Background: Bupivacaine and supraphysiologic temperature can independently reduce cell viability of articular chondrocytes. In combination, these 2 deleterious factors could further impair cell viability.
Hypothesis: Hyaluronan may protect chondrocytes from death induced by bupivacaine at supraphysiologic temperatures.
Study design: Controlled laboratory study.
Methods: Bovine articular chondrocytes were treated with hyaluronan at physiologic (37°C) and supraphysiologic temperatures (45°C and 50°C) for 1 hour and then exposed to bupivacaine for 1 hour at room temperature. Cell viability was assessed at 3 time points: immediately after treatment, 6 hours later, and 24 hours later using flow cytometry and fluorescence microscopy. The effects of hyaluronan on the levels of sulfated glycosaminoglycan in the chondrocytes were determined using Alcian blue staining.
Results: (1) Bupivacaine alone did not induce noticeable chondrocyte death at 37°C; (2) bupivacaine and temperature synergistically increased chondrocyte death, that is, when the chondrocytes were conditioned to 45°C and 50°C, 0.25% and 0.5% bupivacaine increased the cell death rate by 131% to 383% in comparison with the phosphate-buffered saline control group; and (3) addition of hyaluronan reduced chondrocyte death rates to approximately 14% and 25% at 45°C and 50°C, respectively. Hyaluronan's protective effects were still observed at 6 and 24 hours after bupivacaine treatment at 45°C. However, at 50°C, hyaluronan delayed but did not prevent the cell death caused by bupivacaine. One-hour treatment with hyaluronan significantly increased sulfated glycosaminoglycan levels in the chondrocytes.
Conclusion: Bupivacaine and supraphysiologic temperature synergistically increase chondrocyte death, and hyaluronan may protect articular chondrocytes from death caused by bupivacaine.
Clinical relevance: This study provides a rationale to perform preclinical and clinical studies to evaluate whether intra-articular injection of a mixture of bupivacaine and hyaluronan after arthroscopic surgery may protect against bupivacaine's chondrotoxicity.