Mitochondrial injury and caspase activation by the local anesthetic lidocaine.
BACKGROUND
Lidocaine, a local anesthetic, can be neurotoxic. However, the cellular mechanisms of its neurotoxicity at concentrations encountered during spinal anesthesia remain unclear.


METHODS
The authors examined the mechanisms of lidocaine neurotoxicity in the ND7 cell line derived from rat dorsal root ganglion. Individual neurons were assayed by flow cytometry or microscopy using fluorescent probes of plasma membrane integrity, mitochondrial membrane potential, caspase activity, phospholipid membrane asymmetry, and mitochondrial cytochrome c release.


RESULTS
In the ND7 cell line, lidocaine at 185 mm x 10 min to 2.3 mm x 24 h caused necrosis or late apoptosis. Equimolar Tris buffer and equipotent tetrodotoxin controls were not toxic, indicating that neither osmotic nor Na-blocking effects explain lidocaine neurotoxicity. The earliest manifestation of lidocaine neurotoxicity was complete loss of mitochondrial membrane potential within 5 min after exposure to lidocaine at a concentration of 19 mm or greater. Consistent with these data, 37 mm lidocaine (1%) induced release of mitochondrial cytochrome c into the cytoplasm, as well as plasma membrane blebbing, loss of phosphatidylserine membrane asymmetry, and caspase activation, with release of mitochondrial cytochrome c to the cytoplasm within 2 h. Treatment with z-VAD-fmk, a specific inhibitor of caspases, prevented caspase activation and delayed but did not prevent neuronal death, but did not inhibit the other indicators of apoptosis.


CONCLUSIONS
Collectively, these data indicate that lidocaine neurotoxicity involves mitochondrial dysfunction with activation of apoptotic pathways.
Johnson
Michael E
ME
Department of Anesthesiology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA. johnson.michael@mayo.edu
Uhl
Cindy B
CB
Spittler
Karl-Heinz
KH
Wang
Hongxun
H
Gores
Gregory J
GJ
D000779:Anesthetics, Local / Q000494:pharmacology* / Q000633:toxicity*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002021:Buffers; D020169:Caspases / Q000378:metabolism*; D002478:Cells, Cultured; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005434:Flow Cytometry; D005456:Fluorescent Dyes; D008012:Lidocaine / Q000494:pharmacology* / Q000633:toxicity*; D008564:Membrane Potentials / Q000187:drug effects; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology*; D009336:Necrosis; D009475:Neurons, Afferent / Q000187:drug effects / Q000473:pathology; D009498:Neurotoxins; D010101:Oxygen Consumption / Q000187:drug effects; D051381:Rats; D013116:Spinal Cord / Q000166:cytology / Q000473:pathology
D000779:Anesthetics, Local; D002021:Buffers; D005456:Fluorescent Dyes; D009498:Neurotoxins; D045304:Cytochromes c; D008012:Lidocaine; D020169:Caspases