*3.6. Cell Culture and Cell Viability Assay*

The human monocytic cell line, THP-1 (Cell Bank of China Science Academy, Shanghai, China) and *P. acnes* (ATCC6919, Xiangfu biotech, Shanghai, China), were used for the anti-inflammatory assay. THP-1 cells were cultured in RPMI1640 medium with 10% fetal bovine serum (FBS, Gibco, NY, USA) in a humidified incubator (37 ◦C, 5% CO2). *P. acnes* bacteria were incubated in Cooked Meat Medium, containing cooked beef granules (Rishui biotechnology, Qingdao, China) in an anaerobic environment. The THP-1 cells were stimulated by the *P. acnes*, which was harvested at the exponential phase. The viability of THP-1 cells was evaluated by the MTT assay, specifically, seeding the THP-1 cells in 96-well plates at a density of 2 <sup>×</sup> <sup>10</sup><sup>5</sup> cells/well and treated with serially diluted compounds for 36 h (37 ◦C, 5% CO2). After that, we added 20 μL MTT regent (5 mg/mL, Genetimes Technology Inc., Shanghai, China) to each well and incubated the samples at 37 ◦C for 4 h. Removing the supernatant, the formazan crystals were fully solubilized in DMSO (150 μL), and the absorbance was measured at 570 nm and 630 nm.
