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Identification and quantitation of cobalamin and cobalamin analogues in human feces^1,2,3

¹ From the Division of Hematology, Department of Medicine, University of Colorado Health Sciences Center, Denver, CO

Background: Cobalamin (vitamin B-12) and cobalamin analogues are present in human feces, but a complete identification has not been established, and the amounts present have not been determined.

Objectives: We aimed to develop a liquid chromatography–mass spectrometry method for cobalamin and cobalamin analogues and to identify and quantitiate the amounts present in human feces.

Design: Fecal samples were obtained from 20 human subjects in good general health. The samples were analyzed for the presence and amounts of cobalamin and 12 cobalamin analogues that were synthesized with and without the incorporation of stable isotopes.

Results: Cobalamin and 7 cobalamin analogues were identified and quantitated in human feces. The mean for the total amount present in 18 subjects whose daily intake was 25 µg cobalamin from vitamin supplements was 1309 ng cobalamin equivalents/g wet wt of feces. Cobalamin (1.4%) and cobinamide (1.8%) (an incomplete corrinoid) represented a small portion of the total amount. Six cobalamin analogues that contain a base other than the 5,6-dimethylbenzimidizidole in cobalamin were present. The bases and their mean amounts (in %) are 2-methyladenine (60.6%), p-cresol (16.3%), adenine (12.5%), 2-(methylthio)adenine (15.5%), 5-hydroxybenzimidazole (1.8%), and phenol (0.1%). One subject ingested 1 mg cobalamin/d and another ingested 2 mg cobalamin/d, and they appeared to convert most of the cobalamin to cobinamide and the 4 analogues that contain the bases—2-methyladenine, p-cresol, adenine, and 2-(methylthio)adenine.

Conclusions: Cobalamin analogues are present in human feces and account for >98% of the total of cobalamin plus cobalamin analogues. A major portion of large amounts of ingested cobalamin appears to be converted to cobalamin analogues.