Glycine and Uridine Prevent D –Galactosamine Hepatotoxicity in the Rat: Role of Kupffer Cells

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Abstract
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 (GdCl3, 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 GdCl3prevented 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, GdCl3, 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 [Ca2+]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.