張凌云 許國雄
·綜述·
維生素代謝水平對肝癌的影響
張凌云 許國雄
我國是肝癌高發(fā)生率國家之一,晚期肝癌死亡率極高,針對肝癌晚期的治療并沒有減低肝癌患者死亡率,也未能有效地緩解病人的臨床癥狀。臨床工作偏重于常規(guī)物質(zhì)的檢測與補(bǔ)充,往往忽略了維生素的檢測及在肝癌輔助治療中的作用。本文將針對維生素的代謝水平在肝癌發(fā)生發(fā)展及治療中的研究做一綜述,希望可以對未來的肝癌的臨床治療給予一些啟示。
一、肝癌現(xiàn)狀
肝癌是第五大常見的腫瘤,由于乙型肝炎病毒和丙型肝炎病毒的感染增多而呈逐年上升趨勢[1]。據(jù)統(tǒng)計(jì)約54%肝癌發(fā)生在中國[2]。雖然針對肝癌的治療有了長足的進(jìn)步,但是肝癌死亡率仍然很高,5年生存率不足15%[3]。其原因除了晚期肝癌病人的復(fù)發(fā)和轉(zhuǎn)移外,很大程度上是由于患者出現(xiàn)嚴(yán)重的營養(yǎng)不良和代謝紊亂,甚至是惡液質(zhì),但是臨床偏重于蛋白等的檢測,往往忽略了維生素的檢測。
二、維生素概論
維生素是生物的生長和代謝所必需的微量有機(jī)物,分為脂溶性維生素和水溶性維生素兩類。前者包括維生素A、D、E、K等,后者有維生素B1(硫胺素)、B2(核黃素)、B6、B12、泛酸、葉酸、尼克酸、生物素和維生素C。有流行病學(xué)資料顯示機(jī)體的營養(yǎng)狀況與腫瘤的病因與發(fā)病機(jī)制有關(guān),不同的營養(yǎng)狀況既可以促進(jìn)腫瘤的發(fā)生,也可以抑制腫瘤的發(fā)生[4,5]。
三、各類維生素在肝癌中的研究
(一)脂溶性維生素與肝癌
1.維生素A(VA)VA與視力、免疫功能、細(xì)胞生長和分化有關(guān)[6]。早在1983年研究者發(fā)現(xiàn)VA可以通過結(jié)合黃曲霉素B1基因引起相關(guān)酶的改變進(jìn)而導(dǎo)致肝癌和結(jié)腸癌[7]。最新研究顯示VA的紊亂可以導(dǎo)致肝癌、肺癌、乳腺癌的發(fā)生[8]。視黃酸受體可以調(diào)控VA的代謝產(chǎn)物(視黃酸)的多效反應(yīng),而視黃酸受體γ的過度表達(dá)可通過PI3K/Akt和NF-κB信號轉(zhuǎn)導(dǎo)通路促進(jìn)肝癌細(xì)胞的增殖[9]。
2.維生素D(VD)VD是一種甾體類化合物,主要的生理作用是調(diào)控礦物質(zhì)和骨質(zhì)平衡[10]。VD可以通過外部吸收(VD2)和光照后經(jīng)膽固醇合成得到補(bǔ)充(VD3)[11],VD活化的第一步是在肝臟中羥基化形成25-羥基維生素D3[12],1,25-二羥基維生素D3是VD的最佳活性形式,主要在腎臟中合成[13]。一項(xiàng)針對肝癌和慢性肝病的長達(dá)22年的大規(guī)模病例對照研究顯示基線VD水平的不同引起的肝癌發(fā)生率不同:基線高VD水平(>1.485mmol/L)的病人血漿25-羥基維生素D3的濃度與肝癌發(fā)生率呈負(fù)相關(guān)(Q4vs.Q1,OR=0.43,95%CI=0.21~0.89),但在基線低VD水平組(<1.485mmol/L)卻沒有這種關(guān)系;對于慢性肝病病人的致死率卻與基線低VD水平無顯著聯(lián)系,而高血漿25-羥基維生素D3與慢性肝臟疾病的低死亡率呈顯著相關(guān)(Q4vs.Q1,OR=0.34,95%CI=0.21-0.55)[14]。
VD3可通過結(jié)合核因子、維生素D受體[10,15]等起到抑制細(xì)胞增殖、抗血管發(fā)生、促凋亡和免疫調(diào)控的作用[15-17]。維生素D的缺乏和/或維生素D受體的異常可引起肝癌的發(fā)生和發(fā)展[18]。已有文獻(xiàn)證實(shí)1,25-二羥基維生素D3可通過誘導(dǎo)細(xì)胞周期阻滯[19]、抑制肝癌細(xì)胞的增殖[20],但大量應(yīng)用后引起的血鈣紊亂則限制了1,25-二羥基維生素D3在臨床中的應(yīng)用。經(jīng)改良后,1,25-二羥基維生素D3類似物如EB1089、CB1093和MART-10同樣具有抑制肝癌細(xì)胞增殖的作用,還有效避免了血鈣紊亂的發(fā)生[21,22]。另有報(bào)道顯示EB1089還可通過誘導(dǎo)凋亡進(jìn)而抑制肝癌的增殖[23]。檢測血25羥基維生素D3濃度低于50nmol/L視為維生素D缺乏,被認(rèn)為存在肝癌發(fā)生風(fēng)險(xiǎn),但出乎意料的是高濃度的血25羥基維生素D3并不一定會(huì)減少肝癌發(fā)生的風(fēng)險(xiǎn)[24]。
一項(xiàng)針對終末期肝病等待肝移植的99例病人的研究顯示88%患者存在維生素D不足或缺乏[25],可致骨質(zhì)異常??梢奦D與肝臟功能息息相關(guān),肝臟功能差可致VD吸收合成障礙,而VD的不足又可進(jìn)一步導(dǎo)致肝功能惡化。
3.維生素E(VE)VE是有效的抗氧化劑,可以保護(hù)細(xì)胞的結(jié)構(gòu)和功能,抵抗自由基的侵害;同時(shí)也被認(rèn)為參與信號轉(zhuǎn)導(dǎo)通路和基因表達(dá)的調(diào)控[26]。一項(xiàng)針對中國人群的大規(guī)模隨訪研究顯示食物吸收的VE和補(bǔ)充物來源的VE與肝癌發(fā)生風(fēng)險(xiǎn)呈負(fù)相關(guān)(HR=0.52,95%CI=0.30to0.90),在女性中更明顯(HR=0.41,95%CI=0.18to0.96)[27]。CalvisiDF等在轉(zhuǎn)基因小鼠中發(fā)現(xiàn)VE可通過抑制一氧化氮合酶和NADPH酶相關(guān)的活性氧的產(chǎn)生[28],誘導(dǎo)染色質(zhì)損傷[29],抑制肝癌的進(jìn)一步發(fā)生,這意味著VE可用于肝癌的預(yù)防。
4.維生素K(VK)VK最為熟知的功能是作為γ-谷氨酸羧化酶的輔酶,參與將轉(zhuǎn)錄后剩余的與蛋白結(jié)合的谷氨酸殘基轉(zhuǎn)化為γ-羧基谷氨酸[30]。VK缺乏誘導(dǎo)的凝血素增高可以作為診斷肝細(xì)胞肝癌的標(biāo)志物[31]及預(yù)測肝細(xì)胞肝癌復(fù)發(fā)[32]。VK2和VK3可分別通過誘導(dǎo)凋亡并激活MEK/ERK信號轉(zhuǎn)導(dǎo)通路[33],調(diào)控自噬[34]及激活細(xì)胞色素P450[35]抑制肝癌細(xì)胞的增殖[36]。另有研究者認(rèn)為低水平VK的攝入可增加患骨質(zhì)疏松癥的風(fēng)險(xiǎn),VK2(45mg/day)可作為預(yù)防骨質(zhì)流失和脊柱骨質(zhì)的保護(hù)劑[37]。前述VD也可影響骨質(zhì),可見脂溶性維生素不足或缺乏使晚期肝癌患者發(fā)生骨折風(fēng)險(xiǎn)升高。
(二)水溶性維生素與肝癌
1.維生素B(VB)對B族維生素與肝癌的研究最多的是VB6和VB12。針對104位原發(fā)性肝癌患者治療后1個(gè)月的臨床隨訪研究顯示,給予VB6(50mL,QD)聯(lián)合斑蝥酸鈉的治療組較單用斑蝥酸鈉的對照組需要重新治療的例數(shù)明顯減少(P=0.01),治療效果和影像學(xué)下肝癌的形態(tài)維持更好(P<0.05)。但是令人遺憾的是3個(gè)月的隨訪并沒有明顯差別[38]。提示VB6僅僅能在短時(shí)間內(nèi)輔助加強(qiáng)治療效果,其本身無治療作用。
早在1946年Copeland和Salmon發(fā)現(xiàn)甲基供體(包括VB12)的缺乏可誘導(dǎo)嚙齒動(dòng)物肝癌的發(fā)展[39],這些缺少的甲基供體可以通過改變脂類代謝、氧化應(yīng)激反應(yīng)、降解一碳單位等[40]作為癌基因或輔助癌基進(jìn)而導(dǎo)致腫瘤的發(fā)生[41]。VB12及葉酸的異??梢餌NA甲基化的異常而誘導(dǎo)肝細(xì)胞癌變[42]。Lildballe報(bào)道了一名15歲患纖維板層肝細(xì)胞肝癌的男孩,得出血漿VB12結(jié)合蛋白鈷胺素可作為此類疾病的進(jìn)展標(biāo)志物[43];同樣,在日本的一例手術(shù)后復(fù)發(fā)的纖維板層肝細(xì)胞肝癌的病理報(bào)道中作者也得出升高的VB12的結(jié)合容積可以作為此病的標(biāo)志物[44];但是VB12在肝癌中是否可作為標(biāo)志物并沒有系統(tǒng)性研究。直到2014年Simonsen等進(jìn)行了較大規(guī)模(273例)的病例對照研究,發(fā)現(xiàn)維生素B12及B12相關(guān)蛋白在慢性肝病和肝細(xì)胞肝癌中表達(dá)均較正常人群高,雖然作者得出結(jié)論認(rèn)為VB12及相關(guān)蛋白的增高不能最為生物標(biāo)志物來區(qū)分肝細(xì)胞肝癌及慢性肝病,但是在區(qū)分肝臟是否異常上仍有一定的臨床應(yīng)用價(jià)值[45]。在一項(xiàng)對于肝細(xì)胞肝癌的研究中發(fā)現(xiàn)Child-Turcot Pugh score(CTP分級)評分等級的高低與VB12的水平呈正相關(guān)(P=0.016)[46]。
2.維生素C(VC) Zhang等[27]針對國人的一項(xiàng)研究顯示補(bǔ)充物來源的VC可增加肝癌的發(fā)生風(fēng)險(xiǎn)(HR=1.96,95% CI=1.29 to 2.98),而食物中的VC卻與肝癌發(fā)生風(fēng)險(xiǎn)無關(guān)。一些研究顯示VC 可抑制肝癌的發(fā)生[47],也有報(bào)道兩者無關(guān)[48]。Zhang等[27]同時(shí)也發(fā)現(xiàn)入組時(shí)既患散發(fā)肝癌和有家族史的肝癌患者VC水平高,原因可能是這些患者更容易額外補(bǔ)充維生素C,這也可解釋之前作者曾描述的VC會(huì)增加肝癌風(fēng)險(xiǎn)。
四、總結(jié)與展望
綜觀上述研究,在肝癌患者中各類維生素往往是缺乏的,所以晚期肝癌患者的營養(yǎng)匱乏并不僅僅表現(xiàn)白蛋白、血紅蛋白等的減少。在實(shí)際臨床工作中,常規(guī)補(bǔ)充血漿、白蛋白并不能滿足機(jī)體對維生素等物質(zhì)的需求,而即使臨床醫(yī)生給予患者復(fù)合維生素或單一維生素的補(bǔ)充,也往往不能滿足機(jī)體的需要量。有文獻(xiàn)顯示血管的生成可受 VB6(吡哆醇和吡哆醛)的影響,高濃度 VB6可抑制血管的生成,而在腫瘤的發(fā)展中有大量的血管形成[49],肝癌患者往往維生素缺乏,從此角度考慮,只要患者腎功能正常即可給予大量水溶性維生素B6的補(bǔ)充,有可能起到抑制腫瘤血管增生的作用。
可見,維生素代謝與肝癌息息相關(guān),檢測患者維生素水平,系統(tǒng)性的研究、了解維生素的作用機(jī)制,有助于對肝癌進(jìn)行更為有效預(yù)防及治療。
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2015-04-11)
(本文編輯:馮珉)
201508復(fù)旦大學(xué)腫瘤學(xué)碩士研究生(張凌云);復(fù)旦大學(xué)附屬金山醫(yī)院中心實(shí)驗(yàn)室(許國雄)
許國雄,Email:guoxiong.xu@fudan.edu.cn