Abstract
Objective: Calcitonin gene related peptide (CGRP) is a central mediator in migraine and can trigger attacks in susceptible individuals. Therapies targeting CGRP or its receptor provide clinical benefit, but treatment responses vary. This suggests that local factors regulating CGRP availability and signalling within migraine relevant tissues may influence its biological effects. The extent and functional relevance of CGRP degradation at the dura mater, including possible effects on biomarker detection, remain insufficiently characterised.
Methods: Proteomic analyses were used to identify human αCGRP (hαCGRP) degradation fragments generated in rat meningeal preparations. Functional properties of full-length hαCGRP and selected degradation fragments were assessed at the dura mater, in isolated arteries, in mast cell degranulation assays, and at CGRP receptors in vitro. Fragment interactions with a CGRP ELISA were examined to assess potential interference with detection of full-length CGRP. Male Sprague Dawley rats were used for the ex vivo experiments.
Results: hαCGRP disappeared rapidly in the meningeal environment and reduced transdural resistance in the dura mater. Seven predominant degradation fragments accounted for ~ 81.5% of the detected fragment pool. None of the fragments showed agonist activity at the CGRP receptor or altered dural resistance or mast cell degranulation. In vascular assays, the fragments were likewise inactive, with the exception of the C-terminal fragment hαCGRP11-37, which displayed weak competitive antagonism at the CGRP receptor. This was confirmed at both the human and rat CGRP receptor in vitro. Although the identified fragments were not directly detected by the CGRP ELISA, selected fragments interfered with intact hαCGRP measurements, indicating that degradation products can influence biomarker readout.
Conclusion: Local degradation of hαCGRP at the dura mater primarily generates fragments without measurable vascular, immune, or receptor activating effects. The main consequence of this processing appears to be reduced hαCGRP bioavailability rather than formation of secondary bioactive signalling peptides. At the same time, fragment dependent interference in ELISA based detection indicates that local hαCGRP metabolism may affect interpretation of CGRP biomarker measurements in migraine relevant tissues.