Tissue distribution of oral vitamin B12 is influenced by B12 status and B12 form: an experimental study in rats.
OBJECTIVE
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 = kin/kout) 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.
Department of Clinical Biochemistry, Aarhus University Hospital, Palle Juul-Jensens Boulevard 99, 8200, Aarhus N, Denmark. lindajen@rm.dk.
Linda S
LS
Kornerup
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
Sergey N
SN
Fedosov
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
Christian B
CB
Juul
Department of Clinical Biochemistry, Aarhus University Hospital, Palle Juul-Jensens Boulevard 99, 8200, Aarhus N, Denmark.
Eva
E
Greibe
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
Christian W
CW
Heegaard
Department of Clinical Biochemistry, Aarhus University Hospital, Palle Juul-Jensens Boulevard 99, 8200, Aarhus N, Denmark.
Ebba
E
Nexo
D000818:Animals; D002417:Cattle; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D014018:Tissue Distribution; D014805:Vitamin B 12 / Q000008:administration & dosage / Q000378:metabolism*
D014805:Vitamin B 12
Cobalamin deficiency; Cyanocobalamin; Hydroxocobalamin; Intestinal absorption; Kinetic modelling