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Metabolite Card

Note

In vivo, 9-cis-retinal is formed through oxidation of 9-cis-retinol by cis-retinol dehydrogenase (cRDH). (PMID:15572038). The generation of retinoic acid from retinol is a two-step reaction, with the rate-limiting step being the oxidation of retinol into the intermediate retinaldehyde. Two classes of. unrelated enzymes have been implicated in the oxidation of retinol, the classical cytosolic medium chain alcohol dehydrogenases and recently identified microsomal members of the short chain alcohol dehydrogenase reductase (SDR) superfamily. Further oxidation of the retinaldehyde to the retinoic acid is believed to be catalyzed by several cytosolic aldehyde dehydrogenases. Retinoids are micronutrients required to maintain and promote health of vertebrates. They act physiologically by participating in the visual cycle, in regulating cell differentiation, in embryonic development (PMID:10893430), in maintaining normal reproduction, and in the immune response (PMID:8882153). In non-ocular tissues, the effects of retinoids within the body are mediated through retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which act to regulate gene expression as ligand-dependent transcription factors. The naturally occurring ligands for these nuclear receptors are thought to be all-trans-retinoic acid for RARs and 9-cis-retinoic acid for RXRs (PMID:10322133). While many details of the molecular actions of the RARs and RXRs in regulating gene transcription are understood (PMID:10418975), tissue-specific synthetic pathway(s) of their ligands has not been adequately defined. Nevertheless, the therapeutic efficacy of retinoids, including 9-cis-retinoic acid, is well established in both tissue culture and animal models of breast cancer (PMID:8825126, PMID:12743994).