The role of MAP2 kinases and p38 kinase in acute murine liver injury models

Oxidant Stress and Lipid Peroxidation in Acetaminophen Hepatotoxicity

Acetaminophen (APAP) overdose is the most frequent cause of liver injury and acute liver failure in many western countries. The mechanism of APAP-induced hepatocyte necrosis has been investigated extensively. The formation of a reactive metabolite and its binding to cellular proteins was initially thought to be responsible for cell death. A competing hypothesis was introduced that questioned the relevance of protein binding and instead suggested that P450-derived oxidant stress and lipid peroxidation causes APAP-induced liver injury. However, work over the last 15 years has reconciled some of these apparent contradictory hypotheses. This review summarizes the present state of knowledge on the role of reactive oxygen species (ROS) in APAP hepatotoxicity. Detailed investigations into the sources and relevance of the oxidant stress have clearly shown the critical role of the electron transport chain of mitochondria as main source of the oxidant stress. Other potential sources of ROS such as cytochrome P450 enzymes or NADPH oxidase on phagocytes are of limited relevance. The mitochondria-derived superoxide and peroxynitrite formation is initiated by the binding of the reactive metabolite to mitochondrial proteins and the amplification by mitogen activated protein kinases. The consequences of this oxidant stress are the opening of the mitochondrial membrane permeability transition pore with cessation of ATP synthesis, nuclear DNA fragmentation and ultimately cell necrosis. Lipid peroxidation is not a relevant mechanism of cell death but can be a marker of ROS formation. These mechanistic insights suggest that targeting mitochondrial oxidant stress is a promising therapeutic option for APAP hepatotoxicity.

New insights into the role and mechanism of c-Jun-N-terminal kinase signaling in the pathobiology of liver diseases

The c-Jun-N-terminal-kinase (JNK) family is highly conserved across species such as Drosophila, C. elegans, zebrafish and mammals, and plays a central role in hepatic physiologic and pathophysiologic responses. These responses range from cell death to cell proliferation and carcinogenesis, as well as metabolism and survival, depending on the specific context and duration of activation of the JNK signaling pathway. Recently, several investigators identified the key molecules in the JNK activation loop which include apoptosis signal-regulating kinase (ASK1) and SH3-domain binding protein 5 (Sab) and their involvement in acute or chronic liver disease models. Thus, regulating JNK activation through modulating the JNK activation loop may represent an important new strategy in the prevention and treatment of acute and chronic liver diseases. In this review, we will discuss the molecular pathophysiology of the JNK activation loop and its role in the pathogenesis of liver diseases. (Hepatology 2018;67:2013-2024).

Acetaminophen Toxicity: Novel Insights Into Mechanisms and Future Perspectives

Acetaminophen (APAP) overdose is the most common cause of acute liver failure in the US, and decades of intense study of its pathogenesis resulted in the development of the antidote N-acetylcysteine, which facilitates scavenging of the reactive metabolite and is the only treatment in clinical use. However, the narrow therapeutic window of this intervention necessitates a better understanding of the intricacies of APAP-induced liver injury for the development of additional therapeutic approaches that can benefit late-presenting patients. More recent investigations into APAP hepatotoxicity have established the critical role of mitochondrial dysfunction in mediating liver injury as well as clarified mechanisms of APAP-induced hepatocyte cell death. Thus, it is now established that mitochondrial oxidative and nitrosative stress is a key mechanistic feature involved in downstream signaling after APAP overdose. The identification of specific mediators of necrotic cell death further establishes the regulated nature of APAP-induced hepatocyte cell death. In addition, the discovery of the role of mitochondrial dynamics and autophagy in APAP-induced liver injury provides additional insight into the elaborate cell signaling mechanisms involved in the pathogenesis of this important clinical problem. In spite of these new insights into the mechanisms of liver injury, significant controversy still exists on the role of innate immunity in APAP-induced hepatotoxicity.