20-Hydroxyeicosatetraenoic acid mediates calcium/calmodulin-dependent protein kinase II-induced mitogen-activated protein kinase activation in vascular smooth muscle cells

Ca2+/calmodulin-dependent protein kinase II function in vascular remodelling

Vascular smooth muscle (VSM) undergoes a phenotypic switch in response to injury, a process that contributes to pathophysiological vascular wall remodelling. VSM phenotype switching is a consequence of changes in gene expression, including an array of ion channels and pumps affecting spatiotemporal features of intracellular Ca(2+) signals. Ca(2+) signalling promotes vascular wall remodelling by regulating cell proliferation, motility, and/or VSM gene transcription, although the mechanisms are not clear. In this review, the functions of multifunctional Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in VSM phenotype switching and synthetic phenotype function are considered. CaMKII isozymes have complex structural and autoregulatory properties. Vascular injury in vivo results in rapid changes in CaMKII isoform expression with reduced expression of CaMKIIγ and upregulation of CaMKIIδ in medial wall VSM. SiRNA-mediated suppression of CaMKIIδ or gene deletion attenuates VSM proliferation and consequent neointimal formation. In vitro studies support functions for CaMKII in the regulation of cell proliferation, motility and gene expression via phosphorylation of CREB1 and HDACIIa/MEF2 complexes. These studies support the concept, and provide potential mechanisms, whereby Ca(2+) signalling through CaMKIIδ promotes VSM phenotype transitions and vascular remodelling.

The role of 20-HETE in androgen-mediated hypertension

Androgen plays an important role in blood pressure regulation. Epidemiological studies have shown that men have a higher prevalence for developing hypertension than aged-matched, premenopausal women. Interestingly, postmenopausal women and women with polycystic ovary syndrome, both of which have increased endogenous androgen production, have elevated risks for hypertension suggesting that androgen may contribute to its development. Studies from our laboratory and others have provided substantial evidence that 20-hydroxyeicosatetraenoic acid (20-HETE) mediates the hypertension seen in rodents treated with androgen. 20-HETE is the cytochrome P450 (CYP)-derived ω-hydroxylated metabolite of arachidonic acid. 20-HETE plays a complex role in blood pressure regulation. In the kidney tubules, 20-HETE decreases blood pressure by promoting natriuresis, while in the microvasculature it has a pressor effect. In the microcirculation, 20-HETE participates in the regulation of vascular tone by sensitizing the smooth muscle cells to constrictor stimuli and contributes to myogenic, mitogenic and angiogenic responses. In addition, 20-HETE acts on the endothelium to promote endothelial dysfunction and endothelial activation. Recently, we have demonstrated that 20-HETE induces endothelial ACE thus setting forth a potential feed forward mechanism through activation of the renin-angiotensin-aldosterone system. In this review, we will discuss the pro-hypertensive effects of 20-HETE and its role in androgen-induced vascular dysfunction and hypertension.

20-Hydroxyeicosatetraenoic acid inhibits ATP-induced COX-2 expression via peroxisome proliferator activator receptor-α in vascular smooth muscle cells

BACKGROUND AND PURPOSE

20-Hydroxyeicosatetraenoic acid (20-HETE), formed from arachidonate by cytochrome P450, regulates vascular smooth muscle cell (VSMC) function. Because 20-HETE may activate peroxisome proliferator activator receptors (PPARs) and may participate in inflammatory responses, we asked whether 20-HETE may inhibit cyclooxygenase 2 (COX-2) expression by activating PPARs in VSMC.

EXPERIMENTAL APPROACH

Quiescent neonatal VSMC (R22D cell line), were incubated with 20-HETE, synthetic ligands of PPARs, or inhibitors of the extracellular signal regulated kinase (ERK1/2), c-jun N-terminal kinase and the transcription factor activated protein-1 before adding ATPγS. mRNA and protein expression of COX-2 and the promoter luciferase activity of COX-2 and PPAR response element were determined.

KEY RESULTS

Pretreatment with 20-HETE (5-10 µM) significantly inhibited ATPγS-induced COX-2 mRNA and protein expression in VSMC. The inhibitory effect of 20-HETE on COX-2 expression was mimicked by WY14643, a PPARα ligand and inhibited by MK886, a PPARα inhibitor or by transfection of shRNA for PPARα. Both 20-HETE and WY14643 significantly increased the PPAR-response element luciferase activity. Furthermore, ATPγS-induced activation of the COX-2 promoter containing the activated protein-1 site was also inhibited by pretreatment with 20-HETE, which was reversed by MK886 or by transfection with shRNA for PPARα.

CONCLUSIONS AND IMPLICATIONS

The PPARα may mediate the inhibitory effects of 20-HETE on COX-2 expression through a negative cross-talk between PPARα and the COX-2 promoter.

The inhibitor of 20-HETE synthesis, TS-011, improves cerebral microcirculatory autoregulation impaired by middle cerebral artery occlusion in mice

BACKGROUND AND PURPOSE

20-Hydroxyeicosatetraenoic acid is a potent vasoconstrictor that contributes to cerebral ischaemia. An inhibitor of 20-Hydroxyeicosatetraenoic acid synthesis, TS-011, reduces infarct volume and improves neurological deficits in animal stroke models. However, little is known about how TS-011 affects the microvessels in ischaemic brain. Here, we investigated the effect of TS-011 on microvessels after cerebral ischaemia.

EXPERIMENTAL APPROACH

TS-011 (0.3 mg·kg(-1) ) or a vehicle was infused intravenously for 1 h every 6 h in a mouse model of stroke, induced by transient occlusion of the middle cerebral artery occlusion following photothrombosis. The cerebral blood flow velocity and the vascular perfusion area of the peri-infarct microvessels were measured using in vivo two-photon imaging.

KEY RESULTS

The cerebral blood flow velocities in the peri-infarct microvessels decreased at 1 and 7 h after reperfusion, followed by an increase at 24 h after reperfusion in the vehicle-treated mice. We found that TS-011 significantly inhibited both the decrease and the increase in the blood flow velocities in the peri-infarct microvessels seen in the vehicle-treated mice after reperfusion. In addition, TS-011 significantly inhibited the reduction in the microvascular perfusion area after reperfusion, compared with the vehicle-treated group. Moreover, TS-011 significantly reduced the infarct volume by 40% at 72 h after middle cerebral artery occlusion.

CONCLUSIONS AND IMPLICATIONS

These findings demonstrated that infusion of TS-011 improved defects in the autoregulation of peri-infarct microcirculation and reduced the infarct volume. Our results could be relevant to the treatment of cerebral ischaemia.

CYP-eicosanoids--a new link between omega-3 fatty acids and cardiac disease?

Fish oil omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) protect against arrhythmia and sudden cardiac death by largely unknown mechanisms. Recent in vitro and in vivo studies demonstrate that arachidonic acid (AA) metabolizing cytochrome P450-(CYP) enzymes accept EPA and DHA as efficient alternative substrates. Dietary EPA/DHA supplementation causes a profound shift of the cardiac CYP-eicosanoid profile from AA- to EPA- and DHA-derived epoxy- and hydroxy-metabolites. CYP2J2 and other CYP epoxygenases preferentially epoxidize the ω-3 double bond of EPA and DHA. The corresponding metabolites, 17,18-epoxy-EPA and 19,20-epoxy-DHA, dominate the CYP-eicosanoid profile of the rat heart after EPA/DHA supplementation. The (ω-3)-epoxyeicosanoids show highly potent antiarrhythmic properties in neonatal cardiomyocytes, suggesting that these metabolites may specifically contribute to the cardioprotective effects of omega-3 fatty acids. This hypothesis is discussed in the context of recent findings that revealed CYP-eicosanoid mediated mechanisms in cardiac ischemia-reperfusion injury and maladaptive cardiac hypertrophy.

Inhibition of Ras-GTPase farnesylation and the ubiquitin-proteasome system or treatment with angiotensin-(1-7) attenuates spinal cord injury-induced cardiac dysfunction

Cardiovascular diseases are one of the principal causes of death and disability in people with spinal cord injury (SCI). The present study was designed to investigate if acute treatment with FPTIII (an inhibitor of Ras-GTPase farnesylation) or MG132 (an inhibitor of ubiquitin-proteasome pathway [UPS]) or administration of angiotensin-(1-7), also known as Ang-(1-7), (a known inhibitor of cardiac NF-kB) would be cardioprotective. The weight drop technique produced a consistent contusive injury of the spinal cord at the T13 segment. Hearts were isolated from rats either 6 months (SCI-6) or 12 months (SCI-12) after SCI. Hearts were perfused for 30 min and then subjected to 30 min ischemia followed by 30 min reperfusion (I/R). Recovery of cardiac function after I/R was measured as left ventricular developed pressure (P(max)) and coronary flow (CF). Drugs were given during perfusion before hearts were exposed to ischemia and reperfusion. Percent recovery (%R) in P(max) and CF in hearts from control animals were 48±6 and 50±5, respectively, whereas none of the hearts from animals with SCI recovered after 30 min of ischemia. Treatment with FPTIII, MG 132, or Ang-(1-7) before ischemia for 30 min led to significant recovery of heart function following ischemia in SCI-6 but not in SCI-12 animals. Thus we have shown that acute treatments with FPTIII, MG132, or Ang-(1-7) improve cardiac recovery following ischemic insult in animals with SCI and may represent novel therapeutic agents for preventing ischemia-induced cardiac dysfunction in patients with SCI.

Contribution of Ras farnesyl transferase, MAP kinase and cytochrome P-450 metabolites to endothelin-1 induced hypertension

Endothelin 1 (ET-1) is vasoactive peptide that acts via ET-A receptors coupling inducing vascular smooth muscle cell proliferation and contraction. ET-1 is involved in the development and maintenance of hypertension. Aim of this study was to determine the contribution of Ras farnesyl transferase, mitogen activated protein kinase (MAP kinase) and cytochrome P¬450 (CYP450) metabolites to ET-1 induced hypertension. ET-1 (5 pmol/kg per minute) was chronically infused into to the jugular vein by use of mini-osmotic pump for 9 days in male Sprague-Dawley rats. Mean arterial blood pressure (MABP) in ET-1-treated rats was 154±2 mm Hg (hypertensive rats) compared with 98±3 mm Hg in control (normotensive) rats. Infusion of Ras farnesyl transferase inhibitor FPTIII (138 ng/min), MAP kinase inhibitor PD-98059 (694 ng/min) and CYP450 inhibitor 17-ODYA (189 ng/min) significantly attenuated MABP to 115±2.5 mm Hg, 109±3 mm Hg and 118±1.5 mm Hg, respectively. These results suggest that CYP-450 metabolites and Ras/MAP kinase pathway contribute to the development of ET-1 induced hypertension. Further investigation has to be done to confirm whether activation of RAS/MAP kinase pathway by arachidonic acid metabolites plays an important role in the development of ET-1 induced hypertension.

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.

Cytochrome P450-derived eicosanoids: the neglected pathway in cancer

Endogenously produced lipid autacoids are locally acting small molecule mediators that play a central role in the regulation of inflammation and tissue homeostasis. A well-studied group of autacoids are the products of arachidonic acid metabolism, among which the prostaglandins and leukotrienes are the best known. They are generated by two pathways controlled by the enzyme systems cyclooxygenase and lipoxygenase, respectively. However, arachidonic acid is also substrate for a third enzymatic pathway, the cytochrome P450 (CYP) system. This third eicosanoid pathway consists of two main branches: ω-hydroxylases convert arachidonic acid to hydroxyeicosatetraenoic acids (HETEs) and epoxygenases convert it to epoxyeicosatrienoic acids (EETs). This third CYP pathway was originally studied in conjunction with inflammatory and cardiovascular disease. Arachidonic acid and its metabolites have recently stimulated great interest in cancer biology; but, unlike prostaglandins and leukotrienes the link between cytochome P450 metabolites and cancer has received little attention. In this review, the emerging role in cancer of cytochrome P450 metabolites, notably 20-HETE and EETs, are discussed.

Renal function and vasomotor activity in mice lacking the Cyp4a14 gene

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

Endothelin-1 induced vascular smooth muscle cell proliferation is mediated by cytochrome p-450 arachidonic acid metabolites

Endothelins (ETs) are a family of three peptides (ET-1, ET-2, ET-3) that are implicated in the physiological control of vascular smooth muscle cell (VSMC) and myocardial contractility and growth. ET-1 is vasoactive peptide that acts via ET-A receptors coupling inducing vascular smooth muscle cell contraction. ET-1 is involved in the development and maintenance of hypertension. Aim of this study was to investigate whether ET-1 can induce vascular smooth muscle cell proliferation through arachidonic acid (AA) metabolites formed via cytochrome P¬450 (CYP-450). VSMC proliferation was measured by [3H]thymidine incorporation in cultured cells treated by ET-1 (10 to l00 nmol/L) in presence of different inhibitors of CYP-450 (17-ODYA 5 μmol/L), lipoxygenase (LO) (baicalein 20 μmol/L) and cyclooxygenase (COX) (indomethacin 5 μmol/L). ET-1 (10 to 100 nmol/L) induced VSMC proliferation and this effect was attenuated by CYP-450 inhibitor (17-ODYA) and lipoxygenase (LO) inhibitor (baicalein) but not by cyclooxygenase (COX) inhibitor (indomethacin). CYP-450 and LO metabolites of AA, 20-hydroxyeicosatetraenoic acid (HETE) and 12-HETE increased [3H]thymidine incorporation in VSMC. Inhibitors of MAP kinase (PD-98059 50 μmol/L) and cPLA2 (MAFP 50 μmol/L) attenuated ET-1 as well as 20-HETE induced VSMC proliferation. These results suggest AA metabolites via CYP-450 mediates ET-1 induce VSMC proliferation.

Angiotensin II-dependent growth of vascular smooth muscle cells requires transactivation of the epidermal growth factor receptor via a cytosolic phospholipase A(2)-mediated release of arachidonic acid

Angiotensin (Ang) II stimulates vascular smooth muscle cell (VSMC) growth via activation of cytosolic phospholipase A(2) (cPLA(2)), release of arachidonic acid (ArAc) and activation of mitogen-activated protein kinase (MAPK). The mechanism linking AT(1) receptor stimulation of ArAc release with MAPK activation may involve transactivation of the epidermal growth factor receptor (EGFR). In this study, Ang II increased phosphorylation of the EGFR and MAPK in cultured VSMC and these effects were attenuated by the cPLA(2) inhibitor arachidonyl trifluoromethyl ketone (AACOCF(3)), and restored by addition of ArAc. Ang II- or ArAc-induced phosphorylation of the EGFR and MAPK were abolished by the EGFR kinase inhibitor AG1478. Ang II or ArAc also stimulated VSMC growth that was blocked by AG1478 or the MAPK kinase (MEK) inhibitor PD98059. Thus, it appears that the cPLA(2)-dependent release of ArAc may provide a mechanism for the transactivation between the AT(1) receptor and the EGFR signaling cascade.

Combined inhibition of 20-hydroxyeicosatetraenoic acid formation and of epoxyeicosatrienoic acids degradation attenuates hypertension and hypertension-induced end-organ damage in Ren-2 transgenic rats

Recent studies have shown that the renal CYP450 (cytochrome P450) metabolites of AA (arachidonic acid), the vasoconstrictor 20-HETE (20-hydroxyeicosatetraenoic acid) and the vasodilator EETs (epoxyeicosatrienoic acids), play an important role in the pathophysiology of AngII (angiotensin II)-dependent forms of hypertension and the associated target organ damage. The present studies were performed in Ren-2 renin transgenic rats (TGR) to evaluate the effects of chronic selective inhibition of 20-HETE formation or elevation of the level of EETs, alone or in combination, on the course of hypertension and hypertension-associated end-organ damage. Both young (30 days of age) prehypertensive TGR and adult (190 days of age) TGR with established hypertension were examined. Normotensive HanSD (Hannover Sprague-Dawley) rats served as controls. The rats were treated with N-methylsulfonyl-12,12-dibromododec-11-enamide to inhibit 20-HETE formation and/or with N-cyclohexyl-N-dodecyl urea to inhibit soluble epoxide hydrolase and prevent degradation of EETs. Inhibition in TGR of 20-HETE formation combined with enhanced bioavailability of EETs attenuated the development of hypertension, cardiac hypertrophy, proteinuria, glomerular hypertrophy and sclerosis as well as renal tubulointerstitial injury. This was also associated with attenuation of the responsiveness of the systemic and renal vascular beds to AngII without modifying their responses to noradrenaline (norepinephrine). Our findings suggest that altered production and/or action of 20-HETE and EETs plays a permissive role in the development of hypertension and hypertension-associated end-organ damage in this model of AngII-dependent hypertension. This information provides a basis for a search for new therapeutic approaches for the treatment of hypertension.

Effect of cytochrome P450 polymorphism on arachidonic acid metabolism and their impact on cardiovascular diseases

Cardiovascular diseases (CVDs) remain the leading cause of death in the developed countries. Taking into account the mounting evidence about the role of cytochrome P450 (CYP) enzymes in cardiovascular physiology, CYP polymorphisms can be considered one of the major determinants of individual susceptibility to CVDs. One of the important physiological roles of CYP enzymes is the metabolism of arachidonic acid. CYP epoxygenases such as CYP1A2, CYP2C, and CYP2J2 metabolize arachidonic acid to epoxyeicosatrienoic acids (EETs) which generally possess vasodilating, anti-inflammatory, anti-apoptotic, anti-thrombotic, natriuretic, and cardioprotective effects. Therefore, genetic polymorphisms causing lower activity of these enzymes are generally associated with an increased risk of several CVDs such as hypertension and coronary artery disease. EETs are further metabolized by soluble epoxide hydrolase (sEH) to the less biologically active dihydroxyeicosatrienoic acids (DHETs). Therefore, sEH polymorphism has also been shown to affect arachidonic acid metabolism and to be associated with CVDs. On the other hand, CYP omega-hydroxylases such as CYP4A11 and CYP4F2 metabolize arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-HETE) which has both vasoconstricting and natriuretic effects. Genetic polymorphisms causing lower activity of these enzymes are generally associated with higher risk of hypertension. Nevertheless, some studies have denied the association between polymorphisms in the arachidonic acid pathway and CVDs. Therefore, more research is needed to confirm this association and to better understand the pathophysiologic mechanisms behind it.

20-hydroxy-5,8,11,14-eicosatetraenoic acid mediates endothelial dysfunction via IkappaB kinase-dependent endothelial nitric-oxide synthase uncoupling

Endothelial dysfunction and activation occur in the vasculature and are believed to contribute to the pathogenesis of cardiovascular diseases. We have shown that 20-hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE), a cytochrome P450 4A-derived eicosanoid that promotes vasoconstriction in the microcirculation, uncouples endothelial nitric-oxide synthase (eNOS) and reduces nitric oxide (NO) levels via the dissociation of the 90-kDa heat shock protein (HSP90) from eNOS. It also causes endothelial activation by stimulating nuclear factor-kappaB (NF-kappaB) and increasing levels of pro-inflammatory cytokines. In this study, we examined signaling mechanisms that may link 20-HETE-induced endothelial dysfunction and activation. Under conditions in which 20-HETE inhibited NO production, it also stimulated inhibitor of NF-kappaB (IkappaB) phosphorylation. Both effects were prevented by inhibition of tyrosine kinases and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK). It is noteworthy that inhibitor of IkappaB kinase (IKK) activity negated the 20-HETE-mediated inhibition of NO production. Immunoprecipitation experiments revealed that treatment of ionophore-stimulated cells with 20-HETE brings about a decrease in HSP90-eNOS association and an increase in HSP90-IKKbeta association, suggesting that the activation by 20-HETE of NF-kappaB is linked to its action on eNOS. Furthermore, addition of inhibitors of tyrosine kinase MAPK and IKK restored the 20-HETE-mediated impairment of acetylcholine-induced relaxation in rat renal interlobar arteries. The results indicate that 20-HETE mediates eNOS uncoupling and endothelial dysfunction via the activation of tyrosine kinase, MAPK, and IKK, and these effects are linked to 20-HETE-mediated endothelial activation.

The arachidonic acid effect on platelet nitric oxide level

Arachidonic acid can act as a second messenger regulating many cellular processes among which is nitric oxide (NO) formation. The aim of the present study was to investigate the molecular mechanisms involved in the arachidonic acid effect on platelet NO level. Thus NO, cGMP and superoxide anion level, the phosphorylation status of nitric oxide synthase, the protein kinase C (PKC), and NADPH oxidase activation were measured. Arachidonic acid dose-dependently reduced NO and cGMP level. The thromboxane A(2) mimetic U46619 behaved in a similar way. The arachidonic acid or U46619 effect on NO concentration was abolished by the inhibitor of the thromboxane A(2) receptor SQ29548 and partially reversed by the PKC inhibitor GF109203X or by the phospholipase C pathway inhibitor U73122. Moreover, it was shown that arachidonic acid activated PKC and decreased nitric oxide synthase (eNOS) activities. The phosphorylation of the inhibiting eNOSthr495 residue mediated by PKC was increased by arachidonic acid, while no changes at the activating ser1177 residue were shown. Finally, arachidonic acid induced NADPH oxidase activation and superoxide anion formation. These effects were greatly reduced by GF109203X, U73122, and apocynin. Likely arachidonic acid reducing NO bioavailability through all these mechanisms could potentiate its platelet aggregating power.

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

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

Role of 20-hydroxyeicosatetraenoic acid in altering vascular reactivity in diabetes

1 This study examined the role of 20-hydroxyeicosatetraenoic (20-HETE) in altering vascular function in streptozotocin (STZ)-induced diabetic rats. 2 The expression of CYP4A protein and the formation of 20-HETE were elevated in the kidney, but not in the renal or mesenteric vasculature, of diabetic animals. The vasoconstrictor responses to norepinephrine (NE), endothelin-1 (ET-1), and angiotensin II (Ang II) were significantly enhanced in the isolated perfused mesenteric vascular bed and renal artery segments of diabetic rats. Chronic treatment of the diabetic rats with 1-aminobenzotriazole (ABT, 50 mg kg(-1) alt(-1) diem) or N-hydroxy-N'-(4-butyl-2-methylphenyl) formamidine (HET0016, 2.5 mg kg(-1) day(-1)) attenuated the responses to these vasoconstrictors in both vascular beds. 3 The synthesis of 20-HETE in renal microsomes was reduced by >80% confirming that the doses of ABT and HET0016 were sufficient to achieve system blockade. Addition of HET0016 (1 microM) in vitro also normalized the enhanced vascular responsiveness of renal and mesenteric vessels obtained from diabetic animals to NE and inhibited the formation of 20-HETE by >90% while having no effect on the formation of epoxides. Vasodilator responses to carbachol and histamine were reduced in the mesenteric vasculature, but not in renal arteries, of diabetic rats. Treatment of the diabetic animals with HET0016 improved vasodilator responses in both vascular beds. Vascular sensitivity to exogenous 20-HETE was elevated in the mesenteric bed of diabetic animals compared to controls. 4 These results suggest that 20-HETE contributes to the elevation in vascular reactivity in diabetic animals. This effect is not due to increased vascular expression of CYP4A but may be related to either enhanced agonist-induced release of substrate (arachidonic acid) by the CaMKII/Ras-GTPase system and/or elevated vascular responsiveness to 20-HETE by the CaMKII/Ras-GTPase system and/or elevated vascular responsiveness to 20-HETE.

Activation of cytosolic phospholipase A2 in dorsal root ganglion neurons by Ca2+/calmodulin-dependent protein kinase II after peripheral nerve injury

Background

Peripheral nerve injury leads to a persistent neuropathic pain state in which innocuous stimulation elicits pain behavior (tactile allodynia), but the underlying mechanisms have remained largely unknown. We have previously shown that spinal nerve injury induces the activation of cytosolic phospholipase A₂ (cPLA₂) in injured dorsal root ganglion (DRG) neurons that contribute to tactile allodynia. However, little is known about the signaling pathway that activates cPLA₂ after nerve injury. In the present study, we sought to determine the mechanisms underlying cPLA₂ activation in injured DRG neurons in an animal model of neuropathic pain, focusing on mitogen-activated protein kinases (MAPKs) and Ca²⁺/calmodulin-dependent protein kinase II (CaMKII).

Results

Pharmacological inhibition of either p38 or extracellular signal-regulated kinase (ERK) in the injured DRG, which led to suppression of the development of tactile allodynia, did not affect cPLA₂ phosphorylation and translocation after nerve injury. By contrast, a CaMKII inhibitor prevented the development and expression of nerve injury-induced tactile allodynia and reduced both the level of cPLA₂ phosphorylation and the number of DRG neurons showing translocated cPLA₂ in response to nerve injury. Applying ATP to cultured DRG neurons increased the level of both phosphorylated cPLA₂ and CaMKII in the vicinity of the plasma membrane and caused physical association of these two proteins. In addition, ATP-stimulated cPLA₂ and CaMKII phosphorylation were inhibited by both a selective P2X₃R/P2X₂₊₃R antagonist and a nonselective voltage-dependent Ca²⁺ channel (VDCC) blocker.

Conclusion

These results suggest that CaMKII, but not MAPKs, has an important role in cPLA₂ activation following peripheral nerve injury, probably through P2X₃R/P2X₂₊₃R and VDCCs in primary afferent neurons.

Arachidonic acid metabolites inhibit the stimulatory effect of angiotensin II in renal proximal tubules

Angiotensin II (Ang II) regulates renal proximal transport in a biphasic way via Ang II type 1 receptor (AT1). Whereas extracellular signal-regulated kinase (ERK) activation mediates the stimulatory effect, cytosolic phospholipase A2 (cPLA2) mediates the inhibitory effect independently of ERK. In this study, we tested the hypothesis that the cPLA2/P450 epoxygenase pathway might work to suppress the Ang II-mediated ERK activation. In the presence of arachidonic acid or 5,6-epoxyeicosatrienoic acid (EET), Ang II failed to stimulate the Na-HCO3 cotransporter activity in renal proximal tubules isolated from wild-type, AT1A-deficient, and cPLA2-alpha-deficient mice. In addition, Ang II failed to induce a significant ERK phosphorylation in the presence of arachidonic acid or 5,6-EET. Arachidonic acid or 5,6-EET also suppressed the stimulatory effect of Ang II on net proximal tubule bicarbonate absorption without changing cell Ca2+ concentrations. These results indicate that the cPLA2-alpha/P450/EET pathway blocks the stimulatory effect of Ang II by suppressing the ERK activation. Thus, the cPLA2-alpha/P450/EET pathway may operate as a unique negative feedback mechanism to attenuate excessive Ang II activity in the renal proximal tubules, where extremely high concentrations of Ang II are found.

Effect of 20-HETE inhibition on infarct volume and cerebral blood flow after transient middle cerebral artery occlusion

This study examined the effects of an inhibitor of 20-hydroxyeicosatetraenoic acid (20-HETE) synthesis, N-(3-chloro-4-morpholin-4-yl)phenyl-N'-hydroxyimido formamide (TS-011), on infarct volume, volume at risk, cerebral blood flow (CBF), and levels of cytochrome P450 (CYP450) eicosanoids in the brain after transient occlusion of the middle cerebral artery (t-MCAO) in rats. TS-011 (0.1 mg/kg, iv) reduced cortical infarct volume by approximately 70% and total infarct volume by 55%. TS-011 had no effect on the volume at risk or CBF during or up to 30 mins after the ischemic period. TS-011 reduced the delayed fall in CBF seen 2 h after reperfusion. The levels of CYP450 eicosanoids were similar in the ischemic and contralateral hemispheres after t-MCAO. TS-011 reduced 20-HETE levels in cerebral tissue by 80% but had no effect on the levels of EETs. Administration of another 20-HETE inhibitor, HET0016 (0.01 to 1.0 mg/kg, iv) or a 20-HETE antagonist 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (10 mg/kg, iv) also reduced infarct size. These results indicate that inhibitors of the synthesis or vasoconstrictor effects of 20-HETE reduce infarct size in rats after cerebral ischemia. The effects of TS-011 are not associated with changes in the area at risk or CBF and may be because of a potential protective effect in neurons subjected to ischemic stress.

Inhibition of arachidonic acid metabolism and its implication on cell proliferation and tumour-angiogenesis

Arachidonic acid (AA) and its metabolites have recently generated a heightened interest due to growing evidence of their significant role in cancer biology. Thus, inhibitors of the AA cascade, first and foremost COX inhibitors, which have originally been of interest in the treatment of inflammatory conditions and certain types of cardiovascular disease, are now attracting attention as an arsenal against cancer. An increasing number of investigations support their role in cancer chemoprevention, although the precise molecular mechanisms that link levels of AA, and its metabolites, with cancer progression have still to be elucidated. This article provides an overview of the AA cascade and focuses on the roles of its inhibitors and their implication in cancer treatment. In particular, emphasis is placed on the inhibition of cell proliferation and neo-angiogenesis through inhibition of the enzymes COX-2, 5-LOX and CYP450. Downstream effects of inhibition of AA metabolites are analysed and the molecular mechanisms of action of a selected number of inhibitors of catalytic pathways reviewed. Lastly, the benefits of dietary omega-3 fatty acids and their mechanisms of action leading to reduced cancer risk and impeded cancer cell growth are mentioned. Finally, a proposal is put forward, suggesting a novel and integrated approach in viewing the molecular mechanisms and complex interactions responsible for the involvement of AA metabolites in carcinogenesis and the protective effects of omega-3 fatty acids in inflammation and tumour prevention.

Effect of different antihypertensive treatments on Ras, MAPK and Akt activation in hypertension and diabetes

Ras GTPases function as transducers of extracellular signals regulating many cell functions, and they appear to be involved in the development of hypertension. In the present study, we have investigated whether antihypertensive treatment with ARBs (angiotensin II receptor blockers), ACEi (angiotensin-converting enzyme inhibitors) and diuretics induce changes in Ras activation and in some of its effectors [ERK (extracellular-signal-regulated kinase) and Akt] in lymphocytes from patients with hypertension without or with diabetes. ACEi treatment transiently reduced Ras activation in the first month of treatment, but diuretics induced a sustained increase in Ras activation throughout the 3 months of the study. In patients with hypertension and diabetes, ARB, ACEi and diuretic treatment increased Ras activation only during the first week. ACEi treatment increased phospho-ERK expression during the first week and also in the last 2 months of the study; however, diuretic treatment reduced phospho-ERK expression during the last 2 months of the study. In patients with hypertension and diabetes, antihypertensive treatments did not induce changes in phospho-ERK expression in lymphocytes. ACEi treatment reduced phospho-Akt expression in patients with hypertension and diabetes only in the first month of treatment. In conclusion, these findings show that antihypertensive treatments with ACEi, and diuretics to a lesser extent, modify Ras activation and some of its signalling pathways, although in different directions, whereas ARBs do not appear to have any influence on Ras signalling pathways.

20-HETE increases survival and decreases apoptosis in pulmonary arteries and pulmonary artery endothelial cells

20-Hydroxyeicosatetraenoic acid (20-HETE) is an endogenous cytochrome P-450 product present in vascular smooth muscle and uniquely located in the vascular endothelium of pulmonary arteries (PAs). 20-HETE enhances reactive oxygen species (ROS) production of bovine PA endothelial cells (BPAECs) in an NADPH oxidase-dependent manner and is postulated to promote angiogenesis via activation of this pathway in systemic vascular beds. We tested the capacity of 20-HETE or a stable analog of this compound, 20-hydroxy-eicosa-5(Z),14(Z)-dienoic acid, to enhance survival and protect against apoptosis in BPAECs stressed with serum starvation. 20-HETE produced a concentration-dependent increase in numbers of starved BPAECs and increased 5-bromo-2'-deoxyuridine incorporation. Caspase-3 activity, nuclear fragmentation studies, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays supported protection from apoptosis and enhanced survival of starved BPAECs treated with a single application of 20-HETE. Protection from apoptosis depended on intact NADPH oxidase, phosphatidylinositol 3 (PI3)-kinase, and ROS production. 20-HETE-stimulated ROS generation by BPAECs was blocked by inhibition of PI3-kinase or Akt activity. These data suggest 20-HETE-associated protection from apoptosis in BPAECs required activation of PI3-kinase and Akt and generation of ROS. 20-HETE also protected against apoptosis in BPAECs stressed by lipopolysaccharide, and in mouse PAs exposed to hypoxia reoxygenation ex vivo. In summary, 20-HETE may afford a survival advantage to BPAECs through activation of prosurvival PI3-kinase and Akt pathways, NADPH oxidase activation, and NADPH oxidase-derived superoxide.

Chronic blockade of 20-HETE synthesis reduces polycystic kidney disease in an orthologous rat model of ARPKD

20-Hydroxyeicosatetraenoic acid (20-HETE) has been implicated as a potential mediator in epithelial cell proliferation and cyst formation in polycystic kidney disease (PKD). In the present study, we studied the effects of chronic blockade of 20-HETE synthesis in an orthologous rodent model of autosomal recessive polycystic kidney disease (ARPKD), the PCK rat. RT-PCR analysis indicated that the expression of CYP4A1, CYP4A2, CYP4A3, and CYP4A8 mRNA was increased two- to fourfold in cystic PCK compared with noncystic Sprague-Dawley rat kidneys. Daily administration of a 20-HETE synthesis inhibitor, HET-0016 (10 mg x kg(-1) x day(-1) ip) for 4-7 wk significantly reduced kidney size by 24% from 4.95 +/- 0.19 g in vehicle-treated PCK rats to 3.76 +/- 0.15 g (n = 4). Collecting tubule morphometric cystic indices were reduced in HET-0016-treated PCK rats (2.1 +/- 0.2; n = 4) compared with vehicle-treated PCK rats (4.4 +/- 0.1; n = 4). The cellular mechanism by which 20-HETE may play a role in cyst formation has not been well characterized, but there was a significantly lower (P < 0.05) level of intracellular cAMP and decreased phosphorylation (activation) of ERK1/2 protein in PCK rat kidneys (n = 3) treated with HET-0016 . These studies indicate a potential role of 20-HETE in cyst formation in the orthologous rodent PCK model of ARPKD.

Homocysteine decreases platelet NO level via protein kinase C activation

Hyperhomocysteinaemia has been associated with increased risk of thrombosis and atherosclerosis. Homocysteine produces endothelial injury and stimulates platelet aggregation. Several molecular mechanisms related to these effects have been elucidated. The study aimed to deeply investigate the homocysteine effect on nitric oxide formation in human platelets. The homocysteine-induced changes on nitric oxide, cGMP, superoxide anion levels and nitrotyrosine formation were evaluated. The enzymatic activity and the phosphorylation status of endothelial nitric oxide synthase (eNOS) at thr495 and ser1177 residues were measured. The protein kinase C (PKC), assayed by immunofluorescence confocal microscopy technique and by phosphorylation of p47pleckstrin, and NADPH oxidase activation, tested by the translocation to membrane of the two cytosolic subunits p47(phox) and p67(phox), were assayed. Results show that homocysteine reduces platelet nitric oxide and cGMP levels. The inhibition of eNOS activity and the stimulation of NADPH oxidase primed by PKC appear to be involved. PKC stimulates the eNOS phosphorylation of the negative regulatory residue thr495 and the dephosphorylation of the positive regulatory site ser1177. GF109203X and U73122, PKC and phospholipase Cgamma2 pathway inhibitors, respectively, reverse this effect. Moreover, homocysteine stimulates superoxide anion elevation and NADPH oxidase activation. These effects are significantly decreased by GF109203X and U73122, suggesting the involvement of PKC in NADPH oxidase activation. Homocysteine induces formation of the peroxynitrite biomarker nitrotyrosine. Taken together these results suggest that the homocysteine-mediated responses leading to nitric oxide impairment are mainly coupled to PKC activation. Thus homocysteine stimulates platelet aggregation and decreases nitric oxide bioavailability.

Elevated production of 20-HETE in the cerebral vasculature contributes to severity of ischemic stroke and oxidative stress in spontaneously hypertensive rats

Hypertension is a major risk factor for stroke, but the factors that contribute to the increased incidence and severity of ischemic stroke in hypertension remain to be determined. 20-hydroxyeicosatetraenoic acid (20-HETE) has been reported to be a potent constrictor of cerebral arteries, and inhibitors of 20-HETE formation reduce infarct size following cerebral ischemia. The present study examined whether elevated production of 20-HETE in the cerebral vasculature could contribute to the larger infarct size previously reported after transient middle cerebral artery occlusion (MCAO) in hypertensive strains of rat [spontaneously hypertensive rat (SHR) and spontaneously hypertensive stroke-prone rat (SHRSP)]. The synthesis of 20-HETE in the cerebral vasculature of SHRSP measured by liquid chromatography-tandem mass spectrometry was about twice that seen in Wistar-Kyoto (WKY) rats. This was associated with the elevated expression of cytochrome P-450 (CYP)4A protein and CYP4A1 and CYP4A8 mRNA. Infarct volume after transient MCAO was greater in SHRSP (36+/-4% of hemisphere volume) than in SHR (19+/-5%) or WKY rats (5+/-2%). This was associated with a significantly greater reduction in regional cerebral blood flow (rCBF) in SHR and SHRSP than in WKY rats during the ischemic period (78% vs. 62%). In WKY rats, rCBF returned to 75% of control following reperfusion. In contrast, SHR and SHRSP exhibited a large (166+/-18% of baseline) and sustained (1 h) postischemic hyperperfusion. Acute blockade of the synthesis of 20-HETE with N-hydroxy-N'-(4-butyl-2-methylphenyl)-formamidine (HET0016; 1 mg/kg) reduced infarct size by 59% in SHR and 87% in SHRSP. HET0016 had no effect on the fall in rCBF during MCAO but eliminated the hyperemic response. HET0016 also attenuated vascular O2*- formation and restored endothelium-dependent dilation in cerebral arteries of SHRSP. These results indicate the production of 20-HETE is elevated in the cerebral vasculature of SHRSP and contributes to oxidative stress, endothelial dysfunction, and the enhanced sensitivity to ischemic stroke in this hypertensive model.

Transfer of the CYP4A region of chromosome 5 from Lewis to Dahl S rats attenuates renal injury

This study examined the effect of transfer of overlapping regions of chromosome 5 that includes (4A(+)) or excludes (4A(-)) the cytochrome P-450 4A (CYP4A) genes from the Lewis rat on the renal production of 20-hydroxyeicosatetraenoic acid (20-HETE) and the development of hypertension-induced renal disease in congenic strains of Dahl salt-sensitive (Dahl S) rats. The production of 20-HETE was higher in the outer medulla of 4A(+) than in Dahl S or 4A(-) rats. Mean arterial pressure (MAP) rose to 190 +/- 7 and 185 +/- 3 mmHg in Dahl S and 4A(-) rats fed a high-salt (HS) diet for 21 days but only to 150 +/- 5 mmHg in the 4A(+) strain. Protein excretion increased to 423 +/- 40 and 481 +/- 37 mg/day in Dahl S and 4A(-) rats vs. 125 +/- 15 mg/day in the 4A(+) strain. Baseline glomerular capillary pressure (Pgc) was lower in 4A(+) rats (38 +/- 1 mmHg) than in Dahl S rats (42 +/- 1 mmHg). Pgc increased to 50 +/- 1 mmHg in Dahl S rats fed a HS diet, whereas it remained unaltered in 4A(+) rats (39 +/- 1 mmHg). Baseline glomerular permeability to albumin (P(alb)) was lower in 4A(+) rats (0.19 +/- 0.05) than in Dahl S or 4A(-) rats (0.39 +/- 0.02). P(alb) rose to approximately 0.61 +/- 0.03 in 4A(-) and Dahl S rats fed a HS diet for 7 days, but it remained unaltered in the 4A(+) rats. The expression of transforming growth factor-beta2 was higher in glomeruli of Dahl S rats than in 4A(+) rats fed either a low-salt (LS) or HS diet. Chronic administration of a 20-HETE synthesis inhibitor (HET0016; 10 mg.kg(-1).day(-1) sc) reversed the fall in MAP and renoprotection seen in 4A(+) rats. These results indicate that the introgression of the CYP4A genes from Lewis rats into the Dahl S rats increases the renal formation of 20-HETE and attenuates the development of hypertension and renal disease.

New aspects of the role of hydroxyeicosatetraenoic acids in cell growth and cancer development

Lipoxygenase (LOX) pathway leads to the formation of leukotrienes and also catalyses the conversion of arachidonic acid (AA) to hydroperoxyeicosatetraenoic acids that are then reduced to hydroxyeicosatetraenoic acids (HETE) by glutathione peroxidase. There are four mammalian LOXs that produce 5-, 8-, 12- and 15-HETE, respectively. Cytochrome P-450 isozymes are also capable of metabolising AA to HETEs either by bis-allylic oxidation (lipoxygenase-like reaction) to generate 5-, 8-, 9-, 11-, 12- and 15-HETE; or by varpi/varpi-1 hydroxylation to yield 16-, 17-, 18-, 19- and 20-HETEs. It is now widely recognised that HETEs have important physiological and pathological functions that modulate ion transport, renal and pulmonary functions, vascular tone and reactivity, and inflammatory and growth responses. They can be released during the action of growth factors and cytokines, reaching physiological concentrations higher than that of prostanoids and modulating the functions of these factors. Their effects can occur through receptor or non-receptor mechanisms. Recent reviews have summarised the effects of HETEs in vascular homeostasis or lung and renal physiology. The present review focuses on the emerging effects of HETEs on cell signalling and physiological cell growth. It also discusses current observations regarding the role of HETEs in apoptosis, angiogenesis, the proliferation of cancer cells and metastasis, which constitute a potential area for successful therapeutic intervention.

Expression of CYP4F2 in human liver and kidney: assessment using targeted peptide antibodies

P450 enzymes comprising the human CYP4F gene subfamily are catalysts of eicosanoid (e.g., 20-HETE and leukotriene B4) formation and degradation, although the role that individual CYP4F proteins play in these metabolic processes is not well defined. Thus, we developed antibodies to assess the tissue-specific expression and function of CYP4F2, one of four CYP4F P450s found in human liver and kidney. Peptide antibodies elicited in rabbits to CYP4F2 amino acid residues 61-74 (WGHQGMVNPTEEG) and 65-77 (GMVNPTEEGMRVL) recognized on immunoblots only CYP4F2 and not CYP4F3b, CYP4F11 or CYP4F12. Immunoquantitation with anti-CYP4F2 peptide IgG showed highly variable CYP4F2 expression in liver (16.4+/-18.6pmol/mg microsomal protein; n=29) and kidney cortex (3.9+/-3.8 pmol/mg; n=10), with two subjects lacking the hepatic or renal enzyme entirely. CYP4F2 content in liver microsomes was significantly correlated (r> or =0.63; p<0.05) with leukotriene B4 and arachidonate omega-hydroxylase activities, which are both CYP4F2-catalyzed. Our study provides the first example of a peptide antibody that recognizes a single CYP4F P450 expressed in human liver and kidney, namely CYP4F2. Immunoquantitation and correlation analyses performed with this antibody suggest that CYP4F2 functions as a predominant LTB4 and arachidonate omega-hydroxylase in human liver.

20-HETE mediates proliferation of renal epithelial cells in polycystic kidney disease

Polycystic kidney diseases are characterized by abnormal proliferation of renal epithelial cells. In this study, the role of 20-hydroxyeicosatetraenoic acid (20-HETE), an endogenous cytochrome P450 metabolite of arachidonic acid with mitogenic properties, was evaluated in cystic renal disease. Daily administration of HET-0016, an inhibitor of 20-HETE synthesis, significantly reduced kidney size by half in the BPK mouse model of autosomal recessive polycystic kidney disease. In addition, compared with untreated BPK mice, this treatment significantly reduced collecting tubule cystic indices and approximately doubled survival. For evaluation of the role of 20-HETE as a mediator of epithelial cell proliferation, principal cells isolated from cystic BPK and noncystic Balb/c mice were genetically modified using lentiviral vectors. Noncystic Balb/c cells overproducing Cyp4a12 exhibited a four- to five-fold increase in cell proliferation compared with control Balb/c cells, and this increase was completely abolished when 20-HETE synthesis was inhibited; therefore, this study suggests that 20-HETE mediates proliferation of epithelial cells in the formation of renal cysts.

CaM kinase II delta2-dependent regulation of vascular smooth muscle cell polarization and migration

Previous studies indicate involvement of the multifunctional Ca2+/calmodulin-dependent protein kinase II (CaMKII) in vascular smooth muscle (VSM) cell migration. In the present study, molecular loss-of-function studies were used specifically to assess the role of the predominant CaMKII delta2 isoform on VSM cell migration using a scratch wound healing assay. Targeted CaMKII delta2 knockdown using siRNA or inhibition of activity by overexpressing a kinase-negative mutant resulted in attenuation of VSM cell migration. Temporal and spatial assessments of kinase autophosphorylation indicated rapid and transient activation in response to wounding, in addition to a sustained activation in the leading edge of migrating and spreading cells. Furthermore, siRNA-mediated suppression of CaMKII delta2 resulted in the inhibition of wound-induced Rac activation and Golgi reorganization, and disruption of leading edge morphology, indicating an important function for CaMKII delta2 in regulating VSM cell polarization. Numerous previous reports link activation of CaMKII to ERK1/2 signaling in VSM. Wound-induced ERK1/2 activation was also found to be dependent on CaMKII; however, ERK activity did not account for effects of CaMKII in regulating Golgi polarization, indicating alternative mechanisms by which CaMKII affects the complex events involved in cell migration. Wounding a VSM cell monolayer results in CaMKII delta2 activation, which positively regulates VSM cell polarization and downstream signaling, including Rac and ERK1/2 activation, leading to cell migration.

20-HETE increases renal sympathetic nerve activity via activation of chemically and mechanically sensitive muscle afferents

Arachidonic acid and its metabolites produced via cyclooxygenase (COX) and lipoxygenase pathways have been reported to contribute to the cardiovascular reflexes evoked by stimulating thin fibre muscle afferents during muscle contraction. 20-Hydroxyeicosatetraenoic acid (20-HETE), a primarily metabolized product of arachidonic acid by cytochrome P450 enzymes, can be accumulated in contracting muscles. Thus, the purpose of this study was to determine the role of 20-HETE in modulating the reflex sympathetic responses to activation of chemically and mechanically sensitive muscle afferents. The renal sympathetic nerve activity (RSNA) and cardiovascular responses were examined after injections of 20-HETE into the arterial blood supply of the hindlimb muscles of decerebrated rats. This induced a dose-dependent increases in RSNA and mean arterial pressure (MAP). We also tested the hypothesis that 20-HETE would sensitize muscle afferents and, thereby, augment the RSNA and blood pressure response to muscle stretch. The results show that arterial infusion of 20-HETE significantly enhanced the RSNA and MAP responses to muscle stretch. In contrast, N-hydroxy-N'-(4-butyl-2-methylphenyl)formamidine, a potent inhibitor of 20-HETE production, attenuated the reflex muscle responses. Furthermore, the sensitizing effect of 20-HETE on the muscle reflex was significantly attenuated after blocking COX activity with indomethacin. Our data suggest that 20-HETE plays a role in modulating muscle afferent-mediated sympathetic responses, probably through engagement of a COX-dependent mechanism.

20-Hydroxyeicosatetraenoic acid causes endothelial dysfunction via eNOS uncoupling

Nitric oxide (NO), generated from l-arginine by endothelial nitric oxide synthase (eNOS), is a key endothelial-derived factor whose bioavailability is essential to the normal function of the endothelium. Endothelium dysfunction is characterized by loss of NO bioavailability because of either reduced formation or accelerated degradation of NO. We have recently reported that overexpression of vascular cytochrome P-450 (CYP) 4A in rats caused hypertension and endothelial dysfunction driven by increased production of 20-hydroxyeicosatetraenoic acid (20-HETE), a major vasoconstrictor eicosanoid in the microcirculation. To further explore cellular mechanisms underlying CYP4A-20-HETE-driven endothelial dysfunction, the interactions between 20-HETE and the eNOS-NO system were examined in vitro. Addition of 20-HETE to endothelial cells at concentrations as low as 1 nM reduced calcium ionophore-stimulated NO release by 50%. This reduction was associated with a significant increase in superoxide production. The increase in superoxide in response to 20-HETE was prevented by NG-nitro-l-arginine methyl ester, suggesting that uncoupled eNOS is a source of this superoxide. The response to 20-HETE was specific in that 19-HETE did not affect NO or superoxide production, and, in fact, the response to 20-HETE could be competitively antagonized by 19(R)-HETE. 20-HETE had no effect on phosphorylation of eNOS protein at serine-1179 or threonine-497 following addition of calcium ionophore; however, 20-HETE inhibited association of eNOS with 90-kDa heat shock protein (HSP90). In vivo, impaired acetylcholine-induced relaxation in arteries overexpressing CYP4A was associated with a marked reduction in the levels of phosphorylated vasodilator-stimulated phosphoprotein, an indicator of bioactive NO, that was reversed by inhibition of 20-HETE synthesis or action. Because association of HSP90 with eNOS is critical for eNOS activation and coupled enzyme activity, inhibition of this association by 20-HETE may underlie the mechanism, at least in part, by which increased CYP4A expression and activity cause endothelial dysfunction.

cPLA2 phosphorylation at serine-515 and serine-505 is required for arachidonic acid release in vascular smooth muscle cells

Cytosolic phospholipase A(2) (cPLA(2)) is activated by phosphorylation at serine-505 (S505) by extracellular regulated kinase 1/2 (ERK1/2). However, rat brain calcium/calmodulin-dependent kinase II (CaMKII) phosphorylates recombinant cPLA(2) at serine-515 (S515) and increases its activity in vitro. We have studied the sites of cPLA(2) phosphorylation and their significance in arachidonic acid (AA) release in response to norepinephrine (NE) in vivo in rabbit vascular smooth muscle cells (VSMCs) using specific anti-phospho-S515- and -S505 cPLA(2) antibodies and by mutagenesis of S515 and S505 to alanine. NE increased the phosphorylation of cPLA(2) at S515, followed by phosphorylation of ERK1/2 and consequently phosphorylation of cPLA(2) at S505. The CaMKII inhibitor 2-[N-(2-hydroxyethyl)]-N-(4-methoxybenzene-sulfonyl)]amino-N-(4-chlorocinnamyl)-methylbenzylamine attenuated cPLA(2) at S515 and S505, whereas the ERK1/2 inhibitor U0126 reduced phosphorylation at S505 but not at S515. NE in cells transduced with adenovirus carrying enhanced cyan fluorescent protein cPLA(2) wild type caused phosphorylation at S515 and S505 and increased AA release. Expression of the S515A mutant in VSMCs reduced the phosphorylation of S505, ERK1/2, and AA release in response to NE. Transduction with a double mutant (S515A/S505A) blocked the phosphorylation of cPLA(2) and AA release. These data suggest that the NE-stimulated phosphorylation of cPLA(2) at S515 is required for the phosphorylation of S505 by ERK1/2 and that both sites of phosphorylation are important for AA release in VSMCs.

20-Hydroxyeicosatetraenoic acid stimulates nuclear factor-kappaB activation and the production of inflammatory cytokines in human endothelial cells

Endothelial dysfunction is associated with endothelial cell activation, i.e., up-regulation of surface cell adhesion molecules and the release of proinflammatory cytokines. 20-Hydroxyeicosatetraenoic acid (HETE), a major vasoactive eicosanoid in the microcirculation, has been implicated in the regulation of endothelial cell function through its angiogenic and pro-oxidative properties. We examined the effects of 20-HETE on endothelial cell activation in vitro. Cells transduced with adenovirus containing either CYP4A1 or CYP4A2 produced higher levels of 20-HETE, and they demonstrated increased expression levels of the adhesion molecule intercellular adhesion molecule (ICAM) (4-7-fold) and the oxidative stress marker 3-nitrotyrosine (2-3-fold) compared with cells transduced with control adenovirus. Treatment of cells with 20-HETE markedly increased levels of prostaglandin (PG) E(2) and 8-epi-isoprostane PGF(2alpha), commonly used markers of activation and oxidative stress, and most prominently, interleukin-8, a potent neutrophil chemotactic factor whose overproduction by the endothelium is a key feature of vascular injury. 20-HETE at nanomolar concentrations increased inhibitor of nuclear factor-kappaB phosphorylation by 2 to 5-fold within 5 min, which was followed with increased nuclear translocation of nuclear factor-kappaB (NF-kappaB). Likewise, 20-HETE activated the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway by stimulating phosphorylation of ERK1/2. Inhibition of NF-kappaB activation and inhibition of ERK1/2 phosphorylation inhibited 20-HETE-induced ICAM expression. It seems that 20-HETE triggers NF-kappaB and MAPK/ERK activation and that both signaling pathways participate in the cellular mechanisms by which 20-HETE activates vascular endothelial cells.

Cardioprotection from ischemia-reperfusion injury due to Ras-GTPase inhibition is attenuated by glibenclamide in the globally ischemic heart

The present study was designed to see if acute local inhibition of Ras-GTPase before or after ischemia (during perfusion) would produce protection against ischemia and reperfusion (I/R)-induced cardiac dysfunction. The effect of glibenclamide, an inhibitor of cardiac mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels, on Ras-GTPase-mediated cardioprotection was also studied. A 40 min episode of global ischemia followed by a 30 min reperfusion in perfused rat hearts produced significantly impaired cardiac function, measured as left ventricular developed pressure (P(max)) and left ventricular end-diastolic pressure (LVEDP). Perfusion with Ras-GTPase inhibitor FPT III before I/R [FPT(pre)], significantly enhanced cardiac recovery in terms of left ventricular contractility. P(max) was significantly higher at the end of 30 min reperfusion in FPT(pre)-treated hearts compared to pre-conditioned hearts. However, the degree of improvement in left ventricular contractility was significantly less when FPT III was given only after ischemia during reperfusion [FPT(post)]. Combination treatment with FPT III and glibenclamide before I/R resulted in significant reduction of FPT III-mediated cardioprotection. These data suggest that activation of Ras-GTPase signaling pathways during ischemia are critical in the development of left ventricular dysfunction and that opening of mitoK(ATP) channels, at least in part, contributes to cardioprotection produced by Ras-GTPase inhibition.

Functional effects of 20-HETE on human bronchi: hyperpolarization and relaxation due to BKCa channel activation

Airway smooth muscle (ASM) metabolizes arachidonic acid (AA) through various enzymatic pathways, including cytochrome P-450 (CYP-450) omega-hydroxylase, which leads to the production of 20-hydroxyeicosatetraenoic acid (20-HETE). The goal of this study was to delineate the mode of action of 20-HETE in human ASM cells. Isometric tension measurements demonstrated that 20-HETE induced a concentration-dependent relaxant effect in ASM on bronchi precontracted with either methacholine or AA. Relaxing effects of 20-HETE on resting tone were prevented by 10 nM iberiotoxin (IbTx), a BK(Ca) channel inhibitor. Microelectrode measurements showed that exogenous additions of 20-HETE (0.1-10 microM) hyperpolarized the membrane potential of human ASM cells. This concentration-dependent electrophysiological effect induced by the eicosanoid was prevented by 10 nM IbTx. Complementary experiments, using the planar lipid bilayer reconstitution technique, demonstrated that 20-HETE activated reconstituted BK(Ca) channels at low free Ca(2+) concentrations. Together, these results indicate that 20-HETE-dependent activation of BK(Ca) channels is responsible for the hyperpolarization and controlled relaxation of ASM in human distal bronchi.

Vascular cytochrome P450 4A expression and 20-hydroxyeicosatetraenoic acid synthesis contribute to endothelial dysfunction in androgen-induced hypertension

Epidemiological evidence suggests a role for sex-dependent mechanisms in the pathophysiology of hypertension. It has been shown that 5alpha-dihydrotestosterone (DHT) administration (56 mg/kg of body weight per day IP for 14 days) increases blood pressure, cytochrome P450 4A expression, and 20-hydroxyeicosatetraenoic acid synthesis in rats. We examined whether increased vascular 20-hydroxyeicosatetraenoic acid synthesis underlies endothelial dysfunction and hypertension in DHT-treated male Sprague-Dawley rats by using HET0016, a selective cytochrome P450 4A inhibitor. Coadministration of HET0016 (10 mg/kg per day IP for 14 days) to DHT-treated rats markedly reduced DHT-induced interlobar arterial production of 20-hydroxyeicosatetraenoic acid (14.3+/-1.5 versus 1.5+/-0.5 ng/mg of protein per hour; P<0.05), superoxide anion (246+/-47 versus 31+/-8 cpm/microg of protein), and the levels of gp91-phox, p47-phox, and 3-nitrosylated proteins. Moreover, the maximal relaxing response to acetylcholine in phenylephrine-preconstricted renal interlobar arteries from DHT-treated rats (42.8+/-4.8%) significantly (P<0.05) increased in the presence of HET0016 (81.5+/-10.8%). Importantly, the administration of HET0016 negated DHT-induced hypertension; systolic blood pressure was reduced from 146+/-2 mm Hg in DHT-treated rats to 130+/-1 mm Hg (P<0.05). The results strongly implicate vascular cytochrome P450 4A-derived 20-hydroxyeicosatetraenoic acid in the development of androgen-induced endothelial dysfunction and hypertension.

Expression and mechanism of spleen tyrosine kinase activation by angiotensin II and its implication in protein synthesis in rat vascular smooth muscle cells

Syk, a 72-kDa tyrosine kinase, is involved in development, differentiation, and signal transduction of hematopoietic and some non-hematopoietic cells. This study determined if Syk is expressed in vascular smooth muscle cells (VSMC) and contributes to angiotensin II (Ang II) signaling and protein synthesis. Syk was found in VSMC and was phosphorylated by Ang II through AT1 receptor. Ang II-induced Syk phosphorylation was inhibited by piceatannol and dominant negative but not wild type Syk mutant. Syk phosphorylation by Ang II was attenuated by cytosolic phospholipase A(2) (cPLA(2)) inhibitor pyrrolidine-1 and retrovirus carrying small interfering RNAs (shRNAs) of this enzyme. Arachidonic acid (AA) increased Syk phosphorylation, and AA- and Ang II-induced phosphorylation was diminished by inhibitors of AA metabolism (5,8,11,14-eicosatetraynoic acid) and lipoxygenase (LO; baicalein) but not cyclooxygenase (indomethacin). AA metabolites formed via LO, 5(S)-, 12(S)-, and 15(S)-hydroxyeicosatetraenoic acids, which activate p38 MAPK, increased Syk phosphorylation. p38 MAPK inhibitor SB202190, and dominant negative p38 MAPK mutant attenuated Ang II- and AA-induced Syk phosphorylation. Adenovirus dominant negative c-Src mutant abolished Ang II - and AA-induced Syk phosphorylation and SB202190, and dominant negative p38 MAPK mutant inhibited Ang II-induced c-Src phosphorylation. Syk dominant negative mutant but not epidermal growth factor receptor blocker AG1478 also inhibited Ang II-induced VSMC protein synthesis. These data suggest that Syk expressed in VSMC is activated by Ang II through p38 MAPK-activated c-Src subsequent to cytosolic phospholipase A(2) and generation of AA metabolites via LO, and it mediates Ang II-induced protein synthesis independent of epidermal growth factor receptor transactivation (Ang II --> cPLA(2) --> AA metabolites of LO --> p38 MAPK --> c-Src --> Syk --> protein synthesis).

Activation of vascular endothelial growth factor through reactive oxygen species mediates 20-hydroxyeicosatetraenoic acid-induced endothelial cell proliferation

20-Hydroxyeicosatetraenoic acid (20-HETE) is formed by the omega-hydroxylation of arachidonic acid by cytochrome P450 4A and 4F enzymes, and it induces angiogenic responses in vivo. To test the hypothesis that 20-HETE increases endothelial cell (EC) proliferation via vascular endothelial growth factor (VEGF), we studied the effects of WIT003 [20-hydroxyeicosa-5(Z),14(Z)-dienoic acid], a 20-HETE analog on human macrovascular or microvascular EC. WIT003, as well as pure 20-HETE, stimulated EC proliferation by approximately 40%. These proliferative effects were accompanied by increased VEGF expression and release that were observed as early as 4 h after 20-HETE agonist addition. This was accompanied by increased phosphorylation of the VEGF receptor 2. The proliferative effects of 20-HETE were markedly inhibited by a VEGF-neutralizing antibody. Polyethylene glycol-superoxide dismutase (PEG-SOD) markedly inhibited both the increases in VEGF expression and the proliferative effects of 20-HETE. In contrast, administration of the NAD(P)H oxidase inhibitor apocynin had no effect to the proliferative response to 20-HETE. The 20-HETE agonist markedly increased superoxide formation as reflected by an increase in dihydroethidium staining of EC, and this increase was inhibited by PEG-SOD but not by apocynin. 20-HETE also increased the phosphorylation of p42/p44 mitogen-activated protein kinase (MAPK) in EC, whereas an inhibitor of MAPK [U0126, 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene] suppressed the proliferative and the VEGF changes but not the pro-oxidant effects of 20-HETE. These data suggest that 20-HETE stimulates superoxide formation by pathways other than apocynin-sensitive NAD(P)H oxidase, thereby activating MAPK and then enhancing VEGF synthesis that drives EC proliferation. Thus, 20-HETE may be involved in the regulation of EC functions, such as angiogenesis.

20-Hydroxyeicosatetraenoic Acid (20-HETE) Stimulates Migration of Vascular Smooth Muscle Cells

AIM

We tested the hypothesis that 20-HETE production contributes to platelet derived growth factor (PDGF)-BB stimulated migration of VSMC in a cell culture model.

METHODS

Studies were performed with A10 cells which are a rat vascular smooth muscle derived cell line. Migration was determined using a Boyden chamber chemotactic assay.

RESULTS

Pre-treatment of cells with two doses of 20-HETE (100 and 500 nM) significantly increased PDGF-BB stimulated VSMC migration by 34-58% of control; whereas, prior incubation of cells with inhibitors of 20-HETE production, 17-ODYA (1-25 M) or HET0016 (100 nM), significantly decreased PDGF-BB stimulated migration by 40-90%. 20-HETE mediated increase in PDGF-BB migration was completely prevented by the 20-HETE antagonist, WIT-002. In order to determine what second messenger pathways are involved in the 20-HETE mediated stimulation of VSM migration, experiments were performed with specific inhibitors of tyrosine kinase (tyrphostin 25, 10 microM), mitogen-activated extracellular signal-regulated kinase (MEK, PD98059, 20 microM and U0126, 10 microM), protein kinase C (Myr-PKC, 50 microM), and phosphoinositide 3-kinases (PI3Ks) (wortmannin, 50 nM). Blockade of MEK and PI3K all abolished the increase in 20-HETE mediated migration.

CONCLUSION

20-HETE stimulates PDGF-mediated VSM migration acting through pathways that involve MEK and PI3K.

Emerging mechanisms for growth and protection of the vasculature by cytochrome P450-derived products of arachidonic acid and other eicosanoids

Arachidonic acid (AA) is an essential fatty acid that is metabolized by cyclooxygenase (COX), lipoxygenase (LOX) or cytochrome P450 (CYP) enzymes to generate eicosanoids which in turn mediate a number of biological activities including regulation of angiogenesis. While much information on the effects of COX and LOX products is known, the physiological relevance of the CYP-derived products of AA are less well understood. CYP enzymes are highly expressed in the liver and kidney, but have also been detected at lower levels in the brain, heart and vasculature. A number of these enzymes, including members of the CYP 4 family, predominantly catalyze conversion of AA to 20-hydroxyeicosatetraenoic acid (20-HETE) while the CYP epoxygenases generate mainly epoxyeicosatrienoic acids (EETs). This review will focus on the emerging roles of inhibitors of eicosanoid production with emphasis on the CYP pathways, in the regulation of angiogenesis and tumor growth. We also discuss current observations describing the protective effects of EETs for survival of the endothelium.

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.

Signal transduction through Ras-GTPase and Ca2+/ calmodulin-dependent protein kinase II contributes to development of diabetes-induced renal vascular dysfunction

This study examined the role of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and Ras-GTPase in the development of abnormal reactivity to vasoactive agents in the renal artery of diabetic rats. The vasoconstrictor response induced by norepinephrine (NE), endothelin-1 (ET-1) or angiotensin II (Ang II) was significantly increased whereas vasodilator response to carbachol, histamine or sodium nitroprusside (SNP) was not altered in the renal artery segments of the streptozotocin (STZ)-diabetic rats. Chronic intraperitoneal administration of KN-93 (5 mg/kg/ alt diem), an inhibitor of CaMKII or FPTIII (1.5 mg/kg/ alt diem), an inhibitor of Ras-GTPase, produced significant normalization of the altered agonist-induced vasoconstrictor responses without affecting blood glucose levels. All the inhibitors were administered for four weeks starting from day one of diabetes induction. Inhibition of Ras-GTPase or CaMKII did not affect the agonist-induced vasoconstrictor and vasodilator responses in the non-diabetic control animals. These data suggest that inhibition of signal transduction involving CaMKII and Ras-GTPase can prevent development of diabetes-induced abnormal vascular reactivity in the renal artery.