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The mechanisms underlying hepatocellular damage after irradiation are obscure. We identified genes induced by radiation in isolated rat hepatocytes in vitro by cDNA array gene expression analysis and then screened in vivo experiments with those same genes using real-time PCR and Western blotting. Hepatocytes were irradiated and cDNA array analyses were performed 6 h after irradiation. The mRNA of differentially expressed genes was quantitatively analyzed by real-time PCR. cDNA array analyses showed an up-regulation of 10 genes in hepatocytes 6 h after irradiation; this was confirmed by real-time PCR. In vivo, rat livers were irradiated selectively. Treated and sham-irradiated controls were killed humanely 1, 3, 6, 12, 24 and 48 h after irradiation. Liver RNA was analyzed by real-time PCR; expression of in vivo altered genes was also analyzed at the protein level by Western blotting. Up-regulation was confirmed for three of the in vitro altered genes (multidrug resistance protein, proteasome component C3, eukaryotic translation initiation factor 2). Histologically, livers from irradiated animals were characterized by steatosis of hepatocytes. Thus we identified genes that may be involved in liver steatosis after irradiation. The methods shown in this work should help to further clarify the consequences of radiation exposure in the liver.

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.