Augmentation of natriuretic peptide (NP) receptor A and B (NPR-A and NPR-B) and cyclic guanosine monophosphate (cGMP) signalling as a therapeutic strategy in heart failure.

INTRODUCTION: Heart failure is a complex, debilitating condition and despite advances in treatment, it remains a significant cause of morbidity and mortality worldwide. Therefore, the need for alternative treatment strategies is essential. In this review, we explore the therapeutic strategies of augmenting natriuretic peptide receptors (NPR-A and NPR-B) and cyclic guanosine monophosphate (cGMP) in heart failure. AREAS COVERED: We aim to provide an overview of the evidence of preclinical and clinical studies on novel heart failure treatment strategies. Papers collected in this review have been filtered and screened following PubMed searches. This includes epigenetics, modulating enzyme activity in natriuretic peptide (NP) synthesis, gene therapy, modulation of downstream signaling by augmenting soluble guanylate cyclase (sGC) and phosphodiesterase (PDE) inhibition, nitrates, c-GMP-dependent protein kinase, synthetic and designer NP and RNA therapy. EXPERT OPINION: The novel treatment strategies mentioned above have shown great potential, however, large randomized controlled trials are still lacking. The biggest challenge is translating the results seen in preclinical trials into clinical trials. We recommend a multi-disciplinary team approach with cardiologists, geneticist, pharmacologists, bioengineers, researchers, regulators, and patients to improve heart failure outcomes. Future management can involve telemedicine, remote monitoring, and artificial intelligence to optimize patient care.

Dose-Response to Sacubitril/Valsartan in Patients With Heart Failure and Reduced Ejection Fraction.

BACKGROUND: Doses of sacubitril/valsartan (Sac/Val) achieved in clinical trials of heart failure with reduced ejection fraction (HFrEF) are often not reached in clinical practice. OBJECTIVES: The purpose of this study was to investigate associations among Sac/Val doses and changes in prognostic biomarkers, health status, and cardiac remodeling among individuals with HFrEF through 12 months of treatment with Sac/Val administered per usual care. METHODS: A total of 794 persons with HFrEF (ejection fraction [EF] ≤40%) were categorized according to average daily doses of Sac/Val divided into tertiles. Change from baseline to 12 months in biomarkers (N-terminal pro-B-type natriuretic peptide, high-sensitivity cardiac troponin T, soluble ST2, atrial natriuretic peptide, urinary cyclic guanosine monophosphate), Kansas City Cardiomyopathy Questionnaire-23 scores, and parameters of cardiac reverse remodeling (left ventricular EF, indexed left atrial and ventricular volumes, and E/e') were assessed. RESULTS: The average daily dose was 112 mg in Tertile 1 (low dose), 342 mg in Tertile 2 (moderate dose), and 379 mg in Tertile 3 (high dose). Similar changes in prognostic biomarkers were observed in all dose tertiles. Gains in Kansas City Cardiomyopathy Questionnaire-23 scores were comparable regardless of dose category. Consistent reverse cardiac remodeling in all dose categories occurred; the median absolute left ventricular EF improvement across HF dose groups was 9.3%, 8.7%, and 10.2%, for low, moderate, and high doses, respectively; similar improvements in left atrial and ventricular volumes and E/e' were also observed across dose categories. CONCLUSIONS: Among patients with HFrEF, similar improvement in prognostic biomarkers, health status, and cardiac remodeling were observed across various Sac/Val doses. (Effects of Sacubitril/Valsartan Therapy on Biomarkers, Myocardial Remodeling and Outcomes [PROVE-HF]; NCT02887183.

Hemodynamic Effects of Cyclic Guanosine Monophosphate-Dependent Signaling Through ß3 Adrenoceptor Stimulation in Patients With Advanced Heart Failure: A Randomized Invasive Clinical Trial.

BACKGROUND: ß3-AR (ß3-adrenergic receptor) stimulation improved systolic function in a sheep model of systolic heart failure (heart failure with reduced ejection fraction [HFrEF]). Exploratory findings in patients with New York Heart Association functional class II HFrEF treated with the ß3-AR-agonist mirabegron supported this observation. Here, we measured the hemodynamic response to mirabegron in patients with severe HFrEF. METHODS: In this randomized, double-blind, placebo-controlled trial we assigned patients with New York Heart Association functional class III-IV HFrEF, left ventricular ejection fraction <35% and increased NT-proBNP (N-terminal pro-B-type natriuretic peptide) levels to receive mirabegron (300 mg daily) or placebo orally for a week, as add on to recommended HF therapy. Invasive hemodynamic measurements during rest and submaximal exercise at baseline, 3 hours after first study dose and repeated after 1 week's treatment were obtained. Predefined parameters for analyses were changes in cardiac- and stroke volume index, pulmonary and systemic vascular resistance, heart rate, and blood pressure. RESULTS: We randomized 22 patients (age 66±11 years, 18 men, 16, New York Heart Association functional class III), left ventricular ejection fraction 20±7%, median NT-proBNP 1953 ng/L. No significant changes were seen after 3 hours, but after 1 week, there was a significantly larger increase in cardiac index in the mirabegron group compared with the placebo group (mean difference, 0.41 [CI, 0.07-0.75] L/min/BSA; P=0.039). Pulmonary vascular resistance decreased significantly more in the mirabegron group compared with the placebo group (-1.6 [CI, -0.4 to -2.8] Wood units; P=0.02). No significant differences were seen during exercise. There were no differences in changes in heart rate, systemic vascular resistance, blood pressure, or renal function between groups. Mirabegron was well-tolerated. CONCLUSIONS: Oral treatment with the ß3-AR-agonist mirabegron for 1 week increased cardiac index and decreased pulmonary vascular resistance in patients with moderate to severe HFrEF. Mirabegron may be useful in patients with worsening or terminal HF. REGISTRATION: URL: https://www. CLINICALTRIALS: gov; Unique identifier: 2016-002367-34.

Pharmacological developments in antihypertensive treatment through nitric oxide-cGMP modulation.

Treatment of hypertension until now has been directed at inhibition of vasoconstriction, of cardiac contractility and of blood volume regulation. Despite the arsenal of drugs available for this purpose, the control of target blood pressure is still a difficult goal to reach in outpatients. The nitric oxide-cyclic guanosine monophosphate signaling is one of the most important mediators of vasodilation. It might therefore be a potential and most welcome drug target for optimization of the treatment of hypertension. In this chapter we review the problems that can occur in this signaling system, the attempts that have been made to correct these problems, and those that are still under investigation. Recently developed, clinically safe medicines that are currently approved for other applications, such as myocardial infarction, await to be tested for essential systemic hypertension. We conclude that despite many years of research without translation, stimulation of nitric oxide-cyclic guanosine monophosphate is still a viable strategy in the prevention of the health risk posed by chronic hypertension.

Therapeutic augmentation of NO-sGC-cGMP signalling: lessons learned from pulmonary arterial hypertension and heart failure.

The nitric oxide (NO)-guanylate cyclase (GC)-cyclic guanosine monophosphate (cGMP) pathway plays an important role in cardiovascular, pulmonary and renal function. Phosphodiesterase-5 inhibitors (PDE-5i) inhibit cGMP degradation, whereas both soluble guanylate cyclase (sGC) stimulators and sGC activators directly increase sGC. PDE-5i (e.g. sildenafil, tadalafil) and sGC stimulators (e.g. riociguat, vericiguat) have been extensively used in pulmonary artery hypertension (PAH) and heart failure (HF). PDE-5i have also been used in end-stage HF before and after left ventricular (LV) assist device (LVAD) implantation. Augmentation of NO-GC-cGMP signalling with PDE-5i causes selective pulmonary vasodilation, which is highly effective in PAH but may have controversial, potentially adverse effects in HF, including pre-LVAD implant due to device unmasking of PDE-5i-induced RV dysfunction. In contrast, retrospective analyses have demonstrated that PDE-5i have beneficial effects when initiated post LVAD implant due to the improved haemodynamics of the supported LV and the pleiotropic actions of these compounds. sGC stimulators, in turn, are effective both in PAH and in HF due to their balanced pulmonary and systemic vasodilation, and as such they are preferable to PDE-5i if the use of a pulmonary vasodilator is needed in HF patients, including those listed for LVAD implantation. Regarding the effectiveness of PDE-5i and sGC stimulators when initiated post LVAD implant, these two groups of compounds should be tested in a randomized control trial.

Diagnosis and Treatment of Pulmonary Arterial Hypertension: A Review.

Importance: Pulmonary arterial hypertension (PAH) is a subtype of pulmonary hypertension (PH), characterized by pulmonary arterial remodeling. The prevalence of PAH is approximately 10.6 cases per 1 million adults in the US. Untreated, PAH progresses to right heart failure and death. Observations: Pulmonary hypertension is defined by a mean pulmonary artery pressure greater than 20 mm Hg and is classified into 5 clinical groups based on etiology, pathophysiology, and treatment. Pulmonary arterial hypertension is 1 of the 5 groups of PH and is hemodynamically defined by right heart catheterization demonstrating a mean pulmonary artery pressure greater than 20 mm Hg, a pulmonary artery wedge pressure of 15 mm Hg or lower, and a pulmonary vascular resistance of 3 Wood units or greater. Pulmonary arterial hypertension is further divided into subgroups based on underlying etiology, consisting of idiopathic PAH, heritable PAH, drug- and toxin-associated PAH, pulmonary veno-occlusive disease, PAH in long-term responders to calcium channel blockers, and persistent PH of the newborn, as well as PAH associated with other medical conditions including connective tissue disease, HIV, and congenital heart disease. Early presenting symptoms are nonspecific and typically consist of dyspnea on exertion and fatigue. Currently approved therapy for PAH consists of drugs that enhance the nitric oxide-cyclic guanosine monophosphate biological pathway (sildenafil, tadalafil, or riociguat), prostacyclin pathway agonists (epoprostenol or treprostinil), and endothelin pathway antagonists (bosentan and ambrisentan). With these PAH-specific therapies, 5-year survival has improved from 34% in 1991 to more than 60% in 2015. Current treatment consists of combination drug therapy that targets more than 1 biological pathway, such as the nitric oxide-cyclic guanosine monophosphate and endothelin pathways (eg, ambrisentan and tadalafil), and has shown demonstrable improvement in morbidity and mortality compared with the previous conventional single-pathway targeted monotherapy. Conclusions and Relevance: Pulmonary arterial hypertension affects an estimated 10.6 per 1 million adults in the US and, without treatment, typically progresses to right heart failure and death. First-line therapy with drug combinations that target multiple biological pathways are associated with improved survival.

Vericiguat: A New Hope for Heart Failure Patients.

Heart failure with reduced ejection fraction (HFrEF) is the inability of the heart to adequately contract or eject blood. This heart is unable to produce adequate cardiac output to perfuse vital tissues. At a fundamental level, it is known that the cardioprotective pathway of nitric oxide-soluble guanylate cyclase-cyclic guanosine monophosphate is impaired in heart failure patients. Vericiguat is a novel, orally used, small molecule, and direct stimulator of the soluble guanylate cyclase, and thus, it enhances the production of cyclic guanosine monophosphate. Vericiguat was approved by the FDA in January of 2021 to reduce the risk of cardiovascular death and heart failure hospitalization following a hospitalization for heart failure or need for outpatient IV diuretics, in adults with symptomatic chronic heart failure and ejection fraction less than 45%. In this review, we describe the chemical and mechanistic aspects, pharmacokinetics, adverse effects, and contraindications of vericiguat so as to facilitate its optimal therapeutic use.

Targeting Cyclic Guanosine Monophosphate to Treat Heart Failure: JACC Review Topic of the Week.

The significant morbidity and mortality associated with heart failure with reduced ejection fraction (HFrEF) or heart failure with preserved ejection fraction (HFpEF) justify the search for novel therapeutic agents. Reduced cyclic guanosine monophosphate levels contribute to HF progression. Among molecules modulating the nitric oxide (NO)-GMP-phosphodiesterase (PDE) pathway, the evaluation of nitrates, synthetic natriuretic peptides (NP), and NP analogs has yielded mixed results. Conversely, sacubitril/valsartan, combining NP degradation inhibition through neprilysin and angiotensin receptor blockade, has led to groundbreaking findings in HFrEF. Other strategies to increase tissue cyclic guanosine monophosphate have been attempted, such as PDE-3 or PDE-5 inhibition (with negative or neutral results), NO-independent soluble guanylate cyclase (sGC) activation, or enhancement of sGC sensitivity to endogenous NO. Following the positive results of the phase 3 VICTORIA (A Study of Vericiguat in Participants With Heart Failure With Reduced Ejection Fraction) trial on the sGC stimulator vericiguat in HFrEF, the main open questions are the efficacy of the sacubitril/valsartan-vericiguat combination in HFrEF and of vericiguat in HFpEF.

Combinations of two drugs among NS3/4A inhibitors, NS5B inhibitors and non-selective antiviral agents are effective for hepatitis C virus with NS5A-P32 deletion in humanized-liver mice.

BACKGROUND: The emergence of a deletion mutant at hepatitis C virus (HCV) NS5A-P32 (P32del) has recently been reported in a subset of chronic hepatitis C patients who experience virologic failure after direct-acting antiviral drug (DAA) treatment. This mutation confers extremely high resistance to NS5A inhibitors. No effective treatment has been established for cases with this mutation. METHODS: We used a JFH1-based recombinant virus with NS5A from a genotype 1b strain to introduce a P32del mutation. We inoculated human hepatocyte chimeric mice with sera from a patient with ledipasvir/sofosbuvir therapy failure carrying a genotype 1b HCV with NS5A L31M and P32del or from a DAA-naïve patient carrying wild-type virus. RESULTS: JFH1-based chimeric viruses with P32del showed sufficient levels of replication for in vitro assay despite the suppression of viral growth and infectious virus production. Variants with P32del exhibited severe resistance to all tested NS5A inhibitors, including daclatasvir, ledipasvir, elbasvir and velpatasvir, but were as susceptible to NS3/4A inhibitors, NS5B inhibitors, interferon alfa-2b, and ribavirin as wild-type viruses in the in vitro assay. The P32del mutant virus caused persistent infection in all inoculated chimeric mice with high viral titer and frequency. The virus was resistant to the ledipasvir/GS-558093 (a nucleotide analog inhibitor of NS5B polymerase) regimen but susceptible to either simeprevir plus GS-558093 or peg-interferon alfa-2b, compared to the wild-type virus. CONCLUSION: Therapies combining at least two drugs among NS3/4A inhibitors, NS5B inhibitors and non-selective antiviral agents may be effective for HCV-infected patients with NS5A-P32del.

Guanosine 5'-monophosphate-chelated calcium and iron feed additives maintains egg production and prevents Salmonella Gallinarum in experimentally infected layers.

We evaluated the effects of guanosine 5'-monophosphate (GMP)-chelated calcium and iron (CaFe-GMP) on health and egg quality in layers experimentally infected with Salmonella Gallinarum. In this study, a CaFe-GMP feed additive was added to a commercial layer feed and fed to layers over a four-week period. All were inoculated with Salmonella Gallinarum. Body weight, mortality, clinical symptoms, and poultry production including feed intake, egg production, egg loss, and feed conversion rate were observed, and Salmonella Gallinarum was re-isolated from the liver, spleen, and cecum of the layers. All tested internal organs for the CaFe-GMP additive group exhibited significantly lower re-isolation numbers of Salmonella Gallinarum and less severe pathological changes than those in the control group, indicating that the CaFe-GMP feed supplement induced bacterial clearance and increased resistance to Salmonella Gallinarum. Additionally, due to the inhibitory action of CaFe-GMP on the growth of Salmonella Gallinarum, the CaFe-GMP additive group exhibited better egg production, including a higher laying rate and fewer broken eggs. The results suggest that a 0.16% CaFe-GMP additive may help prevent salmonellosis in the poultry industry.

From the Cover: Investigative Nonclinical Cardiovascular Safety and Toxicology Studies with BMS-986094, an NS5b RNA-Dependent RNA Polymerase Inhibitor.

BMS-986094, a 2'-C-methylguanosine prodrug that was in development for treatment of chronic hepatitis C infection was withdrawn from Phase 2 clinical trials because of unexpected cardiac and renal adverse events. Investigative nonclinical studies were conducted to extend the understanding of these findings using more comprehensive endpoints. BMS-986094 was given orally to female CD-1 mice (25 and 150 mg/kg/d) for 2 weeks (53/group) and to cynomolgus monkeys (15 and 30 mg/kg/d) for up to 6 weeks (2-3/sex/group for cardiovascular safety, and 5/sex/group for toxicology). Endpoints included toxicokinetics; echocardiography, telemetric hemodynamics and electrocardiography, and tissue injury biomarkers (monkey); and light and ultrastructural pathology of heart, kidney, and skeletal muscle (mouse/monkey). Dose-related and time-dependent findings included: severe toxicity in mice at 150 mg/kg/d and monkeys at 30 mg/kg/d; decreased left ventricular (LV) ejection fraction, fractional shortening, stroke volume, and dP/dt; LV dilatation, increased QTc interval, and T-wave flattening/inversion (monkeys at ≥ 15 mg/kg/d); cardiomyocyte degeneration (mice at 150 mg/kg/d and monkeys at ≥ 15 mg/kg/d) with myofilament lysis/myofbril disassembly; time-dependent proteinuria and increased urine ß-2 microglobulin, calbindin, clusterin; kidney pallor macroscopically; and tubular dilatation (monkeys); tubular regeneration (mice 150 mg/kg/d); and acute proximal tubule degeneration ultrastructurally (mice/monkeys); and skeletal muscle degeneration with increased urine myoglobin and serum sTnI. These studies identified changes not described previously in studies of BMS-986094 including premonitory cardiovascular functional changes as well as additional biomarkers for muscle and renal toxicities. Although the mechanism of potential toxicities observed in BMS-986094 studies was not established, there was no evidence for direct mitochondrial toxicity.

Zika viral polymerase inhibition using anti-HCV drugs both in market and under clinical trials.

In the last few months, a new Zika virus (ZIKV) outbreak evolved in America. In accordance, World Health Organization (WHO) in February 2016 declared it as Public Health Emergency of International Concern (PHEIC). ZIKV infection was reported in more than 60 countries and the disease was spreading since 2007 but with little momentum. Many antiviral drugs are available in market or in laboratories under clinical trials, could affect ZIKV infection. In silico docking study were performed on the ZIKV polymerase to test some of Hepatitis C Virus (HCV) drugs (approved and in clinical trials). The results show potency of almost all of the studied compounds on ZIKV polymerase and hence inhibiting the propagation of the disease. In addition, the study suggested two nucleotide inhibitors (IDX-184 and MK0608) that may be tested as drugs against ZIKV infection. J. Med. Virol. 88:2044-2051, 2016. © 2016 Wiley Periodicals, Inc.

Single- and repeat-dose toxicity of IDX14184, a nucleotide prodrug with antiviral activity for hepatitis C viral infection, in mice, rats, and monkeys.

The single- and repeat-dose toxicity profile of IDX14184, a novel guanosine nucleotide prodrug with antiviral activity against hepatitis C viral infection, was characterized following once daily oral administration for durations up to 13, 26, and 32 weeks in mouse, rat, and cynomolgus monkey, respectively. The heart, liver, kidney, skeletal muscles, and lower gastrointestinal tract (cecum, colon, and/or rectum) were identified as the primary toxicity targets in these nonclinical species. The mouse was relatively insensitive to IDX14184-induced cardiac toxicity and hepatotoxicity. The rat was very sensitive to IDX14184-induced skeletal muscle, liver, heart, and lower gastrointestinal tract toxicity but relatively insensitive to kidney toxicity. The monkey is a good animal species to detect IDX14184-induced toxicity in the cardiac and skeletal muscles, and in the liver and kidney, but not lower gastrointestinal tract toxicity. The toxicity profile of IDX14184 was most appropriately characterized in rats and monkeys. The conduct of a series of cardiac size and function assessments during a non-rodent toxicology study using echocardiography proved great utility in this work. IDX14184 clinical development was eventually terminated due to suboptimal efficacy and regulatory concerns on potential heart and kidney injury in patients, as seen with a different guanosine nucleotide prodrug, BMS-986094.

Cardiac dysfunction associated with a nucleotide polymerase inhibitor for treatment of hepatitis C.

UNLABELLED: Treatment for chronic hepatitis C virus (HCV) infection is evolving from interferon (IFN)-based therapy to direct-acting antiviral (DAA) agents, yet some safety concerns have arisen involving cardiac toxicity. In this study, we sought to better understand the potential off-target toxicities of new DAAs. We retrospectively evaluated the clinical and pathological findings of the sentinel case in a phase II study that led to clinical development discontinuation for BMS-986094, an HCV nucleotide polymerase (nonstructural 5B) inhibitor. We also report on outcomes from other patients in the same study, including electrocardiogram changes, cardiovascular biomarkers, and transthoracic echocardiograms. Thirty-four patients received IFN-free BMS-986094 regimens. Six patients had left ventricular ejection fractions (LVEFs) <30%, 8 had LVEFs 30%-50%, and 11 required hospitalization for suspected cardiotoxicity. Of the patients with LVEF <50%, 6 had normalization of systolic function after a median of 20 days. T-wave inversions were the most sensitive predictor of LVEF dysfunction. B-type natriuretic peptide levels increased over time and correlated with the degree of LVEF dysfunction. Pathological analysis of cardiac tissue revealed severe myocyte damage with elongated myofibrils without gross necrosis. These findings were consistent with some results of recent primate studies that were conducted to further investigate the potential mechanisms of BMS-986094 toxicity. CONCLUSION: A novel nucleotide analog polymerase inhibitor developed for HCV treatment may cause a toxic cardiomyopathy. Ongoing surveillance of DAAs for cardiotoxicities may be beneficial, especially among patients at higher risk for cardiovascular disease.

IDX184 in combination with pegylated interferon-α2a and ribavirin for 2 weeks in treatment-naive patients with chronic hepatitis C.

BACKGROUND: IDX184 is a liver-targeted nucleotide prodrug that selectively inhibits HCV NS5B polymerase. METHODS: This randomized, double-blind, placebo-controlled, ascending-dose study investigated the antiviral activity, safety and pharmacokinetics of IDX184 plus pegylated interferon-α2a and ribavirin (P/R) in treatment-naive patients with genotype-1 HCV. A total of 81 patients with baseline HCV RNA≥5 log10 IU/ml, alanine aminotransferase ≤3× upper limit of normal and compensated liver disease were dosed. Sequential cohorts of 20 patients, randomized 16:4 (active:placebo), received IDX184 for 14 days at rising daily doses of 50, 100, 150 or 200 mg in combination with P/R for 14 days. RESULTS: At the end of triple dosing, HCV RNA changes from baseline (mean ±sd log10) and proportion of patients achieving undetectable viral load (<15 IU/ml) based on the efficacy-evaluable population were -2.7 ±1.3 (13%), -4.0 ±1.7 (50%), -4.2 ±1.9 (50%), -4.1 ±1.2 (40%), -4.3 ±1.5 (29%) and -3.7 ±1.2 (25%) for the 50 mg once daily, 50 mg twice daily, 100 mg once daily, 150 mg once daily, 100 mg twice daily and 200 mg once daily IDX184 doses, respectively. P/R alone resulted in a reduction of -1.5 ±1.3 log10 with only 6% of patients with undetectable viral load. Patients with genotypes-1a or -1b responded similarly. No viral breakthrough or resistance associated with IDX184 was observed. Anti-HCV activity of IDX184 correlated with plasma exposure of its nucleoside metabolite 2'-methylguanosine. Most adverse events were mild or moderate in severity and were consistent with those associated with P/R. The most common adverse events were fatigue and headache. CONCLUSIONS: IDX184 in combination with P/R for 14 days was well tolerated and demonstrated greater antiviral activity with more patients achieving undetectable viral load than P/R.

Short-term monotherapy with IDX184, a liver-targeted nucleotide polymerase inhibitor, in patients with chronic hepatitis C virus infection.

IDX184 is a liver-targeted prodrug of 2'-methylguanosine (2'-MeG) monophosphate. This study investigated the safety, tolerability, antiviral activity, and pharmacokinetics of IDX184 as a single agent in treatment-naïve patients with genotype-1 chronic hepatitis C virus (HCV) infection. Forty-one patients with baseline HCV RNA ≥ 5 log(10) IU/ml, alanine aminotransferase (ALT) ≤ 2.5× the upper limit of normal, and compensated liver disease were dosed. Sequential cohorts of 10 patients, randomized 8:2 (active:placebo), received 25, 50, 75, and 100 mg of IDX184 once daily for 3 days, with a 14-day follow-up. There were no safety-related treatment discontinuations or serious adverse events. The adverse events and laboratory abnormalities observed for IDX184- and placebo-treated patients were similar. At the end of the 3-day treatment period, changes from baseline in HCV RNA levels (means ± standard deviations) were -0.5 ± 0.6, -0.7 ± 0.2, -0.6 ± 0.3, and -0.7 ± 0.5 log(10) for the 25-, 50-, 75-, and 100-mg doses, respectively, while viral load remained unchanged for the pooled placebo patients (-0.05 ± 0.3 log(10)). Patients with genotype-1a and patients with genotype-1b responded similarly. Serum ALT levels decreased, especially at daily doses ≥ 75 mg. During the posttreatment period, plasma viremia and serum aminotransferase levels returned to near pretreatment levels. No resistance mutations associated with IDX184 were detected. Plasma exposure of IDX184 and its nucleoside metabolite 2'-MeG was dose related and low. Changes in plasma viral load correlated with plasma exposure of 2'-MeG. In conclusion, the results from this proof-of-concept study show that small doses of the liver-targeted prodrug IDX184 were able to deliver significant antiviral activity and support further clinical evaluation of the drug candidate.

Efeitos do sildenafil pela via intraperitoneal na viabilidade de retalhos cutâneos de ratos / Effects of intraperitoneal application of sildenafil on the viability of mice’s skin flap

Introdução: o sildenafil pertence a uma classe relativamente nova de medicamentos, cujo mecanismo de ação ocorre por inibição da fosfodiesterase-5, que é responsável pela degradação intracelular da guanosina monofosfato cíclica (GMPc). A GMPc promove vasodilatação, alteração no perfil de granulação plaquetária e angiogênese. Nesse contexto, seus efeitos vasoativos podem aumentar o fluxo sanguíneo de retalhos, melhorando a sua viabilidade. Este estudo tem como objetivo avaliar a viabilidade de retalhos cutâneos de ratos à McFarlane após a administração de sildenafil pela via intraperitoneal. Métodos: 20 ratos Wistar foram distribuídos em dois grupos - controle (confecção do retalho cutâneo dorsal, aplicação intraperitoneal de solução salina a 0,9%) e estudo (confecção do retalho cutâneo dorsal, aplicação intraperitoneal de sildenafil). Sete dias após a operação, os retalhos foram fotografados e representados graficamente, para serem analisados com o programa AutoCad. Três biópsias (cranial, média e caudal) foram coletadas de cada retalho, para análise histológica. Resultados: à análise macroscópica, o uso do sildenafil pela via intraperitoneal esteve associado à maior contração tecidual (p=0,019). O estudo histológico evidenciou menos granulação associada a polimorfonucleares no terço distal dos retalhos (p=0,001) e mais necrose interpondo os locais de granulação no terço médio dos retalhos (p=0,011). Conclusão: o sildenafil intraperitoneal não se mostrou eficaz para melhorar a viabilidade de retalhos à McFarlane em ratos. Outros estudos talvez possam esclarecer o seu mecanismo de ação para a contração tecidual.

Sildenafil belong to a relatively new class of drugs. Its mechanism of action consists of inhibiting phosphodiesterase-5, which is responsible for the intracellular degradation of cyclic monophosphate guanosine (CMPG). CMPG leads to vasodilation, platelet granulation change, and angiogenesis. CMPG vasoactive effects can increase the blood flows of the flaps, improving their viability. This study aims to assess the viability of McFarland skin flaps after intraperitoneal sildenafil administration. Methods: In total, 20 Wistar mice were distributed in two groups: control (production of dorsal skin flap, intraperitoneal applicatdion of 0.9 % salt solution), and study (production of dorsal skin flap with intraperitoneal application of sildenafil). Skin flaps were photographed seven days after operation and represented graphically with a view to AutoCad-based analysis. Three biopsies (cranial, middle, and caudal) were collected for histological analysis of each flap. Results The macroscopic analysis showed that intraperitoneal application of sildenafil was associated with stronger tissue contraction (p=0.019). The histological study showed less granulation associated with polymorphonuclears in the distal third of the flaps (p=0.001) and more necrosis in granulation sites in the middle third of the flaps (p=0.011). Conclusion: The intraperitoneal application of sildenafil was not effective in improving the viability of McFarlane skin flaps in mice. Other studies may shed light into its mechanism of action for tissue contraction.

The HCV NS5B nucleoside and non-nucleoside inhibitors.

This article introduces one of the most diverse classes of direct-acting antivirals for hepatitis C, the nucleoside and non-nucleoside NS5B polymerase inhibitors. Through a systematic review of the published literature, we describe their structure, mechanism of action, issues with resistance, and clinical effectiveness shown in the latest clinical trials. Direct-acting antiviral combination trials that have already shown some early promising results even in the setting of interferon-sparing antiviral regimens are discussed.

Safety and pharmacokinetics of IDX184, a liver-targeted nucleotide polymerase inhibitor of hepatitis C virus, in healthy subjects.

IDX184 is a nucleotide prodrug designed to enhance formation in the liver of the active triphosphate of 2'-methylguanosine (2'-MeG), a potent and specific polymerase inhibitor of the hepatitis C virus (HCV). In the present study, single ascending oral doses of 5, 10, 25, 50, 75, and 100 mg IDX184 were administered sequentially to cohorts of 8 healthy subjects, randomized 6:2, active/placebo. Plasma and urine pharmacokinetic sampling was performed over a period of 120 h after dosing. Upon absorption, IDX184 rapidly disappeared from plasma, with a mean half-life (t(1/2)) of approximately 1 h, while plasma concentrations of 2'-MeG gradually increased. Consistent with a liver-targeting approach, plasma exposure of IDX184 and 2'-MeG was low and was also dose related: the mean maximum concentrations ranged from 1.1 to 17 ng/ml for IDX184 and 1.7 to 19 ng/ml for 2'-MeG, and the respective mean total area under the curve ranged from 1.2 to 22.7 and 17.3 to 334 ng·h/ml. Mean 2'-MeG plasma concentrations 24 h after dosing were 0.6 to 3 ng/ml for the 25- to 100-mg doses. Mean 2'-MeG t(1/2) values ranged from 18 to 43 h for doses of 25 mg and above. Mean cumulative urine excretion was 0.2% and 12 to 20% of administered doses for the unchanged IDX184 and 2'-MeG, respectively. IDX184 was safe and well tolerated; no serious adverse events (SAEs), dose-dependent adverse events (AEs), or dose-limiting toxicities were observed. The incidence of AEs and laboratory abnormalities was low and was similar among subjects receiving IDX184 or a placebo. All AEs were mild to moderate and resolved at the end of study. The favorable safety and pharmacokinetic profiles support further clinical evaluation of IDX184 in HCV-infected patients.

GMP prevents excitotoxicity mediated by NMDA receptor activation but not by reversal activity of glutamate transporters in rat hippocampal slices.

Glutamate is the main excitatory neurotransmitter in the mammalian nervous system and is essential for its normal functions. However, overstimulation of glutamatergic system due to hyperactivation of NMDA receptors and/or impairment of glutamate reuptake system has been implicated in many acute and chronic neurological diseases. Regulation of extracellular glutamate concentrations relies on the function of glutamate transporters which can be reversed in situations related to excitotoxicity. Guanosine-5'-monophosphate (GMP), a guanine nucleotide which displays important extracellular roles, such as trophic effects to neurons and astrocytes, behaves as antagonist of glutamate receptors and is neuroprotective in hippocampal slices against excitotoxicity or ischemic conditions. Hippocampal slices exposed to 1 or 10 mM glutamate, or 100 microM NMDA with 10 microM glycine for 1 h and evaluated after 6 or 18 h, showed reduced cell viability and DNA fragmentation, respectively. Glutamate- or NMDA-induced cell death was prevented by 50 microM MK-801, but only NMDA-induced cell damage was prevented by GMP (1 mM). Glutamate-induced cell viability impairment and glutamate-induced l-[(3)H]glutamate release were both prevented by adding DL-TBOA (10 microM). Otherwise, NMDA-induced cell viability loss was not prevented by 10 microM of DL-TBOA and NMDA did not induce l-[(3)H]glutamate release. Our results demonstrate that GMP is neuroprotective when acting selectively at NMDA receptors. Glutamate-induced hippocampal slice damage and glutamate release were blocked by glutamate transporter inhibitor, indicating that glutamate-induced toxicity also involves the reversal of glutamate uptake, which cannot be prevented by GMP.