Biological function of cobalamin: causes and effects of hypocobalaminemia at the molecular, cellular, tissue and organism level

Abstract

Cobalamin (vitamin B12) is a complex compound, which is classified as a water-soluble vitamin. Absorption of cobalamin in the gut and its transport to cells is a unique process, in which many proteins are involved. The loss of function of these proteins causes serious cell homeostasis disturbance, which may result in the dysfunction of many tissues and organs. Vitamin B12, a cofactor of methionine synthase, provides methylation process and nucleic acid synthesis. Cobalamin is also necessary for methylmalonyl-CoA mutase activity. The enzyme synthesizes succinyl-CoA, an intermediate in tricarboxylic acid cycle. Vitamin B12 deficiency is an important and current health problem. It may be caused by insufficient dietary intake, age, or disease-related malabsorption and genetic defects of mechanisms involved in the absorption, transport and metabolism of cobalamin. Hypocobalaminemia can also result from long-term pharmacotherapy with medicines: metformin, proton pump inhibitors (e.g. omeprazole) and H2-receptor antagonists (e.g. ranitidine). Significant clinical symptoms of cobalamin deficiency include hematological abnormalities, mainly megaloblastic anemia, as well as neurological disorders resulting from degeneration within the nervous system. Early diagnosis and starting treatment with vitamin B12 increase chances for a complete cure. Therefore, the diagnostically important symptom of hypocobalaminemia may be skin manifestations, mainly hyperpigmentations, but also premature graying of hair. The aim of this review article was to summarize the current state of knowledge on the biological function of cobalamin, as well as the causes and consequences of its deficiency at the molecular, cellular, tissue and organism level.