Contribution of CYP4A8 to the Formation of 20-Hydroxyeicosatetraenoic Acid from Arachidonic Acid in Rat Kidney

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  20-Hydroxyeicosatetraenoic acid (20-HETE) has been shown to be an arachidonic acid metabolite of the cytochrome P450 (CYP) enzymes belonging to the CYP4A subfamily and is a predominant regulator of renal vascular tone and tubular ion reabsorption in rat kidney. CYP4A8 is one of the CYP4A enzymes expressed in rat kidney, but its contribution to 20-HETE formation has not been assessed. In order to clarify that the role of CYP4A8, we have developed bacterial expression systems for the expression of recombinant CYP4A8 (rCYP4A8). We also produced an antibody against rCYP4A8 which was used for immunoinhibition and immunohistochemical studies. In a reconstituted system, rCYP4A8 sufficiently catalyzed 20-HETE formation as well as prostaglandin A₁ ω-hydroxylation, a marker activity for CYP4A8. In addition, anti-rCYP4A8 sera significantly inhibited prostaglandin A₁ ω-hydroxylation and strongly inhibited arachidonic acid ω-hydroxylation in rat kidney microsomes. These observations suggested for the first time that CYP4A8 also contributed to 20-HETE formation in rat kidney. Furthermore, immunohistochemstry suggested that CYP4A8 is present in preglomerular arteries, where 20-HETE has been established to be a vasoconstrictor.