PPAR/RXR Regulation of Fatty Acid Metabolism and Fatty Acid omega-Hydroxylase (CYP4) Isozymes: Implications for Prevention of Lipotoxicity in Fatty Liver Disease. PPAR Res. 2009;2009:952734. [PMID: 20300478 PMCID: PMC2840373 DOI: 10.1155/2009/952734]

Cardiac function and disease: emerging role of small ubiquitin-related modifier

Small ubiquitin-related modifiers, or SUMOs, have emerged as versatile regulators of many biological functions that do so by covalent attachment to a variety of substrates via enzymatic reactions. SUMO conjugation has also been shown to be involved in a number of human pathogenic processes. More recent advances in the SUMO field have indicated a potential role for SUMO conjugation pathway in cardiogenesis. This advanced review will describe the basic features of the SUMO conjugation pathway and will summarize the most recent studies implicating the influence of the sumoylation pathway in cardiac function under both physiological and pathological conditions. WIREs Syst Biol Med 2011 3 446-457 DOI: 10.1002/wsbm.130

Drug-induced toxicity on mitochondria and lipid metabolism: mechanistic diversity and deleterious consequences for the liver

Numerous investigations have shown that mitochondrial dysfunction is a major mechanism of drug-induced liver injury, which involves the parent drug or a reactive metabolite generated through cytochromes P450. Depending of their nature and their severity, the mitochondrial alterations are able to induce mild to fulminant hepatic cytolysis and steatosis (lipid accumulation), which can have different clinical and pathological features. Microvesicular steatosis, a potentially severe liver lesion usually associated with liver failure and profound hypoglycemia, is due to a major inhibition of mitochondrial fatty acid oxidation (FAO). Macrovacuolar steatosis, a relatively benign liver lesion in the short term, can be induced not only by a moderate reduction of mitochondrial FAO but also by an increased hepatic de novo lipid synthesis and a decreased secretion of VLDL-associated triglycerides. Moreover, recent investigations suggest that some drugs could favor lipid deposition in the liver through primary alterations of white adipose tissue (WAT) homeostasis. If the treatment is not interrupted, steatosis can evolve toward steatohepatitis, which is characterized not only by lipid accumulation but also by necroinflammation and fibrosis. Although the mechanisms involved in this aggravation are not fully characterized, it appears that overproduction of reactive oxygen species by the damaged mitochondria could play a salient role. Numerous factors could favor drug-induced mitochondrial and metabolic toxicity, such as the structure of the parent molecule, genetic predispositions (in particular those involving mitochondrial enzymes), alcohol intoxication, hepatitis virus C infection, and obesity. In obese and diabetic patients, some drugs may induce acute liver injury more frequently while others may worsen the pre-existent steatosis (or steatohepatitis).

Fasting-induced oxidative stress in very long chain acyl-CoA dehydrogenase-deficient mice

Hepatopathy and hepatomegaly as consequences of prolonged fasting or illnesses are typical clinical features of very long chain acyl-CoA dehydrogenase (VLCACD) deficiency, the most common long-chain fatty acid β-oxidation defect. Supplementation with medium-chain triglycerides (MCTs) is an important treatment measure in these defects, in order to supply sufficient energy. Little is known about the pathogenetic mechanisms leading to hepatopathy. Here, we investigated the effects of prolonged fasting and an MCT diet on liver function. Wild-type (WT) and VLCAD knockout mice were fed with either a regular long-chain triglyceride diet or an MCT diet for 5 weeks. In both groups, we determined liver and blood lipid contents under nonfasting conditions and after 24 h of fasting. Expression of genes regulating peroxisomal and microsomal oxidation pathways was analyzed by RT-PCR. In addition, glutathione peroxidase and catalase activities, as well as thiobarbituric acid reactive substances, were examined. In VLCAD knockout mice fed with a long-chain triglyceride diet, fasting is associated with excessive accumulation of liver lipids, resulting in hepatopathy and strong upregulation of peroxisomal and microsomal oxidation pathways as well as antioxidant enzyme activities and thiobarbituric acid reactive substances. These effects were even evident in nonfasted mice fed with an MCT diet, and were particularly pronounced in fasted mice fed with an MCT diet. This study strongly suggests that liver damage in fatty acid oxidation defects is attributable to oxidative stress and generation of reactive oxygen species as a result of significant fat accumulation. An MCT diet does not prevent hepatic damage during catabolism and metabolic derangement.