The work, led by Henry Daniell at Penn’s School of Dental Medicine and performed in collaboration with scientists at the Perelman School of Medicine and School of Veterinary Medicine, as well as at The Wistar Institute and Fraunhofer USA, could lead to a low-cost tool in the arsenal against the COVID-19 pandemic. Their study was published in the journal Molecular Therapy.
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A high SARS-CoV-2 viral load is often detected in saliva.9 Highly contagious airborne droplets are the major cause of transmission in respiratory viruses such as influenza, measles, and SARS-CoV-2.10, 11, 12, 13 Human papillomavirus, herpes simplex virus type 1, Epstein-Barr virus, and Kaposi’s sarcoma-associated herpesvirus are orally transmitted, and their life cycle in the oral epithelium is well known.14,15
In SARS-CoV-2 with saliva average load of 7 × 106 copies of RNA virus per milliliter, an oral fluid droplet of 50 μm2 could contain at least one virion.2,14 High SARS-CoV-2 viral loads are detected in saliva of both asymptomatic and symptomatic COVID-19 patients.16,17
In fact, salivary viral burden correlates with the severity of COVID-19 symptoms including the loss of taste and smell, and the virus replicates in salivary glands and oral mucous membranes.18 Thus, the oral mucous membranes and saliva appear] to be a high-risk route for SARS-CoV-2 transmission, and viral inactivation within the oral cavity could be an important strategy to reduce viral infectivity at source.
COVID-19 patients have low angiotensin-converting enzyme 2 (ACE2) activity due to renin-angiotensin-aldosterone dysregulation, which causes respiratory stress,19, 20, 21 and injected ACE2 restores health in COVID-19 patients.22 ACE receptor traps have large binding interfaces capable of blocking the entire receptor interface, thereby facilitating inhibition of different SARS-CoV-1 and SARS-CoV-2 variants.23,24
While nasal sprays could help in reducing viral load in the nose, additional approaches are needed to decrease viral load in saliva because salivary glands are the primary sites of SARS-CoV-2 replication.9,17,18 That salivary glands serve as a reservoir of replication for viruses causing highly prevalent diseases such as Epstein-Barr virus, herpes simplex, HHV-7, cytomegalovirus, hepatitis C, and Zika virus is a known fact.26, 27, 28, 29
Newly evolving strains have higher viral load in saliva and greater transmission.4, 5, 6, 7 The viral load of people infected by the delta variant is 1,260 times higher than in individuals infected with previous strains.4 The Centers for Disease Control and
Prevention have reported a higher basic reproduction rate (R0) of 5–8 for the delta variant, which estimates to 60,466,176 infections as opposed to R0 of 2.79 of the ancestral strain,30 which translates to an estimated 9,536 infections.31
The delta variant is 40%–60% more contagious than the previously dominant alpha strain.31,32 High viral density and transmissibility of these variants, along with the increase in replication potential and serial viral shedding,33 warrants development of novel approaches to curb viral loads in saliva.
Mouthwashes with antimicrobial agents have a short period of contact.32 Therefore, in this study we explore longer duration of contact using the chewing gum topical delivery approach. SARS-CoV-2 utilizes ACE2 and GM1 co-receptors to enter human cells.34, 35, 36, 37, 38
Therefore, in this study we explore receptor binding/blocking proteins cholera toxin B (CTB)-ACE2 chewing gum to minimize transmission and decrease infectivity by binding directly to the spike protein to trap virus particles and saturate both ACE2/GM1 receptors located in close proximity on the surface of human oral epithelial cells.
Furthermore, we explore the impact of SARS-CoV-2 on ACE2 activity in saliva and its potential role as biomarker to distinguish symptomatic from asymptomatic COVID-19 patients. In addition to prophylactic protection against COVID in general social settings or restaurants, the ACE2 gum could be used as a rapid means of reducing SARS-CoV-2 from the oral cavity of infected patients requiring dental procedures. This general concept could be extended to minimize infection or transmission of most oral viruses.
Preparation of chewing gums
Chewing gum tablets containing ground plant powder were prepared by Per Os Biosciences (Hunt Valley, MD) by a compression process but not the traditional gum manufacturing process, which requires higher temperature and extrusion/rolling that introduces variability in the concentration of proteins.
Placebo gum tablets contained the gum base (28.2%), maltitol (20.4%), sorbitol (13%), xylitol (13%), isomalt (13%), natural and artificial flavors, magnesium stearate (3%), silicon dioxide (0.43%), and stevia (0.65%) in order to offer the best flavor, taste, softness, and compression. The gum tablet (2 g weight) chews and performs exactly like conventional chewing gum based on physical characteristics.
Freeze-dried plant cells were ground with five pulses to disrupt plant cells and readily release CTB-ACE2. The ACE2 gum tablet has all the components of the placebo gum but in addition includes 50 mg of CTB-ACE2 freeze-dried 5× ground plant cells. Evaluation of sum total of proteins in all fractions (supernatant and pellet) revealed an insignificant loss of CTB-ACE2 during the gum manufacturing process (Figure S2).