Chlorine Gas Exposure Causes Systemic Endothelial Dysfunction by Inhibiting Endothelial Nitric Oxide Synthase–Dependent Signaling

Abstract

Chlorine gas (Cl 2 ) exposure during accidents or in the military setting results primarily in injury to the lungs. However, the potential for Cl 2 exposure to promote injury to the systemic vasculature leading to compromised vascular function has not been studied. We hypothesized that Cl 2 promotes extrapulmonary endothelial dysfunction characterized by a loss of endothelial nitric oxide synthase (eNOS)-derived signaling. Male Sprague Dawley rats were exposed to Cl 2 for 30 minutes, and eNOS-dependent vasodilation of aorta as a function of Cl 2 dose (0-400 ppm) and time after exposure (0-48 h) were determined. Exposure to Cl 2 (250-400 ppm) significantly inhibited eNOS-dependent vasodilation (stimulated by acetycholine) at 24 to 48 hours after exposure without affecting constriction responses to phenylephrine or vasodilation responses to an NO donor, suggesting decreased NO formation. Consistent with this hypothesis, eNOS protein expression was significantly decreased (z 60%) in aorta isolated from Cl 2 -exposed versus airexposed rats. Moreover, inducible nitric oxide synthase (iNOS) mRNA was up-regulated in circulating leukocytes and aorta isolated 24 hours after Cl 2 exposure, suggesting stimulation of inflammation in the systemic vasculature. Despite decreased eNOS expression and activity, no changes in mean arterial blood pressure were observed. However, injection of 1400W, a selective inhibitor of iNOS, increased mean arterial blood pressure only in Cl 2 -exposed animals, suggesting that iNOS-derived NO compensates for decreased eNOS-derived NO. These results highlight the potential for Cl 2 exposure to promote postexposure systemic endothelial dysfunction via disruption of vascular NO homeostasis mechanisms.

Post-Exposure Antioxidant Treatment in Rats Decreases Airway Hyperplasia and Hyperreactivity Due to Chlorine Inhalation

“…The administration of aerosols with radii of 2-4 mm constitutes the most effective way of replenishing airway and distal lung antioxidants. Second, we showed that the exposure of rats to chlorine causes systemic injury, characterized by inflammation and endothelial dysfunction because of the inactivation of endothelial nitric oxide synthase, an event linked to atherosclerosis and hypertension (31). We thus argued that to augment antioxidant defenses in the plasma would be important.…”

Formation of chlorinated lipids post-chlorine gas exposure

“…Cl 2 gas exposure also leads to tissue inflammation and microcirculatory dysfunction in extrapulmonary tissues. For example, animals exposed to Cl 2 and returned to room air develop endothelial and myocardial dysfunction and failure (13,16). This pattern of injury is observed with many chemically distinct inhaled irritants and pollutants (e.g., ozone, particulate matter) (39)(40)(41)(42).…”

“…Our previous studies have shown that eNOS-dependent vasodilation becomes inhibited post-Cl 2 gas exposure (15,16) and other groups have shown that Cl-lipid addition to cultured endothelial cells inhibits eNOS activity (27). We therefore tested eNOS-dependent vasodilation of aortas isolated 24 h after intranasal Cl-lipid administration.…”

“…Moreover, these fatty acid species have been detected as being free or esterified. Furthermore, emerging studies indicate unique biological effects of Cllipids in stimulating inflammation, promoting cell-death, and dysfunction in eNOS-signaling (19,21,23,(26)(27)(28)(29)(30), which are also all features of post-Cl 2 gas toxicity (4,15). Cl-lipids are predicted to be formed via direct reactions of Cl 2 gas with the vinyl ether bond in plasmalogens, leading us to hypothesize that these species may be mediators of post-Cl 2 gas toxicity.…”

“…While some, such as chloramines, may mediate Cl 2 gas toxicity (18,43), their relatively short lifetimes in vivo preclude them as useful biomarkers. to the periphery to elicit extrapulmonary effects characterized by eNOS inhibition, which leads to the hypothesis that plasma Cl-lipids formed after Cl 2 gas exposure may mediate extrapulmonary toxicities to the vasculature and heart (13,15,16).…”