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Background: Lidocaine exerts antinociceptive effects when applied systemically. The mechanisms are not fully understood but glycinergic mechanisms might be involved. The synaptic glycine concentration is controlled by glycine transporters. Whereas neurons express two types of glycine transporters, astrocytes specifically express glycine transporter 1 (GlyT1). This study focuses on effects of lidocaine and its major metabolites on GlyT1 function.Methods: The effects of lidocaine and its metabolites monoethylglycinexylidide (MEGX), glycinexylidide, and N-ethylglycine on GlyT1 function were investigated in uptake experiments with [¹⁴C]-labeled glycine in primary rat astrocytes. Furthermore, the effect of lidocaine and its metabolites on glycine-induced currents were investigated in GlyT1-expressing Xenopus laevis oocytes.Results: Lidocaine reduced glycine uptake only at toxic concentrations. The metabolites MEGX, glycinexylidide, and N-ethylglycine, however, significantly reduced glycine uptake (P < 0.05). Inhibition of glycine uptake by a combination of lidocaine with its metabolites at a clinically relevant concentration was diminished with increasing extracellular glycine concentrations. Detailed analysis revealed that MEGX inhibits GlyT1 function (P < 0.05), whereas N-ethylglycine was identified as an alternative GlyT1 substrate (EC₅₀ = 55 μM).Conclusions: Although lidocaine does not function directly on GlyT1, its metabolites MEGX and N-ethylglycine [corrected] were shown to inhibit GlyT1-mediated glycine uptake by at least two different mechanisms. Whereas N-ethylglycine [corrected] was demonstrated to be an alternative GlyT1 substrate, MEGX was shown to inhibit GlyT1 activity in both primary astrocytes and in GlyT1-expressing Xenopuslaevis oocytes at clinically relevant concentrations. These findings provide new insights into the possible mechanisms for the antinociceptive effect of systemic lidocaine. [ABSTRACT FROM AUTHOR]

Glycine transporter 1 (GlyT1) plays a crucial role in regulating extracellular glycine concentrations and might thereby constitute a new drug target for the modulation of glycinergic inhibition in pain signaling. Consistent with this view, inhibition of GlyT1 has been found to induce antinociceptive effects in various animal pain models. We have shown previously that the lidocaine metabolite N-ethylglycine (EG) reduces GlyT1-dependent glycine uptake by functioning as an artificial substrate for this transporter. Here, we show that EG is specific for GlyT1 and that in rodent models of inflammatory and neuropathic pain, systemic treatment with EG results in an efficient amelioration of hyperalgesia and allodynia without affecting acute pain. There was no effect on motor coordination or the development of inflammatory edema. No adverse neurological effects were observed after repeated high-dose application of EG. EG concentrations both in blood and spinal fluid correlated with an increase of glycine concentration in spinal fluid. The time courses of the EG and glycine concentrations corresponded well with the antinociceptive effect. Additionally, we found that EG reduced the increase in neuronal firing of wide-dynamic-range neurons caused by inflammatory pain induction. These findings suggest that systemically applied lidocaine exerts antihyperalgesic effects through its metabolite EG in vivo, by enhancing spinal inhibition of pain processing through GlyT1 modulation and subsequent increase of glycine concentrations at glycinergic inhibitory synapses. EG and other substrates of GlyT1, therefore, may be a useful therapeutic agent in chronic pain states involving spinal disinhibition.

Background: Impaired cardiac repolarization, indicated by prolonged QT interval, may cause critical ventricular arrhythmias. Many anesthetics increase the QT interval by blockade of rapidly acting potassium rectifier channels. Although xenon does not affect these channels in isolated cardiomyocytes, the authors hypothesized that xenon increases the QT interval by direct and/or indirect sympathomimetic effects. Thus, the authors tested the hypothesis that xenon alters the heart rate-corrected cardiac QT (QTc) interval in anesthetic concentrations., Methods: The effect of xenon on the QTc interval was evaluated in eight healthy volunteers and in 35 patients undergoing abdominal or trauma surgery. The QTc interval was recorded on subjects in awake state, after their denitrogenation, and during xenon monoanesthesia (FetXe > 0.65). In patients, the QTc interval was recorded while awake, after anesthesia induction with propofol and remifentanil, and during steady state of xenon/remifentanil anesthesia (FetXe > 0.65). The QTc interval was determined from three consecutive cardiac intervals on electrocardiogram printouts in a blinded manner and corrected with Bazett formula., Results: In healthy volunteers, xenon did not alter the QTc interval (mean difference: +0.11 ms [95% CI, -22.4 to 22.7]). In patients, after anesthesia induction with propofol/remifentanil, no alteration of QTc interval was noted. After propofol was replaced with xenon, the QTc interval remained unaffected (417 ± 32 ms vs. awake: 414 ± 25 ms) with a mean difference of 4.4 ms (95% CI, -4.6 to 13.5)., Conclusion: Xenon monoanesthesia in healthy volunteers and xenon/remifentanil anesthesia in patients without clinically relevant cardiovascular disease do not increase QTc interval.

Background: Dysfunction of spinal glycinergic neurotransmission is a major pathogenetic factor in neuropathic pain. The synaptic glycine concentration is controlled by the two glycine transporters (GlyT) 1 and 2. GlyT inhibitors act antinociceptive in various animal pain models when applied as bolus. Yet, in some studies, severe neuromotor side effects were reported. The aim of the current study was to elucidate whether continuous inhibition of GlyT ameliorates neuropathic pain without side effects and whether protein expression of GlyT1, GlyT2, or N-methyl-D-aspartate receptor subunit NR-1 in the spinal cord is affected., Methods: In the chronic constriction injury model of neuropathic pain, male Wistar rats received specific GlyT1 and GlyT2 inhibitors (ALX5407 and ALX1393; Sigma-Aldrich, St. Louis, MO) or vehicle for 14 days via subcutaneous osmotic infusion pumps (n = 6). Mechanical allodynia and thermal hyperalgesia were assessed before, after chronic constriction injury, and every 2 days during substance application. At the end of behavioral assessment, the expression of GlyT1, GlyT2, and NR-1 in the spinal cord was determined by Western blot analysis., Results: Both ALX5407 and ALX1393 ameliorated thermal hyperalgesia and mechanical allodynia in a time- and dose-dependent manner. Respiratory or neuromotor side effects were not observed. NR-1 expression in the ipsilateral spinal cord was significantly reduced by ALX5407, but not by ALX1393. The expression of GlyT1 and GlyT2 remained unchanged., Conclusions: Continuous systemic inhibition of GlyT significantly ameliorates neuropathic pain in rats. Thus, GlyT represent promising targets in pain research. Modulation of N-methyl-D-aspartate receptor expression might represent a novel mechanism for the antinociceptive action of GyT1 inhibitors.

Introduction: Ketamine has been demonstrated to be neurotoxic in animals as well as in patients. Preservatives added to ketamine have been accused to induce this neurotoxicity. Therefore, we investigated whether the most widely used preservative of ketamine-benzethonium chloride-enhances the toxicity of S(+)-ketamine in vitro in lymphoma, neuroblastoma cells and primary astrocytes., Methods: Human Jurkat T-lymphoma- and neuroblastoma cells (SHEP) were incubated for 24 hours with commercially available S-ketamine containing benzethonium, pure S-ketamine and pure benzethonium chloride. The rate of early- and late-apoptotic cells was evaluated by flowcytometry. In a second step the combined toxicity of benzethonium and ketamine was investigated in neuroblastoma cells and primary rat astrocytes in a mitochondrial activity assay (XTT). The additivity of the toxicities was evaluated by employing isobolographic analysis., Results: In Jurkat T-lymphoma and neuroblastoma cells benzethonium increased the toxicity of ketamine from 32% to 80% and from 64% to 84% cell deaths, respectively. In neuroblastoma cells as well as in primary rat astrocytes the measured combined toxicity was within the confidence interval of the calculated pure additive toxicity as seen in the isobolograms., Conclusions: We conclude that benzethonium increases the local toxicity of ketamine in cells of hematopoietic, neuronal and glial origin in an additive manner. Therefore, caution is recommended especially when using preservative containing S-ketamine as an additive for long-term neuraxial analgesia.

Background: Perioperative myocardial ischemia poses a vital threat to surgical patients. Means to protect postischemic myocardium are clinically not available. Lidocaine has been demonstrated to exert antiinflammatory pleiotropic effects. The authors set out to test if lidocaine protects ischemic myocardium from reperfusion injury., Method: A mouse model of transient coronary artery ligation (30 min) and reperfusion (24 h) was used with animal care committee approval. Infarct size and area-at-risk were determined. Leukocyte recruitment was quantified on immunohistochemical stainings. Apoptosis was assessed using enzyme-linked immunosorbent assay to detect histone modifications and terminal deoxynucleotidyl transferase dUTP nick end labeling assays. Lidocaine effects on leukocyte-endothelial interactions were assessed in vitro by using a parallel-plate flow chamber or static adhesion assays., Results: Infarct size per area-at-risk was reduced by 27% in mice treated with a lidocaine bolus (1 mg/kg) before a continuous infusion (0.6 mg . kg(-1) . h(-1)) during ischemia (P < 0.005). Neutrophil density in the infarct and periinfarct zone was not reduced by lidocaine, although the size of the infiltrated area was. Terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cardiomyocytes and endothelial cells were significantly reduced in the periinfarct zone by lidocaine. In vitro, no effect on leukocyte rolling or firm adhesion to resting or activated endothelium was demonstrable. In vitro, lidocaine reduced cardiomyocyte apoptosis induced by hypoxia and reoxygenation (3h/1h) significantly. Infarct size and in vitro cardiomyocyte apoptosis were likewise reduced when lidocaine bolus and infusion were administered after the ischemic insult., Conclusion: Lidocaine exerts cardioprotective effects when administered before or after the ischemic insult. This effect is mediated through an antiapoptotic and not through an antiinflammatory pathway and may be therapeutically exploitable.

Background: Local anesthetics, especially lidocaine, can lead to persistent cauda equina syndrome after spinal anesthesia. Recently, lidocaine has been reported to trigger apoptosis, although the underlying mechanisms remain unknown. To elucidate the pathway of lidocaine-induced apoptosis, the authors used genetically modified cells with overexpression or deficiencies of key regulators of apoptosis., Methods: Human Jurkat T-lymphoma cells overexpressing the antiapoptotic protein B-cell lymphoma 2 as well as cells deficient of caspase 9, caspase 8, or Fas-associated protein with death domain were exposed to lidocaine and compared with parental cells. The authors evaluated cell viability, mitochondrial alterations, cytochrome c release, caspase activation, and early apoptosis. Apoptosis was in addition investigated in neuroblastoma cells., Results: In Jurkat cells, lidocaine reduced viability, associated with a loss of the mitochondrial membrane potential. At low concentrations (3-6 mm) of lidocaine, caspase 3 was activated and release of cytochrome c was detected, whereas at higher concentrations (10 mm), no caspase activation was found. Apoptosis by lidocaine was strongly reduced by B-cell lymphoma-2 protein overexpression or caspase-9 deficiency, whereas cells lacking the death receptor pathway components caspase 8 and Fas-associated protein with death domain were not protected and displayed similar apoptotic alterations as the parental cells. Lidocaine also induced apoptotic caspase activation in neuroblastoma cells., Conclusions: Apoptosis is triggered by concentrations of lidocaine occurring intrathecally after spinal anesthesia, whereas higher concentrations induce necrosis. The data indicate that death receptors are not involved in lidocaine-induced apoptosis. In contrast, the observation that B-cell lymphoma-2 protein overexpression or the lack of caspase 9 abolished apoptosis clearly implicates the intrinsic mitochondrial death pathway in lidocaine-induced apoptosis.

Background: In this prospective, randomized, double-blind trial we investigated the use of stimulating catheters in patients during and after shoulder surgery; functional improvement being the primary outcome measurement., Methods: After eliciting an adequate muscular twitch at < or =0.5 mA nerve stimulation output, the perineural catheter was advanced either blindly (conventional catheter = CC group, n = 20) or guided by stimulation via the catheter (stimulating catheter = SC group, n = 20). A bolus of 40 mL prilocaine 1% and 10 mL ropivacaine 0.75% was injected, followed by a patient-controlled infusion of ropivacaine 0.2% (8 mL/h infusion rate, bolus 2 mL, lockout time 20 min)., Results: Onset of motor block was faster in the SC group, whereas sensory block did not differ between groups. Median pain scores on two postoperative days were equal. Improvement of the objective shoulder function score (Constant Murley Score) 6 wk postoperatively was enhanced to a clinically relevant extent in the SC group compared to the CC group (P < 0.01)., Conclusions: We conclude that the use of a stimulating catheter results in a faster onset of motor block, unaltered postoperative pain, and a significantly improved functional outcome 6 wk after shoulder surgery.

Increase in skin temperature (Ts) occurs early during neuraxial blocks. However, the reliability of Ts to predict successful peripheral block is unknown. Therefore, we investigated whether an increase in Ts more than 1 degrees C precedes or follows an impairment of sensation after combined femoral and sciatic nerve block as well as after epidural anesthesia. In this prospective, nonrandomized study we determined Ts changes in 33 patients undergoing knee or foot surgery under femoral and sciatic nerve block and 10 patients undergoing epidural anesthesia. Perception and motor function were assessed every 5 min. An increase in Ts (> or =1 degrees C) at the foot occurred later after sciatic nerve block than after epidural anesthesia (10.3 +/- 2.8 versus 5.0 min; P < 0.01). Alterations of Ts at skin innervated by the femoral nerve were <1 degrees C. Ts increase preceded sensory block after sciatic nerve block in 6.6% of patients but indicated a successful block (sensitivity, specificity, and accuracy = 100%). We conclude that an increase of Ts is a reliable, but late, sign of successful sciatic nerve block. Therefore it is of limited clinical value. Ts changes after femoral nerve block are negligible and late.