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Published on: August 27, 2015
Nicotinamide adenine dinucleotide phosphate oxidase in experimental liver fibrosis: GKT137831 as a novel potential
Tomonori Aoyama1, Yong-Han Paik, Sumio Watanabe
1Department of Medicine, University of California San Diego, La Jolla, CA 92093-0602, USA.
Unlabelled:
Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) generates reactive oxygen species (ROS) in hepatic stellate cells (HSCs) during liver fibrosis. In response to fibrogenic agonists, such as angiotensin II (Ang II), the NOX1 components form an active complex, including Ras-related botulinum toxin substrate 1 (Rac1). Superoxide dismutase 1 (SOD1) interacts with the NOX-Rac1 complex to stimulate NOX activity. NOX4 is also induced in activated HSCs/myofibroblast by increased gene expression. Here, we investigate the role of an enhanced activity SOD1 G37R mutation (SODmu) and the effects of GKT137831, a dual NOX1/4 inhibitor, on HSCs and liver fibrosis. To induce liver fibrosis, wild-type (WT) and SOD1mu mice were treated with CCl(4) or bile duct ligation (BDL). Then, to address the role of NOX-SOD1-mediated ROS production in HSC activation and liver fibrosis, mice were treated with a NOX1/4 inhibitor. Fibrosis and ROS generation was assessed by histology and measurement of thiobarbituric acid reactive substances and NOX-related genes. Primary cultured HSCs isolated from WT, SODmu, and NOX1 knockout (KO) mice were assessed for ROS production, Rac1 activity, and NOX gene expression. Liver fibrosis was increased in SOD1mu mice, and ROS production and Rac1 activity were increased in SOD1mu HSCs. The NOX1/4 inhibitor, GKT137831, attenuated liver fibrosis and ROS production in both SOD1mu and WT mice as well as messenger RNA expression of fibrotic and NOX genes. Treatment with GKT137831 suppressed ROS production and NOX and fibrotic gene expression, but not Rac1 activity, in SOD1mut and WT HSCs. Both Ang II and tumor growth factor beta up-regulated NOX4, but Ang II required NOX1.
Conclusions:
SOD1mu induces excessive NOX1 activation through Rac1 in HSCs, causing enhanced NOX4 up-regulation, ROS generation, and liver fibrosis. Treatment targeting NOX1/4 may be a new therapy for liver fibrosis.
Insights
A mutation in superoxide dismutase 1 (SOD1) enhances nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) activity, increasing reactive oxygen species (ROS) and liver fibrosis. Targeting NOX1/4 enzymes with GKT137831 may offer a novel therapeutic strategy for liver fibrosis.
Area of Science:
- Hepatology and cellular biology
- Oxidative stress and fibrosis mechanisms
- Enzyme kinetics and drug development
Background:
- Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) enzymes generate reactive oxygen species (ROS) in hepatic stellate cells (HSCs), contributing to liver fibrosis.
- The NOX1 complex, involving Ras-related botulinum toxin substrate 1 (Rac1), and Superoxide dismutase 1 (SOD1) are implicated in fibrogenesis.
- NOX4 expression is also upregulated in activated HSCs during liver fibrosis.
Purpose of the Study:
- To investigate the role of a SOD1 G37R mutation (SODmu) with enhanced activity in HSCs and liver fibrosis.
- To evaluate the therapeutic potential of GKT137831, a dual NOX1/4 inhibitor, in mitigating liver fibrosis.
- To elucidate the specific pathways of NOX-SOD1-mediated ROS production in HSC activation and fibrotic progression.
Main Methods:
- Induction of liver fibrosis in wild-type (WT) and SOD1mu mice using CCl(4) or bile duct ligation (BDL).
- Administration of the NOX1/4 inhibitor GKT137831 to assess its effects on fibrosis and ROS generation.
- Assessment of ROS production, Rac1 activity, and NOX/fibrotic gene expression in primary cultured HSCs from WT, SODmu, and NOX1 knockout mice.
Main Results:
- SOD1mu mice exhibited increased liver fibrosis, ROS production, and Rac1 activity in HSCs.
- GKT137831 treatment significantly attenuated liver fibrosis and ROS production in both SOD1mu and WT mice.
- GKT137831 suppressed ROS and fibrotic gene expression in HSCs, but did not affect Rac1 activity.
Conclusions:
- The SOD1mu mutation drives excessive NOX1 activation via Rac1 in HSCs, leading to increased NOX4 expression, ROS generation, and liver fibrosis.
- Targeting NOX1/4 enzymes represents a promising therapeutic avenue for treating liver fibrosis.
- Understanding the interplay between NOX, SOD1, and ROS is crucial for developing effective anti-fibrotic strategies.
