Superoxide-NO interaction decreases flow- and agonist-induced dilations of coronary arterioles in Type 2 diabetes mellitus

Coronary arterioles in type 2 diabetic (db/db) mice undergo a distinct pattern of remodeling associated with decreased vessel stiffness

Little is known about the impact of type 2 diabetes mellitus (DM) on coronary arteriole remodeling. The aim of this study was to determine the mechanisms that underlie coronary arteriole structural remodeling in type 2 diabetic (db/db) mice. Passive structural properties of septal coronary arterioles isolated from 12- to 16-week-old diabetic db/db and control mice were assessed by pressure myography. Coronary arterioles from 12-week-old db/db mice were structurally similar to age-matched controls. By 16 weeks of age, coronary wall thickness was increased in db/db arterioles (p < 0.01), while luminal diameter was reduced (control: 118 ± 5 μm; db/db: 102 ± 4 μm, p < 0.05), augmenting the wall-to-lumen ratio by 58% (control: 5.9 ± 0.6; db/db: 9.5 ± 0.4, p < 0.001). Inward hypertrophic remodeling was accompanied by a 56% decrease in incremental elastic modulus (p < 0.05, indicating decreased vessel coronary wall stiffness) and a ~30% reduction in coronary flow reserve (CFR) in diabetic mice. Interestingly, aortic pulse wave velocity and femoral artery incremental elastic modulus were increased (p < 0.05) in db/db mice, indicating macrovascular stiffness. Molecular tissue analysis revealed increased elastin-to-collagen ratio in diabetic coronaries when compared to control and a decrease in the same ratio in the diabetic aortas. These data show that coronary arterioles isolated from type 2 diabetic mice undergo inward hypertrophic remodeling associated with decreased stiffness and increased elastin-to-collagen ratio which results in a decreased CFR. This study suggests that coronary microvessels undergo a different pattern of remodeling from macrovessels in type 2 DM.

A flow-cytometry assisted segregation of responding and non-responding population of endothelial cells for enhanced detection of intracellular nitric oxide production

Nitric oxide (NO) is an important paracrine substance released by the endothelium to regulate vasomotor tone. The constitutive levels of endothelium dependent NO production is low. However, it is induced significantly in response to certain environmental and biological stimuli. An accurate evaluation of such stimulus induced NO release is of pharmacological significance. We observed that the sensitivity of NO detection in endothelial cells is compromised by baseline fluorescence emanated from non-activated cells resulting in ambiguous detection. In order to measure NO levels in activated population independent of non-activated cells, we segregated DAF-FM loaded cells based on their fluorescence intensity using flow-cytometry. Specific agonists like bradykinin, VEGF and insulin enhanced the proportion of activated cells. This effect was partially blocked in presence of NO synthase inhibitor, N(G)-nitro-L-arginine-methyl ester (L-NAME). We demonstrate that the fluorescence yield of activated population serves as a sensitive measure to evaluate agonist induced nitric oxide production in endothelial cells. Such increase in NO production in activated cells was also associated with increased eNOS phosphorylation at Ser-1177. While the endothelial cells showed heterogeneity with respect to NO production, immuno-phenotyping for endothelial cell-surface markers revealed a homogenous population.

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.

Coronary microvascular dysfunction in diabetes mellitus: A review

The exploration of coronary microcirculatory dysfunction in diabetes has accelerated in recent years. Cardiac function is compromised in diabetes. Diabetic patients manifest accelerated atherosclerosis in coronary arteries. These data are confirmed in diabetic animal models, where lesions of small coronary arteries have been described. These concepts are epitomized in the classic microvascular complications of diabetes, i.e. blindness, kidney failure and distal dry gangrene. Most importantly, accumulating data indicate that insights gained from the link between inflammation and diabetes can yield predictive and prognostic information of considerable clinical utility. This review summarizes the evidence for the predisposing factors and the mechanisms involved in diabetes, and assesses the current state of knowledge regarding the triggers for inflammation in this disease. We evaluate the roles of hyperglycemia, oxidative stress, polyol pathway, protein kinase C, advanced glycation end products, insulin resistance, peroxisome proliferator-activated receptor-γ, inflammation, and diabetic cardiomyopathy as a "stem cell disease". Furthermore, we discuss the mechanisms responsible for impaired coronary arteriole function. Finally, we consider how new insights in diabetes may provide innovative therapeutic strategies.

Hypoxic relaxation of penile arteries: involvement of endothelial nitric oxide and modulation by reactive oxygen species

Although obesity-related cardiovascular disease and hypoxia are associated with erectile dysfunction, little is known about the direct effects of hypoxia on penile arteries. In the present study, the effects of acute hypoxia (Po(2) = approximately 10 Torr, 20 min) were investigated in isolated penile arteries to determine the influence of endothelium removal, nitric oxide (NO) synthase (NOS), cyclooxygenase (COX), NADPH oxidase, changes in reactive oxygen species (ROS), and a high-fat diet. Hypoxia-relaxed penile arteries contracted with phenylephrine by approximately 50%. Relaxation to hypoxia and acetylcholine was reduced by endothelium removal and by inhibition of NOS (N(omega)-nitro-l-arginine) and COX (indomethacin) but was enhanced by Tempol and by NADPH oxidase inhibition with apocynin and gp91ds-tat. Basal superoxide levels detected by lucigenin chemiluminescence were reduced by Tempol and gp91ds-tat and were enhanced by NOS blockade. Hypoxic relaxant responses were enhanced by catalase and ebselen. Exogenous peroxide evoked relaxations of penile arteries, which were partially inhibited by endothelium removal and by the inhibition of COX and extracellular signal-regulated mitogen-activated protein kinase (MAPK) but enhanced by p38 MAPK blockade. The NO-dependent component of relaxation to hypoxia was impaired in penile arteries from high-fat diet-fed, obese rats associated with increased superoxide production. Thus hypoxic relaxation of penile arteries is partially mediated by endothelial NO in a manner that is normally attenuated by endogenous ROS production. Obesity further increases superoxide production and impairs the influence of NO. Therefore, cardiovascular disease involving decreased NO bioavailability and/or enhanced ROS generation may contribute to erectile dysfunction through impairing the relaxation of penile arteries to hypoxia.

Diabetes impairs arteriogenesis in the peripheral circulation: review of molecular mechanisms

Patients suffering from both diabetes and PAD (peripheral arterial disease) are at risk of developing critical limb ischaemia and ulceration, and potentially requiring limb amputation. In addition, diabetes complicates surgical treatment of PAD and impairs arteriogenesis. Arteriogenesis is defined as the remodelling of pre-existing arterioles into conductance vessels to restore the perfusion distal to the occluded artery. Several strategies to promote arteriogenesis in the peripheral circulation have been devised, but the mechanisms through which diabetes impairs arteriogenesis are poorly understood. The present review provides an overview of the current literature on the deteriorating effects of diabetes on the key players in the arteriogenesis process. Diabetes affects arteriogenesis at a number of levels. First, it elevates vasomotor tone and attenuates sensing of shear stress and the response to vasodilatory stimuli, reducing the recruitment and dilatation of collateral arteries. Secondly, diabetes impairs the downstream signalling of monocytes, without decreasing monocyte attraction. In addition, EPC (endothelial progenitor cell) function is attenuated in diabetes. There is ample evidence that growth factor signalling is impaired in diabetic arteriogenesis. Although these defects could be restored in animal experiments, clinical results have been disappointing. Furthermore, the diabetes-induced impairment of eNOS (endothelial NO synthase) strongly affects outward remodelling, as NO signalling plays a key role in several remodelling processes. Finally, in the structural phase of arteriogenesis, diabetes impairs matrix turnover, smooth muscle cell proliferation and fibroblast migration. The review concludes with suggestions for new and more sophisticated therapeutic approaches for the diabetic population.

Divergent effects of low-O(2) tension and iloprost on ATP release from erythrocytes of humans with type 2 diabetes: implications for O(2) supply to skeletal muscle

Erythrocytes release both O(2) and a vasodilator, ATP, when exposed to reduced O(2) tension. We investigated the hypothesis that ATP release is impaired in erythrocytes of humans with type 2 diabetes (DM2) and that this defect compromises the ability of these cells to stimulate dilation of resistance vessels. We also determined whether a general vasodilator, the prostacyclin analog iloprost (ILO), stimulates ATP release from healthy human (HH) and DM2 erythrocytes. Finally, we used a computational model to compare the effect on tissue O(2) levels of increases in blood flow directed to areas of increased O(2) demand (erythrocyte ATP release) with nondirected increases in flow (ILO). HH erythrocytes, but not DM2 cells, released increased amounts of ATP when exposed to reduced O(2) tension (Po(2) < 30 mmHg). In addition, isolated hamster skeletal muscle arterioles dilated in response to similar decreases in extraluminal O(2) when perfused with HH erythrocytes, but not when perfused with DM2 erythrocytes. In contrast, both HH and DM2 erythrocytes released ATP in response to ILO. In the case of DM2 erythrocytes, amounts of ATP released correlated inversely with glycemic control. Modeling revealed that a functional regulatory system that directs blood flow to areas of need (low O(2)-induced ATP release) provides appropriate levels of tissue oxygenation and that this level of the matching of O(2) delivery with demand in skeletal muscle cannot be achieved with a general vasodilator. These results suggest that the inability of erythrocytes to release ATP in response to exposure to low-O(2) tension could contribute to the peripheral vascular disease of DM2.

Diabetes and microvascular pathophysiology: role of epidermal growth factor receptor tyrosine kinase

Type 2 diabetes is responsible for the increased prevalence of ischaemic heart disease, generally related to coronary artery disease, which is associated with increased morbidity and death in diabetic patients. Epidermal growth factor receptor (EGFR) tyrosine kinase, one of the many factors involved in cell growth and migration, has been shown to be key element in the development of microvessel myogenic tone. In a recent study, we have shown that microvascular dysfunction in type 2 diabetes is dependent on the exacerbation of the EGFR tyrosine kinase phosphorylation. Thus, further elucidation of this EGFR transactivation and down stream signalling will offer a new direction to investigate the mechanism of microvascular dysfunction responsible for heart disease that occurs in type 2 diabetes. In this review, we discuss the link between the EGFR transactivation and microvascular dysfunction that occurs in type 2 diabetes.

Upregulation of TNF-alpha and Receptors Contribute to Endothelial Dysfunction in Zucker Diabetic Rats

Diabetes mellitus is a major risk factor to impair endothelial function and induce cardiovascular diseases. TNF-alpha (TNF) is expressed during a variety of inflammatory conditions. We hypothesized that impairment in coronary endothelial function in type 2 diabetes is due to the overexpression of TNF and TNF receptors (TNFRs). Endothelium-dependent (acetylcholine, ACh) and -independent vasodilation (sodium nitroprusside, SNP) of isolated, pressurized (60 cmH(2)O) coronary arteries (50-100 μm) from lean control and Zucker diabetic fatty (ZDF, the model of type 2 diabetes) rats were determined. In lean rats, SNP and ACh induced dose-dependent vasodilation, but dilation to only ACh was blocked by the NOS inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 10 μM). In ZDF rats, dilation to ACh was blunted compared to lean rats, but SNP-induced dilation was comparable. Neutralizing antibodies to TNF, or blockade of NAD(P)H and xanthine oxidase, partially restored endothelium-dependent, NO-mediated vasodilation in isolated coronary arteries in ZDF rats, but anti-TNF did not alter endothelium-dependent vasodilation in lean rats. The mRNA expression of TNF receptor 1 (TNFR1, but not TNFR2) significantly increased in coronary arteries in ZDF rats. Protein expression of TNF and N-Tyr (ONOO(-)) were higher in coronary arteries in ZDF than those in lean rats. Production of H(2)O(2), NAD(P)H oxidase and xanthine oxidase activity were all higher in ZDF rats than those in lean controls; anti-TNF reduces the production of H(2)O(2), N-Tyr expression, NAD(P)H oxidase and xanthine oxidase activity in ZDF rats. These results demonstrate the endothelial dysfunction occurring in type 2 diabetes is the result of effects of the inflammatory cytokine TNF that activates NAD(P)H oxidase and xanthine oxidase; and perhaps acts mainly through the overexpression of TNFR1.

Reactive oxygen species and cyclooxygenase 2-derived thromboxane A2 reduce angiotensin II type 2 receptor vasorelaxation in diabetic rat resistance arteries

Angiotensin II has a key role in the control of resistance artery tone and local blood flow. Angiotensin II possesses 2 main receptors. Although angiotensin II type 1 receptor is well known and is involved in the vasoconstrictor and growth properties of angiotensin II, the role of the angiotensin II type 2 receptor (AT2R) remains much less understood. Although AT2R stimulation induces vasodilatation in normotensive rats, it induces vasoconstriction in pathological conditions involving oxidative stress and cyclooxygenase 2 expression. Thus, we studied the influence of cyclooxygenase 2 on AT2R-dependent tone in diabetes mellitus. Mesenteric resistance arteries were isolated from Zucker diabetic fatty (ZDF) and lean Zucker rats and studied using in vitro using wire myography. In ZDF rats, AT2R-induced dilation was lower than in lean rats (11% versus 21% dilation). Dilation in ZDF rats returned to the control (lean rats) level after acute superoxide reduction (Tempol and apocynin), cyclooxygenase 2 inhibition (NS398), or thromboxane A(2) synthesis inhibition (furegrelate). Cyclooxygenase 2 expression and superoxide production were significantly increased in ZDF rat arteries compared with arteries of lean rats. After chronic treatment with Tempol, AT2R-dependent dilation was equivalent in ZDF and lean rats. Chronic treatment of ZDF rats with NS398 also restored AT2R-dependent dilation to the control (lean rats) level. Plasma thromboxane B(2) (thromboxane A(2) metabolite), initially high in ZDF rats, was decreased by chronic Tempol and by chronic NS398 to the level found in lean Zucker rats. Thus, in type 2 diabetic rats, superoxide and thromboxane A(2) reduced AT2R-induced dilation. These findings are important to take into consideration when choosing vasoactive drugs for diabetic patients.

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.

Differential structural and functional changes in penile and coronary arteries from obese Zucker rats

Erectile dysfunction frequently coexists with coronary artery disease and has been proposed as a potential marker for silent coronary artery disease in type 2 diabetes. In the present study, we comparatively assessed the structural and functional changes of both penile arteries (PAs) and coronary arteries (CAs) from a prediabetic animal model. PAs and CAs from 17- to 18-wk-old obese Zucker rats (OZRs) and from their control counterparts [lean Zucker rats (LZRs)] were mounted in microvascular myographs to evaluate vascular function, and stained arteries were subjected to morphometric analysis. Endothelial nitric oxide (NO) synthase (eNOS) protein expression was also assessed. The internal diameter was reduced and the wall-to-lumen ratio was increased in PAs from OZRs, but structure was preserved in CAs. ACh-elicited relaxations were severely impaired in PAs but not in CAs from OZRs, although eNOS expression was unaltered. Contractions to norepinephrine and 5-HT were significantly enhanced in both PAs and CAs, respectively, from OZRs. Blockade of NOS abolished endothelium-dependent relaxations in PAs and CAs and potentiated norepinephrine and 5-HT contractions in arteries from LZRs but not from OZRs. The vasodilator response to the phosphodiesterase 5 inhibitor sildenafil was reduced in both PAs and CAs from OZRs. Pretreatment with SOD reduced the enhanced vasoconstriction in both PAs and CAs from OZRs but did not restore ACh-induced relaxations in PAs. In conclusion, the present results demonstrate vascular inward remodeling in PAs and a differential impairment of endothelial relaxant responses in PAs and CAs from insulin-resistant OZRs. Enhanced superoxide production and reduced basal NO activity seem to underlie the augmented vasoconstriction in both PAs and CAs. The severity of the structural and functional abnormalities in PAs might anticipate the vascular dysfunction of the more preserved coronary vascular bed.

Cyclooxygenase-2 derived thromboxane A(2) and reactive oxygen species mediate flow-induced constrictions of venules in hyperhomocysteinemia

OBJECTIVE

Hyperhomocysteinemia (HHcy) has been shown to impair the endothelial function of arterial vessels and promote thrombosis. There are no studies, however, assessing the effects of HHcy on the vasomotor function of venules. We hypothesized that HHcy activates pathophysiological mechanisms impairing flow/shear stress-dependent responses of venules.

METHODS AND RESULTS

Changes in diameter of isolated gracilis muscle venules (diameter: approximately 250 microm at 10 mmHg) of control and HHcy rats (induced by methionine diet for 5 weeks) to increases in intraluminal flow were measured. Increases in flow elicited dilations in control (at max.: 14+/-1%), but induced constrictions in HHcy venules (at max.: -24+/-4%). Flow-induced constrictions in HHcy venules were converted to dilations in the presence of the thromboxane A(2) (TxA(2)) receptor (TP) antagonist SQ 29,548, which were then abolished by the simultaneous administration of nitric oxide (NO) synthase inhibitor, L-NAME and non-selective cyclooxygenase (COX) blocker, indomethacin. In addition, the selective COX-2 inhibitor NS 398 reversed flow-induced constrictions to dilations, which were significantly decreased by additional COX-1 inhibitor, SC 560. Also, as compared to controls, a SOD/CAT sensitive increased ethidium bromide fluorescence was detected in HHcy small veins, indicating substantial production of reactive oxygen species (ROS) in HHcy. Correspondingly, SOD/CAT diminished flow-induced constrictions in venules of HHcy rats.

CONCLUSIONS

In hyperhomocysteinemia increases in flow/shear stress increases the production of COX-2-derived TxA(2), and reactive oxygen species--that overcome the dilator effects of NO and prostaglandins--eliciting constrictions in skeletal muscle venules; changes which can increase vascular resistance and favor thrombus formation in the venular circulation.

Resveratrol improves endothelial function: role of TNF{alpha} and vascular oxidative stress

OBJECTIVE

Oxidative stress plays an important role in type 2 diabetes-related endothelial dysfunction. We hypothesized that resveratrol protects against oxidative stress-induced endothelial dysfunction in aortas of diabetic mice by inhibiting tumor necrosis factor alpha (TNFalpha)-induced activation of NAD(P)H oxidase and preserving phosphorylation of endothelial nitric oxide synthase (eNOS).

METHODS AND RESULTS

We examined endothelial-dependent vasorelaxation to acetylcholine (ACh) in diabetic mice (Lepr(db)) and normal controls (m Lepr(db)). Relaxation to ACh was blunted in Lepr(db) compared with m Lepr(db), whereas endothelial-independent vasorelaxation to sodium nitroprusside (SNP) was comparable. Resveratrol improved ACh-induced vasorelaxation in Lepr(db) without affecting dilator response to SNP. Impaired relaxation to ACh in Lepr(db) was partially reversed by incubating the vessels with NAD(P)H oxidase inhibitor apocynin and a membrane-permeable superoxide dismutase mimetic TEMPOL. Dihydroethidium (DHE) staining showed an elevated superoxide (O(2)(.-)) production in Lepr(db), whereas both resveratrol and apocynin significantly reduced O(2)(.-) signal. Resveratrol increased nitrite/nitrate levels and eNOS (Ser1177) phosphorylation, and attenuated H(2)O(2) production and nitrotyrosine (N-Tyr) content in Lepr(db) aortas. Furthermore, resveratrol attenuated the mRNA and protein expression of TNFalpha. Genetic deletion of TNFalpha in diabetic mice (db(TNF-)/db(TNF-)) was associated with a reduced NAD(P)H oxidase activity and vascular O(2)(.-) production and an increased eNOS (Ser1177) phosphorylation, suggesting that TNFalpha plays a pivotal role in aortic dysfunction in diabetes by inducing oxidative stress and reducing NO bioavailability.

CONCLUSIONS

Resveratrol restored endothelial function in type 2 diabetes by inhibiting TNFalpha-induced activation of NAD(P)H oxidase and preserving eNOS phosphorylation, suggesting the potential for new treatment approaches to promote vascular health in metabolic diseases.

Activation of prostaglandin E2 EP1 receptor increases arteriolar tone and blood pressure in mice with type 2 diabetes

AIMS

Type 2 diabetes mellitus is frequently associated with hypertension, but the underlying mechanisms are not completely understood. We tested the hypothesis that activation of type 1 prostaglandin E(2) (PGE(2)) receptor (EP1) increases skeletal muscle arteriolar tone and blood pressure in mice with type 2 diabetes.

METHODS AND RESULTS

In 12-week-old, male db/db mice (with homozygote mutation in leptin receptor), systolic blood pressure was significantly elevated, compared with control heterozygotes. Isolated, pressurized gracilis muscle arterioles ( approximately 90 microm) of db/db mice exhibited an enhanced pressure- and angiotensin II (0.1-10 nM)-induced tone, which was reduced by the selective EP1 receptor antagonist, AH6809 (10 microM), to the level observed in arterioles of control mice. Exogenous application of PGE(2) (10 pM-100 nM) or the selective agonist of the EP1 receptor, 17-phenyl-trinor-PGE(2) (10 pM-100 nM), elicited arteriolar constrictions that were significantly enhanced in db/db mice (max: 31 +/- 4 and 29 +/- 5%), compared with controls (max: 20 +/- 2 and 14 +/- 3%, respectively). In the aorta of db/db mice, an increased protein expression of EP1, but not EP4, receptor was also detected by western immunoblotting. Moreover, we found that oral administration of the EP1 receptor antagonist, AH6809 (10 mg/kg/day, for 4 days), significantly reduced the systolic blood pressure in db/db, but not in control mice.

CONCLUSION

Activation of EP1 receptors increases arteriolar tone, which could contribute to the development of hypertension in the db/db mice.

Reactive oxygen species and the control of vascular function

This article summarizes perspectives on how reactive oxygen species (ROS) and redox signaling mechanisms participate in regulating vascular smooth muscle function that have resulted from our studies over the past 25 years in areas including oxygen sensing and the regulation of cGMP production by soluble guanylate cyclase (sGC) that were presented in the Robert M. Berne Distinguished Lectureship at the 2008 Experimental Biology Meeting. It considers mechanisms controlling the activity of sources of ROS including Nox oxidases and mitochondria by physiological stimuli, vascular diseases processes, and metabolic mechanisms linked to NAD(P)H redox and hypoxia. Metabolic interactions of individual ROS such as hydrogen peroxide with cellular peroxide metabolizing enzymes are viewed as some of the most sensitive ways of influencing cellular signaling systems. The control of cytosolic NADPH redox also seems to be a major contributor to bovine coronary arterial relaxation to hypoxia, where its oxidation functions to coordinate the lowering of intracellular calcium, whereas increased cytosolic NADPH generation in pulmonary arteries appears to maintain elevated Nox oxidase activity, and relaxation to hydrogen peroxide, which is attenuated by hypoxia. The sensitivity of sGC to nitric oxide seems to be regulated by thiol and heme redox systems controlled by cytosolic NADPH. Heme biosynthesis and metabolism are also important factors regulating the sGC system. The signaling pathways controlling oxidases and their colocalization with redox-regulated systems enables selective activation of numerous regulatory mechanisms influencing vascular function in physiological processes and the progression of aging-associated vascular diseases.

Effects of a Western diet versus high glucose on endothelium-dependent relaxation in murine micro- and macro-vasculature

Vascular contractility and endothelium-dependent vasodilatation were studied in mesenteric, aorta and coronary vasculature from male and female LDL receptor deficient (LDLR(-/-)) and wild type C57BL/6 mice fed either a high-fat Western Diet (WD) or regular animal chow (RD). Endothelium-dependent vasodilatation was also studied in small mesenteric arteries and aorta from C57BL/6 mice following a 20 h exposure in vitro to 30 mM glucose. Compared with RD-fed animals, WD-fed LDLR-/- animals had increased body weights, elevated triglycerides and total cholesterol, but not glucose. Control C57BL6 animals had elevated body weight without increased cholesterol, triglyceride or glucose levels. The contractile sensitivity to cirazoline (pD(2)) of small mesenteric arteries was the same for RD-fed LDLR-/- and RD-fed C57BL6 mice, but was reduced in WD-fed male LDLR-/- and WD-fed female C57BL/6 mice. Maximum mesenteric contractile values for cirazoline (Emax) were unchanged; however, the Emax for phenylephrine in the aorta from WD-fed male C57BL/6 (but not LDLR-/- or female C57BL/6) mice was reduced. The Emax for acetylcholine-mediated endothelium-dependent vasodilatation in micro- and macro vessels (small mesenteric artery, coronary artery and aorta) from WD-fed LDLR-/- and C57BL/6 mice was unaltered, in contrast to the reduction in Emax for glucose-exposed tissues. Furthermore, the component of acetylcholine-mediated vasodilatation resistant to the combination of inhibitors of nitric oxide synthase, cyclooxygenase and guanylyl cyclase (nitro L-arginine methyl ester - 100 microM; indomethacin 10 microM and 1H-[1,2,4]-oxadiazolo[4,3,-a]quinoxalin-1-one, ODQ - 10 microM, respectively) was generally greater in WD-fed mice. Thus, vasculature from WD-fed mice with short-term dyslipidaemia do not exhibit reduced endothelium-dependent vasodilatation, but the WD is associated with changes in the overall endothelial-dependent relaxation and contractile responses thus suggesting an impact of diet rather than dyslipidaemia on cellular signalling pathways in vascular tissue. In contrast, acute hyperglycaemia resulted in endothelial dysfunction in both small mesenteric arteries and thoracic aorta.

Endothelial dysfunction and diabetes: roles of hyperglycemia, impaired insulin signaling and obesity

Endothelial dysfunction comprises a number of functional alterations in the vascular endothelium that are associated with diabetes and cardiovascular disease, including changes in vasoregulation, enhanced generation of reactive oxygen intermediates, inflammatory activation, and altered barrier function. Hyperglycemia is a characteristic feature of type 1 and type 2 diabetes and plays a pivotal role in diabetes-associated microvascular complications. Although hyperglycemia also contributes to the occurrence and progression of macrovascular disease (the major cause of death in type 2 diabetes), other factors such as dyslipidemia, hyperinsulinemia, and adipose-tissue-derived factors play a more dominant role. A mutual interaction between these factors and endothelial dysfunction occurs during the progression of the disease. We pay special attention to the possible involvement of endoplasmic reticulum stress (ER stress) and the role of obesity and adipose-derived adipokines as contributors to endothelial dysfunction in type 2 diabetes. The close interaction of adipocytes of perivascular adipose tissue with arteries and arterioles facilitates the exposure of their endothelial cells to adipokines, particularly if inflammation activates the adipose tissue and thus affects vasoregulation and capillary recruitment in skeletal muscle. Hence, an initial dysfunction of endothelial cells underlies metabolic and vascular alterations that contribute to the development of type 2 diabetes.

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 coronary vascular function independent of myogenic tone or hyperglycemic status in db/db mice

Regulation of coronary function in diabetic hearts is an important component in preventing ischemic cardiac events but remains poorly studied. Exercise is recommended in the management of diabetes, but its effects on diabetic coronary function are relatively unknown. We investigated coronary artery myogenic tone and endothelial function, essential elements in maintaining vascular fluid dynamics in the myocardium. We hypothesized that exercise reduces pressure-induced myogenic constriction of coronary arteries while improving endothelial function in db/db mice, a model of type 2 diabetes. We used pressurized mouse coronary arteries isolated from hearts of control and db/db mice that were sedentary or exercised for 1 h/day on a motorized exercise-wheel system (set at 5.2 m/day, 5 days/wk). Exercise caused a approximately 10% weight loss in db/db mice and decreased whole body oxidative stress, as measured by plasma 8-isoprostane levels, but failed to improve hyperglycemia or plasma insulin levels. Exercise did not alter myogenic regulation of arterial diameter stimulated by increased transmural pressure, nor did it alter smooth muscle responses to U-46619 (a thromboxane agonist) or sodium nitroprusside (an endothelium-independent dilator). Moderate levels of exercise restored ACh-simulated, endothelium-dependent coronary artery vasodilation in db/db mice and increased expression of Mn SOD and decreased nitrotyrosine levels in hearts of db/db mice. We conclude that the vascular benefits of moderate levels of exercise were independent of changes in myogenic tone or hyperglycemic status and primarily involved increased nitric oxide bioavailability in the coronary microcirculation.

Vascular endothelial function in health and diseases

The vascular endothelium constitutes approximately 1% of body mass (1kg) and has a surface area of approximately 5000m(2). The endothelium is a multifunctional endocrine organ strategically placed between the vessel wall and the circulating blood, and has a key role in vascular homeostasis. The endothelium is both a target for and mediator of cardiovascular disease. The endothelium releases several relaxing and constricting factors, which can affect vascular homeostasis. Endothelial dysfunction, whether caused by physical injury or cellular damage, leads to compensatory responses that alter the normal homeostatic properties of the endothelium. In this review, we summarized some physiological aspects of endothelial function and then we discussed endothelial dysfunction during some pathological conditions.

High-fat diet-induced obesity leads to increased NO sensitivity of rat coronary arterioles: role of soluble guanylate cyclase activation

The impact of obesity on nitric oxide (NO)-mediated coronary microvascular responses is poorly understood. Thus NO-mediated vasomotor responses were investigated in pressurized coronary arterioles ( approximately 100 microm) isolated from lean (on normal diet) and obese (fed with 60% of saturated fat) rats. We found that dilations to acetylcholine (ACh) were not significantly different in obese and lean rats (lean, 83 +/- 4%; and obese, 85 +/- 3% at 1 microM), yet the inhibition of NO synthesis with N(omega)-nitro-l-arginine methyl ester reduced ACh-induced dilations only in vessels of lean controls. The presence of the soluble guanylate cyclase (sGC) inhibitor oxadiazolo-quinoxaline (ODQ) elicited a similar reduction in ACh-induced dilations in the two groups of vessels (lean, 60 +/- 11%; and obese, 57 +/- 3%). Dilations to NO donors, sodium nitroprusside (SNP), and diethylenetriamine (DETA)-NONOate were enhanced in coronary arterioles of obese compared with lean control rats (lean, 63 +/- 6% and 51 +/- 5%; and obese, 78 +/- 5% and 70 +/- 5%, respectively, at 1 microM), whereas dilations to 8-bromo-cGMP were not different in the two groups. In the presence of ODQ, both SNP and DETA-NONOate-induced dilations were reduced to a similar level in lean and obese rats. Moreover, SNP-stimulated cGMP immunoreactivity in coronary arterioles and also cGMP levels in carotid arteries were enhanced in obese rats, whereas the protein expression of endothelial NOS and the sGC beta1-subunit were not different in the two groups. Collectively, these findings suggest that in coronary arterioles of obese rats, the increased activity of sGC leads to an enhanced sensitivity to NO, which may contribute to the maintenance of NO-mediated dilations and coronary perfusion in obesity.

Diet-induced obesity and diabetes reduce coronary responses to nitric oxide due to reduced bioavailability in isolated mouse hearts

AIM

The aim of the present study was to examine nitric oxide (NO)-mediated coronary vascular responses in a mouse model of obesity and diabetes induced by a high-fat, high-carbohydrate diet. We hypothesized that endogenous NO bioavailability would be reduced in obese/diabetic mouse hearts due to enhanced superoxide anion production, and that coronary smooth muscle responses to exogenous NO would be reduced.

METHODS

Age-matched, male C57BL/6J mice were fed either a control diet or a high-fat, high-carbohydrate diet. After 15 weeks, the mice were anesthetized and their hearts were removed and perfused by the Langendorff method under constant flow conditions with an oxygenated buffer solution, and changes in coronary vascular resistance were quantified.

RESULTS

Mice fed the high-fat, high-carbohydrate diet became obese, hyperglycaemic and hyperinsulinaemic. Coronary vasoconstrictor responses to NO synthase inhibition by N(omega)-nitro-L-arginine methyl ester were reduced in obese/diabetic mice; normal responses were restored by pretreatment with the superoxide dismutase mimetic 2,2,6,6-tetramethyl-1-piperidinyloxy (Tempol). Coronary endothelium-independent vasodilation to the NO donor (+/-)-S-nitroso-N-acetylpenicillamine (SNAP) was reduced; however, 8-bromo-cyclic guanosine monophosphate (cGMP)-induced vasodilation was unchanged in obese/diabetic hearts.

CONCLUSIONS

These findings suggest that in a diet-induced mouse model of obesity and diabetes, NO bioavailability is reduced by increased superoxide NO scavenging leading to impaired NO-mediated vasodilation. Furthermore, the attenuation of SNAP-induced vasodilation may be due to increased reactive oxygen species scavenging of exogenous NO because normal vascular smooth muscle NO signalling is maintained as indicated by similar 8-bromo-cGMP responses in control and obese/diabetic hearts.

Acute hyperglycaemia does not alter coronary vascular function in isolated, perfused rat hearts

AIM

The purpose of this study was to evaluate the hypothesis that acute hyperglycaemia in hearts of rats without diabetes alters coronary vascular responses to nitric oxide (NO), adenosine (ADO) and phenylephrine (PHE).

METHODS

Coronary function was studied in isolated, Langendorff-perfused, non-beating rat hearts that were perfused with an oxygenated Krebs-Henseleit solution containing 40 mM KCl to arrest the hearts. Changes in coronary vascular resistance were assessed by measuring changes in coronary perfusion pressure under constant flow conditions. Coronary responses to ADO, sodium nitroprusside (SNP), PHE and L-NAME (inhibitor of NO synthase) were studied either under normoglycaemic conditions (100 mg/dl d-glucose) or after 60 min of hyperglycaemic perfusion (500 mg/dl d-glucose). d-mannitol was used as a hyperosmotic control.

RESULTS

Hyperglycaemia did not alter vasodilator responses to ADO or SNP in the presence or absence of L-NAME. Furthermore, hyperglycaemia, compared with normoglycaemia, did not alter vasoconstrictor responses induced by L-NAME or PHE.

CONCLUSIONS

Sixty minutes of exposure to 500 mg/dl of d-glucose in an isolated, non-beating, buffer-perfused rat heart did not significantly affect coronary vascular smooth muscle vasodilator responses to NO and ADO or alter alpha(1)-adrenoceptor-mediated vasoconstrictor responses to PHE. Furthermore, an unchanged vasoconstrictor response to L-NAME suggests that acute hyperglycaemia did not alter NO bioavailability.

Flow-induced remodeling in resistance arteries from obese Zucker rats is associated with endothelial dysfunction

Chronic increases in blood flow increase arterial diameter and NO-dependent dilation in resistance arteries. Because endothelial dysfunction accompanies metabolic syndrome, we hypothesized that flow-mediated remodeling might be impaired in obese rat resistance arteries. Obese and lean Zucker rat mesenteric resistance arteries were exposed to chronic flow increases through arterial ligation in vivo: arteries exposed to high flow were compared with normal flow arteries. Diameter was measured in vitro in cannulated arteries using pressure arteriography. After 7 days, outward remodeling (diameter increased from 346+/-9 to 412+/-11 mum at 100 mm Hg) occurred in lean high-flow arteries. Endothelium-dependent tone was reduced in high-flow arteries from obese rats by contrast with lean animals. On the other hand, diameter enlargement occurred similarly in the 2 strains. The involvement of NO in endothelium-dependent dilation (evidenced by NO blockade) and endothelial NO synthase phosphorylation was smaller in obese than in lean rats. Superoxide anion and reduced nicotinamide-adenine dinucleotide phosphate oxidase subunit expression (p67phox and gp91phox) increased in obese rats and were higher in high-flow than in control arteries. Acute Tempol (a catalase mimetic), catalase plus superoxide dismutase, and l-arginine plus tetrahydrobiopterin restored endothelium-dependent dilation in obese rat normal and high-flow arteries to the level found in lean control arteries. Thus, flow-induced remodeling in obese resistance arteries was associated with a reduced endothelium-mediated dilation because of a decreased NO bioavailability and an excessive superoxide production. This dysfunction might have negative consequences in ischemic diseases in patients with obesity or metabolic syndrome.

Paradoxical role of angiotensin II type 2 receptors in resistance arteries of old rats

The role of angiotensin II type 2 receptors (AT2Rs) remains a matter of controversy. Its vasodilatory and antitrophic properties are well accepted. Nevertheless, in hypertensive rats, AT2R stimulation induces a vasoconstriction counteracting flow-mediated dilation (FMD). This contraction is reversed by hydralazine. Because FMD is also decreased in aging, another risk factor for cardiovascular diseases, we hypothesized that AT2R function might be altered in old-rat resistance arteries. Mesenteric resistance arteries (250 mum in diameter) were isolated from old (24 months) and control (4 months) rats receiving hydralazine (16 mg/kg per day; 2 weeks) or water. FMD, NO-mediated dilation, and endothelial NO synthase expression were lower in old versus control rats. AT2R blockade improved FMD in old rats, suggesting that AT2R stimulation produced vasoconstriction. AT2R expression was higher in old rats and mainly located in the smooth muscle layer. In old rats, AT2R stimulation induced endothelium-independent contraction, which was suppressed by the antioxidant Tempol. Reactive oxygen species level was higher in old-rat arteries than in controls. Hydralazine improved FMD and NO-dependent dilation in old rats without change in AT2R expression and location. In old rats treated with hydralazine, reactive oxygen species level was reduced in endothelial and smooth muscle cells, and AT2R-dependent contraction was abolished. Thus, AT2R stimulation induced vasoconstriction through activation of reactive oxygen species production, contributing to decrease FMD in old-rat resistance arteries. Hydralazine suppressed AT2R-dependent reactive oxygen species production and AT2R-dependent contraction, improving FMD. Importantly, endothelial alterations in aging were reversible. These findings are important to consider in the choice of vasoactive drugs in aging.

The PPARgamma ligand, rosiglitazone, reduces vascular oxidative stress and NADPH oxidase expression in diabetic mice

Oxidative stress plays an important role in diabetic vascular dysfunction. The sources and regulation of reactive oxygen species production in diabetic vasculature continue to be defined. Because peroxisome proliferator-activated receptor gamma (PPARgamma) ligands reduced superoxide anion (O(2)(-.)) generation in vascular endothelial cells in vitro by reducing NADPH oxidase and increasing Cu/Zn superoxide dismutase (SOD) expression, the current study examined the effect of PPARgamma ligands on vascular NADPH oxidase and O(2)(-.) generation in vivo. Lean control (db(+)/db(-)) and obese, diabetic, leptin receptor-deficient (db(-)/db(-)) mice were treated with either vehicle or rosiglitazone (3 mg/kg/day) by gavage for 7-days. Compared to controls, db(-)/db(-) mice weighed more and had metabolic derangements that were not corrected by treatment with rosiglitazone for 1-week. Aortic O(2)(-.) generation and mRNA levels of the NADPH oxidase subunits, Nox-1, Nox-2, and Nox-4 as well as Nox-4 protein expression were elevated in db(-)/db(-) compared to db(+)/db(-) mice, whereas aortic Cu/Zn SOD protein and PPARgamma mRNA levels were reduced in db(-)/db(-) mice. Treatment with rosiglitazone for 1-week significantly reduced aortic O(2)(-.) production and the expression of Nox-1, 2, and 4 but failed to increase Cu/Zn SOD or PPARgamma in aortic tissue from db(-)/db(-) mice. These data demonstrate that the vascular expression of Nox-1, 2, and 4 subunits of NADPH oxidase is increased in db(-)/db(-) mice and that short-term treatment with the PPARgamma agonist, rosiglitazone, has the potential to rapidly suppress vascular NADPH oxidase expression and O(2)(-.) production through mechanisms that do not appear to depend on correction of diabetic metabolic derangements.

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

Our previous study showed that arteriolar tone is enhanced in Type 2 diabetes mellitus (T2-DM) due to an increased level of constrictor prostaglandins. We hypothesized that, in mice with T2-DM, hydrogen peroxide (H2O2) is involved in the increased synthesis of constrictor prostaglandins, hence enhanced basal tone in skeletal muscle arterioles. Isolated, pressurized gracilis muscle arterioles (∼100 μm in diameter) of mice with T2-DM (C57BL/KsJ- db−/ db−) exhibited greater basal tone to increases in intraluminal pressure (20–120 mmHg) than that of control vessels (at 80 mmHg, control: 25 ± 5%; db/ db: 34 ± 4%, P < 0.05), which was reduced back to control level by catalase ( db/ db: 24 ± 4%). Correspondingly, in carotid arteries of db/ db mice, the level of dichlorofluorescein-detectable and catalase-sensitive H2O2 was significantly greater. In control arterioles, exogenous H2O2 (0.1–100 μmol/l) elicited dilations (maximum, 58 ± 10%), whereas in arterioles of db/ db mice H2O2 caused constrictions (−28 ± 8%), which were converted to dilations (maximum, 16 ± 5%) by the thromboxane A2/prostaglandin H2 (TP) receptor antagonist SQ-29548. In addition, arteriolar constrictions in response to the TP receptor agonist U-46619 were not different between the two groups of vessels. Endothelium denudation did not significantly affect basal tone and H2O2-induced arteriolar responses in either control or db/ db mice. Also, in arterioles of db/ db mice, but not in controls, 3-nitrotyrosine staining was detected in the endothelial layer of vessels. Thus we propose that, in mice with T2-DM, arteriolar production of H2O2 is enhanced, which leads to increased synthesis of the constrictor prostaglandins thromboxane A2/prostaglandin H2 in the smooth muscle cells, which enhance basal arteriolar tone. These alterations may contribute to disturbed regulation of skeletal muscle blood flow in Type 2 diabetes mellitus.

Reduced expression of G(i) in erythrocytes of humans with type 2 diabetes is associated with impairment of both cAMP generation and ATP release

Human erythrocytes, by virtue of their ability to release ATP in response to physiological stimuli, have been proposed to participate in the regulation of local blood flow. A signal transduction pathway that relates these stimuli to ATP release has been described and includes the heterotrimeric G protein G(i) and adenylyl cyclase (AC). In this cell, G(i) activation results in increases in cAMP and, ultimately, ATP release. It has been reported that G(i) expression is decreased in animal models of diabetes and in platelets of humans with type 2 diabetes. Here, we report that G(i2) expression is selectively decreased in erythrocytes of humans with type 2 diabetes and that this defect is associated with reductions in cAMP accumulation and ATP release in response to incubation of erythrocytes with mastoparan 7 (10 micromol/l), an activator of G(i). Importantly, this defect in ATP release correlates inversely with the adequacy of glycemic control as determined by levels of HbA(1c) (A1C). These results demonstrate that in erythrocytes of humans with type 2 diabetes, both G(i) expression and ATP release in response to mastoparan 7 are impaired, which is consistent with the hypothesis that this defect in erythrocyte physiology could contribute to the vascular disease associated with this clinical condition.

High-fat diet-induced reduction in nitric oxide-dependent arteriolar dilation in rats: role of xanthine oxidase-derived superoxide anion

Obesity frequently leads to the development of hypertension. We hypothesized that high-fat diet (HFD)-induced obesity impairs the endothelium-dependent dilation of arterioles. Male Wistar rats were fed with normal (control) or HFD (60% of saturated fat, for 10 wk). In rats with HFD, body weight, mean arterial blood pressure, and serum insulin, cholesterol, and glucose were elevated. In isolated gracilis muscle arterioles (diameter: ∼160 μm) of HFD, rat dilations to ACh (at 1 μM, maximum: 83 ± 3%) and histamine (at 10 μM, maximum: 16 ± 4%) were significantly ( P < 0.05) decreased compared with those of control responses (maximum: 90 ± 2 and 46 ± 4%, respectively). Dilations to the NO donor sodium nitroprusside were similar in the two groups. Inhibition of NO synthesis by Nω-nitro-l-arginine methyl ester reduced ACh- and histamine-induced dilations in control arterioles but had no effect on microvessels of HFD rats. The superoxide dismutase mimetic Tiron or xanthine oxidase inhibitor allopurinol enhanced ACh (maximum: 90 ± 2 and 93 ± 2%, respectively)- and histamine (maximum: 30 ± 7 and 37 ± 8%, respectively)-induced dilations in HFD arterioles, whereas the NAD(P)H oxidase inhibitor apocynin had no significant effect. Correspondingly, in carotid arteries of HFD rats, an enhanced superoxide production was shown by lucigenin-enhanced chemiluminescence, in association with an increased xanthine oxidase, but not NAD(P)H oxidase activity. In addition, a marked xanthine oxidase immunostaining was detected in the endothelial layer of the gracilis arterioles of HFD, but not in control rats. These findings suggest that, in obese rats, NO mediation of endothelium-dependent dilation of skeletal muscle arterioles is reduced because of an enhanced xanthine oxidase-derived superoxide production. These alterations demonstrate substantial dysregulation of arteriolar tone by the endothelium in HFD-induced obesity, which may contribute to disturbed tissue blood flow and development of increased peripheral resistance.

Increased cyclooxygenase-2 expression and prostaglandin-mediated dilation in coronary arterioles of patients with diabetes mellitus

Based on findings of experimental models of diabetes mellitus (DM) showing increased expression of vascular cyclooxygenase-2 (COX-2), we hypothesized that in patients with DM changes in COX-2-dependent prostaglandin synthesis affect vasomotor responses of coronary arterioles. Arterioles were dissected from the right atrial appendages obtained at the time of cardiac surgery of patient with DM(+) or without documented diabetes DM(-). Isolated arterioles (89+/-15 microm in diameter) were cannulated and pressurized (at 80 mm Hg), and changes in diameter were measured with video microscopy. After spontaneous tone developed [DM(-): 32+/-7%; DM(+): 37+/-5%; P=NS], arteriolar responses to bradykinin were investigated. Dilations to bradykinin (0.1 nmol/L to 1 micromol/L) were significantly (P<0.05) greater in DM(+) than DM(-) patients (10 nmol/L: 77+/-10% versus 38+/-14%). In both groups, dilations were similar to the NO-donor, sodium nitroprusside. In arterioles of DM(+), but not those of DM(-), patients' bradykinin-induced dilations were reduced by the nonselective COX inhibitor indomethacin or by the selective COX-2 inhibitor NS-398 (DM(+) at 10 nmol/L: to 20+/-4% and 29+/-7%, respectively). Correspondingly, a marked COX-2 immunostaining was detected in coronary arterioles of DM(+), but not in those of DM(-) patients. We conclude that in coronary arterioles of diabetic patients bradykinin induces enhanced COX-2-derived prostaglandin-mediated dilation. These findings are the first to show that in humans diabetes mellitus increases COX-2 expression and dilator prostaglandin synthesis in coronary arterioles, which may serve to increase dilator capacity and maintain adequate perfusion of cardiac tissues.

Copper, oxidative stress, and human health

Copper (Cu), a redox active metal, is an essential nutrient for all species studied to date. During the past decade, there has been increasing interest in the concept that marginal deficits of this element can contribute to the development and progression of a number of disease states including cardiovascular disease and diabetes. Deficits of this nutrient during pregnancy can result in gross structural malformations in the conceptus, and persistent neurological and immunological abnormalities in the offspring. Excessive amounts of Cu in the body can also pose a risk. Acute Cu toxicity can result in a number of pathologies, and in severe cases, death. Chronic Cu toxicity can result in liver disease and severe neurological defects. The concept that elevated ceruloplasmin is a risk factor for certain diseases is discussed. In this paper, we will review recent literature on the potential causes of Cu deficiency and Cu toxicity, and the pathological consequences associated with the above. Finally, we will review some of the potential biochemical lesions that might underlie these pathologies. Given that oxidative stress is a characteristic of Cu deficiency, the role of Cu in the oxidative defense system will receive special attention. The concept that excess Cu may be a precipitating factor in Alzheimer's disease is discussed.

Type 2 Diabetic Mice Have Increased Arteriolar Tone and Blood Pressure

OBJECTIVE

Type 2 diabetes mellitus (T2-DM) is frequently associated with vascular dysfunction and elevated blood pressure, yet the underlying mechanisms are not completely understood. We hypothesized that in T2-DM, the regulation of peripheral vascular resistance is altered because of changes in local vasomotor mechanisms.

METHODS AND RESULTS

In mice with T2-DM (C57BL/KsJ-(db-)/db-), systolic and mean arterial pressures measured by the tail cuff method were significantly elevated compared with those of control (db+/db-) animals (db/db, 146+/-5 and 106+/-2 mm Hg versus control, 133+/-4 and 98+/-4 mm Hg, respectively; P<0.05). Total peripheral resistance, calculated from cardiac output values (measured by echocardiography) and mean arterial pressure were significantly elevated in db/db mice (db/db, 25+/-6 versus control, 15+/-1 mm Hg[middot]mL(-1)[middot]min(-1)). In isolated, pressurized gracilis muscle arterioles (diameter approximately 80 microm) from db/db mice, stepwise increases in intraluminal pressure (from 20 to 120 mm Hg) elicited a greater reduction in diameter than in control vessels at each pressure step (at 80 mm Hg, db/db, 66+/-4% versus control, 79+/-3%). The passive diameters of arterioles (obtained in Ca2+-free solution) and the calculated myogenic index were not significantly different in the 2 groups. The presence of the prostaglandin H2/thromboxane A2 receptor antagonist SQ29548 did not affect arteriolar diameters of control mice but reduced the enhanced arteriolar tone of db/db mice back to control levels (at 80 mm Hg, 80+/-4%). The inhibitor of cyclooxygenase-1 (COX-1), SC-560, did not affect the basal tone of arterioles, whereas NS-398, an inhibitor of COX-2, caused a significant shift in the arteriolar pressure-diameter curve of vessels from db/db mice (at 80 mm Hg, 76+/-3%) but not in those of control mice. Also, in aortas of db/db mice, expression of COX-2 was enhanced compared with controls.

CONCLUSIONS

Collectively, these findings suggest that in mice with T2-DM, the basal tone of skeletal muscle arterioles is increased because of an enhanced COX-2-dependent production of constrictor prostaglandins. These alterations in microvascular prostaglandin synthesis may contribute to the increase in peripheral resistance and blood pressure in T2-DM.

Endothelial dysfunction in Type 2 diabetes correlates with deregulated expression of the tail-anchored membrane protein SLMAP

The Type 2 diabetic db/ db mouse experiences vascular dysfunction typified by changes in the contraction and relaxation profiles of small mesenteric arteries (SMAs). Contractions of SMAs from the db/ db mouse to the α1-adrenoceptor agonist phenylephrine (PE) were significantly enhanced, and acetylcholine (ACh)-induced relaxations were significantly depressed. Drug treatment of db/ db mice with a nonthiazolidinedione peroxisome prolifetor-activated receptor-γ agonist and insulin sensitizing agent 2-[2-(4-phenoxy-2-propylphenoxy)ethyl]indole-5-acetic acid (COOH) completely prevented the changes in endothelium-dependent relaxation, but, with the discontinuation of therapy, endothelial dysfunction returned. Dysfunctional SMAs were found to specifically upregulate the expression of a 35-kDa isoform of sarcolemmal membrane-associated protein (SLMAP), which is a component of the excitation-contraction coupling apparatus and implicated in the regulation of membrane function in muscle cells. Real-time PCR revealed high SLMAP mRNA levels in the db/ db microvasculature, which were markedly downregulated during COOH treatment but elevated again when drug therapy was discontinued. These data reveal that the microvasculature in db/ db mice undergoes significant changes in vascular function with the endothelial component of vascular dysfunction specifically correlating with the overexpression of SLMAP. Thus changes in SLMAP expression may be an important indicator for microvascular disease associated with Type 2 diabetes.

Modulation of potassium currents by angiotensin and oxidative stress in cardiac cells from the diabetic rat

Diabetes induces oxidative stress and leads to attenuation of cardiac K+ currents. We investigated the role of superoxide ions and angiotensin II (ANG II) in generating and linking oxidative stress to the modulation of K+ currents under diabetic conditions. K+ currents were measured using patch-clamp methods in ventricular myocytes from streptozotocin (STZ)-induced diabetic rats. Superoxide ion levels, indicating oxidative stress, were measured by fluorescent labelling with dihydroethidium (DHE). ANG II content was measured using enzyme-linked immunosorbent asssay (ELISA). The results showed DHE fluorescence to be significantly higher in cells from diabetic males, compared to controls. Relief of stress by the NADPH oxidase inhibitor apocynin or by superoxide dismutase (SOD) but not by catalase reversed the attenuation of K+ currents and reduced DHE fluorescence. In cells from diabetic females, neither apocynin nor SOD augmented K+ currents, ANG II was not elevated and DHE fluorescence was significantly weaker than in cells from males. Reduced glutathione (GSH) also augmented K+ currents in cells from diabetic males but not females. In ovariectomized diabetic females K+ currents were augmented by GSH and apocynin. Current augmentation and the attenuation of DHE fluorescence by apocynin were significantly blunted by excess ANG II (300 nm). Diabetic male rats pretreated with the angiotensin-converting enzyme (ACE) inhibitor quinapril were hyperglycaemic, but their cellular ANG II levels and DHE fluorescence were significantly decreased. In cells from these rats, K+ currents were insensitive to apocynin. In conclusion, diabetes-related oxidative stress attenuates K+ currents through ANG II-generated increased superoxide ion levels. When ANG II levels are lower, as in diabetic females or following ACE inhibition in males, oxidative stress is reduced, with blunted alterations in K+ currents.

Impaired endothelium-dependent responses and enhanced influence of Rho-kinase in cerebral arterioles in type II diabetes

BACKGROUND AND PURPOSE

Although the incidence of type II diabetes is increasing, very little is known regarding vascular responses in the cerebral circulation in this disease. The goals of this study were to examine the role of superoxide in impaired endothelium-dependent responses and to examine the influence of Rho-kinase on vascular tone in the cerebral microcirculation in type II diabetes.

METHODS

Diameter of cerebral arterioles (29+/-1 microm; mean+/-SE) was measured in vivo using a cranial window in anesthetized db/db and control mice.

RESULTS

Dilatation of cerebral arterioles in response to acetylcholine (ACh; 1 and 10 micromol/L), but not to nitroprusside, was markedly reduced in db/db mice (eg, 10 micromol/L ACh produced 29+/-1% and 9+/-1% in control and db/db mice, respectively). Superoxide levels were increased (P<0.05) in cerebral arterioles from db/db mice (n=6) compared with controls (n=6). Vasodilatation to ACh in db/db mice was restored to normal by polyethylene glycol-superoxide dismutase (100 U/mL). Y-27632 (1 to 100 micromol/L; a Rho-kinase inhibitor) produced modest vasodilatation in control mice but much greater responses in db/db mice. N(G)-nitro-L-arginine (100 micromol/L; an inhibitor of NO synthase) significantly enhanced Y-27632-induced dilatation in control mice to similar levels as observed in db/db mice.

CONCLUSIONS

These findings provide the first evidence for superoxide-mediated impairment of endothelium-dependent responses of cerebral vessels in any model of type II diabetes. In addition, the influence of Rho-kinase on resting tone appears to be selectively enhanced in the cerebral microcirculation in this genetic model of type II diabetes.

Nitric oxide and H2O2 contribute to reactive dilation of isolated coronary arterioles

The role of metabolic factors derived from cardiac muscle in the development of reactive hyperemia after brief occlusions of the coronary circulation seems to be well established. However, the contribution of occlusion-induced changes in hemodynamic forces to eliciting reactive hyperemia is less known. We hypothesized that in isolated coronary arterioles changes in intraluminal pressure and flow, during and after release of occlusion (O/R), themselves via activating intrinsic mechanosensitive mechanisms, elicit release of vasoactive factors resulting in reactive dilations. Thus in isolated coronary arterioles (diameter: 88 ± 8 μm) changes in diameter to changes in pressure or pressure plus flow (P+F) during and after a brief period (30, 60, and 120 s) of O/R of cannulating tube were measured by videomicroscopy. In response to both types of O/R, diameter first decreased, then, subsequently increased during occlusions. When only pressure was changed (from 80-10-80 mmHg), after release of occlusion, peak dilations increased as a function of the duration of occlusions. After flow was established (30 μl/min), O/R elicited changes in both pressure and flow (from 80-10-80 mmHg and from 0 to 30 μl/min). In these conditions, after the release of occlusions, not only the peak but also the duration of reactive dilation increased significantly as a function of the length of occlusions. The dilations during, and peak dilations after occlusions both in pressure and P+F protocols were significantly reduced by the inhibition of NO synthase with Nω-nitro-l-arginine-methyl-ester (l-NAME) or by endothelium removal, whereas duration of postocclusion dilations were reduced by l-NAME or by endothelium removal only in P+F protocols. Furthermore, in both protocols, catalase significantly reduced the peak but not the duration of reactive dilations. Thus, mechanosensitive mechanisms that are sensitive to deformation, pressure, stretch, and wall shear stress elicit release of NO and H2O2, resulting in reactive dilation of isolated coronary arterioles.

Ghrelin induces vasoconstriction in the rat coronary vasculature without altering cardiac peptide secretion

We administered ghrelin, a novel growth hormone-releasing hormone, to isolated perfused rat hearts, coronary arterioles, and cultured neonatal cardiomyocytes to determine its effects on coronary vascular tone, contractility, and natriuretic peptide secretion and gene expression. We also determined cardiac levels of ghrelin and whether the heart is a source of the circulating peptide. Ghrelin dose dependently increased coronary perfusion pressure (44 ± 9%, P < 0.01), constricted isolated coronary arterioles (12 ± 2%, P < 0.05), and significantly enhanced the pressure-induced myogenic tone of arterioles. These effects were blocked by diltiazem, an L-type Ca2+ channel blocker, and bisindolylmaleimide (Bis), a protein kinase C (PKC) inhibitor. Interestingly, coinfusion of ghrelin with diltiazem completely restored myocardial contractile function that was decreased 30 ± 3% ( P < 0.01) by diltiazem alone. In contrast, combination of ghrelin with diltiazem or Bis did not significantly alter atrial natriuretic peptide (ANP) secretion, which was decreased 40% ( P < 0.01) and 50% ( P < 0.05) by these agents alone, respectively. Administration of ghrelin to cultured cardiomyocytes had no effect on ANP or B-type natriuretic peptide secretion or gene expression. Detectable amounts of low-molecular-weight ghrelin were present in cardiac tissue extracts but not in isolated heart perfusate. Thus we provide the first evidence that ghrelin has a coronary vasoconstrictor action that is dependent on Ca2+ and PKC. Furthermore, the data obtained from diltiazem infusion suggest that ghrelin has a role in regulation of contractility when L-type Ca2+ channels are blocked. Finally, the observation that immunoreactive ghrelin is found in cardiac tissue suggests the presence of a local cardiac ghrelin system.

Microvascular dysfunction after transient high glucose is caused by superoxide-dependent reduction in the bioavailability of NO and BH(4)

We hypothesized that transient high-glucose concentration interferes with mediation by nitric oxide (NO) of flow-induced dilation (FID) of arterioles due to enhanced production of superoxide. In isolated, pressurized (80 mmHg) rat gracilis muscle arterioles ( approximately 130 microm) after transient high-glucose treatment (tHG; incubation with 30 mM glucose for 1 h), FID was reduced (maximum: control, 38 +/- 4%; after tHG, 17 +/- 3%), which was not further diminished by the NO synthase (NOS) inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME; 18 +/- 2%). Correspondingly, an enhanced polyethylene-glycol-SOD (PEG-SOD)-sensitive superoxide production was detected after tHG in carotid arteries by dihydroethydine (DHE) staining. Presence of PEG-SOD during tHG prevented the reduction of FID (41 +/- 3%), which could be inhibited by l-NAME (20 +/- 4%). Administration of PEG-SOD after tHG did not prevent the reduction of FID (22 +/- 3%). Sepiapterin, a precursor of the NO synthase cofactor tetrahydrobiopterin (BH(4)), administered during tHG did not prevent the reduction of FID (maximum, 15 +/- 5%); however, it restored FID when administered after tHG (32 +/- 4%). Furthermore, inhibition of either glycolysis by 2-deoxyglucose or mitochondrial complex II by 2-thenoyltrifluoroacetone reduced the tHG-induced DHE-detectable enhanced superoxide production in carotid arteries and prevented FID reduction in arterioles (39 +/- 5 and 35 +/- 2%). Collectively, these findings suggest that in skeletal muscle arterioles, a transient elevation of glucose via its increased metabolism, elicits enhanced production of superoxide, which decreases the bioavailability of NO and the level of the NOS cofactor BH(4), resulting in a reduction of FID mediated by NO.

Biphasic effect of hydrogen peroxide on skeletal muscle arteriolar tone via activation of endothelial and smooth muscle signaling pathways

We hypothesized that hydrogen peroxide (H2O2) has a role in the local regulation of skeletal muscle blood flow, thus significantly affecting the myogenic tone of arterioles. In our study, we investigated the effects of exogenous H2O2 on the diameter of isolated, pressurized (at 80 mmHg) rat gracilis skeletal muscle arterioles (diameter of approximately 150 microm). Lower concentrations of H2O2 (10(-6)-3 x 10(-5) M) elicited constrictions, whereas higher concentrations of H2O2 (6 x 10(-5)-3 x 10(-4) M), after initial constrictions, caused dilations of arterioles (at 10(-4) M H2O2, -19 +/- 1% constriction and 66 +/- 4% dilation). Endothelium removal reduced both constrictions (to -10 +/- 1%) and dilations (to 33 +/- 3%) due to H2O2. Constrictions due to H2O2 were completely abolished by indomethacin and the prostaglandin H2/thromboxane A2 (PGH2/TxA2) receptor antagonist SQ-29548. Dilations due to H2O2 were significantly reduced by inhibition of nitric oxide synthase (to 38 +/- 7%) but were unaffected by clotrimazole or sulfaphenazole (inhibitors of cytochrome P-450 enzymes), indomethacin, or SQ-29548. In endothelium-denuded arterioles, clotrimazole had no effect, whereas H2O2-induced dilations were significantly reduced by charybdotoxin plus apamin, inhibitors of Ca(2+)-activated K+ channels (to 24 +/- 3%), the selective blocker of ATP-sensitive K+ channels glybenclamide (to 14 +/- 2%), and the nonselective K(+)-channel inhibitor tetrabutylammonium (to -1 +/- 1%). Thus exogenous administration of H2O2 elicits 1) release of PGH2/TxA2 from both endothelium and smooth muscle, 2) release of nitric oxide from the endothelium, and 3) activation of K+ channels, such as Ca(2+)-activated and ATP-sensitive K+ channels in the smooth muscle resulting in biphasic changes of arteriolar diameter. Because H2O2 at low micromolar concentrations activates several intrinsic mechanisms, we suggest that H2O2 contributes to the local regulation of skeletal muscle blood flow in various physiological and pathophysiological conditions.

Cerebrovascular dysfunction in Zucker obese rats is mediated by oxidative stress and protein kinase C

Insulin resistance (IR) impairs vascular function in the peripheral and coronary circulations, but its effects on cerebral arteries are virtually unexplored. We examined the vascular responses of the basilar artery (BA) and its side branches through a cranial window in Zucker lean (ZL) and IR Zucker obese (ZO) rats. Nitric oxide (NO) and K+ channel-mediated dilator responses, elicited by acetylcholine, iloprost, cromakalim, and elevated [K+], were greatly diminished in the ZO rats compared with ZL rats. In contrast, sodium nitroprusside induced similar relaxations in the two experimental groups. Expressions of the K+ channel pore-forming subunits were not affected by IR, while endothelial NO synthase was upregulated in the ZO arteries compared with ZL arteries. Protein kinase C (PKC) activity and production of superoxide anion were increased in the cerebral arteries of ZO rats, and pretreatment with superoxide dismutase restored all examined dilator responses. In contrast, application of PKC inhibitors improved only receptor-linked NO-mediated relaxation, but not K+ channel-dependent responses. Thus, IR induces in ZO rats cerebrovascular dysfunction, which is mediated by oxidative stress and partly by PKC activation. The revealed impairment of NO and K+ channel-dependent dilator responses may be responsible for the increased risk of cerebrovascular events and neurodegenerative disorders in IR.

Potassium Channel Dysfunction in Cerebral Arteries of Insulin-Resistant Rats Is Mediated by Reactive Oxygen Species

Background and Purpose— Insulin resistance (IR) increases the risk of stroke in humans. One possible underlying factor is cerebrovascular dysfunction resulting from altered K + channel function. Thus, the goal of this study was to examine K + channel–mediated relaxation in IR cerebral arteries.

Methods— Experiments were performed on pressurized isolated middle cerebral arteries (MCAs) from fructose-fed IR and control rats.

Results— Dilator responses to iloprost, which are BK Ca channel mediated, were reduced in the IR compared with control arteries (19±2% versus 33±2% at 10 −6 mol/L). Similarly, relaxation to the K ATP opener pinacidil was diminished in the IR MCAs (17±2%) compared with controls (38±2% at 10 −5 mol/L). IR also reduced the K ATP channel–dependent component in calcitonin gene-related peptide–induced dilation; however, the magnitude of the relaxation remained unchanged in IR because of a nonspecified K + channel–mediated compensatory mechanism. In contrast, K ir channel–mediated relaxation elicited by increases in extracellular [K + ] (4 to 12 mmol/L) was similar in the control and IR arteries. Blockade of the K ir and K v channels with Ba 2+ and 4-aminopyridine, respectively, constricted the MCAs in both experimental groups with no significant difference. Pretreatment of arteries with superoxide dismutase (200 U/mL) plus catalase (150 U/mL) restored the dilatory responses to iloprost and pinacidil in the IR arteries. Immunoblots showed that the expressions of the pore-forming subunits of the examined K + channels are not altered by IR.

Conclusions— IR induces a type-specific K + channel dysfunction mediated by reactive oxygen species. The alteration of K ATP and BK Ca channel–dependent vascular responses may be responsible for the increased risk of cerebrovascular events in IR.

PPARgamma activation, by reducing oxidative stress, increases NO bioavailability in coronary arterioles of mice with Type 2 diabetes

We tested the hypothesis that short-term treatment of mice with Type 2 diabetes mellitus (DM) with rosiglitazone (ROSI), an agonist of peroxisome proliferator-activated receptor-gamma, ameliorates the impaired coronary arteriolar dilation by reducing oxidative stress via a mechanism unrelated to its effect on hyperglycemia and hyperinsulinemia. Control and Type 2 DM (db/db) mice were treated with ROSI (3 mg x kg(-1) x day(-1)) for 7 days, which did not significantly affect their serum concentration of glucose and insulin. Compared with controls, in db/db mice serum levels of 8-isoprostane and dihydroethydine-detectable superoxide production in carotid arteries were significantly elevated and were reduced by ROSI treatment. In coronary arterioles (diameter, approximately 80 microm) isolated from db/db mice, the reduced dilations to ACh, the nitric oxide (NO) donor NONOate, and increases in flow were significantly augmented either by in vitro administration of apocynin, an inhibitor of NAD(P)H-oxidase, or by in vivo ROSI treatment, responses that were then significantly reduced by the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester. In aortas of db/db mice, activity of SOD and catalase was reduced, whereas NAD(P)H oxidase activity was enhanced. ROSI treatment enhanced catalase and reduced NAD(P)H oxidase activity but did not affect the activity of SOD. These findings suggest that ROSI treatment enhances NO mediation of coronary arteriolar dilations due to the reduction of vascular NAD(P)H oxidase-derived superoxide production and enhancement of catalase activity. Thus, in addition to the previously revealed beneficial metabolic effects, the antioxidant action of rosiglitazone may protect coronary arteriolar function in Type 2 DM.