Endothelial dysfunction in streptozotocin-diabetic rats is not reversed by dietary probucol or simvastatin supplementation

Vildagliptin/pioglitazone combination improved the overall glycemic control in type I diabetic rats

Type I diabetes (TID) is generally assumed to be caused by an immune associated, if not directly immune-mediated, destruction of pancreatic β-cells. In patients with long-term diabetes, the pancreas lacks insulin-producing cells and the residual β-cells are unable to regenerate. Patients with TID are subjected to a lifelong insulin therapy which shows risks of hypoglycemia, suboptimal control and ketosis. In this study, we investigated the potential role of vildagliptin (Vilda) alone or in combination with pioglitazone (Pio), as treatment regimens for TID using streptozotocin (STZ)-induced TID model in rats. Daily oral administration of Vilda (5 mg/kg) alone or in combination with Pio (20 mg/kg) for 7 weeks significantly reduced blood glucose levels and HbA1c. It increased serum insulin levels and decreased serum glucagon. It also showed a strong antioxidant activity. Immunohistochemical analysis showed a marked improvement in β-cells in treated groups when compared with the diabetic group, which appeared in the normal cellular and architecture restoration of β-cells in the islets of Langerhans. Vilda alone or in combination with Pio has the ability to improve the overall glycemic control in type I diabetic rats and may be considered a hopeful and effective remedy for TID.

Atorvastatin improves systolic function, but does not prevent the development of dilated cardiomyopathy in streptozotocin-induced diabetic rats

BACKGROUND

Therapy with HMG-CoA reductase inhibitors (statins) has been associated with a significant reduction in the number of major cardiovascular (CV) events in diabetic patients. The mechanisms by which these drugs improve cardiac status remain unclear. We assessed the effects of atorvastatin (10 mg/kg/day) on CV function in streptozotocin (STZ)-induced diabetic rats.

METHODS

Age-matched, nondiabetic rats were used as controls. Echocardiographic parameters, systolic blood pressure (SBP), endothelial-dependent relaxation, cardiac and vascular oxidative stress, perivascular fibrosis, and cholesterol levels were evaluated after a 4-week atorvastatin treatment period.

RESULTS

In diabetic rats, SBP was higher than in controls. Atorvastatin decreased SBP in diabetic rats by 14% (n = 10, p < 0.05), and significantly increased stroke volume, ejection fraction, and cardiac output index. Whereas atorvastatin reduced left ventricular end systolic volume (LVESV) by 50% (p < 0.05), it failed to reduce left ventricular end diastolic volume (LVEDV). Total cholesterol was higher in diabetic rats than in controls and atorvastatin was ineffective in reducing cholesterol levels. The statin, however, decreased perivascular fibrosis and media thickness, and the markers of oxidative stress malondialdehyde (MDA) and 4-hidroxyalkenals (4-HAE) in aortic homogenates from diabetic rats. In addition, atorvastatin improved endothelial function by increasing the E _MAX value of the acetylcholine-induced relaxation from 53.7 ± 4.1% in untreated diabetic to 82.1 ± 7.0% in treated diabetic rats (n = 10, p < 0.05). L-NAME fully abolished this improvement, suggesting that the increased vascular relaxation with atorvastatin is NO-dependent.

CONCLUSIONS

Whereas atorvastatin does not reverse ventricular dilatation, it does have a positive hemodynamic effect on the CV system of diabetic rats. This hemodynamic benefit is independent of cholesterol levels, and is observed concomitantly with reduced oxidative stress, vascular remodeling, and improved endothelial function. Together, these results suggest that atorvastatin decreases the workload on the heart and improves systolic performance in type 1 diabetic rats by reducing oxidative stress, vascular tone, and systemic vascular resistance.

Low-molecular-weight fucoidan protects endothelial function and ameliorates basal hypertension in diabetic Goto-Kakizaki rats

Endothelial dysfunction, characterized by impairment of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) bioavailability, has been implicated in diabetic cardiovascular pathogenesis. In this study, low-molecular-weight fucoidan (LMWF), which has multiple biological activities including anti-inflammatory and anti-oxidative properties, was investigated for its protective effect against endothelial dysfunction in Goto-Kakizaki type 2 diabetic rats. LMWF (50, 100, or 200 mg/kg/day) or probucol (100 mg/kg/day) were given to diabetic rats for 12 weeks. Basal blood pressure, acetylcholine- or flow-mediated relaxation of mesenteric and paw arteries, endothelium-dependent dilation of aorta, eNOS phosphorylation, and NO production were measured using laser Doppler flowmetry, force myograph, hematoxylin and eosin staining, western blot analysis, and an NO assay. We found that LMWF robustly ameliorated the basal hypertension and impairment of endothelium-dependent relaxation in the aorta, as well as mesenteric and paw arteries in diabetic rats. In addition, the reduction in eNOS phosphorylation at Ser1177, eNOS expression, and NO production because of diabetes were partially reversed by LMWF treatment. However, probucol, a lipid-modifying drug with antioxidant properties, displayed only mild effects. Moreover, LMWF induced, in a dose-dependent manner, endothelium-dependent vasodilation and eNOS phosphorylation at Ser1177 in normal aorta, and also promoted Ser1177 phosphorylation and NO synthesis in primary cultured vasoendothelial cells. Thus, these data demonstrate for the first time that fucoidan protects vasoendothelial function and reduces basal blood pressure in type 2 diabetes rats via, at least in part, preservation of eNOS function. Fucoidan is therefore a potential candidate drug for protection of endothelium in diabetic cardiovascular complications.

Pyridoxamine analogues scavenge lipid-derived gamma-ketoaldehydes and protect against H2O2-mediated cytotoxicity

Isoketals and levuglandins are highly reactive gamma-ketoaldehydes formed by oxygenation of arachidonic acid in settings of oxidative injury and cyclooxygenase activation, respectively. These compounds rapidly adduct to proteins via lysyl residues, which can alter protein structure/function. We examined whether pyridoxamine, which has been shown to scavenge alpha-ketoaldehydes formed by carbohydrate or lipid peroxidation, could also effectively protect proteins from the more reactive gamma-ketoaldehydes. Pyridoxamine prevented adduction of ovalbumin and also prevented inhibition of RNase A and glutathione reductase activity by the synthetic gamma-ketoaldehyde, 15-E2-isoketal. We identified the major products of the reaction of pyridoxamine with the 15-E2-isoketal, including a stable lactam adduct. Two lipophilic analogues of pyridoxamine, salicylamine and 5'-O-pentylpyridoxamine, also formed lactam adducts when reacted with 15-E2-isoketal. When we oxidized arachidonic acid in the presence of pyridoxamine or its analogues, pyridoxamine-isoketal adducts were found in significantly greater abundance than the pyridoxamine-N-acyl adducts formed by alpha-ketoaldehyde scavenging. Therefore, pyridoxamine and its analogues appear to preferentially scavenge gamma-ketoaldehydes. Both pyridoxamine and its lipophilic analogues inhibited the formation of lysyl-levuglandin adducts in platelets activated ex vivo with arachidonic acid. The two lipophilic pyridoxamine analogues provided significant protection against H2O2-mediated cytotoxicity in HepG2 cells. These results demonstrate the utility of pyridoxamine and lipophilic pyridoxamine analogues to assess the potential contributions of isoketals and levuglandins in oxidant injury and inflammation and suggest their potential utility as pharmaceutical agents in these conditions.

Impairment of dilator responses of cerebral arterioles during diabetes mellitus: role of inducible NO synthase

BACKGROUND AND PURPOSE

During diabetes, expression of inducible nitric oxide synthase (iNOS) plays an important role in the development of endothelial dysfunction in extracranial blood vessels. Progression of vascular dysfunction after the onset of diabetes differs among vascular beds. In this study, the effects of hyperglycemia/diabetes on vasomotor function were examined in cerebral arterioles at 2 different times in control and iNOS-deficient mice and compared with the effects on carotid arteries.

METHODS

Streptozotocin (150 mg/kg IP) was given to induce diabetes. The diameter of cerebral arterioles was measured through a cranial window in diabetic and nondiabetic mice in vivo. Vasomotor function of the carotid artery was examined in vitro.

RESULTS

In diabetic mice, responses of the cerebral arterioles to acetylcholine (1 mumol/L) were normal after 3 weeks of diabetes but were significantly impaired after 5 to 6 weeks of diabetes (4+/-1% [mean+/-SEM] increase in diameter) compared with control mice (14+/-1; P=0.0002). Responses to sodium nitroprusside were similar in diabetic and nondiabetic mice at both time points. In contrast, the vasomotor function of the carotid artery was not affected after 5 to 6 weeks of diabetes. In diabetic iNOS-deficient mice, cerebral arteriolar vasomotor function was not impaired, even after 4 months of diabetes.

CONCLUSIONS

During diabetes, endothelial dysfunction of cerebral arterioles requires expression of iNOS and develops earlier than in carotid arteries.

The beneficial in vitro effects of lovastatin and chelerythrine on relaxatory response to acetylcholine in the perfused mesentric bed isolated from diabetic rats

Diabetes mellitus is associated with an increased risk of cardiovascular disease. Endothelial dysfunction (i.e. decreased endothelium-dependent vasorelaxation) plays a key role in the pathogenesis of diabetic vascular disease. The present study was undertaken to determine whether diabetes induced by streptozotocin alters mesenteric responses to vasodilators and, if so, to study the acute in vitro effects of lovastatin and chelerythrine. Endothelial function was assessed in constantly perfused preparation removed from rats, 12 weeks after treatment with either saline or streptozotocin (45 mg/kg, intraperitoneally). In pre-contracted mesenteric beds (with 100 microM phenylephrine) removed from diabetic rats, the concentration response curve to acetylcholine, but not to sodium nitroprusside, was significantly reduced. Perfusion with lovastatin (10 microM for 20 min) or chelerythrine (1 microM for 20 min) significantly improved the acetylcholine-mediated relaxation in preparations removed from diabetic but not control rats. Pre-incubation of tissue with N(G)-nitro-L-argenine methyl ester hydrochloride (10 microM for 20 min) inhibited the beneficial effect of lovastatin but not chelerythrine. Pre-treatment of tissue with indomethacin (10 microM for 20 min) did not modify the effects of lovastatin or chelerythrine on acetylcholine responses. The present results demonstrate that endothelial dysfunction induced by diabetes (in a resistant vasculature, such as rat mesenteric bed) may be improved by an acute exposure to either lovastatin or chelerythrine. Furthermore, our results suggest that the beneficial effect of lovastatin is mediated via the nitric oxide pathway.

Time-Dependent Changes in Antioxidant Enzymes and Vascular Reactivity of Aorta in Streptozotocin-Induced Diabetic Rats Treated With Curcumin

In the present study changes in oxidative stress and vascular reactivity in aortic rings of chronic streptozotocin-diabetic (STZ-CON) and nondiabetic (ND-CON) rats is studied at 4 weekly intervals up to 24 weeks. The effect of chronic curcumin (200 mg/kg) treatment was also studied. Blood glucose and blood pressure levels were significantly higher in the STZ-CON group and curcumin administration had no significant effect on it. Superoxide dismutase and catalase activity were either unchanged or significantly increased during the early stage of diabetes whereas during the medium and late stage were significantly reduced. Reduced glutathione and lipid peroxidation levels significantly decreased as time after STZ administration increased. Phenylephrine (PE)-induced contraction was significantly (P < 0.05) increased during the early stage of diabetes, whereas it was significantly (P < 0.05) reduced at the medium and late stage of diabetes. Acetylcholine (Ach)-induced relaxation significantly decreased with respect to time after STZ administration. Sodium nitroprusside (SNP)-induced relaxation was unaltered up to initial stage but after medium stage there was a rightward shift and the pD2 value significantly decreased. Though curcumin treatment had no significant effect on superoxide dismutase, catalase, and reduced glutathione levels, it significantly reduced lipid peroxidation compared with diabetic control. Curcumin treatment attenuated the phenylephrine-induced increase in contraction during the early stage. However, curcumin treatment had no significant effect at the medium and late stage. Though curcumin administration improved Ach-induced relaxation it did not restore it to normal. Inability of curcumin to prevent oxidative stress during the late stage may be due to the fact that chronic diabetes (hyperglycemia) leads to excessive production of free radicals. Hence the present study shows that variations reported in antioxidant enzymes and vascular reactivity are due to the duration of diabetes or time after diabetes induction in STZ model and this can not be completely reversed by chronic treatment with curcumin.

Atorvastatin reduces the plasma lipids and oxidative stress but did not reverse the inhibition of prostacyclin generation by aortas in streptozotocin diabetic rats

The effect of atorvastatin (Lipitor) on diabetes-induced changes in plasma lipids, oxidative stress and the ability of aortic tissues to generate prostacyclin was studied in streptozotocin diabetic rats. In diabetic rats, plasma total cholesterol, triglycerides and serum glucose significantly increased compared to nondiabetic rats. Atorvastatin administration to diabetic rats did not affect hyperglycemia but significantly reduced plasma total cholesterol and triglycerides compared to diabetic rats. The oxidative stress markers urinary isoprostane, liver thiobarbituric acid reactive substances (TBARS) and plasma protein carbonyl content significantly increased in diabetic rats compared to nondiabetic rats. Atorvastatin admnistration to diabetic rats significantly reduced oxidative stress levels compared to diabetic rats, but urinary isoprostane and liver TBARS remained significantly higher than nondiabetic rats. Prostacyclin (PGI(2)) generation by aortic tissues significantly decreased in diabetic rats compared to nondiabetic rats. Atorvastatin administration to diabetic rats did not reverse that inhibition. These results were discussed in the light of the possible effects of hyperglycemia and statins on NAD(P)H-oxidase and cyclooxygenase-2 activities and the genetic difference between rats and other mammals regarding the level of vascular superoxide dismutase (SOD) activity.

Tranilast attenuates vascular hypertrophy, matrix accumulation and growth factor overexpression in experimental diabetes

OBJECTIVES

The growth factors transforming growth factor-B (TGF-B) and epidermal growth factor (EGF) have both been implicated in the hypertrophic structural changes in the vasculature that are characteristic features of both human and experimental diabetes. Recently, tranilast (N(3,4-dimethoxycinnamoyl)anthranilic acid), a drug used in the treatment of allergic and dermatological diseases, has also been reported to inhibit transforming growth factor-B (TGF-B)-mediated collagen formation. However, its effects on vascular hypertrophy in diabetes are unknown. The present study thus sought to determine the effects of tranilast on both TGF-B and EGF expression and mast cells in mediating the trophic vascular changes in experimental diabetes.

METHODS

Vessel morphology, growth factors and collagen gene expression and matrix deposition were examined in the mesenteric arteries of control rats treated with or without tranilast, and streptozotocin-induced diabetic Sprague-Dawley rats treated with or without tranilast (200 mg/kg/day) during a 3-week period.

RESULTS

Compared with control animals, diabetic rats had significantly increased vessel weight, wall: lumen ratio, ECM accumulation, gene expression of TGF-B1, EGF, and both alpha1 (I) and alpha1 (IV) collagen. Tranilast treatment did not influence plasma glucose or systemic blood pressure. However, tranilast significantly reduced mesenteric weight, wall: lumen ratio and matrix deposition and also attenuated the overexpression of TGF-B1, EGF, and both alpha1 (I) and alpha1 (IV) collagen mRNA in diabetic rats.

CONCLUSION

These findings indicate that tranilast ameliorates pathological vascular changes observed in experimental diabetes in association with reduced growth factor expression independent of blood glucose or systemic blood pressure.

Endothelial dysfunction in children with type 1 diabetes mellitus

Endothelial dysfunction is defined as the loss of endothelium properties, e.g. alteration of protein synthesis, increased vascular tone and permeability, acquisition of prothrombotic and antifibrinolytic properties. Endothelium, a primary target of unbalanced glycaemic control, is involved in the pathogenesis of vascular complications in patients with type 1 diabetes mellitus (DM). Vascular endothelium damage is characterised by an increase of endothelium-derived regulatory proteins. vWF and t-PA may be useful to investigate early endothelium involvement. However, impaired endothelium-dependent vasodilatation may be a more sensitive marker. Abnormal markers of endothelial cell activation and impaired endothelium-dependent vasodilatation have been observed in young patients with type I DM. Hyperglycaemia may alter normal endothelium functions, either directly or indirectly, by inducing different metabolic pathways. Complete understanding of the pathophysiology of endothelial dysfunction may lead to timely therapeutic intervention to prevent its development and to slow the progression of diabetic complications.

The SOD mimetic tempol restores vasodilation in afferent arterioles of experimental diabetes

BACKGROUND

Endothelium-dependent vasodilation is impaired in large conduit vessels in diabetes mellitus. Oxygen radicals contribute to the impaired endothelium-dependent vasodilation. We tested the hypothesis that stimulated endothelium-dependent vasodilation is reduced in renal afferent arterioles in diabetes and is caused by an increase in vascular superoxide (O2(-)).

METHODS

Renal afferent arterioles from normal and insulin-treated alloxan-diabetic rabbits were microdissected and microperfused in vitro for the study of luminal diameter responses to acetylcholine (Ach; 10(-11) to 10(-6) mol/L). The blood glucose concentration of insulin-treated alloxan-diabetic rabbits was elevated fourfold compared with normal rabbits (319 +/- 23 vs. 79 +/- 6 mg/dL, P < 0.001).

RESULTS

In norepinephrine (NE)-preconstricted afferent arterioles of normal rabbits, Ach significantly (P < 0.001) increased luminal diameter by 165 +/- 44%. The nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (10(-4) mol/L) blocked this Ach-induced vasodilation. In marked contrast, in NE-preconstricted arterioles of diabetic rabbits, Ach significantly (P < 0.01) decreased luminal diameter by 41 +/- 11%. Pretreatment of diabetic afferent arterioles with the superoxide dismutase (SOD) mimetic tempol (10(-3) mol/L) restored a vasodilator response to Ach. In NE-preconstricted diabetic afferent arterioles treated with tempol, Ach significantly (P < 0.001) increased luminal diameter by 25 +/- 6%.

CONCLUSIONS

Ach-induced afferent arteriolar vasodilation is dependent on nitric oxide and is impaired in diabetes. O2(-) contributes to the impaired Ach-induced vasodilation in renal afferent arterioles in diabetes.

Endothelial dysfunction in diabetes

Endothelial dysfunction plays a key role in the pathogenesis of diabetic vascular disease. The endothelium controls the tone of the underlying vascular smooth muscle through the production of vasodilator mediators. The endothelium-derived relaxing factors (EDRF) comprise nitric oxide (NO), prostacyclin, and a still elusive endothelium-derived hyperpolarizing factor (EDHF). Impaired endothelium-dependent vasodilation has been demonstrated in various vascular beds of different animal models of diabetes and in humans with type 1 and 2 diabetes. Several mechanisms of endothelial dysfunction have been reported, including impaired signal transduction or substrate availibility, impaired release of EDRF, increased destruction of EDRF, enhanced release of endothelium-derived constricting factors and decreased sensitivity of the vascular smooth muscle to EDRF. The principal mediators of hyperglycaemia-induced endothelial dysfunction may be activation of protein kinase C, increased activity of the polyol pathway, non-enzymatic glycation and oxidative stress. Correction of these pathways, as well as administration of ACE inhibitors and folate, has been shown to improve endothelium-dependent vasodilation in diabetes. Since the mechanisms of endothelial dysfunction appear to differ according to the diabetic model and the vascular bed under study, it is important to select clinically relevant models for future research of endothelial dysfunction.

Endothelin receptor antagonism ameliorates mast cell infiltration, vascular hypertrophy, and epidermal growth factor expression in experimental diabetes

Vascular hypertrophy, a feature of experimental and human diabetes, has been implicated in the pathogenesis of the microvascular and macrovascular complications of the disease. In the present study, we sought to examine the role of endogenous endothelin and its relation to vascular growth factors in the mediation of vascular hypertrophy in experimental diabetes and to examine the contribution of mast cells to this process. Vessel morphology, endothelin, growth factor gene expression, and matrix deposition were studied in the mesenteric arteries of control and streptozotocin-induced diabetic Sprague-Dawley rats treated with or without the dual endothelin(A/B) receptor antagonist bosentan (100 mg x kg(-1) x d(-1)) during a 3-week period. Compared with control animals, diabetic animals had significant increases in vessel weight, wall-to-lumen ratio, mast cell infiltration, extracellular matrix deposition, and gene expression of epidermal growth factor (EGF) and transforming growth factor-beta(1). In diabetic, but not control, vessels, not only were EGF mRNA and endothelin present in endothelial cells, but also their expression was observed in adventitial mast cells. Immunoreactive endothelin was present in the media of mesenteric vessels of diabetic, but not control, animals. Bosentan treatment significantly reduced mesenteric weight, wall-to-lumen ratio, mast cell infiltration, matrix deposition, and EGF mRNA but did not prevent the overexpression of transforming growth factor-beta(1) mRNA in diabetic rats. These findings suggest that endogenous endothelin and EGF may play a role in diabetes-induced vascular hypertrophy and that mast cells may be pathogenetically involved in this process.

Diabetic dyslipidaemia and coronary heart disease: new perspectives

Atherosclerotic macrovascular disease is the leading cause of both morbidity and mortality in non-insulin dependent diabetes mellitus. Endothelial dysfunction is a key, early and potentially reversible event in pathogenesis of atherosclerosis. Its occurrence in non-insulin dependent diabetes mellitus is well supported by both in-vitro and in-vivo studies. Non-insulin dependent diabetes mellitus results in diverse abnormalities of lipid and lipoprotein metabolism, in particular hypertriglyceridaemia, low levels of high density lipoprotein and abnormalities of post-prandial lipaemia. A variety of studies demonstrate the presence of enhanced oxidative stress in non-insulin dependent diabetes mellitus, with recent data implying an association between oxidative stress, post-prandial lipaemia and endothelial dysfunction in non-diabetic subjects. In this article based on in-vitro and human studies, we develop the hypothesis that endothelial dysfunction in non-insulin dependent diabetes mellitus is the consequence of the diabetic dyslipidaemia, in particular post-prandial lipaemia, and of oxidative stress on the action of nitric oxide. The practical applications of this theory provide potential therapeutic options which may reduce the risk of vascular disease in non-insulin dependent diabetes mellitus.