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Quantitative studies of the interaction of cholecalciferol ((vitamin D3) and its metabolites with different genetic variants of the serum binding protein for these sterols.

ABSTRACT: Cholecalciferol (vitamin D3) and its 25-hydroxy metabolite are transported in plasma bound to a specific protein, the binding protein for cholecalciferol and its metabolites (DBP). DBP is identical with the group-specific component (Gc) proteins, which are known to display genetic polymorphism. Studies were conducted to explore whether or not major differences in the transport of cholecalciferol and its biological metabolites might exist among persons with different Gc phenotypes. Detailed quantitative studies were first carried out on the interaction of 25(OH)D3 with DBP in 21 different samples of serum, representing eight different Gc phenotypes. The studies used a filter disc assay method that provided highly reproducible quantitative results with cholecalciferol-related sterols. The Gc phenotypes studied included the three common types (Gc 1-1, 2-1, and 2-2) and several uncommon genetic variants (Gc Ab-Ab, Ab-1, Ab-2, Chip-1, and Chip-2). The binding affinities for 25(OH)D3 observed with these different sera were all fairly similar to each other. More extensive studies were then conducted to compare the binding of four cholecalciferol-related sterols to each of three genetic variants of DBP, by using sera from homozygous persons with the Gc 1-1, Gc 2-2 and Gc Ab-Ab phenotypes. The ligands tested included cholecalciferol, 25(OH)D3, 1,25(OH)2D3, and 24(R) 25(OH)2D3. The affinities of the three genetic types of DBP/Gc protein were found to be similar for each of the four cholecalciferol-related sterols. The apparent association constants for 25(OH)D3 and 24,25(OH)2D3 were similar (approx. 1--2 x 10(8) M-1); lesser affinities were observed for 1,25(OH)2D3 (kA approx. 1 x 10(7) M-1) and for cholecalciferol (kA approx. 3--4 x 10(5) M-1). Thus the common genetic variants of DBP/Gc protein, and the uncommon genetic variants studied here, all appear to have similar binding properties for cholecalciferol and its several metabolites.

SUBMITTER: Kawakami M

PROVIDER: S-EPMC1186639 | biostudies-other | 1979 May

REPOSITORIES: biostudies-other

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Project description:AIM:To prospectively evaluate the effects of vitamin D3 on disease activity and quality of life in ulcerative colitis (UC) patients with hypovitaminosis D. METHODS:The study was a prospective double-blinded, randomized trial conducted at Community Regional Medical Center, Fresno, CA from 2012-2013. Patients with UC and a serum 25(OH)D level <30 ng/ml were eligible for the study. Enrolled subjects were randomized to receive either 2,000 IU or 4,000 IU of oral vitamin D3 daily for a total of 90 days. The Short IBD Questionnaire (SIBDQ) for quality of life, the Partial Mayo Score for UC disease activity and serum lab tests were compared between the two treatment groups. Matched pair t-tests were computed to assess differences between the vitamin D levels, CRP, UC disease activity and SIBDQ scores before and after vitamin D3 therapy using SPSS version 21. RESULTS:Eight UC patients received 2,000 IU/daily and ten UC patients received 4,000 IU/daily of vitamin D3 for 90 days. Vitamin D levels increased after 90 days of oral vitamin D3 in both dose groups. However, the increase in vitamin D levels after 90 days of oral vitamin D3, in the 4,000 IU group was significantly higher 16.80 ± 9.15 (p < 0.001) compared to the 2,000 IU group of vitamin D 5.00 ± 3.12 (p = 0.008). Normal vitamin D levels (>30 ng/dl) were achieved in four out of the ten UC patients (40%) in the 4,000 IU group and in one out of the eight UC patients (12%) in the 2,000 IU group. In the group receiving 4,000 IU/day of vitamin D3 the increase in quality life scores (SIBDQ) was significant 1.0 ± 1.0 (p = 0.017) but not in the 2,000 IU vitamin D3 group 0.1 ± 1.0 (p = 0.87). In the 2,000 IU of vitamin D3 group the mean decrease in the Partial Mayo UC Score was -0.5 ± 1.5 (p = 0.38) compared to -1.3 ± 2.9 (p = 0.19) in the 4,000 IU vitamin D3 group but this was not statistically significant. CRP levels decreased after 90 days of daily vitamin D3 in both the 2,000 IU group and 4,000 IU group by -3.0 ± 9.4 (p = 0.4) and -10.8 ± 35.0 (p = 0.36) respectively. CONCLUSION:Vitamin D3 at 4,000 IU/day is more effective than 2,000 IU/day in increasing vitamin D to sufficient levels in UC patients with hypovitaminosis D, however higher doses or treatment beyond ninety days may be required. Vitamin D3 may improve the quality of life in UC patients but clinically significant improvement is not yet established. The effect of vitamin D3 on UC disease activity is still unclear. Further larger studies are needed to investigate the effects of vitamin D in ulcerative colitis.

Project description:ContextSingle-nucleotide polymorphisms (SNPs) in genes related to vitamin D metabolism have been associated with serum 25-hydroxyvitamin D [25(OH)D] concentration, but these relationships have not been examined following antenatal cholecalciferol supplementation.ObjectiveTo determine whether SNPs in DHCR7, CYP2R1, CYP24A1, and GC are associated with the response to gestational cholecalciferol supplementation.DesignWithin-randomization group analysis of the Maternal Vitamin D Osteoporosis Study trial of antenatal cholecalciferol supplementation.SettingHospital antenatal clinics.ParticipantsIn total, 682 women of white ethnicity (351 placebo, 331 cholecalciferol) were included. SNPs at rs12785878 (DHCR7), rs10741657 (CYP2R1), rs6013897 (CYP24A1), and rs2282679 (GC) were genotyped.Interventions1000 IU/d cholecalciferol from 14 weeks of gestation until delivery.Main outcome measure25(OH)D at randomization and 34 weeks of gestation were measured in a single batch (Liaison; Diasorin, Dartford, UK). Associations between 25(OH)D and the SNPs were assessed by linear regression using an additive model [β represents the change in 25(OH)D per additional common allele].ResultsOnly rs12785878 (DHCR7) was associated with baseline 25(OH)D [β = 3.1 nmol/L; 95% confidence interval (CI), 1.0 to 5.2 nmol/L; P < 0.004]. In contrast, rs10741657 (CYP2R1) (β = -5.2 nmol/L; 95% CI, -8.2 to -2.2 nmol/L; P = 0.001) and rs2282679 (GC) (β = 4.2 nmol/L; 95% CI, 0.9 to 7.5 nmol/L; P = 0.01) were associated with achieved 25(OH)D status following supplementation, whereas rs12785878 and rs6013897 (CYP24A1) were not.ConclusionsGenetic variation in DHCR7, which encodes 7-dehyrocholesterol reductase in the epidermal vitamin D biosynthesis pathway, appears to modify baseline 25(OH)D. In contrast, the response to antenatal cholecalciferol supplementation was associated with SNPs in CYP2R1, which may alter 25-hydroxylase activity, and GC, which may affect vitamin D binding protein synthesis or metabolite affinity.

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Quantitative studies of the interaction of cholecalciferol ((vitamin D3) and its metabolites with different genetic variants of the serum binding protein for these sterols.

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