Loss of inhibitory growth regulation by TGF-beta1 in preneoplastic lesions in rat liver.

Injection of pig serum into rats twice a week for eight weeks induced transforming growth factor-beta1 (TGF-beta1) mRNA expression and protein production resulting in liver fibrosis without parenchymal cell injury. Eight-week treatment with pig serum reduced bromodeoxyuridine (BrdU) -positive hepatocytes 24 hr after 70% partial hepatectomy compared to that in the livers of rats treated with saline for eight weeks. Administration of a choline-deficient L-amino acid-defined (CDAA) diet for six weeks with pig serum coadministration, after pretreatment with pig serum for eight weeks, led to the development of preneoplastic lesions that were positive for the placental form of glutathione S-transferase (GSTP). Eight-week pretreatment with pig serum induced more GSTP-positive lesions and TGF-beta1 mRNA expression and protein concentration in the livers of rats subsequently fed a CDAA diet for six weeks than in rats fed the CDAA diet with saline treatment. These results indicate that TGF-beta1 induced by pig serum treatment inhibited hepatocyte proliferation but failed to prevent the development of preneoplastic lesions in a CDAA diet model.