To investigate the protective effects of different doses of ulinastatin on sepsis-induced lung injury in rats and their influence on the activation of the NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome.

Seventy-two Sprague Dawley rats were divided into a sham group, a sepsis group, a low-dose group, and a high-dose group, with 18 rats in each group. The sepsis, low-dose, and high-dose groups underwent cecal ligation and puncture (CLP) to establish a sepsis model, while the sham group underwent laparotomy without ligation. After modeling, rats in the low-dose and high-dose groups received intraperitoneal injections of ulinastatin (50 000 or 100 000 U/kg, respectively), whereas rats in the sham and sepsis groups received an equal volume of isotonic NaCl solution. Ten rats in each group were monitored for 7-day survival status. At 24 h post-modeling, the remaining eight rats in each group were euthanized for sample collection. Arterial blood was drawn from the abdominal aorta to measure the partial pressure of oxygen. Lung tissue was collected for histopathological examination (hematoxylin-eosin staining and injury scoring), for enzyme-linked immunosorbent assay (ELISA) to quantify interleukin-1 beta (IL-1β), IL-6 and tumor necrosis factor-alpha (TNF-α) levels, for western-blotting to assess NLRP3, caspase-1 and apoptosis-associated speck-like protein (ASC) expression, and for immunofluorescence to determine the percentage of NLRP3 positive cells.

There was a statistically significant difference in the 7-day survival status of rats among the four groups (Log-rank test: χ² = 7.727, P = 0.005). The 7-day survival status of the sepsis group was significantly worse than that of the low-dose and high-dose groups (both P < 0.05). The lung injury scores, arterial partial pressure of oxygen, levels of IL-1β, IL-6 and TNF-α in lung tissue, expression of NLRP3, caspase-1 and ASC proteins, and percentage of NLRP3 positive cells were compared among the four groups, and the differences were statistically significant (F = 30.691, 11.787, 13.042, 6.669, 18.953, 52.539, 46.265, 61.609, 39.339; all P < 0.05). Further pairwise comparisons revealed that compared with the sham group, the arterial partial pressure of oxygen in the sepsis group was significantly reduced, while the lung tissue injury score, levels of IL-1β, IL-6 and TNF-α, expression of NLRP3, caspase-1 and ASC proteins, and percentage of NLRP3 positive cells were significantly increased (all P < 0.05). Compared with the sepsis group, the arterial partial pressure of oxygen in the low-dose and high-dose groups increased significantly after administration of ulinastain, and the increase was more pronounced in the high-dose group (all P < 0.05). The lung tissue injury score, levels of IL-1β, IL-6 and TNF-α, expression of NLRP3, caspase-1 and ASC proteins, and percentage of NLRP3 positive cells were significantly lower in the low-dose and high-dose groups than in the sepsis group, with the high-dose group showing a more significant decrease (all P < 0.05).

Ustutidine may improve survival status and lung injury in septic rats by inhibiting the activation of NLRP3 inflammasome.