Plasma Pyridoxal Phosphate Concentrations Research Articles

Vitamin B-6 Content of Plasma of Domestic Animals Determined by HPLC, Enzymatic and Radiometric Microbiological Methods

In the course of searching for a good animal model of human vitamin B-6 metabolism, it was discovered that plasma from pigs fed natural diets contained substances that interfered with the HPLC analysis of vitamin B-6. To determine the extent of such interference, plasma from several other species was examined. In addition to the HPLC method, the samples were analyzed by an apotyrosine decarboxylase method and a radiometric microbiological assay. In cats and dogs good correlation was obtained between pyridoxal phosphate concentrations determined by the HPLC and by the enzymatic method (r = 0.973). Also there was good correlation between total vitamin B-6 concentrations determined by HPLC and by radiometric microbiological assay (r = 0.998). Severe interference in the HPLC assay was encountered in plasma from pigs and herbivorous animals including goats, cattle, horses and sheep. The interference was eliminated in a pig fed a purified diet for 5 days. Average plasma pyridoxal phosphate concentrations range from 29 nM in pigs to 2443 nM in cats. This wide range indicates that there may be significant differences between species in dietary B-6 intake and/or metabolism of vitamin B-6.

Apparent vitamin B6 deficiency in sickle cell anemia

In 16 patients with sickle cell anemia, plasma pyridoxal phosphate (PLP) concentrations were significantly lower than in 16 controls (p < 0.0001) whereas sickle cell anemia erythrocyte PLP concentrations were significantly elevated (p < 0.0005), possibly reflecting a greater affinity of PLP to the sickle Hb β chain compared to the normal β chain. Oral supplementation of five patients with 50 mg pyridoxine twice daily for 2 months resulted in increased plasma and erythrocyte PLP levels and a slight, but not significant, increase in erythrocyte cell number, Hb, concentration, and hematocrit. In one subject there was also a reduction in the frequency and duration of painful crises and a virtual elimination of hospitalizations for the treatment of the painful crises. Since pyridoxal and PLP have been shown to have antisickling properties in vitro, these studies suggest that pyridoxine supplementation may also be of therapeutic benefit in vivo in sickle cell anemia.

Vitamin B6 intake and plasma pyridoxal phosphate concentrations in the first 2 weeks of life.

Plasma pyridoxal phosphate concentrations were measured in 178 hospitalised neonates. A reference interval for neonates less than 7 day old, of 25 to 78 nmol/l has been established. Vitamin B6 intakes did not correlate well with plasma pyridoxal concentrations despite 26 neonates receiving less than the Recommended Allowance (0.3 mg/d) and 19 receiving amounts below which convulsions have been associated (0.1 mg/d). Ten percent of those infants fed breast milk had plasma pyridoxal phosphate levels below the reference interval compared with only 4% of those fed milk formulae. Breast milk from mothers with babies less than 14 days old had a total vitamin B6 contents reference interval of 5 to 40 micrograms/l. Twenty percent of breast milk samples had virtually no vitamin B6 detected.

Pyridoxal 5′-phosphate deficiency in uremic undialyzed, hemodialyzed, and non-uremic kidney transplant patients

In this study, we have investigated plasma pyridoxal 5'-phosphate (PLP) concentrations in undialyzed and dialyzed uremic patients and in kidney transplant subjects, using an enzymatic technique with thermal deproteinization to liberate PLP from plasma proteins. The specificity of the reaction indicates no interference with pyridoxal and only 3% interference with pyridoxamine phosphate. In 17 hemodialyzed patients, a deficiency of about 50% of plasma PLP concentration is found as compared to 25 healthy subjects (22.2 +/- 2.47 vs. 48.8 +/- 3.00 nmol . l-1), as mean +/- SEM). In seven undialyzed uremic patients with end-stage renal failure, the plasma PLP concentration is also decreased (29.3 +/- 1.74 nmol . l-1). The absence of PLP in plasma ultrafiltrates demonstrates that no loss of PLP occurs due to hemodialysis. The daily oral supplementation with 250-750 mg pyridoxal induces a supraphysiological increase in plasma PLP concentration in hemodialyzed as well as in undialyzed patients. In 116 non-uremic kidney transplant subjects, the mean plasma PLP concentration was 33.8 +/- 3.50 nmol . l-1). In 65% of these patients, a marked deficit (below 20 nmol . l-1) was observed. In conclusion, uremic patients have a deficient vitamin B6 state. Its correction with pyridoxal to restore physiological plasma PLP concentration necessitates oral supplementation with lower doses that those widely used at present. In kidney transplant patients a similar plasma PLP deficiency is observed in the absence of chronic renal failure.

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

Tryptophan metabolism in bladder cancer patients from Copenhagen.

Urinary excretion before and after a loading dose of tryptophan, plasma pyridoxal phosphate concentration and urinary excretion of 4-pyridoxic acid was studied in 44 male bladder cancer patients from Copenhagen. Six patients (14%) had abnormal tryptophan metabolism, decreased plasma pyridoxal phosphate concentration and in most cases low urinary excretion of 4-pyridoxic acid indicating decreased availability of vitamin B6 or decreased formation of pyridoxal phosphate from vitamin B6. It is concluded that abnormal tryptophan metabolism only plays a minor role for bladder cancer carcinogenesis in Copenhagen. It is, however, stressed that such studies do not rule out the possibility that the aromatic degradation products of tryptophan may be cocarcinogens or promotors as other studies have indicated.

Vitamin B6 deficiency in cancer patients

The plasma pyridoxal phosphate concentration was determined in 30 cases of early breast cancer, 21 patients with locally recurrent disease, and 43 patients with systemic metastases. The two groups of advanced breast cancer had significantly lower plasma pyridoxal phosphate levels than 36 healthy women of similar age. Urinary 4-pyridoxic acid excretion was normal in breast cancer. Plasma pyridoxal phosphate concentrations were also reduced in 34 women with widespread cancer derived from primary sites other than breast, but were normal in 39 with early disease.

Adequacy of vitamin B6 supplementation during pregnancy: a prospective study

This prospective study assesses the effect of 2.5, 4, and 10 mg of pyridoxine supplementation during pregnancy on maternal and fetal plasma levels of pyridoxal 5'-phosphate (PLP) and on the degree of coenzyme saturation (activation factor) of aspartate aminotransferase and alanine aminotransferase (alphaEGOT and alphaEGPT) in maternal erythrocytes. More than 4 mg of pyridoxine supplementation daily was required for most pregnancies to maintain maternal plasma PLP levels within the range observed during the first trimester and in the nonpregnant state. The plasma PLP concentrations in maternal and cord blood were highly correlated and indicated a dependence of fetal vitamin B6 nutrition on maternal circulating PLP. Measurements of alphaEGOT and alphaEGPT were not as reproducible as plasma PLP assays and were less sensitive and quantitative indicators. In the majority of subjects, the changes in alphaEGOT and alphaEGPT with time correlated poorly with the changes in plasma PLP. However, when the data were analyzed without regard for their dependence on time, they demonstrated a negative, linear correlation between alphaEGOT and log plasma PLP and between alphaEGPT and log plasma PLP for the group on 2.5 mg of pyridoxine and for all the subjects combined. Finally, the dietary records showed that most of the subjects consumed less than 2 mg of vitamin B6 daily from their food. The results indicate that the current Recommended Dietary Allowance for vitamin B6 during pregnancy (2.5 mg) is too low and that supplementation of this vitamin in an amount more than 4 mg daily is recommended.

Abnormal Regulation of Plasma Pyridoxal 5'-Phosphate in Patients with Liver Disease

Pyridoxal 5'-phosphate (PLP), the coenzyme form of vitamin B6, is essential for many biochemical reactions in the body. Studies in experimental animals have suggested that the liver is a primary site for the formation of PLP circulating in the plasma, and that it may also participate in its degradation. This study evaluates, for the first time, the effects of liver disease in man on the regulation of plasma PLP. The plasma PLP level was measured before and sequentially after the rapid intravenous administration of 50 mg of pyridoxine to patients with alcoholic cirrhosis, acute hepatitis, and extrahepatic obstruction, and to normal control subjects. The base line plasma PLP concentration was significantly lower in cirrhotic patients than in normal persons (P less than 0.025), and there was a tendency for it to be reduced in patients with extrahepatic obstruction. After administration of pyridoxine there was a significant increase in the plasma PLP level over a 2- to 12-hr period, after which the concentration returned gradually toward the initial value. The area under the concentration/time curve was from 2 to 8 times smaller (P less than 0.002) in the patients with liver disease. To assess possible mechanisms of this change, 5 mg of PLP were intravenously administered to the various patient groups and the pharmacokinetics of the disposition were assessed. The initial and steady state volumes of distribution of PLP were comparable in cirrhotics and controls (P greater than 0.05), but the clearance of plasma PLP in cirrhotics was much faster (63.0 +/- 7.4 versus 31.7 +/- 2.7 ml per min, P less than 0.004). Similar findings were obtained in the other liver disease subjects. The in vitro plasma binding of PLP at supracirculatory concentrations was comparable in cirrhotics and controls (99.4 versus 99.5%, P greater than 0.05). (1) plasma PLP regulation in patients with liver disease is abnormal, (2) a significant factor in the decrease in plasma PLP after intravenous pyridoxine administration in these patients appears to be an increase in the total plasma clearance of the coenzyme, and (3) it is postulated that this may be due to increased degradation of PLP by the diseased liver.

Effect of oral contraceptives and vitamin B6 deficiency on carbohydrate metabolism

Oral glucose tolerance, urinary xanthurenic acid excretion, and plasma pyridoxal phosphate concentrations were determined in nine women taking oral contraceptives and in four controls. The tests were repeated after 4 weeks ingestion of a vitamin B6-deficient diet, and again after pyridoxine supplementation. Vitamin B6 deficiency, as judged by an increased xanthurenic acid excretion and reduced plasma pyridoxal phosphate, was associated with a deterioration in the glucose tolerance of the contraceptive steroid-treated group despite normal or elevated plasma insulin levels. This abnormality was reversed by pyridoxine. There was no change in the glucose tolerance of the vitamin B6-deficient controls. The observed pyridoxine-responsive alteration in carbohydrate metabolism may involve the complexing of insulin with xanthurenic acid with a consequent loss of biological activity. In addition, oral contraceptives may enhance gluconeogensis.

Maternal and fetal plasma levels of pyridoxal phosphate at term: Adequacy of vitamin B6 supplementation during pregnancy

The effect of different amounts of vitamin Be supplementation during pregnancy on maternal and fetal plasma levels of pyridoxal phosphate (PLP) at term has been studied. Ten of I3 subjects given 2 to 2.5 mg. of vitamin Bs daily exhibited plasma PLP levels lower than 4.7 ng. per milliliter (the lower limit of normal for nonpregnant subjects). In contrast, only 4 of II subjects given a supplement of I0 mg. of vitamin Bs daily had plasma PLP less than this value. The mean plasma PLP level (64.4 ng. per milliliter) of I0 cord blood samples from newborn infants whose mothers exhibited plasma PLP levels greater than 4.7 ng. per milliliter was significantly higher (P < 0.005) than that (34.2 ng. per milliliter) from I4 newborn infants whose mothers had abnormally lowered plasma PLP concentrations. In cord plasma, an average venous-arterial gradient of I0.6 ng. per milliliter was observed, indicating that the fetus retains and/or degrades PLP. These results suggest that more than 2 to 2.5 mg. of vitamin B6 supplement daily is required for most pregnancies to restore normal vitamin Bs nutrition in the mother and, perhaps, also in the fetus.

Vitamin B6 metabolism in chronic alcohol abuse. Pyridoxal phosphate levels in plasma and the effects of acetaldehyde on pyridoxal phosphate synthesis and degradation in human erythrocytes.

The plasma pyridoxal-5'-phosphate (PLP) level of alcoholic subjects has been compared with that of non-alcoholic individuals in order to ascertain the incidence of abnormal vitamin B(6) metabolism in chronic alcohol abuse. 66 alcoholic subjects were selected on the basis that they did not exhibit abnormal liver function tests and hematologic findings. 35 of them had plasma PLP concentrations less than 5 ng/ml, the lowest value encountered in 94 control subjects, indicating a high incidence of deranged PLP metabolism in alcoholic patients even when hepatic and hematologic abnormalities are absent. The biochemical basis for the altered PLP metabolism in chronic alcohol abuse was examined. Low plasma PLP levels in alcoholics were not accompanied by decreased pyridoxal kinase and pyridoxine phosphate oxidase activities in erythrocytes. Further studies with erythrocytes demonstrated that the cellular content of PLP is determined not only by the activities of these PLP-synthesizing enzymes but also by the activity of a phosphate-sensitive, membrane-associated, neutral phosphatase, which hydrolyzes phosphorylated B(6) compounds.Acetaldehyde, but not ethanol, impaired the net formation of PLP from pyridoxal, pyridoxine, and pyridoxine phosphate by erythrocytes. However, when the B(6)-phosphate phosphatase activity was inhibited by 80 mM phosphate, this effect of acetaldehyde was abolished. By the use of broken cell preparations, it was possible to demonstrate directly that the action of acetaldehyde is mediated by the phosphatase, resulting in an acceleration of the degradation of the phosphorylated B(6) compounds in erythrocytes.

Pyridoxal phosphate and folic acid concentration in blood and erythrocyte aspartate aminotransferase activity during pregnancy

The plasma pyridoxal phosphate concentrations and folic acid concentration in packed red blood cells have been studied in 58 women during pregnancy and in their children at birth. The material was divided into three groups receiving no, 2 mg and 10 mg extra pyridoxine per day. The study showed a highly significant relationship between the mean plasma pyridoxal phosphate concentration in mother and child at delivery. Addition of 2 mg extra pyridoxine per day was found insufficient to keep the mean pyridoxal phosphate concentration level constant during pregnancy for which addition of between 2 and 10 mg extra pyridoxine per day was found necessary. It was found necessary to add between 2 and 10 mg extra pyridoxine per day to significantly increase the saturation of aspartate aminotransf erase with pyridoxal phosphate. The mean value of pyridoxal phosphate concentration of the newborn children was significantly increased by 2 mg pyridoxine but no further increase was observed by 10 mg pyridoxine per day. No correlation was found between blood pyridoxal phosphate concentration and folic acid concentration. It is recommended to add 10 mg pyridoxine extra per day during pregnancy.

Pyridoxal phosphate concentration in plasma and tryptophan load test during pregnancy

In 35 pregnant women pyridoxal phosphate concentration in plasma, xanthurenic acid excretion in urine after a tryptophan load test and total oestrogen excretion in urine were determined at various stages of pregnancy. Decreasing plasma pyridoxal phosphate concentration and increasing xanthurenic acid excretion were found. Xanthurenic acid excretion was extremely high, and was positively correlated to oestrogen excretion and negatively correlated to pyridoxal phosphate concentration. The abnormal tryptophan degradation is believed to be due to the combined influence of pyridoxal phosphate deficiency and hormonal derangement during pregnancy.