Mercury toxicity and antioxidants: part I: role of glutathione and alpha-lipoic acid in the treatment of mercury toxicity - Mercury Toxicity - Brief Article

Alternative Medicine Review, Dec, 2002 by Lyn Patrick

Elemental Mercury

Elemental mercury, found in thermometers, thermostats, dental amalgams, and mercury added to latex paint, eventually enters a vaporized state. Eighty percent of inhaled elementary mercury vapor is absorbed and can cross the blood-brain barrier or reach the placenta. (2) Mercury vapor in the gastrointestinal tract is converted to mercuric sulfide and excreted in the feces. (6) Mercury vapor in the kidneys, however, the main repository for elemental mercury, is carried to all parts of the central nervous system as a lipid-soluble gas. Mercury vapor can also be oxidized to inorganic mercury by catalase and can attach to the thiol groups in most proteins--enzymes, glutathione, or almost any structural protein. (7) Elemental mercury can also be methylated by microorganisms in soil and water and potentially the human gastrointestinal track, (8) where it can then be transformed into organic methylmercury, the form found in fish, fungicides, and pesticides. Elemental mercury and its metabolites have the toxic effect of denaturing biological proteins, inhibiting enzymes, and interrupting membrane transport and the uptake and release of neurotransmitters. (7) Chronic exposure most commonly manifests as a triad of increased excitability and irritability, tremors, and gingivitis. (2) Less commonly, chronic exposure causes central and peripheral nervous system damage, manifesting as a characteristic fine tremor of the extremities and facial muscles, emotional lability, and irritability. Rarely, significant exposure can cause acrodynia or "pink disease," involving a pink rash on the extremities, pruritis, paresthesias, and pain. (9)

Inorganic Mercury

Inorganic mercury (mercury salts) is found in cosmetic products, laxatives, teething powders, diuretics, and antiseptics. (2) Inorganic mercury can be formed from the metabolism of elemental mercury vapor or methylmercury. (7) Although inorganic mercury does not normally reach the placenta or cross the blood brain barrier, it has been found in the neonatal brain due to the absence of a fully formed blood-brain barrier. (6) Inorganic mercury is complexed with glutathione in the liver and secreted in the bile as a cysteine-mercury or glutathione-mercury complex. Chronic exposure to inorganic mercury salts primarily affects the renal cortex (10) and may manifest as renal failure (dysuria, proteinuria, hematuria, oliguria, and uremia) or gastrointestinal problems (colitis, gingivitis, stomatitis, and excessive salivation). Irritability and occasionally acrodynia can occur. (2)

Organic Mercury

Considered the most toxic and most frequent form of mercury exposure, organic mercury is found in fish, poultry that has been led fishmeal, pesticides, fungicides, insecticides, and thimerosal-containing vaccines. Thimerosal, which is 49.6-percent ethylmercury (a form of organic mercury), has been used as a preservative in vaccinations since the 1930s. It is currently mixed with DTaP, HIB, and hepatitis B vaccines or is used in the manufacturing process for vaccines, with resultant trace amounts being present in the final product. Based on existing Centers for Disease Control (CDC) recommendations for vaccinations, a typical six-month-old child, if receiving all thimerosal-containing vaccines, could potentially be injected with as much as 187.5-200 [micro]g of methylmercury; the equivalent of more than 1.0 [micro]g per day. This amount exceeds the reference limits for exposure to mercury set by the EPA of 0.1 [micro]g/kg/day. (11) In the United States, at the FDA's request, all vaccines are currently being produced as thimerosal-free or thimerosal-reduced (> 95-percent reduction) vaccines. Thimerosal-preserved vaccines are still available and used in clinical practice.

Methylmercury is almost completely absorbed (95-100 percent) in the human gastrointestinal tract, (2,7) 90 percent of which is eventually eliminated through the feces. Methylmercury is present in the body as a water-soluble complex, mainly with the sulfur atom of thiol ligands, (7) and crosses the blood-brain barrier complexed with L-cysteine in a molecule resembling methionine. Methylmercury is absorbed into the placenta and stored in the fetal brain in concentrations that exceed maternal blood levels. (12) After being released from cells in a complex with reduced glutathione, methylmercury is degraded in the bile duct to an L-cysteine complex. Only 10 percent of methylmercury is eliminated through the kidneys. The rest either undergoes enterohepatic recycling or demethylation by microflora in the intestine and immune system and eventual elimination through the feces.