Platycodin D attenuates acute lung injury by suppressing apoptosis and inflammation in vivo and in vitro

Platycodin D (PLD) is the major triterpene saponin in the root of Platycodon grandiflorum (Jacq.) with various pharmacological activities. The purpose of the present study was to evaluate the protective effects and possible mechanisms of PLD on acute lung injury (ALI) both in vivo and in vitro. In vivo, we used two ALI models, lipopolysaccharide (LPS)-induced ALI and bleomycin (BLE)-induced ALI to evaluate the protective effects and possible mechanisms of PLD. Female BALB/c mice were randomly divided into the following groups: control group, LPS group, LPS plus pre-treatment with dexamethasone (2 mg/kg) group, LPS plus pre-treatment with PLD groups (50 mg/kg, 100 mg/kg), LPS plus post-treatment with dexamethasone (2 mg/kg) group, LPS plus post-treatment with PLD groups (50 mg/kg, 100 mg/kg), BLE group, BLE plus pre-treatment with dexamethasone (2 mg/kg) group, BLE plus pre-treatment with PLD groups (50 mg/kg, 100 mg/kg), BLE plus post-treatment with dexamethasone (2 mg/kg) group, and BLE plus post-treatment with PLD groups (50 mg/kg, 100 mg/kg). PLD was orally administered before or after LPS or BLE challenge with mice. Mice were sacrificed, and lung tissues and bronchoalveolar fluid (BALF) were prepared for further analysis. Our results showed that PLD significantly decreased lung wet-to-dry weight ratio (lung W/D weight ratio), total leukocyte number and neutrophil percentage in the BALF, and myeloperoxidase (MPO) activity of lung in a dose-dependent manner. Besides, cytokine levels, including interleukin (IL)-6, tumor neurosis factor (TNF)-α were also found significantly inhibited in BALF. Furthermore, PLD effectively inhibited the expressions of nuclear factor κB (NF-κB), Caspase-3 and Bax in the lung tissues, as well as restored the expression of Bcl-2 in the lungs and improved the superoxide dismutase (SOD) activity in BALF. In vitro, we used LPS-challenged cell model to evaluate the protective effects and possible mechanisms of PLD. MLE-12 cells were stimulated with LPS in the presence and absence of PLD. The levels of TNF-α, IL-6 and the expressions of NF-κB, Caspase-3, and Bax were remarkably down-regulated, while the expression of bcl-2 was significantly up-regulated in PLD treatment groups in MLE-12 cells. These results showed that the administration of PLD improved ALI both in vivo and in vitro, possibly through suppressing apoptosis and inflammation.