MORPHOLOGICAL, MOLECULAR AND GENETICAL ASPECTS OF THE ORAL CAVITY IN COVID-19 DISEASE FOR DIAGNOSIS, SURVEILLANCE, AND TISSUE REGENERATION PURPOSES

The oral cavity often displays signs and/or symptoms of systemic conditions, some of which resolve without consequences, while others may leave sequelae. The present thesis connects the results from anatomical, biological and clinical investigations carried out during the COVID-19 pandemic, designed to describe various aspects of the involvement of the oral cavity in COVID-19’s pathology, diagnosis and course. The aims of the research project were to i) assess the presence of SARS-CoV-2 in the oral cavity through molecular tests to validate Molecular Salivary Testing (MST) as a reliable diagnostic tool for COVID-19 surveillance; ii) study the morphological and immunohistochemical alterations occurring in the lingual tissues of COVID-19 subjects; (iii) investigate the genetic susceptibility to the infection; (iv) contribute to define the pathogenesis of the disease and (v) explore new methodologies such as the use of nanomaterials for regenerative purposes. Salivary samples were analyzed by MST concerning the presence of SARS-CoV-2 and compared to the gold standard, the nasopharyngeal swab. The findings from our study contributed to validate MST for diagnosis and surveillance in communities such as schools, where MST was employed first in 2020, to surveil 401 children and later in 2021 and 2022, with Dried Blood Spot test, to assess the immunological profile of a sample composed by school personnel. Further, the presence of the virus in the oral cavity was described by comparing by RT-PCR samples of lingual tissues from corpses of individuals with or without a history COVID-19. In the same sample, the morphological and immunohistochemical features of the lingual tissues following COVID-19 were investigated and an inflammatory pattern of the lingual gustatory and non-gustatory papillae was observed. The genetic and phenotypical evaluation of the bitter receptor TAS2R38 was evaluated in patients with mild and severe COVID-19 and compared to healthy ones. No correlation between disease’s severity and TAS2R38 expression was observed regarding disease's susceptibility and gene expression. In a further development of the project, nanomaterials were studied to explore their regenerative potential as drug delivery systems and as targetable systems for oral tissues’ repair processes. Nanofibers loaded with Hyaluronic Acid and Vitamin E (NFE) were produced and their effect on Human Gingival Fibroblasts (HGF) was evaluated. NFE induced HGF proliferation, adhesion, collagen cross-linking and reduction of collagen degradation, thus favouring collagen deposition in gingival connective tissue. Furthermore, molecular imprinted nanoparticles were tested on target cells, showing a good affinity. Considering the consequences of some systemic conditions on the oral cavity, among which the long-term consequences of COVID-19, known as Long-COVID, can be considered, nanofibers might be helpful in tissue regeneration procedures of the oral tissues, that we are currently investigating.