Bromelain is a proteolytic enzyme found primarily in the fruit juice and stem of plants belonging to the Bromeliaceae botanical family with pineapple being the one most familiar to us. Its concentration is highest in the pineapple stem which is typically a waste byproduct of pineapple juice extraction. Bromelain seems to be best known as a digestive aid for the breakdown of dietary proteins but the beneficial effects of bromelain aren't limited to this property. This enzyme exerts interesting effects in the lungs suggesting it could be a helpful adjunct used in pulmonary edema bronchitis sinusitis and conditions related to inflammatory airway diseases such as asthma.

In a mouse model of allergic airway disease (AAD) oral supplementation with bromelain at 6mg/kg exerted anti-inflammatory properties as illustrated by significant reduction of inflammatory markers compared to placebo. Reduced inflammatory markers and compounds included bronchoalveolar lavage (BAL) total leukocytes eosinophils and interleukins IL-4 IL-12 IL-17 and IFN-I±. These results confirmed earlier findings that employed intraperitoneal bromelain supplementation which led to attenuated development of AAD and reduced levels of CD4+ T-lymphocytes. This is significant because researchers have concluded that depletion of CD4+ T cells in the animal model prevents pulmonary eosinophilia and airway hyperresponsiveness.

In vitro and in vivo studies suggest the anti-inflammatory properties of bromelain may be due to the enzymes influence on the migration of neutrophils to sites of inflammation. In human neutrophils in vitro bromelain inhibited IL-8-stimulated migration of neutrophils. The predominant effect of bromelain on leukocytes seems to be a reduction in firm adhesion to the site of inflammation via removing cell surface molecules required for adhesion. These adhesion molecules were reduced by almost 50% in bromelain-treated mice compared to those treated with saline. The effects are both short and long-term; bromelain exerts different inhibitory effects on specific adhesion molecules with expression of some of them returning to normal within 30 minutes of treatment while others remained suppressed for up to six hours.

A mouse model of pulmonary edema showed that bioactive bromelain given intravenously at a dose of 10mg/kg prevented this dangerous condition in eight out of nine mice. The opposite held true for a separate experimental group treated with bromelain whose proteolytic activity had been deactivated. This group developed pulmonary edema to the tune of eight out of nine mice leading the authors to conclude that the protective effects of bromelain in this case are connected to its proteolytic properties. 

It's logical that the beneficial effects of bromelain on lung function are a result of its protease activity. Using pulmonary fibrosis as an example thick fibrin deposits on the alveoli prevent normal exchange of carbon dioxide and oxygen leading to shortness of breath upon exertion. If bromelain is successful in degrading some of the fibrin lung capacity and ease of breathing could be improved. 

Allergic rhinitis (AR) is another condition for which bromelain might be a helpful addition to conventional treatment. AR is essentially an inflammatory disease of the nasal mucous membranes which results in sneezing nasal itching and blockage of the nasal passages. As study authors point out “systemic circulation of inflammatory cells allows their infiltration into other tissues where chemoattractant and adhesion molecules already exist. Thus besides local inflammation AR also triggers a systemic inflammation which can in turn augment inflammation in both the upper and lower airways. Consequently AR is linked to various comorbid conditions including asthma rhinosinusitis and nasal polyposis. Bromelain's anti-inflammatory effects could reduce both the local and systemic inflammation that contribute to a variety of lung- and breathing-related conditions.

As a supplement bromelain has been demonstrated to be safe at high doses with no observable side-effects even up to 12g/day. It has been detected undegraded in plasma suggesting it transits the digestive tract intact retaining its biological activity throughout the body. These factors make bromelain an intriguing option for patients with difficult-to-treat conditions that affect breathing.