Propofol reduces acute lung injury by up-regulating gamma-aminobutyric acid type a receptors

Background: We used a two-hit lung injury rat model that involves mechanical ventilation (MV) following lipopolysaccharide exposure to investigate the effects of propofol on the expression of GABAA receptors (GABA(A)R) and cytokine responses, and we then determined the specific effects of GABA on cytokine responses in vitro in alveolar epithelial cells (AECs). Methods: Forty-eight adult male Wister rats were equally and randomly divided into the following 4 groups (n = 12) using a random number table: sham group, sham + propofol group, lipopolysaccharide (LPS) + VILI group, and LPS + VILI + propofol group. All animals were anesthetized, and the animals received a 3.75 mg/kg intratracheal instillation of endotoxins or phosphate-buffered saline (PBS) as the control, as described previously. After 30 min, rats were ventilated for 5 h in a volume-controlled ventilation mode. In the LPS + VILI group, animals were ventilated with a tidal volume (Vt) of 22 ml/kg and zero positive end-expiratory pressure (PEEP) at a respiratory rate of 16-18 breaths/min, whereas control (sham) rats were ventilated with a Vt of 6 ml/kg and PEEP of 5 cmH(2)O at a rate of 45-55 breaths/min. The FiO(2) remained constant as 0.4, propofol was administered intravenously in the LPS + VILI + propofol and sham + propofol groups at a rate of 10 mg.kg(-1).h(-1) while normal saline at the same rate was intravenously administered in the LPS + VILI and sham groups during the entire mechanical ventilation period. Five hours after mechanical ventilation, the rats were killed. Survival rates, histopathology, concentrations of inflammatory mediators in bronchoalveolar lavage fluid (BALF), wet weight/dry weight (W/D) ratio of the lung, myeloperoxidase (MPO) activity in lung tissues, and expression of GAD and GABA(A)R by immunohistochemical detection and Western blotting were assessed. Then, human type II-like alveolar epithelial cells (A549 cells) were cultured to full confluence and incubated with GABA (100 nM) alone, picrotoxin alone, a GABA(A)R antagonist (PTX, 50 nM), or GABA + PTX for 10 min, followed by stimulation with LPS (control) at 100 ng/ml for 4 h. The concentrations of IL-1 beta, IL-2, IL-8, and IL-10 were then measured. Results: Administration of propofol in a two-hit lung injury rat model can increase survival rates and the expression of GAD and GABA(A)R (P<.05). The administration of propofol can attenuate the release of pro-inflammatory cytokines both in vivo and in vitro, and the administration of propofol can attenuate histopathological changes, the W/D ratio, and MPO activity (P<.05). Conclusions: In this study, we found that the administration of propofol improved lung function, alleviated lung injury, and up-regulated the GAD and GABA(A)R expressions in a two-hit model of acute lung injury (ALI) characterized by intratracheal instillation of an endotoxin and prolonged MV. Therefore, the protective effects of propofol may be associated with the up-regulation of GABA(A) receptors in AECs.