Cytochrome P450 4A expression and arachidonic acid omega-hydroxylation in the kidney of the spontaneously hypertensive rat

Urinary 20-HETE: A prospective Non-Invasive prognostic and diagnostic marker for diabetic kidney disease

INTRODUCTION

The identification and validation of a non-invasive prognostic marker for early detection of diabetic kidney disease (DKD) can lead to substantial improvement in therapeutic decision-making.

OBJECTIVES

The main objective of this study is to assess the potential role of the arachidonic acid (AA) metabolite 20-hydroxyeicosatetraenoic (20-HETE) in predicting the incidence and progression of DKD.

METHODS

Healthy patients and patients with diabetes were recruited from the Hamad General Hospital in Qatar, and urinary 20-HETE levels were measured. Data analysis was done using the Statistical Package for Social Sciences (SPSS).

RESULTS

Our results show that urinary 20-HETE-to-creatinine (20-HETE/Cr) ratios were significantly elevated in patients with DKD when compared to patients with diabetes who did not exhibit clinical signs of kidney injury (p < 0.001). This correlation was preserved in the multivariate linear regression accounting for age, diabetes, family history of kidney disease, hypertension, dyslipidemia, stroke and metabolic syndrome. Urinary 20-HETE/Cr ratios were also positively correlated with the severity of kidney injury as indicated by albuminuria levels (p < 0.001). A urinary 20-HETE/Cr ratio of 4.6 pmol/mg discriminated between the presence and absence of kidney disease with a sensitivity of 82.2 % and a specificity of 67.1%. More importantly, a 10-unit increase in urinary 20-HETE/Cr ratio was tied to a 10-fold increase in the risk of developing DKD, suggesting a 20-HETE prognostic efficiency.

CONCLUSION

Taken together, our results suggest that urinary 20-HETE levels can potentially be used as non-invasive diagnostic and prognostic markers for DKD.

Revealing the coexistence of differentiation and communication in an endemic hare, Lepus yarkandensis (Mammalia, Leporidae) using specific-length amplified fragment sequencing

BACKGROUND

The Yarkand hare (Lepus yarkandensis Günther, 1875) is endemic to oasis and desert areas around the Tarim Basin in the Xinjiang Uyghur Autonomous Region of northwest China; however, genome-wide information for this species remains limited. Moreover, the genetic variation, genetic structure, and phylogenetic relationships of Yarkand hare from the plateau mountain regions have not been reported. Thus, we used specific-length amplified fragment sequencing (SLAF-seq) technology to evaluate the genetic diversity of 76 Yarkand hares from seven geographic populations in the northern and southwestern parts of the Tarim Basin to investigate single-nucleotide polymorphism (SNP) marker-based population differentiation and evolutionary processes. Selective sweep analysis was conducted to identify genetic differences between populations.

RESULTS

Using SLAF-seq, a total of 1,835,504 SNPs were initially obtained, of which 308,942 high-confidence SNPs were selected for further analysis. Yarkand hares exhibited a relatively high degree of genetic diversity at the SNP level. Based on pairwise FST estimates, the north and southwest groups showed a moderate level of genetic differentiation. Phylogenetic tree and population structure analyses demonstrated evident systematic phylogeographical structure patterns consistent with the geographical distribution of the hares. Hierarchical analysis of molecular variation further indicated that genetic variation was mainly observed within populations. Low to moderate genetic differentiation also occurred among populations despite a common genomic background, likely due to geographical barriers, genetic drift, and differential selection pressure of distinct environments. Nevertheless, the observed lineage-mixing pattern, as indicated by the evolutionary tree, principal component analysis, population structure, and TreeMix analyses, suggests a certain degree of gene flow between the north and southwest groups. This may be related to the migration of hares to high-altitude water sources southwest of the basin during glacial climatic oscillations, as well as river re-diffusion and oasis restoration in the basin following the glacial period. We also identified candidate genes, and their associated gene ontology terms and pathways, related to the adaptation of Yarkand hares to different environmental habitats.

CONCLUSIONS

The identified genome-wide SNPs, genetic diversity, and population structure of Yarkand hares expand our understanding of the genetic background of this endemic species and provide valuable insights into its environmental adaptation, allowing for further exploration of the underlying mechanisms.

Cyp2j5-Gene Deletion Affects on Acetylcholine and Adenosine-Induced Relaxation in Mice: Role of Angiotensin-II and CYP-Epoxygenase Inhibitor

Previously, we showed vascular endothelial overexpression of human-CYP2J2 enhances coronary reactive hyperemia in Tie2-CYP2J2 Tr mice, and eNOS^−/− mice had overexpression of CYP2J-epoxygenase with adenosine A_2A receptor-induced enhance relaxation, but we did not see the response in CYP2J-epoxygenase knockout mice. Therefore, we hypothesized that Cyp2j5-gene deletion affects acetylcholine- and 5'-N-ethylcarboxamidoadenosine (NECA) (adenosine)-induced relaxation and their response is partially inhibited by angiotensin-II (Ang-II) in mice. Acetylcholine (Ach)-induced response was tested with N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide (MS-PPOH, CYP-epoxygenase inhibitor; 10⁻⁵M) and Ang-II (10⁻⁶M). In Cyp2j5^−/− mice, ACh-induced relaxation was different from C57Bl/6 mice, at 10⁻⁵ M (76.1 ± 3.3 vs. 58.3 ± 5.2, P < 0.05). However, ACh-induced relaxation was not blocked by MS-PPOH in Cyp2j5^−/−: 58.5 ± 5.0%, P > 0.05, but blocked in C57Bl/6: 52.3 ± 7.5%, P < 0.05, and Ang-II reduces ACh-induced relaxation in both Cyp2j5^−/− and C57Bl/6 mice (38.8 ± 3.9% and 45.9 ± 7.8, P <0.05). In addition, NECA-induced response was tested with Ang-II. In Cyp2j5^−/− mice, NECA-induced response was not different from C57Bl/6 mice at 10⁻⁵M (23.1 ± 2.1 vs. 21.1 ± 3.8, P > 0.05). However, NECA-induced response was reduced by Ang-II in both Cyp2j5^−/− and C57Bl/6 mice (−10.8 ± 2.3% and 3.2 ± 2.7, P < 0.05). Data suggest that ACh-induced relaxation in Cyp2j5^−/− mice depends on nitric oxide (NO) but not CYP-epoxygenases, and the NECA-induced different response in male vs. female Cyp2j5^−/− mice when Ang-II treated.

Conflicting roles of 20-HETE in hypertension and renal end organ damage

20-HETE is a cytochrome P450-derived metabolite of arachidonic acid that has both pro- and anti-hypertensive actions that result from modulation of vascular and kidney function. In the vasculature, 20-HETE sensitizes vascular smooth muscle cells to constrictor stimuli and increases myogenic tone. By promoting smooth muscle cell migration and proliferation, as well as by acting on the vascular endothelium to cause endothelial dysfunction, angiotensin converting enzyme (ACE) expression, and inflammation, 20-HETE contributes to adverse vascular remodeling and increased blood pressure. A G protein-coupled receptor was recently identified as the effector for the vascular actions of 20-HETE. In addition, evidence suggests that 20-HETE contributes to hypertension via positive regulation of the renin-angiotensin-aldosterone system, as well as by causing renal fibrosis. On the other hand, 20-HETE exerts anti-hypertensive actions by inhibiting sodium reabsorption by the kidney in both the proximal tubule and thick ascending limb of Henle. This review discusses the pro- and anti-hypertensive roles of 20-HETE in the pathogenesis of hypertension-associated renal disease, the association of gene polymorphisms of cytochrome P450 enzymes with the development of hypertension and renal end organ damage in humans, and 20-HETE related pharmaceutical agents.

Effect of Cytochrome P450 Metabolites of Arachidonic Acid in Nephrology

Thirty-five years ago, a third pathway for the metabolism of arachidonic acid by cytochrome P450 enzymes emerged. Subsequent work revealed that 20-hydroxyeicosatetraenoic and epoxyeicosatrienoic acids formed by these pathways have essential roles in the regulation of renal tubular and vascular function. Sequence variants in the genes that produce 20-hydroxyeicosatetraenoic acid are associated with hypertension in humans, whereas the evidence supporting a role for variants in the genes that alter levels of epoxyeicosatrienoic acids is less convincing. Studies in animal models suggest that changes in the production of cytochrome P450 eicosanoids alter BP. However, the mechanisms involved remain controversial, especially for 20-hydroxyeicosatetraenoic acid, which has both vasoconstrictive and natriuretic actions. Epoxyeicosatrienoic acids are vasodilators with anti-inflammatory properties that oppose the development of hypertension and CKD; 20-hydroxyeicosatetraenoic acid levels are elevated after renal ischemia and may protect against injury. Levels of this eicosanoid are also elevated in polycystic kidney disease and may contribute to cyst formation. Our review summarizes the emerging evidence that cytochrome P450 eicosanoids have a role in the pathogenesis of hypertension, polycystic kidney disease, AKI, and CKD.

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

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

Molecular mechanisms and cell signaling of 20-hydroxyeicosatetraenoic acid in vascular pathophysiology

Cytochrome P450s enzymes catalyze the metabolism of arachidonic acid to epoxyeicosatrienoic acids (EETs), dihydroxyeicosatetraenoic acid and hydroxyeicosatetraeonic acid (HETEs). 20-HETE is a vasoconstrictor that depolarizes vascular smooth muscle cells by blocking K+ channels. EETs serve as endothelial derived hyperpolarizing factors. Inhibition of the formation of 20-HETE impairs the myogenic response and autoregulation of renal and cerebral blood flow. Changes in the formation of EETs and 20-HETE have been reported in hypertension and drugs that target these pathways alter blood pressure in animal models. Sequence variants in CYP4A11 and CYP4F2 that produce 20-HETE, UDP-glucuronosyl transferase involved in the biotransformation of 20-HETE and soluble epoxide hydrolase that inactivates EETs are associated with hypertension in human studies. 20-HETE contributes to the regulation of vascular hypertrophy, restenosis, angiogenesis and inflammation. It also promotes endothelial dysfunction and contributes to cerebral vasospasm and ischemia-reperfusion injury in the brain, kidney and heart. This review will focus on the role of 20-HETE in vascular dysfunction, inflammation, ischemic and hemorrhagic stroke and cardiac and renal ischemia reperfusion injury.

The role of mid-chain hydroxyeicosatetraenoic acids in the pathogenesis of hypertension and cardiac hypertrophy

The incidence, prevalence, and hospitalization rates associated with cardiovascular diseases (CVDs) are projected to increase substantially in the world. Understanding of the biological and pathophysiological mechanisms of survival can help the researchers to develop new management modalities. Numerous experimental studies have demonstrated that mid-chain HETEs are strongly involved in the pathogenesis of the CVDs. Mid-chain HETEs are biologically active eicosanoids that result from the metabolism of arachidonic acid (AA) by both lipoxygenase and CYP1B1 (lipoxygenase-like reaction). Therefore, identifying the localizations and expressions of the lipoxygenase and CYP1B1 and their associated AA metabolites in the cardiovascular system is of major importance in understanding their pathological roles. Generally, the expression of these enzymes is shown to be induced during several CVDs, including hypertension and cardiac hypertrophy. The induction of these enzymes is associated with the generation of mid-chain HETEs and subsequently causation of cardiovascular events. Of interest, inhibiting the formation of mid-chain HETEs has been reported to confer a protection against different cardiac hypertrophy and hypertension models such as angiotensin II, Goldblatt, spontaneously hypertensive rat and deoxycorticosterone acetate (DOCA)-salt-induced models. Although the exact mechanisms of mid-chain HETEs-mediated cardiovascular dysfunction are not fully understood, the present review proposes several mechanisms which include activating G-protein-coupled receptor, protein kinase C, mitogen-activated protein kinases, and nuclear factor kappa B. This review provides a clear understanding of the role of mid-chain HETEs in the pathogenesis of cardiovascular diseases and their importance as novel targets in the treatment for hypertension and cardiac hypertrophy.

Human fetal ventricular cardiomyocyte, RL-14 cell line, is a promising model to study drug metabolizing enzymes and their associated arachidonic acid metabolites

INTRODUCTION

RL-14 cells, human fetal ventricular cardiomyocytes, are a commercially available cell line that has been established from non-proliferating primary cultures derived from human fetal heart tissue. However, the expression of different drug metabolizing enzymes (DMEs) in RL-14 cells has not been elucidated yet. Therefore, the main objectives of the current work were to investigate the capacity of RL-14 cells to express different cytochrome P450 (CYP) isoenzymes and correlate this expression to primary cardiomyocytes.

METHODS

The expression of CYP isoenzymes was determined at mRNA, protein and catalytic activity levels using real time-PCR, Western blot analysis and liquid chromatography-electron spray ionization-mass spectrometry (LC-ESI-MS), respectively.

RESULTS

Our results showed that RL-14 cells constitutively express CYP ω-hydroxylases, CYP1A, 1B, 4A and 4F; CYP epoxygenases, CYP2B, 2C and 2J; in addition to soluble epoxide hydrolayse (EPHX2) at mRNA and protein levels. The basal expression of CYP ω-hydroxylases, epoxygenases and EPHX2 was supported by the ability of RL-14 cells to convert arachidonic acid to its biologically active metabolites, 20-hydroxyeicosatetraenoic acids (20-HETEs), 14,15-epoxyeicosatrienoic acids (14,15-EET), 11,12-EET, 8,9-EET, 5,6-EET, 14,15-dihydroxyeicosatrienoic acid (14,15-DHET), 11,12-DHET, 8,9-DHET and 5,6-DHET. Furthermore, RL-14 cells express CYP epoxygenases and ω-hydroxylase at comparable levels to those expressed in adult and fetal human primary cardiomyocytes cells implying the importance of RL-14 cells as a model for studying DMEs in vitro. Lastly, different CYP families were induced in RL-14 cells using 2,3,7,8-tetrachlorodibenzo-p-dioxin and fenofibrate at mRNA and protein levels.

DISCUSSION

The current study provides the first evidence that RL-14 cells express CYP isoenzymes at comparable levels to those expressed in the primary cells and thus offers a unique in vitro model to study DMEs in the heart.

20-HETE and EETs in diabetic nephropathy: a novel mechanistic pathway

Diabetic nephropathy (DN), a major complication of diabetes, is characterized by hypertrophy, extracellular matrix accumulation, fibrosis and proteinuria leading to loss of renal function. Hypertrophy is a major factor inducing proximal tubular epithelial cells injury. However, the mechanisms leading to tubular injury is not well defined. In our study, we show that exposure of rats proximal tubular epithelial cells to high glucose (HG) resulted in increased extracellular matrix accumulation and hypertrophy. HG treatment increased ROS production and was associated with alteration in CYPs 4A and 2C11 expression concomitant with alteration in 20-HETE and EETs formation. HG-induced tubular injury were blocked by HET0016, an inhibitor of CYPs 4A. In contrast, inhibition of EETs promoted the effects of HG on cultured proximal tubular cells. Our results also show that alteration in CYPs 4A and 2C expression and 20HETE and EETs formation regulates the activation of the mTOR/p70S6Kinase pathway, known to play a major role in the development of DN. In conclusion, we show that hyperglycemia in diabetes has a significant effect on the expression of Arachidonic Acid (AA)-metabolizing CYPs, manifested by increased AA metabolism, and might thus alter kidney function through alteration of type and amount of AA metabolites.

Differential expression of cytochrome P450 omega-hydroxylase isoforms and their association with clinicopathological features in pancreatic ductal adenocarcinoma

BACKGROUND

The cytochrome P450 (CYP) superfamily consists of enzymes that catalyze the oxidation of lipids, steroids, and drugs. In particular, the CYP4 family plays an essential role in lipid metabolism by the ω-hydroxylation of terminal ends of fatty acids. Disturbance of this system has been associated with increased angiogenesis, proliferation, and metastasis of several cancers. This study aimed to detect the expression of CYP4 isoforms (CYP4A11, CYP4F2, CYP4F3) in pancreatic ductal adenocarcinoma (PDA) and their association with clinicopathological features.

METHODS

Pancreatic specimens were collected from 73 patients who underwent surgical resection at the Thomas Jefferson University Hospital. Quantitative polymerase chain reaction was used to examine the cytochrome P450 isoforms in PDA (n = 62), adjacent-normal (n = 30), and benign tissues (n = 11). Logistic regression models were used to analyze gene expression among tissue types. Spearman rank correlations were calculated for isoform expression and for age. Differences in expression by gender were assessed via t test. Other clinicopathological variables (diabetes, smoking, obesity, T stage, perineural invasion, nodal status) were analyzed by Wilcoxon rank sum.

RESULTS

CYP4 expression for isoforms was significantly higher in PDA tissues versus matched-adjacent tissues (p < 0.01). PDA tumors expressed significantly higher levels of CYP4F2 and CYP4F3 when compared to benign lesions (p < 0.01). Significant associations were found between low levels of CYP4F2 and CYP4F3 and increased age of PDA patients. Interestingly, all isoforms were expressed at higher levels in male patients.

CONCLUSIONS

Transcriptional upregulation of cytochrome P450 ω-hydroxylase suggests that these enzymes have the potential to be used as distinguishing markers in pancreatic pathology.

Hormonal regulation of Cyp4a isoforms in mouse liver and kidney

Mouse Cyp4a subfamily, including Cyp4a10, Cyp4a12a, Cyp4a12b and Cyp4a14, demonstrate a gender- and strain-specific expression in liver and kidney. In C57BL/6 mouse liver and kidney, Cyp4a12a and 4a12b are male-predominant, whereas Cyp4a14 is female-predominant. Cyp4a10 is female-predominant in liver, but shows no gender difference in kidney. The present study was aimed to determine whether sex hormones and/or growth hormone (GH) secretion patterns are responsible for the gender-specific Cyp4a expression in C57BL/6 mice. Gonadectomized mice, GH-releasing hormone receptor-deficient little (lit/lit) mice and hypophysectomized mice were used with replacement of sex hormones or GH in male or female secretion patterns. Both androgens and male-pattern GH regulated the gender-divergent Cyp4a10, 4a12a and 4a12b in liver, whereas androgens played an exclusive role in regulating Cyp4a10 and 4a12a in kidney. In contrast, Cyp4a12b was increased by male-pattern GH but not androgens in kidney. The female-predominant Cyp4a14 in liver and kidney was due to a combined effect of male-pattern GH and androgens. In addition, estrogens played a minor role in regulation of Cyp4a isoforms through an indirect pathway. In conclusion, gender-divergent Cyp4a mRNA expression in liver is caused by male-pattern GH secretion pattern and androgens, whereas in kidney, Cyp4a mRNA expression is primarily regulated by androgens.

Epoxyeicosatrienoic acids, 20-hydroxyeicosatetraenoic acid, and renal microvascular function

The development of pharmacological, genetic, and biochemical tools have allowed for detailed studies to determine the contribution of cytochrome P450 (CYP) metabolites of arachidonic acid to renal microvascular function. Renal microvessels can generate CYP hydroxylase metabolites including 20-hydroxyeicosatetraenoic acid (20-HETE) and CYP epoxygenase metabolites, epoxyeicosatrienoic acids (EETs). 20-HETE constricts afferent arterioles and contributes to renal blood flow autoregulation. EETs act as endothelium-dependent hyperpolarizing factors (EDHFs) on the renal microcirculation. 20-HETE inhibits whereas EETs activate renal microvascular smooth muscle cell large-conductance calcium-activated K(+) channels (KCa). Likewise, 20-HETE renal microvascular actions are pro-hypertensive and EET actions are anti-hypertensive. These findings in the renal microvasculature and those of others have provided impetus for the development of enzymatic inhibitors, agonists, and antagonists for 20-HETE and EETs to determine their potential therapeutic value. Initial genetic studies and experimental studies with soluble epoxide hydrolase inhibitors to increase EETs, EET analogs, and 20-HETE inhibitors have demonstrated improved renal microvascular function in hypertension. These findings have demonstrated the important contributions that 20-HETE and EETs play in the regulation of renal microvascular function.

Targeted chiral analysis of bioactive arachidonic Acid metabolites using liquid-chromatography-mass spectrometry

A complex structurally diverse series of eicosanoids arises from the metabolism of arachidonic acid. The metabolic profile is further complicated by the enantioselectivity of eicosanoid formation and the variety of regioisomers that arise. In order to investigate the metabolism of arachidonic acid in vitro or in vivo, targeted methods are advantageous in order to distinguish between the complex isomeric mixtures that can arise by different metabolic pathways. Over the last several years this targeted approach has become more popular, although there are still relatively few examples where chiral targeted approaches have been employed to directly analyze complex enantiomeric mixtures. To efficiently conduct targeted eicosanoid analyses, LC separations are coupled with collision induced dissociation (CID) and tandem mass spectrometry (MS/MS). Product ion profiles are often diagnostic for particular regioisomers. The highest sensitivity that can be achieved involves the use of selected reaction monitoring/mass spectrometry (SRM/MS); whereas the highest specificity is obtained with an SRM transitions between an intense parent ion, which contains the intact molecule (M) and a structurally significant product ion. This review article provides an overview of arachidonic acid metabolism and targeted chiral methods that have been utilized for the analysis of the structurally diverse eicosanoids that arise.

Arachidonic acid ω-hydroxylase CYP4A11: inter-ethnic variations in the 8590T>C loss-of-function variant

The human Cytochrome P450 4A11 (CYP4A11) is a major ω-hydroxylase involved in the regulation of blood pressure in the kidney through the conversion of arachidonic acid into 20-hydroxyeicosatetraenoic acid (20-HETE). Previous studies have reported a significant association between the 8590T>C genetic variant of CYP4A11 and hypertension. Interestingly, several population-based studies have reported ethnic differences in the prevalence of hypertension, with the highest prevalence in African populations. The aim of this work was to determine the frequency and inter-ethnic comparison of the CYP4A11 (8590T>C) functional polymorphism, in five new ethnic groups: European (99 French Caucasians), African (36 Gabonese and 50 Senegalese), South American (60 Peruvians) and North African (53 Tunisians) populations, using polymerase chain reaction-single strand conformational polymorphism and sequencing strategies. We confirmed that the CYP4A11 (8590T>C) functional polymorphism exhibits inter-ethnic frequency differences. Noteworthy, the highest 8590C allele frequency was observed in the Tunisian (30.2%), followed by Senegalese (20%) populations. In addition, the CC genotype was only found in the Gabonese and Tunisian populations (5.6% and 8.4%, respectively). These populations may be of major interest to help to clarify the linkage between hypertension and CYP4A11 (8590T>C) genotype in African populations. These findings provide data for further studies that investigate the potential association of CYP4A11 (8590T>C) variant with an incidence of hypertension genesis in respect of ethnicity.

20-hydroxyeicosatetraeonic acid: a new target for the treatment of hypertension

Arachidonic acid is metabolized by enzymes of the CYP4A and 4F families to 20-hydroxyeicosatetraeonic acid (20-HETE), which plays an important role in the regulation of renal function, vascular tone, and the long-term control of arterial pressure. In the vasculature, 20-HETE is a potent vasoconstrictor, and upregulation of the production of this compound contributes to the elevation in oxidative stress and endothelial dysfunction and the increase in peripheral vascular resistance associated with some forms of hypertension. In kidney, 20-HETE inhibits Na transport in the proximal tubule and thick ascending loop of Henle, and deficiencies in the renal formation of 20-HETE contributes to sodium retention and development of some salt-sensitive forms of hypertension. 20-HETE also has renoprotective actions and opposes the effects of transforming growth factor β to promote proteinuria and renal end organ damage in hypertension. Several new inhibitors of the synthesis of 20-HETE and 20-HETE agonists and antagonists have recently been developed. These compounds along with peroxisome proliferator-activated receptor-α agonists that induce the renal formation of 20-HETE seem to have promise as antihypertensive agents. This review summarizes the rationale for the development of drugs that target the 20-HETE pathway for the treatment of hypertension and associated cardiovascular complications.

Analysis of epoxyeicosatrienoic acids by chiral liquid chromatography/electron capture atmospheric pressure chemical ionization mass spectrometry using [13C]-analog internal standards

The metabolism of arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs) is thought to be mediated primarily by the cytochromes P450 (P450s) from the 2 family (2C9, 2C19, 2D6, and 2J2). In contrast, P450s of the 4 family are primarily involved in omega oxidation of AA (4A11 and 4A22). The ability to determine enantioselective formation of the regioisomeric EETs is important in order to establish their potential biological activities and to asses which P450 isoforms are involved in their formation. It has been extremely difficult to analyze individual EET enantiomers in biological fluids because they are present in only trace amounts and they are extremely difficult to separate from each other. In addition, the deuterium-labeled internal standards that are commonly used for stable isotope dilution liquid chromatography/mass spectrometry (LC/MS) analyses have different LC retention times when compared with the corresponding protium forms. Therefore, quantification by LC/MS-based methodology can be compromised by differential suppression of ionization of the closely eluting isomers. We report the preparation of [(13)C(20)]-EET analog internal standards and the use of a validated high-sensitivity chiral LC/electron capture atmospheric pressure chemical ionization (ECAPCI)-MS method for the trace analysis of endogenous EETs as their pentafluorobenzyl (PFB) ester derivatives. The assay was then used to show the exquisite enantioselectivity of P4502C19-, P4502D6-, P4501A1-, and P4501B1-mediated conversion of AA into EETs and to quantify the enantioselective formation of EETs produced by AA metabolism in a mouse epithelial hepatoma (Hepa) cell line.

Heme oxygenase: the key to renal function regulation

Heme oxygenase (HO) plays a critical role in attenuating the production of reactive oxygen species through its ability to degrade heme in an enzymatic process that leads to the production of equimolar amounts of carbon monoxide and biliverdin/bilirubin and the release of free iron. The present review examines the beneficial role of HO-1 (inducible form of HO) that is achieved by increased expression of this enzyme in renal tissue. The influence of the HO system on renal physiology, obesity, vascular dysfunction, and blood pressure regulation is reviewed, and the clinical potential of increased levels of HO-1 protein, HO activity, and HO-derived end products of heme degradation is discussed relative to renal disease. The use of pharmacological and genetic approaches to investigate the role of the HO system in the kidney is key to the development of therapeutic approaches to prevent the adverse effects that accrue due to an impairment in renal function.

Mechanisms of podocyte injury in diabetes: role of cytochrome P450 and NADPH oxidases

OBJECTIVE

We investigated the role of cytochrome P450 of the 4A family (CYP4A), its metabolites, and NADPH oxidases both in reactive oxygen species (ROS) production and apoptosis of podocytes exposed to high glucose and in OVE26 mice, a model of type 1 diabetes.

RESEARCH DESIGN AND METHODS

Apoptosis, albuminuria, ROS generation, NADPH superoxide generation, CYP4A and Nox protein expression, and mRNA levels were measured in vitro and in vivo.

RESULTS

Exposure of mouse podocytes to high glucose resulted in apoptosis, with approximately one-third of the cells being apoptotic by 72 h. High-glucose treatment increased ROS generation and was associated with sequential upregulation of CYP4A and an increase in 20-hydroxyeicosatetraenoic acid (20-HETE) and Nox oxidases. This is consistent with the observation of delayed induction of NADPH oxidase activity by high glucose. The effects of high glucose on NADPH oxidase activity, Nox proteins and mRNA expression, and apoptosis were blocked by N-hydroxy-N'-(4-butyl-2-methylphenol) formamidine (HET0016), an inhibitor of CYP4A, and were mimicked by 20-HETE. CYP4A and Nox oxidase expression was upregulated in glomeruli of type 1 diabetic OVE26 mice. Treatment of OVE26 mice with HET0016 decreased NADPH oxidase activity and Nox1 and Nox4 protein expression and ameliorated apoptosis and albuminuria.

CONCLUSIONS

Generation of ROS by CYP4A monooxygenases, 20-HETE, and Nox oxidases is involved in podocyte apoptosis in vitro and in vivo. Inhibition of selected cytochrome P450 isoforms prevented podocyte apoptosis and reduced proteinuria in diabetes.

Cellular mediators of renal vascular dysfunction in hypertension

The renal vasculature plays a major role in the regulation of renal blood flow and the ability of the kidney to control the plasma volume and blood pressure. Renal vascular dysfunction is associated with renal vasoconstriction, decreased renal blood flow, and consequent increase in plasma volume and has been demonstrated in several forms of hypertension (HTN), including genetic and salt-sensitive HTN. Several predisposing factors and cellular mediators have been implicated, but the relationship between their actions on the renal vasculature and the consequent effects on renal tubular function in the setting of HTN is not clearly defined. Gene mutations/defects in an ion channel, a membrane ion transporter, and/or a regulatory enzyme in the nephron and renal vasculature may be a primary cause of renal vascular dysfunction. Environmental risk factors, such as high dietary salt intake, vascular inflammation, and oxidative stress further promote renal vascular dysfunction. Renal endothelial cell dysfunction is manifested as a decrease in the release of vasodilatory mediators, such as nitric oxide, prostacyclin, and hyperpolarizing factors, and/or an increase in vasoconstrictive mediators, such as endothelin, angiotensin II, and thromboxane A(2). Also, an increase in the amount/activity of intracellular Ca(2+) concentration, protein kinase C, Rho kinase, and mitogen-activated protein kinase in vascular smooth muscle promotes renal vasoconstriction. Matrix metalloproteinases and their inhibitors could also modify the composition of the extracellular matrix and lead to renal vascular remodeling. Synergistic interactions between the genetic and environmental risk factors on the cellular mediators of renal vascular dysfunction cause persistent renal vasoconstriction, increased renal vascular resistance, and decreased renal blood flow, and, consequently, lead to a disturbance in the renal control mechanisms of water and electrolyte balance, increased plasma volume, and HTN. Targeting the underlying genetic defects, environmental risk factors, and the aberrant renal vascular mediators involved should provide complementary strategies in the management of HTN.

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.

Pharmacological and clinical aspects of heme oxygenase

This review is intended to stimulate interest in the effect of increased expression of heme oxygenase-1 (HO-1) protein and increased levels of HO activity on normal and pathological states. The HO system includes the heme catabolic pathway, comprising HO and biliverdin reductase, and the products of heme degradation, carbon monoxide (CO), iron, and biliverdin/bilirubin. The role of the HO system in diabetes, inflammation, heart disease, hypertension, neurological disorders, transplantation, endotoxemia and other pathologies is a burgeoning area of research. This review focuses on the clinical potential of increased levels of HO-1 protein and HO activity to ameliorate tissue injury. The use of pharmacological and genetic probes to manipulate HO, leading to new insights into the complex relationship of the HO system with biological and pathological phenomena under investigation, is reviewed. This information is critical in both drug development and the implementation of clinical approaches to moderate and to alleviate the numerous chronic disorders in humans affected by perturbations in the HO system.

Gender differences in renal nuclear receptors and aryl hydrocarbon receptor in 5/6 nephrectomized rats

This study was aimed at delineating molecular pathways essential in gender-different pathogenesis of chronic kidney diseases (CKD). Renal transcripts of nuclear receptors and metabolic enzymes in male and female kidneys from 5/6 nephrectomized (Nx) rats 7 weeks post-Nx were examined using branched DNA signal amplification assay. Nx-males had marked kidney injury coupled with anemia and malnutrition. Nx-females had moderate renal injury, and were free of albuminuria, anemia, and malnutrition. Nx-males had systemic and renal inflammation, which were largely absent in Nx-females. Blood 17beta-estradiol, testosterone, and corticosterone did not change, whereas urinary testosterone decreased in both genders. Compared to males, female kidneys had higher androgen receptor (AR) and aryl hydrocarbon receptor (AhR) but lower estrogen receptor alpha (ERalpha). Compared to Nx-males, female remnant kidneys had less decreases in ERalpha and peroxisome proliferator-activated receptor alpha (PPARalpha), had no induction of AR and decrease of acyl-CoA oxidase, whereas had induction of cytochrome P450 4a1 (Cyp4a1) but decrease of AhR. Renal protein expression of a 52-kDa isoform of Wilm's tumor 1 (WT1), transcription factor critical in nephrogenesis, decreased dramatically in Nx-males but largely preserved in Nx-females. In conclusion, gender divergences in basal expression and alteration of ERalpha, AR, AhR, WT1, and PPARalpha/Cyp4a1 during CKD may explain gender differences in CKD progression and outcome of renal transplantation.

Cytochrome P450 4F subfamily: at the crossroads of eicosanoid and drug metabolism

The cytochrome P450 4F (CYP4F) subfamily has over the last few years come to be recognized for its dual role in modulating the concentrations of eicosanoids during inflammation as well as in the metabolism of clinically significant drugs. The first CYP4F was identified because it catalyzed the hydroxylation of leukotriene B(4) (LTB(4)) and since then many additional members of this subfamily have been documented for their distinct catalytic roles and functional significance. Recent evidence emerging in relation to the temporal change of CYP4F expression in response to injury and infection supports an important function for these isozymes in curtailing inflammation. Their tissue-dependent expression, isoform-based catalytic competence and unique response to the external stimuli imply a critical role for them to regulate organ-specific functions. From this standpoint variations in relative CYP4F levels in humans may have direct influence on the metabolic outcome through their ability to generate and/or degrade bioactive eicosanoids or therapeutic agents. This review covers the enzymatic characteristics and regulatory properties of human and rodent CYP4F isoforms and their physiological relevance to major pathways in eicosanoid and drug metabolism.

Eicosanoids and renal vascular function in diseases

Arachidonic acid metabolites are vital for the proper control of renal haemodynamics and, when not properly controlled, can contribute to renal vascular injury and end-stage renal disease. Three major enzymatic pathways, COX (cyclo-oxygenase), CYP450 (cytochrome P450) and LOX (lipoxygenase), are responsible for the metabolism of arachidonic acid metabolites to bioactive eicosanoids. These eicosanoids can dilate or constrict the renal vasculature and maintain vascular resistance in the face of changing vasoactive hormones. Renal vascular generation of eicosanoids is altered in pathophysiological conditions such as hypertension, diabetes, metabolic syndrome and acute renal failure. Experimental evidence supports the concept that altered eicosanoid metabolism contributes to renal haemodynamic alterations and the development and progression of nephropathy. The possible beneficial renal vascular actions of enzymatic inhibitors, eicosanoid analogues and receptor antagonists have been examined in hypertension, diabetes and metabolic syndrome. This review highlights the roles of renal vascular eicosanoids in the pathogenesis of nephropathy and therapeutic targets for renal disease related to hypertension, diabetes, metabolic syndrome and acute renal failure.

Long-term modifications of blood pressure in normotensive and spontaneously hypertensive rats by gene delivery of rAAV-mediated cytochrome P450 arachidonic acid hydroxylase

Arachidonic acid cytochrome P-450 (CYP) hydroxylase 4A isoforms, including 4A1, 4A2, 4A3 and 4A8 in the rat kidney, catalyze arachidonic acid to produce 19/20-Hydroxyeicosatetraenoic acids (20-HETE), a biologically active metabolite, which plays an important role in the regulation of blood pressure. However, controversial results have been reported regarding the exact role of 20-HETE on blood pressure. In the present study, we used recombinant adeno-associated viral vector (rAAV) to deliver CYP 4A1 cDNA and antisense 4A1 cDNA into Sprague-Dawley (SD) rats and spontaneously hypertensive rats (SHR), respectively, to investigate the effects of long-term modifications of blood pressure and the potential for gene therapy of hypertension. The mean systolic pressure increased by 14.2+/-2.5 mm Hg in rAAV.4A1-treated SD rats and decreased by 13.7+/-2.2 mm Hg in rAAV.anti4A1-treated SHR rats 5 weeks after the injection compared with controls and these changes in blood pressure were maintained until the experiments ended at 24 weeks. In 4A1 treated animals CYP4A was overexpressed in various tissues, but preferentially in the kidney at both mRNA and protein levels. In anti-4A1-treated SHR, CYP4A mRNA in various tissues was probed, especially in kidneys, but 4A1 protein expression was almost completely inhibited. These results suggest that arachidonic acid CYP hydroxylases contribute not only to the maintenance of normal blood pressure but also to the development of hypertension. rAAV-mediated anti4A administration strategy has the potential to be used as targeted gene therapy in human hypertension by blocking expression of CYP 4A in kidneys.

Renal localization, expression, and developmental regulation of P450 4F cytochromes in three substrains of spontaneously hypertensive rats

Cytochrome P450 4F isoforms have been shown to metabolize arachidonic acid to generate 20-hydroxyeicosatetraenoic acid (20-HETE), a potent eicosanoid that modulates vascular tone and renal tubular function. 20-HETE production in the kidney is implicated in the development of essential hypertension in the spontaneously hypertensive rat (SHR). In this study, we determined CYP4F mRNA localization and distribution in rat liver and kidney by in situ hybridization and real time quantitative PCR. CYP4Fs are regionally distributed in the kidney with CYP4F1, 4F4, and 4F5 being expressed more in the renal cortex than medulla while CYP4F6 shows higher medullary expression. We investigated developmental CYP4F gene expression in three different substrains of SHR. Distinct age-dependent patterns of expression were seen for individual CYP4F isoforms in Wistar-Kyoto (WKY) and three SHR substrains (B2, C, and A3). A steady increase in CYP4F1 expression with age was seen in each of the three substrains which correlate well with increased 20-HETE levels and elevated blood pressure seen in these animals. CYP4F4 expression increased significantly at 8 weeks followed by a precipitous fall in WKY and A3 strains at 12 weeks of age. In strains B2 and C, CYP4F4 levels started declining as early as 8 weeks of age. CYP4F5 and 4F6 levels fluctuated with age in a biphasic manner with a different profile for each sub-strain. Based on the expression profile and catalytic activity, CYP4F1 seems to be the most critical 4F isoform involved in the production of 20-HETE in the SHR kidney.

Regulation and inhibition of arachidonic acid omega-hydroxylases and 20-HETE formation

Cytochrome P450-catalyzed metabolism of arachidonic acid is an important pathway for the formation of paracrine and autocrine mediators of numerous biological effects. The omega-hydroxylation of arachidonic acid generates significant levels of 20-hydroxyeicosatetraenoic acid (20-HETE) in numerous tissues, particularly the vasculature and kidney tubules. Members of the cytochrome P450 4A and 4F families are the major omega-hydroxylases, and the substrate selectivity and regulation of these enzymes has been the subject of numerous studies. Altered expression and function of arachidonic acid omega-hydroxylases in models of hypertension, diabetes, inflammation, and pregnancy suggest that 20-HETE may be involved in the pathogenesis of these diseases. Our understanding of the biological significance of 20-HETE has been greatly aided by the development and characterization of selective and potent inhibitors of the arachidonic acid omega-hydroxylases. This review discusses the substrate selectivity and expression of arachidonic acid omega-hydroxylases, regulation of these enzymes during disease, and the application of enzyme inhibitors to study 20-HETE function.

Effect of Potassium Channel and Cytochrome P450 Inhibition on Transient Hypotension and Survival during Lipopolysaccharide-Induced Endotoxic Shock in the Rat

The purpose of this study was to determine whether inhibition of potassium channels or cytochrome P450 attenuates the transient phase of hypotension during endotoxic shock in vivo, and to determine whether these interventions improve the rate of survival. Male Sprague-Dawley rats were pretreated with saline (0.2 ml, i.v.), tetraethylammonium chloride (TEA 30 mg/kg; 0.2 ml, i.v.), proadifen (SKF-525 A; 50 mg/kg, i.p.) or ketoconazole (50 mg/kg, i.p.) and challenged with lipopolysaccharide (LPS; 20 mg/kg, i.p.). Changes in heart rate, mean (MAP), systolic (SP) and diastolic (DP) arterial pressures as well as survival rate were then monitored for 45 min. Potassium channel inhibition with TEA had no effect on LPS-induced hypotension at any time point compared with saline (maximal fall in MAP of 79 +/- 18 and 80 +/- 13 mm Hg, respectively). Pretreatment with proadifen or ketoconazole, inhibitors of cytochrome P450, significantly attenuated LPS-induced hypotension compared with saline (maximal fall in MAP of 34, 26 and 63% below baseline, respectively). This effect was evident in all arterial pressures measured, MAP, SP and DP. At 45 min, the survival rate in the saline group was 66%. Pretreatment with TEA significantly reduced survival rate to 50% and pretreatment with proadifen or ketoconazole improved survival to 100% (p < 0.05). These results suggest that an arachidonic acid metabolite produced by a cytochrome P450-catalyzed reaction may contribute to the transient phase of LPS-induced hypotension. However, these effects do not appear to be mediated through potassium channel activation.

Cytochrome P450 4A Isoform Inhibitory Profile of N-Hydroxy-N'-(4-butyl-2-methylphenyl)-formamidine (HET0016), a Selective Inhibitor of 20-HETE Synthesis

We examined the effect of N-hydroxy-N'-(4-butyl-2-methylphenyl)-formamidine) (HET0016), an inhibitor of 20-hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE) synthesis on the omega-hydroxylation and epoxidation of arachidonic acid (AA) catalyzed by recombinant cytochrome P450 4A1 (CYP4A1), CYP4A2 and CYP4A3, and characterized the enzyme inhibitory profile of HET0016. The IC50 values of HET0016 for recombinant CYP4A1-, CYP4A2- and CYP4A3-catalyzed 20-HETE synthesis averaged 17.7 nM, 12.1 nM and 20.6 nM, respectively. The IC50 value for production of 11,12-epoxy-5,8,14-eicosatrienoic acid (11,12-EET) by CYP4A2 and 4A3 averaged 12.7 nM and 22.0 nM, respectively. The IC50 value for CYP2C11 activity was 611 nM which was much greater than that for CYP4As. The initial velocity study showed the Ki value of HET0016 for CYP4A1 was 19.5 nM and a plot of Vmax versus amount of recombinant CYP4A1 added shows HET0016 is an irreversible non-competitive inhibitor. These results indicate that HET0016 is a selective, non-competitive and irreversible inhibitor of CYP4A.

Increased Excretion of Urinary 20-HETE in Rats With Cyclosporine-Induced Nephrotoxicity

The present study examined the contribution of 20-hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE) in cyclosporine A (CsA)-induced renal nephrotoxicity. Treatment of rats with CsA (50 mg/kg) for 9 days induced renal damage as indicated by marked increase in urine flow (from 9.0 +/- 0.3 ml/day to 46.6 +/- 7.1 ml/day) and a 3 - 5-fold rise in blood urea nitrogen (BUN) levels. The urinary excretion of 20-HETE increased from 164 +/- 5 ng/day (N = 5) to 2432 +/- 290 ng/day (N = 5, P<0.01) after 9 days of CsA treatment. The increase in the urinary excretion of 20-HETE in the CsA treated rats was highly correlated with the increase in BUN levels (r = 0.819, P<0.001) and urine volume (r = 0.832, P<0.001). Immunohistochemical examination of kidney revealed that expression of cytochrome P450 4A (CYP4A) protein was markedly enhanced in the proximal tubules of CsA-treated rats. These results indicate that CsA-induced nephrotoxicity in rats is associated with a marked elevation in the renal production of 20-HETE and that 20-HETE may contribute to the pathophysiological condition of CsA-induced nephrotoxicity.

20-HETE-mediated vasoconstriction by hemoglobin-O2 carrier in Sprague-Dawley but not Wistar rats

Hypothetically either decreased nitric oxide (NO) or increased O(2) could initiate 20-HETE-mediated vasoconstriction associated with hemoglobin-based blood substitutes (HBOC). To test this hypothesis, we infused Tm-Hb, an HBOC with low O(2) affinity, into isoflurane-anesthetized Wistar (W) and Sprague-Dawley (SD) rats after exchanging 20% of their blood with Ringer lactate. For comparison we infused an equal amount of BSA or BSA with N(G)-nitro-L-arginine methyl ester (BSA + NAME). Tm-Hb increased blood pressure (BP) and renal vascular resistance (RVR) equally in W and SD rats. Renal blood flow (RBF; Doppler ultrasound) decreased. BSA decreased RVR and raised glomerular filtration rate. BSA + NAME raised BP, RVR, and GFR. HET0016, an inhibitor of 20-HETE production, blunted BP and RVR responses to Tm-Hb and BSA+NAME in SD but not W rats. Arterial O(2) content with BSA was lower than with Tm-Hb but O(2) delivery was 60% higher with BSA because of higher RBF. BSA raised Po(2) (Oxylite) in cortex and medulla and reduced RVR. Tm-Hb decreased Po(2) and increased RVR. Switching rats from breathing air to 100% O(2) raised intrarenal Po(2) two- to threefold and increased BP and RVR. HET0016 did not alter hyperoxic responses. In conclusion, 20-HETE contributes to vasoconstriction by Tm-Hb in SD but not in W rats, and increased 20-HETE activity results primarily from decreased NO.

Inhibition of cytochrome P450omega-hydroxylase: a novel endogenous cardioprotective pathway

Cytochrome P450s (CYP) and their arachidonic acid (AA) metabolites have important roles in regulating vascular tone, but their function and specific pathways involved in modulating myocardial ischemia-reperfusion injury have not been clearly established. Thus, we characterized the effects of several selective CYPomega-hydroxylase inhibitors and a CYPomega-hydroxylase metabolite of AA, 20-hydroxyeicosatetraenoic acid (20-HETE), on the extent of ischemia-reperfusion injury in canine hearts. During 60 minutes of ischemia and particularly after 3 hours of reperfusion, 20-HETE was produced at high concentrations. A nonspecific CYP inhibitor, miconazole, and 2 specific CYPomega-hydroxylase inhibitors, 17-octadecanoic acid (17-ODYA) and N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), markedly inhibited 20-HETE production during ischemia-reperfusion and produced a profound reduction in myocardial infarct size (expressed as a percent of the area at risk) (19.6+/-1.7% [control], 8.4+/-2.5% [0.96 mg/kg miconazole], 5.9+/-2.2% [0.28 mg/kg 17-ODYA], and 10.8+/-1.8% [0.40 mg/kg DDMS], P<0.05, respectively). Conversely, exogenous 20-HETE administration significantly increased infarct size (26.9+/-1.9%, P<0.05). Several CYPomega-hydroxylase isoforms, which are known to produce 20-HETE such as CYP4A1, CYP4A2, and CYP4F, were demonstrated to be present in canine heart tissue and their activity was markedly inhibited by incubation with 17-ODYA. These results indicate an important endogenous role for CYPomega-hydroxylases and in particular their product, 20-HETE, in exacerbating myocardial injury in canine myocardium. The full text of this article is available online at http://circres.ahajournals.org.

20-Hydroxyeicosatetraenoic Acid (20-HETE) Metabolism in Coronary Endothelial Cells

We have investigated the role of endothelial cells in the metabolism of 20-hydroxyeicosatetraenoic acid (20-HETE), a vasoactive mediator synthesized from arachidonic acid by cytochrome P450 omega-oxidases. Porcine coronary artery endothelial cells (PCEC) incorporated 20-[(3)H]HETE primarily into the sn-2 position of phospholipids through a coenzyme A-dependent process. The incorporation was reduced by equimolar amounts of arachidonic, eicosapentaenoic or 8,9-epoxyeicosatrienoic acids, but some uptake persisted even when a 10-fold excess of arachidonic acid was available. The retention of 20-[(3)H]HETE increased substantially when methyl arachidonoyl fluorophosphonate, but not bromoenol lactone, was added, suggesting that a Ca(2+)-dependent cytosolic phospholipase A(2) released the 20-HETE contained in PCEC phospholipids. Addition of calcium ionophore A23187 produced a rapid release of 20-[(3)H]HETE from the PCEC, a finding that also is consistent with a Ca(2+)-dependent mobilization process. PCEC also converted 20-[(3)H]HETE to 20-carboxy-arachidonic acid (20-COOH-AA) and 18-, 16-, and 14-carbon beta-oxidation products. 20-COOH-AA produced vasodilation in porcine coronary arterioles, but 20-HETE was inactive. These results suggest that the incorporation of 20-HETE and its subsequent conversion to 20-COOH-AA in the endothelium may be important in modulating coronary vascular function.

Smooth muscle--specific expression of CYP4A1 induces endothelial sprouting in renal arterial microvessels

Cytochrome P450 (CYP) 4A1 has been characterized as the most efficient arachidonic acid omega-hydroxylase catalyzing the formation of 20-hydroxyeicosatetraenoic acid (20-HETE), a potent constrictor of the renal and cerebral microcirculation and a mitogen for smooth muscle cells. We constructed adenoviruses expressing the CYP4A1 cDNA or LacZ under the control of the smooth muscle cell-specific promoter SM22alpha (Ad-SM22-4A1 and Ad-SM22-nLacZ, respectively). Beta-galactosidase expression was detected in Ad-SM22-nLacZ-transduced vascular smooth muscle A7r5 and PAC1 cells, but not in Ad-SM22-nLacZ-transduced 3T3 fibroblasts or vascular endothelial cells. Likewise, CYP4A1 mRNA and protein were detected in Ad-SM22-4A1-transduced A7r5 and PAC1 cells. Ad-SM22-4A1-transduced A7r5 cells metabolized lauric acid to 12-hydroxy-lauric acid at a rate 5 times greater than that of cells transduced with Ad-SM22-nLacZ (4.79+/-1.77 versus 0.97+/-0.57 nmol 12-hydroxy lauric acid/10(6) cells per h). Smooth muscle-specific LacZ expression was also detected in microdissected renal interlobar arteries transduced with Ad-SM22-nLacZ. Arteries transduced with Ad-SM22-4A1 produced higher levels of 20-HETE (4.04+/-0.29 and 13.43+/-2.84 ng/mg protein in Ad-SM22-nLacZ-transduced and Ad-SM22-4A1-transduced arteries, respectively) and demonstrated a marked angiogenic activity measured as the total length of sprouting neovessels (12.63+/-3.66 mm in Ad-SM22-4A1-transduced vessels versus 1.79+/-0.89 mm in Ad-SM22-nLacZ-transduced vessels). This angiogenic activity represented endothelial cell sprouting and was fully blocked by treatment with HET0016, a selective inhibitor of CYP4A-catalyzed reactions. The inhibitory effect of HET0016 was reversed by addition of a 20-HETE agonist. We conclude that Ad-SM22-4A1 drives a smooth muscle-specific functional expression of CYP4A1 and demonstrates increased angiogenesis, presumably via increased production of 20-HETE.

Regulation of renal CYP4A expression and 20-HETE synthesis by nitric oxide in pregnant rats

20-Hydroxyeicosatetraenoic acid (20-HETE), which promotes renal vasoconstriction, is formed in the rat kidney primarily by cytochrome P-450 (CYP) 4A isoforms (4A1, 4A2, 4A3, 4A8). Nitric oxide (NO) has been shown to bind to the heme moiety of the CYP4A2 protein and to inhibit 20-HETE synthesis in renal arterioles of male rats. However, it is not known whether NO interacts with and affects the activity of CYP4A1 and CYP4A3, the major renal CYP4A isoforms in female rats. Incubation of recombinant CYP4A1 and 4A3 proteins with sodium nitroprusside (SNP) shifted the absorbance at 440 nm, indicating the formation of a ferric-nitrosyl-CYP4A complex. The absorbance for CYP4A3 was about twofold higher than that of CYP4A1. Incubation of SNP or peroxynitrite (PN; 0.01-1 mM) with CYP4A recombinant membranes caused a concentration-dependent inhibition of 20-HETE synthesis, with both chemicals having a greater inhibitory effect on CYP4A3-catalyzed activity. Moreover, incubation of CYP4A1 and 4A3 proteins with PN (1 mM) resulted in nitration of tyrosine residues in both proteins. In addition, PN and SNP inhibited 20-HETE synthesis in renal microvessels from female rats by 65 and 59%, respectively. We previously showed that microvessel CYP4A1/CYP4A3 expression and 20-HETE synthesis are decreased in late pregnancy. Therefore, we investigated whether such a decrease is dependent on NO, the synthesis of which has been shown to increase in late pregnancy. Administration of NG-nitro-l-arginine methyl ester (l-NAME) to pregnant rats for 6 days (days 15-20 of pregnancy) caused a significant increase in systolic blood pressure, which was prevented by concurrent treatment with the CYP4A inhibitor 1-aminobenzotriazole (ABT). Urinary NO2/NO3 excretion decreased by 40 and 52% in l-NAME- and l-NAME + ABT-treated groups, respectively. Interestingly, renal microvessel 20-HETE synthesis showed a marked increase following l-NAME treatment, and this increase was diminished with coadministration of ABT. These results demonstrate that NO interacts with CYP4A proteins in a distinct manner and it interferes with renal microvessel 20-HETE synthesis, which may play an important role in the regulation of blood pressure and renal function during pregnancy.

Androgen-mediated induction of the kidney arachidonate hydroxylases is associated with the development of hypertension

Hypertension is a leading cause of cardiovascular, cerebral, and renal disease morbidity and mortality, and epidemiological evidence suggests a role for sex-dependent mechanisms in the pathophysiology of hypertension. We show here that treatment of rats with 5alpha-dihydrotestosterone increases the activity of the kidney arachidonate omega/omega-1 hydroxylase and the biosynthesis of 20-HETE (165 and 177% of control untreated male and female rats, respectively) and raises the systolic blood pressures of male and females rats by 46 and 57 mmHg, respectively. These androgen effects are associated with an upregulation in the kidney levels of CYP 4A8 mRNA and a decrease in CYP 4A1 transcripts. Dissected renal microvessels, the target tissue for most of the prohypertensive actions of 20-HETE, show an androgen-dependent upregulation of vascular CYP 4A8 mRNA and a fourfold increase in 20-HETE synthase activity. We propose that androgens regulate renal function and systemic blood pressure through a combination of transcriptional and hemodynamic mechanisms that are ultimately responsible for the regulation of renovascular tone and function.

Distribution of cytochrome P-450 4A and 4F isoforms along the nephron in mice

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. 20-HETE production in the kidney has been extensively studied in rats and humans and occurs primarily via the actions of P-450 enzymes of the CYP4A and -4F families. Recent advancements in molecular genetics of the mouse have made it possible to disrupt genes in a cell-type-specific fashion. These advances could help in the creation of models that could distinguish between the vascular and tubular actions of 20-HETE. However, isoforms of the CYP4A and -4F families that may be responsible for the production of 20-HETE in the vascular and tubular segments in the kidney of the mouse are presently unknown. The goal of this study was to identify the isoforms of the CYP4A and -4F families along the nephron by RT-PCR of RNA isolated from microdissected renal blood vessels and nephron segments from 16- to 24-wk-old male and female C57BL/6J mice. CYP4A and -4F isoforms were detected in every segment analyzed, with sex differences only observed in the proximal tubule and glomeruli. In the proximal tubular segments from male mice, the 4A10 and -12 isoforms were present, whereas the 4A10 and -14 isoforms were detected in segments from female mice. In glomeruli, sex differences in the expression pattern of CYP4F isoforms were also observed, with male mice expressing the 4F13, -14, and -15 isoforms, whereas female mice expressed the 4F13, -16, and -18 isoforms. These results demonstrate that isolated nephron and renal vessel segments express multiple isoforms of the CYP4A and -4F families; therefore, elimination of a single CYP4A or -4F isoform may not decrease 20-HETE production in all nephron segments or the renal vasculature of male and female mice. However, the importance of CYP4A vs. -4F isoforms to the production of 20-HETE in each of these renal tubular and vascular segments of the mouse remains to be determined.

Cytochrome P-450 4A isoform expression and 20-HETE synthesis in renal preglomerular arteries

20-Hydroxyeicosatetraenoic acid (20-HETE), a potent vasoconstrictor and mediator of the myogenic response, is a major arachidonic acid metabolite in the microvasculature of the rat kidney formed primarily by the cytochrome P-450 (CYP) 4A isoforms, CYP4A1, CYP4A2, and CYP4A3. We examined CYP4A isoform expression and 20-HETE synthesis in microdissected interlobar, arcuate, and interlobular arteries; mRNA for all CYP4A isoforms was identified by RT-PCR. Western blot analysis indicated that the levels of CYP4A2/4A3-immunoreactive protein increased with decreased arterial diameter, whereas those of CYP4A1-immunoreactive protein remained unchanged. 20-HETE synthesis was the highest in the interlobular arteries (17 +/- 1.62 nmol. mg(-1). h(-1)) and, like CYP4A2/4A3-immunoreactive protein, decreased with increasing vessel diameter (4.5 +/- 1.21, 2.65 +/- 0.58, and 0.81 +/- 0.14 nmol. mg(-1). h(-1) in the arcuate, interlobar, and segmental arteries, respectively). 20-HETE synthesis in the renal artery and the abdominal aorta was undetectable. The observed decreased immunoreactivity of NADPH-cytochrome P-450 (c) oxidoreductase with increased arterial diameter provided a possible explanation for the decreased capacity to generate 20-HETE in the large arteries. The increase in CYP4A isoform expression and 20-HETE synthesis with decreasing diameter along the preglomerular arteries and the potent biological activity of 20-HETE underscore the significance of 20-HETE as a modulator of renal hemodynamics.

Participation of renal and circulating endothelin in salt-sensitive essential hypertension

Salt sensitivity of blood pressure is a cardiovascular risk factor, independent of and in addition to hypertension. In essential hypertension, a conglomerate of clinical and biochemical characteristics defines a salt-sensitive phenotype. Despite extensive research on multiple natriuretic and antinatriuretic systems, there is no definitive answer yet about the major causes of salt-sensitivity, probably reflecting the complexity of salt-balance regulation. The endothelins, ubiquitous peptides first described as potent vasoconstrictors, also have vasodilator, natriuretic and antinatriuretic actions, depending on their site of generation and binding to different receptors. We review the available data on endothelin in salt-sensitive essential hypertension and conclude that abnormalities of renal endothelin may play a primary role. More importantly, the salt-sensitive patient may have blood pressure-dependency on endothelin in all states of salt balance, thus predicting that endothelin receptor blockers will have a major therapeutic role in salt-sensitive essential hypertension.

Contribution of CYP4A8 to the Formation of 20-Hydroxyeicosatetraenoic Acid from Arachidonic Acid in Rat Kidney

20-Hydroxyeicosatetraenoic acid (20-HETE) has been shown to be an arachidonic acid metabolite of the cytochrome P450 (CYP) enzymes belonging to the CYP4A subfamily and is a predominant regulator of renal vascular tone and tubular ion reabsorption in rat kidney. CYP4A8 is one of the CYP4A enzymes expressed in rat kidney, but its contribution to 20-HETE formation has not been assessed. In order to clarify that the role of CYP4A8, we have developed bacterial expression systems for the expression of recombinant CYP4A8 (rCYP4A8). We also produced an antibody against rCYP4A8 which was used for immunoinhibition and immunohistochemical studies. In a reconstituted system, rCYP4A8 sufficiently catalyzed 20-HETE formation as well as prostaglandin A(1) omega-hydroxylation, a marker activity for CYP4A8. In addition, anti-rCYP4A8 sera significantly inhibited prostaglandin A(1) omega-hydroxylation and strongly inhibited arachidonic acid omega-hydroxylation in rat kidney microsomes. These observations suggested for the first time that CYP4A8 also contributed to 20-HETE formation in rat kidney. Furthermore, immunohistochemstry suggested that CYP4A8 is present in preglomerular arteries, where 20-HETE has been established to be a vasoconstrictor.

P-450 metabolites of arachidonic acid in the control of cardiovascular function

Recent studies have indicated that arachidonic acid is primarily metabolized by cytochrome P-450 (CYP) enzymes in the brain, lung, kidney, and peripheral vasculature to 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs) and that these compounds play critical roles in the regulation of renal, pulmonary, and cardiac function and vascular tone. EETs are endothelium-derived vasodilators that hyperpolarize vascular smooth muscle (VSM) cells by activating K(+) channels. 20-HETE is a vasoconstrictor produced in VSM cells that reduces the open-state probability of Ca(2+)-activated K(+) channels. Inhibitors of the formation of 20-HETE block the myogenic response of renal, cerebral, and skeletal muscle arterioles in vitro and autoregulation of renal and cerebral blood flow in vivo. They also block tubuloglomerular feedback responses in vivo and the vasoconstrictor response to elevations in tissue PO(2) both in vivo and in vitro. The formation of 20-HETE in VSM is stimulated by angiotensin II and endothelin and is inhibited by nitric oxide (NO) and carbon monoxide (CO). Blockade of the formation of 20-HETE attenuates the vascular responses to angiotensin II, endothelin, norepinephrine, NO, and CO. In the kidney, EETs and 20-HETE are produced in the proximal tubule and the thick ascending loop of Henle. They regulate Na(+) transport in these nephron segments. 20-HETE also contributes to the mitogenic effects of a variety of growth factors in VSM, renal epithelial, and mesangial cells. The production of EETs and 20-HETE is altered in experimental and genetic models of hypertension, diabetes, uremia, toxemia of pregnancy, and hepatorenal syndrome. Given the importance of this pathway in the control of cardiovascular function, it is likely that CYP metabolites of arachidonic acid contribute to the changes in renal function and vascular tone associated with some of these conditions and that drugs that modify the formation and/or actions of EETs and 20-HETE may have therapeutic benefits.

Modulation by 20-HETE of phenylephrine-induced mesenteric artery contraction in spontaneously hypertensive and Wistar-Kyoto rats

Small mesenteric arteries of spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY) were compared for the production of 20-HETE and the effects of 20-HETE and N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS, 30 micromol/L), a 20-HETE synthesis inhibitor, on contractile responsiveness to phenylephrine (0.1 to 50.0 micromol/L). 20-HETE production was higher in vessels of SHR compared with WKY (1.34+/-0.16 versus 0.27+/-0.09 pmol/mg tissue, P<0.05). Phenylephrine elicited concentration-dependent vascular contraction; the R(max) was similar in vessels of SHR and WKY, but the former were more sensitive as denoted by the lower EC(50) (1.10+/-0.14 versus 1.89+/-0.33 micromol/L, P<0.05). DDMS caused a rightward shift in the concentration-response curve to phenylephrine, increasing (P<0.05) the EC(50) by 258% and 134% in vessels of SHR and WKY, respectively. In contrast, in DDMS-treated vessels, 20-HETE (0.01 to 10.0 micromol/L) caused a leftward shift in the phenylephrine concentration-response curve, decreasing (P<0.05) the EC(50) without affecting the R(max). Importantly, the minimal concentration of 20-HETE that decreased the EC(50) of phenylephrine was much smaller in vessels of SHR that of WKY (0.01 versus 1.0 micromol/L). We conclude that 20-HETE increases the sensitivity of mesenteric arterial vessels to phenylephrine, vessels of SHR are more sensitive to this action of the eicosanoid than vessels of WKY, and vessels of SHR produce more 20-HETE than do vessels of WKY. Hence, 20-HETE of vascular origin may be a determinant of the increased reactivity to constrictor agonists in the vasculature of SHR.

Use of real-time gene-specific polymerase chain reaction to measure RNA expression of three family members of rat cytochrome P450 4A

Exposure of rats to peroxisome proliferators induces members of the cytochrome P450 4A (CYP4A) family. In rats, the CYP4A family consists of four related genes, CYP4A1, CYP4A2, CYP4A3, and CYP4A8. We are specifically interested in examining CYP4A1, CYP4A2, and CYP4A3, each of which is expressed in a tissue-dependent and sex-dependent manner. While CYP4A1 is sufficiently different from the other two members to enable relatively easy specific quantitation, the close similarity between CYP4A2 and CYP4A3 makes quantitative discrimination difficult. We have combined a fluorescent real-time PCR assay (TaqMan) with the sequence-specific mismatch amplification mutation assay (MAMA) to allow us to carry out specific quantitation of all three members of this family. The assay is designed such that a single fluorescent TaqMan(R) probe binds to all three gene products, while specificity is conferred by sequence-specific primers. This specific MAMA technique takes advantage of the ability of Taq polymerase to distinguish between the two cDNAs based on mismatches at the 3' end of a PCR primer. In the 84-base PCR product used for this assay, there is only a single-base difference between CYP4A2 and CYP4A3. Despite this similarity, there is at least a 1000-fold discrimination between the two sequences, using CYP4A2 or CYP4A3 specific standards. Analysis of rat liver RNA from both sexes demonstrates that this discrimination is also achieved in complex RNA mixtures. This technique should be broadly applicable to other areas of research such as allelic discrimination, detecting mutational hotspots in tumors, and discrimination among closely related members of other gene families.

Expression and induction of cytochrome P450s in rabbit parotid glands

Earlier, we isolated and purified five different P450 isoforms from rabbit kidney cortex microsomes, three of which are members of the CYP4A subfamily (CYP4A5, CYP4A6, and CYP4A7), with the others being CYP2B4 and CYP1A1. In contrast, P450s in parotid glands were unknown. The fact that the parotid glands bear a marked morphological and functional resemblance to kidney tissue prompted us to investigate P450s in these glands. The present study was undertaken to determine which P450 isoforms are expressed in this tissue. Microsomes from parotid glands of untreated rabbits were found to contain 42.3 pmol of P450/mg protein and to catalyze the omega-hydroxylation of laurate. Administration of di(2-ethylhexyl) phthalate (DEHP) resulted in a 7-fold increase of laurate omega-hydroxylation. This enzyme activity was greatly inhibited by pretreatment with antibodies against CYP4A5. Furthermore, parotid gland CYP4A5, CYP4A6, and CYP4A7 mRNAs were identified by RT-PCR. Moreover, the CYP4A enzymes were demonstrated immunohistochemically to be localized exclusively in the ducts of these glands. In addition to the CYP4A enzymes, immunoblot analysis revealed that CYP2B4 is constitutively present, and that CYP1A1 is induced in these glands by treatment with 3-methylcholanthrene. Taken together, we can conclude that the P450 isoforms expressed in rabbit kidney cortex and parotid glands are identical in composition.

The kinetic and spectral characterization of the E. coli-expressed mammalian CYP4A7: cytochrome b5 effects vary with substrate

The CYP4A gene subfamily is composed of a number of genes that encode cytochromes P450 from various species, including human, which catalyze the hydroxylation of various saturated and unsaturated fatty acids, including arachidonic acid and prostaglandins. CYP4A7, a fatty acid metabolizing cytochrome P450 from rabbit kidney, was expressed in E. coli by adding the first 10 codons of CYP17alpha producing final yields of 20 nmol/L in order to perform detailed kinetic and spectral studies. CYP4A7 metabolized arachidonate, laurate, and myristate, with maximum turnover numbers of 152, 130, and 64.5 min(-1) and corresponding Km values of 74.5, 27, and 16.7 microM, respectively, in the presence of cytochrome b5. In the absence of cytochrome b5, CYP4A7 metabolized laurate and myristate with turnover numbers of 27.4 and 33.6 min(-1) and corresponding Km values of 3.9 and 33 microM, respectively. Arachidonate was not metabolized in the absence of cytochrome b5. Saturation kinetics studies performed with heme-depleted cytochrome b5 (apo cytochrome b5) yielded turnover numbers of 118 and 74 min(-1) and Km values of 74 and 25 microM with laurate and myristate, respectively, indicating that cytochrome b5 is not involved in electron transfer but rather plays a conformational role. Laurate perturbation of the visible absorption spectrum of CYP4A7 allowed for determination of the spectral binding constant (KS) in the absence and presence of cytochrome b5 (13 and 43 microM, respectively). In stopped-flow kinetics experiments, the flavin reduction (approximately 90 s(-1)) and heme reduction (approximately 9 s(-1)) phases of the monooxygenase reaction of CYP4A7 were not altered by the presence of cytochrome b5. Estimations of the rate of CPR (0.3 s(-1)) or cytochrome b5 (9.1 s(-1)) binding with CYP4A7 were also determined.