Role of insulin in antigen-induced airway eosinophilia and neuronal M2 muscarinic receptor dysfunction

Maternal high-fat diet increases airway sensory innervation and reflex bronchoconstriction in adult offspring

Children born to obese mothers are prone to develop asthma and airway hyperresponsiveness, but the mechanisms behind this are unclear. Here we developed a mouse model of maternal diet-induced obesity that recapitulates metabolic abnormalities seen in humans born to obese mothers. Offspring of dams fed a high-fat diet (HFD) showed increased adiposity, hyperinsulinemia, and insulin resistance at 16 wk of age despite being fed only a regular diet (RD). Bronchoconstriction induced by inhaled 5-hydroxytriptamine was also significantly increased in offspring of HFD-fed versus RD-fed dams. Increased bronchoconstriction was blocked by vagotomy, indicating this reflex was mediated by airway nerves. Three-dimensional (3-D) confocal imaging of tracheas collected from 16-wk-old offspring showed that both epithelial sensory innervation and substance P expression were increased in the offspring of HFD-fed dams compared with offspring of RD-fed dams. For the first time, we show that maternal high-fat diet increases airway sensory innervation in offspring, leading to reflex airway hyperresponsiveness.NEW & NOTEWORTHY Our study reveals a novel potential mechanism, by which maternal high-fat diet increases the risk and severity of asthma in offspring. We found that exposure to maternal high-fat diet in mice leads to hyperinnervation of airway sensory nerves and increased reflex bronchoconstriction in offspring fed a regular diet only. These findings have important clinical implications and provide new insights into the pathophysiology of asthma, highlighting the need for preventive strategies in this patient population.

DJ-1 governs airway progenitor cell/eosinophil interactions to promote allergic inflammation

BACKGROUND

DJ-1 is an antioxidant protein known to regulate mast cell mediated allergic response, but its role in airway eosinophilic interactions and allergic inflammation is not known.

OBJECTIVE

The aim of this study was to investigate the role of DJ-1 in airway eosinophilic inflammation in vitro and in vivo.

METHODS

Ovalbumin-induced airway allergic inflammation was established in mice. ELISA was adopted to analyze DJ-1 and cytokine levels in mouse bronchoalveolar lavage fluid. Transcriptional profiling of mouse lung tissues was conducted by single-cell RNA sequencing technology. The role of DJ-1 in the differentiation of airway progenitor cells into goblet cells was examined by organoid cultures, immunofluorescence staining, quantitative PCR, and cell transplantation in normal, DJ-1 knockout (KO), or conditional DJ-1 KO mice.

RESULTS

We observed that DJ-1 was increased in the lung tissues of ovalbumin-sensitized and challenged mice. DJ-1 KO mice exhibited reduced airway eosinophil infiltration and goblet cell differentiation. Mechanistically, we discovered that eosinophil-club cell interactions are reduced in the absence of DJ-1. Organoid cultures indicated that eosinophils impair the proliferative potential of club cells. Intratracheal transplantation of DJ-1-deficient eosinophils suppresses airway goblet cell differentiation. Loss of DJ-1 inhibits the metabolism of arachidonic acid into cysteinyl leukotrienes in eosinophils while these secreted metabolites promote airway goblet cell fate in organoid cultures and in vivo.

CONCLUSION

DJ-1-mediated interactions between airway epithelial progenitor cells and immune cells are essential in controlling airway goblet cell metaplasia and eosinophilia. Blockade of the DJ-1 pathway is protective against airway allergic inflammation.

Effect of Mori ramulus on the postprandial blood glucose levels and inflammatory responses of healthy subjects subjected to an oral high-fat/sucrose challenge: A double-blind, randomized, crossover clinical trial

Blood glucose is inadequately controlled in diabetes mellitus, causing various inflammation-related complications. This study aimed to investigate responses to an oral sucrose/lipid challenge in the context of glucose metabolism after consumption of Mori ramulus (MR) extract. In this study on healthy subjects, the optimal dose and safety of MR were confirmed in a preliminary pilot trial (n = 24), meanwhile, blood glucose, insulin, and inflammatory marker levels were detected via an oral sucrose/lipid tolerance test in the main trial (n = 36). In the main study, the blood glucose response was significantly decreased after 240 min in the MR group. Compared to the placebo group, the treatment group exhibited plasma insulin levels that were significantly increased at 120 min and decreased at 240 min. In conclusion, a single MR extract dose protects against inflammation induced by high-fat/sugar to maintain normal insulin secretion and thus helps to maintain postprandial blood glucose levels via an inflammatory mechanism.

Metformin prevents airway hyperreactivity in rats with dietary obesity

Increased insulin is associated with obesity-related airway hyperreactivity and asthma. We tested whether the use of metformin, an anti-diabetic drug used to reduce insulin resistance, can reduce circulating insulin, thereby preventing airway hyperreactivity in rats with dietary obesity. Male and female rats were fed a high- or low-fat diet for 5 weeks. Some male rats were simultaneously treated with metformin (100 mg/kg, p.o.). In separate experiments, after 5 weeks of a high-fat diet, some rats were switched to a low-fat diet, while others continued a high-fat diet for an additional 5 weeks. Bronchoconstriction and bradycardia in response to bilateral electrical vagus nerve stimulation or to inhaled methacholine were measured in anesthetized and vagotomized rats. Body weight, body fat, caloric intake, fasting glucose and insulin were measured. Vagally-induced bronchoconstriction was potentiated only in male rats on a high-fat diet. Males gained more body weight, body fat, and had increased levels of fasting insulin, compared to females. Metformin prevented development of vagally-induced airway hyperreactivity in male rats on high-fat diet, in addition to inhibiting weight gain, fat gain and increased insulin. In contrast, switching rats to a low-fat diet for 5 weeks reduced body weight and body fat, it did not reverse fasting glucose, fasting insulin or potentiation of vagally-induced airway hyperreactivity. These data suggest that medications that target insulin may be effective treatment for obesity-related asthma.

Preserving Airway Smooth Muscle Contraction in Precision-Cut Lung Slices

Precision-cut lung slices (PCLS) are ideal for measuring small airway contraction. However, these measurements are currently limited to acute exposure scenarios that typically last a few minutes to a few hours. Using an insulin-supplemented culture medium, we prolong the small airway contractility in mouse PCLS for up to two weeks. Compared to conventional culture medium, insulin-supplemented culture medium provides no additional benefit in preserving cellular viability or airway structure. However, it protects the airway smooth muscle (ASM) against a loss of smooth muscle myosin heavy chain (SMMHC) expression. We elucidate the significance of this new culture medium for chronic disease modeling of IL-13-induced airway hyper-responsiveness.

Lung volume dependence of respiratory function in rodent models of diabetes mellitus

Background

Diabetes mellitus causes the deterioration of smooth muscle cells and interstitial matrix proteins, including collagen. Collagen and smooth muscle cells are abundant in the lungs, but the effect of diabetes on airway function and viscoelastic respiratory tissue mechanics has not been characterized. This study investigated the impact of diabetes on respiratory function, bronchial responsiveness, and gas exchange parameters.

Methods

Rats were allocated randomly to three groups: a model of type 1 diabetes that received a high dose of streptozotocin (DM1, n = 13); a model of type 2 diabetes that received a low dose of streptozotocin with a high-fat diet (DM2, n = 14); and a control group with no treatment (C, n = 14). Forced oscillations were applied to assess airway resistance (Raw), respiratory tissue damping (G), and elastance (H). The arterial partial pressure of oxygen to the inspired oxygen fraction (PaO₂/FiO₂) and intrapulmonary shunt fraction (Qs/Qt) were determined from blood gas samples at positive end-expiratory pressures (PEEPs) of 0, 3, and 6 cmH₂O. Lung responsiveness to methacholine was also assessed. Collagen fibers in lung tissue were quantified by histology.

Results

The rats in groups DM1 and DM2 exhibited elevated Raw, G, H, and Qs/Qt, compromised PaO₂/FiO₂, and diminished airway responsiveness. The severity of adverse tissue mechanical change correlated with excessive lung collagen expression. Increased PEEP normalized the respiratory mechanics, but the gas exchange abnormalities remained.

Conclusions

These findings indicate that diabetes reduces airway and lung tissue viscoelasticity, resulting in alveolar collapsibility that can be compensated by increasing PEEP. Diabetes also induces persistent alveolo-capillary dysfunction and abnormal adaptation ability of the airways to exogenous constrictor stimuli.

Diabetic lung disease: fact or fiction?

Diabetes mellitus is a chronic, progressive, incompletely understood metabolic disorder whose prevalence has been increasing steadily worldwide. Even though little attention has been paid to lung disorders in the context of diabetes, its prevalence has recently been challenged by newer studies of disease development. In this review, we summarize and discuss the role of diabetes mellitus involved in the progression of pulmonary diseases, with the main focus on pulmonary fibrosis, which represents a chronic and progressive disease with high mortality and limited therapeutic options.

Diabetes and Lung Disease: A Neglected Relationship

BACKGROUND

Diabetes mellitus is a systemic disorder associated with inflammation and oxidative stress which may target many organs such as the kidney, retina, and the vascular system. The pathophysiology, mechanisms, and consequences of diabetes on these organs have been studied widely. However, no work has been done on the concept of the lung as a target organ for diabetes and its implications for lung diseases.

AIM

In this review, we aimed to investigate the effects of diabetes and hypoglycemic agent on lung diseases, including asthma, chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis, pulmonary hypertension, and lung cancer. We also reviewed the potential mechanisms by which these effects may affect lung disease patients.

RESULTS

Our results suggest that diabetes can affect the severity and clinical course of several lung diseases.

CONCLUSIONS

Although the diabetes-lung association is epidemiologically and clinically well-established, especially in asthma, the underlying mechanism and pathophysiology are not been fully understood. Several mechanisms have been suggested, mainly associated with the pro-inflammatory and proliferative properties of diabetes, but also in relation to micro- and macrovascular effects of diabetes on the pulmonary vasculature. Also, hypoglycemic drugs may influence lung diseases in different ways. For example, metformin was considered a potential therapeutic agent in lung diseases, while insulin was shown to exacerbate lung diseases; this suggests that their effects extend beyond their hypoglycemic properties.

Deterioration of epithelium mediated mechanisms in diabetic-antigen sensitized airways of guinea pigs

BACKGROUND

The onset of diabetes causes disruption of respiratory epithelial mediators. The present study investigates whether diabetes modifies the epithelium mediated bronchial responses in hyper-reactive airway smooth muscle (ASM) primarily through nitric oxide (NO), cyclooxygenase (COX), and epithelium derived hyperpolarizing factor (EpDHF) pathways.

METHODS

Experimental model of guinea pigs having hyper-reactive airways with or without diabetes were developed. The responses of tracheal rings to cumulative concentrations of acetylcholine (ACh) and isoproterenol (IP) in the presence and absence of epithelium and before and after incubation with NO, K⁺_ATP and COX inhibitors, N-(ω)-Nitro-L-arginine methyl ester (L-NAME; 100 μM), glybenclamide (10 μM) and indomethacin (100 μM) were assessed.

RESULTS

In diabetic guinea pigs with hyper-reactive airways, a decrease in ACh induced bronchoconstriction was observed after epithelium removal and after incubation with L-NAME/indomethacin, suggesting damage to NO/COX pathways. Hyper-reactivity did not alter the response of trachea to ACh but affected the response to IP which was further reduced in hyper-reactive animals with diabetes. The ASM response to IP after glybenclamide treatment did not alter in hyper-reactive guinea pigs and diabetic guinea pigs with hyper-reactive airways, suggesting damage to the EpDHF pathway. Treatment with indomethacin reduced IP response in the hyper-reactive model, and did not produce any change in diabetic model with hyper-reactive airways, indicating further disruption of the COX pathway.

CONCLUSION

EpDHF pathway is damaged in hyper-reactive guinea pigs and in diabetic guinea pigs with hyper-reactive airways. Diabetes further aggravates the NO and COX mediated pathways in diabetic guinea pigs with hyper-reactive airways.

Obesity and asthma: beyond T(H)2 inflammation

Obesity is a major risk factor for asthma. Likewise, obesity is known to increase disease severity in asthmatic subjects and also to impair the efficacy of first-line treatment medications for asthma, worsening asthma control in obese patients. This concept is in agreement with the current understanding that some asthma phenotypes are not accompanied by detectable inflammation, and may not be ameliorated by classical anti-inflammatory therapy. There are growing evidences suggesting that the obesity-related asthma phenotype does not necessarily involve the classical T(H)2-dependent inflammatory process. Hormones involved in glucose homeostasis and in the pathogeneses of obesity likely directly or indirectly link obesity and asthma through inflammatory and non-inflammatory pathways. Furthermore, the endocrine regulation of the airway-related pre-ganglionic nerves likely contributes to airway hyperreactivity (AHR) in obese states. In this review, we focused our efforts on understanding the mechanism underlying obesity-related asthma by exploring the T(H)2-independent mechanisms leading to this disease.

A comparative study of the beneficial effects of ipratropium and beclomethasone against insulin-induced tracheal tissue contraction in a guinea pig model

OBJECTIVE

To evaluate the acute effects of insulin on airway reactivity and the protective effects of beclomethasone and ipratropium against insulin-induced airway hyperresponsiveness on isolated tracheal smooth muscle in a guinea pig model.

MATERIALS AND METHODS

The trachea of each guinea pig was excised; one end of the tracheal strip was attached to the hook of the oxygen tube of a tissue bath and the other end was connected to a research-grade isometric force displacement transducer. The effects of varying concentrations of insulin (10(-7) to 10(-3)M) and insulin pretreated with a fixed concentration of beclomethasone (10(-6)M) and ipratropium (10(-6)M) on the isolated tracheal tissue were studied by constructing cumulative concentration-response curves. Changes in tracheal smooth muscle contractions were recorded on a 4-channel oscillograph.

RESULTS

The means ± standard error of the mean of the maximum amplitude of contraction with increasing concentrations of insulin and of insulin pretreated with fixed concentrations of beclomethasone and ipratropium were 35 ± 1.13, 22 ± 1.15 and 27.8 ± 1.27 mm, respectively.

CONCLUSION

The data showed that beclomethasone inhibited the contractile response of insulin to a greater extent than ipratropium. Thus we suggest that inhalational insulin pretreated with beclomethasone may be more efficacious than with ipratropium for the amelioration of potential respiratory adverse effects such as bronchoconstriction.

Hyperinsulinemia potentiates airway responsiveness to parasympathetic nerve stimulation in obese rats

Obesity is a substantial risk factor for developing asthma, but the molecular mechanisms underlying this relationship are unclear. We tested the role of insulin in airway responsiveness to nerve stimulation using rats genetically prone or resistant to diet-induced obesity. Airway response to vagus nerve stimulation and airway M2 and M3 muscarinic receptor function were measured in obese-prone and -resistant rats with high or low circulating insulin. The effects of insulin on nerve-mediated human airway smooth muscle contraction and human M2 muscarinic receptor function were tested in vitro. Our data show that increased vagally mediated bronchoconstriction in obesity is associated with hyperinsulinemia and loss of inhibitory M2 muscarinic receptor function on parasympathetic nerves. Obesity did not induce airway inflammation or increase airway wall thickness. Smooth muscle contraction to acetylcholine was not increased, indicating that hyperresponsiveness is mediated at the level of airway nerves. Reducing serum insulin with streptozotocin protected neuronal M2 receptor function and prevented airway hyperresponsiveness to vagus nerve stimulation in obese rats. Replacing insulin restored dysfunction of neuronal M2 receptors and airway hyperresponsiveness to vagus nerve stimulation in streptozotocin-treated obese rats. Treatment with insulin caused loss of M2 receptor function, resulting in airway hyperresponsiveness to vagus nerve stimulation in obese-resistant rats, and inhibited human neuronal M2 receptor function in vitro. This study shows that it is not obesity per se but hyperinsulinemia accompanying obesity that potentiates vagally induced bronchoconstriction by inhibiting neuronal M2 muscarinic receptors and increasing acetylcholine release from airway parasympathetic nerves.

Endocrine regulation of airway contractility is overlooked

Asthma is a prevalent respiratory disorder triggered by a variety of inhaled environmental factors, such as allergens, viruses, and pollutants. Asthma is characterized by an elevated activation of the smooth muscle surrounding the airways, as well as a propensity of the airways to narrow excessively in response to a spasmogen (i.e. contractile agonist), a feature called airway hyperresponsiveness. The level of airway smooth muscle (ASM) activation is putatively controlled by mediators released in its vicinity. In asthma, many mediators that affect ASM contractility originate from inflammatory cells that are mobilized into the airways, such as eosinophils. However, mounting evidence indicates that mediators released by remote organs can also influence the level of activation of ASM, as well as its level of responsiveness to spasmogens and relaxant agonists. These remote mediators are transported through circulating blood to act either directly on ASM or indirectly via the nervous system by tuning the level of cholinergic activation of ASM. Indeed, mediators generated from diverse organs, including the adrenals, pancreas, adipose tissue, gonads, heart, intestines, and stomach, affect the contractility of ASM. Together, these results suggest that, apart from a paracrine mode of regulation, ASM is subjected to an endocrine mode of regulation. The results also imply that defects in organs other than the lungs can contribute to asthma symptoms and severity. In this review, I suggest that the endocrine mode of regulation of ASM contractility is overlooked.

May T1 diabetes mellitus protect from asthma?

BACKGROUND

Type 1 diabetes mellitus (T1DM) may be associated with allergy. It was previously reported that >20% of children with T1DM had allergic rhinitis (AR), but none was asthmatic. This finding was surprising as allergic rhinitis is frequently associated with asthma and asthma prevalence is about 10% of the general paediatric population. Thus, it was hypothesized that T1DM could protect from asthma.

OBJECTIVES

The aim of this preliminary study was to evaluate the pulmonary function and the response to bronchodilation testing in children, suffering from T1DM with associated AR, comparing them with a control group of children with AR alone.

METHODS

Twenty children with T1DM and AR were compared with 59 children with AR alone; spirometry and bronchodilation testing were performed in all patients.

RESULTS

There were no statistically significant differences in both "at baseline" and after bronchodilation testing about FVC, FEV1, and FEF25-75 values. However, changes in "post-bronchodilator" values of FEF25-75 (ΔFEF25-75) were significantly higher in children with AR alone than in children with T1DM and AR (p=0.04).

CONCLUSIONS

This preliminary study could sustain the hypothesis that T1DM in children suffering also from AR might exert a protective effect of preventing the possible evolution in asthma.

Eosinophil inversely associates with type 2 diabetes and insulin resistance in Chinese adults

CONTEXT

Limited population-based study focused on relationship between eosinophil and type 2 diabetes (T2D).

OBJECTIVES

We aimed to evaluate the relationship between peripheral eosinophil percentage and glucose metabolism and insulin resistance in a large sample size of Chinese population aged 40 and older.

DESIGN AND METHODS

A cross-sectional study was performed among 9,111 Chinese adults including 3,561 men and 5,550 women. The glucose metabolism status was confirmed by 75-g oral glucose tolerance test. Homeostasis model assessment of insulin resistance index and serum insulin levels were used to evaluate insulin resistance. Homeostasis model assessment-B was used to evaluate β cell function.

RESULTS

The average age of participants was 58.5 years. The prevalence of T2D decreased across the tertiles of eosinophil percentage (21.3%, 18.2% and 16.9%, P<0.0001). Each one tertile increase of eosinophil percentage inversely associated with risk of T2D when referred not only to normal glucose tolerance (NGT) (odds ratio (OR) 0.81, 95% CI 0.76-0.87, P< 0.0001), but also to impaired glucose regulation (OR 0.89, 95% CI 0.83-0.97, P = 0.006), respectively, after adjustment for the confounding factors. Compared with the first tertile, the third tertile of eosinophil percentage associated with a 23% decrease of insulin resistance in NGT participants after full adjustments (P = 0.005). Each 1-standard deviation of increment of eosinophil percentage associated with a 37% decrease of insulin resistance (P = 0.005).

CONCLUSIONS

Higher peripheral eosinophil percentage was associated with decreased risk of T2D. The inverse relation to insulin resistance was detected in NGT participants.

Obesity and asthma: a coincidence or a causal relationship? A systematic review

BACKGROUND AND AIM

Epidemiological data has established increasing adiposity as a risk factor for incident asthma. However, the mechanisms underlying the association between obesity and asthma are incompletely understood. In the present paper, we review current knowledge of possible mechanisms mediating the observed association between obesity and asthma.

METHODS

Systematic literature review.

RESULTS

Obesity and asthma share some etiological factors, such as a common genetic predisposition and effects of in utero conditions, and may also have common predisposing factors such as physical activity and diet. Obesity results in important changes in the mechanical properties of the respiratory system which could explain the occurrence of asthma. However, there are also plausible biological mechanisms whereby obesity could be expected to either cause or worsen asthma. These include co-morbidities such as gastro-oesophageal reflux, complications from sleep-disordered breathing, breathing at low lung volumes, chronic systemic inflammation, and endocrine factors, including adipokines and reproductive hormones. Obesity related asthma is in general not associated with eosinophilic airway inflammation, and adipokines are likely to play important roles in the inflammatory pathogenesis of asthma in obese individuals.

CONCLUSION

The association between obesity and asthma is not straightforward, and further knowledge is clearly needed, as understanding the underlying mechanisms may lead to new therapeutic options for this high-risk part of the asthma population.

Muscarinic receptor antagonists: effects on pulmonary function

In healthy lungs, muscarinic receptors control smooth muscle tone, mucus secretion, vasodilation, and inflammation. In chronic obstructive pulmonary disease (COPD) and asthma, cholinergic mechanisms contribute to increased bronchoconstriction and mucus secretion that limit airflow. This chapter reviews neuronal and nonneuronal sources of acetylcholine in the lung and the expression and role of M₁, M₂, and M₃ muscarinic receptor subtypes in lung physiology. It also discusses the evidence for and against the role of parasympathetic nerves in asthma, and the current use and therapeutic potential of muscarinic receptor antagonists in COPD and asthma.

Airway inflammatory events in diabetic-antigen sensitized guinea pigs

Experimental evidence indicates that the relative lack of insulin in an organism results in an overall reduction in inflammatory reactions. This study was planned to determine the inflammatory events in antigen sensitized diabetic guinea pigs. Twenty-five male guinea pigs were categorized into five groups of five each as follows: diabetic, antigen sensitized, antigen sensitized diabetic, insulin-treated antigen sensitized diabetic and control animals. Induction of experimental diabetes and antigen sensitization was performed by injection of streptozotocin and ovalbumin, respectively. Animals were killed by exsanguination and bronchoalveolar lavage was performed. Bronchoalveolar lavage fluid cellular and protein contents were determined. Airway responsiveness to acetylcholine was assessed using isolated tracheal triple-ring. Histopathological examinations were performed on the lungs. Decreases in the airway reactivity in diabetic and antigen sensitized diabetic animals were found compared with antigen sensitized animals. Experimental diabetes also decreased antigen-induced protein leakage into the airspace as well as the accumulation of inflammatory cells (eosinophils, neutrophils, lymphocytes and macrophages) in bronchoalveolar lavage fluid of antigen sensitized animals. Insulin treatment prevented these decreases in protein content and inflammatory cells infiltration in bronchoalveolar lavage fluid observed in the antigen sensitized guinea pigs with diabetes. Histopathological results showed that coinduction of experimental diabetes significantly reduces the number of eosinophils in the lungs of antigen sensitized animals. Again, treatment with insulin increased the number of eosinophils in the antigen sensitized diabetic animals. Experimental diabetes causes were found to decrease the airway reactivity and inflammatory responsiveness induced by antigen sensitization due to a reduction in the insulin levels.

Association analysis of RGS7BP gene polymorphisms with aspirin intolerance in asthmatic patients

BACKGROUND

Signal-regulated palmitoylation of RGS7BP(regulator of G-protein-signaling 7-binding protein) initiates the activation of G-protein-coupled receptors (GPCRs), including muscarinic receptors, which contribute to the development of asthma and its subphenotypes.

OBJECTIVE

To determine the association of RGS7BP gene polymorphisms with the development of aspirin-exacerbated respiratory disease (AERD).

METHODS

We evaluated the association of RGS7BP gene polymorphisms with response to oral aspirin challenge and with responsiveness to methacholine challenge. RGS7BP messenger RNA splice variants in peripheral blood platelets from patients with different single-nucleotide polymorphisms were analyzed by reverse-transcription polymerase chain reaction.

RESULTS

Logistic regression analysis of RGS7BP gene polymorphisms in patients with AERD (n = 102) and aspirin-tolerant asthma (n = 429) revealed that a haplotype of block 3 consisting of rare alleles +98092 C>G, +98853 C>T, and +104450 T>G of the RGS7BP gene was associated with AERD. Multiple linear regression analysis showed that asthmatic patients carrying ht2/ht2 in block 3 were more responsive to aspirin challenge than those not carrying ht2 (P = .008 in a codominant model). The log-transformed provocation concentration that caused a decrease in forced expiratory volume in 1 second of 20% for methacholine was significantly dependent on the BL3-ht2 haplotype. No significant differences in platelet expression of different RGS7BP messenger RNA splice variants were detected between those with and without the BL3-ht2 haplotype.

CONCLUSION

BL3-ht2 of RGS7BP may be an important genetic variant associated with AERD. The haplotype of block 3 may play a protective role against aspirin hypersensitivity in asthma, perhaps by altering the responsiveness of muscarinic receptors.

Three days after a single exposure to ozone, the mechanism of airway hyperreactivity is dependent on substance P and nerve growth factor

Ozone causes persistent airway hyperreactivity in humans and animals. One day after ozone exposure, airway hyperreactivity is mediated by release of eosinophil major basic protein that inhibits neuronal M(2) muscarinic receptors, resulting in increased acetylcholine release and increased smooth muscle contraction in guinea pigs. Three days after ozone, IL-1β, not eosinophils, mediates ozone-induced airway hyperreactivity, but the mechanism at this time point is largely unknown. IL-1β increases NGF and the tachykinin substance P, both of which are involved in neural plasticity. These experiments were designed to test whether there is a role for NGF and tachykinins in sustained airway hyperreactivity following a single ozone exposure. Guinea pigs were exposed to filtered air or ozone (2 parts per million, 4 h). In anesthetized and vagotomized animals, ozone potentiated vagally mediated airway hyperreactivity 24 h later, an effect that was sustained over 3 days. Pretreatment with antibody to NGF completely prevented ozone-induced airway hyperreactivity 3 days, but not 1 day, after ozone and significantly reduced the number of substance P-positive airway nerve bundles. Three days after ozone, NK(1) and NK(2) receptor antagonists also blocked this sustained hyperreactivity. Although the effect of inhibiting NK(2) receptors was independent of ozone, the NK(1) receptor antagonist selectively blocked vagal hyperreactivity 3 days after ozone. These data confirm mechanisms of ozone-induced airway hyperreactivity change over time and demonstrate 3 days after ozone that there is an NGF-mediated role for substance P, or another NK(1) receptor agonist, that enhances acetylcholine release and was not present 1 day after ozone.

Insulin modulates cytokine release and selectin expression in the early phase of allergic airway inflammation in diabetic rats

BACKGROUND

Clinical and experimental data suggest that the inflammatory response is impaired in diabetics and can be modulated by insulin. The present study was undertaken to investigate the role of insulin on the early phase of allergic airway inflammation.

METHODS

Diabetic male Wistar rats (alloxan, 42 mg/Kg, i.v., 10 days) and controls were sensitized by s.c. injection of ovalbumin (OA) in aluminium hydroxide 14 days before OA (1 mg/0.4 mL) or saline intratracheal challenge. The following analyses were performed 6 hours thereafter: a) quantification of interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha and cytokine-induced neutrophil chemoattractant (CINC)-1 in the bronchoalveolar lavage fluid (BALF) by Enzyme-Linked Immunosorbent Assay, b) expression of E- and P- selectins on lung vessels by immunohistochemistry, and c) inflammatory cell infiltration into the airways and lung parenchyma. NPH insulin (4 IU, s.c.) was given i.v. 2 hours before antigen challenge.

RESULTS

Diabetic rats exhibited significant reduction in the BALF concentrations of IL-1beta (30%) and TNF-alpha (45%), and in the lung expression of P-selectin (30%) compared to non-diabetic animals. This was accompanied by reduced number of neutrophils into the airways and around bronchi and blood vessels. There were no differences in the CINC-1 levels in BALF, and E-selectin expression. Treatment of diabetic rats with NPH insulin, 2 hours before antigen challenge, restored the reduced levels of IL-1beta, TNF-alpha and P-selectin, and neutrophil migration.

CONCLUSION

Data presented suggest that insulin modulates the production/release of TNF-alpha and IL-1beta, the expression of P- and E-selectin, and the associated neutrophil migration into the lungs during the early phase of the allergic inflammatory reaction.

Recent findings on the pathogenesis of bronchial asthma. Part II. The role of hormonal predisposition, environmental influences and conditioning leading to bronchial asthma

In this second part of the review on the pathogenesis of asthma the hormonal factors and adverse external events are shortly reviewed which skew the balance of Th1 vs. Th2 CD4+ lymphocytes towards the latter ones and this way increase the probability of atopic diseases. Among other the role of transplacental priming, insulin, insulin-like and other growth factors, lack of the usual microbial infections in the early childhood (the so-called hygiene hypothesis), gender, diminished testosterone production, gastroesophageal reflux, adverse effects during pregnancy are discussed. A separate chapter deals with the role of central nervous system in the etiology and finally the most common allergizing and airway tissue damaging agents are listed in tabulated form.

Effect of insulin on airway responsiveness in patients with type 2 diabetes mellitus: a cohort study

BACKGROUND

The correlation between low insulin levels and a decreased sensitivity of the muscarinic receptor has been shown on induced-diabetes animal models. We designed a cohort study with the aim of evaluating the effects of insulin therapy on airway responsiveness (AR) in human patients with type 2 diabetes mellitus.

METHODS

We enrolled 92 patients with type 2 diabetes who had switched from oral anti-diabetic therapy to treatment by insulin subcutaneous injection. Patients were administered the methacholine challenge test (MCT) at time 0 (pre-insulin therapy) and at intervals of 15, 30, 90, 180, and 360 days after insulin treatment. The decline of forced expiratory volume in 1 second (FEV(1))% from baseline (Delta FEV(1)) in response to inhaled methacholine (MCH) was determined to assess airway hyper-responsiveness (AHR).

RESULTS

A total of 81 patients (18 women and 63 men) completed the study. Their mean age was 58 +/- 7 years and the mean duration of disease was 13.5 +/- 7.7 years. The mean decrease of FEV(1) at pre-insulin assessment was 2.96 +/- 2.6%. Compared with the pre-insulin value, a significant increase of Delta FEV(1) was observed at 15, 30, and 90 days after treatment (6.25%, CI 95% 5.4 to 7.2, p = 0.0005; 7.64%, CI 95% 6.6 to 8.1, p < 0.001; 6.45%, CI 95% 5.5 to 7.3, p = 0.0004, respectively), while after 180 and 360 days AR was similar to pre-insulin values (Delta FEV(1), 3.62%, CI 95% 2.7 to 3.5 and 3.11%, CI 95% 7.9 to 9.3, respectively).

CONCLUSIONS

The finding of an increased AR in patients with type 2 diabetes during the first 3 months of insulin therapy may underline the importance of monitoring pulmonary function and respiratory symptoms in patients switching from oral anti-diabetic drugs to insulin therapy, especially in the subset of individuals with respiratory disorders.

Discrepancy between sensitization to inhaled allergens and respiratory symptoms in pediatric patients with type 1 diabetes mellitus

According to the 'Th(1)/Th(2) paradigm', children with type 1 diabetes mellitus (T1DM) should have a lower risk of developing allergic sensitization and, because of the involvement of insulin in modulating airway inflammation, different frequency or severity in allergy-related respiratory manifestations. This article aims at evaluating the frequency and type of allergic sensitization and its respiratory manifestation, asthma and/or rhinitis, in a group of pediatric patients with T1DM. Patients (112) with T1DM, 7.8-16.9 yr of age (63 males and 49 females) were evaluated. Skin prick test (SPT) reactivity to the most common classes of aeroallergens were performed and compared with data obtained in 709 school-aged children. The frequency of sensitization was not different in the T1DM and in the control subjects (43.7% and 40.8%, respectively; p = 0.55), with similar proportions of individuals sensitized to one allergen (32.7% and 38.1%, respectively; p = 0.47). In both groups, sensitization to house dust mite allergens was the most frequently detected (69.4% and 65.4%, respectively; p = 0.59), with a higher proportions of individuals sensitized to Graminae (+Cynodon dactylon; p < 0.0001) and a lower, but weakly significant, proportion sensitized to Parietaria (p = 0.03) in the T1DM group, as compared with controls. No differences were found between T1DM and control groups in the proportion of individuals reporting rhinitis (26.8% and 29.2%; p = 0.60). However, comparing separately sensitized and non-sensitized subjects, a lower proportion of rhinitis subjects was detected in the non-sensitized T1DM patients, when compared with the non-sensitized control subjects (p = 0.01). In addition, no differences were detected between T1DM and control groups in frequency of symptoms related to 'lifetime asthma', i.e., asthma episodes during life (14.3% and 16.5%, respectively: p = 0.55), also when sensitized and non-sensitized subjects were evaluated separately (p = 0.12 and p = 1.00, respectively). However, no T1DM patient had 'actual asthma', i.e., asthma episodes in the last year, vs. 5.8% of the individuals in the control group (p = 0.009), the difference being mostly ascribed to sensitized subjects (p = 0.012). Finally, out of the 16 T1DM patients with 'lifetime asthma', 15 had mild intermittent disease and only one mild persistent disease. T1DM does not seem to play a downregulating role on the development of allergic sensitization to aeroallergens, but may lower the frequency or the severity of its clinical manifestations at respiratory level.

IL-1 receptors mediate persistent, but not acute, airway hyperreactivity to ozone in guinea pigs

Ozone exposure in the lab and environment causes airway hyperreactivity lasting at least 3 days in humans and animals. In guinea pigs 1 day after ozone exposure, airway hyperreactivity is mediated by eosinophils that block neuronal M(2) muscarinic receptor function, thus increasing acetylcholine release from airway parasympathetic nerves. However, mechanisms of ozone-induced airway hyperreactivity change over time, so that depleting eosinophils 3 days after ozone makes airway hyperreactivity worse rather than better. Ozone exposure increases IL-1beta in bone marrow, which may contribute to acute and chronic airway hyperreactivity. To test whether IL-1beta mediates ozone-induced airway hyperreactivity 1 and 3 days after ozone exposure, guinea pigs were pretreated with an IL-1 receptor antagonist (anakinra, 30 mg/kg, intraperitoneally) 30 minutes before exposure to filtered air or to ozone (2 ppm, 4 h). One or three days after exposure, airway reactivity was measured in anesthetized guinea pigs. The IL-1 receptor antagonist prevented ozone-induced airway hyperreactivity 3 days, but not 1 day, after ozone exposure. Ozone-induced airway hyperreactivity was vagally mediated, since bronchoconstriction induced by intravenous acetylcholine was not changed by ozone. The IL-1 receptor antagonist selectively prevented ozone-induced reduction of eosinophils around nerves and prevented ozone-induced deposition of extracellular eosinophil major basic protein in airways. These data demonstrate that IL-1 mediates ozone-induced airway hyperreactivity at 3 days, but not 1 day, after ozone exposure. Furthermore, preventing hyperreactivity was accompanied by decreased eosinophil major basic protein deposition within the lung, suggesting that IL-1 affects eosinophil activation 3 days after ozone exposure.

Neutrophil function and metabolism in individuals with diabetes mellitus

Neutrophils act as first-line-of-defense cells and the reduction of their functional activity contributes to the high susceptibility to and severity of infections in diabetes mellitus. Clinical investigations in diabetic patients and experimental studies in diabetic rats and mice clearly demonstrated consistent defects of neutrophil chemotactic, phagocytic and microbicidal activities. Other alterations that have been reported to occur during inflammation in diabetes mellitus include: decreased microvascular responses to inflammatory mediators such as histamine and bradykinin, reduced protein leakage and edema formation, reduced mast cell degranulation, impairment of neutrophil adhesion to the endothelium and migration to the site of inflammation, production of reactive oxygen species and reduced release of cytokines and prostaglandin by neutrophils, increased leukocyte apoptosis, and reduction in lymph node retention capacity. Since neutrophil function requires energy, metabolic changes (i.e., glycolytic and glutaminolytic pathways) may be involved in the reduction of neutrophil function observed in diabetic states. Metabolic routes by which hyperglycemia is linked to neutrophil dysfunction include the advanced protein glycosylation reaction, the polyol pathway, oxygen-free radical formation, the nitric oxide-cyclic guanosine-3'-5'monophosphate pathway, and the glycolytic and glutaminolytic pathways. Lowering of blood glucose levels by insulin treatment of diabetic patients or experimental animals has been reported to have significant correlation with improvement of neutrophil functional activity. Therefore, changes might be primarily linked to a continuing insulin deficiency or to secondary hyperglycemia occurring in the diabetic individual. Accordingly, effective control with insulin treatment is likely to be relevant during infection in diabetic patients.

Insulin increases the expression of contractile phenotypic markers in airway smooth muscle

We have previously demonstrated that long-term exposure of bovine tracheal smooth muscle (BTSM) strips to insulin induces a functional hypercontractile phenotype. To elucidate molecular mechanisms by which insulin might induce maturation of contractile phenotype airway smooth muscle (ASM) cells, we investigated effects of insulin stimulation in serum-free primary BTSM cell cultures on protein accumulation of specific contractile phenotypic markers and on the abundance and stability of mRNA encoding these markers. In addition, we used microscopy to assess insulin effects on ASM cell morphology, phenotype, and induction of phosphatidylinositol (PI) 3-kinase signaling. It was demonstrated that protein and mRNA levels of smooth muscle-specific contractile phenotypic markers, including sm-myosin, are significantly increased after stimulation of cultured BTSM cells with insulin (1 microM) for 8 days compared with cells treated with serum-free media, whereas mRNA stability was unaffected. In addition, insulin treatment promoted the formation of large, elongate ASM cells, characterized by dramatic accumulation of contractile phenotype marker proteins and phosphorylated p70(S6K) (downstream target of PI 3-kinase associated with ASM maturation). Insulin effects on protein accumulation and cell morphology were abrogated by combined pretreatment with the Rho kinase inhibitor Y-27632 (1 microM) or the PI 3-kinase inhibitor LY-294002 (10 microM), indicating that insulin increases the expression of contractile phenotypic markers in BTSM in a Rho kinase- and PI 3-kinase-dependent fashion. In conclusion, insulin increases transcription and protein expression of contractile phenotypic markers in ASM. This could have important implications for the use of recently approved aerosolized insulin formulations in diabetes mellitus.

Insulin induces airway smooth muscle contraction

BACKGROUND AND PURPOSE

Recently, the use of inhaled insulin formulations for the treatment of type I and type II diabetes has been approved in Europe and in the United States. For regular use, it is critical that airway function remains unimpaired in response to insulin exposure.

EXPERIMENTAL APPROACH

We investigated the effects of insulin on airway smooth muscle (ASM) contraction and contractile prostaglandin (PG) production, using guinea-pig open-ring tracheal smooth muscle preparations.

KEY RESULTS

It was found that insulin (1 nM-1 microM) induced a concentration-dependent contraction that was insensitive to epithelium removal. These sustained contractions were susceptible to inhibitors of cyclooxygenase (indomethacin, 3 microM), Rho-kinase (Y-27632, 1 microM) and p42/44 MAP kinase (PD-98059, 30 microM and U-0126, 3 microM), but not of PI-3-kinase (LY-294002,10 microM). In addition, insulin significantly increased PGF(2alpha)-production which was inhibited by indomethacin, but not Y-27632. Moreover, the FP-receptor antagonist AL-8810 (10 microM) and the EP(1)-receptor antagonist AH-6809 (10 microM) strongly reduced insulin-induced contractions, supporting a pivotal role for contractile prostaglandins.

CONCLUSIONS AND IMPLICATIONS

Collectively, the results show that insulin induces guinea-pig ASM contraction presumably through the production of contractile prostaglandins, which in turn are dependent on Rho-kinase for their contractile effects. The data suggest that administration of insulin as an aerosol could result in some acute adverse effects on ASM function.

Treatment with Cyclohexenonic Long-Chain Fatty Alcohol Reverses Diabetes-Induced Tracheal Dysfunction in the Rat

In this study, we tried to elucidate the effect of cyclohexenonic long-chain fatty alcohol (N-hexacosanol) on tracheal dysfunction in diabetic rats. Diabetes was induced in 8-week-old male Sprague-Dawley rats by administering an intraperitoneal injection of 50 mg/kg streptozotocin. Non-diabetic control rats received an injection of citrate-phosphate buffer alone. Four weeks after the induction of diabetes, rats were randomly divided into 5 groups: age-matched non-diabetic control rats (group A); 4-week diabetic rats without N-hexacosanol treatment (group B); diabetic rats treated with vehicle (group C), and diabetic rats treated with N-hexacosanol at a dose of 2 or 8 mg/kg i.p. every day for the following 4 weeks (group D and group E, respectively; n = 6-8 animals in each group). Serum glucose and insulin levels were determined, as were the contractile responses induced by carbachol and 100 mmol/l KCl. The participation of M(2) and M(3) receptors was investigated in the trachea by real-time polymerase chain reaction (PCR), hematoxylin and eosin (HE) and immunohistochemical staining. Hypertrophy of airway smooth muscle was observed in diabetic rats, and was ameliorated by treatment with N-hexacosanol. Treatment with either 2 or 8 mg/kg N-hexacosanol did not alter diabetic rat status, i.e., body weight, serum glucose or serum insulin levels, but it significantly reversed the decrease in tracheal wall thickness and diabetes-induced hypercontractility in the rat trachea. In the immunohistochemical studies, muscarinic M(2) and M(3) receptors were expressed in the airway smooth muscle, the elastic fibers, the fibroblast and the surface of epithelium, and these expressions were not altered by either induction of diabetes or N-hexacosanol treatment. The expression of M(3) muscarinic receptor mRNAs in the trachea tended to be increased by the induction of diabetes and normalized when treated with N-hexacosanol. Our data indicate that N-hexacosanol could reverse diabetes-induced hypercontractility in the rat trachea.

Role of insulin on PGE2 generation during LPS-induced lung inflammation in rats

Alterations in arachidonic acid (AA) metabolism have been reported to occur in diabetes mellitus. The present study was carried out to verify if these alterations are due to the relative lack of insulin or to high levels of blood glucose. Male Wistar rats were rendered diabetic by alloxan injection (42 mg/kg, i.v.), 10 or 30 days before the experiments. Some diabetic rats received a single dose (4 IU, s.c.) of NPH insulin 2 h before an intratracheal instillation of lipopolysaccharide (LPS, 750 microg) or saline. Six hours after LPS challenge, the following parameters were analysed: blood glucose levels, total and differential leukocyte counts in bronchoalveolar lavage (BAL) fluid; linoleic acid and AA content in blood neutrophils (HPLC), and levels of prostaglandin (PG)E(2) in BAL (ELISA). Relative to controls, a reduced number of neutrophils (18%) and decreased amounts of PGE(2) (40%) were observed in the BAL fluid of diabetic rats in response to LPS. A single dose of insulin was not able to reduce blood sugar levels to normal values, but instead resulted in the normalization of both leukocyte migration to the lungs and levels of PGE(2). Accordingly, these abnormalities might be primarily linked to a continuing insulin deficiency rather than to secondary hyperglycaemia occurring in the diabetic rat. In conclusion, data presented suggest that insulin might regulate neutrophil migration and generation of PGE(2) during the course of acute lung injury induced by LPS.

Obesity and asthma

Obesity is an important public health problem. An increasing body of data supports the hypothesis that obesity is a risk factor for asthma. These data include numerous large cross-sectional and prospective studies performed in adults, adolescents, and children throughout the world. With few exceptions, these studies indicate an increased relative risk of asthma in the obese and overweight and demonstrate that obesity antedates asthma. Obesity appears to be a particularly important issue for severe asthma. Studies showing improvements in asthma in subjects who lose weight, as well as studies showing that obese mice have innate airway hyperresponsiveness (AHR) as well as increased responses to certain asthma triggers also suggest a causal relationship between obesity and asthma. The mechanistic basis for this relationship has not been established. It may be that obesity and asthma share some common etiology, such as a common genetic predisposition, common effects of in utero conditions, or that obesity and asthma are both the result of some other predisposing factor such as physical activity or diet. However, there are also plausible biological mechanisms whereby obesity could be expected to either cause or worsen asthma. These include co-morbidities such as gastroesophageal reflux, complications from sleep-disordered breathing (SDB), breathing at low lung volume, chronic systemic inflammation, and endocrine factors, including adipokines and reproductive hormones. Understanding the mechanistic basis for the relationship between obesity and asthma may lead to new therapeutic strategies for treatment of this susceptible population.

The changing role of eosinophils in long-term hyperreactivity following a single ozone exposure

Ozone hyperreactivity over 24 h is mediated by blockade of inhibitory M2 muscarinic autoreceptors by eosinophil major basic protein. Because eosinophil populations in the lungs fluctuate following ozone, the contribution of eosinophils to M2 dysfunction and airway hyperreactivity was measured over several days. After one exposure to ozone, M2 function, vagal reactivity, smooth muscle responsiveness, and inflammation were measured in anesthetized guinea pigs. Ozone-induced hyperreactivity to vagal stimulation persisted over 3 days. Although hyperreactivity one day after ozone is mediated by eosinophils, AbVLA-4 did not inhibit either eosinophil accumulation in the lungs or around the nerves or prevent hyperreactivity at this time point. Two days after ozone, eosinophils in BAL, around airway nerves and in lungs, were decreased, and neuronal M2 receptor function was normal, although animals were still hyperreactive to vagal stimulation. Depleting eosinophils with AbIL-5 prevented hyperreactivity, thus eosinophils contribute to vagal hyperreactivity by mechanisms separate from M2 receptor blockade. Three days after ozone, vagal hyperreactivity persisted, eosinophils were again elevated in BAL in lungs and around nerves, and M2 receptors were again dysfunctional. At this point, airway smooth muscle was also hyperresponsive to methacholine. Eosinophil depletion with AbIL-5, AbVLA-4, or cyclophosphamide protected M2 function 3 days after ozone and prevented smooth muscle hyperreactivity. However, vagal hyperreactivity was significantly potentiated by eosinophil depletion. The site of hyperreactivity, muscle or nerve, changes over 3 days after a single exposure to ozone. Additionally, the role of eosinophils is complex; they mediate hyperreactivity acutely while chronically may be involved in repair.

Insulin induces a hypercontractile airway smooth muscle phenotype

This study aims to investigate the effects of insulin on bovine tracheal smooth muscle phenotype in vitro. Contractility of muscle strips and DNA-synthesis ([3H]thymidine incorporation) of isolated cells were used as parameters for smooth muscle phenotyping. Insulin (1 microM) was mitogenic for bovine tracheal smooth muscle and potentiated DNA-synthesis induced by other growth factors. In contrast, after pretreatment of unpassaged bovine tracheal smooth muscle cells in culture, the mitogenic response induced by growth factors was strongly diminished, with no difference in the basal incorporation. Pretreatment of bovine tracheal smooth muscle strips in organ culture with insulin increased maximal contraction to methacholine and KCl. These results show that insulin acutely augments DNA-synthesis in the presence of other growth factors. In contrast, insulin pretreatment induces a hypercontractile phenotype with a decreased mitogenic capacity. This mechanism may be involved in the putative negative association between asthma and type I diabetes. In addition, these findings may have implications for the use of aerosolized insulin in diabetes mellitus.

Neurotrophins and neurotrophin receptors in allergic asthma

The neurotrophins nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 (NT-3) and NT-4 play a pivotal role in the development of the nervous system. Despite their well-known effects on neurons, elevated neurotrophin concentrations have been observed under pathological conditions in sera of patients with inflammatory disorders. Patients with asthma feature both airway inflammation and an abnormal airway reactivity to many unspecific stimuli, referred to as airway hyperresponsiveness, which is, at least partly, neuronally controlled. Interestingly, these patients show increased levels of neurotrophins in the blood as well as locally in the lung. It has been demonstrated that neurotrophin release from immune cells is triggered by allergen contact. The presence of neurotrophins and the neurotrophin receptors p75 (p75NTR), tyrosine kinase A (TrkA), TrkB and TrkC have been described in several immune cells. There is strong evidence for an involvement of neurotrophins in regulation of hematopoiesis and, in addition, in modulation of immune cell function in mature cells circulating in blood or resting in lymphatic organs and peripheral tissues. The aim of this review is to demonstrate possible roles of neurotrophins during an allergic reaction in consideration of the temporospatial compartimentalization.

Insulin regulates neuronal M2 muscarinic receptor function in the ileum of diabetic rats

Acetylcholine release from cholinergic nerves in the gastrointestinal tract is limited by neuronal M(2) muscarinic receptors. In diabetic animals, M(2) muscarinic receptor function in the ileum is increased, leading to decreased acetylcholine release and smooth muscle contraction in response to nerve stimulation. The mechanisms responsible for increased M(2) muscarinic receptor function are unknown but may contribute to the gastrointestinal dysmotility that occurs frequently in diabetics. In this study, we investigated whether insulin modulates M(2) muscarinic receptor function in the gastrointestinal tract of diabetic rats. M(2) muscarinic receptor function was tested by measuring the ability of an agonist, pilocarpine, to inhibit and an antagonist, methoctramine, to potentiate electrical field stimulation (EFS)-induced contraction of ileum in vitro. Insulin administration (0.2, 0.6, and 2 U s.c. daily for 7 days) reversed the diabetes-induced increase in M(2) muscarinic receptor function and restored normal contractions to EFS. Insulin had no effect on the function of postjunctional M(3) muscarinic receptors, determined by measuring contractile responses to acetylcholine. These data suggest that insulin tonically inhibits neuronal M(2) muscarinic receptors. Thus, loss of insulin removes this inhibition and increases M(2) muscarinic receptor function leading to decreased acetylcholine release and contraction to EFS. In nondiabetic rats, there was a trend that higher insulin doses (0.6 and 2 U) increased M(2) muscarinic receptor function, suggesting a bell-shaped concentration-response relationship for insulin. In conclusion, lack of insulin or excess insulin increases M(2) muscarinic receptor function in rat ileum. This mechanism may contribute to decreased acetylcholine release in the gastrointestinal tract of diabetics, resulting in dysmotility.

Muscarinic acetylcholine receptors and airway diseases

Parasympathetic nerves provide the dominant autonomic innervation of the airways. Release of acetylcholine from parasympathetic nerves activates postjunctional muscarinic receptors present on airway smooth muscle, submucosal glands, and blood vessels to cause bronchoconstriction, mucus secretion, and vasodilatation, respectively. Acetylcholine also feeds back onto prejunctional muscarinic receptors to enhance or inhibit further acetylcholine release. In asthma and chronic obstructive pulmonary disease, bronchoconstriction and mucus secretion is increased and the airways are hyperresponsive to contractile agents. These changes are due to increased parasympathetic nerve activity. The number and function of postjunctional muscarinic receptors in the airways are unchanged in animal models of asthma. Rather, it is the supply of acetylcholine to the postjunctional cells (smooth muscle and submucosal gland) that is increased. The increase in acetylcholine release occurs because prejunctional, inhibitory M(2) muscarinic receptors on the parasympathetic nerves are dysfunctional. M(2) muscarinic receptor dysfunction and subsequent airway hyperreactivity have been demonstrated to occur in animals in response to a variety of triggers, including antigen challenge, virus infection, ozone exposure, and vitamin A deficiency. In humans, there is evidence that loss of M(2) muscarinic receptor function is related to asthma. The mechanisms by which neuronal M(2) muscarinic receptor function is lost and its relevance to human airway disease are discussed in this review.

Role of cholinergic reflexes on the bronchoconstrictor reactivity to neurokinin a in allergic dogs

Neurokinin A (NKA) potentiates airway cholinergic neurotransmission in several species. In this study, the role of cholinergic reflexes on the bronchoconstrictor response to NKA was evaluated in non-sensitized dogs and in allergic dogs neonatally sensitized to ragweed in which heightened bronchoconstrictor reactivity to NKA has previously been observed. Cardiopulmonary functions, including pulmonary resistance (R(L)) were measured in anesthetized, spontaneously breathing dogs before and after increasing concentrations of aerosolized NKA. The provocative concentrations of NKA increasing R(L) by 25% above the baseline (PC(25)) was measured before and after ( approximately 10 min) aerosolized saline or ipratropium bromide (0.01%). This concentration of ipratropium produced a 250-fold shift in the methacholine dose-response curve. In sensitized dogs, NKA bronchoconstrictor reactivity (PC(25)=0.050+/-0.011%) was 2.5 times more potent than that of non-sensitized controls (PC(25)=0.177+/-0.031%). Ipratropium bromide inhibited the bronchoconstrictor response to NKA in both sensitized and non-sensitized dogs and after ipratropium, NKA reactivity was 5.2-fold less in allergic dogs (PC(25)=0.246+/-0.048%) as compared to 3.5 fold less in non-sensitized controls (PC(25)=0.622+/-0.106%). In conclusion, cholinergic reflexes are important components of the bronchoconstrictor response to NKA in dogs particularly in those sensitized neonatally to ragweed. It is speculated that heightened activity of cholinergic reflexes contributes to the bronchial hyperresponsiveness seen in allergic dogs.

Adhesion-dependent interactions between eosinophils and cholinergic nerves

Eosinophils adhere to airway cholinergic nerves and influence nerve cell function by releasing granule proteins onto inhibitory neuronal M(2) muscarinic receptors. This study investigated the mechanism of eosinophil degranulation by cholinergic nerves. Eosinophils were cocultured with IMR32 cholinergic nerve cells, and eosinophil peroxidase (EPO) or leukotriene C(4) (LTC(4)) release was measured. Coculture of eosinophils with nerves significantly increased EPO and LTC(4) release compared with eosinophils alone. IMR32 cells, like parasympathetic nerves, express the adhesion molecules vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 (ICAM-1). Inhibition of these adhesion molecules alone or in combination significantly inhibited eosinophil degranulation. IMR32 cells also significantly augmented the eosinophil degranulation produced by formyl-Met-Leu-Phe. Eosinophil adhesion to IMR32 cells resulted in an ICAM-1-mediated production of reactive oxygen species via a neuronal NADPH oxidase, inhibition of which significantly inhibited eosinophil degranulation. Additionally, eosinophil adhesion increased the release of ACh from IMR32 cells. These neuroinflammatory cell interactions may be relevant in a variety of inflammatory and neurological conditions.

Feeble bronchomotor responses in diabetic rats in association with decreased sensory neuropeptide release

Type I diabetes is associated with a low incidence of asthma. We tested whether a decrease in sensory neuropeptide release is associated with an attenuated bronchoconstrictive response to field stimulation (FS; 100 stimuli, 20 V, 0.1 ms, 20 Hz) in streptozotocin (STZ)-induced diabetes. The organ fluid of the preparations were also tested for substance P, calcitonin gene-related peptide (CGRP), and somatostatin concentrations by RIA. Preparations were from either normal rats or those pretreated with 50 mg/kg STZ iv 8 wk before experiment. A group of STZ-treated animals was supplied with insulin delivery (4 IU/day sc) implants between 4 and 8 wk. A subgroup was formed to study the effect of capsaicin desensitization. The atropine-resistant contraction was attenuated by diabetes without capsaicin-sensitive relaxation response. Exogenous CGRP and substance P potentiated, whereas somatostatin inhibited (1 nM-10 microM) the FS-induced contractions in rings from either group. FS released somatostatin, CGRP, and substance P from 0.17 +/- 0.024, 0.15 +/- 0.022, and 1.65 +/- 0.093 to 0.58 +/- 0.032, 0.74 +/- 0.122, and 5.34 +/- 0.295 in preparations from normal, and from 0.19 +/- 0.016, 0.11 +/- 0.019, and 0.98 +/- 0.116 to 0.22 +/- 0.076, 0.34 +/- 0.099, and 1.84 +/- 0.316 fmol/mg wet wt in preparations from diabetic rats. Insulin supplementation restored neuropeptide release in rings from STZ-treated rats. The results show that the decreased FS-induced contractions occurred with a decrease in sensory neuropeptide release in STZ-diabetic rats.

Increased function of inhibitory neuronal M2 muscarinic receptors in trachea and ileum of diabetic rats

1. Release of acetylcholine from parasympathetic nerves is inhibited by neuronal M(2) muscarinic receptors. The effects of streptozotocin-induced diabetes on prejunctional M(2) and postjunctional M(3) muscarinic receptor function in rat trachea and ileum were investigated in vitro. 2. Neuronal M(2) muscarinic receptor function was tested by measuring the ability of an agonist, pilocarpine, to inhibit and an antagonist, methoctramine, to potentiate electrical field stimulation (EFS)-induced contraction of trachea and ileum. Concentration-response curves to pilocarpine and methoctramine were shifted to the left in both to a greater degree in diabetics than controls. 3. In trachea, post-junctional M(3) muscarinic receptor function was increased since maximum contractile responses to the muscarinic agonists acetylcholine and carbachol were greater in diabetics than controls. This increase offset the increased function of the inhibitory neuronal M(2) muscarinic receptors since EFS-induced, frequency-dependent contraction was equal in control and diabetic rats. 4. In contrast, post-junctional M(3) muscarinic receptor function was unchanged by diabetes since concentration-response curves to acetylcholine and carbachol were not different between groups. Thus, EFS-induced contractions of the ileum were decreased in diabetics versus controls. 5. In conclusion, inhibitory M(2) muscarinic receptors on parasympathetic nerves in the trachea and ileum are hyperfunctional in diabetic rats. The function of post-junctional M(3) muscarinic receptors in the trachea, but not the ileum, is also increased in diabetes. 6. The dysfunction of inhibitory, neuronal M(2) muscarinic receptors in the airways may protect against hyperreactivity and in the ileum may contribute to gastrointestinal dysmotility associated with diabetes.

Effects of dexamethasone on antigen-induced airway eosinophilia and M(2) receptor dysfunction

In antigen-challenged guinea pigs, airway hyperreactivity is due to recruitment of eosinophils to the airway nerves and dysfunction of M(2) muscarinic receptors. M(2) receptor dysfunction is caused by eosinophil major basic protein, which is an allosteric antagonist at the receptor. Because glucocorticoids inhibit airway hyperreactivity in humans and in animal models of asthma, we tested whether dexamethasone treatment (6 microg. kg(-)(1). d(-)(1) for 3 d, intraperitoneal) before antigen challenge prevents M(2) receptor dysfunction and airway hyperreactivity. Guinea pigs were sensitized to ovalbumin via intraperitoneal injections, and were challenged with ovalbumin via inhalation. Twenty-four hours later, hyperreactivity and M(2) receptor function were tested. Antigen-challenged animals were hyperreactive to vagal stimulation, and demonstrated loss of M(2) receptor function. Dexamethasone pretreatment prevented hyperreactivity and M(2) receptor dysfunction in antigen-challenged guinea pigs. Antigen challenge resulted in recruitment of eosinophils to the airways and to the airway nerves. Dexamethasone prevented recruitment of eosinophils to the airway nerves but did not affect total eosinophil influx into the airways. These results demonstrate that dexamethasone prevents antigen-induced hyperreactivity by protecting neuronal M(2) muscarinic receptors from antagonism by eosinophil major basic protein, and this protective mechanism appears to be by specifically inhibiting eosinophil recruitment to the airway nerves.

Eosinophil recruitment to the airway nerves

Increased vagal reflexes contribute to bronchoconstriction in asthma. Antigen challenge of sensitized animals induces vagal hyperresponsiveness. This review will discuss the evidence that eosinophils increase release of acetylcholine from the parasympathetic nerves. After antigen challenge, eosinophils are actively recruited to the airway nerves, possibly through expression of chemotactic substances and adhesion molecules by the nerves. Tachykinins acting on neurokinin 1 receptors activate the eosinophils. Activated eosinophils release eosinophil major basic protein (MBP), which is an endogenous antagonist for M2 muscarinic receptors. The M2 muscarinic receptors on the parasympathetic nerves in the lungs normally inhibit release of acetylcholine. When M2 receptors are blocked by MBP, acetylcholine release is increased, resulting in hyperresponsiveness. Neutralization of MBP with polyanionic substances restores M2 receptor function and eliminates hyperresponsiveness. Antibodies to MBP prevent M2 receptor dysfunction and hyperresponsiveness, as do antibodies to the adhesion molecule very late antigen 4, which prevent eosinophil migration. A low dose of dexamethasone, which does not affect total eosinophil influx into the lungs and airways, prevents eosinophils from clustering around the nerves and prevents antigen-induced M2 dysfunction and hyperresponsiveness. Furthermore, animal studies show that viral infections, which are important precipitants of asthma attacks, and exposure to air pollutants such as ozone can also activate airway eosinophils, leading to a chain of events similar to that seen after antigen challenge. Finally, a similar clustering of eosinophils around airway nerves, as well as release of MBP onto the nerves, is seen in fatal asthma, suggesting that similar mechanisms may be involved in human airway hyperresponsiveness.

Insulin NO-dependent action on airways smooth muscles

In order to find out how insulin acts on airway smooth muscle and which mechanisms could be involved, we studied the effect of insulin on contraction induced, first, by KCl and, second, by Acetylcholine (Ach), before and after epithelium removal, and finally in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor. Tracheal smooth muscle strips from 24 rabbits, 6 being used for each experiment. Each muscle strip was pretreated with a solution containing either 80 mM KCl or 10(-5) Ach and increasing doses of insulin (range 10(-10)--10(-5) M) in the presence or absence of 10(-4) M L-NAME. A reference curve for contraction evoked by 80 mM KCl or 10(-5) M Ach in the presence or absence of 10(-4) M L-NAME was recorded each time before the pretreatment mentioned above. Insulin evoked a concentration-dependent inhibition of tracheal smooth muscle contraction, induced by 80 mM KCl or 10(-5) M Ach. After epithelium removal, insulin (10(-8), 10(-7) M) evoked statistically significant increases to the contractions induced by 10(-5) M Ach compared to the contractions induced by 10(-5) M Ach and insulin in the presence of epithelium (P < 0.05). These increases were higher when 10(-4) M l-NAME was added to the bath (P < 0.05). In conclusion, these results indicate that insulin inhibits tracheal smooth muscle contraction by acting on epithelium and releasing NO.

Substance P-induced airway hyperreactivity is mediated by neuronal M(2) receptor dysfunction

Neuronal muscarinic (M(2)) receptors inhibit release of acetylcholine from the vagus nerves. Hyperreactivity in antigen-challenged guinea pigs is due to blockade of these M(2) autoreceptors by eosinophil major basic protein (MBP) increasing the release of acetylcholine. In vivo, substance P-induced hyperactivity is vagally mediated. Because substance P induces eosinophil degranulation, we tested whether substance P-induced hyperreactivity is mediated by release of MBP and neuronal M(2) receptor dysfunction. Pathogen-free guinea pigs were anesthetized and ventilated. Thirty minutes after intravenous administration of [Sar(9),Met(O(2))(11)]- substance P, guinea pigs were hyperreactive to vagal stimulation and M(2) receptors were dysfunctional. The depletion of inflammatory cells with cyclophosphamide or the administration of an MBP antibody or a neurokinin-1 (NK(1)) receptor antagonist (SR-140333) all prevented substance P-induced M(2) dysfunction and hyperreactivity. Intravenous heparin acutely reversed M(2) receptor dysfunction and hyperreactivity. Thus substance P releases MBP from eosinophils resident in the lungs by stimulating NK(1) receptors. Substance P-induced hyperreactivity is mediated by blockade of inhibitory neuronal M(2) receptors by MBP, resulting in increased release of acetylcholine.

Endotoxin-induced acute lung injury in rats. Role of insulin

Reduced inflammatory responses are frequently associated with diabetes mellitus. In order to investigate the influence of diabetes mellitus on the activation of bronchoalveolar cells, diabetic Wistar rats (alloxan, 40 mg/kg, iv, 30 days) and matched controls were exposed to an aerosol of endotoxin (lipopolysaccharide, LPS) or saline. Bronchoalveolar lavage (BAL) was performed 4 h thereafter. Compared with saline, aerosol administration of LPS significantly increased the number of neutrophils in the BAL fluid of control and diabetic rats. Number of mononuclear cells did not change and eosinophils were absent. A marked increase in luminol-dependent chemiluminescence (LDCL) was observed in control group after stimulation of the cells in vitro with zymosan. In contrast, tests performed with cells from diabetic rats showed a 50% reduction in LDCL generation. Full recovery of cell behaviour to match control values was observed after treatment of diabetic animals with insulin, administered before LPS exposure. Furthermore, relative to controls, level of TNF-alpha in the BAL supernatant of diabetic rats was significantly reduced. Values returned to control levels after treatment of diabetic rats with insulin, prior exposure to LPS. In conclusion, data presented suggest that insulin might regulate superoxide generation and TNF-alpha release by leukocytes upon exposure to LPS in vivo.