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Tissue distribution of oral vitamin B12 is influenced by B12 status and B12 form: an experimental study in rats

Kornerup, Linda S., Fedosov, Sergey N., Juul, Christian B., Greibe, Eva, Heegaard, Christian W., Nexo, Ebba
European journal of nutrition 2018 v.57 no.4 pp. 1459-1469
absorption, animal models, blood, brain, cattle, diet, feces, heart, intestines, kidneys, liver, males, muscles, rats, skeletal muscle, spleen, tissue distribution, urine, vitamin B12
PURPOSE: Hydroxocobalamin (HOCbl) is the dominating Cbl form in food, whereas cyanocobalamin (CNCbl) is common in vitamin pills and oral supplements. This study compares single-dose absorption and distribution of oral HO[⁵⁷Co]Cbl and CN[⁵⁷Co]Cbl in Cbl-deficient and normal rats. METHODS: Male Wistar rats (7 weeks) were fed a 14-day diet with (n = 15) or without (n = 15) Cbl. We compared the uptakes of HO[⁵⁷Co]Cbl (free or bound to bovine transcobalamin) and free CN[⁵⁷Co]Cbl administered by gastric gavage (n = 5 in each diet group). Rats were sacrificed after 24 h. Blood, liver, kidney, brain, heart, spleen, intestines, skeletal muscle, 24-h urine and faeces were collected, and the content of [⁵⁷Co]Cbl was measured. Endogenous Cbl in tissues and plasma was analysed by routine methods. RESULTS: Mean endogenous plasma-Cbl was sevenfold lower in deficient vs. normal rats (190 vs. 1330 pmol/L, p < 0.0001). Cbl depletion increased endogenous Cbl ratios (tissue/plasma = k ᵢₙ/k ₒᵤₜ) in all organs except for the kidney, where the ratio decreased considerably. Twenty-four-hour accumulation of labelled Cbl showed that HOCbl > CNCbl (liver) and CNCbl > HOCbl (brain, muscle and plasma). CONCLUSIONS: The Cbl status of rats and the administered Cbl form influence 24-h Cbl accumulation in tissues and plasma.