Objective: To study the new mechanism of Xuebijing injection improving the function of pulmonary vascular barrier from the perspective of claudin-5 protein.
Methods: Acute lung injury (ALI) model was induced by hydrogen sulfide (H2S) exposure. (1) In vivo study: Sprague-Dawley (SD) rats were divided into control group, H2S exposure group (exposure to 300×10-6 H2S for 3 hours), Xuebijing control group (Xuebijing injection 4 mL/kg , twice a day, for 3 days), and Xuebijing intervention group (H2S exposure after pretreatment of Xuebijing injection) according to random number method, with 6 rats in each group. At different time points (0, 6, 12 and 24 hours) after the model was made successfully, the total protein content in plasma and bronchoalveolar lavage fluid (BALF) of rats were detected respectively, and the pulmonary permeability index (PPI) was calculated (PPI = protein content in BALF/protein content in plasma), lung dry/wet weight ratio (W/D) was detected, and claudin-5 mRNA expression in lung tissue was measured by real time-polymerase chain reaction. (2) In vitro test: human pulmonary microvascular endothelial cells (HPMECs) were divided into blank control group, NaHS treatment group (co-incubated with 500 μmol/L NaHS for 12 hours), Xuebijing control group (2 g/L Xuebijing injection for 24 hours), and Xuebijing intervention group (2 g/L Xuebijing injection pre-treated for 24 hours, then co-incubated with 500 μmol/L NaHS for 12 hours). The HPMECs claudin-5 protein expression and monolayer permeability changes were measured at different co-incubation time (1, 3, 6, 12 and 24 hours) by Western Blot and fluoresceinsodium.
Results: (1) In vivo study: compared with the control group, the lung W/D ratio increased significantly at 6 hours and peaked at 12 hours after H2S exposure in rats (4.67±0.11 vs. 4.26±0.06, P < 0.01). The expression of claudin-5 mRNA in lung tissue was significantly decreased, which was 89% of control group 6 hours after exposure (P < 0.01). The total protein content in BALF and PPI at 12 hours after exposure were significantly higher than those in the control group [total protein content (mg/L): 262.31±14.24 vs. 33.30±3.09, PPI: (11.72±0.57)×10-3 vs. (1.21±0.08)×10-3, both P < 0.01], while the results in Xuebijing intervention group were significantly decreased [total protein content (mg/L): 153.25±7.32 vs. 262.31±14.24, PPI: (5.79±0.23)×10-3 vs. (11.72±0.57)×10-3, both P < 0.01]. (2) In vitro test: compared with the blank control group, after incubating HPMECs with NaHS, the permeability of monolayer endothelial cells gradually increased, reaching the highest level in 12 hours, about twice of that in the blank control group, while claudin-5 protein expression decreased to the lowest level at 12 hours (claudin-5/β-actin: 0.42±0.03 vs. 1.03±0.05, P < 0.01). After intervention with Xuebijing, the permeability of endothelial cells was significantly improved (fluorescence intensity of fluorescein sodium: 1.46±0.10 vs. 1.89±0.11, P < 0.01), and the decrease of claudin-5 protein was reduced (claudin-5/β-actin: 0.68±0.04 vs. 0.38±0.03, P < 0.01).
Conclusions: Xuebijing injection may improve pulmonary vascular barrier function in ALI by upregulating claudin-5 expression.