S. Sakuma, Kumiko Usa, Y. Fujimoto
Aug 1, 2006
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Prostaglandins, leukotrienes, and essential fatty acids
Abstract
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 microM) in rabbit kidney medulla microsomes. The kidney medulla microsomes were incubated with 60 or 5 microM [(14)C]-AA in 0.1M Tris/HCl buffer (pH 8.0) containing cofactors of COX (reduced glutathione and hydroquinone) and cofactors of ACS (ATP, MgCl(2) 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 microM AA. In contrast, 15-HPEPE decreased the PG formation without affecting the AA-CoA formation from 60 microM AA, and increased the AA-CoA formation at the expense of PG formation when 5 microM AA was used as substrate concentration. The experiments utilizing Fe(2+) 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).