Plasma Pyridoxal Phosphate Concentrations Research Articles

Concentration of Vitamin B6 and Activities of Enzymes of B6 Metabolism in the Blood of Alcoholic and Nonalcoholic Men

The purpose of this study was to compare concentrations of vitamin B6 compounds and the activities of enzymes that synthesize or catabolize pyridoxal 5'-phosphate in the plasma and erythrocytes of nonalcoholic and alcoholic subjects. Blood was obtained from male nonalcoholics and chronic alcoholics with minimal liver damage and normal hematology. Plasma, erythrocyte, and urinary B6 compounds were analyzed by high performance liquid chromatography, and pyridoxal phosphate was also measured enzymatically. Erythrocyte pyridoxine kinase and pyridoxine phosphate oxidase and erythrocyte and plasma pyridoxine phosphate phosphatases were assayed. Plasma pyridoxal phosphate concentration was significantly lower in the alcoholics (31.3 +/- 3.6 nmol/liter) than in the nonalcoholics (58.7 +/- 7.5 nmol/liter). The concentrations of the other B6 compounds in plasma, erythrocytes, and urine were not different in the two groups. Plasma alkaline pyridoxine phosphate phosphatase activity was significantly higher in the alcoholics (4.05 +/- 0.36 nmol/(h.mg] than in the nonalcoholics (3.01 +/- 0.18 nmol/(h.mg]. The activities of erythrocyte kinase, oxidase, and phosphatases were not significantly different in the two groups. The relationship of plasma pyridoxal phosphate concentration to its metabolites and the activities of the enzymes involved in its metabolism was determined. Plasma pyridoxine phosphate phosphatase activity assayed at pH 9.0 or 7.4 correlated negatively with plasma pyridoxal phosphate concentration. The low pyridoxal phosphate concentration observed in the plasma of the alcoholic subjects may in part be related to increased plasma phosphatase activity.

Evaluation of Vitamin B-6 Status and Function of Rats Fed Excess Pyridoxine

We compared the vitamin B-6 status of 12-wk-old rats (n = 12) fed excess (1400 mg/kg diet) or the recommended level (7 mg/kg diet, control) of pyridoxine (PN) hydrochloride to test if excess vitamin B-6 would cause tissue depletion of pyridoxal phosphate (PLP), the active coenzyme form of vitamin B-6. Plasma PLP, tryptophan-load test results, food intake, and tissue and body weights were not different at wk 6. Red blood cell endogenous alanine aminotransferase activity and PLP concentration were elevated (P less than 0.01) in rats fed 1400 mg PN.HCl/kg diet. In contrast, PLP concentration in muscle was significantly lower (P = 0.01) in rats fed excess vitamin B-6 (9.7 +/- 0.8 nmol/g, mean +/- SEM) than in controls (14.9 +/- 1.4). PLP concentration in other tissues, including plasma, was not affected. In rats fed excess vitamin B-6, pyridoxal was increased in all tissues examined (P less than 0.05), and total vitamin B-6 was increased in plasma, red blood cells and kidneys (P less than 0.05). Total glycogen phosphorylase (a + b) activity in the gastrocnemius was not affected, but phosphorylase a activity was increased in rats fed excess vitamin B-6 (P = 0.025). Concentrations of dopamine and metabolites in the caudate nucleus of the basal ganglia were not affected. A transient, but significant, elevation in acoustic startle response, a central nervous system reflex, was observed in rats fed excess vitamin B-6. The depletion in muscle PLP could not hae been predicted by either plasma or red blood cell PLP concentration, although the latter did reflect vitamin B-6 intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in Pyridoxal Phosphate and Pyridoxamine Phosphate in Blood, Liver and Brain in the Pregnant Mouse

A decrease in plasma pyridoxal-5'-phosphate (PLP) occurs during pregnancy in humans and experimental animals for reasons that are not known. To determine if mice also develop decreased plasma PLP concentrations during pregnancy, and if plasma PLP levels in pregnancy reflect tissue levels of PLP and pyridoxamine-5'-phosphate (PMP), we measured PLP concentrations in plasma, erythrocytes and whole blood, and liver and brain PLP and PMP in control and pregnant mice. Mice were fed a nonpurified diet containing 8.13 mg pyridoxine-HCl/kg. The PLP analyses were performed in our newly developed apotryptophanase method in which the substrate S-benzyl-L-cysteine is hydrolyzed to benzyl mercaptan, reacted with Ellman's reagent and measured spectrophotometrically. During pregnancy, plasma PLP levels decreased 50% below control levels, but erythrocyte and whole blood PLP levels increased 2.9- and 1.6-fold, respectively. Liver PLP and PMP decreased 25%, in parallel with plasma PLP, but brain PLP and PMP concentrations were unchanged during pregnancy. These results suggest that metabolism or utilization of vitamin B-6 is altered in pregnancy, and that plasma PLP concentrations alone may not be a good indicator of nutritional status in pregnancy.

PLASMA PYRIDOXAL PHOSPHATE CONCENTRATIONS IN RESPONSE TO INGESTING WATER OR GLUCOSE POLYMER DURING A TWO HOUR RUN

PLASMA PYRIDOXAL PHOSPHATE CONCENTRATIONS IN RESPONSE TO INGESTING WATER OR GLUCOSE POLYMER DURING A TWO HOUR RUN

Vitamin B6 repletion in cirrhosis with oral pyridoxine: failure to improve amino acid metabolism.

This study evaluated the effect of daily oral pyridoxine supplementation in patients with cirrhosis. Eight subjects were treated with 25 mg of pyridoxine for 28 days. Before and after the supplementation period, B6 status was assessed by measuring fasting plasma vitamer levels and response to a 25 mg oral pyridoxine load. In addition, a 24-hr urine collection was analyzed during each load study for B6 metabolites. The data indicated that supplementation achieved repletion of peripheral B6 stores, as evidenced by: (i) a significant (p less than 0.005) rise in fasting plasma pyridoxal phosphate after supplementation (mean +/- S.D. = 56.8 +/- 30.5 nmoles per liter) as compared to initial levels (17.0 +/- 17.8 nmoles per liter); (ii) a higher (p less than 0.05) percentage excretion of the pyridoxine load as urinary 4-pyridoxic acid (31.0 +/- 9.3%) compared to the initial load (19.6 +/- 5.8%), and (iii) a postsupplementation area under the plasma concentration vs. time curve for pyridoxal phosphate (377 +/- 529 nmoles.hr per liter), which was decreased (p less than 0.005) from the presupplementation value (934 +/- 756 nmoles.hr per liter). The postsupplementation fasting plasma pyridoxal phosphate concentrations were within the normal range. The consequences of B6 repletion on amino acid metabolism were measured by oral protein loads (n = 4) or oral methionine loads (n = 4). No significant changes were observed for methionine or any other amino acid in regard to plasma fasting concentration, peak concentration or AUC. Although the vitamin B6 deficiency of cirrhosis was corrected by daily oral pyridoxine supplementation, there was apparently no improvement in the deranged amino acid metabolism.

Effect of age on changes in plasma, erythrocyte, and urinary B-6 vitamers after an oral vitamin B-6 load

We investigated the effect of age on indices of vitamin B-6 metabolism in 36 fasting males aged 25-35, 45-55, and 65-75 y who ingested 17.15 mumol vitamin B-6. There were no significant differences among groups in dietary vitamin B-6 intake, base-line erythrocyte pyridoxal 5'-phosphate (PLP), and total vitamin B-6 concentrations, and 24-h and base-line urinary excretion of total vitamin B-6 and 4-pyridoxic acid (4-PA). Base-line plasma PLP and total vitamin B-6 were higher (p less than 0.05) in the youngest group. Increased serum alkaline phosphatase (AP) and decreased dietary vitamin B-6 intake were correlated with decreased base-line plasma PLP and total vitamin B-6. Changes in plasma and erythrocyte PLP concentrations and excretion of 4-PA and total vitamin B-6 postload were not different among groups. Indices of vitamin B-6 absorption, phosphorylation, and excretion were not affected by age.

Plasma pyridoxal phosphate concentrations of men fed different levels of vitamin B-6

The vitamin B-6 status of 12 white, 3 black, and 7 men of other races was evaluated utilizing plasma pyridoxal phosphate concentrations after the males had been on controlled diets for 8 wk. The diets contained averages of 1.22-1.67 mg/d vitamin B-6 as calculated from food composition tables. The actual mean vitamin B-6 content of these diets as analyzed with Saccharomyces uvarum was 0.75-0.98 mg/d; the mean daily protein intakes were 80.8-84.5 g. All subjects had plasma pyridoxal phosphate concentrations (67.6-125.8 nmol/L) well within the normal range; the values of the different race and dietary groups were similar. Vitamin B-6 requirements were satisfied by the consumption of diets analyzed to contain means of 0.75-0.98 mg/d of the vitamin as demonstrated by plasma pyridoxal phosphate levels indicative of adequate status. Dietary vitamin B-6 intakes should be determined by actual analyses when requirements are being determined.

Nutritional evaluation of soldiers subsisting on meal, ready-to-eat operational rations for an extended period: body measurements, hydration, and blood nutrients

To evaluate the nutritional value of a new military operational ration, meal, ready-to-eat (MRE), 27 soldiers were fed the ration as their only food during a 34-d field exercise at an elevation of 1800 m. Thirty soldiers given hot breakfasts and dinners and MREs for lunch served as control subjects. Measurements were made of body height, weight, skinfold thickness at four sites, urine volume and concentration, urinary zinc loss, hemoglobin, hematocrit, serum alkaline phosphatase activity, serum concentrations of albumin, total protein, ascorbic acid, folate, retinol, and Zn, and plasma pyridoxal phosphate concentration. The men fed only MREs experienced significant weight loss compared with those fed hot meals. Neither group appeared to be dehydrated. Hemoglobin and hematocrit values rose in response to increased elevation. Both groups of soldiers displayed normal values, indicative of acceptable nutritional status, of serum proteins, measured vitamins, and Zn.

Maternal aerobic exercise and vitamin B-6 status

Effects of an aerobic walking program during gestational weeks 22-30 on vitamin B-6 status and birth outcome were studied in 28 healthy pregnant women, aged 21-36 y, receiving vitamin-mineral supplements. Mean daily vitamin B-6 intake, excluding a 10-mg supplement, was 1.81 mg. Subjects in the walking (n = 18) and nonwalking (n = 10) groups had similar microbiologically assessed plasma total vitamin B-6 levels and radioenzymatically assessed plasma pyridoxal phosphate concentrations. One walker at 22 wk and at 30 wk and a second walker at 30 wk had plasma total vitamin B-6 concentrations in the low-normal range; the same was true for plasma pyridoxal phosphate levels except that the 30-wk value for the walker who was low at 22 wk was missing. Birth-outcome measurements were similar for both groups. Participation in the walking program slightly improved aerobic fitness without affecting vitamin B-6 status or birth outcome in pregnant women taking vitamin-mineral supplements.

Compartmentalization of pyridoxal-5'-phosphate during the acute phase of myocardial infarction.

Vitamin B6 nutritional status is assessed by measuring the plasma concentration of one of its vitamers, pyridoxal-phosphate (PLP). Several conditions, e.g., myocardial infarction (MI), can disturb the dynamic equilibrium between the different vitamers resulting in transiently low plasma PLP levels. An important question is whether these low plasma PLP levels observed during MI represent a transient state of deficiency and what the possible clinical consequences of such a fall in plasma PLP could be. Since the main metabolic function of PLP is to act as an intracellular coenzyme, it was decided to monitor the changes not only of PLP but also of PL (transport form of vitamin B6) in both the plasma and red blood cells (RBCs) in patients with myocardial infarctions (MI): 16 patients with proven MI were investigated measuring the aforementioned parameters at regular intervals. It was found that the approximately 40% fall in plasma PLP levels was accompanied by an equivalent increase in RBC PLP levels. Subsequently plasma PLP concentrations returned to normal but RBC PLP values were maintained at the newly elevated steady state (without any vitamin supplementation). Since membranes are impermeable to PLP, the only way in which PLP could have been redistributed to the intracellular compartment was through hydrolysis to PL and rephosphorylation once inside the RBCs. This compartmentalization could be an important adaptive response since it has been shown that PLP reduces O2 affinity of deoxygenated hemoglobin, thereby facilitating O2 delivery to the tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of plasma pyridoxal 5′-phosphate concentrations in capillary (finger prick) and venous blood

The purpose of our study was to investigate the validity of using capillary blood plasma to estimate the pyridoxal 5′-phosphate (PLP) concentration of venous blood plasma. To accommodate the small volumes of capillary blood usually obtained, we modified the experimental conditions of the L-tyrosine apodecarboxylase (TDC) assay for PLP by increasing both the specific activity of 14C-tyrosine and the reaction incubation time. Plasma PLP concentrations determined by the TDC assay and the micro-modified TDC assay were highly correlated (r = 0.995, p = 4.0 X 10(-6)). Using the micro-modified TDC assay, we observed no significant difference between the plasma PLP concentrations of venous and capillary (finger prick) blood from 10 healthy adults. Thus, capillary blood plasma can be used to estimate the PLP concentration of venous blood plasma. This observation will aid in verifying data concerning the vitamin B-6 status assessment of individuals as determined by capillary blood plasma PLP concentrations.

A Micromethod for Determination of Plasma Pyridoxal Phosphate and Its Use in Assessment of Storage Stability of the Vitamer

SummaryA widely used macromethod employing tyrosine apodecarboxylase for measurement of pyridoxal phosphate (PLP) concentration in 0.5–1.0‐ml plasma was modified to a microscale utilizing 0.1‐ml plasma. Mean PLP levels in 12 plasma samples were 160.6 ± 32.8 pmol/ml (mean ± SD) when analyzed by the macro‐method, and were not significantly different compared to those obtained by the micromethod (158.4 ± 28.2 pmol/ ml). Results of the two methods were significantly correlated (r = +0.97, p < 0.001). Plasma PLP concentrations of 11 samples determined by the micromethod ( = 151.8 ± 30.0 pmol/ml) were similar and significantly correlated (r = +0.95, p < 0.001) to levels measured in the same samples 1–2 years earlier ( = 145.1 ± 26.2 pmol/ml). This suggests that plasma PLP content of the samples was stable for up to 2 years of storage when the micro‐method was utilized for analysis. The strong significant correlation between macro‐ and micromethods attests that the micromethod is a reliable alternative to the macromethod. The micromethod is useful in instances where only small samples of plasma are available for measurement of PLP.

Pyridoxal phosphate concentrations determined postmortem as an indication of antemortem vitamin B-6 status.

In anticipation of studies relating vitamin B-6 status determined at autopsy to known pathologic causes of death, the postmortem stability of pyridoxal phosphate (PLP) in the plasma, skeletal muscle, and liver of pigs was assessed. Concentrations of plasma K, Mg, Na, and Ca also were examined for postmortem stability using the pig as an experimental model. At 1 hr after death, the mean plasma PLP concentration was essentially unchanged from that observed prior to death. Thereafter, plasma PLP concentration increased with increasing postmortem time interval and was 2.3 times greater than initial by 6 hr postmortem and 7.6 times greater than initial by 12 hr postmortem (P less than 0.01). Skeletal muscle and liver PLP content were 35% lower than initial by 6 hr postmortem (P less than 0.01). Plasma K and Mg were significantly higher by 1 hr postmortem (P less than 0.01) while plasma Na concentration was significantly lower by 1 hr postmortem (P less than 0.01). Plasma Ca concentration was not significantly different at any measured time point. Knowledge of the postmortem time interval appears to be required in order to evaluate the antemortem vitamin B-6 status using pyridoxal phosphate values derived from autopsy samples.

Vitamin B-6 status of a group of cancer patients

The vitamin B-6 status of 12 nonmedicated patients with newly diagnosed malignancies of the oral cavity and thorat, lung, or prostate and bladder and 3 nonhospitalized control subjects was determined by coenzyme stimulation of erythrocyte alanine aminotransferase activities and plasma pyridoxal phosphate levels. The subjects were males except for one female each in the lung and control groups; the mean ages of all groups were about 58 yr. All subjects had smoked for over 25 yr. The status parameter values of the patients with the 3 types of malignancies were similar. The typical vitamin B-6 intakes reported by the cancer patients and control subjects were close to 2 mg daily. All of the cancer patients and none of the control subjects had coenzyme stimulation values indicative of vitamin B-6 inadequacy. Low plasma pyridoxal phosphate concentrations were observed in 67% of the cancer patients and none of the controls. Vitamin B-6 inadequacy was observed in most if not all individuals diagnosed as having cancers of the oral cavity and throat, lung, and prostate and bladder.

Low Levels of Pyridoxal 5'-Phosphate in Patients With Cystic Fibrosis

To determine the effect of cystic fibrosis on the regulation of plasma pyridoxal 5'-phosphate (PLP), the biologically active form of vitamin B6, we measured this compound in plasma from 56 patients with cystic fibrosis. The concentration of PLP in plasma was assayed by a radioenzymatic technique. The results of this study showed that PLP concentration was decreased significantly (6.44 +/- 5.20 ng/mL, mean +/- SD; median 4.45 ng/mL) in patients with cystic fibrosis as compared with a group of hospitalized children with neither cystic fibrosis nor hepatic disease serving as a control group (13.2 +/- 5.04 ng/mL, mean +/- SD; median 12.5 ng/mL). Additionally, 25% of the population with cystic fibrosis exhibited exceedingly low plasma PLP level (less than 2.75 ng/mL). In patients with cystic fibrosis, significant inverse linear associations were found between plasma PLP and serum levels of SGOT and SGPT (PLP v SGOT: r = -.60, P less than .03; PLP v SGPT: r = -.50, P less than .03). This study demonstrated that a deficiency of plasma PLP is a common abnormality in cystic fibrosis and that the low PLP level may be a reflection of impaired vitamin B6 metabolism associated with this disorder.

Effect of oral vitamin B6 supplementation on in vitro platelet aggregation

A randomized, double-blind study was conducted with 12 healthy adult males to determine the effects of oral pyridoxine supplementation on in vitro platelet aggregation. Following a 4-wk baseline period, half the subjects received 100 mg/day of pyridoxine·HCl while the remaining subjects received a placebo for 6 wk. In vitro platelet responses to ADP and collagen and the plasma pyridoxal 5′-phosphate (PLP) concentrations were measured at biweekly intervals. Plasma PLP concentrations increased significantly (p < 0.001) for those receiving the vitamin B6 compared to baseline values or compared to those receiving the placebo. However, there was no significant effect of increased levels of plasma PLP on collagen-stimulated platelet aggregation and only a slight effect on ADP-stimulated aggregation. Acute administration of 100 mg pyridoxine·HCl failed to alter the in vitro response of platelets to either ADP or collagen. Reevaluation of conclusions based solely on in vitro studies suggesting the use of pyridoxine as an effective in vivo antithrombotic agent may be warranted.

A direct assay for pyridoxal 5'-phosphate using pig heart apo-aspartate transaminase.

The development of a simple enzymatic method for the determination of blood and plasma pyridoxal 5'-phosphate (PLP) using pig heart apo-aspartate transaminase (apo-AST) is described. The technique requires three steps: sample extraction using perchloric acid, a binding step in which PLP in the sample extract is attached to the apo-AST and the enzymatic assay of the reconstituted holo-AST. PLP extracts were analysed with and without a known concentration of added PLP to correct for variation in recovery between different specimens. Procedures are outlined for manual and automatic analysis of the PLP extracts. Using the KONE Clinical Analyser after the extraction step, it is possible to measure enzyme activity in 100 specimens (i.e. 400 tubes) in a 5 h period. Results are shown from 185 healthy women aged 20-45 years, in which plasma PLP concentrations ranged from 5 to 165 nmol/L, and 142 men and 56 women in government service aged 17-64 years, whose plasma PLP ranged from 8 to 169 nmol/L. Values less than 20 nmol/L are believed to indicate vitamin B6 deficiency and the method is able to measure 5 nmol/L.

Plasma pyridoxal phosphate concentrations and coenzyme stimulation of erythrocyte alanine aminotransferase activities of white and black adolescent girls

The vitamin B6 status of 96 white and 90 black female adolescents was assessed utilizing plasma pyridoxal phosphate concentrations, coenzyme stimulation of erythrocyte alanine aminotransferase activities, and vitamin B6 intakes. These values were similar for the two race and three age groups. Fifty-eight percent of the girls reported consuming <0.02 mg vitamin B6/g protein daily. The mean coenzyme stimulation and pyridoxal phosphate values of the subjects were 13.5% and 45.2 nM. Coenzyme stimulation values >25% were observed in 18% of the girls and values between 16 and 25%, in 23%. Plasma pyridoxal phosphate concentrations <34.4 nM were observed in 26% of the girls and values from 34.4 to 40.5 nM, in 14%. Vitamin B6 inadequacy was prevalent among white and black southern adolescent girls participating in this study as indicated by plasma pyridoxal phosphate concentrations, coenzyme stimulation of erythrocyte alanine aminotransferase activities, and vitamin B6 intakes.

Nutritionally Relevant Supplementation of Vitamin B6 in Lactating Women: Effect on Plasma Prolactin

Pharmacologic doses of vitamin B6 administered to lactating women have been reported to suppress plasma prolactin. As a result, some physicians have recommended restriction of vitamin B6 intake for lactating women. In the present investigation, 20 lactating women were given supplemental doses of vitamin B6, 0.5 to 4.0 mg/d, beginning 24 hours after delivery. Plasma prolactin, plasma pyridoxal phosphate, and breast milk total vitamin B6 concentrations were determined during the first 9 months postpartum. Women receiving the supplement of 4.0 mg compared with 0.5 mg of vitamin B6 per day had significantly higher plasma pyridoxal phosphate (P less than .01) and breast milk total vitamin B6 concentrations (P less than .05) beginning at 1 month postpartum and continuing through the duration of the study. Plasma prolactin concentrations were not significantly different between the two groups. The percentage of all women, regardless of treatment, in whom lactation persisted at 1 and 2 weeks and 1, 3, 6, and 9 months were 100%, 100%, 100%, 90%, 80%, and 65%, respectively. All women who ceased to lactate during the study reported doing so by choice. Nutritionally relevant doses of vitamin B6 elevated plasma pyridoxal phosphate and breast milk total vitamin B6 concentrations of lactating women without reducing plasma prolactin concentration or halting lactation.

Depressed plasma pyridoxal phosphate concentrations in adult asthmatics

In 15 adult patients with bronchial asthma, plasma and erythrocyte pyridoxal phosphate (PLP) concentrations were significantly lower than in 16 controls (P less than 0.0001 and P less than 0.005, respectively). Oral supplementation of seven asthmatics with 50 mg pyridoxine as pyridoxine X HC1 twice daily failed to produce a sustained elevation of PLP in either the plasma or erythrocytes. However, all subjects reported a dramatic decrease in frequency and severity of wheezing or asthmatic attacks while taking the supplement. The reasons for the failure of a uniform elevation in plasma and erythrocyte PLP concentration and for the apparent beneficial effects of pyridoxine supplementation on the asthmatic symptoms of the patients are unknown at present.