Delayed and persistent suppression of bronchoconstriction by trypsin in the airway lumen

Protease-activated receptors and prostaglandins in inflammatory lung disease

Protease-activated receptors (PARs) are a novel family of G protein-coupled receptors. Signalling through PARs typically involves the cleavage of an extracellular region of the receptor by endogenous or exogenous proteases, which reveals a tethered ligand sequence capable of auto-activating the receptor. A considerable body of evidence has emerged over the past 20 years supporting a prominent role for PARs in a variety of human physiological and pathophysiological processes, and thus substantial attention has been directed towards developing drug-like molecules that activate or block PARs via non-proteolytic pathways. PARs are widely expressed within the respiratory tract, and their activation appears to exert significant modulatory influences on the level of bronchomotor tone, as well as on the inflammatory processes associated with a range of respiratory tract disorders. Nevertheless, there is debate as to whether the principal response to PAR activation is an augmentation or attenuation of airways inflammation. In this context, an important action of PAR activators may be to promote the generation and release of prostanoids, such as prostglandin E(2), which have well-established anti-inflammatory effects in the lung. In this review, we primarily focus on the relationship between PARs, prostaglandins and inflammatory processes in the lung, and highlight their potential role in selected respiratory tract disorders, including pulmonary fibrosis, asthma and chronic obstructive pulmonary disease.

Acid aspiration-induced airways hyperresponsiveness in mice

The role of gastroesophageal reflux and micro-aspiration as a trigger of airways hyperresponsiveness (AHR) in patients with asthma is controversial. The role of acid reflux and aspiration as a direct cause of AHR in normal subjects is also unclear. We speculated that aspiration of a weak acid with a pH (1.8) equivalent to the upper range of typical gastric contents would lead to AHR in naive mice. We further speculated that modest reductions in aspirate acidity to a level expected during gastric acid suppression therapy (pH 4.0) would impede aspiration-induced AHR. BALB/c female mice were briefly anesthetized with isoflurane and allowed to aspirate 75 microl of saline with HCl (pH 1.8, 4.0, or 7.4) or underwent sham aspiration. Mice were re-anesthetized 2 or 24 h later, underwent tracheostomy, and were coupled to a mechanical ventilator. Forced oscillations were used to periodically measure respiratory impedance (Zrs) following aerosol delivery of saline and increasing doses of methacholine to measure for AHR. Values for elastance (H), airways resistance (R(N)), and tissue damping (G) were derived from Zrs. Aspirate pH of 1.8 led to a significant overall increase in peak R(N), G, and H compared with pH 4.0 and 7.4 at 2 and 24 h. Differences between pH 7.4 and 4.0 were not significant. In mice aspirating pH 1.8 compared with controls, airway lavage fluid contained more neutrophils, higher protein, and demonstrated higher permeability. We conclude that acid aspiration triggers an acute AHR, driven principally by breakdown of epithelial barrier integrity within the airways.