METABOLISM AND TOXICITY OF 2-METHYLPROPENE (ISOBUTENE) - A REVIEW

2-Methylpropene (MP) or isobutene is a gaseous chemical used on a larg e scale in the synthetic rubber industry. The present review covers th e rather scarce literature on MP with respect to its metabolic fate an d toxicity in laboratory animals and humans. It has been shown both ir t vivo and in vitro that MP is metabolized to the primary metabolite 2 -methyl-1,2-epoxypropane (MEP) by rodent and human liver tissue. The f ormation of this reactive epoxide intermediate is catalyzed by CYP2E1, while epoxide hydrolase and glutathione S-transferase appear to be in volved in its inactivation. in rats, the capacity to absorb and metabo lize MP is saturable. MP is oxidized to compounds that are mainly excr eted in urine. Data indicate that rodents can tolerate low levels of M P without apparent toxicity. The primary metabolite MEP, however, is a ble to produce genetic damage in both prokaryotic and eukaryotic cells in vitro. MP is thus not toxic per se but elicits metabolic activatio n to become potentially harmful. Consequently, the balance between for mation and detoxification of MEP plays a key role in determining the p otential toxicity of the parent compound. Obviously, further research, including repeated exposure toxicity studies, is required before an e stimation of the risk for man can be made.