Objective To investigate the effects of total flavonoid fraction (TFF) from Nervilia fordii on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in rats, and to explore their protective mechanism. Methods LPS-induced ALI model was established by LPS (5 mg/kg) injection via left cervical vein. Blood samples were collected from the cervical artery of all rats at 5 and 6 h after LPS challenge for arterial blood gas test and cytokines measurements, and pulmonary microvascular permeability

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... P), lung wet/dry weight ratio (W/D), and pathological features were observed. Results Phytochemical study showed that the TFF contained 67.3% of flavonoids expressed in rutin and three flavone glycosides. The TFF pretreatment (6.24 and 12.48 mg/kg) attenuated the partial arterial pressure of oxygen decline in blood significantly, and decreased the PMP and lung W/D in ALI rats. In addition, the TFF (6.24 and 12.48 mg/kg) also ameliorated the LPS-induced lung damages including alveolar edema, neutrophils infiltration, alveolar hemorrhage, and thickening of the alveolar wall. Furthermore, the treatment with the TFF (6.24 and 12.48 mg/kg) also down-regulated the levels of pro-inflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and intercellular adhesion molecule-1 (ICAM-1), and up-regulated the level of anti-inflammatory cytokine IL-10 in serum of ALI rats simultaneously. Conclusion These results suggest that the TFF could protect LPS-induced ALI in rats, which may be mediated, at least in part, by adjusting the production of inflammatory cytokines including TNF-α, IL-6, ICAM-1, and IL-10.