Oxygenation of arachidonic acid by hepatic monooxygenases. Isolation and metabolism of four epoxide intermediates

Intraperitoneally injected d11-11(12)-epoxyeicosatrienoic acid is rapidly incorporated and esterified within rat plasma and peripheral tissues but not the brain

Epoxyeicosatrienoic acids (EpETrEs) are bioactive lipid mediators of arachidonic acid cytochrome P450 oxidation. In vivo, the free (unbound) form of EpETrEs regulate multiple processes including blood flow, angiogenesis and inflammation resolution. Free EpETrEs are thought to rapidly degrade via soluble epoxide hydrolase (sEH); yet, in many tissues, the majority of EpETrEs are esterified to complex lipids (e.g. phospholipids) suggesting that esterification may play a major role in regulating free, bioactive EpETrE levels. This hypothesis was tested by quantifying the metabolism of intraperitoneally injected free d11-11(12)-Epoxyeicosatrienoic acid (d11-11(12)-EpETrE) in male and female rats. Plasma and tissues (liver, adipose and brain) were obtained 3 to 4 min later and assayed for d11-11(12)-EpETrE and its sEH metabolite, d11-11,12-dihydroxyeicosatrienoic acid (d11-11,12-diHETrE) in both the free and esterified lipid fractions. In both males and females, the majority of injected tracer was recovered in liver followed by plasma and adipose. No tracer was detected in the brain, indicating that brain levels are maintained by endogenous synthesis from precursor fatty acids. In plasma, liver, and adipose, the majority (>54 %) of d11-11(12)-EpETrE was found esterified to phospholipids or neutral lipids (triglycerides and cholesteryl esters). sEH-derived d11-11,12-diHETrE was not detected in plasma or tissues, suggesting negligible conversion within the 3-4 min period post tracer injection. This study shows that esterification is the main pathway regulating free 11(12)-EpETrE levels in vivo.

Catalytic and Electrocatalytic Mechanisms of Cytochromes P450 in the Development of Biosensors and Bioreactors

Cytochromes P450 are a unique family of enzymes found in all Kingdoms of living organisms (animals, bacteria, plants, fungi, and archaea), whose main function is biotransformation of exogenous and endogenous compounds. The review discusses approaches to enhancing the efficiency of electrocatalysis by cytochromes P450 for their use in biotechnology and design of biosensors and describes main methods in the development of reconstituted and electrochemical catalytic systems based on the biochemical mechanism of cytochromes P450, as well as and modern trends for their practical application.

Fatty acid dioxygenase-cytochrome P450 fusion enzymes of filamentous fungal pathogens

Oxylipins designate oxygenated unsaturated C₁₈ fatty acids. Many filamentous fungi pathogens contain dioxygenases (DOX) in oxylipin biosynthesis with homology to human cyclooxygenases. They contain a DOX domain, which is often fused to a functional cytochrome P450 at the C-terminal end. A Tyr radical in the DOX domain initiates dioxygenation of linoleic acid by hydrogen abstraction with formation of 8-, 9-, or 10-hydroperoxy metabolites. The P450 domains can catalyze heterolytic cleavage of 8- and 10-hydroperoxides with oxidation of the heme thiolate iron for hydroxylation at C-5, C-7, C-9, or C-11 and for epoxidation of the 12Z double bond; thus displaying linoleate diol synthase (LDS) and epoxy alcohol synthase (EAS) activities. LSD activities are present in the rice blast pathogen Magnaporthe oryzae, Botrytis cinerea causing grey mold and the black scurf pathogen Rhizoctonia solani. 10R-DOX-EAS has been found in M. oryzae and Fusarium oxysporum. The P450 domains may also catalyze homolytic cleavage of 8- and 9-hydroperoxy fatty acids and dehydration to produce epoxides with an adjacent double bond, i.e., allene oxides, thus displaying 8- and 9-DOX-allene oxide synthases (AOS). F. oxysporum, F. graminearum, and R. solani express 9S-DOX-AOS and Zymoseptoria tritici 8S-and 9R-DOX-AOS. Homologues are present in endemic human-pathogenic fungi with extensive studies in Aspergillus fumigatus, A. flavus (also a plant pathogen) as well as the genetic model A. nidulans. 8R-and 10R-DOX appear to bind fatty acids "headfirst" in the active site, whereas 9S-DOX binds them "tail first" in analogy with cyclooxygenases. The biological relevance of 8R-DOX-5,8-LDS (also designated PpoA) was first discovered in relation to sporulation of A. nidulans and recently for development and programmed hyphal branching of A. fumigatus. Gene deletion DOX-AOS homologues in F. verticillioides, A. flavus, and A. nidulans alters, inter alia, mycotoxin production, sporulation, and gene expression.

WITHDRAWN: Fatty acid dioxygenase-cytochrome P450 fusion enzymes of the top 10 fungal pathogens in molecular plant pathology and human-pathogenic fungi

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Invited review: Cytochrome P450 enzyme involvement in health and inflammatory-based diseases of dairy cattle

Dairy cattle are at the greatest risk of developing diseases around the time of calving because of compromised immune responses and the occurrence of oxidative stress. Both the development of compromised immunity and oxidative stress are influenced directly or indirectly by the metabolism of polyunsaturated fatty acids (PUFA) and fat-soluble vitamins. The cytochrome P450 (CYP450) family of enzymes is central to the metabolism of both classes of these compounds, but to date, the importance of CYP450 in the health of dairy cattle is underappreciated. As certain CYP450 isoforms metabolize both PUFA and fat-soluble vitamins, potential interactions may occur between PUFA and fat-soluble vitamins that are largely unexplored. For example, one CYP450 that generates anti-inflammatory oxylipids from arachidonic acid additionally contributes to the activation of vitamin D. Other potential substrate interactions between PUFA and vitamins A and E may exist as well. The intersection of PUFA and fat-soluble vitamin metabolism by CYP450 suggest that this enzyme system could provide an understanding of how immune function and oxidant status interconnect, resulting in increased postpartum disease occurrence. This review will detail the known contributions of bovine CYP450 to the regulation of oxylipids with a focus on enzymes that may also be involved in the metabolism of fat-soluble vitamins A, D, and E that contribute to antioxidant defenses. Although the activity of specific CYP450 is generally conserved among mammals, important differences exist in cattle, such as the isoforms primarily responsible for activation of vitamin D that makes their specific study in cattle of great importance. Additionally, a CYP450-driven inflammatory positive feedback loop is proposed, which may contribute to the dysfunctional inflammatory responses commonly found during the transition period. Establishing the individual enzyme isoform contributions to oxylipid biosynthesis and the regulation of vitamins A, D, and E may reveal how the CYP450 family of enzymes can affect inflammatory responses during times of increased susceptibility to disease. Determining the potential effect of each CYP450 on disease susceptibility or pathogenesis may allow for the targeted manipulation of the CYP450 pathways to influence specific immune responses and antioxidant defenses during times of increased risk for health disorders.

Cytochrome P450 Metabolism of Polyunsaturated Fatty Acids and Neurodegeneration

Due to the aging population in the world, neurodegenerative diseases have become a serious public health issue that greatly impacts patients' quality of life and adds a huge economic burden. Even after decades of research, there is no effective curative treatment for neurodegenerative diseases. Polyunsaturated fatty acids (PUFAs) have become an emerging dietary medical intervention for health maintenance and treatment of diseases, including neurodegenerative diseases. Recent research demonstrated that the oxidized metabolites, particularly the cytochrome P450 (CYP) metabolites, of PUFAs are beneficial to several neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease; however, their mechanism(s) remains unclear. The endogenous levels of CYP metabolites are greatly affected by our diet, endogenous synthesis, and the downstream metabolism. While the activity of omega-3 (ω-3) CYP PUFA metabolites and omega-6 (ω-6) CYP PUFA metabolites largely overlap, the ω-3 CYP PUFA metabolites are more active in general. In this review, we will briefly summarize recent findings regarding the biosynthesis and metabolism of CYP PUFA metabolites. We will also discuss the potential mechanism(s) of CYP PUFA metabolites in neurodegeneration, which will ultimately improve our understanding of how PUFAs affect neurodegeneration and may identify potential drug targets for neurodegenerative diseases.

CYP2J2 Molecular Recognition: A New Axis for Therapeutic Design

Cytochrome P450 (CYP) epoxygenases are a special subset of heme-containing CYP enzymes capable of performing the epoxidation of polyunsaturated fatty acids (PUFA) and the metabolism of xenobiotics. This dual functionality positions epoxygenases along a metabolic crossroad. Therefore, structure-function studies are critical for understanding their role in bioactive oxy-lipid synthesis, drug-PUFA interactions, and for designing therapeutics that directly target the epoxygenases. To better exploit CYP epoxygenases as therapeutic targets, there is a need for improved understanding of epoxygenase structure-function. Of the characterized epoxygenases, human CYP2J2 stands out as a potential target because of its role in cardiovascular physiology. In this review, the early research on the discovery and activity of epoxygenases is contextualized to more recent advances in CYP epoxygenase enzymology with respect to PUFA and drug metabolism. Additionally, this review employs CYP2J2 epoxygenase as a model system to highlight both the seminal works and recent advances in epoxygenase enzymology. Herein we cover CYP2J2's interactions with PUFAs and xenobiotics, its tissue-specific physiological roles in diseased states, and its structural features that enable epoxygenase function. Additionally, the enumeration of research on CYP2J2 identifies the future needs for the molecular characterization of CYP2J2 to enable a new axis of therapeutic design.

19-Hydroxyeicosatetraenoic acid analogs: Antagonism of 20-hydroxyeicosatetraenoic acid-induced vascular sensitization and hypertension

19-Hydroxyeicosatetraenoic acid (19-HETE, 1), a metabolically and chemically labile cytochrome P450 eicosanoid, has diverse biological activities including antagonism of the vasoconstrictor 20-hydroxyeicosatetraenoic acid (20-HETE, 2). A SAR study was conducted to develop robust analogs of 1 with improved in vitro and in vivo efficacy. Analogs were screened in vitro for inhibition of 20-HETE-induced sensitization of rat renal preglomerular microvessels toward phenylephrine and demonstrated to normalize the blood pressure of male Cyp4a14(-/-) mice that display androgen-driven, 20-HETE-dependent hypertension.

Chronic Intermittent Hypoxia Alters Rat Ophthalmic Artery Reactivity Through Oxidative Stress, Endothelin and Endothelium-Derived Hyperpolarizing Pathways

Purpose

Obstructive sleep apnea recently has been associated with a higher frequency of ischemic optic neuropathies. Intermittent hypoxia (IH) has been proposed as a major component of obstructive sleep apnea cardiovascular consequences. However, there currently are no pathophysiologic data regarding the effect of IH on the ocular vascular system. Thus, we assessed the impact of chronic IH exposure on the morphology and vascular reactivity of the rat ophthalmic artery (OA).

Methods

Rats were exposed to 14 days of IH or normoxia (NX). Ophthalmic artery reactivity was studied using wire myography in rats treated or not with tempol (1 mM/day). Expression of endothelin-1 (ET-1) and its receptors, and of the three nitric oxide synthase (NOS) isoform genes was quantified using quantitative polymerase chain reaction (qPCR) in the retina and optic nerve. Structural alterations (optical and electron microscopy) and superoxide anion production were studied in OA sections.

Results

Superoxide ion expression in the OA wall was increased by 23% after IH exposure. Ophthalmic artery contractile response to 3.10-8 M ET-1 was increased by 18.6% and nitric oxide-mediated relaxation was significantly delayed in IH compared to NX rats. In the absence of nitric oxide, cytochrome P450 blockade increased relaxation to acetylcholine in IH rats and delayed it in NX rats. Tempol treatment abolished the IH-induced changes in OA reactivity.

Conclusions

These results strongly suggest that chronic IH induces oxidative stress in the rat OA, associated with endothelial dysfunction through alterations of nitric oxide and endothelium-derived hyperpolarising factors (EDHF) pathways.

CYP2J2 Expression in Adult Ventricular Myocytes Protects Against Reactive Oxygen Species Toxicity

Cytochrome P450 2J2 isoform (CYP2J2) is a drug-metabolizing enzyme that is highly expressed in adult ventricular myocytes. It is responsible for the bioactivation of arachidonic acid (AA) into epoxyeicosatrienoic acids (EETs). EETs are biologically active signaling compounds that protect against disease progression, particularly in cardiovascular diseases. As a drug-metabolizing enzyme, CYP2J2 is susceptible to drug interactions that could lead to cardiotoxicity. CYP2J2 has been shown to be resistant to induction by canonical CYP inducers such as phenytoin and rifampin. It is, however, unknown how cellular stresses augment CYP2J2 expression. Here, we determine the effects of oxidative stress on gene expression in adult ventricular myocytes. Further, we assess the consequences of CYP2J2 inhibition and CYP2J2 silencing on cells when levels of reactive oxygen species (ROS) are elevated. Findings indicate that CYP2J2 expression increases in response to external ROS or when internal ROS levels are elevated. In addition, cell survival decreases with ROS exposure when CYP2J2 is chemically inhibited or when CYP2J2 expression is reduced using small interfering RNA. These effects are mitigated with external addition of EETs to the cells. Finally, we determined the results of external EETs on gene expression and show that only two of the four regioisomers cause an increase in HMOX1 expression. This work is the first to determine the consequence of cellular stress, specifically high ROS levels, on CYP2J2 expression in human ventricular myocytes and discusses how this enzyme may play an important role in response to cardiac oxidative stress.

Enzymatic and free radical formation of cis- and trans- epoxyeicosatrienoic acids in vitro and in vivo

Epoxyeicosatrienoic acids (EETs) are metabolites of arachidonic acid (AA) oxidation that have important cardioprotective and signaling properties. AA is an ω-6 polyunsaturated fatty acid (PUFA) that is prone to autoxidation. Although hydroperoxides and isoprostanes are major autoxidation products of AA, EETs are also formed from the largely overlooked peroxyl radical addition mechanism. While autoxidation yields both cis- and trans-EETs, cytochrome P450 (CYP) epoxygenases have been shown to exclusively catalyze the formation of all regioisomer cis-EETs, on each of the double bonds. In plasma and red blood cell (RBC) membranes, cis- and trans-EETs have been observed, and both have multiple physiological functions. We developed a sensitive ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) assay that separates cis- and trans- isomers of EETs and applied it to determine the relative distribution of cis- vs. trans-EETs in reaction mixtures of AA subjected to free radical oxidation in benzene and liposomes in vitro. We also determined the in vivo distribution of EETs in several tissues, including human and mouse heart, and RBC membranes. We then measured EET levels in heart and RBC of young mice compared to old. Formation of EETs in free radical reactions of AA in benzene and in liposomes exhibited time- and AA concentration-dependent increase and trans-EET levels were higher than cis-EETs under both conditions. In contrast, cis-EET levels were overall higher in biological samples. In general, trans-EETs increased with mouse age more than cis-EETs. We propose a mechanism for the non-enzymatic formation of cis- and trans-EETs involving addition of the peroxyl radical to one of AA's double bonds followed by bond rotation and intramolecular homolytic substitution (S_Hi). Enzymatic formation of cis-EETs by cytochrome P450 most likely occurs via a one-step concerted mechanism that does not allow bond rotation. The ability to accurately measure circulating EETs resulting from autoxidation or enzymatic reactions in plasma and RBC membranes will allow for future studies investigating how these important signaling lipids correlate with heart disease outcomes.

3-methylcholanthrene and benzo(a)pyrene modulate cardiac cytochrome P450 gene expression and arachidonic acid metabolism in male Sprague Dawley rats

BACKGROUND AND PURPOSE

There is a strong correlation between cytochrome P450 (P450)-dependent arachidonic acid metabolism and the pathogenesis of cardiac hypertrophy. Several aryl hydrocarbon receptor (AhR) ligands were found to alter P450-dependent arachidonic acid metabolism. Here, we have investigated the effect of 3-methylcholanthrene (3-MC) and benzo(a)pyrene (BaP), two AhR ligands, on the development of cardiac hypertrophy.

EXPERIMENTAL APPROACH

Male Sprague Dawley rats were injected (i.p.) daily with either 3-MC (10 mg kg(-1)) or BaP (20 mg kg(-1)) for 7 days. Then hearts were removed, and the heart to body weight ratio and the gene expression of the hypertrophic markers and P450 genes were determined. Levels of arachidonic acid metabolites were determined by liquid chromatography-electron spray ionization-mass spectrometry.

KEY RESULTS

Both 3-MC and BaP increased the heart to body weight ratio as well as the hypertrophic markers, atrial natriuretic peptide and brain natriuretic peptide. 3-MC and BaP treatment increased the gene expression of CYP1A1, CYP1B1, CYP2E1, CYP4F4, CYP4F5 and soluble epoxide hydrolase. Both 3-MC and BaP treatments increased the dihydroxyeicosatrienoic acids (DHETs) : epoxyeicosatrienoic acids (EETs) ratio and the 20-hydroxyeicosatetraenoic acid (20-HETE) : total EETs ratio. Treatment with benzo(e)pyrene, an isomer of BaP that is a poor ligand for the AhR, did not induce cardiac hypertrophy in rats, confirming the role of AhR in the development of cardiac hypertrophy. Treatment with the omega-hydroxylase inhibitor, HET0016, significantly reversed BaP-induced cardiac hypertrophy.

CONCLUSIONS AND IMPLICATIONS

3-MC and BaP induce cardiac hypertrophy by increasing the ratio of DHETs : EETs and/or the ratio of 20-HETE : total EETs, through increasing soluble epoxide hydrolase activity.

Novel 14,21-dihydroxy-docosahexaenoic acids: structures, formation pathways, and enhancement of wound healing

Chronic wounds remain a medical challenge, where well-coordinated cellular and molecular processes required by optimal healing are impaired by diabetes, aging, or other diseases. In determining mechanisms that regulate wound healing, we found that wounding induced formation of novel endogenous 14S,21S-dihydroxy-docosa-4Z,7Z,10Z,12E,16Z,19Z-hexaenoic acids (14S,21S-diHDHA);14R,21R-diHDHA; 14S,21R-diHDHA; and/or 14R,21S-diHDHA. 12-lipoxygenase and cytochrome P450 catalysis in tandem converted docosahexaenoic acid to 14S,21R-diHDHA and 14S,21S-diHDHA through the intermediacy of 14S-HDHA; P450 also converted 14R-HDHA to novel 14R,21R-diHDHA and 14R,21S-diHDHA. Macrophages function as the combination of 12-lipoxgenase and P450 to generate these 14,21-diHDHA stereoisomers, as well as their intermediates 14S-HDHA, 14R-HDHA, and 21-HDHA. The structure and formation pathways of 14,21-diHDHA stereoisomers were further confirmed by macrophage biosynthesis of 14,21-diHDHA-21,22,22,22-d(4) stereoisomers, 14S-HDHA-d(5), 14R-HDHA-d(5), and 21-HDHA-d(4) from DHA-21,21,22,22,22-d(5). We found that 14S,21-diHDHA and 14R,21-diHDHA enhanced wound closure, reepithelialization, granulation tissue growth, and capillary vasculature formation of murine wounds. 14S,21-diHDHA and 14R,21-diHDHA produced by macrophages may partially represent the molecular mechanisms for macrophage pro-healing function. Taken together, 14,21-dihydroxy-DHA stereoisomers and their formation pathways may represent a novel mechanism in the orchestration of wound healing processes, which may provide new insight for developing novel therapeutic modalities that counteract impairments to wound healing.

Distribution of soluble and microsomal epoxide hydrolase in the mouse brain and its contribution to cerebral epoxyeicosatrienoic acid metabolism

Epoxide hydrolases comprise a family of enzymes important in detoxification and conversion of lipid signaling molecules, namely epoxyeicosatrienoic acids (EETs), to their supposedly less active form, dihydroxyeicosatrienoic acids (DHETs). EETs control cerebral blood flow, exert analgesic, anti-inflammatory and angiogenic effects and protect against ischemia. Although the role of soluble epoxide hydrolase (sEH) in EET metabolism is well established, knowledge on its detailed distribution in rodent brain is rather limited. Here, we analyzed the expression pattern of sEH and of another important member of the EH family, microsomal epoxide hydrolase (mEH), in mouse brain by immunohistochemistry. To investigate the functional relevance of these enzymes in brain, we explored their individual contribution to EET metabolism in acutely isolated brain cells from respective EH -/- mice and wild type littermates by mass spectrometry. We find sEH immunoreactivity almost exclusively in astrocytes throughout the brain, except in the central amygdala, where neurons are also positive for sEH. mEH immunoreactivity is abundant in brain vascular cells (endothelial and smooth muscle cells) and in choroid plexus epithelial cells. In addition, mEH immunoreactivity is present in specific neuronal populations of the hippocampus, striatum, amygdala, and cerebellum, as well as in a fraction of astrocytes. In freshly isolated cells from hippocampus, where both enzymes are expressed, sEH mediates the bulk of EET metabolism. Yet we observe a significant contribution of mEH, pointing to a novel role of this enzyme in the regulation of physiological processes. Furthermore, our findings indicate the presence of additional, hitherto unknown cerebral epoxide hydrolases. Taken together, cerebral EET metabolism is driven by several epoxide hydrolases, a fact important in view of the present targeting of sEH as a potential therapeutic target. Our findings suggest that these different enzymes have individual, possibly quite distinct roles in brain function and cerebral EET metabolism.

Mammalian epoxide hydrolases in xenobiotic metabolism and signalling

Epoxide hydrolases catalyse the hydrolysis of electrophilic--and therefore potentially genotoxic--epoxides to the corresponding less reactive vicinal diols, which explains the classification of epoxide hydrolases as typical detoxifying enzymes. The best example is mammalian microsomal epoxide hydrolase (mEH)-an enzyme prone to detoxification-due to a high expression level in the liver, a broad substrate selectivity, as well as inducibility by foreign compounds. The mEH is capable of inactivating a large number of structurally different, highly reactive epoxides and hence is an important part of the enzymatic defence of our organism against adverse effects of foreign compounds. Furthermore, evidence is accumulating that mammalian epoxide hydrolases play physiological roles other than detoxification, particularly through involvement in signalling processes. This certainly holds true for soluble epoxide hydrolase (sEH) whose main function seems to be the turnover of lipid derived epoxides, which are signalling lipids with diverse functions in regulatory processes, such as control of blood pressure, inflammatory processes, cell proliferation and nociception. In recent years, the sEH has attracted attention as a promising target for pharmacological inhibition to treat hypertension and possibly other diseases. Recently, new hitherto uncharacterised epoxide hydrolases could be identified in mammals by genome analysis. The expression pattern and substrate selectivity of these new epoxide hydrolases suggests their participation in signalling processes rather than a role in detoxification. Taken together, epoxide hydrolases (1) play a central role in the detoxification of genotoxic epoxides and (2) have an important function in the regulation of physiological processes by the control of signalling molecules with an epoxide structure.

Arabidopsis thaliana CYP77A4 is the first cytochrome P450 able to catalyze the epoxidation of free fatty acids in plants

An approach based on an in silico analysis predicted that CYP77A4, a cytochrome P450 that so far has no identified function, might be a fatty acid-metabolizing enzyme. CYP77A4 was heterologously expressed in a Saccharomyces cerevisiae strain (WAT11) engineered for cytochrome P450 expression. Lauric acid (C(12:0)) was converted into a mixture of hydroxylauric acids when incubated with microsomes from yeast expressing CYP77A4. A variety of physiological C(18) fatty acids were tested as potential substrates. Oleic acid (cis-Delta(9)C(18:1)) was converted into a mixture of omega-4- to omega-7-hydroxyoleic acids (75%) and 9,10-epoxystearic acid (25%). Linoleic acid (cis,cis-Delta(9),Delta(12)C(18:2)) was exclusively converted into 12,13-epoxyoctadeca-9-enoic acid, which was then converted into diepoxide after epoxidation of the Delta(9) unsaturation. Chiral analysis showed that 9,10-epoxystearic acid was a mixture of 9S/10R and 9R/10S in the ratio 33 : 77, whereas 12,13-epoxyoctadeca-9-enoic acid presented a strong enantiomeric excess in favor of 12S/13R, which represented 90% of the epoxide. Neither stearic acid (C(18:0)) nor linolelaidic acid (trans,trans-Delta(9),Delta(12)C(18:2)) was metabolized, showing that CYP77A4 requires a double bond, in the cis configuration, to metabolize C(18) fatty acids. CYP77A4 was also able to catalyze the in vitro formation of the three mono-epoxides of alpha-linolenic acid (cis,cis,cis-Delta(9),Delta(12),Delta(15)C(18:3)), previously described as antifungal compounds. Epoxides generated by CYP77A4 are further metabolized to the corresponding diols by epoxide hydrolases located in microsomal and cytosolic subcellular fractions from Arabidopsis thaliana. The concerted action of CYP77A4 with epoxide hydrolases and hydroxylases allows the production of compounds involved in plant-pathogen interactions, suggesting a possible role for CYP77A4 in plant defense.

Determination of epoxyeicosatrienoic acids in human red blood cells and plasma by GC/MS in the NICI mode

Epoxyeicosatrienoic acids (EETs) are cytochrome P450 metabolites of arachidonic acid involved in the regulation of vascular tone. Despite the importance of EETs in a variety of physiological effects, few methods have been developed to quantify them in human blood. This led us to develop a method by GC/MS with negative ion chemical ionization. As EETs are primarily located in phospholipids, red blood cells (RBCs) and plasma phospholipids were hydrolyzed with phospholipase A(2) after a solid phase extraction. Then, EETs were derivatized as pentafluorobenzyl esters, and [(2)H(8)]-arachidonic acid was used as internal standard for quantification. EETs were found to be at concentrations of 106+/-37ng mL(-1) in plasma and 33.4+/-8.5 ng/10(9) RBCs (mean+/-S.D.) in 10 healthy volunteers. Their amount in RBCs was 3-fold that in plasma; both parameters proved to be well correlated.

Cytochromes P450 from family 4 are the main omega hydroxylating enzymes in humans: CYP4F3B is the prominent player in PUFA metabolism

Human CYP450 omega-hydroxylases of the CYP4 family are known to convert arachidonic acid (AA) to its metabolite 20-hydroxyeicosatetraenoic acid (20-HETE). This study deals with hydroxylations of four PUFAs, eicosatrienoic acid (ETA), AA, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) by either human recombinant CYP4s enzymes or human liver microsomal preparations. CYP4F3A and CYP4F3B were the most efficient omega-hydroxylases of these PUFAs. Moreover, the differences in the number of unsaturations of ETA, AA, and EPA allowed us to demonstrate a rise in the metabolic rate of hydroxylation when the double bond in 14-15 or 17-18 was missing. With the CYP4F enzymes, the main pathway was always the omega-hydroxylation of PUFAs, whereas it was the (omega-1)-hydroxylation with CYP1A1, CYP2C19, and CYP2E1. Finally, we demonstrated that the omega9 and omega3 PUFAs (ETA, EPA, and DHA) could all be used as alternative substrates in AA metabolism by human CYP4F2 and -4F3B. Thus, they decreased the ability of these enzymes to convert AA to 20-HETE. However, although ETA was the most hydroxylated substrate, EPA and DHA were the most potent inhibitors of the conversion of AA to 20-HETE. These findings suggest that some physiological effects of omega3 FAs could partly result from a shift in the generation of active hydroxylated metabolites of AA through a CYP-mediated catalysis.

Antiinflammatory and neuroprotective actions of COX2 inhibitors in the injured brain

Overexpression of COX2 appears to be both a marker and an effector of neural damage after a variety of acquired brain injuries, and in natural or pathological aging of the brain. COX2 inhibitors may be neuroprotective in the brain by reducing prostanoid and free radical synthesis, or by directing arachidonic acid down alternate metabolic pathways. The arachidonic acid shunting hypothesis proposes that COX2 inhibitors' neuroprotective effects may be mediated by increased formation of potentially beneficial eicosanoids. Under conditions where COX2 activity is inhibited, arachidonic acid accumulates or is converted to eicosanoids via lipoxygenases and cytochrome P450 (CYP) epoxygenases. Several P450 eicosanoids have been demonstrated to have beneficial effects in the brain and/or periphery. We suspect that arachidonic acid shunting may be as important to functional recovery after brain injuries as altered prostanoid formation per se. Thus, COX2 inhibition and arachidonic acid shunting have therapeutic implications beyond the suppression of prostaglandin synthesis and free radical formation.

Inhibition of soluble epoxide hydrolase reduces LPS-induced thermal hyperalgesia and mechanical allodynia in a rat model of inflammatory pain

Soluble epoxide hydrolases catalyze the hydrolysis of epoxides in acyclic systems. In man this enzyme is the product of a single copy gene (EPXH-2) present on chromosome 8. The human sEH is of interest due to emerging roles of its endogenous substrates, epoxygenated fatty acids, in inflammation and hypertension. One of the consequences of inhibiting sEH in rodent inflammation models is a profound decrease in the production of pro-inflammatory and proalgesic lipid metabolites including prostaglandins. This prompted us to hypothesize that sEH inhibitors may have antinociceptive properties. Here we tested if sEH inhibitors can reduce inflammatory pain. Hyperalgesia was induced by intraplantar LPS injection and sEH inhibitors were delivered topically. We found that two structurally dissimilar but equally potent sEH inhibitors can be delivered through the transdermal route and that sEH inhibitors effectively attenuate thermal hyperalgesia and mechanical allodynia in rats treated with LPS. In addition we show that epoxydized arachidonic acid metabolites, EETs, are also effective in attenuating thermal hyperalgesia in this model. In parallel with the observed biological activity metabolic analysis of oxylipids showed that inhibition of sEH resulted with a decrease in PGD2 levels and sEH generated degradation products of linoleic and arachidonic acid metabolites with a concomitant increase in epoxides of linoleic acid. These data show that inhibition of sEH may become a viable therapeutic strategy to attain analgesia.

CYP1A in TCDD toxicity and in physiology-with particular reference to CYP dependent arachidonic acid metabolism and other endogenous substrates

Toxicologic and physiologic roles of CYP1A enzyme induction, the major biochemical effect of aryl hydrocarbon receptor activation by TCDD and other receptor ligands, are unknown. Evidence is presented that CYP1A exerts biologic effects via metabolism of endogenous substrates (i.e., arachidonic acid, other eicosanoids, estrogens, bilirubin, and melatonin), production of reactive oxygen, and effects on K(+) and Ca(2+) channels. These interrelated pathways may connect CYP1A induction to TCDD toxicities, including cardiotoxicity, vascular dysfunction, and wasting. They may also underlie homeostatic roles for CYP1A, especially when transiently induced by common chemical exposures and environmental conditions (i.e., tryptophan photoproducts, dietary indoles, and changes in oxygen tension).

Determination of polyunsaturated fatty acid monoepoxides by high performance liquid chromatography-mass spectrometry

Despite the implication of polyunsaturated fatty acid monoepoxides in a large panel of biological effects, few methods allowing their separation in a single run are available. We describe here a simple method based on reversed-phase ion-pair high-performance liquid chromatography (RP-HPLC) and developed to successfully separate the various monoepoxides of eicosatrienoic, arachidonic, eicosapentaenoic and docosahexaenoic acids. These compounds were easily identified by liquid chromatography-mass spectrometry (LC-MS) with atmospheric pressure chemical ionisation owing to the volatility of counter-ion species. Compared to established methods, this new protocol proved its ability to totally resolve, in a single run, all of the different regioisomeric epoxides. In the long run, this method will demonstrate its efficacy to give insights into the cytochrome P450-dependent metabolism of polyunsaturated fatty acids (PUFAs) and the generation of physiologically active epoxy-derivatives.

A Linchpin Approach to Unsaturated Fatty Acids: 11,12-Epoxyeicosatrienoic Acid and 11S,12S-Dihydroxyeicosatrienoic Acid Ethyl Esters

[Chemical reaction: See text] A "linchpin" coupling strategy is described for the construction of long-chain fatty acid metabolites. This strategy led to a short synthesis of the ethyl esters of both 11,12-epoxyeicosatrienoic acid (EET) and 11S,12S-dihydroxyeicosatrienoic acid (DHET).

Oxygenation of polyunsaturated long chain fatty acids by recombinant CYP4F8 and CYP4F12 and catalytic importance of Tyr-125 and Gly-328 of CYP4F8

Recombinant CYP4F8 and CYP4F12 metabolize prostaglandin H2 (PGH2) analogs by omega2- and omega3-hydroxylation and arachidonic acid (20:4n-6) by omega3-hydroxylation. CYP4F8 was found to catalyze epoxidation of docosahexaenoic acid (22:6n-3) and docosapentaenoic acid (22:5n-3) and omega3-hydroxylation of 22:5n-6. CYP4F12 oxidized 22:6n-3 and 22:5n-3 in the same way, but 22:5n-6 was a poor substrate. The products were identified by liquid chromatography-mass spectrometry. The missense mutation 374A>T of CYP4F8 (Tyr125Phe in substrate recognition site-1 (SRS-1)) occurs in low frequency. This variant oxidized two PGH2 analogs, U-51605 and U-44069, in analogy with CYP4F8, but 20:4n-6 and 22:5n-6 were not oxidized. CYP4F enzymes with omega-hydroxylase activity contain a heme-binding Glu residue, whereas CYP4F8 (and CYP4F12) with omega2- and omega 3-hydroxylase activities has a Gly residue in this position of SRS-4. The mutant CYP4F8 Gly328Glu oxidized U-51605 and U-44069 as recombinant CYP4F8, but the hydroxylation of arachidonic acid was shifted from C-18 to C-19. Single amino acid substitutions in SRS-1 and SRS-4 of CYP4F8 may thus influence oxygenation of certain substrates. We conclude that CYP4F8 and CYP4F12 catalyze epoxidation of 22:6n-3 and 22:5n-3, and CYP4F8 omega3-hydroxylation of 22:5n-6.

Arachidonic and eicosapentaenoic acid metabolism by human CYP1A1: highly stereoselective formation of 17(R),18(S)-epoxyeicosatetraenoic acid

Human cytochrome P450 1A1 (CYP1A1) and human NADPH-cytochrome P450 reductase were expressed and purified from Spodoptera frugiperda insect cells. A reconstituted enzymatically active system metabolized polyunsaturated fatty acids such as arachidonic (AA) and eicosapentaenoic acid (EPA). CYP1A1 was an AA hydroxylase which oxidizes this substrate at a rate of 650+/-10 pmol/min/nmol CYP1A1, with over 90% of metabolites accounted for by hydroxylation products and with 19-OH-AA as major product. Epoxyeicosatrienoic acid (EET), mainly 14,15-EET, accounted for about 7% of total metabolites. Unlike rat CYP1A1, the human enzyme exhibited no 20-OH-AA as product. In contrast, with EPA as substrate CYP1A1 was mainly an epoxygenase, oxidizing with over 68% of total metabolites EPA to 17(R),18(S)-epoxyeicosatetraenoic acid (17(R),18(S)-EETeTr). 19-OH-EPA accounted for about 31% of total metabolites. Significantly, the 17,18-olefinic bond of EPA was epoxidized to 17(R),18(S)-EETeTr with nearly absolute regio- and stereoselectivity. Molecular modeling analyses provided rationale for high efficiency of AA hydroxylation at C(19) and its gradual decrease down to C(14), as well as for the limited EPA 17(S),18(R) epoxidation due to unfavorable enzyme-substrate interactions. The absence of omega-hydroxylation for both substrates is not due to steric factors, but probably a consequence of different reactivities of omega and (omega-1) carbons for hydrogen abstraction. It is suggested that the capacity of human CYP1A1 to metabolize AA and EPA and its inducibility by polycyclic aromatic hydrocarbons may affect the production of physiologically active metabolites, in particular, in the cardiovascular system and other extrahepatic tissues including lung.

Polymorphism in soluble epoxide hydrolase and blood pressure in spontaneously hypertensive rats

We measured soluble epoxide hydrolase (sEH) renal gene expression in prehypertensive (4 to 5 weeks old) spontaneously hypertensive rats of the Heidelberg SP substrain (SHR [Heid]) and when blood pressure levels entered the hypertensive plateau (17 to 18 weeks old) and compared expression with matched Wistar-Kyoto (WKY [Heid]) rats. Less expression of the gene encoding sEH (EPHX2) was observed in SHR (Heid) than in WKY (Heid). Analysis of sEH protein abundance showed a similar difference. However, no correlation between sEH abundance and blood pressure was observed in the F(2) progeny of a parental strain cross. Measurement of protein abundance in SHR and WKY obtained from Charles River confirmed a recent report that abundance of sEH was greater in SHR (CRiv) than WKY (CRiv) strains. Polymorphisms were detected in EPHX2. Resequencing revealed that 2 alleles of EPHX2 exist in these 4 rat strains, differing by 4 single nucleotide polymorphisms, of which 3 produce nonsynonymous amino acid substitutions. The ancestral allele was shared by SHR (Heid) and WKY (CRiv), and the variant allele was shared by WKY (Heid) and SHR (CRiv). Activity of sEH was greater in animals carrying the variant allele. However, inheritance of this allele was not correlated with blood pressure in the F(2) progeny of a cross between SHR (Heid) and WKY (Heid). These data indicate that sequence variation determining functional alterations in EPHX2 is not likely to contribute to blood pressure levels in SHR.

Intracellular accumulation of mercury enhances P450 CYP1A1 expression and Cl- currents in cultured shark rectal gland cells

The effects of acute and subchronic exposure to mercury on the Cl- current (ICl) were investigated in cultured shark rectal gland (SRG) cells. The effects of intracellular accumulation of mercury on cytochrome P450 (P450) were also assessed. Bath perfusion of a cocktail solution containing forskolin, 1-isobutyl-3-methylxanthine, and 8-bromoadenosine monophosphate enhanced ICl. Addition of 10 microM HgCl2 significantly inhibited the cAMP-activated ICl (p < 0.05, n = 11). Intracellular dialysis with ATP gamma S did not prevent the inhibitory effect of mercury on ICl. In contrast, incubation of SRG cells with 10 microM HgCl2 for 48 hrs markedly increased ICl (p < 0.01, n = 12). Dephosphorylation of the channel by intracellular dialysis with phosphatase I and II abolished the mercury-incubated increase in ICl. The P450-mediated metabolite of arachidonic acid, 11,12-epoxyeicosatrienoic acid (11,12-EET), significantly increased ICl. However, application of 11,12-dihydroxyeicosatrienoic acid (11,12-DHT) did not alter ICl. Mercury incubation for 48 hrs did not alter the protein expression of Cl- channels, but caused an induction of CYP1A1 in cultured SRG cells. In addition, co-incubation of SRG cells with mercury and the P450 inhibitor clotrimazole prevented the mercury-incubated increase in ICl. Our results demonstrate that acute and subchronic application of mercury has opposing effects on ICl in cultured SRG cells. The acute effect of mercury on ICl may result from mercury blockade of Cl- channels. The subchronic effect of mercury on ICl may be due to an induction of P450 CYP1A1 and its mediated metabolites, but not due to an over-expression of Cl- channels.

CYP2C40, a unique arachidonic acid 16-hydroxylase, is the major CYP2C in murine intestinal tract

We recently identified five different murine CYP2C cDNAs from a murine cDNA library. When expressed in a bacterial cDNA expression system, all five recombinant proteins metabolized arachidonic acid but produced distinctly different profiles. In addition, some CYP2C mRNAs were found in extrahepatic tissues, as well as in liver. Immunoblots with an antibody raised against recombinant CYP2C38, which recognizes all five murine CYP2Cs, demonstrated that among extrahepatic tissues, colon and cecum contained the highest amount of CYP2Cs. The highest concentration of CYP2Cs occurred in cecum and colon (cecum >/= proximal colon >> distal colon), with lower levels in duodenum, jejunum, and ileum. Immunohistochemical studies revealed that CYP2Cs were localized principally in epithelial cells and autonomic ganglia in gut and colon. Polymerase chain reaction amplification of reverse-transcribed mRNA using murine CYP2C-specific primers followed by cloning and sequencing identified CYP2C40 as the major CYP2C isoform expressed in murine intestinal tract. Recombinant CYP2C40 metabolized arachidonic acid in a regio- and stereospecific manner to 16(R)-HETE (hydroxyeicosatetraenoic acid) as the major product. To our knowledge, CYP2C40 is the first enzyme known to produce primarily 16-HETE. We conclude that CYP2C40 is one of the major cytochrome P450 proteins in the mouse intestinal tract. In the light of vasoactive and anti-neutrophilic effects of 16-HETE, we hypothesize that CYP2C40 may play an important role in endogenous biological functions in intestine.

Identification, functional characterization, and regulation of a new cytochrome P450 subfamily, the CYP2Ns

The screening of liver and heart cDNA libraries from the teleost Fundulus heteroclitus with degenerate oligonucleotide probes to conserved alpha-helical regions in mammalian P450s resulted in the identification of two cDNAs that together represent a novel P450 subfamily, the CYP2Ns. Northern analysis demonstrated that CYP2N1 transcripts are most abundant in liver and intestine, whereas CYP2N2 mRNAs are most abundant in heart and brain. CYP2N1 and CYP2N2 proteins were co-expressed with NADPH-cytochrome P450 oxidoreductase in Sf9 insect cells, and their ability to metabolize arachidonic acid and xenobiotic substrates was examined. Both CYP2N1 and CYP2N2 metabolize arachidonic acid to epoxyeicosatrienoic acids. Epoxidation is highly regio- and enantioselective with preferential formation of (8R,9S)-epoxyeicosatrienoic acid (optical purities are 91 and 90% for CYP2N1 and CYP2N2, respectively) and (11R, 12S)-epoxyeicosatrienoic acid (optical purities are 92 and 70% for CYP2N1 and CYP2N2, respectively). CYP2N1 and CYP2N2 also catalyze the formation of a variety of hydroxyeicosatetraenoic acids. Both P450s have benzphetamine N-demethylase activities but show minimal alkoxyresorufin O-dealkylase activities. To investigate factors affecting CYP2N expression in vivo, CYP2N transcripts were examined following starvation and/or treatment with 12-O-tetradecanoyl phorbol-13-acetate. Intestinal CYP2N1 mRNAs decrease in starved and/or phorbol ester-treated fish, whereas intestinal CYP2N2 transcripts decrease only following phorbol ester treatment. Interestingly, cardiac CYP2N2 expression decreases following phorbol ester treatment but increases following starvation. These results demonstrate that members of this novel P450 subfamily encode early vertebrate forms of arachidonic acid catalysts that are widely expressed and are regulated by environmental factors. Given the wealth of information on the functional role of P450-derived arachidonate metabolites in mammals, we postulate that CYP2N1 and CYP2N2 products have similar biological functions in early vertebrates. The identity of the mammalian orthologue(s) of the CYP2Ns remains unknown.

Highly efficient separation of isomeric epoxy fatty acids by micellar electrokinetic chromatography

A capillary electrophoresis (CE) method has been developed for simple and direct separation of cis- and trans-12,13-epoxy-9(Z)-octadecenoic acid and 9,10-epoxy-12(Z)-octadecenoic acid isomers. Separation was performed in micellar electrokinetic capillary chromatography (MEKC) using a buffer consisting of 25 mM borate (pH 9.20), 10 mM sodium dodecyl sulfate (SDS) and 10% v/v acetonitrile. The key variables, concentrations of SDS and organic modifier, were optimized by the application of a factorial experimental design. The use of a low micellar concentration, just above critical micelle concentration (CMC), in a background electrolyte containing an organic modifier not only made it possible to dissolve and separate highly hydrophobic fatty acid isomers, but also resulted in improved separation efficiency and selectivity. Separation efficiency up to 4 x 10(5) theoretical plates/m was achieved under an optimized condition. Also investigated were the influence of temperature on separation and the effect of organic modifier concentration on the dynamic exchange of the analytes between micelles and the bulk of the buffer solution. Direct UV was applied for detection of the fatty acids.

Analysis of cytochrome P450 metabolites of arachidonic and linoleic acids by liquid chromatography-mass spectrometry with ion trap MS

We have used reversed phase-high performance liquid chromatography-mass spectrometry (RP-HPLC-MS) with an ion trap mass spectrometer to study the metabolism of arachidonic and linoleic acids by human recombinant cytochrome P450 (CYP) enzymes. We first recorded the MS2 spectra of the carboxylate anions of epoxides, diols, omega-side chain, and bisallylic hydroxy fatty acids of arachidonic, octadeuterated arachidonic, and linoleic acids. The metabolites formed by CYP2C9 and CYP2C19 were then studied. CYP2C9 converted arachidonic and linoleic acids to epoxides/diols and monohydroxy fatty acids. Some hydroxyeicosatetraenoic acids (HETEs) were studied in detail to investigate the oxygenation mechanism. Incubation of CYP2C9 under oxygen-18 gas showed that all HETEs had incorporated oxygen-18 to the same degree. Chiral HPLC showed that CYP2C9 formed 15R-HETE (72% of the R enantiomer), 13S-HETE (90%), and 11R-HETE (57%). RP-HPLC-MS analysis revealed that CYP2C19 oxygenated arachidonic acid to 19-HETE, 14,15-epoxyeicosatrienoic acid (EET), and 8,9-EET as main metabolites. The method was sufficiently sensitive to identify arachidonic acid metabolites formed by some other isozymes. RP-HPLC-MS with MS2 seems to be useful for rapid identification of fatty acid metabolites in complex mixtures formed by cytochrome P450.

2,3,7,8-Tetrachlorodibenzo-p-dioxin induction of cytochrome P450-dependent arachidonic acid metabolism in mouse liver microsomes: evidence for species-specific differences in responses

Arachidonic acid is biotransformed to metabolites active in signal transduction by cytochrome P450 (CYP) as well as by cyclooxygenase and lipoxygenase enzymes. Inducers of CYP1 enzymes, including 2,3,7,8-tetrachlorodibenzo-p-dioxin and other Ah receptor ligands, markedly increase liver microsomal CYP-dependent arachidonic acid epoxygenation in chicks but depress epoxygenation in rat liver microsomes where they elicit about twofold increases in formation of other CYP products, omega-1 to omega-4-OH arachidonic acid. These studies examined the effect of TCDD on metabolism of [1-14C]-labeled arachidonic acid by mouse liver microsomes. Mouse liver microsomes metabolized arachidonic acid exclusively by a CYP-dependent mechanism as evidenced by lack of metabolism in the absence of NADPH and by formation of specific CYP-dependent metabolites. The major constitutive products were epoxygenase products (EETs and EET-diols) and omega-OH arachidonic acid. Treatment with TCDD increased formation of omega-2- to omega-4-OH arachidonic acid products 23-fold, formation of omega-1-OH arachidonic acid about 5-fold, and formation of epoxygenase products and HETEs each about twofold. In contrast, TCDD treatment decreased formation of omega-OH arachidonic acid by over 70%. EET-diols comprised a greater fraction of total epoxygenase products in mouse liver microsomes than has been found for liver microsomes of other species. The high EET-diol formation was attributable to a non-TCDD-inducible, EET epoxide hydrolase activity in mouse liver microsomes. For comparison, the effect of TCDD on [1-14C]-labeled arachidonic acid was examined in homogenates of spleen, an immune system target of TCDD. While levels of total [1-14C]-arachidonic acid metabolism were comparable in both tissues, virtually all of the metabolism by spleen was CYP-independent, and it was unaffected by TCDD. Western blotting experiments showed that TCDD-induced mouse Cyp1a1 and 1a2 share immunologic epitopes with chick CYP1A4 and 1A5. However, in immunoinhibition studies, an antibody to CYP1A5, the chick arachidonate epoxygenase, was ineffective against TCDD-induced arachidonic acid metabolism in mouse liver microsomes, suggesting that there are differences in the catalytic sites or tertiary structures of CYP1A5 and the CYP-enzyme catalyzing the TCDD-induced arachidonic acid metabolism in mouse liver. This study shows that the effects of TCDD of the profile of CYP-dependent arachidonic acid metabolities and the amounts produced in mouse liver microsomes differ from other species. The findings suggest that species differences in CYP1A catalytic activities including the metabolism of arachidonic acid may contribute to species differences in sensitivity to TCDD toxicity.

Arachidonic acid metabolism in the marine fish Stenotomus chrysops (Scup) and the effects of cytochrome P450 1A inducers

Cytochrome P450-mediated arachidonic acid (AA) metabolism was investigated in the marine fish scup, Stenotomus chrysops. Liver microsomes incubated with AA and NADPH produced epoxyeicosatrienoic acids (EETs) and their hydration products (dihydroxyeicosatrienoic acids, DHETs), midchain conjugated dienols (midchain HETEs), and C16-through C20-alcohols of AA (omega-terminal HETEs), all identified by HPLC and GC/MS. Gravid females had 4-fold lower AA metabolism rates than males but identical metabolite profiles. The 5,6-EET (inferred from stable metabolites) was most abundant (47% of total EETs) followed by 14,15-, 11,12-, and 8,9-EET (27, 13, and 13%, respectively). The 12-HETE represented 25% of total HETEs followed in abundance by 16-, 15-, 11-, 19-, 20-, 8-, and 9-HETE. Antibodies against scup CYP1A and a scup CYP2B-like protein inhibited liver microsomal AA metabolism by 30 and 46%, respectively. GC/MS analysis revealed EETs and DHETs as endogenous constituents in scup liver; the predominant EETs were 8,9- and 14,15-EET, followed by a lesser amount of 11,12-EET. Chiral analysis showed a preference for the S,R-enantiomers of endogenous 8,9-, 11,12-, and 14,15-EET (optical purities 80, 64, and 64%, respectively). Treatment of scup with the CYP1A inducer benzo(a)pyrene (BP) increased liver microsomal formation of EETs and HETEs by 2.7-fold in spring and 1.7-fold in summer. BP treatment did not affect microsomal EET regioselectivity, but shifted hydroxylation in favor of 19-HETE and induced 17-HETE formation. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) treatment in summer did not induce liver microsomal AA metabolism rates, yet BP and TCDD both increased endogenous EET content of liver (5- and 3-fold, respectively), with a shift to 14,15-EET. BP treatment increased the selectivity for the S,R-enantiomers of endogenous 8,9-, 11,12-, and 14,15-EET (optical purities 91, 84, and 83%, respectively). Kidney, gill, and heart microsomes all metabolized AA, at rates 10- to 30-fold less than liver microsomes. Similar amounts of endogenous 8,9- and 14,15-EET and less 11,12-EET were detected in heart and kidney, and there was a strong enantioselectivity for 8(R),9(S)-EET in heart (optical purity 78%) but not in kidney. BP treatment did not alter the total EET content in these organs but did shift the regiochemical profile in heart to favor 14,15-EET. Thus, scup liver and extrahepatic organs metabolize AA via multiple cytochrome P450 (CYP) forms to eicosanoids in vitro and in vivo. BP or TCDD induced endogenous AA metabolism in liver, altering EET regioselectivity and, with BP, stereoselectivity. While AhR agonists alter metabolism of AA in early diverging vertebrates expressing both CYP1A and AhR, the magnitude of effects may depend upon the type of inducer.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces hepatic cytochrome P450-dependent arachidonic acid epoxygenation in diverse avian orders: regioisomer selectivity and immunochemical comparison of the TCDD-induced P450s to CYP1A4 and 1A5

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) markedly induced cytochrome P450 (CYP)-dependent arachidonic acid metabolism in liver microsomes from hatchlings of four avian species belonging to four different orders: chick, pigeon, cormorant, and great blue heron, increasing formation of arachidonic acid epoxides (EETs), monohydroxyeicosatetraenoic acids (HETEs), omega-1, and omega-2 OH arachidonic acid products by fivefold or more. Microsomes from TCDD-induced hatchling chicks had the highest activity and the least restricted EET regioselectivity. omega-OH arachidonic acid, the principal constitutive metabolite in chick and pigeon liver microsomes and a major product for cormorant and great blue heron was not induced by TCDD. Constitutive EET formation in avian liver microsomes was very low except in cormorant microsomes where 8,9-EET was generated almost exclusively. Western blots of liver microsomes using polyclonal antisera to chick embryo-derived CYP1A4 and 1A5 recognized two TCDD-induced bands in each of the species. The chick bands had the same molecular weights as CYP1A4 and 1A5 (55 and 55.5 kDa, respectively) but those of the other species differed. Immunopurified antiserum monospecific for CYP1A5 recognized a band in microsomes from all of the avian species, and monospecific antiserum for CYP1A4 recognized a band in microsomes from chick, pigeon, and great blue heron. AntiCYP1A4 and 1A5 IgG immunoinhibited TCDD-induced mixed function oxidase activity completely in chick and chick embryo microsomes and only partially in the other avian microsomes. The results demonstrate that (1) TCDD causes much greater induction of CYP-dependent arachidonic acid metabolism, and of arachidonic acid epoxygenation in particular, in avian than in mammalian species; (2) TCDD induces two CYP1A-related enzymes in birds as in mammals; (3) CYP1A enzymes in the birds other than chicks are not identical to CYP1A4 and 1A5 but share some enzymatic and immunochemical characteristics with them; (4) constitutive omega-OH arachidonic acid in all of the avian species and 8,9-EET in cormorant are formed by CYP enzymes unrelated to CYP1A; and (5) two distinct characteristics of avian CYP1A enzymes are the acquisition by avian CYP1A4-related P450 of unique epitope(s) and by CYP1A5-related P450 of unusual catalytic effectiveness for arachidonic acid epoxygenation.

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.

Liver microsomes from the yellow rat snake (Elaphe obsoleta) and American bullfrog (Rana catesbeiana) oxidize polyunsaturated fatty acids by NADPH-dependent hydroxylation and epoxidation

Polyunsaturated fatty acids (PUFAs) can be oxygenated by mammalian hepatic P450s to a series of metabolites. The most prominent of these are formed by omega- and (omega-1)-hydroxylation, epoxidation of the double bonds or bisallylic hydroxylation. The object of the present investigation was to determine whether similar oxygenations are catalyzed by liver microsomes of the yellow rat snake (Elaphe obsoleta) and the American bullfrog (Rana catesbeiana). Liver microsomes were incubated with [1-14C]-labeled arachidonic (AA), eicosapentaenoic (EPA), and linoleic acids (LA) in the presence or absence of 1 mM NADPH, and the major metabolites were analyzed by reverse-phase and straight-phase high performance liquid chromatography and capillary gas chromatography-mass spectroscopy. No metabolites were produced in the absence of NADPH. Profiles of metabolites were different depending on the organism and the acclimation state. In all incubations, EPA was the most effective substrate utilized and LA the least effective. The major products from EPA were 19-HEPE, 13-HEPE, and 20-HEPE from cold-acclimated (5 degrees C), warm-acclimated (22 degrees C) frogs, and snakes (22 degrees C), respectively. In contrast, 20-HETE production from AA was greater than 19-HETE in all three. Cold-acclimated frog liver microsomes produced significantly more of all metabolites when compared with microsomes from warm-acclimated frogs. We conclude that amphibian and snake liver can catalyze epoxidation and hydroxylation of PUFAs and that products are species-specific and acclimation-state dependent.

Influence of epoxyeicosatrienoic acids on uterine function

In spite of the large quantities of epoxyeicosatrienoic acids (EEts) released by reproductive tissues, their function has not yet been determined. In order to analyze the influence of epoxygenase products on isolated uterine function, Clotrimazole, a cytochrome P450 inhibitor was used. The drug decreased isolated rat uterine isometric developed tension (IDT) and frequency (FC). 14,15 EEt induced a contractile response when added at 10(11) M, 8,9 EEt and 11,12 EEt produced an increment of IDT when added to 10(-7) M and 5,6 EEt did not modify IDT values. A contractile stimulatory effect was observed when 14,15 EEt (10(-7) M) was added to a tissue bath preparation containing Clotrimazole (20 microM). On the other hand, uterine contractile response to 14,15 EEt addition was partially abolished by indomethacin (10(-6) M), a well known cyclooxygenase inhibitor. Uterine response to 5,6; 8,9 and 11,12 EEts was not modified by indomethacin. This is the first evidence of 14-15 EEt uterotonic properties, possibly exerted in part through the cyclooxygenase pathway.

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.

Identification of a putative microvascular oxygen sensor

The vascular response to changes in oxygen levels in the blood and tissue is a highly adaptive physiological response that functions to match tissue oxygen supply to metabolic demand. Defining the cellular mechanisms that can sense physiologically relevant changes in PO2 and adjust vascular diameter are vital to our understanding of this process. A cytochrome P450 (P450) enzyme of the 4A family of omega-hydroxylases was localized in renal microvessels, renal cortex, and a striated muscle microvascular bed (cremaster) of the rat. In the presence of molecular oxygen, this P450 enzyme catalyzes formation of 20-HETE from arachidonic acid (AA). Prior studies have shown that 20-HETE potently contracts renal and cerebral arteries and arterioles. The present study demonstrates that 20-HETE constricts striated muscle arterioles as well. In both intact renal microvessels and enriched renal cortical microsomal enzyme preparations, the formation of 20-HETE was linearly dependent on PO2 between 20 and 140 mm Hg. Homogenates of cremaster tissue produced 20-oxygen HETE when incubated with AA. They also expressed message for P450 4A enzyme, as determined by Southern and Western blots. Administration of 17-octadecynoic acid (17-ODYA), which is a P450 4A inhibitor, attenuated the constriction of third-order cremasteric arterioles in response to elevation of superfusion solution PO2 from approximately equal to 3 to 5 mm Hg to approximately equal to 35 mm Hg. 17-ODYA had no effect on basal vascular tone or response of cremaster arterioles to vasoactive compounds. These results demonstrate the existence of P450 omega-hydroxylase activity and 20-HETE formation in the vasculature and parenchyma of at least two microvascular beds. Our data suggest that a P450 enzyme of the 4A family has the potential to function as an oxygen sensor in mammalian microcirculatory beds and to regulate arteriolar caliber by generating 20-HETE in an oxygen-dependent manner.

Subcellular localization of docosahexaenoic acid and arachidonic acid omega-hydroxylation activity in the brain, liver and colonic adenocarcinoma

A homogenate of rat brain, rat liver or human colonic well differentiated adenocarcinoma was prepared in 250 mM sucrose isoosmolaric buffer (pH 7.6) and fractionated by differential centrifugation at 10(3), 10(4) and 10(5) g. Each precipitate or supernatant was incubated with NADPH and docosahexaenoic acid or arachidonic acid as a substrate for 30 min at 37 degrees c under aerobic conditions. omega-Hydroxydocosahexaenoic acid or omega-hydroxyeicosatetraenoic acid from an incubation mixture was detected by reversed-phase high-performance liquid chromatography-thermospray mass spectrometry with selected-ion monitoring. omega-Hydroxy polyunsaturated fatty acids were characterized by high intensity of the molecular ion (MH+) although common hydroxy polyunsaturated fatty acids were characterized by high intensity of the MH+ -H2O ion. For the rat brain, omega-hydroxylation activity (the amount of omega-hydroxy product produced in 30 min) was concentrated to a 10(3) g precipitate although the specific activity (the activity per 1 mg of protein) in the 10(3) g precipitate did not indicate superiority over other fractions. However, the specific activity of the rat brain increased on addition of a 10(4) or 10(5) g precipitate. For the rat liver, although omega-hydroxylation activity was concentrated to a 10(3) g precipitate, the specific activity was concentrated to a 10(5) g precipitate and the subcellular localization differed from that of rat brain. In the human colonic well differentiated adenocarcinoma, although omega-hydroxylation activity was relatively high in the 10(3) g supernatant, the specific activity was relatively high in the 10(3) g precipitates. These results suggest that there is a difference regarding subcellular localization of the omega-hydroxylation activity depending on the species of the organs.

Enzymatic production of hydroperoxides of unsaturated fatty acids by injury of mammalian cells

Hydroperoxides of unsaturated fatty acids (LOOHs) are generated by homogenisation of liver tissue, but not if the liver is boiled before homogenisation. This observation indicates that the LOOHs are produced in an enzymatic reaction. This assumption is corroborated by an analysis of the reduction products of LOOHs by gas chromatography/mass spectrometry (GC/MS). A main part of LOOHs is derived from linoleic acid and not from arachidonic acid. Massive cell damage occurs by myocardial infarction or other severe injuries; these events were found to be connected with generation of LOOHs. We suspect--considering the above outlined experiment--that the LOOH production is also mainly caused in these cases by activation of enzymes and not--as postulated--by an autocatalytic process. Increased amounts of LOOHs are found in many chronic diseases, e.g. in rheuma, atherosclerosis or psoriasis, obviously caused by a gradual damage of cells. Thus, the common root of an increased LOOH level might be cell injury.