Assessment of the nitric oxide system in the heart, aorta and kidney of aged Wistar-Kyoto and spontaneously hypertensive rats

Lymphocyte-Specific Protein 1 Regulates Expression and Stability of Endothelial Nitric Oxide Synthase

Nitric oxide (NO), synthesized by endothelial nitric oxide synthase (eNOS), plays a critical role in blood pressure regulation. Genome-wide association studies have identified genetic susceptibility loci for hypertension in human lymphocyte-specific protein 1 (LSP1) gene. LSP1 is recognized as modulator of leukocyte extravasation, and endothelial permeability, however, the role of LSP1 in regulation of NO signaling within endothelial cells (ECs) remains unknown. The present study investigated the role of LSP1 in the regulation of eNOS expression and activity utilizing human macrovascular ECs in vitro and LSP1 knockout (KO) mice. In ECs, specific CRISPR-Cas9 genomic editing deleted LSP1 and caused downregulation of eNOS expression. LSP1 gain-of-function through adenovirus-mediated gene transfer was associated with enhanced expression of eNOS. Co-immunoprecipitation and confocal fluorescence microscopy revealed that eNOS and LSP1 formed a protein complex under basal conditions in ECs. Furthermore, LSP1 deficiency in mice promoted significant upregulation and instability of eNOS. Utilizing a mass-spectrometry-based bottom-up proteomics approach, we identified novel truncated forms of eNOS in immunoprecipitates from LSP1 KO aortae. Our experimental data suggest an important role of endothelial LSP1 in regulation of eNOS expression and activity within human ECs and murine vascular tissues.

Effects of Crocetin Esters and Crocetin from Crocus sativus L. on Aortic Contractility in Rat Genetic Hypertension

Background: Endothelial dysfunction, characterized by an enhancement in vasoconstriction, is clearly associated with hypertension. Saffron (Crocus sativus L.) bioactive compounds have been recognized to have hypotensive properties. Recently, we have reported that crocetin exhibits potent vasodilator effects on isolated aortic rings from hypertensive rats. In this work, we have aimed to analyze the anticontractile ability of crocetin or crocetin esters pool (crocins) isolated from saffron. Thus, we have studied the effects of saffron carotenoids on endothelium-dependent and -independent regulation of smooth muscle contractility in genetic hypertension. Methods: We have measured the isometric responses of aortic segments with or without endothelium obtained from spontaneously hypertensive rats. The effects of carotenoids were studied by assessing the endothelial modulation of phenylephrine-induced contractions (10⁻⁹–10⁻⁵ M) in the presence or absence of crocetin or crocins. The role of nitric oxide and prostanoids was analyzed by performing the experiments with L-NAME (NG-nitro-l-arginine methyl ester) or indomethacin (both 10⁻⁵ M), respectively. Results: Crocetin, and to a minor extent crocins, diminished the maximum contractility of phenylephrine in intact rings, while crocins, but not crocetin, increased this contractility in de-endothelizated vessels. In the intact vessels, the effect of crocetin on contractility was unaffected by indomethacin but was abolished by L-NAME. However, crocetin but not crocins, lowered the already increased contractility caused by L-NAME. Conclusions: Saffron compounds, but especially crocetin have endothelium-dependent prorelaxing actions. Crocins have procontractile actions that take place via smooth muscle cell mechanisms. These results suggest that crocetin and crocins activate different mechanisms involved in the vasoconstriction pathway in hypertension.

Stimulation of nitric oxide production contributes to the antiplatelet and antithrombotic effect of new peptide pENW (pGlu-Asn-Trp)

INTRODUCTION

New peptide pGlu-Asn-Trp (pENW), initially extracted from snake venom, significantly attenuates the formation of arterial and venous thrombi in vivo, and has modest in-vitro antiplatelet activity. This study was designed to investigate the underlying mechanisms.

METHODS

The rat carotid thrombosis model induced by FeCl3 was established to evaluate the antithrombotic activity of pENW. The effects of pENW on the production of nitric oxide (NO), as well as the expression and activity of endothelial nitric oxide synthase (eNOS), were determined. The vasorelaxant effect of pENW was evaluated using isolated rat aortic rings in the absence or presence of N(G)-nitro-L-arginine methyl ester (L-NAME, eNOS inhibitor). Furthermore, the in-vitro antiplatelet activity of pENW was investigated with the addition of sodium nitroprusside (SNP, NO donor) and/or L-NAME to further prove the role of NO and eNOS in the inhibitory effect of pENW on platelet aggregation.

RESULTS

In vivo, pENW inhibited thrombus formation induced by endothelial injury in a dose-dependent manner, with a significantly prolonged time to the occurrence of arterial occlusion. It was shown that pENW offered protection for blood vessels from oxidative injury. pENW significantly increased NO production in rats treated with pENW at 4 or 2mg/kg body weight. Furthermore, the production of NO from the cultured vascular endothelial cells was increased with the treatment of 10(-4)M and 10(-5)M pENW; pENW also enhanced eNOS expression and activity both in vivo and in vitro, and elicited a concentration-dependent vasorelaxation which was significantly inhibited by L-NAME. Notably, pENW inhibited ADP-induced platelet aggregation, and the inhibition was more significant in the presence of NO. The inhibition of platelet aggregation by pENW was significantly abolished by L-NAME.

CONCLUSIONS

The in-vivo antiplatelet and antithrombotic effects of pENW are at least partly mediated by the increased production of endogenous NO via up-regulation and stimulation of eNOS. The findings suggest that pENW could potentially be developed as a novel therapeutic agent in the treatment of platelet-driven disorders.

Endothelium-dependent and -independent vasorelaxant actions and mechanisms induced by total flavonoids of Elsholtzia splendens in rat aortas

Elsholtzia splendens (ES) is, rich in flavonoids, used to repair copper contaminated soil in China, which has been reported to benefit cardiovascular systems as folk medicine. However, few direct evidences have been found to clarify the vasorelaxation effect of total flavonoids of ES (TFES). The vasoactive effect of TFES and its underlying mechanisms in rat thoracic aortas were investigated using the organ bath system. TFES (5-200mg/L) caused a concentration-dependent vasorelaxation in endothelium-intact rings, which was not abolished but significantly reduced by the removal of endothelium. The nitric oxide synthase (NOS) inhibitor N(ω)-nitro-l-arginine methyl ester (100μM) and the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,2-α]quinoxalin-1-one (30μM) significantly blocked the endothelium-dependent vasorelaxation of TFES. Meanwhile, NOS activity in endothelium-intact aortas was concentration-dependently elevated by TFES. However, indomethacin (10μM) did not affect TFES-induced vasorelaxation. Endothelium-independent vasorelaxation of TFES was significantly attenuated by KATP channel blocker glibenclamide. The accumulative Ca(2+)-induced contraction in endothelium-denuded aortic rings primed with KCl or phenylephrine was markedly weakened by TFES. These results revealed that the NOS/NO/cGMP pathway is likely involved in the endothelium-dependent vasorelaxation induced by TFES, while activating KATP channel, inhibiting intracellular Ca(2+) release, blocking Ca(2+) channels and decreasing Ca(2+) influx into vascular smooth muscle cells might contribute to the endothelium-independent vasorelaxation conferred by TFES.

Contribution of caveolin-1 to ventricular nitric oxide in age-related adaptation to hypovolemic state

Our previous results have shown that hypovolemic state induced by acute hemorrhage in young anesthetized rats triggers heterogeneous and dynamic nitric oxide synthase (NOS) activation, modulating the cardiovascular response. Involvement of the nitric oxide pathway is both isoform-specific and time-dependent. The aim of the present study was to investigate changes in activity and protein levels of the different NOS forms, changes in the abundance of caveolin-1 during hypovolemic state and caveolin-1/eNOS association using young and middle-aged rats. Therefore, we studied (i) changes in NOS activity and protein levels and (ii) caveolin-1 abundance, as well as its association with endothelial NOS (eNOS) in ventricles from young and middle-aged rats during hypovolemic state. We used 2-month (young) and 12-month (middle-aged) old male Sprague-Dawley rats. Animals were divided into two groups (n=14/group): (a) sham; (b) hemorrhaged animals (20% blood loss). With advancing age, we observed an increase in ventricle NOS activity accompanied by a decrease in eNOS and caveolin-1 protein levels, but increased inducible NOS (iNOS). We also observed that aging is associated with caveolin-1 dissociation from eNOS. Myocardia from young and middle-aged rats subjected to hemorrhage-induced hypovolemia exhibited an increase in NOS activity and protein levels with a reduction in caveolin-1 abundance, accompanied by a greater dissociation between eNOS and its regulatory protein. Further, an increase in iNOS protein levels after blood loss was observed only in middle-aged rats. Our evidence suggests that aging and acute hemorrhage contribute to the development of upregulation in NOS activity. Our findings demonstrate that specific expression patterns of ventricular NOS isoforms, alterations in the amount of caveolin-1 and caveolin-1/eNOS interaction are involved in aged-related adjustment to hypovolemic state.

Attenuation of oxidative stress-induced vascular endothelial dysfunction by thymoquinone

This study aimed to assess the effects of thymoquinone (TQ) on pyrogallol-induced endothelial dysfunction in isolated rabbit aorta. The protective effects of TQ were examined by incubating aortic rings in TQ concomitant with pyrogallol. The results revealed that pyrogallol produced significant enhancement of phenylephrine-induced contraction and impairment of acetylcholine-induced relaxation. Pyrogallol caused a significant increase in lipid peroxidation and reduction in the level of superoxide dismutase and reduced glutathione in the aortic homogenates. In addition, pyrogallol produced a significant decrease in nitrite/nitrate concentrations (NOx), constitutive nitric oxide synthase (cNOS) activity and an increase in inducible nitric oxide synthase (iNOS) activity in the aortic homogenates. These changes were counteracted by TQ co-incubation as TQ attenuated pyrogallol-induced impairment in vascular reactivity in a dose-dependent manner. Furthermore, TQ showed potent antioxidant activity as well as causing a significant increase in NOx and cNOS activity, and depression in iNOS activity. These results suggest that TQ can protect against pyrogallol-induced endothelial dysfunction which probably results from its potent antioxidant capacity that leads to an increase in NO production as well as its ability to enhance the generation and bioavailability of NO.

Systemic antioxidant properties of L-carnitine in two different models of arterial hypertension

In spite of a wide range of drugs being available in the market, treatment of arterial hypertension still remains a challenge, and new therapeutic strategies could be developed in order to improve the rate of success in controlling this disease. Since oxidative stress has gained importance in the last few years as one of the mechanisms involved in the origin and development of hypertension, and considering that L-carnitine (LC) is a useful compound in different pathologies characterized by increased oxidative status, the aim of the present study was to investigate the systemic antioxidant effect of LC and its correlation to blood pressure in two experimental models of hypertension: (1) spontaneously hypertensive rats (SHR) and (2) rats with hypertension induced by N(omega)-nitro-L-arginine methyl ester (L-NAME). Treatment with captopril was also performed in SHR in order to compare the antioxidant and antihypertensive effects of LC and captopril. The antioxidant defense capacity, in terms of antioxidant enzyme activity, glutathione system availability and plasma total antioxidant capacity, was measured in both animal models with or without an oral, chronic treatment with LC. All the antioxidant parameters studied were diminished in SHR and in L-NAME-treated animals, an alteration that was in general reversed after treatments with LC and captopril. In addition, LC produced a significant but not complete reduction of systolic and diastolic blood pressure levels in these two models of hypertension, whereas captopril was able to normalize blood pressure. Both LC and captopril prevented the reduction in nitric oxide (NO) levels observed in hypertensive animals. This suggests a decrease in the systemic oxidative stress and a higher availability of NO induced by LC in a similar way to captopril's effects, which could be relevant in the management of arterial hypertension eventually.

Chronic antioxidant therapy fails to ameliorate hypertension: potential mechanisms behind

Hypertension in association with oxidative stress belongs to the most discussed topics within the literature on cardiovascular diseases. It is generally believed that elevated production of reactive oxygen species (ROS) plays an important role in hypertension, but clinical studies on chronic antioxidant therapy of hypertension fail to confirm this hypothesis. This discrepancy may be partly determined by the different effects of short and long-lasting treatment with antioxidants or scavengers. Elevated ROS production in hypertension need not be only harmful. It may also stimulate the activity of the antioxidant defence system and improve the nitric oxide (NO)/cyclic 3', 5'-guanosine monophosphate pathway, resulting in the establishment of a new equilibrium between enhanced oxidative load and the stimulated NO pathway, thus maintaining sufficient NO bioavailability. It has been suggested that antioxidant treatment might be beneficial for a short time, until increased NO generation predominates over ROS production. Further weakening of ROS formation by antioxidants may attenuate nuclear factor kappa B activation resulting in decreased endothelial NO synthase expression and activity. Prolonged antioxidant therapy may thus attenuate the beneficial regulatory effect of ROS, leading to decreased NO generation and the re-establishment of the undesirable disproportion between deleterious and protective forces. As a consequence prolonged antioxidant treatment in human hypertension may fail to provide the expected clinical profit.

Apigenin protects endothelium-dependent relaxation of rat aorta against oxidative stress

Apigenin is shown to have cardiovascular effects, but the effects of apigenin on aortas injured by exogenous oxidants are unknown. The objective of this study was to investigate the effect of apigenin on endothelium-dependent vasorelaxation in isolated rat aortic rings exposed to superoxide anion produced by pyrogallol, and its mechanism. The male Sprague-Dawley rat thoracic aorta was rapidly dissected out and the effect of apigenin on tension of aortic rings pretreated with 500 microM pyrogallol, inducing oxidative stress injury, was measured. The activity of nitric oxide synthase (NOS), the level of nitric oxide (NO) and the inhibition of superoxide anion in aortic tissues were measured. We found that pretreatment with pyrogallol concentration-dependently decreased acetylcholine-induced endothelium-dependent vasorelaxation. Apigenin (0.5-72.0 microM) evoked a concentration-dependent relaxation in aortas (pD(2): 5.304+/-0.049), which was weakened by L-NAME (the maximal relaxation fell from 87.6+/-6.7% to 37.1+/-8.8%, P<0.01), but not by aminoguanidine and indomethacin. Apigenin markedly attenuated the inhibition of vasorelaxation induced by pyrogallol (the maximal relaxation elevated from 55.8%+/-6.6% to 69.5%+/-6.4%, and the pD(2) increased from 6.559+/-0.119 to 7.057+/-0.145, P<0.01) and increased the inhibition of superoxide anion (from 94.6% to 74.5%), the NO level (from 77.1% to 94.4%), and the constitutive NOS activity (from 35.1% to 62.5%). These results indicate that pyrogallol decreased endothelium-dependent vasorelaxation in rat aortas via oxidative stress, which was markedly attenuated by apigenin. This may be mediated by weakening the oxidative stress and the NO reduction.

Loss of cardioprotection with ageing

Not only the prevalence, but also the mortality due to ischaemic cardiovascular disease is higher in older than in young humans, and the demographic shift towards an ageing population will further increase the prevalence of age-related cardiovascular disease. In order to develop strategies aimed to limit reversible and irreversible myocardial damage in older patients, there is a need to better understand age-induced alterations in protein expression and cell signalling. Cardioprotective phenomena such as ischaemic and pharmacological pre and postconditioning attenuate ischaemia/reperfusion injury in young hearts. Whether or not pre and postconditioning are still effective in aged organs, animals, or patients, i.e. under conditions where such cardioprotection is most relevant, is still a matter of debate; most studies suggest a loss of protection in aged hearts. The present review discusses changes in protein expression and cell signalling important to ischaemia/reperfusion injury with myocardial ageing. The efficacy of cardioprotective manoeuvres, e.g. ischaemic pre and postconditioning in aged organs and animals will be discussed, and the development of strategies aimed to antagonize the age-induced loss of protection will be addressed.

Effects of pioglitazone and rosiglitazone on aortic vascular function in rat genetic hypertension

Glitazones have beneficial antihypertensive effects independent of their insulin-sensitizing action. We have studied the effects of pioglitazone and rosiglitazone on the endothelial ability to counteract vascular smooth muscle contractility in genetic hypertension. To achieve this, we measured isometric responses of aortic segments obtained from spontaneously hypertensive rats. The effects of glitazones on endothelial function were studied by assessing the endothelial modulation of phenylephrine-induced isometric contractions (10(-9)-10(-5) M) in the presence or absence of pioglitazone or rosiglitazone (10(-5) M), added directly to an organ bath or orally administered to the rats (pioglitazone, 10 mg/kg). The role of both NO and prostanoids was analyzed by performing experiments in the presence of N(G)-nitro-L-arginine methyl ester (L-NAME) and/or indomethacin (both 10(-5) M) in the organ bath. Concentration-dependent contractions to L-NAME (10(-6)-3 x 10(-4) M) in the presence or absence of glitazones were carried out as an estimation of basal NO release. Pioglitazone, but not rosiglitazone, increased contractile responses to phenylephrine in intact vessels. The contractile responses to phenylephrine obtained in the presence of glitazones were markedly diminished by indomethacin, but enhanced by L-NAME. Analogous results were obtained in aortas from pioglitazone-chronically treated animals. L-NAME concentration-dependent contractions were enhanced by both glitazones. Both glitazones lowered the sensitivity to acetylcholine (10(-9)-10(-5) M). In conclusion, pioglitazone and rosiglitazone alter vascular function differentially and through endothelium-dependent mechanisms. These drugs act over the same pathways on the endothelium where they have a dual action, increasing both production of vasoconstrictor prostanoids and NO. The balance between both vasoactive substances determines the vascular response to glitazones.

The senescence-accelerated mouse (SAM-P8) as a model for the study of vascular functional alterations during aging

We studied vascular function in quiescent aortas from senescence-accelerated resistant (SAM-R1) and prone (SAM-P8) mice. Myographical studies of thoracic aorta segments from 6-7 month-old mice showed that the contractility of SAM-P8 aortas was markedly higher than that of SAM-R1 after KCl depolarization or phenylephrine addition. Acetylcholine dose-response relaxation curves revealed that SAM-R1 vessels were slightly more sensitive than those of SAM-P8. In the presence of the NO synthase inhibitor, L-NAME, all vessels displayed contractions to acetylcholine, but these were more distinct in the SAM-R1. Phenylephrine plus L-NAME displayed stronger contractions in both animal strains, but were markedly more pronounced in SAM-R1. The cyclooxygenase inhibitor, indomethacin did not change the vessel responses to acetylcholine or phenylephrine. These data indicate that NO synthase, not cyclooxygenase, was responsible for the differences in contractility. Standard histology and immunohistochemistry of endothelial NO synthase revealed no differences in the expression of this protein. In contrast, increased levels of malondialdehyde were found in SAM-P8 vessels. We conclude that SAM-P8 vessels exhibit higher contractility than those of SAM-R1. Furthermore, our results suggest that the endothelium of SAM-P8 vessels is dysfunctional and lacks normal capability to counteract smooth muscle contraction. Therefore, our findings support SAM-P8 as a suitable model for the study of vascular physiological changes during aging.

Interleukin-2 protects against endothelial dysfunction induced by high glucose levels in rats

AIMS

Interleukin-2 (IL-2) can modulate cardiovascular functions, but the effect of IL-2 on vascular endothelial function in diabetes is not known. We hypothesized that IL-2 may attenuate endothelial dysfunction induced by high glucose or diabetes. So the aim of this study was to investigate the effect of IL-2 on endothelium-response of aortas incubated with high glucose or from diabetic rats and its underlying mechanism.

METHODS

Acetylcholine (ACh)-induced endothelium-dependent relaxation (EDR), sodium nitroprusside (SNP)-induced endothelium-independent relaxation (EIR), superoxide dismutase (SOD) and nitric oxide synthase (NOS) were measured in aortas isolated from non-diabetic rats and exposed to a high glucose concentration and from streptozotocin-induced diabetic rats.

RESULTS

Incubation of aortic rings with high glucose (44 mM) for 4 h resulted in a significant inhibition of EDR, but had no effects on EIR. Co-incubation with IL-2 for 40 min prevented the inhibition of EDR caused by high glucose in a concentration-dependent manner. Similarly, high glucose decreased SOD and NOS activity in aortic tissue. IL-2 (1000 U/ml) significantly attenuated the decrease of SOD and NOS activity caused by high glucose. In addition, EDR declined along with the decrease of serum NO level in aortas from STZ-induced diabetic rats. Injection of IL-2 (5000 and 50,000 U kg(-1) d(-1), s.c.) for 5 weeks prevented the inhibition of EDR and the decrease of serum NO levels caused by diabetes.

CONCLUSIONS

IL-2 significantly ameliorated the endothelial dysfunction induced by hyperglycemia, in which the activation of the NO pathway and SOD may be involved.

Current concepts in diabetic gastroparesis

Diabetic gastroparesis is a common and debilitating condition affecting millions of patients with diabetes mellitus worldwide. Although gastroparesis in diabetes has been known clinically for more than 50 years, treatment options remain very limited. Until recently, the scientific literature has offered few clues regarding the precise aetiology of gastric dysfunction in diabetes.Up to 50% of patients with diabetes may experience postprandial abdominal pain, nausea, vomiting and bloating secondary to gastric dysfunction. There is no clear association between length of disease and the onset of delayed gastric emptying. Gastroparesis affects both type 1 (insulin dependent) and type 2 (non- insulin dependent) forms of diabetes. Diagnosis requires identifying the proper symptom complex, while excluding other entities (peptic ulcer disease, rheumatological diseases, medication effects). The diagnosis of gastroparesis may be confirmed by demonstrating gastric emptying delay during a 4-hour scintigraphic study. Treatment options are limited and rely on dietary modifications, judicious use of available pharmacological agents, and occasionally surgical or endoscopic placement of gastrostomies or jejunostomies. Gastric pacing offers promise for patients with medically refractory gastroparesis but awaits further investigation. Current pharmacological agents for treating gastroparesis include metoclopramide, erythromycin, cisapride (only available via a company-sponsored programme) and domperidone (not US FDA approved). All of these drugs act as promotility agents that increase the number or the intensity of gastric contractions. These medications are not uniformly effective and all have adverse effects that limit their use. Cisapride has been removed from the open market as a result of over 200 reported cases of cardiac toxicity attributed to its use. Unfortunately, there is a paucity of clinical studies that clearly define the efficacy of these agents in diabetic gastroparesis and there are no studies that compare these drugs to each other. The molecular pathophysiology of diabetic gastroparesis is unknown, limiting the development of rational therapies. New studies, primarily in animals, point to a defect in the enteric nervous system as a major molecular cause of abnormal gastric motility in diabetes. This defect is characterised by a loss of nitric oxide signals from nerves to muscles in the gut resulting in delayed gastric emptying. Novel therapies designed to augment nitric oxide signalling are being studied.