Numerical changes in the mitochondrial DNA displacement loop in lung lesions induced by N-nitrosobis(2-hydroxypropyl)amine in rats.

Mutations in the mitochondrial DNA (mtDNA) displacement loop (D-loop) region were investigated to clarify the possible molecular mechanisms underlying the development of lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats. Male Wistar rats, 6 weeks of age, were given 2000 ppm BHP in their drinking water for 12 weeks and then maintained without further treatment until sacrifice at 25 weeks. Genomic DNA was extracted from paraffin-embedded tissues and polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis, followed by nucleotide sequencing, was performed. Eleven out of 24 hyperplasias (45.6%), 8 out of 16 adenomas (50.0%), and 14 out of 21 adenocarcinomas (66.7%) showed numerical changes, in a polymeric C-tract at positions 16,086-16,092 of the mtDNA D-loop, with a one base insertion of cytosine increasing the length of the C-tract, from the seven nucleotides observed in normal lung tissues from non-BHP treated rats, to eight. These changes were all homoplasmic and no changes were found in lung lesions when the length of the C-tract in the normal lung tissues adjacent to the lesions was seven. These results suggest that alterations in the mtDNA D-loop may occur in an early phase of lung carcinogenesis induced in rats by BHP.

Chemopreventive Action by Ethanol-extracted Brazilian Green Propolis on Post-initiation Phase of Inflammation-associated Rat Colon Tumorigenesis.

BACKGROUND/AIM: Propolis has since long been utilized in numerous folk medicines with a variety of medicinal properties. In this study, the effects of ethanol-extracted (EEP) and water-extracted (WEP) Brazilian green propolis on the post-initiation phase of inflammation-associated rat colon tumorigenesis were directly compared. MATERIALS AND METHODS: Male F344 rats at 6 weeks of age were subcutaneously injected with 1,2-dimethylhydrazine (DMH) at 40 mg/kg body weight twice during the first week, followed by 1% dextran sodium sulfate (DSS) in drinking water for one week. After a 1-week no-treatment period, animals were administered either basal Oriental MF powdered diet, or 1% EEP or 1% WEP in the basal diet until week 32. RESULTS: Post-initiation treatment with EEP significantly reduced the multiplicity of colorectal carcinomas compared to the control (0.40±0.13/rat vs. 2.29±0.84/rat, respectively, p<0.05), and EEP also reduced the tumor volume. Immunohistochemically, expression of inflammation-associated proteins inducible nitric oxide synthase, tumor necrotic factor alpha, nuclear factor kappa B and glutathione peroxidase-2 were significantly diminished in colorectal tumors from EEP-treated rats. CONCLUSION: Suppression of inflammation and oxidative stress, which had been triggered by DMH and promoted by DSS, was a primary mechanism by which EEP suppressed carcinogenesis.

Hormonally active doses of isoflavone aglycones promote mammary and endometrial carcinogenesis and alter the molecular tumor environment in Donryu rats.

Our research is focused on modifying effects of an isoflavone aglycones (IAs)-rich extract at a hormonally active dose of 150 mg/kg body weight/day on mammary and endometrial carcinogenesis in female Donryu rats. IA administered for 2 weeks in a phytoestrogen-low diet exerted estrogenic activity and induced cell proliferation in the uterus of ovariectomized rats. Furthermore, administration for 4 weeks resulted in elevation of cell proliferation in the mammary glands of 7,12-dimethylbenz[a]anthracene (DMBA)-treated animals. Forty weeks of postpubertal administration of IA to 5-week-old rats after initiation of mammary and endometrial carcinogenesis with DMBA and N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) caused significant increase of incidence and multiplicity of mammary adenocarcinoma, multiplicities of endometrial atypical hyperplasia, adenomatous polyps, and an increased trend of uterine adenocarcinomas. Liquid chromatography with tandem mass spectrometry and immunohistochemical analyses revealed significant elevation of tumorigenesis-related proteins such as S100 calcium-binding protein A8, kininogen 1, and annexins 1 and 2 in mammary adenocarcinomas and cadherin EGF LAG seven-pass G-type receptor 2, DEAD box polypeptide 1, and cysteine- and glycine-rich protein 1 in uterine proliferative lesions of IA-treated animals. Those changes are likely to be related to modulation of estrogen receptor (ER), AP1, nuclear factor-kappa B, and actin signaling pathways. Our results indicate that the postpubertal exposure of Donryu rats to IA at an estrogenic dose results in promotion of mammary and uterine carcinogenesis induced by DMBA and ENNG, which might be related to the activation of ER-dependent signaling and alteration of the molecular tumor environment in the mammary gland and endometrium.

Disturbance of DNA methylation patterns in the early phase of hepatocarcinogenesis induced by a choline-deficient L-amino acid-defined diet in rats.

The authors investigated the DNA methylation patterns of the E-cadherin, Connexin 26 (Cx26), Rassf1a and c-fos genes in the early phase of rat hepatocarcinogenesis induced by a choline-deficient L-amino acid-defined (CDAA) diet. Six-week-old F344 male rats were continuously fed with the CDAA diet, and three animals were then killed at each of 4 and 8 days and 3 weeks. Genomic DNA was extracted from livers for assessment of methylation status in the 5' upstream regions of E-cadherin, Cx26, Rassf1a and c-fos genes by bisulfite sequencing, compared with normal livers. The livers of rats fed the CDAA diet for 4 and 8 days and 3 weeks were methylated in E-cadherin, Cx26 and Rassf1a genes, while normal livers were all unmethylated. In contrast, normal livers were highly methylated in c-fos gene. Although the livers at 4 days were weakly methylated, those at 8 days and 3 weeks were markedly unmethylated. Methylation patterns of CpG sites in E-cadherin, Cx26 and Rassf1a were sparse and the methylation was not associated with gene repression. These results indicate that gene-specific DNA methylation patterns were found in livers of rats after short-term feeding of the CDAA diet, suggesting gene-specific hypermethylation might be involved in the early phase of rat hepatocarcinogenesis induced by the CDAA diet.

Different mutation patterns of mitochondrial DNA displacement-loop in hepatocellular carcinomas induced by N-nitrosodiethylamine and a choline-deficient l-amino acid-defined diet in rats.

Mutations of the mitochondria DNA (mtDNA) displacement loop (D-loop) were investigated to clarify different changes of exogenous and endogenous liver carcinogenesis in rats. We induced hepatocellular carcinomas (HCCs) in rats with N-nitrosodiethylamine (DEN) and a choline-deficient l-amino acid-defined (CDAA) diet. DNAs were extracted from 10 HCCs induced by DEN and 10 HCCs induced by the CDAA diet. To identify mutations in mtDNA D-loop, polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis, followed by nucleotide sequencing, was performed. Mutations were detected in 5 out of 10 HCCs (50%) induced by DEN. Four out of 5 mutations were G/C to A/T transitions at positions 15707, 15717, 15930, and 16087, and one T/A to C/G transition at position 15559. By contrast, no mutations were found in 10 HCCs induced by the CDAA diet. These results demonstrated that mutations in mtDNA D-loop occur in rat HCCs induced by DEN but not by the CDAA diet, suggesting that mtDNA D-loop is a target of exogenous liver carcinogenesis in rats.