Role of endogenous CYP450 metabolites of arachidonic acid in maintaining the glomerular protein permeability barrier.

This study examined the metabolism of arachidonic acid (AA) by cytochrome P-450 enzymes in isolated glomeruli and the effects of selective inhibitors of the synthesis of 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatetraenoic acids (EETs) on glomerular permeability to albumin (P(alb)). Glomeruli avidly produced 20-HETE, EETs, dihydroxyeicosatetraenoic acids (diHETEs), and HETEs when incubated with exogenous AA. N-hydroxy-N'-(4-butyl-2-methylphenyl)formamidine (HET0016; 10 microM) selectively inhibited the formation of 20-HETE by 95% and increased P(alb) from 0.00 +/- 0.08 to 0.73 +/- 0.10 (n = 43 glomeruli, 4 rats). Addition of a 20-HETE mimetic, 20-hydroxyeicosa-5(Z),14(Z)-dienoic acid (20-5,14-HEDE; 1 microM) opposed the effects of HET0016 (10 microM) to increase P(alb) (0.21 +/- 0.10, n = 36 glomeruli, 4 rats). Preincubation of glomeruli with exogenous AA to increase basal production of 20-HETE had a similar effect. We also examined the effect of an epoxygenase inhibitor, N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MSPPOH; 5 microM), on P(alb). MSPPOH (5 microM) significantly increased P(alb) but had no effect on the synthesis of EETs in glomeruli incubated with AA. However, MSPPOH (5 microM) selectively reduced epoxygenase activity by 50% in glomeruli incubated without added AA. Pretreatment with 8,9-EET (100 nM) attenuated the effects of MSPPOH (5 microM) on P(alb). These results indicate that glomeruli produce 20-HETE, EETs, diHETEs, and HETEs and that endogenously formed 20-HETE and EETs play an essential role in the maintenance of the glomerular permeability barrier to albumin.