High Dosage of Vitamin D Regulates the Energy Metabolism and Increases Insulin Sensitivity, but are Associated with High Levels of Kidney Damage

Mechanisms Linking Vitamin D Deficiency to Impaired Metabolism: An Overview

Vitamin D deficiency is a common health problem worldwide. Despite its known skeletal effects, studies have begun to explore its extra-skeletal effects, that is, in preventing metabolic diseases such as obesity, hyperlipidemia, and diabetes mellitus. The mechanisms by which vitamin D deficiency led to these unfavorable metabolic consequences have been explored. Current evidence indicates that the deficiency of vitamin D could impair the pancreatic β-cell functions, thus compromising its insulin secretion. Besides, vitamin D deficiency could also exacerbate inflammation, oxidative stress, and apoptosis in the pancreas and many organs, which leads to insulin resistance. Together, these will contribute to impairment in glucose homeostasis. This review summarizes the reported metabolic effects of vitamin D, in order to identify its potential use to prevent and overcome metabolic diseases.

Recovery of limb perfusion and function after hindlimb ischemia is impaired by arterial calcification

Medial artery calcification results from deposition of calcium hydroxyapatite crystals on elastin layers, and osteogenic changes in vascular smooth muscle cells. It is highly prevalent in patients with chronic kidney disease, diabetes, and peripheral artery disease (PAD), and when identified in lower extremity vessels, it is associated with increased amputation rates. This study aims to evaluate the effects of medial calcification on perfusion and functional recovery after hindlimb ischemia in rats. Medial artery calcification and acute limb ischemia were induced by vitamin D3 (VitD3 ) injection and femoral artery ligation in rats. VitD3 injection robustly induced calcification in the medial layer of femoral arteries in vivo. Laser Doppler perfusion imaging revealed that perfusion decreased and then partially recovered after hindlimb ischemia in vehicle-injected rats. In contrast, VitD3 -injected rats showed markedly impaired recovery of perfusion following limb ischemia. Accordingly, rats with medial calcification showed worse ischemia scores and delayed functional recovery compared with controls. Immunohistochemical and histological staining did not show differences in capillary density or muscle morphology between VitD3 - and vehicle-injected rats at 28 days after femoral artery ligation. The evaluation of cardiac and hemodynamic parameters showed that arterial stiffness was increased while cardiac function was preserved in VitD3 -injected rats. These findings suggest that medial calcification may contribute to impaired perfusion in PAD by altering vascular compliance, however, the specific mechanisms remain poorly understood. Reducing or slowing the progression of arterial calcification in patients with PAD may improve clinical outcomes.

Vitamin D, sport and health: a still unresolved clinical issue

Vitamin D metabolites have a pleiotropic role in human physiology, both in static and dynamic conditions, and a lot of vitamin D-related biological effects could influence physical and sport performances in athletes. Probably due to different factors (e.g., drugs, doping, nutrition, ultraviolet B radiation exposure), in athletes a very high prevalence of vitamin D inadequacy (i.e., deficiency or insufficiency) has been observed. Vitamin D inadequacy in athletes could be associated with specific health risks and to alterations of functional capacities, potentially influencing the fine adjustment of physical performances during training and sport competitions. When risk factors for vitamin D inadequacy exist, a preventive vitamin D supplementation is indicated, and if a vitamin D inadequacy is diagnosed, its supplementation is recommended. Unfortunately, on these issues many concerns remain unresolved. Indeed, it is not clear if athletes should be classified as a special population at increased risk for vitamin D inadequacy; moreover, in comparison to the non-athletic population, it is still not clear if athletes should have different reference ranges and different optimal target levels for serum vitamin D, if they have additional health risks, and if they need different type of supplementations (doses) for prevention and/or replacement therapy. Moreover, in athletes also the abuse of vitamin D supplements for ergogenic purposes raise different ethical and safety concerns. In this review, the main physio-pathological, functional and clinical issues that relate vitamin D to the world of athletes are described.

Short-Term Combined Exercise Improves Inflammatory Profile in the Retina of Obese Mice

Excess of adipose tissue increases the concentration of proinflammatory cytokines, triggering a subclinical inflammatory condition. This inflammatory profile contributes to retina damage, which can lead to retinal dysfunction and reduced vision. Regularly practicing both aerobic and strength exercises is well known for promoting anti-inflammatory effects on different organs in the peripheral and central regions. However, the effects of combined physical exercise (CPE; strength + aerobic) on the inflammatory process in the retina tissue are not yet known. This study aimed to investigate the effects of CPE on the inflammatory profile of the retina in obese mice. Swiss mice were distributed into control, sedentary obese, and trained obese groups. The trained obese group was subjected to short-term CPE, 1 h/day, for 7 days. The CPE was composed of aerobic and strength exercises in the same exercise session. The strength exercise protocol consisted of 10 climbing series, with 12 ± 1 dynamic climbing movements at 70% of the maximum voluntary carrying capacity (MVCC), and the aerobic exercise protocol consisted of 30 min of treadmill running, with an intensity of 75% of the exhaust velocity. Subsequently, the retina was excised and analyzed by Western blot. Obese animals presented impairment on glucose homeostasis and elevated levels of proinflammatory proteins in the serum and retina; however, CPE was effective in reversing these parameters, independently of changes in body adiposity. Therefore, for the first time, we have shown that short-term CPE can be an important strategy to treat an inflammatory profile in the retina.

1α,25(OH)2 D3 alleviates high glucose-induced lipid accumulation in rat renal tubular epithelial cells by inhibiting SREBPs

Lipid accumulation is a vital event in the progression of diabetic nephropathy. 1,25-Dihydroxyvitamin D3 (1α,25(OH)₂ D₃ ) is considered to have a protective effect on diabetic nephropathy. However, it remains unclear whether 1α,25(OH)₂ D₃ can inhibit lipid accumulation, and the potential mechanisms responsible for lipid metabolism are incompletely understood. In this study, we evaluated the effects of 1α,25(OH)₂ D₃ on lipid metabolism in high glucose-exposed rat renal tubular epithelial NRK-52E cells. Results indicated that high glucose-enhanced lipid accumulation in NRK-52E cells and 1α,25(OH)₂ D₃ can remarkably decrease high glucose-induced lipid accumulation. Western blot showed that 1α,25(OH)₂ D₃ alleviated high glucose-induced upregulation of sterol regulatory element-binding protein-1c (SREBP-1c) and SREBP2, along with their established target genes fatty acid synthase (FASN) and hydroxymethylglutaryl CoA reductases (HMGCR). Overall, these findings suggest that 1α,25(OH)₂ D₃ downregulated the expressions of SREBPs to inhibit high glucose-induced lipid accumulation, which provides new sights into the protective effects of 1α,25(OH)₂ D₃ on diabetic nephropathy.

Intestinal vitamin D receptor modulates lipid metabolism, adipose tissue inflammation and liver steatosis in obese mice

OBJECTIVE

Hypovitaminosis D is common in the obese population and patients suffering from obesity-associated disorders such as type 2 diabetes and fatty liver disease, resulting in suggestions for vitamin D supplementation as a potential therapeutic option. However, the pathomechanistic contribution of the vitamin D-vitamin D receptor (VDR) axis to metabolic disorders is largely unknown.

METHODS

We analyzed the pathophysiological role of global and intestinal VDR signaling in diet-induced obesity (DIO) using global Vdr-/- mice and mice re-expressing an intestine-specific human VDR transgene in the Vdr deficient background (Vdr-/- hTg).

RESULTS

Vdr-/- mice were protected from DIO, hepatosteatosis and metabolic inflammation in adipose tissue and liver. Furthermore, Vdr-/- mice displayed a decreased adipose tissue lipoprotein lipase (LPL) activity and a reduced capacity to harvest triglycerides from the circulation. Intriguingly, all these phenotypes were partially reversed in Vdr-/- hTg animals. This clearly suggested an intestine-based VDR activity on systemic lipid homeostasis. Scrutinizing this hypothesis, we identified the potent LPL inhibitor angiopoietin-like 4 (Angptl4) as a novel transcriptional target of VDR.

CONCLUSION

Our study suggests a VDR-mediated metabolic cross-talk between gut and adipose tissue, which significantly contributes to systemic lipid homeostasis. These results have important implications for use of the intestinal VDR as a therapeutic target for obesity and associated disorders.

Acute physical exercise increases leptin-induced hypothalamic extracellular signal-regulated kinase1/2 phosphorylation and thermogenesis of obese mice

The obesity is a result of energy imbalance and the increase in thermogenesis seems an interesting alternative for the treatment of this disease. The mechanism of energy expenditure through thermogenesis is tightly articulated in the hypothalamus by leptin. The hypothalamic extracellular signal-regulated kinase-1/2 (ERK1/2) is a key mediator of the thermoregulatory effect of leptin and mediates the sympathetic signal to the brown adipose tissue (BAT). In this context, physical exercise is one of the main interventions for the treatment of obesity. Thus, this study aimed to verify the effects of acute physical exercise on leptin-induced hypothalamic ERK1/2 phosphorylation and thermogenesis in obese mice. Here we showed that acute physical exercise reduced the fasting glucose of obese mice and increased leptin-induced hypothalamic p-ERK1/2 and uncoupling protein 1 (UCP1) content in BAT ( P < 0.05). These molecular changes are accompanied by an increased oxygen uptake (VO ₂ ) and heat production in obese exercised mice ( P < 0.05). The increased energy expenditure in the obese exercised animals occurred independently of changes in spontaneous activity. Thus, this is the first study demonstrating that acute physical exercise can increase leptin-induced hypothalamic ERK1/2 phosphorylation and energy expenditure of obese mice.

Can bone-regulating hormones and nutrients help characterize the metabolically healthy obese phenotype

BACKGROUND:

Bone-regulating hormones and nutrients play an important role in influencing metabolic health.

AIM:

The aim of this study was to determine whether bone-regulating hormones and nutrients, such as parathyroid hormone (PTH), 25-hydroxyvitamin D (25OHD), and magnesium (Mg) could be used to characterize the metabolically healthy obese (MHO) phenotype.

METHODS:

This study included 27 overweight or obese participants (14 men/13 women) classified as MHO ( n = 14) or metabolically unhealthy obese (MUO) ( n = 13) based on the presence or absence of metabolic abnormalities, determined by percentage body fat, percentage trunk fat, and waist circumference. Biochemical (serum concentrations of hormones and cytokines such as PTH, 25OHD, ionized Mg (iMg), cytokines, lipids, glycemic indices), physiological (percentage body fat, percentage trunk fat, blood pressure (BP)), and dietary intake (Mg intake, calcium intake) measurements were obtained.

RESULTS:

Serum PTH concentrations were significantly lower ( p = 0.005) in the MHO group (39.68 ± 11.06 pg/mL) compared with the MUO group (63.78 ± 25.82 pg/mL). Serum iMg concentrations were higher ( p = 0.052) in the MHO group (0.565 ± 0.41 mmol/L) than in the MUO group (0.528 ± 0.050 mmol/L). Serum concentrations of osteocalcin were also higher (10.37 ± 3.70 ng/mL) in the MHO compared with the MUO (6.51 ± 4.14 ng/mL) group ( p = 0.017). The MHO group had significantly lower serum insulin concentrations ( p = 0.006) and diastolic BP ( p = 0.035). Concentrations of serum 25OHD, total triglycerides, C-reactive protein and systolic BP did not differ between groups.

CONCLUSIONS:

These findings suggest that bone-regulating hormones and nutrients, especially serum PTH, osteocalcin concentrations, and dietary Mg intakes, can help to characterize the MHO phenotype.