Lipocalin-2 Test in Distinguishing Acute Lung Injury Cases from Septic Mice Without Acute Lung Injury

Objective To explore whether the amount of lipocalin-2 in the biofluid could reflect the onset of sepsis-induced acute lung injury(ALI) in mice. Methods Lipopolysaccharide(LPS, 10 mg/kg) injection or cecal ligation and puncture(CLP) was performed to induce severe sepsis and ALI in C57 BL/6 male mice randomly divided into 5 groups(n=10 in each group): group A(intraperitoneal LPS injection), group B(intravenous LPS injection via tail vein), group C(CLP with 25% of the cecum ligated), group D(CLP with 75% of the cecum ligated), and the control group(6 sham-operation controls plus 4 saline controls). All the mice received volume resuscitation. Measurements of pulmonary morphological and functional alterations were used to identify the presence of experimental ALI. The expressions of lipocalin-2 and interleukin(IL)-6 in serum, bronchoalveolar lavage fluid(BALF), and lung tissue were quantified at both protein and mRNA levels. The overall abilities of lipocalin-2 and IL-6 tests to diagnose sepsis-induced ALI were evaluated by generating receiver operator characteristic curves(ROC) and computing area under curve(AUC). Results In both group B and group D, most of the "main features" of experimental ALI were reproduced in mice, while group A and group C showed septic syndrome without definite evidence for the presence of ALI. Compared with septic mice without ALI(group A+group C), lipocalin-2 protein expression in septic mice with ALI(group B+group D) was significantly up-regulated in BALF(P<0.01) and in serum(P<0.01), and mRNA expression boosted in lung tissues(all P<0.05). Lipocalin-2 tests performed better than IL-6 tests in recognizing sepsis-induced ALI cases, evidenced by the larger AUC of the former(BALF tests, 0.8800 versus 0.6625; serum tests, 0.8500 versus 0.7000). Using a dual cutoff system to diagnose sepsis-induced ALI, BALF lipocalin-2 test exhibited the highest positive likelihood ratio(13.000) and the lowest negative likelihood ratio(0.077) among the tests of lipocalin-2 and IL-6 in blood and BALF. A statistically significant correlation was found between lipocalin-2 concentration in BALF and that in serum(Spearman r=0.8803,P<0.0001). Conclusions Lipocalin-2 expression is significantly up-regulated in septic ALI mice compared with those without ALI. Lipocalin-2 tests with a dual cutoff system could be an effective tool in distinguishing experimental ALI cases.

Lipopolysaccharide Challenge Induces Long Pentraxin 3 Expression in Mice Independently from Acute Lung Injury

Objective To determine whether the onset of acute lung injury （ALl） induces the up-regulation of pentraxin 3 （PTX3） expression in mice and whether PTX3 concentration in the biofluid can help recognizing sepsis-induced ALI. Methods Wild-type C57BL/6 mice （12-14 weeks old） were randomly divided into 3 groups. Mice in the group 1 （n=12） and group 2 （n=12） were instilled with lipopolysaccharide via intratracheal or intraperitoneal routes, respectively. Mice in the group 3 （n=8） were taken as blank controls. Pulmonary morphological and functional alterations were measured to determine the presence of experimental ALl. PTX3 expression in the lung was quantified at both protein and mRNA levels. PTX3 protein concentration in blood and bronchoalveolar lavage fluid was measured to evaluate its ability to diagnose sepsis-induced ALI by computing area under receiver operator characteristic curve （AUROCC）. Results ALl was commonly confirmed in the group 1 but never in the other groups. PTX3 expression was up-regulated indiscriminately among lipopolysaccharide-challenged mice. PTX3 protein concentration in the biofluid was unable to diagnose sepsis-induced ALl evidenced by its small AUROCC. PTX3 concentration in bronchoalveolar lavage fluid did not correlate with that in serum. Conclusions Lipopolysaccharide challenges induced PTX3 expression in mice regardless of the presence ofALI. PTX3 may act as an indicator of inflammatory response instead of organ injury per se.