CNS & Neurological Disorders - Drug Targets (Formerly Current Drug Targets - CNS & Neurological Disorders) - Volume 11, Issue 3, 2012

Palmitoylethanolamide (PEA) is one of a class of naturally occurring lipidic molecules composed of a fatty acid and ethanolamine, namely the fatty acid ethanolamides (FAEs). PEA is abundant in mammalian brain and, for other FAEs, is produced through an ondemand synthesis within the lipid bilayer [1]. The potential benefit of FAEs was first recognized in the early 1940s with the reported antipyretic properties of dried chicken egg yolk in children with rheumatic fever [2]. A decade later, the lipid fraction from egg yolk was identified as the component responsible for this effect [3], with PEA being the active component [4]. The potential applications of this lipid amide remained largely overlooked, however, until the characterization of its anti-inflammatory [5], analgesic [6], and anticonvulsant [7] properties. Indeed, these past 15 years have seen a noteworthy increase in studies dealing with the antiinflammatory actions of PEA [8]. Such was the impetus behind an international conference held in Pozzuoli 9-10 February 2012 and the first ever dedicated to this fast-growing area of biomedical research.....

Parkinson's disease (PD), the most frequent movement disorder, is caused by the progressive loss of the dopamine neurons within the substantia nigra pars compacta and the associated deficiency of the neurotransmitter dopamine in the striatum. Most cases of PD are of a sporadic nature whose cause is unknown, while mutations in several genes have been linked to genetic forms of PD (α-synuclein, Parkin, DJ-1, PINK1, and LRRK2). Epidemiological studies in humans, as well as molecular studies in toxin-induced (e.g. 6-hydroxydopamine (6-OHDA) and rotenone) and genetic animal models of PD show that mitochondrial dysfunction, especially Complex I, is a defect occurring early in the pathogenesis of both sporadic and familial PD. Mitochondrial dynamics (fission, fusion, migration) are important for neurotransmission, synaptic maintenance and neuronal survival.....

Catechol-O-methyltransferase (COMT) [1] is a key enzyme involved in the methylation of catechol structures, including dopamine, norepinephrine, epinephrine, caffeine, and catechol estrogens. In the last decade, there has been renewed interest in this enzyme because of the findings that implicate it in the development and manifestations of mental illnesses. It is now commonly accepted that COMT’s most crucial effects are centered in the modulation of prefrontal cortex (PFC)-mediated functions. This might be explained by the major determinant role of COMT in PFC dopaminergic signaling, which is critical for modulating higher order cognitive functions, thereby impacting many domains of human behavior, thought and emotion. However, also regions of the nervous system other than the PFC and biological effectors apart from dopamine might be affected by COMT. This possibility is still less explored and will need to be addressed in future studies. Nevertheless, COMT pleiotropic behavioral effects seem consistent and real. In particular, from studies conducted in both mouse models and humans, COMT enzyme activity seems to be involved in an apparent evolutionary trade-off between cognitive and affective functions [2-4]. The knowledge acquired so far, indicate COMT as an attractive drug target potentially having important implications for several disorders of the nervous system. Indeed, as it is evident from the review manuscripts in this special issue, the activity of COMT has been linked to a large spectrum of human phenotypes, including cognition, pain sensitivity, personality, anxiety, psychosis and reward processing. Notably, the level of COMT enzyme activity presents individual changes in the human population because of common functional genetic mutations. Genetic variations in COMT may have important implications in the clinical setting, as changing COMT activity could impact the efficacy and dosing of a particular therapeutic treatment and/or intervention. Therefore, functional genetic variations in COMT are factors that will probably need to be considered in the rational design of more effective and personalized healthcare.....

Aging is associated with deficits in several cognitive domains as well as a decline in brain dopamine activity. Catechol-O-methyl transferase (COMT), an enzyme involved in the degradation of dopamine, is a critical determinant of the availability of this neurotransmitter in the prefrontal cortex. A functional single nucleotide polymorphism in the COMT gene, Val158Met, modulates the activity of this enzyme and affects cognition and the brain regions underlying this function. The effects of COMT Val158Met polymorphism are magnified in the aging brain. Here, we review the evidence supporting a role of COMT genetic variation in cognitive as well as structural and functional brain changes associated with senescence. We will address the potential modulatory role of genetic and non-genetic factors on the neural and cognitive effects of COMT Val158Met in late life. Furthermore, we will discuss the viability of a COMT-targeted treatment for improving cognitive efficiency in aging.

Catechol-O-methyltransferase (COMT) is a promising target for modulation of cognitive functions and dysfunctions. COMT dominates the regulation of dopamine metabolism in the prefrontal cortex. Thus, COMT effects are particularly evident in prefrontal cortex-dependent cognitive functions including executive control, working memory, attentional control and long-term memory. This has been determined by both genetic and pharmacological studies that we will highlight in the present review. In particular, we will discuss how common functional variants of the COMT gene may predict individual variation in selective cognitive abilities and vulnerability to cognitive deficits that characterize several neuropsychiatric disorders. Moreover, COMT genetic variants represent one source of individual differences in the cognitive responses to medications such as those used in psychiatric illnesses. COMT genetic testing may then predict some cognitive dysfunctions often seen in certain psychiatric illnesses even from presymptomatic stages and the efficacy/dosage of drugs used to treat them. The consideration of COMT-dependent differences may be important for the development of more efficient personalized healthcare.

The enzyme catechol-O-methyltransferase (COMT) has been shown to play a critical role in pain perception by regulating levels of epinephrine (Epi) and norepinephrine (NE). Although the key contribution of catecholamines to the perception of pain has been recognized for a long time, there is a clear dichotomy of observations. More than a century of research has demonstrated that increasing adrenergic transmission in the spinal cord decreases pain sensitivity in animals. Equally abundant evidence demonstrates the opposite effect of adrenergic signaling in the peripheral nervous system, where adrenergic signaling increases pain sensitivity. Viewing pain processing within spinal and peripheral compartments and determining the directionality of adrenergic signaling helps clarify the seemingly contradictory findings of the pain modulatory properties of adrenergic receptor agonists and antagonists presented in other reviews. Available evidence suggests that adrenergic signaling contributes to pain phenotypes through α1/2 and β2/3 receptors. While stimulation of α2 adrenergic receptors seems to uniformly produce analgesia, stimulation of α1 or β receptors produces either analgesic or hyperalgesic effects. Establishing the directionality of adrenergic receptor modulation of pain processing, and related COMT activity in different pain models are needed to bring meaning to recent human molecular genetic findings. This will enable the translation of current findings into meaningful clinical applications such as diagnostic markers and novel therapeutic targets for complex human pain conditions.

This review provides a short overview of the most significant biologically oriented theories of human personality. Personality concepts of Eysenck, Gray and McNaughton, Cloninger and Panksepp will be introduced and the focal evidence for the heritability of personality will be summarized. In this context, a synopsis of a large number of COMT genetic association studies (with a focus on the COMT Val158Met polymorphism) in the framework of the introduced biologically oriented personality theories will be given. In line with the theory of a continuum model between healthy anxious behavior and related psychopathological behavior, the role of the COMT gene in anxiety disorders will be discussed. A final outlook considers new research strategies such as genetic imaging and epigenetics for a better understanding of human personality.

One of the most important enzymes in the catecholamine cycle, catecholamine-O-methyltransferase (COMT), plays a critical role in the extracellular metabolism of dopamine and norepinephrine both in the periphery and the central nervous system. COMT has attracted strong interest in regards to its role in dopamine-related pathologies, particularly Parkinson’s disease. There are several mechanisms for the potential involvement of COMT-related processes in the pathophysiology of Parkinson’s disease or the consequences of L-DOPA treatment. COMT-mediated metabolism of LDOPA in the periphery influences brain dopamine levels, while the product of central COMT-mediated dopamine metabolism, 3-methoxytyramine, can affect movement via interaction with Trace Amine-Associated Receptor 1 (TAAR1). COMT inhibitors have a long history of clinical use in the treatment of Parkinson’s disease. Several clinical genetic studies have shown that variants of COMT gene contribute to the manifestations or treatment responses of this disorder. Here, we review the basic molecular mechanisms that could be involved in COMT-dependent processes in Parkinson’s disease, the pharmacological properties of COMT inhibitors used in the treatment of this disorder and the clinical genetic observations involving COMT gene variants as modulators of pathological processes and responses to dopamine replacement therapies used in the treatment of the disorder.

Psychiatry is a specialty where the application of pharmacogenomics approaches is made to the study of interindividual differences in response to antidepressants. It is highly applied for improving patient treatment. Major depressive disorder (MDD) is a common and complex disorder resulting from genetic and environmental interactions. Less than 40% of patients with MDD achieve remission, and even after several treatment trials, one in three patients do not fully recover from MDD. Many clinical and genomic association studies suggested that the catechol-Omethyltransferase (COMT) gene region was an important genetic locus for psychiatric disorders, because of the proposed relationship between its function in catecholaminergic neurotransmission and individual response to antidepressants, and vulnerability to psychiatric disorders. Although a number of COMT single nucleotide polymorphisms (SNPs) were observed, the Val108/158Met (rs4680) polymorphism in exon 4 resulted in a change in the enzyme structure which has been intensively investigated in relation to its role of enzyme activity and processes of prefrontal cortex functions in cognition. As serotonin interacts with dopamine and dopamine availability is influenced by COMT SNPs, an association between the COMT gene and response to treatment, based on the various pharmacogenetics/pharmacogenomics studies about COMT gene published to date, is explored in this overview.

22q11.2 deletion syndrome (22q11DS) is a genetic syndrome associated with a microdeletion of the chromosome 22 band q11.2 with an estimated prevalence between 1:2,500 and 1:4,000. Studies of school-age children have shown that individuals with 22q11DS have high rates of psychiatric morbidity. In particular, by late adolescence, about 30% of patients with 22q11DS develop psychotic symptoms. One of the genes located in the microdeletion region of 22q11DS is the catechol-O-methyl transferase (COMT) which codes for an enzyme critically involved in the catabolic clearance of dopamine. COMT is critically involved in cognitive related disturbances, and it has often been suggested as a sensitive factor in the development of psychiatric disorders. Several studies have been conducted on the impact of COMT functional polymorphism in 22q11DS and its related cognitive/psychiatric correlates. In this review, we summarize mainly current knowledge on the correlation between schizophrenia/cognitive related symptoms and COMT genetic variations in 22q11DS. A selective literature review on this topic was undertaken. COMT might play an important role in modulating cognitive functions in 22q11DS but a clear relationship between COMT polimorphism and schizophrenia in 22q11DS need further investigation. Despite controversial results, 22q11DS represent a powerful model for studying the role of COMT and other genetic variations in schizophrenia. This is due to high risk in 22qDS patients of developing this disorder and their relative genetic homogeneity. Further research is needed to evaluate all of the polymorphic markers in the COMT gene and its nearby regulatory elements for association with schizophrenia. Identification of specific COMTdependent molecular, cellular and circuit deficits will provide targets for the development of more efficient treatments for the cognitive and psychiatric symptoms in 22q11DS.

Current antipsychotic drugs lack material efficacy against the negative symptoms and cognitive deficits of schizophrenia. There is considerable uncertainty regarding the optimal pharmacotherapeutic strategy for treating these and other aspects of psychotic illness. The present review summarises clinical, mutant, and psychopharmacological data related to catechol-O-methyltransferase (COMT), an enzyme involved in the catabolism of catecholamine neurotransmitters, with a view to establishing the antipsychotic potential of compounds targeting the action of this enzyme. The review examines clinical and preclinical genetic data linking COMT gene variation with risk for schizophrenia or specific symptoms or disease endophenotypes. We then summarise data concerning the behavioural effects of COMT inhibitors. These genetic and pharmacological data relating to COMT as a therapeutic target have implications for the development of individualised treatments for treatment-resistant symptoms of schizophrenia, including cognitive dysfunction and, potentially, negative symptoms.

Abnormal sleep is an endophenotype of schizophrenia. Here we provide an overview of the genetic mechanisms that link specific sleep physiological processes to schizophrenia-related cognitive defects. In particular, we will review the possible relationships between catechol-O-methyltransferase (COMT), sleep regulation and schizophrenia development. Recent studies validate the hypothesis that COMT mutations may trigger disturbances during adolescence that affect sleep and cortical development. Anomalies in cortical development during this critical developmental phase may increase the susceptibility for schizophrenia. In conclusion, in view of therapeutic efficacy, we can envisage indications for future investigations into the role of COMT for sleep regulation, cognitive performance and sleep-related cognitive deficits.

Alzheimer's disease (AD) is the leading cause of dementia worldwide and is associated with a marked individual, familial and social burden. Catechol-O-mehyltransferase (COMT) is surfacing with a prominent role in AD pathophysiology by affecting the metabolism of catecholamine neurotransmitters and estrogen. COMT gene regulates dopamine levels in the prefrontal cortex which are involved in working memory and executive functioning. Impaired executive functioning is reported in a subgroup of AD patients and is associated with a more severe disorder, a more rapid disease progression and a shorter survival. The COMT rs4680 gene polymorphism has been investigated as a susceptibility factor for AD. No statistically significant results were found in meta-analysis but one study reported that the rs4680 Val allele was associated with AD-related psychosis. The COMT rs4680 polymorphism was also found to modulate declarative episodic memory in normal people and schizophrenic subjects. COMT inhibitors, that are adjunctive drugs in Parkinson's disease treatment, lower homocysteine levels and improve executive memory processes in normal subjects. A preliminary study, which needs replication, demonstrates that COMT inhibitors block beta-amyloid fibrils in vitro. Taken together, these findings suggest that research should focus on the role of COMT in AD pathogenesis and on the feasibility of targeting COMT activity in AD treatment.

Catechol-O-methyltransferase (COMT) catabolises dopamine and is important for regulating dopamine levels in the prefrontal cortex. Consistent with its regulation of prefrontal cortex dopamine, COMT modulates working memory and executive function; however, its significance for other cognitive domains, and in other brain regions, remains relatively unexplored. One such example is reward processing, for which dopamine is a critical mediator, and in which the striatum and corticostriatal circuitry are implicated. Here, we discuss emerging data which links COMT to reward processing, review what is known of the underlying neural substrates, and consider whether COMT is a good therapeutic target for treating addiction. Although a limited number of studies have investigated COMT and reward processing, common findings are beginning to emerge. COMT appears to modulate cortical and striatal activation during both reward anticipation and delivery, and to impact on reward-related learning and its underlying neural circuitry. COMT has been studied as a candidate gene for numerous reward-related phenotypes and there is some preliminary evidence linking it with certain aspects of addiction. However, additional studies are required before these associations can be considered robust. It is premature to consider COMT a good therapeutic target for addiction, but this hypothesis should be revisited as further information emerges. In particular, it will be critical to reveal the precise neurobiological mechanisms underlying links between COMT and reward processing, and the extent to which these relate to the putative associations with addiction.

Since the identification of Catechol-O-Methyltransferase (COMT) by Axelrod in 1957, many inhibitors of this enzyme have been reported. While COMT inhibition may be beneficial in a number of disease states, most of the effort over the years has been directed at boosting L-DOPA concentrations as adjunct treatment for Parkinson’s disease. This review summarizes the major classes of COMT inhibitors, from early catechol and pyrogallol variants to bisubstrate inhibitors. The nitrocatechol substructure has proven to be a particularly productive scaffold, resulting in two marketed drugs and several improved drug candidates working their way through clinical trials.