Nutritional Aspect of Tryptophan Metabolism

Abstract

Mammals, including humans, can synthesize the vitamin nicotinamide from tryptophan in the liver. The resultant nicotinamide is distributed to non-hepatic tissues. We have studied the effects of changes in tryptophan–nicotinamide metabolism on niacin nutritional status. The liver plays a critical role in nicotinamide supply. Animal studies showed that the tryptophan–nicotinamide pathway is affected by physiological conditions, the presence of disease, nutrients, hormones, and chemicals. Human studies have shown that 1 mg of nicotinamide is produced from 67 mg of tryptophan intake, and that the conversion ratio of tryptophan to nicotinamide is enhanced from mid to late pregnancy. These findings have contributed to the determination of dietary reference intakes for niacin recommended in the Dietary Reference Intakes for Japanese 2010. Our findings suggest that the conversion of nicotinamide from tryptophan is important in maintaining niacin nutrition.

Effects of a wide range of dietary nicotinamide riboside (NR) concentrations on metabolic flexibility and white adipose tissue (WAT) of mice fed a mildly obesogenic diet

“…More importantly, requirements were based on studies with rats as no direct data were available for mice. Estimation of vitamin B3 requirements is not straightforward, since NAD + can also be synthesized de novo from the essential amino acid tryptophan (Trp) . Dietary Trp may thus rescue vitamin B3 deficiency.…”

Antidepressants may lead to a decrease in niacin and NAD in patients with poor dietary intake

“…Recent research from Japan reported nicotinamide synthesised from tryptophan in normal healthy Japanese to be almost equal to that from dietary intake [16]. Synthesis from tryptophan has even been suggested as the primary source of NAD in the body [14].…”

“…In the de novo pathway, synthesis from tryptophan occurs as part of the kynurenine pathway in the so-called tryptophan-nicotinamide pathway. NAD can also be generated by recycling degraded NAD components such as nicotinamide, nicotinic acid and nicotinamide riboside in the so-called salvage pathways [6,16].…”

Optimization of the ultrasound-assisted extraction of tryptophan and its derivatives from rice ( Oryza sativa ) grains through a response surface methodology

“…It has been acknowledged that tryptophan is converted into numerous compounds of biological significance such as vitamins, neurotransmitters and auxins (Fukuwatari and Shibata, 2013). Among these biogenetically tryptophan-related compounds, indole-3-acetic acid (IAA) and serotonin (5-hydroxytryptamine, 5HTAM) inspired in-depth research on plant morphogenesis and growth regulators as they contribute to the possible coordinated regulation in plants (Pelagio-Flores et al, 2011;Ramakrishna et al, 2011).…”