Cytochrome P-450-dependent oxygenation of arachidonic acid to hydroxyicosatetraenoic acids.

Abstract

Arachidonic acid is oxidized by a NADPH-dependent oxygenase of rat liver microsomes to a number ofoxygencontaining products, which can be resolved by HPLC. Several of these products have been purified and characterized. They exhibit an absorbance in the UV region of the spectrum that has a maximum at =235 nm, indicative ofthe presence ofa conjugated diene function. Mass spectral analysis of the trimethylsilyl ether derivatives of the methyl esters of the hydrogenated and nonhydrogenated metabolites shows that they are the 9-, 11-, 12-, and 15-monohydroxy derivatives of arachidonic acid, the hydroxyicosatetraenoic acids (HETEs). Their UV absorbance and chromatographic properties suggest that these products possess cis,transdiene geometry characteristic ofHETEs isolated from other mammalian sources. The isolation of these isomeric HETEs suggests that cytochrome P-450 may play a role in the oxidative metabolism of arachidonic acid to physiologically and pharmacologically important hydroxylated unsaturated fatty acids.The oxygenation of arachidonic acid to hydroxyicosatetraenoic acids (HETEs), which contain a conjugated diene function, is catalyzed by enzyme(s) present in several mammalian tissues and has important pathophysiological consequences (1, 2). The isolation of each of the isomeric HETEs has been reported, although significant tissue variation in the composition of the products formed has been observed (3-6). HETEs and their hydroperoxy acid precursors (HPETEs) exhibit diverse biological activities and may play an important role in leukocyte chemotaxis and the inflammatory response (1).HETEs are produced by an oxygenation reaction involving either lipoxygenases (3), singlet molecular oxygen (7), or autooxidation (8). Animal lipoxygenases have not been extensively purified and the nature and properties of this class of mammalian enzymes have scarcely been characterized in most tissues that biosynthesize HETEs. We have recently reported a novel route for the oxidative metabolism ofarachidonic acid (9). The reaction is catalyzed by liver microsomes and requires NADPH and molecular oxygen. The reaction is inhibited by carbon monoxide and metyrapone, suggesting a role for microsomal cytochrome P450 (9). The metabolism ofarachidonic acid can also be demonstrated in reconstitution experiments using purified cytochromes P450 and NADPH-cytochrome P-450 reductase (10).The present paper describes studies to characterize some of the metabolites formed during the rat liver microsomal cytochrome P450-dependent oxidation of arachidonic acid. We report here that the major components of that group of products are the 9-, 11-, 12-, and 15-hydroxy derivatives of arachidonic acid-the HETEs. MATERIALS AND METHODSMicrosomal fractions were prepared from homogenates of rat livers as described (11). Male Sprague-Dawley rats (150-200 g body weight) were treated by four daily intraperitoneal injections ofphenobarbital (75 mg/kg ofbody weight) and starved overnight prior to sacrifice.The oxygenation products of arachidonic m...

Specific action of the lipoxygenase pathway in mediating angiotensin II-induced aldosterone synthesis in isolated adrenal glomerulosa cells.

“…The current results now suggest that AA conversion to products of the 12-LO pathway is a key step in All induced action in the adrenal gland. Our results showing no inhibition of 12-HETE with two structurally distinct cytochrome P450 inhibitors suggests that 12-HETE formation in the rat adrenal glomerulosa cell is not via the P450 epoxygenase system described by others in the kidney and liver (42)(43)(44). However, additional studies will be needed to fully clarify whether other AA metabolites such as epoxides play any role in aldosterone synthesis.…”

Cytochrome P450 metabolites of arachidonic acid are potent inhibitors of vasopressin action on rabbit cortical collecting duct.

“…7 B; 8). Coinjection of an aliquot of the biological material with a known quantity of synthetic [5,6,8,9,11,12,14,1 5-2H] 14,1 5-EET-PFB shows the presence in the mixture of the EET-PFB-derived ion fragments at m/z 319, 303, and 301, and of an ion fragment at m/z 327, derived from the loss of PFB from the octadeuterated standard (Fig. 8 B).…”

“…AA can be metabolized by three distinct enzymatic pathways: (a) by cyclooxygenase to form biologically active PGs and TXs; (b) by lipoxygenases to form hydroperoxy fatty acids, monohydroxy fatty acids, and leukotrienes; and (c) by a recently described cytochrome P450 NADPH-dependent epoxygenase (5)(6)(7)(8)(9)(10). This third pathway of AA metabolism has been documented in the kidney (5,7,8).…”

GPR40 is a low-affinity epoxyeicosatrienoic acid receptor in vascular cells

“…Epoxyeicosatrienoic acids (EETs) are cytochrome P450 metabolites of arachidonic acid (1,2). Four regioisomeric EETs (14,15-, 11,12-, 8,9-and 5,6-EETs) are synthesized by cytochrome P450.…”