Lipopolysaccharide augments aflatoxin B-1-induced liver injury through neutrophil-dependent and -independent mechanisms

Exposure to small, noninjurious doses of the inflammagen, bacterial endotox in (lipopolysaccharide, LPS) augments the toxicity of certain hepatotoxican ts including aflatoxin B-1 (AFB(1)). Mediators of inflammation, in particul ar neutrophils (PMNs), are responsible for tissue injury in a variety of an imal models. This study was conducted to examine the role of PMNs in the pa thogenesis of hepatic injury after AFB(1)/LPS cotreatment. Male, Sprague-Da wley rats (250-350 g) were treated with either 1 mg AFB(1)/kg, ip or its ve hicle (0.5% DMSO/saline), and 4 h later with either E. coli LPS (7.4 x 10(6 ) EU/kg, iv) or its saline vehicle. Over a course of 6 to 96 h after AFB, a dministration, rats were killed and livers were stained immunohistochemical ly for PMNs. LPS resulted in an increase in PMN accumulation in the liver t hat preceded the onset of liver injury. To assess if PMNs contributed to th e pathogenesis, an anti-PMN antibody was administered to reduce PMN numbers in blood and liver, and injury was evaluated. Hepatic parenchymal cell inj ury 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 c oncentration of serum bile acids and activities of gamma -glutamyltransfera se (GGT), alkaline phosphatase (ALP), and 5'-nucleotidase (5'-ND) in serum. Neutrophil depletion protected against hepatic parenchymal cell injury cau sed by AFB(1)/LPS cotreatment but not against markers of biliary tract inju ry. This suggests that LPS augments AFB, hepatotoxicity through two mechani sms: one of which is PMN-dependent, and another that is not.