Moderate food restriction suppresses the conversion of l-tryptophan to nicotinamide in weaning rats

Abstract

Calorie restriction leads to a change in the metabolism of nutrients. Nicotinamide is biosynthesized from l-tryptophan. We attempted to determine the effects of food restriction on the biosynthesis of nicotinamide from l-tryptophan. Weaning male rats were fed a conventional chemically defined diet without preformed niacin for 63 d. However, the food intake was restricted to 80 and 65% of the intake of the ad libitum-fed control group of rats. The 24-h urine samples were periodically collected, and the urinary excretion of nicotinamide and its catabolites was measured. The conversion percentages were lower in both restricted groups than in the ad libitum-fed control group during the experimental period (control group, 1.37 ± 0.24%; 80%-restricted group, 0.20 ± 0.04%; 65%-restricted group, 0.15 ± 0.02%; control vs. restricted groups, p < 0.01). Food restriction, even at mild level, suppressed the conversion of l-tryptophan to nicotinamide when compared to the ad libitum-fed control group.

Graphical Abstract

Moderate food restriction suppressed the conversion of Trp-Nam in rats. The prevalence of pellagra in the 'hungry' season might be associated with a lower conversion percentage of Trp-Nam.

Key words:

• growth
• conversion
• calorie restriction
• nicotinamide
• tryptophan

Acknowledgment

This investigation was part of the project “Studies on the nutritional evaluation of amino acids and B-group vitamins” (Katsumi Shibata was the principal investigator), supported by a scientific research from Japan Society for the Promotion of Science.

Notes

Abbreviations: AMS, α-aminomuconate-ε-semialdehyde; ACMS, α-amino-β-carboxymuconate-ε-semialdehyde; ACMSD, α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase; HPLC, high-performance liquid chromatography; MNA, N¹-methylnicotinamide; 2-py, N¹-methyl-2-pyridone-5-carboxamide; 4-Py, N¹-methyl-4-pyridone-3-carboxamide; Nam, Nicotinamide; l-Trp, l-tryptophan.