Diabetes Physiology 364 Summary PDF

Diabetics Physiology 364 Disclaimer: Please note that these diabetes notes are intended to complement your own study and understanding of the topic. While the content is extensive, only definition and theory questions will be asked in the section. This material represents my personal take and summ...

Diabetics Physiology 364 Disclaimer: Please note that these diabetes notes are intended to complement your own study and understanding of the topic. While the content is extensive, only definition and theory questions will be asked in the section. This material represents my personal take and summaries on the subject and should be used as a supplementary resource. It is not intended to replace your primary study materials or guarantee a passing grade. Note: AI was consulted where information was omitted or unclear. Tests and conversions: Parameters Mechanism Advantage and limits Fasting blood - Normal: Measures the level of Advantage: glucose levels < 5.6 mmol/L glucose in the blood Simple and quick - Pre-diabetic: after an overnight fast. test. 6.0 - 6.9 mmol/L Limitations: - Diabetic: Only provides a > 7.0 mmol/L snapshot of blood (impaired fasting glucose levels. glucose [IFG] Glycosylated - Normal: < 5.7% Glucose rapidly diffuses Advantage: haemoglobin - Pre-diabetic: 5.7 – into RBCs by facilitated Reflects average (HbA1c) 6.4% diffusion. N-terminal blood glucose - Diabetic:  6.5% valine of haemoglobin levels over the alpha chain is available past 2-3 months for irreversible glycation. (RBCs live for 120 Haemoglobin (Hb) -> days). HbA1c. HbA1c level is Limitations: proportional to glucose May be affected concentration in by conditions that plasma. alter red blood cell lifespan. Oral glucose - Impaired glucose 1. Fast overnight Advantage: tolerance test tolerance (IGT) 2. Before the test Can diagnose (OGTT) (pre-diabetic): begins a sample impaired glucose 7.8 – 11mmol/L. of blood taken. tolerance and 3. Consume liquid diabetes. - Diabetic: > 11.1 with fixed Limitations: mmol/L. amount glucose Time consuming (usually 75 and requires grams) fasting and 4. Blood taken multiple blood every 30 to 60 samples. mins after this 5. Test can take up to 3 hours Conversion of glucose values: mg/dL to mmol/L This appears very confusing, but I’ll slim it down for y’all. The conversion factor 18.0182 is derived from the molecular weight of glucose.  𝑚𝑔/𝑑𝐿 × 0.0555 = 𝑚𝑚𝑜𝑙/𝐿 𝑚𝑚𝑜𝑙/𝐿 1  mg/dL = 0.055 = 0.0555 × 𝑚𝑚𝑜𝑙/𝐿  mg/dL = 18.0182 x mmol/L  Therefore, you may use the reverse formula for simplicity 𝑚𝑚𝑜𝑙/𝐿  Mg/dL = 0.0555 2 Postprandial glucose effects: Degree of postprandial glucose excursion (spike) depend on meal type (rich in carbs?). Repetitive and large excursions likely linked to cardio-metabolic disease. o Likely mediated by oxidative stress & inflammation. As can be seen here, patients with Diabetes display elevated ins glucose excursions (spikes), whilst also displaying reduced insulin levels compared to healthy patients. Insulin values usually given as IU/mL (micro international units/mL) or pmol/L To convert pmol/L values: divide it by a factor of 7.715 mean fasting level of insulin 60 pmol/L (US individuals). Review of major metabolic pathways Metabolic Process Reaction Consequence Glycogenesis Glucose → glycogen ↓ Blood glucose Glycogenolysis Glycogen → glucose ↑ Blood glucose Gluconeogenesis Amino acids → glucose ↑ Blood glucose Protein synthesis Amino acids → protein ↓ Blood amino acids Protein degradation Protein → amino acids ↑ Blood amino acids Fat synthesis (lipogenesis or Fatty acids and glycerol → ↓ Blood fatty triglyceride synthesis) triglycerides acids Fat breakdown (lipolysis or Triglycerides → fatty acids ↑ Blood fatty triglyceride degradation) and glycerol acids 3 Recap of insulin & glucagon Insulin is secreted in a biphasic manner Insulin is secreted in an acute first phase, lasting a few minutes, followed by a sustained, lower amplitude/intensity, second phase, which persists for the duration of high-glucose stimulation Why? First phase – rapid & within a few mins; due to readily releasable pool insulin-containing granules at plasma membrane Second phase – takes a little longer as need to synthesize new insulin-containing granules Basically, you are spending your whole savings on a night out at Aandklas, and now you must wait a whole month for your parents to send you half of your original savings back JK 4 Regulation of insulin secretion 5 First phase release of readily available pool of insulin: 6 Effects of insulin on target tissues Glucose Glucose Triglycerides → fatty acids & monoglycerid es Glucose Amino acids 7 Type 1 diabetes type 1 diabetes accounts for a minority of diabetes cases. Diagnosed within first two decades of life, peak at 10-14 years Pathogenesis model The pathogenesis of type 1 diabetes is multifactorial. It involves a combination of genetic, environmental, and immunological factors: 1. Genetic → HLA Region on Chromosome 6: This region is crucial in the development of type 1 diabetes. → HLA Class II Genes: These genes are major genetic contributors. Examples include DR3 and DR4 haplotypes (a group of genes inherited together from a single parent). However, only 30-50% of type 1 diabetes patients have these haplotypes. → Autoantibodies: The most common autoantibodies in type 1 diabetes target the 65 kDa isoform of glutamic acid decarboxylase (GAD65). → Other Genetic Factors: There are lesser genetic predispositions, such as the insulin gene region and the interleukin-2 receptor-α gene. 2. Environmental → Gut Microbiota and Immune System: Most environmental factors influence gut microbiota, which closely interacts with the immune system and can reshape it. i. Increased Gut Permeability: This can allow potentially diabetogenic antigens to pass through, leading to islet-directed autoimmunity. → Enteroviruses: These are prime candidates, especially coxsackieviruses, for triggering type 1 diabetes. → Rubella: Despite being eliminated in wealthy countries, the incidence of type 1 diabetes is still rising. → Disturbed Microbial Balance: An imbalance in the gut microbiota can contribute to the development of type 1 diabetes. → Cow’s Milk: The albumin component in cow’s milk is thought to trigger an immune response if introduced early in life. → Lack of Clear Evidence: There is still no definitive proof of a cause-and-effect relationship. 3. Active autoimmunity → Autoantibody appearance (IAA, GADA, ICA512A, ICA) 4. Immune abnormality and loss of insulin secretion → Loss of first phase of insulin response → Glucose intolerance 5. Overt diabetes with few remaining pancreatic -cells 8 Complete loss of pancreatic -cells → Loss of C peptide (observed) Linear beta-cell hypothesis (refer to above): Referred to as Linear beta-cell decline hypothesis – Eisenbarth (1986) The quantity of autoantibodies is more important than type in disease progression With high genetic risk, environmental triggers play a lesser role, as β-cell mass decreases regardless. Alternate models: pathogenesis of type 1 diabetes 1. Genetic Predisposition and Trigger Event: Individuals with a genetic predisposition experience a trigger event (e.g., infection) that causes inflammation and upregulation of MHC-I (Major Histocompatibility Complex class I) molecules. o Autoantibodies: These appear in the bloodstream, but blood glucose levels remain normal initially. 2. T-Cell Proliferation and Infiltration: T-cells (a type of immune cell) proliferate and infiltrate the pancreatic beta cells. o Waves of Destruction and Survival: This leads to alternating periods of beta- cell destruction and survival. 3. Rapid Beta-Cell Destruction: Immune cells infiltrate the pancreas and rapidly destroy beta cells, reducing their mass. 4. Post-Translational Modifications: These modifications activate cytotoxic T-cells (immune cells that kill infected or damaged cells), leading to further beta-cell destruction. o Insulitis: Significant inflammation of the islets (clusters of pancreatic cells) occurs, known as insulitis. Comparison with the Linear Beta-Cell Decline Hypothesis: The alternate model describes a more dynamic process with waves of beta-cell destruction and survival, influenced by immune responses and environmental triggers. In contrast, the linear beta-cell decline hypothesis suggests a steady, continuous decline in beta-cell function and mass over time, without the fluctuating periods of destruction and survival. Vs. 9 Metabolic effects of type 1 diabetes 1. Starvation in the Midst of Plenty: Despite high plasma glucose levels, tissues have low glucose availability. 2. Hormonal Imbalance: Low insulin and high glucagon levels lead to predominance of glucagon and catabolic effects. 3. Increased Breakdown: This hormonal imbalance causes increased breakdown of carbohydrates, proteins, and fats, resulting in: o Hyperglycemia: High blood sugar levels. o Hypertriglyceridemia: High levels of triglycerides in the blood. o Ketoacidosis: High levels of ketones, leading to acidic blood. o Dehydration: Loss of fluids due to high blood sugar levels. 4. Causes of Hyperglycemia: Hyperglycemia is caused by: o Decreased glucose uptake by tissues. o Increased glycogenolysis (breakdown of glycogen to glucose). o Increased gluconeogenesis (production of glucose from non-carbohydrate sources). Medical Outcomes: ↑ breakdown of muscle protein → ↑ tissue loss. Increased glucose absorption by the kidneys, resulting in excess glucose in urine. o Osmotic diuresis (increased urination), causing dehydration and thirst → Decreased blood pressure → circulatory failure ↑ ketone bodies → Metabolic acidosis. ↑Lipolysis → leading to further tissue loss. 10 Clinical symptoms The 3 Ps o Polyuria – frequent urination o Polydipsia – increased thirst o Polyphagia – increased hunger Ketoacidosis Wight loss, fatigue, nausea, vomiting Testing/Screening 1. Genetic Screening: Check for HLA loci and family history of type 1 diabetes. 2. Autoantibody Screening: Test for autoantibodies, which can fluctuate and even disappear over time. 3. Autoreactive T-Cells: Presence of these T-cells is not routinely assessed due to a lack of robust (tests) assays. 4. Beta-Cell Mass Assessment: Use in vivo tools to improve assessment. Antibodies that bind to beta-cell surfaces can be detected using imaging techniques. 5. Plasma Glucose and C-Peptide Values: Measure these values to assess beta-cell function and glucose metabolism. Treatment 1. Daily insulin injections: rapid-acting, long-acting insulin analogues 2. Regular monitoring of glucose levels 3. Closed-loop system (‘’artificial pancreas’’): continuous glucose monitors + insulin pumps used together 4. Islet transplantation: 2/3 recipients enjoyed insulin independence for 1 year, however long term reverts back to decrease beta cell mass 5. Stem cells: Donor → Adipose Tissue (fat tissue) → Grow MSCs (Mesenchymal Stem Cells) in Culture → Alter Culturing Conditions → MSCs Produce Pancreatic Hormones Primary Prevention Target Group: Individuals with genetic risk but no autoantibodies. Strategy: Dietary modifications early in infancy (e.g., using different baby formula). Outcome: Infants on modified formula are less likely to develop autoantibodies compared to those on conventional formula. 11 Secondary Prevention Target Group: Individuals with multiple autoantibodies but without hyperglycemia. Strategy: Insulin treatment. Outcome: Delays diabetes onset by about 5 years in individuals with elevated autoantibodies. Reversal of Pancreatic Cell Destruction Current Efforts: Focus on limiting immune-mediated damage using single immunosuppressant agents. Outcome: No significant results achieved so far. Two types of Diabetes Type 1 Type 2 Insulin deficient: Insulin resistant: Lack of insulin produced by pancreas Target Cells resistant to influence of insulin Type 2 diabetes Compromied β-cell function Insulin resistance (later during disease progression) Impaires: Insulin secretion -peripheral glucose insufficeit to counter uptake insulin resistance -glucose output by liver 12 Pathogenesis 1. Normal glucose tolerance (NGT): Fasting plasma glucose in normal range, insulin levels rise, due to β-cell compensation. 2. Impaired glucose tolerance (IGT)/impaired fasting glucose (IFG): Patient’s fasting plasma glucose or post oral glucose tolerance test (OGTT) is elevated. Hyperinsulinemia due to β-cell compensation. 3. Type 2 diabetes (T2DM) Fasting plasma glucose elevated, insulin levels are decreased due to β-cell dysfunction. 13 Causes and risk factors: Modifiable: Unmodifiable: Physical activity Ethnicity Sugar intake Age Decreased sleep Low birth weight High fat, low fibre diets History of diabetes (Gestational diabetes, which occurs during pregnancy and usually subsides thereafter). Obesity Family history o Accounts for 80-85% of overall o No single gene is responsible risk of developing type 2 diabetes for susceptibility to T2D o Weight loss greatly improves o It is considered Polygenic patient’s condition o Genes often involved in controlling insulin secretion & action, β-cell proliferation. Energy intake – expenditure = weight gain 1. High intake - low expenditure = weight gain 2. Low intake - high expenditure = negative energy balance ↓ weight 3. Intake = expenditure = constant weight (neutral energy balance) 14  Food intake summarized ↑ blood glucose Body stores fat (adipocytes) Which stimulates Adipocytes secrete ↑ insulin in leptin bloodstream Meal intake NPY-secreting neurons POMC-secreting neurons Ghrelin – released from stomach before meal Neuropeptide Y Melanocortins PYY3-36 released from intestines during meal LHA neurons PVN neurons Orexins Corticotropic releasing hormone Legend ↓ Appetite & food - Stimulates intake - Inhibits - Secretes/ leads to Pathway inhibited (would have worked) 15 Leptin signalling disturbance and obesity: Obese individuals → present with hyperleptinemia o Due to leptin resistance o ↑Fat stores → ↑leptin output → leptin binding faulty o Manifests in hyperphagia (overeating) Genetics o db/db – leptin receptor knockout o ob/ob – leptin deficiency mutation Possible mechanisms of leptin resistance & hyperleptinemia: 1. Circulating Regulators: Factors like serum leptin-binding proteins (SLIPs) can affect the availability of leptin in the bloodstream. 2. Self-Regulation: Leptin itself can induce receptor inhibition, which means that high levels of leptin can lead to a decrease in the sensitivity of leptin receptors. 3. Cellular Signalling Intermediates: Various signalling intermediates within cells can influence how leptin signals are processed. 4. Genetic Variations: Genetic factors, such as mutations in the ob (leptin) or db (leptin receptor) genes, can contribute to leptin resistance. 5. Limited Tissue Access: Issues like saturated CNS (central nervous system) transport can limit leptin’s ability to reach its target tissues effectively. Dietary trans fatty acid consumption - Incremental dietary intake of TFA associated with greater incidence of heart diseases - Link with diabetes less well established & more likely if predisposed (e.g. insulin resistance) or gender-related (women) 16 Excess lipid levels and muscle insulin resistance Under normal physiological conditions: 1. Insulin Binding: Insulin binds to its receptor on the cell membrane. 2. Tyrosine Phosphorylation: This binding triggers the receptor to undergo tyrosine phosphorylation (P- Tyr). 3. IRS-1 Activation: The phosphorylated receptor activates IRS-1 (Insulin Receptor Substrate 1). 4. PI3 Kinase Activation: Activated IRS-1 then activates PI3 kinase. 5. Akt Activation: PI3 kinase activation leads to the activation of Akt, a protein kinase. 6. GLUT4 Vesicle Translocation: Akt facilitates the translocation of GLUT4 vesicles to the cell membrane (sarcolemma). 7. Glucose Uptake: GLUT4 vesicles merge with the membrane, allowing glucose to enter the cell. 17 During high (trans) fat intake 1. High Trans Fat Intake: Consuming a diet high in trans fats leads to an increase in adipose (fat) tissue mass and size. Trans fats are particularly harmful because they can disrupt normal lipid metabolism. 2. Increased Adipose Mass and Size: As adipose tissue expands; it releases more free fatty acids (FFAs) into the bloodstream. This is a key step in the development of insulin resistance. 3. Free Fatty Acid Release: Elevated levels of FFAs in the bloodstream can overwhelm the body’s ability to oxidize these fats. This imbalance leads to a situation where fatty acid uptake by cells exceeds their oxidation. 4. Accumulation of Long-Chain Fatty Acids in Cytosol: When fatty acids accumulate in the cytosol (the fluid part of the cell), they can inhibit mitochondrial fatty acid oxidation. This is because the transport of fatty acids into the mitochondria is impaired, and enzymes involved in oxidation are less active. 5. Decreased Mitochondrial Fatty Acid Oxidation: Reduced oxidation of fatty acids in the mitochondria leads to further accumulation of lipids within cells. This lipid accumulation can interfere with insulin signalling pathways, particularly by promoting the phosphorylation of serine residues on insulin receptor substrate-1 (IRS-1), which impairs insulin action. 18 The image above illustrates the molecular mechanisms behind insulin resistance, which results from increased free fatty acid levels/trans fats: 1. IRS-1 Phosphorylation: In the presence of high levels of FFAs and trans fats, IRS-1 gets phosphorylated on serine residues instead (P-Ser), leading to its inactivation. 2. Inactivation of PI3 Kinase and Akt: Inactive IRS-1 cannot activate PI3 kinase, which in turn leads to inactive Akt. Akt is crucial for the translocation of GLUT4 vesicles to the sarcolemma (cell membrane). 3. Reduced GLUT4 Translocation: Without active Akt, GLUT4 vesicles do not move to the cell membrane, resulting in reduced glucose uptake by cells. 4. Outcome: This entire process leads to reduced glucose uptake, contributing to elevated blood glucose levels and insulin resistance, hallmark features of T2DM. Inflammation leads to development of insulin resistance, mediated by TNFα’s inhibition of AMPK: Obesity/high fat diet → ↑Free fatty acids → Pro-inflammatory state → ↑ TNFα secretion from adipose tissue, inhibits AMPK → ↓AMPK activity (acts as an energy sensor and regulator) → Insulin resistance. Remember from your cancer block AMPK detects a Low energy status in the cell (↑AMP: ATP), leading to upregulation of the Energy producing pathways = glucose + lipid oxidation AMPK enhances glucose oxidation by promoting increased GLUT4 translocation. o AMPK can activate GLUT4 translocation independently of insulin signalling cascade AMPK promotes mitochondrial fatty acid uptake & oxidation o AMPK promotes fatty acid uptake and oxidation by inhibiting ACC, which reduces Malonyl-CoA levels, thereby allowing CPT-1 to transport fatty acids into the mitochondrion for oxidation and ATP production. 19 But TNFα secretion due to a hyper-inflammatory microenvironment as seen in obesity causes the following: 20 Hepatic glucose output during insulin resistance Key Components and Pathways: 1. Diacylglycerol Pathway: o Diacylglycerol: This molecule engages in the pathway leading to glycogen synthesis. o Enzymes: PI3K, Akt2, and GSK3β are key enzymes in this pathway. o Outcome: This pathway ultimately leads to the synthesis of glycogen, a storage form of glucose. 2. Triglyceride Pathway: o Triglycerides: Stored in adipocytes (fat cells) and broken down into Free Fatty Acids (FFAs) and Glycerol. o Gluconeogenesis: Glycerol is used in the liver to produce glucose through a process called gluconeogenesis. Effects of Insulin Resistance: Decreased PI3K Activity: In the liver and muscles, leading to impaired glucose uptake. Increased FOXO-1 Activity: This transcription factor increases the production of enzymes involved in gluconeogenesis, leading to higher glucose production. Decreased Glycogen Synthesis: Due to decreased phosphorylation of GSK3β, which is necessary for glycogen synthesis. Consequences: Increased Gluconeogenesis: More glucose is produced from glycerol. Decreased Glucose Export: Impaired GLUT2-dependent transport reduces glucose export into the bloodstream. Hyperglycemia: High blood sugar levels result from decreased glycogen synthesis and increased gluconeogenesis. 21 Summary: 1. Adipocytes store triglycerides, which are broken down into FFAs and glycerol. 2. Insulin Resistance leads to increased gluconeogenesis and decreased glycogen synthesis, contributing to hyperglycemia. Glycaemic index & risk for type 2 diabetes Glycaemic index (GI) of carbohydrate-containing food refers to the post-prandial glucose response over 2 h vs. a reference food with same amount of carbohydrate Glycaemic load (GL) – amount (serving size) & quality of carbs GL = (grams of carbs X GI)/100 High GI diets linked to higher risk for type 2 diabetes & heart disease vs. low GI (e.g. Mediterranean diet) From the test done above we can deduce that the reduction of Carbohydrates from one’s diet decreases glycosylated haemoglobin levels (refer to white column), as well as reduce the risk of CVD. 22 Mechanisms of high glucose-induced myocardial insulin resistance Oxidative stress implicated In this diagram we observe an increase in Nitrotyrosine (an oxidative stress marker) post-prandially after consuming 75 g of glucose. Here we also see an increase in fluorescent intensity of both intracellular and mitochondrial ROS during hyperglycemia. 23  Here I want you to focus on what is circled in blue: We see during high glucose consumption (25 mM) the administration of antioxidants (4-OHCA and DPI) increase the uptake of glucose, compared to no administration of antioxidants (see orange circle). 24  Generation of mitochondrial superoxide with hyperglycemia Step-by-Step Explanation: 1. Hyperglycemia: o High blood glucose levels lead to an excess of reducing equivalents, specifically NADH and FADH2. 2. Entry into Mitochondrial Electron Transport Chain: o These reducing equivalents enter the mitochondrial electron transport chain at complexes I (NADH) and II (FADH2). 3. Electron Transfer: o Normally, electrons are transferred through complexes III and IV, where complex IV reduces molecular oxygen (O2) to water (H2O). 4. Increased Proton Gradient: o Due to the excess reducing equivalents from hyperglycemia, there is an increased proton gradient across the mitochondrial membrane (ΔμH+). 5. Electron bottleneck: o The increased proton gradient causes a “bottleneck” of electrons within complex III. 6. Superoxide Formation: o Some electrons prematurely react with molecular oxygen, forming superoxide (O2-), a type of reactive oxygen species (ROS). 7. Oxidative Stress: o The accumulation of superoxide contributes to oxidative stress, damaging cellular components and impairing normal cellular functions. 25 Mechanisms of high glucose-induced myocardial insulin resistance – non oxidative glucose pathways (NOGPs) The image illustrates the mechanisms of high glucose-induced myocardial insulin resistance, focusing on non-oxidative glucose pathways (NOGPs): 1. Hyperglycemia and Oxidative Stress: High glucose levels and oxidative stress upregulate NOGPs. 2. Glucose Conversion: Glucose is converted to Glucose-6-Phosphate (Glucose-6P). Glucose-6P is then converted to Fructose-6-Phosphate (Fructose-6P). Conversion of Fructose-6-Phosphate to Glyceraldehyde-3-Phosphate 3. Pyruvate: Formation of Reactive Oxygen Species (ROS) from Excess Pyruvate 4. Mitochondrial Entry: Excess pyruvate enters the mitochondria and is converted to acetyl-CoA by the pyruvate dehydrogenase complex. 5. ROS-Induced PARP Activation and GAPDH Inhibition 6. PARP Activation: ROS cause DNA damage, activating poly (ADP-ribose) polymerase (PARP). 7. Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) Inhibition: An enzyme in glycolysis that converts glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, requiring NAD+ for its activity. Activated PARP consumes NAD+ to repair DNA, depleting cellular NAD+ levels. This inhibits GAPDH, as it requires NAD+ for its activity. 8. Upregulation of Non-Oxidative Glucose Pathways (NOGPs) 9. Glycolytic Blockage: Inhibition of GAPDH causes an accumulation of upstream glycolytic intermediates like G3P and F6P. 10. NOGP Flux: 26  The accumulation of these intermediates diverts glucose metabolism into alternative pathways such as the pentose phosphate pathway (PPP), polyol pathway, and hexosamine biosynthetic pathway (HBP), collectively known as NOGPs. Inhibiting one non-oxidative glucose pathway (NOGP) does not necessarily prevent the activation of other NOGPs. Each pathway can be independently regulated and may still be active even if one is inhibited. This is evident from the image, which shows different inhibitors (AMG, CHE, DON, ZOP) affecting various pathways (Polyol, PKC, HBP) and their differential involvement in insulin resistance. 27 Hexosamine biosynthetic pathway (HBP) – role in the aetiology of insulin resistance Hexosamine Biosynthetic Pathway (HBP) and Insulin Resistance 1. Pathway Overview: o Fructose-6-Phosphate is converted to Glucosamine-6-Phosphate by the enzyme Glutamine: Fructose-6-Phosphate Aminotransferase (GFAT). o Glucosamine-6-Phosphate is further converted to UDP-N-acetylglucosamine (UDP-GlcNAc). 2. Protein Modification: o UDP-GlcNAc is a substrate for O-GlcNAc transferase (OGT), which adds O-GlcNAc to serine and threonine residues on proteins. o This process, known as O-GlcNAcylation, modifies various proteins, including those involved in insulin signalling. 3. Impact on Insulin Signalling: o Excessive O-GlcNAcylation can impair the function of key insulin signalling proteins such as Akt. o Akt is crucial for glucose uptake in cells. When its function is impaired, cells become less responsive to insulin, leading to insulin resistance. 4. Hyperglycemia and HBP Flux: o Elevated glucose levels (hyperglycemia) increase the flux through the HBP. o This results in higher levels of UDP-GlcNAc and increased O-GlcNAcylation of proteins, further contributing to insulin resistance. 5. Clinical Implications: o Understanding the role of HBP in insulin resistance helps in identifying potential therapeutic targets. o Inhibitors of GFAT or OGT could potentially reduce excessive O-GlcNAcylation and improve insulin sensitivity. 28 1. Obesity and Insulin Resistance: Obesity, often due to overnutrition and inactivity, leads to increased insulin resistance. 2. β-cell Response: To counteract this resistance, pancreatic β-cells increase in mass and enhance insulin biosynthesis to maintain normal glucose tolerance (NGT). 3. Genetic Factors, Metabolites, and Incretins: These elements also play a role in influencing β-cell compensation. Metabolites and incretins specifically upregulating insulin secretion and β-cell function. 29  1. Overnutrition/Inactivity: Leads to obesity. 2. Increased Free Fatty Acid (FFA) Levels: Obesity causes higher levels of FFAs. 3. Lipotoxicity and Glucotoxicity: High FFA levels lead to toxic effects on β-cells, known as Lipotoxicity and glucotoxicity. 4. Oxidative Stress, Apoptosis, and Inflammation: These toxic effects cause oxidative stress, cell death (apoptosis), and inflammation in β-cells. 5. Decreased β-cell Mass and Function: The cumulative damage reduces the number and function of β- cells. 6. Insulin Deficiency: As β-cells are exhausted, insulin production decreases, leading to insulin deficiency. The note “Later event? = maladaptive” suggests that these changes can lead to further adverse events if not managed properly. 30 Glucolipotoxicity contributes to β-cell dysfunction. Here’s a detailed breakdown: 1. Glucolipotoxicity: This term refers to the combined harmful effects of high glucose (hyperglycemia) and high lipid levels (hyperlipidaemia) on β-cells. 2. Increased Metabolism and Mitochondrial Respiration: Glucolipotoxicity leads to higher rates of metabolism and mitochondrial activity. 3. Upregulation of UCP-2: This increased activity upregulates Uncoupling Protein 2 (UCP-2), which decreases ATP production. 4. KATP Channel Remains Open: Due to decreased ATP, the KATP channel stays open, preventing the calcium channel from opening. 5. Inhibited Insulin Release: With the calcium channel closed, insulin release is inhibited. 6. Increased ROS Production: The heightened metabolism also increases reactive oxygen species (ROS) production. 7. Oxidative Stress and DNA Damage: ROS leads to oxidative stress, causing DNA damage. 8. Apoptosis: This damage results in apoptosis (cell death), reducing β-cell mass. 9. Decreased Insulin Gene Expression: The overall effect is a decrease in insulin gene expression and insulin release. 31 Some hallmarks of β-cell dysfunction Decreased C peptide o C-peptide and insulin are secreted in equal amounts (equimolar) because they are both derived from the same precursor molecule, proinsulin. When proinsulin is split, it produces one molecule of insulin and one molecule of C-peptide. o The absence of C-peptide indicates a loss of beta cells in the pancreas, as these cells are responsible for producing both insulin and C-peptide. Without functional beta cells, neither insulin nor C-peptide can be produced. Dysregulated biphasic response to glucose o ↓ 1st & 2nd phase release in individuals with IFG o Absent 1st phase & ↓2nd phase release in type 2 diabetic individuals Complications associated with T2DM – cardiovascular disease Increased incidence of myocardial infarction (heart attack) in people with diabetes. Increased blood glucose (even without the onset of diabetes) increased the risk of mortality from myocardial infarction. Damaging effects of hyperglycemia on the cardiovascular system. o Increased Blood Pressure: Hyperglycemia can lead to elevated blood pressure. o Oxidative Stress: High blood sugar levels increase oxidative stress, damaging cells. o Apoptosis: This stress can cause cell death (apoptosis). o Vascular Inflammation: Hyperglycemia induces inflammation in blood vessels. o Endothelial Dysfunction: The inner lining of blood vessels (endothelium) becomes dysfunctional. o Thrombosis: There’s an increased risk of blood clots. o Reduced Collateral Blood Flow: Blood flow through smaller vessels is diminished. o Increased Infarct Size: The size of tissue damage due to lack of blood supply (infarct) is larger. Heart contractile function is reduced under high glucose conditions in rats. Oxidative stress mediates rat myocardial damage with hyperglycemia. Oxidative Stress and Hexosamine Biosynthetic Pathway (HBP) Activity: 32  o Mechanism: Hyperglycemia increases oxidative stress and HBP flux, leading to O-GlcNAc modification of the apoptotic protein BAD. This modification, mediated by reactive oxygen species (ROS), results in increased cardiomyocyte apoptosis. o Inhibitors and Activators: ▪ DON: An inhibitor of the HBP, which can reduce the production of UDP-GlcNAc. ▪ PUGNAc: Inhibits O-GlcNAcase, leading to increased O-GlcNAcylation of proteins. ▪ 4-OHCA: An antioxidant that can reduce oxidative stress by neutralizing ROS. Fat Accumulation in the Heart (Lipotoxicity): o Study Findings: There is a positive correlation between body mass index (BMI) and fat accumulation in the heart. o Research Details: ▪ McGavock et al. (2006): Found a correlation between BMI and heart fat accumulation. ▪ Heart Failure Patients: Study included 27 heart failure patients, categorized into obese (HF + O) and diabetic (HF + DM) groups. ▪ Methodology: Heart tissue biopsies were stained for lipids using Oil Red O, comparing Zucker Diabetic Fatty (ZDF) rats with Zucker Lean (ZL) rats. 33 Therapeutic target: Drug Class Effect on Insulin Secretion/Action Mechanism of action Sulfonylureas & Meglitinides Stimulate insulin secretion Close beta cell KATP channels and depolarize the β-cell to secrete insulin -Glucosidase inhibitors Decrease intestinal glucose uptake Block intestinal enzymes that digest complex- carbohydrates Biguanides (e.g., metformin) Reduce plasma glucose by decreasing hepatic Increase tissue sensitivity to insulin gluconeogenesis PPAR activators (‘glitazones’) Increase gene transcription for proteins that promote Activate PPAR, nuclear receptor activator glucose utilization and fatty acid metabolism Amylin analogues (pramlintide) Reduce plasma glucose Delay gastric emptying, suppress glucagon secretion, and promote satiety Incretin (GLP-1) analogues Reduce plasma glucose and induce weight loss Stimulate insulin secretion, reduce glucagon secretion, (exendin-4) delay gastric emptying, and promote satiety. DPP-4 inhibitors (e.g., Increase insulin secretion and decrease gastric emptying Inhibit dipeptidyl peptidase-5, which breaks down GLP-1 sitagliptin) and GIP. Sodium-glucose co-transporter inhibitors (SGLT2i) 34 Sulfonylureas & Meglitinides 1. Binding to Beta Cells: Both drugs bind to specific receptors on the beta cells in the pancreas. 2. Closure of Potassium Channels: This binding causes the ATP-sensitive potassium channels to close. 3. Cell Depolarization: The closure of these channels leads to the depolarization of the cell membrane. 4. Opening of Calcium Channels: Depolarization opens voltage-gated calcium channels. 5. Calcium Influx: Calcium ions enter the cell, increasing intracellular calcium levels. 6. Insulin Release: The rise in calcium triggers the exocytosis of insulin-containing vesicles, releasing insulin into the bloodstream. 35 α-Glucosidase Inhibitors 1. Inhibition of Enzyme Activity: These drugs inhibit the enzyme α-glucosidase, which is located in the brush border of the small intestine. 2. Slowing Carbohydrate Breakdown: By inhibiting this enzyme, they slow down the breakdown of complex carbohydrates into simple sugars (glucose). 3. Reduced Glucose Absorption: This results in a slower absorption of glucose into the bloodstream. 4. Lower Postprandial Blood Sugar Levels: Consequently, this helps to reduce the rise in blood sugar levels after meals. 36 Biguanides, specifically metformin. 1. Activation of AMPK: Metformin activates AMP-activated protein kinase (AMPK), an enzyme that plays a crucial role in cellular energy homeostasis. 2. Decreased Gluconeogenesis: It reduces the production of glucose in the liver by inhibiting gluconeogenesis. 3. Increased Insulin Sensitivity: Metformin improves insulin sensitivity, allowing cells to better utilize the insulin that is available. 4. Enhanced Glucose Uptake: It increases glucose uptake in muscle and fat tissues. 5. Reduced Intestinal Absorption: Metformin decreases the absorption of glucose from the intestines. Main Sites of Action of Metformin 1. Intestine: o Increased Anaerobic Metabolism: Metformin increases anaerobic glucose metabolism in the intestines, leading to higher lactate production. o Increased Glucose Turnover: This helps in reducing the amount of glucose absorbed from the intestines. 2. Liver: o Decreased Gluconeogenesis: Metformin inhibits gluconeogenesis, which is the process of producing glucose from non-carbohydrate sources. This reduces the amount of glucose released into the bloodstream. o Decreased Glycogenolysis: It also reduces glycogenolysis, the breakdown of glycogen into glucose. 3. Muscle: o Increased Glucose Uptake: Metformin enhances the uptake of glucose into muscle cells. o Increased Glycogen Synthesis: It promotes glycogenesis, the process of converting glucose into glycogen for storage. o Increased Fatty Acid Oxidation: Metformin increases the oxidation of fatty acids in muscle cells, which helps in reducing insulin resistance. Overall Effect 37 These actions collectively help in lowering blood glucose levels and improving insulin sensitivity, making Metformin an effective treatment for managing type 2 diabetes. PPAR activators (‘glitazones’) Mechanisms of Action 1. PPARγ Activation: o Induction of Target Genes: Glitazones bind to PPARγ receptors in adipocytes (fat cells), leading to the induction of specific genes. o Increased Fatty Acid Uptake: This results in increased uptake of fatty acids into adipocytes. o Reduced Lipolysis: There is a reduction in the breakdown of fats (lipolysis). 2. Reduction in Plasma Free Fatty Acids: o Lower Free Fatty Acid Levels: By increasing fatty acid uptake and reducing lipolysis, plasma free fatty acid levels are decreased. o Blunted Harmful Effects: This reduction helps to mitigate harmful effects such as lipid accumulation and impaired insulin-mediated glucose uptake. 3. Activation of AMPK: o Enhanced Glucose Uptake and Metabolism: PPARγ ligands, such as troglitazone, can activate AMP-activated protein kinase (AMPK), leading to enhanced glucose uptake and metabolism. o Increased Fatty Acid Oxidation: AMPK activation also increases fatty acid oxidation, contributing to improved insulin sensitivity. AMPK Mechanisms 1. GLUT4 Translocation: o To Sarcolemma: AMPK activation promotes the translocation of GLUT4 (glucose transporter type 4) to the cell membrane (sarcolemma), facilitating glucose uptake into cells. 2. Inhibition of ACC: o Less Malonyl-CoA: AMPK inhibits acetyl-CoA carboxylase (ACC), leading to decreased levels of malonyl-CoA. o CPT1 Activation: This results in the activation of carnitine palmitoyltransferase 1 (CPT1), enhancing mitochondrial fatty acid uptake and oxidation. 38 Overall Effect These mechanisms collectively lead to improved insulin sensitivity, making glitazones effective in managing conditions like type 2 diabetes by enhancing glucose uptake and reducing lipid-related complications. PPAR activators (‘glitazones’) continued… 39 Amylin analogues (pramlintide) Mechanisms of Action 1. Co-Secretion with Insulin: o Amylin is co-secreted with insulin by pancreatic beta cells in response to meals. 2. Delayed Gastric Emptying: o Pramlintide slows down the rate at which food leaves the stomach, which helps to prevent rapid spikes in blood sugar levels after meals. 3. Reduced Glucagon Secretion: o It decreases the secretion of glucagon, a hormone that signals the liver to release glucose into the bloodstream. This helps to prevent postprandial (after meal) hyperglycemia. 4. Increased Satiety: o Pramlintide promotes a feeling of fullness, which can help reduce overall food intake and assist with weight management. Overall Effects Improved Glycaemic Control: By slowing gastric emptying, reducing glucagon secretion, and increasing satiety, pramlintide helps to smooth out blood sugar levels and improve overall glycaemic control. Weight Management: The increased feeling of fullness can help with weight management, which is beneficial for people with diabetes. 40 GLP-1 analogues and DPP-4 inhibitors: GLP-1 Analogues 1. Stimulation of Insulin Secretion: GLP-1 analogues enhance glucose-dependent insulin secretion from the pancreas. 2. Inhibition of Glucagon Release: They suppress glucagon secretion, which helps to lower blood glucose levels. 3. Slowing Gastric Emptying: These drugs slow down gastric emptying, which helps to prevent rapid spikes in blood sugar after meals. 4. Increased Satiety: GLP-1 analogues promote a feeling of fullness, which can help with weight management. 5. Cardiovascular Benefits: Some GLP-1 analogues have been shown to provide cardiovascular benefits. DPP-4 Inhibitors 1. Prolongation of GLP-1 Activity: DPP-4 inhibitors prevent the breakdown of GLP-1 by inhibiting the enzyme dipeptidyl peptidase-4 (DPP-4), thereby prolonging the action of endogenous GLP-1. 2. Enhanced Insulin Secretion: By increasing the levels of GLP-1, DPP-4 inhibitors enhance glucose-dependent insulin secretion. 3. Reduced Glucagon Secretion: They also help to reduce glucagon levels, which aids in lowering blood glucose. 4. Neutral Effect on Weight: Unlike GLP-1 analogues, DPP-4 inhibitors generally do not have a significant impact on weight. Shared Effects Improved Glycaemic Control: Both classes of drugs help to improve overall glycaemic control by enhancing the incretin effect. Lower Risk of Hypoglycemia: Since their actions are glucose-dependent, they have a lower risk of causing hypoglycemia compared to some other diabetes medications. 41 Sodium-glucose co-transporter inhibitors (SGLT2i) Sodium-glucose co-transporter inhibitors (SGLT2 inhibitors or SGLT2i) are a class of medications used to manage type 2 diabetes by targeting the kidneys. Here’s a summary of their mechanisms and effects: Mechanisms of Action 1. Inhibition of SGLT2: o SGLT2 inhibitors block the sodium-glucose co-transporter 2 (SGLT2) in the proximal tubules of the kidneys. o This prevents the reabsorption of glucose and sodium back into the bloodstream. 2. Increased Urinary Glucose Excretion: o By blocking glucose reabsorption, SGLT2 inhibitors increase the excretion of glucose in the urine. o This helps to lower blood glucose levels. Effects 1. Reduced Plasma Glucose: o The primary effect is a reduction in blood glucose levels, which helps in managing hyperglycemia in type 2 diabetes. 2. Weight Loss: o The excretion of glucose in the urine leads to a loss of calories, which can contribute to weight loss. 3. Lower Blood Pressure: o SGLT2 inhibitors also promote natriuresis (excretion of sodium in the urine), which can help to lower blood pressure. 4. Reduced Uric Acid Levels: o These medications can lower plasma uric acid levels, which may be beneficial for patients with gout. 5. Improved Cardiovascular and Renal Outcomes: 42  o SGLT2 inhibitors have been shown to provide cardiovascular benefits and protect against kidney disease progression in patients with type 2 diabetes. Contraindications & side effects Contraindications & Side Effects 1. Metformin (Biguanides) 4. GLP-1 Analogues o Contraindications: Renal impairment, liver disease, heart o Contraindications: Personal or family history of medullary failure, severe infection, dehydration, metabolic acidosis. thyroid carcinoma, multiple endocrine neoplasia syndrome type 2. o Side Effects: Gastrointestinal issues (nausea, diarrhoea), lactic acidosis (rare but serious). o Side Effects: Nausea, vomiting, diarrhoea, pancreatitis, potential risk of thyroid tumours. 2. PPARγ Activators (Glitazones) 5. DPP-4 Inhibitors o Contraindications: Heart failure, liver disease, bladder cancer. o Contraindications: History of pancreatitis. o Side Effects: Weight gain, oedema, increased risk of heart o Side Effects: Nasopharyngitis, headache, pancreatitis (rare), failure, bone fractures. joint pain. 3. Amylin Analogues (Pramlintide) 6. SGLT2 Inhibitors o Contraindications: Gastroparesis, hypoglycemia o Contraindications: Severe renal impairment, end-stage renal unawareness. disease, dialysis. o Side Effects: Nausea, hypoglycemia (especially when used o Side Effects: Urinary tract infections, genital infections, with insulin), headache. dehydration, ketoacidosis (rare), increased risk of lower limb amputation (specific to some SGLT2 inhibitors). 43 Example of a treatment algorithm for diabetes management 1. Diagnosis: The first step is diagnosing diabetes, which typically involves blood tests to measure glucose levels. 2. Lifestyle Changes: Initial management focuses on lifestyle modifications such as diet, exercise, weight control, and health education. These changes are crucial for managing blood sugar levels and overall health. 3. Oral Agent Monotherapy: If lifestyle changes are insufficient, the next step is usually starting with an oral medication. Metformin is often the first choice unless it’s contraindicated or not tolerated, in which case another class of blood glucose-lowering therapy is considered. 4. Combination Therapy: If monotherapy is not effective, combining two or three different blood glucose-lowering agents with different mechanisms of action is recommended. This approach helps in better managing blood sugar levels. 5. Insulin Therapy: When oral medications and combination therapies are not enough, insulin therapy is introduced. Typically, treatment starts with basal insulin, which may be combined with metformin or another blood glucose-lowering agent. 44 Lifestyle interventions Physical Activity: Engaging in moderate physical activity, such as 30 minutes a day for 5 days a week, can reduce the risk of diabetes by approximately 40-60%. Diet Modifications: Adopting a diet with reduced fat and increased intake of fruits, vegetables, and fibre is beneficial. Weight Management: Effective weight management is the best strategy to prevent the development of type 2 diabetes. Mediterranean diet and weight management High Intake: Legumes, fruit, vegetables, cereals, olive oil, and fish. Low Intake: Meat and dairy products. Benefits: Increased dietary fibre and unsaturated fats lead to lower energy density and increased fat oxidation, contributing to weight control. 45 Mediterranean diet and prevention of T2DM Components: Olive oil, fish, vegetables, fruit, legumes, nuts, and cereals. Benefits: These components provide fibre, antioxidants, and magnesium. Health Outcomes: o Fiber: Delays gastric emptying. o Antioxidants: Increase oxidative capacity. o Magnesium: Supports ATP and P-transfer enzymes. Result: These benefits contribute to weight control, which helps prevent insulin resistance and pancreatic β-cell dysfunction. 46 Resveratrol & insulin sensitizing effects Source: Resveratrol comes from the skin of red grapes (and red wine :-P). Effects: o Activates AMPK: This enzyme plays a role in cellular energy homeostasis. o Increases Mitochondrial Number: More mitochondria can improve cellular energy production. o Increases Insulin Sensitivity: This helps the body use insulin more effectively, which is beneficial for managing blood sugar levels. 47 Reducing risk of type 2 diabetes/CVD by therapeutic/lifestyle interventions Lipid Control: o Reduces coronary heart disease mortality by 36%. o Reduces major coronary heart disease events by 37%. o Reduces any atherosclerotic events by 62%. o Reduces cerebrovascular disease events by 51%. Blood Pressure Control: o Reduces heart failure by 56%. o Reduces stroke by 44%. Blood Glucose Control: o Reduces diabetes-related deaths by 32%. o Reduces heart attacks by 37%. These strategies highlight the importance of managing lipids, blood pressure, and blood glucose levels to prevent serious complications in individuals with type 2 diabetes and CVD. 48