HO-1 has been shown to decrease proinflammatory cytokines, such as tumor necrosis factor alpha (TNF-α), in vitro5, 6 as well as in vivo.7, 8 We could show previously that induction or overexpression of HO-1 reduces liver damage in mouse models of acute inflammation.7, 8 Here, we investigated

the effects of HO-1 induction on chronic inflammation and fibrosis of the liver. Chronic hepatitis, induced by, for example, viral infections or chronic exposure to toxins represents a severe health problem, because it bears a risk of progression to hepatocellular carcinoma (HCC), which represents the fifth most common cancer worldwide.9, 10 To investigate HO-1 effects on chronic hepatitis, we used an animal model selleckchem of chronic portal inflammation and bile duct proliferation with progression to liver fibrosis and HCC (multidrug resistance transporter 2 knockout [Mdr2ko] mouse; FVB.129P2-Abcb4tm1Bor).11 Mdr2ko mice are lacking the Mdr2 P-glycoprotein, a phosphatidylcholine transporter, resulting in dysfunctional phospholipid secretion.12 Signs of inflammation (e.g. intense hepatic leukocyte infiltrations), which appear within the

first weeks of age, are accompanied by an increase in plasma Vadimezan solubility dmso transaminase levels Hydroxychloroquine nmr and followed by enhanced connective tissue storage and progression to fibrosis.13 Fibrogenesis is a dynamic process associated with activation of hepatic stellate cells (HSCs), which is characterized by collagen

and alpha smooth muscle actin (α-SMA) expression as well as chemokine secretion and activation of matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of matrix metalloproteinases (TIMPs).14 As a consequence of chronic inflammation and progressing fibrosis, Mdr2ko mice have been shown to develop HCC within 12-15 months of age.15 We investigated the effect of HO-1 induction on chronic inflammation and fibrogenesis in mice with mild or established fibrosis. Our results show that HO-1 induction decreased chronic inflammation by regulating immune cell infiltration or proliferation, TNF receptor (TNFR) expression, and subsequent events in proinflammatory cytokine signaling, such as extracellular signal-related kinase (ERK) phosphorylation. Liver damage was significantly ameliorated for at least 8 weeks beyond treatment. HO-1 induction improved lobular fibrosis as well as portal inflammation to a state observed before the onset of treatment. In conclusion, induction of HO-1 interfered with chronic inflammation and fibrosis formation.