Identification of 15-hydroxy-11,12-epoxyeicosatrienoic acid as a vasoactive 15-lipoxygenase metabolite in rabbit aorta

Elucidation for the pharmacological effects and mechanism of Shen Bai formula in treating myocardial injury based on energy metabolism and serum metabolomic approaches

ETHNOPHARMACOLOGICAL RELEVANCE

Shen Bai formula (SBF) is a proven effective traditional Chinese medicine for treating viral myocarditis (VMC) sequelae in clinic, and myocardial injury is the pathological basis of VMC sequelae. However, the pharmacological action and mechanism of SBF have not been systematically elucidated.

AIM OF THE STUDY

In present research, the doxorubicin-induced myocardial injury rat model was used to evaluate the efficacy of SBF, and energy metabolism and metabolomics approaches were applied to elucidate the effects of SBF on myocardial injury.

MATERIALS AND METHODS

Through energy metabolism measurement system and UPLC-Q-TOF-MS/MS oriented blood metabolomics, directly reflected the therapeutic effect of SBF at a macro level, and identified biomarkers of myocardial injury in microcosmic, revealing its metabolomic mechanism.

RESULTS

Results showed that SBF significantly improved the electrocardiogram (ECG), heart rate (HR), extent of myocardial tissue lesion, and ratio of heart and spleen. In addition, the serum levels of AST, CK, LDH, α-HBDH, cTnI, BNP, and MDA decreased, whereas SOD and ATP activity and content increased. Moreover, SBF increased locomotor activity and basic daily metabolism in rats with myocardial injury, restoring their usual level of energy metabolism. A total of 45 potential metabolomic biomarkers were identified. Among them, 44 biomarkers were significantly recalled by SBF, including representative biomarkers arachidonic acid (AA), 12-HETE, prostaglandin J2 (PGJ2), 15-deoxy-Δ-12,14-PGJ2, 15-keto-PGE2, 15(S)-HPETE, 15(S)-HETE, 8,11,14-eicosatrienoic acid and 9(S)-HODE, which involved AA metabolism, biosynthesis of unsaturated fatty acids and linoleic acid metabolism.

CONCLUSION

We successfully replicated a myocardial injury rat model with the intraperitoneal injection of doxorubicin, and elucidated the mechanism of SBF in treating myocardial injury. This key mechanism may be achieved by targeting action on COX, Alox, CYP, and 15-PGDH to increase or decrease the level of myocardial injury biomarker, and then emphatically interven in AA metabolism, biosynthesis of unsaturated fatty acids and linoleic acid metabolism, and participate in regulating purine metabolism, sphingolipid metabolism, primary bile acid biosynthesis, and steroid hormone synthesis.

Inhibitory Activity of Natural cis-Khellactone on Soluble Epoxide Hydrolase and Proinflammatory Cytokine Production in Lipopolysaccharides-Stimulated RAW264.7 Cells

The pursuit of anti-inflammatory agents has led to intensive research on the inhibition of soluble epoxide hydrolase (sEH) and cytokine production using medicinal plants. In this study, we evaluated the efficacy of cis-khellactone, a compound isolated for the first time from the roots of Peucedanum japonicum. The compound was found to be a competitive inhibitor of sEH, exhibiting an IC50 value of 3.1 ± 2.5 µM and ki value of 3.5 µM. Molecular docking and dynamics simulations illustrated the binding pose of (-)cis-khellactone within the active site of sEH. The results suggest that binding of the inhibitor to the enzyme is largely dependent on the Trp336-Gln384 loop within the active site. Further, cis-khellactone was found to inhibit pro-inflammatory cytokines, including NO, iNOS, IL-1β, and IL-4. These findings affirm that cis-khellactone could serve as a natural therapeutic candidate for the treatment of inflammation.

Exercise-Induced Changes in Bioactive Lipids Might Serve as Potential Predictors of Post-Exercise Hypotension. A Pilot Study in Healthy Volunteers

Post-exercise hypotension (PEH) is the phenomenon of lowered blood pressure after a single bout of exercise. Only a fraction of people develops PEH but its occurrence correlates well with long-term effects of sports on blood pressure. Therefore, PEH has been suggested as a suitable predictor for the effectivity of exercise as therapy in hypertension. Local vascular bioactive lipids might play a potential role in this context. We performed a cross-over clinical pilot study with 18 healthy volunteers to investigate the occurrence of PEH after a single short-term endurance exercise. Furthermore, we investigated the plasma lipid profile with focus on arachidonic acid (AA)-derived metabolites as potential biomarkers of PEH. A single bout of ergometer cycling induced a significant PEH in healthy volunteers with the expected high inter-individual variability. Targeted lipid spectrum analysis revealed significant upregulation of several lipids in the direct post-exercise phase. Among these changes, only 15- hydroxyeicosatetranoic acid (HETE) correlated significantly with the extent of PEH but in an AA-independent manner, suggesting that 15-HETE might act as specific PEH-marker. Our data indicate that specific lipid modulation might facilitate the identification of patients who will benefit from exercise activity in hypertension therapy. However, larger trials including hypertonic patients are necessary to verify the clinical value of this hypothesis.

Chronic ethanol consumption enhances inducible endothelium-dependent hyperpolarizing factor-mediated relaxation in the rat artery

The inducible endothelium-dependent hyperpolarizing factor (iEDHF) pathway is activated as a compensatory response to adverse changes in the body. It causes vasorelaxation and maintains circulatory homeostasis in the organs. Small to moderate quantities of ethanol enhance vascular relaxation. However, its mechanism and the involvement of the iEDHF pathway in this process are unknown. Therefore, we studied iEDHF-mediated, acetylcholine-induced, endothelium-dependent relaxation in the superior mesenteric arteries (SMAs) of rats chronically fed ethanol. Rats were administered a standard diet (S-Control group), Lieber's control diet (L-Control group), or Lieber's ethanol diet (EtOH group). SMA relaxation was assessed by isometric tension measurements. Arachidonate 15-lipoxygenase (ALOX15) and soluble epoxide hydrolase (sEH) were determined by immunoblot. Acetylcholine-induced, endothelium-dependent relaxation was significantly greater in the EtOH than the control groups. These differences persisted after PGI2 and NO blockade. Thus, the increase in acetylcholine-induced relaxation was EDHF-mediated. In the EtOH group, however, it was prevented by iEDHF inhibitors. ALOX15 and sEH protein expression levels were higher in the EtOH than the L-Control group. The increase in acetylcholine-induced relaxation by chronic ethanol consumption was mediated by the iEDHF pathway. This mechanism may compensate for the blood pressure elevation induced by ethanol. This study suggests that iEDHF is induced during proper drinking and may help prevent the onset of cardiovascular conditions.

Vascular hepoxilin and trioxilins mediate vasorelaxation through TP receptor inhibition in mouse arteries

AIM

12/15-lipoxygenase (12/15-LO) metabolizes arachidonic acid (AA) into several vasoactive eicosanoids. In mouse arteries, we previously characterized the enzyme's 15-LO metabolites 12(S)-hydroxyeicosatetraenoic acid (HETE), 15-HETE, hydroxyepoxyeicosatrienoic acids (HEETAs) and 11,12,15-trihydroxyeicosatrienoic acids (11,12,15-THETAs) as endothelium-derived relaxing factors. However, the observed 12-LO metabolites remained uncharacterized. The purpose of this study was to determine the structure and biological functions of eicosanoids generated by the enzyme's 12-LO activity.

METHODS

Metabolites extracted from aortas of C57BL/6 male mice were separated using a series of reverse and normal phase chromatographic steps and identified as hepoxilin A₃ , trioxilin A₃ and trioxilin C₃ by mass spectrometry. Activities of these natural compounds were tested on isometric tension and intracellular calcium release. The role of thromboxane (TP) receptor was determined in HEK293 cells overexpressing TPα receptor (TPα -HEK).

RESULTS

All identified vascular 12-LO metabolites were biologically active. In mouse mesenteric arteries, trioxilin A₃ , C₃ and hepoxilin A₃ (3 μm) relaxed arteries constricted with the thromboxane mimetic, U46619-constricted arteries (maximum relaxations of 78.9 ± 3.2, 29.7 ± 4.6, 82.2 ± 5.0 and 88.0 ± 2.4% respectively), but not phenylephrine-constricted arteries. In TPα-HEK cells, trioxilin A₃ , C₃ and hepoxilin A₃ (10 μm) inhibited U46619 (10 nM)-induced increases in intracellular calcium by 53.0 ± 7.2%, 32.8 ± 5.0% and 37.9 ± 13.5% respectively. In contrast, trioxilin B₃ and hepoxilin B₃ were not synthesized in arteries and exhibited little biological activity.

CONCLUSION

Trioxilin A₃ and C₃ and hepoxilin A₃ are endogenous vascular relaxing factors. They are not endothelium-derived hyperpolarizing factors but mediate vascular relaxation by inhibiting TP agonist-induced increases in intracellular calcium. Thus, they regulate vascular homeostasis by acting as endogenous TP antagonists.

Endothelium-dependent hyperpolarization: age, gender and blood pressure, do they matter?

Under physiological conditions, the endothelium generates vasodilator signals [prostacyclin, nitric oxide NO and endothelium-dependent hyperpolarization (EDH)], for the regulation of vascular tone. The relative importance of these two signals depends on the diameter of the blood vessels: as the diameter of the arteries decreases, the contribution of EDH to the regulation of vascular tone increases. The mechanism involved in EDH varies with species and blood vessel types; nevertheless, activation of endothelial intermediate- and small-conductance calcium-activated potassium channels (IK_Ca and SK_Ca , respectively) is characteristic of the EDH pathway. IK_Ca - and SK_Ca -mediated EDH are reduced with endothelial dysfunction, which develops with ageing and hypertension, and is less pronounced in female than in age-matched male until after menopause. Impaired EDH-mediated relaxation is related to a reduced involvement of SK_Ca , so that the response becomes more dependent on IK_Ca . The latter depends on the activation of adenosine monophosphate-activated protein kinase (AMPK) and silent information regulator T1 (SIRT1), proteins associated with the process of cellular senescence and vascular signalling in response to the female hormone. An understanding of the role of AMPK and/or SIRT1 in EDH-like responses may help identifying effective pharmacological strategies to prevent the development of vascular complications of different aetiologies.

Plasma 12- and 15-hydroxyeicosanoids are predictors of survival in pulmonary arterial hypertension

This study aimed to characterize alterations in select eicosanoids in experimental and human pulmonary arterial hypertension (PAH) and to assess their potential utility as predictors of outcome. Using liquid chromatography-mass spectrometry, we performed targeted lipidomic analyses of the lungs and right ventricles (RVs) of chronically hypoxic rats and plasma of consecutive PAH patients and healthy controls. In rat lungs, chronic hypoxia was associated with significantly decreased lung prostacyclin (PGI2)/thromboxane B2 (TXB2) ratio and elevated lung 8-hydroxyeicosanoid (HETE) acid concentrations. RV eicosanoids did not exhibit any changes with chronic hypoxia. PAH treatment-naïve patients had significantly increased plasma concentrations of TXB2 and 5-, 8-, 12-, and 15-HETE. The PGI2/TXB2 ratio was lower in PAH patients than in controls, especially in the treatment-naïve cohort (median: 2.1, 0.3, and 1.3 in controls, treatment-naïve, and treated patients, respectively, P = 0.001). Survival was significantly worse in PAH patients with 12-HETEhigh (≥57 pg/mL) and 15-HETEhigh (≥256 pg/mL) in unadjusted and adjusted analyses (hazard ratio [HR]: 2.8 [95% confidence interval (CI): 1.1-7.3], P = 0.04 and HR: 4.3 [95% CI: 1.6-11.8], P = 0.004, respectively; adjustment was performed with the REVEAL [Registry to Evaluate Early and Long-Term PAH Disease Management] risk score). We demonstrate significant alterations in eicosanoid pathways in experimental and human PAH. We found that 12- and 15-HETE were independent predictors of survival in human PAH, even after adjusting for the REVEAL score, suggesting their potential role as novel biomarkers.

The Precise Structures and Stereochemistry of Trihydroxy-linoleates Esterified in Human and Porcine Epidermis and Their Significance in Skin Barrier Function: IMPLICATION OF AN EPOXIDE HYDROLASE IN THE TRANSFORMATIONS OF LINOLEATE

Creation of an intact skin water barrier, a prerequisite for life on dry land, requires the lipoxygenase-catalyzed oxidation of the essential fatty acid linoleate, which is esterified to the ω-hydroxyl of an epidermis-specific ceramide. Oxidation of the linoleate moiety by lipoxygenases is proposed to facilitate enzymatic cleavage of the ester bond, releasing free ω-hydroxyceramide for covalent binding to protein, thus forming the corneocyte lipid envelope, a key component of the epidermal barrier. Herein, we report the transformations of esterified linoleate proceed beyond the initial steps of oxidation and epoxyalcohol synthesis catalyzed by the consecutive actions of 12R-LOX and epidermal LOX3. The major end product in human and porcine epidermis is a trihydroxy derivative, formed with a specificity that implicates participation of an epoxide hydrolase in converting epoxyalcohol to triol. Of the 16 possible triols arising from hydrolysis of 9,10-epoxy-13-hydroxy-octadecenoates, using LC-MS and chiral analyses, we identify and quantify specifically 9R,10S,13R-trihydroxy-11E-octadecenoate as the single major triol esterified in porcine epidermis and the same isomer with lesser amounts of its 10R diastereomer in human epidermis. The 9R,10S,13R-triol is formed by S_N2 hydrolysis of the 9R,10R-epoxy-13R-hydroxy-octadecenoate product of the LOX enzymes, a reaction specificity characteristic of epoxide hydrolase. The high polarity of triol over the primary linoleate products enhances the concept that the oxidations disrupt corneocyte membrane lipids, promoting release of free ω-hydroxyceramide for covalent binding to protein and sealing of the waterproof barrier.

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.

Inducible endothelium-derived hyperpolarizing factor: role of the 15-lipoxygenase-EDHF pathway

Endothelium-derived hyperpolarizing factors (EDHFs) regulate vascular tone by contributing to the vasorelaxations to shear stress and endothelial agonists such as bradykinin and acetylcholine. 15(S)-Hydroxy-11,12-epoxyeicosatrienoic acid (15-H-11,12-EETA) and 11(R),12(S),15(S)-trihydroxyeicosatrienoic acid (11,12,15-THETA) are endothelial metabolites of the 15-lipoxygenase (15-LO) pathway of arachidonic acid metabolism and are EDHFs. 11,12,15-THETA activates small conductance, calcium-activated potassium channels on smooth muscle cells causing membrane hyperpolarization, and relaxation. Expression levels of 15-LO in the endothelium regulate the activity of the 15-LO/15-H-11,12-EETA/11,12,15-THETA pathway and its contribution to vascular tone. Regulation of its expression is by transcriptional, translational, and epigenetic mechanisms. Hypoxia, hypercholesterolemia, atherosclerosis, anemia, estrogen, interleukins, and possibly other hormones increase 15-LO expression. An increase in 15-LO results in increased synthesis of 15-H-11,12-EETA and 11,12,15-THETA, increased membrane hyperpolarization, and enhanced contribution to relaxation by endothelial agonists. Thus, the 15-LO pathway represents the first example of an inducible EDHF. In addition to 15-LO metabolites, a number of chemicals have been identified as EDHFs and their contributions to vascular tone vary with species and vascular bed. The reason for multiple EDHFs has evaded explanation. However, EDHF functioning as constitutive EDHFs or inducible EDHFs may explain the need for chemically and biochemically distinct pathways for EDHF activity and the variation in EDHFs between species and vascular beds. This new EDHF classification provides a framework for understanding EDHF activity in physiological and pathological conditions.

Soluble epoxide hydrolase: gene structure, expression and deletion

Mammalian soluble epoxide hydrolase (sEH) converts epoxides to their corresponding diols through the addition of a water molecule. sEH readily hydrolyzes lipid signaling molecules, including the epoxyeicosatrienoic acids (EETs), epoxidized lipids produced from arachidonic acid by the action of cytochrome p450s. Through its metabolism of the EETs and other lipid mediators, sEH contributes to the regulation of vascular tone, nociception, angiogenesis and the inflammatory response. Because of its central physiological role in disease states such as cardiac hypertrophy, diabetes, hypertension, and pain sEH is being investigated as a therapeutic target. This review begins with a brief introduction to sEH protein structure and function. sEH evolution and gene structure are then discussed before human small nucleotide polymorphisms and mammalian gene expression are described in the context of several disease models. The review ends with an overview of studies that have employed the sEH knockout mouse model.

Differences between basal lung levels of select eicosanoids in rat and mouse

Metabolites of arachidonic acid play an important role in mediating inflammation, cell proliferation, and oxidative stress that contribute to many pulmonary diseases. We hypothesized that the substantial differences between rats and mice in their responses to experimental pulmonary hypertensive stimuli would be associated with parallel differences in their basal eicosanoid profile. Rat and mouse lung extracts were subjected to liquid chromatography tandem mass spectrometry that was optimized for simultaneous separation and rapid quantification of the major hydroxyeicosatetraenoic acids (HETEs) and prostaglandins (PGs). Basal levels (pg/μg protein) of arachidonic acid metabolites differed significantly between rat and mouse lungs. Median values of the following major eicosanoids were significantly higher in mouse than in rat lungs: 5-HETE, 8-HETE, 12-HETE, 15-HETE, PGE₂, and PGI₂, as well as isoprostane-E₂ and -F_2α. In addition, the PGI₂/TXB₂ ratio was increased in mouse relative to rat lungs. On the basis of the important roles that these compounds play in determining pulmonary vascular tone, the differences in select eicosanoid profiles, especially the PGI₂/TXB₂ ratio, between rat and mouse lungs may underlie the interspecies differences in susceptibility to the development of pulmonary hypertension.

Inhibition of soluble epoxide hydrolase limits niacin-induced vasodilation in mice

BACKGROUND

The use of niacin in the treatment of dyslipidemias is limited by the common side effect of cutaneous vasodilation, commonly termed flushing. Flushing is thought to be due to release of the vasodilatory prostanoids prostaglandin D2 (PGD2) and prostaglandin E2 from arachidonic acid metabolism through the cyclooxygenase pathway. Arachidonic acid is also metabolized by the cytochrome P450 system, which is regulated, in part, by the enzyme soluble epoxide hydrolase (sEH).

METHODS

These experiments used an established murine model in which ear tissue perfusion was measured by laser Doppler to test the hypothesis that inhibition of sEH would limit niacin-induced flushing.

RESULTS

Niacin-induced flushing was reduced from 506 ± 126% to 213 ± 39% in sEH knockout animals. Pharmacologic treatment with 3 structurally distinct sEH inhibitors similarly reduced flushing in a dose-dependent manner, with maximal reduction to 143% ± 15% of baseline flow using a concentration of 1 mg/kg TPAU (1-trifluoromethoxyphenyl-3-(1-acetylpiperidin-4-yl) urea). Systemically administered PGD2 caused ear vasodilation, which was not changed by either pharmacologic sEH inhibition or sEH gene deletion.

CONCLUSIONS

Inhibition of sEH markedly reduces niacin-induced flushing in this model without an apparent effect on the response to PGD2. sEH inhibition may be a new therapeutic approach to limit flushing in humans.

Endothelial 12(S)-HETE vasorelaxation is mediated by thromboxane receptor inhibition in mouse mesenteric arteries

Arachidonic acid (AA) metabolites mediate endothelium-dependent relaxation in many vascular beds. Previously, we identified the major AA 12/15-lipoxygenase (12/15-LO) metabolite of mouse arteries as 12-hydroxyeicosatetraenoic acid (12-HETE). The goal was to determine the stereospecific configuration of mouse vascular 12-HETE and characterize the role of 12-HETE stereoisomers in the regulation of vascular tone. Using normal, reverse phase, and chiral HPLC, the stereospecific configuration was identified as 12(S)-HETE. 12(S)-HETE relaxed U46619-, carbocyclic thromboxane A(2)-, PGF(2α)-, and 8-iso PGF(2α)-preconstricted mesenteric arteries, but not phenylephrine-preconstricted arteries. 12(R)-HETE was more potent than 12(S)-HETE in relaxing U46619-preconstricted mouse arteries (maximum relaxations = 91.4 ± 2.7% and 71.8 ± 5.9%, respectively). Neither 12-HETE isomer caused constriction. Pretreatment with 12(S)- or 12(R)-HETE (1 μM) inhibited constrictions to U46619 but not phenylephrine. To investigate the role of thromboxane A(2) (TP) receptors in 12-HETE vascular actions, [(3)H]SQ29548 radioligand binding studies were performed in mouse platelets. U46619, 12(R)-HETE, and 12(S)-HETE displaced [(3)H]SQ29548 binding with IC(50)s of 0.07, 0.32, and 1.73 μM, respectively. Both 12(S)- and 12(R)-HETE inhibited intracellular calcium increases induced by U46619 (10 nM) in HEK293 cells overexpressing TP(α) receptor (65.5% and 45.1%, respectively) and coexpressing prostacyclin (IP) and TP(α) receptors (58.0% and 27.1%, respectively). The LO inhibitor NDGA (10 μM) reduced AA relaxations in arteries preconstricted with U46619 but not phenylephrine. These results indicate that exogenous and endogenous 12(S)-HETE relax mouse mesenteric arteries that are preconstricted with thromboxane agonists. These 12(S)-HETE relaxations are mediated by TP receptor competitive inhibition and inhibition of TP agonist-induced increases in intracellular calcium.

Endothelial nitric oxide and 15-lipoxygenase-1 metabolites independently mediate relaxation of the rabbit aorta

Endothelial 15-lipoxygenase-1 (15-LO-1) metabolites of arachidonic acid (AA), 11,12,15-trihydroxyeicosatrienoic acid (THETA) and 15-hydroxy-11,12-epoxyeicosatrienoic acid (HEETA) and nitric oxide (NO) mediate relaxations to acetylcholine (ACH). However, interactions between NO and the 15-LO-1 pathway have not been explored. Therefore, the effect of physiological and pharmacological concentrations of NO on 15-LO activity and relaxation was studied in rabbit aorta. In indomethacin-treated aortic rings, maximal ACH relaxations of 91.3±4.0%, decreased to 54.5±3.0% by the NO synthase inhibitor, nitro-l-arginine (LNA), to 49.8±3% by the guanylate cyclase (GC) inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, to 63.7±4.9% by the lipoxygenase (LO) inhibitor, nordihydroguaiaretic acid (NDGA) and were completely inhibited by the combination of LNA and NDGA. AA relaxations were not affected by GC inhibition but were reduced by LO inhibition. The NO donor, dipropylenetriamine-NONOate (DPTA) caused concentration-related relaxations (EC(50)=4.7×10(-6)M). Aortic metabolism of (14)C-AA to THETA and HEETA was not altered by EC(50) concentrations of DPTA but were reduced 10-fold by 10(-3)M DPTA. In LNA-treated aorta, DPTA (3×10(-6)M) caused relaxations of 38.2.5±4%. Maximum relaxations to ACH did not differ in the presence and absence 3×10(-6)M DPTA (49.5±5% and 44.2±4%, respectively). These results indicate that NO and 15-LO-1 act in parallel to mediate ACH relaxations and NO does not alter 15-LO-1 activity.

Role of arachidonic acid lipoxygenase metabolites in acetylcholine-induced relaxations of mouse arteries

Arachidonic acid (AA) metabolites function as EDHFs in arteries of many species. They mediate cyclooxygenase (COX)- and nitric oxide (NO)-independent relaxations to acetylcholine (ACh). However, the role of AA metabolites as relaxing factors in mouse arteries remains incompletely defined. ACh caused concentration-dependent relaxations of the mouse thoracic and abdominal aorta and carotid, femoral, and mesentery arteries (maximal relaxation: 57 ± 4%, 72 ± 4%, 82 ± 3%, 80 ± 3%, and 85 ± 3%, respectively). The NO synthase inhibitor nitro-L-arginine (L-NA; 30 μM) blocked relaxations in the thoracic aorta, and L-NA plus the COX inhibitor indomethacin (10 μM) inhibited relaxations in the abdominal aorta and carotid, femoral, and mesenteric arteries (maximal relaxation: 31 ± 10%, 33 ± 5%, 41 ± 8%, and 73 ± 3%, respectively). In mesenteric arteries, NO- and COX-independent relaxations to ACh were inhibited by the lipoxygenase (LO) inhibitors nordihydroguaiaretic acid (NDGA; 10 μM) and BW-755C (200 μM), the K(+) channel inhibitor apamin (1 μM), and 60 mM KCl and eliminated by endothelium removal. They were not altered by the cytochrome P-450 inhibitor N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (20 μM) or the epoxyeicosatrienoic acid antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (10 μM). AA relaxations were attenuated by NDGA or apamin and eliminated by 60 mM KCl. Reverse-phase HPLC analysis revealed arterial [(14)C]AA metabolites that comigrated with prostaglandins, trihydroxyeicosatrienoic acids (THETAs), hydroxyepoxyeicosatrienoic acids (HEETAs), and hydroxyeicosatetraenoic acids (HETEs). Epoxyeicosatrienoic acids were not observed. Mass spectrometry confirmed the identity of 6-keto-PGF(1α), PGE(2), 12-HETE, 15-HETE, HEETAs, 11,12,15-THETA, and 11,14,15-THETA. AA metabolism was blocked by NDGA and endothelium removal. 11(R),12(S),15(S)-THETA relaxations (maximal relaxation: 73 ± 3%) were endothelium independent and blocked by 60 mM KCl. Western immunoblot analysis and RT-PCR of the aorta and mesenteric arteries demonstrated protein and mRNA expression of leukocyte-type 12/15-LO. Thus, in mouse resistance arteries, 12/15-LO AA metabolites mediate endothelium-dependent relaxations to ACh and AA.

Mechanisms underlying increased reactivity of pulmonary arteries contralateral to a localized high-flow anastomosis

OBJECTIVES

Our model of a systemic-pulmonary shunt exhibits enhanced reactivity of pulmonary arteries contralateral to a localized shunt between the left lower lobe pulmonary artery and aorta relative to those of ipsilateral or control pulmonary arteries 48 hours after anastomosis. We examined the contribution of nitric oxide, cyclooxygenase, lipoxygenase, or cytochrome P450 production to mediating this enhanced reactivity.

METHODS

We created a surgical end-to-side anastomosis of the left lower lobe pulmonary artery to the aorta. Forty-eight hours later, we tested tension of pulmonary artery rings from the right and left lower lobes for contraction to the thromboxane mimetic U46619 in the presence of vehicle or inhibitors of nitric oxide synthase, cyclooxygenase, cytochrome P450, or lipoxygenase. Western blots of pulmonary artery homogenates were probed for endothelial nitric oxide synthase or isoforms metabolizing arachidonic acid. Eicosanoid products from intact pulmonary artery rings were detected using labeled arachidonic acid and high-performance liquid chromatography separation.

RESULTS

Enhanced reactivity of unshunted right pulmonary arteries over that of left pulmonary arteries from high-flow hosts was not eliminated by inhibitors of nitric oxide synthase, cyclooxygenase, cytochrome P450. Treatment with 2 different lipoxygenase inhibitors, nordihydroguaiaretic acid and cinnamyl-3,4-dihydroxy-α-cyanocinnamate, closed the difference in contractility of shunted and unshunted pulmonary arteries. Pulmonary arteries contralateral to shunts metabolized arachidonic acid to 12-hydroxyeicosatetraenoic acid in greater quantities than analogous pulmonary arteries from the experimental left or control pulmonary arteries.

CONCLUSIONS

Forty-eight hours after anastomosis, enhanced reactivity of contralateral pulmonary arteries is attributable in part to increased lipoxygenase products as opposed to nitric oxide or other eicosanoid products.

Identification of 13-hydroxy-14,15-epoxyeicosatrienoic acid as an acid-stable endothelium-derived hyperpolarizing factor in rabbit arteries

Arachidonic acid (AA) is metabolized by endothelial 15-lipoxygenase (15-LO) to several vasodilatory eicosanoids such as 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA) and its proposed unstable precursor 15-hydroxy-11,12-epoxyeicosatrienoic acid (15-H-11,12-EETA). In the present study, the acid-stable 13-hydroxy-trans-14,15-epoxy-eicosatrienoic acid (13-H-14,15-EETA) was identified and its vascular activities characterized. Rabbit aorta, mesenteric arteries, and the combination of 15-LO and cytochrome P450 2J2 converted AA to two distinct HEETA metabolites. The HEETA metabolites were resistant to acidic hydrolysis but were hydrolyzed by recombinant sEH to a more polar metabolite identified by mass spectrometry as 13,14,15-THETA. Mass spectrometric analyses and HPLC comigration identified the HEETAs as threo- and erythro-diastereomers of 13-H-trans-14,15-EETA. Erythro- and threo-diastereomers of 13-H-trans-14,15-EETA relaxed endothelium-denuded rabbit small mesenteric arteries with maximum relaxations of 22.6 +/- 6.0% and 8.6 +/- 4.3%, respectively. Apamin (10(-7) m) inhibited the relaxations to the erythro-isomer (maximum relaxation = 1.2 +/- 5.6%) and increasing [K(+)](o) from 4.6 to 30 mm blocked relaxations to both isomers. In cell-attached patches of mesenteric arterial smooth muscle cells (SMCs), erythro-13-H-trans-14,15-EETA (1-3 x 10(-6) m) increased mean open time of small conductance K(+) channels (13-14 pS) from 0.0007 +/- 0.0007 to 0.0053 +/- 0.0042. This activation was inhibited by apamin. The erythro, but not the threo, isomer blocked angiotensin II-stimulated aortic SMC migration. These studies demonstrate that 13-H-14,15-EETAs induces vascular relaxation via K(+) channel activation to cause SMC hyperpolarization. Thus, 13-H-14,15-EETA represents a new endothelial factor.

Role of arachidonic acid lipoxygenase metabolites in the regulation of vascular tone

Stimulation of vascular endothelial cells with agonists such as acetylcholine (ACh) or bradykinin or with shear stress activates phospholipases and releases arachidonic acid (AA). AA is metabolized by cyclooxygenases, cytochrome P-450s, and lipoxygenases (LOs) to vasoactive products. In some arteries, a substantial component of the vasodilator response is dependent on LO metabolites of AA. Nitric oxide (NO)- and prostaglandin (PG)-independent vasodilatory responses to ACh and AA are reduced by inhibitors of LO and by antisense oligonucleotides specifically against 15-LO-1. Vasoactive 15-LO metabolites derived from the vascular endothelium include 15-hydroxy-11,12-epoxyeicosatrienoic acid (15-H-11,12-HEETA) that is hydrolyzed by soluble epoxide hydrolase to 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA). HEETA and THETA are endothelium-derived hyperpolarizing factors that induce vascular relaxations by activation of smooth muscle apamin-sensitive, calcium-activated, small-conductance K(+) channels causing hyperpolarization. In other arteries, the 12-LO metabolite 12-hydroxyeicosatetraenoic acid is synthesized by the vascular endothelium and relaxes smooth muscle by large-conductance, calcium-activated K(+) channel activation. Thus formation of vasodilator eicosanoids derived from LO pathways contributes to the regulation of vascular tone, local blood flow, and blood pressure.

Chronic hypoxia enhances 15-lipoxygenase-mediated vasorelaxation in rabbit arteries

15-Lipoxygenase (15-LO-1) metabolizes arachidonic acid (AA) to 11,12,15-trihydroxyeicosatrienoic acids (THETAs) and 15-hydroxy-11,12-epoxyeicosatrienoic acids (HEETA) that dilate rabbit arteries. Increased endothelial 15-LO-1 expression enhances arterial relaxations to agonists. We tested the effect of hypoxia on 15-LO-1 expression, THETA and HEETA synthesis, and relaxations in rabbit arteries. The incubation of rabbit aortic endothelial cells and isolated aortas in 0.7% O(2) increased 15-LO-1 expression. Rabbits were housed in a hypoxic atmosphere of 12% O(2) for 5 days. 15-LO-1 expression increased in the endothelium of the arteries of rabbits in 12% O(2) compared with room air. THETA and HEETA synthesis was also enhanced in aortas and mesenteric arteries. AA hyperpolarized the smooth muscle cells in indomethacin- and phenylephrine-treated mesenteric arteries of hypoxic rabbits from -29.4 +/- 1 to -50.1 +/- 3 mV. The hyperpolarization to AA was less in arteries of normoxic rabbits (from -26.0 +/- 2 to -37 +/- 2 mV). This AA-induced hyperpolarization was inhibited by the 15-LO inhibitor BW-755C. Nitric oxide and prostaglandin-independent maximum relaxations to acetylcholine (79.7 +/- 2%) and AA (38.3 +/- 4%) were enhanced in mesenteric arteries from hypoxic rabbits compared with the normoxic rabbits (49.7 +/- 6% and 19.9 +/- 2%, respectively). These relaxations were inhibited by BW-755C and nordihydroguaiaretic acid. Therefore, hypoxia increased the relaxations to agonists in the rabbit mesenteric arteries by enhancing endothelial 15-LO-1 expression and synthesis of the hyperpolarizing factors THETA and HEETA.