Expression of the PDE5 enzyme on human retinal tissue: new aspects of PDE5 inhibitors ocular side effects

A real-world pharmacovigilance study of FDA adverse event reporting system events for sildenafil

BACKGROUND

Sildenafil, a selective inhibitor of phosphodiesterase type 5 (PDE5), is widely used for the treatment of erectile dysfunction (ED). However, the safety profile of sildenafil, including adverse event (AEs), requires comprehensive evaluation.

METHODS

This retrospective pharmacovigilance study aimed to evaluate AEs linked to sildenafil by analyzing data sourced from the FDA Adverse Event Reporting System (FAERS) database. A case/non-case design was utilized, and various algorithms including the reporting odds ratio (ROR), the proportional reporting ratio (PRR), the Bayesian confidence propagation neural network (BCPNN), and the multiitem gamma Poisson shrinker (MGPS) were employed to measure the signals indicating the presence of sildenafil-related AEs.

RESULTS

Among 339,230 reports, 33,692 specifically mentioned sildenafil use. Most of AEs occurred in males over 60 years old. The United States accounted for the highest proportion of reported AEs. Severe outcomes, including death, disability, and life-threatening events, were reported. Significant system organ class (SOC) included "Reproductive system and breast disorders" (SOC: 10038604), "Neoplasms benign, malignant and unspecified" (SOC: 10038738), "Vascular disorders" (SOC: 10047065), and "Blood and lymphatic system disorders" (SOC: 10005329). Noteworthy preferred terms (PTs) associated with sildenafil included "Vision blurred," "Flushing," "sudden hearing loss," "Painful erection," and "Priapism." Unexpected AEs, such as "Malignant melanoma," "Pulmonary hypertension," "Malignant melanoma in situ," "Pulmonary arterial hypertension," "Metastatic malignant melanoma," "Malignant melanoma stage III," "Malignant melanoma stage II," "Acquired hemophilia," "Aortic dissection rupture," and "Intracranial artery dissection" were also identified.

CONCLUSIONS

These findings emphasize the importance of monitoring and understanding the potential risks associated with sildenafil. Further investigation is warranted to validate these associations and address previously unrecognized safety concerns.

Histopathology and electron microscopy evaluation of the sildenafil effect on diabetic rats' retinae

PURPOSE

Although there is increasing evidence that phosphodiesterase-5 (PDE-5) inhibitors modify the effect of diabetes on different tissues, its effect on diabetic retinopathy is not well studied.

METHODS

Forty male Sprague-Dawley (SD) rats were divided into four groups: group I = control group that received no treatment; group II (diabetic group), in which diabetes was induced by a single streptozotocin injection; group III (sildenafil small dose, SSD), in which diabetes was similarly introduced (however, rats received daily oral 1 mg/kg sildenafil citrate (SC) for 3 months); and group IV (sildenafil large dose, SLD), which was as in group 3, but SC was 2.5 mg/kg. After 3 months, globes were removed and retinae were dissected; one globe from each rat was examined by light microscopy (LM), and the other by electron microscopy (EM).

RESULTS

In contrast to the control group, diabetic rats in group II demonstrated well-established diabetic changes in the form of capillary congestion, decreased cell population, hyaline changes of capillary walls, and degenerated nerve fiber layer by LM. Similarly, EM demonstrated photoreceptor degeneration, mitochondrial cristolysis, and vacuolated depleted cells among other features in group II. These diabetic features were less prominent in group III and nearly absent in group IV.

CONCLUSION

SC use in the early stages of DR may prevent/delay diabetic retinopathy development or progression in diabetic rat models, an effect that seems to be dose-related.

Exploring the Multifaceted Potential of Sildenafil in Medicine

Phosphodiesterase type 5 (PDE5) is pivotal in cellular signalling, regulating cyclic guanosine monophosphate (cGMP) levels crucial for smooth muscle relaxation and vasodilation. By targeting cGMP for degradation, PDE5 inhibits sustained vasodilation. PDE5 operates in diverse anatomical regions, with its upregulation linked to various pathologies, including cancer and neurodegenerative diseases. Sildenafil, a selective PDE5 inhibitor, is prescribed for erectile dysfunction and pulmonary arterial hypertension. However, considering the extensive roles of PDE5, sildenafil might be useful in other pathologies. This review aims to comprehensively explore sildenafil's therapeutic potential across medicine, addressing a gap in the current literature. Recognising sildenafil's broader potential may unveil new treatment avenues, optimising existing approaches and broadening its clinical application.

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.

Chronic sildenafil citrate use decreases retinal vascular endothelial growth factor expression in diabetic rats: a pilot study

BACKGROUND

Sildenafil citrate (SC) attenuates endothelial dysfunction. However, its effects on diabetic retinopathy (DR), which is mainly a microvascular disease, remain unclear. Vascular endothelial growth factor (VEGF) is known to be a critical mediator of DR. Therefore, we investigated the effects of SC on diabetic retina by measuring VEGF levels.

METHODS

In this study, twenty-eight rats were divided into the following groups: group I, the control group; group II, rats with streptozotocin-induced diabetes; group III, rats with streptozotocin-induced diabetes receiving daily oral sildenafil at 1 mg/kg; and group IV, rats with streptozotocin-induced diabetes receiving high-dose daily sildenafil at 2.5 mg/kg. After 3 months, VEGF was measured in the retina specimen in one eye and the vitreous body in the other eye by immunohistochemistry and enzyme-linked immunosorbent assay, respectively.

RESULTS

We found that VEGF expression in the retina was low in all rats from groups I and IV and in 30% of rats from group III; 80% of rats in group II demonstrated high VEGF expression in the retinae (P < 0.001). VEGF concentrations in the vitreous body samples were 32 ± 2, 61 ± 4, 44 ± 5, and 36 ± 3 pg/l in groups I-IV, respectively (P < 0.001).

CONCLUSION

VEGF decreased significantly in the eyes of diabetic rats after chronic oral sildenafil citrate treatment. SC may have a modifying/attenuating effect on DR. However, further studies are needed to evaluate its use as an adjunctive treatment.

Long-term follow-up of retinal morphology and physiology after 2000 mg sildenafil overdose as a means of attempted suicide: a case report

Background

Few case reports have described sildenafil overdose, particularly ingestion of > 1000 mg, and overdose-induced changes in visual function remain unclear. We report retinal morphology, retinal sensitivity, and findings of electrophysiological evaluation over long-term follow-up in a case of sildenafil overdose (2000 mg).

Case presentation

Our patient developed visual abnormalities in the paracentral visual field accompanied by photophobia, decreased contrast sensitivity, and difficulty distinguishing colors in both eyes, 8 hours after the sildenafil overdose. These symptoms did not improve throughout the course, and although abnormalities of retinal morphology and sensitivity, as well as the electroretinogram findings showed slight improvement, the patient did not recover completely at 6-month follow-up.

Conclusions

We observed that high-dose sildenafil ingestion leads to retinal toxicity; the ocular abnormalities may persist for at least 6 months. Optical coherence tomography, Humphrey perimetry, microperimetry, and multifocal electroretinography are useful to quantitatively monitor temporal changes.

Sildenafil in ophthalmology: An update

Sildenafil citrate, a selective oral phosphodiesterase 5 inhibitor, is a widely used drug for erectile dysfunction that acts by elevating cGMP levels and causing smooth muscle relaxation. It also has 10% activity against PDE6, a key enzyme in phototransduction cascade in the retina. Recent ocular imaging developments have further revealed the influence of sildenafil on ocular hemodynamics, particularly choroidal perfusion. Choroidal thickness is increased, and choroidal perfusion is also enhanced by autoregulatory mechanisms that are further dependent on age and microvascular abnormalities. Studies demonstrating high intraocular pressure via a "parallel pathway" from increased choroidal volume and blood flow to the ciliary body have challenged previous concepts. Another new observation is the effect of sildenafil on bipolar cells and cyclic-nucleotide gated channels. We discuss potential deleterious effects (central serous chorioretinopathy, glaucoma, ischemic optic neuropathy, and risks to recessive carriers of retinitis pigmentosa), potential beneficial effects (ameliorate choroidal ischemia, prevent thickening of Bruch membrane, and promote recovery of the ellipsoid zone) in macular degeneration, as well as potential drug interactions of sildenafil.

Evaluation of Retinal and Choroidal Microcirculation Alterations After a Single Dose of Oral 5-mg Tadalafil: A Prospective Pilot Optical Coherence Tomography Angiography Study

Purpose: To evaluate the effects of a single dose of oral 5-mg tadalafil on macular microcirculation as measured using optical coherence tomography (OCT) and angiography (OCTA) in healthy volunteers. Methods: Twenty-two healthy, middle-aged, sexually active, and male health care worker volunteers were included in this prospective study. All volunteers have a history of occasionally using off-label 5 mg tadalafil to enhance sexual performance. Superficial and deep capillary plexus vascular densities, foveal avascular zone parameters, outer retina, and choriocapillaris flow areas were performed using the OCTA, and subfoveal-choroidal thickness (CT) was performed by using the OCT. Measurements were performed preintake, 30 min, 1, 4, 24 h, 2, 3, 4, and 7 days after the intake of tadalafil off-label. Results: Twenty-two eyes of 22 male volunteers were included in the study. The mean age was 37.16 ± 4.52 years. At 30 min, 1 h, and 4 h after intake, a statistically significant increase was observed in the choriocapillaris flow area and CT compared with preintake (Friedman test, P = 0.034 and P < 0.001, respectively). Conclusion: This study showed that a single dose of oral 5-mg tadalafil causes an increase in choriocapillaris flow and CT. To evaluate the effects of tadalafil on the retina and choroid, an OCTA assessment may be helpful.

Visual Side Effects Linked to Sildenafil Consumption: An Update

Phosphodiesterase type 5 (PDE5) inhibitors such as Viagra^® (sildenafil citrate) have demonstrated efficacy in the treatment of erectile dysfunction (ED) by inducing cyclic guanosine monophosphate (cGMP) elevation followed by vasodilation and increased blood flow. It also exerts minor inhibitory action against PDE6, which is present exclusively in rod and cone photoreceptors. The effects of sildenafil on the visual system have been investigated in a wide variety of clinical and preclinical studies due to the fact that a high dose of sildenafil may cause mild and transient visual symptoms in some patients. A literature review was performed using PubMed, Cochrane Library and Clinical Trials databases from 1990 up to 2020, focusing on the pathophysiology of visual disorders induced by sildenafil. The aim of this review was not only to gather and summarize the information available on sildenafil clinical trials (CTs), but also to spot subpopulations with increased risk of developing undesirable visual side effects. This PDE inhibitor has been associated with transient and reversible ocular side effects, including changes in color vision and light perception, blurred vision, photophobia, conjunctival hyperemia and keratitis, and alterations in the electroretinogram (ERG). Sildenafil may induce a reversible increase in intraocular pressure (IOP) and a few case reports suggest it is involved in the development of nonarteritic ischemic optic neuropathy (NAION). Reversible idiopathic serous macular detachment, central serous retinopathy and ERG disturbances have been related to the significant impact of sildenafil on retinal perfusion. So far, sildenafil does not seem to cause permanent toxic effects on chorioretinal tissue and photoreceptors as long as the therapeutic dose is not exceeded and is taken under a physician’s direction to treat a medical condition. However, the recreational use of sildenafil can lead to harmful side effects, including vision changes.

Sildenafil-evoked photoreceptor oxidative stress in vivo is unrelated to impaired visual performance in mice

Purpose

The phosphodiesterase inhibitor sildenafil is a promising treatment for neurodegenerative disease, but it can cause oxidative stress in photoreceptors ex vivo and degrade visual performance in humans. Here, we test the hypotheses that in wildtype mice sildenafil causes i) wide-spread photoreceptor oxidative stress in vivo that is linked with ii) impaired vision.

Methods

In dark or light-adapted C57BL/6 mice ± sildenafil treatment, the presence of oxidative stress was evaluated in retina laminae in vivo by QUEnch-assiSTed (QUEST) magnetic resonance imaging, in the subretinal space in vivo by QUEST optical coherence tomography, and in freshly excised retina by a dichlorofluorescein assay. Visual performance indices were also evaluated by QUEST optokinetic tracking.

Results

In light-adapted mice, 1 hr post-sildenafil administration, oxidative stress was most evident in the superior peripheral outer retina on both in vivo and ex vivo examinations; little evidence was noted for central retina oxidative stress in vivo and ex vivo. In dark-adapted mice 1 hr after sildenafil, no evidence for outer retina oxidative stress was found in vivo. Evidence for sildenafil-induced central retina rod cGMP accumulation was suggested as a panretinally thinner, dark-like subretinal space thickness in light-adapted mice at 1 hr but not 5 hr post-sildenafil. Cone-based visual performance was impaired by 5 hr post-sildenafil and not corrected with anti-oxidants; vision was normal at 1 hr and 24 hr post-sildenafil.

Conclusions

The sildenafil-induced spatiotemporal pattern of oxidative stress in photoreceptors dominated by rods was unrelated to impairment of cone-based visual performance in wildtype mice.

Progressive Effects of Sildenafil on Visual Processing in Rats

Photoreceptors are light-sensitive cells in the retina converting visual stimuli into electrochemical signals. These signals are evaluated and interpreted in the visual pathway, a process referred to as visual processing. Phosphodiesterase type 5 and 6 (PDE5 and 6) are abundant enzymes in retinal vessels and notably photoreceptors where PDE6 is exclusively present. The effects of the PDE inhibitor sildenafil on the visual system, have been studied using electroretinography and a variety of clinical visual tasks. Here we evaluate effects of sildenafil administration by electrophysiological recordings of flash visual evoked potentials (VEPs) and steady-state visual evoked potentials (SSVEPs) from key regions in the rodent visual pathway. Progressive changes were investigated in female Sprague-Dawley rats at 10 timepoints from 30 min to 28 h after peroral administration of sildenafil (50 mg/kg). Sildenafil caused a significant reduction in the amplitude of VEPs in both visual cortex and superior colliculus, and a significant delay of the VEPs as demonstrated by increased latency of several VEP peaks. Also, sildenafil-treatment significantly reduced the signal-to-noise ratio of SSVEPs. The effects of sildenafil were dependent on the wavelength condition in both assays. Our results support the observation that while PDE6 is a key player in phototransduction, near full inhibition of PDE6 is not enough to abolish the complex process of visual processing. Taken together, VEPs and SSVEPs are effective in demonstrating progressive effects of drug-induced changes in visual processing in rats and as the same paradigms may be applied in humans, representing a promising tool for translational research.

Effects of phosphodiesterase type 5 inhibitors on choroid and ocular vasculature: a literature review

To provide information on the effects of phosphodiesterase type 5 (PDE5) inhibitors on choroidal vessels and central serous chorioretinopathy (CSC) and possible implications for development of exudative age-related macular degeneration (AMD). Two independent investigators conducted a qualitative review of PubMed to identify studies on the choroidal effect of PDE5 inhibitors in June 2019. The search used key words that included PDE5 inhibitors, sildenafil, tadalafil, vardenafil, choroid, choroidal flow, choroidal vessels, choroidal thickness, CSC, AMD or a combination. Only studies which assessed choroidal findings were included. Many ocular diseases are related to changes in choroidal thickness and perfusion. Patients with AMD, who have decreased choroidal perfusion, may manifest more severely diminished choroidal ability to deliver oxygen and other metabolites to the retina, leading to growth of neovascular tissue. As a result of this engorgement of the choroidal vasculature, some patients may have leakage across the retinal pigment epithelium (RPE) and accumulation of subretinal fluid, resulting in CSC. Transient visual symptoms, i.e., changes in color perception and increased light sensitivity, are well-known adverse effects, but there have been rare reports of vision-threatening ocular complications in users of PDE5 inhibitors, such as nonarteritic anterior ischemic optic neuropathy and cilioretinal artery occlusion. The choroid is a vascular tissue analogous in many respects to the corpus cavernosum, and PDE5 inhibitors may increase the choroidal thickness and perfusion. While it is intuitively obvious that thickness of the choroid alone does not guarantee better choriocapillaris oxygenation, it is a reasonable step towards ameliorating ischemia. These drugs have numerous physiologic effects on the choroid related to blood flow, such as clinical consequences in CSC and AMD.

Ethionamide induced blue vision (cyanopsia): Case report

Ethionamide is part of a group of drugs used in the treatment of drug resistant TB. With the advent of increasing drug resistance in pulmonary TB cases, use of Ethionamide, a second line anti tubercular drug is increasing. Vision changes are rare with ethionamide. Cyanopsia i.e., bluish tinted vision of surroundings with ethionamide is not known in literature. Here, we report a case of DRTB patient who developed cyanopsia soon after introducing ethionamide. Although reversible, ethionamide may sometimes need withdrawal because of significant distress caused to patient.

Almond-supplemented diet improves sexual functions beyond Phosphodiesterase-5 inhibition in diabetic male rats

Hyperglycemia, an important feature of diabetes, can cause oxidative stress, which is associated with varieties of diabetic complications including erectile dysfunction. Therefore, this study sought to investigate the effect of almond-supplemented diet on some biochemical indices relevant to erection in diabetic male rats. Forty-two male rats were divided into two groups: A (n = 6) and B (n = 36). Diabetes was induced in Group B via injection of a single dose of STZ (50 mg/kg) intraperitoneally and confirmed 72 h after induction. Diabetic rats (blood glucose ≥250 mg/dL) were subsequently divided into six groups (n = 6). Fourteen days after confirmation of diabetes, rats were fed with diets containing almond drupe and seeds (10 and 20% inclusion) for fourteen days. The effects of the diets on blood glucose, sexual behavior, sexual hormones, phosphodiesterase-5 activity, nitric oxide, H₂S, and AGEs levels were evaluated. Significant increase in blood glucose level, phosphodiesterase-5 activity, and glycated hemoglobin was observed in diabetic rats. Furthermore, diabetes caused a significant decrease in nitric oxide, H₂S, sexual hormones (testosterone, follicle-stimulating hormone and luteinizing hormone) levels, and sexual behavioral indices. However, treatment with diets supplemented with almond drupe and seeds significantly reversed these effects in diabetic rats. Findings in this study revealed that almond-supplemented diets enhance some important biomarkers relevant to erection in diabetic rats. Thus, dietary inclusion of almond (drupe and seeds) could serve as a cheap and readily available nutraceutical in the management of erectile dysfunction associated with diabetes.

Choroidal Thickness Analysis in Patients with Erectile Dysfunction

Purpose

To investigate the morphological features of choroidal vasculature in patients with erectile dysfunction (ED) by analyzing choroidal thickness using optical coherence tomography.

Materials and Methods

We enrolled 39 patients with ED and 19 controls. ED was defined as an erectile function domain score <26 on the International Index of Erectile Function (IIEF) questionnaire. Small-choroidal-vessel-layer (SCVL) thickness was calculated by subtracting large-choroidal-vessel-layer (which corresponded to Haller's layer) thickness from total choroidal thickness. Choroidal thickness was compared between the ED and control groups.

Results

SCVL thickness was lesser in the ED group than in the control group (control, 69.8±24.3 µm vs. ED, 55.1±19.9 µm; p=0.017). Among patients without diabetes, the ED group showed significantly lesser SCVL thickness than did the control group (control, 77.1±22.7 µm vs. ED, 56.5±20.9 µm; p=0.021). However, among patients with diabetes, choroidal thickness showed no significant intergroup difference. Multiple linear regression analysis revealed that spherical equivalent (standardized coefficient β=0.294; p=0.019) and the IIEF erectile function score (standardized coefficient β=0.315; p=0.012) were significantly associated with SCVL thickness.

Conclusions

SCVL thickness, including the choriocapillaris layer and medium-sized choroidal vascular layer, decreased in proportion to ED severity, suggesting that microvascular changes in choroidal vessels may occur before specific ocular diseases in patients with ED.

Sildenafil Administration in Dogs Heterozygous for a Functional Null Mutation in Pde6a: Suppressed Rod-Mediated ERG Responses and Apparent Retinal Outer Nuclear Layer Thinning

This study was designed to assess risk for retinal toxicity associated with administration of high-dose sildenafil citrate to dogs heterozygous for a functionally null mutation in Pde6a over a 4-month period. Three Pde6a +/- dogs were administered 14.3 mg/kg sildenafil per os and two Pde6a +/- dogs placebo once daily for 16 weeks. Three Pde6a +/+ dogs were administered sildenafil for 7 days. Ophthalmic examination, vision testing, and electroretinography (ERG) were regularly performed. At study termination, dogs were euthanized and globes collected. Retinal layer thickness and photoreceptor nuclei counts were determined from plastic sections. In both Pde6a +/- and Pde6a +/+ sildenafil-treated (ST) dogs, elevation of dark-adapted b-wave threshold and unmasking of the scotopic threshold response (STR) were observed. Sildenafil treated Pde6a +/- dogs had significantly thinner ONL (24.90 +/-1.88 μm, p = 0.004) and lower photoreceptor nuclei counts (273.6 +/- 29.3 cells/100 μm, p = 0.008) compared to measurements (35.90 +/- 1.63 μm) and counts (391.5 +/-27.0 cells/100 μm) from archived untreated Pde6a +/- dogs.

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.

Audiometry results and TEOAE and DPOAE amplitudes in men taking a phosphodiesterase type 5 inhibitor for erectile dysfunction

We conducted a prospective study of transient evoked otoacoustic emissions (TEOAEs) and distortion-product otoacoustic emissions (DPOAEs) in men who were taking an oral phosphodiesterase type 5 (PDE5) inhibitor for erectile dysfunction. Our study group was made up of 30 men (60 ears), aged 34 to 60 years (mean: 50.9). They were randomly divided into three groups; 10 men were given sildenafil (Viagra) at 50 mg twice a week, 10 were given tadalafil (Cialis) at 20 mg twice a week, and 10 were given vardenafil (Levitra) at 20 mg twice a week. All patients took their drug for 3 weeks, for a total of 6 tablets for each patient. Audiometric tests and TEOAE and DPOAE measurements were performed before and after treatment. Post-treatment audiometry demonstrated improvement in hearing in all three groups. However, post-treatment TEOAE amplitudes and DPOAE amplitudes differed among the three groups; they were significantly higher in the sildenafil group at 1.0 kHz and the same in the tadalafil group; in the vardenafil group, the DPOAE amplitude was significantly lower at 3.0 kHz while there was no change in the TEOAE amplitude. We speculate that the possible mechanism for these findings is that PDE5 inhibitors block degradation of cyclic guanosine monophosphate (cGMP) and induce dilation of the cochlear microcirculation, resulting in an increase in cochlear blood flow. We also believe that the decrease in DPOAE amplitudes at 3.0 kHz seen in the vardenafil group may be related to an accumulation of nitric oxide/cGMP complex, which is toxic to the cochlea; however, since there was no change in TEOAE amplitude in the vardenafil group, this influence may be minimal. Further studies are needed to obtain a more comprehensive assessment of the effects of PDE5 inhibitors on hearing with the use of higher doses and longer durations of therapy.

Comparative Safety of Drugs Targeting the Nitric Oxide Pathway in Pulmonary Hypertension: A Mixed Approach Combining a Meta-Analysis of Clinical Trials and a Disproportionality Analysis From the World Health Organization Pharmacovigilance Database

BACKGROUND

Recent guidelines recommend riociguat, a soluble guanylate cyclase (sGC) stimulator, and the type 5 phosphodiesterase inhibitor (PDE5i) tadalafil or sildenafil as treatments for pulmonary arterial hypertension. We compared the safety profiles of sildenafil, tadalafil, and riociguat in pulmonary hypertension.

METHODS

We combined two approaches. First, we performed a meta-analysis of safety data extracted from randomized controlled trials. Second, we conducted a disproportionality analysis of data from VigiBase, the World Health Organization's global database of individual case safety reports, to compare the safety profiles with real-life data.

RESULTS

In the meta-analysis, a significant difference between the three drugs was only detected for gastrointestinal disorders, in disfavor of riociguat (P < .01 for interaction). In the disproportionality analysis, the use of riociguat was associated with fewer reports of visual disorders but increased reporting of gastrointestinal, hemorrhagic, and musculoskeletal disorders compared with sildenafil and tadalafil. Pharmacovigilance signals of hearing/vestibular disorders were heterogeneous: vestibular disorders (dizziness) were reported more frequently for riociguat, whereas hearing disorders (deafness) were reported less frequently compared with PDE5is.

CONCLUSIONS

The safety profiles of PDE5is and sGC stimulators significantly differ in pulmonary hypertension. Accordingly, there is a safety rationale in switching between PDE5is and sGC stimulators because of their different side effects.

TRIAL REGISTRY

PROSPERO; No.: CRD42016051986; URL: https://www.crd.york.ac.uk/prospero/.

Investigation of PDE5/PDE6 and PDE5/PDE11 selective potent tadalafil-like PDE5 inhibitors using combination of molecular modeling approaches, molecular fingerprint-based virtual screening protocols and structure-based pharmacophore development

The essential biological function of phosphodiesterase (PDE) type enzymes is to regulate the cytoplasmic levels of intracellular second messengers, 3′,5′-cyclic guanosine monophosphate (cGMP) and/or 3′,5′-cyclic adenosine monophosphate (cAMP). PDE targets have 11 isoenzymes. Of these enzymes, PDE5 has attracted a special attention over the years after its recognition as being the target enzyme in treating erectile dysfunction. Due to the amino acid sequence and the secondary structural similarity of PDE6 and PDE11 with the catalytic domain of PDE5, first-generation PDE5 inhibitors (i.e. sildenafil and vardenafil) are also competitive inhibitors of PDE6 and PDE11. Since the major challenge of designing novel PDE5 inhibitors is to decrease their cross-reactivity with PDE6 and PDE11, in this study, we attempt to identify potent tadalafil-like PDE5 inhibitors that have PDE5/PDE6 and PDE5/PDE11 selectivity. For this aim, the similarity-based virtual screening protocol is applied for the “clean drug-like subset of ZINC database” that contains more than 20 million small compounds. Moreover, molecular dynamics (MD) simulations of selected hits complexed with PDE5 and off-targets were performed in order to get insights for structural and dynamical behaviors of the selected molecules as selective PDE5 inhibitors. Since tadalafil blocks hERG1 K channels in concentration dependent manner, the cardiotoxicity prediction of the hit molecules was also tested. Results of this study can be useful for designing of novel, safe and selective PDE5 inhibitors.

cGMP-Phosphodiesterase Inhibition Prevents Hypoxia-Induced Cell Death Activation in Porcine Retinal Explants

Retinal hypoxia and oxidative stress are involved in several retinal degenerations including diabetic retinopathy, glaucoma, central retinal artery occlusion, or retinopathy of prematurity. The second messenger cyclic guanosine monophosphate (cGMP) has been reported to be protective for neuronal cells under several pathological conditions including ischemia/hypoxia. The purpose of this study was to evaluate whether the accumulation of cGMP through the pharmacological inhibition of phosphodiesterase (PDE) with Zaprinast prevented retinal degeneration induced by mild hypoxia in cultures of porcine retina. Exposure to mild hypoxia (5% O₂) for 24h reduced cGMP content and induced retinal degeneration by caspase dependent and independent (PARP activation) mechanisms. Hypoxia also produced a redox imbalance reducing antioxidant response (superoxide dismutase and catalase activities) and increasing superoxide free radical release. Zaprinast reduced mild hypoxia-induced cell death through inhibition of caspase-3 or PARP activation depending on the cell layer. PDE inhibition also ameliorated the effects of mild hypoxia on antioxidant response and the release of superoxide radical in the photoreceptor layer. The use of a PKG inhibitor, KT5823, suggested that cGMP-PKG pathway is involved in cell survival and antioxidant response. The inhibition of PDE, therefore, could be useful for reducing retinal degeneration under hypoxic/ischemic conditions.

Ocular perfusion pressure and color Doppler imaging of the external ophthalmic artery of rabbits treated with sildenafil citrate

Background

It has been proposed that sildenafil citrate can increase ocular blood flow, and that this property can be used to treat ocular disorders that involve reflex vasoconstriction. This study therefore proposes to ascertain the vasodilator effect of the drug on retrobulbar circulation in healthy rabbits. For this matter rabbits treated with sildenafil citrate or saline solution had their intraocular pressure (IOP), mean arterial pressure (MAP), ocular perfusion pressure (OPP) and color Doppler imaging of the external ophthalmic artery measured prior to treatment and on days one (moment M1), seven (when M2), fourteen (moment M3), twenty-one (moment M4), and thirty (moment M5) of treatment.

Results

The MAP and OPP values of treated group were lower than those of control group at all times, and the mean values differed statistically at moments M1 (S = 71.52 mmHg, C = 84.76 mmHg, p = 0.0356) and M5 (S = 71.38 mmHg, C = 85.52 mmHg, p = 0.0252). The IOP and color Doppler values of the external ophthalmic artery did not differ between tested groups.

Conclusions

The dose of 10 mg of sildenafil citrate administered to healthy rabbits causes systemic vasodilation and consequently lower values of MAP and OPP. However, it does not induce changes in IOP and retrobulbar hemodynamics identifiable by color Doppler assessment of the external ophthalmic artery.

Sildenafil and retinopathy of prematurity risk in very low birth weight infants

OBJECTIVE

To examine the effect of sildenafil therapy on development of severe retinopathy of prematurity (ROP) requiring surgical intervention in premature infants.

STUDY DESIGN

We identified premature infants who were discharged from Pediatrix Medical Group neonatal intensive care units from 2003 to 2012 and who received an ophthalmologic exam. We matched each infant exposed to sildenafil before first eye exam to three nonexposed infants using propensity scoring to control for differences in baseline infant characteristics. We evaluated the association between sildenafil exposure and development of severe ROP using conditional logistic regression.

RESULT

Of the 57 815 infants meeting inclusion criteria, 88 were exposed to sildenafil. We matched 81/88 (92%) sildenafil-exposed with 243 nonexposed infants. There was no difference in the proportion of infants who developed severe ROP in the sildenafil-exposed vs nonexposed groups (17/81 (21%) vs 38/243 (16%), P=0.27). On adjusted analysis, there was no difference in severe ROP in the sildenafil-exposed vs nonexposed infants (odds ratio=1.46, 95% confidence interval=0.76 to 2.82, P=0.26).

CONCLUSION

We did not observe an association between risk of severe ROP and sildenafil exposure before first eye exam in this cohort of premature infants.

Phosphodiesterase type 5 inhibitors: back and forward from cardiac indications

PDE5 inhibitors (PDE5i) are widely known as treatment for erectile dysfunction (ED). This favorable action has emerged as a "side effect" from pioneering studies when PDE5i have been originally proposed as treatment for coronary artery disease (CAD). PDE5i showed marginal benefits for CAD treatment; although disappointing for that indication, they improved systemic and pulmonary vasodilation and ameliorated general endothelial function. Therefore, PDE5i have been approved and licensed also for pulmonary artery hypertension (PAH), besides ED. Nowadays, fine-tuned biomolecular mechanisms of PDE5i are well recognized to be beneficial onto myocardial contractility and geometry, to reduce tissue fibrosis, hypertrophy and apoptosis. PDE5i consistently exert benefits on heart failure, infarct, cardiomyopathy. The concept that PDE5i likely blunt Th1-driven inflammatory processes, which shift the homeostatic balance from health to disease, has emerged; PDE5i seem to decrease the release of active biomolecules from cells to tissues interested by inflammation. In this view, following clinical and basic research progresses, PDE5i can be undoubtedly "re-allocated" for cardiac indications and, hopefully, they could be approved as therapeutic tools to treat and prevent heart disease. This review aims to summarize PDE5i different clinical applications, from past to present and future, focusing on their potential power as treatment for cardiac diseases.

Electroretinography and immunohistochemistry of retina in rabbits treated with sildenafil citrate

Sildenafil citrate is a type-5 phosphodiesterase inhibitor (PDE-5), able to inhibit type-6 phosphodiesterase (PDE-6) as well, providing clinical benefits and paraeffects, some of them potentially related to the retina. The effects of the sildenafil on the retrobulbar and retinal circulation were studied in 27 adult male rabbits of the White New Zealand breed. The electric activity of the retina was evaluated before and at the end of the treatments, and immunohistochemistry studies were conducted. An amplitude increase of the b wave was found in the mixed response of cones and rods after 7 days of treatment with sildenafil citrate. However, in the other evaluations and periods, the values did not differ from the basal ones. Through immunohistochemistry, no significant decrease of the expression of PDE-5 and PDE-6 proteins was observed. Based on the results obtained, it is possible to admit that the sildenafil citrate did not change the expression of PDE-5 and PDE-6, neither the electroretinographic activity of the retina of male rabbits of the White New Zealand breed.

PDE5 inhibition improves acquisition processes after learning via a central mechanism

In previous studies, we have shown that phosphodiesterase type 5 inhibitors (PDE5-Is) can improve early consolidation of object memory. These conclusions were based on the timing of drug administration relative to the learning trial (i.e. before or after). However, there are very little pharmacological data available about the pharmacokinetic profile of orally administered PDE5-Is in the rat. Furthermore, there is still debate whether these effects are achieved via central or peripheral mechanisms and if acquisition processes are improved. In the current study, we tested the effects of the PDE5-I vardenafil in a cholinergic-deficit model and compared the effects after intracerebroventricular (ICV) versus oral (PO) administration. We found that PO vardenafil restored a scopolamine-induced memory impairment when dosed within 2 min after the learning trial while ICV vardenafil was able to restore memory when injected within 4 min after learning. Because the test trial was within 10 min after the learning trial, this suggests that these effects on object memory are related to acquisition processes that may still be ongoing in a time window after the learning trial. To further elucidate the extent of this acquisition window, we investigated the pharmacokinetic profile of vardenafil after PO administration where it was detected within 4 min post-dose. Taken together, our data suggest that PDE5 is involved in acquisition processes, which may linger for at least 4-6 min after learning. Further studies are needed to exclude that these effects could also be explained on basis of an effect on early consolidation processes. Additionally, the effectiveness of ICV-administered vardenafil provides further experimental evidence that PDE5-Is improve memory via a central mechanism.

Regulation of intraocular pressure by soluble and membrane guanylate cyclases and their role in glaucoma

Glaucoma is a progressive optic neuropathy characterized by visual field defects that ultimately lead to irreversible blindness (Alward, 2000; Anderson et al., 2006). By the year 2020, an estimated 80 million people will have glaucoma, 11 million of which will be bilaterally blind. Primary open-angle glaucoma (POAG) is the most common type of glaucoma. Elevated intraocular pressure (IOP) is currently the only risk factor amenable to treatment. How IOP is regulated and can be modulated remains a topic of active investigation. Available therapies, mostly geared toward lowering IOP, offer incomplete protection, and POAG often goes undetected until irreparable damage has been done, highlighting the need for novel therapeutic approaches, drug targets, and biomarkers (Heijl et al., 2002; Quigley, 2011). In this review, the role of soluble (nitric oxide (NO)-activated) and membrane-bound, natriuretic peptide (NP)-activated guanylate cyclases that generate the secondary signaling molecule cyclic guanosine monophosphate (cGMP) in the regulation of IOP and in the pathophysiology of POAG will be discussed.

Sildenafil attenuates vaso-obliteration and neovascularization in a mouse model of retinopathy of prematurity

PURPOSE

We sought to determine the effect of sildenafil on retinal vascular changes in a mouse model of oxygen-induced retinopathy (OIR).

METHODS

Vascular defects in OIR mice were quantified by measuring vaso-obliteration at postnatal days 12 and 17 (P12 and P17) and neovascularization at P17 to compare sildenafil-treated to dextrose-treated OIR mice. Retinal HIF1α protein expression was quantified by Western blotting and normalized to that of β-actin. Right ventricular hypertrophy was measured by Fulton's index as a surrogate for hyperoxia-induced pulmonary hypertension.

RESULTS

At P12, OIR mice treated with sildenafil demonstrated a 24% reduction in vaso-obliteration (P < 0.05), whereas at P17, treated animals showed a 50% reduction in neovascularization (P < 0.05) compared to dextrose-treated controls. Sildenafil-treated OIR mice had stabilization of retinal HIF1α at P12, immediately after hyperoxia. At P17, sildenafil-treated OIR mice had decreased HIF1α relative to untreated mice. OIR mice developed right ventricle hypertrophy that was significant compared to that in room air controls, which was abrogated by sildenafil.

CONCLUSIONS

Sildenafil treatment significantly decreased retinal vaso-obliteration and neovascularization in a mouse OIR model. These effects are likely due to sildenafil-induced HIF1α stabilization during hyperoxia exposure. Furthermore, we confirm disease overlap by showing that OIR mice also develop hyperoxia-induced right ventricular hypertrophy, which is prevented by sildenafil. This study is a first step toward delineating a potential therapeutic role for sildenafil in OIR and further suggests that there may be common pathophysiologic mechanisms underlying hyperoxia-induced retinal and pulmonary vascular disease.

Ocular safety of sildenafil citrate when administered chronically for pulmonary arterial hypertension: results from phase III, randomised, double masked, placebo controlled trial and open label extension

OBJECTIVE

To assess the ocular effects and safety profile of chronic sildenafil oral dosing in patients with pulmonary arterial hypertension.

DESIGN

12 week, double masked, randomised, placebo controlled, phase III trial with open label extension.

SETTING

53 institutions worldwide.

PARTICIPANTS

277 adults with idiopathic pulmonary arterial hypertension or pulmonary arterial hypertension associated with connective tissue disease or after congenital heart disease repair (mean pulmonary artery pressure ≥25 mm Hg; pulmonary capillary wedge pressure ≤15 mm Hg at rest).

INTERVENTIONS

During the double masked study, oral sildenafil 20 mg, 40 mg, or 80 mg or placebo (1:1:1:1) three times daily for 12 weeks was added to baseline drug treatment. In the extension study, the placebo, 20 mg and 40 mg groups received 40 mg three times daily titrated to 80 mg three times daily at week 6. After unmasking, the dose was titrated according to clinical need.

MAIN OUTCOME MEASURE

Ocular safety (ocular examinations, visual function tests, participants' reports of adverse events, and visual disturbance questionnaire completed by investigators) by treatment group at 12 weeks, 24 weeks, 18 months, and yearly.

RESULTS

Findings of the objective assessments-that is, intraocular pressure and visual function tests (visual acuity, colour vision, and visual field)-were similar across groups (20 mg, n=69; 40 mg, n=67; 80 mg, n=71; placebo, n=70). No clinically significant changes occurred between baseline and 12 weeks, except for an efficacy signal in contrast sensitivity for the sildenafil 40 mg three times daily group. In right eyes, changes in intraocular pressure from baseline to week 12 ranged from a mean of -0.5 (95% confidence interval -1.3 to 0.2) mm Hg with placebo, -0.2 (-0.9 to 0.5) mm Hg with sildenafil 40 mg, and -0.1 (-0.7 to 0.5) mm Hg with 80 mg to 0.3 (-0.4 to 0.9) mm Hg with sildenafil 20 mg (the approved dose for pulmonary arterial hypertension). Mean changes from baseline to week 12 in contrast sensitivity in right eyes were -0.02 (SD 0.12) in the sildenafil 20 mg three times daily group compared with -0.05 (0.18) in the placebo group (P=0.044). Percentages of participants with deterioration in visual acuity (Snellen) from baseline to week 12 ranged from 10% (n=7) in the placebo group to 3% (n=2) in the sildenafil 20 mg three times daily group; the same percentages had visual field changes from normal to abnormal during the period in these two groups. The investigators did not deem any findings on colour vision assessment to be clinically significant. Findings of the objective assessments in the 40 mg and 80 mg three times daily sildenafil treatment groups and in left eyes were not substantially different, nor were any measures different throughout the open label extension compared with week 12. However, objective data were limited after month 18, as most participants had missing data or visual parameters were no longer collected by investigators. Incidence of ocular adverse events reported on the case report forms and assessed by the investigator was low with all doses, but a modest, dose related incidence of chromatopsia, cyanopsia, photophobia, and visual disturbance was reported with 80 mg three times daily consistent with the indicated dosing for erectile dysfunction. Retinal haemorrhages, captured on funduscopy, occurred in 2% (4/207) of sildenafil treated participants and none in the placebo group during the double masked study and in 4% (10/259) during the open label extension.

CONCLUSIONS

Sildenafil dosing up to 80 mg three times daily is safe and well tolerated from an ocular perspective in patients with pulmonary arterial hypertension. Daily chronic dosing in this patient population was not associated with visual change and had no detrimental effect on best corrected visual acuity, contrast sensitivity, colour vision, or visual field, or on slit lamp examinations, funduscopy, or intraocular pressure during the duration of this study.

TRIAL REGISTRATION

Clinical trials NCT00644605 and NCT00159887.

Sildenafil accelerates anterior chamber refilling after paracentesis in sheep and rabbits

PURPOSE

Sildenafil increases ocular blood flow. Thus, the authors investigated if it also increases anterior chamber (AC) refilling after paracentesis.

METHODS

Corriedale sheep and albino rabbits were used as animal models. Intraocular pressure (IOP) was measured, paracentesis performed on one eye, and AC refilling followed by observation using oblique illumination. IOP measurements continued as the AC formed. After IOP stabilization, sildenafil (100 mg) was orally administered. Forty to 60 minutes later, AH was withdrawn from the contralateral eye. The point at which IOP recovered was used to determine refilling time. Paracentesis volumes were either 60, 120, or 300 μL in sheep, and 50 or 100 μL in rabbits.

RESULTS

IOP recovered in approximately 49, 56, and 50 minutes after the 60, 120, and 300 μL withdrawals in sheep. The refilling times of the contralateral eye after sildenafil ingestion were approximately 19, 26, and 37 minutes for the respective AH withdrawals. With rabbits, IOP recovered in approximately 13 minutes after the 50 and 100 μL AH withdrawals. After sildenafil, the IOP recovery times of the fellow eye were approximately 6 minutes. AH refilling rates were estimated by dividing the paracentesis volume by IOP recovery time. After sildenafil, such rates were larger than the AH formation rate attributed to secretion by the ciliary epithelium.

CONCLUSIONS

Sildenafil accelerates the rate of AC refilling and might have beneficial utility as an agent enhancing fluid entry into the AC of patients who experienced AH loss during eye surgery, as well as in some cases of ocular hypotony.

Should central serous chorioretinopathy be added to the list of ocular side effects of phosphodiesterase 5 inhibitors?

INTRODUCTION

Rare cases of central serous chorioretinopathy (CSC) associated with the intake of sildenafil citrate have been reported, although CSC is not included in the list of phosphodiesterase 5 (PDE5) inhibitor side effects.

MATERIALS AND METHODS

We present a review of the literature and 2 cases of CSC in 2 men taking PDE5 inhibitors (vardenafil and tadalafil) for erectile dysfunction. In both cases chorioretinopathy appeared after intake of the inhibitor, resolved once the latter was discontinued, reappeared when the inhibitor was restarted and resolved once again after the inhibitor had been discontinued for the second time.

DISCUSSION

PDE5 inhibitors used for male erectile dysfunction have been associated with ocular side effects including lid edema, hyposphagma, photophobia, mydriasis, dyschromatopsia, and nonarteritic anterior ischemic optic neuropathy. CSC was previously described in patients taking sildenafil citrate. Very recently, a case of CSC after tadalafil intake was reported. The relevant literature is reviewed and possible pathophysiologic mechanisms are discussed.

CONCLUSION

The 2 presented cases of CSC after intake of vardenafil or tadalafil with positive dechallenge, rechallenge and second dechallenge reactions provide important arguments for considering CSC as a rare PDE5 inhibitor class-specific side effect.

Contrast sensitivity, ocular blood flow and their potential role in assessing ischaemic retinal disease

PURPOSE

To examine the definition, evaluation methodology, association to ocular blood flow and potential clinical value of contrast sensitivity (CS) testing in clinical and research settings, focusing in patients with ischemic retinal disease.

METHODS

A review of the medical literature focusing on CS and ocular blood flow in ischemic retinal disease.

RESULTS

CS may be more sensitive than other methods at detecting subtle defects or improvements in primarily central retinal ganglion cell function early on in a disease process. CS testing attempts to provide spatial detection differences which are not directly assessed with standard visual acuity chart testing. Analyzing all studies that have assessed both CS change and ocular blood flow, it is apparent that both choroidal circulation and retinal circulation may have an important role in influencing CS.

CONCLUSION

The concept that CS is directly influenced by ocular blood flow is supported by reviewing the studies involving both. Although the studies in the literature have not established a direct cause and effect relationship per se, the literature review makes it logical to assume that changes in retinal and choroidal blood flow influence CS. This raises the possibility that a subjective visual characteristic, specifically CS, may be able to be evaluated more objectively by studying blood flow. It appears appropriate to study the relationship between blood flow and CS more extensively to develop improved ways of measuring various aspects of blood flow to the eye and to best quantify early changes in visual function.

Effect of sildenafil citrate on intraocular pressure and blood pressure in human volunteers

Anecdotal reports have suggested that the vasodilator, sildenafil citrate, which evokes its effect via a select inhibition of PDE5, has the potential to increase intraocular pressure (IOP) in some individuals. An ocular hypertensive effect by sildenafil was also recently described in a sheep animal model. In contrast, clinical studies have not found a direct association between sildenafil ingestion (commonly consumed as Viagra) and changes in IOP. However, some such studies also reported no effects of sildenafil on systemic blood pressure (BP) at the time of the IOP determination. Given this surprising result, our purpose was to repeat a study in human volunteers in the city of Corrientes, Argentina to corroborate the effects of sildenafil on human IOP and systemic BP. For the present study, 9 healthy volunteers (male and female, 18-74 years old) were selected as subjects after ophthalmic and cardiovascular evaluation indicated that they exhibited normal parameters for their age. In a masked, placebo-controlled study, the subjects ingested 100 mg sildenafil citrate (provided as Vorst from Laboratorios Bernabo, Argentina) in one session, and a placebo on a second separate occasion. IOP was measured with a Goldman applanation tonometer by an ophthalmologist, and BP by a second physician, neither of whom witnessed the tablet ingestion by the volunteers, nor provided with information on the nature of the test compounds. A third individual administered the tablets. The average baseline IOP of this group of 9 was 13.1 ± 0.6 mm Hg. Subsequent to sildenafil ingestion, IOP increased by 26% to 16.5 ± 0.8 mm Hg 60 min later (P < 0.005, as paired data), and returned to control values within 2 h. Both systolic and diastolic BP were significantly reduced by sildenafil ingestion. At the point of maximal systemic hypotension (90 min), the systolic and diastolic pressures declined by 15% and 13%, respectively. No significant changes in IOP or BP were recorded after ingestion of the placebo. Our results suggest that sildenafil can elicit a transient IOP increase that may be of importance to patients chronically treated with PDE5 inhibitors for various vascular diseases (e.g., pulmonary hypertension). We discuss possible mechanisms by which PDE5 inhibition might lead to a rise in IOP.

The effects of sildenafil citrate on choroidal thickness as determined by enhanced depth imaging optical coherence tomography

PURPOSE

To investigate the effects of the phosphodiesterase-5 inhibitor, sildenafil citrate, on choroidal thickness using eye-tracked enhanced depth imaging spectral-domain optical coherence tomography.

METHODS

In a prospective interventional study, 8 healthy subjects (4 men and 4 women) with no ocular history underwent enhanced depth imaging spectral-domain optical coherence tomography at baseline, 1 hour, and 3 hours after the ingestion of 100 mg of sildenafil citrate. Choroidal thickness measurements for both eyes using enhanced depth imaging spectral-domain optical coherence tomography were taken by 2 masked readers at baseline, 1-hour, and 3-hour time points. Statistical analysis was performed to compare the measurements of choroidal thickness at each of the three intervals.

RESULTS

The mean age of the subjects was 35.9 years (range 30-46 years). Mean choroidal thickness at baseline was 334 μm (± 57 μm). Mean choroidal thickness increased by 12.3% to 375 μm (± 68 μm) at 1 hour after ingestion (P < 0.001). At 3 hours after ingestion, the mean choroidal thickness remained elevated at 372 μm (± 61 μm), 11.6% thicker than baseline (P < 0.001). There was no significant difference in choroidal thickness between the 1-hour and the 3-hour intervals (P = 0.719).

CONCLUSION

Sildenafil citrate appears to increase choroidal thickness as measured by eye-tracked enhanced depth imaging spectral-domain optical coherence tomography measurements in healthy subjects 1 hour and 3 hours after ingestion. These findings may be of relevance given that increased choroidal thickness appears to be a risk factor for central serous chorioretinopathy and that several reports have suggested an association between phosphodiesterase-5 inhibitors and this disorder.

Phosphodiesterase 6 subunits are expressed and altered in idiopathic pulmonary fibrosis

Background

Idiopathic Pulmonary Fibrosis (IPF) is an unresolved clinical issue. Phosphodiesterases (PDEs) are known therapeutic targets for various proliferative lung diseases. Lung PDE6 expression and function has received little or no attention. The present study aimed to characterize (i) PDE6 subunits expression in human lung, (ii) PDE6 subunits expression and alteration in IPF and (iii) functionality of the specific PDE6D subunit in alveolar epithelial cells (AECs).

Methodology/Principal Findings

PDE6 subunits expression in transplant donor (n = 6) and IPF (n = 6) lungs was demonstrated by real-time quantitative (q)RT-PCR and immunoblotting analysis. PDE6D mRNA and protein levels and PDE6G/H protein levels were significantly down-regulated in the IPF lungs. Immunohistochemical analysis showed alveolar epithelial localization of the PDE6 subunits. This was confirmed by qRT-PCR from human primary alveolar type (AT)II cells, demonstrating the down-regulation pattern of PDE6D in IPF-derived ATII cells. In vitro, PDE6D protein depletion was provoked by transforming growth factor (TGF)-β1 in A549 AECs. PDE6D siRNA-mediated knockdown and an ectopic expression of PDE6D modified the proliferation rate of A549 AECs. These effects were mediated by increased intracellular cGMP levels and decreased ERK phosphorylation.

Conclusions/Significance

Collectively, we report previously unrecognized PDE6 expression in human lungs, significant alterations of the PDE6D and PDE6G/H subunits in IPF lungs and characterize the functional role of PDE6D in AEC proliferation.

Attenuated proliferation and trans-differentiation of prostatic stromal cells indicate suitability of phosphodiesterase type 5 inhibitors for prevention and treatment of benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is characterized by tissue overgrowth and stromal reorganization primarily due to cellular proliferation and fibroblast-to-myofibroblast trans-differentiation. To evaluate the potential of phosphodiesterase type 5 (PDE5) inhibitors like tadalafil for prevention and treatment of BPH, we analyzed the role of the nitric oxide/cyclic GMP (cGMP)/PDE5 pathway for cellular proliferation and TGFbeta1-induced fibroblast-to-myofibroblast trans-differentiation in primary prostate stromal cells. Inhibition by tadalafil of PDE5, which is mainly expressed in the stromal compartment of the prostate, reduced proliferation of primary prostate stromal cells and to a lesser extent of primary prostate basal epithelial cells. Attenuated proliferation due to elevated intracellular cGMP levels was confirmed by inhibition of the cGMP-dependent protein kinase G by its inhibitor KT2358. Moreover, tadalafil strongly attenuated TGFbeta1-induced fibroblast-to-myofibroblast trans-differentiation. The inhibitory effect on trans-differentiation was also observed after small interfering RNA-mediated PDE5 knockdown. As confirmed by the MAPK kinase 1 inhibitor PD98059, this effect was mediated via MAPK kinase 1 signaling. We conclude that BPH patients might benefit from adjuvant therapies with PDE5 inhibitors that inhibit stromal enlargement due to cell proliferation, as well as TGFbeta1-induced trans-differentiation processes.

Phosphatidylethanolamine-binding proteins, including RKIP, exhibit affinity for phosphodiesterase-5 inhibitors

Identifying protein "interactors" of drugs is of great importance to understand their mode of action and possible cross-reactivity to off-target protein binders. In this study, we profile proteins that bind to PF-3717842, a high-affinity phosphodiesterase-5 (PDE5) inhibitor, by using a refined affinity pulldown approach with PF-3717842 immobilized beads. By performing these pulldowns in rat testis tissue lysate, we strongly and specifically enriched for PDE5 and a few other PDEs. In addition to these expected affinity-enriched proteins we also detect rodent-specific phosphatidylethanolamine-binding protein 2 (PEBP2), as a putative binder to the PDE5 inhibitor. By using recombinant forms of the related murine mPEBP2, mPEBP1 and human hPEBP1 (also known as Raf kinase inhibitor protein or RKIP) we confirm that they all can bind strongly to immobilized as well as soluble PF-3717842. As the phosphatidylethanolamine-binding proteins are involved in various important signal transduction pathways, the synthetic PDE5 inhibitor used here might form a platform to synthesize enhanced binders/inhibitors of the family of PEBP proteins. Our approach shows how chemical proteomics might be used to profile the biochemical space (interactome) of small molecule inhibitors.

Phosphodiesterase inhibitors and the eye

Phosphodiesterase type 5 (PDE5) inhibitors are effective oral treatments for erectile dysfunction and have become one of the most widely prescribed medications worldwide. The mechanism of action is to reduce the degradation of cyclic GMP (cGMP) potentiating the effect of nitric oxide in the corpus cavernosum and allowing erectile function to occur by consequent relaxation of penile smooth muscle. Because of the presence of PDE5 in choroidal and retinal vessels these medications increase choroidal blood flow and cause vasodilation of the retinal vasculature. The most common symptoms are a blue tinge to vision and an increased sensitivity to light. There have been reports of non-arteritic anterior ischaemic optic neuropathy and serous macular detachment in users of PDE5 inhibitors, although a causal relationship has not been conclusively shown. Despite the role of cGMP in the production and drainage of aqueous humour these medications do not appear to alter intraocular pressure and are safe in patients with glaucoma. All PDE5 inhibitors weakly inhibit PDE6 located in rod and cone photoreceptors resulting in mild and transient visual symptoms that correlate with plasma concentrations. Psychophysical tests reveal no effect on visual acuity, visual fields or contrast sensitivity; however, some studies show a mild and reversible impairment of blue-green colour discrimination. PDE5 inhibitors transiently alter retinal function on electroretinogram testing but do not appear to be retinotoxic. Despite the role of cyclic nucleotides in tear production there is no detrimental effect on tear film quality. Based on the available evidence PDE5 inhibitors have a good ocular safety profile.