在本次實驗中，大鼠以四氯化碳投予八週並且分別給與高劑量與低
劑量的牛磺酸水溶液，結果顯示高劑量的牛磺酸可以有效的抑制肝臟纖 維化。
GOT、GPT 酵素大量存在肝細胞內，肝臟受到損害時，GOT、GPT 酵素會釋出至血液中，因此，血清中的 GOT、GPT 值最常作為肝損傷 的指標(Sturgill and Lambert, 1997)。其中 GPT 較具專一性，因 GOT 除 了肝臟含有外，心臟、腎臟、骨骼肌、腦部也含有(Sturgill and Lambert, 1997)。大鼠經過八週四氯化碳的處理其血清 GOT、GPT 皆明顯高於正 常組，顯示四氯化碳的確可以誘導慢性肝損傷。牛磺酸的投予在第三及 第六週沒有使血清 GOT、GPT 下降的作用；然在最後第八週出現明顯 的 GOT、GPT 下降作用。此結果有可能是牛磺酸不是保護早期因四氯 化碳代謝活化引起的肝損傷，而是作用於細胞損傷的後期(Waterfield et al., 1993)。
肝硬化時，血流進入肝臟受阻，引起門脈高壓，影響到脾臟的血流，
會使脾臟腫大、門脈高壓及引起腹水(Gill and Kircbain, 1997)。本實驗 中，四氯化碳誘發慢性肝炎，最後引起脾腫大。牛磺酸具改善脾臟腫大 的傾向。
慢性肝炎會引起肝臟纖維化，即結締組織增生。結締組織主要是由 膠原蛋白構成，hydroxyproline 是膠原蛋白特有的成分，測定肝臟中 hydroxyproline 的含量可以反應膠原蛋白的含量，表示肝臟纖維化的程 度(Hanauske-Abel, 1996)。在本實驗，四氯化碳誘發慢性肝炎，其肝臟 hydroxyproline 含量明顯增加，牛磺酸能減少肝臟中 hydroxyproline 含
量，表示有減緩肝纖維化的能力。
四氯化碳引起的肝纖維化，主要是自由基造成脂質過氧化而引起的 肝損傷(Camps et al., 1992)。已有文獻指出牛磺酸具抗氧化作用(John et al., 1995)。在本實驗，四氯化碳誘發慢性肝炎，造成肝臟組織的脂質過 氧化明顯增加，高劑量的牛磺酸能降低脂質過氧化程度，顯示與降低自 由基的傷害有關。
基因微陣列的結果顯示，四氯化碳誘導組的 GSH synthetase 活性
明顯下降，而生化的測定結果卻是 GSH 含量增加，結果相反的原因有 待進一步探討。牛磺酸對 GSH 的影響可以反轉四氯化碳的作用，可推 測 GSH 也參與牛磺酸的護肝作用。在本實驗酵素活性測定及基因微陣列的結果顯示，四氯化碳誘發大 鼠肝纖維化，肝組織中清除自由基的三種酵素 SOD、catalase、GSH-Px 活性明顯下降，牛磺酸對此 SOD 及 catalase 兩種酵素的活性沒有影 響，但會使 GSH-Px 的活性下降，所以牛磺酸抗纖維化是否與 GSH-Px 活性下降有關，有待進一步研究。雖有文獻指出牛磺酸減少 thioacetamide 引起的慢性肝損傷，可能與 GSH-Px 酵素活性的增加有關(Balkan et al., 2002)。但也有報告顯示牛磺酸能減少乙醇及 thioacetamide 造成的慢性 肝損傷，與 SOD、GSH-Px 及 GSH-ST 酵素活性無關(Balkan et al., 2001；Dogru-Abbasoglu et al., 2001)。
先前實驗大鼠的研究顯示牛磺酸有改善肝纖維化的作用，主要可以 明顯抑制四氯化碳所提升的 Procollagen-1 及 TIMP-1 基因表現(Chen, 1999; 陳,1991)。在我們的研究模式中，也獲得相同的結果，證實牛磺酸 明顯抑制四氯化碳所提升的 Procollagen-1 及 TIMP-1 基因表現(Fig.5 (C)(D))。
1998)。 TGF-beta1 的表現增加，可促進 TIMP-1 的表現，進而增強 Procollagen-1 的表現(Eng, 1998)。因此抑制 TGF-beta1 的表現，是目前 抗肝纖維化藥物開發的重點。本實驗以 mRNA 及蛋白質的表現確認牛 磺酸可以抑制四氯化碳所提升的 TGF-beta1 表現。可以證實牛磺酸具抗 肝纖維化作用(Fig.5 (A))。
HGF 是一種具有多種生物學作用的蛋白質分子，實驗證明，在肝 切除和各種肝病血液中 HGF 含量會明顯升高， 肝組織中的 HGF mRNA 亦會表現，其目的是在促進肝臟再生及修復 (Lindroos et al., 1991)。雖然如此，Masson 氏等人的四氯化碳肝纖維化實驗顯示 HGF mRNA 表現不受影響(Masson et al., 1999)。本實驗結果發現在八週四氯 化碳的誘導下，HGF mRNA 的表現明顯下降，高劑量的牛磺酸可以消 除 HGF mRNA 的下降表現。然而此四氯化碳組的結果與 Masson 氏等 人(1999) 的結果不同，其 HGF mRN 在四氯化碳誘導下，與正常組無差 異性，我們認為是四氯化碳損傷到肝細胞的再生功能，真正原因有待進 一步研究。
肝損傷時 MAT 的活性降低(Mato et al., 1997)，調控 MAT 的基因是 mat1a 的表現也會下降 (Avila et al., 2002)。MAT1A 的表現與 SAM 生成 有 關， SAM 與 polyamine 及 glutathione 的生合成有關 (Chen et al., 2000)，此二者對肝細胞有很重要的保護作用(Chen et al., 2000)。本實驗結 果顯示四氯化碳的誘導下，MAT1A 的表現明顯下降，此與其他研究一致 (Avila et al , 2002)，高劑量牛磺酸能明顯提升 MAT1A 的表現，顯示牛 磺酸確實具有保肝的效果。
雖然 MAT2A 在一般肝細胞不會表現，但 MAT1A 及 MAT2A 兩者在肝臟的存在是互相調控的，當肝損傷或肝細胞增生時 MAT2A 會 開始表現，取代 MAT1A，雖然此機轉不明，但仍待研究(Shelly et al.,
2001)。本實驗也發現正常肝組織 MAT2A 沒有表現，四氯化碳誘發的 肝損傷會造成 MAT2A 表現，而 MAT1A 的表現明顯下降。高劑量的 牛磺酸能抑制 MAT2A 表現，更進一步支持牛磺酸具有保護肝細胞避免 肝損傷的功能。
牛磺酸對四氯化碳造成的肝纖維化有明顯減輕現象，其作用機轉可 能經由抗氧化(如: GSH-ST)和肝細胞保護作用(如: MAT1A)，降低肝細 胞損傷 (MAT2A 表現下降)，進而減弱 TGF-beta1 的表現，因此減少 TGF-beta1 所誘發肝纖維化的基因表現(如: TIMP-1、Procollagen-1)，最 後減少細胞外基質的存積，達到改善肝纖維化的效果。
結 論
在 四 氯 化 碳 誘 導 大 鼠 慢 性 肝 損 傷 模 式 下 ， 由 RT-PCR 及 expressed microarray analysis 結果得知適量的牛磺酸可以降低 TGF- beta1、TIMP 及 Procollagen-I mRNA 的表現，提升 HGF、MAT1A 及 GSH-ST mRNA 的表現，因此牛磺酸可能是透過 GSH-ST 催化 GSH 與四氯化碳代謝物結合，並且由 MAT 促進 SAM 的生成來穩定細胞膜 脂質及調節細胞膜通透性，使牛磺酸能保護肝細胞避免受到傷害。
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