aldrin and ethoxyresorufin

The metabolism of three model substrates for the cytochrome P450 dependent mono-oxygenase enzyme system (P450-MMO) was studied in microsomes isolated from skin and liver of young adult and senescent C57B1/6J mice. The substrates chosen were aldrin (AE), 7-ethoxycoumarin (EOC), and 7-ethoxyresorufin (EOR). Both EOC and EOR activities were lower in senescent skin. By contrast, no-age related changes were seen in senescent liver. AE was similar in young and old, in both tissues. We suggest that some important age-related differences in cutaneous xenobiotic metabolism do occur, but that these are not mirrored by hepatic differences, and are substrate specific. Previous work from these laboratories would also suggest significant species differences.

Topics: Aging; Aldrin; Animals; Coumarins; Cytochrome P-450 CYP1A1; Inactivation, Metabolic; Mice; Mice, Inbred C57BL; Microsomes, Liver; Mixed Function Oxygenases; Oxazines; Skin

The clearance of many oxidized drugs falls with age. Whilst factors such as reduced liver size, blood flow and specific enzyme activity may be important, the possibility that reduced enzyme affinity for substrate contributes to this fall has not hitherto been investigated. Using liver microsomes from 12 young adult and 12 elderly male Norwegian Brown rats we defined the kinetics of ethoxyresorufin-O-de-ethylation and aldrin epoxidation, specific substrates for the 3-methylcholanthrene inducible and phenobarbitone inducible forms of cytochrome P450, respectively. Our results show a marked fall in the maximal activity of both enzymes in advanced age whether expressed in terms of microsomal protein or unit of cytochrome P450, but with no change in apparent enzyme affinity (Km). Since Km is unchanged, we feel that qualitative age-related changes in cytochrome P450 are unlikely. Reduced metabolism may be due to age-related alterations in coenzymes or smooth endoplasmic reticulum lipid membranes.

Topics: Aging; Aldrin; Animals; Cytochrome P-450 Enzyme System; Enzyme Induction; In Vitro Techniques; Kinetics; Methylcholanthrene; Microsomes, Liver; Oxazines; Phenobarbital; Rats

The metabolism of nine model substrates for the mixed-function oxidase system was studied in skin and liver microsomes from Balb/C mice. Rates of skin metabolism per mg microsomal protein ranged from 0.5-15% of liver rates depending on the substrate. Relative to liver, mouse skin preferentially metabolized ethoxyresorufin, benzo[alpha]pyrene and diphenyloxazole over aldrin, coumarin and the C1-C4 7-alkyl umbelliferone ethers. NADPH-cytochrome P-450-dependent metabolism of aldrin and ethoxyresorufin was differentially inhibited in skin microsomes by metyrapone and alpha-naphthoflavone, respectively. Biphasic Eadie-Hofstee plots were obtained in both skin and liver microsomes for the metabolism of aldrin, whereas metabolism of ethoxyresorufin in both systems was described by linear kinetics. It is concluded that mouse skin contains multiple forms of cytochrome P-450, and that forms functionally analogous to those induced by polycyclic hydrocarbons in rodent liver are present in untreated mouse skin.

Topics: Aldrin; Animals; Cytochrome P-450 Enzyme System; Female; Kinetics; Mice; Mice, Inbred BALB C; Microsomes; Microsomes, Liver; Mixed Function Oxygenases; Oxazines; Skin; Substrate Specificity; Tissue Distribution

Topics: Aldrin; Animals; Anisoles; Benzoflavones; beta-Naphthoflavone; Butadienes; Coumarins; Cytochrome P-450 Enzyme System; Female; Kidney Tubules, Proximal; Lauric Acids; Male; Mice; Oxazines; Oxygenases; Rats