Thrombin and Protease-Activated Receptor-1 Agonists Promote Lipopolysaccharide-Induced Hepatocellular Injury in Perfused Livers

Abstract

Bacterial lipopolysaccharide (LPS) is a potent inflammatory agent capable of producing liver injury, the pathogenesis of which depends on numerous mediators, including thrombin. Previous studies showed that thrombin promotes LPS-induced liver injury independent of its ability to form fibrin clots. In isolated, buffer-perfused livers from LPS-treated rats, thrombin added to the perfusion buffer caused dose-dependent liver injury with an EC 50 value of 0.4 nM, consistent with activation by thrombin of a protease-activated receptor (PAR). Actions of thrombin at PARs can be mimicked by thrombin receptoractivating peptides (TRAPs). TRAPs for PAR-1 reproduced the injury caused by thrombin in isolated livers, suggesting that one mechanism by which thrombin promotes LPS-induced liver injury is by activating PAR-1. Immunocytochemistry demonstrated the presence of PAR-1 on sinusoidal endothelial cells and Kupffer cells but not on parenchymal cells or neutrophils. Previous studies showed that thrombin interacts with neutrophils in the genesis of liver injury after LPS treatment. To explore this interaction further, the influence of thrombin on mediators that modulate neutrophil function were evaluated. Inhibition of thrombin in LPS-treated rats prevented liver injury but did not prevent up-regulation of cytokine-induced neutrophil chemoattractant-1, macrophage inflammatory protein-2, or intercellular adhesion molecule-1. Thrombin inhibition did, however, prevent neutrophil (PMN) degranulation in vivo as measured by plasma elastase levels. In addition, elastase concentration was increased in the perfusion medium of livers isolated from LPS-treated rats and perfused with TRAPs. These results suggest that activation of PAR-1 after LPS exposure promotes PMN activation and hepatic parenchymal cell injury.

A role for proteinase-activated receptor–1 in inflammatory bowel diseases

“…In lung epithelial cells, PAR 1 agonists stimulate the release of proinflammatory cytokines (IL-6 and IL-8) (8). In vivo, PAR 1 agonists can induce inflammation when injected into the paw, the liver, or the brain of rodents (9)(10)(11)(12).…”

Inflammatory Stress and Idiosyncratic Hepatotoxicity: Hints from Animal Models

“…Perfusion of livers from LPS-treated rats with thrombin or a PAR-1 agonist caused hepatocellular injury in a PMN-dependent manner (Moulin et al, 2001;Copple et al, 2003). Moreover, thrombin inhibition impaired PMN activation in LPStreated rats (Pearson et al, 1996a,b;Copple et al, 2003). These results suggest that thrombin activation of PAR-1 is important for PMN activation in endotoxemia and that both of these events are sufficient for causing inflammatory liver injury in rats given a large, hepatotoxic dose of LPS.…”

“…Indeed, thrombin activation of the tethered-ligand receptor, protease activated receptor-1 (PAR-1), seems to play a critical role in LPS-induced liver injury. Perfusion of livers from LPS-treated rats with thrombin or a PAR-1 agonist caused hepatocellular injury in a PMN-dependent manner (Moulin et al, 2001;Copple et al, 2003). Moreover, thrombin inhibition impaired PMN activation in LPStreated rats (Pearson et al, 1996a,b;Copple et al, 2003).…”

Coagulation-Mediated Hypoxia and Neutrophil-Dependent Hepatic Injury in Rats Given Lipopolysaccharide and Ranitidine

“…This could occur in several ways. For example, thrombin contributes to PMN activation by activating protease-activated receptor-1 (PAR-1) in rats treated with a large dose of LPS (Copple et al, 2003). This receptor is expressed by Kupffer cells, sinusoidal endothelial cells, and hepatic stellate cells but not by rat PMNs (Copple et al, Fig.…”

“…In some of these models, tissue PMN accumulation and/or activation depends on the coagulation system. For example, in the case of large, hepatotoxic doses of LPS, coagulation system activation is required for activation of PMNs and hepatotoxicity, but it is not important for up-regulation of the PMN chemokine, cytokine-induced neutrophil chemoattractant-1 (CINC-1) (Copple et al, 2003). In contrast, coagulation system activation is required for CINC-1 production and liver PMN accumulation in ischemia-reperfusion-induced liver damage (Yamaguchi et al, 1997).…”