LIPOCALIN-2 IS A MAJOR ACUTE-PHASE PROTEIN IN A RAT AND MOUSE MODEL OF STERILE ABSCESS

Lipocalin-2 (LCN-2) is a 25-kDa secretory protein currently used as a biomarker for renal injury and inflammation. Its source and cause of the increased serum levels are unclear. The current study compares LCN-2 gene expression with known major acute-phase proteins in the liver in a rat and mouse model of turpentine oil-induced sterile abscess. Serum LCN-2 concentrations increased dramatically up to 200-fold (20 mu g/mL) at 48 h after turpentine oil injection. A strong elevation of LCN-2 mRNA in rat liver was observed starting from 4 h up to 48 h after injection, with a maximum (8,738 +/- 2,104-fold) at 24 h, which was further confirmed by Western blot analysis. In contrast, the increases in gene expression of alpha 2-macroglobulin, the major acute-phase protein, and hemoxygenase 1, a positive acute-phase protein, were only 1,025 +/- 505-fold and 47 +/- 12-fold, respectively, during acute-phase reaction (APR). No considerable change was observed in LCN-2 mRNA in rat kidney and other organs as compared with liver. Using wild-type mice, a massive increase in gene expression of LCN-2, with a maximum of 2,498 +/- 84-fold in liver, which is similar to that for serum amyloid A (2,825 +/- 233-fold), a major mouse acute-phase protein. However, such an increase was significantly inhibited in interleukin 6 knockout mice during APR. Interleukin 6-treated rat hepatocytes induced a significant time-dependent upregulation of LCN-2. Lipocalin-2 is the major acute-phase protein in rat as compared with alpha 2-macroglobulin and hemoxygenase 1 and comparable with serum amyloid A in mouse whose gene expression is mainly controlled by interleukin 6. The liver is the main source of serum LCN-2 in the case of APR.