Modulation of growth factor binding properties of a2-macroglobulin by enzyme therapy

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Purpose: To investigate the binding of transforming growth factor-beta (TGF-β) to human α2-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 7 days at low dose followed by a bolus application. Before and after medication plasma was immediately withdrawn and binding of 125I-TGF-β to the proteinase inhibitor α2-macroglobulin was determined by electrophoresis and γ-counting. Cell culture experiments were performed to study the effect of transformed α2-macroglobulin on TGF-β-stimulated proliferation of skin fibroblasts. Results: Ingestion of proteinases was found to trigger the formation of intermediate forms of α2-macroglobulin displaying high affinity to TGF-β. Maximum binding of TGF-β was observed 1–2 h after bolus ingestion, and steadily levelled off with time. In vitro experiments demonstrated that complex formation of diverse proteinases (trypsin, α-chymotrypsin, bromelain and plasmin) with α2-macroglobulin conferred binding of 125I-TGF-β. α2-Macroglobulin transformed by methylamine or proteinases was found to abolish the TGF-β effect on fibroblasts in cell culture. Conclusions: Intestinal absorption of proteinases triggers the formation of TGF-β binding species of α2-macroglobulin in blood. Mediated by this process high concentrations of TGF-β might be reduced via enhanced clearance of α2-macroglobulin-TGF-β complexes. Thus, proteinase therapy may have beneficial effects in treatment of fibrosis and certain cancers accompanied by excessively high TGF-β concentrations.