Lymphocytes Assess Exposure to Toxic Drugs

Report:

Lymphocytes to serve as liver surrogates

Investigator: Prahlad K. Seth

Wednesday Jul 10th, 2002

by Anne Jacobson

A novel non-invasive method that uses lymphocytes to assess the effects of exposure to toxic drugs and chemicals could be a boon to both environmental health research and public health, Indian scientists said today.

The research could have a "quite remarkable" impact on "life or death" clinical situations, says a leading expert.

Exposure to toxic drugs and chemicals can be difficult to assess, and usually requires examination of enzymes hidden in the liver. "Lymphocytes have obvious advantage for use in development of non-invasive assays to screen populations for toxicant exposure," said Prahlad K. Seth, a researcher at the Industrial Toxicology Research Centre in Lucknow, India.

To assess the usefulness of blood lymphocytes in screening for environmental exposure, Seth and his colleagues looked for cytochrome P450s (CYPs) - a diverse class of liver enzymes used to metabolize chemicals - in freshly isolated rat lymphocytes.

Seth challenged male rats with a range of toxicants known to induce CYP enzymes. Sixteen hours after the last chemical dose, he isolated lymphocytes and looked for three P450 isozymes known to be involved in xenobiotic metabolism: P450-1A1, -2E1 and -3A.

Using PCR amplification and Western immunoblotting studies, Seth found that exposure to the toxicants showed significant constitutive and inducible mRNA and protein expression of P450-2E1 and -3A, and inducible expression of P450-1A1.

The researchers also detected both inducible and constitutive activity in CYP-associated monooxygenase activity. Using specific CYP inhibitors, Seth also found that P450-1A1, -2E1 and -3A isozymes in lymphocytes catalyze the activity of three specific monooxygenases - EROD, NDMA-d and EMD. In each case, the enzymes induced 1.8- to 3.3-fold increases in monooxygenase activity.

Comparing CYP enzyme regulation in lymphocytes with the liver isoenzymes, the researchers found that enzymes isolated from the two different sources correlated well. Given such strong similarities between the expression of lymphocyte and liver CYP isozymes, P450 expression in peripheral blood lymphocytes can serve as a surrogate for studying tissue isozymes, Seth said.

One of the most challenging tasks facing environmental health research is the identification of genotype changes associated with phenotypes of increased resistance or susceptibility.

Lymphocytes may also be useful phenotypic tools for studying chemical exposure and identifying populations at heightened risk, Seth said. "By generating a P450 expression profile, blood lymphocytes provide a sensitive and mechanistic-based biomarker of chemical exposure," he said.

A blood lymphocyte assay based on this finding may also be useful in identifying environmental agents that cause disease and the true risks associated with their exposure, he added.

This finding, if it holds true in humans, is "potentially very significant," said Kim Rainsford, director of biomedical research at the Sheffield Hallam University in Sheffield, England.

There is tremendous genetic variations in CYP enzymes and different polymorphisms can exert wildly different metabolic properties, Rainsford explained. Such differences can translate to "life or death" clinical situations, he said.

Drugs relatively benign to some patients could be lethal to others, for example. A simple bedside assay designed to pick up differential reactivity of P450 polymorphisms, he said, could have a "quite remarkable" impact on patient treatment.

WCP 2002

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