Therapeutic effects of alprostadil on CCl4-induced hepatic fibrosis in rats and investigation of its molecular mechanisms.

Hepatic fibrosis (HF) is driven by hepatic stellate cell (HSC) activation. Although cyclic adenosine monophosphate (cAMP) is a key antifibrotic signal, whether pharmacological cAMP elevation acts through protein kinase A (PKA) or exchange protein directly activated by cAMP 1 (EPAC1) remains unclear. Alprostadil (PGE1) elevates intracellular cAMP, but its antifibrotic mechanism is undefined. Using CCl₄-induced HF in rats and primary HSCs, we found that Alprostadil markedly reduced liver injury, collagen deposition, and HSC activation. Fibrotic livers showed increased total cAMP but decreased PKA- and EPAC1-bound cAMP, indicating depletion of functional cAMP microdomains. Alprostadil restored effector-bound cAMP, increased EPAC1 expression, and enhanced PKA/CREB phosphorylation. Notably, EPAC1 inhibition-but not PKA inhibition-attenuated the antifibrotic effects of Alprostadil in vivo and in vitro. These findings identify EPAC1 as the dominant downstream effector through which Alprostadil restores localized cAMP signaling to suppress HSC activation and hepatic fibrosis.