Antihypertensive therapy increases tetrahydrobiopterin levels and NO/cGMP signaling in small arteries of angiotensin II-infused hypertensive rats

Endothelial histone deacetylase 1 activity impairs kidney microvascular NO signaling in rats fed a high-salt diet

AIM

We aimed to test the hypothesis that a high-salt diet (HS) impairs NO signaling in kidney microvascular endothelial cells through a histone deacetylase 1 (HDAC1)-dependent mechanism.

METHODS

Male Sprague Dawley rats were fed normal salt diet (NS; 0.49% NaCl) or HS (4% NaCl) for 2 weeks. NO signaling was assessed by measuring L-NAME induced vasoconstriction of the afferent arteriole using the blood perfused juxtamedullary nephron (JMN) preparation. In this preparation, kidneys were perfused with blood from a donor rat on a matching or different diet to that of the kidney donor. Kidney endothelial cells were isolated with magnetic activated cell sorting and HDAC1 activity was measured.

RESULTS

We found HS-induced impaired NO signaling in the afferent arteriole. This was restored by inhibition of HDAC1 with MS-275. Consistent with these findings, HDAC1 activity was increased in kidney endothelial cells. We further found the loss of NO to be dependent upon the diet of the blood donor rather than the diet of the kidney donor and the plasma from HS-fed rats to be sufficient to induce impaired NO signaling. This indicates the presence of a humoral factor we termed plasma-derived endothelial dysfunction mediator (PDEM). Pretreatment with the antioxidants, PEG-SOD and PEG-catalase, as well as the NOS cofactor, tetrahydrobiopterin, restored NO signaling.

CONCLUSION

We conclude that HS activates endothelial HDAC1 through PDEM leading to decreased NO signaling. This study provides novel insights into the molecular mechanisms by which a HS decreases renal microvascular endothelial NO signaling.

Endothelial Histone Deacetylase 1 Activity Impairs Kidney Microvascular NO Signaling in Rats fed a High Salt Diet

Aim

We aimed to identify new mechanisms by which a high salt diet (HS) decreases NO production in kidney microvascular endothelial cells. Specifically, we hypothesized HS impairs NO signaling through a histone deacetylase 1 (HDAC1)-dependent mechanism.

Methods

Male Sprague Dawley rats were fed normal salt diet (NS; 0.49% NaCl) or high salt diet (4% NaCl) for two weeks. NO signaling was assessed by measuring L-NAME induced vasoconstriction of the afferent arteriole using the blood perfused juxtamedullary nephron (JMN) preparation. In this preparation, kidneys were perfused with blood from a donor rat on a matching or different diet to that of the kidney donor. Kidney endothelial cells were isolated with magnetic activated cell sorting and HDAC1 activity was measured.

Results

We found that HS impaired NO signaling in the afferent arteriole. This was restored by inhibition of HDAC1 with MS-275. Consistent with these findings, HDAC1 activity was increased in kidney endothelial cells. We further found the loss of NO to be dependent upon the diet of the blood donor rather than the diet of the kidney donor and the plasma from HS fed rats to be sufficient to induce dysfunction suggesting a humoral factor, we termed Plasma Derived Endothelial-dysfunction Mediator (PDEM), mediates the endothelial dysfunction. The antioxidants, PEG-SOD and PEG-catalase, as well as the NOS cofactor, tetrahydrobiopterin, restored NO signaling.

Conclusion

We conclude that HS activates endothelial HDAC1 through PDEM leading to decreased NO signaling. This study provides novel insights into the molecular mechanisms by which a HS decreases renal microvascular endothelial NO signaling.

Cell-To-Cell Communication in the Resistance Vasculature

The arterial vasculature can be divided into large conduit arteries, intermediate contractile arteries, resistance arteries, arterioles, and capillaries. Resistance arteries and arterioles primarily function to control systemic blood pressure. The resistance arteries are composed of a layer of endothelial cells oriented parallel to the direction of blood flow, which are separated by a matrix layer termed the internal elastic lamina from several layers of smooth muscle cells oriented perpendicular to the direction of blood flow. Cells within the vessel walls communicate in a homocellular and heterocellular fashion to govern luminal diameter, arterial resistance, and blood pressure. At rest, potassium currents govern the basal state of endothelial and smooth muscle cells. Multiple stimuli can elicit rises in intracellular calcium levels in either endothelial cells or smooth muscle cells, sourced from intracellular stores such as the endoplasmic reticulum or the extracellular space. In general, activation of endothelial cells results in the production of a vasodilatory signal, usually in the form of nitric oxide or endothelial-derived hyperpolarization. Conversely, activation of smooth muscle cells results in a vasoconstriction response through smooth muscle cell contraction. © 2022 American Physiological Society. Compr Physiol 12: 1-35, 2022.

Placental Ischemia Says "NO" to Proper NOS-Mediated Control of Vascular Tone and Blood Pressure in Preeclampsia

In this review, we first provide a brief overview of the nitric oxide synthase (NOS) isoforms and biochemistry. This is followed by describing what is known about NOS-mediated blood pressure control during normal pregnancy. Circulating nitric oxide (NO) bioavailability has been assessed by measuring its metabolites, nitrite (NO₂) and/or nitrate (NO₃), and shown to rise throughout normal pregnancy in humans and rats and decline postpartum. In contrast, placental malperfusion/ischemia leads to systemic reductions in NO bioavailability leading to maternal endothelial and vascular dysfunction with subsequent development of hypertension in PE. We end this article by describing emergent risk factors for placental malperfusion and ischemic disease and discussing strategies to target the NOS system therapeutically to increase NO bioavailability in preeclamptic patients. Throughout this discussion, we highlight the critical importance that experimental animal studies have played in our current understanding of NOS biology in normal pregnancy and their use in finding novel ways to preserve this signaling pathway to prevent the development, treat symptoms, or reduce the severity of PE.

Network Pharmacology Prediction and Pharmacological Verification Mechanism of Yeju Jiangya Decoction on Hypertension

Background

Yeju Jiangya decoction (CIF) is an herbal formula from traditional Chinese medicine (TCM) for the treatment of hypertension.

Materials and Methods

Based on the analysis of network pharmacology, combined with in animal experiments, the network pharmacology was used to explore the potential proteins and mechanisms of CIF against hypertension. The bioactive compounds of CIF were screened by using the platform, and the targets of hypertension and CIF were collected. Then, the Kyoto Encyclopedia of Genes and Genomes (KEGG) and protein-protein interaction network (PPI) core targets were carried out, and the useful proteins were found by molecular docking technology. Finally, we used N-nitro-L-arginine (L-NNA) induced hypertension model rats to confirm the effect and mechanism of CIF on hypertension.

Results

14 bioactive compounds of CIF passed the virtual screening criteria, and 178 overlapping targets were identified as core targets of CIF against hypertension. The CIF-related target network with 178 nodes and 344 edges is constructed. The topological results show that quercetin and luteolin are the key components in the network. The key targets NOS3 (nitric oxide synthase 3) and NOS2 (nitric oxide synthase 2) were screened by the protein-protein interaction network. The analysis of target protein pathway enrichment showed that the accumulation pathway is related to the vascular structure of CIF regulation of hypertension. Further verification based on molecular docking results showed that NOS3 had the good binding ability with quercetin and luteolin. On the other hand, NOS3 has an important relationship with the composition of blood vessels. Furthermore, the animal experiment indicated that after the L-NNA-induced hypertension rat model was established, CIF intervention was given by gavage for 3 weeks, and it can decrease serum concentrations of endothelin-1 (ET-1) and thromboxane B2 (TXB₂), increase the expression of nitric oxide (NO) and prostacyclin 2 (PGI₂), and improve renal, cardiac, and aortic lesions. At the same time, it can reduce blood pressure and shorten vertigo time. Western blot (WB) and immunohistochemistry (IHC) analyses indicated that CIF may downregulate the expression of NOS3, guanylyl cyclase-alpha 1 (GC-α1), guanylyl cyclase-alpha 2 (GC-α2), and protein kinase CGMP-dependent 1 (PRKG1). These results suggest that CIF may play an antihypertensive role by inhibiting the activation of the NOS3/PRKG1 pathway.

Conclusions

The results of this study indicate that CIF has the ability to improve target organs, protect endothelial function, and reduce blood pressure and that CIF might be a potential therapeutic drug for the prevention of hypertension. It provides new insight into hypertension and the potential biological basis and mechanism for CIF clinical research.

The Roles of Nitric Oxide Synthase/Nitric Oxide Pathway in the Pathology of Vascular Dementia and Related Therapeutic Approaches

Vascular dementia (VaD) is the second most common form of dementia worldwide. It is caused by cerebrovascular disease, and patients often show severe impairments of advanced cognitive abilities. Nitric oxide synthase (NOS) and nitric oxide (NO) play vital roles in the pathogenesis of VaD. The functions of NO are determined by its concentration and bioavailability, which are regulated by NOS activity. The activities of different NOS subtypes in the brain are partitioned. Pathologically, endothelial NOS is inactivated, which causes insufficient NO production and aggravates oxidative stress before inducing cerebrovascular endothelial dysfunction, while neuronal NOS is overactive and can produce excessive NO to cause neurotoxicity. Meanwhile, inflammation stimulates the massive expression of inducible NOS, which also produces excessive NO and then induces neuroinflammation. The vicious circle of these kinds of damage having impacts on each other finally leads to VaD. This review summarizes the roles of the NOS/NO pathway in the pathology of VaD and also proposes some potential therapeutic methods that target this pathway in the hope of inspiring novel ideas for VaD therapeutic approaches.

Hypertension, dietary salt and cognitive impairment

Dementia is growing at an alarming rate worldwide. Although Alzheimer disease is the leading cause, over 50% of individuals diagnosed with Alzheimer disease have vascular lesions at autopsy. There has been an increasing appreciation of the pathogenic role of vascular risk factors in cognitive impairment caused by neurodegeneration. Midlife hypertension is a leading risk factor for late-life dementia. Hypertension alters cerebrovascular structure, impairs the major factors regulating the cerebral microcirculation, and promotes Alzheimer pathology. Experimental studies have identified brain perivascular macrophages as the major free radical source mediating neurovascular dysfunction of hypertension. Recent evidence indicates that high dietary salt may also induce cognitive impairment. Contrary to previous belief, the effect is not necessarily associated with hypertension and is mediated by a deficit in endothelial nitric oxide. Collectively, the evidence suggests a remarkable cellular diversity of the impact of vascular risk factors on the cerebral vasculature and cognition. Whereas long-term longitudinal epidemiological studies are needed to resolve the temporal relationships between vascular risk factors and cognitive dysfunction, single-cell molecular studies of the vasculature in animal models will provide a fuller mechanistic understanding. This knowledge is critical for developing new preventive, diagnostic, and therapeutic approaches for these devastating diseases of the mind.

Superoxide Dismutase Activity in Small Mesenteric Arteries Is Downregulated by Angiotensin II but Not by Hypertension

Many studies reported reduced antioxidant capacity in the vasculature under hypertensive conditions. However, little is known about the effects of antihypertensive treatments on the regulation of vascular antioxidant enzymes. Thus, we hypothesized that antihypertensive treatments prevent the reduction of antioxidant enzyme activity and expression in the small vessels of angiotensin II-induced hypertensive rats (ANG). We observed the small mesenteric arteries and small renal vessels of normotensive rats (NORM), ANG, and ANG treated with a triple antihypertensive therapy of reserpine, hydrochlorothiazide, and hydralazine (ANG + TTx). Systolic blood pressure was increased in ANG, which was attenuated by 2 weeks of triple therapy (127, 191, and 143 mmHg for NORM, ANG, and ANG + TTx, respectively; p < 0.05). Total superoxide dismutase (SOD) activity in the small mesenteric arteries of ANG was lower than that of NORM. The protein expression of SOD1 was lower in ANG than in NORM, whereas SOD2 and SOD3 expression was not different between the groups. Reduced SOD activity and SOD1 expression in ANG was not restored in ANG + TTx. Both SOD activity and SOD isoform expression in the small renal vessels of ANG were not different from those of NORM. Interestingly, SOD activity in the small renal vessels was reduced by TTx. Between groups, there was no difference in catalase activity or expression in both the small mesenteric arteries and small renal vessels. In conclusion, SOD activity in the small mesenteric arteries decreased by angiotensin II administration, but not by hypertension, which is caused by decreased SOD1 expression.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Impaired Endothelial Nitric Oxide Synthase Homodimer Formation Triggers Development of Transplant Vasculopathy - Insights from a Murine Aortic Transplantation Model

Transplant vasculopathy (TV) represents a major obstacle to long-term graft survival and correlates with severity of ischemia reperfusion injury (IRI). Donor administration of the nitric oxide synthases (NOS) co-factor tetrahydrobiopterin has been shown to prevent IRI. Herein, we analysed whether tetrahydrobiopterin is also involved in TV development. Using a fully allogeneic mismatched (BALB/c to C57BL/6) murine aortic transplantation model grafts subjected to long cold ischemia time developed severe TV with intimal hyperplasia (α-smooth muscle actin positive cells in the neointima) and endothelial activation (increased P-selectin expression). Donor pretreatment with tetrahydrobiopterin significantly minimised these changes resulting in only marginal TV development. Severe TV observed in the non-treated group was associated with increased protein oxidation and increased occurrence of endothelial NOS monomers in the aortic grafts already during graft procurement. Tetrahydrobiopterin supplementation of the donor prevented all these early oxidative changes in the graft. Non-treated allogeneic grafts without cold ischemia time and syngeneic grafts did not develop any TV. We identified early protein oxidation and impaired endothelial NOS homodimer formation as plausible mechanistic explanation for the crucial role of IRI in triggering TV in transplanted aortic grafts. Therefore, targeting endothelial NOS in the donor represents a promising strategy to minimise TV.

Angiotensin II stimulates superoxide production by nitric oxide synthase in thick ascending limbs

Angiotensin II (Ang II) causes nitric oxide synthase (NOS) to become a source of superoxide (O2 (-)) via a protein kinase C (PKC)-dependent process in endothelial cells. Ang II stimulates both NO and O2 (-) production in thick ascending limbs. We hypothesized that Ang II causes O2 (-) production by NOS in thick ascending limbs via a PKC-dependent mechanism. NO production was measured in isolated rat thick ascending limbs using DAF-FM, whereas O2 (-) was measured in thick ascending limb suspensions using the lucigenin assay. Consistent stimulation of NO was observed with 1 nmol/L Ang II (P < 0.001; n = 9). This concentration of Ang II-stimulated O2 (-) production by 50% (1.77 ± 0.26 vs. 2.62 ± 0.36 relative lights units (RLU)/s/μg protein; P < 0.04; n = 5). In the presence of the NOS inhibitor L-NAME, Ang II-stimulated O2 (-) decreased from 2.02 ± 0.29 to 1.10 ± 0.11 RLU/s/μg protein (P < 0.01; n = 8). L-arginine alone did not change Ang II-stimulated O2 (-) (2.34 ± 0.22 vs. 2.29 ± 0.29 RLU/s/μg protein; n = 5). In the presence of Ang II plus the PKC α/β1 inhibitor Gö 6976, L-NAME had no effect on O2 (-) production (0.78 ± 0.23 vs. 0.62 ± 0.11 RLU/s/μg protein; n = 7). In the presence of Ang II plus apocynin, a NADPH oxidase inhibitor, L-NAME did not change O2 (-) (0.59 ± 0.04 vs. 0.61 ± ×0.08 RLU/s/μg protein; n = 5). We conclude that: (1) Ang II causes NOS to produce O2 (-) in thick ascending limbs via a PKC- and NADPH oxidase-dependent process; and (2) the effect of Ang II is not due to limited substrate.

Regulation of myogenic tone and structure of parenchymal arterioles by hypertension and the mineralocorticoid receptor

Proper perfusion is vital for maintenance of neuronal homeostasis and brain function. Changes in the function and structure of cerebral parenchymal arterioles (PAs) could impair blood flow regulation and increase the risk of cerebrovascular diseases, including dementia and stroke. Hypertension alters the structure and function of large cerebral arteries, but its effects on PAs remain unknown. We hypothesized that hypertension increases myogenic tone and induces inward remodeling in PAs; we further proposed that antihypertensive therapy or mineralocorticoid receptor (MR) blockade would reverse the effects of hypertension. PAs from 18-wk-old stroke-prone spontaneously hypertensive rats (SHRSP) were isolated and cannulated in a pressure myograph. At 50-mmHg intraluminal pressure, PAs from SHRSP showed higher myogenic tone (%tone: 39.1 ± 1.9 vs. 28.7 ± 2.5%, P < 0.01) and smaller resting luminal diameter (34.7 ± 1.9 vs. 46.2 ± 2.4 μm, P < 0.01) than those from normotensive Wistar-Kyoto rats, through a mechanism that seems to require Ca(2+) influx through L-type voltage-gated Ca(2+) channels. PAs from SHRSP showed inward remodeling (luminal diameter at 60 mmHg: 55.2 ± 1.4 vs. 75.7 ± 5.1 μm, P < 0.01) and a paradoxical increase in distensibility and compliance. Treatment of SHRSP for 6 wk with antihypertensive therapy reduced PAs' myogenic tone, increased their resting luminal diameter, and prevented inward remodeling. In contrast, treatment of SHRSP for 6 wk with an MR antagonist did not reduce blood pressure or myogenic tone, but prevented inward remodeling. Thus, while hypertensive remodeling of PAs may involve the MR, myogenic tone seems to be independent of MR activity.

An acute rise in intraluminal pressure shifts the mediator of flow-mediated dilation from nitric oxide to hydrogen peroxide in human arterioles

Endothelial nitric oxide (NO) is the primary mediator of flow-mediated dilation (FMD) in human adipose microvessels. Impaired NO-mediated vasodilation occurs after acute and chronic hypertension, possibly due to excess generation of reactive oxygen species (ROS). The direct role of pressure elevation in this impairment of human arteriolar dilation is not known. We tested the hypothesis that elevation in pressure is sufficient to impair FMD. Arterioles were isolated from human adipose tissue and cannulated, and vasodilation to graded flow gradients was measured before and after exposure to increased intraluminal pressure (IILP; 150 mmHg, 30 min). The mediator of FMD was determined using pharmacological agents to reduce NO [N(G)-nitro-l-arginine methyl ester (l-NAME), 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO)], or H2O2 [polyethylene glycol (PEG)-catalase], and mitochondrial (mt) ROS was quantified using fluorescence microscopy. Exposure to IILP decreased overall FMD (max %dilation: 82.7 ± 4.9 vs. 62 ± 5.6; P < 0.05). This dilation was abolished by treatment with l-NAME prepressure and PEG-catalase after IILP (max %dilation: l-NAME: 23.8 ± 6.1 vs. 74.8 ± 8.6; PEG-catalase: 71.8 ± 5.9 vs. 24.6 ± 10.6). To examine if this change was mediated by mtROS, FMD responses were measured in the presence of the complex I inhibitor rotenone or the mitochondrial antioxidant mitoTempol. Before IILP, FMD was unaffected by either compound; however, both inhibited dilation after IILP. The fluorescence intensity of mitochondria peroxy yellow 1 (MitoPY1), a mitochondria-specific fluorescent probe for H2O2, increased during flow after IILP (%change from static: 12.3 ± 14.5 vs. 127.9 ± 57.7). These results demonstrate a novel compensatory dilator mechanism in humans that is triggered by IILP, inducing a change in the mediator of FMD from NO to mitochondria-derived H2O2.

Crucial role for neuronal nitric oxide synthase in early microcirculatory derangement and recipient survival following murine pancreas transplantation

OBJECTIVE

Aim of this study was to identify the nitric oxide synthase (NOS) isoform involved in early microcirculatory derangements following solid organ transplantation.

BACKGROUND

Tetrahydrobiopterin donor treatment has been shown to specifically attenuate these derangements following pancreas transplantation, and tetrahydrobiopterin-mediated protective effects to rely on its NOS-cofactor activity, rather than on its antioxidant capacity. However, the NOS-isoform mainly involved in this process has still to be defined.

METHODS

Using a murine pancreas transplantation model, grafts lacking one of the three NOS-isoforms were compared to grafts from wild-type controls. Donors were treated with either tetrahydrobiopterin or remained untreated. All grafts were subjected to 16 h cold ischemia time and transplanted into wild-type recipients. Following 4 h graft reperfusion, microcirculation was analysed by confocal intravital fluorescence microscopy. Recipient survival was monitored for 50 days.

RESULTS

Transplantation of the pancreas from untreated wild-type donor mice resulted in microcirculatory damage of the transplanted graft and no recipient survived more than 72 h. Transplanting grafts from untreated donor mice lacking either endothelial or inducible NOS led to similar outcomes. In contrast, donor treatment with tetrahydrobiopterin prevented microcirculatory breakdown enabling long-term survival. Sole exception was transplantation of grafts from untreated donor mice lacking neuronal NOS. It resulted in intact microvascular structure and long-term recipient survival, either if donor mice were untreated or treated with tetrahydrobiopterin.

CONCLUSION

We demonstrate for the first time the crucial involvement of neuronal NOS in early microcirculatory derangements following solid organ transplantation. In this model, protective effects of tetrahydrobiopterin are mediated by targeting this isoform.

Tetrahydrobiopterin in cardiovascular health and disease

Tetrahydrobiopterin (BH4) functions as a cofactor for several important enzyme systems, and considerable evidence implicates BH4 as a key regulator of endothelial nitric oxide synthase (eNOS) in the setting of cardiovascular health and disease. BH4 bioavailability is determined by a balance of enzymatic de novo synthesis and recycling, versus degradation in the setting of oxidative stress. Augmenting vascular BH4 levels by pharmacological supplementation has been shown in experimental studies to enhance NO bioavailability. However, it has become more apparent that the role of BH4 in other enzymatic pathways, including other NOS isoforms and the aromatic amino acid hydroxylases, may have a bearing on important aspects of vascular homeostasis, inflammation, and cardiac function. This article reviews the role of BH4 in cardiovascular development and homeostasis, as well as in pathophysiological processes such as endothelial and vascular dysfunction, atherosclerosis, inflammation, and cardiac hypertrophy. We discuss the therapeutic potential of BH4 in cardiovascular disease states and attempt to address how this modulator of intracellular NO-redox balance may ultimately provide a powerful new treatment for many cardiovascular diseases.

Differential regulation of nitric oxide synthase function in aorta and tail artery from 5/6 nephrectomized rats

Chronic renal failure (CRF) is associated with hypertension and concomitant endothelial dysfunction, enhanced vasoconstriction, and nitric oxide synthase (NOS) dysfunction. Vascular function in patients is assessed in peripheral extremity arteries like the finger arteries, whereas animal studies often use the centrally located aorta. Therefore, we examined whether peripheral tail artery and aortic NOS function are differentially regulated by blood pressure in rats with CRF. Using wire myography, arterial function was assessed in 16-week-old Sprague-Dawley rats that were subjected to 5/6 nephrectomy (Nx; arterial ligation model) 8 weeks earlier or non-Nx (control) rats. In aortas from Nx rats, endothelial-dependent vasorelaxation response to acetylcholine (ACh) was blunted and there was enhancement of phenylephrine (PE)-mediated vasoconstriction. Inversely, tail arteries from Nx rats had no change in endothelial function and reduced response to PE. Studies where arterial segments were incubated with the nonspecific NOS inhibitor, L-NAME, showed that Nx reduced NOS function in the aorta but increased NOS function in tail artery for both ACh and PE responses. Furthermore, the observed alterations in NOS function in both aorta and tail artery were abolished when mean arterial blood pressure, as assessed by telemetry, was maintained at normal levels in the 5/6 Nx rats using triple therapy: hydralazine (30 mg/kg per day), hydrochlorothiazide (10 mg/kg per day), and reserpine (0.5 mg/kg per day). In conclusion, differential changes of NOS function in central versus peripheral arteries in CRF are dependent upon hypertension.

Tetrahydrobiopterin has a glucose-lowering effect by suppressing hepatic gluconeogenesis in an endothelial nitric oxide synthase-dependent manner in diabetic mice

Endothelial nitric oxide synthase (eNOS) dysfunction induces insulin resistance and glucose intolerance. Tetrahydrobiopterin (BH4) is an essential cofactor of eNOS that regulates eNOS activity. In the diabetic state, BH4 is oxidized to 7,8-dihydrobiopterin, which leads to eNOS dysfunction owing to eNOS uncoupling. The current study investigates the effects of BH4 on glucose metabolism and insulin sensitivity in diabetic mice. Single administration of BH4 lowered fasting blood glucose levels in wild-type mice with streptozotocin (STZ)-induced diabetes and alleviated eNOS dysfunction by increasing eNOS dimerization in the liver of these mice. Liver has a critical role in glucose-lowering effects of BH4 through suppression of hepatic gluconeogenesis. BH4 activated AMP kinase (AMPK), and the suppressing effect of BH4 on gluconeogenesis was AMPK-dependent. In addition, the glucose-lowering effect and activation of AMPK by BH4 did not appear in mice with STZ-induced diabetes lacking eNOS. Consecutive administration of BH4 in ob/ob mice ameliorated glucose intolerance and insulin resistance. Taken together, BH4 suppresses hepatic gluconeogenesis in an eNOS-dependent manner, and BH4 has a glucose-lowering effect as well as an insulin-sensitizing effect in diabetic mice. BH4 has potential in the treatment of type 2 diabetes.

Female SHR have greater blood pressure sensitivity and renal T cell infiltration following chronic NOS inhibition than males

Nitric oxide is a critical regulator of blood pressure (BP) and inflammation, and female spontaneously hypertensive rats (SHR) have higher renal nitric oxide bioavailability than males. We hypothesize that female SHR will have a greater rise in BP and renal T cell infiltration in response to nitric oxide synthase (NOS) inhibition than males. Both male and female SHR displayed a dose-dependent increase in BP to the nonspecific NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME: 2, 5, and 7 mg·kg(-1)·day(-1) for 4 days each); however, females exhibited a greater increase in BP than males. Treatment of male and female SHR with 7 mg·kg(-1)·day(-1) L-NAME for 2 wk significantly increased BP in both sexes; however, prior exposure to L-NAME only increased BP sensitivity to chronic NOS inhibition in females. L-NAME-induced hypertension increased renal T cell infiltration and indices of renal injury in both sexes, yet female SHR exhibited greater increases in Th17 cells and greater decreases in regulatory T cells than males. Chronic L-NAME was also associated with larger increases in renal cortical adhesion molecule expression in female SHR. The use of triple therapy to block L-NAME-mediated increases in BP attenuated L-NAME-induced increases in renal T cell counts and normalized adhesion molecule expression in SHR, suggesting that L-NAME-induced increases in renal T cells were dependent on both increases in BP and NOS inhibition. Our data suggest that NOS is critical in the ability of SHR, females in particular, to maintain BP and limit a pro-inflammatory renal T cell profile.

Short-term hypercaloric diet induces blunted aortic vasoconstriction and enhanced vasorelaxation via increased nitric oxide synthase 3 activity and expression in Dahl salt-sensitive rats

AIM

To elucidate the role of the O(2)(-), H(2)O(2) or NO pathways in aortic angiotensin (Ang)II-induced vasoconstriction in Dahl salt-sensitive (SS) rats compared with control SS-13(BN) rats on a normal or hypercaloric diet.

METHODS

Aortic function was assessed using wire myography in 16-week-old rats maintained on a normal diet or a 4-week hypercaloric diet. Nitric oxide synthase (NOS) activity and expression was determined by the conversion of radio-labelled arginine to citrulline and Western blot analysis respectively.

RESULTS

On normal diet, AngII-induced vasoconstriction was greater in SS than SS-13(BN) rats. Polyethylene glycol superoxide dismutase (PEG-SOD) reduced the aortic AngII response similarly in both strains on normal diet. Catalase blunted, whereas N(ω)-Nitro-L-arginine methyl ester (L-NAME) did not affect the AngII response in SS rats. In SS-13(BN) rats, catalase had no effect and L-NAME enhanced AngII response. On hypercaloric diet, aortic AngII responsiveness was reduced in SS but unaltered in SS-13(BN) rats compared with their normal diet counterparts. PEG-SOD reduced the AngII response in both rats on hypercaloric diet. Catalase treatment did not alter aortic AngII response, while L-NAME increased the response in SS rats on hypercaloric diet. In SS-13(BN) rats on hypercaloric diet, catalase reduced and L-NAME did not alter the AngII response. Furthermore, aortic endothelial-dependent vasorelaxation was increased in SS rats on hypercaloric diet compared with normal diet and aortic NOS3 activity and expression was increased.

CONCLUSION

A short-term hypercaloric diet induces a blunted vasoconstrictive and enhanced vasodilatory phenotype in SS rats, but not in SS-13(BN) rats, via reduced H(2)O(2) and increased NOS3 function.

Oxidative stress, Noxs, and hypertension: experimental evidence and clinical controversies

Reactive oxygen species (ROS) are signaling molecules that influence many physiological processes. Increased ROS bioavailability and altered redox signaling (oxidative stress) have been implicated in chronic diseases including hypertension. Although oxidative stress may not be the sole cause of hypertension, it amplifies blood pressure elevation in the presence of other prohypertensive factors (salt, renin-angiotensin system, sympathetic hyperactivity). A major source for cardiovascular ROS is a family of non-phagocytic NADPH oxidases (Nox1, Nox2, Nox4, Nox5). Other sources of ROS involve mitochondrial electron transport enzymes, xanthine oxidase, and uncoupled nitric oxide synthase. Although evidence from experimental and animal studies supports a role for oxidative stress in the pathogenesis of hypertension, there is still no convincing proof that oxidative stress is a cause of human hypertension. However, what is clear is that oxidative stress is important in the molecular mechanisms associated with cardiovascular and renal injury in hypertension and that hypertension itself can contribute to oxidative stress. The present review addresses the putative function of ROS in the pathogenesis of hypertension and focuses on the role of Noxs in ROS generation in vessels and the kidney. Implications of oxidative stress in human hypertension are discussed, and clinical uncertainties are highlighted.

Simvastatin ameliorates angiotensin II-induced endothelial dysfunction through restoration of Rho-BH4-eNOS-NO pathway

Endothelial dysfunction contributes to the initiation and development of hypertension. We previously found that simvastatin moderately decreases blood pressure in 2-kidney-2-clip (2k2c) renal hypertension, but the precise mechanisms are still unclear. The present study was designed to examine the protective actions of simvastatin in 2k2c-evoked endothelial dysfunction and also delineate the underlying mechanisms. Here we show that 2k2c-induced elevation in plasma angiotensin II impaired acetylcholine-induced endothelium-dependent vascular relaxation, suppressed endothelial NO synthase (eNOS) activity and reduced nitric oxide (NO) production. Additionally, the levels of tetrahydrobiopterin (BH4), an essential cofactor of eNOS, as well as the activity of GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme for BH4 synthesis, were markedly reduced. Administration of simvastatin significantly improved acetylcholine-induced endothelium-dependent carotid arteries relaxation at 9 weeks in reno-hypertensive rats. Notably, GTPCH I activity, BH4 production, p-eNOS expression and NO levels in the vascular endothelium were elevated as a result of simvastatin administration. In cultured rat arterial endothelial cells, simvastatin restored BH4, GTPCH I activity and NO release impaired by angiotensin II, and pretreatment with mevalonate (MVA) or geranylgeranyl pyrophosphate (GGPP) abolished the beneficial effects exerted by simvastatin. Moreover, RhoA inhibitor C3 exoenzyme, Rho kinase inhibitor Y-27632 and dominant negative mutant of RhoA prevented BH4 and NO loss due to Ang II treatment. Taken together, normalization of BH4-eNOS-NO pathway at least in part accounts for the beneficial actions of simvastatin on vascular endothelium during 2k2c hypertension, and RhoA-Rho kinase pathway is involved in regulation of BH4 production.

Contribution of central nervous system endothelial nitric oxide synthase to neurohumoral activation in heart failure rats

Neurohumoral activation, a hallmark in heart failure (HF), is linked to the progression and mortality of HF patients. Thus, elucidating its precise underlying mechanisms is of critical importance. Other than its classic peripheral vasodilatory actions, the gas NO is a pivotal neurotransmitter in the central nervous system control of the circulation. While accumulating evidence supports a contribution of blunted NO function to neurohumoral activation in HF, the precise cellular sources, and NO synthase (NOS) isoforms involved, remain unknown. Here, we used a multidisciplinary approach to study the expression, cellular distribution, and functional relevance of the endothelial NOS isoform within the hypothalamic paraventricular nucleus in sham and HF rats. Our results show high expression of endothelial NOS in the paraventricular nucleus (mostly confined to astroglial cells), which contributes to constitutive NO bioavailability, as well as tonic inhibition of presympathetic neuronal activity and sympathoexcitatory outflow from the paraventricular nucleus. A diminished endothelial NOS expression and endothelial NOS-derived NO availability were found in the paraventricular nucleus of HF rats, resulting, in turn, in blunted NO inhibitory actions on neuronal activity and sympathoexcitatory outflow. Taken together, our study supports blunted central nervous system endothelial NOS-derived NO as a pathophysiological mechanism underlying neurohumoral activation in HF.