Reactive Oxygen Species and Tumor Cell Adhesion

Objective Resection of primary colorectal cancer is associated with enhanced risk of liver metastases development. We previously demonstrated that surgery initiated an early inflammatory response resulting in elevated tumour cell adhesion in the liver. Because reactive oxygen species (ROS) are shown to be produced and released during surgery, we now investigated the effects of ROS on liver vascular lining and tumour cell adhesion. Methods Human endothelial cell monolayers (HUVEC and HMEC-1) were exposed to ROS production after which electrical impedance, cellular integrity and tumour cell adhesion was investigated. Furthermore, surgery-induced tumour cell adhesion as well as the role of ROS and liver macrophages (Kupffer cells) in this process was studied in vivo. Results Production of ROS decreased cellular impedance of endothelial monolayers dramatically. Moreover, formation of intercellular gaps in endothelial monolayers was observed, exposing sub-endothelial extracellular matrix (ECM) on which colon carcinoma cells adhered via integrin molecules. Endothelial damage was however prevented in the presence of ROS scavenging enzymes. Additionally, surgery induced downregulation of both rat and human liver tight junction molecules. Treatment of rats with the ROS scavenger Edaravone prevented surgery-induced tumour cell adhesion and downregulation of tight junction proteins in the liver. Interestingly, depletion of Kupffer cells prior to surgery significantly reduced numbers of adhered tumour cells and prevented disruption of tight junction proteins expression. Conclusions In the current study we show that surgery-induced ROS production by macrophages damages vascular lining by down regulating tight junction proteins. This leads to exposure of ECM, to which circulating tumour cells bind. As such, peri-operative therapeutic intervention, preventing surgery-induced inflammatory reactions may reduce the risk of developing liver metastases, hereby improving clinical outcome of patients with colorectal cancer. 3 REACTIVE OXYGEN SPECIES AND TUMOR CELL ADHESION