Cobalamin and folate: recent developments

Phytochemical constituents of Inula britannica as potential inhibitors of dihydrofolate reductase: A strategic approach against shigellosis

Shigella dysenteriae type 1 is considered as an epidemic in different developing countries, which is responsible for the most severe form of bacterial dysentery. It habitually can develop to the most severe form of dysentery with deadly complications. Development of drugs against this disease is still ongoing. Therefore, we used in silico studies to screen the Inula britannica phytocompounds that are used in traditional Chinese and Kampo Medicines and have activities against different diseases. Spinacetin, eupatin, chrysoeriol and diosmetin were successfully passed through the docking-based screening and absorption, distribution, metabolism, excretion and toxicity (ADMET) filtration. The estimated docking affinities of eupatin, diosmetin, chrysoeriol and spinacetin with Dihydrofolate reductase type 1 (DHFR-1), were -6.5, -6.5, -6.3 and -6.1 kcal/mol, respectively. Which were selected for further investigations based on their favorable ADME/Tox characteristics. Then, the 100 ns molecular dynamics (MD) simulations of apo DHFR, spinacetin-DHFR, eupatin-DHFR, chrysoeriol-DHFR and diosmetin-DHFR complexes were carried out. The RMSD fluctuations of the spinacetin, eupatin, chrysoeriol and diosmetin inside the binding site were explored. Subsequently, the effect of binding Spinacetin, eupatin, chrysoeriol and diosmetin upon the dynamic stability of protein was assessed. Additionally, Principal Component Analysis (PCA) and Hydrogen bond analysis was performed for the apo protein and the protein ligand complexes. The results revealed that chrysoeriol and eupatin has good inhibitory effects against DHFR-1 as treatment for Shigella dysenteriae type when compared to other compounds under study. Hence this study implies that eupatin and chrysoeriol are a significantly potential drug like molecule for the treatment of Shigellosis and must undergo validation through in vivo and in vitro experiments.Communicated by Ramaswamy H. Sarma.

[A simple algorithm for anemia]

The author presents a novel algorithm for anaemia based on the erythrocyte haemoglobin content. The scheme is based on the aberrations of erythropoiesis and not on the pathophysiology of anaemia. The hemoglobin content of one erytrocyte is between 28-35 picogram. Any disturbance in hemoglobin synthesis can lead to a lower than 28 picogram hemoglobin content of the erythrocyte which will lead to hypochromic anaemia. In contrary, disturbances of nucleic acid metabolism will result in a hemoglobin content greater than 36 picogram, and this will result in hyperchromic anaemia. Normochromic anemia, characterised by hemoglobin content of erythrocytes between 28 and 35 picogram, is the result of alteration in the proliferation of erythropoeisis. Based on these three categories of anaemia, a unique system can be constructed, which can be used as a model for basic laboratory investigations and work-up of anaemic patients.

Current hematological findings in cobalamin deficiency. A study of 201 consecutive patients with documented cobalamin deficiency

With the introduction of automated assays for measuring serum cobalamin levels over the last decades, the hematological manifestations related to cobalamin deficiency have been changed from the description reported in 'old' studies or textbooks. We studied the hematological manifestations or abnormalities in 201 patients (median age: 67 +/- 6 years) with well-documented cobalamin deficiency (mean serum vitamin B12 levels 125 +/- 47 pg/ml) extracted from an observational cohort study (1995-2003). Assessment included clinical features, blood count and morphological review. Hematological abnormalities were reported in at least two-third of the patients: anemia (37%), leukopenia (13.9%), thrombopenia (9.9%), macrocytosis (54%) and hypegmented neutrophils (32%). The mean hemoglobin level was 10.3 +/- 0.4 g/dl and the mean erythrocyte cell volume 98.9 +/- 25.6 fl. Approximately 10% of the patients have life-threatening hematological manifestations with documented symptomatic pancytopenia (5%), 'pseudo' thrombotic microangiopathy (Moschkowitz; 2.5%), severe anemia (defined as Hb levels <6 g/dl; 2.5%) and hemolytic anemia (1.5%). Correction of the hematological abnormalities was achieved in at least two-thirds of the patients, equally well in patients treated with either intramuscular or oral crystalline cyanocobalamin. This study, based on real data from a single institution with a large number of consecutive patients with well-documented cobalamin deficiency, confirms several 'older' findings that were previously reported before the 1990s in several studies and in textbooks.

Cellular folate vitamer distribution during and after correction of vitamin B12 deficiency: a case for the methylfolate trap

Haematological sequellae of vitamin B12 deficiency are attributed to disturbed DNA synthesis, but vitamin B12 itself plays no role in DNA biosynthesis. A proposed explanation for this is the methylfolate trap hypothesis. This hypothesis states that B12 deficiency impairs overall folate metabolism because 5-methyltetrahydrofolate (5MTHF) becomes metabolically trapped. This trap results from the fact that 5MTHF can neither be metabolised via the methionine synthase pathway, nor can it be reconverted to its precursor, methylenetetrahydrofolate. Other manifestations of the methylfolate trap include cellular folate loss because of shorter 5MTHF polyglutamate chains and global hypomethylation. The methylfolate trap has never been demonstrated in humans. We describe a patient with B12 deficiency who was homozygous for the common methylenetetrahydrofolate reductase (MTHFR) C677T mutation. We analysed red blood cell (RBC) folate vitamers and global DNA methylation by liquid chromatography (LC) in combination with tandem mass spectrometry, and 5MTHF polyglutamate length by LC-electrochemical detection. Compared to post-B12 supplementation values, homocysteine was higher (52.9 micromol/l vs. 16.8 micromol/l), RBC folate was lower (268.92 nmol/l vs. 501.2 nmol/l), the 5MTHF fraction of RBC folate was much higher (94.5% vs. 67.4%), polyglutamate chain length was shorter (more tetra- and pentaglutamates), and global DNA methylation was 22% lower. This is the first time that virtually all features of the methylfolate trap hypothesis have been demonstrated in a human with vitamin B12 deficiency.

A systematic approach to the assessment of erythropoiesis

The pathogenesis of anaemia may be simple or complex and the differential diagnosis can be difficult. An appreciation of the erythropoietic processes is required, together with regular review of investigations, to ensure that appropriate protocols are adopted. The application of tests, which define different facets of erythropoiesis, should be appropriate to the clinical circumstances. In some situations, such as the anaemia of chronic disorders, pregnancy and chronic renal failure, a detailed analysis of erythropoiesis is often required. Guidelines for investigating anaemia due to megaloblastosis or haemoglobinopathy are well established, whereas disturbances of iron metabolism are often difficult to classify. These require a clear distinction between storage and functional iron to differentiate whether the defect is due to readily treatable simple iron deficiency or more complex mechanisms, which do not respond to iron supplementation. Determination of red cell haemoglobin content, reticulocyte analysis and the assay of serum transferrin receptors are new generation parameters developed to address this. Practice pressures and new treatment options have contributed to investigations becoming more complex, especially those of the secondary anaemias, as new tests have become more readily available and often automated. This has resulted in reduced turnaround times and clinical demand has driven request patterns. Initiatives to develop evidence-based anaemia management protocols are welcomed but, wherever possible, should be developed through collaboration between the haematology department and the user unit, and based on available guidelines.

Evaluation of Indicators of Cobalamin Deficiency Defined as Cobalamin-induced Reduction in Increased Serum Methylmalonic Acid

Background: Early detection of cobalamin deficiency is clinically important, and there is evidence that such deficiency occurs more frequently than previously anticipated. However, serum cobalamin and other commonly used tests have limited ability to diagnose a deficiency state.

Methods: We investigated the ability of hematological variables, serum cobalamin, plasma total homocysteine (tHcy), serum and erythrocyte folate, gastroscopy, age, and gender to predict cobalamin deficiency. Patients (n = 196; age range, 17–87 years) who had been referred from general practice for determination of serum cobalamin were studied. Cobalamin deficiency was defined as serum methylmalonic acid (MMA) &gt;0.26 μmol/L with at least 50% reduction after cobalamin supplementation. ROC and logistic regression analyses were used.

Results: Serum cobalamin and tHcy were the best predictors, with areas under the ROC curve (SE) of 0.810 (0.034) and 0.768 (0.037), respectively, but age, intrinsic factor antibodies, and gastroscopy gave additional information.

Conclusions: When cobalamin deficiency is suspected in general practice, serum cobalamin should be the first diagnostic test, and the result should be interpreted in relation to the age of the patient. When a definite diagnosis cannot be reached, MMA and tHcy determination will provide additional discriminative information, but MMA, being more specific, is preferable for assessment of cobalamin status.

Epidermal growth factor as a local mediator of the neurotrophic action of vitamin B(12) (cobalamin) in the rat central nervous system

We have recently demonstrated that the myelinolytic lesions in the spinal cord (SC) of rats made deficient in vitamin B(12) (cobalamin) (Cbl) through total gastrectomy (TG) are tumor necrosis factor-alpha (TNF-alpha)-mediated. We investigate whether or not permanent Cbl deficiency, induced in the rat either through TG or by chronic feeding of a Cbl-deficient diet, might modify the levels of three physiological neurotrophic factors-epidermal growth factor (EGF), vasoactive intestinal peptide (VIP), and somatostatin (SS)-in the cerebrospinal fluid (CSF) of these rats. We also investigated the ability of the central nervous system (CNS) in these Cbl-deficient rats to synthesize EGF mRNA and of the SC to take up labeled Cbl in vivo. Cbl-deficient rats, however the vitamin deficiency is induced, show a selective decrease in EGF CSF levels and an absence of EGF mRNA in neurons and glia in various CNS areas. In contrast, radiolabeled Cbl is almost exclusively taken up by the SC white matter, but to a much higher degree in totally gastrectomized (TGX) rats. Chronic administration of Cbl to TGX rats restores to normal both the EGF CSF level and EGF mRNA expression in the various CNS areas examined. This in vivo study presents the first evidence that the neurotrophic action of Cbl in the CNS of TGX rats is mediated by stimulation of the EGF synthesis in the CNS itself. It thus appears that Cbl inversely regulates the expression of EGF and TNF-alpha genes in the CNS of TGX rats.

Effect of hydrazine upon vitamin B12-dependent methionine synthase activity and the sulphur amino acid pathway in isolated rat hepatocytes

The effect of the industrial chemical, hydrazine (4-12 mM), on methionine synthase (EC 2.1.1.13) activity and levels of the sulphur amino acids homocysteine, cysteine, and taurine as well as GSH were investigated in vitro in isolated rat hepatocyte suspensions and monolayers in order to explain some of the adverse in vivo effects of hydrazine. None of the concentrations of hydrazine were overtly cytotoxic in hepatocyte suspensions (measured as lactate dehydrogenase [LDH] leakage) after 3 hr. However, after 24 hr in culture cells treated with 12 mM, hydrazine showed a significant increase in LDH leakage. Methionine synthase activity was reduced by hydrazine (8 and 12 mM) in suspensions (by 45 and 55%, after 3 hr) and monolayers (12 mM; 65-80% after 24 hr). This was not due to nitric oxide production and the inhibitor of nitric oxide synthase, Nomega-nitro-L-arginine, failed to protect against the hydrazine-induced loss of ATP and GSH and the reduction in urea synthesis at 24 hr. Homocysteine export was increased by 6 mM hydrazine, and total taurine content of treated cells was increased by 12 mM hydrazine. Thus, hydrazine was found to have several important and possibly deleterious effects on some parts of the sulphur amino acid pathway.

The role of folate transport and metabolism in neural tube defect risk

Neural tube defects (NTDs) are common congenital malformations in humans. While etiologically heterogeneous, for the most part they are multifactorial in their pathogenesis, having both genetic and environmental factors contributing to their development. In recent years, there has been a great deal of epidemiologic evidence demonstrating that women who received multivitamins containing folic acid periconceptionally had significantly reduced occurrence and recurrence risks for producing infants with such malformations. Unfortunately, the mechanism(s) underlying the beneficial effects of folic acid is not well understood. In this article, we review the fundamental embryological processes involved in closing the neural tube, the relevant epidemiologic data on folic acid supplementation and relative NTD risk, as well as several recent studies of candidate genes for NTD sensitivity that are involved in folate transport and metabolism.

Expression patterns of folate binding proteins one and two in the developing mouse embryo

Expression patterns of mRNAs coding for the murine folate binding proteins one and two (FBP1 and FBP2) were determined by ribonuclease protection assay (RPA) in highly inbred SWV/Fnn mouse embryos. Tissue samples for RPA were collected from the anterior neural tube throughout the period of embryonic development, as well as from maternal- and fetal-derived term placenta. The peak in expression of FBP1 occurred in term placental tissue compared to neural tissue from any time point. This relative increase in FBP1 expression occurred in placental tissue of embryonic, as opposed to maternal, origin. The expression of FBP2 did not differ statistically between any timepoints or tissues examined. Expression of both FBP1 and FBP2 was slightly elevated throughout the period of neural tube closure (Gestational Days 8 through 10), although not significantly. These data fit the anticipated expression patterns of the homologues of human folate receptors alpha and beta, thus helping to resolve some of the confusion secondary to the nomenclature associated with this gene family. Furthermore, the expression of these two genes in the neural tube closure stage of embryological development supports their involvement in regulatory events related to normal neural tube morphogenesis.

The effect of ethanol and its metabolites upon methionine synthase activity in vitro

The association of alcoholism with macrocytic anaemia has lead to investigation of the role of cobalamin-dependent methionine synthase in mediating alcohol toxicity. Several studies have found that long-term ingestion of large quantities of ethanol causes inhibition of liver methionine synthase activity in vivo: however, ethanol has not been found to inhibit the enzyme directly. The effect of ethanol and its breakdown products, acetate and acetaldehyde, on highly purified rat liver methionine synthase was tested in vitro. Enzyme activity was not inhibited by ethanol or acetate. Acetaldehyde was found to inhibit methionine synthase activity, with an apparent IC50 of 2 mM. The reported inhibition by acetaldehyde was found to become irreversible over time. Acetaldehyde-induced inhibition of liver methionine synthase activity is thus proposed as the most likely explanation of the reported in vivo effect of ethanol upon methionine synthase.

Cobalamin

Cobalamin (vitamin B12) is an essential nutrient derived exclusively from bacterial sources. It is an essential cofactor for three known enzymatic reactions. Untreated deficiency, caused by either the autoimmune disease pernicious anemia or nutritional lack, results in a macrocytic anemia and/or subacute combined degeneration of the spinal cord and is eventually fatal. Cobalamin in serum is bound to two proteins, transcobalamin and haptocorrin. The former is responsible for the essential delivery of cobalamin to most tissues. Inadequate tissue availability of cobalamin results in increased concentration of methylmalonic acid and homocyst(e)ine due to inhibition of methylmalonyl-CoA mutase and methionine synthase, respectively. Strict vegetarians have long been known to be at risk of cobalamin deficiency, which develops insidiously over many years. It is now clear that a significant number of the elderly and HIV-positive individuals are also at increased risk of deficiency. Any individual with reduced ability to split cobalamin from food-protein may also become deficient even though intrinsic factor is present. Diagnosis of cobalamin deficiency has frequently relied on total serum cobalamin and the Schilling test. Newer approaches such as analysis of methylmalonic acid, homocyst(e)ine, holotranscobalamin, anti-intrinsic factor antibodies, and serum gastrin may provide more cost-effective testing, as well as identify those with a covert deficiency.

Morphology, biology and biochemistry of cobalamin- and folate-deficient bone marrow cells

B12- or folate-deficient haemopoietic cells display abnormalities in their morphology under both the light and electron microscope, their cell kinetics and their capacity to synthesize protein. These abnormalities are maximal in the last dividing cell class and in non-dividing cells, presumably because B12 and folate uptake is largely confined to the most immature erythroid and granulocyte precursors. In patients with moderate or severe anaemia due to B12 or folate deficiency, erythropoiesis is markedly ineffective; intramedullary cell death occurs mainly in the early and late polychromatic megaloblasts. The damaged erythroblasts appear to display neoantigens or normally-hidden antigens at their cell surface and these react with naturally occurring antibodies. The opsonised erythroblasts are then recognised by macrophages via their IgG-Fc receptors and phagocytosed. Marrow cells from B12- or folate-deficient patients show a subnormal suppression of 3H-thymidine incorporation after pre-incubation with nonradioactive deoxyuridine, suggesting that such cells suffer from an impairment of the 5,10-methylene-THF-dependent methylation of deoxyuridylate to thymidylate. However, the exact mechanism by which B12 deficiency causes a reduced supply of this folate coenzyme is uncertain. Methylcobalamin is required for the 5-methyl-THF-dependent methylation of homocysteine to methionine and an impairment of this reaction will result in both reduced conversion of 5-methyl-THF to THF and in reduced methionine synthesis. There is controversy as to whether the reduced supply of THF or methionine is responsible for the reduced availability of 5,10-methylene-THF. Currently, the balance of evidence favours the hypothesis that the reduced supply of methionine leads to reduced synthesis of formyl-THF and, eventually, of 5,10-methylene-THF. Despite the evidence for impaired thymidylate synthesis, the duration of the S phase of megaloblasts appears to be normal or only modestly increased. Data on rates of DNA strand elongation are inconsistent, with subnormal rates reported in PHA-stimulated B12- or folate-deficient lymphocytes and normal rates in B12- or folate-deficient bone marrow cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Folate metabolism and neural tube defects: a review

The importance of folate in normal fetal development and wellbeing has been recognized only during the past three decades and knowledge concerned is still far from complete. In man, folate acts as a substrate in the transfer of one-carbon moieties and thereby, plays an essential role in the synthesis of several amino acids such as methionine and nucleic acids. Consequently, folate requirements are related to the amount of tissue growth. Epidemiological, clinical and teratological research showed that this B-vitamin is particularly involved in the prevention and pathogenesis of neural tube defects. Therefore, in this review the metabolism of folate has been outlined. Furthermore, the characteristics of the various genically determined folate 'deficiencies' as well as a possible biochemical explanation of the relationship between folate and neural tube defects are being discussed. Finally, the new recommendations launched in November 1993 by the Dutch Health Council as well as the Food and Nutrition Council with regard to folate supplementation in the prevention of neural tube defects are presented.

S-adenosylmethionine levels in psychiatric and neurological disorders: a review

INTRODUCTION

S-adenosylmethionine (SAMe) is an important methyl donor in over 35 methylation reactions involving DNA, proteins, phospholipids and catechol- and indole- amines.

MATERIAL AND METHODS

This article reviews the studies that have examined brain and blood levels of SAMe in several psychological, neurological and metabolic disorders.

RESULTS

Although studies have found no consistent changes in whole blood SAMe levels in psychiatric patients, other investigators have found low cerebrospinal fluid (CSF) SAMe levels in patients with neurological disorders such as Alzheimer's dementia, subacute combined degeneration of the spinal cord (SACD), and HIV-related neuropathies, as well as in patients with metabolic disorders such as 5, 10-CH2-H4 folate reductase deficiency.

CONCLUSION

Intravenous or oral administration of SAMe thus represents a possible treatment for these neurological and metabolic disorders.

The biochemical basis of cobalamin deficiency

OBJECTIVE

In this report, our goal was to summarize the current knowledge of the biochemical basis for the impaired DNA synthesis and neuropathy associated with vitamin B12 deficiency.

MATERIAL AND METHODS

We reviewed the pertinent literature and our clinical experience with cobalamin deficiency.

RESULTS

Studies have established that the megaloblastic hematopoiesis associated with vitamin B12 and folate deficiency is secondary to impaired DNA synthesis. Two mechanisms of impairment of DNA synthesis have been proposed: the "methylfolate trap hypothesis" and the "formate starvation hypothesis." One possibility is that both hypotheses may be contributory--that is, incoming dietary folate may be inaccessible for polyglutamation in accordance with the methylfolate trap hypothesis, whereas the formate starvation hypothesis may explain the failure to use already polyglutamated forms of folate.

CONCLUSION

Although the pathophysiologic mechanisms of vitamin B12 and folate deficiency are not completely understood, nutritional anemias offer suitable models for the study of the biochemical basis of disease.

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.