Delta And Omicron Variants Of SARS-Cov-2 Do Not Stimulate ACE2 Conversion Of Ang II To Ang-(1-7)

ABSTRACT

The Spike domain of SARS-COV-2 binds ACE2 and induces peptidase internalization removing a key regulatory site within the renin-angiotensin system that may exacerbate the effects of SARS-COV-2. However, a recent study finds that an early Beta variant (D614G) of the SARS-COV-2 Spike protein and its receptor-binding domain (RBD) markedly stimulated ACE2 activity using fluorescent substrates. The more dominant forms of SARS-COV-2 include the Delta and Omicron variants and we determined whether these new variants activate ACE2. Delta (B.1.617.1) and Omicron (B.1.1.529) RBDs, and Beta Spike (B1.351) were incubated with human soluble ACE2 for 10 mins at 37degreeC followed by Ang II [2 muM] and 125I-Ang II [0.5 nM] for up to 20 mins, and the Ang-(1-7)/Ang II ratio quantified by HPLC-gamma detection. Ang-(1-7)/Ang II increased linearly over time and doubled with 10 ng of ACE2 (*P<0.01 vs 5 ng;N=4);however, the Delta or Omicron RBD proteins (1 muM) failed to stimulate ACE2 activity at any time point (A). Varying concentrations of the Delta or Omicron RBDs, as well as Spike protein also failed to stimulate ACE2 activity (5 ng), although 200 nM Omicron RBD was inhibitory (B). The newer Spike variants may not activate ACE2;however, the Spike D614G variant also failed to activate ACE2, which questions whether SARS-COV-2 enhances ACE2 activity to metabolize Ang II. We conclude that Delta and Omicron variants do not stimulate the metabolism of Ang II to Ang-(1-7). Moreover, alterations in circulating ACE2 activity in COVID-19 patients likely reflect changes in protein content through shedding of the peptidase, although the interaction of ACE2 autoantibodies to influence peptidase activity is also possible. (Figure Presented).