Determination of cell viability: After the exposure period,
the reaction medium was removed and the adhering
cells washed with PBS. One hundred microliter of MTT
solution (0.5 g.L-1 in medium) was added to each
culture well. After incubating for 4 hours at 37°C, the
MTT reaction medium was removed and formazanblue
was solubilized in 100 μL DMSO. This assay is
based on the reduction of yellow tetrazolium salt MTT
by the mitochondrial succinate dehydrogenase to form
an insoluble formazan-blue product. Only viable cells
with active mitochondria reduce significant amounts of
MTT (Mosmann, 1983) and formazan-blue formation
absorbance was recorded in an ELX800UV, universal
microplate reader spectrophotometer at 570 nm. Values
of absorbance were converted into percentage of
residual viability. Usually, inhibition concentration 50%
(IC50) is chosen as the best biological marker of
cytotoxicity.