Evaluating the role of niacin in human carcinogenesis.

Our understanding of the role of ADP-ribose polymer metabolism in limiting carcinogenic events and the dependence of this metabolism on cellular NAD levels predicts that niacin deficiency leading to reduced NAD levels may enhance carcinogenesis. This prediction has led us to initiate studies to evaluate the potential of niacin as a preventive factor in human cancer. The first approach involves development of a method to assess biochemically niacin status in humans using intracellular NAD derived from whole blood, primarily erythrocytes, as the relevant marker of niacin status. We have shown that erythrocyte NAD content varies by as much as 12-fold within a population and can be modulated readily by supplementation. A second approach to testing this hypothesis involves understanding the relationship of dietary niacin, circulating levels of NAD precursors (nicotinamide and nicotinic acid) and NAD in target tissues for human cancer. Current analytical methods for quantification of plasma levels of nicotinic acid and nicotinamide following intake in the dietary range are not sufficient. Thus, we have developed a GC-MS method for the rapid, sensitive, and selective determination of both nicotinamide and nicotinic acid in plasma. These methods will now allow assessment of niacin metabolism in humans that could lead to a new understanding of niacin in prevention of cancer.