S100B Protein Concentrations in Cord Blood: Correlations with Gestational Age in Term and Preterm Deliveries

S100B is an acidic calcium-binding protein of the EF-hand family concentrated in the nervous system, where it is located mainly in glial cells (1). Although many hypotheses have been formulated, its biological role is still debated, but its appearance in biological fluids has been shown to be a reliable index of brain distress (2). We investigated the relationship between S100B concentrations in cord blood and gestational age in the third trimester of pregnancy in normal preterm and term deliveries. We investigated 58 women with consecutive singleton physiological pregnancies (30 at term and 28 preterm), with normal flow velocimetry waveforms in the uteroplacental vessels, whose delivery was between 27 and 42 weeks of gestation. Gestational age was determined by clinical data and by a first-trimester ultrasound scan. Appropriate growth was defined by the presence of ultrasonographic signs (when biparietal diameter and abdominal circumference were between the 10th and 90th centiles) according to the normograms of Campbell and Thoms (3) and by postnatal confirmation of a birth weight between the 10th and 90th centiles according to our population standards after correction for the mother’s height, weight, and parity, and the sex of the newborn. Exclusion criteria were multiple pregnancies, intrauterine growth retardation, gestational hypertension, diabetes and infections, fetal malformations, chromosomal abnormalities, perinatal asphyxia, and dystocia. The study protocol was approved by the Ethics Committee of the Giannina Gaslini Children’s Hospital, Genoa University; the parents of the subjects examined gave informed consent. At delivery, the umbilical cord was clamped before any signs of breathing, and blood was drawn from the umbilical vein. Heparin-treated blood samples taken from the umbilical cord were centrifuged immediately at 900g for 10 min, and the supernatants were stored at −70 °C before measurement. The S100B protein concentration was measured in all samples, using a commercially available two-site IRMA kit (Sangtec 100; AB Sangtec Medical). This IRMA is specific for the β subunit of the protein, which is known to be predominant (96%) in the human brain (4). Each measurement was performed in duplicate according to the manufacturer’s recommendations, and the averages were reported. The detection limit of the assay was 0.2 μg/L. The imprecision (CV) was <10% for both within and between runs. Concentrations of the cord blood S100B in the groups examined were analyzed by the Mann–Whitney two-sided U-test; P <0.05 was considered significant. The correlation between the blood concentrations of S100B and gestational age was analyzed by linear regression analysis. At birth, all newborns had unremarkable clinical examinations, and no overt neurological injury was observed on discharge from hospital. As expected, gestational age at birth (32.2 ± 3.1 vs 39.4 ± 1.4 weeks) and birth weight (1859 ± 723 g vs 3250 ± 210 g) were higher in the term group (P <0.01 for both), whereas no significant differences were observed regarding delivery mode, the Apgar score at the 1st (8 ± 2 vs 9 ± 1) and 5th min (9 ± 1 vs 8 ± 1), and gender (preterm female/male ratio, 13/15; term, female/male ratio, 16/14). Cord blood S100B concentrations were significantly higher in the preterm group, declining steadily near term and becoming undetectable or at the detection limit in the term group (1.31 ± 0.64 vs 0.47 ± 0.35 μg/L; P <0.001; Fig. 1 ). Cord blood S100B was significantly correlated with gestational age (r = −0.69; P <0.01). S100B protein gender differences were observed in the whole study population (1.14 ± 0.69 vs 0.75 ± 0.51 μg/L; P <0.05) and in both groups (preterm, 1.65 ± 0.48 vs 0.99 ± 0.61 μg/L; term, 0.75 ± 0.60 vs 0.19 ± 0.12 μg/L; P <0.05 for both), with S100B being significantly higher in female preterm and term fetuses. The present data show the relationship between S100B concentrations in the umbilical cord blood and gestational ages in the two genders. The higher concentrations of S100B in preterm fetuses in comparison with fetuses at term could involve blood-brain barrier permeability and cerebral circulation, which could be different in preterm and term fetuses. In this respect, cerebral Doppler velocimetry waveform differences between early and late gestational ages have been reported (5). Among the functions attributed to this protein, all of which are still the subject of debate, the possibility that S100B acts as a cytokine with neurotrophic effects at physiological concentrations appears especially interesting. This hypothesis has been essentially supported in experimental models in laboratory animals and cell cultures (1). The present finding in humans could be related to a higher concentration of the trophic factor in the extracellular compartment in the third trimester of pregnancy, when brain maturation processes are active. It could be relevant in this respect that the peripheral blood of preterm infants without pathological signs had higher S100B concentrations than infants born at term, in whose blood the protein is essentially absent (6). The progressive decrease in S100B concentrations in cord blood at term could reflect a reduced release of the trophic factor at a later stage of fetal-neonatal brain maturation. The origin of S100B in the umbilical cord veins could be the fetal nervous system, which is known to contain the protein at the stages of development under examination. The pattern of accumulation of the protein in human fetal development at these stages is essentially complete, except in the cortex, where the protein appears later (7). It may be noteworthy in this respect that the caudo-rostral pattern of accumulation of the protein has been related to the biochemical, morphological, and electrophysiological maturation of the nervous system (8). S100B could also be released from other sites in which it is concentrated, such as adipose tissue, although the data on the presence of the protein in adipose tissue at this age are not conclusive. Finally, the possibility that S100B is released from placental tissue as a trophic factor should also be taken into account, although its possible presence in the placenta has not yet been studied. The present findings in gender differences in cord blood S100B concentrations constitute the first observation of gender-related differences in S100B concentrations in biological fluids in the perinatal period. These differences could be explained by different patterns of brain maturation in the two sexes (9). In this respect, it could be relevant that the genetically modulated overexpression of S100B has been reported to affect behavior in females, with no appreciable effects in males (10). In any case, the present data suggest the usefulness of investigating S100B dynamics in vivo, with special reference to a possible role of the protein in maturation, which is a matter of speculation. We thank Sangtec Medical and BykGulden Italia for partially supporting this work. Correlation of cord blood S100B protein concentrations (μg/L) with gestational age (weeks) at sampling in female (triangles) and male (circles) preterm (open symbols) and term (filled symbols) fetuses. Values are expressed as median (solid line). The lower and upper dotted lines represent the 10th and 90th centiles, respectively. The lower and upperdashed lines represent the 25th and 75th centiles, respectively.