13,14-Dihydroxy-retinol, a new bioactive retinol metabolite

Deprivation of vitamin A (retinol) leads to reduced potential of B cell proliferation and nearly complete block of T cell activation in vitro. Retinol, which is thought to function as a pro-hormone, is enzymatically converted into intracellular messenger molecules. Thus, 14-hydroxy-retro-retinol (14-HRR) is an intracellular messenger molecule linked to activation and growth regulation of lymphocytes; whereas, anhydroretinol, another natural retro-retinoid, is an antagonist of 14-HRR effects. In this article, we describe the isolation, structure determination, synthesis, and biological properties of a new intracellular retinol derivative, 13,14-dihydroxy-retinol (DHR), which also supports the viability of retinol-deprived lymphocytes. DHR is found in numerous cell lines representing a large cross-section of tissues and animals from insects to mammals. In T lymphocytes the production of DHR and 14-HRR is up-regulated by phorbol ester. DHR is converted to 14-HRR by mild acid treatment, but not by cells; therefore DHR is not a biosynthetic intermediate in the conversion of retinol to 14-HRR. DHR is a distinct end point of retinol metabolism. Although it is linked to cell proliferation, its biological role remains to be determined.