Angiotensin-Converting Enzyme 2, Feedback Systems, and COVID-19

Abstract

Feedback is a central feature of life processes. … The process of feedback governs how we grow, respond to stress and challenge, and regulate factors such as body temperature, blood pressure, and cholesterol level. This apparent purposefulness … operates at every level-from the interaction of proteins in cells to the interactions of organisms in complex ecologies.From Exploring the Way Life Works: The Science of Biology 1Simple causal reasoning about a feedback system is difficult because the first system influences the second and the second system influences the first, leading to a circular argument. This makes reasoning based on cause and effect tricky, and it is necessary to analyze the system as a whole.

COVID-19: Zinc and Angiotensin-Converting Enzyme 2 (ACE2) Deficiencies as Determinants of Risk and Severity of Disease: A Narrative Review

“…In normal functioning, the ACE positive feedback loop leads to amplification of Ang II and increased BP, inflammation, and 1 (see also [15,Table 1]) and [7].…”

“…ACE and ACE2 are key components of the RAS providing homeostasis of blood pressure (BP) (Table 1 ). For details, see [ 15 , Table 1] and [ 16 ].…”

“…In normal functioning, the ACE positive feedback loop leads to amplification of Ang II and increased BP, inflammation, and thrombosis. The ACE2 negative feedback loop modulates the ACE loop, dampening the vasoactive, inflammatory, and thrombogenic actions of the ACE axis, regulating the RAS [ 22 – 24 ] providing homeostasis and smooth fine control, Table 1 (see also [ 15 , Table 1]) and [ 7 ].…”

“…Loss of control in feedback systems occurs when perturbations or delays exceed the limits of the system [ 15 ].…”