Metabolite assays in cobalamin and folate deficiency

Vitamin B12 status and hyperhomocysteinemia in patients with Rheumatoid arthritis treated with methotrexate and folic acid

BACKGROUND

Rheumatoid arthritis (RA) is an inflammatory arthritis in which the immune system targets synovial joints. Methotrexate serves as the mainstay of treatment for RA due to its efficacy. However, patients treated with methotrexate are uniquely at risk for vitamin B12 deficiency and hyperhomocysteinemia due to coincident disease risk factors and the fact that methotrexate use is associated with malabsorption. The objective of this study was to assess for vitamin B12 deficiency among patients with RA treated with methotrexate and folic acid.

METHODS

This cross-sectional study included 50 patients with RA treated with methotrexate and folic acid and 49 patients with RA treated with other therapies. Patients were matched by age, sex, race, renal function, and disease activity. We compared plasma vitamin B12, methylmalonic acid, and homocysteine levels between these two groups utilizing quantitative and categorical analyses.

RESULTS

Thirty-seven (74%) RA patients on methotrexate and folic acid had elevated plasma homocysteine levels compared with only 27 (55%) RA patients receiving other therapies (P < 0.05). The proportion of patients with low vitamin B12 and high methylmalonic acid levels did not differ between the two groups.

CONCLUSIONS

Our data show high plasma homocysteine levels among RA patients treated with methotrexate and folic acid. While plasma vitamin B12 levels were similar between the two groups, high plasma homocysteine is also a sensitive marker of vitamin B12 deficiency. Additional studies should evaluate for the presence of clinical features of vitamin B12 deficiency and hyperhomocysteinemia among RA patients treated with methotrexate and folic acid.

Causes and Risk Factors of Vitamin B12 Deficiency at the Bookends of Life, From Infancy to Old Age

The causes and risk factors of vitamin B12 deficiency are many and varied. Importantly, they vary considerably across the lifespan, from infancy to old age. The complexity of the physiology of vitamin B12 bespeaks the myriad of possible causes of deficiency and possible disruptions of its functional integrity. These lead ultimately to the pathobiological effects witnessed in deficiency of this fascinating micronutrient. This brief overview of the multiplicity of mechanisms that can result in vitamin B12 deficiency, and the panoply of its manifestations explores the underlying reasons for the protean presentations of the disease. As the human organism progresses through the chronology and milestones of age, various susceptibility factors arise resulting from the interplay of environmental and genetic factors. Acting independently and in concert, these factors produce the common denominator of vitamin B12 deficiency. However, the rate at which such deficiency develops and the way in which it presents clinically vary widely, subject to such influences as genetic variability, end-organ susceptibility, and concomitant micronutrient status. Some examples of unusual cases of vitamin B12 deficiency are described. Much has been learned about the last of the numbered vitamins in almost a century. Much yet remains to be discovered.

Vitamin B12 deficiency

Of the water-soluble vitamins, vitamin B12 (B12) has the lowest daily requirement. It also has several unique properties including a complex pathway for its absorption and assimilation requiring intact gastric and terminal small intestinal function, an enterohepatic pathway, and several dedicated binding proteins and chaperons. The many causes of B12 deficiency include malabsorption and defects in cellular delivery and uptake, as well as limited dietary intake. B12 is required as a cofactor for only two reactions in humans, the cytosolic methionine synthase reaction and the mitochondrial methymalonyl CoA mutase reaction. Disruption of either of these reactions gives rise to B12 deficiency. Although more common with advancing age, because of the higher prevalence of malabsorptive disorders in the elderly, B12 deficiency is widely distributed across all age groups particularly where food insecurity occurs. The consequences and severity of B12 deficiency are variable depending on the degree of deficiency and its duration. Major organ systems affected include the blood, bone marrow and nervous system. Megaloblastic anemia results from a defect in thymidine and therefore DNA synthesis in rapidly dividing cells. Nervous system involvement is varied, some of which results from defective myelin synthesis and repair. Cognitive impairment and psychosis may also occur. Diagnosis of B12 deficiency rests on clinical suspicion followed by laboratory testing, which consists of a panel of tests, that together provide clinically reliable predictive indices. B12 metabolism and deficiency is closely intertwined with folate, another B-vitamin. This chapter explores the various aspects of a unique and fascinating micronutrient.

Vitamin B Complex Deficiency After Roux-en-Y Gastric Bypass and Sleeve Gastrectomy-a Systematic Review and Meta-Analysis

Bariatric surgery, although an effective method, still has complications, like nutritional deficiencies. Our aim was to summarize the evidence on the frequency of complex B vitamin deficiencies in studies comparing Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). We included 25 studies for qualitative synthesis and 21 studies for quantitative synthesis. Relevant data was extracted, including proportion of patients with deficiency and mean serum vitamin values in 3 different timeframes. B12 and folate were the most prevalent deficiencies. B12 deficiency was more common after RYGB and folate serum mean levels were higher after RYGB. SG causes less nutrient deficiency and is therefore a better technique from this point of view. More studies are needed on B2, B3, and B6 vitamins to draw better conclusions.

Pernicious anemia: Pathophysiology and diagnostic difficulties

Pernicious anemia (PA) is the most common cause of vitamin B12 (cobalamin) deficiency anemia in the world. It is an autoimmune disease, comprising of salient features of autoimmune chronic atrophic gastritis (CAG) and cobalamin deficiency (CD). Although the anemia was first described as pernicious, it may well be controlled with vitamin B12 replacement. The onset and progression of PA is often insidious. Alternatively, patients may have no anemic symptoms since they become acclimatized to the subtle nature of the disease. Oftentimes, there is a possibility that the underlying disease may be missed unless a full blood count (FBC) is investigated, leading to hindrance in the treatment journey. Diagnostic challenges remain tangible for many practicing clinicians, since there is lack of reliable cobalamin assays to diagnose CD as well as clinical mimics, which simulate many other hematological conditions, such as myelodysplastic syndrome, acute leukemia, sideroblastic anemias, bone marrow failure states, thrombotic microangiopathy, and thromboembolism. Moreover, prompt recognition of the symptoms of CD is also vital, because some neurologic sequalae may become irreversible despite replenishing cobalamin. Herein, we discuss a literature review on the pathophysiology, challenging clinical presentations and diagnostic difficulties of PA. Since the cobalamin replacement therapy for PA is straightforward, it will not be discussed in this review.

Hyperhomocysteinemia is an emerging comorbidity in ischemic stroke

Hyperhomocysteinemia or systemic elevation of the amino acid homocysteine is a common metabolic disorder that is considered to be a risk factor for ischemic stroke. However, it is still unclear whether predisposition to hyperhomocysteinemia could contribute to the severity of stroke outcome. This review highlights the advantages and limitations of the current rodent models of hyperhomocysteinemia, describes the consequence of mild hyperhomocysteinemia on the severity of ischemic brain damage in preclinical studies and summarizes the mechanisms involved in homocysteine induced neurotoxicity. The findings provide the premise for establishing hyperhomocysteinemia as a comorbidity for ischemic stroke and should be taken into consideration while developing potential therapeutic agents for stroke treatment.

Relationship between serum B12 concentrations and mortality: experience in NHANES

BACKGROUND

There is conflicting evidence in the literature on the association between (elevated) serum B12 concentrations and subsequent disease or mortality. We evaluated in the NHANES general population the association of serum B12 concentrations as well as vitamin B12 supplement intake with all-cause, cardiovascular, and cancer-related mortality, while taking into account demographic and lifestyle factors and significant other diseases which are known to be associated with poorer outcome.

METHODS

The main outcomes of our study were all-cause mortality, cardiovascular mortality, and cancer-related mortality. Mortality status and cause of death were determined by NHANES-linked National Death Index public access files through December 31, 2015. The association of serum B12 concentrations and vitamin B12 supplement intake with mortality was assessed with Cox proportional hazard (PH) models, with adjustment for a number of relevant demographic and lifestyle factors and comorbidity.

RESULTS

The final study population of 24,262 participants had a mean age of 48 (SD 19) years; 50.1% were males. The median follow-up duration was 109 months (range 1-201 months). On the census day of December 31, 2015, 3023 participants were determined as deceased (12.5%). The fully adjusted Cox PH model indicated that low serum B12 concentrations < 140 pmol/l were associated with a small increase in all-cause (hazard ratio, HR 1.39, 95% CI 1.08-1.78, p = 0.011) and cardiovascular (HR 1.64, 95% CI 1.08-2.47, p = 0.020) mortality. Similarly, high serum B12 concentrations > 700 pmol/l were associated with an increase in cardiovascular mortality only (HR 1.45, 95% CI 1.01-2.06, p = 0.042). Participants with a diagnosis of hypertension, dyslipidemia, CVD, and cancer more frequently used vitamin B12-containing supplements than those without these diagnoses. We could not demonstrate an association between vitamin B12 supplement intake and mortality, when adjusted for comorbidity.

CONCLUSIONS

In the general population of NHANES, low serum B12 concentrations were associated with a moderate increase in all-cause mortality. There was a small but significant increase in cardiovascular mortality in the groups with low or high serum B12. High intake of vitamin B12 in the form of supplements was not associated with any adverse effect on mortality and therefore can be regarded as safe.

Low Vitamin B12 and Lipid Metabolism: Evidence from Pre-Clinical and Clinical Studies

Obesity is a worldwide epidemic responsible for 5% of global mortality. The risks of developing other key metabolic disorders like diabetes, hypertension and cardiovascular diseases (CVDs) are increased by obesity, causing a great public health concern. A series of epidemiological studies and animal models have demonstrated a relationship between the importance of vitamin B12 (B12) and various components of metabolic syndrome. High prevalence of low B12 levels has been shown in European (27%) and South Indian (32%) patients with type 2 diabetes (T2D). A longitudinal prospective study in pregnant women has shown that low B12 status could independently predict the development of T2D five years after delivery. Likewise, children born to mothers with low B12 levels may have excess fat accumulation which in turn can result in higher insulin resistance and risk of T2D and/or CVD in adulthood. However, the independent role of B12 on lipid metabolism, a key risk factor for cardiometabolic disorders, has not been explored to a larger extent. In this review, we provide evidence from pre-clinical and clinical studies on the role of low B12 status on lipid metabolism and insights on the possible epigenetic mechanisms including DNA methylation, micro-RNA and histone modifications. Although, there are only a few association studies of B12 on epigenetic mechanisms, novel approaches to understand the functional changes caused by these epigenetic markers are warranted.

Fallacies of clinical studies on folic acid hazards in subjects with a low vitamin B12 status

A 2016 plea for revision of the 1 mg/day upper level of folic acid intake prompted us to comprehensively review the 1945-2017 literature on folic acid hazards in subjects with low cyanocobalamin. The concept of folic acid treatment 'masking' the anemia in undiagnosed cyanocobalamin deficiency, thereby delaying the diagnosis of neuropathy, does not account for the dissociation between the deficiency's hematologic and neurologic manifestations. Possible risks of this concept were addressed by 1963-1971 FDA rulings, classifying all folic acid preparations as prescription-only drugs, delivering ≤1 mg daily. The neuropathy in folic acid trials for 'pernicious anemia' is due to the singular use of folic acid-neuropathy improved or disappeared with replacement of folic acid by liver extract or cyanocobalamin. The hypothesis that cognitive impairment in 'subclinical' cyanocobalamin deficiency is folate-mediated is untenable. Of 6 papers specifically investigating this, none could prove that increased cognitive impairment was related to high folate intake. This review fully supports the safety of the 1 mg/day upper level for folic acid intake.

Biomarkers of Nutrition for Development (BOND): Vitamin B-12 Review

This report on vitamin B-12 (B12) is part of the Biomarkers of Nutrition for Development (BOND) Project, which provides state-of-the art information and advice on the selection, use, and interpretation of biomarkers of nutrient exposure, status, and function. As with the other 5 reports in this series, which focused on iodine, folate, zinc, iron, and vitamin A, this B12 report was developed with the assistance of an expert panel (BOND B12 EP) and other experts who provided information during a consultation. The experts reviewed the existing literature in depth in order to consolidate existing relevant information on the biology of B12, including known and possible effects of insufficiency, and available and potential biomarkers of status. Unlike the situation for the other 5 nutrients reviewed during the BOND project, there has been relatively little previous attention paid to B12 status and its biomarkers, so this report is a landmark in terms of the consolidation and interpretation of the available information on B12 nutrition. Historically, most focus has been on diagnosis and treatment of clinical symptoms of B12 deficiency, which result primarily from pernicious anemia or strict vegetarianism. More recently, we have become aware of the high prevalence of B12 insufficiency in populations consuming low amounts of animal-source foods, which can be detected with ≥1 serum biomarker but presents the new challenge of identifying functional consequences that may require public health interventions.

Evaluation of diffusion tensor imaging changes and neurocognitive effects of asymptomatic vitamin B12 deficiency

Vitamin B12 plays an important role in the mechanisms which are responsible for myelinization in the central nervous system. It can particularly lead to hematological and neuropsychiatric symptoms when serum levels fall due to insufficient intake with diet or absorption problems. The purpose of this study was to show the cognitive effects in vitamin B12 deficiency cases that have not reached clinical symptom level using neuropsychological tests, and to show possible cerebral neuronal damage using diffusion tensor imaging (DTI) method. A total of 62 asymptomatic vitamin B12 deficiency patients and 40 healthy subjects were included in the study and both groups were subjected to Standardized Mini-Mental State Examination, Montreal Cognitive Assessment Test, Rey Auditory Verbal Learning Test, forward and backward digit span (WMS-R forward and backward), Visual Reproduction Subtest (WMS-III), Category Fluency Test, Trail Making (Trail A-B) (21) and Similarities (BENZ) tests. DTI examinations were performed on both groups. Patient group was determined to get lower scores in all neuropsychological tests compared to control group. In DTI examination, a significant decrease in FA values of bilateral hippocampus and a prominent increase in apparent diffusion coefficient (ADC) values were determined in the patient group compared to control group. In this study, it was determined that there was microstructural damage in the brain in the presence of vitamin B12 deficiency even in the asymptomatic period, and the patients revealed cognitive decline. In accordance with this result, early treatment of the easily diagnosed and treated vitamin B12 deficiency may prevent possible irreversible damage in the future.

Vitamin B12 deficiency

Vitamin B₁₂ (B12; also known as cobalamin) is a B vitamin that has an important role in cellular metabolism, especially in DNA synthesis, methylation and mitochondrial metabolism. Clinical B12 deficiency with classic haematological and neurological manifestations is relatively uncommon. However, subclinical deficiency affects between 2.5% and 26% of the general population depending on the definition used, although the clinical relevance is unclear. B12 deficiency can affect individuals at all ages, but most particularly elderly individuals. Infants, children, adolescents and women of reproductive age are also at high risk of deficiency in populations where dietary intake of B12-containing animal-derived foods is restricted. Deficiency is caused by either inadequate intake, inadequate bioavailability or malabsorption. Disruption of B12 transport in the blood, or impaired cellular uptake or metabolism causes an intracellular deficiency. Diagnostic biomarkers for B12 status include decreased levels of circulating total B12 and transcobalamin-bound B12, and abnormally increased levels of homocysteine and methylmalonic acid. However, the exact cut-offs to classify clinical and subclinical deficiency remain debated. Management depends on B12 supplementation, either via high-dose oral routes or via parenteral administration. This Primer describes the current knowledge surrounding B12 deficiency, and highlights improvements in diagnostic methods as well as shifting concepts about the prevalence, causes and manifestations of B12 deficiency.

Behavioral alterations are associated with vitamin B12 deficiency in the transcobalamin receptor/CD320 KO mouse

Vitamin B12 (cobalamin) deficiency is prevalent worldwide and causes megaloblastic anemia and neurologic deficits. While the anemia can be treated, the neurologic deficits can become refractive to treatment as the disease progresses. Therefore, timely intervention is critical for a favorable outcome. Moreover, the metabolic basis for the neuro-pathologic changes and the role of cobalamin deficiency in the pathology still remains unexplained. Using a transcobalamin receptor / CD320 knockout mouse that lacks the receptor for cellular uptake of transcobalamin bound cobalamin, we aimed to determine whether cobalamin deficiency in the central nervous system produced functional neurologic deficits in the mouse that would parallel those observed in humans. Our behavioral analyses indicate elevated anxiety and deficits in learning, memory and set-shifting of a spatial memory task in the KO mouse. Consistent with the behavioral deficits, the knockout mouse shows impaired expression of the early phase of hippocampal long-term potentiation along with reduced expression of GluR1, decreased brain mass and a significant reduction in the size of nuclei of the hippocampal pyramidal neurons. Our study suggests that the CD320 knockout mouse develops behavioral deficits associated with cobalamin deficiency and therefore could provide a model to understand the metabolic and genetic basis of neuro-pathologic changes due to cobalamin deficiency.

Vitamin B12 deficiency from the perspective of a practicing hematologist

B₁₂ deficiency is the leading cause of megaloblastic anemia, and although more common in the elderly, can occur at any age. Clinical disease caused by B₁₂ deficiency usually connotes severe deficiency, resulting from a failure of the gastric or ileal phase of physiological B₁₂ absorption, best exemplified by the autoimmune disease pernicious anemia. There are many other causes of B₁₂ deficiency, which range from severe to mild. Mild deficiency usually results from failure to render food B₁₂ bioavailable or from dietary inadequacy. Although rarely resulting in megaloblastic anemia, mild deficiency may be associated with neurocognitive and other consequences. B₁₂ deficiency is best diagnosed using a combination of tests because none alone is completely reliable. The features of B₁₂ deficiency are variable and may be atypical. Timely diagnosis is important, and treatment is gratifying. Failure to diagnose B₁₂ deficiency can have dire consequences, usually neurological. This review is written from the perspective of a practicing hematologist.

Megaloblastic Anemias: Nutritional and Other Causes

Vitamin B₁₂ and folate deficiencies are major causes of megaloblastic anemia. Causes of B₁₂ deficiency include pernicious anemia, gastric surgery, intestinal disorders, dietary deficiency, and inherited disorders of B₁₂ transport or absorption. The prevalence of folate deficiency has decreased because of folate fortification, but deficiency still occurs from malabsorption and increased demand. Other causes include drugs and inborn metabolic errors. Clinical features of megaloblastic anemia include anemia, cytopenias, jaundice, and megaloblastic marrow morphology. Neurologic symptoms occur in B₁₂ deficiency, but not in folate deficiency. Management includes identifying any deficiency, establishing its cause, and replenishing B₁₂ or folate parenterally or orally.

Relationship Between the Levels of Holotranscobalamin and Vitamin B12 in Children

The purpose of this study was to evaluate the relationship between the plasma holoTC and serum vitamin B₁₂ in children and to identify a cutoff cobalamin values according to holoTC. One hundred and fifty-five children were enrolled into the study. All children were evaluated for hemoglobin, vitamin B₁₂, folate, ferritin and holoTC levels. Children were grouped as with low vitamin B₁₂ level (≤200 pg/mL, group I) and normal vitamin B₁₂ (>200 pg/mL, group II). Serum vitamin B₁₂, and holoTC levels were performed in each patient in the study. In 101 patients with low vitamin B₁₂ (group I) the mean holoTC was 21.74 ± 1.14 pmol/L. In 54 children with normal vitamin B₁₂ (group II) mean holoTC was 44.0 ± 2.7 pmol/L (p < 0.01). A ROC curve analysis was performed to delineate the optimum cut-off point for vitamin B₁₂ level and it was found to be 165 pg/mL with a sensitivity of 70% and specificity of 74%; the area under curve was 0.783 (p < 0.01). Our study displayed a positive correlation between vitamin B₁₂ and holoTC, and defined an optimum cutoff value for vitamin B₁₂ as 165 pg/mL. Further studies using the markers both MMA, tHcy and holoTC to confirm the findings are needed.

Early markers of occult megaloblastosis for low-cost detection of hyperhomocysteinemia in patients with ischaemic stroke: preventive approach for primary health care

Recent studies have focussed on the association between elevated homocysteine levels with megaloblastic changes and thromboembolic events, but the relationship between occult megaloblastosis (with normal haemoglobin levels) and ischaemic stroke has not been widely explored. The objective of this study is to establish a simple and economical marker for the detection of occult megaloblastosis at the community health care level in developing countries. A hundred patients who met the inclusion criteria were studied. At the 5% level of significance, the levels of cobalamin and folate were significantly lower, while the number of hypersegmented neutrophils on the peripheral smear was higher in patients from Group A (70 patients with high homocysteine) compared with the patients in Group B (30 patients with normal homocysteine). Forty-five (64.2%) of the 70 patients in Group A showed hypersegmentation of neutrophils in the peripheral smear. The high cost and difficulty in performing the vitamin assays limit their use as early markers of megaloblastosis. Hence, we conclude that in developing countries, the detection of hypersegmented neutrophils can be used at the primary healthcare level for early diagnosis of occult megaloblastosis, so that early therapeutic interventions with vitamins can prevent attacks of hyperhomocysteinemia-induced ischaemic stroke.

CdTe quantum dot as a fluorescence probe for vitamin B(12) in dosage form

We here report the CdTe quantum dot (CdTe QDs)-based sensor for probing vitamin B12 derivatives in aqueous solution. In this paper, simple and sensitive fluorescence quenching measurements has been employed. The Stern-Volmer constant (KSV), quenching rate constant (kq) and binding constant (K) were rationalized from fluorescence quenching measurement. Furthermore, the fluorescence resonance energy transfer (FRET) mechanism was discussed. This method was applicable over the concentration ranging from 1 to 14μg/mL (VB12) with correlation coefficient of 0.993. The limit of detection (LOD) of VB12 was found to be 0.15μg/mL. Moreover, the present approach opens a simple pathway for developing cost-effective, sensitive and selective QD-based fluorescence sensors/probes for biologically significant VB12 in pharmaceutical sample with mean recoveries in the range of 100-102.1%.

Cellular uptake of cobalamin: transcobalamin and the TCblR/CD320 receptor

Cellular uptake of cobalamin is facilitated by a receptor-mediated endocytosis process involving transcobalamin, a plasma protein that binds cobalamin and a cell surface receptor that specifically binds transcobalamin saturated with cobalamin. Intracellular Cbl concentration is maintained by modulating the expression of the receptor, which is cell cycle associated with highest expression in actively proliferating cells and an efflux system that shunts the excess cobalamin out of the cells for mobilization to other tissues where it is most needed. This review describes the process, proteins involved and genes encoding these proteins.

Cobalamin deficiency

Cobalamin (Cbl, vitamin B12) consists of a corrinoid structure with cobalt in the centre of the molecule. Neither humans nor animals are able to synthesize this vitamin. Foods of animal source are the only natural source of cobalamin in human diet. There are only two enzymatic reactions in mammalian cells that require cobalamin as cofactor. Methylcobolamin is a cofactor for methionine synthase. The enzyme methylmalonyl-CoA-mutase requires adenosylcobalamin as a cofactor. Therefore, serum concentrations of homocysteine (tHcy) and methylmalonic acid (MMA) will increase in cobalamin deficiency. The cobalamin absorption from diet is a complex process that involves different proteins: haptocorrin, intrinsic factor and transcobalamin (TC). Cobalamin that is bound to TC is called holotranscobalamin (holoTC) which is the metabolically active vitamin B12 fraction. HoloTC consists 6 and 20% of total cobalamin whereas 80% of total serum cobalamin is bound to another binding protein, haptocorrin. Cobalamin deficiency is common worldwide. Cobalamin malabsorption is common in elderly subjects which might explain low vitamin status. Subjects who ingest low amount of cobalamin like vegetarians develop vitamin deficiency. No single parameter can be used to diagnose cobalamin deficiency. Total serum cobalamin is neither sensitive nor it is specific for cobalamin deficiency. This might explain why many deficient subjects would be overlooked by utilizing total cobalamin as status marker. Concentration of holotranscobalamin (holoTC) in serum is an earlier marker that becomes decreased before total serum cobalamin. Concentrations of MMA and tHcy increase in blood of cobalamin deficient subjects. Despite limitations of these markers in patients with renal dysfunction, concentrations of MMA and tHcy are useful functional markers of cobalamin status. The combined use of holoTC and MMA assays may better indicate cobalamin status than either of them. Because Cbl deficiency is a risk factor for neurodegenerative diseases an early diagnosis of a low B12 status is required which should be followed by an effective treatment in order to prevent irreversible damages.

Indicators for assessing folate and vitamin B-12 status and for monitoring the efficacy of intervention strategies

Deficiencies of folate or of vitamin B-12 are widespread and constitute a major global burden of morbidity that affect all age groups. Detecting or confirming the presence of folate or vitamin B-12 deficiency and distinguishing one from the other depends, ultimately, on laboratory testing. Tests to determine the presence of folate or vitamin B-12 deficiency are used singly or in combination to establish the nutritional status and prevalence of deficiencies of the vitamins in various populations. The efficacy of interventions through the use of fortification or supplements is monitored by using the same laboratory tests. Tests currently in use have limitations that can be either technical or have a biological basis. Consequently, each single test cannot attain perfect sensitivity, specificity, or predictive value. Laboratory indicators of vitamin B-12 or folate status involve the measurement of either the total or a physiologically relevant fraction of the vitamin in a compartment such as blood. Thus, assays to measure vitamin B-12 or folate in plasma or serum as well as folate in red blood cells are in widespread use, and more recently, methods to measure vitamin B-12 associated with the plasma binding protein transcobalamin (holotranscobalamin) have been developed. Alternatively, concentrations of surrogate biochemical markers that reflect the metabolic function of the vitamin can be used. Surrogates most commonly used are plasma homocysteine, for detection of either vitamin B-12 or folate deficiency, and methylmalonic acid for detection of vitamin B-12 deficiency. The general methods as well as their uses, indications, and limitations are presented.

Whole blood propionylcarnitine in newborns with orofacial cleft

Orofacial clefts are thought to be determined by the interplay of genetic and environmental factors. Experiments on animals demonstrated that vitamin B12 supplemented diets antagonize selected teratogens during palatogenesis. Increased propionylcarnitine in neonates is regarded as a marker of maternal vitamin B12 deficiency. The retrospective study was undertaken to determine whether increased propionylcarnitine in newborns is associated with orofacial clefts. Fifty-two newborns with isolated cleft lip with or without cleft palate (CLP) and 107 control newborns without congenital anomalies were investigated. Whole blood propionylcarnitine concentrations were measured using tandem mass spectrometry. The mean concentrations of propionylcarnitine in newborns with clefts and controls were 2.82±1.06µmolL(-1) and 2.68±0.94µmolL(-1), respectively. T-test for equality of means did not confirm any significant differences between both groups (P=0.381). Deficiency of vitamin B12 with metabolic disturbances seems not to be a risk factor for CLP in the investigated group of patients.

Vitamin B12 deficiency, hyperhomocysteinemia and thrombosis: a case and control study

This study aimed at assessing the relationship between thrombosis, hyperhomocysteinemia and vitamin B12 deficiency using a case-control study carried out in 326 patients with thrombosis (case group) and 351 patients from the same hospital (control group). Apart from the classic risk factors, a number of hematological variables were evaluated, including serum vitamin B12 (B12), red cell folate (RCF), and serum homocysteine (Hcy). An evaluation of serum methylmalonic acid (MMA) and a clinical study were carried out to investigate B12 pathology. Results of univariate analysis demonstrated decreased B12 levels in thrombosis (Student's t test, p < 0.0001). Vitamin B12 below 200 pmol/l (LB200) or below 150 pmol/l (LB150), and red cell folate below 600 nmol/l were found in 17.2, 8.6, and 2.2% of cases with thromboembolism, respectively. An increase in Hcy was detected in 86 cases with thrombosis (26.3%). An abnormality in vitamin B12 and/or renal function was found in 80% of cases with hyperHcy and thrombosis. The MMA increase demonstrated that vitamin B12 deficiency was present in these patients with low levels of vitamin B12 in serum, and the MMA levels were in concordance with Hcy levels. The clinical study revealed B12 malabsorption in most cases with LB200. Multivariate analysis showed that serum vitamin B12 (RR 0.998, CI 0.997-0.999) was moderately related to thromboembolism. The results indicated that vitamin B12 deficiency was common among patients with hyperhomocysteinemia and thrombosis. Moreover, HyperHcy was caused by vitamin B12 deficiency and/or chronic renal failure in most patients with thrombosis. As the main cause of vitamin B12 deficiency was vitamin malabsorption, parenteral vitamin B12 with or without folic acid should be administered for the treatment of this condition. However, it remains to be demonstrated whether this treatment approach prevents recurrent thromboses in patients with vitamin B12 deficiency and thrombosis, as suggested by some case reports.

Down-regulation of transcobalamin receptor TCblR/CD320 by siRNA inhibits cobalamin uptake and proliferation of cells in culture

The clinical phenotype of cobalamin (Cbl) deficiency is dictated by the essential role of this vitamin in two key enzymatic reactions. Multiple proteins and receptors participate in the absorption, transport and delivery of this vitamin to tissue cells. Cellular uptake of Cbl is mediated by transcobalamin (TC), a plasma protein and a transmembrane receptor (TCblR) with high affinity for TC saturated with Cbl. Knockdown of TCblR with siRNA results in decreased TC-Cbl uptake. The ensuing Cbl deficiency leads to an increase in doubling time and decreased proliferation of these cells. The study confirms the seminal role of this receptor in the cellular uptake of Cbl and its down-regulation as a potential strategy to inhibit proliferation of cancer cells.

[The role of holotranscobalamin in examination of vitamin B12 status]

INTRODUCTION

Holotranscobalamin contains biologically available cobalamin because only holotranscobalamin promotes the uptake of the cobalamin therein by all cells, via specific receptors. Therefore holotranscobalamin has been proposed as a potentially useful alternative indicator of vitamin B12 status. The aim of the present study was to assess usefulness of holotranscobalamin in the evaluation of vitamin B12 status.

MATERIAL AND METHODS

We examined serum level of holotranscobalamin in 135 subjects divided in four groups according to the serum concentration of vitamin B12: 30 subjects with vitamin B12 <154 pmol/l, 50 subjects with vitamin B12 154-250, 30 subjects with vitamin B12 2251-350 pmol/l, 25 subjects with vitamin B12 >350 pmol/l.

RESULTS

The results show that in subjects with low vitamin B12 serum level there are those with normal holotranscobalamin concentration (60%) and that in subjects with normal vitamin B12 there are those with low holotranscobalamin concentration (22%). The obtained results also show positive significant correlation between levels of holotranscobalamin and vitamin B12 (r = 0.62, p < -0.001).

CONCLUSION

We can conclude that biologically active cobalamin, holotranscobalamin, is a useful tool when examining vitamin B12 status especially in subjects with borderline and low vitamin B12 concentrations. Measurements of the serum holotranscobalamin may be superior to total serum cobalamin.

Indicators for assessing folate and vitamin B12 status and for monitoring the efficacy of intervention strategies

Deficiencies of folate or of vitamin B12 are widespread and constitute a major global burden of morbidity affecting all age groups. Detecting or confirming the presence of folate or vitamin B12 deficiency and distinguishing one from the other depends, ultimately, on laboratory testing. Tests to determine the presence of folate or vitamin B12 deficiency are used singly or in combination to establish the nutritional status and prevalence of deficiencies of the vitamins in various populations. The efficacy of interventions through the use of fortification or supplements is monitored using the same laboratory tests. Tests currently in use have limitations that can be either technical or have a biological basis. Consequently, each single test cannot attain perfect sensitivity, specificity, or predictive value. Laboratory indicators of vitamin B12 or folate status involve measurement of either the total or a physiologically relevant fraction of the vitamin in a compartment such as the blood. Thus, assays to measure vitamin B12 or folate in plasma or serum as well as folate in red blood cells are in widespread use, and more recently, methods to measure vitamin B12 associated with the plasma binding protein transcobalamin (holotranscobalamin) have been developed. Alternatively, levels of surrogate biochemical markers that reflect the metabolic function of the vitamin can be used. Surrogates most commonly used are plasma homocysteine, for detection of either vitamin B12 or folate deficiency and methylmalonic acid for detection of vitamin B12 deficiency. The general methods as well as their uses, indications, and limitations are presented.

Fraction of total plasma vitamin B12 bound to transcobalamin correlates with cognitive function in elderly Latinos with depressive symptoms

BACKGROUND

The fraction of total plasma vitamin B(12) bound to transcobalamin (holoTC/B12 ratio) may reflect tissue levels of the vitamin, but its clinical relevance is unclear.

METHODS

We assessed associations between cognitive function and total B12, holoTC, and holoTC/B12 ratio in a cohort of elderly Latinos (n = 1089, age 60-101 years). We assessed cognitive function using the Modified Mini-Mental State Examination (3MSE) and a delayed recall test; we diagnosed clinical cognitive impairment by neuropsychological and clinical exam with expert adjudication; and we assessed depressive symptoms using the Center for Epidemiological Studies Depression Scale (CES-D). We measured total B12 and holoTC using radioassays.

RESULTS

HoloTC/B12 ratio was directly associated with 3MSE score (P = 0.026) but not delayed recall score. Interactions between holoTC/B12 and CES-D score were observed for 3MSE (P = 0.026) and delayed recall scores (P = 0.013) such that associations between the ratio and cognitive function scores were confined to individuals with CES-D >/=16. For individuals with CES-D > or = 16, the odds ratio for clinical cognitive impairment for the lowest holoTC/B12 tertile was 3.6 (95% CI 1.2-11.2) compared with the highest tertile (P = 0.03). We observed no associations between cognitive function and total B12 or holoTC alone, except between holoTC and 3MSE score (P = 0.021), and no interactions between holoTC or total B12 and CES-D score on cognitive function.

CONCLUSIONS

HoloTC/B12 ratio is associated with cognitive function in elderly Latinos with depressive symptoms and may better reflect the adequacy of B12 for nervous system function than either holoTC or total B12 alone.

Active B12: a rapid, automated assay for holotranscobalamin on the Abbott AxSYM analyzer

BACKGROUND

Conventional tests for vitamin B(12) deficiency measure total serum vitamin B12, whereas only that portion of vitamin B12 carried by transcobalamin (holotranscobalamin) is metabolically active. Measurement of holotranscobalamin (holoTC) may be more diagnostically accurate for detecting B(12) deficiency that requires therapy. We developed an automated assay for holoTC that can be used on the Abbott AxSYM immunoassay analyzer.

METHODS

AxSYM Active B12 is a 2-step sandwich microparticle enzyme immunoassay. In step 1, a holoTC-specific antibody immobilized onto latex microparticles captures holoTC in samples of serum or plasma. In step 2, the captured holoTC is detected with a conjugate of alkaline phosphatase and antiTC antibody.

RESULTS

Neither apoTC nor haptocorrin exhibited detectable cross-reactivity. The detection limit was < or = 0.1 pmol/L. Within-run and total imprecision (CV ranges) were 3.4%-5.1% and 6.3%-8.5%, respectively. Assay CVs were < 20% from at least 3 pmol/L to 107 pmol/L. With diluted serum samples, measured concentrations were 104%-114% of the expected values in the working range of the assay. No interference from bilirubin, hemoglobin, triglycerides, erythrocytes, rheumatoid factor, or total protein was detected at expected (abnormal) concentrations. A comparison of the AxSYM Active B12 assay with a commercial RIA for holoTC yielded the regression equation: AxSYM = 0.98RIA + 4.7 pmol/L (S(y x), 11.4 pmol/L; n = 204). Assay throughput was 45 tests/h. A 95% reference interval of 19-134 pmol/L holoTC was established with samples from 292 healthy individuals.

CONCLUSIONS

The AxSYM Active B12 assay allows rapid, precise, sensitive, specific, and automated measurement of human holoTC in serum and plasma.

Measurement of Total Vitamin B12 and Holotranscobalamin, Singly and in Combination, in Screening for Metabolic Vitamin B12 Deficiency

Background: The standard screening test for vitamin B12 deficiency, measurement of total plasma vitamin B12, has limitations of sensitivity and specificity. Plasma vitamin B12 bound to transcobalamin (holoTC) is the fraction of total vitamin B12 available for tissue uptake and therefore has been proposed as a potentially useful alternative indicator of vitamin B12 status.

Methods: We compared the diagnostic accuracy of total vitamin B12, holoTC, and a combination of both measures to screen for metabolic vitamin B12 deficiency in an elderly cohort (age ≥60 years). Plasma methylmalonic acid and homocysteine were used as indicators of vitamin B12 deficiency.

Results: Low total vitamin B12 (&lt;148 pmol/L) and low holoTC (&lt;35 pmol/L) were observed in 6.5% and 8.0%, and increased methylmalonic acid (&gt;350 nmol/L) and homocysteine (&gt;13 μmol/L) were observed in 12.1% and 17.0% of the study participants. In multiple regression models, holoTC explained 5%–6% more of the observed variance in methylmalonic acid and homocysteine than did total vitamin B12 (P ≤0.004). ROC curve analysis indicated that total vitamin B12 and holoTC were essentially equivalent in their ability to discriminate persons with and without vitamin B12 deficiency. Individuals with low concentrations of both total vitamin B12 and holoTC had significantly higher concentrations of methylmalonic acid and homocysteine than did individuals with total vitamin B12 and/or holoTC within the reference intervals (P &lt;0.001).

Conclusions: HoloTC and total vitamin B12 have equal diagnostic accuracy in screening for metabolic vitamin B12 deficiency. Measurement of both holoTC and total vitamin B12 provides a better screen for vitamin B12 deficiency than either assay alone.

A pediatric patient with recurrent pseudotumor cerebri and vitamin B12 deficiency

Pseudotumor cerebri is a syndrome of increased intracranial pressure, normal cerebrospinal fluid values, and a normal cerebral ventricles on brain imaging studies. A patient with a diagnosis of pseudotumor cerebri was admitted to the authors' hospital twice within a 2.5-year interval and treated with vitamin B12 (vit-B12). At the second admission she also presented with a cerebral venous thrombosis that might have been explained by vit-B12 deficiency, homocysteinemia, and an increased level of lipoprotein-a.

Prevalence of vitamin B12 deficiency in patients with plasma cell dyscrasias: a retrospective review

BACKGROUND

To the authors' knowledge, the prevalence of vitamin B12 deficiency among patients with plasma cell dyscrasias (PCD) is largely unknown. Identifying this vitamin deficiency in such patients could help improve their anemia and increase their tolerance to potentially neurotoxic agents.

METHODS

The authors retrospectively reviewed the charts and laboratory results of 664 consecutive patients diagnosed with PCD who had their vitamin B12 and folate status evaluated between 1997 and 2001 at the Cleveland Clinic Multiple Myeloma Research Program. The patients were screened for vitamin B12 deficiency using serum vitamin B12 and methylmalonic acid.

RESULTS

Of the 664 patients whose medical charts were reviewed, information on vitamin B12 status was available for 522 patients (78%). Among these 522 patients, 71 (13.6%) had laboratory-defined vitamin B12 deficiency and the remaining 451 patients (86.4%) did not. On univariate analysis, vitamin B12 deficiency correlated with immunoglobulin A (IgA) PCD (P = 0.04), higher mean corpuscular volume (P = 0.008), and longer follow-up (P = 0.048). In a covariate adjusted model, only the presence of IgA PCD was associated with an increased prevalence of vitamin B12 deficiency (P = 0.003).

CONCLUSIONS

Vitamin B12 deficiency was prevalent in patients with PCD, especially in patients with the IgA subtype. Serum vitamin B12 measurements should be part of the initial evaluation and subsequent workups for anemia in patients with PCD.

Mild transcobalamin I (haptocorrin) deficiency and low serum cobalamin concentrations

BACKGROUND

Low cobalamin concentrations are common, but their causes are often unknown. Transcobalamin I/haptocorrin (TC I/HC) deficiency, viewed as a rare cause, has not been examined systematically in patients with unexplained low serum cobalamin.

METHODS

Total TC I/HC was measured by RIA in three subgroups of 367, 160, and 38 patients with different categories of low cobalamin concentrations and three comparison subgroups of 112, 281, and 119 individuals with cobalamin concentrations within the reference interval. Additional studies, including family studies, were done in selected patients found to have low TC I/HC concentrations.

RESULTS

Low TC I/HC concentrations suggestive of mild TC I/HC deficiency occurred in 54 of 367 (15%) patients with low cobalamin identified by clinical laboratories and 24 of 160 (15%) patients whose low cobalamin was unexplained after absorption and metabolic evaluation, but in only 2 of 38 patients with malabsorptive causes of low cobalamin concentrations (5%). The prevalence was only 3% (8 of 281 plasma samples) to 5% (6 of 112 sera) in patients with cobalamin concentrations within the reference interval and 3% (4 of 119) in healthy volunteers. Three patients with low cobalamin (0.6%) had severe TC I/HC deficiency with undetectable TC I/HC. Presumptive heterozygotes for severe TC I/HC deficiency in two families had the findings of mild TC I/HC deficiency; mild deficiency was also found in at least three of seven studied families of patients with mild TC I/HC deficiency.

CONCLUSIONS

Mild TC I/HC deficiency is frequently associated with low cobalamin, is often familial, and its biochemical phenotype appears identical to the heterozygous state of severe TC I/HC deficiency. Severe TC I/HC deficiency also appears to be more common than suspected. Both diagnoses should be considered in all patients with unexplained low serum cobalamin.

Vitamin B-12 metabolism in HIV-infected patients in the age of highly active antiretroviral therapy: role of homocysteine in assessing vitamin B-12 status

BACKGROUND

Before the advent of highly active antiretroviral therapy (HAART), 20% and 10% of HIV-infected patients had low vitamin B-12 and red blood cell folate (RBCF) concentrations, respectively. However, few patients had real vitamin B-12 deficiency.

OBJECTIVE

We evaluated the prevalence of low vitamin B-12 and RBCF concentrations in HIV-infected patients receiving HAART and the usefulness of serum homocysteine (sHcy) for differentiating patients with deficiency from those with harmlessly low vitamin B-12.

DESIGN

The prevalence of low vitamin B-12 and RBCF was evaluated in 126 HIV-infected patients receiving HAART. Moreover, sHcy concentrations were evaluated in 40 HIV-infected patients with low vitamin B-12 and in 37 HIV-infected patients with low RBCF and were compared with those in 128 HIV-infected patients with normal vitamin B-12 and RBCF. sHcy was used to monitor treatment with vitamin B-12 and folic acid in 28 patients (24 with low vitamin B-12 and RBCF and 4 with hyperhomocysteinemia but normal vitamin B-12 and RBCF).

RESULTS

The prevalence of low vitamin B-12 was significantly lower in patients receiving HAART than in previously studied patients who did not receive HAART (8.7% compared with 27%). Nine of the 40 patients (22.5%) with low vitamin B-12 (< or = 200 pmol/L) had hyperhomocysteinemia (> 17.5 micromol homocysteine/L). Nineteen (51.4%) of the 37 patients with low RBCF (< or = 580 nmol/L, percentile 10) had hyperhomocysteinemia. Among the 9 patients with an RBCF concentration < or = 450 nmol/L (percentile 2.5), all had hyperhomocysteinemia. The treatment with vitamin B-12 and folic acid normalized sHcy concentrations.

CONCLUSIONS

The prevalence of low vitamin B-12 decreased after the introduction of HAART. The study of sHcy is useful for detecting HIV-infected patients with low vitamin B-12 and real deficiency.

Vegetarian lifestyle and monitoring of vitamin B-12 status

Vegetarians are at risk to develop deficiencies of some essential nutrients, especially vitamin B-12 (cobalamin). Cobalamin occurs in substantial amounts only in foods derived from animals and is essential for one-carbon metabolism and cell division. Low nutritional intake of vitamin B-12 may lead to negative balance and, finally, to functional deficiency when tissue stores of vitamin B-12 are depleted. Early diagnosis of vitamin B-12 deficiency seems to be useful because irreversible neurological damages may be prevented by cobalamin substitution. The search for a specific and sensitive test to diagnose vitamin B-12 deficiency is ongoing. Serum vitamin B-12 measurement is a widely applied standard method. However, the test has poor predictive value. Optimal monitoring of cobalamin status in vegetarians should include the measurement of homocysteine (HCY), methylmalonic acid (MMA), and holotranscobalamin II. Vitamin B-12 deficiency can be divided into four stages. In stages I and II, indicated by a low plasma level of holotranscobalamin II, the plasma and cell stores become depleted. Stage III is characterized by increased levels of HCY and MMA in addition to lowered holotranscobalamin II. In stage IV, clinical signs become recognizable like macroovalocytosis, elevated MCV of erythrocytes or lowered haemoglobin. In our investigations, we have found stage III of vitamin B-12 deficiency in over 60% of vegetarians, thus underlining the importance of cobalamin monitoring in this dietary group.

Human cobalamin deficiency: alterations in serum tumour necrosis factor-alpha and epidermal growth factor

OBJECTIVES

We have previously demonstrated that vitamin B12 (cobalamin)-deficient central neuropathy in the rat is associated with local overexpression of neurotoxic tumour necrosis factor (TNF)-alpha combined with locally decreased synthesis of neurotrophic epidermal growth factor (EGF). The aims of this study were to investigate whether a similar imbalance also occurs in the serum of adult patients with clinically confirmed cobalamin deficiency and whether it can be corrected by vitamin B12 replacement therapy.

PATIENTS AND METHODS

We studied 34 adult patients with severe cobalamin deficiency, 12 patients with pure iron deficiency anaemia and 34 control subjects. Haematological markers of cobalamin deficiency and serum TNF-alpha and EGF levels were measured using commercial kits. Thirteen cobalamin-deficient patients were re-evaluated after 3 and 6 months of parenteral vitamin B12 treatment.

RESULTS

TNF-alpha was significantly higher (p < 0.01) and EGF significantly lower (p < 0.01) in the patients with cobalamin deficiency, but both were unchanged in patients with pure iron deficiency anaemia. In cobalamin-deficient patients the serum TNF-alpha levels correlated significantly with plasma total homocysteine levels (r = 0.425; p < 0.02). In the treated patients TNF-alpha and EGF levels normalised concomitantly with clinical and haematological disease remission.

CONCLUSIONS

In humans, as in rats, cobalamin concentration appears to be correlated with the synthesis and release of TNF-alpha and EGF in a reciprocal manner, because cobalamin deficiency is accompanied by overproduction of TNF-alpha and underproduction of EGF.