Forms of cobalamin and vitamin B 12 analogs in maternal plasma, milk, and cord plasma

Abstract

Corrinoids are nutrients synthesized by microorganisms, both as biologically active compounds (cobalamins: hydroxo-, cyano-[vitamin B 12], and the two vitamin B 12 coenzymatic forms: 5′ adenosyl- and methyl-cobalamin) and as biologically inactive molecules, the so-called analogs (cobinamides). Though the transport system in humans favors the biologically active forms of vitamin B 12, numerous studies have indicated the presence of analogs in human material. The present study was undertaken to compare the number of analogs present in maternal plasma and milk and in cord plasma, and to determine if milk secretion is contaminated with potentially harmful vitamin B 12 analogs. The concentrations of cobalamin and of cobinamides were measured in maternal milk, maternal plasma, and cord plasma. Cobalamin analogs were found in maternal plasma (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 combination of reverse phase high pressure liquid chromatography and radioisotopic dilution assay was used to identify the individual cobalamins. The major peak in cord plasma was identified as CH 3-cobalamin (39%), while the peaks of CH 3-cobalamin (29.75%) and ado-cobalamin (29.56%) were similar in the maternal plasma. The ado-cobalamin peak was higher in milk (41%) than in maternal or umbilical plasma. We have confirmed the presence of analogs in plasma, but shown that milk is protected from vitamin B 12 analogs, as none were found in the exocrine mammary secretion. Thus, biologically active vitamin B 12 is selectively transported into milk. We found cord plasma to contain significantly higher amounts of analogs than maternal plasma. Whether this represents conversion of active forms of the vitamin within the fetus or accumulation of analogs transferred during pregnancy remains to be elucidated.