FORMS OF COBALAMIN AND VITAMIN-B-12 ANALOGS IN MATERNAL PLASMA, MILK,AND CORD PLASMA

Corrinoids are nutrients synthesized by microorganisms, both as biolog ically active compounds (cobalamins: hydroxo-, cyano-[vitamin B-12] an d the two vitamin B-12 coenzymatic forms: 5' adenosyl- and methyl-coba lamin) and as biologically inactive molecules, the so-called analogs ( cobinamides). Though the transport system in humans favors the biologi cally active forms of vitamin B-12, numerous studies have indicated th e presence of analogs in human material. The present study was underta ken to compare the number of analogs present in maternal plasma and mi lk and in cord plasma, and to determine if milk secretion is contamina ted with potentially harmful vitamin B-12 analogs. The concentrations of cobalamin and of cobinamides were measured in maternal milk, matern al plasma, and cord plasma. Cobalamin analogs were found in maternal p lasma (34.6 +/- 28.1 pmol/L) and in cord plasma (62.1 +/- 32.0 pmol/L; P < 0.005), but not in maternal milk (0.6 +/- 0.7 pmol/L). A combinat ion of reverse phase high pressure liquid chromatography and radioisot opic dilution assay was used to identify the individual cobalamins. Th e major peak in cord plasma was identified as CH3-cobalamin (39%), whi le the peaks of CH3- cobalamin (29.75%) and ado-cobalamin (29.56%) wer e similar in the maternal plasma. The ado-cobalamin peak was higher in milk (41%) than in maternal or umbilical plasma. We have confirmed th e presence of analogs in plasma, but shown that milk is protected from vitamin B-12 analogs, as none were found in the exocrine mammary secr etion. Thus, biologically active vitamin B-12 is selectively transport ed into milk. We found cord plasma to contain significantly higher amo unts of analogs than maternal plasma. Whether this represents conversi on of active forms of the vitamin within the fetus or accumulation of analogs transferred during pregnancy remains to be elucidated.