Herbert Desel GIZ-Nord Poisons Centre und Toxicology Laboratory

1. ToxicologyTarget Organs and Mechanism of ActionMaster Programme Molecular Medicine Georg-August-Universität GöttingenModule ‚Special Aspects of Molecular Medicine‘Sub-Module ‚Pharmacology‘November 17,2010www.giz-nord.de Herbert Desel GIZ-Nord Poisons Centre und Toxicology Laboratory

3. Toxicology deals with INTOXICATIONS (poisonings): • adverse effect(s) of a chemical compound on the body: toxic effect • in most cases taken up from the environment (exposure to xenobiotic) • disease caused by a toxic effect • and its clinical treatment

4. Molecular Targets for Toxic Effects (Receptors) • proteins (enzymes,..) • DNA • lipids • small molecules

5. Chemical Basis of Toxic Effects • coordinative binding (electrostatic interaction) • covalent binding, oxidation • directly • activated by metabolism • important role of toxicokinetics

6. Time Scale • Acute toxic effects • direct cause: e.g. neuro receptor binding • Chronic toxic effects • accumulation of subclinical damage • e.g. inhibiting blood coagulation (rodenticides) • accumulation of chemical agent • crossing concentration threshold • e. g. mercury, cadmium in liver

7. Target Organs of Toxic Effects • nervous system • liver • kidney • ... • many toxic agents cause multi organ damage

8. Agent Group Example:Organic Solvents • hydrocarbons • alcohols • carbonic acids • small chlorinated hydrocarbons • esters (lactons), ethers, ketones, aldehyds

9. Example: Organic Solvents • commoneffects • effects caused by onesolvent only

10. Organic Solvents Common Effects Skin / GI mucosa: • extraction of fat (loss of protection) • solvent effect • irritation, inflammation • via cytokines, white blood cells • corrosion • necrosis

11. Corrosion caused by formic acid mixed with dichloro-methane

12. Organic SolventsCommon Effects Skin / mucosa: • ... Central nervous system • Reduced capacity (reaction time, ataxia), drowsiness, coma • nonspecific interaction with neuronal membranes • GABA-A receptor interaction? • Euphoria: excitation • inibiting neurons are more effected in beginning • specific effects in ‚mesolimbic reward system‘ • Risk of substance dependence • tolerance, withdrawal symptoms

13. Most Important: Ethanol • Long tradition in use in many cultures • recreational stimulant • Social importance • 150 fatalities from acute intoxications • 30,000 fatalities from chronic consumption per year in Germany • 2,500,000 people with alcohol dependency • Ethanol consumption plays a role in > 50 % of all legal procedures / cases

14. Organic Solvent With High Neurotoxic Potency: Gamma Hydroxybutyric Acid Users‘ term: liquid ecstasy

15. GHB Case Report (GIZ-Nord Poisons Centre, 1999) • 20yo male to ‚ecstasy and two doses of liquid ecstasy (ostentatious: ‚..a narcotic used for cattle‘) • rapid development of sedation, emergency doctor was called • deep coma, heart rate initially 100 /min, bradycardia developed, insufficient ventilation • sudden awakening 2 h later, leaving the hospital against medical advice • GHB found in blood: 123 mg/l

16. Unusual high Potency: GHB • GHB induces symptoms similar to those induced by ethanol • The dose needed is much higher • 2 g GHB correspond to 200 g ethanol • accidental ingestion may induce severe symptoms

17. Organic SolventsCommon Effects Skin / mucosa: • ... Central nervous system • ... Peripheral nervous system - • Polyneuropathy (long term exposure) • Malerkrankheit (painters‘ disease, occupational)

18. Polyneuropathy • Paraesthesia (tingling, numbness, burning, or prickling sensations in the feet or toes, feeling like wearing gloves) • Failure of muscle action (e.g. ataxia) Mechanism • Axonal swelling (reversible) • Axonal degeneration and demyelination • Failure of nerve signal transmission • Best studied for n-hexane, activated to 2,5-hexanedione,forming pyrrol adducts with primary amino groups leading to cross-linking of neurofilaments

19. Organic Solvents Skin / mucosa • extraction of fat • Irritation, inflammation • (corrosion) Nervous system - central • Reduced brain capacity, euphoria Nervous system - peripheral • Polyneuropathy (long term exposure) Further organ failures ... caused only by chlorinated hydrocarbons and some ‚toxic‘ alcohols

20. Tetrachloromethane (CCl4) • Easily absorbed from gastrointestinal tract or skin • CYP based metabolism in the liver forming CCl4 + e-  CCl3 + Cl-CCl3 + O2 CCl3OO • induces lipid peroxidation • induces liver failure • leads to jaundice and hepatic coma • CCl4 strongly regulated by EU law

21. Toxic Effects of Alcohols • Ethanol: solvent effects, chronic high dose exposure: several organs damaged: liver, brain, pancreas ... (> 100 different diseases) • Methanol: solvent effects, in addition toxic metabolite effects: acidosis, optical nerve damage • Glycols: solvent effects, in addition toxic metabolite effects: acidosis, renal damage

22. Hepatotoxic Effect of Ethanol • EtOH is oxidized to acetaldehyde • acetaldehyde inhibits -oxidation of free fatty acids • Alcoholic fatty liver (90 - 100 %) • EtOH induces CYP 2E1 • CYP 2E1 generates reactive oxygen species (ROS) • ROS induce inflammation • Alcohol hepatitis (30 %) • chronic inflammation induces fibrogenesis • Alcoholic cirrhosis (10 - 20 %) • lipid peroxidation: trans-hydroxy-2-nonenal • DNA adducts: cancerogenesis • Hepatocellular cancer (1 - 2 %)

23. Chemical Carcinogenesis 1st step - Initiation • DNA as target - chemical modification of DNA leads to DNA damage and mutation • Important role of DNA repair • overloaded or impaired 2nd step - Promotion • Stimulation of cell proliferation 3rd step - Progression • Further mutations, invasive growth, metastasis

24. Ethylene Glycol Automotive Antifreeze

25. ADH ethylene glycol glycolic aldehyd glycolic acid ADH glycolic acid glyoxylic acid oxalic acid (3%) Ethylene Glycol Metabolism:Metabolic activation to glycolic acid and oxalic acid

26. Ethylene Glycol Metabolism:Formation of Calcium Oxalate In The Nephron soluble oxalate precipitated calcium oxalate

27. Toxic Effect of Ethylene Glycol • acute euphoria, drowsiness, coma • metabolic acidosis: blood pH below 7.35 • ventilatory dysfunction (Kussmaul respiration) • multi organ failure • acute renal failure • calcium oxalate precipitates in the nephron • polyuria • anuria

28. Therapy of Ethylene Glycol Poisoning • Antidote therapy: fomepizol • Inhibits formation of toxic metabolite(s) • if treatment starts early • Hemodialysis • enhanced elimination of ethylene glycol and accumulated toxic metabolites

29. ethylene glycol glycolic aldehyd glycolic acid Fome-pizol ADH glycolic acid glyoxylic acid oxalic acid (3%) Ethylene Glycol • Toxikokinetics • Metabolic activation to glycolic acid and oxalic acid ADH

30. Methanol • industrial solvent, non-EU parfums • fuel for model aircraft • illegal alcoholic drinks

31. Love Meter

32. ADH folic acid Methanol Metabolism Methanol formaldehyde formic acid carbon dioxide

33. Toxic Effect of Methanol • acute euphoria, drowsiness, coma • metabolic acidosis: blood pH below 7.35 • ventilatory dysfunction (Kussmaul respiration) • multi organ failure • visual disturbances • mechanism unknown (inflammation of optical nerve?) • blindness Therapy: like ethylene glycol poisoning plus folic acid

34. Overview: Target Organs of Important Toxic Effects • Nervous system: solvents, insecticides • Liver: carbon tetrachloride, paracetamol • Lung: particulate matter, herbicides • Several organs: cyanide, glycols, methanol, benzene, heavy metals, dioxins