Lauridsen A L, Vestergaard P, Hermann A P, Brot C, Heickendorff L, Mosekilde L, Nexo E
Department of Clinical Biochemistry, NBG, Aarhus Sygehus, Aarhus University Hospital, Aarhus, Denmark.
Calcif Tissue Int. 2005 Jul;77(1):15-22. doi: 10.1007/s00223-004-0227-5. Epub 2005 May 5.
The major transporter of vitamin D metabolites in the circulation is the multifunctional plasma protein Gc, also known as group-specific component, Gc globulin, vitamin D-binding protein, or DBP. There are several phenotypes of Gc, and we examined the influence of Gc phenotype and Gc concentration on vitamin D status. By using isoelectric focusing we identified the Gc phenotype of 595 caucasian recent postmenopausal women enrolled into the Danish Osteoporosis Prevention Study (DOPS). We measured plasma concentration of Gc by immunonephelometry (coefficient of variation [CV] < 5%), 25-hydroxy vitamin D (25OHD) by a competitive protein-binding assay (CV 10%), and 1,25-dihydroxy-vitamin D (1,25(OH)(2)D) by a radioimmunoassay (CV 6--14%), and calculated index as the molar ratio of vitamin concentration divided by Gc concentration. Plasma levels of Gc, 25OHD, 25OHD index, and 1,25(OH)(2)D, but not 1,25(OH)(2)D index, differed significantly between women with different Gc phenotype, being highest in Gc1-1, intermediate in Gc1-2, and lowest in Gc2-2. In multiple regression analysis, Gc concentration was an independent predictor of 1,25(OH)(2)D, whereas Gc phenotype was a significant predictor of 25OHD concentration, even after adjustment for the effects of season, sunbathing habits, skin thickness, use of vitamin supplements, smoking, and body mass index (BMI). Plasma parathyroid hormone (PTH) level did not differ between Gc phenotypes. Despite the fact that more than 60% of the women with Gc phenotype Gc2-2 had plasma 25OHD levels of less than 50 nmol/L none of them had plasma PTH higher than reference limits. Bone mineral content (BMC), Bone mineral density (BMD), and bone markers did not differ between Gc phenotypes. In conclusion, plasma 1,25(OH)(2)D, 25OHD, and 25OHD index are related to Gc phenotype, and we speculate that the thresholds for vitamin D sufficiency differ between Gc phenotypes.
循环中维生素D代谢产物的主要转运蛋白是多功能血浆蛋白Gc，也称为组特异性成分、Gc球蛋白、维生素D结合蛋白或DBP。Gc有几种表型，我们研究了Gc表型和Gc浓度对维生素D状态的影响。通过等电聚焦，我们确定了纳入丹麦骨质疏松症预防研究（DOPS）的595名白种人近期绝经后女性的Gc表型。我们通过免疫比浊法（变异系数[CV]<5%）测量血浆Gc浓度；通过竞争性蛋白结合测定法（CV 10%）测量25-羟基维生素D（25OHD）；通过放射免疫测定法（CV 6%-14%）测量1,25-二羟基维生素D（1,25(OH)₂D），并计算指数为维生素浓度与Gc浓度的摩尔比。不同Gc表型的女性之间，血浆Gc、25OHD、25OHD指数和1,25(OH)₂D水平存在显著差异，但1,25(OH)₂D指数无差异，在Gc1-1中最高，在Gc1-2中介于两者之间，在Gc2-2中最低。在多元回归分析中，Gc浓度是1,25(OH)₂D的独立预测因子，而Gc表型是25OHD浓度的显著预测因子，即使在调整了季节、日光浴习惯、皮肤厚度、维生素补充剂使用、吸烟和体重指数（BMI）的影响后也是如此。不同Gc表型之间血浆甲状旁腺激素（PTH）水平无差异。尽管超过60%的Gc表型为Gc2-2的女性血浆25OHD水平低于50 nmol/L，但她们中没有一个人的血浆PTH高于参考限值。不同Gc表型之间骨矿物质含量（BMC）、骨矿物质密度（BMD）和骨标志物无差异。总之，血浆1,25(OH)₂D、25OHD和25OHD指数与Gc表型有关，我们推测不同Gc表型的维生素D充足阈值不同。
