The Cobalamin-Binding Proteins Transcobalamin and Haptocorrin in Maternal and Cord Blood Sera at Birth

Abstract

Background: Two proteins carry vitamin B 12 in plasma. Transcobalamin (TC) carries ϳ25% of total plasma vitamin B 12 and is 6% to 20% saturated with cobalamin. Haptocorrin (HC) binds ϳ80% of total cobalamin and is largely saturated with cobalamin. Methods: We investigated the distribution and the relationship between concentrations of cobalamin, total and holo forms of TC, and HC in blood samples from pregnant women just before delivery (n ‫؍‬ 92) and in cord blood samples from their newborn babies. We also investigated the relationship between these proteins and concentrations of methylmalonic acid (MMA), the functional marker of vitamin B 12 status. Results: Concentrations of total serum cobalamin, total HC, holoHC, and percentage of HC saturation were higher in cord blood than in the maternal blood (mean cobalamin, 268 vs 188 pmol/L; total HC, 648 vs 538 pmol/L; holoHC, 441 vs 237 pmol/L; HC saturation, 70% vs 47%). Moreover, total TC was low in cord blood, whereas both holoTC and TC saturation were higher in cord blood than in the maternal blood (mean total TC, 654 vs 1002 pmol/L; holoTC, 118 vs 53 pmol/L; TC saturation, 19.8% vs 5.4%). Higher maternal serum cobalamin was associated with higher cord blood holoTC and TC saturation (P <0.05). Gestational age was also a significant determinant of baby total TC, TC saturation, total HC, and holoHC.

A longitudinal study of serum cobalamins and its binding proteins in lactating women

“…Serum cobalamins decrease during pregnancy (Bartels et al, 1989;Willis et al, 1989;Koebnick et al, 2002), but based on the results from our study and a previous study (Dostálová, 1984), it normalizes within a few weeks post-partum. These observations are confirmed by comparing the level of serum cobalamins just before birth measured in a previous study (Obeid et al, 2005) with the level 3 weeks postpartum obtained in our study. Between 3 weeks and 9 months post-partum, we found no alteration in serum cobalamins, and the levels obtained were well in accordance with established reference intervals for non-lactating women, Table 2.…”

“…Comparing the levels of TC and HC obtained 3 weeks postpartum with the levels obtained just before birth using the same ELISA methods (Obeid et al, 2005), the levels of total proteins (TC and HC) seem to decrease significantly at or just after birth, whereas the levels of holoproteins (TC and HC) seem to increase, significantly. In order to explore this observation, a longitudinal study on pregnant women including samples drawn just before and after birth is needed.…”

Vitamin B-12 and Perinatal Health

“…Several cross-sectional studies have examined the associations between maternal and neonatal vitamin B-12 status at delivery and have found strong correlations for serum vitamin B-12 and related biomarkers. For example, in a cross-sectional study in Germany, maternal and cord blood holotranscobalamin concentrations were significantly correlated (r = 0.68, P < 0.001) (28). Several cohort studies have noted associations between maternal serum and neonatal (or cord blood) vitamin B-12 concentrations, and some studies found that neonatal vitamin B-12 concentrations were significantly higher than maternal concentrations.…”

“…Maternal vitamin B-12 concentrations during pregnancy are thought to be closely associated with fetal (28,29) and early infant (30,31) vitamin B-12 status. Vitamin B-12 is transported by haptocorrin and TC; >70% of vitamin B-12 transport across the placenta is facilitated by TC, whereas the remainder is bound by haptocorrin (32).…”

Markedly Increased Vitamin B12 Concentrations Attributable to IgG–IgM–Vitamin B12 Immune Complexes

“…Vitamin B 12 in serum is bound to 2 proteins, transcobalamin (TC) 3 II and haptocorrin (HC). TC is a 43-kDa nonglycosylated serum protein that is synthesized primarily in the enterocytes and is essential for the transport of vitamin B 12 from ileum into the blood and then into most cells via receptor-mediated endocytosis (1,2 ). TC saturated with vitamin B 12 (holo-TC) constitutes 6%-20% of endogenous circulating vitamin B 12 , whereas unsaturated TC constitutes ϳ90% of TC.…”