Mechanistic Biomarkers in Acute Liver Injury

Abstract

Acute liver failure continues to be a major medical problem. There are many underlying causes of acute liver failure, but drug induced liver injury is the most common. However, ischemic injury secondary to either liver transplantation or hypoxic hepatitis are also commonly encountered clinically. While the pathogenesis of some etiologies of liver failure are well known due to appropriate animal and cell culture models (i.e. acetaminophen toxicity), that of ischemic injury is not as well documented. A major reason for this is the lack of appropriate animal models available to recapitulate these conditions in humans. Furthermore, obtaining multiple liver biopsies to study these conditions at the cellular level is generally not possible owing, in part, to the invasive nature of obtaining the sample, but also to the fact that liver biopsies are contraindicated in acute liver injury patients. Thus, alternative methods which can help diagnose and study liver injury are being explored and refined. Among these methods are the use of circulating biomarkers, which are currently being extensively explored in the field of hepatology. Because biologic specimens in which these biomarkers are being measured can be easily obtained and are non-invasive, they offer a promising means by which to study liver injury, particularly for prolonged periods of time. Indeed, a series of blood collections can provide vital information into various injury-specific aspects of liver pathophysiology including mode of cell death, mitochondrial involvement, degree of liver injury, and presence or absence of a sterile inflammatory component to the injurious process. Here, we use a well-established set of circulating plasma biomarkers to study the pathophysiology of both warm and cold ischemia to better characterize the cellular events which take place during these conditions. Data obtained demonstrates that during both warm and cold ischemia, the majority of injury occurs early in the reperfusion period and that necrosis, rather than apoptosis predominates. Furthermore, we identified the mitochondria as critical mediators of liver injury following ischemia. However, we were unable to find evidence of an inflammatory component of ischemic injury. Furthermore, we conclude that due to advances in surgical technique and organ preservation strategies, future efforts to study injury secondary to liver transplantation should focus on the biliary system and the formation of biliary strictures rather than ischemic injury. HepaRG cells are a human hepatoma cell line which is commonly used in the laboratory. Unlike other liver cell lines, HepaRG cells have a full complement of drug metabolizing enzymes, making them ideal for the study of drug induced liver injury. However, growth, maintenance, and differentiation of conventional HepaRG cells is a timely process. Recently, this lengthy process has been dramatically shortened with the advent of pre-differentiated cryopreserved HepaRG cells. Due to the frequency of acetaminophen toxicity, combined with the fact that liver injury is the most common cause of drug failure and market withdrawal, we set out to compare these two preparations of HepaRG cells. Using acetaminophen as a test substrate, we found both preparations of HepaRG to be similar in all aspects of acetaminophen metabolism. This finding will help advance the study of acetaminophen, as well as help identify idiosyncratic adverse drug reactions earlier in the drug development process.