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

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?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.