Stress Biomarkers: Biological Meaning of Field-Friendly Salivary Measures

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DESCRIPTION (provided by applicant): Stress and emotion impact health. To reduce their costly health consequences, mechanisms through which they alter biological processes must be understood. The hypothalamic-pituitary adrenal (HPA) axis plays a key role in transducing psychosocial experience into bodily changes relevant to health, and HPA stress research is exploding. Salivary cortisol measures provide a stress "biomarker" of HPA activity for use in epidemiological studies, revealing that cortisol is associated with job stress, trauma, depression, fatigue, minority status, cardiovascular disease, and cancer mortality. Laboratory work has dissected HPA activity into biologically important regulatory components (e.g., negative feedback, central drive, stress reactivity) and provides laboratory probes of these components, but there has been little effort to link field and laboratory studies. Psychosocial correlates of field-friendly stress biomarkers are being identified, but we know little about their biological meaning. Markers have been chosen based on ease of use, not on empirical links to specific biological processes of known health relevance. This project will link field and laboratory work, enhancing the value of both, and the value derived from the millions of dollars spent yearly on salivary cortisol assay. The cortisol awakening response (CAR), awakening level, and diurnal decline are commonly used field stress biomarkers. Each likely provides different information about HPA axis regulation, but this has not been explicitly examined. CAR is the most extensively used. Its laboratory correlates have been studied, but are rarely acknowledged - it appears more closely linked to adrenal sensitivity than to theoretically more interesting central HPA measures. Giving biological meaning to field-friendly biomarkers will foster more precise hypotheses, and more efficient bio-sampling to test them. The laboratory probes which will attach biological meaning to salivary measures are themselves influenced by interacting genetic and developmental factors. Childhood adversity, for example, significantly reduces HPA feedback sensitivity, but this effect is only seen in subjects with a particular variant of an HPA gene (CRHR1) and can remain undetected if the genetic effect is ignored. If genes impact laboratory probes, and the field markers link to these probes, genes will impact the field markers. Ignoring this impact will undermine efforts to link psychosocial variables to the stress biomarkers. Documentation of this phenomena and preliminary exploration of relevant genes will be critical to prevent false negative results and replication failures in expensive epidemiological studies that we hope will use the more efficient and biologically meaningful biomarkers we identify in this project. In this study, we will use laboratory probes to give biological meaning to field-friendly HPA biomarkers, identify the most efficient and meaningful set of probes to use, and provide preliminary data on genetic factors that can undermine hypothesis testing in epidemiological stress research using stress biomarkers. This work will deepen understanding of the HPA axis and enhance the value of every future dollar spent on field stress studies.