1. 1 HEAVY METAL TOXICITY Prof. DR. Sri Agus Sudjarwo Knowledge Objectives The student should understand and know: 1.metabolism, absorption, distribution, excretion and mechanism of toxicity for each of the metals. 2. characteristics of a good biological chelating agent. 3. uses of chelating agents in terms of: a. route of administration b. mechanism of action c. specificity d. stability of the heavy metal -chelator complex e. toxicity of chelator and the complex

4. In Utero Exposure Heavy Metals that bioconcentrate in placental tissue: MercuryLeadCadmiumArsenic

7. Hazard + Exposure = Risk Individual Susceptibility Dose / Response

8.  Sources: › copper, lead and zinc smelting auto exhaust › cigarette smoke (a cigarette contains 1-2 ug Cd)  Uses: › metal plating › nickel-cadmium batteries › solders › paint pigments (blue) › plastic stabilizers › photographic chemicals › fungicides  readily absorbed and accumulated in plants From: Klaassen et al., Chap. 19, Philp, Chap. 6

9. pharmacokinetics:  inhalation: › smelters, cigarette smoke › 15-50% absorbed  ingestion:  main source is liver and kidney of meats  6% absorbed, greater if deficient in calcium, zinc or iron

10. pharmacokinetics:  distribution: › bound to albumin in plasma and red blood cells › transported to liver, pancreas, prostate and kidney, with eventual transfer to kidney  50-75% of total body Cd is found in liver and kidney  Metallothionein: protein rich in cysteine  synthesis induced by Cd in kidney  Elimination: urine › half-life in humans is 20 - 30 years

11. Toxicity  mechanisms: › binding to –SH groups › competing with Zn and Se for inclusion into metalloenzymes › competing with calcium for binding sites (calmodulin)  Kidney toxicity: › free Cd binds to kidney glomerulus › proximal tubule dysfunction associated with beta2- macroglobulin From: Klaassen et al., Chap. 19, Philp, Chap. 6

12. Toxicity  Lung toxicity: › edema and emphysema by killing lung macrophages and inhibition alpha 1 antitrypsin  Skeletal effects: › Osteoporosis and osteomalacia (pseudofractures)  Cancer: › carcinogenic in animal studies › 8% of lung cancers may be attributable to Cd From: Klaassen et al., Chap. 19, Philp, Chap. 6

13. Japan (1940s)  effluent (outflow) from a lead-processing plant washed over adjacent rice paddies for many years › rice accumulated high level of Cd › community was poor (and therefore malnourished with respect to calcium) › acute toxicity: renal failure,anemia, severe muscle pain  named "Itai-Itai" disease ("ouch, ouch") From: Klaassen et al., Chap. 19, Philp, Chap. 6 Itai-itai victim

15.  Sources: › smelting of gold, silver, copper, lead and zinc ores › combustion of fossil fuels › agricultural uses as herbicides and fungicides › cigarette smoke  Environmental fate: › accumulates in plants › bioaccumulates in aquatic ecosystems (so fish consumption is a source)

17.  pharmacokinetics and dynamics: › absorbed via inhalation, ingestion and dermal exposure › mimics phosphate in terms of uptake by cells › Detoxified by methylation: decreased rates lead to increased toxicity (individual susceptibility) › Can cross placenta › accumulates in liver, kidney, heart and lung - later in bones, teeth, hair, etc. › half-life is 10 hr, excretion via kidneys From: Klaassen et al., Chap. 19, Philp, Chap. 6

18.  binds to sulfhydryl groups (and disulfide groups), disrupts sulfhydryl-containing enzymes (As (III)) › inhibits pyruvate and succinate oxidation pathways and the tricarboxylic acid cycle, causing impaired gluconeogenesis, and reduced oxidative phosphorylation

19. -substitution for phosphorus in biochemical reactions Replacing the stable phosphorus anion in phosphate with the less stable As(V) anion leads to rapid hydrolysis of high-energy bonds in compounds such as ATP. That leads to loss of high-energy phosphate bonds and effectively "uncouples" oxidative phosphorylation.

21.  acute: severe abdominal pain, fever, cardiac arrhythmia  chronic: muscle weakness and pain, gross edema, gastrointestinal disturbances, liver and kidney damage, swelling of peripheral nerves (neuritis), paralysis › liver injury: jaundice › peripheral vascular disease - blackfoot disease  chronic drinking water exposure in Taiwan and Chile › cancer (skin, lung. Maybe other organs) › Diabetes Melitus

22.  skin disease: › keratosis of palms and soles, and hyperpigmentation

27.  What tests could you do to detect exposure or effects? › Mee's lines: white lines on fingernails can be used to determine chronology of exposure  What could you prescribe for treatment? › Gastric lavage, activated charcoal › Hemodialysis › BAL chelation

29.  Leaded gasoline, paint, pb pipes  Pb affects nervous system, Heam biosynthesis and Kidney  Children are at high risk › Poor blood brain barrier › Absorb 30-40% of ingested Pb ( Pb&Ca) › Decreased iq tests at very low levels of Pb  10-20ug/dL

30. Distribution Initially carried in red cells and distributed to soft tissues (kidney and liver); redistributed to bone, teeth and hair mostly as a phosphate salt. Rates of absorption and distribution are greatly influenced by dietary intake and body stores of phosphate, calcium and iron relative to lead # high PO4, Pb storage in bone # high Vitamin D, Pb storage in soft tissue # low PO4, Pb sequestered in soft tissue # high Ca++, Pb sequestered in soft tissue Half life in blood 30-60 days, bone 20-30 years

31.  Lead binds to enzymes that have functional sulfhydryl groups, rendering them nonfunctional and further contributing to impairment in oxidative balance, leading to:  Autoimmunity  Depletion of glutathione  Increased levels of free radicals in tissue

32.  Adult have well developed BB barrier absorb 7% of ingested Pb and it affects primarily the periferal nervous system  Destroys myelin coating on nerves ( insulation like a wire) affects the conduction velocity of nerves( segmental demyelination, widening of nodes of ranvier)

33.  “ Blood lead concentrations as low as 2.07 µg/dL likely represent a public health hazard.”  In NHANES 1999 to 2000, 38% of US adults had a blood lead level above this threshold. Circulation 2006;114:1347-1349  42% of cataracts are related to bone lead JAMA. 2004;292:2750-2754

34.  Pregnancy and lactation  Lead mobilization during pregnancy is hazardous to the fetus  Lead passes across the placenta almost without hindrance.  Blood lead levels in mother and fetus  Elderly with osteoporosis Environ Health Perspect 1996;104(Suppl 1)

36.  Inorganic Pb goes to the CNS and decreases IQ test scores  Children absorb more Pb because of Ca and growth phase  Most important effects on CNS and they occur at low levels in children ( why Pb was banned from gasoline)

37.  ALA dehydratase is the rate Limiting enzyme in the biosynthesis of Haem  Enzyme has Fe binding site and it is very sensitive to inhibition by Pb  Inhibition by Pb results in porphyrin buildup in the blood and in the urine ( depending upon the degree of inhibition urine may be brown or black)  Inhibition of ALA dehydatase may be used as a biomarker of Pb exposure

38. 38

39.  Usually in adults results in a fanconi syndrome and leakage of phosphate and other nutrients in the urine  Effects are reversible if stop Pb exposure as are the effects of Pb on nerve conduction and Heam biosynthesis

40. WOMEN lead crosses the placenta low infant birth weight retarded mental development miscarriages premature birth MEN impotence sterility altered sperm-birth defects

42.  Pb blood levels indicate relatively recent exposure ( range from 1-20 ug/dL, with >20 dangerous for children, >50 adult toxicity)  Pb redistributes to the bone and behaves Like Ca ( Ca and phosphate mobilization can mobilize Pb, results in episodes of toxicity)  Half life of Pb in bone maybe 10 years and can cause formation of pb lines in bones

43.  Treat symptoms and try to lower Pb levels in blood and urine. Renal. Nueral and Haem effects are reversible  Chelating agents  EDTA ( iv)  DMCA ( oral)

44.  Carcinogenic in rats at high doses induces renal cancers ( may be due to Pb inclusion bodies)  Slightly mutagenic  Teratogenic

45.  Three forms of Hg with very different toxicities ( Inorganic Hg, Organic Hg and Hg Metal)  Hg metal ( thermometers, electrodes for electrolysis)  Organic Hg ( Fungicide, chemical industry)  Inorganic Hg ( fur cutting, felt hat manufacture)

46.  Most of the Environmental levels Of Hg come from natural sources ( valconos etc) › Swordfish accumulate Hg  Metallic Hg ( dental fillings)  Methyl Hg ( Minimatta bay, IraQ)

48.  Activity (mcg)/m³  Chewing Food 68  Tooth Brushing 272  Place Amalgam 2,000  Remove Amalgam 4,000  Polish Amalgam 4,000

49. Source Daily Intake (mcg) Amalgams 3.8 → 21 Fish3.0 Other foods3.6

51.  Inorganic ( effects mainly the Kidney)  Methyl Hg ( CNS effects sensory input loss of hearing, periferal vision delayed onset of symptoms may be related to cellular conversion of Methy Hg to Inorganic Hg Metallic Hg ( psychiatric effects, motor trembling in lips and hands, depression)

53. 53

54. 54

56.  Inorganic Hg binds to SH groups in cells and Inactivates enzymes ( inactivation of enzymes that protect the cell from oxidative stress SOD, Catalase)  Methyl Hg penetrates all cells in the body particularly the CNS  Hg metal may also form inorganic Hg and it also can penetrate many strauctures

57.  Bal Or Pen for Inorganic Hg and methyl Hg  Methyl Hg delayed onset of symptoms can confirm exposure by Hair measurements

58. 58  Water soluble  Resistant to biotransformation  Able to reach sites of metal storage  Capable of forming nontoxic complexes with toxic metals  Be excreted from the body  Have a low affinity for essential metals  the chelator-metal complex should be less toxic than the metal alone

59. 59 2,3-dimercatopropanol (dimercaprol) also known as British Anti Lewisite (BAL)- given IM in peanut oil Use: arsenic, mercury, antimony, lead, gold, zinc, bismuth. Half life is less than onehour. Toxicity: i. CNS convulsions in high dose ii. Increased Blood pressure due to tachycardia and peripheral constriction of arterioles. iii. Renal toxicity can be reduced by alkalizing the urine, which protects against dissociation of the metal-BAL complex. Toxicity is 50% + Anxiety + increased blood pressure + nausea, vomiting and headache

60. 60 Ethylene diamine-tetraacetic acid (EDTA) given IV as the Calcium disodium salt. Uses i. Disodium EDTA binds calcium in blood to prevent clotting- used in blood collection and storage ii. chelator for lead iii. only chelates circulating metal because EDTA cannot enter inside the cell membrane iv. frequently used in combination with BAL or penicillamine for treatment of lead poisoning Toxicity i. tubular destruction due to release of metal or the metal- EDTA complex in the kidney. ii. thrombophlebitis in some cases- too rapid infusion

61. 61

62. 62 d-isomer of beta,beta-dimethylcysteine (Penicillamine) given orally Uses i. lead, mercury, arsenic ii. copper - Wilson’s disease Toxicity i. l-isomer depletes pyridoxine (Vitamin B6), therefore d-isomer is used clinically ii. fever, skin rashes, leukopenia, nausea, vomiting iii. anaphylactic reactions (do not use in the case of allergic to penicillin)

63. 63 Deferoxamine Uses: iron (Fe3+) poisoning IM or slow IV. It has also been used orally to chelate iron poisoning Toxicity i. skin rash ii. histamine release with reduced blood pressure (shock) iii. Cataracts Trientine (triethylenetetramine HCl) is a polydentate chelating agent. It chelates copper and less toxic than penicillamine, but it is teratogenic in long term use. It is used for treating wilson’s disease (hepatolenticular degeneration).

64. 64

65. 65

66. 66

67. 67

68. 68