Targeted disruption of soluble epoxide hydrolase reveals a role in blood pressure regulation

Renal microsomal cytochrome P-450 monooxygenase-dependent metabolism of arachidonic acid generates a series of regioisomeric epoxyeicosatrienoic acids that can be further metabolized by soluble epoxide hydrolase to the corresponding dihydroxyeicosatrienoic acids. Evidence exists that these metabolites affect renal function and, in particular, blood pressure regulation. To examine this possibility, blood pressure and renal arachidonic acid metabolism were examined in mice with a targeted disruption of the soluble epoxide hydrolase gene. Systolic blood pressure of male soluble epoxide hydrolase-null mice was lower compared with wild-type mice in both the absence and presence of dietary salt loading. Both female soluble epoxide hydrolase-null and wild-type female mice also had significantly lower systolic blood pressure than male wild-type mice. Renal formation of epoxyeicosatrienoic and dihydroxyeicosatrienoic acids was markedly lower for soluble epoxide hydrolase-null versus wild-type mice of both sexes. Although disruption of soluble epoxide hydrolase in female mice had minimal effects on blood pressure, deletion of this gene feminized male mice by lowering systolic blood pressure and altering arachidonic acid metabolism. These data provide the first direct evidence for a role for soluble epoxide hydrolase in blood pressure regulation and identify this enzyme as a novel and attractive target for therapeutic intervention in hypertension.     

Decreased epoxygenase and increased epoxide hydrolase expression in the mesenteric artery of obese Zucker rats

Previous studies suggest that epoxyeicosatrienoic acids (EETs) are vasodilators of the mesenteric artery; however, the production and regulation of EETs in the mesenteric artery remain unclear. The present study was designed 1) to determine which epoxygenase isoform may contribute to formation of EETs in mesenteric arteries and 2) to determine the regulation of mesenteric artery cytochrome P-450 (CYP) enzymes in obese Zucker rats. Microvessels were incubated with arachidonic acid, and CYP enzyme activity was determined. Mesenteric arteries demonstrate detectable epoxygenase and hydroxylase activities. Next, protein and mRNA expressions were determined in microvessels. Although renal microvessels express CYP2C23 mRNA and protein, mesenteric arteries lacked CYP2C23 expression. CYP2C11 and CYP2J mRNA and protein were expressed in mesenteric arteries and renal microvessels. In addition, mesenteric artery protein expression was evaluated in lean and obese Zucker rats. Compared with lean Zucker rats, mesenteric arterial CYP2C11 and CYP2J proteins were decreased by 38 and 43%, respectively, in obese Zucker rats. In contrast, soluble epoxide hydrolase mRNA and protein expressions were significantly increased in obese Zucker rat mesenteric arteries. In addition, nitric oxide-independent dilation evoked by acetylcholine was significantly attenuated in mesenteric arteries of obese Zucker rats. These data suggest that the main epoxygenase isoforms expressed in mesenteric arteries are different from those expressed in renal microvessels and that decreased epoxygenases and increased soluble epoxide hydrolase are associated with impaired mesenteric artery dilator function in obese Zucker rats.     

Perinatally administered losartan augments renal ACE2 expression but not cardiac or renal Mas receptor in spontaneously hypertensive rats

Since the identification of the alternative angiotensin converting enzyme (ACE)2/Ang‐(1‐7)/Mas receptor axis, renin‐angiotensin system (RAS) is a new complex target for a pharmacological intervention. We investigated the expression of RAS components in the heart and kidney during the development of hypertension and its perinatal treatment with losartan in young spontaneously hypertensive rats (SHR). Expressions of RAS genes were studied by the RT‐PCR in the left ventricle and kidney of rats: normotensive Wistar, untreated SHR, SHR treated with losartan since perinatal period until week 9 of age (20 mg/kg/day) and SHR treated with losartan only until week 4 of age and discontinued until week 9. In the hypertrophied left ventricle of SHR, cardiac expressions of Ace and Mas were decreased while those of AT1 receptor (Agtr1a) and Ace2 were unchanged. Continuous losartan administration reduced LV weight (0.43 ± 0.02; P < 0.05 versus SHR) but did not influence altered cardiac RAS expression. Increased blood pressure in SHR (149 ± 2 in SHR versus 109 ± 2 mmHg in Wistar; P < 0.05) was associated with a lower renal expressions of renin, Agtr1a and Mas and with an increase in ACE2. Continuous losartan administration lowered blood pressure to control levels (105 ± 3 mmHg; P < 0.05 versus SHR), however, only renal renin and ACE2 were significantly up‐regulated (for both P < 0.05 versus SHR). Conclusively, prevention of hypertension and LV hypertrophy development by losartan was unrelated to cardiac or renal expression of Mas. Increased renal Ace2, and its further increase by losartan suggests the influence of locally generated Ang‐(1‐7) in organ response to the developing hypertension in SHRs.     

Compensatory mechanism for homeostatic blood pressure regulation in Ephx2 gene-disrupted mice

Arachidonic acid-derived epoxides, epoxyeicosatrienoic acids, are important regulators of vascular homeostasis and inflammation, and therefore manipulation of their levels is a potentially useful pharmacological strategy. Soluble epoxide hydrolase converts epoxyeicosatrienoic acids to their corresponding diols, dihydroxyeicosatrienoic acids, modifying or eliminating the function of these oxylipins. To better understand the phenotypic impact of Ephx2 disruption, two independently derived colonies of soluble epoxide hydrolase-null mice were compared. We examined this genotype evaluating protein expression, biofluid oxylipin profile, tissue oxylipin production capacity, and blood pressure. Ephx2 gene disruption eliminated soluble epoxide hydrolase protein expression and activity in liver, kidney, and heart from each colony. Plasma levels of epoxy fatty acids were increased, and fatty acid diols levels were decreased, while measured levels of lipoxygenase- and cyclooxygenase-dependent oxylipins were unchanged. Liver and kidney homogenates also show elevated epoxide fatty acids. However, in whole kidney homogenate a 4-fold increase in the formation of 20-hydroxyeicosatetraenoic acid was measured along with a 3-fold increase in lipoxygenase-derived hydroxylation and prostanoid production. Unlike previous reports, however, neither Ephx2-null colony showed alterations in basal blood pressure. Finally, the soluble epoxide hydrolase-null mice show a survival advantage following acute systemic inflammation. The data suggest that blood pressure homeostasis may be achieved by increasing production of the vasoconstrictor, 20-hydroxyeicosatetraenoic acid in the kidney of the Ephx2-null mice. This shift in renal metabolism is likely a metabolic compensation for the loss of the soluble epoxide hydrolase gene.     

Angiotensin II receptor type 1 (AT1) selective nonpeptidic antagonists--a perspective

Hypertension is a major risk factor for human morbidity and mortality through its effects on target organs like heart, brain and kidneys. More intensive treatment for the effective control of blood pressure significantly reduces the morbidity and mortality. The renin angiotensin system (RAS) is a coordinated hormonal cascade of major clinical importance in the regulation of blood pressure. The principal effector peptide of RAS is angiotensin II, which acts by binding to one of the two major angiotensin II receptors AT(1) and AT(2). Angiotensin II through AT(1) receptor mediates vast majority of biologically detrimental actions. Nonpeptidic angiotensin II (AT(1)) antagonists are the most specific means to block the renin angiotensin enzymatic cascade available presently. Majority of AT(1) antagonists are based on modifications of losartan structure, the first clinically used AT(1) antagonist. In this review, a comprehensive presentation of the literature on AT(1) receptor antagonists has been given.     

Effect of an ACE inhibitor and an AT1 receptor antagonist on cardiac hypertrophy

The effect of long-term administration of delapril, an angiotensin converting enzyme inhibitor, and candesartan, an angiotensin II receptor blocker, on cardiac hypertrophy was investigated in spontaneously hypertensive rats (SHR). Delapril (2 mg/kg/day) and candesartan (2 mg/kg/day) were administered for 5 weeks to 15-week-old male SHR. Echocardiographic estimation of cardiac morphology and function revealed cardiac hypertrophy in SHR compared with Wistar-Kyoto rats (WKY) which were used as normal controls. Both treated groups revealed regression of cardiac hypertrophy estimated by echocardiography. Heart to body weight ratio of treated SHR was also smaller than that of untreated SHR. Plasma BNP and ANP concentrations were increased in untreated SHR and decreased in the treated groups. Histological examination was performed using light microscopy and the area of fibrosis was estimated by computer. Reduction of the fibrotic area was observed in SHR treated with delapril and candesartan, although the latter was not statistically significant. Immunohistochemical examination using anti-collagen monoclonal antibody showed a decrease of type I collagen in treated SHR as compared with untreated SHR. It is concluded that both angiotensin converting enzyme inhibitor and angiotensin II receptor blocker sufficiently reduce blood pressure in SHR associated with regression of cardiac remodeling.     

Genetic disruption of soluble epoxide hydrolase is protective against streptozotocin-induced diabetic nephropathy

Cytochrome P-450 (CYP) epoxygenases metabolize arachidonic acid into epoxyeicosatrienoic acids (EETs), which play important roles in regulating cardiovascular functions. The anti-inflammatory, antiapoptotic, proangiogenic, and antihypertensive properties of EETs suggest a beneficial role for EETs in diabetic nephropathy. Endogenous EET levels are maintained by a balance between synthesis by CYP epoxygenases and hydrolysis by epoxide hydrolases into physiologically less active dihydroxyeicosatrienoic acids. Genetic disruption of soluble epoxide hydrolase (sEH/EPHX2) results in increased EET levels through decreased hydrolysis. This study investigated the effects of sEH gene disruption on diabetic nephropathy in streptozotocin-induced diabetic mice. Streptozotocin-induced diabetic manifestations were attenuated in sEH-deficient mice relative to wild-type controls, with significantly decreased levels of Hb A(1c), creatinine, and blood urea nitrogen and urinary microalbumin excretion. The sEH-deficient diabetic mice also had decreased renal tubular apoptosis that coincided with increased levels of antiapoptotic Bcl-2 and Bcl-xl, and decreased levels of the proapoptotic Bax. These effects were associated with activation of the PI3K-Akt-NOS3 and AMPK signaling cascades. sEH gene inhibition and exogenous EETs significantly protected HK-2 cells from TNFα-induced apoptosis in vitro. These findings highlight the beneficial role of the CYP epoxygenase-EETs-sEH system in the pathogenesis of diabetic nephropathy and suggest that the sEH inhibitors available may be potential therapeutic agents for this condition.     

Nerve stimulation induced overflow of neuropeptide Y and modulation by angiotensin II in spontaneously hypertensive rats

The sympathetic nervous system and renin-angiotensin system are both thought to contribute to the development and maintenance of hypertension in experimental models such as the spontaneously hypertensive rat (SHR). We demonstrated that periarterial nerve stimulation (NS) increased the perfusion pressure (PP) and neuropeptide Y (NPY) overflow from perfused mesenteric arterial beds of SHRs at 4-6, 10-12, and 18-20 wk of age, which correspond to prehypertensive, developing hypertensive, and maintained hypertensive stages, respectively, in the SHR. NS also increased PP and NPY overflow from mesenteric beds of Wistar-Kyoto (WKY) normotensive rats. NS-induced increases in PP and NPY were greater in vessels obtained from SHRs of all three ages compared with WKY rats. ANG II produced a greater increase in PP in preparations taken from SHRs than WKY rats. ANG II also resulted in a greater increase in basal NPY overflow from 10- to 12-wk-old and 18- to 20-wk-old SHRs than age-matched WKY rats. ANG II enhanced the NS-induced overflow of NPY from SHR preparations more than WKY controls at all ages studied. The enhancement of NS-induced NPY overflow by ANG II was blocked by the AT1 receptor antagonist EMD-66684 and the angiotensin type 2 receptor antagonist PD-123319. In contrast, ANG II greatly enhanced norepinephrine overflow in the presence of PD-123319. Both captopril and EMD-66684 decreased neurotransmitter overflow from SHR mesenteric beds; therefore, we conclude that an endogenous renin-angiotensin system is active in this preparation. It is concluded that the ANG II-induced enhancement of sympathetic nerve stimulation may contribute to the development and maintenance of hypertension in the SHR.     

Chronic renin inhibition with aliskiren improves glucose tolerance, insulin sensitivity, and skeletal muscle glucose transport activity in obese Zucker rats

We have demonstrated previously that overactivity of the renin-angiotensin system (RAS) is associated with whole body and skeletal muscle insulin resistance in obese Zucker (fa/fa) rats. Moreover, this obesity-associated insulin resistance is reduced by treatment with angiotensin-converting enzyme inhibitors or angiotensin receptor (type 1) blockers. However, it is currently unknown whether specific inhibition of renin itself, the rate-limiting step in RAS functionality, improves insulin action in obesity-associated insulin resistance. Therefore, the present study assessed the effect of chronic, selective renin inhibition using aliskiren on glucose tolerance, whole body insulin sensitivity, and insulin action on the glucose transport system in skeletal muscle of obese Zucker rats. Obese Zucker rats were treated for 21 days with either vehicle or aliskiren (50 mg/kg body wt ip). Renin inhibition was associated with a significant lowering (10%, P < 0.05) of resting systolic blood pressure and induced reductions in fasting plasma glucose (11%) and free fatty acids (46%) and homeostatic model assessment for insulin resistance (13%). Glucose tolerance (glucose area under the curve) and whole body insulin sensitivity (inverse of the glucose-insulin index) during an oral glucose tolerance test were improved by 15% and 16%, respectively, following chronic renin inhibition. Moreover, insulin-stimulated glucose transport activity in isolated soleus muscle of renin inhibitor-treated animals was increased by 36% and was associated with a 2.2-fold greater Akt Ser(473) phosphorylation. These data provide evidence that chronic selective inhibition of renin activity leads to improvements in glucose tolerance and whole body insulin sensitivity in the insulin-resistant obese Zucker rat. Importantly, chronic renin inhibition is associated with upregulation of insulin action on skeletal muscle glucose transport, and it may involve improved Akt signaling. These data support the strategy of targeting the RAS to improve both blood pressure regulation and insulin action in conditions of insulin resistance.     

Urotensin II-induced hypotensive responses in Wistar-Kyoto (Wky) and spontaneously hypertensive (Shr) rats

Human urotensin II (hU-II) is a potent vasoactive peptide which modulates some of the functions of the cardiovascular and other systems. The in vivo mechanism of action by which hU-II may influence blood pressure in developmental and pathological conditions, is poorly understood. Herein, the blood pressure effects of hU-II (0.1-10 nmol/kg) injected intravenously (i.v.) were studied on ketamine/xylazine anesthetized male WKY and SHR rats aged 4 and 8 weeks. hU-II elicited dose-dependent decreases in mean arterial pressure in both strains of animals. The hypotensive responses to hU-II were, however, significantly higher in SHR rats, independently of age. Four-week-old SHR rats (which are normotensive) were, however, less responsive than their hypertensive 8-week-old counterparts. A series of pharmacological inhibitors were used to identify putative endogenous (endothelial) factors that might account for the hU-II-mediated hypotension in 8-week-old SHR. These include the non-selective nitric oxide synthase inhibitor L-NAME (5 micromol/kg), the non-selective cyclooxygenase inhibitor meclofenamate (16 micromol/kg), the voltage-sensitive and ATP-sensitive K+-channel inhibitors, 4-aminopyridine (5 micromol/kg) and glybenclamide (10 micromol/kg), the cytochrome P450 CYP2C9 inhibitor sulfaphenazole (15 micromol/kg), the cytoskeletal fixation agent phalloidin (15 micromol/kg), the endothelin ETB receptor antagonist BQ-788(35 micromol/kg), the bradykinin B2 receptor antagonist HOE 140 (0.5 micromol/kg), the angiotensin AT2 antagonist PD 123319(10 micromol/kg) and the UT receptor antagonist urantide (10 micromol/kg). These agents were administered i.v. either at 2.5, 10 or 40 min prior hU-II injection (10 nmol/kg). Among these inhibitors, sulfaphenazole and phalloidin were able to reduce hU-II-induced hypotension. This suggests that the vasodepressor effect of hU-II is mediated by UT receptors and relies in part on the release of epoxide related products; increased microvascular permeability may also contribute to the blood pressure lowering effect of hU-II. Since urantide blocks the constrictor effects of hU-II on isolated aorta, but is inactive against the hypotensive action of hU-II in vivo, the results presented in this paper provide, for the first time, evidence for the existence of two different functional sites for hU-II.     

A new look at the renin-angiotensin system--focusing on the vascular system

The renin–angiotensin system (RAS), critically involved in the control of blood pressure and volume homeostasis, is a dual system comprising a circulating component and a local tissue component. The rate limiting enzyme is renin, which in the circulating RAS derives from the kidney to generate Ang II, which in turn regulates cardiovascular function by binding to AT₁ and AT₂ receptors on cardiac, renal and vascular cells. The tissue RAS can operate independently of the circulating RAS and may be activated even when the circulating RAS is suppressed or normal. A functional tissue RAS has been identified in brain, kidney, heart, adipose tissue, hematopoietic tissue, gastrointestinal tract, liver, endocrine system and blood vessels. Whereas angiotensinsinogen, angiotensin converting enzyme (ACE), Ang I and Ang II are synthesized within these tissues, there is still controversy as to whether renin is produced locally or whether it is taken up from the circulation, possibly by the (pro)renin receptor. This is particularly true in the vascular wall, where expression of renin is very low. The exact function of the vascular RAS remains elusive, but may contribute to fine-tuning of vascular tone and arterial structure and may amplify vascular effects of the circulating RAS, particularly in pathological conditions, such as in hypertension, atherosclerosis and diabetes. New concepts relating to the vascular RAS have recently been elucidated including: (1) the presence of functionally active Ang-(1-7)-Mas axis in the vascular system, (2) the importance of the RAS in perivascular adipose tissue and cross talk with vessels, and (3) the contribution to vascular RAS of Ang II derived from immune and inflammatory cells within the vascular wall. The present review highlights recent progress in the RAS field, focusing on the tissue system and particularly on the vascular RAS.     

Alterations in aortic vascular reactivity to angiotensin 1-7 in 17-beta-estradiol-treated female SD rats

Estrogen's suggested cardio-protective effects have come into question following the results of recent clinical trials. Two major components of the renin-angiotensin system (RAS) that are modulated by estrogen are angiotensin converting enzyme, and the angiotensin II type 1 receptor. Further research has revealed several new components of the RAS, including angiotensin converting enzyme 2, its peptide product angiotensin 1-7 (Ang 1-7), and that peptide's receptor, Mas. These components appear to oppose the classical effects of the RAS, and may act to buffer the RAS in vivo. Recent work has shown that during pregnancy, when estradiol levels are elevated, renal and urinary Ang 1-7 are greatly increased. This study examined the effects of estradiol on the efficacy of Ang 1-7 in the rat aorta. Female Sprague-Dawley rats were ovariectomized and a subgroup was chronically treated with subcutaneous pellets of estradiol for 3 weeks. Thoracic aortas were harvested for assessment of in vitro vascular reactivity to Ang 1-7. The results demonstrated that increased estradiol exposure attenuated the relaxation response to Ang 1-7 in a dose-dependent manner. These findings are in contrast to recent work showing potentiated responses to Ang 1-7 in mesenteric arteries from estrogen-manipulated rats, and may suggest a regional specificity in estradiol-mediated changes in the RAS.     

Sexual dimorphism in the renin-angiotensin system in aging spontaneously hypertensive rats

In young adult spontaneously hypertensive rats (SHR), mean arterial pressure (MAP) is higher in males than in females and inhibition of the renin-angiotensin system (RAS) eliminates this sex difference. After cessation of estrous cycling in female SHR, MAP is similar to that in male SHR. The purpose of this study was to determine the role of the RAS in maintenance of hypertension in aging male and female SHR. At 16 mo of age, MAP was similar in male and female SHR (183+/-5 vs. 193+/-8 mmHg), and chronic losartan (40 mg.kg-1.day-1 po for 3 wk) reduced MAP by 52% (to 90+/-8 mmHg, P<0.05 vs. control) in males and 37% (to 123+/-11 mmHg, P<0.05 vs. control) in females (P<0.05, females vs. males). The effect of losartan on angiotensin type 1 (AT1) receptor blockade was similar: MAP responses to acute doses of ANG II (62.5-250 ng/kg) were blocked to a similar extent in losartan-treated males and females. F2-isoprostane excretion was reduced with losartan more in males than in females. There were no sex differences in plasma renin activity, plasma angiotensinogen or ANG II, or renal expression of AT1 receptors, angiotensin-converting enzyme, or renin. However, renal angiotensinogen mRNA and protein expression was higher in old males than females, whereas renal ANG II was higher in old females than males. The data show that, in aging SHR, when blood pressures are similar, there remains a sexual dimorphism in the response to AT1 receptor antagonism, and the differences may involve sex differences in mechanisms responsible for oxidative stress with aging.     

Renal expression of arachidonic acid metabolizing enzymes and RhoA/Rho kinases in fructose insulin resistant hypertensive rats

Fructose feeding has been shown to induce insulin resistance and hypertension. Renal protein expression for the cytochrome P (CYP) 450 arachidonic acid metabolizing enzymes has been shown to be altered in other models of diet-induced hypertension. Of special interest is CYP4A, which produces the potent vasoconstrictor, 20-hydroxyeicosatetraenoic acid and CYP2C, which catalyzes the formation of the potent dilators epoxyeicosatrienoic acids as well as soluble epoxide hydrolase (sEH) which metabolizes the latter to dihydroxyeicosatrienoic acids. The RhoA/Rho kinase (ROCK) signaling pathway is downstream of arachidonic acid and is reported to mediate metabolic-cardio-renal dysfunctions in some experimental models of insulin resistance and diabetes. The aim of the present study was to determine the expression of CYP4A, CYP2C23, CYP2C11, sEH, RhoA, ROCK-1, ROCK-2, and phospho-Lin-11/Isl-1/Mec-3 kinase (LIMK) in kidneys of fructose-fed (F) rats. Male Wistar rats were fed a high fructose diet for 8 weeks. Body weight, systolic blood pressure, insulin sensitivity, and renal expression of the aforementioned proteins were assessed. No change was observed in the body weight of F rats; however, euglycemia and hyperinsulinemia implicating impaired glucose tolerance and significant elevation in systolic blood pressure were observed. Renal expression of CYP4A and CYP2C23 was significantly increased while that of CYP2C11 and sEH was not changed in F rats. Equal expression for RhoA in both control and F rats and an enhanced level of ROCK-1 and ROCK-2 constitutively activate 130 kDa cleavage fragments as well as phospho-LIMK. These data suggest that the kidneys could be actively participating in the pathogenesis of insulin resistance-induced hypertension through the arachidonic acid CYP 450-RhoA/Rho kinase pathway(s).     

Regional differences in sexually dimorphic protein expression in the spontaneously hypertensive rat (SHR)

Hypertension is sexually dimorphic and modified by removal of endogenous sex steroids. This study tested the hypothesis that endogenous gonadal hormones exert differential effects on protein expression in the kidney and mesentery of SHR. At ~5 weeks of age male and female SHR underwent sham operation, orchidectomy, or ovariectomy (OVX). At 20-23 weeks of age, mean arterial pressure (MAP) was measured in conscious rats. The mesenteric arterial tree and kidneys were collected, processed for Western blots, and probed for Cu Zn superoxide dismutase (SOD1), soluble epoxide hydrolase (sEH), and Alpha 2A adrenergic receptor (A2AR) expression. MAP was unaffected by ovariectomy (Sham 164 ± 4: Ovariecttomy 159 ± 3 mm Hg). MAP was reduced by orchidectomy (Sham 189 ± 5:Orchidectomy 167 ± 2 mm Hg). In mesenteric artery, SOD1 expression was greater in male versus female SHR. Orchidectomy increased while ovariectomy decreased SOD1 expression. The kidney exhibited a different pattern of response. SOD1 expression was reduced in male compared to female SHR but gonadectomy had no effect. sEH expression was not significantly different among the groups in mesenteric artery. In kidney, sEH expression was greater in males compared to females. Ovariectomy but not orchidectomy increased sEH expression. A2AR expression was greater in female than male SHR in mesentery artery and kidney. Gonadectomy had no effect in either tissue. We conclude that sexually dimorphic hypertension is associated with regionally specific changes in expression of three key proteins involved in blood pressure control. These data suggest that broad spectrum inhibition or stimulation of these systems may not be the best approach for hypertension treatment. Instead regionally targeted manipulation of these systems should be investigated.     

The adipose tissue renin-angiotensin system and metabolic disorders: a review of molecular mechanisms

The renin-angiotensin system (RAS) is classically known for its role in regulation of blood pressure, fluid and electrolyte balance. In this system, angiotensinogen (Agt), the obligate precursor of all bioactive angiotensin peptides, undergoes two enzymatic cleavages by renin and angiotensin converting enzyme (ACE) to produce angiotensin I (Ang I) and angiotensin II (Ang II), respectively. The contemporary view of RAS has become more complex with the discovery of additional angiotensin degradation pathways such as ACE2. All components of the RAS are expressed in and have independent regulation of adipose tissue. This local adipose RAS exerts important auto/paracrine functions in modulating lipogenesis, lipolysis, adipogenesis as well as systemic and adipose tissue inflammation. Mice with adipose-specific Agt overproduction have a 30% increase in plasma Agt levels and develop hypertension and insulin resistance, while mice with adipose-specific Agt knockout have a 25% reduction in Agt plasma levels, demonstrating endocrine actions of adipose RAS. Emerging evidence also points towards a role of RAS in regulation of energy balance. Because adipose RAS is overactivated in many obesity conditions, it is considered a potential candidate linking obesity to hypertension, insulin resistance and other metabolic derangements.     

The adipose tissue renin-angiotensin system and metabolic disorders: a review of molecular mechanisms

The renin-angiotensin system (RAS) is classically known for its role in regulation of blood pressure, fluid and electrolyte balance. In this system, angiotensinogen (Agt), the obligate precursor of all bioactive angiotensin peptides, undergoes two enzymatic cleavages by renin and angiotensin converting enzyme (ACE) to produce angiotensin I (Ang I) and angiotensin II (Ang II), respectively. The contemporary view of RAS has become more complex with the discovery of additional angiotensin degradation pathways such as ACE2. All components of the RAS are expressed in and have independent regulation of adipose tissue. This local adipose RAS exerts important auto/paracrine functions in modulating lipogenesis, lipolysis, adipogenesis as well as systemic and adipose tissue inflammation. Mice with adipose-specific Agt overproduction have a 30% increase in plasma Agt levels and develop hypertension and insulin resistance, while mice with adipose-specific Agt knockout have a 25% reduction in Agt plasma levels, demonstrating endocrine actions of adipose RAS. Emerging evidence also points towards a role of RAS in regulation of energy balance. Because adipose RAS is overactivated in many obesity conditions, it is considered a potential candidate linking obesity to hypertension, insulin resistance and other metabolic derangements.     

Effects of des-aspartate-angiotensin I on the actions of angiotensin III in the renal and mesenteric vasculature of normo- and hypertensive rats

An earlier study showed that des-aspartate-angiotensin I (DAA-I) attenuated the pressor action of angiotensin III in aortic rings of the spontaneously hypertensive rat (SHR) but not the normotensive Wistar Kyoto (WKY) rat. The present study investigated similar properties of DAA-I in isolated perfused kidneys and mesenteric beds of WKY and SHR. In the renal vasculature, angiotensin III induced a dose-dependent pressor response, which was more marked in the SHR than WKY in terms of significant greater magnitude of response and lower threshold. DAA-I attenuated the pressor action of angiotensin III in both the WKY and SHR. The attenuation in SHR was much more marked, occurring at doses as low as 10⁻¹⁵ M DAA-I, while effective attenuation was only seen with 10⁻⁹ M in WKY. The effects of DAA-I was not inhibited by PD123319 and indomethacin, indicating that its action was not mediated by angiotensin AT₂ receptors and prostaglandins. However, the direct pressor action of angiotensin III in the SHR but not the WKY was attenuated by indomethacin suggesting that this notable difference could be due to known decreased response of renal vasculature to vasodilator prostaglandins in the SHR. Pressor responses to angiotensin III in the mesenteric vascular bed was also dose dependent, but smaller in magnitude compared to the renal response. The responses in the SHR, though generally smaller, were not significantly different from those of the WKY. This trend is in line with the similar observations with angiotensin III and II by other investigators. In terms of the effect of DAA-I, indomethacin and PD123319 on angiotensin III action, similar patterns to those of the renal vasculature were observed. This reaffirms that in the perfused kidney and mesenteric bed, where the majority of the vessels are contractile, femtomolar concentrations of DAA-I attenuates the pressor action of angiotensin III. The attenuation is not indomethacin sensitive and does not involve the angiotensin AT₂ receptor. The findings suggest that DAA-I possesses protective vascular actions and is involved in the pathophysiology of hypertension.     

Synthesis and structure–activity relationship of piperidine-derived non-urea soluble epoxide hydrolase inhibitors

A series of potent amide non-urea inhibitors of soluble epoxide hydrolase (sEH) is disclosed. The inhibition of soluble epoxide hydrolase leads to elevated levels of epoxyeicosatrienoic acids (EETs), and thus inhibitors of sEH represent one of a novel approach to the development of vasodilatory and anti-inflammatory drugs. Structure–activities studies guided optimization of a lead compound, identified through high-throughput screening, gave rise to sub-nanomolar inhibitors of human sEH with stability in human liver microsomal assay suitable for preclinical development.