Chronic cardiac structural damage, diastolic and systolic dysfunction following acute myocardial injury due to bromine exposure in rats

Abstract

Background: Highly reactive halogens such as bromine are more commonly utilized, leading to an increase in quantities that are stocked and transported, therefore increasing the risk of accidental or deliberate exposure. Here we describe progression and potential mechanisms of adverse effects of a single injurious insult on the heart caused by bromine inhalation. Our studies have shown that bromine inhalation causes acute myocardial ischemia-reperfusion-like injury mediated by cytosolic calcium overload and increased calpain activity due to inactivation of SERCA. However, the progression of this injury in survivors is unknown. Our working hypothesis is that the initial injury causes irreversible damage that leads to chronic left ventricular systolic and diastolic dysfunction.Methods: Sprague Dawley rats received bromine exposure of 600 ppm for 45' and the survivors were sacrificed at 14 or 28 days, with matching naïve groups at each time point. Echocardiography, hemodynamic analysis, histology, electron microscopy and biochemical analysis of cardiac tissue were performed to assess functional, structural and molecular effects.Results: At 14 and 28 days, hemodynamic and echocardiographic analysis revealed increases in RV and LV end-diastolic pressure and LV end-diastolic wall stress with increased LV fibrosis at 28 days. TEM images demonstrated myofibrillar loss, cytoskeletal breakdown and mitochondrial damage at both time points. The myofibrillar damage and increased LV wall stress was reflected by increases in cTnI and NT-proBNP at both time points. LV shortening decreased as a function of increasing LV end-systolic wall stress and was accompanied by increased SERCA modification and a striking dephosphorylation of phospholamban with a significant increase in protein phosphatase 1. There was an increased 4-hydroxynonenal content in the myocardium at 28 days suggesting increased oxidative stress. Conclusions:These results indicate that the initial insult of bromine inhalation initiates a continuous process with chronic myocardial damage and subsequent LV systolic and diastolic dysfunction and that oxidative stress and phospholamban dephosphorylation play a central role.

Behavioral and Neuronal Effects of Inhaled Bromine Gas: Oxidative Brain Stem Damage

“…Using a rat model, our studies have shown that a single dose of acute Br 2 exposure causes decreased heart rate, cardiac hypertrophy, increase in cardiac injury markers in blood, and increased ultrastructural damage [1,2]. We also demonstrated that the cardiac damage was caused by the presence of increased brominated fatty acids and aldehydes in the heart along with bromination of cardiac sarco(endo)plasmic reticulum calcium-ATPase (SERCA) and cardiac phosphalamban dephosphorylation that further decreased SERCA activity.…”

“…Interestingly, most of these effects persisted till 28 days of observation in the model and resulted in increased right ventricular (RV) and LV end-diastolic pressure and LV end-diastolic wall stress with increased LV fibrosis. The LV dysfunction in this model at this delayed duration was accompanied by SERCA inactivation that resulted potentially from increased oxidative stress, as shown by increased myocardial hydroxynonenal accumulation and increased NADPH oxidase-2 (Nox-2) [1]. SERCA2 inactivity could also be attributed to a striking loss of phosphalamban (PLN) phosphorylation that started 24 h after Br 2 inhalation and persisted at 7, 14, and 28 days after exposure.…”

“…Age-matched male and female Sprague Dawley rats were purchased from Envigo (Indianapolis, IN, USA). Whole-body bromine (600 ppm in air, 45 min) exposure was performed as described before [1]. These conditions model acute human exposures that occur during industrial or transport accidents [47].…”

“…Br 2 on contact with aqueous media in the body forms bromide, highly oxidizing hydrobromic acid (HBr), hypobromous acid (HOBr), and bromic oxyacids (HBrO 3 ). Br 2 injury to humans is through direct irritant effect with the release of radical species that are damaging to the respiratory mucosa and also distant organs [1,2]. As low as 40-60 ppm is dangerous to human health, and cases of accidental spills with a high concentration of Br 2 have been reported [3].…”

“…We have demonstrated the occurrence of brominated fatty acids and fatty aldehydes, in the tissues of Br 2 -exposed animals, that form upon reaction of Br 2 with pulmonary plasmalogens [2,5]. These circulate in the blood and are transported to other major organs in the body long after exposure [1]. Although not much is known regarding the metabolism of inhaled Br 2 , it has been known to form bromide, its anionic form, in living tissues [3,5].…”