Project description:Viral hepatitis and aflatoxin B1 (AFB1) exposure are common risk factors for hepatocellular carcinoma (HCC). The incidence of HCC in individuals co-exposed to hepatitis C (HCV) or B virus and AFB1 is greater than could be explained by the additive effect, yet the mechanisms are poorly understood due to lack of an animal model. This study investigated the outcomes and mechanisms of combined exposure to HCV and AFB1. We hypothesized that HCV transgenic (HCV-Tg; expressing core, E1, E2, and p7, nucleotides 342-2771) mice will be prone to hepatocarcinogenesis when exposed to AFB1. Neonatal (7 days old) HCV-Tg or C57BL/6J wild-type mice were exposed to AFB1 (6 ug/g bw) or tricaprylin vehicle (15 ul/g bw) and male offspring were followed for up to 12 months. No liver lesions were observed in vehicle-treated wild type or HCV-Tg mice. Tumors (adenomas or carcinomas) and preneoplastic lesions (hyperplasia or foci) were observed in 22.5% (9 of 40) of AFB1-treated wild-type mice. In HCV-Tg, the incidence of tumorous or pre-tumorous lesions was significantly elevated (50%, 18 of 36), with the difference largely due to a 2.5-fold increase in the incidence of adenomas (30.5% vs 12.5%). While oxidative stress and steato-hepatisis were observed in both AFB1-treated groups, molecular changes indicative of the enhanced inflammatory response and altered lipid metabolism were more pronounced in HCV-Tg mice. In summary, HCV proteins core, E1, E2 and p7 are sufficient to reproduce the additive co-carcinogenic effect of HCV and AFB1 which is a known clinical phenomenon. HCV transgenic mice (SL-139 strain, pAlbSVPA-HCV-S, containing the structural genes core, E1, E2, and p7, nucleotides 342-2771 of HCV genotype 1b, strain N, under the control of the murine albumin promoter/enhancer) on C57BL/6J (Jackson Laboratory, Bar Harbor, ME) background were previously reported in Lerat et al (Lerat et al., Gastroenterology 122, 352-365, 2002). Transgenic animals were identified after weaning as detailed in Korenaga et al (Korenaga et al., J Biol. Chem. 280, 37481-37488, 2005). Neonatal (7 days old) mice were administered a single dose of AFB1 (6 ug/g bw) or tricaprylin vehicle (15 ul/g bw) by intra-peritoneal injection. Male mice were maintained on the regular animal chow with free access to food and water for up to 12 months. All animal experiments were approved by the UNC Animal Care and Use Committee.

Project description:Viral hepatitis and aflatoxin B1 (AFB1) exposure are common risk factors for hepatocellular carcinoma (HCC). The incidence of HCC in individuals co-exposed to hepatitis C (HCV) or B virus and AFB1 is greater than could be explained by the additive effect, yet the mechanisms are poorly understood due to lack of an animal model. This study investigated the outcomes and mechanisms of combined exposure to HCV and AFB1. We hypothesized that HCV transgenic (HCV-Tg; expressing core, E1, E2, and p7, nucleotides 342-2771) mice will be prone to hepatocarcinogenesis when exposed to AFB1. Neonatal (7 days old) HCV-Tg or C57BL/6J wild-type mice were exposed to AFB1 (6 ug/g bw) or tricaprylin vehicle (15 ul/g bw) and male offspring were followed for up to 12 months. No liver lesions were observed in vehicle-treated wild type or HCV-Tg mice. Tumors (adenomas or carcinomas) and preneoplastic lesions (hyperplasia or foci) were observed in 22.5% (9 of 40) of AFB1-treated wild-type mice. In HCV-Tg, the incidence of tumorous or pre-tumorous lesions was significantly elevated (50%, 18 of 36), with the difference largely due to a 2.5-fold increase in the incidence of adenomas (30.5% vs 12.5%). While oxidative stress and steato-hepatisis were observed in both AFB1-treated groups, molecular changes indicative of the enhanced inflammatory response and altered lipid metabolism were more pronounced in HCV-Tg mice. In summary, HCV proteins core, E1, E2 and p7 are sufficient to reproduce the additive co-carcinogenic effect of HCV and AFB1 which is a known clinical phenomenon. HCV transgenic mice (SL-139 strain, pAlbSVPA-HCV-S, containing the structural genes core, E1, E2, and p7, nucleotides 342-2771 of HCV genotype 1b, strain N, under the control of the murine albumin promoter/enhancer) on C57BL/6J (Jackson Laboratory, Bar Harbor, ME) background were previously reported in Lerat et al (Lerat et al., Gastroenterology 122, 352-365, 2002). Transgenic animals were identified after weaning as detailed in Korenaga et al (Korenaga et al., J Biol. Chem. 280, 37481-37488, 2005). Neonatal (7 days old) mice were administered a single dose of AFB1 (6 ug/g bw) or tricaprylin vehicle (15 ul/g bw) by intra-peritoneal injection. Male mice were maintained on the regular animal chow with free access to food and water for up to 12 months. All animal experiments were approved by the UNC Animal Care and Use Committee. There were 20 liver samples used for microarray analysis (12 month time point). All samples were run in one batch. There are 4 groups: WT/Control (4 samples - all biological replicates, i.e., different animals); WT/AFB1 (6 samples); HCV/Control (4 samples); HCV/AFB1 (6 samples). This was a 2 color design with a common reference mRNA. No dye swaps or replicate arrays were included.

Project description:Ingestion of aflatoxin B1 (AFB1) represents a major risk factor in the aetiology of human hepatocellular carcinoma. In the rat, the harmful effects of AFB1 can be prevented by the administration of certain drugs which induce hepatic detoxification enzymes. We have previously shown that treatment of rats with the chemoprotector ethoxyquin (EQ) results in a marked increase in expression of the Alpha-class glutathione S-transferase (GST) Yc2 subunit which has high activity towards AFB1-8,9-epoxide [Hayes, Judah, McLellan, Kerr, Peacock and Neal (1991) Biochem. J. 279, 385-398]. To allow an assessment of whether the increased expression of GST Yc2 represents a general adaptive resistance mechanism to chemical stress, that is invoked by both chemoprotectors and carcinogens, we have examined the effects of EQ, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), phenobarbital (PB), AFB1, 3-methylcholanthrene (3-MC) and clofibrate on the AFB1-glutathione-conjugating activity and the GST subunit levels in rat liver. In addition, the effect of these drugs on the hepatic levels of an aldehyde reductase (AFB1-AR) that metabolizes the cytotoxic dialdehydic form of AFB1 has been studied as this enzyme also appears to be important in chemoprotection. Administration of the antioxidants EQ, BHA or BHT, as well as PB, led to a marked increase in levels of the GST Yc2 subunit in rat liver, and this increase coincided with a substantial rise in the GST activity towards AFB1-8,9-epoxide; neither AFB1, 3-MC nor clofibrate caused induction of Yc2 or any of the GST subunits examined. Among the xenobiotics studied, EQ was found to be the most effective inducing agent for the Yc2 subunit as well as Yc1, Yb1 and Yf. However, PB was equally as effective as EQ in increasing levels of the Ya-type subunits, although it was not found to be as potent an inducer of the other GST subunits, including Yc2. In addition to induction of GST, EQ caused a substantial increase in the hepatic content of AFB1-AR. Both BHA and BHT were also able to induce this enzyme but, by contrast, PB was found to be a poor inducer of AFB1-AR. AFB1, 3-MC and clofibrate were unable to serve as inducers of this reductase. The presence of Alpha-class GST, including the Yc2 subunit, was examined in various rat tissues. Constitutive expression of Yc2 was found in the epididymis at levels comparable with that observed in the liver from EQ-treated rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Dataset Information

Dealing with aflatoxin B1 dihydrodiol acute effects: Impact of aflatoxin B1-aldehyde reductase enzyme activity in poultry species tolerant to AFB1 toxic effects.

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Dealing with aflatoxin B1 dihydrodiol acute effects: Impact of aflatoxin B1-aldehyde reductase enzyme activity in poultry species tolerant to AFB1 toxic effects.

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