UMLS:C0596263 - FACTA Search

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Query: UMLS:C0596263 (carcinogenesis)
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We compared the hormonal and epidemiological aspects of ovarian cancer patients in search of the etiology of this neoplasia. Case-control studies of Japanese women with and without cancer were conducted in parallel, with regard to both the excretion of 14 urinary steroids and the pertinent physical and physiological parameters. The results obtained are as follows: 1) premenopausal ovarian cancer patients before and after radical ovariectomy and postmenopausal-postoperative patients were associated with a specified steroid deviation profile characterized by a combination of general depression of androgens, progestins and corticosteroids with sole rescue of tetrahydrocortisol (THF) in urine. 2) The deviation profile of postmenopausal-preoperative cancer patients was distinguished from the 3 partner profiles by its preservation of normalcy in the excretions of androgen and progestin in urine. 3) Ovarian cancer patients were associated with growth retardation, when compared with urban healthy controls and patients with either breast cancer or endometrial cancer by the age-matching method. Ovarian cancer patients were also less fertile than age-matched normal controls, and were as infertile as age-matched patients with either breast cancer or endometrial cancer. 4) Epidemiological evidence was presented to suggest that the incidence of ovarian cancer in Japan was increasing in parallel with the recent increase of social tension in Japan. The possible relevance of the hormonal characteristics of ovarian cancer patients to both the epidemiological characteristics of the same cancer patients and the genesis of this neoplasia is discussed in the light of the 2-step carcinogenesis theory.
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PMID:Relation between the hormonal and epidemiological aspects of ovarian cancer patients in Japan. 144 27

The chemotherapeutic value of methotrexate resides in its ability to perturb folate-dependent one-carbon metabolism and subsequently inhibit DNA synthesis. To assess the functional effect of methotrexate on hepatic one-carbon metabolism, we have developed and applied tracer kinetic techniques in vivo to quantify the carbon flux through the folate-dependent one-carbon pool in rats. Following a 7-day treatment period with methotrexate (0.2 mg/kg body weight), the tracers L-[ring-2-14C] histidine and L-[methyl-3H] methionine were simultaneously infused into control and methotrexate-treated rats. Methotrexate treatment decreased hepatic tetrahydrofolate, methyltetrahydrofolate, and formyltetrahydrofolate, concentrations by 63, 83, and 58%, respectively. Furthermore, the enzymatic activity of 10-formyltetrahydrofolate dehydrogenase, the terminal enzyme in the catabolism of the ring-2-carbon of histidine to CO2, was diminished by 32% in methotrexate-treated animals. These changes in enzyme activity and folate coenzyme concentrations did not result in a significant decrease in the oxidative flow of carbon from histidine to CO2 in methotrexate-treated rats compared to control animals (2.40 and 3.22 micromol/h/kg3/4, respectively). Oxidative carbon flow was reflective of tetrahydrofolate and formyltetrahydrofolate pools when expressed as a percent of total folate: neither coenzyme pool was diminished as a result of methotrexate treatment. In contrast, the reductive carbon flux through the one-carbon pool from histidine to methionine was significantly decreased 59% in methotrexate-treated (7.63 micromol/h/kg3/4) versus control rats (18.73 micromol/h/kg3/4)). Likewise, methyltetrahydrofolate, as a percent of total folate, was reduced 51% in methotrexate-treated rats. Consequently, total measured carbon flow (oxidative+reductive) was 54% lower in rats subjected to subchronic methotrexate treatment. These tracer kinetic experiments quantitatively demonstrate the extent to which methotrexate alters the actual carbon flow through the hepatic folate-dependent one-carbon pool, primarily directed at diminishing the reductive carbon flow towards methyltetrahydrofolate and methionine synthesis.
Carcinogenesis 1996 Aug
PMID:Methotrexate alters carbon flow through the hepatic folate-dependent one-carbon pool in rats. 876 28

Methylenetetrahydrofolate reductase (MTHFR) is an enzyme which converts 5,10-methylene tetrahydrofolate (5,10-MnTHF) to 5-methyl tetrahydrofolate. A common C to T transition (C677T) in the MTHFR gene is reported to reduce the risk for colorectal cancer and acute lymphocytic leukemia in homozygotes (TTs). It is hypothesized that because TTs have reduced MTHFR activity, more 5,10-MnTHF is available to provide methyl groups for the conversion of uracil to thymidine. Folic acid deficiency causes the intracellular accumulation of dUMP and the subsequent incorporation of uracil into DNA. The removal of uracil from DNA may result in double-stranded DNA breaks, the accumulation of which is a putative risk factor for cancer. We tested whether human lymphocytes taken from TTs (n = 10) were more able to resist uracil incorporation into DNA than controls (n = 14 CCs and 6 CTs) when cultured in medium containing 12-120 nM folic acid for 9 days. DNA uracil content of these lymphocytes was measured by CG-MS. TTs and controls showed a dose-dependent increase in DNA uracil content during folic acid deficiency (P < 0.0001, R2 = 0.23 for TTs and P < 0.0001, R2 = 0.19 for controls). DNA uracil content was not different between the two groups at any of the folic acid concentrations (two-way ANOVA: media [folic acid], P < 0.0001; genotype, P = 0.4). The results show that, in this in vitro system, the MTHFR C677T polymorphism does not affect the cell's ability to resist uracil incorporation into DNA. Chromosome breakage, as measured by micronuclei, was also shown to correlate with folic acid concentration in a preliminary experiment (P < 0.0001). Although the results appear not to support the hypothesis that a reduced risk for certain cancers in TTs is due to diversion of folic acid to thymidine synthesis, differences between the in vivo and in vitro situation make this conclusion not definitive.
Carcinogenesis 2001 Jul
PMID:Methylenetetrahydrofolate reductase C677T polymorphism does not alter folic acid deficiency-induced uracil incorporation into primary human lymphocyte DNA in vitro. 1140 44

N-nitrosopiperidine (NPIP) is a potent esophageal carcinogen in rats whereas structurally similar N-nitrosopyrrolidine (NPYR) induces liver, but not esophageal tumors. NPIP is a possible causative agent for human esophageal cancer. Our goal is to explain mechanistically these differing carcinogenic activities in the esophagus. We hypothesize that differences in metabolic activation of these nitrosamines could be one factor accounting for their differing carcinogenicity. alpha-Hydroxylation is the key metabolic activation pathway leading to nitrosamine-induced carcinogenesis. In this study, we examined the alpha-hydroxylation rates of [3,4-(3)H]NPIP and [3,4-(3)H]NPYR by male F344 rat esophageal and liver microsomes. The major alpha-hydroxylation products of NPIP and NPYR, 2-hydroxytetrahydro-2H-pyran (2-OH-THP) and 2-hydroxytetrahydrofuran (2-OH-THF), respectively, were monitored by high performance liquid chromatography with radioflow detection. NPIP or NPYR (4 microM) was incubated with varying concentrations of esophageal microsomes and co-factors. Microsomes converted NPIP to 2-OH-THP with a 40-fold higher velocity than NPYR to 2-OH-THF. Similar results were observed in studies with NPIP and NPYR at substrate concentrations between 4 and 100 micro M. Kinetics of NPIP alpha-hydroxylation were biphasic; K(M) values were 312 +/- 50 and 1600 +/- 312 microM. Expressed cytochrome P450 2A3, found in low levels in rat esophagus, was a good catalyst of NPIP alpha-hydroxylation (K(M) = 61.6 +/- 20.5 microM), but a poor catalyst of NPYR alpha-hydroxylation (K(m) = 1198 +/- 308 micro M). Cytochrome P450 2A3 may play a role in the preferential activation of NPIP observed in rat esophagus. Liver microsomes metabolized NPYR to 2-OH-THF (V(max)/K(M) = 3.23 pmol/min/mg/ microM) as efficiently as NPIP to 2-OH-THP (V(max)/K(M) = 3.80-4.61 pmol/min/mg/ microM). We conclude that rat esophageal microsomes activate NPIP but not NPYR whereas rat liver microsomes activate NPIP and NPYR. These results are consistent with previous findings that tissue-specific activation of nitrosamines contributes to tissue-specific tumor formation.
Carcinogenesis 2003 Feb
PMID:Comparative metabolism of N-nitrosopiperidine and N-nitrosopyrrolidine by rat liver and esophageal microsomes and cytochrome P450 2A3. 1258 80

DNA methylation is the main epigenetic modification after replication in humans. DNA (cytosine-5)-methyltransferase (DNMT) catalyzes the transfer of a methyl group from S-adenosyl-L-methionine (SAM) to C5 of cytosine within CpG dinucleotide sequences in the genomic DNA of higher eukaryotes. There is considerable evidence that aberrant DNA methylation plays an integral role in carcinogenesis. Folic acid or folate is crucial for normal DNA synthesis and can regulate DNA methylation, and through this, it affects cellular SAM levels. Folate deficiency results in DNA hypomethylation. Epidemiological studies have indicated that folic acid protects against gastrointestinal (GI) cancers. Methylene-tetrahydrofolate reductase (MTHFR) and methionine synthase (MS) are the enzymes involved in folate metabolism and are thought to influence DNA methylation. MTHFR is highly polymorphic, and the variant genotypes result in decreased MTHFR enzyme activity and lower plasma folate level. Two common MTHFR polymorphisms, 677CT (or 677TT) and A1298C, and an MS polymorphism, A-->G at 2756, have been identified. Most studies support an inverse association between folate status and the rate of colorectal adenomas and carcinomas. During human GI carcinogenesis, MTHFR is highly polymorphic, and the variant genotypes result in decreased MTHFR enzyme activity and lower plasma folate level, as well as aberrant methylation.
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PMID:Folic acid, polymorphism of methyl-group metabolism genes, and DNA methylation in relation to GI carcinogenesis. 1456 26

We investigated the association of urinary bladder cancer with genetic polymorphisms in the xeroderma pigmentosum complementation group C (XPC), group D (XPD) and group G (XPG), X-ray repair cross-complementing group 1 (XRCC1) and group 3 (XRCC3), Nijmegen breakage syndrome 1 (NBS1), cyclin D1, methylene-tetrahydrofolate reductase (MTHFR), NAD(P)H dehydrogenase quinone 1 (NQO1), H-ras and glutathione S-transferase theta 1 (GSTT1) genes. Bladder cancer patients from the different hospitals in Stockholm County Council area and matching controls were genotyped for different polymorphisms. The frequency of the variant allele for A/C polymorphism in exon 15 of the XPC gene was significantly higher in the bladder cancer cases than in the controls (OR 1.49, 95% CI 1.16-1.92, P = 0.001). The variant allele homozygote genotype for the T/C polymorphism in exon 1 of the H-ras gene was associated with a decreased risk for bladder cancer (OR 0.12, 95% CI 0.02-0.67, P = 0.006). The variant allele genotypes for the single nucleotide polymorphisms (SNPs) in DNA repair genes, XPG and NBS1, showed a marginal association with the occurrence of bladder cancer (OR 0.38, 95% CI 0.15-0.94, P = 0.03 and OR 1.64, 95% CI 0.92-2.90, P = 0.09, respectively). We also report a positive correlation between the null homozygote of GSTT1 with the risk of bladder cancer (OR 2.54, 95% CI 1.32-4.98, P = 0.003). For other polymorphisms included in this study, NBS1 Glu185Gln, XPD Lys751Gln, XPG Asp1104His, XRCC1 Arg399Gln, XRCC3 Thr241Met, cyclin D1 Pro242Pro, MTHFR Ala222Val and Glu429Ala, NQO1 Arg139Trp and Pro187Ser, no significant differences for genotype distributions and allele frequencies between the bladder cancer cases and the controls were observed in the present study.
Carcinogenesis 2004 May
PMID:Polymorphisms in DNA repair and metabolic genes in bladder cancer. 1468 16

Although accumulating evidence suggests a chemopreventive role for folic acid (FA) in colorectal carcinogenesis, the underlying mechanisms are largely unknown. Previously, we reported that supplemental FA inhibits the expression and activation of epidermal growth factor receptor (EGFR) in colon cancer cell lines. To determine the mechanism(s) by which FA affects EGFR function, we have examined whether and to what extent supplemental FA or its metabolites 5-methyltetrahydrofolate (MTF), dihydrofolate (DF), and tetrahydrofolate (TF) will modulate basal and serum-induced activation of the EGFR promoter in the HCT-116 colon cancer cell line. HCT-116 cells were preincubated with or without (control) FA or one of its metabolites (10 microg/ml) for 48 h, transfected with the EGFR promoter luciferase reporter construct, and incubated for 48 h with FA, DF, TF, or 5-MTF in the absence or presence of 10% FBS. Supplemental FA as well as its metabolites markedly inhibited EGFR promoter activity and its methylation status. Exposure of the cells to 10% FBS caused a marked stimulation of EGFR promoter activity and its expression, both of which were greatly abrogated by supplemental FA and 5-MTF. In contrast, serum-induced activation of c-fos promoter activity was unaffected by 5-MTF. The 5-MTF-induced inhibition of serum-mediated stimulation of EGFR promoter activity and EGFR expression was reversed when methylation was inhibited by 5-aza-2'-deoxycytidine. Our data suggest that FA and its metabolite 5-MTF inhibit EGFR promoter activity in colon cancer cells by enhancing methylation. This could partly be responsible for FA-mediated inhibition of growth-related processes in colorectal neoplasia.
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PMID:Folic acid-mediated inhibition of serum-induced activation of EGFR promoter in colon cancer cells. 1507 53

Epidemiological studies have shown an association between low folate intake and an increased cancer risk. Major genes involved in folate metabolism include methylene-tetrahydrofolate reductase (MTHFR) and methionine synthase (MS). We investigated joint effects of polymorphisms of the MTHFR (677 C-->T, 1298A-->C) and MS genes (2756 A-->G), dietary folate intake and cigarette smoking on the risk of bladder cancer in a case-control study. The study population consisted of 457 bladder cancer patients and 457 healthy controls, matched to the cases in terms of age, gender and ethnicity. Genotype data were analyzed in a subset of 410 Caucasian cases and 410 controls. Compared with individuals carrying the MTHFR 677 wild-type (CC) and reporting a high folate intake, those carrying the variant genotype (CT or TT) and reporting a low folate intake were at a significantly 3.51-fold increased risk of bladder cancer (95% CI: 1.59-6.52). In contrast, individuals carrying a variant genotype and reporting a high folate intake were at only a 1.39-fold increased risk (95% CI: 0.71-2.70), and those carrying the wild-type and reporting a low folate intake were at only 1.56-fold increased risk (95% CI: 0.82-2.97). The interaction between genetic polymorphisms and folate intake was significant on the multiplicative scale (P = 0.01). When analyzed in the context of smoking status, compared with never smokers with the MTHFR 677 wild-type, the risk increased to 6.56-fold (95% CI: 3.28-13.12) in current smokers carrying the variant genotype. Analyses of the MTHFR 1298, MS 2756 genes revealed similar results. In addition, age at cancer onset in former smokers increased as the proportion of the heteromorphic haplotype in the individual increased (P = 0.005). Our results strongly suggest that polymorphisms of the MTHFR and MS genes act together with low folate intake and smoking to increase bladder cancer risk. These results have important implications for cancer prevention in susceptible populations.
Carcinogenesis 2004 Sep
PMID:Polymorphisms of folate metabolic genes and susceptibility to bladder cancer: a case-control study. 1511 11

Thymidylate synthase (TS) catalyzes the 5,10-methylene-tetrahydrofolate-mediated conversion of deoxyuridine monophosphate to deoxythymydine monophosphate, a nucleotide required for DNA synthesis and repair. The impaired TS expression has been shown to be related to 28 bp tandem repeats and a G-->C SNP in the 5'-UTR of TS. Folate deficiency has been demonstrated to play a role in gastroesophageal carcinogenesis. This case-control study was to examine the hypothesis that the TS polymorphisms, alone or in combination with serum folate status, may confer susceptibility of the hosts to gastroesophageal cancer. We analyzed TS genotype and serum folate concentration in 324 patients with esophageal squamous cell carcinoma (ESCC), 231 patients with gastric cardia adenocarcinoma (GCA) and 492 controls. It was found that compared with the normal expression TS genotype, the low expression TS genotype alone was significantly associated with increased risk of ESCC [adjusted odds ratio (OR) 1.47; 95% confidence interval (CI) 1.03-2.10] but not GCA (OR=0.98, 95% CI=0.68-1.40). More importantly, a significant interaction between the TS polymorphisms and serum folate status in risk of ESCC and GCA was observed. Among subjects with low serum folate concentration (<3 ng/ml), the ORs of ESCC and GCA for the low expression genotype were 22.63 (95% CI=10.44-49.05) and 4.08 (95% CI=1.94-8.59), which were greater than respective 9.97 (95% CI=5.67-17.53) and 1.88 (95% CI=1.18-3.24) for the normal expression genotype (P=0.002 and 0.029). These results suggest an important role for folate deficiency and impaired TS activity in the etiology of ESCC and GCA.
Carcinogenesis 2005 Aug
PMID:Significant increase in risk of gastroesophageal cancer is associated with interaction between promoter polymorphisms in thymidylate synthase and serum folate status. 1581 9

Concern has been expressed about the safety of formocresol use in pediatric dentistry. Formaldehyde, a primary component in formocresol, is a hazardous substance and is considered a probable human carcinogen by Health Canada. However, humans inhale and ingest formaldehyde daily and also produce this compound as part of normal cellular metabolism. The human body is physiologically equipped to handle this exposure through multiple pathways for oxidation of formaldehyde to formate and incorporation into biological macromolecules via tetrahydrofolate-dependent one-carbon biosynthetic pathways. Recent re-evaluation of earlier research that examined potential health risks associated with formaldehyde exposure has shown that the research was based on flawed assumptions, which resulted in erroneous conclusions. This review examines more recent research about formaldehyde metabolism, pharmacokinetics and carcinogenicity, the results of which indicate that formaldehyde is probably not a potent human carcinogen under conditions of low exposure. Extrapolation of these research results to pediatric dentistry suggests an inconsequential risk of carcinogenesis associated with formaldehyde use in pediatric pulp therapy. Areas for further investigation are suggested.
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PMID:Persuasive evidence that formocresol use in pediatric dentistry is safe. 1669 91

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