Recommendations and quality criteria for micronucleus studies with humans

Micronucleus (MN) analyses in peripheral blood lymphocytes and exfoliated cells from different organs (mouth, nose, bladder and cervix) are at present the most widely used approaches to detect damage of genetic material in humans. MN are extranuclear DNA-containing bodies, which can be identified microscopically. They reflect structural and numerical chromosomal aberrations and are formed as a consequence of exposure to occupational, environmental and lifestyle genotoxins. They are also induced as a consequence of inadequate intake of certain trace elements and vitamins. High MN rates are associated with increased risk of cancer and a range of non-cancer diseases in humans. Furthermore, evidence is accumulating that measurements of MN could be a useful tool for the diagnosis and prognosis of different forms of cancer and other diseases (inflammation, infections, metabolic disorders) and for the assessment of the therapeutic success of medical treatments. Recent reviews of the current state of knowledge suggest that many clinical studies have methodological shortcomings. This could lead to controversial findings and limits their usefulness in defining the impact of exposure concentrations of hazardous chemicals, for the judgment of remediation strategies, for the diagnosis of diseases and for the identification of protective or harmful dietary constituents. This article describes important quality criteria for human MN studies and contains recommendations for acceptable study designs. Important parameters that need more attention include sufficiently large group sizes, adequate duration of intervention studies, the exclusion of confounding factors which may affect the results (sex, age, body mass index, nutrition, etc.), the evaluation of appropriate cell numbers per sample according to established scoring criteria as well as the use of proper stains and adequate statistical analyses.

An automated method for dynamic red blood cell aggregate detection in microfluidic flow

OBJECTIVE

Red blood cell (RBC) aggregation is a unique phenomenon that occurs when red blood cells are subjected to low shear rates. Little is known about the sizes, shapes and behaviour of aggregates flowing in healthy humans. However, excessive aggregation has been shown to be an indication of pathological conditions. Therefore, characterizing RBC aggregates is important to medical research. The objective of this study was to develop a reliable technique based on image processing to assess and characterize human RBC aggregation subjected to controlled and measurable shear rates in a two-fluid flow microfluidic shearing system.

APPROACH

Images of RBC suspensions at [Formula: see text], [Formula: see text] and [Formula: see text] entrained by a phosphate buffered saline solution in a PDMS microchannel were captured with a high speed camera. An algorithm for processing the RBC aggregate images is presented and validated (1) on a sample of known diameter hollow glass microspheres and (2) by comparing RBC aggregate size results with those of an ImageJ image processing technique and those obtained by manual detection by two independent researchers.

MAIN RESULTS

The proposed image processing algorithm provides a very good agreement with the manufacturer data for the glass microspheres. It also performs well on the RBC suspension images, with errors of 2-4 [Formula: see text] with respect to the manual results.

SIGNIFICANCE

The proposed automated method for RBC aggregate detection is found to be reliable and fairly accurate and will serve researchers and, perhaps in the future, clinicians to assess healthy and pathological RBC aggregation under flowing conditions.

Prenatal omega-3 fatty acid supplementation does not affect offspring telomere length and F2-isoprostanes at 12 years: A double blind, randomized controlled trial

BACKGROUND

Oxidative stress and nutritional deficiency may influence the excessive shortening of the telomeric ends of chromosomes. It is known that stress exposure in intrauterine life can produce variations in telomere length (TL), thereby potentially setting up a long-term trajectory for disease susceptibility.

OBJECTIVE

To assess the effect of omega-3 long chain polyunsaturated fatty acid (n-3 LCPUFA) supplementation during pregnancy on telomere length and oxidative stress in offspring at birth and 12 years of age (12y).

DESIGN

In a double-blind, placebo-controlled, parallel-group study, 98 pregnant atopic women were randomised to 4g/day of n-3 LCPUFA or control (olive oil [OO]), from 20 weeks gestation until delivery. Telomere length as a marker of cell senescence and plasma and urinary F2-isoprostanes as a marker of oxidative stress were measured in the offspring at birth and 12y.

RESULTS

Maternal n-3 LCPUFA supplementation did not influence offspring telomere length at birth or at 12y with no changes over time. Telomere length was not associated with F2-isoprostanes or erythrocyte total n-3 fatty acids. Supplementation significantly reduced cord plasma F2-isoprostanes (P<0.001), with a difference in the change over time between groups (P=0.05). However, the differences were no longer apparent at 12y. Between-group differences for urinary F2-isoprostanes at birth and at 12y were non-significant with no changes over time.

CONCLUSIONS

This study does not support the hypothesis that n-3 LCPUFA during pregnancy provides sustained effects on postnatal oxidative stress and telomere length as observed in the offspring.

Design of a microfluidic system for red blood cell aggregation investigation

The purpose of this paper is to design a microfluidic apparatus capable of providing controlled flow conditions suitable for red blood cell (RBC) aggregation analysis. The linear velocity engendered from the controlled flow provides constant shear rates used to qualitatively analyze RBC aggregates. The design of the apparatus is based on numerical and experimental work. The numerical work consists of 3D numerical simulations performed using a research computational fluid dynamics (CFD) solver, Nek5000, while the experiments are conducted using a microparticle image velocimetry system. A Newtonian model is tested numerically and experimentally, then blood is tested experimentally under several conditions (hematocrit, shear rate, and fluid suspension) to be compared to the simulation results. We find that using a velocity ratio of 4 between the two Newtonian fluids, the layer corresponding to blood expands to fill 35% of the channel thickness where the constant shear rate is achieved. For blood experiments, the velocity profile in the blood layer is approximately linear, resulting in the desired controlled conditions for the study of RBC aggregation under several flow scenarios.

Elevated plasma magnesium and calcium may be associated with shorter telomeres in older South Australian women

Telomeres are structures that cap the ends of chromosomes. The integrity of the telomere structure and its DNA hexamer (TTAGGG)n repeat sequence is critical for protecting the ends of chromosomes from degradation and in maintaining overall chromosomal stability. Currently, there are limited data on the influence that nutrition has on telomere length. Recent studies have suggested that micronutrients may influence telomere length. Here we examined the relationship between telomere length in lymphocytes and plasma calcium, magnesium, selenium and zinc status in a healthy cohort of younger and older adults. We report a negative association between telomere length and both plasma calcium and magnesium levels, (r=-0.47, P=0.03 and r=-0.61, P=0.001 respectively), in older females; Intriguingly Ca/Mg ratio was positively associated with telomere length (r=0.55, P=0.007). These relationships were not observed in the younger adults, nor in the older males. In conclusion, our study provides preliminary evidence suggesting that levels of plasma magnesium and calcium may impact on telomere length in lymphocytes in older women.

Contact angle study of blood dilutions on common microchip materials

Biocompatible polymers are commonly used to fabricate microfluidic channels for the study of biological flows such as blood microflows. The most common of these materials is polydimethylsiloxane (PDMS) which is very hydrophobic. Oxygenated plasma is advocated to treat the PDMS with reported decreases in contact angle i.e. increase the hydrophilicity of the material in order to make the liquid flow easily. All contact angle studies have been reported with water. Here the contact angles of blood suspensions, in saline and native plasma, are compared to each other and water on common microfluidic chip materials. The hydrophilic effect of plasma-treatment on PDMS is not found to be as significant with blood suspensions as it is with water. Red blood cells suspended in native plasma are found to have a greater contact angle than those suspended in saline.

Use of haemoglobin A1c to detect impaired fasting glucose or Type 2 diabetes in a United Kingdom community based population

AIMS

To evaluate the diagnostic accuracy of haemoglobin A1c (HbA1c) in screening for impaired fasting glucose and Type 2 diabetes (T2DM).

METHODS

We screened 3904 adults aged 45-70 (mean age 58.6 [standard deviation (SD) 6.9] years, mean body mass index (BMI) 29.9 [SD 4.7]kg/m(2)), with fasting plasma glucose (FPG) and HbA1c as part of a large diabetes prevention programme. We assessed the diagnostic accuracy of HbA1c for predicting impaired fasting glucose (IFG), (defined either as FPG 5.6-6.9 mmol/l, or 6.1-6.9 mmol/l), and T2DM (FPG ≥ 7.0 mmol/l).

RESULTS

The prevalences of IFG were 13.8% (FPG 5.6-6.9 mmol/l) and 4.5% (FPG 6.1-6.9 mmol/l) and of T2DM was 2.1%. Using FPG 5.6-6.9 mmol/l as the IFG reference standard, HbA1c of 39-47 mmol/mol (5.7-6.4%) was 63% sensitive and 81% specific, and HbA1c 43-47 mmol/mol (6.1-6.4%) was 21% sensitive and 98% specific, in diagnosing IFG. HbA1c ≥ 48 mmol/mol (6.5%) was 61% sensitive and 99% specific in diagnosing T2DM. Having HbA1c 39-47 mmol/mol (5.7-6.4%), male sex, and body mass index >29.5 together increased the odds of IFG 6.5-fold (95% confidence interval (CI) 5.5-7.8) compared to the pre-test odds.

CONCLUSION

Defining 'pre-diabetes' at a lower HbA1c threshold of 39 mmol/mol (5.7%) instead of 47 mmol/mol (6.1%) increases its sensitivity in diagnosing IFG, but current American Diabetes Association definitions of 'pre-diabetes' based on HbA1c would fail to detect almost 40% of people currently classified as IFG. This has implications for current and future diabetes prevention programmes, for vascular risk management, and for clinical advice given to people with 'pre-diabetes' based on fasting glucose data.

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.

Transcriptomic network analysis of micronuclei-related genes: a case study

Mechanistically relevant information on responses of humans to xenobiotic exposure in relation to chemically induced biological effects, such as micronuclei (MN) formation can be obtained through large-scale transcriptomics studies. Network analysis may enhance the analysis and visualisation of such data. Therefore, this study aimed to develop a 'MN formation' network based on a priori knowledge, by using the pathway tool MetaCore. The gene network contained 27 genes and three gene complexes that are related to processes involved in MN formation, e.g. spindle assembly checkpoint, cell cycle checkpoint and aneuploidy. The MN-related gene network was tested against a transcriptomics case study associated with MN measurements. In this case study, transcriptomic data from children and adults differentially exposed to ambient air pollution in the Czech Republic were analysed and visualised on the network. Six genes from the network, i.e. BAX, DMNT1, PCNA, HIC1, p21 and CDC20, were retrieved. Based on these six genes and in combination with p53 and IL-6, a dedicated network was created. This dedicated network is possibly suited for the development of a reporter gene assay that could be used to screen populations complementary to the current MN test assay. In conclusion, we have shown that network analysis of transcriptomics data in relation to the formation of MN is possible and provides a novel mechanistic hypothesis by indicating which genes are regulated and influence others.

Flow through a defective mechanical heart valve: a steady flow analysis

Approximately 250,000 valve replacement operations occur annually around the world and more than two thirds of these operations use mechanical heart valves (MHV). These valves are subject to complications such: pannus and/or thrombus formation. Another potential complication is a malfunction in one of the valve leaflets. Although the occurrence of such malfunctions is low, they are life-threatening events that require emergency surgery. It is, therefore, important to develop parameters that will allow an early non-invasive diagnosis of such valve malfunction. In the present study, we performed numerical simulations of the flow through a defective mechanical valve under several flow and malfunction severity conditions. Our results show that the flow upstream and downstream of the defective valve is highly influenced by malfunction severity and this resulted in a misleading improvement in the correlation between simulated Doppler echocardiographic and catheter transvalvular pressure gradients. In this study, we were also able to propose and test two potential non-invasive parameters, using Doppler echocardiography and phase contrast magnetic resonance imaging, for an early detection of mechanical heart valve malfunction. Finally, we showed that valve malfunction has a significant impact on platelet activation and therefore on thrombus formation.

Investigations into the relationship between hemodynamics and vascular alterations in an established arteriovenous fistula

Arteriovenous fistula are specific vessels created by a vascular operation in order to provide sufficient blood access for extracorporeal circulation in hemodialysis. They are subject to numerous pathologies that may be caused by hemodynamic effects. To better understand these effects, a specific patient's arteriovenous fistula was reconstructed from computed tomography angiography. Computational fluid dynamics software made it possible to solve fluid mechanics equations under physiological conditions. An accurate map of unsteady velocity profiles and wall shear stress was drawn up. The computed velocity profiles were successfully confronted with Echo Doppler investigation. Selected regions with or without calcification, the end stage of wall alteration, were examined in terms of the mechanical constraints generated by blood flow. In contrast with other authors, we did not observe any association between calcification and areas of oscillating shear stress. Nevertheless, a statistical analysis of the whole vessel envelop and specific sites of calcification suggested a potential association between calcification and high temporal wall shear stress gradients.

Moderate acute intake of de-alcoholized red wine, but not alcohol, is protective against radiation-induced DNA damage ex vivo -- results of a comparative in vivo intervention study in younger men

Moderate intake of wine is associated with reduced risk of cardiovascular disease and possibly cancer however it remains unclear whether the potential health benefits of wine intake are due to alcohol or the non-alcoholic fraction of wine. We therefore tested the hypothesis that the non-alcoholic fraction of wine protects against genome damage induced by oxidative stress in a crossover intervention study involving six young adult males aged 21-26 years. The participants adhered to a low plant phenolic compound diet for 48 h prior to consuming 300 mL of complete red wine, de-alcoholized red wine or ethanol on separate occasions 1 week apart. Blood samples were collected 0.5, 1.0 and 2.0 h after beverage consumption. Baseline and radiation-induced genome damage was measured using the cytokinesis-block micronucleus assay and total plasma catechin concentration was measured. Consumption of de-alcoholized red wine significantly decreased the gamma radiation-induced DNA damage at 1 and 2 h post-consumption by 20%. In contrast alcohol tended to increase radiation-induced genome damage and complete wine protected against radiation-induced genome damage relative to alcohol. The observed effects were only weakly correlated with the concentration of total plasma catechin (R=-0.23). These preliminary data suggest that only the non-alcoholic fraction of red wine protects DNA from oxidative damage but this effect cannot be explained solely by plasma catechin.

Ovulation failure and double ovulation in dairy cattle: risk factors and effects

Ovulation failure and double ovulation rates were examined in 1917 inseminations performed in high-yielding dairy cows under standard commercial conditions. The ovulation rate was determined 11 days post-insemination by ultrasound detection of at least one corpus luteum in the ovaries. Analyzing the double ovulation and pregnancy rates, the study population consisted only of ovulated cows (n = 1792). Data were analyzed using logistic regression methods. A failure to ovulate was recorded in 125/1917 (6.5%) services: 82/663 (12.4%) during the warm and 43/1254 (3.4%) during the cool period. Based on the odds ratios, the risk of ovulation failure was 3.9 times higher for inseminations performed during the warm period. No significant effects of estrous synchronization, milk production and days in milk at AI, and service and lactation number on ovulation failure were found. Double ovulation was recorded in 277/1792 (15.5%) services: 146 (52.7%) unilateral double ovulations (42.5% left versus 57.5% right); 115 (41.5%) bilateral double ovulations; and 16 (5.8%) triple ovulations. Double ovulation was recorded in 72 (12.4%) and 205 (16.9%) AI during the warm and the cool period, respectively. The percentages of double ovulation for first, second and third or more lactations were 6.7, 16.6 and 25%, respectively. Double ovulation rates for early (less than 90 days), mid- (90-150 days) and late (more than 150 days) lactation periods were 13, 20.7 and 14.2%, respectively. Reaching estrus during the warm period decreased the likelihood of double ovulation by a factor of 0.86; the risk of double ovulation was lower in cows with higher milk production (a 1 kg increase in milk yield led to a 0.97-fold reduced risk of double ovulation); cows in their second and in their third or more lactations showed a likelihood of double ovulation (using the first lactation as reference) increased by factors of 3.4 and 5.6, respectively; and reaching estrus during the early and late lactation period was related to a decreased probability of double ovulation (using the mid-lactation period as reference) by factors of 0.56 and 0.84, respectively. No significant effects of synchronization and service number on the double ovulation rate were found. Pregnancy was recorded in 914/1792 (51%) services: rates of 53.5% (811/1515) were recorded for single ovulations; 37.2% (103/277) for double ovulations: 28.8% (42/146) for unilateral double ovulations; 45.2% (52/115) for bilateral double ovulations; and 56.3% (9/16) for triple ovulations. The likelihood of pregnancy diminished in cows: inseminated during the warm period (by a factor of 0.5); inseminated by one particular bull (by a factor of 0.33); with higher milk production (a 1 kg increase in milk yield decreased the probability of pregnancy by a factor of 0.98); or undergoing unilateral (by a factor of 0.31) and bilateral (by a factor of 0.64) double ovulation. Logistic regression analysis indicated no significant effects of synchronization, days in milk, lactation number and service number on pregnancy rate. Collectively, our results indicate that cows showing estrus in conditions of heat stress had a high risk of ovulation failure. The effect of milk production on double ovulation was negative, whereas lactation number was positively correlated with this factor; the highest incidence of double ovulation occurring during the mid-lactation period.

Comparison of DNA damage and repair following radiation challenge in buccal cells and lymphocytes using single-cell gel electrophoresis

PURPOSE

To develop a reproducible single-cell gel electrophoresis assay for DNA damage and repair in buccal mucosa and sublingual exfoliated cells.

MATERIALS AND METHODS

Buccal mucosa and sublingual cells and lymphocytes from six individuals (three males, three females, aged 34-45 years) were challenged with increasing doses of gamma-rays. DNA strand breaks and DNA repair were measured using the single-cell gel electrophoresis assay.

RESULTS

Baseline DNA strand breaks were significantly greater in buccal mucosa and sublingual cells compared with lymphocytes. Buccal mucosa and sublingual cells did not differ from each other with respect to induction of DNA strand breaks by 2 or 4 Gy gamma-rays. However, they showed a smaller increase in gamma-ray-induced DNA strand breaks compared with lymphocytes (32-53% less than lymphocytes; ANOVA p<0.0001). Unlike lymphocytes, which repaired 83% of DNA strand breaks, buccal mucosa and sublingual cells exhibited only a minimal capacity for DNA repair (approximately 0-14% of the level in lymphocytes).

CONCLUSIONS

Buccal mucosa and sublingual cells exhibit an apparent resistance to the expression of radiation-induced DNA strand breaks in vitro and an apparent lack of DNA strand break repair in the single-cell gel electrophoresis assay.

Reproductive functional anatomy and oestrous cycle pattern of the female brush-tailed porcupine (Atherurus africanus, Gray 1842) from Gabon

In the present study, we examined certain features of the functional anatomy of the female genital tract of the wild brush-tailed porcupine (Atherurus africanus) to obtain data on the reproductive biology of this African forest rodent. Two consecutive experiments were performed. The aim of the first was to establish macroscopic and microscopic features of the genital organs, and to explore correlations between predominant ovarian structures and vaginal contents in 20 wild, mature females. In the second experiment, we inspected the external genitalia and vaginal smears of a further 10 females in captivity on a daily basis for 90 days. The uterus of the brush-tailed porcupine is bicornuate and composed of two separated uterine horns, a uterine body and cervix. The genital tract does not present a vaginal vestibule. Thus, there is no portion common to genital and urinary tracts. Females in the follicular phase of the oestrous cycle showed increased cornification of the vaginal epithelium and a high density of eosinophilic cells in vaginal smears. The vulva and vaginal opening were open, reddish and tumefacted. In luteal phase or in pregnancy, epithelial cornification and eosinophilic features were notably reduced and the vagina presented a pale, non-tumefacted vulva and a vaginal closure membrane. Females in captivity showed spontaneous cycles, a polyoestrous reproduction pattern and, based on features of the external genitalia and vaginal smears, their oestrous cycle length was 27.1+/-6.4 days (n=12).

HUMN project: detailed description of the scoring criteria for the cytokinesis-block micronucleus assay using isolated human lymphocyte cultures

Criteria for scoring micronuclei and nucleoplasmic bridges in binucleated cells in the cytokinesis-block micronucleus assay for isolated human lymphocyte cultures are described in detail. Morphological characteristics of mononucleated cells, binucleated cells, and multinucleated cells as well as necrotic and apoptotic cells and nuclear buds are also described. These criteria are illustrated by a series of schematic diagrams as well as a comprehensive set of colour photographs that are of practical assistance during the scoring of slides. These scoring criteria, diagrams and photographs have been used in a HUman MicronNucleus (HUMN) project inter-laboratory slide-scoring exercise to evaluate the extent of variability that can be attributable to individual scorers and individual laboratories when measuring the frequency of micronuclei and nucleoplasmic bridges in binucleated cells as well as the nuclear division index. The results of the latter study are described in an accompanying paper. It is expected that these scoring criteria will assist in the development of a procedure for calibrating scorers and laboratories so that results from different laboratories for the cytokinesis-block micronucleus assay may be more comparable in the future.

Risk factors for postpartum ovarian cysts and their spontaneous recovery or persistence in lactating dairy cows

Cystic ovarian disease is a major cause of reproductive failure and economic loss for the dairy industry. Many cysts that develop during the early postpartum period regress spontaneously. However, it is difficult to decide at what point it would be more cost effective to treat ovarian cysts than to wait for spontaneous recovery. The objective of this study was to analyze risk factors for the development of the ovarian cystic condition during early and late postpartum, and for its persistence or recovery during the pre-service period in lactating dairy cows. Using multiple logistic regression, we analyzed data derived from 873 lactating dairy cows from a single herd. An ovarian cyst was diagnosed if it was possible to observe a single follicular structure with an antrum diameter > or = 25 mm in the absence of a corpus luteum in three sonograms performed at 7-day intervals. The cystic condition was denoted as early if the cyst was diagnosed 43-49 days postpartum, and late if detected 57-63-day postpartum. Spontaneous cyst regression before 60-day postpartum was regarded as early cystic recovery. For the early cystic group, there were no significant effects of lactation number, body condition score on prepartum Day 60, at parturition or on postpartum Day 30, or of body condition loss from parturition to 30-day postpartum. Cows calving in summer were 2.6 times more likely to develop ovarian cysts than those giving birth in winter. The risk of having a cyst was 1.9 times higher in cows with an abnormal puerperium. A 1-kg increase in milk yield raised the risk of cysts by a factor of 1.05. A 1-unit increase in body condition score (scale from 1 to 5) from prepartum Day 60 to parturition increased the risk of cyst development 8.4 times. Milk production and lactation number were negatively correlated with spontaneous early cyst recovery. A 1-kg decrease in milk production increased the probability of cyst recovery by a factor of 1.06, and a 1-unit drop in lactation number was associated with a 1.4-fold increased probability of cyst recovery. For the late cystic group, there were no significant effects of abnormal puerperium and body score data, except for a prepartum change in body score. Calving season (Odds ratio: 2.3), lactation number (Odds ratio: 1.36), increased milk production (Odds ratio: 1.05) and increased body condition score during the prepartum period (Odds ratio: 4.3) were all related to an increased risk of ovarian cysts. The probability of having a late cyst was 36.6 times greater in cows with early cysts. These findings suggest that it would be profitable to treat multiparous cows having cysts very early in the postpartum period, while treatment of primiparous cows should be delayed, at least until the end of the pre-service period, to provide the opportunity for spontaneous recovery.

Micronutrients and genomic stability: a new paradigm for recommended dietary allowances (RDAs)

Diet as a key factor in determining genomic stability is more important than previously imagined because we now know that it impacts on all relevant pathways, namely exposure to dietary carcinogens, activation/detoxification of carcinogens, DNA repair, DNA synthesis and apoptosis. Current recommended dietary allowances for vitamins and minerals are based largely on the prevention of diseases of deficiency such as scurvy in the case of vitamin C. Because diseases of development, degenerative disease and aging itself are partly caused by damage to DNA it seems logical that we should focus better our attention on defining optimal requirements of key minerals and vitamins for preventing damage to both nuclear and mitochondrial DNA. To date, our knowledge on optimal micronutrient levels for genomic stability is scanty and disorganised. However, there is already sufficient evidence to suggest that marginal deficiencies in folate, vitamin B12, niacin and zinc impact significantly on spontaneous chromosome damage rate. The recent data for folate and vitamin B12 in humans with respect to micronucleus formation in blood and epithelial cells provide compelling evidence of the important role of these micronutrients in maintenance of genome integrity and the need to revise current RDAs for these micronutrients based on minimisation of DNA damage. Appropriately designed in vitro studies and in vivo placebo controlled trials with dose responses using a complementary array of DNA damage biomarkers are required to define recommended dietary allowances for genomic stability. Furthermore these studies would have to be targeted to individuals with common genetic polymorphisms that alter the bioavailability of specific micronutrients and the affinity of specific key enzymes involved in DNA metabolism for their micronutrient co-factor. That there is a need for an international collaborative effort to establish RDAs for genomic stability is self-evident.

Reversibility of artifacts of fluid volume measurements by bioimpedance caused by position changes during dialysis

The effect of temporary position changes, sitting up from supine, on extracellular (ECW) and intracellular (ICW) resistances and fluid volumes calculated from whole body bioimpedance using a Xitron 4200 impedancemeter was investigated on 8 patients during dialysis for a total of 11 tests. It was found that ECW resistance decreased instantaneously by an average of 2.3% when the patient sits up, due to plasma and interstitial fluid shift into the legs which decreases leg resistance, the major contributor to total resistance. This drop in resistance is incorrectly interpreted by the device as an increase in ECW volume which averages 235 ml. But this effect is completely reversible and both ECW resistance and fluid volume rapidly resume their normal course when the patient returns to his initial position. No significant variation in ICW resistance was observed in any of the patients at the position change. We conclude that segmental impedance, which has been proposed to minimize this artifact, is not advisable in dialysis monitoring and that it is simpler to ignore or switch off measurements during the position change so that later data are not affected by it.

The effect of folic acid deficiency and MTHFR C677T polymorphism on chromosome damage in human lymphocytes in vitro

We performed a comprehensive study on the genotoxic and cytotoxic effects of in vitro folic acid deficiency on primary human lymphocytes. Lymphocytes were cultured in medium containing 12-120 nM folic acid for 9 days in a novel cytokinesis-block micronucleus (CBMN) assay system (n = 20). Besides identifying optimal folic acid concentrations for in vitro genomic stability, we tested the hypothesis that lymphocytes from individuals homozygous for the C677T methylenetetrahydrofolate reductase (MTHFR) polymorphism (TTs, n = 10) are protected against chromosome damage relative to controls (CCs, n = 10) under conditions of folic acid deficiency. This hypothesis is based on the assumption that reduced MTHFR activity in TT lymphocytes causes a diversion of 5,10-methylene tetrahydrofolate toward thymidine synthesis, which minimizes uracil-induced double-stranded DNA breakage. Cells were scored for micronuclei, apoptosis, necrosis, nucleoplasmic bridges, and nuclear budding. The latter two endpoints are indicative of chromosome rearrangements and gene amplification, respectively, and to the best of our knowledge, this is the first report of their association with folic acid concentration. Folic acid concentration correlated significantly (P < 0.0001) and negatively (r, -0.63 to -0.74) with all markers of chromosome damage, which were minimized at 60-120 nM folic acid, much greater than concentrations assumed "normal," but not necessarily optimal in plasma. Two-way ANOVA revealed no effect of the MTHFR genotype on any of the endpoints. Results show that the C677T polymorphism does not affect the ability of a cell to resist chromosome damage induced by folic acid deficiency in this in vitro system.

Recommended dietary allowances (RDAs) for genomic stability

Diet as a key factor in determining genomic stability is more important than previously imagined because we now know it impacts on all relevant pathways, i.e. exposure to dietary carcinogens, activation/detoxification of carcinogens, DNA repair, DNA synthesis and apoptosis. Current recommended dietary allowances for vitamins and minerals are based largely on the prevention of diseases of deficiency such as scurvy in the case of Vitamin C. Because diseases of development, degenerative disease and ageing itself are partly caused by damage to DNA, it seems logical that we should focus better our attention on defining optimal requirements of key minerals and vitamins for preventing damage to both nuclear and mitochondrial DNA. To date our knowledge on optimal micronutrient levels for genomic stability is scanty and disorganised. Appropriately designed placebo, controlled trials are required to define recommended dietary allowances for genomic stability. Recently, it has been shown that above RDA intakes of folic acid and Vitamin B12 are required to reduce the micronucleus index in humans by 25%. In the future, clinical trials with a defined wider array of complementary DNA damage end-points would be necessary. That there is a need for an international collaborative group to establish RDAs for genomic stability is self-evident and this paper is a call for such a process to begin.

Normal human lymphocytes exhibit a wide range of methionine-dependency which is related to altered cell division but not micronucleus frequency

The underlying cause(s) of methionine-dependency and its relevance to cancer remains unclear. We aimed to determine whether (i) normal human lymphocytes exhibit methionine-dependency, (ii) baseline levels of genetic damage are related to methionine-dependency and (iii) methionine-dependence can be explained, in part, by common polymorphisms in methionine synthase and methylenetetrahydrofolate reductase (MTHFR). Genetic damage was measured in lymphocytes of 52 volunteers (29--65 years) using the cytokinesis-block micronucleus assay. Methionine-dependency was assessed by culturing cells in serum-free media containing 0.1 mM L-methionine and 0 mM D,L-homocysteine (met(+)hcy(-)) or 0 mM L-methionine and 0.2 or 0.4 mM D,L-homocysteine (0.2/0.4-hcy(+))(met(-)hcy(+)). Mitogenesis was stimulated with phytohaemagglutinin. Cytokinesis was inhibited by adding cytochalasin B at 44 h. Ninety-six hours after PHA, cells were transferred to microscope slides. Cell proliferation was measured by counting binucleated cell frequency and calculating nuclear division index. Volunteers were classified into tertiles of methionine-dependence according to the growth of their cells in met(-)hcy(+) media (relative to growth in met(+)hcy(-) media). Average cell division, as a percentage of division in met(+)hcy(-) media, was approximately 5, 26 and 70% in 0.2-hcy(+) media and 29, 70 and 142% in 0.4-hcy(+) media for the high, mid and low tertiles of methionine-dependence, respectively. Micronucleus frequency did not vary between these tertiles (P > 0.6). In both met(+)hcy(-) and met(-)hcy(+) media, cell division was not affected by polymorphisms in MTHFR (C677T, A1298C) or methionine synthase (A2756G). Cell division in met(-)hcy(+) media was negatively correlated with division in met(+)hcy(-) media (P = 0.05 and 0.007 for 0.2 and 0.4-hcy(+), respectively). Methionine-dependent lymphocytes had higher levels of cell proliferation in met(+)hcy(-) media than methionine-independent lymphocytes (P = 0.089 and 0.01 for 0.2 and 0.4-hcy(+), respectively). However, this difference was not apparent in previous experiments when cells were grown in media containing 10% fetal calf serum. These findings show that there is a wide inter-individual variation in the degree of methionine-dependency of normal human lymphocytes in vitro. Methionine-dependency does not appear to alter the risk for chromosomal mutation as measured by the micronucleus assay. We discuss the possible relevance to cancer of increased cell division in methionine-dependent cells under methionine-replete and serum-free media conditions.

Preliminary study of the genotoxic potential of homocysteine in human lymphocytes in vitro

Homocysteine (Hcy), an immediate precursor of methionine (Met), is considered a risk factor for cardiovascular disease, Alzheimer's disease and neural tube defects. Hcy concentration is also reported to correlate positively with the micronucleus index in lymphocytes in vivo, a marker of chromosome damage. However, it is unclear whether Hcy is genotoxic or simply a biomarker of folate deficiency, a known cause of chromosome damage. We investigated whether high concentrations of Hcy are genotoxic to human lymphocytes in vitro using the cytokinesis-block micronucleus assay. Eighteen lymphocyte cultures were initiated in Met-free and serum-free RPMI 1640 medium for each of four male volunteers aged 22-23 years. At 0, 24, 44 and 72 h, cultures were spiked with L-Hcy or L-Met to achieve concentrations ranging between 50 and 400 microM. The concentration of Hcy at 96 h ranged from 19.45 +/- 2.34 to 149.02 +/- 28.16 microM in Hcy cultures and 0.91 +/- 0.17 to 2.15 +/- 0.9 microM in Met cultures spiked with 50 and 400 microM of metabolite, respectively. Forty-four hours after mitogen stimulation, cytokinesis was inhibited with cytochalasin B. After 96 h, cells were transferred to microscope slides and the frequency of micronucleated-binucleate and necrotic cells was scored. Neither Hcy (P = 0.24) nor Met (P = 0.93) had an apparent dose effect on micronucleus frequency. However, when data were pooled, micronucleus frequency was moderately higher (50.1%) in Hcy- than in Met-spiked cultures (P = 0.04; paired t-test). Hcy concentration was positively correlated with necrosis (P < 0.0005; r(2)= 0.276), however, when data were pooled, levels of necrosis were higher in Met- than in Hcy-spiked cultures (P= 0.01; paired t-test). Further research is required to define more clearly the genotoxic and cytotoxic potential of homocysteine and its metabolites.

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.

Vitamins/minerals and genomic stability in humans

Recommended dietary allowances (RDAs) of micronutrients have been traditionally derived as those levels necessary to prevent symptoms of deficiency diseases. There is increasing evidence that higher levels of many such micronutrients may be necessary for various DNA maintenance reactions, and that the current RDAs for some micronutrients may be inadequate to protect against genomic instability. Supplementation of a normal diet, with either vitamins and/or minerals or with isolated plant polyphenols, is becoming increasingly common in most Western populations. However, there is no clear agreement as to how much supplementation should occur, if at all, and genotypic differences are not accounted for. The 14 mini-reviews in this special issue summarise the role of specific micronutrients in various aspects of DNA maintenance: DNA synthesis, DNA repair, DNA methylation, gene mutation, chromosome breakage, chromosome segregation, gene expression, oxidative stress, necrosis and apoptosis. Evidence has been collated from mammalian and human experiments, both using in vitro cultures and in vivo approaches. Authors were asked to critically assess the strength of evidence as to whether the micronutrient can affect genomic stability in humans at realistic intake levels, and to estimate optimal dietary ranges where possible. Information on further research necessary is also documented. These reviews are an essential step towards a definition of RDAs designed to maintain genomic stability.

Fluid volumes determination by impedance spectroscopy and hematocrit monitoring: application to pediatric hemodialysis

A method for extracting fluid volumes from multifrequency bioimpedance, which takes into account the body geometry and the presence of nonconducting elements, was tested on 12 young dialyzed patients against correlations for total body water volumes (TBW) from Watson et al. and Humes et al. Our calculations of TBW from impedance were found to overestimate Humes' values by 0.25 L (0.8%) postdialysis and by 2.08 L (6.5%) predialysis. Extracellular water (ECW) was found to contribute an average of 93% of ultrafiltered volume. Intracellular water volume (ICW) determination from impedance was found to be too imprecise to predict its variation during dialysis; therefore, ICW variations were calculated as the difference between ultrafiltration and ECW changes. The continuous recording of hematocrit by an optical device monitored changes in plasma and interstitial volumes. In most cases, ultrafiltration was compensated mainly by a contribution from interstitial fluid, and the drop in plasma volume was generally moderate.

Flow cytometric enumeration of micronucleated reticulocytes: high transferability among 14 laboratories

This laboratory previously described a single-laser flow cytometric method, which effectively resolves micronucleated erythrocyte populations in rodent peripheral blood samples. Even so, the rarity and variable size of micronuclei make it difficult to configure instrument settings consistently and define analysis regions rationally to enumerate the cell populations of interest. Murine erythrocytes from animals infected with the malaria parasite Plasmodium berghei contain a high prevalence of erythrocytes with a uniform DNA content. This biological model for micronucleated erythrocytes offers a means by which the micronucleus analysis regions can be rationally defined, and a means for controlling interexperimental variation. The experiments described herein were performed to extend these studies by testing whether malaria-infected erythrocytes could also be used to enhance the transferability of the method, as well as control intra- and interlaboratory variation. For these studies, blood samples from mice infected with malaria, or treated with vehicle or the clastogen methyl methanesulfonate, were fixed and shipped to collaborating laboratories for analysis. After configuring instrumentation parameters and guiding the position of analysis regions with the malaria-infected blood samples, micronucleated reticulocyte frequencies were measured (20,000 reticulocytes per sample). To evaluate both intra- and interlaboratory variation, five replicates were analyzed per day, and these analyses were repeated on up to five separate days. The data of 14 laboratories presented herein indicate that transferability of this flow cytometric technique is high when instrumentation is guided by the biological standard Plasmodium berghei.

Inclusion of micronuclei in non-divided mononuclear lymphocytes and necrosis/apoptosis may provide a more comprehensive cytokinesis block micronucleus assay for biomonitoring purposes

Human biomonitoring of early genetic effects requires accurate, sensitive and, if possible, easy and not too time-consuming methodologies to assess mutations. One of the most promising methodologies at the present time is the cytokinesis block micronucleus (MN) assay (CBMN), which detects both chromosome breakage and chromosome loss in once-divided binucleated (BN) cells. Many studies have been published with this methodology, but before its extensive application is recommended, it is necessary to evaluate its strengths and limitations. Recently, Fenech et al. reviewed the advantages of the CBMN assay for biomonitoring purposes. However, up to now information present in mononucleated (MONO) cells has rarely been taken into account, although it might be complementary to that assessed in BN cells. Indeed, MONO cells should indicate damage which was present in vivo before the start of culture and BN cells may contain pre-existing micronuclei (MNi) plus lesions which are expressed as MNi during in vitro culture. To address this question, the objectives of this paper were as follows. (i) To situate the CBMN assay in a historical and mechanistic perspective. (ii) To consider whether impaired mitotic capacity in vitro may be responsible for false negative biomonitoring studies if MN in MONO cells are not taken into account in the CBMN test. The following factors were considered: division delay for repair and mitotic block, in vitro apoptosis and necrosis of damaged cells, mitotic slippage and correlation between MN expression in vitro versus in vivo. (iii) To analyse the factors which may cause a negative result in the CBMN assay in biomonitoring when exposure to specific genotoxins is evident. The specific effects of aneugens and of adaptive responses to chronic low level exposure were examined. (iv) To compare the sensitivity of MONO and BN cells in relation to the genotoxic mechanism. (v) To propose an adequate sampling scheme to study MN in both MONO and BN cells. It was concluded that a more comprehensive assessment of DNA damage may be achieved if the CBMN assay includes measures of: (i) MNi in MONO cells; (ii) MNi in BN cells; (iii) apoptotic cells; (iv) necrotic cells. It is probable that the 24 h post-phytohaemagglutinin time point may be the optimal time to assess the frequency of MNi in MONO cells, apoptotic cells and necrotic cells. It is also practical to include these measures when scoring MNi in BN cells after cytokinesis block.

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.

Micronucleus induction and chromosome loss in transformed human white cells indicate clastogenic and aneugenic action of the cyanobacterial toxin, cylindrospermopsin

Cylindrospermopsin (CYN) is a potent inhibitor of protein synthesis produced by a number of cyanobacterial species, the most common being Cylindrospermopsis raciborskii. CYN contains a uracil moiety attached to a sulphated guanidino moiety, suggesting that it may have carcinogenic activity. This report describes the use of the WIL2-NS lymphoblastoid cell-line in the well-validated cytokinesis-block micronucleus (CBMN) assay to test this hypothesis. Centromeres (CENs) were identified in micronuclei (MNi) of binucleated cells (BNCs) by fluorescent in situ hybridisation of alpha centromeric DNA sequence repeats. The results indicate that CYN induced a significant increase in the frequency of MNi in BNCs exposed to 6 and 10microg/ml, and a significant increase in CEN-positive MNi at all concentrations of CYN tested (1, 3, 6, and 10microg/ml). However, despite this apparently greater sensitivity of WIL2-NS cells to induction of CEN-positive MNi at low CYN concentrations, at the higher concentrations the magnitude of the increase in CEN-positive MNi did not account for the greater increase in MNi in BNCs, indicating that both CEN-positive and CEN-negative MNi were induced. This suggests that CYN acts to induce cytogenetic damage via two mechanisms, one at the level of the DNA to induce strand breaks, the other at the level of kinetochore/spindle function to induce loss of whole chromosomes (aneuploidy). C. raciborskii occurs in a number of human drinking water sources worldwide and so these findings may have important public health implications.