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

Nicotinamide N-methyltransferase (NNMT): a novel therapeutic target for metabolic syndrome

Metabolic syndrome (MetS) represents a constellation of metabolic abnormalities, typified by obesity, hypertension, hyperglycemia, and hyperlipidemia. It stems from intricate dysregulations in metabolic pathways governing energy and substrate metabolism. While comprehending the precise etiological mechanisms of MetS remains challenging, evidence underscores the pivotal roles of aberrations in lipid metabolism and insulin resistance (IR) in its pathogenesis. Notably, nicotinamide N-methyltransferase (NNMT) has recently surfaced as a promising therapeutic target for addressing MetS. Single nucleotide variants in the NNMT gene are significantly correlated with disturbances in energy metabolism, obesity, type 2 diabetes (T2D), hyperlipidemia, and hypertension. Elevated NNMT gene expression is notably observed in the liver and white adipose tissue (WAT) of individuals with diabetic mice, obesity, and rats afflicted with MetS. Knockdown of NNMT elicits heightened energy expenditure in adipose and hepatic tissues, mitigates lipid accumulation, and enhances insulin sensitivity. NNMT catalyzes the methylation of nicotinamide (NAM) using S-adenosyl-methionine (SAM) as the donor methyl group, resulting in the formation of S-adenosyl-l-homocysteine (SAH) and methylnicotinamide (MNAM). This enzymatic process results in the depletion of NAM, a precursor of nicotinamide adenine dinucleotide (NAD+), and the generation of SAH, a precursor of homocysteine (Hcy). Consequently, this cascade leads to reduced NAD+ levels and elevated Hcy levels, implicating NNMT in the pathogenesis of MetS. Moreover, experimental studies employing RNA interference (RNAi) strategies and small molecule inhibitors targeting NNMT have underscored its potential as a therapeutic target for preventing or treating MetS-related diseases. Nonetheless, the precise mechanistic underpinnings remain elusive, and as of yet, clinical trials focusing on NNMT have not been documented. Therefore, further investigations are warranted to elucidate the intricate roles of NNMT in MetS and to develop targeted therapeutic interventions.

Synthesis, Detection, and Metabolism of Pyridone Ribosides, Products of NAD Overoxidation

Pyridone-containing adenine dinucleotides, ox-NAD, are formed by overoxidation of nicotinamide adenine dinucleotide (NAD+) and exist in three distinct isomeric forms. Like the canonical nucleosides, the corresponding pyridone-containing nucleosides (PYR) are chemically stable, biochemically versatile, and easily converted to nucleotides, di- and triphosphates, and dinucleotides. The 4-PYR isomer is often reported with its abundance increasing with the progression of metabolic diseases, age, cancer, and oxidative stress. Yet, the pyridone-derived nucleotides are largely under-represented in the literature. Here, we report the efficient synthesis of the series of ox-NAD and pyridone nucleotides and measure the abundance of ox-NAD in biological specimens using liquid chromatography coupled with mass spectrometry (LC-MS). Overall, we demonstrate that all three forms of PYR and ox-NAD are found in biospecimens at concentrations ranging from nanomolar to midmicromolar and that their presence affects the measurements of NAD(H) concentrations when standard biochemical redox-based assays are applied. Furthermore, we used liver extracts and 1H NMR spectrometry to demonstrate that each ox-NAD isomer can be metabolized to its respective PYR isomer. Together, these results suggest a need for a better understanding of ox-NAD in the context of human physiology since these species are endogenous mimics of NAD+, the key redox cofactor in metabolism and bioenergetics maintenance.

Defining NAD(P)(H) Catabolism

Dietary vitamin B3 components, such as nicotinamide and nicotinic acid, are precursors to the ubiquitous redox cofactor nicotinamide adenine dinucleotide (NAD⁺). NAD⁺ levels are thought to decline with age and disease. While the drivers of this decline remain under intense investigation, strategies have emerged seeking to functionally maintain NAD⁺ levels through supplementation with NAD⁺ biosynthetic intermediates. These include marketed products, such as nicotinamide riboside (NR) and its phosphorylated form (NMN). More recent developments have shown that NRH (the reduced form of NR) and its phosphorylated form NMNH also increases NAD⁺ levels upon administration, although they initially generate NADH (the reduced form of NAD⁺). Other means to increase the combined levels of NAD⁺ and NADH, NAD(H), include the inhibition of NAD⁺-consuming enzymes or activation of biosynthetic pathways. Multiple studies have shown that supplementation with an NAD(H) precursor changes the profile of NAD(H) catabolism. Yet, the pharmacological significance of NAD(H) catabolites is rarely considered although the distribution and abundance of these catabolites differ depending on the NAD(H) precursor used, the species in which the study is conducted, and the tissues used for the quantification. Significantly, some of these metabolites have emerged as biomarkers in physiological disorders and might not be innocuous. Herein, we review the known and emerging catabolites of the NAD(H) metabolome and highlight their biochemical and physiological function as well as key chemical and biochemical reactions leading to their formation. Furthermore, we emphasize the need for analytical methods that inform on the full NAD(H) metabolome since the relative abundance of NAD(H) catabolites informs how NAD(H) precursors are used, recycled, and eliminated.

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.

Xanthine oxidase and aldehyde oxidase contribute to allopurinol metabolism in rats

BACKGROUND

Allopurinol is used to treat hyperuricemia and gout. It is metabolized to oxypurinol by xanthine oxidase (XO), and aldehyde oxidase (AO). Allopurinol and oxypurinol are potent XO inhibitors that reduce the plasma uric acid levels. Although oxypurinol levels show large inter-individual variations, high concentrations of oxypurinol can cause various adverse effects. Therefore, it is important to understand allopurinol metabolism by XO and AO. In this study we aimed to estimate the role of AO and XO in allopurinol metabolism by pre-administering Crl:CD and Jcl:SD rats, which have known strain differences in AO activity, with XO inhibitor febuxostat.

METHODS

Allopurinol (30 or 100 mg/kg) was administered to Crl:CD and Jcl:SD rats with low and high AO activity, respectively, after pretreatment with or without febuxostat. The serum concentrations of allopurinol and oxypurinol were measured, and the area under the concentration-time curve (AUC) was calculated from the 48 h serum concentration-time profile. In vivo metabolic activity was measured as the ratio AUC_oxypurinol /AUC_allopurinol.

RESULTS

Although no strain-specific differences were observed in the AUC_oxypurinol/AUC_allopurinol ratio in the allopurinol (30 mg/kg)-treated group, the ratio in Jcl:SD rats was higher than that in Crl:CD rats after febuxostat pretreatment. Contrastingly, the AUC ratio of allopurinol (100 mg/kg) was approximately 2-fold higher in Jcl:SD rats than that in Crl:CD rats. These findings showed that Jcl:SD rats had higher intrinsic AO activity than Crl:CD rats did. However, febuxostat pretreatment substantially decreased the activity, as measured by the AUC ratio using allopurinol (100 mg/kg), to 46 and 63% in Crl:CD rats and Jcl:SD rats, respectively, compared to the control group without febuxostat pretreatment.

CONCLUSIONS

We elucidated the role of XO and AO in allopurinol metabolism in Crl:CD and Jcl:SD rats. Notably, AO can exert a proportionately greater impact on allopurinol metabolism at high allopurinol concentrations. AO's impact on allopurinol metabolism is meaningful enough that individual differences in AO may explain allopurinol toxicity events. Considering the inter-individual differences in AO activity, these findings can aid to dose adjustment of allopurinol to avoid potential adverse effects.

Nutritional Factors That Affect the Formation of 5-Aminolevulinic Acid, a Key Intermediate of Heme Biosynthesis

5-Aminolevulinic acid (ALA) is a key intermediate of heme biosynthesis, which is an essential component of the respiratory chain. Therefore, nutrients that affect ALA biosynthesis eventually affect ATP production, which is the basis of mitochondrial function. Although the effects of various non-nutrient components that affect ALA after biosynthesis have been reported, there are few reports on the effects of dietary amino acids/protein on ALA formation and the effects of dietary vitamins that are involved in amino acid metabolism. In mitochondria, ALA is synthesized from succinyl-CoA and glycine by the pyridoxal phosphate-dependent enzyme ALA synthase [EC 2.3.1.37]. In this study, the effects of dietary amino acids/protein and vitamins on the amount of ALA synthesized were investigated using mice, rats, and cultured cells. Amounts of ALA in plasma and urine, and porphyrins in plasma increased with increasing protein intake. Vitamin B₁ insufficiency did not affect ALA synthesis. Vitamin B₆ insufficiency increased the amount of ALA synthesized, while niacin deficiency markedly reduced ALA synthesis. Thus, for heme synthesis, an essential biological substance for life, the amounts of amino acids, as well as the pathways metabolizing amino acids to glycine and succinyl-CoA are very important. Specifically, it is important that niacin is associated with the formation of glycine and succinyl-CoA from amino acids.

Roles of Nicotinamide N-Methyltransferase in Obesity and Type 2 Diabetes

Type 2 diabetes (T2D) is thought to be a complication of metabolic syndrome caused by disorders of energy utilization and storage and characterized by insulin resistance or deficiency of insulin secretion. Though the mechanism linking obesity to the development of T2D is complex and unintelligible, it is known that abnormal lipid metabolism and adipose tissue accumulation possibly play important roles in this process. Recently, nicotinamide N-methyltransferase (NNMT) has been emerging as a new mechanism-of-action target in treating obesity and associated T2D. Evidence has shown that NNMT is associated with obesity and T2D. NNMT inhibition or NNMT knockdown significantly increases energy expenditure, reduces body weight and white adipose mass, improves insulin sensitivity, and normalizes glucose tolerance and fasting blood glucose levels. Additionally, trials of oligonucleotide therapeutics and experiments with some small-molecule NNMT inhibitors in vitro and in preclinical animal models have validated NNMT as a promising therapeutic target to prevent or treat obesity and associated T2D. However, the exact mechanisms underlying these phenomena are not yet fully understood and clinical trials targeting NNMT have not been reported until now. Therefore, more researches are necessary to reveal the acting mechanism of NNMT in obesity and T2D and to develop therapeutics targeting NNMT.

Dual Analysis of N-methyl-2-pyridone-5-carboxamide and N-1-methylnicotinamide in Urine by HPLC with UV Detection

N-methyl-2-pyridone-5-carboxamide (2PYr) and N-1-methylnicotinamide (NMN) are metabolites of the water soluble Vitamin B3 (Nicotinamide). Limited methodologies exist for their dual chromatographic analysis in urine samples. In this study, we developed a method for analysis of both 2PYr and NMN by ultraviolet detection. Urine samples were treated to a salting-out assisted liquid/liquid extraction for the extraction of 2PYr and cation exchange for NMN. Both analytes were separated on a Biphenyl 100 × 2.1 mm, 2.6-μm column. The new assay's performance (specifically 2PYr) was compared against the existing testing protocol (based on a previously published method). Linearity for both analytes was above 0.99 (r  2) up to a concentration range of: 1500 μmol/L (2PYr) and 150 μmol/L (NMN). Intra-assay and inter-assay precision of the method was below 8% (coefficient of variation) except at the lower limit of quantification where it was below 20%. Recovery of 2PYr was above 80% and NMN above 90%. A significant positive bias was observed with 2PYr against the existing method. This new method allows for both 2PYr and NMN to be chromatographed and overcomes sample preparation issues in urine 2PYr analysis.

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.

A Suitable Diet for Recovery from Starvation Is a High-Fat Diet, but Not a High-Protein Diet, in Rats

The present study aims to determine the most suitable dietary balance of energy-producing nutrients for recovery from starvation. Rats were fed their standard high- carbohydrate diet (HCD, carbohydrate energy : protein energy : fat energy=71 : 18 : 11) for 7 d and then deprived of food for 3 d (short-term starvation) or 8 d (long-term starvation). The starved rats were then fed the HCD, a high-protein diet (HPD, 31 : 57 : 12), or a high-fat diet (HFD, 34 : 14 : 52) for 8 d. Rats had ad libitum access to drinking water throughout the experimental period, including the starvation period. The reference group was allowed free access to the HCD throughout the experimental period. Characteristically, increased drinking, increased urea nitrogen in the plasma and urine, and hypertrophy of the kidneys, were observed in the HPD group. Furthermore, the recovery of plasma glucose level was insufficient in this group. Therefore, administration of a HPD was contraindicated in recovery from starvation. The recovery of body weight after starvation was excellent in the HFD group. No effect on the metabolism of B-group vitamins involved in energy metabolism was found with the administration of any diet. The effects of HCD and HFD administration on recovery from starvation were investigated in further detail. No adverse effects were observed on the tissue to body weight mass ratios or biochemical parameters in blood in the HFD group. From the above findings, it is hypothesized that a HFD is most suitable for quickly reversing the influence of starvation.

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.

Hypophosphatemia after Hepatectomy or Pancreatectomy: Role of the Nicotinamide Phosphoribosyltransferase

BACKGROUND

Postoperative hypophosphatemia is common and is associated with a lower risk of liver failure after hepatectomy, but higher morbidity after pancreatectomy. Whether different physiologic mechanisms underlie the hypophosphatemia associated with these very different clinical outcomes is unclear. This study aims to evaluate the underlying mechanism in postoperative hypophosphatemia.

STUDY DESIGN

We prospectively enrolled 120 patients who underwent major hepatectomy (n = 30), minor hepatectomy (n = 30), pancreatectomy (n = 30), and laparotomy without resection (control group, n = 30). Preoperative and postoperative serum and urinary phosphorus, calcium, and creatinine, as well as phosphaturic factors, including serum nicotinamide phosphoribosyltransferase (NAMPT), fibroblast growth factor-23, and parathyroid hormone were measured. In addition, we evaluated urinary levels of nicotinamide catabolites, N-methyl-2-pyridone-5-carboxamide and N-methyl-4-pyridone-3-carboxamide.

RESULTS

We found that significant hypophosphatemia occurred from postoperative day (POD) 1 to POD 2 in all 4 groups and was preceded by hyperphosphaturia from preoperative day to POD 1. Phosphate level alterations were associated with a significant increase in NAMPT levels from preoperative day to POD 2 in all 3 resected groups, but not in the control group. The fibroblast growth factor-23 levels were significantly decreased postoperatively in all 4 groups, and parathyroid hormone levels did not change in any of the 4 groups. Urine levels of N-methyl-2-pyridone-5-carboxamide and N-methyl-4-pyridone-3-carboxamide decreased significantly in all 4 groups postoperatively.

CONCLUSIONS

This study demonstrates that the mechanism of hypophosphatemia is the same for both liver and pancreas resections. Postoperative hypophosphatemia is associated with increased NAMPT. The mechanism that upregulates NAMPT and its role on disparate clinical outcomes in postoperative patients warrant additional investigation.

β-Nicotinamide Mononucleotide, an Anti-Aging Candidate Compound, Is Retained in the Body for Longer than Nicotinamide in Rats

The turnover of the oxidized form of nicotinamide adenine dinucleotide (NAD⁺) has attracted interest in regard to longevity. Thus, compounds that can rapidly increase the cellular NAD⁺ concentration have been surveyed by many researchers. Of those, β-nicotinamide mononucleotide (β-NMN) has been focused on. Studies on the biosynthesis of NAD⁺ from β-NMN have been reported at the cellular level, but not at the whole animal level. In the present study, we investigated whether β-NMN is superior to nicotinamide (Nam) as a precursor of NAD⁺ in whole animal experiments. To this end we compared the NAD⁺ concentration in the blood and the urinary excretion amounts of NAD⁺ catabolites. Rats were intraperitoneally injected with β-NMN or Nam. After the injection, blood samples and urine samples were collected at 3-h intervals. The concentration of blood total NAD (NAD11NADH) in each sample showed no significant differences between the two groups. The urinary excretion amounts of NAD⁺ catabolites in the urine samples collected at 3-6 h after the injection were lower in the β-NMN group than in the Nam group. These results suggest that β-NMN is retained in the body for longer than Nam.

N-methyl-2-pyridone-5-carboxamide (2PY)-Major Metabolite of Nicotinamide: An Update on an Old Uremic Toxin

N-methyl-2-pyridone-5-carboxamide (2PY, a major metabolite of nicotinamide, NAM) was recently identified as a uremic toxin. Recent interventional trials using NAM to treat high levels of phosphorus in end-stage renal disease have highlighted new potential uremic toxicities of 2PY. In the context of uremia, the accumulation of 2PY could be harmful-perhaps by inhibiting poly (ADP-ribose) polymerase-1 activity. Here, we review recently published data on 2PY's metabolism and toxicological profile.

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.

Urinary excretion ratio of xanthurenic acid/kynurenic acid as a functional biomarker of niacin nutritional status

The present study was conducted to survey functional biomarkers for evaluation of niacin nutritional status. Over 500 enzymes require niacin as a coenzyme. Of these, we chose the tryptophan degradation pathway. To create niacin-deficient animals, quinolinic acid phosphoribosyltransferase-knock out mice were used in the present study because wild type mice can synthesize nicotinamide from tryptophan. When the mice were made niacin-deficient, the urinary excretion of xanthurenic acid (XA) was extremely low compared with control mice; however, it increased according to the recovery of niacin nutritional status. The urinary excretion of kynurenic acid (KA) was the reverse of XA. Kynurenine 3-monooxygenase, which needs NADPH, was thought to be suppressed by niacin deficiency. Thus, we calculated the urinary excretion ratio of XA:KA as a functional biomarker of niacin nutrition. The ratio increased according to recovering niacin nutritional status. Low values equate with low niacin nutritional status.

Urinary Branched-Chain 2-Oxo Acids as a Biomarker for Function of B-Group Vitamins in Humans

To find a functional biomarker of B-group vitamins, we collected 24-h urine samples from young Japanese women who lived in the community (n=29) to measure branched-chain 2-oxo acids such as 2-oxo-3-methylbutanoic acid, 2-oxo-3-methylpentanoic acid, and 2-oxo-4-methylpentanoic acid because B-group vitamins are involved in the catabolism of branched-chain amino acids. The relationships between each pair of the three urinary 2-oxo acids were very high (2-oxo-3-methylbutanoic acid and 2-oxo-3-methylpentanoic acid, p<0.001; 2-oxo-3-methylbutanoic acid and 2-oxo-4-methylpentanoic acid, p<0.001; 2-oxo-3-methylpentanoic acid and 2-oxo-4-methylpentanoic acid, p<0.001). The participants were divided into three groups using the upper (n=10), middle (n=9), and lower tertiles (n=10) based on the urinary excretion amounts of the sum of the three branched-chain 2-oxo acids. The administration of capsules containing the daily necessary amounts of B-group vitamins led to a decrease in the urinary excretion of the sum of the three types of branched-chain 2-oxo acids in participants belonging to the upper tertile. A similar phenomenon was observed in the middle tertile, but not in the lower tertile. Intakes of B-group vitamins and the urinary excretion amounts of B-group vitamins were not observed to be significantly different among the upper, middle, and lower tertiles. These results indicate that some young Japanese women need much higher levels of B-group vitamins than the Dietary Reference Intakes for Japanese. Thus, urinary branched-chain 2-oxo acids are useful functional biomarkers for B-group vitamins in humans.

Metabolism alteration in follicular niche: The nexus among intermediary metabolism, mitochondrial function, and classic polycystic ovary syndrome

Classic polycystic ovary syndrome (PCOS) is a high-risk phenotype accompanied by increased risks of reproductive and metabolic abnormalities; however, the local metabolism characteristics of the ovaries and their effects on germ cell development are unclear. The present study used targeted metabolomics to detect alterations in the intermediate metabolites of follicular fluid from classic PCOS patients, and the results indicated that hyperandrogenism but not obesity induced the changed intermediate metabolites in classic PCOS patients. Regarding the direct contact, we identified mitochondrial function, redox potential, and oxidative stress in cumulus cells which were necessary to support oocyte growth before fertilization, and suggested dysfunction of mitochondria, imbalanced redox potential, and increased oxidative stress in cumulus cells of classic PCOS patients. Follicular fluid intermediary metabolic profiles provide signatures of classic PCOS ovary local metabolism and establish a close link with mitochondria dysfunction of cumulus cells, highlighting the role of metabolic signal and mitochondrial cross talk involved in the pathogenesis of classic PCOS.

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.

Tissue vitamin concentrations are maintained constant by changing the urinary excretion rate of vitamins in rats' restricted food intake

We previously reported that mild food restriction induces a reduction in tryptophan-nicotinamide conversion, which helps to explain why death secondary to pellagra is pandemic during the hungry season. In this study, we investigated the levels of B-group vitamins in the liver, kidney, blood, and urine in rats that underwent gradual restriction of food intake (80, 60, 40, and 20% restriction vs. ad libitum food intake). No significant differences in the B-group vitamin concentrations (mol/g tissue) in the liver and kidney were observed at any level of food restriction. However, the urine excretion rates exhibited some characteristic phenomena that differed by vitamin. These results show that the tissue concentrations of B-group vitamins were kept constant by changing the urinary elimination rates of vitamins under various levels of food restriction. Only vitamin B12 was the only (exception).

Relationship Between Urinary Concentrations of Nine Water-soluble Vitamins and their Vitamin Intakes in Japanese Adult Males

Excess water-soluble vitamins are thought to be eliminated in the urine. We have reported a strong relationship between water-soluble vitamin intake and urinary excretion in females. The relationship, however, is not well understood in males. In the present experiment, 10 Japanese male subjects were given a standard Japanese diet for the first week. The subjects remained on the same diet, and a synthesized water-soluble vitamin mixture containing one time the Dietary Reference Intakes (DRIs) for Japanese was given for the second week, three times the DRIs for the third week, and six times the DRIs for the fourth week. Twenty-four-hour urine samples were collected each week. Urinary excretion levels for seven of the nine water-soluble vitamin levels, excluding vitamin B₁₂ and folate, increased linearly and sharply in a dose-dependent manner. These results suggest that measuring urinary water-soluble vitamins can be good nutritional markers for assessing vitamin intakes in humans.

Simultaneous measurement of nicotinamide and its catabolites, nicotinamide N-oxide, N1-methyl-2-pyridone-5-carboxamide, and N1-methyl-4-pyridone-3-carboxamide, in mice urine

Nicotinamide N-oxide is a major nicotinamide catabolite in mice but not in humans and rats. A high-performance liquid chromatographic method for the simultaneous measurement of nicotinamide, nicotinamide N-oxide, N1-methyl-2-pyridone-5-carboxamide, and N1-methyl-4-pyridone-3-carboxamide in mice urine was developed by modifying the mobile phase of a reported method for measurement of nicotinamide N-oxide.

Urine 3-hydroxykynurenine is higher during the postovulatory phase than in the preovulatory phase indicating a higher vitamin B6 requirement

The relationship between l-tryptophan to nicotinamide metabolism and the menstrual cycle of Japanese women was investigated. Nine metabolism intermediates from urine samples collected during the preovulatory and postovulatory phases were measured. Only urine 3-hydroxykynurenine was higher in the postovulatory phase than in the preovulatory phase. This increase in 3-hydroxykynurenine suggests a decreased reaction of 3-hydroxykynurenine → 3-hydroxyanthranilic acid catalyzed by kynureninase, a vitamin B6 enzyme.

Moderate food restriction suppresses the conversion of L-tryptophan to nicotinamide in weaning rats

Calorie restriction leads to a change in the metabolism of nutrients. Nicotinamide is biosynthesized from L-tryptophan. We attempted to determine the effects of food restriction on the biosynthesis of nicotinamide from L-tryptophan. Weaning male rats were fed a conventional chemically defined diet without preformed niacin for 63 d. However, the food intake was restricted to 80 and 65% of the intake of the ad libitum-fed control group of rats. The 24-h urine samples were periodically collected, and the urinary excretion of nicotinamide and its catabolites was measured. The conversion percentages were lower in both restricted groups than in the ad libitum-fed control group during the experimental period (control group, 1.37 ± 0.24%; 80%-restricted group, 0.20 ± 0.04%; 65%-restricted group, 0.15 ± 0.02%; control vs. restricted groups, p < 0.01). Food restriction, even at mild level, suppressed the conversion of L-tryptophan to nicotinamide when compared to the ad libitum-fed control group.

Gender differences in pharmacokinetics of a combination tablet of niacin extended-release/simvastatin in healthy Chinese volunteers

The gender differences in pharmacokinetics of a combination tablet of niacin extended-release/simvastatin were evaluated in healthy Chinese volunteers. Thirty-six healthy male and female volunteers were enrolled in the study receiving a single oral dose of niacin extended-release/simvastatin 1,000/20 mg. The results indicated that the systemic exposure of simvastatin hydroxy acid and the total urine excretion of niacin were significantly higher for females compared with those for males, and the T max of niacin in plasma was significantly shorter for males than that for females. There were no significant differences in the systemic exposure of simvastatin, niacin, and NUA in plasma between males and females.

Hepatectomy-related hypophosphatemia: a novel phosphaturic factor in the liver-kidney axis

Marked hypophosphatemia is common after major hepatic resection, but the pathophysiologic mechanism remains unknown. We used a partial hepatectomy (PH) rat model to investigate the molecular basis of hypophosphatemia. PH rats exhibited hypophosphatemia and hyperphosphaturia. In renal and intestinal brush-border membrane vesicles isolated from PH rats, Na(+)-dependent phosphate (Pi) uptake decreased by 50%-60%. PH rats also exhibited significantly decreased levels of renal and intestinal Na(+)-dependent Pi transporter proteins (NaPi-IIa [NaPi-4], NaPi-IIb, and NaPi-IIc). Parathyroid hormone was elevated at 6 hours after PH. Hyperphosphaturia persisted, however, even after thyroparathyroidectomy in PH rats. Moreover, DNA microarray data revealed elevated levels of nicotinamide phosphoribosyltransferase (Nampt) mRNA in the kidney after PH, and Nampt protein levels and total NAD concentration increased significantly in the proximal tubules. PH rats also exhibited markedly increased levels of the Nampt substrate, urinary nicotinamide (NAM), and NAM catabolites. In vitro analyses using opossum kidney cells revealed that NAM alone did not affect endogenous NaPi-4 levels. However, in cells overexpressing Nampt, the addition of NAM led to a marked decrease in cell surface expression of NaPi-4 that was blocked by treatment with FK866, a specific Nampt inhibitor. Furthermore, FK866-treated mice showed elevated renal Pi reabsorption and hypophosphaturia. These findings indicate that hepatectomy-induced hypophosphatemia is due to abnormal NAM metabolism, including Nampt activation in renal proximal tubular cells.

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.

Supplementing healthy women with up to 5.0 g/d of L-tryptophan has no adverse effects

Because of the frequent use of L-tryptophan (L-Trp) in dietary supplements, determination of the no-observed-adverse-effect-level is desirable for public health purposes. We therefore assessed the no-observed-adverse-effect-level for L-Trp and attempted to identify a surrogate biomarker for excess L-Trp in healthy humans. A randomized, double-blind, placebo-controlled, crossover intervention study was performed in 17 apparently healthy Japanese women aged 18-26 y with a BMI of ≈ 20 kg/m(2). The participants were randomly assigned to receive placebo (0 g/d) or 1.0, 2.0, 3.0, 4.0, or 5.0 g/d of L-Trp for 21 d each with a 5-wk washout period between trials. Food intake, body weight, general biomarkers in blood and urine, and amino acid composition in blood and urine were not affected by any dose of L-Trp. Administration of up to 5.0 g/d L-Trp had no effect on a profile of mood states category measurement. The urinary excretion of nicotinamide and its catabolites increased in proportion to the ingested amounts of L-Trp, indicating that participants could normally metabolize this amino acid. The urinary excretion of L-tryptophan metabolites, including kynurenine (Kyn), anthranilic acid, kynurenic acid, 3-hydroxykynurenine (3-HK), 3-hydroxyanthranilic acid, and quinolinic acid (QA), all of which are intermediates of the L-TRP→Kyn→QA pathway, was in proportion to L-Trp loading. The response of 3-HK was the most characteristic of these L-Trp metabolites. This finding suggests that the urinary excretion of 3-HK is a good surrogate biomarker for excess L-Trp ingestion.

Urinary excretion of B-group vitamins reflects the nutritional status of B-group vitamins in rats

We have reported previously that the urinary excretion of B-group vitamins reflects recent dietary intakes of these vitamins. We also proposed reference values for the urinary levels of B-group vitamins for human subjects, and used these for evaluating human nutritional status. However, the question arises as to whether the urinary excretion of B-group vitamins in animals or human subjects decreases immediately before they become B-group vitamin insufficient or when fed a diet low in vitamins. In the present study, rats were fed a vitamin-free diet for 5 d, and changes in the levels of B-group vitamins in urine and blood were monitored. Urinary excretion of vitamin B₁, vitamin B₂, 4-pyridoxic acid (a catabolite of vitamin B₆), pantothenic acid, folate and biotin steeply decreased, and all of the values reached zero within 1–2 d. With respect to blood, the concentrations of only three of the eight B-group vitamins (vitamin B₁, pyridoxal phosphate and biotin) decreased to 15 % (P < 0·0001), 7 % (P < 0·0001) and 2 % (P < 0·0001) on day 5, respectively, compared with the values at the beginning of the experiment. The decrease was more rapid and the changes were greater in the urine samples than in the blood samples. The present data complement our previous proposal that the urinary excretion of B-group vitamins reflects the nutritional status of these vitamins.

Vitamin B1 Deficiency Does not Affect the Liver Concentrations of the Other Seven Kinds of B-Group Vitamins in Rats

We aimed to determine the effects of vitamin B₁ deficiency on vitamin contents of urine, liver, and blood. In the current study, rats were divided into 3 groups (n = 5, each group): the first was freely fed a complete diet (ad lib-fed control group); the second freely fed a vitamin B₁-free diet (vitamin B₁ deficient group); and the third pair-fed a complete diet with the same amounts of the vitamin B₁ deficient group (pair-fed control group). The experimental period was for 15 days. The blood concentrations of vitamin B₂, PLP, vitamin B₁₂, folic acid, and biotin were lower in the pair-fed control than in the ad lib-fed control and those of nicotinamide and pantothenic acid were the same. We conclude that Vitamin B₁ deficiency did not affect concentrations of the other B-group vitamins.

Increased conversion of tryptophan to nicotinamide in rats by dietary valproate

Valproic acid (VPA) is a short-chained, branched fatty acid that is widely used in humans as an anticonvulsant and mood stabilizer, and has been reported to increase the liver NAD concentration. We investigated the effects of VPA on the conversion of tryptophan to nicotinamide. Rats were fed diets containing various amounts of VPA (0, 0.5, and 1.0% in the diets) for 14 d, 24-h urine samples were collected, and tryptophan and its catabolites were measured. We found that the conversion of tryptophan to nicotinamide was increased by feeding a diet containing VPA (p<0.01; 0% vs. 1.0% VPA). Of the intermediates formed during the conversion of tryptophan to nicotinamide, the tryptophan to 3-hydroxyanthranilic acid step was not affected by the administration of VPA, while such metabolites beyond quinolinic acid as nicotinamide and its catabolites were significantly increased (p<0.01; 0% vs. 1.0% VPA). This increase was dependent on the intake of VPA.

Nutritional Status of Water-soluble Vitamins Did not Differ According to Intake Levels of Wheat and Wheat Alternatives and Rice and Rice Alternatives as a Staple Food in Pregnant Japanese Women

The objective of this study was to investigate whether the intake level of a staple food influences the nutritional status of water-soluble vitamins in pregnant Japanese women. Urinary excretion of water-soluble vitamins was used as a biomarker for nutritional assessment. Twenty-four-hour urine samples were collected and vitamin intake was surveyed using a validated self-administered comprehensive diet history questionnaire. Subjects were categorized into bottom, middle, and upper tertiles according to the percentage of total energy intake from wheat and wheat alternatives or rice and rice alternatives. The present study showed that the nutritional status of water-soluble vitamins did not differ with intake level of wheat and wheat alternatives or rice and rice alternatives as a staple food in pregnant Japanese women.

Establishment of true niacin deficiency in quinolinic acid phosphoribosyltransferase knockout mice

Pyridine nucleotide coenzymes are involved in >500 enzyme reactions and are biosynthesized from the amino acid L-tryptophan (L-Trp) as well as the vitamin niacin. Hence, "true" niacin-deficient animals cannot be "created" using nutritional techniques. We wanted to establish a truly niacin-deficient model animal using a protocol that did not involve manipulating dietary L-Trp. We generated mice that are missing the quinolinic acid (QA) phosphoribosyltransferase (QPRT) gene. QPRT activity was not detected in qprt(-/-)mice. The qprt(+/+), qprt(+/-), or qprt(-/-) mice (8 wk old) were fed a complete diet containing 30 mg nicotinic acid (NiA) and 2.3 g L-Trp/kg diet or an NiA-free diet containing 2.3 g L-Trp/kg diet for 23 d. When qprt(-/-)mice were fed a complete diet, food intake and body weight gain did not differ from those of the qprt(+/+) and qprt(+/-) mice. On the contrary, in the qprt(-/-) mice fed the NiA-free diet, food intake and body weight were reduced to 60% (P < 0.01) and 70% (P < 0.05) of the corresponding values for the qprt(-/-) mice fed the complete diet at d 23, respectively. The nutritional levels of niacin, such as blood and liver NAD concentrations, were also lower in the qprt(-/-) mice than in the qprt(+/+) and the qprt(+/-) mice. Urinary excretion of QA was greater in the qprt(-/-) mice than in the qprt(+/+) and qprt(+/-) mice (P < 0.01). These data suggest that we generated truly niacin-deficient mice.

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.

Effects of ethanol consumption on the B-group vitamin contents of liver, blood and urine in rats

Several studies have shown that blood vitamin levels are lower in alcoholic patients than in control subjects. Acute ethanol exposure enhances the release of vitamins from liver cells in vitro. The aim of the present study is to confirm the effects of ethanol consumption on vitamin contents in vivo. We compared the contents of B-group vitamins in the liver, blood and urine between ethanol-fed and control rats fed a diet containing a sufficient- and low-vitamin mixture. The experimental rats were fed a 15 % ethanol solution freely for 28 d, and then 24 h urine samples were collected, after which the animals were killed. The B-group vitamin contents in the liver, blood and urine were measured. No differences in liver, blood and urine contents were observed between the control and ethanol-fed rats fed a diet containing a sufficient-vitamin mixture. On the contrary, in rats fed a diet containing a low-vitamin mixture, consumption of ethanol caused a decrease in the contents of vitamins B1, B2 and pantothenic acid in the liver; however, the contents of the other vitamins did not decrease. In the blood, the contents of vitamins B1, B2, B6 and pantothenic acid were lower in the ethanol-fed rats than in the controls. Urinary excretion of the B-group vitamins, except for niacin, was lower in the ethanol-fed rats. These results show that ethanol consumption affects the absorption, distribution and excretion of each of the vitamins in rats fed a diet containing a low-vitamin mixture.

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.

Niacin and its metabolites: role of LC-MS/MS bioanalytical methods and update on clinical pharmacology. An overview

Niacin (nicotinic acid), although an old drug, has seen a sudden surge in popularity for treatment of lipid disorders and other associated clinical conditions for the prevention of cardiovascular risk. Also, there has been considerable interest in clarifying the role of metabolic pathways of niacin in explaining the tolerability/adverse affect profile of the agent. Hence, it has become very important to quantify/monitor the levels of niacin and its metabolites in various clinical studies. This review describes the recent trends in the bioanalysis of niacin and its metabolites, where HPLC and LC-MS/MS assays have been successfully employed to measure the drug levels in various biological matrices arising from preclinical and clinical studies. In addition, this review encompass various considerations such as internal standard selection, extraction schemes, matrix effect, selectivity evaluation and optimization of mass spectral conditions to enable the development of sound bioanalytical methods for niacin alone or niacin along with its metabolites. Recent updates pertaining to the clinical pharmacology of niacin and ongoing debate for the clarification of adverse effects are also provided. Overall LC-MS/MS methods have proven to be choice of bioanalytical method for the quantification of niacin alone or with its metabolites in both preclinical and clinical studies.

Urinary excretion of vitamin B1, B2, B6, niacin, pantothenic acid, folate, and vitamin C correlates with dietary intakes of free-living elderly, female Japanese

We hypothesized that 24-hour urinary excretion of water-soluble vitamins might correlate with their intake in free-living Japanese elderly females aged 70 to 84 years. We performed a cross-sectional study composed of 37 healthy, elderly, Japanese females living freely. All foods and the corresponding weights consumed for 4 consecutive days were recorded accurately. A 24-hour urine sample was collected on the fourth day, and the urinary content of water-soluble vitamins was measured. The urinary levels of all vitamins, except for B(12) (r = 0.01; P = .936), were correlated positively with the mean intake over the recent 4 days (vitamin B1: r = 0.62; P < .001; vitamin B2: r = 0.57; P < .001; vitamin B6: r = 0.37; P < .005; niacin: r = 0.54; P < .001; niacin equivalents: r = 0.54; P < .001; pantothenic acid: r = 0.59; P < .001; folate: r = 0.55; P = .001; and vitamin C: r = 0.53; P < .001). Mean estimated intakes of water-soluble vitamins calculated using urinary concentrations and recovery rates showed 96% to 107% of their 3-day mean intake, except for vitamin B12 (65%). We conclude that urinary levels of water-soluble vitamins, except for B12, reflected their recent intake in free-living Japanese elderly females and could be used as a measure of their intake during the previous few days both for group means and for individual rankings within a group.

Twenty-four-hour urinary water-soluble vitamin levels correlate with their intakes in free-living Japanese schoolchildren

OBJECTIVE

To examine the association between 24 h urinary water-soluble vitamin levels and their intakes in free-living Japanese schoolchildren.

DESIGN

All foods consumed for four consecutive days were recorded accurately by a weighed food record. A single 24 h urine sample was collected on the fourth day, and the urinary levels of water-soluble vitamins were measured.

SETTING

An elementary school in Inazawa City, Japan.

SUBJECTS

A total of 114 healthy, free-living, Japanese elementary-school children aged 10-12 years.

RESULTS

The urinary level of each water-soluble vitamin was correlated positively to its mean intake in the past 2-4 d (vitamin B1: r = 0·42, P < 0·001; vitamin B2: r = 0·43, P < 0·001; vitamin B6: r = 0·49, P < 0·001; niacin: r = 0·32, P < 0·001; niacin equivalents: r = 0·32, P < 0·001; pantothenic acid: r = 0·32, P < 0·001; folic acid: r = 0·27, P < 0·01; vitamin C: r = 0·39, P < 0.001), except for vitamin B12 (r = 0·10, P = NS). Estimated mean intakes of water-soluble vitamins calculated using urinary levels and recovery rates were 97-102 % of their 3 d mean intake, except for vitamin B12 (79 %).

CONCLUSIONS

The results show that urinary levels of water-soluble vitamins, except for vitamin B12, reflected their recent intakes in free-living Japanese schoolchildren and could be used as a potential biomarker to estimate mean vitamin intake.

Relationship between uremic toxins and oxidative stress in patients with chronic renal failure

OBJECTIVE

Uremic toxins play a critical role in the manifestation of the uremic syndrome. This is a consequence of retention of such substances in chronic renal failure patients and interactions between them. To date >100 uremic compounds have been discovered. The aim of this study was to elucidate potential relationships between N-methyl-2-pyridone-5-carboxamide (Me2PY) and N-methyl-4-pyridone-5-carboxamide (Me4PY), two uremic compounds, and different parameters of oxidative stress.

MATERIAL AND METHODS

Forty-three non-dialyzed patients at the Nephrological Outpatients Clinic of Gdansk were enrolled and divided into two groups: (i) 20 patients with a mean estimated glomerular filtration rate (eGFR) of 22.7 ml/min/1.73 m(2); and (ii) 23 patients with a mean eGFR of 12.4 ml/min/1.73 m(2). In both groups, the plasma concentrations of uremic toxins (Me2PY, Me4PY, creatinine), malonyldialdehyde (MDA) and carbonyl groups and the erythrocyte concentration of glutathione (GSH) were analyzed. Correlations between uremic toxins and oxidative stress markers were calculated using Pearson's correlation.

RESULTS

We observed significant correlations between serum creatinine and Me2PY (r=0.68; p=0.00001), eGFR and Me2PY (r=-0.55; p=0.00001), Me4PY and serum creatinine (r=0.64, p=0.00001), Me4PY and eGFR (r=-0.59; p=0.00008), MDA and Me2PY (r=0.42; p=0.006), MDA and Me4PY (r=0.38; p=0.02), GSH and Me2PY (r=-0.37; p=0.02) and GSH and Me4PY (r=-0.46; p=0.005), and in particular in patients with severe renal impairment.

CONCLUSIONS

We conclude that there is a relationship between the novel uremic toxins described and oxidative stress markers. However, elucidation of the exact pathogenetic links requires further detailed studies.

[Effects of excess vitamin B1 or vitamin B2 on growth and urinary excretion of water-soluble vitamins in weaning rats]

To determine the tolerable upper intake levels of vitamin B(1) and vitamin B(2) in humans, we investigated the effects of excess thiamin or riboflavin administration on body weight gain, food intake, tissue weights, and urinary excretion of B-group vitamins in weaning rats. The weaning rats were freely fed ordinary diet containing 0.0006% thiamin-HCl or the same diet with 0.006%, 0.03%, 0.18% or 1.0% thiamin-HCl for 30 days, or the diet containing 0.0006% riboflavin or the same diet with 0.1%, 0.5 or 1.0% riboflavin for 22 days. Mild diarrhea was seen only in the rats fed with 1.0% thiamin-HCl diet. Excess thiamin-HCl or riboflavin did not affect body weight gains, food intake or tissue weights. The urinary excretions of water-soluble vitamins also did not differ among the diets. These results clearly showed that feeding a diet containing up to 1.0% thiamin-HCl or 1.0% riboflavin did not induce apparent adverse effects, and the no-observed-adverse-effect-levels (NOAELs) for thiamin-HCl and riboflavin in rats might be 1.0% in diet, corresponding to 900 mg/kg body weight/day.

Age-related alterations of B-group vitamin contents in urine, blood and liver from rats

To investigate how aging alters B-group vitamin metabolism, rats were fed with niacin-free 20% casein diet from 3 to 80 wk old, and the urinary excretions of the B group vitamins were periodically measured. The blood and liver B-group vitamin levels in 80-wk-old rats were also compared with those in 8-wk-old rats. The urinary excretion of thiamin, riboflavin, vitamin B6 metabolite 4-pyridoxic acid, pantothenic acid, folic acid and biotin were not altered during 540 d. The urinary vitamin B12 increased by 8-fold at 29 wk old, and further increased at 80 wk old. Conversion of nicotinamide from tryptophan gradually decreased to 60% from 29 to 48 wk old. Plasma PLP, vitamin B12 and folate levels in 80-wk-old rats were lower than those in 8-wk-old rats, consistent with lower liver vitamin B6 and folate levels in aged rats. Plasma and liver biotin levels in aged rats were higher than those in young rats. Other B-group vitamins such as vitamin B1, vitamin B2, niacin and pantothenic acid levels in blood and liver from aged rats were same as those from young rats. Alteration of vitamin B6 metabolism in particular is similar to the observations in elderly humans reported previously. Our findings suggest that aged rats can be useful models to investigate aging-related B-group vitamin metabolism.

[Effects of excess pyridoxine-HCl on growth and urinary excretion of water-soluble vitamins in weaning rats]

To determine the tolerable upper intake level of pyridoxine-HCl in humans, we investigated the effects of excess pyridoxine-HCl administration on body weight gain, food intake, tissue weight, and urinary excretion of water-soluble vitamins in weaning rats. The weaning rats were freely fed ordinary diet containing 0.0007% pyridoxine-HCl (control diet) or the same diet with 0.1%, 0.5%, 0.8% or 1.0% pyridoxine-HCl for 30 days. The body weight gain in the 0.8% and 1.0% groups, and the total food intake in the 1.0% group were significantly lower than those in the control group. The urinary excretion of pantothenic acid in the pyridoxine-HCl added groups were higher than that in the control group, while excessive pyridoxine-HCl intake did not affect the urinary excretion of other water-soluble vitamins. These results showed that the no-observed-adverse-effect-level (NOAEL) for pyridoxine-HCl was 0.1% in diet, corresponding to 90 mg/kg body weight/day, and lowest-observed-adverse-effect-level (LOAEL) was 0.5% in diet, corresponding to 450 mg/kg body weight/day.