Rodenticides and pesticides pose a significant threat, not only to the environment, but also directly to humans by way of accidental and/or intentional exposure. Metal phosphides, such as aluminum, magnesium, and zinc phosphides, have gained popularity owing to ease of manufacture and application. These agents and their hydrolysis by-product, phosphine gas (PH3), are more than adequate for eliminating pests, primarily in the grain storage industry. In addition to the potential for accidental exposures in the manufacture and use of these agents, intentional exposures must also be considered. Ingestion of metal phosphides is a well-known suicide route, especially in Asia. An intentional release of PH3 in a populated area cannot be discounted. Metal phosphides cause a wide array of effects that include cellular poisoning, oxidative stress, cholinesterase inhibition, circulatory failure, cardiotoxicity, gastrointestinal and pulmonary toxicity, hepatic damage, neurological toxicity, electrolyte imbalance, and overall metabolic disturbances. Mortality rates often exceed 70%. There are no specific antidotes against metal phosphide poisoning. Current therapeutic intervention is limited to supportive care. The development of beneficial medical countermeasures will rely on investigative mechanistic toxicology; the ultimate goal will be to identify specific treatments and therapeutic windows for intervention.
Results of our previous studies on the chemical warfare agent sulfur mustard (2,2'-dichlorodiethyl sulfide) suggested that mustard-induced inhibition of glycolysis is not solely a function of NAD+ depletion. To define the role of NAD+ in mustard-induced metabolic injury, we examined the effects of mustard+/-niacinamide on energy metabolism in cultured human keratinocytes. Sulfur mustard caused concentration-dependent decreases in viable cell number and ATP content at 24 hours, but not earlier, and time- and concentration-dependent glycolytic inhibition and NAD+ depletion as early as 4 hours. Niacinamide partially protected NAD+ levels at all time points, but did not prevent adverse effects on glycolysis, intracellular ATP, or viable cell number. These results support our earlier conclusions and suggest that sulfur mustard may inhibit glycolysis directly.
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