在本實(shí)驗(yàn)中可見(jiàn),隨著供肝冷保存時(shí)間的延長(zhǎng),供肝中NFκB水平顯著增高。其機(jī)制可能是隨冷保存時(shí)間延長(zhǎng),內(nèi)皮細(xì)胞和Kupffer細(xì)胞內(nèi)氧自由基增多,低氧及氧化應(yīng)激介導(dǎo)NFκB激活,調(diào)控TNFα、IL1β表達(dá)增高[11]。再灌注后各組肝組織中NFκB以及血清TNFα、IL1β水平均較冷保存期明顯增高,并隨著冷保存時(shí)間的延長(zhǎng)活性增強(qiáng)。TUNEL顯示肝細(xì)胞凋亡加重,反映肝損傷的酶學(xué)指標(biāo)(ALT、AST)亦明顯升高,表明再灌注后NFκB產(chǎn)生爆發(fā)式激活,轉(zhuǎn)錄大量TNFα、IL1β,進(jìn)一步加重供肝的損傷。其機(jī)制可能與移植肝再灌注后呼吸爆發(fā)、氧化應(yīng)激大大增強(qiáng)有關(guān),而其轉(zhuǎn)錄產(chǎn)物如TNFα、IL1β又可進(jìn)一步激活NFκB,形成正反饋。
可見(jiàn),供肝的冷保存和再灌注是兩個(gè)既獨(dú)立又關(guān)聯(lián)的過(guò)程。供肝的NFκB在冷保存期間就已經(jīng)受到預(yù)激,并表達(dá)多種炎癥介質(zhì),成為再灌注損傷的始動(dòng)因子;在再灌注階段NFκB的效應(yīng)迅速放大,進(jìn)一步激發(fā)并維持炎癥反應(yīng),損傷供肝[12]。其中TNFα在肝損傷中發(fā)揮重要作用,可以直接或誘導(dǎo)肝細(xì)胞壞死、凋亡[13];而IL1β誘導(dǎo)Kuppfer細(xì)胞產(chǎn)生TNFα,上調(diào)中性粒細(xì)胞產(chǎn)生更多的自由基。二者的協(xié)同作用引起血管擴(kuò)張和白細(xì)胞介導(dǎo)的組織壞死,最終導(dǎo)致器官衰竭。NFκB與細(xì)胞凋亡的關(guān)系密切, 其參與多種凋亡相關(guān)基因的轉(zhuǎn)錄調(diào)控, 具有抑制細(xì)胞凋亡作用及促細(xì)胞凋亡的雙向作用,可能與不同亞基的轉(zhuǎn)錄有關(guān),可以不通過(guò)炎性因子的作用,直接導(dǎo)致細(xì)胞凋亡[14]。在本實(shí)驗(yàn)中NFκB顯示出促進(jìn)肝細(xì)胞凋亡的作用。
總之,隨著移植肝冷保存時(shí)間的延長(zhǎng),肝內(nèi)NFκB存在不同程度的預(yù)激,再灌注后大量活化的NFκB通過(guò)上調(diào)TNFα、IL1β的表達(dá)直接或間接導(dǎo)致移植肝的損傷。這可能是移植肝再灌注損傷的重要機(jī)制,而抑制NFκB可能是一條減輕移植肝再灌注損傷的有效方法。
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