EFFECT OF COMBINATION OF THE MAMMALIAN LIGNAN, ENTEROLACTONE, WITH TYROSINE KINASE INHIBITORS ON MARKERS OF HEPATIC FIBROSIS

Abstract

Current treatments for hepatic fibrosis are still elusive because of the lack of efficient and safe drugs. The pathogenesis of hepatic fibrosis suggests multi-target drugs might have therapeutic potential. This dissertation research aimed to confirm the antifibrotic effects of the combination of the bioactive mammalian lignan, enterolactone (ENL), and selected tyrosine kinase inhibitors (TKIs) and to explore whether these effects involve peroxisome proliferator-activated receptor gamma (PPARγ), oxidative stress, and/or endoplasmic reticulum (ER) stress, known pathways of lignan and TKI action. A standard PPARγ competitive binding assay was conducted to assess whether three multi-target TKIs and ENL were PPARγ agonists. Binding affinity to the rosiglitazone binding site of PPARγ was low. However, a PPARγ transactivation assay and PPARγ-related biological functional assays, adipogenesis and glucose uptake assays, provided evidence of potential PPARγ partial agonism by gefitinib and ENL. Evaluation of the expression changes of several fibrotic markers (e.g., collagen I, -SMA, MMP2/MMP9, and TIMP-1,) using human hepatic stellate cells (HSC), LX-2 cells, at both mRNA and protein level by real-time PCR and ELISA/western blot, respectively, demonstrated that Gefitinib had the greatest ability to attenuate HSC activation and ECM production and was chosen as the model TKI for further investigation. Next, qPCR was used to quantify changes in the expression of biomarkers of HSC proliferation and activation (e.g., -SMA, collagen I, TIMP-1, and MMP2) and possible pathways (e.g., PPARγ, β-catenin/Wnt, Nrf2) for the antifibrotic effects of ENL and/or gefitinib in TGF-1-stimulated LX-2 cells. The combination of gefitinib and ENL attenuated the fibrotic biomarkers to a greater extent than using each compound alone. In further experiments evaluating reactive oxygen species (ROS) production, caspase-3/7 apoptosis, and changes in the expression of PPARγ, Nrf2, and ER stress markers, the data suggested that PPARγ, oxidative stress, and ER stress-induced apoptosis might be involved in the antifibrotic response of gefitinib and ENL. The antifibrotic role of secoisolariciresinol diglucoside (SDG) and its metabolites were also investigated in a hypercholesterolemic rat model of hepatic lipidosis. This study indicated that SDG caused modest improvement in serum lipid parameters and hepatic lipidosis, with mild effects on fibrotic biomarkers of non-alcoholic fatty liver disease in hypercholesterolemic rats. In conclusion, these studies suggest the potential of the combination of ENL and gefitinib as a therapeutic approach in hepatic fibrosis. PPARγ, oxidative stress, and the ER stress-induced apoptosis can be potential pathways to attenuate markers of hepatic fibrosis. Further studies should be done to clarify whether ENL and gefitinib attenuate hepatic fibrosis through PPARγ, oxidative stress, and/or the ER stress response in vivo.