Lipopolysaccharide augments aflatoxin B1-induced liver injury through neutrophil-dependent and -independent mechanisms

Abstract

Exposure to small, noninjurious doses of the inflammagen, bacterial endotoxin (lipopolysaccharide, LPS) augments the toxicity of certain hepatotoxicants including aflatoxin B1 (AFB1. Mediators of inflammation, in particular neutrophils (PMNs), are responsible for tissue injury in a variety of animal models. This study was conducted to examine the role of PMNs in the pathogenesis of hepatic injury after AFB1/LPS cotreatment. Male, Sprague-Dawley rats (256-356 g) were treated with either 1 mg AFB1/kg, ip or its vehicle (0.5% DMSO/saline), and 4 h later with either E. coli LPS (7.4 x 106 EU/kg, iv) or its saline vehicle. Over a course of 6 to 96 h after AFB1 administration, rats were killed and livers were stained immunohistochemically for PMNs. LPS resulted in an increase in PMN accumulation in the liver that preceded the onset of liver injury. To assess if PMNs contributed to the pathogenesis, an anti-PMN antibody was administered to reduce PMN numbers in blood and liver, and injury was evaluated. Hepatic parenchymal cell injury was evaluated as increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities in serum and from histologic examination of liver sections. Biliary tract alterations were evaluated as increased concentration of serum bile acids and activities of γ-glutamyltransferase (GGT), alkaline phosphatase (ALP), and 5'-nucleotidase (5'-ND) in serum. Neutrophil depletion protected against hepatic parenchymal cell injury caused by AFB1/LPS cotreatment but not against markers of biliary tract injury. This suggests that LPS augments AFB1 hepatotoxicity through two mechanisms: one of which is PMN-dependent, and another that is not.