Liver fatty acid composition in mice with or without nonalcoholic fatty liver disease

Lipids in Health and Disease Liver fatty acid composition in mice with or without nonalcoholic fatty liver disease Xin Wang 2 Yuzhen Cao 0 Yunwei Fu 0 Guifang Guo 1 Xiuying Zhang 0 0 College of Veterinary Medicine, Northeast Agricultural University , Harbin, China 150030 1 China Institute of Veterinary Drugs Control , Beijing, China 100080 2 College of Animal Sciences and Veterinary Medicine, Heilongjiang Bayi Agricultural University , Daqing, China 163319 Background: Nonalcoholic fatty liver disease (NAFLD) is one of the most frequent causes of abnormal liver function. Because fatty acids can damage biological membranes, fatty acid accumulation in the liver may be partially responsible for the functional and morphological changes that are observed in nonalcoholic liver disease. The aim of this study was to use gas chromatography-mass spectrometry to evaluate the fatty acid composition of an experimental mouse model of NAFLD induced by high-fat feed and CCl4 and to assess the association between liver fatty acid accumulation and NAFLD. C57BL/6J mice were given high-fat feed for six consecutive weeks to develop experimental NAFLD. Meanwhile, these mice were given subcutaneous injections of a 40% CCl4-vegetable oil mixture twice per week. Results: A pathological examination found that NAFLD had developed in the C57BL/6J mice. High-fat feed and CCl4 led to significant increases in C14:0, C16:0, C18:0 and C20:3 (P < 0.01), and decreases in C15:0, C18:1, C18:2 and C18:3 (P < 0.01) in the mouse liver. The treatment also led to an increase in SFA and decreases in other fatty acids (UFA, PUFA and MUFA). An increase in the ratio of product/precursor n-6 (C20:4/C18:2) and n-3 ([C20:5 +C22:6]/C18:3) and a decrease in the ratio of n-6/n-3 (C20:4/[C20:5+C22:6]) were also observed. Conclusion: These data are consistent with the hypothesis that fatty acids are deranged in mice with nonalcoholic fatty liver injury induced by high-fat feed and CCl4, which may be involved in its pathogenesis and/or progression via an unclear mechanism. Fatty acid; Nonalcoholic fatty liver disease; Mouse; High-fat feed; Carbon tetrachloride - Background Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of conditions that are histologically characterized by hepatic steatosis in individuals without significant alcohol consumption and with no viral, congenital, or autoimmune liver disease markers [1]. It is associated with insulin resistance and metabolic syndrome [2,3]. Despite the many possible etiologies of NAFLD [4,5], these results reflect the accumulation of lipids within the hepatocyte cytoplasm. High-fat feed ingestion and hepatic toxins (such as CCl4) may lead to fatty acid accumulation and hepatic damage. Hepatic lipid accumulation in hepatocytes (hepatic steatosis) is the hallmark of NAFLD and an important factor that can induce insulin resistance, lipid peroxidation, changes in energy metabolism, hepatic cell damage and inflammation. Fatty acid are the simplest lipids. They are the basic components of more complex lipids (including triglycerides, phospholipids and sphingolipids) and an important metabolic fuel. The compositions of the lipids that accumulate in livers of subjects with NAFLD are not well characterized. Most of the published literature has focused on triglycerides accumulation as the key defect in NAFLD [6,7]. However, it is unknown whether there are substantial changes in other lipid classes, such as fatty acid. Although an increase in the n-6/n-3 fatty acid ratio in the total lipids has been observed in NAFLD [8,9], the composition of fatty acid in the hepatic lipids has not been extensively characterized. The pathogenic mechanism involved in the development of fatty liver is unclear. In alcoholic patients with asymptomatic fatty liver and in morbidly obese patients, free fatty acid accumulation was observed in liver extracts [10,11]. Non-alcoholic steatohepatitis patients had significantly higher concentrations of total and free fatty acid in their plasma, compared with healthy individuals [12]. Changes in the fatty lipid composition may be implicated in the pathogenesis of NAFLD. As yet, there is little information available concerning the hepatic lipid fatty acid composition in NAFLD [13]. The aim of this study was to compare the liver fatty acid profiles and detailed compositions of healthy mice vs. mice with an experimental model of NAFLD induced by high-fat feed and CCl4. Results and discussion Histological profile All of the sections in the experimental group exhibited diffuse hepatic steatosis (Figure 1) under a light microscope, whereas no fatty liver was observed in the control group The relative sizes of the hepatic cell nuclei were uneven. Hepatic steatosis (mostly microvesicular and macrovesicular mixed steatosis) was most obvious around the portal area and was accompanied by liver cell necrosis and inflammatory cell infiltration. The lobular and portal areas exhibited considerably more inflammatory cell infiltration in the experimental group than in the control group The total histological scores of the livers in the model-group mice reached grade 2 or 3. In contrast to the control mice, a histological analysis of the livers from the mice treated with a high-fat feed and a hepatotoxin (CCl4) confirmed marked fat accumulation and revealed extensive inflammatory cell infiltration, indicating that diffuse hepatic steatosis with moderate inflammation (NAFLD) had developed. Serological profiles Twenty mice in each group were studied (Table 1). The mice with NAFLD had significantly higher TC, HDL, LDL, ALP, AST and ALT levels than did the mice in The data are expressed as the mean SD (n = 20 per treatment group). *P < 0.05, ** P < 0.01 vs. control. ALT, alanine aminotransferase; AST, aspartate aminotransferase; ALP, alkaline phosphatase; TG, triglycerides; TP, total protein; HDL, high-density lipoprotein; LDL, low-density lipoprotein; TC, total cholesterol; ALB, albumin; NAFLD, nonalcoholic fatty liver disease. the control group (P < 0.01), whereas the ALB level was higher in mice with NAFLD than it was in control mice, but this difference did not reach statistical significance. However, the TG, TP and glucose levels were significantly lower in the mice with NAFLD than in the control mice (P < 0.05 or P < 0.01). This study have showed that high-fat feed and CCl4 have pronounced effects on hepatic steatosis, decrease the plasma TG level, and induce hepatocyte necrosis and inflammatory cell infiltration. Serological and pathological examinations confirmed that non-alcoholic fatty liver injury developed in C57BL/6J mice in our study. The blood levels of transaminase (AST, ALT and ALP) were significantly elevated in the model mice, indicating liver dysfunction and confirming the widely held belief that serum transaminase is a sensitive indicator of liver injury. The concentrations of serum TG and TC are known to vary, depending on pathological fac (...truncated)