*2.1. Low Cytotoxicity of 7 rh on Human Articular Chondrocytes Viability*

A pilot study was conducted to choose the optimal concentrations of 7 rh for this experiment. The cytotoxicity of 7 rh on HAC was assessed by CCK8 assay. IC50 (6.9 nM) and IC100 (13.8 nM) of 7 rh were assessed to determine the cytotoxicity. Cell viability assay exhibited that the drug dosage in our study was low cell cytotoxicity to chondrocyte (Figure 1). Therefore, we selected the concentrations of 6.9 nM and 13.8 nM for the subsequent experiments. Additionally, the effects of 7 rh on IL-1β-stimulated HAC were assessed. As shown in Figure 1B, the results showed that the cell viability was suppressed after IL-1β stimulation and 7 rh could significantly prevent the inhibitory effects of IL-1β on cell viability at both selected concentrations (*p* < 0.05 in 6.9 nM and *p* < 0.001 in 13.8 nM).

**Figure 1.** The cytotoxic effects of 7 rh on human articular chondrocytes (HAC). (**A**) The cell viability of HAC that was treated with 6.9 nM and 13.8 nM of 7 rh for 48 h was detected by CCK8 assay. (**B**) The chondrocytes were co-cultured with IL-1β and 7 rh (6.8 nM and 13.9 nM) for 48 h. The cell viability was measured by CCK8 assay. All experiments were performed in quadruplicate and repeated three times with similar results. (\*\* *p* < 0.01 versus the control group; # *p* < 0.05, and ### *p* < 0.001 versus the IL-1β-treated group).
