The measurement of serum pyridoxal by a microbiological assay using Lactobacillus casei

Can black tea influence plasma total homocysteine concentrations?

BACKGROUND

Polyphenols can act as acceptors of methyl groups during the metabolism of methionine to homocysteine. This may result in elevations in plasma total homocysteine (tHcy) concentrations after ingestion of polyphenol-rich beverages such as tea.

OBJECTIVES

Our major objective was to determine whether regular, moderate-to-high intakes of black tea alter tHcy concentrations. We also assessed the relation between the degree of O-methylation of tea-derived polyphenols and the change in tHcy with regular ingestion of tea.

DESIGN

Twenty-two subjects completed a randomized, controlled crossover study. Subjects consumed 1250 mL black tea/d (5 cups each containing 2 g tea leaves in 250 mL boiled water) and 1250 mL hot water/d for 4 wk each. Fasting tHcy concentrations and 24-h urinary excretion of 4-O-methylgallic acid (4OMGA, the major O-methylated metabolite of gallic acid) were measured at the end of each period. 4OMGA was used as a marker of overall O-methylation of tea-derived polyphenols.

RESULTS

Black tea did not significantly alter mean (+/- SEM) tHcy concentrations (9.9 +/- 0.5 and 10.0 +/- 0.5 micro mol/L for the hot water and black tea periods, respectively). However, the increased excretion of 4OMGA as a consequence of black tea consumption was positively associated with the change in tHcy from the hot water period to the black tea period (r = 0.55, P = 0.008). Subjects in the bottom quartile of increase in 4OMGA excretion had a significant decrease in tHcy (-0.28 +/- 0.10 micro mol/L; P = 0.046), and those in the top quartile had a significant increase in tHcy (0.78 +/- 0.16 micro mol/L; P = 0.005).

CONCLUSIONS

Overall, regular ingestion of black tea did not alter mean tHcy concentrations. However, individual differences in O-methylation of polyphenolic compounds may influence the ultimate effects of black tea on tHcy.

Folate-responsive homocystinuria and megaloblastic anaemia in a female patient with functional methionine synthase deficiency (cblE disease)

This first detailed report of a female patient with functional methionine synthase deficiency due to the cblE defect describes treatment with several vitamins and cofactors and clinical progress for 17 years. Before treatment, major findings were microcephaly, psychomotor retardation, episodic reduced consciousness, megaloblastic anaemia, increased plasma free homocystine (> 20 mumol/L), low plasma methionine (< 10 mumol/L) and increased excretion of formiminoglutamate. On high-dose folic acid, biochemical abnormalities such as formiminoglutamate excretion and homocystinuria nearly normalized, but clinical and haematological abnormalities remained. On replacement of folate with methylcobalamin, alertness, motor function, speech and the electroencephalogram improved, biochemical features were similar, but the mean corpuscular volume increased. The best control was observed on a combination of folate and methylcobalamin. At 17 years of age she remains severely mentally retarded. In cultured fibroblasts methionine synthesis was reduced (0.03 nmol/mg/per 16 h, controls 2.4-6.9); methionine synthase activity was normal under high reducing conditions but decreased on limiting the reducing agent, dithiothreitol, to 5 mmol/L (18% of total, controls 51-81%); formation of methylcobalamin was low (4.5% of total cobalamins, control 57.5%) and complementation studies indicated the cblE defect. Methionine formation showed only minor increases in cells grown in folate- or cobalamin-supplemented medium. Serine synthesis, which was low in normal medium, increased with cobalamin supplementation. These studies suggest further heterogeneity within cblE mutants, show the difficulty of establishing the enzyme defect in vitro, and indicate a role for folate in addition to cobalamin in treatment.

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.

A fluorimetric method for the measurement of pyridoxal and pyridoxal phosphate in human plasma and leucocytes, and its application to patients with sideroblastic marrows

A highly sensitive fluorimetric assay for the measurement of pyridoxal and pyridoxal phosphate in biological tissues is described. The method involves the enzymic hydrolysis of pyridoxal phosphate to pyridoxal. The pyridoxal (free or total) is separated on an anion-exchange column, concentrated by cation-exchange chromatography and reacted with potassium cyanide under slightly alkaline conditions to form 4-pyridoxolactone, a highly fluorescent compound. The method is applied to the measurement of pyridoxal, pyridoxal phosphate and total pyridoxal in plasma and neutrophils from control subjects and patients with sideroblastic marrow and identified the patient with pyridoxine-responsive sideroblastic anaemia.

Levels and subcellular localisation of pyridoxal and pyridoxal phosphate in human polymorphonuclear leukocytes and their relationship to alkaline phosphatase activity

Neutrophil leukocytes, isolated from normal subjects and subjected to analytical subcellular fractionation by sucrose density gradient centrifugation, showed very similar cytosol distributions of pyridoxal and pyridoxal phosphate and lactate dehydrogenase. The small amounts of pyridoxal and pyridoxal phosphate associated with the dense granule fractions were not associated with the alkaline phosphatase containing granules. The levels of pyridoxal and pyridoxal phosphate were determined in neutrophils from control subjects, women in the third trimester of pregnancy and patients with chronic granulocytic leukaemia. Neutrophil pyridoxal phosphate was increased in women in the third trimester of pregnancy compared to controls, but there was little variation in the level of pyridoxal between the groups. There was no consistent correlation between the pyridoxal phosphate and the neutrophil alkaline phosphatase activity in the patient groups. Although in vitro neutrophil alkaline phosphatase rapidly hydrolyses pyridoxal phosphate, it is suggested that in vivo this is unlikely to be the principal function of the enzyme.

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.

Fluorometric assay of B6 vitamers in biological material

A method for the separation and assay of all B6 vitamers from a single sample of serum is reported. A new reagent system containing sodium glyoxalate, potassium aluminum, sulfate and manganese dioxide was used for quantitative conversion of pyridoxamine and its phosphate to the corresponding aldehydes by a combination of transamination and oxidation reactions.

Pyridoxine (pyridoxamine) phosphate oxidase activity in the red cell

A method has been developed for the measurement of red cell pyridoxine (pyridoxamine) phosphate oxidase activity. The more stable substrate, pyridoxamine phosphate, was incubated with a red cell haemolysate and the product pyridoxal phosphate was measured by Lactobacillus casei microbiological assay. A wide range of oxidase activities was found in control subjects (6-136 ng pyridoxal phosphate/g Hb x 10(-2)). There is a close correlation between the rate of conversion of pyridoxine to pyridoxal phosphate in whole blood and the oxidase activity. There was a marked increase in both after oral riboflavin. These results suggest that the oxidase plays a large part in the regulation of vitamin B-6 metabolism in red cells.

Hydrolysis of pyridoxal-5'-phosphate in plasma in conditions with raised alkaline phosphate

Hydrolysis of pyridoxal phosphate in plasma was demonstrated in patients with liver disease and other conditions with raised alkaline phosphatase, and this usually closely paralleled the alkaline phosphatase level, whether of liver or bone origin. The endogenous plasma pyridoxal phosphate was inversely related to the alkaline phosphatase, and plasma hydrolysis of pyridoxal phosphate may at least in part be responsible. Very large doses of vitamin B6 may be necessary to compensate for this hydrolysis.

Primary oxalosis: clinical and biochemical response to high-dose pyridoxine therapy

Although pyridoxine hydrochloride (vitamin B6) is known to reduce the endogenous production of oxalate in some individuals with primary oxalosis, the dose for a satisfactory trial of treatment is not established. We report two cases of primary oxalosis on a daily regimen of 1 g pyridoxine hydrochloride, in which 24-hr urinary oxalate excretion decreased by 60% and 70%, respectively, with corresponding clinical benefit. The responses have been sustained up to 2.5 yr in one case, and 20 mo in the other. In the patient with renal failure, serum creatinine decreased from 243 to 146 mumole/liter after 15 mo of treatment. The decrease in glycollic acid excretion in both patients was consistent with an increase of glyoxalate transaminase activity by the vitamin. Supranormal levels of erythrocyte glutamic oxaloacetate transaminase (egot) activity were observed during therapy, and these may be useful as a measure of the effective dose of pyridoxine.

Abnormal red-cell metabolism of pyridoxine associated with beta-thalassaemia

Red-cell conversion of pyridoxine to pyridoxal phosphate was studied in control subjects, and patients with heterozygous and homozygous beta-thalassaemia. In 7% of control subjects the rate of pyridoxine conversion was well below the range found in the other control subjects (5.0-8.6%, mean 6.5%/g Hb x 10(-2)) but in heterozygous beta-thalassaemia was below that range in 63% of the patients. The conversion rate was also slow or borderline in the majority of patients with severe transfusion-dependent homozygous beta-thalassaemia, in spite of the presence of some donor cells; but was normal, or fast as in other anaemias, in all but one patient with mild homozygous thalassaemia. There was a much higher incidence of a slow conversion rate in the parents of the severe homozygotes than in parents of the mild homozygotes, illustrating the familial pattern. This supports our view that the red-cell conversion rate of pyridoxine is an inherited characteristic, independent of thalassaemia. The cause of a reduced rate of pyridoxine conversion was investigated. The increase to a normal rate following riboflavin ingestion suggests a defect in the activity of the flavin mononucleotide (FMN)-dependent pyridoxine phosphate oxidase.

The B-vitamins in malnutrition with alcoholism: A model of intervitamin relationships

1. The B-vitamin status of fifty-nine patients, mainly from the lower socio-economic classes in Bombay, with a history of chronic malnutrition, and of alcoholism of 1·5–20 years’ duration, was studied before and during treatment, and in relation to their clinical, especially neurological, condition. These patients were divided into two neurological categories: (1) those with peripheral neuropathy (mainly sensory and distal) alone, (2) those with mental changes (mainly confusion and disorientation) also. Both categories frequently showed pellagrous pigmentation and mucocutaneous signs of B-vitamin deficiency.

2. Thiamin and erythrocyte transketolase (EC2.2.1.1) activity, riboflavin, nicotinic acid, pantothenic acid, total and pyridoxal fraction of vitamin B6, folate and total vitamin B12were estimated in the blood and the cerebrospinal fluid (CSF) of these patients, and also in the blood of sixty-nine control subjects and in the CSF of some of them. The concentrations of all the vitamins, except vitamin B12, were highly significantly lower in the blood of patients of category 1 compared to the controls, and erythrocyte transketolase activity and pyridoxal concentration in patients of category 2 were significantly lower than those of category 1 patients. Blood pantothenic acid and folate concentrations were reduced less consistently.

3. Serum vitamin B12concentration was significantly increased (though within normal range) in the patients compared to the control group, probably because of the moderate hepatic insufficiency (as assessed by liver function tests) in the former.

4. The concentrations of thiamin, riboflavin, nicotinic acid and total vitamin B6were also highly significantly lower in the CSF in patients of category 1 compared with controls. Furthermore, thiamin, nicotinic acid and total vitamin B6concentrations were significantly lower in patients of category 2 than those of category 1 patients, indicating that CSF levels reflect better the neurological status of these patients.

5. There was a moderate increase in the blood concentration of all the vitamins tested, after a relatively poor hospital diet alone. There was a concurrent increase in the blood levels of thiamin, riboflavin, nicotinic acid and pantothenic acid after parenteral treatment with either thiamin or nicotinic acid. The administration of pyridoxine resulted in a significant increase in the blood levels of riboflavin and the pyridoxal fraction of vitamin B6.

Serum pyridoxal in patients with gastric pathology

Fasting serum pyridoxal was assayed by an automated microbiological system in 60 patients investigated for dyspepsia, patients with active peptic ulceration being excluded from the study. Gastritis was present in 30 patients, gastric carcinoma in 16, six patients had benign polyps, and, in eight patients, radiology, endoscopy, and biopsy failed to shown any abnormality. Of the 52 patients with gastric pathology, 44 had a low serum pyridoxal.

Serum pyridoxal and folate concentrations in diabetics

Serum pyridoxal and folate concentrations were measured in 518 diabetics. There were 185 males and 333 females. The level of pyridoxal was significantly lower in the diabetics when compared with 371 'healthy' controls and 25% had levels below the lower limit of the normal range. No significant difference was observed between diabetics being treated by diet alone, oral hypoglycaemics or insulin. Only 20 patients had a reduced serum folate level and in 6 this was accompanied by a low pyridoxal concentration. The results suggest that diabetics may have an increased demand for pyridoxal.

Serum pyridoxal in active peptic ulceration

Fasting serum pyridoxal was assayed by an automated microbiological system in 50 patients with endoscopically confirmed active peptic ulceration. Thirty patients had gastric ulceration, 14 had duodenal, four had pyloric canal ulceration, and two had both a gastric and a duodenal ulcer. Serum pyridoxal was below normal in 28 of the gastric ulcer group and in one of the duodenal ulcer group. No difference in the age, sex, drug, alcohol intake, or diet could be distinguished between those two groups.

An automated method for the microbiological assay of serum pyridoxal

A fully automated method for the measurement of serum pyridoxal has been developed. Acid phosphatase was used for dephosphorylation and precipitation of the serum proteins was not required. A chloramphenicol-resistant strain of L. casei was used as the test organism and this removed the need for sterilization. The method gives highly reproducible results, and is suitable for population and institutional studies.

Conversion of vitamin B 6 compounds to active forms in the red blood cell

In studies with pyridoxine and other B(6) compounds in blood, the active forms pyridoxal and pyridoxal phosphate were measured by differential assays using Lactobacillus casei. Red cell uptake of tritiated pyridoxine was also measured. A new metabolic pathway for conversion of pyridoxine to active forms was demonstrated in red cells. In vivo studies in normal subjects suggested that pyridoxine was taken up by red cells where it was converted to pyridoxal phosphate and then pyridoxal, followed by gradual release of a proportion of pyridoxal into plasma. In vitro incubation of pyridoxine with blood confirmed this observation. Increasing amounts of pyridoxine were taken up and converted as the amount added to blood was increased, and only very small numbers of red cells were needed to convert appreciable amounts. Conversion was markedly inhibited at temperatures lower than 37 degrees C, and stopped altogether at - 20 degrees C.Release of pyridoxal into plasma was always directly proportional to the amount of pyridoxal formed and to the volume of plasma present. That pyridoxal phosphate was not released into plasma was demonstrated in stored blood, for pyridoxine was converted mainly only as far as pyridoxal phosphate, probably due to inactivation of the phosphatase. Pyridoxal phosphate remained in the red cells. Pyridoxine was converted when incubated with washed red cells in saline or phosphate buffer suspension (0.08 M). In saline suspension, pyridoxal formed but was not released in the absence of plasma. In phosphate buffer suspension, pyridoxal phosphate was formed but was not changed to pyridoxal, probably due to inactivation of phosphatase by excess phosphate. Pyridoxamine was converted to active forms in red cells less efficiently. Pyridoxal entered red cells rapidly, equilibrating between plasma and cells within 1 min in the same ratio as pyridoxal formed inside red cells. Pyridoxal phosphate did not enter red cells in whole blood but did so readily in washed cells in saline.