Selective blockade of phosphodiesterase types 2, 5 and 9 results in cyclic 3'5' guanosine monophosphate accumulation in retinal pigment epithelium cells

Changes in Posterior Ocular Structures in Individuals Using Phosphodiesterase 5 Inhibitor

PURPOSE

To examine posterior ocular structures with optical coherence tomography (OCT) in individuals using a phosphodiesterase 5 inhibitor (PDI, tadalafil).

METHOD

This prospective study included 26 eyes of 26 patients who used 1 tablet of 5-mg tadalafil regularly every day for 1 month due to erectile dysfunction. The routine ophthalmological examinations of the participants were performed at the pre-tadalafil and post-tadalafil first-month visits. At both visits, OCT was used to measure the central retinal thickness (CRT), ganglion cell layer + inner plexiform layer (GCL + IPL) thicknesses, and peripapillary retinal nerve fiber layer (pRNFL; average and superior, temporal, inferior, and nasal quadrants) thicknesses. The disc area, rim area, average and vertical cup/disc ratio, and cup volume of the optic disc head were evaluated. Choroidal thickness was measured from five points: the subfoveal area and the nasal and temporal areas 500 and 1500 microns from the fovea. Choroidal vascular area values and choroidal vascular index (CVI) were calculated using a special binarization technique.

RESULTS

The mean age of the patients was 56 ± 8(range 34-72) years. No significant difference was detected in the CRT,GCL + IPL thicknesses,or pRNFL thicknesses in any of the quadrants before and after tadalafil use. The optic disc head measurements and choroidal thickness values measured from five points were similar between the two visits. The luminal choroidal area was 0.15 ± 0.04 mm2 before tadalafil use and 0.17 ± 0.05 mm2 after 1-month tadalafil use, with no statistically significant difference. The remaining choroidal vascular parameters, namely the stromal and total choroidal area and CVI values, were similar between the two visits.

CONCLUSION

This study showed no significant change in the posterior ocular structures in individuals using tadalafil regular daily use for 1 month due to erectile dysfunction.

Choroidal and retinal alteration after long-term use of tadalafil: a prospective non-randomized clinical trial

OBJECTIVES

The purpose of this study is to investigate choroidal and retinal vascular features in patients taking PDE5is by measuring dynamic vascular alterations and neurostructural features of the retina before and after oral tadalafil administration.

METHODS

The current clinical research involved 22 patients treated with tadalafil 20 mg on alternate days (OAD) after nerve-sparing robotic radical prostatectomy (NS-RARP) for prostate cancer. Patients underwent SD-OCT to assess ganglion cell complex (GCC), retinal nerve fiber layer (RNFL), and subfoveal choroidal thickness (SFCT), as well as OCTA to assess superficial capillary plexus (SCP), deep capillary plexus (DCP), choriocapillaris (CC), foveal avascular zone (FAZ), and radial peripapillary capillary thickness (RPC). All patients were evaluated at baseline (t0), and 3 (t1) and 6 (t2) months after the use of oral tadalafil.

RESULTS

A statistically significant reduction in DCP and CC vessel density was found at t2 compared to baseline. According to the SFCT parameter, a statistically significant increase was observed from t0 to t1, and from t1 to t2. GCC parameter increased at t2 compared to baseline in a statistically significant way. No statistically significant differences were recorded between t0, t1 and t2 for the SCP, RPC, FAZ area, RNFL parameter.

CONCLUSIONS

Retinal and optic disc toxicity may be detected using modifications of capillary vessel density. Further studies are needed to detect the possible progression or regression of ocular or systemic vascular complications in long-term follow-up.

Ophthalmologic profile of patients with systemic sclerosis

PURPOSE

To study the ophthalmologic manifestations of systemic sclerosis (SSc) and its correlation with autoantibody profile.

METHODS

A cross-sectional study on 200 eyes of 100 consecutive adult patients diagnosed with SSc was performed at a tertiary care center in Northern India. The examination of ocular adnexa, anterior segment, and posterior segment with slit-lamp biomicroscopy, tear film break-up time (TBUT), Schirmer's II test, and choroidal thickness measurement by swept-source ocular coherence tomography was done. Autoantibody profile was available for 85 patients, and its statistical association with the ocular examination findings was analyzed.

RESULTS

In total, 100 patients (93 females and 7 males) were included. The mean age was 45.11 ± 11.68 years, and the mean disease duration was 6.93 ± 3.68 years. Meibomian gland disease was more commonly found in patients with the diffuse subtype of SSc ( P = 0.037). Choroidal thickness was increased in 34% and decreased in 7% (reference range = 307 ± 79 µm) patients. Reduced TBUT, meibomian gland dysfunction, and eyelid stiffness had a statistically significant association with the presence of anti-Scl-70 antibody ( P = 0.003, <0.0001, and 0.004, respectively). These patients had ocular fatigue, foreign body sensation, and burning sensation. No significant association was noted with the presence of SS-A/Ro and SS-B/La antibodies.

CONCLUSION

This study highlights the need for an active comprehensive ophthalmic evaluation. Approximately 75% of the patients in our cohort had ocular involvement to varying extent. An isolated presence of anti-Scl70 antibody was also found to have a positive association with dry eye disease.

The Sleep Quality- and Myopia-Linked PDE11A-Y727C Variant Impacts Neural Physiology by Reducing Catalytic Activity and Altering Subcellular Compartmentalization of the Enzyme

Recently, a Y727C variant in the dual-specific 3',5'-cyclic nucleotide phosphodiesterase 11A (PDE11A-Y727C) was linked to increased sleep quality and reduced myopia risk in humans. Given the well-established role that the PDE11 substrates cAMP and cGMP play in eye physiology and sleep, we determined if (1) PDE11A protein is expressed in the retina or other eye segments in mice, (2) PDE11A-Y7272C affects catalytic activity and/or subcellular compartmentalization more so than the nearby suicide-associated PDE11A-M878V variant, and (3) Pde11a deletion alters eye growth or sleep quality in male and female mice. Western blots show distinct protein expression of PDE11A4, but not PDE11A1-3, in eyes of Pde11a WT, but not KO mice, that vary by eye segment and age. In HT22 and COS-1 cells, PDE11A4-Y727C reduces PDE11A4 catalytic activity far more than PDE11A4-M878V, with both variants reducing PDE11A4-cAMP more so than PDE11A4-cGMP activity. Despite this, Pde11a deletion does not alter age-related changes in retinal or lens thickness or axial length, nor vitreous or anterior chamber depth. Further, Pde11a deletion only minimally changes refractive error and sleep quality. That said, both variants also dramatically alter the subcellular compartmentalization of human and mouse PDE11A4, an effect occurring independently of dephosphorylating PDE11A4-S117/S124 or phosphorylating PDE11A4-S162. Rather, re-compartmentalization of PDE11A4-Y727C is due to the loss of the tyrosine changing how PDE11A4 is packaged/repackaged via the trans-Golgi network. Therefore, the protective impact of the Y727C variant may reflect a gain-of-function (e.g., PDE11A4 displacing another PDE) that warrants further investigation in the context of reversing/preventing sleep disturbances or myopia.

The sleep quality- and myopia-linked PDE11A-Y727C variant impacts neural physiology by reducing catalytic activity and altering subcellular compartmentalization of the enzyme

Recently, a Y727C variant in the dual-specific 3',5'-cyclic nucleotide phosphodiesterase 11A (PDE11A-Y727C) was linked to increased sleep quality and reduced myopia risk in humans. Given the well-established role that the PDE11 substrates cAMP and cGMP play in eye physiology and sleep, we determined if 1) PDE11A protein is expressed in the retina or other eye segments in mouse, 2) PDE11A-Y7272C affects catalytic activity and/or subcellular compartmentalization more so than the nearby suicide-associated PDE11A-M878V variant, and 3) Pde11a deletion alters eye growth or sleep quality in male and female mice. Western blots show distinct protein expression of PDE11A4, but not PDE11A1-3, in eyes of Pde11a WT-but not KO mice-that vary by eye segment and age. In HT22 and COS-1 cells, PDE11A4-Y727C reduces PDE11A4 catalytic activity far more than PDE11A4-M878V, with both variants reducing PDE11A4-cAMP more so than PDE11A4-cGMP activity. Despite this, Pde11a deletion does not alter age-related changes in retinal or lens thickness, axial length, nor vitreous or anterior chamber depth. Further, Pde11a deletion only minimally changes refractive error and sleep quality. That said, both variants also dramatically alter the subcellular compartmentalization of human and mouse PDE11A4, an effect occurring independently of dephosphorylating PDE11A4-S117/S124 or phosphorylating PDE11A4-S162. Rather, re-compartmentalization of PDE11A4-Y727C is due to the loss of the tyrosine changing how PDE11A4 is packaged/repackaged via the trans-Golgi network. Therefore, the protective impact of the Y727C variant may reflect a gain-of-function (e.g., PDE11A4 displacing another PDE) that warrants further investigation in the context of reversing/preventing sleep disturbances or myopia.

Retinal and Optic Disc Vascular Changes in Patients Using Long-Term Tadalafil: A Prospective Non-Randomized Matched-Pair Study

Retinal, choroidal and optic disc vascularity has never been evaluated in patients taking PDE5is long-term. The aim of our study was to evaluate the neurostructural and vascular changes after long-term use of tadalafil, using spectral domain (SD)-optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA). In the present clinical trial, 27 patients who have been taking tadalafil 20 mg on alternate days (OAD) for at least 6 months (Group A) were enrolled. The matched group consisted of 27 healthy men (Group B). Both groups of patients underwent SD-OCT to study ganglion cell complex (GCC), retinal nerve fiber layer (RNFL) and choroidal thickness and OCTA for the evaluation of superficial capillary plexus (SCP), deep capillary plexus (DCP), choriocapillaris (CC) and radial peripapillary capillary (RPC). A reduction in SCP, DCP and RPC vessel density was found in patients using tadalafil long-term. Retinal and optic disc toxicity may be detected using modifications of capillary vessel density. Further studies are needed to investigate the possibility of a causal association.

A Surrogate Matrix-Based Approach Toward Multiplexed Quantitation of an sGC Stimulator and cGMP in Ocular Tissue and Plasma

A liquid chromatography-tandem mass spectrometry assay was developed and qualified for the multiplexed quantitation of a small molecule stimulator of soluble guanylate cyclase (sGC) and its target engagement biomarker, 3',5'-cyclic guanosine monophosphate (cGMP), in ocular tissues and plasma from a single surrogate matrix calibration curve. A surrogate matrix approach was used in this assay due to the limited quantities of blank ocular matrices in a discovery research setting. After optimization, the assay showed high accuracy, precision, and recovery as well as parallelism between the surrogate matrix and the biological matrices (rabbit plasma, vitreous, and retina-choroid). This assay provided pharmacokinetic and target engagement data after intravitreal administration of the sGC stimulator. The nitric oxide-sGC-cGMP pathway is a potential target to address glaucoma. Increasing sGC-mediated production of cGMP could improve aqueous humor outflow and ocular blood flow. The sGC stimulator showed dose-dependent exposure in rabbit vitreous, retina-choroid, and plasma. The cGMP exhibited a delayed yet sustained increase in vitreous humor but not retina-choroid. Multiplexed measurement of both pharmacokinetic and target engagement analytes reduced animal usage and provided improved context for interpreting PK and PD relationships.

Can subfoveal choroidal thickness replace subjective tests in patients using tadalafil to treat erectile dysfunction?

We aimed to determine the effect on choroidal thickness of daily 5 mg tadalafil use in patients with erectile dysfunction (ED) and to evaluate agreement between short form of International Index of Erectile Function (IIEF 1-5, 15) scores and choroidal thickness during follow-up. Enhanced depth imaging spectral domain-optical coherence tomography (EDI-OCT) was used to measure full choroidal thickness in the subfoveal area, choroidal thickness (CT) and small-choroidal-vessel-layer (SCVL) thickness. Thirty of the 45 patients included complete their follow-ups and exhibited medication continuity. Patients were divided into two groups, five (16.7%) with ED at any level at third-month follow-up, and 25 (83.3%) with no ED, and subgroup analysis was then performed. Median changes in SCVL thickness at first- and sixth-month follow-ups were 20.5 µm versus 9.0 μm (p = .001) and 23.5 µm versus 12.5 µm (p = .005) in patients without and with ED respectively. The SCVL thickness increased by 20 μm compared with the baseline level, indicating an improvement in the patient's complaints of erectile dysfunction. The level of increase in SCVL thickness can be a useful and objective guide to clinicians if they cannot be present when the IIEF questionnaire is administered.

Hydrogen sulfide: a gaseous signaling molecule modulates tissue homeostasis: implications in ophthalmic diseases

Hydrogen sulfide (H2S) serves as a gasotransmitter in the regulation of organ development and maintenance of homeostasis in tissues. Its abnormal levels are associated with multiple human diseases, such as neurodegenerative disease, myocardial injury, and ophthalmic diseases. Excessive exposure to H2S could lead to cellular toxicity, orchestrate pathological process, and increase the risk of various diseases. Interestingly, under physiological status, H2S plays a critical role in maintaining cellular physiology and limiting damages to tissues. In mammalian species, the generation of H2S is catalyzed by cystathionine beta-synthase (CBS), cystathionine gamma-lyase (CSE), 3-mercapto-methylthio pyruvate aminotransferase (3MST) and cysteine aminotransferase (CAT). These enzymes are found inside the mammalian eyeballs at different locations. Their aberrant expression and the accumulation of substrates and intermediates can change the level of H2S by orders of magnitude, causing abnormal structures or functions in the eyes. Detailed investigations have demonstrated that H2S donors' administration could regulate intraocular pressure, protect retinal cells, inhibit oxidative stress and alleviate inflammation by modulating the function of intra or extracellular proteins in ocular tissues. Thus, several slow-releasing H2S donors have been shown to be promising drugs for treating multiple diseases. In this review, we discuss the biological function of H2S metabolism and its application in ophthalmic diseases.

Experimental and investigational phosphodiesterase inhibitors in development for asthma

INTRODUCTION

Severe, inadequately-controlled asthma remains a clinical challenge. For this reason, clinical trials and preclinical experimental studies on novel agents as an add-on therapies continue emerge. Phosphodiesterases (PDEs) are enzymes that regulate the function of immune cells by hydrolyzing cyclic guanosine monophosphate/cGMP and cyclic adenosine monophosphate/cAMP. PDEs are divided into subfamilies [PDE3, PDE4, PDE5 and PDE7] which are mainly found in the respiratory tract. Inhibitors of PDEs have already been approved for COPD and pulmonary hypertension.

AREAS COVERED

The role of PDE inhibitors in asthma treatment and the possible mechanism of action via their anti-inflammatory and/or bronchodilating effect are discussed.

EXPERT OPINION

Novel PDE inhibitors exhibiting fewer adverse events may have a role as add-on therapies in asthma treatment in the future. More clinical trials are necessary to prove their efficacy and evaluate their safety profile before approval by regulatory bodies is granted.

The Phosphodiesterase 9 Inhibitor PF-04449613 Promotes Dendritic Spine Formation and Performance Improvement after Motor Learning

The cyclic nucleotide cGMP is an intracellular second messenger with important roles in neuronal functions and animals' behaviors. The phosphodiesterases (PDEs) are a family of enzymes that hydrolyze the second messengers cGMP and cAMP. Inhibition of phosphodiesterase 9 (PDE9), a main isoform of PDEs hydrolyzing cGMP, has been shown to improve learning and memory as well as cognitive function in rodents. However, the role of PDE9 in regulating neuronal structure and function in vivo remains unclear. Here we used in vivo two-photon microscopy to investigate the effect of a selective PDE9 inhibitor PF-04449613 on the activity and plasticity of dendritic spines of layer V pyramidal neurons in the mouse primary motor cortex. We found that administration of PF-04449613 increased calcium activity of dendrites and dendritic spines of layer V pyramidal neurons in mice under resting and running conditions. Chronic treatment of PF-04449613 over weeks increased dendritic spine formation and elimination under basal conditions. Furthermore, PF-04449613 treatment over 1-7 days increased the formation and survival of new spines as well as performance improvement after rotarod motor training. Taken together, our studies suggest that elevating the level of cGMP with the PDE9 inhibitor PF-04449613 increases synaptic calcium activity and learning-dependent synaptic plasticity, thereby contributing to performance improvement after learning. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 00: 000-000, 2018.

An immunohistochemical and ultrastructural analysis of the retina in tadalafil (Cialis) treated rats

Tadalafil (Cialis) is one of the most commonly used phosphodiesterase type5 (PDE5) inhibitors. This work aimed to analyze the histological and ultrastructural changes provoked by chronic tadalafil administration in the rat retina, correlate between such changes and PDE5 immunoexpression and to evaluate the possible reversibility of these changes. Thirty Sprague Dawley male rats were randomly distributed into 3 groups. Control group; given 1 ml distilled water daily for 6 weeks. Tadalafil group; given tadalafil in a daily dose of 2.6 mg/kg for 6 weeks. Withdrawal group; given tadalafil 2.6 mg/kg daily for 6 week followed by a withdrawal period of 4 weeks. Retinal specimens were prepared for histological, ultrastructural and immunohistochemical study using anti-PDE5 and anti-Bcl-2 antibodies. Morphometric and statistical studies were performed. Tadalafil group displayed a significant reduction in retinal thickness, diminished cell population of outer and inner nuclear layers, dilated blood capillaries and a significant decline in the number of ganglion cells. Significant reductions of both PDE5 and Bcl-2 immunoexpression were observed. At the ultrastructural level, the photoreceptors showed spacing of outer segments and disorganized membranous discs. Retinal neurons showed ultrastructural degenerative changes in the form of shrunken irregular nuclei, dilated rER, and disrupted mitochondria. Withdrawal group revealed preservation of histological structure and partial restoration of retinal thickness, retinal cells ultrastructure, and PDE5 and Bcl-2 immunoexpressions. In conclusion, chronic use of tadalafil could induce reversible apoptotic and degenerative changes in retinal neurons due to its inhibitory effect on PDE5 expression which affects the metabolism and viability of retinal cells.

Phosphodiesterase 9 (PDE9) regulates bovine tracheal smooth muscle relaxation

The present study was designed to clarify phosphodiesterase 9 (PDE9) expression in bovine tracheal smooth muscle tissue, and to elucidate that PDE9 may contribute to the regulation of airway relaxation. PDE9 mRNA expression was detected in bovine tracheal smooth muscle. Sodium nitroprusside (an NO donor) and BAY 73-6691 (a selective PDE9 inhibitor) reduced high K⁺- and carbachol-induced contraction. BAY 73-6691 relaxed tracheal tissue on the same level with vardenafil (a selective PDE5 inhibitor). These results support our hypothesis that PDE9 plays functional role in the tracheal smooth muscle relaxation. PDE9 inhibitors are expected to be a novel target of the add-on treatment of airway hyperresponsiveness.

Pathophysiology of visual disorders induced by phosphodiesterase inhibitors in the treatment of erectile dysfunction

Aim

The aim of this review was to summarize the ocular action of the most common phosphodiesterase (PDE) inhibitors used for the treatment of erectile dysfunction and the subsequent visual disorders.

Method

This is a literature review of several important articles focusing on the pathophysiology of visual disorders induced by PDE inhibitors.

Results

PDE inhibitors have been associated with ocular side effects, including changes in color vision and light perception, blurred vision, transient alterations in electroretinogram (ERG), conjunctival hyperemia, ocular pain, and photophobia. Sildenafil and tadalafil may induce reversible increase in intraocular pressure and be involved in the development of non-arteritic ischemic optic neuropathy. Reversible idiopathic serous macular detachment, central serous chorioretinopathy, and ERG disturbances have been related to the significant impact of sildenafil and tadalafil on retinal perfusion.

Discussion

So far, PDE inhibitors do not seem to cause permanent toxic effects on chorioretinal tissue and photoreceptors. However, physicians should write down any visual symptom observed during PDE treatment and refer the patients to ophthalmologists.

PDE9A is expressed in the inner retina and contributes to the normal shape of the photopic ERG waveform

The ubiquitous second messenger cGMP is synthesized by guanylyl cyclase and hydrolyzed by phosphodiesterase (PDE). cGMP mediates numerous signaling pathways in multiple tissues. In the retina, cGMP regulates signaling in nearly every cell class including photoreceptors, bipolar cells, amacrine cells, and ganglion cells. In order to understand the specific role of cGMP and its regulating enzymes in different cell types, it is first necessary to localize these components and dissect their influence on the circuits. Here we tested the contribution of PDE9A to retinal processing by recording the electroretinograms (ERG) of PDE9A^™/™ (KO) mice and by localizing the enzyme. We found that while the scotopic ERG of KO was the same as that of wild type (WT) in both amplitude and kinetics, the photopic ERG was greatly affected. The greatest effect was on the recovery of the b-wave; the falling phase and the b-wave duration were significantly longer in the KO mice for all photopic stimuli (UV, green, or saturating white flashes). The rising phase was slower in KO than in WT for UV and green stimuli. For certain stimuli, amplitudes of both the a- and b-waves were smaller than in WT. Using Lac-Z expression in KO retinas as a reporter for PDE9A expression pattern, we found that PDE9A is localized to GABA-positive and GABA-negative amacrine cells, and likely also to certain types of ganglion cells. Our results indicate that PDE9A, by controlling the level of cGMP, modulates inhibitory processes within the cone pathway. We speculate that these circuits involve NO/cGMP signaling pathways.

Inhibition of phosphodiestrase 9 induces cGMP accumulation and apoptosis in human breast cancer cell lines, MCF-7 and MDA-MB-468

OBJECTIVES

Phosphodiesterase 9 (PDE9) is a major isoform of phosphodiesterase hydrolysing cGMP and plays a key role in proliferation of cells, their differentiation and apoptosis, via intracellular cGMP signalling. The study described here was designed to investigate expression, activity and apoptotic effect of PDE9 on human breast cancer cell lines, MCF-7 and MDA-MB-468.

MATERIALS AND METHODS

Activity and expression of PDE9 were examined using colorimetric cyclic nucleotide phosphodiesterase assay and real-time RT-PCR methods respectively; cGMP concentration was also measured. MTT viability test, annexin V-FITC staining, Hoechst 33258 staining and caspase3 activity assay were used to detect apoptosis.

RESULTS

Treatment of both cell lines with BAY 73-6691 lead to reduction in PDE9 mRNA expression, PDE9 cGMP-hydrolytic activity and elevation of the intracellular cGMP response. BAY 73-6691 significantly reduced cell proliferation in a dose- and time-dependent manner and caused marked increase in apoptosis through caspase3 activation.

CONCLUSION

Our results revealed that BAY 73-6691 induced apoptosis in these breast cancer cell lines through the cGMP pathway. These data suggest that BAY 73-6691 could be utilized as an agent in treatment of breast cancer.

cGMP-dependent protein kinases and cGMP phosphodiesterases in nitric oxide and cGMP action

To date, studies suggest that biological signaling by nitric oxide (NO) is primarily mediated by cGMP, which is synthesized by NO-activated guanylyl cyclases and broken down by cyclic nucleotide phosphodiesterases (PDEs). Effects of cGMP occur through three main groups of cellular targets: cGMP-dependent protein kinases (PKGs), cGMP-gated cation channels, and PDEs. cGMP binding activates PKG, which phosphorylates serines and threonines on many cellular proteins, frequently resulting in changes in activity or function, subcellular localization, or regulatory features. The proteins that are so modified by PKG commonly regulate calcium homeostasis, calcium sensitivity of cellular proteins, platelet activation and adhesion, smooth muscle contraction, cardiac function, gene expression, feedback of the NO-signaling pathway, and other processes. Current therapies that have successfully targeted the NO-signaling pathway include nitrovasodilators (nitroglycerin), PDE5 inhibitors [sildenafil (Viagra and Revatio), vardenafil (Levitra), and tadalafil (Cialis and Adcirca)] for treatment of a number of vascular diseases including angina pectoris, erectile dysfunction, and pulmonary hypertension; the PDE3 inhibitors [cilostazol (Pletal) and milrinone (Primacor)] are used for treatment of intermittent claudication and acute heart failure, respectively. Potential for use of these medications in the treatment of other maladies continues to emerge.

Insight into binding of phosphodiesterase-9A selective inhibitors by crystal structures and mutagenesis

PDE9 inhibitors have been studied as therapeutics for treatment of cardiovascular diseases, diabetes, and neurodegenerative disorders. To illustrate the inhibitor selectivity, the crystal structures of the PDE9A catalytic domain in complex with the enantiomers of PDE9 inhibitor 1-(2-chlorophenyl)-6-(3,3,3-trifluoro-2-methylpropyl)-1H-pyrazolo[3,4-d]pyrimidine-4(5H)-one ((R)-BAY73-6691 or (S)-BAY73-6691, 1r or 1s) were determined and mutagenesis was performed. The structures showed that the fluoromethyl groups of 1r and 1s had different orientations while the other parts of the inhibitors commonly interacted with PDE9A. These differences may explain the slightly different affinity of 1r (IC(50) = 22 nM) and 1s (IC(50) = 88 nM). The mutagenesis experiments revealed that contribution of the binding residues to the inhibitor sensitivity varies dramatically, from few-fold to 3 orders of magnitude. On the basis of the crystal structures, a hypothesized compound that simulates the recently published PDE9 inhibitors was modeled to provide insight into the inhibitor selectivity.

Immunohistochemical localization of phosphodiesterase 2A in multiple mammalian species

Phosphodiesterases (PDEs) comprise a family of enzymes that regulate the levels of cyclic nucleotides, key second messengers that mediate a diverse array of functions. PDE2A is an evolutionarily conserved cGMP-stimulated cAMP and cGMP PDE. In the present study, the regional and cellular distribution of PDE2A in tissues of rats, mice, cynomolgus monkeys, dogs, and humans was evaluated by immunohistochemistry. A polyclonal antibody directed to the C-terminal portion of PDE2A specifically detected PDE2A by Western blotting and by immunohistochemistry. The pattern of PDE2A immunoreactivity (ir) was consistent across all species. Western blot analysis demonstrated that PDE2A was most abundant in the brain relative to peripheral tissues. PDE2A ir was heterogeneously distributed within brain and was selectively expressed in particular peripheral tissues. In the brain, prominent immunoreactivity was apparent in components of the limbic system, including the isocortex, hippocampus, amygdala, habenula, basal ganglia, and interpeduncular nucleus. Cytoplasmic PDE2A staining was prominent in several peripheral tissues, including the adrenal zona glomerulosa, neurons of enteric ganglia, endothelial cells in all organs, lymphocytes of spleen and lymph nodes, and pituitary. These studies suggest that PDE2A is evolutionarily conserved across mammalian species and support the hypothesis that the enzyme plays a fundamental role in signal transduction.

Cyclic GMP in the pig vitreous and retina after experimental retinal detachment

PURPOSE

Earlier studies have revealed a decreased level of cGMP in vitreous fluid obtained from patients with a retinal detachment. To further investigate this phenomenon, we developed an experimental retinal detachment model in pigs.

METHODS

Experimental unilateral retinal detachments were induced in pig eyes by subretinal injection of 0.25% sodium hyaluronate. Fourteen days later the vitreous and retinas were analyzed for cGMP expression. Following enucleation, the retinas were incubated in the presence of a nonselective phosphodiesterase inhibitor (IBMX), and the particulate guanylyl cyclase stimulator atrial natriuretic peptide (ANP) or the soluble guanylyl cyclase stimulator sodium nitroprusside (SNP). cGMP was visualized in retinal wholemounts by immunochemistry combined with a computer based stereology system. cGMP levels in vitreous were determined by ELISA.

RESULTS

The mean vitreous cGMP level in pig eyes with a retinal detachment (1.45 pmol/ml) was significantly lower compared to the mean level of cGMP in healthy pig eyes (4.61 pmol/ml; p=0.028 was considered significant). In the inner retina, ANP as well as SNP induced cGMP immunoreactivity in both detached and healthy retinas. After incubation with ANP, cGMP could also be detected in the outer nuclear layer of the detached retina, whereas this was not the case in the normal retina.

CONCLUSIONS

Experimental retinal detachment in the pig eye leads to a decrease of cGMP levels in vitreous similar to that observed in clinical studies. This model may be helpful to analyze the mechanisms involved in cGMP dynamics following retinal detachment.