Gut ACE2 Expression, Tryptophan Deficiency, and Inflammatory Responses The Potential Connection That Should Not Be Ignored During SARS-CoV-2 Infection.

Abstract

An “atypical” physiological function of angiotensin-converting enzyme 2 (ACE2) during COVID-19 is rarely mentioned. In the intestine, where ACE2 is highly expressed,1 it acts as a regulator of the homeostasis of dietary amino acids, particularly tryptophan (Trp). Trp catabolism through the kynurenine (Kyn) pathway plays an important role in regulating the balance between effector and regulatory immune responses; Trp catabolism is increased in inflammatory settings to attenuate excessive systemic immune activation and thus exerts protective effects against many diseases.