Graded, Irreversible Changes in Crayfish Giant Axon as Manifestations of Lidocaine Neurotoxicity In Vitro

Bupivacaine Induces Apoptosis via ROS in the Schwann Cell Line

Local anesthetics have been generally accepted as being safe. However, recent clinical trials and basic studies have provided strong evidence for the neurotoxicity of local anesthetics, especially through apoptosis. We hypothesized that local anesthetics cause neural complications through Schwann cell apoptosis. Among local anesthetics tested on the Schwann cell line, RT4-D6P2T, bupivacaine significantly induced cell death, measured by the methyl tetrazolium (MTT) assay, in a dose- (LD50 = 476 μM) and time-dependent manner. The bupivacaine-induced generation of reactive oxygen species (ROS), which was initiated within 5 hrs and preceded the activation of caspase-3 and poly ADP-ribose polymerase (PARP) degradation, was suggested to trigger apoptosis, exhibited by Hoechst 33258 nuclear staining and DNA fragmentation. Furthermore, concomitant block of ROS by anti-oxidants significantly inhibited bupivacaine-induced apoptosis. Among the local anesthetics for peripheral neural blocks, bupivacaine induced apoptosis in the Schwann cell line, which may be associated with ROS production.

Presentation of Neurolytic Effect of 10% Lidocaine after Perineural Ultrasound Guided Injection of a Canine Sciatic Nerve: A Pilot Study

BACKGROUND

Phenol and alcohol have been used to ablate nerves to treat pain but are not specific for nerves and can damage surrounding soft tissue. Lidocaine at concentrations > 8% injected intrathecal in the animal model has been shown to be neurotoxic. Tests the hypothesis that 10% lidocaine is neurolytic after a peri-neural blockade in an ex vivo experiment on the canine sciatic nerve.

METHODS

Under ultrasound, one canine sciatic nerve was injected peri-neurally with 10 cc saline and another with 10 cc of 10% lidocaine. After 20 minutes, the sciatic nerve was dissected with gross inspection. A 3 cm segment was excised and preserved in 10% buffered formalin fixative solution. Both samples underwent progressive dehydration and infusion of paraffin after which they were placed on paraffin blocks. The sections were cut at 4 µm and stained with hemoxylin and eosin. Microscopic review was performed by a pathologist from Henry Ford Hospital who was blinded to which experimental group each sample was in.

RESULTS

The lidocaine injected nerve demonstrated loss of gross architecture on visual inspection while the saline injected nerve did not. No gross changes were seen in the surrounding soft tissue seen in either group. The lidocaine injected sample showed basophilic degeneration with marked cytoplasmic vacuolation in the nerve fibers with separation of individual fibers and endoneurial edema. The saline injected sample showed normal neural tissue.

CONCLUSIONS

Ten percent lidocaine causes rapid neurolytic changes with ultrasound guided peri-neural injection. The study was limited by only a single nerve being tested with acute exposure.

An inexpensive drivable cannulated microelectrode array for simultaneous unit recording and drug infusion in the same brain nucleus of behaving rats

Neurons are functionally segregated into discrete populations that perform specific computations. These computations, mediated by neuron-neuron electrochemical signaling, form the neural basis of behavior. Thus fundamental to a brain-based understanding of behavior is the precise determination of the contribution made by specific neurotransmitters to behaviorally relevant neural activity. To facilitate this understanding, we have developed a cannulated microelectrode array for use in behaving rats that enables simultaneous neural ensemble recordings and local infusion of drugs in the same brain nucleus. The system is inexpensive, easy to use, and produces robust and quantitatively reproducible drug effects on recorded neurons.

Occurrence of paresthesia after dental local anesthetic administration in the United States

BACKGROUND

Several studies have suggested that the likelihood of paresthesia may depend on the local anesthetic used. The purpose of this study was to determine if the type of local anesthetic administered had any effect on reports of paresthesia in dentistry in the United States.

METHODS

The authors obtained reports of paresthesia involving dental local anesthetics during the period from November 1997 through August 2008 from the U.S. Food and Drug Administration Adverse Event Reporting System. They used chi(2) analysis to compare expected frequencies, on the basis of U.S. local anesthetic sales data, with observed reports of oral paresthesia.

RESULTS

During the study period, 248 cases of paresthesia occurring after dental procedures were reported. Most cases (94.5 percent) involved mandibular nerve block. The lingual nerve was affected in 89.0 percent of cases. Reports involving 4 percent prilocaine and 4 percent articaine were 7.3 and 3.6 times, respectively, greater than expected (chi(2), P < .0001) on the basis of local anesthetic use by U.S. dentists.

CONCLUSIONS

These data suggest that paresthesia occurs more commonly after use of 4 percent local anesthetic formulations. These findings are consistent with those reported in a number of studies from other countries.

CLINICAL IMPLICATIONS

Until further research indicates otherwise, dentists should consider these results when assessing the risks and benefits of using 4 percent local anesthetics for mandibular block anesthesia.

Paresthesias in dentistry

Alterations to normal oral sensory function can occur following restorative and surgical dental procedures. Paresthesia is defined as an abnormal sensation, such as burning, pricking, tickling, or tingling. Paresthesias are one of the more general groupings of nerve disorders known as neuropathies. This article reviews the extent of this oral complication as it relates to dental and surgical procedures, with specific emphasis on paresthesias associated with local anesthesia administration. This review establishes a working definition for paresthesia as it relates to surgical trauma and local anesthesia administration, describes the potential causes for paresthesia in dentistry, assesses the incidence of paresthesias associated with surgery and local anesthesia administration, addresses the strengths and weaknesses in research findings, and presents recommendations for the use of local anesthetics in clinical practice.

Calcineurin and cytoskeleton in low-frequency depression

Transmitter release at high probability phasic synapses of crayfish neuromuscular junctions depresses by over 50% in 60 min when stimulated at 0.2 Hz. Inhibition of the protein phosphatase calcineurin by intracellular pre-synaptic injection of autoinhibitory peptide inhibited low-frequency depression (LFD) and resulted in facilitation of transmitter release. Since this inhibitor had no major effects when injected into the post-synaptic cell, only pre-synaptic calcineurin activity is necessary for LFD. To examine changes in phosphoproteins during LFD we performed a phosphoproteomic screen on proteins extracted from motor axons and nerve terminals after LFD induction or treatment with various drugs that affect kinase and phosphatase activity. Proteins separated by PAGE were stained with phospho-specific/total protein ratio stains (Pro-Q Diamond/SYPRO Ruby) to identify protein bands for analysis by mass spectrometry. Phosphorylation of actin and tubulin decreased during LFD, but increased when calcineurin was blocked. Tubulin and phosphoactin immunoreactivity in pre-synaptic terminals were also reduced after LFD. The actin depolymerizing drugs cytochalasin and latrunculin and the microtubule stabilizer taxol inhibited LFD. Therefore, dephosphorylation of pre-synaptic actin and tubulin and consequent changes in the cytoskeleton may regulate LFD. LFD is unlike long-term depression found in mammalian synapses because the latter requires in most instances post-synaptic calcineurin activity.Thus, this simpler invertebrate synapse discloses a novel pre-synaptic depression mechanism.

Epidural Lidocaine Induces Dose-Dependent Neurologic Injury in Rats

Although epidural lidocaine administered as a bolus has been shown to cause little neurotoxicity, local anesthetics are often administered repetitively or continuously into the epidural space, and in high doses may induce neurologic injury. We investigated whether epidural lidocaine is neurotoxic when a large dose is continuously administered in rats, and whether the functional impairment and histologic damage is dose dependent. In Experiment 1, 13 rats received a 120-min epidural infusion (at 5 microL/min) of saline or 2% lidocaine. Four days after infusion, rats given 2% lidocaine developed significantly more prolonged tail-flick latencies and showed more apparent morphologic damage than those given saline. In Experiment 2, 41 rats were randomly divided into 5 groups to receive an epidural infusion of saline for 120 min or 5% lidocaine for 15, 30, 60, or 120 min at a rate of 5 muL/min. Rats given 5% lidocaine for 120 min developed a significant increase in tail-flick latency. Paw pressure thresholds did not change in any group. Nerve injury scores for rats given 5% lidocaine for 30, 60, and 120 min were significantly higher than those for rats given saline. Significant difference in damage in nerve roots was also observed among rats given the anesthetic for different durations of time; nerve injury scores with 120-min infusion were higher than with 15- and 30-min infusions, and injury with 60-min infusion was greater than with 15-min infusion. In conclusion, these results suggest that epidural lidocaine causes dose-dependent neurotoxicity after continuous infusion in rats.

Neurotoxicity of intrathecal local anaesthetics and transient neurological symptoms

Local anaesthetics have been placed in the intrathecal space for approximately 100 years. Currently used intrathecal local anaesthetics appear to be relatively benign on the basis of the low incidence of permanent neurological deficits. In large retrospective surveys of 4000-10 000 patients, the incidence of persistent neurological sequelae after subarachnoid anaesthesia varies between 0.01 and 0.7%. Since its introduction in 1948, hyperbaric 5% lidocaine has been used for millions of spinal anaesthetics. The predictable onset and limited duration of action have made lidocaine one of the most popular spinal anaesthetics currently available. Concern about the use of spinal lidocaine began in 1991 with published reports of cauda equina syndrome after continuous spinal anaesthesia. In 1993, Schneider published a case report of four patients undergoing spinal anaesthesia who postoperatively experienced aching and pain in the buttocks and lower extremities. This chapter reviews the neurotoxicity of spinal local anaesthetics, as well as the incidence, possible aetiology, and treatment of transient neurological symptoms after lidocaine spinal anaesthesia.

Intracellular Calcium Increases in Growth Cones Exposed to Tetracaine

Neurotoxicity of local anesthetics has been reported for both matured and growing neurons. In the present study, we examined if tetracaine increases Ca(2+) concentration during growth cone collapse. Intracellular Ca(2+) concentration was measured by fura 2/AM after exposure to tetracaine. Tetracaine (1-2 mM) induced increases in intra-growth cone Ca(2+) concentration (P < 0.01). The Ca(2+) hot spot was expanded into the neurite from the periphery towards the cell body. When tetracaine was applied to growth cones in Ca(2+) free media, the increase was minor. However, tetracaine induced growth cone collapse even in the culture media, which did not contain Ca(2+). Ni(2+) (100 microM; a general Ca(2+) channel inhibitor) and BAPTA-AM (5 microM; intracellular Ca(2+) chelator) could not inhibit growth cone collapse induced by 1-2 mM tetracaine. Tetracaine (>1 mM) induces collapse and Ca(2+) increase at growth cones simultaneously; however, these two phenomena might be provoked independently.

IMPLICATIONS

Tetracaine induced intracellular Ca(2+) increases and growth cone collapse in dorsal root ganglion neurons. The Ca(2+) hot spot in the growth cone expanded into the neurite from periphery towards the cell body.

Procaine and mepivacaine have less toxicity in vitro than other clinically used local anesthetics

The neurotoxicity of local anesthetics can be demonstrated in vitro by the collapse of growth cones and neurites in cultured neurons. We compared the neurotoxicity of procaine, mepivacaine, ropivacaine, bupivacaine, lidocaine, tetracaine, and dibucaine by using cultured neurons from the freshwater snail Lymnaea stagnalis. A solution of local anesthetics was added to the culture dish to make final concentrations ranging from 1 x 10(-6) to 2 x 10(-2) M. Morphological changes in the growth cones and neurites were observed and graded 1 (moderate) or 2 (severe). The median concentrations yielding a score of 1 were 5 x 10(-4) M for procaine, 5 x 10(-4) M for mepivacaine, 2 x 10(-4) M for ropivacaine, 2 x 10(-4) M for bupivacaine, 1 x 10(-4) M for lidocaine, 5 x 10(-5) M for tetracaine, and 2 x 10(-5) M for dibucaine. Statistically significant differences (P < 0.05) were observed between mepivacaine and ropivacaine, bupivacaine and lidocaine, lidocaine and tetracaine, and tetracaine and dibucaine. The order of neurotoxicity was procaine = mepivacaine < ropivacaine = bupivacaine < lidocaine < tetracaine < dibucaine. Although lidocaine is more toxic than bupivacaine and ropivacaine, mepivacaine, which has a similar pharmacological effect to lidocaine, has the least-adverse effects on cone growth among clinically used local anesthetics.

IMPLICATIONS

Systematic comparison was assessed morphologically in growth cones and neurites exposed to seven local anesthetics. The order of neurotoxicity was procaine = mepivacaine < ropivacaine = bupivacaine < lidocaine < tetracaine < dibucaine. Although lidocaine is more toxic than bupivacaine and ropivacaine, mepivacaine, which has a similar pharmacological effect to lidocaine, is the safest among clinically used local anesthetics.

Local anesthetics differentially inhibit sympathetic neuron-mediated and C fiber-mediated synovial neurogenic plasma extravasation

Local anesthetics are used for local irrigation after many types of operations. However, recent evidence of toxic effects of local anesthetics at large concentrations during continuous administration suggests an advantage of using decreased local anesthetic concentrations for irrigation solutions. In this study, we determined whether smaller concentrations of local anesthetics may maintain an antiinflammatory and, therefore, analgesic effect without the risk of possible toxicity. Lidocaine and bupivacaine were studied for their ability to inhibit both components of neurogenic inflammation-C fiber-mediated and sympathetic postganglionic neuron (SPGN)-mediated inflammation-in the rat knee joint. Intraarticular lidocaine 0.02% reduced 5-hydroxytryptamine (5-HT)-induced (SPGN-mediated) plasma extravasation (PE) by 35%, and further decreases were obtained by perfusing larger concentrations of lidocaine. Intraarticular bupivacaine 0.025% inhibited 5-HT-induced PE by 60%, and a 95% inhibition was obtained with bupivacaine 0.05%. Larger local anesthetic concentrations were necessary to inhibit C fiber-mediated PE than those required to inhibit SPGN-mediated PE. Lidocaine 0.4% was required to reduce mustard oil-induced PE by 60%. Lidocaine 2% inhibited mustard oil-induced PE to baseline levels. Bupivacaine 0.1% was required for an 80% reduction of PE. Bupivacaine 0.25% inhibited mustard oil-induced PE to baseline levels. Our results demonstrate differential effects of local anesthetics on SPGN- and C fiber-mediated PE but confirm the concept of using smaller concentrations of local anesthetics to achieve inhibition of postoperative inflammation.

IMPLICATIONS

Local anesthetic wound irrigation is often used to treat postoperative surgical pain. Large concentrations of local anesthetics are usually used, and these concentrations may have possible neurotoxic and myotoxic effects. Our results demonstrate antiinflammatory effects of lidocaine and bupivacaine at concentrations smaller than used clinically.

The neuronal lipid membrane permeability was markedly increased by bupivacaine and mildly affected by lidocaine and ropivacaine

We investigated the local anesthetic action on ionic membrane conductance (membrane conductance) and selectivity in membranes formed with neuronal phospholipids in the absence and presence of cholesterol. In membranes without cholesterol, 1 mM bupivacaine and ropivacaine increased the membrane conductance approximately 4.5-fold; and 5 mM lidocaine, ropivacaine and bupivacaine increased the membrane conductance by 2.7-, 2.8- and 22.2-fold, respectively. In the presence of cholesterol, 5 mM ropivacaine had no effect, lidocaine decreased the membrane conductance by 2-fold, and bupivacaine increased the membrane conductance by 17-fold. Local anesthetics did not affect the ion selectivity in membranes without cholesterol, but they all decreased the Na(+) selectivity in membranes with cholesterol. Cholesterol reduced the lidocaine- and ropivacaine-induced membrane conductance increase by eliminating or reversing the Na(+) conductance increase and by lowering the Cl(-) conductance increase. In the absence of cholesterol, 5 mM bupivacaine increased both Na(+) conductance (38-fold) and Cl(-) conductance (19-fold), while in the presence of cholesterol it only increased Cl(-) conductance (26-fold). Of the local anesthetics studied, ropivacaine was the least membrane toxic while bupivacaine was the most toxic.

The neurotoxicity of local anesthetics on growing neurons: a comparative study of lidocaine, bupivacaine, mepivacaine, and ropivacaine

Local anesthetics can be neurotoxic. To test the hypothesis that exposure to local anesthetics produces morphological changes in growing neurons and to compare this neurotoxic potential between different local anesthetics, we performed in vitro cell biological experiments with isolated dorsal root ganglion neurons from chick embryos. The effects of lidocaine, bupivacaine, mepivacaine, and ropivacaine were examined microscopically and quantitatively assessed using the growth cone collapse assay. We observed that all local anesthetics produced growth cone collapse and neurite degeneration. However, they showed significant differences in the dose response. The IC(50) values were approximately, 10(-2.8) M for lidocaine, 10(-2.6) M for bupivacaine, 10(-1.6) M for mepivacaine, and 10(-2.5) M for ropivacaine at 15 min exposure. Some reversibility was observed after replacement of the media. At 20 h after washout, bupivacaine and ropivacaine showed insignificant percentage growth cone collapse in comparison to their control values whereas those for lidocaine and mepivacaine were significantly higher than the control values. Larger concentrations of the nerve growth factor (NGF) did not improve this reversibility. In conclusion, local anesthetics produced morphological changes in growing neurons with significantly different IC(50). The reversibility of these changes differed among the four drugs and was not influenced by the NGF concentration.

IMPLICATIONS

Local anesthetics induce growth cone collapse and neurite degeneration in the growing neurons. Mepivacaine was safer than lidocaine, bupivacaine, and ropivacaine for the primary cultured chick neurons.

Does pregnancy protect against intrathecal lidocaine-induced transient neurologic symptoms?

We investigated the incidence of transient neurologic symptoms (TNS) after the use of hyperbaric lidocaine as compared with hyperbaric bupivacaine in patients undergoing cesarean delivery under spinal anesthesia. Two hundred women scheduled for cesarean delivery were randomly allocated to receive spinal anesthesia with 75 mg hyperbaric lidocaine 5% (n = 100) or 12 mg hyperbaric bupivacaine 0.75% (n = 100). Spinal anesthesia was administered to all patients in the sitting position with a 25-gauge Whitacre needle. The level of sensory blockade, time to full recovery, and intraoperative hemodynamic profile were noted in all patients. The patients were interviewed postoperatively for three consecutive days to detect the occurrence of TNS. The incidence of TNS was zero (95% confidence interval 0%--3%) in both the Lidocaine and the Bupivacaine Groups. Our results indicate that the frequency of postoperative TNS does not exceed 3% in patients undergoing cesarean delivery at term using hyperbaric lidocaine 5% or hyperbaric bupivacaine 0.75%.

Lidocaine disrupts axonal membrane of rat sciatic nerve in vitro

Highly concentrated lidocaine has been reported to induce irreversible loss of membrane potential in crayfish nerve, which implies membrane disruption as one of the direct mechanisms of lidocaine-induced neurotoxicity. To confirm lidocaine-induced membrane disruption in mammalian nerve, a lactate dehydrogenase (LDH) leakage from rat sciatic nerve was measured in vitro. Before applying lidocaine, the desheathed nerve was incubated for 60 min in Krebs-Ringer solution at 37 degrees C to examine basal LDH activity. It was then incubated in 80 mM lidocaine solution at pH 7.3 for 15, 30, 60, or 120 min. Other nerves were immersed in 800 mM choline solution for 120 min. Total LDH activity per wet weight of nerve tissue was assayed using spectrophotometry. It was also determined using nerves cut into 10 segments and incubated in distilled water for 60 min. The LDH activity in the lidocaine group showed a time-dependent increase. After the 60- and 120-min incubation with lidocaine, the amount of LDH activity was significantly increased compared with the choline group and was similar to that of the group incubated in distilled water. We conclude that 80 mM lidocaine may be sufficient to cause membrane damage and facilitate the leakage of enzymes from cytoplasm.

IMPLICATIONS

This study demonstrates that exposing the rat myelinated nerve to lidocaine at a clinically used concentration for more than 30 min causes enough membrane damage to allow enzyme leakage. In clinical practice, the smallest effective dose should be used.

Potential neurotoxicity of spinal anesthesia with lidocaine

Spinal (intrathecal) anesthesia has evolved into a safe, widely accepted method of anesthesia with many advantages. However, the past decade has seen a large number of case reports and incidence studies that implicate the local anesthetic (LA) lidocaine as being more neurotoxic than other commonly used LAs such as bupivacaine and tetracaine, based on patterns of clinical use current at the time of those reports. Available studies suggest a risk of persistent lumbosacral neuropathy after spinal lidocaine by single injection in about 1 in 1300 procedures and a risk as high as about 1 in 200 after continuous spinal anesthesia with lidocaine. While uncommon, this risk is probably an order of magnitude higher than the risk reported for other commonly used LAs or for general anesthesia. Spinal lidocaine is also implicated in the syndrome of transient neurologic symptoms (previously referred to as transient radicular irritation), manifest by pain or dysesthesia in the buttocks or legs after recovery from anesthesia. Although the pain typically resolves within 1 week without lasting sequelae, it can be severe in up to one third of patients with the syndrome. In addition to clinical studies, both whole animal and in vitro studies have shown that lidocaine can be neurotoxic at clinically available concentrations and that lidocaine is more neurotoxic than equipotent concentrations of other commonly used LAs. The mechanism of this neurotoxicity may involve changes in cytoplasmic calcium homeostasis and mitochondrial membrane potential.

The neurotoxicity of drugs given intrathecally (spinal)

Overall, most spinal drugs in clinical use have been poorly studied for spinal cord and nerve root toxicity. Laboratory studies indicate that all local anesthetics are neurotoxic in high concentrations and that lidocaine and tetracaine have neurotoxic potential in clinically used concentrations. However, spinal anesthesia (including lidocaine and tetracaine) has a long and enviable history of safety. Spinal analgesics such as morphine, fentanyl, sufentanil, clonidine, and neostigmine seem to have a low potential for neurotoxicity based on laboratory and extensive clinical use. Most antioxidants, preservatives, and excipients used in commercial formulations seem to have a low potential for neurotoxicity. In addition to summarizing current information, we hope that this review stimulates future research on spinal drugs to follow a systematic approach to determining potential neurotoxicity. Such an approach would examine histologic, physiologic, and behavioral testing in several species, followed by cautious histologic, physiologic, and clinical testing in human volunteers and patients with terminal cancer refractory to conventional therapy.