Nearly one-third of adults 65 years and older have mild cognitive impairment or dementia; correspondingly, Alzheimer's disease and related dementias (ADRD) are now one of the leading causes of morbidity and mortality in the US. Because of global demographic trends toward increasingly older populations, this is a looming public health crisis with associated costs projected to soon exceed $1 trillion. Thus, there is an urgent need to identify the mechanistic underpinnings of modifiable risk factors for ADRD in midlife in order to establish novel biological targets for therapeutic intervention strategies that can be implemented earlier in the aging trajectory and prior to clinically detectable overt cognitive deficits, which are difficult to remediate by current treatments. Accordingly, the long-term goal is to determine whether and to what extent mitochondrial reactive oxygen species (mtROS)-induced impairments in peripheral endothelium-dependent dilation (EDD) explain how daily stress impacts 'real-world' cognitive function in middle-aged adults. As a necessary first step towards developing a competitive NIH R01 empirically investigating this possibility, the objective of this pilot proposal is to (1) establish the feasibility and efficacy of our methodological approach and (2) generate hypothesis-specific micro-longitudinal preliminary data. Aim 1 will examine the stability and temporal patterning of intra-individual dynamic fluctuations in daily stress processes and daily cognitive function in middle-aged adults (within and between bursts). Aim 2 will determine the indicators of daily stress and daily cognitive function most strongly related to peripheral endothelial function in middle-aged adults. The hypotheses are that (1) greater negative affective responsivity to daily stressors, (2) more attentional lapses, and (3) slower processing speed will be related to reductions in peripheral EDD, secondary to increased mtROS production.

A small community sample of cognitively unimpaired middle-aged males and females (n=20; 40-55 yrs) will be recruited. Participants will be recruited from New Castle County, Delaware (DE) and surrounding regions and will be representative of the sex/ethnic/racial population of DE. After providing verbal and written consent, all participants will undergo a clinical exam for signs and symptoms of chronic disease by clinical nursing staff. This will include a complete health history (females will also complete a gynecological history, including a 3-mo menstrual cycle recall), physical exam (anthropometry, resting hemodynamics, and a 12-lead electrocardiogram), and basic blood biochemistry (complete blood count, lipid profile, renal function, electrolytes, HbA1c, fasting glucose and insulin).

The investigators will assess multiple dynamic aspects of daily stress processes and 'real-world' daily cognitive function for 14 consecutive days (mobile app). Using the framework established by the investigative team, this high-resolution phenotyping approach allows for the precise intra-individual quantification of exposure and responsivity to daily stressors as they occur in during routine daily life. Concurrently, the investigators will obtain frequent daily 'snapshots' (i.e., 4 assessments per day) of multiple clinically relevant dimensions of both subjective (self-report) and objective (performance-based) cognitive function. This approach is situated within the Mobile Monitoring of Cognitive Change (M2C2) infrastructure and is a reliable, accurate, sensitive, and ecologically valid approach to detect everyday difficulties in cognitive function in complex real-world environments. Immediately after completion of the ambulatory assessments (i.e., Day 15), the investigataors will use orthogonal laboratory-based techniques to pharmaco-dissect the regulation of microvascular endothelial function (in vivo) and to quantify mitochondrial redox balance (ex vivo). Each participant will complete two 15-day measurement bursts, separated by \~6 months. All laboratory visits will be performed at the same time of day (7a-12p) and 12-hr postprandial. Every attempt will be made to schedule the experimental visits for premenopausal females during the early follicular phase of their menstrual cycle or the low hormone/placebo phase of hormonal contraception; however, given anticipated challenges in this regard, serum concentrations of sex hormones will also be measured at each visit.

Ambulatory Assessment Protocol (Days 1-14): Participants will complete 4 daily assessments; at each, they will complete "brain games" and subjectively report on their cognitive function, as well as on several contextual variables (e.g., affect, stress; shortened for momentary administration). Each assessment will take \~4 min. The first assessment of the day will also include a brief survey (\~2 min) asking about sleep health (quality and quantity; modified Pittsburgh Sleep Quality Inventory), morning outlook (emotions, physical symptoms), and anticipatory stress. Daily stress processes will be assessed each day during the last daily assessment using an adapted version of the Daily Inventory of Stressful Events (DISE; \~8 min). Daily cognitive function will be assessed in multiple domains (subjective and objective).

Laboratory Assessment of Peripheral Endothelial Function (Day 15): Microvascular endothelial function will be assessed using intradermal microdialysis coupled with laser Doppler flowmetry. Two intradermal microdialysis probes (CMA Linear 31 probe, 55 kDa) will be inserted into the dermal layer of the ventral forearm and perfused with either lactated Ringer's solution (control) or MitoTempol (0.5 mM) to scavenge mitochondrial-derived superoxide. Red cell flux will be continuously measured via integrated laser Doppler flowmeters. Mean arterial pressure will be measured via brachial auscultation every 4 min. A standard local heating protocol will be used to elicit EDD and the NO-dependent portion of this response will be determined pharmacologically, as previously described.