Pneumoperitoneum with carbon dioxide inhibits macrophage tumor necrosis factor-α secretion: Source of transitional-cell carcinoma port-site metastasis, with prophylactic irrigation strategies to decrease laparoscopic oncologic risks

Purpose: Peritoneal macrophages play a critical role in maintaining local host resistance to infection and malignancy through the secretion of tumor necrosis factor-alpha (TNF-α).We hypothesized that attenuated TNF-α secretion, as a result of CO₂ pneumoperitoneum, could alter local immune surveillance, thereby contributing to the development of carcinomatosis and incisional metastasis. We further sought to determine if port-site metastasis could be prevented with prophylactic irrigants. Materials and Methods: C57BL/6 mice (n = 50) and the syngenic murine bladder tumor (MBT-2) cell line were used. Experiment 1: Mice were subjected to either CO₂ pneumoperitoneum at 6 mm Hg (n = 10) or a 3-cm midline incision (n = 10). Peritoneal macrophages (1 × 1 0⁶/animal) were collected and subjected to lipopolysaccharide challenge. TNF-α levels were quantified using the Quantikine^® Mouse TNF-α/TNFSF1A Immunoassay. Experiment 2: Peritoneal and port-site metastasis were evaluated 1 week after 1 × 10⁶ MBT-2 cells/animal were spilled in an open group (n = 5) and through 5-mm trocars of a pneumoperitoneal group (n = 5). Experiment 3: 1 × 10⁶ MBT-2 cells/animal were spilled intraperitoneally through 5-mm trocars of four groups (n = 20). Port sites in each group were then irrigated with either sterile water, mitomycin C (1.0 mg/mL), betadine (10%), or heparin (1000 U/mL). At 1 week, incisional sites were evaluated for gross and microscopic metastasis. In each experiment, Student t-test was used to quantify statistical differences. Results: Peritoneal macrophage TNF-α secretion was significantly inhibited in mice subjected to CO₂ pneumoperitoneum v control at 10 and 20 minutes (P = 0.015, P = 0.001, respectively). When 1 × 10⁶ MBT-2 cells were spilled, a significantly higher average tumor burden developed in animals subjected to CO₂ pneumoperitoneum than in controls at 1 week (9.2 gm v 3.8 g, P = 0.002). All irrigants prevented the development of port-site metastasis, yet sterile water did so without toxic effect. Conclusion: In a syngenic murine model, CO₂ pneumoperitoneum causes inhibition of peritoneal macrophage TNF-α secretion. Heavier intraperitoneal and incisional metastasis develops in C57BL/6 mice subjected to CO₂ pneumoperitoneum and a tumor challenge with 1 × 10 ⁶ MBT-2 tumor cells compared with open controls. Inhibition of peritoneal macrophage TNF-α secretion may be considered an adverse event contributing to the development of transitional-cell carcinoma (TCC) port-site metastasis, especially if surgical oncologic principles are violated. Irrigating trocar sites and the peritoneal cavity with sterile water at the conclusion of laparoscopic nephroureterectomy and laparoscopic radical cystectomy may offer a safe prophylactic strategy to prevent this unfavorable event. Our murine model presents a novel avenue for the development of adjunct immunomodulatory therapies to perhaps further reduce oncologic risks during laparoscopic management of TCC.