Wk 2 Slides - MC Questions - Gastrointestinal Embryology PDF

Gastrointestinal Embryology BMS 200 Amna Noor September 11, 2023 Case Study A 14-year-old boy presents with severe lower left quadrant (LLQ) abdominal pain, abdominal distension, nausea, vomiting, and absent bowel movements (signs of bowel obstruction). ▪ What are you thinking? Learning Ou...

Gastrointestinal Embryology BMS 200 Amna Noor September 11, 2023 Case Study A 14-year-old boy presents with severe lower left quadrant (LLQ) abdominal pain, abdominal distension, nausea, vomiting, and absent bowel movements (signs of bowel obstruction). ▪ What are you thinking? Learning Outcomes By the end of this lesson, students will be able to: Describe the contribution of lateral, caudal, and cephalic folding to the development of the foregut, midgut, and hindgut. Describe the development of the septum transversum as it forms the ventral mesentery and diaphragm. Describe the development of the intra-embryonic coelom, splanchnopleure, and somatopleure into the following abdominal structures: (1) abdominal wall, peritoneal cavity, dorsal mesentery, visceral and parietal peritoneum (2) the alimentary canal and accessory organs. Briefly describe the components of the alimentary tract that are derived from the foregut, midgut, and hindgut as well as their arterial vascular supply. Briefly describe how the respiratory tract and accessory Learning Outcomes Continued Describe the development of the hindgut and allantois as it forms the following structures: (1) cloaca, cloacal membrane, urorectal septum, urogenital sinus, proctodeum, pectinate line. Relate the embryologic development of the GI tract to the pathogenesis and basic clinical features of the following congenital disorders: (1) trachea-esophageal fistula, esophageal atresia, pyloric stenosis, duodenal stenosis, extra-hepatic biliary atresia (2) Meckel diverticulum, congenital omphalocele, gastroschisis, congenital diaphragmatic hernia. Relate the embryologic development of the GI tract to the pathogenesis and basic clinical features of the following congenital disorders: annular pancreas, congenital epigastric hernia, umbilical fistula. Relate the embryological structures of the hindgut to selected Pre-Assessment Quiz Which of the following structures is NOT derived from the intra- embryonic coelom? A. Pericardial cavity B. Pleural cavity C. Peritoneal cavity D. Intrathecal cavity Pre-Assessment Quiz Which structure gives rise to the wall of the gut? A. Notochordal process B. Splanchnopleure C. Somatopleure D. Extraembryonic coelom What has happened so far? Dorsally: Neural Tube Ventrally: Gut Tube Tube on top of a tube! Formation of the Body Cavity At the end of the 3rd week: Intraembryonic mesoderm transforms into: ▪ Paraxial mesoderm somitomeres & somites ▪ Intermediate mesoderm Urogenital system ▪ Lateral plate mesoderm Body cavity Formation of the Body Cavity The lateral plate mesoderm splits into: ▪ The parietal (somatic) layer Somatic layer + ectoderm = Somatopleure ▪ The visceral (splanchnic) layer Splanchnic layer + endoderm = Splanchnopleure The space between 2 layers 🡪 primitive body cavity Formation of the Body Wall During the 4th week, the sides of embryo form two lateral body wall folds ▪ Folds consist of the parietal layer of lateral plate mesoderm, overlying the ectoderm, and cells from adjacent somites. ▪ As these folds progress, the endoderm layer folds ventrally and closes to form the gut tube. By the end of the fourth week, the body wall folds meet in the midline and fuse to close the ventral body wall. Formation of the Body Wall Formation of the Body Wall Closure of the body wall is aided by head and tail folds that cause the embryo to curve into a fetal position (cephalocaudal folding).  Formation of the Body Wall Closure of the ventral body wall is complete except in the region of the connecting stalk. Similarly, closure of the gut tube is complete except for a connection from the midgut region to the yolk sac which forms the vitelline duct. ▪ This duct is incorporated into the umbilical cord and degenerates later. Serous Membranes The parietal layer of the lateral plate mesoderm forms the parietal layer of the serous membranes lining outside of the peritoneal, pleural, and pericardial cavities The visceral layer of the lateral plate mesoderm forms the visceral layer of the serous membranes lining outside of the abdominal organs, lungs, and heart.  Serous Membranes Visceral and parietal layers are continuous with each other as the dorsal mesentery. Ventral mesentery exists from the caudal foregut to the upper portion of the duodenum and results from the thinning of mesoderm of the septum transversum. Septum Transversum  Diaphragm & Thoracic Cavity When lung buds grow, they expand within the pericardioperitoneal canals As a result, the canals become too small, and lungs begin to expand into the mesenchyme Ventral and lateral expansion is posterior to the pleuropericardial folds. Diaphragm & Thoracic Cavity With the expansion of lungs, mesoderm splits into the definitive wall of the thorax and the pleuro-pericardial membranes (extensions of the folds which contain the common cardinal veins and phrenic nerves) Descent of the heart and positional changes of the sinus venosus shift the common cardinal veins towards the midline, and the membranes are drawn out like a mesentery They fuse with each other and with the root of the lungs; the thoracic cavity is divided into a definitive pericardial cavity and two pleural cavities ▪ Adults: pleuro-pericardial membranes from the fibrous pericardium Diaphragm & Thoracic Cavity Formation of the Diaphragm Formation of the Diaphragm Overall, the diaphragm is derived from the following structures: ▪ Two pleuroperitoneal membranes ▪ Muscular components from somites at C3-5 ▪ The mesentery of the esophagus 🡪 crura of the diaphragm GI System Overview GI System Overview Four sections: 1. Foregut (1): Pharynx extends from the oropharyngeal membrane to the respiratory diverticulum 2. Foregut (2): Caudal to the pharyngeal tube and extends to the liver outgrowth 3. Midgut: Caudal to the liver bud and extends to the junction of right two- thirds and left third of the transverse colon in adults 4. Hindgut: Extends from the left third of the transverse colon to the cloacal membrane Endoderm: epithelial lining & parenchyma Visceral mesoderm: stroma Quiz Which embryonic layer contributes to the formation of the serous membranes that line the outside of the abdominal organs, lungs, and heart? A. Ectoderm B. Endoderm C. Mesoderm D. Epiblast Quiz The diaphragm develops from the fusion of which of the following structures? A. Mesonephros and metanephros B. Notochord and neural tube C. Somites, pleuroperitoneal membranes, mesentery of the esophagus D. Sclerotome and dermatome Part II - Foregut Esophagus Develops caudal to the primordial pharynx Partitioned by the tracheoesophageal septum Elongates with growth of heart and lungs Upper 2/3rd: striated & innervated by vagus nerve Lower 1/3rd: smooth & innervated by splanchnic plexus Esophageal Atresia & Tracheoesophageal Fistula Stomach Fusiform enlargement of the caudal part of foregut Different rates of growth of borders ▪ Dorsal (faster) 🡪 greater; Ventral (slower) 🡪 lesser curvature Stomach rotates rotates 90° (around the long axis) clockwise: ▪ Ventral (Ant.) border moves to the right (lesser curvature) ▪ Dorsal (Post.) border moves to the left (greater curvature) Innervation? Stomach Stomach & Mesenteries Stomach & Spleen Stomach & Mesenteries Pyloric Stenosis Pylorus hypertrophies and thickens Narrowing of the pyloric lumen 🡪 passage of food is obstructed Symptoms: projectile vomiting https://www.nationwidechildrens.org/conditions/ pyloric-stenosis Duodenum Develops from the caudal part of the foregut and the proximal part of the midgut. The junction of the two parts is directly distal to the origin of the bile duct (major duodenal papilla after birth). ▪ Grows rapidly and forms a C- shaped loop ▪ With rotation of the stomach and duodenum together, it becomes retroperitoneal organ. ▪ Because it is derived from both foregut and midgut, it is supplied by the branches of both celiac and superior mesenteric arteries. Duodenum Duodenum – Recanalization Proliferation of the epithelial cells and obliteration of the lumen of the duodenum ▪ Recanalization (cell death) and re-opening of the lumen Duodenal Stenosis & Atresia Before we are born, Moore Persaud5th E. Fig. 1 Liver & Gallbladder Outgrowth of endodermal epithelium 🡪 hepatic diverticulum (liver bud) infiltrate the septum transversum The bile duct emerges ▪ Ventral outgrowth gives rise to the gallbladder and cystic duct Merging of hepatic epithelial cords with the vitelline and umbilical veins 🡪 hepatic sinusoids Lesser omentum & falciform ligament Liver & Gallbladder Mesenteries & Liver The septum transversum thins to form: ▪ Peritoneum of the liver ▪ Falciform Ligament ▪ Lesser Omentum Epiploic Foramen Mesenteries & Liver Liver & Hematopoiesis Large nests of proliferating cells, which produce red and white blood cells, lie between hepatic cells and and walls of the vessels. This activity gradually subsides during the last 2 months of intrauterine life, and only small hematopoietic islands remain at birth. Extrahepatic Biliary Atresia Pancreas Before we are born, Moore Persaud 6th E. Fig. 13-9 Annular Pancreas Midgut Structures The midgut is suspended from the dorsal abdominal wall by an elongated mesentery and is supplied by the Superior Mesenteric Artery (SMA). Formation of the midgut loop (a ventral U- shaped loop of the gut) with a cranial and a caudal limb due to the elongation of the midgut. The midgut is projected into the proximal part of the umbilical cord. Midgut Loop (Rotation & Retraction) The Midgut loop has two counterclockwise rotations during its development: ▪ A 90-degree rotation during protrusion and a 180-degree rotation during returning to the abdomen. ▪ Rotation occurs around the axis of the SMA. ▪ During the 10th week of development, the intestines return to the abdomen (reduction of the physiological midgut hernia) ▪ The small intestine is the first part that comes back to the abdomen and the large intestine comes after. Midgut Loop Before we are born, Moore Persaud 6th E. Fig.13-12 Volvulus Malrotation of the intestine Meckel’s Diverticulum Outpouching extending from the wall of the intestine Remnant of tissue from embryonic development https://medlineplus.gov/ency/article/ 000234.htm Umbilical Fistula The vitelline duct remains patent over its entire length, forming a direct communication between the umbilicus and the intestinal tract. Omphalocele Failure of the midgut loop to return to the body cavity Covered by amnion Gastroschisis Closure defect in the ventral abdominal wall Not covered by amnion Quiz During the embryonic development of the stomach, which of the following statements is correct regarding its rotation? A. The stomach rotates 180° clockwise around its long axis. B. The stomach rotates 90° clockwise around its long axis. C. The stomach rotation involves the ventral (anterior) border moving to the left. D. The stomach rotation involves the dorsal (posterior) border moving to the right. Quiz Which statement accurately describes innervation of the esophagus? A. Vagus nerve in the upper 2/3rd; Splanchnic plexus in the lower 1/3rd B. Hypoglossal nerve in the upper 2/3rd; Pelvic splanchnic nerves in the lower 1/3rd C. Facial nerve in the upper 2/3rd; Sympathetic trunk in the lower 1/3rd D. Glossopharyngeal nerve in the upper 2/3rd; Lumbar splanchnic nerves in the lower 1/3rd Part III: Congenital Herniation into the Thoracic Cavity Esophageal Hernia: ▪ The esophagus passes through the diaphragm via the esophageal hiatus. If this hiatus fails to close properly, it can lead to a herniation of the stomach into the thoracic cavity. Congenital Diaphragmatic Hernia: ▪ Incomplete closure of the diaphragm and allowing abdominal organs to herniate into the chest. Hindgut Development Gives rise to distal third of the transverse colon, descending colon, sigmoid colon, upper part of the anal canal Hindgut Development Hirschsprung's Disease Affects the movement of stool through the intestines. It is characterized by the absence of nerve cells, known as ganglion cells, in a segment of the colon. Ganglion cells are responsible for coordinating the rhythmic contractions that move feces through the intestines. Ganglion cells usually migrate from the neural crest cells to the entire length of the colon. In Hirschsprung's disease, there is a failure of this migration, resulting in a section of the colon lacking ganglion cells. This segment of the colon becomes unable to relax and can't propel stool forward, causing a functional obstruction. Internal and External Hemorrhoids Dentate Line: Anatomical division separates the upper two-thirds of the anal canal (where internal hemorrhoids occur) from the lower one-third (where external hemorrhoids occur). Internal Hemorrhoids: ▪ Internal hemorrhoids are covered by a mucous membrane that lacks pain receptors. This is why internal hemorrhoids typically don't cause significant pain. External Hemorrhoids: ▪ External hemorrhoids are covered by skin that contains pain receptors. This is why they are often associated with pain and discomfort. Arterial Supply of Foregut Celiac Trunk ▪ Left Gastric: Lesser curvature of the stomach & some esophagus ▪ Common Hepatic: Proper hepatic: Liver Gastroduodenal: Stomach & duodenum ▪ Splenic: Spleen, greater curvature of the stomach, part of the pancreas Arterial Supply of the Midgut Superior Mesenteric Artery ▪ Inferior Pancreaticoduodenal: Head of pancreas & duodenum ▪ Intestinal: Jejunum & ileum ▪ Ileocolic: Terminal ileum, cecum, & appendix ▪ Right colic: Ascending colon ▪ Middle colic: Transverse colon Arterial Supply of the Hindgut Inferior Mesenteric Artery ▪ Left Colic: Descending colon ▪ Sigmoid: Sigmoid colon ▪ Superior Rectal: upper part of the rectum Innervation Overview Area Sympathetic Parasympathetic Foregut Thoracic Splanchnic Nerves Vagus Nerve (Celiac ganglion) Midgut Thoracic Splanchnic Nerves Vagus Nerve (Superior Mesenteric Ganglion) Hindgut Thoracic & Lumbar Splanchnic Pelvic Splanchnic Nerves (S2 Nerves – S4) (Inferior Mesenteric Ganglion) Upper Anal Canal Inferior Mesenteric Plexus Hypogastric Plexus Lower Anal Canal 🡪Pudendal Nerve (Somatic) Amniotic Fluid Volume & Function of Gut Tube 1. Shields gut tube from direct injury and pressure 2. Essential for lung development 3. Nutrient delivery and waste removal 4. Lubrication 5. Swallowing & gut mobility Problems: polyhydramnios (too much) & oligohydramnios (too little) Case Study A 14-year-old boy presents with severe lower left quadrant (LLQ) abdominal pain, abdominal distension, nausea, vomiting, and absent bowel movements (signs of bowel obstruction). ▪ What are you thinking? Symptomatic Meckel’s Diverticulum References Langman’s Medical Embryology: Chapter 15 – Digestive System Chapter 7 – The Gut Tube and Body Cavities Reflections Reflect on the relevance of GI embryology in terms of: ∙ Understanding normal GI anatomy and physiology ∙ Awareness of disorders that present early in life. ∙ Understanding and recognizing disorders that are embryologic in nature and could present later in childhood or adulthood. Some of these disorders are relatively common and contribute to differentials for common complaints. B-vitamins Intro, B1, B2, B3, B5 BMS200  Overall Outcome At the end of the vitamin lectures, you will be able to describe how our bodies absorb vitamins, convert them into a useful form, and use them at a biochemical level to promote optimal health. You will also be able to apply their biochemical mechanisms to treatment of select conditions. Specific objectives to support this outcome can be found in the syllabus and at the start of each vitamin section in the ppts Intro Objectives Classify vitamins as water or lipid soluble, and contrast with respect to general properties of absorption, transport, storage, excretion, toxicity, dosing Discuss general mechanisms of vitamin deficiencies  A patient comes in with fatigue and asking for supplements to help. You know that some vitamins are good for helping for fatigue, but which ones, and why?  What do you already know? Sort the following properties under the headings of “Water Soluble” and “Lipid Soluble”: ▪ Absorbed directly into blood ▪ Typically stored in body ▪ Vitamin A ▪ Typically less chance of toxicity (why?) ▪ Biotin ▪ Frequent dosing (why?)  Background: B-vitamin coenzymes Vitamins are metabolized into larger coenzyme forms ▪ Coenzymes help catalyze specific types of reactions ▪ Example: Review: The FAD coenzyme form of B2 is shown below. What specific reaction does B2 (and B3) coenzymes help catalyze? B2: Riboflavin B2 coenzyme example: FAD  Background: B-vitamin coenzymes Specific Reactions Catalyzed by B2 and B3 Coenzymes: 1. Vitamin B2 (Riboflavin) Coenzymes: FAD and FMN Specific Reactions Oxidation of succinate to fumarate in the citric acid cycle (via succinate dehydrogenase), where FAD is reduced to FADH₂. Fatty acid oxidation, where FAD is reduced during the first step of the beta-oxidation of fatty acids. Electron transport chain (ETC), where FADH₂ is oxidized back to FAD, transferring electrons to the ETC and contributing to ATP production.  Background: B-vitamin coenzymes Vitamin B3 (Niacin) Coenzymes: NAD+ and NADP+ Specific Reactions Glycolysis and citric acid cycle: NAD+ is reduced to NADH during the oxidation of metabolites such as glucose and pyruvate. Lipid and amino acid metabolism: NAD+ and NADP+ participate in the oxidation of lipids and amino acids. Electron transport chain: NADH is oxidized to NAD+, providing electrons that flow through the ETC to ultimately produce ATP.  Background: B-vitamin coenzymes Based on size, which is more likely to diffuse across cell membranes: vitamins or coenzymes? Food Coenzymes Tissues Blood Vitamins Vitamins Coenzymes Trapped in cells, used Intestinal Lumen Keep this in mind when remembering which enzymes help promote absorption, and which help promote  Vitamins vs Co-enzymes Vitamins: Vitamins are typically smaller, simpler molecules compared to their coenzyme forms. For example, riboflavin (vitamin B2) or niacin (vitamin B3) are relatively small and can sometimes diffuse across cell membranes, especially if they are lipid-soluble or have appropriate transport mechanisms. Lipid-soluble vitamins (such as vitamins A, D, E, and K) can readily diffuse across cell membranes because they can dissolve in the lipid bilayer. Coenzymes: Coenzymes, like FAD (flavin adenine dinucleotide), FMN (flavin mononucleotide), NAD+ (nicotinamide adenine dinucleotide), and NADP+ (nicotinamide adenine dinucleotide phosphate), are generally larger and more complex molecules. They often contain multiple components, such as nucleotide groups, making them bulkier and less likely to diffuse across the hydrophobic lipid bilayer of cell membranes without assistance.  Can a Co-enzyme turn back into a Vitamin? No, a coenzyme cannot turn back into a vitamin. The conversion from a vitamin to a coenzyme is a unidirectional process primarily because vitamins and coenzymes serve different roles and functions in the body.  Key Reasons Why Coenzymes Cannot Become Vitamins Biochemical Conversion: When a vitamin is converted into a coenzyme, it undergoes specific biochemical modifications (such as phosphorylation or the addition of other functional groups) that alter its structure to make it suitable for its role in enzymatic reactions. This process is generally not reversible in the body. Functional Specialization: Vitamins are required from dietary sources to maintain various physiological functions. Once a vitamin has been converted into its active coenzyme form, it is committed to fulfilling that specific biochemical function (e.g., facilitating an enzymatic reaction). The body does not have a pathway to reconvert coenzymes back into their original vitamin form. Metabolic Pathways: The pathways that convert vitamins to coenzymes are tightly regulated and designed to meet the body's metabolic needs. There are no known pathways or mechanisms to reverse these processes and regenerate the original vitamin from its coenzyme form. Background: B-vitamin deficiencies Brainstorm general mechanisms that can contribute to B-vit deficiencies ▪ Considering the path of a B-vitamin from food, into your body, into your cells, and out in the urine Considering the above, by what mechanism could the following contribute to deficiencies: ▪ Alcoholism ▪ IBS ▪ Stress  Background: B-vitamin deficiencies Inadequate Dietary Intake Malabsorption Conditions Gastrointestinal disorders, Gastric surgeries, Chronic diarrhea Increased Nutrient Requirements - Pregnancy and lactation Rapid growth: Infants, children, and adolescents undergoing rapid growth may require more B-vitamins. Chronic illnesses Medications and Drugs Genetic Factors Alcohol and Substance Abuse Aging Autoimmune Disorders Impaired Utilization** Loss of Vitamins via Excessive excretion Conditions like **chronic kidney disease or Heat or cooking Thiamin: Vitamin B1  Objectives ▪ Relate B1 absorption, metabolism, excretion and testing to the general properties of B-vitamins ▪ Relate the biochemical function of B1 to carbohydrate metabolism (energy production, PPS products) ▪ Relate antithiamin factors found in common foods to B1 deficiency ▪ Briefly discuss beriberi (wet and dry) and Wernicke- Korsakoff-syndrome in the context of B1 deficiency  What do you already know? Which one or more of the following metabolic pathways use B1? A – Glycolysis B – Pentose Phosphate Shunt C – CAC D – Beta oxidation  Glycolysis: - No Pathways that Use B1 Vitamin B1 is not directly involved in the glycolysis pathway. However, it plays an essential role in the next steps after glycolysis (pyruvate dehydrogenase complex). Pentose Phosphate Shunt (also called the Pentose Phosphate Pathway) - Yes Vitamin B1, in its coenzyme form, is required for the activity of the enzyme transketolase, which is a key enzyme in the non-oxidative phase of the pentose phosphate pathway. Transketolase transfers two-carbon units and requires the vitamin B1 coenzyme to function properly. CAC (Citric Acid Cycle, also known as the Krebs Cycle or TCA Cycle): - Yes Vitamin B1 is essential for the pyruvate dehydrogenase complex and the alpha-ketoglutarate dehydrogenase complex, both of which play crucial roles in linking glycolysis to the citric acid cycle and in catalyzing reactions within the cycle. TPP is a coenzyme required for these dehydrogenase enzymes to function. Beta Oxidation - No Vitamin B1 is not directly involved in the beta-oxidation of fatty acids. Beta-oxidation primarily involves enzymes that do not require thiamine for their function.  Structure and function Coenzyme form = TDP (aka TPP) (thiamin diphosphate/pyrophosphate) 2 phosphoryl groups added to make the coenzyme form  Absorption and Metabolism What type of enzyme takes the TDP from food and turns it into thiamin for absorption? What type of enzyme takes absorbed thiamin and metabolizes it to make the TDP coenzyme?  Enzyme that Converts TDP from Food to Thiamin for Absorption: Enzyme: Phosphatase Function: In the digestive tract, phosphatases (such as alkaline phosphatase) are responsible for removing phosphate groups from TDP (thiamin diphosphate) obtained from food converting it into free thiamin.  Enzyme that Converts Absorbed Thiamin into TDP Coenzyme Enzyme = Thiamin pyrophosphokinase (TPK) Function: Once free thiamin is absorbed into the body, it is phosphorylated by thiamin pyrophosphokinase (TPK) an enzyme that adds two phosphate groupto thiamin, converting it into its active coenzyme form, TDP (thiamin diphosphate) or TPP (thiamin pyrophosphate)* Specific functions B1 and Energy ▪ Citric acid cycle PDH rxn Pyruvate DH (prep step) and α-ketoglutarate DH complexes use B1 FYI Review: ▪ Makes acetyl Acetyl or CoA and succinyl is succinyl CoA transferred for CAC from B1 to lipoic acid to α-KG DH rxn CoA. B2 resets the To Know: PDH and α- lipoic acid, B3 KG DH use B1, lipoic  Vitamin B1 (Thiamine) and the Citric Acid Cycle (CAC) Thiamine Pyrophosphate (TPP) as a Coenzyme and used to help: Pyruvate Dehydrogenase Complex: Location in Pathway: Before the Citric Acid Cycle begins Pyruvate dehydrogenase converts pyruvate (the end product of glycolysis) into acetyl- CoA. Role of Thiamine (TPP):** TPP is required as a coenzyme by the **pyruvate dehydrogenase complex**, which catalyzes the decarboxylation of pyruvate to form acetyl-CoA, with the release of CO₂ and the reduction of NAD+ to NADH. Alpha-Ketoglutarate Dehydrogenase Complex: Location in Pathway: Within the Citric Acid Cycle, α-ketoglutarate dehydrogenase converts α-ketoglutarate to succinyl-CoA.  Specific Functions B1 and energy continued ▪ Succinyl CoA is also a substrate for heme synthesis What is the connection of heme to energy? Oxygen is essential for tissues because it is needed for cellular respiration, a process that produces the energy cells need to function. In cellular respiration, Heme oxygen helps convert glucose and other nutrients into adenosine triphosphate (ATP), which powers Hemoglobin various cellular activities. Without sufficient oxygen, tissues can’t get the energy they need, which can lead to cell damage or death. This is why Carries oxygen to maintaining proper oxygen levels in the body is tissues Needed crucial to health. for overall run __?__  Specific functions B1 and Energy: ▪ Pentose Phosphate Shunt TDP helps transketolase enzymes transfer 2C units in the reactions that connect pentoses back to glycolysis  energy GLUCOS Glucose 6-P E PPS NADP H Glycolysis Fructose 6- transketolases Pentose P s Glyceraldehyde-3- P Pyruvat e  Deficiencies Antithiamine factors found in various foods can help contribute to a thiamin deficiency ▪ Some antithiamin factors can break apart thiamin Sulphur dioxide ▪ Preservative predominantly found in dried fruits/vegetables, as well as alcoholic drinks Thiaminases ▪ Enzymes found in some raw fresh water fish, shellfish, ferns Inactivated by heat  Deficiencies ▪ Other antithiamine factors Polyphenols ▪ Ex: Tannic acid (in tea, betel nuts, etc) and caffeic acid (in coffee, red wine, etc) ▪ Can join 2 thiamines together - Why is this a problem? - It Makes it too big to absorb  Why Joining Two Thiamines Is a Problem 1. Biochemical Specificity: ▪ - Cofactor Role: Thiamine acts as a cofactor for enzymes such as transketolase, pyruvate dehydrogenase, and alpha-ketoglutarate dehydrogenase. These enzymes require thiamine in its active form (thiamine diphosphate or TDP) to facilitate the transfer of 2-carbon units or other biochemical transformations. Joining two thiamine molecules would not produce a functional cofactor for these reactions. 2. Lack of Functional Utility: ▪ - No Enhanced Activity: Combining two thiamine molecules does not result in a form that would be more effective in catalyzing reactions. The enzymatic activity requires thiamine to be present as TDP, and the biochemical activity relies on its specific structure and role in the active site of enzymes. 3. Potential Inhibition: ▪ - Interference with Enzyme Function: If an attempt were made to join two thiamine molecules, the resulting compound could potentially interfere with enzyme function, either by blocking the enzyme's active site or by failing to bind effectively. 4. Metabolic Disruption: ▪ - Deficiency in Function: Thiamine's primary role is to help in energy production and metabolism by aiding in decarboxylation reactions. A non-functional or improperly structured form of thiamine would disrupt these crucial metabolic pathways, leading to symptoms of thiamine deficiency such as fatigue, neurological issues, and metabolic disturbances.  Deficiencies How do you think the following pharmaceuticals could contribute to B1 deficiency? ▪ 5-fluorouracil? Chemotherapeutic agent ▪ Works by inhibiting phosphorylation of thiamin How does this cause a deficiency? ▪ Diuretics?  Deficiencies 5-Fluorouracil: Mechanism: 5-Fluorouracil is a chemotherapeutic agent that primarily works by inhibiting the enzyme thymidylate synthase, which is crucial for DNA synthesis in rapidly dividing cells. This disruption in nucleotide synthesis can indirectly affect various metabolic pathways, including those involving thiamine. Thiamine Phosphorylation Inhibition: Specifically, 5-fluorouracil has been shown to inhibit the phosphorylation of thiamine, which is essential for its conversion into its active form, thiamine diphosphate (TDP). TDP is necessary for the proper function of several key enzymes, including those involved in carbohydrate metabolism. Resulting Deficiency: If thiamine cannot be phosphorylated, it becomes unavailable/trapped in its active form, leading to a functional deficiency. This impairs key enzymatic reactions dependent on TDP, such as those in the Pentose Phosphate Pathway and the Krebs cycle, potentially resulting in symptoms of thiamine deficiency like neurological issues and metabolic disturbances.  Deficiencies Diuretics Mechanism: Diuretics increase urine production, which leads to increased excretion of electrolytes and other nutrients, including thiamine. Thiamine Loss: Prolonged use of diuretics can lead to a loss of thiamine through the urine. This increased loss can deplete the body’s thiamine reserves over time, particularly if dietary intake is not sufficient to compensate for the loss. Resulting Deficiency Chronic thiamine loss due to diuretic use can result in thiamine deficiency if the intake is not adequate. Symptoms of thiamine deficiency, such as fatigue, muscle weakness, and neurological issues, may become evident if the deficiency is severe or prolonged. Excreted thru Urine  Deficiencies B1 deficiency adversely affects highly energy dependent tissues, such as heart and brain ▪ Why is energy production so disrupted by B1 deficiency? B1 deficiency can cause nerve conduction issues ▪ What neurotransmitter would be affected? Review: B1 helps convert pyruvate to acetyl CoA - what NT is made using acetyl CoA? Take home message: Expect to see the CNS and/or cardiovascular system affected by B1 deficiency  Energy Production Disruption: Impact of Deficiency: Without adequate thiamine, pyruvate cannot be efficiently converted to acetyl CoA. This impairs the Krebs cycle and reduces ATP production. Since the heart and brain are highly energy-dependent organs, they are particularly vulnerable to the reduced energy supply. Neurological and Cardiovascular Impact: Nerve Conduction Issues: Thiamine deficiency can cause nerve conduction issues due to its role in maintaining myelin sheath integrity and proper nerve function. This often results in symptoms like peripheral neuropathy and cognitive impairments. Neurotransmitter Affected: Acetyl CoA is a precursor for the synthesis of acetylcholine, a neurotransmitter crucial for many aspects of brain function, including memory and muscle control. A deficiency in acetyl CoA production due to inadequate thiamine can reduce acetylcholine synthesis, affecting cognitive function and muscle coordination. CAC makes: 3 NADH, 1FADH2 and 1 GTP for 12 ATP. Also compromises pentoses from entering glycolysis. Deficiency is likely to affect the central nervous system (CNS) and cardiovascular system. Symptoms may include cognitive disturbances, memory issues, muscle weakness, and cardiovascular problems. Deficiencies B1 deficiency can lead to: ▪ Wernicke-Korsakoff Syndrome May be seen with alcoholism Symptoms include confusion and severe memory impairment (CNS) ▪ Beriberi Main symptoms include: ▪ Sensory and motor nerve conduction issues and muscle weakness when the CNS is more affected (“dry” beriberi) ▪ Heart failure, tachycardia etc when the cardiovascular system is more affected (“wet” beriberi)  Testing Testing ▪ Blood test for transketolase (TK) activity Why might this be more accurate than testing B1 levels directly? Draw blood, separate into two tubes. Add TDP to one tube only, measure activity of TK in both tubes ▪ B1 deficiency: Tube with additional TDP shows a 25% increase in activity What is the rationale here? Why would you not see an increase in activity with the addition of TDP if the patient had adequate B1 levels?  Testing Rationale for Testing TK Activity: Thiamine Dependence of TK Transketolase is an enzyme that requires TDP (the active form of thiamine) as a cofactor. Its activity is directly influenced by the availability of TDP. If thiamine levels are low, the enzyme's activity will be reduced because there is insufficient TDP to enable proper enzyme function. Measurement and Interpretation Increased Activity: If the tube with added TDP shows a significant increase (e.g., 25%) in TK activity compared to the control tube, it indicates that the enzyme's activity was previously limited by a lack of TDP. This suggests a functional deficiency of thiamine. No Increase: If there is no significant increase in activity with the addition of TDP, it could imply that thiamine levels are adequate, and the enzyme's activity is not limited by TDP availability. *Blood Levels can be affected by Recent Intake**  Riboflavin: Vitamin B2 Food sources: Meats (especially liver and organ meats), milk products, brewer’s yeast, legumes, eggs, almonds, leafy greens Objectives Relate B2 absorption, metabolism, excretion and testing to the general properties of B-vitamins Relate the biochemical function of B2 to energy production, catabolism of purines, GSH reduction, NT metabolism Briefly provide a rationale for the use of B2 in treatment of migraines and cataracts What do you already know? Which one or more of the following are coenzyme forms of B2: ▪ FAD ▪ NADH ▪ CoA ▪ PLP ▪ FMN  Absorption and Metabolism Which enzyme would be required for absorption vs metabolism? Dinucleotide Flavin Adenine Bright yellow urine Flavin adenine dinucleotide (FAD) METABOLISM ABSORPTION Riboflavin Flavokinase FMN phosphatase FMN FAD FAD synthetase pyrophosphatase FAD  FAD and FMN Absorption: Dietary riboflavin is absorbed in the small intestine in its free form after enzymatic dephosphorylation of FAD and FMN. It is then converted to FMN and FAD in enterocytes and other tissues. Metabolism: Riboflavin is converted into FMN and FAD, which serve as essential coenzymes in redox reactions, energy metabolism, and antioxidant defense. Distribution: FMN and FAD are distributed throughout the body, especially in metabolically active tissues, where they function as coenzymes for various flavoproteins. Excretion: Excess riboflavin, FMN, and FAD are excreted in the urine, with small amounts potentially excreted in bile or feces.  ENERGY B2 and energy ▪ Which of the following pathways make FADH for 2 energy? ▪ Glycolysis ▪ Beta oxidation ▪ CAC ▪ Cori cycle (anaerobic respiration) ▪ What same type of enzyme produces FADH (and/or 2 NADH) for energy in catabolic pathways?  ENERGY Beta oxidation is the process where fatty acids are broken down to produce acetyl-CoA, and FADH2 is generated during this process. CAC generates FADH2 as one of its products during the oxidation of succinate to fumarate. The same type of enzyme that produces FADH2 (and/or NADH) in these catabolic pathways is known as a **dehydrogenase**. Specifically, in beta oxidation, the enzyme acyl-CoA dehydrogenase produces FADH2 CAC, the enzyme succinate dehydrogenase (which is also part of the electron transport chain complex II) produces FADH2. Similarly, other dehydrogenases in these pathways produce NADH. Beta Oxidation CAC Pyruvate dehydrogenase complex Dehydro- genase Dehydro- genase Alpha-KG Succinate dehydrogenase dehydrogenase (also complex Complex II entry point  ENERGY B2 and energy ▪ In addition to being part of the CAC, succinyl CoA can also feed into heme synthesis How does this provide energy? ▪ How does FADH provide energy? 2 ▪ Does FMN/FMNH2 have a role in energy production?  ENERGY Succinyl-CoA in Heme Synthesis: an intermediate in the citric acid cycle and can also be used in the synthesis of heme, which is a component of hemoglobin and other heme-containing proteins. While the direct role of succinyl-CoA in heme synthesis is not to provide energy, the production of heme is critical for oxygen transport in the blood, which supports aerobic respiration and overall energy metabolism. FADH2 and Energy Production: Role of FADH2: a high-energy electron carrier produced in the citric acid cycle (CAC) and during beta oxidation of fatty acids. It donates electrons to the electron transport chain (ETC) in mitochondria. When FADH2 donates electrons to Complex II of the ETC, it helps to drive the production of ATP through oxidative phosphorylation. Each FADH2 molecule contributes to the creation of about 1.5 ATP molecules. FMN/FMNH2 and Energy Production: FMN/FMNH2 in the Electron Transport Chain: FMN (flavin mononucleotide) is a prosthetic group of Complex I (NADH dehydrogenase) in the electron transport chain. When NADH donates electrons to Complex I, FMN is reduced to FMNH2. FMNH2 then passes electrons through the chain, which helps in generating a proton gradient across the inner mitochondrial membrane. This gradient drives ATP synthesis via ATP synthase. Therefore, FMN (and its reduced form FMNH2) plays a crucial role in the process of energy production by facilitating electron transfer in the ETC. Cytosol FADH2 generated from glycolytic NADH via glycerol phosphate shuttle Cyt. C G-3-P DH Complex IV Complex I Complex III CoQ FMN Complex II (succinate Electron DH) transferrin FADH2 g DH To Know: from NADH from FADH2 from 1) FADH2 supplies electrons to CAC CAC and beta beta ox the ETC, leading to ultimate ox production of ATP 2) FMN acts as an electron carrier in the ETC Matrix OTHER B2 and antioxidation ▪ Along with B3, B2 helps regenerate the antioxidant glutathione HO HO + 2 2 GSH + GSH H2O GS-SG Glutathione 2 reductase FADH2 FAD NADPH + H+ NAD +  OTHER Tyrosine B2 and neurotransmitter Dopamine metabolism NE ▪ Monoamine oxidase uses FAD to oxidize NT’s that Degradation: MAO NE have an amine structure NE such as: ▪ Dopamine, epinephrine, Degradatio Post- norepinephrine n: COMT synaptic Cellula Why do we need to receptor r metabolize NT’s? respon Therapeutic uses and deficiency Given the following therapeutic mechanisms, how might B2 help prevent: ▪ Migraines Migraines may be due to decreased mitochondria energy production in the brain ▪ Cataracts Cataracts may be caused by UV damaged Deficiency ▪ No “hallmark” deficiency. Symptoms include: Fatigue (know this one, provide a rationale) FYI: cheilosis (cracked lips), glossitis (swollen tongue), sore throat Testing Testing ▪ Similar blood test to B1, except the enzyme this time is glutathione reductase If you had a B2 deficiency, would glutathione reductase activity go up or down if additional FAD were added to the test tube?H2O H2O + GSH + GSH H2O GS-SG Glutathione 2 reductase FADH2 FAD NADPH + H+ NAD +  Testing Here's why: Vitamin B2 (Riboflavin) and FAD Riboflavin is a precursor for the coenzyme FAD (flavin adenine dinucleotide). Glutathione reductase, an enzyme that helps maintain the antioxidant glutathione in its reduced form, requires FAD as a cofactor to function properly. Deficiency Effects: In a B2 deficiency, there would be a shortage of FAD, leading to reduced activity of FAD-dependent enzymes, including glutathione reductase. Adding FAD: By adding additional FAD to the test tube, you are essentially supplementing Niacin: Vitamin B3 Objectives Relate B3 absorption, metabolism, excretion and testing to the general properties of B-vitamins Relate the biochemical function of B3 to energy production Relate the biochemical function of B3 to ethanol metabolism, fatty acid synthesis, antioxidation via GSH and Vit C Provide a therapeutic mechanism to rationalize the use of B3 for: Raynaud’s, Elevated TG’s and cholesterol, diabetes Develop a hypothesis regarding the mechanism by which high- dose B3 can cause damage in patients with peptic ulcer disease Relate corn-based diets and carcinoid syndrome to the development of B3 def and pellagra What do you already know? Which one or more of the following are coenzyme forms of B3: ▪ FAD ▪ NADH ▪ CoA ▪ NADP+ ▪ FMN  What do you already know? The coenzyme forms of Vitamin B3 (niacin) are: NADH (Nicotinamide Adenine Dinucleotide, reduced form) NADP+ (Nicotinamide Adenine Dinucleotide Phosphate) This is the reduced form of NAD+ and is involved in various NADH: metabolic processes, including the electron transport chain for ATP production. NADP+: This is the oxidized form of NADPH, which is used primarily in anabolic reactions, including biosynthesis and the antioxidant defense system.  Naming Niacin refers to nicotinic acid and/or nicotinamide: Nicotinic acid and nicotinamide can both be used to make NADH/NAD(P)H coenzymes ▪ Most supplements contain nicotinamide. Any idea why nicotinamide rather than nicotinic acid? ▪ Unique to B3: RDA for niacin includes 1/60mg tryptophan, as can also make NAD+ from tryptophan  why nicotinamide rather than nicotinic acid? Nicotinamide is often used in supplements instead of nicotinic acid for several reasons: Fewer Side Effects: Nicotinic acid can cause flushing, a common side effect characterized by redness and warmth of the skin, especially when taken in higher doses. Nicotinamide does not typically cause flushing, making it a more comfortable option for supplementation. Different Metabolic Pathways: Nicotinamide and nicotinic acid both contribute to the production of NAD+ (nicotinamide adenine dinucleotide), but they enter the metabolic pathways in slightly different ways. Nicotinamide is directly used in the synthesis of NAD+ and is more efficiently converted in the body, whereas nicotinic acid has to be converted to NAD+ through additional steps. Safety Profile: Nicotinamide is considered to have a better safety profile compared to high doses of nicotinic acid. It does not affect blood lipid levels or cause liver toxicity at typical supplementation levels, which can be a concern with high doses of nicotinic acid.  Absorption and metabolism Corn contains niacin bound to carbohydrates (niacytin) and small peptides (niacinogen) ▪ What do you think this does to the bioavailability of niacin obtained from corn? Once nicotinamide and nicotinic acid enter the tissues, they are metabolized into NADH ▪ Nicotinamide adenine dinucleotide  Absorption and metabolism Corn contains niacin bound to carbohydrates as niacytin and to small peptides as niacinogen. This binding affects the bioavailability of niacin in several ways: Reduced Bioavailability (Too big for absorption) Niacytin and niacinogen are forms of niacin that are not as easily absorbed by the body compared to free niacin. The binding to carbohydrates and peptides makes it less accessible for absorption in the digestive tract. As a result, the bioavailability of niacin from corn is lower than from other sources where niacin is present in its free form. Nutritional Implications: Because of this reduced bioavailability, individuals relying heavily on corn as their primary source of niacin might be at risk of niacin deficiency if they do not consume other sources of niacin or if the diet is not well- balanced. This is particularly a concern in populations with a diet primarily consisting of corn and lacking other niacin-rich foods.  FYI Visual Nicotinamide Nicotin- adenine dinucleotide amide NADH Nucleotide Adenine Nucleotide  Energy B3 and energy ▪ Which of the following catabolic pathways produce NADH for energy? ▪ Glycolysis ▪ Beta oxidation ▪ CAC ▪ Anaerobic respiration ▪ What same type of enzyme produces NADH (and/or FADH ) for energy in catabolic pathways? 2  Energy Glycolysis: This pathway breaks down glucose into pyruvate, producing NADH in the process. Beta Oxidation: This pathway breaks down fatty acids into acetyl-CoA, generating NADH as well. Citric Acid Cycle (CAC): This cycle oxidizes acetyl-CoA to produce NADH, along with FADH2. Anaerobic Respiration: While it involves the reduction of other molecules and does not directly produce NADH, it does rely on the regeneration of NAD+ from NADH to maintain glycolysis under anaerobic conditions. The same type of enzyme that produces NADH (and/or FADH2) in these catabolic pathways is a dehydrogenase  Specific functions B3 and energy: Glycolysis ▪ Look at the diagram: find the enzyme that produces NADH Where does NADH go next to make energy in aeroboic conditions? What about anaerobic?  Specific functions In glycolysis the enzyme that produces NADH is glyceraldehyde-3-phosphate dehydrogenase. This enzyme catalyzes the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, and during this reaction, NAD+ is reduced to NADH. Where NADH Goes Next in Aerobic Conditions: Transport into Mitochondria: In aerobic conditions, NADH produced in glycolysis is transported into the mitochondria. This usually involves shuttle systems like the **malate-aspartate shuttle** (in heart and liver cells) or the **glycerol-3-phosphate shuttle** (in muscle cells), which help transfer the electrons from NADH into the mitochondrial matrix. Electron Transport Chain (ETC): Once inside the mitochondria, NADH donates its electrons to **Complex I** of the electron transport chain (ETC). Production of ATP: The electrons transferred from NADH to Complex I pass through the ETC, which is located in the inner mitochondrial membrane. This process generates a proton gradient across the membrane. ATP Synthesis: The proton gradient drives ATP synthesis via ATP synthase, a process known as oxidative phosphorylation. This is how the energy from NADH is ultimately used to produce ATP. Specific functions: B3 and energy: Cori cycle (anaerobic energy) ▪ Lactate dehydrogenase Muscle: Produces NAD to keep glycolysis running + Liver: Uses NADH to make glucose for muscles for glycolysis Glycolysis produces ATP for energy  Anaerobic energy: Cori cycle - FYI review - See previous slide for “what to know” Anaerobic GNG: Liver Conversion of Glycolysis: Muscle NADH back to Glucose Glucose NAD+ allows ATP 1) ATP for: NADH NAD+ NAD+ NADH 1) Continued Pyruvate Oxaloacetate production of ATP via NADH NAD+ Pyruvate glycolysis 2) NAD+ NADH Lactate Lactate 2) Production lactate. Lactate goes to liver for Specific functions: B3 and energy: CAC ▪ All CAC dehydrogenases (including PDH) make NADH, except which one? Hint: This one makes FADH2, and is also part of ETC B3 and energy: Heme ▪ Succinyl CoA (made by alpha KG dehydrogenase) can also be used to make heme Dehydrogenase B3 and energy: Beta ox ▪ Dehydrogenase makes NADH Dehydrogenase Note: one DH makes NADH, and one DH makes FADH2  Specific functions: All CAC dehydrogenases produce NADH except for? Succinate Dehydrogenase which produces FADH2. Succinate dehydrogenase is unique because it also functions as Complex II in the electron transport chain (ETC), where it directly contributes to the production of FADH2. Beta Oxidation Dehydrogenases: In beta oxidation: - Acyl-CoA dehydrogenase produces FADH2. - 3-Hydroxyacyl-CoA dehydrogenase produces **NADH**. These dehydrogenases are crucial for the breakdown of fatty acids and the  Specific functions Other ▪ Dehydrogenases use NAD+ to metabolize alcohol Review slide to follow, details FYI only ▪ NADH (predominantly catabolic) can be converted to NADPH (predominantly anabolic) by what type of enzyme? NADPH can help regenerate antioxidants (vitamin C, GSH) NADPH produced by PPS can beAcetyl used to make fatty acids GLUCO CoA SE NADP FATTY PP F.A. synthesis S H Pentose ACIDS -P- Metabolism of Alcohol: FYI Review NAD NADH NAD NADH+ Ethanol H+ Acetaldehyde H+ E = alcohol E = aldehyde Acetate dehydrogena dehydrogena se se Alcohol consumption Flushing Back to normal Physiological effects & therapeutic uses Nicotinic acid (NAc) and nicotinamide (NAm) each have unique physiological effects separate from their coenzyme forms ▪ Giving high doses of NAc or NAm can ensure there are enough of these forms to be utilized for therapeutic effects Physiological effects Nicotinic acid: ▪ 1) Causes vasodilatory prostaglandin release Responsible for “niacin flush” (transient) ▪ Review from BMS150: What enzyme can block production of vasodilatory PG’s? Therefore, what type of pharmaceutical Cyclooxygenase (COX) can help prevent niacin flush? X Aspirin Arachidonic Vasodilatory Release Niacin promoted by acid PG’s nicotinic acid “flush”  The enzyme that blocks the production of vasodilatory prostaglandins (PGs) is cyclooxygenase (COX). Niacin flush is caused by the release of prostaglandins, which lead to vasodilation and the associated flushing. To prevent niacin flush, a common approach is to use a type of pharmaceutical that inhibits COX. These are known as nonsteroidal anti-inflammatory drugs (NSAIDs). For example, aspirin is an NSAID that can inhibit COX enzymes and reduce the production of prostaglandins. By doing so, aspirin can help prevent or minimize the flushing reaction that occurs with niacin Physiological effects Nicotinic acid: ▪ 2) Causes enhanced fibrinolysis Actions on plasmin (increases) and fibrinogen (decreases) ▪ Nicotinic acid Helps prevent clot buildup, thus improving Nicotinicblood acid flow (-) (+) Thrombin Plasmin Fibrinogen Fibrin Clot Clot Dissolution Physiological effects Nicotinic acid: ▪ 3) Improves lipid profile: Decreases circulating VDLD/LDL and increases HDL ▪ LDL: Carries cholesterol to tissues for use (good) Can become oxidized and contribute to plaque formation  atherosclerosis (bad) ▪ HDL: Picks up excess cholesterol from tissues (including plaques) and can carry back to liver for excretion (good) Physiological effects Nicotinic acid ▪ 3) Improved lipid profile continued NAc can decrease VLDL/LDL by blocking lipolysis in adipose tissue ▪ Diagram the connection between adipose and liver with respect to ffa, VLDL, LDL. Add in effect of NAc. NAc can increase HDL by downregulation of HDL receptors that internalize and catabolize HDL ▪ Allows HDL to circulate longer and pick up more cholesterol  Connecting the Concepts Adipose Tissue → Releases FFAs → Bloodstream → Transports FFAs bound to albumin → Liver Liver: Takes up FFAs → Re-esterifies them to triglycerides → Packages into VLDL → Releases into Bloodstream VLDL is converted to LDL through lipolysis in the bloodstream. NAC: Decreases oxidative stress → Reduces lipolysis in adipose tissue (less FFA release). Enhances antioxidant capacity → Modulates lipid metabolism in the liver (less VLDL production, reduced LDL levels).  Physiological Effects: Review at home Nicotinic acid: Application ▪ Raynaud’s phenomenon Condition characterized by spasm of digital arteries, especially in response to cold or stress, causing numbness and tingling in fingers/toes Nicotinic acid may provide acute relief by promoting vasodilation ▪ Review: What is the vasodilatory mechanism? ▪ Atherosclerosis Condition characterized by narrowing and hardening of arteries Review: Nicotinic can improve blood flow by enhancing fibrinolysis and decreasing ? Physiological effects Histamine Nicotinic acid: Other ▪ 4) Increased histamine release H2-receptor Connect the dots as to why NAc may cause damage in a patient with peptic ulcer disease Parietal ▪ 5) Potential for hyperglycemia Cell Could be partially due to decreased glucokinase phosphorylation of glucose Secretion of ▪ How could this contribute to increased blood ? to make ? sugar? Increases risk of diabetes in pre-diabetic patients Nicotinic Acid and Peptic Ulcer Disease: Increased Histamine Release Nicotinic acid (niacin) can cause increased histamine release, which is a mediator of inflammation and vasodilation. In the context of peptic ulcer disease, this increased histamine release can exacerbate ulcer symptoms because: Histamine Stimulates Gastric Acid Secretion: Histamine binds to H2 receptors in the stomach lining, promoting gastric acid secretion. In patients with peptic ulcer disease, excessive gastric acid can worsen the condition by irritating the ulcerated mucosa and increasing ulcer pain or bleeding. Compounding Existing Gastric Irritation For those already suffering from ulcers, the additional stimulation of gastric acid secretion by histamine can aggravate symptoms and potentially lead to complications such as ulcer bleeding or perforation. Nicotinic Acid and Hyperglycemia: Potential for Hyperglycemia: Niacin can lead to elevated blood glucose levels. One mechanism for this involves decreased phosphorylation of glucose by glucokinase. Here's how this contributes to increased blood sugar: Role of Glucokinase: Glucokinase is an enzyme that helps regulate blood glucose levels by phosphorylating glucose to glucose-6- phosphate in the liver, which is an important step in glucose metabolism and storage. Decreased Glucokinase Activity: When glucokinase activity is reduced, glucose is less efficiently phosphorylated and trapped in the liver cells. This leads to higher levels of free glucose in the bloodstream because less glucose is being converted to glycogen or other metabolic intermediates. Increased Blood Sugar: With decreased glucokinase activity, there is less glucose uptake and storage in the liver, contributing to elevated blood sugar levels. This effect can increase the risk of hyperglycemia and potentially exacerbate diabetes in pre- diabetic patients. Increased Diabetes Risk: For individuals with pre-diabetes or those at risk for diabetes, the impairment in glucose regulation caused by niacin can worsen glycemic control and increase the risk of developing type 2 diabetes.  Physiological effects Nicotinamide ▪ Does not have the same effects just listed for NAc Not associated with niacin flush Not associated with same therapeutic uses ▪ NAm can protect insulin-secreting pancreatic beta cells from damage Does not necessarily protect against development of diabetes ▪ FYI: NAm may also decrease insulin sensitivity, which could explain why improved beta cell function does not translate well to better glycemic control Deficiency Symptoms ▪ Pellagra: dementia, dermatitis, diarrhea, death Causes ▪ Corn-based diet B3 in niacytin or niacinogen form How can each of Low in tryptophan these contribute Why is pellagra is not common in Mexico andto Central America, which pellagra? have largely corn-based diets? ▪ Carcinoid syndrome Condition of increased secretion of serotonin (and other catecholamines) ▪ Why would this cause pellagra? FYI Toxicity FYI: High dose B3 can be associated with liver toxicity, especially nicotinic acid forms Pantothenic acid: Vitamin B5 Objectives Relate B5 absorption, metabolism, excretion and testing to the general properties of B-vitamins Relate the biochemical function of B5 to energy production, synthesis reactions (fatty acids, lipids, cholesterol, ketones) Relate the biochemical function of B5 to the B5 deficiency symptoms of listlessness/fatigue Relate “burning foot syndrome” to B5 deficiency  What do you already know? The most common coenzyme form of B5 is Coenzyme A (CoA). List 2-3 CoA’s you have heard about in BMS so far, and their general functions.  What do you already know? List 2-3 CoA’s you have heard about in BMS so far, and their general functions. Acetyl CoA – CAC, end of beta ox. Creation of HMG CoA for ketones, cholesterol… HMGCoA – cholesterol, ketones Succinyl CoA – CAC, heme Fatty acyl CoA – used for TG and phospholipids synthesis and start of beta ox Structure and function To know: Has S to carry acyl groups To know: What role would kinases and phosphatas es play in absorption vs metabolism ? Phosphate  B5 —> CoA Citric Acid Cycle (CAC:) Acetyl-CoA is a primary substrate that enters the cycle to produce energy. Additionally, succinyl-CoA, another CoA derivative, is an intermediate in the cycle. Vitamin B5 is critical for synthesizing CoA, which is necessary for these processes. Beta Oxidation: This pathway involves the breakdown of fatty acids to produce acetyl-CoA. Fatty acyl-CoA, derived from fatty acids, is the substrate for beta oxidation, and acetyl-CoA is the end product. CoA is vital for this process as it helps in the activation and breakdown of fatty acids. Ketolysis: In ketolysis, acetyl-CoA is generated from ketone bodies, which are alternative energy sources, especially during periods of fasting or prolonged exercise. CoA is essential for the utilization of these ketone bodies. Heme Synthesis Succinyl-CoA, a product of the CAC, is a substrate for the synthesis of heme, a crucial component of hemoglobin. CoA, synthesized from Vitamin B5, is necessary for the production of succinyl-CoA, which in turn supports heme synthesis. Specific Functions B5 and energy ▪ CAC: Acetyl CoA, succinyl CoA (substrates) ▪ Beta oxidation: Fatty acyl CoA (substrate), acetyl CoA (product) ▪ Ketolysis: Acetyl CoA (product) ▪ Heme synthesis: Succinyl CoA (substrate) Acetyl CoA Beta ox Fatty Acyl Keto- lysis CoA Ketone s Energ CAC y Succinyl Also used for heme Specific Functions B5 and synthesis ▪ Fatty acids: Next 2 green CoA: makes acetyl CoA and malonyl CoA slides are review, substrates details are FYI only Also: Part of fatty acid synthetase complex ▪ Phospholipids and triglycerides Fatty acyl CoA substrates Acetyl CoA ▪ Cholesterol and ketones HMG CoA Acetyl CoA = substrate to make HMG-CoA Ketones Cholesterol Specific functions – FYI Review Fatty acid synthesis: 2 roles for B5 ▪ Acetyl CoA and malonyl CoA are substrates ▪ ACP (acyl carrier protein) part of fatty acid synthase includes a portion of CoA (FYI phosphopantethine portion, which is CoA minus the AMP) The S group binds the malonyl substrate Fatty acid synthase B5 S Cys S Malonyl and acetyl C=O C=O groups combine to Malonyl group from CH2 CH3 start the fatty acid malonyl chain COO- Acetyl group Specific functions – FYI Review Lipid synthesis ▪ Fatty acyl CoAs provide the fatty acid chains for triglyceride and phospholipid synthesis O O H2C-OH O O R-C-SCoA H2C-OC-R R-C- O H2C-OC-R HO-CH SCoA HO-CH R-C-O -CH H2C-OPO3 -2 H2C-OPO3-2 H2C-OPO3- 2 Use another Add a head acyl CoA to group to make make a a phospholipid  Deficiency Deficiency symptoms ▪ Burning Foot Syndrome (rare) Burning sensation in feet exacerbated by heat and diminished by cold ▪ FYI – good for hair? ▪ FYI – “antistress” vitamin? To be explored in NMT ▪ Fatigue and listlessness What is the rationale? ▪ Energy pathways – which ones? Acetyl CoA ▪ Heme synthesis – what is the connection to fatigue and listlessness? HMG CoA ▪ Cortisol to help maintain blood glucose – what is the connection to B5? Cholesterol Steroid hormones B-vitamins B6, B7, B9, B12 Dr. Heisel BMS200 Overall Outcome Reminder At the end of the vitamin lectures, you will be able to describe how our bodies absorb vitamins, convert them into a useful form, and use them at a biochemical level to promote optimal health. You will also be able to apply their biochemical mechanisms to treatment of select conditions. Specific objectives to support this outcome can be found in the syllabus and at the start of each vitamin section in the ppts Pyridox- (al, ine, amine): Vitamin B6 Objectives Relate B6 absorption, metabolism, excretion and testing to the general properties of B- vitamins Relate the biochemical function of B6 to synthesis of heme, NAD, neurotransmitters, lipids (unsaturated fatty acids, ceramide) Relate the biochemical function of B6 to carbohydrate metabolism (energy production) and amino acid metabolism Develop hypothesis for the mechanism by which vitamin B can assist in improving depression, inflammation Describe the biochemical relationship between vitamin B6 deficiency and subsequent glutamate decarboxylase deficiency resulting in infantile seizures. Provide a biochemical rationale for fatigue and microcytic anemia as symptoms of B6 def. What do you already know? Name the biochemical reaction catalyzed by B6 that can be used to move amino groups. ▪ Review: What three pairs of molecules can interconvert via this reaction? Alpha Amino Amino Alpha ketoaci acid acid ketoaci d d Review Amino acids Alanine Aspartate Glutamate = = O O O = Pyruvate Oxaloacetat e α- Alpha What do you already know? In addition to transamination, B6 facilitates other types of reactions, including: ▪ Trans- and de- sulfhydration ▪ Decarboxylation Structure and function Six forms = interchangeable “vitamers” ▪ All the same except for the functional group FYI: = Aldehyde (pyridoxal, PL), alcohol (pyridoxine, PN), amine (FYI: pyridoxamine, PM), either with or without an additional phosphate To Know: Coenzyme is phosphorylated aldehyde form = pyridoxal phosphate = PLP ▪ Other B-vitamins can help with vitamer interconversions Ex: B2 helps convert PNP to the PLP ▪ Important, as only PLP acts as a coenzyme  FYI Structure and function visual Blue = functional groups, rest of molecule Redis = the same phosphate added, rest of molecule is the same Yellow = coenzyme Absorption and metabolism What needs to happen for the phosphorylated vitamers to be absorbed? What type of enzyme is used? What type of enzyme helps convert pyridoxal (PL) to the pyridoxal phosphate coenzyme form (PLP)? Specific functions B6 and energy: ▪ Link to B3 B6 helps make the NAD coenzyme from the amino acid + ___________. ▪ Review: NAD+ is converted to NADH by which of the energy producing pathways? A – glycolysis B – beta oxidation C – citric acid cycle NADH can then go to ETC 🡪 energy ▪ Glycogenolysis B6 helps glycogen phosphorylase release glucose ▪ Glucose can then be used for glycolysis 🡪 energy Specific functions B6 and energy ▪ Heme B6 helps condense succinyl CoA and glycine to the start heme synthesis pathway Review: ▪ What vitamins can help make succinyl CoA? ▪ How does heme connect to energy? ?? ? Specific functions B6 and synthesis ▪ Creation of neurotransmitters Which ones? What amino acids are they derived from? What type of B6-assisted reaction is common to all? What is a general function of each of these NTs? Amino acid: ? Amino acid: ? Amino acid: ? * *=? * GABA Inhibitory NT in brain. Serotonin Dopamine Review: Mechanism Specific functions B6 and synthesis ▪ Gluconeogenesis Cys to pyruvate (FYI transamination and desulfhydration) Asp to oxaloacetate (transamination) Ala to pyruvate (transamination) ▪ Part of glucose-alanine cycle, green slide = review Alanine Aspartate GNG Cysteine Pyruvate Oxaloacetate  alpha glutamate B6 KG Glucose-Alanine Cycle - To Know: - Alanine from muscle carries N to liver for urea cycle - Liver makes glucose (gluconeogenesis) to send to muscle for Remaining energy details = FYI review only with - B6 helps (not alanine- testable this term) pyruvate Oxaloaceta te transaminations alpha NH3 KG glutamate B6 Specific functions: B6 and synthesis ▪ Desaturated fatty acid: Gamma-linolenic acid production of anti- linoleic acid gamma-linolenic delta-6- inflammatory acid ▪ Cysteine desaturase, (review) B6 prostaglandins Made from homocysteine (HC) and serine + ▪ HC may be linked to increased Serine risk of cardiovascular disease FYI: Would B6 potentially Transulfhydration increase or decrease this risk? + FYI: Deficiencies Provide a rationale for the following: ▪ A spike in infant seizures in the 1950’s with the advent of formula Due to an error in the sterilization process that destroyed B6 - what the connection to seizures? ▪ Depression (hint: what NT’s might be important?) ▪ Microcytic anemia ▪ Inflammation All the info you need is in the slides!!  To know Testing from figure: Yellow and blue boxes Testing Xanthurenic ▪ Can do a tryptophan loadacid test Requires Test urine before and after PLP tryptophan load for presence of xanthurenic acid ▪ Would levels go up or down in a B6- deficiency? Why? Biotin: Vitamin B7 Objectives ∙ Relate B7 absorption, metabolism, excretion and testing to the general properties of B-vitamins ∙ Relate the biochemical function of B7 to carbohydrate metabolism (GNG), fatty acid synthesis, energy production, heme synthesis, ketone synthesis, cholesterol synthesis ∙ Describe the mechanism by which B7 (biotin) assists in blood sugar regulation (such as in diabetes) What do you already know? What type of reaction does biotin catalyze? A – Redox B – Carboxylation C – Decarboxylation What synthesis pathway below uses B7? a) Fatty acid synthesis b) Gluconeogenesis  Structure and Function Coenzyme form of biotin has a CO2 attached and is linked to its enzyme by a lysine residue (FYI: biotin attached to a lysine =“biocytin”) CO2 comes from bicarbona te, HC03- Absorption To absorb, need to remove the attached carboxylase enzyme via proteolysis ▪ Sometimes lysine is still attached ▪ Removed by biotinidases Back to Gaston… ▪ Eggs have high levels of biotin Why would Gaston’s diet of 4-5 dozen raw eggs have caused him to be biotin deficient? ▪ Why would he have been fine if he had cooked his eggs? Hint: Eggs white contain avidin, a glycoprotein that binds biotin Specific functions B7 and synthesis ▪ Gluconeogenesis Conversion of pyruvate to oxaloacetate Carboxylati on GNG Specific functions B7 and synthesis ▪ Fatty acid synthesis Review: What are the two substrates for fatty acid synthesis? What is the role of biotin? CO2 (transferred over from biotin) Enzym e name?  Specific functions B7 and energy ▪ B7 helps make succinyl CoA (from propionyl CoA) Succinyl CoA 🡪 CAC and heme synthesis CH3 CO2 from biotin Methylmalonyl CoA Propionyl CoA Succinyl CoA energ What is an energy Heme CAC y producing pathway that makes propionyl CoA? Energ  Odd-numbered fatty acyl CoA Beta ox Propiony Acetyl l CoA CoA CH 3 FYI: Also produced by catabolism Heme of various synthesi Specific functions B7 and synthesis ▪ HMG CoA (from leucine) Note the type of enzyme that uses biotin ▪ Rest of diagram is FYI only What two main synthesis pathways does HMG CoA (and therefore biotin) feed into? ? HMG ? CoA Specific functions - other Linked to increased glucokinase activity ▪ Review: What reaction does glucokinase catalyze? What happens to the product? What is the connection to blood sugar levels? Deficiencies FYI: No hallmark condition, but tend to see two types of symptoms: ▪ Neurological Ex: Lethargy, depression ▪ Dermatological Ex: Dermatitis (dry, red, scaly skin) and brittle nails Folate: Vitamin B9 Objectives Relate B9 absorption, metabolism, excretion and testing to the general properties of B- vitamins Relate the biochemical function of B9 to purine and pyrimidine synthesis, then extrapolate to roles of folate in spina bifida, anemia, and cancer Relate the biochemical function of B9 to amino acid metabolism Discuss the implications of the methyl-folate trap Relate the biochemical function of B9 to neurotransmitter synthesis, and link to a possible role in treating depression Relate the genetic polymorphisms in the MTHFR gene to the optimal type of folate supplementation What do you already know? Which best describes the overall biochemical function of folate: A – methylation B – 1-C transfer  Structure and function Coenzyme forms have: ▪ 4 H’s added: “THF” = tetrahydrofolate ▪ Multiple glu’s attached (one shown for simplicity) ▪ A 1-C group added (FYI to N10 and/or N5) Absorption and metabolism Absorption ▪ Look at the previous slide: what do you need to remove prior to absorption? These are removed by hydrolases (aka conjugases) in the small intestine Metabolism ▪ B3 adds the H’s to create the THF form What do you think the enzyme name is? ▪ Polyglu’s and a specific 1-C group are added Various B-vitamins interconvert folate coenzyme forms  To Know: 2) 1-C groups are Points 1-4 then added to the THF form. 1) NADPH helps reductase enzymes add H’s to make DHF, then THF. 4) Some THF forms help make 3) Note all the purines or B-vits involved pyrimidines in folate conversions: Absorption and metabolism Folate undergoes enterohepatic circulation, and small amounts are stored in liver on folate binding proteins (FBP) ▪ Absorption: Small intestine to gut to liver Once in liver, could be: ▪ Converted to coenzyme forms and used by liver ▪ Stored ▪ Sent to other tissues ▪ Cycled back to small intestine in the bile, another chance for absorption back to liver (enterohepatic circulation)  Liver PolyGlu Blood -Trapped. converted to coenzymes - Small Extrahepati Excret MonoGl amounts stored c Tissues ed into u on FBP bile MonoGl Bile u Blood PolyGlu duct -Trapped, converted Poly MonoG Small intestine G to coenzymes Conjuga ses Specific functions B9 and synthesis ▪ Purines and pyrimidines Required to support DNA replication ▪ Cells requiring a high rate of cell division are adversely impacted in a folate deficiency Deficiency can lead to: Spina bifida, cancer Megaloblastic anemia Folate Deficiency Decreased purine and pyrimidine synthesis Megaloblastic anemia Decreased DNA FYI: End up Spina bifida replication & with immature Failure of RBC’s that vertebral laminae Increased replication errors have to fuse during decreased O2 fetal Cancer carrying development, - How can folate help capacity exposing the prevent cervical spinal cord dysplasia from developing into cancer? Important to - Why would you not supplement with treat cancer with folate folate during supplementation? pregnancy to - Note that the Specific functions B9 and synthesis ▪ Various amino acids, including methionine from homocysteine (HC) The 1-C group (methyl) on methionine comes from methyl folate. It is passed onto HC via methyl B12. FYI: HC = cys with an extra CH2 One reason to make methionine is to make the methyl donor “SAM” (S- adenosyl-methionine)  ATP S- SAM = methyl adenosylmethionin donor e B12 Methyl is donated, products include: - Choline - Epinephrine Homocystei - Methylated ne DNA  What vitamin deficiency would cause a Methylatio “methyl folate n reactions trap”? What are the implications? More on methyl folate… It is made from methyleneTHF (MTHF) via the MTHFR enzyme (FYI: methylenetetrahydrofolate reductase) ▪ MTHFR gene is highly polymorphic This can influence MTHFR activity ▪ Reduced activity = “poor converter” What type of folate supplementation would be best? ▪ Can also have increased activity= “over converter” Specific functions: other Folate levels correlate with THB levels ▪ THB (FYI tetrahydrobiopterin) is a redox coenzyme that helps with the synthesis of dopamine and serotonin Indicates a possible role for folate deficiency in depression To Know: high levels of THF correlate with high levels of THB, THB used in serotonin Review at home: Deficiencies Review the presentation ▪ What are four conditions that a folate deficiency might contribute to? Cobalamin: Vitamin B12 FYI: Only in animal products or supplement s/ fortified foods Objectives Relate B12 absorption and metabolism to the general properties of B- vitamins Describe the role of the GIT in the absorption of B12 Relate the biochemical function of B12 to the energy production, the creation of SAM, and the activity of folate Relate B12 excretion and testing to the general properties of B- vitamins Structure and Function Called “cobal”amin due to attached cobalt ▪ FYI: Supplement forms are often either “cyano” (CN) or “hydroxo” (OH) Coenzyme forms have either an adenosyl group or methyl group in place of CN (or OH) Structure and Function Methylcobalamin coenzyme ▪ Methionine synthase reaction: transfers methyl group from methyl folate to HC Makes methionine and regenerates THF ▪ Remember: deficiency leads to methyl folate trap Adenosylcobalamin coenzyme ▪ HelpsB7 CH3 with (CO formation ) of succinyl B12 CoA from propionyl 2 Heme CoA Methylmalonyl CoA (No B12) Propionyl CoA CAC (Methylmalonic Succinyl CoA acid) - can be used to Energ Absorption and metabolism B12 from food needs to be released from proteins ▪ Done by pepsin and HCl in stomach Stomach: B12 carried by R-proteins ▪ Also found in saliva, continue to act in stomach ▪ Protect B12 from hydrolysis and bacterial use Duodenum: B12 released from R-protein and picked up by intrinsic factor (IF) ▪ IF made in stomach, acts in duodenum ▪ Carries B12 to a B12-IF receptor in ileum for absorption  B12 Absorption and metabolism Enterocytes: Uptake of B12-IF-R via Lysosome receptor-mediated endocytosis B12 IF 2 B1 ▪ Receptor is recycled IF ▪ Vesicle fuses with lysosome IF is degraded B-12 is released B12 transported from enterocytes into blood ▪ Carried to tissues bound to transcobalamin II (TCII) Tissues: Uptake via receptor mediated endocytosis Once in cell, chaperone proteins facilitate conversion to adenosyl- and methylcobalamin in the appropriate compartment Absorption and metabolism Like B9, also undergoes enterohepatic circulation and storage ▪ This time, significant amounts are stored for long periods of time Mostly as adenosyl cobalamin Main site = liver, secondary = muscle FYI: A deficiency may not show up for months or years once B12 intake stops, due to use of stored B12 Deficiency Can be caused by hypochlorhydria (more common in elderly patients) – why? Can be secondary due an IF deficiency ▪ What routes of B12 supplementation would be needed in this case, and why? Most symptoms are similar to B9 deficiency, including megalobastic anemia ▪ FYI: megaloblastic anemia due B12 deficiency = pernicious anemia Deficiency Clinical scenario: ▪ A patient with megaloblastic anemia comes to see you. You suspect either a B12 or B9 deficiency, and you decide to try folate supplementation while waiting for lab results. Turns out you picked the wrong vitamin deficiency - the labs indicate a B12 deficiency. However, your B9 supplementation alone still ended up correcting the anemia. How? B12 deficiency = methyl folate trap: can’t regenerate THF from methyl THF Need THF to ultimately feed into purine and pyrimidine synthesis. Can provide THF as a Deficiency Preview: an important deficiency symptom that B-12 does NOT share with B9 is neurological deficits ▪ Looks similar to Alzheimer’s ▪ Can take months/years to appear – why? ▪ Back to your clinical scenario: What is the danger of correcting a B12 deficiency anemia with B9? Excretion and testing Testing ▪ Blood test for B12 ▪ Other options include blood tests for the following: ▪ Homocysteine ▪ Methylmalonic acid What is the rationale for these tests - would levels of each be elevated or decreased in a B12 deficiency? Why?  CH3 B7 (CO2) B12 Methylmalonyl CoA (No B12) Propionyl CoA Methylmalonic acid Succinyl CoA CAC Hem SAM e producti on B12 Homocystei ne