Antioxidative treatment reverses imbalances of nitric oxide synthase isoform expression and attenuates tissue-cGMP activation in diabetic rats

Long-term inorganic nitrate administration protects against myocardial ischemia-reperfusion injury in female rats

BACKGROUND

The favorable effects of nitrate against myocardial ischemia-reperfusion injury (MIRI) have primarily focused on male rats and in short term. Here we determine the impact of long-term nitrate intervention on baseline cardiac function and the resistance to MIRI in female rats.

METHODS

Female Wistar rats were randomly divided into untreated and nitrate-treated (100 mg/L sodium nitrate in drinking water for 9 months) groups (n = 14/group). At intervention end, levels of serum progesterone, nitric oxide metabolites (NOx), heart NOx concentration, and mRNA expressions of NO synthase isoforms (NOS), i.e., endothelial (eNOS), neuronal (nNOS), and inducible (iNOS), were measured. Isolated hearts were exposed to ischemia, and cardiac function indices (CFI) recorded. When the ischemia-reperfusion (IR) period ended, infarct size, NO metabolites, eNOS, nNOS, and iNOS expression were measured.

RESULTS

Nitrate-treated rats had higher serum progesterone (29.8%, P = 0.013), NOx (31.6%, P = 0.035), and higher heart NOx (60.2%, P = 0.067), nitrite (131%, P = 0.018), and eNOS expression (200%, P = 0.005). Nitrate had no significant effects on baseline CFI but it increased recovery of left ventricular developed pressure (LVDP, 19%, P = 0.020), peak rate of positive (+ dp/dt, 16%, P = 0.006) and negative (-dp/dt, 14%, P = 0.014) changes in left ventricular pressure and decreased left ventricular end-diastolic pressure (LVEDP, 17%, P < 0.001) and infarct size (34%, P < 0.001). After the IR, the two groups had significantly different heart nitrite, nitrate, NOx, and eNOS and iNOS mRNA expressions.

CONCLUSIONS

Long-term nitrate intervention increased the resistance to MIRI in female rats; this was associated with increased heart eNOS expression and circulating progesterone before ischemia and blunting ischemia-induced increased iNOS and decreased eNOS after MIRI.

Long-term Ovariectomy Reduces Tolerance of Rats to Myocardial Ischemia-reperfusion Injury

Background

The harmful impact of ovariectomy on myocardial ischemia-reperfusion (M/IR) injury has been established in the short term.

Objectives

In this study, we aimed to investigate the long-term effects of ovariectomy on M/IR injury.

Methods

Two methods involving dorsolateral skin incisions were used to induce the ovariectomized (OVX) rat model. The rats were divided into 2 groups: Control and OVX (n = 6). At the end of the study, the hearts were isolated and subjected to global ischemia using the Langendorff apparatus. Cardiac function indices (CFIs) were recorded, including left ventricular end-diastolic pressure (LVEDP), peak rates of positive (+dp/dt) and negative (-dp/dt) changes in LV pressure, and LV-developed pressure (LVDP). At the end of the reperfusion period, the hearts were used to measure the size of the infarct, levels of nitric oxide metabolites (NOx), and mRNA expression of NO synthase (NOS) enzymes, including endothelial (eNOS), neuronal (nNOS), and inducible (iNOS).

Results

Compared to controls, OVX rats had larger infarct size by 51%, higher LVEDP by 29%, and lower recovery of +dp/dt, -dp/dt, and LVDP by 29%, 22%, and 35%, respectively. Furthermore, in heart tissue, rats that underwent OVX had significantly higher concentrations of nitrate, nitrite, and NOx by 79%, 82%, and 83%, respectively. Additionally, these rats had lower mRNA levels of eNOS by 38% and higher mRNA levels of iNOS by 71%.

Conclusions

The long-term deficiency of estrogen increased the expression of iNOS and decreased the expression of eNOS in the heart tissue of OVX rats. Imbalanced NOS expressions were associated with exacerbated responses to M/IR injury in OVX rats.

Sigesbeckia orientalis Extract Ameliorates the Experimental Diabetic Nephropathy by Downregulating the Inflammatory and Oxidative Stress Signaling Pathways

Diabetes in children and its complications are on the rise globally, which is accompanied by increasing in diabetes-related complications. Oxidative stress and inflammation induced by elevated blood sugar in diabetic patients are considered risk factors associated with the development of diabetes complications, including chronic kidney disease and its later development to end-stage renal disease. Microvascular changes within the kidneys of DM patients often lead to chronic kidney disease, which aggravates the illness. Sigesbeckia orientalis extract (SOE), reported to have strong antioxidative and excellent anti-inflammatory activities, is used in the modern practice of traditional Chinese medicine. Kidneys from three groups of control mice (CTR), mice with streptozotocin (STZ)-induced diabetes (DM), and mice with STZ-induced DM treated with SOE (DMRx) were excised for morphological analyses and immunohistochemical assessments. Only mice in the DM group exhibited significantly lower body weight, but higher blood sugar was present. The results revealed more obvious renal injury in the DM group than in the other groups, which appeared as greater glomerular damage and tubular injury, sores, and plenty of connective tissues within the mesangium. Not only did the DM group have a higher level of cytokine, tumor necrosis factor, and the oxidative stress marker, 8-hydroxyguanosine expression, but also factors of the nuclear factor pathway and biomarkers of microvascular status had changed. Disturbances to the kidneys in DMRx mice were attenuated compared to the DM group. We concluded that SOE is an effective medicine, with antioxidative and anti-inflammatory abilities, to protect against or attenuate diabetic nephropathy from inflammatory disturbances by oxidative stress and to cure vessel damage in a hyperglycemic situation.

Melatonin and Oxidative Stress in the Diabetic State: Clinical Implications and Potential Therapeutic Applications

All living organisms exhibit circadian rhythms, which govern the majority of biological functions, including metabolic processes. Misalignment of these circadian rhythms increases the risk of developing metabolic diseases. Thus, disruption of the circadian system has been proven to affect the onset of type 2 diabetes mellitus (T2DM). In this context, the pineal indoleamine melatonin is a signaling molecule able to entrain circadian rhythms. There is mounting evidence that suggests a link between disturbances in melatonin production and impaired insulin, glucose, lipid metabolism, and antioxidant capacity. Besides, several genetic association studies have causally associated various single nucleotide polymorphysms (SNPs) of the human MT2 receptor with increased risk of developing T2DM. Taken together, these data suggest that endogenous as well as exogenous melatonin may influence diabetes and associated metabolic disturbances not only by regulating insulin secretion but also by providing protection against reactive oxygen species (ROS) since pancreatic β-cells are very susceptible to oxidative stress due to their low antioxidant capacity.

Quercetin improves endothelial function in diabetic rats through inhibition of endoplasmic reticulum stress-mediated oxidative stress

Endoplasmic reticulum (ER) stress attributes a crucial role in diabetes-induced endothelial dysfunction. The present study investigated the effects of quercetin, a potent antioxidant on the attenuation of ER stress-modulated endothelial dysfunction in streptozotocin (STZ)-induced diabetic rats. Oral administration of quercetin for six weeks to diabetic rats dose-dependently reduced the blood glucose levels and improved insulin secretion. Histopathological examination of pancreatic tissues in diabetic rats showed pathological changes such as shrunken islets, reduction in islet area and distorted β-cells, which were found to be restored by quercetin treatment. In addition, quercetin reduced the pancreatic ER stress-induced endothelial dysfunction as assessed by immunohistochemical analysis of C/ERB homologous protein (CHOP) and endothelin-1 (ET-1). Moreover, quercetin administration progressively increased the expression of vascular endothelial growth factor (VEGF) and its receptor, VEGFR2 in diabetes rats. Quercetin-mediated decrease in the nitric oxide (NO∙) and cyclic 3',5'- guanosine monophosphate (cGMP) levels were also observed in the diabetic rats. Quercetin treatment reduced the lipid peroxidation in the diabetic rats, meanwhile increased the total antioxidant capacity in the pancreas from diabetic rats. Altogether, these results demonstrated the vasoprotective effect of quercetin against STZ-induced ER stress in the pancreas of diabetic rats.

Alpha-lipoic acid improves subclinical left ventricular dysfunction in asymptomatic patients with type 1 diabetes

BACKGROUND

Oxidative stress plays an important role in the development of diabetic cardiomyopathy. Alpha-lipoic acid (ALA) is a powerful antioxidant that may have a protective role in diabetic cardiac dysfunction.

AIM

We investigated the possible beneficial effect of alpha-lipoic acid on diabetic left ventricular (LV) dysfunction in children and adolescents with asymptomatic type 1 diabetes (T1D).

SUBJECTS AND METHODS

Thirty T1D patients (aged 10-14) were randomized to receive insulin treatment (n = 15) or insulin plus alpha-lipoic acid 300 mg twice daily (n = 15) for four months. Age and sex matched healthy controls (n = 15) were also included. Patients were evaluated with conventional 2-dimensional echocardiographic examination (2D), pulsed tissue Doppler (PTD), and 2-dimensional longitudinal strain echocardiography (2DS) before and after therapy. Glutathione, malondialdhyde (MDA), nitric oxide (NO), tumor necrosis factor-alpha (TNF-alpha), Fas ligand (Fas-L), matrix metalloproteinase 2 (MMP-2), and troponin-I were determined and correlated to echocardiographic parameters.

RESULTS

Diabetic patients had significantly lower levels of glutathione and significantly higher MDA, NO, TNF-alpha, Fas-L, MMP-2, and troponin-I levels than control subjects. The expression of transforming growth factor beta (TGF-beta) mRNA in peripheral blood mononuclear cells was also increased in diabetic patients. Significant correlations of mitral e'/a' ratio and left ventricular global peak systolic strain with glutathione, MDA, NO, TNF-alpha, and Fas-L were observed in diabetic patients. Alpha-lipoic acid significantly increased glutathione level and significantly decreased MDA, NO, TNF-alpha, Fas-L, MMP-2, troponin-I levels, and TGF-beta gene expression. Moreover, alpha-lipoic acid significantly increased mitral e'/a' ratio and left ventricular global peak systolic strain in diabetic patients.

CONCLUSION

These findings suggest that alpha-lipoic acid may have a role in preventing the development of diabetic cardiomyopathy in type 1 diabetes.

Increased nitric oxide activity compensates for increased oxidative stress to maintain endothelial function in rat aorta in early type 1 diabetes

Hyperglycaemia and oxidative stress are known to acutely cause endothelial dysfunction in vitro, but in the initial stages of diabetes, endothelium-dependent relaxation is preserved. The aim of this study was to investigate how endothelium-dependent relaxation is maintained in the early stages of type 1 diabetes. Diabetes was induced in Sprague-Dawley rats with a single injection of streptozotocin (48 mg/kg, i.v.), and after 6 weeks, endothelium-dependent and endothelium-independent relaxations were examined in the thoracic aorta in vitro. Lucigenin-enhanced chemiluminescence was used to measure superoxide generation from the aorta. Diabetes increased superoxide generation by the aorta (2,180 ± 363 vs 986 ± 163 AU/mg dry tissue weight). Acetylcholine (ACh)-induced relaxation was similar in aortae from control (pEC(50) 7.36 ± 0.09, R (max) 95 ± 3 %) and diabetic rats (pEC(50) 7.33 ± 0.10, R (max) 88 ± 5 %). The ACh-induced relaxation was abolished by the combined presence of the nitric oxide synthase inhibitor N-nitro-L-arginine (L-NNA, 100 μM) and an inhibitor of soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 μM) in control rats, but under the same conditions, the diabetic aortic rings showed significant relaxation to ACh (pEC(50) 6.75 ± 0.15, R (max) 25 ± 4 %, p < 0.05). In diabetic aortae, the addition of haemoglobin, which inactivates nitric oxide, to L-NNA + ODQ abolished the response to ACh. The addition of the potassium channel blockers, apamin and TRAM-34, to L-NNA + ODQ also abolished the relaxation response to ACh. Diabetes significantly elevated plasma total nitrite/nitrate and increased expression of endothelial nitric oxide synthase (eNOS) and calmodulin in aortae. These data indicate that after 6 weeks of diabetes, despite increased oxidant stress, endothelium-dependent relaxation is maintained due to the increased eNOS expression resulting in increased NO synthesis. In diabetic arteries, NO acts both through and independently of cGMP pathways to cause relaxation.

Oxidative stress is not associated with vascular dysfunction in a model of alloxan-induced diabetic rats

OBJECTIVES

To verify if an experimental model of alloxan-diabetic rats promotes oxidative stress, reduces nitric oxide bioavailability and causes vascular dysfunction, and to evaluate the effect of N-acetylcysteine (NAC) on these parameters.

METHODS

Alloxan-diabetic rats were treated or not with NAC for four weeks. Plasmatic levels of malondialdehyde (MDA) and nitrite/nitrate (NOx), the endothelial and inducible nitric oxide synthase (eNOS and iNOS) immunostaining and the vascular reactivity of aorta were compared among diabetic (D), treated diabetic (TD) and control (C) rats.

RESULTS

MDA levels increased in D and TD. NOx levels did not differ among groups. Endothelial eNOS immunostaining reduced and adventitial iNOS increased in D and TD. The responsiveness of rings to acetylcholine, sodium nitroprusside, and phenylephrine did not differ among groups.

CONCLUSIONS

NAC had no effect on the evaluated parameters and this experimental model did not promote vascular dysfunction despite the development of oxidative stress.

Role of melatonin on diabetes-related metabolic disorders

Melatonin is a circulating hormone that is mainly released from the pineal gland. It is best known as a regulator of seasonal and circadian rhythms, its levels being high during the night and low during the day. Interestingly, insulin levels are also adapted to day/night changes through melatonin-dependent synchronization. This regulation may be explained by the inhibiting action of melatonin on insulin release, which is transmitted through both the pertussis-toxin-sensitive membrane receptors MT₁ and MT₂ and the second messengers 3’,5’-cyclic adenosine monophosphate, 3’,5’-cyclic guanosine monophosphate and inositol 1,4,5-trisphosphate. Melatonin may influence diabetes and associated metabolic disturbances not only by regulating insulin secretion, but also by providing protection against reactive oxygen species, since pancreatic β-cells are very susceptible to oxidative stress because they possess only low-antioxidative capacity. On the other hand, in several genetic association studies, single nucleotide polymorphysms of the human MT₂ receptor have been described as being causally linked to an elevated risk of developing type 2 diabetes. This suggests that these individuals may be more sensitive to the actions of melatonin, thereby leading to impaired insulin secretion. Therefore, blocking the melatonin-induced inhibition of insulin secretion may be a novel therapeutic avenue for type 2 diabetes.

Effect of acute topical application of +-pentazocine on the mechanical allodynia in diabetic mice

Mechanical allodynia is a major complication in diabetic mellitus. Peripheral sigma(1) receptors were shown to be involved in nociceptive perception. We therefore investigated the effect of sigma(1) receptor ligand (+)-pentazocine injected into the dorsal surface of the hindpaw on mechanical allodynia in streptozotocin-induced diabetic mice. Injection of (+)-pentazocine (30 microg) into the dorsal surface of the hindpaw did not affect the mechanical threshold and hindpaw NO contents in non-diabetic mice, whereas the mechanical allodynia and hindpaw contents of NO metabolites in diabetic mice were normalized by (+)-pentazocine. These effects of (+)-pentazocine in diabetic mice were inhibited by pretreatment with an sigma receptor antagonist BD1047 into the same area, but not by systemic pretreatment with a kappa-opioid receptor antagonist nor-binaltorphimine. These results suggest that (+)-pentazocine injected into the dorsal surface of the hindpaw increases the lowered mechanical threshold in diabetic mice through the activation of peripheral sigma(1) receptors. This attenuation may be, in part, due to the normalization of increased peripheral NO contents in the hindpaw of diabetic mice.

Effect of Agaricus blazei Murill on the pulmonary tissue of animals with streptozotocin-induced diabetes

The present study was designed to evaluate the oxidative stress as well as the therapeutic effect of Agaricus blazei Muril (A. Blazei) in rats with streptozotocin-induced diabetes. We used 25 Wistar rats, and DM was induced by injecting streptozotocin (70 mg/Kg i.p.). Agaricus blazei Muril was administered daily starting 40 days after disease onset. A. Blazei was tested as an aqueous extract for its phytochemical composition, and its antioxidant activity in vitro was also evaluated. Lipoperoxidation (LPO), and superoxide dismutase (SOD), catalase, and glutathione peroxidase activities were measured in the pulmonary tissue, as well as the presence of inducible nitric oxide synthase (iNOS), through immunohistochemistry. An anatomopathologic study was also performed. Phytochemical screening of A. Blazei detected the presence of alkaloids and saponins. The extract exhibited a significant antioxidant activity in the DPPH-scavenging and the hipoxanthine/xanthine oxidase assays. Pulmonary LPO increased in diabetic animals (0.43 ± 0.09; P < .001) as compared to the control group (0.18 ± 0.02), followed by a reduction in the A. Blazei-treated group (0.33 ± 0.04; P < .05). iNOS was found increased in the lung in diabetic rats and reduced in the A. Blazei-treated group. The pulmonary tissue in diabetic rats showed oxidative alterations related to the streptozotocin treatment. The A. Blazei treatment effectively reduced the oxidative stress and contributed to tissue recovery.

Endothelium-specific GTP cyclohydrolase I overexpression accelerates refractory wound healing by suppressing oxidative stress in diabetes

Refractory wound is a severe complication that leads to limb amputation in diabetes. Endothelial nitric oxide synthase (eNOS) plays a key role in normal wound repair but is uncoupled in streptozotocin (STZ)-induced type 1 diabetes because of reduced cofactor tetrahydrobiopterin (BH(4)). We tested the hypothesis that overexpression of GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme for de novo BH(4) synthesis, retards NOS uncoupling and accelerates wound healing in STZ mice. Blood glucose levels were significantly increased in both male endothelium-specific GTPCH I transgenic mice (Tg-GCH; via a tie-2 promoter) and wild-type (WT) littermates 5 days after STZ regimen. A full-thickness excisional wound was created on mouse dorsal skin by a 4-mm punch biopsy. Wound closure was delayed in STZ mice, which was rescued in STZ Tg-GCH mice. Cutaneous BH(4) level was significantly reduced in STZ mice vs. WT mice, which was maintained in STZ Tg-GCH mice. In STZ mice, constitutive NOS (cNOS) activity and nitrite levels were decreased compared with WT mice, paralleled by increased superoxide anion (O(2)(-)) level and inducible NOS (iNOS) activity. In STZ Tg-GCH mice, nitrite level and cNOS activity were potentiated and O(2)(-) level and iNOS activity were suppressed compared with STZ mice. Thus endothelium-specific BH(4) overexpression accelerates wound healing in type 1 diabetic mice by enhancing cNOS activity and suppressing oxidative stress.

Mitochondria and energetic depression in cell pathophysiology

Mitochondrial dysfunction is a hallmark of almost all diseases. Acquired or inherited mutations of the mitochondrial genome DNA may give rise to mitochondrial diseases. Another class of disorders, in which mitochondrial impairments are initiated by extramitochondrial factors, includes neurodegenerative diseases and syndromes resulting from typical pathological processes, such as hypoxia/ischemia, inflammation, intoxications, and carcinogenesis. Both classes of diseases lead to cellular energetic depression (CED), which is characterized by decreased cytosolic phosphorylation potential that suppresses the cell's ability to do work and control the intracellular Ca(2+) homeostasis and its redox state. If progressing, CED leads to cell death, whose type is linked to the functional status of the mitochondria. In the case of limited deterioration, when some amounts of ATP can still be generated due to oxidative phosphorylation (OXPHOS), mitochondria launch the apoptotic cell death program by release of cytochrome c. Following pronounced CED, cytoplasmic ATP levels fall below the thresholds required for processing the ATP-dependent apoptotic cascade and the cell dies from necrosis. Both types of death can be grouped together as a mitochondrial cell death (MCD). However, there exist multiple adaptive reactions aimed at protecting cells against CED. In this context, a metabolic shift characterized by suppression of OXPHOS combined with activation of aerobic glycolysis as the main pathway for ATP synthesis (Warburg effect) is of central importance. Whereas this type of adaptation is sufficiently effective to avoid CED and to control the cellular redox state, thereby ensuring the cell survival, it also favors the avoidance of apoptotic cell death. This scenario may underlie uncontrolled cellular proliferation and growth, eventually resulting in carcinogenesis.

Chronic inhibition of inducible nitric oxide synthase ameliorates cardiovascular abnormalities in streptozotocin diabetic rats

Previous studies from our lab have demonstrated cardiovascular abnormalities such as depressed mean arterial blood pressure and heart rate, endothelial dysfunction and attenuated pressor responses to vasoactive agents in streptozotocin diabetic rats. We investigated whether these abnormalities are due to diabetes-associated chronic activation of inducible nitric oxide synthase (iNOS). Control and streptozotocin (60 mg/kg, iv) diabetic rats were treated with either vehicle or N6-(1-Iminoethyl)-L-lysine dihydrochloride (L-NIL, 3 mg/kg/day, p.o), a specific inhibitor of iNOS for 8 weeks. At the end of treatment, the mean arterial blood pressure and heart rate were measured in freely moving conscious rats. Further, pressor responses to bolus doses of methoxamine were determined. Endothelial nitric oxide synthase (eNOS) and iNOS expression as well as nitrotyrosine (NT) levels were assessed in the heart and superior mesenteric arteries by western blot and immunohistochemistry. Untreated diabetic rats showed depressed mean arterial blood pressure and heart rate and exhibited vascular hyporeactivity that were significantly improved by treatment with L-NIL. Further, decreased eNOS expression and increased iNOS expression and activity were associated with increased NT levels in the heart and superior mesenteric arteries of untreated diabetic rats. L-NIL treatment of diabetic rats normalized the expression of eNOS and NT levels without any effect on iNOS expression in the heart and superior mesenteric arteries. The results of our study suggest that induction of iNOS in cardiovascular tissues contributes significantly to the depressed mean arterial blood pressure, heart rate and pressor responses to vasoactive agents. Chronic inhibition of iNOS in diabetes may prove beneficial in the treatment of cardiovascular abnormalities.

Oxidative stress as a common mediator for apoptosis induced-cardiac damage in diabetic rats

AIM

To investigate the possible role of oxidative stress as a common mediator of apoptosis and cardiac damage in diabetes.

MATERIALS AND METHODS

This experimental work was conducted on 5 groups of Wistar rats. Group I was the control group. Diabetes type 1 was induced in other groups (by streptozotocin) and animals received insulin or vitamin E (300 mg /kg body weight), both insulin and vitamin E, or no treatment for 4 weeks according to their group. At the end of the study, serum and cardiac tissues were examined for biochemical parameters of cardiac function, oxidative stress and apoptosis. Electron microscopy pictures of cardiac tissue were also evaluated for signs of cardiac damage

RESULTS

Markers of oxidative stress, apoptosis, inflammation as well as manifestations of cardiac damage as assessed by electron microscopy were significantly decreased in rats treated with both insulin and vitamin E when compared with untreated diabetic rats or rats treated with either insulin or vitamin E alone

CONCLUSION

Administration of both vitamin E and insulin was effective in reducing markers of oxidative stress and apoptosis and improving parameters of cardiac function in experiments animals. Antioxidants might prove beneficial as an adjuvant treatment in addition to insulin in type 1 diabetes associated with manifestations of cardiac complications.

Antioxidants and narrow band-UVB in the treatment of vitiligo: a double-blind placebo controlled trial

BACKGROUND

Vitiligo is an acquired depigmenting disease with uncertain aetiopathogenesis, possibly associated with oxidative stress. Narrowband ultraviolet B phototherapy (NB-UVB) is the most widely used and effective treatment.

AIM

To evaluate the clinical effectiveness of NB-UVB and the repairing of oxidative stress-induced damage, using oral supplementation with an antioxidant pool (AP).

METHODS

Patients (n = 35) with nonsegmental vitiligo were enrolled in a randomized, double-blind, placebo-controlled multicentre trial. The treatment group received, for 2 months before and for 6 months during the NB-UVB treatment, a balanced AP containing alpha-lipoic acid, vitamins C and E, and polyunsaturated fatty acids. The area and number of lesions, as well as some parameters of the oxidation-reduction (redox) status of the peripheral blood mononuclear cells (PBMCs) were estimated at the beginning, after 2 months, and at the end of the trial.

RESULTS

In total, 28 patients completed the study. After 2 months of AP supplementation, the catalase activity and the production of reactive oxygen species (ROS) were 121% and 57% of the basal values (P < 0.05 and P < 0.02 vs. placebo, respectively). The AP increased the therapeutic success of NB-UVB, with 47% of the patients obtaining > 75% repigmentation vs. 18% in the placebo group (P < 0.05). An increase in catalase activity to 114% (P < 0.05 vs. placebo) and decrease in ROS level of up to 60% (P < 0.02 vs. placebo) of the basal value was observed in PBMCs. Finally, the AP intake maintained the membrane lipid ratio (saturated : unsaturated fatty acids 1.8 : 3.1; P < 0.05), counteracting phototherapy-induced saturation.

CONCLUSIONS

Oral supplementation with AP containing alpha-lipoic acid before and during NB-UVB significantly improves the clinical effectiveness of NB-UVB, reducing vitiligo-associated oxidative stress.

Lipoic acid significantly restores, in rats, the age-related decline in vasomotion

BACKGROUND AND PURPOSE

The age-related decline in vasorelaxation is largely due to ceramide-induced induction of phosphatase 2A (PP2A), which limits nitric oxide synthase (eNOS) phosphorylation at stimulatory sites. We hypothesized that ceramide accumulation was from an age-related loss of endothelial glutathione (GSH) and subsequent activation of neutral sphingomyelinase (nSMase), an enzyme whose activity increases when GSH is limited.

EXPERIMENTAL APPROACH

Old (30-32 mo) F344xBN rats were given (R)-alpha-lipoic acid (LA), an agent known to induce GSH synthesis. Vasorelaxation was measured in aortic rings; GSH and ceramide levels, activity of nSMase and eNOS phosphorylation (by Western blot) was measured in aortic endothelial cells, isolated from the same aortas.

KEY RESULTS

In old animals, endothelium-dependent relaxation in aortic rings was decreased, GSH levels and its redox state in aortic endothelia were over 30% lower and nSMase activity and endothelial ceramide levels were three-fold increased, relative to young (2-4 mo) rats. LA treatment of old animals improved relaxation in aortic rings, reversed the changes in endothelial GSH, in nSMase activities and in ceramide levels. Similar effects on GSH levels and nSMase activity in old rats were also induced by treatment with GSH monoethylester. Activation (by phosphorylation) of eNOS was decreased by about 50% in old rats and this age-related decrease was partially reversed by LA treatment.

CONCLUSIONS AND IMPLICATIONS

Decreased endothelial GSH was partly responsible for the age-related loss of vascular endothelial function and LA might be therapeutically evaluated to treat endothelial dysfunction.

The effect of alpha-lipoic acid on NOS dispersion in the lung of streptozotocin-induced diabetic rats

Oxidative stress and impaired bioactivity of nitric oxide (NO) play an important role in the organ pathogenesis and angiopathic complications of diabetes mellitus. In this study, we evaluated the effects of alpha-lipoic acid (ALA) on nitric oxide synthase (NOS) in lung tissues. ALA is a strong antioxidant. We wonder how it can affect oxidative stress and NO in the lung cells and vessels of diabetic rats. Wistar rats were divided into four groups; control, diabetic [65 mg/kg streptozotocin (STZ) for 15 days], STZ+ALA-treated (65 mg/kg ALA every 2 days for 15 days), and ALA-only-treated animals. At the end of the experimental period, lipid peroxidation, superoxide dismutase (SOD), and inducible NOS (iNOS) and endothelial NOS (eNOS) distribution were evaluated. Oxidative stress decreased with ALA in diabetic animals, and SOD also increased with ALA. iNOS and eNOS increased in diabetic animals, and ALA prevented iNOS increment in lung tissues. As a result, ALA can prevent some diabetic effects on the lungs and can also protect from vascular damages.

Protective effect of lipoic acid on oxidative and peroxidative damage in cyclosporine A-induced renal toxicity

Free radical generation, including reactive nitrogen and reactive oxygen species, is known to participate in cell physiology in both a positive and negative manner. Moreover, alterations in their concentrations are implicated in a number of renal diseases. However, there is evidence that high concentration of nitric oxide (NO) occurring as a result of iNOS induction and peroxynitrite formation, is capable of causing lipid peroxidation and protein oxidation in cyclosporine A (CsA) induced cellular damage. The present study was conducted to investigate the possible protective role of Lipoic acid (LA) in nitric oxide mediated cellular abnormalities induced by CsA in rat kidney. Adult male albino rats of Wistar strain were given CsA at a dose of 25 mg/kg body weight, orally for 21 days. An extensive elevation in the activities of xanthine oxidase was noted in the renal tissue of the CsA administered rats. These changes were associated with significant increase in the levels of plasma lipid peroxidation with high protein carbonyl contents and 3-nitrotyrosine formation coupled with diminished protein thiols. In addition, plasma nitrite/nitrate (NO(x)), RT-PCR for inducible NOS (iNOS) mRNA, and immunohistochemically demonstrable iNOS protein were evaluated to assess peroxidative damage. Concomitant treatment with LA (20 mg/kg body weight, orally for 21 days showed that the oxidative stress alteration were significantly decreased in CsA treated renal tissue. While the expression of iNOS and the amounts of NO(x) were decreased simultaneously. These results indicate that the antioxidant LA might have a protective effect against CsA-induced peroxidative changes and cellular damage of the renal tissue of the rat.

Rationale for phosphodiesterase 5 inhibitor use post-radical prostatectomy: experimental and clinical review

Erectile dysfunction (ED) is a common complication after radical prostatectomy and results from trauma sustained by the cavernosal nerves. This is a major concern for patients and often affects treatment decisions. The likely mechanism for post-prostatectomy ED is through corporal veno-occlusive dysfunction. There is an increasing amount of evidence to suggest that phosphodiesterase 5 inhibitors (PDE5 inhibitors), when given on a continuous long-term basis, can help to prevent and reverse ED after surgery. In this review article we will examine the pathophysiology of post-prostatectomy ED and discuss the experimental and available clinical evidence for administering PDE5 inhibitors after prostatectomy.

Cyclohexenonic long-chain fatty alcohol has therapeutic effects on diabetes-induced angiopathy in the rat aorta

We studied the effects of cyclohexenonic long-chain fatty alcohol (N-hexacosanol) on diabetes-induced angiopathy in the rat aorta. Male Sprague-Dawley rats were divided into 4 groups, a control group and 3 other groups in which diabetes was induced by streptozotocin (50 mg/kg i.p.). Four weeks after the induction of diabetes, the 3 groups received treatment with either vehicle or N-hexacosanol (2 or 8 mg/kg, i.p. every day) for another 4 weeks. To determine the mechanisms of diabetic vascular dysfunction and the effects of N-hexacosanol, we conducted organ bath studies and real-time polymerase chain reaction on muscarinic M(3) receptor, and endothelial and inducible nitric oxide synthase (eNOS and iNOS) mRNAs in the rat aorta. Treatment with N-hexacosanol did not alter the diabetic status, but improved the diabetes-induced hypercontraction produced by norepinephrine and the damaged endothelium-dependent relaxation of the rat aorta induced by acetylcholine. Furthermore, in the diabetic rats, both muscarinic M(3) receptor and iNOS mRNAs were significantly increased, and N-hexacosanol reversed these upregulations. However, the expression of eNOS mRNA showed no change in all groups. These results indicate that N-hexacosanol has beneficial effects on functional dysfunction and reverses the upregulation of muscarinic M(3) receptor and iNOS mRNAs in the diabetic rat aorta.

A combination of Chinese herbs, Astragalus membranaceus var. mongholicus and Angelica sinensis, enhanced nitric oxide production in obstructed rat kidney

BACKGROUND

The persistent renal hemodynamic maladjustment caused by imbalances between vasoactivators predisposes the kidney to tubulointerstitial injury and ultimate interstitial fibrosis. The decoction (A&A) of a combination of roots of two Chinese herbs, Astragalus membranaceus var. mongholicus and Angelica sinensis, has shown antifibrotic effects in rats with chronic kidney diseases and improvement of renal blood flow in rats with acute ischemic renal injury. In the present study, we investigated the effects and possible mechanisms of A&A on vasoactivators in the process of renal interstitial fibrosis.

METHODS

Male Wistar rats were randomly divided into sham, unilateral ureteral obstruction (UUO) and UAA (UUO plus A&A administration) groups. After oral administration of A&A (14 g/kg/d) for 3, 7 and 10 days, morphological changes were evaluated by HE, Masson and Sirius red staining technique. The levels of Ang-II, ET-1, and the activities of different nitric oxide synthases (NOSs) in renal homogenate were measured by radioimmunoassay. The nitrite concentration as nitric oxide (NO) production was measured using the Griess reagent. Western blot analysis and immunohistochemical staining were performed to determine the expressions of eNOS, nNOS, and iNOS in the kidney. The ability of scavenging reactive oxygen species (ROS) was evaluated by spectrophotometry.

RESULTS

Morphological analysis showed severe interstitial mononuclear cells infiltration, tubular atrophy, renal fibrosis and collagen expression in kidneys of UUO group, which reduced by A&A administration (p<0.05, UAA vs. UUO group). The levels of Ang-II and ET-I were increased in obstructed kidneys, but not significantly changed after A&A administration. NO production did not change in obstructed kidney at day 3 but increased in day 7 and day 10. Administering A&A progressively increased NO production by 2.2, 1.2, and 1.2 fold at days 3, 7 and 10, respectively. The activities of constitutive NOS and iNOS were comparable between UUO group and sham group. In contrast, the activity of constitutive NOS was much higher in UAA than that of UUO rats, which increased 78%, 68% and 78% at days 3, 7 and 10 respectively, although the protein expression of eNOS, nNOS and iNOS in renal tissue had no change in UAA rats. The activities of scavenging ROS in UUO group were not significantly different from the sham group at days 3 and 7, but increased at day 10 (24.1+/-15.0 vs. 10.1+/-0.8 U/min/mg protein, p<0.05). After A&A administration, the activities of scavenging ROS were significantly increased at days 3 and 7 (51.5+/-17.9 vs. 11.7+/-7.4 U/min/mg protein, p<0.05; and 16.1+/-5.6 vs. 7.7+/-1.4 U/min/mg protein, p<0.05) respectively, comparing with the UUO group.

CONCLUSION

The anti-fibrosis effects of A&A might be associated with enhancing NO production via eNOS activation and scavenging ROS, and in turn might improve ischemic microvasculature and attenuate interstitial fibrosis.

Melatonin attenuates metabolic disorders due to streptozotocin-induced diabetes in rats

Enhanced oxidative stress and impairments in nitric oxide synthesis and bioavailability are of considerable importance in the pathogenesis of diabetic vascular diseases. The aim of the present work was to evaluate the metabolic effects of pharmacological doses of the melatonin, a known antioxidant, on streptozotocin-induced diabetic damage in rats. We investigated the indolamine's influence on the cellular redox-balance, nitric oxide (NO) level, and the activities of antioxidative defence enzymes, as well as the activities of enzymes involved in phase II detoxication and NADPH-generating pentose phosphate pathway. Blood glucose, glycated hemoglobin, bilirubin, as well as plasma alanine aminotransferase activities increased and body weight was reduced in rats with streptozotocin-induced (60 mg/kg, i.p.) diabetes (25 days). The NO level was markedly increased in diabetic plasma (by 50%) and aortic tissue (by 30%). The hyperglycemia resulted in reduced activities of glutathione peroxidase (by 25%), catalase (by 20%), glucose-6-phosphate dehydrogenase (by 55%) and transketolase (by 40%) in liver tissue of diabetic animals. Melatonin treatment (10 mg/kg, 18 days) did not influence the level of hyperglycemia or glycated hemoglobin and it had little effect on the activities of antioxidative enzymes. However, melatonin markedly reversed the activities of glucose-6-phosphate dehydrogenase and transketolase in liver tissue of diabetic rats. The most pronounced effect of the melatonin administration was the prevention of an increase in nitric oxide levels in blood plasma and aortic tissue during diabetes. In in vitro experiments, nitrosomelatonin formation in the presence of nitrosodonors was observed. This implies that melatonin might operate as an NO scavenger and carrier. Thus, melatonin treatment may have some beneficial effects in controlling diabetic vascular complications.

Heme oxygenase induction by cyanidin-3-O-β-glucoside in cultured human endothelial cells

The aim of the present research was to investigate the effect of cyanidin-3-O-beta-glucoside (C3G) on heme oxygenase-1 (HO-1), endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS) and dimethylarginine dimethylamino hydrolase-2 (DDAH-2) expression in cultured endothelial cells. Different concentrations (0.00625-250 microM) of C3G were tested in order to investigate possible beneficial and harmful effects of C3G. Our data demonstrated that C3G increased the induction of eNOS and HO-1 in a dose-dependent manner. Higher concentration (62.5-250 microM) also resulted in increase of isoprostane, cGMP and PGE2 levels and in induction of iNOS with consequent oxidative stress. In conclusion, our data evidence that C3G may exert various protective effects against endothelial dysfunction, whereas potentially harmful effects of C3G appear to be limited to concentrations very difficult to be reached in physiological conditions unless there is abundant oral supplementation.

Nitrosative stress and pathogenesis of insulin resistance

Insulin resistance is a major causative factor for type 2 diabetes and is associated with increased risk of cardiovascular disease. Despite intense investigation for a number of years, molecular mechanisms underlying insulin resistance remain to be determined. Recently, chronic inflammation has been highlighted as a culprit for obesity-induced insulin resistance. Nonetheless, upstream regulators and downstream effectors of chronic inflammation in insulin resistance remain unclarified. Inducible nitric oxide synthase (iNOS), a mediator of inflammation, has emerged as an important player in insulin resistance. Obesity is associated with increased iNOS expression in insulin-sensitive tissues in rodents and humans. Inhibition of iNOS ameliorates obesity-induced insulin resistance. However, molecular mechanisms by which iNOS mediates insulin resistance remain largely unknown. Protein S-nitrosylation, a covalent attachment of NO moiety to thiol sulfhydryls, has emerged as a major mediator of a broad array of NO actions. S-nitrosylation is elevated in patients with type 2 diabetes, and increased S-nitrosylation of insulin signaling molecules, including insulin receptor, insulin receptor substrate-1, and Akt/PKB, has been shown in skeletal muscle of obese, diabetic mice. Akt/PKB is reversibly inactivated by S-nitrosylation. Based on these findings, S-nitrosylation has recently been proposed to play an important role in the pathogenesis of insulin resistance.

Carvedilol ameliorates endothelial dysfunction in streptozotocin-induced diabetic rats

The beta-blocker, carvedilol has an additional endothelium-dependent vasodilating properties in patients with hypertension or heart failure. Whether carvedilol can improve endothelium-dependent relaxation in a diabetic animal model and its mechanism of action are unknown. The aim of this study was to investigate the effect of carvedilol on the endothelial-response of aortas from diabetic rats and the underlying mechanism. Acetylcholine-induced endothelium-dependent relaxation, sodium nitroprusside (SNP)-induced endothelium-independent relaxation, and expression of nitric oxide synthase 3 (NOS3) mRNA were measured in aortas isolated from both non-diabetic and streptozotocin-induced diabetic rats. The level of NO in serum was also measured 5 weeks after carvedilol administration (1 or 10 mg/kg/day). Endothelium-dependent relaxation declined along with the decrease of serum NO level in aortas from diabetic rats. Treatment with carvedilol for 5 weeks prevented the inhibition of endothelium-dependent relaxation and the decrease of serum NO levels caused by diabetes. The expression of NOS3 mRNA, protein expression and NOS3 phosphorylation at Ser1177 in diabetic rat aorta was very low in untreated diabetic aortas compared with the healthy group. Administration of carvedilol not only significantly increased the expression of NOS3 mRNA but also protein expression and NOS3 phosphorylation at Ser1177 in the healthy and diabetic groups. In conclusion, chronic carvedilol administration significantly ameliorated the endothelial dysfunction in diabetic rat aortas, in which increased NO level, up-regulated NOS3 mRNA and phosphorylation at Ser1177 may be involved.

Role of nitric oxide-producing and -degrading pathways in coronary endothelial dysfunction in chronic kidney disease

Cardiovascular events are accelerated in chronic kidney disease (CKD). Although deranged nitric oxide (NO) pathways and asymmetric dimethylarginine (ADMA) cause endothelial dysfunction, no direct evidence for coronary artery endothelial dysfunction in CKD has been documented. CKD was induced in male dogs by heminephrectomy (1/2Nx) or five-sixths nephrectomy (5/6Nx). After 4 wk, renal ablation reduced GFR (control 76 [54 to 85]; 1/2Nx 38 [29 to 47]; 5/6Nx 15 [12 to 46] ml/min) and elevated plasma ADMA (control 1.88 [1.68 to 2.54]; 1/2Nx 2.51 [2.11 to 3.55]; 5/6Nx 3.84 [2.16 to 3.95] micromol/L). Coronary circulatory responses to acetylcholine revealed marked increases in coronary blood flow in control group (83 +/- 17% increment) but blunted responses in 1/2Nx (34 +/- 8% increment) and 5/6Nx (20 +/- 4% increment). The acetylcholine-induced changes in epicardial arteriolar diameter, using needle-lens probe charge-coupled device videomicroscopy, showed similar results. The responsiveness to sodium nitroprusside did not differ among three groups. Plasma nitrite/nitrate levels decreased in 1/2Nx and 5/6Nx, and the mRNA expressions of dimethylarginine dimethylaminohydrolase-II (DDAH-II), ADMA-degrading enzyme, and endothelial NO synthase (eNOS) in coronary arteries were downregulated in 1/2Nx and 5/6Nx. Finally, 4-wk treatment with all-trans retinoic acid restored the impaired endothelium-dependent vasodilation and reversed the expression of eNOS but not DDAH-II. Coronary endothelial function is impaired in the early stage of CKD. The dysfunction is attributed to the downregulation of eNOS and/or DDAH-II in coronary arteries. Furthermore, the manipulation of NO pathways may constitute a therapeutic strategy for the prevention of coronary dysfunction in CKD.

N-acetylcysteine prevents nitrosative stress-associated depression of blood pressure and heart rate in streptozotocin diabetic rats

Previous studies have indicated that cardiovascular abnormalities such as depressed blood pressure and heart rate occur in streptozotocin (STZ) diabetic rats. Chronic diabetes, which is associated with increased expression of inducible nitric oxide synthase (iNOS) and oxidative stress, may produce peroxynitrite/nitrotyrosine and cause nitrosative stress. We hypothesized that nitrosative stress causes cardiovascular depression in STZ diabetic rats and therefore can be corrected by reducing its formation. Control and STZ diabetic rats were treated orally for 9 weeks with N-acetylcysteine (NAC), an antioxidant and inhibitor of iNOS. At termination, the mean arterial blood pressure (MABP) and heart rate (HR) were measured in conscious rats. Nitrotyrosine and endothelial nitric oxide synthase (eNOS) and iNOS expression were assessed in the heart and mesenteric arteries by immunohistochemistry and Western blot experiments. Untreated diabetic rats showed depressed MABP and HR that was prevented by treatment with NAC. In untreated diabetic rats, levels of 15-F(2t)-isoprostane, an indicator of lipid peroxidation increased, whereas plasma nitric oxide and antioxidant concentrations decreased. Furthermore, decreased eNOS and increased iNOS expression were associated with elevated nitrosative stress in blood vessel and heart tissue of untreated diabetic rats. N-acetylcysteine treatment of diabetic rats not only restored the antioxidant capacity but also reduced the expression of iNOS and nitrotyrosine and normalized the expression of eNOS to that of control rats in heart and superior mesenteric arteries. The results suggest that nitrosative stress depress MABP and HR following diabetes. Further studies are required to elucidate the mechanisms involved in nitrosative stress mediated depression of blood pressure and heart rate.

Antioxidative enzyme and glutathione S-transferase activities in diabetic rats exposed to long-term ASA treatment

Low-dose acetylsalicylic acid (ASA) treatment is a standard therapeutic approach in diabetes mellitus for prevention of long-term vascular complications. The aim of the present work was to investigate the effect of long-term ASA administration in experimental diabetes on activities of some liver enzymes: glutathione peroxidase (GSHPx), catalase, glucose-6-phosphate dehydrogenase (G6PDH) and glutathione S-transferase (GST). Blood glucose, glycated hemoglobin, as well as plasma ALT and AST activities increased in rats with streptozotocin-induced experimental diabetes. The long-term hyperglycemia resulted in decreased activities of GSHPx (by 26%), catalase (by 34%), GST (by 38%) and G6PDH (by 27%) in diabetic animals. We did not observe increased accumulation of membrane lipid peroxidation products or altered levels of reduced glutathione in livers. The linear correlation between blood glucose and glycated hemoglobin in diabetic animals was distorted upon ASA treatment, which was likely due to a chemical competition between nonenzymatic protein glycosylation and protein acetylation. The long-term ASA administration partially reversed the decrease in GSHPx activity, but did not influence the activities of catalase and GST in diabetic rats. Otherwise, some decrease in these parameters was noted in ASA-treated nondiabetic animals. Increased ASA-induced G6PDH activity was recorded in both diabetic and nondiabetic rats. While both glycation due to diabetic hyperglycemia and ASA-mediated acetylation had very similar effects on the activities of all studied enzymes but G6PDH, we conclude that non-enzymatic modification by either glucose or ASA may be a common mechanism of the observed convergence.

TNF-alpha downregulates eNOS expression and mitochondrial biogenesis in fat and muscle of obese rodents

Obesity is associated with chronic low-grade inflammation. Thus, at metabolically relevant sites, including adipose tissue and muscle, there is abnormal production of proinflammatory cytokines such as TNF-alpha. Here we demonstrate that eNOS expression was reduced, with a concomitant reduction of mitochondrial biogenesis and function, in white and brown adipose tissue and in the soleus muscle of 3 different animal models of obesity. The genetic deletion of TNF receptor 1 in obese mice restored eNOS expression and mitochondrial biogenesis in fat and muscle; this was associated with less body weight gain than in obese wild-type controls. Furthermore, TNF-alpha downregulated eNOS expression and mitochondrial biogenesis in cultured white and brown adipocytes and muscle satellite cells of mice. The NO donors DETA-NO and SNAP prevented the reduction of mitochondrial biogenesis observed with TNF-alpha. Our findings demonstrate that TNF-alpha impairs mitochondrial biogenesis and function in different tissues of obese rodents by downregulating eNOS expression and suggest a novel pathophysiological process that sustains obesity.

Effects of altered nitric oxide availability on rat muscle microvascular oxygenation during contractions

AIM

To explore the role of nitric oxide (NO) in controlling microvascular O2 pressure (P(O2)mv) at rest and during contractions (1 Hz). We hypothesized that at the onset of contractions sodium nitroprusside (SNP) would raise P(O2)mv and slow the kinetics of P(O2)mv change whereas l-nitro arginine methyl ester (L-NAME) would decrease P(O2)mv and speed its kinetics.

METHODS

We superfused the spinotrapezius muscle of female Sprague-Dawley rats (n = 7, body mass = 298 +/- 10 g) with SNP (300 microM) and L-NAME (1.5 mm) and measured P(O2)mv (phosphorescence quenching) during contractions.

RESULTS

SNP decreased mean arterial pressure (92 +/- 5 mmHg) below that of control (CON, 124 +/- 4 mmHg) and L-NAME (120 +/- 4 mmHg) conditions. SNP did not raise P(O2)mv at rest but it did elevate the P(O2)mv-to-MAP ratio (50% increase, P < 0.05) and slow the kinetics by lengthening the time-delay (TD, 14.0 +/- 5.0 s) and time constant (tau, 24.0 +/- 10.0 s) of the response compared with CON (TD, 8.4 +/- 3.3 s; tau, 16.0 +/- 4.5 s, P < 0.05 vs. SNP). L-NAME decreased P(O2)mv at rest and tended to speed tau (10.1 +/- 3.8 s, P = 0.1), while TD (8.1 +/- 1.0 s) was not significantly different. L-NAME also caused P(O2)mv to fall transiently below steady-state contracting values.

CONCLUSIONS

These results indicate that NO availability can significantly affect P(O2)mv at rest and during contractions and suggests that P(O2)mv derangements in ageing and chronic disease conditions may potentially result from impairments in NO availability.

Protection against oxidative stress in diabetic rats: role of angiotensin AT(1) receptor and beta 1-adrenoceptor antagonism

Oxidative stress and low-grade inflammation are hallmarks of diabetes mellitus. We explored protective, blood pressure-independent effects of the angiotensin II type 1 (AT(1)) receptor antagonist candesartan and the selective beta(1)-adrenoceptor antagonist metoprolol. Diabetes mellitus was induced in 8-week-old Sprague-Dawley rats after injection of streptozotocin. Diabetic rats were randomized to treatment with candesartan or metoprolol in sub-antihypertensive doses or to placebo treatment. In the quadriceps, musculature markers of oxidative stress and inflammation were determined. Function of the inherent vascular bed was measured in vivo in the autoperfused hindlimb. Increases in NAD(P)H activity, expression of its cytosolic subunit p22(phox) and of endothelial NO synthase e(NOS) displayed enhanced oxidative stress. Upregulated intercellular (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 and of inducible NOS (iNOS) revealed inflammatory processes. Diabetes was associated with severe impairment of endothelium-dependent and -independent vasodilatation. Candesartan, but not metoprolol, reduced NAD(P)H activity, attenuated diabetes-induced over-expression of p22(phox) and eNOS mRNA as well as ICAM-1, VCAM-1, iNOS and eNOS immunoreactivity and led to a substantial improvement of endothelium-dependent vasodilatation (+46.3% vs. placebo treatment; P<0.05). Angiotensin AT(1) receptor antagonism, but not beta(1)-adrenoceptor antagonism, ameliorates diabetes-generated oxidative stress, indicating a pivotal role of the renin-angiotensin system in the development of diabetic complications.

Bridging advanced glycation end product, receptor for advanced glycation end product and nitric oxide with hormonal replacement/estrogen therapy in healthy versus diabetic postmenopausal women: A perspective

Cardiovascular diseases (CVD) are the most significant cause of death in postmenopausal women. The loss of estrogen biosynthesis with advanced age is suggested as one of the major causes of higher CVD in postmenopausal women. While some studies show beneficial effects of estrogen therapy (ET)/hormonal replacement therapy (HRT) in the cardiovascular system of healthy postmenopausal women, similar studies in diabetic counterparts contradict these findings. In particular, ET/HRT in diabetic postmenopausal women results in a seemingly detrimental effect on the cardiovascular system. In this review, the comparative role of estrogens is discussed in the context of CVD in both healthy and diabetic postmenopausal women in regard to the synthesis or expression of proinflammatory molecules like advanced glycation end products (AGEs), receptor for advanced glycation end products (RAGEs), inducible nitric oxide synthases (iNOS) and the anti-inflammatory endothelial nitric oxide synthases (eNOS). The interaction of AGE-RAGE signaling with molecular nitric oxide (NO) may determine the level of reactive oxygen species (ROS) and influence the overall redox status of the vascular microenvironment that may further determine the ultimate outcome of the effects of estrogens on the CVD in healthy versus diabetic women.

A manganese porphyrin suppresses oxidative stress and extends the life span of streptozotocin-diabetic rats

Enhanced oxidative stress due to hyperglycemia has been implicated in diabetic complications and is considered a major cause of cell and tissue damage. The aim of the present study was to investigate whether synthetic manganese porphyrin, Mn(III) 5,10,15,20-tetrakis(N-methylpyridinium-2-yl)porphyrin (MnTM-2-PyP5+) can ameliorate diabetes-induced oxidative stress and affect life span of diabetic rats. Diabetes was induced by a single (60 mg/kg) intraperitoneal injection of streptozotocin in male Wistar rats. Oxidative stress was monitored by measuring malondialdehyde levels (MDA) in blood plasma and erythrocytes using HPLC. The antioxidant status was assessed by measuring the total radical-trapping potential (TRAP) of blood plasma. Life span of the animals was used as an indication of the overall effect of MnTM-2-PyP5+. MnTM-2-PyP5+ was administered subcutaneously at 1 mg/kg for the duration of the experiment, five times/week followed by one week of rest. Diabetes increased plasma and erythrocyte levels of MDA and decreased TRAP. MnTM-2-PyP5+ had no effect on blood glucose and glycosylated hemoglobin, but significantly increased TRAP and lowered MDA. This Mn porphyrin decreased mortality and markedly extended the life span of the diabetic animals. MnTM-2-PyP5+ suppressed diabetes-induced oxidative stress, which presumably accounts for its beneficial effect on the life span of the diabetic rats. The results indicate that Mn(III) N-alkylpyridylporphyrins can be used as potent therapeutic agents in diabetes.

Antioxidative treatment prevents activation of death-receptor- and mitochondrion-dependent apoptosis in the hearts of diabetic rats

AIMS/HYPOTHESIS

The mechanisms by which glucose injures cells of the cardiovascular system include generation of reactive oxygen species and induction of cellular apoptosis. To date, little is known about the molecular events of hyperglycaemia-induced apoptosis in the heart in vivo.

METHODS

Male Sprague-Dawley rats were rendered diabetic by a single intraperitoneal injection of 60 mg/kg body weight streptozotocin. Caspase activities in cardiac ventricular tissue were determined using fluorometric and immunoassay caspase-activity assay kits respectively. Expression levels of proteins of the apoptotic cascade were determined with western blot analyses using specific antibodies.

RESULTS

Four weeks of hyperglycaemia induced significant apoptosis in cardiac tissue. Determining the initiators of death-receptor-dependent apoptosis revealed induction of CD95/Fas and caspase-8. Examination of the activities of effector caspases revealed increased activity of caspase-6, but not caspase-3 and -7. On evaluating inhibitors of apoptosis, we found up-regulation of caspase-3 and -7-inhibiting X-linked inhibitors of apoptosis in diabetic rats. Hyperglycaemia also induced significant mitochondrion-dependent apoptosis. Our evaluation of expression levels of Bcl-2 family members showed increased expression of pro-apoptotic Bak and Bax in diabetic rats. Antioxidative treatment with lipoic acid significantly suppressed apoptosis and down-regulated caspase-6, -8 and -9 activity, as well as expression levels of pro-apoptotic Bcl-2 proteins without changing blood glucose levels.

CONCLUSIONS/INTERPRETATION

The present study indicates that reactive oxygen species induced by high glucose are involved in both death-receptor- and mitochondrion-dependent apoptosis in the heart in vivo. It also suggests that antioxidants may be a therapeutic option for preventing cardiovascular damage in diabetes mellitus in humans.