HUMAN KERATINOCYTE LINE HACAT METABOLIZES 1-ALPHA-HYDROXYVITAMIN D-3 AND VITAMIN-D-3 TO 1-ALPHA,25-DIHYDROXYVITAMIN D-3 (CALCITRIOL)

Cultured human keratinocytes have the property to hydroxylate exogenou s 25-hydroxyvitamin D-3 (25OHD(3)) at the C-1 alpha position thus prod ucing 1 alpha,25-dihydroxyvitamin D-3 (1 alpha,25(OH)(2)D-3). In this study we investigated whether keratinocytes can also hydroxylate vitam in D-3 and one of its metabolites at the C-25 position. We could demon strate that HaCaT keratinocytes can metabolize 1 alpha-hydroxyvitamin D-3 (1 alpha-OHD3) and vitamin D-3 to 1 alpha,25(OH)(2)D-3. Identifica tion of the generated product as 1 alpha,25(OH)(2)D-3 was based on its elution pattern in two different high performance liquid chromatograp hy systems, on its specific binding in a calf thymus receptor assay an d on its gas chromatography-mass spectrometry characteristics. The hyd roxylation of vitamin D-3 to 1 alpha,25(OH)(2)D-3 was dose- and time-d ependent. Bovine serum albumin added up to 1.5% (w/v) to the culture m edium greatly increased the hydroxylation rates. These results show th at HaCaT cells have the capacity to hydroxylate vitamin D-3 at the C-1 /25 positions. The generation of endogenous 1 alpha,25(OH)(2)D-3 from vitamin D-3 within the skin may indicate a novel pathway which is of i mportance for the regulation of epidermal cell growth and differentiat ion. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.