Target Organ Hepato-Toxicity Lecture 6 (GUC, Spring 2024) PDF

TARGET ORGAN TOXICITY HEPATO-TOXICITY LECTURE 6 TOXICOLOGY (PHTXt 834) SPRING 2024 DR. RAGWA MANSOUR DR. NADIA SHARAF Dr. Ragwa Mansour Spring 2024  COMPETENCIES Fundamental Knowledge Demonstrate understandi...

TARGET ORGAN TOXICITY HEPATO-TOXICITY LECTURE 6 TOXICOLOGY (PHTXt 834) SPRING 2024 DR. RAGWA MANSOUR DR. NADIA SHARAF Dr. Ragwa Mansour Spring 2024  COMPETENCIES Fundamental Knowledge Demonstrate understanding of knowledge of body function in health & disease states as well as basis of genomic pathways regarding their correlation with different diseases. Demonstrate understanding of knowledge of the detoxification methods of acute intoxication in children and their difference to adults. Integrate knowledge of principles of basic toxicology including assessment and management of health & environmental risk caused by chemicals. Use the proper medical scientific language in toxicology practice Pharmaceutical Care Integrate knowledge of etiology, laboratory diagnosis & clinical features of different body systems’ toxicity & their management and treatment approaches Distinguish between the different types of organ injury with respect to the histological examination Distinguish between the different types of organ injury with respect to the histological examination. Compare types of antidotes used for management of toxicity based on diagnosis and clinical manifestations 2 Dr. Ragwa Mansour SS 2023  LECTURE OUTLINE I. Target Organ Toxicity II.Liver vulnerability to toxicity III.Liver structure IV.Factors that affect the development of Hepatotoxicity V.Types of liver Injury: 1) Fatty liver 2) Cell death 3) Cholestasis 4) Cirrhosis 5) Hepatitis Dr. Ragwa Mansour Spring 2024 TARGET ORGAN TOXICITY A target organ is an organ in the body that is most affected by a specific drug, bacteria or xenobiotic & not the organ which absorbs or stores the toxicant. Chemicals absorbed into the bloodstream or lymphatics through any of the major barriers: Skin, Lungs and Alimentary canal. Then Distributed throughout the body, till it reaches the TARGET ORGAN causing TARGET ORAGN TOXICITY. e.g. DDT (Chlorinated hydrocarbon) is highly deposited in fat tissues, and doesn't cause toxicity to them, it causes Neurotoxicity. Chemical may have one or several target organs. Why an organ might be a target for toxicants: a) Blood supply b) The abundancy of a particular enzyme or biochemical reaction c) The function or position of the organ d) The ability to repair Target e) The ability to metabolize a compound & the balance organ of toxication/detoxication systems f) Binding to a particular macromolecule toxicity N.B. highly specialized & vital organs such as CNS are more susceptible to disruption & aren’t easily repaired in comparison with adipose tissue which is less vital & less specialized  Hepato-toxicity  Liver is highly vulnerable to toxic injury due to: 1) Large blood supply to the liver, increasing exposure to the concentration of toxic compounds absorbed from the GIT. 2) Its location at the end of the portal system thus it is the first organ to encounter ingested nutrients, vitamins, metals, drugs, & waste products of bacteria that enter portal blood. 3) Bile secretion: increase toxicity from drugs excreted in bile & due to enterohepatic circulation. 4) It plays a key role in the metabolism and excretion of xenobiotics which makes it highly susceptible to their adverse effects. Dr. Ragwa Mansour Spring 2024 Liver Structure  Cells of the liver are arranged into hexagonal patterns called lobules (STRUCTURAL UNIT). N.B. Types of liver cells: Hepatocyte, Bile canaliculi cells & Sinusoidal cells 1) Hepatocytes are parenchymal cells arranged in columns within a lobule radiating outwards from the central vein, they are responsible for metabolic & secretory functions.  The Central vein is present in the center of each lobule which receives blood from the hepatic portal vein and the hepatic artery via the sinusoidal cells & it drains blood to the hepatic vein.  The Portal triad (portal tract) are present at the corners of the hepatic lobules, it contains a branch of the portal vein, the hepatic artery & a bile duct. 2) Bile canaliculi are fine tubular channels forming 3-dimentional network within the parenchyma of the liver, they join to form bile ductules & eventually the bile duct. * (Hepatocytes *) Bile duct Portal triad Portal Vein * Hepatic Artery Portal triad Hepatic Lobule Histological structure of the hepatic lobule  Liver Structure 3) Sinusoidal cells are small blood vessels between the radiating rows of hepatocytes where they receive oxygen-rich blood from the hepatic artery; and nutrients from the intestine through the portal vein (they carry blood throughout the liver).  Sinusoidal cells have three types of cells: a) The endothelial cells: they represents thin layer cells lining of the sinusoids, they contain pores which permits exchange of fluids & molecules between the sinusoid & the hepatocytes. b) Kupffer cells: (phagocytic cells) they are resident macrophages, and they are a source of cytokines. c) Ito cells: known by fat storing cells & stellate cells; Ito cells synthesize collagen & stores Vit A. * (Hepatocytes *) * Portal triad Histological structure of the hepatic lobule Dr. Ragwa Mansour Spring 2024  Liver Structure Acinus (metabolic lobule) is the BASIC FUNCTIONAL UNIT of the liver. - It contains mass of liver hepatocytes - Acinus comprises a unit bounded by 2 portal triads (portal venule, bile ductile & hepatic artery). Acinus regions (Categorized according to the distance from the blood supply) Zone Location Biochemistry Types of Liver Injury 1 Periportal region - High O2 content (closest to the blood entry) ROS mediated (near portal triad) - High GSH contents Necrosis - Beta-oxidation of fats (Peri-portal necrosis) 2 Mid-zonal Shared functions between zones 1 & 3 (intermediate) 3 Centrilobular - Low O2 content Necrosis caused by (near central vein) - High CYP-450 contents particularly CYP2E1 toxic metabolites isoform (which is responsible for metabolism of (Centri-lobular acetaminophen, benzene, & CCl4). necrosis) - High glucuronidation & Sulfation capacity. - Lipid & TG synthesis. Dr. Ragwa Mansour Spring 2024  Liver Structure Bile formation (one of the main functions of liver):  Bile is a yellow fluid manufactured in the hepatocytes it contains bile Hepatocytes begin the process by transporting salts, glutathione conjugates, phospholipids, cholesterol, METALS, bile salts & other solutes bilirubin & xenobiotics.  The major driving force of bile formation is the active transport of bile salts and other osmolytes into the canalicular lumen (N.B. Excretion through the bile is usually although not exclusively active transport process). Into the canalicular lumen  ACTIVE TRANSPORTERS:. N.B. Canaliculi form channels between a. Transporters at the sinusoidal membranes of the hepatocytes: hepatocytes that connect to a series channels or They transfer solutes from the blood to the hepatocytes. ducts within the liver. The large extrahepatic bile e.g. Organic anion transporter protein (OAT) which transports bile acids ducts merge into the common bile duct & bilirubin b. Transporters at the canalicular membranes of the hepatocytes: They transfer solutes to the lumen of the canaliculi. e.g. i. Multidrug-resistant protein (MDR): transports lipophilic cationic drugs, estrogens, & phospholipids. Bile can be stored and concentrated in the ii. Canalicular multiple organic anion transporter (cMOAT): transports gallbladder before its release into the duodenum conjugates of glutathione, glucuronide & sulphate. sinusoidal membrane of the hepatocytes Canalicular membrane of the hepatocytes cMOAT MDR Transporters on the Sinusoidal & the Canalicular membranes of the hepatocytes Dr. Ragwa Mansour Spring 2024  BILIARY EXCRETION OF METALS  Biliary excretion is important in the homeostasis of multiple metals, notably copper, manganese, cadmium, selenium, gold, silver, & arsenic  Wilson’s disease: An autosomal recessive inherited disorder characterized by the accumulation of COPPER in the liver hepatocytes due to defect or the absence of a copper transporting P-type ATPase (ATP7B).  ATP7B carrier transports copper to: The biliary canaliculi to be excreted into bile The secretory pathway where it binds with apoceruloplasmin then released to the blood circulation as Cu-ceruloplasmin (Ceruloplasmin is a protein that is made in the liver, it stores and carries copper from the liver into the bloodstream and to the parts of your body that need it).  Because biliary excretion is the only way to eliminate copper, a defect in ATP7B results in excessive copper accumulation in hepatocytes, which causes chronic hepatitis and cirrhosis.  As a result of copper accumulation it leaks to the blood & causes toxicity to other organs like brain, kidney & blood. Ceruloplasmin ApoCeruloplasmin  Factors that affect the development of Hepatotoxicity 1) Race: e.g. Blacks are more susceptible to INH toxicity 2) Age: Upon aging the clearance of drugs decrease, hepatic blood flow decreases, & drug binding capabilities differ. 3) Genetic factors: Genetic differences in CYP-450 enzyme activity. 4) Malnourished persons: Low glutathione content 5) Alcohol intake: Alcohol is an enzyme inducer & it depletes GSH. 6) Preexisting liver disease: CYP-450 enzyme is reduced in chronic liver disease. Dr. Ragwa Mansour Spring 2024  Types of liver Injury (Toxicant-induced liver injury) 1) Fatty liver 2) Cell death 3) Cholestasis 4)Cirrhosis 5)Hepatitis Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) 1) Fatty liver (Steatosis):  Definition: it is the abnormal accumulation of fats (TG) in hepatocytes, predominantly in centrilobular region (zone 3).  It occurs due to: a)Disturbance in the uptake & export of lipids & FA into & from the liver. b)Impaired synthesis of lipoproteins & their conjugation to TG. c) Increase TGs production & decrease the release of VLDL from the hepatocytes.  Liver steatosis is often a reversible condition, where it disappears upon the withdrawal of the precipitant agent. Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) 1) Fatty liver (Steatosis): Types Macrovesicular steatosis Microvesicular steatosis Fat droplets displace the nucleus Fat droplets don’t displace the of hepatocytes nucleus of hepatocytes More common More severe Causative agents: Causative agents: Ethanol Zidovudine (nucleoside Obesity analogue, for treatment of HIV Amiodarone infections) causes disruption of mitochondrial DNA synthesis thus inhibiting mitochondrial oxidative phosphorylation & fatty acid –β oxidation.  Fatty liver looks pale & enlarged upon microscopical examination. Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) 2) Cell death :  Liver cells die either by necrosis or apoptosis.  Acute necrosis of hepatocytes disrupts all aspects of its function & excessive necrosis results in functional liver failure.  It is an irreversible liver injury.  Underlying mechanisms hepatic Necrosis: lipid peroxidation, binding to cell macromolecules, mitochondrial damage, & calcium influx. Confined to a limited area with Necrosis of hepatocytes random distribution of single Focal damaged hepatocytes or small clusters of hepatocytes Occurs in certain functional Zonal region Widely distributed cell death scattered throughout the liver Massive with few survival ones in the Centrilobular, midzonal, & periportal zones Dr. Ragwa Mansour Spring 2024 Types of liver Toxicity (Toxicant-induced liver injury) 2) Cell death (necrosis):  Causative agents: CCl4, acetaminophen, chloroform, halogenated hydrocarbons & bromobenzene.  CCl4 mechanism of hepatotoxicity (centrilobular necrosis*): CCl4 is a simple molecule which causes fatty liver & centrilobular necrosis. It is very lipid soluble & consequently well distributed throughout the body but despite this its major toxic effect is on the liver due to its metabolic activation by CYP-450. CCl4 By CYP-450 it forms trichloromethyl free ACUTE EXPOSURE to CCl4 radical CCl3. (low doses) potential outcome is steatosis due to alteration in lipid metabolism & reduction in protein synthesis. It firstly attacks polyunsaturated fatty acids (PUFA) Forming Lipid peroxides & toxic aldehydes CHRONIC EXPOSURE Free radicals’ effect on PUFA will alter the permeability of mitochondria & plasma CC l3. ,toxic aldehydes & lipid radicals membranes resulting in Bind to other macromolecules (nucleic acids, calcium influx, drop in ATP proteins, lipids) production & consequently Impairing important cellular processes & hepatic necrosis. functions & causing Hepatic necrosis Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) 2) Cell death (necrosis):  Acetaminophen mechanism of hepatotoxicity (centrilobular necrosis): Acetaminophen is a safe & effective analgesic in the recommended therapeutic dose BUT if administered in excessive dose it may lead to life-threatening acute liver failure. 2) As a result of iNOS induction forming Peroxynitrite (-OONO) 1) NAPQI will bind radical to hepatic cell proteins & DNA resulting in mitochondrial dysfunction HEPATIC NECROSIS Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) 2) Cell death (necrosis):  Acetaminophen & CCl4 toxicity occurs due to their bio-activation by CYP-450 thus they tends to cause CENTRILOBULAR NECROSIS in liver (Zone-3, rich in CYP-450).  Acetaminophen & CCl4 toxicity is potentiated if administered with any enzyme inducer e.g. ethanol. Acetaminophen toxicity will be EXACERBATED in the presence of kupffer cells activators such as Vitamin A & endotoxins (released from gm –ve bacteria) as a result of signal exchange between primed (damaged) hepatocytes & activated kupffer cells. This signal exchange is considered to be a key event for the hepatotoxicity of many compounds. Key Events in Acetaminophen & other compounds hepatotoxicity  Acetaminophen Antidote is N-acetyl-cystein: It promotes the synthesis of GSH acting as glutathione precursor. Dr. Ragwa Mansour Spring 2024 Types of liver Toxicity (Toxicant-induced liver injury) 3) Cholestasis:  Definition: It is the decrease in the volume of bile formed OR an impaired secretion of specific solutes in the bile.  Cholestasis is characterized biochemically by elevated serum levels of compounds that are normally concentrated in bile, particularly bile salts and bilirubin.  Clinically cholestatic liver disease is characterized by pruritus, jaundice caused by hyperbilirubinemia, altered lipid and cholesterol metabolism, and intestinal malabsorption of fat and fat soluble vitamins.  Toxin-induced cholestasis can be transient or chronic; when substantial, it is associated with cell swelling, cell death, and inflammation.  As a result of bile retention in the liver it becomes green in color. Cholestatic liver Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) 3) Cholestasis: 1) Estrogen & Cyclosporine: At sinusoidal membrane: Both decrease the uptake of bile salts through inhibiting Na+/K+- ATPase (necessary for Na-dependent transport of bile salts across the hepatocyte sinusoidal membranes). At the canalicular membrane: Both inhibits bile acids transportation from hepatocytes into bile canaliculi by interfering with the bile salt export pump (BSEP) (which transports conjugated bile salts). Estrogen only affects Multidrug-resistant protein (MDR) (efflux pump which exudes chemicals out of numerous cells) 2) Rifampicin: It impedes the uptake of bilirubin into hepatocytes (interferes with bilirubin transport & conjugation giving rise to hyper-bilirubinemia) & it inhibits bile salt exporter pump (BSEP). 3) Chlorpromazine: Inhibits Na+/K+-ATPase which decreases canalicular contractility. Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) 3) Cholestasis: Rifampicin (impedes bilirubin uptake) Chlorpromazine Estrogen MDR (inhibiting ATPase, reducing canalicular contractility) Estrogen, Estrogen, Cyclosporine Cyclosporin, (inhibiting Rifampicin Na+/K+- ATPase) Drug Induced Cholestasis Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) 4) Cirrhosis:  Definition: it is the accumulation of extensive amounts of collagen fibers within the hepatocytes in response to direct injury or inflammation.  The destroyed hepatocytes will be replaced by fibrotic scars leading to disruption of the liver architecture.  The accumulation of fibrous scars will transform the liver mass into nodules.  Fibrosis may progress to cirrhosis and the liver has insufficient residual capacity to perform its essential functions.  Cirrhosis results from repeated exposure to a toxicant & is an irreversible liver condition.  Causative agents: Alcohol intake, viruses & fatty liver (progression), & Vitamin A accumulation. Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) 5) Hepatitis  Definition: it is a medical condition characterized by liver inflammation.  It is characterized by migration of neutrophils, lymphocytes & other inflammatory cells to the region of damaged hepatocytes.  Causative agents: Viruses, Isoniazid, Halothane, Alcohol. It is initiated by the activation of kupffer cells which produces AND Neutrophils which cytokines & ROS release cytotoxic proteases & ROS. Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) Alcoholic Liver Injury: Alcohol metabolism Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) Alcoholic Liver Injury: 2) NAD+ depletion causing mitochondrial dysfunction Inducible pathway Major pathway Ethanol metabolism 1) Toxic metabolite & ROS which interact with cellular protein & lipids leading to cell damage ADH: Alcohol dehydrogenase ALDH: Aldehyde dehydrogenase MEOS: Microsomal Ethanol Oxidizing System Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) Alcoholic Liver Injury: causing liver STEATOSIS, CIRRHOSIS & HEPATITIS 1) ADH & ALDH cause elevation in NADH/NAD+ ratio resulting in: Depressed citric acid cycle (mitochondrial dysfunction & ATP depletion) Fatty acids will accumulate as TG in the liver due to: a) Enhanced hepatic lipogenesis (due to acetyl CoA accumulation, which will be used in FA synthesis). b) Decrease the lipoprotein formation CAUSING LIVER STEATOSIS 2) ADH produces Acetaldehyde It is a reactive metabolite which attacks cellular proteins & lipids. Xanthine Oxidase pathway releases superoxide anion O2-. (ROS) Causing excessive hepatocyte damage, increasing the collagen levels & scar tissue formation CAUSING LIVER CIRRHOSIS Dr. Ragwa Mansour Spring 2024  Types of liver Toxicity (Toxicant-induced liver injury) Alcoholic Liver Injury: causing liver STEATOSIS, CIRRHOSIS & HEPATITIS Ethanol damages Gut microflora cell wall: Releasing endotoxins which activates Kupffer cells Which releases activates cytokines e.g.TNF-α & IL-8 & ROS Ethanol will cause neutrophiles recruitment, which releases more ROS & proteolytic enzymes CAUSING LIVER HEPATITIS Treatment of alcoholism: Disulfiram (Antabuse) inhibits ALDH Causing the accumulation of acetaldehyde Thus further alcohol intake will lead to Unpleasant effects like nausea, vomiting & GIT discomfort. Disulfiram & its metabolites inhibits the activity of CYP2E1 Dr. Ragwa Mansour Spring 2024  Drugs withdrawn from the market due to their hepatotoxicity: 1) Troglitazone: Anti-diabetic drug, which was approved by the FDA for clinical use in 1997 & withdrawn from the market in 2000. Both in-vivo & in-vitro toxicological studies revealed its hepatotoxicity which arises from its metabolic bio-activation to quinone metabolite. 2) Kava: Kava is a plant (Piper methysticum) of the pepper family, it was used for the treatment of anxiety. Several in-vitro studies demonstrated that it inhibits various CYP-450 isoforms Dr. Ragwa Mansour Spring 2024 Dr. Ragwa Mansour Spring 2024  Email: [email protected] Room #: B5.120 Dr. Ragwa Mansour Spring 2024