An analysis of the association between the vitamin D pathway and serum 25‐hydroxyvitamin D levels in a healthy Chinese population

Vitamin D deficiency has been recognized as a major public health issue worldwide. Recent studies have indicated that genetic factors might play an important role in determining serum 25‐hydroxyvitamin D [25(OH)D] levels in Caucasians and African Americans. However, the genes that contribute to the variation in serum 25(OH)D levels in Chinese are unknown. In this study, we screened 15 key genes within the vitamin D metabolic pathway using 96 single‐nucleotide polymorphism (SNP) markers in a group of 2897 unrelated healthy Chinese subjects. Significant confounding factors that may influence the variability in serum 25(OH)D levels were used as covariates for association analyses. An association test for quantitative traits was performed to evaluate the association between candidate genes and serum 25(OH)D levels. In the present study, variants and/or haplotypes in GC, CYP2R1, and DHCR7/NADSYN1 were identified as being associated with 25(OH)D levels. Participants with three or four risk alleles of the two variants (GC‐rs4588 and CYP2R1‐rs10766197) had an increased chance of presenting with a 25(OH)D concentration lower than 20 ng/mL (odds ratio 2.121, 95% confidence interval 1.586–2.836, p = 6.1 × 10^?8) compared with those lacking the risk alleles. Each additional copy of a risk allele was significantly associated with a 0.12‐fold decrease in the log‐25(OH)D concentration (p = 3.7 × 10^?12). Haplotype TGA of GC rs705117‐rs2282679‐rs1491710, haplotype GAGTAC of GC rs842999‐rs705120‐rs222040‐rs4588‐rs7041‐rs10488854, haplotype CA of GC rs1155563‐rs222029, and haplotype AAGA of CYP2R1 rs7936142‐rs12794714‐rs2060793‐rs16930609 were genetic risk factors toward a lower 25(OH)D concentration. In contrast, haplotype TGGGCCC of DHCR7/NADSYN1 rs1790349‐rs7122671‐rs1790329‐rs11606033‐rs2276360‐rs1629220‐rs2282618 were genetic protective factors. The results suggest that the GC, CYP2R1, and DHCR7/NADSYN1 genes might contribute to variability in the serum 25(OH)D levels in a healthy Chinese population in Shanghai. These markers could be used as tools in Mendelian randomization analyses of vitamin D, and they could potentially be drug targets in the Chinese population in Shanghai.     

High serum 25‐hydroxyvitamin D is associated with a low incidence of stress fractures

Low serum 25‐hydroxyvitamin D [25(OH)D] concentrations are associated with hip fractures, but the dose‐response relationship of serum 25(OH)D with risk of stress fractures in young women is unknown. This nested case‐control study in a cohort of female Navy recruits was designed to determine whether those with low prediagnostic serum 25(OH)D concentrations had greater risk of stress fracture. Sera were drawn in 2002–2009 from 600 women who were diagnosed subsequently with stress fracture of the tibia or fibula and 600 matched controls who did not experience a stress fracture. The 25(OH)D concentration was measured using the DiaSorin radioimmunoassay method. Controls were individually matched to cases on race (white, black, or other), length of service (±30 days), and day blood was drawn (±2 days). There was approximately half the risk of stress fracture in the top compared with the bottom quintile of serum 25(OH)D concentration (odds ratio [OR] = 0.51, 95% CI 0.34–0.76, p ≤ 0.01). The range of serum 25(OH)D in the lowest quintile was 1.5 to 19.7 (mean 13.9) ng/mL, whereas in the highest it was 39.9 to 112 (mean 49.7) ng/mL. It is concluded that there was a monotonic inverse dose‐response gradient between serum 25(OH)D and risk of stress fracture. There was double the risk of stress fractures of the tibia and fibula in women with serum 25(OH)D concentrations of less than 20 ng/mL compared to those with concentrations of 40 ng/mL or greater. A target for prevention of stress fractures would be a serum 25(OH)D concentration of 40 ng/mL or greater, achievable with 4000 IU/d of vitamin D₃ supplementation. © 2011 American Society for Bone and Mineral Research     

Vitamin D binding protein is a key determinant of 25‐hydroxyvitamin D levels in infants and toddlers

Circulating 25‐hydroxyvitamin D (25‐OHD) levels vary among human populations. Only limited information regarding determinants of these measures is available for infants and children, particularly in minority groups at greatest risk for vitamin D deficiency. We identified demographic determinants of circulating 25‐OHD in a large cohort of minority children, and now extend our studies to examine potential roles of vitamin D binding protein (DBP) as a determinant of 25‐OHD levels. Serum DBP level and common single nucleotide polymorphisms (SNPs) at positions 432 and 436 in the GC gene, encoding DBP, were examined. We confirmed self‐reported ancestry using ancestry informative markers (AIMs), and included quantitative AIMs scores in the analysis. The multivariate model incorporated previously identified demographic and nutritional determinants of 25‐OHD in this cohort, as well as GC SNPs and circulating DBP. Genetic variants in GC differed by self‐reported ancestry. The 1f allele (D432/T436) was enriched in African Americans, occurring in 71%. Homozygosity for the 1f allele (DDTT) occurred in 53% of African Americans but only 6% of Caucasians and 13% of Hispanics. Circulating DBP was significantly correlated with 25‐OHD. GC SNPs were associated with both circulating DBP and 25‐OHD. It appears that progressive substitution of lysine for threonine at the 436 position results in lower circulating 25‐OHD. Multivariate analysis revealed that genetic variance in GC significantly contributes to circulating DBP as well as 25‐OHD. Moreover, the effect of GC SNPs on 25‐OHD are evident after adjusting for their effects on circulating DBP. Thus in young children genetic variance of the common GC T436K SNP affects circulating levels of the DBP protein, which in turn affects circulating 25‐OHD. However, the GC genotype also affects circulating 25‐OHD independently of its effect on circulating DBP. These findings provide data that may be important in the interpretation of vitamin D status in children of varying ancestral backgrounds. © 2013 American Society for Bone and Mineral Research     

老年骨质疏松症患者监测25(OH) D3 水平的临床意义

从老年骨质疏松症发病情况入手,探讨维生素D治疗骨质疏松的作用机制、活性代谢产物种类以及活性维生素D监测的临床意义,有利于指导临床用药,使老年骨质疏松症患者做到个体化治疗。     

Serum 25‐hydroxyvitamin D and clinical fracture risk in a multiethnic cohort of women: The women's health initiative (WHI)

Low 25‐hydroxyvitamin D [25(OH)D] levels have been linked to hip fracture in white women. To study the association of 25(OH)D with risk of fracture in multiethnic women, we performed a nested case‐control study within the prospective Women's Health Initiative (WHI) Observational Study. Incident fractures were identified in 381 black, 192 Hispanic, 113 Asian, and 46 Native American women over an average of 8.6 years. A random sample of 400 white women who fractured was chosen. One control individual was selected per case and matched on age, race/ethnicity, and blood draw date. 25(OH)D, parathyroid hormone, and vitamin D–binding protein (DBP) were measured in fasting baseline serum. Conditional logistic regression models were used to calculate the odds ratio (OR) and 95% CI. In multivariable models, higher 25(OH)D levels compared with levels less than 20 ng/mL were associated with a lower risk of fracture in white women (20 to <30 ng/mL: OR = 0.82, 95% CI 0.58–1.16; ≤30.0 ng/mL: OR = 0.56, 95% CI 0.35–0.90; p trend = 0.02). In contrast, higher 25(OH)D (≥20 ng/mL) compared with levels less than 20 ng/mL were associated with a higher risk of fracture in black women (OR = 1.45, 95% CI 1.06–1.98; p trend = 0.043). Higher 25(OH)D (≥30.0 ng/mL) was associated with higher fracture risk in Asian women after adjusting for DBP (OR = 2.78, 95% CI 0.99–7.80; p trend = 0.04). There was no association between 25(OH)D and fracture in Hispanic or Native American women. Our results suggest divergent associations between 25(OH)D and fracture by race/ethnicity. The optimal level of 25(OH)D for skeletal health may differ in white and black women. © 2011 American Society for Bone and Mineral Research     

Oral supplementation with 25(OH)D3 versus vitamin D3: Effects on 25(OH)D levels,lower extremity function,blood pressure,and markers of innate immunity

To test the effect of 25(OH)D₃ (HyD) compared to vitamin D₃ on serum 25‐hydroxyvitamin D levels (25(OH)D), lower extremity function, blood pressure, and markers of innate immunity. Twenty healthy postmenopausal women with an average 25(OH)D level of 13.2 ± 3.9 ng/mL (mean ± SD) and a mean age of 61.5 ± 7.2 years were randomized to either 20 µg of HyD or 20 µg (800 IU) of vitamin D₃ per day in a double‐blind manner. We measured on 14 visits over 4 months, 25(OH)D serum levels, blood pressure, and seven markers of innate immunity (eotaxin, interleukin [IL]‐8, IL‐12, interferon gamma‐induced protein 10 kDa [IP‐10], monocyte chemotactic protein‐1 [MCP‐1], macrophage inflammatory protein beta [MIP‐1β], and “Regulated upon Activation, Normal T‐cell Expressed, and Secreted” [RANTES]). At baseline and at 4 months, a test battery for lower extremity function (knee extensor and flexor strength, timed up and go, repeated sit‐to‐stand) was assessed. All analyses were adjusted for baseline measurement, age, and body mass index. Mean 25(OH)D levels increased to 69.5 ng/mL in the HyD group. This rise was immediate and sustained. Mean 25(OH)D levels increased to 31.0 ng/mL with a slow increase in the vitamin D₃ group. Women on HyD compared with vitamin D₃ had a 2.8‐fold increased odds of maintained or improved lower extremity function (odds ratio [OR] = 2.79; 95% confidence interval [CI], 1.18–6.58), and a 5.7‐mmHg decrease in systolic blood pressure (p = 0.0002). Both types of vitamin D contributed to a decrease in five out of seven markers of innate immunity, significantly more pronounced with HyD for eotaxin, IL‐12, MCP‐1, and MIP‐1 β. There were no cases of hypercalcemia at any time point. Twenty micrograms (20 µg) of HyD per day resulted in a safe, immediate, and sustained increase in 25(OH)D serum levels in all participants, which may explain its significant benefit on lower extremity function, systolic blood pressure, and innate immune response compared with vitamin D₃. © 2012 American Society for Bone and Mineral Research     

25-OH-D2、25-OH-D3与股骨颈骨密度的相关性研究

目的研究人体内25羟维生素D2(25-OH-D2)、25羟维生素D3(25-OH-D3)含量与股骨颈骨密度的相关性。方法利用双能X线骨密度测量法检测205例患者股骨颈骨密度,同时用高效液相色谱法检测其血清中25-OH-D2及25-OH-D3的含量,并根据维生素D(VitD)含量分析VitD与骨密度的关系。结果人体内VitD(25-OH-D2+25-OH-D3)含量与50岁以下者的股骨颈骨矿含量无相关性(P0.05),与50岁以上者呈正向直线相关(P0.05或P0.01),男女性别均一致。结论对于50岁以上者,随着年龄的增长,其体内血清VitD的含量降低很可能会导致其股骨颈骨矿含量下降。     

Temporal trends and determinants of longitudinal change in 25-hydroxyvitamin D and parathyroid hormone levels

Vitamin D is essential for facilitating calcium absorption and preventing increases in parathyroid hormone (PTH), which can augment bone resorption. Our objectives were to examine serum levels of 25-hydroxyvitamin D [25(OH)D] and PTH, and factors related to longitudinal change in a population-based cohort. This is the first longitudinal population-based study looking at PTH and 25(OH)D levels. We analyzed 3896 blood samples from 1896 women and 829 men in the Canadian Multicentre Osteoporosis Study over a 10-year period starting in 1995 to 1997. We fit hierarchical models with all available data and adjusted for season. Over 10 years, vitamin D supplement intake increased by 317 (95% confidence interval [CI] 277 to 359) IU/day in women and by 193 (135 to 252) IU/day in men. Serum 25(OH)D (without adjustment) increased by 9.3 (7.3 to 11.4) nmol/L in women and by 3.5 (0.6 to 6.4) nmol/L in men but increased by 4.7 (2.4 to 7.0) nmol/L in women and by 2.7 (-0.6 to 6.2) nmol/L in men after adjustment for vitamin D supplements. The percentage of participants with 25(OH)D levels <50 nmol/L was 29.7% (26.2 to 33.2) at baseline and 19.8% (18.0 to 21.6) at year 10 follow-up. PTH decreased over 10 years by 7.9 (5.4 to 11.3) pg/mL in women and by 4.6 (0.2 to 9.0) pg/mL in men. Higher 25(OH)D levels were associated with summer, younger age, lower body mass index (BMI), regular physical activity, sun exposure, and higher total calcium intake. Lower PTH levels were associated with younger age and higher 25(OH)D levels in both women and men and with lower BMI and participation in regular physical activity in women only. We have observed concurrent increasing 25(OH)D levels and decreasing PTH levels over 10 years. Secular increases in supplemental vitamin D intake influenced both changes in serum 25(OH)D and PTH levels.     

23(S)25(R)-1,25-Dihydroxyvitamin D3-lactone, a naturally occurring metabolite of 1,25-dihydroxyvitamin D3, inhibits osteoclast-like cell formation in human bone marrow cultures

We have used a human bone marrow culture system that forms multinucleated cells (MNCs), 50% of which express the osteoclast phenotype, to examine the 23(S)25(R)-1,25-dihydroxyvitamin D₃-26,23-lactone (1,25-D₃-lactone) on osteoclast-like cell formation. The 1,25-D₃-lactone is a vitamin D₃ metabolite that has recently been detected in human serum under physiological conditions at concentrations of approximately 131 pg/ml (3 × 10⁻¹⁰ M) and can inhibit bone resorption induced by 1,25-dihydroxyvitamin D₃ (1,25-D₃) in vivo and in vitro. We examined the effects of the 1,25-D₃-lactone on the formation of MNC that cross-reacted with 23C6 monoclonal antibody (23C6-positive MNC), which preferentially binds to osteoclasts. All metabolites of 1,25-D₃ except the 1,25-D3-lactone increased both total and 23C6-positive MNC formation in a dose-dependent manner. In contrast, the 1,25-D₃-lactone inhibited both total and 23C6-positive MNC formation, whether the cultures were treated with 1,25-D₃, parathyroid hormone, or interleukin-1β, all potent stimulators of MNC formation. This inhibitory action of 1,25-D₃-lactone on MNC formation was very similar to the inhibitory effects of calcitonin. These data suggest that (1) 1,25-D₃-lactone is a potent natural inhibitor of formation of cells with the osteoclast phenotype at physiological concentrations and (2) the inhibition of these cells by 1,25-D₃-lactone may not result solely from its competitive binding to the 1,25-D₃ receptor. Received: April 24, 1997 / Accepted: May 30, 1997     

Serum 25‐hydroxyvitamin D and risk of major osteoporotic fractures in older U.S. adults

Results from previous prospective studies linking serum 25‐hydroxyvitamin D (25OHD) with fracture risk have been inconsistent. The present study examined the relationship between serum 25OHD and risk of incident major osteoporotic fracture (hip, spine, radius, and humerus) in older U.S. adults. The study used a pooled cohort of 4749 men and women ages 65 years and older from the third National Health and Nutrition Examination Survey (NHANES III, 1988–1994) and NHANES 2000–2004. Incident fractures were identified using linked mortality and Medicare records that were obtained for participants from both surveys. Serum 25OHD values were measured by radioimmunoassay in both surveys. Cox proportional hazards models were used to estimate the relative risk (RR) of fracture by serum 25OHD level. There were 525 incident major osteoporotic fractures (287 hip fractures) in the sample. Serum 25OHD was a significant linear predictor of major osteoporotic fracture and significant quadratic predictor of hip fracture in the total sample and among those with less than 10 years of follow‐up, but it was not related to risk of either fracture type among those with ≥10 years of follow‐up. Major osteoporotic fracture risk was increased by 26% to 27% for each SD decrease in serum 25OHD among those with less than 10 years of follow‐up. Serum 25OHD was significantly related to risk of major osteoporotic fractures as a group and to hip fracture alone in this cohort of older U.S. adults from NHANES III and NHANES 2000–2004. However, the predictive utility of serum 25OHD diminished after 10 years. In addition, the relationship appeared to be linear when major osteoporotic fracture risk was considered but quadratic when hip fracture risk was assessed. © 2013 American Society for Bone and Mineral Research.     

Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25‐hydroxyvitamin D

Many patients treated for vitamin D deficiency fail to achieve an adequate serum level of 25‐hydroxyvitamin D [25(OH)D] despite high doses of ergo‐ or cholecalciferol. The objective of this study was to determine whether administration of vitamin D supplement with the largest meal of the day would improve absorption and increase serum levels of 25(OH)D. This was a prospective cohort study in an ambulatory tertiary‐care referral center. Patients seen at the Cleveland Clinic Foundation Bone Clinic for the treatment of vitamin D deficiency who were not responding to treatment make up the stugy group. Subjects were instructed to take their usual vitamin D supplement with the largest meal of the day. The main outcome measure was the serum 259(OH)D level after 2 to 3 months. Seventeen patients were analyzed. The mean age (±SD) and sex (F/M) ratio were 64.5 ± 11.0 years and 13 females and 4 males, respectively. The dose of 25(OH)D ranged from 1000 to 50,000 IU daily. The mean baseline serum 25(OH)D level (±SD) was 30.5 ± 4.7 ng/mL (range 21.6 to 38.8 ng/mL). The mean serum 25(OH)D level after diet modification (±SD) was 47.2 ± 10.9 ng/mL (range 34.7 to 74.0 ng/mL, p < .01). Overall, the average serum 25(OH)D level increased by 56.7% ± 36.7%. A subgroup analysis based on the weekly dose of vitamin D was performed, and a similar trend was observed. Thus it is concluded that taking vitamin D with the largest meal improves absorption and results in about a 50% increase in serum levels of 25(OH)D levels achieved. Similar increases were observed in a wide range of vitamin D doses taken for a variety of medical conditions. © 2010 American Society for Bone and Mineral Research     

Effects of 25‐hydroxyvitamin D3 on proliferation and osteoblast differentiation of human marrow stromal cells require CYP27B1/1α‐hydroxylase

1,25‐Dihydroxyvitamin D₃ [1,25(OH)₂D₃] has many noncalcemic actions that rest on inhibition of proliferation and promotion of differentiation in malignant and normal cell types. 1,25(OH)₂D₃ stimulates osteoblast differentiation of human marrow stromal cells (hMSCs), but little is known about the effects of 25‐hydroxyvitamin D₃ [25(OH)D₃] on these cells. Recent evidence shows that hMSCs participate in vitamin D metabolism and can activate 25(OH)D₃ by CYP27B1/1α‐hydroxylase. These studies test the hypothesis that antiproliferative and prodifferentiation effects of 25(OH)D₃ in hMSCs depend on CYP27B1. We studied hMSCs that constitutively express high (hMSCs^hi‐1α) or low (hMSCs^lo‐1α) levels of CYP27B1 with equivalent expression of CYP24A1 and vitamin D receptor. In hMSCs^hi‐1α, 25(OH)D₃ reduced proliferation, downregulated proliferating cell nuclear antigen (PCNA), upregulated p21^Waf1/Cip1, and decreased cyclin D1. Unlike 1,25(OH)₂D₃, the antiapoptotic effects of 25(OH)D₃ on Bax and Bcl‐2 were blocked by the P450 inhibitor ketoconazole. The antiproliferative effects of 25(OH)D₃ in hMSCs^hi‐1α and of 1,25(OH)₂D₃ in both samples of hMSCs were explained by cell cycle arrest, not by increased apoptosis. Stimulation of osteoblast differentiation in hMSCs^hi‐1α by 25(OH)D₃ was prevented by ketoconazole and upon transfection with CYP27B1 siRNA. These data indicate that CYP27B1 is required for 25(OH)D₃'s action in hMSCs. Three lines of evidence indicate that CYP27B1 is required for the antiproliferative and prodifferentiation effects of 25(OH)D₃ on hMSCs: Those effects were not seen (1) in hMSCs with low constitutive expression of CYP27B1, (2) in hMSCs treated with ketoconazole, and (3) in hMSCs in which CYP27B1 expression was silenced. Osteoblast differentiation and skeletal homeostasis may be regulated by autocrine/paracrine actions of 25(OH)D₃ in hMSCs. © 2011 American Society for Bone and Mineral Research.     

液相色谱-质谱联用法（LC-MS/MS）和酶联免疫法(ELISA)对体内25（OH）D3水平的测定

目的 同时用液相色谱-质谱联用法（LC-MS/MS）和酶联免疫法（ELISA）检测患者体内25（OH）D3水平,分析两者结果的差异。方法 随机选取50例住院患者,对同一血清样本分别用LC-MS/MS法和ELISA法测定25（OH）D3水平,同时用LC-MS/MS法测定25（OH）D2的水平。结果 LC-MS/MS法测定的维生素D3的均数为14.99±6.51ng/ml,酶联免疫法测定的均数为20.91±9.70ng/ml,两者的相关系数为0.725（P＜0.01）,线性相关方程为维生素D3（LC-MS/MS法）=4.829+0.486×维生素D3(ELISA法)。LC-MS/MS法组25（OH）D3浓度高于20ng/ml的比例17%,酶联免疫法组为52%,LC-MS/MS法组的25（OH）D2和25（OH）D3总浓度高于20ng/ml的为24%。25（OH）D2占25（OH）D总量的8.4%。 结论 LC-MS/MS法测定的维生素D3的数值明显低于ELISA法,两者正相关性较高,可经方程互换。酶联免疫法低估了体内维生素D的缺乏,检测25（OH）D3的同时需测定25（OH）D2浓度。     

1,25二羟维生素D3对胆管癌细胞系QBC939增殖和凋亡的影响

目的 探讨1,25二羟维生素D3[1,25(OH)2 D3]对胆管癌细胞系QBC939的体外增殖及凋亡的影响.方法 将不同浓度的1,25(OH)2 D3与胆管癌细胞系QBC939共同培养,采用MTT法测定细胞增殖能力、显微镜观察细胞形态学的改变、流式细胞仪检测细胞周期与凋亡、免疫细胞化学观察bcl-2的表达.结果 0.1～0.5μmol/L的1,25(OH)2 D3对胆管癌细胞QBC939有抑制作用,呈剂量依赖性.经1,25(OH)2 D3作用72h后细胞G1期比例升高,S期比例下降,其中0.5μmol/L组细胞G1期由(50.3±1.0)%上升至(65.5±3.2)%,S期由(39.4±0.5)%下降至(23.6±0.7)%;并且可诱导细胞产生凋亡,0.5μmol/L组作用后细胞凋亡率由0.5%上升至24.6%;bcl-2的表达下调.结论 1,25(OH)2 D3能抑制胆管癌细胞系QBC939增殖并诱导细胞凋亡,其引起凋亡的机制可能与下调bcl-2的表达相关.     

广州地区人群中血清25（OH）VitD的水平

目的评价广州正常人血清25（OH）VitD水平,探讨影响血清25（OH）VitD分布的因素。方法自2010年12月至2011年3月在我院体检人群中检查250名正常人（男性组150例,女性组100例,23～79岁）的血清25（OH）VitD水平。结果 250名正常人血清25（OH）VitD水平为17.80±5.35ng/mL,其中男性：18.54±5.37ng/mL;女性：16.71±5.15ng/mL。男性和女性人群血清25（OH）VitD水平差异无统计学意义（P〉0.05）。男性中VitD缺乏的占67.3%,女性中VitD缺乏的占79.0%。年龄与血清25（OH）VitD水平无线性相关性。结论 72.0%的广州正常成年人25（OH）VitD处于缺乏状态。     

Enhancement of hepatic 4‐hydroxylation of 25‐hydroxyvitamin D3 through CYP3A4 induction in vitro and in vivo: Implications for drug‐induced osteomalacia

Long‐term therapy with certain drugs, especially cytochrome P450 (P450; CYP)‐inducing agents, confers an increased risk of osteomalacia that is attributed to vitamin D deficiency. Human CYP24A1, CYP3A4, and CYP27B1 catalyze the inactivation and activation of vitamin D and have been implicated in the adverse drug response. In this study, the inducibility of these enzymes and monohydroxylation of 25‐hydroxyvitamin D₃ (25OHD₃) were evaluated after exposure to P450‐inducing drugs. With human hepatocytes, treatment with phenobarbital, hyperforin, carbamazepine, and rifampin significantly increased the levels of CYP3A4, but not CYP24A1 or CYP27B1 mRNA. In addition, rifampin pretreatment resulted in an 8‐fold increase in formation of the major metabolite of 25OHD₃, 4β,25(OH)₂D₃. This inductive effect was blocked by the addition of 6′,7′‐dihydroxybergamottin, a selective CYP3A4 inhibitor. With human renal proximal tubular HK‐2 cells, treatment with the same inducers did not alter CYP3A4, CYP24A1, or CYP27B1 expression. 24R,25(OH)₂D₃ was the predominant monohydroxy metabolite produced from 25OHD₃, but its formation was unaffected by the inducers. With healthy volunteers, the mean plasma concentration of 4β,25(OH)₂D₃ was increased 60% (p < 0.01) after short‐term rifampin administration. This was accompanied by a statistically significant reduction in plasma 1α,25(OH)₂D₃ (?10%; p = 0.03), and a nonsignificant change in 24R,25(OH)₂D₃ (?8%; p = 0.09) levels. Further analysis revealed a negative correlation between the increase in 4β,25(OH)₂D₃ and decrease in 1α,25(OH)₂D₃ levels. Examination of the plasma monohydroxy metabolite/25OHD₃ ratios indicated selective induction of the CYP3A4‐dependent 4β‐hydroxylation pathway of 25OHD₃ elimination. These results suggest that induction of hepatic CYP3A4 may be important in the etiology of drug‐induced osteomalacia. © 2013 American Society for Bone and Mineral Research.     

Leptin stimulates fibroblast growth factor 23 expression in bone and suppresses renal 1α,25‐dihydroxyvitamin D3 synthesis in leptin‐deficient ob/ob Mice

Leptin is the LEP (ob) gene product secreted by adipocytes. We previously reported that leptin decreases renal expression of the 25‐hydroxyvitamin D₃ 1α‐hydroxylase (CYP27B1) gene through the leptin receptor (ObRb) by indirectly acting on the proximal tubules. This study focused on bone‐derived fibroblast growth factor 23 (FGF‐23) as a mediator of the influence of leptin on renal 1α‐hydroxylase mRNA expression in leptin‐deficient ob/ob mice. Exposure to leptin (200 ng/mL) for 24 hours stimulated FGF‐23 expression by primary cultured rat osteoblasts. Administration of leptin (4 mg/kg i.p. at 12‐hour intervals for 2 days) to ob/ob mice markedly increased the serum FGF‐23 concentration while significantly reducing the serum levels of calcium, phosphate, and 1α,25‐dihydroxyvitamin D₃ [1,25(OH)₂D₃]. Administration of FGF‐23 (5 µg i.p. at 12‐hour intervals for 2 days) to ob/ob mice suppressed renal 1α‐hydroxylase mRNA expression. The main site of FGF‐23 mRNA expression was the bone, and leptin markedly increased the FGF‐23 mRNA level in ob/ob mice. In addition, leptin significantly reduced 1α‐hydroxylase and sodium‐phosphate cotransporters (NaP_i‐IIa and NaP_i‐IIc) mRNA levels but did not affect Klotho mRNA expression in the kidneys of ob/ob mice. Furthermore, the serum FGF‐23 level and renal expression of 1α‐hydroxylase mRNA were not influenced by administration of leptin to leptin receptor–deficient (db/db) mice. These results indicate that leptin directly stimulates FGF‐23 synthesis by bone cells in ob/ob mice, suggesting that inhibition of renal 1,25(OH)₂D₃ synthesis in these mice is at least partly due to elevated bone production of FGF‐23. © 2010 American Society for Bone and Mineral Research     

Hip bone loss is attenuated with 1000 IU but not 400 IU daily vitamin D3: A 1‐year double‐blind RCT in postmenopausal women

Few year‐long vitamin D supplementation trials exist that match seasonal changes. The aim of this study was to determine whether daily oral vitamin D₃ at 400 IU or 1000 IU compared with placebo affects annual bone mineral density (BMD) change in postmenopausal women in a 1‐year double‐blind placebo controlled trial in Scotland. White women aged 60 to 70 years (n = 305) were randomized to one of two doses of vitamin D or placebo. All participants started simultaneously in January/February 2009, attending visits at bimonthly intervals with 265 (87%) women attending the final visit and an additional visit 1 month after treatment cessation. BMD (Lunar iDXA) and 1,25‐dihydroxyvitamin D[1,25(OH)₂D], N‐terminal propeptide of type 1 collagen [P1NP], C‐terminal telopeptide of type I collagen [CTX], and fibroblast growth factor‐23 [FGF23] were measured by immunoassay at the start and end of treatment. Circulating PTH, serum Ca, and total 25‐hydroxyvitamin D [25(OH)D] (latter by tandem mass spectrometry) were measured at each visit. Mean BMD loss at the hip was significantly less for the 1000 IU vitamin D group (0.05% ± 1.46%) compared with the 400 IU vitamin D or placebo groups (0.57% ± 1.33% and 0.60% ± 1.67%, respectively) (p < 0.05). Mean (± SD) baseline 25(OH)D was 33.8 ± 14.6 nmol/L; comparative 25(OH)D change for the placebo, 400 IU, and 1000 IU vitamin D groups was ?4.1 ± 11.5 nmol/L, +31.6 ± 19.8 nmol/L, and +42.6 ± 18.9 nmol/L, respectively. Treatment did not change markers of bone metabolism, except for a small reduction in PTH and an increase in serum calcium (latter with 1000 IU dose only). The discordance between the incremental increase in 25(OH)D between the 400 IU and 1000 IU vitamin D and effect on BMD suggests that 25(OH)D may not accurately reflect clinical outcome, nor how much vitamin D is being stored. © 2013 American Society for Bone and Mineral Research.     

地塞米松和1，25(OH)2D3对体外人骨髓基质细胞成骨及成脂分化的影响

目的 观察地塞米松（Dex）和1，25（OH）2D3（D3）对骨髓基质细胞（MSCs）成骨及成脂分化的影响。方法 以离心法分离培养人MSCs，以10^-7mol／LDex和，或10^-8mol／Ll，25（OH）2D3作为分化诱导剂对细胞进行干预，分别用细胞碱性磷酸酶（ALP）染液试剂盒及苏丹Ⅲ染液对成骨细胞和脂肪细胞进行组织化学染色，计数；使用RT-PCR技术在转录水平检测成骨细胞标记物骨桥蛋白（OPN）及脂肪细胞标记物过氧化酶体增殖激活受体72（PPARγ2）mRNA的表达。结果细胞染色结果表明各干预组ALP^＋细胞百分比均较对照组增加，与对照组相比有显著性差异（P〈0．05），苏丹Ⅲ^＋细胞百分比Dex组较对照组增多，耽组较对照组减少，差异有显著性（P〈0．05），Dex＋D3组较Dex组苏丹Ⅲ^＋细胞数明显减少，两者相比差异有显著性（P〈0．05）；OPNmRNA及PPARγ2mRNA表达未在对照组测得，Dex诱导了OPNmRNA及PPARγ2mRNA表达，1，25（OH）2D3诱导OPNmRNA表达，并抑制Dex诱导的PPARγ2mRNA的表达。结论 Dex促进MSCs的成骨分化及成脂分化，1，25（OH），D，促进MSCs的成骨分化的同时抑制其成脂分化，与Dex合用抑制Dex成脂分化作用，强化了其成骨分化作用，反映了成骨细胞与脂肪细胞间存在的反变关系，表明两者来源于同一前体细胞的可能性。