OnabotulinumtoxinA effects on trigeminal nociceptors

Animal Models of Chronic Migraine: From the Bench to Therapy

PURPOSE OF REVIEW

Chronic migraine is a disabling progressive disorder without effective management approaches. Animal models have been developed and used in chronic migraine research. However, there are several problems with existing models. Therefore, we aimed to summarize and analyze existing animal models to facilitate translation from basic to clinical.

RECENT FINDINGS

The most commonly used models are the inflammatory soup induction model and the nitric oxide donor induction model. In addition, KATP openers have also been used in model induction. Based on the above models, some molecular targets have been identified, such as glutamate receptors. However, each model has its shortcomings and characteristics, and there are still some common problems that need to be solved, such as spontaneous headache, evaluation criteria after model establishment, and identification methods. In this review, we summarized and highlighted the advantages and limitations of the currently commonly used animal models of chronic migraine with a special focus on drug discovery and current therapeutic strategies, and discussed the directions that can be worked on in the future.

Neurobiological mechanisms of botulinum neurotoxin-induced analgesia for neuropathic pain

Botulinum neurotoxins (BoNTs) are a family of neurotoxins produced by Clostridia and other bacteria that induce botulism. BoNTs are internalized into nerve terminals at the site of injection and cleave soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins to inhibit the vesicular release of neurotransmitters. BoNTs have been approved for multiple therapeutic applications, including the treatment of migraines. They have also shown efficacies for treating neuropathic pain, such as diabetic neuropathy, and postherpetic and trigeminal neuralgia. However, the mechanisms underlying BoNT-induced analgesia are not well understood. Peripherally administered BoNT is taken up by the nerve terminals and reduces the release of glutamate, calcitonin gene-related peptide, and substance P, which decreases neurogenic inflammation in the periphery. BoNT is retrogradely transported to sensory ganglia and central terminals in a microtubule-dependent manner. BoNTs decrease the expression of pronociceptive genes (ion channels or cytokines) from sensory ganglia and the release of neurotransmitters and neuropeptides from primary afferent central terminals, which likely leads to decreased central sensitization in the dorsal horn of the spinal cord or trigeminal nucleus. BoNT-induced analgesia is abolished after capsaicin-induced denervation of transient receptor potential vanilloid 1 (TRPV1)-expressing afferents or the knockout of substance P or the neurokinin-1 receptor. Although peripheral administration of BoNT leads to changes in the central nervous system (e.g., decreased phosphorylation of glutamate receptors in second-order neurons, reduced activation of microglia, contralateral localization, and cortical reorganization), whether such changes are secondary to changes in primary afferents or directly mediated by trans-synaptic, transcytotic, or the hematogenous transport of BoNT is controversial. To enhance their therapeutic potential, BoNTs engineered for specific targeting of nociceptive pathways have been developed to treat chronic pain. Further mechanistic studies on BoNT-induced analgesia can enhance the application of native or engineered BoNTs for neuropathic pain treatment with improved safety and efficacy.

The impact of the migraine treatment onabotulinumtoxinA on inflammatory and pain responses: Insights from an animal model

OBJECTIVE

Migraine, a prevalent and debilitating disease, involves complex pathophysiology possibly including inflammation and heightened pain sensitivity. The current study utilized the complete Freund's adjuvant (CFA) model of inflammation, with onabotulinumtoxinA (BoNT/A) as a treatment of interest due to its use in clinical migraine management. Using an animal model, the study sought to investigate the role of BoNT/A in modulating CFA-induced inflammation, alterations in pain sensitivity, and the regulation of calcitonin gene-related peptide (CGRP) release. Further, we aimed to assess the changes in SNAP-25 through western blot analysis to gain insights into the mechanistic action of BoNT/A.

METHODS

BoNT/A or control was administered subcutaneously at the periorbital region of rats 3 days before the induction of inflammation using CFA. Periorbital mechanical sensitivity was assessed post-inflammation, and alterations in CGRP release were evaluated. Changes in SNAP-25 levels were determined using western blot analysis.

RESULTS

Upon CFA-induced inflammation, there was a marked increase in periorbital mechanical sensitivity, with the inflammation side showing increased sensitivity compared to other periorbital areas. BoNT/A did decrease the withdrawal thresholds in the electronic von Frey test. Despite not being able to observe differences in pain thresholds or CGRP release, BoNT/A reduced baseline release under CFA inflamed conditions. Analysis of SNAP-25 levels in the trigeminal ganglion revealed both intact and cleaved forms that were notably elevated in BoNT/A-treated animals. These findings, derived from western blot analysis, suggest an effect on neurotransmitter release.

CONCLUSION

Our investigation highlights the role of BoNT/A in reducing baseline CGRP in the context of inflammation and its involvement in SNAP-25 cleavage. In contrast, BoNT/A did not appear to alter facial pain sensitivity induced by inflammation, suggesting that mechanisms other than baseline CGRP could be implicated in the elevated thresholds in the CFA model.

Beyond Pain: The Effects of OnabotulinumtoxinA Therapy on Sensitization and Interictal Symptoms in Chronic Migraine

Chronic migraine is a disease with a high burden on patients from both a working and quality of life point of view. The pathophysiology of this subtype of migraine is due to several factors, such as medication overuse. Nevertheless, the detrimental recurring of headache attacks with central and peripheral sensitization plays a central role and explains some additional symptoms complained about by these patients even in the interictal phase. OnabotulinumtoxinA is a therapy indicated for chronic migraine since it has proven to reduce peripheral sensitization, showing even efficacy on central symptoms. The aim of this narrative review is to present the current evidence regarding the effect of OnabotulinumtoxinA on sensitization and interictal symptoms.

Intravesical Botulinum Toxin Injection Plus Hydrodistention Is More Effective in Patients with Bladder Pain-Predominant Interstitial Cystitis/Bladder Pain Syndrome

Intravesical botulinum toxin A (BoNT-A) injections are included in the interstitial cystitis/bladder pain syndrome (IC/BPS) treatment guidelines. However, the IC phenotype suitable for treatment with BoNT-A has not been clarified. Therefore, we identified the factors influencing treatment outcomes for intravesical BoNT-A injections in patients with non-Hunner IC/BPS (NHIC). This retrospective study included patients with NHIC who underwent 100 U BoNT-A intravesical injections over the past two decades. Six months after treatment, treatment outcomes were assessed using the Global Response Assessment (GRA). Outcome endpoints included GRA, clinical symptoms, urodynamic parameters, urine biomarkers, and the identification of factors contributing to satisfactory treatment outcomes. The study included 220 patients with NHIC (42 men, 178 women). The satisfactory group (n = 96, 44%) had significantly higher pain severity scores and IC symptoms index, larger maximum bladder capacity (MBC), and lower 8-isoprostane levels at baseline. Logistic regression revealed that larger MBC (≥760 mL) and bladder pain predominance were associated with satisfactory outcomes after BoNT-A injection. Subjective parameters and pain severity scores improved significantly in patients with bladder pain-predominant IC/BPS after BoNT-A injection. Thus, NHIC patients with bladder or pelvic pain are more likely to experience satisfactory outcomes following intravesical BoNT-A injections.

Method for cryopreservation of trigeminal ganglion for establishing primary cultures of neurons and glia

BACKGROUND

Primary neuronal cultures are used to elucidate cellular and molecular mechanisms involved in disease pathology and modulation by pharmaceuticals and nutraceuticals, and to identify novel therapeutic targets. However, preparation of primary neuronal cultures from rodent embryos is labor-intensive, and it can be difficult to produce high-quality consistent cultures. To overcome these issues, cryopreservation can be used to obtain standardized, high-quality stocks of neuronal cultures.

NEW METHOD

In this study, we present a simplified cryopreservation method for rodent primary trigeminal ganglion neurons and glia from Sprague-Dawley neonates, using a 90:10 (v/v) fetal bovine serum/dimethyl sulfoxide cell freezing medium.

RESULTS

Cryopreserved trigeminal ganglion cells stored for up to one year in liquid nitrogen exhibited similar neuronal and glial cell morphology to fresh cultures and retained high cell viability. Proteins implicated in inflammation and pain signaling were expressed in agreement with the reported subcellular localization. Additionally, both neurons and glial cells exhibited an increase in intracellular calcium levels in response to a depolarizing stimulus. Cryopreserved cells were also transiently transfected with reporter genes.

COMPARISON WITH EXISTING METHODS

Our method is simple, does not require special reagents or equipment, will save time and money, increase flexibility in study design, and produce consistent cultures.

CONCLUSIONS

This method for the preparation and cryopreservation of trigeminal ganglia results in primary cultures of neurons and glia similar in viability and morphology to fresh preparations that could be utilized for biochemical, cellular, and molecular studies, increase reproducibility, and save laboratory resources.

A look at the future-new BoNTs and delivery systems in development: What it could mean in the clinic

Despite the expanding clinical utility of botulinum neurotoxins, there remain problems to be solved for attaining the best outcome. The efficacy and safety need to be reconsidered for commercially available preparations all derived from subtype A1 or B1. Emerging new toxins include A2 or A6 subtypes or engineered toxins with less spread, more potency, longer durations of action, less antigenicity and better safety profile than currently used preparations. Non-toxic BoNTs with a few amino acid replacements of the light chain (LC) may have a role as a drug-delivery system if the toxicity is abolished entirely. At present, efficacy of these BoNTs in animal botulism was demonstrated.