Nicotinamide Adenine Dinucleotide‐Dependent Retinoic Acid Formation From Retinol in the Human Gastric Mucosa: Inhibition by Ethanol, Acetaldehyde, and H2 Blockers

All-trans retinoic acid formation from all-trans retinol (vitamin A) in the human gastric mucosa was studied. When all-trans retinol and the human gastric mucosa were incubated together, all-trans retinoic acid was formed in the presence of nicotinamide adenine dinucleotide (NAD). When the NAD was not added, hardly any formation was observed. The formation of all-trans retinoic acid tended to be attenuated by 10 mM ethanol. Moreover, it was significantly attenuated in a concentration-dependent manner by ethanol at concentrations of 100 mM and above. Acetaldehyde at concentrations of 50 microM and above also significantly attenuated its formation in a concentration-dependent manner. Some H2 blockers, which include ranitidine hydrochloride and cimetidine, significantly attenuated the formation of all-trans retinoic acid, whereas famotidine failed to suppress it. There is an NAD-dependent pathway by which all-trans retinoic acid is produced from all-trans retinol in the human gastric mucosa. Inhibitors of alcohol dehydrogenase, which include ethanol and some H2 blockers, and of aldehyde dehydrogenase, which include acetaldehyde, inhibit its production.