Human vitamin B12 absorption measurement by accelerator mass spectrometry using specifically labeled14C-cobalamin

Colleen Carkeet, Stephen R. Dueker, Jozsef Lango, Bruce A. Buchholz, Joshua W. Miller, Ralph Green, Bruce D. Hammock, John R. Roth, Peter J. Anderson

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


There is a need for an improved test of human ability to assimilate dietary vitamin B12. Assaying and understanding absorption and uptake of B12 is important because defects can lead to hematological and neurological complications. Accelerator mass spectrometry is uniquely suited for assessing absorption and kinetics of carbon-14 (14C)-labeled substances after oral ingestion because it is more sensitive than decay counting and can measure levels of 14C in microliter volumes of biological samples with negligible exposure of subjects to radioactivity. The test we describe employs amounts of B12 in the range of normal dietary intake. The B12 used was quantitatively labeled with 14C at one particular atom of the dimethylbenzimidazole (DMB) moiety by exploiting idiosyncrasies of Salmonella metabolism. To grow aerobically on ethanolamine, Salmonella enterica must be provided with either preformed B12 or two of its precursors, cobinamide and DMB. When provided with 14C-DMB specifically labeled in the C2 position, cells produced 14C-B 12 of high specific activity (2.1 GBq/mmol, 58 mCi/mmol) (1 Ci = 37 GBq) and no detectable dilution of label from endogenous DMB synthesis. In a human kinetic study, a physiological dose (1.5 μg, 2.2 kBq/59 nCi) of purified 14C-B12 was administered and showed plasma appearance and clearance curves consistent with the predicted behavior of the pure vitamin. This method opens new avenues for study of B12 assimilation.

Original languageEnglish (US)
Pages (from-to)5694-5699
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number15
StatePublished - Apr 11 2006
Externally publishedYes

ASJC Scopus subject areas

  • General


  • Dimethylbenzimidazole
  • Ethanolamine
  • Metabolic engineering
  • Salmonella
  • Schilling test


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