Induction of lipid oxidation gene expression by polyunsaturated fatty acids of marine origin in small intestine of mice. Mus musculus

Dietary polyunsaturated fatty acids (PUFA) act as potent natural hypolipidemics and are linked to many health benefits in humans and in animal models. Mice fed long-term a high fat diet, in which medium-chain alpha linoleic acid (ALA) was partially replaced by long-chain docosahexaenoic (DHA) and eicosapentaenoic (EPA) fatty acids, showed reduced accumulation of body fat and prevention of insulin resistance, besides increased mitochondrial beta-oxidation in white adipose tissue and decreased plasma lipids. ALA, EPA and DHA all belong to PUFA of n-3 series. The intestine is a gatekeeper organ for ingested lipids. To examine the potential contribution of the intestine in the beneficial effects of EPA and DHA, this study assessed gene expression changes using whole genome microarray analysis on small intestinal scrapings. The main biological process affected was lipid metabolism. Fatty acid uptake, peroxisomal and mitochondrial beta-oxidation, and omega-oxidation of fatty acids were all increased. Quantitative real time PCR and intestinal fatty acid oxidation measurements ([14C(U)]-palmitate) confirmed significant gene expression differences in a dose-dependent manner. Furthermore, no major changes in the expression of lipid metabolism genes were observed in colonic scrapings. In conclusion, we show that marine n-3 fatty acids regulate small intestinal gene expression patterns. Since this organ contributes significantly to whole organism energy use, this adaptation of the small intestine may contribute to the complex and observed beneficial physiological effects of these natural compounds under conditions that will normally lead to development of obesity and diabetes. Overall design: Male 4-month-old C57BL/6J mice were maintained for 4 weeks on semisynthetic high-fat (20% wt/wt) diets differing in the composition of n-3 PUFA. Two isocaloric diets were used (n=12): control sHFf diet which contained flax-seed oil (rich in ALA) as the only lipid source, or the sHFf-F2 diet, which had the same composition except that 44 % of the lipids were replaced by a n-3 PUFA concentrate (EPA&DHA) containing 6 % EPA and 51 % DHA (EPAX 1050TG; EPAX AS, Lysaker, Norway). Quality control of RNA samples showed that four samples did not pass quality thresholds, and these samples were excluded from array analysis (two control small intestine samples and one EPA&DHA small intestine sample). The remaining RNA samples were pooled per tissue per diet group. Thus; the flax-seed (control) array was hybridized with RNA pooled from of 10 mice, the PUFA array was hybridized with RNA pooled from 11 mice.

膳食多不饱和脂肪酸（polyunsaturated fatty acids, PUFA）是强效的天然降血脂剂，在人类与动物模型中均与多种健康益处相关。长期喂食高脂饲料的小鼠，其饲料中中等链α-亚麻酸（alpha linoleic acid, ALA）被长链二十二碳六烯酸（docosahexaenoic acid, DHA）与二十碳五烯酸（eicosapentaenoic acid, EPA）部分替代后，不仅体脂蓄积减少、胰岛素抵抗得到改善，还出现白色脂肪组织线粒体β氧化增强以及血浆脂质水平降低的现象。ALA、EPA与DHA均属于n-3系列多不饱和脂肪酸。肠道是摄取脂质的门户器官。为探究肠道在EPA与DHA的有益效应中所扮演的潜在角色，本研究采用全基因组微阵列分析（whole genome microarray analysis）对小肠刮取物的基因表达变化进行了评估。受影响的主要生物学过程为脂质代谢：脂肪酸摄取、过氧化物酶体与线粒体β氧化，以及脂肪酸ω氧化均出现上调。实时定量PCR（quantitative real time PCR）与肠道脂肪酸氧化检测（采用[14C(U)]-棕榈酸作为底物）证实，基因表达差异具有显著的剂量依赖性。此外，结肠刮取物中未观察到脂质代谢相关基因表达的显著变化。综上，本研究证实海洋来源n-3脂肪酸可调控小肠的基因表达模式。鉴于肠道对整体机体能量代谢具有重要贡献，在通常会引发肥胖与糖尿病的病理条件下，小肠的这种适应性调控或许是这类天然化合物产生已被观测到的复杂有益生理效应的重要原因之一。整体实验设计：将4月龄雄性C57BL/6J小鼠饲养于半合成高脂饲料（脂肪占比20%质量分数）环境中4周，各组饲料的n-3 PUFA组成存在差异。本研究设置两种等热量饲料（每组n=12）：以亚麻籽油（富含ALA）作为唯一脂质来源的对照sHFf饲料，以及sHFf-F2饲料——后者除44%的脂质被含6% EPA与51% DHA的n-3 PUFA浓缩剂（EPAX 1050TG；EPAX AS, 挪威莱萨克市）替代外，其余成分与对照饲料一致。RNA样本质量质控结果显示，4份样本未达到质量阈值，故被排除出微阵列分析（其中2份为对照组小肠样本，1份为EPA&DHA组小肠样本）。剩余的RNA样本按组织与饲料组进行混合。因此，亚麻籽油（对照）组的微阵列杂交采用10只小鼠的混合RNA，PUFA组的微阵列杂交则采用11只小鼠的混合RNA。