Folate levels determine effect of antioxidant supplementation on micronuclei in subjects with cardiovascular risk

Amelioration of Cytogenotoxic Damage in Drug Abusers Supplemented with Folic Acid

BACKGROUND

Cytogenotoxic damage caused by the consumption of legal and illegal drugs in drug abusers has been demonstrated, primarily due to alterations in their antioxidant capacity, cellular repair mechanisms, and increased production of free radicals. Folic acid shows antioxidant activity by acting as a reducing agent, neutralizing present free radicals, and reducing genomic damage.

METHODS

The intervention involved administering 15 mg of folic acid, divided into three doses per day, to a group of 44 drug abusers. The frequency of nuclear abnormalities (NAs) was determined; micronuclei (MNs), nuclear buds (NBUDs), binucleated cells (BNs), abnormally condensed chromatin (CC), karyorrhexis (KX), pyknotic nuclei (PNs), and karyolysis (KL) were determined at different pre-treatment (baseline) and post-treatment time points at 15 and 30 days. Additionally, a group of 44 healthy individuals was used as the control group.

RESULTS

We observed a statistically significant decrease in the frequency of NAs in the drug abuser group (28.45 ± 17.74 before supplementation vs. 11.18 ± 7.42 at 15 days and 9.11 ± 10.9 at 30 days of supplementation). Specifically, it decreased the frequency of NBUDs, BNs, CC, KX, and PNs (p < 0.05).

CONCLUSION

Our study demonstrates a clear improvement in cytogenotoxic damage in drug abusers supplemented with folic acid.

Protective Effects of Micronutrient Supplements, Phytochemicals and Phytochemical-Rich Beverages and Foods Against DNA Damage in Humans: A Systematic Review of Randomized Controlled Trials and Prospective Studies

Accumulation of deoxyribonucleic acid (DNA) damage diminishes cellular health, increases risk of developmental and degenerative diseases, and accelerates aging. Optimizing nutrient intake can minimize accrual of DNA damage. The objectives of this review are to: 1) assemble and systematically analyze high-level evidence for the effect of supplementation with micronutrients and phytochemicals on baseline levels of DNA damage in humans, and 2) use this knowledge to identify which of these essential micronutrients or nonessential phytochemicals promote DNA integrity in vivo in humans. We conducted systematic literature searches of the PubMed database to identify interventional, prospective, cross-sectional, or in vitro studies that explored the association between nutrients and established biomarkers of DNA damage associated with developmental and degenerative disease risk. Biomarkers included lymphocyte chromosome aberrations, lymphocyte and buccal cell micronuclei, DNA methylation, lymphocyte/leukocyte DNA strand breaks, DNA oxidation, telomere length, telomerase activity, and mitochondrial DNA mutations. Only randomized, controlled interventions and uncontrolled longitudinal intervention studies conducted in humans were selected for evaluation and data extraction. These studies were ranked for the quality of their study design. In all, 96 of the 124 articles identified reported studies that achieved a quality assessment score ≥ 5 (from a maximum score of 7) and were included in the final review. Based on these studies, nutrients associated with protective effects included vitamin A and its precursor β-carotene, vitamins C, E, B1, B12, folate, minerals selenium and zinc, and phytochemicals such as curcumin (with piperine), lycopene, and proanthocyanidins. These findings highlight the importance of nutrients involved in (i) DNA metabolism and repair (folate, vitamin B12, and zinc) and (ii) prevention of oxidative stress and inflammation (vitamins A, C, E, lycopene, curcumin, proanthocyanidins, selenium, and zinc). Supplementation with certain micronutrients and their combinations may reduce DNA damage and promote cellular health by improving the maintenance of genome integrity.

Evaluation of Primary DNA Damage in Young Healthy Females Based on Their Dietary Preferences

DNA damage is known to be associated with many adverse health outcomes, including cancer and chronic diseases, but also with the process of aging. Empirical evidence has shown that environmental exposures, such as certain lifestyle factors, can affect a variety of health-related biomarkers and also impact the stability of DNA through the upregulation of the antioxidant defense system and alteration of its repair capacity. In addition to exercising, diet is an important lifestyle factor that can affect the development of a variety of chronic diseases and growing evidence suggests that plant-based diets, including vegetarianism, may promote health, longevity, and well-being. Therefore, we aimed to assess the primary DNA damage in 32 young healthy females from Zagreb, Croatia, based on their dietary preferences. The participants were divided into two groups: vegetarians and non-vegetarians, where the non-vegetarian group was further divided into omnivores (traditional mixed diet) and pescatarians (consumption of fish and seafood). According to statistical analysis, the DNA damage measured in whole blood cells expressed as the % tail DNA was significantly (p < 0.05) higher in vegetarians (3.6 ± 1.1%) compared to non-vegetarians (2.8 ± 1.0%). When further dividing the participants into specific sub-groups, lower DNA damage was observed amongst omnivorous subjects (3.2 ± 0.8%) compared to vegetarians, with the lowest DNA damage found in females practicing a pescatarian diet (2.4 ± 1.1%). Although a vegetarian diet can lead to a higher intake of specific vitamins and micronutrients, it can also lead to a deficiency of iron, calcium, and total proteins, which may affect genome stability and induce oxidative stress. Even though our results have shown that the pescatarian diet would be more beneficial in terms of maintaining DNA integrity, further research should be carried out to assess how specific dietary preferences affect DNA integrity on a larger scale.

Inflammatory, oxidative and DNA damage status in vegetarians: is the future of human diet green?

The health benefit of a vegetarian diet is still under debate as it may result in a higher intake of some beneficial micronutrients, while others may be reduced, thus influencing various metabolic pathways and health-related biomarkers. This scoping review discusses inflammatory, oxidative and DNA damage status in vegetarians and vegans compared to omnivores. Most of the reviewed studies indicated favorable effects of a vegetarian diet on oxidative status compared to omnivores but did not clearly associate particular dietary habits to genome damage. The evidence on the effect of vegetarian diet on the inflammatory and immunological biomarkers is poor, which could at least partly be explained by methodological constraints such as small sample size, short duration of vegetarianism and inconsistent definitions of the omnivorous diet. The only inflammatory biomarker that seems to be associated with the vegetarian diet was inflammatory mediator C-reactive protein, which in several studies showed lower values in vegetarians as compared to omnivores. There were very few studies on immunological markers and the results on the difference between vegetarians and omnivores were inconclusive. Although several biomarkers involved in oxidative stress and inflammation showed a beneficial association with the vegetarian diet, further research in well-defined and sufficiently sized cohorts is needed to provide more evidence.

Impact of dietary and lifestyle interventions in elderly or people diagnosed with diabetes, metabolic disorders, cardiovascular disease, cancer and micronutrient deficiency on micronuclei frequency - A systematic review and meta-analysis

Chronic diseases such as cardiovascular diseases, type 2 diabetes or cancer are the global leading cause of mortality. Lifestyle interventions are most effective in reducing metabolic risk factors, disease progression or even side effects of a disease. They are also contributing to decelerate the aging process. Genome instability is very often associated with aging or the above-mentioned diseases, and triggered by inflammation and oxidative stress. An established method to measure chromosomal damage is the cytokinesis block micronucleus (CBMN) cytome assay. The aim of this review and meta-analysis is to collect and analyse the current literature regarding the effects of a lifestyle based (dietary) intervention on changes of micronuclei (MNi), nucleoplasmic bridges (NPBs) and nuclear buds (NBUDs) in elderly subjects or people diagnosed with diabetes, metabolic disorders, cardiovascular disease, cancer or micronutrient deficiency. Although the main important diseases were considered as well as the large topic of aging, the number and methodological quality in terms of samples size, duration and rationale of the intervention or an inclusion of a control group of available intervention studies with these backgrounds was low. Most of the studies used antioxidant vitamins or folate, few investigated the whole diet. Only one study showed a physical activity intervention approach. The interventions did not lead to decreased genomic marker despite a few cancer related studies, where particularly MN frequency in mucosa lesions and leukoplakia was reduced by green tea and antioxidants. The performed meta-analysis of the available RCTs did not show a significant reduction of MNi, NBUDs or NPBs of most of the interventions performed, except for green tea. Data show in general a lack of an appropriate number of sound lifestyle based intervention studies linking cytogenetic damage and chronic diseases.

Micronucleus assay for predicting coronary artery disease: A systematic review and meta-analysis

Coronary artery disease (CAD) is the leading cause of morbidity and mortality worldwide. Coronary angiography allows an accurate assessment of the extent and severity of atherosclerotic coronary narrowing, but it provides little characterization of early detection of potentially asymptomatic vulnerable plaque. The identification of the coronary "vulnerable patient" or high-risk plaques remains a major challenge in the treatment of CAD. Recently, growing evidence shows that DNA damage plays a role in the initiation and progression of atherosclerotic plaque. Cytokinesis-block micronucleus (CBMN) assay is one of the most frequently used and validated method for assessing chromosomal damage and genetic instability. Accordingly, the purpose of this systematic review was to retrieve and discuss existing literature on the studies assessing the association between MN and angiographically-proven CAD. A total of 8 studies published between 2001 and 2017 were included in the meta-analysis. Despite a large heterogeneity between studies (I²= 99.7 %, p < 0.0001), an overall increase of MN frequencies was found in patients with CAD compared with control group (meta-MR = 1.96; 95 % CI, 1.5-3.2, p = 0.009). A subgroup analysis showed an increase in the frequency of MN formation for both two- vessel (MR = 2.13, 95 % CI: 0.9-6.9, p = 0.08) and three-vessel disease (MR = 2.89, 95 % CI: 1.84-4.55, P = 0.06). Overall, the results of this meta-analysis provide evidence of an association between CBMN and presence, extent and severity of angiographically-assessed CAD. However, the small number of papers analyzed requires further large and more rigorously designed studies, carefully considering a series of clinical confounding factors, such as the quality of the metabolic control, the influence of drugs and radiation imaging treatments.

A longitudinal study of pre-pregnancy antioxidant levels and subsequent perinatal outcomes in black and white women: The CARDIA Study

BACKGROUND

Although protective associations between dietary antioxidants and pregnancy outcomes have been reported, randomized controlled trials of supplementation have been almost uniformly negative. A possible explanation is that supplementation during pregnancy may be too late to have a beneficial effect. Therefore, we examined the relationship between antioxidant levels prior to pregnancy and birth outcomes.

METHODS AND FINDINGS

Serum carotenoids and tocopherols were assayed in fasting specimens at 1985-86 (baseline) and 1992-1993 (year 7) from 1,215 participants in Coronary Artery Risk Development in Young Adults (CARDIA) study. An interviewer-administered quantitative food-frequency questionnaire assessed dietary intake of antioxidants. Pregnancy outcome was self-reported at exams every 2 to 5 years. Linear and logistic regression modeling was used to assess relationships of low birthweight (LBW; <2,500 g), continuous infant birthweight, preterm birth (PTB; <37 weeks) and length of gestation with antioxidant levels adjusted for confounders, as well as interactions with age and race.

RESULTS

In adjusted models, lycopene was associated with higher odds of LBW (adjusted odds ratio for top quartile, 2.15, 95% confidence interval 1.14, 3.92) and shorter gestational age (adjusted beta coefficient -0.50 weeks). Dietary intake of antioxidants was associated with lower birthweight, while supplement use of vitamin C was associated with higher gestational age (0.41 weeks, 0.01, 0.81).

CONCLUSIONS

Higher preconception antioxidant levels are not associated with better birth outcomes.

Influence of vitamin intake and MTHFR polymorphism on the levels of DNA damage in tobacco farmers

BACKGROUND

Genetic damage may occur spontaneously under normal metabolic circumstances, inadequate intake of nutrients, and excessive exposure to environmental mutagens.

OBJECTIVES

To evaluate the influence of the intake of micronutrients vitamin B12, vitamin B6, and folate and of the polymorphism methylenetetrahydrofolate reductase (MTHFR) C677T on the induction of DNA damage in tobacco farmers.

METHODS

The study involved 66 men and 44 women engaged in tobacco cultivation in the region of Venâncio Aires (Rio Grande do Sul state, Brazil). Peripheral blood samples were collected to analyze DNA damage using the Comet assay, the micronucleus (MN) test and MTHFR C677T polymorphism. Dietary intake was evaluated based on the mean values obtained from three 24-h diet recall questionnaires, and nutrient intake data were computerized and estimated in the Food Processor SQL 10.9 program. The statistical tests used to generate the stated results were Kruskal-Wallis test, Exact Fisher's test, and multivariate linear regression analysis.

RESULTS

DNA damage was significantly higher in individuals who had an inadequate intake of folate, vitamin B12, and vitamin B6 (P < 0.01) assessed by Comet assay. In relation to MN test results, buccal cells showed MN frequency higher in individuals with inadequate intake of vitamin B6 (P < 0.01). No difference was observed in MN lymphocytes frequency. No significant association was detected between MTHFR C677T polymorphism and DNA damage in tobacco farmers.

CONCLUSION

Our results suggest that folate, vitamin B12, and vitamin B6 deficiency may be associated with genotoxic effect in individuals exposed to pesticides.

Interaction between blood selenium concentration and a levels of oxidative stress and antioxidative capacity in healthy children

The study aimed at defining the relationship between blood selenium concentration (Se-B) and levels of oxidative stress and antioxidative capacity in healthy children. The studies were conducted on 337 children (mean age: 8.53±1.92 years). The groups of individuals with Se-B <1st quartile (group I, Se-B<70μg/L), with Se-B fitting the range of 1st quartile and median (group II, Se-B: 70-76.9μg/L), with Se-B between the median and 3rd quartile (group III, Se-B: 77-83.9μg/L) and those with Se-B above the 3rd quartile (group IV, Se-B≥84μg/L) were distinguished. Level of oxidative stress was defined using determination of urine malonyldialdehyde concentration (MDA) and urine 8-hydroxy-2-deoxyguanosine concentration (8-OHdg). Urine total antioxidant status (TAS) was determined. In group IV TAS was significantly higher than in groups I-III. A positive correlation was detected between Se-B and TAS. In healthy children an appropriately high Se-B seems to ensure higher total antioxidative status.

Vitamin complex (ascorbic acid, alpha-tocopherol and beta-carotene) induces micronucleus formation in PBMNC unrelated to ROS production

OBJECTIVES

To evaluate the correlation between reactive oxygen species (ROS) production and micronucleus formation induced by a vitamin complex in peripheral blood mononuclear cells from healthy people aged between 40 and 85 years old.

METHODS

Peripheral blood mononuclear cells (PBMNCs) were purified utilizing ficoll-hypaque gradient. ROS production by PBMNCs was quantified by luminol-dependent chemiluminescence in the presence or in the absence of the vitamin complex. DNA damage in PBMNC by the vitamin complex was detected by the micronucleus technique. Statistical analyses were made with the Student's 't' test and the Pearson correlation. P < 0.05 was considered significant.

RESULTS

The vitamin complex induced MN formation in PBMNC but did not augment ROS production. There was no correlation between ROS production and MN formation either in the presence or in the absence of the vitamin complex.

DISCUSSION

There was no increase in the ROS production in the presence of the vitamin complex. The vitamin complex induced an augmentation in the MN formation. There was no correlation between ROS production and the induction of MN formation. Since no association could be detected between ROS production and MN formation, additional studies are required in order to investigate the possible mechanism of vitamin-induced MN formation.

Extracellular amyloid beta 42 causes necrosis, inhibition of nuclear division, and mitotic disruption under both folate deficient and folate replete conditions as measured by the cytokinesis-block micronucleus cytome assay

Alzheimer's disease is associated with accumulation of extracellular beta amyloid peptide 42 (Aβ42) which may induce DNA damage and reduce cellular regenerative potential. These effects may be exacerbated under conditions of folate deficiency. The aim of this study was to investigate whether extracellular Aβ42 induces DNA damage and cell death in human peripheral lymphocytes and whether there is an interactive effect between extracellular Aβ42 and folic acid status. Peripheral blood lymphocytes were cultured in medium under conditions of both low and high folate (20 and 200 nM, respectively) and challenged with either Aβ42 or the physiologically normal form Aβ40 (both at 5, 10, 15 µM). Genome stability and cytotoxicity events were investigated using the cytokinesis-block micronucleus cytome (CBMN-cyt) assay. Outcome measures scored included the nuclear division index (NDI), necrosis, apoptosis, binucleated cells with micronuclei (MN), nucleoplasmic bridges (NPB), and nuclear buds (NBUD) and abnormally shaped nuclei (circular, (CIR) and horse-shoe, (HS) that may be indicative of mitotic disruption. Folic acid deficiency significantly reduced NDI (P < 0.001) and increased all the DNA damage biomarkers (MN, NPB, NBUD, HS, CIR), (P < 0.001). In contrast, exposure to Aβ40 had no impact on CBMN cytome biomarkers but Aβ42 significantly reduced NDI (P < 0.01), increased necrosis (P < 0.05) and frequency of cells with circular nuclei (P < 0.01). There was no evidence of an interaction between Aβ42 and folic acid with respect to CBMN cytome biomarkers. Extracellular Aβ42 appears to have cytotoxic and cytostatic effects but its effect on chromosomal instability appears to be small relative to folate deficiency.

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.

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.

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.

Dietary and genetic compromise in folate availability reduces acetylcholine, cognitive performance and increases aggression: critical role of S-adenosyl methionine

Folate deficiency has been associated with age-related neurodegeneration. One direct consequence of folate deficiency is a decline in the major methyl donor, S-adenosyl methionine (SAM). We demonstrate herein that pro-oxidant stress and dietary folate deficiency decreased levels of acetylcholine and impaired cognitive performance to various degrees in normal adult mice (9-12 months of age, adult mice heterozygously lacking 5',10'-methylene tetrahydrofolate reductase, homozygously lacking apolipoprotein E, or expressing human ApoE2, E3 or E4, and aged (2-2.5 year old) normal mice. Dietary supplementation with SAM in the absence of folate restored acetylcholine levels and cognitive performance to respective levels observed in the presence of folate. Increased aggressive behavior was observed among some but not all genotypes when maintained on the deficient diet, and was eliminated in all cases supplementation with SAM. Folate deficiency decreased levels of choline and N-methyl nicotinamide, while dietary supplementation with SAM increased methylation of nicotinamide to generate N-methyl nicotinamide and restored choline levels within brain tissue. Since N-methyl nicotinamide inhibits choline transport out of the central nervous system, and choline is utilized as an alternative methyl donor, these latter findings suggest that SAM may maintain acetylcholine levels in part by maintaining availability of choline. These findings suggest that dietary supplementation with SAM represents a useful therapeutic approach for age-related neurodegeneration which may augment pharmacological approaches to maintain acetylcholine levels, in particular during dietary or genetic compromise in folate usage.

Effects of dietary supplementation with N-acetyl cysteine, acetyl-L-carnitine and S-adenosyl methionine on cognitive performance and aggression in normal mice and mice expressing human ApoE4

In addition to cognitive impairment, behavioral changes such as aggressive behavior, depression, and psychosis accompany Alzheimer's Disease. Such symptoms may arise due to imbalances in neurotransmitters rather than overt neurodegeneration. Herein, we demonstrate that combined administration of N-acetyl cysteine (an antioxidant and glutathione precursor that protects against A beta neurotoxicity), acetyl-L-carnitine (which raises ATP levels, protects mitochondria, and buffers A beta neurotoxicity), and S-adenosylmethionine (which facilitates glutathione usage and maintains acetylcholine levels) enhanced or maintain cognitive function, and attenuated or prevented aggression, in mouse models of aging and neurodegeneration. Enhancement of cognitive function was rapidly reversed upon withdrawal of the formulation and restored following additional rounds supplementation. Behavioral abnormalities correlated with a decline in acetylcholine, which was also prevented by this nutriceutical combination, suggesting that neurotransmitter imbalance may contribute to their manifestation. Treatment with this nutriceutical combination was able to compensate for lack of dietary folate and vitamin E, coupled with administration of dietary iron as a pro-oxidant (which collectively increase homocysteine and oxidative damage to brain tissue), indicating that it provided antioxidant neuroprotection. Maintenance of neurotransmitter levels and prevention of oxidative damage underscore the efficacy of a therapeutic approach that utilizes a combination of neuroprotective agents.

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.

The impact of folate status and folic acid supplementation on the micronucleus frequency in human erythrocytes

Folic acid has a well-documented stabilising effect on chromosomes. A correlation between folate status and chromosome stability in humans has been reported in studies that were restricted to certain subpopulations, e.g., folate-deficient persons. The goal of the present investigation was to clarify if there also is a correlation between folate status and chromosome stability among individuals without any folate deficiency. The method used here is the recently developed flow cytometry-based micronucleus assay in human transferrin-positive reticulocytes (MN-Trf-Ret). In a blood sample, separation of the very young reticulocytes from the mature erythrocytes makes this micronucleus assay possible. This investigation comprises three studies (cross-sectional, giving baseline data), two of which are connected to an intervention study. In the three cross-sectional studies (total number of subjects, 99) the frequency of MN-Trf-Ret (fMN-Trf-Ret) was measured and compared with the serum folate status. In two of the studies also serum homocysteine and Vitamin B12 were measured and compared with the baseline fMN-Trf-Ret. Combining the results from the three cross-sectional studies, a negative correlation between folate status and fMN-Trf-Ret was obtained (p<0.05). The goal of the intervention studies was to clarify if different nutritional supplementations had any effect on the fMN-Trf-Ret and the cell proliferation (percentage polychromatic erythrocytes, PCE). Each of the two studies involved two groups, one placebo and one supplemented group. In one of the studies the supplementation was folic acid, 1000 microg/day during 1 week (n=30, both sexes); in the other intervention study, folic acid (800 microg/day), B12 (20 microg/day) and B6 (4 mg/day) were taken during 1 week (n=29, both sexes). No significant difference in %PCE or fMN-Trf-Ret between the two groups was found in either of the two intervention studies.