In vitro, inhibition of mitogen-activated protein kinase pathways protects against bupivacaine- and ropivacaine-induced neurotoxicity

Local anesthetic 'in-situ' toxicity during peripheral nerve blocks: update on mechanisms and prevention

PURPOSE OF REVIEW

Peripheral nerve blocks induce undesired side-effects linked to the toxicity of local anesthetics on neuron and myocytes via different cell targets. The effects of local anesthetics on these targets are now well known and summarized in this review.

RECENT FINDINGS

Local anesthetic-induced local cell toxicity involved different pathways leading to cell death, necrosis and different factors closely associated with the clinical practice modulated this toxicity. High concentration and prolonged duration of local anesthetic administration are closely associated with severe lesions.

SUMMARY

Phenotypic analyses revealed that local anesthetics could induce histological damage with lesions ranging from local to extreme in skeletal muscle. Metabolic alterations were also described involving sarcoplasmic reticulum and calcium dysregulation, alteration of mitochondrial physiology and of oxidative phosphorylation with associated overproduction of harmful reactive oxygen species, typically leading to apoptosis or necrosis. Biochemical and cell biology investigations now indicate that local anesthetics interact with different molecular targets in mammalian cells as respiratory chain complex I or the prosurvival kinase Akt. Functional dysfunction in both muscle and neuron remains to be investigated with caution in patients, as local anesthetic toxicity remains under-evaluated. Likewise, the use of adapted local anesthetics in patients with particular diseases and neuromuscular disorder could further reduce the risk of undesired effect.We need to improve our practice, and the optimization of our clinical protocol could prevent from these side-effects. Lastly, experimental studies highlight the preventive effects of antioxidant drugs or of recombinant human erythropoietin but the pharmacokinetic feature of such strategies remain to be evaluated.

Bupivacaine-induced apoptosis independently of WDR35 expression in mouse neuroblastoma Neuro2a cells

Background

Bupivacaine-induced neurotoxicity has been shown to occur through apoptosis. Recently, bupivacaine was shown to elicit reactive oxygen species (ROS) production and induce apoptosis accompanied by activation of p38 mitogen-activated protein kinase (MAPK) in a human neuroblastoma cell line. We have reported that WDR35, a WD40-repeat protein, may mediate apoptosis through caspase-3 activation. The present study was undertaken to test whether bupivacaine induces apoptosis in mouse neuroblastoma Neuro2a cells and to determine whether ROS, p38 MAPK, and WDR35 are involved.

Results

Our results showed that bupivacaine induced ROS generation and p38 MAPK activation in Neuro2a cells, resulting in apoptosis. Bupivacaine also increased WDR35 expression in a dose- and time-dependent manner. Hydrogen peroxide (H₂O₂) also increased WDR35 expression in Neuro2a cells. Antioxidant (EUK-8) and p38 MAPK inhibitor (SB202190) treatment attenuated the increase in caspase-3 activity, cell death and WDR35 expression induced by bupivacaine or H₂O₂. Although transfection of Neuro2a cells with WDR35 siRNA attenuated the bupivacaine- or H₂O₂-induced increase in expression of WDR35 mRNA and protein, in contrast to our previous studies, it did not inhibit the increase in caspase-3 activity in bupivacaine- or H₂O₂-treated cells.

Conclusions

In summary, our results indicated that bupivacaine induced apoptosis in Neuro2a cells. Bupivacaine induced ROS generation and p38 MAPK activation, resulting in an increase in WDR35 expression, in these cells. However, the increase in WDR35 expression may not be essential for the bupivacaine-induced apoptosis in Neuro2a cells. These results may suggest the existence of another mechanism of bupivacaine-induced apoptosis independent from WDR35 expression in Neuro2a cells.

Repeated Intrathecal Administration of Ropivacaine Causes Neurotoxicity in Rats

Previous studies have shown that ropivacaine is the least neurotoxic local anaesthetic. Most of the data derive from short-term ropivacaine injection into the subarachnoid space. Intrathecal administration for a prolonged period, and the histological changes and behavioural effects of repeated intrathecal administration, have not previously been investigated. We studied the possible neurotoxicity of intrathecal injection of ropivacaine in a rat model.

Rats received 0.12 ml/kg body weight of ropivacaine at concentrations of 0.5 or 1%, or normal saline only, via an implanted intrathecal catheter at 90-minute intervals for 12 hours. On days 1, 3, 5, 7, 14 and 28, the spinal cord was examined by light and electron microscopy at the L3 level. We assessed sensory thresholds to noxious stimulation, behavioural change and protein kinase B immunoreactivity for possible neuronal injury within the spinal cord.

Ropivacaine 1% induced thermal hyperalgesia and mechanical allodynia, neuronal injury characterised by tissue oedema, proliferation of glial cells, neuronal morphology changes and degeneration and protein kinase B expression. There were no significant differences in motor function as a result of different concentrations of ropivacaine.

Repeated intrathecal injection of ropivacaine 1% can induce neurotoxicity in rats. Our data suggests that expression of protein kinase B might be involved in this neurotoxicity.

Local anesthetic Schwann cell toxicity is time and concentration dependent

BACKGROUND

Peripheral nerve blocks with local anesthetics (LAs) are commonly performed to provide surgical anesthesia or postoperative analgesia. Nerve injury resulting in persistent numbness or weakness is a potentially serious complication. Local anesthetics have previously been shown to damage neuronal and Schwann cells via several mechanisms. We sought to test the hypothesis that LAs are toxic to Schwann cells and that the degree of toxicity is directly related to the concentration of LA and duration of exposure. Intraneural injection of LAs has been shown to produce nerve injury. We sought to test the hypothesis that a prolonged extraneural infusion of LA can also produce injury.

METHODS

Schwann cells cultured from neonatal rat sciatic nerves were incubated with LAs at different concentrations (10, 100, 500, and 1000 μM), and each concentration was assessed for toxicity after 4, 24, 48 and 72 hours of exposure. Local anesthetics tested were lidocaine, mepivacaine, chloroprocaine, ropivacaine, and bupivacaine. Cell death was assessed by lactate dehydrogenase release measured by optical density.In a separate experiment, a microcatheter was placed along the sciatic nerves of Sprague-Dawley rats. Rats were randomly assigned to receive either 0.9% saline (n = 8) or bupivacaine (0.5%, n = 4; 0.75%, n = 4) via the perineural catheters for 72 hours. The rats were then killed, and their nerves sectioned and stained for analysis. Sections were stained for myelin and with an antimacrophage (CD68) antibody.

RESULTS

None of the LAs tested produced significant Schwann cell death at very low concentrations (10 μM, or 0.0003%) even after prolonged exposure. With prolonged exposure (48 or 72 hrs) to high concentrations (1000 μM, or 0.03%), all of the LAs tested produced significant Schwann cell death (increased lactate dehydrogenase release relative to control as measured by optical density, 0.384-0.974; all P values < 0.001). Only bupivacaine produced significant cell death (0.482, P < 0.001) after prolonged exposure to low concentrations (100 μM, or 0.003%). At intermediate concentrations (500 μM, or 0.015%), cell death was more widespread with bupivacaine (0.768, P < 0.001) and ropivacaine (0.675, P < 0.001) than the other agents (0.204-0.368; all P values < 0.001). Prolonged extraneural exposure of rat sciatic nerves to bupivacaine caused significant demyelination and infiltration of nerves with inflammatory cells.

CONCLUSIONS

Local anesthetics induce Schwann cell death in a time- and concentration-dependent manner. Bupivacaine and ropivacaine have greater toxicity at intermediate concentrations, and prolonged exposure to bupivacaine produces significant toxicity even at low concentrations. Brief exposure to high concentrations of bupivacaine damages Schwann cells. Prolonged extraneural infusion of bupivacaine results in nerve injury.

Lipophilicity but not stereospecificity is a major determinant of local anaesthetic-induced cytotoxicity in human T-lymphoma cells

BACKGROUND AND OBJECTIVES

Local neurotoxicity of local anaesthetics is a well known phenomenon which is determined by lipophilicity. Recent reports have indicated the relevance of local anaesthetic-induced cytotoxicity also in nonneuronal tissues. This study re-evaluates the role of lipophilicity in local anaesthetic cytotoxicity in nonneuronal cells. In addition, the toxicities of pipecoloxylidine S(-) enantiomers were investigated.

METHODS

Local anaesthetic-induced cytotoxicity was investigated in vitro in T-lymphoma cells (Jurkat). Cells were incubated with each of eight different local anaesthetics, two esters and six amides. Annexin V-fluorescein isothiocyanate and 7-aminoactinomycin D double staining followed by flow cytometry were used to investigate the fraction of early apoptotic cells as well as the overall cell death. The concentrations leading to 50% cell death (LC50) were calculated and compared. In a second step, we compared the toxicities of S(-) bupivacaine and the racemate as well as R(+) and S(-) ropivacaine.

RESULTS

Concentration-dependent cytotoxicity was observed for all investigated local anaesthetics. Apoptosis was seen at low concentrations, whereas necrosis was observed at higher concentrations. LC50 values of the different local anaesthetics yielded the following decreasing order of toxicity: tetracaine, bupivacaine, ropivacaine, prilocaine, procaine, lidocaine, articaine and mepivacaine. Toxicity correlated with octanol/buffer partition coefficients, but was independent of the ester or amide linkage. There was no effect of stereoisomerism on apoptosis and necrosis.

CONCLUSION

Moderate correlations for cytotoxicity with lipophilicity and clinical potency of local anaesthetics can be found in nonneuronal cells that are less than those reported previously with neuronal cells. Structural factors such as ester or amide linkage or stereospecificity do not have any influence on cytotoxicity. Although S(-) enantiomers may be advantageous with regard to systemic toxicity, they have no advantage in respect of local cytotoxicity in vitro.

Coenzyme Q10 does not enhance preadipocyte viability in an in vitro lipotransfer model

BACKGROUND

Autologous fat is an attractive soft-tissue filler in plastic and reconstructive surgery. The success of the procedure relies strongly on the technique of transferring viable preadipocytes. Among other factors, preadipocyte viability is impaired by local anesthetics. Application of coenzyme Q10 is being performed by aesthetic plastic surgeons to enhance the success of lipotransfer. The aim of this study was to evaluate the effect of Q10 on preadipocyte viability with special regard to impairment after lidocaine treatment.

METHODS

Preadipocytes were pretreated with coenzyme Q10 or vehicle control followed by incubation with lidocaine for 30 min. Viability and apoptosis were assessed by FACS analysis and Western blot.

RESULTS

Coenzyme Q10 did not improve viability nor have any effect on investigated apoptosis parameters. Preadipocyte viability was reduced after lidocaine treatment. Surface binding of annexin V, cleavage of caspase-3, and abundance of subdiploid cells were not detectable though, suggesting that necrosis rather than apoptosis is the cause for reduced preadipocyte viability.

CONCLUSION

Our results indicate that Q10 does not improve preadipocyte viability. Preadipocyte cell death induced by lidocaine is not caused by apoptosis but by necrosis, which cannot be prevented by coenzyme Q10. These findings should be taken into account when searching for solutions to improve preadipocyte viability in the context of soft tissue engineering and autologous fat transfer.

Local anesthetics have a major impact on viability of preadipocytes and their differentiation into adipocytes

BACKGROUND

Autologous fat transplantation is a well-established technique in surgery. Moreover, the use of preadipocytes in soft-tissue engineering is currently being intensely investigated. Current efforts focus on identifying maneuvers that may minimize resorption and provide predictable late results. The aim of this study was to investigate the influence of different local anesthetics frequently used in clinical practice on the viability of preadipocytes and their ability to differentiate into adipocytes.

METHODS

Human preadipocytes were isolated from subcutaneous adipose tissue of 15 patients and treated with bupivacaine, mepivacaine, ropivacaine, articaine/epinephrine, and lidocaine for 30 minutes. Viability was determined directly after treatment and during the ensuing cultivation. Differentiation of preadipocytes was determined by expression of the adipocyte marker adiponectin.

RESULTS

Although the immediate effects of mepivacaine and ropivacaine were only moderate, treatment with articaine/epinephrine and lidocaine strongly impaired preadipocyte viability. Cells normally attached to the culture dishes and proliferated irrespective of the previous treatment. During long-term cultivation, articaine/epinephrine-treated cell viability decreased markedly, whereas other local anesthetics had no impact. Despite normal phenotypic appearance of cells treated with bupivacaine, mepivacaine, ropivacaine, and lidocaine, all local anesthetics markedly impaired adipocyte differentiation as determined by adiponectin expression.

CONCLUSIONS

The authors' results show that there is a marked influence of local anesthetics not only on the quantity but also on the quality of viable preadipocytes as determined by their ability to differentiate into mature adipocytes. Therefore, these results should be considered in the context of autologous fat transfer and soft-tissue engineering.

Bupivacaine causes cytotoxicity in mouse C2C12 myoblast cells: involvement of ERK and Akt signaling pathways

AIM

The adverse effects of local anesthetics (LAs) on wound healing at surgical sites have been suggested, and may be related to their cytotoxicity. This study was aimed to compare the cellular toxicity of bupivacaine and lidocaine (two well-known LAs), and to explore the molecular mechanism(s).

METHODS

Toxicity of bupivacaine and lidocaine was assessed in cultured mouse C2C12 myoblasts by cell viability and apoptosis assays. Effects of LAs on extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) activation, which are essential for cell proliferation and survival, were evaluated by immunoblotting.

RESULTS

Both LAs, especially bupivacaine, prevented cell growth and caused cell death in a dose-dependent manner. The half maximal inhibitory concentrations (IC(50)) for bupivacaine and lidocaine were 0.49+/-0.04 and 3.37+/-0.53 mmol/L, respectively. When applied at the same dilutions of commercially available preparations, the apoptotic effect induced by bupivacaine was more severe than that of lidocaine in C2C12 cells. Furthermore, bupivacaine significantly diminished the ERK activation, which may underlie its anti-proliferative actions. Both LAs suppressed Akt activation, which correlated with their effects on apoptosis.

CONCLUSION

Our study demonstrated that, when used at the same dilutions from clinically relevant concentrations, bupivacaine is more cytotoxic than lidocaine in vitro. Anti-proliferation and cell death with concomitant apoptosis mediated by bupivacaine may offer an explanation for its adverse effects in vivo (eg slowing wound healing at the surgical sites). A less toxic, long-acting anesthetic may be needed.