Mechanism In Whichthe Different LCFAs Affect Fatty Acids Transport In Intestinal Epithelial Cells

As one of the TG-rich lipoprotein particles, chylomicron (CM) which is exclusively produced in the enterocytes is indispensable for transporting exogenous lipids absorbed by intestine to the periphery.Hypertriglyceridemia causes or exacerbatesa multitude of health problems, and has been proved to be a potential risk factor contributing to metabolic syndrome.It is noteworthy that phospholipid, triglyceride as well as cholesterol are made up of LCFA.Given that Palmitinic acid (PLA) is classified as saturated long chain fatty acid, while Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA) are recognized as unsaturated long chain fatty acid, the present research investigated the effect of these three fatty acids on chylomicron secretion, nascent triglyceride synthesis and secretion, gene expression involved in fatty acid transport. Consequently, we were enabled to unravel the specific mechanism of fatty acid transport regarding to distinctive fatty acid.1、Impact of different LCFAs on chylomicron secretion by intestinal enterocytes. Caco-2cells cultured for21d were exposed to various concentrations (100μL,200μL and400μL) of [1-14C] PLA,[1-14C] EPA and [1-14C] DHA respectively for24h, followed by medium collection.It was observed that, compared with control cells, chylomicron secretion increased significantly in a concentration-dependent manner in cells incubated with the three fatty acids. Additionally, CM secretion in PLA-treated cells was higher than that in EPA-and DHA-treated cells at any concentration of fatty acid.In the presence of100μM EPA and DHA, no remarkable alteration in CM secretion was observed (P>0.05). While at the fatty acid concentrations of200μM and400μM, DHA was more potent in inhibiting CM secretion compared with EPA (P﹤0.01). It was suggested that EPA and DHA, considered as major PUFAs, could decrease CM secretion by intestinal enterocytes more efficiently than PLA which was classified as saturated fatty acid. When the fatty acid concentration increased to200μM and400μM, longer chain DHA was more powerful in inhibitory effect than EPA.2、Impact of different LCFAs on nascent triglyceride synthesis and secretion. Caco-2cells cultured for21d were exposed to various concentrations (100μL,200μL and400μL) of [1-14C] PLA,[1-14C] EPA and [1-14C] DHA respectively for24h, followed by cell and medium collection.Four hours before terminating the experiment,[l,2,3-3H]glycerol (139μL) was added. After the incubation, labelled TG synthesis and secretion were both detected.It was observed that, compared with control cells, nascent TG synthesis and secretion increased significantly in a concentration-dependent manner in cells incubated with the three fatty acids (P<0.01). Additionally, nascent TG synthesis and secretion in PLA-treated cells were higher than that in EPA-and DHA-treated cells at any concentration of fatty acid. In the presence of100μM EPA and DHA, no remarkable alteration in nascent TG synthesis and secretion was observed (P>0.05). While at the fatty acid concentrations of200μM and400μM, DHA was more potent in inhibiting nascent TG synthesis and secretion compared with EPA (P<0.01). It was suggested that EPA and DHA, considered as major PUFAs, could decrease nascent TG synthesis and secretion by intestinal enterocytes more efficiently than PLA which was classified as saturated fatty acid. When the fatty acid concentration increased to200μM and400μM, longer chain DHA was more powerful in inhibitory effect than EPA.3、Impact of different LCFAs on gene expression involved in fatty acid transport. Caco-2cells cultured for21d were exposed to various concentrations (100μL,200μL and400μL) of [1-14C] PLA,[1-14C] EPA and [1-14C] DHA respectively for24h, followed by cell collection.lt was observed that PLA, EPA and DHA all enhanced the expression of related gene (PPARa, L-FABP, DGAT1and MTP) corresponding to the increasing fatty acid concentration (P<0.01). At the fatty acid concentration of200μM and400μM, the expressions of PPARa, L-FABP and DGAT1were significantly increased. At the fatty acid concentration of100μM and400μM, MTP gene expression was enhanced in EPA-and DHA-treated cells, compared with PLA.It was suggested that, with the increasing fatty acid concentration, gene expression enhanced in a concentration-dependent manner. It was noteworthy that EPA and DHA modified PPARa, L-FABP, DGAT1and MTP expression more efficiently than PLA.Taking these results into account, we concluded that corresponding to increasing fatty acid concentration, gene expression involved in fatty acid transport, nascent TG synthesis and secretion as well as CM secretion were all increased by intestinal enterocytes. EPA and DHA could decrease CM secretion as well as nascent TG synthesis and secretion by intestinal enterocytes more efficiently than PLA which was classified as saturated fatty acid. Moreover, DHA was more powerful in inhibiting fatty acid transport than EPA when the fatty acid concentration between200and400μM.