Vitamin D receptor activation induces peptide YY transcription in pancreatic islets

Vitamin D regulates glucose metabolism in zebrafish (Danio rerio) by maintaining intestinal homeostasis

Vitamin D (VD) is a steroid hormone that is widely known to play an important role in maintaining mineral homeostasis, and regulating various physiological functions. Our previous results demonstrated that the interruption of VD metabolism caused hyperglycemia in zebrafish. In the present study we further explored the mechanism that VD regulates glucose metabolism by maintaining intestinal homeostasis in zebrafish. Our results showed that the expression of several peptide hormones including gastric inhibitory peptide, peptide YY, and fibroblast growth factor 19 in the intestine decreased, while the expression of sodium glucose cotransporter-1 and gcg was increased in the intestine of the zebrafish fed with the VD3-deficient diet. Consistently, similar results were obtained in cyp2r1-/- zebrafish, in which endogenous VD metabolism is blocked. Furthermore, the results obtained from germ-free zebrafish exhibited that VD-regulated glucose metabolism was partly dependent on the microbiota in zebrafish. Importantly, the transplantation of gut microbiota collected from cyp2r1-/- zebrafish to germ-free zebrafish led to hyperglycemic symptoms in the fish, which were associated with the altered structure and functions of the microbiota in cyp2r1-/- zebrafish. Interestingly, the treatments with acetate or Cetobacterium somerae, a potent acetate producer, lowered the glucose contents whereas augmented insulin expression in zebrafish larvae. Notably, acetate supplementation alleviated hyperglycemia in cyp2r1-/- zebrafish and other diabetic zebrafish. In conclusion, our study has demonstrated that VD modulates the gut microbiota-SCFAs-gastrointestinal hormone axis, contributing to the maintenance of glucose homeostasis.

Changes in Appetite-Dependent Hormones and Body Composition After 8 Weeks of High-Intensity Interval Training and Vitamin D Supplementation in Sedentary Overweight Men

Exercise and diet are important factors for energy balance and appetite regulation. The aim of this study was to investigate the effect of 8 weeks High Intensity Interval Training (HIIT) and vitamin D₃ supplementation in sedentary overweight men. Forty-eight participants were randomly assigned to one of the following four groups (n = 12): HIIT + VitD, HIIT + placebo (3 sessions per week, 10 × 1 min interval cycling at 90-100% VO_2peak separated by 1 min active recovery at 15% VO_2peakfor 8 weeks), Vit D and control groups. Participants received 2,000 IU/day 25 (OH) D₃ or placebo. Measurements were taken pre and post training after 10 h overnight fasting. Insulin, weight, BMI and body fat percentage were significantly decreased, but PYY was significantly increased in the HIIT + Vit D and HIIT + placebo groups (p = 0.001 and p = 0.001, respectively) after 8 weeks of HIIT. Insulin (p = 0.009, p = 0.001), weight, BMI and body fat percentage (p = 0.001, p = 0.001) were significantly lower in the HIIT + Vit D and HIIT + placebo groups compared to the Vit D and control groups. However, PYY was significantly higher in the HIIT + Vit D group compared to the Vit D (p = 0.025) and control groups (p = 0.007) and also in the HIIT + placebo group compared to the Vit D (p = 0.037) and control groups (p = 0.032) after 8 weeks of HIIT. The combination of regular HIIT with vitamin D supplementation has a effect on appetite control and body composition.

Frontline Science: Concanavalin A-induced acute hepatitis is attenuated in vitamin D receptor knockout mice with decreased immune cell function

The vitamin D receptor (VDR) is a nuclear receptor for the active form of vitamin D, 1α,25-dihydroxyvitamin D₃ , and regulates various physiologic processes, such as bone and calcium metabolism, cellular proliferation and differentiation, and immunity. VDR is highly expressed in the intestine, kidney, bone, and macrophages, but is expressed at a low level in the liver. The liver is a major metabolic organ and also acts as an immune gateway for dietary nutrients and xenobiotics. In this study, we investigated the function of VDR in hepatic immune cells, such as Kupffer cells/macrophages, utilizing VDR knockout (KO) mice. We showed that VDR is functionally expressed in hepatic mononuclear cells, specifically resident Kupffer cells. We examined the role of VDR in acute hepatitis induced by concanavalin A (Con-A) and found that Con-A-induced hepatitis is attenuated in VDR-KO mice compared to wild-type (WT) mice. Con-A-induced hepatitis is known to be mediated by NKT cell activation, cytokine production, and reactive oxygen species (ROS) production in Kupffer cells/macrophages. However, the proportions of Kupffer cells/macrophages and the NKT cell activation were similar in the liver of WT and VDR-KO mice and inflammatory cytokine gene expression was increased in VDR-KO mice. On the other hand, plasma and hepatic ROS levels were decreased in the liver of VDR-KO mice compared to WT mice. The phagocytic activity of resident Kupffer cells and hepatic neutrophils were also decreased in VDR-KO mice. Therefore, VDR is necessary for Con-A-induced acute hepatitis and plays an important role in hepatic immune cell functions.

Adaptive homeostasis of the vitamin D-vitamin D nuclear receptor axis in 8-methoxypsoralen-induced hepatotoxicity

8-methoxypsoralen (8-MOP) with ultraviolet A radiation therapy (PUVA) is the standard therapy for patients with psoriasis, despite the reported potential risks of 8-MOP-induced cholestatic liver injury in both humans and animals. Usually, patients with chronic cholestasis exhibit lower serum 25-hydroxy vitamin D (25(OH)D) levels. But those patients receiving PUVA for psoriasis showed an increase in serum 25(OH)D levels, probably highlighting that the vitamin D-vitamin D nuclear receptor (VD-VDR) axis play a protective role in 8-MOP-induced hepatotoxicity. The present study confirmed 8-MOP could increase serum 25(OH)D levels in conventional lighting and diet (CLD) and vitamin D deficient (VDD) Sprague-Dawley rats. Potential liver risks were also found in CLD and VDD rats after 8-MOP treatment. We proved that 8-MOP could be a potent ligand for VDR using molecular docking and luciferase report assay. Effect of 8-MOP on VDR subcellular distribution was determined using human liver cell line L02. We found 8-MOP could increase VDR protein expression in the nuclear and cytosol extracts and also total cell extracts in L02. siRNAs for VDR were used to determine the role of VDR in protecting 8-MOP-induced cholestasis and potential cellular mechanisms. The results showed 8-MOP could affect the CYP7A1, SHP and MRP3 expression via VDR, and such effects could be reversed by knockdown of VDR expression, suggesting a vital role of VDR involved in 8-MOP-regulated bile acid synthesis and transportation. In conclusion, these results revealed activation of VD-VDR axis may play a beneficial role in 8-MOP-mediated regulation of bile acid synthesis and transportation.

PTH and Vitamin D

PTH and Vitamin D are two major regulators of mineral metabolism. They play critical roles in the maintenance of calcium and phosphate homeostasis as well as the development and maintenance of bone health. PTH and Vitamin D form a tightly controlled feedback cycle, PTH being a major stimulator of vitamin D synthesis in the kidney while vitamin D exerts negative feedback on PTH secretion. The major function of PTH and major physiologic regulator is circulating ionized calcium. The effects of PTH on gut, kidney, and bone serve to maintain serum calcium within a tight range. PTH has a reciprocal effect on phosphate metabolism. In contrast, vitamin D has a stimulatory effect on both calcium and phosphate homeostasis, playing a key role in providing adequate mineral for normal bone formation. Both hormones act in concert with the more recently discovered FGF23 and klotho, hormones involved predominantly in phosphate metabolism, which also participate in this closely knit feedback circuit. Of great interest are recent studies demonstrating effects of both PTH and vitamin D on the cardiovascular system. Hyperparathyroidism and vitamin D deficiency have been implicated in a variety of cardiovascular disorders including hypertension, atherosclerosis, vascular calcification, and kidney failure. Both hormones have direct effects on the endothelium, heart, and other vascular structures. How these effects of PTH and vitamin D interface with the regulation of bone formation are the subject of intense investigation.

Effects of early enteral micro-feeding on neonatal serum Vitamin D levels

Objective:

To evaluate the effects of early enteral micro-feeding on neonatal serum vitamin D levels, and to analyze the application value of glutamine.

Methods:

One hundred ninty neonates enrolled in intensive care unit were randomly divided into a treatment group and a control group (n=95) that were both given enteral and parenteral nutrition support. Meanwhile, the treatment group was fed formula milk containing 0.3 g/(kg·d) glutamine as enteral nutrition support for 14 days.

Results:

The weight of the treatment group increased significantly faster than that of the control group did (P<0.05). The treatment group had significantly higher milk amount and calorie intake than those of the control group (P<0.05), and neonates in the treatment group who reached calorie intake of 50/80/100 kcal/kg/d were significantly younger (P<0.05). Meanwhile, the treatment group was significantly less prone to feeding intolerance than the control group (P<0.05). After 14 days of feeding, the serum motilin, gastrin and vitamin D levels of both groups all increased, with significant intra-group and inter-group differences. Such levels of the treatment group significantly exceeded those of the control group (P<0.05).

Conclusion:

Supplementing early enteral micro-feeding with glutamine promoted the absorption of neonatal routine nutrients and vitamin D, obviously regulated gastrointestinal hormones, and elevated weight as a result.

Decreased serum vitamin D levels are associated with diabetic peripheral neuropathy in a rural area of Turkey

Data examining the association between vitamin D and diabetic peripheral neuropathy are limited. This study investigated the serum levels of vitamin D, vitamin D-binding protein (VDBP), and vitamin D receptor (VDR) in diabetics in the Yozgat region of Turkey, and assessed their relationships with diabetic peripheral neuropathy. 69 diabetic patients and 49 age- and sex-matched control subjects were enrolled in this clinical prospective study. All the diabetics underwent conventional sensory and motor nerve conduction studies, and diabetic peripheral neuropathy was confirmed or ruled out according to the electromyography findings and Douleur Neuropathique 4 questions. Serum vitamin D, VDBP and VDR levels were measured using commercial enzyme-linked immunosorbent assay kits. The serum vitamin D levels (p = 0.001) were significantly lower, while the VDR levels (p = 0.003) were higher, in diabetics than in controls. The serum VDBP levels were similar in both groups (p > 0.05). The serum vitamin D levels were significantly lower in diabetics with diabetic peripheral neuropathy than in those without (p = 0.032), whereas the serum VDBP and VDR levels were similar in these two groups (p > 0.05). The lower serum vitamin D levels in diabetics, especially in those with peripheral neuropathy, may suggest a neurotrophic effect of vitamin D.

Vitamin D and energy homeostasis: of mice and men

The vitamin D endocrine system has many extraskeletal targets, including adipose tissue. 1,25-Dihydroxyvitamin D₃, the active form of vitamin D, not only increases adipogenesis and the expression of typical adipocyte genes but also decreases the expression of uncoupling proteins. Mice with disrupted vitamin D action--owing to gene deletion of the nuclear receptor vitamin D receptor (Vdr) or the gene encoding 1α-hydroxylase (Cyp27b1)--lose fat mass over time owing to an increase in energy expenditure, whereas mice with increased Vdr-mediated signalling in adipose tissue become obese. The resistance to diet-induced obesity in mice with disrupted Vdr signalling is caused at least partially by increased expression of uncoupling proteins in white adipose tissue. However, the bile acid pool is also increased in these animals, and bile acids are known to be potent inducers of energy expenditure through activation of several nuclear receptors, including Vdr, and G-protein-coupled receptors, such as GPBAR1 (also known as TGR5). By contrast, in humans, obesity is strongly associated with poor vitamin D status. A causal link has not been firmly proven, but most intervention studies have failed to demonstrate a beneficial effect of vitamin D supplementation on body weight. The reasons for the major discrepancy between mouse and human data are unclear, but understanding the link between vitamin D status and energy homeostasis could potentially be very important for the human epidemic of obesity and the metabolic syndrome.

Enhanced transcription of pancreatic peptide YY by 1α-hydroxyvitamin D3 administration in streptozotocin-induced diabetic mice

Peptide YY (PYY) is a peptide hormone secreted from L cells in the intestine in response to food intake that regulates appetite and gastrointestinal function. PYY is also produced in the pancreatic islets. The vitamin D receptor (VDR) is a nuclear receptor for the active form of vitamin D3 that regulates numerous physiological processes. VDR is expressed in the pancreatic islets and pharmacological VDR activation increases PYY expression in mouse peripheral islet cells. Although VDR is present in insulin-producing β cells as well as non-β cells, the role of β cell VDR in Pyy transcription remains unknown. We treated mice with streptozotocin to ablate β cells in the pancreas. Pancreatic Vdr mRNA expression was decreased in streptozotocin-induced diabetic mice. Interestingly, streptozotocin-treated mice exhibited increased basal Pyy expression and 1α-hydroxyvitamin D3 treatment further increased expression. Moreover, 1α-hydroxyvitamin D3 increased mRNA expression of pancreatic polypeptide and decreased that of neuropeptide Y in streptozotocin-induced diabetic mice but not in control mice. 1α-Hydroxyvitamin D3 slightly increased mRNA expression of insulin but transcript levels were nearly undetectable in the pancreas of streptozotocin-treated mice. Thus, VDR in non-β islet cells is involved in Pyy expression in the mouse pancreas. The findings from this β cell ablation study suggest a hormone transcription regulatory network composed of β cells and non-β cells.