15-Hydroperoxyeicosapentaenoic acid, but not eicosapentaenoic acid, shifts arachidonic acid away from cyclooxygenase pathway into acyl-CoA synthetase pathway in rabbit kidney medulla microsomes

Under physiological conditions, small amounts of free arachidonic acid (AA) are released from membrane phospholipids, and cyclooxygenase (COX) and acyl-CoA synthetase (ACS) competitively act on this fatty acid to form prostaglandins (PGs) and arachidonoyl-CoA (AA-CoA). In the present study, we investigated the effects of eicosapentaenoic acid (EPA) and 15-hydroperoxyeicosapentaenoic acid (15-HPEPE) on the PG and AA-CoA formations from high and low concentrations of AA (60 and 5 μM) in rabbit kidney medulla microsomes. The kidney medulla microsomes were incubated with 60 or 5 μM [14C]-AA in 0.1 M Tris/HCl buffer (pH 8.0) containing cofactors of COX (reduced glutathione and hydroquinone) and cofactors of ACS (ATP, MgCl2 and CoA). After incubation, PG (as total PGs), AA-CoA and residual AA were separated by selective extraction using petroleum ether and ethyl acetate. EPA reduced the PG and AA-CoA formations from both 60 and 5 μM AA. In contrast, 15-HPEPE decreased the PG formation without affecting the AA-CoA formation from 60 μM AA, and increased the AA-CoA formation at the expense of PG formation when 5 μM AA was used as substrate concentration. The experiments utilizing Fe2+ and an electron spin resonance (ESR) revealed that 15-HPEPE elicits these effects in the form of hydroperoxy adduct. These results suggest that 15-HPEPE, but not EPA, has the potential to shift AA away from COX pathway into ACS pathway at low substrate concentration (close to the physiological concentration of AA).