Impact and Therapeutic Potential of PPARs in Alzheimer's Disease

Peroxisome proliferator activated receptors (PPARs) are well studied for their role of peripheral metabolism, but they also may be involved in the pathogenesis of various disorders of the central nervous system (CNS) including multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer's and, Parkinson's disease. The observation that PPARs are able to suppress the inflammatory response in peripheral macrophages and in several models of human autoimmune diseases, lead to the idea that PPARs might be beneficial for CNS disorders possessing an inflammatory component. The neuroinflammatory response during the course of Alzheimer's disease (AD) is triggered by the deposition of the β-amyloid peptide in extracellular plaques and ongoing neurodegeneration. Non-steroidal anti-inflammatory drugs (NSAIDs) have been considered to delay the onset and reduce the risk to develop Alzheimer’s disease, while they also directly activate PPARγ. This led to the hypothesis that NSAID protection in AD may be partly mediated by PPARγ. Several lines of evidence have supported this hypothesis, using AD related transgenic cellular and animal models. Stimulation of PPARγ by synthetic agonist (thiazolidinediones) inducing anti-inflammatory, anti-amyloidogenic and insulin sensitizing effects may account for the observed effects. Several clinical trials already revealed promising results using PPARγ agonists, therefore PPARγ represents an attractive therapeutic target for the treatment of AD

PDE 7 Inhibitors: New Potential Drugs for the Therapy of Spinal Cord Injury

BACKGROUND: Primary traumatic mechanical injury to the spinal cord (SCI) causes the death of a number of neurons that to date can neither be recovered nor regenerated. During the last years our group has been involved in the design, synthesis and evaluation of PDE7 inhibitors as new innovative drugs for several neurological disorders. Our working hypothesis is based on two different facts. Firstly, neuroinflammation is modulated by cAMP levels, thus the key role for phosphodiesterases (PDEs), which hydrolyze cAMP, is undoubtedly demonstrated. On the other hand, PDE7 is expressed simultaneously on leukocytes and on the brain, highlighting the potential crucial role of PDE7 as drug target for neuroinflammation. METHODOLOGY/PRINCIPAL FINDINGS: Here we present two chemically diverse families of PDE7 inhibitors, designed using computational techniques such as virtual screening and neuronal networks. We report their biological profile and their efficacy in an experimental SCI model induced by the application of vascular clips (force of 24 g) to the dura via a four-level T5-T8 laminectomy. We have selected two candidates, namely S14 and VP1.15, as PDE7 inhibitors. These compounds increase cAMP production both in macrophage and neuronal cell lines. Regarding drug-like properties, compounds were able to cross the blood brain barrier using parallel artificial membranes (PAMPA) methodology. SCI in mice resulted in severe trauma characterized by edema, neutrophil infiltration, and production of a range of inflammatory mediators, tissue damage, and apoptosis. Treatment of the mice with S14 and VP1.15, two PDE7 inhibitors, significantly reduced the degree of spinal cord inflammation, tissue injury (histological score), and TNF-α, IL-6, COX-2 and iNOS expression. CONCLUSIONS/SIGNIFICANCE: All these data together led us to propose PDE7 inhibitors, and specifically S14 and VP1.15, as potential drug candidates to be further studied for the treatment of SCI

Specific Inhibition of Phosphodiesterase-4B Results in Anxiolysis and Facilitates Memory Acquisition

Cognitive dysfunction is a core feature of dementia and a prominent feature in psychiatric disease. As non-redundant regulators of intracellular cAMP gradients, phosphodiesterases (PDE) mediate fundamental aspects of brain function relevant to learning, memory, and higher cognitive functions. Phosphodiesterase-4B (PDE4B) is an important phosphodiesterase in the hippocampal formation, is a major Disrupted in Schizophrenia 1 (DISC1) binding partner and is itself a risk gene for psychiatric illness. To define the effects of specific inhibition of the PDE4B subtype, we generated mice with a catalytic domain mutant form of PDE4B (Y358C) that has decreased ability to hydrolyze cAMP. Structural modelling predictions of decreased function and impaired binding with DISC1 were confirmed in cell assays. Phenotypic characterization of the PDE4BY358C mice revealed facilitated phosphorylation of CREB, decreased binding to DISC1, and upregulation of DISC1 and β-Arrestin in hippocampus and amygdala. In behavioural assays, PDE4BY358C mice displayed decreased anxiety and increased exploration, as well as cognitive enhancement across several tests of learning and memory, consistent with synaptic changes including enhanced long-term potentiation and impaired depotentiation ex vivo. PDE4BY358C mice also demonstrated enhanced neurogenesis. Contextual fear memory, though intact at 24 hours, was decreased at 7 days in PDE4BY358C mice, an effect replicated pharmacologically with a non-selective PDE4 inhibitor, implicating cAMP signalling by PDE4B in a very late phase of consolidation. No effect of the PDE4BY358C mutation was observed in the pre-pulse inhibition and forced swim tests. Our data establish specific inhibition of PDE4B as a promising therapeutic approach for disorders of cognition and anxiety, and a putative target for pathological fear memory

Selective phosphodiesterase inhibitors: a promising target for cognition enhancement

# The Author(s) 2008. This article is published with open access at Springerlink.com Rationale One of the major complaints most people face during aging is an impairment in cognitive functioning. This has a negative impact on the quality of daily life and is even more prominent in patients suffering from neurodegenerative and psychiatric disorders including Alzheimer’s disease, schizophrenia, and depression. So far, the majority of cognition enhancers are generally targeting one particular neurotransmitter system. However, recently phosphodiesterases (PDEs) have gained increased attention as a potential new target for cognition enhancement. Inhibition of PDEs increases the intracellular availability of the second messengers cGMP and/or cAMP. Objective The aim of this review was to provide an overvie

Emerging targets for addiction neuropharmacology: From mechanisms to therapeutics

Drug abuse represents a considerable burden of disease and has enormous economic impacts on societies. Over the years, few medications have been developed for clinical use. Their utilization is endowed with several limitations, including partial efficacy or significant side effects. On the other hand, the successful advancement of these compounds provides an important proof of concept for the feasibility of drug development programs in addiction. In recent years, a wealth of information has been generated on the psychological mechanisms, genetic or epigenetic predisposing factors, and neurobiological adaptations induced by drug consumption that interact with each other to contribute to disease progression. It is now clear that addiction develops through phases, from initial recreational use to excessive consumption and compulsive drug seeking, with a shift from positive to negative reinforcement driving motivated behaviors. A greater understanding of these mechanisms has opened new vistas in drug development programs. Researchers' attention has been shifted from investigation of classical targets associated with reward to biological substrates responsible for negative reinforcement, impulse loss of control, and maladaptive mechanisms resulting from protracted drug use. From this research, several new biological targets for the development of innovative therapies have started to emerge. This chapter offers an overview of targets currently under scrutiny for the development of new medications for addiction. This work is not exhaustive but rather it provides a few examples of how this research has advanced in recent years by virtue of studies carried out in our laboratory

Fosfodiesterasas del AMPc y del GMPc en el cerebro: Expresión en procesos neuroinflamatorios y neurodegenerativos

[spa] Los nucleótidos cíclicos, AMPc y GMPc, están considerados segundos mensajeros que participan en la transducción de las vías de señalización intracelular, contribuyendo de esta manera en una gran variedad de procesos celulares. Los niveles del AMPc están regulados por la adenilato ciclasa y los del GMPc por la guanilato ciclasa a nivel de su síntesis, y para ambos por las fosfodiesterasas, a nivel de su degradación. Entre la gran variedad de procesos fisiológicos en los que están involucrados, se ha demostrado su participación en reacciones inflamatorias. Niveles elevados de ambos nucleótidos cíclicos desencadenan respuestas antiiflamatorias y/o neuroprotectoras, por lo tanto, es de esperar que la regulación de los enzimas involucrados en su degradación, las fosfodiesterasas, influya indirectamente en estos procesos. En este trabajo determinamos la expresión de los ARNm de fosfodiesterasas específicas de AMPc, como las variantes de splicing de la PDE4B y el isoenzima de la PDE7, la PDE7B, en cerebros controles de ratas para posteriormente determinar su regulación en cerebros de modelos animales con componente inflamatorio (LPS y EAE). Por otro lado estudiamos la expresíón de los ARNm de la PDE2 y de la PDE9, fosfodiesterasas que son capaces de hidolizar el GMPc, en cerebros postmortem de humanos control, y comparamos su expresión con cerebros de pacientes con enfermedad de Alzheimer. La distribución de los ARNm de las cuatro variantes de splicing de la PDE4B en el cerebro de la rata presenta estructuras en común, como el núcleo anterior olfatorio, o la corteza piriforme. Sin embargo existen regiones en las que no encontramos todas isoformas como en el área postrema, donde no se expresa la PDE4B4, en diversos tractos de materia blanca, que hibrida intensamente con el oligonucleótido para la PDE4B3 y no presenta señal para la PDE4B1, o en el giro dentado del hipocampo, donde sólo se expresa la PDE4B2. Su estudio en los modelos animales utilizados reveló un aumento exclusivo de la PDE4B2 a las 2 y 3 h después de la administración de la toxina en los plexos coroideos en el modelo animal de inflamación por LPS, y en áreas perivasculares de cerebro en el modelo animal de EAE. La expresión de esta variante de splicing en este último modelo se localizó en algunos linfocitos T y macrófagos/microglía. El ARNm de la PDE7B se localiza a lo largo de todo el cerebro de la rata, siendo más abundante en regiones cerebrales anteriores, especialmente en el tubérculo olfativo, los núcleo caudado-putamen, el giro dentado del hipocampo, algunos núcleos talámicos y las células de Purkinje del cerebelo. En estas áreas se expresa preferentemente en neuronas glutamatérgicas y GABAérgicas, pero no en colinérgicas. La expresión de los dos isoenzimas de la PDE7, la PDE7A y PDE7B, no presenta cambios en la expresión en áreas perivasculares del cerebro de los animales EAE. Los ARNm de la PDE2 y de la PDE9 en el cerebro humano se localiza en áreas como la corteza cerebral, la formación hipocampal, el claustrum y los núcleos caudado y putamen. Sin embargo en el cerebelo encontramos expresión de la PDE9, pero no de la PDE2, en las células de Purkinje, en la capa granular del cerebelo y en el núcleo dentado. La comparación de su expresión entre cerebros postmortem control y cerebros diagnosticados con la enfermedad de Alzheimer en las regiones estudiadas (corteza frontal, cerebelo y diferentes regiones del área hipocampal) no mostró diferencias estadísticamente significativas.[eng] "cAMP and cGMP fosfodiesterases in brain: Expression in neuroinflammatory and neurodegenerative processes" cAMP and cGMP are second messengers involved in intracellular signalling pathways, contributing in a variety of cellular processes. Their synthesis is regulated by adenilyl-cyclase and guanilyl-cyclase, and their degradation by phosphodiesterases. High levels of both nucleotides develop antiinfammatory and/or neuroprotective actions, so that, we would expect that the regulation of the enzymes involved in their degradation, phosphodiesterases, will act indirectly in those processes. In this work we determined cAMP specific phosphodiesterase mRNA expression, PDE4B splicing variants and PDE7B isozyme, first, in control rat brain, and then in neuroinflammatory animal model brains (LPS and EAE) in order to determine their regulation. We also studied PDE2 and PDE9 mRNA expression, phosphodiesterases hydrolyzing cGMP, in post-mortem control human brains comparing with Alzheimer disease patient brains. PDE4B splicing variant mRNA distribution in rat brain presents common structures: anterior olfactory nucleus or piriform cortex. However, some regions do not express all PDE4B isoforms. PDE4B4 is not expressed in area postrema; some white fibre tracts do not hybridize for PDE4B1 mRNA, or hippocampal dentate gyrus expresses exclusively PDE4B2 mRNA. Their expression in our animal models showed an exclusive increase for PDE4B2 mRNA levels in choroid plexus after toxin administration in the LPS inflammatory model, and in brain perivascular areas in the EAE animal model, where we found this splicing variant expression in some T cells and some macrophages/microglia. PDE7B mRNA is localized along de whole rat brain, abundantly in anterior brain regions: olfactory tubercle, caudate-putamen nucleus, dentate gyrus of the hipocampus, some thalamic nucleus and Purkinje cells. This isoenzyme is preferently expressed in glutamatergic and GABAergic neurons, but not in cholinergic cells. PDE7 isoenzymes expression does not change in perivascular regions of the EAE animal brains. PDE2 and PDE9 mRNA are localized in human brain regions: cerebral cortex, hipocampal formation, claustrum and caudate and putamen nuclei. However, we find PDE9 mRNA expression, but no PDE2 mRNA expression, in Purkinje cells, in granule cerebellar layer and in dentate nucleus of the cerebellum. When comparing their expression between post-mortem control and Alzheimer disease brains in studied regions we do not find statistically significant differences

Selective induction of cAMP phosphodiesterase PDE4B2 expression in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) in Lewis rats is the most widely used animal model for multiple sclerosis. Cyclic adenosine monophosphate (cAMP) has been associated with neuroinflammation. The aim of this study was to investigate the possible involvement of different cAMP-specific phosphodiesterase (PDE) isoenzymes by analyzing their expression in the brain of EAE rats. We found in the brain of EAE animals that there was a dramatic increase in the mRNA expression levels of the PDE4B isozyme detected around blood vessels from the spinal cord to the upper midbrain. There was a single splicing form of the 4 splice variants that are known for PDE4B: PDE4B2, which showed increased expression levels. This overexpression is localized around the blood vessels and parenchyma in infiltrating T cells and macrophages/microglia. These results support the role played by the activation of the PDE4B2 gene in the neuroinflammatory process in EAE rats. © 2007 American Association of Neuropathologists, Inc.Peer Reviewe

Comparison of cAMP-specific phosphodiesterase mRNAs distribution in mouse and rat brain

There are eleven families of phosphodiesterases that regulate cellular levels of cyclic nucleotides by degradation of cAMP or cGMP. Knowledge of the expression sites of different PDE genes in brain is of special importance for studies on development of specific inhibitors considering that, for example, PDE4 inhibitor treatments exhibit profound anti-inflammatory effects. To address possible species differences we examined the expression of mRNAs coding for the cAMP specific PDE4 and PDE7 families since inhibitors have been used in clinic for schizophrenia, mood disorders, cognition and inflammatory diseases treatment. We have compared the expression of these PDEs in mouse brain by . in situ hybridization histochemistry in comparison with rat brain and found that their neuroanatomical distribution differs in a few areas. © 2012 Elsevier Ireland Ltd.This work was supported by grants awarded by the Spanish Ministerio de Educación y Ciencia and FEDER Funds (SAF2010-01874; SAF2009-11052; PI10/01874). Emily Johansson was a recipient of a fellowship from the Ministerio de Educación y Ciencia.Peer Reviewe

Neuronal expression of cAMP-specific phosphodiesterase 7B mRNA in the rat brain

cAMP plays an important role as second messenger molecule controlling multiple cellular processes in the brain. cAMP levels depend critically on the phosphodiesterases (PDE) activity, enzymes responsible for the clearance of intracellular cAMP. We have examined the regional distribution and cellular localization of mRNA coding for the cAMP-specific phosphodiesterase 7B (PDE7B) in rat brain by in situ hybridization histochemistry. PDE7B mRNA is specifically distributed in rat brain, preferentially in neuronal cell populations. The highest levels of hybridization are observed in olfactory tubercle, islands of Calleja, dentate gyrus, caudate-putamen and some thalamic nuclei. Positive hybridization signals are also detected in other areas, such as cerebral cortex, Purkinje cells of the cerebellum and area postrema. By double in situ hybridization histochemistry, we found that 74% and 79% of the cells expressing PDE7B mRNA in striatum and olfactory tubercle, respectively, were GABAergic cells (expressing glutamic acid decarboxylase mRNA), in contrast with the lack of expression in the few cholinergic cells (expressing choline acetyltransferase mRNA) present in those two areas (around 0.4% in olfactory tubercle). In the thalamic nuclei, a majority of cells containing PDE7B mRNA also expresses a glutamatergic marker (76.7% express vesicular glutamate transporter vGluT1 and 76% express vGluT2 mRNAs). Almost all PDE7B expressing cells in dentate gyrus (93%) were glutamatergic. These results offer a neuroanatomical and neurochemical base that will support the search for specific functions for cAMP dependent PDEs and for the development of specific PDE7 inhibitors. © 2005 IBRO. Published by Elsevier Ltd. All rights reserved.This work was supported, by grants from CICYT (SAF1999-0123, SAF2003-02083) and Red CIEN IDIBAPS-ISCIII RTIC C03/06. S.P.-T was a recipient of a fellowship from CIRIT (Generalitat de Catalunya)Peer Reviewe