Green tea suppresses lipopolysaccharide-induced liver injury in d-galactosamine-sensitized rats.
We conducted a series of in vivo experiments to clarify the hepatoprotective activity of green tea against lipopolysaccharide (LPS) + D-galactosamine (GalN)-induced liver injury and to elucidate the mechanism by which green tea exerts its effect in 7-wk-old male Wistar rats. Liver injury was assessed by plasma alanine aminotransferase and aspartate aminotransferase activities. Green tea extract significantly suppressed LPS + GalN-induced liver injury when added to the diet (30 or 35 g/kg) and fed to rats for 14 d or when force-fed alone (0.4-1.2 g/kg body) 1.5 h before the injection of drugs. Although all five of the fractions extracted from green tea extract with different organic solvents had significant suppressive effects, the caffeine-containing fraction exhibited the strongest effect, suggesting that the protective effect of green tea against LPS + GalN-induced liver injury is attributable mainly to caffeine. Authentic caffeine also significantly suppressed LPS + GalN-induced liver injury when added to the diet (2 g/kg) and fed to rats for 14 d. Dietary green tea suppressed LPS + GalN-induced apoptosis of liver cells, as assessed by DNA fragmentation. However, dietary green tea did not suppress LPS-induced enhancement of plasma concentration of tumor necrosis factor (TNF)-alpha, the cytokine that is thought to play a pivotal role in the pathogenesis of LPS-induced liver injury, although it significantly suppressed plasma concentrations of interleukin (IL)-1beta, IL-2, IL-4, IL-6, IL-10 and interferon (IFN)-gamma. TNF-alpha + GalN-induced liver injury and apoptosis were also suppressed by dietary green tea. In contrast, dietary caffeine significantly suppressed LPS-induced enhancement not only of plasma IL-1beta, IL-6, IL-10 and IFN-gamma concentrations, but also of TNF-alpha concentration. The results suggest that green tea might suppress LPS + GalN-induced liver injury mainly through the inhibition of TNF-alpha-induced apoptosis of hepatocytes, rather than through the suppression of TNF-alpha production, although the suppressed production of TNF-alpha may be associated with the hepatoprotective effect of caffeine.
He
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Department of Applied Biological Chemistry, Faculty of Agriculture, Shizuoka University, Shizuoka 422-8529, Japan.
Noda
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Sugiyama
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D000410:Alanine Transaminase / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D001219:Aspartate Aminotransferases / Q000378:metabolism; D001835:Body Weight / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D004032:Diet; D005688:Galactosamine / Q000037:antagonists & inhibitors / Q000633:toxicity*; D007378:Interleukins / Q000097:blood; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors / Q000633:toxicity*; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D008517:Phytotherapy; D051381:Rats; D017208:Rats, Wistar; D013662:Tea / Q000737:chemistry / Q000627:therapeutic use*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D007378:Interleukins; D008070:Lipopolysaccharides; D013662:Tea; D014409:Tumor Necrosis Factor-alpha; D002110:Caffeine; D005688:Galactosamine; D001219:Aspartate Aminotransferases; D000410:Alanine Transaminase