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Abuyaman O, Hatmal MM, Hijjawi N, Deeb AA, Abuothman M, Taha M. Vitamin B12 binding to mutated human transcobalamin, in-silico study of TCN2 alanine scanning and ClinVar missense mutations/SNPs. J Biomol Struct Dyn 2022; 41:3222-3233. [PMID: 35261335 DOI: 10.1080/07391102.2022.2046638] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Many missense mutations/SNPs of the TCN2 gene (which yield Transcobalamin (TC)) were reported in the literature but no study is available about their effect on binding to vitamin B12(B12) at the structural level experimentally nor computationally. Predict the effect of TC missense mutations/SNPs on binding affinity to B12 and characterize their contacts to B12 at the structural level. TC-B12 binding energy difference from the wildtype (ΔΔGmut) was calculated for 378 alanine scanning mutations and 76 ClinVar missense mutations, repeated on two distinct X-ray structures of holoTC namely 2BB5 and 4ZRP. Destabilizing mutations then went through 100 ns molecular dynamics simulation to study their effect on TC-B12 binding at the structural level employing 2BB5 structure. Out of the studied 454 mutations (378 alanine mutations + 76 ClinVar mutations), 19 were destabilizing representing 17 amino acid locations. Mutation energy results show a neutral effect on B12 binding of several missense SNPs reported in the literature including I23V, G94S, R215W, P259R, S348F, L376S, and R399Q. Compared to the wildtype, all the destabilizing mutations have higher average RMSD-Ligand in the last 25% of the MD simulation trajectories and lower average hydrogen bond count while the other parameters vary. Previously reported TCN2 SNPs with an unknown effect on TC-B12 binding were found to have a neutral effect in the current study based on mutation energy calculations. Also, we reported 17 possible amino acids that destabilize TC-B12 binding upon mutation (four listed in ClinVar) and studied their structural effect computationally. Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Omar Abuyaman
- Department of Medical Laboratory Sciences, Faculty of Applied Medical Sciences, The Hashemite University, Zarqa, Jordan
| | - Ma'mon M Hatmal
- Department of Medical Laboratory Sciences, Faculty of Applied Medical Sciences, The Hashemite University, Zarqa, Jordan
| | - Nawal Hijjawi
- Department of Medical Laboratory Sciences, Faculty of Applied Medical Sciences, The Hashemite University, Zarqa, Jordan
| | - Ahmad A Deeb
- Faculty of Pharmacy, Department of Pharmacy, Al-Zaytoonah University of Jordan, Amman, Jordan
| | | | - Mutasem Taha
- Faculty of Pharmacy, Department of Pharmaceutical Sciences, University of Jordan, Amman, Jordan
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Sobczyńska-Malefora A, Delvin E, McCaddon A, Ahmadi KR, Harrington DJ. Vitamin B 12 status in health and disease: a critical review. Diagnosis of deficiency and insufficiency - clinical and laboratory pitfalls. Crit Rev Clin Lab Sci 2021; 58:399-429. [PMID: 33881359 DOI: 10.1080/10408363.2021.1885339] [Citation(s) in RCA: 55] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Vitamin B12 (cobalamin) is an essential cofactor for two metabolic pathways. It is obtained principally from food of animal origin. Cobalamin becomes bioavailable through a series of steps pertaining to its release from dietary protein, intrinsic factor-mediated absorption, haptocorrin or transcobalamin-mediated transport, cellular uptake, and two enzymatic conversions (via methionine synthase and methylmalonyl-CoA-mutase) into cofactor forms: methylcobalamin and adenosylcobalamin. Vitamin B12 deficiency can masquerade as a multitude of illnesses, presenting different perspectives from the point of view of the hematologist, neurologist, gastroenterologist, general physician, or dietician. Increased physician vigilance and heightened patient awareness often account for its early presentation, and testing sometimes occurs during a phase of vitamin B12 insufficiency before the main onset of the disease. The chosen test often depends on its availability rather than on the diagnostic performance and sensitivity to irrelevant factors interfering with vitamin B12 markers. Although serum B12 is still the most commonly used and widely available test, diagnostics by holotranscobalamin, serum methylmalonic acid, and plasma homocysteine measurements have grown in the last several years in routine practice. The lack of a robust absorption test, coupled with compromised sensitivity and specificity of other tests (intrinsic factor and gastric parietal cell antibodies), hinders determination of the cause for depleted B12 status. This can lead to incorrect supplementation regimes and uncertainty regarding later treatment. This review discusses currently available knowledge on vitamin B12, informs the reader about the pitfalls of tests for assessing its deficiency, reviews B12 status in various populations at different disease stages, and provides recommendations for interpretation, treatment, and associated risks. Future directions for diagnostics of B12 status and health interventions are also discussed.
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Affiliation(s)
- Agata Sobczyńska-Malefora
- The Nutristasis Unit, Viapath, St. Thomas' Hospital, London, UK.,Faculty of Life Sciences and Medicine, King's College London, London, UK
| | - Edgard Delvin
- Sainte-Justine UHC Research Centre, Montreal, Canada.,Department of Biochemistry and Molecular Medicine, University of Montreal, Montreal, Canada
| | | | - Kourosh R Ahmadi
- Department of Nutrition & Metabolism, School of Biosciences and Medicine, University of Surrey, Guildford, UK
| | - Dominic J Harrington
- The Nutristasis Unit, Viapath, St. Thomas' Hospital, London, UK.,Faculty of Life Sciences and Medicine, King's College London, London, UK
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Akış M, Kant M, Işık İ, Kısa PT, Köse E, Arslan N, İşlekel H. Functional vitamin B12 deficiency in phenylketonuria patients and healthy controls: An evaluation with combined indicator of vitamin B12 status as a biochemical index. Ann Clin Biochem 2020; 57:291-299. [PMID: 32482081 DOI: 10.1177/0004563220935140] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Vitamin B12 deficiency frequently appears in phenylketonuria patients having a diet poor in natural protein. The aims of this study were to evaluate vitamin B12 status in phenylketonuria patients by using combined indicator of vitamin B12 status (cB12) as well as methylmalonic acid and homocysteine, more specific and sensitive markers, in comparison with healthy controls. METHODS Fifty-three children and adolescents with phenylketonuria under dietary treatment and 30 healthy controls were assessed cross-sectionally. Serum vitamin B12 and folate concentrations were analysed by chemiluminescence immunoassay. Plasma methylmalonic acid and total homocysteine concentrations were measured by liquid chromatography-tandem mass spectrometry and liquid chromatography, respectively. cB12 was calculated by using a formula involving blood parameters. RESULTS Methylmalonic acid and folate concentrations in phenylketonuria group were higher compared with controls. Methylmalonic acid concentrations were high in 56.5% of the patients and 26.7% of the controls with normal vitamin B12 concentrations. Based on cB12, a significant difference within the normal values was detected between the groups. However, although 24.5% of phenylketonuria patients and 13.3% of controls had decreased vitamin B12 status according to cB12, there was no significant difference. CONCLUSION Children and adolescents with phenylketonuria having a strict diet can be at risk of functional vitamin B12 deficiency. This deficiency can be accurately determined by measuring methylmalonic acid concentrations. Calculation of cB12 as a biochemical index did not provide additional information compared with the measurement of methylmalonic acid alone, but may be helpful for classification of some patients with increased methylmalonic acid as having adequate vitamin B12 status.
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Affiliation(s)
- Merve Akış
- Department of Medical Biochemistry, School of Medicine, Balikesir University, Balikesir, Turkey
| | - Melis Kant
- Department of Medical Biochemistry, Institute of Health Sciences, School of Medicine, Dokuz Eylul University, Izmir, Turkey
| | - İshak Işık
- Department of Pediatric Gastroenterology, Hepatology and Nutrition, Health Sciences University Antalya Training and Research Hospital, Antalya, Turkey
| | - Pelin Teke Kısa
- Division of Pediatric Metabolism and Nutrition, Dokuz Eylul University, Izmir, Turkey
| | - Engin Köse
- Division of Pediatric Metabolism and Nutrition, Dokuz Eylul University, Izmir, Turkey
| | - Nur Arslan
- Division of Pediatric Metabolism and Nutrition, Dokuz Eylul University, Izmir, Turkey
| | - Hüray İşlekel
- Department of Medical Biochemistry, School of Medicine, Dokuz Eylul University, Izmir, Turkey.,Department of Molecular Medicine, Institute of Health Sciences, Dokuz Eylul University, Izmir, Turkey
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Vitamin B12 Status Upon Short-Term Intervention with a Vegan Diet-A Randomized Controlled Trial in Healthy Participants. Nutrients 2019; 11:nu11112815. [PMID: 31752105 PMCID: PMC6893687 DOI: 10.3390/nu11112815] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Revised: 11/06/2019] [Accepted: 11/13/2019] [Indexed: 02/07/2023] Open
Abstract
Vegans are at an increased risk for certain micronutrient deficiencies, foremost of vitamin B12. Little is known about the short-term effects of dietary change to plant-based nutrition on vitamin B12 metabolism. Systemic biomarkers of vitamin B12 status, namely, serum vitamin B12 and holotranscobalamin, may respond quickly to a reduced intake of vitamin B12. To test this hypothesis, 53 healthy omnivore subjects were randomized to a controlled unsupplemented vegan diet (VD, n = 26) or meat-rich diet (MD, n = 27) for 4 weeks. Vitamin B12 status was examined by measurement of serum vitamin B12, holotranscobalamin (holo-TC), methylmalonic acid (MMA) and total plasma homocysteine (tHcy). Holo-TC decreased significantly in the VD compared to the MD group after four weeks of intervention, whereas metabolites MMA and tHcy were unaffected. Body weight remained stable in both groups. VD intervention led to a significant reduction of cholesterol intake, and adequate profiles of nutrient and micronutrient status. Lower intake of vitamin B12 was observed in VD, which was mirrored by a lower concentration of serum vitamin B12 and reduced holo-TC after 4 weeks. Plasma holo-TC may be a fast-responding biomarker to monitor adequate supply of vitamin B12 in plant-based individuals.
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Renard E, Chéry C, Oussalah A, Josse T, Perrin P, Tramoy D, Voirin J, Klein O, Leheup B, Feillet F, Guéant-Rodriguez RM, Guéant JL. Exome sequencing of cases with neural tube defects identifies candidate genes involved in one-carbon/vitamin B12 metabolisms and Sonic Hedgehog pathway. Hum Genet 2019; 138:703-713. [DOI: 10.1007/s00439-019-02015-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Accepted: 04/13/2019] [Indexed: 12/13/2022]
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Griffioen PH, van Dam-Nolen DHK, Lindemans J, Heil SG. Measurement of total Transcobalamin employing a commercially available assay for Active B12. Clin Biochem 2017; 50:1030-1033. [PMID: 28823760 DOI: 10.1016/j.clinbiochem.2017.08.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2017] [Revised: 08/15/2017] [Accepted: 08/16/2017] [Indexed: 11/17/2022]
Abstract
INTRODUCTION Vitamin B12 deficiency is mostly caused by insufficient gastro-intestinal absorption and in rare conditions by Transcobalamin (TC) deficiency. Unsaturated Transcobalamin (apoTC) can be measured by a binding assay using radiolabeled cobalamin. The Active B12 test analyzes saturated Transcobalamin (holoTC) and we hypothesize that this test can be used to measure total TC by additional in vitro saturation with cobalamin. METHODS Serum was saturated in vitro (16 times dilution) with a cyanocobalamin solution and total TC was selectively measured with the Abbott Active B12 test. ApoTC was calculated by subtracting endogenous holoTC from total TC after correction for dilution. Linearity was determined with a pool serum dilution series. Precision was investigated according to the CLSI EP15 protocol. Method comparison was performed against a binding assay using radiolabeled cobalamin. Reference values were determined in 100 healthy controls. RESULTS The method was linear in the range of 240 to 1933pmol/L (R2=0.997, lack of fit F=1.61). Precision of low- and high-pool total TC in serum were; 5.2% and 4.3% respectively. Method comparison against a radiolabeled cobalamin binding assay showed a proportional bias of 30% (y=0.70x+126). Total TC reference values were determined at 500-1276pmol/L. CONCLUSION We describe a rapid method to quantify total TC, which can be implemented on routine platforms using commercial Active B12 tests. In addition, apoTC can be assessed by subtracting endogenous holoTC concentration which can be measured in the same run, securing the same calibration level for all three parameters (holoTC, apoTC and total TC). This method is applicable in clinical diagnostics and in larger epidemiological studies.
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Affiliation(s)
- Pieter H Griffioen
- Erasmus MC University Medical Center Rotterdam, Department of Clinical Chemistry, PO box 2040, 3000 CA Rotterdam, The Netherlands
| | - Dianne H K van Dam-Nolen
- Erasmus MC University Medical Center Rotterdam, Department of Clinical Chemistry, PO box 2040, 3000 CA Rotterdam, The Netherlands
| | - Jan Lindemans
- Erasmus MC University Medical Center Rotterdam, Department of Clinical Chemistry, PO box 2040, 3000 CA Rotterdam, The Netherlands
| | - Sandra G Heil
- Erasmus MC University Medical Center Rotterdam, Department of Clinical Chemistry, PO box 2040, 3000 CA Rotterdam, The Netherlands.
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Harrington DJ. Laboratory assessment of vitamin B12 status. J Clin Pathol 2016; 70:168-173. [PMID: 27169753 DOI: 10.1136/jclinpath-2015-203502] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2016] [Revised: 04/19/2016] [Accepted: 04/20/2016] [Indexed: 11/04/2022]
Abstract
The detection and correction of vitamin B12 (B12) deficiency prevents megaloblastic anaemia and potentially irreversible neuropathy and neuropsychiatric changes. B12 status is commonly estimated using the abundance of the vitamin in serum, with ∼148 pmol/L (200 ng/L) typically set as the threshold for diagnosing deficiency. Serum B12 assays measure the sum of haptocorrin-bound and transcobalamin-bound (known as holotranscobalamin) B12 It is only holotranscobalamin that is taken up by cells to meet metabolic demand. Although receiver operator characteristic curves show holotranscobalamin measurement to be a moderately more reliable marker of B12 status than serum B12, both assays have an indeterminate range. Biochemical evidence of metabolic abnormalities consistent with B12 insufficiency is frequently detected despite an apparently sufficient abundance of the vitamin. Laboratory B12 status markers that reflect cellular utilisation rather than abundance are available. Two forms of B12 act as coenzymes for two different reactions. Methionine synthase requires methylcobalamin for the remethylation of methionine from homocysteine. A homocysteine concentration >20 µmol/L may suggest B12 deficiency in folate-replete patients. In the second B12-dependent reaction, methylmalonyl-CoA mutase uses adenosylcobalamin to convert methylmalonyl-CoA to succinyl-CoA. In B12 deficiency excess methylmalonyl-CoA is hydrolysed to methylmalonic acid. A serum concentration >280 nmol/L may suggest suboptimal status in young patients with normal renal function. No single laboratory marker is suitable for the assessment of B12 status in all patients. Sequential assay selection algorithms or the combination of multiple markers into a single diagnostic indicator are both approaches that can be used to mitigate inherent limitations of each marker when used independently.
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Affiliation(s)
- Dominic J Harrington
- The Nutristasis Unit, St Thomas' Hospital NHS Foundation Trust, London, UK.,Division of Women's Health, School of Medicine, King's College London, London, UK
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