Project Summary Daily low-dose aspirin is routinely prescribed to prevent cardiovascular (CV) events, despite conflicting data on its efficacy, especially with increasing body weight. While intended to inhibit platelet aggregation, aspirin has other effects that may be important in reducing CV risk that are influenced by body weight. Obesity and atherosclerosis are both characterized by chronic, low-grade inflammation and some treatments aimed at reducing inflammation improve CV outcomes. The resolution of inflammation requires specialized pro-resolving lipid mediators (SPMs). Several SPMs and their precursors are termed “aspirin- triggered” (AT), as their production is stimulated in the presence of acetylated COX-2. We and others have shown that AT-SPMs, including 15-epi-lipoxin A4 (15R-LXA4), are reduced in blood and tissues from obese humans. Pre-clinical models have established that AT-SPMs inhibit atherosclerosis progression and have plaque stabilizing effects. Small cross-sectional human cohorts have shown AT-SPMs inversely associated with severity of atherosclerosis, but a potential association with prospective CV outcomes has not been tested. The largest meta-analysis of aspirin trials showed that low-dose aspirin was effective at reducing major adverse CV events (MACE) only in those weighing <70kg, whereas doses >300mg exhibited increasing efficacy as body weight increased. While suggested to explain these findings, data on incomplete platelet COX-1 inhibition from low-dose aspirin with increasing body weight are inconclusive. Thus, aspirin-mediated factors extrinsic to platelet function in aggregation and thrombosis, such as deficient AT-SPMs, may mediate obesity’s role in CVD and reduced benefit from low-dose aspirin with increasing body weight. Our central hypothesis is that reduced levels of AT-SPMs contribute to excess CV risk and worse CV outcomes with low-dose aspirin therapy. In our first Aim, we will test the effects of low- and regular-dose aspirin regimens on AT-SPM levels and cellular function in humans across a wide range of body weights using a randomized, placebo-controlled, crossover trial. We will measure lipid mediators, including thromboxanes, leukotrienes, and SPMs, in serum and neutrophils before and after treatment with aspirin. We will also assess measures of cellular inflammation including platelet activity, platelet-leukocyte aggregates, and leukocyte surface expression of SPM receptors. In Aim 2, we will assess a predictive capacity of 15R-LXA4 for MACE in persons with stable ischemic heart disease taking aspirin. Using a nested case-control design, we will assess serum SPM profiles in 402 subjects in the ISCHEMIA randomized controlled trial and evaluate the capacity of SPM profiles to predict CV outcomes in these subjects. We will also assess a mediating effect of body weight on 15R-LXA4 levels. This work will evaluate a novel mechanistic role for aspirin in CVD treatment, separate from thrombosis, that may...