麻豆传媒

Production of vitamin D in the skin. Vitamin D3 (D3) is synthesized in keratinocytes from the precursor 7-dehydrocholesterol in response to ultraviolet radiation in sunlight. D3 is metabolized to 25 hydroxy vitamin D (25(OH)D), the form most commonly measured in the blood as a marker of vitamin D status, by CYP27A1. 25(OH)D is metabolized to 1,25-dihydroxyvitamin D (1,25(OH)2D), the hormonally active form of vitamin D, by CYP27B1. The enzyme CYP24A1 inactivates both 25(OH)D and 1,25(OH)2D. Transcription of the gene encoding CYP24A1 is induced by 1,25(OH)2D, which serves as a feedback loop to modulate levels of active vitamin D. The inhibitors ketoconazole and VID400 block the activity of CYP24A1, which may lead to decreased profibrotic gene expression by decreasing inactivation of 1,25(OH)2D. 159x134mm (300 x 300 DPI)