Release patterns of astrocytic and neuronal biochemical markers in serum during and after experimental settings of cardiac surgery

OBJECTIVE: Brain injury and altered psychomotor development in infants, children and adults after cardiac surgery using cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA) is still a matter of concern. Early diagnosis and identification of brain injury that has occurred or is ongoing by measurement of biochemical markers in serum may have diagnostic and prognostic value. The aim of the experimental studies in an animal model was therefore to investigate the release patterns of astroglial and neuronal markers in serum and to determine the morphological and immunohistochemical changes in the brain of animals undergoing similar perfusion conditions of CPB and a period of DHCA. METHODS: Fourteen New Zealand rabbits, (weight, 3.1 +/- 0.25 kg) were anesthetized, intubated and mechanically ventilated. Four animals were sham operated and served as controls. After median sternotomy the animals were connected to CPB by cannulation of the aorta and right atrium. Full flow CPB (200-250 ml/kg/min) was initiated to achieve homogeneous systemic cooling. Circulatory arrest of 60 minutes was induced when rectal and nasopharyngeal temperature of 14 degrees C was achieved. After rewarmed reperfusion and establishment of stable cardiac ejection the animals were weaned from CPB and monitored for 6 hours. Then the animals were killed, the brain was immediately removed and cut in standardized sections. These were fixated, embedded in paraffin and stained for further quantitative histological studies. In the brain astrocyte reactivity for S-100B was assessed immunocytochemically (DPC Immustain Los Angeles, USA). Monoclonal mouse anti-human neurospecific enolase (NSE) antibody was used for the localization of NSE in the fixed and paraffin embedded brain (NSE-DAKO, H14). The concentrations of S-100B protein and neurospecific enolase (NSE) in the serum were analyzed using a commercially available immunoluminometric assay (LIA-mat, Sangtec 100, Byk-Sangtec). Immunospecific monoclonal anti-parvalbumin antibody was used for the detection of parvalbumin in the brain. Serum concentrations of parvalbumin were analyzed using a newly developed ELISA method. RESULTS: In all experimental animals a significant increase of the serum concentration of the astroglial protein S-100B was found immediately after reperfusion and the termination of CPB. In contrast the serum levels of the neuronal proteins parvalbumin and NSE were not increased, but rather decreased. Light microscopy and electron microscopy revealed perivascular astrocytic swelling and minor neuronal cell injury. In comparison to the sham operated animals, increased immunohistochemical staining of S-100B was found. This increased reactivity of S100B antibody was found in the astrocytic processes with immediate connection to the perivascular space and around the perivascular oedema. The immunocytochemical stainings for NSE and parvalbumin in the neuronal cells was not different from that of sham-operated animals and indicated well preserved neurons