The complexity of vitamin D metabolism with its many vitamin D metabolites and cytochrome P450-mediated steps has fascinated scientists and clinicians for the past four decades. The emergence of liquid-chromatography tandem mass spectrometry (LC-MS/MS), with its ever-improving sensitivity, has enabled its use for detection, identification and quantitation of vitamin D metabolites in human and animal tissues. Not only does this new approach permit accurate assay of the main circulating form 25-OH-D3, but also the simultaneous assay of dihydroxyvitamin D metabolites: 1,25-(OH)2D3 and 24,25-(OH)2D3. We have used this new metabolic profiling approach to study genetic defects of vitamin D metabolism in humans and to understand the metabolic consequences of targeted gene ablation in the mouse. Knockout of CYP2R1 & CYP27A1(25-hydroxylases), CYP27B1(1-hydroxylase), CYP24A1(24-hydroxylase) and VDR (vitamin D receptor) genes all have profound effects on the vitamin D metabolic profile. The LC-MS/MS assay of 24,25-(OH)2D3 is a reliable screening test to detect loss-of-function mutations of CYP24A1 which lead to idiopathic infantile hypercalcemia, which often results in renal stones in children and adults. The talk will provide an overview of the LC-MS/MS technology, show examples from various clinical diseases and animal models and allow us to reevaluate current knowledge of vitamin D metabolism.

LC-MS/MS offers new insights into vitamin D metabolism in humans and knockout animal models

249th National Meeting (2015)

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