Tear fluid, saliva and urine as biological matrices for assessing free radical homeostasis (literature review)

Free radical homeostasis is a state of a biological system characterized by a balance between the production of free radicals and their neutralization by the body’s antioxidant defense systems. A disruption of this balance leads to a change in the redox state of the cell, which contributes to the development of oxidative stress, a key link in the pathogenesis of many diseases. Considering that most current studies assess the parameters of the redox system in venous blood samples, the collection procedure of which is invasive and, accordingly, has a number of limitations, there is a need to search for alternative biological matrices suitable for the analysis of redox parameters.

Aim. To analyze current concepts regarding the potential use of tear fluid, saliva, and urine as promising biological matrices for assessing the state of free radical homeostasis. This review examines the characteristics of the formation and composition of tear fluid, saliva, and urine, as well as the sources of free radicals, products of oxidative modification of biomolecules, and components of the antioxidant defense system detected in them. The factors influencing the interpretation of free radical homeostasis parameters in these biological matrices are analyzed, including formation specifics, sample collection methods, the impact of local and systemic pathological processes, approaches to data normalization, and external factors. It is shown that tear fluid provides high diagnostic value for assessing local changes occurring on the ocular surface and in the anterior segment of the eye. Saliva reflects a combination of local and systemic changes, while urine is the most extensively studied and standardized biological matrix, with parameters primarily reflecting established systemic alterations in free radical homeostasis.

Thus, tear fluid, saliva, and urine possess varying diagnostic utility for assessing local and systemic changes in free radical homeostasis. Future prospects in this field are associated with the development of standardized approaches to the analysis of these biological matrices and a comprehensive assessment of free radical homeostasis.

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