Effects of Subchronic Exposures to Concentrated Ambient Particles in Mice: IX. Integral Assessment and Human Health Implications of Subchronic Exposures of Mice to CAPs

Abstract

In order to examine the biologic plausibility of adverse chronic cardiopulmonary effects in humans associated with ambient particulate matter (PM) exposure, we exposed groups of normal mice (C57) and knockout mice that develop atherosclerotic plaques (ApoE^−/− and ApoE^−/− LDLr^−/−) for 6 h/day, 5 days/wk for 5 or 6 mo during the spring/summer of 2003 to either filtered air or 10-fold concentrated ambient particles (CAPs) in Tuxedo, NY (average PM_2.5 concentration during exposure = 110 μ g/m³). Some of the mice had implanted electocardiographic monitors. We demonstrated that: (1) this complex interdisciplinary study was technically feasible in terms of daily exposures, collection of air quality monitoring data, the collection, analysis, and interpretation of continuous data on cardiac function, and the collection and analyses of tissues of the animals sacrificed at the end of the study; (2) the daily variations in CAPs were significantly associated, in ApoE^−/− mice, with daily variations in cardiac function; (3) there were significant differences between CAPs and sham-exposed ApoE^−/− mice in terms of cardiac function after the end of the exposure period, as well as small differences in atherosclerotic plaque density, coronary artery disease, and cell density in the substantia nigra in the brain in the ApoE^−/− mice; and (4) there are suggestive indications of gene expression changes for genes associated with the control of circadian rhythm in the ApoE^−/− LDLr^−/− double knockout (DK) mice. These various CAPs-related effects on cardiac function and the development of histological evidence of increased risk of clinically significant disease at the end of the exposures in animal models of atherosclerosis provide biological plausibility for the premature mortality associated with PM_2.5 exposure in human subjects and provide suggestive evidence for neurogenic disease as well.