Researchers looking for prevention and treatment strategies for COVID-19 that are not impacted by SARS-CoV-2 mutations published findings in Pathogens that showed that a combination of diphenhydramine (the active ingredient antihistamine in Benadryl) with lactoferrin (an immunologically active protein found in human and cow milk) reduced SARS-COV-2 replication by 99% in human cells.

Background

The key to the researchers’ findings related to proteins called the sigma receptors. These receptor proteins are located in the endoplasmic reticulum (ER), an organelle responsible for protein folding and transportation. Sigma receptors have multiple functions, including regulation of the ER stress response.

The ER stress response occurs when the ER is overwhelmed with unfolded or misfolded proteins. This triggers the unfolded protein response (UPR), which seeks to return the cell to a normal state by increasing protein folding, autophagy (destruction of damaged proteins), and in the case of prolonged UPR, apoptosis (cell suicide).

ER stress usually occurs when the ER is overwhelmed with unfolded or misfolded proteins. Cells mitigate ER stress by provoking the unfolded protein response (UPR), which includes increased protein folding, autophagy (destruction of damaged proteins) and, in prolonged cases, apoptosis (cell suicide).

When the UPR causes autophagy, it does so by forming sites near the ER called autophagosomes. Coronaviruses (CoV) have been found to bind directly to the sigma-2 receptor to cause ER stress, enabling them to hijack autophagosomes for use as virus replication sites.

Implication

Researchers found that by binding a drug molecule to the sigma-2 receptor, SARS-CoV-2 would no longer be able to bind to it to cause ER stress (and ultimately virus replication). This is made even more effective by also binding to and activating the function of the sigma-1 receptor.

Results

By using molecular docking software, the team identified a ligand called AZ66 as being able to bind to both sigma-1 and sigma-2 receptors. In experiments with human lung cells infected with SARS-CoV-2, AZ66 completely blocked virus production. However, the safety of AZ66 is unknown, as the drug candidate has not been tested in clinical trials.

Molecular docking model of human sigma-2 receptor (orange) bound to AZ66 (yellow).

Searching for common compounds with proven records of safety, the researchers identified diphenhydramine (DPH), the active ingredient antihistamine in Benadryl, as having effects on the sigma-1 receptor. DPH was found to reduce replication of SARS-CoV-2 in the infected human lung cells by about 30%.

Lactoferrin, a broadly antimicrobial protein found in human and cow milk, was brought to a researcher’s attention by the Global Virus Network’s COVID-19 task force as having antiviral effects on SARS-CoV-2. When tested, it was also found to reduce replication by about 30%. The milk protein has a proven safety record as a supplement widely used to treat stomach ulcers.

When a diphenhydramine/lactoferrin combination was tested in human and monkey epithelial lung cells, they found that a synergistic effect occurred, reducing virus replication by 99%.

Commentary

The study’s first author, David A. Ostrov, Ph.D. of the University of Florida, hailed the diphenhydramine and lactoferrin combination as “effective, economical,” and unlike AZ66, “[having] a long history of safety.” The combination could be used to prevent infection as well as decrease recovery time from COVID-19.

While the researchers await potential interest from pharmaceutical companies, Ostrov told the University of Florida Health Newsroom that he cautions against self-medicating with diphenhydramine or lactoferrin as a COVID-19 prevention or treatment, as the commercially available lactoferrin used for treatment of stomach ulcers is not exactly the same as the lactoferrin used in the study.

This article is based on the following sources – Bennett, D. (2021, November 22). Two common compounds show effectiveness against COVID-19 virus in early testing. University of Florida Health Newsroom. https://ufhealth.org/news/2021/two-common-compounds-show-effectiveness-against-covid-19-virus-early-testing

– Ostrov, D. A., Bluhm, A. P., Li, D., Norris, M. H., et al. (2021, November 20). Highly specific sigma receptor ligands exhibit anti-viral properties in SARS-Cov-2 infected cells. Pathogens. https://doi.org/10.3390/pathogens10111514

– Vela, J. M. (2020). Repurposing sigma-1 receptor ligands for COVID-19 therapy? Frontiers in Pharmacology. https://doi.org/10.3389/fphar.2020.582310