H2O2 increases production of constrictor prostaglandins in smooth muscle leading to enhanced arteriolar tone in Type 2 diabetic mice

Regional heterogeneity in vascular contractile dysfunction in diabetic mice

Oxidative stress underlies many diabetic complications, including diabetic vasculopathy. It is unclear if oxidative stress has different effects in regionally distant arteries. We compared the contractile function of three arteries from diabetic mice and elucidated the mechanisms underlying their differential adaptation. We examined responses of the aorta, carotid and femoral arteries, isolated from the same diabetic (db/db) or normoglycemic control mice, to different vasoconstrictors in the presence and absence of indomethacin, apocynin, sulfaphenazole, L-NAME or a reactive oxygen species generating system to identify the enzyme(s) contributing to vascular dysfunction. Expression of superoxide dismutase (SOD) isoforms was measured. db/db aortae showed augmented contractile responses to KCl, phenylephrine, A23197 and U-46619 likely due to activated cyclooxygenases and hypersensitivity to thromboxane A2. Contractile responses of db/db carotid arteries were unaltered, likely due to higher SOD3 and SOD1 levels compared to the aortae. Femoral arteries were more vulnerable to oxidative stress, lacked SOD3 expression, and showed higher basal potassium channels activity. Phenylephrine contractions in femoral arteries were dependent on extracellular calcium entry; while contractions in aortae were dependent on extracellular calcium entry and intracellular calcium release. Femoral arteries from db/db mice exhibited higher basal potassium channels activity and attenuated contractility compared to control mice likely due to lower SOD levels. Heterogeneity exists between the three arteries at functional and molecular levels due to different signalling pathways and antioxidant defense mechanisms. Understanding regional differences in vasomotor control coupled with advanced delivery systems can help in developing therapies targeting specific vascular beds.

Reduction of vascular reactivity in rat aortas following pilocarpine-induced status epilepticus

OBJECTIVE

The authors investigated changes in vascular reactivity in rats following pilocarpine-induced status epilepticus.

METHOD

Male Wistar rats weighing between 250g and 300g were used. Status epilepticus was induced using 385 mg/kg i.p. pilocarpine. After 40 days the thoracic aorta was dissected and divided into 4 mm rings and the vascular smooth muscle reactivity to phenylephrine was evaluated.

RESULTS

Epilepsy decreased the contractile responses of the aortic rings to phenylephrine (0.1 nM-300 mM). To investigate if this reduction was induced by increasing NO production with/or hydrogen peroxide L-NAME and Catalase were used. L-NAME (N-nitro-L arginine methyl ester) increased vascular reactivity but the contractile response to phenylephrine increased in the epileptic group. Catalase administration decreased the contractile responses only in the rings of rats with epilepsy.

CONCLUSIONS

Our findings demonstrated for the first time that epilepsy is capable of causing a reduction of vascular reactivity in rat aortas. These results suggest that vascular reactivity reduction is associated with increased production of Nitric Oxide (NO) as an organic attempt to avoid hypertension produced by excessive sympathetic activation.

Exercise protects vascular function by countering senescent cells in older adults

Blood vessels are key conduits for the transport of blood and circulating factors. Abnormalities in blood vessels promote cardiovascular disease (CVD), which has become the most common disease as human lifespans extend. Aging itself is not pathogenic; however, the decline of physiological and biological function owing to aging has been linked to CVD. Although aging is a complex phenomenon that has not been comprehensively investigated, there is accumulating evidence that cellular senescence aggravates various pathological changes associated with aging. Emerging evidence shows that approaches that suppress or eliminate cellular senescence preserve vascular function in aging-related CVD. However, most pharmacological therapies for treating age-related CVD are inefficient. Therefore, effective approaches to treat CVD are urgently required. The benefits of exercise for the cardiovascular system have been well documented in basic research and clinical studies; however, the mechanisms and optimal frequency of exercise for promoting cardiovascular health remain unknown. Accordingly, in this review, we have discussed the changes in senescent endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) that occur in the progress of CVD and the roles of physical activity in CVD prevention and treatment.

Oxidative Regulation of Vascular Cav1.2 Channels Triggers Vascular Dysfunction in Hypertension-Related Disorders

Blood pressure is determined by cardiac output and peripheral vascular resistance. The L-type voltage-gated Ca²⁺ (Ca_v1.2) channel in small arteries and arterioles plays an essential role in regulating Ca²⁺ influx, vascular resistance, and blood pressure. Hypertension and preeclampsia are characterized by high blood pressure. In addition, diabetes has a high prevalence of hypertension. The etiology of these disorders remains elusive, involving the complex interplay of environmental and genetic factors. Common to these disorders are oxidative stress and vascular dysfunction. Reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria are primary sources of vascular oxidative stress, whereas dysfunction of the Ca_v1.2 channel confers increased vascular resistance in hypertension. This review will discuss the importance of ROS derived from NOXs and mitochondria in regulating vascular Ca_v1.2 and potential roles of ROS-mediated Ca_v1.2 dysfunction in aberrant vascular function in hypertension, diabetes, and preeclampsia.

Role of Caveolae in the Development of Microvascular Dysfunction and Hyperglycemia in Type 2 Diabetes

In type 2 diabetes (T2D) microvascular dysfunction can interfere with tissue glucose uptake thereby contributing to the development of hyperglycemia. The cell membrane caveolae orchestrate signaling pathways that include microvascular control of tissue perfusion. In this study, we examined the role of caveolae in the regulation of microvascular vasomotor function under the condition of hyperglycemia in T2D patients and rodent models. Human coronary arterioles were obtained during cardiac surgery from T2D patients, with higher perioperative glucose levels, and from normoglycemic, non-diabetic controls. The coronary arteriole responses to pharmacological agonists bradykinin and acetylcholine were similar in T2D and non-diabetic patients, however, exposure of the isolated arteries to methyl-β-cyclodextrin (mβCD), an agent known to disrupt caveolae, reduced vasodilation to bradykinin selectively in T2D subjects and converted acetylcholine-induced vasoconstriction to dilation similarly in the two groups. Dilation to the vascular smooth muscle acting nitric oxide donor, sodium nitroprusside, was not affected by mβCD in either group. Moreover, mβCD reduced endothelium-dependent arteriolar dilation to a greater extent in hyperglycemic and obese db/db mice than in the non-diabetic controls. Mechanistically, when fed a high-fat diet (HFD), caveolin-1 knockout mice, lacking caveolae, exhibited a significantly reduced endothelium-dependent arteriolar dilation, both ex vivo and in vivo, which was accompanied by significantly higher serum glucose levels, when compared to HFD fed wild type controls. Thus, in T2D arterioles the role of caveolae in regulating endothelium-dependent arteriole dilation is altered, which appears to maintain vasodilation and mitigate the extent of hyperglycemia. While caveolae play a unique role in microvascular vasomotor regulation, under the condition of hyperglycemia arterioles from T2D subjects appear to be more susceptible for caveolae disruption-associated vasomotor dysfunction and impaired glycemic control.

Modulation of Renal Function in a Metabolic Syndrome Rat Model by Antioxidants in Hibiscus sabdariffa L

Metabolic syndrome (MS) is the association of three or more pathologies among which obesity, hypertension, insulin resistance, dyslipidemia, and diabetes are included. It causes oxidative stress (OS) and renal dysfunction. Hibiscus sabdariffa L. (HSL) is a source of natural antioxidants that may control the renal damage caused by the MS. The objective of this work was to evaluate the effect of a 2% HSL infusion on renal function in a MS rat model induced by the administration of 30% sucrose in drinking water. 24 male Wistar rats were divided into 3 groups: Control rats, MS rats and MS + HSL rats. MS rats had increased body weight, systolic blood pressure, triglycerides, insulin, HOMA index, and leptin (p ≤ 0.04). Renal function was impaired by an increase in perfusion pressure in the isolated and perfused kidney, albuminuria (p ≤ 0.03), and by a decrease in clearance of creatinine (p ≤ 0.04). The activity of some antioxidant enzymes including the superoxide dismutase isoforms, peroxidases, glutathione peroxidase, glutathione-S-transferase was decreased (p ≤ 0.05). Lipoperoxidation and carbonylation were increased (p ≤ 0.001). The nitrates/nitrites ratio, total antioxidant capacity, glutathione levels and vitamin C were decreased (p ≤ 0.03). The treatment with 2% HSL reversed these alterations. The results suggest that the treatment with 2% HSL infusion protects renal function through its natural antioxidants which favor an improved renal vascular response. The infusion contributes to the increase in the glomerular filtration rate, by promoting an increase in the enzymatic and non-enzymatic antioxidant systems leading to a decrease in OS and reestablishing the normal renal function.

The effects of physical activity on adipokines in individuals with overweight/obesity across the lifespan: A narrative review

This narrative review summarizes current knowledge on the effects of physical activity (PA) on adipokine levels in individuals with overweight and obesity. Approximately 90 investigations including randomized control, cross-sectional and longitudinal studies that reported on the effects of a single session of PA (acute) or long-term PA (chronic) on adipokine levels in individuals with overweight/obesity were reviewed. The findings support the notion that there is consensus on the benefits of chronic exercise training-regardless of the mode (resistance vs. aerobic), intensity and cohort (healthy vs. diabetes)-on adipokine levels (such as tumour necrosis factor-alpha, interleukin-6, adiponectin, visfatin, omentin-1 and leptin). However, several confounding factors (frequency, intensity, time and type of exercise) can alter the magnitude of the effects of an acute exercise session. Available evidence suggests that PA, as a part of routine lifestyle behaviour, improves obesity complications by modulating adipokine levels. However, additional research is needed to help identify the most effective interventions to elicit the most beneficial changes in adipokine levels in individuals with overweight/obesity.

Curcumin analogs (B2BrBC and C66) supplementation attenuates airway hyperreactivity and promote airway relaxation in neonatal rats exposed to hyperoxia

BACKGROUND

This study was undertaken to test the hypothesis that the newly synthesized curcuminoids B2BrBC and C66 supplementation will overcome hyperoxia-induced tracheal hyperreactivity and impairment of relaxation of tracheal smooth muscle (TSM).

MATERIALS AND METHODS

Rat pups (P5) were exposed to hyperoxia (>95% O2 ) or normoxia for 7 days. At P12, tracheal cylinders were used to study in vitro contractile responses induced by methacholine (10-8 -10-4 M) or relaxation induced by electrical field stimulation (5-60 V) in the presence/absence of B2BrBC or C66, or to study the direct relaxant effects elicited by both analogs.

RESULTS

Hyperoxia significantly increased contraction and decreased relaxation of TSM compared to normoxia controls. Presence of B2BrBC or C66 normalized both contractile and relaxant responses altered by hyperoxia. Both, curcuminoids directly induced dose-dependent relaxation of preconstricted TSM. Supplementation of hyperoxic animals with B2BrBC or C66, significantly increased catalase activity. Lung TNF-α was significantly increased in hyperoxia-exposed animals. Both curcumin analogs attenuated increases in TNF-α in hyperoxic animals.

CONCLUSION

We show that B2BrBC and C66 provide protection against adverse contractility and relaxant effect of hyperoxia on TSM, and whole lung inflammation. Both analogs induced direct relaxation of TSM. Through restoration of catalase activity in hyperoxia, we speculate that analogs are protective against hyperoxia-induced tracheal hyperreactivity by augmenting H2 O2 catabolism. Neonatal hyperoxia induces increased tracheal contractility, attenuates tracheal relaxation, diminishes lung antioxidant capacity, and increases lung inflammation, while monocarbonyl CUR analogs were protective of these adverse effects of hyperoxia. Analogs may be promising new therapies for neonatal hyperoxic airway and lung disease.

Ganglioside GM3 content in skeletal muscles is increased in type 2 but decreased in type 1 diabetes rat models: Implications of glycosphingolipid metabolism in pathophysiology of diabetes

BACKGROUND

Ganglioside GM3 is found in the plasma membrane, where its accumulation attenuates insulin receptor signaling. Considering the role of skeletal muscles in insulin-stimulated glucose uptake, the aim of the present study was to determine the expression of GM3 and its precursors in skeletal muscles of rat models of type 1 and type 2 diabetes mellitus (T1DM and T2DM, respectively).

METHODS

Diabetes was induced in male Sprague-Dawley rats by streptozotocin injection (55 mg/kg, i.p., for T1DM induction; 35 mg/kg, i.p., for T2DM induction), followed by feeding of rats with either a normal pellet diet (T1DM) or a high-fat diet (T2DM). Rats were killed 2 weeks after diabetes induction and samples of skeletal muscle were collected. Frozen quadriceps muscle sections were stained with a primary antibody against GM3 (Neu5Ac) and visualized using a secondary antibody coupled with Texas Red. The muscle content of ganglioside GM3 and its precursors was analyzed by high-performance thin-layer chromatography (HPTLC) followed by GM3 immunostaining.

RESULTS

Muscle GM3 content was significantly higher in T2DM compared with control rats (P < 0.001). Furthermore, levels of the GM3 precursors ceramide, glucosylceramide, and lactosylceramide were significantly higher in T2DM compared with control rats (P < 0.05), whereas ceramide content was significantly lower in T1DM rats (P < 0.05). The intensity of the GM3 band on HPTLC was significantly higher in T2DM rats (P < 0.001) and significantly lower in T1DM rats (P < 0.05) compared with control.

CONCLUSIONS

The expression patterns of GM3 ganglioside and its precursors in diabetic rats suggest that the role of glycosphingolipid metabolism may differ between T2DM and T1DM.

Hyperglycaemia disrupts conducted vasodilation in the resistance vasculature of db/db mice

Vascular dysfunction in small resistance arteries is observed during chronic elevations in blood glucose. Hyperglycaemia-associated effects on endothelium-dependent vasodilation have been well characterized, but effects on conducted vasodilation in the resistance vasculature are not known. Small mesenteric arteries were isolated from healthy and diabetic db/db mice, which were used as a model of chronic hyperglycaemia. Endothelium-dependent vasodilation via the G_q/11-coupled proteinase activated receptor 2 (PAR2) was stimulated with the selective agonist SLIGRL. The Ca²⁺-sensitive fluorescent indicator fluo-8 reported changes in endothelial cell (EC) [Ca²⁺]_i, and triple cannulated bifurcating mesenteric arteries were used to study conducted vasodilation. Chronic hyperglycaemia did not affect either EC Ca²⁺ or local vasodilation to SLIGRL. However, both acute and chronic exposure to high glucose or the mannitol osmotic control attenuated conducted vasodilation to 10μM SLIGRL. This investigation demonstrates for the first time that a hypertonic solution containing glucose or mannitol can interfere with the spread of a hyperpolarizing current along the endothelium in a physiological setting. Our findings reiterate the importance of studying the effects of hyperglycaemia in the vasculature, and provide the basis for further studies regarding the modulation of junctional proteins involved in cell to cell communication by diseases such as diabetes.

Role of Perivascular Adipose Tissue in Health and Disease

Perivascular adipose tissue (PVAT) is cushion of fat tissue surrounding blood vessels, which is phenotypically different from other adipose tissue depots. PVAT is composed of adipocytes and stromal vascular fraction, constituted by different populations of immune cells, endothelial cells, and adipose-derived stromal cells. It expresses and releases an important number of vasoactive factors with paracrine effects on vascular structure and function. In healthy individuals, these factors elicit a net anticontractile and anti-inflammatory paracrine effect aimed at meeting hemodynamic and metabolic demands of specific organs and regions of the body. Pathophysiological situations, such as obesity, diabetes or hypertension, induce changes in its amount and in the expression pattern of vasoactive factors leading to a PVAT dysfunction in which the beneficial paracrine influence of PVAT is shifted to a pro-oxidant, proinflammatory, contractile, and trophic environment leading to functional and structural cardiovascular alterations and cardiovascular disease. Many different PVATs surrounding a variety of blood vessels have been described and exhibit regional differences. Both protective and deleterious influence of PVAT differs regionally depending on the specific vascular bed contributing to variations in the susceptibility of arteries and veins to vascular disease. PVAT therefore, might represent a novel target for pharmacological intervention in cardiovascular disease. © 2018 American Physiological Society. Compr Physiol 8:23-59, 2018.

Thrombospondin-1, Free Radicals, and the Coronary Microcirculation: The Aging Conundrum

SIGNIFICANCE

Successful matching of cardiac metabolism to perfusion is accomplished primarily through vasodilation of the coronary resistance arterioles, but the mechanism that achieves this effect changes significantly as aging progresses and involves the contribution of reactive oxygen species (ROS). Recent Advances: A matricellular protein, thrombospondin-1 (Thbs-1), has been shown to be a prolific contributor to the production and modulation of ROS in large conductance vessels and in the peripheral circulation. Recently, the presence of physiologically relevant circulating Thbs-1 levels was proven to also disrupt vasodilation to nitric oxide (NO) in coronary arterioles from aged animals, negatively impacting coronary blood flow reserve.

CRITICAL ISSUES

This review seeks to reconcile how ROS can be successfully utilized as a substrate to mediate vasoreactivity in the coronary microcirculation as "normal" aging progresses, but will also examine how Thbs-1-induced ROS production leads to dysfunctional perfusion and eventual ischemia and why this is more of a concern in advancing age.

FUTURE DIRECTIONS

Current therapies that may effectively disrupt Thbs-1 and its receptor CD47 in the vascular wall and areas for future exploration will be discussed. Antioxid. Redox Signal. 27, 785-801.

Diabetes converts arterial regulation by perivascular adipose tissue from relaxation into H(2)O(2)-mediated contraction

This study aims to reveal the reason for the increased force of 5-hydroxytryptamine-induced contraction of endothelium-denuded skeletal muscle arteries of diabetic rats in the presence of perivascular adipose tissue (PVAT). Our data on rat gracilis arteries show that i) PVAT of skeletal muscle arteries of healthy and diabetic rats releases hydrogen peroxide (H(2)O(2)), ii) higher concentrations of 5-hydroxytryptamine increase the production of H(2)O(2) in PVAT; iii) an enhanced PVAT production of H(2)O(2) is the main, if not the only, reason for the sensitization of arterial contraction to 5-hydroxytriptamine-induced contraction in diabetes and iv) endothelium antagonizes the effect of PVAT-derived H(2)O(2).

AST IV inhibits H₂O₂-induced human umbilical vein endothelial cell apoptosis by suppressing Nox4 expression through the TGF-β1/Smad2 pathway

Endothelial cell apoptosis plays an important role in the pathophysiological mechanisms of vascular complications in diabetes mellitus (DM). NADPH oxidase 4 (Nox4)-dependent reactive oxygen species (ROS) aggregation is the main cause of vascular endothelial cell apoptosis. The transforming growth factor-β1 (TGF-β1)/Smad2 signaling pathway is involved in the apoptosis of several types of cells. However, the association between vascular endothelial cell apoptosis and Nox4, and the involvement of the TGF-β1/Smad2 signaling pathway in vascular endothelial cell apoptosis remain unclear. In the present study, we aimed to investigate the role of Nox4-dependent ROS production and to determine the involvement of the TGF-β1/Smad2 signaling pathway in endothelial cell apoptosis induced by oxidative stress which causes vascular injury in DM. We demonstrated that hydrogen peroxide (H2O2) increased Nox4-dependent-ROS aggregation, as well as the expression of TGF-β1, Smad2, Bax and caspase-3, decreased Bcl-2 expression and increased the apoptosis of human umbilical vein endothelial cells (HUVECs). Treatment with diphenyliodonium (DPI), a specific inhibitor of Nox4 or astragaloside IV (AST IV), a monomer located in an extract of astragaloside, decreased Nox4 expression and the levels of ROS, decreased TGF-β1 and Smad2 expression, altered the expression of apoptosis-related genes and decreased the apoptosis of HUVECs. Treatment with LY2109761, a selective inhibitor of the TGF-β1/Smad2 pathway, produced results similar to those of DPI; however, LY2109761 had no effect on Nox4 expression and ROS levels. Taken together, the findings of the present study suggest that H2O2 contributes to HUVEC apoptosis by inducing Nox4-dependent ROS aggregation and activating the TGF-β1/Smad2 signaling pathway. Our data indicate that the protective effects of AST IV against vascular endothelial cell apoptosis in DM are mainly associated with the decrease in Nox4 expression through the TGF-β1/Smad2 signaling pathway. Furthermore, the inhibition of the activation of the TGF-β1/Smad2 signaling pathway may be another potential therapeutic strategy in the treatment of DM.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Ca(2+) handling alterations and vascular dysfunction in diabetes

More than 65% of patients with diabetes mellitus die from cardiovascular disease or stroke. Hyperglycemia, due to either reduced insulin secretion or reduced insulin sensitivity, is the hallmark feature of diabetes mellitus. Vascular dysfunction is a distinctive phenotype found in both types of diabetes and could be responsible for the high incidence of stroke, heart attack, and organ damage in diabetic patients. In addition to well-documented endothelial dysfunction, Ca(2+) handling alterations in vascular smooth muscle cells (VSMCs) play a key role in the development and progression of vascular complications in diabetes. VSMCs provide not only structural integrity to the vessels but also control myogenic arterial tone and systemic blood pressure through global and local Ca(2+) signaling. The Ca(2+) signalosome of VSMCs is integrated by an extensive number of Ca(2+) handling proteins (i.e. channels, pumps, exchangers) and related signal transduction components, whose function is modulated by endothelial effectors. This review summarizes recent findings concerning alterations in endothelium and VSMC Ca(2+) signaling proteins that may contribute to the vascular dysfunction found in the diabetic condition.

Hydrogen peroxide elicits constriction of skeletal muscle arterioles by activating the arachidonic acid pathway

Aims

The molecular mechanisms of the vasoconstrictor responses evoked by hydrogen peroxide (H₂O₂) have not been clearly elucidated in skeletal muscle arterioles.

Methods and Results

Changes in diameter of isolated, cannulated and pressurized gracilis muscle arterioles (GAs) of Wistar-Kyoto rats were determined under various test conditions. H₂O₂ (10–100 µM) evoked concentration-dependent constrictions in the GAs, which were inhibited by endothelium removal, or by antagonists of phospholipase A (PLA; 100 µM 7,7-dimethyl-(5Z,8Z)-eicosadienoic acid), protein kinase C (PKC; 10 µM chelerythrine), phospholipase C (PLC; 10 µM U-73122), or Src family tyrosine kinase (Src kinase; 1 µM Src Inhibitor-1). Antagonists of thromboxane A2 (TXA2; 1 µM SQ-29548) or the non-specific cyclooxygenase (COX) inhibitor indomethacin (10 µM) converted constrictions to dilations. The COX-1 inhibitor (SC-560, 1 µM) demonstrated a greater reduction in constriction and conversion to dilation than that of COX-2 (celecoxib, 3 µM). H₂O₂ did not elicit significant changes in arteriolar Ca²⁺ levels measured with Fura-2.

Conclusions

These data suggest that H₂O₂ activates the endothelial Src kinase/PLC/PKC/PLA pathway, ultimately leading to the synthesis and release of TXA2 by COX-1, thereby increasing the Ca²⁺ sensitivity of the vascular smooth muscle cells and eliciting constriction in rat skeletal muscle arterioles.

Increase in insulin-induced relaxation of consecutive arterial segments toward the periphery: Role of vascular oxidative state

RATIONALE

The oxidative state has been implicated in the signaling of various vasomotor functions, yet its role regarding the vasomotor action of insulin is less known.

OBJECTIVE

To investigate the insulin-evoked relaxations of consecutive arterial segments of different oxidative state and the role of extracellular signal-regulated kinase (ERK) pathway.

METHODS AND RESULTS

The oxidative state, as assessed by the level of ortho-tyrosine, was higher in the thoracic aorta of rats than in the abdominal aorta, and was the lowest in the femoral artery. The vasomotor function of vessels of same origin was studied using a small-vessel myograph. Insulin-induced relaxations increased toward the periphery (i.e., thoracic < abdominal < femoral). Aortic banding and hydrogen peroxide/aminotriazole increased the oxidative state of the thoracic aorta that was accompanied by ERK activation and decreased relaxation to insulin, and vice versa, acutely lowered oxidative state by superoxide dismutase/catalase improved relaxation. In contrast, insulin-induced relaxation of the femoral artery could be enhanced with a higher oxidative state, and reduced with a lower state.

CONCLUSIONS

Oxidative state of vessels modulates the magnitude of vasomotor responses to insulin, which appears to be mediated via the ERK signaling pathway.

Mechanisms of vascular dysfunction in mice with endothelium-specific deletion of the PPAR-δ gene

Peroxisome proliferator-activated receptor (PPAR)-δ is a nuclear hormone receptor that is mainly involved in lipid metabolism. Recent studies have suggested that PPAR-δ agonists exert vascular protective effects. The present study was designed to characterize vascular function in mice with genetic inactivation of PPAR-δ in the endothelium. Mice with vascular endothelial cell-specific deletion of the PPAR-δ gene (ePPARδ(-/-) mice) were generated using loxP/Cre technology. ePPARδ(-/-) mice were normotensive and did not display any sign of metabolic syndrome. Endothelium-dependent relaxations to ACh and endothelium-independent relaxations to the nitric oxide (NO) donor diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate were both significantly impaired in the aorta and carotid arteries of ePPARδ(-/-) mice (P < 0.05). In ePPARδ(-/-) mouse aortas, phosphorylation of endothelial NO synthase at Ser(1177) was significantly decreased (P < 0.05). However, basal levels of cGMP were unexpectedly increased (P < 0.05). Enzymatic activity of GTP-cyclohydrolase I and tetrahydrobiopterin levels were also enhanced in ePPARδ(-/-) mice (P < 0.05). Most notably, endothelium-specific deletion of the PPAR-δ gene significantly decreased protein expressions of catalase and glutathione peroxidase 1 and resulted in increased levels of H2O2 in the aorta (P < 0.05). In contrast, superoxide anion production was unaltered. Moreover, treatment with catalase prevented the endothelial dysfunction and elevation of cGMP detected in aortas of ePPARδ(-/-) mice. The findings suggest that increased levels of cGMP caused by H2O2 impair vasodilator reactivity to endogenous and exogenous NO. We speculate that chronic elevation of H2O2 predisposes PPAR-δ-deficient arteries to oxidative stress and vascular dysfunction.

Maintenance of hypertensive hemodynamics does not depend on ROS in established experimental chronic kidney disease

While the presence of oxidative stress in chronic kidney disease (CKD) is well established, its relation to hypertensive renal hemodynamics remains unclear. We hypothesized that once CKD is established blood pressure and renal vascular resistance (RVR) no longer depend on reactive oxygen species. CKD was induced by bilateral ablation of 2/3 of each kidney. Compared to age-matched, sham-operated controls all ablated rats showed proteinuria, decreased glomerular filtration rate (GFR), more renal damage, higher mean arterial pressure (MAP), RVR and excretion of oxidative stress markers and hydrogen peroxide, while excretion of stable nitric oxide (NO) metabolites tended to decrease. We compared MAP, RVR, GFR and fractional excretion of sodium under baseline and during acute Tempol, PEG-catalase or vehicle infusion in rats with established CKD vs. controls. Tempol caused marked reduction in MAP in controls (96±5 vs.79±4 mmHg, P<0.05) but not in CKD (130±5 vs. 127±6 mmHg). PEG-catalase reduced MAP in both groups (controls: 102±2 vs. 94±4 mmHg, P<0.05; CKD: 118±4 vs. 110±4 mmHg, P<0.05), but did not normalize MAP in CKD rats. Tempol and PEG-catalase slightly decreased RVR in both groups. Fractional excretion of sodium was increased by both Tempol and PEG-catalase in both groups. PEG-catalase decreased TBARS excretion in both groups. In sum, although oxidative stress markers were increased, MAP and RVR did not depend more on oxidative stress in CKD than in controls. Therefore reactive oxygen species appear not to be important direct determinants of hypertensive renal hemodynamics in this model of established CKD.

Exercise induced adipokine changes and the metabolic syndrome

The lack of adequate physical activity and obesity created a worldwide pandemic. Obesity is characterized by the deposition of adipose tissue in various parts of the body; it is now evident that adipose tissue also acts as an endocrine organ capable of secreting many cytokines that are though to be involved in the pathophysiology of obesity, insulin resistance, and metabolic syndrome. Adipokines, or adipose tissue-derived proteins, play a pivotal role in this scenario. Increased secretion of proinflammatory adipokines leads to a chronic inflammatory state that is accompanied by insulin resistance and glucose intolerance. Lifestyle change in terms of increased physical activity and exercise is the best nonpharmacological treatment for obesity since these can reduce insulin resistance, counteract the inflammatory state, and improve the lipid profile. There is growing evidence that exercise exerts its beneficial effects partly through alterations in the adipokine profile; that is, exercise increases secretion of anti-inflammatory adipokines and reduces proinflammatory cytokines. In this paper we briefly describe the pathophysiologic role of four important adipokines (adiponectin, leptin, TNF-α, and IL-6) in the metabolic syndrome and review some of the clinical trials that monitored these adipokines as a clinical outcome before and after exercise.

Selective up-regulation of arginase-1 in coronary arteries of diabetic patients

Coronary artery disease (CAD) remains the leading cause of death in the Western societies. Diabetes mellitus (DM) is one of the highly prevalent diseases, which remarkably accelerates the development of CAD. Experimental evidence indicates that decreased bioavailability of coronary endothelial nitric oxide (NO) contributes to the development of CAD in DM. There are recent studies showing that a selective impairment of NO synthesis occurs in coronary arteries of DM patients, which is mainly due to the limited availability of endothelial NO synthase (eNOS) precursor, l-arginine. Importantly, these studies demonstrated that DM, independent of the presence of CAD, leads to selective up-regulation of arginase-1. Arginase-1 seems to play an important role in limiting l-arginine availability in the close proximity of eNOS in vessels of DM patients. This brief review examines recent clinical studies demonstrating the pathological role of vascular arginase-1 in human diabetes. Whether arginase-1, which is crucial in the synthesis of various fundamental polyamines in the body, will represent a potent therapeutic target for prevention of DM-associated CAD is still debated.

Exercise and the aging endothelium

The endothelium plays a critical role in the maintenance of cardiovascular health by producing nitric oxide and other vasoactive materials. Aging is associated with a gradual decline in this functional aspect of endothelial regulation of cardiovascular homeostasis. Indeed, age is an independent risk factor for cardiovascular diseases and is in part an important factor in the increased exponential mortality rates from vascular disease such as myocardial infarction and stroke that occurs in the ageing population. There are a number of mechanisms suggested to explain age-related endothelial dysfunction. However, recent scientific studies have advanced the notion of oxidative stress and inflammation as the two major risk factors underlying aging and age-related diseases. Regular physical activity, known to have a favorable effect on cardiovascular health, can also improve the function of the ageing endothelium by modulating oxidative stress and inflammatory processes, as we discuss in this paper.

Signaling pathways involved in the H2O2-induced vasoconstriction of rat coronary arteries

Hydrogen peroxide (H2O2) is an endogenous endothelium-derived hyperpolarizing factor released by flow and involved in the regulation of coronary blood flow. Because opposing vasoactive effects have been reported for H2O2 depending on the vascular bed and experimental conditions, the aim of this study was to assess whether H2O2 may act as a coronary vasoconstrictor and if so to determine the underlying signaling mechanisms. Intramyocardial arteries from male Wistar rats were mounted on microvascular myographs for simultaneous measurements of intracellular Ca(2+) ([Ca(2+)]i) and tension. On coronary arteries precontracted with the thromboxane A2 (TxA2) analogue U46619, H2O2 (1-300μM) elicited further moderate contractions in the proximal arterial segments and relaxed the more distal coronary branches, the contractions being markedly augmented in arteries depolarized by raising extracellular K(+). H2O2-elicited vasoconstriction on K(+)30-precontracted coronary arteries was blunted by catalase and significantly reduced by endothelial cell removal and by inhibitors of cyclooxygenase (COX) and of the TxA2 receptor (TP). H2O2 (50μM) increased by about 10-fold basal superoxide anion (O2(-)) production in coronary arteries measured by lucigenin-enhanced chemiluminescence, and H2O2-elicited contractions were reduced by the superoxide dismutase mimetic tempol and by NADPH oxidase inhibition. Furthermore, blockade of the ERK and p38 mitogen-activated protein (MAP) kinases significantly reduced the contractions elicited by high and low concentrations of peroxide, respectively, whereas Rho kinase inhibition nearly abolished these responses. H2O2 (50μM) elicited simultaneous and similar sustained increases in [Ca(2+)]i and tension that were blunted by blockade of voltage-dependent L-type channels, but resistant to the nonselective Ca(2+) channel blocker 2-aminoethoxydiphenyl borate. Moreover, endothelial cell removal reduced the increases in [Ca(2+)]i and contraction elicited by peroxide. The present data demonstrate that H2O2 is an endothelium-dependent vasoconstrictor in rat coronary arteries that activates smooth muscle Ca(2+) entry through L-type and non-L-type channels and various intracellular signaling pathways including the release of a COX-derived TP agonist, stimulation of the MAP and Rho kinase pathways, and production of NADPH oxidase-derived superoxide.

Defective Nrf2-dependent redox signalling contributes to microvascular dysfunction in type 2 diabetes

AIMS

In type 2 diabetes, antioxidant depletion contributes to increased oxidative stress in the microvasculature. The current study was designed to assess how oxidative stress contributes to functional changes in the microvasculature, and determine the importance, and the effects of pharmacologically targeting, the transcription factor Nrf2.

METHODS AND RESULTS

Pressure myography was used to measure myogenic constriction in mesenteric arterioles from diabetic (db/db) and non-diabetic (db/m) mice. Compared with db/m, myogenic constriction was larger in db/db, independent of the endothelial cell layer, and directly correlated with elevated basal and pressure-induced reactive oxygen species (ROS) production. Nrf2 was depleted in db/db vessels and associated with down-regulation of Nrf2-regulated genes. Notably, expression of GCLC and GCLM, enzymes important for glutathione (GSH) synthesis, was dramatically reduced, as was total cellular GSH. Normal myogenic function was restored to db/db arterioles by incubation with cell-permeant GSH. Similarly, the db/db myogenic phenotype was recapitulated in the db/m vessels by pharmacological GSH depletion. Treatment with the Nrf2-activator sulforaphane increased Nrf2 and promoted its nuclear localization and increased GCLC and GCLM expression in both db/m and db/db. Sulforaphane dramatically lowered ROS signalling in db/db and reduced myogenic tone to levels similar to that seen in db/m vessels.

CONCLUSION

Depleted Nrf2 and expression of its dependent genes compromises antioxidant capacity resulting in dysfunctional myogenic tone in diabetes that is reversed by the Nrf2-activator sulforaphane.

Potential mechanisms of exercise in gestational diabetes

Gestational diabetes mellitus (GDM) is defined as glucose intolerance first diagnosed during pregnancy. This condition shares same array of underlying abnormalities as occurs in diabetes outside of pregnancy, for example, genetic and environmental causes. However, the role of a sedentary lifestyle and/or excess energy intake is more prominent in GDM. Physically active women are less likely to develop GDM and other pregnancy-related diseases. Weight gain in pregnancy causes increased release of adipokines from adipose tissue; many adipokines increase oxidative stress and insulin resistance. Increased intramyocellular lipids also increase cellular oxidative stress with subsequent generation of reactive oxygen species. A well-planned program of exercise is an important component of a healthy lifestyle and, in spite of old myths, is also recommended during pregnancy. This paper briefly reviews the role of adipokines in gestational diabetes and attempts to shed some light on the mechanisms by which exercise can be beneficial as an adjuvant therapy in GDM. In this regard, we discuss the mechanisms by which exercise increases insulin sensitivity, changes adipokine profile levels, and boosts antioxidant mechanisms.

Abnormal Ca2+ spark/STOC coupling in cerebral artery smooth muscle cells of obese type 2 diabetic mice

Diabetes is a major risk factor for stroke. However, the molecular mechanisms involved in cerebral artery dysfunction found in the diabetic patients are not completely elucidated. In cerebral artery smooth muscle cells (CASMCs), spontaneous and local increases of intracellular Ca2+ due to the opening of ryanodine receptors (Ca2+ sparks) activate large conductance Ca2+-activated K+ (BK) channels that generate spontaneous transient outward currents (STOCs). STOCs have a key participation in the control of vascular myogenic tone and blood pressure. Our goal was to investigate whether alterations in Ca(2+) spark and STOC activities, measured by confocal microscopy and patch-clamp technique, respectively, occur in isolated CASMCs of an experimental model of type-2 diabetes (db/db mouse). We found that mean Ca(2+) spark amplitude, duration, size and rate-of-rise were significantly smaller in Fluo-3 loaded db/db compared to control CASMCs, with a subsequent decrease in the total amount of Ca(2+) released through Ca(2+) sparks in db/db CASMCs, though Ca(2+) spark frequency remained. Interestingly, the frequency of large-amplitude Ca(2+) sparks was also significantly reduced in db/db cells. In addition, the frequency and amplitude of STOCs were markedly reduced at all voltages tested (from -50 to 0 mV) in db/db CASMCs. The latter correlates with decreased BK channel β1/α subunit ratio found in db/db vascular tissues. Taken together, Ca(2+) spark alterations lead to inappropriate BK channels activation in CASMCs of db/db mice and this condition is aggravated by the decrease in the BK β1 subunit/α subunit ratio which underlies the significant reduction of Ca(2+) spark/STOC coupling in CASMCs of diabetic animals.

Exercise in the metabolic syndrome

The metabolic syndrome is a clustering of obesity, diabetes, hyperlipidemia, and hypertension that is occurring in increasing frequency across the global population. Although there is some controversy about its diagnostic criteria, oxidative stress, which is defined as imbalance between the production and inactivation of reactive oxygen species, has a major pathophysiological role in all the components of this disease. Oxidative stress and consequent inflammation induce insulin resistance, which likely links the various components of this disease. We briefly review the role of oxidative stress as a major component of the metabolic syndrome and then discuss the impact of exercise on these pathophysiological pathways. Included in this paper is the effect of exercise in reducing fat-induced inflammation, blood pressure, and improving muscular metabolism.

Exercise and the cardiovascular system

There are alarming increases in the incidence of obesity, insulin resistance, type II diabetes, and cardiovascular disease. The risk of these diseases is significantly reduced by appropriate lifestyle modifications such as increased physical activity. However, the exact mechanisms by which exercise influences the development and progression of cardiovascular disease are unclear. In this paper we review some important exercise-induced changes in cardiac, vascular, and blood tissues and discuss recent clinical trials related to the benefits of exercise. We also discuss the roles of boosting antioxidant levels, consequences of epicardial fat reduction, increases in expression of heat shock proteins and endoplasmic reticulum stress proteins, mitochondrial adaptation, and the role of sarcolemmal and mitochondrial potassium channels in the contributing to the cardioprotection offered by exercise. In terms of vascular benefits, the main effects discussed are changes in exercise-induced vascular remodeling and endothelial function. Exercise-induced fibrinolytic and rheological changes also underlie the hematological benefits of exercise.

Antioxidant and anti-inflammatory effects of exercise in diabetic patients

Diabetes is a chronic metabolic disease which is characterized by absolute or relative deficiencies in insulin secretion and/or insulin action. The key roles of oxidative stress and inflammation in the progression of vascular complications of this disease are well recognized. Accumulating epidemiologic evidence confirms that physical inactivity is an independent risk factor for insulin resistance and type II diabetes. This paper briefly reviews the pathophysiological pathways associated with oxidative stress and inflammation in diabetes mellitus and then discusses the impact of exercise on these systems. In this regard, we discuss exercise induced activation of cellular antioxidant systems through “nuclear factor erythroid 2-related factor.” We also discuss anti-inflammatory myokines, which are produced and released by contracting muscle fibers. Antiapoptotic, anti-inflammatory and chaperon effects of exercise-induced heat shock proteins are also reviewed.

Pulmonary arterial responses to reactive oxygen species are altered in newborn piglets with chronic hypoxia-induced pulmonary hypertension

Reactive oxygen species (ROS) have been implicated in the pathogenesis of pulmonary hypertension. ROS might mediate vascular responses, at least in part, by stimulating prostanoid production. Our goals were to determine whether the effect of ROS on vascular tone is altered in resistance pulmonary arteries (PRAs) of newborn piglets with chronic hypoxia-induced pulmonary hypertension and the role, if any, of prostanoids in ROS-mediated responses. In cannulated, pressurized PRA, ROS generated by xanthine (X) plus xanthine oxidase (XO) had minimal effect on vascular tone in control piglets but caused significant vasoconstriction in hypoxic piglets. Both cyclooxygenase inhibition with indomethacin and thromboxane synthase inhibition with dazoxiben significantly blunted constriction to X+XO in hypoxic PRA. X+XO increased prostacyclin production (70 ± 8%) by a greater degree than thromboxane production (50 ± 6%) in control PRA; this was not the case in hypoxic PRA where the increases in prostacyclin and thromboxane production were not statistically different (78 ± 13% versus 216 ± 93%, respectively). Thromboxane synthase expression was increased in PRA from hypoxic piglets, whereas prostacyclin synthase expression was similar in PRA from hypoxic and control piglets. Under conditions of chronic hypoxia, altered vascular responses to ROS may contribute to pulmonary hypertension by a mechanism that involves the prostanoid vasoconstrictor, thromboxane.

Weight and inflammation are the major determinants of vascular dysfunction in the aortae of db/db mice

The key roles that obesity, hyperglycemia, hyperlipidemia, inflammation, and oxidative stress play in the progression of diabetes vascular complications are well recognized; however, the relative contribution and importance of these individual factors remain uncertain. At 6, 10, or 14 weeks old, blood samples and thoracic aortae were collected from db/db mice and their non-diabetic controls. Plasma samples were analyzed for glucose, 8-isoprostane, CRP, triglycerides, LDL, and HDL as markers of glycemic status, oxidative stress, inflammation, and dyslipidemia, respectively. The responses of the aortic rings to high KCl, phenylephrine (PE), acetylcholine (ACh), and sodium nitroprusside were examined. Statistical methods were used to estimate the strength of the association between plasma variables and vascular functions. Systemic inflammation occurred in db/db mice at an earlier age than did hyperglycemia or oxidative stress. Aortae of db/db showed augmented contractions to PE which were positively correlated with weight, plasma glucose, 8-isoprostane, and CRP. Also, db/db mice showed impaired endothelium-dependent ACh vasorelaxation which was negatively correlated with weight, plasma glucose, and 8-isoprostane. Multivariate analysis and stepwise modeling show that CRP is the major determinant of the contractile responses, while weight and HDL are the major determinants of ACh-induced relaxation. Among the traditional risk factors of obesity, hyperglycemia, oxidative stress, inflammation, and dyslipidemia, our study reveals that weight and inflammation are the major determinants of vascular dysfunction in the aortae of db/db mice. Our findings partially resolve the complexity of diabetes vasculopathies and suggest targeting weight loss and inflammation for effective therapeutic approaches.

Superoxide dismutase mimetic drug tempol aggravates anti-GBM antibody-induced glomerulonephritis in mice

Oxidative stress plays an important role in the pathogenesis of anti-glomerular basement membrane antibody-induced glomerulonephritis (anti-GBM-GN). Superoxide dismutase (SOD) is the first line of defense against oxidative stress by converting superoxide to hydrogen peroxide (H(2)O(2)). We investigated the effect of the SOD mimetic drug tempol on anti-GBM-GN in mice. 129/svJ mice were challenged with rabbit anti-mouse-GBM sera to induce GN and subsequently divided into tempol (200 mg.kg(-1).day(-1), orally) and vehicle-treated groups. Routine histology, SOD and catalase activities, malondialdehyde (MDA), H(2)O(2), and immunohistochemical staining for neutrophils, lymphocytes, macrophages, p65-NF-kappaB, and osteopontin were performed. Mice with anti-GBM-GN had significantly reduced renal SOD and catalase activities and increased H(2)O(2) and MDA levels. Unexpectedly, tempol administration exacerbated anti-GBM-GN as evidenced by intensification of proteinuria, the presence of severe crescentic GN with leukocyte influx, and accelerated mortality in the treated group. Tempol treatment raised SOD activity and H(2)O(2) level in urine, upregulated p65-NF-kappaB and osteopontin in the kidney, but had no effect on renal catalase activity. Thus tempol aggravates anti-GBM-GN by increasing production of H(2)O(2) which is a potent NF-kappaB activator and as such can intensify inflammation and renal injury. This supposition is supported by increases seen in p65-NF-kappaB, osteopontin, and leukocyte influx in the kidneys of the tempol-treated group.

Physical activity maintains aortic endothelium-dependent relaxation in the obese type 2 diabetic OLETF rat

We tested the hypothesis that physical activity can attenuate the temporal decline of ACh-induced endothelium-dependent relaxation during type 2 diabetes mellitus progression in the Otsuka Long-Evans Tokushima fatty (OLETF) rat. Sedentary OLETF rats exhibited decreased ACh-induced abdominal aortic endothelium-dependent relaxation from 13 to 20 wk of age (20-35%) and from 13 to 40 wk of age (35-50%). ACh-induced endothelium-dependent relaxation was maintained in the physically active OLETF group and control sedentary Long-Evans Tokushima Otsuka (LETO) group from 13 to 40 wk of age. Aortic pretreatment with N(G)-nitro-l-arginine (l-NNA), indomethacin (Indo), and l-NNA + Indo did not alter the temporal decline in ACh-induced endothelium-dependent relaxation. Temporal changes in the protein expression of SOD isoforms in the aortic endothelium or smooth muscle did not contribute to the temporal decline in ACh-induced endothelium-dependent relaxation in sedentary OLETF rats. A significant increase in the 40-wk-old sedentary LETO and physically active OLETF rat aortic phosphorylated endothelial nitric oxide (p-eNOS)-to-eNOS ratio was observed versus 13- and 20-wk-old rats in each group that was not seen in the 40- versus 13- and 20-wk-old sedentary OLETF rats. These results suggest that temporal changes in the antioxidant system, EDHF, and cycloxygenase metabolite production in sedentary OLETF rat aortas do not contribute to the temporal decline in sedentary OLETF rat aortic ACh-induced endothelium-dependent relaxation seen with type 2 diabetes mellitus progression. We also report that physical activity in conjunction with aging in the OLETF rat results in a temporal increase in the aortic endothelial p-eNOS-to-eNOS ratio that was not seen in sedentary OLETF rats. These results suggest that the sustained aortic ACh-induced endothelium-dependent relaxation in aged physically active OLETF rats may be the result of an increase in active aortic eNOS.

Mechanisms of coronary microvascular adaptation to obesity

The metabolic syndrome (MetS) is associated with clustering of cardiovascular risk factors in individuals that may greatly increase their risk of developing coronary artery disease. Obesity and related metabolic dysfunction are the driving forces in the prevalence of MetS. It is believed that obesity has detrimental effects on cardiovascular function, but its overall impact on the vasomotor regulation of small coronary arteries is still debated. Emerging evidence indicates that in obesity coronary arteries adapt to hemodynamic changes via maintaining and/or upregulating cellular mechanism(s) intrinsic to the vascular wall. Among other factors, endothelial production of cyclooxygenase-2-derived prostacyclin and reactive oxygen species, as well as increased nitric oxide sensitivity and potassium channel activation in smooth muscle cells, have been implicated in maintaining coronary vasodilator function. This review aims to examine studies that have been primarily focused on alterations in coronary vasodilator function in obesity. A better understanding of cellular mechanisms that may contribute to coronary microvascular adaptation may provide insight into the sequence of pathological events in obesity and may allow the harnessing of these effects for therapeutic purposes.

Pyrrolidine dithiocarbamate reduces vascular prostanoid-induced responses in aged type 2 diabetic rat model

It has been shown that enhancement of vasoconstrictor prostanoids plays an important role in the development of cardiovascular diseases. The aim of the present study was to examine the effects of pyrrolidine dithiocarbamate (PDTC), a low-molecular-weight thiol antioxidant and a potent inhibitor of nuclear factor-kappaB (NF-kappaB), on both the response to and production of prostanoids in arterial vessels isolated from rats at the chronic stage of type 2 diabetes. Using aortas from type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats, control Long-Evans Tokushima Otsuka (LETO) rats, and LETO and OLETF rats treated with PDTC (30 mg/kg, s.c., daily, for 1 week), we measured the production of prostanoids and NF-kappaB activity. The arachidonic acid-induced contraction and the acetylcholine-induced endothelium-derived contracting factor (EDCF)-mediated contraction in mesenteric arteries were also compared among these groups. OLETF rats exhibited (vs. age-matched LETO rats) the following: increased responses to both arachidonic acid and EDCF and greater productions of PGE(2) and TXA(2). Treatment with PDTC resulted in the following: 1) reduced arachidonic acid- and EDCF-mediated contractions, 2) suppressed the production of prostanoids, and 3) normalized NF-kappaB activity. These results suggest that PDTC has beneficial effects against the abnormal vasoconstrictor prostanoid signaling present in rats at the chronic stage of type 2 diabetes.

Preserved coronary arteriolar dilatation in patients with type 2 diabetes mellitus: implications for reactive oxygen species

Type 2 diabetes mellitus is associated with clustering of cardiovascular risk factors that may greatly increase individuals' risk of developing coronary artery disease. Type 2 diabetes is believed to impair coronary function. However, its impact on the vasomotor function of coronary resistance vessels in humans is still debated. Reduced, preserved or even augmented dilations of coronary arterioles have been reported in subjects with type 2 diabetes. Interestingly, recent studies have suggested that reactive oxygen species (ROS), particularly hydrogen peroxide, may compensate for the loss of the vasodilatory function of coronary microvessels during disease development. Recent interventional clinical trials have yielded largely negative results, and there has even been some suggestion of harm caused by attempts to reduce ROS. Thus, it is possible that interference with ROS-related signaling might paradoxically temper the function of coronary microvessels, predisposing patients to myocardial ischemia. In this review, we aim to highlight current findings supporting a potential role for ROS in preserving coronary arteriolar dilation in type 2 diabetes mellitus.

Renal and metabolic effects of tempol in obese ZSF1 rats--distinct role for superoxide and hydrogen peroxide in diabetic renal injury

Oxidative stress, that is, overproduction of reactive oxygen species and reduced antioxidant system activity, is implicated in the pathogenesis of diabetic complications; and therefore, superoxide dismutase (SOD) mimetic tempol should be protective in diabetic kidney. However, the effects of tempol in metabolic syndrome-associated renal injury have not been thoroughly examined. In this study, we examined the effects of 9 weeks of treatment with tempol on metabolic status, renal oxidative stress, and kidney function and structure in obese, diabetic, hypertensive ZSF(1) rats and their nondiabetic, hypertensive, lean littermates. The obese rats had significantly reduced total SOD and catalase activity, increased peroxidase activity and lipid peroxidation, and higher level of protein oxidation in renal cortical tissue compared with their lean littermates. These changes were accompanied by renal injury (proteinuria; reduced excretory function; and markedly increased glomerular and interstitial inflammation, proliferation, and collagen IV synthesis). Tempol treatment slightly increased total SOD activity, significantly reduced lipid peroxidation and peroxidase activity, but had no effect on catalase and protein oxidation. Tempol had no effects on blood pressure, renal hemodynamics and excretory function, and proteinuria in obese rats, yet improved insulin sensitivity and reduced renal inflammatory, proliferative, and fibrotic changes. Because tempol possesses no catalase activity and, in diabetes, not only SOD but also catalase is inhibited, it is possible that the toxicity of hydrogen peroxide (H(2)O(2)) remains unaltered under tempol treatment. This study suggests that superoxide and H(2)O(2) may have distinct roles in the pathogenesis of diabetic renal injury, with superoxide mainly being involved in inflammatory, proliferative, and fibrotic changes, and H(2)O(2) in glomerular hemodynamics and proteinuria.

Reactive oxygen species from NADPH oxidase contribute to altered pulmonary vascular responses in piglets with chronic hypoxia-induced pulmonary hypertension

Our main objective was to determine whether reactive oxygen species (ROS), such as superoxide (O(2)(-)) and hydrogen peroxide (H(2)O(2)), contribute to altered pulmonary vascular responses in piglets with chronic hypoxia-induced pulmonary hypertension. Piglets were raised in either room air (control) or hypoxia for 3 days. The effect of the cell-permeable superoxide dismutase mimetic (SOD; M40403) and/or PEG-catalase (PEG-CAT) on responses to acetylcholine (ACh) was measured in endothelium-intact and denuded pulmonary resistance arteries (PRAs; 90-to-300-microm diameter). To determine whether NADPH oxidase is an enzymatic source of ROS, PRA responses to ACh were measured in the presence and absence of a NADPH oxidase inhibitor, apocynin (APO). A Western blot technique was used to assess expression of the NADPH oxidase subunit, p67phox. A lucigenin-derived chemiluminescence technique was used to measure ROS production stimulated by the NADPH oxidase substrate, NADPH. ACh responses, which were dilation in intact control arteries but constriction in both intact and denuded hypoxic arteries, were diminished by M40403, PEG-CAT, the combination of M40403 plus PEG-CAT, as well as by APO. Although total amounts were not different, membrane-associated p67phox was greater in PRAs from hypoxic compared with control piglets. NADPH-stimulated lucigenin luminescence was nearly doubled in PRAs from hypoxic vs. control piglets. We conclude that ROS generated by NADPH oxidase contribute to the aberrant pulmonary arterial responses in piglets exposed to 3 days of hypoxia.

Exercise restores endothelial function independently of weight loss or hyperglycaemic status in db/db mice

AIMS/HYPOTHESIS

Exercise ameliorates oxidative stress-mediated diabetic vascular endothelial dysfunction through poorly defined mechanisms. We hypothesised that, in addition to improving metabolic parameters, upregulation of antioxidants such as superoxide dismutase (SOD) mediates exercise-induced reductions of oxidative stress and increased nitric oxide (NO) bioavailability, and also restores vasodilatation.

METHODS

Type 2 diabetic db/db and normoglycaemic wild-type mice were exercised at moderate intensity for 1 h a day for 7 weeks, leading to a 10% body weight loss. Sedentary animals or those undergoing a low-intensity exercise regimen causing non-significant weight loss were also used. We examined aortic endothelial cell function, NO bioavailability and various biomarkers of oxidative stress.

RESULTS

Moderate-intensity exercise lowered body weight, increased mitochondrial manganese SOD (MnSOD) and both total and phosphorylated (Ser1177) endothelial nitric oxide synthase (eNOS) protein production; it also reduced whole-body (plasma 8-isoprostane) and tissue oxidative stress (nitrotyrosine immunostaining or protein carbonyl levels in the aorta). Low-intensity exercise did not alter body weight; however, it upregulated cytosolic Cu/Zn-SOD instead of MnSOD, and still demonstrated all the above benefits in the db/db aorta. Importantly, both exercise protocols improved endothelial-dependent vasodilatation and NO bioavailability without altering hyperglycaemic status in db/db mice.

CONCLUSIONS/INTERPRETATION

Exercise reverses diabetic vascular endothelial dysfunction independently of improvements in body weight or hyperglycaemia. Our data suggest that upregulation of eNOS and specific SOD isoforms could play important roles in improving NO bioavailability, as well as in reversing endothelial dysfunction in type 2 diabetes patients through lifestyle modifications in the management of diabetes.

Contribution of polyol pathway to arteriolar dysfunction in hyperglycemia. Role of oxidative stress, reduced NO, and enhanced PGH(2)/TXA(2) mediation

Hyperglycemia increases glucose metabolism via the polyol pathway, which results in elevations of intracellular sorbitol concentration. Thus we hypothesized that elevated level of sorbitol contributes to the development of hyperglycemia-induced dysfunction of microvessels. In isolated, pressurized (80 mmHg) rat gracilis muscle arterioles (approximately 150 microm), high glucose treatment (25 mM) induced reduction in flow-dependent dilation (from maximum of 39 +/- 2% to 15 +/- 1%), which was significantly mitigated by an aldose reductase inhibitor, zopolrestat (maximum 27 +/- 2%). Increasing doses of sorbitol (10(-10)-10(-4) M) elicited dose-dependent constrictions (maximum 22 +/- 3%), which were abolished by endothelium removal, a prostaglandin H(2)/thromboxane A(2) (PGH(2)/TXA(2)) receptor (TP) antagonist SQ-29548, or superoxide dismutase (SOD) plus catalase (CAT). Incubation of arterioles with sorbitol (10(-7) M) reduced flow-dependent dilations (from maximum of 39 +/- 2% to 20 +/- 1.5%), which was not further affected by inhibition of nitric oxide synthase by N(omega)-nitro-l-arginine methyl ester but was prevented by SOD plus CAT and mitigated by SQ-29548. Nitric oxide donor sodium nitroprusside-induced (10(-9)-10(-6) M) dilations were also decreased in a SQ-29548 and SOD plus CAT-reversible manner, whereas adenosine dilations were not affected by sorbitol exposure. Sorbitol significantly increased arterial superoxide production detected by lucigenin-enhanced chemiluminescence, which was inhibited by SOD plus CAT. Sorbitol treatment also increased arterial formation of 3-nitrotyrosine. We suggest that hyperglycemia by elevating intracellular sorbitol induces oxidative stress, which interferes with nitric oxide bioavailability and promotes PGH(2)/TXA(2) release, both of which affect regulation of vasomotor responses of arterioles. Thus increased activity of the polyol pathway may contribute to the development of microvascular dysfunction in diabetes mellitus.

Imbalance between endothelium-derived relaxing and contracting factors in mesenteric arteries from aged OLETF rats, a model of Type 2 diabetes

We investigated whether the balance between endothelium-derived relaxing factors (EDRFs) and endothelium-derived contracting factors (EDCFs) might be altered in mesenteric arteries from aged Otsuka Long-Evans Tokushima Fatty (OLETF) rats (a Type 2 diabetic model) [vs. age-matched control Long-Evans Tokushima Otsuka (LETO) rats]. ACh-induced relaxation was impaired in the OLETF group, and a tendency for the relaxation to reverse at high ACh concentrations was observed in both groups. This tendency was abolished by indomethacin. Nitric oxide- and/or endothelium-derived hypolarizing factor-mediated relaxation and the protein expressions of phospho-endothelial nitric oxide synthase (Ser1177) and extracellular superoxide dismutase were also reduced in OLETF. An ACh-induced contraction was observed at higher ACh concentrations in the presence of NG-nitro-l-arginine (l-NNA) but was greater in OLETF rats. This contraction in OLETF rats was reduced by cyclooxygenase (COX) inhibitors and by prostanoid-receptor antagonists. The ACh-induced productions of thromboxane A2 and PGE2 were greater in OLETF than LETO rats, as were the mesenteric artery COX-1 and COX-2 protein expressions. Moreover, tert-butyl hydroperoxide ( t-BOOH) (membrane-permeant oxidant) induced a concentration-dependent contraction that was greater in OLETF rats. The t-BOOH-mediated contraction was increased both by l-NNA and by endothelium removal in LETO but not OLETF rats, suggesting that a negative modulatory role of the endothelium was lost in OLETF rats. These results suggest that an imbalance between EDRFs and EDCFs may be implicated in the endothelial dysfunction seen in aged OLETF mesenteric arteries, and may be attributable to increased oxidative stress.

High oxygen tension constricts epineurial arterioles of the rat sciatic nerve via reactive oxygen species

Microcirculation of the sheath of the rat sciatic nerve fiber was investigated by using an intravital microscope, and changes in the diameter of the epineurial arterioles in response to highly oxygenated Krebs-bicarbonate solution were evaluated. Superfusion of low-oxygen (0%) Krebs-bicarbonate solution (LKS) onto rat sciatic nerves did not affect changes in the diameter of the arterioles. Nifedipine, a Ca(2+)-channel blocker, caused a dose-dependent dilation of the epineurial arterioles in LKS. In contrast, superfusion of high-oxygen (21%) Krebs-bicarbonate solution (HKS) onto rat sciatic nerves significantly constricted the epineurial arterioles in a time-dependent manner. The HKS-induced constriction of the epineurial arterioles was significantly reduced by treatment with 120 U/ml superoxide dismutase (SOD) alone or 5,000 U/ml catalase alone. In the presence of 120 U/ml SOD plus 5,000 U/ml catalase, 10(-4) M tempol, 10(-6) M diphenyleneiodium, 2 x 10(-4) M apocynin, or 10(-6) M allopurinol, the HKS-induced constriction of the epineurial arterioles completely disappeared. These results suggest that superfusion of highly oxygenated solution onto rat sciatic nerves constricts the epineurial arterioles through reactive oxygen species (ROS), including superoxide and hydrogen peroxide, and that production of superoxide involves a NADPH oxidase- or xanthine oxidase-dependent pathway. In conclusion, ROS play significant roles in the regulation of microcirculation of rat sciatic nerves in vivo.