Review: Precision Cut Liver Slices for the Evaluation of Fatty Liver and Fibrosis.

Introduction: Ethanol metabolism in the liver results in oxidative stress, altered cytokine production and fat accumulation in the liver. Thus, it is thought that the accumulation of benign fat into the liver in conjunction with a second hit leads to liver failure. However, we have recently developed the use of precision-cut liver slices (PCLSs) as an in vitro culture model in which to investigate the pathophysiology of alcohol-induced liver injury. In this review, these studies will be discussed and newer data presented.

Methods: Original investigations into the use of PCLS were obtained from chow fed rats (200-300g). PCLSs were cultured 24-96h in media, 25 mM ethanol, or 25 mM ethanol and 0.5 mM 4- methylpyrazole (4-MP). PCLSs were examined for at different times and evaluated for glutathione (GSH) levels, extent of lipid peroxidation (TBARS assay), cytokine production (ELISA and RT-PCR) and myofibroblast activation. Age-matched rats were fed high fat diets for 13 months, PCLSs were prepared, and evaluated as outlined above. In recently, human and mouse PCLSs were cut, equilibrated, and evaluated using the methods outlined as above.

Results: In these studies, it was shown that the PCLSs from rats, mice and human livers retained excellent viability over a 96 hour period of incubation. During this time period, alcohol dehydrogenase, aldehyde dehydrogenase, and cytochrome P4502E1 levels were viable. After 24 hours of ethanol exposure, fatty livers and fibrogenic responses developed and could be prevented/reversed with the 4-MP. In a separate study using overly obese rats, ethanol metabolism was decreased in PCLSs as compared to age-matched controls (AMC). However, higher levels of triglycerides and lipid peroxidation were found in PCLSs from obese rats compared to AMC. Also, increased concentrations of the proinflammatory cytokines (TNF-α and IL-6) were found in the culture supernatants. In contrast, decreased levels of reduced glutathione (GSH) and heme oxygenase I (HO-1) levels were detected.

Conclusion: Within 24h of incubation, ethanol metabolism by PCLSs initiates fat accumulation in the liver at which point there is an activation of myofibroblasts. Thus, fatty liver is the first response to ethanol and sensitizes the liver to other products of oxidative stress that result in inflammation and the start of liver failure ending in cirrhosis. Thus, from these studies it appears that PCLSs can be utilized to determine the mechanisms(s) by which ethanol exposure leads to the development and/or progression of alcoholic liver disease (ALD).