Induction of chemokines and cytokines before neutrophils and macrophage recruitment in different regions of rat liver after TAA administration

Single-dose thioacetamide (TAA) administration induces inflammation and acute liver damage. The mechanism of inflammatory cell recruitment in the liver is still unclear. The aim of this study was to examine the sequence and recruitment of inflammatory cells in different liver regions in relation to CXC- and CC-chemokine and cytokine expression during acute liver injury. Single-dose TAA was administered to rats intraperitoneally, and animals were killed at different time points thereafter. Serum and liver tissue were taken and frozen immediately. Tissue was used for immunostaining cryostat sections, RNA, and protein extraction. RT-PCR and western blotting were performed for RNA and protein analysis, respectively. An early increase (3 h) in CXCL8/IL-8 levels was measured followed by a marked release in MCP1/CCL2 (24h) serum levels after TAA administration compared with controls. Similarly, an early increase in specific RNA of hepatic chemokines CXCL1/KC and CXCL8/IL-8 was found at 3 h, followed by an upregulation of CXCL5/LIX (6 h), CXCL2/MIP-2 (12 h), and MCP1/CCL2 gene expression at 24-48 h. Further, an induction of pro-inflammatory cytokines IFN-gamma and IL-1 beta followed by IL-6 and TNF-alpha was observed with a maximum at 12 h. The magnitude of increase in gene expression of TNF-alpha and MCP1/CCL2 was the highest among all cytokines and chemokines, respectively. By means of immunohistochemistry, an early (12-24 h) increase in the number of only neutrophil granulocytes (NGs) attached to and around portal vessel walls was observed, followed by increased numbers of mononuclear phagocytes (24-48 h) along the sinusoids. Treatment of the human monocytic cell line U-937 with TNF-alpha increased the gene expression of CXCL1/KC, CXCL8/IL-8, and MCP1/CCL2. Conversely, adding of infliximab (IFX) to the culture medium inhibited this upregulation significantly. In conclusion, single-dose TAA administration induces a sequence of events with a defined upregulation of gene expression of inflammatory chemokines and cytokines and a transient accumulation of NGs within the portal area and macrophages along the sinusoids throughout the liver. Periportal inflammation seems to precede hepatocellular damage.