Oxidative damage to extracellular fluids by ozone and possible protective effects of thiols

Environmental levels of ozone (O3) frequently exceed air quality standards in many urban areas, and much research has been devoted to pathophysiological effects of O3 inhalation. Inhaled O3 will interact primarily with respiratory tract lining fluids (RTLF) and with constituents therein. It is believed that interaction of O3 with constituents in RTLF occurs by reactive absorption. We investigated interactions of O3 with human blood plasma, used as a model extracellular fluid representing RTLF, and studied oxidation of plasma antioxidants, proteins, and lipids. Plasma was exposed to various concentrations of O3 in humidified air, supplied at a continuous flow, in a system that mimics exposure of RTLF to inhaled O3 in vivo. Interaction of O3 with plasma appeared to be caused by reactive absorption of O3 by plasma. It was found that O3 reacts primarily with the aqueous antioxidants ascorbate and urate. Reactive absorption of O3 by plasma ascorbate and urate was found to be more efficient at low (2 ppm) O3 levels than at high (16 ppm) levels. We were also able to detect oxidative damage to plasma proteins and lipids after prolonged exposure to O3. Second, we investigated whether GSH or dihydrolipoic acid (DHLA) could prevent oxidative damage to plasma proteins and lipids by O3, under our exposure conditions. In contrast to plasma, RTLF contain relatively high amounts of GSH, which may contribute to antioxidant protection to respiratory tract epithelial cells. DHLA is an endogenous dithiol and has potent antioxidant properties. Addition of either GSH or DHLA to plasma (at concentrations up to 1 mM) prior to O3 exposure did not inhibit oxidation of plasma proteins and lipids during exposure to O3, nor did it attenuate depletion rates of ascorbate or urate. Our results indicate that added thiols cause increased reactive absorption of O3, rather than preventing reaction of O3 with other plasma constituents. Thiol supplementation could afford protection against O3-induced injury in vivo by increasing reactive absorption of O3 in the upper respiratory tract, thereby protecting the epithelia of lower airways and gas-exchanging portions of the lungs from exposure to toxic levels of O3.(ABSTRACT TRUNCATED AT 400 WORDS)