Effects of mild hypothermia on the expression of high mobility group protein B1 in lung tissues of septic mice / 中国综合临床

ABSTRACT

Objective:To investigate the effects of naturally occurring mild hypothermia and artificial mild hypothermia on the expression of high mobility group box 1(HMGB1) in lung tissues of septic mice.Methods:One hundred and twenty BALB/C mice (SPF level) were randomly numbered.Twelve mice with integer multiples of 10 were used as the normal control (NC) group, and the remaining 108 mice were chosen as the septic group.The septic mouse model was established by intra abdominal injection of lipopolysaccharide (LPS) 10 mg/kg.The NC group was given the same dose of normal saline.Anal temperature of the septic mice were measured 1 hour after the model was established successfully, and then were divided into naturally occurring mild hypothermia group and non-mild hypothermia group according to T≤36℃ and T>36℃.In the naturally occurring mild hypothermia group, the mice with T<34℃ were eliminated, and the remaining septic mice were randomly divided into the naturally occurring mild hypothermia(NOMH) observation group and the keep normothermia (KN) group.NOMH group was not given preheating intervention, while KN group was placed in an incubator to maintain the anal temperature between 36.0℃ and 37.5℃.Septic mice in the non-mild hypothermia group were randomly divided into the nonhypothermia (NH) observation group and the artificial mild hypothermia (ATMH) group.The NH group was not treated with hypothermia, while the ATMH group was treated with physical hypothermia, so that the anal temperature of the mice were maintained at 34℃-36℃.Four mice in each group were randomly selected at 6 and 12 hours after modeling, and the concentrations of tumor necrosis factor-α(TNF-α), interleukin-6(IL-6) and HMGB1 in serum were detected by enzyme-linked immunosorbent assay(ELISA). At 12 hours, the survival rate of each group of mice was observed.Then 4 mice of each group were sacrificed and lung tissues were taken.The pathological changes of lung tissues were observed by hematoxylin-eosin (HE) staining, and the expression of HMGB1 in lung tissues was observed by immunohistochemical staining.Real time fluorescence quantitative PCR and Western blot were used to detect the relative expression of HMGB1 at mRNA and protein levels.Results:(1)Twelve hours after modeling, the survival number of NOMH group, ATMH group, KN group and NH group were 36(40), 6(11), 27(40), 4(11), respectively, and there were differences between the four groups (χ 2=32.286, P=0.002). Compared with the other three groups of septic mice, the survival rate was highest in the NOMH group (compared with ATMH group χ 2=5.222, P=0.022; compared with the KN group χ 2=6.050, P=0.013; and the NH group χ 2=11.672, P=0.001), but the differences between the other two groups were not statistically significant (all P>0.05). (2)Compared with the NC group, the concentrations of serum TNF-α, IL-6 and HMGB1 of septic mice in each group were significantly increased at 6 h and 12 h (all P<0.05). Compared with NOMH group, the concentrations of TNF-α, IL-6 and HMGB1 in ATMH group, KN group and NH group were significantly increased at 6 h and 12 h(all P<0.05), and the concentrations of TNF-α, IL-6 and HMGB1 in NH group were the highest at all time points (all P<0.05). The concentrations of TNF-α at 12 h decreased compared with 6 h (all P<0.05), while the concentrations of IL-6 and HMGB1 at 12 h increased compared with 6 h (all P<0.05). (3)HE staining showed that the lung tissue damage were minimal in NOMH group, followed by ATMH group.(4)Immunohistochemical staining showed that the expression of HMGB1 protein was in order of NOMH group, ATMH group, KN group and NH group; (5)The relative expressions of HMGB1 protein in lung tissues of septic mice in NOMH group, ATMH group, KN group, and NH group was 0.280±0.013, 0.320±0.016, 0.340±0.018, and 0.380±0.014, respectively, and the relative expression level of HMGB1 mRNA was 4.86±0.22, 6.02±0.18, 6.26±0.20, and 7.98±0.28, respectively, compared with NC group (HMGB1 protein content was 0.240±0.013, and the relative expression level of HMGB1 mRNA was 2.21±0.12) significantly increased (all P<0.05). Cmpared with NOMH group, the relative expression levels of HMGB1 protein and HMGB1 mRNA in the lung tissues of the ATMH group, KN group and NH group were significantly increased(all P<0.05), with the highest expression level in the NH group(all P<0.05). Conclusion:Mild hypothermia may reduce lung tissue damage by down-regulating the expression of HMGB1 in lung tissues of septic mice, and the improvement of spontaneous mild hypothermia was more significant.