MTT Assay for Cell Viability

Cell viability was determined with the thiazolyl blue tetrazolium bromide (MTT) assay as previously described [22 (link)]. Briefly, 1 × 10⁴ cells were seeded in the wells of a 96-well microplate and cultured with α-syn, p-α-syn, sonicated OW, OP, PFF, and pPFF for 1, 3, and 6 h. Afterward, the medium was replaced with MTT (M2128; Sigma-Aldrich Corporation) at a final concentration of 0.5 mg/mL and incubation was continued for 4 h. Then, the medium was discarded and replaced with 100 μL of dimethyl sulfoxide to dissolve the formazan crystals. Absorbance was measured at 490 nm with a microplate reader (PerkinElmer, Inc., Waltham, MA, USA). Three independent experiments were performed.