Characteristic behavioural alterations in rats induced by rolipram and other selective adenosine cyclic 3', 5'-monophosphate phosphodiesterase inhibitors

Phosphodiesterase-4 Inhibition in Parkinson's Disease: Molecular Insights and Therapeutic Potential

Clinicians and researchers are exploring safer and novel treatment strategies for treating the ever-prevalent Parkinson's disease (PD) across the globe. Several therapeutic strategies are used clinically for PD, including dopamine replacement therapy, DA agonists, MAO-B blockers, COMT blockers, and anticholinergics. Surgical interventions such as pallidotomy, particularly deep brain stimulation (DBS), are also employed. However, they only provide temporal and symptomatic relief. Cyclic adenosine monophosphate (cAMP) is one of the secondary messengers involved in dopaminergic neurotransmission. Phosphodiesterase (PDE) regulates cAMP and cGMP intracellular levels. PDE enzymes are subdivided into families and subtypes which are expressed throughout the human body. PDE4 isoenzyme- PDE4B subtype is overexpressed in the substantia nigra of the brain. Various studies have implicated multiple cAMP-mediated signaling cascades in PD, and PDE4 is a common link that can emerge as a neuroprotective and/or disease-modifying target. Furthermore, a mechanistic understanding of the PDE4 subtypes has provided perceptivity into the molecular mechanisms underlying the adverse effects of phosphodiesterase-4 inhibitors (PDE4Is). The repositioning and development of efficacious PDE4Is for PD have gained much attention. This review critically assesses the existing literature on PDE4 and its expression. Specifically, this review provides insights into the interrelated neurological cAMP-mediated signaling cascades involving PDE4s and the potential role of PDE4Is in PD. In addition, we discuss existing challenges and possible strategies for overcoming them.

Positive effects of roflumilast on behavior, neuroinflammation, and white matter injury in mice with global cerebral ischemia

Inhibition of phosphodiesterase 4 (PDE4) is a promising pharmacological strategy for the treatment of cerebral ischemic conditions. To increase the relevance and increase the translational value of preclinical studies, it is important to conduct experiments using different animal species and strains, different animal models, and to evaluate long-term functional outcomes after cerebral ischemia. In the present study, the effects of the selective PDE4 inhibitor roflumilast were evaluated in vivo and in vitro. Balb/c mice were subjected to bilateral common carotid artery occlusion (BCCAO) and tested during 21 days in multiple behavioral tasks to investigate the long-term effects of roflumilast on functional recovery. The effects of roflumilast were also investigated on hippocampal cell loss, white matter injury, and expression of neuroinflammatory markers. Roflumilast prevented cognitive and emotional deficits induced by BCCAO in mice. Roflumilast also prevented neurodegeneration and reduced the white matter damage in the brain of ischemic animals. Besides, roflumilast decreased Iba-1 (microglia marker) levels and increased Arginase-1 (Arg-1; microglia M2 phenotype marker) levels in the hippocampus of these mice. Likewise, roflumilast suppressed inducible nitric oxide synthase (microglia M1 phenotype marker) expression and increased Arg-1 levels in a primary mouse microglia culture. These findings support evidence that PDE4 inhibition by roflumilast might be beneficial in cerebral ischemic conditions. The neuroprotective effects of roflumilast appear to be mediated by a decrease in neuroinflammation.

The long and winding road of designing phosphodiesterase inhibitors for the treatment of heart failure

Cyclic nucleotide phosphodiesterases (PDEs) are a superfamily of enzymes known to play a critical role in the indirect regulation of several intracellular metabolism pathways through the selective hydrolysis of the phosphodiester bonds of specific second messenger substrates such as cAMP (3',5'-cyclic adenosine monophosphate) and cGMP (3',5'-cyclic guanosine monophosphate), influencing the hypertrophy, contractility, apoptosis and fibroses in the cardiovascular system. The expression and/or activity of multiple PDEs is altered during heart failure (HF), which leads to changes in levels of cyclic nucleotides and function of cardiac muscle. Within the cardiovascular system, PDEs 1-5, 8 and 9 are expressed and are interesting targets for the HF treatment. In this comprehensive review we will present a briefly description of the biochemical importance of each cardiovascular related PDE to the HF, and cover almost all the "long and winding road" of designing and discovering ligands, hits, lead compounds, clinical candidates and drugs as PDE inhibitors in the last decade.

Phosphodiesterase 4B: Master Regulator of Brain Signaling

Phosphodiesterases (PDEs) are the only superfamily of enzymes that have the ability to break down cyclic nucleotides and, as such, they have a pivotal role in neurological disease and brain development. PDEs have a modular structure that allows targeting of individual isoforms to discrete brain locations and it is often the location of a PDE that shapes its cellular function. Many of the eleven different families of PDEs have been associated with specific diseases. However, we evaluate the evidence, which suggests the activity from a sub-family of the PDE4 family, namely PDE4B, underpins a range of important functions in the brain that positions the PDE4B enzymes as a therapeutic target for a diverse collection of indications, such as, schizophrenia, neuroinflammation, and cognitive function.

PDE3 Inhibitors Repurposed as Treatments for Age-Related Cognitive Impairment

As the population of older individuals grows worldwide, researchers have increasingly focused their attention on identifying key molecular targets of age-related cognitive impairments, with the aim of developing possible therapeutic interventions. Two such molecules are the intracellular cyclic nucleotides, cAMP and cGMP. These second messengers mediate fundamental aspects of brain function relevant to memory, learning, and cognitive function. Consequently, phosphodiesterases (PDEs), which hydrolyze cAMP and cGMP, are promising targets for the development of cognition-enhancing drugs. Inhibitors that target PDEs work by elevating intracellular cAMP. In this review, we provide an overview of different PDE inhibitors, and then we focus on pharmacological and physiological effects of PDE3 inhibitors in the CNS and peripheral tissues. Finally, we discuss findings from experimental and preliminary clinical studies and the potential beneficial effects of the PDE3 inhibitor cilostazol on age-related cognitive impairments. In the innovation pipeline of pharmaceutical development, the antiplatelet agent cilostazol has come into the spotlight as a novel treatment for mild cognitive impairment. Overall, the repurposing of cilostazol may represent a potentially promising way to treat mild cognitive impairment, Alzheimer's disease, and vascular dementia. In this review, we present a brief summary of cAMP signaling and different PDE inhibitors, followed by a discussion of the pharmacological and physiological role of PDE3 inhibitors. In this context, we discuss the repurposing of a PDE3 inhibitor, cilostazol, as a potential treatment for age-related cognitive impairment based on recent research.

[Phosphodiesterase 4 inhibition for treatment of endothelial barrier and microcirculation disorders in sepsis]

Sepsis is commonly associated with loss of microvascular endothelial barrier function (capillary leak) and dysfunctional microcirculation, which both promote organ failure. The development of a distinct therapy of impaired endothelial barrier function and disturbed microcirculation is highly relevant because both of these phenomena constitute crucial processes which critically influence the prognosis of patients. Numerous in vivo and in vitro trials over the past years have fostered a better understanding of the pathophysiology of capillary leak. Furthermore, promising data in animal models show that therapeutic modulation of endothelial barrier function and microcirculation can be achieved by stabilizing endothelial cAMP (cyclic adenosine monophosphate) levels followed by activation of Rho-GTPase Rac1, e. g. by phosphodiesterase 4 inhibitors. This review summarizes and discusses recent findings of cellular mechanisms and in vivo trials.

The Regulatory Role of Rolipram on Inflammatory Mediators and Cholinergic/Adrenergic Stimulation-Induced Signals in Isolated Primary Mouse Submandibular Gland Cells

Exposure to bacterial lipopolysaccharides (LPS) induces inflammatory signals in salivary glands. We investigated the regulatory role of phosphodiesterase 4 (PDE4) inhibitor rolipram on inflammatory mediators and cholinergic/adrenergic stimulation-induced intracellular Ca(2+) signaling in salivary acinar and ductal cells. Submandibular gland (SMG) expressed PDE4A through 4D mRNA and PDE4 was localized in the luminal membrane of SMG. LPS induced Ca(2+) signaling and ROS production in SMG. Treatment with rolipram blocked LPS-induced Ca(2+) increase and ROS production. The application of histamine evoked Ca(2+) signals and ROS production, which were attenuated by rolipram in SMG cells. Moreover, LPS-induced NLRP3 inflammasome and cleaved caspase-1 were inhibited by rolipram. The inhibitory role of rolipram in ROS-induced Ca(2+) signaling was mainly observed in acinar cells and not in ductal cells. Rolipram also protected SMG acinar but not ductal cells from LPS-induced cell membrane damage. In the case of cholinergic/adrenergic stimulation, carbachol/isoproterenol-induced Ca(2+) signals were upregulated by the treatment of rolipram in SMG. In the case of cAMP-dependent ductal bicarbonate secretion by rolipram, no effect was observed on the modulation of ductal chloride/bicarbonate exchange activity. Rolipram could suppress the inflammatory signals and could be a potential therapeutic strategy against LPS-induced inflammation to protect the salivary gland cells.

Functional testing in animal models of spinal cord injury: not as straight forward as one would think

When exploring potential treatments for spinal cord injury (SCI), functional recovery is deemed the most relevant outcome measure when it comes to translational considerations. Yet, assessing such recovery and potential treatment effects is challenging and the pitfalls are frequently underestimated. The consequences are that in many cases positive results cannot be reliably replicated, and likely treatments that appear to lack effects have been dismissed prematurely. In this article we review the relationships between lesion location/severity and functional outcomes with specific consideration given to floor and ceiling effects. The roles of compensatory strategies, the challenges of distinguishing them from bona fide recovery, and of comparing function to pre-injury levels given the variability inherent in animal testing are discussed. Ultimately, we offer a series of considerations to enhance the power of functional analysis in animal models of SCI.

PDE4 as a target for cognition enhancement

INTRODUCTION

The second messengers cAMP and cGMP mediate fundamental aspects of brain function relevant to memory, learning, and cognitive functions. Consequently, cyclic nucleotide phosphodiesterases (PDEs), the enzymes that inactivate the cyclic nucleotides, are promising targets for the development of cognition-enhancing drugs.

AREAS COVERED

PDE4 is the largest of the 11 mammalian PDE families. This review covers the properties and functions of the PDE4 family, highlighting procognitive and memory-enhancing effects associated with their inactivation.

EXPERT OPINION

PAN-selective PDE4 inhibitors exert a number of memory- and cognition-enhancing effects and have neuroprotective and neuroregenerative properties in preclinical models. The major hurdle for their clinical application is to target inhibitors to specific PDE4 isoforms relevant to particular cognitive disorders to realize the therapeutic potential while avoiding side effects, in particular emesis and nausea. The PDE4 family comprises four genes, PDE4A-D, each expressed as multiple variants. Progress to date stems from characterization of rodent models with selective ablation of individual PDE4 subtypes, revealing that individual subtypes exert unique and non-redundant functions in the brain. Thus, targeting specific PDE4 subtypes, as well as splicing variants or conformational states, represents a promising strategy to separate the therapeutic benefits from the side effects of PAN-PDE4 inhibitors.

Molecular Neurobiology of Depression: PET Findings on the Elusive Correlation with Symptom Severity

Molecular mechanisms in the brain are assumed to cause the symptoms and severity of neuropsychiatric disorders. This review concerns the elusive nature of relationships between the severity of depressive disorders and neuromolecular processes studied by positron emission tomography (PET). Recent PET studies of human depression have focused on serotonergic, dopaminergic, muscarinic, nicotinic, and GABAergic receptors, as well as central processes dependent on monoamine oxidase, phosphodiesterase type 4, amyloid plaques, neurofibrillar tangles, and P-glycoprotein. We find that reliable causal links between neuromolecular mechanisms and relief from depressive disorders have yet to be convincingly demonstrated. This situation may contribute to the currently limited use of PET for exploring the neuropathways that are currently viewed as being responsible for beneficial effects of antidepressant treatment regimes.

Analgesia mediated by soluble epoxide hydrolase inhibitors is dependent on cAMP

Pain is a major health concern even though numerous analgesic agents are available. Side effects and lack of wide-spectrum efficacy of current drugs justify efforts to better understand pain mechanisms. Stabilization of natural epoxy-fatty acids (EFAs) through inhibition of the soluble epoxide hydrolase (sEH) reduces pain. However, in the absence of an underlying painful state, inhibition of sEH is ineffective. Surprisingly, a pain-mediating second messenger, cAMP, interacts with natural EFAs and regulates the analgesic activity of sEH inhibitors. Concurrent inhibition of sEH and phosphodiesterase (PDE) dramatically reduced acute pain in rodents. Our findings demonstrate a mechanism of action of cAMP and EFAs in the pathophysiology of pain. Furthermore, we demonstrate that inhibition of various PDE isozymes, including PDE4, lead to significant increases in EFA levels through a mechanism independent of sEH, suggesting that the efficacy of commercial PDE inhibitors could result in part from increasing EFAs. The cross-talk between the two major pathways-one mediated by cAMP and the other by EFAs-paves the way to new approaches to understand and control pain.

A fission yeast-based platform for phosphodiesterase inhibitor HTSs and analyses of phosphodiesterase activity

Fission yeast strains have been engineered so that their growth behavior reflects the activity of heterologous cyclic nucleotide phosphodiesterases (PDEs). These strains can be used in High-Throughput Screens (HTSs) for PDE inhibitors that possess "drug-like" characteristics, displaying activity in a growth stimulation assay over a 48-h period. Through three generations of development, a collection of strains expressing 10 of the 11 mammalian PDE families that is appropriate for small molecule inhibitor screening has been generated in our laboratory. Strains unable to synthesize cyclic nucleotides allow characterization of PDE activity in that the enzyme's potency is reflected in the amount of either cAMP or cGMP that must be added to the growth medium to stimulate cell growth. In the future, this system could be used to screen cDNA libraries for biological regulators of target PDEs and for the construction of strains that co-express PDEs and associated regulatory proteins to facilitate molecular and genetic studies of their functions and, in particular, to identify whether different PDE-partner protein complexes show distinct patterns of inhibitor sensitivity.

Phosphodiesterases in the central nervous system: implications in mood and cognitive disorders

Cyclic nucleotide phosphodiesterases (PDEs) are a superfamily of enzymes that are involved in the regulation of the intracellular second messengers cyclic AMP (cAMP) and cyclic GMP (cGMP) by controlling their rates of hydrolysis. There are 11 different PDE families and each family typically has multiple isoforms and splice variants. The PDEs differ in their structures, distribution, modes of regulation, and sensitivity to inhibitors. Since PDEs have been shown to play distinct roles in processes of emotion and related learning and memory processes, selective PDE inhibitors, by preventing the breakdown of cAMP and/or cGMP, modulate mood and related cognitive activity. This review discusses the current state and future development in the burgeoning field of PDEs in the central nervous system. It is becoming increasingly clear that PDE inhibitors have therapeutic potential for the treatment of neuropsychiatric disorders involving disturbances of mood, emotion, and cognition.

Involvement of phosphodiesterase 4 in beta-adrenoceptor agonist-induced amylase release in parotid acinar cells

beta-Adrenoceptor activation increases intracellular cAMP levels and consequently induces exocytotic amylase release in parotid acinar cells. Phosphodiesterase (PDE) catalyses the hydrolysis of cAMP, which terminates the downstream signaling of this second messenger. We investigated the involvement of PDE4, a cAMP-PDE, in beta-adrenoceptor agonist-induced amylase release in mouse, rat and rabbit parotid acinar cells by using the specific PDE4 inhibitor rolipram. cAMP-PDE activity was detected in mouse, rat and rabbit parotid acinar cells. In the presence of rolipram, cAMP-PDE activity was reduced by about 31%, 38% and 33% in mouse, rat and rabbit parotid acinar cells, respectively. The increase in cAMP levels induced by the beta-adrenoceptor agonist isoproterenol was enhanced in the presence of rolipram in mouse, rat and rabbit parotid acinar cells. Isoproterenol-induced amylase release, but not constitutive amylase release, was also enhanced in the presence of rolipram in mouse, rat and rabbit parotid acinar cells. These results suggest that the rolipram-sensitive cAMP-PDE, PDE4, is involved in beta-adrenoceptor agonist-induced amylase release in parotid acinar cells.

Local delivery of rolipram, a phosphodiesterase-4-specific inhibitor, augments bone morphogenetic protein-induced bone formation

Recombinant human bone morphogenetic protein (rhBMP) is a promising therapeutic cytokine for the induction of bone formation, but a weak response in humans remains a major hurdle in its therapeutic application. We have previously reported an rhBMP-2-induced increase in the bone mass of mice receiving systemic rolipram, a specific inhibitor of phosphodiesterase-4. To overcome the side effects of systemic administration of rolipram, we examined the effects of its local release. Polyethylene glycol discs were used as a delivery system. The discs were impregnated with rhBMP-2 and rolipram and implanted into the dorsal muscle pouches in mice. Bone formation was assessed by measuring the bone mineral content (BMC) of the formed bone. First, to determine the optimal dose of rolipram, we added 0-5000 nmol rolipram and 5 microg rhBMP-2 to the pellets and found that 500 nmol rolipram was the most effective concentration for inducing bone formation after 4 weeks. Second, to examine the time course of bone formation, we implanted 5 microg rhBMP-2 with 0 or 500 nmol rolipram and killed mice 5, 7, 10, 14, or 21 days after implantation. Bone formation was accelerated in the rolipram group. Finally, to determine the rolipram-induced increase in the effect of BMP, BMC obtained after treatment with 5 microg rhBMP-2 and 500 nmol rolipram was compared with that obtained after treatment with 5-9 microg rhBMP-2 without rolipram, 4 weeks after implantation. The results indicated that 500 nmol rolipram enhanced the effect of rhBMP-2 by almost 1.5-fold. In summary, locally released rolipram enhanced the capacity of rhBMP-2 to induce bone formation, an effect previously reported with systemic administration. These findings may decrease the cost and increase the efficacy of rhBMP-2 treatment.

The involvement of type IV phosphodiesterases in cocaine-induced sensitization and subsequent pERK expression in the mouse nucleus accumbens

RATIONALE

Cocaine exposure produces sensitization that is partly mediated by cyclic adenosine monophosphate (cAMP) pathways within the nucleus accumbens (NAc). Type IV phosphodiesterases (PDE4s) break down cAMP and are required for cocaine-induced conditioned place preference. Whether PDE4 disruption attenuates induction of behavioral sensitization to cocaine and subsequent NAc expression of phosphorylated extracellular signal-regulated kinase (ERK), which is involved in cocaine-induced sensitization, is unknown.

OBJECTIVES

The objective of this study was to determine whether inhibition of PDE4s prevents cocaine-induced locomotor sensitization and if reduced behavioral sensitization is accompanied by decreased expression of phosphorylated ERK (pERK) within the NAc.

METHODS

Mice were administered the PDE4 inhibitor, rolipram, or vehicle before or after five daily injections of cocaine or saline, and activity was monitored on days 1 and 5. After nine drug-free days, locomotor sensitization was tested. Some subjects were sacrificed following testing for behavioral sensitization to measure pERK expression in the NAc.

RESULTS

PDE4 inhibition, during the induction of sensitization, reduced behavioral sensitization only if rolipram (1.0 mg/kg) was administered before cocaine. Re-exposure to the cocaine-paired environment following a 9-day drug-free period enhanced pERK expression in the NAc core and shell. Rolipram did not alter pERK induction despite blocking behavioral sensitization.

CONCLUSIONS

Rolipram given during, but not following, cocaine treatment prevents development of locomotor sensitization to cocaine but does not affect subsequent pERK activation induced by exposure to a cocaine-paired context or following a cocaine challenge. Although PDE4 inhibition during the induction of sensitization blocks the locomotor component of sensitization, other long-term changes induced by repeated cocaine treatment remain.

The novel distribution of phosphodiesterase-4 subtypes within the rat retina

Phosphodiesterases (PDEs) are important regulators of signal transduction processes. While much is known about the function of cyclic GMP-specific PDEs in the retina, much less is known about the closely related, cyclic AMP-specific PDEs. The purpose of the present study is to characterize and localize PDE4 within the adult rat retina. We have used Western blotting, RT-PCR, and immunohistochemistry together with retrograde labeling to determine the presence and location of each PDE4 subtype. Western blot analysis revealed that multiple isoforms of PDE4A, B, and D subtypes are present within the retina, whereas the PDE4C subtype was absent. These data were confirmed by RT-PCR. Using immunohistochemistry we show that all three PDE4s are abundantly expressed within the retina where they all colocalize with retrograde-labeled retinal ganglion cells, as well as bipolar cells, horizontal cells, and cholinergic amacrine cells, whereas Müller cells lack PDE4 expression. Uniquely, PDE4B was expressed by the inner and outer segments of rod photoreceptors as well as their terminals within the outer plexiform layer. Collectively, our results demonstrate that PDE4s are abundantly expressed throughout the rodent retina and this study provides the framework for further functional studies.

Evaluating the antipsychotic profile of the preferential PDE10A inhibitor, papaverine

RATIONALE

Prepulse inhibition (PPI) is an operational measure of sensorimotor gating that is deficient in schizophrenia patients. In rats, PPI deficits induced by dopamine (DA) agonists are reversed by antipsychotics. Inhibition of the striatum-rich phosphodiesterase (PDE)10A may represent a novel antipsychotic mechanism. Previous studies were controversial, showing antipsychotic-like profiles in measures of PPI for the preferential PDE10A inhibitor papaverine (PAP) but not the novel PDE10A inhibitor TP-10.

OBJECTIVE

The aim of the study was to evaluate the antipsychotic profile of PAP in rats using PPI.

MATERIALS AND METHODS

PPI deficits were induced in rats by apomorphine (APO; 0.1, 0.5 mg/kg) or D: -amphetamine (AMPH; 4 mg/kg). PAP (3, 10, 30 mg/kg) or haloperidol (HAL; 0.1 mg/kg) was tested against these agonists in Sprague-Dawley (SD) or Wistar (WI) rats. Prepulse intervals ranged from 10 to 120 ms. Further tests evaluated the effects of PAP on spontaneous locomotion, AMPH (1 mg/kg)-induced hyperlocomotion, and core body temperature (T degrees ).

RESULTS

HAL reversed APO-induced PPI deficits but PAP failed to reverse APO- and AMPH-induced PPI deficits at all doses, strains, pretreatment times, and prepulse intervals. PAP (30 mg/kg) significantly reduced AMPH hyperlocomotion in SD rats, and a similar pattern was detected in WI rats. This PAP dose also strongly reduced spontaneous locomotion and T degrees in SD rats.

CONCLUSION

Our study does not support an antipsychotic-like profile of PAP in dopaminergic PPI models.

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.

Development of a fission yeast-based high-throughput screen to identify chemical regulators of cAMP phosphodiesterases

Cyclic nucleotide phosphodiesterases (PDEs) comprise a superfamily of enzymes that serve as drug targets in many human diseases. There is a continuing need to identify high-specificity inhibitors that affect individual PDE families or even subtypes within a single family. The authors describe a fission yeast-based high-throughput screen to detect inhibitors of heterologously expressed adenosine 3',5'-cyclic monophosphate (cAMP) PDEs. The utility of this system is demonstrated by the construction and characterization of strains that express mammalian PDE2A, PDE4A, PDE4B, and PDE8A and respond appropriately to known PDE2A and PDE4 inhibitors. High-throughput screens of 2 bioactive compound libraries for PDE inhibitors using strains expressing PDE2A, PDE4A, PDE4B, and the yeast PDE Cgs2 identified known PDE inhibitors and members of compound classes associated with PDE inhibition. The authors verified that the furanocoumarin imperatorin is a PDE4 inhibitor based on its ability to produce a PDE4-specific elevation of cAMP levels. This platform can be used to identify PDE activators, as well as genes encoding PDE regulators, which could serve as targets for future drug screens.

Alterations in proteoglycan synthesis selectively impair FSH-induced particulate cAMP-phosphodiesterase 4 (PDE4) activation in immature rat Sertoli cells

FSH-induced upregulation of cAMP-PDE4 activities was decreased in cultured Sertoli cells when alteration of cell proteoglycans (PGs) metabolism was simultaneously induced either by para-nitrophenyl beta-d-xyloside (PNPX) or by sodium chlorate. This effect was restricted to the particulate PDE4 activities and its timing was consistent with the half-life of Sertoli cell PGs. It did not result from alterations in Pde4d variants expression, the major FSH-regulated PDE4 in Sertoli cells. Moreover, lack of changes in the particulate levels of major immunoreactive 75 kDa and 90 kDa PDE4D proteins, corresponding likely to short PDE4D1 and long PDE4D3/D8/D9 isoforms respectively, suggested that the decrease in FSH-stimulated of PDE4 activities in chlorate- and PNPX-treated cells at the end of the 24-h incubation period resulted from the increased reversal of the activated particulate PDE4(D) activities back to unstimulated levels. By controlling FSH-stimulated particulate PDE4 inactivation through a still unknown mechanism (sustained activation of PKA or reduction of phosphoprotein phosphatase activities), cell PGs could be involved in the alteration of cAMP response to FSH accompanying the transition of Sertoli cells from proliferative to non-proliferative differentiated state.

Roflumilast: a phosphodiesterase-4 inhibitor for the treatment of respiratory disease

Asthma and chronic obstructive pulmonary disease (COPD) are two of the most common chronic diseases worldwide, yet the classes of drug licensed to treat these conditions have not changed appreciably over the last 20 years. Inhaled bronchodilators and glucocorticosteroids (often in combination) form the mainstay of therapy for respiratory diseases, but many patients (including the elderly and children) can have problems using inhaler devices and there is a clear preference for oral therapy. The prevalence of these respiratory diseases is on the increase worldwide and continues to represent an area of medicine with unmet medical needs, particularly in the treatment of COPD. Despite this increase, very few new classes of drugs have been introduced into clinical practice. Phosphodiesterase-4 inhibitors are a novel class of drugs in development for the treatment of respiratory diseases and there are a number of lead compounds in late clinical development. This review focuses on one of the most promising drugs in development, roflumilast, which has undergone extensive clinical evaluation.

Expression of the cAMP-phosphodiesterase PDE4D isoforms and age-related changes in follicle-stimulating hormone-stimulated PDE4 activities in immature rat sertoli cells

Major changes in the cAMP-dependent signal transduction pathway triggered by FSH take place during transition of rat Sertoli cells from proliferative to the quiescent/terminally differentiated state. Using Sertoli cell cultures isolated from 10-, 20-, and 30-day-old rats, we recorded a specific increase in PDE4 activity in both the soluble and particulate subcellular fractions of 20-day-old Sertoli cells, which also displayed the highest cAMP response to FSH and the highest FSH-induced increase in PDE4 activity in both subcellular compartments. RT-PCR and immunoblotting experiments showed that almost all the PDE4D isoforms, known as the main cAMP-regulated rolipram-sensitive PDE in Sertoli cells, were expressed throughout the early postpartum period, whereas only the short PDE4D isoforms (PDE4D1 and PDE4D2) were transcriptionally regulated by FSH. Unexpectedly, the immunoblot data also revealed that the soluble PDE4 activities were mainly related to the long PDE4D isoforms and that short PDE4D1 was predominantly particulate. The subcellular distribution and expression of PDE4D proteins were unaffected by the developmental status of the Sertoli cells. Only the expression of short PDE4D1 appeared to be upregulated by FSH and only in 20-day-old Sertoli cells, which suggests phenotype-dependent differential regulation of Pde4d1 mRNA translation. Resensitization of the cAMP response to FSH in 20-day-old Sertoli cells was also associated with the highest FSH-induced transient increase in both soluble and particulate PDE4 activities, which suggests developmental changes in the PKA-mediated upregulation of the catalytic activities of long PDE4D. Such alterations may be involved in the phenotype-dependent alterations in FSH receptor coupling with its associated G proteins in rat Sertoli cells.

Regulierte Hypothermie nach Herz-Kreislauf-Stillstand

The introduction of therapeutic mild hypothermia after cardiac arrest allows the neuronal damage caused by global cerebral ischemia to be advantageously influenced for the first time. Currently, hypothermia is induced by external or internal cooling of the patient (forced hypothermia). However, this results in activation of counter-regulation mechanisms which could be possible risk factors for the patient. The aim of this article is to give a review of possible, but at present only experimental, methods which could allow the body temperature set point to be decreased pharmacologically (regulated hypothermia). Various classes of substances will be discussed based on their effect on thermoregulation and their performance in animal experiments on cerebral ischemia.

Cyclic Nucleotide Phosphodiesterases: Molecular Regulation to Clinical Use

Cyclic nucleotide phosphodiesterases (PDEs) are enzymes that regulate the cellular levels of the second messengers, cAMP and cGMP, by controlling their rates of degradation. There are 11 different PDE families, with each family typically having several different isoforms and splice variants. These unique PDEs differ in their three-dimensional structure, kinetic properties, modes of regulation, intracellular localization, cellular expression, and inhibitor sensitivities. Current data suggest that individual isozymes modulate distinct regulatory pathways in the cell. These properties therefore offer the opportunity for selectively targeting specific PDEs for treatment of specific disease states. The feasibility of these enzymes as drug targets is exemplified by the commercial and clinical successes of the erectile dysfunction drugs, sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra). PDE inhibitors are also currently available or in development for treatment of a variety of other pathological conditions. In this review the basic biochemical properties, cellular regulation, expression patterns, and physiological functions of the different PDE isoforms will be discussed. How these properties relate to the current and future development of PDE inhibitors as pharmacological agents is especially considered. PDEs hold great promise as drug targets and recent research advances make this an exciting time for the field of PDE research.

Local anti-inflammatory effect and behavioral studies on new PDE4 inhibitors

Phosphodiesterase 4 (PDE4) inhibitors are effective anti-inflammatory drugs, although some adverse effects are observed in animals and humans. These effects have forced researchers to find new PDE4 inhibitors with less adverse effects. We recently reported the synthesis of novel heterocyclic-fused pyridazinones that inhibit PDE4. As a first step in the study of the anti-inflammatory properties of these compounds, we studied the effects of local administration of these pyridazinone derivatives in a mouse model of acute inflammation. We found that 6-Benzyl-3-methyl-4-phenylpyrazolo[3,4-d]pyridazin-7(6H)-one (CC4), ethyl 6,7-dihydro-6-ethyl-3-methyl-7-oxo-4-phenyl-thieno[2,3-d]pyridazine-2-carboxylate (CC6) and ethyl 6,7-dihydro-6-ethyl-3-methyl-4-phenyl-1H-pyrrolo[2,3-d]pyridazine-2-carboxylate (CC12) reduced the paw edema induced by zymosan in mice as rolipram (the PDE4 inhibitor prototype with anti-inflammatory activity) and indomethacin did. It is well known that rolipram locally administered induces some adverse effects such as hyperalgesia. Thus, we studied this effect after local administration of CC4, CC6 and CC12 in the formalin test. We found that CC6 induced hyperalgesic effects, whereas CC4 and CC12 did not change the nociceptive threshold. Furthermore, we found that rolipram and CC6 reduced locomotor activity, whereas CC4 and CC12 did not change locomotor performance of the mice. Since CC4 and CC12 neither affected the nociceptive threshold nor changed the locomotor performance of mice, they appear more suitable than CC6 for future studies on animals and could be developed as an anti-inflammatory drug for humans.

Type 4 phosphodiesterase inhibition impairs detection of low odor concentrations in mice

The cAMP-specific phosphodiesterase PDE4A is abundant in the dendrites, soma and axons of olfactory receptor neurons of the mouse, but it is not present in the cilia, where olfactory transduction initiates. Although the function of PDE4A in mammalian olfaction is unknown, patch clamp studies on deciliated olfactory receptor cells in the newt have shown that adrenaline or cAMP analogs can increase the contrast sensitivity to current injection. We used mice to ask whether increasing the levels of cAMP in sensory neurons by inhibiting PDE4A activity with rolipram could lead to changes in the perception of odorants that correspond to the in vitro cellular responses seen in newts. In an automated olfactometer, rolipram treatment (1mg/kg, i.p.) significantly impaired the detection accuracy of 1-propanol at relatively high dilutions but did not affect detection at lower dilutions. Meanwhile, the ability to discriminate amyl acetate alone from a mixture of amyl acetate+citronellal was not affected by rolipram at any odor dilution. In a different task in which mice were trained to discriminate between cups of scented versus unscented sand, rolipram treatment resulted in poorer discrimination at high and better discrimination at low, odor dilutions. In sum, PDE4 inhibition resulted in a consistent decrement in the ability of mice to detect low concentrations of odorants, but the effects of rolipram on detection of higher concentrations were task-dependent.

Effects of repeated administration of rolipram, a cAMP-specific phosphodiesterase inhibitor, on acetylcholinergic indices in the aged rat brain

The effects of repeated treatment of rolipram, a cAMP specific phosphodiesterase inhibitor (0.1 mg/kg/day i.p., 14 days), on several neuronal cholinergic indices, especially on those in aged rats were examined. In young-adult rats, rolipram treatment increased choline acetyltransferase (ChAT) activity (V(max)value) in the striatum as well as in thalamus + midbrain, whereas it decreased choline esterase activity in the hippocampus. The ChAT activity (V(max)value) and the M1-R binding (B(max)value) in the aged control rats were significantly reduced in all the brain regions examined, compared with the young-adult rats, but consecutive rolipram treatment ameliorated the reductions of both indices in the frontal cortex and the hippocampus to approximately the young-adult control levels. Since high membrane binding site concentrations for rolipram itself were revealed in the frontal cortex and the hippocampus, where the rolipram treatment showed ameliorating effects on the ChAT activity and the M1-R binding, the present findings indicate that repeated rolipram administration easily affects these two brain regions. Thus, repeated rolipram administration could restore both the presynaptic ChAT activity and the postsynaptic muscarinic cholinergic M1-R binding which are decreased with aging.

The toxicity of SCH 351591, a novel phosphodiesterase-4 inhibitor, in Cynomolgus monkeys

SCH351591, a novel phosphodiesterase-4 inhibitor under investigation as a potential therapeutic for asthma and chronic obstructive pulmonary disease (COPD), was evaluated in a 3-month rising-dose study in Cynomolgus monkeys. Four groups, containing four monkeys/sex, received vehicle control or rising doses up to 12, 24, or 48 mg/kg of SCH351591 daily. Although initial exposure produced clinical signs of emesis, reduced food intake, and reduced body weight, tachyphylaxis to the emesis allowed dose escalation up to 48 mg/kg/day. Two monkeys died and 3 were sacrificed in moribund condition over the course of the study. Early mortality, involving monkeys dosed with 12 or 24 mg/kg, was attributed to sepsis (2 monkeys) or colon inflammation (3 monkeys). Leukocyte function assays on low- and mid-dose group survivors revealed an inhibition of T lymphocyte proliferation for 12 mg/kg group males and 24 mg/kg group monkeys of both sexes. Necropsy findings, unassociated with early mortality, included reduced size and weight of the thymus, depletion of body fat, red discoloration of the gastric mucosa, and perivascular hemorrhage of the stomach and heart. Stomach and heart gross findings were present in the high-dose group only. Histopathologic lesions, in addition to those attributed to concurrent bacterial infection, included thymic atrophy, serous atrophy of fat, myocardial degeneration and acute to chronic inflammation of small to medium-sized arteries in various organs and tissues including the heart, kidneys, stomach, salivary glands, pancreas, esophagus, gallbladder, and mesentery. The findings of this study demonstrate the potential of a PDE4 inhibitor to alter immunologic response as well as to produce arteriopathy in nonhuman primates.

The induction of cyclic nucleotide phosphodiesterase 4 gene (PDE4D) impairs memory in a water maze task

In this study, the effects on memory of intraperitoneal post-training administration of cyclic nucleotide phosphodiesterase (PDE) inhibitors, DC-TA 46 and rolipram, were tested using a visible/hidden-platform water maze task. The effects of these compounds on cyclic nucleotide levels in the hippocampal formation (HF) and striatum (CP) were also assessed, by enzymatic immunoassay (EIA). The results obtained from rats trained in the visible-platform task were not significantly different from controls. On the contrary, the animals trained in the hidden-platform water maze task showed a memory impairment, when injected with DC-TA 46 at maximal dose of 20mg/kg and with rolipram at 3 and 30 mg/kg doses. The effects of these drugs on cyclic nucleotide levels in HF and CP were observed at 30 min and at 24h after drug administration. Thirty minutes after drug injection, we observed an increase of cAMP level, both in HF and in CP. Twenty-four hours after the retention test, we observed that in CP the cAMP intracellular level remained high, while in the HF at effective doses both inhibitors induced cAMP PDE activity, determining a decrease of cyclic nucleotide. Semi-quantitative RT-PCR analysis, together with Western blot immunodetection, showed a mRNA and protein induction of PDE4D PDE isoforms, that may account for the increase of PDE activity observed. Our data suggest that, despite cyclic nucleotide increase at 30 min, the fundamental event causing memory impairment, came from the subsequent long time decrease of cAMP levels, due to the post-translational PDE4D induction.

Transient focal ischemia affects the cAMP second messenger system and coupled dopamine D1 and 5-HT1A receptors in the living monkey brain: a positron emission tomography study using microdialysis

Using positron emission tomography (PET) and microdialysis, the present study showed that neuronal damages after transient focal ischemia was partly induced by hyperactivation of the cyclic adenosine 3',5'-monophosphate (cAMP) second messenger system through modulations of dopamine D, and serotonin 5-HT1A receptors in the living brains of cynomolgus monkeys. Occlusion of the right middle cerebral artery for 3 hours suppressed CBF in the striatum, and reperfusion induced hyperperfusion in the neocortex and striatum of the occluded side. Six hours after reperfusion, the activity of the cAMP second messenger system assayed with [11C]rolipram was significantly facilitated in the neocortex and striatum where CBF was lowered more than 40% of normal during occlusion ("ischemic" area). Seven days later, impaired dopamine D1 and 5-HT1A receptor binding, measured with [11C]SCH23390 and [carbonyl-11C]WAY-100635, respectively, was observed in the ischemic area. Microdialysis analysis revealed that the striatal dopamine level provided a transient and marked increased during occlusion and after reperfusion, whereas the cortical serotonin level transiently increased only after reperfusion, and was at an undetectable level thereafter. Administration of rolipram (0.1 and 1 mg/kg, intravenously) during occlusion facilitated reduction of dopamine D1 binding, whereas rolipram administration 6 hours after reperfusion induced a further decrease in 5-HT1A receptor binding. These results suggest that the activation of cAMP second messenger system modulated by dopamine D1 and 5-HT1A receptors could be involved in the neuronal degeneration after transient cerebral ischemic insult.

Inhibition of osteoclastogenesis by a phosphodiesterase 4 inhibitor XT-611 through synergistic action with endogenous prostaglandin E2

We examined the effect of a phosphodiesterase 4 (PDE4) inhibitor, 3,4-dipropyl-4,5,7,8-tetrahydro-3H-imidazo[1,2-i]-purin-5-one (XT-611) on osteoclast formation in three different mouse bone-marrow cell (BMC) culture systems. We confirmed that selective inhibitors of PDE4, including XT-611, among several PDE inhibitors decreased osteoclast formation in the BMC culture system. XT-611 also inhibited osteoclast formation in co-culture of mouse bone-marrow stromal cell line ST2 and adherent cell-depleted (ACD)-BMCs. However, it did not inhibit osteoclastogenesis in culture of ACD-BMCs alone in the presence of macrophage-colony stimulating factor (M-CSF) and soluble receptor activator of NF-kappaB ligand (sRANKL). XT-611 significantly increased prostaglandin E(2) (PGE(2)) production from ST2 cells and, in combination with PGE(2), synergistically increased cAMP concentration in osteoclast progenitors. In the ST2 co-culture system, XT-611 did not influence the expression of RANKL, osteoprotegerin and RANK mRNAs. By combined treatment with XT-611 and PGE(2) of ACD-BMCs, osteoclast multinucleation was clearly inhibited with decrease in the expression of calcitonin receptor mRNA, while the expression of RANK and c-fms (an M-CSF receptor) mRNAs was unchanged. These results indicate that the PDE4 inhibitor inhibits osteoclastogenesis by acting on osteoclast progenitors synergistically with PGE(2) secreted from stromal cells, but not by influencing the cell-to-cell interaction between stromal cells and osteoclast progenitors.

Tissue transglutaminase directly regulates adenylyl cyclase resulting in enhanced cAMP-response element-binding protein (CREB) activation

Tissue transglutaminase (tTG) is present in the human nervous system and is predominantly localized to neurons. Treatment of human neuroblastoma SH-SY5Y cells with retinoic acid results in increased tTG expression, which is both necessary and sufficient for differentiation. The goal of the present study was to determine whether tTG modulates the activation of the cyclic AMP-response element (CRE)-binding protein, CREB, an event that likely plays a central role in the differentiation of SH-SY5Y cells. SH-SY5Y cells stably transfected with active wild type tTG, tTG without transamidating activity (C277S), an antisense tTG construct that depleted the endogenous levels of tTG, or vector only were used for the study. Treatment with forskolin, an adenylyl cyclase activator, increased that activation-associated phosphorylation of CREB, which was prolonged by tTG overexpression. CRE-reporter gene activity was also significantly elevated in the tTG cells compared with the other cells. The enhancement of CREB phosphorylation/activation in the tTG cells is likely due to the fact that tTG significantly potentiates cAMP production, and our findings indicate that tTG enhances adenylyl cyclase activity by modulating the conformation state of adenylyl cyclase. This is the first study to provide evidence of the mechanism by which tTG may contribute to neuronal differentiation.

PDE4 cAMP phosphodiesterases: modular enzymes that orchestrate signalling cross-talk, desensitization and compartmentalization

cAMP is a second messenger that controls many key cellular functions. The only way to inactivate cAMP is to degrade it through the action of cAMP phosphodiesterases (PDEs). PDEs are thus poised to play a key regulatory role. PDE4 cAMP-specific phosphodiesterases appear to have specific functions with selective inhibitors serving as potent anti-inflammatory agents. The recent elucidation of the structure of the PDE4 catalytic unit allows for molecular insight into the mode of catalysis as well as substrate and inhibitor selectivity. The four PDE4 genes encode over 16 isoforms, each of which is characterized by a unique N-terminal region. PDE4 isoforms play a pivotal role in controlling functionally and spatially distinct pools of cAMP by virtue of their unique intracellular targeting. Targeting occurs by association with proteins, such as arrestins, SRC family tyrosyl kinases, A-kinase anchoring proteins ('AKAPs') and receptor for activated C kinase 1 ('RACK1'), and, in the case of isoform PDE4A1, by a specific interaction (TAPAS-1) with phosphatidic acid. PDE4 isoforms are 'designed' to be regulated by extracellular-signal-related protein kinase (ERK), which binds to anchor sites on the PDE4 catalytic domain that it phosphorylates. The upstream conserved region 1 (UCR1) and 2 (UCR2) modules that abut the PDE4 catalytic unit confer regulatory functions by orchestrating the functional outcome of phosphorylation by cAMP-dependent protein kinase ('PKA') and ERK. PDE4 enzymes stand at a crossroads that allows them to integrate various signalling pathways with that of cAMP in spatially distinct compartments.

Antagonism of adenosine receptors by caffeine and caffeine metabolites in equine forebrain tissues

OBJECTIVE

To determine the presence of adenosine receptor subtypes A1 and A2a in equine forebrain tissues and to characterize the interactions of caffeine and its metabolites with adenosine receptors in the CNS of horses.

SAMPLE POPULATION

Brain tissue specimens obtained during necropsy from 5 adult male research horses.

PROCEDURE

Membrane-enriched homogenates from cerebral cortex and striatum were evaluated by radioligand binding assays with the A1-selective ligand [3H]DPCPX and the A2a-selective ligand [3H]ZM241385. Functional responses to adenosine receptor agonists and antagonists were determined by a nucleotide exchange assay using [35S]-guanosine 5'-(gamma-thio) triphosphate ([35S]GTPgammaS).

RESULTS

Saturable high affinity [3H]DPCPX binding (A1) sites were detected in cerebral cortex and striatum, whereas high-affinity [3H]ZM241385 binding (A2a) sites were detected only in striatum. Caffeine and related methylxanthines had similar binding affinities at A1 and A2a sites with rank orders of drug binding affinities (theophylline > paraxanthine > or = caffeine >> theobromine) similar to other species. [35S]GTPgammaS exchange revealed that caffeine and its metabolites act as pure adenosine receptor antagonists at concentrations that correspond to A1 and A2a receptor binding affinities.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of our study affirm the presence of guanine nucleotide binding protein linked adenosine receptors (ie, high-affinity A1 and A2a adenosine receptors) in equine forebrain tissues and reveal the antagonistic actions by caffeine and several biologically active caffeine metabolites. Antagonism of adenosine actions in the equine CNS by these stimulants may be responsible for some central actions of methylxanthine drugs, including motor stimulation and enhanced racing performance.

Age differences in phosphodiesterase type-IV and its functional response to dopamine D1 receptor modulation in the living brain: a PET study in conscious monkeys

The present study demonstrated the age-related changes in the striatal dopamine D1 receptor binding and its related cAMP second-messenger system in the living brains of conscious young (6.4 +/- 1.8 years old) and aged (19.5 +/- 3.3 years old) monkeys (Macaca mulatta) using positron emission tomography (PET). For quantitative analysis of D1 receptors, [11C]SCH23390 was used and phosphodiesterase type-IV (PDE-IV) activity, as an index of cAMP system, was estimated by two scans with R- and S-[11C]rolipram. Significant age-related decreases in D1 receptor binding were observed in the striatum and frontal cortex. Analysis of uptake of R- and S-[11C]rolipram indicated age-related decreases in PDE-IV activity showing 22.0 and 25.2% decreases in the striatum and frontal cortex, respectively, while no significant changes were observed in the cerebellum. With systemic preadministration of the dopamine D1 receptor antagonist SCH23390 (0.2, 0.6, and 2 mg/kg), the PDE-IV activities in the striatum and frontal cortex were dose-dependently suppressed in both age groups. However, the degree of suppression by SCH23390 was more marked in young than in aged monkeys. These results demonstrate that the striatal cAMP second-messenger system activity as well as its functional response to dopamine D1 antagonist showed age-related impairment in the brain.

Facilitation of dopaminergic neural transmission does not affect [(11)C]SCH23390 binding to the striatal D(1) dopamine receptors, but the facilitation enhances phosphodiesterase type-IV activity through D(1) receptors: PET studies in the conscious monkey brain

The present study evaluated the effects of methamphetamine and scopolamine on the striatal dopamine D(1) receptor binding, measured by [(11)C]SCH23390, and D(1) receptor-coupled cAMP messenger system, determined as phosphodiesterase type-IV (PDE-IV) activity, were evaluated in the brains of conscious monkeys using positron emission tomography (PET) with microdialysis. When methamphetamine (0.1, 0.3, and 1 mg/kg) or scopolamine (0.01, 0.03, and 0.1 mg/kg) was systemically administered, [(11)C]SCH23390 binding to D(1) receptors was not affected. With administration of methamphetamine, the striatal PDE-IV activity, as measured with R-[(11)C]rolipram (active form) and S-[(11)C]rolipram (inactive form), was dose-dependently facilitated with enhanced dopamine level in the striatal ECF. Administration of scopolamine also induced facilitated PDE-IV activity without any apparent changes in the ECF dopamine. These facilitations of PDE-IV activity were abolished by preadministration of SCH23390, but not by raclopride. These results demonstrate that, as evaluated by PDE-IV activity, the inhibition of muscarinic cholinergic receptors actually facilitated dopamine neuronal signal transduction through D(1) receptors, as observed previously on D(2) receptors with no apparent increase in the striatal ECF dopamine level, but the enhanced dopamine transmission could not detected by [(11)C]SCH23390.

The antidepressant and antiinflammatory effects of rolipram in the central nervous system

Rolipram is a selective inhibitor of phosphodiesterases (PDE) IV, especially of the subtype PDE IVB. These phosphodiesterases are responsible for hydrolysis of the cyclic nucleotides cAMP and cGMP, particularly in nerve and immune cells. Consequences of rolipram-induced elevation of intracellular cAMP are increased synthesis and release of norepinephrine, which enhance central noradrenergic transmission, and suppress expression of proinflammatory cytokines and other mediators of inflammation. In humans and animals rolipram produces thereby a variety of biological effects. These effects include attenuation of endogenous depression and inflammation in the central nervous system (CNS), both effects are of potential clinical relevance. There are some discrepancies between in vitro and in vivo effects of rolipram, as well as between results obtained in animal models and clinical studies. The clinical use of rolipram is limited because of its behavioral and other side effects. Newly developed selective PDE IV inhibitors with presumably higher potency and lower toxicity are currently under investigation.

The novel long PDE4A10 cyclic AMP phosphodiesterase shows a pattern of expression within brain that is distinct from the long PDE4A5 and short PDE4A1 isoforms

In situ hybridisation methods were used to map the distribution of the novel long PDE4A10 isoform in the brain. PDE4A10 distribution was compared to that of the long PDE4A5 isoform and the short PDE4A1 isoform using probes specific for unique sequences within each of these isoforms. Coronal sections of the brain, taken at the level of the olfactory bulb, prefrontal cortex, striatum, thalamus, hippocampus and cerebellum, were analysed. Strongest expression of PDE4A isoforms was found in the olfactory bulb granular layer with high signals also in the piriform cortex, the dentate gyrus and the CA1 and CA2 pyramidal cells. For the two long forms, level general staining was noted throughout the striatum, thalamus and hippocampus but no signal was evident in the cerebellum. The long PDE4A10 and PDE4A5 isoforms localised to essentially the same regions throughout the brain, although PDE4A10 was uniquely expressed in the major island of Calleja. A signal for the short PDE4A1 isoform was found in regions in which the two long isoforms were both expressed, with the exception of the medial nucleus of the amygdala where weak signals for PDE4A5 and PDE4A10 were detected but PDE4A1 was absent. Uniquely, strong signals for PDE4A1 were detected in the glomerular layer of the olfactory bulb, the CA3 pyramidal cell region and the cerebellum; areas where signals for the two long forms were not evident. PDE4A transcripts for both PDE4A5 and PDE4A10 were not apparent in the brain stem and those for PDE4A1 were low. PDE4A isoforms are present in several key areas of the brain and therefore present valid targets for therapeutic interventions. Whilst the two long PDE4A isoforms show a remarkably similar distribution, in at least three regions there is clear segregation between their pattern of expression and that of the PDE4A1 short form. This identifies differential regulation of the expression of PDE4A long and short isoforms. We suggest that specific PDE4A isoforms may have distinct functional roles in the brain, indicating that PDE4A isoform-selective inhibitors may have specific therapeutic and pharmacologic properties.

Effects of rolipram on the elevated plus-maze test in rats: a preliminary study

The objective of the present study was to assess the behavioural effects of rolipram, a specific cAMP phosphodiesterase (PDE4) inhibitor, in the elevated plus-maze (EPM) test in rats. Results showed that rolipram at the highest dose tested (0.1 mg/kg) increased the percentage of both time spent and entries into open arms, although a decrease of locomotor activity in the EPM test was also observed. In contrast, diazepam (3.0 mg/kg) exhibited the typical profile of an anxiolytic in the EPM test, increasing the percentage of time spent and entries into open arms as well as locomotor activity. A posterior statistical analysis, however, established that the effects of both rolipram and diazepam on parameters denoting anxiolytic-like activity were statistically independent from those reflecting locomotor activity reduction. Furthermore, the effects of both rolipram and diazepam were shown to be distinct from those exhibited by tricyclic antidepressant imipramine which did not show any anxiolytic-like effects in the EPM test, although a reduction of locomotor activity was also detected. Although these preliminary results suggest that rolipram may have some anxiolytic-like properties on the EPM test in rats, such an interpretation should be taken cautiously due to the observed effects on locomotor activity, which could complicate the interpretation of results from rolipram and other PDE4 inhibitors in the current test and in other anxiety animal models.

Preliminary evidence for an involvement of the cholinergic system in the sedative effects of rolipram in rats

Rolipram is a specific cAMP phosphodiesterase type 4 (PDE4) inhibitor in the brain, which induces an increase in the intracellular levels of cAMP. Rolipram produces characteristic alterations in animal behavior, which have been suggested to be mediated mainly through an intracellular mechanism involving an increase in cAMP. However, specific mechanisms mediating the sedative effects of this compound have not yet been investigated. Because several lines of evidence indicate that the acetylcholine neural system may be involved in some effects of PDE4 inhibitors, the aim of this study was to elucidate whether the neurotransmitter acetylcholine is involved in the sedative effects induced by rolipram. The present study assessed the motor effects of rolipram in an exploratory behavioral test, the open field, in Wistar rats. The results show that rolipram (0.1-3.0 mg/kg SC) induced potent and dose-dependent hypoactivity, decreasing both locomotion and rearing. Physostigmine (0.03-0.3 mg/kg SC) potentiated a subeffective dose of rolipram (0.03 mg/kg SC), resulting in strong sedation, similar to that following higher doses of either rolipram or physostigmine alone, whereas the reduction in locomotor activity induced by rolipram (0.3 mg/kg SC) was completely reversed by scopolamine (0.03-0.3 mg/kg SC). These data provide preliminary evidence suggesting the involvement of the acetylcholinergic system in the sedative effects of rolipram.

Treatment with BBB022A or rolipram stabilizes the blood-brain barrier in experimental autoimmune encephalomyelitis: an additional mechanism for the therapeutic effect of type IV phosphodiesterase inhibitors

We examined the treatment effects of two structurally distinct phosphodiesterase type IV (PDE IV) inhibitors, BBB022 and rolipram, in murine and rat models of experimental autoimmune encephalomyelitis (EAE). Based on our data, we propose a mechanism of action which may supplement immunomodulatory effects of PDE IV inhibitors. In particular, PDE inhibitors promote elevation of intracellular cAMP levels, increasing the electrical resistance of endothelial monolayers by stabilizing intercellular junctional complexes. Such an effect on central nervous system (CNS) vascular endothelium has the potential to reduce disease severity in EAE, because both inflammatory cells and humoral factors readily cross a disrupted blood-brain barrier (BBB). In this report, we demonstrate the capacity of BBB022 and rolipram to decrease clinical severity of EAE. further, PDE IV inhibitors significantly reduced BBB permeability in the spinal cords of mice with EAE. These results provide evidence that PDE IV-inhibitors may exert therapeutic effects in EAE by modifying cerebrovascular endothelial permeability, reducing tissue edema as well as entry of inflammatory cells and factors.

The type IV phosphodiesterase inhibitors, Ro 20-1724 and rolipram, block the initiation of cocaine self-administration

The hypothesis that the selective activation of cyclic AMP (cAMP) signal transduction pathways will suppress the initiation of cocaine self-administration was examined in this investigation. To test this hypothesis, the effects of the administration of the cAMP-specific (type IV) phosphodiesterase inhibitors, rolipram and Ro 20-1724, on cocaine self-administration were determined. The effects of Ro 20-1724 treatment on operant responding for food also were examined. Both cocaine and food were delivered following a fixed-ratio 5 schedule. A significant increase in the latency for the delivery of the first cocaine infusion and a reduction in the number of infusions obtained per session were produced by treatment with either rolipram or Ro 20-1724. Similar effects on responding for food were seen with Ro 20-1724 administration. Responding after drug-induced delays tended to be at control levels. These results suggest that cAMP-specific phosphodiesterase inhibitors may inhibit the initiation of operant responding for either cocaine or food. However, the extent to which these actions involve specific effects on central motivational systems as opposed to other mechanisms remains to be determined.

Rolipram, a type IV-specific phosphodiesterase inhibitor, facilitates the establishment of long-lasting long-term potentiation and improves memory

In an attempt to improve behavioral memory, we devised a strategy to amplify the signal-to-noise ratio of the cAMP pathway, which plays a central role in hippocampal synaptic plasticity and behavioral memory. Multiple high-frequency trains of electrical stimulation induce long-lasting long-term potentiation, a form of synaptic strengthening in hippocampus that is greater in both magnitude and persistence than the short-lasting long-term potentiation generated by a single tetanic train. Studies using pharmacological inhibitors and genetic manipulations have shown that this difference in response depends on the activity of cAMP-dependent protein kinase A. Genetic studies have also indicated that protein kinase A and one of its target transcription factors, cAMP response element binding protein, are important in memory in vivo. These findings suggested that amplification of signals through the cAMP pathway might lower the threshold for generating long-lasting long-term potentiation and increase behavioral memory. We therefore examined the biochemical, physiological, and behavioral effects in mice of partial inhibition of a hippocampal cAMP phosphodiesterase. Concentrations of a type IV-specific phosphodiesterase inhibitor, rolipram, which had no significant effect on basal cAMP concentration, increased the cAMP response of hippocampal slices to stimulation with forskolin and induced persistent long-term potentiation in CA1 after a single tetanic train. In both young and aged mice, rolipram treatment before training increased long- but not short-term retention in freezing to context, a hippocampus-dependent memory task.