Broad spectrum neuroprotection profile of phosphodiesterase inhibitors as related to modulation of cell-cycle elements and caspase-3 activation

Therapeutic efficacy of rolipram delivered by PgP nanocarrier on secondary injury and motor function in a rat TBI model

Aim: To develop poly(lactide-co-glycolide)-graft-polyethylenimine (PgP) as a nanocarrier for the delivery of rolipram (Rm) and evaluate the therapeutic efficacy of Rm-loaded PgP (Rm-PgP) on secondary injury and motor function in a rat traumatic brain injury (TBI) model. Materials & methods: Rm-PgP was injected in the injured brain lesion immediately after TBI using a microinjection pump. Secondary injury pathologies such as inflammatory response, apoptosis and astrogliosis were assessed by histological analysis and functional recovery was assessed by assorted motor function tests. Results: Rm-PgP restored cyclic adenosine monophosphate level in the injured brain close to the sham level and Rm-PgP treatment reduced lesion volume, neuroinflammation and apoptosis and improved motor function at 7 days post-TBI. Conclusion: One single injection of Rm-PgP can be effective for acute mild TBI treatment.

Formulation of Medicated Chewing Gum Containing Sceletium tortuosum and Process Optimization Utilizing the SeDeM Diagram Expert System

Sceletium tortuosum is one of the most promising medicinal plant species for treating anxiety and depression. Traditionally, aerial parts are chewed (masticatory herbal medicine) providing fast relief and rendering the masticatory route for delivery, ideal. This study intended formulating novel medicated chewing gum containing S. tortuosum to alleviate depression and anxiety. S. tortuosum extract was formulated into directly compressed medicated chewing gum (MCG) containing different Health-in-Gum® (HIG) bases through process optimization with the SeDeM Diagram Expert System. Physical properties of MCGs were characterized, and specialized drug release studies performed. According to the manufacturer, only HIG-03 was specifically developed for direct compression; however, the SeDeM System was successfully applied to all HIG-bases investigated. HIG-01 and HIG-04 are also considered useful in direct compression as no considerable differences in these MCG formulations' physical properties were recognized. Inclusion of a lubricant, however, is deemed essential, and MCG comprising HIG-01, most suited for direct compression. Dissolution experiments found only two alkaloids used as markers, mesembrine and mesembrenone, were released in quantifiable concentrations regardless formulation constituents. Novel directly compressed MCG-containing S. tortuosum extract was successfully formulated by which the biologically active phytochemicals of S. tortuosum can be scientifically delivered through the traditionally applied mastication method.

Novel therapeutic targets in mood disorders: Pentoxifylline (PTX) as a candidate treatment

Numerous pharmacological treatments for mood disorders are currently available; however, rates of treatment resistance, relapse and recurrence remain high. Therefore, novel treatments acting outside of the conventionally targeted monoamine system are urgently needed to improve patient outcomes. Emerging and converging evidence suggests that immune dysfunction, oxidative stress, impaired cerebral blood flow (CBF) and decreased neurotrophic factors all contribute to mood disorder pathophysiology and are therefore treatment targets of interest. Pentoxifylline (PTX) is a phosphodiesterase inhibitor with potent anti-inflammatory and antioxidant effects, with additional pleiotropic effects that lead to improved CBF and increases in brain derived neurotrophic factor (BDNF) levels. The direct effect of non-specific phosphodiesterase inhibition may also improve alertness and cognitive function through enhancing second messenger systems. Replicated preclinical studies have demonstrated antidepressant-like effects in animal models. Small preliminary clinical trials have demonstrated promising results for antidepressant and procognitive effects, however, have yet to be replicated in larger mood disorder samples. Only one randomized clinical trial (RCT) specifically assessed the effects of adjunctive PTX in major depressive disorder (MDD), showing clinically and statistically significant antidepressant effects compared to placebo. No studies have assessed PTX in bipolar disorder (BD), where inflammation and altered CBF have also been strongly implicated. Taken together, PTX presents as a promising pleiotropic agent with several potential novel mechanisms of action meriting further evaluation in clinical trials to evaluate target engagement, antidepressant, procognitive and mood stabilizing effects.

Elevated intracellular cAMP concentration mediates growth suppression in glioma cells

Supressed levels of intracellular cAMP have been associated with malignancy. Thus, elevating cAMP through activation of adenylyl cyclase (AC) or by inhibition of phosphodiesterase (PDE) may be therapeutically beneficial. Here, we demonstrate that elevated cAMP levels suppress growth in C6 cells (a model of glioma) through treatment with forskolin, an AC activator, or a range of small molecule PDE inhibitors with differing selectivity profiles. Forskolin suppressed cell growth in a PKA-dependent manner by inducing a G₂/M phase cell cycle arrest. In contrast, trequinsin (a non-selective PDE2/3/7 inhibitor), not only inhibited cell growth via PKA, but also stimulated (independent of PKA) caspase-3/-7 and induced an aneuploidy phenotype. Interestingly, a cocktail of individual PDE 2,3,7 inhibitors suppressed cell growth in a manner analogous to forskolin but not trequinsin. Finally, we demonstrate that concomitant targeting of both AC and PDEs synergistically elevated intracellular cAMP levels thereby potentiating their antiproliferative actions.

The protective and therapeutic effects of vinpocetine, a PDE1 inhibitor, on oxidative stress and learning and memory impairment induced by an intracerebroventricular (ICV) injection of amyloid beta (aβ) peptide

Alzheimer's disease (AD) is a neurodegenerative disease leading to cognitive and memory impairment. This study aimed at investigating the therapeutic and preserving effects of vinpocetine on amyloid beta (Aβ)-induced rat model of AD. Sixty male adult Wistar rats were randomly divided into 6 groups (n = 10 per group) as follows: 1; control, 2; sham, 3; Aβ, 4; pre-treatment (vinpocetine + Aβ): oral gavage administration of vinpocetine at 4 mg/kg for 30 days followed by intracerebroventricular (ICV) injection of Aβ, 5; treatment (Aβ + vinpocetine): Aβ ICV injection followed by vinpocetine administration for 30 days, 6; pre-treatment + treatment (vinpocetine + Aβ + vinpocetine): vinpocetine administration for 30 days before and 30 days after AD induction. Following treatments, the animals' learning and memory were investigated using passive avoidance learning (PAL) task, Morris water maze (MWM), and novel object recognition (NOR) tests. The results demonstrated that Aβ significantly enhanced escape latency and the distance traveled in the MWM, decreased step-through latency, and increased time spent in the dark compartment in PAL. Vinpocetine ameliorated the Aβ-infused memory deficits in both MWM and PAL tests. Administration of vinpocetine in the Aβ rats increased the discrimination index of the NOR test. It also significantly diminished the nitric oxide and malondialdehyde levels and restored the reduced glutathione (GSH) levels. Vinpocetine can improve memory and learning impairment following Aβ infusion due to its different properties, including antioxidant effects, which indicates that vinpocetine administration can lead to the amelioration of cognitive dysfunction in AD.

Pharmacological manipulation of cGMP and NO/cGMP in CNS drug discovery

The development of small molecule modulators of NO/cGMP signaling for use in the CNS has lagged far behind the use of such clinical agents in the periphery, despite the central role played by NO/cGMP in learning and memory, and the substantial evidence that this signaling pathway is perturbed in neurodegenerative disorders, including Alzheimer's disease. The NO-chimeras, NMZ and Nitrosynapsin, have yielded beneficial and disease-modifying responses in multiple preclinical animal models, acting on GABAA and NMDA receptors, respectively, providing additional mechanisms of action relevant to synaptic and neuronal dysfunction. Several inhibitors of cGMP-specific phosphodiesterases (PDE) have replicated some of the actions of these NO-chimeras in the CNS. There is no evidence that nitrate tolerance is a phenomenon relevant to the CNS actions of NO-chimeras, and studies on nitroglycerin in the periphery continue to challenge the dogma of nitrate tolerance mechanisms. Hybrid nitrates have shown much promise in the periphery and CNS, but to date only one treatment has received FDA approval, for glaucoma. The potential for allosteric modulation of soluble guanylate cyclase (sGC) in brain disorders has not yet been fully explored nor exploited; whereas multiple applications of PDE inhibitors have been explored and many have stalled in clinical trials.

Role of cAMP and phosphodiesterase signaling in liver health and disease

Liver disease is a significant health problem worldwide with mortality reaching around 2 million deaths a year. Non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) are the major causes of chronic liver disease. Pathologically, NAFLD and ALD share similar patterns of hepatic disorders ranging from simple steatosis to steatohepatitis, fibrosis and cirrhosis. It is becoming increasingly important to identify new pharmacological targets, given that there is no FDA-approved therapy yet for either NAFLD or ALD. Since the evolution of liver diseases is a multifactorial process, several mechanisms involving parenchymal and non-parenchymal hepatic cells contribute to the initiation and progression of liver pathologies. Moreover, certain protective molecular pathways become repressed during liver injury including signaling pathways such as the cyclic adenosine monophosphate (cAMP) pathway. cAMP, a key second messenger molecule, regulates various cellular functions including lipid metabolism, inflammation, cell differentiation and injury by affecting gene/protein expression and function. This review addresses the current understanding of the role of cAMP metabolism and consequent cAMP signaling pathway(s) in the context of liver health and disease. The cAMP pathway is extremely sophisticated and complex with specific cellular functions dictated by numerous factors such abundance, localization and degradation by phosphodiesterases (PDEs). Furthermore, because of the distinct yet divergent roles of both of its effector molecules, the cAMP pathway is extensively targeted in liver injury to modify its role from physiological to therapeutic, depending on the hepatic condition. This review also examines the behavior of the cAMP-dependent pathway in NAFLD, ALD and in other liver diseases and focuses on PDE inhibition as an excellent therapeutic target in these conditions.

Isatin, an endogenous nonpeptide biofactor: A review of its molecular targets, mechanisms of actions, and their biomedical implications

Isatin (indole-2,3-dione) is an oxidized indole. It is widely distributed in mammalian tissues and body fluids, where isatin concentrations vary significantly from <0.1 to > 10 µM. Isatin output is increased under conditions of stress. Exogenously administered isatin is characterized by low toxicity, mutagenicity, and genotoxicity in vivo. Cytotoxic effects of isatin on various cell cultures are usually observed at concentrations exceeding 100 µM. Binding of [³ H]isatin to rat brain sections is consistent with its physiological concentrations. Proteomic analysis of mouse and rat brain isatin-binding proteins revealed about 90 individual proteins, which demonstrated significant interspecies differences (rat versus mouse). Certain evidence exist that redox state(s) and possibly other types of posttranslational modifications regulate affinity of target proteins to isatin. Recent data suggest that interacting with numerous intracellular isatin binding proteins, isatin can act as a regulator of complex protein networks in norm and pathology. Physiological concentrations of isatin in vitro inhibit monoamine oxidase B and natriuretic peptide receptor guanylate cyclase, higher (neuroprotective) concentrations (50-400 μM) cause apoptosis of various (including malignant tumor) cell lines and influence expression of certain apoptosis-related genes. Being administered in vivo, isatin exhibits various behavioral effects; it attenuates manifestations of MPTP-induced parkinsonism and tumor growth in experimental animal models. © 2017 BioFactors, 44(2):95-108, 2018.

Preservation of neuronal function as measured by clinical and MRI endpoints in relapsing-remitting multiple sclerosis: how effective are current treatment strategies?

INTRODUCTION

Approved medications for relapsing-remitting multiple sclerosis have shown to be effective in terms of their anti-inflammatory potential. However, it is also crucial to evaluate what long-term effects a patient can expect from current MS drugs in terms of preventing neurodegeneration. Here we aim to provide an overview of the current treatment strategies in MS with a specific focus on potential neuroprotective effects. Areas covered: Randomized, double-blind and placebo or referral-drug controlled phase 2a/b and phase 3 trials were examined; non-blinded phase 4 studies (extension studies) were included to provide long-term data, if not otherwise available. Endpoints considered were expanded disability status scale, various neuropsychological tests, percent brain volume change and T1-hypointense lesions as well as multiple sclerosis functional composite, confirmed disease progression, and no evidence of disease activity. Expert commentary: Overall, neuroprotective functions of classical MS therapeutics are not sufficiently investigated, but available data show limited effects. Thus, further research and development in neuroprotection are warranted. When counselling patients, potential long-term beneficial effects should be presented more conservatively.

Rolipram-Loaded Polymeric Micelle Nanoparticle Reduces Secondary Injury after Rat Compression Spinal Cord Injury

Among the complex pathophysiological events following spinal cord injury (SCI), one of the most important molecular level consequences is a dramatic reduction in neuronal cyclic adenosine monophosphate (cAMP) levels. Many studies shown that rolipram (Rm), a phosphodiesterase IV inhibitor, can protect against secondary cell death, reduce inflammatory cytokine levels and immune cell infiltration, and increase white matter sparing and functional improvement. Previously, we developed a polymeric micelle nanoparticle, poly(lactide-co-glycolide)-graft-polyethylenimine (PgP), for combinatorial delivery of therapeutic nucleic acids and drugs for SCI repair. In this study, we evaluated PgP as an Rm delivery carrier for SCI repair. Rolipram's water solubility was increased ∼6.8 times in the presence of PgP, indicating drug solubilization in the micelle hydrophobic core. Using hypoxia as an in vitro SCI model, Rm-loaded PgP (Rm-PgP) restored cAMP levels and increased neuronal cell survival of cerebellar granular neurons. The potential efficacy of Rm-PgP was evaluated in a rat compression SCI model. After intraspinal injection, 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indotricarbocyanine Iodide-loaded PgP micelles were retained at the injection site for up to 5 days. Finally, we show that a single injection of Rm-PgP nanoparticles restored cAMP in the SCI lesion site and reduced apoptosis and the inflammatory response. These results suggest that PgP may offer an efficient and translational approach to delivering Rm as a neuroprotectant following SCI.

An update on vinpocetine: New discoveries and clinical implications

Vinpocetine, a derivative of the alkaloid vincamine, has been clinically used in many countries for treatment of cerebrovascular disorders such as stroke and dementia for more than 30 years. Currently, vinpocetine is also available in the market as a dietary supplement to enhance cognition and memory. Due to its excellent safety profile, increasing efforts have been put into exploring the novel therapeutic effects and mechanism of actions of vinpocetine in various cell types and disease models. Recent studies have revealed a number of novel functions of vinpocetine, including anti-inflammation, antagonizing injury-induced vascular remodeling and high-fat-diet-induced atherosclerosis, as well as attenuating pathological cardiac remodeling. These novel findings may facilitate the repositioning of vinpocetine for preventing or treating relevant disorders in humans.

Phosphodiesterase Inhibitors as a Therapeutic Approach to Neuroprotection and Repair

A wide diversity of perturbations of the central nervous system (CNS) result in structural damage to the neuroarchitecture and cellular defects, which in turn are accompanied by neurological dysfunction and abortive endogenous neurorepair. Altering intracellular signaling pathways involved in inflammation and immune regulation, neural cell death, axon plasticity and remyelination has shown therapeutic benefit in experimental models of neurological disease and trauma. The second messengers, cyclic adenosine monophosphate (cyclic AMP) and cyclic guanosine monophosphate (cyclic GMP), are two such intracellular signaling targets, the elevation of which has produced beneficial cellular effects within a range of CNS pathologies. The only known negative regulators of cyclic nucleotides are a family of enzymes called phosphodiesterases (PDEs) that hydrolyze cyclic nucleotides into adenosine monophosphate (AMP) or guanylate monophosphate (GMP). Herein, we discuss the structure and physiological function as well as the roles PDEs play in pathological processes of the diseased or injured CNS. Further we review the approaches that have been employed therapeutically in experimental paradigms to block PDE expression or activity and in turn elevate cyclic nucleotide levels to mediate neuroprotection or neurorepair as well as discuss both the translational pathway and current limitations in moving new PDE-targeted therapies to the clinic.

From Age-Related Cognitive Decline to Alzheimer's Disease: A Translational Overview of the Potential Role for Phosphodiesterases

Phosphodiesterase inhibitors (PDE-Is) are pharmacological compounds enhancing cAMP and/or cGMP signaling. Both these substrates affect neural communication by influencing presynaptic neurotransmitter release and postsynaptic intracellular pathways after neurotransmitter binding to its receptor. Both cAMP and cGMP play an important role in a variety of cellular functions including neuroplasticity and neuroprotection. This chapter provides a translational overview of the effects of different classes of PDE-Is on cognition enhancement in age-related cognitive decline and Alzheimer's disease (AD). The most effective PDE-Is in preclinical models of aging and AD appear to be PDE2-Is, PDE4-Is and PDE5-Is. Clinical studies are relatively sparse and so far PDE1-Is and PDE4-Is showed some promising results. In the future, the demonstration of clinical proof of concept and the generation of isoform selective PDE-Is are the hurdles to overcome in developing safe and efficacious novel PDE-Is for the treatment of age-related cognitive decline and cognitive dysfunction in AD.

Design, rationale, and baseline characteristics of the randomized double-blind phase II clinical trial of ibudilast in progressive multiple sclerosis

BACKGROUND

Primary and secondary progressive multiple sclerosis (MS), collectively called progressive multiple sclerosis (PMS), is characterized by gradual progression of disability. The current anti-inflammatory treatments for MS have little or no efficacy in PMS in the absence of obvious active inflammation. Optimal biomarkers for phase II PMS trials is unknown. Ibudilast is an inhibitor of macrophage migration inhibitor factor and phosphodiesterases-4 and -10 and exhibits possible neuroprotective properties. The goals of SPRINT-MS study are to evaluate the safety and efficacy of ibudilast in PMS and to directly compare several imaging metrics for utility in PMS trials.

METHODS

SPRINT-MS is a randomized, placebo-controlled, phase II trial of ibudilast in patients with PMS. Eligible subjects were randomized 1:1 to receive either ibudilast (100mg/day) or placebo for 96weeks. Imaging is conducted every 24weeks for whole brain atrophy, magnetization transfer ratio, diffusion tensor imaging, cortical brain atrophy, and retinal nerve fiber layer thickness. Clinical outcomes include neurologic disability and patient reported quality of life. Safety assessments include laboratory testing, electrocardiography, and suicidality screening.

RESULTS

A total of 331 subjects were enrolled, of which 255 were randomized onto active study treatment. Randomized subjects were 53.7% female and mean age 55.7 (SD 7.3) years. The last subject is projected to complete the study in May 2017.

CONCLUSION

SPRINT-MS is designed to evaluate the safety and efficacy of ibudilast as a treatment for PMS while simultaneously validating five different imaging biomarkers as outcome metrics for use in future phase II proof-of-concept PMS trials.

Efficient Synthesis of β-Aryl-γ-lactams and Their Resolution with (S)-Naproxen: Preparation of (R)- and (S)-Baclofen

An efficient synthesis of enantiomerically-pure β-aryl-γ-lactams is described. The principal feature of this synthesis is the practical resolution of β-aryl-γ-lactams with (S)-Naproxen. The procedure is based on the Michael addition of nitromethane to benzylidenemalonates, which was easily obtained, followed by the reduction of the γ-nitroester in the presence of Raney nickel and the subsequent saponification/decarboxylation reaction. The utility of this methodology was highlighted by the preparation of enantiomerically-pure (R)- and (S)-Baclofen hydrochloride.

Cyclic nucleotide phosphodiesterases: important signaling modulators and therapeutic targets

By catalyzing hydrolysis of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), cyclic nucleotide phosphodiesterases are critical regulators of their intracellular concentrations and their biological effects. As these intracellular second messengers control many cellular homeostatic processes, dysregulation of their signals and signaling pathways initiate or modulate pathophysiological pathways related to various disease states, including erectile dysfunction, pulmonary hypertension, acute refractory cardiac failure, intermittent claudication, chronic obstructive pulmonary disease, and psoriasis. Alterations in expression of PDEs and PDE-gene mutations (especially mutations in PDE6, PDE8B, PDE11A, and PDE4) have been implicated in various diseases and cancer pathologies. PDEs also play important role in formation and function of multimolecular signaling/regulatory complexes, called signalosomes. At specific intracellular locations, individual PDEs, together with pathway-specific signaling molecules, regulators, and effectors, are incorporated into specific signalosomes, where they facilitate and regulate compartmentalization of cyclic nucleotide signaling pathways and specific cellular functions. Currently, only a limited number of PDE inhibitors (PDE3, PDE4, PDE5 inhibitors) are used in clinical practice. Future paths to novel drug discovery include the crystal structure-based design approach, which has resulted in generation of more effective family-selective inhibitors, as well as burgeoning development of strategies to alter compartmentalized cyclic nucleotide signaling pathways by selectively targeting individual PDEs and their signalosome partners.

Ibudilast (AV411), and its AV1013 analog, reduce HIV-1 replication and neuronal death induced by HIV-1 and morphine

OBJECTIVE

We explored the antiviral therapeutic potential of ibudilast (AV411, MN-166) and its amino analog, AV1013.

METHODS

We analyzed whether Ibudilast, a nonselective cyclic AMP phosphodiesterase inhibitor that has been used clinically in Asia for bronchial asthma, poststroke dizziness, and ocular allergies, and AV1013, attenuate HIV-1 replication and the synergistic interactions seen with opiate abuse-HIV-1 comorbidity in neuronal death and inflammation.

RESULTS

AV411 and AV1013 inhibited replication by HIV-1 in microglia and significantly suppressed Tat ± morphine-induced tumor necrosis factor-α and MIF production, the activation of the nuclear factor-kappa B subunit p65, and neuronal death. AV411 and AV1013 prevented HIV-1 replication, and attenuated tumor necrosis factor-α and MIF release at concentrations of 100  nmol/l and 1  μmol/l, which are likely achievable at clinical doses. More importantly, co-exposure with morphine did not negate the inhibitory actions of AV411.

CONCLUSION

Collectively, our data suggest that AV411 and its amino analog, AV1013, may be useful neuroprotective agents counteracting neurotoxicity caused by infected and activated glia, and implicate them as potential therapies for the management of HIV-associated neurocognitive disorders in an opioid-abusing population.

Phosphodiesterases: Regulators of cyclic nucleotide signals and novel molecular target for movement disorders

Movement disorders rank among the most common neurological disorders. During the last two decades substantial progress has been made in understanding of the pathological basis of these disorders. Although, several mechanisms have been proposed, downregulation of cyclic nucleotide mediated signaling cascade has consistently been shown to contribute to the striatal dysfunctioning as seen in movement disorders. Thus, counteracting dysregulated cyclic nucleotide signaling has been considered to be beneficial in movement disorders. Cyclic nucleotide phosphodiesterases (PDEs) are the enzymes responsible for the breakdown of cyclic nucleotides and upregulation in PDE activity has been reported in various movement disorders. Thus, PDE inhibition is considered to be a novel strategy to restore cerebral cyclic nucleotide levels and their downstream signalling cascade. Indeed, various PDE inhibitors have been tested pre-clinically and were reported to be neuroprotective in various neurodegenerative disorders associated with movement disabilities. In this review, we have discussed a putative role of PDE inhibitors in movement disorders and associated abnormalities.

Effects of combining methylprednisolone with rolipram on functional recovery in adult rats following spinal cord injury

Methylprednisolone (MP) has been widely used as a standard therapeutic agent for the treatment of spinal cord injury (SCI). Because of its controversial beneficial effects, the combination of MP and other pharmacological agents aimed at enhancing functional recovery is desirable. The phosphodiesterase 4 (PDE4) inhibitor rolipram has been implicated in promotion of regeneration due to elevating cAMP. In the present study, we sought to determine the effects of MP and rolipram, administered in combination, after spinal cord injury (SCI) in adult rats. Here we show that in vitro administration of rolipram and MP significantly increased neuron survival and promoted neurite outgrowth of neurons on the inhibitory substrate CSPGs by upregulation of MMP-2 expression; in vivo administration of rolipram and MP inhibited CSPG expression and increase CSPG digestion after rat SCI. Rolipram and MP combining treatment promoted significant neuroprotection through reduced motoneuron death, minimized lesion cavity, and increased regeneration of lesioned corticospinal tract (CST) axons beyond the lesion site after SCI. Enhanced functional recovery was also observed. Overall, our study strongly suggested that the combination treatment of MP and rolipram may represent a promising strategy for clinically applicable pharmacological therapy for rapid initiation of neuroprotection after SCI.

Phosphodiesterases in neurodegenerative disorders

Cyclic nucleotide phosphodiesterases (PDEs) are responsible for the breakdown of cyclic nucleotides, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). As such, they are crucial regulators of levels of cyclic nucleotide-mediated signaling. cAMP signaling and cGMP signaling have been associated with neuroplasticity and protection, and influencing their levels in the cell by inhibition of PDEs has become a much studied target for treatment in a wide array of disorders, including neurodegenerative disorders. In this review, we will focus on the involvement of PDEs in neurodegenerative disorders. In comparison with preclinical work, data on human patients are scarce. Alzheimer's disease is associated with changes in PDE4, PDE7, and PDE8 expression in the brain. Altered functioning of PDE4 as well as PDE11 is associated with major depressive disorder. In multiple sclerosis, there are indications of alterations in expression of several PDE subtypes in the central nervous system; however, evidence is indirect. In Huntington's disease and Parkinson's disease, most research has focused on PDE1B and PDE10, because of their abundant presence in striatal neurons. In another rare, neurodegenerative striatal motor disorder, that is, autosomal-dominant striatal degeneration, genetic defects in PDE8B gene are thought to underlie the neurodegenerative processes. Although the latter disorder has showed a causative dysfunction of PDEs, this does not hold for the neurodegenerative disorders discussed above, in which changes in PDE levels seemingly rather represent secondary changes and compensation to prior existing dysfunction. However, normalizing cyclic nucleotide signaling via PDE inhibition remains interesting for the treatment of neurodegenerative disorders.

cGMP Signaling, Phosphodiesterases and Major Depressive Disorder

Deficits in neuroplasticity are hypothesized to underlie the pathophysiology of major depressive disorder (MDD): the effectiveness of antidepressants is thought to be related to the normalization of disrupted synaptic transmission and neurogenesis. The cyclic adenosine monophosphate (cAMP) signaling cascade has received considerable attention for its role in neuroplasticity and MDD. However components of a closely related pathway, the cyclic guanosine monophosphate (cGMP) have been studied with much lower intensity, even though this signaling transduction cascade is also expressed in the brain and the activity of this pathway has been implicated in learning and memory processes. Cyclic GMP acts as a second messenger; it amplifies signals received at postsynaptic receptors and activates downstream effector molecules resulting in gene expression changes and neuronal responses. Phosphodiesterase (PDE) enzymes degrade cGMP into 5’GMP and therefore they are involved in the regulation of intracellular levels of cGMP. Here we review a growing body of evidence suggesting that the cGMP signaling cascade warrants further investigation for its involvement in MDD and antidepressant action.

Comparative monitoring of oral theophylline treatment in blood serum, saliva, and nasal mucus

BACKGROUND

Theophylline, used in the treatment for various pulmonary pathologies, is usually given orally with drug levels measured primarily in blood serum and occasionally in saliva. Although theophylline treatment is now not commonly used it has been effective to correct smell loss (hyposmia). This is important because 21 million people in the United States exhibit hyposmia and oral theophylline has corrected hyposmia in about 50% of these patients. This result suggests that oral theophylline may result in the drug not only appearing in the serum but also in nasal mucus, thereby playing a role in correcting hyposmia. No prior report of theophylline in nasal mucus has been made and no comparison of levels in nasal mucus, blood serum, or saliva has been previously reported.

PURPOSE

The aim was to determine, after oral theophylline treatment, if it is present in nasal mucus and, if present, to compare the levels with those in serum and saliva.

METHODS

Oral theophylline was given to 23 hyposmic patients at daily doses of 200, 300, 400, 600, and 800 mg for periods of 2-10 months. During each period, blood serum, saliva, and nasal mucus were collected and theophylline measured in each fluid.

RESULTS

Theophylline was found in nasal mucus and in saliva and blood serum at each drug dose in each patient to whom it was given. The mean level of theophylline in nasal mucus was 74% that of serum; mean level in saliva was 67% of serum; mean level in nasal mucus was 111% that in saliva.

CONCLUSIONS

Theophylline is present in nasal mucus after oral administration. Levels in nasal mucus reflect blood and saliva levels in a consistent manner and offer a simple convenient noninvasive method to monitor theophylline doses of the oral drug.

Phosphodiesterase 4B mediates extracellular signal-regulated kinase-dependent up-regulation of mucin MUC5AC protein by Streptococcus pneumoniae by inhibiting cAMP-protein kinase A-dependent MKP-1 phosphatase pathway

Otitis media (OM) is the most common childhood bacterial infection and the major cause of conductive hearing loss in children. Mucus overproduction is a hallmark of OM. Streptococcus pneumoniae is the most common gram-positive bacterial pathogen causing OM. Among many mucin genes, MUC5AC has been found to be greatly up-regulated in the middle ear mucosa of human patients with OM. We previously reported that S. pneumoniae up-regulates MUC5AC expression in a MAPK ERK-dependent manner. We also found that MAPK phosphatase-1 (MKP-1) negatively regulates S. pneumoniae-induced ERK-dependent MUC5AC up-regulation. Therapeutic strategies for up-regulating the expression of negative regulators such as MKP-1 may have significant therapeutic potential for treating mucus overproduction in OM. However, the underlying molecular mechanism by which MKP-1 expression is negatively regulated during S. pneumoniae infection is unknown. In this study we show that phosphodiesterase 4B (PDE4B) mediates S. pneumoniae-induced MUC5AC up-regulation by inhibiting the expression of a negative regulator MKP-1, which in turn leads to enhanced MAPK ERK activation and subsequent up-regulation of MUC5AC. PDE4B inhibits MKP-1 expression in a cAMP-PKA-dependent manner. PDE4-specific inhibitor rolipram inhibits S. pneumoniae-induced MUC5AC up-regulation both in vitro and in vivo. Moreover, we show that PDE4B plays a critical role in MUC5AC induction. Finally, topical and post-infection administration of rolipram into the middle ear potently inhibited S. pneumoniae-induced MUC5AC up-regulation. Collectively, these data demonstrate that PDE4B mediates ERK-dependent up-regulation of mucin MUC5AC by S. pneumoniae by inhibiting cAMP-PKA-dependent MKP-1 pathway. This study may lead to novel therapeutic strategy for inhibiting mucus overproduction.

Oligodendrocyte-protection and remyelination post-spinal cord injuries: a review

In the past four decades, the main focus of investigators in the field of spinal cord regeneration has been to devise therapeutic measures that enhance neural regeneration. More recently, emphasis has been placed on enhancing remyelination and providing oligodendrocyte-protection after a spinal cord injury (SCI). Demyelination post-SCI is part of the cascading secondary injury that takes place immediately after the primary insult; therefore, therapeutic measures are needed to reduce oligodendrocyte death and/or enhance remyelination during the acute stage, preserving neurological functions that would be lost otherwise. In this review a thorough investigation of the oligodendrocyte-protective and remyelinative molecular therapies available to date is provided. The advent of new biomaterials shown to promote remyelination post-SCI is discussed mainly in the context of a combinatorial approach where the biomaterial also provides drug delivery capabilities. The aim of these molecular and biomaterial-based therapies is twofold: (1) oligodendrocyte-protective therapy, which involves protecting already existing oligodendrocytes from undergoing apoptosis/necrosis; and (2) inductive remyelination, which involves harnessing the remyelinative capabilities of endogenous oligodendrocyte precursor cells (OPCs) at the lesion site by providing a suitable environment for their migration, survival, proliferation and differentiation. From the evidence reported in the literature, we conclude that the use of a combinatorial approach including biomaterials and molecular therapies would provide advantages such as: (1) sustained release of the therapeutic molecule, (2) local delivery at the lesion site, and (3) an environment at the site of injury that promotes OPC migration, differentiation and remyelination.

Therapeutic utility of phosphodiesterase type I inhibitors in neurological conditions

Neuronal plasticity is an essential property of the brain that is impaired in different neurological conditions. Phosphodiesterase type 1 (PDE1) inhibitors can enhance levels of the second messengers cAMP/cGMP leading to the expression of neuronal plasticity-related genes, neurotrophic factors, and neuroprotective molecules. These neuronal plasticity enhancement properties make PDE1 inhibitors good candidates as therapeutic agents in many neurological conditions. However, the lack of specificity of the drugs currently available poses a challenge to the systematic evaluation of the beneficial effect of these agents. The development of more specific drugs may pave the way for the use of PDE1 inhibitors as therapeutic agents in cases of neurodevelopmental conditions such as fetal alcohol spectrum disorders and in degenerative disorders such as Alzheimer's and Parkinson's.

Therapeutic targets for neuroprotection and/or enhancement of functional recovery following traumatic brain injury

Traumatic brain injury (TBI) is a significant public health concern. The number of injuries that occur each year, the cost of care, and the disabilities that can lower the victim's quality of life are all driving factors for the development of therapy. However, in spite of a wealth of promising preclinical results, clinicians are still lacking a therapy. The use of preclinical models of the primary mechanical trauma have greatly advanced our knowledge of the complex biochemical sequela that follow. This cascade of molecular, cellular, and systemwide changes involves plasticity in many different neurochemical systems, which represent putative targets for remediation or attenuation of neuronal injury. The purpose of this chapter is to highlight some of the promising molecular and cellular targets that have been identified and to provide an up-to-date summary of the development of therapeutic compounds for those targets.

Glial restricted precursor cell transplant with cyclic adenosine monophosphate improved some autonomic functions but resulted in a reduced graft size after spinal cord contusion injury in rats

Transplantation of glial restricted precursor (GRP) cells has been shown to reduce glial scarring after spinal cord injury (SCI) and, in combination with neuronal restricted precursor (NRP) cells or enhanced expression of neurotrophins, to improve recovery of function after SCI. We hypothesized that combining GRP transplants with rolipram and cAMP would improve functional recovery, similar to that seen after combining Schwann cell transplants with increasing cAMP. A short term study, (1) uninjured control, (2) SCI+vehicle, and (3) SCI+cAMP, showed that spinal cord [cAMP] was increased 14days after SCI. We used 51 male rats subjected to a thoracic SCI for a 12-week survival study: (1) SCI+vehicle, (2) SCI+GRP, (3) SCI+cAMP, (4) SCI+GRP+cAMP, and (5) uninjured endpoint age-matched control (AM). Rolipram was administered for 2weeks after SCI. At 9days after SCI, GRP transplantation and injection of dibutyryl-cAMP into the spinal cord were performed. GRP cells survived, differentiated, and formed extensive transplants that were well integrated with host tissue. Presence of GRP cells increased the amount of tissue in the lesion; however, cAMP reduced the graft size. White matter sparing at the lesion epicenter was not affected. Serotonergic input to the lumbosacral spinal cord was not affected by treatment, but the amount of serotonin immediately caudal to the lesion was reduced in the cAMP groups. Using telemetric monitoring of corpus spongiosum penis pressure we show that the cAMP groups regained the same number of micturitions per 24hours when compared to the AM group, however, the frequency of peak pressures was increased in these groups compared to the AM group. In contrast, the GRP groups had similar frequency of peak pressures compared to baseline and the AM group. Animals that received GRP cells regained the same number of erectile events per 24hours compared to baseline and the AM group. Since cAMP reduced the GRP transplant graft, and some modest positive effects were seen that could be attributable to both GRP or cAMP, future research is required to determine how cAMP affects survival, proliferation, and/or function of progenitor cells and how this is related to function. cAMP may not always be a desirable addition to a progenitor cell transplantation strategy after SCI.

A novel structure-based multimode QSAR method affords predictive models for phosphodiesterase inhibitors

Quantitative structure-activity relationship (QSAR) methods aim to build quantitatively predictive models for the discovery of new molecules. It has been widely used in medicinal chemistry for drug discovery. Many QSAR techniques have been developed since Hansch's seminal work, and more are still being developed. Motivated by Hopfinger's receptor-dependent QSAR (RD-QSAR) formalism and the Lukacova-Balaz scheme to treat multimode issues, we have initiated studies that focus on a structure-based multimode QSAR (SBMM QSAR) method, where the structure of the target protein is used in characterizing the ligand, and the multimode issue of ligand binding is systematically treated with a modified Lukacova-Balaz scheme. All ligand molecules are first docked to the target binding pocket to obtain a set of aligned ligand poses. A structure-based pharmacophore concept is adopted to characterize the binding pocket. Specifically, we represent the binding pocket as a geometric grid labeled by pharmacophoric features. Each pose of the ligand is also represented as a labeled grid, where each grid point is labeled according to the atom types of nearby ligand atoms. These labeled grids or three-dimensional (3D) maps (both the receptor map (R-map) and the ligand map (L-map)) are compared to each other to derive descriptors for each pose of the ligand, resulting in a multimode structure-activity relationship (SAR) table. Iterative partial least-squares (PLS) is employed to build the QSAR models. When we applied this method to analyze PDE-4 inhibitors, predictive models have been developed, obtaining models with excellent training correlation (r(2) = 0.65-0.66), as well as test correlation (R(2) = 0.64-0.65). A comparative analysis with 4 other QSAR techniques demonstrates that this new method affords better models, in terms of the prediction power for the test set.

Nanofibrous Patches for Spinal Cord Regeneration

The difficulty in spinal cord regeneration is related to the inhibitory factors for axon growth and the lack of appropriate axon guidance in the lesion region. Here we developed scaffolds with aligned nanofibers for nerve guidance and drug delivery in spinal cord. Blended polymers including Poly (l-lactic acid) (PLLA) and Poly (lactide-co-glycolide) (PLGA) were used to electrospin nanofibrous scaffolds with two-layer structure: aligned nanofibers in the inner layer and random nanofibers in the outer layer. Rolipram, a small molecule that can enhance cAMP activity in neurons and suppress inflammatory responses, was immobilized onto nanofibers. To test the therapeutic effects of nanofibrous scaffolds, the nanofibrous scaffolds loaded with rolipram were used to bridge the hemisection lesion in 8-week old athymic rats. The scaffolds with rolipram increased axon growth through the scaffolds and in the lesion, promoted angiogenesis through the scaffold, and decreased the population of astrocytes and chondroitin sulfate proteoglycans in the lesion. Locomotor scale rating analysis showed that the scaffolds with rolipram significantly improved hindlimb function after 3 weeks. This study demonstrated that nanofibrous scaffolds offered a valuable platform for drug delivery for spinal cord regeneration.

Spinal cord injury and neural repair: focus on neuroregenerative approaches for spinal cord injury

BACKGROUND

This review discusses the urgent need for improved therapeutic approaches aimed at restoring function following traumatic spinal cord injury (SCI). The focus of this paper is neuroregenerative approaches for SCI, with a highlighted comparison of recent advances in the field and comparisons to that made by Cethrin (Alseres Pharmaceuticals, Inc.), the leading nerve repair product.

OBJECTIVE

This review first provides the reader with an understanding of SCI. The market for promising therapeutics that can either intervene in secondary etiological mechanisms or ameliorate symptoms associated with SCI are then discussed. The reader will also learn about Cethrin and its current status in clinical evaluation.

METHODS

Review of the preclinical literature and clinical SCI trials relevant to the discovery and current development of Cethrin.

RESULTS/CONCLUSION

In a recently concluded Phase I/IIa clinical trial involving 37 patients with either cervical or thoracic SCIs, the evidence for Cethrin indicates that topical administration of either 0.3, 1, 3 or 6 mg of the recombinant rho inhibitor following surgical decompression is safe. Alseres has announced that planning is underway for a Phase IIB trial of Cethrin to include a placebo arm to assess better the drugs' clinical efficacy.

Cyclic AMP-specific PDEs: A promising therapeutic target for CNS repair

Research to date has indicated that cAMPspecific PDEs, particularly the members of PDE4 family, play a crucial role in the pathogenesis of CNS injury and neurodegeneration by downregulating intracellular levels of cAMP in various cell types. Reduced cAMP signaling results in immune cell activation, inflammation, secondary tissue damage, scar formation and axon growth failure, ultimately leading to an exacerbation of injury, the prevention of endogenous repair and limited functional recovery. Although inhibition of cAMPspecific-PDE activity through the use of drugs like Rolipram has been shown to reverse these deficiencies and mediate neurorepair, an inability to develop selective agents and/or reduce dose-limiting side-effects associated with PDE4 inhibition has hampered their clinical translation. Recent work with more selective pharmacological inhibitors of cAMP-specific PDEs and molecular targeting approaches, along with improved understanding of the basic biology and role of PDEs in pathological processes may enable this promising therapeutic approach to advance clinically and have a similar impact on CNS injury and disease as PDE5 inhibitors have had on the treatment of sexual dysfunction.

Development of improved models for phosphodiesterase-4 inhibitors with a multi-conformational structure-based QSAR method

Phosphodiesterase-4 (PDE-4) is an important drug target for several diseases, including COPD (chronic obstructive pulmonary disorder) and neurodegenerative diseases. In this paper, we describe the development of improved QSAR (quantitative structure-activity relationship) models using a novel multi-conformational structure-based pharmacophore key (MC-SBPPK) method. Similar to our previous work, this method calculates molecular descriptors based on the matching of a molecule's pharmacophore features with those of the target binding pocket. Therefore, these descriptors are PDE4-specific, and most relevant to the problem under study. Furthermore, this work expands our previous SBPPK QSAR method by explicitly including multiple conformations of the PDE-4 inhibitors in the regression analysis, and thus addresses the issue of molecular flexibility. The nonlinear regression problem resulted from including multiple conformations has been transformed into a linear equation and solved by an iterative partial least square (iPLS) procedure, according to the Lukacova-Balaz scheme. 35 PDE-4 inhibitors have been analyzed with this new method, and predictive models have been developed. Based on the prediction statistics for both the training set and the test set, these new models are more robust and predictive than those obtained by traditional ligand-based QSAR techniques as well as that obtained with the SBPPK method reported in our previous work. As a result, multiple predictive models have been added to the collection of QSAR models for PDE4 inhibitors. Collectively, these models will be useful for the discovery of new drug candidates targeting the PDE-4 enzyme.

A new therapeutic approach in Parkinson's disease: some novel quinazoline derivatives as dual selective phosphodiesterase 1 inhibitors and anti-inflammatory agents

The increasing life expectancy in our population makes Parkinson's disease (PD) a growing public health problem. There is a great need to find a way to prevent and delay the disease. It was shown that selective phosphodiesterase 1 (PDE1) inhibitors and anti-inflammatory agents might be effective in treating PD. Therefore, a novel 1,2,9,11-tetrasubstituted-7H-thieno[2',3':4,5]pyrimido[6,1-b]-quinazolin-7-one (1-15) and 1,3,10,12-tetrasubstituted-8H-pyrido[2',3':4,5]pyrimido[6,1-b]quinazolin-8-one (16-36) derivatives were synthesized by reported method and investigated for their ability to inhibit PDE1. Most of the synthesized compounds have shown good activity against PDE1 and were less effective than 3-isobutyl-1-methylxanthine. All the compounds were also tested for their in vitro anti-inflammatory activity by carrageenan-induced oedema in rats. In addition, ulcerogenic activity was determined. The combined anti-inflammatory data from in vitro animal model showed that compounds, 9,11-dibromo-1-(2-furyl)-3-(4-tolyl)-8H-pyrido[2',3':4,5]pyrimido[6,1-b]quinazolin-8-one 23, 9,11-dibromo-1-(4-methoxy-phenyl)-3-phenyl-8H-pyrido[2',3':4,5]pyrimido[6,1-b]quinazolin-8-one 24, 9,11-dibromo-1-(4-chloro-phenyl)-3-(4-tolyl)-8H-pyrido[2',3':4,5]pyrimido[6,1-b]quinazolin-8-one 29 and 9-bromo-1-(4-chloro-phenyl)-3-(4-tolyl)-8H-pyrido[2',3':4,5]pyrimido[6,1-b]quinazolin-8-one 36 exhibited even more potent anti-inflammatory activity and low gastric ulceration incidence compare to reference standard Indomethacin. Since compound 23, 24, 29 and 36 exhibits both anti-inflammatory activity and PDE1 inhibition, it needs further detailed studies.

A new structure-based QSAR method affords both descriptive and predictive models for phosphodiesterase-4 inhibitors

We describe the application of a new QSAR (quantitative structure-activity relationship) formalism to the analysis and modeling of PDE-4 inhibitors. This new method takes advantage of the X-ray structural information of the PDE-4 enzyme to characterize the small molecule inhibitors. It calculates molecular descriptors based on the matching of their pharmacophore feature pairs with those (the reference) of the target binding pocket. Since the reference is derived from the X-ray crystal structures of the target under study, these descriptors are target-specific and easy to interpret. We have analyzed 35 indole derivative-based PDE-4 inhibitors where Partial Least Square (PLS) analysis has been employed to obtain the predictive models. Compared to traditional QSAR methods such as CoMFA and CoMSIA, our models are more robust and predictive measured by statistics for both the training and test sets of molecules. Our method can also identify critical pharmacophore features that are responsible for the inhibitory potency of the small molecules. Thus, this structure-based QSAR method affords both descriptive and predictive models for phosphodiesterase-4 inhibitors. The success of this study has also laid a solid foundation for systematic QSAR modeling of the PDE family of enzymes, which will ultimately contribute to chemical genomics research and drug discovery targeting the PDE enzymes.

Emerging drugs for spinal cord injury

BACKGROUND

This review summarizes several promising pharmacological approaches for the therapeutic management of traumatic spinal cord injury (SCI), which are either in early-phase clinical trials or nearing clinical translation.

OBJECTIVE

This review provides the reader with an understanding of the key pathophysiological mechanisms that contribute to neurological deficits after SCI. Through discussion of the mechanism(s) of action of the selected therapeutic approaches potentially important targets to aid further drug discovery will be highlighted.

METHODS

Systematic literature review of the pre-clinical literature and clinical SCI trials related to neuroprotective, immunomodulatory and regenerative therapeutic approaches.

RESULTS/CONCLUSION

The next decade will witness an unprecedented number of clinical trials which will seek to translate key biomedical research discoveries. The promising drug-based therapeutic approaches include regenerative strategies to neutralize myelin-mediated neurite outgrowth inhibition, neuroprotective strategies to reduce apoptotic triggers, the targeting of cationic/glutamatergic toxicity, anti-inflammatory strategies and the use of approaches to stabilize disrupted cell membranes.

Rolipram attenuates acute oligodendrocyte death in the adult rat ventrolateral funiculus following contusive cervical spinal cord injury

Rolipram, an inhibitor of phosphodiesterase 4 (PDE4) proteins that hydrolyze cAMP, increases axonal regeneration following spinal cord injury (SCI). Recent evidence indicate that rolipram also protects against a multitude of apoptotic signals, many of which are implicated in secondary cell death post-SCI. In the present study, we used immunohistochemistry and morphometry to determine potential spinal cord targets of rolipram and to test its protective potential in rats undergoing cervical spinal cord contusive injury. We found that 3 PDE4 subtypes (PDE4A, B, D) were expressed by spinal cord oligodendrocytes. OX-42 immunopositive microglia only expressed the PDE4B subtype. Oligodendrocyte somata were quantified within the cervical ventrolateral funiculus, a white matter region critical for locomotion, at varying time points after SCI in rats receiving rolipram or vehicle treatments. We show that rolipram significantly attenuated oligodendrocyte death at 24 h post-SCI continuing through 72 h, the longest time point examined. These results demonstrate for the first time that spinal cord glial cells express PDE4 subtypes and that the PDE4 inhibitor rolipram protects oligodendrocytes from secondary cell death following contusive SCI. They also indicate that further investigations into neuroprotection and axonal regeneration with rolipram are warranted for treating SCI.

Beneficial effects of rolipram in the R6/2 mouse model of Huntington's disease

We have previously showed that rolipram, a phosphodiesterase type IV inhibitor, displays a neuroprotective effect in a rat quinolinic acid model of HD [DeMarch Z., Giampa C., Patassini S., Martorana A., Bernardi G. and Fusco F.R., (2007) Beneficial effects of rolipram in a quinolinic acid model of striatal excitotoxicity. Neurobiol. Dis. 25:266-273.]. In this study, we sought to determine if rolipram exerts a neuroprotective effect in R6/2 mutant mice, which recapitulates, in many aspects, human HD [Mangiarini L., Sathasivam K., Seller M., Cozens B., Harper A., Hetherington C., Lawton M., Trottier Y., Lehrach H., Davies S.W. and Bates G.P. (1996) Exon 1 of the HD gene with an expanded CAG repeat is sufficient to cause a progressive neurological phenotype in transgenic mice. Cell. 87:493-506]. Transgenic mice were treated with rolipram 1.5 mg/kg daily starting from 4 weeks of age. After transcardial perfusion, histological and immunohistochemical studies were performed. We found that rolipram-treated R6/2 mice survived longer and displayed less severe signs of neurological dysfunction than the vehicle treated ones. Primary outcome measures such as brain volume, striatal atrophy, size and morphology of striatal neurons, neuronal intranuclear inclusions and microglial reaction confirmed a neuroprotective effect of the compound. Rolipram was effective in increasing significantly the levels of activated CREB and of BDNF the striatal spiny neurons, which might account for the beneficial effects observed in this model. Our findings show that rolipram could be considered as a valid therapeutic approach for HD.

PDE inhibitors in psychiatry--future options for dementia, depression and schizophrenia?

Phosphodiesterases are key enzymes in cellular signalling pathways. They degrade cyclic nucleotides and their inhibition via specific inhibitors offers unique 'receptor-independent' opportunities to modify cellular function. An increasing number of in vitro and animal model studies point to innovative treatment options in neurology and psychiatry. This review critiques a selection of recent studies and developments with a focus on dementia/neuroprotection, depression and schizophrenia. Despite increased interest among the clinical neurosciences, there are still no approved PDE inhibitors for clinical use in neurology or psychiatry. Adverse effects are a major impediment for clinical approval. It is therefore necessary to search for more specific inhibitors at the level of different PDE sub-families and isoforms.