Blockade of renin-angiotensin system in antifibrotic therapy

Recent studies have shown that the renin-angiotensin system (RAS) plays a pivotal role in liver fibrosis. An intrahepatic RAS is expressed in chronically damaged livers, and angiotensin-II (AT-II) reportedly stimulates contraction and proliferation of the activated hepatic stellate cells (Ac-HSC), and increases the transforming growth factor-beta (TGF-beta) expression through angiotensin type-I receptors (AT1-R). Some studies have demonstrated that the clinically used angiotensin-converting enzyme (ACE) inhibitor (ACE-I), and AT1-R blockers (ARB) significantly attenuated experimental liver fibrosis along with suppression of the Ac-HSC and hepatic TGF-beta expression. Angiotensin-II also stimulates the tissue inhibitor of metalloproteinases-1 (TIMP-1) in a dose- and time-dependent manner via protein kinase-C as an intracellular signaling cascade in the Ac-HSC, and these effects are completely suppressed by ARB. Combination treatment with low-dose interferon (IFN) and ACE-I exerts a stronger inhibitory effect than either single agent on its own. In humans it has been reported that ARB markedly improved the liver fibrosis score and TGF-beta expression in patients with chronic hepatitis C and non-alcoholic steatohepatitis. Serum fibrosis markers also significantly improved by treatment with low-dose IFN and ACE-I in patients with chronic hepatitis C, refractory to IFN monotherapy. Collectively, these data suggest that the interaction between AT-II and AT1-R plays a pivotal role in liver fibrosis development. Because both ACE-I and ARB are widely used in clinical practice without serious side-effects, these drugs in combination with IFN may provide a new strategy for antifibrosis therapy.