Dietary vitamin D3 improves postprandial hyperglycemia in aged mice

Effect of Liraglutide on Osteoporosis in a Rat Model of Type 2 Diabetes Mellitus: A Histological, Immunohistochemical, and Biochemical Study

Diabetic osteoporosis (DOP) is a diabetic complication associated with a significant disability rate. Liraglutide, a glucagon-like peptide-1 receptor agonist, is a promising and innovative drug for type 2 diabetes mellitus (T2DM), with potential therapeutic implications for bone disorders. This investigation examined the impact of liraglutide on osteoporosis in rats with T2DM and studied the influence of vitamin D receptor Bsm1 polymorphism on liraglutide-induced outcomes. Thirty rats were divided into control, T2DM induced by a combination of a high-fat diet and 25 mg/kg streptozotocin, and T2DM-liraglutide (T2DM treated with 0.4 mg/kg/day liraglutide) groups. After 8 weeks of liraglutide treatment, femurs and blood samples were obtained from all rats for subsequent investigations. Diabetes induced a remarkable rise in the serum levels of receptor activator of nuclear factor kappa B ligand (RANKL) and C-telopeptide of type I collagen (CTX-1) associated with a remarkable decline in osteocalcin and osteoprotegerin (OPG). Impaired bone architecture was also demonstrated by light and scanning electron microscopic study. The immune expression of OPG was down-regulated, while RANKL was up-regulated. Interestingly, the administration of liraglutide ameliorated the previous changes induced by diabetes mellitus. In conclusion, liraglutide can prevent DOP, mostly due to liraglutide's ability to increase bone growth, while inhibiting bone resorption.

Vitamin D mitigates diabetes-associated metabolic and cognitive dysfunction by modulating gut microbiota and colonic cannabinoid receptor 1

INTRODUCTION

Obesity is associated with elevated endocannabinoid tone, gut dysbiosis, and inflammation predisposing to diabetes. The endocannabinoid system mediates the effects of gut microbiota and regulates the gut barrier integrity. We examined the effects of vitamin D (VD) on colonic cannabinoid receptor 1(CB1R), tight junction proteins, gut dysbiosis, metabolic and cognitive dysfunction in a model of type 2 diabetes compared with metformin.

METHODS

Rats received high-fat, high-sucrose diet (HFSD) and either VD (500 IU/kg/day; p.o.), or metformin (200 mg/kg/day; p.o.) for 8 weeks. After 6 weeks, streptozotocin (STZ) (40 mg/kg; i.p) was injected. Behavioral, cognitive, and metabolic assessments were carried out. Finally, fecal, blood, and tissue samples were collected to examine Bacteroidetes/Firmicutes ratio, colonic CB1R, zonula occludens-1 (ZO-1), occludin, and Toll-like receptor 4 (TLR4); serum lipopolysaccharides (LPS), peptidoglycan (PGN), tumor necrosis factor-alpha (TNF-ɑ), glucagon-like peptide-1 (GLP-1), lipids, and VD; hippocampal brain-derived neurotrophic factor (BDNF) and inflammatory markers.

RESULTS

VD ameliorated HFSD/STZ-induced dysbiosis/gut barrier dysfunction as indicated by lower circulating LPS, PGN and TNF-ɑ levels, likely by downregulating colonic CB1R and upregulating ZO-1 and occludin expressions. Additionally, VD suppressed HFSD/STZ-induced hyperglycemia, hyperinsulinemia, dyslipidemia, and hippocampal neuroinflammation. These changes culminated in improved glycemic control and cognitive function. VD was more effective than metformin in decreasing serum LPS and TNF-ɑ levels; whereas metformin resulted in better glycemic control.

CONCLUSION

Targeting gut microbiota by VD could be a successful strategy in the treatment of diabetes and associated cognitive deficit. The crosstalk between VD axis and the endocannabinoid system needs further exploration.

Efficacy of Mesenchymal Stem Cell and Vitamin D in the Treatment of Diabetes Mellitus Induced in a Rat Model: Pancreatic Tissues

Treatment with mesenchyme stem cells (MSCs) plays a significant role in the therapies of many diseases such as diabetics. Vitamin D plays a significant role in the development of insulin and can increase the insulin action sensitivity of peripheral tissues. Moreover, there is limited research concerning the mechanism of the therapeutic action of MSCs with the combination of vitamin D (vit. D). Therefore, we evaluated the effect of MSC intervention in a diabetic animal model. Diabetes was induced by streptozotocin (STZ) injection at a dose of 50 mg/kg in adult male rats The diabetic rats were injected with MSCs derived from bone marrow (2 × 106 per rat), either alone or in combination with vit. D through the tail vein for four weeks. Serum insulin, glucose, C-peptide, glycosylated hemoglobin, and lipid profile levels were determined. Pancreatic oxidative stress, histology, and electron microscopy were evaluated, and the gene expression of cytokines was assessed by real-time polymerase chain reaction PCR. MSC treatment suppressed pancreatic inflammatory cytokine secretion and oxidative stress in diabetic rats, resulting in improved pancreatic histology and cellular structure, and the complication of hyperglycemia was observed. Engrafted MSCs were found inside degraded pancreatic regions and regulated inflammatory cytokines. Our results demonstrated that treatment with MSCs and vit. D in combination prevented pancreatic injury via antioxidant and immune regulation in diabetic rats, contributing to the prevention of pancreatic dysfunction, improvement of lipid metabolism, and regulation of cytokine gene expression compared with each one separately. All these mechanisms also improved the histological structure of the pancreas based on transmission electron microscopy. The combination of MSCs and vit. D appears to have contributed to a greater improvement in the diabetic pancreatic complication of rats than was observed by each one separately. Therefore, this association can be used as antidiabetic therapy.

Renoprotective effects of vitamin D3 supplementation in a rat model of metabolic syndrome

PURPOSE

The study aimed to investigate the potential nephroprotective effects of vitamin D3 in metabolic syndrome (MetS) and the molecular basis of the underlying mechanisms of its action.

METHODS

MetS was induced in adult male Wistar rat‏s by adding fructose (10%) to every day drinking water and salt (3%) to the diet. Six weeks after fructose/salt consumption, fasting serum lipid profile and uric acid levels were determined, an oral glucose tolerance test (OGTT) was performed and kidney function was checked. MetS rats were then treated orally with vitamin D3 (10 µg/kg/day) for 6 weeks. At the end of the study period (12 weeks), the OGTT test was reperformed, anthropometrical parameters were measured, urine, blood and tissue samples were collected and the animals were euthanised.

RESULTS

The incidence of MetS was confirmed 6 weeks after fructose/salt consumption, when the rats exhibited significant weight gain, dyslipidemia, hyperuricemia, insulin resistance, hyperinsulinemia and impaired glucose tolerance. After 12 weeks, MetS rats displayed markedly declined renal function alongside with extravagant renal histopathological damages and interstitial fibrosis. Furthermore, significantly enhanced renal oxidative stress and inflammation were manifested. Vitamin D3 supplementation in MetS rats significantly reversed all the above-mentioned deleterious effects.

CONCLUSION

The study has indeed provided mounting evidence of the promising therapeutic potential of vitamin D3 against development and progression of MetS-induced nephropathy. A new insight has been introduced into the crucial role of dipeptidyl peptidase-4 inhibition and sirtuin-1/5'adenosine monophosphate-activated protein kinase activation in the renoprotective effects of vitamin D3.

Evaluation of Serum Glucagon-Like Peptide 1 and Vitamin D Levels in Elderly Patients with Bone Fractures

OBJECTIVES

To evaluate the correlation between levels of serum vitamin D and glucagon-like peptide-1 (GLP-1) in elderly patients with bone fractures.

MATERIALS AND METHODS

This study included 56 patients and 31 control subjects. The patients included were those aged ≥65 years who were admitted to our hospital with a diagnosis of bone fracture. The control group comprised age-matched, healthy individuals. Levels of serum vitamin D and GLP-1 were measured and compared between the 2 groups.

RESULTS

Significant differences were noted between the groups in terms of serum levels of vitamin D (p < 0.001) and serum levels of GLP-1 (p < 0.001). A positive correlation was observed between serum levels of vitamin D and GLP-1.

CONCLUSION

Serum levels of GLP-1 were found to be significantly lower in elderly patients with bone fracture compared to healthy adults. In addition, a significant correlation was found between decreased vitamin D and GLP-1 levels. These results may therefore demonstrate the protective effects of GLP-1 on bone structure and metabolism, similar to those of vitamin D.

Effect of denosumab, a human monoclonal antibody of receptor activator of nuclear factor kappa-B ligand (RANKL), upon glycemic and metabolic parameters: Effect of denosumab on glycemic parameters

Osteoporosis is a complication of type 2 diabetes mellitus (T2DM). Blockade of receptor activator of nuclear factor kappa-B ligand (RANKL) improves osteoporosis, but might also improve glucose tolerance through reduction of hepatic insulin resistance. However, the effect of denosumab (a human monoclonal antibody of RANKL) upon glycemic and metabolic parameters is controversial. We revealed the effect of denosumab upon glycemic and metabolic parameters for 52 weeks. We evaluated 20 individuals diagnosed with both osteoporosis (male and female: postmenopausal) and T2DM. We measured glycemic and metabolic parameters before and 26/52 weeks after administration of denosumab (60 mg per 26 weeks) without changing any other medication each patient was taking. All patients completed the study without complications and the T-score (lumbar spine and femoral neck) improved significantly from baseline to 52 weeks after denosumab administration (P < .001, .001, respectively). None of the glycemic parameters changed significantly from baseline to 26 weeks after denosumab administration, but levels of glycated hemoglobin and homeostasis model assessment of insulin resistance improved significantly from baseline to 52 weeks after administration (P = .019, .008, respectively). The levels of liver enzymes did not change significantly from baseline to 26 weeks after denosumab administration, but levels of aspartate transaminase and alanine aminotransferase improved significantly from baseline to 52 weeks after administration (P = .014, .004, respectively). None of the markers of lipid metabolism and body mass index changed significantly from baseline to 26/52 weeks after denosumab administration. These data demonstrated that denosumab is useful for T2DM patients with osteoporosis for glycemic control via improvement of insulin resistance. Also, the effect of denosumab might be due to improvement of hepatic function.

Chlorpyrifos stimulates expression of vitamin D3 receptor in skin cells irradiated with UVB

Skin, the organ responsible for vitamin D synthesis, is fully exposed to many xenobiotics, e.g. polycyclic aromatic hydrocarbons and pesticides. A broad spectrum organophosphorus insecticides (OP's), such as chlorpyrifos (CPS), are commonly used in agriculture and to control domestic insects. Thus, the aim of this study was to investigate the effect of chlorpyrifos, on the expression of vitamin D₃ receptor (VDR) in human keratinocytes cell line HaCaT and fibroblasts cell line BJ. The impact of CPS and UVB radiation on cell viability were examined by Neutral Red assay. The effect of CPS on VDR expression was evaluated by RT-qPCR and flow cytometry (FC). The presented study demonstrated that exposure to CPS and UVB significantly affects the viability of HaCaT and BJ cells lines. Results also revealed that exposure to CPS induced the expression at mRNA and protein level of VDR nuclear receptor in both cell lines exposed to UVB. In HaCaT incubated with 250 μM CPS and 15 mJ/cm² UVB, the relative VDR expression was ∼2-fold higher; whereas in BJ incubated with 250 μM CPS and 20 mJ/cm², UVB was∼3-fold higher. Results from FC confirmed this result, as VDR expression increased by ~250% in HaCaT incubated with 250 μM CPS and 20 mJ/cm² UVB, and in BJ incubated with 250 μM CPS, and 20 mJ/cm² UVB cells VDR expression increased by ~190%, compared with control. It can therefore be concluded that OPs pesticide might interfere with vitamin D₃ metabolism in skin cells.

Effects of vitamin D supplementation on advanced glycation end products signaling pathway in T2DM patients: a randomized, placebo-controlled, double blind clinical trial

BACKGROUND

Several researches have recommended vitamin D possible health benefits on diabetic complications development, but a few number of studies have been accomplished on the molecular and cellular mechanisms. Certain cellular pathways modification and also some transcription factors activation may protect cells from hyperglycemia condition induced damages. This study purpose was to determine the vitamin D supplementation effect on some key factors [advanced glycation end products (AGEs) signaling pathway] that were involved in the diabetic complications occurrence and progression for type-2 diabetes participants.

METHODOLOGY

48 type-2 diabetic patients (T2DM) randomly divided into two groups (n = 24 per group), receiving: 100-µg vitamin D or placebo for 3 months. At this study beginning and the end, the receptor expression for advanced glycation end products (RAGE) and glyoxalase I (GLO1) enzyme from peripheral blood mononuclear cells (PBMCs) and AGEs and tumor necrosis factor-α (TNF-α) serum levels were measured by the use of real-time PCR and ELISA methods, respectively.

RESULTS

This study results demonstrated that vitamin D supplementation could down-regulate RAGE mRNA [fold change = 0.72 in vitamin D vs. 0.95 in placebo) P = 0.001)]. In addition, no significant changes were observed for GLO1 enzyme expression (P = 0.06). This study results also indicated that vitamin D serum level significantly increased in vitamin D group (P < 0.001). Moreover, AGES and TNF-α serum levels significantly reduced in vitamin D group, but they were remained unchanged in the placebo group.

CONCLUSION

In conclusion, vascular complications are more frequent in diabetic patients, and vitamin D treatment may prevent or delay the complications onset in these patients by AGEs serum level and RAGE gene expression reducing.Trial registration NCT03008057. Registered December 2016.

Ultraviolet radiation, vitamin D and the development of obesity, metabolic syndrome and type-2 diabetes

Obesity is increasing in prevalence in many countries around the world. Its causes have been traditionally ascribed to a model where energy intake exceeds energy consumption. Reduced energy output in the form of exercise is associated with less sun exposure as many of these activities occur outdoors. This review explores the potential for ultraviolet radiation (UVR), derived from sun exposure, to affect the development of obesity and two of its metabolic co-morbidities, type-2 diabetes and metabolic syndrome. We here discuss the potential benefits (or otherwise) of exposure to UVR based on evidence from pre-clinical, human epidemiological and clinical studies and explore and compare the potential role of UVR-induced mediators, including vitamin D and nitric oxide. Overall, emerging findings suggest a protective role for UVR and sun exposure in reducing the development of obesity and cardiometabolic dysfunction, but more epidemiological and clinical research is required that focuses on measuring the direct associations and effects of exposure to UVR in humans.

Vitamin D increases IGF-I and insulin levels in experimental diabetic rats

INTRODUCTION AND OBJECTIVE

Previous studies have found that IGF-I may play an important role in glucose metabolism. The aim of this study is to examine the effect of vitamin D intake on the serum levels of glucose, insulin, and IGF-I in experimental diabetic rats.

MATERIAL AND METHODS

A total of 24 male Sprague-Dawley rats aged six to seven months, with an average weight of 300±30g, were randomly divided into three groups (eight rats per group). The first group served as control and the other two groups received an intraperitoneal injection of 45mg/kg streptozotocin (STZ) to develop diabetes. Then groups were treated for four weeks either with placebo or vitamin D (two injections of 20,000IU/kg).

RESULTS

At the end of the experiment, two injection of vitamin D were found to result in a significant increase in plasma cholecalciferol, which could improve hyperglycaemia and hypoinsulinemia in diabetic rats. HbA1c concentration had a slight and insignificant decrease following vitamin D intake. In addition, a significant decline was observed in the serum IGF-I level of STZ-treated rats in comparison to the controls, which was compensated in the vitamin D group. The serum vitamin D concentration was positively correlated to the changes in IGF-I level by Pearson test.

CONCLUSIONS

These data showed for the first time that vitamin D intake could significantly improve fasting plasma glucose, insulin, and IGF-I in an experimental type 1 diabetes model.

Role of vitamin D in energy and bone metabolism in postmenopausal women with type 2 diabetes mellitus: A 6-month follow-up evaluation

AIMS/INTRODUCTION

Resting energy expenditure was associated with a serum bone turnover marker in postmenopausal women with type 2 diabetes (T2DMPW) in the present cross-sectional study. To clarify the fundamental pathological factor for the correlation of bone metabolism and basal metabolism in type 2 diabetes, a 6-month prospective follow-up study was carried out with supplementation of vitamin D.

MATERIALS AND METHODS

A total of 44 T2DMPW were enrolled. The following factors were evaluated at the beginning and the end of the summer: procollagen type 1 N-terminal propeptide, carboxy-terminal collagen crosslinks-1, intact parathyroid hormone and 25-hydroxyvitamin D (25[OH]D), as well as diabetic complications, body composition, respiratory quotient and resting energy expenditure. A total of 23 patients with low 25(OH)D levels (˂20 ng/mL) were instructed to increase vitamin D levels by lifestyle change. Among them, 15 patients with osteoporosis were also administered alfacalcidol.

RESULTS

Serum 25(OH)D increased in 25 patients and decreased in 19 patients. Patients who did not receive the study intervention at the start tended to have a decreased 2525(OH)D level; therefore, the average 25(OH)D level of all patients was not changed. Changes in resting energy expenditure were positively correlated with those of procollagen type 1 N-terminal propeptide/carboxy-terminal collagen crosslinks-1. Changes in the respiratory quotient correlated with the mean glycated hemoglobin levels; procollagen type 1 N-terminal propeptide levels positively correlated with serum 25(OH)D after the intervention. These correlations were prominent in patients with increased 25(OH)D and those with alfacalcidol supplementation.

CONCLUSIONS

Restoration of vitamin D level might be a prerequisite for a normal correlation between bone and basal metabolism in T2DMPW. Lifestyle intervention for retention of vitamin D level is important even in summer, in T2DMPW.

Effects of vitamin D and resveratrol on metabolic associated markers in liver and adipose tissue from SAMP8 mice

SAMP8 mice exhibit multiple metabolic characteristics associated with age, and it is a suitable candidate for researching aging associated metabolic dysfunction.

OBJECTIVES

We aimed to 1) explore how key metabolic markers will be altered in both liver and adipose tissue with aging in SAMP8 mice; and 2) how the combination of vitamin D (VD) with resveratrol (RSV) will affect aging associated metabolic impairment in liver and adipose tissue from SAMP8 mice.

METHODS

SAMP8 mice and their control SAMR1 mice were divided into 5 groups, i.e. SAMR1, SAMP8, SAMP8 mice supplemented with VD, RSV and VD combined with RSV group, respectively. At the end of the intervention, glucose and insulin tolerance, p-AMP-activated protein kinase (AMPK) and amyloid precursor protein (APP), and endoplasmic reticulum (ER) stress markers in liver and adipose tissue, adiponectin secretion, p-NF-κBp65 and TNF-α protein expression in adipose tissue were determined.

RESULTS

Compared to SAMR1 control, SAMP8 mice demonstrate impaired glucose tolerance and reduction in circulating adiponectin level; in the liver, SAMP8 mice have reduction in p-Aktser473, elevation in PTP1B and APP, p-eIF2α, GRP78 and p-JNK protein expression. In epididymal (EPI) fat, SAMP8 mice also have elevated p-Aktser473 and PTP1B compared to SAMR1 mice. In both epididymal (EPI) and subcutaneous (SC) fat, there were elevated ER stress markers, reduced p-AMPK and elevated APP, as well as elevated p-NF-κBp65 and TNF-α protein expression from SAMP8 compared to SAMR1 mice. In liver, the combined intervention significantly restored p-Aktser473, p-eIF2α and p-JNK protein expression. In both EPI and SC fat, the combined intervention is effective for reducing p-NF-κB p65 and TNF-α in both fat depot, while only partially reduced ER stress markers in SC fat. As for adiponectin, their combination is unable to reverse reduction in adiponectin level. Adiponectin secretion in SC fat from VD, RSV and VDRSV group were also significantly reduced compared to SAMR1.

CONCLUSION

The combined intervention might exert greater beneficial effects for reversing aging associated metabolic dysfunction in liver and adipose tissue from SAMP8 mice.

The Potential Protective Action of Vitamin D in Hepatic Insulin Resistance and Pancreatic Islet Dysfunction in Type 2 Diabetes Mellitus

Vitamin D deficiency (i.e., hypovitaminosis D) is associated with increased insulin resistance, impaired insulin secretion, and poorly controlled glucose homeostasis, and thus is correlated with the risk of metabolic diseases, including type 2 diabetes mellitus (T2DM). The liver plays key roles in glucose and lipid metabolism, and its dysregulation leads to abnormalities in hepatic glucose output and triglyceride accumulation. Meanwhile, the pancreatic islets are constituted in large part by insulin-secreting β cells. Consequently, islet dysfunction, such as occurs in T2DM, produces hyperglycemia. In this review, we provide a critical appraisal of the modulatory actions of vitamin D in hepatic insulin sensitivity and islet insulin secretion, and we discuss the potential roles of a local vitamin D signaling in regulating hepatic and pancreatic islet functions. This information provides a scientific basis for establishing the benefits of the maintenance, or dietary manipulation, of adequate vitamin D status in the prevention and management of obesity-induced T2DM and non-alcoholic fatty liver disease.