Angiotensin II modulates ion transport in rat proximal tubules through CYP metabolites

Elevated 20-HETE impairs coronary collateral growth in metabolic syndrome via endothelial dysfunction

Coronary collateral growth (CCG) is impaired in metabolic syndrome (MetS). microRNA-145 (miR-145-Adv) delivery to our rat model of MetS (JCR) completely restored and neutrophil depletion significantly improved CCG. We determined whether low endogenous levels of miR-145 in MetS allowed for elevated production of 20-hydroxyeicosatetraenoic acid (20-HETE), which, in turn, resulted in excessive neutrophil accumulation and endothelial dysfunction leading to impaired CCG. Rats underwent 0-9 days of repetitive ischemia (RI). RI-induced cardiac CYP4F (neutrophil-specific 20-HETE synthase) expression and 20-HETE levels were increased (4-fold) in JCR vs. normal rats. miR-145-Adv and 20-HETE antagonists abolished and neutrophil depletion (blocking antibodies) reduced (~60%) RI-induced increases in CYP4F expression and 20-HETE production in JCR rats. Impaired CCG in JCR rats (collateral-dependent blood flow using microspheres) was completely restored by 20-HETE antagonists [collateral-dependent zone (CZ)/normal zone (NZ) flow ratio was 0.76 ± 0.07 in JCR + 20-SOLA, 0.84 ± 0.05 in JCR + 20-HEDGE vs. 0.11 ± 0.02 in JCR vs. 0.84 ± 0.03 in normal rats]. In JCR rats, elevated 20-HETE was associated with excessive expression of endothelial adhesion molecules and neutrophil infiltration, which were reversed by miR-145-Adv. Endothelium-dependent vasodilation of coronary arteries, endothelial nitric oxide synthase (eNOS) Ser1179 phosphorylation, eNOS-dependent NO^·- production and endothelial cell survival were compromised in JCR rats. These parameters of endothelial dysfunction were completely reversed by 20-HETE antagonism or miR-145-Adv delivery, whereas neutrophil depletion resulted in partial reversal (~70%). We conclude that low miR-145 in MetS allows for increased 20-HETE, mainly from neutrophils, which compromises endothelial cell survival and function leading to impaired CCG. 20-HETE antagonists could provide viable therapy for restoration of CCG in MetS.NEW & NOTEWORTHY Elevated 20-hydroxyeicosatetraenoic acid (20-HETE) impairs coronary collateral growth (CCG) in metabolic syndrome by eliciting endothelial dysfunction and apoptosis via excessive neutrophil infiltration. 20-HETE antagonists completely restore coronary collateral growth in metabolic syndrome. microRNA-145 (miR-145) is an upstream regulator of 20-HETE production in metabolic syndrome; low expression of miR-145 in metabolic syndrome promotes elevated production of 20-HETE.

20-HETE and blood pressure regulation: clinical implications

20-Hydroxy-5, 8, 11, 14-eicosatetraenoic acid (20-HETE) is a cytochrome P450 (CYP)-derived omega-hydroxylation metabolite of arachidonic acid. 20-HETE has been shown to play a complex role in blood pressure regulation. In the kidney tubules, 20-HETE inhibits sodium reabsorption and promotes natriuresis, thus, contributing to antihypertensive mechanisms. In contrast, in the microvasculature, 20-HETE has been shown to play a pressor role by sensitizing smooth muscle cells to constrictor stimuli and increasing myogenic tone, and by acting on the endothelium to further promote endothelial dysfunction and endothelial activation. In addition, 20-HETE induces endothelial angiotensin-converting enzyme, thus, setting forth a potential feed forward prohypertensive mechanism by stimulating the renin-angiotensin-aldosterone system. With the advancement of gene sequencing technology, numerous polymorphisms in the regulatory coding and noncoding regions of 20-HETE-producing enzymes, CYP4A11 and CYP4F2, have been associated with hypertension. This in-depth review article discusses the biosynthesis and function of 20-HETE in the cardiovascular system, the pharmacological agents that affect 20-HETE action, and polymorphisms of CYP enzymes that produce 20-HETE and are associated with systemic hypertension in humans.

CYP4F2 genetic polymorphisms are associated with coronary heart disease in a Chinese population

BACKGROUND

To explore the relationship between CYP4F2 gene polymorphism and coronary heart disease (CHD) in a Chinese Han population.

METHODS

We selected 440 CHD patients and 440 control subjects to perform a case - control study. Four SNPs (rs2108622, rs3093100, rs3093105 and rs3093135) in CYP4F2 gene were genotyped using polymerase chain reaction - restriction fragment length polymorphism (PCR - RFLP) methods. The genotype and haplotype distributions were compared between the case and the control group.

RESULTS

We found both rs2108622 and rs3093105 in CYP4F2 gene were associated with the risk for CHD (P <0.01). Haplotype analysis indicated that GGGT haplotype consisted by rs2108622-rs3093100-rs3093105-rs3093135 was associated with CHD risk (OR = 4.367, 95% CI: 2.241 ~ 8.510; P < 0.001), but GGTA haplotype was associated with decreased risk for CHD (OR = 0.450, 95% CI: 0.111 ~ 0.777; P <0.001).

CONCLUSION

CYP4F2 gene polymorphisms were associated with the risk of CHD in Chinese population.

How do glucocorticoids cause hypertension: role of nitric oxide deficiency, oxidative stress, and eicosanoids

The exact mechanism by which glucocorticoid induces hypertension is unclear. Several mechanisms have been proposed, although there is evidence against the role of sodium and water retention as well as sympathetic nerve activation. This review highlights the role of nitric oxide-redox imbalance and their interactions with arachidonic acid metabolism in glucocorticoid-induced hypertension in humans and experimental animal models.

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.

Advanced glycation end products inhibit Na+ K+ ATPase in proximal tubule epithelial cells: role of cytosolic phospholipase A2alpha and phosphatidylinositol 4-phosphate 5-kinase gamma

Chronic hyperglycaemia during diabetes leads to non-enzymatic glycation of proteins to form advanced glycation end products (AGEs) that contribute to nephropathy. In diabetes, renal Na+ K+ ATPase (NKA) activity is downregulated and phosphoinositide metabolism is upregulated. We examined the effects of AGEs on NKA activity in porcine LLC-PK1 and human HK2 proximal tubule epithelial cells. AGE-BSA increased cellular phosphoinositol 4,5 bisphosphate (PIP2) production as determined by immunofluorescence microscopy and thin layer chromatography. AGE-BSA (40 microM) induced 3H-arachidonic acid release and reactive oxygen species (ROS) production via cytosolic phospholipase A2 (cPLA2) activation. Within minutes, AGE-BSA significantly inhibited NKA surface expression and activity in a dose- and time-dependent manner as determined by immunofluorescence staining and [86Rb+] uptake, respectively, suggesting AGEs inhibit NKA by stimulating its endocytosis. The AGE-BSA-induced decrease in cell surface NKA was reversed by a cPLA2alpha inhibitor, neomycin, a PIP2 inhibitor, and PP2, a Src inhibitor. AGE-BSA increased binding of NKA to the alpha-adaptin but not beta2- or mu2-adaptin subunits of the AP-2 clathrin pit adaptor complex. Transfection of HK2 cells with PIP5Kgamma siRNA prevented AGE-BSA inhibition of NKA activity. AGEs may stimulate PIP5Kgamma to increase PIP2 production, which may enhance AP-2 localisation to clathrin pits, increase clathrin pit formation, enhance NKA cargo recognition by AP-2 and/or stimulate cPLA2alpha activity. These results suggest AGEs modulate arachidonic acid and phosphoinositide metabolism to inhibit NKA via clathrin-mediated endocytosis. Elucidation of new intracellular AGE signaling pathways may lead to improved therapies for diabetic nephropathy.

Functional polymorphism in human CYP4F2 decreases 20-HETE production

20-Hydroxyeicosatetraenoic acid (20-HETE) plays an important role in the regulation of renal tubular and vascular function and a deficiency in the renal formation of 20-HETE has been linked to the development of hypertension. The cytochrome P450 4F2 ( CYP4F2) gene encodes for the major CYP enzyme responsible for the synthesis of 20-HETE in the human kidney. We screened two human sampling panels (African and European Americans: n = 24 and 23 individuals, respectively) using PCR and DNA resequencing to identify informative SNPs in the coding region of the CYP4F2 gene. Two nonsynonymous SNPs that lead to amino acid changes at position 12 (W12G) and 433 (V433M), were identified. Both of these variants were found to be frequent in both African and European American sampling panels (9–21% minor allele frequency), and the W12G polymorphism exhibited extensive linkage disequilibrium with surrounding SNPs. To determine the functional significance of these mutations on the ability of the CYP4F2 enzyme to metabolize arachidonic acid and leukotriene B4(LTB4), recombinant baculoviruses containing four different human CYP4F2 variants (i.e., W12/V433, W12/M433, G12/V433, G12/M433) were generated and the proteins were expressed in Sf9 insect cells. The presence of the M433 allele, W12/M433, or G12/M433 decreased 20-HETE production to 56–66% of control. In contrast these variants had no effect on the ω-hydroxylation of LTB4. These findings are the first to identify a functional variant in the human CYP4F2 gene that alters the production of 20-HETE.

Cytochrome P450 enzymes: Central players in cardiovascular health and disease

Cardiovascular disease (CVD) is a human health crisis that remains the leading cause of death worldwide. The cytochrome P450 (CYP) class of enzymes are key metabolizers of both xenobiotics and endobiotics. Many CYP enzyme families have been identified in the heart, endothelium and smooth muscle of blood vessels. Furthermore, mounting evidence points to the role of endogenous CYP metabolites, such as epoxyeicosatrienoic acids (EETs), hydroxyeicosatetraenoic acids (HETEs), prostacyclin (PGI(2)), aldosterone, and sex hormones, in the maintenance of cardiovascular health. Emerging science and the development of genetic screening have provided us with information on the differences in CYP expression among populations and groups of individuals. With this information, a link between CYP expression and activity and CVD, such as hypertension, coronary artery disease (CAD), myocardial infarction, heart failure, stroke, and cardiomyopathy and arrhythmias, has been established. In fact many currently used therapeutic modalities in CVD owe their therapeutic efficacy to their effect on CYP metabolites. Thus, the evidence for the involvement of CYP in CVD is numerous. Concentrating on treatment modalities that target the CYP pathway makes ethical sense for the affected individuals and decreases the socioeconomic burden of this disease. However, more research is needed to allow the integration of this information into a clinical setting.

Inhibition of the formation of EETs and 20-HETE with 1-aminobenzotriazole attenuates pressure natriuresis

This study examined the effects of chronic blockade of the renal formation of epoxyeicosatrienoic acids and 20-hydroxyeicosatetraenoic acid with 1-aminobenzotriazole (ABT; 50 mg·kg−1· day−1ip for 5 days) on pressure natriuresis and the inhibitory effects of elevations in renal perfusion pressure (RPP) on Na+-K+-ATPase activity and the distribution of the sodium/hydrogen exchanger (NHE)-3 in the proximal tubule of rats. In control rats ( n = 15), sodium excretion rose from 2.3 ± 0.4 to 19.4 ± 1.8 μeq·min−1·g kidney weight−1when RPP was increased from 114 ± 1 to 156 ± 2 mmHg. Fractional excretion of lithium rose from 28 ± 3 to 43 ± 3% of the filtered load. Chronic treatment of the rats with ABT for 5 days ( n = 8) blunted the natriuretic response to elevations in RPP by 75% and attenuated the increase in fractional excretion of lithium by 45%. In vehicle-treated rats, renal Na+-K+-ATPase activity fell from 31 ± 5 to 19 ± 2 μmol Pi·mg protein−1·h−1and NHE-3 protein was internalized from the brush border of the proximal tubule after an elevation in RPP. In contrast, Na+-K+-ATPase activity and the distribution of NHE-3 protein remained unaltered in rats treated with ABT. These results suggest that cytochrome P-450 metabolites of arachidonic acid contribute to pressure natriuresis by inhibiting Na+-K+-ATPase activity and promoting internalization of NHE-3 protein from the brush border of the proximal tubule.

Angiotensin II-dependent increased expression of Na+-glucose cotransporter in hypertension

Glucose uptake is increased in hypertension. Thus we investigated Na+-glucose cotransporter (SGLT2) activity and expression in proximal tubules from renovascular hypertensive rats. Sham-operated rats, aortic coarctation rats, and aortic coarctation rats treated with either ramipril (2.5 mg.kg-1.day-1 for 21 days) or losartan (10 mg.kg-1.day-1 for 21 days) were used. Na+-dependent glucose uptake was measured in brush-border membrane vesicles (BBMV). Vmax in BBMV from hypertensive rats was greater compared with those from normotensive rats (3 +/- 0.2 vs. 1.5 +/- 0.1 nmol.mg protein-1.min-1) without a change in Km. Renal immunostaining was greater, and Western blot analysis and RT-PCR showed a higher expression of SGLT2 in hypertensive rats than in normotensive rats (1,029 +/- 71 vs. 5,003 +/- 292, 199 +/- 15 vs. 95 +/- 10, and 1.4 +/- 0.2 vs. 0.3 +/- 0.1 arbitrary units, respectively). In rats treated with either ramipril or losartan, Vmax decreased to 2.1 +/- 0.3 and 1.8 +/- 0.4 nmol.mg protein-1.min-1, respectively, as well as did the intensity of immunostaining and levels of protein and mRNA. We suggest that in renovascular hypertension, angiotensin II induced SGLT2 via the AT1 receptor, which was evidenced at both the functional and expression levels, probably contributing to increased absorption of Na+ and thereby to the development or maintenance of hypertension.

20-HETE-induced contraction of small coronary arteries depends on the activation of Rho-kinase

20-HETE is a potent constrictor of small blood vessels and has been suggested to play a crucial role in the generation of myogenic tone and the development of hypertension. In the present study, we investigated the mechanisms by which exogenously applied 20-HETE modulates vascular tone in small porcine coronary arteries. In organ chamber experiments, 20-HETE elicited a concentration-dependent contraction of small porcine coronary artery rings that was partially inhibited by the cyclooxygenase inhibitor diclofenac, the thromboxane and endoperoxide receptor antagonist SQ29548, and the thromboxane A2 synthase inhibitor furegrelate. Removal of endothelium attenuated the response to 20-HETE, whereas preconstriction of endothelium-denuded vessels to 25% of the maximum response with KCl markedly enhanced the response to 20-HETE. This 20-HETE-induced contraction was not associated with a significant increase in the intracellular concentration of Ca2+. 20-HETE-induced contraction was also observed in beta-escin-permeabilized arteries precontracted with a submaximal concentration of Ca2+ and was abolished by the Rho-kinase inhibitor Y27632, but was insensitive to the PKC inhibitor RO 31-8220. 20-HETE elicited the phosphorylation of the myosin light chain (MLC20) in coronary artery rings, an effect that was sensitive to Y27632 and mimicked by the thromboxane analog U46619. These data suggest that in small porcine coronary arteries, 20-HETE can induce contraction by 2 mechanisms, one endothelium-dependent involving the cyclooxygenase-dependent generation of vasoconstrictor prostanoids, and the other endothelium-independent. The latter response is associated with the activation of Rho-kinase, phosphorylation of MLC20, and sensitization of the contractile apparatus to Ca2+.

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.

20-hydroxyeicosatetraenoic acid and epoxyeicosatrienoic acids and blood pressure

The properties of 20-hydroxyeicosatetraenoic acid and epoxyeicosatrienoic acids, vasoactivity and modulation of ion transport and mediation/modulation of the effects of vasoactive hormones, such as angiotensin II and endothelin, underscore their importance to renal vascular mechanisms and electrolyte excretion. 20-Hydroxyeicosatetraenoic acid is an integral component of renal autoregulation and tubuloglomerular feedback as well as cerebral autoregulation, eliciting vasoconstriction by the inhibition of potassium channels. Nitric oxide inhibits 20-hydroxyeicosatetraenoic acid formation, the removal of which contributes to the vasodilator effect of nitric oxide. In contrast, epoxyeicosatrienoic acids are generally vasodilatory by activating potassium channels and have been proposed as endothelium-derived hyperpolarizing factors. 20-Hydroxyeicosatetraenoic acid modulates ion transport in key nephron segments by influencing the activities of sodium--potassium-ATPase and the sodium--potassium--chloride co-transporter; however, the primacy of the various arachidonate oxygenases that generate products affecting these activities changes with age. The range and diversity of activity of 20-hydroxyeicosatetraenoic acid is influenced by its metabolism by cyclooxygenase to products affecting vasomotion and salt/water excretion. 20-Hydroxyeicosatetraenoic acid is the principal renal eicosanoid that interacts with several hormonal systems that are central to blood pressure regulation. This article reviews the most recent studies that address 20-hydroxyeicosatetraenoic acid and epoxyeicosatrienoic acids in vascular and renal tubular function and hypertension.

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

Recent studies indicate that arachidonic acid is primarily metabolized by cytochrome P450 enzymes of the 4A and 2C families in the kidney to 20-hydroxyeicosatetraenoic acid (HETE), epoxyeicosatrienoic acids (EETs) and dihydroxyeicosatrienoic acids. These compounds play central roles in the regulation of renal tubular and vascular function. 20-HETE is produced by renal vascular smooth muscle (VSM) cells and is a potent constrictor that depolarizes VSM cells by blocking the calcium-activated potassium channel. Inhibition of the formation of 20-HETE blocks the myogenic response of isolated renal arterioles in vitro, and autoregulation of renal blood flow and tubuloglomerular feedback responses in vivo. EETs are products formed in the endothelium and are potent dilators that activate the calcium-activated potassium channel in renal VSM. Endothelial-dependent vasodilators stimulate the release of EETs, and these compounds appear to serve as an endothelial-derived hyperpolarizing factor. EETs and 20-HETE are produced in the proximal tubule. There, they regulate sodium/potassium-ATPase activity and serve as second messengers for the natriuretic effects of dopamine, parathyroid hormone and angiotensin II. 20-HETE is also produced in the thick ascending loop of Henle. It regulates sodium-potassium-chloride transport in this nephron segment. The renal production of cytochrome P450 metabolites of arachidonic acid is altered in hypertension, diabetes, toxemia of pregnancy, and hepatorenal syndrome. Given the importance of cytochrome P450 metabolites of arachidonic acid in the control of renal function, it is likely that changes in this system contribute to the abnormalities in renal function that are associated with many of these conditions.