Spinal nociceptive sensitization and plasma palmitoylethanolamide levels during experimentally induced migraine attacks

A Decades-Long Journey of Palmitoylethanolamide (PEA) for Chronic Neuropathic Pain Management: A Comprehensive Narrative Review

Palmitoylethanolamide (PEA) has been prescribed in neuropathic pain management for over 20 years. This study aims to summarize what has been published on the topic in the last 15 years and determine the appropriateness of the prescribing. It describes the pharmacological aspect of PEA, especially focusing on its pharmacodynamics and pharmacokinetics. Then, it deeply explores why PEA may be useful in the pharmacological management of both neuropathic and mixed pain. Finally, it examines some innovative patent, which aims to address obstacles encountered with conventional PEA formulations, for its pharmacodynamic characteristics. One of them (Equisetum-PEA) seems promising. It partially ameliorates the bioavailability and the targeted distribution. It seems to introduce novel advancements that can potentially enhance the therapeutic effectiveness of PEA in terms of its anti-inflammatory, antioxidant, and analgesic properties. The deep literature analysis aims to examine the potential advantages of PEA, in the context of several pathological conditions that may benefit from this molecule. It focuses on various published data regarding the clinical efficacy of PEA in managing neuropathic and mixed pain. Also, it tries to understand if it can modernize the field of therapy based on PEA, thus offering a better treatment option for individuals with chronic long-term inflammation, oxidative stress, and neuropathic or mixed pain with a neuropathic component. The study examines the possible impact of PEA on personalized medicine strategies and its potential for translation into clinical practice. It analyses the possibilities that PEA has in enhancing patient outcomes in a range of central nervous system and inflammatory conditions. A complete analysis of the therapeutic potentialities of this product was missing. This extensive narrative review makes a valuable contribution to the ongoing comprehension of PEA therapy. It establishes a foundation for further exploration in research and potential uses in clinical settings.

Maladaptive changes in the homeostasis of AEA-TRPV1/CB1R induces pain-related hyperactivity of nociceptors after spinal cord injury

BACKGROUND

Neuropathic pain resulting from spinal cord injury (SCI) is associated with persistent hyperactivity of primary nociceptors. Anandamide (AEA) has been reported to modulate neuronal excitability and synaptic transmission through activation of cannabinoid type-1 receptors (CB1Rs) and transient receptor potential vanilloid 1 (TRPV1). However, the role of AEA and these receptors in the hyperactivity of nociceptors after SCI remains unclear.

RESULTS

In this study, we investigated the effects of AEA and its receptors on the hyperexcitability of mouse dorsal root ganglion (DRG) neurons after SCI. Using a whole-cell patch-clamp technique, we found that the timing of SCI-induced hyperexcitability in nociceptors paralleled an increase in the endocannabinoid AEA content. The expression of TRPV1 and CB1R was also upregulated at different time points after SCI. High-dose extracellular administration of AEA increased the excitability of naive DRG neurons, leading to the transition from a rapidly accommodating (RA) hypoexcitable state to a highly excitable non-accommodating (NA) state. These AEA-induced transitions were facilitated by increased TRPV1 transcription. Pharmacological and Ca2+ imaging experiments revealed that AEA induced hyperexcitability in nociceptors after SCI via the AEA-TRPV1-Ca2+ pathway, whereas activation of CB1Rs reduced SCI-induced hyperexcitability and maintained cytosolic Ca2+ concentration ([Ca2+]cyto) at low levels in the early stages of SCI. As the AEA and TRPV1 levels increased after SCI, adaptive neuroprotection transitioned to a maladaptive hyperactive state, leading to sustained pain.

CONCLUSIONS

Taken together, this study provides new insights into how endocannabinoids regulate nociceptor activity after SCI, offering potential targets for the treatment of neuropathic pain.

High-frequency episodic migraine: Time for its recognition as a migraine subtype?

BACKGROUND

High-frequency episodic migraine (HFEM) has gained attention in the field of headache research and clinical practice. In this narrative review, we analyzed the available literature to assess the evidence that could help decide whether HFEM may represent a distinct clinical and/or biological entity within the migraine spectrum.

METHODS

The output of the literature search included 61 papers that were allocated to one of the following topics: (i) socio-demographic features and burden; (ii) clinical and therapeutic aspects; (iii) pathophysiology; and (iv) classification.

RESULTS

Multiple features differentiate subjects with HFEM from low-frequency episodic migraine and from chronic migraine: education, employment rates, quality of life, disability and psychiatric comorbidities load. Some evidence also suggests that HFEM bears a specific profile of activation of cortical and spinal pain-related pathways, possibly related to maladaptive plasticity.

CONCLUSIONS

Subjects with HFEM bear a distinctive clinical and socio-demographic profile within the episodic migraine group, with a higher disease burden and an increased risk of transitioning to chronic migraine. Recognizing HFEM as a distinct entity is an opportunity for the better understanding of migraine and the spectrum of frequency with which it can manifest, as well as for stimulating further research and more adequate public health approaches.

Ultramicronized N-palmitoylethanolamine associated with analgesics: Effects against persistent pain

Current epidemiological data estimate that one in five people suffers from chronic pain with considerable impairment of health-related quality of life. The pharmacological treatment is based on first- and second-line analgesic drugs, including COX-2 selective and nonselective nonsteroidal anti-inflammatory drugs, paracetamol, antidepressants, anti-seizure drugs and opioids, that are characterized by important side effects. N-palmitoylethanolamine (PEA) is a body's own fatty-acid ethanolamide belonging to the family of autacoid local injury antagonist amides. The anti-inflammatory and pain-relieving properties of PEA have been recognized for decades and prompted to depict its role in the endogenous mechanisms of pain control. Together with its relative abundance in food sources, this opened the way to the use of PEA as a pain-relieving nutritional intervention. Naïve PEA is a large particle size lipid molecule with low solubility and bioavailability. Reducing particle size is a useful method to increase surface area, thereby improving dissolution rate and bioavailability accordingly. Micron-size formulations of PEA (e.g., ultramicronized and co-(ultra)micronized) have shown higher oral efficacy compared to naïve PEA. In particular, ultramicronized PEA has been shown to efficiently cross the intestinal wall and, more importantly, the blood-brain and blood-spinal cord barrier. Several preclinical and clinical studies have shown the efficacy, safety and tolerability of ultramicronized PEA. This narrative review summarizes the available pharmacokinetic/pharmacodynamic data on ultramicronized PEA and focuses to its contribution to pain control, in particular as 'add-on' nutritional intervention. Data showing the ability of ultramicronized PEA to limit opioid side effects, including the development of tolerance, have also been reviewed.

Duality in response of intracranial vessels to nitroglycerin revealed in rats by imaging photoplethysmography

Among numerous approaches to the study of migraine, the nitroglycerin (NTG) model occupies a prominent place, but there is relatively insufficient information about how NTG affects intracranial vessels. In this study we aim to assess the effects of NTG on blood-flow parameters in meningeal vessels measured by imaging photoplethysmography (iPPG) in animal experiments. An amplitude of the pulsatile component (APC) of iPPG waveform was assessed before and within 2.5 h after the NTG administration in saline (n = 13) or sumatriptan (n = 12) pretreatment anesthetized rats in conditions of a closed cranial window. In animals of both groups, NTG caused a steady decrease in blood pressure. In 7 rats of the saline group, NTG resulted in progressive increase in APC, whereas decrease in APC was observed in other 6 rats. In all animals in the sumatriptan group, NTG administration was accompanied exclusively by an increase in APC. Diametrically opposite changes in APC due to NTG indicate a dual effect of this drug on meningeal vasomotor activity. Sumatriptan acts as a synergist of the NTG vasodilating action. The results we obtained contribute to understanding the interaction of vasoactive drugs in the study of the headache pathophysiology and methods of its therapy.

Biomarkers of Migraine: An Integrated Evaluation of Preclinical and Clinical Findings

In recent years, numerous efforts have been made to identify reliable biomarkers useful in migraine diagnosis and progression or associated with the response to a specific treatment. The purpose of this review is to summarize the alleged diagnostic and therapeutic migraine biomarkers found in biofluids and to discuss their role in the pathogenesis of the disease. We included the most informative data from clinical or preclinical studies, with a particular emphasis on calcitonin gene-related peptide (CGRP), cytokines, endocannabinoids, and other biomolecules, the majority of which are related to the inflammatory aspects and mechanisms of migraine, as well as other actors that play a role in the disease. The potential issues affecting biomarker analysis are also discussed, such as how to deal with bias and confounding data. CGRP and other biological factors associated with the trigeminovascular system may offer intriguing and novel precision medicine opportunities, although the biological stability of the samples used, as well as the effects of the confounding role of age, gender, diet, and metabolic factors should be considered.

Exploring Novel Therapeutic Targets in the Common Pathogenic Factors in Migraine and Neuropathic Pain

Migraine and neuropathic pain (NP) are both painful, disabling, chronic conditions which exhibit some symptom similarities and are thus considered to share a common etiology. The calcitonin gene-related peptide (CGRP) has gained credit as a target for migraine management; nevertheless, the efficacy and the applicability of CGRP modifiers warrant the search for more effective therapeutic targets for pain management. This scoping review focuses on human studies of common pathogenic factors in migraine and NP, with reference to available preclinical evidence to explore potential novel therapeutic targets. CGRP inhibitors and monoclonal antibodies alleviate inflammation in the meninges; targeting transient receptor potential (TRP) ion channels may help prevent the release of nociceptive substances, and modifying the endocannabinoid system may open a path toward discovery of novel analgesics. There may exist a potential target in the tryptophan-kynurenine (KYN) metabolic system, which is closely linked to glutamate-induced hyperexcitability; alleviating neuroinflammation may complement a pain-relieving armamentarium, and modifying microglial excitation, which is observed in both conditions, may be a possible approach. Those are several potential analgesic targets which deserve to be explored in search of novel analgesics; however, much evidence remains missing. This review highlights the need for more studies on CGRP modifiers for subtypes, the discovery of TRP and endocannabinoid modulators, knowledge of the status of KYN metabolites, the consensus on cytokines and sampling, and biomarkers for microglial function, in search of innovative pain management methods for migraine and NP.

Measuring the Content of Endocannabinoid-Like Compounds in Biological Fluids: A Critical Overview of Sample Preparation Methodologies

Different mass spectrometric techniques have been used over the past decade to quantify endocannabinoids (eCBs) and related lipids. Even with the level of molecular fingerprinting accuracy of an instrument like the most advanced triple quadrupole mass spectrometer, if one is not getting the most optimized sample to the detector in a way that this improved technology can be of use, then advancements can be stymied. Here, our focus is on review and discussion of sample preparation methodologies used to isolate the eCB anandamide and its close congeners N-acyl ethanolamines and structural congeners (i.e., lipo amino acids, lipoamines, N-acyl amides) in biological fluids. Most of our focus will be on the analysis of these lipids in plasma/serum, but we will also discuss how the same techniques can be used for the analysis of saliva and breast milk.

Oculo-vestibular signs in experimentally induced migraine attacks: an exploratory analysis

Vestibular symptoms accompanying headache are quite common in migraine patients. Based on the association of vertigo with migraine, vestibular migraine was included in the appendix of the 3rd edition of the International Classification of Headache Disorders as a possible migraine subtype worthy of further investigation. In this post hoc, exploratory analysis, we investigated the occurrence of oculo-vestibular signs (OVSs) during experimentally induced migraine attacks in 24 episodic migraine patients and 19 healthy controls exposed to sublingual nitroglycerin (NTG - 0.9 mg). A comprehensive clinical examination was performed at baseline, at the onset of the migraine-like attack, and immediately before hospital discharge (180 minutes after NTG administration). Three of the 13 migraine patients who developed a spontaneous-like migraine attack during the hospital observation period (23.1%) also developed OVSs during the induction test. Noteworthy, none of the patients with a negative induction test developed OVSs and no OVSs were reported in healthy subjects at any time point. The exploratory nature of our study does not allow to draw definite conclusions on the possible implications of a vestibular dysfunction in migraine pathophysiology. Our results however suggest that NTG administration may lend itself to investigate vestibular dysfunction in migraine, at least in a subset of patients. The present findings represent a starting point for designing future ad hoc and well-powered studies.

Triggers of migraine: where do we stand?

PURPOSE OF REVIEW

In this review, we illustrate and discuss the recent findings regarding the epidemiology and pathophysiology of migraine triggers and their implications in clinical practice.

RECENT FINDINGS

Data from the literature suggest that individual triggers fail to provoke migraine attack in experimental settings. It is therefore possible that more triggers acting in combination are needed to induce an attack by promoting some degree of brain dysfunction and thus increasing the vulnerability to migraine. Caution is however needed, because some of the factors rated as triggers by the patients may actually be a component of the clinical picture of migraine attacks.

SUMMARY

Trigger factors of migraine are endogenous or exogenous elements associated with an increased likelihood of an attack in a short period of time and are reported by up to 75.9% of patients. Triggers must be differentiated from premonitory symptoms that precede the headache phase but do not have a causative role in attack provocation, being rather the very first manifestations of the attack. Identification of real triggers is an important step in the management of migraine. Vice versa, promoting an active avoiding behaviour toward factors whose role as triggers is not certain would be ineffective and even frustrating for patients.

Clinical Evidence of Cannabinoids in Migraine: A Narrative Review

The endocannabinoid system (ECS) influences many biological functions, and hence, its pharmacological modulation may be useful for several disorders, such as migraine. Preclinical studies have demonstrated that the ECS is involved in the modulation of trigeminal excitability. Additionally, clinical data have suggested that an endocannabinoid deficiency is associated with migraine. Given these data, phytocannabinoids, as well as synthetic cannabinoids, have been tried as migraine treatments. In this narrative review, the current clinical evidence of potential ECS involvement in migraine pathogenesis is summarized. Furthermore, studies exploring the clinical effects of phytocannabinoids and synthetic cannabinoids on migraine patients are reviewed.