COVID-19 has impacted virtually everyone‘s lives, whether through personal experience of infection or the impacts of other people’s illnesses. But how is Severe Acute Respiratory Syndrome Coronaviruses 2 (SARS-CoV-2) able to enter our cells?
The answer lies in the external part of the angiotensin-converting enzyme 2 (ACE2) receptor protein, which is present in a wide range of cells throughout the body and acts as a gateway for the virus.
ACE2 can be found in epithelial cells such as those in the lung alveoli, small intestine, colon, kidney, liver, pancreas and vascular system, as well as in cell membranes in the nasopharynx, nasal and oral mucosa.
This protein also plays a key role in the hormone system known as the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure by controlling fluid and salt levels. A number of pathological processes, such as acute respiratory distress syndrome (ARDS), fibrosis, hypertension and cardiac dysfunction are also related to this system.
Bachem, an industry leading expert in the development and production of peptides and oligonucleotides analyses the findings from leading scientists about the relationship between ACE2 and SARS-CoV-2.
Patients who suffer with the conditions mentioned above are more likely to experience severe illness if infected with COVID-19. This has led to concern that they could be at risk if drugs which tend to raise levels of the ACE2 protein are linked to greater susceptibility to the virus.
These drugs − such as angiotensin-II blockers (ARBs) and angiotensin-converting enzyme inhibitors (ACEi) − are often prescribed to these patients, and experts want to investigate their connection to SARS-CoV-2 infection. Some are even considering the possibility that these drugs could have benefits for those suffering with COVID-19, as the viral entry process causes a down-regulation of ACE2.
ACE2 boosts levels of angiotensin 1-7 (Ang 1-7), an anti-inflammatory peptide, and reduces levels of the inflammatory vasoconstrictor peptide angiotensin II (Ang II). As a result, ACE2 is seen as a protective agent against inflammation.
More specifically, ACE2 is a membrane bound receptor which turns the octapeptide Ang II and the decapeptide angiotensin I into the anti-inflammatory Ang 1-7 and angiotensin 1-9 (Ang 1-9). The angiotensin-converting enzyme (ACE) then also converts Ang 1-9 to Ang 1-7, which then counters inflammation and triggers vasodilation when it binds to the mitochondrial assembly receptor (MasR) on the surface of the cell.
Elevated levels of Ang II in the plasma of COVID-19 patients were first picked up by Chinese researchers using commercial ELISA tests, and reported on in March 2020. The strong correlation between the ang II and lung injury and viral load in COVID-19 patients was also noted.1
The Chinese scientists proposed that SARS-CoV-2 was disrupting patients’ RAAS, and that drugs like ARBs and ACEi could help to right their RAAS balance. Studies on how the drugs impacted the severity of illness among COVID-19 patients produced mixed results; some showing negative or negligible effects, and some showing benefits.
Research into the impacts of ending the treatment of hypertension with RAAS inhibitors for COVID-19 patients has, however, supported the case for continuing to use the drugs. Consequently, the recommendations of major American and European medical societies have been to continue with these therapies for patients infected with COVID-19. Nevertheless, there is still a need for more investigation, including thorough investigation of the angiotensins.
The significance of the relationship between ACE2 and SARS-CoV-2 infection lies in its consequences for the decision making of physicians based on patients’ angiotensins. In the US, scientists used Ang 1-7 and Ang II standards from Bachem Torrance CA3 to produce results from commercial ELISA tests which they compared with those from a validated radioimmunoassay.2
The highly sensitive radioimmunoassay has been the standard means of measurement for 40 years. Working with peptides like Ang 1-7 and Ang II is challenging because they are quantified in terms of picograms per millilitre of plasma, or per gram of tissue. The research above was conducted by scientists at the Hypertension and Vascular Research Centre at the Wake Forest University School of Medicine and was published in 2021.
In their findings, they conclude: “As to the inability of these ELISAs to recognise the Bachem Ang (1–7) and Ang II standards, either the sensitivities of the ELISAs are far lower (worse) than stated by the manufacturer or these assays do not detect authentic Ang (1–7) and Ang II. This may also explain the failure of both ELISAs to detect Ang (1–7) and Ang II in the extracted plasma samples. Nonetheless, we cannot recommend that these assays provide an accurate assessment of Ang (1–7) or Ang II in direct or extracted plasma samples.”
From their report, the conclusion is that even for commercial clinical testing kits, plasma samples should be used rather than serum, and reference standards should be validated.
It’s possible that blocking the interaction between SARS-CoV and ACE2 with other peptide molecules or antibodies could be the basis of a therapy for COVID-19.3 At the University of Cambridge, researchers have been trying to screen potential inhibitors of COVID-19 infection using stem cells from a beating heart infected with the virus.
In their work, the scientists drew products from Bachem’s catalogue of angiotensin peptides, including ACE2 peptide antagonist DX600, from the application field cardiovascular system and diseases.
This research shows not only that DX600 can be used, with this screening approach, to “prevent SARS-CoV-2 from entering the heart cells,” but that its efficacy is seven times that of an antibody against ACE2.
The University of Cambridge scientists reported that “DX600 is a highly selective peptide that has not been tested previously as a viral entry inhibitor. It forms multiple interactions with the catalytic site of the ACE2 receptor that is distinct from the receptor-binding domain of the virus.”4
In summary, they determine that the COVID-19 virus can be prevented from interacting with receptors on cells and thereby entering them, by using the binding of DX600 to change the confirmation of ACE2. As a result, there is reason to be hopeful that this research could support the development of an effective treatment for COVID-19 patients.