CGRP and Brain Functioning: Cautions for Migraine Treatment

Background Calcitonin gene‐related peptide has emerged as a therapeutic target in migraine. Monoclonal antibodies and small molecule receptor antagonists (gepants) directed against CGRP have been approved or are in Phase II or III clinical trials. For monitoring the long‐term safety of these drugs, it is helpful to consider the role of CGRP in brain functioning. Methods Qualitative review of the preclinical literature on CGRP in brain physiology and pathophysiology. Results Within the brain, CGRP is upregulated by stresses such as ischemia, injury, hyperthermia, and seizure, and activates neuroprotective processes. Thus, CGRP buffers intracellular calcium, triggers antiapoptotic signaling, upregulates a number of neurotrophins (including insulin‐like growth factor‐1/IGF‐1, basic fibroblast growth factor/bFGF, and nerve growth factor/NGF), reduces brain edema, and likely increases antioxidant defenses. When released outside the blood‐brain barrier, CGRP likely protects the endothelium, upregulates growth factor signaling from the endothelium to the brain parenchyma, strengthens the blood‐brain barrier, protects the immune privilege of the brain by inhibiting the movement of neutrophils and monocytes, and facilitates neurogenesis and angiogenesis at stem cell niches. Conclusions CGRP participates in a wide range of neuroprotective processes. In theory, migraineurs with comorbid brain pathology might be at increased risk from CGRP inhibition. However, the extent of compensating processes is unknown and will determine whether these risks materialize in practice.