Glycine and uridine prevent D-galactosamine hepatotoxicity in the rat: Role of Kupffer cells

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 GdCl3 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, 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.