Theophylline suppresses human alveolar macrophage respiratory burst through phosphodiesterase inhibition

cAMP-PDE signaling in COPD: Review of cellular, molecular and clinical features

Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death among non-contagious diseases in the world. PDE inhibitors are among current medicines prescribed for COPD treatment of which, PDE-4 family is the predominant PDE isoform involved in hydrolyzing cyclic adenosine monophosphate (cAMP) that regulates the inflammatory responses in neutrophils, lymphocytes, macrophages and epithelial cells The aim of this study is to investigate the cellular and molecular mechanisms of cAMP-PDE signaling, as an important pathway in the treatment management of patients with COPD. In this review, a comprehensive literature review was performed about the effect of PDEs in COPD. Generally, PDEs are overexpressed in COPD patients, resulting in cAMP inactivation and decreased cAMP hydrolysis from AMP. At normal amounts, cAMP is one of the essential agents in regulating metabolism and suppressing inflammatory responses. Low amount of cAMP lead to activation of downstream inflammatory signaling pathways. PDE4 and PDE7 mRNA transcript levels were not altered in polymorphonuclear leukocytes and CD8 lymphocytes originating from the peripheral venous blood of stable COPD subjects compared to healthy controls. Therefore, cAMP-PDE signaling pathway is one of the most important signaling pathways involved in COPD. By examining the effects of different drugs in this signaling pathway critical steps can be taken in the treatment of this disease.

Pharmacological potential of methylxanthines: Retrospective analysis and future expectations

Methylated xanthines (methylxanthines) are available from a significant number of different botanical species. They are ordinarily included in daily diet, in many extremely common beverages and foods. Caffeine, theophylline and theobromine are the main methylxanthines available from natural sources. The supposedly relatively low toxicity of methylxanthines, combined with the many beneficial effects that have been attributed to these compounds through time, generated a justified attention and a very prolific ground for dedicated scientific reports. Methylxanthines have been widely used as therapeutical tools, in an intriguing range of medicinal scopes. In fact, methylxanthines have been/were medically used as Central Nervous System stimulants, bronchodilators, coronary dilators, diuretics and anti-cancer adjuvant treatments. Other than these applications, methylxanthines have also been hinted to hold other beneficial health effects, namely regarding neurodegenerative diseases, cardioprotection, diabetes and fertility. However, it seems now consensual that toxicity concerns related to methylxanthine consumption and/or therapeutic use should not be dismissed. Taking all the knowledge and expectations on the potential of methylxanthines into account, we propose a systematic look at the past and future of methylxanthine pharmacologic applications, discussing all the promise and anticipating possible constraints. Anyways, methylxanthines will still substantiate considerable meaningful research and discussion for years to come.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Association of pre-hospital theophylline use and mortality in chronic obstructive pulmonary disease patients with sepsis

BACKGROUND

Although theophylline has been shown to have anti-inflammatory effects, the therapeutic use of theophylline before sepsis is unknown. The aim of our study was to determine the effect of theophylline on COPD patients presenting with sepsis.

METHODS

This nationwide, population-based, propensity score-matched analysis used data from the linked administrative databases of Taiwan's National Health Insurance program. Patients with COPD who were hospitalized for sepsis between 2000 and 2011 were divided into theophylline users and non-users. The primary outcome was 30-day mortality. The secondary outcome was in-hospital death, intensive care unit admission, and need for mechanical ventilation. Cox proportional hazard model and conditional logistic regression were used to calculate the risk between groups.

RESULTS

A propensity score-matched cohort of 51,801 theophylline users and 51,801 non-users was included. Compared with non-users, the 30-day (HR 0.931, 95% CI 0.910-0.953), 180-day (HR 0.930, 95% CI 0.914-0.946), 365-day (HR 0.944, 95% CI 0.929-0.960) and overall mortality (HR 0.965, 95% CI 0.952-0.979) were all significantly lower in theophylline users. Additionally, the theophylline users also had lower risk of in-hospital death (OR 0.895, 95% CI 0.873-0.918) and need for mechanical ventilation (OR 0.972, 95% CI 0.949-0.997).

CONCLUSIONS

Theophylline use is associated with a lower risk of sepsis-related mortality in COPD patients. Pre-hospital theophylline use may be protective to COPD patients with sepsis.

Structure-Bioactivity Relationships of Methylxanthines: Trying to Make Sense of All the Promises and the Drawbacks

Methylxanthines are a group of phytochemicals derived from the purine base xanthine and obtained from plant secondary metabolism. They are unobtrusively included in daily diet in common products as coffee, tea, energetic drinks, or chocolate. Caffeine is by far the most studied methylxanthine either in animal or epidemiologic studies. Theophylline and theobromine are other relevant methylxanthines also commonly available in the aforementioned sources. There are many disseminated myths about methylxanthines but there is increased scientific knowledge to discuss all the controversy and promise shown by these intriguing phytochemicals. In fact, many beneficial physiologic outcomes have been suggested for methylxanthines in areas as important and diverse as neurodegenerative and respiratory diseases, diabetes or cancer. However, there have always been toxicity concerns with methylxanthine (over)consumption and pharmacologic applications. Herein, we explore the structure-bioactivity relationships to bring light those enumerated effects. The potential shown by methylxanthines in such a wide range of conditions should substantiate many other scientific endeavors that may highlight their adequacy as adjuvant therapy agents and may contribute to the advent of functional foods. Newly designed targeted molecules based on methylxanthine structure may originate more specific and effective outcomes.

The cAMP Pathway as Therapeutic Target in Autoimmune and Inflammatory Diseases

Nucleotide signaling molecules contribute to the regulation of cellular pathways. In the immune system, cyclic adenosine monophosphate (cAMP) is well established as a potent regulator of innate and adaptive immune cell functions. Therapeutic strategies to interrupt or enhance cAMP generation or effects have immunoregulatory potential in autoimmune and inflammatory disorders. Here, we provide an overview of the cyclic AMP axis and its role as a regulator of immune functions and discuss the clinical and translational relevance of interventions with these processes.

Activation of Cyclic Adenosine Monophosphate Pathway Increases the Sensitivity of Cancer Cells to the Oncolytic Virus M1

Oncolytic virotherapy is a novel and emerging treatment modality that uses replication-competent viruses to destroy cancer cells. Although diverse cancer cell types are sensitive to oncolytic viruses, one of the major challenges of oncolytic virotherapy is that the sensitivity to oncolysis ranges among different cancer cell types. Furthermore, the underlying mechanism of action is not fully understood. Here, we report that activation of cyclic adenosine monophosphate (cAMP) signaling significantly sensitizes refractory cancer cells to alphavirus M1 in vitro, in vivo, and ex vivo. We find that activation of the cAMP signaling pathway inhibits M1-induced expression of antiviral factors in refractory cancer cells, leading to prolonged and severe endoplasmic reticulum (ER) stress, and cell apoptosis. We also demonstrate that M1-mediated oncolysis, which is enhanced by cAMP signaling, involves the factor, exchange protein directly activated by cAMP 1 (Epac1), but not the classical cAMP-dependent protein kinase A (PKA). Taken together, cAMP/Epac1 signaling pathway activation inhibits antiviral factors and improves responsiveness of refractory cancer cells to M1-mediated virotherapy.

Phagosomal Acidification Prevents Macrophage Inflammatory Cytokine Production to Malaria, and Dendritic Cells Are the Major Source at the Early Stages of Infection: IMPLICATION FOR MALARIA PROTECTIVE IMMUNITY DEVELOPMENT

Inflammatory cytokines produced at the early stages of malaria infection contribute to shaping protective immunity and pathophysiology. To gain mechanistic insight into these processes, it is important to understand the cellular origin of cytokines because both cytokine input and cytokine-producing cells play key roles. Here, we determined cytokine responses by monocytes, macrophages, and dendritic cells (DCs) to purified Plasmodium falciparum and Plasmodium berghei ANKA, and by spleen macrophages and DCs from Plasmodium yoelii 17NXL-infected and P. berghei ANKA-infected mice. The results demonstrate that monocytes and macrophages do not produce inflammatory cytokines to malaria parasites and that DCs are the primary source early in infection, and DC subsets differentially produce cytokines. Importantly, blocking of phagosomal acidification by inhibiting vacuolar-type H(+)-ATPase enabled macrophages to elicit cytokine responses. Because cytokine responses to malaria parasites are mediated primarily through endosomal Toll-like receptors, our data indicate that the inability of macrophages to produce cytokines is due to the phagosomal acidification that disrupts endosomal ligand-receptor engagement. Macrophages efficiently produced cytokines to LPS upon simultaneously internalizing parasites and to heat-killed Escherichia coli, demonstrating that phagosomal acidification affects endosomal receptor-mediated, but not cell surface receptor-mediated, recognition of Toll-like receptor agonists. Enabling monocytes/macrophages to elicit immune responses to parasites by blocking endosomal acidification can be a novel strategy for the effective development of protective immunity to malaria. The results have important implications for enhancing the efficacy of a whole parasite-based malaria vaccine and for designing strategies for the development of protective immunity to pathogens that induce immune responses primarily through endosomal receptors.

Choosing wisely: practical considerations on treatment efficacy and safety of asthma in the elderly

The prevalence of asthma in the most advanced ages is similar to that of younger ages. However, the concept that older individuals may suffer from allergic asthma has been largely denied in the past, and a common belief attributes to asthma the definition of "rare" disease. Indeed, asthma in the elderly is often underdiagnosed or diagnosed as COPD, thus leading to undertreatment of improper treatment. This is also due to the heterogeneity of clinical and functional presentations of geriatric asthma, including the partial loss of reversibility and the lower occurrence of the allergic component in this age range. The older asthmatic patients are also characterized the coexistence of comorbid conditions that, in conjunction with age-associated structural and functional changes of the lung, may contribute to complicate the management of asthma. The current review addresses the main issues related to the management of allergic asthma in the geriatric age. In particular, the paper aims at revising current pharmacological and non pharmacological treatments for allergic asthmatics of advanced ages, primarily focusing on their safety and efficacy, although most behaviors are an arbitrary extrapolation of what has been tested in young ages. In fact, age has always represented an exclusion criterion for eligibility to clinical trials. Experimental studies and real life observations specifically testing the efficacy and safety of therapeutic approaches in allergic asthma in the elderly are urgently needed.

Theophylline

Theophylline (dimethylxanthine) has been used to treat airway diseases for more than 80 years. It was originally used as a bronchodilator, but the relatively high doses required are associated with frequent side effects, so its use declined as inhaled β2-agonists became more widely used. More recently it has been shown to have antiinflammatory effects in asthma and chronic obstructive pulmonary disease (COPD) at lower concentrations. The molecular mechanism of bronchodilatation is inhibition of phosphodiesterase (PDE)3, but the antiinflammatory effect may be due to inhibition of PDE4 and histone deacetylase-2 activation, resulting in switching off of activated inflammatory genes. Through this mechanism, theophylline also reverses corticosteroid resistance, and this may be of particular value in severe asthma and COPD, wherein histone deacetylase-2 activity is reduced. Theophylline is given systemically (orally as slow-release preparations for chronic treatment and intravenously for acute exacerbations of asthma). Efficacy is related to blood concentrations, which are determined mainly by hepatic metabolism, which may be increased or decreased in several diseases and by concomitant drug therapy. Theophylline is now usually used as an add-on therapy in patients with asthma not well controlled on inhaled corticosteroids with or without long-acting β2-agonists and in patients with COPD with severe disease not controlled by bronchodilator therapy. Side effects are related to plasma concentrations and include nausea, vomiting, and headaches due to PDE inhibition and at higher concentrations to cardiac arrhythmias and seizures due to adenosine A1-receptor antagonism. In the future, low-dose theophylline may be useful in reversing corticosteroid resistance in COPD and severe asthma.

Tetomilast attenuates elastase-induced pulmonary emphysema through inhibition of oxidative stress in rabbits

Tetomilast was originally identified as a potent inhibitor of superoxide production in human neutrophils, and is of interest because it may relieve oxidative stress related to chronic obstructive pulmonary disease (COPD). Our objective was to determine whether tetomilast effectively protects against the development of porcine pancreatic elastase (PPE)-induced emphysema in rabbits. Rabbits were divided into three groups (sham n=19, PPE n=19, PPE/Tetomilast n=18). The rabbits were once daily orally administered vehicle solution or tetomilast 5 d/week for 4 weeks before the PPE instillation. We compared pulmonary function, inflammatory cell infiltration, oxidative stress, and the incidences of apoptosis among the three groups. Tetomilast suppressed PPE-induced increases in the incidence of apoptosis and the production of 8-hydroxy-deoxyguanosine (8-OHdG) in lung tissues. PPE-instilled rabbits treated with tetomilast showed significantly less mean linear intercept and significantly better pulmonary function than rabbits administered PPE alone. Tetomilast may inhibit the development of emphysema by attenuating pulmonary inflammation and apoptosis caused by PPE-induced oxidative stress.

The increase in rat ventricular automaticity induced by salbutamol is mediated through β(1)- but not β(2)-adrenoceptors: role of phosphodiesterases

AIMS

While β(2)-adrenoceptor (AR) agonists are useful bronchodilators, they also produce cardiac arrhythmias. These agents are not fully selective and also activate β(1)-AR, but the involvement of β(1)-AR and β(2)-AR in the observed pro-arrhythmic effect has not been established. We studied the effect of β(1)-AR and β(2)-AR activation on ventricular automaticity and the role of phosphodiesterases (PDE) in regulating this effect.

MAIN METHODS

Experiments were performed in the spontaneously beating isolated right ventricle of the rat heart. We also measured cAMP production in this tissue.

KEY FINDINGS

The β(2)-AR agonist salbutamol (1-100 μM) produced a concentration-dependent increase in ventricular automaticity that was not affected by 50nM of the β(2)-AR antagonist ICI 118551. This effect was enhanced by the non-selective PDE inhibitor theophylline (100 μM) and by the selective PDE4 inhibitors rolipram (1 μM) and Ro 201724 (2 μM), but not modified by the selective PDE3 inhibitors cilostamide (0.3 μM) or milrinone (0.2 μM). The effects of salbutamol alone and in the presence of either theophylline or rolipram were virtually abolished by 0.1 μM β(1)-AR antagonist CGP 20712A. Salbutamol (10 μM) increased the cAMP concentration, and this effect was abolished by CGP 20712A (0.1 μM) but enhanced by theophylline (100 μM) or rolipram (1 μM). Cilostamide (0.3 μM) failed to modify the effect of salbutamol on cAMP concentration.

SIGNIFICANCE

These results indicate that the increase of ventricular automaticity elicited by salbutamol was exclusively mediated through β(1)-AR and enhanced by non-selective PDE inhibition with theophylline or selective PDE4 inhibition. However, PDE3 did not appear to regulate this effect.

Inhibition of cyclic nucleotide phosphodiesterases by methylxanthines and related compounds

Naturally occurring methylxanthines were the first inhibitors of cyclic nucleotide (cN) phosphodiesterases (PDEs) to be discovered. To improve potency and specificity for inhibition of various PDEs in research and for treatment of diseases, thousands of compounds with related structures have now been synthesized. All known PDE inhibitors contain one or more rings that mimic the purine in the cN substrate and directly compete with cN for access to the catalytic site; this review focuses on inhibitors that contain a nucleus that is closely related to the xanthine ring of theophylline and caffeine and the purine ring of cNs. The specificity and potency of these compounds for blocking PDE action have been improved by appending groups at positions on the rings as well as by modification of the number and distribution of nitrogens and carbons in those rings. Several of these inhibitors are highly selective for particular PDEs; potent and largely selective PDE5 inhibitors are used clinically for treatment of erectile dysfunction [sildenafil (Viagra™), tadalafil (Cialis™) and vardenafil (Levitra™)] and pulmonary hypertension [sildenafil (Revatio™) and tadalafil (Adenocirca)]. Related compounds target other PDEs and show therapeutic promise for a number of maladies.

Immunomodulatory properties of pentoxifylline are mediated via adenosine-dependent pathways

The phosphodiesterase inhibitor pentoxifylline (PTX) exerts multiple beneficial immunomodulatory effects in states of hyperinflammation. However, the exact mechanism of action still remains elusive, and the clinical effects of PTX cannot be reliably predicted. In immune cells, the G protein-coupled adenosine A2A receptor (A2AR) exerts strong anti-inflammatory effects. As PTX amplifies signaling pathways downstream of Gs protein-coupled receptors, the A2AR-signaling pathway might be involved in the mediation of immune-suppressive effects of PTX. Here, we investigated this assumption in LPS-stimulated human polymorphonuclear (PMN) leukocytes and in anti-CD3/CD28-stimulated human T cells. In stimulated PMN leukocytes, PTX treatment led to a 4.5-fold decrease of the 50% inhibitory concentrations of adenosine on the H2O2 production; i.e., for adenosine plus PTX (in clinically relevant concentrations), an overadditive increase of inhibitory effects from less than 20% (estimated for each) to 56% (+/-5%) was found. In T cells, adenosine plus PTX revealed similar synergistic inhibitory effects on proinflammatory cytokine production. Inhibition of interferon gamma and TNF-alpha production increased from 7% (+/-1%) and 31% (+/-6%) (PTX alone) to 49% (+/-2%) and 69% (+/-6%), respectively. In T cells and PMN leukocytes, mRNA transcription of the A2AR was significantly increased upon stimulation, which was not influenced by PTX. In human PMN leukocytes and T cells, clinically relevant anti-inflammatory effects of PTX can be achieved only in the presence of sufficient adenosine concentrations. Sufficient adenosine levels might be a prerequisite for the accessibility of sepsis patients to treatment with PTX.

Theophylline

Theophylline (3-methyxanthine) has been used to treat airway diseases for over 70 years. It was originally used as a bronchodilator but the relatively high doses required are associated with frequent side effects, so its use declined as inhaled β₂-agonists became more widely used. More recently it has been shown to have anti-inflammatory effects in asthma and COPD at lower concentrations. The molecular mechanism of bronchodilatation is inhibition of phosphodiesterase(PDE)3 and PDE4, but the anti-inflammatory effect may be due to histone deacetylase (HDAC) activation, resulting in switching off of activated inflammatory genes. Through this mechanism theophylline also reverses corticosteroid resistance and this may be of particular value in severe asthma and COPD where HDAC2 activity is markedly reduced. Theophylline is given systemically (orally as slow-release preparations for chronic treatment and intravenously for acute exacerbations of asthma) and blood concentrations are determined mainly by hepatic metabolism, which may be increased or decreased in several diseases and by concomitant drug therapy. Theophylline is now usually used as an add-on therapy in asthma patients not well controlled on inhaled corticosteroids and in COPD patients with severe disease not controlled by bronchodilator therapy. Side effects are related to plasma concentrations and include nausea, vomiting and headaches due to PDE inhibition and at higher concentrations to cardiac arrhythmias and seizures due to adenosine A₁-receptor antagonism.

Milk peptides and immune response in the neonate

Bioactive peptides encrypted within the native milk proteins can be released by enzymatic proteolysis, food processing, or gastrointestinal digestion. These peptides possess a wide range of properties, including immunomodulatory properties. The first months of life represent a critical period for the maturation of the immune system because a tolerance for nutrient molecules should be developed while that for pathogen-derived antigens is avoided. Evidence has accumulated to suggest that milk peptides may regulate gastrointestinal immunity, guiding the local immune system until it develops its full functionality. Our data using the weaning piglet as the model suggest that several milk peptides can downregulate various immune properties at a time (one to two weeks after weaning) that coincides with immaturity of the immune system. The protein kinase A system and/or the exchange protein directly activated by cyclic AMP (Epac-1) are implicated in the mechanism through which milk peptides can affect immune function in the early postweaning period. Despite the fact that the research in this field is in its infancy, the evidence available suggests that milk protein peptides may promote development of neonatal immune competence. Milk contains a variety of components that provide immunological protection and facilitate the development of neonatal immune competence. Two main categories of milk compounds are thought to be associated with immunological activity. The first category includes cytokines, which neonates do not produce efficiently. Cytokines present in milk are thought to be protected against intestinal proteolysis and could alleviate immunological deficits, aiding immune system maturation (Kelleher & Lonnerdal, 2001; Bryan et al., 2006). The second category of milk compounds includes milk protein peptides. Milk peptides may affect mucosal immunity possibly by guiding local immunity until it develops its full functionality (Baldi et al., 2005). This chapter focuses on the effects of milk peptides on immune function and attempts to provide an overview of the knowledge available in this field.

Norepinephrine suppresses wound macrophage phagocytic efficiency through alpha- and beta-adrenoreceptor dependent pathways

BACKGROUND

The systemic response to injury is characterized by massive release of norepinephrine (NE) into the circulation as a result of global sympathetic activation. We have recently demonstrated that NE modulates the recruitment of macrophages to the cutaneous wound. We hypothesized that NE suppresses wound macrophage phagocytic function through canonical adrenergic signaling pathways.

METHODS

Murine wound macrophages were harvested at 5 days after injury and treated with physiologic and pharmacologic dose norepinephrine. Phagocytosis of green fluorescent protein-labeled Escherichia coli was assayed by flow cytometry. The signaling pathways mediating NE modulation of wound macrophage phagocytosis were interrogated by pharmacologic manipulation of alpha- and beta-adrenoreceptors (ARs), intracellular cyclic adenosine monophosphate (cAMP), and protein kinase A (PKA). Tissue specificity was determined by comparison of wound macrophages to splenic macrophages.

RESULTS

Both physiologic and pharmacologic dose NE suppressed wound macrophage phagocytic efficiency. This effect was mediated by alpha- and beta-ARs in a dose-dependent fashion. Direct stimulation of cAMP-suppressed phagocytic efficiency and blockade of PKA signaling prevented NE-mediated suppression of phagocytic efficiency. Splenic macrophage phagocytic efficiency was less than that of wound macrophages and was not altered by NE.

CONCLUSIONS

NE has a profound immunosuppressive effect on wound macrophage function that is tissue specific and appears to be mediated through adrenergic receptors and their canonical downstream signaling pathway. Attenuation of post-injury immunosuppression represents another potential mechanism by which beta-AR blockade may reduce morbidity and mortality after severe injury.

Mechanisms of adenosine-induced cytotoxicity and their clinical and physiological implications

Extracellular ATP (ATPo) and adenosine are cytotoxic to several cancer cell lines, suggesting their potential use for anticancer therapy. Adenosine causes cytotoxicity, either when added exogenously or when generated from ATPo hydrolysis, via mechanisms which are not mutually exclusive and which involve, adenosine receptor activation, pyrimidine starvation and/or increases in intracellular S-adenosylhomocysteine: S-adenosylmethionine ratio. Given that adenosine also appears to protect against cytotoxicity via mechanisms including immunity against damage by oxygen free radicals, an understanding of the contribution of adenosine to ATPo-induced cytotoxicity is thus crucial, when considering any potential therapeutic use for these compounds. However, such an understanding has been largely hindered by the fact that many studies have not focused enough on the possibility that both ATPo and adenosine may mediate cytotoxicity in the same system. Such studies can benefit from use a range of ATPo concentrations when assessing the contribution of adenosine to ATPo-induced cytotoxicity. Whilst future molecular and pharmacological studies are needed to establish the nature of the cytotoxic adenosine receptor, it is possible that more than just one adenosine receptor type is involved and that the cytotoxic receptor(s) type is more likely to have a low affinity for adenosine. Activation of the adenosine receptor(s) would thus lead to cytotoxicity only at relatively high adenosine concentrations, while lower adenosine concentrations mediate non-cytotoxic physiological effects.

Natural ozone scavenger prevents asthma in sensitized rats

The assumption that ozone is not only a strong oxidant, but also an important inflammatory mediator, is heavily supported by the ample literature on the pulmonary toxicity and biological effects of environmental ozone and by the recent discovery that antibodies, human neutrophils, and inflammatory lesions catalyze the formation of ozone in vivo. We hypothesized that the pulmonary inflammation in asthma involves a vicious circle of ozone production and recruitment of white blood cells, which produce more ozone. Accordingly, we predicted that electron-rich olefins, which are known ozone scavengers, could be used for prophylactic treatment of asthma. In particular, volatile, unsaturated monoterpenes, could saturate the pulmonary membranes and thereby equip the airways with local chemical protection against either exogenous or endogenous ozone. Here we present experimental evidence using a sensitized rat model to support this hypothesis. Examination of the pulmonary function of sensitized rats that inhaled either limonene (unsaturated, ozone scavenger) or eucalyptol (saturated, inert to ozone) showed that limonene inhalation significantly prevents bronchial obstruction while eucalyptol inhalation does not cause any effect. The anti-inflammatory effect of limonene was also evident from pathological parameters, such as diminished peribronchiolar and perivascular inflammatory infiltrates.

Effects of piclamilast, a selective phosphodiesterase-4 inhibitor, on oxidative burst of sputum cells from mild asthmatics and stable COPD patients

Oxidative stress associated with increased presence of neutrophils is an important feature of inflammatory airways diseases like asthma or chronic obstructive pulmonary disease. We studied the in vitro effect of piclamilast (RP73401), a selective phosphodiesterase (PDE)-4 inhibitor, compared to theophylline and prednisolone, on respiratory burst of sputum cells from mild asthmatics and COPD patients. Sputum cells were harvested from mild asthmatics and stable COPD patients and treated with piclamilast, theophylline or prednisolone. Respiratory burst was assessed by luminol-dependent chemoluminescence after stimulation with 10 microM n-formyl-met-leu-phe (FMLP). Piclamilast inhibited FMLP-induced respiratory burst of sputum cells in a concentration-dependent manner (asthma: EC50 approximately 100 nM, max. inhibition: 97.5+/-5% at 100 microM; COPD: EC50 approximately 1 microM, max. inhibition: 70.6+/-4.5% at 100 microM), whereas maximal inhibition observed with theophylline (asthma: max. inhib. 27+/-15%; COPD: 6+/-2%, both p < 0.05 vs. piclamilast) and prednisolone (asthma: 16+/-6%; COPD: 7.8+/-6.2%, both p < 0.05 vs. piclamilast) was weaker. Inhibition by piclamilast was largely reversed through pretreatment of cells with the adenylcyclase inhibitor SQ22536. We concluded that piclamilast, a selective PDE-4 inhibitor, attenuates the respiratory burst of sputum cells from mild asthmatics and COPD patients in vitro. These data underline the potential of PDE-4 inhibition as a novel therapeutic approach to inflammatory airway diseases like asthma or COPD.

Cutting edge: macrophage inhibition by cyclic AMP (cAMP): differential roles of protein kinase A and exchange protein directly activated by cAMP-1

cAMP has largely inhibitory effects on components of macrophage activation, yet downstream mechanisms involved in these effects remain incompletely defined. Elevation of cAMP in alveolar macrophages (AMs) suppresses FcgammaR-mediated phagocytosis. We now report that protein kinase A (PKA) inhibitors (H-89, KT-5720, and myristoylated PKA inhibitory peptide 14-22) failed to prevent this suppression in rat AMs. We identified the expression of the alternative cAMP target, exchange protein directly activated by cAMP-1 (Epac-1), in human and rat AMs. Using cAMP analogs that are highly specific for PKA (N6-benzoyladenosine-3',5'-cAMP) or Epac-1 (8-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-cAMP), we found that activation of Epac-1, but not PKA, dose-dependently suppressed phagocytosis. By contrast, activation of PKA, but not Epac-1, suppressed AM production of leukotriene B(4) and TNF-alpha, whereas stimulation of either PKA or Epac-1 inhibited AM bactericidal activity and H(2)O(2) production. These experiments now identify Epac-1 in primary macrophages, and define differential roles of Epac-1 vs PKA in the inhibitory effects of cAMP.

Elevated exhalation of hydrogen peroxide and thiobarbituric acid reactive substances in patients with community acquired pneumonia

BACKGROUND

Bacterial pneumonia involves influx of activated phagocytes into distal airways. These cells release oxidants including H2O2, that may be exhaled or induce peroxidative damage to lung tissues with formation of thiobarbituric reactive substances (TBARs).

STUDY OBJECTIVES

To determine whether concentrations of H2O2 and TBARs in exhaled breath condensate (EBC) is elevated and correlate with systemic response to pneumonia during 10 days of hospital treatment.

DESIGN

The concentration of H2O2 and TBARs was measured in EBC of 43 inpatients with community acquired pneumonia (CAP) and 20 healthy never smoked subjects over 10 days and were accompanied by monitoring of WBC count, serum concentration of C-reactive protein (CRP) and peroxyl radical-trapping capacity.

RESULTS

Patients with CAP exhaled 4.6-, 3.7-, 3.9-, 3.3-times more H2O2 than healthy controls at 1st, 3rd, 5th and 10th day of treatment (P<0.05), respectively. EBC concentrations of TBARs were elevated at 1st and 3rd day. H2O2 and TBARs levels decreased along with treatment course. Correlation (P<0.05) was found between H2O2 levels and CRP and WBC count (r = 0.31) at 1st day and between TBARs and CRP at 5th (r = 0.34) and 10th day (r = 0.46). The mean H2O2 exhalation estimated over ten days of treatment correlated with pneumonic chest X-ray score (r = 0.42), CRP levels (r = 0.46) and WBC count (r = 0.33) at admission (P<0.05).

CONCLUSIONS

Pneumonia is accompanied by oxidative stress in airways that moderately correlates with intensity of systemic inflammatory response. Determination of H2O2 in EBC may be helpful for non-invasive monitoring of oxidants production during lower respiratory tract infection.

Alveolar Macrophages as Orchestrators of COPD

Alveolar macrophages play a critical role in the pathophysiology of COPD and are a major target for future anti-inflammatory therapy. Macrophage numbers are markedly increased in the lung and alveolar space of patients with COPD and are localized to sites of alveolar destruction. The increased numbers of macrophages may result from increased recruitment of blood monocytes, prolonged survival in the lung and to a lesser extent to increased proliferation in the lung. Alveolar macrophages from COPD patients have an increased baseline and stimulated secretion of inflammatory proteins, including certain cytokines, chemokines, reactive oxygen species and elastolytic enzymes, which together could account for all of the pathophysiological features of COPD. Alveolar macrophages form COPD appear to be resistant to the anti-inflammatory effects of corticosteriods and this is linked to reduced activity and expression of histone deacetylase 2, a nuclear enzyme that switches off inflammatory genes activated through the transcription factor nuclear factor-KB. Alternative anti-inflammatory therapies that inhibit macrophages are therefore needed in the future to deal with the chronic inflammation of COPD. These drugs may include resveratrol, theophylline derivatives, MAP kinase inhibitors and phosphodiesterase-4 inhibitors.

Blockade of LTC4 synthesis caused by additive inhibition of gIV-PLA2 phosphorylation: Effect of salmeterol and PDE4 inhibition in human eosinophils

BACKGROUND

Prior investigations have demonstrated that beta(2)-adrenoceptor stimulation is ineffective in inhibiting synthesis of eicosanoids in human eosinophils. This effect has been postulated to relate to density or structural differences in the beta(2)-adrenoceptor or its coupled G-protein. However, recent reports indicate that cAMP-specific PDE4 activity in eosinophils is 10-fold that of other inflammatory cells. We postulated that selective blockade of PDE4 in eosinophils would unmask the inhibitory effect of beta(2)-adrenoceptor stimulation and that this inhibition would result from decreased phosphor-ylation of cytosolic group IV-PLA(2) (gIV-PLA(2)).

OBJECTIVE

To determine (a) whether PDE4 inhibition alone with rolipram blocked secretions of arachidonic acid (AA) and leukotriene C(4) (LTC(4)) caused by activation of eosinophils with formyl-met-leu-phe plus cytochalasin B (FMLP/B), (b) to determine if PDE4 inhibition plus beta(2)-adrenoceptor agonist act additively to augment endogenous cAMP concentration, and (c) to determine the mechanism by which additive inhibition of AA and LTC(4) synthesis is regulated by cAMP.

METHODS

Human eosinophils were pretreated with buffer, salmeterol or rolipram (singly or combination) before FMLP/B activation. Release of AA and LTC(4), intracellular cAMP concentration, and phosphorylation and activation of gIV-PLA(2) were determined.

RESULTS

Rolipram unmasked the inhibitory effect of beta(2)-adrenoceptor stimulation with salmeterol and significantly attenuated the stimulated release of AA and subsequent LTC(4). Inhibition corresponded to increased cAMP production caused by rolipram alone or rolipram plus salmeterol and blocked proportionately the phosphorylation and activation of gIV-PLA(2) in FMLP/B-activated eosinophils.

CONCLUSIONS

Inhibition of PDE4 by rolipram unmasks beta(2)-adrenergic blockade of LTC(4) synthesis caused by FMLP/B.

Inhibition of lipopolysaccharide-induced apoptosis by cilostazol in human umbilical vein endothelial cells

This work describes the pharmacological inhibition by cilostazol and its metabolites, OPC-13015 and OPC-13213, of the apoptosis in the human umbilical vein endothelial cells (HUVECs) damaged by lipopolysaccharide (LPS) in comparison with its analog, cilostamide. Cilostazol and OPC-31213 caused a significant suppression of cell death induced by LPS (1 microg/ml) in a concentration-dependent manner but a modest suppression by cilostamide and OPC-13015. These compounds potently inhibited the 5,5-dimethyl-1-pyrroline-1-oxide (DMPO)/(*)OH adduct formation and significantly reduced the increased intracellular reactive oxygen species (ROS) and tumor necrosis factor-alpha (TNF-alpha) production induced by LPS (1 microg/ml). An apoptotic death of HUVECs by 1 microg/ml LPS (DNA ladders on electrophoresis) was strongly suppressed by all these compounds. Incubation with LPS caused a marked decrease in Bcl-2 protein, which was significantly reversed by cilostazol and its analogs. The greatly increased Bax protein expression and cytochrome c release by LPS were, in contrast, suppressed by cilostazol and, to a lesser degree, by others. In conclusion, cilostazol and its analogs exert a strong protection against apoptotic cell death by scavenging hydroxyl radicals and intracellular ROS with reduction in TNF-alpha formation and by increasing Bcl-2 protein expression and decreasing Bax protein and cytochrome c release.

Evidence that the anti-spasmogenic effect of the beta-adrenoceptor agonist, isoprenaline, on guinea-pig trachealis is not mediated by cyclic AMP-dependent protein kinase

1. The spasmolytic and anti-spasmogenic activity of beta-adrenoceptor agonists on airways smooth muscle is thought to involve activation of the cyclic AMP/cyclic AMP-dependent protein kinase (PKA) cascade. Here we have tested the hypothesis that PKA mediates the anti-spasmogenic activity of isoprenaline and other cyclic AMP-elevating agents in guinea-pig isolated trachea by utilizing a number of cell permeant cyclic AMP analogues that act as competitive 'antagonists' of PKA. 2. Anion-exchange chromatography of guinea-pig tracheae resolved two peaks of PKA activity that corresponded to the type I ( approximately 5%) and type II ( approximately 93%) isoenzymes. 3. Pre-treatment of tracheae with zardaverine (30 microM), vasoactive intestinal peptide (VIP) (1 microM) and the non-selective activator of PKA, Sp-8-CPT-cAMPS (10 microM), produced a non-parallel rightwards shift in the concentration-response curves that described acetylcholine (ACh)-induced tension generation. The type II-selective PKA inhibitor, Rp-8-CPT-cAMPS (300 microM), abolished this effect. 4. Pre-treatment of tracheae with Sp-8-Br-PET-cGMPS (30 microM) produced a non-parallel rightwards shift of the concentration-response curves that described ACh-induced tension generation. The selective cyclic GMP-dependent protein kinase (PKG) inhibitor, Rp-8-pCPT-cGMPS (300 microM), abolished this effect. 5. Pre-treatment of tracheae with isoprenaline (1 microM) produced a 10 fold shift to the right of the ACh concentration-response curve by a mechanism that was unaffected by Rp-8-Br-cAMPS (300 microM, selective inhibitor of type I PKA), Rp-8-CPT-cAMPS (300 microM) and Rp-8-pCPT-cGMPS (300 microM). 6. We conclude that the anti-spasmogenic activity of Sp-8-CPT-cAMPS, zardaverine and VIP in guinea-pig trachea is attributable to activation of the cyclic AMP/PKA cascade whereas isoprenaline suppresses ACh-induced contractions by a mechanism(s) that is independent of PKA and PKG.

Role of the epithelium in opposing H(2)O(2)-induced modulation of acetylcholine-induced contractions in rabbit intrapulmonary bronchiole

1. The role played by the epithelium in H(2)O(2)-induced modulation of the mechanical responses induced by acetylcholine (ACh) in rabbit intrapulmonary bronchioles was investigated in epithelium-intact and -denuded strips. 2. When ACh (3 microM) was applied intermittently, H(2)O(2) (30 microM) enhanced the ACh-induced contractions in epithelium-intact strips. In contrast, in epithelium-denuded strips H(2)O(2) (30 microM) inhibited such contractions. At higher concentrations, H(2)O(2) concentration-dependently attenuated the ACh-induced contractions in both epithelium-intact and -denuded strips, its action being more potent in the latter strips than in the former. 3. Diclofenac (a cyclo-oxygenase inhibitor; 3 microM) reduced the H(2)O(2)-induced enhancement of ACh-contractions in epithelium-intact strips but had no effect on the H(2)O(2)-induced inhibition in epithelium-denuded strips. N(G)-nitro-L-arginine did not alter the effect of H(2)O(2) on ACh-induced contractions in epithelium-intact strips. 4. Catalase (500 u ml(-1)) completely blocked both H(2)O(2)-induced effects on ACh-contractions (enhancement and inhibition). Neither superoxide dismutase (200 u ml(-1)) nor deferoxamine (0.5 mM) had any effect on H(2)O(2)-induced inhibition in epithelium-denuded strips. 5. Aminotriazole (an inhibitor of catalase; 50 mM) significantly potentiated the H(2)O(2)-induced inhibition of ACh-contractions in epithelium-intact strips but not in epithelium-denuded strips. 6. The density ratio for catalase (epithelium-intact over -denuded strips) analysed by Western blot was about 2.1, suggesting that epithelium contains more catalase than smooth muscle. 7. It is concluded that in rabbit intrapulmonary bronchioles, H(2)O(2) has dual actions on ACh-contractions. It is suggested that the epithelium may act as a powerful biochemical barrier via both the action of catalase (scavenging H(2)O(2)) and the release of bronchoconstrictor prostaglandins, thus attenuating the H(2)O(2)-induced modulation of ACh-contractions.

Selective phosphodiesterase inhibitors for the treatment of bronchial asthma and chronic obstructive pulmonary disease

Theophylline is commonly used in the treatment of obstructive airway diseases. The identification and functional characterization of different phosphodiesterase (PDE) isoenzymes has led to the development of various isoenzyme-selective inhibitors as potential anti-asthma drugs. Considering the distribution of isoenzymes in target tissues, with high activity of PDE3 and PDE4 in airway smooth muscle and inflammatory cells, selective inhibitors of these isoenzymes may add to the therapy of chronic airflow obstruction. However, initial data from clinical trials with selective PDE3 and PDE4 inhibitors have been somewhat disappointing and have tempered the expectations considerably since these drugs had limited efficacy and their use was clinically limited through side effects. The improved understanding of the molecular biology of PDEs enabled the synthesis of novel drugs with an improved risk/benefit ratio. These 'second generation' selective drugs have produced more promising clinical results not only for the treatment of bronchial asthma but also for the treatment of chronic obstructive pulmonary disease.

Anti-oxidative effects of theophylline on human neutrophils involve cyclic nucleotides and protein kinase A

The effects were studied of the non-specific phosphodiesterase inhibitor, theophylline (37.5-300 microM), on intracellular levels of cyclic adenosine monophosphate (cAMP) and superoxide generation following exposure of human neutrophils to four different stimuli of neutrophil membrane-associated oxidative metabolism, each of which utilizes a different transductional mechanism to activate NADPH-oxidase, in vitro. Exposure of neutrophils to FMLP (1 microM), the calcium ionophore A23187 (1 microM), and opsonized zymosan (OZ, 0.5 mg/ml) was accompanied by activation of superoxide production and increased concentrations of intracellular cAMP. Inclusion of theophylline resulted in augmentation of cAMP and inhibition of superoxide production by these stimuli. These negative effects of theophylline on neutrophil superoxide generation were mimicked by dibutyryl cAMP and 8-bromo-cGMP, while the inhibitory activity of all 3 agents was antagonized by the protein kinase A inhibitor KT 5720, but not by the G-kinase inhibitor KT 5823. Unlike FMLP, OZ and A23187, intracellular cAMP levels did not increase in cells activated with phorbol-12-myristate-13-acetate (PMA, 25 ng/ml), while oxidant production activated by this stimulus was insensitive to the inhibitory effects of theophylline. These observations suggest that the beneficial, anti-inflammatory interactions of theophylline with human neutrophils are related to the phosphodiesterase inhibitory properties of this agent, and are selective for those pro-inflammatory stimuli which elevate cAMP, resulting in enhanced activity of protein kinase A and inhibition of the production of potentially harmful reactive oxidants by these cells.

A comparison of low-dose inhaled budesonide plus theophylline and high-dose inhaled budesonide for moderate asthma

BACKGROUND

Inhaled glucosteroids and oral theophylline are widely used to treat asthma. We compared the benefits of adding theophylline to inhaled glucosteroid with those of doubling the dose of inhaled glucosteroid in patients with persistent symptoms despite the use of inhaled glucosteroid.

METHODS

In a double-blind, placebo-controlled trial, we randomly assigned 62 patients to receive either 400 microg of inhaled budesonide (low-dose budesonide) with 250 or 375 mg of theophylline (depending on body weight) or 800 microg of inhaled budesonide (high-dose budesonide). All doses were given twice daily for three months. Lung function was measured serially, and patients kept records of peak expiratory flow, symptoms, and albuterol use. The effects of treatment on endogenous cortisol levels were also assessed.

RESULTS

Both treatments resulted in improvements in lung function that were sustained throughout the study. As compared with treatment with high-dose budesonide, treatment with low-dose budesonide plus theophylline resulted in greater improvements in forced vital capacity (P=0.03) and forced expiratory volume in one second (P= 0.03). There were significant and similar reductions in beta2-agonist use and the variability of peak expiratory flow, a correlate of bronchial hyperresponsiveness and the severity of asthma. Serum cortisol concentrations were significantly reduced in the group given high-dose budesonide (from a mean [+/-SE] of 18.4+/-2.4 microg per deciliter to 15.9+/-2.1 microg per deciliter, P=0.02) but were unchanged in the other group. The median serum theophylline concentration was 8.7 microg per milliliter (therapeutic range, 10 to 20) among those who received theophylline. Both treatments were well tolerated.

CONCLUSIONS

For patients with moderate asthma and persistent symptoms, low-dose inhaled budesonide with theophylline and high-dose inhaled budesonide produced similar benefits. Effects were achieved at theophylline concentrations below the recommended therapeutic range. The addition of low-dose theophylline to inhaled glucosteroid may be preferable to and cheaper than increasing the dose of inhaled glucosteroid.

Augmentation of human neutrophil and alveolar macrophage LTB4 production by N-acetylcysteine: role of hydrogen peroxide

1. The actions of N-acetylcysteine (NAC) on hydrogen peroxide (H2O2) and leukotriene B4 (LTB4) production by human resting and stimulated peripheral blood neutrophils and alveolar macrophages were investigated. 2. At a concentration of 100 microM, NAC significantly (P < 0.01) suppressed the accumulation of H2O2 in the incubation medium of resting and opsonized zymosan (OZ; 0.5 mg ml[-1])- or N-formylmethionyl-leucyl-phenylalanine (fMLP; 1 microM)-stimulated neutrophils and of resting and OZ-stimulated macrophages. At concentrations of 10 microM and above, NAC augmented significantly the level of LTB4 in the supernatants of OZ- and fMLP-stimulated neutrophils (P < 0.01 and P < 0.05, respectively) and OZ-stimulated macrophages (P < 0.05 at 10 microM, P < 0.01 at 100 microM NAC). 3. NAC (100 microM) caused a significant (P < 0.01) reduction in the quantity of measurable H2O2 when incubated with exogenous H2O2 concentrations equivalent to those released from OZ-stimulated neutrophils and macrophages. At no concentration did NAC affect quantitites of measurable LTB4 when incubated with exogenous LTB4. 4. Superoxide dismutase (SOD), which catalyzes the conversion of superoxide anion to H2O2 had no significant effect on LTB4 production by human neutrophils. In contrast, catalase, which catalyzes the conversion of H2O2 to H2O and O2, caused a pronounced, statistically significant (P < 0.01) increase in the levels of LTB4 measured in the supernatants of OZ- and fMLP-stimulated neutrophils. 5. H2O2 (12.5 microM and 25 microM, concentrations equivalent to those measured in the supernatants of activated neutrophils and alveolar macrophages, respectively) caused a small (13%) decrease in the quantity of measurable LTB4 (P = 0.051 and P < 0.05 at 12.5 microM and 25 microM, respectively) that was inhibited by NAC (100 microM) but not by catalase (400 u ml[-1]). 6. In conclusion, the anti-oxidant drug, NAC, increases LTB4 production by human neutrophils and alveolar macrophages, probably through the elimination of cell-derived H2O2. LTB4 undergoes a H2O2-dependent oxidation that is inhibited by NAC but this is unlikely to account fully for the increased levels of LTB4, suggesting that NAC may increase LTB4 production by blocking the H2O2-dependent inhibition of a synthetic enzyme, such as 5-lipoxygenase.

Differential efficacy of lymphocyte- and monocyte-selective pretreatment with a type 4 phosphodiesterase inhibitor on antigen-driven proliferation and cytokine gene expression

Elevations of intracellular cyclic AMP, achieved with the use of phosphodiesterase (PDE) inhibitors, cause functional downregulation of most inflammatory cells. Rolipram, an inhibitor selective for the PDE4 isozyme, can markedly downregulate antigen-driven proliferation and cytokine gene expression of unfractionated human peripheral blood mononuclear cells. However, it is unclear whether PDE4 inhibitors in a mixed-cell system exert their immunosuppressive effect on the lymphocyte or on the monocyte fraction. We have used an adherence-based protocol for separating peripheral blood mononuclear cells, isolated from atopic individuals, into lymphocyte and monocyte fractions and have selectively treated these populations with rolipram prior to reconstituting the cell cultures to their original lymphocyte/monocyte proportions. Cellular responses to both ragweed and tetanus toxoid were analyzed for both proliferation and gene expression of proinflammatory cytokines. A dose-dependent downregulation of ragweed- and tetanus toxoid-driven proliferative responses was achieved by pretreatment of lymphocytes from peripheral blood with rolipram. This downregulation was significantly greater than that achieved with pretreatment of monocytes. Pretreatment of both populations failed to show synergistic downregulation of proliferation. Lymphocyte pretreatment with rolipram also resulted in marked downregulation of gene expression for IL-4, IL-5, and interferon-gamma compared to monocyte pretreatment in both ragweed- and tetanus toxoid-driven systems. Interestingly, monocyte pretreatment in these systems resulted in significant downregulation of IL-2 gene expression compared to lymphocyte pretreatment. Flow cytometric analysis failed to show alterations in any of a panel of surface activation and signal transducing molecules by rolipram treatment with or without antigen stimulation. We conclude that, in a mixed cell system, PDE4 inhibitors downregulate antigen-driven proliferation and gene expression of proinflammatory cytokines predominantly through their effects on lymphocytes rather than monocytes.

Effects of theophylline and rolipram on leukotriene C4 (LTC4) synthesis and chemotaxis of human eosinophils from normal and atopic subjects

1. The effects of the non-selective phosphodiesterase (PDE) inhibitor theophylline and the selective PDE4 inhibitor rolipram on leukotriene C4 (LTC4) synthesis and chemotaxis of complement 5a (C5a)- and platelet-activating factor (PAF)-stimulated human eosinophils obtained from normal and atopic donors were investigated. 2. Eosinophils were purified from peripheral venous blood of normal and atopic subjects by an immunomagnetic procedure to a purity > 99%. Eosinophils were stimulated with PAF (0.1 microM) or C5a 0.1 microM for 15 min and LTC4 was measured by radioimmunoassay (RIA). Eosinophil chemotaxis in response to PAF and C5a was assessed with 48-well microchambers (Boyden). 3. Under these conditions substantial amounts of LTC4 (about 300-1000 pg per 10(6) cells) were only detectable in the presence of indomethacin (0.1-10 microM). To explain this finding it was hypothesized that indomethacin reversed the inhibition of LTC4 synthesis by endogenously synthesized prostaglandins, in particular prostaglandin E2 (PGE2). In fact, eosinophils release 23 pg PGE2 per 10(6) cells following PAF stimulation; this PGE2 synthesis was completely inhibited by indomethacin and readdition of PGE2 inhibited eosinophil LTC4 synthesis (IC50 = 3 nM). The following experiments were performed in the presence of 10 microM indomethacin. 4. Theophylline (IC50 approximately 50 microM) and rolipram (IC50 approximately 0.03-0.2 microM) suppressed PAF- and C5a-stimulated LTC4 synthesis. This PDE inhibitor-induced suppression of LTC4 generation is mediated by activation of protein kinase A, since it was reversed by the protein kinase A inhibitor Rp-8-Br-cyclic AMPS. In addition, exogenous arachidonic acid concentration-dependently (0.3 microM-3 microM) reversed the inhibition of LTC4 synthesis by the PDE inhibitors, indicating that theophylline and rolipram suppress the mobilization of arachidonic acid. The beta 2-adrenoceptor agonist salbutamol inhibited eosinophil LTC4 synthesis (IC50 = 0.08 microM). The combination of salbutamol with theophylline (10 microM) or rolipram (3 nM) appeared to be additive. 5. Theophylline (IC50 approximately 40 microM), rolipram (IC50 approximately 0.02 microM [C5a], approximately 0.6 microM [PAF]) and PGE2 (IC50 approximately 3 nM) inhibited C5a- and PAF-stimulated eosinophil chemotaxis. The combination of PGE2 with theophylline resulted in an additive effect. 6. Both C5a- and PAF-stimulated eosinophil chemotaxis and LTC4 generation were significantly elevated in eosinophils from atopic individuals compared to normal subjects. However, eosinophils from normal and atopic individuals were not different with respect to their total cyclic AMP-PDE and PDE4 isoenzyme activities as well as the potencies of theophylline and rolipram to suppress LTC4 generation and chemotaxis.

Theophylline: potential antiinflammatory effects in nocturnal asthma

BACKGROUND

Recent information suggests that one of the therapeutic properties of theophylline is an antiinflammatory effect.

OBJECTIVE

We evaluated this potential effect of theophylline in eight patients with nocturnal asthma.

METHODS

The study design was a randomized, double-blind, placebo-controlled crossover of 2-week treatment periods, separated by a 1-week washout period. Spirometry and bronchoscopy were performed.

RESULTS

Theophylline, compared with placebo, significantly improved the overnight decrement in lung function. The higher the nocturnal theophylline level, the greater the improvement in lung function. Theophylline also significantly decreased the percentage of neutrophils in the 4:00 AM bronchoalveolar lavage fluid and stimulated leukotriene B4 levels from macrophages obtained at 4:00 AM. The greater change in neutrophils correlated with increasing serum theophylline concentration. Also, the change in leukotriene B4 production was significantly correlated with the theophylline-induced decrement in lavage granulocytes (neutrophils and eosinophils).

CONCLUSION

This study suggests that one action of theophylline is to alter inflammatory cell number and function in nocturnal asthma and that it may do this through an leukotriene B4-mediated mechanism.

Phosphodiesterase inhibitors suppress proliferation of peripheral blood mononuclear cells and interleukin-4 and -5 secretion by human T-helper type 2 cells

It has been suggested that interleukin-4 and -5 (IL-4 and IL-5) are instrumental in the control of allergic disease. Elevated levels of IL-4 messenger RNA (mRNA) have been detected in numerous foci of atopic activity, including bronchoalveolar lavage (BAL) fluid from atopic asthmatics and skin of atopic dermatitis patients. IL-5 is important in eosinophil activation, which is a common feature of atopic disease. IL-5 mRNA has been detected in BAL fluid from both atopic and non-atopic asthmatics, indicating that IL-5 may be a common feature of the two disease states. Production of IL-4 and IL-5 by T cells appears to be associated with a high affinity cyclic AMP (cAMP) phosphodiesterase (PDE). This study was designed to compare the effects of PDE inhibitors Ro20-1724 and theophylline on (1) the mitogenic response of peripheral blood mononuclear cells from atopic and non-atopic individuals and (2) secretion of IL-4 and IL-5 by TH(2) cells after activation with PMA and anti-CD3. Both Ro20-1724 and theophylline inhibited proliferation of PBMC in a dose-dependent manner. There was no significant difference between proliferation of PBMC from atopic versus non-atopic donors, but Ro20-1724, a specific PDE IV inhibitor, was more potent at a concentration of 10(-5)M than theophylline in suppressing lymphocyte proliferation. Similarly, both PDE inhibitors suppressed secretion of IL-4 and IL-5 from TH(2)-like cell lines in a dose-dependent manner. In conclusion, as Ro20-1724 and theophylline inhibit proliferation of PBMC and secretion of IL-4 and IL-5 from human TH(2) cell lines, the development of a selective cyclic nucleotide PDE IV inhibitor may provide a promising new approach for asthma prophylaxis.

Oral vs inhaled asthma therapy. Pros, cons and combinations

A number of oral and inhaled drugs are available for the long term management of patients with persistent asthma, yet the disease continues to be associated with significant morbidity and mortality. Over the past years, inhaled glucocorticoids have become established as a cornerstone of maintenance therapy because of their demonstrated clinical efficacy, ability to reduce bronchial inflammation and good tolerability. Other inhaled drugs (e.g. sodium cromoglycate, nedocromil, long-acting beta 2 agonists) also play a role in the long term treatment of patients with asthma. However, many patients (especially children and the elderly) find inhalers difficult to use, and poor inhalation technique can affect the amount of drug reaching the lungs and response to therapy. Oral drug administration is simple, but, until recently, oral asthma therapy has primarily consisted of sustained-release theophylline and glucocorticoids. Theophylline has a narrow therapeutic index, necessitating regular monitoring of serum drug concentrations, and long term oral glucocorticoid therapy is associated with potentially serious adverse events including osteoporosis with bone fracture. The recent development of orally administered leukotriene receptor antagonists (e.g. zafirlukast) and 5-lipoxygenase inhibitors (e.g. zileuton) offers novel mechanisms of action and potential solutions to compliance issues associated with regular administration of inhaled asthma therapy. These drugs have demonstrated efficacy as maintenance therapy in patients with asthma and, importantly, lack the adverse effects associated with long term systemic glucocorticoid therapy. Further clinical trials and the increasing use of these new therapies will help to establish the precise role of orally administered leukotriene receptor antagonists and 5-lipoxygenase inhibitors in the long term management of patients with asthma.

Differential effect of phosphodiesterase 4 inhibitors on the proliferation of human peripheral blood mononuclear cells from normals and subjects with atopic dermatitis

1. The aims of this study were to compare the effects of selective inhibitors of the type 3, type 4 and type 5 phosphodiesterase (PDE) isoenzymes on the phytohaemagglutinin (PHA)-stimulated proliferation of human peripheral blood mononuclear cells (HPBM) from normals and subjects with atopic dermatitis (AD). 2. Mononuclear cells were isolated from peripheral venous blood of normals and subjects with AD. A concentration-response curve was carried out with PHA (0.5-5 micrograms ml-1) and a concentration which produced a submaximal stimulation of proliferation (2 micrograms ml-1) was selected for further experiments. HPBM (10(5) cells per well) were stimulated with PHA (2 micrograms ml-1) in the absence or presence of PDE inhibitor (0.01 microM-10 microM) and 24 h later [3H]-thymidine (0.1 microCi per well) was added. Cells were incubated for an additional 24 h period and [3H]-thymidine incorporation measured. 3. The type 4 PDE inhibitors (rolipram, RO 20-1724 and denbufylline) produced a concentration-related inhibition of proliferation of HPBM from normal and AD subjects. The IC50 for rolipram was significantly (P < 0.05) lower in HPBM from AD patients 0.28 microM (95% confidence limits (CL): 0.158-0.499, n = 5) vs normal subjects 2.6 microM (95% CL: 0.867-7.05, n = 5, P < 0.05) as were the IC50 values for denbufylline: 0.26 microM (95% CL: 0.152-0.440, n = 5) vs 1.84 microM (95% CL: 0.467-7.23, n = 5, P < 0.05) respectively and RO 20-1724: 1.49 microM (95% CL: 0.61 microM-3.64 microM) vs 6.46 microM (95% CL: 2.03 microM-20.46 microM), respectively. 4. The mixed type 3/4 inhibitors (zardaverine and benzafentrine) produced a concentration-related inhibition of proliferation of HPBM from normal and AD subjects. The IC50 value for zardaverine in HPBM from normal subjects: 1.8 microM (95% CL: 0.43 microM-7.85 microM, n = 4) was similar to that in AD subjects: 1.03 microM (95% CL: 0.48 microM-2.28 microM) as was the IC50 value for benzafentrine in normal 3.8 microM (95% CL: 2.45 microM-5.9 microM) and atopic 5.5 microM (95% CL: 3.84 microM-7.78 microM) HPBM. The type 5 PDE inhibitor, zaprinast was ineffective at inhibiting the proliferation of normal HPBM. The type 3 PDE inhibitor, siguazodan only inhibited [3H]-thymidine incorporation at a concentration of 10 microM. 5. These results show that combined inhibition of the type 3 and 4 PDE isoenzymes in HPBM from normal subjects has a greater antiproliferative effect than inhibition of the type 4 isoenzyme alone. In addition these data indicate that the proliferative response of HPBM from AD subjects is more sensitive to PDE 4 inhibition than the proliferation of HPBM from normals.

Cyclic nucleotide phosphodiesterases in the human lung

Although theophylline has been used in the treatment of lung diseases, particularly bronchial asthma, since the nineteenth century, the mechanisms underlying its effectiveness remained poorly understood until quite recently. The identification of cyclic nucleotide phosphodiesterase (PDE)--the enzyme responsible for breaking down cyclic AMP and cyclic GMP within cells--as a target for methylxanthines such as theophylline led to a research effort that has resulted in the characterization of multiple forms of the PDE enzyme and the development of selective inhibitors for some of these forms. Using these drugs, it has been possible to identify the PDE "isoenzymes" in a number of tissues and cells and to demonstrate the functional effects of the inhibition of different PDEs upon these tissues. Studies on the smooth muscle of human airways and pulmonary arteries have identified isoenzyme-selective PDE inhibitors that are effective broncho- and vasorelaxants in vitro, and it is hoped that these agents may be effective in relieving airway obstruction and pulmonary hypertension in patients. In addition, selective inhibitors of certain PDE isoenzymes suppress the proinflammatory functions of a range of immune cells, including the lung mast cell and the alveolar macrophage. Selective inhibitors of PDE isoenzymes are beginning to undergo clinical trials for the treatment of asthma. The advancing understanding of the PDE distribution in the lung and the ever more precise characterization of distinct enzyme proteins should allow the development of site-selective drugs for the treatment of lung diseases, while minimizing the systemic side effects associated with nonselective PDE inhibitors such as theophylline.