Methylenetetrahydrofolate reductase C677T polymorphism, folic acid and riboflavin are important determinants of genome stability in cultured human lymphocytes

The in vitro MN assay in 2011: origin and fate, biological significance, protocols, high throughput methodologies and toxicological relevance

Micronuclei (MN) are small, extranuclear bodies that arise in dividing cells from acentric chromosome/chromatid fragments or whole chromosomes/chromatids lagging behind in anaphase and are not included in the daughter nuclei at telophase. The mechanisms of MN formation are well understood; their possible postmitotic fate is less evident. The MN assay allows detection of both aneugens and clastogens, shows simplicity of scoring, is widely applicable in different cell types, is internationally validated, has potential for automation and is predictive for cancer. The cytokinesis-block micronucleus assay (CBMN) allows assessment of nucleoplasmic bridges, nuclear buds, cell division inhibition, necrosis and apoptosis and in combination with FISH using centromeric probes, the mechanistic origin of the MN. Therefore, the CBMN test can be considered as a "cytome" assay covering chromosome instability, mitotic dysfunction, cell proliferation and cell death. The toxicological relevance of the MN test is strong: it covers several endpoints, its sensitivity is high, its predictivity for in vivo genotoxicity requires adequate selection of cell lines, its statistical power is increased by the recently available high throughput methodologies, it might become a possible candidate for replacing in vivo testing, it allows good extrapolation for potential limits of exposure or thresholds and it is traceable in experimental in vitro and in vivo systems. Implementation of in vitro MN assays in the test battery for hazard and risk assessment of potential mutagens/carcinogens is therefore fully justified.

Molecular mechanisms of micronucleus, nucleoplasmic bridge and nuclear bud formation in mammalian and human cells

Micronuclei (MN) and other nuclear anomalies such as nucleoplasmic bridges (NPBs) and nuclear buds (NBUDs) are biomarkers of genotoxic events and chromosomal instability. These genome damage events can be measured simultaneously in the cytokinesis-block micronucleus cytome (CBMNcyt) assay. The molecular mechanisms leading to these events have been investigated over the past two decades using molecular probes and genetically engineered cells. In this brief review, we summarise the wealth of knowledge currently available that best explains the formation of these important nuclear anomalies that are commonly seen in cancer and are indicative of genome damage events that could increase the risk of developmental and degenerative diseases. MN can originate during anaphase from lagging acentric chromosome or chromatid fragments caused by misrepair of DNA breaks or unrepaired DNA breaks. Malsegregation of whole chromosomes at anaphase may also lead to MN formation as a result of hypomethylation of repeat sequences in centromeric and pericentromeric DNA, defects in kinetochore proteins or assembly, dysfunctional spindle and defective anaphase checkpoint genes. NPB originate from dicentric chromosomes, which may occur due to misrepair of DNA breaks, telomere end fusions, and could also be observed when defective separation of sister chromatids at anaphase occurs due to failure of decatenation. NBUD represent the process of elimination of amplified DNA, DNA repair complexes and possibly excess chromosomes from aneuploid cells.

Cytokinesis-blocked micronucleus assay and cancer risk assessment

Cancer risk assessment is a multidisciplinary process that goes beyond the scope of classical epidemiology to include the biological evaluation of individual differences to carcinogenic exposures. The inclusion of genetic biomarkers such as mutagen sensitivity or cytokinesis-blocked micronucleus (CBMN) assay end points into risk assessment models allows for a more comprehensive determination of cancer risk that includes known demographic (age and gender), lifestyle exposures (smoking and alcohol) and occupational or environmental exposures. The CBMN assay generates multiple correlated end points that, after applying data reduction methods, could be combined into a summary measure that incorporates information from each individual variable into a single (or possible multiple, uncorrelated) measure of risk. In this article, we highlight the use of the CBMN assay in radiosensitivity assessment. In addition, we demonstrate the potential use of the combined summary measures in cancer risk assessment as a result of chronic exposure to tobacco carcinogens. The simplicity, rapidity and sensitivity of the CBMN assay not only make it a valuable tool for screening but also the multiple end points simultaneously generated lead to a better understanding of the underlying mechanisms involved in the carcinogenic process that could in turn substantially improve risk predictions.

Micronucleus assay and labeling of centromeres with FISH technique

The cytokinesis-block micronucleus (CBMN) assay has since many years been applied for in vitro genotoxicity testing and biomonitoring of human populations. The standard in vitro/ex vivo micronucleus test is usually performed on human lymphocytes and has become a comprehensive method to assess genetic damage, cytostasis, and cytotoxicity. The predictive association between the frequency of micronuclei (MN) in cytokinesis-blocked lymphocytes and cancer risk has recently been demonstrated. MN frequencies can be influenced by inherited (or acquired) genetic polymorphisms (or mutations) in genes responsible for the metabolic activation, detoxification of clastogens, and for the fidelity of DNA replication. An important advantage of the CBMN assay is its ability to detect both clastogenic and aneugenic events by centromere and kinetochore identification and contributes to the high sensitivity of the method. The objective of the present chapter is to review the mechanisms of induction of micronuclei, the method of the micronucleus assay and its combination with centromeric labeling in the FISH technique. Furthermore, an overview is given of recent results obtained by our laboratory by the application of the micronucleus assay.

Reflections on the development of micronucleus assays

These are personal reflections on the development of methods to use micronuclei as a measure of genetic damage and their use in research and in toxicology by four people who have been intimately involved with this work, a personal rather than a comprehensive history. About 6000 papers have been published using such methods in many tissues in vivo or in cultured cells of many organisms from plants to humans, but the majority of the work has been on mammalian erythrocytes and human lymphocytes, the areas in which we have worked primarily. Although this is by no means a complete history, those working in the field may be interested in some of the personal events that lie behind the development and acceptance of methods that are now standard.

Nutriomes and nutrient arrays - the key to personalised nutrition for DNA damage prevention and cancer growth control

DNA damage at the base-sequence, epigenome and chromosome level is a fundamental cause of developmental and degenerative diseases. Multiple micronutrients and their interactions with the inherited and/or acquired genome determine DNA damage and genomic instability rates. The challenge is to identify for each individual the combination of micronutrients and their doses (i.e. the nutriome) that optimises genome stability and DNA repair. In this paper I describe and propose the use of high-throughput nutrient array systems with high content analysis diagnostics of DNA damage, cell death and cell growth for defining, on an individual basis, the optimal nutriome for DNA damage prevention and cancer growth control.

Folate and methionine metabolism in autism: a systematic review

BACKGROUND

Autism is a complex neurodevelopmental disorder that is increasingly being recognized as a public health issue. Recent evidence has emerged that children with autism may have altered folate or methionine metabolism, which suggests the folate-methionine cycle may play a key role in the etiology of autism.

OBJECTIVE

The objective was to conduct a systematic review to examine the evidence for the involvement of alterations in folate-methionine metabolism in the etiology of autism.

DESIGN

A systematic literature review was conducted of studies reporting data for metabolites, interventions, or genes of the folate-methionine pathway in autism. Eighteen studies met the inclusion criteria, 17 of which provided data on metabolites, 5 on interventions, and 6 on genes and their related polymorphisms.

RESULTS

The findings of the review were conflicting. The variance in results can be attributed to heterogeneity between subjects with autism, sampling issues, and the wide range of analytic techniques used. Most genetic studies were inadequately powered to provide more than an indication of likely genetic relations.

CONCLUSIONS

The review concluded that further research is required with appropriately standardized and adequately powered study designs before any definitive conclusions can be made about the role for a dysfunctional folate-methionine pathway in the etiology of autism. There is also a need to determine whether functional benefits occur when correcting apparent deficits in folate-methionine metabolism in children with autism.

Dietary reference values of individual micronutrients and nutriomes for genome damage prevention: current status and a road map to the future

Damage to the genome is recognized as a fundamental cause of developmental and degenerative diseases. Several micronutrients play an important role in protecting against DNA damage events generated through endogenous and exogenous factors by acting as cofactors or substrates for enzymes that detoxify genotoxins as well as enzymes involved in DNA repair, methylation, and synthesis. In addition, it is evident that either micronutrient deficiency or micronutrient excess can modify genome stability and that these effects may also depend on nutrient-nutrient and nutrient-gene interaction, which is affected by genotype. These observations have led to the emerging science of genome health nutrigenomics, which is based on the principle that DNA damage is a fundamental cause of disease that can be diagnosed and nutritionally prevented on an individual, genetic subgroup, or population basis. In this article, the following topics are discussed: 1) biomarkers used to study genome damage in humans and their validation, 2) evidence for the association of genome damage with developmental and degenerative disease, 3) current knowledge of micronutrients required for the maintenance of genome stability in humans, 4) the effect of nutrient-nutrient and nutrient-genotype interaction on DNA damage, and 5) strategies to determine dietary reference values of single micronutrients and micronutrient combinations (nutriomes) on the basis of DNA damage prevention. This article also identifies important knowledge gaps and future research directions required to shed light on these issues. The ultimate goal is to match the nutriome to the genome to optimize genome maintenance and to prevent pathologic amounts of DNA damage.

Folate-mediated one-carbon metabolism and its effect on female fertility and pregnancy viability

This review summarizes current knowledge of the effect of folate-mediated one-carbon metabolism and related genetic variants on female fertility and pregnancy viability. Insufficient folate status disrupts DNA methylation and integrity and increases blood homocysteine levels. Elevated levels of follicular fluid homocysteine correlate with oocyte immaturity and poor early embryo quality, while methylenetetrahydrofolate reductase (MTHFR) gene variants are associated with lower ovarian reserves, diminished response to follicular stimulation, and reduced chance of live birth after in vitro fertilization. Embryos carrying multiple MTHFR variants appear to have a selective disadvantage; however, the heterozygous MTHFR 677CT genotype in the mother and fetus provides the greatest chance for a viable pregnancy and live birth, possibly due to a favorable balance in folate cofactor distribution between methyl donor and nucleotide synthesis. The results of previous studies clearly emphasize that imbalances in folate metabolism and related gene variants may impair female fecundity as well as compromise implantation and the chance of a live birth.

Telomere length in lymphocytes of older South Australian men may be inversely associated with plasma homocysteine

Deficiencies in folate (FOL) and vitamin B12 (B12) result in increased chromosomal aberrations, a validated biomarker of cancer risk. Telomeres, the regions of DNA that cap the ends of each chromosome, are critical for maintaining chromosomal stability but the impact of micronutrients on telomere structure and function remains unclear. We hypothesized that telomere length maintenance might be compromised if the status of FOL and B12 was inadequate and plasma homocysteine (HCY) was increased. We investigated the relationship between telomere length in peripheral blood lymphocytes and plasma FOL, B12, and HCY status, and tested whether any such relationship was dependent on age, gender, body mass index, and common polymorphisms in folate metabolism genes. A single blood sample was collected from 43 younger (18-32 years) and 47 older (65-83 years) adults in South Australia. The younger cohort consisted of 18 males and 25 females, whereas the older group included 24 males and 23 females. Telomere length was determined in lymphocytes by flow cytometry. Telomere length in the younger cohort was 11.52% greater than in the older cohort (p = 0.015). In the older cohort, telomere length in females was 12.5% greater than in males (p = 0.028). In older males, there was a significant inverse correlation between telomere length and HCY (r = -0.57, p = 0.004), but this effect was not observed in the younger cohort or in the older female group. These results provide evidence that telomere length of lymphocytes in older men may be adversely affected by HCY in vivo.

Folate deficiency in human peripheral blood lymphocytes induces chromosome 8 aneuploidy but this effect is not modified by riboflavin

Chromosome 8 aneuploidy is a common event in certain cancers but whether folate (F) deficiency induces chromosome 8 aneuploidy is not known. Furthermore the impact of riboflavin (R) deficiency, which may alter activity of a key enzyme in folate metabolism, on these events is unknown. Therefore, the aim of our research was to test the following hypotheses: (a) F deficiency induces chromosome 8 aneuploidy; (b) chromosome 8 aneuploidy is affected by F deficiency to a similar degree as chromosome 17 and (c) R deficiency aggravates the risk of aneuploidy caused by F deficiency. These hypotheses were tested in long-term cultures of lymphocytes from twenty female healthy volunteers (aged 30-48 years). Lymphocytes were cultured in each of the four possible combinations of low (L) and high (H) F (LF, 20 nmol/L, HF 200 nmol/L, respectively) and L and H R (LR 1 nmol/L, HR 500 nmol/L, respectively) media (LFLR, LFHR, HFLR, HFHR) for 9 days. Chromosomes 8 and 17 aneuploidy was measured in mononucleated (MONO) and cytokinesis-blocked binucleated (BN) cells using dual-color fluorescence in situ hybridization (FISH) with fluorescent centromeric probes specific for chromosomes 8 and 17. Culture in LF media (LFLR or LFHR) induced significant and similar increases in frequencies of aneuploidy of chromosomes 8 and 17 (P < 0.001) relative to culture in HF media (HFLR or HFHR). There was no significant effect of R concentration on aneuploidy frequency for either chromosome. We conclude that F deficiency is a possible cause of chromosome 8 aneuploidy.

Role of the MTHFR polymorphisms in cancer risk modification and treatment

The role of folate, a water-soluble B vitamin, and single nucleotide polymorphisms (SNPs) in the folate metabolic pathway in human health and disease has been rapidly expanding. Recently, functionally significant SNPs in 5,10-methylenetetrahydrofolate reductase (MTHFR), a critical enzyme for intracellular folate homeostasis and metabolism, have been identified and characterized. The MTHFR SNPs are ideal candidates for investigating the role of SNPs in cancer risk modification and treatment because of their well-defined and highly relevant biochemical effects on intracellular folate composition and one-carbon transfer reactions. Indeed, a large body of molecular epidemiologic evidence suggests that the MTHFR 677 variant T allele is associated with cancer risk in a site-specific manner. Furthermore, biologically plausible mechanisms based on the functional consequences of changes in intracellular folate cofactors resulting from the MTHFR 677T variant exist to readily explain cancer risk modification associated with this variant. In addition, a growing body of in vitro and clinical evidence suggests that the MTHFR SNPs may be an important pharmacogenetic determinant of response to and toxicity of 5-fluorouracil (5FU) and methotrexate (MTX)-based cancer and anti-inflammatory chemotherapy. Furthermore, studies suggest that MTHFR inhibition may be a potential target for increasing chemosensitvity of cancer cells to 5FU-based chemotherapy. Because the MTHFR SNPs are prevalent and MTX and 5FU are widely used for the treatment of common cancers and inflammatory conditions, the pharmacogenetic role of the MTHFR SNPs has significant clinical implications. MTHFR SNPs may play an important role in providing rational, effective and safe tailored treatment to patients with cancer and inflammatory disorders requiring 5FU and MTX-based therapy. As such, largescale human studies and in vitro mechanistic studies are warranted to clarify the pharmacogenetic role of the MTHFR SNPs.

Increased consumption of wheat biofortified with selenium does not modify biomarkers of cancer risk, oxidative stress, or immune function in healthy Australian males

Increased intake of selenium (Se) may reduce the risk of degenerative diseases including cancer but excessive intake may be toxic. Wheat is a major source of dietary Se in humans. However, the effect of Se from wheat that is agronomically biofortified with Se on biomarkers of human health status is unknown. This study aimed to investigate whether improving Se status, by increased dietary intake of Se-biofortified wheat, affects biomarkers of cancer risk, cardiovascular disease risk, oxidative stress, and immune function in healthy South Australian men. A 24-week placebo-controlled double-blind intervention was performed in healthy older men (n = 62), with increased dose of Se intake every 8 weeks. Wheat was provided as 1, 2, and 3 puffed wheat biscuits, during weeks 1-8, 9-16, and 17-24, respectively. Blood was collected to measure a wide range of disease risk biomarkers. Consumption of Se-biofortified wheat was found to increase plasma Se concentration from a baseline level of 122 to 192 microg/L following intake of three biscuits/day, which provided 267 microg Se. Platelet glutathione peroxidase, chromosome aberrations, and DNA damage in lymphocytes measured using the cytokinesis-block micronucleus cytome assay and with the Comet assay, plasma F2-isoprostanes, protein carbonyls, plasma C-reactive protein, and leukocyte number were unaffected by the improved Se status. Improvement of Se status by consumption of Se-biofortified wheat did not substantially modify the selected biomarkers of degenerative disease risk and health status in this apparently selenium-replete cohort of healthy older men in South Australia.

Chromosomal aberrations in railroad transit workers: effect of genetic polymorphisms

Complex chemical mixtures are transported by train from Russia to Finland for further shipment. Here, we studied if exposure to genotoxic components among these substances could affect chromosomal aberrations (CAs) in peripheral lymphocytes of workers handling the tank cars. An initial survey among 48 railroad workers and 39 referents (male smokers and nonsmokers) showed an elevation of CAs. A campaign was started to reduce exposures through preventive measures. Five years later, 51 tank car workers and 40 age-matched referents (all nonsmoking men) were studied for CAs and genetic polymorphisms of xenobiotic metabolism (EPHX1, GSTM1, GSTP1, GSTT1, NAT1, NAT2), DNA repair (ERCC2, ERCC5, XPA, XPC, XRCC1, XRCC3), and folate metabolism (MTHFR, MTR). No increase in CAs was seen in the exposed group, suggesting that the preventive measures had been successful. However, a positive association existed between exposure duration and CA level among the exposed subjects. The level of chromosome-type breaks was actually lower in the exposed workers than the referents, particularly among MTHFR wild-type homozygotes or XRCC3 codon 241 variant allele carriers, suggesting modulation of CA frequency by folate metabolism and DNA repair. An interaction was observed between the occupational exposure and MTHFR, EPHX1, and MTR genotypes in determining CA level. The NAT2, ERCC2 exon 10, and XRCC1 codon 194 polymorphisms also affected CA frequency. Our findings suggest that handling of tank cars containing complex chemical mixtures poses a genotoxic risk, which may be reduced by preventive measures. Several genetic polymorphisms seem to modify the genotoxic effect or baseline CA level.

The methylenetetrahydrofolate reductase C677T mutation induces cell-specific changes in genomic DNA methylation and uracil misincorporation: a possible molecular basis for the site-specific cancer risk modification

The C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene is associated with a decreased risk of colon cancer although it may increase the risk of breast cancer. This polymorphism is associated with changes in intracellular folate cofactors, which may affect DNA methylation and synthesis via altered one-carbon transfer reactions. We investigated the effect of this mutation on DNA methylation and uracil misincorporation and its interaction with exogenous folate in further modulating these biomarkers of one-carbon transfer reactions in an in vitro model of the MTHFR 677T mutation in HCT116 colon and MDA-MB-435 breast adenocarcinoma cells. In HCT116 cells, the MTHFR 677T mutation was associated with significantly increased genomic DNA methylation when folate supply was adequate or high; however, in the setting of folate insufficiency, this mutation was associated with significantly decreased genomic DNA methylation. In contrast, in MDA-MB-435 cells, the MTHFR 677T mutation was associated with significantly decreased genomic DNA methylation when folate supply was adequate or high and with no effect when folate supply was low. The MTHFR 677T mutation was associated with a nonsignificant trend toward decreased and increased uracil misincorporation in HCT116 and MDA-MB-435 cells, respectively. Our data demonstrate for the first time a functional consequence of changes in intracellular folate cofactors resulting from the MTHFR 677T mutation in cells derived from the target organs of interest, thus providing a plausible cellular mechanism that may partly explain the site-specific modification of colon and breast cancer risks associated with the MTHFR C677T mutation.

A lifetime passion for micronucleus cytome assays--reflections from Down Under

A brief account of an improbable career in the field of genetic toxicology is given, extending from my early years in Malta through a life-changing decision to study in Australia (Down Under). I describe the circumstances that led to the discovery of the cytokinesis-block micronucleus (CBMN) assay and its evolution into a cytome assay of chromosome breakage and loss (micronuclei), asymmetrical chromosome rearrangements or telomere end fusions (nucleoplasmic bridges), gene amplification (nuclear buds), cell death (necrosis, apoptosis) and cytostasis (nuclear division index). This paper also describes the role of my laboratory in the beginning of the HUMN project, its achievements, and the applications of CBMN cytome assays in the fields of radiation biology, genetic toxicology, epidemiology, biodosimetry and genome health nutrigenomics, leading to the Genome Health Clinic concept. Along the way I mention my encounters with some of the influential people in the field of mutagenesis who provided me with the motivation and guidance needed to realise these achievements. I hope this account provides some inspiration to the next generation of scientists who may be fortunate to see the realisation of the application of the principles of mutagenesis in health optimisation or disease prevention and eventually in mainstream medicine.

Effect of common polymorphisms in folate uptake and metabolism genes on frequency of micronucleated lymphocytes in a South Australian cohort

Single nucleotide polymorphisms (SNPs) in genes that control folate uptake and metabolism may have an important effect on chromosomal stability. The present study investigated the effect of common SNPs in some of these critical genes on frequency of lymphocytes with micronuclei, a biomarker of chromosome breakage or loss. 164 individuals (94 males and 70 females) of different age ranging from 18 to 73 years participated in this study. Polymorphisms in GCPII (C1561T), RFC (G80A), MTR (A2756G), MTRR (A66G and C524T), TS (tandem repeats, 6bp deletion in 3'-UTR region) and MTHFR (C677T and A1298C) were detected using PCR-based methods. Frequency of binucleated (BN) lymphocytes containing one or more micronuclei (BN-MN) was determined using the cytokinesis-block micronucleus (CBMN) assay and adjusted for the effects of age and gender. We did not find any significant association between BN-MN frequency and the common SNPs in GCPII, MTRR, TS and MTHFR genes. BN-MN frequency in individuals who carried at least one copy of the rarer G allele for MTR (A2756G) or were homozygotes for the more common G allele for RFC (G80A) had a 14% or 19% lower BN-MN frequency compared to the alternative genotypes for that SNP respectively. It was evident from genotype combination analyses that BN-MN frequency per 1000 BN cells was highest in those with the combined MTR (2756) AA and RFC (80) GA or AA genotype (13.6 per thousand) and lowest in those with the combined MTR (2756) AG or GG and RFC (80) GG genotypes (9.5 per thousand) (P trend=0.015). The RFC G80A and MTR A2756G polymorphisms and their combinations may be important variables that substantially affect lymphocyte BN-MN frequency in this South Australian cohort.

The effect of selenium, as selenomethionine, on genome stability and cytotoxicity in human lymphocytes measured using the cytokinesis-block micronucleus cytome assay

A supranutritional intake of selenium (Se) may be required for cancer prevention, but an excessively high dose could be toxic. Therefore, the effect on genome stability of seleno-L-methionine (Se-met), the most important dietary form of Se, was measured to determine its bioefficacy and safety limit. Peripheral blood lymphocytes were isolated from six volunteers and cultured with medium supplemented with Se-met in a series of Se concentrations (3, 31, 125, 430, 1880 and 3850 microg Se/litre) while keeping the total methionine (i.e. Se-met + L-methionine) concentration constant at 50 microM. Baseline genome stability of lymphocytes and the extent of DNA damage induced by 1.5-Gy gamma-ray were investigated using the cytokinesis-block micronucleus cytome assay after 9 days of culture in 96-microwell plates. High Se concentrations (>or=1880 microg Se/litre) caused strong inhibition of cell division and increased cell death (P < 0.0001). Baseline frequency of nucleoplasmic bridges and nuclear buds, however, declined significantly (P trend < 0.05) as Se concentration increased from 3 to 430 microg Se/litre. Se concentration (<or=430 microg Se/litre) had no significant effect on baseline frequency of micronuclei and had no protective effect against genome damage induced by exposure to 1.5-Gy gamma-ray irradiation. In conclusion, Se, as Se-met, may improve genome stability at concentrations up to 430 microg Se/litre, but higher doses may be cytotoxic. Therefore, a cautious approach to supplementation with Se-met is required to ensure that optimal genome health is achieved without cytotoxic effects.

Methionine-dependence phenotype in the de novo pathway in BRCA1 and BRCA2 mutation carriers with and without breast cancer

Methionine-dependence phenotype (MDP) refers to the reduced ability of cells to proliferate when methionine is restricted and/or replaced by its immediate precursor homocysteine. MDP is a characteristic of human tumors in vivo, human tumor cell lines, and normal somatic tissue in some individuals. It was hypothesized that MDP is a risk factor for developing breast cancer in BRCA (BRCA1 and BRCA2) germline mutation carriers. To test the hypothesis, human peripheral blood lymphocytes of BRCA carriers with and without breast cancer and healthy non-carrier relatives (controls) were cultured for 9 days in medium containing either 0.1 mmol/L L-methionine or 0.2 mmol/L D,L-homocysteine, with the ratio of viable cell growth in both types of medium after 9 days used to calculate the methionine-dependence index (MDI), a measure of MDP. We also tested whether MDP was associated with common polymorphisms in methionine metabolism. Viable cell growth, MDI, and polymorphism frequency in MTRR (A66G and C524T) and MTHFR (A1298C and A1793G) did not differ among the study groups; however, MDI tended to be higher in BRCA carriers with breast cancer than those without and was significantly increased in MTHFR 677T allele carriers relative to wild-type carriers (P=0.017). The presence of MTR A2756G mutant allele and MTHFR C677T mutant allele in carriers was associated with increased breast cancer risk [odds ration, 3.2 (P=0.16; 95% confidence interval, 0.76-13.9) and 3.9 (P=0.09; 95% confidence interval, 0.93-16.3), respectively]. The results of this study support the hypothesis that defects in methionine metabolism may be associated with breast cancer risk in BRCA carriers.

Single-step surface functionalization of polymeric nanoparticles for targeted drug delivery

Targeted drug delivery using nanocarriers is achieved by functionalizing the carrier surface with a tissue-recognition ligand. Current surface modification methods require tedious and inefficient synthesis and purification steps, and are not easily amenable to incorporating multiple functionalities on a single surface. In this report, we describe a versatile, single-step surface functionalizing technique for polymeric nanoparticles. The technique utilizes the fact that when a diblock copolymer like polylactide-polyethylene glycol (PLA-PEG) is introduced in the oil/water emulsion used in polymeric nanoparticle formulation, the PLA block partitions into the polymer containing organic phase and PEG block partitions into the aqueous phase. Removal of the organic solvent results in the formation of nanoparticles with PEG on the surface. When a PLA-PEG-ligand conjugate is used instead of PLA-PEG copolymer, this technique permits a 'one-pot' fabrication of ligand-functionalized nanoparticles. In the current study, the IAASF approach facilitated the simultaneous incorporation of biotin and folic acid, known tumor-targeting ligands, on drug-loaded nanoparticles in a single step. Incorporation of the ligands on nanoparticles was confirmed by using NMR, surface plasmon resonance, transmission electron microscopy and tumor cell uptake studies. Simultaneous functionalization with both ligands significantly enhanced nanoparticle accumulation in tumors in vivo, and resulted in greatly improved efficacy of paclitaxel-loaded nanoparticles in a mouse xenograft tumor model. This new surface functionalization approach will enable the development of targeting strategies based on the use of multiple ligands on a single surface to target a tissue of interest.

One-carbon metabolism enzyme polymorphisms and uteroplacental insufficiency

OBJECTIVES

This study was undertaken to test novel genetic polymorphisms involved in 1-carbon metabolism for a potential association with increased risk of developing pregnancy complications associated with uteroplacental insufficiency.

STUDY DESIGN

This was a prospective cohort study consisting of 50 women at low risk and 93 women at high risk for having a pregnancy complication develop. Maternal and fetal DNA samples were genotyped for methionine synthase (MTR) A2756G, methionine synthase reductase (MTRR) A66G and methylenetetrahydrofolate dehydrogenase (MTHFD1) G1958A. A chi squared or chi(2) analysis was used to compare genotypes and pregnancy outcome, 1-way analysis of variance and linear regression were used to compare genotype with continuous variables.

RESULTS

The fetal MTR 2756 G allele was associated with uteroplacental insufficiency (P = .022, likelihood ratio = 10.4) and maternal homocysteine (P = .017). The maternal MTR A2756G polymorphism was associated with uteroplacental insufficiency (P = .049, likelihood ratio = 6.0), but only in mothers not supplementing with high-dose B-vitamins. The maternal MTHFD1 AA genotype was associated with intrauterine growth restriction (P = .047, likelihood ratio = 5.8).

CONCLUSION

This study suggests the maternal and fetal MTR 2756 G allele is an important risk factor in the development of uteroplacental insufficiency. In addition, the maternal MTHFD1 1958 AA genotype may be associated with intrauterine growth restriction.

Genome-health nutrigenomics and nutrigenetics: nutritional requirements or ‘nutriomes’ for chromosomal stability and telomere maintenance at the individual level

It is becoming increasingly evident that (a) risk for developmental and degenerative disease increases with more DNA damage, which in turn is dependent on nutritional status, and (b) the optimal concentration of micronutrients for prevention of genome damage is also dependent on genetic polymorphisms that alter the function of genes involved directly or indirectly in the uptake and metabolism of micronutrients required for DNA repair and DNA replication. The development of dietary patterns, functional foods and supplements that are designed to improve genome-health maintenance in individuals with specific genetic backgrounds may provide an important contribution to an optimum health strategy based on the diagnosis and individualised nutritional prevention of genome damage, i.e. genome health clinics. The present review summarises some of the recent knowledge relating to micronutrients that are associated with chromosomal stability and provides some initial insights into the likely nutritional factors that may be expected to have an impact on the maintenance of telomeres. It is evident that developing effective strategies for defining nutrient doses and combinations or ‘nutriomes’ for genome-health maintenance at the individual level is essential for further progress in this research field.

Chromosomal aberration frequency in lymphocytes predicts the risk of cancer: results from a pooled cohort study of 22 358 subjects in 11 countries

Mechanistic evidence linking chromosomal aberration (CA) to early stages of cancer has been recently supported by the results of epidemiological studies that associated CA frequency in peripheral lymphocytes of healthy individuals to future cancer incidence. To overcome the limitations of single studies and to evaluate the strength of this association, a pooled analysis was carried out. The pooled database included 11 national cohorts and a total of 22 358 cancer-free individuals who underwent genetic screening with CA for biomonitoring purposes during 1965–2002 and were followed up for cancer incidence and/or mortality for an average of 10.1 years; 368 cancer deaths and 675 incident cancer cases were observed. Subjects were classified within each laboratory according to tertiles of CA frequency. The relative risk (RR) of cancer was increased for subjects in the medium [RR = 1.31, 95% confidence interval (CI) = 1.07–1.60] and in the high (RR = 1.41; 95% CI = 1.16–1.72) tertiles when compared with the low tertile. This increase was mostly driven by chromosome-type aberrations. The presence of ring chromosomes increased the RR to 2.22 (95% CI = 1.34–3.68). The strongest association was found for stomach cancer [RR_medium = 1.17 (95% CI = 0.37–3.70), RR_high = 3.13 (95% CI = 1.17–8.39)]. Exposure to carcinogens did not modify the effect of CA levels on overall cancer risk. These results reinforce the evidence of a link between CA frequency and cancer risk and provide novel information on the role of aberration subclass and cancer type.

Maternal and offspring genetic variants of AKR1C3 and the risk of childhood leukemia

The aldo-keto reductase 1C3 (AKR1C3) gene located on chromosome 10p15-p14, a regulator of myeloid cell proliferation and differentiation, represents an important candidate gene for studying human carcinogenesis. In a prospectively enrolled population-based case-control study of Han Chinese conducted in Kaohsiung in southern Taiwan, a total of 114 leukemia cases and 221 controls <20 years old were recruited between November 1997 and December 2005. The present study set out to evaluate the association between childhood leukemia and both maternal and offspring's genotypes. To do so, we conducted a systematic assessment of common single-nucleotide polymorphisms (SNPs) at the 5' flanking 10 kb to 3' UTR of AKR1C3 gene. Gln5His and three tagSNPs (rs2245191, rs10508293 and rs3209896) and one multimarker (rs2245191, rs10508293 and rs3209896) were selected with average 90% coverage of untagged SNPs by using the HapMap II data set. Odds ratios and 95% confidence intervals were adjusted for age and gender. After correcting for multiple comparisons, we observed that risk of developing childhood leukemia is significantly associated with rs10508293 polymorphism on intron 4 of the AKR1C3 gene in both offspring alone and in the combined maternal and offspring genotypes (nominal P < 0.0001, permutation P < 0.005). The maternal methylenetetrahydrofolate reductase A1298C polymorphism was found to be an effect modifier of the maternal intron 4 polymorphism of the AKR1C3 gene (rs10508293) and the childhood leukemia risk. In conclusion, this study suggests that AKR1C3 polymorphisms may be important predictive markers for childhood leukemia susceptibility.

Low dietary riboflavin but not folate predicts increased fracture risk in postmenopausal women homozygous for the MTHFR 677 T allele

The MTHFR C677T polymorphism is associated with mildly elevated homocysteine levels when folate and/or riboflavin status is low. Furthermore, a mildly elevated homocysteine level is a risk factor for osteoporotic fractures. We studied whether dietary intake of riboflavin and folate modifies the effects of the MTHFR C677T variant on fracture risk in 5,035 men and women from the Rotterdam Study. We found that the MTHFR C677T variant interacts with dietary riboflavin intake to influence fracture risk in women.

INTRODUCTION

The MTHFR C677T polymorphism is associated with mildly elevated homocysteine (Hcy) levels in the presence of low folate and/or riboflavin status. A mildly elevated Hcy level was recently identified as a modifiable risk factor for osteoporotic fracture. We studied whether dietary intake of riboflavin and folate modifies the effects of the MTHFR C677T polymorphism on BMD and fracture risk.

MATERIALS AND METHODS

We studied 5,035 individuals from the Rotterdam Study, >or=55 yr of age, who had data available on MTHFR, nutrient intake, and fracture risk. We performed analysis on Hcy levels in a total of 666 individuals, whereas BMD data were present for 4,646 individuals (2,692 women).

RESULTS

In the total population, neither the MTHFR C677T polymorphism nor low riboflavin intake was associated with fracture risk and BMD. However, in the lowest quartile of riboflavin intake, female 677-T homozygotes had a 1.8 (95% CI: 1.1-2.9, p = 0.01) times higher risk for incident osteoporotic fractures and a 2.6 (95% CI: 1.3-5.1, p = 0.01) times higher risk for fragility fractures compared with the 677-CC genotype (interaction, p = 0.0002). This effect was not seen for baseline BMD in both men and women. No significant influence was found for dietary folate intake on the association between the MTHFR C677T genotype and fracture risk or BMD. In the lowest quartile of dietary riboflavin intake, T-homozygous individuals (men and women combined) had higher (22.5%) Hcy levels compared with C-homozygotes (mean difference = 3.44 microM, p = 0. 01; trend, p = 0.02).

CONCLUSIONS

In this cohort of elderly whites, the MTHFR C677T variant interacts with dietary riboflavin intake to influence fracture risk in women.

Polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene, intakes of folate and related B vitamins and colorectal cancer: a case-control study in a population with relatively low folate intake

Folate is key in one-carbon metabolism, disruption of which can interfere with DNA synthesis, repair, and methylation. Efficient one-carbon metabolism requires other B vitamins and the optimal activity of enzymes including 5,10-methylenetetrahydrofolate reductase (MTHFR). We report a population-based case-control study of folate intake, related dietary factors and MTHFR polymorphisms (C677T, A1298C) and colorectal cancer in a population with relatively high colorectal cancer incidence and relatively low folate intake. A total of 264 cases with histologically confirmed incident colorectal cancer and 408 controls participated. There was no clear trend in risk with reported intakes of total, or dietary, folate, riboflavin, vitamin B12 or vitamin B6, nor were there interactions between folate intake and the other B vitamins or alcohol. For C677T, risk decreased with increasing variant alleles (multivariate OR for CT v. CC = 0.77 (95 % CI 0.52, 1.16); OR for TT v. CC = 0.62 (95 % CI 0.31, 1.24)), which, although not statistically significant, was consistent with previous studies. For A1298C, compared with AA subjects, CC subjects had modest, non-significant, reduced risk (multivariate OR = 0.81 (95 % CI 0.45, 1.49)). There were significant interactions between total folate and C677T (P = 0.029) and A1298C (P = 0.025), and total vitamin B6 and both polymorphisms (C677T, P = 0.016; A1298C, P = 0.033), although the patterns observed differed from previous studies. Seen against the setting of low folate intake, the results suggest that the role of folate metabolism in colorectal cancer aetiology may be more complex than previously thought. Investigation of particular folate vitamers (for example, tetrahydrofolate, 5,10-methylenetetrahydrofolate) may help clarify carcinogenesis pathways.

Genetic polymorphisms and micronucleus formation: a review of the literature

The formation of micronuclei (MN) is extensively used in molecular epidemiology as a biomarker of chromosomal damage, genome instability, and eventually of cancer risk. The occurrence of MN represents an integrated response to chromosome-instability phenotypes and altered cellular viabilities caused by genetic defects and/or exogenous exposures to genotoxic agents. The present article reviews human population studies addressing the relationship between genetic polymorphisms and MN formation, and provides insight into how genetic variants could modulate the effect of environmental exposures to genotoxic agents, host factors (gender, age), lifestyle characteristics (smoking, alcohol, folate), and diseases (coronary artery disease, cancer). Seventy-two studies measuring MN frequency either in peripheral blood lymphocytes or exfoliated cells were retrieved after an extensive search of the MedLine/PubMed database. The effect of genetic polymorphisms on MN formation is complex, influenced to a different extent by several polymorphisms of proteins or enzymes involved in xenobiotic metabolism, DNA repair proteins, and folate-metabolism enzymes. This heterogeneity reflects the presence of multiple external and internal exposures, and the large number of chromosomal alterations eventually resulting in MN formation. Polymorphisms of EPHX, GSTT1, and GSTM1 are of special importance in modulating the frequency of chromosomal damage in individuals exposed to genotoxic agents and in unexposed populations. Variants of ALDH2 genes are consistently associated with MN formation induced by alcohol drinking. Carriers of BRCA1 and BRCA2 mutations (with or without breast cancer) show enhanced sensitivity to clastogens. Some evidence further suggests that DNA repair (XRCC1 and XRCC3) and folate-metabolism genes (MTHFR) also influence MN formation. As some of the findings are based on relatively small numbers of subjects, larger scale studies are required that include scoring of additional endpoints (e.g., MN in combination with fluorescent in situ hybridization, analysis of nucleoplasmic bridges and nuclear buds), and address gene-gene interactions.

Folate and colorectal cancer: an evidence-based critical review

Currently available evidence from epidemiologic, animal, and intervention studies does not unequivocally support the role of folate, a water-soluble B vitamin and important cofactor in one-carbon transfer, in the development and progression of colorectal cancer (CRC). However, when the portfolio of evidence from these studies is analyzed critically, the overall conclusion supports the inverse association between folate status and CRC risk. It is becoming increasingly evident that folate possesses dual modulatory effects on colorectal carcinogenesis depending on the timing and dose of folate intervention. Folate deficiency has an inhibitory effect whereas folate supplementation has a promoting effect on the progression of established colorectal neoplasms. In contrast, folate deficiency in normal colorectal mucosa appears to predispose it to neoplastic transformation, and modest levels of folic acid supplementation suppress, whereas supraphysiologic supplemental doses enhance, the development of cancer in normal colorectal mucosa. Several potential mechanisms relating to the disruption of one-carbon transfer reactions exist to support the dual modulatory role of folate in colorectal carcinogenesis. Based on the lack of compelling supportive evidence and on the potential tumor-promoting effect, routine folic acid supplementation should not be recommended as a chemopreventive measure against CRC at present.

Effect of coenzyme Q10, riboflavin and niacin on serum CEA and CA 15-3 levels in breast cancer patients undergoing tamoxifen therapy

In breast cancer patients, it is not the primary tumour, but its metastases at distant sites that are the main cause of death. Circulating breast cancer tumour markers such as carcinoembryonic antigen (CEA) and carbohydrate antigen 15-3 (CA 15-3) are reliable indicators of impending relapse, in which an increasing tumour marker level is associated with a very likelihood of developing recurrence. In the present study, 84 breast cancer patients were randomized to receive a daily supplement of 100 mg coenzyme Q10 (CoQ10), 10 mg riboflavin and 50 mg niacin (CoRN) one dosage per day along with 10 mg tamoxifen (TAM) twice a day. Serum CEA and CA 15-3 levels were elevated in untreated breast cancer patients (group II) and their tumour marker levels significantly reduced upon tamoxifen therapy for more than 1 year (group III). Group III patients supplemented with CoRN for 45 d (group IV) and 90 d (group V) along with tamoxifen significantly reduced CEA and CA 15-3 levels. This study suggests supplementing CoRN to breast cancer patients along with tamoxifen reduces the serum tumour marker level and thereby reduce the risk of cancer recurrence and metastases.

Protective association of MTHFR polymorphism on cervical intraepithelial neoplasia is modified by riboflavin status

OBJECTIVES

We previously reported that women polymorphic for the methylenetetrahydrofolate reductase (MTHFR) gene were less likely to have cervical intraepithelial neoplasia (CIN) 2 or 3 (odds ratio [OR] 0.40, 95% confidence interval [CI] 0.21-0.78, P = 0.007). In the present study, we tested whether this protective association is modified by circulating riboflavin status in the same study population.

METHODS

Riboflavin status was assessed by the erythrocyte glutathione reductase assay and expressed in terms of an erythrocyte glutathione reductase activity coefficient. The status of MTHFR polymorphism, riboflavin, and circulating concentrations of folate, vitamins B12, A, E, and C, and total carotene were ascertained in 170 White and 265 African-American women positive for the cervical presence of high-risk human papilloma virus. Presence/absence of CIN 2 or 3 was determined histologically, and associations with risk factors were examined using multiple logistic regression. Eighty women with CIN 2 or 3 lesions were compared with 355 women without cervical lesions. Based on the median erythrocyte glutathione reductase activity coefficient of 1.4, women were grouped into low (>1.4) and high (< or =1.4) riboflavin status.

RESULTS

Women with MTHFR polymorphism and low riboflavin status were significantly less likely to have CIN 2 or 3 than was the referent group of women without the polymorphism and high riboflavin status (OR 0.35, 95% CI 0.13-0.92, P = 0.034). MTHFR polymorphism was not associated with CIN 2 or 3 in women with high riboflavin status (OR 0.51, 95% CI 0.22-1.19, P = 0.119), nor were any of the associations influenced by folate levels.

CONCLUSION

A further inactivation of polymorphic MTHFR by low riboflavin status and a resulting shift in the folate metabolic pathway toward DNA synthesis may explain these observations. The practical implications of this complex gene-nutrient-disease interaction will require further investigation.

Localized depletion: the key to colorectal cancer risk mediated by MTHFR genotype and folate?

Dietary folate has been consistently associated with reduced risk of colorectal cancer (CRC). One of the known biochemical roles of folate is donation of methyl moieties. DNA hypomethylation is an early and almost ubiquitous occurrence in tumor tissue. Therefore, it was originally suggested that adequate folate intake contributed to reduced risk of CRC by facilitating methyl-mediated silencing of oncogenes. Methylene tetrahydrofolate reductase (MTHFR) metabolizes 5,10-MTHF (important in DNA synthesis) to 5-MTHF (contributes to downstream methylation reactions by regeneration of methionine from homocysteine). A common polymorphism in the MTHFR gene (C677T) results in a thermolabile phenotype associated with increased homocysteine levels and DNA hypomethylation. Consistent with the folate/methylation hypothesis, it was originally proposed that C677T may increase risk of CRC due to hypomethylation of oncogenes. However, most subsequent studies have reported a reduced risk associated with this polymorphism. This is inconsistent with methylation as the mechanism by which folate and MTHFR genotype mediate CRC risk. The hypothesis presented here proposes that localized folate depletion combined with the effect of the C677T polymorphism on enzyme stability, impacts on the DNA synthesis pathway and accounts for the observed variation in risk associated with genotype and folate status.

Dietary intake of folate and co-factors in folate metabolism, MTHFR polymorphisms, and reduced rectal cancer

Little is known about the contribution of polymorphisms in the methylenetetrahydrofolate reductase gene (MTHFR) and the folate metabolism pathway in rectal cancer alone. Data were from participants in a case-control study conducted in Northern California and Utah (751 cases and 979 controls). We examined independent associations and interactions of folate, B vitamins, methionine, alcohol, and MTHFR polymorphisms (MTHFR C677T and A1298C) with rectal cancer. Dietary folate intake was associated with a reduction in rectal cancer OR 0.66, 95% CI 0.48-0.92 (>475 mcg day compared to < or = 322 mcg) as was a combination of nutrient intakes contributing to higher methyl donor status (OR 0.79, 95% CI 0.66-0.95). Risk was reduced among women with the 677 TT genotype (OR 0.54, 95% CI 0.30-0.9), but not men (OR 1.11, 95% CI 0.70-1.76) and with the 1298 CC genotype in combined gender analysis (OR 0.67, 95% CI 0.46-0.98). These data are consistent with a protective effect of increasing dietary folate against rectal cancer and suggest a protective role of the MTHFR 677 TT genotype in women and 1298 CC in men and women. Folate intake, low methyl donor status, and MTHFR polymorphisms may play independent roles in the etiology of rectal cancer.

Lack of mutagenicity and clastogenicity of PNAEmu-NLS targeted to a regulatory sequence of the translocated c-myc oncogene in Burkitt's lymphoma

Peptide nucleic acids (PNAs) are synthetic homolog of nucleic acids in which the phosphate-sugar polynucleotide backbone is replaced by a flexible polyamide. They bind complementary polynucleotide sequences with higher affinity and specificity than their natural counterparts. PNAs linked to the appropriate nuclear localization signal (NLS) peptide have been used to selectively down-regulate the expression of several genes in viable cells. For example in Burkitt's lymphoma (BL) cells the c-myc oncogene is translocated in proximity to the Emu enhancer of the Ig gene locus and upregulated. PNAs complementary to the second exon of c-myc or to the Emu enhancer sequence (PNAEmu-NLS), selectively and specifically block the expression of the c-myc oncogene and inhibit cell growth in vitro and in vivo. PNAEmu-NLS administration to mice did not exhibit toxic effects even at the highest concentration allowed by the experimental conditions. Because of the accumulating data confirming PNAEmu-NLS potential therapeutic value, PNAEmu-NLS was evaluated for the inability to induce mutations in tester strains of Salmonella typhimurium, Escherichia coli, and at the hprt locus in Chinese hamster ovary cells (CHO). Moreover, the induction of chromosomal aberrations in CHO cells and of micronuclei in human lymphocytes were investigated. We may conclude that PNAEmu-NLS neither induces mutations nor has clastogenic effects as detectable by treatment under the standard test conditions.