Endothelium dependent hyperpolarization-type relaxation compensates for attenuated nitric oxide-mediated responses in subcutaneous arteries of diabetic patients

Vitamin D deficiency enhances vascular oxidative stress, inflammation, and angiotensin II levels in the microcirculation of diabetic patients

Low vitamin D (vitD) levels have been reported to be a risk factor for diabetes-related cardiovascular complications. This study examined the effects of vitD deficiency on oxidative stress (OS), inflammation, and levels of the vasoconstrictor angiotensin II (Ang II) in the microvascular tissue of type 2 diabetic patients. Patients were categorized into (i) vitD non-deficient diabetics (DNP, n = 10) and (ii) vitD-deficient diabetics (DDP, n = 10), based on their serum 25(OH)D levels. Subcutaneous fat tissues with intact blood vessels were collected during lower limb surgical procedures. The blood vessel were isolated; measurements of the antioxidant enzyme superoxide dismutase (SOD) activity, OS marker malondialdehyde (MDA), Ang II, and the inflammatory marker, TNF-α of the microvascular tissues were determined. Elevated MDA levels and reduced SOD activity, with higher levels of TNF-α and Ang II were observed in the microvascular tissues of DDP compared to DNP. VitD deficiency did not associate with glycemic parameters (fasting blood glucose and glycated hemoglobin) levels. In conclusion, vitD deficiency was correlated with higher microvascular tissue OS, inflammation, and Ang II levels in type 2 diabetic patients. This may contribute to early vasculopathy that occurs in diabetic patients, thus, may contribute to the planning of therapeutic strategies to delay or prevent cardiovascular complications.

Impact of aging on vascular ion channels: perspectives and knowledge gaps across major organ systems

Individuals aged ≥65 yr will comprise ∼20% of the global population by 2030. Cardiovascular disease remains the leading cause of death in the world with age-related endothelial "dysfunction" as a key risk factor. As an organ in and of itself, vascular endothelium courses throughout the mammalian body to coordinate blood flow to all other organs and tissues (e.g., brain, heart, lung, skeletal muscle, gut, kidney, skin) in accord with metabolic demand. In turn, emerging evidence demonstrates that vascular aging and its comorbidities (e.g., neurodegeneration, diabetes, hypertension, kidney disease, heart failure, and cancer) are "channelopathies" in large part. With an emphasis on distinct functional traits and common arrangements across major organs systems, the present literature review encompasses regulation of vascular ion channels that underlie blood flow control throughout the body. The regulation of myoendothelial coupling and local versus conducted signaling are discussed with new perspectives for aging and the development of chronic diseases. Although equipped with an awareness of knowledge gaps in the vascular aging field, a section has been included to encompass general feasibility, role of biological sex, and additional conceptual and experimental considerations (e.g., cell regression and proliferation, gene profile analyses). The ultimate goal is for the reader to see and understand major points of deterioration in vascular function while gaining the ability to think of potential mechanistic and therapeutic strategies to sustain organ perfusion and whole body health with aging.

Endothelium dysfunction in hind limb arteries of male Zucker Diabetic-Sprague Dawley rats

Endothelium dysfunction produces peripheral vascular disease comorbidities in type 2 diabetes, including hypertension, and critical limb ischemia. In this study we aimed to test endothelial dysfunction, the vasodilator effects of a proteinase-activated receptor 2 (PAR2) agonist (2fLIGRLO), and thromboxane A₂ synthase inhibitor (ozagrel) on PAR2 vasodilation in hind limb arteries ex vivo, using Zucker Diabetic-Sprague Dawley (ZDSD) rats, a model of type 2 diabetes. Male Sprague Dawley rats (SD) and ZDSD were fed a high-fat content 'Western diet' from 16 to 20 weeks of age (wks) then fed a standard laboratory diet. We identified diabetic ZDSD rats by two consecutive blood glucose measurements > 12.5 mM, based on weekly monitoring. We used acetylcholine, 2fLIGRLO, and nitroprusside with wire-myograph methods to compare relaxations of femoral, and saphenous arteries from diabetic ZDSD (21-23 wks) to age-matched normoglycemic SD. All arteries showed evidence of endothelium dysfunction using acetylcholine (reduced maximum relaxations, reduced sensitivity), and higher sensitivities to 2fLIGRLO, and nitroprusside in ZDSD vs SD. Ozagrel treatment of ZDSD distal segments, and end-branches of saphenous arteries decreased their sensitivities to 2fLIGRLO. We tested aortas for altered expression of endothelium-specific gene targets using PCR array and qPCR. PAR2, and placental growth factor gene transcripts were 1.5, and 4-times higher in ZDSD than SD aortas. Hind limb arteries of ZDSD exhibit endothelium dysfunction having less GPCR agonist induced vasodilation by endothelial NO-release. Different expression of several endothelial genes in ZDSD vs SD aortas, including PAR2, suggests altered inflammatory, and angiogenesis signaling pathways in the endothelium of ZDSD.

High altitude differentially modulates potassium channel-evoked vasodilatation in pregnant human myometrial arteries

High-altitude (>2500 m or 8200 ft) residence reduces uterine artery blood flow during pregnancy, contributing to an increased incidence of preeclampsia and intrauterine growth restriction. However, not all pregnancies are affected by the chronic hypoxic conditions of high-altitude residence. K+ channels play important roles in the uterine vascular adaptation to pregnancy, promoting a reduction in myogenic tone and an increase in blood flow. We hypothesized that, in pregnancies with normal fetal growth at high altitude, K+ channel-dependent vasodilatation of myometrial arteries is increased compared to those from healthy pregnant women at a lower altitude (∼1700 m). Using pharmacological modulation of two K+ channels, ATP-sensitive (KATP ) and large-conductance Ca2+ -activated (BKCa ) K+ channels, we assessed the vasodilatation of myometrial arteries from appropriate for gestational age (AGA) pregnancies in women living at high or low altitudes. In addition, we evaluated the localization of these channels in the myometrial arteries using immunofluorescence. Our results showed an endothelium-dependent increase in KATP -dependent vasodilatation in myometrial arteries from high versus low altitude, whereas vasodilatation induced by BKCa activation was reduced in these vessels. Additionally, KATP channel co-localization with endothelial markers was reduced in the high-altitude myometrial arteries, which suggested that the functional increase in KATP activity may be by mechanisms other than regulation of channel localization. These observations highlight an important contribution of K+ channels to the human uterine vascular adaptation to pregnancy at high altitude serving to maintain normal fetal growth under conditions of chronic hypoxia. KEY POINTS: High-altitude (>2500 m or 8200 ft) residence reduces uterine blood flow during pregnancy and fetal growth. Animal models of high altitude/chronic hypoxia suggest that these reductions are partially due to reduced vascular K+. channel responses, such as those elicited by large conductance Ca2+ -activated (BKCa ) and ATP-sensitive (KATP ) K+ channel activation. We found that women residing at high versus low altitude during pregnancy showed diminished myometrial artery vasodilatory responses to endothelium-independent BKCa channel activation but greater responses to endothelium-dependent KATP channel activation. Our observations indicate that KATP channels play an adaptive role in maintaining myometrial artery vasodilator sensitivity under chronic hypoxic conditions during pregnancy. Thus, KATP channels represent potential therapeutic targets for augmenting uteroplacental blood flow and, in turn, preserving fetal growth in cases of uteroplacental hypoperfusion.

Vasoactive Effects of Chronic Treatment with Fructose and Slow-Releasing H2S Donor GYY-4137 in Spontaneously Hypertensive Rats: The Role of Nitroso and Sulfide Signalization

Increased fructose consumption induces metabolic-syndrome-like pathologies and modulates vasoactivity and the participation of nitric oxide (NO) and hydrogen sulfide (H₂S). We investigated whether a slow-releasing H₂S donor, GYY-4137, could exert beneficial activity in these conditions. We examined the effect of eight weeks of fructose intake on the blood pressure, biometric parameters, vasoactive responses, and NO and H₂S pathways in fructose-fed spontaneously hypertensive rats with or without three weeks of GYY-4137 i.p. application. GYY-4137 reduced triacylglycerol levels and blood pressure, but not adiposity, and all were increased by fructose intake. Fructose intake generally enhanced endothelium-dependent vasorelaxation, decreased adrenergic contraction, and increased protein expression of interleukin-6 (IL-6), tumor necrosis factor alpha (TNFα), and concentration of conjugated dienes in the left ventricle (LV). Although GYY-4137 administration did not affect vasorelaxant responses, it restored disturbed contractility, LV oxidative damage and decreased protein expression of TNFα in fructose-fed rats. While the participation of endogenous H₂S in vasoactive responses was not affected by fructose treatment, the expression of H₂S-producing enzyme cystathionine β-synthase in the LV was increased, and the stimulation of the NO signaling pathway improved endothelial function in the mesenteric artery. On the other hand, chronic treatment with GYY-4137 increased the expression of H₂S-producing enzyme cystathionine γ-lyase in the LV and stimulated the beneficial pro-relaxant and anti-contractile activity of endogenous H₂S in thoracic aorta. Our results suggest that sulfide and nitroso signaling pathways could trigger compensatory vasoactive responses in hypertensive rats with metabolic disorder. A slow H₂S-releasing donor could partially amend metabolic-related changes and trigger beneficial activity of endogenous H₂S.

Differential contribution of renal cytochrome P450 enzymes to kidney endothelial dysfunction and vascular oxidative stress in obesity

Arachidonic acid (AA)-derived cytochrome P450 (CYP) derivatives, epoxyeicosatrienoic acids (EETs) and 20-hidroxyeicosatetranoic acid (20-HETE), play a key role in kidney tubular and vascular functions and blood pressure. Altered metabolism of CYP epoxygenases and CYP hydroxylases has differentially been involved in the pathogenesis of metabolic disease-associated vascular complications, although the mechanisms responsible for the vascular injury are unclear. The present study aimed to assess whether obesity-induced changes in CYP enzymes may contribute to oxidative stress and endothelial dysfunction in kidney preglomerular arteries. Endothelial function and reactive oxygen species (ROS) production were assessed in interlobar arteries of obese Zucker rats (OZR) and their lean counterparts lean Zucker rats (LZR) and the effects of CYP2C and CYP4A inhibitors sulfaphenazole and HET0016, respectively, were examined on the endothelium-dependent relaxations and O2- and H2O2 levels of preglomerular arteries. Non-nitric oxide (NO) non-prostanoid endothelium-derived hyperpolarization (EDH)-type responses were preserved but resistant to the CYP epoxygenase blocker sulfaphenazole in OZR in contrast to those in LZR. Sulfaphenazole did not further inhibit reduced arterial H2O2 levels, and CYP2C11/CYP2C23 enzymes were downregulated in intrarenal arteries from OZR. Renal EDH-mediated relaxations were preserved in obese rats by the enhanced activity and expression of endothelial calcium-activated potassium channels (KCa). CYP4A blockade restored impaired NO-mediated dilatation and inhibited augmented O2- production in kidney arteries from OZR. The current data demonstrate that both decreased endothelial CYP2C11/ CYP2C23-derived vasodilator H2O2 and augmented CYP4A-derived 20-HETE contribute to endothelial dysfunction and vascular oxidative stress in obesity. CYP4A inhibitors ameliorate arterial oxidative stress and restore endothelial function which suggests its therapeutic potential for the vascular complications of obesity-associated kidney injury.

Increased Fetal Cardiovascular Disease Risk: Potential Synergy Between Gestational Diabetes Mellitus and Maternal Hypercholesterolemia

Cardiovascular diseases (CVD) remain a major cause of death worldwide. Evidence suggests that the risk for CVD can increase at the fetal stages due to maternal metabolic diseases, such as gestational diabetes mellitus (GDM) and maternal supraphysiological hypercholesterolemia (MSPH). GDM is a hyperglycemic, inflammatory, and insulin-resistant state that increases plasma levels of free fatty acids and triglycerides, impairs endothelial vascular tone regulation, and due to the increased nutrient transport, exposes the fetus to the altered metabolic conditions of the mother. MSPH involves increased levels of cholesterol (mainly as low-density lipoprotein cholesterol) which also causes endothelial dysfunction and alters nutrient transport to the fetus. Despite that an association has already been established between MSPH and increased CVD risk, however, little is known about the cellular processes underlying this relationship. Our knowledge is further obscured when the simultaneous presentation of MSPH and GDM takes place. In this context, GDM and MSPH may substantially increase fetal CVD risk due to synergistic impairment of placental nutrient transport and endothelial dysfunction. More studies on the separate and/or cumulative role of both processes are warranted to suggest specific treatment options.

Cell therapy rescues aging-induced beta-1 adrenergic receptor and GRK2 dysfunction in the coronary microcirculation

Our past study showed that coronary arterioles isolated from adipose-derived stromal vascular fraction (SVF)-treated rats showed amelioration of the age-related decrease in vasodilation to beta-adrenergic receptor (β-AR) agonist and improved β-AR-dependent coronary flow and microvascular function in a model of advanced age. We hypothesized that intravenously (i.v.) injected SVF improves coronary microvascular function in aged rats by re-establishing the equilibrium of the negative regulators of the internal adrenergic signaling cascade, G-protein receptor kinase 2 (GRK2) and G-alpha inhibitory (Gαi) proteins, back to youthful levels. Female Fischer-344 rats aged young (3 months, n = 24), old (24 months, n = 26), and old animals that received 1 × 10⁷ green fluorescent protein (GFP+) SVF cells (O + SVF, n = 11) 4 weeks prior to sacrifice were utilized. Overnight urine was collected prior to sacrifice for catecholamine measurements. Cardiac samples were used for western blotting while coronary arterioles were isolated for pressure myography studies, immunofluorescence staining, and RNA sequencing. Coronary microvascular levels of the β1 adrenergic receptor are decreased with advancing age, but this decreased expression was rescued by SVF treatment. Aging led to a decrease in phosphorylated GRK2 in cardiomyocytes vs. young control with restoration of phosphorylation status by SVF. In vessels, there was no change in genetic transcription (RNAseq) or protein expression (immunofluorescence); however, inhibition of GRK2 (paroxetine) led to improved vasodilation to norepinephrine in the old control (OC) and O + SVF, indicating greater GRK2 functional inhibition of β1-AR in aging. SVF works to improve adrenergic-mediated vasodilation by restoring the β1-AR population and mitigating signal cascade inhibitors to improve vasodilation.

Aging Alters Cerebrovascular Endothelial GPCR and K+ Channel Function: Divergent Role of Biological Sex

Age-related dementia entails impaired blood flow to and throughout the brain due, in part, to reduced endothelial nitric oxide signaling. However, it is unknown whether sex affects cerebrovascular Gq-protein-coupled receptors (GPCRs) and K+ channels underlying endothelium-derived hyperpolarization (EDH) during progressive aging. Thus, we simultaneously evaluated intracellular Ca2+ ([Ca2+]i) and membrane potential (Vm) of intact endothelial tubes freshly isolated from posterior cerebral arteries of young (4-6 mo), middle-aged (12-16 mo), and old (24-28 mo) male and female C57BL/6 mice. Purinergic receptor function (vs. muscarinic) was dominant and enhanced for [Ca2+]i increases in old females versus old males. However, Ca2+-sensitive K+ channel function as defined by NS309-evoked Vm hyperpolarization was mildly impaired in females versus males during old age. This sex-based contrast in declined function of GPCRs and K+ channels to produce EDH may support a greater ability for physiological endothelial GPCR function to maintain optimal cerebral blood flow in females versus males during old age. As reflective of the pattern of cerebral blood flow decline in human subjects, inward-rectifying K+ (KIR) channel function decreased with progressive age regardless of sex. Combined age-related analyses masked male versus female aging and, contrary to expectation, hydrogen peroxide played a minimal role. Altogether, we conclude a sex-based divergence in cerebrovascular endothelial GPCR and K+ channel function while highlighting a previously unidentified form of age-related endothelial dysfunction as reduced KIR channel function.

Diabetes Attenuates the Contribution of Endogenous Nitric Oxide but Not Nitroxyl to Endothelium Dependent Relaxation of Rat Carotid Arteries

Endothelial dysfunction is a major risk factor for several of the vascular complications of diabetes, including ischemic stroke. Nitroxyl (HNO), the one electron reduced and protonated form of nitric oxide (NO•), is resistant to scavenging by superoxide, but the role of HNO in diabetes mellitus associated endothelial dysfunction in the carotid artery remains unknown. Aim: To assess how diabetes affects the role of endogenous NO• and HNO in endothelium-dependent relaxation in rat isolated carotid arteries. Methods: Male Sprague Dawley rats were fed a high-fat-diet (HFD) for 2 weeks prior to administration of low dose streptozotocin (STZ; 35 mg/kg i. p./day) for 2 days. The HFD was continued for a further 12 weeks. Sham rats were fed standard chow and administered with citrate vehicle. After 14 weeks total, rats were anesthetized and carotid arteries collected to assess responses to the endothelium-dependent vasodilator, acetylcholine (ACh) by myography. The combination of calcium-activated potassium channel blockers, TRAM-34 (1 μmol/L) and apamin (1 μmol/L) was used to assess the contribution of endothelium-dependent hyperpolarization to relaxation. The corresponding contribution of NOS-derived nitrogen oxide species to relaxation was assessed using the combination of the NO• synthase inhibitor, L-NAME (200 μmol/L) and the soluble guanylate cyclase inhibitor ODQ (10 μmol/L). Lastly, L-cysteine (3 mmol/L), a selective HNO scavenger, and hydroxocobalamin (HXC; 100 μmol/L), a NO• scavenger, were used to distinguish between NO• and HNO-mediated relaxation. Results: At study end, diabetic rats exhibited significantly retarded body weight gain and elevated blood glucose levels compared to sham rats. The sensitivity and the maximal relaxation response to ACh was significantly impaired in carotid arteries from diabetic rats, indicating endothelial dysfunction. The vasorelaxation evoked by ACh was abolished by L-NAME plus ODQ, but not affected by the apamin plus TRAM-34 combination, indicating that NOS-derived nitrogen oxide species are the predominant endothelium-derived vasodilators in sham and diabetic rat carotid arteries. The maximum relaxation to ACh was significantly decreased by L-cysteine in both sham and diabetic rats, whereas HXC attenuated ACh-induced relaxation only in sham rats, suggesting that diabetes impaired the contribution of NO•, whereas HNO-mediated vasorelaxation remained intact. Conclusion: Both NO• and HNO contribute to endothelium-dependent relaxation in carotid arteries. In diabetes, NO•-mediated relaxation is impaired, whereas HNO-mediated relaxation was preserved. The potential for preserved HNO activity under pathological conditions that are associated with oxidative stress indicates that HNO donors may represent a viable therapeutic approach to the treatment of vascular dysfunction.

KCa channel activation normalizes endothelial function in Type 2 Diabetic resistance arteries by improving intracellular Ca2+ mobilization

BACKGROUND

Endothelial dysfunction is an early pathogenic event in the progression of cardiovascular disease in patients with Type 2 Diabetes (T2D). Endothelial KCa2.3 and KCa3.1 K⁺ channels are important regulators of arterial diameter, and we thus hypothesized that SKA-31, a small molecule activator of KCa2.3 and KCa3.1, would positively influence agonist-evoked dilation in myogenically active resistance arteries in T2D.

METHODOLOGY

Arterial pressure myography was utilized to investigate endothelium-dependent vasodilation in isolated cremaster skeletal muscle resistance arteries from 22 to 24 week old T2D Goto-Kakizaki rats, age-matched Wistar controls, and small human intra-thoracic resistance arteries from T2D subjects. Agonist stimulated changes in cytosolic free Ca²⁺ in acutely isolated, single endothelial cells from Wistar and T2D Goto-Kakizaki cremaster and cerebral arteries were examined using Fura-2 fluorescence imaging.

MAIN FINDINGS

Endothelium-dependent vasodilation in response to acetylcholine (ACh) or bradykinin (BK) was significantly impaired in isolated cremaster arteries from T2D Goto-Kakizaki rats compared with Wistar controls, and similar results were observed in human intra-thoracic arteries. In contrast, inhibition of myogenic tone by sodium nitroprusside, a direct smooth muscle relaxant, was unaltered in both rat and human T2D arteries. Treatment with a threshold concentration of SKA-31 (0.3 μM) significantly enhanced vasodilatory responses to ACh and BK in arteries from T2D Goto-Kakizaki rats and human subjects, whereas only modest effects were observed in non-diabetic arteries of both species. Mechanistically, SKA-31 enhancement of evoked dilation was independent of vascular NO synthase and COX activities. Remarkably, SKA-31 treatment improved agonist-stimulated Ca²⁺ elevation in acutely isolated endothelial cells from T2D Goto-Kakizaki cremaster and cerebral arteries, but not from Wistar control vessels. In contrast, SKA-31 treatment did not affect intracellular Ca²⁺ release by the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) inhibitor cyclopiazonic acid.

CONCLUSIONS

Collectively, our data demonstrate that KCa channel modulation can acutely restore endothelium-dependent vasodilatory responses in T2D resistance arteries from rats and humans, which appears to involve improved endothelial Ca²⁺ mobilization.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Role of Caveolin-1 in Diabetes and Its Complications

It is estimated that in 2017 there were 451 million people with diabetes worldwide. These figures are expected to increase to 693 million by 2045; thus, innovative preventative programs and treatments are a necessity to fight this escalating pandemic disorder. Caveolin-1 (CAV1), an integral membrane protein, is the principal component of caveolae in membranes and is involved in multiple cellular functions such as endocytosis, cholesterol homeostasis, signal transduction, and mechanoprotection. Previous studies demonstrated that CAV1 is critical for insulin receptor-mediated signaling, insulin secretion, and potentially the development of insulin resistance. Here, we summarize the recent progress on the role of CAV1 in diabetes and diabetic complications.

Vascular adenosine monophosphate-activated protein kinase: Enhancer, brake or both?

Adenosine monophosphate-activated protein kinase (AMPK), expressed/present ubiquitously in the body, contributes to metabolic regulation. In the vasculature, activation of AMPK is associated with several beneficial biological effects including enhancement of vasodilatation, reduction of oxidative stress and inhibition of inflammatory reactions. The vascular protective effects of certain anti-diabetic (metformin and sitagliptin) or lipid-lowering (simvastatin and fenofibrate) therapeutic agents, of active components of Chinese medicinal herbs (resveratrol and berberine) and of pharmacological agents (AICAR, A769662 and PT1) have been attributed to the activation of AMPK (in endothelial cells, vascular smooth muscle cells and/or perivascular adipocytes), independently of changes in the metabolic profile (eg glucose tolerance and/or plasma lipoprotein levels), leading to improved endothelium-derived nitric oxide-mediated vasodilatation and attenuated endothelium-derived cyclooxygenase-dependent vasoconstriction. By contrast, endothelial AMPK activation with pharmacological agents or by genetic modification is associated with reduced endothelium-dependent relaxations in small blood vessels and elevated systolic blood pressure. Indeed, AMPK activators inhibit endothelium-dependent hyperpolarization (EDH)-type relaxations in superior mesenteric arteries, partly by inhibiting endothelial calcium-activated potassium channel signalling. Therefore, AMPK activation is not necessarily beneficial in terms of endothelial function. The contribution of endothelial AMPK in the regulation of vascular tone, in particular in the microvasculature where EDH plays a more important role, remains to be characterized.

Differential contribution of Nox1, Nox2 and Nox4 to kidney vascular oxidative stress and endothelial dysfunction in obesity

Oxidative stress-associated endothelial dysfunction is a key pathogenic factor underlying the microvascular complications of metabolic disease. NADPH oxidase (Nox) is a major source of oxidative stress in diabetic nephropathy and chronic kidney disease, despite Nox4 and Nox2 have been identified as relevant sources of vasodilator endothelial H₂O₂.The present study was sought to investigate the role of Nox enzymes in renal vascular oxidative stress and endothelial dysfunction in a rat model of genetic obesity. Endothelial function was assessed in intrarenal arteries of obese Zucker rats (OZR) and their counterparts lean Zucker rats (LZR) mounted in microvascular myographs, and superoxide (O₂^.-) and H₂O₂ production were measured. Impaired endothelium-dependent relaxations to acetylcholine (ACh) were associated to augmented O₂^.- generation, but neither ROS scavengers nor the Nox inhibitor apocynin significantly improved these relaxant responses in renal arteries of OZR. Whereas NO contribution to endothelial relaxations was blunted, catalase-sensitive non-NO non-prostanoid relaxations were enhanced in obese rats. Interestingly, NADPH-dependent O₂^.- production was augmented while NADPH-dependent H₂O₂ generation was reduced, and cytosolic and mitochondrial SOD were up-regulated in kidney of obese rats. Nox4 was down-regulated in renal arteries and Nox4-dependent H₂O₂ generation and endothelial relaxation were reduced in OZR. Up-regulation of both Nox2 and Nox1 was associated with augmented O₂^.- production but reduced H₂O₂ generation and blunted endothelial Nox2-derived H₂O₂-mediated in obese rats. Moreover, increased Nox1-derived O₂^.- contributed to renal endothelial dysfunction in OZR. In summary, the current data support a main role for Nox1-derived O₂^.- in kidney vascular oxidative stress and renal endothelial dysfunction in obesity, while reduced endothelial Nox4 expression associated to decreased H₂O₂ generation and H₂O₂-mediated vasodilatation might hinder Nox4 protective renal effects thus contributing to kidney injury. This suggests that effective therapies to counteract oxidative stress and prevent microvascular complications must identify the specific Nox subunits involved in metabolic disease.

Endothelium-Dependent Hyperpolarization (EDH) in Diabetes: Mechanistic Insights and Therapeutic Implications

Diabetes mellitus is one of the major risk factors for cardiovascular disease and is an important health issue worldwide. Long-term diabetes causes endothelial dysfunction, which in turn leads to diabetic vascular complications. Endothelium-derived nitric oxide is a major vasodilator in large-size vessels, and the hyperpolarization of vascular smooth muscle cells mediated by the endothelium plays a central role in agonist-mediated and flow-mediated vasodilation in resistance-size vessels. Although the mechanisms underlying diabetic vascular complications are multifactorial and complex, impairment of endothelium-dependent hyperpolarization (EDH) of vascular smooth muscle cells would contribute at least partly to the initiation and progression of microvascular complications of diabetes. In this review, we present the current knowledge about the pathophysiology and underlying mechanisms of impaired EDH in diabetes in animals and humans. We also discuss potential therapeutic approaches aimed at the prevention and restoration of EDH in diabetes.

Oxymatrine ameliorates diabetes-induced aortic endothelial dysfunction via the regulation of eNOS and NOX4

AIM

Oxymatrine (OMT) is the major quinolizidine alkaloid extracted from the root of Sophora flavescens Ait (the Chinese herb Kushen) and exhibits diverse pharmacological actions. In this study, we investigated the effects of OMT on diabetes-associated aortic endothelial dysfunction in a rat model of diabetes and its mechanisms.

METHODS

Male Sprague-Dawley rats were randomly divided into five groups: control, diabetic rats, diabetic rats treated with OMT (60, 120 mg/kg per day, by gavage), and diabetic rats treated with metformin (20 mg/kg per day, by gavage). The serum fasting blood glucose, insulin, total cholesterol, triglyceride, and nitric oxide (NO) levels were determined with commercial kits. Biochemical indices reflecting oxidative stress, such as malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) were analyzed with commercial kits. Mitochondrial reactive oxygen species 2',7'-dichlorofluorescein diacetate (DCFH-DA) was measured by fluorescence microscopy. Histological analyses were conducted to observe morphological changes. Western blot analysis was applied to detect the expression levels of eNOS and NOX4. Reverse transcription polymerase chain reaction was used to detect the expressions of eNOS and NOX4 messenger RNA (mRNA).

RESULTS

The diabetic rats exhibited markedly reduced body weight and increased plasma glucose levels. Moreover, the diabetic rats showed oxidative stress (significantly increased MDA and decreased SOD, CAT, GSH-Px, and serum NO levels). Hyperglycemia caused significant endothelial injury and dysfunction, including vasodilative and histologic changes in the diabetic rats. The expressions of phospho-eNOS protein and mRNA were significantly decreased, while the NOX4 protein expression was increased in the aortas of the diabetic rats. All of these diabetes-induced effects were reversed by OMT in the diabetic rats.

CONCLUSION

The OMT treatment ameliorates diabetic endothelial dysfunction through enhanced NO bioavailability by upregulating eNOS expression and downregulating expression of NOX4.

Functional Interaction among KCa and TRP Channels for Cardiovascular Physiology: Modern Perspectives on Aging and Chronic Disease

Effective delivery of oxygen and essential nutrients to vital organs and tissues throughout the body requires adequate blood flow supplied through resistance vessels. The intimate relationship between intracellular calcium ([Ca²⁺]_i) and regulation of membrane potential (V_m) is indispensable for maintaining blood flow regulation. In particular, Ca²⁺-activated K⁺ (K_Ca) channels were ascertained as transducers of elevated [Ca²⁺]_i signals into hyperpolarization of V_m as a pathway for decreasing vascular resistance, thereby enhancing blood flow. Recent evidence also supports the reverse role for K_Ca channels, in which they facilitate Ca²⁺ influx into the cell interior through open non-selective cation (e.g., transient receptor potential; TRP) channels in accord with robust electrical (hyperpolarization) and concentration (~20,000-fold) transmembrane gradients for Ca²⁺. Such an arrangement supports a feed-forward activation of V_m hyperpolarization while potentially boosting production of nitric oxide. Furthermore, in vascular types expressing TRP channels but deficient in functional K_Ca channels (e.g., collecting lymphatic endothelium), there are profound alterations such as downstream depolarizing ionic fluxes and the absence of dynamic hyperpolarizing events. Altogether, this review is a refined set of evidence-based perspectives focused on the role of the endothelial K_Ca and TRP channels throughout multiple experimental animal models and vascular types. We discuss the diverse interactions among K_Ca and TRP channels to integrate Ca²⁺, oxidative, and electrical signaling in the context of cardiovascular physiology and pathology. Building from a foundation of cellular biophysical data throughout a wide and diverse compilation of significant discoveries, a translational narrative is provided for readers toward the treatment and prevention of chronic, age-related cardiovascular disease.

Calcium and electrical signaling in arterial endothelial tubes: New insights into cellular physiology and cardiovascular function

The integral role of the endothelium during the coordination of blood flow throughout vascular resistance networks has been recognized for several decades now. Early examination of the distinct anatomy and physiology of the endothelium as a signaling conduit along the vascular wall has prompted development and application of an intact endothelial "tube" study model isolated from rodent skeletal muscle resistance arteries. Vasodilatory signals such as increased endothelial cell (EC) Ca²⁺ ([Ca²⁺ ]_i ) and hyperpolarization take place in single ECs while shared between electrically coupled ECs through gap junctions up to distances of millimeters (≥2 mm). The small- and intermediate-conductance Ca²⁺ activated K⁺ (SK_Ca /IK_Ca or K_Ca 2.3/K_Ca 3.1) channels function at the interface of Ca²⁺ signaling and hyperpolarization; a bidirectional relationship whereby increases in [Ca²⁺ ]_i activate SK_Ca /IK_Ca channels to produce hyperpolarization and vice versa. Further, the spatial domain of hyperpolarization among electrically coupled ECs can be finely tuned via incremental modulation of SK_Ca /IK_Ca channels to balance the strength of local and conducted electrical signals underlying vasomotor activity. Multifunctional properties of the voltage-insensitive SK_Ca /IK_Ca channels of resistance artery endothelium may be employed for therapy during the aging process and development of vascular disease.

KMUP-1 protects against streptozotocin-induced mesenteric artery dysfunction via activation of ATP-sensitive potassium channels

BACKGROUND

Diabetes mellitus is a metabolic disorder characterized by chronic hyperglycemia accompanied by impaired vascular and endothelial function. Activation of ATP-sensitive potassium (K_ATP) channels can protect endothelial function against hypertension and hyperglycemia. KMUP-1, a xanthine derivative, has been demonstrated to modulate K⁺-channel activity in smooth muscles. This study investigated protective mechanisms of KMUP-1 in impaired mesenteric artery (MA) reactivity in streptozotocin (STZ)-induced diabetic rats.

METHODS

Rats were divided into three groups: control, STZ (65 mg/kg, ip) and STZ + KMUP-1 (5 or 10 mg/kg/day, ip). MA reactivity was measured by dual wire myograph. MA smooth muscle cells (MASMCs) were enzymatically dissociated and the K_ATP currents recorded by a whole-cell patch-clamp technique.

RESULTS

STZ decreased MA K_ATP currents in a time-course dependent manner and achieved steady inhibition at day 14. In the MASMCs of STZ-treated rats, KMUP-1 partially recovered the K_ATP currents, suggesting that vascular K_ATP channels were activated by KMUP-1. K⁺ (80 mM KCl)-induced MA contractions in STZ-treated rats were higher than those of control rats. KMUP-1 significantly attenuated STZ-stimulated MA contractions in response to high K⁺, suggesting that KMUP-1 may partly restore the vascular reactivity of MAs. In addition, STZ decreased the expression of endothelial nitric oxide synthase (eNOS) and this effect was reversed by KMUP-1, suggesting that KMUP-1 could improve STZ-induced vascular endothelial dysfunction.

CONCLUSION

KMUP-1 prevents STZ impairment of MA reactivity, eNOS levels and K_ATP channels, and accordingly protects against vascular dysfunction in diabetic rats.

Impact of Aging on Calcium Signaling and Membrane Potential in Endothelium of Resistance Arteries: A Role for Mitochondria

Impaired blood flow to peripheral tissues during advanced age is associated with endothelial dysfunction and diminished bioavailability of nitric oxide (NO). However, it is unknown whether aging impacts coupling between intracellular calcium ([Ca2+]i) signaling and small- and intermediate K+ channel (SKCa/IKCa) activity during endothelium-derived hyperpolarization (EDH), a signaling pathway integral to dilation of the resistance vasculature. To address the potential impact of aging on EDH, Fura-2 photometry and intracellular recording were applied to evaluate [Ca2+]i and membrane potential of intact endothelial tubes (width, 60 µm; length, 1-3 mm) freshly isolated from superior epigastric arteries of young (4-6 mo) and old (24-26 mo) male C57BL/6 mice. In response to acetylcholine, intracellular release of Ca2+ from the endoplasmic reticulum (ER) was enhanced with aging. Further, treatment with the mitochondrial uncoupler FCCP evoked a significant increase of [Ca2+]i with membrane hyperpolarization in an SKCa/IKCa-dependent manner in the endothelium of old but not young mice. We conclude that the ability of resistance artery endothelium to release Ca2+ from intracellular stores (ie, ER and mitochondria) and hyperpolarize Vm via SKCa/IKCa activation is augmented as compensation for reduced NO bioavailability during advanced age.

Serelaxin treatment reverses vascular dysfunction and left ventricular hypertrophy in a mouse model of Type 1 diabetes

Serelaxin prevents endothelial dysfunction in the mouse aorta ex vivo and inhibits apoptosis in cardiomyocytes under acute hyperglycaemia. Less is known about the effects of serelaxin in an in vivo mouse model of diabetes. Therefore, we tested the hypothesis in streptozotocin (STZ)-treated mice that serelaxin is able to reverse diabetes-induced vascular dysfunction and cardiac remodelling. Mice were divided into citrate buffer + placebo, STZ + placebo and STZ + serelaxin (0.5 mg/kg/d, 2 weeks) groups. After 12 weeks of diabetes, sensitivity to the endothelium-dependent agonist acetylcholine (ACh) was reduced in the mesenteric artery. This was accompanied by an enhanced vasoconstrictor prostanoid contribution and a decrease in endothelium-derived hyperpolarisation (EDH)-mediated relaxation. Serelaxin restored endothelial function by increasing nitric oxide (NO)-mediated relaxation but not EDH. It also normalised the contribution of vasoconstrictor prostanoids to endothelial dysfunction and suppressed diabetes-induced hyper-responsiveness of the mesenteric artery to angiotensin II. Similarly, diabetes reduced ACh-evoked NO-mediated relaxation in the aorta which was reversed by serelaxin. In the left ventricle, diabetes promoted apoptosis, hypertrophy and fibrosis; serelaxin treatment reversed this ventricular apoptosis and hypertrophy, but had no effect on fibrosis. In summary, serelaxin reversed diabetes-induced endothelial dysfunction by enhancing NO-mediated relaxation in the mouse vasculature and attenuating left ventricular hypertrophy and apoptosis.