Transduction of transactivator of transcription (Tat)-superoxide dismutase (SOD) fusion protein into monolayer cultured chondrocytes. Chondrocytes were obtained from the femoral condyle and the tibial plateau from osteoarthritis (OA) patients and cultured in monolayers. First passage chondrocytes were used in subsequent experiments. (a) Dose-dependent and (b) time-dependent transduction of Tat-SOD into chondrocytes. Transduction of Tat-SOD into the cells was analyzed by western blotting with a rabbit anti-polyhistidine IgG. Tat-SOD (1 to 7 μM) and control SOD were added to the culture medium for 1 hour (a), or 3 μM of Tat-SOD and control SOD were added to the culture medium for 1 to 9 hours (b). (c) Localization of transduced Tat-SOD protein. After FITC-labeled Tat-SOD (3 μM) was transduced into chondrocytes, the cells were washed with PBS and immediately observed by fluorescence microscopy (×100 original magnification; inset, ×400 original magnification). Data are representative of four samples from different donors. (d) The specific activities of SOD in cultured chondrocytes treated with Tat-SOD; 1 to 7 μM of Tat-SOD and control SOD were added to the culture medium for 1 hours. Bars represent the mean ± standard error of the mean obtained from duplicate experiments from three donors. Asterisks denote p < 0.05 compared to control.