Asthma is an increasingly common chronic illness with higher rates of hospitalization for exacerbation than many other chronic conditions. In 2009, total asthma costs in the U.S. were estimated at $56 billion per year, and over half the overall asthma-related costs were attributed to inpatient hospitalization. Allergen exposure and viral infection are among the most common triggers for asthma exacerbations. Exacerbations of allergic asthma are characterized by an early phase response (EPR), mediated by release of preformed mediators like histamine from mast cells, and a late phase response (LPR) 3-7 hours later mediated by chemokines and cytokines, including IL-1β, that attract leukocytes such as neutrophils and eosinophils to the airways, increase mucus production, trigger airway smooth muscle contraction, and result in airway constriction and airway hyper-reactivity (AHR). The LPR is thought to be predominantly responsible for the symptoms associated with acute exacerbations of allergic asthma.
While corticosteroids are considered a mainstay of treatment for asthma exacerbation regardless of the trigger, there are limitations to their effectiveness in the acute setting including the initial lag period of 4-6 hours or more before therapeutic effect and the concern for broad immune suppression. Corticosteroids are often ineffective in treating the neutrophilic component of airway inflammation seen with viral infection and allergen-induced airway inflammation . Finally, mucus plugging is a known hallmark of severe and fatal asthma, yet there is a notable lack of effective mucolytic treatments for asthma. Time to therapeutic benefit is key in preventing patient morbidity and mortality. Currently there is an urgent need for anti-inflammatory treatments that work quickly and effectively in acute asthma exacerbations.
The investigators propose that IL-1 blockade can achieve these ends and perhaps complement corticosteroid actions. Anakinra is an FDA-approved recombinant form of human IL-1 receptor antagonist (IL-1RA), a natural anti-inflammatory cytokine that competes with agonist binding to the IL-1 receptor, suppressing IL-1β and IL-1a signaling. Numerous studies indicate that IL-1 signaling mediates key features of viral- and allergen-induced airway inflammation. IL-1 signaling can directly impact three aspects of an airway inflammatory response: granulocyte (neutrophil/eosinophil) recruitment; non-specific and allergen-specific airway reactivity; and mucin production. Numerous IL-1 blocking agents are FDA-approved for conditions where the IL-1β pathway predominates disease pathophysiology, such as in systemic juvenile idiopathic arthritis and the cryopyrin-associated periodic syndromes.
Anakinra is an ideal candidate to test as a rescue treatment for acute asthma exacerbation due to its fast onset of action (reaching peak concentrations in 3-7 hours), and a short 4-6 hour half-life. A single 1mg/kg dose (up to 100mg) of anakinra or placebo will be administered at the onset of the LPR to model anakinra use in an emergency care setting. This dose was chosen because it is the current FDA-approved dose for rheumatoid arthritis (RA). Notably, the investigators have previously demonstrated that a 1 mg/kg dose resulted in significant reduction in airway granulocyte recruitment following lipopolysaccharide (LPS) challenge in a study of healthy volunteers. The investigators' objective is to determine if a single 1 mg/kg dose of Anakinra can mitigate key features of asthma exacerbations, namely AHR, airway constriction, airway inflammation, and mucous secretion/clearance.
