PM-induced cardiac oxidative stress and dysfunction are mediated by autonomic stimulation

Epidemiological studies show that increases in particulate air pollution (PM) are associated with increases in cardiopulmonary morbidity and mortality. However, the mechanism(s) underlying the cardiac effects of PM remain unknown. We used pharmacological strategies to determine whether oxidants are implicated in PM-dependent cardiac dysfunction and whether PM-induced increase in autonomic stimulation on the heart mediates cardiac oxidative stress and toxicity. Adult Sprague-Dawley rats were exposed to either intratracheal instillation of urban air particles (UAP 750 μg) or to inhalation of concentrated ambient particles (CAPs mass concentration 700 ± 180 μg/m3) for 5 h. Oxidative stress and cardiac function were evaluated 30 min after UAP instillation or immediately after exposure to CAPs. Instillation of UAP led to significant increases in heart oxidants measured as organ chemiluminescence (UAP: 38 ± 5 cps/cm2, sham: 10 ± 1 cps/cm2) or thiobarbituric acid reactive substances (TBARS, UAP: 76 ± 10, Sham 30 ± 6 pmol/mg protein). Heart rate increased immediately after exposure (UAP: 390 ± 20 bpm, sham: 350 ± 10 bpm) and returned to basal levels over the next 30 min. Heart rate variability (SDNN) was unchanged immediately after exposure, but significantly increased during the recovery phase (UAP: 3.4 ± 0.2, Sham: 2.4 ± 0.3). To determine the role of ROS in the development of cardiac malfunction, rats were treated with 50 mg/kg N-acetylcysteine (NAC) 1 h prior to UAP instillation or CAPs inhalation. NAC prevented changes in heart rate and SDNN in UAP-exposed rats (340 ± 8 and 2.9 ± 0.3, respectively). To investigate the role of the autonomic nervous system in PM-induced oxidative stress, rats were given 5 mg/kg atenolol (β-1 receptor antagonist), 0.30 mg/kg glycopyrrolate (muscarinic receptor antagonist) or saline immediately before exposure to CAPs aerosols. Both atenolol and glycopyrrolate effectively prevented CAPs-induced cardiac oxidative stress (CLATEN: 11 ± 1 cps/cm2, CLGLYCO: 10 ± 1 cps/cm2, TBARSATEN: 40 ± 6 pmol/mg protein, TBARSGLYCO: 38 ± 6 pmol/mg protein). These data indicate that PM exposure increases cardiac oxidants via autonomic signals and the resulting oxidative stress is associated with significant functional alterations in the heart.