Bromelain, a mixture of
proteases derived from pineapple stem, has been reported to have therapeutic benefits in a variety of inflammatory diseases, including murine
inflammatory bowel disease. The purpose of this work was to understand potential mechanisms for this anti-inflammatory activity. Exposure to
bromelain in vitro has been shown to remove a number of cell surface molecules that are vital to leukocyte trafficking, including CD128a/CXCR1 and CD128b/CXCR2 that serve as receptors for the neutrophil
chemoattractant IL-8 and its murine homologues. We hypothesized that specific proteolytic removal of CD128 molecules by
bromelain would inhibit neutrophil migration to
IL-8 and thus decrease acute responses to inflammatory stimuli. Using an in vitro chemotaxis assay, we demonstrated a 40% reduction in migration of
bromelain- vs.
sham-treated human neutrophils in response to rhIL-8. Migration to the bacterial
peptide analog fMLP was unaffected, indicating that
bromelain does not induce a global defect in leukocyte migration. In vivo
bromelain treatment generated a 50-85% reduction in neutrophil migration in 3 different murine models of leukocyte migration into the inflamed peritoneal cavity. Intravital microscopy demonstrated that although in vivo
bromelain treatment transiently decreased leukocyte rolling, its primary long-term effect was abrogation of firm adhesion of leukocytes to blood vessels at the site of
inflammation. These changes in adhesion were correlated with rapid re-expression of the
bromelain-sensitive CD62L/
L-selectin molecules that mediate rolling following in vivo
bromelain treatment and minimal re-expression of CD128 over the time period studied. Taken together, these studies demonstrate that
bromelain can effectively decrease neutrophil migration to sites of acute
inflammation and support the specific removal of the CD128
chemokine receptor as a potential mechanism of action.