Environmentally persistent free radicals decrease cardiac function before and after ischemia/reperfusion injury in vivo

Abstract

Exposure to airborne particles is associated with increased cardiovascular morbidity and mortality. During the combustion of chlorine-containing hazardous materials and fuels, chlorinated hydrocarbons chemisorb to the surface of transition metal-oxide-containing particles, reduce the metal, and form an organic free radical. These radical-particle systems can survive in the environment for days and are called environmentally persistent free radicals (EPFRs). This study determined whether EPFRs could decrease left ventricular function before and after ischemia and reperfusion (I/R) in vivo. Male Brown-Norway rats were dosed (8 mg/kg, intratracheal) 24 h prior to testing with particles containing the EPFR of 1, 2-dichlorobenzene (DCB230). DCB230 treatment decreased systolic and diastolic function. DCB230 also produced pulmonary and cardiac inflammation. After ischemia, systolic, but not diastolic function was significantly decreased in DCB230-treated rats. Ventricular function was not affected by I/R in control rats. There was greater oxidative stress in the heart and increased 8-isoprostane (biomarker of oxidative stress) in the plasma of treated vs. control rats after I/R. These data demonstrate for the first time that DCB230 can produce inflammation and significantly decrease cardiac function at baseline and after I/R in vivo. Furthermore, these data suggest that EPFRs may be a risk factor for cardiac toxicity in healthy individuals and individuals with ischemic heart disease. Potential mechanisms involving cytokines/chemokines and/or oxidative stress are discussed.

Figure 1

EPFRs decrease baseline diastolic left ventricular function in closed chest rats. Rats were treated with DCB230 (8 mg/kg, i.t.) or vehicle 24 hrs prior to the experiment. Left ventricular function was measured using Millar pressure-volume catheters. Data are mean ± SEM. Abbreviations: EDV, end diastolic volume; EDP, end diastolic pressure; −dP/dt_min, diastolic decrease in pressure vs time; Tau (G). ***p<0.001, **p<0.01, and * p<0.05.

Figure 2

EPFRs decrease baseline systolic left ventricular function in closed chest rats. Rats were treated with DCB230 or vehicle as in figure 1. Data are reported as mean ± SEM. Abbreviations: ESP, end systolic pressure; dP/dt_max, change in pressure vs change in time during systole; SW, stroke work; SV, stroke volume; CO, cardiac output. ***p<0.001, **p<0.01, and *p<0.05.

Figure 3

EPFRs do not alter diastolic function after a brief myocardial ischemia. Rats were treated with DCB230 (n=6) or vehicle (n=6) 24 hr prior, as described in figure 1. Ventricular function was measured at baseline (B) before occluding the lower anterior descending coronary artery for 90s followed by reperfusion (I/R). Ventricular function was also measured 1, 5, 30 and 60 minutes after starting reperfusion. Data are means ± SEM. Abbreviations: as in figure 1.

Figure 4

EPFRs decrease left ventricular systolic function after brief cardiac ischemia and reperfusion. These are the same rats and experimental set up as described in figure 3. Data are means ± SEM. Abbreviations: as in figure 2. **p<0.01, and *p<0.05.

Figure 5

EPFRs increase oxidative stress in heart and plasma after I/R. Rats are the same as reported in figures 1–4. Levels GSH and GSSG in the heart and 8-iosprostane in plasma were measured using HPLC with electrochemical detection. Data are means ± SEM. ** p<0.01, and *p<0.05.

Figure 6

Section of the left ventricle of a vehicle-treated (A) and a DCB230-treated (B) rat showing increased macrophage infiltration (darkly stained cells) 24 hours after i.t. instillation of DCB230.