Inhibitory cytokines in asthma

Although research in asthma has concentrated on complex proinflammatory mechanisms, it is likely that defective expression of cytokines that inhibit allergic inflammation, such as interleukin 10, interleukin 12 and interferon γ, might also be important, particularly in determining disease severity and persistence of inflammation in the airways. Therapy based on these cytokines might also be useful, with the advantage that it restores the balance of endogenous cytokines. We discuss the therapeutic potential of these and other inhibitory cytokines in the treatment of asthma, particularly in patients with severe disease that is poorly responsive to conventional therapy, or as a disease-modifying treatment when used early.     

Identification and management of adults with asthma prone to exacerbations: can we do better?

Exacerbations are a major cause of morbidity in asthma and generate high health costs. Identification and management of adults with asthma who are prone to exacerbations is of considerable importance as by this means it should be possible to reduce the number of patients who currently experience inadequately controlled disease. Exacerbations occur most frequently in individuals with severe disease. Other risk factors include a history of a recent exacerbation, co-morbidities such as a raised body mass index and psychological problems as well as current smoking and lower socio-economic status. A low FEV₁, particularly if combined with the additional information from questionnaires helps predict exacerbations. Despite the association between these risk factors and exacerbations it remains difficult to accurately predict in an individual patient with asthma whether they will go on to develop an exacerbation in the future. A major aim of international guidelines on the management of asthma is to prevent future risks of exacerbations, but some patients, particularly those with severe disease, respond poorly to current therapies and continue to experience recurrent exacerbations. There is an unmet need for improved management strategies and drugs targeted at preventing asthma exacerbations. Monitoring induced sputum eosinophil cell counts is helpful in preventing exacerbations in some patient with severe asthma. Future developments are likely to include the identification of better biomarkers to predict exacerbations or the cause of exacerbations, augmentation of the immunological response to viruses at the time of the exacerbation, the use of telemonitoring in patients with severe asthma and the development of improved therapies targeted at reducing exacerbations.     

Leptin, adiponectin and pulmonary diseases

Adipose tissue produces leptin and adiponectin - energy-regulating adipokines that may also play a role in inflammatory pulmonary conditions, as suggested by some murine studies. Leptin and adiponectin and their respective receptors are expressed in the human lung. The association between systemic or airway leptin and asthma in humans is currently controversial, particularly among adults. The majority of the evidence among children however suggests that systemic leptin may be associated with greater asthma prevalence and severity, particularly among prepubertal boys and peripubertal/postpubertal girls. Systemic and airway leptin concentrations may also be disproportionately higher in chronic obstructive pulmonary disease (COPD) patients, particularly among women, and reflect greater airway inflammation and disease severity. Quite like leptin, the association between systemic and airway adiponectin and asthma in humans is also controversial. Some but not all studies, demonstrate that serum adiponectin concentrations are protective against asthma among premenopausal women and peripubertal girls. On the other hand, serum adiponectin concentrations are inversely associated with asthma severity among boys but positively associated among men. Further, systemic and airway adiponectin concentrations are higher in COPD patients than controls, as demonstrated by case-control studies of men. Systemic adiponectin is also positively associated with lung function in healthy adults but inversely associated with lung function in subjects with COPD. It is therefore possible that pro-inflammatory effects of adiponectin dominate under certain physiologic conditions and anti-inflammatory effects under others. The adipokine-lung disease literature has critical gaps that include a lack of adequately powered longitudinal or weight-intervention studies; inadequate adjustment for confounding effect of obesity; and unclear understanding of potential sex interactions. It is also uncertain whether adipokine derangements precede pulmonary disease or are a consequence of it. Future research will determine whether modulation of adipokines, independent of BMI, may allow novel ways to prevent or treat inflammatory pulmonary conditions.     

The increase in the prevalence of asthma and allergy: food for thought

Since about 1960, the prevalence of asthma and allergic disease has increased sufficiently to become a major public-health concern. Concurrently, there have been marked changes in our diet, and it has been proposed that these changes have contributed to the increase in the prevalence of asthma and allergy. In this article, these hypotheses about diet are described, together with the postulated mechanisms and the evidence for and against, leading to the most recent evidence indicating that maternal diet during pregnancy might be particularly important in the development of childhood asthma.     

A comparison between intratracheal and inhalation delivery of Aspergillus fumigatus conidia in the development of fungal allergic asthma in C57BL/6 mice

Allergic asthma is a debilitating disease of the airways characterized by airway hyperresponsiveness, eosinophilic inflammation, goblet cell metaplasia with associated mucus hypersecretion,?and airway wall remodelling events, particularly subepithelial fibrosis and smooth muscle cell hyperplasia. Animal models that accurately mimic these hallmarks of allergic airways disease are critical for studying mechanisms associated with the cellular and structural changes that lead to disease pathogenesis. Aspergillus fumigatus, is a common aeroallergen of human asthmatics. The intratracheal (IT) delivery of A. fumigatus conidia into the airways of sensitized mice has been described as a model of allergic disease. Here, we compared the IT model with a newly developed inhalation (IH) challenge model. The IH model allowed multiple fungal exposures, which resulted in an exacerbation to the allergic asthma phenotype. Increased recruitment of eosinophils and lymphocytes, the hallmark leukocytes of asthma, was noted with the IH model as compared to the IT model in which macrophages and neutrophils were more prominent. Immunoglobulin E (IgE) production was significantly greater after IH challenge, while that of IgG(2a) was higher after IT challenge. Airway wall remodelling was pronounced in IH-treated mice, particularly after multiple allergen challenges. Although the IT model may be appropriate for the examination of the played by innate cells in the acute response to fungus, it fails to consistently reproduce the chronic remodelling hallmarks of allergic asthma. The ability of the IH challenge to mimic these characteristics recommends it as a model suited to study these important events.     

Heparin antagonists are potent inhibitors of mast cell tryptase

Tryptase may be a key mediator in mast cell-mediated inflammatory reactions. When mast cells are activated, they release large amounts of these tetrameric trypsin-like serine proteases. Tryptase is present in a macromolecular complex with heparin proteoglycan where the interaction with heparin is known to be essential for maintaining enzymatic activity. Recent investigations have shown that tryptase has potent proinflammatory activity, and inhibitors of tryptase have been shown to modulate allergic reactions in vivo. Many of the tryptase inhibitors investigated previously are directed against the active site. In the present study we have investigated an alternative approach for tryptase regulation. We show that the heparin antagonists Polybrene and protamine are potent inhibitors of both human lung tryptase and of recombinant mouse tryptase (mouse mast cell protease 6). Protamine inhibited tryptase in a competitive manner whereas Polybrene showed noncompetitive inhibition kinetics. Treatment of tetrameric, active tryptase with Polybrene caused dissociation into monomers, accompanied by complete loss of enzymatic activity. The present report thus suggests that heparin antagonists potentially may be used in treatment of mast cell-mediated diseases such as asthma.     

NONALLERGIC ASTHMA—Differential Diagnosis and Treatment

A classification of asthma into allergic and nonallergic has gained support from the more recent studies on the underlying causes of the disease.The majority of instances of nonallergic asthma occur after middle life and result from recurrent infections of the upper and lower respiratory tract. Status asthmaticus is a frequent complication of infectious asthma.Chronic and intractable asthma may be present also in a patient with allergic asthma complicated by a superimposed infection of the sinuses, bronchi and lungs.There are many secondary or precipitating causes that may bring on asthmatic paroxysms. The most important of these are acute respiratory infections, mechanical and chemical irritants, autonomic imbalance, hormonal deficiencies and psychogenic influences. These secondary causes play a more important role in nonallergic asthma because of the greater tendency to chronicity in this form of the disease.The effective treatment of chronic asthma depends largely on the successful control of the secondary or precipitating causes of the asthmatic attacks.The introduction of the antibiotics and corticosteroids in the treatment of infectious asthma has supplied potent weapons to combat the disease. The use of these therapeutic agents makes possible the control of two of the important pathologic lesions of asthma—bronchial infection and bronchial inflammation.At present combined antibiotic and cortisone or hydrocortisone therapy of asthma seems to be the most rational method of preventing the disease from becoming chronic and intractable. Their value in infectious asthma is due to their anti-infective and antiflammatory action.When prolonged treatment is essential, combined therapy also lessens the dangers arising from the presence of masked infections.     

Histidines are critical for heparin-dependent activation of mast cell tryptase

Mast cell tryptase is a tetrameric serine protease that is stored in complex with negatively charged heparin proteoglycans in the secretory granule. Tryptase has potent proinflammatory properties and has been implicated in diverse pathological conditions such as asthma and fibrosis. Previous studies have shown that tryptase binds tightly to heparin, and that heparin is required in the assembly of the tryptase tetramer as well as for stabilization of the active tetramer. Because the interaction of tryptase with heparin is optimal at acidic pH, we investigated in this study whether His residues are of importance for the heparin binding, tetramerization, and activation of the tryptase mouse mast cell protease 6. Molecular modeling of mouse mast cell protease 6 identified four His residues, H35, H106, H108, and H238, that are conserved among pH-dependent tryptases and are exposed on the molecular surface, and these four His residues were mutated to Ala. In addition, combinations of different mutations were prepared. Generally, the single His-Ala mutations did not cause any major defects in heparin binding, activation, or tetramerization, although some effect of the H106A mutation was observed. However, when several mutations were combined, large defects in all of these parameters were observed. Of the mutants, the triple mutant H106A/H108A/H238A was the most affected with an almost complete inability to bind to heparin and to form active tryptase tetramers. Taken together, this study shows that surface-exposed histidines mediate the interaction of mast cell tryptase with heparin and are of critical importance in the formation of active tryptase tetramers.     

Cutting edge: the absence of C3 demonstrates a role for complement in Th2 effector functions in a murine model of pulmonary allergy

Asthma is a chronic disease of the lung resulting from airway obstruction. Although the initiating causes are not entirely clear, the airway inflammation in asthma is associated with Th2 lymphocytes and their cytokines, particularly IL-4, which play a prominent role in this disease by regulating airway hyperresponsiveness, eosinophil activation, and IgE synthesis. Historically, complement was not thought to contribute to the pathogenesis of asthma. However, using C3-deficient mice in an allergen-induced model of pulmonary allergy, we demonstrate that complement may impact key features of this disease. When challenged with allergen, mice deficient in C3 exhibit diminished airway hyperresponsiveness and lung eosinophilia. Furthermore, these mice also have dramatically reduced numbers of IL-4-producing cells and attenuated Ag-specific IgE and IgG1 responses. Collectively, these results demonstrate that C3-deficient mice have significantly altered allergic lung responses and indicate a role for the complement system in promoting Th2 effector functions in asthma.     

Nonallergic asthma; differential diagnosis and treatment

A classification of asthma into allergic and nonallergic has gained support from the more recent studies on the underlying causes of the disease. The majority of instances of nonallergic asthma occur after middle life and result from recurrent infections of the upper and lower respiratory tract. Status asthmaticus is a frequent complication of infectious asthma. Chronic and intractable asthma may be present also in a patient with allergic asthma complicated by a superimposed infection of the sinuses, bronchi and lungs. There are many secondary or precipitating causes that may bring on asthmatic paroxysms. The most important of these are acute respiratory infections, mechanical and chemical irritants, autonomic imbalance, hormonal deficiencies and psychogenic influences. These secondary causes play a more important role in nonallergic asthma because of the greater tendency to chronicity in this form of the disease. The effective treatment of chronic asthma depends largely on the successful control of the secondary or precipitating causes of the asthmatic attacks. The introduction of the antibiotics and corticosteroids in the treatment of infectious asthma has supplied potent weapons to combat the disease. The use of these therapeutic agents makes possible the control of two of the important pathologic lesions of asthma-bronchial infection and bronchial inflammation. At present combined antibiotic and cortisone or hydrocortisone therapy of asthma seems to be the most rational method of preventing the disease from becoming chronic and intractable. Their value in infectious asthma is due to their anti-infective and antiflammatory action. When prolonged treatment is essential, combined therapy also lessens the dangers arising from the presence of masked infections.     

Molecular and cellular mechanisms in the viral exacerbation of asthma

The aetiology of asthma associated with viral infection is complex. The dynamics that contribute to disease pathogenesis are multifactorial and involve overlapping molecular and cellular mechanisms, particularly the immune response to respiratory virus infection or allergen sensitization. This review summarizes the evidence associated with factors that may contribute to the development or exacerbation of asthma including age, host factors, genetic polymorphisms, altered immune responses, and aspects of viral antigen expression. This review also provides an important perspective of key events linked to the development of asthmatic disease and related pulmonary inflammation from human and animal studies, and discusses their relationship as targets for disease intervention strategies.     

ATOPIC DERMATITIS—ETIOLOGY AND CLINICAL MANAGEMENT

Atopic dermatitis is primarily an allergic problem, similar in most of its aspects to that of allergic bronchial asthma. It should be studied and treated like asthma, with especial emphasis on the significance of inhalant allergens. It is doubtful that psychic factors are of importance in primary genesis of the disease although they may be involved in exacerbation of it.     

Atopic dermatitis-etiology and clinical management

Atopic dermatitis is primarily an allergic problem, similar in most of its aspects to that of allergic bronchial asthma. It should be studied and treated like asthma, with especial emphasis on the significance of inhalant allergens. It is doubtful that psychic factors are of importance in primary genesis of the disease although they may be involved in exacerbation of it.     

Inhibition of apolipoprotein E-related neurotoxicity by glycosaminoglycans and their oligosaccharides

Apolipoprotein E (apoE) has been genetically linked to late-onset Alzheimer's disease (AD). The role of this lipid-transport protein in AD remains to be established. One hypothesis is that apoE, particularly the apoE4 isoform, may have neurotoxic effects as demonstrated using apoE-related synthetic peptides and the N-terminal fragment of apoE. ApoE is a heparan-sulfate binding protein, and apoE peptide neurotoxicity can be blocked by heparin and prevented by degrading heparan sulfate or inhibiting its biosynthesis. The possibility that heparin inhibition of toxicity is mediated by a specific oligosaccharide sequence was investigated using a bioassay to determine the inhibition of apoE peptide toxicity by glycosaminoglycans and purified glycosaminoglycan oligosaccharides. Studies on modified heparins showed that the presence of N-sulfo groups and either 2- or 6-O sulfo groups were required for inhibition of toxicity. Heparin oligosaccharides with eight or more saccharide residues with seven O-sulfo groups and four N-sulfo groups exhibited potent inhibition. Larger oligosaccharides, and heparin and heparan sulfate polymers, afforded comparable, or somewhat better, protective effects but also caused clumping and detachment of cells when administrated alone.     

Heparin as a Therapy for Atherosclerosis: Preliminary Observations on the Intrapulmonary Administration of Low-Dose Heparin in the Morning Versus Evening Gauged by Its Effect on Blood Variables

Reports on clinical trials with subcutaneous and intrapulmonary administration of low-dose heparin suggest that it may be an attractive therapeutic modality for the treatment of coronary artery disease because of unprecedented reduction in mortality of treated subjects. As a preliminary to a clinical trial with low-dose intrapulmonary heparin, a pilot study was conducted on three subjects. It compares overall circadian responses of 37 blood variables following intrapulmonary administration of heparin (10,500-18,800 U) in the morning (0800 h) and in the evening (2000 h). After each of these times, blood samples, mostly at 3 h intervals for the ensuing 27 h, were analyzed for heparin, APTT, TT, functional fibrinogen, CBC, enzymes, lipids, electrolytes, and hormones. Each time series was analyzed for circadian rhythm by the least-squares fit of a 24 h cosine and circadian mesors were compared by the Bingham test of rhythm parameters. Following heparin in the evening, but not in the morning, a statistically significant increase in circulating heparin levels, as well as directional increases in APTT and TT and decreases in fibrinogen, were observed in all three subjects. Same direction changes in several other variables were also observed. It is concluded that inhalation of heparin in low-dose levels results in variable circadian effects on blood parameters measured, ranging from no changes in their levels to minimal within normal range changes, and that these effects are dependent upon the timing of dose administration. It is suggested that the timed self-administration of low-dose heparin by inhalation be seriously considered for long-term clinical trials in the treatment and prevention of atherosclerosis.     

Analysis of novel disease-related genes in bronchial asthma

Bronchial asthma is a complex disease characterized by airway inflammation involving interleukin (IL)-4 and IL-13. We have applied microarray analyses to human bronchial epithelial cultures to probe for genes regulated by these cytokines and have identified a subset of disease-relevant genes by comparison with cDNA libraries derived from normal and asthmatic bronchial biopsies. Squamous cell carcinoma antigen-1 (SCCA1) and SCCA2, the cysteine and serine protease inhibitors, respectively, showed the highest expression by IL-4 and IL-13, and particularly, SCCA1 was significantly increased in the asthmatic cDNA library. STAT6 was shown to be involved in expression of SCCA1 and SCCA2 in vitro. Furthermore, serum levels of SCCA were also elevated in asthmatic patients. Taken together, it was supposed that SCCA may play some role in the pathogenesis of bronchia asthma, and measuring its serum level may be relevant for diagnosing or monitoring the status of bronchial asthma. In a complex disorder such as asthma, this combination of in vitro and in vivo genomic approaches is a powerful discriminatory method enabling identification of novel disease-related genes and their mechanisms of regulation.     

Metabolic effects of heparin on rat cervical epithelial cells

The glycosaminoglycan heparin inhibits the growth of a number of different cell types in vitro including smooth muscle cells, mesangial cells, fibroblasts, and rat cervical epithelial cells (RCEC). Studies investigating the antiproliferative effects of heparin on smooth muscle cells have demonstrated the site of the cell cycle block and revealed several metabolic alterations that could be causally associated with growth inhibition. We have investigated these metabolic parameters in RCEC to determine whether they are also associated with the antiproliferative effects of heparin in epithelial cells. Heparin acts rapidly to inhibit RCEC growth with inhibition detectable by autoradiography 7 h after the addition of heparin. Heparin treated RCEC begin to enter S-phase 12 h after the removal of heparin. These findings suggest that heparin blocks RCEC in the early-to-mid G1 phase of the cell cycle rather than late in G1 or early in S-phase as has previously been demonstrated for smooth muscle cells. Unlike smooth muscle cells, the uptake of thymidine and uridine is not inhibited by heparin in RCEC. Treatment of medium with heparin-Sepharose does not reduce the subsequent growth of RCEC; heparin inhibits the growth of RCEC in heparin-Sepharose treated medium in a manner identical to that in nontreated medium. Therefore the growth inhibitory effects of heparin cannot be explained by the inactivation of mitogens present in serum. In contrast to its effects on smooth muscle cells, heparin treatment of RCEC does not result in a reduction in the binding of epidermal growth factor (EGF) to the cells. These results indicate that although heparin inhibits the growth of a variety of cell types, significant differences exist in the responses of the different cells to heparin.     

Regulation of pathologic retinal angiogenesis in mice and inhibition of VEGF-VEGFR2 binding by soluble heparan sulfate

Development of the retinal vascular network is strictly confined within the neuronal retina, allowing the intraocular media to be optically transparent. However, in retinal ischemia, pro-angiogenic factors (including vascular endothelial growth factor-A, VEGF-A) induce aberrant guidance of retinal vessels into the vitreous. Here, we show that the soluble heparan sulfate level in murine intraocular fluid is high particularly during ocular development. When the eyes of young mice with retinal ischemia were treated with heparan sulfate-degrading enzyme, the subsequent aberrant angiogenesis was greatly enhanced compared to PBS-injected contralateral eyes; however, increased angiogenesis was completely antagonized by simultaneous injection of heparin. Intraocular injection of heparan sulfate or heparin alone in these eyes resulted in reduced neovascularization. In cell cultures, the porcine ocular fluid suppressed the dose-dependent proliferation of human umbilical vein endothelial cells (HUVECs) mediated by VEGF-A. Ocular fluid and heparin also inhibited the migration and tube formation by these cells. The binding of VEGF-A and HUVECs was reduced under a high concentration of heparin or ocular fluid compared to lower concentrations of heparin. In vitro assays demonstrated that the ocular fluid or soluble heparan sulfate or heparin inhibited the binding of VEGF-A and immobilized heparin or VEGF receptor 2 but not VEGF receptor 1. The recognition that the high concentration of soluble heparan sulfate in the ocular fluid allows it to serve as an endogenous inhibitor of aberrant retinal vascular growth provides a platform for modulating heparan sulfate/heparin levels to regulate angiogenesis.     

Fibrillin-1 interactions with heparin. Implications for microfibril and elastic fiber assembly

Fibrillin-1 assembly into microfibrils and elastic fiber formation involves interactions with glycosaminoglycans. We have used BIAcore technology to investigate fibrillin-1 interactions with heparin and with heparin saccharides that are analogous to S-domains of heparan sulfate. We have identified four high affinity heparin-binding sites on fibrillin-1, localized three of these sites, and defined their binding kinetics. Heparin binding to the fibrillin-1 N terminus has particularly rapid kinetics. Hyaluronan and chondroitin sulfate did not interact significantly with fibrillin-1. Heparin saccharides with more than 12 monosaccharide units bound strongly to all four fibrillin-1 sites. Heparin did not inhibit fibrillin-1 N- and C-terminal interactions or RGD-dependent cell attachment, but heparin and MAGP-1 competed for binding to the fibrillin-1 N terminus, and heparin and tropoelastin competed for binding to a central fibrillin-1 sequence. By regulating these key interactions, heparin can profoundly influence microfibril and elastic fiber assembly.