Vitamin D3 production by cultured human keratinocytes and fibroblasts.

We have demonstrated that monolayers of human cultured newborn foreskin keratinocytes and fibroblasts elaborate vitamin D3 following exposure to UV-B. This in vitro system provides a new means to study those factors (hormones, ions, vitamin D3 metabolites, etc.) that regulate the production of vitamin D3 by human skin cells. Vitamin D3 production was enhanced greatly by using cells that were pre-treated with AY-9944, a non-toxic drug that inhibits cholesterologenesis while elevating cellular levels of 7-dehydrocholesterol, the sterol precursor of vitamin D3. The pre-D3 formed within viable, irradiated cells is transformed to D3 within a matter of hours at 37 degrees C, and keratinocytes proved to be more proficient sources of the vitamin and its metabolites than corresponding skin fibroblasts.