乾燥洋蔥粉對高脂飲食誘發之大鼠肥胖的影響

由於飲食習慣和生活方式的改變，體重過重和肥胖的發生率逐年增加，已經成為全球和台灣重要的健康問題。然而目前只有少數藥物可以用來幫助減輕體重，但是效果有限且可能有一些副作用。洋蔥(Allium cepa L.)為全球常見的經濟作物，在台灣中南部亦盛產，富含類黃酮(包括quercetin, Q)、植物固醇、皂苷、含硫胺基酸及多醣體等成分，有多個研究顯示洋蔥油、洋蔥有機溶劑萃取物及quercetin具抗肥胖的作用，但完整的乾燥洋蔥粉效果如何研究的並不多，因此本研究主要目的是探討乾燥洋蔥粉抑制高脂飲食(HFD)誘發的大鼠肥胖的作用及其可能機制。我們將大鼠隨機分為五組(各組n = 9-11)：控制組(control)、高脂飲食組(HFD)、HFD + DO (dried onion powder；1 % 乾燥洋蔥粉)組、HFD + 5DO組(5 % 乾燥洋蔥粉)及HFD + Q (quercetin)組(180 mg Q / kg diet，Q含量與5 % 乾燥洋蔥粉相當)，處理12週，實驗期間或犧牲後我們紀錄體重、進食量、體脂肪量及器官重量，並分析血清生化數值、氧化壓力指標、促發炎激素及肝臟與糞便脂質含量等。結果顯示，與control組相比，HFD雖然降低進食量，但仍顯著增加大鼠熱量攝取、體重、腓腸肌重量、內臟與皮下脂肪組織重量以及副睪與腎周脂肪細胞面積，而乾燥洋蔥粉(DO及5DO)劑量依賴性的改善HFD造成的這些改變，且5DO效果較Q好。血清生化數值方面，HFD組僅顯著降低HDL-C濃度而增加血中酮體濃度。反之，與control組及HFD組相比，乾燥洋蔥粉降低總膽固醇(total cholesterol, TC)、LDL-C (low density lipoprotein-cholesterol)、三酸甘油酯(triglyceride, TG)、游離脂肪酸、酮體及血糖濃度，5DO效果較Q好或相似。乾燥洋蔥粉亦降低血清氧化壓力指標及促發炎細胞激素濃度，效果與Q相當。然而單獨給予HFD及HFD合併乾燥洋蔥粉或Q均不會影響腎功能以及血清中鈉、鉀離子濃度。此外，我們發現DO及5DO降低肝臟中脂質推積、TC和TG含量以及ACC-α (一種脂肪酸合成相關酵素) mRNA表現量，並增加了糞便中TC及TG含量，5DO效果優於Q。綜合以上結果，我們的研究發現乾燥洋蔥粉能夠抑制餵食HFD大鼠體重、內臟與皮下脂肪重量增加及肝臟脂肪堆積，且效果比Q好，其機制與增加糞便中脂質排出及降低氧化壓力、促發炎細胞激素和ACC-α mRNA表現量有關。

Because of the change of dietary habits and lifestyles, the prevalence of overweight and obesity is increasing and becoming an important health problem worldwide including Taiwan. So far, only a few drugs are available for anti-obesity and may have some side effects. Onion (Allium cepa L.) is a common vegetable crop grown around the world including the mid-south part of Taiwan. Onion is rich in flavonoids (particularly quercetin), phytosterols, saponins, sulfur amino acids, and polysaccharides. Several studies show that the extract of onion, onion oil, and quercetin possess anti-obesity activities. However, the studies regarding the effects of dried onion powder on obesity are limited. Thus, the purposes of the present study were to investigate the inhibition of dried onion powder on a high-fat diet (HFD)-induced obesity in rats as well as the possible mechanisms. We also compared the efficiency of dried onion powder with that of quercetin (Q). The animals were randomly assigned to the following five groups (n = 9-11 per group) for 12 weeks: control, HFD alone (a diet containing 43% fat), HFD + DO (1% dried onion powder, w/w), HFD + 5DO (5% dried onion powder, w/w) or HFD + Q (180 mg/ kg diet). We determined body weights, food intake, serum biochemistries, oxidative stress marker, proinflammatory cytokines, body fat weight, organ weight, liver, and fecal fat levels during or after the experiment. The results showed that despite decreasing food intake, HFD significantly increased the calories intake, body weight, gastrocnemius weight, visceral and subcutaneous fat accumulations as well as adipocyte area in epididymal and perirenal adipose compared with the control group. DO and 5DO dose-dependently suppressed these increases in mice exposed to HFD. In general, the efficiencies of 5DO were better than Q. Regarding serum biochemists, HFD only significantly decreased serum HDL-C level and increased ketone body level; however, dried onion powder tended to decreased total cholesterol (TC), LDL-C, triglyceride (TG), free fatty acid and ketone body, blood sugar compared with the control group. The effects of 5DO were better than or similar to Q. Dried onion powder also decreased the levels of oxidative stress marker and proinflammatory cytokines in serum with efficiencies similar to those of Q. Neither HFD alone nor HFD in combination with dried onion powder quercetin affected renal function as well as serum sodium and potassium levels. Furthermore, we found that DO and 5DO decreased fat accumulation, TC, and TG levels as well as ACC-α (a fatty acid synthesis associated enzyme) mRNA level in liver but increased TC and TG levels in feces. Consistently, the efficiencies of 5DO were tended to better than Q, especially in fecal TC and TG levels. Taken together, the present study demonstrates that dried onion powder suppresses weight gain, body visceral and subcutaneous, and liver fat accumulation in rats better than Q does. The mechanisms are associated with increasing fecal excretion and decreasing oxidative stress, proinflammatory cytokines and ACC-α mRNA levels.