Effect of repeated inhalations of gaseous hypochlorous acid on the antioxidant properties of rat blood plasma

The development of disinfection systems based on the introduction of a gaseous antimicrobial agent into indoor air represents an effective strategy to prevent airborne infections. Gaseous hypochlorous acid HOCl(g) is an attractive candidate for this purpose. However, its high oxidizing capacity necessitates a thorough investigation of its inhalation toxicity. In this study, Wistar Han rats (n=6 per group per time point) were exposed to daily 5-hour inhalations of 0.32±0.03 ppm HOCl(g) for 25 days, followed by a 7-day recovery period. To assess oxidative stress, the activities of catalase (CAT) and superoxide dismutase (SOD), total antioxidant capacity (TAC), and malondialdehyde (MDA) levels were measured in blood plasma on days 2, 7, 14, 25 and 32. A sharp increase in MDA was observed 24 hours after the first inhalation, indicating intense lipid peroxidation. Plasma antioxidant capacity increased from day 1, reaching a maximum on day 7, substantially exceeding control values: CAT by 1.9-fold, SOD by 2.3-fold, and TAC by 4-fold. This allowed MDA to return to control levels by day 14. After day 7, antioxidant enzyme activities and TAC gradually declined, and by day 32 (one week post-exposure), all parameters were indistinguishable from controls. These findings suggest that repeated HOCl(g) inhalations do not cause severe oxidative stress but rather induce a hormetic response that stimulates the antioxidant system. This may be exploitable not only for airborne disinfection but also for therapeutic preconditioning against oxidative damage. Further research is required to establish an HOCl(g) concentration with an optimal safety/antimicrobial efficacy ratio.