Peripheral Gene Expression of Endocannabinoid System Components in Episodic and Chronic Migraine Patients: a Pilot Study

Migraine is a neurovascular disease whose pathophysiology is far from being completely clarified. This is mainly due to the complex mechanisms that underlie migraine attack as well as its recurrence. The endocannabinoid system (ES) is a complex signalling system involved in different biological processes (e.g. neuronal activity, pain sensation and immune functions) and it plays a crucial role in the maintenance of body homeostasis. The ES components include the endogenous lipids, the most studied ones being N-arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG), their metabolic enzymes and at least two cannabinoid receptors (CB1 and CB2). The biosynthesis of AEA mainly occurs by N-acylphosphatidylethanolamide-phospholipase D (NAPE-PLD), whereas 2-AG is produced through the action of diacylglycerol lipase (DAGL). AEA is metabolized by fatty acid amide hydrolase (FAAH) and 2-AG mainly by monoacylglycerol lipase (MAGL).

Alterations in gene expression of ES components may involve various cell types, multiple catabolic pathways and the generation of active metabolites via epigenetic mechanisms, under both physiological and pathological conditions. CB genes, for instance, may interact with different transcriptional factors, many of which are related to DNA methylation and histone post-translational modifications. A dysfunctional ES has been associated to numerous disorders including migraine. The ES, indeed, modulates multiple activities and neuromodulators/neurotransmitters that play a crucial role in migraine pathogenesis. ES is also implicated in the descending modulation of the trigeminovascular nociceptive transmission from the brainstem afferents. Previous studies from the Laboratory of Neurophysiology of Integrative Autonomic Systems, Headache Science Centre, IRCCS Mondino Foundation, Pavia (Italy), using the migraine-specific animal model based on nitroglycerin administration in rat, demonstrated the existence of interactions between the ES and pain mediation. In particular, the investigators showed a key role for AEA and for FAAH-regulated AEA activity in the processing of trigeminal nociceptive signals. AEA inhibits neurogenic dural vasodilatation, as well as calcitonin gene-related peptide-induced and nitric oxide-induced dural vessel dilation, an activity that is reversed by CB1 antagonism. The interaction between the ES and migraine pain is also suggested by clinical observations. FAAH activity was higher in platelets of women with episodic migraine (EM) to suggest a more marked degradation of AEA. Subjects with chronic migraine (CM) and medication overuse (MO) showed an altered endocannabinoid metabolism not only in platelets, but also in the CSF. Although the above clinical findings are scattered and replicated, their re-consideration in the light of more recent data from the increasing pre-clinical evidence prompt the need to investigate in more depth the role of ES in migraine pathophysiology.

Several studies suggest that changes in ES components detected in peripheral blood mononuclear cells (PBMCs) are reliable indicators of a central dysfunction of the ES in different neurological diseases. For instance, in patients with Parkinson disease or multiple sclerosis, increased CSF levels of AEA were associated with a reduction in the activity and protein content of FAAH in PBMCs, which is indicative of an increased AEA tone. AEA levels were elevated in the CSF and in the blood of schizophrenic subjects, with a significant drop in AEA blood levels and in mRNA transcripts of CB2 and FAAH in PBMCs following clinical remission.

The aim of this study, was the identification of specific functional patterns of ES activity in subjects with migraine. To this end, the investigators performed a thorough evaluation of multiple peripheral components of the ES (gene expression, protein expression and DNA methylation) in PBMCs of representative samples of subjects with EM without aura, CM-MO and in healthy controls (CT).

Twenty-five subjects with EM, 26 with CM-MO and 24 CT were enrolled in the headache center of the IRCCS Mondino Foundation of Pavia (Italy). The study was approved by the local Ethics Committee and all subjects enrolled signed a written informed consent.