Another way for NADPH oxidase to send a signal for liver injury

Angiotensin II increases mRNA levels of all TGF-beta isoforms in quiescent and activated rat hepatic stellate cells

AII (angiotensin II) is a vasoactive peptide that plays an important role in the development of liver fibrosis mainly by regulating profibrotic cytokine expression such as TGF-beta (transforming growth factor-beta). Activated HSCs (hepatic stellate cells) are the major cell type responsible for ECM (extracellular matrix) deposition during liver fibrosis and are also a target for AII and TGF-beta actions. Here, we studied the effect of AII on the mRNA levels of TGF-beta isoforms in primary cultures of rat HSCs. Both quiescent and activated HSCs were stimulated with AII for different time periods, and mRNA levels of TGF-beta1, TGF-beta2 and TGF-beta3 isoforms were evaluated using RNaseI protection assay. The mRNA levels of all TGF-beta isoforms, particularly TGF-beta2and TGF-beta3, were increased after AII treatment in activated HSCs. In addition, activated HSCs were able to produce active TGF-beta protein after AII treatment. The mRNA expression of TGF-beta isoforms induced by AII required both ERK1/2 and Nox (NADPH oxidase) activation but not PKC (protein kinase C) participation. ERK1/2 activation induced by AII occurs via AT1 receptors, but independently of either PKC and Nox activation or EGFR (epidermal growth factor receptor) transactivation. Interestingly, AII has a similar effect on TGF-beta expression in quiescent HSCs, although it has a smaller but significant effect on ERK1/2 activation in these cells.

Hyperhomocysteinemia induces liver injury in rat: Protective effect of folic acid supplementation

Hyperhomocysteinemia, a condition of elevated blood homocysteine level, is an independent risk factor for cardiovascular diseases. Hyperhomocysteinemia is also found in patients with liver diseases. However, the direct effect of homocysteine on liver injury is not well known. Folic acid supplementation is a promising approach for improving endothelial function in patients with hyperhomocysteinemia. The aim of this study was to investigate the direct effect of hyperhomocysteinemia on liver injury and whether folic acid could offer any protective effect to the liver. Hyperhomocysteinemia was induced in rats fed a high-methionine diet for 4 weeks. There was a significant increase in the serum aspartate aminotransferase and alanine aminotransferase activities reflecting liver injury in hyperhomocysteinemic rats. Hepatic NAD(P)H oxidase was activated during hyperhomocysteinemia leading to increased superoxide anion production and peroxynitrite formation in the liver. As a consequence, the level of lipid peroxides was significantly elevated in livers of hyperhomocysteinemic rats. Folic acid supplementation effectively inhibited NAD(P)H oxidase-mediated superoxide anion production leading to reduced lipid peroxidation in the liver. Folic acid supplementation also alleviated hyperhomocysteinemia-induced liver injury. These results suggest that hyperhomocysteinemia can cause liver injury and supplementation of folic acid offers a hepatoprotective effect.