探討大蒜汁對於人體腸道菌相與氧化三甲胺 (TMAO) 生成的影響

Abstract

根據世界衛生組織 (World Health Organization, WHO) 的統計，心血管疾病是 2016 年造成世界人口死亡原因的榜首。而台灣衛生福利部所公佈的 107 年國人十大死亡原因中，心血管疾病所造成的死亡人數居高不下，可見相關研究被探討的必要性。近期因腸道菌相關研究的興起，腸道菌及其代謝產物如氧化三甲胺 (Trimethylamine N-oxide, TMAO) 、短鏈脂肪酸 (Short chain fatty acids, SCFAs) 及次級膽酸都被證實與心血管疾病的發生有關 。其中 TMAO 已被許多研究證實具有致粥狀動脈硬化及血栓形成的潛力。先前本實驗室在動物實驗中發現大蒜素的介入能透過調節腸道菌相，降低肉鹼飲食所造成血漿 TMAO 濃度的提高，然而相關的人體試驗卻相當缺乏。因此本次實驗想要探討於 high TMAO producers 飲食中介入新鮮大蒜汁是否能透過調節腸道菌相，來降低其血漿 TMAO 濃度及血小板過度活化的現象，進而降低心血管疾病的風險。結果顯示，在介入了一週的大蒜汁後，high TMAO producers 的血漿 TMAO 濃度有下降的趨勢，血漿 γ -丁基甜菜鹼 (gamma-butyrobetaine, ϒ-BB) 則有顯著地上升，推測大蒜汁的介入可以抑制腸道菌利用 ϒ-BB 生成 TMA 的能力。此外，大蒜汁的介入顯著降低了受試者的尿液 TMAO 濃度，且與血漿 TMAO 濃度也有顯著相關性，暗示未來可以以非侵入性的尿液檢測代替血漿 TMAO 的檢測。 High TMAO producers 的血小板凝集反應在大蒜汁介入後並無顯著差異，與預期有落差，說明人體血小板凝集反應的複雜性，靠單一因子無法造成整體的影響。菌相分析的結果顯示，high TMAO producers α-多樣性中的 Shannon index 有顯著地上升，說明大蒜汁的介入提高了受試者腸道菌相的多樣性及均勻度。主座標分析 (PCoA) 的結果顯示大蒜汁的介入對於 high TMAO producers 整體的腸道菌相組成並無造成顯著地影響，但對於特定菌相的相對豐度仍造成顯著地改變。體外試驗的結果顯示 2.5% 的大蒜汁濃度為抑制腸道菌群利用 carnitine 生成 TMA 的最低有效劑量。綜上所述，本次研究的結論為飲食中大蒜汁的介入可以透過調節腸道菌相，抑制腸道菌利用 ϒ-BB 生成 TMA 的能力，藉此減少 TMAO 的產生，進而降低心血管疾病的風險。

According to the estimations made by World Health Organizations (WHO) in 2016, cardiovascular diseases (CVD) were the main cause of death worldwide. Taiwan Ministry of Health and Welfare also stated that CVD remained one of the greatest cause of death in Taiwan population. Recently, gut microbiota related metabolites, trimethylamine N-oxide (TMAO) has gain more attentions with its proatherogenic and prothrombic potentials. Many studies have showed that elevated plasma TMAO increased the risk of major adverse cardiovascular events (MACE). Recently, our laboratory works showed that synthesized allicin, a major bioactive compound in garlic can prevent the elevation of plasma TMAO caused by carnitine diet in animal studies. However, the effects of garlic on the production of TMAO in human studies were yet to prove. Therefore, the aim of this study is to investigate whether fresh garlic juice can decrease the elevation of plasma TMAO in high TMAO producers after consuming carnitine supplements and lower the platelet aggregation through modulation of gut microbiota. The results showed that garlic juice intervention reduced plasma TMAO and significantly increased plasma gamma-butyrobetaine (ϒ-BB) in high TMAO producers indicating the transformation of ϒ-BB into TMA in our gut microbiota was inhibited. Urine TMAO exhibited a strong correlation with plasma TMAO. Hence, urine can be an alternative non-invasive test for TMAO measurement. Platelet aggregation of high TMAO producers showed no significant differences after garlic juice intervention suggested that there are many other factors like thromboxane A2 and serotonin affecting platelet aggregation in human. Gut microbiota analysis of high TMAO producers showed that the Shannon index increased significantly after garlic juice intervention. Principal coordinate analysis (PCoA) showed no significant differences of overall gut microbiota composition after garlic juice intervention in high TMAO producers. However, the relative abundances of specific gut microbiota like Akkermansia, Lachnospiraceae and Christensenellaceae in genus level showed significant differences after garlic juice intervention. In vitro study showed that 2.5% of garlic juice concentration would inhibit the growth of bacteria and thus prevent the formation of TMA. In conclusion, fresh garlic juice reduced production of TMAO by preventing the transformation of ϒ-BB to TMA through modulation of gut microbiota indicating garlic as a potential food therapy to decrease CVD risk.