Markedly Increased Vitamin B12 Concentrations Attributable to IgG–IgM–Vitamin B12 Immune Complexes

Enhanced detection of immune complexed vitamin B12 in human serum by size-exclusion fractionation (SEF): An upgraded tool for reliable diagnosis

BACKGROUND

The elevated concentration of vitamin B12 in blood has important diagnostic implications since it is associated with different pathologies such as liver and kidney diseases and solid tumours. However, the presence of immune complexed forms of this vitamin (Ig-B12), which have no pathological implications, significantly alters its diagnostic utility because of the overestimation of B12 levels. Thus, developing efficient and selective clinical methodologies for separating Ig-B12 complexes in human serum is crucial to ensure accurate diagnosis of elevated B12 levels and avoid artificial "enrichment" of medically insignificant vitamin forms.

RESULTS

In this work, we present a new method based on the miniaturisation of the size-exclusion chromatography (SEC) gold-standard technique, capable of easily separating the Ig-B12 complexes from non-complexed vitamins (free-B12). A compact system of size-exclusion fractionation (SEF) columns has been designed, developed and tested to separate Ig-B12 and free-B12 resourcefully by rapid gel filtration. These columns are based on centrifugal filtration through a cross-linked dextran Sephadex G-100 resin. The SEF method was validated with sera from 30 patients, showing similar behaviour to the reference SEC technique for Ig-B12 detection (Pearson's coefficient 0.937, 90 % agreement). Furthermore, SEF was superior to polyethylene glycol (PEG) precipitation (Pearson's coefficient 0.769, 80 % agreement), the most utilised and standardised technique in clinical, both in correlation and concordance at a quantitative level.

SIGNIFICANCE

SEF columns allow the rapid and selective separation of Ig-B12 from free vitamin B12. This technique permits mimicking the gold-standard SEC technique but on a smaller scale, both in size and time, making it applicable in any clinical laboratory. The effective quantification of free-B12 allows the unadulterated diagnosis of the vitamin B12 concentration in blood serum.

Impact of laboratory involvement in the characterization of B12 hypervitaminosis in clinical practice

Objectives

Unexplained B12 hypervitaminosis (HB12) in asymptomatic patients leads to a cascade of medical consultations and diagnostic tests aimed at determining its etiology. The objective of this study was to assess the efficacy of the laboratory getting involved in the detection and elimination of immune complexes with vitamin B12 in clinical practice and its economic impact.

Methods

A retrospective longitudinal study was undertaken to assess the laboratory strategy of detecting B12 macrovitamin (macro-B12) in patients with HB12 >1,000 pg/mL. The clinical characteristics of patients with HB12 referred to Internal Medicine (IM) in the pre- and post-implantation period of the new strategy were compared. Additionally, the healthcare costs of one-year follow-up were estimated.

Results

The prevalences of HB12 in the pre- and post-implantation period were 3.9 % and 3 %, respectively. Macro-B12 explained 25 % of the HB12 cases initially detected. A 41 % reduction was observed in the number of patients with HB12 after the implantation of the new strategy, thereby resulting in a cost reduction of 5,000 €.

Conclusions

The laboratory intervention for the detection of macro-B12 provides clear economic and clinical benefits in clinical practice.

Impacto de la intervención del laboratorio en la caracterización de la hipervitaminosis B12 en la práctica asistencial

Objectivos

El hallazgo de hipervitaminosis B12 (HB12) no justificado en pacientes asintomáticos desencadena consultas médicas y pruebas diagnósticas, a fin de determinar la etiología. Nuestro objetivo fue probar la eficacia de la intervención del laboratorio en la detección y eliminación de inmunocomplejos con vitamina B12 en la práctica clínica, así como su impacto económico.

Métodos

Es un estudio retrospectivo y longitudinal diseñado para evaluar la estrategia del laboratorio para detectar macrovitamina B12 (macro-B12) en aquellos pacientes con HB12 mayor a 1.000 pg/mL. Se compararon las características clínicas de los pacientes con HB12 derivados a las consultas de Medicina Interna (MI) en el año anterior y posterior a la implantación de la estrategia y se calcularon los costes asistenciales generados en el año de seguimiento de los pacientes.

Resultados

La prevalencia de HB12 en el periodo previo y posterior a la implantación fue del 3,9 % y 3 %, respectivamente. La macro-B12 fue responsable del 25 % de la HB12 iniciales detectadas. El número de pacientes con HB12 derivados a las consultas de MI se redujo en el 41 % tras la implantación, traduciéndose en un ahorro de más de 5.000€.

Conclusiones

La intervención del laboratorio de detección de macro-B12 tiene un claro beneficio asistencial y económico en la práctica clínica.

Macro-B12 and Unexpectedly High Levels of Plasma B12: A Critical Review

A low total plasma vitamin B12 supports a clinical suspicion of B12 deficiency, while the interpretation of an unexpectedly normal/high level is marred by controversies. Here, we critically review current knowledge on B12 in blood plasma, including the presence of the so-called "macro-B12". The latter form is most often defined as the fraction of B12 that can be removed by precipitation with polyethylene glycol (PEG), a nonspecific procedure that also removes protein polymers and antibody-bound analytes. Plasma B12 includes B12 attached to transcobalamin and haptocorrin, and an increased concentration of one or both proteins almost always causes an elevation of B12. The total plasma B12 is measured by automated competitive binding assays, often incorrectly referred to as immunoassays, since the binding protein is intrinsic factor and not an antibody. An unexpectedly high level of B12 may be further explored using immunological measurements of haptocorrin and transcobalamin (optionally combined with e.g., size-exclusion chromatography). Nonspecific methods, such as PEG precipitation, are likely to give misleading results and cannot be recommended. Currently, the need for evaluation of a high B12 of unknown etiology is limited since other tests (such as measurements of methylmalonic acid) may better guide the diagnosis of B12 deficiency.

Challenges in the diagnosis of hypervitaminemia B12. Interference by immunocomplexes

BACKGROUND-AIM

High vitamin B12 concentrations are considered a common finding in clinical practice. Thanks to immunoassay accessibility, vitamin B12 has become a usual test in routine health checkups. However, these analytical methods usually present antibody-mediated interferences. Our aim was to propose an algorithm for the screening of antibody-mediated analytical interferences on vitamin B12 immunoassays on the Alinity platform.

METHODS

Observational, prospective, case-control study was performed during 12 months. Individuals with persistently elevated cobalamin concentrations [>554 pmol/L] were considered as cases in the absence of supplementation or other justifying cause. Individuals under treatment with vitamin B12, or in the context of alcoholism were included as controls. A thorough interference study by macromolecules in immunoassays was performed in serum samples: PEG precipitation, rheumatoid factor, heterophile antibodies and gel permeation chromatography (GPC). Albumin, total B12, IgG and IgM were measured in every GPC collected fraction and chromatograms were drafted.

RESULTS

Up to 45% of cases presented interference by B12-immunocomplexes and the precipitation for all of them was >50%. The individual with the lowest interfered vitamin B12 result was 661 pmol/L.

CONCLUSION

The presence of antibody-mediated interferences, mainly B12-immunocomplexes, is a relatively common phenomenon. A simple algorithm for the screening of interferences is useful and reliable in ruling out healthy individuals and highly cost-effective.

Approaches to expand the conventional toolbox for discovery and selection of antibodies with drug-like physicochemical properties

Antibody drugs should exhibit not only high-binding affinity for their target antigens but also favorable physicochemical drug-like properties. Such drug-like biophysical properties are essential for the successful development of antibody drug products. The traditional approaches used in antibody drug development require significant experimentation to produce, optimize, and characterize many candidates. Therefore, it is attractive to integrate new methods that can optimize the process of selecting antibodies with both desired target-binding and drug-like biophysical properties. Here, we summarize a selection of techniques that can complement the conventional toolbox used to de-risk antibody drug development. These techniques can be integrated at different stages of the antibody development process to reduce the frequency of physicochemical liabilities in antibody libraries during initial discovery and to co-optimize multiple antibody features during early-stage antibody engineering and affinity maturation. Moreover, we highlight biophysical and computational approaches that can be used to predict physical degradation pathways relevant for long-term storage and in-use stability to reduce the need for extensive experimentation.

Relationship between high dose intake of vitamin B12 and glaucoma: Evidence from NHANES 2005-2008 among United States adults

Objective

Glaucoma has currently become the second leading cause of blindness in the world. Serum vitamin B12 level has been found to be involved in the development and progression of glaucoma. We performed the present study to confirm this association.

Methods

This cross-sectional study included 594 participants aged 40 years and older in the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2008. Retinal imaging was performed using the Ophthalmic Digital Imaging system (Retinography) to assess the retina for the presence of features of glaucomatous lesions. Logistic regression models were used to assess the association between dietary vitamin intake and glaucoma.

Results

After screening, 594 subjects were finally included. Among all vitamin intakes, we observed significant differences between the two groups for vitamin B12 intake (5.93 vs. 4.77 mg, p = 0.033). According to the logistic regression results, the intake of vitamin B12 was significantly positively associated with glaucoma (model 1: OR = 1.078, 95% CI = 1.019-1.141; model 2: OR = 1.092, 95% CI = 1.031-1.158; model 3: OR = 1.092, 95% CI = 1.029-1.158). After performing a quantile regression, we observed a significant positive association between vitamin B12 intake and incident glaucoma in the fourth quartile (model 1: OR = 1.133, 95% CI = 1.060-1.210; model 2: OR = 1.141, 95% CI = 1.072-1.215; model 3: OR = 1.146, 95% CI = 1.071-1.226).

Conclusions

Therefore, the above results, high-dose intake of vitamin B12 may promote the development of glaucoma.

High Plasma Vitamin B12 and Cancer in Human Studies: A Scoping Review to Judge Causality and Alternative Explanations

Patients with cancer have been reported to show elevated plasma concentrations of vitamin B12, thus causing uncertainties regarding safety of vitamin B12. We conducted a systematic literature search and a scoping review of human studies published in PubMed between January 2005 and March 2022, to investigate the association between vitamin B12 (concentrations of B12 biomarkers, intake, and genetic determinants) and cancer. Except for liver cancer, the association between plasma vitamin B12 concentrations and cancer was not consistent across the studies. Vitamin B12 intake from food, or food and supplements, showed even less consistent associations with cancer. There was no evidence for temporality, coherence, or a biologically meaningful dose-response relationship between plasma vitamin B12 concentrations and cancer. Genetically determined high plasma vitamin B12 was likely to be associated with cancer. Available randomized controlled trials have used a high dose of multivitamin supplements and cancer was the unplanned outcome, thus the causality of B12 in cancer cannot be judged based on these trials. Additionally, low plasma vitamin B12 concentrations were common in patients with cancer. Therefore, there is not sufficient evidence to assume that high plasma vitamin B12, high B12 intake, or treatment with pharmacological doses of vitamin B12, is causally related to cancer. Low vitamin B12 status in patients with cancer needs to be diagnosed and treated in order to prevent the hematological and neurological sequela of the deficiency.

Total serum vitamin B12 (cobalamin) LC-MS/MS assay as an arbiter of clinically discordant immunoassay results

Objectives

Measurement of the serum levels of vitamin B12 (VB12) is key for evaluating VB12 deficiency-dependent anemia. Immunoassay, the major method for determining VB12, tends to give false-normal results because of the presence of anti-intrinsic factor (IF-Ab) or other factors such as heterophilic antibodies et al. This study aimed to develop a liquid chromatography tandem mass spectrometry (LC-MS/MS) method that is helpful for distinguish false normal VB12 results measured by the immunoassay.

Methods

Different forms of VB12 were derivatized into CN-B12, which was collected through solid-phase extraction and analyzed via LC-MS/MS. 236 serum samples were measured both by LC-MS/MS and immunoassay, results were compared, and the IF-Ab effect was evaluated.

Results

The LC-MS/MS assay afforded a linear slope from 20 to 4,000 pmol/L for CN-B12. OH-VB12, methyl-VB12, and CoA-VB12 showed recovery within 89.3–109.5%. The intra-assay CV of VB12 was 2.6–4.1%, whereas the total CV was 9.3–9.8%. Passing–Bablok regression between LC-MS/MS and immunoassay results showed that the slope was 1.085 and the intercept was −15.691. The Bland–Altman plot showed that the mean difference and difference% were −34.6 pmol/L and 0.3%, respectively. Inter-rater agreement analysis showed that the linear weighted kappa value was 0.885, implying good agreement between the two methods. However, two samples were falsely elevated and one sample was falsely normal in the immunoassay compared with LC-MS/MS. The LC-MS/MS method helped in the distinction of false-normal VB12 results shown by the immunoassay.

Conclusions

The VB12 LC-MS/MS method can be used as an arbiter of clinically discordant immunoassay results.

Serum vitamin B12 levels and glycemic fluctuation in patients with type 2 diabetes mellitus

PURPOSE

The aim of the study was to explore the correlation between serum vitamin B12 levels and glycemic fluctuation in patients with type 2 diabetes mellitus (T2DM).

METHODS

This study included 202 T2DM patients in whom blood glucose levels were recorded using a continuous glucose monitoring system retrospectively. Glycemic fluctuation was determined using the average daily risk range (ADRR), a diabetes-specific measure of the risk for hyper- and hypoglycemia.

RESULTS

Serum vitamin B12 levels were higher in T2DM patients with wider glycemic fluctuations than in those with minor glycemic fluctuations (p < 0.001). We observed a positive correlation between serum vitamin B12 levels and ADRR in both T2DM patients who received and did not receive metformin therapy (r = 0.388, p < 0.001 and r = 0.280, p = 0.004, respectively). Multiple linear regression analysis showed that serum vitamin B12 levels were independently correlated with ADRR in T2DM patients who received and did not receive metformin therapy (beta = 0.367, p < 0.001 and beta = 0.410, p < 0.001, respectively).

CONCLUSIONS

Serum vitamin B12 levels are correlated with glycemic fluctuation in patients with T2DM and may serve as an underlying useful biomarker of glycemic fluctuation in T2DM patients, treated with or without metformin therapy.

"Macro transcobalamin causing raised vitamin B12: Case-based laboratory investigation"

Determination of plasma vitamin B12 (B12) is a frequently requested laboratory analysis, mainly employed to establish B12 deficiency. However, an increased level of B12 is a common unexpected finding that may be related to an increased concentration of one of the B12 binding proteins, haptocorrin or transcobalamin. This paper describes the extensive laboratory evaluation of a patient with an elevated level of plasma B12 with various well-established assays. Initial studies suggested the presence of a macromolecule consisting of haptocorrin bound B12. Specific determinations of the B12-binding proteins revealed normal amounts of haptocorrin but a markedly increase in both total and B12 saturated transcobalamin (holo-TC). The results are in accord with the presence of macro-transcobalamin. These experiments reveal that determination of the nature of the B12-macromolecules is troublesome due to differences in assays applied to measure these proteins. In addition, this publication creates awareness of macro-holo-TC as a cause of an unexplained increased B12 level.

Macro-B12 masking B12 deficiency

In clinical practice, the finding of an elevated serum B₁₂ concentration is often the consequence of supplementation with B₁₂ in either oral form or injections. Also, elevated serum B₁₂ may be associated with underlying disorders, like liver diseases or a (haematologic) malignancy. Only a few studies have shown that it may also be the consequence of complex formation of B₁₂-vitamin binding proteins with immunoglobulins, the so-called macro-B₁₂. We describe a young woman who previously was diagnosed with B₁₂ deficiency, and in whom, after cessation of B₁₂ injection treatment, neurologic symptoms re-appeared, and despite this, repeatedly elevated serum B₁₂ concentrations above the upper limit of the assay were found. We demonstrated that this was caused by the presence of macro-B₁₂, which not only resulted in erroneous and longstanding elevated serum B₁₂, but also masked her underlying B₁₂ deficiency.

Macro vitamin B12: an underestimated threat

Background The correct identification of the macro-B12 interference (macroforms) is paramount to avoid potential erroneous clinical decisions. Our objectives were to determine whether immunoassays are affected by the presence of macro-B12 and to validate a polyethylene glycol (PEG) precipitation procedure to detect it. Methods Sixty-two serum samples obtained from healthy volunteers were analyzed to determine recovery and reference intervals (RIs) following PEG precipitation. Thereafter, 50 serum samples with very high levels of B12 (>1476 pmol/L) were randomly selected to search for macro-B12 interferences. Serum samples obtained from healthy volunteers and related PEG aliquots were analyzed on a Cobas® immunoassay. Patients' samples were analyzed on both Cobas® and Architect® immunoassays. Finally, samples suspected to contain macro-B12 were analyzed by size-exclusion chromatography (SEC) to confirm the presence of macro-B12. Results Recovery and post-PEG RIs determined on a Cobas 8000® in healthy volunteers ranged from 68.3% to 108.4% and from 122.1 to 514.4 pmol/L, respectively. Fifteen samples (30%) were found to show macro-B12 while using the recovery criteria, and nine samples (18%) while using the post-PEG RI. The other immunoassay ran on the Architect i2000® was also affected by the presence of macro-B12. Size-exclusion chromatography studies confirmed the presence of macro-B12 (immunoglobulin-B12 complexes). Conclusions The prevalence of macro-B12 in elevated B12 samples is high. We suggest to systematically screen for the presence of macro-B12 with PEG precipitation procedure in samples with elevated B12 levels to avoid potential misdiagnosis or harmful clinical consequences.

Interaction of clinical-stage antibodies with heme predicts their physiochemical and binding qualities

Immunoglobulin repertoires contain a fraction of antibodies that recognize low molecular weight compounds, including some enzymes' cofactors, such as heme. Here, by using a set of 113 samples with variable region sequences matching clinical-stage antibodies, we demonstrated that a considerable number of these antibodies interact with heme. Antibodies that interact with heme possess specific sequence traits of their antigen-binding regions. Moreover they manifest particular physicochemical and functional qualities i.e. increased hydrophobicity, higher propensity of self-binding, higher intrinsic polyreactivity and reduced expression yields. Thus, interaction with heme is a strong predictor of different molecular and functional qualities of antibodies. Notably, these qualities are of high importance for therapeutic antibodies, as their presence was associated with failure of drug candidates to reach clinic. Our study reveled an important facet of information about relationship sequence-function in antibodies. It also offers a convenient tool for detection of liabilities of therapeutic antibodies.

B Vitamins and One-Carbon Metabolism: Implications in Human Health and Disease

Vitamins B9 (folate) and B12 are essential water-soluble vitamins that play a crucial role in the maintenance of one-carbon metabolism: a set of interconnected biochemical pathways driven by folate and methionine to generate methyl groups for use in DNA synthesis, amino acid homeostasis, antioxidant generation, and epigenetic regulation. Dietary deficiencies in B9 and B12, or genetic polymorphisms that influence the activity of enzymes involved in the folate or methionine cycles, are known to cause developmental defects, impair cognitive function, or block normal blood production. Nutritional deficiencies have historically been treated with dietary supplementation or high-dose parenteral administration that can reverse symptoms in the majority of cases. Elevated levels of these vitamins have more recently been shown to correlate with immune dysfunction, cancer, and increased mortality. Therapies that specifically target one-carbon metabolism are therefore currently being explored for the treatment of immune disorders and cancer. In this review, we will highlight recent studies aimed at elucidating the role of folate, B12, and methionine in one-carbon metabolism during normal cellular processes and in the context of disease progression.

Prevalence and clinical relevance of hypercobalaminaemia in dogs and cats

Hypocobalaminaemia is common in dogs and cats with exocrine pancreatic insufficiency and/or chronic enteropathy. While hypocobalaminaemia has been extensively studied, naturally-occurring serum hypercobalaminaemia (i.e. without supplementation) might be an underestimated finding in small animal medicine. Studies in human medicine have associated hypercobalaminaemia with neoplastic, hepatic and renal disease. Medical records of all dogs and cats with serum cobalamin concentration measurements (2007-2019) were retrospectively analysed; any that had received supplemental cobalamin were excluded from the analysis. Of 654 dogs, 3% (n = 21) were hypercobalaminaemic (median serum cobalamin concentration, 1307 ng/L [965 pmol/L]; range, 914-3561 ng/L [675-2628 pmol/L]). Chronic gastrointestinal signs were common in hypercobalaminaemic dogs (48%). Two of the 21 hypercobalaminaemic dogs were diagnosed with hypoadrenocorticism. Of 323 cats, 11% (n = 34) were hypercobalaminaemic (median serum cobalamin concentration, 1713 ng/L [1264 pmol/L]; range, 1370-3107 ng/L [1011-2293 pmol/L]). The following comorbidities were diagnosed in hypercobalaminaemic cats: chronic enteropathy, 65% (n = 22); acute or chronic pancreatitis, 24% (n = 8); cholangiohepatopathy, 18% (n = 6); gastric lymphoma, 6% (n = 2); and 3% hyperthyroidism (n = 1). Naturally-occurring increased serum cobalamin concentrations occurred infrequently in cats and even less often in dogs. Since hypercobalaminaemia can occur in dogs and cats with severe inflammatory, immune-mediated, and neoplastic conditions, it should not be ignored.

Elevated Plasma Vitamin B12 in Patients with Hepatic Glycogen Storage Diseases

Background: Hepatic glycogen storage diseases (GSDs) are inborn errors of metabolism affecting the synthesis or breakdown of glycogen in the liver. This study, for the first time, systematically assessed vitamin B₁₂ status in a large cohort of hepatic GSD patients. Methods: Plasma vitamin B₁₂, total plasma homocysteine (tHcy) and methylmalonic acid concentrations were measured in 44 patients with hepatic GSDs and compared to 42 healthy age- and gender-matched controls. Correlations of vitamin B₁₂ status with different disease markers of GSDs (including liver transaminase activities and triglycerides) as well as the vitamin B₁₂ intake were studied. Results: GSD patients had significantly higher plasma vitamin B₁₂ concentrations than healthy controls (p = 0.0002). Plasma vitamin B₁₂ concentration remained elevated in GSD patients irrespective of vitamin B₁₂ intake. Plasma vitamin B₁₂ concentrations correlated negatively with triglyceride levels, whereas no correlations were detected with liver transaminase activities (GOT and GPT) in GSD patients. Merging biomarker data of healthy controls and GSD patients showed a positive correlation between vitamin B₁₂ status and liver function, which suggests complex biomarker associations. A combined analysis of biomarkers permitted a reliable clustering of healthy controls versus GSD patients. Conclusions: Elevated plasma concentration of vitamin B₁₂ (irrespective of B₁₂ intake) is a common finding in patients with hepatic GSD. The negative correlation of plasma vitamin B₁₂ with triglyceride levels suggests an influence of metabolic control on the vitamin B₁₂ status of GSD patients. Elevated vitamin B₁₂ was not correlated with GOT and GPT in our cohort of GSD patients. Merging of data from healthy controls and GSD patients yielded positive correlations between these biomarkers. This apparent dichotomy highlights the intrinsic complexity of biomarker associations and argues against generalizations of liver disease and elevated vitamin B₁₂ in blood. Further studies are needed to determine whether the identified associations are causal or coincidental, and the possible impact of chronically elevated vitamin B₁₂ on GSD.

Blood concentrations of vitamins B1, B6, B12, C and D and folate in palliative care patients: Results of a cross-sectional study

Objective

The main purpose of palliative care is symptom relief. Frequently, the symptoms of patients requiring palliative care are the same as common symptoms of vitamin deficiency (e.g. pain, weakness, fatigue, depression). The study aim was to investigate whether patients in palliative care are vitamin deficient.

Method

This was a monocentre cross-sectional study. Patients attending the palliative care unit of a general hospital in Germany from October 2015 to April 2016 were examined for vitamin blood concentrations and symptoms. Data were analysed using univariate analysis and bivariate correlations.

Results

Data were available from 31 patients. Vitamin D3 deficiency (<62.5 nmol/L) affected 93.5% of patients, vitamin B6 deficiency (<4.1 ng/mL) 48.4%, vitamin C deficiency (<4.5 mg/L) 45.2%, vitamin B1 deficiency (<35 µg/L) 25.8% and vitamin B12 deficiency (<193 pg/mL) 12.9%. There was a significant negative correlation between vitamin B1 ranges and pain (r = −0.384) and depression (r = −0.439) symptoms.

Conclusion

All patients showed a deficiency in at least one of the measured vitamins; 68% had concurrent deficiencies in >1 vitamin. A follow-up study using validated questionnaires and a larger sample is needed to investigate the effects of targeted vitamin supplementation on quality of life and symptom burden.

Hypervitaminosis B12 - a new marker and predictor of prognostically unfavorable diseases

A high serum vitamin B12 level (hypercobalaminemia) is a underestimated anomaly. Clinically, it can be paradoxically accompanied by signs of deficiency, which are related to defects in tissue uptake of vitamin B12. The increase in the level of serum cobalamin occurs mainly in serious diseases that require early diagnosis: hemoblastosis, liver and kidney diseases, etc. This review presents data on the metabolism of vitamin B12 and the potential significance of increasing its level as a marker for the early diagnosis of these diseases.

Characterization of the complex between native and reduced bovine serum albumin with aquacobalamin and evidence of dual tetrapyrrole binding

Serum albumin binds to a variety of endogenous ligands and drugs. Human serum albumin (HSA) binds to heme via hydrophobic interactions and axial coordination of the iron center by protein residue Tyr161. Human serum albumin binds to another tetrapyrrole, cobalamin (Cbl), but the structural and functional properties of this complex are poorly understood. Herein, we investigate the reaction between aquacobalamin (H₂OCbl) and bovine serum albumin (BSA, the bovine counterpart of HSA) using Ultraviolet-Visible and fluorescent spectroscopy, and electron paramagnetic resonance. The reaction between H₂OCbl and BSA led to the formation of a BSA-Cbl(III) complex consistent with N-axial ligation (amino). Prior to the formation of this complex, the reactants participate in an additional binding event that has been examined by fluorescence spectroscopy. Binding of BSA to Cbl(III) reduced complex formation between the bound cobalamin and free cyanide to form cyanocobalamin (CNCbl), suggesting that the β-axial position of the cobalamin may be occupied by an amino acid residue from the protein. Reaction of BSA containing reduced disulfide bonds with H₂OCbl produces cob(II)alamin and disulfide with intermediate formation of thiolate Cbl(III)-BSA complex and its decomposition. Finally, in vitro studies showed that cobalamin binds to BSA only in the presence of an excess of protein, which is in contrast to heme binding to BSA that involves a 1:1 stoichiometry. In vitro formation of BSA-Cbl(III) complex does not preclude subsequent heme binding, which occurs without displacement of H₂OCbl bound to BSA. These data suggest that the two tetrapyrroles interact with BSA in different binding pockets.

The role of oxidative stress, inflammation and acetaminophen exposure from birth to early childhood in the induction of autism

The wide range of factors associated with the induction of autism is invariably linked with either inflammation or oxidative stress, and sometimes both. The use of acetaminophen in babies and young children may be much more strongly associated with autism than its use during pregnancy, perhaps because of well-known deficiencies in the metabolic breakdown of pharmaceuticals during early development. Thus, one explanation for the increased prevalence of autism is that increased exposure to acetaminophen, exacerbated by inflammation and oxidative stress, is neurotoxic in babies and small children. This view mandates extreme urgency in probing the long-term effects of acetaminophen use in babies and the possibility that many cases of infantile autism may actually be induced by acetaminophen exposure shortly after birth.

Unexpected high plasma cobalamin : proposal for a diagnostic strategy

It is well-established that more than 8% of patients examined for vitamin B12 deficiency unexpectedly have increased plasma levels of the vitamin, but so far there are no guidelines for the clinical interpretation of such findings. In this review, we summarise known associations between high plasma cobalamin and diseases. We report associations mainly with cancer, liver and kidney diseases, but also with a number of other diagnostic entities. The pathogenic background is poorly understood and is likely to be multi-factorial, involving increased concentrations of one or both of the circulating cobalamin binding proteins, transcobalamin and haptocorrin. Based on current knowledge, we suggest a strategy for the clinical interpretation of unexpected high plasma cobalamin. Since a number of the associated diseases are critical and life-threatening, the strategy promotes the concept of 'think the worst first'. It is important to realise that high cobalamin levels can be an unspecific marker for cancer. If this can be ruled out, diseases of the liver and kidney should be considered.

Hydroxocobalamin association during cell culture results in pink therapeutic proteins

Process control of protein therapeutic manufacturing is central to ensuring the product is both safe and efficacious for patients. In this work, we investigate the cause of pink color variability in development lots of monoclonal antibody (mAb) and Fc-fusion proteins. Results show pink-colored product generated during manufacturing is due to association of hydroxocobalamin (OH-Cbl), a form of vitamin B12. OH-Cbl is not part of the product manufacturing process; however we found cyanocobalamin (CN-Cbl) in cell culture media converts to OH-Cbl in the presence of light. OH-Cbl can be released from mAb and Fc-fusion proteins by conversion with potassium cyanide to CN-Cbl, which does not bind. By exploiting the differential binding of CN-Cbl and OH-Cbl, we developed a rapid and specific assay to accurately measure B12 levels in purified protein. Analysis of multiple products and lots using this technique gives insight into color variability during manufacturing.

The pathophysiology of elevated vitamin B12 in clinical practice

Hypercobalaminemia (high serum vitamin B12 levels) is a frequent and underestimated anomaly. Clinically, it can be paradoxically accompanied by signs of deficiency, reflecting a functional deficiency linked to qualitative abnormalities, which are related to defects in tissue uptake and action of vitamin B12. The aetiological profile of high serum cobalamin predominantly encompasses severe disease entities for which early diagnosis is critical for prognosis. These entities are essentially comprised of solid neoplasms, haematological malignancies and liver and kidney diseases. This review reflects the potential importance of the vitamin B12 assay as an early diagnostic marker of these diseases. A codified approach is needed to determine the potential indications of a search for high serum cobalamin and the practical clinical strategy to adopt upon discovery of elevated cobalamin levels. While low serum cobalamin levels do not necessarily imply deficiency, an abnormally high serum cobalamin level forms a warning sign requiring exclusion of a number of serious underlying pathologies. Functional cobalamin deficiency can thus occur at any serum level.

An IgG complexed form of vitamin B12 is a common cause of elevated serum concentrations

OBJECTIVES

To report detailed investigations in a case of elevated serum B(12) due to the presence of an IgG-B(12) complex, to determine the prevalence of this phenomenon and to review the literature.

DESIGN AND METHODS

431 samples with elevated B(12) (median 1250 ng/L, range 901-114,480 ng/L) were treated with polyethylene glycol to precipitate immunoglobulin complexes. Samples with >50% of precipitable B(12) (PPB(12)) were further investigated by protein G adsorption, gel filtration chromatography and measurement of B(12) on different analytical platforms.

RESULTS

Median PPB(12) was 22.6%, but in 35 samples (8.1%), median PPB(12) was more than 50%. Investigation of 27 of these samples with protein G-Sepharose confirmed the presence of an IgG-B(12) complex in 24, and in 15 cases, B(12) fell to within the reference range. After treatment of serum with reagents releasing B(12) from binding proteins, immunoreactivity co-eluted with free B(12). Immunoreactivity of the IgG-bound form of B(12) was confirmed using five B(12) assays in common use in the UK.

CONCLUSIONS

At least 8% of samples with elevated vitamin B(12) contain an immunoglobulin complexed form of circulating B(12); this possibility should be considered in the interpretation of results.