Supraphysiologic Temperature Enhances Cytotoxic Effects of Bupivacaine on Bovine Articular Chondrocytes in an In Vitro Study

Abstract

The purpose of this study was to determine the effects of temperature or 0.25% bupivacaine treatment in combination with supraphysiologic temperatures on chondrocyte viability. Bovine articular chondrocytes in suspension culture were treated with phosphate-buffered saline solution at 20°C, 37°C, 40°C, 42°C, 45°C, 47°C, and 50°C for 15, 30, and 60 minutes or with phosphate-buffered saline solution at 37°C, 45°C, and 50°C for 30 and 60 minutes followed by 0.25% bupivacaine at 20°C for 60 minutes. Chondrocyte viability was analyzed by flow cytometry with the LIVE/DEAD Viability/Cytotoxicity Kit (Molecular Probes, Eugene, OR). Annexin V and ethidium double staining determined whether apoptosis or necrosis occurred. Temperatures from 20°C to 42°C did not cause chondrocyte death. Temperatures at or above 45°C caused significant chondrocyte death, particularly at 50°C for 60 minutes, compared with 37°C at 60 minutes (P < .01). When the chondrocytes were incubated at 50°C, subsequent exposure to bupivacaine significantly increased chondrocyte death compared with the saline solution-treated control group (P < .001). There were additive cytotoxic effects when bupivacaine was combined with supraphysiologic temperatures. It was also found that bupivacaine at supraphysiologic temperatures caused necrosis of articular chondrocytes. Temperatures at or above 45°C caused significant chondrocyte death. Bupivacaine treatment in the presence of 45°C and 50°C temperatures significantly increased necrosis of bovine articular chondrocytes in this in vitro study. Immediate intra-articular injection of bupivacaine after heat-generating procedures may cause damage to the cartilage because of the additive cytotoxic effects of bupivacaine and elevated temperature.