| Summary: | 碩士 === 國立中正大學 === 分子生物研究所 === 99 === Sepsis remains a serious clinical problem accompanied with unpredictable disease outcome. Septic shock and multiorgan dysfunction are the most common causes of death in patients with sepsis under intensive care. As previous reports indicated that the level of extracellular histone in plasma is elevated in systemic inflammation and sepsis, probably due to damages inflicted to the inflamed tissues by neutrophils or other inflammatory cells. Moreover, elevated extracellular histone is associated with cytotoxicity of endothelial cells and leads to death of mice in experimental septic model.
We speculate that extracellular histone is an important mediator of the septic syndrome and set out to investigate the mechanism of histone-dependent cytotoxicity. In vitro, addition of histone mixture in the culture medium caused the death of human endothelial cells in a dosage-dependent manner. In addition, the cytotoxic effect of histone can be blocked by serum albumin, suggesting that serum albumin is able to reduce the adverse effect of histone to endothelial cells. In order to identify the response of endothelial cells to extracellular histone, the expression levels of a cohort of genes functioning in inflammation were determined by RT-PCR, and the result shows that the levels of DR5 and XIAPF were increased and decreased, respectively, upon histone treatment. Increase of DR5 expression is suppressed if albumin is present during histone treatment, confirming regulation of DR5 expression specifically in response to extracellular histone. To support the notion that serum histone plays a role in increasing the severity of sepsis, we discovered that, in a cecal ligation and puncture mouse model, injection of histone mixture leads to drastic increase in mortality rate in a dosage-dependent pattern. We are currently collecting the data in patients suffering from sepsis to correlate serum histone concentration with progression and severity of sepsis.
In conclusion, we have demonstrated that extracellular histone exhibits cytotoxic effect toward endothelial cells in dosage and time dependent manner in vitro and that additional albumin protects endothelial cells from histone-induced cellular damage. It is likely that DR5 and XIAPF, members of tumor necrosis factor family, are involved in activation of histone-induced cytotoxicity. Finally, extracellular histone exacerbates progression and severity of sepsis and increase the mortality rate in a sepsis mouse model, strongly supporting our hypothesis that histone is a negative indicator for the outcome of sepsis in patients.
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