Comparision of the inotropic effects of levosimendan, rolipram, and dobutamine on human atrial trabeculae

The aim of this study was to compare the positive inotropic effects of 3 different agents with 3 different mechanisms of actions-levosimendan, rolipram, and dobutamine-on human atrial trabecular muscles. Samples of right atrial appendage (1 cm, 500-1000 mg) were removed and immersed in preoxygenated and modified Tyrode solution. In oxygenated Tyrode solution, preparations were used to investigate the concentration-effect relationship of levosimendan, dobutamine, and rolipram on percentage developed tension (DT), from 10 to 10 M, each concentration for 15 minutes. All 3 agents produced concentration-dependent increments in DT. We found that levosimendan was the most efficacious positive inotropic agent on isolated human atrial trabeculae. Both the sensitivity (pD2) and maximum response (Emax) of human atrial trabeculae to levosimendan (6.711 +/- 0.26 and 23.2 +/- 2.2 mN, respectively) were significantly greater than those of dobutamine (6.663 +/- 0.19 and 17.6 +/- 2.8 mN) and rolipram (6.497 +/- 0.18 and 15.0 +/- 1.0 mN). pD2 and Emax values for dobutamine were significantly higher than those for rolipram. It was suggested that because of its potential to enhance cardiac performance without predisposition to calcium-induced arrhythmias, levosimendan might be more useful as a positive inotropic agent in clinical practice.

Persistent accumulation of calcium/calmodulin-dependent protein kinase II in dendritic spines after induction of NMDA receptor-dependent chemical long-term potentiation

Calcium/calmodulin-dependent protein kinase II (CaMKII) is a leading candidate for a synaptic memory molecule because it is persistently activated after long-term potentiation (LTP) induction and because mutations that block this persistent activity prevent LTP and learning. Previous work showed that synaptic stimulation causes a rapidly reversible translocation of CaMKII to the synaptic region. We have now measured green fluorescent protein (GFP)-CaMKIIalpha translocation into synaptic spines during NMDA receptor-dependent chemical LTP (cLTP) and find that under these conditions, translocation is persistent. Using red fluorescent protein as a cell morphology marker, we found that there are two components of the persistent accumulation. cLTP produces a persistent increase in spine volume, and some of the increase in GFP-CaMKIIalpha is secondary to this volume change. In addition, cLTP results in a dramatic increase in the bound fraction of GFP-CaMKIIalpha in spines. To further study the bound pool, immunogold electron microscopy was used to measure CaMKIIalpha in the postsynaptic density (PSD), an important regulator of synaptic function. cLTP produced a persistent increase in the PSD-associated pool of CaMKIIalpha. These results are consistent with the hypothesis that CaMKIIalpha accumulation at synapses is a memory trace of past synaptic activity.

A novel mechanism for the modulation of luteinizing hormone receptor mRNA expression in the rat ovary

Luteinizing hormone receptor (LHR) is a G-protein-coupled receptor that exerts its effects mainly through increased cAMP synthesis. Our previous studies have shown that a ovarian cytosolic protein, designated as LHR mRNA binding protein (LRBP) is an important regulator of the steady state levels of LHR expression. To test whether LHR mRNA expression is modulated by cAMP through LRBP activity, we used rolipram, a type IV phosphodiesterase inhibitor that is known to promote intracellular cAMP accumulation. On day 4 of pseudopregnancy, rats were treated with rolipram (1.25 mg/injection) to raise intracellular levels of cAMP. In order to maintain higher cAMP levels, up to four injections of rolipram were given, with the last injection 4 h before collecting the ovaries. Measurement of cAMP levels showed an increase (p< or =0.05) at 8, 12, and 24 h after rolipram injections at total dosages of 2.5, 3.75 and 5.0 mg/rat, respectively. Northern blot analysis of LHR mRNA showed that rolipram treatment also markedly reduced ovarian LHR mRNA levels by up to 75%. LHR mRNA binding activity of LRBP, assayed by RNA electrophoretic mobility shift analysis, using S-100 fractions from control or rolipram-treated ovaries showed increased LHR mRNA binding activity in the S-100 fractions from rolipram treated groups. These data indicate that chronic elevation of ovarian cAMP leads to a decreased expression of LHR mRNA with a concomitant increase in LHR mRNA binding activity of LRBP.

A2A adenosine receptor agonist and PDE4 inhibition delays inflammation but fails to reduce injury in experimental obstructive nephropathy

BACKGROUND

Renal interstitial inflammation is a consequence of unilateral ureteral obstruction (UUO). Following ischemia/reperfusion, adenosine reduces renal inflammation and injury, effects which are potentiated by type 4 phosphodiesterase inhibitors. We therefore studied the effects of A2A adenosine receptor agonist (ATL146e), and PDE4 inhibitor (rolipram) in mice subjected to UUO.

METHODS

Mice were subjected to UUO or sham operation, and received either vehicle or ATL146e + rolipram by osmotic minipump for 1 or 7 days. At 1, 3, 7, or 14 days after operation, renal macrophage infiltration, apoptosis, proliferation, tubular atrophy, and interstitial fibrosis were quantitated, and expressions of IL-6 and TGF-beta mRNA were determined.

RESULTS

ATL146e + rolipram reduced macrophage infiltration by 40% after 3 days UUO (p < 0.05). Tubular apoptosis, tubular atrophy, and interstitial fibrosis were increased by 7 or 14 days UUO, but were unaffected by ATL146e + rolipram. However, cellular proliferation was increased by ATL146e + rolipram in the obstructed kidney. ATL146e + rolipram had no effect on the renal expression of IL-6 and TGF-beta mRNA.

CONCLUSIONS

A2A receptor activation and PDE4 inhibition transiently reduce renal macrophage infiltration, but do not ameliorate the renal response to UUO. We speculate that the persistent stimulus for inflammation triggered by UUO cannot be reversed by agents that suppress inflammatory cell activation alone.

The type IV-specific phosphodiesterase inhibitor rolipram and its effect on hippocampal long-term potentiation and synaptic tagging

We investigated the effects of rolipram, a selective cAMP phosphodiesterase (PDE) inhibitor, on late plastic events during functional CA1 plasticity in vitro in rat hippocampal slices. We present data showing that an early form of long-term potentiation (LTP) (early-LTP) that normally decays within 2-3 hr can be converted to a lasting LTP (late-LTP) if rolipram is applied during tetanization. This rolipram-reinforced LTP (RLTP) was NMDA receptor and protein synthesis dependent. cAMP formation in region CA1 during late-LTP requires dopaminergic receptor activity (Frey et al., 1989, 1990). Thus, we studied whether RLTP was influenced by inhibitors of the D(1)/D(5) receptor. Application of the specific D(1)/D(5) antagonist SCH23390 (0.1 microm) did not prevent RLTP, suggesting that the phosphodiesterase inhibitor acts downstream of the D(1)/D(5) receptors. We also studied whether rolipram can interact with processes of synaptic tagging, because RLTP was also dependent on protein synthesis, similar to late-LTP. Inhibition of PDE and subsequent induction of RLTP in one synaptic population were able to transform early-LTP into late-LTP in a second, independent synaptic population of the same neurons. This supports our hypothesis that cAMP-dependent processes are directly involved in the synthesis of plasticity-related proteins.

Cyclic AMP-phosphodiesterases inhibitor improves sodium excretion in rats with cirrhosis and ascites

BACKGROUND

The mechanisms responsible for renal dysfunction and sodium retention in cirrhosis remain unclear. Cyclic AMP (cAMP) regulates sodium reabsorption in the proximal nephron. This study investigates the role of cAMP metabolism in renal dysfunction in cirrhosis.

METHODS

Renal function was studied by the clearance technique in anesthetized control and cirrhotic rats with or without ascites. cAMP phosphodiesterase (PDE) activity was measured in the renal cortex in vitro. Moroever, the effects on renal function of the intravenous administration of cAMP and rolipram, a powerful and specific cAMP-PDE4 inhibitor, were evaluated.

RESULTS

In control and in non-ascitic cirrhotic rats, cAMP administration significantly increased sodium and phosphate excretions, but did not change these excretions in cirrhotic rats with ascites. cAMP-PDE activity was higher in ascitic than in control rats (P < 0.05). Rolipram infusion significantly increased sodium and phosphate excretion only in cirrhotic rats with ascites.

CONCLUSION

These results suggest that increased renal cAMP-PDE activity is responsible for resistance to the natriuretic effects of cAMP in cirrhosis and plays a role in the development of ascites.

Essential role of a Ca2+-selective, store-operated current (ISOC) in endothelial cell permeability: determinants of the vascular leak site

Store-operated calcium (SOC) entry is sufficient to disrupt the extra-alveolar, but not the alveolar, endothelial cell barrier. Mechanism(s) underlying such insensitivity to transitions in cytosolic calcium ([Ca2+]i) in microvascular endothelial cells are unknown. Depletion of stored Ca2+ activates a larger SOC entry response in extra-alveolar (pulmonary artery; PAECs) than alveolar (pulmonary microvascular; PMVECs) endothelial cells. In vivo permeation studies revealed that Ca2+ store depletion activates similar nonselective cationic conductances in PAECs and PMVECs, while only PAECs possess the calcium-selective, store-operated Ca2+ entry current, I(SOC). Pretreatment with the type 4 phosphodiesterase inhibitor, rolipram, abolished thapsigargin-activated I(SOC) in PAECs, and revealed I(SOC) in PMVECs. Rolipram pretreatment shifted the thapsigargin-induced fluid leak site from extra-alveolar to alveolar vessels in the intact pulmonary circulation. Thus, our results indicate I(SOC) provides a [Ca2+]i source that is needed to disrupt the endothelial cell barrier, and demonstrate that intracellular events controlling I(SOC) activation coordinate the site-specific vascular response to inflammation.

Altered activities of cyclic nucleotide phosphodiesterases and soluble guanylyl cyclase in cultured RFL-6 cells

We utilized rat fetal lung fibroblasts (RFL-6) to evaluate our PDE5 inhibitors at cellular level and observed a decrease in cGMP accumulation induced by sodium nitroprusside (SNP) and PDE5 inhibitors with passage. To further investigate this observation, we examined cGMP synthesis via soluble guanylyl cyclase (sGC) and degradation via phosphodiesterases (PDEs) at different passages. At passage (p)4, p9, p14, major cGMP and cAMP degradation activities were contributed by PDE5 and PDE4, respectively. The PDE5 activity decreased 50% from p4 to p14, while PDE4 activity doubled. The cGMP accumulation was evaluated in the presence of sodium nitroprusside (SNP) and/or PDE inhibitors in p4 and p14 cells. SNP together with sildenafil, a PDE5 inhibitor, induced dose-dependent increase in cGMP levels in cells at p4, but showed little effect on cells at p14. The possible down regulation of sGC at mRNA level was explored using real-time RT-PCR. The result showed the mRNA level of the alpha1 subunit of sGC decreased about 98% by p9, while the change on beta1 mRNA was minimal. Consistently, sGC activities in cell lysate decreased by 94% at p9. Forskolin stimulated a dramatic increase in cAMP levels in cells at all passages examined. Our results show that sGC activity decreased significantly and rapidly with passage due to a down regulation of the alpha1 subunit mRNA, yet the adenylyl cyclase activity was not compromised. This study further emphasized the importance of considering passage number when using cell culture as a model system to study NO/cGMP pathway.

A2A adenosine receptor induction inhibits IFN-gamma production in murine CD4+ T cells

Incubation of purified C57BL/6 murine CD4(+) T lymphocytes with anti-CD3 mAb serves as a model of TCR-mediated activation and results in increased IFN-gamma production and cell surface expression of CD25 and CD69. We demonstrate here that signaling through the TCR causes a rapid (4-h) 5-fold increase in A(2A) adenosine receptor (AR) mRNA, which is correlated with a significant increase in the efficacy of A(2A)AR-mediated cAMP accumulation in these cells. A(2A)AR activation reduces TCR-mediated production of IFN-gamma by 98% with a potency order of 4-{3-[6-amino-9-(5-ethylcarbamoyl-3,4-dihydroxytetrahydrofuran-2-yl)-9H-purin-2-yl]prop-2-ynyl}cyclohexanecarboxylic acid methyl ester (ATL146e; EC(50) = 0.19 +/- 0.03 nM) > 4-{3-[6-amino-9-(5-cyclopropyl-carbamoyl-3,4-dihydroxytetrahydrofuran-2-yl)-9H-purin-2-yl]prop-2-ynyl}piperidine-1-carboxylic acid methyl ester (ATL313; 0.43 +/- 0.06 nM) > 5'-N-ethylcarboxamidoadenosine (3.5 +/- 0.77 nM) > 2-[4-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosine (CGS21680; 7.2 +/- 1.4 nM) >> N(6)-cyclohexyladenosine (110 +/- 33 nM) > 2-chloro-N(6)-(3-iodobenzyl)-5'-N-methylcarboxamide (390 +/- 160 nM), similar to the potency order to compete for radioligand binding to the recombinant murine A(2A)AR but not the A(3)AR. The selective A(2A)AR antagonist, 4-(2-[7-amino-2-[2-furyl][1,2,4]triazolo[2,3-a][1,3,5]triazin-5-yl-amino]ethyl)phenol (ZM241385), inhibits the effect of ATL146e with a pA(2) of 0.34 nM and also inhibits the effects of N(6)-cyclohexyl-adenosine and 2-chloro-N(6)-(3-iodobenzyl)-5'-N-methylcarboxamide. In CD4(+) T cells derived from A(2A)AR(-/-) and A(2A)AR(+/-) mice, the IFN-gamma release response to ATL146e is reduced by 100 and 50%, respectively, indicative of a gene dose effect. The response of T cells to the phosphodiesterase inhibitor, 4-(3'-cyclopentyloxy-4'-methoxyphenyl)-2-pyrrolidone (rolipram), is not affected by A(2A)AR deletion. We conclude that the rapid induction of the A(2A)AR mRNA in T cells provides a mechanism for limiting T cell activation and secondary macrophage activation in inflamed tissues.

Phosphodiesterase 4D Forms a cAMP Diffusion Barrier at the Apical Membrane of the Airway Epithelium

We demonstrated previously that Calu-3 airway epithelial cells sense adenosine on their luminal surface through adenosine A2B receptors coupled to adenylyl cyclase. Occupancy of these receptors leads to activation of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel through protein kinase A (PKA) anchored at the apical membrane. Because luminal A2B receptor activation does not raise total cellular cAMP levels, we hypothesized that activation of phosphodiesterases (PDEs) confines cAMP generated by apical A2B receptors to a microdomain that includes the CFTR channel. Using reverse transcription-PCR, Western blotting, and activity measurements, PDE4D was identified as the major PDE species in airway epithelia. Consistent with these results, inhibitors of PDE4, but not PDE3, selectively abolished the lateral confinement of cAMP signaling in apical membrane patches during cell-attached recordings. Furthermore, stimulation of the CFTR in excised apical patches by rolipram and RS25344 indicated that PDE4 is localized in close proximity to the CFTR channel. Indeed, immunohistochemistry of human airway sections revealed that PDE4D is localized in the apical domain of the cell. PDE4 was activated after luminal adenosine exposure in a PKA-dependent manner. Because PDE4 activity is positively regulated by PKA, our results support a model whereby the PDE diffusion barrier is proportional to the degree of receptor stimulation. These findings underscore the concept that subcellular localization of individual PDE isozymes is an important mechanism for confining cAMP signaling to functional domains within cells.

Rolipram, a phosphodiesterase 4 inhibitor, stimulates inducible cAMP early repressor expression in osteoblasts

Phosphodiesterase (PDE) 4 inhibitors have been shown to induce the cAMP-mediated signaling pathway by inhibiting cAMP hydrolysis. This study investigated the effect of a PDE4 inhibitor on the expression of the inducible cAMP early repressor (ICER), which is an endogenous inhibitor of CRE- mediated transcription, in osteoblastic cells. RT-PCR analysis revealed that rolipram, a PDE4 inhibitor, stimulates the ICER mRNA in a dose dependent manner. The induction of ICER mRNA expression by rolipram was suppressed by the inhibitors of protein kinase A (PKA) and p38 MAPK, suggesting the involvement of PKA and p38 MAPK activation in ICER expression by rolipram. It was previously shown that rolipram induced the expression of TNF-related activation-induced cytokine (TRANCE, also known as RANKL, ODF, or OPGL) in osteoblasts. This paper provides evidences that a transcriptional repressor like ICER might modulate TRANCE mRNA expression by rolipram in osteoblasts.

Effect of phosphodiesterase 4 inhibitors on NFAT-dependent cyclooxygenase-2 expression in human T lymphocytes

Transcriptional induction of cyclooxygenase-2 (COX-2) occurs early after T cell receptor triggering and has functional implications in inflammation. Here, we show that phosphodiesterase (PDE)-4 inhibitors block COX-2 induction and prostaglandin synthesis in activated T cells. COX-2 inhibition by PDE4 inhibitors occurs mainly at the transcriptional level. Two response elements for the nuclear factor of activated T cells (NFAT) in the COX-2 promoter were required for inhibition by these drugs. PDE4 inhibitors did not affect NFAT nuclear translocation upon T cell activation; rather they prevented NFAT binding to DNA and induction of the transactivation function of GAL4-NFAT. These effects seem to be cAMP/PKA independent as they were not mimicked by the permeable analog dBcAMP or by forskolin, neither can be reverted by the PKA inhibitors H89 or KT-5720. These results may explain some of the anti-inflammatory properties of PDE4 inhibitors through the blockade of NFAT-mediated transactivation of pro-inflammatory genes such as COX-2.

Persistent improvement in synaptic and cognitive functions in an Alzheimer mouse model after rolipram treatment

Evidence suggests that Alzheimer disease (AD) begins as a disorder of synaptic function, caused in part by increased levels of amyloid beta-peptide 1-42 (Abeta42). Both synaptic and cognitive deficits are reproduced in mice double transgenic for amyloid precursor protein (AA substitution K670N,M671L) and presenilin-1 (AA substitution M146V). Here we demonstrate that brief treatment with the phosphodiesterase 4 inhibitor rolipram ameliorates deficits in both long-term potentiation (LTP) and contextual learning in the double-transgenic mice. Most importantly, this beneficial effect can be extended beyond the duration of the administration. One course of long-term systemic treatment with rolipram improves LTP and basal synaptic transmission as well as working, reference, and associative memory deficits for at least 2 months after the end of the treatment. This protective effect is possibly due to stabilization of synaptic circuitry via alterations in gene expression by activation of the cAMP-dependent protein kinase (PKA)/cAMP regulatory element-binding protein (CREB) signaling pathway that make the synapses more resistant to the insult inflicted by Abeta. Thus, agents that enhance the cAMP/PKA/CREB pathway have potential for the treatment of AD and other diseases associated with elevated Abeta42 levels.

Rolipram, a phosphodiesterase 4 inhibitor, stimulates osteoclast formation by inducing TRANCE expression in mouse calvarial cells

Phosphodiesterase (PDE) 4 is an enzyme that degrades intracellular cAMP. In the present study, the effect of rolipram, a specific phosphodiesterase (PDE) 4 inhibitor, on osteoclast formation was investigated. Rolipram induced osteoclast formation in cocultures of mouse bone marrow cells and calvarial osteoblasts. This activity was not observed in the absence of calvarial osteoblasts, suggesting that calvarial osteoblasts are likely target cells of rolipram. Osteoclast formation by rolipram was completely blocked by the addition of osteoprotegerin (OPG), a soluble decoy receptor for the osteoclast differentiation factor, TNF-related activation-induced cytokine (TRANCE, identical to RANKL, ODF, and OPGL). Northern blot analysis revealed the effect of rolipram to be associated with the increased expression of TRANCE mRNA in mouse calvarial osteoblasts. Collectively, these data indicate that PDE4 inhibitor up-regulates the TRANCE mRNA expression in osteoblasts, which in turn controls osteoclast formation.

Type 4 cAMP phosphodiesterase (PDE4) inhibitors augment glucocorticoid-mediated apoptosis in B cell chronic lymphocytic leukemia (B-CLL) in the absence of exogenous adenylyl cyclase stimulation

cAMP-mediated signaling potentiates glucocorticoid-mediated apoptosis in lymphoid cells, but an effective means by which to take advantage of this observation in the treatment of lymphoid malignancies has not been identified. The primary objective of the current study was to determine whether PDE4 inhibitors, a class of compounds in late clinical development that raise intracellular cAMP levels by inhibiting type 4 cyclic nucleotide phosphodiesterases (PDE4), increase the efficacy of glucocorticoid-mediated apoptosis in leukemic cells from patients with B cell chronic lymphocytic leukemia (B-CLL). Rolipram, a prototypic PDE4 inhibitor, synergized with glucocorticoids in inducing B-CLL but not T cell apoptosis. Rolipram also augmented glucocorticoid receptor element (GRE) transactivation in B-CLL cells. In contrast, inhibition of protein kinase A (PKA) with the cAMP antagonist Rp-8Br-cAMPS reversed both glucocorticoid-induced apoptosis and GRE transactivation. CCRF-CEM cells, a well-studied model of glucocorticoid and cAMP-induced apoptosis, differed from B-CLL cells in that stimulation of adenylyl cyclase with the diterpene forskolin was required to increase both glucocorticoid-mediated apoptosis and GRE activation, while PDE4 inhibition had no effect. Consistent with these results, inhibition of PDE4 induced cAMP elevation in B-CLL but not CCRF-CEM cells, while forskolin augmented cAMP levels in CCRF-CEM but not B-CLL cells. While rolipram treatment up-regulated PDE4B in B-CLL, forskolin treatment up-regulated PDE4D in CCRF-CEM cells. These studies suggest that PKA is required for and enhances glucocorticoid-induced apoptosis in B-CLL by modulating glucocorticoid receptor signal transduction. Clinical trials that examine whether PDE4 inhibitors enhance the efficacy of glucocorticoid-containing chemotherapy regimens in B-CLL are indicated.

Upregulation of phosphodiesterase-4 in the lung of allergic rats

Inhibitors of phosphodiesterase-4 (PDE4) are efficacious for allergic asthma in animal models and have shown some efficacy in human asthma. Regulation of PDE4 in allergy and asthma has been widely investigated in blood leukocytes, with discrepant results. This study investigated PDE4 regulation in the lung in a rat model of allergic asthma. Ovalbumin sensitization and challenge significantly increased pulmonary resistance and lung interleukin (IL)-4 production. The increases in pulmonary resistance and IL-4 production were both suppressed by the PDE4-selective inhibitor rolipram or the corticosteroid drug dexamethasone. Furthermore, cAMP-PDE enzyme activity in the lung was also significantly increased by the sensitization and challenge. mRNA analysis confirmed that PDE4 gene expression was increased in the lung of the allergic rats. A highly significant correlation was observed between the increases in PDE activity and IL-4 production. Our data suggest, for the first time, that PDE4 may be upregulated in the lung and play a role in the pathogenesis of allergic asthma.

PDE4-regulated cAMP degradation controls the assembly of integrin-dependent actin adhesion structures and REF52 cell migration

Plating of REF52 cells onto extracellular matrix components leads to the formation of integrin-dependent actin adhesion microspikes. We show that the formation of these structures is sensitive to chemical agents that regulate cAMP levels, such as forskolin and IBMX. In particular, by using the specific inhibitor rolipram, we identify the PDE4 family of cAMP-specific phosphodiesterases as critical regulators of this process. The effect of PDE4 on microspike formation is mediated by actions exerted through the activation of PKA - rather than through the alternative cAMP effector, Epac. We provide evidence that peripheral microspikes are RhoA-, ROCK- and myosin-dependent, and that this pathway is suppressed by PDE4 inhibition. In addition, PDE4 inhibition impairs cell locomotion that requires dynamic protrusion and retraction of peripheral spike structures. Our data demonstrate that PDE4 activity is a key modulator of integrin-induced actin assembly at the cell periphery which, in turn, controls cell migration.

Phosphodiesterase inhibitors: a novel mechanism for receptor-independent antipsychotic medications

OVERVIEW

All current antipsychotic medications work by binding to Gi-coupled dopamine (DA) D2 receptors. Such medications are thought to affect cellular function primarily by decreasing DA-mediated regulation of intracellular cyclic adenosine monophosphate (cAMP).However, several studies indicate that cAMP signal transduction abnormalities in schizophrenia may not be limited to D2-containing cells. The current study examines the potential of using non-receptor-based agents that modify intracellular signal transduction as potential antipsychotic medications.

METHODS

The indirect DA agonist amphetamine has been used to model the auditory sensory processing deficits in schizophrenia. Such pharmacologically induced abnormalities are reversed by current antipsychotic treatments. This study examines the ability of the phosphodiesterase-4 inhibitor, rolipram, to reverse amphetamine-induced abnormalities in auditory-evoked potentials that are characteristic of schizophrenia.

RESULTS

Rolipram reverses amphetamine-induced reductions in auditory-evoked potentials.

CONCLUSION

This finding could lead to novel approaches to receptor-independent treatments for schizophrenia.

cAMP response element-binding protein activation in ligation preconditioning in neonatal brain

Perinatal hypoxic-ischemic (HI) brain injury is a major cause of permanent neurological dysfunction in children. An approach to study the treatment of neonatal HI encephalopathy that allows for neuroprotection is to investigate the states of tolerance to HI. Twenty-four-hour carotid-artery ligation preconditioning established by delaying the onset of hypoxia for 24 hours after permanent unilateral carotid ligation rats markedly diminished the cerebral injury, however, the signaling mechanisms of this carotid-artery ligation preconditioning in neonatal rats remain unknown. Ligation of the carotid artery 24 hours before hypoxia provided complete neuroprotection and produced improved performance on the Morris water maze compared with ligation performed 1 hour before hypoxia. Carotid artery ligation 6 hours before hypoxia produced intermediate benefit. The 24-hour carotid-artery ligation preconditioning was associated with a robust and sustained activation of a transcription factor, the cAMP response element-binding protein (CREB), on its phosphorylation site on Ser133. Intracerebroventricular infusions of antisense CREB oligodeoxynucleotides significantly reduced the 24-hour carotid-artery ligation-induced neuroprotection effects by decreasing CREB expressions. Pharmacological activation of the cAMP-CREB signaling with rolipram 24 hours before hypoxia protected rat pups at behavioral and pathological levels by sustained increased CREB phosphorylation. This study suggests that 24-hour carotid-artery ligation preconditioning provides important mechanisms for potential pharmacological preconditioning against neonatal HI brain injury.

Potentiation and prolongation of long-term odor memory in neonate rats using a phosphodiesterase inhibitor

Cyclic AMP has been shown to have a critical role in learning and memory in invertebrates. Here we use the rat pup odor preference learning model in which odor acts as a conditioned stimulus and beta-adrenoceptor stimulation acts as an unconditioned stimulus to test the role of cyclic AMP in an associative mammalian paradigm. A phosphodiesterase inhibitor that prevents cyclic AMP breakdown (cilomilast) makes a low, learning-ineffective dose of a beta-adrenoceptor agonist (isoproterenol, 1mg/kg) an effective unconditioned stimulus in pup odor preference learning. A dose of the phosphodiesterase inhibitor (cilomilast, 1 mg/kg) that induces learning with a weak unconditioned stimulus interferes with learning using a normally optimal unconditioned stimulus (isoproterenol, 2 mg/kg). Cilomilast (3 mg/kg) paired with peppermint odor during learning, prolonged memory at least four times longer than without the drug (24 h vs. 96 h). These data demonstrate a causal role for cyclic AMP in the acquisition and duration of odor preference learning in the rat pup.

The potential of PDE4 inhibitors in respiratory disease

Glucocorticosteroids remain the gold standard therapy for the prophylactic treatment of asthma. Concerns regarding its long-term use particularly in young children has provided an impetus for discovering novel anti-inflammatory molecules with high tolerability and clinical efficacy. Whilst for chronic obstructive pulmonary disease (COPD), there exist no pharmacological treatment for the prevention of decline in lung function. Targeting phosphodiesterase (PDE)4 is one example of this approach and inhibitors of this enzyme are the most advanced drug class in the respiratory pipeline. A number of potent PDE4 inhibitors have undergone clinical trials with moderate success. Tolerability and clinical efficacy issues have dampened enthusiasm in this area. However, with the prospect of newer potent and side effect free inhibitors on the horizon give this area guarded optimism. This review will summarise the most recent information concerning the effectiveness of PDE4 inhibitors as novel anti-inflammatory agents for the treatment of respiratory diseases.

Irsogladine, an anti-ulcer drug, suppresses superoxide production by inhibiting phosphodiesterase type 4 in human neutrophils

Neutrophil superoxide production is implicated in the pathogenesis of gastric mucosal damage induced by various ulcerative agents and Helicobacter pylori infection. We investigated here the effects of an anti-ulcer drug irsogladine [2, 4-diamino-6-(2, 5-dichlorophenyl)-s-triazine maleate] on cAMP formation in isolated human neutrophils. The cAMP level in human neutrophils was elevated by a phosphodiesterase (PDE) type 4 selective inhibitor rolipram, but not by any inhibitors of PDE1, PDE2 and PDE3. Irsogladine also increased cAMP formation in a concentration-dependent manner in neutrophils. A non-selective PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX) alone significantly increased cAMP level, whereas irsogladine was unable to further increase cAMP level in the presence of IBMX. Irsogladine inhibited concentration-dependently the superoxide (O(2)(-)) production induced by various stimuli including formyl-methionyl-leucyl-phenylalanine, opsonized zymosan, guanosine 5'-[gamma-thio] triphosphate, A23187 and phorbol 12-myristate 13-acetate. These effects of irsogladine were mimicked by rolipram, IBMX and dibutyryl cAMP. The inhibitory effects of irsogladine and rolipram on the O(2)(-) production were reversed by a protein kinase A inhibitor H-89. These results indicate that irsogladine inhibits the superoxide production in human neutrophils by the increase of cAMP content by PDE 4 inhibition, which in turn contributing to the anti-ulcer effects of irsogladine on gastric mucosal lesions associated with oxidative stress.

Reduction of infarct size and postischemic inflammation from ATL-146e, a highly selective adenosine A2A receptor agonist, in reperfused canine myocardium

Adenosine and adenosine A(2A) receptor agonists have been shown to limit myocardial infarct size when given at vasodilatory doses during reperfusion. This beneficial effect is thought to be due, in part, to stimulation of adenosine A(2A) receptors on inflammatory cells. The specific aims of this study were to determine whether the anti-inflammatory and cardioprotective properties of a novel adenosine A(2A) receptor agonist, ATL-146e (ATL), alone or in combination with the phosphodiesterase IV inhibitor rolipram would occur using very low, nonvasodilating doses. In a canine model of reperfused myocardial infarction, low-dose ATL given alone reduced infarct size by 45% (P < 0.05 vs. control). When ATL was combined with a very low dose of rolipram (0.001 microg.kg(-1).min(-1)), a marked reduction in P-selectin expression and neutrophil infiltration (51% lower; P < 0.001 vs. control) was seen and the infarct size reduction (58% lower; P < 0.01 vs. control) was greater than observed with ATL (45% lower; P < 0.05) or rolipram (33% lower; P < 0.05) alone. In conclusion, a low, nonvasodilating dose of ATL, a highly selective adenosine A(2A) receptor agonist, reduced infarct size after reperfusion. Furthermore, combining ATL and the phosphodiesterase IV inhibitor rolipram reduced infarct size even more than either agent alone. Such combination therapy may be beneficial clinically by potentiating cardioprotection after coronary reperfusion at doses far below those producing vasodilatation or side effects.

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

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

Increased levels of cyclic adenosine monophosphate contribute to the hyporesponsiveness of mast cells in alloxan diabetes

In this study, we investigated the influence of intracellular cyclic adenosine monophosphate (cAMP) changes on the rat mast cell hyporesponsiveness following immunological and non-immunological stimuli. Compared with mast cells from normal rats, those recovered from 21-day diabetic animals showed a significant augmentation in the intracellular levels of cAMP, in directly correlated with secretion of lower amounts of histamine after stimulation with antigen, bradykinin and compound 48/80 in vitro. Incubation of normal mast cells with selective inhibitors of phosphodiesterase type 4 (PDE 4) rolipram, NCS 613 and RP 73401, or the cell permeable analogue N6-2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (db cAMP), led to a decrease of histamine secretion in vitro. However, the effectiveness of either NCS 613 or db cAMP in inhibiting antigen-induced degranulation is comparable in both normal and diabetic mast cells. We suggest that (a) there is a close correlation between higher levels of intracellular cAMP and hyporesponsiveness of diabetic mast cells, phenomena probably associated with a reduction in the expression and/or activity of PDE 4 and that (b) the mechanism of cAMP-mediated down-regulation of mast cell function is saturated in diabetic rats.