title: Lipocalin-2 test in distinguishing acute lung injury cases from septic mice without acute lung injury.
abstract: 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.
authors.affiliation: Department of Emergency,Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China.
authors.forename: Gao
authors.initials: G
authors.lastname: Zeng
authors.affiliation: Department of Pathology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China.
authors.forename: Cong-Wei
authors.initials: CW
authors.lastname: Jia
authors.affiliation: Department of Emergency,Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Emergency,Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China.
authors.forename: Shu-Bin
authors.initials: SB
authors.lastname: Guo
mesh_terms: D000209:Acute-Phase Proteins / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D001992:Bronchoalveolar Lavage Fluid; D017931:DNA Primers; D000071068:Lipocalin-2; D054834:Lipocalins / Q000378:metabolism*; D055370:Lung Injury / Q000150:complications / Q000175:diagnosis*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D015513:Oncogene Proteins / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D018805:Sepsis / Q000150:complications*
chemical_list: D000209:Acute-Phase Proteins; D017931:DNA Primers; D000071068:Lipocalin-2; D054834:Lipocalins; D015513:Oncogene Proteins; C071332:Lcn2 protein, mouse