Occurrence of isoprostane receptors activating fibrogenic effects on hepatic stellate cells

The connection between oxidative stress (OS) and hepatic fibrosis has been well studied. F2-isoprostanes (Iso) are considered as the most reliable markers of OS. Recently we investigated the role of Iso as possible mediators of CCl4-induced hepatic fibrosis. Plasma levels of Iso were found to be elevated in rat chronically treated with CCl4 and correlated with hepatic collagen content. Also, Iso induced a marked increase in DNA and collagen synthesis in cultured hepatic stellate cells (HSC), in the concentration range found in the in vivo studies (1-10 nM). Besides markers of OS, Iso proved to be mediators of important biological effects and would act through the activation of receptors analogous to those for tromboxane A2 (TxA2r). Thus, the possible occurrence of TxA2r on HSC was investigated. For binding studies, HSC were treated with [3H]SQ29548 with or without the addition of cold SQ29548. Scatchard analysis indicated the presence of a single class of binding sites for this ligand on HCS. Competition binding experiments demonstrated that I-BOP (a specific agonist of TxA2r) displaced [3H]SQ29548 binding with more binding potency (IC50=6.98x10-8M) than 8-epi-PGF2alpha IC50=9.31x10-6M) and suggested that both ligands bind to the same receptor. Finally, SQ29548 suppressed almost completely the Iso-induced stimulation of DNA and collagen synthesis in HSC. This is the first study demonstrating the existence of TxA2r in HSC and the involvement of TxA2r in Iso-evoked responses.