Interactions of new lactoglobulin variants with tetracaine: crystallographic studies of ligand binding to lactoglobulin mutants possessing single substitution in the binding pocket

β-Lactoglobulin (BLG) like other lipocalins can be modified by mutagenesis to re-direct its ligand binding properties. Local site-directed mutagenesis was used to change the geometry of the BLG ligand binding pocket and therefore change BLG ligand preferences. The presented studies are focused on previously described mutants L39Y, I56F, L58F, F105L, and M107L and two new BLG variants, L39K and F105A, and their interactions with local anesthetic drug tetracaine. Binding of tetracaine to BLG mutants was investigated by X-ray crystallography. Structural analysis revealed that for tetracaine binding, the shape of the binding pocket seems to be a more important factor than the substitutions influencing the number of interactions. Analyzed BLG mutants can be classified according to their binding properties to variants: capable of binding tetracaine in the β-barrel (L58F, M107L); capable of accommodating tetracaine on the protein surface (I56F) and unable to bind tetracaine (F105L). Variants L39K, L39Y, and F105A, had a binding pocket blocked by endogenous fatty acids. The new tetracaine binding site was found in the I56F variant. The site localized on the surface near Arg124 and Trp19 was previously predicted by in silico studies and was confirmed in the crystal structure.

Prolonged Duration Local Anesthesia by Combined Delivery of Capsaicin- and Tetrodotoxin-Loaded Liposomes

BACKGROUND

Capsaicin, the active component of chili peppers, can produce sensory-selective peripheral nerve blockade. Coadministration of capsaicin and tetrodotoxin, a site-1 sodium channel blocker, can achieve a synergistic effect on duration of nerve blocks. However, capsaicin can be neurotoxic, and tetrodotoxin can cause systemic toxicity. We evaluated whether codelivery of capsaicin and tetrodotoxin liposomes can achieve prolonged local anesthesia without local or systemic toxicity.

METHODS

Capsaicin- and tetrodotoxin-loaded liposomes were developed. Male Sprague-Dawley rats were injected at the sciatic nerve with free capsaicin, capsaicin liposomes, free tetrodotoxin, tetrodotoxin liposomes, and blank liposomes, singly or in combination. Sensory and motor nerve blocks were assessed by a modified hotplate test and a weight-bearing test, respectively. Local toxicity was assessed by histologic scoring of tissues at the injection sites and transmission electron microscopic examination of the sciatic nerves. Systemic toxicity was assessed by rates of contralateral nerve deficits and/or mortality.

RESULTS

The combination of capsaicin liposomes and tetrodotoxin liposomes achieved a mean duration of sensory block of 18.2 hours (3.8 hours) [mean (SD)], far longer than that from capsaicin liposomes [0.4 hours (0.5 hours)] (P < .001) or tetrodotoxin liposomes [0.4 hours (0.7 hours)] (P < .001) given separately with or without the second drug in free solution. This combination caused minimal myotoxicity and muscle inflammation, and there were no changes in the percentage or diameter of unmyelinated axons. There was no systemic toxicity.

CONCLUSIONS

The combination of encapsulated tetrodotoxin and capsaicin achieved marked prolongation of nerve block. This combination did not cause detectable local or systemic toxicity. Capsaicin may be useful for its synergistic effects on other formulations even when used in very small, safe quantities.

Nano-engineered microcapsules boost the treatment of persistent pain

Persistent pain remains a major health issue: common treatments relying on either repeated local injections or systemic drug administration are prone to concomitant side-effects. It is thought that an alternative could be a multifunctional cargo system to deliver medicine to the target site and release it over a prolonged time window. We nano-engineered microcapsules equipped with adjustable cargo release properties and encapsulated the sodium-channel blocker QX-314 using the layer-by-layer (LbL) technology. First, we employed single-cell electrophysiology to establish in vitro that microcapsule application can dampen neuronal excitability in a controlled fashion. Secondly, we used two-photon excitation imaging to monitor and adjust long-lasting release of encapsulated cargo in target tissue in situ. Finally, we explored an established peripheral inflammation model in rodents to find that a single local injection of QX-314-containing microcapsules could provide robust pain relief lasting for over a week. This was accompanied by a recovery of the locomotive deficit and the amelioration of anxiety in animals with persistent inflammation. Post hoc immunohistology confirmed biodegradation of microcapsules over a period of several weeks. The overall remedial effect lasted 10-20 times longer than that of a single focal drug injection. It depended on the QX-314 encapsulation levels, involved TRPV1-channel-dependent cell permeability of QX-314, and showed no detectable side-effects. Our data suggest that nano-engineered encapsulation provides local drug delivery suitable for prolonged pain relief, which could be highly advantageous compared to existing treatments.

Reduced graphene oxide as an efficient sorbent in microextraction by packed sorbent: Determination of local anesthetics in human plasma and saliva samples utilizing liquid chromatography-tandem mass spectrometry

Herein, reduced graphene oxide (RGO) has been utilized as an efficient sorbent in microextraction by packed sorbent (MEPS). The combination of MEPS and liquid chromatography-tandem mass spectrometry has been used to develop a method for the extraction and determination of three local anesthetics (i.e. lidocaine, prilocaine, and ropivacaine) in human plasma and saliva samples. The results showed that the utilization of RGO in MEPS could minimize the matrix effect so that no interfering peaks at the retention times of the analytes or internal standard was observed. The high extraction efficiency of this method was approved by mean recoveries of 97.26-106.83% and 95.21-105.83% for the studied analytes in plasma and saliva samples, respectively. Intra- and inter-day accuracies and precisions for all analytes were in good accordance with the international regulations. The accuracy values (as percentage deviation from the nominal value) of the quality control samples were between -2.1 to 13.9 for lidocaine, -4.2 to 11.0 for prilocaine and between -4.5 to -2.4 for ropivacaine in plasma samples while the values were ranged from -4.6 to 1.6 for lidocaine, from -4.2 to 15.5 for prilocaine and from -3.3 to -2.3 for ropivacaine in human saliva samples. Lower and upper limit of quantification (LLOQ, ULOQ) were set at 5 and 2000 nmol L^-1 for all of the studied drugs. The correlation coefficients values were ≥0.995. The limit of detection values were obtained 4 nmol L^-1 for lidocaine and prilocaine, and 2 nmol L^-1 for ropivacaine.

Median and Dorsal Raphe Serotonergic Neurons Control Moderate Versus Compulsive Cocaine Intake

BACKGROUND

Reduced expression of the serotonin transporter (SERT) promotes anxiety and cocaine intake in both humans and rats. We tested the hypothesis that median raphe nucleus (MRN) and dorsal raphe nucleus (DRN) serotonergic projections differentially mediate these phenotypes.

METHODS

We used virally mediated RNA interference to locally downregulate SERT expression and compared the results with those of constitutive SERT knockout. Rats were allowed either short access (ShA) (1 hour) or long access (LgA) (6 hours) to cocaine self-administration to model moderate versus compulsive-like cocaine taking.

RESULTS

SERT knockdown in the MRN increased cocaine intake selectively under ShA conditions and, like ShA cocaine self-administration, reduced corticotropin-releasing factor (CRF) immunodensity in the paraventricular nucleus of the hypothalamus. In contrast, SERT knockdown in the DRN increased cocaine intake selectively under LgA conditions and, like LgA cocaine self-administration, reduced CRF immunodensity in the central nucleus of the amygdala. SERT knockdown in the MRN or DRN produced anxiety-like behavior, as did withdrawal from ShA or LgA cocaine self-administration. The phenotype of SERT knockout rats was a summation of the phenotypes generated by MRN- and DRN-specific SERT knockdown.

CONCLUSIONS

Our results highlight a differential role of serotonergic projections arising from the MRN and DRN in the regulation of cocaine intake. We propose that a cocaine-induced shift from MRN-driven serotonergic control of CRF levels in the hypothalamus to DRN-driven serotonergic control of CRF levels in the amygdala may contribute to the transition from moderate to compulsive intake of cocaine.

Pattern of Anesthetic Diffusion during Peribulbar Infiltration: A Ct Evaluation

PURPOSE

The aim of this study was to evaluate the changes undergone by orbital structures during peribulbar anesthesia.

METHODS

CT-thin slices were acquired and 8-9 ml of anesthetic, with a small part of low-density non-ionic water-soluble contrast medium were injected under CT guide once to follow extraconal spreading and diffusion to intraconal structures and above all, the surgically important structures such as recti muscles, orbicular and optic nerve sheath. Conjunctival sack involvement was assessed and conjunctival chemosis was rated. Induced ptosis was evaluated, verifying change before and after eyepressure.

RESULTS

The results help in optimizing anesthetic technique, above all concerning the site, materials and quantity, and suggest the amount of anesthesia could be reduced.

CONCLUSIONS

The peribulbar anesthetic technique proved effective and safe for patients.

Local anaesthetic pain relief therapy: In vitro and in vivo evaluation of a nanotechnological formulation co-loaded with ropivacaine and dexamethasone

Combination therapy is frequently applied to anesthesia and analgesia for its benefits, which includes prolonged analgesia following peripheral nerve blockade, and reduced side effects. The aim of this study was to develop chitosan (CH) coated poly(ε-caprolactone) (PCL) nanoparticles to co-deliver ropivacaine (RPV) and dexamethasone (DEM) (RPV/DEM CH-PCL NPs) for the prolongation of anesthesia and pain relief. In the present study, RPV/DEM CH-PCL NPs were fabricated. The properties of CH-PCL NPs were evaluated for their particle sizes, zeta potential, drug loading capacity and in vitro drug release profile. In vitro skin permeation and in vivo therapeutic effect in an animal model were further investigated. The results showed that the NPs was around 190nm, with PDI of less than 0.20. The zeta potentials of NPs were about 36mV. In vitro drug release of both RPV and DEM from NPs complied with sustained behaviors. All of the drugs loaded NPs samples studied exhibited no obvious L929 cells cytotoxicity. In vitro skin penetration profiles showed the amount of RPV permeated through the skin from NPs was significantly higher than free RPV. RPV and DEM co-loaded NPs induced remarkably better anesthetic effect than non DEM loaded RPV CH-PCL NPs. The results suggested that adding a small dosage of DEM could improve the anesthesia efficacy of RVP to a large content. The resulting formulation could be applied as a promising anesthesia system for local anesthetics therapy.

The AMPK Activator A769662 Blocks Voltage-Gated Sodium Channels: Discovery of a Novel Pharmacophore with Potential Utility for Analgesic Development

Voltage-gated sodium channels (VGSC) regulate neuronal excitability by governing action potential (AP) generation and propagation. Recent studies have revealed that AMP-activated protein kinase (AMPK) activators decrease sensory neuron excitability, potentially by preventing sodium (Na⁺) channel phosphorylation by kinases such as ERK or via modulation of translation regulation pathways. The direct positive allosteric modulator A769662 displays substantially greater efficacy than other AMPK activators in decreasing sensory neuron excitability suggesting additional mechanisms of action. Here, we show that A769662 acutely inhibits AP firing stimulated by ramp current injection in rat trigeminal ganglion (TG) neurons. PT1, a structurally dissimilar AMPK activator that reduces nerve growth factor (NGF) -induced hyperexcitability, has no influence on AP firing in TG neurons upon acute application. In voltage-clamp recordings, application of A769662 reduces VGSC current amplitudes. These findings, based on acute A769662 application, suggest a direct channel blocking effect. Indeed, A769662 dose-dependently blocks VGSC in rat TG neurons and in Na_v1.7-transfected cells with an IC₅₀ of ~ 10 μM. A769662 neither displayed use-dependent inhibition nor interacted with the local anesthetic (LA) binding site. Popliteal fossa administration of A769662 decreased noxious thermal responses with a peak effect at 5 mins demonstrating an analgesic effect. These data indicate that in addition to AMPK activation, A769662 acts as a direct blocker/modulator of VGSCs, a potential mechanism enhancing the analgesic property of this compound.

[Transdermal Local Anesthetics]

Taking EMLA cream and Penles tape 18 mg as examples, this article describes the conditions for skin penetration of topical anesthetics, with their onset time of action, duration of effect and a precautions for their use. EMLA cream is a unique cream for topical anesthesia which is the eutectic mixture of lidocaine and propitocaine to increase skin penetration. The safety study demonstrated that blood concentrations of active ingredients of EMLA cream were below toxic levels. EMLA cream, with confirmed high skin penetrability and safety, should be used for pain reduction of various treatments for many diseases. Here in Japan, EMLA cream has indications not only for pain reduction of skin laser therapy but also for reduction of needle puncture pain. This means the use of topical anesthesia would be expanded to wider ranges of treatments.

Coating solid dispersions on microneedles via a molten dip-coating method: development and in vitro evaluation for transdermal delivery of a water-insoluble drug

This study demonstrates for the first time the ability to coat solid dispersions on microneedles as a means to deliver water-insoluble drugs through the skin. Polyethylene glycol (PEG) was selected as the hydrophilic matrix, and lidocaine base was selected as the model hydrophobic drug to create the solid dispersion. First, thermal characterization and viscosity measurements of the PEG-lidocaine mixture at different mass fractions were performed. The results show that lidocaine can remain stable at temperatures up to ∼130°C and that viscosity of the PEG-lidocaine molten solution increases as the mass fraction of lidocaine decreases. Differential scanning calorimetry demonstrated that at lidocaine mass fraction less than or equal to 50%, lidocaine is well dispersed in the PEG-lidocaine mixture. Uniform coatings were obtained on microneedle surfaces. In vitro dissolution studies in porcine skin showed that microneedles coated with PEG-lidocaine dispersions resulted in significantly higher delivery of lidocaine in just 3 min compared with 1 h topical application of 0.15 g EMLA®, a commercial lidocaine-prilocaine cream. In conclusion, the molten coating process we introduce here offers a practical approach to coat water-insoluble drugs on microneedles for transdermal delivery.

[Local invasive treatment of chronic pain]

The literature on methods of invasive local treatment of chronic pain was analyzed. We reviewed 14 publications including meta-analyses and systematic reviews. The use of regional anesthesia conducted by anesthesiologists in pain clinics demonstrated the evidence based efficacy of different types of peridural injections of local anesthetics with steroids in patients with root pain syndromes at cervical and lumbar levels. Therapeutic blockades of the occipital nerve is effective method of treatment of cervicogenic and cluster headache as well as occipital nerve neuralgia. There are clear indications of the efficacy of local injections in primary chronic cephalgia (migraine and headache of tension). The possibility of the abortion of the pain information flow in peripheral nociceptive pathways and, as a consequence, breaking the vicious circle is emphasized. Issues on the efficacy of local injections at trigger points in the treatment of chronic pain are highlighted.

Bisphenol A binds to the local anesthetic receptor site to block the human cardiac sodium channel

Bisphenol A (BPA) has attracted considerable public attention as it leaches from plastic used in food containers, is detectable in human fluids and recent epidemiologic studies link BPA exposure with diseases including cardiovascular disorders. As heart-toxicity may derive from modified cardiac electrophysiology, we investigated the interaction between BPA and hNav1.5, the predominant voltage-gated sodium channel subtype expressed in the human heart. Electrophysiology studies of heterologously-expressed hNav1.5 determined that BPA blocks the channel with a K_d of 25.4±1.3 µM. By comparing the effects of BPA and the local anesthetic mexiletine on wild type hNav1.5 and the F1760A mutant, we demonstrate that both compounds share an overlapping binding site. With a key binding determinant thus identified, an homology model of hNav1.5 was generated based on the recently-reported crystal structure of the bacterial voltage-gated sodium channel NavAb. Docking predictions position both ligands in a cavity delimited by F1760 and contiguous with the DIII–IV pore fenestration. Steered molecular dynamics simulations used to assess routes of ligand ingress indicate that the DIII–IV pore fenestration is a viable access pathway. Therefore BPA block of the human heart sodium channel involves the local anesthetic receptor and both BPA and mexiletine may enter the closed-state pore via membrane-located side fenestrations.

An effective way to biosynthesize α-glucosyl eugenol with a high yield by Xanthomonas maltophilia

CONTEXT

Eugenol is known for its analgesic, local anesthetic, anti-inflammatory, antibacterial, and hair growing effects, the application of which, however, is limited by its low solubility, liability of sublimating, and its pungent smell. Compared to eugenol, its glycosylated derivate [eugenol α-glucoside (α-EG)] has more advantages in application.

OBJECTIVE

The biosynthesis of α-EG by Xanthomonas maltophilia Hugh (Xanthomonadaceae) BT-112 and the optimum conditions for α-EG production are investigated here.

MATERIALS AND METHODS

The α-EG was obtained by fermentation using Xanthomonas maltophilia BT-112 and purified by macroporous absorption resin. The identity of α-EG is confirmed by high performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR).

RESULTS

The maximum yield of α-EG reached 10.62 g/L broth when the suspension of Xanthomonas maltophilia strain was incubated at 30°C with 70 mM eugenol and 1.0 M maltose.

DISCUSSION AND CONCLUSION

Bio-fermentation was applied in this work to get α-EG with a high mole conversion, which is a potentially efficient and highly promising approach to modify phenolic compounds into glucosides.

Occurrence and removal of lidocaine, tramadol, venlafaxine, and their metabolites in German wastewater treatment plants

PURPOSE

Some of the pharmaceuticals that are not extensively investigated in the aquatic environment are the anesthetic lidocaine (LDC), the analgesic tramadol (TRA), and the antidepressant venlafaxine (VEN). LDC metabolizes to 2,6-xylidine (2,6-DMA) and monoethylglycinexylidine (MEGX), TRA to O-desmethyltramadol (ODT), and VEN to O-desmethylvenlafaxine (ODV). Within this study, the distribution and behavior of these compounds in German wastewater treatment plants (WWTPs) were investigated.

METHODS

Samples of influents and effluents from WWTPs in Hesse, Germany were collected between January and September 2010. Analytes were extracted from wastewater samples by solid-phase extraction and from solid samples by sonication. Extracts were measured using gas chromatography/mass spectrometry.

RESULTS

LDC, TRA, VEN, ODT, and ODV were detected in all analyzed influent and effluent samples. 2,6-DMA could not be identified. MEGX was not detected. TRA and ODV were present in untreated wastewater at the highest concentrations (max, 1,129 (TRA) and 3,302 ng L⁻¹ (ODV)), while the concentrations of LDC and VEN were all significantly lower (mean, 135 (LDC) and 116 ng L⁻¹ (VEN)). All of the analytes were only partially removed in the WWTPs. The mean ratios between the concentrations of the metabolites and their respective parent compounds in influents were 4.7 (ODV/VEN) and 0.7 (ODT/TRA). These values remain approximately constant comparing influents and effluents.

CONCLUSIONS

LDC, TRA, VEN, ODT, and ODV are only partially removed from sewage water by WWTPs and thus are continuously discharged in respective recipient rivers. A further transformation of TRA and VEN into the known metabolites during treatment in the WWTPs is not observed.

Analysis of the action of lidocaine on insect sodium channels

A new class of sodium channel blocker insecticides (SCBIs), which include indoxacarb, its active metabolite, DCJW, and metaflumizone, preferably block inactivated states of both insect and mammalian sodium channels in a manner similar to that by which local anesthetic (LA) drugs block mammalian sodium channels. A recent study showed that two residues in the cockroach sodium channel, F1817 and Y1824, corresponding to two key LA-interacting residues identified in mammalian sodium channels are not important for the action of SCBIs on insect sodium channels, suggesting unique interactions of SCBIs with insect sodium channels. However, the mechanism of action of LAs on insect sodium channels has not been investigated. In this study, we examined the effects of lidocaine on a cockroach sodium channel variant, BgNa(v)1-1a, and determined whether F1817 and Y1824 are also critical for the action of LAs on insect sodium channels. Lidocaine blocked BgNa(v)1-1a channels in the resting state with potency similar to that observed in mammalian sodium channels. Lidocaine also stabilized both fast-inactivated and slow-inactivated states of BgNa(v)1-1a channels, and caused a limited degree of use- and frequency-dependent block, major characteristics of LA action on mammalian sodium channels. Alanine substitutions of F1817 and Y1824 reduced the sensitivity of the BgNa(v)1-1a channel to the use-dependent block by lidocaine, but not to tonic blocking and inactivation stabilizing effects of lidocaine. Thus, similar to those on mammalian sodium channels, F1817 and Y1824 are important for the action of lidocaine on cockroach sodium channels. Our results suggest that the receptor sites for lidocaine and SCBIs are different on insect sodium channels.

Effect of 4% topical lidocaine applied to the face on the serum levels of lidocaine and its metabolite, monoethylglycinexylidide

BACKGROUND

Topical lidocaine is a common form of anesthesia for a wealth of procedures across a large number of disciplines, including laser treatments. Preparations can be purchased over the counter with no prescription necessary. It is considered a safer and more acceptable form of anesthetic than hypodermic injections; however, there have been reports of fatalities following its application. Above certain serum lidocaine concentrations, patients may experience effects of toxicity such as lightheadedness and paraesthesia; these effects can progress to seizures and cardiorespiratory depression, which can ultimately lead to death. The active metabolite of lidocaine, monoethylglycinexylidide (MEGX), can be almost as potent as lidocaine in terms of toxicity.

OBJECTIVES

The authors examine the levels of both lidocaine and MEGX in blood serum after application of topical lidocaine.

METHODS

Twenty-five healthy volunteers were assigned to one of four groups (A, B, C, D). Group A had 2.5 g of 4% lidocaine topical anesthetic cream applied to the face for one hour without occlusion, Group B had 5 g applied to the face for one half-hour without occlusion, Group C had 5 g applied to the face for one hour without occlusion, and Group D had 5 g applied to the face for one hour with occlusion. To evaluate serum concentrations, blood was drawn every 30 minutes for four hours.

RESULTS

Group D showed the highest serum levels of lidocaine and MEGX, a three-fold increase compared with group C, which received the same dose (5g topical 4% lidocaine) but without occlusion. In group D, peak serum levels occurred at 90 minutes for serum lidocaine, which was also the fastest of the four groups. Serum MEGX levels peaked much later than serum lidocaine levels, at 210 minutes. Individual serum levels did not exceed 0.6 µg/mL. Across the groups, there was significant interindividual variation in both lidocaine and MEGX serum levels (P = .061). Applications of 5 g of 4% lidocaine resulted in higher serum concentration of both lidocaine and MEGX. When comparing group A to group C, doubling the dose of 4% lidocaine from 2.5 g to 5 g resulted in double the serum levels of MEGX and a 50% increase in the serum lidocaine levels (P = .021). When comparing groups C and D, the addition of an occlusive dressing resulted in a tripling of the serum lidocaine levels and a doubling of the serum MEGX levels, both of which were statistically significant (P < .001). When comparing all four groups, there were significant differences between the combined serum concentrations of lidocaine and MEGX (P < .001).

CONCLUSIONS

Topical lidocaine preparations are increasingly being employed to provide a patient-friendly form of noninvasive analgesia for a multitude of procedures. Some preparations are available over the counter for unsupervised patient application. Our study has demonstrated significant interindividual variability for a given dose, especially when occlusion is applied. There have been fatalities resulting from topical lidocaine application, and our study suggests that this is the result of the unpredictability of lidocaine metabolism between individuals. Therefore, we recommend that caution be exercised with topical lidocaine preparations, in particular when applied in conjunction with occlusive dressings.

[Decomposition kinetics of bupivacaine in biological specimens]

OBJECTIVE

To study on the decomposition kinetics of bupivacaine in brain, blood and urine, which were collected from dogs executed by bupivacaine and stored in different conditions.

METHODS

Dogs were given arachnoid cavity anesthesia with bupivacaine. Then the brain, blood and urine were collected and divided equally to three groups stored in 20, 4 and -20 degrees C respectively. The concentrations of bupivacaine at different days were determined by the GC. The equation and half-time period of decomposition kinetics were imitated and calculated with WinNolin program.

RESULTS

The decomposition kinetics of bupivacaine in the dogs' brain, blood and urine were fit to the first order kinetics. The common equation was lgC = lgCo-kt/2.303 and k was the decomposition constant of first order reaction.

CONCLUSION

Bupivacaine in the brain, blood and urine specimens were found to be decomposed at various environments for storage. The higher temperature for storage, the faster of decomposition reaction.

[Determination of lidocaine and its metabolites in human plasma by liquid chromatography in combination with tandem mass spectrometry]

OBJECTIVE

To establish a liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method for the determination of lidocaine (LDC) and its metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX), in human plasma. METHODS; The assay was conducted with an API 3000 HPLC-MS/MS system consisted of a Ultimate C18 column (50 x 4.6 mm, 5 microm). The mobile phase consisted of methanol: 5 mmol/ L ammonium acetate (50:50, pH was adjusted to 5.0 by formic acid) and the flow rate was set at 0.2 mL/min. The alkalinized sample was extracted with ethyl acetate. After evaporation of the organic layer, the residue was dissolved in mobile phase and the drug was determined by HPLC-MS/MS using electrospray ionization.

RESULTS

The calibration curve was linear in a range from 15.625 to 2000 ng/mL for LDC. Linear calibration curves were obtained in the range of 1.5625 to 200 ng/mL for both for MEGX and GX. The limit of quantification for LDC, MEGX and GX was set at 15.625, 1.5625 and 1.5625 ng/mL.

CONCLUSION

This method for the quantitative determination of lidocaine and its metabolites in human plasma is simple, rapid, sensitive and accurate. Therefore it can be used for the determination of lidocaine and its metabolites in clinical practice.

Bioadhesive films containing benzocaine: correlation between in vitro permeation and in vivo local anesthetic effect

PURPOSE

The aim of this work was to develop anesthetic bioadhesive films containing benzocaine and study their in vitro skin permeation and in vivo performance, in comparison with commercial formulations.

METHODS

Films containing 3% and 5% w/w of benzocaine were prepared and characterized by weight, drug content, thickness and morphology. In vitro permeation assays were performed in vertical diffusion cells using full-thickness pig ear skin as barrier. Intensity and duration of analgesia were evaluated in rats by tail-flick test, and skin histological analysis was carried out.

RESULTS

Tail-flick test showed that the duration of benzocaine-induced analgesia was significantly prolonged with the films compared to commercial creams, in agreement with the higher in vitro permeation. Histological analysis of the rat tail skin did not reveal morphological tissue changes nor cell infiltration signs after application of the commercial creams or films.

CONCLUSIONS

Results from our study indicate that the films developed in this work can be considered as innovative dermal/transdermal therapeutic systems for benzocaine local delivery.

[Preparation of lidocaine nanoemulsion and its transdermal absorption by rat skin ex vivo]

OBJECTIVE

To prepare lidocaine nanoemulsion and investigate its transdermal delivery ability in vitro.

METHODS

The optimal Km (surfactant/cosurfactant) value and the component proportion were determined by pseudoternary phase diagrams combined with Origin software analysis. The diameter and distribution range were detected by Zeta particle size analysis instrument, and the morphology of the nanoemulsion was observed by electron microscope. The permeation flux of lidocaine was determined in vitro using the modified Franz diffusion cell combined with HPLC, and the cumulative transdermal absorption amount and the apparent skin transdermal velocity were compared among nanoemulsion, gel and tincture containing 5% lidocaine. The permeation mode of lidocaine nanoemulsion was analyzed.

RESULTS

The average drop size of lidocaine nanoemulsion was 29.8-/+14.4 nm, and 98% of the drop sizes ranged from 15.1 to 45.5 nm and 2% from 77.9 to 261.3 nm. The nanoemulsion drop showed a spherical morphology in a polydisperse system. The Kp value of the nanoemulsion (3.07-/+0.74 cm/h) was significantly higher than that of gel (1.27-/+0.35 cm/h) and tincture (0.97-/+0.18 cm/h), and the permeation rate of the nanoemulsion was 69.82-/+7.48 microg x cm(-2) x h(-1), which fitted the the Zero-order release dynamic procedure.

CONCLUSIONS

The component proportion of lidocaine nanoemulsion can be conveniently obtained through pseudoternary phase diagrams and Origin software analysis, and the drop size, distribution, morphology and system type can be determined by Malvern Zetasizer combined with electron microscopy. The results also indicate that the nanoemulsion system with high permeation rate may provide a new promising means for local anesthesia.

Lidocaine metabolism in isolated perfused liver from streptozotocin-induced diabetic rats

Insulin deficiency can trigger not only an altered glucose metabolic state but may also affect drug metabolism. The formation rate of the major lidocaine metabolite monoethylglycinxylidide (MEGX) has been shown to reflect the activity of CYP3A2 and CYP1A2. In the present study the effects of streptozotocin-induced diabetes on lidocaine elimination and MEGX formation in a model of isolated, non-recirculated, perfused rat liver with constant flow was evaluated. The parameters describing hepatic lidocaine elimination studied 10 days after streptozotocin administration, i.e. hepatic extraction coefficient (EH), hepatic clearance (ClH) and elimination rate (VL), were significantly decreased in diabetic livers in comparison with the controls. The EH in the controls varied between 0.88±0.07 and 0.93±0.06, whereas in diabetic livers it was markedly reduced to between 0.27±0.15 and 0.39±0.23. The ClH dropped to 8.04±4.12-11.66±2.99mLmin 1 in diabetic rats in comparison to 26.29±2.07–27.94±0.92 mL min−1 in the control animals. The VL was estimated to be 128.08±18.60–136.44±17.59 μg mL−1 in the controls and from 40.87±28.31 μg mL−1 to 56.83±22.16 μg mL−1 in diabetic perfused livers. The major lidocaine metabolite, i.e. MEGX, concentrations were significantly decreased in diabetic rats compared to the controls. The observed changes indicate an impairment of N-deethylation metabolic pathway in streptozotocin-induced diabetic rats, i.e. a possible decrease in the enzymatic activity of CYP3A2 and CYP1A2.

Epidural spread after continuous cervical paravertebral block: a case report

BACKGROUND AND OBJECTIVE

This report illustrates epidural spread after continuous cervical paravertebral block (CCPVB). By fluoroscopy, it also explains the mechanism of the complication.

CASE REPORT

A healthy 22-year-old male developed bilateral upper-extremity motor weakness immediately after placement of a continuous cervical paravertebral block for postoperative pain control after shoulder stabilization surgery. The tip of the stimulating catheter was demonstrated in the C7 neuroforamen. Contrast injected through the catheter demonstrated epidural spread. The contralateral block resolved after 4 hours and the patient suffered no respiratory embarrassment or other untoward sequelae.

CONCLUSION

Continuous cervical paravertebral block is a relatively new, but generally well-accepted, modality for postoperative pain control after major surgery to the upper limb. Epidural spread is recognized as a complication. In this particular case, medial placement of the catheter was possibly caused by unintentional medial direction of the bevel of the Tuohy needle. Meticulous attention to the direction of the needle bevel and early recognition and management of adverse events are mandatory. The same principles may apply for continuous thoracic, lumbar, and sacral paravertebral blocks.

A critical review of local anesthetic sensitivity

With their ability to block pain signals to the brain, local anesthetics (LAs) have made possible many surgical procedures and interventions once thought impossible. LAs are generally safe and well tolerated when used correctly by trained professionals. However, adverse reactions do occur, and may generate a referral to an Allergist for evaluation of LA allergy. LA structure, classification, and metabolism will be briefly reviewed. A critical analysis of the studies and case reports involving LA allergy found via PubMed search for "local anesthetic allergy" and "local anesthetic hypersensitivity" will be discussed. In addition, the clinical evaluation of a patient with concern for a LA allergy will be examined.

Continuous Positive Airway Pressure Breathing Increases Cranial Spread of Sensory Blockade After Cervicothoracic Epidural Injection of Lidocaine

BACKGROUND

Continuous positive airway pressure (CPAP) increases the caudad spread of sensory blockade after low-thoracic epidural injection of lidocaine. We hypothesized that CPAP would increase cephalad spread of blockade after cervicothoracic epidural injection.

METHODS

Twenty patients with an epidural catheter at the C6-7 or C7-T1 interspace received an epidural dose of lidocaine while breathing at ambient pressure (control group), or while breathing with 7.5 cm H2O CPAP. After injection, we evaluated the spread of sensory blockade. Spirometry variables before and after epidural injection were also measured.

RESULTS

Data are presented as median (interquartile range) values. Sensory block ranged from C7 (C4-7) to T4 (T4-6) in the control group and from C2 (C2-4) to T4 (T2-5) in the CPAP group (P = 0.003 for the cranial border). The total number of segments blocked was 7.5 (6.8-9.8) in the control group and 10 (8-12) in the CPAP group (P = 0.13). The number of segments blocked cranial to the injection site was one (0.8-3.5) in the control group and five (3.5-7) in the CPAP group (P = 0.006). The number of patients with a maximal cranial block (up to C2) was one in the control group and seven in the CPAP group (P = 0.02). In both groups, there was a small but significant decrease from baseline in spirometry values, with no differences between groups.

CONCLUSION

Applying CPAP during cervicothoracic epidural injection of lidocaine resulted in a more cranial extension of sensory blockade when compared with breathing at ambient pressure.

Multiway Partial Least-Squares Coupled to Residual Trilinearization: A Genuine Multidimensional Tool for the Study of Third-Order Data. Simultaneous Analysis of Procaine and Its Metabolitep-Aminobenzoic Acid in Equine Serum

A new third-order multivariate calibration approach, based on the combination of multiway-partial least-squares with a separate procedure called residual trilinearization (N-PLS/RTL), is presented and applied to multicomponent analysis using third-order data. The proposed chemometric algorithm is able to predict analyte concentrations in the presence of unexpected sample components, which require strict adherence to the second-order advantage. Results for the determination of procaine and its metabolite p-aminobenzoic acid in equine serum are discussed, based on kinetic fluorescence excitation-emission four-way measurements and application of the newly developed multiway methodology. Since the analytes are also the reagent and product of the hydrolysis reaction followed by fast-scanning fluorescence spectroscopy, the classical approach based on parallel factor analysis is challenged by strong linear dependencies and multilinearity losses. In comparison, N-PLS/RTL appears an appealing genuine multiway alternative that avoids the latter complications, yielding analytical results that are statistically comparable to those rendered by related unfolded algorithms, which are also able to process four-way data. Prediction was made on validation samples with a qualitative composition similar to the calibration set and also on test samples containing unexpected equine serum components.

Point mutations at the local anesthetic receptor site modulate the state-dependent block of rat Nav1.4 sodium channels by pyrazoline-type insecticides

Pyrazoline-type insecticides (PTIs) selectively block sodium channels at membrane potentials that promote slow sodium channel inactivation and are proposed to interact with a site that overlaps the local anesthetic (LA) receptor site. Mutagenesis studies identified two amino acid residues in the S6 segment of homology domain IV (Phe-1579 and Tyr-1586 in the rat Na(v)1.4 sodium channel) as principal elements of the LA receptor. To test the hypothesis that PTIs bind to the LA receptor, we constructed mutated Na(v)1.4/F1579A and Na(v)1.4/Y1586A cDNAs, expressed native and mutated channels in Xenopus oocytes, and examined the effects of these mutations on channel block by three PTIs (indoxacarb, its bioactivation product DCJW, and RH3421) by two-electrode voltage clamp. DCJW and RH3421 had no effect on Na(v)1.4 channels held at -120mV but caused a slowly developing block upon depolarization to -30mV. Estimated IC(50) values following 15min of exposure were 1 and 4muM for DCJW and RH3421, respectively. Indoxacarb failed to block Na(v)1.4 channels under all experimental conditions. Sensitivity to block by DCJW and RH3421 at -30mV was significantly reduced in Na(v)1.4/F1579A channels, a finding that is consistent with the impact of this mutation on drug binding. In contrast to its effect on drug binding, the Y1586A mutation increased the sensitivity of Na(v)1.4 channels held at -30mV to all three compounds, conferring modest sensitivity to indoxacarb and increasing sensitivity to DCJW and RH3421 by 58- and 16-fold, respectively. These results provide direct evidence for the action of PTIs at the LA receptor.

A Nav1.7 channel mutation associated with hereditary erythromelalgia contributes to neuronal hyperexcitability and displays reduced lidocaine sensitivity

Mutations in the TTX-sensitive voltage-gated sodium channel subtype Nav1.7 have been implicated in the painful inherited neuropathy, hereditary erythromelalgia. Hereditary erythromelalgia can be difficult to treat and, although sodium channels are targeted by local anaesthetics such as lidocaine (lignocaine), some patients do not respond to treatment with local anaesthetics. This study examined electrophysiological differences in Nav1.7 caused by a hereditary erythromelalgia mutation (N395K) that lies within the local anaesthetic binding site of the channel. The N395K mutation produced a hyperpolarized voltage dependence of activation, slower kinetics of deactivation, and impaired steady-state slow inactivation. Computer simulations indicate that the shift in activation is the major determinant of the hyperexcitability induced by erythromelalgia mutations in sensory neurons, but that changes in slow inactivation can modulate the overall impact on excitability. This study also investigated lidocaine inhibition of the Nav1.7-N395K channel. We show that the N395K mutation attenuates the inhibitory effects of lidocaine on both resting and inactivated Nav1.7. The IC50 for lidocaine was estimated at 500 microM for inactivated wild-type Nav1.7 and 2.8 mM for inactivated Nav1.7-N395K. The N395K mutation also significantly reduced use-dependent inhibition of lidocaine on Nav1.7 current. In contrast, a different hereditary erythromelalgia mutation (F216S), not located in the local anaesthetic binding site, had no effect on lidocaine inhibition of Nav1.7 current. Our observation of reduced lidocaine inhibition on Nav1.7-N395K shows that the residue N395 is critical for lidocaine binding to Nav1.7 and suggests that the response of individuals with hereditary erythromelalgia to lidocaine treatment may be determined, at least in part, by their specific genotype.

Anesthetic and procedural sedation techniques for wound management

Emergency physicians come across a wide variety of painful conditions and perform a large number of uncomfortable procedures on a typical shift. This article describes the local anesthetic agents and their potential applications. The peripheral nerve blocks that are regularly done in the emergency department are described. Lastly, procedural sedation and analgesia are covered, to include general principles and specific agents for its use in the emergency department.

Charge at the lidocaine binding site residue Phe-1759 affects permeation in human cardiac voltage-gated sodium channels

Our homology molecular model of the open/inactivated state of the Na(+) channel pore predicts, based on extensive mutagenesis data, that the local anaesthetic lidocaine docks eccentrically below the selectivity filter, such that physical occlusion is incomplete. Electrostatic field calculations suggest that the drug's positively charged amine produces an electrostatic barrier to permeation. To test the effect of charge at this pore level on permeation in hNa(V)1.5 we replaced Phe-1759 of domain IVS6, the putative binding site for lidocaine's alkylamino end, with positively and negatively charged residues as well as the neutral cysteine and alanine. These mutations eliminated use-dependent lidocaine block with no effect on tonic/rested state block. Mutant whole cell currents were kinetically similar to wild type (WT). Single channel conductance (gamma) was reduced from WT in both F1759K (by 38%) and F1759R (by 18%). The negatively charged mutant F1759E increased gamma by 14%, as expected if the charge effect were electrostatic, although F1759D was like WT. None of the charged mutations affected Na(+)/K(+) selectivity. Calculation of difference electrostatic fields in the pore model predicted that lidocaine produced the largest positive electrostatic barrier, followed by lysine and arginine, respectively. Negatively charged glutamate and aspartate both lowered the barrier, with glutamate being more effective. Experimental data were in rank order agreement with the predicted changes in the energy profile. These results demonstrate that permeation rate is sensitive to the inner pore electrostatic field, and they are consistent with creation of an electrostatic barrier to ion permeation by lidocaine's charge.

Serine-401 as a batrachotoxin- and local anesthetic-sensing residue in the human cardiac Na+ channel

Sequence alignment of four S6 segments in the human cardiac Na+ channel suggests that serine-401 (hNav1.5-S401) at D1S6 along with asparagine-927 (N927) at D2S6, serine-1458 (S1458) at D3S6, and phenylalanine-1760 (F1760) at D4S6 may jointly form a pore-facing S(401)N(927)S(1458)F(1760) ring. Importantly, this pore-facing structure is adjacent to the putative gating-hinge (G(400)G(926)G(1457)S(1759)) and close to the selectivity filter. Within this SNSF ring, only S401 has not yet been identified as a batrachotoxin (BTX) sensing residue. We therefore created S401 mutants with 12 substitutions (S401C,W,P,A,K,F,R,E,L,N,D,G) and assayed their BTX sensitivity. All S401 mutants expressed Na+ currents but often with altered gating characteristics. Ten mutants were found sensitive to 5 muM BTX, which eliminated Na+ channel fast inactivation after repetitive pulses. However, S401K and S401R became BTX resistant. In addition, the block of open and inactivated hNav1.5-S401K Na+ channels by local anesthetic bupivacaine was reduced by approximately 8-10-fold, but not the block of resting Na+ channels. Qualitatively, these ligand-sensing phenotypes of hNav1.5-S401K channels resemble those of S1458K and F1760K channels reported earlier. Together, our results support that residue hNav1.5-S401 at D1S6 is facing the inner cavity and is in close proximity to the receptor sites for BTX and for local anesthetics.

Hemoglobin adducts of the human bladder carcinogen o-toluidine after treatment with the local anesthetic prilocaine

Prilocaine, a widely used local anesthetic, is metabolized to o-toluidine which is classified as human carcinogen. We aimed to assess the impact of prilocaine-treatment on hemoglobin adducts from o-toluidine. Blood samples were obtained before and 24h after receiving prilocaine local anesthesia (Xylonest, 100mg) from 20 head and neck surgery patients and 6 healthy volunteers. Hemoglobin adducts of o-toluidine and 4-aminobiphenyl were determined by gas chromatography/mass spectrometry. Hemoglobin adducts of o-toluidine were significantly increased 24h after 100mg prilocaine-treatment by 21.6+/-12.8ng/g hemoglobin (mean+/-S.D., N=26; P<0.0001). This corresponds to a 6-360-fold increase of o-toluidine adduct levels in 25 patients from 0.54+/-0.95ng/g before treatment to 22.0+/-13.2ng/g 24h after surgery (mean+/-S.D.). Because of an extremely high background level the increase was only 1.6-fold in one patient (40.9ng/g before and 64.4ng/g 24h after prilocaine injection). Current smoking had no influence on background values and on the increase of o-toluidine adducts. No treatment-related differences were seen in mean hemoglobin adduct levels of 4-aminobiphenyl which were significantly higher in smokers, 0.149+/-0.096ng/g (mean+/-S.D., N=8) as compared to nonsmokers 0.036+/-0.035ng/g (mean+/-S.D., N=16; P<0.01). In conclusion, prilocaine anesthesia leads to a massive increase of hemoglobin adducts of the carcinogenic arylamine o-toluidine. This implies a carcinogenic risk which should be taken into account in preventive hazard minimization.

Voltage-gated Na+ channel ligands and ATP: relative molecular similarity and implications for channel function

The voltage-gated sodium channel (VGNC) is targeted by naturally occurring ligands and drugs of diverse structure. ATP modulates VGNC current in-vitro but is given little prominence in models describing channel function. This computational study uses superimposition and molecular fitting to investigate relative molecular similarity within the structures of ATP and VGNC ligands. A motif of 3 linked atoms (C-N-C) in the adenine ring of ATP satisfies the fitting of a wide range of anticonvulsant structures. An alternative group (N-C-N) provides one fitting motif for the ester and amide groups of local anaesthetic drugs; protonated amine and aromatic groups in the same conformers fit to a second motif in the adenine ring. Analogous structures from other drug classes with VGNC blocking activity give the same molecular fits to ATP. Structures fitted to the adenine ring of ATP occlude the intra-molecular space between the nucleoside and triphosphate chain in approximation to their established blocking, activating or neutral effects on Na+ current. The findings are discussed in terms of drug preferences for VGNC states and channel requirements for ATP.

[In vitro investigations of phase I metabolism of the fomocaine derivative Oe 9000 with pig liver homogenates]

2,2'-[4-(4-Phenoxymethylphenyl)butylimino]diethanol (Oe 9000) is a new, highly potent local anaesthetic related to fomocaine. It displays a long duration of action, low toxicity and is superior to fomocaine with regard to aqueous solubility and efficacy. In view of the development of new application forms, e.g. for the treatment of postoperative pain, the elucidation of the biotransformation of the drug is required. Therefore, experiments with 10000 x g supernatants and microsomes from pig liver homogenates were conducted. Using specifically synthesized reference compounds six phase I metabolites could be identified by LC-MS. Apart from the predominating oxidative desamination of the compound, that led after redox reactions to the corresponding butyric acid and butanol derivatives, oxygenation of the exocycle, oxidative N-desalkylation, and N-oxidation were observed. Thus, with the exception of one compound only metabolites are generated, that are expected to have no local anaesthetic activity due to their reduced basicity.

Lipid infusion accelerates removal of bupivacaine and recovery from bupivacaine toxicity in the isolated rat heart

BACKGROUND AND OBJECTIVES

Infusion of a lipid emulsion has been advocated for treatment of severe bupivacaine cardiac toxicity. The mechanism of lipid rescue is unknown. These studies address the possibility that lipid infusion reduces cardiac bupivacaine content in the context of cardiac toxicity.

METHODS

We compared the effects of a 1% lipid emulsion with standard Krebs buffer after inducing asystole in isolated rat heart with 500 micromol/L bupivacaine. We compared times to first heart beat and recovery of 90% of baseline rate pressure product (RPP = heart rate x [left ventricular systolic pressure - left ventricular diastolic pressure]) between controls and hearts receiving 1% lipid immediately after bupivacaine. We also used minibiopsies to compare control bupivacaine tissue content with hearts getting lipid immediately after an infusion of radiolabeled bupivacaine. We then compared bupivacaine efflux from hearts with and without lipid infusion started 75 seconds after radiolabeled bupivacaine was administered.

RESULTS

Infusion of lipid resulted in more rapid return of spontaneous contractions and full recovery of cardiac function. Average (+/- SEM) times to first beat and to 90% recovery of rate pressure product were 44.6 +/- 3.5 versus 63.8 +/- 4.3 seconds (P < .01) and 124.7 +/- 12.4 versus 219.8 +/- 25.6 seconds (P < .01) for lipid and controls, respectively. Lipid treatment resulted in more rapid loss of bupivacaine from heart tissue (P < .0016). Late lipid infusion, 75 seconds after bupivacaine infusion ended, increased the release of bupivacaine measured in effluent for the first 15-second interval compared with controls (183 vs. 121 nmol, n = 5 for both groups, P < .008).

CONCLUSIONS

Lipid emulsion speeds loss of bupivacaine from cardiac tissue while accelerating recovery from bupivacaine-induced asystole. These findings are consistent with the hypothesis that bupivacaine partitions into the emulsion and supports the concept of a "lipid sink." However, the data do not exclude other possible mechanisms of action.

Activities of rat cytochrome P450 3A and 2C isoforms are increased in vivo by magnesium sulfate as evidenced by enhanced oxidation of bupivacaine and testosterone in liver microsomes

We previously reported that magnesium sulfate (MgSO(4)) increases the threshold dose of bupivacaine in inducing seizure in rats. Cytochrome P450 (P450) isoforms involved in the biotransformation of bupivacaine to three oxidative metabolites and the effects of MgSO(4) in vivo on the P450 activities in rats were investigated. Of six cDNA-expressed rat P450 isoforms tested, CYP3A2 and CYP2C11 had high rates for N-debutlylation and 3'-hydroxylation of bupivacaine, respectively. The liver microsomes prepared from male rats pretreated with intravenous administration of MgSO(4) (a bolus dose of 25 mg/kg, followed by infusion of 2.0 mg/kg/min for 6 h) showed increased V(max) values for N-debutylation and 3'-hydroxylaiton of bupivacaine compared to the liver microsomes from control rats. Administration of MgSO(4) also increased the activities of testosterone 6beta- and 16alpha-hydroxylation. Although the level of expression of CYP3A and CYP2C isoforms in the liver microsomes were unchanged, NADPH-P450 reductase and cytochrome b(5) were found to be induced by intravenous administration of MgSO(4). These results suggest that CYP3A and CYP2C isoforms are activated by MgSO(4) in vivo as a consequence of enhanced microsomal electron transfer due to induction of NADPH-P450 reductase and cytochrome b(5), leading to the increased metabolism and clearance of bupivacaine.

Evaluation of chemical enhancers in the transdermal delivery of lidocaine

The effect of various classes of chemical enhancers was investigated for the transdermal delivery of the anesthetic lidocaine across pig and human skin in vitro. The lipid disrupting agents (LDA) oleic acid, oleyl alcohol, butenediol, and decanoic acid by themselves or in combination with isopropyl myristate (IPM) showed no significant flux enhancement. However, the binary system of IPM/n-methyl pyrrolidone (IPM/NMP) improved drug transport. At 2% lidocaine dose, this synergistic enhancement peaked at 25:75 (v/v) IPM:NMP with a steady state flux of 57.6 +/- 8.4 microg cm(-2) h(-1) through human skin. This observed flux corresponds to a four-fold enhancement over a 100% NMP solution and over 25-fold increase over 100% IPM at the same drug concentration (p < 0.001). NMP was also found to co-transport through human skin with lidocaine free base and improve enhancement due to LDA. These findings allow a more rational approach for designing oil-based formulations for the transdermal delivery of lidocaine free base and similar drugs.

Ropivacaine: a pharmacological review

Ropivacaine (Naropin, AstraZeneca) a new long-acting amide local anaesthetic agent, is a pure S-enantiomer, with a high pKa and relatively low-lipid solubility. Since its clinical introduction in 1996, it has been the focus of intense interest because of its increased CNS and cardiovascular safety compared with bupivacaine. This article reviews the pharmacology of ropivacaine with particular emphasis placed on toxicological issues. Compared with bupivacaine (the drug of choice for many years), ropivacaine is equally effective for subcutaneous infiltration, epidural, intrathecal and peripheral nerve block surgery, and obstetrics and postoperative analgesia. Ropivacaine is virtually identical to bupivacaine in terms of onset, quality and duration of sensory block, but seems to produce less motor block. The lesser toxicity of ropivacaine compared with bupivacaine has been confirmed in numerous animal experiments as well as human studies, including studies considering the presumed lower potency of ropivacaine. In fact, the reduced cardiovascular toxicity compared with bupivacaine may be a distinct feature of ropivacaine. So far, the increased cost of ropivacaine compared with bupivacaine has limited its wider clinical use -- in spite of the improved safety profile. During the last few years, cost differences between bupivacaine and ropivacaine have been minimized, thus making pharmacoeconomical speculations a much lesser concern when choosing a local anaesthetic drug. In conclusion, ropivacaine appears to be a safer local anaesthetic agent than bupivacaine. It seems particularly indicated for major peripheral nerve blocks and obstetrics. Ropivacaine should be considered when regional blocks are used in neonates and young infants. With the current trend in the cost development, ropivacaine will most likely be used increasingly in the future.

A mutation in the local anaesthetic binding site abolishes toluene effects in sodium channels

Toluene is a solvent of abuse that inhibits cardiac sodium channels in a manner that resembles the action of local anaesthetics. The purpose of this work was to analyze toluene effects on skeletal muscle sodium channels with and without beta1 subunit (Nav1.4+beta1 and Nav1.4-beta1, respectively) expressed in Xenopus laevis oocytes and to compare them with those produced in the F1579A mutant channel lacking a local anaesthetic binding site. Toluene inhibited Nav1.4 sodium currents (IC50=2.7 mM in Nav1.4+beta1 and 2.2 mM in Nav1.4-beta1 in a concentration dependent way. Toluene (3 mM) blocked sodium currents in Nav1.4 channels proportionally throughout the entire current-voltage relationship producing inactivation at more negative potentials. Minimal inhibition was produced by 3 mM toluene in F1579A mutant channels. Recovery from inactivation was slower both in Nav1.4 and F1579A channels in the presence of 3 mM toluene. The solvent blocked sodium currents in a use-dependent and frequency-dependent manner in Nav1.4 channels. A single mutation in the local anaesthetic binding site of Nav1.4 channels almost abolished toluene effects. These results suggest that this site is important for toluene action.

Antinociception following application of DAMGO to the basolateral amygdala results from a direct interaction of DAMGO with Mu opioid receptors in the amygdala

Previous studies from our laboratory have shown that application of the mu opioid agonist DAMGO into the basolateral region of the amygdala (BLA) suppresses the radiant heat tail flick (TF) reflex in anesthetized rats. This antinociceptive effect can be blocked by lesions of brainstem regions such as the periaqueductal gray (PAG) or the rostral ventromedial medulla (RVM) or by functional inactivation of neurons in these regions, suggesting the activation of brainstem-descending antinociceptive systems from the amygdala. However, little is known about the direct interaction of DAMGO with mu receptors in the amygdala. In the present series of experiments, the BLA was pretreated with opioid receptor antagonists and a G protein inhibitor prior to TF testing with application of DAMGO into the same site. Rats pretreated with the non-selective opioid antagonist naltrexone (1.25-3.75 microg/0.25 microl per side) or the G protein inhibitor pertussis toxin (0.25 microg) failed to show inhibition of TF reflexes following infusion of DAMGO (0.168-0.50 microg), indicating that DAMGO works through G-protein-coupled opioid receptors in the BLA. Furthermore, pretreatment with the mu antagonist beta-FNA (1.00-2.00 microg) attenuated antinociception induced by DAMGO injection, suggesting DAMGO's action on mu receptors in the BLA. Accordingly, we confirm a direct interaction of DAMGO with G-protein-coupled mu receptors in the BLA contributing to induction of opioid antinociception in the amygdala.

Equilibrium sampling through membrane based on a single hollow fibre for determination of drug–protein binding and free drug concentration in plasma

The determination of drug-protein binding and free drug concentration in plasma applying the equilibrium sampling through membrane (ESTM) technique has been studied using supported liquid membrane extraction in a single hollow fibre without any membrane carrier. In the extraction setup, the donor phase (plasma or buffer) was placed in the vial, into which was immersed the hollow fibre with the acceptor phase situated in the lumen. This proposed technique was applied to study the drug-protein binding of five local anaesthetics and two antidepressants as model substances, and the influence of the total drug concentration on the drug-protein binding was investigated. The brief theoretical background for determination of the drug-protein binding under equilibrium conditions is described. The developed method shows a new, improved and simple procedure for determination of free drug concentration in plasma and extent of drug-protein binding.

Effect of pressure on nucleotide binding to yeast alcohol dehydrogenase

Binding of reduced nicotinamide adenine dinucleotide to yeast alcohol dehydrogenase results in a hypsochromic shift of its absorbance maximum at 340 nm. Application of high hydrostatic pressure to the enzyme-nucleotide complex returns the absorbance maximum to longer wavelengths. This pressure-dependent bathochromic shift validates one of two assignments on the effects of pressure on the kinetics of the enzymatic oxidation of benzyl alcohol, namely the protein-ligand conformational change of the capturing form of enzyme.

Interferon subtype gene therapy for regulating cytomegalovirus disease

Delivery of type I interferon (IFN) subtypes by intramuscular inoculation of mice with a recombinant mammalian expression vector encoding IFN stimulates the immune response. Such immunomodulation drives towards a Th1-like response. The degree of stimulation of the immune response was influenced by several parameters of the naked deoxyribonucleic acid (DNA) vaccination protocol. Pretreatment of mice with bupivacaine increased transgene expression in situ. The specific subtype gene of type I IFN, the DNA concentration, the combined use of two or more subtypes, and the timing of the DNA immunisations were all found to influence the level of efficacy of IFN gene therapy in a mouse model for cytomegalovirus (CMV) infection and disease. In addition, adjuvant therapy, using type I IFN genes, for DNA virus vaccination (CMV glycoprotein B) enhanced viral-specific immunity and reduced the severity of myocarditis in mice. Thus, type I IFN gene therapy has potent adjuvant properties when delivered as DNA and can be used to regulate virus infection and disease via pleiotropic actions in the stimulation of immune responses.

Local Anesthetic Interaction with Human Ether-a-go-go –related Gene (HERG) Channels

Background

Human ether-a-go-go-related gene (HERG) potassium channels constitute a potential target involved in cardiotoxic side effects of amino-amide local anesthetics. The molecular interaction site of these low-affinity blockers with HERG channels is currently unknown. The aim of this study was to determine the effect of the mutations Y652A and F656A in the putative drug binding region of HERG on the inhibition by bupivacaine, ropivacaine, and mepivacaine.

Methods

The authors examined the inhibition of wild-type and mutant HERG channels, transiently expressed in Chinese hamster ovary cells by bupivacaine, ropivacaine, and mepivacaine. Whole cell patch clamp recordings were performed at room temperature.

Results

Inhibition of HERG wild-type and mutant channels by the different local anesthetics was concentration dependent, stereoselective, and reversible. The sensitivity decreased in the order bupivacaine &gt; ropivacaine &gt; mepivacaine for wild-type and mutant channels. The mutant channels were approximately 4-30 times less sensitive to the inhibitory action of the different local anesthetics than the wild-type channel. The concentration-response data were described by Hill functions (bupivacaine: wild-type IC50 = 22 +/- 2 microm, n = 38; Y652A IC50 = 95 +/- 5 microm, n = 31). The mutations resulted in a change of the stereoselectivity of HERG channel block by ropivacaine. The potency of the local anesthetics to inhibit wild-type and mutant channels correlated with the lipophilicity of the drug (r &gt; 0.9).

Conclusions

These results indicate that local anesthetics specifically but not exclusively interact with the aromatic residues Y652 and F656 in S6 of HERG channels.