Delayed O-methylation of L-DOPA in MB-COMT-deficient mice after oral administration of L-DOPA and carbidopa

1.Catechol-O-methyltransferase (COMT) is involved in the O-methylation of l-DOPA, dopamine, and other catechols. The enzyme is expressed in two isoforms: soluble (S-COMT), which resides in the cytoplasm, and membrane-bound (MB-COMT), which is anchored to intracellular membranes. 2.To obtain specific information on the functions of COMT isoforms, we studied how a complete MB-COMT deficiency affects the total COMT activity in the body, peripheral l-DOPA levels, and metabolism after l-DOPA (10mg kg(-1)) plus carbidopa (30mg kg(-1)) administration by gastric tube in wild-type (WT) and MB-COMT-deficient mice. l-DOPA and 3-O-methyl-l-DOPA (3-OMD) levels were assayed in plasma, duodenum, and liver. 3.We showed that the selective lack of MB-COMT did not alter the total COMT activity, COMT enzyme kinetics, l-DOPA levels, or the total O-methylation of l-DOPA but delayed production of 3-OMD in plasma and peripheral tissues.Peer reviewe

Catechol-O-methyltransferase

Peer reviewe

Generation of membrane-bound catechol-O-methyl transferase deficient mice with disctinct sex dependent behavioral phenotype.

PMID: 28195063Catechol-O-methyltransferase (COMT) has two isoforms: soluble (S-COMT), which resides in the cytoplasm, and membrane-bound (MB-MT), anchored to intracellular membranes. COMT is involved in the O-methylation of L-DOPA, dopamine and other catechols. The exact role of MB-COMT is still mostly unclear. We wanted to create a novel genetically modified mouse model that specifically lacks MB-COMT activity and to study their behavioral phenotype. MB-COMT knock-in mutant mice were generated by introducing two point mutations in exon 2 of the Comt gene (ATGCTG->GAGCTC disabling the function of the P2 promoter and allowing only the P1-regulated S-COMT transcription. The first mutation changes methionine to glutamic acid whereas the second one does not affect coding. The expression of the two COMT isoforms, total COMT activity in several areas of the brain and peripheral tissues and extracellular dopamine concentrations after L-DOPA (10 mg/kg) and carbidopa (30 mg/kg) subcutaneous administration were assessed. A battery of behavioral tests was performed to compare MB-COMT deficient mice and their wild type littermates of both sexes. MB-COMT deficient mice were seemingly normal, bred usually and had unaltered COMT activity in the brain and periphery despite a complete lack of the MB-COMT protein. MB-COMT deficient male mice showed higher extracellular dopamine levels than their wild-type littermates in the striatum, but not in the mPFC. In addition, the MB-COMT deficient male mice exhibited a distinct endophenotype characterized by schizophrenia-related behaviors like aggressive behavior and reduced prepulse inhibition. They also had prolonged immobility in the tail suspension test. Both sexes were sensitized to acute pain and had normal motor activity but disturbed short-term memory. Hence the behavioral phenotype was not limited to schizophrenia-related endophenotype and some behavioural findings were not sex-dependent. Our findings indicate that MB-COMT is critical for behavior, and its function in COMT-dependent brain areas cannot be entirely substituted by the remaining S-COMT.Peer reviewe

Prolyl Oligopeptidase Regulates Dopamine Transporter Phosphorylation in the Nigrostriatal Pathway of Mouse

Alpha-synuclein is the main component of Lewy bodies, a histopathological finding of Parkinson's disease. Prolyl oligopeptidase (PREP) is a serine protease that binds to alpha-synuclein and accelerates its aggregation in vitro. PREP enzyme inhibitors have been shown to block the alpha-synuclein aggregation process in vitro and in cellular models, and also to enhance the clearance of alpha-synuclein aggregates in transgenic mouse models. Moreover, PREP inhibitors have induced alterations in dopamine and metabolite levels, and dopamine transporter immunoreactivity in the nigrostriatal tissue. In this study, we characterized the role of PREP in the nigrostriatal dopaminergic and GABAergic systems of wild-type C57Bl/6 and PREP knockout mice, and the effects of PREP overexpression on these systems. Extracellular concentrations of dopamine and protein levels of phosphorylated dopamine transporter were increased and dopamine reuptake was decreased in the striatum of PREP knockout mice, suggesting increased internalization of dopamine transporter from the presynaptic membrane. Furthermore, PREP overexpression increased the level of dopamine transporters in the nigrostriatal tissue but decreased phosphorylated dopamine transporters in the striatum in wild-type mice. Our results suggest that PREP regulates the function of dopamine transporter, possibly by controlling the phosphorylation and transport of dopamine transporter into the striatum or synaptic membrane.Peer reviewe

Influence of the COMT Genotype on Working Memory and Brain Activity Changes During Development

Background: The Valine158Methionine (Val158Met) polymorphism of the COMT gene leads to lower enzymatic activity and higher dopamine availability in Met carriers. The Met allele is associated with better performance and reduced prefrontal cortex activation during working memory (WM) tasks in adults. Dopaminergic system changes during adolescence may lead to a reduction of basal dopamine levels, potentially affecting Met allele benefits during development. Methods: We investigated the association of COMT genotype with behavioral (n = 322) and magnetic resonance imaging data (n = 81–84) collected during performance of a visuospatial WM task and potential changes in these effects during development (reflected in age × genotype interactions). Data were collected from a cross-sectional and longitudinal typically developing sample of 6- to 20-year-olds. Results: Visuospatial WM capacity exhibited an age × genotype interaction, with a benefit of the Met allele emerging after 10 years of age. There was a parallel age × genotype interaction on WM-related activation in the right inferior frontal gyrus and intraparietal sulcus (IPS), with increases in activation with age in the Val/Val group only. Main effects of COMT genotype were also observed in the IPS, with greater gray matter volumes bilaterally and greater right IPS activation in the Val/Val group compared with the Met carriers. Conclusions: These results suggest that COMT genotype effects on WM brain activity and behavior are not static during development. The full developmental picture should be considered when trying to understand the impact of genetic polymorphisms on the mature cognition of healthy adult or psychiatric populations

Monoaminergic and histaminergic strategies and treatments in brain diseases

The monoaminergic systems are the target of several drugs for the treatment of mood, motor and cognitive disorders as well as neurological conditions. In most cases, advances have occurred through serendipity, except for Parkinson's disease where the pathophysiology led almost immediately to the introduction of dopamine restoring agents. Extensive neuropharmacological studies first showed that the primary target of antipsychotics, antidepressants, and anxiolytic drugs were specific components of the monoaminergic systems. Later, some dramatic side effects associated with older medicines were shown to disappear with new chemical compounds targeting the origin of the therapeutic benefit more specifically. The increased knowledge regarding the function and interaction of the monoaminergic systems in the brain resulting from in vivo neurochemical and neurophysiological studies indicated new monoaminergic targets that could achieve the efficacy of the older medicines with fewer side-effects. Yet, this accumulated knowledge regarding monoamines did not produce valuable strategies for diseases where no monoaminergic drug has been shown to be effective. Here, we emphasize the new therapeutic and monoaminergic-based strategies for the treatment of psychiatric diseases. We will consider three main groups of diseases, based on the evidence of monoamines involvement (schizophrenia, depression, obesity), the identification of monoamines in the diseases processes (Parkinson's disease, addiction) and the prospect of the involvement of monoaminergic mechanisms (epilepsy, Alzheimer's disease, stroke). In most cases, the clinically available monoaminergic drugs induce widespread modifications of amine tone or excitability through neurobiological networks and exemplify the overlap between therapeutic approaches to psychiatric and neurological conditions. More recent developments that have resulted in improved drug specificity and responses will be discussed in this review.peer-reviewe

Pakotetun nikotiinialtistuksen ja Comt-geenipuutoksen vaikutus riippuvuuteen liittyvien neurokemiallisten ja käyttäytymismuutosten kehittymisessä hiirissä

Activation of midbrain dopamine systems is thought to be critically involved in the addictive properties of abused substances. Drugs of abuse increase dopamine release in the nucleus accumbens and dorsal striatum, which are the target areas of mesolimbic and nigrostriatal dopamine pathways, respectively. Dopamine release in the nucleus accumbens is thought to mediate the attribution of incentive salience to rewards, and dorsal striatal dopamine release is involved in habit formation. In addition, changes in the function of prefrontal cortex (PFC), the target area of mesocortical dopamine pathway, may skew information processing and memory formation such that the addict pays an abnormal amount of attention to drug-related cues. In this study, we wanted to explore how long-term forced oral nicotine exposure or the lack of catechol-O-methyltransferase (COMT), one of the dopamine metabolizing enzymes, would affect the functioning of these pathways. We also wanted to find out how the forced nicotine exposure or the lack of COMT would affect the consumption of nicotine, alcohol, or cocaine. First, we studied the effect of forced chronic nicotine exposure on the sensitivity of dopamine D2-like autoreceptors in microdialysis and locomotor activity experiments. We found that the sensitivity of these receptors was unchanged after forced oral nicotine exposure, although an increase in the sensitivity was observed in mice treated with intermittent nicotine injections twice daily for 10 days. Thus, the effect of nicotine treatment on dopamine autoreceptor sensitivity depends on the route, frequency, and time course of drug administration. Second, we investigated whether the forced oral nicotine exposure would affect the reinforcing properties of nicotine injections. The chronic nicotine exposure did not significantly affect the development of conditioned place preference to nicotine. In the intravenous self-administration paradigm, however, the nicotine-exposed animals self-administered nicotine at a lower unit dose than the control animals, indicating that their sensitivity to the reinforcing effects of nicotine was enhanced. Next, we wanted to study whether the Comt gene knock-out animals would be a suitable model to study alcohol and cocaine consumption or addiction. Although previous work had shown male Comt knock-out mice to be less sensitive to the locomotor-activating effects of cocaine, the present study found that the lack of COMT did not affect the consumption of cocaine solutions or the development of cocaine-induced place preference. However, the present work did find that male Comt knock-out mice, but not female knock-out mice, consumed ethanol more avidly than their wild-type littermates. This finding suggests that COMT may be one of the factors, albeit not a primary one, contributing to the risk of alcoholism. Last, we explored the effect of COMT deficiency on dorsal striatal, accumbal, and prefrontal cortical dopamine metabolism under no-net-flux conditions and under levodopa load in freely-moving mice. The lack of COMT did not affect the extracellular dopamine concentrations under baseline conditions in any of the brain areas studied. In the prefrontal cortex, the dopamine levels remained high for a prolonged time after levodopa treatment in male, but not female, Comt knock-out mice. COMT deficiency induced accumulation of 3,4-dihydroxyphenylacetic acid, which increased further under levodopa load. Homovanillic acid was not detectable in Comt knock-out animals either under baseline conditions or after levodopa treatment. Taken together, the present results show that although forced chronic oral nicotine exposure affects the reinforcing properties of self-administered nicotine, it is not an addiction model itself. COMT seems to play a minor role in dopamine metabolism and in the development of addiction under baseline conditions, indicating that dopamine function in the brain is well-protected from perturbation. However, the role of COMT becomes more important when the dopaminergic system is challenged, such as by pharmacological manipulation.Huumeiden ja muiden riippuvuutta aiheuttavien aineiden yhteinen nimittäjä on kyky aktivoida keskiaivojen dopamiiniratoja. Ne lisäävät dopamiinin vapautumista akkumbens-tumakkeessa ja dorsaalisessa striatumissa, jotka ovat mesolimbisen ja nigrostriataalisen dopamiiniradan päätealueet. Akkumbens-tumakkeessa dopamiinin ajatellaan välittävän palkitsevien tapahtumien muuttumista halutuiksi, ja dorsaalisessa striatumissa sen on todettu osallistuvan tapojen muodostukseen. Lisäksi muutokset mesokortikaalisen radan päätealueen, etuaivokuoren, toiminnassa voivat vääristää tiedonkäsittelyä ja muistin toimintaa siten, että riippuvainen yksilö kiinnittää suhteettoman paljon huomiota huumeisiin liittyviin ympäristön tekijöihin. Tässä tutkimuksessa haluttiin selvittää, kuinka pitkäkestoinen pakotettu juomaveden kautta tapahtuva nikotiinialtistus tai dopamiinin hajottamiseen osallistuvan katekoli-O-metyylitransferaasientsyymin (COMT) puutos vaikuttaa näiden dopamiiniratojen toimintaan. Lisäksi halusimme tutkia, miten pakotettu nikotiinialtistus tai COMT-puutos vaikuttaa nikotiinin, alkoholin tai kokaiinin kulutukseen. Tässä tutkimuksessa havaittiin, että krooninen pakotettu nikotiinialtistus lisäsi dopamiinin ja dopamiinimetaboliittien määrää dorsaalisessa striatumissa. Se myös lisäsi hiirten liikeaktiivisuutta. Nämä havainnot osoittavat, että pakotetustikin annettu nikotiini aktivoi nigrostriataalista dopamiinirataa vielä useiden viikkojen altistuksen jälkeenkin. Muutokset tämän radan toiminnassa osoittautuivat kuitenkin olevan erilaisia kuin annettaessa nikotiinia perinteisellä tavalla toistettuina injektioina. Havaitsimme myös, että nikotiinialtistetut eläimet itseannostelivat nikotiinia matalammalla annostasolla kuin verrokkihiiret. Tämä viittaa siihen, että nikotiinialtistetut hiiret olivat verrokkeja herkempiä nikotiinin palkitseville vaikutuksille. Passiivinenkin nikotiinialtistus voi siis lisätä riippuvuusriskiä. Näin ollen esimerkiksi altistuminen huoneilman tupakansavulle saattaa kasvattaa nikotiiniriippuvuuden kehittymisen todennäköisyyttä myöhempien tupakointikokeilujen seurauksena. Aiemmissa tutkimuksissa oli todettu COMT-entsyymipuutoksen vähentävän kokaiinin liikeaktiivisuutta lisäävää vaikutusta hiirissä. Tässä tutkimuksessa COMT-puutoksen ei kuitenkaan todettu vaikuttavan kokaiiniliuoksen kulutukseen tai kokaiinin palkitseviin vaikutuksiin. Alkoholiliuoksia Comt-poistogeeniset hiiriurokset kuitenkin joivat runsaammin kuin verrokkihiiret, mutta tätä vaikutusta ei havaittu naarashiirissä. Tulosten perusteella näyttäisi siltä, että COMT saattaa olla yksi, vaikkakaan ei keskeisin, osatekijä alkoholismin kehittymisessä. COMT-puutos ei vaikuttanut dorsaalistriatumin, akkumbens-tumakkeen eikä etuaivokuoren solunulkoiseen dopamiinipitoisuuteen. Dopamiinin ensisijaisen hajoamistuotteen, 3,4-dihydroksifenyylietikkahapon, kumuloituminen sen sijaan korostui Comt-poistogeenisisssä hiirissä. Levodopa-annoksen jälkeen Comt-poistogeenisien hiiriuroksien etuaivokuoren dopamiinitasot säilyivät kuitenkin pidempään korkeina kuin verrokkihiirien, mutta samanlaista vaikutusta ei ollut nähtävissä naarashiirissä. Etanoli saattaa siis aiheuttaa Comt-poistogeenisten uroshiirien aivoissa voimakkaamman dopamiinin vapautumisen, jolloin ne joisivat enemmän alkoholia kuin naaraat. Voidaan myös todeta, että COMT-entsyymin merkitys dopamiinin hajottamisessa kasvaa etenkin etuaivokuorella, kun dopamiiniratoja rasitetaan farmakologisin keinoin