Preliminary Studies On The Relationship Between Fatty Liver And Atherosclerosis In New Zealand Rabbits

Fatty liver is closely correlated with atherosclerosis. Several clinical studies have demonstrated that fatty liver is associated with increased cardiovascular disease (CVD) risk, and raised the possibility that fatty liver may be not only a marker but also an early mediator of atherosclerosis. Current research studies concentrate more on clinical area rather than animal aspect with a uncertain results. Therefore, this study aims to investigate the relationship between fatty liver and arteriosclerosis and its possibly underlying mechanism from the view of pathology and molecular biology by use of rabbit model.Part One:ESTABLISHMENT OF NON-ALCOHOLIC STEATOHEPATITIS AND ATHEROSCLEROSIS MODEL IN NEW ZEALAND WHITE RABBITSObjectives To establish non-alcoholic steatohepatitis (NASH) and atherosclerosis animal model induced by high lipid diet in New Zealand white rabbits. Methods Normal male New Zealand white rabbits (n=14) were randomly divided into two groups: control group (n=12) and atherosclerosis group (n=8). Atherosclerosis was induced by high lipid diet (92% normal rabbit chow with 2% cholesterol and 6% lard). Rabbits were sacrificed at the end of week 10. Serum aminotransferase, lipid levels and fasting plasma glucose (FPG) levels were examined dynamically and morphology changes in ascending aortas and livers were observed. The intima-to-media (I/M) ratio of ascending aortas was also measured. Results The levels of serum aminotransferase, lipid and FPG in the atherosclerosis group were significantly higher than those of the control group (P<0.05). Compared with the control group, the livers in atherosclerosis group presented the typical histological changes of steatohepatitis, and ascending aortas showed overt atherosclerosis changes. The mean I/M ratio in ascending aortas of the atherosclerosis group was higher than that in the control group (1.13±0.32 vs. 0.12±0.04, P< 0.05). Conclusions High lipid diet can induce an ideal model of atherosclerosis in rabbits, accompanied with typical changes of NASH.Part Two:EXPLORATION THE RELATIONSHIP BETWEEN FATTY LIVER AND ATHEROSCLEROSIS AND THE UNDERLYING MECHANISM Objectives To investigate relationship between fatty liver and atherosclerosis and the underlying mechanism. Methods Liver superoxide dismutase (SOD) activity, glutathione (GSH), malonyl-dialdehyde (MDA) contents were determined spectrophotometrically. The expression of monocyte chemoattractant protein-1 (MCP-1) and vascular adhesion molecule-1 (VCAM-1) message RNA were determined by reverse transcription polymerase chain reaction (RT-PCR), and the expression of C-reactive protein (CRP) was determined by enzyme linked immunosorbent assay (ELISA). Results Compared with the control group, activity of SOD and content of GSH in the atherosclerosis group were decreased, but MDA content in the liver increased (P <0.01). The levels of serum CRP and the expression of VCAM-1 mRNA in the atherosclerosis group were significant higher than those in the control group (P<0.05), but the expression of MCP-1 had no statistically significance between the two groups. Ascending aortas intima-media thickness (IMT) showed a positive correlation with the degree of liver steatosis, inflammation and the levels of liver MDA, serum CRP (r=0.784, 0.850, 0.722, 0.454, respectively, all P<0.05), and a negative correlation with the liver SOD, GSH contents (r=-0.819, -0.604, respectively, both P<0.05) in the atherosclerosis group. Conclusions Fatty liver is closely correlated with atherosclerosis. The severity of liver steatosis and inflammation could aggravate the development of atherosclerosis, and the liver oxidative stress and the production and release of inflammatory cytokine such as CRP may be involved in the underlying mechanism.Part Three : IMPACT OF NON-ALCOHOLIC FATTY LIVER CIRRHOSIS INDUCED BY CARBON TETRACHLORIDE ON ATHEROSCLEROSISObjectives To investigate the effect of non-alcoholic fatty liver cirrhosis on the development of atherosclerosis. Methods Normal male New Zealand white rabbits (n=40) were randomly divided into four groups: control group (n=12), high lipid group (n=8), carbon tetrachloride (CCl4) group (n=12) and complex model group (n=14). Rabbits were sacrificed at the end of week 10. Serum aminotransferase, lipid levels and FPG were examined dynamically and morphology changes in ascending aortas and livers were observed. The levels of SOD, GSH, MDA in the liver, serum CRP, and the expression of VCAM-1 mRNA were also determined. The expression of VCAM-1 protein was determined by immune histochemistry staining. Results Atherosclerosis was induced by high lipid diet in high lipid group and complex model group, while steatohepatitis-related cirrhosis was induced by CCl4 in complex model group. Compared with the control group, serum lipid levels and alanine aminotransferase (ALT) in CCl4 group were increased significantly (P<0.05), significant liver steatosis, inflammation and fibrosis could be observed, but atherosclerosis could not be found in ascending aortas. There were no difference of CRP, the expression of VCAM-1 mRNA and protein in these two groups. The levels of serum aminotransferase, lipid and FPG in two high lipid diet groups were significantly higher than those of the control group (P<0.05). Significant liver steatosis, inflammation and fibrosis could also be observed, and typical atherosclerosis plaques could be found in ascending aortas. Serum CRP, the expression of VCAM-1 mRNA and protein were increased. There were significant difference of serum aminotransferase and intima-to-media (I/M) ratio of ascending aortas between the high lipid group and the complex model group, but IMT otherwise. There was no association with liver fibrosis and serum CRP, ascending aortas IMT in the animals fed with high lipid diet. Conclusions Rabbits treated with CCl4 can elevate serum lipid levels, but can not induce atherosclerosis. High lipid diet can induce atherosclerosis and NASH, and even cirrhosis when treated with CCl4 synchronously. Though the activity of liver inflammation was aggravated in the complex model group, it has no effect on atherosclerosis possibly partly because of malnutrition.