Activation of Angiotensin Converting Enzyme 2 (ACE2) Mitigates Gastrointestinal Acute Radiation Syndrome (GI-ARS)

Purpose: In a radiation mass casualty event, exposed populations will suffer dose-dependent toxicity to multiple-organ systems. Although several therapies are FDA-approved for treatment of the hematopoietic acute radiation syndrome (H-ARS), there are no FDA-approved medical countermeasures (MCM) for either acute gastrointestinal injury (GI) or multi-organ delayed effects of acute radiation exposure (DEARE). Prior data suggest activation of the alternative Renin angiotensin system (Ras) enzyme angiotensin-converting enzyme 2 (ACE2) has therapeutic potential for mitigating multi-organ radiation injury, including GI-ARS. Here, we evaluated whether activation of ACE2 mitigates GI-ARS in rodent models and protects against DEARE in GI-ARS survivors.

Methods and materials: GI recovery was assessed following treatment with ACE2 activator diminazene aceturate (DIZE) or an engineered form of the ACE2 protein with enhanced catalytic activity (ACE2 T371L/Y510Ile) in rodent partial body irradiation (PBI) models. Single cell RNA Sequencing was performed following irradiation and DIZE treatment to assess the cellular target of ACE2 activation. Mitigation of DEARE was assessed in a cohort of ARS survivors following DIZE-treatment.

Results: Radiation induced a marked loss of GI ACE2 expression, most notably within mature enterocyte populations. ACE2 activation accelerated recovery of intestinal progenitor cells with high proliferative capacity and mucosal defense function. Following 13.5 Gy PBI, DIZE improved survival in male rats during both ARS (days 0-30; p=0.0008) and DEARE (days 30-200; p<0.0001) compared to vehicle control. In female rats exposed to 13.5 Gy PBI, DIZE-treatment improved all-cause morbidity through ARS and DEARE following 13.5 Gy PBI (p=0.0025). Treatment with catalytically enhanced ACE2 variant T371L/Y510Ile accelerated recovery of ACE2 expression and improved survival during GI-ARS in male C57BL/6 mice exposed to 12.5 Gy PBI (p=0.038).

Conclusions: Activation of ACE2 promotes GI recovery during GI-ARS and mitigates lethal DEARE. Together, these data demonstrate alternative Ras enzyme ACE2 expression within the GI tract regulates radiation response and the alternative Ras axis is targetable for development of MCM.

acute radiation syndrome (ARS); delayed effects of acute radiation exposure, renin angiotensin system, radiation medical countermeasures, ACE2; radiation-induced gastrointestinal injury.