Effects of L-arginine and phosphodiesterase-5 inhibitor, sildenafil, on inflammation and airway responsiveness of sensitized BP2 mice

Exploring the Multifaceted Potential of Sildenafil in Medicine

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

Review - Nutraceuticals Can Target Asthmatic Bronchoconstriction: NADPH Oxidase-Dependent Oxidative Stress, RhoA and Calcium Dynamics

Activation of various isoforms of NADPH oxidase contributes to the pathogenesis of asthma at multiple levels: promoting hypercontractility, hypertrophy, and proliferation of airway smooth muscle; enabling lung influx of eosinophils via VCAM-1; and mediating allergen-induced mast cell activation. Free bilirubin, which functions physiologically within cells as a feedback inhibitor of NADPH oxidase complexes, has been shown to have a favorable impact on each of these phases of asthma pathogenesis. The spirulina chromophore phycocyanobilin (PhyCB), a homolog of bilirubin’s precursor biliverdin, can mimic the inhibitory impact of biliverdin/bilirubin on NADPH oxidase activity, and spirulina’s versatile and profound anti-inflammatory activity in rodent studies suggests that PhyCB may have potential as a clinical inhibitor of NADPH oxidase. Hence, spirulina or PhyCB-enriched spirulina extracts merit clinical evaluation in asthma. Promoting biosynthesis of glutathione and increasing the expression and activity of various antioxidant enzymes – as by supplementing with N-acetylcysteine, Phase 2 inducers (eg, lipoic acid), selenium, and zinc – may also blunt the contribution of oxidative stress to asthma pathogenesis. Nitric oxide (NO) and hydrogen sulfide (H₂S) work in various ways to oppose pathogenic mechanisms in asthma; supplemental citrulline and high-dose folate may aid NO synthesis, high-dose biotin may mimic and possibly potentiate NO’s activating impact on soluble guanylate cyclase, and NAC and taurine may boost H₂S synthesis. The amino acid glycine has a hyperpolarizing effect on airway smooth muscle that is bronchodilatory. Insuring optimal intracellular levels of magnesium may modestly blunt the stimulatory impact of intracellular free calcium on bronchoconstriction. Nutraceutical regimens or functional foods incorporating at least several of these agents may have utility as nutraceutical adjuvants to standard clinical management of asthma.

Sildenafil beyond erectile dysfunction and pulmonary arterial hypertension: Thinking about new indications

Sildenafil, approved two decades ago, is the inhibitor of phosphodiesterase 5 (PDE5). First of all, it was designated for angina pectoris, but soon it showed a wonderful efficacy in erectile dysfunction (ED) and then pulmonary arterial hypertension (PAH). Due to the distribution of phosphodiesterase (PDE) in almost all organs, maybe it effects other diseases. Hence, a great number of investigations began to understand the role of PDEi in different organs. Preliminary research on sildenafil in cell culture and animal models has yielded promising results. Soon, a greater number of animal researches and clinical trials joined them. The results disclosed sildenafil can have beneficial effects in each organ such as heart, liver, kidney, brain, and intestines. Furthermore, it has significantly improved the prognosis of organ ischemia in various animal models. Clinical trials in several diseases, such as recurrent spontaneous miscarriage, fatty liver disease, bronchopulmonary dysplasia (BPD), heart failure, and premature ejaculation (PE) brought promising results. Although some clinical trials are available on the effects of sildenafil on various diseases, further studies on humans are needed to consolidate the ultimate effects of sildenafil. The aim of this review was to describe the effects of sildenafil on each organ and explain its mechanisms of action. Further, other PDE inhibitors such as tadalafil and vardenafil have been briefly discussed in parts of this review.

Use of Melatonin in Oxidative Stress Related Neonatal Diseases

Reactive oxygen species have a crucial role in the pathogenesis of perinatal diseases. Exposure to inflammation, infections, or high oxygen concentrations is frequent in preterm infants, who have high free iron levels that enhance toxic radical generation and diminish antioxidant defense. The peculiar susceptibility of newborns to oxidative stress supports the prophylactic use of melatonin in preventing or decreasing oxidative stress-mediated diseases. Melatonin, an effective direct free-radical scavenger, easily diffuses through biological membranes and exerts pleiotropic activity everywhere. Multiple investigations have assessed the effectiveness of melatonin to reduce the “oxygen radical diseases of newborn” including perinatal brain injury, sepsis, chronic lung disease (CLD), and necrotizing enterocolitis (NEC). Further studies are still awaited to test melatonin activity during perinatal period.

Phosphodiesterases as therapeutic targets for respiratory diseases

Chronic respiratory diseases, such as chronic obstructive pulmonary disease (COPD) and asthma, affect millions of people all over the world. Cyclic adenosine monophosphate (cAMP) which is one of the most important second messengers, plays a vital role in relaxing airway smooth muscles and suppressing inflammation. Given its vast role in regulating intracellular responses, cAMP provides an attractive pharmaceutical target in the treatment of chronic respiratory diseases. Phosphodiesterases (PDEs) are enzymes that hydrolyze cyclic nucleotides and help control cyclic nucleotide signals in a compartmentalized manner. Currently, the selective PDE4 inhibitor, roflumilast, is used as an add-on treatment for patients with severe COPD associated with bronchitis and a history of frequent exacerbations. In addition, other novel PDE inhibitors are in different phases of clinical trials. The current review provides an overview of the regulation of various PDEs and the potential application of selective PDE inhibitors in the treatment of COPD and asthma. The possibility to combine various PDE inhibitors as a way to increase their therapeutic effectiveness is also emphasized.

Dose dependent effects of tadalafil and roflumilast on ovalbumin-induced airway hyperresponsiveness in guinea pigs

INTRODUCTION

Chronic obstructive diseases of airways associated with cough and/or airway smooth muscle hyperresponsiveness are usually treated with bronchodilating and anti-inflammatory drugs. Recently, selective phosphodiesterase (PDE) 4 inhibitors have been introduced into the therapy of chronic obstructive pulmonary disease. Several studies have demonstrated their ability to influence the airway reactivity and eosinophilic inflammation by increasing the intracellular cAMP concentrations also in bronchial asthma. Furthermore, the expression of PDE5 in several immune cells suggests perspectives of PDE5 inhibitors in the therapy of inflammation, as well.

PURPOSE

The aim of this study was to assess the dose-dependent effects of PDE4 and PDE5 inhibitors in allergic inflammation. Therefore, the effects of 7-days administration of PDE4 inhibitor roflumilast and PDE5 inhibitor tadalafil at two different doses in experimentally-induced allergic inflammation were evaluated.

MATERIALS AND METHODS

In the study, male adult guinea pigs were used. Control group was non-sensitized. Other animals were sensitized with ovalbumin over two weeks and thereafter treated intraperitoneally for 7 days with roflumilast or tadalafil (daily dose 0.5 mg/kg or 1.0 mg/kg b.w.), or with vehicle.

RESULTS

Both roflumilast and tadalafil reduced specific airway resistance after nebulization of histamine (marker of in vivo airway reactivity) at both doses used. The in vitro airway reactivity to cumulative doses of acetylcholine was significantly reduced for roflumilast at higher dose, predominantly in the lung tissue strips. Histamine-induced contractile responses were significantly influenced in both lung and tracheal tissue strips, predominantly at the higher doses. Tadalafil led to a decrease in contractile responses induced by both acetylcholine and histamine, with more significant effects in the lung tissue strips. These changes were associated with decreased numbers of circulating leukocytes and eosinophils and concentrations of interleukin (IL)-4, IL-5 and TNF-α in the lung homogenate.

CONCLUSIONS

The selective PDE4 and PDE5 inhibitors alleviated allergic airway inflammation, with more significant effects at the higher doses.

Treatment with a combination of ginger, L-citrulline, muira puama and Paullinia cupana can reverse the progression of corporal smooth muscle loss, fibrosis and veno-occlusive dysfunction in the aging rat

AIMS

Aging associated erectile dysfunction is characterized within the corpora by a progressive apoptosis of the smooth muscle cells and their replacement by collagen. Nitric oxide from iNOS has been shown to inhibit these histological changes in the corpora while PDE5 inhibitors as well as certain nutraceuticals such as ginger, paullinia cupana, muira puama and L-citrulline are known to enhance the effects of NO. We evaluated whether the daily oral administration for 2 months with a combination of ginger, paullinia cupana, muira puama and L-citrulline (COMP-4) can effectively delay the ongoing corporal fibrosis, smooth muscle cell apoptosis and cavernosal veno-occlusive dysfunction (CVOD) seen in middle aged rats similar to that seen with tadalafil.

METHODS

10 Month old Fisher 344 rats were treated or not for two months with COMP-4, tadalafil or a combination of tadalafil plus COMP-4. CVOD was determined by dynamic infusion cavernosometry. Penile sections of the corpora cavernosa were subjected to Masson trichrome staining to evaluate fibrosis and immunohistochemistry for desmin as a marker of smooth muscle content and inducible nitric oxide synthase (iNOS) followed by image analysis. Oxidative stress levels were determined by GSH/GSSG ratio in whole blood.

RESULTS

a decline in the non-treated rat's erectile function is evident by 10-12 months of age and is accompanied by a decrease in the corporal smooth muscle content determined by desmin expression and an increase in corporal fibrosis. The daily treatment for two months with COMP-4 reverses this process by reducing systemic oxidative stress and increasing desmin and iNOS expression, similar to that seen with tadalafil or the combination of COMP-4 plus tadalafil.

CONCLUSION

An oral combination of ginger, muira puama, Paullinia cupana and L-citrulline seems to be as effective as daily PDE5 inhibitor therapy in either delaying or reversing the onset of the histological and functional characteristics of aging related erectile dysfunction.

Protective role of melatonin in neonatal diseases

Oxidative stress contributes to the severity of several newborn conditions to the extent that Saugstad coined the phrase “oxygen radical diseases of neonatology.” In order to counteract free radicals damage many strategies to augment antioxidant status in ill-term and preterm infants have been proposed and several medications have been experimented with mixed results. Several studies have tested the efficacy of melatonin to counteract oxidative damage in diseases of newborns such as chronic lung disease, perinatal brain injury, necrotizing enterocolitis, and retinopathy of prematurity, giving promising results. The peculiar perinatal susceptibility to oxidative stress indicates that prophylactic use of antioxidants as melatonin could help to prevent or at least reduce oxidative stress related diseases in newborns. However, more studies are needed to confirm these beneficial effects.

Novel therapies in asthma: leukotriene antagonists, biologic agents, and beyond

Asthma is one of the most common conditions seen in clinical practice and carries both a significant disease burden in terms of patient morbidity and a high economic burden in both direct and indirect costs. Despite this, it remains a comparatively poorly understood disease, with only modest advances in treatment over the past decade. Corticosteroids remain the cornerstone of therapy. Both patient compliance with medications and physician adherence to evidence-based guidelines are often poor, and a high percentage of patients continue to have inadequately controlled disease even with optimal therapy. Following a contextual overview of the current treatment guidelines, this review focuses on novel asthma therapies, beginning with the introduction of the leukotriene receptor antagonist zafirlukast in the 1990s, continuing through advanced endoscopic therapy and into cytokine-directed biologic agents currently in development. Along with clinically relevant biochemistry and pharmacology, the evidence supporting the place of these therapies in current guidelines will be highlighted along with data comparing these agents with more conventional treatment. A brief discussion of other drugs, such as those developed for unrelated conditions and subsequently examined as potential asthma therapies, is included.

Choice of mouse strain influences the outcome in a mouse model of chemical-induced asthma

Background

The development of occupational asthma is the result of interactions between environmental factors and individual susceptibility. We assessed how our model of chemical-induced asthma is influenced by using different mouse strains.

Methodology/Principal Findings

On days 1 and 8, male mice of 7 different strains (BALB/c, BP/2, A/J, C57Bl/6, DBA/2, CBA and AKR) were dermally treated with toluene-2,4-diisocyanate (TDI) (0.3%) or vehicle (acetone/olive oil, AOO, 2∶3) on each ear (20 µl). On day 15, they received an oropharyngeal instillation of TDI (0.01%) or AOO (1∶4). Airway reactivity to methacholine, total and differential cell counts in bronchoalveolar lavage (BAL) and total serum IgE and IgG_2a levels were measured. Lymphocyte subpopulations in auricular lymph nodes and in vitro release of cytokines by ConA stimulated lymphocytes were assessed. In TDI-sensitized and challenged mice, airway hyper-reactivity was only observed in BALB/c, BP/2, A/J and AKR mice; airway inflammation was most pronounced in BALB/c mice; numbers of T-helper (CD4⁺), T-activated (CD4⁺CD25⁺), T-cytotoxic (CD8⁺) and B- lymphocytes (CD19⁺) were increased in the auricular lymph nodes of BALB/c, BP/2, A/J and CBA mice; elevated concentrations of IL-4, IL-10, IL-13 and IFN-γ were detected in supernatant of lymphocytes from BALB/c, BP/2, A/J, C57Bl/6 and CBA mice cultured with concanavaline A, along with an increase in total serum IgE.

Conclusion

The used mouse strain has considerable and variable impacts on different aspects of the asthma phenotype. The human phenotypical characteristics of chemically-induced occupational asthma were best reproduced in Th2-biased mice and in particular in BALB/c mice.

Melatonin protects against oxidative damage in a neonatal rat model of bronchopulmonary dysplasia

BACKGROUND

Oxidative stress plays an important role in the pathogenesis of bronchopulmonary dysplasia (BPD). Melatonin (MT) has direct and indirect free radical detoxifying activity. The present study was to investigate whether treatment with MT would attenuate hyperoxia-induced lung injury and the effect of MT on imbalance of oxidants/antioxidants in the lung of neonatal rats.

METHODS

BPD was induced by exposure to hyperoxia in neonatal rats (n=90). The rats were divided randomly into three groups (n=30 each): air-exposed control group, hyperoxia-exposed group, and hyperoxia-exposed MT-treated group. Lung specimens were obtained respectively on day 3, day 7, and day 14 after exposure (n=10 each). Activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT), and levels of myeloperoxidase (MPO), nitrite/nitrate, and malondialdehyde (MDA) were assayed. Histopathologic changes were observed in the tissues stained with hematoxylin and eosin and Masson's trichrome stain.

RESULTS

Increased levels of MPO, nitrite/nitrate, and MDA in the hyperoxia-exposed rats were significantly reduced by MT (P<0.05). Activities of GSH-Px, SOD, and CAT which did not change after exposure to hyperoxia were increased by MT (P<0.05). Furthermore, BPD associated histopathological alterations such as reduced total number of alveoli and interstitial fibrosis were obviously abated in the MT-treated group.

CONCLUSIONS

MT can reverse oxidants/antioxidants imbalance in damaged lung tissue and thus exert a beneficial effect on hyperoxia-induced lung disease in neonatal rats. With regard to humans, there may be a protective effect of MT on BPD.

Arginine homeostasis in allergic asthma

Allergic asthma is a chronic disease characterized by early and late asthmatic reactions, airway hyperresponsiveness, airway inflammation and airway remodelling. Changes in l-arginine homeostasis may contribute to all these features of asthma by decreased nitric oxide (NO) production and increased formation of peroxynitrite, polyamines and l-proline. Intracellular l-arginine levels are regulated by at least three distinct mechanisms: (i) cellular uptake by cationic amino acid (CAT) transporters, (ii) metabolism by NO-synthase (NOS) and arginase, and (iii) recycling from l-citrulline. Ex vivo studies using animal models of allergic asthma have indicated that attenuated l-arginine bioavailability to NOS causes deficiency of bronchodilating NO and increased production of procontractile peroxynitrite, which importantly contribute to allergen-induced airway hyperresponsiveness after the early and late asthmatic reaction, respectively. Decreased cellular uptake of l-arginine, due to (eosinophil-derived) polycations inhibiting CATs, as well as increased consumption by increased arginase activity are major causes of substrate limitation to NOS. Increasing substrate availability to NOS by administration of l-arginine, l-citrulline, the polycation scavenger heparin, or an arginase inhibitor alleviates allergen-induced airway hyperresponsiveness by restoring the production of bronchodilating NO. In addition, reduced l-arginine levels may contribute to the airway inflammation associated with the development of airway hyperresponsiveness, which similarly may involve decreased NO synthesis and increased peroxynitrite formation. Increased arginase activity could also contribute to airway remodelling and persistent airway hyperresponsiveness in chronic asthma via increased synthesis of l-ornithine, the precursor of polyamines and l-proline. Drugs that increase the bioavailability of l-arginine in the airways - particularly arginase inhibitors - may have therapeutic potential in allergic asthma.