The metabolism of high intakes of tryptophan, nicotinamide and nicotinic acid in the rat

Abstract

1. The metabolic fate of high dietary intakes of nicotinamide, nicotinic acid and tryptophan, and of acute doses of nicotinamide and nicotinic acid, has been studied in the rat. A new high-pressure liquid chromatography method for measurement of the principal urinary metabolites of niacin is described.2. Administration to rats of a single oral dose of nicotinamide or nicotinic acid (up to 100 mg/kg body-weight), or maintenance for 3 weeks on diets providing 150 mg nicotinamide or nicotinic acid/kg diet, resulted in only a small increase in the liver content of nicotinamide nucleotide coenzymes (NAD and NADP). The quantitative metabolism of nicotinamide and nicotinic acid differed, suggesting that intestinal bacterial deamidation is not the major fate of nicotinamide.3. A high dietary intake of tryptophan (5.9 g/kg diet) led to a considerable increase in liver NAD(P) and also in urinary excretion of niacin metabolites. The results suggest that, as indicated by enzyme kinetic studies (Bender et al. 1982), the utilization of nicotinamide and nicotinic acid for nucleotide synthesis is limited, while there is little or no limitation of NAD(P) synthesis from the tryptophan metabolite quinolinic acid.

Sirtuins as novel players in the pathogenesis of diabetes mellitus

“…In energy rich conditions, NAD + is reduced to nicotine-amide adenine di nucleotide (NADH) and the proportion of NAD + to NADH is reduced during glycolysis, cyclic acid cycling, lipid β-oxidation and protein catabolism [11] . Two main sources of NAD + are the salvage pathway of nicotinamide catalyzed by the enzyme, nicotinamide phosphoribosyltransferase, and de novo synthesis from tryptophan metabolism [12] . Recent experimental studies showed that sirtuins can be found and activated in kidney, liver, spleen, lung, heart, muscle, brain, testis, ovary, thymus, pancreas, white and brown adipose tissue [13] .…”

Biocidal action of chlorhexidine is annulled by nicotinic acid

“…In the latter pharmacologic situation, as opposed to nutritional circumstances, different biotransformations for NAmide and NA may explain why they do not have the same pharmacologic action (9). Similarly, in our study (Table 1) NAmide apparently could not be biotransformed into NA in the presence of CLX if CLX inhibited NAmide deamidase activity (9,15).…”

Thiamin and Niacin in Ruminant Nutrition

“…Harmeyer, unpublished results) it was shown that nicotinamide administered into the rumen was almost instantly hydrolysed to nicotinic acid and ammonia, probably due to the presence of microbial deamidases (Warner, 1964) which have also been found in the rat intestines (McCreanor & Bender, 1986). There is also evidence that most tissues can utilize both nicotinic acid and nicotinamide for synthesis of NAD and NADP ).…”

“…A method for quantification of niacin metabolites from urine using cation-exchange chromatography is, however, available (McCreanor & Bender, 1986). Pertinent methods for determination of the oxidized and reduced forms of the coenzymes in blood and other tissues have been reviewed (Chytil & McCormick, 1986).…”