Age-related modifications in human unstimulated whole saliva: a biochemical study

Saliva as Biomarker for Oral and Chronic Degenerative Non-Communicable Diseases

Saliva is a very complex fluid and it is essential to maintain several physiological processes and functions, including oral health, taste, digestion and immunological defenses. Saliva composition and the oral microbiome can be influenced by several factors, like diet and smoking habits, and their alteration can represent an important access point for pathogens and, thus, for systemic illness onset. In this review, we explore the potentiality of saliva as a new tool for the early detection of some pathological conditions, such as oral diseases, chronic degenerative non-communicable diseases, among these chronic kidney disease (CKD). We also examined the possible correlation between oral and systemic diseases and oral and gut microbiota dysbiosis. In particular, we deeply analyzed the relationship between oral diseases and CKD. In this context, some salivary parameters can represent a new device to detect either oral or systemic pathologies. Moreover, the positive modulation of oral and gut microbiota induced by prebiotics, postbiotics, or symbiotics could represent a new possible adjuvant therapy in the clinical management of oral diseases and CKD.

Salivary Proteomics Reveals Significant Changes in Relation to Alzheimer's Disease and Aging

BACKGROUND

Aging is a risk factor for several pathologies as Alzheimer's disease (AD). Great interest exists, therefore, in discovering diagnostic biomarkers and indicators discriminating biological aging and health status. To this aim, omic investigations of biological matrices, as saliva, whose sampling is easy and non-invasive, offer great potential.

OBJECTIVE

Investigate the salivary proteome through a statistical comparison of the proteomic data by several approaches to highlight quali-/quantitative variations associated specifically either to aging or to AD occurrence, and, thus, able to classify the subjects.

METHODS

Salivary proteomic data of healthy controls under-70 (adults) and over-70 (elderly) years old, and over-70 AD patients, obtained by liquid chromatography/mass spectrometry, were analyzed by multiple Mann-Whitney test, Kendall correlation, and Random-Forest (RF) analysis.

RESULTS

Almost all the investigated proteins/peptides significantly decreased in relation to aging in elderly subjects, with or without AD, in comparison with adults. AD subjects exhibited the highest levels of α-defensins, thymosin β4, cystatin B, S100A8 and A9. Correlation tests also highlighted age/disease associated differences. RF analysis individuated quali-/quantitative variations in 20 components, as oxidized S100A8 and S100A9, α-defensin 3, P-B peptide, able to classify with great accuracy the subjects into the three groups.

CONCLUSION

The findings demonstrated a strong change of the salivary protein profile in relation to the aging. Potential biomarkers candidates of AD were individuated in peptides/proteins involved in antimicrobial defense, innate immune system, inflammation, and in oxidative stress. RF analysis revealed the feasibility of the salivary proteome to discriminate groups of subjects based on age and health status.

Lactoferrin as Immune-Enhancement Strategy for SARS-CoV-2 Infection in Alzheimer's Disease Patients

Coronavirus 2 (SARS-CoV2) (COVID-19) causes severe acute respiratory syndrome. Severe illness of COVID-19 largely occurs in older people and recent evidence indicates that demented patients have higher risk for COVID-19. Additionally, COVID-19 further enhances the vulnerability of older adults with cognitive damage. A balance between the immune and inflammatory response is necessary to control the infection. Thus, antimicrobial and anti-inflammatory drugs are hopeful therapeutic agents for the treatment of COVID-19. Accumulating evidence suggests that lactoferrin (Lf) is active against SARS-CoV-2, likely due to its potent antiviral and anti-inflammatory actions that ultimately improves immune system responses. Remarkably, salivary Lf levels are significantly reduced in different Alzheimer's disease (AD) stages, which may reflect AD-related immunological disturbances, leading to reduced defense mechanisms against viral pathogens and an increase of the COVID-19 susceptibility. Overall, there is an urgent necessity to protect AD patients against COVID-19, decreasing the risk of viral infections. In this context, we propose bovine Lf (bLf) as a promising preventive therapeutic tool to minimize COVID-19 risk in patients with dementia or AD.

Standardizing salivary lactoferrin measurements to obtain a robust diagnostic biomarker for Alzheimer's disease

The search for new, robust, and reproducible biomarkers for Alzheimer's disease (AD) diagnosis is a challenge. We recently reported that salivary lactoferrin (Lf) could be presented as new biomarker candidate for AD, being both non-invasive and cost-effective, as well as having appropriate diagnostic performance for the clinical detection of AD subjects. Saliva is an attractive sample type for biomarker-based testing approaches for several other diseases; however, its composition may change under certain circumstances. It is therefore critical to maintain a consistent salivary handling protocol, considering possible extrinsic factors that may influence salivary Lf concentration. In this work, we analyzed salivary Lf concentration under different handling conditions and donor-dependent factors including age, inter-diurnal variations, physical activity, and pharmacological treatments. Our aim was to evaluate the influence of such conditions on salivary Lf concentration. In conclusion, we found that most of these extrinsic factors should be considered in the future when using Lf as a predictive biomarker for AD.

Xanthine oxidase-lactoperoxidase system and innate immunity: Biochemical actions and physiological roles

The innate immune system in mammals is the first-line defense that plays an important protective role against a wide spectrum of pathogens, especially during early life before the adaptive immune system develops. The enzymes xanthine oxidase (XO) and lactoperoxidase (LPO) are widely distributed in mammalian tissues and secretions, and have a variety of biological functions including in innate immunity, provoking much interest for both in vitro and in vivo applications. The enzymes are characterized by their generation of reactive oxygen and nitrogen species, including hydrogen peroxide, hypothiocyanite, nitric oxide, and peroxynitrite. XO is a major generator of hydrogen peroxide and superoxide that subsequently trigger a cascade of oxidative radical pathways, including those produced by LPO, which have bactericidal and bacteriostatic effects against pathogens including opportunistic bacteria. In addition to their role in host microbial defense, reactive oxygen and nitrogen species play important physiological roles as second messenger cell signaling molecules, including cellular proliferation, differentiation and gene expression. There are several indications that the reactive species generated by peroxide have positive effects on human health, particularly in neonates; however, some important in vivo aspects of this system remain obscure. The primary dependence of the system on hydrogen peroxide has led us to propose it is particularly relevant to neonate mammals during milk feeding.

The Significance of Lactoperoxidase System in Oral Health: Application and Efficacy in Oral Hygiene Products

Lactoperoxidase (LPO) present in saliva are an important element of the nonspecific immune response involved in maintaining oral health. The main role of this enzyme is to oxidize salivary thiocyanate ions (SCN^-) in the presence of hydrogen peroxide (H₂O₂) to products that exhibit antimicrobial activity. LPO derived from bovine milk has found an application in food, cosmetics, and medical industries due to its structural and functional similarity to the human enzyme. Oral hygiene products enriched with the LPO system constitute an alternative to the classic fluoride caries prophylaxis. This review describes the physiological role of human salivary lactoperoxidase and compares the results of clinical trials and in vitro studies of LPO alone and complex dentifrices enriched with bovine LPO. The role of reactivators and inhibitors of LPO is discussed together with the possibility of using nanoparticles to increase the stabilization and activity of this enzyme.

Aging-related changes in quantity and quality of saliva: Where do we stand in our understanding?

Saliva is crucial to oral processing of food and consequently is also related to the sensory and textural experience. It is often assumed that the secretion and properties of saliva change with age, which can result in dry mouth conditions, taste aberrations. Such changes may result in reduced nutrient intake and malnutrition besides adversely affecting the quality of life. Based on some recent research findings, this article reviews our current understandings on age-dependent changes on quantity (bulk salivary flow rate) as well as quality of saliva (e.g., composition, viscosity, lubrication) in healthy elderly individuals. The review begins with a short introduction to histological changes of salivary glands upon aging. This is followed by covering different aspects of salivary changes with key articles highlighting decreased flow rate, increased ionic concentration, decreased calcium and mucin content in saliva of elderly subjects consequently affecting the oral coating and flavor perception. We also highlight issues in data associated with respect to variance in saliva collection protocols as well as factors influencing such results other than age, such as health conditions and polypharmacy. Clear gaps in literature have been highlighted with respect to lack of quantitative data in viscoelasticity, rheology, and lubrication properties of saliva in healthy elderly population and the potential impact of changes in these material properties on sensory and textural perception of food and consequently food intake. Such insights will not only have clinical implications for maintaining optimal oral health in elderly population but also serve to optimize food for elderly population. PRACTICAL APPLICATIONS: The population has undergone a fundamental change in its age structure globally, with a rapid increase in elderly population. Innovation of tailored foods is still in its early stage to satisfy the needs of growing aging population. One of the biggest challenges in such food product development is lack of adequate understanding and characterization of endogenous factors, that is, age-related changes in saliva, which may influence oral processing of food and subsequently nutrient intake. Aging affects the salivary glands and alters quantity (flow rate) and quality (e.g., ion and protein composition, rheology, tribology) of saliva. Thus, older adults may suffer from dry mouth, taste aberration, and poor oral hygiene, greatly affecting their quality of life. This review provides insights into how age versus other health conditions influence salivary properties. Understanding of age-dependent changes in salivary rheology and tribology will be of paramount importance to optimize food for elderly population.

Salivary markers of oxidative stress are related to age and oral health in adult non-smokers

BACKGROUND

Salivary concentrations of thiobarbituric acid-reacting substances (TBARS) are associated with the periodontal status assessed as papillary bleeding index (PBI). Whether this association is age independent is currently unclear. Salivary concentrations of advanced oxidation protein products (AOPPs) and advanced glycation end products (AGEs) have not been assessed in relation to age or oral health yet. The aim of our study was to analyse salivary markers of oxidative stress in dental patients in relation to age, gender and oral health.

METHODS

Consecutive adult non-smoking dental patients were enrolled (n = 204; aged 19-83 years). PBI and the caries index (CI) were assessed. Markers of oxidative stress, such as TBARS, AOPPs and AGEs, and the total antioxidant capacity (TAC) were measured in saliva samples taken before clinical examination.

RESULTS

Linear regression showed that salivary TBARS, AGEs and TAC significantly increase with age (r squared = 5.3%, 2.1% and 5%, respectively). PBI is an independent predictor of salivary TBARS (r squared = 5.5%), and the CI negatively affected AOPPs (r = 3.2%) and positively affected TBARS (r = 2.5%). Gender did not affect any of the analysed parameters.

CONCLUSIONS

Age as a significant contributor to the variance should be taken into account in studies focusing on salivary markers of oxidative stress. The relationship between PBI and salivary TBARS confirms results from previous studies. In addition, our results show that the association is age independent. Negative association between the CI and AOPPs might be related to recent findings that AOPP might be actually a marker of non-enzymatic antioxidant status.