No evidence that RAS blockers facilitate SARS-CoV-2 entry into cells
Renin-Angiotensin System Blockers and the COVID-19 Pandemic
The commentary article by Danser et al. in Hypertension provides an in-dept description of the properties and function of ACE2, the receptor responsible for SARS-CoV-2 entry into cells. Furthermore, the authors describe the currently available scientific evidence on the effects of RAS blockers on ACE2 and motivate why RAS blockers should not be discontinued because of concerns related to coronavirus infection.
ACE inhibitors do not inhibit ACE2
Angiotensin-converting enzyme 2 (ACE2) is the receptor responsible for entry of SARS-CoV-2, the virus causing COVID-19, into cells [1,2]. A surface unit of a viral spike protein is required for binding to ACE2 and priming by the serine protease TMPRSS2 is needed for subsequent cell entry [3,4 ].
ACE2 converts angiotensin II (Ang II) to Ang-(1-7) and Ang I to Ang-(1-9) [5,6]. ACE2 and ACE are two different enzymes with 2 different active sites. ACE inhibitors prevent the conversion of Ang I to Ang II by ACE, but ACE inhibitors do not inhibit ACE2.
ACE2 is a membrane-bound enzyme [7,8]. The membrane-anchor can be cleaved by a disintegrin and metalloprotease 17 (ADAM17). The shorter (soluble) form of ACE2 can subsequently be found in body fluids, albeit at very low levels [7,8]. SARS-CoV-2 entry depends on membrane-bound ACE2. Shedding of ACE2 is often increased in pathological states, resulting in elevated levels of ACE2 in body fluids [9,10]. A doubling of soluble ACE2 has for instance been reported in patients with hypertension . However, the fast majority of ACE2 is membrane-bound and it is therefore unlikely that a doubling of soluble ACE2 can significantly alter the amount of membrane-bound ACE2. In theory, RAS blockage could (partly) reverse this increase in shedding. However, it is unlikely that this will seriously affect SARS-CoV-2 entry.
Effects of RAS blockers on ACE2
Since ACE inhibitors do not inhibit ACE2, any effect of ACE inhibitors on ACE2 activity must be of indirect nature. There are limited reports from animal studies that ACE inhibitors affect the expression of ACE2 in the heart and kidney . Some animal studies showed that AT1 receptor blockers (ARBs) alter ACE2 expression at the mRNA and protein level. However, high doses were required, and results differed per ARB and per organ [12-14].
Measuring membrane-bound ACE2 in vivo is technically challenging. Most publications in humans have therefore reported levels of ACE2 activity in blood, reflecting soluble ACE2 circulating at very low levels . Even if upregulation of tissue ACE2 by ARBs at high doses as reported in animal studies could be extrapolated to humans, this would not provide evidence that increased ACE2 expression is sufficient to facilitate SARS-CoV-2 entry into cells.
The authors also address a potentially beneficial pulmonary effect of ARBs. Alveolar ACE2 appears to be downregulated during acute lung injury [16,17]. This would result in lower Ang II metabolism and consequently higher local Ang II levels, which increases alveolar permeability and fosters lung injury. The authors speculate that, in this context, increased ACE2 expression by ARBs could potentially have protective effects during a SARS-CoV-2 infection.
RAS blockers should not be discontinued due to coronavirus concerns
A notion has been popularized via social media and in the general public that treatment with RAS blockers might increase the risk of SARS-CoV-2 infection and severity of infection. However, as explained in this article there is no evidence that ACE inhibitors or ARBs facilitate SARS-CoV-2 entry by increasing ACE2 expression in either animals or humans. The authors therefore strongly recommend that patients who are taking ACE inhibitors or ARBs should not withdraw their current treatment unless specifically advised to do so by their physician or healthcare provider. The therapeutic benefit outweighs any potential risk related to a coronavirus infection, according to the authors. The advice on continued use of RAS blockers is in line with position statements released by the ESC and HFSA/ACC/AHA.
A prospective cohort study with incidence rates of SARS-CoV-2 infection in patients with and without hypertension, with similar exposure history, is required to investigate whether hypertensive patients are more likely to get serious and fatal SARS-CoV-2 infections.
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