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A novel pathway for hormonally active calcitriol
B Lehmann1, P Knuschke, M Meurer
1Department of Dermatology, Carl Gustav Carus Medical School, Dresden University of Technology, Dresden, Germany. Bodo.lehmann@mailbox.tu-dresden.de
Hormone Research
|October 12, 2001
Summary
Human skin produces calcitriol (1alpha,25(OH)2D3), the active form of vitamin D3, when exposed to UVB light. This process converts 7-dehydrocholesterol into calcitriol within epidermal cells.
Area of Science:
- Dermatology
- Endocrinology
- Biochemistry
Background:
- Calcitriol (1alpha,25(OH)2D3) is the active form of vitamin D3, crucial for calcium homeostasis.
- Vitamin D3 is synthesized in the skin and also produced in renal and extrarenal tissues.
Purpose of the Study:
- To investigate the capacity of human skin to synthesize calcitriol (1alpha,25(OH)2D3) autonomously.
- To determine the role of UVB radiation in the cutaneous production of calcitriol.
Main Methods:
- Exposure of human epidermal keratinocytes to physiological doses of UVB radiation (300 nm).
- Measurement of calcitriol formation using microdialysis technique in vivo.
- Assessment of the effect of ketoconazole, a P450 inhibitor, on calcitriol synthesis.
Main Results:
- UVB radiation induced the conversion of 7-dehydrocholesterol (7-DHC) to pre-vitamin D3, vitamin D3, and finally calcitriol in epidermal keratinocytes.
- Calcitriol was produced in the pmol range.
- Ketoconazole significantly suppressed the hydroxylation of vitamin D3 to calcitriol.
- UVB-induced calcitriol formation in human skin was confirmed in vivo.
Conclusions:
- Human skin possesses the autonomous capacity to produce calcitriol (1alpha,25(OH)2D3) from UVB exposure.
- The skin acts as an independent source of hormonally active calcitriol.
- This finding has implications for understanding vitamin D3 metabolism and skin physiology.