Effects of dietary lipids against carbon tetrachloride-induced liver fibrosis in rats : a proteomic approach

Abstract

Liver fibrosis is an important reversible stage in progress of most chronic liver diseases (CLDs). The excess hepatic wound healing response against chronic liver injury results in extracellular matrix proteins accumulation and fibrosis. Oxidative stress, liver inflammation and/or hepatic steatosis contribute to this process. Until now, little is known how dietary lipids can influence liver’s pathophysiology. The effects of lipids on CLD progression may depend on their amount and the quality of fatty acids as well as the degrees of saturation. The investigation of liver fibrosis will help to understand the pathogenesis of CLDs and develop potential nutritional therapeutic approaches.

The specific aim of this study was to investigate the effects of different high fats consumption in liver fibrosis by feeding the normal and carbon tetrachloride (CCl4)-treated animals with the diets enriched with following oils: corn oil rich in ω-6 polyunsaturated fatty acids (PUFAs), extra virgin olive oil (EVOO) high in ω-9 monounsaturated fatty acids (MUFAs), and lard enriched with saturated fatty acids (SFAs) for 4 weeks. The differentially expressed liver proteins in this process were identified by two-dimensional gel electrophoresis based proteomics to explore the molecular mechanisms.

The proteomic analysis revealed characteristic differences between (i) normal and fibrotic livers (Chapter 3), and between the fibrotic livers treated with (ii) low fat versus high fat (20% w/w corn oil, Chapter 4) and among the high fats, between the diet enriched with corn oil versus (iii) EVOO (Chapter 5) and lard (Chapter 6).

Among the identified proteins, collagen synthesis related protein prolyl 4-hydroxylase, oxidative stress related protein alpha-1-antitrypsin, free radical scavenger Cu/Zn superoxide dismutase and Calcium homeostasis regulator calreticulin and regucalcin were found to involve in CCl4-induced liver fibrosis. The results show that corn oil enhanced the hepatic steatosis but had no significant effects on fibrogenesis; the expression of several stress proteins like heat shock protein 75 kDa, and lipid metabolism related protein enoyl-CoA hydratase domain-containing protein 3 were found increased in high corn oil consumption animals with CCl4-treatment.

Histological evaluations showed that olive oil could attenuate, and lard oil aggravate the liver damage induced by CCl4. Compared to corn oil, high EVOO diet rich in MUFAs decreased the lipid peroxidation and collagen accumulation in liver. Several protein related to antioxidant effects, including peroxiredoxin-1, thiosulfate sulfurtransferase and thioredoxin domain-containing protein 12 were found have higher expression level in high EVOO intake animals. In contrast, lard rich in SFAs intake leaded to macrovesicular steatosis and advanced fibrosis, and decreased the expression of antioxidant related glutathione S-transferases. Interestingly, S-adenosylmethionine synthesis related enzyme methionine adenosyltransferase was found up-regulated in lard intake animals, suggests the modification of DNA methylation was implicated in lard fed animals, while the demethylation on the promoter of profibrogenic gene was found, confirmed the lard consumption has the epigenetic modification effects in liver injury.

Together, these findings give further insight into the pathobiology of CLDs. The data also helped to address the issue that different degrees of saturation of dietary lipids may affect liver fibrosis with different mechanistic actions.