Novel αO-conotoxin GeXIVA[1,2] Nonaddictive Analgesic with Pharmacokinetic Modelling-Based Mechanistic Assessment

BrSPR-20-P1 peptide isolated from Brevibacillus sp. developed into liposomal hydrogel as a potential topical antimicrobial agent

A novel BrSPR-20-P1 antimicrobial peptide (P1-AMP; NH2-VVVNVLVKVLPPPVV-COOH) isolated from Brevibacillus sp. SPR-20 was encapsulated in a liposome containing varying proportions of l-α-phosphatidylcholine (PC) and cholesterol (CH). P1-AMP liposomes were incorporated into a chitosan hydrogel to achieve a peptide concentration of 0.02%. P1-AMP has been tested for its antibacterial and in vitro wound healing activities. The physicochemical characteristics of liposomes and hydrogel were investigated, including in vitro drug release, permeability, cell toxicity, antimicrobial activities, and stability studies. P1-AMP showed higher antimicrobial and wound-healing activities than the negative control. A toxicity test of P1-AMP in keratinocyte cell lines revealed cell viability of 100% at a concentration range of 1.96-1000 μg mL-1. The empty liposomes exhibited an average particle size ranging from 324.5 ± 8.6 to 1823.7 ± 288.2 nm. The size range of P1-AMP liposomes was 378.6 ± 14.0 to 2363.0 ± 255.6 nm. The zeta potential of the blank liposome ranged from -40.43 ± 2.51 to -60.17 ± 0.93 mV and it decreased to -57.33 ± 0.72 to -70.33 ± 0.15 mV of the liposome loaded with peptide. SEM images showed liposomes were ovoid spheres with smooth surfaces. The chosen formulation, composed of PC to CH in an 18 : 1 ratio (formulation F3), had the highest entrapment effectiveness with small particle size and possessed an acceptable zeta potential. The developed P1-AMP liposome-loaded hydrogels exhibited a yellowish-clear appearance with a viscosity of 758.0 ± 149.8 cPs. The P1-AMP was rapidly released from the P1-AMP-loaded liposome hydrogel formulation. The P1-AMP-loaded liposome showed high permeability compared to P1-AMP alone or P1-AMP in hydrogel without the incorporation of liposomes. The minimum inhibitory concentration (MIC) against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) of P1-AMP-loaded liposome hydrogel was 2 μg mL-1, equivalent to P1-AMP. It completely killed S. aureus at 10× and 5× MIC after 6 and 12 h of incubation, respectively. The formulation did not induce cytotoxicity to the tested keratinocyte cell and remained stable for at least 6 months under the studied conditions.

Aspartic acid mutagenesis of αO-Conotoxin GeXIVA isomers reveals arginine residues crucial for inhibition of the α9α10 nicotinic acetylcholine receptor

The two most active disulfide bond isomers of the analgesic αO-conotoxin GeXIVA, namely GeXIVA[1, 2] and GeXIVA[1, 4], were subjected to Asp-scanning mutagenesis to determine the key amino acid residues for activity at the rat α9α10 nicotinic acetylcholine receptor (nAChR). These studies revealed the key role of arginine residues for the activity of GeXIVA isomers towards the α9α10 nAChR. Based on these results, additional analogues with 2-4 mutations were designed and tested. The analogues [T1A,D14A,V28K]GeXIVA[1, 2] and [D14A,I23A,V28K]GeXIVA[1, 4] were developed and showed sub-nanomolar activity for the α9α10 nAChR with IC50 values of 0.79 and 0.38 nM. The latter analogue had exceptional selectivity for the α9α10 receptor subtype over other nAChR subtypes and can be considered as a drug candidate for further development. Molecular dynamics of receptor-ligand complexes allowed us to make deductions about the possible causes of increases in the affinity of key GeXIVA[1, 4] mutants for the α9α10 nAChR.

Dual Antagonism of α9α10 nAChR and GABAB Receptor-Coupled CaV2.2 Channels by an Analgesic αO-Conotoxin Analogue

Pain severely affects the physical and mental health of patients. The need to develop nonopioid analgesic drugs to meet medical demands is urgent. In this study, we designed a truncated analogue of αO-conotoxin, named GeX-2, based on disulfide-bond deletion and sequence truncation. GeX-2 retained the potency of its parent peptide at the human α9α10 nAChR and exhibited potent inhibitory activity at CaV2.2 channels via activation of the GABAB receptor (GABABR). Importantly, GeX-2 significantly alleviated pain in the rat model of chronic constriction injury. The dual inhibition of GeX-2 at both α9α10 nAChRs and CaV2.2 channels is speculated to synergistically mediate the potent analgesic effects. Results from site-directed mutagenesis assay and computational modeling suggest that GeX-2 preferentially interacts with the α10(+)α10(-) binding site of α9α10 nAChR and favorably binds to the top region of the GABABR2 subunit. The study offers vital insights into the molecular action mechanism of GeX-2, demonstrating its potential as a novel nonopioid analgesic.

αO-Conotoxin GeXIVA[1,2] Reduced Neuropathic Pain and Changed Gene Expression in Chronic Oxaliplatin-Induced Neuropathy Mice Model

Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting painful neuropathy that occurs commonly during cancer management, which often leads to the discontinuation of medication. Previous studies suggest that the α9α10 nicotinic acetylcholine receptor (nAChR)-specific antagonist αO-conotoxin GeXIVA[1,2] is effective in CIPN models; however, the related mechanisms remain unclear. Here, we analyzed the preventive effect of GeXIVA[1,2] on neuropathic pain in the long-term oxaliplatin injection-induced CIPN model. At the end of treatment, lumbar (L4-L6) spinal cord was extracted, and RNA sequencing and bioinformatic analysis were performed to investigate the potential genes and pathways related to CIPN and GeXIVA[1,2]. GeXIVA[1,2] inhibited the development of mechanical allodynia induced by chronic oxaliplatin treatment. Repeated injections of GeXIVA[1,2] for 3 weeks had no effect on the mice's normal pain threshold or locomotor activity and anxiety-like behavior, as evaluated in the open field test (OFT) and elevated plus maze (EPM). Our RNA sequencing results identified 209 differentially expressed genes (DEGs) in the CIPN model, and simultaneously injecting GeXIVA[1,2] with oxaliplatin altered 53 of the identified DEGs. These reverted genes were significantly enriched in immune-related pathways represented by the cytokine-cytokine receptor interaction pathway. Our findings suggest that GeXIVA[1,2] could be a potential therapeutic compound for chronic oxaliplatin-induced CIPN management.

α7- and α9-Containing Nicotinic Acetylcholine Receptors in the Functioning of Immune System and in Pain

Nicotinic acetylcholine receptors (nAChRs) present as many different subtypes in the nervous and immune systems, muscles and on the cells of other organs. In the immune system, inflammation is regulated via the vagus nerve through the activation of the non-neuronal α7 nAChR subtype, affecting the production of cytokines. The analgesic properties of α7 nAChR-selective compounds are mostly based on the activation of the cholinergic anti-inflammatory pathway. The molecular mechanism of neuropathic pain relief mediated by the inhibition of α9-containing nAChRs is not fully understood yet, but the role of immune factors in this process is becoming evident. To obtain appropriate drugs, a search of selective agonists, antagonists and modulators of α7- and α9-containing nAChRs is underway. The naturally occurring three-finger snake α-neurotoxins and mammalian Ly6/uPAR proteins, as well as neurotoxic peptides α-conotoxins, are not only sophisticated tools in research on nAChRs but are also considered as potential medicines. In particular, the inhibition of the α9-containing nAChRs by α-conotoxins may be a pathway to alleviate neuropathic pain. nAChRs are involved in the inflammation processes during AIDS and other viral infections; thus they can also be means used in drug design. In this review, we discuss the role of α7- and α9-containing nAChRs in the immune processes and in pain.