Estimating the viral loads of SARS-CoV-2 in the oral cavity when complicated with periapical lesions

Abstract

Background The oral cavity represents a main entrance of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Angiotensin-converting enzyme 2 (ACE-2), neuropilin-1 (NRP-1), and transmembrane serine protease 2 (TMPRSS2) are essential for the entry of SARS-CoV-2 to the host cells. Both ACE-2 and NRP-1 receptors and TMPRSS2 have been identified in the oral cavity. However, there is limited knowledge about the impact of periapical lesions and their metabolites on the expression of these critical genes. This study aims to measure the impact of periapical lesions and their unique fatty acids (FAs) metabolites on the expression of the aforementioned genes, in addition to interleukin 6 (IL-6) gene and hence SARS-CoV-2 infection loads can be estimated. Methods Gene expression of ACE-2, NRP-1, TMPRSS2, and IL-6 was performed in periapical lesions in comparison to healthy oral cavity. Since FAs are important immunomodulators required for the lipid synthesis essential for receptors synthesis and viral replication, comparative FAs profiling was determined in oral lesions and healthy pulp tissues using gas chromatography–mass spectrometry (GC–MS). The effect of major identified and unique FAs was tested on mammalian cells known to express ACE-2, NRP-1, and TMPRSS2 genes. Results Gene expression analysis indicated that ACE-2, NRP-1, and TMPRSS2 were significantly upregulated in healthy clinical samples compared to oral lesions, while the reverse was true with IL-6 gene expression. Saturated and monounsaturated FAs were the major identified shared and unique FAs, respectively. Major shared FAs included palmitic, stearic and myristic acids with the highest percentage in the healthy oral cavity, while unique FAs included 17-octadecynoic acid in periapical abscess, petroselinic acid and l-lactic acid in periapical granuloma, and 1-nonadecene in the radicular cyst. Computational prediction showed that the binding affinity of identified FAs to ACE-2, TMPRSS2 and S protein were insignificant. Further, FA-treated mammalian cells showed significant overexpression of ACE-2, NRP-1 and TMPRSS2 genes except with l-lactic acid and oleic acid caused downregulation of NRP-1 gene, while 17-octadecynoic acid caused insignificant effect. Conclusion Collectively, a healthy oral cavity is more susceptible to viral infection when compared to that complicated with periapical lesions. FAs play important role in viral infection and their balance can affect the viral loads. Shifting the balance towards higher levels of palmitic, stearic and 1-nonadecene caused significant upregulation of the aforementioned genes and hence higher viral loads. On the other hand, there is a reverse correlation between inflammation and expression of SARS-CoV-2 receptors. Therefore, a mouth preparation that can reduce the levels of palmitic, stearic and 1-nonadecene, while maintaining an immunomodulatory effect can be employed as a future protection strategy against viral infection.

Oral Pathology in COVID-19 and SARS-CoV-2 Infection—Molecular Aspects

“…A global transcriptomic analysis reported that the SARS-CoV-2 entry factors, i.e., ACE2 and TMPRSS2, are expressed in healthy and inflamed human dental pulp without significant differences between healthy control and diseased biopsies [19]. These findings were confirmed by Altaie et al in an RNA expression study, which revealed the expression of ACE2, TMPRSS2 and NRP1 in healthy pulp tissues [20]. It can be suggested that healthy and inflamed pulp tissues have a similar tendency to be infected by SARS-CoV-2.…”

“…The response of periapical tissues to inflammatory factors, including IL-6, seems to be opposite to the periodontal tissues cited above. Altaie et al [20] indicated that the expression of ACE2 and TMPRSS2 (also NRP-1) was significantly reduced in oral periapical lesions (periapical abscesses, preapical granulomas, radicular cysts) compared with healthy pulp tissues. A reverse correlation between IL6 and ACE2, NRP1 and TMPRSS2 gene expression in periapical abscesses and granuloma was noted.…”

“…Dental practitioners can be, in additionally to the abovementioned factors of saliva being a risk for the general population, exposed during routine oral cavity-related procedures to other infectious material. The SARS-CoV-2 entry and transmission factors were found in pulp tissues and periapical lesions (periapical abscesses, preapical granulomas, radicular cysts) [19,20]. It can be hypothesized that the virus is able to populate pulp tissues when access to it is possible due to pathological processes (e.g., caries) or a blood-borne pulp infection.…”

Advances in the Prophylaxis of Respiratory Infections by the Nasal and the Oromucosal Route: Relevance to the Fight with the SARS-CoV-2 Pandemic

“…The oral cavity may become an entry point for respiratory pathogens through the oral–lung axis, oromucosal infection and/or absorption, or even the oral–gut axis [ 70 , 71 , 72 , 73 ]. The former mechanism relates to the act of oral inhalation (mouth breathing) or microaspiration, by which a respiratory pathogen bypasses the antigen-resilient nasopharyngeal zone and reaches the lower airways [ 74 , 75 ].…”

“…One eloquent example could be given again for the novel Coronavirus , which is currently reported to adhere to and infect salivary glands cells and oromucosal epithelial cells, especially in the tongue and gingival area (a mechanism related to the commonly observed loss-of-taste symptom of COVID-19 infection). This fact is explained by the high density of the SARS-CoV-2 entry factors in the oral tissues in question, i.e., the ACE2 receptor and the transmembrane serine proteases 2 (TMPRSS2) [ 70 , 71 , 86 , 87 , 88 ]. Furthermore, although a respiratory virus by definition, the SARS-CoV-2 is described to infect the intestinal enterocytes (also expressing the coronaviral cell entry factors) through the oral–gut axis and systemically spread through the gut–lung axis [ 89 , 90 , 91 , 92 ].…”