Detection of initiation activity of 1,2-dimethylhydrazine in in vivo medium-term liver initiation assay system using 4-week-old rats without hepatocellular proliferative stimuli during the test chemical treatment period

Ameliorative Effects of Aspergillus awamori against the Initiation of Hepatocarcinogenesis Induced by Diethylnitrosamine in a Rat Model: Regulation of Cyp19 and p53 Gene Expression

Hepatocellular carcinoma (HCC) is the most common cancer in humans. Despite advances in its treatment, liver cancer remains one of the most difficult cancers to treat. This study aimed to investigate the ameliorative action and potential mechanism of Aspergillus awamori (ASP) administration against the initiation process of liver carcinogenesis induced by diethylnitrosamine (DEN) in male Wistar rats. Seventy-two male rats were divided equally into eight groups as follows, Group 1: untreated control; Group 2: DEN (200 mg/kg bw) intra-peritoneally for the initiation of HCC; Groups 3-5: DEN + ASP at a dose of 1, 0.5, and 0.25 mg/kg bw and groups 6-8: ASP at a dose of 1, 0.5, and 0.25 mg/kg bw. Supplementation of A. awamori significantly lightened the adverse impacts induced by DEN via restoring the leukogram to normal, lowering the elevated serum aspartate aminotransferase (AST), alanine transaminase (ALT), and γ-glutamyl transferase (GGT), and alkaline phosphatase (ALP). Furthermore, it enhanced the hepatic antioxidant capacity through increasing the reduced glutathione (GSH) level and catalase (CAT) activity with a marked reduction in malondialdehyde (MDA) level. In addition, it decreased the positive GST-P foci. Likewise, a significant alteration of DEN-associated hepatocarcinogenesis occurred through inhibiting cytochrome P450 (Cyp19) and activating p53 gene expression. In conclusion, supplementation of A. awamori counteracts the negative effects of DEN, inhibits the early development of GST-P-positive foci and could be used as a new alternative strategy for its chemo-preventive effect in liver cancer. To the best of our knowledge, the present study is the first to report the hepato-protective effect of A. awamori in induced hepatocarcinogenesis.

Early molecular events associated with liver and colon sub-acute responses to 1,2-dimethylhydrazine: Potential implications on preneoplastic and neoplastic lesion development

This study unveiled the early cellular and molecular events induced by 1,2-dimethylhydrazine (DMH) in the colon and liver and their implications on pre- and neoplastic lesion burden in a late timepoint. Male Wistar rats received four DMH injections (40 mg/kg body weight) for 2 weeks and were sacrificed 24 h (short-term study) or 22 (medium-term study) weeks after the last DMH administration. In the short-term study, DMH led to increased leukocyte (comet assay) and colon (H2AX) genotoxicity, enhanced proliferation (Ki-67) and apoptosis (caspase-3) indexes in both liver and colon. Furthermore, the expression of mRNA (Cat, Gsta1, Gsta2, Gpx1, Gstm1, Sod1, Sod2 and Sod3) and the activity of antioxidant agents were diminished in the colon and liver of DMH-induced rats, eliciting an environment of oxidative stress featuring elevated lipid hydroperoxide levels. Apoptosis effectors were upregulated in the liver (Bax, Casp3 and Fas), and developmental genes were downregulated in both colon and liver (Foxa1, Foxa2, Smad2 and Smad4). In the medium-term study, DMH led to a high number of preneoplastic colonic aberrant crypt foci and tumors (adenomas and invasive adenocarcinomas) but few preneoplastic hepatic glutathione S-transferase (GST-P)-positive foci. Our novel gene expression data highlights overlooked mechanisms in the liver (main metabolizing organ) and colon (main target organ) on toxicity and carcinogenesis induced by repeated doses of DMH, as both organs should be considered in further interventions on the initiation stage of colon carcinogenesis.

Augmentation of diethylnitrosamine-induced early stages of rat hepatocarcinogenesis by 1,2-dimethylhydrazine

Diethylnitrosamine (DEN) and 1,2-dimethylhydrazine (DMH) are classical carcinogens used in experimental rodent carcinogenesis. However, the interaction effects of these carcinogens on biochemical and molecular changes during carcinogenesis have not been investigated. Therefore, the effect of DEN and DMH co-administration on preneoplastic lesion formation and its molecular mechanism in rats were determined. Triple intraperitoneal administrations of DEN were made before, during or after double subcutaneous injections of DMH. At week 8 of the experiment, the preneoplastic hepatic glutathione-S-transferase placental form (GST-P) positive foci and colonic aberrant crypt foci (ACF) were analyzed. The combined treatment of these carcinogens increased toxicity to rats. Administration of DMH alone did not induce hepatic GST-P positive foci, while co-treatment with DMH enhanced hepatic GST-P positive foci formation. However, DEN did not influence the size or number of colonic ACF. The treatment with DMH alone induced CYP2E1 and P450 reductase, demonstrating that DMH enhanced DEN metabolism in DEN- and DMH-treated rats. These findings were related to increases in hepatic O⁶-methylguanine DNA adducts and hepatotoxicity, which are associated with the induction of cell proliferation and liver cancer development. DEN-induced early stages of rat hepatocarcinogenesis were synergistically promoted by DMH via metabolic enzyme induction leading to enhanced DNA mutation and hepatocarcinogenicity.

Changes in the gene expression and enzyme activity of hepatic cytochrome P450 in juvenile Sprague-Dawley rats

The developmental changes in the hepatic cytochrome P450 (CYP) content, mRNA expression of 12 hepatic CYP subtypes, and the enzyme activities of 5 hepatic CYP subfamilies in rats were investigated using non-treated male and female Sprague-Dawley rats of ages postnatal day (PD) 4, 16, 30 and 8 and 12 weeks. The hepatic proliferation kinetics was also determined by using the phospho-histone H3 (p-histon)-labeled hepatocyte index. The developmental changes in the enzyme activities of hepatic expression of CYP1A and CYP3A in rats were similar to those in humans, although there is no fetal-neonatal dominant CYP3A subtype in rat livers unlike human CYP3A7. On the other hand, the developmental pattern of expression of the CYP2C subfamily differed between humans and rats. Enzyme activity and mRNA expression of each hepatic CYP subtype in rats on PD 30 was similar to that after 8 weeks of age, except in the case of sex-dependent CYP subtypes. The p-histon-labeled hepatocyte index was approximately 10-fold higher in PD 30 rats than in 8-week-old rats. Therefore, the livers of juvenile rats, which have high hepatocellular proliferation activity and a sufficient amount of metabolic enzymes such as CYP, may be more sensitive to the cytotoxic and carcinogenic effects of chemicals than the livers of adult rats. Thus, our results on developmental difference of hepatic CYPs in juvenile rats are useful to identify underlying age-dependent susceptibility of chemical-induced toxicity, and to understand developmental change of chemical disposition.