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.

词 汇

tentative n.&adj.假设，实验，尝试；不确定的，暂定的，踌躇的，犹豫不定的，不果断的，试探性的

commentary n. 评注，评论，议论

surpass v.超过，胜过，优于

exponential adj.指数的，幂的，越来越快的

pandemic n.&adj.（全国或全球性）流行病，大流行病；大流行的，普遍的，全球的

materialize v.实现，发生，成为现实

immunopathology n.免疫病理学

vaccine n.疫苗，菌苗

ternary n.&adj.三个一组；三元的，由三部分组成的

glycyl n.甘氨酰，氨基乙酰

prolyl n.脯氨酰，脯胺酰基

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，服务;雇用，应用，运用，使用

superinfection n.重复感染，重複感染，双重感染

endocytosis n.（细胞）内吞作用，内噬作用

confer v.商讨，协商，交换意见，授予

注 释

1.spike protein称棘突蛋白，又称S蛋白，位于冠状病毒的表面，因病毒表面众多的棘突看上去像皇冠，故名为冠状病毒。棘突蛋白有S1和S2两个亚单位，S1与宿主细胞表面的受体结合，S2与宿主细胞膜融合，使得病毒的基因组进入宿主细胞，这是病毒感染过程的第一步，也是关键的一步。

2.Mas receptor称Mas受体，是血管紧张素系统中Ang-(1-7)的受体，由血管紧张素转换酶2（ACE2）分解血管紧张素Ⅱ而产生，其介导的作用能对抗血管紧张素Ⅱ通过AT1受体介导的作用如血管收缩、炎症反应和纤维化过程。

参考译文

第94课 血管紧张素受体阻断剂或成新冠肺炎治疗药

在撰写这一述评（2020年2月）时，2019年12月下旬暴发、由SARS-CoV-2引起的新冠病毒肺炎（COVID-19）流行死亡人数已超过2002-2003年SARS（严重急性呼吸综合征）与2013年MERS（中东呼吸综合征）的死亡总人数。本次流行似乎呈指数速率蔓延，倍增时间为1.8d，令人恐惧的是这将扩散至全球范围。目前SARS-CoV-2还缺乏有效的治疗，虽然已公布一些等待批准的治疗措施，包括几种广谱的抗病毒药物如法匹拉韦和瑞德西韦，抗疟疾药物氯喹，以及传统的中药配方。显然，最主要的解决方案是开发SARS-CoV-2疫苗。然而，自18年前SARS-CoV暴发以来，尚未开发出获得批准的产品。另外，不乏担心疫苗介导的疾病加重，比如SARS-CoV导致的肺部免疫病理学变化。此外，即使疫苗获得批准用于人体，病毒的高度突变性意味着每次暴发均需开发新疫苗，类似于每年新流感疫苗这种状况。下面我阐述可供替代的方案，如果证实有效，将可迅速应用于临床。

近来推测，也许血管紧张素受体1（AT1R）阻断剂有益于感染COVID-19的肺炎患者。不过，这一文章只有中文文本，英文摘要提及SARS-CoV-2引起肾素-血管紧张素系统调节紊乱，但没有阐述其中的逻辑。2020年2月4日《英国医学杂志》“快速在线反应”栏目线上刊登类似的文章，提出用AT1R阻断剂治疗COVID-19患者。这些试探性建议是建立在观察到SARS-CoV-2利用血管紧张素转换酶2（ACE2）作为其棘突蛋白受体结合域的基础上，类似于2002～2003年SARS流行时的冠状病毒株。况且，这两种冠状病毒拥有72%的相同氨基酸序列。分子仿真已表明相似的三元结构。然而，SARS-CoV-2包含有截然不同的环形柔性甘氨酰残基，取代了SARS-CoV中的硬性脯氨酰残基。分子模型显示，与SARS-CoV相比较，SARS-CoV-2的受体结合域与ACE2的关系更密切。

值得注意的是血管紧张素转换酶（ACE）与其密切同系物ACE2虽然同属二肽基羧基二肽酶ACE家族，但生理作用相反。ACE剪切血管紧张素Ⅰ而产生血管紧张素Ⅱ，该肽结合并激活AT1R引起血管收缩，从而提升血压。相反，ACE2灭活血管紧张素Ⅱ而产生血管紧张素1-7，此七肽血管紧张素通过激活它的Mas受体而具备扩血管功能，因此成为血管紧张素系统的负向调节器。

冠状动脉结扎引起心肌梗死的小鼠，给予常用于高血压患者降压治疗的AT1R阻断剂氯沙坦和奥美沙坦治疗长达28d后显示，心脏的ACE2表达增加3倍。长期治疗的小鼠显示，氯沙坦也上调肾脏的ACE2表达。与这些观察相一致的是接受AT1R阻断剂奥美沙坦治疗的高血压患者尿中ACE2含量较高。综合这些结果表明，长期AT1R阻断引发小鼠和人的ACE2上调。

如上所述，ACE2是 2002-2003年 SARS流行时的SARS-CoV以及更有可能是引起当前COVID-19流行的SARS-CoV-2的共同结合部位。因此，建议用AT1R阻断剂治疗SARS患者来提高他们ACE2的表达似乎是反常的。不过，来自SARS-CoV的一些研究观察似乎不以为然，这些观察很可能也与SARS-CoV-2相关联。已证实冠状病毒棘突蛋白与其细胞结合部位ACE2结合而导致ACE2下调，随之，相关酶ACE即产生过量的血管紧张素，仅有少量的ACE2能将其转化为具有血管扩张作用的七肽血管紧张素1-7，从而导致肺损伤，这是因为血管紧张素刺激AT1R引发肺血管渗透性增加，由此引发加重肺病理过程。因此，SARS-CoV-2感染患者经长期AT1R阻断剂治疗后的较高ACE2表达，虽然看似矛盾，将能保护患者免遭肺损伤，而非置他们于发生SARS的较高风险中。这可由两种互补机制加以解释：阻断病毒引起的血管紧张素介导AT1R过度激活，以及上调ACE2，从而减少ACE产生的血管紧张素和增加扩血管的血管紧张素1-7。有关ACE2调节障碍对SARS-CoV病理过程的影响de Wit等学者于2016年作了详细的综述。顺便提一下，2002-2003年SARS-CoV流行后，曾建议ACE2抑制剂作为SARS的治疗药，然而，这一建议并未带来新药。

此外，有关人类免疫缺陷病毒（HIV），已证实HIV结合部位CCR5和CD4的高水平表达是具有保护作用，而不是增强HIV的毒性。Michel等报告，HIV凭借其早期基因Nef产物，通过下调CCR5而避免病毒进入步骤中的重复感染。Nef介导的下调作用加速CCR5和CD4两者的内噬过程，随之，加大HIV病毒的高效复制和传播，从而促进AIDS的疾病过程。仍需研究的是如果冠状病毒中已经形成为避免重复感染的类似机制，在此情况下，认为如同SARS治疗一样，应用AR1R阻断剂似乎并不矛盾，尽管AR1R阻断剂上调ACE2病毒结合部位的表达。

1990年代以来，为控制高血压和肾病，氯沙坦、替米沙坦、奥美沙坦（和其他AT1R拮抗剂）广泛用于临床，已知为一类安全而少有副作用的药物。不过，值得注意的是约一半SARS-CoV患者在其住院期间出现低血压。在写此述评时，尚无有关SARS-CoV-2住院患者低血压发生率的详尽资料，对目前正在流行的SARS患者安全接受AR1R阻断剂治疗而不加重低血压风险的百分比进行估算为时过早。

将AT1R拮抗剂如氯沙坦和替米沙坦用作SARS-CoV-2的治疗药物，用于治疗尚未出现急性呼吸综合征患者的尝试建议仍未得到批准。在撰写此简短述评时，尚看不到COVID-19流行的结束，需要强有力的行动（已在实施中）来控制其蔓延和死亡人数。因此，分析可行性最为快速的方法是分析临床患者的记录、利用数据挖掘技术来确定是否在诊断前已接受AT1R拮抗剂治疗（因高血压、糖尿病性肾病或其他指证）的患者预后较好。此外，对比总体人群中长期接受AT1R拮抗剂治疗的人群占比与因SARS-CoV-2感染住院并出现严重症状患者中长期接受AT1R拮抗剂治疗的占比。如能发现后者的占比呈显著偏小，这将支持AT1R拮抗剂防范SARS-CoV-2感染患者严重症状作用的想法。通过这种临床记录数据攫取的知识对于降低SARS-CoV-2的病死率和发病率似乎是至关重要的。同时，应努力开发SARS-CoV-2疫苗。