Changes in the urinary excretion of the metabolites of the tryptophan-niacin pathway during pregnancy in Japanese women and rats

The effect of dietary niacin deficiency on reproduction of European brown hares: An experimental study

Large plots of maize in agricultural landscapes are associated with reduced reproductive output of females and impaired population development of free-living populations of European brown hares (Lepus europaeus, Pallas 1778). We investigated in captive brown hares experimentally whether these effects could result from an undersupply of niacin due to a suspected maize-biased diet in such areas. We repeatedly mated adult female hares, fed ad libitum either with a niacin deficient pellet mainly consisting of maize plant parts, or with the same pellet enriched with niacin to meet physiological requirements. We measured effects of the experimental feeding on body mass of females, reproductive output, growth and survival of leverets. We found significantly higher body mass of females fed the control pellet, and faster body mass gain of their leverets until standardized weaning. We found no significant difference between niacin deficient and control diet groups in reproductive output of females and survival rates of leverets. Our results show that even a diet severely depauperate of niacin affects reproductive success of female brown hares only slightly, presumably because of sufficient conversion of tryptophan to niacin, or of additional supply of niacin by caecal microorganism.

Beyond Pellagra-Research Models and Strategies Addressing the Enduring Clinical Relevance of NAD Deficiency in Aging and Disease

Research into the functions of nicotinamide adenine dinucleotide (NAD) has intensified in recent years due to the insight that abnormally low levels of NAD are involved in many human pathologies including metabolic disorders, neurodegeneration, reproductive dysfunction, cancer, and aging. Consequently, the development and validation of novel NAD-boosting strategies has been of central interest, along with the development of models that accurately represent the complexity of human NAD dynamics and deficiency levels. In this review, we discuss pioneering research and show how modern researchers have long since moved past believing that pellagra is the overt and most dramatic clinical presentation of NAD deficiency. The current research is centered on common human health conditions associated with moderate, but clinically relevant, NAD deficiency. In vitro and in vivo research models that have been developed specifically to study NAD deficiency are reviewed here, along with emerging strategies to increase the intracellular NAD concentrations.

The Significance of NAD+ Biosynthesis Alterations in Acute Kidney Injury

Acute kidney injury (AKI) is a serious and highly prevalent disease, yet only supportive treatment is available. Nicotinamide adenine dinucleotide (NAD+) is a cofactor necessary for adenosine triphosphate (ATP) production and cell survival. Changes in renal NAD+ biosynthesis and energy utilization are features of AKI. Targeting NAD+ as an AKI therapy shows promising potential. However, the pursuit of NAD+-based treatments requires deeper understanding of the unique drivers and effects of the NAD+ biosynthesis derangements that arise in AKI. This article summarizes the NAD+ biosynthesis alterations in the kidney in AKI, chronic disease, and aging. To enhance this understanding, we explore instances of NAD+ biosynthesis alterations outside the kidney in inflammation, pregnancy, and cancer. In doing so, we seek to highlight that the different NAD+ biosynthesis pathways are not interconvertible and propose that the way in which NAD+ is synthesized may be just as important as the NAD+ produced.

Metabolite trajectories across the perinatal period and mental health: A preliminary study of tryptophan-related metabolites, bile acids and microbial composition

Depression and anxiety during pregnancy and postpartum are common, but affected women differ in timing, trajectories, and extent of symptoms. The objective of this pilot, feasibility study is to analyze trajectories of serotonin and tryptophan-related metabolites, bile acid metabolites, and microbial composition, in relation to psychiatric history and current symptoms across the perinatal period. Serum and fecal samples were collected from 30 women at three times points in the perinatal period and assayed with LC-MS/MS and 16S sequencing respectively. We defined mean trajectories for each metabolite, clustered individuals by metabolite trajectories, tested associations between metabolites, and examined metabolite levels in relation to microbial composition. Findings of note include: (1) changes in kynurenine and the ratio of kynurenic acid to kynurenine from second trimester to third trimester were strongly associated with baseline primary and secondary bile acids. (2) Secondary bile acid UDCA and its conjugated forms were associated with lower bacterial diversity and levels of Lachnospiraceae, a taxa known to produce Short Chain Fatty Acids. (3) History of anxiety was associated with UDCA levels, but history of major depression was not associated with any of the bile acids. (4) There was a trend towards lower dietary fiber for those with history of anxiety or depression. Overall, our results reveal substantial temporal variation in tryptophan-related metabolites and in bile acid metabolites over the perinatal period, with marked inter-individual variability. Trajectories of TRP -related metabolites, primary and secondary bile acids, and the absence or presence of microbes that produce Short Chain Fatty Acids (SCFAs) considered in concert have the potential to differentiate individuals based on perinatal adaptations that may impact mental and overall health.

Developmental Programming and Reprogramming of Hypertension and Kidney Disease: Impact of Tryptophan Metabolism

The concept that hypertension and chronic kidney disease (CKD) originate in early life has emerged recently. During pregnancy, tryptophan is crucial for maternal protein synthesis and fetal development. On one hand, impaired tryptophan metabolic pathway in pregnancy impacts fetal programming, resulting in the developmental programming of hypertension and kidney disease in adult offspring. On the other hand, tryptophan-related interventions might serve as reprogramming strategies to prevent a disease from occurring. In the present review, we aim to summarize (1) the three major tryptophan metabolic pathways, (2) the impact of tryptophan metabolism in pregnancy, (3) the interplay occurring between tryptophan metabolites and gut microbiota on the production of uremic toxins, (4) the role of tryptophan-derived metabolites-induced hypertension and CKD of developmental origin, (5) the therapeutic options in pregnancy that could aid in reprogramming adverse effects to protect offspring against hypertension and CKD, and (6) possible mechanisms linking tryptophan metabolism to developmental programming of hypertension and kidney disease.

NAD deficiency due to environmental factors or gene-environment interactions causes congenital malformations and miscarriage in mice

Causes for miscarriages and congenital malformations can be genetic, environmental, or a combination of both. Genetic variants, hypoxia, malnutrition, or other factors individually may not affect embryo development, however, they may do so collectively. Biallelic loss-of-function variants in HAAO or KYNU, two genes of the nicotinamide adenine dinucleotide (NAD) synthesis pathway, are causative of congenital malformation and miscarriage in humans and mice. The variants affect normal embryonic development by disrupting the synthesis of NAD, a key factor in multiple biological processes, from its dietary precursor tryptophan, resulting in NAD deficiency. This study demonstrates that congenital malformations caused by NAD deficiency can occur independent of genetic disruption of NAD biosynthesis. C57BL/6J wild-type mice had offspring exhibiting similar malformations when their supply of the NAD precursors tryptophan and vitamin B3 in the diet was restricted during pregnancy. When the dietary undersupply was combined with a maternal heterozygous variant in Haao, which alone does not cause NAD deficiency or malformations, the incidence of embryo loss and malformations was significantly higher, suggesting a gene-environment interaction. Maternal and embryonic NAD levels were deficient. Mild hypoxia as an additional factor exacerbated the embryo outcome. Our data show that NAD deficiency as a cause of embryo loss and congenital malformation is not restricted to the rare cases of biallelic mutations in NAD synthesis pathway genes. Instead, monoallelic genetic variants and environmental factors can result in similar outcomes. The results expand our understanding of the causes of congenital malformations and the importance of sufficient NAD precursor consumption during pregnancy.

Organ Co-Relationship in Tryptophan Metabolism and Factors That Govern the Biosynthesis of Nicotinamide from Tryptophan

The pathway of tryptophan (Trp)-nicotinamide is very important nutritionally because a vitamin nicotinamide is biosynthesized from an amino acid Trp. Until we started studying the factors that affect the Trp-nicotinamide conversion rate, little data existed. Data obtained from TDO (Trp 2,3-dioxygenase)-KO (knock-out) mice have revealed that mice can biosynthesize a necessary amount of nicotinamide from Trp by indoleamine 2,3-dioxygenase (IDO) even when TDO is lacking. It has also been shown that 3-hydroxyanthranilic acid is a key intermediate. Urine upper metabolites such as kynurenic acid and xanthurenic acid originate from non-hepatic tissues but not from the liver. Data obtained from quinolinic acid phosphoribosyltransferase (QPRT)-KO mice indicated that the Trp→quinolinic acid conversion ratio was 6%. Urine quinolinic acid levels and the conversion ratio of Trp to nicotinamide were the same between hetero and wild mice. These findings indicate that QPRT is not the rate-limiting enzyme in the conversion. Thus, the limiting factors in the conversion of Trp to nicotinamide are the amounts of 3-hydroxyanthranilic acid and quinolinic acid in the liver and the activity of liver 3-hydroxyanthranilic acid 3,4-dioxygenase. Studies on factors have shown that conversion of Trp to nicotinamide is increased by adequate intake of good quality protein, and adequate intake of unsaturated fatty acids and starch. However, conversion was decreased by deficient niacin, vitamin B₂, or vitamin B₆, excessive intake of protein, saturated fatty acids, or glucose and fructose, or intake of protein with low Trp content, and insufficient mineral intake.

Redox Properties of Tryptophan Metabolism and the Concept of Tryptophan Use in Pregnancy

During pregnancy, tryptophan (Trp) is required for several purposes, and Trp metabolism varies over time in the mother and fetus. Increased oxidative stress (OS) with high metabolic, energy and oxygen demands during normal pregnancy or in pregnancy-associated disorders has been reported. Taking the antioxidant properties of Trp and its metabolites into consideration, we made four hypotheses. First, the use of Trp and its metabolites is optional based on their antioxidant properties during pregnancy. Second, dynamic Trp metabolism is an accommodation mechanism in response to OS. Third, regulation of Trp metabolism could be used to control/attenuate OS according to variations in Trp metabolism during pregnancy. Fourth, OS-mediated injury could be alleviated by regulation of Trp metabolism in pregnancy-associated disorders. Future studies in normal/abnormal pregnancies and in associated disorders should include measurements of free Trp, total Trp, Trp metabolites, and activities of Trp-degrading enzymes in plasma. Abnormal pregnancies and some associated disorders may be associated with disordered Trp metabolism related to OS. Mounting evidence suggests that the investigation of the use of Trp and its metabolites in pregnancy will be meanful.

Tryptophan metabolism, disposition and utilization in pregnancy

Tryptophan (Trp) requirements in pregnancy are several-fold: (1) the need for increased protein synthesis by mother and for fetal growth and development; (2) serotonin (5-HT) for signalling pathways; (3) kynurenic acid (KA) for neuronal protection; (4) quinolinic acid (QA) for NAD(+) synthesis (5) other kynurenines (Ks) for suppressing fetal rejection. These goals could not be achieved if maternal plasma [Trp] is depleted. Although plasma total (free + albumin-bound) Trp is decreased in pregnancy, free Trp is elevated. The above requirements are best expressed in terms of a Trp utilization concept. Briefly, Trp is utilized as follows: (1) In early and mid-pregnancy, emphasis is on increased maternal Trp availability to meet the demand for protein synthesis and fetal development, most probably mediated by maternal liver Trp 2,3-dioxygenase (TDO) inhibition by progesterone and oestrogens. (2) In mid- and late pregnancy, Trp availability is maintained and enhanced by the release of albumin-bound Trp by albumin depletion and non-esterified fatty acid (NEFA) elevation, leading to increased flux of Trp down the K pathway to elevate immunosuppressive Ks. An excessive release of free Trp could undermine pregnancy by abolishing T-cell suppression by Ks. Detailed assessment of parameters of Trp metabolism and disposition and related measures (free and total Trp, albumin, NEFA, K and its metabolites and pro- and anti-inflammatory cytokines in maternal blood and, where appropriate, placental and fetal material) in normal and abnormal pregnancies may establish missing gaps in our knowledge of the Trp status in pregnancy and help identify appropriate intervention strategies.

Maternal and fetal tryptophan metabolism in gestating rats: effects of intrauterine growth restriction

L-Tryptophan (L-Trp) is a precursor for serotonin (5-HT) and nicotinamide adenine dinucleotide (NAD) synthesis. Both 5-HT and NAD may impact energy metabolism during gestation given that recent studies have demonstrated that increased 5-HT production is crucial for increasing maternal insulin secretion, and that sirtuin, an NAD(+)-dependent protein deacetylase, regulates endocrine signaling. Infants born with intrauterine growth restriction (IUGR) are at a higher risk of metabolic disease once they reach adulthood. IUGR is associated with altered maternal-fetal amino acid transfer. Whether IUGR affects L-Trp metabolism in mother and fetus has not been fully elucidated. Recently, we developed an analytical method using stable isotope-labeled L-Trp to explore the metabolism of L-Trp and its main metabolites, L-kynurenine (L-Kyn), 5-HT and quinolinic acid (QA). In this study, dams submitted to dietary protein restriction throughout gestation received intravenous infusions of stable isotope-labeled (15)N2-L-Trp to determine whether L-Trp metabolism is affected by IUGR. Samples were obtained from maternal, fetal and umbilical vein plasma, as well as the amniotic fluid (AF), placenta and liver of the mother and the fetus after isotope infusion. We observed evidence for active L-Trp transfer from mother to fetus, as well as de novo synthesis of 5-HT in the fetus. Plasma 5-HT was decreased in undernourished mothers. In IUGR fetuses, maternal-fetal L-Trp transfer remained unaffected, but conversion to QA was impaired, implying that NAD production also decreased. Whether such alterations in tryptophan metabolism during gestation have adverse consequences and contribute to the increased risk of metabolic disease in IUGR remains to be explored.

Method for Evaluation of the Requirements of B-group Vitamins Using Tryptophan Metabolites in Human Urine

Tryptophan metabolism is directly involved with B-group vitamins such as vitamin B2, niacin, and vitamin B6, and indirectly with vitamin B1 and pantothenic acid. We evaluated the validity of requirements of B-group vitamins set by the Dietary Reference Intakes for the Japanese (DRI-J). We investigated the fate of dietary tryptophan in 10 Japanese adult men who ate the same diet based on DRI-J during a 4-week study. Vitamin mixtures were administered based on the amounts in the basal diet during weeks 2, 3, and 4. Daily urine samples were collected eight times (days 1 and 5 in each week). Administration of vitamin mixtures had no effect on tryptophan metabolites such as anthranilic acid, kynurenic acid, xanthurenic acid, 3-hydroxyanthranilic acid, and quinolinic acid within individuals. Surplus administration of B-group vitamins against DRI-J requirements did not elicit beneficial effects on tryptophan metabolism. Our findings supported the requirements of B-group vitamins set by the DRI-J.

Conversion Percentage of Tryptophan to Nicotinamide is Higher in Rice Protein Diet than in Wheat Protein Diet in Rats

We reported previously that the pellagragenic property of corn protein is not only low l-tryptophan concentration but also the lower conversion percentage of l-tryptophan to nicotinamide; the amino acid composition greatly affected the conversion percentage. The amino acid value of wheat protein is lower than that of rice protein. In the present study, we compare the conversion percentages of l-tryptophan to nicotinamide between wheat protein and rice protein diets in growing rats. The body weight gain for 28 days in rats fed with a 10% amino acid mixture diet with wheat protein was lower than that of rats fed with a 10% amino acid diet with rice protein (68.1 ± 1.6 g vs 108.4 ± 1.9 g; P < 0.05). The conversion percentage of l-tryptophan to nicotinamide was also lower for the wheat protein diet compared with the rice protein diet (1.44 ± 0.036% vs 2.84 ± 0.19%; P < 0.05). The addition of limiting amino acids (l-isoleucine, l-lysine, l-tryptophan, l-methionine, l-threonine) to the wheat protein diet improved growth and the conversion percentage. In conclusion, our result supports the thinking that the composition of amino acids affects the conversion ratio of l-tryptophan to nicotinamide.

Vitamin B1 deficiency inhibits the increased conversion of tryptophan to nicotinamide in severe food-restricted rats

The conversion of tryptophan (Trp) → nicotinamide (Nam) is an important pathway for supplying vitamin niacin. We reported the following two phenomena: (1) severe food restriction led to an increase in the Trp → Nam conversion compared with free-access control group; (2) the conversion of Trp → Nam is also increased by vitamin B1 deficiency compared with free-access control group. The present study was done to clarify whether or not a true reason about an increase in the Trp → Nam conversion is a vitamin B1 deficiency or severe food restriction. The present results showed that vitamin B1 deficiency suppressed the increased conversion of Trp → Nam induced by severe food restriction, probably by suppressing 3-hydroxyanthranilic acid 3,4-dioxygenase protein synthesis in liver.

Changes in plasma pyridoxal 5'-phosphate concentration during pregnancy stages in Japanese women

Most Japanese women do not consume the estimated average requirement of vitamin B6 (1.7 mg/d) during pregnancy. Nevertheless, these deficiencies are not reported. We investigated a nutritional biomarker of vitamin B6 in pregnant Japanese women as well as their vitamin B6 intakes. Vitamin B6 intakes in the first, second, and third trimesters of pregnancy, and 1 mo after delivery were 0.79±0.61 (n=56), 0.81±0.29 (n=71), 0.90±0.35 (n=92), and 1.00±0.31 (n=44) mg/d, respectively. Plasma pyridoxal 5'-phosphate (PLP) concentrations in the first, second, and third trimesters of pregnancy, and 1 mo after delivery were 57.1±27.6 (n=56), 23.3±16.7 (n=71), 18.3±12.5 (n=92), and 43.9±33.4 (n=44) nmol/L, respectively. The plasma concentrations significantly decreased in the second and third trimesters of pregnancy compared to values from the first trimester (p<0.05), and these concentrations returned to the values of the first trimester of pregnancy 1 mo after birth.

Simultaneous detection of stable isotope-labeled and unlabeled L-tryptophan and of its main metabolites, L-kynurenine, serotonin and quinolinic acid, by gas chromatography/negative ion chemical ionization mass spectrometry

A method for the detection of unlabeled and (15)N2 -labeled L-tryptophan (L-Trp), L-kynurenine (L-Kyn), serotonin (5-HT) and quinolinic acid (QA) in human and rat plasma by GC/MS is described. Labeled and unlabeled versions of these four products were analyzed as their acyl substitution derivatives using pentafluoropropionic anhydride and 2,2,3,3,3-pentafluoro-1-propanol. Products were then separated by GC and analyzed by selected ion monitoring using negative ion chemical ionization mass spectrometry. L-[(13)C11, (15)N2]-Trp, methyl-serotonin and 3,5-pyridinedicarboxylic acid were used as internal standards for this method. The coefficients of variation for inter-assay repeatability were found to be approximately 5.2% for L-Trp and (15)N2-Trp, 17.1% for L-Kyn, 16.9% for 5-HT and 5.8% for QA (n = 2). We used this method to determine isotope enrichments in plasma L-Trp over the course of a continuous, intravenous infusion of L-[(15) N2 ]Trp in pregnant rat in the fasting state. Plasma (15)N2-Trp enrichment reached a plateau at 120 min. The free Trp appearance rate (Ra) into plasma was 49.5 ± 3.35 µmol/kg/h. The GC/MS method was applied to determine the enrichment of (15)N-labeled L-Trp, L-Kyn, 5-HT and QA concurrently with the concentration of non-labeled L-Trp, L-Kyn, 5-HT and QA in plasma. This method may help improve our understanding on L-Trp metabolism in vivo in animals and humans and potentially reveal the relative contribution of the four pathways of L-Trp metabolism.

Nutritional aspect of tryptophan metabolism

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.

Fate of dietary tryptophan in young Japanese women

The purpose of this study was to determine, using the high-performance liquid chromatographic methods recently modified by us, the fate of dietary tryptophan in 17 healthy female Japanese adults who ate self-selected food. The experimental period was 22 days. The habitual intake of tryptophan was 3328.4 μmol/day. 24-hour urine samples were collected at the beginning of the experiment and then once per week. Blood was collected at the beginning and end of the experiment. Levels of tryptophan and its metabolites were measured in blood and urine. Tryptophan, nicotinamide and 2-oxoadipic acid were the major compounds of the blood. The urinary excretion amounts of tryptophan, 5-hydroxyindole-3-acetic acid, kynurenine, anthranilic acid, kynurenic acid, 3-hydroxykynurenine, xanthurenic acid, 3-hydroxyanthranilic acid and quinolinic acid were about 40, 20, 4, 1, 10, 4, 3, 5 and 20 μmol/day, respectively.

High tryptophan diet reduces extracellular dopamine release via kynurenic acid production in rat striatum

At endogenous brain concentrations, the neuroinhibitory tryptophan metabolite kynurenic acid (KYNA) is a preferential antagonist of the α7 nicotinic acetylcholine receptor (α7nAChR). In the present study, male Wistar rats were fed a high tryptophan diet (adding 0.1-1.5% tryptophan) for 24 h to examine (i) the effect of increased tryptophan on extracellular dopamine (DA) and KYNA levels and (ii) to determine any possible interactions between DA and KYNA. Brain KYNA levels were dose-dependently increased by tryptophan intake, and these increase were consistent with kynurenine (KYN), the precursor to KYNA, levels in the brain, plasma and liver. Administration of the 1.5% tryptophan added diet reduced the extracellular DA level to 60%, and increased the extracellular KYNA to 320% in the striatum. The DA reduction was attenuated through inhibiting KYNA synthesis with 2-aminoadipic acid. These results indicate that a high tryptophan diet can induce KYNA production and suppress DA release. One possible mechanism is that as more KYN is metabolized from the high doses of tryptophan in the liver and released into the blood stream, KYNA production in astrocytes is enhanced and the increased extracellular KYNA inhibits DA release by blocking α7nAChRs. Dietary manipulation of KYNA formation in astrocytes may offer a unique strategy to modulate DA.