Vitamins B2 and B6 and genetic polymorphisms related to one-carbon metabolism as risk factors for gastric adenocarcinoma in the European prospective investigation into cancer and nutrition

B vitamins and polymorphisms in genes coding for enzymes involved in one-carbon metabolism may affect DNA synthesis and methylation and thereby be implicated in carcinogenesis. Previous data on vitamins B2 and B6 and genetic polymorphisms other than those involving MTHFR as risk factors for gastric cancer (GC) are sparse and inconsistent. In this case-control study nested within the European Prospective Investigation into Cancer and Nutrition cohort, cases (n = 235) and controls (n = 601) were matched for study center, age, sex, and time of blood sampling. B2 and B6 species were measured in plasma, and the sum of riboflavin and flavin mononucleotide was used as the main exposure variable for vitamin B2 status, whereas the sum of pyridoxal 5'-phosphate, pyridoxal, and 4-pyridoxic acid was used to define vitamin B6 status. In addition, we determined eight polymorphisms related to one-carbon metabolism. Relative risks for GC risk were calculated with conditional logistic regression, adjusted for Helicobacter pylori infection status and smoking status. Adjusted relative risks per quartile (95% confidence interval, P(trend)) were 0.85 (0.72-1.01, 0.06) for vitamin B2 and 0.78 (0.65-0.93, <0.01) for vitamin B6. Both relations were stronger in individuals with severe chronic atrophic gastritis. The polymorphisms were not associated with GC risk and did not modify the observed vitamin-cancer associations. In summary, results from this large European cohort study showed an inverse association between vitamin B2 and GC risk, which is borderline significant, and a significant inverse association between vitamin B6 and GC risk.

Dietary factors of one-carbon metabolism and prostate cancer risk

BACKGROUND

Folate is hypothesized to be inversely associated with the risk of several cancers, but such a potential association has not been well studied for prostate cancer. Vitamin B-6, vitamin B-12, methionine, and alcohol can influence folate-related metabolism.

OBJECTIVE

The objective was to investigate the associations between dietary factors of one-carbon metabolism and prostate cancer risk within the alpha-Tocopherol, beta-Carotene Cancer Prevention Study.

DESIGN

Of the cohort's 27 111 Finnish male smokers aged 50-69 y who had complete dietary data, 1270 had a diagnosis of incident prostate cancer between 1985 and 2002. Folate, vitamin B-6, vitamin B-12, methionine, and alcohol intakes were estimated from a 276-item modified dietary history questionnaire. Cox proportional hazard models, adjusted for age and vitamin supplement use, estimated relative risks (RR) and 95% CIs.

RESULTS

Vitamin B-6 intake was inversely associated with prostate cancer risk (RR for highest versus lowest quintile: 0.88; 95% CI: 0.72, 1.07; P for trend = 0.045), whereas vitamin B-12 intake was associated with significantly increased risk (RR = 1.36; 95% CI: 1.14, 1.96; P for trend = 0.01). No association between folate or alcohol intake and prostate cancer risk was observed. No differences were found in the above associations according to stage of disease or subgroups of several potential effect modifiers.

CONCLUSIONS

We found no convincing evidence for a protective role of one-carbon metabolism against prostate cancer, although these observations can be generalized only to smokers. The possible modest protective association with vitamin B-6 and the significantly elevated risk with vitamin B-12 intake warrant further investigation.

Downregulation of CD44v6 in colorectal carcinomas is associated with hypermethylation of the CD44 promoter region

Overexpression of the cell adhesion protein CD44v6 has been demonstrated in colorectal cancer and other gastrointestinal tumors. While CD44v6 is upregulated in benign colorectal adenomas and well-differentiated colorectal cancer tissues, downregulation frequently occurs during disease progression. The mechanism of downregulation, however, is unknown. Therefore, we evaluated the methylation status of the CD44 promoter as a mechanism for decreased CD44v6 expression in advanced colorectal carcinomas. We demonstrated by methylation-sensitive restriction enzyme digestion that the CpG islands of the CD44 promoter were methylated in 6/21 (28%) of benign colorectal adenomas. Interestingly, in colorectal carcinomas the frequency of promoter methylation was significantly increased (10/19; 53%) compared to 7/21 (33%) in the corresponding normal mucosa. Methylation seems to be associated with a more advanced cancer stage, but the trend did not reach statistical significance. In colorectal carcinomas with CD44 promoter methylation CD44v6 mRNA was detected by reverse transcription-polymerase chain reaction in 3/10 carcinomas, whereas in tumors without CD44 promoter methylation CD44v6 expression was observed in 8/9 (P <or= 0.05). These results demonstrated that methylation of the 5'CpG island of the CD44 gene is closely associated with decreased expression of CD44v6 in human colorectal carcinomas.

Vitamin B6-mediated suppression of colon tumorigenesis, cell proliferation, and angiogenesis (review)

This review describes current research on the preventive effect of dietary vitamin B(6) against colon tumorigenesis and its possible mechanisms. Studies in cell culture have demonstrated that high levels of vitamin B(6) suppress growth of some cancer cells. From these studies it has been considered that supraphysiological doses of vitamin B(6) suppress tumor growth and metastasis. However, recent rodent study has indicated that azoxymethane-induced colon tumorigenesis in mice is suppressed by moderate doses of dietary vitamin B(6.) Epidemiological studies also support an inverse relationship between vitamin B(6) intake and colon cancer risk. Potential mechanisms underlying the preventive effect of dietary vitamin B(6) have been suggested to include the suppression of cell proliferation, oxidative stress, nitric oxide (NO) synthesis, and angiogenesis.

CpG methylation of promoter region inactivates E-cadherin gene in renal cell carcinoma

CpG methylation in the promoter region has been shown to be important in the regulation of genes implicated in malignant transformation. The present study was designed to test the hypothesis that CpG methylation of the promoter region of the E-cadherin gene may inactivate its expression in renal cell carcinoma. To test this hypothesis, five kidney cancer cell lines and 34 microdissected renal cell carcinoma samples were analyzed for gene and protein expression by reverse transcription-polymerase chain reaction and immunohistochemistry, respectively. CpG methylation in the promoter regions of the E-cadherin gene was analyzed by the sodium bisulfite genome sequencing technique. Our results show that all normal renal tissue expressed the E-cadherin gene and protein. Of the renal cancer tissues analyzed, 67% (23 of 34) lacked E-cadherin expression, with an associated increase in methylation, compared with normal tissue. E-cadherin gene promoter was methylated in all renal cancer cell lines and was accompanied by a loss of E-cadherin gene and protein expression. The treatment of renal cancer cell lines with the demethylating agent 5-aza-2'-deoxycytidine restored E-cadherin mRNA expression in all renal cancer cell lines. This is the first report that shows inactivation of the E-cadherin gene and protein in renal cell carcinoma through CpG hypermethylation in the promoter region of this gene. The results of these experiments may contribute to an understanding of the role of E-cadherin inactivation in renal cell carcinoma.

Association of the B-vitamins pyridoxal 5'-phosphate (B(6)), B(12), and folate with lung cancer risk in older men

A nested case-control study was conducted within the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study cohort to test for associations between selected B-vitamins (folate, vitamin B(6), vitamin B(12)) and incident lung cancer. This trial was conducted in Finland between 1985 and 1993. Serum was analyzed for these nutrients and homocysteine among 300 lung cancer cases and matched controls (1:1). Odds ratios and 95% confidence intervals were determined in conditional and unconditional (controlling for the matching factors) logistic regression models, after adjusting for body mass index, years of smoking, and number of cigarettes smoked per day. No significant associations were seen between serum folate, vitamin B(12), or homocysteine and lung cancer risk. The authors found significantly lower risk of lung cancer among men who had higher serum vitamin B(6) levels. Compared with men with the lowest vitamin B(6) concentration, men in the fifth quintile had about one half of the risk of lung cancer (odds ratio = 0.51; 95% confidence interval: 0.23, 0.93; p-trend = 0.02). Adjusting for any of the other serum factors (folate, B(12), and homocysteine) either alone or jointly did not significantly alter these estimates. This is the first report from a prospectively conducted study to suggest a role for vitamin B(6) in lung cancer.

Methyl group metabolism gene polymorphisms and susceptibility to prostatic carcinoma

BACKGROUND

Alterations of DNA methylation are very frequent in prostatic carcinoma. A possible cause underlying altered DNA methylation could be an insufficient level of S-adenosylmethionine as a consequence of nutritional imbalances or of weaker alleles of genes for its synthesis, i.e., encoding methylene-tetrahydrofolate reductase (MTHFR), methionine synthase (MS), and beta-cystathione synthetase (CBS). Therefore, homozygosity or heterozygosity for such weaker alleles may underlie susceptibility to prostatic carcinoma.

METHODS

The distribution of the two most frequent MTHFR, MS, and CBS alleles was determined in 132 prostatic carcinoma patients and 150 population controls by restriction fragment length polymorphism-(RFLP) PCR.

RESULTS

In the controls, a Hardy-Weinberg equilibrium was observed for each allele pair. No significant differences were observed with respect to age or gender. No significant differences for single genes or combinations were found between prostatic carcinoma patients and controls, although the MTHFR Val allele was slightly overrepresented among the tumor patients. Neither did the allele distribution significantly differ among the prostatic carcinoma patients stratified according to age, clinical stage, or presence of metastases. However, the MTHFR Val allele tended to be associated with higher tumor grade.

CONCLUSIONS

In general, the data do not support the hypothesis that weaker alleles in methyl group metabolism genes constitute a major factor in the high prevalence of DNA methylation alterations found in prostatic carcinoma. However, a potential association with the MTHFR genotype deserves further study.

Morphological identification of the patterns of prostatic intraepithelial neoplasia and their importance

High grade prostatic intraepithelial neoplasia (PIN) is the most likely precursor of prostatic carcinoma. PIN has a high predictive value as a marker for carcinoma, and its identification in biopsy specimens warrants repeat biopsy for concurrent or subsequent carcinoma. The only methods of detection are biopsy and transurethral resection; PIN does not greatly raise the concentration of serum prostate specific antigen (PSA) or its derivatives, does not induce a palpable mass, and cannot be detected by ultrasound. Androgen deprivation decreases the prevalence and extent of PIN, suggesting that this form of treatment might play a role in chemoprevention. Radiotherapy is also associated with a decreased incidence of PIN.

Silencing of CD44 expression in prostate cancer by hypermethylation of the CD44 promoter region

Loss of the CD44 transmembrane glycoprotein in primary prostate cancer has been shown to be associated with unfavorable clinical behavior. Moreover, the majority of prostate cancer metastases lack expression of this molecule. The mechanism of CD44 silencing in prostate cancer was investigated using both patient material and in vivo-propagated human prostate cancer xenografts. In 9 of 11 lymph node metastases of prostate cancer, we demonstrated by methylation-sensitive restriction enzyme digestion that the promoter region of the CD44 gene is methylated, indicating that this represents a major mechanism of CD44 silencing. Similarly, in 6 out of 12 in vivo-growing human prostate carcinoma xenograft models, hypermethylation of the CD44 gene was found. The extent of CpG island methylation was investigated by nucleotide sequencing after bisulphite modification of the CD44 promoter region. In the xenografts displaying hypermethylation, the examined 14 CpG sites in the CD44 transcription regulatory domain, including a Sp1 binding site, were consistently methylated. This correlated with reduced CD44 expression or lack of CD44 expression at mRNA and protein levels. In the xenografts lacking hypermethylation of the CD44 gene, high levels of CD44 mRNA and protein were expressed in some models, whereas in others CD44 mRNA expression was only detectable by RT-PCR and the CD44 protein could hardly be detected or was not detected at all. The results indicate that, in most prostate cancers, loss of CD44 expression is associated with extensive hypermethylation of the CpG island of the CD44 promoter region, but other, posttranscriptional mechanisms may also lead to CD44 loss.

High frequency of alterations in DNA methylation in adenocarcinoma of the prostate

BACKGROUND

Alterations of DNA methylation have been reported in many human cancers. In prostatic carcinoma, hypermethylation of the GST P gene promoter and an overall decrease in methylcytosine content have been reported. The aim of the present study was to investigate the frequency and extent of these alterations in relation to tumor stage and grade, in order to explore their clinical relevance and to determine their relationship to each other.

METHODS

DNA from 32 histologically verified adenocarcinomas of the prostate was analyzed for GST P hypermethylation by a semiquantitative PCR method and for overall DNA methylation by quantitative Southern blot analysis or LM-PCR of LINE-1 repetitive sequence methylation.

RESULTS

GST P hypermethylation was detected in 24/32 (75%) specimens, and LINE-1 hypomethylation in 17/32 (53%). Both alterations tended to increase in frequency and extent with tumor stage. All but 1 of 8 carcinomas with lymph node involvement were positive for GST P hypermethylation. Six of these as compared to 2 out of 24 showed strong hypomethylation (P = 0.005). Hypermethylation and hypomethylation did not show a quantitative correlation, but all except two samples with weak LINE-1 hypomethylation also displayed GST P hypermethylation.

CONCLUSIONS

GST P hypermethylation is an extremely frequent change in prostatic carcinoma which most probably precedes genome-wide hypomethylation. It appears useful for sensitive detection of prostatic carcinoma, whereas pronounced LINE-1 hypomethylation may be associated with progressive tumors.

Differences in p16 gene methylation and expression in benign and malignant ovarian tumors

OBJECTIVE

The aim of this study was to test the hypothesis that DNA methylation is important for silencing the p16 tumor suppressor gene in ovarian epithelial tumors and to compare the prevalence of this mechanism among different ovarian epithelial tumor subtypes.

METHOD

Methylation-specific PCR was used to analyze the p16 gene for DNA methylation in 20 ovarian cystadenomas, 15 low malignant potential (LMP) tumors, and 37 carcinomas. p16 expression was determined immunohistochemically in 58 of these tumors (16 cystadenomas, 13 LMP tumors, 29 carcinomas). Differences in methylation or expression rates between specific tumor subgroups were examined by Fisher's exact test.

RESULTS

Fragments from the distal promoter and beginning of the first exon of the p16 gene were both methylated in 5 of 15 (33%) LMP tumors compared to 2 of 37 (5%) carcinomas (P = 0. 02). Those sites were also methylated in 5 of 20 (25%) cystadenomas. Lack of p16 expression was present in 7 of 16 cystadenomas, 4 of 13 LMP tumors, and 22 of 29 carcinomas (P [LMPs versus carcinomas] = 0. 01) and correlated with methylation changes in LMP tumors (P = 0.05). p16 expression was correlated with mucinous differentiation in cystadenomas (P = 0.001).

CONCLUSION

p16 silencing may be important for the development of ovarian carcinomas and a subset of LMP tumors. Changes in DNA methylation may be more important for inactivation of this gene (and perhaps other tumor suppressor genes) in LMP tumors, which lack many of the alternative mechanisms present in carcinomas. p16 expression is primarily related to mucinous differentiation in cystadenomas.

The cadherin cell-cell adhesion pathway in prostate cancer progression

Cadherins are a family of calcium-dependent cell-cell adhesion molecules involved in cell-cell aggregation and morphoregulatory cell function. Dysfunction of the cadherin pathway is involved in tumour invasiveness and disease progression for a variety of carcinomas. E-cadherin is a prognostic marker in prostatic cancer, based on the correlation of the grade of E-cadherin expression and tumour grade, stage, metastasis and survival, as well as recurrence after radical prostatectomy. P-cadherin was shown to be lost in all prostatic cancers, although this most likely reflects loss of the basal cell population rather than a transcriptional down-regulation, suggesting that loss of P-cadherin expression is an early event in the tumorigenesis of prostatic carcinomas. Catenins, particularly alpha-catenin, also play an important role in the dysfunction of the cell adhesion complex. Mechanisms of inactivation of the cadherin-catenin pathway include LOH, gene deletions and gene promoter hypermethylation. Therapeutic strategies have been investigated in tumour models, i.e. the use of demethylating agents for the hypermethylated promoter region of E-cadherin or gene transfer in PC-3 cells with homozygous deletion of the alpha-catenin gene. The complexity of neoplastic changes cannot be explained by alterations of cell adhesion molecules alone; but as demonstrated, cadherins and catenins play an important role in this process.

Characterization and glutamyl preferring carboxypeptidase function of prostate specific membrane antigen: a novel folate hydrolase

We have cloned the gene encoding the prostate-specific membrane (PSM) antigen, which is recognized by the 7E11C-5 antibody. The antigen is strongly expressed in prostate cancer, and the antibody has been approved for use as an imaging agent for detection of prostatic cancer metastasis. The gene was unique and encoded a type II membrane protein. The only clue to its potential function was found in the cDNA coding sequences from 1250 to 1700, which had a modest but significant homology with transferrin-receptor, demonstrating a 54% homology of nucleic acid sequence. In comparing the mRNA obtained from normal prostate with that obtained from cancerous or lymph node carcinoma of the prostate (LNCaP) cells, normal cells produced a shorter alternative spliced species that encoded a cytosolic form of the protein, and not a membrane protein. It appeared that, as the prostatic cells became cancerous, there was a nearly 100-fold difference in expression of the ratio of the messages encoding the 2 forms, with the cytosolic form (PSM') predominant in normal cells and the membrane form (PSM) predominant in cancer cells. The other tissue in which the membrane antigen form of PSM is highly expressed is the membrane brush border of the small intestine of the proximal, but not distal, small intestine. This is the location of a unique membrane form of a folate hydrolase. This membrane folate hydrolase and its location are necessary in human nutrition because humans require folate, and the folate in foods is poly-gamma-glutamated. Polyglutamated folates cannot be taken into the cells by folate-transporter systems. The ability to take up folate from foods requires the membrane folate hydrolase to sequentially remove the gamma-linked glutamates, freeing folate that can then be transported. PSM antigen has a similar folate hydrolase activity. Others have reported finding an enzyme in the rat brain that functions as an alpha-neurocarboxypeptidase and acts on the abundant brain peptide N-acetylaspartylglutamate to generate glutamate and N-acetylaspartate. The 3'-end of the rat brain enzyme had 84% sequence homology with PSM antigen. Because this enzyme liberates glutamate in the brain, the enzyme is considered to have regulatory activity related to glutamate receptors. Current investigations are underway to determine whether glutamate receptors are present in prostate. Thus, PSM antigen is a unique folate hydrolase-carboxypeptidase that can release glutamate with either gamma-or alpha-linkage. Its enzymatic activity raises a number of questions for consideration. In the normal prostate where the protein is intracellular, is PSM' antigen keeping folate in nonglutamated forms? If so, folate should be able to readily diffuse out of prostate cells, making the prostate gland an organ at risk for localized folate deficiency and carcinogenesis. In prostate tumor cells, with the enzyme outside of the cell, can PSM antigen be used for the activation of cytotoxic prodrugs?