Selenium restores defective beta-adrenergic receptor response of thoracic aorta in diabetic rats

Effects of sitagliptin on ß-adrenoceptor mediated relaxation in streptozotocin-diabetic rat aorta

Background/aim

Dipeptidyl peptidase-4 (DPP4) inhibitors, a class of oral antidiabetic drugs, have been shown to be protective on the vascular system because of their antiinflammatory, antiatherosclerotic, and vasodilatory effects. ß2-adrenoceptors (ß2-ARs) mediate the vasorelaxation in the aorta. However, ß3-adrenoceptor-mediated relaxation has not been studied in diabetic aorta yet. Thus, we aimed to study the effect of sitagliptin treatment on ß2- and ß3-adrenoceptor-mediated relaxations in the diabetic rat aorta.

Materials and methods

Eight-week old Sprague Dawley rats were divided into three groups: control, diabetic, sitagliptin treated diabetic. Diabetes was induced by injection of streptozotocin (35 or 40 mg/kg, intraperitoneally). After 10 weeks of diabetes, some of the diabetic rats were treated with sitagliptin (orally, 10mg/kg/day). ß2- and ß3-AR-mediated relaxation responses were evaluated by using isoprenaline and CL 316,243, respectively. ß3-AR-mediated relaxation experiments were repeated in presence of L-NAME. Western blotting and immunohistochemistry were performed to determine the abundance of ß3-adrenoceptor and endothelial nitric oxide synthase (eNOS).

Results

The isoprenaline-mediated relaxation response was impaired in the diabetic group and sitagliptin treatment did not improve it. There was no significant change in CL316,243 mediated-relaxation or protein expression of ß3-ARs among the groups. However, the ratio of phosphorylated eNOS/NOS protein was increased markedly in the sitagliptin treated group, which points the stimulating effect of this drug towards the eNOS pathway.

Conclusion

Our results indicate that sitagliptin treatment does not alter ß-AR-mediated relaxation in streptozotocin-diabetic rat aorta; however, it significantly stimulates the eNOS pathway. Future studies are needed to clarify the relationship between the eNOS pathway and DPP-4 inhibition.

Selenium and selenoproteins: from endothelial cytoprotection to clinical outcomes

The role of the vascular endothelium in inflammation was demonstrated experimentally through biomarkers of endothelial dysfunction and cytoprotection. Selenium is a trace element essential for cell protection against oxidative lesions triggered by reactive oxygen species or inflammatory responses. Preclinical studies have demonstrated a relationship between adhesion molecules as biomarkers of endothelial dysfunction and selenoproteins as biomarkers of selenium status under conditions that mimic different diseases. Most studies in humans indicate an association between selenium deficiency and increased risk of morbidity and mortality, yet the pathophysiology of selenium in endothelial activation remains unknown. Here, we summarize selenium-dependent endothelial function evaluation techniques and focus on the role of selenium in endothelial cytoprotection according to current scientific knowledge. Most studies on the role of selenium in endothelial processes show selenium-dependent endothelial functions and explain how cells and tissues adapt to inflammatory insults. Taken together, these studies show an increase in adhesion molecules and a decrease in the expression of selenoproteins following a decreased exposure to selenium. Few clinical trials have enough methodological quality to be included in meta-analysis on the benefits of selenium supplementation. Furthermore, the methodology adopted in many studies does not consider the relevant findings on the pathophysiology of endothelial dysfunction. Preclinical studies should be more frequently integrated into clinical studies to provide clearer views on the role of selenium status in endothelial cytoprotection.

In vitro influence of selenium on the proliferation of and steroidogenesis in goat luteinized granulosa cells

In this study, we investigated the effects of Selenium (Se) on the proliferation of and steroidogenesis in goat luteinized granulosa cells (LGCs) and elucidated the mechanisms underlying these effects. Our results showed that proliferating cell nuclear antigen (PCNA), Akt, and phosphoinositide 3-kinase (PI3K) were expressed mainly in ovarian oocytes and granulosa cells (GCs). We observed that 5 ng/mL Se significantly stimulated LGC proliferation, which could be attributed to increases in PCNA, cyclin-dependent kinase 1 (CDK1), phosphorylated adenosine monophosphate-activated protein kinase (p-AMPK; Thr172), and phosphorylated Akt (p-Akt; Ser473) and decreases in p21 (P < 0.05). Se treatment also significantly increased estradiol (E₂) production, which could be, at least partially, due to increased levels of 3β-hydroxysteroid dehydrogenase(3β-HSD), steroidogenic acute regulatory protein (StAR), p-Akt (Ser473), and cyclic adenosine monophosphate (cAMP) (P < 0.05); however, follicle-stimulating hormone (FSH) significantly enhanced the production of E₂, progesterone (P₄) and cAMP (P < 0.05). Moreover, Se treatment stimulated proliferation and the synthesis of E₂ and cAMP in the presence of FSH (P < 0.05). Additionally, the expression of antioxidant-related genes [glutathione peroxidase (GSH-Px) and superoxide dismutase 2 (SOD2)] and the activity of GSH-Px and SOD were progressively elevated by Se treatment (P < 0.05). These data suggested that Se plays an important role in the proliferation of and steroidogenesis in LGC by activating the PI3K/Akt and AMPK pathways, thereby increasing the expression of its downstream cell-cycle- and steroid-synthesis-related genes, as well as regulating cellular oxidative stress.

Supplementation of Micronutrient Selenium in Metabolic Diseases: Its Role as an Antioxidant

Selenium is an essential mineral naturally found in soil, water, and some of the food. As an antioxidant, it is one of the necessary trace elements in human body and has been suggested as a dietary supplement for health benefit. Although the human body only needs a trace amount of selenium every day, plenty of recent studies have revealed that selenium is indispensable for maintaining normal functions of metabolism. In this study, we reviewed the antioxidant role of nutritional supplementation of selenium in the management of major chronic metabolic disorders, including hyperlipidaemia, hyperglycaemia, and hyperphenylalaninemia. Clinical significance of selenium deficiency in chronic metabolic diseases was elaborated, while clinical and experimental observations of dietary supplementation of selenium in treating chronic metabolic diseases, such as diabetes, arteriosclerosis, and phenylketonuria, were summarized. Toxicity and recommended dose of selenium were discussed. The mechanism of action was also proposed via inspecting the interaction of molecular networks and predicting target protein such as xanthine dehydrogenase in various diseases. Future direction in studying the role of selenium in metabolic disorders was also highlighted. In conclusion, highlighting the beneficial role of selenium in this review would advance our knowledge of the dietary management of chronic metabolic diseases.

Administration of Selenium Decreases Lipid Peroxidation and Increases Vascular Endothelial Growth Factor in Streptozotocin Induced Diabetes Mellitus

Objective

The imbalance in oxidant/antioxidant status plays a pivotal role in diabetes mellitus (DM). Selenium is a integral component of the antioxidant enzyme glutathione peroxidase. Se treatment induces angiogenesis and improves endothelial function through increased expression of vascular endothelial growth factor (VEGF). The aim of this study is to investigate the effect of selenium on oxidative stress, VEGF, and endothelin 1 (ET1) in a DM rat model.

Materials and Methods

We performed an experimental animal study with 64 adult male Wistar-Albino rats. Rats were divided into the following groups (n=8): control (C)7, C21, C+sodium selenite (Se)7, and C+Se21 (control rats), and DM7, DM21, DM+Se7, and DM+Se21 (diabetic rats). Diabetes was induced by 2-deoxy-2-(3-methyl-3-nitrosoureido)- D-glucopyranose [streptozotocin (STZ)]. Three weeks after STZ, DM+Se7 rats received intraperitoneal (i.p.) injections of 0.4 mg/kg Se for 7 days. The DM+Se21 rats received these injections for 21 days. The same dose/duration of Se was administered to the C+Se7 and C+Se21 groups. The remaining rats (C7, C21, DM7, DM21) received physi- ologic saline injections for 7 or 21 days. Ferric reducing antioxidant power (FRAP), malon- dialdehyde (MDA), advanced oxidation protein products (AOPP), and endothelial function markers (VEGF and ET1) in plasma samples were measured.

Results

Diabetic rats (DM7 and DM21) had significantly increased plasma FRAP (P=0.002, P=0.001), AOPP (P=0.024, P=0.01), MDA (P=0.004, P=0.001), and ET1 (P=0.028, P=0.003) levels compared with C7 and C21 control rats. VEGF (P=0.02, P=0.01) significantly decreased in DM7 and DM21 diabetic rats compared with their controls (C7, C21). Se administration reversed the increased MDA and decreased VEGF levels, and lowered plasma glucose levels in the DM+Se7 and DM+Se21 diabetic groups compared with diabetic rats (DM7, DM21). We observed positive correlations between FRAP-AOPP (r=0.460), FRAP-ET1 (r=0.510), AOPP-MDA (r=0.270), and AOPP-ET1 (r=0.407), and a negative correlation between MDA-VEGF (r=-0.314).

Conclusion

We observed accentuated oxidative stress and impaired endothelial function in diabetes. Se treatment reduced lipid peroxidation and hyperglycemia. Se probably improved endothelial dysfunction in diabetic rats because of the increased VEGF levels.

Di-peptidyl peptidase-4 inhibitor sitagliptin protects vascular function in metabolic syndrome: possible role of epigenetic regulation

Metabolic syndrome (MetS) is a complex medical disorder characterized by insulin resistance, hypertension, and high risk of coronary disease and stroke. Microvascular rarefaction and endothelial dysfunction have also been linked with MetS, and recent evidence from clinical studies supports the efficacy of incretin-based antidiabetic therapies for vascular protection in diabetes. Previous studies pointed out the importance of dipeptidyl peptidase-4 (DPP-4) inhibition in endothelial cells due to getting protection against metabolic pathologies. We therefore aimed to investigate the acute effects of a DPP-4 inhibitor, sitagliptin, on vascular function in rats with high-sucrose diet-induced MetS. In order to elucidate the mechanisms implicated in the effects of DPP-4 inhibition, we tested the involvement of NO pathway and epigenetic regulation in the MetS. Acute use of sitagliptin protects the vascular function in the rats with MetS in part due to NO pathway via restoring the depressed aortic relaxation responses mediated by receptors. Application of sitagliptin enhanced the depressed phosphorylation levels of both the endothelial NO synthase and the apoptotic status of protein kinase B, known as Akt, in endothelium-intact thoracic aorta from rats with MetS. One-hour application of sitagliptin on aortic rings from rats with MetS also induced remarkable histon posttranslational modifications such as increased expression of H3K27Me3, but not of H3K27Me2, resulting in an accumulation of the H3K27Me3. Our findings suggest that, in addition to its well-known hypoglycemic action, sitagliptin may also have beneficial effects on hyperglycemia-induced vascular changes in an endotheium-dependent manner. These present results with sitagliptin aside from the glycaemic control, may demonstrate its important role in the treatment of patients with MetS.

Effects of selenium on endothelial dysfunction and metabolic profile in low dose streptozotocin induced diabetic rats fed a high fat diet

Endothelial dysfunction develops as a result of oxidative stress and is responsible for diabetic vascular complications. We investigated the effects of selenium on endothelial dysfunction and oxidative stress in type 2 diabetic rats. Male Wistar rats were divided into five groups: controls, untreated diabetics, and diabetics treated with 180, 300, 500 mcg/kg selenium each day. Diabetes was induced by a single intraperitoneal injection of low dose streptozotocin to rats fed a high fat diet. Endothelium-dependent and -independent relaxations were measured in the thoracic aorta. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and endothelial nitric oxide synthase (eNOS) mRNA expressions were analyzed using real-time polymerase chain reaction (RT-PCR). Fasting blood glucose, lipid profile, lipid oxidation, insulin and nitric oxide were measured in blood samples. Malondialdehyde, superoxide dismutase, catalase and glutathione peroxidase levels were measured in liver samples. RT-PCR showed that selenium reversed increased NADPH oxidase expression and decreased eNOS expression to control levels. Selenium also improved the impairment of endothelium-dependent vasorelaxation in the diabetic aorta. Selenium treatment significantly decreased blood glucose, cholesterol and triglyceride levels, and enhanced the antioxidant status in diabetic rats. Our findings suggest that selenium restores a normal metabolic profile and ameliorates vascular responses and endothelial dysfunction in diabetes by regulating antioxidant enzyme and nitric oxide release.

Comparative investigation of kidney mesangial cells from increased oxidative stress-induced diabetic rats by using different microscopy techniques

High glucose and increased oxidative stress levels are the known important mediators of diabetic nephropathy. However, the effects of these mediators on tissue damage basically due to extracellular matrix expansion in mesangial cells have yet to be fully examined within the context of early stage diabetic nephropathy. In this study, we attempted to characterize changes in mesangial cells of streptozotocin-induced diabetic rats with a comparative investigation of kidney tissue by using different microscopy techniques. The serum levels of urea and creatinine of diabetic rats, as biomarkers of kidney degeneration, decreased significantly compared to those of age-matched controls. In diabetic rats, there are increased malondialdehyde and oxidized-glutathione levels as well as reduced-glutathione and glutathione-peroxidase activity levels in renal tissue compared to those of the controls. By using light and electron microscopies, we showed that there were marked thickening in Bowman's membrane and glomerular capillary wall, increased amount of extracellular matrix often occupying Bowman's space, degenerations in tubules, an increased number of mesangial cells in the network of glomerular capillary walls, and increased amount of lipid accumulation in proximal tubules in the renal tissue of diabetic rats. Our confocal microscopy data confirmed also the presence of irregularity and widened in glomerular capillaries, their attachment to the Bowman's capsule, degenerated heterochromatin, thickening in foci of glomerular basement membrane, and marked increase in mesangial cells. These results suggest that a detailed structural investigation of kidney tissue provides further information on the important role of mesangial cells in pathogenesis of diabetic nephropathy.

Role of ROCK upregulation in endothelial and smooth muscle vascular functions in diabetic rat aorta

Background

The RhoA/ROCK signaling pathway mediates vascular smooth muscle contraction while endogenous NO induces vasodilation through its inhibition. Since myosin light chain phosphatase (MLCP) and eNOS are targeted by RhoA/ROCK upregulation then turn to lead abnormalities in vasculature, we aimed to examine whether less endothelial NO-production and inhibited eNOS together with an upregulation of RhoA/ROCK signaling pathway in thoracic aorta can play an important role in vascular dysfunction under hyperglycemia.

Methods

We used streptozotocin-injected rats, as a model of type 1 diabetes, and their lean controls to investigate the role of ROCK upregulation in the function of toracic aorta by using electrophysiological and biochemical techniques.

Results

The protein level of ROCK isoform ROCK2 was found to be 2.5-fold higher in endothelium-intact aortic rings of the diabetic rats compared to those of the controls while its level in endothelium-denuded rings was similar among these two groups. Phosphorylation level of eNOS in endothelium-intact rings from the diabetics was 50% less compared to that of the control. ROCK inhibitors, either Y27632 or HA1077, induced concentration-dependent relaxation with a marked left-shift in phenylephrine pre-contracted endothelium-intact rings from either diabetics or high glucose incubated controls while pretreatment of these rings with L-NAME abolished this shift, fully. Moreover, phosphorylation levels of both MLCP and MLC in endothelium-denuded rings were markedly higher in the diabetics than the controls.

Conclusion

We demonstrated that diabetes-induced vascular dysfunction can arise due to either inbition of eNOS, thereby less endothelial NO-production, either directly or indirectly, in part, due to an upregulation of ROCK2 by hyperglycemia. Additionally, our data demonstrate that high phosphorylation levels of both MLC and MLCP in endothelium-denuded rings can be due to a less endothelial NO-production dependent ROCK upregulation in the smooth muscle cells under hyperglycemia, as well.

Selenium-vitamin E combination modulates endometrial lipid peroxidation and antioxidant enzymes in streptozotocin-induced diabetic rat

Diabetes mellitus is associated with diabetic impairment of uterine function, ultimately leading to reduced fertility. Its etiology may involve oxidative damage by reactive oxygen substances, and protection against this damage can be offered by antioxidant supplementation. In the present study, the effects of a vitamin E-plus-selenium (VESe) combination on lipid peroxidation (MDA) and the scavenging enzyme activity in the uterine endometrium of streptozotocin (STZ)-induced diabetic rats were investigated. Twenty-four female rats were equally divided into three groups as follows: group I (control); group II (diabetic); group III (diabetic + VESe), STZ + vitamin E (60 mg/kg over 1 day) + selenium-treated (Na2SeO3, 1 mg/kg over 1 day). After 4 weeks of receiving the VESe treatment, endometrium samples were taken from the uterus. Although the VESe treatment decreased the MDA and blood glucose levels in the STZ group, the observed values remained significantly higher than in the controls. Catalase, superoxide dismutase, and glutathione peroxidase activities and body weight gain were significantly (p < 0.01) lower in STZ groups as compared to control group, whereas their activities were (p < 0.01) increased by VESe treatment. However, there was no significant difference on body weight gain and uterine weights between control and STZ + VESe groups. In conclusion, the endometrial complications caused by oxidative stress, and the abnormal blood glucose levels in diabetic of rats, can be alleviated by strengthening the physiological antioxidative defense through the administration of vitamin E and Se.

Alpha lipoic acid treatment improved endothelium-dependent relaxation in diabetic rat aorta

The aim of this study was to ascertain the effects of α-lipoic acid (ALA) treatment on relaxant responses of acetylcholine (ACh) and isoprenaline (ISO) in aortic rings precontracted with serotonin (5-HT, 10(-6) M) obtained from streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in the rats by 50 mg/kg streptozotocin (STZ) via an intraperitoneal injection. Rat body and aorta weights were measured. The isometric tension to ACh (10(-9)-3×10(-6) M) and ISO (10(-9)-10(-4) M) of 5-HT-precontracted diabetic and non-diabetic rat (control), diabetic-ALA-treated, and ALA-treated aortas, in organ baths were recorded. Six weeks after STZ treatment blood glucose was elevated compared to control rats. In aortic rings from diabetic rats ACh and ISO-induced relaxations were impaired whereas endothelium-independent relaxation to sodium nitroprusside (SNP) was unaffected. ALA (100 mg/kg/day) treatment for 5 weeks enhanced ACh and ISO-induced relaxation in diabetic aortas. This recovering effect was via NO because prevented by incubating the vessels with N(G)-nitro-L-arginine methyl ester (L-NAME, a NOS inhibitor). It may be assumed that ALA treatment in vivo, can protect against impaired vascular responsiveness in STZ-induced diabetic rats.

Attenuation of beta2-adrenergic receptors and homocysteine metabolic enzymes cause diabetic cardiomyopathy

Although adrenergic receptors (AR) and hyperhomocysteinemia (HHcy) are implicated in heart failure, their role in diabetic cardiomyopathy is not completely understood. We tested the hypothesis that glucose mediated depletion of beta2-AR and HHcy impair contractile function of cardiomyocytes leading to diabetic cardiomyopathy. To prove the hypothesis, cardiac function was assessed in 12week male diabetic Ins2+/- Akita and C57BL/6J mice by echocardiography, pressure-volume loop, and contractile function of cardiomyocytes. The results revealed cardiac dysfunction in Akita. To investigate the mechanism, the levels of beta2-AR, GLUT4, sarcoplasmic reticulum calcium ATP-ase-isoform 2 (SERCA-2) and homocysteine (Hcy) metabolic enzymes-cystathionine beta synthase (CBS), cystathionine gamma lyase (CTH), and methyl tetrahydrofolate reductase (MTHFR) were determined in the heart. It revealed down-regulation of beta2-AR, GLUT4, SERCA-2, CBS, CTH, and MTHFR in Akita. Attenuation of beta2-AR in hyperglycemic condition was also confirmed in cardiomyocytes at in vitro level. Interestingly, the ex vivo treatment of cardiomyocytes with beta2-AR antagonist deteriorated whereas beta-AR agonist ameliorated contractile function. It points to the involvement of beta2-AR in diabetic cardiomyopathy. We conclude that degradation of beta2-AR and impairment of Hcy metabolism is implicated in diabetic cardiomyopathy.