Lipid Metabolism Part 1 PDF

Semester 1 2024/2025 VPP3021 VETERINARY BIOCHEMISTRY LIPID METABOLISM PART 1 Nazhan Ilias (DVM, PhD) Dept. of Veterinary Preclinical Sciences Faculty of Veterinary Medicine...

Semester 1 2024/2025 VPP3021 VETERINARY BIOCHEMISTRY LIPID METABOLISM PART 1 Nazhan Ilias (DVM, PhD) Dept. of Veterinary Preclinical Sciences Faculty of Veterinary Medicine Universiti Putra Malaysia [email protected]  Lipid De novo fatty acids synthesis Lecture Beta-oxidation Outline Ketogenesis Ketolysis Clinical relevance Lipids DEFINITION A divers group of structurally distinct Fatty Acids (FA) amphipathic molecules. Triacylglycerides (TAG) ELEMENTS Phospholipids Composed mainly of hydrocarbons. It may also Steroids contain oxygen, nitrogen, sulfur, and phosphorus. Ketone bodies SOLUBILITY Terpenes Insoluble (hydrophobic) in water (polar) ; soluble in organic (non-polar) solvents such as ether, Prostaglandins (PG) benzene, acetone, and chloroform. Classification of lipids Simple Compound Derived FA + alcohol FA + alcohol Hydrolysis of and other groups simple or compound lipids Fats Phospholipids Fatty acids Oils Glycolipids Glycerol Waxes Lipoproteins Steroids/sterols Ketone bodies Lipid soluble vitamins Hormones  Energy storage Structural components of CM Metabolic regulators Functions Thermal insulator Protection of lipids Improve palatability Fatty acids Amphipathic Carboxyl group (-COOH) Hydrocarbon chain Methyl end (hydrophilic head) (hydrophobic tail) General formula: R - COOH (R is a hydrocarbon chain) Basic structure of fatty acids Monounsaturated Fatty Acid Contain one double bonds Palmitic acid 16:0 Oleic acid 18:1;9 Saturated Fatty Acid Carbon atoms saturated with hydrogen atoms No double bonds Polyunsaturated Fatty Acid Multiple double bonds Linoleic acid 18:2;9,12 Biosynthesis DE NOVO SYNTHESIS Occurs mainly in the liver and adipose tissue. of Substrate: Acetyl-CoA. Key Enzyme: Fatty acid synthase (FAS). Fatty Acids REGULATION Activation: Insulin. Combines 8 acetyl groups Inhibition: Glucagon, epinephrine. from acetyl CoA to form 16-C saturated fatty acids ELONGATION AND DESATURA TI O N (palmitate) Fatty acids can be elongated or desaturated in the endoplasmic reticulum. Desaturases introduce double bonds, but Modified to create other mammals cannot create ω−3\omega-3 or fatty acids ω−6\omega-6 (essential FA). - WHY? Acetyl-CoA PRODUCTS Glycolysis Amino acids Ketone bodies Fatty acids Fatty acids Ketone bodies Cholesterol Eicosanoids SOURCES Phospholipids Triglycerides De novo synthesis Excess carbohydrates Oxidation 4 ! 1. Synthesis of Acetyl-CoA​ 2. Formation of Malonyl-CoA 3 3. Fatty Acid Chain Elongation 4. Termination 1 2 Synthesis of Acetyl-CoA​ 1 1. CoA portion of acetyl-CoA cannot cross the inner 2 mitochondrial membrane; Oxidation only acetyl portion enters the cytosol. 2. Oxaloacetate and acetyl- CoA condense to citrate catalyze by citrate synthase. 3 3. Translocation of citrate from mitochondria to cytosol; cleaved by ATP- citrate lyase → cytosolic acetyl-CoA and OAA. Formation of Malonyl-CoA Glucagon, Epinephrin, Palmitoyl-CoA, AMPK Insulin, Citrate, ChREBP Oxidation Acetyl-CoA Acetyl-CoA Carboxylase Malonyl-CoA Production of Malonyl-CoA involved carboxylation and requires biotin and ATP. ChREBP STEPS Transcription factors are proteins involved in the process of converting, or transcribing, DNA into RNA. Step 1 – Carboxylation of biotin involving ATP. Step 2 – Transfer of carboxyl group to Acetyl-CoA to form Malonyl-CoA. Fatty Acid Chain Elongation Fatty acid synthase enzyme complex SH B5 ACP FAS KS-SH Cysteine ACP - Acyl Carrier Protein SH - Thiol group KS - Beta-ketoacyl synthase domain Palmitate synthesis: FAS Product: Malonyl-ACP Product: Acetyl-ACP CoASH 1 Acetyl-CoA SH B5 ACP 3 H AS o Condensation C 2 FAS 4 Malonyl-CoA ACP-SH KS-SH Cysteine Product: Acetyl-KS  Fatty acid elongation CoA CoA Transferred to ACP Acetyl-CoA Malonyl-CoA located on FAS enzyme Acetyl-CoA Carboxylase Acyltransferase This release CoA Post transfer acetyl-KS Malonyl-ACP Acetyl-ACP to First cycle = 4 carbon Acetyl-ACP malonyl-ACP Sixth cycle = 2 carbon x 6 = 14 serves as a primer, provide 2 intial carbon Total = 16 carbon 1 CYCLE = INCREMENT OF 2 CARBON 6 CYCLE CO2 NADPH NADP+ H2O NADPH NADP+ Palmitate Chain elongation Condensation Reduction Dehydration Reduction Termination 3 ketoacyl synthase 3 ketoacyl reductase dehydratase enoyl reductase palmitoyl thioesterase SUMMARY 1. Loading: Acetyl-CoA and malonyl-CoA attach to FAS. OF KEY 2. Condensation: Acetyl and malonyl groups combine with CO₂ release. 3. Reduction, dehydration, reduction: STEPS Sequential modification of the intermediate. 4. Elongation: Cycle repeats with malonyl-CoA as a two-carbon donor. IMPORTANT 5. Termination: Release of palmitate by thioesterase.  LOCATION Primarily in the mitochondria. B-Oxidation Peroxisomes handle very long-chain fatty acids before transferring shorter chains to mitochondria. Beta oxidation degradation of fatty acids IMPORTANCE to generate acetyl-CoA, Provides a significant energy source during NADH, and FADH2. fasting, exercise, or when glucose is scarce. Especially vital for animals like ruminants and carnivores with fat-rich diets. STEPS Activation of fatty acids (occurs in the Cytosol) Transport into the Mitochondria Beta-Ox Cycle (occurs in the Mitochondrial Matrix) Activation of fatty acids Enzyme: Acyl-CoA synthetase Notes: These FA are inert; thus must first be activated by conversion to fatty acyl-CoA Fatty acid + CoA + ATP → Fatty acyl-CoA + AMP + PPi​ Requires ATP (converted to AMP, equivalent to 2 ATP) Transport into the mitochondria Fatty acyl-CoA cannot cross the mitochondrial membrane directly. Carnitine Shuttle System: Carnitine palmitoyltransferase I (CPT-I) 1. converts fatty acyl-CoA to acyl-carnitine 1 3 Acyl-carnitine is transported 2 into the mitochondria via 2. carnitine-acylcarnitine translocase CPT-II regenerates fatty acyl- 3. CoA inside the mitochondria. Beta oxidation cycle 1 Each cycle removes two carbons from the fatty acid chain as acetyl-CoA. Step 1: Oxidation Converts fatty acyl-CoA to trans-Δ2-enoyl-CoA. 2 Step 2: Hydration Converts trans-Δ2-enoyl-CoA to L-3-hydroxyacyl-CoA. Step 3: Oxidation 3 Converts 3-L-hydroxyacyl-CoA to B-ketoacyl-CoA. Step 4: Thiolysis Cleaves B-ketoacyl-CoA to release acetyl-CoA and a shorter fatty acyl-CoA. 4 Beta Oxidation Cycle: O-HOT  ACETOACETATE The primary ketone body formed in the liver. Ketone Can be converted to: β-hydroxybutyrate for transport. bodies Acetone, a byproduct expelled through breath or urine. Liver mitochondria have the capacity to convert acetyl- Β-HYDROXYBUTYRATE CoA derived from FA The most abundant ketone body in circulation. oxidation into KB: Formed from the reduction of acetoacetate. Provides energy upon oxidation back to Acetoacetate acetoacetate. 3-hydroxybutyrate Acetone ACETONE Biosynthesis of Ketone Bodies A non-metabolizable byproduct. (Ketogenesis) Volatile and excreted via breath or urine, giving a Occurs in the mitochondria of "fruity" smell characteristic of ketosis. hepatocytes. Regulation of KB production Prolonged fasting KETOLYSIS Increased glucose and insulin levels Low-carbohydrate diets (postprandial state) Uncontrolled diabetes mellitus KETOGENESIS Ketogenesis 1 Step 1: Condensation of Acetyl-CoA 2 Acetyl-CoA → Acetoacetyl-CoA Step 2: Formation of HMG-CoA 2 Acetoacetyl-CoA + Acetyl-CoA → HMG-CoA Step 3: Production of Acetoacetate HMG-CoA → Acetoacetate + Acetyl-CoA 3 Step 4: Conversion to Other Ketone Bodies Acetoacetate → β-hydroxybutyrate 4 Acetoacetate → Acetone (via spontaneous decarboxylation) Ketolysis Catabolizing ketones. Released into bloodstream. Transported to and occurred in tissues like brain, heart, and muscles (but not hepatocytes!). The SCOT enzyme (aka thiophorase) is required for ketolysis, and is present in the mitochondria of all mammalian cells except for hepatocytes. CLINICAL RELEVANCE  KETOSIS Small Companion Bovine Ruminants Animals Bovine Pregnancy Diabetic Ketoacidosis Toxemia ketoacidosis NEB Pregnancy Hormonal Insulin Milk production Multiple fetuses deficiency Case 1: Bovine ketoacidosis This metabolic disorder affects high-producing dairy cows during early lactation, characterized by elevated ketone body levels in blood, urine, and milk due to a negative energy balance (NEB). It occurs when energy demands, such as high milk production, exceed energy intake, leading to low blood glucose concentrations. A common issue in dairy cows during the first few weeks of lactation is the mismatch between energy input and output, as energy is lost in milk production. Case 1: Bovine ketoacidosis Fat mobilization β-Oxidation Ketogenesis Compensatory Ketone bodies pH? mechanism (weak acid) Clinical components: clinical signs, diagnosis/diagnostic testing, treatment (GOOD TO KNOW) "Seek knowledge from the cradle to the grave"