Occult Cardiotoxicity: Subtoxic Dosage of Bis(2-chloroethoxy)methane Impairs Cardiac Response to Simulated Ischemic Injury

Abstract

The effect of Bis(2-chloroethoxy)methane (CEM) on myocardial response to ischemia was tested in rats. CEM was dermally applied for 3 days to F344/N male rats, at 0, 100, 400, or 600 mg/kg/d. Subsequently, left ventricular sections were prepared from each rat heart. Part of the sections from each heart were exposed to 90 minutes of simulated ischemia, followed by 90 minutes of reoxygenation. The rest of the sections were continuously oxygenated. Mitochondrial activity was assessed in the sections by the MTT colorimetric assay, reflecting dehydrogenases redox activity. Myocardial toxicity occurred in response to 400 and 600 mg/kg, characterized by myofiber vacuoles, necrosis, and mononuclear infiltrates. The latter dose was lethal. In sections from rats treated with 400 mg/kg CEM, redox activity was decreased by 21% (p<0.01) in oxygenated conditions and by 45% (p<0.01) in ischemia-reoxygenation, compared to controls. Hearts of rats treated with 100 mg/kg/d CEM showed normal histology. Their mitochondrial activity did not differ from that of untreated rat hearts in oxygenated conditions. However, in ischemia-reoxygenation, their redox activity was significantly lower (by 46%, p<0.01) than that of untreated rat hearts. These results demonstrate that subtoxic dosage of a cardiotoxic agent may cause occult cardiotoxicity, reflected by impaired response to ischemia.

Myocardial Mitochondrial Injury Induced by Pulmonary Exposure to Particulate Matter in Rats

“…(Ad et al 2005;Golomb et al 2009Golomb et al , 2007Tong et al 2009). We hypothesized that functional acute and potentially reversible impairment in cardiac mitochondria cannot be detected by light microscopic analysis of the myocardium and that TEM might detect evidence of mitochondrial toxicity following PM exposure.…”

“…The use of rat ventricular sections in an ex vivo experimental system simulating ischemia and reoxygenation (I/R) was previously described in our earlier studies involving isolated human right atrial sections (Schneider et al 2003) and rat left ventricular (LV) sections (Golomb et al 2007). Briefly, 2 millimeter cubes from the midsection of the LV were exposed to 30 min of oxygenated equilibration in 25 ml of glucose supplemented phosphate buffered saline (G-PBS) bubbled with oxygen at 37 o C (O 2 -G-PBS), then washed in PBS and transferred for 90 min to conditions of simulated ischemia: PBS without glucose bubbled with nitrogen (N 2 -PBS, at 37 o C), and then to 90 min of reoxygenation with glucose (O 2 -G-PBS, 37 o C), in the presence of MTT obtained from Sigma (St. Louis, MO, USA).…”

“…The ratio between the optical densities following I/R to that of its oxygenated controls, normalized to dry weight of the myocardial tissue, reflects the myocardial tolerance to ischemia/reoxygenation, and is referred to as the ischemic tolerance index (ITI) (Golomb et al 2007). …”

“…Therefore, ischemic injury can be viewed, at least partially, as a failure of the mitochondrial defense mechanisms (Golomb et al 2009). Exogenous agents may injure the heart by decreasing its ischemic tolerance (Golomb et al 2007(Golomb et al , 2009.…”

“…For this purpose, we administered a respirable oil combustion fly ash PM sample rich in water-soluble vanadium (HP-10); collected from a power plant in Boston, MA), by intratracheal instillation into rats (Kodavanti et al 1998). We used an ex vivo technique to simulate ischemia in isolated cardiac tissue sections (Ad et al 2005;Golomb et al 2009Golomb et al , 2007. The viability of the myocardium was then examined in vitro, in oxygenated conditions and in simulated ischemia/reoxygenation (I/R).…”