Inflammation and airway hyperresponsiveness after chlorine exposure are prolonged by Nrf2 deficiency in mice.

Rationale: Chlorine gas (Cl) is a potent oxidant and trigger of irritant induced asthma. We explored NF-E2-related factor 2 (Nrf2)-dependent mechanisms in the asthmatic response to Cl, using Nrf2-deficient mice, buthionine sulfoximine (BSO), an inhibitor of glutathione (GSH) synthesis and sulforaphane (SFN), a phytochemical regulator of Nrf2.

Methods: Airway inflammation and airway hyperresponsiveness (AHR) were assessed 24 and 48h after a 5-min nose-only exposure to 100ppm Cl of Nrf2-deficient and wild type Balb/C mice treated with BSO or SFN. Animals were anesthetized, paralyzed and mechanically ventilated (FlexiVent™) and challenged with aerosolized methacholine. Bronchoalveolar lavage (BAL) was performed and lung tissues were harvested for assessment of gene expression.

Results: Cl exposure induced a robust AHR and an intense neutrophilic inflammation that, although similar in Nrf2-deficient mice and wild-type mice at 24h after Cl exposure, were significantly greater at 48h post exposure in Nrf2-deficient mice. Lung GSH and mRNA for Nrf2-dependent phase II enzymes (NQO-1 and GPX2) were significantly lower in Nrf2-deficient than wild-type mice after Cl exposure. BSO reduced GSH levels and promoted Cl-induced airway inflammation in wild-type mice, but not in Nrf2-deficient mice, whereas SFN suppressed Cl-induced airway inflammation in wild-type but not in Nrf2-deficient mice. AHR was not affected by either BSO or SFN at 48h post Cl exposure.

Conclusions: Nrf2-dependent phase II enzymes play a role in the resolution of airway inflammation and AHR after Cl exposure. Moderate deficiency of GSH affects the magnitude of acute inflammation but not AHR.