Emulsion-induced polymersomes taming tetrodotoxin for prolonged duration local anesthesia

Tetrodotoxin Delivery Pen Safely Uses Potent Natural Neurotoxin to Manage Severe Cutaneous Pain

Clinically available therapies often inadequately address severe chronic cutaneous pain due to short anesthetic duration, insufficient intensity, or side effects. This study introduces a pen device delivering tetrodotoxin (TTX), a potent neurotoxin targeting nerve voltage-gated sodium channels, as a safe and effective topical anesthetic to treat severe chronic cutaneous pain. Chemical permeation enhancers, such as sodium dodecyl sulfate (SDS) and limonene (LIM), are incorporated to enhance TTX skin permeability. The device ensures precise TTX dosing down to the nanogram level, essential to avoid TTX overdose. In rats, the pen device treatment produces TTX-dose-dependent anesthetic effectiveness. An administration of 900 ng of TTX with SDS and LIM to the rat back skin produces a 393.25% increase (measurement limit) in the nociceptive skin pressure threshold, and the hypoalgesia lasts for 11.25 h, outperforming bupivacaine (28 µg), of which are 25.24% and under 1 h. Moreover, the pen device provides on-demand therapy for multiple treatments, consistently achieving prolonged anesthesia over ten sessions (1 treatment per day) without noted toxicity. Furthermore, a single topical administration of 16 µg of TTX exhibits no TTX-related toxicity in rats. The TTX delivery pen paves the way for clinical trials, offering a promising solution for severe cutaneous pain.

Molecular Dynamics Insights into Peptide-Based Tetrodotoxin Delivery Nanostructures

Tetrodotoxin (TTX), a potent Site-1 sodium channel blocker (S1SCB), offers highly effective local anesthetic properties with minimal addiction potential. To fully leverage TTX's capabilities as a local anesthetic, it is crucial to develop a drug delivery system that balances its systemic toxicity with its therapeutic efficacy. Recent studies have shown that peptide mixtures, derived from fragments of Site-1 sodium channel proteins and enhanced with hydrophobic tails (designated MP1 and MP2), can self-assemble into nanostructures that exhibit remarkable sustained-release capabilities for TTX. Despite the profound impact that the addition of a hydrophobic tail has on altering the release behavior of the original peptides, the atomic-level interactions and mechanisms underlying this phenomenon remain poorly understood. In this study, a combination of ColabFold and molecular dynamics (MD) simulations were used to investigate the binding interactions between TTX and the nanostructures formed by MP1 and MP2 at an atomic level. Our findings agree with experimental observations and indicate that the MP1/MP2 nanostructure demonstrates greater stability and higher binding affinity for TTX compared to their non-modified counterparts, P1 and P2. The analysis of the simulations revealed that charged amino acids, specifically aspartic acid (ASP) and glutamic acid (GLU), on the peptides are crucial for strong TTX binding and serve as the primary functional sites. Additionally, the stability of the nanostructure significantly affects TTX binding affinity, elucidating why P1, P2, MP1, and MP2 exhibit different binding capabilities despite containing identical charged residues. The results reported here may provide fundamental information to drive future research and enhance the development of TTX-based drug delivery systems.

Tetrodotoxin: The State-of-the-Art Progress in Characterization, Detection, Biosynthesis, and Transport Enrichment

Tetrodotoxin (TTX) is a neurotoxin that binds to sodium channels and blocks sodium conduction. Importantly, TTX has been increasingly detected in edible aquatic organisms. Because of this and the lack of specific antidotes, TTX poisoning is now a major threat to public health. However, it is of note that ultra-low dose TTX is an excellent analgesic with great medicinal value. These contradictory effects highlight the need for further research to elucidate the impacts and functional mechanisms of TTX. This review summarizes the latest research progress in relation to TTX sources, analogs, mechanisms of action, detection methods, poisoning symptoms, therapeutic options, biosynthesis pathways, and mechanisms of transport and accumulation in pufferfish. This review also provides a theoretical basis for reducing the poisoning risks associated with TTX and for establishing an effective system for its use and management to ensure the safety of fisheries and human health.

Capsaicin-Loaded Melanin Nanoparticles for Long-Lasting Nociceptive-Selective Nerve Blockade

Clinically used amino-ester and amino-amide local anesthetics, such as bupivacaine and lidocaine, face two primary challenges: inadequate duration of action and nonselective action on both sensory and motor neurons, resulting in motor function loss alongside pain relief. In this work, we developed capsaicin-loaded melanin nanoparticles (Cap-MNPs) to address these two challenges. Capsaicin selectively acts on sensory neurons without affecting motor neurons, thereby achieving nociceptive-selective nerve blockade. Melanin is known for its exceptional biocompatibility, biodegradability, and abundance in pigmented human tissue. Melanin's inherent chemical structure and hydrophobic nature enable the encapsulation and sustained release of amino-ester and amino-amide local anesthetics with aromatic rings through π-π interactions and hydrophobic interactions. The drug loading efficiency of Cap-MNPs was 82.99 ± 1.55%, the drug loading capacity was 67.47 ± 4.24%, and capsaicin was continuously released for more than 360 h. In rats, a single injection of Cap-MNPs containing 8.04 mg of capsaicin produced a sciatic sensory nerve block lasting for 6 h without causing any local toxicity and capsaicin-related systemic toxicity. Cap-MNPs show promise as clinically useful therapeutics for pain management.

Hydration-induced Void-containing Hydrogels for Encapsulation and Sustained Release of Small Hydrophilic Molecules

Efficient encapsulation and sustained release of small hydrophilic molecules from traditional hydrogel systems have been challenging due to the large mesh size of 3D networks and high water content. Furthermore, the encapsulated molecules are prone to early release from the hydrogel prior to use, resulting in a short shelf life of the formulation. Here, we present a hydration-induced void-containing hydrogel (HVH) based on hyperbranched polyglycerol-poly(propylene oxide)-hyperbranched polyglycerol (HPG-PPG-HPG) as a robust and efficient delivery system for small hydrophilic molecules. Specifically, after the HPG-PPG-HPG is incubated overnight at 4 °C in the drug solution, it is hydrated into a hydrogel containing micron-sized voids, which could encapsulate hydrophilic drugs and achieve 100% drug encapsulation efficiency. In addition, the voids are surrounded by a densely packed polymer matrix, which restricts drug transport to achieve sustained drug release. The hydrogel/drug formulation can be stored for several months without changing the drug encapsulation and release properties. HVH hydrogels are injectable due to shear thinning properties. In rats, a single injection of the HPG-PPG-HPG hydrogel containing 8 μg of tetrodotoxin (TTX) produced sciatic nerve block lasting up to 10 hours without any TTX-related systemic toxicity nor local toxicity to nerves and muscles.