Phosphodiesterase 4 inhibitors and inflammatory bowel disease: emerging therapies in inflammatory bowel disease

Hypersampsonone H attenuates ulcerative colitis via inhibition of PDE4 and regulation of cAMP/PKA/CREB signaling pathway

BACKGROUND AND OBJECTIVES

Ulcerative colitis (UC) is a recurrent intestinal inflammatory disease which poses a serious threat to the life of patients. However, there are no specific drugs for UC yet. Hypericum sampsonii Hance (HS) is a Chinese herbal medicine traditionally used to treat enteritis and dysentery. Our previous studies have demonstrated that HS holds potential anti-UC effects, and a novel compound named Hypersampsonone H (HS-1) isolated from HS possesses significant anti-inflammatory activity. However, the beneficial effects of HS-1 on UC remain unclear. This study aimed to investigate the therapeutic effects of HS-1 on UC and its potential mechanisms, both in vitro and in vivo.

METHODS

The in vitro model was employed using LPS-induced RAW264.7 cells to investigate the anti-inflammatory effects of HS-1 and its possible mechanisms. Furthermore, the therapeutic efficacy and potential mechanisms of HS-1 against dextran sulfate sodium (DSS)-induced acute colitis were assessed through histopathological examination, biochemical analysis, and molecular docking.

RESULTS

In vitro, HS-1 significantly reduced LPS-induced inflammatory responses, as indicated by inhibiting NO production, down-regulating the overexpression of COX-2 and iNOS, as well as regulating the imbalanced levels of IL-6, TNF-α, and IL-10. Moreover, HS-1 also inhibited the expression of PDE4, elevated the intracellular cAMP level, and promoted the phosphorylation of CREB, thereby activating the PKA/CREB pathway in RAW264.7 cells. In vivo, HS-1 demonstrated therapeutic capacity against DSS-induced colitis by alleviating the symptoms of colitis mice, regulating the abnormal expression of inflammatory mediators, protecting the integrity of intestinal epithelial barrier, and reducing tissue fibrosis. Consistently, HS-1 was found to decrease the expression of PDE4 isoforms, subsequently activating the cAMP/PKA/CREB signaling pathway. Furthermore, the molecular docking results indicated that HS-1 exhibited a high affinity for PDE4, particularly PDE4D. Further mechanistic validation in vitro demonstrated that HS-1 possessed a synergistic effect on forskolin and an antagonistic effect on H-89 dihydrochloride, thereby exerting anti-inflammatory effects through the cAMP/PKA/CREB signaling pathway.

CONCLUSION

We disclose that HS-1 serves as a promising candidate drug for the treatment of UC by virtue of its ability to reduce DSS-induced colitis via the inhibition of PDE4 and the activation of cAMP/PKA/CREB signaling pathway.

Intestinal barrier in inflammatory bowel disease: A bibliometric and knowledge-map analysis

BACKGROUND

Barrier surfaces composed of specialized epithelial cells separate the host body from the external environment, and are essential for maintaining proper intestinal physiologic and immune homeostasis.

AIM

To explore the development trends and research hotspots of intestinal barrier research in inflammatory bowel disease (IBD).

METHODS

The publications related to the intestinal barrier in IBD were obtained from the Web of Science Core Collection database. Bibliometric analysis and visualization were conducted using VOSviewer, CiteSpace and R software.

RESULTS

A total of 4482 articles published between 2002 and 2022 were identified. The United States is dominant in intestinal barrier research, whereas the University of Chicago is the most active institution. Jerrold from Harvard Medical School was the most productive authors with the most citations. The journals Inflammatory Bowel Disease and Gastroenterology have made significant contributions in this field. The keywords appearing at high frequency related to the intestinal barrier in IBD were detected, including nuclear factor kappa B, tumor necrosis factor-α, apoptosis, oxidative stress and probiotics. Among them, antioxidants, Akkermansia muciniphila, nanoparticles, short-chain fatty acids and extracellular vesicles have received growing interest in recent research.

CONCLUSION

The intestinal barrier field is developing rapidly with extensive cooperation. Targeting the gut microbiota and dietary metabolism to regulate the intestinal barrier has shown promising prospective applications and has generated broad interest. The importance of the intestinal barrier in IBD is gradually being fully recognized, providing a new therapeutic perspective for improving inflammation and prognosis.

Protective effect of Apremilast against LPS-induced acute lung injury via modulation of oxidative stress and inflammation: Possible involvement of Akt and ERK signaling pathways

Lung injuries are attributed due to exposure to Drugs or chemicals. One of the important challenging situations for the clinicians is to manage treatments of different diseases with acute lung injury (ALI). The objective of this study was to investigate the possible protective mechanisms and action of a novel Phosphodiesterase-4 inhibitor “Apremilast” (AP) in lipopolysaccharide (LPS)-induced lung injury. Blood sample from each animals were collected in a vacuum blood collection tube. The rat lungs were isolated for oxidative stress assessment, western blot analysis and their mRNA expressions using RT-PCR. Exposure of LPS in rats causes significant increase in oxidative stress, activates the pro-inflammatory cytokines release like tissue necrotic factor-alpha (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6), modulated gene expression, protein expression and histopathological changes which were reversed by administration of AP. Finding of the research enlighten the protective role of AP against LPS-induced ALI.

Research progress of phosphodiesterase inhibitors in inflammatory bowel disease treatment

Inflammatory bowel disease is a recurrent chronic intestinal inflammatory disease with unknown etiology and no effective treatment. Phosphodiesterase (PDE) regulates a variety of physiological and pathophysiological processes by mediating the hydrolysis of intracellular second messengers cyclic adenosine monophosphate and cyclic guanosine monophosphate. In recent years, a series of researches suggest that PDE inhibitors such as several PDE4 inhibitors, PDE5 inhibitors (sildenafil, tadalafil and vardenafil), PDE3 inhibitors (cilostazol), PDE9 inhibitor (PF-04447943) and PDE3/PDE4 double inhibitor (pumafentrine) have ameliorating effect on experimental colitis in animals. In clinical trials, PDE4 inhibitor apremilast showed more therapeutic advantage than tetomilast. This article reviews the recent research progress of PDE inhibitors in treatment of inflammatory bowel disease.

Apremilast Normalizes Gene Expression of Inflammatory Mediators in Human Keratinocytes and Reduces Antigen-Induced Atopic Dermatitis in Mice

Background

Apremilast, an oral phosphodiesterase (PDE) 4 inhibitor, has demonstrated efficacy in psoriasis, while its efficacy in atopic dermatitis (AD) was found to be modest. AD is a chronic inflammatory skin disease associated with activation of T helper (Th) 2 and Th17 immunity and a compromised epidermal barrier.

Objective

The objectives of this study were to examine the expression of PDE4 isoforms in skin from healthy subjects and AD patients, and to determine the effects of apremilast on AD-related inflammatory markers in vitro and in murine models of AD.

Methods

The expression of PDE4 isoforms (A, B, C, and D) in skin biopsies from healthy subjects and AD patients was evaluated using immunohistochemistry and digital image analysis. Using quantitative real-time reverse-transcriptase polymerase chain reaction, we evaluated the effects of apremilast on gene expression in adult human epidermal keratinocytes (HEKa) stimulated by Th2 and Th17 cytokines, and in two mouse models of antigen-induced AD.

Results

Expression of PDE4 isoforms increased up to three-fold in the epidermis of AD patients versus healthy skin. In interleukin (IL)-4 and IL-17-stimulated HEKa cells, apremilast significantly changed the expression of ILs, including IL-12/IL-23p40 and IL-31, and alarmins S100A7, S100A8, and S100A12. In mouse models of AD, apremilast significantly reduced ear swelling and monocyte chemoattractant protein-1 expression.

Conclusion

PDE4 is overexpressed in AD skin compared with normal skin, and inflammatory gene expression by human keratinocytes and mouse dermatitis can be modulated by apremilast.

TGF-β activity restoration and phosphodiesterase 4 inhibition as therapeutic options for inflammatory bowel diseases

In the last decades, the better understanding of inflammatory bowel diseases (IBD) pathogenesis has contributed to the identification of new therapeutic targets that can be modulated to induce and maintain disease remission. Monoclonal antibodies against tumor necrosis factor, interleukin (IL)-12/IL-23p40, and the integrin α4β7 and inhibitors of Janus kinase molecules are valid compounds to limit the function of molecules implicated in the control of IBD-related inflammation. However, not all patients respond to treatment with such drugs, some of them lose response over time and others develop serious side effects, such as infections or malignancies, which lead to the discontinuation of the therapy. Thus, an intensive research is ongoing with the goal to identify new targets and develop novel therapeutic options. In this context, restoration of TGF-β activity and inhibition of phosphodiesterase 4 (PD4) represent two relevant strategies. TGF-β is an immunesuppressive cytokine, whose activity is severely impaired in IBD due to the abundance of the intracellular inhibitor Smad7. Knockdown of Smad7 with a specific antisense oligonucleotide restores TGF-β signalling and dampens effector immune responses in pre-clinical studies and initial clinical trials in Crohn's disease patients, even though a recent phase 3 trial was discontinued due to an apparent inefficacy. PD4 inhibition determines the increase of intracellular levels of cyclic adenosine monophosphate, a mechanism that decreases pro-inflammatory cytokine production. A recent phase 2 study has shown that oral administration of PD4 associates with clinical benefit in patients with ulcerative colitis. In this article, we review the rationale and the available data relative to the use of these two agents in IBD.

PDE4 Inhibition and Inflammatory Bowel Disease: A Novel Therapeutic Avenue

BACKGROUND

In the last few decades, a better knowledge of the inflammatory pathways involved in the pathogenesis of Inflammatory Bowel Disease (IBD) has promoted biological therapy as an important tool to treat IBD patients. However, in spite of a wider spectrum of biological drugs, a significant proportion of patients is unaffected by or lose their response to these compounds, along with increased risks of infections and malignancies. For these reasons there is an urgent need to look for new pharmacological targets. The novel Phosphodiesterase 4 (PDE4) inhibitors have been recently introduced as new modulators of intracellular signals and gene transcription for the treatment of IBD.

AIM

To discuss and describe the state of the art of this new class of compounds in the IBD field, with particular attention to apremilast.

METHODS

Published articles selected from PubMed were comprehensively reviewed, with key words including apremilast, inflammatory disease, IBD, psoriasis, psoriatic arthritis, pathogenesis, therapies, and treatment.

RESULTS

PDE4 inhibitors generate elevated intracellular levels of cyclic Adenosine Monophosphate (cAMP), that consequently down-regulate the release of pro-inflammatory cytokines in the mucosa of IBD patients. The newly developed apremilast is one of these drugs and has already been approved for the treatment of dermatologic/rheumatologic inflammatory conditions; studies in psoriasis and psoriatic arthritis have in fact demonstrated its clinical activity. However, no clinical trials have yet been published on the use of apremilast in IBD.

CONCLUSION

In light of the similarity of pro-inflammatory signaling pathways across the gut, the skin, and joints, apremilast is likely supposed to show its efficacy also in IBD.

DrugGenEx-Net: a novel computational platform for systems pharmacology and gene expression-based drug repurposing

Background

The targeting of disease-related proteins is important for drug discovery, and yet target-based discovery has not been fruitful. Contextualizing overall biological processes is critical to formulating successful drug-disease hypotheses. Network pharmacology helps to overcome target-based bottlenecks through systems biology analytics, such as protein-protein interaction (PPI) networks and pathway regulation.

Results

We present a systems polypharmacology platform entitled DrugGenEx-Net (DGE-NET). DGE-NET predicts empirical drug-target (DT) interactions, integrates interaction pairs into a multi-tiered network analysis, and ultimately predicts disease-specific drug polypharmacology through systems-based gene expression analysis. Incorporation of established biological network annotations for protein target-disease, −signaling pathway, −molecular function, and protein-protein interactions enhances predicted DT effects on disease pathophysiology. Over 50 drug-disease and 100 drug-pathway predictions are validated. For example, the predicted systems pharmacology of the cholesterol-lowering agent ezetimibe corroborates its potential carcinogenicity.

When disease-specific gene expression analysis is integrated, DGE-NET prioritizes known therapeutics/experimental drugs as well as their contra-indications. Proof-of-concept is established for immune-related rheumatoid arthritis and inflammatory bowel disease, as well as neuro-degenerative Alzheimer’s and Parkinson’s diseases.

Conclusions

DGE-NET is a novel computational method that predicting drug therapeutic and counter-therapeutic indications by uniquely integrating systems pharmacology with gene expression analysis. DGE-NET correctly predicts various drug-disease indications by linking the biological activity of drugs and diseases at multiple tiers of biological action, and is therefore a useful approach to identifying drug candidates for re-purposing.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-016-1065-y) contains supplementary material, which is available to authorized users.

Phosphodiesterase 4 in inflammatory diseases: Effects of apremilast in psoriatic blood and in dermal myofibroblasts through the PDE4/CD271 complex

Phosphodiesterases 4 (PDE4) act as proinflammatory enzymes via degradation of cAMP, whereas PDE4 inhibitors play an anti-inflammatory role in vitro and in vivo. In particular, apremilast has been recently approved for the treatment of psoriasis and psoriatic arthritis. However, little is known on the expression pattern of PDE4 in psoriasis. We report that PDE4B and PDE4D mRNA are overexpressed in peripheral blood mononuclear cells (PBMC) from psoriasis, as compared with normal controls, while apremilast reduces PBMC production of a number of pro-inflammatory cytokines and increases the levels of anti-inflammatory mediators. PDE4 expression is up-regulated in psoriatic dermis as compared with normal skin, with particular regard to fibroblasts. This is confirmed in vitro, where both dermal fibroblasts (DF) and, to a greater extent, myofibroblasts (DM) express all PDE4 isoforms at the mRNA and protein level. Because PDE4 interacts with the nerve growth factor (NGF) receptor CD271 in lung fibroblasts, we evaluated the relationship and function of PDE4 and CD271 in normal human skin fibroblasts. All PDE4 isoforms co-immunoprecipitate with CD271 in DM, while apremilast inhibits apoptosis induced by β-amyloid, a CD271 ligand, in DM. Furthermore, apremilast significantly reduces NGF- and transforming growth factor-β1 (TGF-β1)-induced fibroblast migration, and inhibits DF differentiation into DM mediated by NGF or TGF-β1. Finally, in DM, apremilast significantly reduces cAMP degradation induced by treatment with β-amyloid. Taken together, these results indicate that PDE4 play an important role in psoriasis. In addition, the study reveals that the PDE4/CD271 complex could be important in modulating fibroblast functions.

cAMP ameliorates inflammation by modulation of macrophage receptor for advanced glycation end-products

Clarification of the roles of PAMPs (pathogen-associated molecular patterns) and DAMPs (damage-associated molecular patterns) is indispensable for therapeutic strategies against various inflammatory diseases. RAGE (receptor for advanced glycation end-products) is one of the PRRs (pattern recognition receptors) and has been implicated in autoimmune and inflammatory diseases. Effective remedies targeting RAGE are required for the diseases. In the present study, we show that cAMP-induced modulation of the RAGE isoform in macrophages can control the inflammatory state in both in vitro and in vivo experimental conditions. The RAGE ligand S100B stimulated MCP-1 (monocyte chemoattractant protein-1) secretion from peritoneal macrophages, but cAMP elevation suppressed it by converting the RAGE isoform from a membrane-bound into a soluble form. This shedding is the result of ectodomain cleavage of mRAGE (membrane-bound RAGE) by MMP9 (matrix metalloproteinase 9). Furthermore, forskolin significantly inhibited peritoneal macrophage accumulation in a mouse S100B-induced peritonitis model. These results suggest that cAMP serves as a negative regulator of ligand-RAGE signalling and macrophage recruitment by mRAGE down-regulation and formation of decoys as soluble receptors. The present study should deepen our understanding of the pathogenesis of RAGE-mediated tissue derangement and provide new clues for overcoming RAGE-related inflammatory diseases.

cAMP-specific phosphodiesterase inhibitors: promising drugs for inflammatory and neurological diseases

INTRODUCTION

PDEs are key enzymes in the adenosine and guanosine cyclic nucleotides (cAMP and cGMP) signaling cascade. Their inhibition increases cyclic nucleotide levels inside the cell. Thus, pharmacological modulation of PDE activity can have profound effects on the function of cells and organ systems throughout the body.

AREAS COVERED

Among the large PDE families, only PDE4, PDE7 and PDE8 are cAMP-specific hydrolyzing enzymes. cAMP is an important second messenger not only by its involvement in a vast number of physiological processes but also by activation of protein kinase A, exchange protein activated by cAMP (Epac) and cAMP response element-binding (CREB) or cyclic nucleotide-gated channels. Clearly, such enzymes represent ideal drug targets for the pharmacological treatment of many pathologies. The discovery and development of small molecules targeting cAMP-specific PDEs reported in the last 5 years is the focus of the present review.

EXPERT OPINION

The first PDE4 inhibitors recently reached the market, having avoided, by different strategies, their dose-limiting side effects (after more than two decades of drug development). Meanwhile, new cAMP-specific PDE7 and PDE8 inhibitors emerged as effective and safe drugs for severe unmet diseases. The therapeutic potential of these inhibitors will be tested in the near future, as many of these drug candidates are ready to start clinical trials.

Synergistic effect of vaginal trauma and ovariectomy in a murine model of stress urinary incontinence: upregulation of urethral nitric oxide synthases and estrogen receptors

The molecular mechanisms underlying stress urinary incontinence (SUI) are unclear. We aimed to evaluate the molecular alterations in mice urethras following vaginal trauma and ovariectomy (OVX). Twenty-four virgin female mice were equally distributed into four groups: noninstrumented control; vaginal distension (VD) group; OVX group; and VD + OVX group. Changes in leak point pressures (LPPs), genital tract morphology, body weight gain, plasma 17β-estradiol level and expressions of neuronal nitric oxide synthase (nNOS), induced nitric oxide synthase (iNOS), and estrogen receptors (ERs—ERα and ERβ) were analyzed. Three weeks after VD, the four groups differed significantly in genital size and body weight gain. Compared with the control group, the plasma estradiol levels were significantly decreased in the OVX and VD + OVX groups, and LPPs were significantly decreased in all three groups. nNOS, iNOS, and ERα expressions in the urethra were significantly increased in the VD and VD + OVX groups, whereas ERβ expression was significantly increased only in the VD + OVX group. These results show that SUI following vaginal trauma and OVX involves urethral upregulations of nNOS, iNOS, and ERs, suggesting that NO- and ER-mediated signaling might play a role in the synergistic effect of birth trauma and OVX-related SUI pathogenesis.

Selective Phosphodiesterase 4B Inhibitors: A Review

Phosphodiesterase 4B (PDE4B) is a member of the phosphodiesterase family of proteins that plays a critical role in regulating intracellular levels of cyclic adenosine monophosphate (cAMP) by controlling its rate of degradation. It has been demonstrated that this isoform is involved in the orchestra of events which includes inflammation, schizophrenia, cancers, chronic obstructive pulmonary disease, contractility of the myocardium, and psoriatic arthritis. Phosphodiesterase 4B has constituted an interesting target for drug development. In recent years, a number of PDE4B inhibitors have been developed for their use as therapeutic agents. In this review, an up-to-date status of the inhibitors investigated for the inhibition of PDE4B has been given so that this rich source of structural information of presently known PDE4B inhibitors could be helpful in generating a selective and potent inhibitor of PDE4B.

Clinical and molecular genetics of the phosphodiesterases (PDEs)

Cyclic nucleotide phosphodiesterases (PDEs) are enzymes that have the unique function of terminating cyclic nucleotide signaling by catalyzing the hydrolysis of cAMP and GMP. They are critical regulators of the intracellular concentrations of cAMP and cGMP as well as of their signaling pathways and downstream biological effects. PDEs have been exploited pharmacologically for more than half a century, and some of the most successful drugs worldwide today affect PDE function. Recently, mutations in PDE genes have been identified as causative of certain human genetic diseases; even more recently, functional variants of PDE genes have been suggested to play a potential role in predisposition to tumors and/or cancer, especially in cAMP-sensitive tissues. Mouse models have been developed that point to wide developmental effects of PDEs from heart function to reproduction, to tumors, and beyond. This review brings together knowledge from a variety of disciplines (biochemistry and pharmacology, oncology, endocrinology, and reproductive sciences) with emphasis on recent research on PDEs, how PDEs affect cAMP and cGMP signaling in health and disease, and what pharmacological exploitations of PDEs may be useful in modulating cyclic nucleotide signaling in a way that prevents or treats certain human diseases.

Phosphodiesterase 4-targeted treatments for autoimmune diseases

Advancements in phosphodiesterase (PDE)-targeted therapies have shown promise in recent years for treating patients with a variety of autoimmune diseases. This review summarizes the development of PDE4 inhibitors and the associated literature with a focus on treatments for autoimmune diseases. After the initial investigations of the prototypic PDE inhibitor, rolipram, more selective inhibitors targeting the PDE4 isozyme have been developed. With phase II and phase III clinical trials currently underway to evaluate the safety and efficacy of the latest generation of PDE4 inhibitors, namely apremilast, a new class of treatments may be around the corner for patients suffering from chronic, autoimmune diseases.

Design and synthesis of 3,5-disubstituted-1,2,4-oxadiazoles as potent inhibitors of phosphodiesterase4b2

A series of 3,5-disubstituted-1,2,4-oxadiazoles has been prepared and evaluated for phosphodiesterase inhibition (PDE4B2). Among the prepared 3,5-disubstituted-1,2,4-oxadiazoles, compound 9a is the most potent inhibitor (PDE4B2 IC(50)  = 5.28 μm). Structure-activity relationship studies of 3,5-disubstituted-1,2,4-oxadiazoles revealed that substituents 3-cyclopentyloxy-4-methoxyphenyl group at 3-position and cyclic ring bearing heteroatoms at 5-position are important for activity. Molecular modeling study of the 3,5-disubstituted-1,2,4-oxadiazoles with PDE4B has shown similar interactions of 3-cyclopentyloxy-4-methoxyphenyl group; however, heteroatom ring is slightly deviating when compared to Piclamilast. 3-(3-Cyclopentyloxy-4-methoxyphenyl)-5-(piperidin-4-yl)-1,2,4-oxadiazole (9a) exhibited good analgesic and antiinflammatory activities in formalin-induced pain in mice and carrageenan-induced paw edema model in rat.

Phosphodiesterase inhibitors in inflammatory bowel disease

Inflammatory bowel disease (IBD) is fundamentally a relapsing and remitting disease appearing in forms of ulcerative colitis (UC) or Crohn's disease (CD) with a non-well-known etiology. With the hope to prevent adverse drug events and to increase the efficacy of therapies for IBD, in the recent years, other than new monoclonal antibodies such as infliximab, the novel phosphodiesterase inhibitors (PDEIs) have been introduced. Among PDE4Is, rolipram, OPC-6535, mesopram, roflumilast and tetomilast have shown beneficial effects in experimental colitis. Unfortunately until now, human studies have not been successful in showing significant superiority of PDE4Is in the treatment of IBD. Parallel with discovery of PDE4Is and their anti-inflammatory properties, inhibiting other PDE isoenzymes in immune and proinflammatory cells is on the way. PDE7Is have shown synergistic effect with PDE4Is and they may act similar to PDE3Is in experimental settings. Sildenafil as the PDE5I has shown good effects in experimental colitis by balancing oxidant-antioxidant status. Although the present data about PDE superfamily and their specific roles in gastrointestinal tract is limited but inhibitors of PDE4, PDE5 and PDE7 seem good candidates as the next generation of effective drugs. The synergistic anti-inflammatory effect of PDE4Is and PDE7Is is also important.

Apremilast mechanism of action and application to psoriasis and psoriatic arthritis

Psoriasis and psoriatic arthritis are common clinical conditions that negatively impact health-related quality of life and are linked to serious medical comorbidities. Disease mechanisms involve local and systemic chronic inflammatory processes. Available biologic therapies specifically target single inflammatory mediators, such as tumor necrosis factor-α (TNF-α), in the context of a larger inflammatory signaling cascade. To interrupt this pathological cascade earlier in the response or further upstream, and return pro-inflammatory and anti-inflammatory signaling to a homeostatic balance, the use of a phosphodiesterase4 (PDE4) inhibitor has been explored. PDE4 is the major enzyme class responsible for the hydrolysis of cyclic adenosine monophosphate (cAMP), an intracellular second messenger that controls a network of pro-inflammatory and anti-inflammatory mediators. With PDE4 inhibition, and the resulting increases in cAMP levels in immune and non-immune cell types, expression of a network of pro-inflammatory and anti-inflammatory mediators can be modulated. Apremilast is an orally available targeted PDE4 inhibitor that modulates a wide array of inflammatory mediators involved in psoriasis and psoriatic arthritis, including decreases in the expression of inducible nitric oxide synthase, TNF-α, and interleukin (IL)-23 and increases IL-10. In phase II studies of subjects with psoriasis and psoriatic arthritis, apremilast reversed features of the inflammatory pathophysiology in skin and joints and significantly reduces clinical symptoms. The use of an oral targeted PDE4 inhibitor for chronic inflammatory diseases, like psoriasis and psoriatic arthritis, represents a novel treatment approach that does not target any single mediator, but rather focuses on restoring a balance of pro-inflammatory and anti-inflammatory signals.

Phosphodiesterase inhibitors in the treatment of inflammatory diseases

Phosphodiesterase 4 (PDE4) belongs to a family of enzymes which catalyzes the breakdown of 3, 5'-adenosine cyclic monophosphate (cAMP) and is ubiquitously expressed in inflammatory cells. There is little evidence that inflammatory diseases are caused by increased expression of this isoenzyme, although human inflammatory cell activity can be suppressed by selective PDE4 inhibitors. Consequently, there is intense interest in the development of selective PDE4 inhibitors for the treatment of a range of inflammatory diseases, including asthma, chronic obstructive pulmonary disease (COPD), inflammatory bowel disease, and psoriasis. Recent clinical trials with roflumilast in COPD have confirmed the therapeutic potential of targeting PDE4 and recently roflumilast has been approved for marketing in Europe and the USA, although side effects such as gastrointestinal disturbances, particularly nausea and emesis as well as headache and weight loss, may limit the use of this drug class, at least when administered by the oral route. However, a number of strategies are currently being pursued in attempts to improve clinical efficacy and reduce side effects of PDE4 inhibitors, including delivery via the inhaled route, development of nonemetic PDE4 inhibitors, mixed PDE inhibitors, and/or antisense biologicals targeted toward PDE4.

Update on roflumilast, a phosphodiesterase 4 inhibitor for the treatment of chronic obstructive pulmonary disease

Phosphodiesterase 4 (PDE4) is a member of the PDE enzyme superfamily that inactivates cyclic adenosine monophosphate and cyclic guanosine monophosphate, and is the main PDE isoenzyme occurring in cells involved in inflammatory airway disease such as chronic obstructive pulmonary disease (COPD). COPD is a preventable and treatable disease and is characterized by airflow obstruction that is not fully reversible. Chronic progressive symptoms, particularly dyspnoea, chronic bronchitis and impaired overall health are worse in those who have frequent, acute episodes of symptom exacerbation. Although several experimental PDE4 inhibitors are in clinical development, roflumilast, a highly selective PDE4 inhibitor, is the first in its class to be licensed, and has recently been approved in several countries for oral, once-daily treatment of severe COPD. Clinical trials have demonstrated that roflumilast improves lung function and reduces exacerbation frequency in COPD. Furthermore, its unique mode of action may offer the potential to target the inflammatory processes underlying COPD. Roflumilast is effective when used concomitantly with all forms of bronchodilator and even in patients treated with inhaled corticosteroids. Roflumilast thus represents an important addition to current therapeutic options for COPD patients with chronic bronchitis, including those who remain symptomatic despite treatment. This article reviews the current status of PDE4 inhibitors, focusing on the pharmacokinetics, efficacy and safety of roflumilast. In particular, it provides an overview of the effects of roflumilast on lung function and exacerbations, glucose homoeostasis and weight loss, and the concomitant use of long-acting beta(2)-adrenergic receptor agonists and short-acting muscarinic receptor antagonists.

Pharmacology, clinical efficacy, and tolerability of phosphodiesterase-4 inhibitors: impact of human pharmacokinetics

Since more than two decades anti-inflammatory effects of inhibitors of phosphodiesterase-4 have been described in numerous cellular and animal studies and were finally confirmed in clinical trials. The path from an early, pioneering study with Ro20-1724 showing reduction of psoriatric plaque size in 1979 to modern PDE4 inhibitors such as oral apremilast in development for psoriasis, the inhaled PDE4 inhibitor GSK256066 in development for asthma and COPD and finally roflumilast, the first PDE4 inhibitor approved and currently marketed as an oral, once-daily remedy for severe COPD was marked by large progress in chemical optimization based on improved understanding of PDE4 biology and drug-like properties determining the appropriate pharmacokinetic profile. In this chapter aspects of the pharmacology and clinical efficacy of PDE4 inhibitors, which have been in clinical development over the years are summarized with specific emphasis on their clinical pharmacokinetic properties.

Bacterial heat-stable enterotoxins: translation of pathogenic peptides into novel targeted diagnostics and therapeutics

Heat-stable toxins (STs) produced by enterotoxigenic bacteria cause endemic and traveler’s diarrhea by binding to and activating the intestinal receptor guanylyl cyclase C (GC-C). Advances in understanding the biology of GC-C have extended ST from a diarrheagenic peptide to a novel therapeutic agent. Here, we summarize the physiological and pathophysiological role of GC-C in fluid-electrolyte regulation and intestinal crypt-villus homeostasis, as well as describe translational opportunities offered by STs, reflecting the unique characteristics of GC-C, in treating irritable bowel syndrome and chronic constipation, and in preventing and treating colorectal cancer.

Apremilast, a cAMP phosphodiesterase-4 inhibitor, demonstrates anti-inflammatory activity in vitro and in a model of psoriasis

BACKGROUND AND PURPOSE

Apremilast is an orally administered phosphodiesterase-4 inhibitor, currently in phase 2 clinical studies of psoriasis and other chronic inflammatory diseases. The inhibitory effects of apremilast on pro-inflammatory responses of human primary peripheral blood mononuclear cells (PBMC), polymorphonuclear cells, natural killer (NK) cells and epidermal keratinocytes were explored in vitro, and in a preclinical model of psoriasis.

EXPERIMENTAL APPROACH

Apremilast was tested in vitro against endotoxin- and superantigen-stimulated PBMC, bacterial peptide and zymosan-stimulated polymorphonuclear cells, immunonoglobulin and cytokine-stimulated NK cells, and ultraviolet B light-activated keratinocytes. Apremilast was orally administered to beige-severe combined immunodeficient mice, xenotransplanted with normal human skin and triggered with human psoriatic NK cells. Epidermal skin thickness, proliferation index and inflammation markers were analysed.

KEY RESULTS

Apremilast inhibited PBMC production of the chemokines CXCL9 and CXCL10, cytokines interferon-gamma and tumour necrosis factor (TNF)-alpha, and interleukins (IL)-2, IL-12 and IL-23. Production of TNF-alpha by NK cells and keratinocytes was also inhibited. In vivo, apremilast significantly reduced epidermal thickness and proliferation, decreased the general histopathological appearance of psoriasiform features and reduced expression of TNF-alpha, human leukocyte antigen-DR and intercellular adhesion molecule-1 in the lesioned skin.

CONCLUSIONS AND IMPLICATIONS

Apremilast displayed a broad pattern of anti-inflammatory activity in a variety of cell types and decreased the incidence and severity of a psoriasiform response in vivo. Inhibition of TNF-alpha, IL-12 and IL-23 production, as well as NK and keratinocyte responses by this phosphodiesterase-4 inhibitor suggests a novel approach to the treatment of psoriasis.

Chronic lymphocytic leukemia and B and T cells differ in their response to cyclic nucleotide phosphodiesterase inhibitors

Phosphodiesterase (PDE)4 inhibitors, which activate cAMP signaling by reducing cAMP catabolism, are known to induce apoptosis in B lineage chronic lymphocytic leukemia (CLL) cells but not normal human T cells. The explanation for such differential sensitivity remains unknown. In this study, we report studies contrasting the response to PDE4 inhibitor treatment in CLL cells and normal human T and B cells. Affymetrix gene chip analysis in the three cell populations following treatment with the PDE4 inhibitor rolipram identified a set of up-regulated transcripts with unusually high fold changes in the CLL samples, several of which are likely part of compensatory negative feedback loops. The high fold changes were due to low basal transcript levels in CLL cells, suggesting that cAMP-mediated signaling may be unusually tightly regulated in this cell type. Rolipram treatment augmented cAMP levels and induced ATF-1/CREB serine 63/133 phosphorylation in both B lineage cell types but not T cells. As treatment with the broad-spectrum PDE inhibitor 3-isobutyl-1-methylxanthine induced T cell CREB phosphorylation, we tested a series of family-specific PDE inhibitors for their ability to mimic 3-isobutyl-1-methylxanthine-induced ATF-1/CREB phosphorylation. Whereas PDE3 inhibitors alone had no effect, the combination of PDE3 and PDE4 inhibitors induced ATF-1/CREB serine 63/133 phosphorylation in T cells. Consistent with this observation, PDE3B transcript and protein levels were low in CLL cells but easily detectable in T cells. Combined PDE3/4 inhibition did not induce T cell apoptosis, suggesting that cAMP-mediated signal transduction that leads to robust ATF-1/CREB serine 63/133 phosphorylation is not sufficient to induce apoptosis in this lymphoid lineage.

The effect of sildenafil, a phosphodiesterase-5 inhibitor, on acetic acid-induced colonic inflammation in the rat

BACKGROUND AND AIM

Sildenafil, a selective and potent inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase (PDE)5, has a relaxant effect on the smooth muscle cells of the arterioles supplying the human corpus cavernosum acting via nitric oxide (NO)-dependent mechanism. This study aimed to investigate the possible protective effect of sildenafil citrate on the extent of tissue integrity, oxidant-antioxidant status and neutrophil infiltration to the inflamed organ in a rat model of acetic acid-induced colitis.

METHODS

Colitis was induced by intrarectal administration of 1 mL of 5% acetic acid to Sprague-Dawley rats (200-250 g; n = 7-8/group). Control rats received an equal volume of saline intrarectally. In treatment groups, the rats were treated with either sildenafil citrate (5 mg/kg/day; subcutaneously) or saline for 3 days. After decapitation, distal colon was weighed and scored macroscopically and microscopically. Tissue samples were used for the measurement of malondialdehyde (MDA) and glutathione (GSH) levels, myeloperoxidase (MPO) activity, and oxidant production. Trunk blood was collected for the assessment of serum tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta levels.

RESULTS

In the colitis group, the colonic tissue was characterized by lesions, increased lipid peroxidation with a concomitant reduction in GSH content, increased MPO activity and oxidant production. Serum TNF-alpha and IL-1beta levels were higher in the colitis group compared to control values. Sildenafil reversed these inflammatory parameters nearly back to control values.

CONCLUSIONS

Sildenafil citrate administration to rats with acetic acid-induced colitis seems to be beneficial via prevention of lipid peroxidation, oxidant generation, cytokine production and neutrophil accumulation.

Identification of a potent new chemotype for the selective inhibition of PDE4

A series of substituted 3,6-diphenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines were prepared and analyzed as inhibitors of phosphodiesterase 4 (PDE4). Synthesis, structure-activity relationships, and the selectivity of a highly potent analogue against related phosphodiesterase isoforms are presented.