Electron spin resonance spectroscopy has been used to study
free radical generation in rats with acute
sodium formate poisoning. The in vivo spin-trapping technique was used with alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone (
POBN), which reacts with
free radical metabolites to form radical adducts, which were detected in the bile and urine samples from Fischer rats. The use of [(13)C]-
sodium formate and computer simulations of the spectra identified the 12-line spectrum as arising from the
POBN/
carbon dioxide anion radical adduct. The identification of
POBN/*CO(2)(-) radical adduct provides direct electron spin resonance spectroscopy evidence for the formation of *CO(2)(-) radicals during acute intoxication by
sodium formate, suggesting a
free radical metabolic pathway. To study the mechanism of
free radical generation by
formate, we tested several known inhibitors. Both
allopurinol, an inhibitor of
xanthine oxidase, and aminobenzotriazole, a
cytochrome P450 inhibitor, decreased
free radical formation from
formate, which may imply a dependence on
hydrogen peroxide. In accord with this hypothesis, the
catalase inhibitor 3-aminotriazole caused a significant increase in
free radical formation. The
iron chelator Desferal decreased the formation of
free radicals up to 2-fold. Presumably,
iron plays a role in the mechanism of
free radical generation by
formate via the Fenton reaction. The detection of
formate free radical metabolites generated in vivo and the key role of the Fenton reaction in this process may be important for understanding the pathogenesis of both
formate and
methanol intoxication.