Enumeration of micronucleated reticulocytes in rat peripheral blood: a flow cytometric study

In vitro and in vivo assessment of the genotoxic effects of ceric ammonium nitrate and 1,3-propane sultone

A variety of methods have been developed for accurate and systematic evaluation of chemical genotoxicity. Ceric ammonium nitrate (CAN) and 1,3-propane sultone (1,3-PS) have been extensively applied in industrial fields. Although 1,3-PS, but not CAN, has been reported as a potent carcinogen, systematic assessment of the genotoxic properties of these chemicals has not been conducted. The purpose of this study was to establish a decision tree for evaluating genotoxicity based on the good laboratory practices (GLP) system using 1,3-PS and CAN as test chemicals. In vitro studies were performed including the bacterial reverse mutation assay, chromosomal aberration assay, and micronucleus assay. We conducted in vivo studies using a combined micronucleus and alkaline comet (MN-CMT) assay and the Pig-a gene mutation assay, which is a promising method for detecting gene mutations in vivo. CAN showed negative responses in all in vitro genotoxicity assays and the in vivo combined MN-CMT assay. Meanwhile, 1,3-PS had positive results in all in vitro and in vivo genotoxicity assays. In this study, we confirmed the genotoxicity of 1,3-PS and CAN using both in vitro and in vivo assays. We propose a decision tree for evaluating chemical-induced genotoxicity.

Micronucleus Analysis by Flow Cytometry

During the last two decades the micronucleus (MN) test has been extensively used as a genotoxicity screening tool of chemicals and in a variety of exploratory and mechanistic investigations. The MN is a biomarker for chromosomal damage or mitotic abnormalities since it can originate from chromosome fragments or whole chromosomes that fail to be incorporated into daughter nuclei during mitosis (Fenech et al., Mutagenesis 26: 125-132, 2011; Kirsch-Volders et al., Arch Toxicol 85: 873-899, 2011). The simplicity of scoring, accuracy, amenability to automation by image analysis or flow cytometry and the readiness to be applied to a variety of cell types either in vitro or in vivo made it a versatile tool that contributed to a large extent in our understanding of key toxicological issues related to genotoxins and their effects at the cellular and organism levels. Recently, the final acceptance of the in vitro MN test Organization for Economic Cooperation and Development (OECD) guideline 487 (OECD, Guideline for testing of chemicals: in vitro mammalian cell micronucleus test 487: in vitro mammalian cell micronucleus test (MNVIT). Organization for Economic Cooperation and Development, Paris, 2010) together with the standard in vivo MN test OECD guideline 474 (OECD, Guideline for the testing of chemicals no. 474 mammalian erythrocyte micronucleus test. Organization for Economic Cooperation and Development, Paris, 1997) further positioned the assay as a key driver in the determination of the genotoxicity potential in exploratory research as well as in the regulatory environment. This book chapter covers to some extent the protocol designs and experimental steps necessary for a successful performance of the MN test and an accurate analysis of the MN by the flow cytometry technique.

Flow cytometry in peripheral blood reticulocytes as a marker of chromosome instability in highgrade glioma patients

Introduction: The quantification of chromosomal instability is an important parameter to assess genotoxicity and radiosensitivity. Most conventional techniques require cell cultures or laborious microscopic analyses of chromosomes or nuclei. However, a flow cytometry that selects the reticulocytes has been developed as an alternative for in vivo studies, which expedites the analytical procedures and increases up to 20 times the number of target cells to be analyzed. Objectives: To standardize the flow cytometry parameters for selecting and quantifying the micronucleated reticulocytesCD71+ (MN-RET) from freshly drawn peripheral blood and to quantify the frequency of this abnormal cell subpopulation as a measure of cytogenetic instability in populations of healthy volunteers (n =25), and patients (n=25), recently diagnosed with high-grade gliomas before the onset of treatment. Materials and methods: Blood cells were methanol-fixed and labeled with anti-CD-71-PE for reticulocytes, antiCD-61-FITC for platelet exclusion, and propidium iodide for DNA detection in reticulocytes. The MN-RETCD71+ cell fraction was selected and quantified with an automatic flow cytometer. Results: The standardization of cytometry parameters was described in detail, emphasizing the selection and quantification of the MN-RETCD71+ cellular fraction. The micronuclei basal level was established in healthy controls. In patients, a 5.2-fold increase before the onset of treatment was observed (p <0.05). Conclusion: The data showed the usefulness of flow cytometry coupled with anti-CD-71-PE and anti-CD-61-FITC labeling in circulating reticulocytes as an efficient and high resolution method to quantify chromosome instability in vivo. Finally, possible reasons for the higher average of micronuclei in RETCD71+ cells from untreated high-grade glioma patients were discussed.

Flow cytometric determination of micronucleus frequency

During the last two decades the micronucleus (MN) test has been extensively used as a genotoxicity screening tool of chemicals and in a variety of exploratory and mechanistic investigations. The MN is a biomarker for chromosomal damage or mitotic abnormalities, since it can originate from chromosome fragments or whole chromosomes that fail to be incorporated into daughter nuclei during mitosis (Fenech et al., Mutagenesis 26:125-132, 2011; Kirsch-Volders et al., Arch Toxicol 85:873-899, 2011). The simplicity of scoring, accuracy, amenability to automation by image analysis or flow cytometry, and readiness to be applied to a variety of cell types either in vitro or in vivo have made it a versatile tool that has contributed to a large extent in our understanding of key toxicological issues related to genotoxins and their effects at the cellular and organism levels. Recently, the final acceptance of the in vitro MN test guideline 487 (OECD Guideline for Testing of Chemicals, In vitro mammalian cell micronucleus test 487. In vitro mammalian cell micronucleus test (MNVIT). Organization for Economic Cooperation and Development, Paris, 2010) together with the standard in vivo MN test OECD guideline 474 (OECD Guideline for The Testing of Chemicals, Mammalian erythrocyte micronucleus test no. 474. Organization for Economic Cooperation and Development, Paris, 1997) will further position the assay as a key driver in the determination of the genotoxicity potential in exploratory research as well as in the regulatory environment. This chapter covers to some extent the protocol designs and experimental steps necessary for a successful performance of the MN test and an accurate analysis of the MN by the flow cytometry technique.

Cytogenetic in vivo assays in somatic cells

Chromosome aberration assays are employed to detect the induction of chromosome breakage (clastogenesis) in somatic and germ cells by direct observation of the chromosomal damage during metaphase analysis, or by indirect observation of chromosomal fragments. Thus, various types of cytogenetic change can be detected such as structural chromosome aberrations (CA), sister chromatid exchanges (SCE), ploidy changes, and micronuclei. Following the induction of the chromosomal damage, most of the aberrations and abnormalities detected by these assays can be detrimental or even lethal to the cell. Their presence, however, indicates a potential to also induce more subtle and therefore transmissible chromosomal damage which survives cell division to produce heritable cytogenetic changes. Usually, induced cytogenetic damage is accompanied by other genotoxic damage such as gene mutations.

Trimethoprim-sulfamethoxazole increase micronuclei formation in peripheral blood from weanling well-nourished and malnourished rats

The combination of trimethoprim and sulfamethoxazole (TMP-SMX) is a widely used drug. In spite of this, there are few reports on its genotoxicity, and the results are controversial. Severe malnutrition is a complex condition that increases the susceptibility to infections. Consequently, drugs are extensively used in malnutrition cases. Experimental animal models have been widely used to study the effects of malnutrition. Neonatal rats were experimentally malnourished (UN) during lactation. The UN rats weighed 51.1% less than the well-nourished (WN) controls and had lower concentrations of serum protein and blood lipids. The micronucleus (MN) assay is useful for detecting chromosome damage induced by nutritional deficiencies. In vivo rodent MN assays have been widely used to screen genotoxic agents. In this study, we have evaluated the frequency of spontaneous and TMP-SMX-induced micronuclei in the peripheral blood of weanling (21 days of age) rats using a flow cytometric analysis technique. The spontaneous frequency of micronucleated reticulocytes (MN-RETs) was 2.7 times greater in the UN rats than in the WN rats. In rats that were not treated with TMP-SMX, the percentage of reticulocytes was significantly lower (41.1%) in the UN rats than the WN controls. A therapeutic dose of TMP-SMX (80 mg/kg (TMP), 400 mg/kg (SMX) for 48 hr) increased MN-RETs in the WN and in the UN rats. The data demonstrate the genotoxic effect of this drug. The results indicate that severe protein-calorie restriction and drug treatment enhance DNA damage in rat peripheral blood reticulocytes, potentially increasing the risk of negative effects on health.

The rat gut micronucleus assay: a good choice for alternative in vivo genetic toxicology testing strategies

The in vivo bone marrow (BM) micronucleus assay is one of the three tests in the standard test battery to assess the genotoxic potential of a pharmaceutical candidate. In some cases, depending on results of in vitro studies, the route of administration or the degree of systemic exposure, in vivo assessment of genotoxicity in the BM alone may not be sufficient. Based on the potential for high gut exposures to orally administered compounds with low systemic exposures as well as the potential susceptibility of rapidly dividing cells of the intestinal tissues, we have developed a modified technique for evaluating micronuclei formation in both the duodenum and colon of rats based on earlier publications. Adult male Sprague Dawley rats were treated once daily for 2 days with either vehicle control or with the test articles acetyl salicylic acid (ASA), carbendazim (CAR), cyclophosphamide (CP), dimethylhydrazine (DMH), mitomycin C (MMC) or vinblastine sulfate (VIN). The duodenum, colon, and BM were harvested, processed, and analyzed for micronucleus induction. Results from these studies demonstrated differences in the susceptibility for different test compounds in the three tissues tested. When MMC and VIN were dosed by different routes at the same dose levels both compounds produced positive results in all three tissues by intraperitoneal injection but not oral administration. These studies suggest that overall the GI micronucleus assay might be a useful tool for clastogenic and aneugenic compounds that are expected to produce high sustained concentrations in the gastrointestinal tract with little systemic exposure.

New and emerging technologies for genetic toxicity testing

The International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute (HESI) Project Committee on the Relevance and Follow-up of Positive Results in In Vitro Genetic Toxicity (IVGT) Testing established an Emerging Technologies and New Strategies Workgroup to review the current State of the Art in genetic toxicology testing. The aim of the workgroup was to identify promising technologies that will improve genotoxicity testing and assessment of in vivo hazard and risk, and that have the potential to help meet the objectives of the IVGT. As part of this initiative, HESI convened a workshop in Washington, DC in May 2008 to discuss mature, maturing, and emerging technologies in genetic toxicology. This article collates the abstracts of the New and Emerging Technologies Workshop together with some additional technologies subsequently considered by the workgroup. Each abstract (available in the online version of the article) includes a section addressed specifically to the strengths, weaknesses, opportunities, and threats associated with the respective technology. Importantly, an overview of the technologies and an indication of how their use might be aligned with the objectives of IVGT are presented. In particular, consideration was given with regard to follow-up testing of positive results in the standard IVGT tests (i.e., Salmonella Ames test, chromosome aberration assay, and mouse lymphoma assay) to add weight of evidence and/or provide mechanism of action for improved genetic toxicity risk assessments in humans.

Rationale of genotoxicity testing of nanomaterials: regulatory requirements and appropriateness of available OECD test guidelines

The development of an environmental health and safety risk management system for nanoscale particle-types requires a base set of hazard data. Accurate determination of health and environmental risks of nanomaterials is a function of the integration of hazard and exposure datasets. Recently, a nanoparticle risk assessment strategy was promulgated and the components are described in a document entitled “Nanorisk framework” (www.nanoriskframework.com). A major component of the hazard evaluation includes a proposed minimum base set of toxicity studies. Included in the suggested studies were substantial particle characterization, a variety of acute hazard and environmental tests, concomitant with screening-type genotoxicity studies. The implementation of well-accepted genotoxicity assays for testing nanomaterials remains a controversial issue. This is because many of these genotoxicity tests were designed for screening general macroparticle chemicals and might not be suitable for the screening of nanomaterials (even of the same compositional material). Furthermore, no nanoparticle-type positive controls have been established or universally accepted for these tests. Although it is the comparative results of the test material vs. the negative or vehicle control that forms the basis for interpreting the results and potency of test materials in genetic toxicology assays, the lack of a nanoparticle-type positive control questions the suitability of the tests to identify nanomaterials with genotoxic properties. It is also not possible to establish historical positive control ranges that would confirm the sensitivity of the tests. Although several genetic toxicology tests have been validated for chemicals according to the Organisation for Economic Co-operation and Development (OECD) test guidelines, the relevance of these assays for nanoparticulate materials remains to be determined. In an attempt to remedy this issue, the OECD has established current projects designed to evaluate the relevance and reproducibility of safety hazard tests for representative nanomaterials, including genotoxicity assays (i.e., Steering Group 3 – Safety Testing of Representative Nanomaterials). In this article, we discuss our past approaches and experience in conducting genotoxicity assays (1) for a newly developed ultrafine TiO₂ particle-type; and (2) in a recent inhalation study, evaluating micronucleus formation in rat erythrocytes following exposures to engineered amorphous nanosilica particles. It seems clear that the development of standardized approaches will be necessary in order to determine whether exposures to specific nanoparticle-types are associated with genotoxic events. The appropriateness of available genotoxicity test systems for nanomaterials requires confirmation and standardization. Accordingly, it seems reasonable to conclude that any specific regulatory testing requirements for nanoparticles would be premature at this time.

Reflections on the development of micronucleus assays

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

Evaluation of a modified CD71 MicroFlow method for the flow cytometric analysis of micronuclei in rat bone marrow erythrocytes

The aim of this study was to evaluate a modified flow cytometric method for the quantification of micronuclei in rat bone marrow reticulocytes. The method identified uses the erythrocyte pure fraction from cellulose filtered bone marrow with slight modifications to the widely published MicroFlow(®) method developed by Litron Laboratories, Rochester, NY for the detection of micronuclei in peripheral blood. A number of experiments were conducted to compare the micronucleus induction measured by flow cytometry with traditional microscopic analysis in male rats treated daily for 2 days with appropriate vehicle controls or various doses of cyclophosphamide (CP), mitomycin C (MMC), vinblastine sulfate (VBS), 1,2-dimethylhydrazine (DMH), etoposide (ETO), colchicine (COL), or 4-nitroquinoline-1-oxide (4NQO). In addition, for a subset of chemical we compared the induction of micronuclei in bone marrow and peripheral blood. The results from this study showed a very good correlation of micronucleus frequencies in bone marrow between microscopic analysis and the flow cytometry as well as between blood and bone marrow. In general, micronucleus frequencies of test compound treated animals and inter-animal variability were slightly lower by flow cytometric analysis compared to manual slide analysis. The data presented in this study support the use of the CD71 flow method for the analysis of micronuclei in rat bone marrow and also suggest that peripheral blood may be equally as sensitive as bone marrow in detecting a micronucleus response in short term studies.

Flow cytometry peripheral blood micronucleus test in vivo: determination of potential thresholds for aneuploidy induced by spindle poisons

Non-DNA binding genotoxins (e.g., aneugens), unlike DNA-binding genotoxins, are theoretically expected to show thresholded concentration-effect response curves. This is a major issue in genetic toxicology testing because the identification of thresholds in vivo can provide a safety margin for exposure to a particular compound. In the current study we measured micronucleus induction by flow cytometry to determine the dose-response curves for tubulin interacting agents, a specific class of aneugens. All experiments with aneugens, which include colchicine, vinblastine, vincristine, as well as the clastogen cyclophosphamide (CP) were performed in mice to avoid the splenic elimination of micronucleated reticulocytes, which has been described in rats. Flow cytometry analysis revealed a non-linear dose-dependent increase in micronuclei frequencies for all tested aneugens, and a linear dose response curve for the clastogen, CP. To determine whether micronucleus induction at higher doses was due to chromosome loss (aneuploidy) or chromosome breakage (clastogenicity), flow sorting of the micronucleated reticulocytes and fluorescent in situ hybridization (FISH) with a mouse pan centromeric probe were performed for vinblastine, vincristine, and colchicine. Statistical evaluation of the flow cytometry and FISH data was performed to determine the threshold levels for chromosome loss in vivo. The threshold concentrations for vinblastine, vincristine, and colchicine were found at 0.35, 0.017, and 0.49 mg kg(-1), respectively.

No increases in biomarkers of genetic damage or pathological changes in heart and brain tissues in male rats administered methylphenidate hydrochloride (Ritalin) for 28 days

Following a 2005 report of chromosomal damage in children with attention deficit/hyperactivity disorder (ADHD) who were treated with the commonly prescribed medication methylphenidate (MPH), numerous studies have been conducted to clarify the risk for MPH-induced genetic damage. Although most of these studies reported no changes in genetic damage endpoints associated with exposure to MPH, one recent study (Andreazza et al. [2007]: Prog Neuropsychopharmacol Biol Psychiatry 31:1282-1288) reported an increase in DNA damage detected by the Comet assay in blood and brain cells of Wistar rats treated by intraperitoneal injection with 1, 2, or 10 mg/kg MPH; no increases in micronucleated lymphocyte frequencies were observed in these rats. To clarify these findings, we treated adult male Wistar Han rats with 0, 2, 10, or 25 mg/kg MPH by gavage once daily for 28 consecutive days and measured micronucleated reticulocyte (MN-RET) frequencies in blood, and DNA damage in blood, brain, and liver cells 4 hr after final dosing. Flow cytometric evaluation of blood revealed no significant increases in MN-RET. Comet assay evaluations of blood leukocytes and cells of the liver, as well as of the striatum, hippocampus, and frontal cortex of the brain showed no increases in DNA damage in MPH-treated rats in any of the three treatment groups. Thus, the previously reported observations of DNA damage in blood and brain tissue of rats exposed to MPH for 28 days were not confirmed in this study. Additionally, no histopathological changes in brain or heart, or elevated serum biomarkers of cardiac injury were observed in these MPH-exposed rats.

Gamma-radiation induces micronucleated reticulocytes in 3D bone marrow bioreactors in vitro

Radiation injury to the bone marrow is potentially lethal due to the potent DNA-damaging effects on cells of the hematopoietic system, including bone marrow stem cell, progenitor, and the precursor cell populations. Investigation of radiation genotoxic effects on bone marrow progenitor/precursor cells has been challenged by the lack of optimal in vitro surrogate organ culture systems, and the overall difficulty to sustain lineage-specific proliferation and differentiation of hematopoiesis in vitro. We report the investigation of radiation genotoxic effects in bone marrow cultures of C57Bl/6 mice established in 3D bioreactors, which sustain long-term bone marrow cultures. For these studies, genotoxicity is measured by the induction of micronucleated reticulocytes (MN-RETs). The kinetics and dose-response relationship of MN-RET induction in response to gamma-radiation of bioreactor-maintained bone marrow cultures are presented. Our data showed that 3D long-term bone marrow cultures had sustained erythropoiesis capable of generating reticulocytes up to 8 weeks. The peak time-interval of viable cell output and percentage of reticulocytes increased steadily and reached the initial peak between the 14th and 21st days after inoculations. This was followed by a rebound or staying relatively constant until week 8. The percentage of MN-RET reached the maximum between 24 h and 32 h post 1 Gy gamma-ray. There was a near linear MN-RET induction by gamma-radiation from 0 Gy to 1.0 Gy, followed by an attenuated increase to 1.5-2.0 Gy. The MN-RET response showed a downtrend beyond 2 Gy. Our data suggest that bone marrow culture in the 3D bioreactor may be a useful organ culture system for the investigation of radiation genotoxic effect in vitro.

Evaluation of the micronucleus assay in bone marrow and peripheral blood of rats for the determination of cigarette mainstream-smoke activity

The mammalian in vivo micronucleus assay is widely used as part of the genotoxicity testing battery required during the development of new drugs. As such, the in vivo micronucleus assay has been used in a battery of assays for the assessment of cigarette ingredients or design modifications to help ensure that there is no increase in risk or any new risk introduced by these additions or modifications. The present series of studies was conducted to optimize and evaluate this assay for the assessment of the effects of mainstream smoke on the micronucleus frequency in the bone marrow and peripheral blood of rats. In a first experiment, the optimal conditions for performing the micronucleus assay in these tissues were determined. This was done by use of two compounds known for their micronucleus-inducing activity, i.e., the clastogen cyclophosphamide and the aneugen colchicine. In a second experiment, the effects of tube restraint on untreated control rats were investigated. In a third experiment, the optimal conditions were used to assess the clastogenic/aneugenic activity of cigarette smoke in Sprague-Dawley rats. The rat micronucleus assay in both bone marrow and peripheral blood is able to detect clastogenic and aneugenic activity. The flow cytometric determination of micronucleated cells in rat blood is at least as sensitive as determinations in bone marrow. No statistically significant differences were observed in micronucleus frequencies between rats with and without the additional stress of tube restraint; however, the cautious approach would be to use a fresh-air-exposed group (with tube restraint) as the negative control in inhalation experiments. Using the conditions identified as optimal in the above-mentioned experiments, the micronucleus assay was not able to detect effects induced by smoke from conventional cigarettes. Nevertheless, the micronucleus assay will remain a valuable tool as part of a testing battery used to investigate possible adverse effects related to product modifications.

Palladium alters cigarette smoke toxicological profile, but accumulates in the lungs of rats during inhalation exposure

The use of a palladium (Pd) catalyst has been proposed to promote combustion of tobacco, thereby reducing concentrations of certain toxic components of smoke, including polyaromatic hydrocarbons (PAHs). In the present work, toxicological comparisons were made using experimental cigarettes containing no added Pd, against otherwise similar cigarettes containing three different amounts of Pd as potassium tetrachloropalladate added to the tobacco. A full analysis of smoke chemistry was made, along with a subchronic 90-day inhalation study with mainstream smoke (rats exposed to 150 mg/m(3) of total particulate matter, 6 h/day for 90 consecutive days) and in vitro evaluations of Salmonella mutagenicity, cytotoxicity, and in vivo clastogenicity (micronucleus). Addition of Pd to the tobacco resulted in 20-30% reductions in the concentrations of 6 PAHs and 2 aromatic amines, but it also resulted in transfer of Pd to smoke and in 10-50% increases in concentrations of several tobacco-specific nitrosamines. Mutagenicity was reduced by about 50% in 2 of 5 strains of Salmonella (with S9 only), while the cytotoxicity and micronucleus assays showed no changes. Histopathology responses were similar across the four smoke inhalation groups. Smoke Cd was reduced by 40-70% in the smoke, leading to lower lung concentrations; however, the presence of Pd in smoke led to accumulation of Pd in the lungs increasing in both a dose-and an exposure-related manner. While catalysts such as Pd addition may alter the typical chemical/toxicological profile of smoke, a concern arises regarding the "risk-benefit" of the addition of such chemically active materials as Pd to cigarette tobacco, leading to potential pulmonary accumulation with unknown consequences.

Quantitative analysis of Howell-Jolly bodies in children with sickle cell disease

OBJECTIVES

Although functional asplenia in sickle cell disease (SCD) begins early in life and has important clinical consequences, quantitative measurement of splenic function is not readily available. A novel high-throughput flow cytometric method for quantitating Howell-Jolly bodies (HJB) has been developed which isolates HJB-containing CD71(+) and CD71(-) erythrocytes. Analysis of these cell populations allows quantitative measurement of splenic filtrative function and possible chromosomal damage.

METHODS

Blood specimens from 147 children with SCD were analyzed using a high-throughput flow cytometric method. Enumeration of the following populations was accomplished: 1) CD71(+) reticulocytes among total erythrocytes, identifying the youngest erythroid cell population; 2) HJB-containing CD71(+) reticulocytes, which isolate young erythrocytes containing micronuclei as an index of cytogenetic damage; and 3) HJB-containing CD71(-) erythrocytes, identifying older erythrocytes containing micronuclei, indirectly measuring splenic function.

RESULTS

Children with HbSC (n = 24) had slightly elevated HJB frequencies, while children with HbSS (n = 125) had highly elevated frequencies within CD71(+) cells (0.44% +/- 0.40%, normal 0.12% +/- 0.06%, p < 0.001) and CD71(-) cells (2493 +/- 2303 per million RBC, normal 20 +/- 11, p < 0.001). Using a multiple regression model, the frequency of HbSS CD71(+) reticulocytes containing HJB was significantly influenced by hydroxyurea use (p < 0.0001), age (p = 0.0288), and splenectomy (p = 0.0498). Similarly, mature CD71(-) erythrocytes containing HJB were positively correlated with hydroxyurea (p = 0.0001), age (p < 0.0001), and splenectomy (p = 0.0104).

CONCLUSIONS

HJB quantitation by flow cytometry is a novel assay for measuring splenic function and may be valuable for investigating the efficacy and safety of therapeutic options for children with SCD.

Automated human blood micronucleated reticulocyte measurements for rapid assessment of chromosomal damage

This study evaluated the utility of human blood micronucleated reticulocyte (MNCD71+) frequency measurement as a cytogenetic damage biomarker. The analytical methodology was flow cytometry in conjunction with a previously described three color fluorescence labeling technique that includes anti-CD71 to focus analyses on the most immature fraction of reticulocytes [S.D. Dertinger, K. Camphausen, J.T. MacGregor, M.E. Bishop, D.K. Torous, S. Avlasevich, et al., Three-color labeling method for flow cytometric measurement of cytogenetic damage in rodent and human blood, Environ. Mol. Mutagen. 44 (2004) 427-435]. Blood specimens from 50 self-reported healthy adult volunteers were studied. In addition to MNCD71+ measurements, blood plasma folate and B12 levels were assessed, since these variables tend to influence other indices of cytogenetic damage. Time-course data are also provided for 10 cancer patients undergoing treatment. For these subjects, frequency of MNCD71+ was measured immediately before therapy, and daily during the first week of chemotherapy and/or fractionated radiotherapy. For the group of healthy volunteers, the variables of age, and folate and B12 levels demonstrated no significant effect on MNCD71+ frequency. In addition, no difference was observed between pre-treatment MNCD71+ values for cancer patients compared with healthy volunteers. Regarding chemotherapy and/or partial body radiotherapy, elevated frequencies were observed upon initiation of treatment for 9 of the 10 patients studied. Maximal effects were observed 3-5 days following initiation of therapy. The largest increases in frequency of MNCD71+ (up to 25.9-fold) were observed in those patients exposed to anti-neoplastic drugs, presumably due to the systemic red marrow exposure provided by these agents. Taken together, these data support the hypothesis that the MNCD71+ endpoint represents a valuable biomarker of cytogenetic damage that does not require cell culture or microscopy-based scoring.

In vivo micronucleus test with flow cytometry after acute and chronic exposures of rats to chemicals

The use of flow cytometry with rat peripheral blood erythrocytes is expected to increase the sensitivity of the in vivo micronucleus test and allows assessment of the genotoxic effects at doses that may be equal or close to those relevant to human exposure. However, there was a limitation to the use of rat peripheral blood erythrocytes since the spleen selectively removes micronucleated erythrocytes from circulation. In the present study, the selective analysis by flow cytometry of young MN-PCEs (micronucleated polychromatic erythrocytes or reticulocytes) by use of anti-CD71 antibodies was intended to compensate for the splenic clearance of micronucleated erythrocytes. The young polychromatic erythrocytes have on their surface a specific marker (CD71 antigen) that decreases in density during the maturation process. To investigate the usefulness of the flow cytometric micronucleus analysis combined with anti-CD71 staining of reticulocytes several compounds were tested in acute or sub-chronic treatment regimens. Furthermore, an evaluation was conducted in comparison with the standard rat bone-marrow micronucleus test with additional compounds. The results of acute studies with intraperitoneal application of ethyl methanesulfonate (EMS) (50, 100 and 200 mg/kg) and mitomycin C (MMC) (0.5, 1 and 2 mg/kg), were comparable to data published in the literature. Sub-chronic experiments were performed with cyclophosphamide (CP) (1, 2, 4 and 8 mg/(kg day)), colchicine (6, 8 mg/(kg day)) and mitomycin C (0.1 mg/(kg day)) and showed dose- and time-dependent accumulation of MN-PCEs. Parallel analysis of micronucleus induction in peripheral blood and bone marrow performed with Novartis compounds up to the highest tested dose (5 mg/kg of compound A, 200 mg/kg of compound B and 1250 mg/kg of compound C) showed concordant results. Furthermore, we performed kinetic studies of micronucleus induction in peripheral blood samples obtained at various times after a single treatment with 10 mg/kg CP and with 6 or 8 mg/kg of colchicine. Such experiments gave important supplementary information about the time course of micronucleus induction. Our data suggest that the peripheral blood flow-cytometry micronucleus test can be used for the assessment of micronucleus induction after acute and chronic exposures of rats to chemicals.

Practical threshold for micronucleated reticulocyte induction observed for low doses of mitomycin C, Ara-C and colchicine

Micronucleus induction was studied for the DNA target clastogens mitomycin C (MMC) and 1-beta-D-arabinofuranosylcytosine (Ara-C), and also the non-DNA target aneugen colchicine (COL) in order to evaluate the dose-response relationship at very low dose levels. The acridine orange (AO) supravital staining method was used for microscopy and the anti-CD71-FITC based method was used for flow cytometric analysis. In the AO method, 2000 reticulocytes were analysed as commonly advised, but in the flow cytometric method, 2000, 20,000, 200,000 and 1,000,000 reticulocytes were analysed for each sample to increase the detecting power (i.e. sensitivity) of the assay. The present data show that increasing the number of cells scored increases the statistical power of the assay when the cell was considered as a statistical unit. Even so, statistically significant differences from respective vehicle controls were not observed at the lowest dose level for MMC and Ara-C, or the lower four dose levels for COL, even after one million cells were analysed. When the animal was considered as a statistical unit, only the top dose group for each chemical showed significant increase of micronucleated reticulocytes frequency. As non-linear dose-response curves were obtained for each of the three chemicals studied, these observations provide evidence for the existence of a practical threshold for the DNA target clastogens as well as the non-DNA target aneugen studied.

Analysis of micronuclei in the transferrin-receptor positive reticulocytes from peripheral blood of nasopharyngeal cancer patients undergoing radiotherapy by a single-laser flow cytometer

The automated micronucleus test is now accepted as a simple, objective, and accurate method for evaluating potential mutagenic effects caused by physical, chemical or biotic factors. This paper describes a single-laser flow cytometry, based on an immunomagnetic isolation technique in combination with acridine orange staining, to detect frequencies of micronucleated transferrin-receptor positive reticulocytes from human peripheral blood. Using this flow cytometric system, we detected the frequencies of micronucleated transferrin-receptor positive reticulocytes from 10 nasopharyngeal cancer patients undergoing radiotherapy and the baseline of the frequencies of micronucleated transferrin-receptor positive reticulocytes from 7 healthy donors. The results showed that the mean frequency of micronucleated transferrin-receptor positive reticulocytes from healthy donors was 0.236% and that from nasopharyngeal cancer patients before radiotherapy was 0.297%. After radiotherapy it was significantly elevated. When the cumulative dose of radiotherapy was about 20Gy, it reached a maximum of 6.905%, and then, as the cumulative dose of radiotherapy continued to increase to 30Gy, 40Gy and 50Gy, the frequency decreased to 6.258%, 5.119% and 5.007% respectively. Our results indicated that the single-laser flow cytometric system was quick, reasonable and acceptable for detecting the frequency of micronucleated transferrin-receptor positive reticulocytes from human peripheral blood.

Spontaneous and mitomycin C-induced micronuclei in peripheral blood reticulocytes from severely malnourished rats

Severe malnutrition caused by deficiencies in protein, calorie, and micronutrient intake is widely distributed throughout the world and is a particular problem in developing countries. Animal models have been useful for studying the effects of malnutrition under different experimental conditions. In this study, we have evaluated the effect of malnutrition on the frequency of spontaneous and mitomycin C (MMC)-induced micronuclei in the peripheral blood of rats measured using a flow cytometric analysis technique. Neonatal rats were experimentally malnourished during lactation and assayed at weaning (21 days of age). The malnourished rats weighed 49.2% less than well-nourished controls and had lower concentrations of serum protein, triglycerides, and cholesterol. In rats not treated with MMC, the frequency of micronucleated reticulocytes (MN-RETs) was 1.6 times greater in malnourished rats than in well-nourished rats (0.48% +/- 0.16% vs. 0.31% +/- 0.09%). The mean MN-RET frequency measured 32 hr after treatment with single i.p. doses of 0.5, 0.75, or 1.0 mg/kg of MMC was 0.60 +/- 0.10 vs. 0.84 +/- 0.14, 1.21 +/- 0.52 vs. 2.36 +/- 0.47, and 2.50 +/- 0.06 vs. 4.64 +/- 1.14 for well-nourished vs. malnourished rats, respectively. Statistical comparisons indicate significant differences between the two groups of rats at all doses tested. Malnourishment and MMC treatment had no significant effects on the frequencies of RETs or micronucleated normochromatic erythrocytes. The data indicate that protein-calorie malnutrition during lactation is associated with increased frequencies of MN-RETs, which are indicative of chromosome damage. These findings suggest that malnutrition could result in greater susceptibility to environmental damage.

Micronucleated CD71-positive reticulocytes: a blood-based endpoint of cytogenetic damage in humans

The frequency of micronuclei (also known as Howell-Jolly bodies) in peripheral blood erythrocytes of humans is extremely low due to the efficiency with which the spleen sequesters and destroys these aberrant cells. In the past, this has precluded erythrocyte-based analyses from effectively measuring chromosome damage. In this report, we describe a high-throughput, single-laser flow cytometric system for scoring the incidence of micronucleated reticulocytes (MN-RET) in human blood. Differential staining of these cells was accomplished by combining the immunochemical reagent anti-CD71-FITC with a nucleic acid dye (propidium iodide plus RNase). The immunochemical reagent anti-CD42b-PE was also incorporated into the procedure in order to exclude platelets which can interfere with analysis. This analytical system was evaluated with blood samples from ten healthy volunteers, one splenectomized subject, as well as samples collected from nine cancer patients before and over the course of radio- or chemotherapy. The mean frequency of MN-RET observed for the healthy subjects was 0.09%. This value is nearly two orders of magnitude higher than frequencies observed in mature erythrocytes, and is approximately half the MN-RET frequency observed for the splenectomized subject (0.20%). This suggests that the spleen's effect on micronucleated cell incidence can be minimized by restricting analyses to the youngest (CD71-positive) fraction of reticulocytes. Furthermore, MN-RET frequencies were significantly elevated in patients undergoing cancer therapy. Collectively, these data establish that micronuclei can be quantified in human peripheral blood reticulocytes with a single-laser flow cytometer, and that these measurements reflect the level of chromosome damage which has occurred in red marrow space.

Comparative scoring of micronucleated reticulocytes in rat peripheral blood by flow cytometry and microscopy

A flow cytometric technique for scoring the incidence of micronucleated reticulocytes in rat peripheral blood was compared to a standard microscopy-based procedure. For these studies, groups of five male Sprague-Dawley rats were treated with vehicle or a broad range of chemical genotoxicants: 6-thioguanine, N-methyl-N'-nitro-N-nitrosoguanidine, vincristine, methylaziridine, acetaldehyde, methyl methanesulfonate, benzene, monocrotaline, and azathioprine. Animals were treated once a day for up to 2 days, and peripheral blood was collected between 24 and 48 h after the final administration. These samples were processed for flow cytometric scoring and microscopy-based analysis using supravital acridine orange staining, and the percentage of reticulocytes and micronucleated reticulocytes was determined for each sample. The resulting data demonstrate good agreement between these scoring methodologies, although careful execution of the flow cytometric method was found to enhance the micronucleus assay by reducing both scoring time and scoring error. These data add further support to the premise that the peripheral blood compartment of rats can be used effectively to detect genotoxicant-induced micronuclei.

Enumeration of micronucleated CD71-positive human reticulocytes with a single-laser flow cytometer

The extreme rarity of micronucleated reticulocytes (RETs) in the peripheral blood of non-splenectomized humans has precluded facile enumeration of these cells, as well as evaluation of this endpoint as an index of cytogenetic damage. In this report, we describe a high-throughput, single-laser flow cytometric system for scoring the incidence of micronuclei (MN) in newly formed human RETs. The procedure is based on an immunochemical reagent that differentially labels the most immature fraction of RETs from mature erythrocytes based on the expression level of the transferrin receptor (also known as CD71). The resolution of four erythrocyte populations (young RETs and mature erythrocytes, with and without MN) was achieved for human blood cells treated with phycoerythrin-conjugated anti-CD71, RNase, and either SYTOX Green or SYBR Green I nucleic acid dyes. Anti-glycophorin A labeling of erythroid cells (CyChrome conjugate) was also incorporated into the staining procedure to ensure that debris or other potential artifacts did not adversely impact the analyses. Instrument calibration procedures utilizing malaria-infected rodent erythrocytes were also developed, and are described. Using this analytical system, blood samples from 10 healthy non-splenectomized human volunteers were analyzed for micronucleus frequencies with a single-laser flow cytometer. Average micronucleus frequencies in the mature and most immature fraction of RETs were 0.016 and 0.19%, respectively. Blood samples from three healthy splenectomized volunteers were also evaluated. As expected, these samples exhibited higher micronucleus frequencies in the mature subset of erythrocytes (range 0.03-0.18%). The resulting data suggest that MN can be quantified in human erythrocyte populations with a single-laser flow cytometer, and that the frequency of MN cells in the youngest reticulocyte population approaches values expected in the absence of splenic selection against MN-erythrocytes. This high throughput system is potentially important for evaluating the value of the micronucleated reticulocyte endpoint as an index of chromosome breakage and/or chromosome segregational abnormalities in human populations.

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.