| 摘要: | 腦部的氧化壓力、發炎反應及血腦障壁通透性增加、周邊的胰島素抗性誘導、肝臟的代謝異常、腸道的菌相失衡與更年期時雌激素的分泌減少有關。本研究的目的以雙側卵巢切除 (ovariectomy, OVX)小鼠模擬婦女停經狀態，並利用D-半乳糖注射合併果糖糖水餵食的多重致病因子模式，探討將飲食中油脂組成由大豆油替換成苦茶油，或合併米糠的介入，是否能改善小鼠的腦部神經發炎、肝臟脂肪堆積及腸道菌相組成。本實驗動物為雌性C57BL/6小鼠，以8週大的小鼠為年輕對照組，以6-8個月的退役雌鼠為年長對照組及實驗組，實驗分組如下：年輕假手術控制組(sham + young mice, SY)、年長假手術控制組 (sham + old mice, SO)、實驗誘導組 (OVX + soybean oil diet, OS)；卵巢切除大豆油合併米糠介入組 (OVX + soybean oil combined rice bran diet, OSR)；卵巢切除苦茶油介入組 (OVX + tea seed oil diet, OT)；卵巢切除苦茶油合併米糠介入組 (OVX + tea seed oil combined rice bran diet, OTR)。其中OVX四組會給予D-半乳糖注射 (100 mg/kg/day)及果糖糖水 (15% v/v)，米糠及苦茶油的介入劑量為飼料重量百分比10% (w/w)，共餵食8週後犧牲。結果顯示，OS組顯著降低小鼠的學習而非記憶能力。相較OS組，OSR、OT及OTR組雖可降低空腹血糖值，但無法改善小鼠的認知功能。其中OSR組會造成小鼠體重的增加，但可減少腦中前額葉的丙二醛 (malondialdehyde, MDA)、肝臟骨髓過氧化酶 (myeloperoxidase, MPO)活性及三酸甘油酯 (triglycerides, TG)濃度，提升腸道菌群α-多樣性、負責分解飲食中膳食纖維之c_Clostridia相對含量及總短鏈脂肪酸生成；OT組顯著增加肝臟相對重量、肝臟內TG及膽固醇 (total cholesterol, TC)濃度、血漿肝功能指標天門冬胺酸轉胺酶 (aspartate transaminase, AST)及丙胺酸轉胺酶 (alanine transaminase, ALT)活性，並伴隨腸道中負責生成內毒素的f_Tannerellaceae及g_Parabacteroides相對含量的上升。由於在本實驗同時發現腦部促發炎細胞激素、肝臟脂肪堆積及肝功能指標與腸道的f_Tannerellaceae相對含量彼此呈正相關，因此推測OT組可以透過增加f_Tannerellaceae相對含量，經由肝–腸軸及腦–腸軸之相互影響，加劇肝臟中的脂肪堆積及腦部介白素 (interleukin, IL)-1β、介白素(IL)-6及腫瘤壞死因子 (tumor necrosis factor, TNF)-α的分泌；而OTR組相較OT組，可降低腸道f_Tannerellaceae、g_Parabacteroides相對含量，同時增加腸道屏障緊密連結蛋白occludin、c_Clostridia相對含量及丁酸的產生，透過腦–肝–腸軸，使肝臟相對重量、肝臟內TG及TC、肝功能指標AST及ALT下降，周邊氧化傷害指標8-羥基去氧鳥糞嘌呤 (8-hydroxy-2’deoxyguanosine, 8-OHdG)生成減少，並減緩腦部促發炎細胞激素IL-1β及TNF-α的產生。因此，本研究結果顯示苦茶油合併米糠飲食可能會藉由減少周邊8-OHdG濃度，以及腸道f_Tannerellaceae與g_Parabacteroides相對含量，以降低僅介入苦茶油對於D-半乳糖注射合併果糖糖水餵食之卵巢切除小鼠其肝臟的脂肪堆積及腦部的發炎反應。
Increased oxidative stress, inflammation and blood brain barrier permeability in the brain, peripheral insulin resistance, abnormal liver metabolism, and gut dysbiosis are all related to the estrogen deficiency after menopause. This study aimed to investigate a tea seed oil-based diet combined with rice bran on neuroinflammation, liver steatosis and gut microbiota in a fructose drink fed D-galactose injected ovariectomized (OVX) mice model. Eight weeks old young female C57BL/6 mice for young control and 6-8 months old female C57BL/6 mice for old control and OVX were used in this study. All mice were divided into six groups: sham + young mice (SY), sham + old mice (SO), OVX + soybean oil diet (OS), OVX + soybean oil combined rice bran diet (OSR), OVX + tea seed oil diet (OT) and OVX + tea seed oil combined rice bran diet (OTR). Four OVX groups were injected D-galactose (100 mg/kg/day) by subcutaneous (s.c.) and provided 15% (v/v) fructose drink to induce multiple factors associated with aging and neurodegenerative diseases, and the intervention of rice bran and tea seed oil was 10% (w/w). After eight weeks of feeding, the impairment of learning ability but not memory ability was found in the OS group. Fasting glucose was significantly lower in OSR, OT and OTR groups than the OS group, with no effect on the cognitive function. In the OSR group, the MDA level of the brain, the activity of MPO, and the concentration of TG in the liver were lower. The α-diversity, the relative abundance of dietary fiber-degrading microbiota - c_Clostridia in the cecal content, and the level of total short-chain fatty acids of the feces in the OSR group were higher than those in the OS group, accompanied by the elevation of the body weight. The relative weight of the liver, the hepatic TG and TC content, the plasma AST and ALT level, and the relative abundance of endotoxin-producing microbiota - f_Tannerellaceae and g_Parabacteroides in the cecal content significantly increased in the OT group. The relative abundance of f_Tannerellaceae in the cecal content were found positively associated with the level of pro-inflammatory cytokines of the brain, the content of the hepatic lipids, and the plasma liver function biomarkers in this study. These results existed the relation among the brain-liver-gut axis. Thus, we suggested that the elevation of the relative abundance of f_Tannerellaceae in the OT group resulted in the exaggeration of lipid accumulation in the liver and the secretion of IL-1β, IL-6 and TNF-α in the brain via the liver-gut axis and brain-gut axis, respectively. Compared with the OT group, mice in OTR group decreased the relative abundance of f_Tannerellaceae and g_Parabacteroides in the cecal content. Moreover, the occludin gene expression of the colon, the relative abundance of c_Clostridia in the cecal content, the amount of butyric acid in the feces were also higher in the OTR group. Through the brain-liver-gut axis, the alteration of gut microbiota and their metabolites in the OTR group could lower the relative weight of the liver, the hepatic TG and TC, the plasma AST, ALT and 8-OHdG level. These might influence and alleviated IL-1β and TNF-α in the brain. In conclusion, compared with the tea seed oil-based diet, a diet containing rice bran in tea seed oil-based diet may ameliorate hepatic fat accumulation and brain inflammatory responses through downregulating circulating 8-OHdG level as well as the relative abundance of f_Tannerellaceae and g_Parabacteroides in the gut in ovariectomized mice combined with D-galactose injection and fructose drink feeding. |
