Note: This page was an email, sent on 2020-3-5, which is shared publicly here for cross-reference and archival purposes. Some of the information contained below may be now known to be inaccurate, but no effort has been made to update the content below.
Professor Gurwitz, Dr. Argyropoulos, Dr. Brzósko, Dr. Kruse, Dr. Moskowitz-
I wanted to invite a group email discussion among you experts on this pressing matter. I apologize if group email is an academic faux pas. I am not an academic, physician, or other expert on disease or biology; I'm simply a concerned layman who's been researching SARS-CoV-2 and the usage of ARBs/other therapeutics. Please take everything I write below with a grain of salt - I am only hoping to spark a conversation.
Dr. Kruse, this email relates to the "increased viral entry w/ higher ACE2" ARB question I asked in my previous email.
Professor Gurwitz, I read your commentary with great interest. I have collected some information on this topic on my twitter account.
As you note in your commentary, some papers indicate that AT1R blockade may increase ACE2 expression. As you indicate, I see resolving "upregulated ACE2" as "good" or "bad" as the central question as to whether there is risk to ARB trial in COVID-19 patients beyond hypotension.
Notably, in this paper ARB usage increased ACE2 expression in lung tissue (Figure 1F). Unrelated to lungs, I found papers saying ARBs increase ACE2 expression in retina, renal cortical tissue[1], but also found the opposite in cardiofibroblasts. But let’s just assume ARBs upregulate ACE2 expression in the lungs, would this ever be a bad thing?
The reason I was thinking it could be bad is because it seems intuitively that with more ACE2 expression, the virus would have more opportunity to enter cells via the ACE2 receptor. But besides this intuitive guess -- and the fact ACE2-KO mice don't get disease -- I don't find evidence that a higher ACE2 expression is correlated with disease severity. But of course absence of evidence is not evidence of absence.
There was a preprint making the rounds on Twitter RE: smoking and ACE2 gene expression[2], which may have set the "higher ACE2 = more severe disease" thinking in motion.
So the line of thinking is that a higher ACE2 expression could be bad because it could lead to more viral entry, if having more receptors means the virus has a higher probability of cell entry. And if more viral entry itself is bad. I have seen this line of thinking all over, so it seems important to discuss.
My thinking on why it may not be bad to have higher ACE2 (from AT1R blockade) with COVID19:
- This paper shows the proportion of ACE2 decrease as being correlated with disease severity. And also most interesting is that Figure 1 indicates “outcomes did not correlate with differences in viral replication efficiencies.” So while the two groups had the same viral replication efficiency (meaning, I'm guessing, that both had enough ACE2 for cell entry and viral replication..?)
If a higher ACE2 expression levels correlated with disease severity (due to “more viral entry points” thinking), I would expect the viral replication efficiency to differ between the two groups. But I am not an expert. - Case study of COVID-19 on Feb 28th in a six month old shows high viral load, no severe disease: which makes me think the child had plenty of cells expressing ACE2 for the virus to enter and replicate via, right? The only other explanation I can think of (as a non-expert) is perhaps there is a tissue based expression difference of ACE2 the child, but the fact the infant has similar viral load as the mother makes me think this is probably unlikely?
- ACE2-KO mice experience severe lung injury with other viral diseases, and a higher ACE2/ACE ratio is protective in inhibiting pulmonary apoptosis:
- ACE2 deficiency worsens pathogenesis of influenza A (AT1R blockade attenuated lung injury).
- Angiotensin II receptor (AT1R) inhibition prevents pneumocystis apoptosis after lung injury, and higher ACE2/ACE ratio “important for inhibiting pulmonary apoptosis” (& ACE inhibitor had protective effect)
- ACE2 protects from lethal influenza A H5N1 Infections. Virus doesn’t use ACE2 receptor. Recombinant ACE2 ameliorates lung injury. But effects may be via angiotensin II, as “high levels appear to be linked to the severity & lethality of infection.
- Recombinant ACE2 attenuates RSV lung injury, and AT1R blockade also attenuated.
These papers consistently show a role for ACE2 in protecting against (probably? AT1R) induced lung injury.
Intuitively to me as a layman it seems like other viruses may have plenty of receptors to enter cells with. So would the number of available receptors be the determining factor for a virus' severity in the host?
- Professor Gurwitz, as you mentioned in your commentary, for HIV, an increase in the expression of the binding sites protects from virulence.
- This paper shows that for influenza A and HRV, a higher viral load isn't associated with disease severity, but it is associated with severity in influenza B. But I guess we're really interested about viral replication rate, not 'viral load', per se.
- This study on SARS data says: "The consistent clinical progression, shifting radiological infiltrates and an inverted V viral load profile suggested that deterioration during the second week is not related to uncontrolled viral replication but may rather be related to immunopathological damage"
As noted in the Chinese paper:
"Although animal experiments have shown that the use of olmesartan or telmisartan in the treatment of hypertension or vascular injury, reversed the expression of ACE2, but did not exceed the normal level of ACE2 expression in vivo. This indicates that the recovery of ACE2 expression after administration may be related to the regression of cellular inflammation and functional recovery. The expression of ACE2 in children and young people is significantly higher than that of elderly people, while the expression of elderly women is higher than that of elderly male patients. Severe SARS-CoV infection patients are concentrated in young and middle-aged patients, while COVID-19 severe infections present more elderly patients" (via Google translate).
They don't cite a source for "did not exceed the normal level of ACE2 expression" (and I haven't seen the paper they're referencing). If you know the reference I would love to see it.
For children and infants, a source also was not cited. I wasn't able to find direct data on ACE2 expression in human infants/children, but I found this paper (mice) which says "The expressions of PRR, ACE, and Ang II, and AT1R-positive area significantly increased, whereas expressions of ACE2 and MasR and AT2R-positive area decreased with age." I found some data on human children and RAS: this paper says children have higher Ang II (but are normotensive), which suggests to me (not expert) that they may have a higher AT2R:AT1R ratio than adults (or perhaps just a ton of ACE2?)
The data on infants and children and COVID-19 is remarkable. Based on what we know, they are effectively immune to severe COVID-19 symptoms, with zero reported deaths thus far. But as the case study above shows, there is a high viral load, so they must have ACE2 receptors, right? This incredible age difference seems unusual for a disease. I looked at Ebola, which looks like: "< 5 years old: 77% fatal; 6-15: 38% fatal; 16-21 42% fatal;" I think Ebola is around 50% fatal in adults. So there is an age difference, but it's nowhere near as pronounced as COVID-19.
Couldn't this suggest there is something beyond the difference in the immune system of children and adults at play, e.g. differences in children's RAS configuration? Again, I am not an expert. I found this paper on human children's RAS which says children have dramatically higher Ang II than adults. This suggests to me that their RAS configuration could be much different than adults', perhaps with much more AT2R (and/or way more ACE2? as suggested in the mice papers, etc)
The paper on estrogen and a SARS model in mice shows a similar incredible discrepancy. Female mice are practically immune from the mouse model of SARS, which is mediated entirely by the estrogen receptor. Giving mice estrogen makes them effectively immune to death[3]. This paper also looked at RAG1 knockout mice, which shows similar sex differences: "Sex-dependent SARS outcomes are independent of adaptive immunity". This would suggest to me (not expert) that changes in the RAS could account for these group differences. We know that estrogen induces RAS changes with a higher AT2R:AT1R ratio in women than men. This one paper says estrogen increases ACE2 activity in mouse cardiac myocytes & fibroblasts and another paper says estrogen in increased ACE2 mRNA expression, increased Ang (1-7) in human endothelial cells. But I haven't personally dug in enough to the ACE2/estrogen question.
Gut feeling as a total (!!) non-expert: the human coronavirus strains that have been circulating the human population (for practically ever?) have presumably been mutating as they circulate, but these coronavirsus do not cause severe disease; they're common colds. They have had many chances to mutate into nasty forms, right? But these common coronaviruses have never turned into a spanish flu. These common human coronaviruses do not use the ACE2 receptor[4]. Based on my quick research, common cold human coronavirus OC43 uses the Neu5Ac receptor, which seems to be widely expressed, including in the lungs.
Perhaps it is the fact that SARS, SARS-CoV-2 use the ACE2 receptor, downregulating its expression, that causes the severity of disease. Given all of the evidence of the beneficial role of ACE2 in other viral lung disease, it seems to be the simplest explanation.
Unfortunately, I could not find any studies on animal models of SARS and AT1R blockade. Even one of this MA15 mouse studies + ARB might settle this question. We know from this paper that in a SARS mouse model, the SARS spike binding protein itself (without virus) downregulates ACE2, and that AT1R blockade stops the additional damage from ACE2 loss when the mice endure lung damage. But this study does not tell us what happens when viral replication is occurring. But if we look at the available evidence, I don't find anything to suggest that a higher ACE2 expression would correlate with disease severity, and I see lots of indications that ACE2 may attenuate viral lung damage.
Dr. David Moskowitz has an alternative theory of AT1R blockade for COVID-19 that centers on the role of Ang II and immune response. He believe that ACEi/ARBs may represent a broad-spectrum anti-viral drug, and see his thoughts on AT1R blockade and SARS.
Dr. Moskowitz told me he trialed Losartan in 30 West Nile patents (21/30 got better). 8 patents described here in Table 2. Perhaps this immune system theory is related to the Keiji Kuba SARS / AT1R pathophysiological model somehow?
There is also literature on the usage of ACEi/ARB to fight host response in the context of a pandemic:
- Treating the host response to emerging virus diseases: lessons learned from sepsis, pneumonia, influenza and Ebola
- Clinician-initiated research on treating the host response to pandemic influenza
- Treating influenza with statins and other immunomodulatory agents.
As a gut feeling as a layman is it seems possible COVID-19 could respond extremely well -- maybe much more so than influenza (some papers collected here) -- to AT1R blockade, due to the downregulation of ACE2 with infection?
I would love any and all of your thoughts on the question of whether increased ACE2 expression brought on by ARB usage would be likely to increase or decrease the severity of COVID-19. I know all on this email thread are interested in finding short-term therapeutic options for COVID-19.
—Philip Neustrom
2. I am not sure what to make of this preprint. In this study of smoke exposed rats, ACE2 decreased and Ang II increased. ARB usage attenuated ACE2 reduction & ameliorated pulmonary vascular remodeling. I couldn't find any other direct data on ACE2 and smoking besides this rat study.
3. Estrogen could also play a role in male survival, as the author notes that testosterone decreased markedly in male SARS-model infected mice; estrogen is produced via aromatization of testosterone in men, thus men infected may have less estrogen than non-infected. In my correspondence with the author, he stated "As for the role of estrogen in male mice: It is possible that estrogen can protect male, as male myeloid cells in mice ( and humans??) do express estrogen receptor (ESR1)." The castrated male rats didn't differ from the intact male mice. If the infection didn't markedly decrease testosterone, perhaps intact male mice would out survive castrated male mice due to the effects of estrogen in the male rats (my own speculation, shared with author). I saw this study on the protective effect of testosterone (via estrogen would be my guess) with influenza in mice.
4. Except for NL63. This human coronavirus is reported to cause common cold symptoms in almost all cases, but very occasionally leads to severe respiratory symptoms. NL63 has reduced affinity for ACE2, and may lose affinity at higher temperatures (fever?). So perhaps it is this weak affinity for ACE2, and even weaker affinity with fever, that makes NL63 tame. I think NL63 was widely circulating around the world before it was detected, so it must be dramatically more mild than SARS-CoV-2, and probably is almost always a common cold. Source: "2002..2003, evaluated.. specimens..9.3% were positive for HCoV-NL63", but was "first isolated in Amsterdam in 2004 from the nasopharyngeal aspirate of a seven-month old child."
