Targeting caspase-1 by inhalation-therapy:: effects of Ac-YVAD-CHO on IL-1β, IL-18 and downstream proinflammatory parameters as detected in rat endotoxaemia

Objective: We set out to investigate whether the nebulized and inhaled specific caspase-1 inhibitor Ac-YVAD-CHO has the potential to attenuate the pulmonary and systemic release of the caspase-1-dependent cytokines interleukin-1 beta (IL-1 beta) and interleukin-18 (IL-18) as well as their downstream enzymes iNOS and COX-2 in rat experimental endotoxaemia. Design and setting: Controlled, randomized animal study in a university research facility. Subject: Male Sprague-Dawley rats (n = 32) were randomly treated as follows: Inhaled Ac-YVAD-CHO was administered in eight rats at a inhaled total dosage of 5 mg and in eight rats at a inhaled total dose of 0.5 mg before infusion of lipopolysaccharide (LPS; 5 mg/kg, i.v.). Eight animals received LPS only. Eight animals served as controls without endotoxaemia. Measurements and results: After 4 h of endotoxaemia, levels of IL-1 beta, IL-18 and TNF-alpha in plasma and bronchoalveolar fluid (BALF) were analyzed. Nitric oxide (NO) release from alveolar macrophages was measured by Griess assay. Amounts of iNOS protein in alveolar macrophages and COX-2 protein in lung homogenates were determined by Western blotting. Significant reductions in release of IL-1 beta (-58%, p < 0.05) and IL-18 (-51%, p < 0.05) in plasma and IL-1 beta (-59%, p < 0.05) in BALF were found in animals pretreated with inhaled caspase-1 inhibitor compared with animals without therapy. Expression of iNOS in alveolar macrophages and COX-2in lung tissue was concurrently decreased in the treatment groups compared with control animals. Conclusions: Our data demonstrate that administration of the caspase-1 inhibitor Ac-YVAD-CHO by inhalation is able to reduce the pulmonary and systemic release of proinflammatory mediators in rat endotoxaemia. These results further underscore that inhalation may constitute an effective route of anti-inflammatory drug administration, beneficial in the clinical setting of ARDS.