Endocannabinoids in chronic migraine: CSF findings suggest a system failure

Inhibition of monoacylglycerol lipase: Another signalling pathway for potential therapeutic targets in migraine?

Background

Drugs that modulate endocannabinoid signalling are effective in reducing nociception in animal models of pain and may be of value in the treatment of migraine.

Methods

We investigated the anti-nociceptive effects of inhibition of monoacylglycerol lipase (MGL), a key enzyme in the hydrolysis of the 2-arachidonoylglycerol, in a rat model of migraine based on nitroglycerin (NTG) administration. We evaluated c-fos expression in specific brain areas and nociceptive behavior in trigeminal and extra-trigeminal body areas.

Results

URB602, a reversible MGL inhibitor, did not show any analgesic effect in the tail flick test, but it inhibited NTG-induced hyperalgesia in both the tail flick test and the formalin test applied to the hind paw or to the orofacial area. Quite unexpectedly, URB602 potentiated formalin-induced hyperalgesia in the trigeminal area when used alone. The latter result was also confirmed using a structurally distinct, irreversible MGL inhibitor, JZL184. URB602 did not induce neuronal activation in the area of interest, but significantly reduced the NTG-induced neuronal activation in the ventrolateral column of the periaqueductal grey and the nucleus trigeminalis caudalis.

Conclusions

These findings support the hypothesis that modulation of the endocannabinoid system may be a valuable approach for the treatment of migraine. The topographically segregated effect of MGL inhibition in trigeminal/extra-trigeminal areas calls for further mechanistic research.

Interactions between the Kynurenine and the Endocannabinoid System with Special Emphasis on Migraine

Both the kynurenine and the endocannabinoid systems are involved in several neurological disorders, such as migraine and there are increasing number of reports demonstrating that there are interactions of two systems. Although their cooperation has not yet been implicated in migraine, there are reports suggesting this possibility. Additionally, the individual role of the endocannabinoid and kynurenine system in migraine is reviewed here first, focusing on endocannabinoids, kynurenine metabolites, in particular kynurenic acid. Finally, the function of NMDA and cannabinoid receptors in the trigeminal system-which has a crucial role in the pathomechanisms of migraine-will also be discussed. The interaction of the endocannabinoid and kynurenine system has been demonstrated to be therapeutically relevant in a number of pathological conditions, such as cannabis addiction, psychosis, schizophrenia and epilepsy. Accordingly, the cross-talk of these two systems may imply potential mechanisms related to migraine, and may offer new approaches to manage the treatment of this neurological disorder.

Plasma levels of the endocannabinoid anandamide, related N-acylethanolamines and linoleic acid-derived oxylipins in patients with migraine

There is evidence that patients with migraine have deficient levels of the endogenous cannabinoid receptor ligand anandamide (AEA). It is not known, however, if this is a localised or generalised phenomenon. In the present study, levels of AEA, related N-acylethanolamines (NAEs) and linoleic acid-derived oxylipins have been measured in the blood of 26 healthy women and 38 women with migraine (26 with aura, 12 without aura) who were matched for age and body-mass index. Blood samples were taken on two occasions: the first sample near the start of the menstrual cycle (when present) and the second approximately fourteen days later. For a subset of migraine patients, two additional blood samples were taken, one during a migraine attack and one approximately 1 month later (to be at the same stage in the menstrual cycle, when present). NAEs and oxylipins were measured by liquid chromatography coupled to mass spectrometry. Twenty-nine lipids were quantified, of which 16 were found to have a high reproducibility of measurement. There were no significant differences in the levels of AEA, the related NAEs stearoylethanolamide and oleoylethanolamide or any of the nine linoleic acid-derived oxylipins measured either between migraine patients with vs. without aura, or between controls and migraine patients (after stratification to take into account whether or not the individuals had regular menstruation cycles) in either of the first two samples. Levels of linoleoylethanolamide were lower in the patients with vs. without aura on the second sample but not in the first sample, but the biological importance of this finding is unclear. Due to time-dependent increases in their concentrations ex vivo prior to centrifugation, AEA and oleoylethanolamide levels in the samples collected during migraine attacks were not analysed, but for the other fourteen lipids, there were no significant differences in plasma concentrations during migraine vs. one month later. It is concluded that migraine is not associated with a generalised (as opposed to localised) deficiency in these lipids.

The Use of Cannabis for Headache Disorders

Headache disorders are common, debilitating, and, in many cases, inadequately managed by existing treatments. Although clinical trials of cannabis for neuropathic pain have shown promising results, there has been limited research on its use, specifically for headache disorders. This review considers historical prescription practices, summarizes the existing reports on the use of cannabis for headache, and examines the preclinical literature exploring the role of exogenous and endogenous cannabinoids to alter headache pathophysiology. Currently, there is not enough evidence from well-designed clinical trials to support the use of cannabis for headache, but there are sufficient anecdotal and preliminary results, as well as plausible neurobiological mechanisms, to warrant properly designed clinical trials. Such trials are needed to determine short- and long-term efficacy for specific headache types, compatibility with existing treatments, optimal administration practices, as well as potential risks.

Variants in the CNR1 gene predispose to headache with nausea in the presence of life stress

One of the main effects of the endocannabinoid system in the brain is stress adaptation with presynaptic endocannabinoid receptor 1 (CB1 receptors) playing a major role. In the present study, we investigated whether the effect of the CB1 receptor coding CNR1 gene on migraine and its symptoms is conditional on life stress. In a cross-sectional European population (n = 2426), recruited from Manchester and Budapest, we used the ID-Migraine questionnaire for migraine screening, the Life Threatening Experiences questionnaire to measure recent negative life events (RLE), and covered the CNR1 gene with 11 SNPs. The main genetic effects and the CNR1 × RLE interaction with age and sex as covariates were tested. None of the SNPs showed main genetic effects on possible migraine or its symptoms, but 5 SNPs showed nominally significant interaction with RLE on headache with nausea using logistic regression models. The effect of rs806366 remained significant after correction for multiple testing and replicated in the subpopulations. This effect was independent from depression- and anxiety-related phenotypes. In addition, a Bayesian systems-based analysis demonstrated that in the development of headache with nausea all SNPs were more relevant with higher a posteriori probability in those who experienced recent life stress. In summary, the CNR1 gene in interaction with life stress increased the risk of headache with nausea suggesting a specific pathological mechanism to develop migraine, and indicating that a subgroup of migraine patients, who suffer from life stress triggered migraine with frequent nausea, may benefit from therapies that increase the endocannabinoid tone.

Migraine biomarkers in cerebrospinal fluid: A systematic review and meta-analysis

Objective To perform a meta-analysis of migraine biomarkers in cerebrospinal fluid (CSF) and of corresponding blood concentrations. Methods We conducted a systematic search for studies that measured biochemical compounds in CSF of chronic or episodic migraineurs and non-headache controls. Subsequent searches retrieved studies with blood measurements of selected CSF biomarkers. If a compound was assessed in three or more studies, results were pooled in a meta-analysis with standardised mean differences (SMD) as effect measures. Results Sixty-two compounds were measured in 40 CSF studies. Most important results include: increased glutamate (five studies, SMD 2.22, 95% CI: 1.30, 3.13), calcitonin gene-related peptide (CGRP) (three studies, SMD: 3.80, 95% CI: 3.19, 4.41) and nerve growth factor (NGF) (three studies, SMD: 6.47, 95% CI: 5.55, 7.39) in chronic migraine patients and decreased β-endorphin (β-EP) in both chronic (four studies, SMD: -1.37, 95% CI: -1.80, -0.94) and interictal episodic migraine patients (three studies, SMD: -1.12, 95% CI: -1.65, -0.58). In blood, glutamate (interictal) and CGRP (chronic, interictal and ictal) were increased and β-EP (chronic, interictal and ictal) was decreased. Conclusions Glutamate, β-EP, CGRP and NGF concentrations are altered in CSF and, except for NGF, also in blood of migraineurs. Future research should focus on the pathophysiological roles of these compounds in migraine.

FABP-1 gene ablation impacts brain endocannabinoid system in male mice

Liver fatty acid-binding protein (FABP1, L-FABP) has high affinity for and enhances uptake of arachidonic acid (ARA, C20:4, n-6) which, when esterified to phospholipids, is the requisite precursor for synthesis of endocannabinoids (EC) such as arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG). The brain derives most of its ARA from plasma, taking up ARA and transporting it intracellularly via cytosolic fatty acid-binding proteins (FABPs 3,5, and 7) localized within the brain. In contrast, the much more prevalent cytosolic FABP1 is not detectable in the brain but is instead highly expressed in the liver. Therefore, the possibility that FABP1 outside the central nervous system may regulate brain AEA and 2-AG was examined in wild-type (WT) and FABP1 null (LKO) male mice. LKO increased brain levels of AA-containing EC (AEA, 2-AG), correlating with increased free and total ARA in brain and serum. LKO also increased brain levels of non-ARA that contain potentiating endocannabinoids (EC*) such as oleoyl ethanolamide (OEA), PEA, 2-OG, and 2-PG. Concomitantly, LKO decreased serum total ARA-containing EC, but not non-ARA endocannabinoids. LKO did not elicit these changes in the brain EC and EC* as a result of compensatory up-regulation of brain protein levels of enzymes in EC synthesis (NAPEPLD, DAGLα) or cytosolic EC chaperone proteins (FABPs 3, 5, 7, SCP-2, HSP70), or cannabinoid receptors (CB1, TRVP1). These data show for the first time that the non-CNS fatty acid-binding protein FABP1 markedly affected brain levels of both ARA-containing endocannabinoids (AEA, 2-AG) as well as their non-ARA potentiating endocannabinoids. Fatty acid-binding protein-1 (FABP-1) is not detectable in brain but instead is highly expressed in liver. The possibility that FABP1 outside the central nervous system may regulate brain endocannabinoids arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG) was examined in wild-type (WT) and FABP-1 null (LKO) male mice. LKO increased brain levels of arachidonic acid-containing endocannabinoids (AEA, 2-AG), correlating with increased free and total arachidonic acid in brain and serum. Read the Editorial Highlight for this article on page 371.

Clinical Endocannabinoid Deficiency Reconsidered: Current Research Supports the Theory in Migraine, Fibromyalgia, Irritable Bowel, and Other Treatment-Resistant Syndromes

Medicine continues to struggle in its approaches to numerous common subjective pain syndromes that lack objective signs and remain treatment resistant. Foremost among these are migraine, fibromyalgia, and irritable bowel syndrome, disorders that may overlap in their affected populations and whose sufferers have all endured the stigma of a psychosomatic label, as well as the failure of endless pharmacotherapeutic interventions with substandard benefit. The commonality in symptomatology in these conditions displaying hyperalgesia and central sensitization with possible common underlying pathophysiology suggests that a clinical endocannabinoid deficiency might characterize their origin. Its base hypothesis is that all humans have an underlying endocannabinoid tone that is a reflection of levels of the endocannabinoids, anandamide (arachidonylethanolamide), and 2-arachidonoylglycerol, their production, metabolism, and the relative abundance and state of cannabinoid receptors. Its theory is that in certain conditions, whether congenital or acquired, endocannabinoid tone becomes deficient and productive of pathophysiological syndromes. When first proposed in 2001 and subsequently, this theory was based on genetic overlap and comorbidity, patterns of symptomatology that could be mediated by the endocannabinoid system (ECS), and the fact that exogenous cannabinoid treatment frequently provided symptomatic benefit. However, objective proof and formal clinical trial data were lacking. Currently, however, statistically significant differences in cerebrospinal fluid anandamide levels have been documented in migraineurs, and advanced imaging studies have demonstrated ECS hypofunction in post-traumatic stress disorder. Additional studies have provided a firmer foundation for the theory, while clinical data have also produced evidence for decreased pain, improved sleep, and other benefits to cannabinoid treatment and adjunctive lifestyle approaches affecting the ECS.

Fatty Acid Binding Protein-1 (FABP1) and the Human FABP1 T94A Variant: Roles in the Endocannabinoid System and Dyslipidemias

The first discovered member of the mammalian FABP family, liver fatty acid binding protein (FABP1, L-FABP), occurs at high cytosolic concentration in liver, intestine, and in the case of humans also in kidney. While the rat FABP1 is well studied, the extent these findings translate to human FABP1 is not clear-especially in view of recent studies showing that endocannabinoids and cannabinoids represent novel rat FABP1 ligands and FABP1 gene ablation impacts the hepatic endocannabinoid system, known to be involved in non-alcoholic fatty liver (NAFLD) development. Although not detectable in brain, FABP1 ablation nevertheless also impacts brain endocannabinoids. Despite overall tertiary structure similarity, human FABP1 differs significantly from rat FABP1 in secondary structure, much larger ligand binding cavity, and affinities/specificities for some ligands. Moreover, while both mouse and human FABP1 mediate ligand induction of peroxisome proliferator activated receptor-α (PPARα), they differ markedly in pattern of genes induced. This is critically important because a highly prevalent human single nucleotide polymorphism (SNP) (26-38 % minor allele frequency and 8.3 ± 1.9 % homozygous) results in a FABP1 T94A substitution that further accentuates these species differences. The human FABP1 T94A variant is associated with altered body mass index (BMI), clinical dyslipidemias (elevated plasma triglycerides and LDL cholesterol), atherothrombotic cerebral infarction, and non-alcoholic fatty liver disease (NAFLD). Resolving human FABP1 and the T94A variant's impact on the endocannabinoid and cannabinoid system is an exciting challenge due to the importance of this system in hepatic lipid accumulation as well as behavior, pain, inflammation, and satiety.

Effects of Medical Marijuana on Migraine Headache Frequency in an Adult Population

STUDY OBJECTIVE

No clinical trials are currently available that demonstrate the effects of marijuana on patients with migraine headache; however, the potential effects of cannabinoids on serotonin in the central nervous system indicate that marijuana may be a therapeutic alternative. Thus, the objective of this study was to describe the effects of medical marijuana on the monthly frequency of migraine headache.

DESIGN

Retrospective chart review.

SETTING

Two medical marijuana specialty clinics in Colorado.

PATIENTS

One hundred twenty-one adults with the primary diagnosis of migraine headache who were recommended migraine treatment or prophylaxis with medical marijuana by a physician, between January 2010 and September 2014, and had at least one follow-up visit.

MEASUREMENTS AND RESULTS

The primary outcome was number of migraine headaches per month with medical marijuana use. Secondary outcomes were the type and dose of medical marijuana used, previous and adjunctive migraine therapies, and patient-reported effects. Migraine headache frequency decreased from 10.4 to 4.6 headaches per month (p<0.0001) with the use of medical marijuana. Most patients used more than one form of marijuana and used it daily for prevention of migraine headache. Positive effects were reported in 48 patients (39.7%), with the most common effects reported being prevention of migraine headache with decreased frequency of migraine headache (24 patients [19.8%]) and aborted migraine headache (14 patients [11.6%]). Inhaled forms of marijuana were commonly used for acute migraine treatment and were reported to abort migraine headache. Negative effects were reported in 14 patients (11.6%); the most common effects were somnolence (2 patients [1.7%]) and difficulty controlling the effects of marijuana related to timing and intensity of the dose (2 patients [1.7%]), which were experienced only in patients using edible marijuana. Edible marijuana was also reported to cause more negative effects compared with other forms.

CONCLUSION

The frequency of migraine headache was decreased with medical marijuana use. Prospective studies should be conducted to explore a cause-and-effect relationship and the use of different strains, formulations, and doses of marijuana to better understand the effects of medical marijuana on migraine headache treatment and prophylaxis.

Endocannabinoids and acute pain after total knee arthroplasty

Osteoarthritis (OA) of the knee is a progressive disease that is associated with inflammation of the joints and lower extremity pain. Total knee arthroplasty (TKA) is a surgical procedure that aims to reduce pain and restore motor function in patients suffering from OA. The immediate postoperative period can be intensely painful leading to extended recovery times including persistent pain. The endocannabinoid system regulates nociception, and the activation of cannabinoid receptors produces antinociceptive effects in preclinical models of OA. To date, the influence of the endocannabinoid tone on pain and disability in OA patients and on acute postoperative pain in humans has not been explored. In this study, we provide the first comprehensive profile of endocannabinoids in serum, cerebrospinal fluid, and synovial fluid of patients with painful end-stage OA undergoing TKA and examine correlations between endocannabinoid levels, interleukin 6, functional disability, acute postoperative pain, and postoperative opioid use. Our results reveal that central (cerebrospinal fluid) and peripheral (synovial fluid) levels of the endocannabinoid 2-arachidonoyl glycerol were significantly elevated in patients who developed higher postoperative pain after TKA. In addition, synovial fluid 2-arachidonoyl glycerol levels were positively correlated with postoperative opioid use. Similarly, synovial fluid levels of the anti-inflammatory lipid palmitoylethanolamide correlated with functional disability in OA. Taken together, our results are the first to reveal associations between central and peripheral endocannabinoid levels and postoperative pain. This suggests that endocannabinoid metabolism may serve as a target for the development of novel analgesics both for systemic or local delivery into the joint.

Medical marijuana in neurology

Constituents of the Cannabis plant, cannabinoids, may be of therapeutic value in neurologic diseases. The most abundant cannabinoids are Δ(9)-tetrahydrocannabinol, which possesses psychoactive properties, and cannabidiol, which has no intrinsic psychoactive effects, but exhibits neuroprotective properties in preclinical studies. A small number of high-quality clinical trials support the safety and efficacy of cannabinoids for treatment of spasticity of multiple sclerosis, pain refractory to opioids, glaucoma, nausea and vomiting. Lower level clinical evidence indicates that cannabinoids may be useful for dystonia, tics, tremors, epilepsy, migraine and weight loss. Data are also limited in regards to adverse events and safety. Common nonspecific adverse events are similar to those of other CNS 'depressants' and include weakness, mood changes and dizziness. Cannabinoids can have cardiovascular adverse events and, when smoked chronically, may affect pulmonary function. Fatalities are rare even with recreational use. There is a concern about psychological dependence, but physical dependence is less well documented. Cannabis preparations may presently offer an option for compassionate use in severe neurologic diseases, but at this point, only when standard-of-care therapy is ineffective. As more high-quality clinical data are gathered, the therapeutic application of cannabinoids will likely expand.

Migraine and neuropeptides

Migraine is a common disabling neurovascular primary headache disorder. The pathomechanism is not clear, but extensive preclinical and clinical studies are ongoing. The structural basis of the leading hypothesis is the trigeminovascular system, which includes the trigeminal ganglion, the meningeal vasculature, and the distinct nuclei of the brainstem, the thalamus and the somatosensory cortex. This review covers the effects of sensory (calcitonin gene-related peptide, pituitary adenylate cyclase-activating polypeptide and substance P), sympathetic (neuropeptide Y) and parasympathetic (vasoactive intestinal peptide) migraine-related neuropeptides and the functions of somatostatin, nociceptin and the orexins in the trigeminovascular system. These neuropeptides may take part in neurogenic inflammation (plasma protein extravasation and vasodilatation) of the intracranial vasculature and peripheral and central sensitization of the trigeminal system. The results of human clinical studies are discussed with regard to the alterations in these neuropeptides in the plasma, saliva and cerebrospinal fluid during or between migraine attacks, and the therapeutic possibilities involving migraine-related neuropeptides in the acute and prophylactic treatment of migraine headache are surveyed.

Comprehensive Review of Medicinal Marijuana, Cannabinoids, and Therapeutic Implications in Medicine and Headache: What a Long Strange Trip It's Been …

BACKGROUND

The use of cannabis, or marijuana, for medicinal purposes is deeply rooted though history, dating back to ancient times. It once held a prominent position in the history of medicine, recommended by many eminent physicians for numerous diseases, particularly headache and migraine. Through the decades, this plant has taken a fascinating journey from a legal and frequently prescribed status to illegal, driven by political and social factors rather than by science. However, with an abundance of growing support for its multitude of medicinal uses, the misguided stigma of cannabis is fading, and there has been a dramatic push for legalizing medicinal cannabis and research. Almost half of the United States has now legalized medicinal cannabis, several states have legalized recreational use, and others have legalized cannabidiol-only use, which is one of many therapeutic cannabinoids extracted from cannabis. Physicians need to be educated on the history, pharmacology, clinical indications, and proper clinical use of cannabis, as patients will inevitably inquire about it for many diseases, including chronic pain and headache disorders for which there is some intriguing supportive evidence.

OBJECTIVE

To review the history of medicinal cannabis use, discuss the pharmacology and physiology of the endocannabinoid system and cannabis-derived cannabinoids, perform a comprehensive literature review of the clinical uses of medicinal cannabis and cannabinoids with a focus on migraine and other headache disorders, and outline general clinical practice guidelines.

CONCLUSION

The literature suggests that the medicinal use of cannabis may have a therapeutic role for a multitude of diseases, particularly chronic pain disorders including headache. Supporting literature suggests a role for medicinal cannabis and cannabinoids in several types of headache disorders including migraine and cluster headache, although it is primarily limited to case based, anecdotal, or laboratory-based scientific research. Cannabis contains an extensive number of pharmacological and biochemical compounds, of which only a minority are understood, so many potential therapeutic uses likely remain undiscovered. Cannabinoids appear to modulate and interact at many pathways inherent to migraine, triptan mechanisms ofaction, and opiate pathways, suggesting potential synergistic or similar benefits. Modulation of the endocannabinoid system through agonism or antagonism of its receptors, targeting its metabolic pathways, or combining cannabinoids with other analgesics for synergistic effects, may provide the foundation for many new classes of medications. Despite the limited evidence and research suggesting a role for cannabis and cannabinoids in some headache disorders, randomized clinical trials are lacking and necessary for confirmation and further evaluation.

Leptin levels are negatively correlated with 2-arachidonoylglycerol in the cerebrospinal fluid of patients with osteoarthritis

BACKGROUND

There is compelling evidence in humans that peripheral endocannabinoid signaling is disrupted in obesity. However, little is known about the corresponding central signaling. Here, we have investigated the relationship between gender, leptin, body mass index (BMI) and levels of the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) in the serum and cerebrospinal fluid (CSF) of primarily overweight to obese patients with osteoarthritis.

METHODOLOGY/PRINCIPAL FINDINGS

Patients (20 females, 15 males, age range 44-78 years, BMI range 24-42) undergoing total knee arthroplasty for end-stage osteoarthritis were recruited for the study. Endocannabinoids were quantified by liquid chromatography - mass spectrometry. AEA and 2-AG levels in the serum and CSF did not correlate with either age or BMI. However, 2-AG levels in the CSF, but not serum, correlated negatively with CSF leptin levels (Spearman's ρ -0.48, P=0.0076, n=30). No such correlations were observed for AEA and leptin.

CONCLUSIONS/SIGNIFICANCE

In the patient sample investigated, there is a negative association between 2-AG and leptin levels in the CSF. This is consistent with pre-clinical studies in animals, demonstrating that leptin controls the levels of hypothalamic endocannabinoids that regulate feeding behavior.

Mast cells, glia and neuroinflammation: partners in crime?

Glia and microglia in particular elaborate pro-inflammatory molecules that play key roles in central nervous system (CNS) disorders from neuropathic pain and epilepsy to neurodegenerative diseases. Microglia respond also to pro-inflammatory signals released from other non-neuronal cells, mainly those of immune origin such as mast cells. The latter are found in most tissues, are CNS resident, and traverse the blood-spinal cord and blood-brain barriers when barrier compromise results from CNS pathology. Growing evidence of mast cell-glia communication opens new perspectives for the development of therapies targeting neuroinflammation by differentially modulating activation of non-neuronal cells that normally control neuronal sensitization - both peripherally and centrally. Mast cells and glia possess endogenous homeostatic mechanisms/molecules that can be up-regulated as a result of tissue damage or stimulation of inflammatory responses. Such molecules include the N-acylethanolamine family. One such member, N-palmitoylethanolamine is proposed to have a key role in maintenance of cellular homeostasis in the face of external stressors provoking, for example, inflammation. N-Palmitoylethanolamine has proven efficacious in mast-cell-mediated experimental models of acute and neurogenic inflammation. This review will provide an overview of recent progress relating to the pathobiology of neuroinflammation, the role of microglia, neuroimmune interactions involving mast cells and the possibility that mast cell-microglia cross-talk contributes to the exacerbation of acute symptoms of chronic neurodegenerative disease and accelerates disease progression, as well as promoting pain transmission pathways. We will conclude by considering the therapeutic potential of treating systemic inflammation or blockade of signalling pathways from the periphery to the brain in such settings.

Care and feeding of the endocannabinoid system: a systematic review of potential clinical interventions that upregulate the endocannabinoid system

Background

The “classic” endocannabinoid (eCB) system includes the cannabinoid receptors CB₁ and CB₂, the eCB ligands anandamide (AEA) and 2-arachidonoylglycerol (2-AG), and their metabolic enzymes. An emerging literature documents the “eCB deficiency syndrome” as an etiology in migraine, fibromyalgia, irritable bowel syndrome, psychological disorders, and other conditions. We performed a systematic review of clinical interventions that enhance the eCB system—ways to upregulate cannabinoid receptors, increase ligand synthesis, or inhibit ligand degradation.

Methodology/Principal Findings

We searched PubMed for clinical trials, observational studies, and preclinical research. Data synthesis was qualitative. Exclusion criteria limited the results to 184 in vitro studies, 102 in vivo animal studies, and 36 human studies. Evidence indicates that several classes of pharmaceuticals upregulate the eCB system, including analgesics (acetaminophen, non-steroidal anti-inflammatory drugs, opioids, glucocorticoids), antidepressants, antipsychotics, anxiolytics, and anticonvulsants. Clinical interventions characterized as “complementary and alternative medicine” also upregulate the eCB system: massage and manipulation, acupuncture, dietary supplements, and herbal medicines. Lifestyle modification (diet, weight control, exercise, and the use of psychoactive substances—alcohol, tobacco, coffee, cannabis) also modulate the eCB system.

Conclusions/Significance

Few clinical trials have assessed interventions that upregulate the eCB system. Many preclinical studies point to other potential approaches; human trials are needed to explore these promising interventions.

Endocannabinoids in the brainstem modulate dural trigeminovascular nociceptive traffic via CB1 and "triptan" receptors: implications in migraine

Activation and sensitization of trigeminovascular nociceptive pathways is believed to contribute to the neural substrate of the severe and throbbing nature of pain in migraine. Endocannabinoids, as well as being physiologically analgesic, are known to inhibit dural trigeminovascular nociceptive responses. They are also involved in the descending modulation of cutaneous-evoked C-fiber spinal nociceptive responses from the brainstem. The purpose of this study was to determine whether endocannabinoids are involved in the descending modulation of dural and/or cutaneous facial trigeminovascular nociceptive responses, from the brainstem ventrolateral periaqueductal gray (vlPAG). CB1 receptor activation in the vlPAG attenuated dural-evoked Aδ-fiber neurons (maximally by 19%) and basal spontaneous activity (maximally by 33%) in the rat trigeminocervical complex, but there was no effect on cutaneous facial receptive field responses. This inhibitory vlPAG-mediated modulation was inhibited by specific CB1 receptor antagonism, given via the vlPAG, and with a 5-HT1B/1D receptor antagonist, given either locally in the vlPAG or systemically. These findings demonstrate for the first time that brainstem endocannabinoids provide descending modulation of both basal trigeminovascular neuronal tone and Aδ-fiber dural-nociceptive responses, which differs from the way the brainstem modulates spinal nociceptive transmission. Furthermore, our data demonstrate a novel interaction between serotonergic and endocannabinoid systems in the processing of somatosensory nociceptive information, suggesting that some of the therapeutic action of triptans may be via endocannabinoid containing neurons in the vlPAG.

Acute reduction of anandamide-hydrolase (FAAH) activity is coupled with a reduction of nociceptive pathways facilitation in medication-overuse headache subjects after withdrawal treatment

OBJECTIVES

We investigated (1) a possible relationship between the functional activity of the endocannabinoid system and the facilitation of pain processing in migraineurs with medication-overuse headache, and (2) the effect of withdrawal treatment on both.

BACKGROUND

The endocannabinoid system antinociception effect includes prevention of nociceptive pathways sensitization. The sensitization of the pain pathways has been demonstrated to be pivotal in the development and maintenance of chronic form of migraine, including medication-overuse headache.

METHODS

We used the temporal summation threshold of the nociceptive withdrawal reflex to explore the spinal cord pain processing, and the platelet activity of the enzyme fatty acid amide hydrolase to detect the functional state of the endocannabinoid system in 27 medication-overuse headache subjects before and 10 and 60 days after a standard withdrawal treatment and compared results with those of 14 controls.

RESULTS

A significantly reduced temporal summation threshold and increased related pain sensation was found in subjects before withdrawal treatment when compared with controls. A significant fatty acid amide hydrolase activity reduction coupled with a significant improvement (reduction) in facilitation of spinal cord pain processing (increase in temporal summation threshold and reduction in related pain sensation) was found in medication-overuse headache subjects at both 10 and 60 days after withdrawal treatment when compared with medication-overuse headache subjects before withdrawal treatment.

CONCLUSIONS

We demonstrated a marked facilitation in spinal cord pain processing in medication-overuse headache before withdrawal treatment when compared with controls. Furthermore, the acute reduction of the fatty acid amide hydrolase activity coupled with a reduction of the facilitation in pain processing immediately (10 days) after withdrawal treatment and its persistence 60 days after withdrawal treatment could represent the consequence of a mechanism devoted to acutely reduce the degradation of endocannabinoids and aimed to increase the activity of the endocannabinoid system that results in an antinociceptive effect.

Dependent behavior in patients with medication-overuse headache

Two thirds of patients with medication-overuse headache (MOH) fulfilled criteria for dependence on acute symptomatic treatments for pain, not exclusive of psychoactive medications, based on the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders. Several questionnaires have been used to assess dependent behavior in patients with MOH. Findings regarding underlying psychological profiles of dependence and MOH are not consistent. Nevertheless, several neuroimaging, genetic, and neurobiological studies support the existence of the common pathophysiological features of dependence and MOH and suggest a link between them. This review highlights recent studies on the relationship between dependence and MOH. This issue is important because it implies a treatment strategy in managing patients with MOH by providing the treatment of dependence.

Interictal type 1 cannabinoid receptor binding is increased in female migraine patients

OBJECTIVE

To compare binding of the type 1 cannabinoid receptor (CB1R) between migraine patients and healthy volunteers.

BACKGROUND

It has been suggested that endocannabinoid deficiency may play a role in the pathophysiology of migraine. Nonetheless, biochemical studies substantiating this idea remain scarce and are faced with methodological shortcomings partly because of the difficulty to perform measurements of endocannabinoids within the central nervous system itself.

METHODS

An observational cross-sectional study was conducted in 20 female migraine patients and 18 healthy women matched for age and body mass index. Positron emission tomography acquisition was performed 90 minutes after intravenous injection of the radioligand [(18)F]MK-9470 to assess binding of [(18)F]MK-9470 to CB1R.

RESULTS

Binding of CB1 R was globally increased in migraine patients vs healthy controls (average gray matter difference +16%; P = .009, 2-sample 2-sided Student's t-test). There were no correlations between CB1R binding and any predefined migraine characteristics. Increases in CB1R binding were most pronounced in the anterior cingulate, mesial temporal, prefrontal, and superior frontal cortices.

CONCLUSION

The increased interictal CB1R binding, especially in brain regions that exert top-down influences to modulate pain, supports the idea that endocannibinoid deficiency is present in female patients suffering from episodic migraine.

Deciphering the mechanism(s) of action of natural products: analgesic peroxide oil as example

BACKGROUND

There are multiple reports of natural products having therapeutic effect. In an era of evidence-based medicine, clinical trials inform clinical decisions regarding use of the product, but prevailing preference is to identify and use a single 'active ingredient'. Yet, the clinical benefit of a natural product might derive from the fortuitous combination of its multiple components. Therefore, the elucidation of the mechanism(s) of action of natural products is important, but presents significant challenges. This article examines this issue using peroxide oil (essential oxygen oil) as an illustrative example.

OBJECTIVE

To review the published literature of a natural product in an effort to elucidate postulated mechanism(s) of action of a complex mixture.

METHODS

The clinical and preclinical literature was reviewed from the perspective of its contribution to elucidating a mechanism of analgesic action of a natural product.

RESULTS

Peroxide oil contains ingredients that are associated with analgesic mechanisms, such inhibition of lipid peroxidation and arachidonic acid metabolism and non-opioid, glibenclamide-sensitive receptor-mediated and K(ATP) -NO-cGMP channel pathways.

CONCLUSION

Although its exact mechanism remains unknown, peroxide oil provides an example of how a natural product can be evaluated for plausible mechanistic explanation of its purported therapeutic efficacy. Such an approach seems valuable, since, as in this case, the constituents appear to contribute in an additive or synergistic manner, something not possible with a single substance.

What is the role of dependence-related behavior in medication-overuse headache?

Medication-overuse headache (MOH) can be viewed as an interaction between the worsening of the primary headache course and individual predispositions for dependence. We present here a review of the clinical and biological data raising the role of dependence-related behavior in MOH. Indeed, several clinical studies show that acute headache medications containing psychoactive components (barbiturates, opiates) are associated with an increased risk of MOH. Diagnostic and Statistical Manual of Mental Disorders, 4th edition substance dependence criteria were identified in a sub-group of MOH patients. Comorbidity between MOH and substance-related disorders has also been showed. Recent neuroimaging, biological, and pharmacogenetic studies suggest the existence of an overlap between the pathophysiological mechanisms of MOH and those of substance-related disorders. These data support the proposition of separating 2 sets of MOH patients: the first one in which the illness is mainly due to the worsening of the headache course, and the second one in which behavioral issues are a major determinant of the illness. Detection of a psychological dependence component in a sub-group of MOH patients should have direct relevance to disease management.

Palmitoylethanolamide and other anandamide congeners. Proposed role in the diseased brain

Acylethanolamides are formed in the brain "on demand" from membrane phospholipids called N-acylated phosphatidylethanolamines. The acylethanolamides are signaling molecules of lipid nature, and this lipofilicity suggests an autocrine function. The acylethanolamides include palmitoylethanolamide (PEA), oleoylethanolamide (OEA), stearoylethanolamide (SEA), and several other quantitative minor species including anandamide (= arachidonoylethanolamide). PEA and OEA can activate several different receptors and inhibit some ion channels, e.g., PPARalpha, vanilloid receptor, K(+) channels (Kv4.3, Kv1.5), and OEA can activate GPR119 and inhibit ceramidases. Targets for SEA are less clear, but it has some cannabimimetic actions in rats in vivo. All acylethanolamides accumulate during neuronal injury, and injected OEA has neuroprotective effects, and PEA has anti-inflammatory effects as studied in the peripheral system. Several of the pharmacological effects seem to be mediated via activation of PPARalpha. Recently, injected OEA has been found to consolidate memories in rats. Inhibitors of the acylethanolamide-degrading enzyme FAAH can increase levels of all acylethanolamides including annandamide, and some of the pharmacological effects caused by these inhibitors may be explained by increased cerebral levels of OEA and PEA, e.g., suppression of nicotine-induced activation of dopamine neurons. Furthermore, through activation of PPARalpha, OEA and PEA may stimulate neurosteroid synthesis, thereby modulating several biological functions mediated by GABA(A) receptors. The existence of acylethanolamides in the mammalian brain has been known for decades, but it is first within the last few years that the putative biological functions of the three most abundant acylethanolamides species are starting to emerge.

Role of calcitonin gene-related peptide in light-aversive behavior: implications for migraine

Migraine is a chronic neurological disorder characterized by recurrent episodes of severe unilateral throbbing head pain and associated symptoms, such as photophobia. Our current understanding of the mechanisms underlying migraine has been hampered by limitations in ascertaining migraine symptoms in animal models. Clinical studies have established the neuropeptide calcitonin gene-related peptide (CGRP) as a key player in migraine. Here, we establish a genetic model of photophobia by engineering increased sensitivity to CGRP in mice. These transgenic mice (nestin/hRAMP1) display light-aversive behavior that is greatly enhanced by intracerebroventricular injection of CGRP and blocked by coadministration of the CGRP receptor antagonist olcegepant. This behavior appears to be an indicator of photophobia and cannot be fully explained by gross abnormality of ocular anatomy or differences in general anxiety or motor activity. Our findings demonstrate that a single gene, receptor activity-modifying protein 1 (RAMP1), can be a modifier of photophobia and, by extension, suggest that genetic or epigenetic modulation of RAMP1 levels may contribute to migraine susceptibility. Moreover, they validate CGRP hypersensitive mice as a tool for exploring the neurobiology and novel therapies for migraine and other disorders involving photophobia.

Variations in the cannabinoid receptor 1 gene predispose to migraine

In animal models endogenous cannabinoids have an inhibitory effect on trigeminovascular activation through the cannabinoid receptor 1 (CB1), although there is no evidence of the potential role of CB1 in human migraine. In this study we applied single marker association and haplotypic trend regression analysis to investigate the relationship between the CB1 gene (CNR1) and headache with migraine symptoms (nausea, photophobia and disability, measured by the ID-migraine questionnaire). We identified our controls (CO=684) as those who have not reported ID-migraine symptoms at all and defined migraine headache sufferers (M=195) as those who reported all three symptoms. The CNR1 was covered by 10 SNPs located throughout the gene based on haplotype tagging (htSNP) and previous literature. Our results demonstrated a significant haplotypic effect of CNR1 on migraine headaches (p=0.008, after permutation p=0.017). This effect was independent of reported depression or drug/alcohol abuse although using neuroticism in the analysis as covariant slightly decreased this association (p=0.027, permutated p=0.052). These results suggest a significant effect of CNR1 on migraine headaches that might be related to the alteration of peripheral trigeminovascular activation. In addition, this is the first study to demonstrate the effectiveness of using trait components combinations to define extreme phenotypes with haplotype analysis in genetic association studies for migraine. However, further studies are needed to elucidate the role of CNR1 and the cannabinoid system in migraine.

Endocannabinoids in Alzheimer's disease and their impact on normative cognitive performance: a case-control and cohort study

BACKGROUND

Neuropathological, animal, and cell culture studies point to a role for the body's own endogenous cannabinoids (eCBs) system in Alzheimer's disease (AD) pathology and treatment. To date, no published studies have investigated the potential utility of circulating eCBs as diagnostic biomarkers for AD or the impact of central eCBs on cognition.

RESULTS

In comparison with healthy controls, there were no significant differences in measured eCB concentrations in plasma samples from patients with AD. Detectable eCBs in cerebrospinal fluid (CSF) had no relationship to cognitive performance in healthy controls at risk for AD. In pooled plasma samples, an inverse correlation was observed between plasma levels of the eCB 2-AG (2-arachidonoylglycerol) and TNF-alpha (r = -0.41, p < 0.02).

CONCLUSION

These results suggest that circulating endocannabinoids do not have utility as diagnostic biomarkers for AD and do not have a robust correlation with cognitive performance. Circulating levels of 2-AG may downregulate TNF-alpha production.

Targeting the endocannabinoid system in Alzheimer's disease

The endocannabinoid system is rapidly emerging as a potential drug target for a variety of immune-mediated central nervous system diseases. There is a growing body of evidence suggesting that endocannabinoid interventions may have particular relevance to Alzheimer's disease. Here we present a review of endocannabinoid physiology, the evidence that underscores its utility as a potential target for intervention in Alzheimer's disease, and suggest future pathways of research.

Cannabinoids in the management of difficult to treat pain

This article reviews recent research on cannabinoid analgesia via the endocannabinoid system and non-receptor mechanisms, as well as randomized clinical trials employing cannabinoids in pain treatment. Tetrahydrocannabinol (THC, Marinol((R))) and nabilone (Cesamet((R))) are currently approved in the United States and other countries, but not for pain indications. Other synthetic cannabinoids, such as ajulemic acid, are in development. Crude herbal cannabis remains illegal in most jurisdictions but is also under investigation. Sativex((R)), a cannabis derived oromucosal spray containing equal proportions of THC (partial CB(1) receptor agonist ) and cannabidiol (CBD, a non-euphoriant, anti-inflammatory analgesic with CB(1) receptor antagonist and endocannabinoid modulating effects) was approved in Canada in 2005 for treatment of central neuropathic pain in multiple sclerosis, and in 2007 for intractable cancer pain. Numerous randomized clinical trials have demonstrated safety and efficacy for Sativex in central and peripheral neuropathic pain, rheumatoid arthritis and cancer pain. An Investigational New Drug application to conduct advanced clinical trials for cancer pain was approved by the US FDA in January 2006. Cannabinoid analgesics have generally been well tolerated in clinical trials with acceptable adverse event profiles. Their adjunctive addition to the pharmacological armamentarium for treatment of pain shows great promise.

Degradation of endocannabinoids in chronic migraine and medication overuse headache

Chronic migraine (CM) is frequently associated with medication overuse headache (MOH). The endocannabinoid system plays a role in modulating pain including headache and is involved in the common neurobiological mechanism underlying drug addiction and reward system. Anandamide (AEA) and 2-arachidonoylglycerol are the most biologically active endocannabinoids, which bind to both central and peripheral cannabinoid receptors. The level of AEA in the extracellular space is controlled by cellular uptake via a specific AEA membrane transporter (AMT), followed by intracellular degradation by the enzyme AEA hydrolase (fatty acid amide hydrolase, FAAH). AMT and FAAH have also been characterized in human platelets. We assayed the activity of AMT and of FAAH in platelets isolated from four groups of subjects: MOH, CM without MOH, episodic migraine and controls. AMT and FAAH were significantly reduced in CM and MOH, compared to either controls or episodic migraine group. This latter finding was observed in both males and females with CM and MOH. Changes observed in the biochemical mechanisms degrading endogenous cannabinoids may reflect an adaptative behaviour induced by chronic headache and/or drug overuse.

Short- and long-term plasticity of the endocannabinoid system in neuropsychiatric and neurological disorders

The activity of the endocannabinoid system, in terms of the levels of the endocannabinoids and of cannabinoid receptors, or of the functional coupling of the latter to a biological response, undergoes to remodelling during pathological conditions. In the CNS, these changes, depending also on the nature of the disorder, can be transient or long-lasting, occur only in those tissues involved in the pathological condition and usually aim at restoring the physiological homeostasis by reducing excitotoxicity, inflammation and neuronal death. However, during chronic disorders, prolonged activation of the endocannabinoid system might also contribute to the symptoms of the pathology. Whilst acute changes of the tissue levels of the endocannabinoids reflect the "on demand" nature of their biosynthesis and release, and hence are effected mostly through regulation of the biosynthetic enzymes, chronic changes seem to be mostly due to longer-lasting alterations in the expression of anabolic and catabolic enzymes. The possibility of obtaining therapeutic advantage from endocannabinoid plasticity in neuropsychiatric and neurological disorders is discussed in this review article.