Bacterial lipopolysaccharide enhances aflatoxin B1 hepatotoxicity in rats by a mechanism that depends on tumor necrosis factor alpha.

Exposure to a nontoxic dose of bacterial endotoxin (lipopolysaccharide [LPS]) potentiates the hepatotoxicity of aflatoxin B(1) (AFB(1)). Because some of the pathophysiologic effects associated with LPS are mediated through tumor necrosis factor alpha (TNF-alpha), this study was conducted to explore the role of TNF-alpha in the AFB(1)/LPS model. Male Sprague-Dawley rats (250-300 g) were treated with either 1 mg AFB(1)/kg, intraperitoneally, or its vehicle (0.5% dimethyl sulfoxide [DMSO]/water), and 4 hours later with either Escherichia coli lipopolysaccharide (7.4 x 10(6)EU/kg, intravenously) or its saline vehicle. LPS administration resulted in a marked rise in TNF-alpha levels at 6 hours, which preceded the onset of liver injury. TNF-alpha messenger RNA (mRNA) in liver was increased by LPS treatment. The mRNA of receptors (R1 and R2) for TNF-alpha was also examined. R1 mRNA levels were not altered; however, R2 mRNA levels were increased by either AFB(1) or LPS administration. To determine if TNF-alpha plays a causal role in the development of liver injury, the increase in TNF-alpha was attenuated by administration of either pentoxifylline or anti-TNF-alpha serum, and liver injury was assessed. Administration of either of these agents resulted in protection. LPS treatment resulted in the upregulation of gene transcription for cyclooxygenase-2 (COX-2). However, administration of the selective COX-2 inhibitor NS-398 did not decrease injury. TNF-alpha and COX-2 inhibitors did not affect hepatic sequestration of neutrophils. Furthermore, it did not appear that TNF-alpha contributed to injury through inhibition of tissue repair. These data support the hypothesis that LPS-induced expression of TNF-alpha underlies the potentiation of AFB(1)-induced hepatotoxicity.

Bacterial lipopolysaccharide exposure augments aflatoxin B(1)-induced liver injury.

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.