1
|
Stackpole BJ, Fredericksen JM, Brasch NE. Exploring the potential of the vitamin B 12 derivative azidocobalamin to undergo Huisgen 1,3-dipolar azide-alkyne cycloaddition reactions. J Inorg Biochem 2024; 254:112504. [PMID: 38412777 DOI: 10.1016/j.jinorgbio.2024.112504] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 02/08/2024] [Accepted: 02/09/2024] [Indexed: 02/29/2024]
Abstract
There is considerable interest in using the metalloprotein cofactor vitamin B12 as a vehicle to deliver drugs and diagnostic agents into mammalian or bacterial cells by exploiting the B12-specific active uptake pathways. Conjugation of the cargo via the β-axial site or the 5'-OH of the ribose of the nucleotide are the most desirable sites, to maximise intracellular uptake. Herein we show the potential of conjugation at the beta-azido ligand of the vitamin B12 derivative azidocobalamin via a click-type azide-alkyne 1,3-dipolar cycloaddition (Huisgen cycloaddition) reaction. Reacting azidocobalamin with dimethyl acetylenedicarboxylate at 40 °C results in essentially stoichiometric conversion of azidocobalamin to the corresponding triazolato complex. The stability of the complex as a function of pH and in the presence of cyanide were investigated. The complex is stable in pD 7.0 phosphate buffer for 24 h. The rate of beta-axial ligand substitution was found to be one order of magnitude slower for the triazolatocobalamin complex compared with azidocobalamin.
Collapse
Affiliation(s)
- Ben J Stackpole
- School of Science, Auckland University of Technology, Private Bag 92006, Auckland 1142, New Zealand; The Dodd-Walls Centre for Quantum and Photonic Technologies, Dunedin 9054, New Zealand; The Maurice Wilkins Centre for Molecular Biodiscovery, Private Bag 92019, Auckland 1142, New Zealand
| | - Jessica M Fredericksen
- School of Science, Auckland University of Technology, Private Bag 92006, Auckland 1142, New Zealand; The Dodd-Walls Centre for Quantum and Photonic Technologies, Dunedin 9054, New Zealand; The Maurice Wilkins Centre for Molecular Biodiscovery, Private Bag 92019, Auckland 1142, New Zealand
| | - Nicola E Brasch
- School of Science, Auckland University of Technology, Private Bag 92006, Auckland 1142, New Zealand; The Dodd-Walls Centre for Quantum and Photonic Technologies, Dunedin 9054, New Zealand; The Maurice Wilkins Centre for Molecular Biodiscovery, Private Bag 92019, Auckland 1142, New Zealand.
| |
Collapse
|
2
|
Abstract
The recently delineated structure- and reactivity-based concept of antivitamins B12 has begun to bear fruit by the generation, and study, of a range of such B12 -dummies, either vitamin B12 -derived, or transition metal analogues that also represent potential antivitamins B12 or specific B12 -antimetabolites. As reviewed here, this has opened up new research avenues in organometallic B12 -chemistry and bioinorganic coordination chemistry. Exploratory studies with antivitamins B12 have, furthermore, revealed some of their potential, as pharmacologically interesting compounds, for inducing B12 -deficiency in a range of organisms, from hospital resistant bacteria to laboratory mice. The derived capacity of antivitamins B12 to induce functional B12 -deficiency in mammalian cells and organs also suggest their valuable potential as growth inhibitors of cancerous human and animal cells.
Collapse
Affiliation(s)
- Bernhard Kräutler
- Institute of Organic Chemistry and Center for Molecular Biosciences (CMBI)University of Innsbruck6020InnsbruckAustria
| |
Collapse
|
3
|
Frawley KL, Carpenter Totoni S, Bae Y, Pearce LL, Peterson J. A Comparison of Potential Azide Antidotes in a Mouse Model. Chem Res Toxicol 2020; 33:594-603. [PMID: 31922405 DOI: 10.1021/acs.chemrestox.9b00422] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Three cobalt-containing macrocyclic compounds previously shown to antagonize cyanide toxicity have been comparatively evaluated for the amelioration of sublethal azide toxicity in juvenile (7-8 weeks) Swiss-Webster mice. The lowest effective doses were determined for hydroxocobalamin, a cobalt porphyrin, and a cobalt-Schiff base macrocycle by giving the antidotes 5 min prior to the toxicant, 27 mg (415 μmol) /kg sodium azide. Both male and female mice were evaluated for their response to the toxicant as well as the antidotes, and no significant differences were noted once weight differences were taken into account. Two of the three compounds significantly decreased the recovery time of azide-intoxicated mice at 10 min after the administration of sodium azide, as determined by a behavioral test (pole climbing). Additionally, azide was determined to cause a several degree drop (∼3 °C) in measured tail temperature, and warming the mice led to a more rapid recovery. The mice were also shown to recover more rapidly when given sodium nitrite, 24 mg (350 μmol)/kg, 5 min after the toxicant; this treatment also suppressed the azide-induced tail temperature decrease. Electron paramagnetic resonance (EPR) measurements of mouse blood treated with sodium azide demonstrated the presence of nitrosylhemoglobin at levels of 10-20 μM which persisted for ∼300 min. The presence of the methemoglobin azide adduct was also detected by EPR at a maximum level of ∼300 μM, but these signals disappeared around 200 min after the administration of azide. The treatment of mice with 15N sodium azide proved that the nitrosylhemoglobin was a product of the administered azide by the appearance of a two-line hyperfine (due to the 15N) in the EPR spectrum of mouse blood.
Collapse
Affiliation(s)
- Kristin L Frawley
- Department of Environmental and Occupational Health, Graduate School of Public Health , The University of Pittsburgh , 130 DeSoto Street , Pittsburgh , Pennsylvania 15219 , United States
| | - Samantha Carpenter Totoni
- Department of Environmental and Occupational Health, Graduate School of Public Health , The University of Pittsburgh , 130 DeSoto Street , Pittsburgh , Pennsylvania 15219 , United States
| | - Yookyung Bae
- Department of Environmental and Occupational Health, Graduate School of Public Health , The University of Pittsburgh , 130 DeSoto Street , Pittsburgh , Pennsylvania 15219 , United States
| | - Linda L Pearce
- Department of Environmental and Occupational Health, Graduate School of Public Health , The University of Pittsburgh , 130 DeSoto Street , Pittsburgh , Pennsylvania 15219 , United States
| | - Jim Peterson
- Department of Environmental and Occupational Health, Graduate School of Public Health , The University of Pittsburgh , 130 DeSoto Street , Pittsburgh , Pennsylvania 15219 , United States
| |
Collapse
|
4
|
M Al-Daghri N, Abd-Alrahman S, Wani K, Krishnaswamy S, Alenad A, Hassan MA, S Al-Attas O, Alokail MS. Strong parent-child correlation in circulating vitamin B12 levels and its association with inflammatory markers in Saudi families. INT J VITAM NUTR RES 2019; 90:430-438. [PMID: 30932791 DOI: 10.1024/0300-9831/a000585] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Vitamin B12 deficiency leads to adverse effects on human health, but limited information is available as to whether abnormal vitamin B12 levels are associated between parents and offspring. The present study aimed to assess the association between circulating levels of vitamin B12 in Saudi parents and their children as well as its association with pro-inflammatory markers. A total of 104 Saudi families: 49 fathers, 63 mothers, 94 sons and 79 daughters were selected for the study. Fasting blood samples and anthropometrics were collected. Biochemical parameters, various pro-inflammatory markers and vitamin B12 were measured. Results showed a significant positive correlation between B12 levels in most parent-offspring pairs: mother-daughter (N = 46 pairs, r = 0.72, p < 0.0001); father-daughter (N = 39, r = 0.62, p < 0.0001) and mother-son (N = 51, r = 0.42, p < 0.01). This association was absent in father-son pairs (N = 48, r = 0.26, p = 0.09). Also, B12 was inversely associated with tumor necrosis factor-α and plasminogen activator inhibitor-1 in parents (r = -0.32; p < 0.01 and r = -0.31; p < 0.01 respectively) and children (r = -0.14; p < 0.01 and r = -0.19; p < 0.01 respectively). A significant inverse correlation was found between vitamin B12 and leptin in mothers (r = -0.31, p < 0.05). Our study suggests a strong familial component between B12 levels indicating a possible genetic influence on individual B12 status. Our study also suggests an inverse correlation between circulating levels of vitamin B12 and pro-inflammatory markers. The present study highlights the importance of extending screening in families of patients with abnormal B12 levels and expanding treatment, if necessary, to maximize clinical benefits.
Collapse
Affiliation(s)
- Nasser M Al-Daghri
- Chair for Biomarkers of Chronic Diseases, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia
| | - Sherif Abd-Alrahman
- Chair for Biomarkers of Chronic Diseases, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia
| | - Kaiser Wani
- Chair for Biomarkers of Chronic Diseases, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia
| | - Soundararajan Krishnaswamy
- Chair for Biomarkers of Chronic Diseases, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia
| | - Amal Alenad
- Chair for Biomarkers of Chronic Diseases, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia
| | - Mohammed A Hassan
- Chair for Biomarkers of Chronic Diseases, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia
| | - Omar S Al-Attas
- Chair for Biomarkers of Chronic Diseases, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia
| | - Majed S Alokail
- Chair for Biomarkers of Chronic Diseases, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia
| |
Collapse
|
5
|
Benoit CR, Stanton AE, Tartanian AC, Motzer AR, McGaughey DM, Bond SR, Brody LC. Functional and phylogenetic characterization of noncanonical vitamin B 12-binding proteins in zebrafish suggests involvement in cobalamin transport. J Biol Chem 2018; 293:17606-17621. [PMID: 30237171 PMCID: PMC6231144 DOI: 10.1074/jbc.ra118.005323] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2018] [Revised: 09/13/2018] [Indexed: 12/19/2022] Open
Abstract
In humans, transport of food-derived cobalamin (vitamin B12) from the digestive system into the bloodstream involves three paralogous proteins: transcobalamin (TC), haptocorrin (HC), and intrinsic factor (IF). Each of these proteins contains two domains, an α-domain and a β-domain, which together form a cleft in which cobalamin binds. Zebrafish (Danio rerio) are thought to possess only a single cobalamin transport protein, referred to as Tcn2, which is a transcobalamin homolog. Here, we used CRISPR/Cas9 mutagenesis to create null alleles of tcn2 in zebrafish. Fish homozygous for tcn2-null alleles were viable and exhibited no obvious developmentally or behaviorally abnormal phenotypes. For this reason, we hypothesized that previously unidentified cobalamin-carrier proteins encoded in the zebrafish genome may provide an additional pathway for cobalamin transport. We identified genes predicted to code for two such proteins, Tcn-beta-a (Tcnba) and Tcn-beta-b (Tcnbb), which differ from all previously characterized cobalamin transport proteins as they lack the α-domain. These β-domain-only proteins are representative of an undescribed class of cobalamin-carrier proteins that are highly conserved throughout the ray-finned fishes. We observed that the genes encoding the three cobalamin transport homologs, tcn2, tcnba, and tcnbb, are expressed in unique spatial and temporal patterns in the developing zebrafish. Moreover, exogenously expressed recombinant Tcnba and Tcnbb bound cobalamin with high affinity, comparable with binding by full-length Tcn2. Taken together, our results suggest that this noncanonical protein structure has evolved to fully function as a cobalamin-carrier protein, thereby allowing for a compensatory cobalamin transport mechanism in the tcn2-/- zebrafish.
Collapse
Affiliation(s)
- Courtney R Benoit
- From the Gene and Environment Interaction Section, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892 and
| | - Abigail E Stanton
- From the Gene and Environment Interaction Section, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892 and
| | - Aileen C Tartanian
- From the Gene and Environment Interaction Section, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892 and
| | - Andrew R Motzer
- From the Gene and Environment Interaction Section, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892 and
| | - David M McGaughey
- From the Gene and Environment Interaction Section, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892 and
| | - Stephen R Bond
- Computational and Statistical Genomics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892
| | - Lawrence C Brody
- From the Gene and Environment Interaction Section, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892 and
| |
Collapse
|
6
|
Abstract
Nine compounds are classified as water-soluble vitamins, eight B vitamins and one vitamin C. The vitamins are mandatory for the function of numerous enzymes and lack of one or more of the vitamins may lead to severe medical conditions. All the vitamins are supplied by food in microgram to milligram quantities and in addition some of the vitamins are synthesized by the intestinal microbiota. In the gastrointestinal tract, the vitamins are liberated from binding proteins and for some of the vitamins modified prior to absorption. Due to their solubility in water, they all require specific carriers to be absorbed. Our current knowledge concerning each of the vitamins differs in depth and focus and is influenced by the prevalence of conditions and diseases related to lack of the individual vitamin. Because of that we have chosen to cover slightly different aspects for the individual vitamins. For each of the vitamins, we summarize the physiological role, the steps involved in the absorption, and the factors influencing the absorption. In addition, for some of the vitamins, the molecular base for absorption is described in details, while for others new aspects of relevance for human deficiency are included. © 2018 American Physiological Society. Compr Physiol 8:1291-1311, 2018.
Collapse
Affiliation(s)
- Hamid M Said
- University of California-School of Medicine, Irvine, California, USA.,VA Medical Center, Long Beach, California, USA
| | - Ebba Nexo
- Department of Clinical Medicine, Clinical Biochemistry, Aarhus University Hospital, Aarhus, Denmark
| |
Collapse
|
7
|
Lie KK, Tørresen OK, Solbakken MH, Rønnestad I, Tooming-Klunderud A, Nederbragt AJ, Jentoft S, Sæle Ø. Loss of stomach, loss of appetite? Sequencing of the ballan wrasse (Labrus bergylta) genome and intestinal transcriptomic profiling illuminate the evolution of loss of stomach function in fish. BMC Genomics 2018; 19:186. [PMID: 29510660 PMCID: PMC5840709 DOI: 10.1186/s12864-018-4570-8] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 02/28/2018] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND The ballan wrasse (Labrus bergylta) belongs to a large teleost family containing more than 600 species showing several unique evolutionary traits such as lack of stomach and hermaphroditism. Agastric fish are found throughout the teleost phylogeny, in quite diverse and unrelated lineages, indicating stomach loss has occurred independently multiple times in the course of evolution. By assembling the ballan wrasse genome and transcriptome we aimed to determine the genetic basis for its digestive system function and appetite regulation. Among other, this knowledge will aid the formulation of aquaculture diets that meet the nutritional needs of agastric species. RESULTS Long and short read sequencing technologies were combined to generate a ballan wrasse genome of 805 Mbp. Analysis of the genome and transcriptome assemblies confirmed the absence of genes that code for proteins involved in gastric function. The gene coding for the appetite stimulating protein ghrelin was also absent in wrasse. Gene synteny mapping identified several appetite-controlling genes and their paralogs previously undescribed in fish. Transcriptome profiling along the length of the intestine found a declining expression gradient from the anterior to the posterior, and a distinct expression profile in the hind gut. CONCLUSIONS We showed gene loss has occurred for all known genes related to stomach function in the ballan wrasse, while the remaining functions of the digestive tract appear intact. The results also show appetite control in ballan wrasse has undergone substantial changes. The loss of ghrelin suggests that other genes, such as motilin, may play a ghrelin like role. The wrasse genome offers novel insight in to the evolutionary traits of this large family. As the stomach plays a major role in protein digestion, the lack of genes related to stomach digestion in wrasse suggests it requires formulated diets with higher levels of readily digestible protein than those for gastric species.
Collapse
Affiliation(s)
- Kai K. Lie
- Institute of Marine Research, P.O. Box. 1870, Nordnes, 5817 Bergen, NO Norway
| | - Ole K. Tørresen
- Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, P.O. Box 1066, Blindern, 0316 Oslo, NO Norway
| | - Monica Hongrø Solbakken
- Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, P.O. Box 1066, Blindern, 0316 Oslo, NO Norway
| | - Ivar Rønnestad
- Department of Biology, University of Bergen, P.O. Box 7803, 5020 Bergen, NO Norway
| | - Ave Tooming-Klunderud
- Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, P.O. Box 1066, Blindern, 0316 Oslo, NO Norway
| | - Alexander J. Nederbragt
- Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, P.O. Box 1066, Blindern, 0316 Oslo, NO Norway
- Biomedical Informatics Research Group, Department of Informatics, University of Oslo, P.O. Box 1066, Blindern, 0316 Oslo, Norway
| | - Sissel Jentoft
- Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, P.O. Box 1066, Blindern, 0316 Oslo, NO Norway
| | - Øystein Sæle
- Institute of Marine Research, P.O. Box. 1870, Nordnes, 5817 Bergen, NO Norway
| |
Collapse
|
8
|
Lopes-Marques M, Ruivo R, Delgado I, Wilson JM, Aluru N, Castro LFC. Basal Gnathostomes provide unique insights into the evolution of vitamin B12 binders. Genome Biol Evol 2014; 7:457-64. [PMID: 25552533 PMCID: PMC4350170 DOI: 10.1093/gbe/evu289] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The uptake and transport of vitamin B12 (cobalamin; Cbl) in mammals involves a refined system with three evolutionarily related transporters: transcobalamin 1 (Tcn1), transcobalamin 2 (Tcn2), and the gastric intrinsic factor (Gif). Teleosts have a single documented binder with intermediate features to the human counterparts. Consequently, it has been proposed that the expansion of Cbl binders occurred after the separation of Actinopterygians. Here, we demonstrate that the diversification of this gene family took place earlier in gnathostome ancestry. Our data indicates the presence of single copy orthologs of the Sarcopterygii/Tetrapoda duplicates Tcn1 and Gif, and Tcn2, in Chondrichthyes. In addition, a highly divergent Cbl binder was found in the Elasmobranchii. We unveil a complex scenario forged by genome, tandem duplications and lineage-specific gene loss. Our findings suggest that from an ancestral transporter, exhibiting large spectrum and high affinity binding, highly specific Cbl transporters emerged through gene duplication and mutations at the binding pocket.
Collapse
Affiliation(s)
- Mónica Lopes-Marques
- CIIMAR-Interdisciplinary Centre of Marine and Environmental Research, CIMAR Associate Laboratory, UPorto-University of Porto, Portugal ICBAS-Institute of Biomedical Sciences Abel Salazar, UPorto-University of Porto, Portugal
| | - Raquel Ruivo
- CIIMAR-Interdisciplinary Centre of Marine and Environmental Research, CIMAR Associate Laboratory, UPorto-University of Porto, Portugal
| | - Inês Delgado
- CIIMAR-Interdisciplinary Centre of Marine and Environmental Research, CIMAR Associate Laboratory, UPorto-University of Porto, Portugal
| | - Jonathan M Wilson
- CIIMAR-Interdisciplinary Centre of Marine and Environmental Research, CIMAR Associate Laboratory, UPorto-University of Porto, Portugal Department of Biology, Wilfred Laurier University-Waterloo, Ontario, Canada
| | | | - L Filipe C Castro
- CIIMAR-Interdisciplinary Centre of Marine and Environmental Research, CIMAR Associate Laboratory, UPorto-University of Porto, Portugal Department of Biology, Faculty of Sciences, UPorto-University of Porto, Portugal
| |
Collapse
|
9
|
Furger E, Frei DC, Schibli R, Fischer E, Prota AE. Structural basis for universal corrinoid recognition by the cobalamin transport protein haptocorrin. J Biol Chem 2013; 288:25466-25476. [PMID: 23846701 PMCID: PMC3757208 DOI: 10.1074/jbc.m113.483271] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Revised: 07/08/2013] [Indexed: 12/25/2022] Open
Abstract
Cobalamin (Cbl; vitamin B12) is an essential micronutrient synthesized only by bacteria. Mammals have developed a sophisticated uptake system to capture the vitamin from the diet. Cbl transport is mediated by three transport proteins: transcobalamin, intrinsic factor, and haptocorrin (HC). All three proteins have a similar overall structure but a different selectivity for corrinoids. Here, we present the crystal structures of human HC in complex with cyanocobalamin and cobinamide at 2.35 and 3.0 Å resolution, respectively. The structures reveal that many of the interactions with the corrin ring are conserved among the human Cbl transporters. However, the non-conserved residues Asn-120, Arg-357, and Asn-373 form distinct interactions allowing for stabilization of corrinoids other than Cbl. A central binding motif forms interactions with the e- and f-side chains of the corrin ring and is conserved in corrinoid-binding proteins of other species. In addition, the α- and β-domains of HC form several unique interdomain contacts and have a higher shape complementarity than those of intrinsic factor and transcobalamin. The stabilization of ligands by all of these interactions is reflected in higher melting temperatures of the protein-ligand complexes. Our structural analysis offers fundamental insights into the unique binding behavior of HC and completes the picture of Cbl interaction with its three transport proteins.
Collapse
Affiliation(s)
| | - Dominik C Frei
- Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institut, CH-5232 Villigen PSI and
| | - Roger Schibli
- From the Center for Radiopharmaceutical Sciences and; the Institute of Pharmaceutical Sciences, Eidgenössische Technische Hochschule (ETH) Zürich, CH-8093 Zürich, Switzerland
| | | | - Andrea E Prota
- Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institut, CH-5232 Villigen PSI and.
| |
Collapse
|
10
|
Abstract
BACKGROUND Vitamin B12 (cobalamin) is a cobalt-containing compound synthesized by bacteria and an essential nutrient in mammals, which take it up from diet. The absorption and distribution of dietary vitamin B12 to the organism is a complex process involving several gene products including carrier proteins, plasma membrane receptors and transporters. Disturbed cellular entry, transit or egress of vitamin B12 may lead to low vitamin B12 status or deficiency and eventually hematological and neurological disorders. OBJECTIVE The aim of this review is to summarize the causes leading to vitamin B12 deficiency including decreased intake, impaired absorption and increased requirements. Under physiological conditions, vitamin B12 bound to the gastric intrinsic factor is internalized in the ileum by a highly specific receptor complex composed by Cubilin (Cubn) and Amnionless (Amn). Following exit of vitamin B12 from the ileum, general cellular uptake from the circulation requires the transcobalamin receptor CD320 whereas kidney reabsorption of cobalamin depends on Megalin (Lrp2). Whereas malabsorption of vitamin B12 is most commonly seen in the elderly, selective pediatric, nondietary-induced B12 deficiency is generally due to inherited disorders including the Imerslund-Gräsbeck syndrome and the much rarer intrinsic factor deficiency. Biochemical, clinical and genetic research on these disorders considerably improved our knowledge of vitamin B12 absorption. This review describes basic and recent findings on the intestinal handling of vitamin B12 and its importance in health and disease.
Collapse
|