High-fat diet decreases activity of the oxidative phosphorylation complexes and causes nonalcoholic steatohepatitis in mice

Abstract

Nonalcoholic fatty liver disease (NAFLD) is the most frequent histological finding in individuals with abnormal liver-function tests in the Western countries. In previous studies, we have shown that oxidative phosphorylation (OXPHOS) is decreased in individuals with NAFLD, but the cause of this mitochondrial dysfunction remains uncertain. The aims of this study were to determine whether feeding mice a high-fat diet (HFD) induces any change in the activity of OXPHOS, and to investigate the mechanisms involved in the pathogenesis of this defect. To that end, 30 mice were distributed between five groups: control mice fed a standard diet, and mice on a HFD and treated with saline solution, melatonin (an antioxidant), MnTBAP (a superoxide dismutase analog) or uric acid (a scavenger of peroxynitrite) for 28 weeks intraperitoneously. In the liver of these mice, we studied histology, activity and assembly of OXPHOS complexes, levels of subunits of these complexes, gene expression of these subunits, oxidative and nitrosative stress, and oxidative DNA damage. In HFD-fed mice, we found nonalcoholic steatohepatitis, increased gene expression of TNFα, IFNγ, MCP-1, caspase-3, TGFβ1 and collagen α1(I), and increased levels of 3-tyrosine nitrated proteins. The activity and assembly of all OXPHOS complexes was decreased to about 50–60%. The amount of all studied OXPHOS subunits was markedly decreased, particularly the mitochondrial-DNA-encoded subunits. Gene expression of mitochondrial-DNA-encoded subunits was decreased to about 60% of control. There was oxidative damage to mitochondrial DNA but not to genomic DNA. Treatment of HFD-fed mice with melatonin, MnTBAP or uric acid prevented all changes observed in untreated HFD-fed mice. We conclude that a HFD decreased OXPHOS enzymatic activity owing to a decreased amount of fully assembled complexes caused by a reduced synthesis of their subunits. Antioxidants and antiperoxynitrites prevented all of these changes, suggesting that nitro-oxidative stress played a key role in the pathogenesis of these alterations. Treatment with these agents might prevent the development of NAFLD in humans.

MnTBAP stimulates angiogenic functions in endothelial cells through mitofusin-1

“…One factor could be an insufficient dosage of MnTBAP. Although most published in vivo studies also treated mice with MnTBAP at a dosage of 5mg/kg BW, some studies have used dosages up to 15mg/kg BW [4, 8, 10]. However, our data suggest, that higher concentration of MnTBAP may elicit toxic effects on the cellular level.…”

Role of CYP2E1 in Mitochondrial Dysfunction and Hepatic Injury by Alcohol and Non-Alcoholic Substances

“…In addition, mitochondrial DNA and proteins are more susceptible to nitroxidative damage due to the absence of protective antioxidant protein catalase, the low activity of DNA repair enzymes, and the absence of histones and polyamines [178]. The damage of mitochondrial DNA, which is essential for normal formation of the ETC components, and inefficient repair are thought to be important in both alcohol- and HFD-induced hepatic cellular damage [179–182]. Enhanced mitochondrial generation of ROS has been reported in obese (ob/ob) mice [183] and a rat model of steatosis and steatohepatitis exposed to a choline-deficient diet [184, 185].…”

“…Further, mitochondrial DNA damage and/or PTMs of mitochondrial proteins by nitroxidative stress would result in decreased expression, assembly and activity of the mitochondrial ETC complexes. Indeed, under high levels of ROS/RNS in AFLD, NAFLD as observed with HFD or in obese (ob/ob) mice and in DILI by APAP, the activities of the hepatic mitochondrial ETC complexes were significantly compromised, ultimately contributing to more hepatocellular ROS production and the development of a vicious cycle of ROS/RNS production [19, 179–182, 189–192]. …”

ShenFu Preparation Protects AML12 Cells Against Palmitic Acid-Induced Injury Through Inhibition of Both JNK/Nox4 and JNK/NFκB Pathways

“…Nox4 mRNA level was also upregulated in PA-treated HepG2 cell [25]. In the liver tissue of obsess mice, TGFβ is increased, leading to upregulation of Nox4 [26, 27]. Reduced MMP and elevated ROS levels were also described in treatment of primary rat hepatocytes with PA [10].…”