| α-linolenic acid(ALA)is an important plant originated n-3 polyunsaturated fatty acid and an essential fatty acid for human health, which means that ALA cannot be synthesized in human and it must be supplied via the diet. ALA is cheap and can be found mostly in plant seeds and plant oils. Several studies indicated that part of ALA in human can be desaturated and elongated into long chain polyunsaturated fatty acids such as EPA and DHA, which may play a decisive role in biological function of ALA. The efficiency of the ALA absorption and the machanisms of low conversion rate is not yet clear. In this study, we systematically analyzed the efficiency of absorption and conversion of ALA to LC-PUFAs in vivo and in vitro, and preliminarily explored the mechanism of low efficiency on ALA conversion. Based on the principle of total energy balance and fixed LA input, the experimental diets were divided into groups with different content of ALA and ALA plus different amount of EPA. Blood samples were collected with different time points during the experimental period. Tissue samples such as blood, liver, prostate and epididymal fat pad were dissected and collected at the end of animal experiments. Fatty acids composition of all samples were analyzed by GC-MS. The relative expression of key genes related to ALA/EPA conversion were analyzed by quantitative PCR(q PCR) method. Cellular experiment was conducted to confirm the conclusions from animal studies. The main conclusions we made are as follows:(1)The uptake of ALA in liver, prostate and epididymal fat pad or related tissues was positively correlated with the amount of ALA fed in diets, the same with the blood samples collected at any time of the experimental period. These results suggest that the uptake of ALA in vivo are efficient, and the ALA content in blood and tissues can perfectly respond to the ALA content in diets.(2)The increase of EPA concentration in vivo was strictly correlated with dietary ALA input up to 5%, then the conversion reached saturation. While the DHA level in vivo is quite steady. Our results indicate that ALA can be biotransformed into EPA to certain extent in vivo, but conversion saturation occurs while further increasing the intake of dietary ALA. Although dietary ALA can not increase DHA concentration, it is important for keeping a balanced DHA level in vivo.(3)EPA concentration in blood was further increased after animals were prolonged fed with ALA diet. It suggests that converted EPA in mice accumulated over time, a time-accumulation effects.(4)Experiments with human liver cells in vitro demonstrated that the absorption of ALA was positively correlated with exogenous ALA input, the convesion of ALA to EPA was efficient, higher input of ALA led to the saturation of ALA to EPA conversion. Thus, the phenomenons of absorption efficiency, conversion rate of ALA and accumulation of converted EPA are similar in mouse and human cells, occur both in vivo and in vitro.(5)Not only the dietary composition of fatty acids, but also the expression level of liver genes such as FADS1, FADS2, ELOVL5 affected the LC-PUFAs biosynthetic process of ALA. When the expression level of related genes was up-regulated, the conversion of ALA to EPA was enhanced, and accompanied with an increased EPA concentration in vivo and in vitro. When the genes were down-regulated, the conversion was inefficient, and accompanied with a decreased EPA concentration.In summary the results from this project found that dietary supplementation of ALA can boost ALA level linearly. The conversion of ALA to EPA is limited and concentration dependent. The accumulation of converted EPA is time dependent. Thus, prolonged supplementation of definite amount of dietary ALA does improve the levels of both ALA and EPA and does keep a balanced level of DHA in vivo, which provides a theoretical basis for the ALA supplement in the food industry. |
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