Catalase: its role in xenobiotic detoxification.

Catalase activity is found primarily in peroxisomes although in some species and in some organ systems, cytosolic catalase also may be involved in intracellular oxidant stress protection. Toxicology studies with repeat exposures to xenobiotics producing hydrogen peroxide either directly or indirectly generally indicate that the organisms develop resistance to the toxin (adaptation). This adaptation would result from induction of catalase activity in most target organs. The induction of hepatic peroxisomes accompanied by less than compensatory increase in catalase activity is now recognized as suggesting a potential for hepatotoxic and hepatocarcinogenic effects. Although these effects seem to also require mobilization of fatty acids, it is not clear if such mobilization is an absolute requirement. As would be expected, there are great differences among species in catalase activity thus making animal-human extrapolations difficult. Finally, with the exception of premature and neonatal animals, age-related variations in catalase activity do not seem to be large enough to have toxicological relevance. However, in old animals, their apparent inability to replace lost catalase activity after repeated stress may have major significance in explaining observed young-old differences in toxicity resulting from oxidant stress.