Subanesthetic Dose Of Isoflurane Protects Against Zymosan-induced Generalized Inflammation And Its Associated Acute Lung Injury In Mice.

BackgroundMultiple organ dysfunction syndrome (MODS) is one of the leading causes of death in the intensive care unit (ICU). Lung is frequently the first failing organ during the development of MODS. Volatile anesthetic isoflurane (ISO) is one of the most widely used anesthetic agents, and ISO anesthesia has been reported to improve the survival rate and organ function in sepsis/MODS models. It is reported that ISO, at anesthetic concentration ranging from 1.2% to 2.5%, reduces inflammatory cytokines and protects against sepsis and organ injuries including lung injury [3-9]. However, anesthetic dose of ISO is limited to be applied to critically ill patients who may not tolerate the hemodynamic effects of anesthesia including vasodilation, myocardial depression, and bradycardia[9].PurposeThe present study was designed to investigate the effects of ISO at subanesthetic dose (0.7%, 0.5 MAC) on ZY-induced generalized inflammationand its associated lung injury in mice and the roles of antioxidant enzymes in the effects.Methods1. Effects of 0.7% ISO treatment on the survival rate in ZY-challenged mice.One hundred and sixty animals were randomly divided into eight groups (n=20 per group): NS, NS + PT, NS + 0.7% ISO, NS + 1.4% ISO, ZY, ZY + PT, ZY + 0.7% ISO, and ZY + 1.4% ISO groups. Generalized inflammation wasinduced in all the animals of ZY, ZY + PT, ZY + 0.7% ISO, and ZY + 1.4% ISOgroups. The animals from the other four groups were given the same volume ofNS as the control. Isoflurane treatment was performed in the NS + 0.7% ISO, NS+ 1.4% ISO, ZY + 0.7% ISO, and ZY + 1.4% ISO groups, with the animalsexposed to 0.7% or 1.4% ISO for 1 h starting at 1 and 6 h after the NS or ZYinjection, respectively. As a control, the animals from NS + PT and ZY + PTgroups were given an aseptic i.p. injection of PT (12.5 mg/kg) at 1 and 6 h afterthe NS or ZY injection, respectively. The survival rate was observed on days 1, 2,3 and 7 after the NS or ZY administration (Fig. 1).To study the effects of 0.7% ISO treatment on ZY-induced lung injury,additional animals were used to observe lung myeloperoxidase (MPO) activity (n= 6 per group), lung wet/dry (W/D) weight ratio (n = 6 per group), proteinconcentration in bronchoalveolar lavage fluid (BALF; n = 6 per group), serumand lung tissue proinflammatory cytokine TNF-α(n = 6 per group) and lunghistopathology (n = 6 per group) at 24 h after the NS or ZY injection. Thegrouping method and experimental protocols were the same as it was describedabove.2. Effects of 0.7% ISO treatment on oxidant and antioxidant system inZY-challenged miceAdditional animals were used in this study. The grouping method and experimental protocols were the same as it was described above. According toour previous experiments (14), serum and lung tissue antioxidant enzymesuperoxide dismutase (SOD) (n = 6 per group), catalase (CAT) (n = 6 per group),and oxidation product 8-iso-prostaglandin F2α(8-iso-PGF2α) (n = 6 per group)were detected at 24 h after the NS or ZY injection.To investigate the effects of CAT activity antagonist 3-amino-1,2,4-triazole(AT; Sigma-Aldrich Co, St Louis, Mo) on the protection of ISO treatment againstZY-induced generalized inflammation, animals were randomly divided into fourgroups (n = 20 per group): ZY, ZY + 0.7% ISO, ZY + 0.7% ISO + 0.09 g/kg AT,and ZY + 0.09 g/kg AT groups. Generalized inflammation was induced in allanimals. Isoflurane treatment was performed in the ZY + 0.7% ISO and ZY +0.7% ISO + 0.09 g/kg AT groups with animals exposed to 0.7% (0.5 MAC) ISOfor 1 h starting at 1 and 6 h after the ZY injection, respectively. In the ZY + 0.7%ISO + 0.09 g/kg AT and ZY + 0.09 g/kg AT groups, animals wereintraperitoneally administered with 0.09 g/kg AT. In the animals of ZY + 0.7%ISO + 0.09 g/kg AT groups, an i.p. injection of AT was performed before 0.7%ISO inhalation, which was repeated before the second 0.7% ISO inhalation (16). In the ZY + 0.09 g/kg AT group, AT was given at the same time points as that in the ZY + 0.7% ISO + 0.09 g/kg group. The survival rate was observed on days 1, 2, 3 and 7 after the NS or ZY administration.ResultsCompared with i.v. anesthetic pentobarbital treatment, we showed that twiceinhalation of ISO at subanesthetic dose (0.7%, 0.5 minimum alveolarconcentration) alleviated lung injury at 24 h after zymosan (ZY) injection andincreased the 7-day survival rate from 10% to 45% in mice. We also showed thatISO exerted its protection by significantly improving the activities of superoxide dismutase and catalase in lung and serum when compared with those inpentobarbital-treated mice. The catalase inhibitor 3-amino-1, 2, 4-triazolepartially abolished the protective effect of ISO in ZY-challenged mice.ConclusionsWe conclude that subanesthetic dose ISO protects against ZY-induced generalized inflammation and its associated lung injury via enhancing the activities of antioxidant enzymes in mice, which may provide a new strategy for the treatment of critically ill patients.