Glycyrrhizin and its metabolite inhibit Smad3-mediated type I collagen gene transcription and suppress experimental murine liver fibrosis.
OBJECTIVE
Glycyrrhizin has been widely used for the treatment of chronic hepatitis C. It decreases the serum levels of aminotransferases, and suppresses progression of liver fibrosis as well as subsequent occurrence of hepatocellular carcinoma. Although previous studies have shown that glycyrrhizin and its metabolite inhibit collagen gene expression, its underlying mechanisms are virtually unknown. This study was aimed to explore molecular mechanisms responsible for the inhibitory effect of glycyrrhizin on type I collagen gene transcription.


METHODS
Effects of glycyrrhizin and its metabolite, glycyrrhetinic acid, on collagen promoter activity were examined by using transgenic reporter mice harboring alpha2(I) collagen gene (COL1A2) promoter. Their effects on the TGF-beta/Smad signaling pathway were studied by cell transfection assays and immunofluorescence studies using cultured hepatic stellate cells.


RESULTS
Administration of glycyrrhizin or its metabolite, glycyrrhetinic acid, significantly suppressed COL1A2 promoter activation and progression of liver fibrosis induced by repeated carbon tetrachloride injections. In cultured hepatic stellate cells, glycyrrhetinic acid, but not glycyrrhizin, inhibited type I collagen synthesis mostly at the level of gene transcription. This inhibitory effect of glycyrrhetinic acid was abolished by a mutation introduced into a Smad3-binding region within the COL1A2 promoter. Glycyrrhetinic acid did not affect gene expression of TGF-beta receptors or Smad proteins, but inhibited nuclear accumulation of Smad3 in activated hepatic stellate cells. In addition to those direct inhibitory effects on COL1A2 transcription, glycyrrhetinic acid also suppressed activation of quiescent hepatic stellate cells in primary culture.


CONCLUSIONS
The results provide a molecular basis for the anti-fibrotic effect of glycyrrhizin treatment.
Moro
Tadashi
T
Tokai University School of Medicine, 143 Shimo-kasuya, Isehara, Kanagawa 259-1193, Japan.
Shimoyama
Yoshihito
Y
Kushida
Miwa
M
Hong
Yun Yu
YY
Nakao
Sachie
S
Higashiyama
Reiichi
R
Sugioka
Yoshihiko
Y
Inoue
Hideo
H
Okazaki
Isao
I
Inagaki
Yutaka
Y
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000378:metabolism / Q000494:pharmacology*; D015153:Blotting, Western; D002252:Carbon Tetrachloride Poisoning / Q000473:pathology / Q000517:prevention & control; D006528:Carcinoma, Hepatocellular / Q000517:prevention & control; D002478:Cells, Cultured; D024042:Collagen Type I / Q000235:genetics*; D005455:Fluorescent Antibody Technique; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism; D019695:Glycyrrhizic Acid / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D007202:Indicators and Reagents; D008103:Liver Cirrhosis / Q000517:prevention & control*; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D050506:Mutant Chimeric Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D051900:Smad3 Protein / Q000037:antagonists & inhibitors*; D014158:Transcription, Genetic
D000893:Anti-Inflammatory Agents; D024042:Collagen Type I; D007202:Indicators and Reagents; D050506:Mutant Chimeric Proteins; D051900:Smad3 Protein; D019695:Glycyrrhizic Acid; D008156:Luciferases; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D020928:Mitogen-Activated Protein Kinases