Vitamin B12 transport from food to the body's cells—a sophisticated, multistep pathway

Abstract

Vitamin B(12) (B(12); also known as cobalamin) is a cofactor in many metabolic processes; deficiency of this vitamin is associated with megaloblastic anaemia and various neurological disorders. In contrast to many prokaryotes, humans and other mammals are unable to synthesize B(12). Instead, a sophisticated pathway for specific uptake and transport of this molecule has evolved. Failure in the gastrointestinal part of this pathway is the most common cause of nondietary-induced B(12) deficiency disease. However, although less frequent, defects in cellular processing and further downstream steps in the transport pathway are also known culprits of functional B(12) deficiency. Biochemical and genetic approaches have identified novel proteins in the B(12) transport pathway--now known to involve more than 15 gene products--delineating a coherent pathway for B(12) trafficking from food to the body's cells. Some of these gene products are specifically dedicated to B(12) transport, whereas others embrace additional roles, which explains the heterogeneity in the clinical picture of the many genetic disorders causing B(12) deficiency. This Review describes basic and clinical features of this multistep pathway with emphasis on gastrointestinal transport of B(12) and its importance in clinical medicine.

Tumor Imaging in Patients with Advanced Tumors Using a New 99mTc-Radiolabeled Vitamin B12 Derivative

“…Haptocorrin carries the major part of circulating cobalamin, but interestingly haptocorrin is not filtered in the kidney and no receptor recognizing haptocorrin has been identified in the kidney. The function of haptocorrin in the transport and use of cobalamin is unsettled (2,13). However, 2 unique features of haptocorrin are important for the concept of the present paper.…”

“…A complex transport process involving several soluble binding proteins and corresponding receptors ensure the transport of the vitamin from the intestine through the bloodstream to the target cell (2,3). Intrinsic factor, present only in the gastrointestinal tract, mediates the intestinal absorption of cobalamin.…”

Vitamin B12: Could It Be a Promising Immunotherapy?

“…IFs represent stomach-speciic glycoproteins secreted by the stomach parietal cells and are essential for the absorption of B12 from the intestinal lumen into the bloodstream [17,21]. Some genetic Immunotherapy -Myths, Reality, Ideas, Futuredefects or pathological changes in gastric and intestinal mucosa may lead to a deiciency of IF, in which case the transport of vitamin B12 is impeded and deiciency is present [17].…”

History of the therapy of pernicious anemia

“…Az élővilágban B 12 -(kobalamin) vitamint egyedül mikroorganizmusok állítanak elő, amelyek a növényevő álla-tokba jutva nagy mennyiségben termelnek B 12 -t. A B 12 felszívódásához és a szervezet sejtjeibe történő bejutá-sához több transzportfehérjére van szükség, amelyek homológ kobalamint megkötő, valamint receptort felismerő szekvenciát tartalmaznak [26,27,28]. A kobalamintranszport-fehérjék közül említést érdemel a genetikailag jól jellemzett transzkobalamin-I (haptocorin R-protein, R-faktor, TC-I), a gastric intrinsic factor (GIF) és a transzkobalamin-II (TC-II).…”

“…Ez a körforgalom -a többi vitamintól eltérően -elvileg hosszú időre biztosítja a szervezet kobalaminigényét (napi 2-3 μg.) Említésre méltó, hogy a szervezetbe jutott kobalamin 1-2%-a passzív diffúzió útján is felszívódhat [26,27].…”