Initiation Of Carcinogenic Process Research Articles

Mandatory fortification with folic acid in the United States appears to have adverse effects on histone methylation in women with pre-cancer but not in women free of pre-cancer

To evaluate whether mandatory fortification of grain products with folic acid in the US is associated with changes in histone methylation in cells involved in cervical carcinogenesis. Cervical specimens obtained before (1990 to 1992) and after mandatory folic acid fortification (2000 to 2002) were used to examine the degree of histone methylation (H3 Lys-9) by immunohistochemistry. 91 women (51 before and 40 after fortification) were diagnosed with cervical intraepithelial neoplasia (CIN) grade 3 or carcinoma in situ (CIS) and sections utilized in the study also contained normal, reactive or metaplastic cervical epithelium, CIN 1 or CIN 2. 64 women (34 before and 30 after fortification) were free of CIN and these sections contained only normal or reactive cervical epithelium. Immunohistochemical staining for H3 Lys-9, its assessment in different cell or lesion types and data entry were blinded for fortification status. For each cell type or lesion category we used PROC MIXED in SAS with the specimen identifier as a random effect and the robust variance estimator to estimate age- and race-adjusted intensity score for H3 Lys-9 in the pre- and post-fortification periods. Degree of H3 Lys-9 methylation was significantly higher (P < 0.0001) in ≥CIN 2 lesions (CIN 2, CIN 3 and CIS) than in ≤CIN 1 lesions (CIN 1, normal, reactive and metaplastic), in both pre- and post-fortification CIN 3/CIS specimens. Age- and race-adjusted mean H3 Lys-9 score was significantly higher in all cell or lesion types in CIN 3/CIS specimens obtained in the post-fortification period compared to pre-fortification period (P < 0.05, all comparisons). In contrast, in specimens obtained from women free of CIN, Lys-9 methylation in normal/reactive cervical epithelium was significantly lower in post-fortification specimens than in pre-fortification specimens (P = 0.03). Higher levels of Lys-9 methylation in ≥CIN 2 compared to ≤CIN 1 lesions suggest that higher Lys-9 methylation is associated with progression of lower grade CIN to higher grade CIN. Higher Lys-9 methylation in cervical tissues of women diagnosed with CIN 3 in the post-fortification period than in pre-fortification period suggest that fortification may adversely affect histone methylation in already initiated cells. Lower Lys-9 methylation in normal/reactive cervical cells of women free of CIN in the post-fortification period than pre-fortification on the other hand suggests that fortification is likely to protect against initiation of carcinogenic process in the cervix. These results suggest that mandatory fortification with folic acid in the US seems to have different effects on cancer depending on the stage of carcinogenesis. Because this is the first study to report folic acid fortification-associated differences in histone methylation and because of the limitations inherent to the approach we have taken to demonstrate these differences, validation of the results in other study populations or with other techniques for assessing histone methylation is necessary.

Mandatory fortification with folic acid in the United States appear to have adverse effects on histone methylation in women with pre‐cancer but not in women free of pre‐cancer

The objective of this study was to evaluate whether mandatory fortification of grain products with folic acid in the USA is associated with changes in histone methylation in cells involved in cervical carcinogenesis. Cervical specimens (free of pre‐cancer or diagnosed with pre‐cancer cervical intraepithelial neoplasia grade 3 [CIN 3]) obtained before (1990‐92) or after mandatory folic acid fortification (2000‐02) were used to examine the degree of histone methylation (H3 Lys‐9) by immunohistochemistry. Age‐ and race‐adjusted mean H3 Lys‐9 score was significantly higher in CIN 3 specimens obtained in the post‐fortification period compared to pre‐fortification period (P &lt; 0.05). In contrast, in specimens obtained from women free of CIN, H3 Lys‐9 scores were significantly lower in post‐fortification specimens compared to pre‐fortification specimens (P &lt; 0.05). Altered histone methylation has emerged as key to DNA methylation‐related gene silencing and this type of gene silencing in cancer is accompanied by an increase in H3 Lys9 methylation. Therefore, higher Lys‐9 methylation in cervical tissues of women diagnosed with CIN 3 in the post‐fortification period compared to pre‐fortification period suggest that fortification may have adverse effects on histone methylation in already initiated cells. Lower Lys‐9 methylation in cervical cells of women free of CIN in the post fortification period compared to pre fortification on the other hand suggest that fortification is likely to protect against the initiation of carcinogenic process in the cervix.Supported by NCI R03 CA 102893

5-azacytidine potentiates initiation induced by carcinogens in rat liver.

To test the validity of the hypothesis that hypomethylation of DNA plays an important role in the initiation of carcinogenic process, 5-azacytidine (5-AzC) (10 mg/kg), an inhibitor of DNA methylation, was given to rats during the phase of repair synthesis induced by the three carcinogens, benzo[a]-pyrene (200 mg/kg), N-methyl-N-nitrosourea (60 mg/kg) and 1,2-dimethylhydrazine (1,2-DMH) (100 mg/kg). The initiated hepatocytes in the liver were assayed as the gamma-glutamyltransferase (gamma-GT) positive foci formed following a 2-week selection regimen consisting of dietary 0.02% 2-acetylaminofluorene coupled with a necrogenic dose of CCl4. The results obtained indicate that with all three carcinogens, administration of 5-AzC during repair synthesis increased the incidence of initiated hepatocytes, for example 10-20 foci/cm2 in 5-AzC and carcinogen-treated rats compared with 3-5 foci/cm2 in rats treated with carcinogen only. Administration of [3H]-5-azadeoxycytidine during the repair synthesis induced by 1,2-DMH further showed that 0.019 mol % of cytosine residues in DNA were substituted by the analogue, indicating that incorporation of 5-AzC occurs during repair synthesis. In the absence of the carcinogen, 5-AzC given after a two thirds partial hepatectomy, when its incorporation should be maximum, failed to induce any gamma-GT positive foci. The results suggest that hypomethylation of DNA per se may not be sufficient for initiation. Perhaps two events might be necessary for initiation, the first caused by the carcinogen and a second involving hypomethylation of DNA.