Galcanezumab modulates Capsaicin-induced C-fiber reactivity

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.

Double-blind, randomized, placebo-controlled study to evaluate erenumab-specific central effects: an fMRI study

OBJECTIVE

Given the findings of central effects of erenumab in the literature, we aimed to conduct a rigorous placebo-controlled, double-blind, randomized study to elucidate whether the observed changes are directly attributable to the drug.

METHODS

We recruited 44 patients with migraine, randomly assigning them to either the erenumab 70 mg or the placebo group. 40 patients underwent fMRI scanning using a trigeminal nociceptive paradigm both, pre- and four weeks post-treatment. Participants kept a headache diary throughout the whole study period of two months in total. A clinical response was defined as a ≥30% reduction in headache frequency at follow-up. Details of this study have been preregistered in the open science framework: https://osf.io/ygf3t .

RESULTS

Seven participants of the verum group (n=33.33%) and 4 of the placebo group (21.05%) experienced improvements in migraine activity, characterized by a minimum of 30% reduction in monthly headache frequency compared to baseline. The imaging data show an interaction between the verum medication and the response. Whilst numbers were too small for individual analyses (Verum vs. Placebo and Responder vs. Non-Responder), the variance-weighted analysis (Verum vs Placebo, scan before vs after weighted for response) revealed specific decrease in thalamic, opercular and putamen activity.

INTERPRETATION

The central effects of erenumab could be reproduced in a placebo randomized design, further confirming its central role in migraine modulation. The mechanism, whether direct or secondary to peripheral mode of action, needs further exploration. It is important to note that the response rate to erenumab 70mg in this study was not as substantial as anticipated in 2019, when this study was planned. This resulted in a too small sample size for a subgroup analysis based on the responder status was associated with both the verum drug and the relative reduction in headache days.

Characterization of trigeminal C-fiber reactivity through capsaicin-induced release of calcitonin gene-related peptide

OBJECTIVE

We hypothesized that the response of trigeminal dermal blood flow (DBF) in the trigeminal system and consecutive expansion of flare response to capsaicin would differ from the somatosensory system (arm). We also investigated whether there are differences between patients with migraine and healthy controls (HC).

BACKGROUND

Functional differences between the trigeminal and extracephalic somatosensory systems may partly explain the susceptibility for headaches in patients with migraine. Capsaicin-induced activation of nociceptive C-fibers in the skin is mainly mediated by calcitonin gene-related peptide (CGRP) and induces cutaneous vessel dilatation and flare response.

METHODS

Female patients with migraine (n = 38) and age-matched HC (n = 35) underwent DBF measurement at baseline and after topical capsaicin administration using laser speckle imaging. DBF before and after capsaicin stimulation was analyzed over ophthalmic nerve/maxillary nerve/mandibular nerve (V1/V2/V3) dermatomes and the forearm as an extracephalic control.

RESULTS

Capsaicin-induced DBF increased more in the trigeminal dermatomes than on the forearm. The V1 dermatome showed a smaller increase of DBF in patients with migraine compared to HC.

CONCLUSION

Our results suggest that the trigeminovascular system reacts differently from extracephalic areas, which may explain the trigeminal susceptibility to CGRP-mediated pain attacks. By demonstrating a different reactivity of the V1 dermatome in patients with migraine, our finding suggests that the first trigeminal branch is functionally different from the second and third branches; however, only in patients with migraine.