Synthesis and characterization of cytochrome P-450 epoxygenase metabolites of eicosapentaenoic acid

Novel Unspecific Peroxygenase from Truncatella angustata Catalyzes the Synthesis of Bioactive Lipid Mediators

Lipid mediators, such as epoxidized or hydroxylated eicosanoids (EETs, HETEs) of arachidonic acid (AA), are important signaling molecules and play diverse roles at different physiological and pathophysiological levels. The EETs and HETEs formed by the cytochrome P450 enzymes are still not fully explored, but show interesting anti-inflammatory properties, which make them attractive as potential therapeutic target or even as therapeutic agents. Conventional methods of chemical synthesis require several steps and complex separation techniques and lead only to low yields. Using the newly discovered unspecific peroxygenase TanUPO from the ascomycetous fungus Truncatella angustata, 90% regioselective conversion of AA to 14,15-EET could be achieved. Selective conversion of AA to 18-HETE, 19-HETE as well as to 11,12-EET and 14,15-EET was also demonstrated with known peroxygenases, i.e., AaeUPO, CraUPO, MroUPO, MweUPO and CglUPO. The metabolites were confirmed by HPLC-ELSD, MS1 and MS2 spectrometry as well as by comparing their analytical data with authentic standards. Protein structure simulations of TanUPO provided insights into its substrate access channel and give an explanation for the selective oxyfunctionalization of AA. The present study expands the scope of UPOs as they can now be used for selective syntheses of AA metabolites that serve as reference material for diagnostics, for structure-function elucidation as well as for therapeutic and pharmacological purposes.

Functional fluxolipidomics of polyunsaturated fatty acids and oxygenated metabolites in the blood vessel compartment

Synthesis of bioactive oxygenated metabolites of polyunsaturated fatty acids and their degradation or transformation products are made through multiple enzyme processes. The kinetics of the enzymes responsible for the different steps are known to be quite diverse, although not precisely determined. The location of the metabolites biosynthesis is diverse as well. Also, the biological effects of the primary and secondary products, and their biological life span are often completely different. Consequently, phenotypes of cells in response to these bioactive lipid mediators must then depend on their concentrations at a given time. This demands a fluxolipidomics approach that can be defined as a mediator lipidomics, with all measurements done as a function of time and biological compartments. This review points out what is known, even qualitatively, in the blood vascular compartment for arachidonic acid metabolites and number of other metabolites from polyunsaturated fatty acids of nutritional value. The functional consequences are especially taken into consideration.

Arachidonic acid-metabolizing cytochrome P450 enzymes are targets of {omega}-3 fatty acids

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) protect against cardiovascular disease by largely unknown mechanisms. We tested the hypothesis that EPA and DHA may compete with arachidonic acid (AA) for the conversion by cytochrome P450 (CYP) enzymes, resulting in the formation of alternative, physiologically active, metabolites. Renal and hepatic microsomes, as well as various CYP isoforms, displayed equal or elevated activities when metabolizing EPA or DHA instead of AA. CYP2C/2J isoforms converting AA to epoxyeicosatrienoic acids (EETs) preferentially epoxidized the ω-3 double bond and thereby produced 17,18-epoxyeicosatetraenoic (17,18-EEQ) and 19,20-epoxydocosapentaenoic acid (19,20-EDP) from EPA and DHA. We found that these ω-3 epoxides are highly active as antiarrhythmic agents, suppressing the Ca(2+)-induced increased rate of spontaneous beating of neonatal rat cardiomyocytes, at low nanomolar concentrations. CYP4A/4F isoforms ω-hydroxylating AA were less regioselective toward EPA and DHA, catalyzing predominantly ω- and ω minus 1 hydroxylation. Rats given dietary EPA/DHA supplementation exhibited substantial replacement of AA by EPA and DHA in membrane phospholipids in plasma, heart, kidney, liver, lung, and pancreas, with less pronounced changes in the brain. The changes in fatty acids were accompanied by concomitant changes in endogenous CYP metabolite profiles (e.g. altering the EET/EEQ/EDP ratio from 87:0:13 to 27:18:55 in the heart). These results demonstrate that CYP enzymes efficiently convert EPA and DHA to novel epoxy and hydroxy metabolites that could mediate some of the beneficial cardiovascular effects of dietary ω-3 fatty acids.

Synthesis and NMR characterization of the methyl esters of eicosapentaenoic acid monoepoxides

The activities of cytochrome P450-derived epoxide metabolites of omega-6 polyunsaturated fatty acids (PUFAs) in cellular homeostasis have generated considerable topical interest, but there is less information on the effects of omega-3 PUFA epoxides. Mass spectroscopic data on the epoxides of the omega-3 PUFA eicosapentaenoic acid (EPA) have been reported but the absence of corresponding NMR data currently hinders their biological assessment. In the present study five monoepoxy derivatives of EPA methyl ester were synthesized by treating EPA methyl ester with m-chloroperbenzoic acid. The individual regioisomers were purified by normal-phase chromatography and characterized by LC-MS/MS and a combination of NMR approaches including (1)H-, (13)C-, (1)H-(1)H-COSY, (1)H-(13)C-HSQC, and (1)H-(13)C-HMBC. The chromatographic properties for these monoepoxides were studied in normal-phase and reversephase-HPLC systems and the MS/MS fragmentation patterns using electrospray ionization were established. This paper also focuses on the NMR characterization of epoxide, olefinic and methylenic moieties and the complete assignments of the isomers.

EET homologs potently dilate coronary microvessels and activate BKCa channels

Epoxyeicosatrienoic acids (EETs) are released from endothelial cells and potently dilate small arteries by hyperpolarizing vascular myocytes. In the present study, we investigated the structural specificity of EETs in dilating canine and porcine coronary microvessels (50–140 μm ID) and activating large-conductance Ca2+-activated K+(BKCa) channels. The potencies and efficacies of EET regioisomers and enantiomers were compared with those of two EET homologs: epoxyeicosaquatraenoic acids (EEQs), which are made from eicosapentaenoic acid by the same cytochrome P-450 epoxygenase that generates EETs from arachidonic acid, and epoxydocosatetraenoic acids (EDTs), which are EETs that are two carbons longer. With EC50 values of 3–120 pM but without regio- or stereoselectivity, EETs potently dilated canine and porcine microvessels. Surprisingly, the EEQs and EDTs had comparable potencies and efficacies in dilating microvessels. Moreover, 50 nM 13,14-EDT activated the BKCa channels with the same efficacy as either 11,12-EET enantiomer at 50 nM. We conclude that coronary microvessels and BKCa channels possess low structural specificity for EETs and suggest that EEQs and EDTs may thereby also be endothelium-derived hyperpolarizing factors.

Stereospecific metabolism of isomeric epoxyoctadecanoic acids in the lactone-producing yeast Sporidiobolus salmonicolor

The metabolic course of four isomeric epoxyfatty acids derived from oleic-, elaidic-, (Z)-, and (E)-vaccenic acids in the lactone-producing yeast, Sporidiobolus salmonicolor, was studied by using the deuterium-labeled precursors. Dihydroxy-, hydroxyoxo-, and hydroxy fatty acids as well as gamma-lactones were identified as metabolic intermediates. Quantitative analysis of the label content and estimation of the enantiomeric composition of the lactones established that, in the first step, the racemic epoxyfatty acids were enantiospecifically hydrolyzed by an epoxide hydrolase. During the subsequent metabolism, the stereochemical orientation of the hydroxy groups of the dihydroxyfatty acids were modified by an oxidation/reduction step.

Cytochrome P450 metabolites of arachidonic acid: rapid incorporation and hydration of 14,15-epoxyeicosatrienoic acid in arterial smooth muscle cells

Arachidonic acid is converted to epoxyeicosatrienoic acids (EETs) by cytochrome P450 monooxygenases. EETs produce arterial vasodilatation, and recent evidence suggests that they are endothelium-derived hyperpolarizing factors. In porcine coronary arteries contracted with a thromboxane mimetic agent, we find that relaxation is rapidly initiated by exposure to 14,15-EET. The relaxation slowly increases in magnitude, resulting in a response which is sustained for more than 10 min. Cultured porcine aortic smooth muscle cells rapidly take up [3H]14,15-EET. After 3 min, radioactivity is present in neutral lipids, phosphatidylcholine, and phosphatidylinositol. The cells also convert 14,15-EET to 14,15-dihydroxyeicosatrienoic acid (14,15-DHET), and some DHET is detected in the medium after only 1 min of incubation. Like 14,15-EET, 14,15-DHET produces relaxation of the contracted coronary artery rings. These findings suggest that the incorporation into phospholipids and conversion to 14,15-DHET can occur at a rate that is fast enough to modulate the vasorelaxation produced by 14,15-EET.

Evidence for the involvement of docosahexaenoic acid in cholinergic stimulated signal transduction at the synapse

[4,5-3H]Docosahexaenoic acid ([3H]DHA) or [9,10-3H]palmitic acid ([3H]PAM) was infused intravenously for 5 min to awake, adult male rats before and after treatment with arecoline (15 mg/kg, i.p.), a cholinergic agonist. Animals were killed 15 min post-infusion, the brains were rapidly removed and subcellular fractions were obtained after sucrose density centrifugation. In control animals, [3H]DHA and [3H]PAM were incorporated into the synaptosomal fractions, representing 50%-60% of total membrane label. Most remaining membrane label (30%-40%) was in the microsomal fraction. Both fractions contained the synaptic marker synaptophysin. The remaining 10% of radioactivity was in the myelin and mitochondrial fractions. Arecoline significantly increased [3H]DHA entry into the synaptosomal fractions by 100% and into the microsomal fraction by 50%. In these fractions 60%-65% of the [3H]DHA was in phospholipid, the rest corresponding to free fatty acid and diacylglycerol. In contrast, arecoline did not change [3H]PAM incorporation into any brain fraction. These results demonstrate that plasma [3H]DHA incorporation is selectively increased into synaptic membrane phospholipids of the rat brain in response to cholinergic activation. The increased incorporation of DHA but not of PAM into synaptic membranes in response to cholinergic stimulation indicates a primary role for DHA in phospholipid mediated signal transduction at the synapse involving activation of phospholipase A2 and/or C.

Bisallylic hydroxylation and epoxidation of polyunsaturated fatty acids by cytochrome P450

Polyunsaturated fatty acids can be oxygenated by cytochrome P450 to hydroxy and epoxy fatty acids. Two major classes of hydroxy fatty acids are formed by hydroxylation of the omega-side chain and by hydroxylation of bisallylic methylene carbons. Bisallylic cytochrome P450-hydroxylases transform linoleic acid to 11-hydroxylinoleic acid, arachidonic acid to 13-hydroxyeicosa-5Z,8Z,11Z,14Z-tetraenoic acid, 10-hydroxyeicosa-5Z,8Z,11Z,14Z-tetraenoic acid and 7-hydroxyeicosa-5Z,8Z,11Z,14Z-tetraenoic acid and eicosapentaenoic acid to 16-hydroxyeicosa-5Z,8Z,11Z,14Z,17Z-pent aenoic acid, 13-hydroxyeicosa-5Z,8Z,11Z,14Z,17Z-pent aenoic acid and 10-hydroxyeicosa-5Z,8Z,11Z,14Z,17Z-pent aenoic acid as major metabolites. The bisallylic hydroxy fatty acids are chemically unstable and decompose rapidly to cis-trans conjugated hydroxy fatty acids during acidic extractive isolation. Bisallylic hydroxylase activity appears to be augmented in microsomes induced by the synthetic glucocorticoid dexamethasone and by some other agents, but the P450 gene families of these hydroxylases have yet to be determined. The fatty acid epoxides, which are formed by cytochrome P450, are chemically stable, but are hydrolyzed to diols by soluble epoxide hydrolases. Epoxidation of polyunsaturated fatty acids is a prominent pathway of metabolism in the liver and the renal cortex and epoxy-genase activity appears to be under homeostatic control in the kidney. Many arachidonate epoxygenases have been identified belonging to the CYP2C gene subfamily. Epoxygenases have also been found in the central nervous system, endocrine organs, the heart and endothelial cells. Epoxides of arachidonic acid have been found to exert pharmacological effects on many cells.

Arachidonic acid diols produced by cytochrome P-450 monooxygenases are incorporated into phospholipids of vascular endothelial cells

Epoxyeicosatrienoic acids (EETs) are synthesized by cytochrome P-450 monooxygenases and released into the blood. When taken up by vascular endothelial and smooth muscle cells, the EETs are primarily esterified to phospholipids or converted to dihydroxyeicosatetraenoic acids (DHETs) and released. In the present studies, radiolabeled 8,9-, 11,12-, and 14,15-DHETs released into the medium from vascular smooth muscle cells were isolated and incubated for 4-16 h with cultured bovine aortic endothelial cells. The uptake ranged from 2 to 50% for the three regioisomers. Hydrolysis of the endothelial lipids and gas chromatographic-mass spectral analyses of the products indicated that all three DHET regioisomers were incorporated intact into phosphatidylcholine and phosphatidylinositol. Similar incubations with EETs confirmed that small amounts of DHETs were also esterified to endothelial phospholipids. These studies indicate that DHETs are incorporated into phospholipids either at the time of EET conversion to DHET or upon release and re-uptake of DHETs. Beside demonstrating for the first time that fatty acid diols are incorporated intact into endothelial lipids, these studies raise the possibility that both EETs and DHETs remain long enough in the vascular wall to produce chronic vasoactive effects.

Dietary fish oil and cytochrome P-450 monooxygenase activity in rat liver and kidney

Lauric acid hydroxylation and aminopyrine N-demethylation were studied in kidney and liver microsomes from rats treated with fish oil. Different doses of fish oil containing 20% eicosapentaenoic acid and 10% docosahexaenoic acid were provided daily to the rats for seven days. In all the groups studied, the lauric acid metabolism was higher in kidney microsomes and the aminopyrine metabolism in the liver microsomes. Although no effect on the renal cytochrome P-450 concentration was detectable, all four fish oil doses increased the hepatic concentration of cytochrome P-450 by a mean 27%. The higher fish oil doses used increased the renal and hepatic microsomal metabolism of aminopyrine. The lauric acid metabolism was increased by fish oil only in the liver. Fish oil, a known inducer of fatty acid peroxisomal beta-oxidation, also induced microsomal activity. These results show that liver and kidney respond in different ways to dietary factors such as fish oil. In addition, our study would suggest that fish oil increased the activity of two different families of liver cytochrome P-450. The activity of kidney lauric acid 11- and 12-hydroxylation, however, was not modulated by fish oil.

Optimization of epoxyeicosatrienoic acid syntheses to test their effects on cerebral blood flow in vivo

Epoxyeicosatrienoic acids (EETs), normally present in brain and blood, appear to be released from atherosclerotic vessels in large amounts. Once intravascular, EETs can constrict renal arteries in vivo and dilate cerebral and coronary arteries in vitro. Whether EETs in blood will alter cerebral blood flow (CBF) in vivo is unknown. In the present study, the chemical synthesis of four EET regioisomers was optimized, and their identity and structural integrity established by chromatographic and mass spectral methods. The chemically labile EETs were converted to a sodium salt, complexed with albumin, and infused into anesthetized rats via the common carotid. The objective was to test whether sustained, high levels of intravascular EETs alter CBF. The CBF (cortical H2 clearance) was measured before and 30 min after the continuous infusion of 14,15- (n = 5), 11,12- (n = 5), 8,9- (n = 7) and 5,6-EET (unesterified or as the methyl ester, n = 5 for each). Neither the CBF nor the systemic blood pressure was affected by EETs. Because the infusions elevated the plasma concentrations of EETs about 700-fold above normal levels (1.0 nM), it is unlikely that EETs released from atherosclerotic vessels will alter CBF.

Effect of n-3 fatty acid ethyl ester supplementation on fatty acid composition of the single platelet phospholipids and on platelet functions

Twenty healthy male volunteers were randomly assigned to receive either four 1-g capsules of n-3 polyunsaturated fatty acids (PUFA) ethyl esters or four 1-g capsules of olive oil (as placebo) for a period of 4 months, followed by a 3-month wash-out period. Fatty acids of platelet phospholipid fractions, platelet aggregation, and thromboxane B2 (TXB2) formation were analyzed at 0, 2, and 4 months of treatment and at 1, 2, and 3 months of wash-out. During n-3 PUFA supplementation, accumulations of eicosapentaenoic (EPA), docosapentaenoic (DPA), and docosahexaenoic (DHA) acids were markedly increased after 2 months, with slight differences in further accumulation up to 4 months among the various phospholipid fractions. Significant decreases in platelet sensitivity to collagen, serum TXB2 levels, and urinary TXB2 metabolites were also observed following n-3 PUFA treatment. During the first and second month of wash-out, slight differences were observed in changes of various fatty acids among different phospholipid fractions, but after 3 months of wash-out, alterations were no longer detectable with respect to pretreatment values. After 3 months of wash-out, platelet function parameters also were returned to baseline. Thus, both platelet lipids and function are influenced by n-3 PUFA ethyl ester supplementation, and significant alterations are still detectable after 2 months of wash-out.

High-performance liquid chromatography-thermospray mass spectrometry of epoxy polyunsaturated fatty acids and epoxyhydroxy polyunsaturated fatty acids from an incubation mixture of rat tissue homogenate

A method for the analysis of epoxy polyunsaturated fatty acids (EpPUFAs) and epoxyhydroxy polyunsaturated fatty acids (EpHPUFAs) in rat tissue homogenate, with homo-gamma-linolenic acid (20:3, n - 6), arachidonic acid (20:4, n - 6), eicosapentaenoic acid (20:5, n - 3) or docosahexaenoic acid (22:6, n - 3) as a substrate, has been developed. Extraction with dichloromethane at pH 4-5 and concentration in the presence of pyridine were performed. Spectral analysis of chromatograms obtained with high-performance liquid chromatography-thermospray mass spectrometry showed the presence of EpPUFAs, EpHPUFAs and dihydroxy metabolites (DiHPUFAs) of EpPUFAs corresponding to each precursor fatty acid. On a selected-ion monitoring chromatogram, many EpPUFAs, EpHPUFAs and DiHPUFAs in an extract from an incubation mixture of each precursor fatty acid in aged rat tissue homogenate were detected simultaneously within 70 min. EpPUFAs and DiHPUFAs derived from 20:3 (n - 6) or 20:5 (n - 3) were detected in significant amounts. From these results, a highly active cytochrome P450 system or non-enzymic oxidative reactions in aged rat tissue homogenate were suggested.

Oxygenation of polyunsaturated fatty acids by cytochrome P450 monooxygenases

Polyunsaturated fatty acids can be oxygenated by P450 in different ways--by epoxidation, by hydroxylation of the omega-side chain, by allylic and bis-allylic hydroxylation and by hydroxylation with double bond migration. Major organs for these oxygenations are the liver and the kidney. P450 is an ubiquitous enzyme. It is therefore not surprising that some of these reactions have been found in other organs and tissues. Many observations indicate that P450 oxygenates arachidonic acid in vivo in man and in experimental animals. This is hardly surprising. omega-Oxidation was discovered in vivo 60 years ago. It was more unexpected that biological activities have been associated with many of the P450 metabolites of arachidonic acid, at least in pharmacological doses. Epoxygenase metabolites of arachidonic acid have attracted the largest interest. In their critical review on epoxygenase metabolism of arachidonic acid in 1989, Fitzpatrick and Murphy pointed out some major differences between the PGH synthase, the lipoxygenase and the P450 pathways of arachidonic acid metabolism. Their main points are still valid and have only to be modified slightly in the light of recent results. First, lipoxygenases show a marked regiospecificity and stereospecificity, while many P450 seem to lack this specificity. There are, however, P450 isozymes which catalyse stereospecific epoxidations or hydroxylations. Many hydroxylases and at least some epoxygenases also show regiospecificity, i.e. oxygenate only one double bond or one specific carbon of the fatty acid substrate. In addition, preference for arachidonic acid and eicosapentaenoic acid may occur in the sense that other fatty acids are oxygenated with less regiospecificity. A more important difference is that prostaglandins and leukotrienes affect specific and well characterised receptors in cell membranes, while receptors for epoxides of arachidonic acid or other P450 metabolites have not been characterised. Nevertheless, epoxides of arachidonic acid have been found to induce a large number of different pharmacological effects. In some systems, effects have been noted at pm concentrations which might conceivably be in the physiological concentration range of these epoxides, e.g. after release from phospholipids by phospholipase A2. An intriguing possibility is that the effects of [Ca]i on different ion channels might possibly explain their biological actions. In situations when pharmacological doses are used, metabolism to epoxyprostanoids or other interactions with PGH synthase could also be of importance. Finally, one report on a specific receptor for 14R,15S-EpETrE in mononuclear cell membranes has just been published.(ABSTRACT TRUNCATED AT 400 WORDS)

Enantioselective separation of some polyunsaturated epoxy fatty acids by high-performance liquid chromatography on a cellulose phenylcarbamate (Chiralcel OC) stationary phase

cis-Epoxides of linoleic acid, alpha-linolenic acid, arachidonic acid and the omega 3-epoxide of eicosapentaenoic acid were chromatographed on a cellulose trisphenylcarbamate (Chiralcel OC) stationary phase in the normal-phase mode. The R,S and S,R enantiomers of methyl-14(15)epoxyeicosatrienoate, methyl-9(10)epoxyoctadecadienoate and methyl-9(10)epoxyoctadecenoate could be partly resolved. The R,S enantiomer of methyl-14(15)epoxyeicosatrienoate eluted before the S,R enantiomer. [14C]14(15)Epoxyeicosatrienoic acid was isolated from an incubation of [14C]20:4n-6 with microsomes of rabbit kidney cortex and the S,R enantiomer was found to predominate (about 2:1).

Biosynthesis of prostaglandins from 17(18)epoxy-eicosatetraenoic acid, a cytochrome P-450 metabolite of eicosapentaenoic acid

Eicosapentaenoic acid (20:5(n - 3)) is oxygenated to 17S(18R)epoxyeicosatetraenoic acid (EpETE) by microsomes of monkey seminal vesicles, which also are rich in prostaglandin (PG) H synthase. The metabolism of racemic [14C]17(18)EpETE by PGH synthase of sheep vesicular glands was investigated in the present report. The two main metabolites were identified by GC-MS as 17(18)epoxyprostagland E2 (17(18)EpPGE2) and 17(18)EpPGF2 alpha. The structures were confirmed by chemical synthesis of these prostaglandins from PGE3. 17(18)EpPGE1 was synthesized from 17,18-dehydro-PGE1 by the same method. Alkali treatment of 17(18)EpPGE2 yielded 17(18)EpPGB2, which could be resolved by RP-HPLC into the 17R(18S) and 17S(18R) stereoisomers. The 17S(18R) stereoisomer was identified by co-chromatography with [14C]17S(18R)EpPGB2, which was formed by PGH synthase from biosynthetic [14C]17S(18R)EpETE. The 17(18)epoxyprostaglandins were found to be relatively unstable during acidic extractive isolation. 17(18)EpPGE1 and 17(18)EpPGE2 could not be detected in seminal vesicles of the cynomolgus monkey in significant amounts relative to 19-hydroxy-PGE1. Nevertheless, biosynthesis of 17(18)epoxyprostaglandins should be considered when the biological effects of 17S(18R)EpETE are investigated.

Docosahexaenoic acid inhibits PAF and LTD4 stimulated [Ca2+]i-increase in differentiated monocytic U937 cells

We investigated the effects of different polyunsaturated fatty acids (PUFAs) of the n-6 and n-3 family on the PAF and LTD4 stimulated increase in cytosolic free Ca(2+)-concentration [Ca2+]i in retinoic acid (RA) differentiated, human monocytic U937 cells. Docosahexaenoic acid (10 microM DHA) reduced the PAF induced increase in [Ca2+]i from 455 +/- 25 nM to 319 +/- 24 nM (P less than 0.01). DHA also significantly attenuated the LTD4 induced increase in [Ca2+]. However [Ca2+]i-increase stimulated by f-MLP, ATP, or ionophore A 23187 was not affected by DHA. Other PUFAs like eicosapentaenoic acid (EPA), alpha-linolenic acid (LnA), arachidonic acid (AA) or gamma-linoleic acid (LA) were ineffective. Cellular differentiation as assessed by nitrobluetetrazolium reduction and enhanced expression of specific PAF binding sites in RA treated cells were not altered by DHA. Fatty acid composition in cellular phospholipids revealed effective incorporation of each PUFA. The DHA-effect on [Ca2+]i was time dependent and occurred at 48 h, whereas the DHA-content in phospholipids reached a plateau already at 24 h. The antioxidant vitamin E, the lipoxygenase inhibitor NDGA and the cytochrome P-450 inhibitor SKF 525A completely prevented the DHA induced reduction of PAF stimulated [Ca2+]i-increase. In contrast, the cyclooxygenase inhibitor indomethacin had no effect. Our results indicate that DHA selectively reduces intracellular [Ca2+]i-increases induced by PAF and LTD4 in RA-treated U937 cells, presumably involving an oxidative modification of DHA.

Metabolism of polyunsaturated (n-3) fatty acids by monkey seminal vesicles: isolation and biosynthesis of omega-3 epoxides

Monooxygenases of monkey seminal vesicles can metabolize arachidonic acid (20:4(n-6)) by w3-hydroxylation to 18(R)-hydroxyeicosatetraenoic acid (18(R)-HETE) and eicosapentaenoic acid (20:5(n-3)) to 17,18-dihydroxyeicosatetraenoic acid (Oliw, E.H. (1989) J. Biol. Chem. 264, 17845-17853). The present study aimed to further characterize the oxygenation of (n-3) polyunsaturated fatty acids. 14C-Labelled 22:6(n-3), 20:5(n-3), 20:4-(n-3) and 18:3(n-3) were incubated with microsomes of seminal vesicles of the cynomolgus monkey, NADPH and a cyclooxygenase inhibitor, diclofenac, and the main metabolites were identified by capillary gas chromatography-mass spectrometry. 22:6(n-3) was slowly metabolized to 19,20-dihydroxy-4,7,10,13,16-docosapentaenoic acid, while 20:5(n-3), 20:4(n-3) and 18:3(n-3) were metabolized more efficiently to the corresponding w4,w3-diols. The w3 epoxides, which were obtained from 20:5(n-3) and 18:3(n-3), were isolated in the presence of an epoxide hydrolase inhibitor, 1(2)epoxy-3,3,3-trichloropropane, and the geometry of the epoxides was determined to be 17S, 18R and 15S, 16R, respectively. While 20:5(n-3) was metabolized almost exclusively to the epoxide and diol pair of metabolites, 18:3(n-3) was metabolized not only to the w3 epoxide and the corresponding diol, but also to the w2 alcohol, 17(R)-hydroxy-9,12,15-octadecatrienoic acid. 22:6(n-3) and 5,8,11,14-eicosatetraynoic acid inhibited the biosynthesis of 18(R)-HETE from arachidonic acid (IC50 0.16 and 0.14 mM, respectively). In comparison with 20:4 or 18:3(n-3), 18:1(n-9) and 22:5(n-6) appeared to be slowly metabolized by seminal monooxygenases, while 18:2(n-6) was converted to the w3 alcohol and to smaller amounts of the w2 alcohol (4:1). Together, the results indicate that the w3-hydroxylase and w3-epoxygenase enzyme(s) metabolize 20:4(n-6) and 20:5(n-3) almost exclusively to the w3(R) alcohol and the w3(R, S) epoxide, respectively, while longer and shorter fatty acids either are poor substrates or metabolized with a lesser degree of position specificity.

17R(18S)epoxyeicosatetraenoic acid, a cytochrome P-450 metabolite of 20:5n-3 in monkey seminal vesicles, is metabolized to novel prostaglandins

Eicosapentaenoic acid (20:5n-3) is metabolized by cytochrome P-450w3 of monkey seminal vesicles to 17R(18S)epoxy-5,8,11,14-eicosatetraenoic acid (17R(18S)EpETE). PGH synthase is abundant in this tissue. Racemic 17(18)EpETE was therefore investigated as a substrate of PGH synthase. The main products were identified as two diastereoisomers of 17(18)epoxyprostaglandin E2, which were formed in a 4:5 ratio. The structures were confirmed by authentic material. The natural epoxide enantiomer can thus be metabolized to novel 17R(18S)epoxyprostaglandins.