Alcohol metabolism and associated metabolic changes when drinking alcohol Seminar 3 Nguyễn Dương Sang Lê Nguyễn Bảo Trân Tăng Bảo Trân Dương Triều Nghi Ngô Tuấn Kiệt Nguyễn Thành Thái
Alcohol metabolism and associated metabolic changes when drinking alcohol Seminar 3 1. What is alcohol?
2. Alcohol metabolism
3. Polymorphisms
4. Acute effects of increased NADH/NAD+
5. Acetaldehyde toxicity Alcohol metabolism and associated metabolic changes when drinking alcohol Seminar 3 1. What is alcohol?
Drinking alcohol – Ethanol – 퐶2퐻5푂퐻
• Small molecule • Water AND Lipid –soluble
=> Passive diffusion 2. Alcohol metabolism
Absorption rate:
• Upper GI tract: 0-5%
• Lower GI tract: 85-98%
• Excreted through lungs/kidneys: 2-10% 2. Alcohol metabolism 2. Alcohol metabolism
3 Phases: 1. Ethanol → Acetaldehyde 2. Acetaldehyde → Acetate 3. Acetate → … 2. Alcohol metabolism 1. Ethanol → Acetaldehyde Mainly 2 principle routes, occur at different ethanol concentration 1. Alcohol dehydrogenase (ADH) 2. The Microsomal Ethanol-Oxidizing System (MEOS) 2. Alcohol metabolism 1. Ethanol → Acetaldehyde 1. Alcohol dehydrogenase (ADH) • Mainly ADH1 family – high concentration in the liver • Low Km => High affinities 2. Alcohol metabolism 1. Ethanol → Acetaldehyde 2. The Microsomal Ethanol-Oxidizing System (MEOS) Cytochrome P450 enzymes • 2 major catalytic protein components: • Cytochrome P450 reductase • Cytochrome P450 • Present in the Endoplasmic Reticulum (ER) 2. Alcohol metabolism 1. Ethanol → Acetaldehyde 2. The Microsomal Ethanol-Oxidizing System (MEOS) Main CYP that has the highest activity toward ethanol:
• Much higher Km than ADH1 (low affinity) • High ethanol concentration => A greater proportion of ethanol is metabolized through CYP2E1 2. Alcohol metabolism 1. Ethanol → Acetaldehyde 2. The Microsomal Ethanol-Oxidizing System (MEOS) 2. Alcohol metabolism 2. Acetaldehyde → Acetate By acetaldehyde dehydrogenase (ALDH) In the liver: • 80%: in mitochondria • Mitochondria ALDH (ALDH2) • High affinity; Highly specific • 20%: in cytosol • Cytosolic ALDH (ALDH1) 2. Alcohol metabolism 3. Acetate → … 2. Alcohol metabolism 3. Acetate → … Can occur 2 places: 1. At the liver: • In the cytosol • Through ACSI • Similar to fatty acyl-CoA synthetase • In the mitochondria • Through ACSII 2. Other tissues: • In the mitochondria • Through ACSII ASCI: the principal isoform of acetyl-CoA synthetase ASCII: the mitochondria acetyl-CoA synthetase 3. Polymorphisms
• Variations in the Pattern of Ethanol Metabolism • Genotype o ADH o ALDH o Cytochrome P450 o Single-nucleotide polymorphism (SNP) • Drinking History • Gender • Quantity 3. Polymorphisms
• Variations in the Pattern of Ethanol Metabolism • Genotype GENE TISSUE PROPERTIES DISTRIBUTION o ADH ADH1 Mostly in the liver Active with ethanol ▪ ADH2, ADH4, ADH2 Primary liver, Active with ethanol ▪ ADH3 lower levels in GI (lower affinity) tract ▪ ADH1B*2: ADH3 Higher levels in Active with long- rapid ethanol liver chain alcohol and ꞷ-OH fatty acids oxidation ADH4 High levels in Active with upper GI tract, not medium-chain in the liver alcohols 3. Polymorphisms
• Variations in the Pattern of Ethanol Metabolism • Genotype o ALDH ▪ ALDH1 ▪ ALDH2*2: decreased capacity for acetaldehyde o Cytochrome P450 ▪ CYP2B1 ▪ CYP2B2 o Single-nucleotide polymorphism (SNP) 3. Polymorphisms
• Variations in the Pattern of Ethanol Metabolism • Genotype • Drinking History • Gender • Quantity 4. Acute effects of increased NADH/NAD+
• Hepatic steatosis • Ketoacidosis • Lactic acidosis • Hyperureciema • Hypoglycemia 4. Acute effects of increased NADH/NAD+
Hepatic steatosis
Ketoacidosis
Lactic acidosis
Hyperureciema
Hypoglycemia 4. Acute effects of increased NADH/NAD+
• Hypoglycemia ↑ NADH/NAD+ → ↑ conversion OAA => Malate ↓ OAA → TCA cycle
Gluconeogenesis 4. Acute effects of increased NADH/NAD+
Hepatic steatosis
Ketoacidosis
Lactic acidosis
Hyperureciema
Hypoglycemia 4. Acute effects of increased NADH/NAD+
• Lactic acidosis ↑ NADH/NAD+ → ↑ Pyruvate => Lactate. Can not enter gluconeogenesis. 4. Acute effects of increased NADH/NAD+
Hepatic steatosis
Ketoacidosis
Lactic acidosis
Hyperureciema
Hypoglycemia 4. Acute effects of increased NADH/NAD+
• Hyperureciema ↑ NADH/NAD+ → ↑ Lactate → Lactic acidosis Decreased excretion of uric acid by the kidney. 4. Acute effects of increased NADH/NAD+
Hepatic steatosis
Ketoacidosis
Lactic acidosis
Hyperureciema
Hypoglycemia 4. Acute effects of increased NADH/NAD+
• Ketoacidosis ↑ NADH/NAD+ → ↑ conversion OAA => Malate → ↓ OAA → TCA cycle → Acetyl-CoA enters ketone body synthesis. 4. Acute effects of increased NADH/NAD+
Hepatic steatosis
Ketoacidosis
Lactic acidosis
Hyperureciema
Hypoglycemia 4. Acute effects of increased NADH/NAD+
• Hepatic steatosis ↑ NADH/NAD+ → fatty acids oxidation → Fatty acids + glycerol 3-P => triacylglycerols (TAG). → TAG => VLDLs that accumulate in the liver and enter the blood → Hyperlipidemia 5. Acetaldehyde toxicity
• Adducts • Free-radicals • Induction of Kuffer cell • Sirtuin 1 (SIRT-1) 5. Acetaldehyde toxicity
• Adducts Acetaldehyde binds covalently to amino groups, sulfhydryl groups, nucleotides, and phospholipids
=> Form “adducts” 5. Acetaldehyde toxicity
• Adducts The accumulation of proteins -> An influx in the liver within hepatocytes and a swelling of the liver. => Contribute to portal hypertension and a disruption of hepatic architecture. 5. Acetaldehyde toxicity
• Adducts 5. Acetaldehyde toxicity
• Free-radicals • Can be defined as any molecular species capable of independent existence that contains an unpaired electron in an atomic orbital.
• Through several enzymatic and nonenzymatic processes that routinely occur in cells, O2 accepts single electrons to form reactive oxygen species (ROS). 5. Acetaldehyde toxicity
• Free-radicals The effects of ROS 5. Acetaldehyde toxicity
• Free-radicals Damage • Acetaldehyde-adduct formation enhances free-radical damage • Lipid peroxidation -> destroy the cell membrane. => Damage to mitochondria 5. Acetaldehyde toxicity
• The Kuffer cell
Hepatic stellate cells (here HSC) = perisinusoidal cells = Ito cells
• The lipid droplets in the cell body store vitamin A as retinol ester • Respond to cell damage to the liver 5. Acetaldehyde toxicity
• Sirtuin 1 (SIRT-1) • DNA methylation inhibition Alcohol
Sirtuin 1 (SIRT-1): o is a histone deacetylase o uses NAD+ as a substrate
Liver injury ↑ Key Concepts Ethanol metabolism • Occurs primarily at the liver • Through 2-step oxidation sequence => Acetate (+ NADH) • Acetate => Acetyl-CoA => Energy generation • Alcohol dehydrogenase (ADH) – 1st step of alcohol oxidation Acetaldehyde dehydrogenase (ALDH) – 2nd step of alcohol oxidation • High ethanol levels => MEOS (consisting of CYP2E1) is induced Polymorphism Metabolism pathway is the same with everyone. Only the efficiency is different due to the polymorphisms of the pathway. Key Concepts Toxic effects of ethanol
Acute effects (↑ NADH/NAD+) Chronic effects • Hypoglycemia • Hepatic steatosis • Lactic acidosis • Hepatitis => Inhibiton of gluconeogenesis • Fibrosis • Ketoacidosis • Cirrhois • Hyperureciema Chronic effects are caused by • Inhibition of fatty acid oxidation acetaldehyde and reactive oxygen => Hyperlipidemia species (ROS) Questions ADH vs MEOS ADH MEOS In the liver Cytoplasma Microsome Substrate EtOH, NAD+ EtOH, NADPH, O2 Km to EtOH 0.02 – 5 mM (0.09 – 22.5 mg/dL) 11 mM (51 mg/dL) Induced by EtOH No Yes Energy Release Consume
CYP2E1 has a much higher Km for ethanol than the ADH1 family members (11 mM [51 mg/dL] compared with 0.02 to 5 mM [0.09 to 22.5 mg/dL]). Thus, a greater proportion of ingested ethanol is metabolized through CYP2E1 at high levels of ethanol consumption than at low levels.
Mark’s Basic Medical Biochemistry – A Clinical Approach (5th Edition) – Chapter 33: Metabolism of Ethanol Questions Mixing Different Types of Alcohol Increases Your Risk of Getting Sick? Simply mixing different types of alcohol is unlikely to make you sick. True or False: Mixing Different Types of Alcohol Increases Your Risk of Getting Sick – Beth Israel Lahey Health Winchester Hospital Alcohol flushing reaction 80% of East Asians carry an allele of the gene coding for ADH1B*2 => alcohol converted to toxic acetaldehyde more 30–50% of East Asians have the mitochondrial ALDH2*2 allele => decreased acetaldehyde converted to acetate Alcohol flush reaction - Wikipedia How alcohol affects the stomach? Common symptoms of acute gastritis include: mild stomach upset, ulcers, stomach irritability, nausea and vomiting, bloating and gas, hemorrhage. These are due to bacterial overgrowth, alcohol-induced intestinal hyperpermeability, alcohol modulation of mucosal immunity. Alcohol and Gut-Derived Inflammation - NCBI Alcoholic Gastritis Symptoms, Causes & Treatment – American Addiction Centers Alcoholic Gastritis: Causes, Symptoms And Addiction Treatment Options – Vertava Health How ethanol and phenobarbital relate to each other? Ethanol is an inhibitor of the phenobarbital-oxidizing P450 system. When large amounts of ethanol are consumed, the inactivation of phenobarbital is directly or indirectly inhibited. Therefore, when high doses of phenobarbital and ethanol are consumed at the same time, toxic levels of the barbiturate can accumulate in the blood. Mark’s Basic Medical Biochemistry – A Clinical Approach (5th Edition) – Chapter 33: Metabolism of Ethanol Questions ADHs in our body and their Km?
Mark’s Basic Medical Biochemistry – A Clinical Approach (5th Edition) – Chapter 33: Metabolism of Ethanol
Alcohol and Cancer – Samir Zakhari; Vasilis Vasiliou; Q. Max Guo Editors Questions ATP from ethanol metabolism: The ATP yield from ethanol oxidation to acetate varies with the route of ethanol metabolism. If ethanol is oxidized by the major route of cytosolic ADH and mitochondrial ALDH, one cytosolic and one mitochondrial NADH are generated, with a maximum yield of 5 ATP. Oxidation of acetyl-CoA in the TCA cycle and the electron-transport chain leads to the generation of 10 high-energy phosphate bonds. However, activation of acetate to acetyl-CoA requires two high-energy phosphate bonds (one in the cleavage of ATP to adenosine monophosphate [AMP] + pyrophosphate and one in the cleavage of pyrophosphate to phosphate), which must be subtracted. Thus, the maximum total energy yield is 13 mol of ATP per mole of ethanol. Mark’s Basic Medical Biochemistry – A Clinical Approach (5th Edition) – Chapter 33: Metabolism of Ethanol
Potential benefits of drinking wine: • Rich in antioxidants: polyphenols which have been shown to reduce oxidation stress and inflammation • Wine has resveratrol, a natural antioxidant in the skin of grapes => Increase HLD • Wine has a high amount of some vitamins and minerals Because red wine grapes are higher in antioxidants than white grape varieties, drinking red wine may increase your blood antioxidant levels to a greater extent than drinking white wine. (Red wine has up to 10 times more resveratrol than white wine) Is red wine good for you? - MedicalNewsToday References
• Mark’s Basic Medical Biochemistry – A Clinical Approach (5th Edition) – Chapter 33: Metabolism of Ethanol • Duke University – The Alcohol Pharmacology Education Partnership – Module 4: Alcohol and the Breathalyzer Test • Liver (AMBOSS US); The Cell (AMBOSS US) • Exocytosis – ScienceDirect Thank you for listening! Seminar 3