Lipopolysaccharide “two-hit” induced refractory hypoxemia acute respiratory distress model in rats

Abstract

To establish a stable and reliable model of refractory hypoxemia acute respiratory distress syndrome (ARDS) and examine its pathological mechanisms, a total of 144 healthy male Wistar rats were randomized into 4 groups: group I (saline control group), group II (LPS intravenous “single-hit” group), group III (LPS intratracheal “single-hit” group) and Group IV (LPS “two-hit” group). Rats were intravenously injected or intratracheally instilled with a large dose of LPS (10 mg/kg in 0.5 mL) to simulate a single attack of ARDS, or intraperitoneally injected with a small dose of LPS (1 mg/kg) followed by tracheal instillation with median dose of LPS (5 mg/kg) to establish a “two-hit” model. Rats in each group were monitored by arterial blood gas analysis and visual inspection for three consecutive days. Arterial blood gas values, lung wet/dry weight ratio and pathological pulmonary changes were analyzed to determine the effects of each ALI/ARDS model. Concentrations of TNF-α, IL-1 and IL-10 in the bronchoalveolar lavage fluid (BALF) and blood plasma were measured by using enzyme-linked immunosorbent assays (ELISA). Our resulsts showed that single LPS-stimulation, whether through intravenous injection or tracheal instillation, could only induce ALI and temporary hypoxemia in rats. A two-hit LPS stimulation induces prolonged hypoxemia and specific pulmonary injury in rats, and is therefore a more ideal approximation of ARDS in the animal model. The pathogenesis of LPS two-hit-induced ARDS is associated with an uncontrolled systemic inflammatory response and inflammatory injury. It is concluded that the rat ARDS model produced by our LPS two-hit method is more stable and reliable than previous models, and closer to the diagnostic criteria of ARDS, and better mimics the pathological process of ARDS.

Keywords

acute respiratory distress syndrome (ARDS) / acute lung injury (ALI) / lipopolysaccharide (LPS) / rat / animal model / systemic inflammatory response syndrome (SIRS) / tumor necrosis factor-α (TNF-α) / IL-1 / IL-10

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