Hepatic effects of 2-butoxyethanol in rodents

Abstract

Chronic inhalation of 2-butoxyethanol resulted in an increase in liver hemangiosarcomas and hepatic carcinomas in male mouse liver. No increase in liver neoplasia was observed in similarly exposed male and female rats or female mice. We proposed that the production of liver neoplasia in the male mouse is the result of oxidative damage secondary to the hemolytic deposition of iron in the liver. This occurs selectively in the male mouse and leads either directly or indirectly to liver neoplasia. To address this proposal, male B6C3F1 mice and male F344 rats were treated with 2-butoxyethanol (via daily gavage; five times per week) at doses of 0, 225, 450, and 900 mg/kg/day (mice) and 0, 225, and 450 mg/kg/day (rats) respectively. Following treatment for 7, 14, 28, and 90 days, DNA synthesis, oxidative damage, hematocrit, and iron deposition were measured in the livers. An increase in hemolysis (measured by a decrease in hematocrit and increase in relative spleen weight) was observed in 2-butoxyethanol-treated rats and mice in a dose-dependent manner. An increase in the percentage of iron-stained Kupffer cells was observed following treatment with 450 and 900 mg/kg of 2-butoxyethanol in mice and 225 and 450 mg/kg of 2-butoxyethanol in rats. A biphasic increase in oxidative damage (8-hydroxydeoxyguanosine and malondialdehyde) was seen in mouse liver after 7 and 90 days of treatment with 2-butoxyethanol, whereas no increases were observed in treated rat liver. Vitamin E levels were reduced by 2-butoxyethanol treatment in both mice and rat liver; however, the basal level of vitamin E was approximately 2.5-fold higher in rat than in mouse liver. A similar biphasic induction of DNA synthesis was seen following 2-butoxyethanol treatment in the mouse. In the mouse liver, increased DNA synthesis was observed in hepatocytes at 90 days and in endothelial cells at 7 and 14 days at all doses. No change in DNA synthesis was seen in 2-butoxyethanol-treated rat liver. No apparent differences in apoptosis and mitosis in the liver were observed in mouse and rat liver between 2-butoxyethanol treatment groups and untreated controls. These results suggest that DNA synthesis, possibly from oxidative stress or Kupffer cell activation, occurs selectively in the mouse liver, primarily in endothelial cells (a target of 2-butoxyethanol neoplasia), following exposure to 2-butoxyethanol.