title: Macrophage activation by factors released from acetaminophen-injured hepatocytes: potential role of HMGB1.
abstract: Toxic doses of acetaminophen (AA) cause hepatocellular necrosis. Evidence suggests that activated macrophages contribute to the pathogenic process; however, the factors that activate these cells are unknown. In these studies, we assessed the role of mediators released from AA-injured hepatocytes in macrophage activation. Treatment of macrophages with conditioned medium (CM) collected 24hr after treatment of mouse hepatocytes with 5mM AA (CM-AA) resulted in increased production of reactive oxygen species (ROS). Macrophage expression of heme oxygenase-1 (HO-1) and catalase mRNA was also upregulated by CM-AA, as well as cyclooxygenase (COX)-2 and 12/15-lipoxygenase (LOX). CM-AA also upregulated expression of the proinflammatory chemokines, MIP-1α and MIP-2. The effects of CM-AA on expression of COX-2, MIP-1α and MIP-2 were inhibited by blockade of p44/42 MAP kinase, suggesting a biochemical mechanism mediating macrophage activation. Hepatocytes injured by AA were found to release HMGB1, a potent macrophage activator. This was inhibited by pretreatment of hepatocytes with ethyl pyruvate (EP), which blocks HMGB1 release. EP also blocked CM-AA induced ROS production and antioxidant expression, and reduced expression of COX-2, but not MIP-1α or MIP-2. These findings suggest that HMGB1 released by AA-injured hepatocytes contributes to macrophage activation. This is supported by our observation that expression of the HMGB1 receptor RAGE is upregulated in macrophages in response to CM-AA. These data indicate that AA-injured hepatocytes contribute to the inflammatory environment in the liver through the release of mediators such as HMGB1. Blocking HMGB1/RAGE may be a useful approach to limiting classical macrophage activation and AA-induced hepatotoxicity.
authors.affiliation: Department of Pharmacology and Toxicology, Rutgers University, Ernest Mario School of Pharmacy, Piscataway, NJ 08854, USA.
authors.forename: Ana-Cristina
authors.initials: AC
authors.lastname: Dragomir
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Laskin
authors.forename: Debra L
authors.initials: DL
authors.lastname: Laskin
mesh_terms: D000082:Acetaminophen / Q000633:toxicity*; D018712:Analgesics, Non-Narcotic / Q000633:toxicity*; D000818:Animals; D018932:Chemokine CCL2 / Q000502:physiology; D051546:Cyclooxygenase 2 / Q000502:physiology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology; D024243:HMGB1 Protein / Q000502:physiology*; D051547:Heme Oxygenase-1 / Q000502:physiology; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D008262:Macrophage Activation / Q000502:physiology*; D008297:Male; D008565:Membrane Proteins / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL
chemical_list: D018712:Analgesics, Non-Narcotic; C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; D024243:HMGB1 Protein; D008565:Membrane Proteins; D000082:Acetaminophen; D051547:Heme Oxygenase-1; C496542:Hmox1 protein, mouse; C077623:Ptgs2 protein, mouse; D051546:Cyclooxygenase 2; D048049:Extracellular Signal-Regulated MAP Kinases