Cytochrome P-450IIE1 is a constitutive, hepatic enzyme that has been implicated in the activation of pro-toxins and pro-carcinogens. Studies with animals have shown that P-450IIE1 can be significantly induced by a class of compounds that include ethanol, acetone, and isoniazid, as well as by abnormal metabolic states such as fasting, obesity, and diabetes. The major hypothesis to be tested in this proposal is that humans exposed to the same class of chemicals, or with a similar altered metabolic state, will have elevated levels of P-450IIE1 enzyme and can be identified with an in vivo catalytic probe. Four compounds (enflurane, chlorzoxazone, 4-methylpyrazole, and acetone) have been identified as potential probes based on literature reports and preliminary results. The utility of probes based on literature reports and preliminary results. The utility of probe candidate(s) will be validated by: a) determining the in vitro catalytic specificity of the probe towards human liver P-450IIE1, b) identifying an in vivo metabolic clearance parameter that reflects intrinsic P-450IIE1 catalytic activity, and c) determining whether the in vivo clearance parameter predicts direct measurements of hepatic P-450IIE1 levels in normal and isoniazid-treated populations. Once developed, the in vivo probe will be used to study the inducibility of functional P-450IIE1 enzyme in people with Type I and Type II diabetes, the morbidity obese, and obese people experiencing rapid weight loss. If P-450IIE1 levels are significantly elevated in selected human populations, those persons will be at greater risk for developing the carcinogenicities and cytotoxicities thought to be related to P-450IIE1 catalytic activity. This proposal will provide a safe and facile method for their identification.
