Transduction of transactivator of transcription (Tat)-superoxide dismutase (SOD) fusion protein into explant cultured chondrocytes. Chondrocytes were obtained from a relatively lesion-free area of femoral condyles in OA patients and cultured in explants. (a) Transduction of Tat-SOD into the cells was analyzed by western blotting with a rabbit anti-polyhistidine IgG. Tat-SOD (1 to 7 μM) or control SOD were added to the culture medium for 6 hours. The tissues were milled in liquid nitrogen after transduction and protein was extracted in 4 M guanidine hydrochloride buffer and dialyzed. (b) Immunohistochemistry of cartilage explant transduced with Tat-SOD fusion protein (3 μM concentration of fusion protein added to the culture medium for 6 hours). The explants were fixed and sectioned in a cryotome after extensive washing. Cartilage sections were incubated with a mouse monoclonal anti-human Cu, Zn-SOD IgG and then visualized with a confocal scanning fluorescent microscope. Data are representative of seven samples from different donors. Scale bar = 100 μm.