From micro- to nanostructured implantable device for local anesthetic delivery

Highly Efficient Loading of Procaine on Water-Soluble Carbon Dots toward Long-Acting Anesthesia

Safe and efficient local anesthetic delivery carriers are crucial for long-term anesthesia and analgesics in clinical treatment. But currently, most of the local anesthetic carriers still have some disadvantages such as low drug-loading capacity, drug leakage, and potential side effects. Here, we report red-emissive carbon dots (Cys-CDs) synthesized by choosing cysteine and citric acid as precursors, which contain a large and intact sp2-domain with rich hydrophilic groups around the edge. The special structure of Cys-CDs is conducive to the efficient loading of procaine (PrC) via strong π-π stacking interactions. Based on the strong noncovalent interactions between them, the PrC loaded on Cys-CDs achieved slow release in vitro and had a long-lasting nerve blocking effect in vivo, which is 4-fold more than that of free PrC. More importantly, PrC/Cys-CDs do not cause any toxicity and inflammation during treatment owing to slow release of PrC and good water solubility of Cys-CDs, thus demonstrating the potential clinical application of CDs in long-lasting analgesia.

Recent Research Advances in Nano-Based Drug Delivery Systems for Local Anesthetics

From a clinical perspective, local anesthetics have rather widespread application in regional blockade for surgery, postoperative analgesia, acute/chronic pain control, and even cancer treatments. However, a number of disadvantages are associated with traditional local anesthetic agents as well as routine drug delivery administration ways, such as neurotoxicity, short half-time, and non-sustained release, thereby limiting their application in clinical practice. Successful characterization of drug delivery systems (DDSs) for individual local anesthetic agents can support to achieve more efficient drug release and prolonged duration of action with reduced systemic toxicity. Different types of DDSs involving various carriers have been examined, including micromaterials, nanomaterials, and cyclodextrin. Among them, nanotechnology-based delivery approaches have significantly developed in the last decade due to the low systemic toxicity and the greater efficacy of non-conventional local anesthetics. Multiple nanosized materials, including polymeric, lipid (solid lipid nanoparticles, nanostructured lipid carriers, and nanoemulsions), metallic, inorganic non-metallic, and hybrid nanoparticles, offer a safe, localized, and long-acting solution for pain management and tumor therapy. This review provides a brief synopsis of different nano-based DDSs for local anesthetics with variable sizes and structural morphology, such as nanocapsules and nanospheres. Recent original research utilizing nanotechnology-based delivery systems is particularly discussed, and the progress and strengths of these DDSs are highlighted. A specific focus of this review is the comparison of various nano-based DDSs for local anesthetics, which can offer additional indications for their further improvement. All in all, nano-based DDSs with unique advantages provide a novel direction for the development of safer and more effective local anesthetic formulations.

Using Chitosan-Coated Polymeric Nanoparticles-Thermosensitive Hydrogels in association with Limonene as Skin Drug Delivery Strategy

Topical delivery of local anesthetics (LAs) is commonly used to decrease painful sensations, block pain throughout procedures, and alleviate pain after surgery. Dermal and/or transdermal delivery of LAs has other advantages, such as sustained drug delivery and decreased systemic adverse effects. This study reports the development of poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles coated with chitosan for the sustained release and topicality of benzocaine (BZC) and topical delivery. BZC PLGA nanoparticles or nonencapsulated drugs were further incorporated into Poloxamer hydrogels (Pluronic™ F-127). The nanoparticles showed a mean diameter of 380 ± 4 nm, positive zeta potential after coating with chitosan (23.3 ± 1.7 mV), and high encapsulation efficiency (96.7 ± 0.02%). Cellular viability greater than 70% for both fibroblasts and keratinocytes was observed after treatment with nanoparticles, which is in accordance with the preconized guidelines for biomedical devices and delivery systems. Both the nanoparticles and hydrogels were able to modulate BZC delivery and increase drug permeation when compared to the nonencapsulated drug. Furthermore, the incorporation of limonene into hydrogels containing BZC-loaded nanoparticles increased the BZC permeation rates. Non-Newtonian and pseudoplastic behaviors were observed for all hydrogel nanoformulations with or without nanoparticles. These results demonstrate that the hydrogel-nanoparticle hybrids could be a promising delivery system for prolonged local anesthetic therapy.

Strontium-loaded titanium implant with rough surface modulates osseointegration by changing sfrp4 in canonical and noncanonical Wnt signaling pathways

A rough morphology and strontium can activate the Wnt pathway to regulate bone mesenchymal stem cells (rBMSCs) osteogenic differentiation, but the mechanism remains unclear. We constructed smooth Ti (ST) surfaces, rough Ti (RT) surfaces subjected to hydrofluoric acid etching, strontium-loaded smooth Ti (ST-Sr) surfaces subjected to magnetron sputtering, and rough strontium-loaded Ti (RT-Sr) surfaces. We systematically studied the in vitro osteogenic differentiation of rBMSCs on these four surfaces by alkaline phosphatase measurement, Alizarin Red staining and PCR. We also investigated whether crosstalk of the canonical and noncanonical Wnt signaling pathways regulated by sfrp4, which is an inhibitor of canonical and noncanonical Wnt, is the underlying mechanism via PCR on rBMSCs in different stages of osteogenic differentiation. We confirmed the effect of sfrp4 through an in vivo sfrp4-siRNA test. The in vitro osteogenic differentiation of rBMSCs decreased in the order RT-Sr, RT, ST-Sr, and ST. Regarding the mechanism, rough morphology and strontium both enhanced the canonical Wnt pathway to promote osseointegration. Additionally, rough morphology can inhibit sfrp4 to activate the noncanonical Wnt pathway, and then, the activated noncanonical Wnt pathway can suppress the canonical Wnt pathway at the early stage of osteogenic differentiation. Strontium continuously enhanced sfrp4 to inhibit the canonical Wnt pathway instead of activating the noncanonical Wnt pathway. Interestingly, the effect of rough morphology on sfrp4 changed from inhibition to enhancement, and the enhancing effect of strontium on sfrp4 was gradually attenuated. The results of the in vivo sfrp4-siRNA test showed that osseointegration decreased in the order RT-Sr, RT-Sr-siRNA, and ST. Our results suggest that the lack of sfrp4 could suppress osseointegration, indicating that sfrp4 acts as a crucial regulatory molecule for the canonical and noncanonical Wnt pathways during the response of rBMSCs to rough morphology and strontium.

Combination therapy with ropivacaine-loaded liposomes and nutrient deprivation for simultaneous cancer therapy and cancer pain relief

Autophagy allows cancer cells to respond changes in nutrient status by degrading and recycling non-essential intracellular contents. Inhibition of autophagy combined with nutrient deprivation is an effective strategy to treat cancer. Pain is a primary determinant of poor quality of life in advanced cancer patients, but there is currently no satisfactory treatment. In addition, effective treatment of cancer does not efficiently relieve cancer pain, but may increase pain in many cases. Hence, few studies focus on simultaneous cancer therapy and pain relief, and made this situation even worse.

Method: Ropivacaine was loaded into tumor-active targeted liposomes. The cytotoxicity of ropivacaine-based combination therapy in B16 and HeLa cells were tested. Moreover, a mice model of cancer pain which was induced by inoculation of melanoma near the sciatic nerve was constructed to assess the cancer suppression and pain relief effects of ropivacaine-based combination therapy.

Results: Ropivacaine and ropivacaine-loaded liposomes (Rop-DPRL) were novelly found to damage autophagic degradation. Replicated administration of Rop-DPRL and calorie restriction (CR) could efficiently repress the development of tumor. In addition, administration of Rop-DPRL could relieve cancer pain with its own analgestic ability in a short duration, while repeated administration of Rop-DPRL and CR resulted in continuous alleviation of cancer pain through reduction of VEGF-A levels in advanced cancer mice. Further, dual inhibition of phosphorylation of STAT3 at Tyr705 and Ser727 by Rop-DPRL and CR contribute to the reduction of VEGF-A.

Conclusion: Combination therapy with Rop-DPRL and nutrient deprivation simultaneously suppresses cancer growth and relieves cancer pain.

Advances of Nano-Structured Extended-Release Local Anesthetics

Extended-release local anesthetics (LAs) have drawn increasing attention with their promising role in improving analgesia and reducing adverse events of LAs. Nano-structured carriers such as liposomes and polymersomes optimally meet the demands of/for extended-release, and have been utilized in drug delivery over decades and showed satisfactory results with extended-release. Based on mature technology of liposomes, EXPAREL, the first approved liposomal LA loaded with bupivacaine, has seen its success in an extended-release form. At the same time, polymersomes has advances over liposomes with complementary profiles, which inspires the emergence of hybrid carriers. This article summarized the recent research successes on nano-structured extended-release LAs, of which liposomal and polymeric are mainstream systems. Furthermore, with continual optimization, drug delivery systems carry properties beyond simple transportation, such as specificity and responsiveness. In the near future, we may achieve targeted delivery and controlled-release properties to satisfy various analgesic requirements.

In vitro and in vivo quantification of chloroprocaine release from an implantable device in a piglet postoperative pain model

Background

The pharmacokinetic properties and clinical advantages of the local anesthetic chloroprocaine are well known. Here, we studied the pharmacokinetic profile of a new hydrogel device loaded with chloroprocaine to investigate the potential advantages of this new strategy for postoperative pain (POP) relief.

Materials and methods

We performed both in vitro and in vivo analyses by considering plasma samples of four piglets receiving slow-release chloroprocaine. To quantify chloroprocaine and its inactive metabolite 4-amino-2-chlorobenzoic acid (ACBA), a HPLC–tandem mass spectrometry (HPLC-MS/MS) analytical method was used. Serial blood samples were collected over 108 hours, according to the exposure time to the device.

Results

Chloroprocaine was consistently found to be below the lower limit of quantification, even though a well-defined peak was observed in every chromatogram at an unexpected retention time. Concerning ACBA, we found detectable plasma concentrations between T₀ and T_12h, with a maximum plasma concentration (C_max) observed 3 hours after the device application. In the in vitro analyses, the nanogel remained in contact with plasma at 37°C for 90 minutes, 3 hours, 1 day, and 7 days. Chloroprocaine C_max was identified 1 day following exposure and C_min after 7 days, respectively. Additionally, ACBA reached the C_max following 7 days of exposure.

Conclusion

A thorough review of the literature indicates that this is the first study analyzing both in vivo and in vitro pharmacokinetic profiles of a chloroprocaine hydrogel device and is considered as a pilot study on the feasibility of including this approach to the management of POP.

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.

Nanoparticles administered intrapericardially enhance payload myocardial distribution and retention

Pharmacological therapies for cardiovascular diseases are limited by short-term pharmacokinetics and extra-cardiac adverse effects. Improving delivery selectivity specifically to the heart, wherein therapeutic drug levels can be maintained over time, is highly desirable. Nanoparticle (NP)-based pericardial drug delivery could provide a strategy to concentrate therapeutics within a unique, cardiac-restricted compartment to allow sustained drug penetration into the myocardium. Our objective was to explore the kinetics of myocardial penetration and retention after pericardial NP drug delivery. Fluorescently-tagged poly(lactic-co-glycolic acid) (PLGA) NPs were loaded with BODIPY, a fluorophore, and percutaneously administered into the pericardium via subxiphoid puncture in rabbits. At distinct timepoints hearts were examined for presence of NPs and BODIPY. PLGA NPs were found non-uniformly distributed on the epicardium following pericardial administration, displaying a half-life of ~2.5days in the heart. While NPs were mostly confined to epicardial layers, BODIPY was capable of penetrating into the myocardium, resulting in a transmural gradient. The distinct architecture and physiology of the different regions of the heart influenced BODIPY distribution, with fluorophore penetrating more readily into atria than ventricles. BODIPY proved to have a long-term presence within the heart, with a half-life of ~7days. Our findings demonstrate the potential of utilizing the pericardial space as a sustained drug-eluting reservoir through the application of nanoparticle-based drug delivery, opening several exciting avenues for selective and prolonged cardiac therapeutics.