Effect Of α-linolenic Acid On Plasma Lipid Of Rats With High Fat Diet And Mechanism Of Increasing Hepatocyte SR-BI Expression

BackgroundAlpha-linolenic acid (all-cis-(9,12,15)- octadecatrienoic acid , ALA) is a kind of n-3 polyunsaturated fatty acid (PUFA).α- linolenic acid is the precursor for longer chain n-3 PUFA such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The majority of the biological effects of ALA are generally attributed to conversion to EPA and then DHA via desaturation and elongation. A number of epidemiological and laboratory studies have showed that ALA favorably affects atherosclerosis through regulation of plasma lipid, such as decreasing plasma triglyceride and total cholesterol. But there were few reports about the effects of ALA on plasma HDL metabolism.Male SD rats were used as the object treated by Camelina sativa oil which contains ALA up to 56.1% to investigate the effect of ALA on plasma lipid and to explore the possible mechanism. Part I Effects of ALA on blood lipid and oxidative damage of rats with high fat dietObjectObserve the effects ofα- linolenic acid on plasma lipid and oxidative damage of rats with high fat diet.MethodThe rats were divided into 6 groups: normal diet group, high fat diet group, high fat-diet mixed with fish oil group, high fat diet mixed with ALA of low, middle and high dose groups, labeled as group 1, 2, 3, 4, 5, 6 respectively. The rats were killed 6 weeks later and their livers were weighed. Cholesterol, triglyeride, some oxadation and anti-oxadation indexes of plasma and liver were detected with commercial kits, and plasma ALT, AST level were also detected with commercial kits. The HDL level and the ratio of HDL3/HDL were detected by means of PEG 20000 precipitation. The creep of HDL particle was observed by means of agarose gel electrophoresis of lipoprotein.ResultThe body weight of the rats rose with the time, but no significant difference among the groups; and the ratio of liver/body weight in groups 2,3,4,5,6 was higher than that of group 1 significantly. Compared with the normal diet group, cholesterol, triglyeride in plasma and liver in other groups was higher significantly, while ALA and fish oil decreased the plasma TG and TC significantly and trended to decrease the liver cholesterol. There were not significant effects on oxadation and anti-oxadation to plasma of the rats with normal diet, high fat-diet, high fat-diet mixed with fish oil, and high fat-diet mixed with ALA; while the oxidative damage was found to the liver of the all rats with high fat, and fish oil and ALA had no further damage to liver. Furthermore, the plasma AST level of the rats with high fat diet mixed with fish oil or ALA was lower significantly than that of the rats with high fat diet which led to the plasma AST level increase. The plasma HDL level and HDL3/HDL of rats with high fat diet was lower significantly than that of rats with normal diet, and the plasma HDL level of rats with high fat diet mixed with fish oil or ALA was lower but HDL3/HDL was higher significantly than that of rats with high fat diet. ALA increased the creep of the HDL particle which means that the HDL particle had the tendency to getsmaller.ConclusionALA could regulate plasma lipid of rats with high fat diet effectively. It decreased the level of PG, TC and HDL-C in plasma, increased the ratio of HDL3/HDL, and drived the HDL particle smaller. ALA did not increase the oxidative damage of plasma and liver of rats with high fat diet.Part II Mechanism of ALA increasing hepatocyte SR-BI expression ObjectExplore the possible mechanism of ALA increasing hepatocyte SR-BI expression.MethodThe rats were divided into 7 groups: normal diet group, high fat diet group, high fat diet mixed with ALA of low, middle and high dose groups, high fat diet mixed with Rosiglitazone group and basic control mixed with Rosiglitazone group. 6 weeks later, the expression of mRNA and protein of PPARγ,SR-BI in liver of rats were detected by means of RT-PCR and Westen blotting, and the expression of PDZK1 mRNA and apoAI mRNA in liver of rats were determined through RT-PCR. Result(1) There was PPARγexpression in Rat liver. ALA moderately increased rat liver PPARγmRNA and protein expression, and rosiglitazone significantly increased it. (2) ALA markedly enhanced the transcription of SR-BI mRNA and the protein expression of SR-BI in rat liver, rosiglitazone enhanced the transcription of SR-BI mRNA significantly but just slightly enhanced the protein expression of SR-BI in rat liver. (3) ALA enhanced the transcription of PDZK1 mRNA in rat liver and rosiglitazone had no effect on it. (4) ALA decreased the transcription of apoAI mRNA in rat liver and rosiglitazone had no effect on it.ConclusionActivated PPARγby ALA (maybe with its derivatives) up-regulated SR-BI expression by which ALA promoted metabolism of HDL-C and then increased reverse cholesterol transport (RCT). PDZK1 also played an important role in this process.