Inhibition of chondrocyte and synovial cell death after exposure to commonly used anesthetics: Chondrocyte apoptosis after anesthetics

Background: An intra-articular injection of local anesthetics is a common procedure for diagnostic and therapeutic purposes. It has been shown that these agents are toxic to articular cartilage and synovial tissue in a dose- and time-dependent fashion, and in some cases, they may lead to postarthroscopic glenohumeral chondrolysis (PAGCL). However, the role of apoptosis in cell death is still unclear, and the potential role of apoptosis inhibition in minimizing chondrocyte and synovial cell death has not been reported. Purpose: (1) To quantify the degree of apoptotic cell death in chondrocytes and synovial cells exposed to local anesthetics, and (2) to determine whether caspase inhibition could reduce cell death. Study Design: Controlled laboratory study. Methods: Human chondrocytes and synovial cells were expanded in vitro and exposed to normal saline, 0.5% bupivacaine, 0.5% ropivacaine, 1% lidocaine, or 1:1000 epinephrine for 90 minutes. Apoptosis was then detected at 1, 3, 5, and 7 days after exposure using terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) and immunohistochemistry. Apoptosis was then inhibited using the pan-caspase inhibitor z-vad-fmk. Results were normalized to normal saline controls and analyzed by generalized regression models and pairwise confidence intervals. Results: Analysis of cumulative chondrocyte apoptosis relative to controls after anesthetic exposure demonstrated more than 60% cell death with 0.5% bupivacaine and 1:1000 epinephrine. The greatest chondroprotective effect of caspase inhibition occurred with 0.5% ropivacaine. Similarly, in synovial cells, epinephrine was also very cytotoxic; however, 1% lidocaine induced the most apoptosis. Synovial cells exposed to 0.5% ropivacaine were again most sensitive to protective caspase inhibition. Conclusion: Local anesthetics induce chondrocyte and synovial cell apoptosis in a time-dependent fashion, with peak apoptosis occurring 5 days after exposure. Both chondrocytes and synovial cells are most sensitive to caspase inhibition after exposure to 0.5% ropivacaine. Clinical Relevance: Apoptosis inhibition may be an effective strategy in minimizing chondrocyte and synovial cell death after exposure to anesthetics. Further investigation is clinically warranted.