CNS & Neurological Disorders - Drug Targets (Formerly Current Drug Targets - CNS & Neurological Disorders) - Volume 12, Issue 1, 2013

Ethanolamides of long-chain fatty acids are a class of endogenous lipid mediators generally referred to as Nacylethanolamines (NAEs). NAEs include anti-inflammatory and analgesic palmitoylethanolamide, anorexic oleoylethanolamide, and the endocannabinoid anandamide. Since the endogenous levels of NAEs are principally regulated by enzymes responsible for their biosynthesis and degradation, these enzymes are expected as targets for the development of therapeutic agents. Thus, a better understanding of these enzymes is indispensable. The classic “N-acylationphosphodiesterase pathway” for NAE biosynthesis is composed of two steps; the formation of Nacylphosphatidylethanolamine (NAPE) by N-acyltransferase and the release of NAE from NAPE by NAPE-hydrolyzing phospholipase D (NAPE-PLD). However, recent studies, including the analysis of NAPE-PLD-deficient (NAPE-PLD-/-) mice, revealed the presence of NAPE-PLD-independent multi-step pathways to form NAEs from NAPE in animal tissues. Our recent studies using NAPE-PLD-/- mice also suggest that NAE is formed not only from NAPE, but also from Nacylated plasmalogen-type ethanolamine phospholipid (N-acyl-plasmenylethanolamine) through both NAPE-PLDdependent and -independent pathways. Here, we present recent findings on NAE biosynthetic pathways mainly occurring in the brain.

Palmitoylethanolamide (PEA) as well as the other N-acylethanolamines (NAEs), e.g. anandamide, oleoylethanolamide, stearoylethanolamide and linoleoylethanolamide, appear to exist in every mammalian cell at low levels, e.g. a few hundred pmol/g tissue for PEA. Their formation can be stimulated by cellular injury and inflammation. In the brain PEA and other NAEs may have neuroprotective functions. PEA levels in tissues seem hardly to be influenced by variation in intake of dietary fatty acids, except in the small intestine where dietary fat results in decreased levels of PEA and other NAEs. In rat small intestine, PEA, oleoylethanolamide and linoleoylethanolamide have anorectic properties. Of other dietary components, only ethanol is known to influence tissue levels of PEA. Thus, an acute intoxicating dose of ethanol will decrease PEA levels in various areas in the brain of rats. The mechanism behind this effect is not known.

Palmitoylethanolamide (PEA) belongs to the N-acyl ethanolamines (NAEs), a group of endogenous compounds involved in a variety of physiological processes, including energy homeostasis and inflammation. This review focuses on the analysis of PEA in plasma and tissues and discusses effects of diet and some pathological processes on PEA levels. Originally isolated from egg yolk, PEA has been detected in a variety of tissues and plasma of different species. The compound is present at relatively high levels compared to other NAEs and now mostly analysed using liquid chromatography coupled to mass spectrometry. PEA plasma concentrations show marked fluctuations during the day. However, concentrations in tissues are likely to be more relevant than those in plasma. Most studies suggest that compared to other NAEs, tissue PEA tissue levels are not influenced by changes in dietary fatty acid composition. Effects of inflammation and disease on PEA tissue levels show differences between different models and studies. Therefore, more research is needed on the endogenous role and tissue kinetics of PEA during disease. The rediscovery of the therapeutic potential of PEA has fuelled research and the development of new pharmaceutical formulations. With regard to this there is a need for better kinetic data and models, preferably also on its tissue disposition. Moreover, it is important to learn more about effects of exogenous PEA on the kinetics of other NAEs (and endocannabinoids) and effects of inhibiting its breakdown using inhibitors of the degrading enzymes fatty acid amide hydrolase or N-acylethanolamine-hydrolyzing acid amidase.

We have previously shown that the endogenous lipid palmitoylethanolamide (PEA) induced relief of neuropathic pain through an action upon receptors located on the nociceptive pathway. Recently, it has been proposed that immune cells, in particular mast cells, and microglia, by releasing algogen mediators interact with neurons to alter pain sensitivity thereby contributing to the development and maintenance of chronic pain states. The aim of this work was to explore whether the anti-nociceptive properties of PEA might be accompanied by modulation of these non-neuronal cells. Mice were subjected to a chronic constriction injury model of neuropathic pain and treated with PEA. The data show that at the earlier (3 days) time-point after nerve injury there was a substantial recruitment of mast cells whose activation was not yet pronounced. In contrast, at the later time point (8 days) there was no further increase in mast cell number, but rather a marked activation of these cells. An up-regulation of activated microglia was found in the spinal cord of neuropathic pain mice. PEA delayed mast cell recruitment, protected mast cells against degranulation and abolished the nerve growth factor increase in sciatic nerve concomitantly preserving the nerve from degeneration, while reducing microglia activation in the spinal cord. These findings support the idea that non-neuronal cells may be a valuable pharmacological target to treat neuropathic pain since the current neuronal-direct drugs are still unsatisfactory. In this context PEA could represent an innovative molecule, combining a dual analgesic activity, both on neurons and on nonneuronal cells.

Palmitoylethanolamide (PEA) is an endogenous cannabinoid-like compound in the central nervous system, which can modulate several functions in different pathological states, such as inflammation and pain response. We have here investigated the effect of PEA (5-10 mg/kg, intraperitoneally) on mechanical allodynia and thermal hyperalgesia 3 and 7 days following peripheral injection of formalin. Formalin induced a significant decrease of thermal and mechanical threshold in the injected and contralateral paw. PEA chronic treatment (once per day) significantly reduced mechanical allodynia and thermal hyperalgesia in a dose-dependent manner. Consistently, in vivo electrophysiological analysis revealed a significant increase of the duration and frequency, and a rapid decrease in the onset of evoked activity of the spinal nociceptive neurons 7 days after formalin. PEA normalized the electrophysiological parameters in a dosedependent manner. Moreover, we investigated PEA effect on the glial/microglial phenotypical changes associated with spinal neuronal sensitization. We found that formalin induced a significant microglia and glia activation normalized by PEA, together with increased expression of glial interleukin 10. Finally, primary microglial cell cultures, conditioned with PEA or vehicle, where transplanted in naive and formalin-treated mice, and nociceptive neurons were recorded. We observed that only PEA-conditioned cells normalized the activity of sensitized nociceptive neurons. In conclusion these data confirm the potent anti-inflammatory and anti-allodynic effect of PEA, and highlight a possible targeted microglial/glial effect of this drug in the spinal cord.

The role of palmitoylethanolamide (PEA) in the regulation of complex systems involved in the inflammatory response, pruritus, neurogenic and neuropathic pain is well understood. Growing evidence indicates that this Nacylethanolamine also exerts neuroprotective effects within the central nervous system (CNS), i.e. in spinal cord and traumatic brain injuries and in age-related pathological processes. PEA is abundant in the CNS, and is produced by glial cells. Several studies show that administering PEA during the first few hours after injury significantly limits CNS damage, reduces loss of neuronal tissue and improves functional recovery. PEA appears to exert its protective effect by decreasing the development of cerebral edema, down-regulating the inflammatory cascade, and limiting cellular necrosis and apoptosis. All these are plausible mechanisms of neuroprotection. This review provides an overview of current knowledge of PEA effect on glial functions in the brain and how targeting glial-specific pathways might ultimately impact the development of therapies for clinical management of neurodegenerative disorders. The diverse signaling mechanisms are also summarized.

The growth of knowledge about the molecular mechanisms underlying Alzheimer's disease (AD) has highlighted the role of neuroinflammation in the pathophysiology of this disorder. AD is classically characterized by the deposit of misfolded proteins: the extracellular accumulation of beta amyloid peptide (Aβ), and the formation of intracellular neurofibrillary tangles. However, it is clear that many other cellular dysfunctions occur. Among these, a prominent role is exerted by the inflammatory process which is a consequence of the over-activation of glial cells. Indeed, several models of AD have demonstrated that glia modify their functions, losing the physiological supportive role. These cells instead acquire a pro-inflammatory phenotype, thus contributing to exacerbate Aβ toxicity. The relationship between neurodegeneration and neuroinflammation is strictly interdependent, and research efforts are now addressed to antagonize both processes simultaneously. Along this line palmitoylethanolamide (PEA) has attracted much attention because of its numerous pharmacological properties, particularly those related to the modulation of peripheral inflammation through the peroxisome proliferator activated receptor-α involvement. In light of these considerations, we explored the antiinflammatory and neuroprotective effects of PEA in rat neuronal cultures and organotypic hippocampal slices challenged with Aβ, and treated with PEA in the presence or absence of a selective peroxisome proliferator activated receptor-α antagonist. The data indicate that PEA is able to blunt Aβ-induced astrocyte activation and to exert a marked protective effect on neurons. These findings highlight new pharmacological properties of PEA and suggest that this compound may provide an effective strategy for AD.

The discovery that N-acylethanolamines, such as oleoylethanolamide (OEA) and palmitoylethanolamide (PEA), acting as endogenous ligands of alpha-type peroxisome proliferator-activated receptors (PPARα), block nicotineinduced excitation of dopamine neurons revealed their role as important endogenous negative modulators of nicotinic receptors containing β2 subunits (denoted β2*-nAChRs) on dopamine neurons, which are key to the brain reward system. Using mass-spectrometry data analysis from rodent brain slices containing the midbrain, we characterized the effects induced by modulation of PPARα on PEA and OEA levels. PEA and OEA constitutive levels in the midbrain are higher than endocannabinoids (e.g. anandamide, 2-arachidonoylglycerol), and depend upon excessive input drive and the metabolic state of the cells. Accordingly, OEA and PEA synthesis is affected when adding low concentrations of fatty acids (endogenous PPARα ligands), most likely through activation of PPARα. Indeed, PPARα activation increases PEA and OEA levels, which may further sustain PPARα activity. Given this, it is likely that these molecules dynamically affect dopamine function and excitability, as well as their dependent behaviour. Consequently, N-acylethanolamines may confer less vulnerability towards disruption of dynamic balance of dopamine-acetylcholine systems through PPARα activation. Finally, using pharmacological and/or nutritional strategies which target PPARα might represent a promising therapeutic approach to prevent disorders often related to neuro-inflammation, stress and abnormal β2*-nAChR function.

Since its discovery palmitoylethanolamide was considered as an endogenous compound able to negatively modulate the inflammatory process. Its effects have been extensively investigated in in vitro, in vivo and in clinical studies. Notwithstanding some discrepancy, nowadays the efficacy of palmitoylethanolamide in controlling mast cell behaviour, which likely accounts for its many anti-inflammatory, anti-angiogenic and analgesic effects, is well recognized. In view of their strategic localization at sites directly interfacing with the external environment, mast cells act as surveillance antennae against different types of injury and can undergo activation, thereby regulating both innate and adaptive immune reactions through the release of several preformed and newly synthesized mediators. Mast cells are now viewed as key players in orchestrating several disorders including both acute and chronic inflammatory processes, and have a role in angiogenesis and hyperalgesia. Since mast cells exert also important physiological, homeostatic functions, the most recent goal for pharmacologists is to control, rather than block, mast cell degranulation in order to modulate the pathological scenario. The aim of the present review is to summarise the evidence regarding the role played by palmitoylethanolamide in the control of mast cell activation, starting from in vitro studies, going through in vivo evidence in animal models of disease sustained by mast cell activation, and finally reviewing recent clinical studies using this molecule.

Hepatic encephalopathy (HE) is a severe neuropsychiatric complication of liver failure, in which there is injury to brain cells, particularly neurons and glia. Brain cells and their function are greatly influenced by omega-3 polyunsaturated fatty acids, essential components of cell membrane phospholipids in the brain that are crucial to normal function. This study assessed the effect of chronic fish oil (FO) supplementation (rich in omega-3 polyunsaturated fatty acids) on behavior and oxidative stress of Wistar rats subjected to HE due to a liver failure caused by thioacetamide (TAA) intoxication. The FO supplementation started in an early phase of brain development, that is, at the 21st day of life, and extended to the 122th day of life. The results indicated that cognitive function, specifically spatial memory, was markedly affected in the group that received TAA. Most notably, the ill effects caused by TAA administration were counteracted by FO supplementation. In addition to behavioral improvements, FO also promoted reduction in levels of thiobarbituric acid-reactive substances and superoxide dismutase activity in hippocampus and cerebral cortex. In summary, FO protected against spatial memory deficits and oxidative stress caused by HE in rats subjected to liver lesion due to TAA intoxication. Further studies are necessary to understand the mechanism underlying FO behaviors in rats subjected to encephalopathy.

Choline-containing phospholipids were proposed as cognition enhancing agents, but evidence on their activity is controversial. CDP-choline (cytidine-5´-diphosphocholine, CDP) and choline alphoscerate (L-alpha-glycerylphosphorylcholine, GPC) represent the choline-containing phospholipids with larger clinical evidence in the treatment of sequelae of cerebrovascular accidents and of cognitive disorders. These compounds which display mainly a cholinergic profile interfere with phospholipids biosynthesis, brain metabolism and neurotransmitter systems. Dated preclinical studies and clinical evidence suggested that CDP-choline may have also a monoaminergic profile. The present study was designed to assess the influence of treatment for 7 days with choline-equivalent doses (CDP-choline: 325 mg/Kg/day; GPC: 150 mg/Kg/day) of these compounds on brain dopamine (DA), and serotonin (5-HT) levels and on DA plasma membrane transporter (DAT), vesicular monoamine transporters (VMAT1 and VMAT2), serotonin transporter (SERT), and norepinephrine transporter (NET) in the rat. Frontal cortex, striatum and cerebellum were investigated by HPLC with electrochemical detection, immunohistochemistry, Western blot analysis and ELISA techniques. CDP-choline did not affect DA levels, which increased after GPC administration in frontal cortex and cerebellum. GPC increased also 5-HT levels in frontal cortex and striatum. DAT was stimulated in frontal cortex and cerebellum by both CDP and GPC, whereas VMAT2, SERT, NET were unaffected. VMAT1 was not detectable. The above data indicate that CDP-choline and GPC possess a monoaminergic profile and interfere to some extent with brain monoamine transporters. This activity on a relevant drug target, good tolerability and safety of CDP-choline and GPC suggests that these compounds may merit further investigations in appropriate clinical settings.

Background: Inflammation is known to play a role in cererovascular risk. Multiple sclerosis (MS) is a neurodegenerative disease that is initially characterized by inflammatory changes in the brain. We hypothesized that due to chronic inflammation, MS patients would present with a higher levels of cardiovascular (CV) risk factors than non-MS patients. Methods: We performed a retrospective chart review on 206 MS patients and 142 control patients suffering from meningiomas and acoustic neuromas, non inflammatory, non autoimmune diseases of the brain. The obtained data included fasting lipid profiles, plasma glucose, systolic and diastolic blood pressure (BP), serum levels of homocysteine and uric acid, data on iron status, smoking habit, and list of medications. In addition, data on indicators of MS disease severity was obtained for MS patients. Results: MS patients had significantly higher total plasma cholesterol, p = 0.01, and plasma high density lipoprotein, P <0.001, but lower plasma glucose, P <0.001, and systolic BP, P = 0.001, than non-MS patients. In addition, MS patients had lower erythrocyte sedimentation rate and serum vitamin B12, but higher serum folic acid and vitamin D3 than non-MS patients. A positive correlation was observed between plasma glucose and the extended disability status scale (EDSS), P = 0.008, and between plasma glucose and the rate of clinical relapse, P = 0.001. Conclusion: The MS pathophysiology may be among factors for the lower CV risk factors in MS patients. Future studies should examine whether the chronic use of many pharmacological agents influence CV risk factors in MS patients.

Opioid withdrawal syndrome is a debilitating manifestation of opioid dependence and responds poorly to the available clinical therapies. Studies from various in vivo and in vitro animal models of opioid withdrawal syndrome have led to understanding of its pathobiology which includes complex interrelated pathways leading to adenylyl cyclase superactivation based central excitation. Advancements in the elucidation of opioid withdrawal syndrome mechanisms have revealed a number of key targets that have been hypothesized to modulate clinical status. The present review discusses the neurobiology of opioid withdrawal syndrome and its therapeutic target recptors like calcitonin gene related peptide receptors (CGRP), N-methyl-D-aspartate (NMDA) receptors, gamma aminobutyric acid receptors (GABA), G-proteingated inwardly rectifying potassium (GIRK) channels and calcium channels. The present review further details the potential role of second messengers like calcium (Ca2+) / calmodulin-dependent protein kinase (CaMKII), nitric oxide synthase, cytokines, arachidonic acid metabolites, corticotropin releasing factor, fos and src kinases in causing opioid withdrawal syndrome. The exploitation of these targets may provide effective therapeutic agents for the management of opioid dependence-induced abstinence syndrome.

Epigenetics is key to understanding modulation of gene expression at specific stages and conditions in nervous system development and function. In epigenetic processes, a variety of enzymes contribute to modify chromatin with methyl, acetyl or other chemical marks, leading to repression or activation of the targeted gene without altering the original sequence. Aberrant activities of these epigenetic enzymes are implicated in many nervous system diseases, including neurodevelopmental disorders, brain cancer, neurodegenerative diseases, and mental illnesses. Thus, they have emerged as new targets for treating a variety of nervous system disorders. In this review, we briefly summarize the association between various epigenetic mechanisms and discuss recent progress in drug discovery efforts involving epigenetic regulators.