Objective
Research has shown that celastrol can effectively treat a variety of diseases, yet when passing a certain dosage threshold, celastrol becomes toxic, causing complications such as liver and kidney damage and erythrocytopenia, among others. With this dichotomy in mind, it is extremely important to find ways to preserve celastrol’s efficacy while reducing or preventing its toxicity.

Methods
In this study, insulin-resistant HepG2 (IR-HepG2) cells were prepared using palmitic acid and used for in vitro experiments. IR-HepG2 cells were treated with celastrol alone or in combination with N-acetylcysteine (NAC) or ferrostatin-1 (Fer-1) for 12, 24 or 48 h, at a range of doses. Cell counting kit-8 assay, Western blotting, quantitative reverse transcription-polymerase chain reaction, glucose consumption assessment, and flow cytometry were performed to measure celastrol’s cytotoxicity and whether the cell death was linked to ferroptosis.

Results
Celastrol treatment increased lipid oxidation and decreased expression of anti-ferroptosis proteins in IR-HepG2 cells. Celastrol downregulated glutathione peroxidase 4 (GPX4) mRNA. Molecular docking models predicted that solute carrier family 7 member 11 (SLC7A11) and GPX4 were covalently bound by celastrol. Importantly, we found for the first time that the application of ferroptosis inhibitors (especially NAC) was able to reduce celastrol’s toxicity while preserving its ability to improve insulin sensitivity in IR-HepG2 cells.

Conclusion
One potential mechanism of celastrol’s cytotoxicity is the induction of ferroptosis, which can be alleviated by treatment with ferroptosis inhibitors. These findings provide a new strategy to block celastrol’s toxicity while preserving its therapeutic effects.

Key words: Celastrol, Insulin resistance, Ferroptosis, N-Acetylcysteine, Palmitic acid, Molecular docking