Correlation between niacin equivalent intake and urinary excretion of its metabolites, N'-methylnicotinamide, N'-methyl-2-pyridone-5-carboxamide, and N'-methyl-4-pyridone-3-carboxamide, in humans consuming a self-selected food

N'-methyl-4-pyridone-3-carboxamide (4-py) is the major metabolite of nicotinamide and nicotinic acid in rats. However, because it is complicated to determine 4-py in humans, there is only one report on its excretion. Recently we developed a method for the microdetermination of 4-py by high-performance liquid chromatography. Urinary excretion of 4-py in Japanese students from Teikoku Women's University who consumed self-selected foods was 7.12 +/- 3.25 mumol/d, which is about one-fourth of N'-methylnicotinamide (MNA) and about one-ninth of N'-methyl-2-pyridone-5-carboxamide (2-py) excretion. The correlation coefficient between daily niacin equivalent (NE) intake and daily 4-py excretion was 0.529, which was about the same as the correlation coefficient between daily NE intake and daily 2-py excretion and which was two times higher than the correlation coefficient between daily NE intake and daily MNA excretion.     

The metabolism of high intakes of tryptophan, nicotinamide and nicotinic acid in the rat

1. The metabolic fate of high dietary intakes of nicotinamide, nicotinic acid and tryptophan, and of acute doses of nicotinamide and nicotinic acid, has been studied in the rat. A new high-pressure liquid chromatography method for measurement of the principal urinary metabolites of niacin is described. 2. Administration to rats of a single oral dose of nicotinamide or nicotinic acid (up to 100 mg/kg body-weight), or maintenance for 3 weeks on diets providing 150 mg nicotinamide or nicotinic acid/kg diet, resulted in only a small increase in the liver content of nicotinamide nucleotide coenzymes (NAD and NADP). The quantitative metabolism of nicotinamide and nicotinic acid differed, suggesting that intestinal bacterial deamidation is not the major fate of nicotinamide. 3. A high dietary intake of tryptophan (5.9 g/kg diet) led to a considerable increase in liver NAD(P) and also in urinary excretion of niacin metabolites. The results suggest that, as indicated by enzyme kinetic studies (Bender et al. 1982), the utilization of nicotinamide and nicotinic acid for nucleotide synthesis is limited, while there is little or no limitation of NAD(P) synthesis from the tryptophan metabolite quinolinic acid.     

Exposure assessment of phthalate esters in Japanese pregnant women by using urinary metabolite analysis

Objectives  Our objectives were (1) to evaluate whether single spot urine is suitable media for longer-term phthalate esters exposure assessment, and (2) to estimate intake level of phthalate esters of Japanese pregnant women using urinary metabolites as an indicator of prenatal exposure level in their offspring. Methods  We analyzed nine metabolites (MMP, MEP, MnBP, MBzP, MEHP, MEOHP, MEHHP, MINP, MnOP) of seven phthalate esters in spot urine samples from 50 pregnant women by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Using four urine samples collected from each of 12 subjects from 50 pregnant women within 5–12 weeks, we compared intra- and interindividual variation in urinary metabolites by calculation of intraclass correlation coefficient (ICC). We estimated daily intakes of 50 pregnant women from their urinary metabolite concentrations. Results  ICCs for seven phthalate metabolite concentrations in single spot urine samples were: MMP (0.57), MEP (0.47), MnBP (0.69), MBzP (0.28), MEHP (0.51), MEHHP (0.43), and MEOHP (0.41) in 12 pregnant women. Phthalate ester metabolites had high detection rates in 50 subjects. The mean daily intake ranged from 0.01 to 2 μg/kg per day. The daily intake levels in all subjects were lower than corresponding tolerable daily intake (TDI) set by the European Food Safety Authority (EFSA), though maximum value for DnBP of 6.91 μg/kg per day accounted for 70% of TDI value. Conclusions  Higher ICCs indicated that phthalate metabolite levels in single spot urine could reflect longer-term exposure to the corresponding diesters of subjects. Although the current exposure level was less than TDIs, further studies and exposure monitoring are needed to reveal the toxicity of phthalate esters to sensitive subpopulation.     

Methylated niacin derivatives in plasma and urine after an oral dose of nicotinamide given to subjects fed a low-methionine diet

Five healthy males, age 25-32 y, were fed in sequence a diet of ordinary foods (10 d, PI), a low-methionine diet (285 mg/d, 14 d, PII), and an adequate-methionine diet (725 mg/d, 7 d, PIII). Diets contained 9 g nitrogen (N) per day with soy protein and synthetic L-amino acids as the N sources in PII and PIII. In PII, subjects were in negative N balance whereas, in PIII, four subjects were in positive N balance. On the last day of each period, fasting subjects ingested a dose of nicotinamide (NAM, 102 mumol/kg body wt). Plasma and urine samples were analyzed for methylated derivatives of NAM by high-performance liquid chromatography (HPLC) methods. Mean values of methylated metabolites in urine from the three diet periods (for four subjects in N balance during PIII) were not different (59.8, 56.7, and 59.9 mumol/(kg body wt X 24 h) for PI, PII, and PIII, respectively). Plasma values of these metabolites also were similar. Results suggest that during a 2-wk period of negative N balance due to a low-methionine intake hepatic methylation processes are not impaired. These processes appear to have a higher metabolic priority than maintenance of the net protein synthesis rate.     

Conversion ratio of tryptophan to niacin in Japanese women fed a purified diet conforming to the Japanese Dietary Reference Intakes

In order to establish the human requirements of niacin, it is first important to know how much tryptophan is converted to niacin in the human body. In a general, 60 mg of tryptophan is equivalent to 1 mg of niacin, whereas the conversion ratio of tryptophan to niacin is yet to be confirmed. The aim of this study was to know the conversion ratio of tryptophan to niacin in Japanese females fed a purified diet, which followed the Japanese Dietary Reference Intakes. Ten young Japanese females were housed in the same facility and given the same daily living activity schedule for 7 d. The composition of their purified diet was conformed to the Dietary Reference Intakes in Japan. The diet was niacin free. In order to investigate the conversion ratio, daily urinary outputs were collected. Tryptophan-niacin metabolites in the urine were measured and the conversion ratio of tryptophan to niacin calculated. The conversion ratio was calculated by comparing the dietary intake of tryptophan and the sum of the niacin catabolites such as N1-methylnicotinamide, N1-methyl-2-pyridone-5-carboxamide, and N1-methyl-4-pyridone-3-carboxamide, which were derived only from the dietary intake of tryptophan. The ratio was calculated as 1.5 +/- 0.1 (mean +/-SE for 10 women; in molar basis) on the last day of the experiment. It was calculated that if the excretory percentage of niacin metabolites in the urine were 60%, of the tryptophan ingested, the conversion factor would be a value of 67, meaning that is 67 mg of tryptophan is equal to 1 mg of niacin.     

Excretion of tryptophan-niacin metabolites by young men: effects of tryptophan, leucine, and vitamin B6 intakes

Three human metabolic studies, each 35 days in length, were performed to investigate the relationship between tryptophan intake and the proportion of dietary tryptophan converted to niacin and the effect of supplements of L-leucine and vitamin B6 on this conversion. Nine college men consumed a basal diet that provided 8 mg of niacin, 1 mg of vitamin B6, and either 245, 548, or 845 mg of tryptophan from proteins per day. During each 35-day study, for one 15-day period basal diet alone was consumed, for another 15-day period basal diet plus 10 g of L-leucine per day was consumed, and for the last 5-day period, 20 mg of vitamin B6 per day was added to the diets of both groups. N1-methylnicotinamide, N1-methyl-2-pyridone-5-carboxamide, and quinolinic acid were measured in 24-hr urine samples. There were no significant or consistent effects of L-leucine or vitamin B6 supplements on the excretin of any of the metabolites measured. The proportion of tryptophan converted to niacin tended to increase as tryptophan consumption increased; however, this change was small and was probably not significant over the range of tryptophan intakes studied. The average conversion ration of tryptophan to niacin was approximately 72:1 in these subjects.     

Effects of niacin source on epinephrine stimulation of plasma nonesterified fatty acid and glucose concentrations, on diet digestibility and on rumen protozoal numbers in lactating dairy cows

Effects of niacin (nicotinic acid or nicotinamide) supplementation of dairy cow diets on apparent total tract nutrient digestibility, milk yield and milk composition were determined using six mid-lactation Holstein cows in a replicated 3 x 3 Latin square design arranged to test for residual treatment effects. Treatments were control, 12 g/d of nicotinic acid or 12 g/d of nicotinamide. Periods were 14 d long; d 1 to 4 served as an adaptation period before treatment administration commenced (d 5 to 14). Effects of supplemental niacin on plasma nonesterified fatty acid (NEFA) concentrations and plasma glucose concentrations were tested following saline injection on d 10. Blood was then sampled for 5.5 h at 15-min intervals. On d 13, cows were treated similarly except that epinephrine replaced saline. The area below d-10 curves was subtracted from the area below d-13 curves to serve as an indicator of niacin's effect on plasma NEFA and glucose concentration responses to epinephrine injection. Niacin treatments did not change the area differences for plasma glucose compared to the control treatment; however, there was a trend for niacin to reduce the area difference compared to the control treatment for plasma NEFA. Niacin treatments did not alter dry matter intake, nutrient digestibility, milk yield or composition. Niacin supplementation increased the number of entodinia protozoa in rumen fluid.     

Effects of stress on the urinary excretory pattern of niacin catabolites,the most reliable index of niacin status,in humans

Urinary output of water-soluble vitamins has been used as an indices for vitamin nutrition. It has been pointed out that the coefficient variance of these values is high, especially for niacin catabolites. Thus, we investigated what kinds of stress affect the catabolism using female subjects. The effects of cold exposure (as a typical physical stress), calculation exercise (a typical mental stress) and dark exposure (a typical emotional stress) on the metabolism of niacin were investigated. Of the stresses, cold exposure significantly increased urinary excretory output of the niacin metabolites. The biosynthesis of nicotinamide from Trp seemed to be increased by cold exposure.     

Fate of excess nicotinamide and nicotinic acid differs in rats

Rats administered excess nicotinamide and nicotinic acid were studied to determine the metabolic fate of pharmacological levels of these compounds. When a large amount of nicotinamide (500 mg/kg body wt) was intraperitoneally injected into rats, 32% of the dose was excreted as nicotinamide, 11% as N1-methylnicotinamide (MNA), 10% as nicotinuric acid, 5% as nicotinic acid, 3% as N1-methyl-4-pyridone-3-carboxamide (4-pyr) and 2% as N1-methyl-2-pyridone-5-carboxamide (2-pyr) during d 1 after the injection. Urinary excretion of these compounds gradually decreased with time and returned to normal by d 3. Urinary excretion of nicotinic acid and nicotinuric acid was observed only on d 1. When a large amount of nicotinic acid (500 mg/kg body wt) was intraperitoneally injected into rats, 55% of the dose was excreted as nicotinic acid and 15% as nicotinuric acid during d 1, and no excretion of these compounds was observed thereafter. The increase in excretion of nicotinamide, MNA, 2-pyr and 4-pyr was slight even on d 1. Excretion of nicotinic acid, nicotinuric acid, nicotinamide, MNA, 2-pyr and 4-pyr returned to normal levels on d 2. From these results, the different fates of excess nicotinamide and nicotinic acid are discussed.     

Urinary water-soluble vitamins and their metabolite contents as nutritional markers for evaluating vitamin intakes in young Japanese women

Little information is available to estimate water-soluble vitamin intakes from urinary vitamins and their metabolite contents as possible nutritional markers. Determination of the relationships between the oral dose and urinary excretion of water-soluble vitamins in human subjects contributes to finding valid nutrition markers of water-soluble vitamin intakes. Six female Japanese college students were given a standard Japanese diet in the first week, the same diet with a synthesized water-soluble vitamin mixture as a diet with approximately onefold vitamin mixture based on Dietary Reference Intakes (DRIs) for Japanese in the second week, with a threefold vitamin mixture in the third week, and a sixfold mixture in the fourth week. Water-soluble vitamins and their metabolites were measured in the 24-h urine collected each week. All urinary vitamins and their metabolite levels except vitamin B(12) increased linearly in a dose-dependent manner, and highly correlated with vitamin intake (r=0.959 for vitamin B(1), r=0.927 for vitamin B(2), r=0.965 for vitamin B(6), r=0.957 for niacin, r=0.934 for pantothenic acid, r=0.907 for folic acid, r=0.962 for biotin, and r=0.952 for vitamin C). These results suggest that measuring urinary water-soluble vitamins and their metabolite levels can be used as good nutritional markers for assessing vitamin intakes.     

Association between dietary folate-rich food intake and folate status of elderly Taiwanese

To investigate the relationship between folate status and dietary folate intake in the Taiwanese elderly, we analyzed plasma folate levels and dietary folate intake in 725 males and 705 females aged 65-90 years, sampled from the Elderly Nutrition and Health Survey in Taiwan (1999-2000) (Elderly NAHSIT). Results showed that the mean plasma folate levels were 22.9+/-1.4 nmol/L (10.1+/-0.6 ng/ml) for males and 29.5+/-1.6 nmol/L (13.0+/-0.7 ng/ml) for females. The average plasma folate concentrations of males from all age groups were significantly lower than those of females (P<0.0001). None of the study subjects had a plasma folate below 7 nmol/L (3 ng/ml). However, 18.6% of males and 12.1% of females had marginal folate deficiency, with plasma folate between 7-14 nmol/L (3-6 ng/ml). This suggests that elderly males have a poorer folate status than elderly females in the Taiwanese population. The percentage of marginal folate deficiency tended to increase with age among females (P trend=0.0137). The average estimated folate intakes were 379+/-18 microg/d in males and 351+/-27 microg/d in females. However, 45.5% of males and 48.8% of females had a dietary folate intake below 2/3 of the RDA of 400 microg/d. Our results indicated that dietary folate intake is positively correlated with plasma folate levels (r=0.10, P<0.05). In addition, dietary folate intake increased with increased intakes of vegetables, mushrooms and fruit. A lower intake of fruit appeared to be responsible for the higher prevalence of marginal folate deficiency among females over the age of 80 years.     

Interaction of niacin and zinc metabolism in patients with alcoholic pellagra

The effect of zinc supplementation on the metabolism of tryptophan conversion to niacin was studied in 14 alcoholic patients with pellagra and in 7 male control subjects aged 21-45 y. The pellagrins received chemically defined diets based on crystalline amino acids through an enteral tube for 7 d. Patients were divided into two groups (A and B), both receiving a diet from which tryptophan, Zn, and niacin were excluded. Patients in group B, however, received 220 mg Zn sulfate orally. Upon admission the pellagra patients had low plasma Zn levels and low urinary excretion values of N'methylnicotinamide (N'MN) and N'methyl-2-pyridone-5-carboxamide (2-PYR) in relation to the control subjects (p less than 0.01). During the experimental period there was an increase in plasma Zn levels (p less than 0.005) and in urinary N'MN (p less than 0.05) and 2-PYR (p less than 0.05) excretion in the patients receiving Zn supplementation (group B). These results suggest that Zn interacts with niacin metabolism in alcoholic patients with pellagra through a probable mediation by vitamin B-6.     

Low and deficient niacin status and pellagra are endemic in postwar Angola

BACKGROUND: Outbreaks of pellagra were documented during the civil war in Angola, but no contemporary data on the incidence of pellagra or the prevalence of niacin deficiency were available. OBJECTIVE: The objective was to investigate the incidence of pellagra and the prevalence of niacin deficiency in postwar Angola and their relation with dietary intake, poverty, and anthropometric status. DESIGN: Admissions data from 1999 to 2004 from the pellagra treatment clinic in Kuito, Angola, were analyzed. New patients admitted over 1 wk were examined, and urine and blood samples were collected. A multistage cluster population survey collected data on anthropometric measures, household dietary intakes, socioeconomic status, and clinical signs of pellagra for women and children. Urinary excretion of 1-methylnicotinamide, 1-methyl-2-pyridone-5-carboxymide, and creatinine was measured and hemoglobin concentrations were measured with a portable photometer. RESULTS: The incidence of clinical pellagra has not decreased since the end of the civil war in 2002. Low excretion of niacin metabolites was confirmed in 10 of 11 new clinic patients. Survey data were collected for 723 women aged 15-49 y and for 690 children aged 6-59 mo. Excretion of niacin metabolites was low in 29.4% of the women and 6.0% of the children, and the creatinine-adjusted concentrations were significantly lower in the women than in the children (P < 0.001, t test). In children, niacin status was positively correlated with the household consumption of peanuts (r = 0.374, P = 0.001) and eggs (r = 0.290, P = 0.012) but negatively correlated with socioeconomic status (r = -0.228, P = 0.037). CONCLUSIONS: The expected decrease in pellagra incidence after the end of the civil war has not occurred. The identification of niacin deficiency as a public health problem should refocus attention on this nutritional deficiency in Angola and other areas of Africa where maize is the staple.     

Effect of nicotinamide administration on the tryptophan-nicotinamide pathway in humans

The vitamin nicotinamide is synthesized in the liver from tryptophan, and distributed to non-hepatic tissues. Although it is generally accepted that 60 mg tryptophan is equivalent to 1 mg nicotinamide in humans, the conversion ratio of tryptophan to nicotinamide is changeable. To determine if de novo nicotinamide synthesis from tryptophan is influenced by nicotinamide intake itself, six young women consumed controlled diets containing 30.4 or 24.8 mg niacin-equivalent nicotinamide supplements with 0, 89, 310, or 562 micromol/day (0, 10.9, 37.8, or 68.6 mg/day, respectively), and urinary excretion of intermediates and metabolites of the tryptophan-nicotinamide pathway were measured. Urinary excretion of nicotinamide metabolites increased linearly in a dose-dependent manner. None of the intermediates, including anthranilic acid, kynurenic acid, xanthurenic acid, 3-hydroxyanthranilic acid, and quinolinic acid, changed at all, even when up to 562 micromol/day nicotinamide was given. That is, exogenous nicotinamide did not affect de novo nicotinamide synthesis. Therefore, when niacin equivalent is calculated, the intake of nicotinamide itself need not be considered as a factor that changes the tryptophan-nicotinamide conversion ratio.     

Interaction among niacin, vitamin B6 and zinc in rats receiving ethanol

The interaction of niacin, vitamin B6 and zinc was studied in Wistar rats. Seventy animals were submitted to a four-week depletion period during which they were fed a corn grits diet with no niacin, vitamin B6 or zinc added. These animals also received a 32% ethanol solution. Thirty additional rats were used as controls. After the period of depletion, the deficient animals were divided into five subgroups of 10 animals each. Each group received either the deficient diet, the deficient diet plus niacin, the deficient diet plus vitamin B6, the deficient diet plus zinc, or the control diet for the following two weeks. Five rats from each group were killed weekly after 24-hour urine collection. N'methylnicotinamide (N'MN), N'methyl-2-pyridone-5-carboxamide (2 PYR) and 4-pyridoxic acid (4 PYR) were measured in urine by HPLC. Niacin repletion increased the excretion of niacin metabolites, N'MN and 2 PYR (p less than 0.01), in relation to deficient animals. Niacin and vitamin B6 metabolites increased with vitamin B6 repletion (p less than 0.01). Repletion with zinc alone was followed by an increase in urinary excretion of N'MN (p less than 0.05), 2 PYR (p less than 0.01) and 4 PYR (p less than 0.01). When the deficient rats were fed the control diet containing the three nutrients, all three metabolites increased (p less than 0.01). The main conclusion is that zinc repletion per se caused activation of niacin metabolism, increasing the excretion of niacin metabolites. This emphasizes the role of zinc in the function of these vitamins.     

Effects of different levels of vitamin C intake on the vitamin C concentration in human milk and the vitamin C intakes of breast-fed infants

The influence of maternal intake of vitamin C on the vitamin C concentration in human milk and on the vitamin C intakes of breast-fed infants has not been demonstrated conclusively. This study examined these influences of diet and supplementation in 25 lactating women administered 90 mg of ascorbic acid for 1 day followed by 250, 500 or 1000 mg/day for 2 days or unsupplemented for 1 day followed by either 0 or 90 mg ascorbic acid supplement for 2 days. Vitamin C content in milk and urine was determined by the 2,4-dinitrophenylhydrazine method. Vitamin C intakes of infants were calculated from milk volume, as determined by the test-weighing method and from vitamin C levels in milk samples obtained at each feeding. Total maternal intakes of vitamin C, which exceeded 1000 mg/day or 10-fold the RDA for lactation (100 mg/day), did not significantly influence the vitamin C content in milk or the vitamin C intakes of infants. However, maternal vitamin C intake was positively correlated (r = 0.7) with maternal urinary excretion. These differences in milk and urine response to vitamin C intake suggest a regulatory mechanism for vitamin C levels in milk.     

Changes in vitamin and mineral intakes and serum concentrations among free-living men on cholesterol-lowering diets: the Dietary Alternatives Study

Nutritional adequacy of diets with 18-30% of calories from fat was investigated in men with elevated serum cholesterol (n = 396) at the end of diet classes and 1 and 2 y later. On 4-d food records, intakes of vitamin A, beta-carotene, folate, vitamin C, magnesium, vitamin B-6, iron, thiamin, and riboflavin increased from baseline whereas niacin, selenium, vitamin E, and zinc decreased. Median zinc intake, 80% of the recommended dietary allowance (RDA) at baseline, decreased to approximately 75% of the RDA, most markedly when intakes of meat, fish, and poultry were limited to 85 g/d. Nutrient densities generally increased. Of the serum nutrients measured, median beta-carotene and vitamin C increased, whereas vitamin B-6, iron, and zinc were unchanged. Below-normal values were fewer for vitamin C and magnesium. Diets similar to the National Cholesterol Education Program Step-Two Diet [less than 7% saturated fatty acids, less than 200 mg cholesterol/d] appeared to provide increased levels of most micronutrients both short and long term to men receiving comprehensive dietary counseling.     

Validation of a phytoestrogen food frequency questionnaire with urinary concentrations of isoflavones and lignan metabolites in premenopausal women

OBJECTIVE: The purpose of this study was to examine the association between dietary intake of phytoestrogens estimated by a food frequency questionnaire (FFQ) with urinary metabolites. METHODS: Participants were 26 premenopausal, Caucasian women aged 25 to 42 years. Dietary intake of isoflavones (genistein and daidzein) and lignans (secoisolariciresinol and matairesinol) were estimated by a 53-item interviewer-administered FFQ on two occasions, reflecting 'habitual' (previous 2 months) and 'recent' (previous 2 days) dietary intake. Isoflavone (genistein, daidzein) and lignan (enterolactone, enterodiol and secoisolariciresinol) concentrations were measured in 24-hour urine samples by gas chromatography-mass spectrometry. Correlations between FFQ (habitual and recent, separately) and urinary metabolite values were assessed using Spearman correlation coefficients. RESULTS: Mean habitual isoflavone and lignan intakes were 13.7 mg/day and 13.8 mg/day, respectively. Mean urinary concentrations of isoflavones and lignans were 17.4 micromol/day and 20.6 micromol/day, respectively. Recent and habitual isoflavone intakes were correlated with urinary excretion of metabolites (r = 0.64, p < 0.001 and r = 0.54, p = 0.004, respectively). Urinary excretion of lignans was also modestly correlated with recent and habitual lignan intakes (r = 0.46, p = 0.02 and r = 0.40, p = 0.05, respectively). CONCLUSIONS: Our results support the use of this FFQ as a measure of dietary isoflavone and lignan intake in epidemiological studies.     

Effects of dietary fat and protein on the activity of alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase and the urinary excretion of niacin metabolites in rats

The effects of dietary protein and soybean oil on the metabolism of L-tryptophan through the NAD pathway and the activity of alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) [EC4.1.1.45] in rat liver and kidney were investigated. The animals were fed on the following niacin-free diets for 11 days: group 1, a fat-free 20% casein diet (20% Cas); group 2, a fat-free 40% casein diet (40% Cas); group 3, a 40% casein diet containing 20% soybean oil (40% Cas + 20% F). After feeding on each diet for 7 days, the urine was collected during 48 h. On day 9, L-tryptophan was force-fed and the urine was collected during 48 h. Niacin metabolites such as N-methylnicotinamide (MNA), N-methyl-2-pyridone-5-carboxamide (2-Py) and N-methyl-4-pyridone-3-carboxamide (4-Py) in the urine samples were analyzed by chromatography. The activity of ACMSD in the liver and kidney was assayed immediately after the last urine collection. The results indicate that the urinary excretion of the niacin metabolites in the 40% Cas group was lower than that of the 20% Cas group in spite of the more intake of tryptophan in the former group. On the other hand, in the 40% Cas+ 20% F group, tryptophan intake was lower and the excretion of the metabolites was significantly higher than that in the 40% Cas group. The hepatic ACMSD activity in the 40% Cas group was 5.8 times that of the 20% Cas group and that in the 40% Cas + 20% F group was one tenth that of the 20% Cas group. These results indicate that the ratio of the excreted metabolites to the tryptophan intake was reduced by the high dietary protein level, but increased by the addition of high soybean oil. The data analysis shows that the amount of urinary total niacin metabolites ([TNM]: MNA + 2-Py + 4-Py) could be expressed in the following equation in the rats fed on each diet: [TNM] = 0.090 ([Trp] -22.5.delta w) [1/(1 + 2.4 [ACMSD])], where [ACMSD] is the hepatic ACMSD activity, [Trp] the tryptophan intake, and delta w the body weight gain.     

Quantitation of urinary niacin metabolites by reversed-phase liquid chromatography

The niacin metabolites N1-methyl-2-pyridone-5-carboxamide (2-PYR) and N1-methylnicotinamide (N-MN) have been quantified in human urine using isocratic reversed-phase high-performance liquid chromatography with ultraviolet detection after a simple anion-exchange clean-up procedure. The coefficients of variation (%) of the method for 2-PYR and N-MN were 6.3 and 6.8, respectively, and the limits of detection (mg/1 urine) were 0.05 for 2-PYR and 0.20 for N-MN. Results by this method compared favorably with those obtained by established techniques. It is a straight forward, rapid, and sensitive procedure for the assessment of niacin status.