Inhibition of matrix metalloproteinases increases PPAR-α and IL-6 and prevents dietary-induced hepatic steatosis and injury in a murine model

Abstract

Steatosis is a prominent feature of nonalcoholic fatty liver disease and a potential promoter of inflammation. Injury leading to cirrhosis is partly mediated by dysregulation of matrix protein turnover. Matrix metalloproteinase (MMP) inhibitors protect mice from lethal TNF-α induced liver injury. We hypothesized that Marimastat, a broad-spectrum MMP and TNF-α converting enzyme (TACE) inhibitor, might modulate this injury through interruption of inflammatory pathways. Triglyceride and phospholipid levels (liver, serum) and fatty acid profiles were used to assess essential fatty acid status and de novo lipogenesis as mechanisms for hepatic steatosis. Mice receiving a fat-free, high-carbohydrate diet (HCD) for 19 days developed severe fatty liver infiltration, demonstrated by histology, magnetic resonance spectroscopy, and elevated liver function tests. Animals receiving HCD plus Marimastat (HCD+MAR) were comparable to control animals. Increased tissue levels of peroxisome proliferator activated receptor-α (PPAR-α), higher levels of serum IL-6, and decreased levels of serum TNF-α receptor II were also seen in the HCD+MAR group compared with HCD-only. In addition, there was increased phosphorylation, and likely activation, of PPAR-α in the HCD+MAR group. PPAR-α is a transcription factor involved in β-oxidation of fatty acids, and IL-6 is a hepatoprotective cytokine. Liver triglyceride levels were higher and serum triglyceride and phospholipid levels lower with HCD-only but improved with Marimastat treatment. HCD-only and HCD+MAR groups were essential fatty acid deficient and had elevated rates of de novo lipogenesis. We therefore conclude that Marimastat reduces liver triglyceride accumulation by increasing fat oxidation and/or liver clearance of triglycerides. This may be related to increased expression and activation of PPAR-α or IL-6, respectively.