Mechanisms Of Brain Injury Associated-CPB And Cerebroprotective Effects Of GM₁ During CPB

Mordern cardiac surgery, heralded by the advent of cardiopulmonary bypass (CPB) more than 50 years ago, continues to be challenged by the risk of organ dysfunction and the morbidity and mortality that accompanies it. Advances in medical equipment, perfusion, anesthesia, and surgical techniques have allowed most patients to undergo surgery with decreasing morbidity or mortality, but the incidence of stroke and cognitive dysfunction has remained relatively unchanged. Overt and subclinical perioperative cerebral injury remains an unresolved problem. At present, CPB-related physiological changes and mechanisms for the occurrence of central nervous system complications are still a lack of thorough understanding, and is still a lack of effective treatment and preventive measures. So, increasing attention is also being paid to the role of perioperative neuropsychological dysfunction triggered during exposure to surgry and CPB.The purpose of this study was to investigate the central nervous system dysfunction after CPB and to evaluate the neuroprotective effects of monosialoteterahexosyl ganglioside 1 (GM₁) on rats during CPB in morphological, functional and molecular biology aspects, with the successful establishment of a good recoverable rat model of CPB. And we also observed the effect of GM₁ as priming solution on the levels of S100B, Tau protein and cerebral metabolism of oxygen in elderly patients undergoing open cardiac surgery using CPB, to evaluate the protective effect of GM₁ on cerebral injury associated with CPB.Part A. Establishment of animal model of cardiopulmonary bypass in the rats SPF-class adult male Sprague-Dawley rats were anesthetized and intubated. The right external jugular vein, femoral artery and tail artery were cannulated. The blood was drained from the the right atrium via the right jugular vein and further transferred by a small roller pump to a miniaturized hollow fiber oxgenator and return to the systemic circulation through the tail artery. CPB were performed for 60 min at a flow rate of 100 to 180 ml/(kg·min). During the whole process,the hemodynamics,electrocardiograph (ECG) and blood-gas analysis were observed. The result showed that 90% CPB animals were performed successfully. The hemodynamic parameters were stable throughout the procedure and the blood-gas analysis at different time points were within a normal range. After CPB weaning,cardiovascular and respiratory functions recovered gradually. The rat model of CPB can be established successfuly. It is an ideal model which may open the field for various studies on multiple organ pathophisiological process produced by CPB, especially for the study of central nervous system injury after CPB.Part B. Morphological and functional aspects of basic reaseach in the rat.SPF-class adult male SD rats were randomly divided into CPB group, CPB+GM₁ group, transfusion group and Sham-oprated group. After establishing a rat model of cardiopulmonary bypass, GM₁ with 20mg/kg was added to the priming solution. All rats were anesthetized to collect the whole cerebral tissues for detection after 24 hours.1. To explore the protective effects of GM₁ on brain damage after CPB, we used electron microscopy technique to observe ultrastructure of the hippocampus and cortex, especially the structural parameters of synaptic interface changes. The results showed: after CPB, neural cell rough endoplasmic reticulum and free ribosomes were markedly decreased, mitochondriosome was swelled, vacuolated and destructed, cristae were ruptured, dissolved and disappeared, cellular membrane disintegrated; synaptic cleft was obviously vague, and neuronal apoptosis occur more frequently. Compared with the CPB group, the the intervention of GM₁ could slightly improved the above morphological changes, slightly narrowing synaptic cleft, and apoptotic cells decreased.2. To investigate the effect of GM₁ on the oxidative stress of brain tissue after CPB, we detected the contents of lactate dehydrogenase (LDH), malonadehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GRH-Px) in the brain tissue. The results showed that, compared with the control groups, the level of LHD and MDA increased significantly (P<0.05), while the SOD, GSH-Px activity decreased significantly (P<0.05) in the CPB group. The data suggestes that oxygen free radicals may be important pathogenic factors for the central nervous system dysfunction after CPB. GM₁ can mitigate brain injuries after CPB by alleviating the lipid peroxidation.3. The activity of Na⁺-K⁺-ATPase in cerebral tissues was descended from the normal17.03±4.17 mol·Pi/g·protein/h to 12.45±2.64 mol·Pi/g·protein/h, GM₁ administration obviously enhanced the activity of Na⁺-K⁺-ATPase to 14.72±3.29 mol·Pi/g·protein/h. GM₁ can stabilize the functional activity of Na⁺-K⁺-ATPase of neuronal cytomembrane, and moderate cerebral edema from the brain injuries associated with CPB.4. This study was to observe the effect of GM₁ on nitric oxide synthase (NOS), including constitutive nitric oxide synthase (cNOS) and induced nitric oxide synthase (iNOS) following cerebral damage induced CPB. The rise of iNOS activity could correlate closely with brain injury after CPB, and GM₁ could reduce iNOS activity and NO content. GM₁ has the effect of brain protection against the neurotoxicity of NO.5. The purpose of the present study is to evaluate the effect and the mechanism of GM₁ on the expression of inflammatory mediators in hippocampus and cortex after CPB, by the means of semi-quantitative reverse transcriptionpolymerase chain reation (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) method. The results showed that CPB can induce the expression of TNF-α, ICAM-1, IL-1β, IL-10 mRNA in hippocampus and cortex, resulting in a corresponding increase in protein secretion of cytokines, which activated the immunologic inflammatory response pathway, causing brain damage, in particular the more obvious damage to the hippocampus. GM₁ did not affect the expression of TNF-α, ICAM-1, IL-1β, IL-10 mRNA, could not lead to a corresponding reduction in protein secretion of cytokines.Part C. Clinical researchThe aim of this study was to explore the effect of GM₁ on the levels of S100B, Tau protein and cerebral metabolism of oxygen in elderly patients undergoing open cardiac surgery using CPB. Forty ASAâ…¡-â…¢patients older than 60 years old scheduled for elective aortic and/or mitral valve replacement undergoing CPB were randomly divided into two groups of 20 each: control group and GM₁ group. Blood samples were obtained from jugular bulb and radial artery before CPB (T0), 5 minute after clamping the aorta (T1), 5 minute after declamping the aorta (T2), at the end of CPB (T3), 1h (T4) and 24h(T5) after termination of CPB for the measurements of CBF/CMRO2 and CMRO2/CMRGLU. The jugular bulb blood samples were taken at the same time point for determination of the serum concentrations of S100B and Tau protein by means of ELISA method. The results showed that the serum levels of S100B and Tau protein of both groups were significantly increased after cardiopulmonary bypass in elderly patients. GM₁ can decrease the serum levels of S100B and Tau protein. There happen imbalance of cerebral oxygen metabolism in the process of CPB, GM₁ are better able to maintain the balance between cerebral oxygen supply and demand, and has cerebral protetive effect during cadiac valve replacement with CPB in elderly patients to a degree.Conclusions:In summary, the studies have shown some degree of cerebral injuries induced by CPB in both basic animal model and clinical cardiac surgical patients. The mechanisms for neurologic injury after CPB include initiation of oxidative stress, inhibiting Na⁺-K⁺-ATPase activity, NO neurotoxicity mediated by iNOS, inflammatory response with the release of various injurious inflammatory mediators, as well as imbalance of cerebral oxygen supply and demand in the process of CPB. GM₁ may decrese cerebral injury associated with CPB, by attenuating the morphological changes, inhibiting the oxidative stress and iNOS, enhancing the Na⁺-K⁺-ATPase activity, stabilizing balance of cerebral oxygen supply and demand.