Correlation of Urine Concentration of S100B in Extremely Premature Infants With Gestational Age and Severity of Intraventricular Hemorrhage

S100B is a low molecular weight calcium binding protein found predominantly in the central nervous system, specifically astroglial cells.[1] S100B plays a role in calcium-dependent information processing and intracellular is involved in the regulation of cytoskeleton and cell morphology.[1] S100B is secreted by astrocytes and exhibits dose dependent extracellular cytokine functions. In tissue culture at nanomolar concentration, S100B stimulates neuronal growth, development, and regeneration and protects against degeneration. At micromolar concentration, S100B is neurotoxic [2] and stimulates apoptosis potentially through interaction with RAGE receptor, by induction of NO synthase, and through the caspase cascade. Thus, markedly elevated concentration of S100B, released from damaged astrocytes, may propagate neuronal death. To support this hypothesis, over expression of S100B is present in wobble mice, an animal model for neuronal degeneration.[3] S100B is also increased in brains of patients with Alzheimer's disease [1] and in the amniotic fluid of fetuses [4] and brains of patients with Down's syndrome.[1]

S100B is released from damaged astroglial cells and may indirectly reflect neuronal damage.[5,6] S100B is elevated in cerebrospinal fluid (CSF) of adult patients within 48 hours after infarction and remains elevated for at least 7 days after the event.[6] S100B is also elevated in CSF for the first 3 days after traumatic brain injury [7] and subarachnoid hemorrhage.[8] S100B readily crosses a dysfunctional blood-brain barrier and serum concentration of S100B is significantly increased in adult patients after traumatic brain injury [9], stroke [10], or cardiac arrest.[5] Serum S100B rises for 2-4 days after brain trauma or infarct and its concentration correlates with size of damage as identified by CT scan. [9,10] For patients with traumatic brain injury, elevated concentration of S100B was noted on admission and significantly predicted development of increased intracranial pressure 4-5 days later. [9] After cardiac arrest, serum S100B concentration was statistically elevated by 30 minutes after initiation of CPR and continued to be significantly elevated in those patients who later exhibited brain damage by CT scan or neurological exam.[5] This significant elevation in serum S100B lasted for at least 7 days. In addition, serum S100B concentration correlated with morbidity [9] and neurological outcome. [10] While the t1/2 of S100B is ~2 hours in adults, persistent increased concentration of S100B in serum indicates continuous release from damaged cells.

S100B has been shown to be differentially distributed in different cortical regions of the brain during fetal development and increases in concentration during gestation, supporting its role in the development and maturation of the CNS.[11] It is postulated that early in development, S100B leads to glial cell proliferation while later it leads to extension of neurites, regulation of fiber sprouting, formation/maintenance of synapses, and maturation of glial cells.[1] Cord blood concentration of S100B has been shown to be inversely related to gestational age between 27 to 42 weeks gestation.[12] Thirty term infants (37-42 weeks) had cord blood S100B levels < 1 ug/L while 28 preterm infants (27-36 weeks) had cord blood levels between 0.5 and 2.7 ug/L. Higher serum concentration of S100B may be due to the lack of integrity of the blood-brain barrier in preterm infants in conjunction with an increased secretion of S100B from astroglial cells.

Due to its low molecular weight (10.5 kD) and high degree of solubility, S100B is excreted through the kidneys. It has been detected in the first void urine of infants between 26-42 weeks gestation with the most preterm infant exhibiting the highest concentration of S100B (3.17 ug/L). [13] Urine S100B concentration was at the detection limit of the assay (0.02 ug/L) for term infants. There was a significant negative correlation between S100B concentration in the urine and gestational age (r=-.79, p<0.001), but the data was not shown. Only 23 preterm infants (gestational age 26-36 weeks) were enrolled in the study and the average gestational age was not stated. Previous study from this laboratory demonstrated that urine S100B concentration did not significantly vary between 23-28 weeks gestation. {spr}

Infants with CNS injury have increased CSF, serum, and urine concentration of S100B. In asphyxiated term infants who later developed intracranial hemorrhage, S100B was shown to be elevated at 12 hours after birth when compared to asphyxiated term infants who did not develop intracranial pathology and to control term infants.[14] In another report, asphyxiated term infants, who at 3 months exhibited abnormal neurologic outcome or death, had markedly elevated S100B levels 12-24 hours after birth.[15] However, that study was limited by a small number of patients. Serum concentration of S100B was also significantly elevated (2.9 ug/L) in 8 term infants 3 days after initiating ECMO therapy. Daily cranial ultrasound evaluation identified intracranial hemorrhage in these infants by day 5-6. In other words, significant elevation of serum concentration of S100B occurred at least 2-3 days prior to ultrasound evidence of intracranial hemorrhage. Eight control infants, who also received ECMO therapy, had no ultrasonic evidence of intracranial hemorrhage and had no change in S100B above baseline (0.5 ug/L).[16]