Dihydrokaempferol attenuates CCl4-induced hepatic fibrosis by inhibiting PARP-1 to affect multiple downstream pathways and cytokines.

The pathophysiological mechanism of hepatic fibrosis (HF) is related to the excessive activation of the DNA repair enzyme poly ADP-ribose polymerase-1 (PARP-1). The drugs, targeting PARP-1, are scarce. Therefore, the lead compound, moderately inhibiting PARP-1, with anti-HF properties should be identified. This study screened dihydrokaempferol (DHK) from herbs based on preliminary studies to intervene in a CCl4-induced liver injury and HF model in mice. In vitro, the expression levels of PARP-1-regulated related proteins and phosphorylation were examined. The binding pattern of DHK and PARP-1 was analyzed using molecular docking and molecular dynamics platforms. The results showed that DHK could significantly attenuate CCl4-induced liver injury and HF in mice. Moreover, it could also attenuate the toxic effects of CCl4 on HepG2 and inhibit α-SMA and Collagen 1/3 synthesis of LX-2 cells in-vitro. Molecular docking revealed that DHK could competitively bind to the Glu-988 and His-862 residues of the upstream DNA repair enzyme PARP-1, moderately inhibiting its overactivation. This led to maintaining NAD+ levels and energy metabolism in hepatocytes and inhibiting the activation of PARP-1-regulated downstream signaling pathways (TGF-β1, etc.), related proteins (p-Smd2/3, etc.), and inflammatory mediators while acting indirectly. Thus, DHK could attenuate CCl4-induced liver injury and HF in mice in a different mechanism from those of the existing reported flavonoids. It was associated with inhibiting the expression of downstream pathways and related cytokines by competitively binding to PARP-1. This study might provide a basis and direction for the design and exploration of anti-HF lead compounds.