F2- Isoprostane receptors and hepatic fibrosis

The discovery of F2-isoprostanes (F2-IsoPs) as specific markers of oxidative stress is briefly summarized. F2-IsoPs are also agonists of important biological effects. Since a relation between oxidative stress and collagen hyperproduction has been suggested, we investigated whether collagen synthesis is induced by F2-IsoPs, the most proximal products of lipid peroxidation. In a rat model of carbon tetrachloride-induced hepatic fibrosis, plasma F2-IsoPs were markedly elevated for the entire experimental period; hepatic collagen content was also increased. When hepatic stellate cells (HSC) from normal liver were cultured up to activation (expression of alpha-smooth muscle actin) and then treated with F2-IsoPs in the concentration range found in the in vivo studies (10-9 to 10-8M), a striking increase in DNA synthesis, in cell proliferation and in collagen synthesis was observed. Moreover, F2-IsoPs increased the production of transforming growth factor- β1 by U937 cells, assumed as a model of Kupffer cells or liver macrophages. F2-IsoPs generated by lipid peroxidation in hepatocytes may therefore mediate HSC proliferation and collagen hyperproduction seen in hepatic fibrosis. In addition, binding studies suggested that the stimulatory effects of 8-epi-PGF2 (the most represented isomer of F2-IsoPs) on DNA and collagen synthesis are mediated by TxA2 receptor (TP). Moreover, western blotting and immunocytochemistry analysis revealed the expression of TP in HSC both on plasma membranes and within the cells. Further experiments, carried out in HSC to clarify the signal transduction pathways set into motion by F2-IsoPs showed that 8-epi-PGF2induced an increase of Ins(1,4,5)P3 and the activation of ERK1/2, p38 and cyclin D1 in HSC. It is known that these pathways are involved in cell proliferation and collagen gene expression.