4.12. Assessment of Neuroprotective Activity and MTT Assay

The MTT assay evaluated the SH-SY5Y cell viability after treatment with S. officinalis extracts, Aβ_25–35 peptides, or the combination of both extracts and peptides, as previously described [50]. The SH-SY5Y cells were cultured for 24 h at a density of 2 × 10⁵ cells/well in a 96-well plate. The next day, the cells were treated with different concentrations of the S. officinalis extracts, or 25 μM of Aβ_25–35 peptides, or a combination of both for 48 h. Then, the cells were incubated in DMEM without phenol red that contained 45 μg/mL MTT for 4 h at 37 °C. Following aspiration of the medium, 150 μL of DMSO was added to each well. After covering the plate with foil and shaking it for 15 min, the absorbance was measured at 590 nm using a Synergy H1 microplate reader (BioTek^® Instruments, Inc., Winooski, VT, USA). Cell viability was calculated using the following equation:

At least four independent experiments were performed.