The CYP P450 Arachidonate Monooxygenases: Enzymatic Relays for the Control of Kidney Function and Blood Pressure

During P450-dependent metabolism, arachidonic acid (AA) is: a) hydroxylated at its ω or ω-1 carbons to 19- and 20-hydroxyeicosatetraenoic acids (HETEs)(AA ω/ω-1 hydroxylase), or b) epoxidized at any one of its four olefins to 5,6-, 8,9-, 11,12-, or 14,15-epoxyeicosatrienoic acids (EETs)(AA epoxygenase). The demonstration that many of these P450- derived eicosanoids, were formed endogenously by several rat, rabbit, and human tissues, and that they were present in human and rat plasma and/or urine, established the P450 AA monooxygenase as a formal metabolic pathway, and stimulated an extensive functional characterization of its metabolites [1, 2, 3, 4, 5, 6, 7]. During the last 15 years, the list of biological activities attributed to the P450-eicosanoids has increased at a rapid pace, and led to an extensive in vitro characterization of their vasoactive properties, roles in cell and organ ion transport, and of their participation in hormone signaling cascades [1, 2, 3, 4, 5, 6, 7]. In male Sprague-Dawley rats, AA ω/ω-1 hydroxylation and epoxidation account for 70–80, and 20–30% of the total kidney microsomal monooxygenase activity, respectively, and 20-HETE and 11(R), 12(S)-EET (88% optical purity) are recovered as the major ω-hydroxylase and epoxygenase metabolites, respectively [[3]]. The high degree of structural homology displayed by the members of a P450 gene family [8] has complicated the identification of the P450 isoforms responsible for the metabolism of endogenous AA pools [[3],[5],[9]–[11]]. Nevertheless, extensive enzymatic, biochemical, immunological, and functional evidence indicates that CYPs of the 2 and 4 gene families are responsible for AA metabolism, and that, in rat kidney, CYPs 2C and 4A are the predominant and functionally significant AA epoxygenases and ω/ω-1 hydroxylases, respectively [[3],[9]–[19]]. For example, CYPs, 2C23, 2C24, and 2C11 are expressed in the rat kidney in decreasing order of abundance [[17]] but, of these, only CYP 2C23 metabolizes AA with a regio- and enantioselectivity that matches that of the microsomal enzymes [[16],[17]]. Furthermore, as shown in Figure 1,antibodies raised against CYP 2C23 inhibited better than 95% of the microsomal epoxygenase activity present in rat kidney microsomes, and had no effect on microsomal AA ω/ω-1 hydroxylation. The recognition of CYPs 2C and 4A as endogenous AA epoxygenases and ω/ hydroxylases, as well the early proposal of a role for these isoforms in the pathophysiology of experimental hypertension [1,[4]–[7]], open the way to the introduction of molecular approaches for the study of the functional roles of the AA monooxygenases, and the characterization of P450-isoform/gene-dependent phenotypes of renal dysfunction.