Prolonged duration local anesthesia with minimal toxicity

Polymeric Prodrugs using Dynamic Covalent Chemistry for Prolonged Local Anesthesia

Depot-type drug delivery systems are designed to deliver drugs at an effective rate over an extended period. Minimizing initial "burst" can also be important, especially with drugs causing systemic toxicity. Both goals are challenging with small hydrophilic molecules. The delivery of molecules such as the ultrapotent local anesthetic tetrodotoxin (TTX) exemplifies both challenges. Toxicity can be mitigated by conjugating TTX to polymers with ester bonds, but the slow ester hydrolysis can result in subtherapeutic TTX release. Here, we developed a prodrug strategy, based on dynamic covalent chemistry utilizing a reversible reaction between the diol TTX and phenylboronic acids. These polymeric prodrugs exhibited TTX encapsulation efficiencies exceeding 90 % and the resulting polymeric nanoparticles showed a range of TTX release rates. In vivo injection of the TTX polymeric prodrugs at the sciatic nerve reduced TTX systemic toxicity and produced nerve block lasting 9.7±2.0 h, in comparison to 1.6±0.6 h from free TTX. This approach could also be used to co-deliver the diol dexamethasone, which prolonged nerve block to 21.8±5.1 h. This work emphasized the usefulness of dynamic covalent chemistry for depot-type drug delivery systems with slow and effective drug release kinetics.

Nanozyme-assisted molecularly imprinted polymer-based indirect competitive ELISA for the detection of marine biotoxin

Saxitoxin (STX), which is produced by certain dinoflagellate species, is a type of paralytic shellfish poisoning toxin that poses a serious threat to human health and the environment. Therefore, developing a technology for the convenient and cost-effective detection of STX is imperative. In this study, we developed an affinity peptide-imprinted polymer-based indirect competitive ELISA (ic-ELISA) without using enzyme-toxin conjugates. AuNP/Co3O4@Mg/Al cLDH was synthesized by calcining AuNP/ZIF-67@Mg/Al LDH, which was obtained by combining AuNPs, ZIF-67, and flower-like Mg/Al LDH. This synthesized nanozyme exhibited high catalytic activity (Km = 0.24 mM for TMB and 132.5 mM for H2O2). The affinity peptide-imprinted polymer (MIP) was imprinted with an STX-specific template peptide (STX MIP) on a multi-well microplate and then reacted with an STX-specific signal peptide (STX SP). The interaction between the STX SP and MIP was detected using a streptavidin-coated nanozyme (SA-AuNP/Co3O4@Mg/Al cLDH). The developed MIP-based ic-ELISA exhibited excellent selectivity and sensitivity, with a limit of detection of 3.17 ng/mL (equivalent: 0.317 μg/g). Furthermore, the system was validated using a commercial ELISA kit and mussel tissue samples, and it demonstrated a high STX recovery with a low coefficient of variation. These results imply that the developed ic-ELISA can be used to detect STX in real samples.

Supramolecular interaction in the action of drug delivery systems

Complex diseases and diverse clinical needs necessitate drug delivery systems (DDSs), yet the current performance of DDSs is far from ideal. Supramolecular interactions play a pivotal role in various aspects of drug delivery, encompassing biocompatibility, drug loading, stability, crossing biological barriers, targeting, and controlled release. Nevertheless, despite having some understanding of the role of supramolecular interactions in drug delivery, their incorporation is frequently overlooked in the design and development of DDSs. This perspective provides a brief analysis of the involved supramolecular interactions in the action of drug delivery, with a primary emphasis on the DDSs employed in the clinic, mainly liposomes and polymers, and recognized phenomena in research, such as the protein corona. The supramolecular interactions implicated in various aspects of drug delivery systems, including biocompatibility, drug loading, stability, spatiotemporal distribution, and controlled release, were individually analyzed and discussed. This perspective aims to trigger a comprehensive and systematic consideration of supramolecular interactions in the further development of DDSs. Supramolecular interactions embody the true essence of the interplay between the majority of DDSs and biological systems.

Size control of ropivacaine nano/micro-particles by soft-coating with peptide nanosheets for long-acting analgesia

Rationale: To meet the need of long-acting analgesia in postoperative pain management, slow-releasing formulations of local anesthetics (LAs) have been extensively investigated. However, challenges still remain in obtaining such formulations in a facile and cost-effective way, and a mechanism for controlling the release rate to achieve an optimal duration is still missing. Methods: In this study, nanosheets formed by a self-assembling peptide were used to encapsulate ropivacaine in a soft-coating manner. By adjusting the ratio between the peptide and ropivacaine, ropivacaine particles with different size were prepared. Releasing profile of particles with different size were studied in vitro and in vivo. The influence of particle size and ropivacaine concentration on effective duration and toxicity were evaluated in rat models. Results: Our results showed that drug release rate became slower as the particle size increased, with particles of medium size (2.96 ± 0.04 μm) exhibiting a moderate release rate and generating an optimal anesthetic duration. Based on this size, formulations at different ropivacaine concentrations generated anesthetic effect with different durations in rat sciatic nerve block model, with the 6% formulation generated anesthetic duration of over 35 h. Long-acting analgesia up to 48 h of this formulation was also confirmed in a rat total knee arthroplasty model. Conclusion: This study provided a facile strategy to prepare LA particles of different size and revealed the relationship between particle size, release rate and anesthetic duration, which provided both technical and theoretical supports for developing long-acting LA formulations with promising clinical application.

A hybrid nanoparticle-protein hydrogel system for prolonged local anesthesia

Local anesthetics are effective in relieving pain, but their duration of action is short. Therefore, the development of injectable sustained release systems to prolong the effect of local anesthetics has been of interest. In such systems delivering conventional local anesthetics, it has been challenging to achieve long durations of effect, particularly without incurring tissue toxicity. To overcome these challenges, we created a platform comprising a protein hydrogel incorporating hydrophobic local anesthetic (bupivacaine) nanoparticles. The nanoparticles were prepared by anti-solvent precipitation stabilized with bovine serum albumin (BSA), followed by crosslinking with glutaraldehyde (GA). The resulting BSA hydrogels prolonged release of bupivacaine in vitro. When bupivacaine nanoparticles within crosslinked BSA were injected at the sciatic nerve in rats, a duration of nerve block of 39.9 h was obtained, compared to 5.5 h for the commercial bupivacaine liposome suspension EXPAREL®. Tissue reaction was benign. We further demonstrated that this system could control the release of the amphiphilic drug diphenhydramine and the hydrophobic paclitaxel.

Marine Toxins as Pharmaceutical Treasure Troves: A Focus on Saxitoxin Derivatives from a Computational Point of View

This work highlights the significant potential of marine toxins, particularly saxitoxin (STX) and its derivatives, in the exploration of novel pharmaceuticals. These toxins, produced by aquatic microorganisms and collected by bivalve mollusks and other filter-feeding organisms, offer a vast reservoir of chemical and biological diversity. They interact with sodium channels in physiological processes, affecting various functions in organisms. Exposure to these toxins can lead to symptoms ranging from tingling sensations to respiratory failure and cardiovascular shock, with STX being one of the most potent. The structural diversity of STX derivatives, categorized into carbamate, N-sulfocarbamoyl, decarbamoyl, and deoxydecarbamoyl toxins, offers potential for drug development. The research described in this work aimed to computationally characterize 18 STX derivatives, exploring their reactivity properties within marine sponges using conceptual density functional theory (CDFT) techniques. Additionally, their pharmacokinetic properties, bioavailability, and drug-likeness scores were assessed. The outcomes of this research were the chemical reactivity parameters calculated via CDFT as well as the estimated pharmacokinetic and ADME properties derived using computational tools. While they may not align directly, the integration of these distinct datasets enriches our comprehensive understanding of the compound's properties and potential applications. Thus, this study holds promise for uncovering new pharmaceutical candidates from the considered marine toxins.

Harmful and beneficial properties of cyanotoxins: Two sides of the same coin

Cyanotoxins are by definition "harmful agents" produced by cyanobacteria. Their toxicity has been extensively studied and reviewed over the years. Cyanotoxins have been commonly classified, based on their poisonous effects on mammals, into three main classes, neurotoxins, hepatotoxins and dermatotoxins, and, considering their chemical features, mainly identified as peptides, alkaloids and lipopolysaccharides. Here we propose a broader subdivision of cyanotoxins into eight distinct classes, taking into account their molecular structures, biosynthesis and modes of action: alkaloids, non-ribosomal peptides, polyketides, non-protein amino acids, indole alkaloids, organophosphates, lipopeptides and lipoglycans. For each class, the structures and primary mechanisms of toxicity of the main representative cyanotoxins are reported. Despite their powerful biological activities, only recently scientists have considered the biotechnological potential of cyanotoxins, and their applications both in medical and in industrial settings, even if only a few of these have reached the biotech market. In this perspective, we discuss the potential uses of cyanotoxins as anticancer, antimicrobial, and biocidal agents, as common applications for cytotoxic compounds. Furthermore, taking into account their mechanisms of action, we describe peculiar potential bioactivities for several cyanotoxin classes, such as local anaesthetics, antithrombotics, neuroplasticity promoters, immunomodulating and antifouling agents. In this review, we aim to stimulate research on the potential beneficial roles of cyanotoxins, which require interdisciplinary cooperation to facilitate the discovery of innovative biotechnologies.

Aromatized liposomes for sustained drug delivery

Insufficient drug loading and leakage of payload remain major challenges in designing liposome-based drug delivery systems. These phenomena can limit duration of effect and cause toxicity. Targeting the rate-limiting step in drug release from liposomes, we modify (aromatized) them to have aromatic groups within their lipid bilayers. Aromatized liposomes are designed with synthetic phospholipids with aromatic groups covalently conjugated onto acyl chains. The optimized aromatized liposome increases drug loading and significantly decreases the burst release of a broad range of payloads (small molecules and macromolecules, different degrees of hydrophilicity) and extends their duration of release. Aromatized liposomes encapsulating the anesthetic tetrodotoxin (TTX) achieve markedly prolonged effect and decreased toxicity in an application where liposomes are used clinically: local anesthesia, even though TTX is a hydrophilic small molecule which is typically difficult to encapsulate. Aromatization of lipid bilayers can improve the performance of liposomal drug delivery systems.

Materials for Controlled Release of Local Anesthetics

Controlled release systems for prolonged duration local anesthesia have long been an area of research interest, and now are entering clinical practice, in part driven by the opioid epidemic. We discuss the design considerations and material properties of systems for controlled release of local anesthetics, from relatively simple systems to covalent binding of drugs to materials and delivery triggered by external stimuli.

An aptamer-based depot system for sustained release of small molecule therapeutics

Delivery of hydrophilic small molecule therapeutics by traditional drug delivery systems is challenging. Herein, we have used the specific interaction between DNA aptamers and drugs to create simple and effective drug depot systems. The specific binding of a phosphorothioate-modified aptamer to drugs formed non-covalent aptamer/drug complexes, which created a sustained release system. We demonstrated the effectiveness of this system with small hydrophilic molecules, the site 1 sodium channel blockers tetrodotoxin and saxitoxin. The aptamer-based delivery system greatly prolonged the duration of local anesthesia and reduced systemic toxicity. The beneficial effects of the aptamers were restricted to the compounds they were specific to. These studies establish aptamers as a class of highly specific, modifiable drug delivery systems, and demonstrate potential usefulness in the management of postoperative pain.

Emerging drugs for the treatment of postsurgical pain

INTRODUCTION

Postoperative pain is a distressful experience and remains to be a significant concern after surgery. Current agents either fail to prevent or minimize postoperative pain or cause a series of adverse effects, addiction, or abuse. Opioids have been the gold standard in the treatment of postoperative pain despite their well-described adverse effects. Many new agents with different mechanisms of action have been recently introduced to address this issue.

AREAS COVERED

This current review summarizes the list of new and emerging drugs investigated for their efficacy in controlling the postoperative pain and decreasing the need for rescue opioid use, adverse effect profile, abuse, and addiction potential.

EXPERT OPINION

Opioids have unrivaled analgesic efficacy. However adverse effects of opioids led to the search for better options. In mild pain most of the emerging drugs have been shown to control postoperative pain and decrease the use of rescue opioid, however fail to control pain after major surgeries causing severe pain. Specific agents such as Oliceridine, new local anesthetics, etc., are effective in controlling severe pain and hold a promise to replace opioids in the near future.

Voltage-Gated Sodium Channels: A Prominent Target of Marine Toxins

Voltage-gated sodium channels (VGSCs) are considered to be one of the most important ion channels given their remarkable physiological role. VGSCs constitute a family of large transmembrane proteins that allow transmission, generation, and propagation of action potentials. This occurs by conducting Na⁺ ions through the membrane, supporting cell excitability and communication signals in various systems. As a result, a wide range of coordination and physiological functions, from locomotion to cognition, can be accomplished. Drugs that target and alter the molecular mechanism of VGSCs’ function have highly contributed to the discovery and perception of the function and the structure of this channel. Among those drugs are various marine toxins produced by harmful microorganisms or venomous animals. These toxins have played a key role in understanding the mode of action of VGSCs and in mapping their various allosteric binding sites. Furthermore, marine toxins appear to be an emerging source of therapeutic tools that can relieve pain or treat VGSC-related human channelopathies. Several studies documented the effect of marine toxins on VGSCs as well as their pharmaceutical applications, but none of them underlined the principal marine toxins and their effect on VGSCs. Therefore, this review aims to highlight the neurotoxins produced by marine animals such as pufferfish, shellfish, sea anemone, and cone snail that are active on VGSCs and discuss their pharmaceutical values.

Emerging Optical Materials in Sensing and Discovery of Bioactive Compounds

Optical biosensors are used in numerous applications and analytical fields. Advances in these sensor platforms offer high sensitivity, selectivity, miniaturization, and real-time analysis, among many other advantages. Research into bioactive natural products serves both to protect against potentially dangerous toxic compounds and to promote pharmacological innovation in drug discovery, as these compounds have unique chemical compositions that may be characterized by greater safety and efficacy. However, conventional methods for detecting these biomolecules have drawbacks, as they are time-consuming and expensive. As an alternative, optical biosensors offer a faster, simpler, and less expensive means of detecting various biomolecules of clinical interest. In this review, an overview of recent developments in optical biosensors for the detection and monitoring of aquatic biotoxins to prevent public health risks is first provided. In addition, the advantages and applicability of these biosensors in the field of drug discovery, including high-throughput screening, are discussed. The contribution of the investigated technological advances in the timely and sensitive detection of biotoxins while deciphering the pathways to discover bioactive compounds with great health-promoting prospects is envisaged to meet the increasing demands of healthcare systems.

Distinct neurotoxic effects of select local anesthetics on facial nerve injury and recovery

BACKGROUND

Local anesthetic toxicity has been well-documented to cause neuronal injury, death, and dysfunction, particularly in a susceptible nerve.

OBJECTIVE

To determine whether select local anesthetics affect neuron survival and/or functional recovery of an injured nerve.

METHODS

This report describes 6 separate experiments that test immediate or delayed application of local anesthetics in 3 nerve injury models. Adult C57/black6 male mice underwent a facial nerve sham, transection, or crush injury. Local anesthetic or saline was applied to the facial nerve at the time of injury (immediate) or 1 day after injury (delayed). Average percent facial motoneuron (FMN) survival was evaluated four-weeks after injury. Facial nerve regeneration was estimated by observing functional recovery of eye blink reflex and vibrissae movement after facial nerve crush injury.

RESULTS

FMN survival after: transection + immediate treatment with ropivacaine (54.8%), bupivacaine (63.2%), or tetracaine (66.9%) was lower than saline (85.5%) and liposomal bupivacaine (85.0%); crush + immediate treatment with bupivacaine (92.8%) was lower than saline (100.7%) and liposomal bupivacaine (99.3%); sham + delayed treatment with bupivacaine (89.9%) was lower than saline (96.6%) and lidocaine (99.5%); transection + delayed treatment with bupivacaine (67.3%) was lower than saline (78.4%) and liposomal bupivacaine (77.6%); crush + delayed treatment with bupivacaine (85.3%) was lower than saline (97.9%) and lidocaine (96.0%). The average post-operative time for mice to fully recover after: crush + immediate treatment with bupivacaine (12.83 days) was longer than saline (11.08 days) and lidocaine (10.92 days); crush + delayed treatment with bupivacaine (16.79 days) was longer than saline (12.73 days) and lidocaine (11.14 days).

CONCLUSIONS

Our data demonstrate that some local anesthetics, but not all, exacerbate motoneuron death and delay functional recovery after a peripheral nerve injury. These and future results may lead to clinical strategies that decrease the risk of neural deficit following peripheral nerve blocks with local anesthetics.

Nanogels with High Loading of Anesthetic Nanocrystals for Extended Duration of Sciatic Nerve Block

The development of thermoresponsive nanogels loaded with nanocrystals of the local anesthetic bupivacaine nanocrystals (BNCs) for prolonged peripheral nerve pain relief is reported here. BNCs were prepared using the antisolvent precipitation method from the hydrophobic form of bupivacaine (bupivacaine free base). The as-prepared BNCs were used stand-alone or encapsulated in temperature-responsive poly(ethylene glycol) methyl ether methacrylate (OEGMA)-based nanogels, resulting in bupivacaine NC-loaded nanogels (BNC-nanogels) of monodisperse size. The synthesis protocol has rendered high drug loadings (i.e., 93.8 ± 1.5 and 84.8 ± 1.2 wt % for the NC and BNC-nanogels, respectively) and fast drug dissolution kinetics in the resulting composite material. In vivo tests demonstrated the efficacy of the formulation along with an extended duration of sciatic nerve block in murine models of more than 8 h with a formulation containing only 2 mg of the local anesthetic thanks to the thermoresponsive character of the polymer, which, at body temperature, becomes hydrophobic and acts as a diffusion barrier for the encapsulated drug nanocrystals. The hydrophobicity of the encapsulated bupivacaine free base probably facilitates its pass through cell membranes and also binds strongly to their hydrophobic lipid bilayer, thereby protecting molecules from diffusion to extracellular media and to the bloodstream, reducing their clearance. When using BNC-nanogels, the duration of the anesthetic blockage lasted twice as long as compared to the effect of just BNCs or a conventional bupivacaine hydrochloride solution both containing equivalent amounts of the free drug. Results of the in vivo tests showed enough sensory nerve block to potentially relieve pain, but still having mobility in the limb, which enables motor function when required. The BNC-nanogels presented minimal toxicity in the in vivo study due to their sustained drug release and excellent biocompatibility. The encapsulation of nano-sized crystals of bupivacaine provides a prolonged regional anesthesia with reduced toxicity, which could be advantageous in the management of chronic pain.

Lidocaine-loaded reduced graphene oxide hydrogel for prolongation of effects of local anesthesia: In vitro and in vivo analyses

Lidocaine is widely used as a local anesthetic for alleviation of post-operative pain and for management of acute and chronic painful conditions. Although several approaches are currently used to prolong the duration of action, an effective strategy to achieve neural blockage for several hours remains to be identified. In this study, a lidocaine-loaded Pluronic® F68-reduced graphene oxide hydrogel was developed to achieve sustained release of lidocaine. Fourier transform infrared spectroscopy, X-ray diffraction, and Raman spectroscopy confirmed the synthesis of Pluronic® F68-reduced graphene oxide. Transmission electron microscopy showed wrinkled, flat nanosheets with micelles attached. The developed hydrogel showed desirable pH, viscosity, adhesiveness, hardness, and cohesiveness for topical application. The ex vivo release study demonstrated the ability of the Pluronic® F68-reduced graphene oxide hydrogel to prolong release up to 10 h, owing to the strong π-π interactions between the graphene oxide and the lidocaine. In comparison with a commercial lidocaine ointment, the developed graphene oxide hydrogel showed sustained anesthetic effect in the radiant heat tail flick test and sciatic nerve block model. Thus, this study demonstrates the potential of using Pluronic® F68-reduced graphene oxide nanocarriers to realize prolonged effects of local anesthesia for effective pain management.

Neurotoxicity of bupivacaine and liposome bupivacaine after sciatic nerve block in healthy and streptozotocin-induced diabetic mice

Background

Long-acting local anaesthetics (e.g. bupivacaine hydrochloride) or sustained-release formulations of bupivacaine (e.g. liposomal bupivacaine) may be neurotoxic when applied in the setting of diabetic neuropathy. The aim of the study was to assess neurotoxicity of bupivacaine and liposome bupivacaine in streptozotocin (STZ) - induced diabetic mice after sciatic nerve block. We used the reduction in fibre density and decreased myelination assessed by G-ratio (defined as axon diameter divided by large fibre diameter) as indicators of local anaesthetic neurotoxicity.

Results

Diabetic mice had higher plasma levels of glucose (P < 0.001) and significant differences in the tail flick and plantar test thermal latencies compared to healthy controls (P < 0.001). In both diabetic and nondiabetic mice, sciatic nerve block with 0.25% bupivacaine HCl resulted in a significantly greater G-ratio and an axon diameter compared to nerves treated with 1.3% liposome bupivacaine or saline (0.9% sodium chloride) (P < 0.01). Moreover, sciatic nerve block with 0.25% bupivacaine HCl resulted in lower fibre density and higher large fibre and axon diameters compared to the control (untreated) sciatic nerves in both STZ-induced diabetic (P < 0.05) and nondiabetic mice (P < 0.01). No evidence of acute or chronic inflammation was observed in any of the treatment groups.

Conclusions

In our exploratory study the sciatic nerve block with bupivacaine HCl (7 mg/kg), but not liposome bupivacaine (35 mg/kg) or saline, resulted in histomorphometric indices of neurotoxicity. Histologic findings were similar in diabetic and healthy control mice.

Effect of Peritumoral Bupivacaine on Primary and Distal Hyperalgesia in Cancer-Induced Bone Pain

Background

Cancer-induced bone pain (CIBP) is a debilitating chronic pain condition caused by injury to bone nerve terminals due to primary or metastasized bone tumors. Pain manifests as enhanced sensitivity, not only over the affected bone site but also at distal areas that share common nerve innervation with the tumor. In this study, we aim to understand how tumor-induced primary and distal pain sensitivities are affected by bupivacaine-induced block of bone nerve endings in a rat model of CIBP.

Methods

MRMT-1 breast cancer cells were injected into the proximal segment of tibia in female Sprague–Dawley rats. Radiograms and micro-CT images were obtained to confirm tumor growth. Bupivacaine was injected peritumorally at day 7 or day 14 post-tumor induction, and withdrawal thresholds in response to pressure and punctate mechanical stimulus were recorded from the knee and hind-paw, respectively. Immunohistochemical studies for the determination of ATF3 and GFAP expression in DRG and spinal cord sections were performed.

Results

Rats developed primary and distal hyperalgesia after MRMT-1 administration that was sustained for 2 weeks. Peritumoral administration of bupivacaine in 7-day post-tumor-induced (PTI) rats resulted in a reversal of both primary and distal hyperalgesia for 20–30 mins. However, bupivacaine failed to reverse distal hyperalgesia in 14 day-PTI rats. ATF3 and GFAP expression were much enhanced in 14 day-PTI animals, compared to 7 day-PTI group.

Conclusion

Results from this study strongly suggest that distal hyperalgesia of late-stage CIBP demonstrates differential characteristics consistent with neuropathic pain as compared to early stage, which appears more inflammatory in nature.

HYR-PB21-LA, a potential extended-release bupivacaine formulation, produces long-lasting local anesthesia in rats and guinea pigs

BACKGROUND

Effective postoperative pain management plays a key role in enhancing recovery of patients after surgery. Bupivacaine hydrochloride is one of the most commonly local anesthetics used for the postoperative pain control. However, the relatively short anesthesia duration of bupivacaine preparations limited their clinical application.

METHODS

Both guinea pig pin-prick study and rat tail-flick test were performed to evaluate the local anesthesia efficacy of HYR-PB21-LA, a new microparticle suspension injection of bupivacaine pamoate.

RESULTS

In the pin-prick test, the complete cutaneous trunci muscle reflex inhibitions were observed at 30 min in all treatment groups containing bupivacaine. In comparison with 6.7 mg/mL HYR-PB21-LA, both 10 and 20 mg/mL HYR-PB21-LA groups had significantly higher area under effect time curve (AUEC) values (p<0.001 and p<0.0001) and slower offset time (p<0.0001). Significantly higher AUEC (p<0.0001) and slower offset time (p<0.0001) were also found in 10 mg/mL HYR-PB21-LA treatment group compared with bupivacaine liposome injectable suspension (liposomal bupivacaine). In the rat tail-flick test, significantly increased local anesthesia effect was lasted for 5 hours after 2.5 mg/mL HYR-PB21-LA administration, which was fivefold longer than bupivacaine hydrochloride. The longer lasted efficacy of significantly increased local anesthesia was also observed in 5 mg/mLHYR-PB21-LA than those in liposomal bupivacaine (8 hour vs 1 hour).

CONCLUSIONS

The results demonstrated that the HYR-PB21-LA produced longer local anesthesia effect than current clinical preparations of bupivacaine in two animal models. These findings raise the potential clinical value of HYR-PB21-LA as a long-lasting local anesthesia for controlling postsurgical pain in humans.

[Stocktaking of local anesthetics 2020]

For decades local anesthetics have proven to be safe and effective drugs in the clinical practice, crucially promoting the enormous achievements in regional anesthesia. Meanwhile, it is a well-known fact that local anesthetics are much more than just "simple" sodium channel blockers. They also interact with numerous other ion channels and subcellular structures, enhancing nerve blockade and resulting in systemic "alternative" effects, which can sometimes even be clinically used. By the simultaneous administration of various adjuvants (e.g., opioids, corticosteroids and α₂-receptor agonists) attempts are made to prolong the time of action of local anesthetics after a single administration in order to achieve the best possible improvement in postoperative analgesia. In this context, ultralong-acting local anesthetics, such as liposomal bupivacaine, which at least theoretically can provide a sensory nerve block for several days, have been developed and clinically introduced. The coming years will show whether these approaches will develop into genuine alternatives to the personnel and cost-intensive continuous nerve blockades.Local anesthetic-induced systemic toxicity is meanwhile rare but still a potentially life-threatening event, frequently resulting from accidental intravascular injection or extensive systemic resorption. Consequently, slow and fractional application of these agents with intermittent aspiration helps to prevent toxic sequelae. If toxic symptoms occur, however, the intravenous infusion of 20% lipid solutions in addition to basic treatment measures can enhance the success of treatment.

Identification of promoter elements in the Dolichospermum circinale AWQC131C saxitoxin gene cluster and the experimental analysis of their use for heterologous expression

Background

Dolichospermum circinale is a filamentous bloom-forming cyanobacterium responsible for biosynthesis of the paralytic shellfish toxins (PST), including saxitoxin. PSTs are neurotoxins and in their purified form are important analytical standards for monitoring the quality of water and seafood and biomedical research tools for studying neuronal sodium channels. More recently, PSTs have been recognised for their utility as local anaesthetics. Characterisation of the transcriptional elements within the saxitoxin (sxt) biosynthetic gene cluster (BGC) is a first step towards accessing these molecules for biotechnology.

Results

In D. circinale AWQC131C the sxt BGC is transcribed from two bidirectional promoter regions encoding five individual promoters. These promoters were identified experimentally using 5′ RACE and their activity assessed via coupling to a lux reporter system in E. coli and Synechocystis sp. PCC 6803. Transcription of the predicted drug/metabolite transporter (DMT) encoded by sxtPER was found to initiate from two promoters, PsxtPER1 and PsxtPER2. In E. coli, strong expression of lux from PsxtP, PsxtD and PsxtPER1 was observed while expression from Porf24 and PsxtPER2 was remarkably weaker. In contrast, heterologous expression in Synechocystis sp. PCC 6803 showed that expression of lux from PsxtP, PsxtPER1, and Porf24 promoters was statistically higher compared to the non-promoter control, while PsxtD showed poor activity under the described conditions.

Conclusions

Both of the heterologous hosts investigated in this study exhibited high expression levels from three of the five sxt promoters. These results indicate that the majority of the native sxt promoters appear active in different heterologous hosts, simplifying initial cloning efforts. Therefore, heterologous expression of the sxt BGC in either E. coli or Synechocystis could be a viable first option for producing PSTs for industrial or biomedical purposes.

Clinical Management of Pain in Rodents

The use of effective regimens for mitigating pain remain underutilized in research rodents despite the general acceptance of both the ethical imperative and regulatory requirements intended to maximize animal welfare. Factors contributing to this gap between the need for and the actual use of analgesia include lack of sufficient evidence-based data on effective regimens, under-dosing due to labor required to dose analgesics at appropriate intervals, concerns that the use of analgesics may impact study outcomes, and beliefs that rodents recover quickly from invasive procedures and as such do not need analgesics. Fundamentally, any discussion of clinical management of pain in rodents must recognize that nociceptive pathways and pain signaling mechanisms are highly conserved across mammalian species, and that central processing of pain is largely equivalent in rodents and other larger research species such as dogs, cats, or primates. Other obstacles to effective pain management in rodents have been the lack of objective, science-driven data on pain assessment, and the availability of appropriate pharmacological tools for pain mitigation. To address this deficit, we have reviewed and summarized the available publications on pain management in rats, mice and guinea pigs. Different drug classes and specific pharmacokinetic profiles, recommended dosages, and routes of administration are discussed, and updated recommendations are provided. Nonpharmacologic tools for increasing the comfort and wellbeing of research animals are also discussed. The potential adverse effects of analgesics are also reviewed. While gaps still exist in our understanding of clinical pain management in rodents, effective pharmacologic and nonpharmacologic strategies are available that can and should be used to provide analgesia while minimizing adverse effects. The key to effective clinical management of pain is thoughtful planning that incorporates study needs and veterinary guidance, knowledge of the pharmacokinetics and mechanisms of action of drugs being considered, careful attention to individual differences, and establishing an institutional culture that commits to pain management for all species as a central component of animal welfare.

The Duration of Nerve Block from Local Anesthetic Formulations in Male and Female Rats

PURPOSE

It is unknown whether there are sex differences in response to free or encapsulated local anesthetics.

METHODS

We examined nerve block duration and toxicity following peripheral nerve blockade in male and female rats. We studied the local anesthetic bupivacaine (free or encapsulated) as well as tetrodotoxin, which acts on a different site of the same voltage-gated channel.

RESULTS

Sensory nerve blockade was 158.5 [139-190] minutes (median [interquartile range]) (males) compared to 173 [134-171] minutes (females) (p = 0.702) following bupivacaine injection, N = 8 male, 8 female. Motor nerve blockade was 157 [141-171] minutes (males) compared to 172 [146-320] minutes (females) (p = 0.2786). Micellar bupivacaine (N = 8 male, 8 female) resulted in sensory nerve blockade of 266 [227-320] minutes (males) compared to 285 [239-344] minutes (females) (p = 0.6427). Motor nerve blockade was 264 [251-264] minutes (males) compared to 287 [262-287] minutes (females) (p = 0.3823). Liposomal bupivacaine (N = 8 male, 8 female) resulted in sensory nerve blockade of 240 [207-277] minutes (males) compared to 289 [204-348] minutes (females) (p = 0.1654). Motor nerve blockade was 266 [237-372] minutes (males) compared to 317 [251-356] minutes (females) (p = 0.6671). Following tetrodotoxin injection (N = 12 male,12 female) sensory nerve blockade was 54.8 [5-117] minutes (males) compared to 54 [14-71] minutes (females) (p = 0.6422). Motor nerve blockade was 72 [40-112] minutes (males) compared to 64 [32-143] minutes (females) (p = 0.971).

CONCLUSIONS

We found no statistically significant sex differences associated with the formulations tested. In both sexes, durations of nerve block were similar between micellar and liposomal bupivacaine formulations, despite the micellar formulation containing less drug.

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.

The "nano to micro" transition of hydrophobic curcumin crystals leading to in situ adjuvant depots for Au-liposome nanoparticle mediated enhanced photothermal therapy

Photothermal therapy (PTT) is emerging as a promising treatment for skin cancer. Plasmon-resonant gold-coated liposome nanoparticles (Au Lipos NPs) specifically absorb Near Infra-Red (NIR) light resulting in localized hyperthermia (PTT). In the current study, curcumin (a hydrophobic anticancer agent) was entrapped in Au Lipos NPs as nanocrystals to act as an adjuvant for the PTT of melanoma. NIR light irradiation on Au Lipos Cur NPs triggered the release of curcumin nanocrystals which coalesce to form curcumin microcrystals (CMCs). An in situ"nano to micro" transition in the crystal state of curcumin was observed. This in situ transition leads to the formation of CMCs. These CMCs exhibited sustained release of curcumin for a prolonged duration (>10 days). The localized availability of curcumin aids in enhancing PTT by inhibiting the growth and mobility of cancer cells that escape PTT. In the in vitro modified scratch assay, the Au Lipos Cur NP + Laser group showed >1.5 fold enhanced therapeutic coverage when compared with the Au Lipos NP + Laser group. In vivo PTT studies performed in a B16 tumor model using Au Lipos Cur NPs showed a significant reduction of the tumor volume along with the localized release of curcumin in the tumor environment. It was observed that the localized release of curcumin enables an immediate adjuvant effect resulting in the enhancement of PTT.

Polymer-tetrodotoxin conjugates to induce prolonged duration local anesthesia with minimal toxicity

There is clinical and scientific interest in developing local anesthetics with prolonged durations of effect from single injections. The need for such is highlighted by the current opioid epidemic. Site 1 sodium channel blockers such as tetrodotoxin (TTX) are extremely potent, and can provide very long nerve blocks but the duration is limited by the associated systemic toxicity. Here we report a system where slow release of TTX conjugated to a biocompatible and biodegradable polymer, poly(triol dicarboxylic acid)-co-poly(ethylene glycol) (TDP), is achieved by hydrolysis of ester linkages. Nerve block by the released TTX is enhanced by administration in a carrier with chemical permeation enhancer (CPE) properties. TTX release can be adjusted by tuning the hydrophilicity of the TDP polymer backbone. In vivo, 1.0–80.0 µg of TTX released from these polymers produced a range of durations of nerve block, from several hours to 3 days, with minimal systemic or local toxicity.

There is interest in developing long-lasting local anaesthetics for a range of applications. Here, the authors report on the application of tetrodotoxin conjugated to amphiphilic biodegradable polymer to reduce systemic toxicity, achieve sustained release and investigate application as a local anaesthetic.

Prolonged Duration Local Anesthesia Using Liposomal Bupivacaine Combined With Liposomal Dexamethasone and Dexmedetomidine

BACKGROUND

The relatively short duration of effect of local anesthetics has been addressed by encapsulation in drug delivery systems. Codelivery with a single compound that produces an adjuvant effect on nerve block but without intrinsic local anesthetic properties can further prolong the nerve block effect. Here, we investigated whether codelivery of more than 1 encapsulated adjuvant compound can further enhance nerve blockade.

METHODS

Liposomes loaded with bupivacaine (Bup), dexamethasone phosphate (DexP), or dexmedetomidine (DMED) were synthesized and its in vitro drug release profiles were determined. Animals (Sprague-Dawley rats) were injected with liposomal Bup (Lipo-Bup) and adjuvants at the sciatic nerve and underwent a modified hot plate test to assess the degree of nerve block. The duration of block was monitored and the tissue reaction was assessed.

RESULTS

Coinjection of Lipo-Bup with liposomal DexP (Lipo-DexP) and liposomal DMED (Lipo-DMED) prolonged the duration of sciatic nerve block 2.9-fold compared to Lipo-Bup alone (95% confidence interval, 1.9- to 3.9-fold). The duration of the block using this combination was significantly increased to 16.2 ± 3.5 hours compared to Lipo-Bup with a single liposomal adjuvant (8.7 ± 2.4 hours with Lipo-DMED, P = .006 and 9.9 ± 5.9 hours with Lipo-DexP, P = .008). The coinjection of Lipo-Bup with liposomal adjuvants decreased tissue inflammation (P = .014) but did not have a significant effect on myotoxicity when compared to Lipo-Bup alone. Coinjection of Lipo-Bup with unencapsulated adjuvants prolonged the duration of nerve block as well (25.0 ± 6.3 hours; P < .001) however was accompanied by systemic side effects.

CONCLUSIONS

Codelivery of Lipo-DexP and Lipo-DMED enhanced the efficacy of Lipo-Bup. This benefit was also seen with codelivery of both adjuvant molecules in the unencapsulated state, but with marked systemic toxicity.

Natural Voltage-Gated Sodium Channel Ligands: Biosynthesis and Biology

Natural product biosynthetic pathways are composed of enzymes that use powerful chemistry to assemble complex molecules. Small molecule neurotoxins are examples of natural products with intricate scaffolds which often have high affinities for their biological targets. The focus of this Minireview is small molecule neurotoxins targeting voltage-gated sodium channels (VGSCs) and the state of knowledge on their associated biosynthetic pathways. There are three small molecule neurotoxin receptor sites on VGSCs associated with three different classes of molecules: guanidinium toxins, alkaloid toxins, and ladder polyethers. Each of these types of toxins have unique structural features which are assembled by biosynthetic enzymes and the extent of information known about these enzymes varies among each class. The biosynthetic enzymes involved in the formation of these toxins have the potential to become useful tools in the efficient synthesis of VGSC probes.

Research Progress on Conducting Polymer-Based Biomedical Applications

Conducting polymers (CPs) have attracted significant attention in a variety of research fields, particularly in biomedical engineering, because of the ease in controlling their morphology, their high chemical and environmental stability, and their biocompatibility, as well as their unique optical and electrical properties. In particular, the electrical properties of CPs can be simply tuned over the full range from insulator to metal via a doping process, such as chemical, electrochemical, charge injection, and photo-doping. Over the past few decades, remarkable progress has been made in biomedical research including biosensors, tissue engineering, artificial muscles, and drug delivery, as CPs have been utilized as a key component in these fields. In this article, we review CPs from the perspective of biomedical engineering. Specifically, representative biomedical applications of CPs are briefly summarized: biosensors, tissue engineering, artificial muscles, and drug delivery. The motivation for use of and the main function of CPs in these fields above are discussed. Finally, we highlight the technical and scientific challenges regarding electrical conductivity, biodegradability, hydrophilicity, and the loading capacity of biomolecules that are faced by CPs for future work. This is followed by several strategies to overcome these drawbacks.

Heterologous expression and biochemical characterisation of cyanotoxin biosynthesis pathways

This review discusses cyanotoxin biosynthetic pathways and highlights the heterologous expression and biochemical studies used to characterise them.

Addressing the Issue of Tetrodotoxin Targeting

This review is devoted to the medical application of tetrodotoxin (TTX), a potent non-protein specific blocker of voltage-gated sodium (NaV) channels. The selectivity of action, lack of affinity with the heart muscle NaV channels, and the inability to penetrate the blood–brain barrier make this toxin an attractive candidate for anesthetic and analgesic drug design. The efficacy of TTX was shown in neuropathic, acute and inflammatory pain models. The main emphasis of the review is on studies focused on the improvement of TTX efficacy and safety in conjunction with additional substances and drug delivery systems. A significant improvement in the effectiveness of the toxin was demonstrated when used in tandem with vasoconstrictors, local anesthetics and chemical permeation enhancers, with the best results obtained with the encapsulation of TTX in microparticles and liposomes conjugated to gold nanorods.

Long-lasting, reversible and non-neurotoxic inactivation of hippocampus activity induced by neosaxitoxin

BACKGROUND

Neosaxitoxin (NeoSTX) and related paralytics shellfish toxins has been successfully used as local anesthetic and muscle relaxants to treat a variety of ailments. The primary mechanism of action of these toxins occurs by blocking voltage-gated sodium channels with compounds such as TTX, lidocaine, or derivatives. However, most of these non-classical sodium channel blockers act with a reduced time effect as well as ensuing neurotoxicity.

NEW METHOD

In this report, we show that the use of local NeoSTX injections inactivates the hippocampal neuronal activity reversibly with a by long-term dynamics, without neuronal damage.

RESULTS

A single 10 ng/μl injection of NeoSTX in the dorsal CA1 region abolished for up to 48 h memory capacities and neuronal activity measured by the neuronal marker c-fos. After 72 h of toxin injection, the animals fully recover their memory capacities and hippocampal neuronal activity. The histological inspection of NeoSTX injected brain regions revealed no damage to the tissue or reactive gliosis, similar to vehicle injection. Acute electrophysiological recording in vivo shows, also, minimal spreading of the NeoSTX in the cerebral tissue.

COMPARISON WITH EXISTING METHODS

Intracerebral NeoSTX injection showed longer effects than other voltage sodium channel blocker, with minimal spreading and no neuronal damage.

CONCLUSION

NeoSTX is a new useful tool that reversibly inactivates different brains region for a long time, with minimal diffusion and without neuronal damage. Moreover, NeoSTX can be used as a valuable sodium channel blocker for many studies in vivo and with potential therapeutic uses.

Long-acting liposomal corneal anesthetics

Eye drops producing long-acting ocular anesthesia would be desirable for corneal pain management. Here we present liposome-based formulations to achieve very long ocular anesthetic effect after a single eye drop instillation. The liposomes were functionalized with succinyl-Concanavalin A (sConA-Lip), which can bind corneal glycan moieties, to significantly prolong the dwell time of liposomes on the cornea. sConA-Lip were loaded with tetrodotoxin and dexmedetomidine (sConA-Lip/TD), and provided sustained release for both. A single topical instillation of sConA-Lip/TD on the cornea could achieve 105 min of complete analgesia and 608 min of partial analgesia, which was significantly longer than analgesia with proparacaine, tetrodotoxin/dexmedetomidine solution or unmodified liposomes containing tetrodotoxin and dexmedetomidine. sConA-Lip/TD were not cytotoxic in vitro to human corneal limbal epithelial cells or corneal keratocytes. Topical administration of sConA-Lip/TD provided prolonged corneal anesthesia without delaying corneal wound healing. Such a formulation may be useful for the management of acute surgical and nonsurgical corneal pain, or for treatment of other ocular surface diseases.

An in Vivo Mouse Model to Investigate the Effect of Local Anesthetic Nanomedicines on Axonal Conduction and Excitability

Peripheral nerve blocks (PNBs) using local anesthetic (LA) are superior to systemic analgesia for management of post-operative pain. An insufficiently short PNB duration following single-shot LA can be optimized by development of extended release formulations among which liposomes have been shown to be the least toxic. In vivo rodent models for PNB have focused primarily on assessing behavioral responses following LA. In a previous study in human volunteers, we found that it is feasible to monitor the effect of LA in vivo by combining conventional conduction studies with nerve excitability studies. Here, we aimed to develop a mouse model where the same neurophysiological techniques can be used to investigate liposomal formulations of LA in vivo. To challenge the validity of the model, we tested the motor PNB following an unilamellar liposomal formulation, filled with the intermediate-duration LA lidocaine. Experiments were carried out in adult transgenic mice with fluorescent axons and with fluorescent tagged liposomes to allow in vivo imaging by probe-based confocal laser endomicroscopy. Recovery of conduction following LA injection at the ankle was monitored by stimulation of the tibial nerve fibers at the sciatic notch and recording of the plantar compound motor action potential (CMAP). We detected a delayed recovery in CMAP amplitude following liposomal lidocaine, without detrimental systemic effects. Furthermore, CMAP threshold-tracking studies of the distal tibial nerve showed that the increased rheobase was associated with a sequence of excitability changes similar to those found following non-encapsulated lidocaine PNB in humans, further supporting the translational value of the model.

Injectable nanocomposite analgesic delivery system for musculoskeletal pain management

Musculoskeletal pain is a major health issue which results from surgical procedures (i.e. total knee and/or hip replacements and rotator cuff repairs), as well as from non-surgical conditions (i.e. sympathetically-mediated pain syndrome and occipital neuralgia). Local anesthetics, opioids or corticosteroids are currently used for the pain management of musculoskeletal conditions. Even though local anesthetics are highly preferred, the need for multiple administration presents significant disadvantages. Development of unique delivery systems that can deliver local anesthetics at the injection site for prolonged time could significantly enhance the therapeutic efficacy and patient comfort. The goal of the present study is to evaluate the efficacy of an injectable local anesthetic nanocomposite carrier to provide sustained analgesic effect. The nanocomposite carrier was developed by encapsulating ropivacaine, a local anesthetic, in lipid nanocapsules (LNC-Rop), and incorporating the nanocapsules in enzymatically crosslinked glycol chitosan (0.3GC) hydrogels. Cryo Scanning Electron Microscopic (Cryo SEM) images showed the ability to distribute the LNCs within the hydrogel without adversely affecting their morphology. The study demonstrated the feasibility to achieve sustained release of lipophilic molecules from the nanocomposite carrier in vitro and in vivo. A rat chronic constriction injury (CCI) pain model was used to evaluate the efficacy of the nanocomposite carrier using thermal paw withdrawal latency (TWL). The nanocomposite carriers loaded with ropivacaine and dexamethasone showed significant improvement in pain response compared to the control groups for at least 7 days. The study demonstrated the clinical potential of these nanocomposite carriers for post-operative and neuropathic pain.

STATEMENT OF SIGNIFICANCE

Acute or chronic pain associated with musculoskeletal conditions is considered a major health issue, with healthcare costs totaling several billion dollars. The opioid crisis presents a pressing clinical need to develop alternative and effective approaches to treat musculoskeletal pain. The goal of this study was to develop a long-acting injectable anesthetic formulation which can sustain a local anesthetic effect for a prolonged time. This in turn could increase the quality of life and rehabilitation outcome of patients, and decrease opioid consumption. The developed injectable nanocomposite demonstrated the feasibility to achieve prolonged pain relief in a rat chronic constriction injury (CCI) model.

Precision-guided long-acting analgesia by Gel-immobilized bupivacaine-loaded microsphere

Peripheral nerve blockade (PNB) is a conventional strategy for the management of acute postoperative pain. However, the short duration of the associated analgesia and the potential systemic toxicity due to the low molecular weights of local anesthetics limit their application. Methods: An in situ forming injectable Gel-microsphere (Gel-MS) system consisting of PLGA-PEG-PLGA Gel (Gel) and Gel-immobilized bupivacaine-loaded microsphere (MS/BUP) was prepared for precision-guided long-acting analgesia. A series of in vitro characterizations, such as scanning electron microscopy, rheology analysis, confocal laser scanning microscopy, drug release, and erosion and degradation, were carried out. After that, the in vivo analgesia effect of the Gel-MS system, the immobilization effect of Gel on the MS, and biocompatibility of the system were evaluated using a sciatic nerve block model. Results: The BUP release from the Gel-MS system was regulated by both the inner MS and the outer Gel matrix, demonstrating sustained BUP release in vitro for several days without an initial burst release. More importantly, incorporation of the Gel immobilized the MS and hindered the diffusion of MS from the injection site because of its in situ property, which contributed to a high local drug concentration and prevented systemic side effects. In vivo, a single injection of Gel-MS/BUP allowed rats to maintain sensory and motor blockade significantly longer than treatment with MS/BUP (P < 0.01) or BUP-loaded Gel (Gel-BUP, P < 0.01). Histopathological results demonstrated the excellent biodegradability and biocompatibility of the Gel-MS system without neurotoxicity. Conclusion: This precision-guided long-acting analgesia, which provides an in situ and sustained release of BUP, is a promising strategy for long-acting analgesia, and could represent a potential alternative for clinical pain management.

Hollow Silica Nanoparticles Penetrate the Peripheral Nerve and Enhance the Nerve Blockade from Tetrodotoxin

The efficacy of tetrodotoxin (TTX), a very potent local anesthetic, is limited by its poor penetration through barriers to axonal surfaces. To address this issue, we encapsulated TTX in hollow silica nanoparticles (TTX-HSN) and injected them at the sciatic nerve in rats. TTX-HSN achieved an increased frequency of successful blocks, prolonged the duration of the block, and decreased the toxicity compared to free TTX. In animals injected with fluorescently labeled HSN, the imaging of frozen sections of nerve demonstrated that HSN could penetrate into nerve and that the penetrating ability of silica nanoparticles was highly size-dependent. These results demonstrated that HSN could deliver TTX into the nerve, enhancing efficacy while improving safety.

Systemic Safety of Liposomal Bupivacaine in Simultaneous Bilateral Total Knee Arthroplasty

BACKGROUND

Intraoperative periarticular injections (PAIs) with local anesthetic are an important component of multimodal pain control in total joint arthroplasty. Liposomal bupivacaine is an extended-release formulation of bupivacaine designed to provide extended pain relief, approved for use in a single surgical site. The systemic safety profile for use in simultaneous bilateral TKA (bTKA) with a full dose in each knee has not been evaluated. The purpose of this study was to determine the safety and pharmacokinetics of bilateral full-dose PAI liposomal bupivacaine in the blood collected in patients undergoing simultaneous bTKA.

METHODS

In this prospective study, patients had an identical PAI consisting of 20 cc of liposomal bupivacaine (266 mg), 30 cc of 0.25% bupivacaine (75 mg) with epinephrine, and 10 cc of normal saline injected into each knee during bTKA. Blood samples were collected at predefined intervals until patient discharge. No exogenous bupivacaine was administered. Pharmacokinetic evaluations were subsequently performed and compared to bupivacaine toxicity levels. Patients were monitored for adverse events related to anesthetic toxicity (cardiac and neurologic).

RESULTS

Fifteen patients (mean age, 60.7 years; range, 57-64 years) were enrolled in the study. The mean peak level (Cmax) was 0.8 μg/mL (range, 0.4-1.2 μg/mL). All patients were well below the reported systemic cardiac and toxicity levels reported as 2-4 μg/mL. There were no reported cardiac and neurotoxic events in any patients.

CONCLUSION

The use of full-dose PAI with liposomal bupivacaine placed into each knee during simultaneous bTKA is safe with systemic bupivacaine levels well below reported cardiac and neurotoxic levels.

Biotechnological and Pharmacological Applications of Biotoxins and Other Bioactive Molecules from Dinoflagellates

The long-lasting interest in bioactive molecules (namely toxins) produced by (microalga) dinoflagellates has risen in recent years. Exhibiting wide diversity and complexity, said compounds are well-recognized for their biological features, with great potential for use as pharmaceutical therapies and biological research probes. Unfortunately, provision of those compounds is still far from sufficient, especially in view of an increasing demand for preclinical testing. Despite the difficulties to establish dinoflagellate cultures and obtain reasonable productivities of such compounds, intensive research has permitted a number of advances in the field. This paper accordingly reviews the characteristics of some of the most important biotoxins (and other bioactive substances) produced by dinoflagellates. It also presents and discusses (to some length) the main advances pertaining to dinoflagellate production, from bench to large scale-with an emphasis on material published since the latest review available on the subject. Such advances encompass improvements in nutrient formulation and light supply as major operational conditions; they have permitted adaptation of classical designs, and aided the development of novel configurations for dinoflagellate growth-even though shearing-related issues remain a major challenge.

Enhanced Triggering of Local Anesthetic Particles by Photosensitization and Photothermal Effect Using a Common Wavelength

On-demand pain relief systems would be very helpful additions to the armamentarium of pain management. Near-infrared triggered drug delivery systems have demonstrated the potential to provide such care. However, challenges remain in making such systems as stimulus-sensitive as possible, to enhance depth of tissue penetration, repeatability of triggering, and safety. Here we developed liposomes containing the local anesthetic tetrodotoxin and also containing a photosensitizer and gold nanorods that were excitable at the same near-infrared wavelength. The combination of triggering mechanisms enhanced the photosensitivity and repeatability of the system in vitro when compared with liposomes with a single photoresponsive component. In vivo, on-demand local anesthesia could be induced with a low irradiance and short irradiation duration, and liposomes containing both photosensitizer and gold nanorods were more effective than those containing just one photoresponsive component. Tissue reaction was benign.