The hepatotrophic growth factor Augmenter of liver regeneration (ALR) is protective against metabolic damage via the PI3K/AKT pathway

Abstract

The liver is a highly metabolic organ with a great potential of regeneration. Beside mitogenic signals via hepatotrophic growth factors like EGF (epidermal growth factor), HGF (hepatocyte growth factor) and ALR, liver regeneration is also triggered through metabolites of intracellular reactive oxygen species (ROS) and anti-apoptotic mechanisms. Aim of this study was to investigate the protective effect of ALR in vitro against different hepatotoxic agents. Primary human hepatocytes (phH) and hepatic cell lines were exposed to different concentrations of ethanol, 5-FU and actinomycin D and (pre) co-incubated with or without ALR. The influence on cell proliferation was analyzed by MTT assay. As an indicator of irreversible cell death, the leakage of intracellular LDH into the culture medium was measured as well as the intracellular GSH (glutathione)/GSSG (oxidized glutathione) ratio (indicator of cellular oxidative stress). The amount of induced apoptosis was evaluated by FACS analysis with propidium iodid (PI) staining. In Western Blot studies the corresponding signal pathways were analyzed. Pre-incubation of culture media with rhALR showed an increase in proliferation of HepG2 cells and primary human hepatocytes. The collected data revealed a concentration dependent increase of cell damage by ethanol, ActD and 5-FU as well as a protective effect of rhALR (FACS analysis, enzyme leakage). Anti-apoptotic effects of rhALR were shown by increased phosphorylation of Akt and phosphorylation of GSK-3ß, a downstream protein of the Akt/PKB survival pathway. In summary, we have demonstrated that rhALR acts liver specific and excerts not only mitogenic but also protective effects through the PI3K/AKT signaling pathway.