Quantification of the B6 vitamers in human plasma and urine in a study with pyridoxamine as an oral supplement; pyridoxamine as an alternative for pyridoxine.

BACKGROUND AND AIMS: Vitamin B6 is involved in a large spectrum of physiological processes and comprises of the vitamers pyridoxamine (PM), pyridoxal (PL), pyridoxine (PN), and their phosphorylated derivatives including the biological active pyridoxal 5'-phosphate (PLP). While PN toxicity is known to complicate several treatments, PM has shown promise in relation to the treatment of metabolic and age-related diseases by blocking oxidative degradation and scavenging toxic dicarbonyl compounds and reactive oxygen species. We aimed to assess the metabolization of oral PM supplements in a single and three daily dose. MATERIALS AND METHODS: We optimized and validated a method for the quantification of the B6 vitamers in plasma and urine using ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Five healthy volunteers were recruited to study PM metabolization after a single oral dose of 200 mg PM or a three daily dose of 67 mg PM. A third protocol was implemented as control for dietary intake. Venous blood samples, 24 h urine and fasted second void urine samples were collected. RESULTS: After a single oral dose of 200 mg PM, plasma PM increased in the first 3 h to a maximum of 2324 ± 266 nmol/L. While plasma PM levels returned to baseline after ~10 h of PM intake, PLP increased to a maximum of 2787 ± 329 nmol/L and reached a plateau. We found a small increase of PN to a maximum of 13.5 ± 2.1 nmol/L; it was nearly undetectable after ~12 h. With a three daily dose of 67 mg PM we observed an increase and decline of plasma PM, PL, and PN concentrations after each PM intake. PLP showed a similar increase as in the single dose protocol and accumulated over time. CONCLUSION: In this study we showed high plasma levels of PM after oral PM supplementation. We found steadily increasing levels of the biologically active PLP, with minimal formation of PN. The B6 vitamer PM is an interesting supplement as an inhibitor of harmful processes in metabolic diseases and for the treatment of vitamin B6 deficiency. CLINICAL TRIAL REGISTRY: The study was approved by the Medical Ethics Committee of Maastricht University (NL) and was registered at ClinicalTrials.gov as NCT02954588.

Novel synthesis of a dual fluorimetric sensor for the simultaneous analysis of levodopa and pyridoxine.

Herein, a fluorimetric sensor was fabricated based on molecularly imprinted polymers (MIPs) with two types of carbon dots as fluorophores. The MIPs produced had similar excitation wavelengths (400 nm) and different emission wavelengths (445 and 545 nm). They were used for the simultaneous analysis of levodopa and pyridoxine. First, two types of carbon dots, i.e. nitrogen-doped carbon dots (NCDs) with a quantum yield of 43%, and carbon dots from o-phenylenediamine (O-CDs) with a quantum yield of 17%, were prepared using the hydrothermal method. Their surfaces were then covered with MIPs through the reverse microemulsion method. Finally, a mixture of powdered NCD@MIP and O-CD@MIP nanocomposites was used for the simultaneous fluorescence measurement of levodopa and pyridoxine. Under optimal conditions using response surface methodology and Design-Expert software, a linear dynamic range of 38 to 369 nM and 53 to 457 nM, and detection limits of 13 nM and 25 nM were obtained for levodopa and pyridoxine, respectively. The capability of the proposed fluorimetric sensor was investigated in human blood serum and urine samples. Graphical Abstract Schematic representation of nitrogen-doped carbon dots (NCDs), carbon dots from o-phenylenediamine (O-CDs), NCDs coated with imprinted polymers (NCD@MIPs), and O-CDs coated with imprinted polymers (O-CD@MIPs) in the presence and absence of levodopa and pyridoxine.

Development and validation of a liquid chromatography method for the simultaneous determination of eight water-soluble vitamins in multivitamin formulations and human urine.

A simple, precise, and rapid RPLC method has been developed without incorporation of any ion-pair reagent for the simultaneous determination of vitamin C (C) and seven B-complex vitamins, viz, thiamine hydrochloride (B1), pyridoxine hydrochloride (B6), nicotinamide (B3), cyanocobalamine (B12), folic acid, riboflavin (B2), and 4-aminobenzoic acid (Bx). Separations were achieved within 12.0 min at 30 degrees C by gradient elution on an RP C18 column using a mobile phase consisting of a mixture of 15 mM ammonium formate buffer and 0.1% triethylamine adjusted to pH 4.0 with formic acid and acetonitrile. Simultaneous UV detection was performed at 275 and 360 nm. The method was validated for system suitability, LOD, LOQ, linearity, precision, accuracy, specificity, and robustness in accordance with International Conference on Harmonization guidelines. The developed method was implemented successfully for determination of the aforementioned vitamins in pharmaceutical formulations containing an individual vitamin, in their multivitamin combinations, and in human urine samples. The calibration curves for all analytes showed good linearity, with coefficients of correlation higher than 0.9998. Accuracy, intraday repeatability (n = 6), and interday repeatability (n = 7) were found to be satisfactory.

Epilepsy as a pyridoxine-dependent condition: quantified urinary biomarkers for status evaluation and monitoring antiepileptic treatment.

The study testifies an assumption on epilepsy as an inborn error of pyridoxine metabolism and suggests non-invasive quantitative biomarkers for clarified evaluation of clinical status and monitoring an individual treatment by antiepileptic drugs. Urinary parameters of pyridoxal-phosphate (PLP)-dependent tryptophan degradation and the level of 4-pyridoxic acid, the end product of pyridoxine metabolism, were measured by HPLC method with simultaneous ultraviolet and fluorimetric detection in children with different forms of epilepsy and matched healthy controls. The concentrations of compounds formed or metabolized in the course of tryptophan degradation (kynurenines, indoxyl-sulfate) along with correlations between them turned out to be quantitative biomarkers useful for both clarifying patient's clinical state and monitoring antiepileptic treatment. In particular, the value of the ratio of 4-pyridoxic acid to kynurenine appears to be an index of an experienced seizure attack, while the ratio of 3-hydroxyanthranilic acid to 3-hydroxykynurenine reflects activity of kynureninase, the enzyme of critical sensitivity to PLP supply. Growing progressively worse, epilepsy is accompanied by aggravation of PLP-dependent disturbances of tryptophan metabolism and expanding inhibition of kynureninase. The affected pyridoxine metabolism is discussed as an inborn genetic trait in epilepsy in general, rather than a specific sign of pyridoxine-dependent epilepsy solely.

Development of simultaneous enzymatic assay method for all six individual vitamin B6 forms and pyridoxine-beta-glucoside.

A method for determining all of the six natural vitamin B(6) compounds and pyridoxine-beta-glucoside in urine from humans consuming their usual diet was developed. These compounds were specifically converted with 5 enzymes into a high fluorescent 4-pyridoxolactone which was supersensitively determined by an isocratic HPLC. All of the compounds in urine from humans consuming their usual diets were for the first time determined together. The preparation procedure for urine samples was easy without HCl-hydrolysis, and the enzyme reactions took only 2 or 3 h. It required only 5 microL of the urine sample for analysis of one of the compounds. Urine samples from five young Japanese males consuming their usual diet contained pyridoxal, pyridoxamine, and pyridoxine-beta-glucoside but not pyridoxine or phosphoester forms. The contents of 4-pyridoxic acid and pyridoxal correlate well with a correlation coefficient of 0.98. On the other hand, the content of pyridoxamine did not correlate with that of 4-pyridoxic acid.

A capillary zone electrophoretic method for simultaneous determination of seven drugs in pharmaceuticals and in human urine.

A simple, sensitive, and novel method has been developed and validated for the separation and simultaneous quantitation of seven structurally different drugs-pipemidic acid and ofloxacin quinolone antibiotics, pseudoephedrine decongestant, piroxicam anti-inflammatory, thiamin, pyridoxine, and cobalamin-in a mixture by capillary zone electrophoresis. Factors affecting the separation were pH, concentration of buffer, and applied voltage. Separation was carried out in < 9 min with a 50 mM sodium tetraborate buffer, pH 10, and an applied voltage of 30 kV in an uncoated silica capillary tube. The carrier electrolyte gave baseline separation with good resolution, reproducibility, and accuracy. Calibration plots were linear over at least three orders of magnitude of analyte concentrations, and the lower LODs were within the range of 1-5 microg/mL. Detection was performed by UV absorbance at 230 nm. The method was validated for the analysis of drugs in pharmaceutical preparations and in urine samples with RSD of 0.5-2.4% and recovery of > 99%.

Separation of three water-soluble vitamins by poly(dimethylsiloxane) microchannel electrophoresis with electrochemical detection.

A method for rapid separation and sensitive determination of three water-soluble vitamins, pyridoxine, ascorbic acid (VC), and p-aminobenzoic acid (PABA) has been developed by PDMS microchannel electrophoresis integrated with amperometric detection. After treatment of the microchip with oxygen plasma, the peak shapes of the three analytes were essentially improved. Pyridoxine, VC, and PABA were well separated within only 80 s in a running buffer of 20 mM borate solution (pH 8.5). Good linearity was obtained within the concentration range of 2-200 microM for the three water-soluble vitamins. The detection limits were 1.0 microM for pyridoxine and VC, and 1.5 microM for PABA. The proposed method has been successfully applied to real human urine sample, without solid phase extraction, with recoveries of 80-122% for the three water-soluble vitamins.

[Urine levels of thiamine and riboflavine in diuretic therapy of patients with cardiovascular diseases]. / Vyvedenie tiamina i riboflavina s mochoi pri provedenii diureticheskoi terapii u patsientov s zabolevaniiami serdechno-sosudistoi sistemy.

Diuretic therapy entails decreased plasma concentrations of thiamine and riboflavine. Vitamins eliminated with urine more rapidly when diuresis accelerates. This process is not related to diuresis cause. A linear relationship exists between diuresis intensity and amount of eliminated thiamine and riboflavine. Thus it is shown that diuretic therapy provokes thiamine and riboflavine elimination from the body.

Assessment of vitamin B-6 status in young women consuming a controlled diet containing four levels of vitamin B-6 provides an estimated average requirement and recommended dietary allowance.

The Recommended Dietary Allowance (RDA) of vitamin B-6 for young women was recently reduced from 1.6 to 1.3 mg/d based on an adequate plasma pyridoxal phosphate (PLP) concentration of 20 nmol/L. To assess vitamin B-6 requirements and suggest recommendations for intake, seven healthy young women consumed a controlled diet providing 1.2 g protein/kg body weight for a 7-d adjustment period (1.0 mg vitamin B-6/d) and three successive 14-d experimental periods (1.5, 2.1 and 2.7 mg/d, respectively). Direct and indirect vitamin B-6 status indicators were measured in plasma, erythrocytes and urine. Indicators most strongly correlated with vitamin B-6 intake [i.e., plasma and erythrocyte PLP, urinary 4-pyridoxic acid (4-PA) and total vitamin B-6] were regressed on vitamin B-6 intake and the dietary vitamin B-6 to protein ratio. Inverse prediction using adequate and baseline values estimated vitamin B-6 requirement. Adequate values were determined for plasma PLP and urinary 4-PA from baseline values of 60 previous subjects, using the statistical method suggested by Sauberlich. The current study suggests a vitamin B-6 Estimated Average Requirement (EAR) for young women of 1.1 mg/d or 0.016 mg/g protein, and a RDA of 1.5 mg/d or 0.020 mg/g protein. When results from this study are combined with data from four other recent studies, the combined data predict an EAR of 1.2 mg/d or 0.015 mg/g protein, and a RDA of 1.7 mg/d or 0.018 mg/g protein. This study suggests that the current vitamin B-6 RDA may not be adequate.

Influence of water and sodium diuresis and furosemide on urinary excretion of vitamin B(6), oxalic acid and vitamin C in chronic renal failure.

Urinary excretion of vitamin B(6), oxalic acid and vitamin C was investigated in 15 healthy subjects during maximal water diuresis and in the group of 12 patients in polyuric stage of chronic renal failure without dialysis treatment receiving a diet containing high sodium chloride (15g/day). Urinary excretions of the same parameters were investigated in another group of 15 patients in polyuric stage of chronic renal failure without dialysis treatment after i.v. administration of 20 mg furosemide. Urinary excretion of vitamin B(6), oxalic acid and vitamin C significantly increased during maximal water diuresis while during high intake of sodium chloride the urinary excretions of these substances were not affected. The results suggest that urinary excretion of vitamin B(6), oxalic acid and vitamin C depends on the urinary excretion of water. Intravenous administration of 20 mg furosemide led to an increase of urinary excretion of vitamin B(6), oxalic acid and vitamin C in patients with chronic renal failure. The increased urinary excretion of vitamin B(6) and vitamin C is a new negative side effect of furosemide and increased urinary excretion of oxalic acid is a new positive side effect in patients with chronic renal failure.

[The effect of furosemide on urinary excretion of oxalic acid, vitamin C and vitamin B6 in chronic kidney failure]. / Vplyv furosemidu na vylucovanie kyseliny oxalovej, vitamínu C a vitamínu B6 do mocu pri chronickom zlyhaní obliciek.

The authors describe the effect of a single i.v. dose of 20 mg furosemide on the excretion of oxalic acid, vitamin C and vitamin B6 in a control group and in patients with chronic renal failure without dialyzation treatment. An increased urinary excretion of oxalic acid, vitamin C and vitamin B6 was found during the first three hours after furosemide administration in both groups. The effect of furosemide persisted for six hours in patients with chronic renal failure without dialyzation treatment. The authors described a new hitherto unknown positive side-effect of furosemide, i.e. enhanced urinary oxalic acid excretion in the control group and in patients with chronic renal failure without dialyzation treatment and a negative side-effect of furosemide, i.e. increased urinary vitamin B6 excretion in both examined groups. With regard to the assembled results the authors recommend in addition to monitoring of vitamin C also monitoring of vitamin B6 in plasma during long-term administration of large doses of furosemide to patients with chronic renal failure as deficiency of these vitamins could develop.

[Study of the relationship between indicators of provision with vitamins B2 and B6 of children 7-10 years of age with mental retardation]. / Izuchenie vzaimosviazi mezhdu pokazateliami obespechennosti vitaminami B2 i B6 detei 7-10 let s zaderzhkoi psikhicheskogo razvitiia.

Study of the vitamin status of 34 children of both sexes aged 7 to 10, pupils of a school for children with mental retardation in the city of Krasnoyarsk revealed that the values of riboflavin and 4-pyridoxic acid excretion per g of creatinine, which are in good correlation with the content of the respective vitamins in the blood, reflect the saturation with these nutrients and may be used for assessing vitamin supply. Excretion of at least 200 mg of riboflavin per g of creatinine corresponds to normal provision of a child with this vitamin.

Micronutrient status, with special reference to vitamin B6.

OBJECTIVE: To assess the adequacy of micronutrient status among the adult population, with special reference to vitamin B6 status. DESIGN AND SUBJECTS: Micronutrient status was assessed among a random sample of the adult Dutch population (reference group, n = 300), aged 20-79 y, stratified for age and gender, and among a group with a low vitamin B6 intake (n = 144). RESULTS: Low vitamin B6 groups had lower mean levels of erythrocyte and plasma pyridoxal (PL) and pyridoxal-5'-phosphate (PLP), urinary excretion of 4-pyridoxic acid, basal and stimulated erythrocyte aspartate aminotransferase (EAST) and erythrocyte alanine aminotransferase (EALT) activities and EAST stimulation coefficients but not of EALT stimulation coefficients, handgripstrength and 24 h homocysteine excretion before and after a methionin load test. Besides, plasma levels of vitamin C, B12 and folate were lower among low B6 than among reference groups indicating a combined low vitamin status. Direct biomarkers of vitamin B6 intake (plasma PLP and 4-pyridoxic acid excretion) were significantly related to more functional parameters (EAST, EALT and alpha-EAST). Among random reference groups the prevalence of plasma PLP values below 19 nmol/l was 3-7% for different age-gender groups, with the highest value of 16% among men aged 50-79 years. The prevalence of high values of erythrocyte glutathion reductase stimulation coefficient (alpha-EGR) and low levels of serum vitamin B12 and C was not more than 5% among different age-gender reference groups. CONCLUSIONS: Direct biomarkers of vitamin B6 intake confirmed the preselection of a group with a low vitamin B6 intake. The results suggest that the sensitivity of vitamin B6 status parameters for low vitamin B6 intake was highest for the direct vitamin B6 status parameters and lowest for handgripstrength and homocysteine excretion after a methionin load; results for enzyme stimulation coefficients were intermediate. The prevalence of below adequate status parameters for vitamin B2, B6, B12 and C was not more than 7% among the different age-gender groups, with the exception of a value of 16% for plasma PLP levels below 19 nmol/l among men aged 50-79.

Vitamin B-6 status indicators decrease in women consuming a diet high in pyridoxine glucoside.

Previous research has shown that the pyridoxine glucoside (PNG) form of vitamin B-6 has a reduced bioavailability compared with pyridoxine, but its effect on vitamin B-6 status has not been assessed. Following an 8-d adjustment period, nine women consumed diets containing a high or low amount of PNG for 18 d each, in a crossover design. The high and low PNG diets provided 1.52 mg/d (8.98 micromol/d) and 1.44 mg/d (8.57 micromol/d) of vitamin B-6, of which 27% and 9% was PNG, respectively. The dietary vitamin B-6 to protein ratio of both diets was 0.017 mg/g. Urinary excretions of 4-pyridoxic acid and total vitamin B-6 were significantly lower (P < 0.05) during the high PNG diet period than when the low PNG diet was consumed. Urinary PNG excretion was equal to about 9% of the total PNG intake during both periods. Plasma total vitamin B-6 (P < 0.01) and red blood cell pyridoxal 5'-phosphate (PLP) (P < 0.05) were significantly lower when the high PNG diet was consumed than during the low PNG diet period. Fecal total vitamin B-6 excretion was significantly higher (P < 0.001) when the high PNG diet was consumed. Women consuming a diet containing a higher percentage of the total vitamin B-6 intake as PNG exhibited a decrease in vitamin B-6 status indicators, consistent with the reduced bioavailability of PNG demonstrated in other studies, equal to a loss of 15-18% of the total vitamin B-6 intake. During the determination of Recommended Dietary Allowances, the reduced bioavailability of PNG and its presence in higher amounts in some diets should be considered.

Plasma and urine riboflavin and pyridoxine concentrations in enterally fed very-low-birth-weight neonates.

Preterm infant formulas (PIFs) for very-low-birth-weight (VLBW) infants (birth weight, < 1,500 g) are augmented to provide daily riboflavin and pyridoxine at levels up to five-fold greater than in term infant formula and 18-fold greater than in human milk. We evaluated plasma riboflavin and pyridoxine concentrations in VLBW infants who received PIF during their first postnatal month. Eighty-eight plasma and 124 urine samples were collected for riboflavin- and pyridoxine-concentration measurements from 57 clinically healthy VLBW infants weekly during their first postnatal month. Concentrations were measured using high-performance liquid chromatography. At the time of the sample, patients were receiving > or = 80% of their total calories via enteral feedings. Plasma riboflavin concentrations rose from 45.3 +/- 7.3 ng/ml at baseline (mean +/- SEM) to 173.5 +/- 20.3 ng/ml by 1 week of age and remained at 177.3-199.7 ng/ml during the following three weekly measurements; values were up to 14-fold above baseline concentration. Urine riboflavin concentration increased from 534 +/- 137 ng/ml at baseline to 3,521 +/- 423 ng/ml by 1 week of age and remained at 4,451-5,216 ng/ml during the next 3 weeks. In a similar pattern, baseline plasma (69.4 +/- 10.4 ng/ml) and urine (145 +/- 30 ng/ml) pyridoxine concentrations were significantly increased by 1 week postnatal age; they remained at 163-248 ng/ml (plasma) and 1,573-2,394 ng/ml (urine) through the first postnatal month. Plasma and urine riboflavin and pyridoxine concentrations in enterally fed VLBW infants increased from baseline concentrations by 1 week of postnatal age and remained elevated for the first postnatal month. High daily intake and immature renal development are probable contributing causes of the elevated plasma riboflavin and pyridoxine concentrations. We suggest that lower daily enteral administration of riboflavin and pyridoxine should maintain adequate blood concentrations and minimize potential toxicity.

[Refining criteria for supplying the body with vitamin B6]. / Utochnenie kriteriev obespechennosti organizma vitaminom B6.

As shown by many-year experience of human vitaminization with vitamin B6 and by mathematical analysis of a relationship between content of pyridoxal phosphate in blood plasma, excretion of 4-pyridoxic acid with urine and the rate of PALP-effect as well as after calculation and mathematical interpretation of statistical variations in distribution of those pyridoxal phosphate content in blood plasma and the rate of PALP-effect in man after additional vitaminization, the value of PALP-effect not exceeding 2.5 and content of PALP more than 8ng/ml in blood plasma should be recommended as a criterion of normal vitamin B6 consumption. Excretion of 4-pyridoxic acid with urine more than 60mg/h in children 5-7 years old and 70 mg/h in adults and children 9 years appear to serve as a criterion of normal vitamin B6 consumption.

Vitamin B-6 status of school-aged patients with phenylketonuria.

A triad of measures of vitamin B-6 (B6) status (diet, plasma, and urine) was evaluated in 15 patients with phenylketonuria (PKU) and six control subjects (6-17 y): 1) 4-d reported dietary intakes of protein and B6; 2) fasting plasma concentrations of pyridoxal 5'-phosphate (PLP), total B6 (TB6), and alkaline phosphatase (AP) activity; and 3) 24-h urinary excretions of TB6 and 4-pyridoxic acid (4-PA). Compared with control subjects, patients had a significantly reduced mean protein intake (P < 0.001) and increased mean B6 intake (P < 0.05). Mean dietary B6:protein in patients, 0.043 mg/g protein, was over twice that of control subjects, 0.018 mg/g protein (P < 0.001). Mean plasma PLP and PLP/TB6 in patients were significantly increased compared with control subjects (P < or = 0.05). As a percent of B6 intake, mean urine TB6 was similar between the groups (6.8% patients vs 6.5% control subjects). These findings, along with a lower mean plasma AP activity in patients, support the possibility of a reduced turnover of the vitamin in PKU.

Pyridoxine-5'-beta-D-glucoside: metabolic utilization in rats during pregnancy and availability to the fetus.

Pyridoxine-5'-beta-D-glucoside (PNG), which is abundant in various plant-derived food products, has been shown to be poorly utilized in male rats and adult men. To assess the metabolic utilization of PNG during pregnancy and the availability to the fetus, [3H]PNG and [14C]pyridoxine (PN) were orally administered to 15-d pregnant rats for direct assessment of the intestinal absorption, tissue distribution, and urinary excretion of the radioisotopes. The level of 3H was significantly greater in the liver, and urinary excretion of 3H tended to be lower than that of 14C. The relative distribution of 3H among the groups of B-6 vitamers within the liver was similar to that for 14C. There was greater uptake by the fetus of 3H than of 14C. There was no difference in the relative concentrations of 3H and 14C among the groups of B-6 vitamers within the fetus. Results of this study suggest that the metabolic utilization of PNG is similar to that of PN during pregnancy. Therefore, the availability of vitamin B-6 derived from maternal PNG seems to be similar to that of vitamin B-6 derived from maternal PN.

[Metabolism of B group vitamins in patients with insulin-dependent and non-insulin dependent forms of diabetes mellitus]. / Obmen vitaminov gruppy B u bol'nykh s insulinzavisimoi i insulinnezavisimoi formami sakharnogo diabeta.

Metabolism of vitamins B, involving evaluation of these vitamins content in blood and excretion of their metabolites with urine, was studied in adult healthy persons as well as in patients with insulin-dependent and -independent forms of diabetes mellitus. Distinct alterations in metabolism of vitamin B2 were detected in the insulin-dependent diabetes: its content in erythrocytes and the rate of excretion with urine were increased. This phenomenon made some problems in evaluation of riboflavin consumption in patients with diabetes mellitus of the I type, while parameters of vitamin consumption in insulin-independent diabetes were similar to those of healthy persons. Parameters of metabolism of vitamins B1, B6 and PP were not different in patients with insulin-dependent and -independent forms of diabetes mellitus. Rates of excretion of 4-pyridoxic acid, 1-methyl nicotinamide, thiamine with urine as well as concentration of the corresponding vitamins in blood were similar to those parameters of healthy persons.

[Assessment of vitamin B2, B6, and PP supply from data on excretion of vitamins and their metabolites in alimentary iron and riboflavin deficiency]. / K otsenke obespecehnnosti organizma vitaminami B2, B6, i PP po dannym ékskretsii vitaminov i ikh metabolitov pri alimentarnom defitsite zheleza i riboflavina.

Alimentary deficiency in riboflavin and/or iron in rats involved distinct decrease in excretion of 4-pyridoxylic acid and 1-N-methyl nicotinamide--the metabolites considered as the indices of vitamins B6 and PP consumption. The effect observed appears to occur due to a decrease in activity of some iron- and flavin-containing enzymes participating in the metabolism of pyridoxine and niacin. Addition to the diet of the deficient component normalized these patterns. Use of the data on excretion of 4-pyridoxylic acid and 1-N-methyl nicotinamide as criteria of consumption of pyridoxine and niacin is discussed.