Effect of Dietary Supplements With Fish Oil on Mannitol-induced Airway Sensitivity & Inflammation in Persons With Asthma

Asthma is a chronic inflammatory disorder of the airways characterized by recurrent episodes of dyspnea, wheeze and chest tightness and is associated with variable airway obstruction. Exercise-induced bronchoconstriction (EIB) is a feature specific to asthma. Exercise testing protocols have been developed to identify the presence of asthma as well as to assess asthma therapy. Airway narrowing following exercise in persons with asthma is thought to result from dry air hyperpnoea-induced dehydration of the airway surface, leading to the release of mediators from inflammatory cells residing in the airway. Regular treatment with inhaled corticosteroids inhibits the airway response to exercise by decreasing the number of inflammatory cells and thus the source of bronchoconstricting mediators. Therefore, a decrease in the source of mediator may be the reason for this eventual inhibition of the airway response to exercise.

It has recently been demonstrated that fish oil supplementation in capsule form, taken daily over three weeks, provides significant protection against EIB. This protection appears to be of equal or greater efficacy than inhaled corticosteroids treatment over a similar period. This may have positive implications in the treatment of asthma as inhaled corticosteroids are known to have some unwanted side effects. Fish oil supplementation in the high doses given in previous studies have not demonstrated any side effects and may lead to an alternative treatment, or a decrease in the dose of inhaled steroids required in the treatment of asthma.

A new bronchial provocation test using inhaled mannitol, derived from the mechanism of EIB, has been recently developed and is now registered in Australia and the European Union. Mannitol causes airway narrowing in a similar manner to exercise in persons with asthma and is effective in identifying responsiveness to inhaled corticosteroids. We wish to use inhaled mannitol as a model for EIB in an effort to further investigate the use of fish oil supplementation in the treatment of asthma. Our hypothesis is that daily orally administered encapsulated fish oil will attenuate the airway response to mannitol over a 3-week treatment period. We also wish to measure associated markers of inflammation in the blood, urine, sputum and exhaled condensate as well as monitor clinical outcomes such as symptoms and daily beta2 agonist use.

Inclusion criteria

• Male or female (medically or surgically postmenopausal or practicing an accepted form of barrier or hormonal contraception) subjects age 18-55.
• Stable, mild atopic asthma with forced expiratory volume in one second (FEV1) greater than 70% of predicted for age and height, and not requiring any medical treatment other than short acting inhaled beta2-agonists as required or for those on steroids, taking < 1000 mcg of inhaled corticosteroid per day.
• No recent or significant history of cigarette smoking (no smoking within six months prior to entry into the study; less than 10 pack-years cumulative history of cigarette smoking).
• Signed written informed consent to participate in the study; ability to return to the clinic for repeated visits.
• No history of asthma exacerbations or acute intercurrent respiratory illness (viral respiratory syndrome, bronchitis, pneumonia) for a four week period preceding entry into the screening phase of the study.
• Subjects who take inhales steroids regularly must demonstrate reproducibility to inhaled mannitol (PD15<1.0 doubling doses) during a 2 week run-in period.
• A PD15 to the mannitol challenge < 315mg

Exclusion criteria

• Significant gastrointestinal (including hepatic), hematological, cardiovascular, cerebrovascular, metabolic such as including type II diabetes or other body system disorder.
• Regular consumption of fish consisting more than 1 meal of fish per week or regular fish oil supplements during the trial and for at least 2 weeks prior to the first study visit.
• Subjects who have taken oral corticosteroids or a leukotriene receptor antagonist in 4 weeks prior to entry into the study.
• Psychosis, alcoholism, active substance abuse, or any personality disorder, which would make compliance with this protocol problematic.
• Pregnant or nursing females.
• Any other medical or social condition which, in the opinion of the investigator, could confound the interpretation of the data derived from this study.
• Subjects taking >1000 mcg of inhaled steroids daily in those subjects taking inhaled steroids.
• Subjects requiring regular anti-histamines for allergies.
• Subjects who have allergy to fish or any other ingredient in the study products.
• Subjects using anti-coagulants (warfarin, heparin)
• Subjects who have surgery planned over the course of the trial.
• Subjects who use medications to lower LDL cholesterol levels
• Subjects using non-steroidal anti-inflammatory medications (e.g., aspirin, ibuprofen)