Influence of serum micronutrients on the incidence of kinetochore-positive or -negative micronuclei in human peripheral blood lymphocytes

The Cytokinesis-Block Micronucleus Assay on Human Isolated Fresh and Cryopreserved Peripheral Blood Mononuclear Cells

The cytokinesis-block micronucleus (CBMN) assay is a standardized method used for genotoxicity studies. Conventional whole blood cultures (WBC) are often used for this assay, although the assay can also be performed on isolated peripheral blood mononuclear cell (PBMC) cultures. However, the standardization of a protocol for the PBMC CBMN assay has not been investigated extensively. The aim of this study was to optimize a reliable CBMN assay protocol for fresh and cryopreserved peripheral blood mononuclear cells (PBMCS), and to compare micronuclei (MNi) results between WBC and PBMC cultures. The G₀ CBMN assay was performed on whole blood, freshly isolated, and cryopreserved PBMCS from healthy human blood samples and five radiosensitive patient samples. Cells were exposed to 220 kV X-ray in vitro doses ranging from 0.5 to 2 Gy. The optimized PBMC CBMN assay showed adequate repeatability and small inter-individual variability. MNi values were significantly higher for WBC than for fresh PBMCS. Additionally, cryopreservation of PBMCS resulted in a significant increase of MNi values, while different cryopreservation times had no significant impact. In conclusion, our standardized CBMN assay on fresh and cryopreserved PBMCS can be used for genotoxicity studies, biological dosimetry, and radiosensitivity assessment.

Analysis of Genetic Damage in Lymphocytes of Former Uranium Processing Workers

The frequency of cells containing micronuclei (MN) and the presence of centromeres in these MN were analyzed in lymphocytes of 98 men from Southern Bohemia. Forty-six of them had worked at the uranium processing plant ‘MAPE Mydlovary' which was closed in 1991, and 52 men were controls from the same area. FISH using human pan-centromeric chromosome paint was employed to detect centromere-positive (CEN+) and -negative (CEN-) MN. A total of 1,000 binucleated cells (BNC) per participant were analyzed after cytochalasin B treatment. All BNC with MN (CEN+ or CEN-) were recorded. No differences were found between formerly exposed workers and the control group, neither in the total frequency of cells with MN per 1,000 BNC (mean levels ± SD, 9.1 ± 3.1 and 9.8 ± 2.5, respectively) nor in the percentage of CEN- MN, which were equal (50 ± 18 and 49 ± 17, respectively). Also, there was no difference between individuals living in the 3 villages closest to the uranium processing plant and those living further away. Considering the fact that effective doses of the workers at MAPE Mydlovary were overall similar to those of former uranium miners in whom higher frequencies of CEN- MN have been found more than 10 years after they had finished working underground, these results are somewhat surprising. A more detailed analysis of the exposures indicates that uranium miners received a greater percentage of their effective dose from the inhalation of radon and its daughters, whereas uranium processing workers received it from the incorporation of long-lived radioactive nuclides such as uranium. If, as has been suggested before, the higher level of DNA damage in miners is due to induced genomic instability, then this phenomenon may be related to radon exposure rather than exposure to uranium.

A combination of micronucleus assay and fluorescence in situ hybridization analysis to evaluate the genotoxicity of formaldehyde

A genotoxic effect of formaldehyde (FA), particularly micronucleus (MN) induction, has been shown in several previous studies. The aim of the present study was to assess the frequency of micronuclei and to identify the type of chromosomal damage in Tunisian staff members working in the Pathologic Anatomy Laboratory of Farhat Hached hospital (Sousse, Tunisia) who were exposed to FA. Assessment of chromosomal damage was performed in peripheral lymphocytes of 31 FA-exposed employees compared with 31 control employees working in the administrative department of the same hospital. The clastogenic/aneugenic effect of FA was evaluated using the standard MN assay in combination with fluorescence in situ hybridization (FISH) using pan-centromeric probes. The mean level of exposure to FA was 3.4 ppm. The results showed a significant increase of MN frequency in lymphocytes of exposed workers compared with the control group (25.35 ± 6.28 ‰ vs. 7.08  ± 4.62 ‰, p < 0.05). As assessed by FISH, the frequency of centromeric micronuclei (C+MN) was greater in exposed subjects than in controls (18.38 ± 5.94 ‰ vs. 5.03 ± 3.64 ‰). Among the C+MN, the frequency of MN containing one centromere (C1+MN) was significantly greater in pathologists and anatomists than in controls (15.35 ± 6.0 ‰ vs. 3.33 ± 2.74 ‰, p < 0.05). The results showed an effect of sex and time of FA exposure with significantly increased frequencies of all end points measuring aneuploidy (C+MN, C1+MN, and Cx+MN [more then one MN]). The increased frequency of C1+MN observed in the exposed group may suggest a slight aneugenic effect of FA exposure.

Folate (vitamin B9) and vitamin B12 and their function in the maintenance of nuclear and mitochondrial genome integrity

Folate plays a critical role in the prevention of uracil incorporation into DNA and hypomethylation of DNA. This activity is compromised when vitamin B12 concentration is low because methionine synthase activity is reduced, lowering the concentration of S-adenosyl methionine (SAM) which in turn may diminish DNA methylation and cause folate to become unavailable for the conversion of dUMP to dTMP. The most plausible explanation for the chromosome-breaking effect of low folate is excessive uracil misincorporation into DNA, a mutagenic lesion that leads to strand breaks in DNA during repair. Both in vitro and in vivo studies with human cells clearly show that folate deficiency causes expression of chromosomal fragile sites, chromosome breaks, excessive uracil in DNA, micronucleus formation, DNA hypomethylation and mitochondrial DNA deletions. In vivo studies show that folate and/or vitamin B12 deficiency and elevated plasma homocysteine (a metabolic indicator of folate deficiency) are significantly correlated with increased micronucleus formation and reduced telomere length respectively. In vitro experiments indicate that genomic instability in human cells is minimised when folic acid concentration in culture medium is greater than 100nmol/L. Intervention studies in humans show (a) that DNA hypomethylation, chromosome breaks, uracil incorporation and micronucleus formation are minimised when red cell folate concentration is greater than 700nmol/L and (b) micronucleus formation is minimised when plasma concentration of vitamin B12 is greater than 300pmol/L and plasma homocysteine is less than 7.5μmol/L. These concentrations are achievable at intake levels at or above current recommended dietary intakes of folate (i.e. >400μg/day) and vitamin B12 (i.e. >2μg/day) depending on an individual's capacity to absorb and metabolise these vitamins which may vary due to genetic and epigenetic differences.

Cytogenetic methods in human biomonitoring: principles and uses

Cellular phenotypes can be applied as biomarkers to differentiate normal from abnormal biological -conditions. Several cytogenetic methods have been developed and allow the accurate detection of such phenotypic changes.Based on their mechanisms of formation, cellular phenotypes may be used either as biomarkers of exposure or as biomarkers of effect. Therefore, it is important that cytogenetic methods implemented in human biomonitoring should be based on a good knowledge of these mechanisms.In this chapter, we aim to review the mechanistic basis, the methodology, and the use in human biomonitoring studies of four major cytogenetic endpoints: sister chromatid exchanges (SCEs), high frequency cells (HFCs), chromosomal aberrations (CAs), and micronuclei (MN). In addition, an overview of potential confounding factors on the induction of these cytogenetic makers is presented. Furthermore, the combination of cytogenetics with molecular methods, which allows chromosome and gene identification on metaphase as well as in interphase cells with high resolution, is discussed. Finally, practical recommendations for an efficient application of these cytogenetic assays and a correct interpretation of the results on the basis of cellular phenotype(s) assessment in human biomonitoring are highlighted.

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.

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.

Genotoxic effects of X-rays on keratinized mucosa cells during panoramic dental radiography

OBJECTIVES

The aim of this study was to evaluate the genotoxic effects of X-rays on epithelial gingival cells during panoramic dental radiography using a differentiated protocol for the micronucleus test.

METHODS

40 healthy individuals who underwent this procedure for diagnostic purposes on request from their dentists agreed to participate in this study. All of them answered a questionnaire before the examination. Epithelial gingival cells were obtained from the keratinized mucosa of the upper dental arcade by gentle scraping with a cervical brush immediately before exposure and 10 days later. Cytological preparations were stained according to the Feulgen-Rossenbeck reaction, counterstained with fast green 1% for 1 min and analysed under a light microscope. Micronuclei, nuclear projections (broken eggs) and degenerative nuclear alterations (pyknosis, karyolysis, karyorrhexis and condensed chromatin) were scored.

RESULTS

The frequency of micronuclei was significantly higher after exposure (P < 0.05), as were the frequencies of nuclear alterations indicative of apoptosis (P < 0.001).

CONCLUSIONS

These results indicate that X-ray radiation emitted during panoramic dental radiography induces a genotoxic effect on epithelial gingival cells that increases the frequency of chromosomal damage and nuclear alterations indicative of apoptosis.

Chromosomal changes: induction, detection methods and applicability in human biomonitoring

The objective of this state of the art paper is to review the mechanisms of induction, the fate, the methodology, the sensitivity/specificity and predictivity of two major cytogenetic endpoints applied for genotoxicity studies and biomonitoring purposes: chromosome aberrations and micronuclei. Chromosomal aberrations (CAs) are changes in normal chromosome structure or number that can occur spontaneously or as a result of chemical/radiation treatment. Structural CAs in peripheral blood lymphocytes (PBLs), as assessed by the chromosome aberration (CA) assay, have been used for over 30 years in occupational and environmental settings as a biomarker of early effects of genotoxic carcinogens. A high frequency of structural CAs in lymphocytes (reporter tissue) is predictive of increased cancer risk, irrespective of the cause of the initial CA increase. Micronuclei (MN) are small, extranuclear bodies that arise in dividing cells from acentric chromosome/chromatid fragments or whole chromosomes/chromatids that lag behind in anaphase and are not included in the daughter nuclei in telophase. The cytokinesis-block micronucleus (CBMN) assay is the most extensively used method for measuring MN in human lymphocytes, and can be considered as a "cytome" assay covering cell proliferation, cell death and chromosomal changes. The key advantages of the CBMN assay lie in its ability to detect both clastogenic and aneugenic events and to identify cells which divided once in culture. Evaluation of the mechanistic origin of individual MN by centromere and kinetochore identification contributes to the high sensitivity of the method. A number of findings support the hypothesis of a predictive association between the frequency of MN in cytokinesis-blocked lymphocytes and cancer development. Recent advances in fluorescence in situ hybridization (FISH) and microarray technologies are modifying the nature of cytogenetics, allowing chromosome and gene identification on metaphase as well as in interphase. Automated scoring by flow cytometry and/or image analysis will enhance their applicability.

The Genome Health Clinic and Genome Health Nutrigenomics concepts: diagnosis and nutritional treatment of genome and epigenome damage on an individual basis

The evidence of a direct link between increased genome/epigenome damage and elevated risk for adverse health outcomes during the various stages of life, such as infertility, foetal development and cancer is becoming increasingly stronger. The latter is briefly reviewed against a background of evidence indicating that genome and epigenome damage biomarkers, in the absence of overt exposure of genotoxins, are themselves sensitive indicators of deficiency in micronutrients required as cofactors or as components of DNA repair enzymes, for maintenance methylation of CpG sequences and prevention of DNA oxidation and/or uracil incorporation into DNA. The latter is illustrated with cross-sectional and dietary intervention data obtained using the micronucleus assay and other efficient biomarkers for diagnosing genome and/or epigenome instability. The concept of recommended dietary allowances for genome stability and how this could be achieved is discussed. The 'Genome Health Nutrigenomics' concept is also introduced to define and focus attention on the specialized research area of how diet impacts on genome stability and how genotype determines nutritional requirements for genome health maintenance. The review concludes with a vision for a paradigm shift in disease prevention strategy based on the diagnosis and nutritional treatment of genome/epigenome damage on an individual basis, i.e. The Genome Health Clinic.

Genetic damage in exfoliated cells from oral mucosa of individuals exposed to X-rays during panoramic dental radiographies

The genotoxic effects of X-ray emitted during dental panoramic radiography were evaluated in exfoliated cells from oral epithelium through a differentiated protocol of the micronucleus test. Thirty-one healthy individuals agreed to participate in this study and were submitted to this procedure for diagnosis purpose after being requested by the dentist. All of them answered a questionnaire before the examination. Cells were obtained from both sides of the cheek by gentle scrapping with a cervical brush, immediately before the exposure and after 10 days. Cytological preparations were stained according to Feulgen-Rossenbeck reaction and analyzed under light and laser scanning confocal microscopies. Micronuclei, nuclear projections (buds and broken eggs) and degenerative nuclear alterations (condensed chromatin, karyolysis and karyorrhexis) were scored. The frequencies of micronuclei, karyolysis and pycnosis were similar before and after exposure (P > 0.90), whereas the condensation of the chromatin and the karyorrhexis increased significantly after exposure (P < 0.0001). In contrast, both bud and broken egg frequencies were significantly higher before the examination (P < 0.005), suggesting that these structures are associated to the normal epithelium differentiation. The results suggest that the X-ray exposure during panoramic dental radiography induces a cytotoxic effect by increasing apoptosis. We also believe that the score of other nuclear alterations in addition to the micronucleus improves the sensitivity of genotoxic effects detection.

Bilirubin UDP-glucuronosyltransferase 1A1 (UGT1A1) gene promoter polymorphisms and HPRT, glycophorin A, and micronuclei mutant frequencies in human blood

A dinucleotide repeat polymorphism (5-, 6-, 7-, or 8-TA units) has been identified within the promoter region of UDP-glucuronosyltransferase 1A1 (UGT1A1) gene. The 7-TA repeat allele has been associated with elevated serum bilirubin levels that cause a mild hyperbilirubinemia (Gilbert's syndrome). Studies suggest that promoter transcriptional activity of UGT1A1 is inversely related to the number of TA repeats, and that unconjugated bilirubin concentration increases directly with the number of TA repeat elements. Because bilirubin is a known antioxidant, we hypothesized that UGT1A1 repeats associated with higher bilirubin may be protective against oxidative damage. We examined the effect of UGT1A1 genotype on somatic mutant frequency in the hypoxanthine-guanine phosphoribosyl-transferase (HPRT) gene in human lymphocytes and the glycophorin A (GPA) gene of red blood cells (both N0, NN mutants), and the frequency of lymphocyte micronuclei (both kinetochore (K)-positive or micronuclei K-negative) in 101 healthy smoking and nonsmoking individuals. As hypothesized, genotypes containing 7- and 8-TA displayed marginally lower GPA_NN mutant frequency relative to 5/5, 5/6, 6/6 genotypes ( [Formula: see text] ). In contrast, our analysis showed that lower expressing UGT1A1 alleles (7- and 8-TA) were associated with modestly increased HPRT mutation frequency ( [Formula: see text] ), while the same low-expression genotypes were not significantly associated with micronuclei frequencies (K-positive or K-negative) when compared to high-expression genotypes (5- and 6-TA). We found weak evidence that UGT1A1 genotypes containing 7- and 8-TA were associated with increased GPA_NØ mutant frequency relative to 5/5, 5/6, 6/6 genotypes ( [Formula: see text] ). These data suggest that UGT1A1 genotype may modulate somatic mutation of some types, in some cell lineages, by a mechanism not involving bilirubin antioxidant activity. More detailed studies examining UGT1A1 promoter variation, oxidant/antioxidant balance and genetic damage will be needed.

DNA lesions and cytogenetic changes induced by N-nitrosomorpholine in HepG2, V79 and VH10 cells: the protective effects of Vitamins A, C and E

INTRODUCTION

N-Nitrosomorpholine (NMOR), present in the workplace of tyre chemical factories, is a known hepatocarcinogen. This compound belongs to the group of N-nitrosamines, which are indirect-acting and require metabolic activation. However, the mechanism of its carcinogenic effect is not completely clear.

AIMS

The objective of this study was (i) to compare the DNA-damaging and clastogenic effects of NMOR in three cell lines (HepG2, V79 and VH10) with different levels of metabolizing enzymes and (ii) to determine the protective effects of Vitamins A, C and E against deleterious effects of NMOR.

METHODS

The exponentially growing cells were pre-treated with Vitamins A, C and E and treated with NMOR. Genotoxic effects of NMOR were evaluated by single-cell gel electrophoresis (SCGE, comet assay), while the chromosomal aberration assay was used for the study of clastogenic effects.

KEY RESULTS

NMOR-induced a significant dose-dependent increase of DNA damage as analyzed by SCGE, but the extent of DNA migration in the electric field was unequal in the different cell lines. Although the results obtained by SCGE confirmed the genotoxicity of NMOR in all cell lines studied, the number of chromosomal aberrations was significantly increased only in HepG2 and V79 cells, while no changes were observed in VH10 cells. In HepG2 cells pre-treated with Vitamins A, C and E we found a significant decrease of the percentage of tail DNA induced by NMOR. The reduction of the clastogenic effects of NMOR was observed only after pretreatment with Vitamins A and E; Vitamin C did not alter the frequency of NMOR-induced chromosomal aberrations under the experimental conditions of this study.

CONCLUSIONS

The fat-soluble Vitamins A and E, which are dietary constituents, reduce the harmful effects of N-nitrosomorpholine in human hepatoma cells HepG2, which are endowed with the maximal capacity for metabolic activation of several drugs.

Ascorbic acid potentiates mitomycin C-induced micronuclei and sister chromatid exchanges in human peripheral blood lymphocytes in vitro

Vitamin C (l-ascorbic acid), an effective free radical scavenger present as ascorbate in most biological systems, is one of the most extensively studied antioxidant vitamins. Vitamin C acts as either a free radical scavenger or a pro-oxidant producing hydrogen peroxide and free radicals. The modulatory effect of L-ascorbic acid (AA) on Mitomycin C (MMC) induced chromosome damage has been evaluated in human peripheral blood lymphocytes in vitro. The effect of L-ascorbic acid, 200 microg/ml as 1- and 2-h pretreatment on the frequencies of the biomarkers micronuclei (MN), sister chromatid exchanges (SCEs), and chromosome aberrations (CA) induced by mitomycin C 0.1 and 0.2 microg/ml has been studied. AA pretreatment caused a statistically significant increase in MMC-induced MN and SCE frequencies for all treatment groups, but did not show an increase in induced chromosome aberrations compared to MMC treatment alone. Cell division delays caused by MMC was reversed in the presence of AA. Interindividual variability in MMC as well as AA plus MMC-induced MN, SCE, and CA frequencies were evident. Ascorbic acid potentiated MMC-induced chromosome damage in human lymphocytes in vitro. The potentiation observed has to be viewed in the light of metal ion catalysed autooxidation of AA in oxygenated media and the existence of an antioxidant system in vivo that inactivates oxyradicals before their interaction with DNA.

Dietary folate deficiency enhances induction of micronuclei by arsenic in mice

Folate deficiency increases background levels of DNA damage and can enhance the genotoxicity of chemical agents. Arsenic, a known human carcinogen present in drinking water supplies around the world, induces chromosomal and DNA damage. The effect of dietary folate deficiency on arsenic genotoxicity was evaluated using a mouse peripheral blood micronucleus (MN) assay. In duplicate experiments, male C57Bl/6J mice were fed folate-deficient or folate-sufficient diets for 7 weeks. During week 7, mice on each diet were given four consecutive daily doses of sodium arsenite (0, 2.5, 5, or 10 mg/kg) via oral gavage. Over the course of the study the folate-deficient diet produced an approximate 60% depletion of red blood cell folate. Folate deficiency by itself was associated with small but significant increases in MN in normochromatic erythrocytes (NCEs) and polychromatic erythrocytes (PCEs). Arsenic exposure was associated with significant increases in MN-PCEs in both folate-deficient and folate-sufficient mice. MN-PCE frequencies at the 10 mg/kg dose of arsenic were increased 4.5-fold over vehicle control in folate-deficient mice and 2.1-fold over control in folate-sufficient mice. At the 5 and 10 mg/kg doses of arsenic, MN-PCE levels were significantly higher (1.3-fold and 2.4-fold, respectively) in folate-deficient mice compared to folate-sufficient mice. Very few MN from either control or treated animals in either experiment exhibited kinetochore immunostaining, suggesting that the MN were derived from chromosome breakage rather than from whole chromosome loss. These results indicate that folate deficiency enhances arsenic-induced clastogenesis at doses of 5 mg/kg and higher.

Vitamin C and genomic stability

Vitamin C, a water-soluble glucose derivative, has considerable antioxidant activity in vitro, in part because of its ease of oxidation and because the semidehydroascorbate radical derived from it is of low reactivity. Vitamin C in vivo is an essential cofactor for a range of enzymes involved in diverse metabolic pathways, but much recent literature has focused on its antioxidant effects. Consumption of foods rich in Vitamin C (fruits and vegetables) is associated with decreased risk of cardiovascular disease, of many types of cancer and possibly of neurodegenerative disease, but the extent to which Vitamin C contributes to these effects is uncertain. Data using biomarkers of oxidative damage to DNA bases have given no compelling evidence to date that ascorbate supplements can decrease the levels of oxidative DNA damage in vivo, except perhaps in subjects with very low Vitamin C intakes. Similarly, there is no conclusive evidence from studies of strand breaks, micronuclei, or chromosomal aberrations for a protective effect of Vitamin C. There is limited evidence that supplements of Vitamin C might have beneficial effects in disorders of vascular function, and that diet-derived Vitamin C may decrease gastric cancer incidence in certain populations, but it is not clear whether it is the antioxidant or other properties of ascorbate that are responsible for these two actions.

The role of folic acid and Vitamin B12 in genomic stability of human cells

Folic acid plays a critical role in the prevention of chromosome breakage and hypomethylation of DNA. This activity is compromised when Vitamin B12 (B12) concentration is low because methionine synthase activity is reduced, lowering the concentration of S-adenosyl methionine (SAM) which in turn may diminish DNA methylation and cause folate to become unavailable for the conversion of dUMP to dTMP. The most plausible explanation for the chromosome-breaking effect of low folate is excessive uracil misincorporation into DNA, a mutagenic lesion that leads to strand breaks in DNA during repair. Both in vitro and in vivo studies with human cells clearly show that folate deficiency causes expression of chromosomal fragile sites, chromosome breaks, excessive uracil in DNA, micronucleus formation and DNA hypomethylation. In vivo studies show that Vitamin B12 deficiency and elevated plasma homocysteine are significantly correlated with increased micronucleus formation. In vitro experiments indicate that genomic instability in human cells is minimised when folic acid concentration in culture medium is >227nmol/l. Intervention studies in humans show: (a) that DNA hypomethylation, chromosome breaks, uracil misincorporation and micronucleus formation are minimised when red cell folate concentration is >700nmol/l folate; and (b) micronucleus formation is minimised when plasma concentration of Vitamin B12 is >300pmol/l and plasma homocysteine is <7.5micromol/l. These concentrations are achievable at intake levels in excess of current RDIs i.e. more than 200-400microgram folic acid per day and more than 2microgram Vitamin B12 per day. A placebo-controlled study with a dose-response suggests that based on the micronucleus index in lymphocytes, an RDI level of 700microgram/day for folic acid and 7microgram/day for Vitamin B12 would be appropriate for genomic stability in young adults. Dietary intakes above the current RDI may be particularly important in those with extreme defects in the absorption and metabolism of these Vitamins, for which ageing is a contributing factor.

HUman MicroNucleus project: international database comparison for results with the cytokinesis-block micronucleus assay in human lymphocytes: I. Effect of laboratory protocol, scoring criteria, and host factors on the frequency of micronuclei

Micronucleus (MN) expression in peripheral blood lymphocytes is well established as a standard method for monitoring chromosome damage in human populations. The first results of an analysis of pooled data from laboratories using the cytokinesis-block micronucleus (CBMN) assay and participating in the HUMN (HUman MicroNucleus project) international collaborative study are presented. The effects of laboratory protocol, scoring criteria, and host factors on baseline micronucleated binucleate cell (MNC) frequency are evaluated, and a reference range of "normal" values against which future studies may be compared is provided. Primary data from historical records were submitted by 25 laboratories distributed in 16 countries. This resulted in a database of nearly 7000 subjects. Potentially significant differences were present in the methods used by participating laboratories, such as in the type of culture medium, the concentration of cytochalasin-B, the percentage of fetal calf serum, and in the culture method. Differences in criteria for scoring micronuclei were also evident. The overall median MNC frequency in nonexposed (i.e., normal) subjects was 6.5 per thousand and the interquartile range was between 3 and 12 per thousand. An increase in MNC frequency with age was evident in all but two laboratories. The effect of gender, although not so evident in all databases, was also present, with females having a 19% higher level of MNC frequency (95% confidence interval: 14-24%). Statistical analyses were performed using random-effects models for correlated data. Our best model, which included exposure to genotoxic factors, host factors, methods, and scoring criteria, explained 75% of the total variance, with the largest contribution attributable to laboratory methods.

Increased nondisjunction of chromosome 21 with age in human peripheral lymphocytes

Fluorescence in situ hybridization (FISH) on binucleated cells with chromosome-specific DNA probes provides a convenient way to visualize reciprocal segregation patterns in daughter nuclei, and overcomes most problems related to the artefactual loss or gain of chromosomes that flaw chromosome preparations. In this study, FISH was employed to evaluate age- and sex-effects on spontaneous malsegregation, nondisjunction and loss of chromosome 21 in human lymphocytes after the first division in culture. A total of 68 healthy nonsmokers and nondrinkers of alcohol (37 males and 31 females) were grouped by age as Group I (0-10 years), Group II (20-30 years), Group III (40-50 years) and Group IV (60-70 years), with at least seven subjects per group and sex. FISH with a pericentric chromosome 21 specific DNA probe was carried out on binucleated lymphocytes, cytokinesis-blocked by cytochalasin B (6 microg/ml for 26 h) at 44 h after initiation of cultures. Linear regression analyses demonstrated a significant age-related increase in the frequency of micronuclei without chromosome 21 (MN-21)(r=0.73, p<0.001 in females; r=0.69, p<0.001 in males) in all binucleated cells, with a steeper slope in females (0.1758) than in males (0. 1241). Analysis using the 2x2 chi-square (chi(2)) test on the frequencies of MN-21 showed significant age-related differences in both males and females, except males in Group III and Group IV (p>0. 05). A significant sex-related difference was found only in subjects over 60 years (p<0.05), with females having more MN-21 (12.57 per thousand vs. 8.43 per thousand) than males. Loss of chromosome 21, occurring at mean levels of 0.38 per thousand in all binucleated cells and 0.24 per thousand in binucleated cells containing four FISH signals, was shown not to be age- or sex-related. A positive age-related increase in nondisjunction of chromosome 21 was shown in males (r=0.50, p<0.01), females (r=0.61, p<0.001) and all subjects (r=0.55, p<0.001) by linear regression analysis. An age effect was found only between children and adults (p<0.01 for females, p<0.05

Dietary carotenoids and lung cancer: a review of recent research

Several hundred carotenoid research studies have been published since 1996, when two major intervention trials showed a lack of protective effect of beta-carotene supplements against lung cancer. Recent epidemiologic studies continue to show an association between high dietary intake of beta-carotene and lower risk of lung cancer. New research is attempting to clarify the apparently contradictory results of intervention and epidemiologic studies. Promising areas of investigation include characterizing biologic activities of carotenoids and gaining further insight into whether they may serve primarily as markers for a healthy lifestyle or diet.