Cytochrome P450 metabolites of arachidonic acid in the control of renal function

The potential mechanisms underlying the modulating effect of perirenal adipose tissue on hypertension: Physical compression, paracrine, and neurogenic regulation

Hypertension, a prevalent global cardiovascular disease, affects approximately 45.4 % of adults worldwide. Despite advances in therapy, hypertension continues to pose a significant health risk due to inadequate management. It has been established that excessive adiposity contributes majorly to hypertension, accounting for 65 to 75 % of primary cases. Fat depots can be categorised into subcutaneous and visceral adipose tissue based on anatomical and physiological characteristics. The metabolic impact and the risk of hypertension are determined more significantly by visceral fat. Perirenal adipose tissue (PRAT), a viscera enveloping the kidney, is known for its superior vascularisation and abundant innervation. Although traditionally deemed as a mechanical support tissue, recent studies have indicated its contributing potential to hypertension. Hypertensive patients tend to have increased PRAT thickness compared to those without, and there is a positive correlation between PRAT thickness and elevated systolic blood pressure. This review encapsulates the anatomical characteristics and biogenesis of PRAT. We provide an overview of the potential mechanisms where PRAT may modulate blood pressure, including physical compression, paracrine effects, and neurogenic regulation. PRAT has become a promising target for hypertension management, and continuous effort is required to further explore the underlying mechanisms.

Adenosine A2A receptor and vascular response: role of soluble epoxide hydrolase, adenosine A1 receptor and angiotensin-II

Previously, we have reported that the coronary reactive hyperemic response was reduced in adenosine A_2A receptor-null (A_2AAR^-/-) mice, and it was reversed by the soluble epoxide hydrolase (sEH) inhibitor. However, it is unknown in aortic vascular response, therefore, we hypothesized that A_2AAR-gene deletion in mice (A_2AAR^-/-) affects adenosine-induced vascular response by increase in sEH and adenosine A₁ receptor (A₁AR) activities. A_2AAR^-/- mice showed an increase in sEH, A_I AR and CYP450-4A protein expression but decrease in CYP450-2C compared to C57Bl/6 mice. NECA (adenosine-analog) and CCPA (adenosine A₁ receptor-agonist)-induced dose-dependent vascular response was tested with t-AUCB (sEH-inhibitor) and angiotensin-II (Ang-II) in A_2AAR^-/- vs. C57Bl/6 mice. In A_2AAR^-/-, NECA and CCPA-induced increase in dose-dependent vasoconstriction compared to C57Bl/6 mice. However, NECA and CCPA-induced dose-dependent vascular contraction in A_2AAR^-/- was reduced by t-AUCB with NECA. Similarly, dose-dependent vascular contraction in A_2AAR^-/- was reduced by t-AUCB with CCPA. In addition, Ang-II enhanced NECA and CCPA-induced dose-dependent vascular contraction in A_2AAR^-/- with NECA. Similarly, the dose-dependent vascular contraction in A_2AAR^-/- was also enhanced by Ang-II with CCPA. Further, t-AUCB reduced Ang-II-enhanced NECA and CCPA-induced dose-dependent vascular contraction in A_2AAR^-/- mice. Our data suggest that the dose-dependent vascular contraction in A_2AAR^-/- mice depends on increase in sEH, A₁AR and CYP4A protein expression.

CYP450 Mediates Reactive Oxygen Species Production in a Mouse Model of β-Thalassemia through an Increase in 20-HETE Activity

Oxidative damage by reactive oxygen species (ROS) is one of the main contributors to cell injury and tissue damage in thalassemia patients. Recent studies suggest that ROS generation in non-transfusion-dependent (NTDT) patients occurs as a result of iron overload. Among the different sources of ROS, the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase family of enzymes and cytochrome P450 (CYP450) have been proposed to be major contributors for oxidative stress in several diseases. However, the sources of ROS in patients with NTDT remain poorly understood. In this study, Hbbth3/+ mice, a mouse model for β-thalassemia, were used. These mice exhibit an unchanged or decreased expression of the major NOX isoforms, NOX1, NOX2 and NOX4, when compared to their C57BL/6 control littermates. However, a significant increase in the protein synthesis of CYP4A and CYP4F was observed in the Hbbth3/+ mice when compared to the C57BL/6 control mice. These changes were paralleled by an increased production of 20-hydroxyeicosatetraenoic acid (20-HETE), a CYP4A and CYP4F metabolite. Furthermore, these changes corroborate with onset of ROS production concomitant with liver injury. To our knowledge, this is the first report indicating that CYP450 4A and 4F-induced 20-HETE production mediates reactive oxygen species overgeneration in Hbbth3/+ mice through an NADPH-dependent pathway.

The Systems Biology of Drug Metabolizing Enzymes and Transporters: Relevance to Quantitative Systems Pharmacology

Quantitative systems pharmacology (QSP) has emerged as a transformative science in drug discovery and development. It is now time to fully rethink the biological functions of drug metabolizing enzymes (DMEs) and transporters within the framework of QSP models. The large set of DME and transporter genes are generally considered from the perspective of the absorption, distribution, metabolism, and excretion (ADME) of drugs. However, there is a growing amount of data on the endogenous physiology of DMEs and transporters. Recent studies—including systems biology analyses of “omics” data as well as metabolomics studies—indicate that these enzymes and transporters, which are often among the most highly expressed genes in tissues like liver, kidney, and intestine, have coordinated roles in fundamental biological processes. Multispecific DMEs and transporters work together with oligospecific and monospecific ADME proteins in a large multiorgan remote sensing and signaling network. We use the Remote Sensing and Signaling Theory (RSST) to examine the roles of DMEs and transporters in intratissue, interorgan, and interorganismal communication via metabolites and signaling molecules. This RSST‐based view is applicable to bile acids, uric acid, eicosanoids, fatty acids, uremic toxins, and gut microbiome products, among other small organic molecules of physiological interest. Rooting this broader perspective of DMEs and transporters within QSP may facilitate an improved understanding of fundamental biology, physiologically based pharmacokinetics, and the prediction of drug toxicities based upon the interplay of these ADME proteins with key pathways in metabolism and signaling. The RSST‐based view should also enable more tailored pharmacotherapy in the setting of kidney disease, liver disease, metabolic syndrome, and diabetes. We further discuss the pharmaceutical and regulatory implications of this revised view through the lens of systems physiology.

Identification of the Perturbed Metabolic Pathways Associating With Renal Fibrosis and Evaluating Metabolome Changes of Pretreatment With Astragalus polysaccharide Through Liquid Chromatography Quadrupole Time-Of-Flight Mass Spectrometry

Renal fibrosis is glomerulosclerosis and renal tubulointerstitial fibrosis caused by the increase of interstitial cells and intercellular substances and the accumulation of extracellular matrix, and is a common pathological manifestation of renal disease progressing to end-stage renal failure. It has proved that Astragalus polysaccharide (AP) has curative effect on renal disease; however, its therapeutic mechanism on renal fibrosis is still unclear. Metabolomics approach provides an opportunity to identify novel molecular biomarkers. The purpose of this study is to study the changes of serum metabolic profile of rats with unilateral tubal ligation and replication of renal fibrosis model and the therapeutic effect of AP on it. The blood samples of rats in the control group, renal fibrosis model group, and AP treatment group collected on the 21st day were analyzed by metabolomics method based on UPLC-Q-TOF-MS. Principal component analysis (PCA) showed that clustering was obvious and significantly separated, and paired partial least squares discriminant analysis (OPLS-DA) was used for further analysis. Combined with the network databases such as HMDB and KEGG and a large number of literatures, 32 potential biomarkers related to renal fibrosis were preliminarily screened out and further verified by MS/MS secondary debris information. After pretreatment with AP, 20 biomarkers were significantly regulated, and correlated with phenylalanine, tyrosine, and tryptophan biosynthesis, phenylalanine metabolism, arachidonic acid metabolism, etc. It also revealed the metabolic changes of renal fibrosis and intervention effect of AP. These data uncover a link between metabolism and the molecular mechanism with potential implications in the understanding of the intervention effect of AP. Conclusively, UPLC-Q-TOF-MS-based metabolomics can be valuable and promising strategy to understand the disease mechanism and natural drug pretreatment.

Transcriptome analysis of Rana chensinensis liver under trichlorfon stress

Trichlorfon is a selective organophosphate insecticide that is widely applied in aquaculture and agriculture for control of various parasites. However, repeated and excess applications of trichlorfon often lead to water pollution and threaten non-targeted species. Our previous studies showed that trichlorfon could cause oxidative stress, lipid peroxidation and hepatic lesions in the liver of Rana chensinensis, but the related molecular mechanisms remain unclear. To explore the interference of trichlorfon in gene transcription, the differentially expressed genes in the liver of R. chensinensis exposed to trichlorfon were characterized using the RNA-seq platform. A search of all unigenes against non-redundant protein sequence (Nr), non-redundant nucleotide (Nt), Swiss-Prot, Kyoto Encyclopaedia of Genes and Genomes (KEGG), Clusters of Orthologous Groups (COG) and Gene Ontology (GO) databases resulted in 22,888, 21,719, 20,934, 16,923, 7375 and 15,631 annotations, respectively, and provided a total of 27,781 annotated unigenes. Among the annotated unigenes, 16,923 were mapped to 257 signalling pathways. A set of 3329 differentially expressed unigenes was identified by comparison of the two groups in liver. Notably, relative expression of metabolism-related genes, including both up- and down-regulated genes, were also validated by qPCR. The present study depicts the high degree of transcriptional complexity in R. chensinensis under trichlorfon stress and provides new insights into the molecular mechanisms of organophosphate insecticide toxicology. Some of these metabolism-responsive genes could be useful for understanding the toxicological mechanism of trichlorfon on non-target aquatic organisms and will contribute to the conservation of aquatic life.

Clinical Implications of 20-Hydroxyeicosatetraenoic Acid in the Kidney, Liver, Lung and Brain: An Emerging Therapeutic Target

Cytochrome P450-mediated metabolism of arachidonic acid (AA) is an important pathway for the formation of eicosanoids. The ω-hydroxylation of AA generates significant levels of 20-hydroxyeicosatetraenoic acid (20-HETE) in various tissues. In the current review, we discussed the role of 20-HETE in the kidney, liver, lung, and brain during physiological and pathophysiological states. Moreover, we discussed the role of 20-HETE in tumor formation, metabolic syndrome and diabetes. In the kidney, 20-HETE is involved in modulation of preglomerular vascular tone and tubular ion transport. Furthermore, 20-HETE is involved in renal ischemia/reperfusion (I/R) injury and polycystic kidney diseases. The role of 20-HETE in the liver is not clearly understood although it represents 50%-75% of liver CYP-dependent AA metabolism, and it is associated with liver cirrhotic ascites. In the respiratory system, 20-HETE plays a role in pulmonary cell survival, pulmonary vascular tone and tone of the airways. As for the brain, 20-HETE is involved in cerebral I/R injury. Moreover, 20-HETE has angiogenic and mitogenic properties and thus helps in tumor promotion. Several inhibitors and inducers of the synthesis of 20-HETE as well as 20-HETE analogues and antagonists are recently available and could be promising therapeutic options for the treatment of many disease states in the future.

Gene expression study of phase I and II metabolizing enzymes in RPTEC/TERT1 cell line: application in in vitro nephrotoxicity prediction

1. The phase I and II metabolizing enzymes of kidneys play an important role in the metabolism of xenobiotic as well as endogenous compounds and proximal tubules of kidney constitute high concentration of these metabolizing enzymes compared with the other parts. 2. It has been shown previously that differential enzyme expression among human and rodent/non-rodent species can be a roadblock in drug discovery and development process. Currently, proximal tubule cell lines of human origin such as RPTEC/TERT1 and HK-2 are used to understand the pathophysiology of kidney diseases, therapeutic efficacy of drugs, and nephrotoxicity of compounds. 3. The purpose of the present study is to understand the metabolic enzymes present in RPTEC/TERT1 and HK-2 cell lines that would help to interpret and predict probable in vitro behavior of the molecule being tested. 4. We analyzed the expression of phase I and II metabolizing enzymes of RPTEC/TERT1 and HK-2 cell lines. We found equal expression of CYP1B1, 2J2, 3A4, 3A5, UGT1A9, SULT2A1 and GSTA, higher expression of 2B6, 2D6, 4A11, 4F2, 4F8, 4F11, UGT2B7, SULT1E1 in RPTEC/TERT1 and absence of GSTT in RPTEC/TERT1 compared to HK-2 at mRNA level. Such differences can affect the outcome of in vitro nephrotoxicity prediction.

20-HETE and CYP4A2 ω-hydroxylase contribute to the elevated blood pressure in hyperandrogenemic female rats

In male rats, androgen supplements increase 20-hydroxyeicosatetraenoic acid (20-HETE) via cytochrome P-450 (CYP)4A ω-hydroxylase and cause an increase in blood pressure (BP). In the present study, we determined the roles of 20-HETE and CYP4A2 on the elevated BP in hyperandrogenemic female rats. Chronic dihydrotestosterone (DHT) increased mean arterial pressure (MAP) in female Sprague-Dawley rats (96 ± 2 vs. 108 ± 2 mmHg, P < 0.05) and was associated with increased renal microvascular CYP4A2 mRNA expression (15-fold), endogenous renal 20-HETE (5-fold), and ω-hydroxylase activity (3-fold). Chronic DHT also increased MAP in low salt-fed Dahl salt-resistant female rats (81 ± 4 vs. 95 ± 1 mmHg, P < 0.05) but had no effect on MAP in Dahl salt-sensitive female rats (154 ± 3 vs. 153 ± 3 mmHg), which are known to be 20-HETE deficient. To test the role of CYP4A2, female CYP4A2(-/-) and SS.5(Bn) (wild type) rats were treated with DHT. DHT increased MAP in SS.5(Bn) female rats (104 ± 1 vs. 128 ± 1 mmHg, P < 0.05) but had no effect in CYP4A2(-/-) female rats (118 ± 1 vs. 120 ± 1 mmHg). Renal microvascular 20-HETE was reduced in control CYP4A2(-/-) female rats and was increased with DHT in SS.5(Bn) female rats (6-fold) but not CYP4A2(-/-) female rats. ω-Hydroxylase activity was 40% lower in control CYP4A2(-/-) female rats than in SS.5(Bn) female rats, and DHT decreased ω-hydroxylase activity in SS.5(Bn) female rats (by 50%) but significantly increased ω-hydroxylase activity in CYP4A2(-/-) female rats (3-fold). These data suggest that 20-HETE via CYP4A2 contributes to the elevation in BP in hyperandrogenemic female rats. The data also suggest that 20-HETE synthesis inhibition may be effective in treating the elevated BP in women with hyperandrogenemia, such as women with polycystic ovary syndrome.

Association between the maternal serum levels of 19 eicosanoids and pre-eclampsia

OBJECTIVE

To investigate whether serum levels of 19 eicosanoids are associated with pre-eclampsia.

METHODS

A case-control study was performed using data for pregnant women with pre-eclampsia, normotensive pregnant women, and nonpregnant women, for all of whom serum samples had been collected at a hospital in Shanghai, China, between December 2012 and December 2013. Ultra-performance liquid chromatography-tandem mass spectrometry was used to measure the serum levels of 19 eicosanoids.

RESULTS

Overall, 49 pregnant women with pre-eclampsia, 26 normotensive pregnant women, and 14 nonpregnant women were included. Women with pre-eclampsia had significantly higher serum levels of 11,12-epoxyeicosatrienoic acid (11,12-EET), the hydroxyeicosatetraenoic acids 5-HETE, 8-HETE, 12-HETE, and 15-HETE, and leukotriene B4 than did women with a normal pregnancy and nonpregnant women, both before and after the onset of pre-eclampsia (P<0.01 for all comparisons). Women with severe pre-eclampsia had significantly higher serum levels of 5-HETE, 15-HETE, and leukotriene B4 than did women with mild pre-eclampsia, women with a normal pregnancy, and nonpregnant women (P<0.01 for all comparisons).

CONCLUSION

The eicosanoids 11,12-EET, 5-HETE, 8-HETE, 12-HETE, 15-HETE, and leukotriene B4 might play important parts in the occurrence and development of pre-eclampsia.

Fragment Screening of Soluble Epoxide Hydrolase for Lead Generation-Structure-Based Hit Evaluation and Chemistry Exploration

Soluble epoxide hydrolase (sEH) is involved in the regulation of many biological processes by metabolizing the key bioactive lipid mediator, epoxyeicosatrienoic acids. For the development of sEH inhibitors with improved physicochemical properties, we performed both a fragment screening and a high-throughput screening aiming at an integrated hit evaluation and lead generation. Followed by a joint dose-response analysis to confirm the hits, the identified actives were then effectively triaged by a structure-based hit-classification approach to three prioritized series. Two distinct scaffolds were identified as tractable starting points for potential lead chemistry work. The oxoindoline series bind at the right-hand side of the active-site pocket with hydrogen bonds to the protein. The 2-phenylbenzimidazole-4-sulfonamide series bind at the central channel with significant induced fit, which has not been previously reported. On the basis of the encouraging initial results, we envision that a new lead series with improved properties could be generated if a vector is found that could merge the cyclohexyl functionality of the oxoindoline series with the trifluoromethyl moiety of the 2-phenylbenzimidazole-4-sulfonamide series.

Modulation of arachidonic Acid metabolism in the rat kidney by sulforaphane: implications for regulation of blood pressure

Background. We investigated the effects of sulforaphane (SF), the main active isothiocyanate in cruciferous vegetables, on arachidonic acid (AA) metabolism in the kidney and its effect on arterial blood pressure, using spontaneously hypertensive rats (SHR) as models. Methods. Rats were treated for 8 weeks with either drinking water alone (control) or SF (20 or 40 mg/kg) added to drinking water. Mean arterial pressure (MAP) was measured at 7-day intervals throughout the study. At the end of treatment rats were euthanized, and kidneys were harvested to prepare microsomes and measure enzymes involved in regulation of vasoactive metabolites: CYP4A, the key enzyme in the formation of 20-hydroxyeicosatetraenoic acid, and the soluble epoxide hydrolase, which is responsible for the degradation of the vasodilator metabolites such as epoxyeicosatetraenoic acids. Effect of SF on kidney expression of CYP4A was investigated by immunoblotting. Results. We found that treatment with SF leads to significant reductions in both, the expression and activity of renal CYP4A isozymes, as well as the activity of soluble epoxide hydrolase (sEH). Consistent with these data, we have found that treatment with SF resisted the progressive rise in MAP in the developing SHR in a dose-dependent manner. Conclusion. This is the first demonstration that SF modulates the metabolism of AA by both P450 enzymes and sEH in SHR rats. This may represent a novel mechanism by which SF protects SHR rats against the progressive rise in blood pressure.

Cytochrome P450 2J2: distribution, function, regulation, genetic polymorphisms and clinical significance

Cytochrome P450 2J2 (CYP2J2) is an enzyme mainly found in human extrahepatic tissues, with predominant expression in the cardiovascular systems and lower levels in the intestine, kidney, lung, pancreas, brain, liver, etc. During the past 15 years, CYP2J2 has attracted much attention for its epoxygenase activity in arachidonic acid (AA) metabolism. It converts AA to four epoxyeicosatrienoic acids (EETs) that have various biological effects, especially in the cardiovascular systems. In recent publications, CYP2J2 is shown highly expressed in various human tumor cells, and its EET metabolites are demonstrated to implicate in the pathologic development of human cancers. CYP2J2 is also a human CYP that involved in phase I xenobiotics metabolism. Antihistamine drugs and many other compounds were identified as the substrates of CYP2J2, and studies have demonstrated that these substrates have a broad structural diversity. CYP2J2 is found not readily induced by known P450 inducers; however, its expression could be regulated in some pathological conditions, might through the activator protein-1(AP-1), the AP-1-like element and microRNA let-7b. Several genetic mutations in the CYP2J2 gene have been identified in humans, and some of them have been shown to have potential associations with some diseases. With the increasing awareness of its roles in cancer disease and drug metabolism, studies about CYP2J2 are still going on, and various inhibitors of CYP2J2 have been determined. Further studies are needed to delineate the roles of CYP2J2 in disease pathology, drug development and clinical practice.

An eicosanoid-centric view of atherothrombotic risk factors

Cardiovascular disease is the foremost cause of morbidity and mortality in the Western world. Atherosclerosis followed by thrombosis (atherothrombosis) is the pathological process underlying most myocardial, cerebral, and peripheral vascular events. Atherothrombosis is a complex and heterogeneous inflammatory process that involves interactions between many cell types (including vascular smooth muscle cells, endothelial cells, macrophages, and platelets) and processes (including migration, proliferation, and activation). Despite a wealth of knowledge from many recent studies using knockout mouse and human genetic studies (GWAS and candidate approach) identifying genes and proteins directly involved in these processes, traditional cardiovascular risk factors (hyperlipidemia, hypertension, smoking, diabetes mellitus, sex, and age) remain the most useful predictor of disease. Eicosanoids (20 carbon polyunsaturated fatty acid derivatives of arachidonic acid and other essential fatty acids) are emerging as important regulators of cardiovascular disease processes. Drugs indirectly modulating these signals, including COX-1/COX-2 inhibitors, have proven to play major roles in the atherothrombotic process. However, the complexity of their roles and regulation by opposing eicosanoid signaling, have contributed to the lack of therapies directed at the eicosanoid receptors themselves. This is likely to change, as our understanding of the structure, signaling, and function of the eicosanoid receptors improves. Indeed, a major advance is emerging from the characterization of dysfunctional naturally occurring mutations of the eicosanoid receptors. In light of the proven and continuing importance of risk factors, we have elected to focus on the relationship between eicosanoids and cardiovascular risk factors.

Dopamine and renal function and blood pressure regulation

Dopamine is an important regulator of systemic blood pressure via multiple mechanisms. It affects fluid and electrolyte balance by its actions on renal hemodynamics and epithelial ion and water transport and by regulation of hormones and humoral agents. The kidney synthesizes dopamine from circulating or filtered L-DOPA independently from innervation. The major determinants of the renal tubular synthesis/release of dopamine are probably sodium intake and intracellular sodium. Dopamine exerts its actions via two families of cell surface receptors, D1-like receptors comprising D1R and D5R, and D2-like receptors comprising D2R, D3R, and D4R, and by interactions with other G protein-coupled receptors. D1-like receptors are linked to vasodilation, while the effect of D2-like receptors on the vasculature is variable and probably dependent upon the state of nerve activity. Dopamine secreted into the tubular lumen acts mainly via D1-like receptors in an autocrine/paracrine manner to regulate ion transport in the proximal and distal nephron. These effects are mediated mainly by tubular mechanisms and augmented by hemodynamic mechanisms. The natriuretic effect of D1-like receptors is caused by inhibition of ion transport in the apical and basolateral membranes. D2-like receptors participate in the inhibition of ion transport during conditions of euvolemia and moderate volume expansion. Dopamine also controls ion transport and blood pressure by regulating the production of reactive oxygen species and the inflammatory response. Essential hypertension is associated with abnormalities in dopamine production, receptor number, and/or posttranslational modification.

Measurement of vasoactive metabolites (hydroxyeicosatetraenoic and epoxyeicosatrienoic acids) in uterine tissues of normal and compromised human pregnancy

BACKGROUND

Preeclampsia and intrauterine growth restriction define two disorders of a multifactorial etiology that compromise maternal and fetal well being as well as cardiovascular health in later life. Many of the overt symptoms of preeclampsia are attributable to the systemic endothelial dysfunction observed in the uteroplacental and systemic circulation, leading to a generalized vasoconstriction, hypertension and inadequate placental perfusion. Mounting evidence implicates nonprostanoid eicosanoids, epoxyeicosatrienoic acids (EETs) and hydroxyeicosatetraenoic acids (HETEs) in the control of vascular function and dysfunction.

OBJECTIVE

To determine whether levels of EETs and HETEs are altered in preeclampsia and intrauterine growth restriction compared with normal term pregnancy.

METHODS

An analytical liquid chromatography-tandem mass spectrometry profiling method was utilized in order to analyze differential levels of EETs and HETEs in intrauterine tissues of term nonlaboring, laboring and preeclamptic women as well as women with a growth-restricted pregnancy.

RESULTS

Placentae of preeclamptic women contained significantly (P < 0.05) larger amounts of 5-HETE, 12-HETE and 15-HETE known to possess either vasoconstrictive or proinflammatory actions. Laboring tissues were characterized by significantly higher (P < 0.05) EET levels in the amnion compared with the other clinical groups. EET and HETE levels in preeclampsia and intrauterine growth restriction were positively correlated (P < 0.05), whereas in normal and laboring pregnancies, EETs and HETEs were negatively correlated.

CONCLUSION

Increased production of 5-HETE, 12-HETE and 15-HETE metabolites in preeclamptic placentae indicates an important role for this family of eicosanoids in the cause of this disease.

Renal function and vasomotor activity in mice lacking the Cyp4a14 gene

The production of 20-hydroxyeicosatetraenoic acid (20-HETE) in the kidney is thought to be involved in the control of renal vascular tone and tubular sodium and chloride reabsorption. Cytochrome (Cyp) P-450 enzymes of the Cyp4a family in the mouse, namely 4a10, -12 and 14, are involved in 20-HETE synthesis. Recent advances in the molecular genetics of the mouse have produced mice in which Cyp4a isoforms have been disrupted and the consequence of such an approach is examined. This study evaluated the effect of deletion of the Cyp4a14 gene on blood pressure, renal vascular responses and tubular function. When compared with the wild-type (WT) litter mates, systolic blood pressure was greater in Cyp4a14 null (KO) mice as were renal vascular responses to angiotensin II or phenyephrine, G protein-coupled receptor (GPCR) agonists, but not KCl, a non-GPCR agonist. Renal vascular responses to guanosine 5'-O-(gamma-thio)triphosphate, a non-hydrolyzable GTP analog, or NaF(4), an activator of G-proteins, were also enhanced. However, vasodilation to bradykinin or apocynin but not sodium nitroprusside was blunted in Cyp4a14 null (KO) kidneys. These changes in KO mice were accompanied by increased 20-HETE synthesis, reduced renal production of nitric oxide (NO), increased lipid hydroperoxides and increased apocynin-inhibitable vascular NADPH oxidase activity that was prevented by administration of NO synthase (NOS) inhibitor, suggesting endothelial nitric oxide synthase (eNOS) uncoupling. Cyp4a14 KO mice also exhibited a diminished capacity to excrete an acute sodium load (0.9% NaCl, 2.5 mL/kg). These data suggest that deletion of the Cyp4a gene conferred a prohypertensive status via mechanisms involving increased 20-HETE synthesis and eNOS uncoupling leading to increased oxidative stress, enhanced vasoconstriction but diminished vasodilation as well as a defect in the renal excretory capacity in Cyp4a14 KO mice. These mechanisms suggest that the Cyp4a14-deficient mouse may be a useful model for evaluation of NO/20-HETE interactions.

Soluble epoxide hydrolase inhibitors: a patent review

IMPORTANCE OF THE FIELD

Soluble epoxide hydrolase (sEH) inhibitors have been shown to effectively increase the levels of epoxyeicosatrienoic acids and reduce the levels of dihydroxyeicosatrienoic acids, which may be translated to therapeutic potentials for multiple disease indications. It has been claimed that sEH inhibitors can be used to treat hypertension, diabetes, stroke, dyslipidemia, pain, immunological disorders, eye diseases, neurological diseases and other indications.

AREAS COVERED IN THIS REVIEW

A comprehensive synopsis of patent literature on sEH inhibitors is provided.

WHAT THE READER WILL GAIN

A total of more than 100 patent publications describing multiple classes of sEH inhibitors are analyzed. These include amides, ureas, thioamides, thioureas, carbamates, acyl hydrazones, chalcone oxdies, etc. In addition to selected in vitro and in vivo data of representative sEH inhibitors, a wide range of proposed applications of sEH inhibitors are also summarized.

TAKE HOME MESSAGE

Several sEH inhibitors with potent in vitro and in vivo target inhibition appear promising, including one Phase II clinical candidate. The clinical evaluation will be critical to assess the proclaimed therapeutic utility of sEH inhibition.

20-HETE increases NADPH oxidase-derived ROS production and stimulates the L-type Ca2+ channel via a PKC-dependent mechanism in cardiomyocytes

The production of 20-hydroxyeicosatetraenoic acid (20-HETE) is increased during ischemia-reperfusion, and inhibition of 20-HETE production has been shown to reduce infarct size caused by ischemia. This study was aimed to discover the molecular mechanism underlying the action of 20-HETE in cardiac myocytes. The effect of 20-HETE on L-type Ca(2+) currents (I(Ca,L)) was examined in rat isolated cardiomyocytes by patch-clamp recording in the whole cell mode. Superfusion of cardiomyocytes with 20-HETE (10-100 nM) resulted in a concentration-dependent increase in I(Ca,L), and this action of 20-HETE was attenuated by a specific NADPH oxidase inhibitor, gp91ds-tat (5 μM), or a superoxide scavenger, polyethylene glycol-superoxide dismutase (25 U/ml), suggesting that NADPH-oxidase-derived superoxide is involved in the stimulatory action of 20-HETE on I(Ca,L). Treatment of cardiomyocytes with 20-HETE (100 nM) increased both NADPH oxidase activity and superoxide production by approximately twofold. To study the molecular mechanism mediating the 20-HETE-induced increase in NADPH oxidase activity, PKC activity was measured in cardiomyocytes. Incubation of the cells with 20-HETE (100 nM) significantly increased PKC activity, and pretreatment of cardiomyocytes with a selective PKC inhibitor, GF-109203 (1 μM), attenuated the 20-HETE-induced increases in I(Ca,L) and in NADPH oxidase activity. In summary, 20-HETE stimulates NADPH oxidase-derived superoxide production, which activates L-type Ca(2+) channels via a PKC-dependent mechanism in cardiomyocytes. 20-HETE and 20-HETE-producing enzymes could be novel targets for the treatment of cardiac ischemic diseases.

Rapid synthesis of an array of trisubstituted urea-based soluble epoxide hydrolase inhibitors facilitated by a novel solid-phase method

A 270-membered library of trisubstituted ureas was synthesized and evaluated for inhibition of soluble epoxide hydrolase. Library design and reagent selection was guided by the use of a pharmacophore model and synthesis of the array was enabled with a general solid-phase method. This array approach facilitated multi-dimensional SAR around this series and identified functionality responsible for binding affinity, as well as opportunities for modulating the overall in vitro profiles of this class of soluble epoxide hydrolase inhibitors.

ATP, P2 receptors and the renal microcirculation

Purinoceptors are rapidly becoming recognised as important regulators of tissue and organ function. Renal expression of P2 receptors is broad and diverse, as reflected by the fact that P2 receptors have been identified in virtually every major tubular/vascular element. While P2 receptor expression by these renal structures is recognised, the physiological functions that they serve remains to be clarified. Renal vascular P2 receptor expression is complex and poorly understood. Evidence suggests that different complements of P2 receptors are expressed by individual renal vascular segments. This unique distribution has given rise to the postulate that P2 receptors are important for renal vascular function, including regulation of preglomerular resistance and autoregulatory behaviour. More recent studies have also uncovered evidence that hypertension reduces renal vascular reactivity to P2 receptor stimulation in concert with compromised autoregulatory capability. This review will consolidate findings related to the role of P2 receptors in regulating renal microvascular function and will present areas of controversy related to the respective roles of ATP and adenosine in autoregulatory resistance adjustments.

A strategy of employing aminoheterocycles as amide mimics to identify novel, potent and bioavailable soluble epoxide hydrolase inhibitors

Distinct from previously reported urea and amide inhibitors of soluble epoxide hydrolase (sEH), a novel class of inhibitors were rationally designed based on the X-ray structure of this enzyme and known amide inhibitors. The structure-activity relationship (SAR) study was focused on improving the sEH inhibitory activity. Aminobenzisoxazoles emerged to be the optimal series, of which a potent human sEH inhibitor 7t was identified with a good pharmacokinetics (PK) profile. The strategy of employing aminoheterocycles as amide replacements may represent a general approach to develop mimics of known hydrolase or protease inhibitors containing an amide moiety.

Expression and characterization of CYP4V2 as a fatty acid omega-hydroxylase

Bietti's crystalline dystrophy is an ocular disease that is strongly associated with polymorphisms in the CYP4V2 gene. CYP4 enzymes are typically microsomal fatty acid omega-hydroxylases that function together with mitochondrial and peroxisomal beta-oxidation enzymes to degrade cellular lipids. Indeed, ocular and peripheral cells cultured from patients with Bietti's have been reported to exhibit abnormal lipid metabolism. However, CYP4V2 possesses low sequence homology to other members of the CYP4 family. Therefore, we cloned and expressed CYP4V2 and analyzed the functional characteristics of this new cytochrome P450 enzyme. We find that CYP4V2 is a selective omega-hydroxylase of saturated, medium-chain fatty acids with relatively high catalytic efficiency toward myristic acid. Moreover, N-hydroxy-N'-(4-n-butyl-2-methylphenyl formamidine) (HET0016) is a nanomolar inhibitor of the enzyme. Therefore, CYP4V2 exhibits catalytic functions typical of a human CYP4 enzyme, but with a distinctive chain-length selectivity coupled with high omega-hydroxylase specificity. Consequently, defective omega-oxidation of ocular fatty acids/lipids secondary to mutations in the CYP4V2 gene appears to be a plausible mechanism underlying Bietti's crystalline dystrophy.

20-HETE activates the Raf/MEK/ERK pathway in renal epithelial cells through an EGFR- and c-Src-dependent mechanism

20-Hydroxyeicosatetraenoic acid (20-HETE) has been reported to promote mitogenicity in a variety of cell types, including renal epithelial cells. However, the signal transduction pathways activated by 20-HETE have not been fully defined. The present study evaluated the effects of 20-HETE and its more stable agonist analogs 20-hydroxyeicosa-5(Z),14(Z)-dienoic acid (5,14-20-HEDE) and N-[20-hydroxyeicosa-5(Z),14(Z)-dienoyl]glycine (5,14-20-HEDGE) on the Raf/MEK/ERK and phosphatidylinositol 3-kinase (PI3K)-Akt pathway in LLC-PK(1) renal epithelial cells. 20-HETE (20 microM) increased phosphorylation of Raf-1 (2.5 +/- 0.2-fold), MEK1/2 (6.3 +/- 1.6-fold), and ERK1/2 (5.8 +/- 0.3-fold) compared with vehicle-treated cells. Similarly, the 20-HETE analogs also strongly activated ERK1/2 in a Raf-1- and MEK1/2-dependent manner. Moreover, 5,14-20-HEDE increased Akt phosphorylation by 2.2 +/- 0.3-fold. 20-HETE and 5,14-20-HEDE also promoted activation (Y1086) of epidermal growth factor receptor (EGFR; Y1086) by 1.9 +/- 0.2- and 2.5 +/- 0.2-fold, respectively. These effects were completely blocked by the EGFR inhibitor EKB-569 (0.1 microM). Moreover, EKB-569 (0.1 microM), as well as a c-Src inhibitor, SKI-606 (0.05 microM), completely abolished the 20-HETE-mediated activation of the Raf/MEK/ERK and PI3K-Akt pathways. Blockade of PKC with bisindolylmaleimide I had no effect on 20-HETE-induced ERK1/2 activation. This study demonstrated that 20-HETE activated the Raf/MEK/ERK and Akt pathways in renal epithelial cells secondary to the activation of c-Src and EGFR.

Vascular control in humans: focus on the coronary microcirculation

Myocardial perfusion is regulated by a variety of factors that influence arteriolar vasomotor tone. An understanding of the physiological and pathophysiological factors that modulate coronary blood flow provides the basis for the judicious use of medications for the treatment of patients with coronary artery disease. Vasomotor properties of the coronary circulation vary among species. This review highlights the results of recent studies that examine the mechanisms by which the human coronary microcirculation is regulated in normal and disease states, focusing on diabetes. Multiple pathways responsible for myogenic constriction and flow-mediated dilation in human coronary arterioles are addressed. The important role of endothelium-derived hyperpolarizing factors, their interactions in mediating dilation, as well as speculation regarding the clinical significance are emphasized. Unique properties of coronary arterioles in human vs. other species are discussed.

Physiological Significance and Expression of P450s in the Developing Eye

Expression of 10 CYP orthologs (Families 1-3) in developing mouse conceptus is constitutive. These forms have specific temporal and spatial expression. Studies on CYP1B1 indicate its requirement for normal eye development, both in human and mouse. The distribution of the enzyme in the mouse eye is in three regions, which may reflect three different, perhaps equally important, functions in this organ. Its presence in the inner ciliary and lens epithelia appears to be necessary for normal development of the trabecular meshwork and its function in regulating intraocular pressure. Its expression in the retinal ganglion and inner nuclear layers may reflect a role in maintenance of the visual cycle. Its expression in the corneal epithelium may indicate a function in metabolism of environmental xenobiotics.

Role of CYP epoxygenases in A2A AR-mediated relaxation using A2A AR-null and wild-type mice

We hypothesized that A2A adenosine receptor (A2A AR) activation causes vasorelaxation through cytochrome P-450 (CYP) epoxygenases and endothelium-derived hyperpolarizing factors, whereas lack of A2A AR activation promotes vasoconstriction through Cyp4a in the mouse aorta. Adenosine 5'-N-ethylcarboxamide (NECA; 10(-6) M), an adenosine analog, caused relaxation in wild-type A2A AR (A2A AR+/+; +33.99 +/- 4.70%, P < 0.05) versus contraction in A2A AR knockout (A2A AR(-/-); -27.52 +/- 4.11%) mouse aortae. An A2A AR-specific antagonist (SCH-58261; 1 microM) changed the NECA (10(-6) M) relaxation response to contraction (-35.82 +/- 4.69%, P < 0.05) in A2A AR+/+ aortae, whereas no effect was noted in A2A AR(-/-) aortae. Significant contraction was seen in the absence of the endothelium in A2A AR+/+ (-2.58 +/- 2.25%) aortae compared with endothelium-intact aortae. An endothelial nitric oxide synthase inhibitor (N-nitro-L-arginine methyl ester; 100 microM) and a cyclooxygenase inhibitor (indomethacin; 10 microM) failed to block NECA-induced relaxation in A2A AR+/+ aortae. A selective inhibitor of CYP epoxygenases (methylsulfonyl-propargyloxyphenylhexanamide; 10 microM) changed NECA-mediated relaxation (-22.74 +/- 5.11% at 10(-6) M) and CGS-21680-mediated relaxation (-18.54 +/- 6.06% at 10(-6) M) to contraction in A2A AR+/+ aortae, whereas no response was noted in A2A AR(-/-) aortae. Furthermore, an epoxyeicosatrienoic acid (EET) antagonist [14,15-epoxyeicosa-5(Z)-enoic acid; 10 microM] was able to block NECA-induced relaxation in A2A AR+/+ aortae, whereas omega-hydroxylase inhibitors (10 microM dibromo-dodecenyl-methylsulfimide and 10 microM HET-0016) changed contraction into relaxation in A2A AR(-/-) aorta. Cyp2c29 protein was upregulated in A2A AR+/+ aortae, whereas Cyp4a was upregulated in A2A AR(-/-) aortae. Higher levels of dihydroxyeicosatrienoic acids (DHETs; 14,15-DHET, 11,12-DHET, and 8,9-DHET, P < 0.05) were found in A2A AR+/+ versus A2A AR(-/-) aortae. EET levels were not significantly different between A2A AR+/+ and A2A AR(-/-) aortae. It is concluded that CYP epoxygenases play an important role in A2A AR-mediated relaxation, and the deletion of the A2A AR leads to contraction through Cyp4a.

Increased blood pressure in mice lacking cytochrome P450 2J5

The cytochrome P450 (CYP) enzymes participate in a wide range of biochemical functions, including metabolism of arachidonic acid and steroid hormones. Mouse CYP2J5 is abundant in the kidney where its products, the cis-epoxyeicosatrienoic acids (EETs), modulate sodium transport and vascular tone. To define the physiological role of CYP2J5 in the kidney, knockout mice were generated using a conventional gene targeting approach. Cyp2j5 (-/-) mice develop normally and exhibit no overt renal pathology. While renal EET biosynthesis was apparently unaffected by the absence of CYP2J5, deficiency of this CYP in female mice was associated with increased blood pressure, enhanced proximal tubular transport rates, and exaggerated afferent arteriolar responses to angiotensin II and endothelin I. Interestingly, plasma 17beta-estradiol levels were reduced in female Cyp2j5 (-/-) mice and estrogen replacement restored blood pressure and vascular responsiveness to normal levels. There was no evidence of enhanced estrogen metabolism, or altered expression or activities of steroidogenic enzymes in female Cyp2j5 (-/-) mice, but their plasma levels of luteinizing hormone and follicle stimulating hormone were inappropriately low. Together, our findings illustrate a sex-specific role for CYP2J5 in regulation of blood pressure, proximal tubular transport, and afferent arteriolar responsiveness via an estrogen-dependent mechanism.

Quantitative profiling of epoxyeicosatrienoic, hydroxyeicosatetraenoic, and dihydroxyeicosatetraenoic acids in human intrauterine tissues using liquid chromatography/electrospray ionization tandem mass spectrometry

A reversed-phase liquid chromatography negative ion electrospray tandem mass spectrometry (LC/ESI-MS/MS) method was developed and validated to quantify a range of physiologically relevant eicosanoids, including 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs); 5-, 8-, 9-, 12-, and 15-hydroxyeicosatetraenoic acids (HETEs), and 5,6-, 8,15-, and 12,20-dihydroxyeicosatetraenoic acids (DiHETEs) in human intrauterine tissues. A solid-phase extraction method was employed to extract the eicosanoids, and gradient LC separation was performed on a Kromasil C(18) column. Mass spectrometric detection was performed by multiple reaction monitoring over a 31-min run time. The calibration curves were linear over the range of 4-400pmol/g tissue, and the intra- and interday precision and accuracy were within a coefficient of variation of 2.0 to 27.4% and 4.6 to 17.9%, respectively. The lower limit of quantitation was 1.0pmol/g tissue. The method was applied successfully to the characterization and quantitation of eicosanoids in the different compartments of human intrauterine tissues. Our results demonstrate significantly greater amounts of HETEs than of either the EETs or DiHETEs (P<0.001), irrespective of tissue type. Specifically, the metabolite 12-HETE was significantly more abundant (P<0.001) than all other HETEs. Of the EET metabolites, 5,6-EET predominated (P<0.001). A significant negative correlation between EETs and HETEs for all tissues (rho=-0.390, P<0.001) was identified, implying a biological feedback mechanism between these two arachidonate metabolite classes.

P450 CYP2C epoxygenase and CYP4A omega-hydroxylase mediate ciprofibrate-induced PPARalpha-dependent peroxisomal proliferation

Peroxisomal proliferators, such as ciprofibrate, are used extensively as effective hypolipidemic drugs. The effects of these compounds on lipid metabolism require ligand binding activation of the peroxisome proliferator-activated receptor (PPAR) alpha subtype of nuclear receptors and involve transcriptional activation of the metabolic pathways involved in lipid oxidative metabolism, transport, and disposition. omega-Hydroxylated-eicosatrienoic acids (HEETs), products of the sequential metabolism of arachidonic acid (AA) by the cytochrome P450 CYP2C epoxygenase and CYP4A omega-hydroxylase gene subfamilies, have been identified as potent and high-affinity ligands of PPARalpha in vitro and as PPARalpha activators in transient transfection assays. Using isolated rat hepatocytes in culture, we demonstrate that specific inhibition of either the CYP2C epoxygenase or the CYP4A omega-hydroxylase abrogates ciprofibrate-induced peroxisomal proliferation, whereas inhibition of other eicosanoid-synthesizing pathways had no effect. Conversely, overexpression of the rat liver CYP2C11 epoxygenase leads to spontaneous peroxisomal proliferation, an effect that is reversed by a CYP inhibitor. Based on these results, we propose that HEETs may serve as endogenous PPARalpha ligands and that the P450 AA monooxygenases participate in ciprofibrate-induced peroxisomal proliferation and the activation of PPARalpha downstream targets.

Oxygenation of omega-3 fatty acids by human cytochrome P450 4F3B: effect on 20-hydroxyeicosatetraenoic acid production

Cytochrome P450 (CYP) omega-oxidases convert arachidonic acid (AA) to 20-hydroxyeicosatetraenoic acid (20-HETE), a lipid mediator that modulates vascular tone. We observed that a microsomal preparation containing recombinant human CYP4F3B, which converts AA to 20-HETE, converted eicosapentaenoic acid (EPA) to 20-OH-EPA. Likewise, docosahexaenoic acid (DHA) was converted to 22-OH-DHA, indicating that human CYP4F3B also can oxidize 22-carbon omega-3 fatty acids. Consistent with these findings, addition of 0.5-5 microM EPA, DHA or omega-3 docosapentaenoic acid (DPA) to incubations containing 0.5 microM [3H]AA inhibited [3H]20-HETE production by 15-65%. [3H]20-OH-EPA was rapidly taken up by COS-7 cells, and almost all of the incorporated radioactivity remained as unmodified 20-OH-EPA. The 20-OH-EPA stimulated luciferase activity in COS-7 cells that express peroxisome proliferator-activated receptor alpha, indicating that this EPA metabolite may function as a lipid mediator. These findings suggest that some functional effects of omega-3 fatty acid supplementation may be due to inhibition of 20-HETE formation or the conversion of EPA to the corresponding omega-oxidized product.

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

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

ω-Oxidation of 20-Hydroxyeicosatetraenoic Acid (20-HETE) in Cerebral Microvascular Smooth Muscle and Endothelium by Alcohol Dehydrogenase 4

20-Carboxyeicosatetraenoic acid (20-COOH-AA) is a bioactive metabolite of 20-hydroxyeicosatetraenoic acid (20-HETE), an eicosanoid that produces vasoconstriction in the cerebral circulation. We found that smooth muscle (MSMC) and endothelial (MEC) cultures obtained from mouse brain microvessels convert [3H]20-HETE to 20-COOH-AA, indicating that the cerebral vasculature can produce this metabolite. The [3H]20-COOH-AA accumulated primarily in the culture medium, together with additional radiolabeled metabolites identified as the chain-shortened dicarboxylic acids 18-COOH-18:4, 18-COOH-18:3, and 16-COOH-16:3. N-Heptylformamide, a potent inhibitor of alcohol dehydrogenase (ADH), decreased the conversion of [3H]20-HETE to 20-COOH-AA by the MSMC and MEC and also by isolated mouse brain microvessels. Purified mouse and human ADH4, human ADH3, and horse liver ADH1 efficiently oxidized 20-HETE, and ADH4 and ADH3 were detected in MSMC and MEC by Western blotting. N-Heptylformamide inhibited the oxidation of 20-HETE by mouse and human ADH4 but not by ADH3. These results demonstrated that cerebral microvessels convert 20-HETE to 20-COOH-AA and that ADH catalyzes the reaction. Although ADH4 and ADH3 are expressed in MSMC and MEC, the inhibition produced by N-heptylformamide suggests that ADH4 is primarily responsible for 20-COOH-AA formation in the cerebral microvasculature.

Soluble epoxide hydrolase is a main effector of angiotensin II-induced hypertension

The soluble epoxide hydrolase (sEH) metabolizes vasodilatory epoxyeicosatrienoic acids (EETs) to their di-hydroxy derivatives. We hypothesized that the metabolism of EETs by the sEH contributes to angiotensin II-induced hypertension and tested the effects of a water-soluble sEH inhibitor, 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA) on blood pressure. AUDA (130 microg/mL in drinking water) did not affect blood pressure in normotensive animals but markedly lowered it in mice with angiotensin II-induced hypertension (1 mg/kg per day). The effect of AUDA was accompanied by an increase in urinary salt and water excretion. Intravenous application of AUDA (8 mg/kg) acutely lowered blood pressure and heart rate in animals with angiotensin II-induced hypertension but failed to affect blood pressure in animals with phenylephrine-induced hypertension (29 mg/kg per day). AUDA (0.1 micromol/L) selectively lowered vascular resistance in an isolated perfused kidney preparation from angiotensin II-pretreated mice but not from control mice. In the perfused hind limb and in isolated carotid arteries from angiotensin II-treated mice, AUDA was without effect. The omega-hydroxylase inhibitor N-methylsulfonyl-12,12-dibromododec-11-enamide, which attenuates formation of the potent vasoconstrictor 20-hydroxyeicosatetraenoic acid, decreased tone in carotid arteries from angiotensin II-treated but not from control mice. These data demonstrate that the decrease in blood pressure observed after sEH inhibition in angiotensin II-induced hypertension can be attributed to an initial reduction in heart rate followed by pressure diuresis resulting from increased perfusion of the kidney. Direct vasodilatation of resistance arteries in skeletal muscles does not appear to contribute to the antihypertensive effects of sEH inhibition in mice.

Fenofibrate prevents the development of angiotensin II-dependent hypertension in mice

Previous studies have indicated that the production of 20-hydroxyecisatatraenoic acid (20-HETE) is similar in the liver of C57/B6 mice and rats, but the renal production of 20-HETE is very low in this strain of mice. The present study examined the effects of induction of the renal production of 20-HETE with fenofibrate (FF) on the development of angiotensin II (Ang II)-dependent hypertension in C57BL/6J mice. The mice were divided into 4 groups and treated with vehicle (control), FF (90 mg/kg per day, IP), Ang II (1000 ng/kg per minute, SC), and Ang II plus FF. Mean arterial blood pressure (MAP) averaged 109+/-4 and 106+/-2 mm Hg in control and FF-treated mice (n=7). MAP was significantly increased in the Ang II-treated mice to 144+/-4 mm Hg (n=7). However, FF treatment prevented the development of Ang II-dependent hypertension, with MAP averaging 115+/-5 mm Hg in mice treated with both Ang II plus FF (n=7). Renal production of 20-HETE was very low in control (n=7) and Ang II-treated (n=7) mice and was increased by >2-fold in FF-treated (n=7) and Ang II plus FF-treated (n=7) mice. The levels of Cyp4A proteins were markedly increased in the kidneys of mice treated with FF and Ang II plus FF but not in the renal vasculature. These results suggest that upregulation of the production of 20-HETE in renal tubules may contribute to the blood pressure-lowering effects of FF treatment in Ang II-dependent hypertension in C57BL/6J mice.

Epoxide hydrolases: their roles and interactions with lipid metabolism

The epoxide hydrolases (EHs) are enzymes present in all living organisms, which transform epoxide containing lipids by the addition of water. In plants and animals, many of these lipid substrates have potent biologically activities, such as host defenses, control of development, regulation of inflammation and blood pressure. Thus the EHs have important and diverse biological roles with profound effects on the physiological state of the host organisms. Currently, seven distinct epoxide hydrolase sub-types are recognized in higher organisms. These include the plant soluble EHs, the mammalian soluble epoxide hydrolase, the hepoxilin hydrolase, leukotriene A4 hydrolase, the microsomal epoxide hydrolase, and the insect juvenile hormone epoxide hydrolase. While our understanding of these enzymes has progressed at different rates, here we discuss the current state of knowledge for each of these enzymes, along with a distillation of our current understanding of their endogenous roles. By reviewing the entire enzyme class together, both commonalities and discrepancies in our understanding are highlighted and important directions for future research pertaining to these enzymes are indicated.

Carbon monoxide and hypertension

The enzymatic action of heme oxygenase yields carbon monoxide, biliverdin and iron. Carbon monoxide is implicated in many physiological processes, including the regulation of vascular tissue contractility and apoptosis. By stimulating the soluble guanylyl cyclase (sGC)/cGMP pathway and activating K channels in vascular smooth muscle cells (SMCs), carbon monoxide relaxes vascular tissues under physiological conditions. Altered metabolism and functions of carbon monoxide have been linked to the pathogenesis and maintenance of hypertension. The expression and activity of heme oxygenase-1, sGC and cGMP in vascular SMCs are associated with different stages of development of hypertension in spontaneously hypertensive rats (SHRs). The importance of altered heme oxygenase-2 expression in vascular tissues in hypertension remains unclear. Increased vascular contractility, unbalanced cellular apoptosis and proliferation in the vascular wall, increased oxidative stress, and the altered interaction of carbon monoxide and nitric oxide are among the consequences of heme oxygenase/carbon monoxide system dysfunction in hypertension. Acute application of pharmacological inducers to upregulate the expression of heme oxygenase-1 or the use of gene delivery method to overexpress heme oxygenase-1 decreases blood pressure in young SHRs and other animal models of hypertension. These blood pressure-decreasing effects are annulled by metalloporphyrins. In adult SHRs, the heme oxygenase/carbon monoxide system appears to be normalized as a compensatory reaction. To date, acute manipulation of the expression of heme oxygenase-1 has not been successful in decreasing blood pressure in adult SHRs. In conclusion, abnormality of the heme oxygenase/carbon monoxide system has a critical role in the pathogenesis of hypertension, and novel therapeutic approaches should be pursued to achieve selective improvement in the function of this system in hypertension.