T-lymphocyte and glycemic status after vitamin D treatment in type 1 diabetes: A randomized controlled trial with sequential crossover.

BACKGROUND: Type 1 diabetes mellitus (T1D) is mediated by autoaggressive T effector cells with an underlying regulatory T-cell (Treg) defect. Vitamin D deficiency is highly prevalent in T1D, which can aggravate immune dysfunction. High-dose vitamin D treatment may enhance Tregs and improve metabolism in T1D patients. METHODS: In a randomized double-blind placebo-controlled trial with crossover design, patients received either for 3 months cholecalciferol 4000 IU/d followed by 3 months placebo or the sequential alternative. Thirty-nine T1D patients (19 women and 20 men) completed the trial. RESULTS: Primary outcome was a change of Tregs, secondary HbA1C, and insulin demand. Effects were evaluated based on intra-individual changes between treatment and placebo periods for outcome measures. Exploratory analyses included vitamin D system variant genotyping and C-peptide measurements. Median 25(OH)D3 increased to 38.8 ng/ml with males showing a significantly stronger increase (p = .003). T-lymphocyte profiles did not change significantly (p > 2); however, the intra-individual change of Tregs between males and females was different with a significantly stronger increase in men (p = .017), as well as between genotypes of the vitamin D receptor (Apa, Taq, and Bsm: genotypes aa, TT, and bb; p = .004-0.015). Insulin demands declined significantly (p = .003-.039) and HbA1C improved (p < .001). Random C-peptide levels were low but rising (median, 0.125 ng/ml; range, 0.02-0.3) in 6 patients. No toxicity was observed. CONCLUSION: A daily vitamin D dose of 4000 IU for 3 months was well tolerated and enhanced Tregs in males. Glucometabolic control improved in all. Subsequent larger trials need to address ß-cell function and genotyping for individualized vitamin D doses.

IL28B gene variants and glucose metabolism in Type 2 Diabetes.

Type 2 Diabetes (T2D) develops, when ß-cell insulin response fails to compensate for insulin resistance. Recent studies reported associations between the IL28B polymorphisms (rs12979860 and rs8099917) and T2D development in Hepatitis C virus (HCV) patients. To identify possible association with T2D independent from virus infection, we investigated both IL28B polymorphisms in T2D patients and healthy controls (HC). No association was found comparing the genotype and allele frequencies of both IL28B polymorphisms between T2D patients and HC. However, higher glucose levels were found in T2D patients carrying the IL28B CT/TT rs12979860 and GT/GG rs8099917 HCV risk genotypes compared to those with the protective CC and TT genotype (p=0.06 and p=0.02, respectively). Moreover, T2D patients with CT/TT rs12979860 HCV risk genotypes possessed significantly higher HbA1c levels than CC carriers (p=0.04). In conclusion, the IL28B HCV risk genotypes may influence glucose homeostasis in T2D patients without HCV.

VDR FokI polymorphism is associated with a reduced T-helper cell population under vitamin D stimulation in type 1 diabetes patients.

BACKGROUND: Type 1 diabetes (T1D) is an autoimmune disease mediated by T-helper (Th) cells. Additionally, the immune system regulator vitamin D, exerts its modulatory effects through the vitamin D receptor (VDR) expressed in Th cells. Furthermore, several genetic variants in the VDR gene including the VDR FokI (rs10735810) polymorphism have been implicated in T1D susceptibility in some Caucasian populations. Aim of the present study was to investigate the possible functional role of the VDR FokI gene polymorphism in Th cells from T1D patients and healthy controls (HC). METHODS: Isolated Th cells from 23 HC and 20 T1D patients were stimulated for 72h with 25-hydroxyvitamin D3 (25(OH)D3) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). After in vitro culture CD3(+)CD4(+) (CD4(+)) Th cell subsets were characterized by flow cytometry and gene expression of VDR was measured by Taqman assay. Finally, the VDR FokI polymorphism was genotyped. RESULTS: Significant lower VDR gene expression was observed in non-stimulated and 25(OH)D3 stimulated Th cells from T1D compared to HC (p=0.04 and p=0.005, respectively). In addition, by stratifying subjects into VDR FokI genotypes, significant lower percentage of CD4(+) cells was observed in 25(OH)D3 and 1,25(OH)2D3 stimulated Th cells from T1D patients carrying the "FF" genotype compared to those with the genotypes "Ff/ff" (p=0.02 and p=0.05, respectively). Moreover, looking at vitamin D effects according to VDR FokI genotypes, CD4(+) cells were significantly down-regulated by 25(OH)D3 and 1,25(OH)2D3 only in T1D "FF" carriers (p=0.01 and p=0.02; respectively). CONCLUSION: According to these results, T1D patients carrying the "FF" genotype with an adequate vitamin D therapy may benefit from a more balanced T cell immunity. However, further research is needed to confirm these premilinary findings and to elucidate functional mechanisms of genetic variation in the vitamin D system. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Vitamin D status and gene transcription in immune cells.

BACKGROUND: Vitamin D is a modulator of the immune system. Its insufficiency has been implicated in type 1 diabetes (T1D) and studies showed significant associations with polymorphisms of vitamin D genes. Aim of the study was to investigate whether gene expression in immune cells, vitamin D status and genetic variants are correlated in healthy controls (HC). METHODS: From 23 HC monocytes (Mo), T-helper cells (Th) and natural killer cells (NK) were isolated. In all immune cells gene expression of vitamin D receptor (VDR), 25-vitamin-D-hydroxylase (CYP2R1) and 25-hydroxyvitamin-D3-1a-hydroxylase (CYP27B1) were measured by Taqman assay. Furthermore, CYP2R1 (rs10741657), CYP27B1 (rs10877012) and the VDR-FokI (rs10735810) polymorphisms in HC were genotyped. Finally, 25-hydroxyvitamin D3 (25(OH)D3) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) plasma levels in HC were measured by radioimmunoassay. RESULTS: All studied immune cells showed a significantly different gene expression of CYP2R1 and CYP27B1 (p=1×10(-6), respectively). When stratifying the HC according to vitamin D deficiency and vitamin D sufficiency, within the 25(OH)D3 deficient group significantly lower 1,25(OH)2D3 plasma levels (p=0.02) in HC and a significant down-regulation of the VDR expression only in Mo were observed (p=0.04). Furthermore, a significant correlation between CYP2R1 gene transcription and 1,25(OH)2D3 plasma levels in Th cells was found (p=0.04). No associations between the gene expression levels and the investigated polymorphism in all different immune cells were detected. However, vitamin D deficiency in combination with the "AC" CYP27B1 genotype appeared to inhibit the CYP27B1 expression in NK cells (p=0.03). CONCLUSION: both 25(OH)D3 deficiency and low 1,25(OH)2D3 levels appear to interact with its system gene transcription illustrating the relevance for targeted vitamin D therapy. This article is part of a Special Issue entitled 'Vitamin D Workshop'.