University of Wisconsin Hospital and Clinics Clinical Toxicology Laboratory, Madison, Wisconsin 53705, USA
J Clin Endocrinol Metab. 2012 Jan;97(1):163-8. doi: 10.1210/jc.2011-0584. Epub 2011 Oct 19.
Epimers have identical molecular structure but differ in stereochemical configuration. It is widely believed that the C-3 epimer of 25-hydroxyvitamin D(3) [3-epi-25(OH)D(3)] is found only in neonates. However, this epimer was recently detected in a limited number of adults. The physiological importance of 3-epi-25(OH)D(3) is uncertain but might affect 25-hydroxyvitamin D test results and thereby reliability of the 25-hydroxyvitamin D(3) [25(OH)D(3)] measurement.
This project describes development of a highly sensitive method for 3-epi-25(OH)D(3) measurement and establishes the prevalence of this epimer in adult clinical serum specimens. DESIGN, SETTING, PARTICIPANTS, AND MAIN OUTCOME MEASURE: Serum 25(OH)D(3), 3-epi-25(OH)D(3), and 25(OH)D(2) concentrations were determined in a cohort of patients (n = 214; age neonate to 80+ yr). High-performance liquid chromatography with ultraviolet detection and high-performance liquid chromatography tandem mass spectrometry with atmospheric pressure chemical ionization equipped with cyanopropyl analytical columns were used to baseline separate and quantitate 25(OH)D(3), 3 epi-25(OH)D(3), and 25(OH)D(2).
The C-3 epimer was detected in 212 of 214 (99%) of samples. Concentrations ranged from 1 to 93 ng/ml for 25(OH)D(3) and 0.1 to 23.7 ng/ml for 3-epi-25(OH)D(3). The relative amounts of epimer to 25(OH)D(3) ranged from 0 to 25.5% (mean 4.75%). The epimer amount increased as 25(OH)D(3) increased in a nonlinear mode. In sera with approximately the same 25(OH)D(3) concentration, the ratio of epimer to 25(OH)D(3) varied, e.g. at 25(OH)D(3) values of 20-22 ng/ml, the ratio varied from 2-8.5%.
3-Epi-25(OH)D(3) is present in the majority of human serum specimens. Although this concentration is generally low, further work must investigate the impact of 3-epi-25(OH)D(3) on the various 25-hydroxyvitamin D assays and ultimately what information, if any, C-3 epimer measurement can provide clinically.
差向异构体具有相同的分子结构，但立体化学构型不同。人们普遍认为，25-羟维生素 D（3）的 C-3 差向异构体（3-差向-25（OH）D（3））仅存在于新生儿中。然而，最近在少数成年人中检测到这种差向异构体。3-差向-25（OH）D（3）的生理重要性尚不确定，但可能会影响 25-羟维生素 D 检测结果，从而影响 25-羟维生素 D（3）[25（OH）D（3）]的测量结果。
本项目描述了一种用于 3-差向-25（OH）D（3）测量的高灵敏度方法的开发，并确定了这种差向异构体在成人临床血清标本中的流行程度。
设计、地点、参与者和主要观察结果：对 214 例患者（年龄从新生儿到 80 岁以上）的血清 25（OH）D（3）、3-差向-25（OH）D（3）和 25（OH）D（2）浓度进行了测定。使用配备氰丙基分析柱的高效液相色谱法（HPLC）与紫外检测和配备大气压化学电离的高效液相色谱串联质谱法（HPLC-MS/MS）进行基线分离和定量。
在 214 个样本中的 212 个（99%）样本中检测到 C-3 差向异构体。25（OH）D（3）浓度范围为 1-93ng/ml，3-差向-25（OH）D（3）浓度范围为 0.1-23.7ng/ml。差向异构体与 25（OH）D（3）的相对量范围为 0-25.5%（平均值为 4.75%）。差向异构体的量以非线性模式随 25（OH）D（3）的增加而增加。在血清中 25（OH）D（3）浓度大致相同的情况下，差向异构体与 25（OH）D（3）的比值不同，例如在 25（OH）D（3）值为 20-22ng/ml 时，比值范围为 2-8.5%。
3-差向-25（OH）D（3）存在于大多数人血清标本中。尽管这种浓度通常较低，但需要进一步研究 3-差向-25（OH）D（3）对各种 25-羟维生素 D 检测的影响，以及最终 C-3 差向异构体检测能为临床提供哪些信息。
