Characterization of the rolipram-sensitive, cyclic AMP-specific phosphodiesterases: identification and differential expression of immunologically distinct forms in the rat brain

An Overview of PDE4 Inhibitors in Clinical Trials: 2010 to Early 2022

Since the early 1980s, phosphodiesterase 4 (PDE4) has been an attractive target for the treatment of inflammation-based diseases. Several scientific advancements, by both academia and pharmaceutical companies, have enabled the identification of many synthetic ligands for this target, along with the acquisition of precise information on biological requirements and linked therapeutic opportunities. The transition from pre-clinical to clinical phase was not easy for the majority of these compounds, mainly due to their significant side effects, and it took almost thirty years for a PDE4 inhibitor to become a drug i.e., Roflumilast, used in the clinics for the treatment of chronic obstructive pulmonary disease. Since then, three additional compounds have reached the market a few years later: Crisaborole for atopic dermatitis, Apremilast for psoriatic arthritis and Ibudilast for Krabbe disease. The aim of this review is to provide an overview of the compounds that have reached clinical trials in the last ten years, with a focus on those most recently developed for respiratory, skin and neurological disorders.

Selective Inhibition of PDE4B Reduces Binge Drinking in Two C57BL/6 Substrains

Cyclic AMP (cAMP)-dependent signaling is highly implicated in the pathophysiology of alcohol use disorder (AUD), with evidence supporting the efficacy of inhibiting the cAMP hydrolyzing enzyme phosphodiesterase 4 (PDE4) as a therapeutic strategy for drinking reduction. Off-target emetic effects associated with non-selective PDE4 inhibitors has prompted the development of selective PDE4 isozyme inhibitors for treating neuropsychiatric conditions. Herein, we examined the effect of a selective PDE4B inhibitor A33 (0–1.0 mg/kg) on alcohol drinking in both female and male mice from two genetically distinct C57BL/6 substrains. Under two different binge-drinking procedures, A33 pretreatment reduced alcohol intake in male and female mice of both substrains. In both drinking studies, there was no evidence for carry-over effects the next day; however, we did observe some sign of tolerance to A33’s effect on alcohol intake upon repeated, intermittent, treatment (5 injections of 1.0 mg/kg, every other day). Pretreatment with 1.0 mg/kg of A33 augmented sucrose intake by C57BL/6NJ, but not C57BL/6J, mice. In mice with a prior history of A33 pretreatment during alcohol-drinking, A33 (1.0 mg/kg) did not alter spontaneous locomotor activity or basal motor coordination, nor did it alter alcohol’s effects on motor activity, coordination or sedation. In a distinct cohort of alcohol-naïve mice, acute pretreatment with 1.0 mg/kg of A33 did not alter motor performance on a rotarod and reduced sensitivity to the acute intoxicating effects of alcohol. These data provide the first evidence that selective PDE4B inhibition is an effective strategy for reducing excessive alcohol intake in murine models of binge drinking, with minimal off-target effects. Despite reducing sensitivity to acute alcohol intoxication, PDE4B inhibition reduces binge alcohol drinking, without influencing behavioral sensitivity to alcohol in alcohol-experienced mice. Furthermore, A33 is equally effective in males and females and exerts a quantitatively similar reduction in alcohol intake in mice with a genetic predisposition for high versus moderate alcohol preference. Such findings further support the safety and potential clinical utility of targeting PDE4 for treating AUD.

A Novel PDE4D Inhibitor BPN14770 Reverses Scopolamine-Induced Cognitive Deficits via cAMP/SIRT1/Akt/Bcl-2 Pathway

A global, quantitative proteomics/systems-biology analysis of the selective pharmacological inhibition of phosphodiesterase-4D (PDE4D) revealed the differential regulation of pathways associated with neuroplasticity in memory-associated brain regions. Subtype selective inhibitors of PDE4D bind in an allosteric site that differs between mice and humans in a single amino acid (tyrosine vs. phenylalanine, respectively). Therefore to study selective inhibition of PDE4D by BPN14770, a subtype selective allosteric inhibitor of PDE4D, we utilized a line of mice in which the PDE4D gene had been humanized by mutating the critical tyrosine to phenylalanine. Relatively low doses of BPN14770 were effective at reversing scopolamine-induced memory and cognitive deficits in humanized PDE4D mice. Inhibition of PDE4D alters the expression of protein kinase A (PKA), Sirt1, Akt, and Bcl-2/Bax which are components of signaling pathways for regulating endocrine response, stress resistance, neuronal autophagy, and apoptosis. Treatment with a series of antagonists, such as H89, sirtinol, and MK-2206, reversed the effect of BPN14770 as shown by behavioral tests and immunoblot analysis. These findings suggest that inhibition of PDE4D enhances signaling through the cAMP-PKA-SIRT1-Akt -Bcl-2/Bax pathway and thereby may provide therapeutic benefit in neurocognitive disorders.

Principal component analysis of routine blood test results with Parkinson's disease: A case-control study

This study aimed to explore the association of routine blood test values and blood cell ratios with the risk or severity of Parkinson's disease (PD). The medical records of 453 PD patients and 436 controls were retrospectively reviewed. The severity of PD was quantified by the modified Hoehn-Yahr (HY) scale. We performed principal component analysis (PCA) of significant values/ratios and used logistic regression analysis to explore the relationship between principal components (PCs) and the risk of PD. Spearman correlation and ordinal logistic regression analyses were performed to explore the relationship between indicators and the severity of PD. The PCA generated 9 PCs, which contributed to 90.86% of the total variance. Logistic regression analysis revealed positive associations of PC2 (a measure monocyte ratios) and PC6 (a measure of platelet ratios and volume) and negative associations of PC1 (a comprehensive measure of lymphocyte, eosinophil, neutrophil, and red blood cell values), PC4 (a measure of red blood cell values), and PC7 (a measure of red blood cell values and platelet volume) with the risk of PD. However, we observed no associations of variables with the severity of PD. In conclusion, PCA reduced the dimensionality of the data. Peripheral blood disorders may be associated with PD.

PAN-selective inhibition of cAMP-phosphodiesterase 4 (PDE4) induces gastroparesis in mice

Inhibitors of cAMP-phosphodiesterase 4 (PDE4) exert a number of promising therapeutic benefits, but adverse effects, in particular emesis and nausea, have curbed their clinical utility. Here, we show that PAN-selective inhibition of PDE4, but not inhibition of PDE3, causes a time- and dose-dependent accumulation of chow in the stomachs of mice fed ad libitum without changing the animals' food intake or the weight of their intestines, suggesting that PDE4 inhibition impairs gastric emptying. Indeed, PDE4 inhibition induced gastric retention in an acute model of gastric motility that traces the passage of a food bolus through the stomach over a 30 minutes time period. In humans, abnormal gastric retention of food is known as gastroparesis, a syndrome predominated by nausea (>90% of cases) and vomiting (>80% of cases). We thus explored the abnormal gastric retention induced by PDE4 inhibition in mice under the premise that it may represent a useful correlate of emesis and nausea. Delayed gastric emptying was produced by structurally distinct PAN-PDE4 inhibitors including Rolipram, Piclamilast, Roflumilast, and RS25344, suggesting that it is a class effect. PDE4 inhibitors induced gastric retention at similar or below doses commonly used to induce therapeutic benefits (e.g., 0.04 mg/kg Rolipram), thus mirroring the narrow therapeutic window of PDE4 inhibitors in humans. YM976, a PAN-PDE4 inhibitor that does not efficiently cross the blood-brain barrier, induced gastroparesis only at significantly higher doses (≥1 mg/kg). This suggests that PDE4 inhibition may act in part through effects on the autonomic nervous system regulation of gastric emptying and that PDE4 inhibitors that are not brain-penetrant may have an improved safety profile. The PDE4 family comprises four subtypes, PDE4A, B, C, and D. Selective ablation of any of these subtypes in mice did not induce gastroparesis per se, nor did it protect from PAN-PDE4 inhibitor-induced gastroparesis, indicating that gastric retention may result from the concurrent inhibition of multiple PDE4s. Thus, potentially, any of the four PDE4 subtypes may be targeted individually for therapeutic benefits without inducing nausea or emesis. Acute gastric retention induced by PDE4 inhibition is alleviated by treatment with the widely used prokinetic Metoclopramide, suggesting a potential of this drug to alleviate the side effects of PDE4 inhibitors. Finally, given that the cause of gastroparesis remains largely idiopathic, our findings open the possibility that a physiologic or pathophysiologic downregulation of PDE4 activity/expression may be causative in a subset of patients.

Phosphodiesterase 4 and 7 inhibitors produce protective effects against high glucose-induced neurotoxicity in PC12 cells via modulation of the oxidative stress, apoptosis and inflammation pathways

Diabetic neuropathy (DN) is the most common diabetic complication. It is estimated diabetic population will increase to 592 million by the year 2035. This is while at least 50-60% of all diabetic patients will suffer from neuropathy in their lifetime. Oxidative stress, mitochondrial dysfunction, apoptosis, and inflammation are crucial pathways in development and progression of DN. Since there is also no selective and effective therapeutic agent to prevent or treat high glucose (HG)-induced neuronal cell injury, it is crucial to explore tools by which one can reduce factors related to these pathways. Phosphodiesterase 4 and 7 (PDE 4 and 7) regulate oxidative damage, neurodegenaration, and inflammatory responses through modulation of cyclic adenosine monophosphate (cAMP) level, and thus can be as important drug targets for regulating DN. The aim of this study was to evaluate the protective effects of inhibitors of PDE 4 and 7, named rolipram and BRL5048, on HG-induced neurotoxicity in PC12 cells as an in vitro cellular model for DN and determine the possible mechanisms for theirs effects. We report that the PC12 cells pre-treatment with rolipram (2 μM) and/or BRL5048 (0.2 μM) for 60 min and then exposing the cells to HG (4.5 g/L for 72 h) or normal glucose (NG) (1 g/L for 72 h) condition show: (1) significant attenuation in ROS, MDA and TNF-a levels, Bax/Bcl-2 ratio, expression of caspase 3 and UCP2 proteins; (2) significant increase in viability, GSH/GSSG ratio, MMP and ATP levels. All these data together led us to propose PDE 4 and 7 inhibitors, and specifically, rolipram and BRL5048, as potential drugs candidate to be further studied for the prevention and treatment of DN.

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.

Rolipram, a Selective Phosphodiesterase 4 Inhibitor, Ameliorates Mechanical Hyperalgesia in a Rat Model of Chemotherapy-Induced Neuropathic Pain through Inhibition of Inflammatory Cytokines in the Dorsal Root Ganglion

Chemotherapy-induced neuropathic pain is a significant side effect of chemotherapeutic agents and is the most common reason for stopping chemotherapy. The aim of the present study was to find the major site and mechanisms of action by which rolipram, a selective phosphodiesterase-4 inhibitor, alleviates paclitaxel-induced neuropathic pain. Chemotherapy-induced neuropathic pain was induced in adult male Sprague-Dawley rats by intraperitoneal injection of paclitaxel on four alternate days. Rolipram was administered systemically or locally into the lumbar spinal cord, L5 dorsal root ganglion, sciatic nerve, or skin nerve terminal. The mechanical threshold, the protein level of several inflammatory cytokines, and the cellular locations of phosphodiesterase-4 and interleukin-1β in the dorsal root ganglion were measured by using behavioral testing, Western blotting, and immunohistochemistry, respectively. The local administration (0.03-mg) of rolipram in the L5 dorsal root ganglion ameliorated paclitaxel-induced pain behavior more effectively than did local administration in the other sites. Paclitaxel significantly increased the expression of inflammatory cytokines including tumor necrosis factor-α (2.2 times) and interleukin-1β (2.7 times) in the lumbar dorsal root ganglion, and rolipram significantly decreased it. In addition, phosphodiesterase-4 and interleukin-1β were expressed in the dorsal root ganglion neurons and satellite cells and paclitaxel significantly increased the intensity of interleukin-1β (2 times) and rolipram significantly decreased it. These results suggest that the major site of action of rolipram on paclitaxel-induced neuropathic pain in rats was the dorsal root ganglion. Rolipram decreased the expression of inflammatory cytokines in the dorsal root ganglion. Thus, phosphodiesterase-4 inhibitors may ameliorate chemotherapy-induced neuropathic pain by decreasing expression of inflammatory cytokines in the dorsal root ganglion.

FFPM, a PDE4 inhibitor, reverses learning and memory deficits in APP/PS1 transgenic mice via cAMP/PKA/CREB signaling and anti-inflammatory effects

Thus far, phosphodiesterase-4 (PDE4) inhibitors have not been approved for application in Alzheimer's disease (AD) in a clinical setting due to severe side effects, such as nausea and vomiting. In this study, we investigated the effect of FFPM, a novel PDE4 inhibitor, on learning and memory abilities, as well as the underlying mechanism in the APP/PS1 mouse model of AD. Pharmacokinetic studies have revealed that FFPM efficiently permeates into the brain, and reached peak values in plasma 2 h after orally dosing. A 3-week treatment with FFPM, at doses of 0.25 mg/kg and 0.5 mg/kg, significantly improved the learning and memory abilities of APP/PS1 transgenic mice in the Morris water maze and the Step-down passive avoidance task. Interestingly, we found that while rolipram (0.5 mg/kg) reduced the duration of the α2 adrenergic receptor-mediated anesthesia induced by xylazine/ketamine, FFPM (0.5 mg/kg) or the vehicle did not have an evident effect. FFPM increased the cAMP, PKA and CREB phosphorylation and BDNF levels, and reduced the NF-κB p65, iNOS, TNF-α and IL-1β levels in the hippocampi of APP/PS1 trangenic mice, as observed by ELISA and Western blot analysis. Taken together, our data demonstrated that the reversal effect of FFPM on cognitive deficits in APP/PS1 transgenic mice might be related to stimulation of the cAMP/PKA/CREB/BDNF pathway and anti-inflammatory effects. Moreover, FFPM appears to have potential as an effective PDE4 inhibitor in AD treatment with little emetic potential.

Comparison of the Pharmacological Profiles of Selective PDE4B and PDE4D Inhibitors in the Central Nervous System

Inhibition of cyclic AMP (cAMP)-specific phosphodiesterase 4 (PDE4) has been proposed as a potential treatment for a series of neuropsychological conditions such as depression, anxiety and memory loss. However, the specific involvement of each of the PDE4 subtypes (PDE4A, 4B and 4C) in different categories of behavior has yet to be elucidated. In the present study, we compared the possible pharmacological effects of PDE4B and PDE4D selective inhibitors, A-33 and D159687, in mediating neurological function in mice. Both compounds were equally potent in stimulating cAMP signaling in the mouse hippocampal cell line HT-22 leading to an increase in CREB phosphorylation. In contrast, A-33 and D159687 displayed distinct neuropharmacological effects in mouse behavioral tests. A-33 has an antidepressant-like profile as indicated by reduced immobility time in the forced swim and tail suspension tasks, as well as reduced latency to feed in the novelty suppressed feeding test. D159687, on the other hand, had a procognitive profile as it improved memory in the novel object recognition test but had no antidepressant or anxiolytic benefit. The present data suggests that inhibitors targeting specific subtypes of PDE4 may exhibit differential pharmacological effects and aid a more efficient pharmacotherapy towards neuropsychological conditions.

Genomic Response to Selection for Predatory Behavior in a Mammalian Model of Adaptive Radiation

If genetic architectures of various quantitative traits are similar, as studies on model organisms suggest, comparable selection pressures should produce similar molecular patterns for various traits. To test this prediction, we used a laboratory model of vertebrate adaptive radiation to investigate the genetic basis of the response to selection for predatory behavior and compare it with evolution of aerobic capacity reported in an earlier work. After 13 generations of selection, the proportion of bank voles (Myodes [=Clethrionomys] glareolus) showing predatory behavior was five times higher in selected lines than in controls. We analyzed the hippocampus and liver transcriptomes and found repeatable changes in allele frequencies and gene expression. Genes with the largest differences between predatory and control lines are associated with hunger, aggression, biological rhythms, and functioning of the nervous system. Evolution of predatory behavior could be meaningfully compared with evolution of high aerobic capacity, because the experiments and analyses were performed in the same methodological framework. The number of genes that changed expression was much smaller in predatory lines, and allele frequencies changed repeatably in predatory but not in aerobic lines. This suggests that more variants of smaller effects underlie variation in aerobic performance, whereas fewer variants of larger effects underlie variation in predatory behavior. Our results thus contradict the view that comparable selection pressures for different quantitative traits produce similar molecular patterns. Therefore, to gain knowledge about molecular-level response to selection for complex traits, we need to investigate not only multiple replicate populations but also multiple quantitative traits.

The glial cell modulator ibudilast attenuates neuroinflammation and enhances retinal ganglion cell viability in glaucoma through protein kinase A signaling

Glaucoma is a neurodegenerative disease and the leading cause of irreversible blindness worldwide. Vision deficits in glaucoma result from the selective loss of retinal ganglion cells (RGC). Glial cell-mediated neuroinflammation has been proposed to contribute to disease pathophysiology, but whether this response is harmful or beneficial for RGC survival is not well understood. To test this, we characterized the role of ibudilast, a clinically approved cAMP phosphodiesterase (PDE) inhibitor with preferential affinity for PDE type 4 (PDE4). Here, we demonstrate that intraocular administration of ibudilast dampened macroglia and microglia reactivity in the retina and optic nerve hence decreasing production of proinflammatory cytokines in a rat model of ocular hypertension. Importantly, ibudilast promoted robust RGC soma survival, prevented axonal degeneration, and improved anterograde axonal transport in glaucomatous eyes without altering intraocular pressure. Intriguingly, ocular hypertension triggered upregulation of PDE4 subtype A in Müller glia, and ibudilast stimulated cAMP accumulation in these cells. Co-administration of ibudilast with Rp-cAMPS, a cell-permeable and non-hydrolysable cAMP analog that inhibits protein kinase A (PKA), completely blocked ibudilast-induced neuroprotection. Collectively, these data demonstrate that ibudilast, a safe and well-tolerated glial cell modulator, attenuates gliosis, decreases levels of proinflammatory mediators, and enhances neuronal viability in glaucoma through activation of the cAMP/PKA pathway. This study provides insight into PDE4 signaling as a potential target to counter the harmful effects associated with chronic gliosis and neuroinflammation in glaucoma.

The Analgesic Effect of Rolipram, a Phosphodiesterase 4 Inhibitor, on Chemotherapy-Induced Neuropathic Pain in Rats

BACKGROUND

Chemotherapy-induced neuropathic pain is a significant side effect of chemotherapeutic agents. Currently, there are no effective analgesics for chemotherapy-induced neuropathic pain. Rolipram is a selective phosphodiesterase 4 inhibitor, which increases intracellular cyclic AMP in nerve and immune cells. The aim of our study was to determine the analgesic effects of rolipram on paclitaxel (PAC)-induced neuropathic pain in rats.

METHODS

Chemotherapy-induced neuropathic pain was produced by intraperitoneal injection of PAC on 4 alternate days in male Sprague-Dawley rats. Mechanical allodynia was measured by using von Frey filaments.

RESULTS

After the rats developed PAC-induced pain behavior (such as mechanical allodynia), a single intraperitoneal injection and continuous infusion of rolipram ameliorated PAC-induced pain behavior. In addition, systemic infusion of the drug during the early phase of developing pain behavior did not prevent the development of mechanical allodynia induced by PAC.

CONCLUSIONS

These results suggest that rolipram alleviated mechanical allodynia induced by PAC in rats. Thus, phosphodiesterase 4 inhibitors may prove useful in the treatment of chemotherapy-induced neuropathic pain. However, further studies are needed to clarify their effects in clinical settings.

Effects of an Immunomodulatory Therapy and Chondroitinase After Spinal Cord Hemisection Injury

BACKGROUND:

Individually, immunomodulatory therapy and chondroitinases have demonstrated neuroprotective and potential neuroregenerative effects following spinal cord injury.

OBJECTIVE:

To investigate the therapeutic potential of combined immunomodulatory and chondroitin sulfate-glycosaminoglycan degradation therapy in spinal cord injury.

METHODS:

A combined immunomodulatory treatment using (1) liposome-encapsulated clodronate (selectively depletes peripheral macrophages), and (2) rolipram (a selective type 4 phosphodiesterase inhibitor), along with the chondroitin sulfate proteoglycan-glycosaminoglycan-degrading enzyme, chondroitinase ABC (ChABC), was assessed for its potential to promote axonal regrowth and improve locomotor recovery following midthoracic spinal cord hemisection injury in adult rats.

RESULTS:

We demonstrate that combined treatment with liposomal clodronate, rolipram, and ChABC attenuates macrophage accumulation at the site of injury, reduces axonal die-back of injured dorsal column axons, and produces the greatest improvement in locomotor recovery at 6 weeks postinjury compared with controls and noncombined therapy. Anterograde and retrograde tracing revealed that delivery of clodronate, rolipram, and ChABC did not promote substantial axonal regeneration through the site of injury, although the treatment did limit the extent of axonal die-back. Histological assessments revealed that combined treatment with clodronate/rolipram and/or ChABC resulted in a significant reduction in lesion size and cystic cavitation in comparison with injured controls. Combined clodronate, rolipram, and ChABC treatment reduced the accumulation of macrophages within the injured spinal cord 7 weeks after injury.

CONCLUSION:

The present data suggest that delivery of an immunomodulatory therapy consisting of clodronate and rolipram, in combination with ChABC, reduces axonal injury and enhances neuroprotection, plasticity, and hindlimb functional recovery after hemisection spinal cord injury in adult rats.

Phosphodiesterase type 4 inhibitor rolipram improves survival of spiral ganglion neurons in vitro

Sensorineural deafness is caused by damage of hair cells followed by degeneration of the spiral ganglion neurons and can be moderated by cochlear implants. However, the benefit of the cochlear implant depends on the excitability of the spiral ganglion neurons. Therefore, current research focuses on the identification of agents that will preserve their degeneration. In this project we investigated the neuroprotective effect of Rolipram as a promising agent to improve the viability of the auditory neurons. It is a pharmaceutical agent that acts by selective inhibition of the phosphodiesterase 4 leading to an increase in cyclic AMP. Different studies reported a neuroprotective effect of Rolipram. However, its significance for the survival of SGN has not been reported so far. Thus, we isolated spiral ganglion cells of neonatal rats for cultivation with different Rolipram concentrations and determined the neuronal survival rate. Furthermore, we examined immunocytologically distinct proteins that might be involved in the neuroprotective signalling pathway of Rolipram and determined endogenous BDNF by ELISA. When applied at a concentration of 0.1 nM, Rolipram improved the survival of SGN in vitro. According to previous studies, our immunocytological data showed that Rolipram application induces the phosphorylation and thereby activation of the transcription factor CREB. This activation can be mediated by the cAMP-PKA-signalling pathway as well as via ERK as a part of the MAP-kinase pathway. However, only in cultures pre-treated with BDNF, an endogenous increase of BDNF was detected. We conclude that Rolipram has the potential to improve the vitality of neonatal auditory nerve cells in vitro. Further investigations are necessary to prove the effect of Rolipram in vivo in the adult organism after lesion of the hair cells and insertion of cochlear implants.

Pharmacological basis for medicinal use of Lens culinaris in gastrointestinal and respiratory disorders

Crude extract of Lens culinaris (Lc.Cr), which tested positive for presence of anthraquinones, flavonoids, saponins, sterol, tannins, and terpenes exhibited protective effect against castor oil-induced diarrhea in mice at 100-1000 mg/kg. In rabbit jejunum preparations, Lc.Cr caused relaxation of spontaneous contractions at 0.03-5.0 mg/mL. Lc.Cr inhibited carbachol (CCh, 1 μM) and K(+) (80 mM)-induced contractions in a pattern similar to dicyclomine, but different from verapamil and atropine. Lc.Cr shifted the Ca(++) concentration-response curves to the right, like dicyclomine and verapamil. Pretreatment of tissues with Lc.Cr (0.03-0.1 mg/mL) caused leftward shift of isoprenaline-induced inhibitory CRCs, similar to papaverine. In guinea-pig ileum, Lc.Cr produced rightward parallel shift of CCh curves, followed by non-parallel shift at higher concentration with suppression of maximum response, similar to dicyclomine, but different from verapamil and atropine. Lc.Cr (3.0-30 mg/kg) caused suppression of carbachol (CCh, 100 µg/kg)-induced increase in inspiratory pressure of anesthetized rats. In guinea-pig trachea, Lc.Cr relaxed CCh and high K(+) -induced contractions, shifted CCh curves to right and potentiated isoprenaline response. These results suggest that L. culinaris possesses antidiarrheal, antispasmodic, and bronchodilator activities mediated possibly through a combination of Ca(++) antagonist, anticholinergic, and phosphodiesterase inhibitory effects, and this study provides sound mechanistic background to its medicinal use in disorders of gut and airways hyperactivity, like diarrhea and asthma.

The PDE1/5 Inhibitor SCH-51866 Does Not Modify Disease Progression in the R6/2 Mouse Model of Huntington's Disease

Huntington's disease is a neurodegenerative disorder caused by mutations in the CAG tract of huntingtin. Several studies in HD cellular and rodent systems have identified disturbances in cyclic nucleotide signaling, which might be relevant to pathogenesis and therapeutic intervention. To investigate whether selective phosphodiesterase (PDE) inhibitors can improve some aspects of disease pathogenesis in HD models, we have systematically evaluated the effects of a variety of cAMP and cGMP selective PDE inhibitors in various HD models. Here we present the lack of effect in a variety of endpoints of the PDE subtype selective inhibitor SCH-51866, a PDE1/5 inhibitor, in the R6/2 mouse model of HD, after chronic oral dosing.

Select 3',5'-cyclic nucleotide phosphodiesterases exhibit altered expression in the aged rodent brain

3',5'-cyclic nucleotide phosphodiesterases (PDEs) are the only known enzymes to compartmentalize cAMP and cGMP, yet little is known about how PDEs are dynamically regulated across the lifespan. We mapped mRNA expression of all 21 PDE isoforms in the adult rat and mouse central nervous system (CNS) using quantitative polymerase chain reaction (qPCR) and in situ hybridization to assess conservation across species. We also compared PDE mRNA and protein in the brains of old (26 months) versus young (5 months) Sprague-Dawley rats, with select experiments replicated in old (9 months) versus young (2 months) BALB/cJ mice. We show that each PDE isoform exhibits a unique expression pattern across the brain that is highly conserved between rats, mice, and humans. PDE1B, PDE1C, PDE2A, PDE4A, PDE4D, PDE5A, PDE7A, PDE8A, PDE8B, PDE10A, and PDE11A showed an age-related increase or decrease in mRNA expression in at least 1 of the 4 brain regions examined (hippocampus, cortex, striatum, and cerebellum). In contrast, mRNA expression of PDE1A, PDE3A, PDE3B, PDE4B, PDE7A, PDE7B, and PDE9A did not change with age. Age-related increases in PDE11A4, PDE8A3, PDE8A4/5, and PDE1C1 protein expression were confirmed in hippocampus of old versus young rodents, as were age-related increases in PDE8A3 protein expression in the striatum. Age-related changes in PDE expression appear to have functional consequences as, relative to young rats, the hippocampi of old rats demonstrated strikingly decreased phosphorylation of GluR1, CaMKIIα, and CaMKIIβ, decreased expression of the transmembrane AMPA regulatory proteins γ2 (a.k.a. stargazin) and γ8, and increased trimethylation of H3K27. Interestingly, expression of PDE11A4, PDE8A4/5, PDE8A3, and PDE1C1 correlate with these functional endpoints in young but not old rats, suggesting that aging is not only associated with a change in PDE expression but also a change in PDE compartmentalization.

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.

Therapeutic Strategies for Huntington's Disease

Huntington's disease (HD) is a devastating autosomal dominant neurodegenerative disease, caused by expansion of the CAG repeat in the huntingtin (HTT) gene and characterized pathologically by the loss of pyramidal neurons in several cortical areas, of striatal medium spiny neurons, and of hypothalamic neurons. Clinically, a distinguishing feature of the disease is uncontrolled involuntary movements (chorea, dyskensias) accompanied by progressive cognitive, motor, and psychiatric impairment. This review focuses on the current state of therapeutic development for the treatment of HD, including the preclinical and clinical development of small molecules and molecular therapies.

Phosphodiesterase isoform-specific expression induced by traumatic brain injury

Traumatic brain injury (TBI) results in significant inflammation which contributes to the evolving pathology. Previously, we have demonstrated that cyclic AMP (cAMP), a molecule involved in inflammation, is down-regulated after TBI. To determine the mechanism by which cAMP is down-regulated after TBI, we determined whether TBI induces changes in phosphodiesterase (PDE) expression. Adult male Sprague Dawley rats received moderate parasagittal fluid-percussion brain injury (FPI) or sham injury, and the ipsilateral, parietal cortex was analyzed by western blotting. In the ipsilateral parietal cortex, expression of PDE1A, PDE4B2, and PDE4D2, significantly increased from 30 min to 24 h post-injury. PDE10A significantly increased at 6 and 24 h after TBI. Phosphorylation of PDE4A significantly increased from 6 h to 7 days post-injury. In contrast, PDE1B, PD4A5, and PDE4A8 significantly decreased after TBI. No changes were observed with PDE1C, PDE3A, PDE4B1/3, PDE4B4, PDE4D3, PDE4D4, PDE8A, or PDE8B. Co-localization studies showed that PDE1A, PDE4B2, and phospho-PDE4A were neuronally expressed, whereas PDE4D2 was expressed in neither neurons nor glia. These findings suggest that therapies to reduce inflammation after TBI could be facilitated with targeted therapies, in particular for PDE1A, PDE4B2, PDE4D2, or PDE10A.

The therapeutic profile of rolipram, PDE target and mechanism of action as a neuroprotectant following spinal cord injury

The extent of damage following spinal cord injury (SCI) can be reduced by various neuroprotective regimens that include maintaining levels of cyclic adenosine monophosphate (cyclic AMP), via administration of the phosphodiesterase 4 (PDE4) inhibitor Rolipram. The current study sought to determine the optimal neuroprotective dose, route and therapeutic window for Rolipram following contusive SCI in rat as well as its prominent PDE target and putative mechanism of protection. Rolipram or vehicle control (10% ethanol) was given subcutaneously (s.c.) daily for 2 wk post-injury (PI) after which the preservation of oligodendrocytes, neurons and central myelinated axons was stereologically assessed. Doses of 0.1 mg/kg to 1.0 mg/kg (given at 1 h PI) increased neuronal survival; 0.5 mg to 1.0 mg/kg protected oligodendrocytes and 1.0 mg/kg produced optimal preservation of central myelinated axons. Ethanol also demonstrated significant neuronal and oligo-protection; though the preservation provided was significantly less than Rolipram. Subsequent use of this optimal Rolipram dose, 1.0 mg/kg, via different routes (i.v., s.c. or oral, 1 h PI), demonstrated that i.v. administration produced the most significant and consistent cyto- and axo- protection, although all routes were effective. Examination of the therapeutic window for i.v. Rolipram (1.0 mg/kg), when initiated between 1 and 48 h after SCI, revealed maximal neuroprotection at 2 h post-SCI, although the protective efficacy of Rolipram could still be observed when administration was delayed for up to 48 h PI. Importantly, use of the optimal Rolipram regimen significantly improved locomotor function after SCI as measured by the BBB score. Lastly we show SCI-induced changes in PDE4A, B and D expression and phosphorylation as well as cytokine expression and immune cell infiltration. We demonstrate that Rolipram abrogates SCI-induced PDE4B1 and PDE4A5 production, PDE4A5 phosphorylation, MCP-1 expression and immune cell infiltration, while preventing post-injury reductions in IL-10. This work supports the use of Rolipram as an acute neuroprotectant following SCI and defines an optimal administration protocol and target for its therapeutic application.

Adenylate cyclase 5 coordinates the action of ADP, P2Y1, P2Y13 and ATP-gated P2X7 receptors on axonal elongation

In adult brains, ionotropic or metabotropic purinergic receptors are widely expressed in neurons and glial cells. They play an essential role in inflammation and neurotransmission in response to purines secreted to the extracellular medium. Recent studies have demonstrated a role for purinergic receptors in proliferation and differentiation of neural stem cells although little is known about their role in regulating the initial neuronal development and axon elongation. The objective of our study was to investigate the role of some different types of purinergic receptors, P2Y1, P2Y13 and P2X7, which are activated by ADP or ATP. To study the role and crosstalk of P2Y1, P2Y13 and P2X7 purinergic receptors in axonal elongation, we treated neurons with specific agonists and antagonists, and we nucleofected neurons with expression or shRNA plasmids. ADP and P2Y1-GFP expression improved axonal elongation; conversely, P2Y13 and ATP-gated P2X7 receptors halted axonal elongation. Signaling through each of these receptor types was coordinated by adenylate cyclase 5. In neurons nucleofected with a cAMP FRET biosensor (ICUE3), addition of ADP or Blue Brilliant G, a P2X7 antagonist, increased cAMP levels in the distal region of the axon. Adenylate cyclase 5 inhibition or suppression impaired these cAMP increments. In conclusion, our results demonstrate a crosstalk between two metabotropic and one ionotropic purinergic receptor that regulates cAMP levels through adenylate cyclase 5 and modulates axonal elongation triggered by neurotropic factors and the PI3K-Akt-GSK3 pathway.

Differential expression of cyclic nucleotide phosphodiesterases 4 in developing rat lung

During the perinatal period, lungs undergo changes to adapt to air breathing. The genes involved in these changes are developmentally regulated by various signaling pathways, including the cyclic nucleotide cAMP. As PDE4s are critical enzymes for regulation of cAMP levels, the objective of this study was to investigate PDE4's ontogeny in developing rat lung during the perinatal period. Pulmonary PDE4 activity, PDE4A-D, PDE4B, and PDE4D variant expression levels, PDE4B and PDE4D protein levels, and PDE4D localization in distal lung were determined. PDE4 activity increased towards term, dropped at birth, and increased thereafter to reach a plateau at the end of the second week of life. PDE4B2 and PDE4D long forms demonstrated a pattern of expression that increased markedly at birth. After birth, PDE4D was expressed in alveolar epithelial and mesenchymal cells. The study, therefore, evidenced striking variations in expression patterns among the PDE4 family that differed from changes in global PDE4 activity.

Neuroplasticity signaling pathways linked to the pathophysiology of schizophrenia

Schizophrenia is a severe mental illness that afflicts nearly 1% of the world's population. One of the cardinal pathological features of schizophrenia is perturbation in synaptic connectivity. Although the etiology of schizophrenia is unknown, it appears to be a developmental disorder involving the interaction of a potentially large number of risk genes, with no one gene producing a strong effect except rare, highly penetrant copy number variants. The purpose of this review is to detail how putative schizophrenia risk genes (DISC-1, neuregulin/ErbB4, dysbindin, Akt1, BDNF, and the NMDA receptor) are involved in regulating neuroplasticity and how alterations in their expression may contribute to the disconnectivity observed in schizophrenia. Moreover, this review highlights how many of these risk genes converge to regulate common neurotransmitter systems and signaling pathways. Future studies aimed at elucidating the functions of these risk genes will provide new insights into the pathophysiology of schizophrenia and will likely lead to the nomination of novel therapeutic targets for restoring proper synaptic connectivity in the brain in schizophrenia and related disorders.

Bronchodilatory effect of Acorus calamus (Linn.) is mediated through multiple pathways

AIM OF THE STUDY

This study was undertaken to provide a pharmacological basis for traditional use of Acorus calamus in airways disorders.

MATERIALS AND METHODS

Isolated guinea-pig trachea and atria were suspended in organ baths bubbled with carbogen and mechanisms were found using different parameters.

RESULTS

In isolated guinea-pig tracheal segments, crude extract of Acorus calamus was more effective than carbachol in causing relaxation of high K(+) (80 mM) precontractions, similar to verapamil, suggesting blockade of calcium channels. The n-hexane fraction was equipotent against both precontractions, similar to papaverine, while ethylacetate fraction was more potent against carbachol precontractions but had a negligible dilator effect against K(+), similar to atropine and or rolipram. Pretreatment of tracheal preparations with n-hexane or ethylacetate fractions potentiated isoprenaline-induced inhibitory concentration-response curves, similar to papaverine or rolipram. Pretreatment of tracheal preparations with ethylacetate fraction caused a rightward parallel shift in carbachol response curve at lower concentration (0.003 mg/mL) similar to atropine and a non-parallel shift at higher concentrations (0.01 mg/mL), with reduction of maximum response, similar to rolipram. In isolated guinea-pig atrial preparations, crude extracts, its fractions and papaverine inhibited force and rate of contractions at higher concentrations than the smooth muscle while verapamil was equipotent.

CONCLUSION

These data indicate the presence of unique combination of airways relaxant constituents in crude extract of Acorus calamus, a papaverine-like dual inhibitor of calcium channels and phosphodiesterase in n-hexane fraction and a novel combination of anticholinergic, rolipram-like phosphodiesterase4 inhibitor in ethylacetate fraction and associated cardiac depressant effect, provide a pharmacological basis for traditional use of Acorus calamus in disorders of airways.

Differential function of phosphodiesterase families in the brain: gaining insights through the use of genetically modified animals

Phosphodiesterases (PDEs) are the only known enzymes to degrade cAMP and cGMP, intracellular signaling molecules key to numerous cellular functions. There are 11 PDE families identified to date, and each is expressed in a unique pattern across brain regions. Here, we review genetic mouse models in which PDEs are either directly manipulated (e.g., genetically deleted) or are changed in a compensatory manner due to the manipulation of another target. We believe these genetic mouse models have contributed to our understanding of how the PDE1, PDE4, and PDE10 families contribute uniquely to overall brain function.

Decreased expression and activity of cAMP phosphodiesterases in cardiac hypertrophy and its impact on beta-adrenergic cAMP signals

RATIONALE

Multiple cyclic nucleotide phosphodiesterases (PDEs) degrade cAMP in cardiomyocytes but the role of PDEs in controlling cAMP signaling during pathological cardiac hypertrophy is poorly defined.

OBJECTIVE

Evaluate the beta-adrenergic regulation of cardiac contractility and characterize the changes in cardiomyocyte cAMP signals and cAMP-PDE expression and activity following cardiac hypertrophy.

METHODS AND RESULTS

Cardiac hypertrophy was induced in rats by thoracic aortic banding over a time period of 5 weeks and was confirmed by anatomic measurements and echocardiography. Ex vivo myocardial function was evaluated in Langendorff-perfused hearts. Engineered cyclic nucleotide-gated (CNG) channels were expressed in single cardiomyocytes to monitor subsarcolemmal cAMP using whole-cell patch-clamp recordings of the associated CNG current (I(CNG)). PDE variant activity and protein level were determined in purified cardiomyocytes. Aortic stenosis rats exhibited a 67% increase in heart weight compared to sham-operated animals. The inotropic response to maximal beta-adrenergic stimulation was reduced by approximately 54% in isolated hypertrophied hearts, along with a approximately 32% decrease in subsarcolemmal cAMP levels in hypertrophied myocytes. Total cAMP hydrolytic activity as well as PDE3 and PDE4 activities were reduced in hypertrophied myocytes, because of a reduction of PDE3A, PDE4A, and PDE4B, whereas PDE4D was unchanged. Regulation of beta-adrenergic cAMP signals by PDEs was blunted in hypertrophied myocytes, as demonstrated by the diminished effects of IBMX (100 micromol/L) and of both the PDE3 inhibitor cilostamide (1 micromol/L) and the PDE4 inhibitor Ro 201724 (10 micromol/L).

CONCLUSIONS

Beta-adrenergic desensitization is accompanied by a reduction in cAMP-PDE and an altered modulation of beta-adrenergic cAMP signals in cardiac hypertrophy.

Reduced adiposity and high-fat diet-induced adipose inflammation in mice deficient for phosphodiesterase 4B

The concept that obesity is an inflammatory state has changed our understanding of this condition and suggested that pharmacological interventions targeting inflammation may be useful strategies to improve metabolic complications of obesity. Phosphodiesterase 4 (PDE4) inhibitors exhibit profound antiinflammatory effects, but whether PDE4 inhibition suppresses obesity-induced inflammation is unknown. Among PDE4 isoforms, PDE4B is the major species mediating inflammatory responses. We therefore examined obesity-related phenotypes in mice deficient for PDE4B. Compared with wild-type littermates, PDE4B-null mice were leaner, with lower fat pad weights, smaller adipocytes, and decreased serum leptin levels on both chow and high-fat diets (HFDs). PDE4B deficiency suppressed TNF-alpha mRNA levels and macrophage infiltration in white adipose tissue in mice on HFD, but insulin sensitivity was unaltered. PDE4B-null mice on HFDs had increased locomotor activity. These results suggest a previously unappreciated role for PDE4B in the regulation of energy balance and that PDE4B inhibitors could have utility in treatment of obesity and for suppression of obesity-induced inflammation in white adipose tissue.

The role of phosphodiesterases in schizophrenia : therapeutic implications

Recent studies have suggested that currently available antipsychotic medications, while useful in treating some aspects of schizophrenia, still possess considerable limitations. Improving the treatment of negative symptoms and cognitive dysfunction, and decreasing adverse effects remain significant challenges. Many new drug strategies have been proposed in recent years and increasing evidence suggests that members of the phosphodiesterase (PDE) gene family may play a role in the aetiology or treatment of schizophrenia. PDEs are key enzymes responsible for the degradation of the second messengers cAMP (3',5'-cyclic adenosine monophosphate) and cGMP (3',5'-cyclic guanosine monophosphate). Mammalian PDEs are composed of 21 genes and are categorized into 11 families based on sequence homology, enzymatic properties and sensitivity to pharmacological inhibitors. Representatives from most families have been identified in the brain by the presence of protein or RNA, and numerous studies suggest that PDEs play an important role in the regulation of intracellular signalling downstream of receptor activation in neurons. Insights into the multiple brain processes to which PDEs contribute are emerging from the phenotype of genetically engineered mice that lack activity of specific PDEs (knockout mice), as well as from in vitro and in vivo studies with PDE inhibitors.This article provides a brief overview of recent studies implicating PDE inhibition, focusing on PDE4 and PDE10, as targets for treating the positive, negative or cognitive symptoms associated with schizophrenia.

Phosphodiesterase-4A expression is reduced in cerebella of patients with bipolar disorder

OBJECTIVE

The cAMP-specific phosphodiesterase-4 (PDE4) gene family has four members (PDE4 A, B, C, and D) and is the target of several potential therapeutic inhibitors. Recently, PDE4A5 has been shown to bind with disrupted in schizophrenia 1 (DISC1), which has been identified as a risk factor for schizophrenia, bipolar disorder, and major depression. We sought to examine whether PDE4A5 expression was altered in cerebella of patients with schizophrenia, bipolar disorder, and major depression.

METHODS

We measured protein levels of PDE4A isoforms in cerebella of patients with schizophrenia, bipolar disorder, and major depression versus matched controls using sodium dodecyl sulfate polyacrylamide gel electrophoresis and western blotting.

RESULTS

We observed that specific isoforms of PDE4A were reduced in cerebella of patients with bipolar disorder, whereas there was no change in patients with schizophrenia or major depression.

CONCLUSION

Our results are the first to show that PDE4A expression is altered in patients with bipolar disorder and provide potential new therapeutic avenues for treatment of this disorder.

Increased particulate phosphodiesterase 4 in the prefrontal cortex supports 5-HT4 receptor-induced improvement of object recognition memory in the rat

RATIONALE

Serotonin receptors (5-HT4Rs) are critical to both short-term and long-term memory processes. These receptors mainly trigger the cyclic adenosine monophosphate (cAMP)/protein kinase A signaling pathway, which is regulated by cAMP phosphodiesterases (PDEs).

OBJECTIVES

We investigated the mechanisms underlying the effect of the selective activation of 5-HT4R on information acquisition in an object recognition memory task and the putative regulation of PDE.

MATERIALS AND METHODS

The effect of RS 67333 (1 mg/kg, intraperitoneally [i.p.], injected 30 min before the sample phase) was examined at different delay intervals in an object recognition task in Sprague-Dawley rats. After the testing trial, PDE activity of brain regions implicated in this task was assayed.

RESULTS

RS 67333-treated rats spent more time exploring the novel object after a 15-min (P < 0.001) or 4-h delay (P < 0.01) but not after a 24-h delay, whereas control animals showed no preference for the novel object for delays greater than 15 min. We characterized the specific patterns and kinetic properties of PDE in the prefrontal and perirhinal cortices as well as in the hippocampus. We demonstrated that particulate PDE activities increase in both the prefrontal cortex and hippocampus following 5-HT4R stimulation. In the prefrontal cortex, PDE4 activities support the RS 67333-induced modification of PDE activities, whereas in the hippocampus, all cAMP-PDE activities varied. In contrast, particulate PDE variation in the hippocampus was not found to support improvement of recognition memory after a 4-h delay.

CONCLUSIONS

We provide evidence that the increase in particulate PDE4 activity in the prefrontal cortex supports the 5-HT4R-induced increase in information acquisition.

Effects of phosphodiesterase 4 inhibition on alveolarization and hyperoxia toxicity in newborn rats

BACKGROUND

Prolonged neonatal exposure to hyperoxia is associated with high mortality, leukocyte influx in airspaces, and impaired alveolarization. Inhibitors of type 4 phosphodiesterases are potent anti-inflammatory drugs now proposed for lung disorders. The current study was undertaken to determine the effects of the prototypal phosphodiesterase-4 inhibitor rolipram on alveolar development and on hyperoxia-induced lung injury.

METHODOLOGY/FINDINGS

Rat pups were placed under hyperoxia (FiO2>95%) or room air from birth, and received rolipram or its diluent daily until sacrifice. Mortality rate, weight gain and parameters of lung morphometry were recorded on day 10. Differential cell count and cytokine levels in bronchoalveolar lavage and cytokine mRNA levels in whole lung were recorded on day 6. Rolipram diminished weight gain either under air or hyperoxia. Hyperoxia induced huge mortality rate reaching 70% at day 10, which was prevented by rolipram. Leukocyte influx in bronchoalveolar lavage under hyperoxia was significantly diminished by rolipram. Hyperoxia increased transcript and protein levels of IL-6, MCP1, and osteopontin; rolipram inhibited the increase of these proteins. Alveolarization was impaired by hyperoxia and was not restored by rolipram. Under room air, rolipram-treated pups had significant decrease of Radial Alveolar Count.

CONCLUSIONS

Although inhibition of phosphodiesterases 4 prevented mortality and lung inflammation induced by hyperoxia, it had no effect on alveolarization impairment, which might be accounted for by the aggressiveness of the model. The less complex structure of immature lungs of rolipram-treated pups as compared with diluent-treated pups under room air may be explained by the profound effect of PDE4 inhibition on weight gain that interfered with normal alveolarization.

The PDE4 inhibitor rolipram prevents NF-kappaB binding activity and proinflammatory cytokine release in human chorionic cells

Spontaneous preterm delivery is linked to intrauterine inflammation. Fetal membranes are involved in the inflammatory process as an important source of mediators, and the chorion leave produces high levels of the proinflammatory cytokine TNF-alpha when stimulated by LPS. The transcription factor NF-kappaB is the main regulator of this inflammatory process and controls the production of cytokines by the chorion leave. Phosphodiesterase 4 inhibitors are recognized for their anti-inflammatory and myorelaxant effects. The purpose of this study was to investigate whether PDE4 inhibition affects the LPS signaling in human cultured chorionic cells. We showed that these cells express TLR4, the main LPS receptor, and exhibit a predominant PDE4 activity. Upon LPS challenge, PDE4 activity increases concomitantly to the induction of the specific isoform PDE4B2 and chorionic cells secrete TNF-alpha. LPS induces the nuclear translocation of the NF-kappaB p65 subunit and the activation of three different NF-kappaB complexes in chorionic cells. The presence of the PDE4 inhibitor rolipram reduces the TNF-alpha production and the activation of the three NF-kappaB complexes. These data indicate that the PDE4 family interacts with the LPS signaling pathway during the inflammatory response of chorionic cells. PDE4 selective inhibitors may thus represent a new therapeutic approach in the management of inflammation-induced preterm delivery.

Diastolic dysfunction in alveolar hypoxia: a role for interleukin-18-mediated increase in protein phosphatase 2A

AIMS

Chronic obstructive pulmonary disease with alveolar hypoxia is associated with diastolic dysfunction in the right and left ventricle (LV). LV diastolic dysfunction is not caused by increased afterload, and we recently showed that reduced phosphorylation of phospholamban at serine (Ser) 16 may explain the reduced relaxation of the myocardium. Here, we study the mechanisms leading to the hypoxia-induced reduction in phosphorylation of phospholamban at Ser16.

METHODS AND RESULTS

In C57Bl/6j mice exposed to 10% oxygen, signalling molecules were measured in cardiac tissue, sarcoplasmic reticulum (SR)-enriched membrane preparations, and serum. Cardiomyocytes isolated from neonatal mice were exposed to interleukin (IL)-18 for 24 h. The beta-adrenergic pathway in the myocardium was not altered by alveolar hypoxia, as assessed by measurements of beta-adrenergic receptor levels, adenylyl cyclase activity, and subunits of cyclic AMP-dependent protein kinase. However, alveolar hypoxia led to a significantly higher amount (124%) and activity (234%) of protein phosphatase (PP) 2A in SR-enriched membrane preparations from LV compared with control. Serum levels of an array of cytokines were assayed, and a pronounced increase in IL-18 was observed. In isolated cardiomyocytes, treatment with IL-18 increased the amount and activity of PP2A, and reduced phosphorylation of phospholamban at Ser16 to 54% of control.

CONCLUSION

Our results indicate that the diastolic dysfunction observed in alveolar hypoxia might be caused by increased circulating IL-18, thereby inducing an increase in PP2A and a reduction in phosphorylation of phospholamban at Ser16.

PDE4B polymorphisms and decreased PDE4B expression are associated with schizophrenia

Schizophrenia has a complex genetic underpinning and variations in a number of candidate genes have been identified that confer risk of developing the disorder. We report in the present studies that several single nucleotide polymorphisms (SNPs) and a two-SNP haplotype in PDE4B are associated with an increased incidence of schizophrenia in two large populations of Caucasian and African American patients. The SNPs in PDE4B associated with schizophrenia occur in intronic sequences in the vicinity of a critical splice junction that gives rise to the expression of PDE4B isoforms with distinct regulation and function. We also observed specific decreases in phosphodiesterase 4B (PDE4B) isoforms in brain tissue obtained postmortem from patients diagnosed with schizophrenia and bipolar disorder. PDE4B metabolically inactivates the second messenger cAMP to regulate intracellular signaling in neurons throughout the brain. Thus, the present observations suggest that dysregulation of intracellular signaling mediated by PDE4B is a significant factor in the cause and expression, respectively, of schizophrenia and bipolar disorder and that targeting PDE4B-regulated signaling pathways may yield new therapies to treat the totality of these disorders.

Behavioral and neurochemical characterization of mice deficient in the phosphodiesterase-4B (PDE4B) enzyme

RATIONALE

Phosphodiesterases (PDEs) belonging to the PDE4 family control intracellular concentrations of cyclic adenosine monophosphate (cAMP) by catalyzing its hydrolysis. Four separate PDE4 genes (PDE4A, PDE4B, PDE4C, and PDE4D) have been identified. PDE4 has been reported to be involved in various central nervous system (CNS) functions including depression, memory, and schizophrenia, although the specific subtype mediating these effects remains unclear.

OBJECTIVE

To investigate the role of PDE4B in the CNS, PDE4B wild-type and knockout mice (C57BL/6N background) were assessed in a variety of well-characterized behavioral tasks, and their brains were assayed for monoamine content.

RESULTS

Knockout mice showed a significant reduction in prepulse inhibition. Spontaneous locomotor activity was decreased (16%) in knockout mice. Furthermore, when challenged with amphetamine, both groups of mice responded similarly to a low dose of d-amphetamine (1.0 mg/kg), but knockout mice showed an enhanced response to a higher dose (1.78 mg/kg). Decreases in baseline levels of monoamines and their metabolites within the striatum of knockout mice were also observed. PDE4B knockout mice showed a modest decrease in immobility time in the forced swim test that approached significance. In several other tests, including the elevated plus maze, hot plate, passive avoidance, and Morris water maze, wild-type and knockout mice performed similarly.

CONCLUSION

The present studies demonstrate decreased striatal DA and 5-HT activity in the PDE4B knockout mice associated with decreased prepulse inhibition, decreased baseline motor activity, and an exaggerated locomotor response to amphetamine. These data further support a role for PDE4B in psychiatric diseases and striatal function.

Expression of phosphodiesterase 4 is altered in the brains of subjects with autism

The cyclic adenosine monophosphate-specific phosphodiesterase-4 (PDE4) gene family is the target of several potential therapeutic inhibitors and the PDE4B gene has been associated with schizophrenia and depression. Little, however, is known of any connection between this gene family and autism, with limited effective treatment being available for autism. We measured the expression of PDE4A and PDE4B by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting in Brodmann's area 40 (BA40, parietal cortex), BA9 (superior frontal cortex), and cerebellum from subjects with autism and matched controls. We observed a lower expression of PDE4A5, PDE4B1, PDE4B3, PDE4B4, and PDE4B2 in the cerebella of subjects with autism when compared with matched controls. In BA9, we observed the opposite: a higher expression of PDE4AX, PDE4A1, and PDE4B2 in subjects with autism. No changes were observed in BA40. Our results demonstrate altered expressions of the PDE4A and PDE4B proteins in the brains of subjects with autism and might provide new therapeutic avenues for the treatment of this debilitating disorder.

The DISC locus in psychiatric illness

The DISC locus is located at the breakpoint of a balanced t(1;11) chromosomal translocation in a large and unique Scottish family. This translocation segregates in a highly statistically significant manner with a broad diagnosis of psychiatric illness, including schizophrenia, bipolar disorder and major depression, as well as with a narrow diagnosis of schizophrenia alone. Two novel genes were identified at this locus and due to the high prevalence of schizophrenia in this family, they were named Disrupted-in-Schizophrenia-1 (DISC1) and Disrupted-in-Schizophrenia-2 (DISC2). DISC1 encodes a novel multifunctional scaffold protein, whereas DISC2 is a putative noncoding RNA gene antisense to DISC1. A number of independent genetic linkage and association studies in diverse populations support the original linkage findings in the Scottish family and genetic evidence now implicates the DISC locus in susceptibility to schizophrenia, schizoaffective disorder, bipolar disorder and major depression as well as various cognitive traits. Despite this, with the exception of the t(1;11) translocation, robust evidence for a functional variant(s) is still lacking and genetic heterogeneity is likely. Of the two genes identified at this locus, DISC1 has been prioritized as the most probable candidate susceptibility gene for psychiatric illness, as its protein sequence is directly disrupted by the translocation. Much research has been undertaken in recent years to elucidate the biological functions of the DISC1 protein and to further our understanding of how it contributes to the pathogenesis of schizophrenia. These data are the main subject of this review; however, the potential involvement of DISC2 in the pathogenesis of psychiatric illness is also discussed. A detailed picture of DISC1 function is now emerging, which encompasses roles in neurodevelopment, cytoskeletal function and cAMP signalling, and several DISC1 interactors have also been defined as independent genetic susceptibility factors for psychiatric illness. DISC1 is a hub protein in a multidimensional risk pathway for major mental illness, and studies of this pathway are opening up opportunities for a better understanding of causality and possible mechanisms of intervention.

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.

Inhibition of Phosphodiesterase Type 4 Decreases Stress-Induced Defecation in Rats and Mice

BACKGROUND/AIMS

Phosphodiesterase type 4 (PDE4) has been previously shown to regulate colonic contractile activity in vitro. In this study, the effects of PDE4 inhibition were assessed in a model of stress-induced defecation previously demonstrated to be due to increased colonic transit/evacuation.

METHODS

Rats were individually placed in a mild restraint cage and placed into a 12 degrees C environment (cold-restraint stress) for 60 min. Mice received restraint (only) stress at room temperature for 30 min. Loperamide (positive control compound) or two different PDE4 inhibitors (rolipram and roflumilast) were administered orally at several doses to the rodents 1 h before stress began. Vehicle alone was administered for comparison. The number of fecal pellets expelled during stress (fecal pellet output), total fecal pellet wet weight and total fecal water content were measured.

RESULTS

Loperamide produced a dose-related decrease (ID(50)s in mg/kg) in fecal pellet output (rat = 7.4, mouse = 0.7) and significantly decreased fecal wet weight (72.9%) and decreased fecal percent water content (9.4%). The two PDE4 inhibitors produced a similar dose-related inhibition of fecal pellet output. Rolipram exhibited ID(50)s in rat and mouse of 14.1 and 27.1, respectively. Rolipram significantly decreased fecal wet weight (58.8%) but increased fecal percent water content (15.0%). For roflumilast, ID(50)s were 24.2 mg/kg and 12.4 in the rat and mouse, respectively. Although roflumilast also significantly (p < 0.05) decreased fecal wet weight (47.2%), it did not significantly increase fecal percent water content.

CONCLUSIONS

These data indicate that PDE4 inhibition is effective in reducing rodent stress-induced defecation, provides the first functional data on a potential role for PDE4 activity in the colonic evacuation response to stress, and indicates the potential utility of PDE4 inhibitors in functional bowel disease such as irritable bowel syndrome requires further evaluation.

The role of cyclic AMP signaling in promoting axonal regeneration after spinal cord injury

The failure of axons to regenerate after spinal cord injury remains one of the greatest challenges facing both medicine and neuroscience, but in the last 20 years there have been tremendous advances in the field of spinal cord injury repair. One of the most important of these has been the identification of inhibitory proteins in CNS myelin, and this has led to the development of strategies that will enable axons to overcome myelin inhibition. Elevation of intracellular cyclic AMP (cAMP) has been one of the most successful of these strategies, and in this review we examine how cAMP signaling promotes axonal regeneration in the CNS. Intracellular cAMP levels can be increased through a peripheral conditioning lesion, administration of cAMP analogues, priming with neurotrophins or treatment with the phosphodiesterase inhibitor rolipram, and each of these methods has been shown to overcome myelin inhibition both in vitro and in vivo. It is now known that the effects of cAMP are transcription dependent, and that cAMP-mediated activation of CREB leads to upregulated expression of genes such as arginase I and interleukin-6. The products of these genes have been shown to directly promote axonal regeneration, which raises the possibility that other cAMP-regulated genes could yield additional agents that would be beneficial in the treatment of spinal cord injury. Further study of these genes, in combination with human clinical trials of existing agents such as rolipram, would allow the therapeutic potential of cAMP to be fully realized.

Antipsychotic profile of rolipram: efficacy in rats and reduced sensitivity in mice deficient in the phosphodiesterase-4B (PDE4B) enzyme

RATIONALE

Recent studies provide evidence for reduced phosphodiesterase-4B (PDE4B) as a genetic susceptibility factor as well as suggesting an association of several single nucleotide polymorphisms (SNPs) in PDE4B that are associated with an increased incidence of schizophrenia.

OBJECTIVES

The aim of the current study was to assess the activity of rolipram, a nonsubtype-selective PDE4 inhibitor, in several animal models predictive of antipsychotic-like efficacy and side-effect liability and to use PDE4B wild-type and knockout mice to begin to understand the subtypes involved in the activity of rolipram.

RESULTS

In rats, rolipram antagonized both phencyclidine hydrochloride- and D-amphetamine-induced hyperactivity and inhibited conditioned avoidance responding (CAR). In PDE4B wild-type mice, rolipram dose-dependently suppressed CAR (ED(50) = 2.4 mg/kg); however, in knockout mice, their sensitivity to rolipram at the higher doses (1.0 and 3.2 mg/kg) was reduced, resulting in a threefold shift in the ED(50) (7.3 mg/kg), suggesting PDE4B is involved, at least in part, with the activity of rolipram. Only the highest dose of rolipram (3.2 mg/kg) produced a modest but significant degree of catalepsy.

CONCLUSIONS

Rolipram has a pharmacologic profile similar to that of the atypical antipsychotics and has low extrapyramidal symptom liability. These results suggest that PDE4B mediates the antipsychotic effects of rolipram in CAR and that the PDE4B-regulated cyclic adenosine monophosphate signaling pathway may play a role in the pathophysiology and pharmacotherapy of psychosis.

Differential expression and function of phosphodiesterase 4 (PDE4) subtypes in human primary CD4+ T cells: predominant role of PDE4D

Type 4 phosphodiesterases (PDE4) are critical regulators in TCR signaling by attenuating the negative constraint of cAMP. In this study, we show that anti-CD3/CD28 stimulation of human primary CD4(+) T cells increases the expression of the PDE4 subtypes PDE4A, PDE4B, and PDE4D in a specific and time-dependent manner. PDE4A and PDE4D mRNAs as well as enzyme activities were up-regulated within 5 days, PDE4B showed a transient up-regulation with highest levels after 24 h. The induction was shown to be independent of different stimulation conditions and was similar in naive and memory T cell subpopulations. To elucidate the functional impact of individual PDE4 subtypes on T cell function, we used PDE4 subtype-specific short-interfering RNAs (siRNAs). Knockdown of either PDE4B or PDE4D inhibited IL-2 release 24 h after stimulation (time point of maximal IL-2 concentrations) to an extent similar to that observed with the panPDE4 inhibitor RP73401 (piclamilast). Substantial amounts of IFN-gamma or IL-5 were measured only at later time points. siRNA targeting PDE4D showed a predominant inhibitory effect on these cytokines measured after 72 h. However, the inhibition of all cytokines was most effective when PDE4 siRNAs were applied in combination. Although the effect of PDE4 inhibition on T cell proliferation is small, the PDE4D-targeting siRNA alone was as effective as the panPDE4 inhibitor, whereas PDE4A or PDE4B siRNAs had hardly an effect. In summary, individual PDE4 subtypes have overall nonredundant, but complementary, time-dependent roles in propagating various T cell functions and PDE4D is the form likely playing a predominant role.

PDE4 inhibition prevents preterm delivery induced by an intrauterine inflammation

The aim of this study was to explore the anti-inflammatory properties of phosphodiesterase-4 (PDE4) inhibitors in vivo and their potential ability to prevent inflammation-induced preterm delivery. Indeed, intrauterine inflammation is the major etiology of very preterm delivery, the leading cause of neonatal mortality and morbidity. Intrauterine injection of Escherichia coli LPS in 15-day-pregnant mice induced an increase of PDE4 activity and PDE4B expression at the maternofetal interface, a rise of amniotic fluid levels of TNF-alpha, IL-1beta, IL-6, and IL-10 and provoked massive preterm delivery and fetal demise. Selective PDE4 inhibition by rolipram prevented the rise in the proinflammatory cytokines. Following the nuclear translocation of the transcription factor NFkappaB, as a marker of cellular activation after the inflammatory challenge, showed a time-dependent sequential activation of the gestational tissues, from the uterine mesometrial to the fetal compartment, particularly in the glycogen-trophoblastic cells of the placenta. This activation was disrupted by PDE4 inhibition, and inflammation-induced preterm delivery and fetal demise were prevented. PDE4 selective inhibitors may thus represent a novel effective treatment to delay inflammation-induced preterm delivery and to prevent adverse outcomes in infants.

Dynamic regulation of cystic fibrosis transmembrane conductance regulator by competitive interactions of molecular adaptors

Disorganized ion transport caused by hypo- or hyperfunctioning of the cystic fibrosis transmembrane conductance regulator (CFTR) can be detrimental and may result in life-threatening diseases such as cystic fibrosis or secretory diarrhea. Thus, CFTR is controlled by elaborate positive and negative regulations for an efficient homeostasis. It has been shown that expression and activity of CFTR can be regulated either positively or negatively by PDZ (PSD-95/discs large/ZO-1) domain-based adaptors. Although a positive regulation by PDZ domain-based adaptors such as EBP50/NHERF1 is established, the mechanisms for negative regulation of the CFTR by Shank2, as well as the effects of multiple adaptor interactions, are not known. Here we demonstrate a physical and physiological competition between EBP50-CFTR and Shank2-CFTR associations and the dynamic regulation of CFTR activity by these positive and negative interactions using the surface plasmon resonance assays and consecutive patch clamp experiments. Furthermore whereas EBP50 recruits a cAMP-dependent protein kinase (PKA) complex to CFTR, Shank2 was found to be physically and functionally associated with the cyclic nucleotide phosphodiesterase PDE4D that precludes cAMP/PKA signals in epithelial cells and mouse brains. These findings strongly suggest that balanced interactions between the membrane transporter and multiple PDZ-based adaptors play a critical role in the homeostatic regulation of epithelial transport and possibly the membrane transport in other tissues.

Reduced PDE4 expression and activity contributes to enhanced catecholamine-induced cAMP accumulation in adipocytes from FOXC2 transgenic mice

Overexpression of forkhead transcription factor FOXC2 in white adipose tissue (WAT) leads to a lean phenotype resistant to diet-induced obesity. This is due, in part, to enhanced catecholamine-induced cAMP-PKA signaling in FOXC2 transgenic mice. Here we show that rolipram treatment of adipocytes from FOXC2 transgenic mice did not increase isoproterenol-induced cAMP accumulation to the same extent as in wild type cells. Accordingly, phosphodiesterase-4 (PDE4) activity was reduced by 75% and PDE4A5 protein expression reduced by 30-50% in FOXC2 transgenic WAT compared to wild type. Thus, reduced PDE4 activity in adipocytes from FOXC2 transgenic mice contributes to amplified beta-AR induced cAMP responses observed in these cells.

Regulation of phosphodiesterase-4 (PDE4) expression in mouse brain by repeated antidepressant treatment: Comparison with rolipram

Cyclic nucleotide phosphodiesterase-4 (PDE4) is a component of signaling pathways involved in the mediation of antidepressant activity. Of the four PDE4 subtypes, PDE4D appears to be of particular importance, given the finding that PDE4D-deficient mice exhibit an antidepressant-like behavioral phenotype. In mouse hippocampus and cerebral cortex, the effects of repeated treatment with the antidepressants desipramine and fluoxetine or the PDE4 inhibitor rolipram on the expression of PDE4D was compared to that of PDE4A and PDE4B, the other two subtypes expressed in the brain. Expression of PDE4D was increased by all drugs tested, with the exception of desipramine in hippocampus. By contrast, these treatments affected PDE4A and PDE4B expression differentially. In hippocampus, antidepressants increased PDE4A and decreased PDE4B, whereas ROL decreased PDE4A and did not change PDE4B. In cerebral cortex, antidepressants increased PDE4A and did not change PDE4B, whereas ROL did not change PDE4A and increased PDE4B. 3H-Rolipram binding was increased in cytosolic, but not in membrane, fractions of cerebral cortex by all drugs tested; there were no changes observed in hippocampus. Overall, the present results suggest some species-dependence of the regulation of PDE4 subtypes, based on data obtained previously using rats. They also suggest that the PDE4D subtype may be of particular importance as an antidepressant target in that it is regulated by repeated treatment with both norepinephrine and serotonin reuptake inhibitors as well as by the PDE4 inhibitor rolipram, drugs that produce antidepressant effects via different neuropharmacological mechanisms.