Screening Countermeasures to Resolve Metabolic Toxicity

Sodium monofluoroacetate is a metabolic poison which has been used since World War II to control rodent and predator populations. Though it is widely used in many countries, its use in the United States is regulated due to safety concerns. Signs of intoxication include cardiac, pulmonary, neurologic, renal and gastrointestinal complaints. No medical treatment for fluoroacetate poisoning has been identified, and exposure is usually fatal. In recent years, this toxin has been linked to terrorist organizations. It has also been smuggled into and sold illegally in the United States. The mechanism of action of fluoroacetate has been understood for decades. Via lethal synthesis, fluoroacetate is converted in cellulo to fluorocitrate, a tightly binding competitive inhibitor of aconitase which effectively halts the citric acid cycle. This blockade results in cellular and mitochondrial dysfunction. In response to inhibited pyruvate metabolism, previous studies have recommended supporting alternative energy pathways by introducing substrates of amino acid or fatty acid metabolism. Previous studies have also suggested antioxidants may be effective countermeasures to fluoroacetate intoxication. However, in animal studies investigating these approaches, results have been inconclusive. We have developed a model of fluorocitrate exposure to characterize intoxication at the cellular level and to screen candidate countermeasures. Previous work has shown fluoroacetate is not efficiently metabolized to fluorocitrate ex vivo; as such, fluorocitrate toxicity serves as a better model. In metabolically active cardiac myocytes, introduction of fluorocitrate rapidly affects multiple metabolic parameters. Cells show dose‐dependent decreases in basal respiration, ATP production, maximal respiration, and coupling efficiency. These data recommend this model to screen antioxidants for their ability to mediate mitochondrial dysfunction. Our work also shows that dependence on fatty acid metabolism increases over a period of 8 hours after exposure to fluorocitrate. Complementary data show that glucose metabolic capacity decreases after exposure. These data suggest fluorocitrate causes cells to shift their metabolic profile to avoid the compromised citric acid cycle and utilize alternative energy sources. It seems, in response to fluorocitrate exposure, inhibited glucose metabolism is countered by increasing metabolic dependence on fatty acid oxidation for energy. These data recommend a treatment strategy which supports alternative energy pathways by providing cells with substrates that enter glutamine or fatty acid metabolism. Future directions will examine amino acid oxidation and evaluate mediators of alternativeenergy pathways as candidate countermeasures.