The role of endotoxin/lipopolysaccharide in surgically induced tumour growth in a murine model of metastatic disease

Abstract

Summary Surgical removal of a primary tumour is often followed by rapid growth of previously dormant metastases. Endotoxin or lipopolysaccharide, a cell wall constituent of Gram-negative bacteria, is ubiquitously present in air and may be introduced during surgery. BALB/c mice received a tail vein injection of 10 5 4T1 mouse mammary carcinoma cells. Two weeks later, animals were subjected to surgical trauma or an intraperitoneal injection of endotoxin (10 µg per animal). Five days later, animals which underwent open surgery, laparoscopy with air sufflation or received an endotoxin injection displayed increased lung metastasis compared to anaesthetic controls. These increases in metastatic tumour growth were reflected in increased tumour cell proliferation and decreased apoptosis within lung metastases. Circulating levels of the angiogenic cytokine, vascular endothelial growth factor (VEGF), were also elevated in these groups and correlated with increased plasma levels of endotoxin. Endotoxin treatment for 18 h (>10 ng ml -1 ) directly up-regulated VEGF production by the 4T1 tumour cells in vitro. Metastatic tumour growth in mice undergoing carbon dioxide laparoscopy, where air is excluded, was similar to anaesthetic controls. These data indicate that endotoxin introduced during surgery is associated with the enhanced growth of metastases following surgical trauma, by altering the critical balances governing cellular growth and angiogenesis.

Lipopolysaccharide‐induced metastatic growth is associated with increased angiogenesis, vascular permeability and tumor cell invasion

“…We previously reported that LPS exposure resulted in increased circulating VEGF in the same murine model used here. 9 Pleural effusions are associated with increased VEGF and vessel permeability and inhibition of VEGF receptor tyrosine phosphorylation reduced the formation of pleural effusions suppressing vascular hyperpermeability in a murine model of lung adenocarcinoma. 25 LPS has previously been reported to have angiogenic activity in a number of angiogenesis models.…”

“…9 Table I shows that LPS exposure 1 week after tumor cell injection resulted in increased lung tumor burden, evidenced by increased lung weight (0.262 Ϯ 0.05 vs. 0.229 Ϯ 0.03 g in controls) and incidence of lesions in the pleural cavity or on chest wall and ribs (10/15 vs. 1/13 in the saline control group). The normal lung weight of 8-week-old female BALB/c mice is 0.139 -0.177 g; thus these lung weights represent a significant tumor burden.…”

“…7 Endotoxin is ubiquitously present in air, and we previously implicated endotoxin in surgically induced tumor growth. 8,9 Endogenous gut bacteria are a major source of endotoxin, which can translocate across the gut into the circulation following surgical trauma or thermal injury. 10 -12 Vascular endothelial growth factor (VEGF), also known as vascular permeability factor (VPF), is a potent angiogenic cytokine stimulating growth and differentiation of endothelial cells.…”

“…20 We previously reported increased plasma LPS in mice following surgery and that surgery or LPS exposure increased metastatic tumor growth in an experimental murine metastasis model. 9 To clarify the mechanisms underlying LPS-induced metastatic growth, we have extended those studies to examine the effect of LPS on key determinants of the metastatic process, namely angiogenesis, tumor cell invasion, vascular permeability, NOS and MMP expression. In addition, we assessed the effect of NO blockade on tumor cell invasion in vivo.…”

Exploitation of the Toll-like receptor system in cancer: a doubled-edged sword?

“…Following laparotomy and air laparoscopy, LPS contaminates the peritoneal cavity and enters the systemic circulation due to perioperative bacterial gut translocation. In a murine metastatic breast carcinoma model, mice undergoing laparotomy or air laparoscopy had increased serum levels of LPS and metastatic tumour burden compared to those in the CO2 laparoscopy group (which was not contaminated with endotoxin), a result replicated by intraperitoneal LPS injection (Pidgeon et al, 1999;Harmey et al, 2002). Luo et al used TLR-4 deficient CT-26 murine colorectal cancer cells in their study and suggested that the tumour promoting effect of LPS is subservient to inflammatory cytokines produced primarily by the innate immune system, as the LPS-induced enhanced tumour burden was TNF-a dependent and abolished with super-repressormediated NF-kB inhibition.…”