Acute Homeostatic Changes Following Vitamin D2 Supplementation

Indian ASD probands with 25(OH)D and vitamin D binding protein deficiency exhibited higher severity

The severity of autism spectrum disorder (ASD) shows wide variations, though the reason remains unclear. Vitamin D (VitD) deficiency is considered a risk factor for ASD and its supplementation was reported to reduce symptom severity. Since VitD, either synthesized in the skin or absorbed from the food, is transported to the liver by the vitamin D binding protein (DBP), we have analyzed DBP genetic polymorphisms [rs7041 (A/C), rs4588 (G/T), and rs3755967 (C/T)] affecting DBP function [Case = 411; Control = 397], levels of plasma 25(OH)D and DBP [Case = 25; Control = 26], and DBP mRNA expression [Case = 74; Control = 44] in a group of Indo-Caucasoid ASD probands and neurotypical subjects. ASD probands with rs7041'CC', rs4588 'TT', and rs3755967 'TT' genotypes exhibited higher scores for a few traits. Scores for Imitation and Listening response were also higher in the presence of the "A-T" haplotype (rs7041-rs4588). Plasma 25(OH)D and DBP levels as well as DBP mRNA expressions were significantly lower in the ASD probands as compared to the neurotypical subjects. We infer that DBP deficiency, in the presence of risk genetic variants, could be one of the reasons for the reported 25(OH)D deficiency of the ASD probands.

Vitamin D Supplementation Modulates Platelet-Mediated Inflammation in Subjects With Type 2 Diabetes: A Randomized, Double-Blind, Placebo-Controlled Trial

Background

Recently, our group identified increased platelet-mediated inflammation in type 2 diabetes (T2DM) patients, and it is a well-established risk factor for diabetes complications, particularly for the development of cardiovascular diseases (CVD). Furthermore, vitamin D is reported to play an important role in the modulation of platelet hyperactivity and immune function, although the effect of vitamin D on platelet-mediated inflammation is not well studied. Hence, we aimed to investigate the effect of vitamin D supplementation on platelet-mediated inflammation in T2DM patients.

Methods

After screening a total of 201 subjects, our randomized, double-blind, placebo-controlled trial included 59 vitamin-D-deficient T2DM subjects, and the participants were randomly assigned to placebo (n = 29) or vitamin D3 (n = 30) for 6 months. Serum vitamin D metabolite levels, immunome profiling, platelet activation, and platelet-immune cell aggregate formation were measured at baseline and at the end of the study. Similarly, the serum levels of inflammatory cytokines/chemokines were assessed by a multiplex assay.

Results

Six months of vitamin D supplementation increases the serum vitamin D3 and total 25(OH)D levels from the baseline (p < 0.05). Vitamin D supplementation does not improve glycemic control, and no significant difference was observed in immune cells. However, platelet activation and platelet immune cell aggregates were altered after the vitamin D intervention (p < 0.05). Moreover, vitamin D reduces the serum levels of IL-18, TNF-α, IFN-γ, CXCL-10, CXCL-12, CCL-2, CCL-5, CCL-11, and PF-4 levels compared to the baseline levels (p < 0.05). Our ex vivo experiment confirms that a sufficient circulating level of vitamin D reduces platelet activation and platelet intracellular reactive oxygen species.

Conclusion

Our study results provide evidence that vitamin D supportive therapy may help to reduce or prevent the disease progression and cardiovascular risk in T2DM patients by suppressing oxidative stress and platelet-mediated inflammation.

Clinical Trial Registration

Clinical Trial Registry of India: CTRI/2019/01/016921.

Differential effects of phosphate binders on vitamin D metabolism in chronic kidney disease

BACKGROUND

Phosphate binders are commonly used in the treatment of patients with hyperphosphatemia. While phosphate binders are used to lower phosphate, the effects of specific phosphate binder types on vitamin D metabolism are unknown.

METHODS

We performed a secondary analysis of the Phosphate Normalization Trial in which patients with moderate to advanced chronic kidney disease were randomized to receive either placebo, sevelamer carbonate, lanthanum carbonate or calcium acetate for 9 months. We evaluated changes in serum concentrations of vitamin D metabolites including 24,25-dihydroxyvitamin D3 [24,25(OH)2D3], 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the ratio of 24,25(OH)2D3 to 25-hydroxyvitamin D [the vitamin D metabolite ratio (VMR)] and the ratio of serum 1,25(OH)2D to 25-hydroxyvitamin D.

RESULTS

Compared with placebo, randomization to the calcium acetate arm was associated with a 0.6 ng/mL (95% CI 0.2, 1) and 13.5 pg/ng (95% CI 5.5, 21.5) increase in 24,25(OH)2D and VMR, respectively, and a 5.2 pg/mL (95% CI 1.1, 9.4) reduction in 1,25(OH)2D. Randomization to sevelamer carbonate was associated with a 0.5 ng/mL (95% CI -0.9, -0.1) and 11.8 pg/ng (95% CI -20, -3.5) reduction in 24,25(OH)2D3 and VMR, respectively. There was no association of the sevelamer arm with the change in 1,25(OH)2D3, and randomization to lanthanum carbonate was not associated with a change in any of the vitamin D metabolites.

CONCLUSION

Administration of different phosphate binders to patients with moderate to severe CKD results in unique changes in vitamin D metabolism.

Vitamin D Binding Protein and the Biological Activity of Vitamin D

Vitamin D has a long-established role in bone health. In the last two decades, there has been a dramatic resurgence in research interest in vitamin D due to studies that have shown its possible benefits for non-skeletal health. Underpinning the renewed interest in vitamin D was the identification of the vital role of intracrine or localized, tissue-specific, conversion of inactive pro-hormone 25-hydroxyvitamin D [25(OH)D] to active 1,25-dihydroxyvitamin D [1,25(OH)₂D]. This intracrine mechanism is the likely driving force behind vitamin D action resulting in positive effects on human health. To fully capture the effect of this localized, tissue-specific conversion to 1,25(OH)₂D, adequate 25(OH)D would be required. As such, low serum concentrations of 25(OH)D would compromise intracrine generation of 1,25(OH)₂D within target tissues. Consistent with this is the observation that all adverse human health consequences of vitamin D deficiency are associated with a low serum 25(OH)D level and not with low 1,25(OH)₂D concentrations. Thus, clinical investigators have sought to define what concentration of serum 25(OH)D constitutes adequate vitamin D status. However, since 25(OH)D is transported in serum bound primarily to vitamin D binding protein (DBP) and secondarily to albumin, is the total 25(OH)D (bound plus free) or the unbound free 25(OH)D the crucial determinant of the non-classical actions of vitamin D? While DBP-bound-25(OH)D is important for renal handling of 25(OH)D and endocrine synthesis of 1,25(OH)₂D, how does DBP impact extra-renal synthesis of 1,25(OH)₂D and subsequent 1,25(OH)₂D actions? Are their pathophysiological contexts where total 25(OH)D and free 25(OH)D would diverge in value as a marker of vitamin D status? This review aims to introduce and discuss the concept of free 25(OH)D, the molecular biology and biochemistry of vitamin D and DBP that provides the context for free 25(OH)D, and surveys in vitro, animal, and human studies taking free 25(OH)D into consideration.