Acridine orange induces binucleation in chondrocytes

Objective: Although it is well known that binuclear cells commonly appear a mong the chondrocytes of normal cartilages as well as among neoplastic chon drocytes of chondrosarcomas, the mechanism of binucleation is still unclear . Therefore, this study was undertaken to clarify the mechanism of binuclea tion in chondrocytes, using primary culture cells of growth plate cartilage . Design: These chondrocytes were exposed to acridine orange (AO) which is a fluorescent dye for differentiating certain DNAs and RNAs in nuclei and cyt oplasm, and which inhibits mitosis. After exposure to 0.5 mug/ml AO, for 0, 6, 24, 48, and 96 h, the following parameters were investigated: (1) cell growth rate (GR); (2) frequency of hyperdiploid cells (%HDC) by DNA cytoflu orometry; (3) mitotic index (MI); (4) BrdU labeling index (FI), (5) frequen cy of binuclear cells (%BNC). Results: Compared with the control cells, which were cultured in AO-free me dium, the GR was remarkably inhibited at 24 h. MI was also decreased from 6 to 24 h, and LI decreased at 48 h. However, these parameters were recovere d at 96 h. The %HDC was increased from 8 to 96 h, and the %BNC was also inc reased to a maximum of six times that of the control cells at 96 h. Discussion: These results suggested that the binuclear cells observed among the cultured chondrocytes may be formed from G2 arrested cells by amitotic nuclear division, but not by mitosis without cytoplasmic division or cell fusion. (C) 2001 OsteoArthritis Research Society International.