Evaluation of the in vitro effects of local anesthetics on equine chondrocytes and fibroblast-like synoviocytes

Abstract

OBJECTIVE To investigate the in vitro effects of clinically relevant concentrations of the local anesthetics (LAs) bupivacaine, lidocaine, lidocaine with preservative (LP), mepivacaine, and ropivacaine on equine chondrocyte and fibroblast-like synoviocyte (FLS) viability. SAMPLE Chondrocytes and FLSs of the metacarpophalangeal joints of 4 healthy adult horses. PROCEDURES Viability of chondrocytes and FLSs was determined with 3 assays: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH), and trypan blue (TB) exclusion (only FLS). Viability was assessed after 30- and 60-minute exposures to 0.0625%, 0.125%, and 0.25% bupivacaine; 0.25%, 0.5%, and 1% lidocaine; 0.25%, 0.5%, and 1% LP; 0.25%, 0.5%, and 1% mepivacaine; and 0.125%, 0.25%, and 0.5% ropivacaine. RESULTS Viability of chondrocytes was significantly decreased with exposure to 0.25% bupivacaine, 1% lidocaine, 1% LP, 1% mepivacaine, and 0.25% ropivacaine. Viability of FLSs was significantly decreased with exposure to 0.25% bupivacaine, 1% mepivacaine, 1% LP, and 0.5% ropivacaine. CONCLUSIONS AND CLINICAL RELEVANCE Clinically relevant concentrations of LAs had in vitro time- and concentration-dependent cytotoxicity for chondrocytes and FLSs isolated from the metacarpophalangeal joints of healthy horses. Bupivacaine was more toxic to chondrocytes than lidocaine, mepivacaine, and ropivacaine, whereas bupivacaine, LP, mepivacaine, and ropivacaine were more toxic to FLSs than preservative-free lidocaine. Several LAs may negatively affect chondrocyte and FLS viability.

The concentration of lidocaine and mepivacaine measured in synovial fluid of different joints of horses after single intra-articular injection

“…The results of the present study show that after a mean of 7 min the lidocaine concentrations of the majority of joints exceed those concentrations previously associated with toxic effects on fibroblast-like synoviocytes and chondrocytes in vitro ( 11 ). After a mean of 7 min, mepivacaine concentrations were either above concentrations previously associated with cytotoxicity (≥10 mg/ml) or within a two-fold dilution of that concentration (between 5 and 10 mg/ml), suggesting that not only mepivacaine administration of 10 mL to the DIP joint but also mepivacaine administration of 10 mL to the MC and MCP joint have the potential to result in toxic effects ( Table 1 ).…”

“…Our study reveals that SF concentrations of lidocaine and mepivacaine after routine intra-articular injections are above concentrations associated with cytotoxicity to articular cells but also sufficiently high to possess antimicrobial activities against common equine pathogens ( 11 , 16 ).…”

“…Adverse effects of LAs on articular cartilage were first established after continuous intra-articular administration of bupivacaine in joints of humans ( 26 ) and have been recently established in horses after single intra-articular lidocaine and mepivacaine injection ( 12 ). A number of in vitro studies have confirmed toxicity of LAs to articular cells and sought to establish concentrations at which LAs exert their harmful effects ( 7 – 9 , 11 , 27 – 30 ). Toxic insults to equine chondrocytes and synoviocytes have been seen in vitro at concentrations as low as >5–10 mg/mL of mepivacaine and lidocaine ( 11 ).…”

“…A number of in vitro studies have confirmed toxicity of LAs to articular cells and sought to establish concentrations at which LAs exert their harmful effects ( 7 – 9 , 11 , 27 – 30 ). Toxic insults to equine chondrocytes and synoviocytes have been seen in vitro at concentrations as low as >5–10 mg/mL of mepivacaine and lidocaine ( 11 ). In vitro , investigations of cytotoxicity are carried out as two-fold dilutions, meaning that when in vitro results show cytotoxic effects after exposure to 10 mg/mL and not after exposure to 5 mg/mL, the exact concentrations at which a drug exhibits its cytotoxic effects lie somewhere in between the two investigated concentrations.…”

“…As early as 1963, their use for abolishing lameness in the horse was described ( 4 ), but it was not until the past decades, that LAs were associated with detrimental effects on joints ( 5 – 8 ). Specifically, concentrations of 1–2% lidocaine and mepivacaine possess chondrotoxic and synoviotoxic effects in vitro ( 7 – 11 ). In vivo , single intra-articular injections of 2% mepivacaine and lidocaine as used during lameness diagnosis resulted in a catabolic cartilage response as well as in joint inflammation in horses ( 12 ).…”