Liquid chromatographic-electrospray ionization-mass spectrometric analysis of cytochrome P450 metabolites of arachidonic acid

Pharmacodynamics and Pharmacokinetics of HSK3486, a Novel 2,6-Disubstituted Phenol Derivative as a General Anesthetic

Background: The purpose of this study was to characterize the novel sedative/hypnotic agent HSK3486, a 2,6-disubstituted alkylphenol analogue.

Methods: The mechanism of action of HSK3486 was studied in competitive binding assays and whole-cell patch clamp assays. HSK3486 was administered by bolus intravenous injection to dogs and rats, and the loss of righting reflex as well as effects on the cardiovascular and respiratory systems were assessed. The in vitro metabolism of HSK3486 was analyzed by CYP450 genotyping and enzyme inhibition.

Results: HSK3486 competed with t-butylbicycloorthobenzoate (TBOB) and t-butylbicyclophosphorothionate (TBPS) for binding to the gamma-aminobutyric acid type A (GABA_A) receptor. HSK3486 potentiated GABA-evoked chloride currents at lower concentrations while activating GABA_A receptor at higher concentrations. HSK3486 induced hypnosis in rats and dogs, and had a higher therapeutic index than propofol in rats. The hypnotic potency of HSK3486 was approximately 4-5 fold higher than that of propofol. HSK3486 exerted minimal effects on the cardiovascular system.

Conclusions: HSK3486 is a positive allosteric regulator and direct agonist of GABA_A receptor. It has a promising sedative/hypnotic effect and good in vivo pharmacokinetic properties, which justify further studies towards its clinical application.

Simultaneous Quantitation of Lipid Biomarkers for Inflammatory Bowel Disease Using LC-MS/MS

Eicosanoids are key mediators and regulators of inflammation and oxidative stress that are often used as biomarkers for severity and therapeutic responses in various diseases. We here report a highly sensitive LC-MS/MS method for the simultaneous quantification of at least 66 key eicosanoids in a widely used murine model of colitis. Chromatographic separation was achieved with Shim-Pack XR-ODSIII, 150 × 2.00 mm, 2.2 µm. The mobile phase was operated in gradient conditions and consisted of acetonitrile and 0.1% acetic acid in water with a total flow of 0.37 mL/min. This method is sensitive, with a limit of quantification ranging from 0.01 to 1 ng/mL for the various analytes, has a large dynamic range (200 ng/mL), and a total run time of 25 min. The inter- and intraday accuracy (85-115%), precision (≥85%), and recovery (40-90%) met the acceptance criteria per the US Food and Drug Administration guidelines. This method was successfully applied to evaluate eicosanoid metabolites in mice subjected to colitis versus untreated, healthy control mice. In summary, we developed a highly sensitive and fast LC-MS/MS method that can be used to identify biomarkers for inflammation and potentially help in prognosis of the disease in inflammatory bowel disease (IBD) patients, including the response to therapy.

Regulation of Cerebral Blood Flow: Response to Cytochrome P450 Lipid Metabolites

There have been numerous reviews related to the cerebral circulation. Most of these reviews are similar in many ways. In the present review, we thought it important to provide an overview of function with specific attention to details of cerebral arterial control related to brain homeostasis, maintenance of neuronal energy demands, and a unique perspective related to the role of astrocytes. A coming review in this series will discuss cerebral vascular development and unique properties of the neonatal circulation and developing brain, thus, many aspects of development are missing here. Similarly, a review of the response of the brain and cerebral circulation to heat stress has recently appeared in this series (8). By trying to make this review unique, some obvious topics were not discussed in lieu of others, which are from recent and provocative research such as endothelium-derived hyperpolarizing factor, circadian regulation of proteins effecting cerebral blood flow, and unique properties of the neurovascular unit. © 2018 American Physiological Society. Compr Physiol 8:801-821, 2018.

Multiplex quantitative analysis of eicosanoid mediators in human plasma and serum: Possible introduction into clinical testing

Eicosanoid mediators play important roles in maintaining the physiological and pathophysiological homeostasis in the body. Their measurements, however, are rarely performed in clinical practice. In the present study, we analyzed 30 varieties of eicosanoid mediators that were detectable in human plasma and serum collected from healthy donors, using liquid chromatography-tandem mass spectrometry from the viewpoint of the clinical application of the multiplex quantitation of eicosanoid mediators. Wider variety of eicosanoid mediators were detected in serum (27 out of 30) than in plasma (14 out of 30), since the serum was thought to contain lipid mediators released from activated platelets. Larger inter-individual variations were observed in the plasma and serum eicosanoid levels. On the other hand, the concentrations of eicosanoids were not affected by the platelet count but were affected by the concentration of arachidonic acid (AA) within the reference interval (17.4-40.5×10¹⁰/L). When serum samples from patients with hematological disorders were analyzed, the concentrations of AA were positively correlated with the platelet count. When the patients underwent ASA therapy, a marked decrease in the concentrations of thromboxane B₂ (TXB₂) and 12-hydroxyl-heptadecatrienoic acid (12-HHT) was observed. Considering the availability of serum samples in clinical settings, the serum analysis of eicosanoids may be clinically useful.

Inhibition of soluble epoxide hydrolase augments astrocyte release of vascular endothelial growth factor and neuronal recovery after oxygen-glucose deprivation

Epoxyeicosatrienoic acids (EETs) are synthesized in astrocytes, and inhibitors of soluble epoxide hydrolase (sEH), which hydrolyzes EETs, reduce infarct volume in ischemic stroke. Astrocytes can release protective neurotrophic factors, such as vascular endothelial growth factor (VEGF). We found that addition of sEH inhibitors to rat cultured astrocytes immediately after oxygen-glucose deprivation (OGD) markedly increased VEGF concentration in the medium 48 h later and the effect was blocked by an EET antagonist. The sEH inhibitors increased EET concentrations to levels capable of increasing VEGF. When the sEH inhibitors were removed from the medium at 48 h, the increase in VEGF persisted for an additional 48 h. Neurons exposed to OGD and subsequently to astrocyte medium previously conditioned with OGD plus sEH inhibitors showed increased phosphorylation of their VEGF receptor-2, less TUNEL staining, and increased phosphorylation of Akt, which was blocked by a VEGF receptor-2 antagonist. Our findings indicate that sEH inhibitors, applied to cultured astrocytes after an ischemia-like insult, can increase VEGF secretion. The released VEGF then enhances Akt-enabled cell survival signaling in neurons through activation of VEGF receptor-2 leading to less neuronal cell death. These results suggest a new strategy by which astrocytes can be leveraged to support neuroprotection.

Development of cellular hypertrophy by 8-hydroxyeicosatetraenoic acid in the human ventricular cardiomyocyte, RL-14 cell line, is implicated by MAPK and NF-κB

Recent studies have established the role of mid-chain hydroxyeicosatetraenoic acids (mid-chain HETEs) in the development of cardiovascular disease. Among these mid-chains, 8-HETE has been reported to have a proliferator and proinflammatory action. However, whether 8-HETE can induce cardiac hypertrophy has never been investigated before. Therefore, the overall objectives of the present study are to elucidate the potential hypertrophic effect of 8-HETE in the human ventricular cardiomyocytes, RL-14 cells, and to explore the mechanism(s) involved. Our results showed that 8-HETE induced cellular hypertrophy in RL-14 cells as evidenced by the induction of cardiac hypertrophy markers ANP, BNP, α-MHC, and β-MHC in a concentration- and time-dependent manner as well as the increase in cell surface area. Mechanistically, 8-HETE was able to induce the NF-κB activity as well as it significantly induced the phosphorylation of ERK1/2. The induction of cellular hypertrophy was associated with a proportional increase in the formation of dihydroxyeicosatrienoic acids (DHETs) parallel to the increase of soluble epoxide hydrolase (sEH) enzyme activity. Blocking the induction of NF-κB, ERK1/2, and sEH signaling pathways significantly inhibited 8-HETE-induced cellular hypertrophy. Our study provides the first evidence that 8-HETE induces cellular hypertrophy in RL-14 cells through MAPK- and NF-κB-dependent mechanism

Expression of CYP 4A ω-hydroxylase and formation of 20-hydroxyeicosatetreanoic acid (20-HETE) in cultured rat brain astrocytes

Astrocytes secrete vasodilator and vasoconstrictor factors via end feet processes, altering blood flow to meet neuronal metabolic demand. Compared to what is known about the ability of astrocytes to release factors that dilate local cerebral vasculature, very little is known regarding the source and identity of astrocyte derived constricting factors. The present study investigated if astrocytes express CYP 4A ω-hydroxylase and metabolize arachidonic acid (AA) to 20-hydroxyeicotetraenoic acid (20-HETE) that regulates KCa channel activity in astrocytes and cerebral arterial myocyte contractility. Here we report that cultured astrocytes express CYP 4A2/3 ω-hydroxylase mRNA and CYP 4A protein and produce 20-HETE and the CYP epoxygenase metabolites epoxyeicosatrienoic acids (EETs) when incubated with AA. The production of 20-HETE and EETs was enhanced following stimulation of metabotropic glutamate receptors (mGluR) on the astrocytes. Exogenous application of 20-HETE attenuated, whereas inhibition of 20-HETE production with HET-0016 increased the open state probabilities (NPo) of 71pS and 161pS KCa single-channel currents recorded from astrocytes. Exposure of isolated cerebral arterial myocytes to conditioned media from cultured astrocytes caused shortening of the length of freshly isolated cerebral arterial myocytes that was not evident following inhibition of astrocyte 20-HETE synthesis and action. These findings suggest that astrocytes not only release vasodilator EETs in response to mGluR stimulation but also synthetize and release the cerebral arterial myocyte constrictor 20-HETE that also functions as an endogenous inhibitor of the activity of two types of KCa channel currents found in astrocytes.

Development and Validation of a High-Throughput Ultrahigh-Performance Liquid Chromatography-Mass Spectrometry Approach for Screening of Oxylipins and Their Precursors

Lipid mediators, highly bioactive compounds synthesized from polyunsaturated fatty acids (PUFAs), have a fundamental role in the initiation and signaling of the inflammatory response. Although extensively studied in isolation, only a limited number of analytical methods offer a comprehensive coverage of the oxylipin synthetic cascade applicable to a wide range of human biofluids. We report the development of an ultrahigh-performance liquid chromatography-electrospray ionization triple quadrupole mass spectrometry (UHPLC-MS) assay to quantify oxylipins and their PUFA precursors in 100 μL of human serum, plasma, urine, and cell culture supernatant. A single 15 min UHPLC run enables the quantification of 43 oxylipins and 5 PUFAs, covering pro and anti-inflammatory lipid mediators synthesized across the cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP450) pathways. The method was validated in multiple biofluid matrixes (serum, plasma, urine, and cell supernatant) and suppliers, ensuring its suitability for large scale metabonomic studies. The approach is accurate, precise, and reproducible (RSD < 15%) over multiple days and concentrations. Very high sensitivity is achieved with limits of quantification inferior to picograms for the majority of analytes (0.05-125 pg) and linear range spanning up to 5 orders of magnitude. This enabled the quantification of the great majority of these analytes at their low endogenous level in human biofluids. We successfully applied the procedure to individuals undergoing a fasting intervention; oxylipin profiles highlighted significantly altered PUFA and inflammatory profiles in accordance with previously published studies as well as offered new insight on the modulation of the biosynthetic cascade responsible for the regulation of oxylipins.

Early Changes in Cytochrome P450s and Their Associated Arachidonic Acid Metabolites Play a Crucial Role in the Initiation of Cardiac Hypertrophy Induced by Isoproterenol

Cytochrome P450 enzymes (P450s), along with their cardioprotective metabolites the epoxyeicosatrienoic acids (EETs) and cardiotoxic metabolite 20-hydroxyeicosatetraeonic acid (20-HETE), were found to be altered in cardiac hypertrophy; however, it is unclear whether these changes are causal or epiphenomenon. Therefore, we hypothesized that P450s and their metabolites play a crucial role in the initiation of cardiac hypertrophy. To test our hypothesis, rats and RL-14 cells were treated with the hypertrophic agonist isoproterenol for different time periods. Thereafter, in vivo heart function and wall thickness were assessed using echocardiography. Moreover, the role of P450 epoxygenases, ω-hydroxylases, and soluble epoxide hydrolase (sEH) were determined at mRNA, protein, and activity levels using real-time polymerase chain reaction, Western blot, and liquid chromatography-mass spectrometry, respectively. Our results show that in vivo and in vitro hypertrophy was initiated after 72 hours and 6 hours of isoproterenol treatment, respectively. Studies performed at the prehypertrophy phase showed a significant decrease in P450 epoxygenases along with a significant induction of sEH activity. Consequently, lower EET and higher dihydroxyeicosatrienoic acid levels were observed during this phase. However, significant increases in P450 ω-hydroxylase along with its associated metabolite, 20-HETE, were detected only in vivo. Interestingly, increasing EET levels by P450 epoxygenase induction, sEH inhibition, or exogenous administration of EET prevented the initiation of cardiac hypertrophy through a nuclear factor-κB-mediated mechanism. Taken together, these findings reveal a crucial role of P450 epoxygenases and EETs in the development of cardiac hypertrophy, which could uncover novel targets for prevention of heart failure at early stages.

Soluble epoxide hydrolase inhibitor, TUPS, protects against isoprenaline-induced cardiac hypertrophy

BACKGROUND AND PURPOSE

We have previously shown that isoprenaline-induced cardiac hypertrophy causes significant changes in the expression of cytochromes P450 (CYP) and soluble epoxide hydrolase (sEH) genes. Therefore, it is important to examine whether the inhibition of sEH by 1-(1-methanesulfonyl-piperidin-4-yl)-3-(4-trifluoromethoxy-phenyl)-urea (TUPS) will protect against isoprenaline-induced cardiac hypertrophy.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were treated with TUPS (0.65 mg kg(-1) day(-1), p.o.), isoprenaline (5 mg kg(-1) day(-1), i.p.) or the combination of both. In vitro H9c2 cells were treated with isoprenaline (100 μM) in the presence and absence of either TUPS (1 μM) or 11,12 EET (1 μM). The expression of hypertrophic, fibrotic markers and different CYP genes were determined by real-time PCR.

KEY RESULTS

Isoprenaline significantly induced the hypertrophic, fibrotic markers as well as the heart to body weight ratio, which was significantly reversed by TUPS. Isoprenaline also caused an induction of CYP1A1, CYP1B1, CYP2B1, CYP2B2, CYP4A3 and CYP4F4 gene expression and TUPS significantly inhibited this isoprenaline-mediated effect. Moreover, isoprenaline significantly reduced 5,6-, 8,9-, 11,12- and 14,15-EET and increased their corresponding 8,9-, 11,12- and 14,15-dihydroxyeicosatrienoic acid (DHET) and the 20-HETE metabolites. TUPS abolished these isoprenaline-mediated changes in arachidonic acid (AA) metabolites. In H9c2 cells, isoprenaline caused a significant induction of ANP, BNP and EPHX2 mRNA levels. Both TUPS and 11,12-EET significantly decreased this isoprenaline-mediated induction of ANP, BNP and EPHX2.

CONCLUSIONS AND IMPLICATIONS

TUPS partially protects against isoprenaline-induced cardiac hypertrophy, which confirms the role of sEH and CYP enzymes in the development of cardiac hypertrophy.

Contribution of epoxyeicosatrienoic acids to the cerebral blood flow response to hypoxemia

Adenosine A2A receptors and ATP-activated K(+) (KATP) channels contribute to part of the cerebral vasodilatory response to systemic hypoxia, but other mediators are likely involved. Epoxyeicosatrienoic acids (EETs) are cerebral vasodilators and are released from astrocytes exposed to hypoxia. Moreover, stimulation of metabotropic glutamate receptors (mGluR) produces vasodilation by an EET-dependent mechanism. Here, we tested the hypothesis that EET signaling and mGluR activation contribute to hypoxic vasodilation. Laser-Doppler flow was measured over cerebral cortex of anesthetized rats subjected to stepwise reductions in arterial oxygen saturation to 50-70%. Hypoxic reactivity was calculated as the slope of the change in laser-Doppler flow vs. the reciprocal of arterial oxygen content. Hypoxic reactivity significantly decreased from 9.2 ± 1.9 (±95% confidence interval) in controls with vehicle treatment to 2.6 ± 1.4 with the EET antagonist 14,15-epoxyeicosa-5(Z)-enoic acid, to 3.0 ± 1.5 with the EET synthesis inhibitor MS-PPOH, to 1.9 ± 2.3 with the combined mGluR subtype 1 and 5 antagonists 2-methyl-6-(phenylethynyl)pyridine and LY367385, to 5.6 ± 1.2 with the KATP channel inhibitor glibenclamide, and to 5.8 ± 2.3 with the A2A receptor antagonist SCH58261. However, reactivity was not significantly altered by the A2B receptor antagonist MRS1754 (6.7 ± 1.8; P = 0.28 Dunnett's test) or by the 20-hydroxyeicosatetraenoic acid synthesis inhibitor HET0016 (7.5 ± 2.3; P = 0.6). These data indicate that, in addition to the known contributions of A2A receptors and KATP channels to the increase in cerebral blood flow during hypoxia, EETs and mGluRs make a major contribution, possibly by mGluR stimulation and hypoxia-induced release of EETs. In contrast, A2B receptors do not make a major contribution, and 20-hydroxyeicosatetraenoic acid does not significantly limit hypoxic vasodilation.

Ethanol at low concentrations protects glomerular podocytes through alcohol dehydrogenase and 20-HETE

Clinical studies suggest cardiovascular and renal benefits of ingesting small amounts of ethanol. Effects of ethanol, role of alcohol dehydrogenase (ADH) or of 20-hydroxyeicosatetraenoic acid (20-HETE) in podocytes of the glomerular filtration barrier have not been reported. We found that mouse podocytes at baseline generate 20-HETE and express ADH but not CYP2e1. Ethanol at high concentrations altered the actin cytoskeleton, induced CYP2e1, increased superoxide production and inhibited ADH gene expression. Ethanol at low concentrations upregulated the expression of ADH and CYP4a12a. 20-HETE, an arachidonic acid metabolite generated by CYP4a12a, blocked the ethanol-induced cytoskeletal derangement and superoxide generation. Ethanol at high concentration or ADH inhibitor increased glomerular albumin permeability in vitro. 20-HETE and its metabolite produced by ADH activity, 20-carboxy-arachidonic acid, protected the glomerular permeability barrier against an ADH inhibitor, puromycin or FSGS permeability factor. We conclude that ADH activity is required for glomerular function, 20-HETE is a physiological substrate of ADH in podocytes and that podocytes are useful biosensors to understand glomeruloprotective effects of ethanol.

Ultrahigh-performance liquid chromatography/tandem mass spectrometry method for evaluating enzyme activity and screening inhibitors of cyclooxygenase-2

RATIONALE

Prostaglandin E2 is an important biomarker in many biological systems. The development of sensitive and reliable analytical methods for monitoring PGE2 contents in various samples is of great interest. Here we developed an improved method for evaluating the enzyme activity and screening COX-2 inhibitors using ultrahigh-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) combined with PGE2 derivatization.

METHODS

Girard's reagent-T was used as the derivatization reagent and the reaction conditions were optimized. The established method was performed to screen the COX-2 inhibitors from effective constituents of herbs and detect the concentration of PGE2 in biological tissue samples (liver and kidney). The IC50 values of celecoxib, rofecoxib, sinomenine, bulleyaconitine A, tetrandrine, fangchinoline, berberine hydrochloride and sophocarpidine towards COX-2 were determined.

RESULTS

This method improves the quantitative ability for PGE2 , including the linearly dependent coefficient, linearity range and limit of detection. After derivatization, the derivatized PGE2 could be detected in positive ion mode of electrospray ionization (ESI), which improves the detection sensitivity 10-fold compared to that of the direct detection of underivatized PGE2 in negative ESI mode. Besides the positive control, sinomenine (IC50 =113 μM) and bulleyaconitine A (IC50=53 μM) were found to be potent COX-2 inhibitors.

CONCLUSIONS

All the results indicate that the present derivatization quantification method of PGE2 could be used as the detection method of COX-2 enzyme activity and as the screening method for COX-2 inhibitors.

Simultaneous tissue profiling of eicosanoid and endocannabinoid lipid families in a rat model of osteoarthritis

We describe a novel LC method for the simultaneous and quantitative profiling of 43 oxylipins including eicosanoids, endocannabinoids, and structurally related bioactive lipids with modified acyl groups. The LC-MS/MS method uses switching at a defined time between negative and positive electrospray ionization modes to achieve optimal detection sensitivity for all the lipids. The validated method is linear over a range of 0.01–5 nmol/g (0.1–50 nmol/g for 2-arachidonoyl glycerol) with intra- and interday precision and accuracy between 1.38 and 26.76% and 85.22 and 114.3%, respectively. The method successfully quantified bioactive lipids in different tissue types in the rat, including spinal cord, dorsal root ganglia (DRGs), knee joint, brain, and plasma. Distinct regional differences in the pattern of lipid measured between tissue types were observed using principle component analysis. The method was applied to analyze tissue samples from an established preclinical rat model of osteoarthritis (OA) pain and showed that levels of 12-hydroxyeicosatetraenoic acid were significantly increased in the OA rat knee joint compared with controls, and that 15-hydroxyeicosatetraenoic acid was significantly increased in the DRGs in the model of OA compared with controls. The developed LC-MS/MS method has the potential to provide detailed pathway profiling in tissues and biofluids where the disruption of bioactive oxylipins may be involved in disease states.

A novel activity of microsomal epoxide hydrolase: metabolism of the endocannabinoid 2-arachidonoylglycerol

Microsomal epoxide hydrolase (EPHX1, EC 3.3.2.9) is a highly abundant α/β-hydrolase enzyme that is known for its catalytical epoxide hydrolase activity. A wide range of EPHX1 functions have been demonstrated including xenobiotic metabolism; however, characterization of its endogenous substrates is limited. In this study, we present evidence that EPHX1 metabolizes the abundant endocannabinoid 2-arachidonoylglycerol (2-AG) to free arachidonic acid (AA) and glycerol. The EPHX1 metabolism of 2-AG was demonstrated using commercially available EPHX1 microsomes as well as PC-3 cells overexpressing EPHX1. Conversely, EPHX1 siRNA markedly reduced the EPHX1 expression and 2-AG metabolism in HepG2 cells and LNCaP cells. A selective EPHX1 inhibitor, 10-hydroxystearamide, inhibited 2-AG metabolism and hydrolysis of a well-known EPHX1 substrate, cis-stilbene oxide. Among the inhibitors studied, a serine hydrolase inhibitor, methoxy-arachidonyl fluorophosphate, was the most potent inhibitor of 2-AG metabolism by EPHX1 microsomes. These results demonstrate that 2-AG is an endogenous substrate for EPHX1, a potential role of EPHX1 in the endocannabinoid signaling and a new AA biosynthetic pathway.

Regulation of KCa2.3 and endothelium-dependent hyperpolarization (EDH) in the rat middle cerebral artery: the role of lipoxygenase metabolites and isoprostanes

Background and Purpose. In rat middle cerebral arteries, endothelium-dependent hyperpolarization (EDH) is mediated by activation of calcium-activated potassium (K_Ca) channels specifically K_Ca2.3 and K_Ca3.1. Lipoxygenase (LOX) products function as endothelium-derived hyperpolarizing factors (EDHFs) in rabbit arteries by stimulating K_Ca2.3. We investigated if LOX products contribute to EDH in rat cerebral arteries.

Methods. Arachidonic acid (AA) metabolites produced in middle cerebral arteries were measured using HPLC and LC/MS. Vascular tension and membrane potential responses to SLIGRL were simultaneously recorded using wire myography and intracellular microelectrodes.

Results. SLIGRL, an agonist at PAR2 receptors, caused EDH that was inhibited by a combination of K_Ca2.3 and K_Ca3.1 blockade. Non-selective LOX-inhibition reduced EDH, whereas inhibition of 12-LOX had no effect. Soluble epoxide hydrolase (sEH) inhibition enhanced the K_Ca2.3 component of EDH. Following NO synthase (NOS) inhibition, the K_Ca2.3 component of EDH was absent. Using HPLC, middle cerebral arteries metabolized ¹⁴C-AA to 15- and 12-LOX products under control conditions. With NOS inhibition, there was little change in LOX metabolites, but increased F-type isoprostanes. 8-iso-PGF_2α inhibited the K_Ca2.3 component of EDH.

Conclusions. LOX metabolites mediate EDH in rat middle cerebral arteries. Inhibition of sEH increases the K_Ca2.3 component of EDH. Following NOS inhibition, loss of K_Ca2.3 function is independent of changes in LOX production or sEH inhibition but due to increased isoprostane production and subsequent stimulation of TP receptors. These findings have important implications in diseases associated with loss of NO signaling such as stroke; where inhibition of sEH and/or isoprostane formation may of benefit.

Astrocyte regulation of cerebral vascular tone

Cerebral blood flow is controlled by two crucial processes, cerebral autoregulation (CA) and neurovascular coupling (NVC) or functional hyperemia. Whereas CA ensures constant blood flow over a wide range of systemic pressures, NVC ensures rapid spatial and temporal increases in cerebral blood flow in response to neuronal activation. The focus of this review is to discuss the cellular mechanisms by which astrocytes contribute to the regulation of vascular tone in terms of their participation in NVC and, to a lesser extent, CA. We discuss evidence for the various signaling modalities by which astrocytic activation leads to vasodilation and vasoconstriction of parenchymal arterioles. Moreover, we provide a rationale for the contribution of astrocytes to pressure-induced increases in vascular tone via the vasoconstrictor 20-HETE (a downstream metabolite of arachidonic acid). Along these lines, we highlight the importance of the transient receptor potential channel of the vanilloid family (TRPV4) as a key molecular determinant in the regulation of vascular tone in cerebral arterioles. Finally, we discuss current advances in the technical tools available to study NVC mechanisms in the brain as it relates to the participation of astrocytes.

Determination of the dominant arachidonic acid cytochrome p450 monooxygenases in rat heart, lung, kidney, and liver: protein expression and metabolite kinetics

Cytochrome P450 (P450)-derived arachidonic acid (AA) metabolites serve pivotal physiological roles. Therefore, it is important to determine the dominant P450 AA monooxygenases in different organs. We investigated the P450 AA monooxygenases protein expression as well as regioselectivity, immunoinhibition, and kinetic profile of AA epoxygenation and hydroxylation in rat heart, lung, kidney, and liver. Thereafter, the predominant P450 epoxygenases and P450 hydroxylases in these organs were characterized. Microsomes from heart, lung, kidney, and liver were incubated with AA. The protein expression of CYP2B1/2, CYP2C11, CYP2C23, CYP2J3, CYP4A1/2/3, and CYP4Fs in the heart, lung, kidney, and liver were determined by Western blot analysis. The levels of AA metabolites were determined by liquid chromatography-electrospray ionization mass spectroscopy. This was followed by determination of regioselectivity, immunoinhibition effect, and the kinetic profile of AA metabolism. AA was metabolized to epoxyeicosatrienoic acids and 19- and 20-hydroxyeicosatetraenoic acid in the heart, lung, kidney, and liver but with varying metabolic activities and regioselectivity. Anti-P450 antibodies were found to differentially inhibit AA epoxygenation and hydroxylation in these organs. Our data suggest that the predominant epoxygenases are CYP2C11, CYP2B1, CYP2C23, and CYP2C11/CYP2C23 for the heart, lung, kidney, and liver, respectively. On the other hand, CYP4A1 is the major ω-hydroxylase in the heart and kidney; whereas CYP4A2 and/or CYP4F1/4 are probably the major hydroxlases in the lung and liver. These results provide important insights into the activities of P450 epoxygenases and P450 hydroxylases-mediated AA metabolism in different organs and their associated P450 protein levels.

Quantitative profiling of oxylipins through comprehensive LC-MS/MS analysis: application in cardiac surgery

Oxylipins, including eicosanoids, affect a broad range of biological processes, such as the initiation and resolution of inflammation. These compounds, also referred to as lipid mediators, are (non-) enzymatically generated by oxidation of polyunsaturated fatty acids such as arachidonic acid (AA). A plethora of lipid mediators exist which makes the development of generic analytical methods challenging. Here we developed a robust and sensitive targeted analysis platform for oxylipins and applied it in a biological setting, using high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) operated in dynamic multiple reaction monitoring (dMRM). Besides the well-described AA metabolites, oxylipins derived from linoleic acid, dihomo-γ-linolenic acid, α-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid were included. Our comprehensive platform allows the quantitative evaluation of approximately 100 oxylipins down to low nanomolar levels. Applicability of the analytical platform was demonstrated by analyzing plasma samples of patients undergoing cardiac surgery. Altered levels of some of the oxylipins, especially in certain monohydroxy fatty acids such as 12-HETE and 12-HEPE, were observed in samples collected before and 24 h after cardiac surgery. These findings indicate that this generic oxylipin profiling platform can be applied broadly to study these highly bioactive compounds in relation to human disease.

The complex contribution of NOS interneurons in the physiology of cerebrovascular regulation

Following the discovery of the vasorelaxant properties of nitric oxide (NO) by Furchgott and Ignarro, the finding by Bredt and coll. of a constitutively expressed NO synthase in neurons (nNOS) led to the presumption that neuronal NO may control cerebrovascular functions. Consequently, numerous studies have sought to determine whether neuraly-derived NO is involved in the regulation of cerebral blood flow (CBF). Anatomically, axons, dendrites, or somata of NO neurons have been found to contact the basement membrane of blood vessels or perivascular astrocytes in all segments of the cortical microcirculation. Functionally, various experimental approaches support a role of neuronal NO in the maintenance of resting CBF as well as in the vascular response to neuronal activity. Since decades, it has been assumed that neuronal NO simply diffuses to the local blood vessels and produce vasodilation through a cGMP-PKG dependent mechanism. However, NO is not the sole mediator of vasodilation in the cerebral microcirculation and is known to interact with a myriad of signaling pathways also involved in vascular control. In addition, cerebrovascular regulation is the result of a complex orchestration between all components of the neurovascular unit (i.e., neuronal, glial, and vascular cells) also known to produce NO. In this review article, the role of NO interneuron in the regulation of cortical microcirculation will be discussed in the context of the neurovascular unit.

11,12,20-Trihydroxy-eicosa-8(Z)-enoic acid: a selective inhibitor of 11,12-EET-induced relaxations of bovine coronary and rat mesenteric arteries

Arachidonic acid is metabolized to four regioisomeric epoxyeicosatrienoic acids (EETs) by cytochrome P-450. 5,6-, 8,9-, 11,12-, and 14,15-EET are equipotent in relaxing bovine coronary arteries (BCAs). Vasorelaxant effects of EETs are nonselectively antagonized by 14,15-epoxyeicosa-5(Z)-enoic acid. The 11,12-EET analogs, 20-hydroxy-11,12-epoxyeicosa-8(Z)-enoic acid (20-H-11,12-EE8ZE) and 11,12,20-trihydroxyeicosa-8(Z)-enoic acid (11,12,20-THE8ZE) were synthesized and tested for antagonist activity against EET-induced relaxations in BCAs. In U-46619-preconstricted arterial rings, 5,6-, 8,9-, 11,12-, and 14,15-EET caused concentration-dependent relaxations with maximal relaxations ranging from 80 to 96%. Preincubation of arteries with 20-H-11,12-EE8ZE (10(-5) M) inhibited relaxations to 14,15- and 11,12-EET, but not 5,6- and 8,9-EET; however, greatest inhibitory effect was against 11,12-EET (maximal relaxation = 80.6 ± 4.6 vs. 26.7 ± 7.4% without and with 20-H-11,12-EE8ZE, respectively). Preincubation with the soluble epoxide hydrolase inhibitor (tAUCB, 10(-6) M) significantly enhanced the antagonist effect of 20-H-11,12-EE8ZE against 14,15-EET-induced relaxations (maximal relaxation = 86.6 ± 4.4 vs. 27.8 ± 3.3%, without and with 20-H-11,12-EE8ZE and tAUCB) without any change in its effect against 11,12-EET-induced relaxations. In contrast to the parent compound, the metabolite, 11,12,20-THE8ZE (10(-5) M), significantly inhibited relaxations to 11,12-EET and was without effect on other EET regioisomers. Mass spectrometric analysis revealed conversion of 20-H-11,12-EE8ZE to 11,12,20-THE8ZE by incubation with BCA. The conversion was blocked by tAUCB. 14,15-Dihydroxy-eicosa-5Z-enoic acid (a 14,15-EET antagonist), but not 11,12,20-THE8ZE (an 11,12-EET antagonist), inhibited BCA relaxations to arachidonic acid and flow-induced dilation in rat mesenteric arteries. These results indicate that 11,12,20-THE8ZE is a selective antagonist of 11,12-EET relaxations and a useful pharmacological tool to elucidate the function of 11,12-EET in the cardiovascular system.

Relative contribution of cyclooxygenases, epoxyeicosatrienoic acids, and pH to the cerebral blood flow response to vibrissal stimulation

The increase in cerebral blood flow (CBF) during neuronal activation can be only partially attenuated by individual inhibitors of epoxyeicosatrienoic acids (EETs), cyclooxgenase-2, group I metabotropic glutamate receptors (mGluR), neuronal nitric oxide synthase (nNOS), N-methyl-D-aspartate receptors, or adenosine receptors. Some studies that used a high concentration (500 μM) of the cyclooxygenase-1 inhibitor SC-560 have implicated cyclooxygenase-1 in gliovascular coupling in certain model systems in the mouse. Here, we found that increasing the concentration of SC-560 from 25 μM to 500 μM over whisker barrel cortex in anesthetized rats attenuated the CBF response to whisker stimulation. However, exogenous prostaglandin E(2) restored the response in the presence of 500 μM SC-560 but not in the presence of a cyclooxygenase-2 inhibitor, thereby suggesting a limited permissive role for cyclooxygenase-1. Furthermore, inhibition of the CBF response to whisker stimulation by an EET antagonist persisted in the presence of SC-560 or a cyclooxygenase-2 inhibitor, thereby indicating that the EET-dependent component of vasodilation did not require cyclooxygenase-1 or -2 activity. With combined inhibition of cyclooxygenase-1 and -2, mGluR, nNOS, EETs, N-methyl-D-aspartate receptors, and adenosine 2B receptors, the CBF response was reduced by 60%. We postulated that the inability to completely block the CBF response was due to tissue acidosis resulting from impaired clearance of metabolically produced CO2. We tested this idea by increasing the concentration of superfused bicarbonate from 25 to 60 mM and found a markedly reduced CBF response to hypercapnia. However, increasing bicarbonate had no effect on the initial or steady-state CBF response to whisker stimulation with or without combined inhibition. We conclude that the residual response after inhibition of several known vasodilatory mechanisms is not due to acidosis arising from impaired CO2 clearance when the CBF response is reduced. An unidentified mechanism apparently is responsible for the rapid, residual cortical vasodilation during vibrissal stimulation.

Involvement of cytochrome P-450 1B1 in renal dysfunction, injury, and inflammation associated with angiotensin II-induced hypertension in rats

We investigated the contribution of cytochrome P-450 1B1 (CYP1B1) to renal dysfunction and organ damage associated with ANG II-induced hypertension in rats. ANG II (300 ng·kg(-1)·min(-1)) or vehicle were infused for 2 wk, with daily injections of a selective CYP1B1 inhibitor, 2,4,3',5'-tetramethoxystilbene (TMS; 300 μg/kg ip), or its vehicle. ANG II increased blood pressure and renal CYP1B1 activity that were prevented by TMS. ANG II also increased water intake and urine output, decreased glomerular filtration rate, increased urinary Na(+) and K(+) excretion, and caused proteinuria, all of which were prevented by TMS. ANG II infusion caused hypertrophy, endothelial dysfunction, and increased reactivity of renal and interlobar arteries to vasoconstrictor agents and renal vascular resistance and interstitial fibrosis as indicated by accumulation of α-smooth muscle actin, fibronectin, and collagen, and inflammation as indicated by increased infiltration of CD-3(+) cells; these effects were inhibited by TMS. ANG II infusion also increased production of reactive oxygen species (ROS) and activities of NADPH oxidase, ERK1/2, p38 MAPK, and c-Src that were prevented by TMS. TMS alone had no effect on any of the above parameters. These data suggest that CYP1B1 contributes to the renal pathophysiological changes associated with ANG II-induced hypertension, most likely via increased ROS production and activation of ERK1/2, p38 MAPK, and c-Src and that CYP1B1 could serve as a novel target for treating renal disease associated with hypertension.

Soluble epoxide hydrolase contamination of specific catalase preparations inhibits epoxyeicosatrienoic acid vasodilation of rat renal arterioles

Cytochrome P-450 metabolites of arachidonic acid, the epoxyeicosatrienoic acids (EETs) and hydrogen peroxide (H(2)O(2)), are important signaling molecules in the kidney. In renal arteries, EETs cause vasodilation whereas H(2)O(2) causes vasoconstriction. To determine the physiological contribution of H(2)O(2), catalase is used to inactivate H(2)O(2). However, the consequence of catalase action on EET vascular activity has not been determined. In rat renal afferent arterioles, 14,15-EET caused concentration-related dilations that were inhibited by Sigma bovine liver (SBL) catalase (1,000 U/ml) but not Calbiochem bovine liver (CBL) catalase (1,000 U/ml). SBL catalase inhibition was reversed by the soluble epoxide hydrolase (sEH) inhibitor tAUCB (1 μM). In 14,15-EET incubations, SBL catalase caused a concentration-related increase in a polar metabolite. Using mass spectrometry, the metabolite was identified as 14,15-dihydroxyeicosatrienoic acid (14,15-DHET), the inactive sEH metabolite. 14,15-EET hydrolysis was not altered by the catalase inhibitor 3-amino-1,2,4-triazole (3-ATZ; 10-50 mM), but was abolished by the sEH inhibitor BIRD-0826 (1-10 μM). SBL catalase EET hydrolysis showed a regioisomer preference with greatest hydrolysis of 14,15-EET followed by 11,12-, 8,9- and 5,6-EET (V(max) = 0.54 ± 0.07, 0.23 ± 0.06, 0.18 ± 0.01 and 0.08 ± 0.02 ng DHET·U catalase(-1)·min(-1), respectively). Of five different catalase preparations assayed, EET hydrolysis was observed with two Sigma liver catalases. These preparations had low specific catalase activity and positive sEH expression. Mass spectrometric analysis of the SBL catalase identified peptide fragments matching bovine sEH. Collectively, these data indicate that catalase does not affect EET-mediated dilation of renal arterioles. However, some commercial catalase preparations are contaminated with sEH, and these contaminated preparations diminish the biological activity of H(2)O(2) and EETs.

Rapid simultaneous analysis of cyclooxygenase, lipoxygenase and cytochrome P-450 metabolites of arachidonic and linoleic acids using high performance liquid chromatography/mass spectrometry in tandem mode

Eicosanoids are oxidized arachidonate-derived lipid products generated by cyclooxygenase, lipoxygenase and cytochrome P-450 pathways. They are involved in diverse processes in health and disease and they are highly bioactive. Gas chromatography and enzyme immunoassays were used to quantify these mediators in the past. However, the recent availability of high-sensitivity liquid chromatography-mass spectrometry has provided a new approach for quantification that minimizes the sample size and the required preparation. This paper describes a rapid and simple technique for the simultaneous quantitative analysis of prostaglandin (PG) E(2) and PGJ(2); leukotrienes (LT) B(4) and D(4); 5-, 12-, 15- and 20-hydroxyeicosatetraenoic acids (HETEs); 13-hydroxyoctadecadienoic acid (13-HODE); 5,6-, 8,9-, 11,12- and 14,15-epoxyeicosatrienoic acids (EETs); and 11,12- and 14,15-dihydroxieicosatrienoic acids (DHETs) in cell culture supernatants and urine. We simultaneously analyzed 14 arachidonic acid metabolites representative from the three pathways, together with 13-HODE, a linoleic-derived product. Solid phase extraction was used for the sample preparation. The recoveries obtained ranged from 25% to 100%, depending on the metabolites. The LC/MS/MS method used the gradient on a C(18) column and electrospray ionization in negative ion detection mode. The method was optimized for sensitivity and for separation within 20 min. The linear ranges of the calibration curves were 0.1-200 ng/ml for PGE(2), PGJ(2), LTB(4), 5-HETE, 12-HETE, 15-HETE, 13-HODE, 11,12-EET, 11,12-DHET and 14,15-DHET, and 1-200ng/ml for LTD(4), 20-HETE, 5,6-EET, 8,9-EET and 14,15-EET. The advantages of this method include minimal sample preparation, high sensitivity and elimination of the problem associated with thermal instability in gas chromatography analysis.

Epoxyeicosatrienoic acid-dependent cerebral vasodilation evoked by metabotropic glutamate receptor activation in vivo

Group I metabotropic glutamate receptors (mGluR) on astrocytes have been shown to participate in cerebral vasodilation to neuronal activation in brain slices. Pharmacological stimulation of mGluR in brain slices can produce arteriolar constriction or dilation depending on the initial degree of vascular tone. Here, we examined whether pharmacological stimulation of mGluR in vivo increases cerebral blood flow. A 1-mM solution of the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG) superfused at 5 μl/min over the cortical surface of anesthetized rats produced a 30 ± 2% (±SE) increase in blood flow measured by laser-Doppler flowmetry after 15-20 min. The response was completely blocked by superfusion of group I mGluR antagonists and attenuated by superfusion of an epoxyeicosatrienoic acid (EET) antagonist (5 ± 4%), an EET synthesis inhibitor (11 ± 3%), and a cyclooxygenase-2 inhibitor (15 ± 3%). The peak blood flow response was not significantly affected by administration of inhibitors of cyclooxygenase-1, neuronal nitric oxide synthase, heme oxygenase, adenosine A(2B) receptors, or an inhibitor of the synthesis of 20-hydroxyeicosatetraenoic acid (20-HETE). The blood flow response gradually waned following 30-60 min of DHPG superfusion. This loss of the flow response was attenuated by a 20-HETE synthesis inhibitor and was prevented by superfusion of an inhibitor of epoxide hydrolase, which hydrolyzes EETs. These results indicate that pharmacological stimulation of mGluR in vivo increases cerebral blood flow and that the response depends on the release of EETs and a metabolite of cyclooxygenase-2. Epoxide hydrolase activity and 20-HETE synthesis limit the duration of the response to prolonged mGluR activation.

Pressure-induced myogenic tone and role of 20-HETE in mediating autoregulation of cerebral blood flow

While myogenic force in response to a changing arterial pressure has been described early in the 20th century, it was not until 1984 that the effect of a sequential increase in intraluminal pressure on cannulated cerebral arterial preparations was found to result in pressure-dependent membrane depolarization associated with spike generation and reduction in lumen diameter. Despite a great deal of effort by different laboratories and investigators, the identification of the existence of a mediator of the pressure-induced myogenic constriction in arterial muscle remained a challenge. It was the original finding by our laboratory that demonstrated the capacity of cerebral arterial muscle cells to express the cytochrome P-450 4A enzyme that catalyzes the formation of the potent vasoconstrictor 20-hydroxyeicosatetraenoic acid (20-HETE) from arachidonic acid, the production of which in cerebral arterial muscle cells increases with the elevation in intravascular pressure. 20-HETE activates protein kinase C and causes the inhibition of Ca(²+)-activated K(+) channels, depolarizes arterial muscle cell membrane, and activates L-type Ca(²+) channel to increase intracellular Ca(²+) levels and evoke vasoconstriction. The inhibition of 20-HETE formation attenuates pressure-induced arterial myogenic constriction in vitro and blunts the autoregulation of cerebral blood flow in vivo. We suggest that the formation and action of cytochrome P-450-derived 20-HETE in cerebral arterial muscle could play a critically important role in the control of cerebral arterial tone and the autoregulation of cerebral blood flow under physiological conditions.

Role of superoxide and thromboxane receptors in acute angiotensin II-induced vasoconstriction of rabbit vessels

This study explored the hypothesis that a portion of angiotensin II-induced contractions is dependent on superoxide generation and release of a previously unidentified arachidonic acid metabolite that activates vascular smooth muscle thromboxane receptors. Treatment of rabbit aorta or mesentery artery with the thromboxane receptor antagonist SQ29548 (10 μM) reduced angiotensin II-induced contractions (maximal contraction in aorta; control vs. SQ29548: 134 ± 16 vs. 93 ± 10%). A subset of rabbits deficient in vascular thromboxane receptors also displayed decreased contractions to angiotensin II. The superoxide dismutase mimetic Tiron (30 mM) attenuated angiotensin II-induced contractions only in rabbits with functional vascular thromboxane receptors (maximal contraction in aorta; control vs. Tiron: 105 ± 5 vs. 69 ± 11%). Removal of the endothelium or treatment with a nitric oxide synthase inhibitor, nitro-l-arginine (30 μM) did not alter angiotensin II-induced contractions. Tiron and SQ29548 decreased angiotensin II-induced contractions in the denuded aortas by a similar percentage as that observed in intact vessels. The cyclooxygenase inhibitor indomethacin (10 μM) or thromboxane synthase inhibitor dazoxiben (10 μM) had no effect on angiotensin II-induced contractions indicating that the vasoconstrictor was not thromboxane. Angiotensin II increased the formation of a 15-series isoprostane. Isoprostanes are free radical-derived products of arachidonic acid. The unidentified isoprostane increased when vessels were incubated with the superoxide-generating system xanthine/xanthine oxidase. Pretreatment of rabbit aorta with the isoprostane isolated from aortic incubations enhanced angiotensin II-induced contractions. Results suggest the factor activating thromboxane receptors and contributing to angiotensin II vasoconstriction involves the superoxide-mediated generation of a 15-series isoprostane.

Role of lipoxygenase metabolites of arachidonic acid in enhanced pulmonary artery contractions of female rabbits

Pulmonary arterial hypertension is characterized by elevated pulmonary artery pressure and vascular resistance. In women the incidence is 4-fold greater than that in men. Studies suggest that sustained vasoconstriction is a factor in increased vascular resistance. Possible vasoconstrictor mediators include arachidonic acid-derived lipoxygenase (LO) metabolites. Our studies in rabbits showed enhanced endothelium-dependent contractions to arachidonic acid in pulmonary arteries from females compared with males. Because treatment with a nonspecific LO inhibitor reduced contractions in females but not males, the present study identified which LO isoform contributes to sex-specific pulmonary artery vasoconstriction. The 15- and 5- but not 12-LO protein expressions were greater in females. Basal and A23187-stimulated release of 15-, 5-, and 12-hydroxyeicosatetraenoic acids (HETEs) from females and males were measured by liquid chromatography/mass spectrometry. Only 15-HETE synthesis was greater in females compared with males under both basal and stimulated conditions. Vascular contractions to 15-HETE were enhanced in females compared with males (maximal contraction: 44±6%versus 25±3%). The specific 15-LO inhibitor PD146176 (12 μmol/L) decreased arachidonic acid-induced contractions in females (maximal contraction: 93±4% versus 57±10%). If male pulmonary arteries were incubated with estrogen (1 μmol/L, 18 hours), protein expression of 15-LO and 15-HETE production increased. Mechanisms to explain the increased incidence of pulmonary hypertension in women are not known. Results suggest that the 15-LO pathway is different between females and males and is regulated by estrogen. Understanding this novel sex-specific mechanism may provide insight into the increased incidence of pulmonary hypertension in females.

Comprehensive lipidomics analysis of bioactive lipids in complex regulatory networks

In the present work we describe the development of an analytical technique for simultaneous profiling of over 100 biochemically related lipid mediators in biological samples. A multistep procedure was implemented to extract eicosanoids and other bioactive lipids from the biological matrix, chromatographically separate them using fast reversed-phase liquid chromatography, tentatively identify new candidate eicosanoids through a matching process of retention times, isotope distribution patterns, and high-resolution orbitrap MS/MS fragmentation patterns, and subsequently quantify tentative candidates by means of analytical reference standards. Key new aspects of this profiling technique included the classification of bioactive lipids into 12 groups according to their calculated exact masses and the development of optimized liquid chromatographic conditions for these groups to achieve sufficient separation of the numerous isobaric and isomeric species, many of which exhibited virtually identical collision-induced dissociation behavior. Importantly, no analytical standards were required at this screening stage of the assay, and tentative identifications were achieved by matching results to selected reference species from each of the groups. The analytical figures of merit for the orbitrap assay such as linear dynamic range, limit of detection, limit of quantitation, and precision demonstrated that the performance of the assay was very similar to that of a quadrupole linear ion trap assay, which was used for validation purposes. The method allowed us to examine eicosanoid profiles within the signaling cascade in chronic lymphocytic leukemia (CLL) cells under basal conditions and following arachidonic acid stimulation. The preliminary screening based on high-resolution tandem mass spectrometry data along with isotope pattern and retention time matching revealed the presence of 15 bioactive lipids, belonging to a range of prostaglandin, leukotriene, and hydroxy and epoxy fatty acid lipid mediators produced by CLL cells.

Angiotensin II regulates adrenal vascular tone through zona glomerulosa cell-derived EETs and DHETs

Elevated concentrations of aldosterone are associated with several cardiovascular diseases. Angiotensin II (Ang II) increases aldosterone secretion and adrenal blood flow. This concurrent increase in steroidogenesis and adrenal blood flow is not understood. We investigated the role of zona glomerulosa (ZG) cells in the regulation of vascular tone of bovine adrenal cortical arteries by Ang II. ZG cells enhanced endothelium-dependent relaxations to Ang II. The ZG cell-dependent relaxations to Ang II were unchanged by removing the endothelium-dependent response to Ang II. These ZG cell-mediated relaxations were ablated by cytochrome P450 inhibition, epoxyeicosatrienoic acid (EET) antagonism, and potassium channel blockade. Analysis of ZG cell EET production by liquid chromatography/mass spectrometry demonstrated an increase in EETs and dihydroxyeicosatrienoic acids with Ang II stimulation. These EETs and dihydroxyeicosatrienoic acids produced similar concentration-dependent relaxations of adrenal arteries, which were attenuated by EET antagonism. Whole-cell potassium currents of adrenal artery smooth muscle cells were increased by Ang II stimulation in the presence of ZG cells but decreased in the absence of ZG cells. This increase in potassium current was abolished by iberiotoxin. Similarly, 14,15-EET induced concentration-dependent increases in potassium current, which was abolished by iberiotoxin. ZG cell aldosterone release was not directly altered by EETs. These data suggest that Ang II stimulates ZG cells to release EETs and dihydroxyeicosatrienoic acids, resulting in potassium channel activation and relaxation of adrenal arteries. This provides a mechanism by which Ang II concurrently increases adrenal blood flow and steroidogenesis.

14,15-Dihydroxy-eicosa-5(Z)-enoic acid selectively inhibits 14,15-epoxyeicosatrienoic acid-induced relaxations in bovine coronary arteries

Cytochrome P-450 epoxygenases metabolize arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs). EETs relax vascular smooth muscle by membrane hyperpolarization. 14,15-Epoxyeicosa-5(Z)-enoic acid (14,15-EE5ZE) antagonizes many vascular actions of EETs. EETs are converted to the corresponding dihydroxyeicosatrienoic acids by soluble epoxide hydrolase (sEH). sEH activity in the bovine arterial endothelium and smooth muscle regulates endogenous EETs. This study examined sEH metabolism of 14,15-EE5ZE to 14,15-dihydroxy-eicosa-5(Z)-enoic acid (14,15-DHE5ZE) and the resultant consequences on EET relaxations of bovine coronary arteries (BCAs). BCAs converted 14,15-EE5ZE to 14,15-DHE5ZE. This conversion was blocked by the sEH inhibitor 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA). 14,15-EET relaxations (maximal relaxation, 83.4 ± 4.5%) were inhibited by 14,15-DHE5ZE (10 μM; maximal relaxation, 36.1 ± 9.0%; p < 0.001). In sharp contrast with 14,15-EE5ZE, 14,15-DHE5ZE is a 14,15-EET-selective inhibitor and did not inhibit 5,6-, 8,9-, or 11,12-EET relaxations. 14,15-EET and 11,12-EET relaxations were similar in the presence and absence of AUDA (1 μM). 14,15-EE5ZE inhibited 14,15-EET relaxations to a similar extent with and without AUDA pretreatment. However, 14,15-EE5ZE inhibited 11,12-EET relaxations to a greater extent with than without AUDA pretreatment. These observations indicate that sEH converts 14,15-EE5ZE to 14,15-DHE5ZE, and this alteration influences antagonist selectivity against EET-regioisomers. 14,15-DHE5ZE inhibited endothelium-dependent relaxations to AA but not endothelium-independent relaxations to sodium nitroprusside. A series of sEH-resistant ether analogs of 14,15-EE5ZE was developed, and analogs with agonist and antagonist properties were identified. The present study indicates that conversion of 14,15-EE5ZE to 14,15-DHE5ZE produces a 14,15-EET-selective antagonist that will be a useful pharmacological tool to identify EET receptor(s) and EET function in the cardiovascular system.

Inhibition of carcinoma cell motility by epoxyeicosatrienoic acid (EET) antagonists

Cytochrome P450 (CYP) epoxygenases, CYP2C8, 2C9 and 2J2 mRNA and proteins, were expressed in prostate carcinoma (PC-3, DU-145 and LNCaP) cells. 11,12-Epoxyeicosatrienoic acid (11,12-EET) was the major arachidonic acid metabolite in these cells. Blocking EET synthesis by a selective CYP epoxygenase inhibitor (N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide [MS-PPOH]) inhibited tonic (basal) invasion and migration (motility) while exogenously added EET induced cell motility in a concentration-dependent manner. An epidermal growth factor receptor (EGFR) kinase inhibitor (AG494) or a PI3 kinase inhibitor (LY294002) inhibited cell migration and reduced 11,12-EET-induced cell migration. Importantly, synthetic EET antagonists (14,15-epoxyeicosa-5(Z)-enoic acid [14,15-EEZE], 14,15-epoxyeicosa-5(Z)-enoic acid 2-[2-(3-hydroxy-propoxy)-ethoxy]-ethyl ester [14,15-EEZE-PEG] and 14,15-epoxyeicosa-5(Z)-enoic-methylsulfonylimide [14,15-EEZE-mSI]) inhibited EET-induced cell invasion and migration. 11,12-EET induced cell stretching and myosin-actin microfilament formation as well as increased phosphorylation of EGFR and Akt (Ser473), while 14,15-EEZE inhibited these effects. These results suggest that EET induce and EET antagonists inhibit cell motility, possibly by putative EET receptor-mediated EGFR and PI3K/Akt pathways, and suggest that EET antagonists are potential therapeutic agents for prostate cancer.

Effects of a commonly occurring genetic polymorphism of human CYP3A4 (I118V) on the metabolism of anandamide

The endocannabinoid system plays an important role in numerous physiological processes including mood, appetite, and pain sensation. A critical compound in maintaining cannabinoid tone is the endocannabinoid anandamide (AEA). We have recently shown that AEA is metabolized by several different human cytochromes P450 (P450) to form a number of metabolites, one of which exhibits increased biological activity. CYP3A4, one of the major P450s involved in the metabolism of AEA, produces four major metabolites. One of these metabolites, 5,6-epoxyeicosatrienoic acid ethanolamide (5,6-EET-EA), exhibits a much higher affinity than AEA for the cannabinoid 2 receptor (CB-2), which leads to a marked decrease in intracellular cAMP levels in cells expressing CB-2. There are multiple human alleles of CYP3A4, and the CYP3A4.4 allele has been shown to exhibit a significant decrease in activity. Recombinant CYP3A4*4 was expressed in Escherichia coli and was demonstrated to produce 60% less 6-hydroxytestosterone than the wild-type (WT) 3A4 in a reconstituted system. The metabolism of AEA by the WT and the CYP3A4.4 variant was investigated. The mutant produced 60% less of the four EET-EA metabolites than the WT. The mutant also produced a new peak on liquid chromatography-mass spectrometry not seen with the WT, which corresponded to 19-hydroxyeicosatetraenoic acid-ethanolamide. In addition, the mutant produces four novel peaks at m/z 380, which correspond to the addition of two oxygen atoms, possibly to form a peroxide bond. These data indicate that individuals expressing the CYP3A4.4 allele may exhibit significant variations in the metabolism of AEA as well as any other compounds resembling AEA.

Role of epoxyeicosatrienoic acids as autocrine metabolites in glutamate-mediated K+ signaling in perivascular astrocytes

Epoxyeicosatrienoic acids (EETs), synthesized and released by astrocytes in response to glutamate, are known to play a pivotal role in neurovascular coupling. In vascular smooth muscle cells (VSMC), EETs activate large-conductance, Ca(2+)-activated K(+) (BK) channels resulting in hyperpolarization and vasodilation. However, the functional role and mechanism of action for glial-derived EETs are still to be determined. In this study, we evaluated the effect of the synthetic EET analog 11-nonyloxy-undec-8(Z)-enoic acid (NUD-GA) on outward K(+) currents mediated by calcium-activated K(+) channels. Addition of NUD-GA significantly increased intracellular Ca(2+) and outward K(+) currents in perivascular astrocytes. NUD-GA-induced currents were significantly inhibited by BK channel blockers paxilline and tetraethylammonium (TEA) (23.4 ± 2.4%; P < 0.0005). Similarly, NUD-GA-induced currents were also significantly inhibited in the presence of the small-conductance Ca(2+)-activated K(+) channel inhibitor apamin along with a combination of blockers against glutamate receptors (12.8 ± 2.70%; P < 0.05). No changes in outward currents were observed in the presence of the channel blocker for intermediate-conductance K(+) channels TRAM-34. Blockade of the endogenous production of EETs with N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH) significantly blunted (dl)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (t-ACPD)-induced outward K(+) currents (P < 0.05; n = 6). Both NUD-GA and t-ACPD significantly increased BK channel single open probability; the later was blocked following MS-PPOH incubation. Our data supports the idea that EETs are potent K(+) channel modulators in cortical perivascular astrocytes and further suggest that these metabolites may participate in NVC by modulating the levels of K(+) released at the gliovascular space.

Adrenic acid metabolites as endogenous endothelium-derived and zona glomerulosa-derived hyperpolarizing factors

Adrenic acid (docosatetraenoic acid), an abundant fatty acid in the adrenal gland, is identical to arachidonic acid except for 2 additional carbons on the carboxyl end. Adrenic acid is metabolized by cyclooxygenases, cytochrome P450s, and lipoxygenases; however, little is known regarding the role of adrenic acid and its metabolites in vascular tone. Because of its abundance in the adrenal gland, we investigated the role of adrenic acid in vascular tone of bovine adrenal cortical arteries and its metabolism by bovine adrenal zona glomerulosa cells. In adrenal cortical arteries, adrenic acid caused concentration-dependent relaxations, which were inhibited by the epoxyeicosatrienoic acid antagonist 14,15-epoxyeicosa-5(Z)-enoic acid and the cytochrome P450 inhibitor SKF-525A. The large-conductance calcium-activated potassium channel blocker iberiotoxin or removal of the endothelium abolished these relaxations. Reverse-phase high-pressure liquid chromatography and liquid chromatography/mass spectrometry isolated and identified numerous adrenic acid metabolites from zona glomerulosa cells, including dihomo-epoxyeicosatrienoic acids and dihomo-prostaglandins. In denuded adrenal cortical arteries, adrenic acid caused concentration-dependent relaxations in the presence of zona glomerulosa cells but not in their absence. These relaxations were inhibited by SKF-525A, 14,15-epoxyeicosa-5(Z)-enoic acid, and iberiotoxin. Dihomo-16,17-epoxyeicosatrienoic acid caused concentration-dependent relaxations of adrenal cortical arteries, which were inhibited by 14,15-epoxyeicosa-5(Z)-enoic acid and high potassium. Our results suggest that adrenic acid relaxations of bovine adrenal cortical arteries are mediated by endothelial and zona glomerulosa cell cytochrome P450 metabolites. Thus, adrenic acid metabolites could function as endogenous endothelium-derived and zona glomerulosa-derived hyperpolarizing factors in the adrenal cortex and contribute to the regulation of adrenal blood flow.

Rapid, simultaneous quantitation of mono and dioxygenated metabolites of arachidonic acid in human CSF and rat brain

Currently, there are few biomarkers to predict the risk of symptomatic cerebral vasospasm (SV) in subarachnoid hemorrhage (SAH) patients. Mono and dioxygenated arachidonic acid metabolites, involved in the pathogenesis of ischemic injury, may serve as indicators of SV. This study developed a quantitative UPLC-MS/MS method to simultaneously measure hydroxyeicosatetraenoic acid (HETE), dihydroxyeicosatrienoic acid (DiHETrE), and epoxyeicosatrienoic acid (EET) metabolites of arachidonic acid in cerebrospinal fluid (CSF) samples of SAH patients. Additionally, we determined the recovery of these metabolites from polyvinylchloride (PVC) bags used for CSF collection. Linear calibration curves ranging from 0.208 to 33.3 ng/ml were validated. The inter-day and intra-day variance was less than 15% at most concentrations with extraction efficiency greater than 73%. The matrix did not affect the reproducibility and reliability of the assay. In CSF samples, peak concentrations of 8,9-DiHETrE, 20-HETE, 15-HETE, and 12-HETE ranged from 0.293 to 24.9 ng/ml. In rat brain cortical tissue samples, concentrations of 20-, 15-, 12-HETE, 8,9-EET, and 14,15-, 11,12-DiHETrE ranged from 0.57 to 23.99 pmol/g wet tissue. In rat cortical microsomal incubates, all 10 metabolites were measured with formation rates ranging from 0.03 to 7.77 pmol/mg/min. Furthermore, 12-HETE and EET metabolites were significantly altered by contact with PVC bags at all time points evaluated. These data demonstrate that the simultaneous measurement of these compounds in human CSF and rat brain can be achieved with a UPLC-MS/MS system and that this method is necessary for evaluation of these metabolites as potential quantitative biomarkers in future clinical trials.

Quantitative profiling method for oxylipin metabolome by liquid chromatography electrospray ionization tandem mass spectrometry

Cyclooxygenase, lipoxygenase, and epoxygenase derived oxylipins, especially eicosanoids, play important roles in many physiological processes. Assessment of oxidized fatty acid levels is important for understanding their homeostatic and pathophysiological roles. Most reported methods examine these pathways in isolation. The work described here employed a solid phase extraction-liquid chromatography-electrospray ionization MS/MS (SPE-LC-ESI MS/MS) method to monitor these metabolites. In 21 min, 39 oxylipins were quantified along with eight corresponding internal standards. The limits of quantification were between 0.07 and 32 pg (20 pM-10 nM). Finally, the validated method was used to evaluate oxylipin profiles in lipopolysaccharide-exposed mice, an established septic inflammatory model. The method described here offers a useful tool for the evaluation of complex regulatory oxylipin responses in in vitro or in vivo studies.