Platelets and protease-activated receptor-4 contribute to acetaminophen-induced liver injury in mice

Abstract

Key Points• Platelets and PAR-4 contribute to the progression of APAPinduced liver injury in mice through independent pathways.Acetaminophen (APAP)-induced liver injury in humans is associated with robust coagulation cascade activation and thrombocytopenia. However, it is not known whether coagulation-driven platelet activation participates in APAP hepatotoxicity. Here, we found that APAP overdose in mice caused liver damage accompanied by significant thrombocytopenia and accumulation of platelets in the liver. These changes were attenuated by administration of the direct thrombin inhibitor lepirudin. Platelet depletion with an anti-CD41 antibody also significantly reduced APAP-mediated liver injury and thrombin generation, indicated by the concentration of thrombin-antithrombin (TAT) complexes in plasma. Compared with APAP-treated wild-type mice, biomarkers of hepatocellular and endothelial damage, plasma TAT concentration, and hepatic platelet accumulation were reduced in mice lacking protease-activated receptor (PAR)-4, which mediates thrombin signaling in mouse platelets. However, selective hematopoietic cell PAR-4 deficiency did not affect APAP-induced liver injury or plasma TAT levels. These results suggest that interconnections between coagulation and hepatic platelet accumulation promote APAP-induced liver injury, independent of platelet PAR-4 signaling. Moreover, the results highlight a potential contribution of nonhematopoietic cell PAR-4 signaling to APAP hepatotoxicity. (Blood. 2015;126(15):1835-1843 Introduction Acetaminophen (APAP) hepatotoxicity is the leading cause of druginduced liver injury and acute liver failure in the United States and other developed countries.1-4 Even though APAP hepatotoxicity has been recognized for more than 50 years, the main treatment options for overdose have been limited to early treatment with N-acetylcysteine and liver transplantation in the most severe cases. Many studies have been conducted to understand the mechanisms of APAP hepatotoxicity and to seek alternative therapies. It is commonly understood from early studies in murine models that APAP overdose leads to excessive production of the reactive metabolite, N-acetyl-p-benzoquinoneimine (NAPQI), and consequent depletion of hepatic glutathione (GSH), which is responsible for detoxifying NAPQI. This depletion of GSH permits NAPQI binding to cellular proteins, and this initiating event is followed by a myriad of cellular and molecular events involving parenchymal and nonparenchymal cells that ultimately determine the severity of liver damage. 5-10Evidence supports a role for numerous mediators in the pathogenesis of APAP-induced liver injury, including nitric oxide (NO) and peroxynitrite formation, oxidative stress, mitochondrial injury, alteration in hepatic blood flow, and the innate immune response. [8][9][10][11] APAP overdose is associated with activation of the coagulation cascade in mice and in humans.12-14 Indeed, consumptive coagulopathy is one of the major clinical signs in acute liver failure from AP...

Mechanisms of platelet-mediated liver regeneration

“…[55][56][57][58] In line with these results, a retrospective clinical study showed that use of aspirin was associated with a decreased progression of fibrosis in liver transplant recipients transplanted for hepatitis C (in whom fibrosis frequently recurs after transplantation). 59 Furthermore, platelets contribute to ischemia/reperfusion injury, 60 which is relevant in the context of liver transplantation and partial hepatectomy.…”

Fibrin(ogen) drives repair after acetaminophen-induced liver injury via leukocyte αMβ2 integrin-dependent upregulation of Mmp12

“…Discovery of a putative role for fibrin(ogen) in liver repair is somewhat at odds with prior publications indicating that anticoagulation (i.e., heparin, lepirudin) reduced early APAP-induced hepatotoxicity [7, 28]. However, these previous studies only examined the effect of anticoagulants at early times (≤ 6 hours post-APAP), well before peak injury and likely preceding profound activation of liver repair pathways.…”

Thrombocytopenia Is Associated With Multi-organ System Failure in Patients With Acute Liver Failure

“…Evidence of activation of hemostasis (fibrin) has long been noted in liver biopsy specimens from patients with acetaminophen-induced ALF 27 , leading to an early trial of heparin to treat the disorder 28 . More recently, two studies have shown that administering heparin to mice with APAP-induced acute liver injury ameliorated the severity of hepatic necrosis 1,29 , and a third documented platelet sequestration within the necrotic liver (at the expense of peripheral platelet numbers) also contributes to liver injury 30 . These observations suggest that intra-sinusoidal activation of hemostasis may lead to a secondary ischemic injury.…”