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

European Journal of Nutrition, Mar 2017

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.

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

Linda S. Kornerup 0 1 Sergey N. Fedosov 0 1 Christian B. Juul 0 1 Eva Greibe 0 1 Christian W. Heegaard 0 1 Ebba Nexo 0 1 0 Department of Molecular Biology and Genetics, Aarhus University , Aarhus , Denmark 1 Department of Clinical Biochemistry, Aarhus University Hospital , Palle Juul-Jensens Boulevard 99 8200 Aarhus N , Denmark 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 = 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). Hydroxocobalamin; Cyanocobalamin; Intestinal absorption; Cobalamin deficiency; Kinetic modelling - Vitamin B12 (cobalamin, Cbl) is essential for a normal neurological function and formation of blood cells. The vitamin is supplied via dietary animal products and increasingly through food fortification or vitamin pills [1]. The Cbl forms present in foods are the coenzymes methyl- and 5′-deoxyadenosyl-Cbl (MeCbl, AdoCbl). A brief exposure to light converts both coenzymes to hydroxo-Cbl (HOCbl), making HOCbl the ubiquitous food form of Cbl [2]. CyanoCbl (CNCbl) is chemically stable, and it is the predominant Cbl form used in industrial Cbl products (food fortification and vitamin pills) [3]. The general concept is that HOCbl and CNCbl are comparable concerning their absorption and tissue distribution patterns, while free Cbl is absorbed more efficiently than food bound Cbl (for a review see ref. [3]). Our recent data in normal rats challenge both of these statements [4]. We compared 24-h oral absorption of CN[57Co] Cbl (free or bound to bovine transcobalamin (TC), the Cbl binding protein in milk) and free HO[57Co]Cbl. We found no difference between TC-bound and free CN[57Co]Cbl, as well as no difference in the total absorption levels of the two Cbl forms. However, the liver HO[57Co]Cbl accumulation was twice as high as the CN[57Co]Cbl accumulation. Notably, this result challenges the concept that CN[57Co] Cbl and HO[57Co]Cbl behave alike and thereby are of equal value for treatment/prevention of Cbl deficiency. The current study was undertaken to investigate whether the observed differences in distribution of HOCbl and CNCbl also were mirrored in other tissues than liver and kidney and whether this distribution was dependent on Cbl status. In addition, we wanted to explore whether the food form of Cbl (HOCbl) was absorbed alike when administered free or bound to bovine TC. Materials and methods Thirty male Wistar rats (Taconic Bioscience Inc., Denmark) were used for the experiments; 7 weeks old, weighing approx. 200  g upon arrival to the animal facilities. The rats were housed in pairs in standard cages (Makrolon 1291  H type III H, 800  cm2, Tecniplast, Italy) with free access to food and tap water. The room temperature was 19–20 °C and the humidity 60% with a 12/12  h light/ dark cycle. Bedding material (asp chips, Tapvei, Finland) and soft paper wool (LBS biotech, United Kingdom) were changed daily. Rats were kept for 2  weeks, during which half (n = 15) were randomized to a Cbl-deficient diet (Altromin C1024, Brogaarden, Denmark) and the other half (n = 15) to the control diet (Altromin C1000, Brogaarden, Denmark). The calorie contents of the two diets were equal, but the Cbl-deficient diet contained less cellulose and corn starch and more sucrose compared with the control diet. The manufacturer assessed Cbl content by using the tabulated values for Cbl in different food sources. Therefore, we quantified Cbl in the diets by extracting 0.3 g of solids with 1.5 mL of water. After centrifugation, Cbl was measured in the supernatant employing a Cobas 6000 (Roche Diagnostics). During the analysis, all Cbl is converted to CNCbl; thus, the Cbl content was calculated employing the molecular weight for CNCbl, MW: 1355. The mean of two independent measures is shown (Cbl-deficient diet: <0.5 (<0.5, <0.5) µg/kg, control diet: 60 (69, 51) µg/kg). All experiments were conducted in agreement with EU Directive 2010/63/E (...truncated)


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Linda S. Kornerup, Sergey N. Fedosov, Christian B. Juul, Eva Greibe, Christian W. Heegaard, Ebba Nexo. Tissue distribution of oral vitamin B12 is influenced by B12 status and B12 form: an experimental study in rats, European Journal of Nutrition, 2017, pp. 1-11, DOI: 10.1007/s00394-017-1424-0