Correction of the DNA synthesis defect in vitamin B12 deficiency by tetrahydrofolate: evidence in favour of the methyl-folate trap hypothesis as the cause of megaloblastic anaemia in vitamin B12 deficiency

The critical disturbance of folate metabolism caused by vitamin B12 deficiency which results in megaloblastic anaemia remains controversial. Vitamin B12 is required in the methionine synthase reaction in which homocysteine is converted to methionine and methyl tetrahydrofolate (methyl THF) to THF. The 'methyl-folate trap' hypothesis suggested that failure of demethylation of methyl THF with consequent deficiency of folate co-enzymes derived from THF is the crucial lesion caused by vitamin B12 deficiency. A more recent theory suggested that reduced supply of methionine leads to reduced availability of 'activated formate' and hence of formyl THF and it is this defect that results in failure of folate co-enzyme synthesis. The present results, based on deoxyuridine suppression tests on 103 cases of megaloblastic anaemia, show that THF itself is equally capable of correcting the failure of thymidylate synthesis in vitamin B12 deficiency as in folate deficiency. Although not as effective as formyl THF in correcting the dU blocking test in vitamin B12 deficiency, this is equally so for the correction of the test by THF compared with formyl THF in folate deficiency. The results therefore favour the theory that it is in the supply of THF and not of 'active formate' or formyl THF that vitamin B12 plays a critical role in folate metabolism.     

The growth and development of the Annals of Human Biology: a 25-year retrospective

Several fundamental questions relating to the biochemical basis of megaloblastic hemopoiesis in vitamin B12 (B12) and folate deficiency and neurological damage in B12 deficiency remain to be answered. Among them is the explanation underlying (1) the failure of B12-deficient animals to develop megaloblastic hemopoiesis despite indirect evidence of impaired thymidylate synthesis and (2) the inverse relationship between the extent of hematologic and neurological damage in B12 deficiency. Diagnostic advances have led to the awareness that many patients with B12 or folate deficiency are hematologically normal and that subtle hematologic or neuropsychiatric manifestations may be found at a fairly early stage of developing B12 deficiency. Studies of the mechanism of absorption of B12 in food have identified the syndrome of food B12 malabsorption in which the degree of B12 deficiency is commonly, although not invariably, mild. Folate intake influences the prevalence of neural tube defects (NTDs) and a suboptimal folate status may be associated with an increased risk for dysplasia and cancer. The latter may be at least partly the result of uracil misincorporation into DNA and consequent DNA strand breaks. Folate status has also been linked to arteriosclerotic vascular disease through its effect on serum homocysteine levels. Uracil misincorporation into DNA and increased serum homocysteine levels may also be found in B12 deficiency. These adverse associations form the basis of a case for improving B12 or folate status in individuals with a mild degree of deficiency. Because inadequate folate intake is relatively common, especially in the elderly and the poor, the fortification of staple foods with folate is currently under active consideration.     

Review article: the diagnosis and treatment of haematinic deficiency in gastrointestinal disease

Deficiency of any of the vitamins and minerals essential for normal erythropoiesis (haematinics), including iron, copper, cobalt, vitamins A, B12, B6, C, E, folic acid, riboflavin and nicotinic acid, may be associated with defective erythropoiesis and anaemia. Iron, vitamin B12 and folate are the haematinics for which deficiency states manifest most often clinically and are the focus of this review. The normal absorption of these haematinics and gastrointestinal causes of their deficiency are described. Investigations, including the use of homocysteine metabolite levels and new techniques such as serum transferrin receptor assays, and treatment of haematinic deficiency are discussed in detail.     

Changes in erythroblast morphology as an index of response to cyanocobalamin in patients with megaloblastic anaemia

Fifty-three patients with megaloblastic anaemia treated with cyanocobalamin and folic acid have been studied. Repeat marrow examination was found to be of value in assessing response to treatment. The early improvement in marrow morphology in patients with pernicious anaemia was greater with 1000 mug than with 5 mug doses of cyanocobalamin. The effect of folate deficiency in delaying marrow response to cyanocobalamin in patients with pernicious anaemia is described and combined cyanocobalamin and folic acid treatment was found to be more effective than either alone. The response to large doses of cyanocobalamin in folate deficient patients was unrelated to the initial serum vitamin B12 level.     

The danger of B12 deficiency in the elderly

Vitamin B12 deficiency damages nerve cells and aggravates nervous system disorders even in the absence of evidence of anaemia. Prevalence of B12 deficiency increases with age especially over 65 and is frequently associated with Alzheimer's disease. Recent American surveys record a higher prevalence of B12 deficiency and of undiagnosed and untreated pernicious anaemia in the elderly than reported earlier. B12 deficiency is also reported to be a risk factor for heart disease, stroke and accelerated ageing.     

Computed tomography-guided central venous catheter placement in a patient with superior vena cava and inferior vena cava occlusion

Erythropoietin (EPO) is a glycoprotein hormone produced principally by the kidney and is the major stimulus for erythropoiesis. Recombinant human EPO has now been biosynthesized and is available for clinical use, particularly in patients with renal failure. EPO has been reported to be effective in treating anaemia due to chronic renal failure. It has been used in pregnancy to correct anaemia following renal transplantation with graft dysfunction. We report here the case of a post-renal transplant patient who became pregnant and developed severe anaemia which was not related to iron, B12, or folate deficiency. Her anaemia was successfully treated with EPO with no evidence of rejection or significant graft dysfunction following therapy. She tolerated EPO very well, and there was a successful outcome of the pregnancy. This case has encouraged us to conclude that EPO has a useful role in the treatment of anaemia in pregnant women following renal transplantation.     

Practical applications of electromapping]

The serum "uracil+uridine" level, expressed as uracil, has been measured in 21 cases of vitamin B12 deficiency, in which the serum folate was normal, and compared with the level in 97 normal subjects. The level in the vitamin B12 deficient group (11.9 mumol/1). was significantly lower than in the controls (15.7 mumol/1., P less than 0.005). Nine of the former were complicated by stystemic illness but the clinical and haematological features in the remaining 12 were consistent with the diagnosis of pernicious anaemia in relapse. The serum uracil level in this group was even lower (10.21 mumol/1., P less than 0.01). This finding is unexpected in view of the generally accepted indirect role of vitamine B12 in the methylation of deoxyuridine monophosphate to deoxythymidine monophosphate. Reasons are given for not accepting these results as reflecting the main biochemical lesion in vitamin B12 deficiency. Although they do not give direct support to an impairment in the methylation of deoxyuridine monophosphate, they do not exclude it as they test only one possible metabolic pathway and moreover they could represent the result of more than one action of vitamin B12 on uracil metabolism. They do show, however, that some aspect of uracil metabolism other than methylation is affected in vitamin B12 deficiency in man.     

Methionine synthase deficiency without megaloblastic anaemia

We report findings on a child presenting with neonatal homocystinuria, hypomethioninaemia and severe neurological symptoms, including developmental delay and seizures. Methylmalonic aciduria was not present. The activity of methionine synthase in fibroblasts was severely deficient and formation of methylcobalamin from 57Co labelled cyanocobalamin was very low. The patients cells complemented with those of a cblE patient but not with those of two cblG patients. No biochemical or clinical response to injections of hydroxycobalamin was found. Both off treatment and on betaine and methionine supplementation the patient, at age 8 years, has not developed megaloblastic anaemia. In addition, the patient is homozygous for the C677T polymorphism in the 5,10 methylenetetrahydrofolate reductase (MTHFR) gene and the concomitant existence of this mutation with the methionine synthase defect may prevent folate and thus anaemia. CONCLUSION: We report the lack of megaloblastic anaemia in a patient with severe methionine synthase deficiency who is also homozygous for C677T in MTHFR, hypothesize that the MTHFR polymorphism protects the patient against anaemia and speculate that homozygosity for MTHFR C677T could cause the dissociation between haematological and neurological disease seen in some patients with vitamin B12 deficiency.     

Microcytosis, anisocytosis and the red cell indices in iron deficiency

Red cell volume distribution curves have been used to measure microcytosis and anisocytosis in normal subjects, blood donors and patients with iron deficiency anaemia. These measurements were more sensitive than the conventional red cell indices for detecting blood donors with a low transferrin saturation. Three stages are suggested as iron deficiency progressively interferes with haemopoietic function. Anisocytosis and an increased percentage of microcytic cells are the first haematological abnormalities to occur and at this stage haemoglobin concentration is usually normal and trasferrin saturation less than 32%. At the second stage the MCV and MCH decline, haemoglobin concentration is generally sub-normal, though not below 9 g/dl, and transferrin saturation is usually below 16%. The final stage of iron deficiency is associated with a low MCHC, a haemoglobin concentration below 9 g/dl and a transferrin saturation of less than 16%.     

Pernicious anaemia patients should be screened for iron deficiency during follow up

AIMS: To investigate if patients with pernicious anaemia (PA) are prone to develop iron deficiency and if there is a difference for this manifestation between younger and older age groups. METHODS: Ninety-five patients with pernicious anaemia were evaluated for body iron status at the time of diagnosis and during follow up. Patients were also divided into two groups; younger than 60 (53 patients) and older than 60 (42 patients) years of age. Groups were compared for iron deficiency both at the time of diagnosis and at the end of follow up period. RESULTS: Iron deficiency was a common finding in patients with pernicious anaemia. This deficiency state was more common in the elderly. During B12 therapy, iron deficiency increased in all groups, but the increased rate of iron deficiency was more prominent in the elderly patients. CONCLUSION: Pernicious anaemia is an atrophic gastropathy in which gastric parietal cells no longer produce hydrochloric acid. These patients with achlorhydria demonstrate impaired absorption of iron. On the other hand, with ageing, gastric acidity is already diminished. Iron deficiency commonly accompanies patients with pernicious anaemia and this is more pronounced in the elderly group. We suggest that all patients with pernicious anaemia, especially the elderly, should be screened for iron deficiency both at the beginning and during the follow up.     

Absorption of xylose, glucose, glycine, and folic (pteroylglutamic) acid in Zambian Africans with anaemia

Rates of glucose, glycine, and folic (pteroylglutamic) acid absorption were determined for a 30 cm jejunal segment in vivo, with a double-lumen tube perfusion system, in 10 Zambian African women with a mean haemoglobin concentration of 5-1 (3-5-9-2) g/dl. In four the anaemia was megaloblastic (due to folate deficiency) and in six hypochromic. Perfusion solutions contained (1) glucose 200 mmol/1, (2) glycine 100 mmol/1, and (3) folic acid 250 mug/1. D-xylose absorption after a 25 g oral load was determined in them, and also in 18 additional patients (11 had megaloblastic and seven either hypochromic or haemolytic anaemia). Xylose absorption tests were significantly impaired in the patients with megaloblastic compared with hypochromic or haemolytic anaemia (P less than 0-001); those with untreated megaloblastic anaemia had a greater abnormality than those who had started treatment. Mean glucose, glycine, and folic acid absorption rates were similar to those in controls, and the rates in patients with megaloblastic and hypochromic anaemia were not significantly different. Correlation between glucose absorption rate and xylose excretion was, however, significantly (P less than 0-02). If more patients had been studied it seems likely therefore that a significant impairment of glucose absorption rate in the presence of megaloblastic anaemia would also have been demonstrated. In this investigation anaemia per se did not affect glucose, glycine, or folic acid absorption rates or xylose absorption, but xylose absorption was reduced in patients with megaloblastic anaemia. That abnormality was probably related to folate deficiency, and the underlying mechanism seems to be different from that causing impairment of monosaccharide absorption in patients with systemic bacterial infections. Mean glycine and folic acid absorption rates were not altered by megaloblastic anaemia, indicating that folate deficiency does not cause a general depression of absorption.     

Features of the parasitic system of Ixodid ticks--Borrelia--small mammals in the Russian Northwest

BACKGROUND AND AIMS: Long-term treatment with H(+)-K(+)-adenotriphosphatase (ATPase) inhibitors, such as omeprazole or lansoprazole, for severe gastroesophageal reflux disease is now widely used. Whether such treatment will result in vitamin B12 deficiency is controversial. We studied whether long-term treatment with omeprazole alters serum vitamin B12 levels in patients with Zollinger-Ellison syndrome. METHODS: In 131 consecutive patients treated with either omeprazole (n = 111) or histamine H2-receptor antagonists (n = 20), serum vitamin B12 and folate levels and complete blood counts were determined after acid secretion had been controlled for at least 6 months. These studies were repeated yearly. Serum vitamin B12 and folate levels were correlated with the type of antisecretory drug and the extent of inhibition of acid secretion. RESULTS: The mean duration of omeprazole treatment was 4.5 years, and for H2-receptor antagonists 10 years. Vitamin B12 levels, but not serum folate levels or any hematological parameter, were significantly (P = 0.03) lower in patients treated with omeprazole, especially those with omeprazole-induced sustained hyposecretion (P = 0.0014) or complete achlorhydria (P < 0.0001). In 68 patients with two determinations at least 5 years apart, vitamin B12 levels decreased significantly (30%; P = 0.001) only in patients rendered achlorhydric. The duration of omeprazole treatment was inversely correlated with vitamin B12 levels (P = 0.013), but not folate levels. Eight patients (6%) developed subnormal B12 levels during follow-up. CONCLUSIONS: Long-term omeprazole treatment leads to significant decreases in serum vitamin B12 but not folate levels. These results suggest patients with Zollinger-Ellison syndrome treated with H(+)-K(+)-ATPase inhibitors should have serum vitamin B12 levels monitored. Furthermore, these results raise the possibility that other patients treated chronically with H(+)-K(+)-ATPase inhibitors may develop B12 deficiency.     

Radiofrequency ablation in a patient with tachycardia incorporating triple free wall accessory pathways and atrioventricular nodal reentrant tachycardia

Bone marrow cells from 15 patients with normal deoxyuridine (dU) suppression test results, 3 healthy subjects, and 11 patients with megaloblastic anemia caused by vitamin B12 or folate deficiency were examined for misincorporation of uracil into DNA. Cells were incubated with [5-3H] uridine for 2 hours and their DNA extracted. The DNA was hydrolyzed to deoxyribonucleosides with DNase 1, phosphodiesterase and alkaline phosphatase, and any dU present was separated from other deoxyribonucleosides by Aminex A6 chromatography. The quantity of dU/mg DNA and the radioactivity in the dU peak/mg DNA were then calculated. The results clearly showed that there was markedly increased uracil misincorporation into the DNA of vitamin B12- or folate-deficient marrow cells. Misincorporation of uracil into DNA may be an important biochemical lesion underlying both the megaloblastic change and the ineffectiveness of hematopoiesis in vitamin B12 and folate deficiency.     

The cytotoxic effect of the vitamin B12 inhibitor cyanocobalamin [c-lactam], and a review of other vitamin B12 antagonists

The vitamin B12 antagonist cyanocobalamin [c-lactam] was cytotoxic to cultured human leukemia cells, grown in methylfolate, homocysteine, and vitamin B12, but not in the presence of methionine. Small concentrations of methionine were effective in restoring the growth rate in a dose-dependent fashion, confirming methionine deficiency as the cytotoxic principle. Cyanocobalamin [c-lactam] prevented utilization of the methyl group of methylfolate, but no evidence of folate deficiency developed in long-term culture. High concentrations of non-methylated folate were unable to reverse the cytotoxicity, excluding a methylfolate 'trap' as the cause. Low concentrations of serine in the medium induced transient biochemical megaloblastosis. Cyanocobalamin [c-lactam] caused this to occur earlier, and persist. In high concentrations of serine, the inhibitor caused only transient changes in deoxyuridine suppression. Homocysteine cannot be remethylated without vitamin B12, and condensation with serine is the only other excretory pathway for this toxic amino acid. We hypothesize that impaired DNA synthesis in vitamin B12 deficiency is the result of diverting serine away from thymidylate synthesis, into homocysteine metabolism.     

Vitamin B12 and folate levels and lithium administration in patients with affective disorders

BACKGROUND: It is unclear whether there is a relationship between lithium administration and vitamin B12 metabolism. METHODS: We compared serum B12, serum folate, and red blood cell folate concentrations in patients receiving and not receiving lithium at two Mood Disorders Clinics. As the two centers differed in vitamin assay methods, data were first analyzed separately and then combined. To rule out an in vitro effect of lithium on the assays, we also added varying amounts of lithium to lithium-free blood samples and measured vitamin concentrations. RESULTS: Mean serum B12 concentrations were approximately 20% lower in the lithium than in the nonlithium group at each center. This difference was statistically significant for each center and on combination (two-tailed p = .017, .021, and .0009). The parametric effect size for each center and the combined weighted mean effect size were moderate in magnitude (.605, .523, and .565). There was a nonsignificant trend toward an increased prevalence of assay-defined B12 deficiency in the lithium group at one center only, with no cases in either group at the other center and a nonsignificant combined relative risk. CONCLUSIONS: Our data may represent a lithium-associated decrease in serum B12 concentration. The clinical significance of these findings is not yet clear.     

What are the consequences of the new American guidelines for the diagnosis of diabetes mellitus in The Netherlands?

Anaemia is a commonly encountered medical condition, although associated ophthalmic manifestations are not often sought or recognised. The authors present a case report of a patient with severe vitamin B12 deficiency anaemia with florid retinal changes classical of anaemic retinopathy. A review of the ocular involvement in anaemia is also presented.     

Epithelial cell folate depletion occurs in neoplastic but not adjacent normal colon mucosa

BACKGROUND & AIMS: Restricted folate supply is associated with the development of carcinoma, and folate supplements have a protective effect in colorectal carcinoma. This effect may be mediated through correction of local folate deficiency. The aim of this study was to define the folate content of neoplastic colonic epithelial cells and its relation to that of adjacent normal tissue and circulating levels. METHODS: Epithelial cells were isolated from endoscopic biopsy specimens of normal, adenocarcinoma, adenoma, and adjacent normal colonic mucosa by ion chelation. Intracellular folate levels were determined by microbiological assay. RESULTS: Folate levels in carcinoma specimens were lower than in adjacent normal tissue (P < 0.02). Levels in adenoma epithelial cells were lower than in adjacent normal tissue, although this did not reach statistical significance (P < 0.06). Epithelial cells from normal tissue and mucosa adjacent to tumors and adenomata had similar folate contents. Blood folate and vitamin B12 indices for all groups were normal. CONCLUSIONS: Malignant colon epithelial cells show a relative localized folate deficiency. However, there is no evidence for the occurrence of generalized mucosal folate deficiency. This finding suggests that folate supplements do not inhibit carcinogenesis through correction of localized folate depletion.     

Vitamin nutrition status and homocysteine: an atherogenic risk factor

In an epidemiologic survey, a marginal status of folic acid, vitamin B12, and vitamin B6 was shown to be associated with hyperhomocysteinemia. In a case-control study, a low plasma folate concentration was associated with increased coronary heart disease risk. This phenomenon appears to be mediated by folate's effect on homocysteine metabolism. Both studies offer further perspectives on homocysteine as an atherogenic risk factor.     

Mechanisms by which histamine stimulates rapidly adapting receptors in dog lungs

The relative amounts of folate compounds having 1--3--, 4--, 5-- and 6--glutamic acid residues in the molecule were measured in red blood cells. The results were expressed in relation to methyltetrahydrofolate pentaglutamate (5-glutamic acid residues) which is the analogue present in highest concentration. When the concentration of pentaglutamate is given a value of 100 the relative concentration of folates with 1--3--, 4--, 5-- and 6--glutamic acid residues in control subjects are 48, 48, 100 and 50 respectively. In folate deficiency there is a fall in the relative amount of the short chain glutamic acid chain compounds in addition to having an overall fall in the amount of folate present, the values for 1--3, 4, 5 and 6 chain folates being 16, 14, 100 and 39. By contrast, in untreated pernicious anaemia there is an accumulation of the short chain folates as well as an overall fall in polyglutamate concentration and the relative concentrations were 72, 44, 100 and 30. Folate polyglutamate appears to be the active coenzyme and the reltive amounts of glutamic acid residues may serve to regulate the rate of enzyme activity. In pernicious anaemia the amount of enzyme is reduced and on this hypothesis the regulatory function impaired.     

Significance of lymphadenectomy in renal cancer]

BACKGROUND: This study was done to determine the prevalence of folate deficiency and macrocytosis in patients admitted to the hospital medicine service with alcohol and nonalcohol-related illnesses. METHODS: Two groups of patients, with and without alcohol-related illnesses, were included. Patients were excluded if they received folate therapy, medications known to alter folate concentrations, or if they had an uncertain diagnosis. Complete blood count and erythrocyte folate concentrations were determined from each patient. A Fisher's Exact Test and odds ratio were used to determine the prevalence of macrocytosis and correlation between folate deficiency and macrocytosis in the alcoholic group, respectively. RESULTS: Of the 36 alcoholic patients, 11.1% were folate deficient, and 33.3% had macrocytosis. Only 2 of 12 patients with macrocytosis were folate deficient. No control patient had macrocytosis or folate deficiency. CONCLUSION: The prevalence of folate deficiency among patients with alcohol-related illness is low. There is no correlation detected between macrocytosis and folate deficiency. Our findings suggest that it may be inappropriate to routinely supplement all alcoholics with folic acid, but certainly a small minority may benefit from it.