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-galact osamine hepatotoxicity in rats and determine whether uridine, a compound th at rescues animals from D-galactosamine toxicity, affects Kupffer cells. Ra ts were fed control or glycine (5%) containing diets to prevent Kupffer cel l activation or treated with gadolinium chloride (GdCl3, 20 mg/kg) to destr oy Kupffer cells selectively before injection of D-galactosamine (500 mg/kg , intraperitoneally). D-galactosamine caused panlobular focal hepatocellula r necrosis, polymorphonuclear cell infiltration, and increased serum transa minases significantly at 24 hours. Dietary glycine or pretreatment with GdC l3 prevented these effects. D-galactosamine caused a transient increase in circulating endotoxin that was maximal at 1 hour and was blunted significan tly by dietary glycine, Additionally, antisera to tumor necrosis factor-alp ha (TNF-alpha) prevented hepatotoxicity caused by D-galactosamine, Moreover , apoptosis in hepatocytes caused by D-galactosamine occurred before necros is (6 hours) and was prevented by glycine, GdCl3, TNF-alpha antiserum, and uridine. Thus, it was hypothesized that TNF-alpha from Kupffer cells causes apoptosis after D-galactosamine administration in the rat, Indeed, increas es in TNF-alpha. messenger RNA (mRNA) were detected as early as 2.5 hours a fter D-galactosamine treatment. Previous work proposed that uridine blocks D-galactosamine toxicity by preventing inhibition of mRNA synthesis. In vie w 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-alpha 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 hepatotoxicit y not only by rescuing the hepatocyte in the late phases of the injury but also preventing TNF-alpha release from Kupffer cells thereby blocking apopt osis that occurs early after D-galactosamine treatment. Taken together, the se data strongly support the role of Kupffer cell activation by endotoxin e arly after D-galactosamine treatment as an important event in the mechanism of hepatotoxicity in the rat.