Chronic Ethanol Intake Impairs Niacin Nutritional Status in Mice

Niacin is involved in many biological reactions relating energy metabolism, redox reactions, DNA repair and longevity. Since niacin deficiency has been reported in alcoholic patients, and niacin coenzyme NAD is used as substrate to dehydrogenate ethanol in the liver, ethanol consumption can be a factor to impair niacin nutritional status. We have recently established the niacin insufficient model mice using kynurenine 3-monooxygenase knock out (KMO^-/-) mice with niacin-limited diet, which lack the de novo NAD synthesis pathway from tryptophan. To evaluate the effects of chronic ethanol intake on niacin nutritional status, 4 wk old KMO^-/- mice were fed 4 or 30 mg/kg nicotinic acid containing diets with or without 15% ethanol for 35 d. The mice fed 4 mg/kg nicotinic acid diet with ethanol showed lower body weight gain and niacin nutritional markers such as liver and blood NAD, and urine nicotinamide metabolites than the mice without ethanol. These animals did not show any difference in the NAD synthesis, NAD salvage and nicotinamide catabolic pathways. Chronic ethanol intake failed to affect any indices in the mice fed the 30 mg/kg nicotinic acid diet. When the diet was exchanged the 4 mg/kg for 30 mg/kg nicotinic acid diet to the mice showed chronic ethanol-induced growth retardation, their body weight rapidly increased. These results show that chronic ethanol intake impairs niacin nutritional status in the niacin insufficient mice, and enough niacin intake can prevent this impairment. Our findings also suggest that chronic ethanol intake increases niacin requirement by increase of NAD consumption.