INFECTIOUS HYPOTHESIS OF NEURODEGENERATIVE DISEASES. WHAT WAITS US AFTER THE COVID-19 PANDEMIC?

Since the description of the first clinical cases of the most common neurodegenerative diseases, numerous hypotheses have been proposed for their development. At the same time, the failure of therapeutic strategies in various directions of clinical research indicates the fallacy of most theories. In this regard, in recent years, various infectious agents are increasingly considered as a trigger of neuronal inflammation and a factor inducing the onset of the neurodegenerative process. Infectious agents differ in their mechanisms of invasion into the central nervous system and can even enter the brain perineurally. Reactivation of latent viral infection induces the production of viral proteins and the accumulation of abnormal proteins that are markers of Alzheimer's disease and Parkinson's disease. Both bacterial (chlamydia, causative agents of chronic periodontitis, E. coli) and viral (herpes viruses, noroviruses) infectious agents are considered. However, for the development of neurodegeneration, it is not enough just a simple invasion and reactivation of the infectious process: the genetic characteristics of the main histocompatibility complex also play a huge role. Currently, several studies have been initiated on the possible efficacy of antibacterial and antiviral drugs in Alzheimer's disease. Data obtained over the past year suggests that the brain may act as a target for SARS-CoV-2. Neurological manifestations of COVID-19 can occur as a result of both the direct cytopathic action of the pathogen and the activation of neuroinflammation, accompanied by a violation of the integrity of the blood-brain barrier. Further study of the molecular and cellular mechanisms of neuroinflammation and neurodegeneration in COVID-19 will form the basis for the development of treatments for neurological complications.

Physicochemical indicators of dental patient saliva who have undergone an uncomplicated coronavirus infection

Today, it has been proven that saliva is the main medium through which the new COVID-19 coronavirus infection spreads. Since the oral cavity is the gateway for the SARS-CoV-2 virus, the degree of change in the physicochemical parameters of the saliva of people who have had coronavirus infection compared to people who have not had COVID-19 is of interest. This study involved dental patients of the first and second health groups with a history of chronic generalized periodontitis of moderate degree in the stage of remission. We studied physicochemical parameters of saliva such as pH, surface tension and base buffering capacity. The results of this stage of the study showed saliva acidification, that is a decrease in pH in people who had had a new coronavirus infection compared to the indicators of people from the control group. The average values of the surface tension of saliva in patients of the control group are 30% less than in those who have had COVID-19. This indicates that the saliva of people who have not been sick with the new coronavirus contains more surface-active agents (surfactants). Surfactants provide rinsing and disinfecting functions of saliva, therefore, it can be concluded that these functions are less pronounced in patients who have recovered from COVID-19. The base buffering capacity of the saliva of patients who have had COVID-19 is, on average, 35% higher than that of people from the control group. Thus, the pH and the base buffering capacity are in correlation: the lower the pH value, the higher the acidity of the saliva and the higher the base buffering capacity is. At the second stage of the study, similar physicochemical parameters of patients’ saliva were measured after the application of an oral spray containing a synthetic peptide (ZP2) of the active center of granulo-cyte-macrophage colony-stimulating factor. This spray was used as an antibacterial therapy for the oral cavity after professional hygiene of patients. In 5 minutes after spray irrigation, an increase in saliva pH was observed in all test subjects within the physiological norm. In patients, regardless of their anamnesis, the surface tension of saliva changed in different ways. In a number of people, it increased, which indicates an increase in the concentration of surfactants in saliva, while in others it decreased, which can be explained by the high rate of penetration of surfactants from saliva through the gums into the blood. After the application of the ZP-2 peptide, the base buffering capacity of saliva decreases or remains unchanged. In patients of the control group, the indicators of the base buffering capacity of saliva change less than in patients who have undergone COVID-19. All the studied physicochemical parameters of saliva in patients who had had uncomplicated COVID-19, three months after receiving two negative results for the SARS-CoV-2 virus, remained within the physiological norm.

Relationship between the oral cavity and respiratory diseases: Aspiration of oral bacteria possibly contributes to the progression of lower airway inflammation.

The global population is aging, and elderly people have a higher incidence of lower airway diseases owing to decline in swallowing function, airway ciliary motility, and overall immunity associated with aging. Furthermore, lower airway diseases in the elderly tend to have a high mortality rate. Their prevention is important for extending healthy life expectancy and improving the quality of life of each individual. In recent years, the relationship between "chronic periodontitis and oral bacteria, especially the periodontopathic ones" and "respiratory diseases" (e.g., pneumonia, chronic obstructive pulmonary disease, and influenza) has become clear. In addition, the association of several periodontal pathogens with the onset and aggravation of coronavirus disease 2019 (COVID-19) is also being reported. In support of these findings, oral health management has shown to reduce deaths from pneumonia and prevent influenza in nursing homes and inpatient wards. This has led to clinical and multidisciplinary cooperation between physicians and dentists, among others. However, to date, the mechanisms by which "chronic periodontitis and oral bacteria" contribute to lower airway diseases have not been well understood. Clarifying these mechanisms will lead to a theoretical basis for answering the question, "Why is oral health management effective in preventing lower airway diseases?"