FROM HORMONES TO RESILIENCE: ENDOCRINE BIOMARKERS OF ADAPTIVE RESPONSES IN HUMANS AND ANIMALS WITHIN A ONE HEALTH FRAMEWORK

Life, across biological systems, is characterized not by the absence of stressors but by the continuous capacity to adapt to them. Within this framework, resilience represents a dynamic, multilevel biological process that determines whether exposure to stressors results in adaptive regulation or allostatic overload. Particular attention is given to the “stress resilience signature,” conceptualized as an individual profile emerging from the dynamic interplay among endocrine, metabolic, and neuroimmune systems. Although humans and animals are exposed to different categories of stressors, these challenges—whether clinical, occupational, environmental, or nutritional—engage shared adaptive pathways that shape resilience. The assessment of resilience may be approached through the use of biomarkers, which provide insight into the dynamic and multilevel interactions underlying individual variability in stress responses. Among these, hormonal biomarkers represent key indicators of endocrine regulation and can be quantified in different biological matrices, including both point-based and retrospective samples, offering complementary insights into endocrine function over time. In this context, the first goal of the present research was to develop and validate some useful assays for the measurement of endocrine biomarkers in both invasive and non-invasive matrices, apart from those already available. An in-house radioimmunoassay (RIA) was validated for the quantification of cortisol in buffalo milk, a commercially enzyme-linked immunosorbent assays (ELISA) kit for the measurement of the cortisol metabolite 11-oxoetiocholanolone in equine and bovine feces, and another one for allopregnanolone in human and equine hair. Proper validation under these circumstances ensures reliable, reproducible, and biologically meaningful results. Building on these methodological foundations, the second aim was to study biological resilience by measuring steroid hormones in hair in humans suffering from neurological and occupational stressors, and in an animal model exposed to nutritional stress. This approach allowed the evaluation of endocrine adaptations and highlighted individual variability in resilience across different physiological and psychosocial conditions. Third, the study extended the application of hair steroid measurements to pig farming. Environmental, social, and management-related stressors—such as confinement systems, social interactions, tail docking, and diet—were assessed for their impact on adaptive capacity. Hair steroid profiles provided cumulative, non-invasive indicators of allostatic load and resilience, emphasizing the importance of integrative approaches for evaluating welfare and adaptive responses under multifactorial stress. Fourth, hair steroid analysis was applied to critical developmental windows in equine and bovine species, including late gestation, parturition, and early postnatal life. These periods involve intense metabolic, immunological, and environmental demands, and steroid hormone profiles reflect both physiological adaptation and the capacity to cope with internal and external challenges. Hair steroid measurements offered cumulative, non-invasive insights into resilience and adaptive capacity, supporting the understanding of feto-maternal interactions and early-life development. This thesis examines biological resilience as a multi-level adaptive process within a One Health perspective, focusing primarily on endocrine biomarkers measured in non-invasive matrices. These biomarkers were investigated across different environmental, occupational and health condition in human populations as well management, nutritional and feto-maternal challenges in animal models. The study focuses on identifying and characterizing hormonal signatures associated with adaptive responses to stressors, offering a framework for interpreting individual resilience across species.