A novel phosphodiesterase 5 inhibitor, CPD1, alleviates liver fibrosis by modulating the Akt/NF-κB pathway to inhibit activated hepatic stellate cells.

Hepatic fibrosis is a progressive disorder marked by abnormal extracellular matrix buildup, with no effective antifibrotic drugs currently available. Recent evidence indicates that inhibiting phosphodiesterase 5 (PDE5) can have significant benefits for fibrotic diseases, suggesting PDE5 inhibitors may be effective antifibrotic agents. This study aimed to develop a new PDE5 inhibitor, potassium salt crystal form B (CPD1), which has much greater aqueous solubility than sildenafil. We assessed CPD1's efficacy in inhibiting hepatic stellate cells (HSCs) activation and investigated its mechanism of action. The therapeutic effect of CPD1 was studied in a carbon tetrachloride-induced liver fibrosis model, exploring its antifibrotic mechanisms via cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG1) or Akt inhibitors and PKG1 overexpression in LX-2 cells. As anticipated, the expression of PDE5A was significantly elevated in both human and mouse fibrotic liver tissues, as well as in LX-2 cells induced by transforming growth factor-beta 1 (TGFβ1). In vivo, CPD1 reduced serum transaminases in a dose-dependent manner, mitigated liver damage, decreased collagen deposition, and suppressed the activation of HSCs. Additionally, CPD1 is more effective than sildenafil at a lower dosage. In vitro, CPD1 inhibited TGFβ1-induced activation of LX-2 and reduced the expression of fibrotic marker proteins and genes. Notably, the anti-fibrotic effects of CPD1 were completely negated following the administration of a PKG1 inhibitor. Mechanistically, the CPD1 intervention effectively countered the TGFβ1-induced increase in p-IκBα and p-P65. This study demonstrated that CPD1 mitigates liver fibrosis by activating the cGMP/PKG pathway, which in turn inhibits the AKT/NF-κB pathway. Therefore, it may be considered a potential therapeutic agent that warrants further investigation for the treatment of liver fibrosis.