AbstractPurpose: To investigate the binding of transforming growth factor-beta (TGF-) to human 2-macroglobulin upon oral treatment of patients with proteases. Methods: Volunteers were given a cocktail of active proteinases (Phlogenzym) composed of trypsin, bromelain and the additive rutoside orally over a period of 7days at low dose followed by a bolus application. Before and after medication plasma was immediately withdrawn and binding of 125I-TGF- to the proteinase inhibitor 2-macroglobulin was determined by electrophoresis and -counting. Cell culture experiments were performed to study the effect of transformed 2-macroglobulin on TGF--stimulated proliferation of skin fibroblasts. Results: Ingestion of proteinases was found to trigger the formation of intermediate forms of 2-macroglobulin displaying high affinity to TGF-. Maximum binding of TGF- was observed 12h after bolus ingestion, and steadily levelled off with time. In vitro experiments demonstrated that complex formation of diverse proteinases (trypsin, -chymotrypsin, bromelain and plasmin) with 2-macroglobulin conferred binding of 125I-TGF-. 2-Macroglobulin transformed by methylamine or proteinases was found to abolish the TGF- effect on fibroblasts in cell culture. Conclusions: Intestinal absorption of proteinases triggers the formation of TGF- binding species of 2-macroglobulin in blood. Mediated by this process high concentrations of TGF- might be reduced via enhanced clearance of 2-macroglobulin-TGF- complexes. Thus, proteinase therapy may have beneficial effects in treatment of fibrosis and certain cancers accompanied by excessively high TGF- concentrations.