山苦瓜上調C57BL/6J公鼠肝Fgf21 mRNA並誘發副睪脂褐化

肥胖與代謝異常為許多慢性疾病的危險因子 (Risk factor)，更可能導致死亡發生，加上近年來盛行率急遽增加，使其成為全球公共衛生之重要議題。苦瓜(Momordica charantia L.) 含有PPAR的活化物質，為具有抗肥胖及代謝症候群潛力之機能性食品。本實驗室發現長期餵食C57BL/6J公鼠山苦瓜全果凍乾粉可以促進白色脂肪組織褐化，而目前認為白脂褐化能增加個體能量消耗並對抗肥胖。FGF21賀爾蒙可增進個體胰島素敏感度，誘發白脂褐化，在肝臟中表現量受到PPARα調控而增加。本實驗旨在初步以代謝體學研究評估山苦瓜餵食造成的代謝影響，並觀察山苦瓜造成的白脂褐化是否與FGF21相關。首先進行代謝體分析，設計高蔗糖以及高脂飲食的2×2雙因子實驗，C57BL/6J公鼠分別餵食AIN-93G改良高蔗糖飲食 (HS group) 或高脂飲食 (HF group)，並添加 (BGP or FBGP group) 或不添加5% 山苦瓜全果凍乾粉餵食8週。山苦瓜添加可顯著降低脂肪塊相對重量、血糖及血清三酸甘油酯。以LC-MS分析尿液、血清、肝臟、脂肪與骨骼肌組織樣本代謝體，根據現有資料庫預測山苦瓜補充後分別與對應之對照組含量有顯著差異的化合物。於餵食苦瓜組的肝臟中偵測到山苦瓜可能的活性成分（三萜類）含量改變，也觀察到Tryptophan代謝路徑中的代謝物 (Tryptophan、3-Hydroxy-DL-kynurenine、nicotinamide adenine dinucleotide、serotonin) 含量改變，推測Tryptophan代謝路徑可能受到山苦瓜餵食影響。再來評估山苦瓜與白色脂肪褐化，三組C57BL/6J公鼠分別餵食AIN-93G改良高蔗糖飲食 (HS組)、高蔗糖飼料添加5% 山苦瓜粉 (BG組) 或chow diet餵食25週。BG組肝臟Fgf21 mRNA表現量為HS組的2.8倍 (P<0.05)，BG組副睪脂 (EWAT) 中Ucp1 mRNA表現大幅提高，並且Pgc1α, Cidea, Prdm16等褐化基因mRNA表現量與粒線體DNA含量皆顯著較高。相較HS組，BG組有顯著較低的飼料/能量利用率、脂肪塊相對重、禁食血糖/胰島素及胰島素阻抗指標 (HOMA-IR index)，並有較高的個體氧氣消耗及二氧化碳排出量。綜合以上結果，我們認為山苦瓜添加可能透過上調肝臟Fgf21 mRNA與EWAT中Ucp1等生熱、粒線體生合成相關基因mRNA表現，與提高能量消耗，來降低小鼠受飲食誘發的肥胖與代謝異常情形，提升代謝健康。

關鍵字

山苦瓜；白色脂肪組織；褐化；粒線體

並列摘要

Obesity and metabolic disorder are linked to high risks of various chronic diseases and mortality. They have been recognized as a world-wide public health issue due to the rapid increasing prevalence in recent years. Bitter gourd (Momordica charantia L., BG) contains PPAR activators and is considered a potential functional food for ameliorating obesity and metabolic syndrome. Previous studies in our lab demonstrated that dietary BG might induce “browning” of the white adipose tissue which is considered an effective way to increase energy expenditure and combat obesity. The FGF21 (fibroblast growth factor 21) is a hormone that can be up-regulated by PPARα in liver and can improve systemic insulin sensitivity and induce browning of white fat. This study aims to preliminarily evaluate the metabolic changes from BG feeding using metabolomic approach and to examine whether FGF21 is involved in the WAT browning effect of BG. Using a 2×2 factorial design, 4 groups of C57BL/6J male mice were fed an AIN-93G modified high sucrose diet (HS group) or a high fat diet (HF group) supplemented with (BGP or FBGP group) or without 5% BGP for 8 weeks. BG supplementation reduced adipose mass, serum glucose and triglycerides. The metabolome of urine, serum, liver, adipose and skeletal muscle tissues samples were analyzed by LC-MS. Metabolites that were significantly different between the BG supplemented and the respective control groups were predicted based on available data base. Putative active compounds (triterpenoids) in BG were detected in the liver of BG fed mice. Changes in metabolites of tryptophan metabolism (Tryptophan, 3-Hydroxy-DL-kynurenine, nicotinamide adenine dinucleotide, serotonin) were also noted, suggesting tryptophan metabolic pathway may be affected by BG. To examine the WAT browning, 3 groups of C57BL/6J male mice were respectively fed the AIN-93G modified high sucrose diet (HS group) or HS diet supplemented with 5% BGP (BG group) or a chow diet for 25 weeks. The liver Fgf21 mRNA of the BG group was 2.8 folds higher than that of the HS group (P<0.05). The Ucp1 mRNA level was significantly higher in the EWAT of the BG group, and the mRNA expression levels of browning genes (Pgc-1α, Cidea, Prdm16) and mitochondrial DNA content were also higher. The BG group had significantly lower feed/energy efficiency, adipose mass, fasting serum glucose/insulin and HOMA-IR index, higher O2 consumption/CO2 production than the HS group. In conclusion, these data suggest that BG might improve metabolic health through the up-regulation of liver Fgf21 mRNA, EWAT Ucp1 browning genes and mitochondrial biogenic genes and increases in energy expenditure, which ameliorated the diet-induced obesity and metabolic disorder in mice.