Absorption and Transport of Cobalamin (Vitamin B₁₂)

Abstract

This review apprises the reader of recent advances in cobalamin absorption and transport since 1970. This field has been of interest to gastroenterologists, hematologists, and biochemists as well as nutritionists. Clinical conditions leading to cobalamin deficiency present especially to the first two of these specialties. Many recent advances involve biochemical definition of the specific transport proteins themselves. Full understanding of the multiple clinical conditions associated with cobalamin deficiency requires some knowledge of these proteins. We do not discuss every paper in the field, especially the early literature (see 47, 61, 150). Despite rapid strides in understanding the mechanism of absorption and transport of cobalamin both in prokaryotic and eukaryotic cells, the complete sequence of events during cellular absorption at the plasma membrane level and events in the cells that mediate intracellular movement of cobalamin have not been elucidated completely. Here we emphasize the current state of knowledge about cobalamin absorption and transport in man and other mammalian systems, particularly the physiological role and biochemical nature of proteins involved (intrinsic factor, intrinsic factor-cobalamin receptor, transcobalamins).

Increased Serum Corrinoids Correlates with Disease Severity and IgA Levels in Alcoholic Cirrhosis

“…A release of corrinoids from the liver into the blood circulation occurs certainly in cyto lytic hepatitis. In this case, it is associated with an increased seric level of unsaturated TC [24], Concerning our patients we did not observe any significant change of seric con centration of unsaturated TC and He, nei ther in HV nor in IVC nor in SVC. More over, the saturated TC was enhanced in the same proportion as the saturated He, in group C. suggesting that the elevated seric level of corrinoids in alcoholic liver disease is only in part the result of an inhibition of hepatic clearance of He by circulating glyco proteins.…”

“…An in crease in plasma vitamin B12 levels has also been reported in other liver disorders, e.g. viral hepatitis [12,24] and alcoholic hepati tis where hepatic cytolysis is a common fea ture [5], In the same way, Baker et al [5] observed recently that high plasma vitamin B12 levels correlated significantly with the standard liver function tests, including bili rubin, cholylglycin, alkaline phosphatase, al anine serum transferase and prothrombin time, in case of alcoholic hepatitis. They concluded that the increased plasma vitamin B12 levels were correlated to the severity and the mortality of alcoholic hepatitis.…”

Bipolar Functional Expression of Transcobalamin II Receptor in Human Intestinal Epithelial Caco-2 Cells

“…However, it is not known whether TC II like IF in some species (28) is secreted from the pancreas and mediate luminal uptake of Cbl via TC II-R. 2) patients with inherited disorders (29,30) of IF or IFCR develop Cbl deficiency, suggesting that IF/IFCR-mediated Cbl transport system is the only physiologically operational intestinal uptake system for Cbl transport in man. Despite its lack of importance in the normal uptake of dietary Cbl, it is possible that apical TC II-R can mediate uptake of TC II-Cbl when presented orally, particularly in patients who malabsorb Cbl due to several inherited disorders (29,30) or to surgical procedures such as gastrectomy and ileal resection (31). A child who malabsorbed Cbl due to inherited TC II deficiency responded well in Schilling test (32) (which measures Cbl absorption) when the child was orally fed with Cbl complexed to TC II.…”

Effects of Vitamin B12Analogues with Alternations in the Side Chains of the Corrin Ring on Urinary Methylmalonate Excretion in Vitamin B12-Deficient Rats

“…14 ) The order of the contribution of these propionamides for the binding of Cbl to IF and TC has been shown to be d>b>e.…”