Vitamin D3 improves glucose metabolism and attenuates inflammation in prediabetic human and mice

Prediabetes is a crucial stage for prevention and treatment of diabetes, and vitamin D (VD) has been found to be linked to the development of prediabetes and diabetes. Thus, we aimed to identify the effect of VD supplementation on glucose metabolism in prediabetic participants and mice. A 1:1 paired design of randomized, placebo-controlled trial with 1600 IU/day VD3 or placebo was administered to individuals with prediabetes, two-way repeated-measures ANCOVA was used to analyze glycolipid and inflammatory factors. A high-fat diet induced prediabetic KKay mice were utilized to evaluate the effects of VD3 with 16 weeks supplementation. Generalized estimation equation, one way ANOVA were used to analyze continuous monitoring indexes and terminal indexes, respectively. Exercise capacity, skeletal muscle pathological features and relevant proteins were examined. The clinical results showed that VD3 could improve insulin secretion and decrease inflammation. Results of KKay mice exhibited that VD3 not only ameliorate glycolipid metabolism and inflammatory indicators, but also regulated pathological changes of skeletal muscle and exercise capacity. Mechanistically, our results demonstrated that VD3 could inhibit the TLR4/NFκB and activate PI3K/AKT signaling pathway. Collectively, the study indicated that VD3 exerts its beneficial effects by inhibiting TLR4/NFκB to decrease inflammatory response, and activating PI3K/AKT signaling pathway to regulate glucose homeostasis.

Interplay between Vitamin D and Adipose Tissue: Implications for Adipogenesis and Adipose Tissue Function

Adipose tissue encompasses various types, including White Adipose Tissue (WAT), Brown Adipose Tissue (BAT), and beige adipose tissue, each having distinct roles in energy storage and thermogenesis. Vitamin D (VD), a fat-soluble vitamin, maintains a complex interplay with adipose tissue, exerting significant effects through its receptor (VDR) on the normal development and functioning of adipocytes. The VDR and associated metabolic enzymes are widely expressed in the adipocytes of both rodents and humans, and they partake in the regulation of fat metabolism and functionality through various pathways. These encompass adipocyte differentiation, adipogenesis, inflammatory responses, and adipokine synthesis and secretion. This review primarily appraises the role and mechanisms of VD in different adipocyte differentiation, lipid formation, and inflammatory responses, concentrating on the pivotal role of the VD/VDR pathway in adipogenesis. This insight furnishes new perspectives for the development of micronutrient-related intervention strategies in the prevention and treatment of obesity.

A randomized controlled trial of Vitamin D supplementation in Iranian patients with schizophrenia: Effects on serum levels of glycogen synthase kinase-3β and symptom severity

BACKGROUND

Growing evidence has shown that hypovitaminosis D is a risk factor for developing schizophrenia and comorbid conditions. Therefore, this study aimed to examine the effect of vitamin D supplementation on serum levels of vitamin D, metabolic factors related to insulin resistance (IR) and the severity of the disorder in patients with schizophrenia.

METHODS

Forty-eight chronic male patients with schizophrenia with vitamin D deficiency (≤20 ng/mL= (≤50 nmol/l) were selected and randomly assigned to vitamin D treatment and placebo groups. Subjects were supplemented for 8 weeks with vitamin D (2000 IU/day) or placebo.

RESULTS

Within-group comparison revealed that the vitamin D group had a significant reduction in waist circumference, Positive and Negative Syndrome Scale - total score (PANSS-TS), and glycogen synthase kinase 3 beta (GSK-3β) levels (P = .022, P = <.001 and P = .013, respectively). On the other hand, the placebo group showed a significant increase in the level of fasting serum insulin and Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) (P = .003 and P = .003). The between-group comparison showed a significant difference in terms of PANSS-TS, GSK-3β, fasting serum insulin (FSI), and HOMA-IR (P = .022, P = .048, P = .013 and P = .014 respectively).

CONCLUSIONS

Among vitamin D deficient patients with schizophrenia, vitamin D supplementation may affect GSK-3 β, an important biomarker in schizophrenia and insulin resistance. In addition, vitamin D supplementation in such patients may reduce the disorder's symptom severity.

The role of vitamin D on redox regulation and cellular senescence

Vitamin D is considered an essential micronutrient for human health that is metabolized into a multifunctional secosteroid hormone. We can synthesize it in the skin through ultraviolet B (UVB) rays or acquire it from the diet. Its deficiency is a major global health problem that affects all ages and ethnic groups. Furthermore, dysregulation of vitamin D homeostasis has been associated with premature aging, driven by various cellular processes, including oxidative stress and cellular senescence. Various studies have shown that vitamin D can attenuate oxidative stress and delay cellular senescence, mainly by inducing the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and Klotho and improving mitochondrial homeostasis, proposing this vitamin as an excellent candidate for delaying aging. However, the mechanisms around these processes are not yet fully explored. Therefore, in this review, the effects of vitamin D on redox regulation and cellular senescence are discussed to propose new lines of research and clinical applications of vitamin D in the context of age-related diseases.

Vitamin D and Obesity/Adiposity—A Brief Overview of Recent Studies

Observational studies classically find an inverse relationship between human plasma 25-hydroxyvitamin D concentration and obesity. However, interventional and genetic studies have failed to provide clear conclusions on the causal effect of vitamin D on obesity/adiposity. Likewise, vitamin D supplementation in obese rodents has mostly failed to improve obesity parameters, whereas several lines of evidence in rodents and prospective studies in humans point to a preventive effect of vitamin D supplementation on the onset of obesity. Recent studies investigating the impact of maternal vitamin D deficiency in women and in rodent models on adipose tissue biology programming in offspring further support a preventive metabolically driven effect of vitamin D sufficiency. The aim of this review is to summarize the state of the knowledge on the relationship between vitamin D and obesity/adiposity in humans and in rodents and the impact of maternal vitamin D deficiency on the metabolic trajectory of the offspring.

Pancreatic islet cells disarray, apoptosis, and proliferation in obese mice. The role of Semaglutide treatment

There are significant injuries of pancreatic islets due to obesity and insulin resistance. Therefore, GLP-1 receptor agonists like Semaglutide might benefit the islet structural remodeling and its endocrine function in diet-induced obese mice. One-month-old male C57BL/6 mice were allotted into two dietary groups (n = 60/group) and fed for 16 weeks a control diet (C) or a high‒fat diet (HF). Then, for an additional four weeks, the main groups were resampled to include treatment (Semaglutide, S, 40 μg/kg), or paired feed with the treated group (PF), totaling six groups (n = 20/group): C, CS, CPF, HF, HFS, HFPF. Biochemistry, stereology, immunohistochemistry/immunofluorescence, confocal microscopy, and RT-qPCR were used in the study. The mouse model reproduced metabolism and bodily changes due to diet-induced obesity. Pancreatic islet hypertrophy was observed with alpha- and beta-cell remodeling, cell disarray, and apoptosis. Semaglutide increased islet cell proliferation and recovered islet size and alpha- and beta-cell masses. The changes include recovery of glucose and hormone levels, reduction of pro-inflammatory markers, improvement of pancreatic duodenal homeobox 1 (PDX-1), glucose transporter 2 (GLUT-2), v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MAF-A), and peroxisome proliferator-activated receptors (PPAR) -gamma. In conclusion, damage to the pancreatic islet caused by insulin resistance and the attempt to adapt the islet of obese mice involved different pathways, especially the pro-inflammatory pathway, PDX1, and PPAR-alpha and gamma. Semaglutide showed beneficial effects on these pathways, reducing the lesion on the islet. However, the weight loss influence of Semaglutide was of little relevance in the pancreatic islet.

Vitamin D Rescues Pancreatic β Cell Dysfunction due to Iron Overload via Elevation of the Vitamin D Receptor and Maintenance of Ca2+ Homeostasis

SCOPE

Accumulating evidence indicates that micronutrients are related to metabolic diseases. However, comparatively less attention has been devoted to their influence on each other during the development of metabolic diseases. To investigate the underlying mechanisms, the effects of iron and vitamin D on pancreatic β cell functions are examined.

METHODS AND RESULTS

Iron overload is induced in INS-1 rat insulinoma pancreatic β cells and it is found that iron overload dramatically reduce expression of the vitamin D receptor (VDR). Iron overload-induced β cell dysfunction is rescued by 1,25-dihydroxyvitamin D3 (1,25(OH)2 D3 ) cotreatment via restoration of VDR level and the consequent maintenance of Ca2+ homeostasis. Iron accumulation is also observed in the islets of 22-month-old C57BL/6 mice fed with a chow diet (1000 IU vitamin D3 per kg). In contrast, islet iron accumulation and hyperinsulinemia are ameliorated in mice fed with a vitamin D3 -supplemented diet (20 000 IU kg-1 ).

CONCLUSION

The authors show that functional failure of β cells due to iron accumulation is rescued by 1,25(OH)2 D3 , and iron overload significantly reduces VDR levels in β cells. These results suggest that iron and vitamin D inversely influence pancreatic β cell function.

Vitamin D actions in neurons require the PI3K pathway for both enhancing insulin signaling and rapid depolarizing effects

Despite correlations between low vitamin D levels and diabetes incidence/severity, supplementation with vitamin D has not been widely effective in improving glucose parameters. This may be due to a lack of knowledge regarding how low vitamin D levels physiologically affect glucose homeostasis. We have previously shown that the brain may be a critical area for vitamin d-mediated action on peripheral glucose levels. However, the mechanisms for how vitamin D acts in the brain are unknown. We utilized a multimodal approach to determine the mechanisms by which vitamin D may act in the brain. We first performed an unbiased search (RNA-sequencing) for pathways affected by vitamin D. Vitamin D (125-dihydroxyvitamin D3; 1,25D3) delivered directly into the third ventricle of obese animals differentially regulated multiple pathways, including the insulin signaling pathway. The insulin signaling pathway includes PI3K, which is important in the brain for glucose regulation. Since others have shown that vitamin D acts through the PI3K pathway in non-neuronal cells (muscle and bone), we hypothesized that vitamin D may act in neurons through a PI3K-dependent pathway. In a hypothalamic cell-culture model (GT1-7 cells), we demonstrate that 1,25D3 increased phosphorylation of Akt in the presence of insulin. However, this was blocked with pre-treatment of wortmannin, a PI3K inhibitor. 1,25D3 increased gene transcription of several genes within the PI3K pathway, including Irs2 and p85, without affecting expression of InsR or Akt. Since we had previously shown that 1,25D3 has significant effects on neuronal function, we also tested if the PI3K pathway could mediate rapid actions of vitamin D. We found that 1,25D3 increased the firing frequency of neurons through a PI3K-dependent mechanism. Collectively, these data support that vitamin D enhances insulin signaling and neuronal excitability through PI3K dependent processes which involve both transcriptional and membrane-initiated signaling events.

Intermittent fasting benefits on alpha- and beta-cell arrangement in diet-induced obese mice pancreatic islet

AIMS

There is a pancreatic islet adaptation in obese subjects, resulting in insulin resistance and diabetes type 2. We studied the effect of intermittent fasting (IntF) on the islet structure of diet-induced obese (DIO) mice.

METHODS

Three-month-old male mice fed a control diet (C, 10% Kcal fat) or a high-fat diet (HF, 50% Kcal fat) for two months (n = 20 each group). Then, half of each group did IntF (alternating 24 h fed/24 h fast), continuing in their diets four more weeks: C, C-IntF, HF, HF-IntF. Islets were prepared to microscopy or isolated for molecular analysis.

RESULTS

HF group (vs. C group) showed hyperglycemia, hyperinsulinemia, hyperleptinemia, hypoadiponectinemia, glucose intolerance, insulin resistance, and islet hypertrophy with a consequent higher both the alpha-cell and beta-cell masses. In the HF group (vs. C), there was low PDX1 (pancreatic and duodenal homeobox 1), and IntF did not alter PDX1. There was a low p-AKT/AKT ratio (protein kinase B), and IntF enhanced it. Also, tumor suppressor p53 was increased, and IntF decreased it. IL (interleukin) -6 was higher in the HF group (vs. C), and HF-IntF (vs. C-IntF). Any significant change in NFkB was seen among groups.

CONCLUSIONS

IntF improves pancreatic islet structure in DIO mice, even with continued HF diet intake, primarily considering on the alpha- and beta-cell masses regulation, then improving insulin signaling and decreasing cell apoptosis. Future research should explore whether the shortening of the IntF extend could maintain the benefits observed in the long term.

The deficiency and the supplementation of vitamin D and liver: Lessons of chronic fructose-rich diet in mice

The fructose added to soft drinks and processed food, as well as frequent detection of vitamin D deficiency in the body, are two insults increasingly considered to cause lesions in target organs. We studied the liver after a chronic high-fructose diet deficient and supplemented with vitamin D. Sixty C57BL/6 mature male mice were allocated into six groups (n = 10) for ten weeks: control (C), control deficient in vitamin D (CDD), control supplemented with vitamin D (CDS), fructose (F), fructose deficient in vitamin D (FDD), and fructose supplemented with vitamin D (FDS). The gene expressions of vitamin D receptor and CYP27B1 and 25 hydroxyvitamin D plasma level ensured that the diets caused vitamin D deficiency or supplementation. Body mass did not change, but blood pressure (BP) increased in CDD, F, and FDD, whereas BP was controlled in FDS. Insulinemia, insulin tolerance and resistance were seen in both vitamin D deficiency and fructose groups but improved with vitamin D supplementation. The steatosis and fibrosis were observed in the CDD, F and FDD groups. Also, F and FDD showed activation of stellate cells (HSC). Lipogenesis and inflammation gene expressions were enhanced in the CDD, F and FDD groups, but diminished with vitamin D supplementation. In conclusion, we demonstrated the adverse effects of vitamin D deficiency on metabolism, liver steatosis and, combined with fructose intake, liver interstitial fibrosis with hepatic stellate cell activation, and alteration of the lipogenesis, beta-oxidation, and liver inflammation. All these data improved when vitamin D was supplemented in the animals.

Vitamin D and the paraventricular nucleus: Relevance for type 2 diabetes

Vitamin D deficiency is linked to type 2 diabetes and we recently showed this may be through action of vitamin D in the paraventricular nuclei (PVN) in the hypothalamus of the brain. This review focuses on the known roles of the PVN in glucose control and how previously discovered actions of vitamin D in other tissues may translate to action in the PVN. Specifically, we focus on the role of insulin and inflammation in the hypothalamus and how these may be modified through vitamin D action.

The Relationship between Vitamin D and Type 2 Diabetes Is Intriguing: Glimpses from the Spect-China Study

OBJECTIVE

Vitamin D is a multifunctional vitamin for our body. Type 2 diabetes mellitus (T2DM) is a common metabolic disease. Whether T2DM affects the serum 25(OH)D level has not been reported. The objective of this study was to reveal the extent to which vitamin D is present in the population in East China and to explore the relationship between serum 25(OH)D and T2DM.

METHODS

The cohort was selected based on a large investigation named Survey on Prevalence in East China including 12,702 participants aged 21-92 years old. All the participants completed the questionnaire and went through a physical examination. Fasting blood samples were collected to test serum 25(OH)D and other metabolism-related indicators. AVONA was used to test the significance of differences among groups. Multinomial logistic regression was used to assess the association of T2DM with serum 25(OH)D level.

RESULTS

The overall percentage of vitamin D deficiency was 80.55% (male 74.1%, female 85.0%). Men with lower serum 25(OH)D level had high value in homeostasis model assessment of insulin resistance and HbA1c. The serum 25(OH)D level of those who were diagnosed with T2DM was higher than that in non-diabetics. The serum 25(OH)D level of pre-diabetes was the highest. T2DM patients trended to have higher serum 25(OH)D levels.

CONCLUSION

Vitamin D deficiency is common among the people in East-China. T2DM patients had higher levels of serum 25(OH)D. The relationship between vitamin D and T2DM is intriguing. It seemed that vitamin D was either irrelevant directly to T2DM or resisted in T2DM patients.

Differential effects of angiotensin receptor blockers on pancreatic islet remodelling and glucose homeostasis in diet-induced obese mice

Obesity leads to adverse endocrine pancreas remodelling, reduced islet lifespan and early type 2 diabetes onset. AT1R blockade shows beneficial pleiotropic effects. This study sought to compare the effects of losartan and telmisartan on pancreatic islets remodelling and glucose homeostasis in diet-induced obese mice. High-fat diet yielded overweight, insulin resistance, islet apoptosis and hypertrophy. Suitable insulin levels and preserved endocrine pancreas structure were correlated to adequate AKT-FOXO1 pathway functioning in losartan-treated animals. Conversely, telmisartan yielded enhanced PDX1 and GLP-1 islet expression along with greater GLP-1 levels, with the consequent better islet glucose sensing and uptake. Greater islet vascularisation coupled with reduced apoptosis and macrophage infiltration seems to underlie the beneficial findings in both treatments. In conclusion, these results provide compelling evidence that two antihypertensive drugs (telmisartan and losartan) ameliorate pancreatic islet structure, glucose handling, and vascularisation in obese mice. Although only telmisartan countered overweight, both drugs yielded reduced apoptosis and islet preservation, with translational potential.

Maternal vitamin D-restricted diet has consequences in the formation of pancreatic islet/insulin-signaling in the adult offspring of mice

The maternal deficiency of vitamin D can act on organogenesis in mice offspring, being a risk factor for chronic diseases in adulthood. This study investigates the effects of maternal deficiency of vitamin D on structural islet remodeling and insulin-signaling pathway in the offspring. We studied male C57Bl/6 offspring at 3-month old (n = 10/group) from mother fed one of the two diets: control diet (C) or vitamin D-restricted diet (VitD^-). After weaning, offspring only fed the control diet ad libitum. In the offspring, we studied insulin production, islet remodeling, and islet protein expression of the insulin-signaling pathway (Western blotting, isolated islet, n = 5/group). VitD^- offspring showed greater glycemia (P = 0.012), smaller beta-cell mass (P = 0.014), and hypoinsulinemia (P = 0.024) than C offspring. Comparing VitD^- offspring with C offspring, we observed lower protein levels in islet of insulin (P = 0.003), insulin receptor substrate-1 (P = 0.025), phosphatidylinositol-3-kinases (P = 0.045), 3-phosphoinositide-dependent protein kinase 1 (P = 0.017), protein kinase B (P = 0.028), with reduced expression of pancreas/duodenum homeobox-1 (PDX-1) (P = 0.016), glucose transporter-2 (P = 0.003), and glucokinase (P = 0.045). The maternal vitamin D-restricted diet modifies the development of the pancreas of the offspring, leading to islet remodeling and altered insulin-signaling pathway. The decrease of PDX-1 is probably significant to the changes in the beta-cell mass and insulin secretion in adulthood.

Chronic over-nutrition and dysregulation of GSK3 in diseases

Loss of cellular response to hormonal regulation in maintaining metabolic homeostasis is common in the process of aging. Chronic over-nutrition may render cells insensitive to such a hormonal regulation owing to overstimulation of certain signaling pathways, thus accelerating aging and causing diseases. The glycogen synthase kinase 3 (GSK3) plays a pivotal role in relaying various extracellular and intracellular regulatory signals critical to cell growth, survival, regeneration, or death. The main signaling pathway regulating GSK3 activity through serine-phosphorylation is the phosphoinositide 3-kinase (PI3K)/phosphoinositide-dependent kinase-1 (PDK1)/Akt relay that catalyzes serine-phosphorylation and thus inactivation of GSK3. In addition, perilipin 2 (PLIN2) has recently been shown to regulate GSK3 activation through direct association with GSK3. This review summarizes current understanding on environmental and nutritional factors contributing to GSK3 regulation (or dysregulation) through the PI3K/PDK1/Akt/GSK3 axis, and highlights the newly discovered role that PLIN2 plays in regulating GSK3 activity and GSK3 downstream pathways.