I. Haller

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

BACKGROUND:Animal models show us that specific activation of the p38 mitogen-activated protein kinase (MAPK) may be a pivotal step in lidocaine neurotoxicity, but this has not been investigated in the case of two very widely used local anesthetics, bupivacaine and ropivacaine. We investigated the hypotheses that these drugs (A) are less neurotoxic than the prototype local anesthetic, lidocaine (B) are selectively toxic for subcategories of dorsal root ganglion neurons and (C) induce activation of either p38 MAPK or related enzymes, such as the c-jun terminal N-kinase (JNK) and extracellular signal-regulated kinase (ERK). METHODS:We incubated primary sensory neuron cultures with doses of lidocaine, bupivacaine, and ropivacaine equipotent at blocking sodium currents. Next, we sought to determine potential selectivity of bupivacaine and ropivacaine toxicity on neuron categories defined by immunohistochemical staining, or size. Subsequently, the involvement of p38 MAPK, JNK, and ERK was tested using enzyme-linked immunosorbent assays. Finally, the relevance of MAPK pathways in bupivacaine- and ropivacaine-induced neurotoxicity was determined by selectively inhibiting activity of p38 MAPK, JNK, and ERK. RESULTS:We found that the neurotoxic potency of bupivacaine and ropivacaine is dose-dependent and similar in vitro, but is not selective for any of the investigated subgroups of neurons. Neurotoxicity of bupivacaine and ropivacaine was mediated, at least in part, by MAPKs. Specifically, we demonstrated the relevance of both p38 MAPK and JNK pathways for the neurotoxicity of bupivacaine and characterized the involvement of the p38 MAPK pathway in the neurotoxicity of ropivacaine. CONCLUSIONS:Given equipotent doses, the neurotoxic potential of lidocaine does not appear to be significantly different from that of bupivacaine and ropivacaine in vitro. Moreover, bupivacaine and ropivacaine do not exert their neurotoxicity differently on specific subsets of dorsal root ganglion neurons. Their neurotoxic effects are brought about through the activation of specific MAPKs; the specific pharmacologic inhibition of these kinases attenuates toxicity in vitro.

Mitigation of direct neurotoxic effects of lidocaine and amitriptyline by inhibition of p38 mitogen-activated protein kinase in vitro and in vivo

Background:Local anesthetic–induced direct neurotoxicity (paresthesia, failure to regain normal sensory and motor function) is a potentially devastating complication of regional anesthesia. Local anesthetics activate the p38 mitogen-activated protein kinase (MAPK) system, which is involved in apoptotic cell death. The authors therefore investigated in vitro (cultured primary sensory neurons) and in vivo (sciatic nerve block model) the potential neuroprotective effect of the p38 MAPK inhibitor SB203580 administered together with a clinical (lidocaine) or investigational (amitriptyline) local anesthetic. Methods:Cell survival and mitochondrial depolarization as marker of apoptotic cell death was assessed in rat dorsal root ganglia incubated with lidocaine or amitriptyline either with or without the addition of SB203580. Similarly, in a sciatic nerve block model, the authors assessed wallerian degeneration by light microscopy to detect a potential mitigating effect of MAPK inhibition. Results:Lidocaine at 40 mm/approximately 1% and amitriptyline at 100 &mgr;m reduce neuron count, but coincubation with the p38 MAPK inhibitor SB203580 at 10 &mgr;m significantly reduces cytotoxicity and the number of neurons exhibiting mitochondrial depolarization. Also, wallerian degeneration and demyelination induced by lidocaine (600 mm/approximately 15%) and amitriptyline (10 mm/approximately 0.3%) seem to be mitigated by SB203580. Conclusions:The cytotoxic effect of lidocaine and amitriptyline in cultured dorsal root ganglia cells and the nerve degeneration in the rat sciatic nerve model seem, at least in part, to be mediated by apoptosis but seem efficiently blocked by an inhibitor of p38 MAPK, making it conceivable that coinjection might be useful in preventing local anesthetic-induced neurotoxicity.

The neurotoxic effects of amitriptyline are mediated by apoptosis and are effectively blocked by inhibition of caspase activity

Oral tricyclic antidepressants, widely used as adjuncts in the treatment of chronic pain, block sodium channels in vitro and nerve conduction in vivo. However, toxicity of amitriptyline has been observed after neural application. We therefore investigated the mechanism and possible prevention of amitriptyline neurotoxicity. To assess dose-dependent neurotoxicity of amitriptyline, we incubated neuron cultures from adult rat dorsal root ganglia with amitriptyline and quantified neuronal survival. Additionally, we investigated accepted markers of apoptosis (mitochondrial membrane potential, cytosolic cytochrome c, and activated caspase-3) and co-incubated amitriptyline with an inhibitor of caspase activity, z-vad-fmk, to assess the effect on cell survival. We found a dose-dependent neurotoxic effect of amitriptyline. Neurons incubated with amitriptyline exhibited loss of mitochondrial membrane potential, release of cytochrome c into the cytoplasm, and activation of caspase-3. Co-incubation with z-vad-fmk substantially improved neuronal survival in culture. In conclusion, amitriptyline-induced neurotoxicity is mediated by apoptosis and is attenuated by inhibition of caspase activity, suggesting that inhibition of apoptotic pathways may be efficient at alleviating local anesthetic–induced neurotoxicity. In vivo studies will have to corroborate whether the co-injection of anti-apoptotic drugs with local anesthetics decreases neurotoxic side effects.

Neurotoxicity of Lidocaine Involves Specific Activation of the p38 Mitogen-activated Protein Kinase, but Not Extracellular Signal–regulated or c-jun N-terminal Kinases, and Is Mediated by Arachidonic Acid Metabolites

Background:Pharmacologic inhibition of the p38 mitogen-activated protein kinase (MAPK) leads to a reduction in lidocaine neurotoxicity in vitro and in vivo. The current study investigated in vitro the hypotheses that lidocaine neurotoxicity is specific for dorsal root ganglion cells of different size or phenotype, involves time-dependent and specific activation of the p38 MAPK, that p38 MAPK inhibitors are only effective if applied with local anesthetic, and that p38 MAPK activation triggers activation of lipoxygenase pathways. Methods:The authors used primary sensory neuron cultures and pheochromocytoma cell line cultures to detect time-dependent activation of the p38 MAPK or related pathways such as extracellular signal–regulated kinases and c-jun N-terminal kinases. Cells were divided by size or by immunoreactivity for calcitonin gene–related peptide or isolectin B4, indicative of nociceptive phenotype. The authors also investigated whether arachidonic acid pathways represent a downstream effector of the p38 MAPK in local anesthetic–induced neurotoxicity. Results:All types of dorsal root ganglion cells were subject to neurotoxic effects of lidocaine, which were mediated by specific activation of the p38 MAPK but not extracellular signal–regulated kinases or c-jun N-terminal kinases. Neuroprotective efficacy of p38 MAPK inhibitors declined significantly when administered more than 1 h after lidocaine exposure. Activation of p38 MAPK preceded activation of arachidonic acid pathways. Neurotoxicity of lidocaine, specific activation of p38 MAPK, and neuroprotective effects of a p38 MAPK inhibitor were further confirmed in pheochromocytoma cell line cultures. Conclusions:Specific and time-dependent activation of the p38 MAPK is involved in lidocaine-induced neurotoxicity, most likely followed by activation of lipoxygenase pathways.

In Vitro, Lidocaine-Induced Axonal Injury Is Prevented by Peripheral Inhibition of the p38 Mitogen-Activated Protein Kinase, but Not by Inhibiting Caspase Activity

BACKGROUND:All local anesthetics (LAs) are, to some extent, neurotoxic. Toxicity studies have been performed in dissociated neuron cultures, immersing both axon and soma in LA. This approach, however, does not accurately reflect the in vivo situation for peripheral nerve blockade, where LA is applied to the axon alone. METHODS:We investigated lidocaine neurotoxicity in compartmental sensory neuron cultures, which are composed of one central compartment containing neuronal cell bodies and a peripheral compartment containing their axons, allowing for selective incubation. We applied lidocaine ± neuroprotective drugs to neuronal somata or axons, and assessed neuron survival and axonal outgrowth. RESULTS:Lidocaine applied to the peripheral compartment led to a decreased number of axons (to 59% ± 9%), without affecting survival of cell bodies. During axonal incubation with lidocaine, the p38 mitogen-activated protein kinase inhibitor SB203580 (10 &mgr;M) attenuated axonal injury when applied to the axon (insignificant reduction of maximal axonal distance to 93% ± 9%), but not when applied to the cell body (deterioration of maximal axonal length to 48% ± 6%). Axonal co-incubation of lidocaine with the caspase inhibitor z-vad-fmk (20 &mgr;M) was not protective. CONCLUSIONS:Whereas inhibition of either p38 mitogen-activated protein kinase or caspase activity promote neuronal survival after LA treatment of dissociated neuronal cultures, axonal degeneration induced by lidocain (40 mM) is prevented by p38 MAP kinase but not by caspase inhibition. We conclude that processes leading to LA-induced neurotoxicity in dissociated neuronal culture may be different from those observed after purely axonal application.

In Zucker Diabetic Fatty rats, subclinical diabetic neuropathy increases in vivo lidocaine block duration but not in vitro neurotoxicity

Background and Objectives Application of local anesthetics may lead to nerve damage. Increasing evidence suggests that risk of neurotoxicity is higher in patients with diabetic peripheral neuropathy. In addition, block duration may be prolonged in neuropathy. We sought to investigate neurotoxicity in vitro and block duration in vivo in a genetic animal model of diabetes mellitus type 2. Methods In the first experiments, neurons harvested from control Zucker diabetic fatty (ZDF) rats were exposed to acute (24 hours) or chronic (72 hours) hyperglycemia, followed by incubation with lidocaine 40 mM (approximately 1%). In a second experiment, neurons harvested from control ZDF rats, or diabetic ZDF rats, were incubated with lidocaine, with or without SB203580, an inhibitor of the p38 mitogen-activated protein kinase. Finally, we performed sciatic nerve block (lidocaine 2%, 0.2 mL) in control or diabetic ZDF rats and measured motor and nociceptive block duration. Results In vitro, neither acute nor chronic hyperglycemia altered neurotoxic properties of lidocaine. In vitro, incubation of neurons with lidocaine resulted in a slightly decreased survival ratio when neurons were harvested from diabetic (57% ± 19%) as compared with control (64% ± 9%) rats. The addition of SB203580 partly reversed this enhanced neurotoxic effect and raised survival to 71% ± 12% in diabetic neurons and 66% ± 9% in control rats, respectively. In vivo, even though no difference was detected at baseline testing, motor block was significantly prolonged in diabetic as compared with control rats (137 ± 16 vs 86 ± 17 min). Conclusions In vitro, local anesthetic neurotoxicity was more pronounced on neurons from diabetic animals, but the survival difference was small. In vivo, subclinical neuropathy leads to substantial prolongation of block duration. We conclude that early diabetic neuropathy increases block duration, whereas the observed increase in toxicity was small.

Acute Pulmonary Artery Embolism During Transcatheter Embolization : Successful Resuscitation with Veno-Arterial Extracorporeal Membrane Oxygenation

Versatile particles from transcatheter embolization may accidentally enter the pulmonary circulation, causing severe pulmonary embolism. A 36-yr-old woman patient suffering from an arteriovenous malformation in the left shoulder underwent embolization with micro coils, N-butyl-2-cyanoacrylate/lipiodol and polyvinyl alcohol particles. During embolization, acute onset of tachycardia, hypotension, and decline in oxygen saturation indicated right ventricular failure and decreased pulmonary perfusion confirmed by angiography. As mechanical resuscitation failed to stabilize cardiocirculatory function, veno-arterial extracorporeal membrane oxygenation support was preformed until hemodynamic stability was regained. Extracorporeal membrane oxygenation should be considered for cases where pulmonary embolism causes right ventricular failure and circulatory arrest during transcatheter embolization.

Differential neurotoxicity of tricyclic antidepressants and novel derivatives in vitro in a dorsal root ganglion cell culture model

Background and objective: Tricyclic antidepressants are commonly employed orally to treat major depressive disorders and have been shown to be of substantial benefit in various chronic pain conditions. Among other properties they are potent Na+ channel blockers in vitro and show local anaesthetic properties in vivo. The present study aimed to determine their differential neurotoxicity, and that of novel derivatives as prerequisite for their potential use in regional anaesthesia. Methods: To directly test neurotoxicity in adult peripheral neurons, the culture model of dissociated adult rat primary sensory neurons was employed. Neurons were incubated for 24 h with amitriptyline, N‐methyl‐amitriptyline, doxepin, N‐methyl‐doxepin, N‐propyl‐doxepin, desipramine, imipramine and trimipramine at 100 &mgr;mol, and at concentrations correlating to their respective potency in blocking sodium channels. Results: All investigated substances showed considerable neurotoxic potency as represented in significantly decreased neuron numbers in cultures as compared to controls. Specifically, doxepin was more neurotoxic than amitriptyline, and both imipramine and trimipramine were more toxic than desipramine or amitriptyline. Novel derivatives of tricyclic antidepressants were, in general, more toxic than the parent compound. Conclusions: Tricyclic antidepressants and novel derivatives thereof show differential neurotoxic potential in vitro. The rank order of toxicity relative to sodium channel blocking potency was desipramine < amitriptyline < N‐methyl amitriptyline < doxepin < trimipramine < imipramine < N‐methyl doxepin < N‐propyl doxepin.

Management of spinal anaesthesia-induced hypotension for caesarean delivery: a European survey.

Hypotension following administration of spinal anaesthesia for caesarean delivery is common; the reported incidence varies between 50 and 100%. Several strategies have been suggested to reduce the incidence or mitigate the severity of hypotension, such as patient positioning, fluid administration, and use of prophylactic or therapeutic vasopressors. No recent data exist on the clinical practice among anaesthesiologists providing care for parturients in Europe.