Acute phase inflammatory response promotes liver tumor recurrence and metastasis by mobilization of circulating EPCs and activation of TAMs

Abstract

OBJECTIVE: We aim to explore the precise mechanism of liver tumor recurrence and metastasis under surgical stress by investigating the impact of hepatic I/R injury on mobilization of circulating endothelial progenitor cells (EPCs) and activation of tumor-associated macrophages (TAMs). METHODS: Othotopic rat liver tumor model was established in male Buffalo rats with cirrhotic liver. Major hepatectomy was performed at 3 weeks after tumor implantation in the left lobe with (I/R injury group) or without (Control group) partial hepatic ischemia/reperfusion (20/20 minutes duration on right and median lobes). The tumor recurrence and metastases were longitudinally monitored by Xenogen in vivo imaging system (IVIS) in live animals. Blood samples at different time points after major hepatectomy were used for detection of IP10 level, and circulating endothelial progenitor cells (CD133+CD34+VEGFR2+). Circulating protein markers linking to I/R injury and tumor recurrence and metastasis were identified by proteomic screening. Tumor recurrence and metastasis were confirmed by histology. TAMs in recurrent and metastatic tumor nodules were detected by immunostaining. In vitro and in vivo functional studies were conducted to further confirm the role of inflammatory chemokine (IP10) on angiogenesis potency of EPCs. RESULTS: Significant high incidence of lung metastasis was present in I/R injury group (50%, 16/32) compared to the control group (10%, 2/20; p=0.000) at 4 weeks after major hepatectomy. The early occurrence of lung metastasis was found in I/R injury group at 2 weeks after operation detected by IVIS. Significant higher levels of IP10 induced by hepatic I/R injury subsequently mobilized more bone marrow derived EPCs to circulation compared to the control group. CD133+ cells were also found in lung metastatic nodules in I/R injury group. Numbers of Tregs (FOXP3+) and activated TAMs were presented in the recurrent and metastatic tumor nodules. The circulating protein marker linking to hemopoietic progenitor cell - myelin basic protein (MBP) was also over-expressed in I/R injury group. In vitro functional studies confirmed that IP10 could not only enrich the EPC population from bone marrow cells (BMCs), but also promoted its angiogenesis potency. In vivo functional study further verified that IP10 treated EPCs/BMCs promoted tumor recurrence and metastasis through its high angiogenesis potency. CONCLUSION: Hepatic ischemia/reperfusion injury promoted liver tumor recurrence and lung metastasis after major hepatectomy by mobilization of circulating EPCs and activation of TAMs.