Immunoglobulin M, C-Reactive Protein and Complement Activation in Rat Hepatic Ischemia-Reperfusion Injury

Abstract

Background: Ischemia-reperfusion (I/R) models have shown that C-reactive protein (CRP) and immunoglobulin M (IgM) are involved in complement activation. Binding of CRP and IgM to damaged cell membranes initiates complement activation and aggravates I/R injury in various organs. However, the time course of CRP- and IgM-mediated complement activation and the relation to hepatocellular injury and inflammation in liver I/R are unknown. Aim: To evaluate the time course of IgM- and CRP-related complement activation and the relation to hepatocellular injury and inflammation in a hepatic I/R rat model. Methods: Male Wistar rats were allocated to (1) five groups of animals exposed to 60 min of partial ischemia (70%) induced via clamping of the left segmental portal triad, followed by 0, 3, 6, 12 or 24 h of reperfusion (n = 6 in each group); (2) five groups of sham-operated animals with corresponding reperfusion times (n = 5), and (3) a control group sacrificed before ischemia (n = 5). Hepatocellular injury, inflammatory response, rat plasma CRP and IgM levels and immunohistochemical depositions of CRP, IgM and C3 were assessed for each group. Results: Histopathological injury scores of hematoxylin and eosin sections of ischemic liver lobes demonstrated increasing values throughout the reperfusion time with a peak at 12 h. Plasma aminotransferases (alanine aminotransferase and aspartate aminotransferase) significantly increased after 3 h of reperfusion, peaking at 6 h (3,100 ± 800 U/l; p < 0.05). Hepatic neutrophil influx significantly increased from 3 to 6 h of reperfusion (p < 0.05) and demonstrated the highest value at 12 h (1.1 ± 0.2 U/mg of protein). Plasma IL-6 levels in the ischemia groups showed peak values after 6 h of reperfusion, decreasing significantly thereafter (p < 0.05). Plasma CRP values reached highest levels after 3 h of reperfusion (mean 91 ± 5% of control pool), decreasing significantly thereafter. Rat IgM concentrations in plasma did not significantly change throughout the reperfusion time. Immunohistochemical depositions of IgM, CRP and C3 in ischemic lobes demonstrated a similar pattern in time, reaching maximum values at 12 h of reperfusion. The percentages of depositions of CRP and IgM were significantly correlated [r(S) = 0.569; p < 0.001; Spearman test]. The time course of C3 and CRP depositions throughout reperfusion and C3 and IgM staining were significantly similar [r(S) = 0.797 and r(S) = 0.656, respectively; p < 0.0001; ANOVA]. Conclusions: CRP and IgM depositions demonstrate a parallel time course throughout the reperfusion to hepatocellular damage, inflammatory response and activated complement deposition in this rat hepatic I/R model. Furthermore, the time course of CRP and IgM depositions was significantly similar to that of activated complement depositions.