Improvement of Hepatic fibrosis/cirrhosis and impaired liver regeneration using protease inhibitors

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Transforming growth factor-β(TGF-β), a potent fibrogenic and growth-suppressing cytokine, is composed of two different gene products, and secreted as latent form. It must be activated before binding to receptors and exerting its activities. Latent TGF-β is physiologically activated by specific cleavage of latency-associated peptide (LAP) portion with proteases such as plasmin (PLN) or plasma kallikrein (PLK). In the current study, using animal models, we have established that TGF-β is secreted and activated either by PLN in liver fibrosis/cirrhosis or by PLK in impaired liver regeneration, and therefore that inhibition of the activation with protease inhibitors including FOY305 (camostat mesilate) prevents the development of the diseases. We then determined different cleavage sites by PLN and PLK in LAP portion and raised antibodies in rabbits by immunizing LAP sequence peptides beginning from or ending at these cleavage sites. Purified antibody against N-terminus of PLK-cleaved site specifically recognized PLK-cleaved LAP, but not uncleaved LAP, and weakly recognized PLN-cleaved LAP in Western Blot. Liver sections from LPS-pretreated and partial hepatectomized mice were specifically immunostained with this antibody as well as anti-active TGF-β antibody. The anti-cleaved LAP antibody also weakly but significantly stained liver sections from patients with fulminant hepatitis compared to pre-immune antibody, suggesting that PLK-dependent activation reaction may occur to produce active TGF-β, which suppresses regeneration of the patient liver. In addition, we discovered a compound CXZ, which interferes with TGF-β signaling and thus exerts a synergism in suppressing the activation of hepatic stellate cells with the protease inhibitor, suggesting a promising combination therapy of CXZ and protease inhibitors against the liver diseases.