Researches On Differences In Triglyceride Metabolism In Hyperlipidemic Guinea Pigs And Rats & Hypolipidemic Effect And Mechanisms Of LRTG

ObjectiveThe present study was designed to determine the charecterristics of triglyceride metabolism in hyperlipidemic guinea pigs and rats induced by high-fat diets and to compare the enzyme activities and gene expression of molecules that closely related to triglyceride metabolism using systems and molecule biological techniques. To better support the usages of guinea pigs and rats on researches of hypolipidemic drugs.Furthermore, the aim of this study was to evaluate the hypolipidemic effect of LRTG in reducing serum and hepatic lipids levels. And to explore the mechanisms of its hypolipidemic effect by determining the mRNA expressions of the enzymes, proteins and receptors that involved in lipid metabolism.MethodsGuinea pigs and rats were randomly assigned to two groups:a control group and a model group respectively. Guinea pigs and rats in the control groups were fed control diets, while animals of both model groups were fed high-fat diets containing 0.1% cholesterol and 10% lard for 4 weeks. At the end of the experiment, half of the animals were used to detect the VLDL-TG secretion rate; blood and live samples of the remainder were collected. Plasma lipids levels and LPL activity were measured. Hepatic lipids concentrations and FAS, DGAT, CPT-1 activities were measured using enzymatic methods. The relative expressions of PPARa and MTTP mRNA in liver were detected by real-time PCR.Guinea pigs and rats were assigned randomly to groups of normal control, hyperlipidemia model, positive control (gemfibrozil 0.3g/kg) and high (1.2g/kg), middle (0.6g/kg), low (0.3g/kg) doses of LRTG respectively. Animals of the normal control groups were fed with the normal diets. The rest were fed with the high-fat diets (guinea pig:0.1% cholesterol,10% lard and 89.9% normal diets;rat:1% cholesterol,0.3% bile salt,10% lard and 88.7% normal diets). A week later, the groups treated were intragastrically administrated with drugs according to the prescribed dosage respectively for three weeks. The hypolipidemic effect of LRTG was evaluated through detecting the serum lipids (TC、TG、LDL-C、HDL-C and FFA), hepatic lipids (TC. TG and FFA) concentrations and hepatic histomorphology. Furthermore, rat genome-wide oligonucleotide microarray was used to screen the hypolipidemic targets. The relative expressions of the differently expressed genes were further detected by real-time PCR.ResultsFed the high-fat diet for 4 weeks led to significant increases in plasma TC, TG, LDL-C, HDL-C and FFA in guinea pigs but not in rats. But hepatic TG levels in rats were greatly increased in response to the high-fat diet, while it remained unchanged in guinea pigs. Mechanisms researches showed that the hepatic acyl coenzyme A:diacylglycerol acyltransferase (DGAT) activity, microsomal triglyceride transfer protein (MTTP) mRNA levels and very-low-density lipoprotein (VLDL)-TG secretion rate in guinea pigs fed a high-fat diet were significantly higher than those in the control group. Hepatic carnitine palmitoyltransferase-1 (CPT-1) activity and peroxisome proliferator-activated receptor-a (PPARa) mRNA levels were upregulated in guinea pigs, but not rats, fed a high-fat diet.Serum and hepatic TG concentrations were reduced, hydropic and fatty degenerations of hepatic cells were alleviated by gemfibrozil and LRTG in hyperlipidemic rats. Also serum TG levels were reduced by three doses of LRTG in hyperlipidemic guinea pigs.The differently expressed genes involved in lipid metabolism such as SCD1、CYP4A3、SREBP-1c were discovered with rat genome-wide oligonucleotide microarray. Further real-time PCR results confirmed that hepatic SCD1、SREBP-lc mRNA exprssions were down-regulated by LRTG.ConclusionThe characteristics of TG metabolism were different in guinea pigs and rats fed with high-fat diets (0.1% cholesterol and 10% lard). These differences are as following: hepatic DGAT activity and MTTP mRNA expressions were upregulated in guinea pigs fed with high-fat diets, to promote the biosynthesis of TG and VLDL-TG secretion, those led to an elevation of plasma TG concentration in guinea pigs. Second, the high-fat diet increases mitochondrial fatty acidβ-oxidation in guinea pigs by enhancing hepatic CPT-1 activity and PPARαtranscription but not in rats, which induced a typical fatty liver in rats. Consequently, guinea pigs could be a good hyperlipidemic animal model with hypertriglyceridemia, whereas rats could develop a typical fatty liver model. Guinea pigs and rats have different characteristics for research on lipid metabolism disorders and hypolipidemic drugsLRTG has specialty of hypolipidemic effect that it can reduce serum and hepatic TG concentrations significantly. And its hypolipidemic targets might be SCD1 and SREBP-1c.