Bacterial endotoxin (lipopolysaccharide; LPS) given to animals in large doses results in pronounced, midzonal liver injury. Exposure to smaller, non-injurious doses of LPS augments the toxicity of certain hepatotoxicants. This study was conducted to delineate the development of injury in a rat model of augmentation of aflatoxin B(1) (AFB(1)) hepatotoxicity by LPS. At large doses (i.e., > 1 mg/kg, ip), AFB(1) administration resulted in pronounced injury to the periportal regions of the liver. Male, Sprague-Dawley rats (250-350 g) were treated with 1 mg AFB(1)/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. Liver injury was assessed 6, 12, 24, 48, 72, or 96 h after AFB(1) administration. 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 gamma-glutamyltransferase (GGT), alkaline phosphatase (ALP), and 5'-nucleotidase (5'-ND) in serum. At all times and for all markers, injury in rats treated with either AFB(1) or LPS alone was absent or modest. In the AFB(1)/LPS cotreated group, hepatic parenchymal cell injury was pronounced by 24 h and had returned to control values by 72 h. The injury began in the periportal region and spread midzonally with time. Furthermore, changes in serum markers indicative of biliary tract alterations were evident by 12 h and had returned to control values by 72 h. Thus, the nature of the hepatic lesions suggested that LPS potentiated the effects of AFB(1) on both parenchymal and bile duct epithelial cells.

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Exposure to small, noninjurious doses of the inflammagen, bacterial endotoxin (lipopolysaccharide, LPS) augments the toxicity of certain hepatotoxicants including aflatoxin B(1) (AFB(1)). 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 AFB(1)/LPS cotreatment. Male, Sprague-Dawley rats (250-350 g) were treated with either 1 mg AFB(1)/kg, ip or its vehicle (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(1) 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 gamma-glutamyltransferase (GGT), alkaline phosphatase (ALP), and 5'-nucleotidase (5'-ND) in serum. Neutrophil depletion protected against hepatic parenchymal cell injury caused by AFB(1)/LPS cotreatment but not against markers of biliary tract injury. This suggests that LPS augments AFB(1) hepatotoxicity through two mechanisms: one of which is PMN-dependent, and another that is not.