Bromelain treatment alters leukocyte expression of cell surface molecules involved in cellular adhesion and activation.

Bromelain is a natural proteinase preparation derived from pineapple stem that is marketed for oral use as a digestive aid and as an antiinflammatory agent. Bromelain treatment in vitro has been previously shown to selectively remove certain cell surface molecules that may affect lymphocyte migration and activation. This study reports the effects of bromelain on a broad range of cell surface molecules and on lymphocytes, monocytes, and granulocytes under physiologically relevant conditions. In vitro bromelain treatment of leukocytes in whole blood proteolytically altered 14 of 59 leukocyte markers studied. Constitutively expressed bromelain-sensitive molecules included CD7, CD8alpha, CD14, CD16, CD21, CD41, CD42a, CD44, CD45RA, CD48, CD57, CD62L, CD128a, and CD128b. The proteolytic effect of bromelain increased as the concentration of plasma decreased, with EC50 ranging from >1000 microg/ml for 100% plasma to approximately 1 microg/ml in the absence of plasma, indicating the presence of an inhibitor of bromelain in plasma. alpha2-macroglobulin purified from plasma mimicked the inhibitory effect of whole plasma on bromelain activity. If proteolysis is required for the antiinflammatory actions of oral bromelain, these data suggest that the required concentrations are more likely to be achieved locally in the gastrointestinal tract or in other tissue sites where the plasma concentration is low, rather than in the bloodstream. The cell surface molecules altered by bromelain are involved in leukocyte homing and cellular adhesion and activation. Thus bromelain could potentially exert an antiinflammatory effect by multiple mechanisms, including alterations in leukocyte migration and activation.