Stem bromelain-induced macrophage apoptosis and activation curtail Mycobacterium tuberculosis persistence

Mycobacterium tuberculosis, the causative agent of tuberculosis, has a remarkable ability to usurp its host's innate immune response, killing millions of infected people annually. One approach to manage infection is prevention through the use of natural agents. In this regard, stem bromelain (SBM), a pharmacologically active member of the sulfhydryl proteolytic enzyme family, obtained from Ananas comosus and possessing a remarkable ability to induce the innate and acquired immune systems, is important.

We evaluated SBM's ability to induce apoptosis and free-radical generation in macrophages. We also studied antimycobacterial properties of SBM and its effect on foamy macrophages.

SBM treatment of peritoneal macrophages resulted in the upregulation of proapoptotic proteins and downregulation of antiapoptotic proteins. Additionally, SBM treatment activated macrophages, curtailed the levels of free glutathione, and augmented the production of hydrogen peroxide, superoxide anion, peroxynitrite, and nitric oxide. SBM cleaves CD36 and reduced the formation of foam cells, the hallmark of M. tuberculosis infection. These conditions created an environment for the increased clearance of M. tuberculosis.

Together these data provide a mechanism for antimycobacterial activity of SBM and provide important insights for the use of cysteine proteases as immunomodulatory agents.