Key words: proinflammatory cytokines; colon carcinoma; microvascular endothelium; adhesionLocoregional recurrence as well as recurrence to distant sites following intentionally curative surgery is a major problem in colorectal cancer. Recurrence rates up to 40% have been reported in colorectal cancer. 1 Among the sites of recurrences, the most frequent are liver, lung and locoregional sites. [2][3][4][5] Resection handling of the tumor can provoke detachment of tumor cells. Circulating tumor cells are often found in patients with gastrointestinal cancer, not only during resection of the primary tumor. 6 -8 Although the amount of circulating tumor cells is enhanced during resection of the primary tumor, it will not entirely explain the high recurrence rate found after intentionally curative surgery. Implantation of circulating tumor cells appears to be highly inefficient and most circulating tumor cells are rapidly destroyed. 9,10 It is possible that the surgical trauma itself influences the development of recurrences. Surgical peritoneal trauma provokes an inflammatory reaction, in which leukocytes are activated and cytokines and reactive oxygen species are released. We recently demonstrated that these factors enhance locoregional tumor recurrences. 11,12 However, these factors are released not only locally but also in the circulation. After major abdominal surgery, the proinflammatory cytokines interleukin-6 (IL-6), interleukin-1␤ (IL-1␤) and tumor necrosis factor-␣ (TNF-␣) in peripheral blood are elevated. [13][14][15][16][17] We hypothesize that these factors are not only involved in locoregional tumor recurrence after peritoneal trauma, but also in recurrences at distant sites.The lung is a frequent site for tumor recurrence in many gastrointestinal tumors. The process of hematogenous metastasis formation to the lung is a multistep event in which tumor cells first have to detach from the primary tumor, invade the bloodstream, subsequently adhere to the endothelium within the lung and finally invade and multiply to form lung metastases. 18,19 An important step in this process is the adhesion of tumor cells to the endothelium. It is known that the cytokines IL-1␤ and TNF-␣ enhance tumor cell adhesion to human umbilical venous endothelial cells (HUVECs) in vitro by upregulation of adhesion molecules on HUVECs. 20 -25 HUVECs are embryonic macrovascular cells used in many models studying the pathophysiology of the endothelium. However, the adhesion of tumor cells to endothelium does not occur in the macrovascular circulation, but in the microvascular circulation. 26 Microvascular endothelial cells react differently to stimuli compared to macrovascular endothelial cells. [27][28][29][30][31][32][33] Furthermore, it is believed that endothelial cells from different organs have their own pattern of adhesion molecules. 34 -37 Because of these differences, general extrapolation from data obtained from the HUVEC model to the microcirculation is most certainly invalid.We developed a reproducible human in vitro model...

We hypothesise that reactive oxygen species (ROS) released from activated polymorphonuclear leucocytes during surgery play a crucial role in enhanced tumour recurrence seen after surgery. Therefore, the effect of ROS on adhesion of tumour cells to microvascular endothelium in a reproducible human in vitro model was studied. Preincubation of microvascular endothelial cells with the superoxide anion producing xanthine -xanthine oxidase complex significantly increased adhesion of the human colon carcinoma cells HT29 (167% vs control, Po0.01), Caco2 (164% vs control, Po0.01) and of the pancreas carcinoma cells PanC1 (180% vs control, Po0.01). Addition of the antioxidant enzymes superoxide dismutase or catalase significantly decreased tumour cell adhesion (Po0.01). Exposure of endothelial cells to superoxide anions increased the apoptotic rate to 7.9 times the normal rate. Additionally, exposure increased expression of the endothelial adhesion molecules E-Selectin, ICAM-1, and VCAM-1 of maximally 170% vs control (Po0.01). In conclusion, this study shows that superoxide anions promote the adherence of tumour cells to the microvasculature by inducing endothelial apoptosis that subsequently induces the expression of various adhesion molecules for tumour cells. This indicates that by tackling the production of ROS preventing tumour recurrence at distant sites might be feasible.

Postoperative peritoneal carcinomatosis is a significant clinical problem after "curative" resection of pancreatic carcinoma. Preoperative surgical trauma activates a cascade of peritoneal defense mechanisms responsible for postoperative intra-abdominal tumor recurrence. Reactive oxygen species (ROS) play a pivotal role in this postoperative inflammatory reaction. This study explores the influence of ROS on adhesion of human pancreatic carcinoma cells to human mesothelial cells. Furthermore this study explores the influence of ROS on the presentation of adhesion molecules on Panc-1 and mesothelial cells. ROS were produced using the enzymatic reaction of xanthine with xanthine oxidase (X/XO). A reproducible in vitro assay to study adhesion of human Panc-1 carcinoma tumor cells to a mesothelial cell monolayer of primary human mesothelial cells was used. Mesothelial monolayers were incubated with ROS produced prior to adhesion of the tumor cells. Incubation of the mesothelial cells with X/XO resulted in a significant increase (69.5%) in adhesion of Panc-1 in all patients. SOD/catalase, anti-oxidants, could reduce this increase by 56.7%. ROS significantly influenced the expression of the adhesion molecules ICAM-1, VCAM-1 and CD44h on mesothelial cells, but did not influence adhesion molecule expression on Panc-1. The ROS released during the post-operative inflammatory reaction may play an important role in the adhesion of pancreatic tumor cells to the mesothelium-possibly by influencing adhesion molecule expression on mesothelial cells. Therefore ROS can partly be responsible for the enhanced post-operative intra-abdominal tumor recurrence.

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