High-performance liquid chromatographic determination of nicotinamide in rat tissue samples and blood after extraction with diethyl ether

Establishment of Model Mice to Evaluate Low Niacin Nutritional Status

Niacin is involved in many biological reactions relating energy metabolism, redox reactions, DNA repair and longevity, and low NAD levels with aging and feeding high fat diets develop and progress age-related diseases. Although recent findings suggest the requirement of niacin insufficient animal model to further study, appropriate animal models have not been established yet because niacin is biosynthesized from tryptophan via tryptophan-nicotinamide pathway. To establish model mice to evaluate niacin nutritional status, we used kynurenine 3-monooxygenase knock out (KMO-/-) mice which lack NAD biosynthesis pathway from tryptophan. To determine the niacin requirement and assess niacin nutritional markers, 4 wk old KMO-/- mice were fed 2-30 mg/kg nicotinic acid containing diets for 28 d. More than 4 mg/kg but not less than 3 mg/kg nicotinic acid containing diets induced maximum growth, and niacin nutritional markers in the blood, liver and urine increased with increase of dietary nicotinic acid. These results showed that several niacin nutritional markers reflect niacin nutritional status, niacin nutritional status can be controlled by dietary nicotinic acid, and niacin requirement for maximum growth is 4 mg/kg nicotinic acid diets in the KMO-/- mice. This animal model useful to investigate pathophysiology and mechanism of niacin deficiency, clarify the relationships between niacin nutritional status and age-related and lifestyle diseases, and evaluate factors affecting niacin nutritional status.

Blood concentrations and renal clearance of water-soluble vitamins in outpatients with ulcerative colitis

Few studies have investigated the association between dietary intake and blood concentrations of water-soluble vitamins in patients with ulcerative colitis (UC). In the present study, vitamin concentrations were measured in the blood and urinary excretion of 23 outpatients with UC and compared against a control group of 20 healthy participants. A weighed food record procedure was used to ensure controlled macronutrient and vitamin intakes of the UC cohort. Individuals in the control group were given a semi-purified diet for 8 days prior to assessment. Multiple linear regression analysis was used to identify important differences in vitamin concentrations, independent of sex, age and other confounding variables. The blood concentrations of vitamins B2, C, niacin and folate were markedly lower in the patients with UC than those in the control group, and the renal clearance of vitamins B1, B6, B12 and folate was notably higher in the UC cohort. It was concluded that vitamins B2, C, niacin and folate were at significantly lower concentrations in patients with UC following adjustment for coexisting factors. The lower levels of niacin may be partially due to impaired reabsorption. Chronic inflammation, common in patients with UC, with may contribute to the lower levels of other vitamins by rendering amino acid and carbohydrate metabolism into a hypermetabolic state. As the role of vitamins in metabolic activity is constant and pervasive, nutritional management including the application of water-soluble vitamins appears important for patients suffering from UC.

Oral Glucose Tolerance and Tryptophan Metabolism in Non-Obese and Non-Insulin-Dependent Diabetic Goto-Kakizaki Rats Fed High-Tryptophan Diets

We investigated oral glucose tolerance and tryptophan (Trp) metabolism in non-obese and non-insulin-dependent diabetic Goto-Kakizaki (GK) rats fed high-Trp diets. Five-week-old male Wistar and GK rats were fed a 20% casein diet (control diet) or the same diet supplemented with 1%, 2%, 3%, or 5% Trp for 58 d. Oral glucose tolerance tests were performed on Days 14 and 28 of the experimental period. Urine as well as livers and blood were collected on the last day of the experiment. The glucose concentration and the amount of Trp metabolites were measured. On Day 14 of the experiment, the incremental blood glucose concentrations integrated over a period of 2 h (ΔAUC_0-2h) of blood glucose in rats fed the 3% and 5% Trp diets had decreased by 13% and 18%, respectively, compared with that of the control-GK rats. However, no significant differences were found in the rats fed +1% or +2% Trp diets compared with control-GK rats. On Day 28, there were no significant differences found in the ΔAUC_0-2h of blood glucose levels in any group including the control-GK group. On the last day, the concentrations of plasma glucose, total cholesterol, and triglyceride did not show differences in any group. There were no specific phenomena observed in the metabolism of Trp in GK rats even when fed an excess of Trp, compared with that of Wistar rats. Oral Trp administration and its continuous use may not improve blood glucose levels in type 2 diabetic rats.

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.

Concentrations of Water-Soluble Vitamins in Blood and Urinary Excretion in Patients with Diabetes Mellitus

We examined the concentrations of water-soluble vitamins in blood and urinary excretion of 22 patients with type 2 diabetes mellitus (type 2DM) and 20 healthy control participants. Macronutrient and vitamin intakes of type 2DM subjects were measured using a weighed food record method. Control participants consumed a semipurified diet for eight days. Multiple linear regression models were used to determine whether significant differences existed in vitamin concentrations in blood independent of age, sex, and other confounding factors. Concentrations of vitamins B2, B6, C, niacin, and folate in blood were significantly lower in type 2DM subjects than in controls, independent of confounding factors. Renal clearances of vitamins B6, C, niacin, and folate were significantly higher in type 2DM subjects than in controls. In conclusion, concentrations of vitamins B2, B6, C, niacin, and folate in blood were significantly lower in type 2DM subjects than in controls, independent of confounding factors; based on the evidence of increased urinary clearance of these vitamins, the lower levels were likely due to impaired reabsorption processes.

The niacin required for optimum growth can be synthesized from L-tryptophan in growing mice lacking tryptophan-2,3-dioxygenase

In mammals, nicotinamide (Nam) is biosynthesized from l-tryptophan (l-Trp). The enzymes involved in the initial step of the l-Trp→Nam pathway are l-Trp-2,3-dioxygenase (TDO) and indoleamine-2,3-dioxygenase (IDO). We aimed to determine whether tdo-knockout (tdo(-/-)) mice fed a diet without preformed niacin can synthesize enough Nam to sustain optimum growth. Wild-type (WT) and tdo(-/-) mice were fed a chemically defined 20% casein diet with or without preformed niacin (30 mg nicotinic acid/kg) for 28 d. Body weight, food intake, and liver NAD concentrations did not differ among the groups. In the groups of mice fed the niacin-free diet, urinary concentrations of the upstream metabolites kynurenine (320% increase, P < 0.0001), kynurenic acid (270% increase, P < 0.0001), xanthurenic acid (770% increase, P < 0.0001), and 3-hydroxyanthranilic acid (3-HA; 450% increase, P < 0.0001) were higher in the tdo(-/-) mice than in the WT mice, while urinary concentrations of the downstream metabolite quinolinic acid (QA; 50% less, P = 0.0010) and the sum of Nam and its catabolites (10% less, P < 0.0001) were lower in the tdo(-/-) mice than in the WT mice. These findings show that the kynurenine formed in extrahepatic tissues by IDO and subsequent enzymes can be metabolized up to 3-HA, but not into QA. However, the tdo(-/-) mice sustained optimum growth even when fed the niacin-free diet for 1 mo, suggesting they can synthesize the minimum necessary amount of Nam from l-Trp, because the liver can import blood kynurenine formed in extrahepatic tissues and metabolize it into Nam via NAD and the resulting Nam is then distributed back into extrahepatic tissues.

Different variations of tissue B-group vitamin concentrations in short- and long-term starved rats

Prolonged starvation changes energy metabolism; therefore, the metabolic response to starvation is divided into three phases according to changes in glucose, lipid and protein utilisation. B-group vitamins are involved in energy metabolism via metabolism of carbohydrates, fatty acids and amino acids. To determine how changes in energy metabolism alter B-group vitamin concentrations during starvation, we measured the concentration of eight kinds of B-group vitamins daily in rat blood, urine and in nine tissues including cerebrum, heart, lung, stomach, kidney, liver, spleen, testis and skeletal muscle during 8 d of starvation. Vitamin B1, vitamin B6, pantothenic acid, folate and biotin concentrations in the blood reduced after 6 or 8 d of starvation, and other vitamins did not change. Urinary excretion was decreased during starvation for all B-group vitamins except pantothenic acid and biotin. Less variation in B-group vitamin concentrations was found in the cerebrum and spleen. Concentrations of vitamin B1, vitamin B6, nicotinamide and pantothenic acid increased in the liver. The skeletal muscle and stomach showed reduced concentrations of five vitamins including vitamin B1, vitamin B2, vitamin B6, pantothenic acid and folate. Concentrations of two or three vitamins decreased in the kidney, testis and heart, and these changes showed different patterns in each tissue and for each vitamin. The concentration of pantothenic acid rapidly decreased in the heart, stomach, kidney and testis, whereas concentrations of nicotinamide were stable in all tissues except the liver. Different variations in B-group vitamin concentrations in the tissues of starved rats were found. The present findings will lead to a suitable supplementation of vitamins for the prevention of the re-feeding syndrome.

Energy-modulating vitamins--a new combinatorial therapy prevents cancer cachexia in rat mammary carcinoma

Mitochondria are the major intracellular organelles producing ATP molecules via the electron transport chain. Cancer cells have a deviant energy metabolism, and a high rate of glycolysis is related to a high degree of dedifferentiation and proliferation. The overall net ATP production is diminished with cancer, which ultimately leads to cancer cachexia. The present study was designed to investigate the altered energy metabolism in cancer cells and to enhance ATP production in the normal host cell metabolism by enhancing the activities of mitochondrial enzymes, using energy-modulating vitamins, and thus prevent cancer cachexia. Female Sprague-Dawley rats were selected for the experimental study. Mammary carcinoma was induced by the oral administration of 7,12-dimethylbenz[a]anthracene (25 mg/kg body weight), and treatment was started by the oral administration of the energy-modulating vitamins riboflavin (45 mg/kg body weight per d), niacin (100 mg/kg body weight per d) and coenzyme Q10 (40 mg/kg body weight per d) for 28 d. Mitochondria were isolated from the mammary gland and liver of all four groups, and the Krebs cycle and oxidative phosphorylation enzymes were assayed. In mammary carcinoma-bearing animals, the activities of the Krebs cycle and oxidative phosphorylation enzymes were significantly decreased. These activities were restored to a greater extent in animals treated with energy-modulating vitamins. From these experimental results, one may hypothesize that the combination therapy of energy-modulating vitamins could be of major therapeutic value in breast cancer.

Effect of arylformamidase (kynurenine formamidase) gene inactivation in mice on enzymatic activity, kynurenine pathway metabolites and phenotype

The gene coding for arylformamidase (Afmid, also known as kynurenine formamidase) was inactivated in mice through the removal of a shared bidirectional promoter region regulating expression of the Afmid and thymidine kinase (Tk) genes. Afmid/Tk -deficient mice are known to develop sclerosis of glomeruli and to have an abnormal immune system. Afmid-catalyzed hydrolysis of N-formyl-kynurenine is a key step in tryptophan metabolism and biosynthesis of kynurenine-derived products including kynurenic acid, quinolinic acid, nicotinamide, NAD, and NADP. A disruption of these pathways is implicated in neurotoxicity and immunotoxicity. In wild-type (WT) mice, Afmid-specific activity (as measured by formyl-kynurenine hydrolysis) was 2-fold higher in the liver than in the kidney. Formyl-kynurenine hydrolysis was reduced by approximately 50% in mice heterozygous (HZ) for Afmid/Tk and almost completely eliminated in Afmid/Tk knockout (KO) mice. However, there was 13% residual formyl-kynurenine hydrolysis in the kidney of KO mice, suggesting the existence of a formamidase other than Afmid. Liver and kidney levels of nicotinamide plus NAD/NADP remained the same in WT, HZ and KO mice. Plasma concentrations of formyl-kynurenine, kynurenine, and kynurenic acid were elevated in KO mice (but not HZ mice) relative to WT mice, further suggesting that there must be enzymes other than Afmid (possibly in the kidney) capable of metabolizing formyl-kynurenine into kynurenine. Gradual kidney deterioration and subsequent failure in KO mice is consistent with high levels of tissue-specific Afmid expression in the kidney of WT but not KO mice. On this basis, the most significant function of the kynurenine pathway and Afmid in mice may be in eliminating toxic metabolites and to a lesser extent in providing intermediates for other processes.

Chromatographic and capillary electrophoretic methods for the analysis of nicotinic acid and its metabolites

Methods for the assay of nicotinic acid (NiAc) and its metabolites in biological fluids using high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) are reviewed. Most of the references cited in this review concern HPLC methods. A few CE methods that have been recently reported are also included. As these compounds are relatively polar and have a wide range of physico-chemical properties, the sample pre-treatment or clean-up process prior to analysis is included. Most HPLC methods using an isocratic elution system allow determination of a single or few metabolites, but gradient HPLC methods enable simultaneous determination of five to eight compounds. Simultaneous determination of NiAc including many metabolites in a single run can be achieved by CE. We also discuss the pharmacokinetics of NiAc and some of its metabolites.

Nicotinic acid supplementation: effects on niacin status, cytogenetic damage, and poly(ADP-ribosylation) in lymphocytes of smokers

As a substrate for poly(ADP-ribose) polymerase (PARP; EC, 2.4.2.30), an enzyme that is activated by DNA strand breaks and is thought to facilitate efficient DNA repair, NAD+ and its precursor nicotinic acid (niacin) are involved in the cellular defense against DNA damage by genotoxic compounds. In this study, the effect of nicotinic acid supplementation on cytogenetic damage and poly(ADP-ribosylation) was evaluated in a human population that is continuously exposed to genotoxic agents, e.g., smokers. By use of a placebo-controlled intervention design, 21 healthy smokers received supplementary nicotinic acid at 0-100 mg/day for 14 weeks. An increased niacin status, as assessed from blood nicotinamide concentrations and lymphocyte NAD+ concentrations, was observed in groups supplemented with 50 and 100 mg/day. This effect was most pronounced in subjects with lower initial NAD+ levels. An increased niacin status did not result in decreased hypoxanthine guanine phosphoribosyltransferase variant frequencies and micronuclei induction in peripheral blood lymphocytes (PBLs). Sister chromatid exchanges in PBLs, however, were increased after supplementation with nicotinic acid. This increase was positively associated with the daily dose of nicotinic acid. No effects of nicotinic acid supplementation were found for ex vivo (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene-induced poly(ADP-ribosylation), although the small number of samples that could be analyzed (n = 12) does not allow firm conclusions. Because no evidence was found for a decrease in cigarette smoke-induced cytogenetic damage in PBLs of smokers after nicotinic acid supplementation of up to 100 mg/day, it is concluded that supplemental niacin does not contribute to a reduced genetic risk in healthy smokers.

Effects of nicotinamide on milk composition and production in dairy cows fed supplemental fat

Thirty-two cows, averaging 112 DIM, were assigned to four dietary treatments: 1) control, 2) Ca salts of fatty acids, 3) nicotinamide, and 4) Ca salts of fatty acids blended with nicotinamide during manufacture. Preliminary studies showed that nicotinamide survives blending with Ca salts of fatty acids during manufacture and that a blended mixture of nicotinamide and Ca salts of fatty acids gave results similar to those from nicotinamide plus Ca salts of fatty acids supplemented separately. Calcium salts of fatty acids increased milk fat percentage, decreased milk protein percentage, but had no effect on production of milk, FCM, fat, or protein. Nicotinamide increased production of milk and protein, decreased fat percentage, but had no effect on either production of FCM and protein or percentage of protein. Calcium salts of fatty acids increased NEFA in blood, and dietary nicotinamide increased concentrations of nicotinamide in blood, but glucose and BHBA in blood were unaffected by either dietary ingredient. Therefore, in these midlactation cows, the decreased milk protein percentage caused by supplemental dietary fat was prevented by nicotinamide. Supplementation with only nicotinamide increased total production of milk protein.

High-performance liquid chromatographic and capillary electrophoretic determination of free nicotinic acid in human plasma and separation of its metabolites by capillary electrophoresis

Two methods are described based on high-performance liquid chromatography and capillary electrophoresis that provide the selective and sensitive determination of nicotinic acid in human plasma. Moreover, the capillary electrophoresis system was used for the separation of nicotinic acid, nicotinamide, nicotinamide N-oxide, N'-methylnicotinamide, 6-hydroxynicontinic acid, nicotinuric acid and barbital (internal standard). The extraction procedure is simple; no gradient elution or derivatization is required. Both methods can be useful for clinical and biomedical investigations.

High-performance liquid chromatographic determination of nicotinamide and its metabolites in human and murine plasma and urine

A high-performance liquid chromatographic method is described which enables the determination of nicotinamide and eight of its possible metabolites in human and murine plasma and urine, using ion-pairing on a base-deactivated reversed-phase column. Calibration curves were linear up to 2 mumol/ml for nicotinamide and 200 nmol/ml for the metabolites; both the intra- and inter-assay relative standard deviations ranged between 1 and 8%. In murine plasma, the N-oxide was the major nicotinamide metabolite, but in man, formation of 1-methylnicotinamide and the 2- and 4-pyridones was also significant. In urine, nicotinuric acid was seen in the mouse, but no nicotinic acid metabolites were seen in man.

High-performance liquid chromatographic determination of 3-hydroxykynurenine with fluorimetric detection; comparison of preovulatory phase and postovulatory phase urinary excretion

A high-performance liquid chromatographic assay for 3-hydroxykynurenine in human urine is described. A fluorescent derivative of 3-hydroxykynurenine was prepared, based on the reaction of the compound with p-toluenesulphonyl chloride in a basic medium. The analytical method for the measurement of the fluorescent compound employed a Tosoh ODS 80 column eluted with 10 mM potassium dihydrogenphosphate (pH 4.5) and acetonitrile (3:2, v/v) and detection at an excitation wavelength of 375 nm (10 nm bandpass) and an emission wavelength of 455 nm (10 nm bandpass). The column temperature was maintained at 25 degrees C. The detection limit was 3 pmol (673 pg) at a signal-to-noise ratio of 5:1. The fluorescent derivative of 3-hydroxykynurenine was eluted at ca. 12.5 min. The technique was applied to the analysis of human urine. The total analysis time was ca. 15 min.

Simultaneous micro-determination of nicotinamide and its major metabolites, N1-methyl-2-pyridone-5-carboxamide and N1-methyl-4-pyridone-3-carboxamide, by high-performance liquid chromatography

A simultaneous micro-determination of nicotinamide and its major metabolites, N1-methyl-2-pyridone-5-carboxamide (2-py) and N1-methyl-4-pyridone-3-carboxamide (4-py) by high-performance liquid chromatography is described. The method employs a 7-ODS-L (250 mm X 4.6 mm I.D., particle size 7 microns) column eluted with 10 mM potassium dihydrogenphosphate-acetonitrile (96:4, v/v; pH adjusted to 3.0 by the addition of concentrated phosphoric acid) at a flow-rate of 1.0 ml/min. The UV detector was set at 260 nm. The detection limits for nicotinamide, 2-py and 4-py were 10 pmol (1.22 ng), 2 pmol (304 pg) and 2 pmol (304 pg), respectively, at a signal-to-noise ratio 5:1. Isonicotinamide was used as an internal standard. The technique was applied to the analysis of rat and human urines. The total analysis time was ca. 15 min.