Zaprinast consolidates long-term memory when administered to neonate chicks trained using a weakly reinforced single trial passive avoidance task

Cilostazol as an adjunctive treatment in major depressive disorder: a pilot randomized, double-blind, and placebo-controlled clinical trial

BACKGROUND

Cilostazol, a phosphodiesterase-3 inhibitor, has been reported to improve depressive-like behavior in experimental studies of depression. We investigated the safety and efficacy of cilostazol combination therapy with sertraline in treating patients with major depressive disorder (MDD) in a 6-week, parallel, randomized controlled trial.

METHOD

Among patients referred to the outpatient clinic of a tertiary hospital, those with a diagnosis of MDD with moderate to severe severity (a score of >19 on the Hamilton depression rating scale (HAM-D)) were enrolled. A total of 54 MDD patients aged 18-65 years were randomly assigned to either the cilostazol (100 mg daily) or the placebo group. Both groups received sertraline 100 mg per day similarly. Changes in HAM-D at weeks 2, 4, and 6 were the primary outcome. Participants and outcome assessors were blinded.

RESULTS

At week 6, patients in the cilostazol group had significantly lower HAM-D score (p value= 0.015). General linear model repeated-measure analysis showed significant effect for treatment in improving MDD severity (p value <0.001). The remission rate at the study endpoint and number of responders at week 4 were significantly higher in the cilostazol group (p value= 0.047, p value= 0.032, respectively). The cilostazol group demonstrated a significantly shorter time to response. No significant difference was observed in treatment response at the study endpoint, and there were no serious adverse effects.

CONCLUSION

Our study supports safety and efficacy of cilostazol in treating MDD patients.

TRIAL REGISTRATION

This trial was registered at the Iranian registry of clinical trials (IRCT: www.irct.ir ; registration number: IRCT20090117001556N130).

PDE5 Exists in Human Neurons and is a Viable Therapeutic Target for Neurologic Disease

Phosphodiesterase 5 (PDE5) is a critical component of the cGMP-PKG axis of cellular signaling in neurons, and inhibition of PDE5 has been shown to be therapeutic in a wide range of neurologic conditions in animal models. However, enthusiasm for PDE5 inhibitors in humans is limited by data suggesting that PDE5 may not exist in human neurons. Here, we first show that past attempts to quantify PDE5 mRNA were flawed due to the use of incorrect primers, and that when correct primers are used, PDE5 mRNA is detectable in human brain tissue. We then show that PDE5 protein exists in human brain by western blot and ELISA. Most importantly, we performed immunohistochemistry and demonstrate that PDE5 is present in human neurons. We hope that this work will trigger a renewed interest in the development of PDE5 inhibitors for neurologic disease.

Phosphodiesterase-5 inhibitor sildenafil prevents neuroinflammation, lowers beta-amyloid levels and improves cognitive performance in APP/PS1 transgenic mice

Memory deficit is a marker of Alzheimer's disease (AD) that has been highly associated with the dysfunction of cyclic GMP (cGMP) signaling and an ongoing inflammatory process. Phosphodiesterase-5 (PDE5) inhibitors prevent the breakdown of cGMP and are currently studied as a possible target for cognitive enhancement. However, it is still unknown whether inhibition of PDE5 reversed β-amyloid peptide (Aβ)-induced neuroinflammation in APP/PS1 transgenic (Tg APP/PS1) mice. The present study evaluated the cognitive behaviors, inflammatory mediators, and cGMP/PKG/pCREB signaling in 15-month-old Tg APP/PS1 mice and age-matched wild-type (WT) mice that were treated with PDE5 inhibitor sildenafil and the inhibitor of cGMP-dependent protein kinase Rp-8-Br-PET-cGMPS. In comparison with WT mice, Tg APP/PS1 mice were characterized by impaired cognitive ability, neuroinflammatory response, and down-regulated cGMP signaling. Sildenafil reversed these memory deficits and cGMP/PKG/pCREB signaling dysfunction; it also reduced both the soluble Aβ1-40 and Aβ1-42 levels in the hippocampus. These effects of sildenafil were prevented by intra-hippocampal infusion of the Rp-8-Br-PET-cGMPS. These results suggest that sildenafil could restore cognitive deficits in Tg APP/PS1 mice by the regulation of PKG/pCREB signaling, anti-inflammatory response and reduction of Aβ levels.

Evaluation of antidepressant and anxiolytic activity of phosphodiesterase 3 inhibitor - cilostazol

BACKGROUND

Cyclic nucleotide Phosphodiesterases (PDEs) are ubiquitously distributed in mammalian tissues and play a major role in cell signaling by hydrolyzing cyclic Adenosine Monophosphate (cAMP) and cyclic Guanosine Monophosphate (cGMP). Impairments in signal transduction have been implicated as possible mechanism of reduced plasticity and neuronal survival in major depressive disorders. PDE inhibitors possess a potentially powerful means to manipulate secondary messengers involved in learning, memory and mood. Cilostazol is an antiplatelet agent indicated for the treatment of intermittent claudication with peripheral artery occlusion and for the prevention of ischemic stroke worldwide. Various animal studies have reported neuroprotective, anti apoptotic, cognition and cerebral blood flow improvement properties of cilostazol.

MATERIALS AND METHODS

In this study, the antidepressant and anxiolytic effects of cilostazol were evaluated in mice using behavioral tests sensitive to clinically effective antidepressant compound.

RESULTS

Cilostazol, administered intraperitoneally (20 mg/kg), decreased immobility time of mice when subjected to forced swim test and tail suspension test as compared to standard fluoxetine (20 mg/kg). Cilostazol also produced significant decrease in the number of marbles buried as compared to fluoxetine in marble burying model.

CONCLUSION

The present study suggests that cilostazol possesses potential antidepressant and anxiolytic activity, which could be of therapeutic interest for use in patients with depressive disorders.

Effects of protein kinase A and G inhibitors on hippocampal cholinergic markers expressions in rolipram- and sildenafil-induced spatial memory improvement

Although there are number of studies showing that phosphodiesterase (PDE) 4 and 5 inhibitors affect different kinds of memory, their effects on spatial memory consolidation in conjunction with the cholinergic activity in the hippocampus have not been studied before. In the present study firstly, rats were evaluated for the effects of different doses of the PDE4 inhibitor rolipram and the PDE5 inhibitor sildenafil on spatial memory consolidation in the water maze task. Rolipram or sildenafil was daily administered intraperitoneally 3 or 0 h after the last trial of training, respectively. Then in a separate related experiment the effect of the most efficient doses of rolipram or sildenafil accompanied by an intrahippocampally injected protein kinase A (PKA) or protein kinase G (PKG) inhibitor, respectively, was examined. Finally for determination of the hippocampal cholinergic activity the protein expression of hippocampal vesicular acetylcholine transporter (VAChT) and cholineacetyltransferase (ChAT) was measured. Rolipram at 0.03 mg/kg as well as sildenafil at 3 mg/kg increased spatial memory and their enhancing effect was completely blocked following inhibition of PKA and PKG, respectively. Furthermore, none of the treatments had a significant effect on the hippocampal ChAT and VAChT levels. Our data showed that rolipram and sildenafil enhanced spatial memory consolidation in an inverted U-shaped dose-response curve. This effect is dependent on the activity of cAMP/PKA- and cGMP/PKG-mediated pathways, respectively in the hippocampus. However, we did not find evidence for a chronic increase of cholinergic activity in the observed PDE inhibitor-induced memory improvement.

Selective phosphodiesterase inhibitors: a promising target for cognition enhancement

RATIONALE

One of the major complaints most people face during aging is an impairment in cognitive functioning. This has a negative impact on the quality of daily life and is even more prominent in patients suffering from neurodegenerative and psychiatric disorders including Alzheimer's disease, schizophrenia, and depression. So far, the majority of cognition enhancers are generally targeting one particular neurotransmitter system. However, recently phosphodiesterases (PDEs) have gained increased attention as a potential new target for cognition enhancement. Inhibition of PDEs increases the intracellular availability of the second messengers cGMP and/or cAMP.

OBJECTIVE

The aim of this review was to provide an overview of the effects of phosphodiesterase inhibitors (PDE-Is) on cognition, the possible underlying mechanisms, and the relationship to current theories about memory formation.

MATERIALS AND METHODS

Studies of the effects of inhibitors of different PDE families (2, 4, 5, 9, and 10) on cognition were reviewed. In addition, studies related to PDE-Is and blood flow, emotional arousal, and long-term potentiation (LTP) were described.

RESULTS

PDE-Is have a positive effect on several aspects of cognition, including information processing, attention, memory, and executive functioning. At present, these data are likely to be explained in terms of an LTP-related mechanism of action.

CONCLUSION

PDE-Is are a promising target for cognition enhancement; the most suitable candidates appear to be PDE2-Is or PDE9-Is. The future for PDE-Is as cognition enhancers lies in the development of isoform-specific PDE-Is that have limited aversive side effects.

Selective PDE inhibitors rolipram and sildenafil improve object retrieval performance in adult cynomolgus macaques

RATIONALE

Selective phosphodiesterase (PDE) inhibitors improve the formation of hippocampus-dependent memories in several rodent models of cognition. However, studies evaluating the effects of PDE inhibition on prefrontal cortex-dependent cognition and in monkeys are rare.

OBJECTIVES

The present study investigates the effect of the PDE4 inhibitor rolipram and the PDE5 inhibitor sildenafil on object retrieval performance. Object retrieval is a prefrontal cortical-mediated task, which is likely to capture attention and response inhibition.

MATERIALS AND METHODS

The ability to retrieve a food reward from a clear box with an open side positioned in various orientations was assessed in adult male cynomolgus monkeys (Macaca fascicularis).

RESULTS

Rolipram (0.003-0.03 mg/kg, intramuscular [i.m.]) and sildenafil (0.3-3 mg/kg, i.m.) dose-dependently increased correct first reaches during difficult trials, reaching significance at 0.01 and 1 mg/kg, respectively. For both drugs, correct reaches were increased approximately 20%; that is, performance was improved from approximately 50 to approximately 70% correct.

CONCLUSIONS

Both rolipram and sildenafil improved object retrieval performance, thus demonstrating the cognition-enhancing effects of PDE inhibition on a prefrontal task of executive function in monkeys.

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

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

Effect of gestational ethanol exposure on long-term memory formation in newborn chicks

Fetal alcohol syndrome (FAS), a condition occurring in some children of mothers who have consumed alcohol during pregnancy, is characterized by craniofacial malformations, and physical and mental retardation. It is significant that even children with history of gestational ethanol exposure but relatively unaffected overall IQ performance, often exhibit learning difficulties and behavioral problems, suggestive of impaired memory formation. Hence, the specific aim of this study was to examine memory formation in chicks exposed to ethanol during early gestation toward the understanding of neurobehavioral disturbances in FAS. Chicks were exposed to alcohol on gestational days 1-3 by injection of ethanol into the airspace of freshly fertilized eggs. The effects of prenatal ethanol on physical growth and development, and memory formation were studied. The one-trial passive avoidance learning paradigm in 1-day-old chicks was used to study memory formation in these chicks. It was observed that chick embryos exposed to 10% ethanol on gestational days 1-3 had significant reduction in all body parameters when compared with appropriate controls. Further, ethanol-exposed chick embryos had significantly impaired (P<.05) long-term memory (LTM) formation after training, though short-term or intermediate-term memory formation was unimpaired. Thus, the findings of the current study demonstrate the detrimental effects of ethanol exposure during early pregnancy on developing chick embryos in general and on memory formation in particular. Hence, it is suggested that impairment in LTM could be a fundamental mechanism for learning disorders and neurobehavioral abnormalities observed in FAS.

Time-dependent involvement of cAMP and cGMP in consolidation of object memory: studies using selective phosphodiesterase type 2, 4 and 5 inhibitors

The present study investigated the time-dependent memory enhancing properties of three selective phosphodiesterase inhibitors (PDE-I) vardenafil (PDE5-I), rolipram (PDE4-I) and BAY 60-7550 (PDE2-I) in the object recognition task. In particular, the time-dependent involvement of cAMP and cGMP in memory consolidation was assessed by altering the time points of drug administration. Vardenafil (1 mg/kg, p.o.), rolipram (0.03 mg/kg, i.p.), and BAY 60-7550 (3 mg/kg, p.o.) were tested in rats with a 24 h delay between the learning and the test trial. The PDE-Is were administered at different time points, i.e. directly after, 1 h, 3 h and 6 h after the first trial. Using a 24 h interval, vardenafil only showed an effect on object memory when injected directly after trial 1, rolipram only showed an improvement when injected 3 h after trial 1 and BAY 60-7550 improved memory when injected either directly after or 3 h after trial 1. No treatment effects were found when the compounds were administered 1 h or 6 h after the first trial. Our results extend our previous data that different types of PDE-Is affect different stages of memory consolidation. Moreover, the present study provides further support that selective PDE-Is can influence memory consolidation in a time-dependent manner, assumingly by elevating central cAMP and cGMP levels.

New perspectives on the mechanisms through which nitric oxide may affect learning and memory processes

Nitric oxide (NO) has been well established as a molecule necessary for memory consolidation. Interestingly, the majority of research has focused on only a single mechanism through which NO acts, namely the up-regulation of guanylate cyclase (GC). However, since NO and NO-derived reactive nitrogen species are capable of interacting with a broad array of enzymes, ion channels and receptors, a singular focus on GC appears short-sighted. Although NO inhibits the action of a number of molecules there are four, in addition to GC, which are up-regulated by the direct presence of NO, or NO-derived radicals, and implicated in memory processing. They are: cyclic nucleotide-gated channels; large conductance calcium-activated potassium channels; ryanodine receptor calcium release (RyR) channels; and the enzyme mono(ADP-ribosyl) transferase. This review presents evidence that not only are these four molecules worthy of investigation as GC-independent mechanisms through which NO may act, but that behavioural evidence already exists suggesting a relationship between NO and the RyR channel.