Animal models are crucial for improving our understanding of human pathogenesis, enabling researchers to identify therapeutic targets and test novel drugs. In the current review, we provide a comprehensive summary of the most widely used experimental models of chronic liver disease, starting from early stages of fatty liver disease (non-alcoholic and alcoholic) to steatohepatitis, advanced cirrhosis and end-stage primary liver cancer. We focus on aspects such as reproducibility and practicality, discussing the advantages and weaknesses of available models for researchers who are planning to perform animal studies in the near future. Additionally, we summarise current and prospective models based on human tissue bioengineering.

Alcoholic liver disease (ALD) is a major cause of acute and chronic liver injury. Extensive evidence has been accumulated on the pathological process of ALD during the past decades. However, effective treatment options for ALD are very limited due to the lack of suitable in vivo models that recapitulate the full spectrum of ALD. Experimental animal models of ALD, particularly rodents, have been used extensively to mimic human ALD. An ideal animal model should recapitulate all aspects of the ALD process, including significant steatosis, hepatic neutrophil infiltration, and liver injury. A better strategy against ALD depends on clear diagnostic biomarkers, accurate predictor(s) of its progression and new therapeutic approaches to modulate stop or even reverse the disease. Numerous models employing rodent animals have been established in the last decades to investigate the effects of acute and chronic alcohol exposure on the initiation and progression of ALD. Although significant progress has been made in gaining better knowledge on the mechanisms and pathology of ALD, many features of ALD are unknown, and require further investigation, ideally with improved animal models that more effectively mimic human ALD. Although differences in the degree and stages of alcoholic liver injury inevitably exist between animal models and human ALD, the acquisition and translational relevance will be greatly enhanced with the development of new and improved animal models of ALD.

Background&Aims c-Jun N-terminal kinase (JNK)1 and JNK2 are expressed in hepatocytes and have overlapping and distinct functions. JNK proteins are activated, via phosphorylation, in response to acetaminophen- or CCl4-induced liver damage; the level of activation correlates with the degree of injury. SP600125, a JNK inhibitor, has been reported to block acetaminophen-induced liver injury. We investigated the role of JNK in drug-induced liver injury (DILI) in liver tissues from patients and in mice with genetic deletion of JNK in hepatocytes. Methods We studied liver sections from patients with DILI (due to acetaminophen, phenprocoumon, non-steroidal anti-inflammatory drugs or autoimmune hepatitis), or patients without acute liver failure (controls), collected from a DILI Biobank in Germany. Levels of total and activated (phosphorylated) JNK were measured by immunohistochemistry and western blotting. Mice with hepatocyte-specific deletion of Jnk1 (Jnk1Δhepa) or combination of Jnk1 and Jnk2 (JnkΔhepa), as well as Jnk1- floxed C57BL/6 (control) mice, were given injections of CCl4 (to induce fibrosis) or acetaminophen (to induce toxic liver injury). We performed gene expression microarray, and phosphoproteomic analyses to determine mechanisms of JNK activity in hepatocytes. Results Liver samples from DILI patients contained more activated JNK, predominantly in nuclei of hepatocytes and in immune cells, than healthy tissue. Administration of acetaminophen to JnkΔhepa mice produced a greater level of liver injury than that observed in Jnk1Δhepa or control mice, based on levels of serum markers and microscopic and histologic analysis of liver tissues. Administration of CCl4 also induced stronger hepatic injury in JnkΔhepa mice, based on increased inflammation, cell proliferation, and fibrosis progression, compared to Jnk1Δhepa or control mice. Hepatocytes from JnkΔhepa mice given acetaminophen had an increased oxidative stress response, leading to decreased activation of AMPK, total protein AMPK levels, and pJunD and subsequent necrosis. Administration of SP600125 before or with acetaminophen protected JnkΔhepa and control mice from liver injury. Conclusions In hepatocytes, JNK1 and JNK2 appear to have combined effects in protecting mice from CCl4- and acetaminophen-induced liver injury. It is important to study the tissue-specific functions of both proteins, rather than just JNK1, in the onset of toxic liver injury. JNK inhibition with SP600125 shows off-target effects.