[Assessment of Vitamin D Metabolism by LC-MS/MS]

Vitamin D is pro-hormone that has important roles in calcium metabolism in the intestine, kidneys, and bone. Many studies have indicated that vitamin D deficiency causes not only rickets and osteomalacia, but also increases the risk of various diseases such as cancer and autoimmune disease. Of the many vitamin D metabolites, 25-hydroxyvitamin D[25OH-D], 1α,25-dihydroxyvitamin D[1,25(OH)2-D], and 24,25-dihydroxyvitamin D [24,25 (OH) 2-D] are important for assessing vitamin D metabolism. They are circulating, biologically active, and major inactive forms of vitamin D metabolite, respectively. Immunoassays are widely used for the measurement of serum/plasma vitamin D metabolites. With such an assay, however, the accurate quantification of these metabolites is difficult because of cross-reactivity. Liquid chromatography-tandem mass spectrometry [LC-MS/MS] is the gold standard method for analyzing these metabolites due to its high sensitivity and selectivity. Derivatization with a Cookson-type reagent is a key technique for robust and sensitive analysis by LC-MS/MS. A Cookson-type reagent rapidly and quantitatively reacts with the s-cis-diene structure of vitamin D metabolites, and markedly enhances the ionization efficiency. Using a recently developed Cookson-type reagent (DAPTAD), we successfully established an LC-MS/MS-based method for analyzing serum vitamin D metabolites including 250H-D, 1,25 (OH) 2-D, and 24,25 (OH) 2-D. Thus, LC-MS/MS can be a powerful tool for the accurate determination of vitamin D metabolism. In this review, we describe the advantages of LC-MS/MS for the determination of vitamin D metabolites.