5 mg/mL) for 4 h at 37 °C in a 5% CO2 atmosphere.

The plate was centrifuged at 1500 rpm for 10 min. The medium was removed and replaced by 100 μL of dimethyl sulfoxide (DMSO), followed by mixing to dissolve the formazan CHIR-99021 mouse crystals. Absorbance was measured at 570 nm on a microenzyme-linked immunosorbent assay (ELISA) reader (Spectramax, Molecular Devices®) and the reduction of cell viability was expressed as the percentage compared with the negative control group designated as 100%. A control experiment carried out using only PAMAM in the culture medium did not induced cytotoxicity (data not shown). Nanoparticle-induced DNA damage was performed by the comet assay (also referred to as the single-cell gel electrophoresis – SCGE analysis) under alkaline conditions (Singh et al., 1988). The negative control was

exposed without AuNps under the same conditions. HepG2 cells and PBMC were cultured in 12-well culture plates as described above, and then pretreated for 3 h with 1.0 and 50.0 μM of AuNps-citrate and AuNps-PAMAM. Microscope slides were prepared in duplicate and coated with 1% normal melting point agarose (NMA). 60 μL of each cell suspension with 300 μL of low melting point agarose 1% (LMPA) were placed on these microscope slides containing NMA, deposited over the agarose layer. Coverslips were placed on the gels, which were left to set on ice. After gently removing the coverslips, the slides were immediately submersed in cold lysis solution (2.5 M NaCl, 100 mM EDTA,

10 mM Tris, 1% Tritron click here oxyclozanide X-100, pH 10) for 12 h in the dark. DNA was then allowed to unwind for 20 min in alkaline electrophoresis solution (300 mM NaOH, 1 mM EDTA, pH > 13). Electrophoresis was performed under 25 V and 300 mA for 20 min. Subsequently, the slides were placed in a cold neutralizing buffer (400 mM Tris buffer, pH 7.5) for 15 min, dried in 100% methanol for 5 min, and stained with 50 μL of 20 μg/mL ethidium bromide in the dark. At least 50 comets per slide were analyzed under a fluorescence microscope (Nikon Eclipse E200, Japan) equipped with an excitation filter of 515–560 nm and a barrier filter of 590 nm, connected to a digital camera (Nikon DS Qi1, Japan). The classical visual analysis scoring of the comet assay was analyzed by a single analyst, in order to minimize scoring images variation. Data were based on 150 cells for each test or control that were visually scored as belonging to one of five classes, according to tail size and intensity. Classes 0, 1, 2, 3, or 4 were given, with 0 = no detectable damage and 4 = maximum damage. The damage index was obtained by the formula, damage index = (0 × n0) + (1 × n1) + (2 × n2) + (3 × n3) + (4 × n4). The variables n0–n4 represent the number of nucleoids with 0–4 damage level, and each experiment was performed in triplicate. The AuNps cellular uptake was investigated using flow cytometry (Suzuki et al., 2007).