Shikonin from lithospermum erythrorhizon induces pyroptosis in trophoblast cells by activating the CTSB-NLRP3 inflammasome.

Background: With the decline of global fertility, drug therapeutic of ectopic pregnancy is of great significance. Lithospermum erythrorhizon is using for embryo killing as herbal medicine. Shikonin is the critical nucleus of Lithospermum erythrorhizon; however, the mechanism is still unclear. The study aimed to explore the mechanism of shikonin against ectopic pregnancy.

Material and methods: In this study, we examined the viability and LDH release of HTR-8/SVneo cells by assays, observed pore formation in cell membranes by microscopy imaging and PI staining, and IL-1β release by WB and ELISA assay kit. Then, we used network pharmacology to analyse the potential interaction between shikonin, ectopic pregnancy and pyroptosis and used molecular docking techniques to verify interactions between shikonin and core common targets. Finally, western blotting and immunofluorescence assay were used to explore the mechanism of shikonin-inducing pyroptosis of HTR-8/SVneo cells.

Results: Shikonin could cause a significant inhibition of HTR-8/SVneo cell viability in a concentration- and time-dependent manner. In HTR-8/SVneo cells, shikonin-induced cell swelling, bubble formation, an increase in the release of lactate dehydrogenase (LDH) and up-regulation of several pyroptosis-associated factors. And network pharmacology showed that The main targets of shikonin-ectopic pregnancy-pyroptosis were IL-1β and caspase-1, and molecular docking results showed that shikonin can closely bind to IL-1β, caspase-1 and GSDMD. Additionally, the necroptosis inhibitor GSK'872 could not suppress the expression of mature-IL-1β and prevent the pyroptosis phenotype from developing. However, the nucleotide oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) inhibitor MCC-950 could downregulate the expression of pyroptosis-associated factors and prevent the pyroptosis phenotype from developing. Shikonin led to an elevation in the expression of cathepsin B (CTSB), and the CTSB inhibitor CA-074 abolished pyroptosis induced by shikonin; however, the NLRP3 inhibitor MCC-950 could not inhibit the expression of CTSB.

Conclusions: Our results suggest that shikonin activates CTSB to induce NLRP3-dependent pyroptosis in HTR-8/SVneo cells. This study has important clinical implications for the treatment of ectopic pregnancy.