Lesson Ninety-four Angiotensin receptor blockers as tentative SARS-CoV-2 therapeutics

At the time of writing this commentary,the death tollfrom the COVID-19 epidemic caused by coronavirus SARS-CoV-2,which emerged in late December 2019,has surpassed the combined death toll of the SARS (Severe Acute Respiratory Syndrome)epidemic of 2002-2003 and the MERS (Middle East Respiratory Syndrome)epidemic of 2013 combined.This epidemic seems to be spreading at an exponential rate,with a doubling period of 1.8 days,and there are fears that it might progress to pandemic scales.Yet,no SARS-CoV-2 therapeutics are presently available,albeit some treatment options which await validation have been published,including several broad spectrum antivirals such as favipiravir and remdesivir,the anti-malaria drug chloroquine,and a traditional Chinese herbal formula.The ultimate solution is,obviously, developing a SARS-CoV-2 vaccine.However,vaccines for the SARS-CoV developed since its outbreak 18 years ago have not materialized to an approved product.In addition,there have been concerns about vaccine-mediated enhancement of disease,for example,due to pulmonary immunopathology upon challenge with SARS-CoV.Moreover,even once a vaccine is approved for human use,high virus mutation rates mean that new vaccines may need to be developed for each outbreak,similarly to the situation with new annualinfluenza vaccines.Below,Idescribe an alternative option which,if proven to be effective,would allow a rapid application in the clinic.

A recent hypothesis suggested that angiotensin receptor 1 (AT1R)inhibitors might be beneficial for patientsinfected by COVID-19 who experience pneumonia.This article,however,is only available in Chinese with an English abstract that does not describe its logic besides the notion that the renin-angiotensin system is dysregulated by SARS-CoV-2.A similar suggestion proposingthetreatmentofCOVID-19 patients with AT1R blockers was put forward in a"rapid online response"posted online by the British Medical Journalon February 4,2020.These tentative suggestions were based on the observation that SARS-CoV-2 uses angiotensin-converting enzyme 2(ACE2)as the receptor binding domain for its spike protein1,similarly to the coronavirus strain implicated in the 2002-2003 SARS epidemic.Moreover,the receptor binding domains of these two coronaviruses share 72%amino acid sequence identity,and molecular simulation has indicated similar ternary structures.However,SARS-CoV-2 includes a distinct loop with flexible glycylresidues replacing rigid prolylresidues in SARS-CoV,and molecular modeling indicated that the receptor binding domain of SARS-CoV-2 has higher affinity for ACE2 compared with SARS-CoV.

Notably,angiotensin-converting enzyme(ACE)and its close homologue ACE2,while both belonging to the ACE family of dipeptidyl carboxydipeptidases,serve two opposing physiological functions.ACE cleaves angiotensin I to generate angiotensin II,the peptide which binds to and activates AT1R to constrict blood vessels,thereby elevating blood pressure.By contract,ACE2 inactivatesangiotensin IIwhile generating angiotensin 1-7,aheptapeptidehavingapotent vasodilator function via activation of its Mas receptor2,and thus serving as a negative regulator of the renin-angiotensin system.

The AT1R antagonists losartan and olmesartan,commonly applied for reducing blood pressure in hypertensive patients,were shown to increase cardiac ACE2 expression about three-fold following chronic treatment(28 days)after myocardial infarction induced by coronary artery ligation of rats.Losartan was also shown to upregulate renalACE2 expression in chronically treated rats.In agreementwith these observations,higher urinary ACE2 levels were observed in hypertensive patientstreated with the AT1R antagonist olmesartan. Taken together, these observations suggest that chronic AT1R blockade results in ACE2 upregulation in both rats and humans.

As described above,ACE2 is the common binding site for both the SARS-CoV of the 2002-2003 SARS epidemic and,most likely,also the SARS-CoV-2 strain underlying the current COVID-19 epidemic.Hence,the suggestion to treat SARS patients with AT1R antagonists for increasing their ACE2 expression seems counterintuitive.However,several observations from studies on SARS-CoV,which very likely are relevant also for SARS-CoV-2,seem to suggest otherwise.It has been demonstrated that the binding of the coronavirus spike protein to ACE2,its cellular binding site,leads to ACE2 downregulation,which in turn results in excessive production of angiotensin by the related enzyme ACE,while less ACE2 is capable of converting it to the vasodilator heptapeptide angiotensin 1-7.This in turn contributes to lung injury,as angiotensin-stimulated AT1R results in increased pulmonary vascular permeability, thereby mediating increased lung pathology.Therefore,higher ACE2 expression following chronically medicating SARS-CoV-2 infected patients with AT1R blockers,while seemingly paradoxical,may protect them against acute lung injury rather than putting them at higher risk to develop SARS.This may be accounted for by two complementary mechanisms:blocking the excessive angiotensin-mediated AT1R activation caused by the viral infection,as well as upregulating ACE2,thereby reducing angiotensin production by ACE and increasing the production of the vasodilator angiotensin 1-7.These aspects on the role of dysregulated ACE2 in SARS-CoV pathogenesis are reviewed in detail by de Wit et al.,2016.Incidentally,following the SARS-CoV epidemic of 2002-2003,ACE2 inhibitors were suggested as SARS therapeutics;however,this proposal has not led to new drugs.

Incidentally,in the contextofthe human immunodeficiency viruses (HIV), it has been demonstrated that higher expression levels of the HIV binding sites CCR5 and CD4 protect from,rather than increase,HIV virulence.Michel et al.reported that HIV employs its early gene Nef product foravoiding superinfection during the viral entry step by downregulating CCR5. This Nef-mediated downregulation enhances the endocytosis rate of both CCR5 and CD4,which in turn facilitates efficient replication and spread of HIV,thereby promoting AIDS pathogenesis.It remains to be studied if a comparable mechanism for avoiding superinfection has evolved in coronaviruses;in which case,the suggestion of applying AT1R blockers as SARS therapeutics,even that they upregulate the expression of the ACE2 virus binding site,will not seem paradoxical.

Losartan,telmisartan,olmesartan (and additional AT1R antagonists)are widely applied in the clinic since the 1990s for control of hypertension and kidney disorders,and are known as safe drugs that are rarely implicated in adverse drugs events.However,it should be noted that around half of SARS-CoV patients developed hypotension during their hospitalization.At time of writing this commentary,no comprehensive information is available on hypotension rates among hospitalized SARS-CoV-2 patients;it is thus premature to estimate what percentage of SARS patients of the currently ongoing epidemic can be safely treated with AT1R blockers without risking exacerbated hypotension.

The tentative suggestion to apply AT1R antagonists such as losartan and telmisartan as SARS-CoV-2 therapeutics for treating patients prior to the development of acute respiratory syndrome remains unproven until tried.At time of writing this brief commentary,the end of the COVID-19 epidemic is not in sight and drastic actions are required(and being done)for containing its spread and death toll.Hence,the most rapid approach for assessing its feasibility is to analyze clinical patient records and apply datamining technologies to determine whether patients who were prescribed with AT1R antagonists prior to their diagnosis(for treating their hypertension,diabetic kidney disease,or other indications)had betterdisease outcome.Moreover, the percentage of people chronically medicated with AT1R blockers in the general population should be compared with the percentage among hospital admissions of SARS-CoV-2 infected patients presenting serious symptoms.If the latter percentage would be found to be significantly smaller,this would support the notion that AT1R antagonists confer protection from severe symptoms among SARSCoV-2 infected individuals.Knowledge gained from such datamining of clinical records seems crucial for reducing the mortality and morbidity of SARS-CoV-2.At the same time,efforts must be made for developing a SARS-CoV-2 vaccine.

詞 匯

tentative n.&adj.假設，實驗，嘗試；不確定的，暫定的，躊躇的，猶豫不定的，不果斷的，試探性的

commentary n. 評注，評論，議論

surpass v.超過，勝過，優(yōu)于

exponential adj.指數(shù)的，冪的，越來越快的

pandemic n.&adj.（全國或全球性）流行病，大流行??；大流行的，普遍的，全球的

materialize v.實現(xiàn)，發(fā)生，成為現(xiàn)實

immunopathology n.免疫病理學

vaccine n.疫苗，菌苗

ternary n.&adj.三個一組；三元的，由三部分組成的

glycyl n.甘氨酰，氨基乙酰

prolyl n.脯氨酰，脯胺?；?/p>

homologue n.同源物，同系物

dipeptidyl n.二肽基

carboxydipeptidase n.羧基二肽酶

heptapeptide n.七肽

counterintuitive adj.反常的;

virulence n.毒力，毒性，致命性

employ n.&v.雇用，受雇，服務;雇用，應用，運用，使用

superinfection n.重復感染，重複感染，雙重感染

endocytosis n.（細胞）內(nèi)吞作用，內(nèi)噬作用

confer v.商討，協(xié)商，交換意見，授予

注 釋

1.spike protein稱棘突蛋白，又稱S蛋白，位于冠狀病毒的表面，因病毒表面眾多的棘突看上去像皇冠，故名為冠狀病毒。棘突蛋白有S1和S2兩個亞單位，S1與宿主細胞表面的受體結(jié)合，S2與宿主細胞膜融合，使得病毒的基因組進入宿主細胞，這是病毒感染過程的第一步，也是關鍵的一步。

2.Mas receptor稱Mas受體，是血管緊張素系統(tǒng)中Ang-(1-7)的受體，由血管緊張素轉(zhuǎn)換酶2（ACE2）分解血管緊張素Ⅱ而產(chǎn)生，其介導的作用能對抗血管緊張素Ⅱ通過AT1受體介導的作用如血管收縮、炎癥反應和纖維化過程。

參考譯文

第94課 血管緊張素受體阻斷劑或成新冠肺炎治療藥

在撰寫這一述評（2020年2月）時，2019年12月下旬暴發(fā)、由SARS-CoV-2引起的新冠病毒肺炎（COVID-19）流行死亡人數(shù)已超過2002-2003年SARS（嚴重急性呼吸綜合征）與2013年MERS（中東呼吸綜合征）的死亡總?cè)藬?shù)。本次流行似乎呈指數(shù)速率蔓延，倍增時間為1.8d，令人恐懼的是這將擴散至全球范圍。目前SARS-CoV-2還缺乏有效的治療，雖然已公布一些等待批準的治療措施，包括幾種廣譜的抗病毒藥物如法匹拉韋和瑞德西韋，抗瘧疾藥物氯喹，以及傳統(tǒng)的中藥配方。顯然，最主要的解決方案是開發(fā)SARS-CoV-2疫苗。然而，自18年前SARS-CoV暴發(fā)以來，尚未開發(fā)出獲得批準的產(chǎn)品。另外，不乏擔心疫苗介導的疾病加重，比如SARS-CoV導致的肺部免疫病理學變化。此外，即使疫苗獲得批準用于人體，病毒的高度突變性意味著每次暴發(fā)均需開發(fā)新疫苗，類似于每年新流感疫苗這種狀況。下面我闡述可供替代的方案，如果證實有效，將可迅速應用于臨床。

近來推測，也許血管緊張素受體1（AT1R）阻斷劑有益于感染COVID-19的肺炎患者。不過，這一文章只有中文文本，英文摘要提及SARS-CoV-2引起腎素-血管緊張素系統(tǒng)調(diào)節(jié)紊亂，但沒有闡述其中的邏輯。2020年2月4日《英國醫(yī)學雜志》“快速在線反應”欄目線上刊登類似的文章，提出用AT1R阻斷劑治療COVID-19患者。這些試探性建議是建立在觀察到SARS-CoV-2利用血管緊張素轉(zhuǎn)換酶2（ACE2）作為其棘突蛋白受體結(jié)合域的基礎上，類似于2002～2003年SARS流行時的冠狀病毒株。況且，這兩種冠狀病毒擁有72%的相同氨基酸序列。分子仿真已表明相似的三元結(jié)構(gòu)。然而，SARS-CoV-2包含有截然不同的環(huán)形柔性甘氨酰殘基，取代了SARS-CoV中的硬性脯氨酰殘基。分子模型顯示，與SARS-CoV相比較，SARS-CoV-2的受體結(jié)合域與ACE2的關系更密切。

值得注意的是血管緊張素轉(zhuǎn)換酶（ACE）與其密切同系物ACE2雖然同屬二肽基羧基二肽酶ACE家族，但生理作用相反。ACE剪切血管緊張素Ⅰ而產(chǎn)生血管緊張素Ⅱ，該肽結(jié)合并激活AT1R引起血管收縮，從而提升血壓。相反，ACE2滅活血管緊張素Ⅱ而產(chǎn)生血管緊張素1-7，此七肽血管緊張素通過激活它的Mas受體而具備擴血管功能，因此成為血管緊張素系統(tǒng)的負向調(diào)節(jié)器。

冠狀動脈結(jié)扎引起心肌梗死的小鼠，給予常用于高血壓患者降壓治療的AT1R阻斷劑氯沙坦和奧美沙坦治療長達28d后顯示，心臟的ACE2表達增加3倍。長期治療的小鼠顯示，氯沙坦也上調(diào)腎臟的ACE2表達。與這些觀察相一致的是接受AT1R阻斷劑奧美沙坦治療的高血壓患者尿中ACE2含量較高。綜合這些結(jié)果表明，長期AT1R阻斷引發(fā)小鼠和人的ACE2上調(diào)。

如上所述，ACE2是 2002-2003年 SARS流行時的SARS-CoV以及更有可能是引起當前COVID-19流行的SARS-CoV-2的共同結(jié)合部位。因此，建議用AT1R阻斷劑治療SARS患者來提高他們ACE2的表達似乎是反常的。不過，來自SARS-CoV的一些研究觀察似乎不以為然，這些觀察很可能也與SARS-CoV-2相關聯(lián)。已證實冠狀病毒棘突蛋白與其細胞結(jié)合部位ACE2結(jié)合而導致ACE2下調(diào)，隨之，相關酶ACE即產(chǎn)生過量的血管緊張素，僅有少量的ACE2能將其轉(zhuǎn)化為具有血管擴張作用的七肽血管緊張素1-7，從而導致肺損傷，這是因為血管緊張素刺激AT1R引發(fā)肺血管滲透性增加，由此引發(fā)加重肺病理過程。因此，SARS-CoV-2感染患者經(jīng)長期AT1R阻斷劑治療后的較高ACE2表達，雖然看似矛盾，將能保護患者免遭肺損傷，而非置他們于發(fā)生SARS的較高風險中。這可由兩種互補機制加以解釋：阻斷病毒引起的血管緊張素介導AT1R過度激活，以及上調(diào)ACE2，從而減少ACE產(chǎn)生的血管緊張素和增加擴血管的血管緊張素1-7。有關ACE2調(diào)節(jié)障礙對SARS-CoV病理過程的影響de Wit等學者于2016年作了詳細的綜述。順便提一下，2002-2003年SARS-CoV流行后，曾建議ACE2抑制劑作為SARS的治療藥，然而，這一建議并未帶來新藥。

此外，有關人類免疫缺陷病毒（HIV），已證實HIV結(jié)合部位CCR5和CD4的高水平表達是具有保護作用，而不是增強HIV的毒性。Michel等報告，HIV憑借其早期基因Nef產(chǎn)物，通過下調(diào)CCR5而避免病毒進入步驟中的重復感染。Nef介導的下調(diào)作用加速CCR5和CD4兩者的內(nèi)噬過程，隨之，加大HIV病毒的高效復制和傳播，從而促進AIDS的疾病過程。仍需研究的是如果冠狀病毒中已經(jīng)形成為避免重復感染的類似機制，在此情況下，認為如同SARS治療一樣，應用AR1R阻斷劑似乎并不矛盾，盡管AR1R阻斷劑上調(diào)ACE2病毒結(jié)合部位的表達。

1990年代以來，為控制高血壓和腎病，氯沙坦、替米沙坦、奧美沙坦（和其他AT1R拮抗劑）廣泛用于臨床，已知為一類安全而少有副作用的藥物。不過，值得注意的是約一半SARS-CoV患者在其住院期間出現(xiàn)低血壓。在寫此述評時，尚無有關SARS-CoV-2住院患者低血壓發(fā)生率的詳盡資料，對目前正在流行的SARS患者安全接受AR1R阻斷劑治療而不加重低血壓風險的百分比進行估算為時過早。

將AT1R拮抗劑如氯沙坦和替米沙坦用作SARS-CoV-2的治療藥物，用于治療尚未出現(xiàn)急性呼吸綜合征患者的嘗試建議仍未得到批準。在撰寫此簡短述評時，尚看不到COVID-19流行的結(jié)束，需要強有力的行動（已在實施中）來控制其蔓延和死亡人數(shù)。因此，分析可行性最為快速的方法是分析臨床患者的記錄、利用數(shù)據(jù)挖掘技術來確定是否在診斷前已接受AT1R拮抗劑治療（因高血壓、糖尿病性腎病或其他指證）的患者預后較好。此外，對比總體人群中長期接受AT1R拮抗劑治療的人群占比與因SARS-CoV-2感染住院并出現(xiàn)嚴重癥狀患者中長期接受AT1R拮抗劑治療的占比。如能發(fā)現(xiàn)后者的占比呈顯著偏小，這將支持AT1R拮抗劑防范SARS-CoV-2感染患者嚴重癥狀作用的想法。通過這種臨床記錄數(shù)據(jù)攫取的知識對于降低SARS-CoV-2的病死率和發(fā)病率似乎是至關重要的。同時，應努力開發(fā)SARS-CoV-2疫苗。