Impaired contraction and relaxation in aorta from streptozotocin-diabetic rats: role of polyol pathway

Oxidative and Nitrous Stress Underlies Vascular Malfunction Induced by Ionizing Radiation and Diabetes

Oxidative stress results from the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in quantities exceeding the potential activity of the body's antioxidant system and is one of the risk factors for the development of vascular dysfunction in diabetes and exposure to ionizing radiation. Being the secondary products of normal aerobic metabolism in living organisms, ROS and RNS act as signaling molecules that play an important role in the regulation of vital organism functions. Meanwhile, in high concentrations, these compounds are toxic and disrupt various metabolic pathways. The various stress factors (hyperglycemia, gamma-irradiation, etc.) trigger free oxygen and nitrogen radicals accumulation in cells that are capable to damage almost all cellular components including ion channels and transporters such as Na+/K+-ATPase, BKCa, and TRP channels. Vascular dysfunctions are governed by interaction of ROS and RNS. For example, the reaction of ROS with NO produces peroxynitrite (ONOO-), which not only oxidizes DNA, cellular proteins, and lipids, but also disrupts important signaling pathways that regulate the cation channel functions in the vascular endothelium. Further increasing in ROS levels and formation of ONOO- leads to reduced NO bioavailability and causes endothelial dysfunction. Thus, imbalance of ROS and RNS and their affect on membrane ion channels plays an important role in the pathogenesis of vascular dysfunction associated with various disorders.

Mechanisms and clinical implications of endothelium-dependent vasomotor dysfunction in coronary microvasculature

Coronary microvascular disease (CMD), which affects the arterioles and capillary endothelium that regulate myocardial perfusion, is an increasingly recognized source of morbidity and mortality, particularly in the setting of metabolic syndrome. The coronary endothelium plays a pivotal role in maintaining homeostasis, though factors such as diabetes, hypertension, hyperlipidemia, and obesity can contribute to endothelial injury and consequently arteriolar vasomotor dysfunction. These disturbances in the coronary microvasculature clinically manifest as diminished coronary flow reserve, which is a known independent risk factor for cardiac death, even in the absence of macrovascular atherosclerotic disease. Therefore, a growing body of literature has examined the molecular mechanisms by which coronary microvascular injury occurs at the level of the endothelium and the consequences on arteriolar vasomotor responses. This review will begin with an overview of normal coronary microvascular physiology, modalities of measuring coronary microvascular function, and clinical implications of CMD. These introductory topics will be followed by a discussion of recent advances in the understanding of the mechanisms by which inflammation, oxidative stress, insulin resistance, hyperlipidemia, hypertension, shear stress, endothelial cell senescence, and tissue ischemia dysregulate coronary endothelial homeostasis and arteriolar vasomotor function.

13C Metabolic Flux Analysis Indicates Endothelial Cells Attenuate Metabolic Perturbations by Modulating TCA Activity

Disrupted endothelial metabolism is linked to endothelial dysfunction and cardiovascular disease. Targeted metabolic inhibitors are potential therapeutics; however, their systemic impact on endothelial metabolism remains unknown. In this study, we combined stable isotope labeling with ¹³C metabolic flux analysis (¹³C MFA) to determine how targeted inhibition of the polyol (fidarestat), pentose phosphate (DHEA), and hexosamine biosynthetic (azaserine) pathways alters endothelial metabolism. Glucose, glutamine, and a four-carbon input to the malate shuttle were important carbon sources in the baseline human umbilical vein endothelial cell (HUVEC) ¹³C MFA model. We observed two to three times higher glutamine uptake in fidarestat and azaserine-treated cells. Fidarestat and DHEA-treated HUVEC showed decreased ¹³C enrichment of glycolytic and TCA metabolites and amino acids. Azaserine-treated HUVEC primarily showed ¹³C enrichment differences in UDP-GlcNAc. ¹³C MFA estimated decreased pentose phosphate pathway flux and increased TCA activity with reversed malate shuttle direction in fidarestat and DHEA-treated HUVEC. In contrast, ¹³C MFA estimated increases in both pentose phosphate pathway and TCA activity in azaserine-treated cells. These data show the potential importance of endothelial malate shuttle activity and suggest that inhibiting glycolytic side branch pathways can change the metabolic network, highlighting the need to study systemic metabolic therapeutic effects.

Aldose Reductase: An Emerging Target for Development of Interventions for Diabetic Cardiovascular Complications

Diabetes is a leading cause of cardiovascular morbidity and mortality. Despite numerous treatments for cardiovascular disease (CVD), for patients with diabetes, these therapies provide less benefit for protection from CVD. These considerations spur the concept that diabetes-specific, disease-modifying therapies are essential to identify especially as the diabetes epidemic continues to expand. In this context, high levels of blood glucose stimulate the flux via aldose reductase (AR) pathway leading to metabolic and signaling changes in cells of the cardiovascular system. In animal models flux via AR in hearts is increased by diabetes and ischemia and its inhibition protects diabetic and non-diabetic hearts from ischemia-reperfusion injury. In mouse models of diabetic atherosclerosis, human AR expression accelerates progression and impairs regression of atherosclerotic plaques. Genetic studies have revealed that single nucleotide polymorphisms (SNPs) of the ALD2 (human AR gene) is associated with diabetic complications, including cardiorenal complications. This Review presents current knowledge regarding the roles for AR in the causes and consequences of diabetic cardiovascular disease and the status of AR inhibitors in clinical trials. Studies from both human subjects and animal models are presented to highlight the breadth of evidence linking AR to the cardiovascular consequences of diabetes.

Heme oxygenase-1 contributes to the protective effect of resveratrol against endothelial dysfunction in STZ-induced diabetes in rats

Endothelial dysfunction is a common complication of diabetes that mainly stems from increased reactive oxygen species, which makes antioxidants of great benefit. Resveratrol (RSV) is an antioxidant that shows protective effects in a variety of disease models where the ameliorative effect appears to be mediated, in part, via heme oxygenase-1 (HO-1) induction. However, the pathophysiological relevance of HO-1 in the ameliorative response of RSV in endothelial dysfunction is not clearly defined. The present study was conducted to investigate whether HO-1 plays a role in diabetes-induced vascular dysfunction. Streptozotocin-diabetic rats were treated with RSV (10 mg/kg) in presence or absence of an HO-1 blocker, Zinc protoporphyrin (ZnPP) to assess vascular function and indicators of disease status. We found that RSV treatment significantly abrogated diabetes induced vascular dysfunction. This improvement was associated with the ability of RSV to decrease oxidative stress markers alongside a reduction in the aortic TGF-β expression, elevation of NOS3 expression and aortic nitrite concentration as well as HO activity. These ameliorative effects were diminished when ZnPP was administered prior to RSV. Our results clearly demonstrate the protective effects of RSV in diabetes-associated endothelial dysfunction and verified a causal role of HO-1 in this setting.

Normalization of organ bath contraction data for tissue specimen size: does one approach fit all?

Organ bath experiments are a key technology to assess contractility of smooth muscle. Despite efforts to standardize tissue specimen sizes, they vary to a certain degree. As it appears obvious that a larger piece of tissue should develop greater force, most investigators normalize contraction data for specimen size. However, they lack agreement which parameter should be used as denominator for normalization. A pre-planned analysis of data from a recent study was used to compare denominators used for normalization, i.e., weight, length, and cross-sectional area. To increase robustness, we compared force with denominator in correlation analysis and also coefficient of variation with different denominators. This was done concomitantly with urinary bladder strips and aortic rings and with multiple contractile stimuli. Our urinary bladder data show that normalization for strip weight yielded the tightest but still only moderate correlation (e.g., r² = 0.3582 for peak carbachol responses based on 188 strips). In aorta, correlations were even weaker (e.g., r² = 0.0511 for plateau phenylephrine responses normalized for weight based on 200 rings). Normalization for strip size is less effective in reducing data variability than previously assumed; the normalization denominator of choice must be identified separately for each preparation.

Blockade of sigma 1 receptors alleviates sensory signs of diabetic neuropathy in rats

BACKGROUND

E-52862 (S1RA, 4-[2-[[5-methyl-1-(2-naphthalenyl)-1H-pyrazol-3-yl]oxy]ethyl]-morpholine), a novel selective sigma 1 receptor (σ1R) antagonist, has demonstrated efficacy in nociceptive and neuropathic pain models. Our aim was to test if σ1R blockade with E-52862 may modify the signs of neuropathy in Zucker diabetic fatty (ZDF) rats, a type 2 diabetes model.

METHODS

Mechanical and thermal response thresholds were tested on 7-, 13-, 14- and 15-week-old ZDF rats treated with saline or with E-52862 acutely administered on week 13, followed by sub-chronic administration (14 days). Axonal peripheral activity (skin-saphenous nerve preparation) and isolated aorta or mesenteric bed reactivity were analysed in 15-week-old ZDF rats treated with saline or E-52862 and in LEAN rats.

RESULTS

Zucker diabetic fatty rats showed significantly decreased thermal withdrawal latency and threshold to mechanical stimulation on week 13 compared to week 7 (prediabetes) and with LEAN animals; single-dose and sub-chronic E-52862 administration restored both parameters to those recorded on week 7. Regarding axonal peripheral activity, E-52862 treatment increased the mean mechanical threshold (77.3 ± 21 mN vs. 19.6 ± 1.5 mN, saline group) and reduced the response evoked by mechanical increasing stimulation (86.4 ± 36.5 vs. 352.8 ± 41.4 spikes) or by repeated mechanical supra-threshold steps (39.4 ± 1.4 vs. 83.5 ± 0.9). E-52862 treatment also restored contractile response to phenylephrine in aorta and mesenteric bed.

CONCLUSIONS

E-52862 administration reverses neuropathic (behavioural and electrophysiological) and vascular signs in the ZDF rat.

SIGNIFICANCE

Blockade of σ1R avoids the development of diabetic neuropathy in rats, and may represent a potentially useful therapeutic approach to peripheral neuropathies in diabetic patients. WHAT DOES THIS STUDY ADD?: This study presents evidences for the potential usefulness of sigma receptor blockade on diabetic neuropathy in rats. The methodology includes behavioural evidences, electrophysiological data and vascular-isolated models.

Damaging effects of hyperglycemia on cardiovascular function: spotlight on glucose metabolic pathways

The incidence of cardiovascular complications associated with hyperglycemia is a growing global health problem. This review discusses the link between hyperglycemia and cardiovascular diseases onset, focusing on the role of recently emerging downstream mediators, namely, oxidative stress and glucose metabolic pathway perturbations. The role of hyperglycemia-mediated activation of nonoxidative glucose pathways (NOGPs) [i.e., the polyol pathway, hexosamine biosynthetic pathway, advanced glycation end products (AGEs), and protein kinase C] in this process is extensively reviewed. The proposal is made that there is a unique interplay between NOGPs and a downstream convergence of detrimental effects that especially affect cardiac endothelial cells, thereby contributing to contractile dysfunction. In this process the AGE pathway emerges as a crucial mediator of hyperglycemia-mediated detrimental effects. In addition, a vicious metabolic cycle is established whereby hyperglycemia-induced NOGPs further fuel their own activation by generating even more oxidative stress, thereby exacerbating damaging effects on cardiac function. Thus NOGP inhibition, and particularly that of the AGE pathway, emerges as a novel therapeutic intervention for the treatment of cardiovascular complications such as acute myocardial infarction in the presence hyperglycemia.

Toll-like receptor 2 mediates vascular contraction and activates RhoA signaling in vascular smooth muscle cells from STZ-induced type 1 diabetic rats

Increased vascular smooth muscle cell (VSMC) contraction is an early and critical contributor to the pathogenesis of vascular dysfunction in diabetes; however, knowledge regarding the underlying mechanisms is scarce. Toll-like receptor 2 (TLR2), a well-known component of the innate immunity, is expressed in VSMC and recently has been identified to be systemically activated in diabetes. Whether TLR2 is locally activated in the diabetic blood vessels and have effect on contraction is not known. In the current study, we examined the role of TLR2 in increased vascular contraction in diabetes. Utilizing rat model of type 1 diabetes (induced by streptozotocin (STZ)), we demonstrated that aortas from STZ-diabetic rats exhibit increased expression of TLR2 and its adaptor protein, myeloid differentiation primary response 88 (MyD88), as well as enhanced protein-protein interaction between TLR2 and MyD88, suggesting a TLR2 signaling activation. Blockade of TLR2 in intact aortas using anti-TLR2 antibody attenuated increased vascular contraction in STZ-diabetic rat as assessed by wire myograph. Activation of TLR2 by specific ligand in primary aortic VSMC cultures triggered activation of RhoA which was exacerbated in cells from STZ-diabetic rats than control rats. Activation of RhoA was accompanied by phosphorylation and therefore activation of its downstream targets myosin phosphatase target subunit I and myosin light chain (markers of VSMC contraction). Taken together, these results provide evidence for the role of TLR2 in increased contraction in diabetic blood vessels that involves RhoA signaling. Thus, targeting vascular TLR2 offers a promising drug target to treat vascular dysfunction in diabetes.

Diabetic complications in obese type 2 diabetic rat models

We overviewed the pathophysiological features of diabetes and its complications in obese type 2 diabetic rat models: Otsuka Long-Evans Tokushima fatty (OLETF) rat, Wistar fatty rat, Zucker diabetic fatty (ZDF) rat and Spontaneously diabetic Torii (SDT) fatty rat. Pancreatic changes with progression of diabetes were classified into early changes, such as islet hypertrophy and degranulation of β cells, and degenerative changes, such as islet atrophy and fibrosis of islet with infiltration of inflammatory cells. Renal lesions in tubuli and glomeruli were observed, and nodular lesions in glomeruli were notable changes in OLETF and SDT fatty rats. Among retinal changes, folding and thickening were interesting findings in SDT fatty rats. A decrease of motor nerve conduction velocity with progression of diabetes was presented in obese diabetic rats. Other diabetic complications, osteoporosis and sexual dysfunction, were also observed. Observation of bone metabolic abnormalities, including decrease of osteogenesis and bone mineral density, and sexual dysfunction, including hypotestosteronemia and erectile dysfunction, in obese type 2 diabetic rats have been reported.

Recent advances in understanding the biochemical and molecular mechanism of diabetic cardiomyopathy

Cardiovascular complications account for significant morbidity and mortality in the diabetic population. Diabetic cardiomyopathy (DCM), a prominent cardiovascular complication, has been recognized as a microvascular disease that may lead to heart failure. During the past few decades, research progress has been made in investigating the pathophysiology of the disease; however, the exact molecular mechanism has not been elucidated, making therapeutic a difficult task. In this review article, we have discussed a number of diabetes-induced metabolites such as glucose, advanced glycation end products, protein kinase C, free fatty acid and oxidative stress and other related factors that are implicated in the pathophysiology of the DCM. An understanding of the biochemical and molecular changes especially early in the DCM may lead to new and effective therapies toward prevention and amelioration of DCM, which is important for the millions of individuals who already have or are likely to develop the disease before a cure becomes available.

Simultaneous renal hypertension and type 2 diabetes exacerbate vascular endothelial dysfunction in rats

Despite the high rate of occurrence of both diabetes and hypertension in humans, the cardiovascular effects of the two conditions have not been investigated when they occur simultaneously. Thus this study examined the vascular effects of simultaneous type 2 diabetes and renal hypertension on endothelial function. Serum malondialdehyde and systolic blood pressure (SBP) were measured, glucose tolerance test (GTT) was performed, and concentration-response to phenylephrine (PE) in the absence and presence of nitro-l-arginine methyl ester (l-NAME), acetylcholine and sodium nitroprusside were conducted on aortic rings from diabetic control, type 2 diabetes, sham-operated, renal hypertensive, and simultaneous type 2 diabetes plus hypertension rats respectively. Hypertension, diabetes, and simultaneous diabetes and hypertension were associated with either increased or decreased maximal responses (E(max)) of PE dependent on in the presence or absence of l-NAME. There was also increased serum malondialdehyde and decreased E(max) of acetylcholine. Thus simultaneous hypertension and diabetes caused a greater decrease in E(max) of acetylcholine compared to that seen with either diabetes or hypertension alone higher than that seen in hypertension. The blood glucose during GTT was lower than that seen in diabetes groups. Thus simultaneous type 2 diabetes and the SBP was renal hypertension is associated with improved glucose tolerance, but with further deterioration of endothelial dysfunction compared with either condition alone.

Human aldose reductase expression accelerates atherosclerosis in diabetic apolipoprotein E-/- mice

OBJECTIVE

There are several pathways that mediate the aberrant metabolism of glucose and that might induce greater vascular damage in the setting of diabetes. The polyol pathway mediated by aldose reductase (AR) has been postulated to be one such pathway. However, it has been reported that AR reduces toxic lipid aldehydes and, under some circumstances, might be antiatherogenic.

METHODS AND RESULTS

Atherosclerosis development was quantified in 2 lines of transgenic mice expressing human AR (hAR) crossed on the apolipoprotein E knockout background. The transgenes were used to increase the normally low levels of this enzyme in wild-type mice. Both generalized hAR overexpression and hAR expression via the Tie 2 promoter increased lesion size in streptozotocin diabetic mice. In addition, pharmacological inhibition of AR reduced lesion size.

CONCLUSIONS

Although in some settings AR expression might reduce levels of toxic aldehydes, transgenic expression of this enzyme within the artery wall leads to greater atherosclerosis.

Gender differences in vascular reactivity of aortas from streptozotocin-induced diabetic mice

The aim of the present study was to assess gender differences in diabetes-related vascular reactivity in murine aortas. Diabetes is a risk factor for ischemic heart disease, cerebral ischemia, and atherosclerosis, conditions in which endothelial dysfunction plays a pathogenetic role. We examined vascular responses in aortas isolated from streptozotocin (STZ)-induced type 1 diabetic mice and age-matched control mice, and looked for gender differences in the diabetes-induced changes in these responses. For each gender, the plasma adiponectin levels were lower in diabetic mice than in the controls, and they were significantly higher in females than in males. The acetylcholine (ACh)-induced endothelium-dependent relaxation of aortic rings was impaired (vs. that in the age-matched controls) in diabetic male mice, but not in diabetic female mice. The sodium nitroprusside-induced endothelium-independent aortic relaxation was not altered by diabetes in either male or female mice. The norepinephrine-induced aortic contraction was enhanced (vs. that in the control group) in diabetic female mice, but not in diabetic male mice, whereas in the presence of N(G)-nitro-L-arginine neither gender exhibited a significant diabetes-induced change in this contraction. The clonidine-induced and insulin-induced endothelium-dependent aortic relaxations were impaired only in the diabetic female group (vs. the age-matched controls). These results suggest that: a) in male diabetic mice, which exhibited low adiponectin levels, these were impairments of both the aortic relaxation and nitric oxide (NO) production induced by ACh, whereas b) in female diabetic mice, there were impairments of the aortic relaxations induced by both insulin and clonidine.

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.

Aldose reductase and AGE-RAGE pathways: central roles in the pathogenesis of vascular dysfunction in aging rats

Aging is inevitably accompanied by gradual and irreversible innate endothelial dysfunction. In this study, we tested the hypothesis that accentuation of glucose metabolism via the aldose reductase (AR) pathway contributes to age-related vascular dysfunction. AR protein and activity levels were significantly increased in aged vs. young aortic homogenates from Fischer 344 rats. Immunostaining revealed that the principal site of increased AR protein was the aortic endothelium as well as smooth muscle cells. Studies revealed that endothelial-dependent relaxation (EDR) in response to acetylcholine was impaired in aged rats compared to young rats and that treatment with the AR inhibitor (ARI) zopolrestat significantly improved EDR in aged rats. Methylglyoxal (MG), a key precursor of advanced glycation endproducts (AGEs), was significantly increased in the aortas of aged rats vs. young rats. Consistent with central roles for AR in generation of MG in aging, ARI treatment significantly reduced MG levels in aged rat aorta to those in young rats. Treatment of aged rats with soluble(s) RAGE, a soluble form of the chief signal transduction receptor for AGEs, RAGE, significantly improved EDR in aged rats, thus establishing the contribution of age-related increases in AGEs to endothelial dysfunction. These findings reveal that significant increases in AR expression and activity in aged rat vasculature linked to endothelial dysfunction may be mitigated, at least in part, via ARI and that aging-linked increased flux via AR generates AGEs; species which transduce endothelial injury consequent to their interaction with RAGE. These data demonstrate for the first time that AR mediates aging-related vascular dysfunction, at least in part, via RAGE.

Sevoflurane does not alter norepinephrine-induced intracellular Ca²(+) changes in the diabetic rat aorta

PURPOSE

The effect of volatile anesthetics on the mechanism(s) of vascular contraction in diabetes mellitus (DM) has not been fully understood. The current study was designed to determine the effects of sevoflurane on the norepinephrine (NE)-induced changes in contractile state and intracellular Ca²(+) concentrations ([Ca²(+)](i)) in the spontaneously developing type 2 DM rat.

METHODS

The effects of sevoflurane on NE (10⁻⁶M)-induced vasoconstriction and increase in [Ca²(+)](i) in the aortas from Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a type 2 DM model, and from age-matched control Long-Evans Tokushima Otsuka (LETO) rats were investigated using an isometric force transducer and fluorometer with fura-2 as an indicator of [Ca²(+)](i).

RESULTS

Norepinephrine-induced increases in tension and [Ca²(+)](i) in OLETF rats were 54.8%, 95% confidence interval (CI) 36.9-72.6% and 58.8%, 95% CI 51.5-66.1%, respectively, and in LETO rats they were 46.4%, 95% CI 39.0-53.7% and 53.8%, 95% CI 46.9-60.7%, respectively, when expressed as the percentage relative to that induced by KCl 30 mM. In LETO rats, sevoflurane at a concentration of 3.4% inhibited the vascular contraction (9.4%, 95% CI 6.3-12.6%; P < 0.001) and the increase in [Ca²(+)](i) (33.3%, 95% CI 27.4-39.2%; P = 0.002). In OLETF rats, however, sevoflurane failed to affect either the NE-induced contraction (43.6%, 95% CI 28.3-58.9%; P = 0.68) or the elevation in [Ca²(+)](i) (60.5%, 95% CI 56.3-64.8%; P = 0.93).

CONCLUSION

Sevoflurane at clinically relevant concentrations inhibited the NE-induced increase in [Ca²(+)](i) in the aortic smooth muscle from normal rats but not in that from type 2 DM rats. Thus, a Ca²(+)- signalling pathway resistant to sevoflurane appears to exist in the type 2 DM rat aorta.

Sciatic nerve of diabetic rat treated with epoetin delta: effects on C-fibers and blood vessels including pericytes

In diabetes mellitus (DM) reduced motor and sensory properties of peripheral nerves are linked with the dysfunction of neural vasculature. We investigated C-fibers and microvessels of sciatic nerve of normal, DM, and DM + epoetin delta-treated rats. C-fibers immunoreactive for calcitonin gene-related peptide (CGRP), tyrosine hydroxylase (TH), epoetin receptor (EpoR), and common beta receptor subunit of the interleukin 3 receptor (IL-3Rbeta) were present in all rats, whereas in DM and epoetin-treated rats C-fibers also showed neuronal (nNOS) and inducible (iNOS) nitric oxide synthases. The cross-sectional area of CGRP-positive C-fibers was decreased in DM, but it recovered after epoetin treatment. In all conditions, vascular endothelium showed scarce immunolabeling for endothelial nitric oxide synthase (eNOS); the profound immunoreactivity for eNOS, EpoR, and IL-3Rbeta was in pericytes. Some perivascular autonomic nerves were damaged and IL-3Rbeta positive. Findings are discussed in terms of declined sensory conduction velocity in DM, its improvement after epoetin treatment, and the possible vascular contribution to these phenomena.

Effect of L-arginine on the microcirculation in the neuropathic diabetic foot in Type 2 diabetes mellitus: a double-blind, placebo-controlled study

OBJECTIVE

To investigate the effect of L-arginine on endothelial function, transcutaneous oxygen and clinical neuropathy in patients with peripheral neuropathy as a result of diabetes.

RESEARCH DESIGN AND METHODS

Thirty diabetic patients with peripheral neuropathy were randomized to receive L-arginine (3 g three times daily) or placebo (3 g three times daily) for 3 months. All patients had foot microcirculation and foot transcutaneous oxygen pressure (TcPO(2)), neuropathy disability score (NDS) and vibration perception threshold (VPT) assessed at baseline and follow-up.

RESULTS

No difference was observed in endothelium-dependent and -independent vasodilation, TcPO(2), NDS and VPT.

CONCLUSIONS

L-arginine has no effect on endothelial dysfunction, TcPO(2) and clinical neuropathy.

The endothelium of basilar artery of diabetic rat treated with epoetin delta

Erythropoiesis-stimulating agents (ESAs) are used to treat anemia associated with renal failure. It is now known that these agents also show a broad range of cell- and tissue-protective effects. In the current study, we explored whether an ESA, epoetin delta, affects vascular pathology linked to diabetes mellitus (DM). In a rat model of streptozotocin-induced DM, we investigated, by pre-embedding electron-immunocytochemistry, whether epoetin delta affects DM-induced structural changes in cerebrovascular endothelium of the rat basilar artery and influences the subcellular distribution of endothelial nitric oxide synthase (eNOS). Epoetin delta treatment influenced DM-induced changes to the distribution of eNOS in, and the structure of, the endothelial cell. This may indicate potential beneficial effects of epoetin delta on cerebrovascular endothelium and suggests eNOS as a possible target molecule of epoetin delta in DM.

Ionizing non-fatal whole-body irradiation inhibits Ca2+-dependent K+channels in endothelial cells of rat coronary artery: Possible contribution to depression of endothelium-dependent vascular relaxation

PURPOSE

The goal of this study was to evaluate the influence of ionizing irradiation on large conductance Ca2+-dependent potassium (BKCa) channels in rat coronary endothelial cells.

MATERIALS AND METHODS

Rats were exposed to a 6 Gy dose from a cobalt60 source. Experimental design of this study comprised recording of contractile force using isolated rat aortic rings and whole-cell patch clamp techniques to study whole-cell potassium currents in isolated rat coronary artery endothelial cells.

RESULTS

It has been shown that outward potassium currents in endothelial cells 9 days after irradiation appear to be suppressed or even totally abolished. The reversal potential for these currents in irradiated cells was shifted to more positive values. Paxilline (500 nM), an inhibitor of BKCa channels, had no or only a negligible effect on irradiated cells. The experiments using isolated aortic rings demonstrated that both paxilline and irradiation significantly shifted the acetylcholine dependent concentration-relaxation response curve to the right. Irradiated tissues were insensitive to paxilline.

CONCLUSION

The results suggest that non-fatal, whole-body gamma-irradiation suppresses large conductance, calcium-activated potassium channels, which control the driving force for Ca2+ entry and therefore Ca2+ dependent nitric oxide (NO) synthesis in endothelial cells. This may contribute, in part, to radiation-induced endothelium dysfunction and an increase in arterial blood pressure.

Effects of streptozotocin-induced diabetes on the pharmacology of rat conduit and resistance intrapulmonary arteries

Background

Poor control of blood glucose in diabetes is known to promote vascular dysfunction and hypertension. Diabetes was recently shown to be linked to an increased prevalence of pulmonary hypertension. The aim of this study was to determine how the pharmacological reactivity of intrapulmonary arteries is altered in a rat model of diabetes.

Methods

Diabetes was induced in rats by the β-cell toxin, streptozotocin (STZ, 60 mg/kg), and isolated conduit and resistance intrapulmonary arteries studied 3–4 months later. Isometric tension responses to the vasoconstrictors phenylephrine, serotonin and PGF_2α, and the vasodilators carbachol and glyceryl trinitrate, were compared in STZ-treated rats and age-matched controls.

Results

STZ-induced diabetes significantly blunted the maximum response of conduit, but not resistance pulmonary arteries to phenylephrine and serotonin, without a change in pEC₅₀. Agonist responses were differentially reduced, with serotonin (46% smaller) affected more than phenylephrine (32% smaller) and responses to PGF_2α unaltered. Vasoconstriction caused by K⁺-induced depolarisation remained normal in diabetic rats. Endothelium-dependent dilation to carbachol and endothelium-independent dilation to glyceryl trinitrate were also unaffected.

Conclusion

The small resistance pulmonary arteries are relatively resistant to STZ-induced diabetes. The impaired constrictor responsiveness of conduit vessels was agonist dependent, suggesting possible loss of receptor expression or function. The observed effects cannot account for pulmonary hypertension in diabetes, rather the impaired reactivity to vasoconstrictors would counteract the development of pulmonary hypertensive disease.

Impairment of endothelium-dependent ACh-induced relaxation in aorta of diabetic db/db mice--possible dysfunction of receptor and/or receptor-G protein coupling

Diabetes is a risk factor of ischemic heart disease, cerebral ischemia, and atherosclerosis, in which endothelial dysfunction plays a role in the pathogenesis. We examined vascular responses in the aorta of pre-diabetic db/db mice with normoglycemia, hyperlipidemia, and hyperinsulinemia (6 weeks old), and diabetic db/db mice with hyperglycemia, hyperlipidemia, and hyperinsulinemia (11 weeks old) in comparison with age-matched non-diabetic db/+ mice. Prostaglandin F2alpha (PGF2alpha)-induced contraction was significantly enhanced in the aorta of diabetic but not pre-diabetic db/db mice compared to age-matched non-diabetic db/+ mice. Acetylcholine (ACh), adenosine-5'-diphosphate (ADP), NaF, a G protein activator and A-23187, a Ca-ionophore, caused endothelium-dependent and nitric oxide (NO)-mediated relaxation, and sodium nitroprusside (SNP), an NO donor, caused endothelium-independent relaxation in the pre-contracted aorta of db/db mice. Maximal endothelium-dependent ACh-induced relaxation was reduced in diabetic but not pre-diabetic db/db mice compared to age-matched db/+ mice, while maximal SNP-induced relaxation was not different between diabetic and non-diabetic mice. ACh-induced relaxation in diabetic db/db mice was not affected by ozagrel, a thromboxane A2 (TXA2) synthetase inhibitor, or acetylsalicylic acid (aspirin), a cyclooxygenase inhibitor, suggesting no involvement of endogenous TXA2 or prostanoids in the reduction of relaxation. Maximal endothelium-dependent ADP-, A-23187-, and NaF-induced relaxation was not reduced in diabetic db/db mice. EC50 values for ACh- and SNP-induced relaxation were increased in diabetic but not pre-diabetic db/db mice, suggesting decreases in sensitivity to NO in diabetic mice. Two-week treatment with KV-5070, a PPARgamma agonist, lowered plasma glucose, triglyceride (TG), and insulin but not cholesterol, and reversed the reduced ACh-induced relaxation. In conclusion, ACh-induced endothelium-dependent relaxation is impaired in diabetic db/db mice, probably due to the dysfunction of ACh receptors and/or receptor-G protein coupling. Endothelial dysfunction was not genetic and was considered to be initiated primarily by hyperglycemia, and was improved by anti-diabetic treatment with a PPARgamma agonist.

Diabetic complications and dysregulated innate immunity

Diabetes mellitus is a metabolic disorder that leads to the development of a number of complications. The etiology of each diabetic complication is undoubtedly multifactorial. We will focus on one potential component that may be common in many diabetic complications, dysregulation of innate immunity associated with an increased inflammatory response. High glucose levels lead to shunting through the polyol pathway, an increase in diacylglycerol which activates protein kinase C, an increase in the release of electrons that react with oxygen molecules to form superoxides, and the non-enzymatic glycosylation of proteins that result in greater formation of advanced glycation end products. Each of these can lead to aberrant cell signalling that affects innate immunity for example, by activating the MAP kinase pathway or inducing activation of transcription factors such as NF-kappaB. This may be a common feature of several complications including periodontal disease, atherosclerosis, nephropathy, impaired healing and retinopathy. These complications are frequently associated with increased expression of inflammatory cytokines such as TNF-alpha, IL-1beta and IL-6 and enhanced generation of reactive oxygen species. Cause and effect relationship between dysregulation of key components of innate immunity and diabetic complications in many instances have been demonstrated with the use of cytokine blockers and antioxidants.

Time-dependent alteration in cromakalim-induced relaxation of corpus cavernosum from streptozocin-induced diabetic rats

The purpose of the present study was to investigate the relaxant responses to the ATP-sensitive potassium (K(ATP)) channel opener cromakalim in corpus cavernosum strips from 1-, 2-, 4-, 6-, and 8-week streptozocin-induced diabetic rats. Cromakalim (1 nM-0.1 mM) produced concentration-dependent relaxation in phenylephrine (7.5 microM)-precontracted isolated rat corporal strips. Compared with age-matched control animals, a significant enhancement in cromakalim-induced relaxation of corpus cavernosum was observed in 2-week diabetic animals, whereas the relaxant responses to cromakalim were decreased in 6-and 8-week diabetic animals. However, the cromakalim-induced relaxation was not altered in either 1-week or 4-week rat corporal strips in comparison with corresponding age-matched non-diabetic groups. Preincubation with the K(ATP) channel blocker glibenclamide (10 microM) significantly inhibited the cromakalim-induced relaxation in both non-diabetic and diabetic rat corpus cavernosum, but neither the voltage-dependent K(+) channel (K(V)) antagonist 4-aminopyridine (1 mM) nor the calcium-activated K(+) channel (K(Ca)) antagonist charybdotoxin (0.1 microM) had significant effect on cromakalim-induced relaxation in both control and diabetic rat corporal strips. Relaxation responses to the nitric oxide donor sodium nitroprusside (1 nM-0.1 mM) in diabetic rat corpus cavernosum were similar to that of age-matched controls. These data demonstrated that the relaxant responses to cromakalim were altered in diabetic cavernosal strips in a time dependent manner, suggesting that the period of diabetes mellitus may play a key role in the K(ATP) channels function in rat corpus cavernosum.

The calcium ionophore A23187 induces endothelium-dependent contractions in femoral arteries from rats with streptozotocin-induced diabetes

BACKGROUND AND PURPOSE

To study the importance of endothelium-derived contracting factors (EDCFs) in arteries of rats with type I diabetes.

EXPERIMENTAL APPROACH

Rat femoral arteries were collected four or twelve weeks after induction of diabetes with streptozotocin. Rings, with or without endothelium, were suspended in organ chambers for isometric tension measurement. COX protein levels were determined by Western blotting.

KEY RESULTS

Four weeks after the injection of streptozotocin, the endothelium-dependent relaxations (during contractions to phenylephrine) to A23817 were attenuated, but the endothelium-dependent contractions (quiescent preparations) to the ionophore were augmented. Indomethacin and S18886 prevented the endothelium-dependent contractions, while dazoxiben reduced them in rings from streptozotocin-treated rats, suggesting that thromboxane A2, activating TP- receptors, is involved. Twelve weeks after the injection of streptozotocin, the changes in endothelium-dependent relaxations and contractions to A23187 were even more noticeable. The protein expression of COX-1 was increased in femoral arteries of the diabetic rats. Valeryl salicylate and SC560 inhibited the contractions, suggesting that the EDCFs are produced by COX-1. At that time, a combination of S18886 with EP1-blockers was required to abolish the contractions, suggesting that the EDCFs involved act at both TP- and EP-receptors. Rings without endothelium from streptozotocin-treated rats exhibited a reduced maximal contraction to potassium chloride and U46619, combined with hyper-responsiveness to the latter, suggesting that more prolonged diabetes also alters the responsiveness of vascular smooth muscle.

CONCLUSION AND IMPLICATIONS

The production of EDCFs is progressively increased in the course of type I diabetes. Eventually, the disease also damages vascular smooth muscle.

Treatment with the xanthine oxidase inhibitor, allopurinol, improves nerve and vascular function in diabetic rats

Several putative sources of reactive oxygen species could potentially contribute to diabetic neuropathy and vasculopathy. The aim was to assess the involvement of elevated xanthine oxidase activity. After 6 weeks of streptozotocin-diabetes, groups of rats were given 2 weeks of high-dose allopurinol treatment (50 and 250 mg/kg) to gauge the effect of maximal blockade of xanthine oxidase. In the final experiments, rats were subjected to sensory testing and, under butabarbital anaesthesia, measurements were made on nerve conduction velocities and neural tissue blood flow estimated by hydrogen clearance microelectrode polarography. Further groups were used to study detailed responses of the isolated mesenteric vascular bed after 4 weeks of diabetes and allopurinol (150 mg/kg) treatment. Diabetes caused 20% and 14% reduction in motor and sensory conduction velocity, which were 78% and 81% corrected by allopurinol treatment respectively, both doses giving similar results. Diabetic rats showed tactile allodynia and thermal hyperalgesia, which were completely corrected by allopurinol, whereas mechanical hyperalgesia was only 45% ameliorated. Sciatic nerve and superior cervical ganglion blood flow was halved by diabetes and allopurinol corrected this by approximately 63%. Mesenteric endothelium-dependent vascular responses to acetylcholine, which depend upon nitric oxide and endothelium derived hyperpolarizing factor, were attenuated by diabetes. Allopurinol treatment gave approximately 50% protection for both components. Thus, xanthine oxidase is an important source of reactive oxygen species that contributes to neurovascular dysfunction in experimental diabetes. Inhibition of xanthine oxidase could be a potential therapeutic approach to diabetic neuropathy and vasculopathy.

Alteration of aortic function from streptozotocin-diabetic rats with Kilham’s virus is associated with inducible nitric oxide synthase

Kilham's rat virus (KRV) is a parvovirus commonly known to affect laboratory rats. Qualitative immunohistochemical analysis revealed that aorta isolated from KRV-infected streptozotocin (STZ)-induced diabetic adult rats expressed markedly greater levels of inducible nitric oxide synthase (iNOS) than aorta from KRV-infected controls. In contrast with the prevailing literature, nitric oxide-mediated endothelium-dependent relaxation to acetylcholine was not blunted by STZ-diabetes, but was comparable to relaxations of aorta from controls. However, with increasing ex vivo duration, a decreased response to acetylcholine was observed in the STZ-diabetic aorta. In addition, whereas contraction responses to phenylephrine were not significantly altered over time in control tissue, aorta from STZ-diabetic rats developed increased tensions. The data suggest that increased iNOS-derived nitric oxide masks expected acetylcholine-mediated relaxation deficits as a result of KRV-infection, and that the deficit is unmasked by iNOS turnover ex vivo.

The role of polyol pathway in high glucose-induced endothelial cell damages

To clarify the mechanism by which hyperglycemia in diabetes mellitus causes endothelial cell damages, the effects of high glucose on DNA fragmentation and caspase-3 activity of cultured endothelial cells and on the generation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) were studied. Furthermore, the involvement of the polyol pathway in this process was investigated using aldose reductase inhibitor (SNK-860). Human umbilical vein endothelial cells (HUVECs) were incubated with 5.5mmol/L (low glucose medium) or 28mmol/L (high glucose medium) of glucose. The amounts of fragmented DNA, caspase-3 activity and 8-OHdG in the medium increased in significantly greater extent in high glucose-incubated HUVECs than in low glucose-incubated HUVECs. No significant increase in fragmented DNA or 8-OHdG was observed when HUVECs were incubated with mannitol (500mg/mL). The concentration of intracellular sorbitol was significantly higher in HUVECs incubated in high glucose medium than that in low glucose medium. Addition of the aldose reductase inhibitor SNK-860 dose-dependently decreased the intracellular sorbitol concentration in HUVECs incubated in high glucose medium, and also significantly suppressed the increases in fragmented DNA, caspase-3 activity and 8-OHdG by conditioning with high glucose medium. These results suggest that high glucose-induced endothelial cell damages may be mediated by activation of the polyol pathway accompanied by augmented oxidative stress.

The effects of age and streptozotocin diabetes on the sympathetic innervation in the rat penis

The objective was to describe the changes in catecholamine levels, noradrenaline (NA) release and the ultrastructural and immunohistochemical changes in the sympathetic nerves in the penis of STZ-diabetic rats. Amines were measured using HPLC. Nerves were studied using immunocytochemistry for tyrosine hydroxylase, and electron microscopy. Diabetic animals were compared with age-matched controls. The concentration of penile NA increases at least 2.5-fold after about 10 weeks of hyperglycaemia, is maintained for over 40 weeks. The rate of release of NA in the diabetics also increases approximately by fourfold. Immunohistochemical staining for tyrosine hydroxylase showed either no change or an increase in the levels of the enzyme around the central arteries and the outer coverings of the corpus cavernosum. Cavernosal nerves show increased intensity of staining for tyrosine hydroxylase, and the presence of dilated nerve fibres and engorged endings. The axons of the dorsal nerve of the diabetic penis have a smaller cross-sectional area that is most marked in unmyelinated axons. In the diabetic penis, the nerve endings appear to contain significantly more NA than the controls, and the turnover of noradrenaline is increased substantially. There is immunocytochemical evidence of an increase in staining for tyrosine hydroxylase, suggesting an increase in synthetic activity. These results are discussed in relation to the existing literature on the role of amines in normal and disordered erectile function. In particular, the increased concentration and turnover of NA in the diabetic rat contrasts with the fall in NA in cavernosal blood described during normal erection in humans.

Diabetic neuropathy and oxidative stress

This review will focus on the impact of hyperglycemia-induced oxidative stress in the development of diabetes-related neural dysfunction. Oxidative stress occurs when the balance between the production of reactive oxygen species (ROS) and the ability of cells or tissues to detoxify the free radicals produced during metabolic activity is tilted in the favor of the former. Although hyperglycemia plays a key role in inducing oxidative stress in the diabetic nerve, the contribution of other factors, such as endoneurial hypoxia, transition metal imbalances, and hyperlipidemia have been also suggested. The possible sources for the overproduction of ROS in diabetes are widespread and include enzymatic pathways, auto-oxidation of glucose, and mitochondrial superoxide production. Increase in oxidative stress has clearly been shown to contribute to the pathology of neural and vascular dysfunction in diabetes. Potential therapies for preventing increased oxidative stress in diabetic nerve dysfunction will be discussed.

Correction of endothelial dysfunction in diabetic female rats by tetrahydrobiopterin and chronic insulin

Diabetes-induced vascular dysfunction has mainly been studied in males. However, the mechanisms involved may not correspond to those in females. Here we analyzed the effects of tetrahydrobiopterin (BH(4)) and chronic insulin on the physiology of mesenteric arterioles of alloxan-diabetic female rats. The parameters studied were the mesenteric arteriolar reactivity (intravital microscopy), nitric oxide synthase (NOS) activity (conversion of L-arginine to L-citrulline), eNOS gene expression (RT-PCR), NO production (diaminofluorescein), reactive oxygen species (ROS) generation (intravital fluorescence microscopy) and Cu/Zn superoxide dismutase (SOD) activity (spectrophotometry) and gene expression (RT-PCR). The reduced endothelium-dependent vasodilation of diabetic females was corrected by both BH(4) and insulin. NOS activity was decreased by diabetes, but insulin did not correct it. However, NOS expression was not modified by either diabetes or insulin. Arterioles of diabetic rats exhibited lower NO production, which was fully corrected by BH(4) and only partially by insulin. ROS generation was increased in diabetic rats, and both BH(4) and insulin normalized it. Diabetes did not change SOD activity and gene expression. However, insulin increased SOD activity but not its expression. Our data suggest that, similarly to males, endothelial dysfunction in female diabetic rats involves an altered ROS/NO imbalance. In contrast to males, however, insulin does not regulate NOS in the microcirculation of diabetic females.

Aldose reductase pathway inhibition improved vascular and C-fiber functions, allowing for pressure-induced vasodilation restoration during severe diabetic neuropathy

Pressure-induced vasodilation, a neurovascular mechanism relying on the interaction between mechanosensitive C-fibers and vessels, allows skin blood flow to increase in response to locally nonnociceptive applied pressure that in turn may protect against pressure ulcers. We expected that severe neuropathy would dramatically affect pressure-induced vasodilation in diabetic mice, and we aimed to determine whether pressure-induced vasodilation alteration could be reversed in 8-week diabetic mice. Control and diabetic mice received no treatment or sorbinil, an aldose reductase inhibitor, or alagebrium, an advanced glycation end product breaker, the last 2 weeks of diabetes. Laser Doppler flowmetry was used to evaluate pressure-induced vasodilation and endothelium-dependent vasodilation after iontophoretic delivery of acetylcholine (ACh). We assessed the nervous function with measurements of motor nerve conduction velocity (MNCV) as well as the C-fiber-mediated nociception threshold. Pressure-induced vasodilation, endothelial response, C-fiber threshold, and MNCV were all altered in 8-week diabetic mice. None of the treatments had a significant effect on MNCV. Although sorbinil and alagebrium both restored ACh-dependent vasodilation, sorbinil was the sole treatment to restore the C-fiber threshold as well as pressure-induced vasodilation development. Therefore, the inhibition of aldose reductase pathway by sorbinil improved vascular and C-fiber functions that allow pressure-induced vasodilation restoration that could limit neuropathic diabetic cutaneous pressure ulcers.

L-Arginine Supplementation Prevents the Development of Endothelial Dysfunction in Hyperglycaemia

Diabetes mellitus leads to the development of endothelial dysfunction which finally contributes to diabetic angiopathy. We investigated the effects of hyperglycaemia on nitric oxide (NO) liberation and a possible influence of L-arginine supplementation. Porcine endothelial aortic cells (PAEC) were cultured in Medium 199 containing 0.33 mmol/l L-arginine. During the entire third culture passage (= 4 days) cells were either exposed to 5 or 20 mmol/l D-glucose with or without additional 3 mmol/l L-arginine. For osmotic control, cells were exposed to 15 mmol/l mannitol. NO liberation was measured under basal conditions and after stimulation with 1 mmol/l ATP using the spectrophotometrical methemoglobin assay. Cells released 35 +/- 8 pmol NO/1 x 10(6) cells/10 min under basal conditions while hyperglycaemia led to a significant reduction in NO release to 16 +/- 6 pmol/1 x 10(6) cells/10 min. In osmotic control, NO release was unchanged (37 +/- 10 pmol/1 x 10(6) cells/10 min). Stimulation with 1 mmol/l ATP led to a significant increase in NO release to 103 +/- 11 pmol/1 x 10(6) cells/10 min (normoglycaemia) which was unchanged in osmotic controls. Under normoglycaemic conditions, additional L-arginine supplementation did not influence NO release from PAEC. In hyperglycaemia (0.33 mmol/l L-arginine) ATP stimulated NO release was reduced (48 +/- 8 pmol/1 x 10(6) cells/10 min, p < 0.05), which was completely prevented by 3 mmol/l L-arginine treatment (98 +/- 15 pmol/ 1 x 10(6) cells/10 min). Hyperglycaemia (but not enhanced osmotic pressure) leads to endothelial dysfunction with reduced NO release which is completely prevented by L-arginine. L-Arginine utilisation may be impaired in hyperglycaemia and L-arginine supplementation might be an interesting additional therapeutic tool in diabetic patients.

Chronic treatment with vascular endothelial growth factor preserves agonist-evoked vascular responses in the streptozotocin-induced diabetic rat

AIMS/HYPOTHESIS

Vascular dysfunction is a hallmark of diabetes mellitus and endothelial dysfunction is considered to be a key early component of vascular dysfunction. Attenuated agonist-evoked responses are considered to be a barometer of endothelial/vascular dysfunction. We sought to determine whether vascular endothelial growth factor (VEGF) could prevent dysfunction from developing in the streptozotocin (STZ)-induced rat model of type 1 diabetes.

MATERIALS AND METHODS

One week after induction of diabetes, STZ rats began a 4-week treatment protocol of twice-weekly i.v. injections of 2 microg VEGF or inactivated VEGF. Corresponding non-diabetic rats served as controls. Agonist-evoked vascular responses were recorded 1 day after the last treatment in anaesthetised rats.

RESULTS

Acetylcholine (0.1-12.5 microg/kg) evoked increases in superior mesenteric arterial conductance and decreases in mean blood pressure, while methoxamine (12.5-100 microg/kg) and endothelin-1 (100-1,200 pmol/kg) evoked decreases in superior mesenteric arterial conductance and increases in mean blood pressure. These responses to all three agonists were attenuated in STZ rats, and chronic treatment with VEGF improved these responses dramatically. Both the reduction in plasma nitrate and nitrite and the elevation in aortic superoxide associated with STZ diabetes were normalised with VEGF treatment. VEGF also prevented the apparent paradoxical increased endothelial nitric oxide synthase expression seen in untreated STZ rats.

CONCLUSIONS/INTERPRETATION

Chronic treatment with VEGF early in diabetes is able to prevent the attenuated agonist-evoked vascular responses in STZ rats and normalise the oxidative environment associated with the disease.

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.

Effect of Glucagon-Like Peptide-1(7–36) and Exendin-4 on the Vascular Reactivity in Streptozotocin/Nicotinamide-Induced Diabetic Rats

We investigated the vascular effects of glucagon-like peptide-1 (GLP-1) and Exendin-4 in type 2 diabetic rat aortae. Studies were performed in a normal control group (NC) (0.2 ml i.p. saline, n = 10), streptozotocin (STZ)/nicotinamide diabetic control group (DC) (a single dose of 80 mg/kg STZ i.p. injection 15 min after administration of 230 mg/kg nicotinamide i.p.), GLP-1 (GLPC) control group (1 microg/kg twice daily i.p. for 1 month, n = 10), Exendin-4 control group (EXC) (0.1 microg/kg twice daily i.p. for 1 month, n = 10), GLP-1-treated diabetic group (GLPT) (1 microg/kg twice daily i.p. for 1 month, n = 10), and Exendin-4-treated diabetic group (EXT) (0.1 microg/kg twice daily i.p. for 1 month, n = 10). One month of GLP-1 and Exendin-4 treatment significantly decreased the blood glucose levels of diabetic rats (113 +/- 2 mg/dl, p < 0.001, and 117 +/- 1 mg/dl, p < 0.001, respectively versus 181 +/- 9 mg/dl in the DC group). Sensitivity (pD2) and maximum response (% Max. Relax) of acetylcholine-stimulated relaxations in the DC group (pD2: 6.73 +/- 0.12 and 55 +/- 6, respectively) were decreased compared with the non-diabetic NC group (pD2: 7.41 +/- 0.25, p < 0.05, and 87 +/- 4, p < 0.01). Treating diabetic rats with GLP-1, pD2 values and with Exendin-4, Max. Relax %values of aortic strips to acetylcholine returned to near non-diabetic NC values (pD2: 7.47 +/- 0.15, p < 0.05, and 87 +/- 3, p < 0.01, respectively). Maximal contractile responses (Emax) to noradrenaline in aortic strips from the diabetic DC group (341 +/- 27 mg tension/mg wet weight) were significantly decreased compared with the non-diabetic NC (540 +/- 66 mg tension/mg wet weight, p < 0.001) and the GLPT group (490 +/- 25 mg tension/mg wet weight, p < 0.05). There were no significant differences in pD2 values of aortic strips to noradrenaline from all groups. Emax to KCl in aortic strips from the DC group (247 +/- 10 mg tension/mg wet weight, p < 0.01) was significantly decreased compared with non-diabetic NC group (327 +/- 26 mg tension/mg wet weight). Treating diabetic rats with GLP-1 (GLPT), Emax values of aortic strips to KCl returned to near non-diabetic NC values (271 +/- 12 mg tension/mg wet weight). GLP-1 and (partially) Exendin-4 treatment could improve the increased blood glucose level and normalize the altered vascular tone in type 2 diabetic rats.

Calcium dobesilate attenuates vascular injury and the progression of diabetic retinopathy in streptozotocin-induced diabetic rats

BACKGROUND

Diabetic retinopathy (DR) is a highly specific vascular complication of type 1 and type 2 diabetes mellitus. Calcium dobesilate (DOBE) has been tested in the treatment of diabetic retinopathy showing a slowdown of the progression of the disease after long-term oral treatment. The aim of this study was to determine the effects of DOBE on vascular and diabetic retinopathy in streptozotocin (STZ) diabetic rats.

METHODS

Diabetes was induced in wistar rats by the administration of STZ (60 mg/kg, i.p.). Rats were divided into three groups (n = 30). Group 0 (GO): nondiabetic rats. Group 1 (G1): 14 months of insulin treatment after diabetes development. Group 2 (G2): 14 months of insulin treatment after diabetes development plus DOBE (500 mg/kg/day). At the end of the treatment, vascular reactivity was tested. The study of the vascularization of the retina was performed on wholemounts of trypsin retinal digest preparations and retinal sections.

RESULTS

Relaxation induced by acetylcholine decreased in the aorta arteries from diabetic rats but it was restored to control values in the DOBE-treated group (71.8 +/- 4.5%, 53.3 +/- 0.5%, 67.4 +/- 4.6% in group 0, 1 and 2 respectively). DOBE treatment also restored noradrenaline (1.08 +/- 0.05 g, 1.70 +/- 0.08 g, 1.13 +/- 0.05 g in group 0, 1 and 2 respectively) and caffeine-induced contractions. Diabetic state did not cause any alteration in mesenteric arteries. The analysis of the retinal digests showed vascular tortuosity, acellular capillaries, focal accumulations of capillaries and reduction of the number of pericytes in G1. The vascular changes observed in G2 seem to be intermediate between the control and the diabetic rats.

CONCLUSIONS

We showed that long-term treatment with DOBE attenuated the progression of diabetic retinopathy and the alterations in vascular reactivity in streptozotocin-induced diabetic rats.

C-peptide corrects endoneurial blood flow but not oxidative stress in type 1 BB/Wor rats

Oxidative stress and neurovascular dysfunction have emerged as contributing factors to the development of experimental diabetic neuropathy (EDN) in streptozotocin-diabetic rodents. Additionally, depletion of C-peptide has been implicated in the pathogenesis of EDN, but the mechanisms of these effects have not been fully characterized. The aims of this study were therefore to explore the effects of diabetes on neurovascular dysfunction and indexes of nerve oxidative stress in type 1 bio-breeding Worcester (BB/Wor) rats and type 2 BB Zucker-derived (ZDR)/Wor rats and to determine the effects of C-peptide replacement in the former. Motor and sensory nerve conduction velocities (NCVs), hindlimb thermal thresholds, endoneurial blood flow, and indicators of oxidative stress were evaluated in nondiabetic control rats, BB/Wor rats, BB/Wor rats with rat II C-peptide replacement (75 nmol C-peptide.kg body wt(-1).day(-1)) for 2 mo, and diabetes duration-matched BBZDR/Wor rats. Endoneurial perfusion was decreased and oxidative stress increased in type 1 BB/Wor rats. C-peptide prevented NCV and neurovascular deficits and attenuated thermal hyperalgesia. Inhibition of nitric oxide (NO) synthase, but not cyclooxygenase, reversed the C-peptide-mediated effects on NCV and nerve blood flow. Indexes of oxidative stress were unaffected by C-peptide. In type 2 BBZDR/Wor rats, neurovascular deficits and increased oxidative stress were unaccompanied by sensory NCV slowing or hyperalgesia. Therefore, nerve oxidative stress is increased and endoneurial perfusion decreased in type 1 BB/Wor and type 2 BBZDR/Wor rats. NO and neurovascular mechanisms, but not oxidative stress, appear to contribute to the effects of C-peptide in type 1 EDN. Sensory nerve deficits are not an inevitable consequence of increased oxidative stress and decreased nerve perfusion in a type 2 diabetic rodent model.

Alterations in vascular endothelial function in the aorta and mesenteric artery in type II diabetic rats

We used the partial protection exerted by suitable dosages of nicotinamide against the β-cytotoxic effect of streptozotocin (STZ) to create an experimental diabetic syndrome in adult rats that appears closer to type II diabetes mellitus than other available animal models. The dosage of 230 mg/kg of nicotinamide given intraperitoneally 15 min before STZ administration (65 mg/kg i.v.) yielded animals with hyperglycemia (187.8 ± 17.8 vs. 103.8 ± 2.8 mg/dL in controls; P < 0.001) and preservation of plasma insulin levels. This study assessed the relationship between endothelial dysfunction and agonist-induced contractile responses in such rats. In the thoracic aorta, the acetylcholine (ACh) induced relaxation was significantly reduced and the noradrenaline (NA) induced contractile response was significantly increased in diabetic rats compared with age-matched control rats. In the superior mesenteric artery, the ACh-induced relaxation was similar in magnitude between diabetic and age-matched control rats; however, the ACh-induced endothelium-derived hyperpolarizing factor (EDHF) type relaxation was significantly weaker in diabetic rats than in the controls. The phenylephrine (PE) induced contractile response was not different between the two groups. The plasma concentration of NOx (NO2– + NO3–) was significantly lower in diabetic rats than in control rats. We conclude that vasomotor activities in conduit arteries are impaired in this type II diabetes model.Key words: aorta, contraction, endothelium-derived hyperpolarizing factor, endothelium-mediated relaxation, mesenteric artery, type II diabetes.

Protein kinase C beta inhibition and aorta and corpus cavernosum function in streptozotocin-diabetic mice

Increased activity of the beta-isoform of protein kinase C (PKC) has been linked to the vascular and neural complications of diabetes mellitus. Treatment with the PKCbeta inhibitor, (s)-13-[(dimethylamino)methyl]-10,11,14,15-tetrahydro-4,9:16,21-dimetheno-1H,13H-dibenzo[e,k]pyrrolo[3,4-h][1,4,13]oxadiazacyclohexadecene-1,3(2H)-dione, (LY333531), improves somatic nerve function and blood flow in diabetic rats. The aim was to assess whether LY333531 treatment could prevent nitric oxide-dependent autonomic nerve and vascular dysfunction in a diabetic mouse model. Diabetes was induced by streptozotocin; duration was 4 weeks. Aorta and corpus cavernosum were isolated and mounted in organ baths and agonist or electrical stimulation-evoked nerve-mediated tension responses were examined. Maximum nitric oxide-mediated endothelium-dependent relaxation of phenylephrine-precontracted aorta and cavernosum to acetylcholine were more than 30% reduced by diabetes. LY333531 treatment (10 mg kg(-1) day(-1)) completely prevented the diabetic deficit in cavernosum, and 75% prevented the deficit in aorta. Maximum nitric oxide-dependent non-adrenergic, non-cholinergic (NANC) nerve-mediated relaxation of phenylephrine-precontracted cavernosum was approximately 43% reduced by diabetes; LY333531 attenuated the deficit by 44%. For diabetic aorta, but not cavernosum, sensitivity (EC50) to phenylephrine-mediated contraction was increased by approximately 0.85 log10 M units; LY333531 treatment completely prevented this effect. Thus, PKCbeta activation contributes to nitric oxide-dependent vascular and autonomic nerve dysfunction in diabetic mice and could prove suitable for further study in clinical trials of diabetic autonomic neuropathy and vasculopathy.

The effect of agmatine on the vascular reactivity in streptozotocin-diabetic rats

AIM

We investigated the vascular effects of agmatine (decarboxylated arginine=AGM), an endogenous ligand for alpha(2)-adrenoceptors and imidazoline receptors, present in endothelium and smooth muscle, using the diabetic rat aortae.

MATERIALS AND METHODS

Studies were performed in control group (0.2 ml i.p. saline, n=10), streptozotocin (STZ)-diabetic control group (60 mg kg(-1) STZ i.p., n=10), agmatine (AGM)-control group (5 mg kg(-1)day(-1) i.p. AGM for 1 month, n=10), citrate-control group (0.2 ml 0.01 M, n=10), insulin-treated diabetic group ((3 U kg(-1) NPH+1 U kg(-1) regular insulin) twice per day, for 1 month, n=10) and AGM-treated diabetic group (5 mg kg(-1)day(-1) i.p. for 1 month, n=10). All values are expressed as means+/-S.E.M. Statistical analysis of the data was performed using ANOVA followed by Tukey multiple comparisons test.

RESULTS

One-month AGM-treatment significantly decreased the blood glucose levels of diabetic rats (502+/-44 mg dl(-1) to 343+/-31 mg dl(-1), P<0.001). Fast, slow and total components of responses to noradrenaline in all the experimental groups were not significantly affected by AGM-treatment. AGM reversed the decreased responses of acetylcholine (pD(2) and Inh.%, P<0.001 and P<0.05) in diabetic rats although it did not affect the responses of sodium nitroprusside in all groups. The contraction values of KCl in all groups were not affected by AGM-treatment.

CONCLUSION

AGM-treatment could improve the increased blood glucose level, reverse the endothelial dysfunction and normalize the endothelium-dependent relaxation responses in STZ-diabetic rats.

Minalrestat and leukocyte migration in diabetes mellitus

BACKGROUND

We recently demonstrated that aldose reductase inhibition was effective in restoring the reduced migratory capacity of leukocytes in diabetic rats. To investigate the mechanism(s) involved in the restoring effect, we used minalrestat, an aldose reductase inhibitor.

METHODS

In sodium pentobarbital-anesthetized (40 mg/kg, intraperitoneally) alloxan-diabetic or galactosemic male Wistar rats, the internal spermatic fascia was exteriorized, and the number of leukocytes rolling along the venular endothelium and the number of leukocytes sticking to the vascular wall after topical application of zymosan-activated plasma or leukotriene B(4) (1 ng/ml), as well as after the application of a local irritant stimulus (carrageenan, 100 microg), were determined using intravital microscopy. Data from animals that were treated with and those that were not treated with minalrestat (10 mg/kg/d by gavage) were compared.

RESULTS

The reduced number of leukocytes rolling along the venular endothelium (by about 70%) and the number of adhered and migrated leukocytes in postcapillary venules (by 60%) were significantly restored to control values after minalrestat treatment. Total or differential leukocyte counts, venular blood flow velocity or wall shear rate were not altered by minalrestat treatment. The expression of ICAM-1 and P-selectin, cell adhesion molecules involved in the interaction of leukocyte-endothelium, reduced in diabetic rats was restored by minalrestat treatment.

CONCLUSION

We conclude that an enhanced flux through the polyol pathway might be involved in the reduced expression of ICAM-1 and P-selectin contributing to the impaired leukocyte-endothelial interactions in diabetes mellitus and that aldose reductase inhibition restores the defect, restoring the reduced expression.

Effect of chronic treatment with vitamin E on endothelial dysfunction in a type I in vivo diabetes mellitus model and in vitro

Diabetes mellitus often leads to generalized vasculopathy. Because of the pathophysiological role of free radicals we investigated the effects of vitamin E. Twenty-eight rats were rendered diabetic by streptozotocin injection and were fed either with a diet with low (10 mg/kg of chow), medium (75 mg/kg of chow) or high amounts of vitamin E (1300 mg/kg of chow). Nine age-matched nondiabetic rats receiving 75 mg of vitamin E/kg chow served as controls. After 7 months, mesenteric microcirculation was investigated. Smooth muscle contractile function was not altered in diabetic versus nondiabetic vessels. Endothelial function was significantly reduced in diabetics; relaxation upon 1 micro M acetylcholine was reduced by 50% in diabetics with a medium and high vitamin E diet. In vitamin E-deprived rats, a complete loss of endothelium-dependent relaxation was observed, and instead, acetylcholine elicited vasoconstriction. L-N(G)-Nitro-arginine-induced vasoconstriction was reduced in small arteries in diabetics, which was not prevented by vitamin E, but was aggravated by vitamin E deprivation. In a subchronic endothelial cell culture model, cells were cultivated with 5 or 20 mM D-glucose for an entire cell culture passage (4 days) with or without vitamin E (20 mg/l versus 0.01 mg/l). Hyperglycemia led to significant reduction in basal and ATP-stimulated nitric oxide (NO)-production. Hyperglycemia-induced reduction in basal NO-release was significantly prevented by vitamin E, whereas reduction in stimulated NO-release was not influenced. NADPH-diaphorase activity was reduced by 40% by hyperglycemia, which was completely prevented by vitamin E. We conclude that 1) vitamin E has a potential to prevent partially hyperglycemia-induced endothelial dysfunction, 2) under in vivo conditions vitamin E deficiency enhanced diabetic endothelial dysfunction dramatically, and 3) positive effects of vitamin E may be attenuated with a longer disease duration.

Minalrestat, an aldose reductase inhibitor, corrects the impaired microvascular reactivity in diabetes

We demonstrated that aldose reductase inhibition corrects the impaired microvascular responses to inflammatory mediators in diabetic rats. To study the mechanism involved in the restoring effect of aldose reductase inhibition, we examined the effects of minalrestat, another aldose reductase inhibitor, on the responses of mesenteric microvessels studied in vivo to permeability-increasing agents in diabetic and galactosemic rats. The diabetic group was treated from 3 days after the alloxan injection with minalrestat (10 mg/kg/day) for 30 days and the minalrestat treatment (10 mg/kg/day/7 days) of galactosemic rats started concomitantly with the induction of galactosemia. The mesenteric microvessel reactivity was studied using intravital microscopy and changes in vessel diameters were estimated after the topical application of vasoactive agents. The impaired responses to bradykinin, histamine, and platelet-activating factor of arterioles and venules observed in diabetic and galactosemic rats were completely prevented by minalrestat. Neither diabetes nor galactosemia affected responses to acetylcholine and sodium nitroprusside. Responses to these agents were not modified by aldose reductase inhibition. The restoring effect of minalrestat was reversed by inhibition of nitric oxide (NO) synthesis with N(omega)-nitro-L-arginine methyl ester, by blocking K(+) channel with tetraethylammonium but not by cyclooxygenase inhibition with diclofenac. Therefore, we concluded that NO, membrane hyperpolarization, but not cyclooxygenase products are involved in the beneficial effect of minalrestat on the microvascular reactivity in diabetes. Together, these findings led us to suggest that aldose reductase inhibition might ameliorate diabetic complications through the correction of the altered microvascular reactivity by a mechanism that involves NO and membrane hyperpolarization.

Diabetes mellitus impairs vasodilation to hypoxia in human coronary arterioles: reduced activity of ATP-sensitive potassium channels

ATP-sensitive K+ channels (K(ATP)) contribute to vasomotor regulation in some species. It is not fully understood the extent to which K(ATP) participate in regulating vasomotor tone under physiological and pathophysiological conditions in the human heart. Arterioles dissected from right atrial appendage were studied with video microscopy, membrane potential recordings, reverse transcription-polymerase chain reaction, and immunohistochemistry. Hypoxia produced endothelium-independent vasodilation and membrane hyperpolarization of vascular smooth muscle cells, both of which were attenuated by glibenclamide. Aprikalim, a selective K(ATP) opener, also induced a potent endothelium-independent and glibenclamide-sensitive vasodilation with membrane hyperpolarization. Reverse transcription-polymerase chain reaction detected mRNA expression for K(ATP) subunits, and immunohistochemistry confirmed the localization of the inwardly rectifying Kir6.1 protein in the vasculature. In patients with type 1 or type 2 diabetes mellitus (DM), vasodilation was reduced to both aprikalim (maximum dilation, DM(+) 90+/-2% versus DM(-) 96+/-1%, P<0.05) and hypoxia (maximum dilation, DM(+) 56+/-8% versus DM(-) 85+/-5%, P<0.01) but was not altered to sodium nitroprusside or bradykinin. Baseline myogenic tone and resting membrane potential were not affected by DM. We conclude that DM impairs human coronary arteriolar dilation to K(ATP) opening, leading to reduced dilation to hypoxia. This reduction in K(ATP) function could contribute to the greater cardiovascular mortality and morbidity in DM.