Glycine and uridine prevent d ‐galactosamine hepatotoxicity in the rat: Role of kupffer cells

Extrahepatic factors, such as increased gut permeability and bacteria from the gut, have been shown to play a role in d ‐galactosamine toxicity in rats. Because bacterial endotoxin activates Kupffer cells, the purpose of this study was to clarify the role of Kupffer cells in the mechanism of d ‐galactosamine hepatotoxicity in rats and determine whether uridine, a compound that rescues animals from d ‐galactosamine toxicity, affects Kupffer cells. Rats were fed control or glycine (5%) containing diets to prevent Kupffer cell activation or treated with gadolinium chloride (GdCl 3 , 20 mg/kg) to destroy Kupffer cells selectively before injection of d ‐galactosamine(500 mg/kg, intraperitoneally). d ‐galactosamine caused panlobular focal hepatocellular necrosis, polymorphonuclear cell infiltration, and increased serum transaminases significantly at 24 hours. Dietary glycine or pretreatment with GdCl 3 prevented these effects. d ‐galactosamine caused a transient increase in circulating endotoxin that was maximal at 1 hour and was blunted significantly by dietary glycine. Additionally, antisera to tumor necrosis factor‐α (TNF‐α) prevented hepatotoxicity caused by d ‐galactosamine. Moreover, apoptosis in hepatocytes caused by d ‐galactosamine occurred before necrosis (6 hours) and was prevented by glycine, GdCl 3 , TNF‐α antiserum, and uridine. Thus, it was hypothesized that TNF‐α from Kupffer cells causes apoptosis after d ‐galactosamine administration in the rat. Indeed, increases in TNF‐α messenger RNA (mRNA) were detected as early as 2.5 hours after d ‐galactosamine treatment. Previous work proposed that uridine blocks d ‐galactosamine toxicity by preventing inhibition of mRNA synthesis. In view of these results, the possibility that uridine might affect Kupffer cells was investigated. Uridine significantly blunted the increase in [Ca 2+ ] i and release of TNF‐α caused by endotoxin in isolated Kupffer cells and prevented apoptosis caused by d ‐galactosamine treatment in vivo . These data support the hypothesis that uridine prevents d ‐galactosamine hepatotoxicity not only by rescuing the hepatocyte in the late phases of the injury but also preventing TNF‐α release from Kupffer cells thereby blocking apoptosis that occurs early after d ‐galactosamine treatment. Taken together, these data strongly support the role of Kupffer cell activation by endotoxin early after d ‐galactosamine treatment as an important event in the mechanism of hepatotoxicity in the rat.