Abstract
Background: Vitamin A is a family of derivatives synthesized from carotenoids acquired from the diet and can be converted in animals to bioactive forms essential for life. The vitamin A1 (all-trans-retinol / ATROL) and provitamin A1 (all-trans-β,β-carotene / ATBC) are precursors of all-trans-retinoic acid acting as a ligand for the retinoic acid receptors. The contribution of ATROL and ATBC to formation of 9-cis-13,14-dihydroretinoic acid (9CDHRA), the only endogenous retinoid acting as retinoid X receptor ligand remains unknown. Methods: Novel and well know retinoids and carotenoids were synthesized via organic chemical synthesis. Further, novel and well know retinoids / carotenoids were administered to in vitro oligodendrocyte cell culture and to in vivo oral supplemented mice with following HPLC-MS / UV-Vis based metabolomic evaluation of these administered retinoids / carotenoids. In addition, working memory analyses were performed in a mouse study. Results: In this study, we show that ATROL and ATBC are at best only weak and non-selective precursors of 9CDHRA. Instead, we identify 9-cis-13,14-dihydroretinol (9CDHROL) and 9-cis-13,14-dihydro-β,β-carotene (9CDHBC) as novel direct nutritional precursors of 9CDHRA, which are present endogenously in humans and the human food chain matrix. We also propose that the endogenous carotenoid 9-cis-β,β-carotene (9CBC) can also act as weak, indirect precursor of 9CDHRA via hydrogenation to 9CDHBC and further metabolism to 9CDHROL and/or 9CDHRA.Conclusion: In summary, since classical vitamin A1 is not an efficient 9CDHRA precursor, we conclude that this group of molecules constitutes as a new class of vitamin or a new independent member of the vitamin A family, named “Vitamin A5/X”.
A new approach to the assessment of marginal vitamin A deficiency in children in suburban Guwahati, India: hydrolysis of retinoyl glucuronide to retinoic acid