The interaction between polyphyllin I and SQLE protein induces hepatotoxicity through SREBP-2/HMGCR/SQLE/LSS pathway

Polyphyllin I (PPI) and polyphyllin II (PII) are the main active substances in the Paris polyphylla. However, liver toxicity of these compounds has impeded their clinical application and the potential hepatotoxicity mechanisms remain to be elucidated. In this work, we found that PPI and PII exposure could induce significant hepatotoxicity in human liver cell line L-02 and zebrafish in a dose-dependent manner. The results of the proteomic analysis in L-02 cells and transcriptome in zebrafish indicated that the hepatotoxicity of PPI and PII was associated with the cholesterol biosynthetic pathway disorders, which were alleviated by the cholesterol biosynthesis inhibitor lovastatin. Additionally, 3-hydroxy-3-methy-lglutaryl CoA reductase (HMGCR) and squalene epoxidase (SQLE), the two rate-limiting enzymes in the cholesterol synthesis, selected as the potential targets, were confirmed by the molecular docking, the overexpression, and knockdown of HMGCR or SQLE with siRNA. Finally, the pull-down and surface plasmon resonance technology revealed that PPI could directly bind with SQLE but not with HMGCR. Collectively, these data demonstrated that PPI-induced hepatotoxicity resulted from the direct binding with SQLE protein and impaired the sterol-regulatory element binding protein 2/HMGCR/SQLE/lanosterol synthase pathways, thus disturbing the cholesterol biosynthesis pathway. The findings of this research can contribute to a better understanding of the key role of SQLE as a potential target in drug-induced hepatotoxicity and provide a therapeutic strategy for the prevention of drug toxic effects with similar structures in the future.