Effect of tetraethylthiuramdisulphide and diethyl-dithiocarbamate on nickel toxicokinetics in mice

A review of pitfalls and progress in chelation treatment of metal poisonings

Most acute and chronic human metal poisonings are due to oral or inhalation exposure. Almost 80% of published animal experiments on chelation in metal poisoning used single or repeated intraperitoneal, intramuscular or intravenous administration of metal and chelator, impeding extrapolation to clinical settings. Intramuscular administration of dimercaptopropanol (BAL) has until now been used in acute arsenic, lead, and mercury poisonings, but repeated BAL administration increased the brain uptake of As, Pb and Hg in experimental animals. Also, diethyl dithiocarbamate (DDC) has been used as antidote in acute experimental animal parenteral Cd poisoning, and both DDC and tetraethylthiuram disulfide (TTD, disulfiram, Antabuse) have been used in nickel allergic patients. However, even one dose of DDC given immediately after oral Cd or Ni increased their brain uptake considerably. The calcium salt of ethylenediamminetetraacetic acid (CaEDTA) but not dimercaptosuccinic acid (DMSA) increased the brain uptake of Pb. In oral Cd or Hg poisoning, early oral administration of DMSA or dimercaptopropane sulfonate (DMPS) increased survival and reduced intestinal metal uptake. Oral administration of Prussian Blue or resins with fixed chelating groups that are not absorbed offer chelation approaches for decorporation after oral exposure to various metals. Diethylenetriaminepentaacetic acid (DTPA) nebulizers for pulmonary chelation after inhalation exposure need further development. Also, combined chelation with more than one compound may offer extensive advances. Solid knowledge on the chemistry of metal chelates together with relevant animal experiments should guide development of chelation procedures to alleviate and not aggravate the clinical status of poisoned patients.

Disturbance of aerobic metabolism accompanies neurobehavioral changes induced by nickel in mice

The oral ingestion of soluble nickel compounds leads to neurological symptoms in humans. Deficiencies in aerobic metabolism induced by neurotoxic stimulus can cause an energy crisis in the brain that results in a variety of neurotoxic effects. In the present study, we focused on the aerobic metabolic states to investigate whether disturbance of aerobic metabolism was involved in nickel-induced neurological effects in mice. Mice were orally administered nickel chloride, and neurobehavioral performance was evaluated using the Morris water maze and open field tests at different time points. Aerobic metabolic states in the cerebral cortex were analyzed at the same time points at which neurobehavioral changes were evident. We found that nickel exposure caused deficits in both spatial memory and exploring activity in mice and that nickel was deposited in their cerebral cortex. Deficient aerobic metabolism manifested as decreased O2 consumption and ATP concentrations, lactate and NADH accumulation, and oxidative stress. Meanwhile, the activity of prototypical iron-sulfur clusters (ISCs) containing enzymes that are known to control aerobic metabolism, including complex I and aconitase, and the expression of ISC assembly scaffold protein (ISCU) were inhibited following nickel deposition. Overall, these data suggest that aerobic metabolic disturbances, which accompanied the neurobehavioral changes, may participate in nickel-induced neurologic effects. The inactivation of ISC containing metabolic enzymes may result in the disturbance of aerobic metabolism. A better understanding of how nickel impacts the energy metabolic processes may provide insight into the prevention of nickel neurotoxicity.

Preventing disulfiram hepatitis in alcohol abusers: inappropriate guidelines and the significance of nickel allergy

Disulfiram hepatitis, although sometimes fatal, is a very rare complication of alcoholism treatment. A disproportionate number of cases are associated with disulfiram treatment for nickel allergy and unrecognized nickel sensitivity may partly explain the surprisingly high proportion of female victims- about 60%. US guidelines formulated in 1988 suggest that alcoholic patients should not be started on disulfiram unless liver toxicity tests have been done and, if elevated, returned to normal. This advice is unsound and contrasts with medical attitudes to the prevention of other rare side effects. It has led to significant delays in starting treatment which are probably much more hazardous than the very slight risks of hepatotoxicity. We recommend that the guidelines be modified in favour of an approach which emphasizes the education of patients and their carers and clinical rather than laboratory monitoring.

Nickel

Nickel is an essential element for at least several animal species. These animal studies associate nickel deprivation with depressed growth, reduced reproductive rates, and alterations of serum lipids and glucose. Although there is substantial evidence of an essential status for nickel in animals, a deficiency state in humans has not been clearly defined. Nickel is a silver-white metal with siderophilic properties that facilitate the formation of nickel-iron alloys. In contrast to the soluble nickel salts (chloride, nitrate, sulfate), metallic nickel, nickel sulfides, and nickel oxides are poorly water-soluble. Nickel carbonyl is a volatile liquid at room temperature that decomposes rapidly into carbon monoxide and nickel. Drinking water and food are the main sources of exposure for the general population with the average American diet containing about 300 micrograms Ni/d. Nickel is highly mobile in soil, particularly in acid soils. There is little evidence that nickel compounds accumulate in the food chain. Nickel is not a cumulative toxin in animals or in humans. Almost all cases of acute nickel toxicity result from exposure to nickel carbonyl. The initial effects involve irritation of the respiratory tract and nonspecific symptoms. Patients with severe poisoning develop intense pulmonary and gastrointestinal toxicity. Diffuse interstitial pneumonitis and cerebral edema are the main cause of death. Sodium diethyldithiocarbamate is an investigational drug used to chelate nickel following exposure to nickel carbonyl. Nickel is a common sensitizing agent with a high prevalence of allergic contact dermatitis. Nickel and nickel compounds are well-recognized carcinogens. However, the identity of the nickel compound or compounds, which cause the increased risk of cancer, remains unclear. Currently, there are little epidemiological data to indicate that exposure to metallic nickel increases the risk of cancer, or that exposure to the carcinogenic forms of nickel causes cancer outside the lung and the nasal cavity.