Activity of vitamin A analogues in cell cultures of mouse epidermis and organ cultures of hamster trachea

Abstract

FIFTY years after the discovery that vitamin A controls cel differentiation in epithelial tissues the mechanism involved is still unknown. The recent introduction of two-cell and organ culture systems, involving serum-free medium, for the assay of vitamin A activity in vitro may help. One assay uses epidermal cell cultures derived from mouse skin¹ and the other uses tracheal organ cultures from vitamin A-deficient hamsters². In both, the observed cellular response depends on the addition of vitamin A, which induces a marked increase in the cellular RNA of the skin cultures and a change from the production of keratin to the production of cilia and mucus in the tracheal organ cultures. We have now investigated the Biological activity of seven analogues of natural vitamin A ester (β-retinyl acetate) and vitamin A acid (β-retinoic acid), in line with the common practice of assaying physiological and pharmacological actions of vitamins, hormones and drugs using structural analogues of a parent compound. In the analogues we used, the 5,6-cyclohexenyl ring system of natural vitamin A is modified substantially. Although data obtained in vivo show that modification of the ring portion of the molecule can reduce growth-promoting activity^3–5, we found that several vitamin A analogues with alterations in the ring, including a shift of the 5,6-double bond of the cyclohexene ring to the 4,5-position and replacement of the cyclohexene ring with substituted aromatic and cyclopentene rings, have substantial activity in the skin and tracheobronchial assays. Because of the sensitivity of the two assays it is now possible to assay vitamin A activity in the 10⁻⁹–10⁻¹⁰M range (30–300 pg ml⁻¹). Moreover, there is excellent correlation between the results of the two assays in terms of the evaluation of Biol.ogical activity of new analogues.