QUANTITATIVE-DETERMINATION OF URINARY LIPID METABOLITES BY HIGH-PRESSURE LIQUID-CHROMATOGRAPHY AS INDICATORS OF MENADIONE-INDUCED IN-VIVO LIPID-PEROXIDATION

The one- and two-electron-reduction reactions of menadione result in t he generation of reactive oxygen species which are believed to mediate the cytotoxicity of this xenobiotic. The induction of lipid peroxidat ion in liver and isolated hepatocytes occurs in response to the menadi one-mediated formation of reactive oxygen species. However, studies on the effects of menadione on the urinary excretion of lipid metabolite s have not been conducted. The effect of a single oral dose of 60 mg m enadione/kg to rats on the urinary excretion of the lipid metabolites malondialdehyde (MDA), formaldehyde (FA), acetaldehyde (ACT), and acet one (ACON) has been examined over 48 h post-treatment. The urinary met abolites were identified by gas chromatography-mass spectrometry and q uantitated by high pressure liquid chromatography. Time-dependent incr eases in the urinary excretion of the four metabolites were observed a fter menadione administration. Over the 48 h of the study, the menadio ne-induced urinary excretion of MDA, FA, ACT, and ACON increased by ap proximately 1.5-, 2.0-, 1.7-, and 3.2-fold, respectively, relative to control animals. The data were expressed in nmoles/kg body weight/4.5 h. The results clearly demonstrate that menadione increases the urinar y excretion of four lipid metabolites. These metabolites may have wide spread applicability as biomarkers of altered lipid metabolism in dise ase states and exposure to environmental pollutants/xenobiotics which induce enhanced lipid peroxidation. The non-invasive methods offer adv antages over most other methods for assessing oxidative stress in vivo .