Vitamin D dietary supplementation ameliorates the complications associated with type 2 diabetes induced by streptozotocin

Combined resveratrol and vitamin D treatment ameliorate inflammation-related liver fibrosis, ER stress, and apoptosis in a high-fructose diet/streptozotocin-induced T2DM model

A high fructose diet is a major cause of diabetes and various metabolic disorders, including fatty liver. In this study, we investigated the effects of resveratrol and vitamin D (VitD) treatments on endoplasmic reticulum (ER) stress, oxidative stress, inflammation, apoptosis, and liver regeneration in a rat model of type 2 diabetes mellitus, namely, T2DM Sprague-Dawley rats. This T2DM rat model was created through a combination treatment of a 10% fructose diet and 40 mg/kg streptozotocin (STZ). Resveratrol (1 mg/kg/day) and VitD (170/IU/week) were administered alone and in combination to both the diabetic and control groups. Immunohistochemical staining was performed to evaluate PCNA, NF-κB, TNF-α, IL-6, IL-1β, GRP78, and active caspase-3 in liver tissue. The TUNEL method and Sirius red staining were used to determine apoptosis and fibrosis, respectively. G6PD, 6-PGD, GR, and GST activities were measured to determine oxidative stress status. We found that the expressions of cytokines (TNF-α, IL-6, and IL-1β) correlated with NF-κB activation and were significantly increased in the T2DM rats. Increased GRP78 expression, indicating ER stress, increased in apoptotic cells, enhanced caspase-3 activation, and collagen accumulation surrounding the central vein were observed in the T2DM group compared with the other groups. The combination VitD + resveratrol treatment improved antioxidant defense via increasing G6PD, 6-PGD, GR, and GST activities compared to the diabetic groups. We concluded that the combined administration of resveratrol with VitD ameliorates the adverse effects of T2DM by regulating blood glucose levels, increasing antioxidant defense mechanisms, controlling ER stress, enhancing tissue regeneration, improving inflammation, and reducing apoptosis in liver cells. In conclusion, this study indicates that the combination treatment of resveratrol + VitD can be a beneficial option for preventing liver damage in fructose-induced T2DM.

Vitamin D Supplementation Could Enhance the Effectiveness of Glibenclamide in Treating Diabetes and Preventing Diabetic Nephropathy: A Biochemical, Histological and Immunohistochemical Study

Diabetes mellitus is an oxidative stress-related disease characterized by hyperglycemia and a variety of complications, including nephropathy. Vitamin D has variable functions extending beyond the calcium metabolism to prevent oxidative tissue damage. We aimed to investigate whether vitamin D supplements could enhance Glibenclamide's effectiveness in treating diabetes and minimize the risk of associated pathology. Wistar rats were divided into normal control (n = 10) and diabetic (n = 30), where animals received two low doses of Streptozotocin 30 mg/kg/BW intraperitoneally to develop diabetes. The diabetic rats were then randomly divided into three equal groups: untreated, treated with Glibenclamide (0.6 mg/kg), and treated with Glibenclamide and Vitamin D3 (500 IU/kg). After eight weeks, the animals were sacrificed, and blood samples and kidney tissues were collected to evaluate biochemical, anti-oxidant, and pro-inflammatory cytokine levels and histological and immunohistochemical changes. Diabetic animals had significantly increased fasting blood glucose, lipid profile, blood urea, serum creatinine, and Malondialdehyde levels, whereas serum insulin, albumin, and the anti-oxidant enzymes superoxide dismutase and catalase were significantly decreased compared to normal control (p < 0.01). Furthermore, some renal histological changes were observed together with significantly increased immunoreactivity of anti-p53, anti-TNF-α, and anti-IL-6 antibodies when compared to the normal control. All abnormal parameters improved significantly with Glibenclamide therapy (p < 0.01), but combination therapy with vitamin D produced a much better result. In conclusion, vitamin D supplementation along with anti-diabetic medication can help prevent or reduce the severity of diabetic nephropathy due to its potent antioxidant, anti-inflammatory, and anti-apoptotic properties.

1α,25-(OH)2 vitamin D3 prevents insulin resistance and regulates coordinated exocytosis and insulin secretion

Vitamin D₃ is associated with improvements in insulin resistance and glycemia. In this study, we investigated the short-term effect of 1α,25(OH)₂ Vitamin D₃ (1,25-D₃) and cholecalciferol (vitamin D₃) on the glycemia and insulin sensitivity of control and dexamethasone-induced insulin-resistance rats. ⁴⁵Ca²⁺ influx responses to 1,25-D₃ and its role in insulin secretion were investigated in isolated pancreatic islets from control rats. In vivo, 5 d treatment with 1,25-D₃ (i.p.) prevented insulin resistance in dexamethasone-treated rats. Treatment with 1,25-D₃ improved the activities of hepatic enzymes, serum lipids and calcium concentrations in insulin-resistant rats. 25-D₃ (o.g.) does not affect insulin resistance. In pancreatic islets, 1,25-D₃ increased insulin secretion and stimulated rapid response ⁴⁵Ca²⁺ influx. The stimulatory effect of 1,25-D₃ on ⁴⁵Ca²⁺ influx was decreased by diazoxide, apamine, thapsigargin, dantrolene, 2-APB, nifedipine, TEA, PKA, PKC, and cytoskeleton inhibitor, while it was increased by glibenclamide and N-ethylmaleimide. The stimulatory effect of 1,25-D₃ on ⁴⁵Ca²⁺ influx involves the activation of L-type VDCC, K⁺-ATP, K⁺-Ca^2+, and Kv channels, which augment cytosolic calcium. These ionic changes mobilize calcium from stores and downstream activation of PKC, PKA tethering vesicle traffic and fusion at the plasma membrane for insulin secretion. This is the first study highlighting the unprecedented role of 1,25-D₃ (short-term effect) in the regulation of glucose homeostasis and on prevention of insulin resistance. Furthermore, this study shows the intracellular β-cell signal transduction of 1,25-D₃ through the modulation of pivotal ionic channels and proteins exhibiting a coordinated exocytosis of vesicles for insulin secretion.

Vitamin D supplementation decreases visceral adiposity and normalizes leptinemia and circulating TNF-α levels in western diet-fed obese rats

AIMS

Vitamin (Vit) D regulates various organic processes, including adipose tissue morphofunction and lipid metabolism. Studies indicate that Vit D bioavailability is reduced in obesity, which could contribute to obesity development; however, the effects of Vit D supplementation on increased adiposity in western diet (WD)-obese rats (an experimental model that better resembles the obesogenic human obesity condition) have not been studied, to date. Thus, we hypothesized that Vit D supplementation following the induction of obesity in WD rats might reduce their body weight (BW) and adiposity.

MAIN METHODS

Male Wistar rats were fed on a standard chow [control (CTL) group] or a WD to induce obesity (WD group), from 21 to 59 days of age. Subsequently, from 60 to 90-days, half of the CTL and of the WD rats were randomly submitted, or not, to oral Vit D supplementation (CTL-VD and WD-VD groups, respectively).

KEY FINDINGS

At 91 days of age, WD rats were obese, displaying higher abdominal circumference and white fat stores, dyslipidemia, hyperleptinemia and greater plasma levels of tumor necrosis factor (TNF)-α. Vit D supplementation decreased BW gain, abdominal fat deposition and ameliorated the plasma lipid profile in WD-VD rats. These effects were accompanied by reductions in leptinemia and in circulating TNF-α levels in these rodents.

SIGNIFICANCE

Vit D supplementation, following the induction of obesity, may represent a good strategy to attenuate BW gain and abdominal adiposity, and ameliorate the plasma lipid profile in WD rats. These effects may be mediated, at least in part, by reductions in circulating levels of leptin and TNF-α.