高效聯(lián)合抗反轉(zhuǎn)錄病毒治療引發(fā)繼發(fā)性骨質(zhì)疏松的研究進(jìn)展

劉浩，李瑋，魏強，周永勝*

(1. 北京大學(xué)口腔醫(yī)學(xué)院·口腔醫(yī)院, 北京 100081； 2. 中國醫(yī)學(xué)科學(xué)院醫(yī)學(xué)實驗動物研究所，北京協(xié)和醫(yī)學(xué)院比較醫(yī)學(xué)中心，北京 100021)

自從高效聯(lián)合抗反轉(zhuǎn)錄病毒治療(highly active anti-retroviral therapy，HAART)廣泛應(yīng)用以來，艾滋病病毒(human immunodeficiency virus，HIV)感染者的期望壽命顯著延長[1-3]。然而，越來越多的證據(jù)表明許多年齡相關(guān)的并發(fā)癥如骨骼肌肉失能、心血管疾病、腎損傷以及非艾滋病(acquired immune deficiency syndrome，AIDS)相關(guān)的惡性腫瘤等疾病在HIV感染群體中呈現(xiàn)高風(fēng)險和低齡化的特點[4-6]。其中，AIDS相關(guān)的骨質(zhì)疏松和骨量減少引起了越來越多的學(xué)者們關(guān)注。

骨質(zhì)疏松癥(osteoporosis，OP)是一種以骨量減少、骨微結(jié)構(gòu)損壞、骨強度下降、易發(fā)生脆性骨折為特征的全身性骨代謝疾病。骨質(zhì)疏松骨折相關(guān)的病死率和病殘率的增加給社會、家庭帶來沉重的經(jīng)濟(jì)負(fù)擔(dān)。目前，世界衛(wèi)生組織(World Health Organization, WHO)骨質(zhì)疏松診斷標(biāo)準(zhǔn)為：使用雙能X線骨密度儀(dual energy X-ray absorptiometry, DEXA)檢測腰椎或髖部的骨密度(bone mineral density, BMD)，與健康的同性別人群BMD平均值相比較，檢測值介于1-2.5個標(biāo)準(zhǔn)差的為骨量減低(-2.5SD

目前研究已經(jīng)確定HIV感染是骨質(zhì)疏松和骨量減少的高危因素[8-10]，但發(fā)病機制仍不清楚。歐美國家的多項大樣本量隊列研究表明HIV感染者骨折發(fā)病率較未感染人群上升2～5倍，而且這種發(fā)病率的上升并沒有性別差異[11-13]。雖然我國關(guān)于HIV感染和骨質(zhì)疏松的大樣本量隊列研究沒有報道，但是小樣本量的研究也表明HIV感染者骨量減少的比率較健康對照者增高1.52～2倍[14]。綜合大量研究表明，艾滋病患者罹患骨質(zhì)疏松主要有以下三類原因：(1)年齡增長和激素變化導(dǎo)致的原發(fā)性骨質(zhì)疏松，這也是所有人群骨質(zhì)疏松發(fā)病的危險因素[15]；(2)病毒感染導(dǎo)致的繼發(fā)性骨質(zhì)疏松[16]；(3)HAART引發(fā)的繼發(fā)性骨質(zhì)疏松[17]。這三類骨質(zhì)疏松誘因共同作用導(dǎo)致了HIV感染者骨量快速下降，進(jìn)而導(dǎo)致骨質(zhì)疏松。目前，原發(fā)性骨質(zhì)疏松仍無持續(xù)有效的治療方法，藥物治療所帶來的副作用也不容忽視[18]；而HIV病毒感染到如今也沒有有效的清除辦法。所以前兩種骨質(zhì)疏松的危險因素現(xiàn)階段無法有效解決。而HAART雖然會誘發(fā)繼發(fā)性骨質(zhì)疏松，但卻是目前唯一有效的AIDS治療方法，無法替代。因此，在保證HAART抗病毒療效的前提下，減少HAART誘發(fā)的骨質(zhì)疏松發(fā)病率已經(jīng)成為諸多科學(xué)家的研究方向。下面，本文將就HAART引發(fā)繼發(fā)性骨質(zhì)疏松的流行病學(xué)和機制的研究進(jìn)展做一綜述。

1 HAART引發(fā)繼發(fā)性骨質(zhì)疏松的流行病學(xué)調(diào)查

既往研究表明，在HAART治療的前兩年，相比較絕經(jīng)后骨質(zhì)疏松的HIV未感染人群，藥物因素額外貢獻(xiàn)了2%～6%的BMD降低率[19]。另一項研究也證明，相較于HIV未感染人群，HIV感染人群由于HAART引發(fā)骨質(zhì)疏松的比值比(odds ratio，OR)為2.5，而該研究對象所有骨質(zhì)疏松誘因的比值比僅為3.7 [95%置信區(qū)間(confidence interval，CI)2.3-5.9][20]。不僅如此，這種藥物相關(guān)的骨毒性是廣泛存在于不同年齡段的兩性人群中[9, 21]。目前，針對抗反轉(zhuǎn)錄病毒藥物和骨質(zhì)疏松之間關(guān)系的研究幾乎囊括了所有的抗病毒藥物的種類，但主要研究還是集中在核苷類反轉(zhuǎn)錄酶抑制劑(nucleotide reverse transcriptase inhibitor，NRTI)和蛋白酶抑制劑(protease inhibitors，PI)上。

1.1 NRTI引發(fā)繼發(fā)性骨質(zhì)疏松的流行病學(xué)調(diào)查

NRTI是合成HIV過程中DNA逆轉(zhuǎn)錄酶底物脫氧核苷酸的類似物，在體內(nèi)可通過與天然的三磷酸脫氧核苷競爭HIV逆轉(zhuǎn)錄酶的結(jié)合位點來阻礙前病毒的合成。在該類藥物中，替諾福韋酯(tenofovir disoproxil fumarate，TDF)是公認(rèn)的骨量降低/骨質(zhì)疏松的禁忌藥物。有研究表明采用TDF進(jìn)行抗病毒治療的患者比用其他NRTI藥物治療的患者，其BMD要多下降1%～3%[22, 23]。Assoumou L的研究也表明TDF與髖骨BMD(OR 2.8, 95% CI 1.3-5.9)和椎體BMD(OR 2.4, 95% CI 1.2-4.9)下降顯著相關(guān)[24]。

1.2 PI引發(fā)繼發(fā)性骨質(zhì)疏松的流行病學(xué)調(diào)查

PI是基于肽類的化合物，PI能競爭性抑制蛋白酶活性或作為互補蛋白酶活性點的抑制劑。其主要作用于艾滋病病毒復(fù)制的最后階段，使HIV病毒無法從感染的CD4細(xì)胞核中形成DNA進(jìn)而病毒不能聚集和釋放。目前，絕大部分研究已經(jīng)確認(rèn)PI和BMD降低存在相關(guān)性[25-27]。例如，一項隊列研究表明使用PI藥物與腰椎和股骨頸低骨量的OR值分別為1.100 [95% CI 1.003-1.207]和1.187 [95% CI 1.043-1.351][25]；此外，Bedimo等[28]學(xué)者認(rèn)為洛匹那韋/利托那韋(lopinavir/ ritonavir，LPV/r)是骨質(zhì)疏松骨折的獨立預(yù)測因子。但是，也有學(xué)者持反對意見。例如，艾滋病臨床研究小組(AIDS Clinical Trials Group，ACTG)一項研究顯示，兩組患者分別服用依法韋侖(efavirenz，EFV)或奈非那韋/利托那韋(nelfinavir/ ritonavir，NFV/r)，服藥前后兩組患者全身平均BMD差值沒有顯著性差異。由于之前研究表明EFV并不會導(dǎo)致骨質(zhì)疏松，所以研究者推斷NFV/r 也不會造成骨質(zhì)疏松[29]。當(dāng)然，這或許與此研究測量的是全身體平均BMD而不是WHO推薦的椎體或髖骨等特異性位點有關(guān)。此外，還有少量研究探索了不同PI藥物對BMD降低的影響。ACTG的另一項研究認(rèn)為服用阿扎那韋/利托那韋(atazanavir/ ritonavir，ATV/r)或地瑞那韋/利托那韋(darunavir/ ritonavir，DRV/r)的患者的椎體和髖骨BMD下降程度沒有顯著性差異，但這兩類PIs導(dǎo)致椎體和髖骨BMD下降程度比整合酶鏈轉(zhuǎn)移抑制劑(integrase strand transfer inhibitor，INSTI)雷特格韋(raltegravir，RAL)要大得多[30]。

2 HAART引發(fā)繼發(fā)性骨質(zhì)疏松的可能機制

骨組織重塑終生持續(xù)存在，其維持正常生理功能是通過成骨細(xì)胞介導(dǎo)的骨形成和破骨細(xì)胞介導(dǎo)的骨吸收之間的動態(tài)平衡來實現(xiàn)的[31-32]。骨吸收和骨形成受多種因素調(diào)節(jié)。雖然目前HAART引發(fā)繼發(fā)性骨質(zhì)疏松的可能機制仍不清楚，但是這種作用必然是骨吸收速率大于骨形成速率的結(jié)果。目前，研究者們認(rèn)為HAART引發(fā)繼發(fā)性骨質(zhì)疏松的可能機制有以下四種：

2.1 抗病毒藥物直接影響骨細(xì)胞代謝

抗病毒藥物對骨細(xì)胞的作用體現(xiàn)在兩個方面——影響來源于造血干細(xì)胞的破骨細(xì)胞和來源于骨髓間充質(zhì)干細(xì)胞的成骨細(xì)胞。破骨細(xì)胞方面，有研究表明TDF通過下調(diào)Gnas，Got2和Snord32 a基因的表達(dá)導(dǎo)致原代破骨細(xì)胞功能紊亂[33]；利托那韋(ritonavir，RTV)可以通過上調(diào)生長因子的表達(dá)來促進(jìn)外周血單核淋巴細(xì)胞(peripheral blood mononuclear cells，PBMCs)分化成破骨細(xì)胞[34]。成骨細(xì)胞方面，Grigsby IF的研究認(rèn)為TDF在體外影響了原代成骨細(xì)胞的多條成骨信號通路、細(xì)胞周期、氨基酸和能量代謝的多個基因[35]。Vincenzo Esposito的研究也表明TDF和阿巴卡韋(abacavir，ABC)通過降低I型膠原基因和p21 mRNA的表達(dá)減少了骨肉瘤細(xì)胞的鈣沉積量[36]。Hernandez-Vallejo SJ的研究表明ATV和LPV會通過誘導(dǎo)人骨髓間充質(zhì)干細(xì)胞(mesenchymal stem cells, MSCs)沉默而導(dǎo)致干細(xì)胞成骨細(xì)胞向分化能力下降，這與臨床觀察相一致[32]。

此外，也有研究者有不一致的觀點。Gibellini等[37]認(rèn)為膦沙那韋(fosamprenavir，F(xiàn)PV)作用于成骨樣細(xì)胞時導(dǎo)致其增加了OPG的表達(dá)，降低了RANKL的表達(dá)，這樣的結(jié)果應(yīng)該是導(dǎo)致BMD增加而不是降低。但是，由于成骨和破骨是類似蹺蹺板式的關(guān)系，單純觀測成骨或破骨一方的升高或降低不足以推斷出最終的骨變化。進(jìn)一步全面深入的研究才有可能解釋抗病毒藥物對骨代謝的影響。

2.2 HAART通過抑制HIV感染和促進(jìn)免疫恢復(fù)導(dǎo)致繼發(fā)性骨質(zhì)疏松

因為HAART誘發(fā)骨質(zhì)疏松具有普遍性，所以推斷可能是由于HAART抑制了HIV感染和促進(jìn)免疫恢復(fù)的原因。Ofotokun等[37]研究表明HAART治療12周后T細(xì)胞數(shù)量達(dá)到峰值，與此同時，在這個時間點骨吸收也達(dá)到了峰值。通過免疫重構(gòu)動物模型觀察到，免疫重構(gòu)后小鼠BMD確實出現(xiàn)了顯著下降，這是由于T細(xì)胞和其他免疫細(xì)胞產(chǎn)生了RANKL和TNF-α等促破骨的細(xì)胞因子[38]。但是，也有研究表明，利用TDF進(jìn)行健康兩性人群HIV暴露前的預(yù)防時，TDF導(dǎo)致的骨丟失可以逆轉(zhuǎn)，據(jù)此可以推斷TDF的骨毒性或許跟HIV感染或免疫重構(gòu)無關(guān)[39-41]。

2.3 HAART通過改變維生素D代謝誘發(fā)繼發(fā)性骨質(zhì)疏松

維生素D對于骨代謝和血清鈣含量的維持具有重要作用。在HIV感染人群中，維生素D缺乏非常常見，特別是在使用TDF和EFV進(jìn)行抗病毒治療時[42-44]。有研究表明，在體外，PIs通過抑制肝細(xì)胞和單核細(xì)胞的25-和1α-羥化酶來降低活性代謝產(chǎn)物1,25-二羥維生素D [1,25-(OH)2D]的含量[45]。此外，多項研究也表明了PIs和25-羥維生素D [25-(OH)D]存在顯著正相關(guān)，這或許與PIs抑制了25-(OH)D轉(zhuǎn)化為活性產(chǎn)物1,25-(OH)2D有關(guān)[46-48]。

2.4 TDF通過腎毒性導(dǎo)致繼發(fā)性骨質(zhì)疏松

目前研究發(fā)現(xiàn)，TDF在腎近曲小管上皮細(xì)胞處累積會造成近曲腎小管的功能紊亂，嚴(yán)重時可引起范可尼綜合征(高磷酸鹽尿癥、高氨基酸尿癥和糖尿)，導(dǎo)致骨質(zhì)降低、骨軟化以及骨質(zhì)疏松[14]。

3 結(jié)語

HAART導(dǎo)致骨質(zhì)疏松具有普遍性，其中NRTI和PI仍是兩類對BMD影響最大的抗病毒藥物，也是HAART療法的重要組成部分。這類藥物的骨毒性可能是由于HAART治療后抑制HIV感染和促進(jìn)T細(xì)胞恢復(fù)有關(guān)，也可能與藥物影響了骨細(xì)胞或維生素D代謝相關(guān)。當(dāng)前，HAART療法是AIDS治療的主要方法且具有不可替代性，因此，通過研究HAART療法中抗病毒藥物導(dǎo)致骨質(zhì)疏松的機制和相關(guān)防治方法來降低藥物的骨毒性具有重要的臨床意義。

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