Reversal of Endothelial Nitric Oxide Synthase Uncoupling and Up-Regulation of Endothelial Nitric Oxide Synthase Expression Lowers Blood Pressure in Hypertensive Rats

Studies on the Effects of Hypercholesterolemia on Mouse Ophthalmic Artery Reactivity

Atherogenic lipoproteins may impair vascular reactivity, leading to tissue damage in various organs, including the eye. This study aimed to investigate whether ophthalmic artery reactivity is affected in mice lacking the apolipoprotein E gene (ApoE-/-), a model for hypercholesterolemia and atherosclerosis. Twelve-month-old male ApoE-/- mice and age-matched wild-type controls were used to assess vascular reactivity using videomicroscopy. Moreover, the vascular mechanics, lipid content, levels of reactive oxygen species (ROS), and expression of pro-oxidant redox enzymes and the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) were determined in vascular tissue. Unlike the aorta, the ophthalmic artery of ApoE-/- mice developed no signs of endothelial dysfunction and no signs of excessive lipid deposition. Remarkably, the levels of ROS, nicotinamide adenine dinucleotide phosphate oxidase 1 (NOX1), NOX2, NOX4, and LOX-1 were increased in the aorta but not in the ophthalmic artery of ApoE-/- mice. Our findings suggest that ApoE-/- mice develop endothelial dysfunction in the aorta by increased oxidative stress via the involvement of LOX-1, NOX1, and NOX2, whereas NOX4 may participate in media remodeling. In contrast, the ophthalmic artery appears to be resistant to chronic apolipoprotein E deficiency. A lack of LOX-1 expression/overexpression in response to increased oxidized low-density lipoprotein levels may be a possible mechanism of action.

The Triple Crown: NO, CO, and H2S in cancer cell biology

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are three endogenously produced gases with important functions in the vasculature, immune defense, and inflammation. It is increasingly apparent that, far from working in isolation, these three exert many effects by modulating each other's activity. Each gas is produced by three enzymes, which have some tissue specificities and can also be non-enzymatically produced by redox reactions of various substrates. Both NO and CO share similar properties, such as activating soluble guanylate cyclase (sGC) to increase cyclic guanosine monophosphate (cGMP) levels. At the same time, H2S both inhibits phosphodiesterase 5A (PDE5A), an enzyme that metabolizes sGC and exerts redox regulation on sGC. The role of NO, CO, and H2S in the setting of cancer has been quite perplexing, as there is evidence for both tumor-promoting and pro-inflammatory effects and anti-tumor and anti-inflammatory activities. Each gasotransmitter has been found to have dual effects on different aspects of cancer biology, including cancer cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and immunomodulation. These seemingly contradictory actions may relate to each gas having a dual effect dependent on its local flux. In this review, we discuss the major roles of NO, CO, and H2S in the context of cancer, with an effort to highlight the dual nature of each gas in different events occurring during cancer progression.

Targeting cytokine-like protein FAM3D lowers blood pressure in hypertension

Current antihypertensive options still incompletely control blood pressure, suggesting the existence of uncovered pathogenic mechanisms. Here, whether cytokine-like protein family with sequence similarity 3, member D (FAM3D) is involved in hypertension etiology is evaluated. A case-control study exhibits that FAM3D is elevated in patients with hypertension, with a positive association with odds of hypertension. FAM3D deficiency significantly ameliorates angiotensin II (AngII)-induced hypertension in mice. Mechanistically, FAM3D directly causes endothelial nitric oxide synthase (eNOS) uncoupling and impairs endothelium-dependent vasorelaxation, whereas 2,4-diamino-6-hydroxypyrimidine to induce eNOS uncoupling abolishes the protective effect of FAM3D deficiency against AngII-induced hypertension. Furthermore, antagonism of formyl peptide receptor 1 (FPR1) and FPR2 or the suppression of oxidative stress blunts FAM3D-induced eNOS uncoupling. Translationally, targeting endothelial FAM3D by adeno-associated virus or intraperitoneal injection of FAM3D-neutralizing antibodies markedly ameliorates AngII- or deoxycorticosterone acetate (DOCA)-salt-induced hypertension. Conclusively, FAM3D causes eNOS uncoupling through FPR1- and FPR2-mediated oxidative stress, thereby exacerbating the development of hypertension. FAM3D may be a potential therapeutic target for hypertension.

Endothelial cell vasodilator dysfunction mediates progressive pregnancy-induced hypertension in endothelial cell tetrahydrobiopterin deficient mice

BACKGROUND AND PURPOSE

Pregnancy-associated vascular remodelling is essential for both maternal and fetal health. We have previously shown that maternal endothelial cell tetrahydrobiopterin (BH4) deficiency causes poor pregnancy outcomes. Here, we investigated the role and mechanisms of endothelial cell-mediated vasorelaxation function in these outcomes.

EXPERIMENTAL APPROACH

The vascular reactivity of mouse aortas and uterine arteries from non-pregnant and pregnant endothelial cell-specific BH4 deficient mice (Gch1fl/flTie2cre mice) was assessed by wire myography. Systolic blood pressure was assessed by tail cuff plethysmography.

KEY RESULTS

In late pregnancy, systolic blood pressure was significantly higher (∼24 mmHg) in Gch1fl/flTie2cre mice compared with wild-type littermates. This was accompanied by enhanced vasoconstriction and reduced endothelial-dependent vasodilation in both aorta and uterine arteries from pregnant Gch1fl/flTie2cre mice. In uterine arteries loss of eNOS-derived vasodilators was partially compensated by upregulation of intermediate and large-conductance Ca2+-activated K+ channels. In rescue experiments, oral BH4 supplementation alone did not rescue vascular dysfunction and pregnancy-induced hypertension in Gch1fl/flTie2cre mice. However, combination with the fully reduced folate, 5-methyltetrahydrofolate (5-MTHF), restored endothelial cell vasodilator function and blood pressure.

CONCLUSIONS AND IMPLICATIONS

We identify a critical requirement for maternal endothelial cell Gch1/BH4 biosynthesis in endothelial cell vasodilator function in pregnancy. Targeting vascular Gch1 and BH4 biosynthesis with reduced folates may provide a novel therapeutic target for the prevention and treatment of pregnancy-related hypertension.

Stretchable Oxygen-Tolerant Sensor Based on a Single-Atom Fe-N4 Electrocatalyst for Observing the Role of Oxidative Stress in Hypertension

Oxidative stress and related oxidative damage have a causal relation with the pathogenesis of hypertension. Therefore, it is crucial to determine the mechanism of oxidative stress in hypertension by applying mechanical forces on cells to simulate hypertension while monitoring the release of reactive oxygen species (ROS) from cells under an oxidative stress environment. However, cellular level research has rarely been explored because monitoring the ROS released by cells is still challenging owing to the interference of O₂. In this study, an Fe single-atom-site catalyst anchored on N-doped carbon-based materials (Fe SASC/N-C) was synthesized, which exhibits excellent electrocatalytic activity for the reduction of hydrogen peroxide (H₂O₂) at a peak potential of +0.1 V and can effectively avoid the interference of O₂. Furthermore, we constructed a flexible and stretchable electrochemical sensor based on the Fe SASC/N-C catalyst to study the release of cellular H₂O₂ under simulated hypoxic and hypertension conditions. Density functional theory calculations show that the highest transition state energy barrier from the oxygen reduction reaction (ORR), i.e., O₂ to H₂O, is 0.38 eV. In comparison, the H₂O₂ reduction reaction (HPRR) can be completed only by overcoming a lower energy barrier of 0.24 eV, endowing the HPRR to be more favorable on Fe SASC/N-C compared with the ORR. This study provided a reliable electrochemical platform for real-time investigation of H₂O₂-related underlying mechanisms of the hypertension process.

Photo-controlled and photo-calibrated nanoparticle enabled nitric oxide release for anti-bacterial and anti-biofilm applications

After numerous efforts to elucidate the biological role of nitric oxide (NO), NO treatments have become a hotspot at the forefront of medicine. NO-releasing substances are constantly needed, while the direct use of NO gas is unattainable in bio-systems. An ideal NO donor should possess controllable and visible NO-release capability. The reported NO donating nanoparticles, prepared via encapsulating a hydrophobic NO-releasing compound into DSPE-PEG2000, meet the criteria mentioned previously. The localization and flux of NO released from these nanoparticles could be manipulated by UV or blue light. Meanwhile, NOD-NPs emit a dose-dependent fluorescence intensity to calibrate the generation of NO. While the good biocompatibility of NOD-NPs has been validated, the NO from our nanoparticles demonstrates efficient anti-bacterial and anti-biofilm effects toward Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Therefore, the NOD-NPs developed in this work have potential application in evaluating the regulation of microbes by NO.

Utility of NO and H2S donating platforms in managing COVID-19: Rationale and promise

Viral infections are a continuing global burden on the human population, underscored by the ramifications of the COVID-19 pandemic. Current treatment options and supportive therapies for many viral infections are relatively limited, indicating a need for alternative therapeutic approaches. Virus-induced damage occurs through direct infection of host cells and inflammation-related changes. Severe cases of certain viral infections, including COVID-19, can lead to a hyperinflammatory response termed cytokine storm, resulting in extensive endothelial damage, thrombosis, respiratory failure, and death. Therapies targeting these complications are crucial in addition to antiviral therapies. Nitric oxide and hydrogen sulfide are two endogenous gasotransmitters that have emerged as key signaling molecules with a broad range of antiviral actions in addition to having anti-inflammatory properties and protective functions in the vasculature and respiratory system. The enhancement of endogenous nitric oxide and hydrogen sulfide levels thus holds promise for managing both early-stage and later-stage viral infections, including SARS-CoV-2. Using SARS-CoV-2 as a model for similar viral infections, here we explore the current evidence regarding nitric oxide and hydrogen sulfide's use to limit viral infection, resolve inflammation, and reduce vascular and pulmonary damage.

Oxidative Stress: Meeting Multiple Targets in Pathogenesis of Vascular Endothelial Dysfunction

Vascular endothelium is the innermost lining of blood vessels, which maintains vasoconstriction and vasodilation. Loss of vascular tone is a hallmark for cardiovascular disorders. Though there are numerous factors, such as over activation of renin angiotensin aldosterone system, kinases, growth factors, etc. play crucial role in induction and progression of vascular abrasion. Interestingly, dysregulation of these pathways either enhances the intensity of oxidative stress, or these pathways are affected by oxidative stress. Thus, oxidative stress has been considered a key culprit in the progression of vascular endothelial dysfunction. Oxidative stress induced by reactive oxygen and nitrogen species causes abnormal gene expression, alteration in signal transduction, and the activation of pathways leading to induction and progression of vascular injury. In addition, numerous antioxidants have been noted to possess promising therapeutic potential in preventing the development of vascular endothelial dysfunction. Therefore, we have focused on current perspectives in oxidative stress signalling to evaluate common biological processes whereby oxidative stress plays a crucial role in the progression of vascular endothelial dysfunction.

Compensatory role of endogenous sulfur dioxide in nitric oxide deficiency-induced hypertension

OBJECTIVE

This study aimed to determine the communicational pattern of gaseous signaling molecules sulfur dioxide (SO2) and nitric oxide (NO) between vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs), and elucidate the compensatory role and significance of endogenous SO2 in the development of hypertension due to NO deficiency.

APPROACH AND RESULTS

Blood pressure was monitored by the tail-cuff and implantable physiological signal telemetry in L-nitro-arginine methyl ester (l-NAME)-induced hypertensive mice, and structural alterations of mouse aortic vessels were detected by the elastic fiber staining method. l-NAME-treated mice showed decreased plasma NO levels, increased SO2 levels, vascular remodeling, and increased blood pressure, and application of l-aspartate-β-hydroxamate, which inhibits SO2 production, further aggravated vascular structural remodeling and increased blood pressure. Moreover, in a co-culture system of HAECs and HASMCs, NO from HAECs did not influence aspartate aminotransferase (AAT)1 protein expression but decreased AAT1 activity in HASMCs, thereby resulting in the inhibition of endogenous SO2 production. Furthermore, NO promoted S-nitrosylation of AAT1 protein in HASMCs and purified AAT1 protein. Liquid chromatography with tandem mass spectrometry showed that the Cys192 site of AAT1 purified protein was modified by S-nitrosylation. In contrast, dithiothreitol or C192S mutations in HASMCs blocked NO-induced AAT1 S-nitrosylation and restored AAT1 enzyme activity.

CONCLUSION

Endothelium-derived NO inhibits AAT activity by nitrosylating AAT1 at the Cys192 site and reduces SO2 production in HASMCs. Our findings suggest that SO2 acts as a compensatory defense system to antagonize vascular structural remodeling and hypertension when the endogenous NO pathway is disturbed.

B Lymphocyte-Deficiency in Mice Causes Vascular Dysfunction by Inducing Neutrophilia

B lymphocytes have been implicated in the development of insulin resistance, atherosclerosis and certain types of hypertension. In contrast to these studies, which were performed under pathological conditions, the present study provides evidence for the protective effect of B lymphocytes in maintaining vascular homeostasis under physiological conditions. In young mice not exposed to any known risk factors, the lack of B cells led to massive endothelial dysfunction. The vascular dysfunction in B cell-deficient mice was associated with an increased number of neutrophils in the circulating blood. Neutrophil depletion in B cell-deficient mice resulted in the complete normalization of vascular function, indicating a causal role of neutrophilia. Moreover, vascular function in B cell-deficient mice could be restored by adoptive transfer of naive B-1 cells isolated from wild-type mice. Interestingly, B-1 cell transfer also reduced the number of neutrophils in the recipient mice, further supporting the involvement of neutrophils in the vascular pathology caused by B cell-deficiency. In conclusion, we report in the present study the hitherto undescribed role of B lymphocytes in regulating vascular function. B cell dysregulation may represent a crucial mechanism in vascular pathology.

Butterfly Pea Flower (Clitoria ternatea Linn.) Extract Ameliorates Cardiovascular Dysfunction and Oxidative Stress in Nitric Oxide-Deficient Hypertensive Rats

In this study, we examine whether Clitoria ternatea Linn. (CT) can prevent Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME)-induced cardiac and vascular dysfunction in rats. Male Sprague Dawley rats were given L-NAME (40 mg/kg, drinking water) and orally administered with CT extract (300 mg/kg/day) or lisinopril (2.5 mg/kg/day) for 5 weeks. The main phytochemical components of the CT extract were found to be flavonoids. The CT extract alleviated the high blood pressure in rats receiving L-NAME. Decreased vasorelaxation responses to acetylcholine and enhanced contractile responses to sympathetic nerve stimulation in aortic rings and mesenteric vascular beds of L-NAME treated rats were ameliorated by CT extract supplementation. Left ventricular hypertrophy and dysfunction were developed in L-NAME rats, which were partially prevented by CT extract treatment. The CT extract alleviated upregulated endothelial nitric oxide synthase expression, decreased plasma nitrate/nitrite levels, and increased oxidative stress in L-NAME rats. It suppressed high levels of serum angiotensin-converting enzyme activity, plasma angiotensin II, and cardiac angiotensin II type 1 receptor, NADPH oxidases 2, nuclear factor-kappa B, and tumor necrosis factor-alpha expression. The CT extract, therefore, partially prevented L-NAME-induced hypertension and cardiovascular alterations in rats. These effects might be related to a reduction in the oxidative stress and renin-angiotensin system activation due to L-NAME in rats.

Renin-angiotensin system overactivation in perivascular adipose tissue contributes to vascular dysfunction in heart failure

Perivascular adipose tissue (PVAT) dysfunction is associated with vascular damage in cardiometabolic diseases. Although heart failure (HF)-induced endothelial dysfunction is associated with renin-angiotensin system (RAS) activation, no data have correlated this syndrome with PVAT dysfunction. Thus, the aim of the present study was to investigate whether the hyperactivation of the RAS in PVAT participates in the vascular dysfunction observed in rats with HF after myocardial infarction surgery. Wire myograph studies were carried out in thoracic aorta rings in the presence and absence of PVAT. An anticontractile effect of PVAT was observed in the rings of the control rats in the presence (33%) or absence (11%) of endothelium. Moreover, this response was substantially reduced in animals with HF (5%), and acute type 1 angiotensin II receptor (AT1R) and type 2 angiotensin II receptor (AT2R) blockade restored the anticontractile effect of PVAT. In addition, the angiotensin-converting enzyme 1 (ACE1) activity (26%) and angiotensin II levels (51%), as well as the AT1R and AT2R gene expression, were enhanced in the PVAT of rats with HF. Associated with these alterations, HF-induced lower nitric oxide bioavailability, oxidative stress and whitening of the PVAT, which suggests changes in the secretory function of this tissue. The ACE1/angiotensin II/AT1R and AT2R axes are involved in thoracic aorta PVAT dysfunction in rats with HF. These results suggest PVAT as a target in the pathophysiology of vascular dysfunction in HF and provide new perspectives for the treatment of this syndrome.

Oxidative Stress, GTPCH1, and Endothelial Nitric Oxide Synthase Uncoupling in Hypertension

Significance: Hypertension has major health consequences, which is associated with endothelial dysfunction. Endothelial nitric oxide synthase (eNOS)-produced nitric oxide (NO) signaling in the vasculature plays an important role in maintaining vascular homeostasis. Considering the importance of NO system, this review aims to provide a brief overview of the biochemistry of members of NO signaling, including GTPCH1 [guanosine 5'-triphosphate (GTP) cyclohydrolase 1], tetrahydrobiopterin (BH4), and eNOS. Recent Advances: Being NO signaling activators and regulators of eNOS signaling, BH4 treatment is getting widespread attention either as potential therapeutic agents or as preventive agents. Recent clinical trials also support that BH4 treatment could be considered a promising therapeutic in hypertension. Critical Issues: Under conditions of BH4 depletion, eNOS-generated superoxides trigger pathological events. Abnormalities in NO availability and BH4 deficiency lead to disturbed redox regulation causing pathological events. This disturbed signaling influences the development of systemic hypertension as well as pulmonary hypertension. Future Directions: Considering the importance of BH4 and NO to improve the translational significance, it is essential to continue research on this field to manipulate BH4 to increase the efficacy for treating hypertension. Thus, this review also examines the current state of knowledge on the effects of eNOS activators on preclinical models and humans to utilize this information for potential therapy.

Reactive oxygen species in renal vascular function

Reactive oxygen species (ROS) are produced by the aerobic metabolism. The imbalance between production of ROS and antioxidant defence in any cell compartment is associated with cell damage and may play an important role in the pathogenesis of renal disease. NADPH oxidase (NOX) family is the major ROS source in the vasculature and modulates renal perfusion. Upregulation of Ang II and adenosine activates NOX via AT1R and A1R in renal microvessels, leading to superoxide production. Oxidative stress in the kidney prompts renal vascular remodelling and increases preglomerular resistance. These are key elements in hypertension, acute and chronic kidney injury, as well as diabetic nephropathy. Renal afferent arterioles (Af), the primary resistance vessel in the kidney, fine tune renal hemodynamics and impact on blood pressure. Vice versa, ROS increase hypertension and diabetes, resulting in upregulation of Af vasoconstriction, enhancement of myogenic responses and change of tubuloglomerular feedback (TGF), which further promotes hypertension and diabetic nephropathy. In the following, we highlight oxidative stress in the function and dysfunction of renal hemodynamics. The renal microcirculatory alterations brought about by ROS importantly contribute to the pathophysiology of kidney injury, hypertension and diabetes.

Modulation of the lifespan of C. elegans by the controlled release of nitric oxide

The frontier of nitric oxide biology has gradually shifted from mechanism elucidation to biomanipulation, e.g. cell-proliferation promotion, cell-apoptosis induction, and lifespan modulation. This warrants biocompatible nitric oxide (NO) donating materials, whose NO release is not only controlled by a bioorthogonal trigger, but also self-calibrated allowing real-time monitoring and hence an onset/offset of the NO release. Additionally, the dose of NO release should be facilely adjusted in a large dynamic range; flux and the dose are critical to the biological outcome of NO treatment. Via self-assembly of a PEGylated small-molecule NO donor, we developed novel NO-donating nanoparticles (PEG-NORM), which meet all the aforementioned criteria. We showcased that a low flux of NO induced cell proliferation, while a high flux induced cell oxidative stress and, ultimately, death. Notably, PEG-NORM was capable of efficiently modulating the lifespan of C. elegans. The average lifespan of C. elegans could be fine-tuned to be as short as 15.87 ± 0.29 days with a high dose of NO, or as long as 21.13 ± 0.41 days with a low dose of NO, compared to an average life-span of 18.87 ± 0.46 days. Thus, PEG-NORM has broad potential in cell manipulation and life-span modulation and could drive the advancement of NO biology and medicine.

Renal Effects of Fetal Reprogramming With Pentaerythritol Tetranitrate in Spontaneously Hypertensive Rats

Aims

Current antihypertensive therapies cannot cure hypertension and a life-long medication is necessary. Maternal treatment may represent a promising strategy for hypertension treatment. We have previously shown that maternal treatment of spontaneously hypertensive rats (SHR) with pentaerythritol tetranitrate (PETN) leads to a persistent blood pressure reduction in the female offspring. The underlying mechanisms include improved endothelial function resulting from long-lasting epigenetic changes. In the present study, we address the renal effects of maternal PETN treatment.

Methods and Results

F0 parental SHR were fed with either normal chow or PETN-containing (1 g/kg) chow ad libitum from the time point of mating to the end of lactation period. The F1 offspring received normal chow without PETN from the time point of weaning (at the age of 3 weeks). At the age of 16 weeks, female PETN offspring showed lower blood pressure than the control. No difference was observed in male offspring. All following experiments were performed with kidneys from 16-week-old female offspring. Maternal PETN treatment reduced the mRNA and protein expression of angiotensin-converting enzyme (ACE) and basic fibroblast growth factor (FGF2), resulting from epigenetic modifications found at the proximal promoter regions. The expression levels of mineralocorticoid receptor (MR) and factors in the MR signalling pathway (Rac1 and Sgk1) were also reduced by PETN. Major profibrotic cytokines, including Wnt4, TNF-alpha, TGF-beta, and MMP9, were downregulated by PETN, which was associated with reduced collagen deposition and glomerulus sclerosis in the kidney of PETN offspring. In addition, PETN treatment also decreased the markers of inflammation and immune cell infiltration in the kidneys.

Conclusions

PETN maternal treatment leads to epigenetic changes in the kidney of female SHR offspring. The reduced renal inflammation, alleviated kidney fibrosis, and decreased MR signalling are potential mechanisms contributing to the observed blood pressure-lowering effect.

Phosphorylation and activation of endothelial nitric oxide synthase by red fruit (Pandanus conoideus Lam) oil and its fractions

ETHNOPHARMACOLOGICAL RELEVANCE

Red fruit (Pandanus conoideus Lam) oil (RFO) is utilized by inhabitants of the Papua Island to treat diseases such as infections, cancer, and cardiovascular disease, but the mechanism of action is unknown.

AIM OF THE STUDY

We have recently shown that RFO stimulates nitric oxide (NO) production in endothelial cells. The present study was conducted to investigate the molecular mechanism of endothelial NO synthase (eNOS) activation by RFO.

MATERIALS AND METHODS

NO production by endothelial cells was determined with electron paramagnetic resonance. The vascular function of isolated mouse aorta was examined using a wire myograph system. Phosphorylation of eNOS was studied with Western blot analyses.

RESULTS

RFO induced concentration-dependent vasodilation in isolated mouse aorta. The vasodilator effect of RFO was lost in endothelium-denuded aorta and in aorta from mice deficient in eNOS. Treatment of human EA.hy 926 endothelial cells with RFO led to an enhancement of eNOS phosphorylation at serine 1177 and NO production. The RFO-induced eNOS phosphorylation and NO production were reduced by inhibitors of Akt or AMPK, but not by an inhibitor of CaMKII. The effects of RFO were decreased by pharmacological inhibition of PI3K, indicating an involvement of the PI3K-Akt pathway. Moreover, acetone-soluble fractions and oily fractions of RFO showed higher efficacies than the RFO polar fraction in activating eNOS.

CONCLUSIONS

RFO contains highly active compounds that enhance NO production through Akt- or AMPK-mediated eNOS phosphorylation. The increase in endothelial NO production is likely to represent one of the molecular mechanisms responsible for the therapeutic effects of RFO.

Elevated Intraocular Pressure Causes Abnormal Reactivity of Mouse Retinal Arterioles

Objective

Glaucoma is a leading cause of severe visual impairment and blindness. Although high intraocular pressure (IOP) is an established risk factor for the disease, the role of abnormal ocular vessel function in the pathophysiology of glaucoma gains more and more attention. We tested the hypothesis that elevated intraocular pressure (IOP) causes vascular dysfunction in the retina.

Methods

High IOP was induced in one group of mice by unilateral cauterization of three episcleral veins. The other group received sham surgery only. Two weeks later, retinal vascular preparations were studied by video microscopy in vitro. Reactive oxygen species (ROS) levels and expression of hypoxia markers and of prooxidant and antioxidant redox genes as well as of inflammatory cytokines were determined.

Results

Strikingly, responses of retinal arterioles to stepwise elevation of perfusion pressure were impaired in the high-IOP group. Moreover, vasodilation responses to the endothelium-dependent vasodilator, acetylcholine, were markedly reduced in mice with elevated IOP, while no differences were seen in response to the endothelium-independent nitric oxide donor, sodium nitroprusside. Remarkably, ROS levels were increased in the retinal ganglion cell layer including blood vessels. Expression of the NADPH oxidase isoform, NOX2, and of the inflammatory cytokine, TNF-α, was increased at the mRNA level in retinal explants. Expression of NOX2, but not of the hypoxic markers, HIF-1α and VEGF-A, was increased in the retinal ganglion cell layer and in retinal blood vessels at the protein level.

Conclusion

Our data provide first-time evidence that IOP elevation impairs autoregulation and induces endothelial dysfunction in mouse retinal arterioles. Oxidative stress and inflammation, but not hypoxia, appear to be involved in this process.

Buddhist meditation for vascular function: A narrative review

Background

High blood pressure represents an important risk factor for diseases related to cardiovascular system and is directly associated with high oxidative stress, inflammation and vascular endothelial dysfunction. Recently, there is promising data available to suggest that meditation-based low-cost and low-risk lifestyle modification strategies may provide beneficial effects on chronic inflammation, oxidative stress and maintenance of blood pressure, both in young and older adults. This review aims to summarize the evidence regarding the effectiveness of Buddhist meditation for vascular endothelial function and blood pressure.

Method

A search was conducted using Ovid MEDLINE, Scopus, CINAHL and PsycINFO for articles published from 1990 to 2018.

Results

Relevant articles (n = 407) were reviewed and 5 met selection criteria. Several lines of studies have provided compelling data showing that Buddhist meditation approach was effective in improving inflammation and vascular function (endothelial vasodilation and arterial stiffness) in both young and elderly cohorts. Particularly, Buddhist meditation approach has shown to be effective in reducing plasma inflammatory markers, increasing nitric oxide concentration and improving vascular endothelial function and glycemic control, which in turn can be favorable factors for demonstrated positive effects of Buddhist meditation on blood pressure and vascular function.

Conclusion

This paper presents brief overview of clinical outcomes of complementary therapeutic approach of Buddhist meditation in vascular function. In future, well-structured systematic reviews are essential to report specificity of Buddhist mindfulness-based approach on vascular function, blood pressure and other cardiovascular risk factors.

Central Glucagon-like Peptide-1 Receptor Signaling via Brainstem Catecholamine Neurons Counteracts Hypertension in Spontaneously Hypertensive Rats

Glucagon-like peptide-1 receptor (GLP-1R) agonists, widely used to treat type 2 diabetes, reduce blood pressure (BP) in hypertensive patients. Whether this action involves central mechanisms is unknown. We here report that repeated lateral ventricular (LV) injection of GLP-1R agonist, liraglutide, once daily for 15 days counteracted the development of hypertension in spontaneously hypertensive rats (SHR). In parallel, it suppressed urinary norepinephrine excretion, and induced c-Fos expressions in the area postrema (AP) and nucleus tractus solitarius (NTS) of brainstem including the NTS neurons immunoreactive to dopamine beta-hydroxylase (DBH). Acute administration of liraglutide into fourth ventricle, the area with easy access to the AP and NTS, transiently decreased BP in SHR and this effect was attenuated after lesion of NTS DBH neurons with anti-DBH conjugated to saporin (anti-DBH-SAP). In anti-DBH-SAP injected SHR, the antihypertensive effect of repeated LV injection of liraglutide for 14 days was also attenuated. These findings demonstrate that the central GLP-1R signaling via NTS DBH neurons counteracts the development of hypertension in SHR, accompanied by attenuated sympathetic nerve activity.

PPARδ agonist prevents endothelial dysfunction via induction of dihydrofolate reductase gene and activation of tetrahydrobiopterin salvage pathway

BACKGROUND AND PURPOSE

Impaired endothelium-dependent relaxation (EDR) is a hallmark of endothelial dysfunction. A deficiency of tetrahydrobiopterin (BH4 ) causes endothelial NOS to produce ROS rather than NO. PPARδ is an emerging target for pharmacological intervention of endothelial dysfunction. Thus, the present study examined the role of PPARδ in the regulation of dihydrofolate reductase (DHFR), a key enzyme in the BH4 salvage pathway.

EXPERIMENTAL APPROACH

Gene expression was measured by using qRT-PCR and western blotting. Biopterins and ROS were determined by using HPLC. NO was measured with fluorescent dye and electron paramagnetic resonance spectroscopy. Vasorelaxation was measured by Multi Myograph System.

KEY RESULTS

The PPARδ agonist GW501516 increased DHFR and BH4 levels in endothelial cells (ECs). The effect was blocked by PPARδ antagonist GSK0660. Chromatin immunoprecipitation identified PPAR-responsive elements within the 5'-flanking region of the human DHFR gene. The promoter activity was examined with luciferase assays using deletion reporters. Importantly, DHFR expression was suppressed by palmitic acid (PA, a saturated fatty acid) but increased by docosahexaenoic acid (DHA, a polyunsaturated fatty acid). GSK0660 prevented DHA-induced increased DHFR expression. Conversely, the suppressive effect of PA was mitigated by GW501516. In mouse aortae, GW501516 ameliorated the PA-impaired EDR. However, this vasoprotective effect was attenuated by DHFR siRNA or methotrexate. In EC-specific Ppard knockout mice, GW501516 failed to improve vasorelaxation.

CONCLUSION AND IMPLICATIONS

PPARδ prevented endothelial dysfunction by increasing DHFR and activating the BH4 salvage pathway. These results provide a novel mechanism for the protective roles of PPARδ against vascular diseases.

Lancemaside A from Codonopsis lanceolata prevents hypertension by inhibiting NADPH oxidase 2-mediated MAPK signalling and improving NO bioavailability in rats

OBJECTIVES

This study investigated whether lancemaside A (LMA) can prevent hypertension and assessed the mechanisms of action of LMA in rats.

METHODS

Hypertension was induced by chronic immobilization stress and nicotine administration. Hypertensive vehicle rats were treated with LMA (1, 20, or 40 mg/kg) or nifedipine (10 mg/kg) as a positive control daily for 3 weeks.

KEY FINDINGS

In hypertensive vehicle rats, LMA dose-dependently reduced systolic blood pressure. LMA doses of 20 and 40 mg/kg reduced the aortic expression of nicotinamide adenine dinucleotide phosphate oxidase (NOX)2 (both P < 0.01), and 40 mg/kg LMA reduced serum malondialdehyde (P < 0.01). Serum nitrite levels were significantly higher in LMA treated rats than in hypertensive vehicle rats, with LMA doses of 20 and 40 mg/kg reducing the expression of endothelial nitric oxide synthase in rat aortas (P < 0.001 and P < 0.01, respectively). LMA also reduced the aortic levels of nuclear factor kappa B and the activation of the three isoforms of mitogen-activated protein kinase (MAPK).

CONCLUSIONS

Lancemaside A prevents hypertension in rats by inhibiting the activation of MAPK signalling and the impairment in nitric oxide bioavailability due to NOX2-mediated oxidative stress. Thus, LMA may act as a preventive agent for hypertension.

Nitric Oxide and Hydrogen Sulfide Regulation of Ischemic Vascular Growth and Remodeling

Ischemic vascular remodeling occurs in response to stenosis or arterial occlusion leading to a change in blood flow and tissue perfusion. Altered blood flow elicits a cascade of molecular and cellular physiological responses leading to vascular remodeling of the macro- and micro-circulation. Although cellular mechanisms of vascular remodeling such as arteriogenesis and angiogenesis have been studied, therapeutic approaches in these areas have had limited success due to the complexity and heterogeneous constellation of molecular signaling events regulating these processes. Understanding central molecular players of vascular remodeling should lead to a deeper understanding of this response and aid in the development of novel therapeutic strategies. Hydrogen sulfide (H₂ S) and nitric oxide (NO) are gaseous signaling molecules that are critically involved in regulating fundamental biochemical and molecular responses necessary for vascular growth and remodeling. This review examines how NO and H₂ S regulate pathophysiological mechanisms of angiogenesis and arteriogenesis, along with important chemical and experimental considerations revealed thus far. The importance of NO and H₂ S bioavailability, their synthesis enzymes and cofactors, and genetic variations associated with cardiovascular risk factors suggest that they serve as pivotal regulators of vascular remodeling responses. © 2019 American Physiological Society. Compr Physiol 9:1213-1247, 2019.

The M1 muscarinic acetylcholine receptor subtype is important for retinal neuron survival in aging mice

Muscarinic acetylcholine receptors have been implicated as potential neuroprotective targets for glaucoma. We tested the hypothesis that the lack of a single muscarinic receptor subtype leads to age-dependent neuron reduction in the retinal ganglion cell layer. Mice with targeted disruption of single muscarinic acetylcholine receptor subtype genes (M₁ to M₅) and wild-type controls were examined at two age categories, 5 and 15 months, respectively. We found no differences in intraocular pressure between individual mouse groups. Remarkably, in 15-month-old mice devoid of the M₁ receptor, neuron number in the retinal ganglion cell layer and axon number in the optic nerve were markedly reduced. Moreover, mRNA expression for the prooxidative enzyme, NOX2, was increased, while mRNA expression for the antioxidative enzymes, SOD1, GPx1 and HO-1, was reduced in aged M₁ receptor-deficient mice compared to age-matched wild-type mice. In line with these findings, the reactive oxygen species level was also elevated in the retinal ganglion cell layer of aged M₁ receptor-deficient mice. In conclusion, M₁ receptor deficiency results in retinal ganglion cell loss in aged mice via involvement of oxidative stress. Based on these findings, activation of M₁ receptor signaling may become therapeutically useful to promote retinal ganglion cell survival.

New Therapeutic Implications of Endothelial Nitric Oxide Synthase (eNOS) Function/Dysfunction in Cardiovascular Disease

The Global Burden of Disease Study identified cardiovascular risk factors as leading causes of global deaths and life years lost. Endothelial dysfunction represents a pathomechanism that is associated with most of these risk factors and stressors, and represents an early (subclinical) marker/predictor of atherosclerosis. Oxidative stress is a trigger of endothelial dysfunction and it is a hall-mark of cardiovascular diseases and of the risk factors/stressors that are responsible for their initiation. Endothelial function is largely based on endothelial nitric oxide synthase (eNOS) function and activity. Likewise, oxidative stress can lead to the loss of eNOS activity or even “uncoupling” of the enzyme by adverse regulation of well-defined “redox switches” in eNOS itself or up-/down-stream signaling molecules. Of note, not only eNOS function and activity in the endothelium are essential for vascular integrity and homeostasis, but also eNOS in perivascular adipose tissue plays an important role for these processes. Accordingly, eNOS protein represents an attractive therapeutic target that, so far, was not pharmacologically exploited. With our present work, we want to provide an overview on recent advances and future therapeutic strategies that could be used to target eNOS activity and function in cardiovascular (and other) diseases, including life style changes and epigenetic modulations. We highlight the redox-regulatory mechanisms in eNOS function and up- and down-stream signaling pathways (e.g., tetrahydrobiopterin metabolism and soluble guanylyl cyclase/cGMP pathway) and their potential pharmacological exploitation.

Oxidative stress induces BH4 deficiency in male, but not female, SHR

We previously published that female spontaneously hypertensive rats (SHR) have significantly greater nitric oxide (NO) bioavailability and NO synthase (NOS) enzymatic activity in the renal inner medulla (IM) compared with age-matched males, although the mechanism responsible remains unknown. Tetrahydrobiopterin (BH₄) is a critical cofactor required for NO generation, and decreases in BH₄ as a result of increases in oxidative stress have been implicated in the pathogenesis of hypertension. As male SHR are known to have higher levels of oxidative stress compared with female SHR, we hypothesized that relative BH₄ deficiency induced by oxidative stress in male SHR results in lower levels of NOS activity in renal IM compared with females. Twelve-week-old male and female SHR were randomized to receive tempol (30 mg/kg/day via drinking water) or vehicle for 2 weeks. Tempol treatment did not affect blood pressure (BP) in either sex, but reduced peroxynitrite levels only in males. Females had more total biopterin, dihydrobiopterin (BH₂), and BH₄ levels in renal IMs than males, and tempol treatment eliminated these sex differences. Females had greater total NOS activity in the renal IM than males, and adding exogenous BH₄ to the assay increased NOS activity in both sexes. This sex difference in total NOS and the effect of exogenous BH₄ were abolished with tempol treatment. We conclude that higher oxidative stress in male SHR results in a relative deficiency of BH₄ compared with females, resulting in diminished renal NOS activity in the male.

Aerobic exercise enhanced endothelium-dependent vasorelaxation in mesenteric arteries in spontaneously hypertensive rats: the role of melatonin

Melatonin, a neuroendocrine hormone synthesized primarily by the pineal gland, provides various cardiovascular benefits. Regular physical activity is an effective non-pharmacological therapy for the prevention and control of hypertension. In the present study, we hypothesized that melatonin plays an important role in the aerobic exercise-induced increase of endothelium-dependent vasorelaxation in the mesenteric arteries (MAs) of spontaneously hypertensive rats (SHRs) in a melatonergic receptor-dependent manner. To test this hypothesis, we evaluated the vascular mechanical and functional properties in normotensive Wistar Kyoto (WKY), SHRs, and SHRs that were trained on a treadmill (SHR-EX) for 8 weeks. Exercise training produced a significant reduction in blood pressure and heart rate in SHR, which was significantly attenuated by the intraperitoneal administration of luzindole, a non-selective melatonin receptor (MT1/MT2) antagonist. Serum melatonin levels in the SHR group were significantly lower than those in the WKY group at 8:00-9:00 and 21:00-22:00, while exercise training reduced this difference. Endothelium-dependent vessel relaxation induced by acetylcholine was significantly blunted in SHR compared with age-matched WKY. Both exercise training and luzindole ameliorated this endothelium-dependent impairment of relaxation in hypertension. Immunohistochemistry and Western blotting showed that the protein expression of the MT2 receptor and eNOS, as well as their colocalization in the endothelial cell layer in SHRs, was significantly decreased; as exercise training suppressed this reduction. These results provide evidence that regular exercise has a beneficial effect on improving endothelium-dependent vasorelaxation in MAs, in which melatonin plays a critical role by acting on MT2 receptors to increase NO production and/or NO bioavailability.

l-Phenylalanine Restores Vascular Function in Spontaneously Hypertensive Rats Through Activation of the GCH1-GFRP Complex

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Tetrahydrobiopterin is an essential cofactor for NO production.

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Limitation of endogenous tetrahydrobiopterin reduces NO bioavailability, enhances oxidative stress, and impairs vascular function.

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Orally supplemented tetrahydrobiopterin has therapeutic challenges because it is rapidly oxidized in vivo.

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Here, the authors demonstrate that l-phenylalanine, when administered orally, raises vascular tetrahydrobiopterin, restores NO, reduces superoxide, and enhances vascular function in spontaneously hypertensive rats.

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This effect is achieved by activation of a protein complex (GCH1-GFRP) involved in the biosynthesis of tetrahydrobiopterin.

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Activation of this protein complex by l-phenylalanine or its analogues represents a novel therapeutic target for vascular disorders underpinned by reduced NO bioavailability.

Reduced nitric oxide (NO) bioavailability correlates with impaired cardiovascular function. NO is extremely labile and has been challenging to develop as a therapeutic agent. However, NO bioavailability could be enhanced by pharmacologically targeting endogenous NO regulatory pathways. Tetrahydrobiopterin, an essential cofactor for NO production, is synthesized by GTP cyclohydrolase-1 (GCH1), which complexes with GCH1 feedback regulatory protein (GFRP). The dietary amino acid l-phenylalanine activates this complex, elevating vascular BH₄. Here, the authors demonstrate that l-phenylalanine administration restores vascular function in a rodent model of hypertension, suggesting the GCH1-GFRP complex represents a rational therapeutic target for diseases underpinned by endothelial dysfunction.

Reciprocal regulation of eNOS and caveolin-1 functions in endothelial cells

We hypothesized that the maintenance of vascular homeostasis is critically dependent on the expression and reciprocal regulation of caveolin-1 (Cav-1) and endothelial nitric oxide synthase (eNOS) in endothelial cells (ECs). Skeletal muscle biopsies from subjects with type 2 diabetes showed 50% less Cav-1 and eNOS than those from lean healthy controls. The Cav-1:eNOS expression ratio was 200:1 in primary culture human ECs. Cav-1 small interfering RNA (siRNA) reduced eNOS protein and gene expression in association with a twofold increase in eNOS phosphorylation and nitrate production per molecule of eNOS, which was reversed in cells overexpressing Adv-Cav-1-GFP. Upon addition of the Ca²⁺ ionophore A23187 to activate eNOS, we observed eNOS Ser1177 phosphorylation, its translocation to β-catenin-positive cell–cell junctions, and increased colocalization of eNOS and Cav-1 within 5 min. We also observed Cav-1 S-nitrosylation and destabilization of Cav-1 oligomers in cells treated with A23187 as well as insulin or albumin, and this could be blocked by L-NAME, PP2, or eNOS siRNA. Finally, caveola-mediated endocytosis of albumin or insulin was reduced by Cav-1 or eNOS siRNA, and the effect of Cav-1 siRNA was rescued by Adv-Cav-1-GFP. Thus, Cav-1 stabilizes eNOS expression and regulates its activity, whereas eNOS-derived NO promotes caveola-mediated endocytosis.

Inhibition of endothelial nitric oxide synthase reverses the effect of exercise on improving cognitive function in hypertensive rats

Hypertension-induced endothelial dysfunction is associated with β-amyloid (Aβ) deposition, a typical pathology of Alzheimer's disease (AD). Endothelial nitric oxide synthase (eNOS) phosphorylation, impaired by phosphatidylinositol 3-kinase (PI3K)/protein kinase-B(Akt) pathway abnormalities in hypertensive rats, has a critical role in endothelial function. However, it is unknown whether eNOS participates in the hypertension-induced pathology of AD. In this study, we investigated the role of eNOS in Aβ deposition and cognitive function in stroke-prone spontaneously hypertensive (SHRSP) rats. Physical exercise was used as a promoter, and N^ω-nitro L-arginine methyl ester (L-NAME) was used as an inhibitor of eNOS to determine the effects of eNOS on SHRSP rats. Compared with Wistar Kyoto (WKY) rats, the hypertensive challenge caused cognitive impairment, decreased eNOS levels and increased amyloid precursor protein (APP), β-secretase, and Aβ levels in the cortex and hippocampus. Sixteen weeks of exercise lowered blood pressure (BP), promoted eNOS expression, ameliorated Alzheimer's pathology, and improved cognitive function in 29-week-old SHRSP rats. Furthermore, daily treatment with L-NAME reversed the beneficial effects of exercise on SHRSP rats. Exercise also decreased the protein levels of insulin-like growth factor-1 (IGF-1), PI3K, and phospho-Akt (p-Akt, ser473). In addition, long-term exercise increased the expression levels of IGF-1, PI3K, and p-Akt (ser473) in the brains of SHRSP rats. In conclusion, eNOS downregulation contributed to hypertension-induced Alzheimer pathology and cognitive impairment. Long-term exercise initiated in rats at a young age promoted eNOS expression and attenuated vascular-related Alzheimer's pathology via the IGF-1/PI3K/p-Akt pathway in SHRSP rats.

Nitric oxide signalling in cardiovascular health and disease

Nitric oxide (NO) signalling has pleiotropic roles in biology and a crucial function in cardiovascular homeostasis. Tremendous knowledge has been accumulated on the mechanisms of the nitric oxide synthase (NOS)-NO pathway, but how this highly reactive, free radical gas signals to specific targets for precise regulation of cardiovascular function remains the focus of much intense research. In this Review, we summarize the updated paradigms on NOS regulation, NO interaction with reactive oxidant species in specific subcellular compartments, and downstream effects of NO in target cardiovascular tissues, while emphasizing the latest developments of molecular tools and biomarkers to modulate and monitor NO production and bioavailability.

Gallic Acid Reduces Blood Pressure and Attenuates Oxidative Stress and Cardiac Hypertrophy in Spontaneously Hypertensive Rats

Gallic acid (GA) has been reported to have beneficial effects on cancer, vascular calcification, and diabetes-induced myocardial dysfunction. We hypothesized that GA controls hypertension via oxidative stress response regulation in an animal model for essential hypertension. Spontaneously hypertensive rats (SHRs) were administered GA for 16 weeks. GA treatment lowered elevated systolic blood pressure in SHRs through the inhibition of vascular contractility and components of the renin-angiotensin II system. In addition, GA administration reduced aortic wall thickness and body weight in SHRs. In SHRs, GA attenuated left ventricular hypertrophy and reduced the expression of cardiac-specific transcription factors. NADPH oxidase 2 (Nox2) and GATA4 mRNA expression was induced in SHR hearts and angiotensin II-treated H9c2 cells; this expression was downregulated by GA treatment. Nox2 promoter activity was increased by the synergistic action of GATA4 and Nkx2-5. GA seems to regulate oxidative stress by inhibiting the DNA binding activity of GATA4 in the rat Nox2 promoter. GA reduced the GATA4-induced Nox activity in SHRs and angiotensin II-treated H9c2 cells. GA administration reduced the elevation of malondialdehyde levels in heart tissue obtained from SHRs. These findings suggest that GA is a potential therapeutic agent for treating cardiac hypertrophy and oxidative stress in SHRs.

The Future Challenge of Reactive Oxygen Species (ROS) in Hypertension: From Bench to Bed Side

Reactive oxygen species (ROS) act as signaling molecules that control physiological processes, including cell adaptation to stress. Redox signaling via ROS has quite recently become the focus of much attention in numerous pathological contexts, including neurodegenerative diseases, kidney and cardiovascular disease. Imbalance in ROS formation and degradation has also been implicated in essential hypertension. Essential hypertension is characterized by multiple genetic and environmental factors which do not completely explain its associated risk factors. Thereby, even if advances in therapy have led to a significant reduction in hypertension-associated complications, to interfere with the unbalance of redox signals might represent an additional therapeutic challenge. The decrease of nitric oxide (NO) levels, the antioxidant activity commonly found in preclinical models of hypertension and the ability of antioxidant approaches to reduce ROS levels have spurred clinicians to investigate the contribution of ROS in humans. Indeed, particular effort has recently been devoted to understanding how redox signaling may contribute to vascular pathobiology in human hypertension. However, although biomarkers of oxidative stress have been found to positively correlate with blood pressure in preclinical model of hypertension, human data are less convincing. We herein provide an overview of the most relevant mechanisms via which oxidative stress might contribute to the pathophysiology of essential hypertension. Moreover, alternative approaches, which are directed towards improving antioxidant machinery and/or interfering with ROS production, are also discussed.

Impact of Oxidative Stress on the Heart and Vasculature: Part 2 of a 3-Part Series

Vascular disease and heart failure impart an enormous burden in terms of global morbidity and mortality. Although there are many different causes of cardiac and vascular disease, most causes share an important pathological mechanism: oxidative stress. In the failing heart, oxidative stress occurs in the myocardium and correlates with left ventricular dysfunction. Reactive oxygen species (ROS) negatively affect myocardial calcium handling, cause arrhythmia, and contribute to cardiac remodeling by inducing hypertrophic signaling, apoptosis, and necrosis. Similarly, oxidative balance in the vasculature is tightly regulated by a wealth of pro- and antioxidant systems that orchestrate region-specific ROS production and removal. Reactive oxygen species also regulate multiple vascular cell functions, including endothelial and smooth muscle cell growth, proliferation, and migration; angiogenesis; apoptosis; vascular tone; host defenses; and genomic stability. However, excessive levels of ROS promote vascular disease through direct and irreversible oxidative damage to macromolecules, as well as disruption of redox-dependent vascular wall signaling processes.

Taking up the cudgels for the traditional reactive oxygen and nitrogen species detection assays and their use in the cardiovascular system

Reactive oxygen and nitrogen species (RONS such as H2O2, nitric oxide) confer redox regulation of essential cellular functions (e.g. differentiation, proliferation, migration, apoptosis), initiate and catalyze adaptive stress responses. In contrast, excessive formation of RONS caused by impaired break-down by cellular antioxidant systems and/or insufficient repair of the resulting oxidative damage of biomolecules may lead to appreciable impairment of cellular function and in the worst case to cell death, organ dysfunction and severe disease phenotypes of the entire organism. Therefore, the knowledge of the severity of oxidative stress and tissue specific localization is of great biological and clinical importance. However, at this level of investigation quantitative information may be enough. For the development of specific drugs, the cellular and subcellular localization of the sources of RONS or even the nature of the reactive species may be of great importance, and accordingly, more qualitative information is required. These two different philosophies currently compete with each other and their different needs (also reflected by different detection assays) often lead to controversial discussions within the redox research community. With the present review we want to shed some light on these different philosophies and needs (based on our personal views), but also to defend some of the traditional assays for the detection of RONS that work very well in our hands and to provide some guidelines how to use and interpret the results of these assays. We will also provide an overview on the "new assays" with a brief discussion on their strengths but also weaknesses and limitations.

Redox regulation of the actin cytoskeleton and its role in the vascular system

The actin cytoskeleton is critical for form and function of vascular cells, serving mechanical, organizational and signaling roles. Because many cytoskeletal proteins are sensitive to reactive oxygen species, redox regulation has emerged as a pivotal modulator of the actin cytoskeleton and its associated proteins. Here, we summarize work implicating oxidants in altering actin cytoskeletal proteins and focus on how these alterations affect cell migration, proliferation and contraction of vascular cells. Finally, we discuss the role of oxidative modification of the actin cytoskeleton in vivo and highlight its importance for vascular diseases.

Role for reactive oxygen species in flow-stimulated inner medullary collecting duct endothelin-1 production

Inner medullary collecting duct (IMCD)-derived endothelin-1 (ET-1) is stimulated by volume expansion, in part through augmented luminal flow, whereupon it can elicit natriuresis and diuresis. Since flow can alter nitric oxide (NO) and reactive oxygen species (ROS), both of which can affect collecting duct salt transport, we asked whether NO and/or ROS mediate flow-stimulated IMCD ET-1. Mouse IMCD3 cells were exposed to flow, and ET-1/GAPDH mRNA was assessed. A shear stress of 10 dyn/cm2 for 1 h increased ET-1 mRNA by fourfold compared with no flow (ET-1 flow response). Global NO synthase (NOS) inhibition [NG-nitro-l-arginine methyl ester (l-NAME)] reduced the ET-1 flow response; however, pharmacological inhibition of NOS1 or NOS2, inhibition of NOS3 siRNA, inhibition of arginase inhibition, removal of media l-Arg, or inhibition of NO-dependent signaling pathways (PKG, guanylyl cyclase, or NF-κB) did not affect the ET-1 flow response. Tempol reduced the ET-1 flow response; no further inhibition occurred with l-NAME. Superoxide dismutase, but not catalase, reduced the ET-1 flow response. Inhibition of NAPDH oxidase (NOX) (apocynin), pharmacological inhibition of NOX1/4, or NOX4 siRNA reduced the ET-1 flow response. Finally, flow increased IMCD3 ROS production and this was inhibited by apocynin, NOX1/4 inhibition, and, to a small extent, by l-NAME. Taken together, these data suggest that NOX4-derived ROS in general, and possibly superoxide in particular, are involved in flow-stimulated IMCD ET-1 production. To our knowledge, this is the first report of flow-stimulated ROS production by the CD, as well as the first report of such flow-stimulated CD ROS exerting a biological effect.

Angiogenesis is VEGF-independent in the aged striatum of male rats exposed to acute hypoxia

Brain hypoxia is involved in many diseases. The activation of angiogenesis is one of the major adaptive mechanisms to counteract the adverse effects of hypoxia. In a previous work, we have shown that the adult rat striatum promotes angiogenesis in response to hypoxia via upregulation of the most important proangiogenic factor, the vascular endothelial growth factor (VEGF). However, the effects of hypoxia on angiogenesis in the aged striatum remain unknown and constitute our aim. Here we show the upregulation of hypoxia-inducible factor-1α in the striatum of aged (24-25 months old) Wistar rats exposed to acute hypoxia and analysed during a reoxygenation period ranging from 0 h to 5 days. While the mRNA expression of the proangiogenic factors VEGF, transforming growth factor-β1 (TGF-β1), and adrenomedullin dropped at 0 h post-hypoxia compared to normoxic control, no changes were detected at the protein level, showing an impaired response of these proangiogenic factors to hypoxia in the aged striatum. However, the striatal blood vessel network increased at 24 h of reoxygenation, suggesting that mechanisms independent from these proangiogenic factors may be involved in hypoxia-induced angiogenesis in the striatum of aged rats. A thorough understanding of the factors involved in the response to hypoxia is essential to guide the design of therapies for hypoxia-related diseases in the aged brain.

A key role for tetrahydrobiopterin-dependent endothelial NOS regulation in resistance arteries: studies in endothelial cell tetrahydrobiopterin-deficient mice

BACKGROUND AND PURPOSE

The cofactor tetrahydrobiopterin (BH4) is a critical regulator of endothelial NOS (eNOS) function, eNOS-derived NO and ROS signalling in vascular physiology. To determine the physiological requirement for de novo endothelial cell BH4 synthesis for the vasomotor function of resistance arteries, we have generated a mouse model with endothelial cell-specific deletion of Gch1, encoding GTP cyclohydrolase 1 (GTPCH), an essential enzyme for BH4 biosynthesis, and evaluated BH4-dependent eNOS regulation, eNOS-derived NO and ROS generation.

EXPERIMENTAL APPROACH

The reactivity of mouse second-order mesenteric arteries was assessed by wire myography. High performance liquid chromatography was used to determine BH4, BH2 and biopterin. Western blotting was used for expression analysis.

KEY RESULTS

Gch1fl/fl Tie2cre mice demonstrated reduced GTPCH protein and BH4 levels in mesenteric arteries. Deficiency in endothelial cell BH4 leads to eNOS uncoupling, increased ROS production and loss of NO generation in mesenteric arteries of Gch1fl/fl Tie2cre mice. Gch1fl/fl Tie2cre mesenteric arteries had enhanced vasoconstriction to U46619 and phenylephrine, which was abolished by L-NAME. Endothelium-dependent vasodilatations to ACh and SLIGRL were impaired in mesenteric arteries from Gch1fl/fl Tie2cre mice, compared with those from wild-type littermates. Loss of eNOS-derived NO-mediated vasodilatation was associated with increased eNOS-derived H2 O2 and cyclooxygenase-derived vasodilator in Gch1fl/fl Tie2cre mesenteric arteries.

CONCLUSIONS AND IMPLICATIONS

Endothelial cell Gch1 and BH4-dependent eNOS regulation play pivotal roles in maintaining vascular homeostasis in resistance arteries. Therefore, targeting vascular Gch1 and BH4 biosynthesis may provide a novel therapeutic target for the prevention and treatment of microvascular dysfunction in patients with cardiovascular disease.

The potential of stimulating nitric oxide formation in the treatment of hypertension

INTRODUCTION

Hypertension is a leading cause of morbidity and mortality worldwide. A major pathophysiological factor contributing to hypertension is reduced nitric oxide (NO) bioavailability. Strategies to address this pathophysiological mechanism could offer significant advantages. Areas covered: In this review we aimed at examining a variety of drugs (statins, beta-adrenergic receptor blockers, calcium channel blockers, angiotensin converting enzyme inhibitors, angiotensin II type-1 receptor blockers) used to treat hypertension and other cardiovascular diseases, particularly with respect to their potential of increasing NO bioavailability and activity in the cardiovascular system. There is now evidence supporting the notion that many cardiovascular drugs activate NO signaling or enhance NO bioavailability as a contributing mechanism to their beneficial cardiovascular effects. Moreover, other drugs may attenuate NO inactivation by superoxide and other reactive oxygen species by exerting antioxidant effects. More recently, the NO oxidation products nitrite and nitrate have been acknowledged as sources of NO after recycling back to NO. Activation of the nitrate-nitrite-NO pathway is an alternate pathway that may generate NO from both anions and exert antihypertensive effects. Expert opinion: In this review, we provide an overview of the possible mechanisms by which these drugs enhance NO bioavailability and help in the therapy of hypertension.

Roles of Vascular Oxidative Stress and Nitric Oxide in the Pathogenesis of Atherosclerosis

Major reactive oxygen species (ROS)–producing systems in vascular wall include NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidase, xanthine oxidase, the mitochondrial electron transport chain, and uncoupled endothelial nitric oxide (NO) synthase. ROS at moderate concentrations have important signaling roles under physiological conditions. Excessive or sustained ROS production, however, when exceeding the available antioxidant defense systems, leads to oxidative stress. Animal studies have provided compelling evidence demonstrating the roles of vascular oxidative stress and NO in atherosclerosis. All established cardiovascular risk factors such as hypercholesterolemia, hypertension, diabetes mellitus, and smoking enhance ROS generation and decrease endothelial NO production. Key molecular events in atherogenesis such as oxidative modification of lipoproteins and phospholipids, endothelial cell activation, and macrophage infiltration/activation are facilitated by vascular oxidative stress and inhibited by endothelial NO. Atherosclerosis develops preferentially in vascular regions with disturbed blood flow (arches, branches, and bifurcations). The fact that these sites are associated with enhanced oxidative stress and reduced endothelial NO production is a further indication for the roles of ROS and NO in atherosclerosis. Therefore, prevention of vascular oxidative stress and improvement of endothelial NO production represent reasonable therapeutic strategies in addition to the treatment of established risk factors (hypercholesterolemia, hypertension, and diabetes mellitus).

Restoration of perivascular adipose tissue function in diet-induced obese mice without changing bodyweight

Background and Purpose

We have recently shown that a reduced function of endothelial nitric oxide synthase (eNOS) in the perivascular adipose tissue (PVAT) contributes crucially to obesity‐induced vascular dysfunction in mice. The current study was conducted to test the hypothesis that vascular dysfunction in obesity can be reversed by in vivo improvement of PVAT eNOS activity.

Experimental Approach

Male C57BL/6J mice were fed a high‐fat diet (HFD) for 22 weeks to induce obesity. During the last 4 weeks of HFD feeding, the obese mice were treated p.o. with the standardized Crataegus extract WS® 1442, which has been shown previously to improve eNOS activity.

Key Results

Diet‐induced obesity in mice markedly reduced the vasodilator response of thoracic aorta to acetylcholine in wire myograph experiments. Strikingly, this vascular dysfunction was only evident in PVAT‐containing aorta but not in PVAT‐free aorta. In vivo treatment of obese mice with WS® 1442 had no effect on body weight or epididymal fat mass, but completely restored the vascular function of PVAT‐containing aorta. Feeding a HFD led to a reduced phosphorylation and an enhanced acetylation of PVAT eNOS, both effects were reversed by WS® 1442 treatment.

Conclusion and Implications

PVAT plays a key role in vascular dysfunction in diet‐induced obese mice. Not obesity itself, but a PVAT dysfunction is responsible for obesity‐induced vascular disorders. Improving PVAT function by pharmacological means (e.g. with WS® 1442) can ameliorate vascular function even without reducing body weight or fat mass.

Linked Articles

This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue – Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc

Nitrosyl-Cobinamide, a New and Direct Nitric Oxide–Releasing Drug Effective In Vivo

A limited number of nitric oxide (NO)-generating drugs are available for clinical use for acute and chronic conditions. Most of these agents are organic nitrates, which do not directly release NO; tolerance to the drugs develops, in part, as a consequence of their conversion to NO. We synthesized nitrosyl-cobinamide (NO-Cbi) from cobinamide, a structural analog of cobalamin (vitamin B12). NO-Cbi is a direct NO-releasing agent that we found was stable in water, but under physiologic conditions, it released NO with a half-life of 30 mins to 1 h. We show in five different biological systems that NO-Cbi is an effective NO-releasing drug. First, in cultured rat vascular smooth muscle cells, NO-Cbi induced phosphorylation of vasodilator-stimulated phosphoprotein, a downstream target of cGMP and cGMP-dependent protein kinase. Second, in isolated Drosophila melanogaster Malpighian tubules, NO-Cbi–stimulated fluid secretion was similar to that stimulated by Deta-NONOate and a cGMP analog. Third, in isolated mouse hearts, NO-Cbi increased coronary flow much more potently than nitroglycerin. Fourth, in contracted mouse aortic rings, NO-Cbi induced relaxation, albeit to a lesser extent than sodium nitroprusside. Fifth, in intact mice, a single NO-Cbi injection rapidly reduced blood pressure, and blood pressure returned to normal after 45 mins; repeated NO-Cbi injections induced the expected fall in blood pressure. These studies indicate that NO-Cbi is a useful NO donor that can be used experimentally in the laboratory; moreover, it could be developed into a vasodilating drug for treating hypertension and potentially other diseases such as angina and congestive heart failure.

Response of the Nitric Oxide System to Hypobaric Hypoxia in the Aged Striatum

BACKGROUND

Nitric oxide (NO) appears to play a key role in the hypoxic injury to the brain. We have previously reported that hypoxia/reoxygenation downregulated NO synthases (NOS) in the adult striatum. Until now, no data were available concerning the influence of aging in conjunction with hypoxia/reoxygenation on the NO system in the striatum.

OBJECTIVE

The aim of this study was to assess the role of the NO pathway in the hypoxic aged striatum.

METHODS

Wistar rats 24-25 months old were submitted to hypobaric hypoxia (20 min)/reoxygenation (0 h, 24 h, 5 days). Expression (PCR, immunohistochemistry/image analysis) and activity (NADPH-diaphorase/image analysis) of NOS isoforms (neuronal NOS or nNOS, endothelial NOS or eNOS, inducible NOS or iNOS) were analyzed together with nitrated protein expression (immunohistochemistry/image analysis). NO levels were indirectly quantified as nitrates/nitrites (NOx).

RESULTS

The mRNA levels of NOS isoforms were undetectable at 0 h after hypoxia in the striatum compared to the control. At later reoxygenation times, nNOS mRNA decreased, while eNOS mRNA augmented. Protein levels of nNOS and eNOS rose at 24 h after hypoxia, and iNOS protein increased at 5 days. NOx levels remained unchanged, whereas in situ NOS activity and protein nitration diminished during reoxygenation in the aged striatum.

CONCLUSION

The aged striatum may overexpress NOS isoforms as a neuroprotective-adaptive mechanism to hypoxia. However, this mechanism may not work properly in the aged striatum, since no changes in NO levels were detected after hypoxia. This may be related to the low activity of NOS isoforms in the hypoxic striatum.

Targeting Nitric Oxide with Natural Derived Compounds as a Therapeutic Strategy in Vascular Diseases

Within the family of endogenous gasotransmitters, nitric oxide (NO) is the smallest gaseous intercellular messenger involved in the modulation of several processes, such as blood flow and platelet aggregation control, essential to maintain vascular homeostasis. NO is produced by nitric oxide synthases (NOS) and its effects are mediated by cGMP-dependent or cGMP-independent mechanisms. Growing evidence suggests a crosstalk between the NO signaling and the occurrence of oxidative stress in the onset and progression of vascular diseases, such as hypertension, heart failure, ischemia, and stroke. For these reasons, NO is considered as an emerging molecular target for developing therapeutic strategies for cardio- and cerebrovascular pathologies. Several natural derived compounds, such as polyphenols, are now proposed as modulators of NO-mediated pathways. The aim of this review is to highlight the experimental evidence on the involvement of nitric oxide in vascular homeostasis focusing on the therapeutic potential of targeting NO with some natural compounds in patients with vascular diseases.

The Endothelium-Dependent Nitric Oxide-cGMP Pathway

Nitric oxide (NO)-cyclic 3'-5' guanosine monophosphate (cGMP) signaling plays a critical role on smooth muscle tone, platelet activity, cardiac contractility, renal function and fluid balance, and cell growth. Studies of the 1990s established endothelium dysfunction as one of the major causes of cardiovascular diseases. Therapeutic strategies that benefit NO bioavailability have been applied in clinical medicine extensively. Basic and clinical studies of cGMP regulation through activation of soluble guanylyl cyclase (sGC) or inhibition of cyclic nucleotide phosphodiesterase type 5 (PDE5) have resulted in effective therapies for pulmonary hypertension, erectile dysfunction, and more recently benign prostatic hyperplasia. This section reviews (1) how endothelial dysfunction and NO deficiency lead to cardiovascular diseases, (2) how soluble cGMP regulation leads to beneficial effects on disorders of the circulation system, and (3) the epigenetic regulation of NO-sGC pathway components in the cardiovascular system. In conclusion, the discovery of the NO-cGMP pathway revolutionized the comprehension of pathophysiological mechanisms involved in cardiovascular and other diseases. However, considering the expression "from bench to bedside" the therapeutic alternatives targeting NO-cGMP did not immediately follow the marked biochemical and pathophysiological revolution. Some therapeutic options have been effective and released on the market for pulmonary hypertension and erectile dysfunction such as inhaled NO, PDE5 inhibitors, and recently sGC stimulators. The therapeutic armamentarium for many other disorders is expected in the near future. There are currently numerous active basic and clinical research programs in universities and industries attempting to develop novel therapies for many diseases and medical applications.

Differential contribution of endothelium-derived relaxing factors to vascular reactivity in conduit and resistance arteries from normotensive and hypertensive rats

The endothelium contributes to the maintenance of vasodilator tone by releasing nitric oxide (NO), prostacyclin (PGI2), and endothelium-derived hyperpolarizing factor (EDHF). In hypertension, endothelium-dependent relaxation is attenuated (a phenomenon referred to as endothelial dysfunction) and contributes to the increased peripheral resistance. However, which vasodilator among NO, PGI2, and EDHF is impaired in hypertension remains largely unknown. The present study was designed to study the exact contribution of NO, PGI2, and EDHF to vascular reactivity in conduit and resistance artery, under physiological and pathological conditions. The aorta and the second-order mesenteric artery from spontaneous hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were used to measure the vasorelaxation with myograph technology, in the presence or absence of different inhibitors. The results showed that the endothelium-dependent vasodilatation in the conduit artery was mediated mainly by NO, whereas the resistant artery by NO, PGI2, and EDHF together. In hypertension, both NO-mediated relaxation in the conduit artery and NO-, PGI2-, and EDHF-mediated dilation in the resistant artery were markedly impaired. Furthermore, the endothelium-dependent and the endothelium-independent vasorelaxation in conduit artery was attenuated more pronouncedly than that in the resistant artery from hypertensive rats, suggesting that the conduit artery is more vulnerable to hypertensive condition. In conclusion, vasodilators including NO, PGI2, and EDHF contribute distinctively to endothelium-dependent relaxation in conduit and resistance artery under physiological and pathological conditions.