Assessment of the effect of betaine on p16 and c-myc DNA methylation and mRNA expression in a chemical induced rat liver cancer model.
BACKGROUND
The development and progression of liver cancer may involve abnormal changes in DNA methylation, which lead to the activation of certain proto-oncogenes, such as c-myc, as well as the inactivation of certain tumor suppressors, such as p16. Betaine, as an active methyl-donor, maintains normal DNA methylation patterns. However, there are few investigations on the protective effect of betaine in hepatocarcinogenesis.


METHODS
Four groups of rats were given diethylinitrosamine (DEN) and fed with AIN-93G diets supplemented with 0, 10, 20 or 40 g betaine/kg (model, 1%, 2%, and 4% betaine, respectively), while the control group, received no DEN, fed with AIN-93G diet. Eight or 15 weeks later, the expression of p16 and c-myc mRNA was examined by Real-time PCR (Q-PCR). The DNA methylation status within the p16 and c-myc promoter was analyzed using methylation-specific PCR.


RESULTS
Compared with the model group, numbers and areas of glutathione S-transferase placental form (GST-p)-positive foci were decreased in the livers of the rats treated with betaine (P < 0.05). Although the frequency of p16 promoter methylation in livers of the four DEN-fed groups appeared to increase, there is no difference among these groups after 8 or 15 weeks (P > 0.05). Betaine supplementation attenuated the down-regulation of p16 and inhibited the up-regulation of c-myc induced by DEN in a dose-dependent manner (P < 0.01). Meanwhile, increases in levels of malondialdehyde (MDA) and glutathione S-transferase (GST) in model, 2% and 4% betaine groups were observed (P < 0.05). Finally, enhanced antioxidative capacity (T-AOC) was observed in both the 2% and 4% betaine groups.


CONCLUSIONS
Our data suggest that betaine attenuates DEN-induced damage in rat liver and reverses DEN-induced changes in mRNA levels.
Du
Yan-ping
YP
School of public health, Sun Yat-Sen University, Guangzhou 510080, PR China. ypdu518@163.com
Peng
Jun-sheng
JS
Sun
Ai
A
Tang
Zhi-hong
ZH
Ling
Wen-hua
WH
Zhu
Hui-lian
HL
D000818:Animals; D001622:Betaine / Q000494:pharmacology*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism*; D019175:DNA Methylation; D004052:Diethylnitrosamine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D015227:Lipid Peroxidation; D008099:Liver / Q000201:enzymology; D008113:Liver Neoplasms / Q000139:chemically induced* / Q000188:drug therapy*; D008745:Methylation; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction
D019941:Cyclin-Dependent Kinase Inhibitor p16; D016271:Proto-Oncogene Proteins c-myc; D004052:Diethylnitrosamine; D001622:Betaine