Chronic treatment with polyethylene-glycolated superoxide dismutase partially restores endothelium-dependent vascular relaxations in cholesterol-fed rabbits

"Sticki-ER": Functions of the Platelet Endoplasmic Reticulum

Significance: The primary role of platelets is to generate a thrombus by platelet activation. Platelet activation relies on calcium mobilization from the endoplasmic reticulum (ER). ER resident proteins, which are externalized upon platelet activation, are essential for the function of platelet surface receptors and intercellular interactions. Recent Advances: The platelet ER is a conduit for changes in cellular function in response to the extracellular milieu. ER homeostasis is maintained by an appropriate redox balance, regulated calcium stores and normal protein folding. Alterations in ER function and ER stress results in ER proteins externalizing to the cell surface, including members of the protein disulfide isomerase family (PDIs) and chaperones. Critical Issues: The platelet ER is central to platelet function, but our understanding of its regulation is incomplete. Previous studies have focused on the function of PDIs in the extracellular space, and much less on their intracellular role. How platelets maintain ER homeostasis and how they direct ER chaperone proteins to facilitate intercellular signalling is unknown. Future Directions: An understanding of ER functions in the platelet is essential as these may determine critical platelet activities such as secretion and adhesion. Studies are necessary to understand the redox reactions of PDIs in the intracellular versus extracellular space, as these differentially affect platelet function. An unresolved question is how platelet ER proteins control calcium release. Regulation of protein folding in the platelet and downstream pathways of ER stress require further evaluation. Targeting the platelet ER may have therapeutic application in metabolic and neoplastic disease.

Dual role of the L-arginine-ADMA-NO pathway in systemic hypoxic vasodilation and pulmonary hypoxic vasoconstriction

In healthy vascular endothelium, nitric oxide acts as a vasodilator paracrine mediator on adjacent smooth muscle cells. By activating soluble guanylyl cyclase, nitric oxide stimulates cyclic guanosine monophosphate (cGMP) which causes relaxation of vascular smooth muscle (vasodilation) and inhibition of platelet aggregation. This mechanism is active in both, the systemic and pulmonary circulation. In the systemic circulation, hypoxia results in local vasodilation, which has been shown to be brought about by stabilization of hypoxia-inducible factor-1α (HIF1α) and concomitant upregulation of endothelial nitric oxide synthase. By contrast, the physiological response to hypoxia in the pulmonary circulation is vasoconstriction. Hypoxia in the lung primarily results from hypoventilation of circumscript areas of the lung, e.g. by bronchial tree obstruction or inflammatory infiltration. Therefore, hypoxic pulmonary vasoconstriction is a mechanism preventing distribution of blood to hypoventilated areas of the lungs, thereby maintaining maximal oxygenation of blood. The exact molecular mechanism of hypoxic pulmonary vasoconstriction is less well understood than hypoxic vasodilation in the systemic circulation. While alveolar epithelial cells may be key in sensing low oxygen concentration, and pulmonary vascular smooth muscle cells obviously are the effectors of vasoconstriction, the pulmonary vascular endothelium plays a crucial role as an intermediate between these cell types. Indeed, dysfunctional endothelial nitric oxide release was observed in humans exposed to acute hypoxia, and animal studies suggest that hypoxic pulmonary vasoconstriction is enhanced by nitric oxide synthase inhibition. This may be caused, in part, by elevation of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthesis. High asymmetric dimethylarginine levels are associated with endothelial dysfunction, vascular disease, and hypertension.

Redox Regulation of the Microcirculation

The microcirculation maintains tissue homeostasis through local regulation of blood flow and oxygen delivery. Perturbations in microvascular function are characteristic of several diseases and may be early indicators of pathological changes in the cardiovascular system and in parenchymal tissue function. These changes are often mediated by various reactive oxygen species and linked to disruptions in pathways such as vasodilation or angiogenesis. This overview compiles recent advances relating to redox regulation of the microcirculation by adopting both cellular and functional perspectives. Findings from a variety of vascular beds and models are integrated to describe common effects of different reactive species on microvascular function. Gaps in understanding and areas for further research are outlined. © 2020 American Physiological Society. Compr Physiol 10:229-260, 2020.

Chronic statin therapy is associated with enhanced cutaneous vascular responsiveness to sympathetic outflow during passive heat stress

KEY POINTS

Impairments in both central sympathetic and peripheral microvascular function contribute to blunted reflex cutaneous vasodilatation during heat stress in healthy older adults. Hypercholesterolaemia is associated with decrements in neurovascular function; however, little is known about the impact of hypercholesterolaemia on the integrated responses to heat stress. Further, whether chronic statin therapy alters skin sympathetic outflow or its relation to cutaneous vascular conductance during heat stress is unknown. We demonstrate that reflex cutaneous vasodilatation is impaired in older hypercholesterolaemic adults but not in formerly hypercholesterolaemic adults currently treated with a statin compared to age-matched controls. Additionally, chronic statin treatment-induced improvements in reflex vasodilatation are mediated, in part, by increases in end-organ responsiveness to efferent sympathetic outflow during whole-body heating. These data add to the growing body of literature substantiating the beneficial pleiotropic neurovascular effects of chronic statin treatment and provide further support for the use of statins to confer additional cardioprotective benefits in older adults.

ABSTRACT

Attenuated reflex cutaneous vasodilatation in healthy human ageing is mediated by alterations in both central (sympathetic outflow) and peripheral (microvascular endothelial) function. Hypercholesterolaemia is associated with further impairments in neurovascular function. HMG-CoA reductase inhibitors (statins) improve cutaneous endothelium-dependent dilatation; however, whether statin therapy alters skin sympathetic nervous system activity (SSNA) or its relation to cutaneous vascular conductance (CVC) during passive heat stress is unknown. We hypothesized that (1) hypercholesterolaemic older adults would demonstrate blunted increases in both SSNA and CVC during passive heating and (2) chronic statin treatment would improve the response range and sensitivity of the SSNA:CVC relation. Reflex vasodilatation in response to a 1.0°C rise in oral temperature (T_or ; water perfused suit) was induced in 13 healthy normocholesterolaemic adults (62 ± 2 years; LDL = 113 ± 7 mg/dl), 10 hypercholesterolaemic adults (60 ± 1 years; LDL = 183 ± 2 mg/dl), and 10 previously hypercholesterolaemic adults (64 ± 1 years; LDL = 102 ± 2 mg/dl) treated with lipophilic statin (10-40 mg daily). SSNA (peroneal microneurography) and red cell flux (laser-Doppler flowmetry) in the innervated dermatome (dorsum of foot) were continuously measured. Reflex vasodilatation was blunted in hypercholesterolaemic adults, but not in statin-treated adults, compared to normocholesterolaemic adults (at ∆T_or  = 1.0°C: normal = 36 ± 1%CVC_max , high = 32 ± 1%CVC_max , statin = 38 ± 1%CVC_max ; P < 0.01). ∆SSNA was not different (at ∆T_or  = 1.0°C: normal: ∆ = 393 ± 96%, high: ∆ = 311 ± 120%, statin: ∆ = 256 ± 90%; P = 0.11). The slope of the SSNA:CVC relation was blunted in hypercholesterolaemic adults (0.02 ± 0.03%CVC_max /%_baseline ) compared to both normocholesterolaemic (0.09 ± 0.02%CVC_max /%_baseline ; P = 0.024) and statin-treated (0.12 ± 0.05%CVC_max /%_baseline ; P = 0.03) adults. Chronic statin treatment improves reflex cutaneous vasodilatation in formerly hypercholesterolaemic older adults by increasing end-organ responsiveness to sympathetic outflow during passive heat stress.

Oral administration of Zuccagnia punctata extract improves lipid profile, reduces oxidative stress and prevents vascular dysfunction in hypercholesterolemic rabbits

BACKGROUND

The consumption of flavonoids has been shown to prevent cardiovascular diseases including atherosclerosis. In this sense, in a recent in vitro study we demonstrated that a rich in flavonoids extract from Zuccagnia punctata has beneficial effects on vascular function in aorta from hypercholesterolemic rabbits.

PURPOSE

The aim of this study was to evaluate the ability of a hydroalcoholic extract from Z.puncata (ZpE) to prevent alterations induced by high cholesterol diet in rabbits.

METHODS

The major components of the ZpE, flavonoids, were analyzed by using a validated reversed phase HPLC method. Rabbits were separated in five groups: fed standard chow (CD); CD orally administrated 2.5 mg, 5 mg or 10 mg GAE/day ZpE (ZpE- CD); fed 1% cholesterol-enriched chow (HD); HD orally administrated 2.5 mg GAE/day ZpE (ZpE-HD); HD orally administrated 2.5 mg rosuvastatin/day (Ro-HD). All diets were administrated by 6 weeks. Body weights (BW), mean blood pressure (MAP), heart rate (HR), visceral abdominal fat (VAF), organ weight (heart, kidney, liver) and vascular morphology were determined. Total cholesterol (TC), triglycerides (TG), fasting glucose (FG), aspartate amino transferase (AST), alanine amino transferase (ALT), bilirubin, creatinine, thiobarbituric acids reactive substances (TBARS) and glutathione reduced/oxidized index were measured in serum. Abdominal aorta was excised and vascular function was assessed by acetylcholine and sodium nitroprusiate relaxation and contractile response to norepinephrine and angiotensin II.

RESULTS

The major compounds of ZpE identified were chalcones: 2',4'-dihydroxy-3'-methoxychalcone and 2',4'-dihydroxychalcone. Oral treatment with ZpE reduced MAP, TC, TG, TBARS, aortic intima/media ratio and increased glutathione reduced/oxidized index in HD rabbits. No differences were found in AST, ALT, bilirubin or creatinine. Acetylcholine relaxation was normalized and contractile response to norepinephrine and angiotensin II was reduced in ZpE-HD.

CONCLUSION

Oral administration of ZpE as natural product in the prevention of cardiovascular disease related with hypercholesterolemia and endothelial dysfunction is very promising.

Endothelial function is disturbed in a hypertensive diabetic animal model of HFpEF: Moderate continuous vs. high intensity interval training

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is associated with endothelial dysfunction, but the molecular mechanisms still remain unclear. Whether exercise training (ET) along with which optimal modality can improve endothelial function is controversial. The present study used a hypertensive, diabetic-driven HFpEF animal model (ZSF1 rats) to determine whether different training modalities (moderate-continuous (MCT) and high-intensity interval training (HIIT)) could reverse endothelial dysfunction and to understand the underlying molecular mechanisms.

METHODS AND RESULTS

The development of HFpEF in ZSF1 obese animals was confirmed by echocardiography and hemodynamic measurements. Thereafter, animals were randomized into following groups: 1) sedentary, 2) 8 weeks of MCT, 3) 8 weeks of HIIT. ZSF1 lean animals served as control. In vitro measurement of endothelial function in aortic rings revealed significantly impaired endothelial-dependent and -independent vasodilation in HFpEF, which was reversed by MCT and HIIT. At the molecular level, the development of endothelial dysfunction was associated with a reduced expression / activation of endothelial nitric oxide synthase (eNOS), an increase in NADPH and activation of c-Jun N-terminal protein kinase (JNK), a reduced collagen I/III ratio and a reduced lining of the vessel wall by endothelial cells. ET primarily decreased NADPH oxidase expression, and JNK activation, elevated collagen I/III ratio while further improving aortic endothelial cell coverage.

CONCLUSIONS

The present study provides evidence that endothelial dysfunction occurs in experimental HFpEF and that ET, independent of the studied training modality, reverses endothelial dysfunction and specific molecular alterations. ET may therefore provide an important therapeutic intervention for HFpEF patients.

Cellular redox dysfunction in the development of cardiovascular diseases

To meet its exceptionally high energy demands, the heart relies largely on fatty acid oxidation, which then drives the oxidative phosphorylation system in mitochondria. Each day, this system produces about 6kg of ATP to sustain heart function. Fatty acid oxidation is sometimes associated with high rates of mitochondrial reactive oxygen species (ROS) production. By definition, ROS are singlet electron intermediates formed during the partial reduction of oxygen to water and they include radical and non-radical intermediates like superoxide, hydrogen peroxide and hydroxyl radical. Superoxide can also interact with nitric oxide to produce peroxynitrite that in turn can give rise to other radical or non-radical reactive nitrogen species (RNS) like nitrogen dioxide, dinitrogen trioxide and others. While mitochondrial and cellular functions can be impaired by ROS if they accumulate, under normal physiological conditions ROS are important signaling molecules in the cardiovascular system. A fine balance between ROS production and antioxidant systems, including glutathione redox, is essential in the heart; otherwise the ensuing damage can contribute to pathogenic processes, which can culminate in endothelial dysfunction, atherosclerosis, hypertension, cardiac hypertrophy, arrhythmias, myocardial ischemia/reperfusion damage, and heart failure. Here we provide a succinct review of recent findings.

Correlation between ambulatory blood pressure variability and vasodilator function in middle-aged normotensive individuals

OBJECTIVE

The aim of this study was to investigate the association between ambulatory blood pressure variability and vasodilator function in a cohort of normotensive middle-aged individuals.

PARTICIPANTS AND METHODS

This was a cross-sectional study of 285 randomly selected 40-59-year-old normotensive participants who underwent 24-h ambulatory blood pressure monitoring and brachial artery ultrasound assessment. Systolic and diastolic blood pressure variability (BPV) of 24-h, daytime, and night-time were calculated using the coefficients of variation (CV) and the average real variability (ARV) index. Brachial arterial endothelium-dependent vasodilation (EDD) was assessed in response to increased flow and endothelium-independent vasodilation (EID) was assessed in response to nitroglycerin. Relationships were explored using univariate and multivariate linear regression.

RESULTS

The EDD were negatively associated with the CV of 24-h systolic blood pressure (SBP), the ARV of 24-h SBP, and diastolic blood pressure (DBP) in univariate analysis. However, the CV and ARV of 24-h SBP remained associated independently with % EDD in multivariate analysis. In addition, the mean levels of 24-h SBP and DBP, the CV of 24-h SBP and DBP, the ARV of 24-h SBP and DBP, the CV of daytime SBP, and the ARV of daytime DBP were all associated with % EID. However, in a multiple linear regression model, adjusting for covariates, only the CV and ARV of 24-h SBP, and the ARV of 24-h DBP were correlated negatively but weakly with % EID.

CONCLUSION

Our results indicated that a higher 24-h BPV was associated independently with decreased endothelial-dependent and endothelial-independent vasodilator functions in a middle-aged normotensive population. Although 24-h BPV was associated with vasodilator function, relationships were attenuated after adjusting for covariates.

ADMA: its role in vascular disease

Endothelium-derived nitric oxide (NO) is the most potent endogenous vasodilator and, by virtue of its anti-inflammatory and anti-thrombotic effects, it is an endogenous anti-atherogenic agent. Accordingly, impairment of NO synthesis or bioactivity may increase the risk of vascular disease. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of the NO synthase pathway. Plasma levels of ADMA are increased in patients with vascular disease, or with risk factors for vascu lar disease. Preclinical and clinical studies indicate that ADMA may mediate the adverse effects of traditional risk factors on endothelial vasodilator function. By impairing endothelial function, ADMA may contribute to pulmonary or systemic hypertension, as well as to vascular disease. Several drugs known to treat cardiovas cular disease also reduce plasma ADMA levels, such as angiotensin receptor antag onists, converting enzyme inhibitors, and insulin sensitizing agents. Plasma ADMA may be a common mediator of endothelial dysfunction induced by vascular risk factors. Insights into the mechanisms by which plasma ADMA is regulated may lead to new therapeutic knowledge.

ADMA: its role in vascular disease

Endothelium-derived nitric oxide (NO) is the most potent endogenous vasodilator and, by virtue of its anti-inflammatory and anti-thrombotic effects, it is an endogenous anti-atherogenic agent. Accordingly, impairment of NO synthesis or bioactivity may increase the risk of vascular disease. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of the NO synthase pathway. Plasma levels of ADMA are increased in patients with vascular disease, or with risk factors for vascular disease. Preclinical and clinical studies indicate that ADMA may mediate the adverse effects of traditional risk factors on endothelial vasodilator function. By impairing endothelial function, ADMA may contribute to pulmonary or systemic hypertension, as well as to vascular disease. Several drugs known to treat cardiovascular disease also reduce plasma ADMA levels, such as angiotensin receptor antagonists, converting enzyme inhibitors, and insulin sensitizing agents. Plasma ADMA may be a common mediator of endothelial dysfunction induced by vascular risk factors. Insights into the mechanisms by which plasma ADMA is regulated may lead to new therapeutic knowledge.

Nitric Oxide Signaling and Clinical Alternatives to Nitric Oxide

Nitric oxide has been implicated in numerous biological processes, particularly those involved with the cardiovascular system. Nitric oxide production is closely regulated and influenced by a number of factors in both health and disease. Nitric oxide is involved in maintaining the vascular system in its healthy, nondiseased state by producing vasorelaxation which enhances blood flow and prevents both leukocyte and platelet adhesion to the vascular wall. Dysfunctional endothelial cell nitric oxide production has been implicated in a number of disease states, including hypertension and atherosclerosis, and has been associated with adverse cardiac events. Various recent therapies may exert their beneficial effects in part by enhancing endothelial nitric oxide bloavallability. Nitric oxide has been used therapeutically in a number of cardiorespiratory disease states. An improved understanding of the pathologic processes underlying these diseases has resulted in several alternative agents being investigated and used clinically.

Genetic Deletion of ACE2 Induces Vascular Dysfunction in C57BL/6 Mice: Role of Nitric Oxide Imbalance and Oxidative Stress

Accumulating evidence indicates that angiotensin-converting enzyme 2 (ACE2) plays a critical role in cardiovascular homeostasis, and its altered expression is associated with major cardiac and vascular disorders. The aim of this study was to evaluate the regulation of vascular function and assess the vascular redox balance in ACE2-deficient (ACE2^-/y) animals. Experiments were performed in 20–22 week-old C57BL/6 and ACE2^-/y male mice. Evaluation of endothelium-dependent and -independent relaxation revealed an impairment of in vitro and in vivo vascular function in ACE2^-/y mice. Drastic reduction in eNOS expression at both protein and mRNA levels, and a decrease in ^•NO concentrations were observed in aortas of ACE2^-/y mice in comparison to controls. Consistently, these mice presented a lower plasma and urine nitrite concentration, confirming reduced ^•NO availability in ACE2-deficient animals. Lipid peroxidation was significantly increased and superoxide dismutase activity was decreased in aorta homogenates of ACE2^-/y mice, indicating impaired antioxidant capacity. Taken together, our data indicate, that ACE2 regulates vascular function by modulating nitric oxide release and oxidative stress. In conclusion, we elucidate mechanisms by which ACE2 is involved in the maintenance of vascular homeostasis. Furthermore, these findings provide insights into the role of the renin-angiotensin system in both vascular and systemic redox balance.

Ameliorative effect of statin therapy on oxidative damage in heart tissue of hypercholesterolemic rabbits

The aim of this study was to investigate the effects of a high-cholesterol diet in the presence and absence of statin on Cu-Zn-superoxide dismutase (Cu,Zn-SOD), malondialdehyde (MDA), protein carbonyl (PCO), and nitric oxide (NO) of blood and heart tissue, the antioxidant activity of serum paraoxonase-1 (PON-1), and on the blood lipid profile of rabbits. The animals were divided into four groups each of which included 10 rabbits. Rabbits in group 1 received a regular rabbit chow diet (normal diet) for 8 weeks; those in group 2 received atorvastatin (0.3 mg atorvastatin per day/kg body weight) for 8 weeks; those in group 3 received high-cholesterol diet for 8 weeks; and those in group 4 received high-cholesterol diet for 4 weeks, a high-cholesterol diet + atorvastatin (0.3 mg atorvastatin per day/kg body weight) for 8 weeks. The parameters were measured by spectrophotometric methods. As expected, the atherogenic diet caused a pronounced increase in lipid profile (not HDL) parameters. Rabbits in group 3 showed higher PCO, MDA, and NO levels in circulating and heart tissue compared to the rabbits in group 1. Atorvastatin has prevented or limited LDL oxidation and has showed constitutively beneficial effects in group 4. Increased LDL-C, PCO, MDA, and NO levels leading to decreasing PON-1 activity thus create a predisposition to atherogenesis in this model. But atorvastatin administration partly ameliorated oxidative damage in heart injury of hypercholesterolemic rabbits. Atorvastatin which functions as a potent antioxidant agent may inhibit this LDL-C oxidation by increasing PON-1 activity in atherogenesis.

Immunosuppressive/anti-inflammatory cytokines directly and indirectly inhibit endothelial dysfunction--a novel mechanism for maintaining vascular function

Endothelial dysfunction is a pathological status of the vascular system, which can be broadly defined as an imbalance between endothelium-dependent vasoconstriction and vasodilation. Endothelial dysfunction is a key event in the progression of many pathological processes including atherosclerosis, type II diabetes and hypertension. Previous reports have demonstrated that pro-inflammatory/immunoeffector cytokines significantly promote endothelial dysfunction while numerous novel anti-inflammatory/immunosuppressive cytokines have recently been identified such as interleukin (IL)-35. However, the effects of anti-inflammatory cytokines on endothelial dysfunction have received much less attention. In this analytical review, we focus on the recent progress attained in characterizing the direct and indirect effects of anti-inflammatory/immunosuppressive cytokines in the inhibition of endothelial dysfunction. Our analyses are not only limited to the importance of endothelial dysfunction in cardiovascular disease progression, but also expand into the molecular mechanisms and pathways underlying the inhibition of endothelial dysfunction by anti-inflammatory/immunosuppressive cytokines. Our review suggests that anti-inflammatory/immunosuppressive cytokines serve as novel therapeutic targets for inhibiting endothelial dysfunction, vascular inflammation and cardio- and cerebro-vascular diseases.

Evaluation of the Associations between Vascular Endothelial Function and Coronary Artery Stenosis in Patients with Elevated Blood Pressure during Coronary Angiography

<p><b>Objectives:</b> The aim of the present study is to explore the correlation between vascular endothelial function and coronary artery stenosis in non-hypertensive patients with elevated blood pressure under stress.</p><p><b>Methods:</b> This study included 1141 patients suspected of having coronary artery disease (CAD) without hypertension. Coronary arteriography and ultrasonic detection were used to measure the flow-mediated dilatation (FMD) function in the brachial artery. Patients were divided into 2 groups according to coronary angiography: experiment group, patients with blood pressure ? 140/90 mm Hg; control group, patients with blood pressure <140/90 mm Hg. The correlation between vascular endothelial function and coronary artery stenosis was observed.</p><p><b>Results:</b> The majority of the patients in the control group were found to have either normal coronary arteries or stenosis <50%. Patients in the experiment group (those with invasive blood pressure [IBP] >140/90) were more likely to have some degree of coronary artery stenosis. Specifically, there were significantly more patients with >50% stenosis in the experiment when compared with the control group (<i>P</i> < .05). The FMD in the experiment group was significantly lower than that in the control group (<i>P</i> < .05).</p><p><b>Conclusion:</b> The non-hypertensive patients with elevated blood pressure under stress had coronary artery stenosis, which was associated with vascular endothelial dysfunction.</p>

Changes in arterial function in a mouse model of human familial hypercholesterolaemia

AIM

Atherosclerosis is the most common cause of cardiovascular disease. The ApoB mouse is a model for human familial hypercholesterolaemia and has a lipoprotein profile similar to that of humans with atherosclerosis. Therefore, it is a suitable model to investigate the changes in vasoreactivity during atherogenesis. This study investigates contractile and dilatative properties of arteries in this model in relation to age.

METHODS

Male ApoB mice and B6, wild-type (WT), mice were examined at age four or 18 months. Isometric measurements of 2-mm ring preparations of the aorta thoracica were performed using a wire myograph. Histological and biochemical methods served to determine atherosclerosis, lipid status and endothelial markers respectively.

RESULTS

Morphometric analysis showed that all old ApoB mice had severe atherosclerosis in the aorta. Atherosclerotic alteration of the aorta of the ApoB mice coincided with a diminished vasodilatation to acetylcholine. The phenylephrine response was significantly attenuated already to the same degree in the non-atherosclerotic aorta of the young ApoB mice as in the atherosclerotic aorta of the older ApoB mice. Serum parameters showed a rise in total cholesterol and triglycerides in the ApoB strain compared to WT mice. Soluble intercellular adhesion molecule (sICAM)-1 and soluble vascular adhesion molecule (sVCAM)-1 were increased in old compared to young ApoB mice.

CONCLUSION

The study shows that reduced acetylcholine-induced dilatation is related to the presence of atherosclerosis in old ApoB mice. Remarkably, the impaired vessel reactivity to phenylephrine already in young ApoB mice indicates early changes in vascular function in this model.

In vitro model suggests oxidative stress involved in keratoconus disease

Keratoconus (KC) affects 1:2000 people and is a disorder where cornea thins and assumes a conical shape. Advanced KC requires surgery to maintain vision. The role of oxidative stress in KC remains unclear. We aimed to identify oxidative stress levels between human corneal keratocytes (HCKs), fibroblasts (HCFs) and keratoconus cells (HKCs). Cells were cultured in 2D and 3D systems. Vitamin C (VitC) and TGF-β3 (T3) were used for 4 weeks to stimulate self-assembled extracellular matrix (ECM). No T3 used as controls. Samples were analyzed using qRT-PCR and metabolomics. qRT-PCR data showed low levels of collagen I and V, as well as keratocan for HKCs, indicating differentiation to a myofibroblast phenotype. Collagen type III, a marker for fibrosis, was up regulated in HKCs. We robustly detected more than 150 metabolites of the targeted 250 by LC-MS/MS per condition and among those metabolites several were related to oxidative stress. Lactate levels, lactate/malate and lactate/pyruvate ratios were elevated in HKCs, while arginine and glutathione/oxidized glutathione ratio were reduced. Similar patterns found in both 2D and 3D. Our data shows that fibroblasts exhibit enhanced oxidative stress compared to keratocytes. Furthermore the HKC cells exhibit the greatest level suggesting they may have a myofibroblast phenotype.

Hemodynamic regulation of reactive oxygen species: implications for vascular diseases

SIGNIFICANCE

Arterial blood vessels functionally and structurally adapt to altering hemodynamic forces in order to accommodate changing needs and to provide stress homeostasis. This ability is achieved at the cellular level by converting mechanical stimulation into biochemical signals (i.e., mechanotransduction). Physiological mechanical stress helps maintain vascular structure and function, whereas pathologic or aberrant stress may impair cellular mechano-signaling, and initiate or augment cellular processes that drive disease.

RECENT ADVANCES

Reactive oxygen species (ROS) may represent an intriguing class of mechanically regulated second messengers. Chronically enhanced ROS generation may be induced by adverse mechanical stresses, and is associated with a multitude of vascular diseases. Although a causal relationship has clearly been demonstrated in large numbers of animal studies, an effective ROS-modulating therapy still remains to be established by clinical studies.

CRITICAL ISSUES AND FUTURE DIRECTIONS

This review article focuses on the role of various mechanical forces (in the form of laminar shear stress, oscillatory shear stress, or cyclic stretch) as modulators of ROS-driven signaling, and their subsequent effects on vascular biology and homeostasis, as well as on specific diseases such as arteriosclerosis, hypertension, and abdominal aortic aneurysms. Specifically, it highlights the significance of the various NADPH oxidase (NOX) isoforms as critical ROS generators in the vasculature. Directed targeting of defined components in the complex network of ROS (mechano-)signaling may represent a key for successful translation of experimental findings into clinical practice.

From ST segments to endothelial pathophysiology: hypercholesterolemia and endothelial superoxide production

As a young medical resident, I encountered a patient suffering from spontaneous coronary vasospasm and was puzzled by these dramatic alterations in vasomotion. This encounter piqued my interest in understanding the drivers of vascular reactivity. In a paper published in the JCI, my colleagues and I revealed a role for superoxide production in the vascular dysfunction associated with hypercholesterolemia. Subsequent work by our group and others has unveiled complex associations between ROS generation and vascular disease.

Redox signaling in cardiovascular health and disease

Spatiotemporal regulation of the activity of a vast array of intracellular proteins and signaling pathways by reactive oxygen species (ROS) governs normal cardiovascular function. However, data from experimental and animal studies strongly support that dysregulated redox signaling, resulting from hyperactivation of various cellular oxidases or mitochondrial dysfunction, is integral to the pathogenesis and progression of cardiovascular disease (CVD). In this review, we address how redox signaling modulates the protein function, the various sources of increased oxidative stress in CVD, and the labyrinth of redox-sensitive molecular mechanisms involved in the development of atherosclerosis, hypertension, cardiac hypertrophy and heart failure, and ischemia-reperfusion injury. Advances in redox biology and pharmacology for inhibiting ROS production in specific cell types and subcellular organelles combined with the development of nanotechnology-based new in vivo imaging systems and targeted drug delivery mechanisms may enable fine-tuning of redox signaling for the treatment and prevention of CVD.

Nitric oxide function in atherosclerosis

Atherosclerosis is a chronic inflammatory process in the intima of conduit arteries, which disturbs the endothelium-dependent regulation of the vascular tone by the labile liposoluble radical nitric oxide (NO) formed by the constitutive endothelial nitric oxide synthase (eNOS). This defect predisposes to coronary vasospasm and cardiac ischaemia, with anginal pain as the typical clinical manifestation. It is now appreciated that endothelial dysfunction is an early event in atherogenesis and that it may also involve the microcirculation, in which atherosclerotic lesions do not develop. On the other hand, the inflammatory environment in atherosclerotic plaques may result in the expression of the inducible NO synthase (iNOS) isozyme. Whether the dysfunction in endothelial NO production is causal to, or the result of, atherosclerotic lesion formation is still highly debated. Most evidence supports the hypothesis that constitutive endothelial NO release protects against atherogenesis e.g. by preventing smooth muscle cell proliferation and leukocyte adhesion. Nitric oxide generated by the inducible isozyme may be beneficial by replacing the failing endothelial production but excessive release may damage the vascular wall cells, especially in combination with reactive oxygen intermediates.

Effects of glutathione-depleting drug buthionine sulfoximine and aging on activity of endothelium-derived relaxing and contracting factors in carotid artery of Sprague-Dawley rats

The role of the antioxidant glutathione (GSH) in mediating endothelial (dys)function, and how that role may depend on age, is unclear. The main purpose of the current study was to investigate the effect of 10-day treatment with the GSH-depleting drug l-buthionine sulfoximine (BSO) on endothelium-derived relaxing factor and endothelium-derived contracting factor activities in the isolated common carotid artery (CCA) of Adult and Aging animals. CCA blood pressure and flow were unaffected by age or BSO. Endothelium-derived relaxing factor activity, examined in precontracted CCA as relaxation to cumulative acetylcholine (ACh), was largely nitric oxide synthase (NOS) mediated and was not different between Adult and Aging animals at lower ACh; however, at higher ACh, relaxation was blunted in Aging CCA, an effect abolished by cyclooxygenase (COX) inhibition but not by NOS inhibition nor by the reactive oxygen species (ROS) inhibitors 4-hydroxy-TEMPO or Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin,tetratosylate,hydroxide. Specific examination of endothelium-derived contracting factor activity in quiescent NOS-inhibited CCA established that higher ACh elicited a contractile response, ∼3.5-fold greater in Aging versus Adult CCA, which was abolished by COX-1-specific inhibition but unaffected by ROS inhibitors. Aging was unrelated to changes in liver or vascular tissue GSH or ROS content. BSO was effective in significantly decreasing GSH and increasing ROS content in both animal cohorts. However, NOS-mediated endothelium-derived relaxing factor activity was well preserved and age-related COX-mediated endothelium-derived contracting factor activity was unaffected in response to these BSO-induced perturbations, as were exogenous H2O2-stimulated NOS/non-NOS-mediated relaxation and COX-mediated contractile activities. These data suggest that, regardless of age, chronic partial depletion of GSH in vivo does not necessarily cause endothelium-dependent vasomotor dysfunction.

Scavenging ROS: superoxide dismutase/catalase mimetics by the use of an oxidation-sensitive nanocarrier/enzyme conjugate

Reactive Oxygen Species (ROS) are quintessential inflammatory compounds with oxidizing behavior. We have successfully developed a micellar system with responsiveness at the same time to two of the most important ROS: superoxide and hydrogen peroxide. This allows for an effective and selective capture of the two compounds and, in perspective, for inflammation-responsive drug release. The system is composed of superoxide dismutase (SOD) conjugated to oxidation-sensitive amphiphilic polysulfide/PEG block copolymers; the conjugate combines the SOD reactivity toward superoxide with that of hydrophobic thioethers toward hydrogen peroxide. Specifically, here we have demonstrated how this hybrid system can efficiently convert superoxide into hydrogen peroxide, which is then "mopped-up" by the polysulfides: this modus operandi is functionally analogous to the SOD/catalase combination, with the advantages of (a) being based on a single and more stable system, and (b) a higher overall efficiency due the physical proximity of the two ROS-reactive centers (SOD and polysulfides).

Hypercholesterolemia and microvascular dysfunction: interventional strategies

Hypercholesterolemia is defined as excessively high plasma cholesterol levels, and is a strong risk factor for many negative cardiovascular events. Total cholesterol levels above 200 mg/dl have repeatedly been correlated as an independent risk factor for development of peripheral vascular (PVD) and coronary artery disease (CAD), and considerable attention has been directed toward evaluating mechanisms by which hypercholesterolemia may impact vascular outcomes; these include both results of direct cholesterol lowering therapies and alternative interventions for improving vascular function. With specific relevance to the microcirculation, it has been clearly demonstrated that evolution of hypercholesterolemia is associated with endothelial cell dysfunction, a near-complete abrogation in vascular nitric oxide bioavailability, elevated oxidant stress, and the creation of a strongly pro-inflammatory condition; symptoms which can culminate in profound impairments/alterations to vascular reactivity. Effective interventional treatments can be challenging as certain genetic risk factors simply cannot be ignored. However, some hypercholesterolemia treatment options that have become widely used, including pharmaceutical therapies which can decrease circulating cholesterol by preventing either its formation in the liver or its absorption in the intestine, also have pleiotropic effects with can directly improve peripheral vascular outcomes. While physical activity is known to decrease PVD/CAD risk factors, including obesity, psychological stress, impaired glycemic control, and hypertension, this will also increase circulating levels of high density lipoprotein and improving both cardiac and vascular function. This review will provide an overview of the mechanistic consequences of the predominant pharmaceutical interventions and chronic exercise to treat hypercholesterolemia through their impacts on chronic sub-acute inflammation, oxidative stress, and microvascular structure/function relationships.

Curcumin supplementation could improve diabetes-induced endothelial dysfunction associated with decreased vascular superoxide production and PKC inhibition

Background

Curcumin, an Asian spice and food-coloring agent, is known for its anti-oxidant properties. We propose that curcumin can improve diabetes-induced endothelial dysfunction through superoxide reduction.

Methods

Diabetes (DM) was induced in rats by streptozotocin (STZ). Daily curcumin oral feeding was started six weeks after the STZ injection. Twelve weeks after STZ injection, mesenteric arteriolar responses were recorded in real time using intravital fluorescence videomicroscopy. Superoxide and vascular protein kinase C (PKC-βII) were examined by hydroethidine and immunofluorescence, respectively.

Results

The dilatory response to acetylcholine (ACh) significantly decreased in DM arterioles as compared to control arterioles. There was no difference among groups when sodium nitroprusside (SNP) was used. ACh responses were significantly improved by both low and high doses (30 and 300 mg/kg, respectively) of curcumin supplementation. An oxygen radical-sensitive fluorescent probe, hydroethidine, was used to detect intracellular superoxide anion (O₂^●-) production. O₂^●- production was markedly increased in DM arterioles, but it was significantly reduced by supplementation of either low or high doses of curcumin. In addition, with a high dose of curcumin, diabetes-induced vascular PKC-βII expression was diminished.

Conclusion

Therefore, it is suggested that curcumin supplementation could improve diabetes-induced endothelial dysfunction significantly in relation to its potential to decrease superoxide production and PKC inhibition.

Endothelial dysfunction in the microcirculation of patients with obstructive sleep apnea

RATIONALE

Obstructive sleep apnea (OSA) is a risk factor for cardiovascular disease. We hypothesized that patients with OSA and no cardiovascular disease have oxidant-related microcirculatory endothelial dysfunction.

OBJECTIVES

To evaluate the microcirculation in OSA.

METHODS

This study included seven patients with OSA and seven age- and weight-matched control subjects (mean age, 38 yr; mean body mass index, 32.5 kg/m²). All participants were free of cardiovascular risk factors. Participants received measurement of brachial artery flow-mediated dilation and forearm subcutaneous biopsy. Patients underwent repeated tests 12 weeks after treatment. Microcirculatory endothelial cells were isolated, and immunohistochemistry staining for peroxynitrite in the microcirculation was performed.

MEASUREMENTS AND MAIN RESULTS

Flow-mediated dilation was lower in patients than in control subjects at baseline (mean ± SEM: 5.7 ± 0.5 vs. 9.5 ± 0.6; P = 0.02) and increased after treatment (5.7-7.3; change, 1.7 ± 0.6; P = 0.04). Microcirculatory peroxynitrite deposit was higher in patients compared with control subjects (44.0 ± 1.6 vs. 21.8 ± 1.9 stain density units; P < 0.001) and decreased after treatment from 44.0 to 30.5 stain density units (change, -13.5 ± 2.9; P = 0.009). In patients, transcription of endothelial nitric oxide synthase decreased from 5.2 to -1.3 after treatment (change, 6.5 ± 2.5; P = 0.05), and transcription of superoxide dismutase1 decreased from -4.0 to -12.3 after treatment (change, -8.3 ± 2.1; P = 0.01). These changes persisted after adjustment for weight and underlying severity of OSA.

CONCLUSIONS

This is the first direct evaluation of the microcirculation in OSA. Patients with OSA with low cardiovascular risk status had increased oxidant production in the microcirculation and endothelial dysfunction, both of which improved with treatment. Endothelial nitric oxide synthase transcription decreased with treatment.

Regulation of endothelial cell tetrahydrobiopterin pathophysiological and therapeutic implications

Tetrahydrobiopterin (BH(4)) is a critical cofactor for the nitric oxide synthases. In the absence of BH(4), these enzymes become uncoupled, fail to produce nitric oxide, and begin to produce superoxide and other reactive oxygen species (ROS). BH(4) levels are modulated by a complex biosynthetic pathway, salvage enzymes, and by oxidative degradation. The enzyme GTP cyclohydrolase-1 catalyzes the first step in the de novo synthesis of BH(4) and new evidence shows that this enzyme is regulated by phosphorylation, which reduces its interaction with its feedback regulatory protein (GFRP). In the setting of a variety of common diseases, such as atherosclerosis, hypertension, and diabetes, reactive oxygen species promote oxidation of BH(4) and inhibit expression of the salvage enzyme dihydrofolate reductase (DHFR), promoting accumulation of BH(2) and NOS uncoupling. There is substantial interest in therapeutic approaches to increasing tissue levels of BH(4), largely by oral administration of this agent. BH(4) treatment has proved effective in decreasing atherosclerosis, reducing blood pressure, and preventing complications of diabetes in experimental animals. While these basic studies have been very promising, there are only a few studies showing any effect of BH(4) therapy in humans in treatment of these common problems. Whether BH(4) or related agents will be useful in treatment of human diseases needs additional study.

Suppression of Oxidative Stress in the Endothelium and Vascular Wall

There is growing evidence that oxidative stress, meaning an excessive production of reactive oxygen and nitrogen species, underlies many forms of cardiovascular disease. The major source of oxidative stress in the artery wall is an NADPH oxidase. This enzyme complex in vascular cells, including endothelium, differs from that in phagocytic leucocytes in both biochemical structure and functions. The crucial flavin-containing catalytic subunits Nox1 and Nox4 are not present in leucocytes, but are highly expressed in vascular cells and upregulated in vascular remodeling, such as that found in hypertension and atherosclerosis. This offers the opportunity to develop "vascular specific" NADPH oxidase inhibitors that do not compromise the essential physiological signaling and phagocytic function carried out by reactive oxygen and nitrogen molecules. Although many conventional antioxidants fail to significantly affect outcomes in cardiovascular disease, targeted inhibitors of NADPH oxidase that block the source of oxidative stress in the vasculature are more likely to prevent the deterioration of vascular function that leads to stroke and heart attack.

Effects of allopurinol, a xanthine oxidase inhibitor, on renal injury in hypercholesterolemia‐induced hypertensive rats

To investigate if increased lipid peroxidation is involved in hypercholesterolemia-induced hypertension and renal injury, we examined the effects of allopurinol, a xanthine oxidase inhibitor, on these conditions. Groups of male Sprague--Dawley rats were fed for 8 weeks with a high-cholesterol diet (4% cholesterol), a high-cholesterol plus allopurinol (10 mg/kgBW/day) diet or a normal diet. Systolic blood pressure (SBP), serum lipids, uric acid (UA) and malondialdehyde (MDA) as a measure of lipid peroxides, and urinary excretion of protein (UP) were measured after 0, 4 and 8 weeks. Urinary excretion of nitrite plus nitrate (UNOx) and iron (UFe), and MDA in the kidney were measured after 8 weeks. The renal injury was evaluated by the glomerular sclerosis score (SS). The high-cholesterol diet increased SBP, serum total cholesterol and UA, MDA in the serum and kidney, UP, UNOx, UFe and SS. Allopurinol ameliorated cholesterol-induced elevation in serum UA, MDA in the serum and kidney, UP, UNOx, UFe and SS, but did not affect SBP. Hence, our results suggest that lipid peroxidation may be involved in hypercholesterolemia-induced renal injury, and that suppression of lipid peroxidation can reduce such injury.

Effects of acute hypercholesterolemia on blood pressure and pressor response to norepinephrine in rats

To examine if high cholesterol in blood acutely affects the blood pressure, we partly exchanged the blood of normal rats for that of hypercholesterolemic rats. Male Sprague-Dawley rats were fed for 8 weeks with a high-cholesterol diet (4% cholesterol; HC) or a normal diet (NC). The rats were catheterized; and blood of animals in NC was partly exchanged with that of HC (N-H) or other animals in NC (N-N). Systolic blood pressure (SBP) and the pressor response to norepinephrine (NE) in N-H were compared with those of N-N. Serum lipids and malondialdehyde (MDA), and urinary excretion of protein (UP) and NE (UNE) were determined. After 8 weeks, SBP, serum total cholesterol (TC), MDA, UP and UNE were higher in the HC. Blood exchange caused an increase in TC, MDA and SBP in only the N-H. Increases in SBP caused by NE injection were rather less in the N-H than in the N-N. The blood pressure increase induced by a high-cholesterol diet seemed to be caused by certain factors in the blood of hypercholesterolemic rats. Excessive lipid oxidation induced by hypercholesterolemia may be involved in the blood pressure elevation.

A randomized placebo-controlled study on the effect of nifedipine on coronary endothelial function and plaque formation in patients with coronary artery disease: the ENCORE II study

AIMS

Endothelial dysfunction and plaque formation are features of atherosclerosis. Inhibition of L-type calcium channels or HMG-CoA pathway improves endothelial function and reduces plaque size. Thus, we investigated in stable coronary artery disease (CAD) the effects of a calcium antagonist on coronary endothelial function and plaque size.

METHODS AND RESULTS

In 454 patients undergoing PCI, acetylcholine (10(-6) to 10(-4) M) was infused in a coronary segment without significant CAD. Changes in coronary diameter were measured and an intravascular ultrasound examination (IVUS) was performed. On top of statin therapy, patients were randomized in a double-blind fashion to placebo or nifedipine GITS 30-60 mg/day and followed for 18-24 months. Blood pressure was lower on nifedipine than on placebo by 5.8/2.1 mmHg (P < 0.001) as was total and LDL cholesterol (4.8 mg/dL; P = 0.495), while HDL was higher (3.6 mg/dL; P = 0.026). In the most constricting segment, nifedipine reduced vasoconstriction to acetylcholine (14.0% vs. placebo 7.7%; P < 0.0088). The percentage change in plaque volume with nifedipine and placebo, respectively, was 1.0 and 1.9%, ns.

CONCLUSION

The ENCORE II trial demonstrates in a multi-centre setting that calcium channel blockade with nifedipine for up to 2 years improves coronary endothelial function on top of statin treatment, but did not show an effect of nifedipine on plaque volume.

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

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

Chemistry and antihypertensive effects of tempol and other nitroxides

Nitroxides can undergo one- or two-electron reduction reactions to hydroxylamines or oxammonium cations, respectively, which themselves are interconvertible, thereby providing redox metabolic actions. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (tempol) is the most extensively studied nitroxide. It is a cell membrane-permeable amphilite that dismutates superoxide catalytically, facilitates hydrogen peroxide metabolism by catalase-like actions, and limits formation of toxic hydroxyl radicals produced by Fenton reactions. It is broadly effective in detoxifying these reactive oxygen species in cell and animal studies. When administered intravenously to hypertensive rodent models, tempol caused rapid and reversible dose-dependent reductions in blood pressure in 22 of 26 studies. This was accompanied by vasodilation, increased nitric oxide activity, reduced sympathetic nervous system activity at central and peripheral sites, and enhanced potassium channel conductance in blood vessels and neurons. When administered orally or by infusion over days or weeks to hypertensive rodent models, it reduced blood pressure in 59 of 68 studies. This was accompanied by correction of salt sensitivity and endothelial dysfunction and reduced agonist-evoked oxidative stress and contractility of blood vessels, reduced renal vascular resistance, and increased renal tissue oxygen tension. Thus, tempol is broadly effective in reducing blood pressure, whether given by acute intravenous injection or by prolonged administration, in a wide range of rodent models of hypertension.

Redox control of renal function and hypertension

Loss of redox homeostasis and formation of excessive free radicals play an important role in the pathogenesis of kidney disease and hypertension. Free radicals such as reactive oxygen species (ROS) are necessary in physiologic processes. However, loss of redox homeostasis contributes to proinflammatory and profibrotic pathways in the kidney, which in turn lead to reduced vascular compliance and proteinuria. The kidney is susceptible to the influence of various extracellular and intracellular cues, including the renin-angiotensin-aldosterone system (RAAS), hyperglycemia, lipid peroxidation, inflammatory cytokines, and growth factors. Redox control of kidney function is a dynamic process with reversible pro- and anti-free radical processes. The imbalance of redox homeostasis within the kidney is integral in hypertension and the progression of kidney disease. An emerging paradigm exists for renal redox contribution to hypertension.

Effect of endothelium-specific insulin resistance on endothelial function in vivo

OBJECTIVE

Insulin resistance is an independent risk factor for the development of cardiovascular atherosclerosis. A key step in the development of atherosclerosis is endothelial dysfunction, manifest by a reduction in bioactivity of nitric oxide (NO). Insulin resistance is associated with endothelial dysfunction; however, the mechanistic relationship between these abnormalities and the role of impaired endothelial insulin signaling versus global insulin resistance remains unclear.

RESEARCH DESIGN AND METHODS

To examine the effects of insulin resistance specific to the endothelium, we generated a transgenic mouse with endothelium-targeted overexpression of a dominant-negative mutant human insulin receptor (ESMIRO). This receptor has a mutation (Ala-Thr(1134)) in its tyrosine kinase domain that disrupts insulin signaling. Humans with the Thr(1134) mutation are insulin resistant. We performed metabolic and vascular characterization of this model.

RESULTS

ESMIRO mice had preserved glucose homeostasis and were normotensive. They had significant endothelial dysfunction as evidenced by blunted aortic vasorelaxant responses to acetylcholine (ACh) and calcium ionophore. Furthermore, the vascular action of insulin was lost in ESMIRO mice, and insulin-induced endothelial NO synthase (eNOS) phosphorylation was blunted. Despite this phenotype, ESMIRO mice demonstrate similar levels of eNOS mRNA and protein expression to wild type. ACh-induced relaxation was normalized by the superoxide dismutase mimetic, Mn(III)tetrakis(1-methyl-4-pyridyl) porphyrin pentachloride. Endothelial cells of ESMIRO mice showed increased superoxide generation and increased mRNA expression of the NADPH oxidase isoforms Nox2 and Nox4.

CONCLUSIONS

Selective endothelial insulin resistance is sufficient to induce a reduction in NO bioavailability and endothelial dysfunction that is secondary to increased generation of reactive oxygen species. This arises independent of a significant metabolic phenotype.

Redox control of endothelial function and dysfunction: molecular mechanisms and therapeutic opportunities

The endothelium is essential for the maintenance of vascular homeostasis. Central to this role is the production of endothelium-derived nitric oxide (EDNO), synthesized by the endothelial isoform of nitric oxide synthase (eNOS). Endothelial dysfunction, manifested as impaired EDNO bioactivity, is an important early event in the development of various vascular diseases, including hypertension, diabetes, and atherosclerosis. The degree of impairment of EDNO bioactivity is a determinant of future vascular complications. Accordingly, growing interest exists in defining the pathologic mechanisms involved. Considerable evidence supports a causal role for the enhanced production of reactive oxygen species (ROS) by vascular cells. ROS directly inactivate EDNO, act as cell-signaling molecules, and promote protein dysfunction, events that contribute to the initiation and progression of endothelial dysfunction. Increasing data indicate that strategies designed to limit vascular ROS production can restore endothelial function in humans with vascular complications. The purpose of this review is to outline the various ways in which ROS can influence endothelial function and dysfunction, describe the redox mechanisms involved, and discuss approaches for preventing endothelial dysfunction that may highlight future therapeutic opportunities in the treatment of cardiovascular disease.

Relation of nitrite to structural and mechanical adaptation of arteries during postnatal development

Mammalian arteries undergo rapid remodeling during postnatal growth and development. The high wall shear stress at birth is an important mediator of postnatal endothelial nitric oxide (NO) and consequently of growth and remodeling. The objective of this study was to quantify the NO production in relation to geometric and mechanical remodeling of aorta and pulmonary artery during postnatal development. Fifty-one C57BL/6 mice aged from 1 to 33 days were divided into 8 age groups for measurements of nitrite (NO(x)). Systematic measurements of NO(x) in each rings were made in the main pulmonary artery and primary branch as well as along the length of aorta using the combination of a diazo coupling method and high-performance liquid chromatography. The NO(x) data on the aorta were correlated with data on the geometry (diameter, wall thickness) and mechanical properties (stress, strain, elastic modulus) in the same strain of mice under the same conditions. Our findings show postnatal age and vessel size affects the NO production; i.e., the NO(x) decreased with age and diameter. Furthermore, there is a significant positive correlation between strain and NO(x) but negative correlation between both wall thickness and elastic modulus and NO(x) levels. These findings suggest an important interplay between NO(x) and geometric and mechanical remodeling during postnatal growth and development.

Reduced antioxidant capacity and diet-induced atherosclerosis in uncoupling protein-2-deficient mice

Vascular dysfunction in response to reactive oxygen species (ROS) plays an important role in the development and progression of atherosclerotic lesions. In most cells, mitochondria are the major source of cellular ROS during aerobic respiration. Under most conditions the rates of ROS formation and elimination are balanced through mechanisms that sense relative ROS levels. However, a chronic imbalance in redox homeostasis is believed to contribute to various chronic diseases, including atherosclerosis. Uncoupling protein-2 (UCP2) is a mitochondrial inner membrane protein shown to be a negative regulator of macrophage ROS production. In response to a cholesterol-containing atherogenic diet, C57BL/6J mice significantly increased expression of UCP2 in the aorta, while mice lacking UCP2, in the absence of any other genetic modification, displayed significant endothelial dysfunction following the atherogenic diet. Compared with wild-type mice, Ucp2(-/-) mice had decreased endothelial nitric oxide synthase, an increase in vascular cell adhesion molecule-1 expression, increased ROS production, and an impaired ability to increase total antioxidant capacity. These changes in Ucp2(-/-) mice were associated with increased aortic macrophage infiltration and more numerous and larger atherosclerotic lesions. These data establish that in the vasculature UCP2 functions as an adaptive antioxidant defense to protect against the development of atherosclerosis in response to a fat and cholesterol diet.

Role of oxidative stress and nitric oxide in atherothrombosis

During the last decade basic and clinical research has highlighted the central role of reactive oxygen species (ROS) in cardiovascular disease. Enhanced production or attenuated degradation of ROS leads to oxidative stress, a process that affects endothelial and vascular function, and contributes to vascular disease. Nitric oxide (NO), a product of the normal endothelium, is a principal determinant of normal endothelial and vascular function. In states of inflammation, NO production by the vasculature increases considerably and, in conjunction with other ROS, contributes to oxidative stress. This review examines the role of oxidative stress and NO in mechanisms of endothelial and vascular dysfunction with an emphasis on atherothrombosis.

Unresolved roles of platelet nitric oxide synthase

Endothelial-derived nitric oxide (NO) is a key regulator of platelet function, inhibiting both adhesion to the extracellular matrix and aggregation at sites of vascular injury. Platelets also have the capacity to synthesize and release bioactive NO, which is thought to make a significant contribution to the vascular pool of NO. The regulation of platelet NO production is poorly understood and studies examining the physiological role of platelet-derived NO have produced contradictory and controversial findings. In the present article, we discuss the current understanding of the biochemical and molecular regulation of platelet NO synthesis and outline the potential physiological and clinical significance of this molecule.