CYTOCHROME P450-DERIVED ARACHIDONIC-ACID METABOLISM IN THE RAT-KIDNEY- CHARACTERIZATION OF SELECTIVE INHIBITORS

We characterized the inhibitory activity of several acetylenic and ole finic compounds on cytochrome P450 (CYP)-derived arachidonic acid omeg a-hydroxylation and epoxidation using rat renal cortical microsomes an d recombinant CYP proteins. Among the acetylenic compounds, 6-(2-propa rgyloxyphenyl)hexanoic acid (PPOH) and -methylsulfonyl-6-(2-propargylo xyphenyl)hexanamide were found to be potent and selective inhibitors o f microsomal epoxidation with IC50 values of 9 and 13 mu M, respective ly. On the other hand, 17-octadecynoic acid inhibited both omega-hydro xylation and epoxidation of arachidonic acid with IC50 values of 7 and 5 mu M, respectively. The olefinic compounds N-methylsulfonyl-12,12-d ibromododec-11-enamide (DDMS) and 12,12-dibromododec-11-enoic acid (DB DD) exhibited a high degree of selectivity inhibiting microsomal omega -hydroxylation with an IC50 value of 2 mu M, whereas the IC50 values f or epoxidation were 60 and 51 mu M for DDMS and DBDD, respectively. St udies using recombinant rat CYP4A isoforms showed that PPOH caused a c oncentration-dependent inhibition of omega-hydroxylation and 11,12-epo xidation by CYP4A3 or CYP4A2 but had no effect on CYP4A1-catalyzed ome ga-hydroxylase activity. On the other hand, DDMS inhibited both CYP4A1 - and CYP4A3- or CYP4A2-catalyzed arachidonic acid oxidations. Inhibit ion of microsomal activity by PPOH, but not DDMS, was time- and NADPH- dependent, a result characteristic of a mechanism-based irreversible i nhibitor. These studies provide information useful for evaluating the role of the CYP-derived arachidonic acid metabolites in the regulation of renal function and blood pressure.