Decrease of histamine induced bronchoconstriction by caffeine in mild asthma

Different cutoff values of methacholine bronchial provocation test depending on age in children with asthma

BACKGROUND

Bronchial hyperresponsiveness (BHR) is a fundamental pathophysiological characteristic of asthma. Although several factors such as airway caliber can affect BHR, no study has established age-dependent cutoff values of BHR to methacholine for the diagnosis of asthma in children. We investigated the cutoff values of the methacholine challenge test (MCT) in the diagnosis of asthma according to age.

METHODS

A total of 2383 individuals aged from 6 to 15 years old were included in this study. MCTs using the five-breath technique were performed in 350 children with suspected asthma based on symptoms by pediatric allergists and in 2033 healthy children from a general population-based cohort. We determined the provocative concentration of methacholine producing a 20% decrease in forced expiratory volume in 1 second from baseline (PC₂₀). A modified Korean version of the International Study of Asthma and Allergies in Childhood questionnaire was used to distinguish asthmatics and healthy subjects. Receiver-operator characteristic curve analysis was used to assess the cutoff value of PC₂₀ for the diagnosis of asthma.

RESULTS

Cutoff values of methacholine PC₂₀, which provided the best combination of diagnostic sensitivity and specificity, showed an increasing pattern with age: 5.8, 9.1, 11.8, 12.6, 14.9, 21.7, 23.3, 21.1, 21.1, and 24.6 mg/mL at ages 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 years, respectively.

CONCLUSION

The application of different cutoff values of methacholine PC₂₀ depending on age might be a practical modification for the diagnosis of asthma in children and adolescents with asthmatic symptoms.

The effect of dietary components on inflammatory lung diseases - a literature review

Anti-inflammatory treatment in chronic inflammatory lung diseases usually involves glucocorticosteroids. With patients suffering from serious side effects or becoming resistant, specific nutrients, that are suggested to positively influence disease progression, can be considered as new treatment options. The dietary inflammatory index is used to calculate effects of dietary components on inflammation and lung function to identify most potent dietary components, based on 162 articles. The positive effects of n-3 PUFAs and vitamin E on lung function can at least partially be explained by their anti-inflammatory effect. Many other dietary components showed only small or no effects on inflammation and/or lung function, although the number of weighted studies was often too small for a reliable assessment. Optimal beneficial dietary elements might reduce the required amounts of anti-inflammatory treatments, thereby decreasing both side effects and development of resistance as to improve quality of life of patients suffering from chronic inflammatory lung diseases.

Taste receptors in asthma

PURPOSE OF REVIEW

Although today's cornerstone therapies for asthma (inhaled bronchodilators and corticosteroids) target airway narrowing and lung inflammation, about half of treated asthmatic patients do not achieve good disease control. There is a clear need for new therapeutic approaches and novel drug targets. Recent research has unexpectedly revealed that certain taste receptors (particularly those involved in bitter taste transduction) are expressed in lung tissue.

RECENT FINDINGS

Bitter taste receptors are expressed in several cell types in the lungs (such as chemosensory cells, epithelial cells, smooth muscle cells, lymphocytes, and macrophages) and variously involved in ciliary beating, muscle relaxation, and/or inhibition of the production of inflammatory mediators. Here, we review recent research on the role of bitter taste receptors in experimental models of asthma and in asthmatics.

SUMMARY

The currently available data suggest that bitter taste receptor agonists have therapeutic potential in chronic obstructive airway diseases such as asthma.

[Taste receptors in the lungs: interesting or anecdotal?]

The receptors responsible for taste perception distinguish the four basic tastes : salty, sweet, bitter and umami. Among them, the bitter taste receptors (TAS2R) are G protein coupled receptors, including 25 subtypes identified in humans to date. Although the existence of endogenous agonists remains uncertain, the TAS2R receptors have the ability to recognize natural or synthetic molecules, as various molecules produced by bacteria, or caffeine, chloroquine, or erythromycin. The expression of these receptors, initially thought to be confined to the oral cavity, has recently been described in extra-oral tissues such as the gastrointestinal tract and the lungs. The effects in the lung tissue are essentially at three levels : TAS2R receptors expressed on the cilia of epithelial cells increase the cilia vibration frequency; the stimulation of TAS2R receptors expressed in bronchial smooth muscle cells leads to bronchial relaxation; while TAS2R receptors expressed on immune cells in the lung tissue, including macrophages, are involved in the modulation of the production of pro-inflammatory cytokines. In conclusion, in view of these complementary mechanisms, TAS2R receptors may become a pharmacological target of interest for the treatment of obstructive lung diseases.

Current clinical diagnostic tests for asthma

Asthma involves variable airflow obstruction in both large and small airways. The physiological consequences of obstruction include increased airway resistance and decreased expiratory flow rates, which lead to air trapping and dynamic hyperinflation. This chapter reviews current methods for pulmonary function testing to detect these physiological changes for both diagnosis and monitoring.

The effect of caffeinated coffee on airway response to methacholine and exhaled nitric oxide

BACKGROUND

The bronchoprotective effect of caffeine on histamine challenge testing (HCT) has been studied with equivocal results. Current guidelines for bronchoprovocation testing recommend exclusion of caffeine the day of testing. The effects of caffeine on methacholine challenge testing (MCT), now more commonly performed than histamine challenge, are unknown.

METHODS

Sixteen well-controlled asthmatics with a forced expiratory volume in 1 s (FEV(1)) > 65% predicted and methacholine provocation concentration causing a 20% fall in FEV(1) (PC(20)) ≤ 16 mg/ml participated in a randomized single-blind crossover study. The two treatments included 16 ounces of caffeinated and decaffeinated coffee given on two separate days. The fraction of exhaled nitric oxide (eNO) and FEV(1) were measured before and 1 h after each treatment. One hour post treatment blood was drawn for serum caffeine level and the MCT was done.

RESULTS

Fourteen subjects completed the study; there were no adverse events. No significant bronchodilation was seen between the mean FEV(1) values before and after the caffeinated treatment (3.31 ± 0.75 L and 3.36 ± 0.74 L, respectively). No significant bronchoprotection was seen between the caffeinated and decaffeinated treatment's geometric mean PC(20) values (1.35 mg/ml and 1.36 mg/ml, respectively). Mean eNO values before and after caffeinated treatment were not significantly different (31.2 ± 19.6 ppb and 31.5 ± 20.4 ppb).

CONCLUSION

The amount of caffeine in a normal dietary serving of a 16 oz cup of coffee is not enough to cause significant bronchoprotection, bronchodilation, or decrease eNO values. Registered at http://clinicaltrials.gov: NCT01057875.

Caffeine for asthma

BACKGROUND

Caffeine has a variety of pharmacological effects; it is a weak bronchodilator and it also reduces respiratory muscle fatigue. It is chemically related to the drug theophylline which is used to treat asthma. It has been suggested that caffeine may reduce asthma symptoms and interest has been expressed in its potential role as an asthma treatment. A number of studies have explored the effects of caffeine in asthma, this is the first review to systematically examine and summarise the evidence.

OBJECTIVES

To assess the effects of caffeine on lung function and identify whether there is a need to control for caffeine consumption prior to either lung function or exhaled nitric oxide testing.

SEARCH STRATEGY

We searched the Cochrane Airways Group trials register and the reference lists of articles (August 2009). We also contacted study authors.

SELECTION CRITERIA

Randomised clinical trials of oral caffeine compared to placebo or coffee compared to decaffeinated coffee in adults with asthma.

DATA COLLECTION AND ANALYSIS

Trial selection, quality assessment and data extraction were done independently by two reviewers.

MAIN RESULTS

Seven trials involving a total of 75 people with mild to moderate asthma were included. The studies were all of cross-over design .Six trials involving 55 people showed that in comparison with placebo, caffeine, even at a 'low dose' (< 5mg/kg body weight), appears to improve lung function for up to two hours after consumption. Forced expiratory volume in one minute showed a small improvement up to two hours after caffeine ingestion (SMD 0.72; 95% CI 0.25 to 1.20), which translates into a 5% mean difference in FEV1. However in two studies the mean differences in FEV1 were 12% and 18% after caffeine. Mid-expiratory flow rates also showed a small improvement with caffeine and this was sustained up to four hours.One trial involving 20 people examined the effect of drinking coffee versus a decaffeinated variety on the exhaled nitric oxide levels in patients with asthma and concluded that there was no significant effect on this outcome.

AUTHORS' CONCLUSIONS

Caffeine appears to improve airways function modestly, for up to four hours, in people with asthma . People may need to avoid caffeine for at least four hours prior to lung function testing, as caffeine ingestion could cause misinterpretation of the results. Drinking caffeinated coffee before taking exhaled nitric oxide measurements does not appear to affect the results of the test, but more studies are needed to confirm this.

Bronchoprovocation testing

Airway smooth muscles of asthmatics tend to be hyperresponsive when provoked. The exaggerated bronchial constriction can be measured by the airflow limitation seen following bronchial provocation. Measuring bronchial hyperresponsiveness by broncho provocation testing is helpful in diagnosing and optimizing therapy. While numerous agents have been used to provoke a measurable airflow limitation, standardized protocols are available for only a few. This article aims to discuss the various methods that have been reported for bronchoprovocation testing.

Methacholine challenge testing: identifying its diagnostic role, testing, coding, and reimbursement

Methacholine challenge testing (MCT), also sometimes described as bronchoprovocation testing, is widely performed for both research and diagnostic purposes. MCT is clinically useful when the patient presents with a history of symptoms suggesting asthma, but spirometry findings are normal. Typically, MCT is performed in a pulmonary function laboratory, a clinic, or a physician's office. MCT requires time, effort, and understanding. Two standard testing regimes are identified along with proper coding and reimbursement methodologies.

RT-PCR study of purinergic P2 receptors in hematopoietic cell lines

Seven P2X and fifteen P2Y receptors have been identified to date, partly on the basis of amino acid sequence homologies. The expression of all cloned human purinergic P2 receptors was investigated on the messenger RNA level in promonocytic U937 cells, erythroblastic K562 cells, and undifferentiated, dimethyl sulfoxide-differentiated granulocytic, and phorbol-12-myristate-13-acetate-differentiated monocytic HL60 cells. RT-PCR assays showed expression of several P2X receptors, whereas all P2Y receptors were found in at least some of the analyzed cells lines. Granulocytic and monocytic differentiation of HL60 cells lead to a partly dramatic up- or downregulation of receptor transcripts. The number of different P2 receptors expressed in each cell type showed a significant rise from U937 cells via K562 cells, undifferentiated and granulocytic, to monocytic HL60 cells. The total mRNA amounts being normalized to the glyceraldehyde-3-phosphate dehydrogenase levels demonstrated an even more distinct variability of absolute transcript levels. An increased number of different P2 receptors expressed were associated with an increased total average P2 receptor mRNA amount in each cell. This phenomenon of overexpression suggests self-inductive effects of purinergic signaling indicating its involvement in hematopoiesis and possibly in immunoreactive mediation.

Identification and characterization of a cell-surface receptor, P2Y15, for AMP and adenosine

AMP and adenosine are found in all cell types and can be released by cells or created extracellularly from the breakdown of ATP and ADP. We have identified an orphan G protein-coupled receptor with homology to the P2Y family of nucleotide receptors that can respond to both AMP and adenosine. Based on its ability to functionally bind the nucleotide AMP, we have named it P2Y15. Upon stimulation, P2Y15 induces both Ca2+ mobilization and cyclic AMP generation, suggesting coupling to at least two different G proteins. It is highly expressed in mast cells and is found predominantly in the tissues of the respiratory tract and kidneys, which are known to be affected by AMP, adenosine, and adenosine antagonists. Until now, the effects of AMP have been thought to depend on its dephosphorylation to adenosine but we demonstrate here that P2Y15 is a bona fide AMP receptor by showing that it binds [(32)P]AMP. Because AMP and adenosine have bronchoconstrictive effects that can be inhibited by theophylline, we tested whether theophylline and other adenosine receptor antagonists can block P2Y15. We found inhibition at a theophylline concentration well within the therapeutic dose range, indicating that P2Y15 may be a clinically important target of this drug.

Bronchoprovocation testing

Bronchoprovocation testing has been performed for more than 50 years. Challenge testing with nonselective agents has been used widely for the assessment of airflow limitation in patients, and has been used in the research setting to better characterize the pathophysiology of bronchial responsiveness. Based on this large body of literature, detailed guidelines are now available to allow for standardization of testing methodology. Such standardization is critical to achieve safe, accurate, and reproducible test results that may be interpreted meaningfully. Currently, bronchoprovocation testing with direct-acting stimuli such as methacholine is used most frequently in the clinical arena, but, in recent years, considerable interest has been developing in the use of indirect stimuli. (57) It now is recognized that bronchial hyperresponsiveness to indirect stimuli (e.g., exercise, cold air, and AMP) is highly specific for asthma and may have greater clinical relevance than does responsiveness to direct stimuli. (8) As a result, testing with indirect agents may become employed more widely in the future.

The role of n-6 polyunsaturated fat in stable asthmatics

We investigated in a clinical setting whether increased intake of linoleic acid alters respiratory function in 26 mild asthmatics. Subjects completed a 16-week-dietary intervention comprising 8 weeks eating an enriched n-6 polyunsaturated fat diet (9.2% energy from linoleic acid) and consuming either a high monounsaturated or saturated fat diet in a random cross-over resign for 8 weeks. Neither FEV1 nor PC20 values changed significantly after increased linoleic acid consumption when compared with the other diets. Increased consumption of linoleic acid caused a 20% rise (p < or = 0.01) in plasma linoleic acid, a 38% decrease (p < or = 0.01) in plasma eicosapentaenoic acid, but no change in arachidonic acid. There were no changes in symptom scores or bronchodilator use.

Caffeine for asthma

BACKGROUND

Caffeine has a variety of pharmacological effects. It is chemically related to the drug theophylline which is used to treat asthma. Accordingly, interest has been expressed in its potential role as an asthma treatment. A number of studies have explored the effects of caffeine in asthma, this is the first review to systematically examine and summarise the evidence.

OBJECTIVES

Caffeine is a weak bronchodilator and it also reduces respiratory muscle fatigue. It has been suggested that caffeine may reduce asthma symptoms. The objective of this review was to assess the effects of caffeine on lung function and identify whether there is a need to control for caffeine consumption prior to lung function testing.

SEARCH STRATEGY

We searched the Cochrane Airways Group trials register and the reference lists of articles. We also contacted study authors.

SELECTION CRITERIA

Randomised trials of oral caffeine compared to placebo in adults with asthma.

DATA COLLECTION AND ANALYSIS

Trial quality assessment and data extraction were done independently by two reviewers.

MAIN RESULTS

Six trials involving a total of 55 people were included. The studies were all of cross-over design and of high quality. In comparison with placebo, caffeine appears to improve lung function for up to two hours after consumption. Forced expiratory volume in one minute showed a small improvement up to two hours after caffeine use (standardised mean difference -0.73, 95% confidence interval -1.20 to -0.25). Mid-expiratory flow rates also showed a small improvement with caffeine and this was sustained up to four hours.

REVIEWER'S CONCLUSIONS

Caffeine appears to improve airways function modestly in people with asthma for up to four hours. People may need to avoid caffeine for at least four hours prior to lung function testing.

Daily psychosocial factors predict levels and diurnal cycles of asthma symptomatology and peak flow

This study examines the relationship among psychosocial factors, asthma symptoms, and peak expiratory flow rate (PEFR) in the natural environment. Twenty adult asthmatics wore preprogrammed wristwatches that prompted them to assess PEFR, asthma symptoms, and psychosocial factors five times a day for 10 days. Psychosocial variables (activities, locations, social contacts, mood, and stressors) were strongly related to PEFR and asthma symptoms, suggesting that they may play a more important role in disease expression than has been previously thought. Diurnal cycles of asthma symptoms and PEFR were observed. However, statistically controlling for psychosocial factors eliminated diurnal cycles for PEFR or asthma symptoms, indicating that psychosocial factors are a major contributor to the observed diurnal cycle in PEFR and symptoms. These relationships underscore the need to include psychosocial factors in future asthma research.

Dose equivalence and bronchoprotective effects of salmeterol and salbutamol in asthma

BACKGROUND

Salbutamol is the most widely prescribed short acting beta 2 agonist and salmeterol is the first long acting inhaled beta 2 agonist. The dose equivalence of salmeterol and salbutamol is disputed. Estimates of weight-for-weight dose ratio have ranged from 1:2 to 1:16. A study was undertaken to clarify the true dose ratio.

METHODS

The bronchoprotection afforded against repeated methacholine challenge by inhaled salmeterol 25 micrograms and 100 micrograms and salbutamol 100 micrograms and 400 micrograms was compared in a randomised, double blind, placebo controlled, crossover trial. Subjects were 16 stable asthmatics with a baseline forced expiratory volume in one second (FEV1) of > or = 65% predicted, screening concentration provoking a fall in FEV1 of 20% (PC20FEV1) of < or = 8mg/ml, and a shift in PC20FEV1 of more than two doubling concentration steps following inhalation of salbutamol 400 micrograms. On five separate occasions subjects underwent methacholine challenge before and 30 and 120 minutes after drug administration. PD20FEV1 was calculated for each challenge. FEV1 at 90 minutes after drug administration was also recorded.

RESULTS

Bronchoprotection afforded by salmeterol was increased at 120 minutes compared with 30 minutes and protection by salbutamol was decreased. Protection by both doses of salmeterol was similar to salbutamol 100 micrograms at 30 minutes but significantly greater at 120 minutes. FEV1 at 90 minutes was significantly greater after salmeterol 100 micrograms than after placebo, but there were no other significant differences between treatments. Maximal observed protection was equivalent for salmeterol 100 micrograms and salbutamol 400 micrograms.

CONCLUSIONS

The data are compatible with a weight-for-weight dose ratio for salmeterol:salbutamol of < or = 1:4.