Rolipram, a cyclic AMP-selective phosphodiesterase inhibitor, reduces neuronal damage following cerebral ischemia in the gerbil

Chronic traumatic encephalopathy and the nucleus basalis of Meynert

Due to the growing number of chronic traumatic encephalopathy (CTE) cases in the military and contact sports, defining the cellular and molecular substrate of this disorder is crucial. Most classic neuropathological investigations describe cortical tau and, to a lesser extent, amyloid lesions, which may underlie the clinical sequela associated with CTE. The application of modern molecular biologic technology to postmortem human brain tissue has made it possible to evaluate the genetic signature of specific neuronal phenotypes at different stages of CTE pathology. Most recently, molecular pathobiology has been used in the field of CTE, with an emphasis on the cholinergic neurons located within the nucleus basalis of Meynert, which develop tau pathology and are associated with cognitive dysfunction similar to that found in Alzheimer's disease (AD). Quantitative findings derived from single-cell transcript investigations provide clues to our understanding of the selective vulnerability of neurons containing AD-like tau pathology at different stages of CTE. Since human tissue-based studies provide a gold standard for the field of CTE, continued molecular pathological studies are needed to reveal novel drug targets for the treatment of this disorder.

Phosphodiesterase-4 enzyme as a therapeutic target in neurological disorders

Phosphodiesterases (PDE) are a diverse family of enzymes (11 isoforms so far identified) responsible for the degradation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) which are involved in several cellular and biochemical functions. Phosphodiesterase 4 (PDE4) is the major isoform within this group and is highly expressed in the mammalian brain. An inverse association between PDE4 and cAMP levels is the key mechanism in various pathophysiological conditions like airway inflammatory diseases-chronic obstruction pulmonary disease (COPD), asthma, psoriasis, rheumatoid arthritis, and neurological disorders etc. In 2011, roflumilast, a PDE4 inhibitor (PDE4I) was approved for the treatment of COPD. Subsequently, other PDE4 inhibitors (PDE4Is) like apremilast and crisaborole were approved by the Food and Drug Administration (FDA) for psoriasis, atopic dermatitis etc. Due to the adverse effects like unbearable nausea and vomiting, dose intolerance and diarrhoea, PDE4 inhibitors have very less clinical compliance. Efforts are being made to develop allosteric modulation with high specificity to PDE4 isoforms having better efficacy and lesser adverse effects. Interestingly, repositioning PDE4Is towards neurological disorders including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), multiple sclerosis (MS) and sleep disorders, is gaining attention. This review is an attempt to summarize the data on the effects of PDE4 overexpression in neurological disorders and the use of PDE4Is and newer allosteric modulators as therapeutic options. We have also compiled a list of on-going clinical trials on PDE4 inhibitors in neurological disorders.

Transcriptional Factors and Protein Biomarkers as Target Therapeutics in Traumatic Spinal Cord and Brain Injury

Traumatic injury to the spinal cord (SCI) and brain (TBI) are serious health problems and affect many people every year throughout the world. These devastating injuries are affecting not only patients but also their families socially as well as financially. SCI and TBI lead to neurological dysfunction besides continuous inflammation, ischemia, and necrosis followed by progressive neurodegeneration. There are well-established changes in several other processes such as gene expression as well as protein levels that are the important key factors to control the progression of these diseases. We are not yet able to collect enough knowledge on the underlying mechanisms leading to the altered gene expression profiles and protein levels in SCI and TBI. Cell loss is hastened by the induction or imbalance of pro- or anti-inflammatory expression profiles and transcription factors for cell survival after or during trauma. There is a sequence of events of dysregulation of these factors from early to late stages of trauma that opens a therapeutic window for new interventions to prevent/restrict the progression of these diseases. There has been increasing interest in the modulation of these factors for improving the patient’s quality of life by targeting both SCI and TBI. Here, we review some of the recent transcriptional factors and protein biomarkers that have been developed and discovered in the last decade in the context of targeted therapeutics for SCI and TBI patients.

Time-Dependent Bidirectional Neuroprotection by Adenosine 2A Receptor in Experimental Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) results in both focal and diffuse brain pathological features that become severely exacerbated after the initial injury. Owing to this disease complexity, no effective therapeutic measure has yet been devised aimed directly at these pathological processes. We developed a clinically relevant model of TBI and tested the bidirectional neuroprotective role of adenosine 2A receptors (A2ARs) at different times.

METHODS

Wistar rats were divided into 4 treatment groups (sham, TBI, A2AR agonist [CGS-21680], and A2AR antagonist [SCH-58261]) and 4 post-TBI intervals (15 minutes and 1, 12, and 24 hours). A2AR agonist and antagonist effects were tested by the neurological functional score (NFS) and levels of cyclic adenosine monophosphate, interleukin-1β, oxidative stress antioxidant markers, and caspase-3.

RESULTS

The A2AR agonist-treated group showed significant NFS improvement at 15 minutes and 1 hour after TBI compared with the TBI group. However, no improvement was observed at 12 and 24 hours. The A2AR antagonists resulted in no NFS improvement at 15 minutes and 1 hour, and significant improvement observed at 12 and 24 hours. Significant neuroprotective effect with an A2AR agonist were observed with cyclic adenosine monophosphate, interleukin-1β, oxidative stress markers, catalase, and caspase-3 levels at 15 minutes and 1 hour after TBI. The A2AR antagonist showed no effect at these intervals but showed a protective effect at 12 and 24 hours after TBI.

CONCLUSIONS

The A2AR agonist showed a beneficial neuroprotective effect at the early stages after TBI, and the A2AR antagonist showed a benefit at the later stages after TBI. These findings suggest that A2AR agonists and antagonists should be used in accordance with the point at which the TBI occurred.

Targeting phosphodiesterase 4 as a potential therapeutic strategy for enhancing neuroplasticity following ischemic stroke

Sensorimotor recovery following ischemic stroke is highly related with structural modification and functional reorganization of residual brain tissues. Manipulations, such as treatment with small molecules, have been shown to enhance the synaptic plasticity and contribute to the recovery. Activation of the cAMP/CREB pathway is one of the pivotal approaches stimulating neuroplasticity. Phosphodiesterase 4 (PDE4) is a major enzyme controlling the hydrolysis of cAMP in the brain. Accumulating evidences have shown that inhibition of PDE4 is beneficial for the functional recovery after cerebral ischemia; i. subtype D of PDE4 (PDE4D) is viewed as a risk factor for ischemic stroke; ii. inhibition of PDE4 enhances neurological behaviors, such as learning and memory, after stroke in rodents; iii.PDE4 inhibition increases dendritic density, synaptic plasticity and neurogenesis; iv. activation of cAMP/CREB signaling by PDE4 inhibition causes an endogenous increase of BDNF, which is a potent modulator of neuroplasticity; v. PDE4 inhibition is believed to restrict neuroinflammation during ischemic stroke. Cumulatively, these findings provide a link between PDE4 inhibition and neuroplasticity after cerebral ischemia. Here, we summarized the possible roles of PDE4 inhibition in the recovery of cerebral stroke with an emphasis on neuroplasticity. We also made some recommendations for future research.

Gene Profiling of Nucleus Basalis Tau Containing Neurons in Chronic Traumatic Encephalopathy: A Chronic Effects of Neurotrauma Consortium Study

Military personnel and athletes exposed to traumatic brain injury may develop chronic traumatic encephalopathy (CTE). Brain pathology in CTE includes intracellular accumulation of abnormally phosphorylated tau proteins (p-tau), the main constituent of neurofibrillary tangles (NFTs). Recently, we found that cholinergic basal forebrain (CBF) neurons within the nucleus basalis of Meynert (nbM), which provide the major cholinergic innervation to the cortex, display an increased number of NFTs across the pathological stages of CTE. However, molecular mechanisms underlying nbM neurodegeneration in the context of CTE pathology remain unknown. Here, we assessed the genetic signature of nbM neurons containing the p-tau pretangle maker pS422 from CTE subjects who came to autopsy and received a neuropathological CTE staging assessment (Stages II, III, and IV) using laser capture microdissection and custom-designed microarray analysis. Quantitative analysis revealed dysregulation of key genes in several gene ontology groups between CTE stages. Specifically, downregulation of the nicotinic cholinergic receptor subunit β-2 gene (CHRNB2), monoaminergic enzymes catechol-O-methyltransferase (COMT) and dopa decarboxylase (DDC), chloride channels CLCN4 and CLCN5, scaffolding protein caveolin 1 (CAV1), cortical development/cytoskeleton element lissencephaly 1 (LIS1), and intracellular signaling cascade member adenylate cyclase 3 (ADCY3) was observed in pS422-immunreactive nbM neurons in CTE patients. By contrast, upregulation of calpain 2 (CAPN2) and microtubule-associated protein 2 (MAP2) transcript levels was found in Stage IV CTE patients. These single-population data in vulnerable neurons indicate alterations in gene expression associated with neurotransmission, signal transduction, the cytoskeleton, cell survival/death signaling, and microtubule dynamics, suggesting novel molecular pathways to target for drug discovery in CTE.

Transcription factors Tp73, Cebpd, Pax6, and Spi1 rather than DNA methylation regulate chronic transcriptomics changes after experimental traumatic brain injury

Traumatic brain injury (TBI) induces a wide variety of cellular and molecular changes that can continue for days to weeks to months, leading to functional impairments. Currently, there are no pharmacotherapies in clinical use that favorably modify the post-TBI outcome, due in part to limited understanding of the mechanisms of TBI-induced pathologies. Our system biology analysis tested the hypothesis that chronic transcriptomics changes induced by TBI are controlled by altered DNA-methylation in gene promoter areas or by transcription factors. We performed genome-wide methyl binding domain (MBD)-sequencing (seq) and RNA-seq in perilesional, thalamic, and hippocampal tissue sampled at 3 months after TBI induced by lateral fluid percussion in adult male Sprague-Dawley rats. We investigated the regulated molecular networks and mechanisms underlying the chronic regulation, particularly DNA methylation and transcription factors. Finally, we identified compounds that modulate the transcriptomics changes and could be repurposed to improve recovery. Unexpectedly, DNA methylation was not a major regulator of chronic post-TBI transcriptomics changes. On the other hand, the transcription factors Cebpd, Pax6, Spi1, and Tp73 were upregulated at 3 months after TBI (False discovery rate < 0.05), which was validated using digital droplet polymerase chain reaction. Transcription regulatory network analysis revealed that these transcription factors regulate apoptosis, inflammation, and microglia, which are well-known contributors to secondary damage after TBI. Library of Integrated Network-based Cellular Signatures (LINCS) analysis identified 118 pharmacotherapies that regulate the expression of Cebpd, Pax6, Spi1, and Tp73. Of these, the antidepressant and/or antipsychotic compounds trimipramine, rolipramine, fluspirilene, and chlorpromazine, as well as the anti-cancer therapies pimasertib, tamoxifen, and vorinostat were strong regulators of the identified transcription factors, suggesting their potential to modulate the regulated transcriptomics networks to improve post-TBI recovery.

Genetic Understanding of Stroke Treatment: Potential Role for Phosphodiesterase Inhibitors

Phosphodiesterase (PDE) gene family is a large family having at least 21 genes and multiple versions (isoforms) of the phosphodiesterase enzymes. These enzymes catalyze the inactivation of intracellular mediators of signal transduction such as cAMP and cGMP and therefore, play a pivotal role in various cellular functions. PDE inhibitors (PDEI) are drugs that block one or more of the five subtypes of the PDE family and thereby prevent inactivation of the intracellular cAMP and cGMP by the respective PDE-subtypes. The first clinical use of PDEI was reported almost three decades ago. Studies later found the ability of these compounds to increase the levels of ubiquitous secondary messenger molecules that can cause changes in vascular tone, cardiac function and other cellular events and thus these findings paved the way for their use in various medical emergencies. PDEs are found to be distributed in many tissues including brain. Therefore, new therapeutic agents in the form of PDEI are being explored in neurodegenerative diseases including stroke. Although studies have revealed their use in cerebral infarction prevention, their full-fledged application in times of neurological emergency or stroke in specific has been very limited so far. Nevertheless, recent investigations suggest PDE4 and PDE5 inhibitors to play a vital role in mitigating stroke symptoms by modulating signaling mechanisms in PDE pathway. Further, extensive research in terms of their pharmacological properties like dosing, drug specific activities, use of simultaneous medications, ancillary properties of these compounds and studies on adverse drug reactions needs to be carried out to set them as standard drugs of use in stroke.

Traumatic Brain Injury Upregulates Phosphodiesterase Expression in the Hippocampus

Traumatic brain injury (TBI) results in significant impairments in hippocampal synaptic plasticity. A molecule critically involved in hippocampal synaptic plasticity, 3′,5′-cyclic adenosine monophosphate, is downregulated in the hippocampus after TBI, but the mechanism that underlies this decrease is unknown. To address this question, we determined whether phosphodiesterase (PDE) expression in the hippocampus is altered by TBI. Young adult male Sprague Dawley rats received sham surgery or moderate parasagittal fluid-percussion brain injury. Animals were analyzed by western blotting for changes in PDE expression levels in the hippocampus. We found that PDE1A levels were significantly increased at 30 min, 1 h and 6 h after TBI. PDE4B2 and 4D2 were also significantly increased at 1, 6, and 24 h after TBI. Additionally, phosphorylation of PDE4A was significantly increased at 6 and 24 h after TBI. No significant changes were observed in levels of PDE1B, 1C, 3A, 8A, or 8B between 30 min to 7 days after TBI. To determine the spatial profile of these increases, we used immunohistochemistry and flow cytometry at 24 h after TBI. PDE1A and phospho-PDE4A localized to neuronal cell bodies. PDE4B2 was expressed in neuronal dendrites, microglia and infiltrating CD11b⁺ immune cells. PDE4D was predominantly found in microglia and infiltrating CD11b⁺ immune cells. To determine if inhibition of PDE4 would improve hippocampal synaptic plasticity deficits after TBI, we treated hippocampal slices with rolipram, a pan-PDE4 inhibitor. Rolipram partially rescued the depression in basal synaptic transmission and converted a decaying form of long-term potentiation (LTP) into long-lasting LTP. Overall, these results identify several possible PDE targets for reducing hippocampal synaptic plasticity deficits and improving cognitive function acutely after TBI.

Phosphodiesterase 4D gene polymorphisms in sudden sensorineural hearing loss

The phosphodiesterase 4D (PDE4D) gene has been reported as a risk gene for ischemic stroke. The vascular factors are between the hypothesized etiologies of sudden sensorineural hearing loss (SSNHL), and this genetic effect might be attributed for its role in SSNHL. We hypothesized that genetic variants of the PDE4D gene are associated with susceptibility to SSNHL. We conducted a case-control study with 362 SSNHL cases and 209 controls. Three single nucleotide polymorphisms (SNPs) were selected. The genotypes were determined using TaqMan technology. Hardy-Weinberg equilibrium (HWE) was tested for each SNP, and genetic effects were evaluated according to three inheritance modes. We carried out sex-specific analysis to analyze the overall data. All three SNPs were in HWE. When subjects were stratified by sex, the genetic effect was only evident in females but not in males. The TT genotype of rs702553 exhibited an adjusted odds ratio (OR) of 3.83 (95 % confidence interval = 1.46-11.18) (p = 0.006) in female SSNHL. The TT genotype of SNP rs702553 was associated with female SSNHL under the recessive model (p = 0.004, OR 3.70). In multivariate logistic regression analysis, TT genotype of rs702553 was significantly associated with female SSNHL (p = 0.0043, OR 3.70). These results suggest that PDE4D gene polymorphisms influence the susceptibility for the development of SSNHL in the southern Taiwanese female population.

Phosphodiesterase inhibitors as therapeutics for traumatic brain injury

Developing therapeutics for traumatic brain injury remains a challenge for all stages of recovery. The pathological features of traumatic brain injury are diverse, and it remains an obstacle to be able to target the wide range of pathologies that vary between traumatic brain injured patients and that evolve during recovery. One promising therapeutic avenue is to target the second messengers cAMP and cGMP with phosphodiesterase inhibitors due to their broad effects within the nervous system. Phosphodiesterase inhibitors have the capability to target different injury mechanisms throughout the time course of recovery after brain injury. Inflammation and neuronal death are early targets of phosphodiesterase inhibitors, and synaptic dysfunction and circuitry remodeling are late potential targets of phosphodiesterase inhibitors. This review will discuss how signaling through cyclic nucleotides contributes to the pathology of traumatic brain injury in the acute and chronic stages of recovery. We will review our current knowledge of the successes and challenges of using phosphodiesterase inhibitors for the treatment of traumatic brain injury and conclude with important considerations in developing phosphodiesterase inhibitors as therapeutics for brain trauma.

Effects of early rolipram treatment on histopathological outcome after controlled cortical impact injury in mice

Traumatic brain injury (TBI) pathology includes contusions, cavitation, cell death, all of which can be exacerbated by inflammation. We hypothesized that an anti-inflammatory drug, rolipram, may reduce pathology after TBI, since in several CNS injury models rolipram reduces inflammation and improves cell survival and functional recovery. Adult male C57BL/6 mice received a craniotomy over the right parietotemporal cortex. Vertically directed controlled cortical impact (CCI) injury was delivered. Naïve controls were used for comparison. At 30 min post-surgery, animals were treated with vehicle or rolipram (1 mg/kg), and then once per day for 3 days. On day 3, the brains were systematically sectioned and stained to visualize the resulting pathology using hematoxylin and eosin (H&E) staining and NeuN immunocytochemistry. Total parietotemporal cortical contusion and cavity volume were significantly increased in rolipram-treated as compared to vehicle-treated CCI animals. Contusion areas at specific bregma levels indicated a significant effect of drug across bregma levels. Neuronal cell loss in the dentate hilus and area CA3 of the hippocampus were similar between vehicle and rolipram-treated animals. Although rolipram is well known to reduce pathology and inflammation in several other CNS injury models, the pathology resulting from CCI was worsened with rolipram at this particular dose and administration schedule. These studies suggest that consideration of the unique characteristics of TBI pathology is important in the extrapolation of promising therapeutic interventions from other CNS injury models.

Association of SNP41, SNP56 and a novel SNP in PDE4D gene with stroke and its subtypes

An association between phosphodiesterase 4D (PDE4D) gene and risk of stroke has been suggested by deCODE group in an Icelandic population. In the present case-control study we investigated the association of SNP41 (rs12153798) and SNP56 (rs702553) with ischemic stroke and stroke subtypes. Five hundred and sixteen ischemic stroke patients and 513 healthy age and sex matched controls were included in the study. The genotypes were determined by subjecting the PCR products to sequencing. Both the SNPs 56 and 41 associated significantly with stroke [adjusted OR=1.97; 95% CI (1.262-3.082); p=0.003: adjusted OR=5.42; 95% CI (3.45-8.5); p<0.001 respectively]. In addition to this, a novel SNP at position 59736747 T>G was found while sequencing the PCR products including SNP56. This novel SNP was found in patients as well as controls but did not show a significant association with the disease. We found significant association of SNPs 56 and 41 with large artery atherosclerosis, lacunar and cardioembolic stroke. In conclusion PDE4D gene plays a key part in the pathogenesis of ischemic stroke in the South Indian population from Andhra Pradesh.

Postinjury treatment with rolipram increases hemorrhage after traumatic brain injury

The pathology caused by traumatic brain injury (TBI) is exacerbated by the inflammatory response of the injured brain. Two proinflammatory cytokines that contribute to inflammation after TBI are tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). From previous studies using the parasagittal fluid-percussion brain injury model, we reported that the anti-inflammatory drug rolipram, a phosphodiesterase 4 inhibitor, reduced TNF-α and IL-1β levels and improved histopathological outcome when administered 30 min prior to injury. We now report that treatment with (±)-rolipram given 30 min after injury significantly reduced TNF-α levels in the cortex and hippocampus. However, postinjury administration of (±)-rolipram significantly increased cortical contusion volume and increased atrophy of the cortex compared with vehicle-treated animals at 10 days postinjury. Thus, despite the reduction in proinflammatory cytokine levels, histopathological outcome was worsened with post-TBI (±)-rolipram treatment. Further histological analysis of (±)-rolipram-treated TBI animals revealed significant hemorrhage in the contused brain. Given the well-known role of (±)-rolipram of increasing vasodilation, it is likely that (±)-rolipram worsened outcome after fluid-percussion brain injury by causing increased bleeding.

Prevention of cerebral ischemia-induced memory deficits by inhibition of phosphodiesterase-4 in rats

Inhibition of phosphodiesterase-4 (PDE4) by rolipram, a prototypical PDE4 inhibitor, reverses memory impairment produced pharmacologically or genetically. Comparably, much less is known about the effect of rolipram on cerebral ischemia-induced memory deficits. The objective of this study was to determine the effects of rolipram on ischemia-induced memory deficit, neuronal damage, and alteration of PDE4 activity in the hippocampus. Memory was examined using Morris water-maze and step-through passive avoidance tests in rats subjected to global cerebral ischemia with or without repeated treatment with rolipram (0.3 or 1 mg/kg, i.p.); neuronal damage in the hippocampus and PDE4 activity in hippocampal tissues were determined using Nissl staining and HPLC, respectively. In the water-maze test, cerebral ischemia significantly increased the escape latency to reach the platform during acquisition training and decreased the exploration time in the target quadrant in the probe trial test; these were blocked by rolipram in a dose-dependent manner. Rolipram also reduced the distracted platform searches induced by cerebral ischemia. In the passive avoidance test, ischemia decreased the 24-h latency to the dark compartment, which was also blocked by rolipram treatment. In addition, Nissl staining revealed ischemia-induced neuron loss in hippocampal CA1; this was blocked by rolipram. Further, cerebral ischemia led to increases in activity of PDE, primarily PDE4, in the hippocampus, which also was antagonized by rolipram. These results suggest that rolipram prevents cerebral ischemia-induced memory deficits via inhibition of increased PDE4 activity and attenuation of hippocampal, neuronal damages induced by ischemia. PDE4 may be a target for treatment of cognitive disorders associated with cerebral ischemia.

A large-scale chemical screen for regulators of the arginase 1 promoter identifies the soy isoflavone daidzeinas a clinically approved small molecule that can promote neuronal protection or regeneration via a cAMP-independent pathway

An ideal therapeutic for stroke or spinal cord injury should promote survival and regeneration in the CNS. Arginase 1 (Arg1) has been shown to protect motor neurons from trophic factor deprivation and allow sensory neurons to overcome neurite outgrowth inhibition by myelin proteins. To identify small molecules that capture Arg1's protective and regenerative properties, we screened a hippocampal cell line stably expressing the proximal promoter region of the arginase 1 gene fused to a reporter gene against a library of compounds containing clinically approved drugs. This screen identified daidzein as a transcriptional inducer of Arg1. Both CNS and PNS neurons primed in vitro with daidzein overcame neurite outgrowth inhibition from myelin-associated glycoprotein, which was mirrored by acutely dissociated and cultured sensory neurons primed in vivo by intrathecal or subcutaneous daidzein infusion. Further, daidzein was effective in promoting axonal regeneration in vivo in an optic nerve crush model when given intraocularly without lens damage, or most importantly, when given subcutaneously after injury. Mechanistically, daidzein requires transcription and induction of Arg1 activity for its ability to overcome myelin inhibition. In contrast to canonical Arg1 activators, daidzein increases Arg1 without increasing CREB phosphorylation, suggesting its effects are cAMP-independent. Accordingly, it may circumvent known CNS side effects of some cAMP modulators. Indeed, daidzein appears to be safe as it has been widely consumed in soy products, crosses the blood-brain barrier, and is effective without pretreatment, making it an ideal candidate for development as a therapeutic for spinal cord injury or stroke.

The effects of the phosphodiesterase inhibitor olprinone on global cerebral ischemia

BACKGROUND

The phosphodiesterase III inhibitor olprinone has been confirmed to improve myocardial function and increase cerebral blood flow; therefore, if olprinone exerts direct neuroprotective effects against global cerebral ischemia to the same degree as cilostazol, olprinone could be useful for cerebral resuscitation after cardiac arrest. We examined whether olprinone directly protected neuronal cells from global cerebral ischemia both in vivo and in vitro.

METHODS

In a rat model of 10-minute global cerebral ischemia induced by 4-vessel occlusion, 0.3, 3, or 30 microg x kg(-1) x min(-1) olprinone or saline was infused for a periischemic period of 40 minutes (n = 6 for each group). Hippocampal CA1 neuronal cells were then counted 3 days after reperfusion, and the phosphorylation of cyclic adenosine 3'5'-monophosphate response element-binding protein was examined using Western blotting analyses of specimens obtained 15 minutes after reperfusion. In vitro, cultured cerebral neurons were exposed to 4 hours of hypoxia and glucose deprivation and then 24 hours of recovery in the absence or presence of olprinone (10(-11)-10(-5) mol x L(-1)). Cell viability was measured using the Cell Counting Kit-8 (Dojindo Molecular Technologies, Gaithersburg, MD).

RESULTS

In the rat model of global ischemia, the number of surviving CA1 neurons counted under a microscopic field in the 30 microg x kg(-1) x min(-1) olprinone-treated group (49.9 +/- 9.2) was significantly higher than that in the saline infusion control group (7.2 +/- 3.4), and olprinone treatment increased the phosphorylation of cyclic adenosine 3'5'-monophosphate response element-binding protein. The survival fraction of the neuronal cells cultured in the presence of olprinone was also significantly higher than that of cells cultured in the absence of olprinone in a dose-dependent manner.

CONCLUSIONS

Our study successfully demonstrated, for the first time, that olprinone had a protective effect on neuronal cells in vitro and in vivo, especially against global cerebral ischemia. These results suggest that olprinone might be useful for the treatment of patients experiencing global cerebral ischemia.

Association between the PDE4D gene and ischaemic stroke in the Chinese Han population

Recent findings suggests that PDE4D (gene encoding phosphodiesterase 4D) is a stroke-related gene in the Icelandic population, but it is still very controversial as to whether it is a susceptible gene for stroke in other populations. In the present study, we attempted to explore the role of the gene in the pathogenesis of stroke in the Chinese Han population of eastern China. A total of 649 ischaemic stroke patients and 761 unrelated control individuals with no history of stroke or transient ischaemic attack were examined in a case-control study. Four SNPs (single nucleotide polymorphisms) rs152312 (C/T), SNP56 (A/T), SNP83 (C/T) and SNP87 (C/T) with a minor allele frequency over 5% were genotyped and the corresponding haplotypes were constructed. In an analysis of the combined cardiogenic and carotid stroke group, both the allele (P=0.0060) and genotype (P=0.0160) frequencies between cases and controls at SNP83 showed significant differences. However, no difference in haplotype frequencies was observed between cases and controls at rs152312 and SNP56. In the analysis of the small-artery-occlusive stroke group, no difference in allele or genotype frequencies was observed at any marker between cases and controls; the global haplotype frequency in rs152312 and SNP56 had a significant difference between cases and controls (P=0.0162); the frequency of haplotype C-A was higher in cases than in controls (P=0.0122). In conclusion, our present findings show that polymorphisms in the PDE4D gene are associated with an increased risk of ischaemic stroke in the Chinese Han population. The present study adds further support to the role of PDE4D in stroke.

Systemic administration of rolipram increases medullary and spinal cAMP and activates a latent respiratory motor pathway after high cervical spinal cord injury

BACKGROUND/OBJECTIVE

High cervical spinal cord hemisection interrupts descending respiratory drive from the rostral ventral respiratory group in the medulla to the ipsilateral phrenic motoneurons. Hemisection results in the paralysis of the ipsilateral hemidiaphragm. Chronic administration of rolipram, a specific phosphodiesterase-IV inhibitor, promotes synaptic plasticity and restores phrenic nerve function after a high cervical spinal cord lesion. Here, we test the hypothesis that an acute administration of rolipram will increase spinal and medullary levels of 3',5'-cyclic adenosine monophosphate (cAMP) and induce phrenic nerve recovery after cervical (C2) spinal cord hemisection.

METHODS

Male Sprague-Dawley rats were subjected to left C2 hemisection surgery 1 week before experimentation. Bilateral phrenic nerve activity was recorded in anesthetized, vagotomized, and pancuronium paralyzed rats, and rolipram was intravenously applied (2 mg/kg).

RESULTS

Intravenous administration of rolipram increased phrenic nerve output in uninjured control and left C2 spinal cord-hemisected rats. In addition, rolipram restored respiratory-related activity to the left phrenic nerve made quiescent by the hemisection. In both uninjured and hemisected rats, rolipram significantly enhanced phrenic inspiratory burst amplitude and burst area compared with predrug values. Also, rolipram concomitantly increased spinal and medullary cAMP.

CONCLUSIONS

These results suggest that a phosphodiesterase inhibitor capable of elevating cAMP levels can enhance phrenic nerve output and restore respiratory-related phrenic nerve function after high cervical spinal cord injury. Thus, targeting the cAMP signaling cascade can be a useful therapeutic approach in promoting synaptic efficacy and respiratory recovery after cervical spinal cord injury.

Modulation of the cAMP signaling pathway after traumatic brain injury

Traumatic brain injury (TBI) results in both focal and diffuse brain pathologies that are exacerbated by the inflammatory response and progress from hours to days after the initial injury. Using a clinically relevant model of TBI, the parasagittal fluid-percussion brain injury (FPI) model, we found injury-induced impairments in the cyclic AMP (cAMP) signaling pathway. Levels of cAMP were depressed in the ipsilateral parietal cortex and hippocampus, as well as activation of its downstream target, protein kinase A, from 15 min to 48 h after moderate FPI. To determine if preventing hydrolysis of cAMP by administration of a phosphodiesterase (PDE) IV inhibitor would improve outcome after TBI, we treated animals intraperitoneally with rolipram (0.3 or 3.0 mg/kg) 30 min prior to TBI, and then once per day for 3 days. Rolipram treatment restored cAMP to sham levels and significantly reduced cortical contusion volume and improved neuronal cell survival in the parietal cortex and CA3 region of the hippocampus. Traumatic axonal injury, characterized by beta-amyloid precursor protein deposits in the external capsule, was also significantly reduced in rolipram-treated animals. Furthermore, levels of the pro-inflammatory cytokines, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), were significantly decreased with rolipram treatment. These results demonstrate that the cAMP-PKA signaling cascade is downregulated after TBI, and that treatment with a PDE IV inhibitor improves histopathological outcome and decreases inflammation after TBI.

The Phosphodiesterase Inhibitor Rolipram Promotes Survival of Newborn Hippocampal Neurons After Ischemia

BACKGROUND AND PURPOSE

Brain ischemia stimulates neurogenesis. However, newborn neurons show a progressive decrease in number over time. Under normal conditions, the cAMP-cAMP responsive element binding protein (CREB) pathway regulates the survival of newborn neurons. Constitutive activation of CREB after brain ischemia also stimulates hippocampal neurogenesis. Thus, activation of cAMP-CREB signaling may provide a promising strategy for enhancing the survival of newborn neurons. We examined whether treatment of mice with the phosphodiesterase-4 inhibitor rolipram enhances hippocampal neurogenesis after ischemia.

METHODS

Both common carotid arteries in mice were occluded for 12 minutes. Bromodeoxyuridine (BrdU) was used to label proliferating cells. Mice were perfused transcardially with 4% paraformaldehyde, and immunohistochemistry was performed. To evaluate the role of CREB in the survival of newborn neurons after ischemia, intrahippocampal injection of a CRE-decoy oligonucleotide was delivered for 1 week. We examined whether the activation of cAMP-CREB signaling by rolipram enhanced the proliferation and survival of newborn neurons.

RESULTS

Phospho-CREB immunostaining was markedly upregulated in immature neurons, decreasing to low levels in mature neurons. The number of BrdU-positive cells 30 days after ischemia was significantly less in the CRE-decoy treatment group than in the vehicle group. Rolipram enhanced the proliferation of newborn cells under physiologic conditions but not under ischemic conditions. Rolipram significantly increased the survival of nascent BrdU-positive neurons, accompanied by an enhancement of phospho-CREB staining and decreased newborn cell death after ischemia.

CONCLUSIONS

CREB phosphorylation regulates the survival of newborn neurons after ischemia. Chronic pharmacological activation of cAMP-CREB signaling may be therapeutically useful for the enhancement of neurogenesis after ischemia.

The therapeutic potential of PDE4 inhibitors

Phosphodiesterase enzymes are responsible for the inactivation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Phosphodiesterase 4 (PDE4) is a cAMP specific phosphodiesterase expressed in inflammatory cells such as eosinophils. Inhibition of PDE4 results in an elevation of cAMP in these cells, which in turn downregulates the inflammatory response. The anti-inflammatory effects of PDE4 inhibitors have been well documented both in vitro and in vivo in a variety of animal models. The potential use of PDE4 inhibitors as anti-inflammatory agents for the treatment of asthma and other inflammatory disorders has received considerable attention from the pharmaceutical industry, but to date, there are no selective PDE4 inhibitors on the market. Early PDE4 inhibitors, typified by rolipram, suffered from dose-limiting side effects, including nausea and emesis, which severely restricted their therapeutic utility. Second generation compounds, including CDP840 and SB207499 (Ariflo), have been identified with reduced side effect liability. Recent evidence suggests a correlation between side effects and the ability of compounds to bind at the so-called high affinity rolipram binding site (HPDE), whilst beneficial effects appear to correlate with binding at the catalytic site. A number of companies are actively pursuing compounds which exhibit improved affinity for the catalytic site and reduced affinity for the HPDE, in the expectation that this will provide compounds with an improved therapeutic index.

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.

Multiple actions of the human immunodeficiency virus type-1 Tat protein on microglial cell functions

The human immunodeficiency virus type-1 (HIV-1) regulatory protein Tat is produced in the early phase of infection and is essential for virus replication. Together with other viral products, Tat has been implicated in the pathogenesis of HIV-1-associated dementia (HAD). As HIV-1 infection in the brain is very limited and macrophage/microglial cells are the only cellular type productively infected by the virus, it has been proposed that many of the viral neurotoxic effects are mediated by microglial products. We and others have shown that Tat affects the functional state of microglial cells, supporting the hypothesis that activated microglia play a role in the neuropathology associated with HIV-1 infection. This review describes the experimental evidence indicating that Tat stimulates microglia to synthesize potentially neurotoxic molecules, including proinflammatory cytokines and free radicals, and interferes with molecular mechanisms controlling cAMP levels, intracellular [Ca2+], and ion channel expression.

Inhibitory effects of group II mGluR-related drugs on memory performance in mice

The cAMP/protein kinase A signaling pathway is negatively modulated by group II metabotropic glutamate receptors (mGluRs), and the cross-talk that occurs between these receptors may modulate learning and memory. To examine the relationship among cAMP/PKA-signaling pathway activity, group II mGluRs, and learning and memory, mice were trained to perform a step-through-type passive avoidance task, and 10 min before each avoidance trial the following drugs were injected intracisternally (i.cist.): vehicle (0.05% dimethylsulfoxide); a specific group II mGluR agonist, DCG-IV (1-50 ng/mouse); a specific group II mGluR antagonist, LY341495 (10-300 ng); a selective inhibitor of cAMP-specific phosphodiesterase, rolipram (100-1000 ng); an activator of adenylyl cyclase, forskolin (25-250 ng); a specific inhibitor of PKA, H-89 (150 or 300 ng) or; an activator of protein kinase C, phorbol 12-myristate 13-acetate (PMA 200 ng). DCG-IV (25 and 50 ng) or LY341495 (150 and 300 ng) reduced the latency in the avoidance task. The reduction of latency by DCG-IV was not observed in mice coinjected with DCG-IV (50 ng) together with rolipram (500 ng) or forskolin (25 ng). Conversely, coinjection of LY341495 with 100 or 1000 ng rolipram, or with 25 or 250 ng forskolin tended to potentiate the LY341495-induced shortening of latency. In addition, the reduction of latency by DCG-IV (50 ng) was not observed in mice coinjected with DCG-IV and PMA together. However, the reduction of latency by LY341495 (300 ng) was potentiated when the drug was coadministered with PMA. These results suggest that changes in the cAMP/PKA-signaling pathway, mediated by group II mGluRs, influence memory in the passive avoidance task, and that both the excessive activation and deactivation of this pathway may induce the impairment of learning and memory.

Association between inflammation and nigral neuronal damage following striatal excitotoxic lesion

We examined the expression of TNF-alpha within the substantia nigra pars reticulata (SNR) following intrastriatal injection of quinolinic acid (QA) and studied the effect of rolipram, a TNF-alpha-inhibitor, on the secondary neuronal damage. QA (240 nmol in 1 microl) was injected stereotactically into the striatum of male Wistar rats. After survival of 1, 3 or 10 days, the animals were sacrificed and immunohistochemical staining with an antibody against TNF-alpha was performed. From day 1 to day 10 after striatal QA injection TNF-alpha positive cells were observed within ipsilateral substantia nigra which were neither present on the contralateral side nor in sham-operated controls. Double labeling with antibodies against TNF-alpha and NeuN, keratan sulfate proteoglycan or GFAP displayed a good overlap between TNF-alpha and NeuN, which suggests that TNF-alpha positive cells are neurons. For the pharmacological approach, three groups of QA rats were treated intraperitoneally with either solvent (n=5), the NMDA receptor antagonist MK 801 (4 mg/kg, n=6) or the TNF-alpha inhibitor rolipram (0.3 mg/kg, n=6), which was started 24 h after QA-injection and continued with daily applications for 14 days. The amount of striatal damage did not differ between the three groups. The number of intact neurons within the ipsilateral substantia nigra of the solvent treated group was reduced by approximately 30% compared to the contralateral side. Both MK 801 and rolipram ameliorated this secondary damage and reduced the number of TNF-alpha positive cells. The observed association between expression of TNF-alpha and secondary neuronal damage within the substantia nigra induced by intrastriatal QA application might hint towards an involvement of this cytokine in transneuronal degeneration.

Regulation of cAMP phosphodiesterase mRNAs expression in rat brain by acute and chronic fluoxetine treatment. An in situ hybridization study

Changes in brain cyclic AMP (cAMP) have been suggested to underlie the clinical action of antidepressant treatments. Also, a regionally-selective regulation of cAMP-specific phosphodiesterases (PDEs) has been demonstrated for some antidepressants. To further investigate the effects of antidepressant treatments on PDEs, we examined the expression of different cAMP-specific PDEs in the brain of rats treated (1 and 14 days) with fluoxetine 3 mg/kg day. The mRNAs coding for PDE4A, PDE4B, PDE4D, and the five known PDE4D splice variants were analyzed by in situ hybridization on 45 brain structures of acute and chronic fluoxetine-treated rats. We also examined the binding sites for the putative antidepressant drug [(3)H]rolipram, a PDE4-selective inhibitor. In some brain areas single fluoxetine administration increased the density of the mRNA of all PDE4 isozymes, except PDE4D and PDE4D5. Chronic fluoxetine treatment increased PDE4A mRNA levels and decreased those for PDE4B, PDE4D and PDE4D1 mRNAs in some brain regions. The study was complemented with the analysis of the expression of the transcripts of BDNF. Chronic fluoxetine treatment down-regulated the expression of BDNF. These results show that the expression of PDE4 isozymes is modulated by a clinically relevant fluoxetine dose. The significance of these changes in PDE4 expression to the antidepressant effect of fluoxetine is discussed.

Differential distribution of PDE4D splice variant mRNAs in rat brain suggests association with specific pathways and presynaptical localization

cAMP plays an important role as a second-messenger molecule controlling multiple cellular processes. Its hydrolysis provides an important mechanism by which cAMP levels are regulated. This is performed by a large multigene family of cyclic nucleotide phosphodiesterases (PDEs). Members of the PDE4 enzyme family are selectively inhibited by rolipram. Five different mRNA splice forms for PDE4D have been isolated. Here, we analyzed the regional distribution of the mRNAs coding for the splice variants PDE4D1, PDE4D2, PDE4D3, PDE4D4, and PDE4D5 in the rat brain by in situ hybridization histochemistry using specific radiolabeled oligonucleotides. We found that all five splice variants showed a distinct distribution pattern and, in some cases, in association with specific brain pathways. The most relevant differences were in hippocampal formation, medial habenula, basal ganglia, and area postrema, at both the regional and cellular level. The dorsal and median raphe nuclei exclusively contained PDE4D2 mRNA transcripts, probably located on serotonergic cells. PDE4D1 mRNA was expressed in some white matter cells. PDE4D1 and PDE4D2 mRNA splice forms presented a similar distribution in the area postrema, whereas for PDE4D4 and PDE4D5 the cellular distribution presented a complementary pattern. The differential expression of PDE4D mRNA splice variants in the area postrema is consistent with their possible involvement in emesis control and suggests new molecular targets for a more selective drug design.

Hydrolysis of N-methyl-D-aspartate receptor-stimulated cAMP and cGMP by PDE4 and PDE2 phosphodiesterases in primary neuronal cultures of rat cerebral cortex and hippocampus

Stimulation of N-methyl-D-aspartate (NMDA) receptors on neurons activates both cAMP and cGMP signaling pathways. Experiments were carried out to determine which phosphodiesterase (PDE) families are involved in the hydrolysis of the cyclic nucleotides formed via this mechanism, using primary neuronal cultures prepared from rat cerebral cortex and hippocampus. The nonselective PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX) potentiated the ability of NMDA to increase cAMP and cGMP. However, among the family-selective inhibitors, only the PDE4 inhibitor rolipram enhanced the ability of NMDA to increase cAMP in the neurons. In contrast, only the PDE2 inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) enhanced the ability of NMDA to increase cGMP. Neither adenosine nor an adenosine deaminase inhibitor mimicked the effect of EHNA; this suggests that EHNA's inhibition of PDE2, not its effects on adenosine metabolism, mediates its effects on NMDA-stimulated cGMP concentrations. The PDE inhibitor-augmented effects of NMDA on cAMP and cGMP formation were antagonized by 5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine maleate (MK-801), verifying NMDA receptor mediation. In contrast, only NMDA-mediated cGMP formation was affected by altering either nitric oxide signaling or guanylyl cyclase; this suggests that NMDA-induced changes in cAMP are not secondary to altered cGMP concentrations. Overall, the present findings indicate that cAMP and cGMP formed in neurons as a result of NMDA receptor stimulation are hydrolyzed by PDE4 and PDE2, respectively. Selective inhibitors of the two PDE families will differentially affect the functional consequences of activation of these two signaling pathways by NMDA receptor stimulation.

Effects of a phosphodiesterase IV inhibitor rolipram on microsphere embolism-induced defects in memory function and cerebral cyclic AMP signal transduction system in rats

The effects of treatment with rolipram, a specific phosphodiesterase IV inhibitor, on learning and memory function and on the cyclic AMP/PKA/CREB signal transduction system were examined in rats with microsphere embolism (ME)-induced cerebral ischaemia. Sustained cerebral ischaemia was induced by the injection of 900 microspheres (48 microm in diameter) into the right hemisphere of the rat brain. The animals were treated once daily with 3 mg kg(-1) rolipram i.p. from 6 h after the onset of the operation for consecutive 10 days. Microsphere-embolized rats showed prolongation of the escape latency in the water maze task starting from day 7 after the operation and lasting for 3 consecutive days. Treatment with rolipram reduced the escape latency. ME decreased the cyclic AMP content, cytosolic PKA Cbeta level, and nuclear PKA Calpha and Cbeta levels, as well as reduced the pCREB level and the DNA-binding activity of CREB in the cerebral cortex and hippocampus on day 10 after the operation. These alterations were attenuated by treatment with rolipram. These results suggest that ME-induced failure in learning and memory function may be mediated by dysfunction of the cyclic AMP/PKA/CREB signal transduction system, that rolipram may ameliorate ME-induced impairment of learning and memory function, and that the drug effect may be partly attributed to activation of the cyclic AMP/PKA/CREB signal transduction system.

Chondrocytes respond to adenosine via A(2)receptors and activity is potentiated by an adenosine deaminase inhibitor and a phosphodiesterase inhibitor

OBJECTIVE

To test the mechanisms by which adenosine and adenosine analogues stimulate adenylate cyclase and suppress lipopolysaccharide (LPS)-induced production of nitric oxide (NO) by chondrocytes.

METHODS

Primary chondrocytes isolated from equine articular cartilage were plated in monolayer. Intracellular cyclic-AMP (cAMP) accumulation was measured following exposure to medium containing adenosine, the non-hydrolyzable adenosine analogue N(6)-methyladenosine, the A(2A)specific agonist N(6)-(dimethoxyphenyl)-ethyl]adenosine (DPMA), the adenosine deaminase inhibitor erythro-9-(2-Hydroxy-3-nonyl)adenine hydrochloride (EHNA), or forskolin, a potent stimulator of adenylate cyclase. Regulation of NO production by LPS-stimulated chondrocytes, as determined by nitrite concentration, was assessed in the presence of adenosine, N(6)-methyladenosine, DPMA, the broad agonist 5'-N-ethylcarboxamidoadenosine (NECA), or forskolin. Alternatively, LPS-stimulated chondrocytes were exposed to EHNA or the phosphodiesterase inhibitor rolipram in the presence or absence of supplemental adenosine.

RESULTS

Adenosine, N(6)-methyladenosine, DPMA, and forskolin each increased intracellular cAMP accumulation in a concentration-dependent manner and suppressed NO production by LPS-stimulated chondrocytes. NECA also decreased NO production by chondrocytes stimulated with LPS. Incubation with EHNA, to protect endogenously produced adenosine, or rolipram, which prevents the degradation of cAMP, similarly suppressed LPS-stimulated NO production. The addition of exogenous adenosine with EHNA or rolipram further suppressed NO production.

CONCLUSIONS

This study documents functional responses to adenosine by articular chondrocytes. These responses are mimicked by the A(2A)receptor agonist, DPMA. Effects were enhanced by protecting adenosine using an adenosine deaminase inhibitor or by potentiating the cAMP response with rolipram. These experiments suggest that adenosine may play a physiological role in regulation of chondrocytes and that adenosine pathways could represent a novel target for therapeutic intervention.

Effects of inhibition of PDE4 and TNF-alpha on local and remote injuries following ischaemia and reperfusion injury

1. The effects of phosphodiesterase (PDE)4 and TNF-alpha inhibition were assessed on the local and remote injuries following intestinal ischaemia and reperfusion (I/R) injury in rats. 2. The PDE4 inhibitor rolipram dose-dependently (1 - 10 mg kg(-1)) suppressed the local (intestine) and remote (lung) increases in vascular permeability and neutrophil recruitment following mild I/R injury. SB207499 (ariflo), a structurally-distinct PDE4 inhibitor, also suppressed the injuries following mild I/R injury. 3. In a severe model of I/R injury, treatment with rolipram (10 mg kg(-1)) partially reversed the local and remote increases in vascular permeability, neutrophil recruitment, intestinal haemorrhage and intestinal LTB(4) concentrations. The anti-TNF-alpha anti-serum was more effective than rolipram at inhibiting local and remote injuries and prevented the lethality associated with severe I/R. 4. Rolipram and anti-TNF-alpha prevented the increase in the concentrations of TNF-alpha in the lung and intestine, but rolipram only partially inhibited the elevation of this cytokine in serum. Rolipram had little effect on the increases of IL-1 beta concentrations in lung and serum, whereas treatment with anti-TNF-alpha markedly increased the concentration of this cytokine. Concentrations of IL-10 rose significantly in the lung and serum and these increases were blocked by rolipram or anti-TNF-alpha. 5. The capacity of PDE4 inhibitors to block the recruitment of neutrophils into tissues, the production of LTB(4) and of the pro-inflammatory cytokines TNF-alpha, IL-1 beta and IL-6 appear to underlie their anti-inflammatory effects in our model of I/R injury. Overall, PDE4 inhibition was less effective than inhibition of TNF-alpha for protection against I/R injury.

Differential distribution of cAMP-specific phosphodiesterase 7A mRNA in rat brain and peripheral organs

We investigated the regional distribution and cellular localization of mRNA coding for the cAMP-specific phosphodiesterase 7A (PDE7A) in rat brain and several peripheral organs by in situ hybridization histochemistry. The regional expression of two splice variants, PDE7A1 and PDE7A2, was examined by RT-PCR using RNA extracted from several brain regions. PDE7A mRNA was found to be widely distributed in rat brain in both neuronal and nonneuronal cell populations. The highest levels of hybridization were observed in the olfactory bulb, olfactory tubercle, hippocampus, cerebellum, medial habenula nucleus, pineal gland, area postrema, and choroid plexus. Positive hybridization signals were also detected in other areas, such as raphe nuclei, temporal and entorhinal cortex, pontine nuclei, and some cranial nerve motor nuclei. Both mRNA splice forms were differentially distributed in several areas of the brain with the striatum expressing only PDE7A1 and the olfactory bulb and spinal cord expressing PDE7A2 exclusively. In peripheral organs the highest levels of PDE7A hybridization were seen in kidney medulla, although testis, liver, adrenal glands, thymus, and spleen also presented high hybridization signal. These results are consistent with PDE7A being involved in the regulation of cAMP signaling in many brain functions. The consistent colocalization with PDE4 mRNAs suggests that PDE7A could have an effect on memory, depression, and emesis. The results offer clear anatomical and functional systems in which to investigate future specific PDE7 inhibitors.

Rolipram reduces excitotoxic neuronal damage

Proinflammatory cytokines are supposed to be involved in the pathophysiology of neuronal damage following excitotoxic lesions. We examined the effect of rolipram, a TNF-alpha-inhibitor, on excitotoxic neuronal damage. Quinolinic acid (240 nmol in 1 microl) was injected stereotactically into the striatum of male Wistar rats. Four groups of QA rats were treated i.p. with solvent, MK-801 (4 mg/kg) or rolipram (0.3 mg/kg) which was started either 6 or 24 h after QA injection and continued with daily applications for 14 days. QA injection induced neuronal damage which affected 93% of the striatal area. MK-801 reduced this damage to 12% of the striatal area. Treatment with rolipram when started at 6 h after QA injection resulted in neuronal damage amounting to 60%; the result after starting at 24 h was not different from solvent (91%). The present results demonstrate that rolipram reduces neuronal damage induced by intrastriatal QA application.

Human immunodeficiency virus type 1 Tat protein decreases cyclic AMP synthesis in rat microglia cultures

We have studied the modulation of cyclic AMP (cAMP) accumulation by the human immunodeficiency virus type 1 (HIV 1) protein Tat in microglia and astrocyte cultures obtained from neonatal rat brain. Pretreatment of microglia with recombinant Tat resulted in a dose- and time-dependent decrease of cAMP accumulation induced by subsequent exposure to isoproterenol (1 microM). The inhibitory action of 100 ng/mL Tat approached 50% after 4 h of preincubation and reached a maximum of 70% after 24 h. The Tat-induced time- and dose-dependent decrease of cAMP accumulation was observed also when microglial cultures were stimulated with the adenylyl cyclase activator forskolin (100 microM). In both cases, Tat inhibitory action was 70% reverted by a specific monoclonal anti-Tat antibody, but was not prevented either by the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xantine (100 microM) or by a 16-h pretreatment of microglial cultures with the Gi protein inhibitor pertussis toxin (10 ng/mL). All these results suggested that the viral protein acts at a step of the cAMP transduction pathway other than receptors, G proteins and phosphodiesterases. The target of Tat appeared to be adenylyl cyclase, whose activity was markedly reduced (up to 60%) in membranes prepared from Tat-treated microglial cells, both in basal conditions and after stimulation with isoproterenol and forskolin. The inability of the competitive inhibitor of nitric oxide synthase N(G)-monometyl- L-arginine (20 and 200 microM) to revert Tat action on forskolin-induced cAMP accumulation, and of two potent nitric oxide donors, PAPA and DETA (0.1-2 m M), to alter forskolin-induced cAMP accumulation, excluded an involvement of nitric oxide in Tat-induced adenylyl cyclase inhibition. On the contrary, two inhibitors of nuclear factor kappaB activation, N-tosyl-( L)-phenylalanine chloromethyl ketone (10 microM) and SN50 (25 microM), markedly prevented the reduction of forskolin-evoked cAMP accumulation by Tat, suggesting a possible role for this nuclear transcriptional factor in the regulation of adenylyl cyclase by Tat in microglia. This assumption was strengthened by the ability of lipopolysaccharide (100 ng/mL, 4 h) to mimic the inhibitory effect of the viral protein. Conversely, astrocyte cAMP accumulation was unaffected by the viral protein, as tested at various concentrations and time points. Finally, Tat inhibition of microglial adenylyl cyclase was not due to non-specific cytotoxicity. As cAMP has been reported to exert a neuroprotective role in several in vivo and in vitro models of brain pathologies, and microglia is believed to mediate Tat-induced neurotoxicity, these results suggest that the ability of Tat to inhibit cAMP synthesis in microglia may contribute to neuronal degeneration and cell death associated with HIV infection.

Involvement of cyclic AMP systems in morphine physical dependence in mice: prevention of development of morphine dependence by rolipram, a phosphodiesterase 4 inhibitor

In this study, we examined whether morphine dependence was inhibited by rolipram, a cyclic AMP selective phosphodiesterase inhibitor in mice, since a role for the cyclic AMP systems in the development of morphine dependence has been reported. Mice, which received morphine (10 mg kg(-1) s.c.) twice a day for 5 days showed withdrawal syndromes such as jumping, rearing and forepaw tremor following naloxone challenge (5 mg kg(-1) i.p.) on the 6th day. Such mice exhibited a significant elevation of cyclic AMP levels in the thalamus compared to control mice. However, co-administration of rolipram (1 mg kg(-1) i.p.) with morphine for 5 days significantly attenuated the severity of the withdrawal syndrome and the increase in the cyclic AMP levels after the administration of naloxone. In naïve mice, acute morphine treatment (10 mg kg(-1) s.c.) decreased cyclic AMP levels in the thalamus and cerebral cortex 10 min later. The decrease of cyclic AMP levels induced by acute morphine treatment was blocked by co-administration of rolipram (1 mg kg(-1) i.p.). However, acute rolipram did not affect the naloxone-precipitated morphine withdrawal syndrome. These results suggest that the elevation of the cyclic AMP levels is involved in the development of morphine withdrawal syndrome and that blockade of the morphine-induced reduction of cyclic AMP levels by chronic rolipram inhibits the development of dependence and the behavioural and biochemical changes induced by naloxone. Furthermore, rolipram may be a useful drug for attenuating the development of morphine dependence.

Inflammation contributes to the postponed ischemic neuronal damage following treatment with a glutamate antagonist in rats

The present study examined whether anti-inflammatory drugs can ameliorate the postponed neuronal damage which has been observed following treatment of ischemic animals with 2,3-dihydro-6-nitro-7-sulfamoyl-benz (F) quinoxaline (NBQX). Global cerebral ischemia was induced in male Wistar rats by four-vessel occlusion for 20 min. The animals were treated either with NBQX, rolipram, doxycycline or a combination of NBQX and rolipram or doxycycline. Four weeks after ischemia neuronal damage in the hippocampus was assessed. Treatment with NBQX or doxycycline did not affect ischemic neuronal damage whereas rolipram alone or combination of NBQX with either rolipram or doxycycline reduced neuronal damage. The present study shows that combining NBQX with an anti-inflammatory drug leads to long-lasting protection. These results suggest that inflammation contributes to the postponed neuronal damage following treatment with NBQX.

Phosphodiesterase type 4 isozymes expression in human brain examined by in situ hybridization histochemistry and[3H]rolipram binding autoradiography. Comparison with monkey and rat brain

We have examined the distribution of four different cyclic AMP-specific phosphodiesterase isozyme (PDE4A, PDE4B, PDE4C and PDE4D) mRNAs in the brain of different species by in situ hybridization histochemistry and by autoradiography with [3H]rolipram. We have compared the localization of each isozyme in human brain with that in rat and monkey brain. We have found that the four PDE4 isoforms display a differential expression pattern at both regional and cellular level in the three species. PDE4A, PDE4B and PDE4D are widely distributed in human brain, with the two latter appearing more abundant. In contrast, PDE4C in human brain, presents a more restricted distribution, limited to cortex, some thalamic nuclei and cerebellum. This is at variance with the distribution of PDE4C in rat brain, where it is found exclusively in olfactory bulb. In monkey brain, the highest expression for this isoform is found in the claustrum, and at lower levels in cortical areas and cerebellum. PDE4B presented a broad distribution, being expressed in both neuronal and non neuronal cell populations. In general, the distribution of binding sites visualized with [3H]rolipram correlated well with the expression of each PDE4 isozyme.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Age-related effects of rolipram on [3H]quinuclidinyl benzilate and [3H]phorbol 12,13-dibutyrate binding in the rat brain

Cholinergic neurotransmission and protein kinase C (PKC) in the brain play important roles in the processes of cognitive function. In this study, we examined the effect of chronic treatment with rolipram, a 3',5'-cyclic adenosine monophosphate (cyclic AMP)-selective phosphodiesterase inhibitor, on age-related changes in [3H]quinuclidinyl benzilate (QNB) and [3H]phorbol 12,13-dibutyrate (PDBu) binding, which labeled brain muscarinic cholinergic receptors and PKC, respectively. Rolipram was administered per os to young (15 weeks old) and old (80 weeks old) Wistar rats at dosage of 0.01 mg/kg and 0.1 mg/kg once a day over 4 weeks. Then, quantitative in vitro autoradiography was performed. Control old rats showed elevations in [3H]PDBu binding in the hippocampus and the cerebellum compared to young rats, but [3H]QNB binding was largely unchanged. Chronic treatment of the old rats with the higher dose of rolipram led to reductions in [3H]QNB and [3H]PDBu binding in many brain regions. However, the same treatment of the young rats induced no or minimal effect. Thus, the response of the brain to rolipram was different between young and old rats. These results suggest that the cyclic AMP-selective phosphodiesterase system in the brain is modified during aging, modulating subsequently cholinergic neurotransmission and PKC activity exclusively in old rat brains.

Protection against blood-brain barrier disruption in focal cerebral ischemia by the type IV phosphodiesterase inhibitor BBB022: a quantitative study

We examined the effect of BBB022, a type IV phosphodiesterase inhibitor, on blood-brain barrier (BBB) integrity after transient middle cerebral artery occlusion (MCAo) in rats. Male Sprague-Dawley rats were anesthetized with halothane and subjected to 120 min of temporary MCAo by retrograde intraluminal insertion of a nylon suture coated with poly-L-lysine. The drug (BBB022 in saline, 1 mg kg-1 h-1, i.v.) or vehicle (0.9% saline, 1-2 ml kg-1 h-1) was administered by infusion after the onset of MCAo. Four animal groups were studied: Groups A and B were treated by infusion of vehicle or drug over 5 h, and groups C and D over 48 h. Damage to the BBB was judged by extravasation of Evans blue (EB) dye, which was administered i.v. at 3 h after the onset of MCAo in groups A and B; and at 46 h in groups C and D. Fluorometric quantitation of EB was performed 1 or 2 h later in six brain regions. In the 5-h infusion series (group B), BBB022 decreased dye extravasation in the ipsilateral cortex, striatum and hemisphere (hemisphere mean+/-S.E.M. : 41.2+/-5.4 vs. 82.4+/-9.2 microg/g, p=0.005) compared to the vehicle-treated group (A). The 48-h infusion of BBB022 (group D) also decreased dye extravasation in the ipsilateral cortex (7.4+/-2. 5 vs. 29.0+/-8.3 microg/g, p=0.05), striatum (17.2+/-2.2 vs. 50. 8+/-12.1 microg/g, p=0.03) and hemisphere (30.7+/-4.0 vs. 93.2+/-18 microg/g, p=0.01) compared to the vehicle-treated group (C). BBB022 also significantly improved the neurological score at 3 and 5 h after MCAo (in the 5-h infusion group) and at 60 min, 24 h and 48 h (in the 48-h infusion group) compared to the vehicle groups. These data indicate that BBB022 prevents ischemic damage to the BBB after focal cerebral ischemia in rats.

Phosphodiesterase (PDE)4 inhibitors: anti-inflammatory drugs of the future?

Phosphodiesterase type 4 (PDE4) plays a major role in modulating the activity of virtually all cells involved in the inflammatory process. Inhibitors of this enzyme family display impressive anti-inflammatory and disease-modifying effects in a variety of experimental models. In this review, Mauro Teixeira, Robert Gristwood, Nicola Cooper and Paul Hellewell examine the capacity of PDE4 inhibitors to exert anti-inflammatory actions in vivo and discuss the potential of this class of drugs to take their place as novel therapeutic agents for a variety of inflammatory diseases.

Up-regulation of cyclooxygenase-2 expression in cultured microglia by prostaglandin E2, cyclic AMP and non-steroidal anti-inflammatory drugs

Cyclooxygenase-2, the inducible isoform of cyclooxygenase, is highly expressed in microglial cells activated by bacterial lipopolysaccharide and is a major regulatory factor in the synthesis of prostanoids, such as prostaglandins, prostacyclin and thromboxanes. Since prostanoids are potent modulators of inflammation, immune responses and neurotoxicity, the regulation of their synthesis may be crucial for balancing microglial neuroprotective and neurotoxic activities. The present study shows that expression of cyclooxygenase-2 and prostanoid production in cultured rat microglia activated by lipopolysaccharide is up-regulated by cyclic AMP (cAMP), as indicated by experiments performed in the presence of adenylyl cyclase activators, cAMP analogues and protein kinase A-specific inhibitors. Exogenous prostaglandin E2 (PGE2), which elevates the cAMP level in microglial cells, also increased the lipopolysaccharide-induced expression of cyclooxygenase-2 and production of thromboxane in a dose- and time-dependent manner. The observations that the lipopolysaccharide-induced prostanoid production was specifically increased by 11-deoxy-16,16-dm PGE2, a selective agonist at the PGE2 receptor EP2 coupled to the activation of adenylyl cyclase, and that the enhancing effect of PGE2 was partially prevented by specific inhibitors of adenylyl cyclase and protein kinase A, suggest that the up-regulation of cyclooxygenase-2 expression by PGE2 is mediated by cAMP, through a putative microglial EP2 receptor. Unexpectedly, non-steroidal anti-inflammatory drugs such as indomethacin and 6-methoxy naphthalene acetic acidic, which inhibit cyclooxygenase enzymatic activity and abrogate prostanoid synthesis, caused a moderate but consistent up-regulation of cyclooxygenase-2 expression. In conclusion, while the strong up-regulation of cyclooxygenase-2 expression by exogenous PGE2 appears to be mediated by EP2 receptors and cAMP, the limited down-regulation caused by anti-inflammatory drug treatments may be either due to arachidonic acid metabolites other than PGE2, or to PGE2 itself, acting through a distinct cAMP-independent signalling pathway.