DNA damage kinetics and apoptosis in ivermectin-treated Chinese hamster ovary cells

A comet assay was used to analyze DNA damage kinetics in Chinese hamster ovary (CHO-K1) cells induced by antiparasitic ivermectin (IVM) and the IVM-containing technical formulation Ivomec® (IVO; 1% IVM). Cells were treated with 50 µg ml(-1) IVM and IVO for 80 min, washed and re-incubated in antiparasiticide-free medium for 0-24 h until assayed using the single-cell gel electrophoresis assay (SCGE). Cell viability remained unchanged up to 3 h of incubation. After 6 h of treatment, cell survival decreased up to 75% and 79% in IVM- and IVO-treated cultures, respectively, remaining unchanged within 12-24 h after treatment. For both anthelmintics, biphasic behavior in DNA damage occurred during the incubation time. A time-dependent increase of IVM- and IVO-induced DNA damage was observed within 0 to 3 h after pulse treatment, revealed by a progressive decrease of undamaged cells and an increase in slightly damaged and damaged cells. Finally, a time-dependent decrease in IVM- and IVO-induced DNA damage was revealed by a progressive decrease of slightly damaged cells and the absence of damaged cells simultaneously with an increase in the frequency of undamaged cells during the final 18 h of incubation. Flow cytometry analysis revealed that both compounds are able to induce a marked increase in early and late apoptosis. Based on our observations, we could conclude that the decrease in DNA lesions is mostly related to IVM-induced cytotoxicity rather than attributable to a repair process.