In Vitro Metabolism of 1,1-Dichloroethylene By Rat Hepatic Mitochondria and Microsomes (Cytochrome P-450, Chlorinated Hydrocarbon, Hepatotoxicity).

1,1-Dichloroethylene (vinylidene chloride, VDC) is widely used in the production of plastics. It is also a potent, acute hepatotoxin. The in vitro metabolism of VDC by rat hepatic microsomes and mitochondria was investigated by quantitating changes in microsomal cytochrome P-450 and heme contents, cytochrome P-450 linked enzyme activities; headspace disappearance of VDC over mitochondria and microsomes, and metabolite (monochloroacetate) formation in these two preparations. Microsomal cytochrome P-450 has been shown to have an important role in oxidative metabolism of VDC. Microsomal cytochrome P-450 content was decreased by in vitro exposure of VDC in a concentration and NADPH dependent manner, possibly as a consequence of heme destruction. There was no observable VDC-induced lipid peroxidation. VDC exposure caused concentration dependent decreases of benzphetamine N-demethylase, ethoxycoumarin O-deethylase, and aniline hydroxylase activities. Differences in the destructive effect of VDC on these enzyme activities suggest that multiple cytochrome P-450 isozymes participate in the microsomal metabolism of VDC. Headspace disappearance of VDC was used as an indirect measure of VDC metabolism. Headspace disappearance of VDC occurred at a faster rate in mitochondria than in microsomes on a nmole per mg protein per minute basis. Headspace disappearance of VDC over microsomes was NADPH dependent while that over mitochondria was partially NADPH dependent. Headspace disappearance of VDC over mitoplasts (mitochondria without outer membrane) was similar to that over mitochondria, indicating mitochondrial metabolism of VDC takes place in the inner membrane and matrix compartment of mitochondria. The microsomal and mitochondrial VDC metabolite monochloroacetate was identified quantitatively by GC and qualitatively by GC-MS. The relative rate of monochloroacetate formation was greater in mitochondria than in microsomes. Production of monochloroacetate in mitochondria and microsomes appeared to be an enzymatic process. Phenobarbital induction increased the formation of monochloroacetate in microsomes but not in mitochondria. Production of monochloroacetate in mitochondria may be by cytochrome P-450 or some other NADPH dependent system.Ph.D.Environmental scienceUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/160103/1/8422205.pd