LIVER CLINICAL BIOCHEMISTRY

LIVER STRUCTURE sinusoids central vein portal vein bile canaliculi hepatic artery bile duct sinusoids bile canaliculi central vein

LIVER FUNCTIONS Distribution of nutrients All types of metabolism (protein, lipid, carbohydrate, vitamin, mineral) Excretory (bile acids, urea synthesis) Destruction of toxic substances Depot of iron, vitamins

METABOLISM OF CARBS IN LIVER glycolisis metabolism of fructose and galactose gluconeogenesis release of glucose into blood (maintain the stable glucose concentration in blood) conversion of pyruvate into acetyl CoA tricarboxylic acid cycle pentose phosphate pathway glycogenolysis, glycogenogenesis

METABOLISM OF LIPIDS IN LIVER synthesis of lipoproteins synthesis of triacylglyserols synthesis of phospholipids synthesis of fatty acids, elongation of fatty acids chain, desaturation synthesis of cholesterol ketone bodies formation lipolysis fatty acids oxidation

METABOLISM OF PROTEINS IN LIVER protein synthesis, including blood plasma proteins protein decomposition; urea synthesis conversion of proteins into carbs and lipids interconversion of aminoacids conversion of proteins into low molecular weight nitrogen containing substances

Vitamin metabolism in liver Formation of active form of vitamin D Formation of vitamin A from carotins Depo of cyanocobalamine and folic acid Depo of vitamin E Phosphorilation of vitamins B, formation of coenzyme forms

DETOXIFICATION OF TOXIC SUBSTANCES IN LIVER Phase I and phase II. Phase I: hydrolysis, reduction, oxidation. These reactions introduce functional group (—OH, —NH2, —SH, or —COOH) and usually result in a little increase of hydrophylic properties

Phase II includes: glucuronation, sulfation, acetylation, methylation, conjugation with glutathione, conjugation with aminoacids (glycin, taurin, glutamic acid) Phase II results in the marked increase of hydrophylic properties of xenobiotic.

General ways of xenobiotics biotransformation and their localization in cell REACTION ENZYME LOCALIZATION PHASE I Hydrolysis Reduction Oxidation Esterase Peptidase Epoxide hydrolase Azo- and nitro-reduction Carbonyl reduction Disulfide reduction Sulfoxide reduction Alcohol dehydrogenase Aldehyde dehydrogenase Aldehyde oxidase Xanthine oxidase Monoamine oxidase Diamine oxidase Flavin-monooxygenases Cytochrome P450 Microsomes, cytosol, lysosomes, blood lysosomes Microsomes, cytosol Microflora, microsomes, cytosol Cytosol, blood, microsomes Cytosol Mitochondria, cytosol Mitochondria Microsomes PHASE II Glucuronide conjugation Sulfate conjugation Glutathione conjugation Amino acid conjugation Acetylation Methylation Cytosol, microsomes Mitochondria, microsomes Cytosol, microsomes, blood

PHASE I Hydrolysis Reduction Esterases (carboxyesterases, cholinesterases, phosphatases) Peptidases Reduction Metals and xenobiotics containing aldehyde, keto, disulfide, alkyn, azo, or nitro group are often reduced Reducing agents: Reduced glutathione, FADH2, FMN, NADH NADPH.

Alcohol dehydrogenase Oxidation Alcohol dehydrogenase

Aldehyde dehydrogenase Xanthine dehydrogenase-Xanthine oxidase Oxidizes aldehydes to carbonic acids Xanthine dehydrogenase-Xanthine oxidase Monoaminooxidase Oxidative deamination of amines (serotonin) and many xenobiotics

Cytochrom P450 The highest concentration – in endoplasmic reticulum of hepatocytes (microsomes). Hem containing protein. Catalyzes monooxigenation of oxygen atom into substrate; another oxygen atom is reduced to water Electrons are transferred from NADPH to cytochrome P450 through flavoprotein NADPH-cytochrome P450 reductase.

SCHEME OF MONOOXYGENASE SYSTEM

SCHEME OF MONOOXYGENASE SYSTEM IN ENDOPLASMIC RETICULUM

The example of reaction that is catalyzed by cytochrome P450: hydroxylation of aliphatic carbon

The example of reaction that is catalyzed by cytochrome P450: hydroxylation of aromatic carbon

Examples of reactions catalyzed by cytochrome P450: heteroatom oxygenation

Examples of reactions catalyzed by cytochrome P450: oxidative group transfer

JAUNDICES

NORMAL METABOLISM OF BILE PIGMENTS CELLS OF RES Indirect bilirubin NADP+ NADPH2 Biliverdin reductase Biliverdin Iron Globin Verdoglobin Hemoxi-genase Hemoglobin ERYTHROCYTES KIDNEYS Stercobilinogen URINE Stercobilin Indirect bilirubin 1,7-20,5 mkmol/l albumin UDP-glucoronil-transferase Direct bilirubin 0.8-4.3 mkmol/l BLOOD LIVER Bilirubin mono-glucoronid, 20 % Bilirubin di-glucoronid, 80 % Dipyrols -glucoro-nidase Glucoronic acid Direct bilirubin BILE INTESTINE Mesobilirubin Mesobilirubin (urobilinogen) STOOL

Bilirubin di-glucoronid

HEMOLYTIC (PREHEPATIC) JAUNDICE Jaundice due to the excessive breakdown of red blood cells. Causes: sickle cell anemia, malaria, thalassemia, autoimmune disorders, massive hemorrhage

METABOLISM OF BILE PIGMENTS IN HEMOLYTIC JAUNDICE CELLS OF RES Indirect bilirubin albumin Biliverdin reductase UDP-glucoronil-transferase Direct bilirubin NADP+ NADPH2 Biliverdin Iron Globin Verdoglobin Hemoglobin Hemoxi- genase BLOOD LIVER Bilirubin mono-glucoronid, 20 % Bilirubin diglucoronid, 80 % -glucoro- nidase Glucoronic acid BILE ERYTHROCYTES KIDNEYS INTESTINE STOOL Stool hypercholic URINE Urine dark Mesobilirubin Mesobilinogen (urobilinogen) Stercobilinogen Stercobilin Urobilin

PARENCHYMAL (HEPATIC) JAUNDICE occurs due to the liver disease and inability of liver to metabolize and remove bilirubin from the biliary system Causes: cirrhosis, cancer, viral hepatitis, Gilbert’s syndrome, toxins or drugs, etc.

METABOLISM OF BILE PIGMENTS IN HEPATIC JAUNDICE CELLS OF RES Indirect bilirubin albumin Biliverdin reductase UDP-glucoronil-transferase Direct bilirubin NADP+ NADPH2 Biliverdin Iron Globin Verdoglobin Hemoglobin Hemoxi- genase BLOOD LIVER Bilirubin mono-glucoronid, 20 % Bilirubin diglucoronid, 80 % -glucoro- nidase Glucoronic acid BILE ERYTHROCYTES KIDNEYS Urobilinogen INTESTINE STOOL Stool hypocholic URINE Urine dark Stercobi-linogen Stercobilin Bilirubin Urobilin Mesobilirubin Mesobilinogen (urobilinogen) Stercobilinogen

ОBSTRUCTIVE (POST-HEPATIC) JAUNDICE is caused by obstruction of bile flow from the liver Causes: carcinoma in the bile duct or gall bladder, presence of gallstones in the biliary system, infection by parasites, pancreatitis, etc.

METABOLISM OF BILE PIGMENTS IN OBSTRUCTIVE JAUNDICE CELLS OF RES Indirect bilirubin albumin Biliverdin reductase UDP-glucoronil-transferase Direct bilirubin NADP+ NADPH2 Biliverdin Iron Globin Verdoglobin Hemoglobin Hemoxi- genase BLOOD LIVER Bilirubin mono-glucoronid, 20 % Bilirubin diglucoronid, 80 % Bile acids -glucoro- nidase Glucoronic acid BILE ERYTHROCYTES KIDNEYS INTESTINE STOOL Stool acholic, steatorhea URINE Direct bilirubin Bile acids Urine dark, foaming