Methylglyoxal-induced glycation changes liver lipid content in high-fat diet-fed rats, causing glucose and lipid systemic dysmetabolism

• Autor(a) principal: Neves, Christian André Fernandes
• Data de Publicação: 2015
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/14597
• topic: Biomedicina; Fígado - Metabolismo de lípidos; Diabetes; Obesidade; Glicosilação

Fatty liver disease is simultaneously a cause and a consequence of type 2 diabetes. Hepatic lipid metabolism is altered in obese patients, causing insulin resistance. More, inhibition of insulin signaling may also affect hepatic lipid metabolism, causing a feedback that may lead to hepatic steatosis, common in such patients. In this work, we intended to assess the role of glycation (methylglyoxal-induced) in the hepatic lipid metabolism of high-fat diet-fed rats, using lipidomic approaches and magnetic resonance imaging, which identify hepatic lipid species, including phospholipids (PL), triglycerids (TG), diacylglycerols (DAG) and fatty acids (FA). Wistar rats were maintained during 4 months with methylglyoxal (MG) supplementation (100mg/Kg/day) (MG group), a high-fat diet rich in TG (HFD group) or both (HFDMG group) and compared with controls feeding a standard diet (n=6/ group). Lipidomic approaches, namely liquid chromatography - mass spectrometry (LC-MS) and gas chromatography (GC) were used to determine liver composition in PL, TG and FA. Non-invasive 1H nuclear magnetic resonance (NMR) spectroscopy (9 Tesla) of liver tissues in vivo was used to determine lipid species, such as TG and DAG. The total and phosphorylated levels of the mediators of the insulin receptor pathway and lipid oxidation were determined by western blotting. High-fat diet-fed (HFD) rats showed increased body weight in relation to controls, but this effect was partially inhibited by MG supplementation (HFDMG group). Moreover, HFDMG group showed increased plasma free fatty acid levels, hyperinsulinemia, insulin resistance and glucose intolerance. In liver, lipidomic techniques and 1H NMR showed increased fat mass in the liver of HFD and HFDMG rats. HFD rats, but not HFDMG, showed increased total levels of the 18:1 fatty acid (common in high-fat diets). Despite no differences were observed for HFD group, HFDMG rats showed decreased fraction of unsaturated lipids and increased fraction of saturated lipids. This difference was obtained due to a decrease in monounsaturated FA. Regarding lipid esterification, HFDMG group showed lower percentage of esterified glycerol carbons, suggesting an increased concentration of DAG in relation to TG. In accordance, this group showed higher fatty acids/glycerol ratio, suggesting increased liver non-esterified fatty acid levels. Western Blotting analyses showed decreased activation of insulin pathway, especially HFDMG group, as well as decreased activation of the insulin receptor in HFDMG group. Data suggest that glycation changes lipid metabolism in a context of hyperlipidemia, possibly contributing to hepatic lipotoxicity and to accelerate progression of insulin resistance and fatty liver disease.