Hepatocyte regeneration after partial liver irradiation in rats

Liver has a strong potential for regeneration after physical, biological or chemical injury, but no data have been reported so far on liver regeneration in response to irradiation injury. The present experiment in rats was designed to clarify whether partial liver irradiation could induce and stimulate the unirradiated part of liver to regenerate. The left-half of rat liver was irradiated with a single dose of 25 Gy. Liver tissues from the irradiated and unirradiated liver, and blood sample were collected at different time points after irradiation. Radiation injury was evaluated by serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, histopathologic features and trichrome stain. The hepatic regeneration was assessed by serum hepatic growth factor (HGF), mitotic index and proliferation cell nuclear antigen (PCNA) immunohistochemical stain. Expression of transforming growth factor-β1 (TGF-β1) by immunohistochemistry assay was also performed. Results showed that 25 Gy of single-dose irradiation produced severe hepatic injury in the irradiated liver, and the unirradiated liver had been stimulated to regenerate, demonstrated by significant increases of serum HGF 30 days after irradiation, and increase of mitotic index and the number of PCNA-positive hepatocytes 60 days after irradiation. TGF-β1 was strongly and uniformly expressed in the irradiated liver 90-day-post-irradiation, and it was also expressed slightly in unirradiated liver region. In summary, partial liver irradiation could stimulate the unirradiated liver to regenerate, and the role of TGF-β1 in hepatic injury and proliferation needs further investigation.