Quantification of the asymmetric migration of the lipophilic dyes, DiO and DiD, in homotypic co-cultures of chondrosarcoma SW-1353 cells.

DiO and DiD are lipophilic cell labelling dyes used in the staining of cells in vivo and in vitro. The aim of the present study was to quantify the asymmetrical distribution of dyes in co‑cultured cells and to measure the intercellular transfer of DiO and DiD. DiO and DiD were applied separately to stain two identical populations of SW‑1353 human chondrosarcoma cells that were subsequently co‑cultured (homotypic co‑culture). The intercellular migration of dyes in the co‑cultured cells was measured by flow cytometry and recorded under a fluorescent microscope. DiD and DiO caused no effect on the proliferation of cells, the degradation rate of the two dyes was comparable and crossover effects between dyes were negligible. The results of the present study suggested that asymmetrical intercellular migration of DiD and DiO was responsible for the asymmetrical distribution of these dyes in co‑cultured cells. To take advantage of the lipophilic dyes migration in the double-stained co-cultured cells we suggest to apply mixed-dyes controls prior to the flow cytometric analysis. These controls are performed by staining cells with a 1:1 mix of the two dyes and would enable the estimation of the intensity of intercellular contact in co‑culture systems. A 1:1 premix of DiO and DiD was applied to estimate cellular effect on intercellular exchange of lipid dyes in co‑cultures incubated with cycloheximide and cytochalasin B. The cellular effect contributed 6‑7% of intercellular migration of the lipophilic dyes, DiO and DiD. The majority of the observed intercellular transfer of these dyes was due to non‑cellular, passive transfer.