Hepatic ischemia/reperfusion injury promotes lung metastasis after major hepatectomy by mobilization of circulating endothelial progenitor cells (EPCs) - application of optical imaging system in rat and mouse models with othotopic liver cancer

Abstract

Objective: We aim to explore the precise mechanism of tumor metastasis under surgical stress by investigating the impact of hepatic I/R injury on mobilization of circulating endothelial progenitor cells and regulatory T cells. 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 (I/R injury - 20/20 minutes duration on right and median lobes). The tumor growth and metastases were longitudinally monitored by Xenogen in vivo imaging system (IVIS) in live animals by detection of luminance signals from tumor cells, which stably labeled with luciferase gene. Blood samples were taken at day0, 3, 7, 17, 21 and 28 after hepatectomy for detection of circulating endothelial progenitor cells (CD133+CD34+CXCR4+). Intra hepatic and circulating gene/protein markers linking to I/R injury and lung metastasis were identified. To further validate the role of EPCs with inflammatory chemokine IP10 treatment on liver tumor growth and metastasis, the EPCs with or without IP10 treatment from a rat model with green fluorescence protein (GFP) labeling were further injected into an orthotopic nude mice liver cancer model. The liver tumor growth and metastasis in nude mice were longitudinally monitored by IVIS system. The EPCs were also traced with their GFP signals. 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/CXCR4/VEGF induced by hepatic I/R injury subsequently mobilized more bone marrow derived endothelial progenitor cells (CD133+CD34+CXCR4+) to circulation compared to the control group (day14: 12.21% vs 7,73%, p=0.002; day21: 12.25% vs 4.47%, p=0.004; day28: 9.64% vs 2.27%, p=0.004). The circulating protein marker linking to hemopoietic progenitor cell - myelin basic protein (MBP) was also over-expressed in I/R injury group. IP10 treated EPCs has greater potential to promote liver tumor growth and metastasis via increasing anigogenesis in the orthotpic nude mice liver tumor model. Conclusion: Hepatic ischemia/reperfusion injury promoted lung metastasis after major hepatectomy by mobilization of circulating endothelial progenitor cells.