Using retinoic acid derivative molecules to antagonize the TGF-beta induced early liver fibrosis

• Main Authors: Kun-Lin Yang, 楊昆霖
• Other Authors: Eric I. Li
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/51948157471200925280

博士 === 國立成功大學 === 基礎醫學研究所 === 96 === At present, the only curative treatment for end stage liver cirrhosis is organtransplantation. However, the availability of donor organ limits the application of this treatment. The current anti-fibrotic effect of antioxidants is disappointing in vivo due probably to the fact that once liver fibrosis is established it is too advanced to be reversed by medical intervention. Many studies of liver fibrosis consist of animal testing with various hepatotoxins such as carbon tetrachloride (CCl4). Although this method is often used, the model at which cirrhosis or extensive fibrosis becomes irreversible has not been well defined and is not represen- tative of early-stage fibrogenesis. Therefore, it is of imperative importance to establish a suitable fibrosis model for studying the prevention of liver fibrosis at the initiation stage. This thesis investigation addresses this problem and sets out firstly to establish a different animal model for studying the early liver fibrosis. It has been well documented that transforming growth factor-beta-1 (TGF-β1) up regulates the expression of α(1) collagen (Col 1A2) gene in the liver via the reactive oxygen species (ROS). The process triggers inflammation (cycloxygenase-2; Cox-2), leading to hepatic stellate cells (HSC) damages and liver fibrogenesis. We hence screened small molecules isolated from some herbal medicines with the hope that they may antagonize fibrosis. We used ROS, Col 1A2 and Cox-2 promoter assays as screening targets. Out of a panel of approximately 96 chemical compounds for possible candidate that may inhibit liver fibrosis, a small retinoic acid molecule isolated from the mycelia of Phellinus linteus (denoted here as PL) was found to be a promising candidate molecule for inhibiting liver fibrogenesis when assayed by our newly established animal model where a plasmid containing TGF-β1 cDNA was“hydro-dynamically” transferred into an animal to generate a transient liver fibrosis. The procedure involves a large-volume and high-speed intravenous injection of naked plasmid DNA into the animal tail vein; the whole procedure was finished within 5-7 seconds. We found that PL could strongly alleviate the expressions of hydroxyproline and Col 1A2 mRNA, making their expressions only about 50% and 0.001%,respectively, as compared to the pPK9a-transferred mice upon induction by ZnSO4. PL also markedly improves the expressions of alanine transaminase (ALT), Cox-2, α-SMA, p-Smad2/3 and trans- cription factor Sp1. Our results suggest that the retinoic acid derivative of Phellinus linteus prevents liver fibrosis from happening at an early phase both in vitro and in vivo through the inhibition of ROS, inflammation and the acti- vation of HSC. Our model is more unique to the liver and may have its usefulness in clinical study for prevention of early stage liver fibrosis. As for its effects on advanced fibrosis or cirrhosis further studies are warranted.