Pulsatilla chinensis saponins cause liver injury through interfering ceramide/sphingomyelin balance that promotes lipid metabolism dysregulation and apoptosis.

Background: P. chinensis saponins (PRS) are pentacyclic triterpenoid bioactive constituents from Pulsatilla chinensis (Bunge) Regel. In our previous study, PRS caused chronic liver injury (CLI) with the significant changes of lipid metabolites including sphingomyelin (SM) in serum after long-term administration. The SM in the hepatocytes membrane plays an indispensable role in maintaining cell membrane stability and regulating the extracellular and intracellular signal transduction. However, it is still unknown the pathway related to SM and the mechanism of CLI on hepatocyte.

Purpose: The purpose of this study was to explore the hepatotoxicity mechanism of PRS in vivo and in vitro, to reveal the action of mechanism of SM and the pathway related to liver injury.

Methods: SD rats were orally administered with PRS for 240 days and liver injury was evaluated by histological examinations. Metabolomics analysis was used to explore the liver metabolic pathway affected by PRS, and the expressions of related proteins were evaluated by western blots. To discover and elucidate the underlying mechanisms of metabolites changes induced by PRS at the cellular level, cellular morphology, MTT assays, western blots and cell membrane potential measurements were carried out using LO2 cells. Furthermore, the roles of SM and cholesterol (Chol) in hepatocyte injury were investigated individually in overload Chol and SM groups. Sphingolipid metabolic pathway related with ceramide/sphingomyelin (Cer/SM) balance was explored using cellular lipidomics and RT-PCR.

Results: PRS gradually damaged the rat's liver in a time-dependent manner. The analysis of liver metabolism profiles showed that lipids metabolites were changed, including sphingolipid, bile acid, linoleic acid and fatty acid. We found that PRS induced apoptosis by interfering with bile acid-mediated sphingolipid metabolic pathway and Cer/SM balance in CLI. In in vitro experiments, PRS led to the increase of LDH leakage, depolarized cell membrane potential and caused cell membrane toxicity. Furthermore, PRS inducedG0/G1 phase cell cycle arrest in LO2 cells, simultaneously activated cellular extrinsic and intrinsic apoptosis pathways. PRS acted on SM and interfered with Cer/SM balance, which promote lipid metabolism dysregulation and apoptosis.

Conclusion: PRS acted on SM to interfere Cer/SM balance on LO2 cell. Both in vivo and in vitro, PRS induced Cer/SM imbalance which promoted lipid metabolism disorder and apoptosis. Apoptosis and lipids changes gradually damaged the rats liver, and ultimately developed into CLI.