Irradiation leads to susceptibility of hepatocytes to TNF-alpha mediated apoptosis

Background and purpose The pathogenesis of radiation-induced-liver-disease (RILD) is still unknown. We tested the hypothesis that irradiated liver macrophages influence the viability of radiation stressed hepatocytes. Patients and methods Hepatocytes and liver macrophages were isolated from rat liver, cultured and irradiated with doses of 2, 8, and 25Gy. Cell viability was measured by trypan blue exclusion, and by annexin V/propidium iodide staining. TNF-α in the supernatants from liver macrophage cell culture was quantitatively detected by ELISA. TNF-α mRNA from liver macrophages was measured by real time PCR. Results Irradiation had no influence on cell viability. Apoptosis of irradiated hepatocytes was detected 24h after replacing 50% of medium with supernatants of irradiated liver macrophages 6h after irradiation (32.0±5.8% compared to solely irradiated cells (12±2.9%, P =0.02)). In supernatants of hepatocytes, no TNF-α secretion could be measured. A radiation dependent increase was found in supernatants of liver macrophages. Addition of anti-TNF-α-antibodies to the supernatants of irradiated liver macrophages reduced apoptosis (20±0.9%). Incubation of irradiated hepatocytes with purified recombinant TNF-α increased apoptosis in irradiated hepatocytes. This effect could be abrogated by additional administration of TNF-α-antibodies. Conclusions Irradiation leads to susceptibility of hepatocytes to TNF-α mediated apoptosis. Liver macrophages may be one of the sources of TNF-α in case of liver-irradiation. This cell–cell-interaction may be an important initial step towards RILD and liver fibrosis.