Standardization of a resazurin-based assay for the evaluation of metabolic activity in oral squamous carcinoma and glioblastoma cells.

The widely accepted resazurin-based assay can be used, prior to in vivo studies, as an inexpensive method to determine cytotoxicity. The aim of this study was to evaluate and standardize the assay conditions for oral squamous cancer cell (OSCC) and glioblastoma (U87-MG) lines by UV-vis spectroscopy. The cells were treated with 25 µgmL-1 of resazurin sodium salt and then incubated for 4 h, 6 h, and 6.5 h. All absorbance measurements were carried out at 21 ± 1 °C on a spectrophotometer with a microplate reader. After 4-hs of incubation, resazurin was completely reduced by OSCC cells, as demonstrated by the suppression of the absorbance at 380 nm. However, the U87-MG cells needed 6.5 h of incubation to demonstrate the same behavior. The Statistical analysis did not indicate significant differences between the OSCC and U87-MG cell lines' viability after 4 and 6.5 h respectively. We concluded that spectroscopic analysis is an efficient method for the standardization of the resazurin assay. In addition, without the implementation of suitable protocols, there could be an increase in the chance of errors or false positives or negatives that would reduce the usefulness of the data.

Rose Bengal located within liposome do not affect the activity of inside-out oriented Na,K-ATPase.

DPPC:DPPE-proteoliposomes (in which the enzyme is inside-out oriented) and DLOPC:DLOPE-proteoliposomes (in which the enzyme is only 40% inside-out oriented) is an excellent model for studying the selective effect of the reactive oxygen species, produced by the photo-activation of Rose Bengal. Both proteoliposomes used, when submitted to photo-irradiation with laser using 1200 mJ/cm2 energy dose, in the absence of the Rose Bengal, did not shown any effect in the ATPase activity and in the integrity of its systems. Also, no effect was observed using 50 microM of Rose Bengal encapsulated in the interior of the DPPC:DPPE-proteoliposome system. But, when we use 50 microM of Rose Bengal, present only in the extravesicular environment, and photo-irradiation with a laser dose of 200 mJ/cm2, it results in the loss of 40-50% of the ATPase activity, with damage of the DPPC:DPPE-proteoliposome integrity. Using a dose of 400 mJ/cm2 the ATPase activity was totality lost. Consequently, these effects could be correlated with direct damage in the peptide structure. The photo-irradiation of the system constituted by DLOPC:DLOPE-proteoliposome in the presence of Rose Bengal, encapsulated only in the interior compartment or in the extra-liposomal environments, revealed a gradual decrease of the ATPase activity, maintaining it at 30% after a dose of 1200 mJ/cm2 and losing total ATPase activity at 800 mJ/cm2, respectively, with the loss of integrity of this vesicular system in both conditions studied. The generated singlet oxygen could attack the double linkage present in the fatty acid structure of the lipid instead of the amino acid in the protein structure and, in a second step, result in an indirect inactivation of the enzyme activity. In summary, these results indicated that singlet oxygen species produced by photo-oxidation of Rose Bengal using laser light could act in protein and lipid structure depending on its proportion or distribution.