Effects of tadalafil on skeletal muscle tissue: exploring interactions and novel mechanisms of action.

Beside its mechanical roles in controlling posture and locomotion, skeletal muscle system, the largest insulin and steroid hormones target tissue, plays a key role in influencing thermoregulation, secondary sexual characteristics, hormones metabolism, and glucose uptake and storage, as well as energetic metabolism. Indeed, in addition to insulin, several hormones influence the skeletal muscle metabolism/function and/or are influenced by skeletal muscles activity (i.e., physical exercise). Particularly, steroid hormones play a key role in modulating many biological processes in muscles, essential for overall muscle's function and homeostasis, both at rest and during all physical activities (i.e., physical exercise, muscular work). Phosphodiesterase type 5 (PDE5) is the enzyme engaged to hydrolyze cyclic guanosine monophosphate (cGMP) in inactive 5'-GMP form. Therefore, through the inhibition of this enzyme, the intracellular level of cGMP increases, and the cGMP-related cellular responses are prolonged. Different drugs inhibiting PDE5 (PDE5i) exist, and the commercially available PDE5i are sildenafil, vardenafil, tadalafil, and avanafil. The PDE5i tadalafil may influence cellular physiology and endocrine-metabolic pathways in skeletal muscles and exerts its functions both by activating the cell signaling linked to the insulin-related metabolic pathways and modulating the endocrine responses, protein catabolism and hormone-related anabolism/catabolism during and after physical exercise-related stress. Based on recent in-vivo and in-vitro findings, in this narrative review the aim was to summarize the available evidence describing the interactions between the PDE5i tadalafil and steroid hormones in skeletal muscle tissue and physical exercise adaptation, focusing our interest on their possible synergistic or competitive action(s) on muscle metabolism and function.

The PDE5 inhibitor, vardenafil, ameliorates progressive pathological changes in a focal segmental glomerulosclerosis mouse model.

AIMS: Phosphodiesterase 5 inhibitors (PDE5is) inhibit the hydrolysis of cyclic guanosine 5'-monophosphate in smooth muscle cells and are a widely known treatment for erectile dysfunction. Accumulating evidence also suggests that PDE5is exhibit potential benefits in cardiovascular and chronic kidney diseases. In this study, we examined the therapeutic effects of a PDE5i, vardenafil (VAR), in a focal segmental glomerulosclerosis (FSGS) mouse model. MATERIALS AND METHODS: FSGS was induced in BALB/c mice by the intravenous administration of Adriamycin (AD, 11 mg/kg of body weight). After 24 h, VAR (at 12.5 µg/ml) was given in drinking water ad libitum until the animals were sacrificed. At the end of the experiment, plasma and kidney samples were harvested to evaluate clinical parameters, histopathological changes, and alterations in transcriptome and protein expressions. KEY FINDINGS: In this study, VAR treatment attenuated the deterioration of proteinuria, renal dysfunction, and hypercholesterolemia in AD-induced FSGS. Treatment with VAR exhibited reductions in the severity of both glomerulosclerosis and tubulointerstitial injury in the histological analysis. In addition to relieving AD-induced podocyte loss, VAR also preserved endothelial cells in glomerular capillaries and ameliorated the accumulation of collagen fibers in the mesangial area and Bowman's capsule basement membrane. In addition, VAR showed an ability to suppress transforming growth factor-ß-induced fibroblast-to-myofibroblast transdifferentiation. SIGNIFICANCE: Our data suggest that VAR exhibited reno-therapeutic effects via attenuating podocyte loss, preserving the integrity of the glomerular vasculature, and ameliorating fibrotic changes. These findings suggest that PDE5is might be a promising treatment modality for nephrotic syndrome.

The NO/cGMP/PKG pathway in platelets: The therapeutic potential of PDE5 inhibitors in platelet disorders.

Platelets are the "guardians" of the blood circulatory system. At sites of vessel injury, they ensure hemostasis and promote immunity and vessel repair. However, their uncontrolled activation is one of the main drivers of thrombosis. To keep circulating platelets in a quiescent state, the endothelium releases platelet antagonists including nitric oxide (NO) that acts by stimulating the intracellular receptor guanylyl cyclase (GC). The latter produces the second messenger cyclic guanosine-3',5'-monophosphate (cGMP) that inhibits platelet activation by stimulating protein kinase G, which phosphorylates hundreds of intracellular targets. Intracellular cGMP pools are tightly regulated by a fine balance between GC and phosphodiesterases (PDEs) that are responsible for the hydrolysis of cyclic nucleotides. Phosphodiesterase type 5 (PDE5) is a cGMP-specific PDE, broadly expressed in most tissues in humans and rodents. In clinical practice, PDE5 inhibitors (PDE5i) are used as first-line therapy for erectile dysfunction, pulmonary artery hypertension, and lower urinary tract symptoms. However, several studies have shown that PDE5i may ameliorate the outcome of various other conditions, like heart failure and stroke. Interestingly, NO donors and cGMP analogs increase the capacity of anti-platelet drugs targeting the purinergic receptor type Y, subtype 12 (P2Y12) receptor to block platelet aggregation, and preclinical studies have shown that PDE5i inhibits platelet functions. This review summarizes the molecular mechanisms underlying the effect of PDE5i on platelet activation and aggregation focusing on the therapeutic potential of PDE5i in platelet disorders, and the outcomes of a combined therapy with PDE5i and NO donors to inhibit platelet activation.

Effects of phosphodiesterase 5 inhibition on cardiovascular function in resistant hypertension: A systematic review.

Approximately 12-18% of hypertensive patients are diagnosed with resistant hypertension (RH). The risk of having worse cardiovascular outcomes is twice higher in those patients. The low effectiveness of conventional antihypertensive drugs in RH emphasizes the need to evaluate complementary drug therapies to achieve blood pressure (BP) control. Previous studies have demonstrated that phosphodiesterase 5 (PDE-5) inhibitors improve hemodynamics and reduce BP on essential hypertension. So, the authors aimed to summarize current clinical trials-based evidence published concerning the use of PDE-5 inhibitors on BP, cardiovascular function, and hemodynamics of patients with RH. We searched MEDLINE, EMBASE, LILACS, ClinicalTrials.gov, and WHO International Clinical Trials Registry databases on May 15th, 2020 using pre-defined search terms. Two independent reviewers assessed and extracted data from clinical trials that evaluated the effect of PDE-5 inhibitors on BP. We have included five articles in this systematic review. Four of them developed a single-day protocol, while one has developed a 14-day study. The main findings indicate that PDE-5 inhibitors ameliorate BP, vascular hemodynamics, and diastolic function parameters. Some data demonstrated improvement of endothelial function, but it was not a consensus. The side effects seemed to be limited and well-tolerated. In brief, our systematic review highlights the potential of PDE-5 inhibitors as a therapeutic alternative in addition to the multiple-drug regime for RH. Larger studies are still needed to determine whether the beneficial effects of PDE-5 inhibitors on RH would be maintained with chronic administration.

High frequency of potential phosphodiesterase type 5 inhibitor drug interactions in males with HIV infection and erectile dysfunction.

OBJECTIVES: We sought to determine the prevalence of phosphodiesterase type 5 inhibitor (PDE-5) mediated drug-drug interactions (DDIs) in males with HIV infection receiving antiretroviral therapy (ART) and identify factors associated with PDE-5-mediated DDIs. METHODS: Male US Military HIV Natural History Study participants diagnosed with erectile dysfunction (ED) and having a PDE-5 inhibitor and potentially-interacting ART co-dispensed within 30 days were included. DDIs were defined according to criteria found in published guidelines and drug information resources. The primary outcome of interest was overall PDE-5 inhibitor-mediated DDI prevalence and episode duration. A secondary logistic regression analysis was performed on those with and without DDIs to identify factors associated with initial DDI episode. RESULTS: A total of 235 male participants with ED met inclusion criteria. The majority were White (50.6%) or African American (40.4%). Median age at medication co-dispensing (45 years), duration of HIV infection (14 years), and duration of ED (1 year) did not differ between the two groups (p>0.05 for all). PDE-5 inhibitors included sildenafil (n = 124), vardenafil (n = 99), and tadalafil (n = 14). ART regimens included RTV-boosted protease inhibitors (PIs) atazanavir (n = 83) or darunavir (n = 34), and COBI-boosted elvitegravir (n = 43). Potential DDIs occurred in 181 (77.0%) participants, of whom 122 (67.4%) had multiple DDI episodes. The median DDI duration was 8 (IQR 1-12) months. In multivariate analyses, non-statistically significant higher odds of DDIs were observed with RTV-boosted PIs or PI-based ART (OR 2.13, 95% CI 0.85-5.37) and in those with a diagnosis of major depressive disorder (OR 1.74, 95% CI 0.83-3.64). CONCLUSIONS: PDE-5-mediated DDIs were observed in the majority of males with HIV infection on RTV- or COBI-boosted ART in our cohort. This study highlights the importance of assessing for DDIs among individuals on ART, especially those on boosted regimens.

From Celecoxib to a Novel Class of Phosphodiesterase 5 Inhibitors: Trisubstituted Pyrazolines as Novel Phosphodiesterase 5 Inhibitors with Extremely High Potency and Phosphodiesterase Isozyme Selectivity.

A ligand-based approach involving systematic modifications of a trisubstituted pyrazoline scaffold derived from the COX2 inhibitor, celecoxib, was used to develop novel PDE5 inhibitors. Novel pyrazolines were identified with potent PDE5 inhibitory activity lacking COX2 inhibitory activity. Compound d12 was the most potent with an IC50 of 1 nM, which was three times more potent than sildenafil and more selective with a selectivity index of >10,000-fold against all other PDE isozymes. Sildenafil inhibited the full-length and catalytic fragment of PDE5, while compound d12 only inhibited the full-length enzyme, suggesting a mechanism of enzyme inhibition distinct from sildenafil. The PDE5 inhibitory activity of compound d12 was confirmed in cells using a cGMP biosensor assay. Oral administration of compound d12 achieved plasma levels >1000-fold higher than IC50 values and showed no discernable toxicity after repeated dosing. These results reveal a novel strategy to inhibit PDE5 with unprecedented potency and isozyme selectivity.

NCX 1741, a Novel Nitric Oxide-Donating Phosphodiesterase-5 Inhibitor, Exerts Rapid and Long-Lasting Intraocular Pressure-Lowering in Cynomolgus Monkeys.

Purpose: We studied the IOP-lowering effects of NCX 1741, a novel nitric oxide (NO)-donating derivative of the phosphodiesterase type-5 inhibitor, avanafil, in Cynomolgus monkey with laser-induced ocular hypertension (OHT-monkeys). NCX 1193 (NO-donating moiety), NCX 1744 (NCX 1741 without ester nitrate moiety), and travoprost (PGF2α analogue) were used for comparison. Ocular exposure after NCX 1741 dosing also was addressed. Methods: Vehicle (phosphate buffer pH 6.0, Kolliphor® 5%, DMSO 0.3%, benzalkonium chloride 0.02%), NCX 1741, NCX 1193, NCX 1744, or travoprost were instilled (30 µL; single dose) masked and conscious IOPs were measured by pneumatonometry. LC-MS/MS-based methods were employed to monitor ocular exposure of NCX 1741 and main metabolites after ocular dosing in New Zealand White rabbits. Results: NCX 1741 (2.2%, 0.8 µmol/eye) lowered IOP with an Emax (ΔΔIOP, IOP change vs. pre-dose and vehicle) between 5 and 8 h post-dosing (ΔΔIOP5h, -5.3 ± 2.0 mmHg and ΔΔIOP8h, -6.0 ± 2.1 mmHg). Conversely, equimolar (0.47%, 0.8 µmol/eye) NCX 1193 IOP-lowering effects were maximal 3 h post-dosing (ΔΔIOP3h, -4.7 ± 1.6 mmHg) and declined thereafter (ΔΔIOP5h, -1.6 ± 1.1 mmHg). In a follow-up study, NCX 1741 (1.5%, 0.5 µmol/eye) was more effective than NCX 1744 despite a similar duration. Further, NCX 1741 was as effective as travoprost (0.1%, 0.06 µmol/eye) at 5 and 8 h post-dosing (travoprost, ΔΔIOP5h, -3.4 ± 2.2 mmHg and ΔΔIOP8h, -4.9 ± 1.3 mmHg) but had shorter duration (NCX 1741, ΔΔIOP24h, -1.5 ± 1.1 mmHg; travoprost, ΔΔIOP24h, -7.1 ± 2.8 mmHg). NCX 1741 resulted in significant aqueous humor exposure, as determined by the levels of the main metabolite, avanafil. Conclusions: NCX 1741 rapidly and effectively lowers IOP in OHT-monkeys for several hours post-dosing. How these effects translate in humans is still to be defined.

The utility of CYP3A activity endogenous markers for evaluating drug-drug interaction between sildenafil and CYP3A inhibitors in healthy subjects.

Cytochrome P450 (CYP) 3A-related drug-drug interaction (DDI) studies are needed during drug development to determine clinical interaction effects. We aimed to evaluate DDI between sildenafil and two CYP3A inhibitors, clarithromycin and itraconazole, regarding the changes in pharmacokinetics and endogenous markers. An open-label, one-sequence, one-period, two-treatment parallel study was conducted in 32 healthy Korean subjects. Each of 16 subjects were randomly assigned to the clarithromycin and itraconazole groups. Both groups received a single dose of sildenafil 25 mg as a control, and either clarithromycin 250 mg or itraconazole 100 mg was administered four times to inhibit CYP3A activity. Pharmacokinetics of sildenafil showed the similar magnitude of inhibitory effects of the two inhibitors on total CYP3A activity; both inhibitors similarly increased systemic exposure of sildenafil by 2-fold. Urinary 6ß-OH-cortisone/cortisone and plasma 4ß-OH-cholesterol were significantly decreased after clarithromycin administration but not after itraconazole. A significant correlation between sildenafil CL/F and metabolic markers of CYP3A activity was observed after clarithromycin administration. We confirmed that sildenafil has moderate pharmacokinetic interaction with clarithromycin and itraconazole. Endogenous markers well reflected the CYP3A inhibition of clarithromycin, suggesting possible utility in DDI study with moderate to strong CYP3A inhibition; however, there are limitations in predicting intestinal CYP3A mediated DDI.

Gender differences and dose proportionality in the toxicokinetics of udenafil and its active metabolite following oral administration in rodents.

Udenafil is a long-acting oral phosphodiesterase type 5 inhibitor used to treat erectile dysfunction which may also have beneficial effects on cardiovascular diseases. Udenafil is mainly biotransformed to the active metabolite N-dealkylated udenafil via cytochrome P450 3A. The aim of this study was to investigate the gender differences and dose proportionality of the toxicokinetics of udenafil and its metabolite N-dealkylated udenafil in rodents. Udenafil was administered orally by gavage to male and female B6C3F1/N mice (100, 240, 350, and 500 mg/kg) and F344 rats (60, 120, and 240 mg/kg). Plasma concentrations of udenafil and N-dealkylated udenafil were simultaneous measured via liquid chromatography-tandem mass spectrometry. Female mice showed higher systemic exposure to udenafil than male mice, whereas female rats showed lower systemic exposure to udenafil than male rats after repeated administration at high dose. Systemic exposure to the metabolite, N-dealkylated udenafil, was lower in female than male mice and rats. A dose proportionality assessment by power model revealed a lack of dose proportionality in systemic exposure (Cmax, AUC24h and AUCinf) after administration of 100-500 mg/kg of udenafil in mice and 60-240 mg/kg in rats. This study thus demonstrates gender and species differences with regard to the toxicokinetic profiles of udenafil and its active metabolite N-dealkylated udenafil after oral administration of udenafil to mice and rats of both sexes. Our findings suggest the possibility of gender differences in the toxicokinetics of udenafil in humans and suggests that further study is needed in this cohort.

Species differences in the CYP3A-catalyzed metabolism of TPN729, a novel PDE5 inhibitor.

TPN729 is a novel phosphodiesterase 5 (PDE5) inhibitor used to treat erectile dysfunction in men. Our previous study shows that the plasma exposure of metabolite M3 (N-dealkylation of TPN729) in humans is much higher than that of TPN729. In this study, we compared its metabolism and pharmacokinetics in different species and explored the contribution of its main metabolite M3 to pharmacological effect. We conducted a combinatory approach of ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry-based metabolite identification, and examined pharmacokinetic profiles in monkeys, dogs, and rats following TPN729 administration. A remarkable species difference was observed in the relative abundance of major metabolite M3: i.e., the plasma exposure of M3 was 7.6-fold higher than that of TPN729 in humans, and 3.5-, 1.2-, 1.1-fold in monkeys, dogs, and rats, respectively. We incubated liver S9 and liver microsomes with TPN729 and CYP3A inhibitors, and demonstrated that CYP3A was responsible for TPN729 metabolism and M3 formation in humans. The inhibitory activity of M3 on PDE5 was 0.78-fold that of TPN729 (The IC50 values of TPN729 and M3 for PDE5A were 6.17 ± 0.48 and 7.94 ± 0.07 nM, respectively.). The plasma protein binding rates of TPN729 and M3 in humans were 92.7% and 98.7%, respectively. It was astonishing that the catalyzing capability of CYP3A4 in M3 formation exhibited seven-fold disparity between different species. M3 was an active metabolite, and its pharmacological contribution was equal to that of TPN729 in humans. These findings provide new insights into the limitation and selection of animal model for predicting the clinical pharmacokinetics of drug candidates metabolized by CYP3A4.

Discovery of Evodiamine Derivatives as Highly Selective PDE5 Inhibitors Targeting a Unique Allosteric Pocket.

Clinical use of phosphodiesterase-5 (PDE5) inhibitors is limited by several side effects due to weak isoform selectivity. Herein, a unique allosteric pocket of PDE5 is identified by molecular modeling and structural biology, which enables the discovery of highly selective PDE5 inhibitors from natural product evodiamine (EVO). The crystal structure of PDE5 with bound EVO derivative (S)-7e revealed that binding of (S)-7e to the novel allosteric pocket induced dramatic conformation changes in the H-loop with a maximum 24 Å movement of their Cα atoms. This movement directly blocks the binding of substrate/inhibitors to the PDE5 active site, which is different from all traditional PDE5 inhibitors such as sildenafil, tadalafil, and vardenafil. These derivatives showed >570-fold selectivity over PDE6C and PDE11A and achieved potent efficacy for the effective treatment of pulmonary hypertension in vivo.

Iridoids and Amino Acid Derivatives from the Paraguayan Crude Drug Adenocalymma marginatum (ysypó hû).

The crude drug ysypó hû (Adenocalymma marginatum DC., Bignoniaceae) is used traditionally by the Guarani of Eastern Paraguayan as a male sexual enhancer. The aim of the present study was to identify the main constituents of the crude drug and to evaluate the in vitro inhibitory activity towards the enzyme phosphodiesterase-5 (PDE-5). The main compounds were isolated by counter-current chromatography (CCC). The metabolites were identified by spectroscopic and spectrometric means. The chemical profiling of the extracts was assessed by high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS/MS). The crude extract and main isolated compounds were tested for their PDE-5 inhibitory activity using commercial kits. The iridoid theviridoside and 4-hydroxy-1-methylproline were isolated as the main constituent of the crude drug. Four chlortheviridoside hexoside derivatives were detected for the first time as natural products. Chemical profiling by HPLC-MS/MS led to the tentative identification of nine iridoids, six phenolics, and five amino acids. The crude extracts and main compounds were inactive towards PDE-5 at concentrations up to 500 µg/mL. Iridoids and amino acid derivatives were the main compounds occurring in the Paraguayan crude drug. The potential of ysypó hû as a male sexual enhancer cannot be discarded, since other mechanisms may be involved.

Effect of Combination Therapy of Endothelin Receptor Antagonist and Phosphodiesterase-5 Inhibitor on Clinical Outcome and Pulmonary Haemodynamics in Patients with Pulmonary Arterial Hypertension: A Meta-Analysis.

BACKGROUND: The combination of an endothelin receptor antagonist and a phosphodiesterase-5 inhibitor having different biological targets has become an integral part of the treatment of pulmonary arterial hypertension; however, several clinical studies have reported conflicting results. OBJECTIVE: The objective of this meta-analysis was to evaluate the effect of an endothelin receptor antagonist and phosphodiesterase-5 inhibitor combination in pulmonary arterial hypertension. METHODS: After performing a comprehensive literature search in MEDLINE, Cochrane and the International Clinical Trial Registry Platform, reviewers assessed eligibility and extracted data from seven relevant articles (publications till December 2018). PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines were followed in the selection, analysis and reporting of findings. The odds ratio and mean difference were calculated to estimate the difference in clinical worsening, 6-minute walking distance, pulmonary vascular resistance and N-terminal pro-brain natriuretic peptide between the groups. Quality assessment was performed using the risk of bias assessment tool and a meta-regression for probable variables affecting effect size. RESULTS: The random-effect model analysis revealed an odds ratio of 0.56 [95% confidence interval (CI) 0.41-0.76; p = 0.0002] for clinical worsening, mean difference of 15.64 (95% CI 2.67-28.61; p = 0.02) for 6-minute walking distance, - 1.66 (95% CI - 3.82 to 0.50; p = 0.13) for pulmonary vascular resistance and - 21.04 (95% CI - 26.87 to - 15.22; p < 0.00001) for N-terminal pro-brain natriuretic peptide. The meta-regression showed no statistically significant association between the dose and duration of treatment and outcomes (odds ratio of clinical worsening and mean difference of 6-minute walking distance). CONCLUSIONS: In pulmonary arterial hypertension, endothelin receptor antagonist and phosphodiesterase-5 inhibitor combination therapy significantly improved 6-minute walking distance, clinical worsening and N-terminal pro-brain natriuretic peptide compared with the monotherapy but did not offer any advantage in improving pulmonary vascular resistance. PROSPERO REGISTRATION NO: CRD42018091133.

Placental effects and transfer of sildenafil in healthy and preeclamptic conditions.

BACKGROUND: The phosphodiesterase-5 inhibitor (PDE5) sildenafil has emerged as a promising treatment for preeclampsia (PE). However, a sildenafil trial was recently halted due to lack of effect and increased neonatal morbidity. METHODS: Ex vivo dual-sided perfusion of an isolated cotyledon and wire-myography on chorionic plate arteries were performed to study the effects of sildenafil and the non-selective PDE inhibitor vinpocetine on the response to the NO donor sodium nitroprusside (SNP) under healthy and PE conditions. Ex vivo perfusion was also used to study placental transfer of sildenafil in 6 healthy and 2 PE placentas. Furthermore, placental mRNA and protein levels of eNOS, iNOS, PDE5 and PDE1 were quantified. FINDINGS: Sildenafil and vinpocetine significantly enhanced SNP responses in chorionic plate arteries of healthy, but not PE placentas. Only sildenafil acutely decreased baseline tension in arteries of both healthy and PE placentas. At steady state, the foetal-to-maternal transfer ratio of sildenafil was 0·37 ±â€¯0·03 in healthy placentas versus 0·66 and 0·47 in the 2 PE placentas. mRNA and protein levels of PDE5, eNOS and iNOS were comparable in both groups, while PDE1 levels were lower in PE. INTERPRETATION: The absence of sildenafil-induced NO potentiation in arteries of PE placentas, combined with the non-PDE-mediated effects of sildenafil and the lack of PDE5 upregulation in PE, argue against sildenafil as the preferred drug of use in PE. Moreover, increased placental transfer of sildenafil in PE might underlie the neonatal morbidity in the STRIDER trial. FUND: This study was funded by an mRACE Erasmus MC grant.

The efficacy and underlying mechanism of phosphodiesterase- 5 inhibitors in preventing cognitive impairment and Alzheimer pathology: A systematic review of animal studies.

BACKGROUND: Alzheimer disease (AD) initially presents with cognitive decline that affects the affected individual's daily activities. Cognitive decline reversal represents an important medical need, where Phosphodiesterase-5 inhibitors (PDE-5Is) might play a role. AIM: This systematic review was performed to verify the efficacy of PDE-5Is in preventing cognitive impairment and to elucidate the underlying mechanism. METHODS: Preclinical animal studies assessing the efficacy of PDE-5Is in preventing cognitive impairment and pathological changes by measuring Aß-42 ß42 and p-Tau were included in the analysis. CAMARADES Checklist was used to assess study quality. Further, various signaling pathways in different studies were examined. RESULTS AND OUTCOMES: Data of behavioral tests were extracted and a meta-analysis was conducted. Fifteen animal trials met the inclusion criteria, and all reported the prevention of cognitive deficits by PDE-5Is in Alzheimer's disease. A significant effect of PDE-5Is in increasing the time spent in the target quadrant was reported in four of seven studies using the water maze. Four studies showed significant improvement in contextual fear memory freezing time, and three studies showed improvement in the 14 unit maze number of errors. CONCLUSIONS: Cognitive decline in preclinical AD finds tauopathy has a more impact than Aß-42. This systematic review showed that PDE-5 inhibitors might help prevent cognitive impairment in AD, and while its mechanism of action is non-related to Aß-42, it might include decrease p-Tau, increase CREB and BDNF or suppressing apoptosis and inflammation. However, the efficacy of PDE-5 inhibitors in preventing cognitive impairment remains unclear due to various limitations, such as the small number of included studies, the high risk of bias, the lack of an integrated study design, and low reporting quality.

Characterization of TPN171 metabolism in humans via ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry.

TPN171 is a novel potent pyrimidinone phosphodiesterase type 5 (PDE5) inhibitor with high selectivity and long duration of action. It has been used to treat patients suffering from pulmonary arterial hypertension and entered phase I clinical trials in 2016. Considering the potential therapeutic value of TPN171, its metabolism in humans is necessary to be elucidated during early-stage of drug development. This study aimed to establish a rapid and reliable method based on ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry for the characterization of TPN171 metabolites in human plasma, urine and stool samples. A total of 17 metabolites, including 14 from phase I and 3 from phase II metabolic reactions, were identified and characterized. TPN171 was found to be the predominant component in all plasma, urine and stool samples. Seven proposed metabolites were validated by comparing with synthetic reference standards. N-demethylation, O-depropylation, N-oxidation and dehydrogenation were demonstrated to be the main metabolic pathways of TPN171 in humans, yielding metabolites M4, M3, M7-2 and M5-3, respectively. Notably, M5-3 (a dehydrogenation product) and M3 (an O-depropylation product) were the main metabolites in human plasma while M5-3 (produced via dehydrogenation) and M7-2 (produced via N-oxidation) were the major metabolites in human urine. Besides, O-depropylation product M3 and N-demethylation product M4 were the main metabolites in human stool. In overall, this study assessed the metabolic fate of TPN171 in humans, which may yield considerably benefits for subsequent studies focusing on TPN171 metabolism and development of other PDE5 inhibitors.

Pharmacological evidence for the relationship between the NMDA receptor and nitric oxide pathway and the antidepressant-like effects of glucagon-like peptide-2 in the mouse forced-swim test.

We previously demonstrated that glucagon-like peptide-2 (GLP-2) exerted antidepressant-like effects in mice. The aim of the present study was to investigate the relationship between N-methyl-D-aspartate (NMDA) receptor-nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway and the antidepressant-like effects of GLP-2 in the forced-swim test (FST) in mice. Intracerebroventricularly administered GLP-2 (3 µg/mouse) decreased the immobility time in the FST. The pretreatment of mice with l-arginine (750 mg/kg, i.p.), a substrate for nitric oxide synthase, sildenafil (5 mg/kg, i.p.), a phosphodiesterase 5 inhibitor, or d-serine (300 mg/kg, i.p.), a NMDA receptor co-agonist, inhibited the antidepressant-like effects of GLP-2 (3 µg/mouse) in the FST. Meanwhile, l-nitroarginine methyl ester (10 mg/kg, i.p.), a non-specific nitric oxide synthase (NOS) inhibitor, 7-nitroindazole (30 mg/kg, i.p.), a neuronal NOS inhibitor, methylene blue (10 mg/kg, i.p.), an inhibitor of both NOS and soluble guanylate cyclase (sGC), ODQ (30 pmol/site, i.c.v.), a sGC inhibitor, or MK-801 (0.05 mg/kg, i.p.), an NMDA receptor antagonist, in combination with a sub-effective dose of GLP-2 (1.5 µg/mouse) also decreased the immobility time in the FST. The present study provided evidence for the synergistic antidepressant-like effects of GLP-2 and inhibition of the NMDA receptor-l-arginine-NO-cGMP pathway in the FST, thereby contributing to our understanding of the mechanisms underlying the antidepressant-like effects of GLP-2.

Probing the Effect of Sildenafil on Progesterone and Testosterone Production by an Intracellular FRET/BRET Combined Approach.

Forster resonance energy transfer (FRET)-based biosensors have been recently applied to the study of biological pathways. In this study, a new biosensor was validated for the first time in live HEK293 and steroidogenic MLTC-1 cell lines for studying the effect of the PDE5 inhibitor on the hCG/LH-induced steroidogenic pathway. The sensor improves FRET between a donor (D), the fluorescein-like diarsenical probe that can covalently bind a tetracysteine motif fused to the PDE5 catalytic domain, and an acceptor (A), the rhodamine probe conjugated to the pseudosubstrate cGMPS. Affinity constant ( Kd) values of 5.6 ± 3.2 and 13.7 ± 0.8 µM were obtained with HEK293 and MLTC-1 cells, respectively. The detection was based on the competitive displacement of the cGMPS-rhodamine conjugate by sildenafil; the Ki values were 3.6 ± 0.3 nM (IC50 = 2.3 nM) in HEK293 cells and 10 ± 1.0 nM (IC50 = 3.9 nM) in MLTC-1 cells. The monitoring of both cAMP and cGMP by bioluminescence resonance energy transfer allowed the exploitation of the effects of PDE5i on steroidogenesis, indicating that sildenafil enhanced the gonadotropin-induced progesterone-to-testosterone conversion in a cAMP-independent manner.

Q817G mutation in phosphodiesterase type 5: Conformational analysis and dissociation profile of the inhibitor Tadalafil.

Phosphodiesterase type 5 (PDE-5) is an important enzyme involved in the hydrolysis of cyclic guanosine monophosphate (cGMP) to guanosine monophosphate (GMP). The inhibition of this protein leads to the accumulation of cGMP in cells with various biological and therapeutic effects. Several PDE-5 inhibitors exist, with Tadalafil being one of the most commonly studied and used in clinical therapy. In this study, we applied Molecular Dynamics simulations coupled to the ABF (Adaptive Biasing Force) method to study the effect of the mutation on the Gln817 residue (Q817G). The results of the free energy profiles made clear that the affinity of the inhibitor for PDE-5 is dependent on the amino acid residue Gln817. The hydrogen bond made between the side chain of glutamine and the indole ring of Tadalafil results in the stabilization of the ligand in the catalytic site. Despite the prominent role of this interaction, it is important to highlight the contribution of other residues of the catalytic domain for the stabilization of the compound, due to the set of polar, hydrophobic and electrostatic interactions performed by specific amino acid residues.

Targeted therapy of pulmonary arterial hypertension: Updated recommendations from the Cologne Consensus Conference 2018.

In the summer of 2016, delegates from the German Respiratory Society, the German Society of Cardiology and the German Society of Pediatric Cardiology met in Cologne, Germany, to define consensus-based practice recommendations for the management of patients with pulmonary arterial hypertension (PAH). These recommendations were built on the 2015 European Pulmonary Hypertension guidelines and included new evidence, where available. The treatment algorithm for PAH was modified based on the observation that there are now many patients diagnosed with IPAH who are at an advanced age and have significant cardiopulmonary comorbidities. For patients newly diagnosed with classic forms of PAH, i.e. younger patients without significant cardiopulmonary comorbidities, the consensus-based recommendation was to use initial combination therapy as the standard approach. The use of monotherapies was no longer considered appropriate in such patients. The choice of treatment strategies should be based on the risk assessment as proposed in the European guidelines. In patients presenting with a low or intermediate risk, oral combination therapy with endothelin receptor antagonists and phosphodiesterase-5 inhibitors or soluble guanylate cyclase stimulators, respectively, should be used. In high-risk patients, triple combination therapy including a subcutaneous or intravenous prostacyclin analogue should be considered. For patients who suffer from PAH and significant cardiopulmonary comorbidities, initial monotherapy is recommended and the use of combination therapies should be considered on an individual basis. The latter recommendations are based on the scarcity of evidence supporting the use of combination therapy and the higher risk of drug-related adverse events in such patients.