2.3. Cell Viability

The effects of LPS and quercetin on cell viability of HGFs were measured by MTT assay based on the reduction of MTT to formazan by mitochondrial succinate dehydrogenase in viable cells. In brief, HGFs were seeded in a 96-well plate at a density of 1×10⁴ cells/well and treated with different concentrations of quercetin (final concentration at 5 μM, 10 μM and 20 μM, respectively) with and without LPS (final concentration at 1 μg/mL) for 24 h. Pre-treatment of quercetin was performed prior to the stimulation of LPS. Then 20 uL MTT (5 mg/mL) was added to each well, followed by incubation for another 4 h at 37°C with 5% CO₂. After the medium was removed, 150 uL DMSO was added to each well to dissolve the insoluble formazan crystals in viable cells. Then the formazan concentrations were quantified by measuring the absorbance at 450 nm using a microplate spectraphotometer (Multiskan GO, Thermo, USA). Cell viability was expressed relative to the untreated control group which was regarded as 100%.