Role of Sildenafil in Neurological Disorders

Neuronal nitric oxide synthase activation by tadalafil protects neurological impairments in a zebrafish larva model of hyperammonemia

AIMS

Hyperammonaemia (HA) is a metabolic disorder characterized by increased ammonia levels in the blood and is associated with severe neurological impairments. Some previous findings have shown the involvement of the nitric oxide pathway in HA-induced neurological impairments. The current study explored the impact of tadalafil on neurological impairments induced by HA in a zebrafish larval model due to its reported indirect interactions with the nitric oxide pathway.

MATERIAL AND METHODS

HA was induced in zebrafish larvae by ammonium acetate exposure from 2 to 9 days post fertilization (dpf). Locomotor and cognitive functions were analysed following the treatment. The levels of gamma-aminobutyric acid (GABA), glutamate, and dopamine were measured in the larval head. The expression of genes associated with apoptosis (baxa and bcl2a), selected neurotransmitter receptors and bdnf was analysed. The protein levels of CREB and nNOS were also quantified.

KEY FINDINGS

Tadalafil incubation reversed the HA-associated locomotor and cognitive impairments in larvae. The treatment modulated GABA, dopamine, and glutamate levels. An upregulation in the expression of grin1a, gria2b, drd1b, drd2b, bdnf, and bcl2a, and downregulation of gabrz, gabrd, gabrg2 and baxa was observed following tadalafil treatment. The protein expression showed increased nNOS, p-CREB(Ser133), and decreased p-nNOS(Ser847) levels in the larvae incubated with tadalafil.

SIGNIFICANCE

The study concluded that tadalafil mitigates HA-induced neurological impairments by activating neuronal nitric oxide synthase. The study highlighted the possible application of tadalafil in the symptomatic management of neurological impairments in HA provided its efficacy and safety are further ensured in higher mammals.

Multimodal action of phosphodiesterase 5 inhibitors against neurodegenerative disorders: An update review

Phosphodiesterase type 5 (PDE5) is an enzyme primarily found in the smooth muscle of the corpus cavernosum and also highly expressed in the substantia nigra, cerebellum, caudate, hippocampal regions and cerebellar purkinje cells, responsible for selectively breaking down cyclic guanosine monophosphate (cGMP) into 5'-GMP and regulate intracellular cGMP levels. As a second messenger, cyclic GMP enhances signals at postsynaptic receptors and triggers downstream effector molecules, leading to changes in gene expression and neuronal responses. Additionally, cGMP signaling transduction cascade, present in the brain, is also essential for learning and memory processes. Mechanistically, PDE5 inhibitors share structural similarities with cGMP, competitively binding to PDE5 and inhibiting cGMP hydrolysis. This action enhances the effects of nitric oxide, resulting in anti-inflammatory and neuroprotective effects. Neurodegenerative disorders entail the progressive loss of neuron structure, culminating in neuronal cell death, with currently available drugs providing only limited symptomatic relief, rendering neurodegeneration considered incurable. PDE5 inhibitors have recently emerged as a potential therapeutic approach for neurodegeneration, neuroinflammation, and diseases involving cognitive impairment. This review elucidates the principal roles of 3',5'-cyclic adenosine monophosphate (cAMP) and cGMP signaling pathways in neuronal functions, believed to play pivotal roles in the pathogenesis of various neurodegenerative disorders. It provides an updated assessment of PDE5 inhibitors as disease-modifying agents for conditions such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, cerebral ischemia, Huntington's disease, and neuroinflammation. The paper aims to review the current understanding of PDE5 inhibitors, which concurrently regulate both cAMP and cGMP signaling pathways, positing that they may exert complementary and synergistic effects in modifying neurodegeneration, thus presenting a novel direction in therapeutic discovery. Moreover, the review provides critical about biological functions, therapeutic potentials, limitations, challenges, and emerging applications of selective PDE5 inhibitors. This comprehensive overview aims to guide future academic and industrial endeavors in this field.

Sildenafil-induced spinal cord infarction: a case report

Spinal cord infarction is a rare condition, accounting for only a small percentage of strokes. It can be classified into cervical and thoracolumbar infarctions, with various factors contributing to its occurrence. Sildenafil, a phosphodiesterase type 5 inhibitor commonly used for erectile dysfunction, has been associated with cardiovascular side effects, including transient hypotension. In this case report, we present the unusual occurrence of spinal cord infarction in a 65-year-old man who had self-administered high doses of sildenafil without a doctor's prescription. The patient experienced severe radicular pain in the lumbar region and subsequent weakness in the lower limbs. Evaluation revealed an anterior spinal cord infarction in the thoracic region, confirmed by MRI imaging. After excluding other potential causes, it was concluded that the intake of sildenafil likely led to systemic hypotension, resulting in spinal cord infarction. This case highlights the importance of considering sildenafil as a possible contributor to spinal cord infarction, particularly when used at high doses. Further studies are needed to better understand the relationship between sildenafil and vascular complications, including spinal cord infarction.

Unmasking hidden risks: The surprising link between PDE5 inhibitors and seizure susceptibility

BACKGROUND

Phosphodiesterase 5 inhibitors (PDE5i) are the first line treatment for erectile dysfunction; however, several articles and case reports have shown central nervous system effects, that can cause seizures in susceptible patients. This study aims to describe the changes caused by the use of Sildenafil and Tadalafil through the analysis of abnormalities expressed in the electrocorticogram (ECoG) of rats and evaluate the seizure threshold response and treatment of seizures with anticonvulsants.

MATERIALS AND METHODS

The study used 108 rats (Wistar). Before surgery for electrode placement in dura mater, the animals were randomly separated into 3 experiments for electrocorticogram analysis. Experiment 1: ECoG response to using PD5i (Sildenafil 20mg/kg and Tadalafil 2.6mg/kg p.o.). Experiment 2: ECoG response to the use of PD5i in association with Pentylenetetrazole (PTZ-30 mg/kg i.p.), a convulsive model. Experiment 3: ECoG response to anticonvulsant treatment (Phenytoin, Phenobarbital and Diazepam) of seizures induced by association IPDE5 + PTZ. All recordings were made thirty minutes after administration of the medication and analyzed for ten minutes, only once. We considered statistical significance level of *p<0.05, **p<0.01 and ***p < 0.001.

RESULTS

After administration of Sildenafil and Tadalafil, there were increases in the power of recordings in the frequency bands in oscillations in alpha (p = 0.0920) and beta (p = 0.602) when compared to the control group (p<0.001). After the use of Sildenafil and Tadalafil associated with PTZ, greater potency was observed in the recordings during seizures (p<0.001), however, the Sildenafil group showed greater potency when compared to Tadalafil (p<0.05). Phenobarbital and Diazepam showed a better response in controlling discharges triggered by the association between proconvulsant drugs.

CONCLUSIONS

PDE5i altered the ECoG recordings in the rats' motor cortexes, demonstrating cerebral asynchrony and potentiating the action of PTZ. These findings demonstrate that PDE5i can lower the seizure threshold.

Migraine Is Associated With High Risk of Erectile Dysfunction: A Systematic Review and Cumulative Analysis

BACKGROUND

Migraine, a common chronic primary headache, has been found to be associated with a high risk of erectile dysfunction (ED).

AIM

The present study aims to summarize all the evidence related to this topic and demonstrate a quantified result on the association between migraine and ED, which has not been reported in the literature.

METHODS

MEDLINE, Excerpta Medica Database, and Cochrane Library were systematically searched for identifying the eligible studies (2000-2021). This study was registered in the PROSPERO (ID: CRD42021248013).

OUTCOMES

The combined effects were synthesized with the relative risks (RR) or standard mean differences (SMD) with 95% confidence intervals (CI).

RESULTS

6 trials with a total of 51,657 participants were included, of which 6,175 were men with migraine. The pooled analysis indicated that migraine was associated with a significantly higher risk of ED as compared to the non-migraine general population (RR = 1.63, 95%CI: 1.34 to 2.0, P < .001). Consistently, men with migraine have a significantly lower IIEF-5 score than healthy controls (SMD = -3.64, 95%CI: -6.4 to -0.89, P = .01). Stratification analysis on the mean age indicated that the association between migraine and ED was much stronger in the migraine patients with age < 40 years (RR = 32.29, 95% CI: 6.41-162.64, P < .001; I2 = 0.0 %, P = .837) than in those with age > 40 years (RR = 1.75, 95% CI: 1.11-2.78, P = .017; I2 = 89.2%, P = .002). Sensitivity analysis indicated that no single study had dominated the combined RR and the heterogeneity.

CLINICAL IMPLICATIONS

ED is a common disease among migraine men, especially those patients whose age is under 40 years old. It shows a 32-fold increased risk of ED compared to the healthy controls. Migraine-induced ED may be correlated with multiple factors, that is, chronic illnesses, chronic pain, and psychosocial causes (like anxiety and depression). Since phosphodiesterase-5 inhibitors (ie, sildenafil) might induce or exacerbate migraine, thus it is not recommended to prescribe these drugs for patients with migraine-mediated ED.

CONCLUSION

The present study provides evidence that migraine is associated with a significantly high risk of ED, especially in those aged < 40 years. The pathophysiological mechanisms of this action deserve further study. He W, Yang Y, Liang H, et al. Migraine Is Associated With High Risk of Erectile Dysfunction: A Systematic Review and Cumulative Analysis. J Sex Med 2022;19:430-440.

Phosphodiesterase Type 5 Inhibitors and Visual Side Effects: A Narrative Review

Phosphodiesterase type 5 inhibitors such as sildenafil citrate and tadalafil are well known for the treatment of erectile dysfunction. However, their use in the presence of pulmonary hypertension can cause ophthalmologic side effects, including non-arteritic optic ischemic neuropathy, chorioretinopathy, glaucoma, and optic atrophy. The present review aimed to identify these visual side effects and provide recommendations. We identified articles published from January 2000 to March 2019 on diseases arising from the management of sexual dysfunction in urology or pulmonary hypertension in pneumonia that could cause pathologic alterations in eye structure based on a literature search of the MEDLINE electronic database using keywords for the most common adverse effects and different kinds of phosphodiesterase 5 inhibitors. After applying the exclusion criteria, we selected 36 of the 77 articles initially identified to write the narrative review and added 20 additional articles to completely describe the pathological entities. Phosphodiesterase type 5 inhibitors can cause side effects in the eye including ocular surface abnormalities, increased intraocular pressure and glaucoma, uveitis, non-arteritic ischemic neuropathy, chorioretinopathy, retinal occlusion, and visual field changes. There is an increased need for well-performed studies to better understand these side effects, which are common due to the wide use of sildenafil.

Neuroprotective Effects of Sildenafil on Traumatic Brain Injury in an Experimental Rat Model

Objective Not only primary injuries, secondary injuries such as posttraumatic biochemical cascades, ischemia, and hypoxia also affect the morbidity and mortality of traumatic brain injury (TBI). Sildenafil released the vasodilatation by relaxing the smooth muscle of the systemic artery and vein. Also, the effects of sildenafil are evidenced in multiple sclerosis, Alzheimer's disease, and memory loss as a part of experimental studies. Sildenafil decreases oxidative stress by increasing the cGMP level. We aimed to examine the protective effects of sildenafil on TBI with histopathological and biochemical parameters.

Method 21 Sprague–Dawley rats were separated into three groups (n = 7). “The weight drop injury model,” which was described by Marmou, was used for the head injury. Group 1: nontraumatic sham group, Group 2: nontreated TBI group, Group 3: sildenafil (100 mg/kg) treated TBI group. The whole brain and serum were collected for histopathological and biochemical study. The histopathological sections were examined under a light microscope.

Results On comparison of total antioxidant status (TAS), total oxidant status (TOS), nitric oxide (NO), and plasma nitrite/nitrate (PNOx) between groups, NO level was significantly high in group 3 (p = 0.013). Even though the TAS level was significantly high in group 3 (p = 0.02), there were no significant differences in TOS level in groups (p = 0.225). Disappearing Nissle granules occurred in a pyknotic situation in the cell nucleus, and acidophilic staining in neuron cells, which describe the neuron degeneration observed in the trauma group. The neuron degeneration markers were not seen in the sildenafil-treated trauma group.

Conclusion Our study has shown that sildenafil decreases the oxygen radicals and affects the recovery of experimental TBI in rats.

Phosphodiesterase Type 5 Inhibitors Synergize Vincristine in Killing Castration-Resistant Prostate Cancer Through Amplifying Mitotic Arrest Signaling

Combination therapies that display cancer-killing activities through either coexistent targeting of several cellular factors or more efficient suppression of a specific pathway are generally used in cancer treatment. Sildenafil, a specific phosphodiesterase type 5 (PDE5) inhibitor, has been suggested to display both cardioprotective and neuroprotective activities that provide a rationale for the combination with vincristine on the treatment against castration-resistant prostate cancer (CRPC). In the present work, vincristine arrested cells in the metaphase stage of mitosis. Vincristine-induced mitotic arrest was identified by Cdk1 activation (i.e., increased Cdk1^Thr161 phosphorylation and decreased Cdk1^Tyr15 phosphorylation), cyclin B1 upregulation, and increased phosphorylation of multiple mitotic proteins and stathmin. Sildenafil synergistically potentiated vincristine-induced mitotic arrest and a dramatic increase of mitotic index. Furthermore, sildenafil potentiated vincristine-induced mitochondrial damage, including Mcl-1 downregulation, Bcl-2 phosphorylation and downregulation, Bak upregulation and loss of mitochondrial membrane potential, and sensitized caspase-dependent apoptotic cell death. Sildenafil-mediated synergistic effects were mimicked by other PDE5 inhibitors including vardenafil and tadalafil, and also by PDE5A knockdown in cells, suggesting PDE5-involved mechanism. Notably, sildenafil amplified vincristine-induced phosphorylation and cleavage of BUBR1, a protein kinase in spindle assembly checkpoint (SAC) function and chromosome segregation. Sildenafil also significantly decreased kinetochore tension during SAC activation. Moreover, sildenafil synergized with vincristine on suppressing tumor growth in an in vivo model. In conclusion, the data suggest that sildenafil, in a PDE5-dependent manner, potentiates vincristine-induced mitotic arrest signaling, and sensitizes mitochondria damage–involved apoptosis in CRPC. Both in vitro and in vivo data suggest the combination potential of PDE5 inhibitors and vincristine on CRPC treatment.

Sildenafil promotes the anti-amnesic activity of estrogen receptor alpha agonist in animals with estrogen insufficiency

The cognitive function in the females is observed to modulate with the fluctuation in plasma estrogen level. The specific estrogen receptor alpha (ERα) agonist, (4,4',4″-(4-propyl-[1H] pyrazole-1,3,5-triyl) tris phenol (PPT), exerts similar therapeutic activity to that of estrogen replacement therapy. It can also exert cyclic adenosine monophosphate (cAMP)-dependent carcinogenic activity in the uterus of the ovariectomized animals. However, there is no report of cGMP on the ERα-mediated phosphorylation of Akt in the experimental condition. Sildenafil increases the level of cGMP in most of the tissues including brain. Hence, the present study evaluated the therapeutic effect of Sildenafil with or without PPT in rats with experimentally-induced estrogen insufficiency. The condition of estrogen insufficiency was induced in female rats through bilateral ovariectomy on day-1 (D-1) of the experimental schedule. Sildenafil (1.0 and 10.0 mg/kg) and PPT attenuated ovariectomy-induced cognitive deficits in behavioural tests and increase in body weight in the rodents. Sildenafil and PPT increased the cholinergic function and the ratio of cGMP/cAMP in the hippocampus, pre-frontal cortex and amygdala of the animals. Further, the ovariectomy-induced decrease in the extent of phosphorylation of ERα in all the brain regions was attenuated with the monotherapy of either Sildenafil or PPT. Interestingly, the combination of Sildenafil and PPT exhibited better therapeutic effectiveness than their monotherapy. However, Sildenafil attenuated the PPT-induced increase in the level of expression of phosphorylated protein kinase-B (Akt) in the discrete brain regions and the weight of uterus of these rodents. Hence, it can be assumed that the combination could be a better therapeutic alternative with minimal side effect in the management of estrogen insufficiency-induced disorders.

The effect of sildenafil on retinal blood velocity in healthy subjects

Purpose

It has been suggested that Sildenafil may have beneficial therapeutic effects in the treatment of neurodegenerative disorders. The retinal circulation is of significant interest as a marker of cerebral vascular disease since the retinal and cerebral vasculatures share many morphological and physiological properties, yet only the retinal circulation can be directly visualized. Therefore, our aim was to assess the change induced by Sildenafil on retinal blood velocity.

Methods

Retinal flow velocity was measured 0.5, 3 and 6 h following administration of 100 mg of Sildenafil using the Retinal Function Imager.

Results

No clinical change in either systemic blood pressure or retinal flow velocities were observed. However, when controlling for heart rate and blood pressure, a significant drop in venous flow velocity 6 h following treatment (mean drop 0.3 ± 0.07; 95% CI: 0.44–0.56, P = 0.023) was revealed.

Conclusions

In healthy volunteers, retinal venous flow velocity was significantly reduced at the 6-h time point following Sildenafil treatment. No effect was observed on arterial retinal flow velocity.

Sildenafil protective effects on high glucose-induced neurotoxicity in PC12 cells: the role of oxidative stress, apoptosis, and inflammation pathways in an in vitro cellular model for diabetic neuropathy

Objectives Diabetic neuropathy (DN) induces lifetime disability and there is currently no effective therapy to treat or to minimize patients suffering, so it is thereby imperative to develop therapeutic strategies for this disease. Since oxidative stress, mitochondrial dysfunction, apoptosis, and inflammation are crucial mechanisms in development and progression of DN, it is important to explore tools by which one can reduce factors related to these pathways. Herein, the understandings of the sildenafil neuroprotective effect through increase of cGMP level and the mediation of oxidative stress, apoptosis, and inflammation pathways on neurotoxicity induced by high glucose (HG) in PC12 cells as an in vitro cellular model for DN were investigated. Methods We reported that the PC12 cells pre-treatment with sildenafil (0.008 μM) for 60 min and then exposing the cells to HG (25 mM for 72 h) or normal glucose (NG) (5 mM for 72 h) condition, show: Results (1) significant attenuation in reactive oxygen species, MDA and TNF-a levels, Bax/Bcl-2 ratio, expression of caspase 3 and UCP2 proteins; (2) significant increase in viability, GSH/GSSG ratio, mitochondrial membrane potential, and ATP levels. Conclusion All these data together led us to propose neuroprotective effect of sildenafil is probably through its antioxidant, antiapoptotic, and anti-inflammatory activities. Of course, further studies are required to explain the underlying mechanism of the sildenafil effects.

Effect of chronic administration of sildenafil citrate (Viagra) on the histology of the retina and optic nerve of adult male rat

BACKGROUND

Abnormal vision has been reported by 3% of patients treated with sildenafil citrate (Viagra). Although many men use Viagra for an extended period for treatment of erectile dysfunction, the implications of the long term-daily use of it on the retina and optic nerve are unclear.

AIM OF THE WORK

To investigate the effect of chronic daily use of sildenafil citrate in a dose equivalent to men preferred therapeutic dose on the histology of the retina and optic nerve of adult male rat.

MATERIAL & METHODS

Eighteen adult male Wistar rats were equally divided into three groups. Group I: control. Group II: treated with sildenafil citrate orally (10mg/kg/day) for 8 weeks. Group III (withdrawal): treated as group II and then left for 4 weeks without treatment. Specimens from the retina and optic nerve were processed for light and electron microscopy.

RESULTS

In sildenafil citrate treated group, the retina and optic nerve revealed vacuolations and congested blood capillaries with apoptotic endothelial and pericytic cells, and thickened basal lamina. Caspase-3 (apoptotic marker) and CD31 (endothelial marker) expression increased. Glial cells revealed morphological changes: Müller cells lost their processes, activated microglia, astrocytic clasmatodendrosis, degenerated oligodendrocytes surrounded by disintegrated myelin sheathes of the optic nerve fibers. The retina and optic nerve of the withdrawal group revealed less vacuolations and congestion, and partial recovery of the glial cells.

CONCLUSION

Chronic treatment with sildenafil citrate (Viagra) caused toxic effect on the structure of the retina and optic nerve of the rat. Partial recovery was observed after drug withdrawal.

Useful Implications of Low-dose Long-term Use of PDE-5 Inhibitors

INTRODUCTION

Phosphodiesterase type 5 (PDE-5) hydrolyzes cyclic guanylate monophosphate (cGMP) specifically to 5' GMP, promoting successful corporeal vascular relaxation and penile erection during sexual stimulation. Oral PDE-5 inhibitors such as sildenafil, vardenafil, tadalafil, and avanafil have provided noninvasive, effective, well-tolerated treatment for erectile dysfunction (ED) patients and, at the same time, stimulated both academic and clinical interests. Lately, some oral PDE-5 inhibitors were released as low-dose preparations with the concept of potential daily administration and long-term use.

AIM

To highlight the possible potential implications of low-dose long-term use of PDE-5 inhibitors.

METHOD

A systematic review was carried out until December 2015 based on a search of all concerned articles in MEDLINE, medical subjects heading (MeSH) databases, Scopus, The Cochrane Library, EMBASE, and CINAHL databases without language restriction. Key words used to assess the outcome and estimates for concerned associations were: PDE-5 inhibitors; erectile dysfunction; low-dose; long-term; sildenafil; tadalafil; vardenafil; avanafil.

MAIN OUTCOME MEASURES

Demonstrating different implications for low-dose long-term use of PDE-5 inhibitors.

RESULTS

Low-dose and/or long-term use of PDE-5 inhibitors was shown to put forth beneficial sound effects in different medical implications with potentials that could be extended for different utilities. These implications included sexual, urogenital, cardiovascular, pulmonary, cutaneous, gastrointestinal, and reproductive, as well as neurological disorders. However, it is evident that most potential appliances were carried out experimentally on preclinical studies with off-label indications.

CONCLUSION

Making use of and exploring low-dose and/or long-term use of several PDE-5 inhibitors for their possible implications seem to be valuable in different medical disorders. Increased knowledge of the drug characteristics, comparative treatment regimens, optimal prescribing patterns, and well-designed clinical trials are needed before these agents can be recommended for use.

A Phase I proof-of-concept and safety trial of sildenafil to treat cerebral vasospasm following subarachnoid hemorrhage

OBJECTIVE

Studies show that phosphodiesterase-V (PDE-V) inhibition reduces cerebral vasospasm (CVS) and improves outcomes after experimental subarachnoid hemorrhage (SAH). This study was performed to investigate the safety and effect of sildenafil (an FDA-approved PDE-V inhibitor) on angiographic CVS in SAH patients.

METHODS

A2-phase, prospective, nonrandomized, human trial was implemented. Subarachnoid hemorrhage patients underwent angiography on Day 7 to assess for CVS. Those with CVS were given 10 mg of intravenous sildenafil in the first phase of the study and 30 mg in the second phase. In both, angiography was repeated 30 minutes after infusion. Safety was assessed by monitoring neurological examination findings and vital signs and for the development of adverse reactions. For angiographic assessment, in a blinded fashion, pre- and post-sildenafil images were graded as "improvement" or "no improvement" in CVS. Unblinded measurements were made between pre- and post-sildenafil angiograms.

RESULTS

Twelve patients received sildenafil; 5 patients received 10 mg and 7 received 30 mg. There were no adverse reactions. There was no adverse effect on heart rate or intracranial pressure. Sildenafil resulted in a transient decline in mean arterial pressure, an average of 17% with a return to baseline in an average of 18 minutes. Eight patients (67%) were found to have a positive angiographic response to sildenafil, 3 (60%) in the low-dose group and 5 (71%) in the high-dose group. The largest degree of vessel dilation was an average of 0.8 mm (range 0-2.1 mm). This corresponded to an average percentage increase in vessel diameter of 62% (range 0%-200%).

CONCLUSIONS

The results from this Phase I safety and proof-of-concept trial assessing the use of intravenous sildenafil in patients with CVS show that sildenafil is safe and well tolerated in the setting of SAH. Furthermore, the angiographic data suggest that sildenafil has a positive impact on human CVS.

Neuroprotective effects of sildenafil in experimental spinal cord injury in rabbits

Neuroprotective agents such as methylprednisolone and sildenafil may limit damage after spinal cord injury. We evaluated the effects of methylprednisolone and sildenafil on biochemical and histologic changes after spinal cord injury in a rabbit model. Female New Zealand rabbits (32 rabbits) were allocated to 4 equal groups: laminectomy only (sham control) or laminectomy and spinal trauma with no other treatment (trauma control) or treatment with either methylprednisolone or sildenafil. Gelsolin and caspase-3 levels in cerebrospinal fluid and plasma were determined, and spinal cord histology was evaluated at 24 hours after trauma. There were no differences in mean cerebrospinal fluid or plasma levels of caspase-3 between the groups or within the groups from 0 to 24 hours after injury. From 0 to 24 hours after trauma, mean cerebrospinal fluid gelsolin levels significantly increased in the sildenafil group and decreased in the sham control and the trauma control groups. Mean plasma gelsolin level was significantly higher at 8 and 24 hours after trauma in the sildenafil than other groups. Histologic examination indicated that general structural integrity was better in the methylprednisolone in comparison with the trauma control group. General structural integrity, leptomeninges, white and grey matter hematomas, and necrosis were significantly improved in the sildenafil compared with the trauma control group. Caspase-3 levels in the cerebrospinal fluid and blood were not increased but gelsolin levels were decreased after spinal cord injury in trauma control rabbits. Sildenafil caused an increase in gelsolin levels and may be more effective than methylprednisolone at decreasing secondary damage to the spinal cord. 

Regional cerebral blood flow following single-dose and continuous-dose tadalafil after stroke

PURPOSE

Tadalafil is a potent and selective phosphodiesterase type 5 inhibitor that provides effective treatment for erectile dysfunction (ED). The purpose of this study was to explore the effect of a single on-demand dose of tadalafil compared to low-dose continuous administration on regional cerebral blood flow (rCBF), in patients after stroke.

METHODS

Thirty consecutive male patients (mean age 58.3 ± 7.9 years) with ED and a history of stroke were included in the study. The baseline single-photon emission computed tomography (SPECT) study was performed 15 min after iv injection of 740 MBq Tc-99m-HMPAO (Ceretec; GE Healthcare Ltd. Chalfont St. Giles, UK). Fifteen randomized patients received a single dose of 20 mg tadalafil in the morning, and a second SPECT study was performed 6 h later. Fifteen other patients received 5 mg of tadalafil each morning for seven consecutive days, and the second SPECT study was performed 6 h after the last dose. The imaging data were evaluated using SPM software (Wellcome Department of Cognitive Neurology, University College, London).

RESULTS

Associations between any of the risk factors/comorbidities and the perfusion changes were not detected. All patients showed areas of reduced relative rCBF in the affected hemisphere after tadalafil administration compared to baseline (P < 0.001). No significant difference was found between patients on 5 mg tadalafil and 20 mg dose.

CONCLUSION

Tadalafil administration after cerebral stroke may be associated with diminished blood flow to areas adjacent to the stroke. The alterations in perfusion suggest a need for caution in prescribing tadalafil to patients with a history of stroke, especially with continuous administration that may impose constant stress on the cerebral circulation.

Regulating the ubiquitin/proteasome pathway via cAMP-signaling: neuroprotective potential

The cAMP-signaling pathway has been under intensive investigation for decades. It is a wonder that such a small simple molecule like cAMP can modulate a vast number of diverse processes in different types of cells. The ubiquitous involvement of cAMP-signaling in a variety of cellular events requires tight spatial and temporal control of its generation, propagation, compartmentalization, and elimination. Among the various steps of the cAMP-signaling pathway, G-protein-coupled receptors, adenylate cyclases, phosphodiesterases, the two major cAMP targets, i.e., protein kinase A and exchange protein activated by cAMP, as well as the A-kinase anchoring proteins, are potential targets for drug development. Herein we review the recent progress on the regulation and manipulation of different steps of the cAMP-signaling pathway. We end by focusing on the emerging role of cAMP-signaling in modulating protein degradation via the ubiquitin/proteasome pathway. New discoveries on the regulation of the ubiquitin/proteasome pathway by cAMP-signaling support the development of new therapeutic approaches to prevent proteotoxicity in chronic neurodegenerative disorders and other human disease conditions associated with impaired protein turnover by the ubiquitin/proteasome pathway and the accumulation of ubiquitin-protein aggregates.

Stimulation of neural stem cell proliferation by inhibition of phosphodiesterase 5

The involvement of nitric oxide (NO) and cyclic GMP (cGMP) in neurogenesis has been progressively unmasked over the last decade. Phosphodiesterase 5 (PDE5) specifically degrades cGMP and is highly abundant in the mammalian brain. Inhibition of cGMP hydrolysis by blocking PDE5 is a possible strategy to enhance the first step of neurogenesis, proliferation of neural stem cells (NSC). In this work, we have studied the effect on cell proliferation of 3 inhibitors with different selectivity and potency for PDE5, T0156, sildenafil, and zaprinast, using subventricular zone-(SVZ-) derived NSC cultures. We observed that a short- (6 h) or a long-term (24 h) treatment with PDE5 inhibitors increased SVZ-derived NSC proliferation. Cell proliferation induced by PDE5 inhibitors was dependent on the activation of the mitogen-activated protein kinase (MAPK) and was abolished by inhibitors of MAPK signaling, soluble guanylyl cyclase, and protein kinase G. Moreover, sildenafil neither activated ERK1/2 nor altered p27^Kip1 levels, suggesting the involvement of pathways different from those activated by T0156 or zaprinast. In agreement with the present results, PDE5 inhibitors may be an interesting therapeutic approach for enhancing the proliferation stage of adult neurogenesis.

PDE5 inhibitors: considerations for preference and long-term adherence

INTRODUCTION

Erectile dysfunction (ED) is a highly prevalent condition affecting nearly one in five men worldwide. The advent of phosphodiesterase type 5 inhibitors (PDE5i) has revolutionised the ED treatment landscape and provided effective, minimally invasive therapies to restore male sexual function.

MATERIALS AND METHODS

A pubmed search was performed of all English language articles from 1996 to present reviewing PDE5i, including pharmacokinetics, efficacy profiles and comparisons, where available.

RESULTS

Currently available PDE5i in the United States include sildenafil, vardenafil, tadalafil and avanafil, each of which has unique side effect, pharmacokinetic and outcome profiles. Sildenafil is associated with increased rate of visual changes, vardenafil with QT prolongation and tadalafil with lower back pain. Avanafil and vardenafil orodispersible tablet rapidly achieve peak plasma concentration, which results in faster onset of action, whereas tadalafil exhibits the longest half-life. First time response to PDE5i is approximately 60-70%, with no significant differences in efficacy noted among therapies. The literature does not clearly demonstrate a preference for one drug. High-treatment success rates (89%) were reported when patients were prescribed all available PDE5i. Daily dosing with tadalafil is associated with improved erectile function (EF) over time. Finally, novel modes of patient-provider interaction, including internet-based education, communication and prescribing, may also improve long-term adherence.

CONCLUSIONS

PDE5i represent first line therapy for ED with excellent overall efficacy and satisfactory side effect profiles. Enhanced communciation, coupled with increased knowledge of drug characteristics, comparative treatment regimens and optimal prescribing patterns, offer compelling tools to improve long-term treatment success.

Neuroprotective role of PDE4 and PDE5 inhibitors in 3-nitropropionic acid induced behavioral and biochemical toxicities in rats

Phosphodiesterase inhibitors have been reported to be beneficial in cognitive and motor disorders. In the present study, we have investigated the effects of RO 20-1724 (PDE4 inhibitor) and sildenafil (PDE5 inhibitor) in 3-nitropropionic acid (3-NP) induced experimental Huntington's disease in rats. 3-Nitropropionic acid was administered for 14 days (10 mg/kg i.p.) 1h following 3-NP administration, the rats were treated with either vehicle, RO 20-1724 (0.25 and 0.5 mg/kg i.p.) or sildenafil (2 and 4 mg/kg i.p.) for 14 days. Cognitive functions were assessed by using Morris water maze whereas, motor functions were assessed by spontaneous locomotor activity, limb withdrawal and suspended wire test at different time points. Biochemically, markers of oxidative stress and cell damage, such as reduced glutathione, malondialdehyde, nitrite and lactate dehydrogenase levels were assessed terminally in the brain homogenate. Chronic administration of 3-NP produced significant decrease in body weight, showed marked abnormalities in cognitive and motor functions. Further, significant oxidative-nitrosative stress and cell damage was also observed. Chronic administration of RO 20-1724 and sildenafil in 3-NP treated rats significantly and dose dependently attenuated 3-NP induced behavioral and biochemical abnormalities in rats. Both these drugs were equally effective in attenuating 3-NP induced neurotoxicity. These results suggesting that the inhibition of PDE4 and PDE5 would be therapeutic in neurodegenerative disorders associated with cognitive and motor dysfunction.

Partial motor restoration upon administration of sildenafil: a case study

OBJECTIVE

Extensive research in the past decade has confirmed that the adult brain maintains some plasticity, including neural cell birth, migration and integration. Pre-clinical data strongly suggest that phosphodiesterase type 5 (PDE5) inhibitors promote cerebral neovascularization and neurogenesis. Animal studies of cerebral stroke suggest potential regenerative benefits following treatment with sildenafil citrate, a PDE5 inhibitor. This study reports a case in which compassionate use of sildenafil was investigated as a treatment to improve physical functioning, more than 4 decades after development of spastic quadriplegia during the 1st-2nd year of life.

METHODS

Sildenafil 100 mg was administered every 24 hours for 7 months.

RESULTS

Sildenafil treatment was associated with clinical (functional) improvement.

CONCLUSIONS

The activity of sildenafil on cerebral neovascularization and neurogenesis may be the mechanism for the observed functional benefits.

Sildenafil improves epicenter vascular perfusion but not hindlimb functional recovery after contusive spinal cord injury in mice

Nitric oxide (NO) is an important regulator of vasodilation and angiogenesis in the central nervous system (CNS). Signaling initiated by the membrane receptor CD47 antagonizes vasodilation and angiogenesis by inhibiting synthesis of cyclic guanosine monophosphate (cGMP). We recently found that deletion of CD47 led to significant functional locomotor improvements, enhanced angiogenesis, and increased epicenter microvascular perfusion in mice after moderate contusive spinal cord injury (SCI). We tested the hypothesis that improving NO/cGMP signaling within the spinal cord immediately after injury would increase microvascular perfusion, angiogenesis, and functional recovery, with an acute, 7-day administration of the cGMP phosphodiesterase 5 (PDE5) inhibitor sildenafil. PDE5 expression is localized within spinal cord microvascular endothelial cells and smooth muscle cells. While PDE5 antagonism has been shown to increase angiogenesis in a rat embolic stroke model, sildenafil had no significant effect on angiogenesis at 7 days post-injury after murine contusive SCI. Sildenafil treatment increased cGMP concentrations within the spinal cord and improved epicenter microvascular perfusion. Basso Mouse Scale (BMS) and Treadscan analyses revealed that sildenafil treatment had no functional consequence on hindlimb locomotor recovery. These data support the hypothesis that acutely improving microvascular perfusion within the injury epicenter by itself is an insufficient strategy for improving functional deficits following contusive SCI.

Sildenafil-induced cervical spinal cord infarction

We present a patient with an acute cervical spinal cord infarction resulting from the use of sildenafil (Viagra) in combination with his hypertension medication. Symptoms were acute and rapidly progressive, and MR imaging with DWI was crucial in confirming the diagnosis.

Effects of sildenafil and tadalafil on ischemia/reperfusion injury in fetal rat brain

OBJECTIVE

The aim of the present study was to evaluate the effects of phosphodiesterase type 5 (PDE5) inhibitory drugs, sildenafil and tadalafil, in ischemia/reperfusion (I/R)-induced oxidative injury in fetal rat brain.

METHODS

Timed pregnant adult Wistar rats were randomly assigned to the following groups (n = 6 for each group): saline + none I/R (1), saline + I/R (2), sildenafil + none I/R (3); sildenafil + I/R (4), tadalafil + none I/R (5) and tadalafil + I/R (6). Fetal ischemia was induced by clamping the utero-ovarian artery bilaterally. Fetuses were delivered and 268 fetal rats were decapitated. Malondialdehyde (MDA) levels and, superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities were assessed in fetal brain tissue homogenates by spectrophotometric methods.

RESULTS

In saline + I/R group, MDA levels were increased and, SOD and GSH-Px activities were decreased significantly comparing with saline + none I/R group. Both tadalafil and sildenafil treatment decreased the MDA levels significantly in ischemia/reperfusion groups, whereas this effect was significantly more potent with tadalafil. SOD levels were significantly decreased in all groups after I/R. Tadalafil seems to be more effective than sildenafil by means of increasing GSH-Px activity significantly after I/R.

CONCLUSION

Our results indicate some beneficial effects of PDE5 inhibitory drugs, especially tadalafil, on oxidative I/R injury in fetal rat brains.

Stem cell-based neuroprotective and neurorestorative strategies

Stem cells, a special subset of cells derived from embryo or adult tissues, are known to present the characteristics of self-renewal, multiple lineages of differentiation, high plastic capability, and long-term maintenance. Recent reports have further suggested that neural stem cells (NSCs) derived from the adult hippocampal and subventricular regions possess the utilizing potential to develop the transplantation strategies and to screen the candidate agents for neurogenesis, neuroprotection, and neuroplasticity in neurodegenerative diseases. In this article, we review the roles of NSCs and other stem cells in neuroprotective and neurorestorative therapies for neurological and psychiatric diseases. We show the evidences that NSCs play the key roles involved in the pathogenesis of several neurodegenerative disorders, including depression, stroke and Parkinson’s disease. Moreover, the potential and possible utilities of induced pluripotent stem cells (iPS), reprogramming from adult fibroblasts with ectopic expression of four embryonic genes, are also reviewed and further discussed. An understanding of the biophysiology of stem cells could help us elucidate the pathogenicity and develop new treatments for neurodegenerative disorders. In contrast to cell transplantation therapies, the application of stem cells can further provide a platform for drug discovery and small molecular testing, including Chinese herbal medicines. In addition, the high-throughput stem cell-based systems can be used to elucidate the mechanisms of neuroprotective candidates in translation medical research for neurodegenerative diseases.

Subarachnoid Hemorrhage and Intracerebral Hematoma due to Sildenafil Ingestion in a Young Adult

Sildenafil citrate (Viagra(R); Pfeizer US Pharmaceutical Group, New York, NY, USA) is a potent vasodilating agent to treat male erectile dysfunction. Among its adverse effects, hemorrhagic stroke has not been widely reported yet. We present a case of a 33-year-old healthy man who ingested 50 mg sildenafil a half hour before onset of headache, nervousness and speech disturbance. Head computed tomogram of this stuporous man showed huge intracerebral hemorrhage and thick subarachnoid hemorrhage, but angiography failed to disclose any vascular anomalies. Subsequent surgical procedure was followed, and rehabilitation was provided thereafter. Sildenafil seems to act by redistributing arterial blood flow, and concurrent sympathetic hyperactivity, which lead to such hemorrhagic presentation. Extreme caution should be paid on even in a young adult male patient wven without known risk factors.