Bioengineered soluble ACE2 for brain protection against SARS-CoV-2 infection

In a recent study posted to the bioRxiv* preprint server, researchers compared the efficiency of bioengineered soluble angiotensin converting enzyme-2 (ACE-2) concerning brain protection during coronavirus disease 2019 (COVID-19).

Background

Studies have noted the potential of ACE2 proteins in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) neutralization using human organoids. The cellular model proposed in the present study expressed human ACE2, an important receptor of SARS-CoV-2 entry in human cells, and transmembrane serine protease 2 (TMPRSS2), which is a protease important for SARS-CoV-2-ACE2 complex internalization.

The k18-hACE2 model has proven deadly when infected with wild-type (WT) SARS-CoV-2 and mimics severe lung disease observed in humans. While there is sufficient evidence of significant brain injury reported by the model, the reason for the universal lethality is yet unknown.

About the study

In the present study, researchers examined the impact of an ACE2 618-DDC-ABD, a bioengineered soluble ACE2 protein with a sufficient duration of action and strong SARS-CoV-2 binding affinity.

In the k18-human ACE2 (hACE2) mouse, the team compared the impact of intraperitoneal (IP) versus intranasal (IN) delivery of the soluble ACE2 protein called ACE2 618-DDC-ABD. As per the study protocol, animals that exhibited a weight loss of over 20% of their body weight or displayed a clinical score of three or more were euthanized.

Four of the nine healthy mice from the IN-pre group were euthanized on day 5 to harvest organs for comparison with the IP-pre group, while the other five mice belonging to the IN-pre group lived until day 14, which was the final day of the study. In contrast, the surviving mice in the IP-pre-group had to be euthanized by the seventh day due to deteriorating clinical ratings and weight loss.

The team utilized k18-hACE2 mice, which expressed human ACE2 in its entirety and are sensitive to SARS-CoV-2 infection. Five to nine days after infection, animals with this viral load always succumb to the disease. The researchers examined the effects of pre-and post-treatment with the ACE2 618-DDC-ABD protein and compared intranasal (IN) and intraperitoneal (IP) delivery effects using distinct methodologies. In the pre-treatment cohorts, ACE2 618-DDC-ABD was delivered IV or IP to k18-hACE2 mice one hour before SARS-CoV-2 infection and then subsequently 24 and 48 hours for three doses. Control animals were administered bovine serum albumin (BSA) in phosphate-buffered saline (PBS), both IP and IN, at dosages and intervals similar to the ACE2 618-DDC-ABD post-treated mice.

Results

All infected untreated control mice had to be euthanized on the fifth day, had serious body weight loss, and received a high clinical score. In the subject mice administered ACE2 618-DDC-ABD before and after viral inoculation, the day 5 survival rate was 90% across the IN-pre group and 40% across the IP-pre group. The survival rate was 0% among untreated infected controls on day 5. In addition, the IN-pre-group had minimal weight loss and superior clinical scores. In contrast, the IP-pre-group reported weight loss and poor clinical ratings.

In mice administered ACE2 618-DDC-ABD after viral inoculation, the survival rate was 30% on day 5 and 20% on day 14 in the IN+IP-post group. Furthermore, in the IN-post cohort, the survival rate on day 5 was 20% and on day 14 was 10%. The IP-post group had a 20% survival rate on day 5 but a 0% survival rate on day 14.

On day five, 0% of untreated and infected mice survived. Most mice that were administered ACE2 618-DDC-ABD post-viral inoculation experienced significant weight loss and deteriorating clinical score, while a few recovered and survived up to day 14.

In the IN-pre group, there were no detectable brain antibodies. On the other hand, brain titers were elevated in five out of eight mice in the IP-pre cohort, which was considerably greater than that in the IN-pre group. The brain virus titers of post-treated mice were slightly and not significantly lower than those of infected untreated animals. Brain titers, however, were undetectable on the fourteenth day within the few survivors of the post-treatment groups. The lung SARS-CoV-2 titers of animals treated with ACE2 618-DDC-ABC.

Conclusion

Overall, the study findings showed that ACE2 618-DDC-ABD provided significantly superior survival and organ protection when administered IN than IP or after viral inoculation and that reducing brain titers is a crucial predictor of survival and organ protection.

*Important notice

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.