Tryptophan-niacin Metabolism Research Articles

Effect of Dietary Phytol on the Expression of α-Amino-β-carboxymuconate-ε-semialdehyde Decarboxylase, a Key Enzyme of Tryptophan-niacin Metabolism, in Rats

α-Amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD) plays a key role in the regulation of NAD biosynthesis or the production of quinolinate from tryptophan (Trp). We investigated in this study the effect of phytol, a phytochemical known as a peroxisome proliferator-activated receptor α (PPARα) ligand, on NAD synthesis and ACMSD expression in rats. Male Sprague-Dawley rats were fed a diet containing 0.5%, 1%, or 2% phytol for 7 d. Phytol decreased the ACMSD activity and its mRNA expression in a dose-dependent manner in the liver. Phytol similarly and significantly suppressed ACMSD mRNA expression in primary rat hepatocytes. However, the mRNA expression of ACO (a known PPARα target gene) was higher in the low-phytol groups than in the high-phytol group in vivo and in vitro. Phytol increased the blood NAD level by suppressing ACMSD mRNA expression in the liver of the rats. It is possible that this mechanism occurred by the activation of PPARα and also of other transcriptional factors.

Effects of hepatic injury or kidney injury on the tryptophan–niacin metabolism in rats

Abstract Hepatic α-amino-β-carboxymuconate-e-semialdehyde decarboxylase (ACMSD) plays a key role in regulating NAD biosynthesis. In normal rats, ACMSD has been generally detectable only in the liver and kidneys. Therefore, there is a possibility that liver or kidney injury affects tryptophan–niacin metabolism. We previously reported the significant change of tryptophan–niacin metabolism in rats with liver cirrhosis or in rats with d -galactosamine injected liver injury. In this experiment, we investigated the change of tryptophan–niacin metabolism in rats treated with puromycin aminonucleoside (PAN)-induced nephrosis, the mechanisms responsible for their change of urinary excretion of nicotinamide and its metabolites, and the role of the kidney in tryptophan–niacin conversion. In PAN-treated rats, the sum of urinary excretion of nicotinamide and its metabolites was significantly lower compared with controls. Although kidney ACMSD activity was reduced, the conversion of tryptophan to niacin tended to be lower in the PAN-treated rats. The reduction of urinary excretion of niacin in nephrotic rats may be due to the reduction of blood tryptophan concentration. The role of the kidney ACMSD may be insignificant concerning tryptophan–niacin conversion under this experimental condition.

Characterization of tryptophan–niacin metabolism in rats fed with an excessive tryptophan diet

Abstract We investigated tryptophan–niacin metabolism in rats when fed with an excessive tryptophan diet. Male rat of the Wistar strain (3 weeks old) were divided into the four groups of five rats each, and one of the group was fed with a 20% casein diet added with 0, 0.5, 1, 2, and 5% tryptophan for 30 days. The last day urine samples (24-h urine) were collected for analyses for the metabolites of tryptophan such as kynurenic acid (KA), xanthurenic acid (XA), 3-hydroxyanthranilic acid (3-HA), quinolinic acid (QA), nicotinamide (Nam), N 1 -methylnicotinamide (MNA), N 1 -methyl-4-pyridone-3-carboxamide(4-Py), and N 1 -methyl-2-pyridone-5-carboxamide (2-Py). The urinary excretion of KA, XA, and 3-HA were increased according to the intake of tryptophan. However, the excretion of QA was almost the same in the groups between the groups of 2 and 5% tryptophan diets. The sum metabolites of Nam + MNA + 2-Py + 4-Py were almost the same in the 1–5% tryptophan diets. The value of (2-Py + 4-Py)/MNA decreased sharply in the 0.5 and 1% Trp diets. Therefore the adverse effects of dietary Trp were observed from the diet containing 0.5% Trp, which was calculated as 0.45 g/kg of rat body weight.

Tryptophan-Niacin Metabolism in Rat with Puromycin Aminonucleoside-Induced Nephrosis

We investigated the change of tryptophan-niacin metabolism in rats with puromycin aminonucleoside PAN-induced nephrosis, the mechanisms responsible for their change of urinary excretion of nicotinamide and its metabolites, and the role of the kidney in tryptophan-niacin conversion. PAN-treated rats were intraperitoneally injected once with a 1.0% (w/v) solution of PAN at a dose of 100 mg/kg body weight. The collection of 24-hour urine was conducted 8 days after PAN injection. Daily urinary excretion of nicotinamide and its metabolites, liver and blood NAD, and key enzyme activities of tryptophan-niacin metabolism were determined. In PAN-treated rats, the sum of urinary excretion of nicotinamide and its metabolites was significantly lower compared with controls. The kidney alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) activity in the PAN-treated group was significantly decreased by 50%, compared with the control group. Although kidney ACMSD activity was reduced, the conversion of tryptophan to niacin tended to be lower in the PAN-treated rats. A decrease in urinary excretion of niacin and the conversion of tryptophan to niacin in nephrotic rats may contribute to a low level of blood tryptophan. The role of kidney ACMSD activity may be minimal concerning tryptophan-niacin conversion under this experimental condition.

Estimated Conversion Ratio of Tryptophan-Niacin in Nursing Rats Using the Enzyme Activities Involved in the Tryptophan-Niacin Metabolism

Estimated Conversion Ratio of Tryptophan-Niacin in Nursing Rats Using the Enzyme Activities Involved in the Tryptophan-Niacin Metabolism

Changes in the Urinary Excretion of the Metabolites of the Tryptophan-Niacin Pathway during Pregnancy in Japanese Women and Rats

NAD is biosynthesized from tryptophan. Therefore, experimental studies including tryptophan metabolism studies could provide insight into niacin nutrition in pregnancy. Our aim was to determine the change in niacin metabolism during pregnancy by a systemic investigation of how pregnancy alters the tryptophan-niacin metabolism in Japanese women and rats. For the human study, spot urine samples were collected from a total of 434 pregnant Japanese women who were at 5-40 wk of gestation, 50 women at 4-6 wk postpartum, and 10 nonpregnant women as the controls. For the animal study, pregnant rats were fed with a niacin-free diet, and daily urine samples were collected from day 6 of gestation to day 6 postpartum. The intermediates and metabolites of the tryptophan-niacin pathway in the urine samples were measured. The urinary excretions of niacin metabolites in humans and rats increased from mid pregnancy in a time-dependent manner, reached a peak of 2-3-fold during late pregnancy, and declined to control levels after childbirth.

The effects of phthalate esters on the tryptophan-niacin metabolism.

Several phthalate esters (PhE), used as a plasticizer for numerous plastic devices, induce liver tumors and testicular atrophy, although the precise nature and mechanism for the action of PhE on these organs have remained unclear. We have previously reported that the administration of a large amount of di(n-butyl)phthalate (DBP) increased the conversion ratio of tryptophan to niacin in rats. To clarify the mechanism for the toxicity of PhE, we investigated the effects of di(2-ethylhexyl) phthalate (DEHP), one of the most frequently used additives, on the conversion ratio and how altering the conversion ratio of tryptophan to niacin depended on the concentration of DEHP. Rats were fed with a diet containing 0%, 0.01%, 0.05%, 0.1%, 0.5%, 1.0%, or 3.0% DEHP for 21 days. To assess the conversion ratio of tryptophan to niacin, urine samples were collected at the last day of the experiment and measured for metabolites on the tryptophan-niacin pathway. The conversion ratio increased with increasing dietary concentration of DEHP above 0.05%; the conversion ratio was about 2% in the control group, whereas it was 28% in the 3.0% DEHP group. It is suggested that the inhibition of alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) by DEHP or its metabolites caused this increase in the conversion ratio. We conclude that PhE such as DEHP and DBP disturbed the Tryptophan-niacin metabolism.

Purification and molecular cloning of rat 2-amino-3-carboxymuconate-6-semialdehyde decarboxylase.

2-Amino-3-carboxymuconate-6-semialdehyde decarboxylase (ACMSD; EC 4.1.1.45) is one of the important enzymes regulating tryptophan-niacin metabolism. In the present study, we purified the enzyme from rat liver and kidney, and cloned the cDNA encoding rat ACMSD. The molecular masses of rat ACMSDs purified from the liver and kidney were both estimated to be 39 kDa by SDS/PAGE. Analysis of N-terminal amino acid sequences showed that these two ACMSDs share the same sequence. An expressed sequence tag (EST) of the mouse cited from the DNA database was found to be identical with this N-terminal sequence. Reverse transcription-PCR (RT-PCR) was performed using synthetic oligonucleotide primers having the partial sequences of the EST, and then cDNAs encoding rat ACMSDs were isolated by using subsequent 3'-rapid amplification of cDNA ends and RT-PCR methods. ACMSD cDNAs isolated from liver and kidney were shown to be identical, consisting of a 1008 bp open reading frame (ORF) encoding 336 amino acid residues with a molecular mass of 38091 Da. The rat ACMSD ORF was inserted into a mammalian expression vector, before transfection into human hepatoma HepG2 cells. The transfected cells expressed ACMSD activity, whereas the enzyme activity was not detected in uninfected parental HepG2 cells. The distribution of ACMSD mRNA expression in various tissues was investigated in the rat by RT-PCR. ACMSD was expressed in the liver and kidney, but not in the other principal organs examined.

Purification and molecular cloning of rat 2-amino-3-carboxymuconate-6-semialdehyde decarboxylase

2-Amino-3-carboxymuconate-6-semialdehyde decarboxylase (ACMSD; EC 4.1.1.45) is one of the important enzymes regulating tryptophan—niacin metabolism. In the present study, we purified the enzyme from rat liver and kidney, and cloned the cDNA encoding rat ACMSD. The molecular masses of rat ACMSDs purified from the liver and kidney were both estimated to be 39kDa by SDS/PAGE. Analysis of N-terminal amino acid sequences showed that these two ACMSDs share the same sequence. An expressed sequence tag (EST) of the mouse cited from the DNA database was found to be identical with this N-terminal sequence. Reverse transcription-PCR (RT-PCR) was performed using synthetic oligonucleotide primers having the partial sequences of the EST, and then cDNAs encoding rat ACMSDs were isolated by using subsequent 3′-rapid amplification of cDNA ends and RT-PCR methods. ACMSD cDNAs isolated from liver and kidney were shown to be identical, consisting of a 1008bp open reading frame (ORF) encoding 336 amino acid residues with a molecular mass of 38091Da. The rat ACMSD ORF was inserted into a mammalian expression vector, before transfection into human hepatoma HepG2 cells. The transfected cells expressed ACMSD activity, whereas the enzyme activity was not detected in uninfected parental HepG2 cells. The distribution of ACMSD mRNA expression in various tissues was investigated in the rat by RT-PCR. ACMSD was expressed in the liver and kidney, but not in the other principal organs examined.

Elucidation of the toxic mechanism of the plasticizers, phthalic acid esters, putative endocrine disrupters: effects of dietary di(2-ethylhexyl)phthalate on the metabolism of tryptophan to niacin in rats.

We have previously reported that the administration of a large amount of di(n-butyl)phthalate (DBP) increased the conversion ratio of tryptophan to niacin in rats. In the present experiment, the effect of di(2-ethylhexyl)phthalate (DEHP) on the conversion ratio and how altering the conversion ratio of tryptophan to niacin depended on the concentration of DEHP were investigated to elucidate the toxic mechanism of phthalic acid esters (PhE). Rats were fed with a diet containing 0%, 0.01%, 0.05%, 0.1%, 0.5%, 1.0%, or 3.0% DEHP for 21 days. To assess the conversion ratio of tryptophan to niacin, urine samples were collected at the last day of the experiment and measured for metabolites on the tryptophan-niacin pathway. The conversion ratio increased with increasing dietary concentration of DEHP above 0.05%; the conversion ratio was about 2% in the control group, whereas it was 28% in the 3.0% DEHP group. It is suggested that the inhibition of alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) by DEHP or its metabolites caused this increase in the conversion ratio. We conclude that PhE such as DEHP and DBP disturbed the tryptophan-niacin metabolism.

Influence of adenine-induced renal failure on tryptophan-niacin metabolism in rats.

To discover the role of the kidney in tryptophan degradation, especially tryptophan to niacin, rat kidneys were injured by feeding a diet containing a large amount of adenine. The kidney contains very high activity of aminocarboxymuconate-semialdehyde decarboxylase (ACMSD), which leads tryptophan into the glutaric acid pathway and then the TCA cycle, but not to the niacin pathway. On the other hand, kidneys contain significant activity of quinolinate phosphoribosyltransferase (QPRT), which leads tryptophan into the niacin pathway. The ACMSD activity in kidneys were significantly lower in the adenine group than in the control group, while the QPRT activity was almost the same, however, the formations of niacin and its compounds such as N1-methylnicotinamide and its pyridones did not increase, and therefore, the conversion ratio of tryptophan to niacin was lower in the adenine group than in the control group. The contents of NAD and NADP in liver, kidney, and blood were also lower in the adenine group. The decreased levels of niacin and the related compounds were consistent with the changes in the enzyme activities involved in the tryptophan-niacin metabolism in liver. It was concluded from these results that the conversion of tryptophan to niacin is due to only the liver enzymes and that the role of the kidney would be extremely low.

Tryptophan-niacin metabolism in liver cirrhosis rat caused by carbon tetrachloride.

We investigated the change of tryptophan-niacin metabolism induced by carbon tetrachloride (CCl4) in rats with liver cirrhosis. The rats were injected with CCl4 (0.5 or 1 mL of 50% olive oil solution/kg body weight) twice a week for 1 or 2 mo and given phenobarbital water simultaneously. The urinary excretions of nicotinamide (Nam) and its metabolites were assayed. As the result, the urinary excretion of Nam, N1-methyl-4-pyridone-3-carboxamide (4-Py), Nam + N1-methylnicotinamide (MNA) + N1-methyl-2-pyridone-5-carboxamide (2-Py) + 4-Py was lower in the CCl4-treated groups than in the non-treated group (control) regardless of the experimental period (1 mo and 2 mo) or dosing amount of CCl4 (0.5 and 1 mL). Moreover, we investigated which pathway of tryptophan-niacin metabolism was affected in CCl4-treated rat. As the result, the possibility that the MNA-->4-Py reaction is inhibited by CCl4 treatment was suggested in this experiment.

Change of tryptophan-niacin metabolism in D-galactosamine-induced liver injury in rat.

The change of tryptophan-niacin metabolism in D-galactosamine (D-galN) injected rats was investigated. Rats fed with niacin-free diets containing 40% casein for 11 days were injected with D-galN (0.8 g/kg body weight). The urinary excretions of nicotinamide and its metabolites, and the activity of liver alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) (EC 4.1.1.45), a key enzyme of tryptophan-niacin metabolism, were assayed. As the result, the urinary excretions of N1-methylnicotinamide (MNA), N1-methyl-2-pyridone-5-carboxamide (2-Py), N1-methyl-4-pyridone-3-carboxamide (4-Py) and their sum (nicotinamide+MNA+2-Py+4-Py) were higher in the D-galN-injected group than in the control group. Hepatic ACMSD activity in the D-galN-injected group was lower than that of the control group. These results suggest that the increase in urinary excretion of nicotinamide and its metabolites after the injection of D-galN is considered to be attributable to a decrease in liver ACMSD activity.

Effect of dietary linoleic acid on the tryptophanniacin metabolism in streptozotocin diabetic rats

To make clear the mechanism of change of tryptophan-niacin metabolism in diabetic rats, we investigated the effect of dietary linoleic acid on the tryptophan-niacin metabolites and the activity of liver, alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD), a key enzyme of tryptophan-niacin metabolism, in streptozotocin diabetic rats. Moreover, we investigated the involvement of linoleic acid in the induction of hepatic ACMSD activity by streptozotocin diabetes. In diabetic rats, the sum of urinary excretion of nicotinamide, N1-methylnicotinamide (MNA), N1-methyl-2-pyridone-5-carboxamide (2-Py) and N1-methyl-4-pyridone-3-carboxamide (4-Py) was higher in the fat free diet group than in the linoleic acid group, that was accompanied by the increase of tryptophan intake and reduction of body weight in the fat free diet group. In diabetic rats, hepatic ACMSD activity was higher in the fat free diet group than in the linoleic acid group. The results indicated that the induction of hepatic ACMSD activity by diabetes was not due to removal of the suppressive effect of the linoleic acid on the enzyme. In the diabetic+insulin group, hepatic ACMSD activity was significantly lower than in the diabetic group.

Suppression of Rat Hepatic α-Amino-β-carboxymuconate-ε-semialdehyde Decarboxylase (ACMSD) Activity by Linoleic Acid in Relation to Its Induction by Glucocorticoids and Dietary Protein

Hepatic α-amino-β-carboxymuconate-ɛ-semialdehyde decarboxylase [EC 4.1.1.45] (ACMSD), a key enzyme for tryptophan-niacin metabolism, is known to be suppressed by dietary polyunsaturated fatty acids. This enzyme is induced by glucocorticoid or dietary protein. We investigated the effect of linoleic acids on the induction of ACMSD activity by glucocorticoid at 40% or 10% casein levels and the effect of dietary linoleic acid on ACMSD activity in puromycin-treated rats to investigate the action of dietary linoleic acid. Dietary linoleic acid suppressed the hepatic ACMSD activity in the groups treated with and without glucocorticoid. However, in the case of the 10% casein diet, the ACMSD elevation ratio caused by glucocorticoid in the linoleic acid diet group was as large as that in the fat-free diet group. Puromycin suppressed ACMSD activity, but no additional suppression of hepatic ACMSD was observed by dietary linoleic acid.

Effects of Various Dietary Fatty Acids onα-Amino-β-carboxymuconate-ε-semialdehyde Decarboxylase Activity in Rat Liver

In this study, we investigated the effects of short-chain, middle-chain, and long-chain fatty acids on the activity of rat liver α-amino-β-carboxymuconate-e-semialdehyde decarboxylase [EC 4.1.1.45] (ACMSD), a key enzyme of tryptophan-niacin metabolism. Moreover, we examined the cholesterol metabolism and lipid peroxidation in relation to ACMSD activity in rats. When diets containing 2%, 5%, and 10% levels of fatty acids were given to rats for a week, saturated fatty acids and elaidic acid (trans form) did not suppress the ACMSD activity in liver. But polyunsaturated fatty acids such as linoleic acid, linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) strongly suppressed the liver ACMSD activity. Five % sorbic acid and oleic acid tended to suppress the liver ACMSD activity weakly. On the other hand, this report indicated that there is no correlation between liver ACMSD activity and cholesterol levels of serum or liver, but there is a weak negative correlation between liver malondia...

Effects of ethanol feeding and growth on the tryptophan-niacin metabolism in rats.

The effects of ethanol feeding on the tryptophan-niacin metabolism were investigated in rats. Male rats of the Wistar strain (3 weeks old) were fed with a 20% casein diet and 15% ethanol ad libitum for 56 days. Urine samples were collected every week during the experimental period. Urinary excretion of N1-methylnicotinamide (MNA) was always higher in the ethanol-fed group than in the control group, but urinary excretion of its oxidized metabolites N1-methyl-2-pyridone-5-carboxamide (2-Py) and N1-methyl-4-pyridone-3-carboxamide (4-Py) was always lower. Therefore, the ratio of (2-Py + 4-Py)/MNA excretion was lower in the ethanol-fed group than in the control group. The rats were killed on day 57 and liver enzyme activities involved in the tryptophan-niacin metabolism were also measured. Tryptophan oxygenase, kynureninase, nicotinamide mononucleotide adenylyltransferase, NAD+ synthetase, and nicotinamide methyltransferase activities were similar in both groups, but, 2-Py-forming MNA oxidase and 4-Py-forming ...

Lack of Influence of Aflatoxins in the Development of Pellagra

Some of the most important plant foods consumed by humans, such as cereals, millets and oil seeds are susceptible to mycotoxin contamination. The highest levels and incidence of contamination are found in tropical and sub-tropical regions, although mycotoxins have also been frequently encountered in temperate zones. Several agricultural commodities have been screened in India for possible occurrence of aflatoxins and to some extent other mycotoxins. Sorghum (Sorghum vulgare) is one of the important food crops in the semiarid regions of India. Sorghum is susceptible to fungal attack and mycotoxin elaboration in conducive climatic conditions. In the recent past, it has been suggested that consumption of mycotoxin contaminated sorghum may be involved in the development of the disease pellagra in sorghum eating population. The present study relates to the metabolic effect of aflatoxins on tryptophan-niacin pathway in rats, which is found to be altered in pellagrins. The experimental evidence suggests that, the effect of aflatoxins on tryptophan-niacin metabolism may be more of a non-specific effect rather than a direct effect as none of the changes seen in nicotinamide nucleotide synthesis are similar to changes seen in pellagrins. Aflatoxins may not have any relationship with the disease pellagra.

Effects of dietary protein levels on the enzyme activities involved in tryptophan-niacin metabolism in rats.

Effects of dietary protein levels on the enzyme activities involved in tryptophan-niacin metabolism in rats.

Effect of dietary paraquat on the enzyme activities involved in tryptophan-niacin metabolism in rats.

Effect of dietary paraquat on the enzyme activities involved in tryptophan-niacin metabolism in rats.