Niacin nucleotide synthesis and glycolytic activity in erythrocytes of patients suffering from pellagra

Whole blood NAD and NADP concentrations are not depressed in subjects with clinical pellagra

Population surveys for niacin deficiency are normally based on clinical signs or on biochemical measurements of urinary niacin metabolites. Status may also be determined by measurement of whole blood NAD and NADP concentrations. To compare these methods, whole blood samples and spot urine samples were collected from healthy subjects (n = 2) consuming a western diet, from patients (n = 34) diagnosed with pellagra and attending a pellagra clinic in Kuito (central Angola, where niacin deficiency is endemic), and from female community control subjects (n = 107) who had no clinical signs of pellagra. Whole blood NAD and NADP concentrations were measured by microtiter plate-based enzymatic assays and the niacin urinary metabolites 1-methyl-2-pyridone-5-carboxamide (2-PYR) and 1-methylnicotinamide (1-MN) by HPLC. In healthy volunteers, inter- and intra-day variations for NAD and NADP concentrations were much lower than for the urinary metabolites, suggesting a more stable measure of status. However, whole blood concentrations of NAD and NADP or the NAD:NADP ratio were not significantly depressed in clinical pellagra. In contrast, the concentrations of 2-PYR and 1-MN, expressed relative to either creatinine or osmolality, were lower in pellagra patients and markedly higher following treatment. The use of the combined cut-offs (2-PYR <3.0 micromol/mmol creatinine and 1-MN <1.3 micromol/mmol creatinine) gave a sensitivity of 91% and specificity of 72%. In conclusion, whole blood NAD and NADP concentrations gave an erroneously low estimate of niacin deficiency. In contrast, spot urine sample 2-PYR and 1-MN concentrations, relative to creatinine, were a sensitive and specific measure of deficiency.

Dietary tryptophan level and the enzymes of tryptophan NAD pathway

1. Dietary tryptophan was found to regulate the activities of tryptophan oxygenase (EC 1.13.1.12) and quinolinate phosphoribosyltransferase (EC 2.4.2a) in liver. 2. With increasing tryptophan concentration in the diet containing 100 g protein/kg, tryptophan oxygenase activity increased while that of quinolinate phosphoribosyltransferase decreased. The response of these enzymes to dietary tryptophan at lower dietary protein level (25 g/kg) was not significant. 3. Liver nicotinate phosphoribosyltransferase (EC 2.4.2.11) activity and kidney picolinate carboxylase (EC 4.1.1.45) activity were unaltered with different tryptophan concentrations in the diet. 4. The response of various biochemical measurements was dependent on the tryptophan intake and the changes were marked below and above the requirement level of tryptophan. 5. It is suggested that the urinary excretion of quinolinic acid and N'-methylnicotinamide may be useful in assessing the tryptophan nutritional status and its requirement.

Effect of dietary protein level on some key enzymes of the tryptophan-NAD pathway

1. Six groups of rats were given diets containing protein at three levels (50, 100 and 200 g/kg), with and without nicotinic acid. After 4 weeks on these diets some key enzymes of the tryptophan and nicotinic acid-NAD pathway, liver nicotinamide nucleotide concentration, and urinary metabolites of tryptophan and nicotinic acid were studied. 2. Liver nicotinamide nucleotide levels were lower in rats given the diet with 50 g protein/kg as compared to those in rats given diets with 100 and 200 g protein/kg. The addition of nicotinic acid to the diet resulted in a significant increase in the levels of nicotinamide nucleotides only in rats given 50 g protein/kg diet but not in those given either 100 or 200 g protein/kg diet. 3. Liver tryptophan oxygenase (EC 1.13.1.12) activity increased with increasing dietary protein level. Niconitic acid in the diet had no effect on its activity. 4. Quinolinate phosphoribosyltransferase (EC 2.4.2.a) activity in liver was inversely related to dietary protein level, and nicotinic acid in the diet had no effect on its activity. 5. Liver nicotinate phosphoribosyltransferase (EC 2.4.2.11) activity and kidney picolinate carboxylase (EC 4.1.1.45) activity were not altered either by dietary protein level or nicotinic acid in the diet. 6. The addition of nicotinic acid to the diet resulted in increased excretion of N'-methylnicotinamide at all dietary protein levels. 7. The inverse relationship between protein level in the diet and liver quinolinate phosphoribosyltransferase activity, the rate-limiting enzyme of the tryptophan-NAD pathway suggests that the efficiency of conversion of tryptophan to NAD is related to protein level in the diet, the efficiency decreasing with an increase in the level of dietary protein.