BUTYLATED HYDROXYTOLUENE MODULATES DNA METHYLATION IN RATS

The major observation of this investigation is that a single intraperi toneal injection of butylated hydroxytoluene (BHT 60 mg/kg body mass) results within a few hours in a strong increase in nuclear DNA(cytosin e-5)-methyl transferase (methyl transferase) activity in the liver, ki dneys, heart, spleen, brain and lungs of male rats In most organs, the rise in methyl transferase activity is observed as early as 4 h after BHT injection, it reaches a maximum at 8 h and then, except for lungs and brain, gradually decreases to its initial level at 16 h. At the m aximum induction times, the methyl transferase activity in liver, kidn ey and spleen increases by about 16-, 3- and 5-fold, respectively. A s econd BHT injection at 96 h results in a secondary rise in hepatic met hyl transferase activity. Isoelectric focusing electrophoresis of cont rol rat liver nuclear extracts showed methyl transferase activity in t he pi 4.7 and 7.4 protein fractions. Both fractions methylate calf thy mus DNA better than they do Drosophila melanogaster DNA. In similar ex tracts from BHT-treated rats, the methyl transferase activity is found in three protein fractions with pi values equal to 4.0, 6.2 and 9.5, respectively. Most of the methyl transferase fractions from the livers of BHT-treated rats methylate the completely unmethylated D. melanoga ster DNA better than they do calf thymus DNA. Thus, BHT induces methyl transferase activity that preferably provides de novo DNA methylation . BHT injection had no significant effect on the hepatic contents of S -adenosylmethionine (AdoMet), S-adenosylhomocysteine (AdoHcy) and AdoM et/AdoHcy ratios. While BHT injection did not alter the 5-methyldeoxyc ytidine content in liver DNA, it did appear to alter such content in o ther organs. BHT appears to cause the reversible changes in the methyl ation status of an internal cytosine residue in some CCGG sites of the rat liver cytosine DNA-methyl transferase gene. BHT induces also hypo methylation of the renal methyl transferase gene and the hepatic c-Ha- ms gene. While BHT also increases the hepatic mRNA transcripts for the S-adenosylmethionine synthetase and the p53 genes, it had no detectab le effects on the corresponding mRNA transcripts for methyl transferas e homologous to murine methyl transferase. Thus, BHT induces tissue-sp ecific reversible changes in methyl transferase activity and methylati on of total DNA and various genes in rats. A strong increase in methyl transferase activity in rat liver is accompanied with BHT-induced cha nge in the methyl transferase set observed in this organ.