Malaria-infected erythrocytes serve as biological standards to ensure reliable and consistent scoring of micronucleated erythrocytes by flow cytometry

Revitalize splenic functions. Following a splenectomy for trauma, a small amount of splenic autotransplantation was performed

INTRODUCTION

The spleen is a responsible significant part of the immune system; after Splenectomy following trauma, the immune system changes; splenic autotransplantation can preserve the immune system after trauma and Splenectomy.

BACKGROUND

Patients can be protected from immune dysfunction by autotransplanting splenic tissues after splenectomy following trauma because their immune systems and spleens are changed. Patients can gain their immune function after splenic autotransplantation.

METHODS

Patient classification methods are into three categories, Group A, 6 cases with auto-translation; Group B, 6 cases without transplantation; Group C, seven regular people serving as the control.

AIM OF WORK

The aim of the work is not to compare outcome methods or compare types of autotransplantation; This work aims to document postoperative radiological, immunological, clinical, and hematological investigations. We concentrated on the results of investigations more than the types of operation or approach or types of autotransplantation.

RESULTS

We showed that, after comparing each group with normal individuals subjects, patients who did not undergo autotransplantation had significantly higher platelet counts, a more significant percentage of micronucleated reticulocytes, increased levels of naive B lymphocytes, changes in class-switched memory and class-unswitched memory B cells, and higher levels of PD1 on CD8 + T lymphocytes. Nevertheless, neither splenic autotransplant patients nor the average general population showed any appreciable variations in any of the parameters.

CONCLUSIONS

Spleen's activities with adequate hemocatheter activity and recovery of the immunological deficit after splenic autotransplantation.

Rodent Malaria Erythrocyte Preference Assessment by an Ex Vivo Tropism Assay

Circulating red blood cells consist of young erythrocytes (early and late reticulocytes) and mature erythrocytes (normocytes). The human malaria parasites, Plasmodium falciparum and P. vivax, have a preference to invade reticulocytes during blood-stage infection. Rodent malaria parasites that also prefer reticulocytes could be useful tools to study human malaria reticulocyte invasion. However, previous tropism studies of rodent malaria are inconsistent from one another, making it difficult to compare cell preference of different parasite species and strains. In vivo measurements of cell tropism are also subjected to many confounding factors. Here we developed an ex vivo tropism assay for rodent malaria with highly purified fractions of murine reticulocytes and normocytes. We measured invasion into the different erythrocyte populations using flow cytometry and evaluated the tropism index of the parasite strains. We found that P. berghei ANKA displayed the strongest reticulocyte preference, followed by P. yoelii 17X1.1, whereas P. chabaudi AS and P. vinckei S67 showed mixed tropism. These preferences are intrinsic and were maintained at different reticulocyte and normocyte availabilities. Our study shed light on the true erythrocyte preference of the parasites and paves the way for future investigations on the receptor-ligand interactions mediating erythrocyte tropism.

Assessment of systemic genetic damage in pediatric inflammatory bowel disease

The etiology of distal site cancers in inflammatory bowel disease (IBD) is not well understood and requires further study. We investigated whether pediatric IBD patients' blood cells exhibit elevated levels of genomic damage by measuring the frequency of mutant phenotype (CD59-/CD55-) reticulocytes (MUT RET) as a reporter of PIG-A mutation, and the frequency of micronucleated reticulocytes (MN-RET) as an indicator of chromosomal damage. IBD patients (n = 18 new-onset disease, 46 established disease) were compared to age-matched controls (constipation or irritable bowel syndrome patients from the same clinic, n = 30) and young healthy adults age 19-24 (n = 25). IBD patients showed no indication of elevated MUT RET relative to controls (mean ± SD = 3.1 ± 2.3 × 10^-6 vs. 3.6 ± 5.6 x 10^-6 , respectively). In contrast, 59 IBD patients where %MN-RET measurements were obtained, 10 exceeded the upper bound 90% tolerance interval derived from control subjects (i.e., 0.42%). Furthermore, each of the 10 IBD patients with elevated MN-RET had established disease (10/42), none were new-onset (0/17) (p = .049). Interestingly, each of the subjects with increased chromosomal damage was receiving anti-TNF based monotherapy at the time blood was collected (10/10, 100%), whereas this therapy was less common (20/32, 63%) among patients that exhibited ≤0.42% MN-RET (p = .040). The results clearly indicate the need for further work to understand whether the results presented herein are reproducible and if so, to elucidate the causative factor(s) responsible for elevated MN-RET frequencies in some IBD patients.

Single segment of spleen autotransplantation, after splenectomy for trauma, can restore splenic functions

Background

Splenectomy is sometimes necessary after abdominal trauma, but splenectomized patients are at risk of sepsis due to impaired immunological functions.

To overcome this risk, autotransplantation of the spleen by using a new technique has been proposed, but so far, a demonstration of functionality of the transplanted tissue is lacking.

Methods

We therefore evaluated 5 patients who underwent a splenic autotransplant in comparison with 5 splenectomized patients without splenic autotransplant and 7 normal subjects.

Results

We confirmed that the patients not undergoing autotransplantation, when compared to normal subjects, had a higher platelet count, higher percentage of micronucleated reticulocytes (p = 0.002), increased levels of naive B lymphocytes (p = 0.01), a defect of class-switched memory (p = 0.001) and class-unswitched memory B cells (p = 0.002), and increased levels of PD1 on T lymphocytes CD8+ (p = 0.08). In contrast, no significant differences for any of the abovementioned parameters were recorded between patients who underwent spleen autotransplantation and normal subjects.

Conclusion

These findings suggest that splenic autotransplantation is able to restore an adequate hemocatheretic activity as well as recover the immunological deficit after splenectomy.

3Rs friendly study designs facilitate rat liver and blood micronucleus assays and Pig-a gene mutation assessments: Proof-of-concept with 13 reference chemicals

Regulatory guidance documents stress the value of assessing the most appropriate endpoints in multiple tissues when evaluating the in vivo genotoxic potential of chemicals. However, conducting several independent studies to evaluate multiple endpoints and/or tissue compartments is resource intensive. Furthermore, when dependent on visual detection, conventional approaches for scoring genotoxicity endpoints can be slow, tedious, and less objective than the ideal. To address these issues with current practices we attempted to (1) devise resource sparing treatment and harvest schedules that are compatible with liver and blood micronucleus endpoints, as well as the Pig-a gene mutation assay, and (2) utilize flow cytometry-based methods to score each of these genotoxicity biomarkers. Proof-of-principle experiments were performed with 4-week-old male and female Crl:CD(SD) rats exposed to aristolochic acids I/II, benzo[a]pyrene, cisplatin, cyclophosphamide, diethylnitrosamine, 1,2-dimethylhydrazine, dimethylnitrosamine, 2,6-dinitrotoluene, hydroxyurea, melphalan, temozolomide, quinoline, or vinblastine. These 13 chemicals were each tested in two treatment regimens: one 3-day exposure cycle, and three 3-day exposure cycles. Each exposure, blood collection, and liver harvest was accomplished during a standard Monday-Friday workweek. Key findings are that even these well-studied, relatively potent genotoxicants were not active in both tissues and all assays (indeed only cisplatin was clearly positive in all three assays); and whereas the sensitivity of the Pig-a assay clearly benefitted from three versus one treatment cycle, micronucleus assays yielded qualitatively similar results across both study designs. Collectively, these results suggest it is possible to significantly reduce animal and other resource requirements while improving assessments of in vivo genotoxicity potential by simultaneously evaluating three endpoints and two important tissue compartments using fit-for-purpose study designs in conjunction with flow cytometric scoring approaches. Environ. Mol. Mutagen., 60:704-739, 2019. © 2019 Wiley Periodicals, Inc.

Integration of liver and blood micronucleus and Pig-a gene mutation endpoints into rat 28-day repeat-treatment studies: Proof-of-principle with diethylnitrosamine

Regulatory guidance documents stress the value of assessing multiple tissues and the most appropriate endpoints when evaluating chemicals for in vivo genotoxic potential. However, conducting several independent studies to consider multiple endpoints and/or tissue compartments is resource intensive. Furthermore, conventional approaches for scoring genotoxicity endpoints are slow, tedious, and less objective than what would be considered ideal. In an effort to address these issues with current practices, we attempted to i) employ flow cytometry-based methods to score liver micronuclei, blood micronuclei, and blood Pig-a gene mutation, and ii) integrate the endpoints into a common general toxicology study design-the rat 28-day repeat dose study. A proof-of-principle experiment was performed with 6-week old male Crl:CD(SD) rats exposed to diethylnitrosamine (DEN) for 28 consecutive days. One day later blood was collected for micronucleated reticulocyte (MN-RET) and Pig-a mutation assays, and liver tissue was obtained for micronucleated hepatocyte (MNHEP) scoring. MN-RET frequencies were not affected by DEN exposure, and mean Pig-a mutant cell frequencies were only slightly elevated. On the other hand, % MNHEP showed marked, dose-related increases (2.2, 7.2, and 9.1 mean fold-increase for 5, 10, 15 mg DEN/kg/day, respectively). Concurrent with MNHEP analyses, assessments of Ki-67-positive events and the proportion of 8n nuclei provided evidence for treatment-related changes to hepatocyte proliferation. Collectively, these results reinforce the importance of evaluating chemicals' genotoxic potential in liver in addition to hematopoietic cells, and suggest that several automated measurements can be successfully integrated into repeat-dose studies for higher efficiencies and better utilization of fewer animals.

Turf wars: exploring splenomegaly in sickle cell disease in malaria-endemic regions

Sickle cell disease (SCD) is a group of recessively inherited disorders of erythrocyte function that presents an ongoing threat to reducing childhood and adult morbidity and mortality around the world. While decades of research have led to improved survival for SCD patients in wealthy countries, survival remains dismal in low- and middle-income countries. Much of the early mortality associated with SCD is attributed to increased risk of infections due to early loss of splenic function. In the West, bacterial infections with encapsulated organisms are a primary concern. In sub-Saharan Africa, where the majority of infants with SCD are born, the same is true. However malaria presents an additional threat to survival. The search for factors that define variability in sickle cell phenotypes should include environmental modifiers, such as malaria. Further exploration of this relationship could lead to novel strategies to reduce morbidity and mortality attributable to infections. In this review, we explore the interactions between SCD, malaria and the spleen to better understand how splenomegaly and splenic (dys)function may co-exist in patients with SCD living in malaria-endemic areas.

Rat Pig-a mutation assay responds to the genotoxic carcinogen ethyl carbamate but not the non-genotoxic carcinogen methyl carbamate

Determination of the mode of action of carcinogenic agents is an important factor in risk assessment and regulatory practice. To assess the ability of the erythrocyte-based Pig-a mutation assay to discriminate between genotoxic and non-genotoxic modes of action, the mutagenic response of Sprague Dawley rats exposed to methyl carbamate (MC) or ethyl carbamate (EC) was investigated. EC, a potent carcinogen, is believed to induce DNA damage through the formation of a DNA-reactive epoxide group, whereas the closely structurally related compound, MC, cannot form this epoxide and its weaker carcinogenic activity is thought to be secondary to inflammation and promotion of cell proliferation. The frequency of Pig-a mutant phenotype cells was monitored before, during, and after 28 consecutive days of oral gavage exposure to either MC (doses ranging from 125 to 500 mg/kg/day) or EC (250 mg/kg/day). Significant increases in the frequency of mutant reticulocytes were observed from Days 15 through 43, with a peak mean frequency of 19.9×10(-6) on Day 29 (i.e. 24.9-fold increase relative to mean vehicle control across all four sampling times). As expected, mutant erythrocyte responses lagged behind mutant reticulocyte responses, with a maximal mean frequency of 8.2×10(-6) on Day 43 (i.e. 16.4-fold increase). No mutagenic effects were observed with MC. A second indicator of in vivo genotoxicity, peripheral blood micronucleated reticulocytes, was also studied. This endpoint was responsive to EC (3.3-fold mean increase), but not to MC. These results support the hypothesis that genotoxicity contributes to the carcinogenicity of EC but not of MC, and illustrates the value of the Pig-a assay for discriminating between genotoxic and non-genotoxic modes of action.

Haematological and genotoxic responses in an urban adapter, the banana bat, foraging at wastewater treatment works

Wastewater Treatment Works (WWTWs) are a ubiquitous feature of the urban landscape. The Banana Bat, Neoromicia nana specifically exploits the high abundance of chironomid midge prey available at WWTWs but these populations also have higher levels of non-essential metals (Cd, Cr and Ni) in their tissues than bats foraging at unpolluted sites. Pollutant exposure may elicit primary physiological responses such as DNA damage and haematological changes. We investigated whether pollutant exposure from foraging at WWTWs impacts haematological and genotoxic parameters in N. nana. We compared four measures of haematological/genotoxic damage between N. nana foraging at three WWTWs and two unpolluted sites located in KwaZulu-Natal, South Africa: DNA damage measured by the Comet assay, total antioxidant capacity as indicated by the FRAP assay, chromosomal aberration indicated by micronuclei formation and blood oxygen capacity based on haematocrits. There was significantly higher DNA damage in N. nana at WWTWs than in bats from unpolluted sites, suggesting inadequate repair to double stranded DNA breaks. In addition, WWTW bats had a significantly lower antioxidant capacity than bats from unpolluted sites. This suggests that bats at WWTWs may have a diminished capacity to cope with the excess reactive oxidative species (ROS) produced from pollutants such as metals. There was no increase in micronucleus frequency in WWTW bats, indicating that cellular functioning has not yet been disrupted by chemical exposure. Haematocrits, however, were significantly higher in WWTW bats, possibly due to erythrocyte production in response to certain pollutants. Thus, effects of pollutant exposure in bats foraging at WWTWs elicit sub-lethal haematological and genotoxic responses which may pose serious long-term risks. This provides evidence that WWTWs, that are aimed to remove pollutants from the environment, can themselves act as a source of contamination and pose a threat to animals exploiting these habitats.

Inter-laboratory validation of the in-vivo flow cytometric micronucleus analysis method (MicroFlow®) in China

Although inter-laboratory validation efforts of the in-vivo micronucleus (MN) assay based on flow cytometry (FCM) have taken place in the EU and US, none have been organized in China. Therefore, an inter-laboratory study that included eight laboratories in China and one experienced reference laboratory in the US was coordinated to validate the in-vivo FCM MicroFlow(®) method to determine the frequency of micro-nucleated reticulocytes (MN-RETs) in rat blood. Assay reliability and reproducibility were evaluated with four known genotoxicants, and the results obtained with the FCM method were compared with the outcome of the traditional evaluation of bone-marrow micronuclei by use of microscopy. Each of the four chemicals was tested at three sites (two in China and the one US reference laboratory). After three consecutive daily exposures to a genotoxicant, blood and bone-marrow samples were obtained from rats 24h after the third dose. MN-RET frequencies were measured in 20,000 RET in blood by FCM, and micro-nucleated polychromatic erythrocyte (MN-PCE) frequencies were measured in 2,000 PCEs in bone marrow by microscopy. For both methods, each genotoxicant was shown to induce a statistically significant increase in the frequency of MN after treatment with at least one dose. Where more doses than one caused an increase, responses occurred in a dose-dependent manner. Spearman's correlation coefficient (rs) for FCM-based MN-RET vs microscopy-based MN-PCE measurements (eight experiments, 200 paired measurements) was 0.723, indicating a high degree of correspondence between methods and compartments. The rs value for replicate FCM MN-RET measurements performed at the eight collaborative laboratories was 0.940 (n=200), and between the eight FCM laboratories with the reference laboratory was 0.933 (n=200), suggesting that the automated method is very well transferable between laboratories. The FCM micronucleus analysis method is currently used in many countries worldwide, and these data support its use for evaluating the in-vivo genotoxic potential of test chemicals in China.

In vitro micronucleus assay for the analysis of total particulate matter in cigarette smoke: comparison of flow cytometry and laser scanning cytometry with microscopy

The possible genotoxicity of the total particulate matter (TPM) in cigarette smoke has typically been evaluated using the in vitro micronucleus assay. In recent years, automated scoring techniques have been developed to replace the manual counting process in this assay. However, these automated scoring techniques have not been applied in routine genotoxicity assays for the analysis of TPM to improve the assay efficiency. Chinese hamster ovary (CHO) cells were treated with TPM produced from 14 types of cigarettes at five concentrations (25-200μg/ml) without exogenous metabolic activation. The three following methods were used to score the micronucleus (MN) frequency: (a) flow cytometry with SYTOX and EMA dyes, which differentially stain micronuclei and apoptotic/necrotic chromatin to enhance assay reliability; (b) laser scanning cytometry with FITC and PI dyes, which is a system that combines the analytical capabilities of flow and image cytometry; and (c) visual microcopy with Giemsa dye. The test results obtained using the three methods were compared using correlation analysis. The key findings for this set of compounds include the following: (a) both flow cytometry- and laser scanning cytometry-based methods were effective for MN identification, (b) the three scoring methods could detect dose-dependent micronucleus formation for the 14 types of TPM, and (c) the MN frequencies that were measured in the same samples by flow cytometry, laser scanning cytometry, and visual microscopy were highly correlated, and there were no significant differences (p>0.05). In conclusion, both flow cytometry and laser scanning cytometry can be used to evaluate the MN frequency induced by TPM without exogenous metabolic activation. The simpler and faster processing and the high correlation of the results make these two automatic methods appropriate tools for use in in vitro micronucleus assays for the analysis of TPM using CHO cells.

Effects of pneumonia and malnutrition on the frequency of micronuclei in peripheral blood of pediatric patients

The aim of this study was to evaluate the effects of bacterial pneumonia and malnutrition on the frequency of micronuclei (MN) in peripheral blood of pediatric patients through flow cytometric analysis. The study was an analytical case-control study carried out on 35 malnourished children with bacterial pneumonia and 20 well-nourished children with bacterial pneumonia, in addition to 20 healthy children as controls. Complete physical examination including; anthropometric measurement, Chest roentgenograms were done for all cases. Assessment of MN was done by FACSCalibur flow cytometry. The frequency of micronucleated reticulocytes (MN-RETs) was higher both in the malnourished children with pneumonia and well-nourished children with pneumonia than the controls. Within the malnourished children with pneumonia, patients with kwashiorkor had more micronucleated mature erythrocytes (MN-RBCs) and MN-RETs than patients with marasmus.

IN CONCLUSION

Pneumonia is associated with an increased frequency of MN and this increment is more pronounced in children with severe malnutrition especially kwashiorkor group.

In vivo flow cytometric Pig-a and micronucleus assays: highly sensitive discrimination of the carcinogen/noncarcinogen pair benzo(a)pyrene and pyrene using acute and repeated-dose designs

Combining multiple genetic toxicology endpoints into a single in vivo study, and/or integrating one or more genotoxicity assays into general toxicology studies, is attractive because it reduces animal use and enables comprehensive comparative analysis using toxicity, metabolism, and pharmacokinetic information from the same animal. This laboratory has developed flow cytometric scoring techniques for monitoring two blood-based genotoxicity endpoints-micronucleated reticulocyte frequency and gene mutation at the Pig-a locus-thereby making combination and integration studies practical. The ability to effectively monitor these endpoints in short-term and repeated dosing schedules was investigated with the carcinogen/noncarcinogen pair benzo(a)pyrene (BP) and pyrene (Pyr). Male Sprague-Dawley rats were treated via oral gavage for 3 or 28 consecutive days with several dose levels of Pyr, including maximum tolerated doses. BP exposure was administered by the same route but at one dose level, 250 or 125 mg/kg/day for 3-day and 28-day studies, respectively. Serial blood samples were collected up to Day 45, and were analyzed for Pig-a mutation with a dual labeling method (SYTO 13 in combination with anti-CD59-PE) that facilitated mutant cell frequency measurements in both total erythrocytes and the reticulocyte subpopulation. A mutant cell enrichment step based on immunomagnetic column separation was used to increase the statistical power of the assay. BP induced robust mutant reticulocyte responses by Day 15, and elevated frequencies persisted until study termination. Mutant erythrocyte responses lagged mutant reticulocyte responses, with peak incidences observed on Day 30 of the 3-day study (43-fold increase) and on Day 42 of the 28-day study (171-fold increase). No mutagenic effects were apparent for Pyr. Blood samples collected on Day 4, and Day 29 for the 28-day study, were evaluated for micronucleated reticulocyte frequency. Significant increases in micronucleus frequencies were observed with BP, whereas Pyr had no effect. These results demonstrate that Pig-a and micronucleus endpoints discriminate between these structurally related carcinogenic and noncarcinogenic agents. Furthermore, the high sensitivity demonstrated with the enrichment protocol indicates that the Pig-a endpoint is suitable for both repeated-dose and acute studies, allowing integration of mutagenic and clastogenic endpoints into on-going toxicology studies, and use as a short-term assay that provides efficient screening and mechanistic information in vivo.

Malnutrition and infection influence the peripheral blood reticulocyte micronuclei frequency in children

Malnutrition is a serious public health problem that affects approximately one third of all children. Developing countries have the highest incidence of malnourished children, and approximately 60% of deaths that occur in children under five are directly related to malnutrition and associated diseases. The relationship between malnutrition and genetic damage has been widely studied in humans and animal models. The micronucleus (MN) assay is useful in detecting chromosome damage induced by several factors. The aim of this study was to evaluate the effects of infection and malnutrition on the frequency of MN in erythrocytes from the peripheral blood of well-nourished, uninfected (WN) and well-nourished, infected (WNI) children, and moderately malnourished (UNM) and severely malnourished (UNS) children, both with infection, using a flow cytometric analysis technique. The percentage of reticulocytes (RETs) was significantly higher (1.5-fold) in WNI children than well-nourished controls. In addition, the UNS group had a 2.2-fold increase in the percentage of RETs compared to the WNI group. The frequency of micronucleated reticulocytes (MN-RETs) was 2.5 times greater, in WNI group compared to the WN group. These frequencies were significantly higher (1.7- and 2.1-fold) in UNM and UNS, respectively, compared to the WNI group. The results suggest that infection and malnutrition induce DNA damage in children.

Genotoxic effects in blood cells of Mus musculus and Iguana iguana living near coal mining areas in Colombia

Coal is a mixture of chemicals with the capacity of promoting biochemical changes that may lead to DNA damage. In this study, the comet assay in peripheral blood cells, and the micronucleus test in blood smears were used to evaluate potential genotoxic effects derived from exposure to coal mining activities on wild populations of Mus musculus and Iguana iguana. Four locations from Colombia were evaluated: La Loma and La Jagua de Ibirico, two municipalities located near coal mining fields at the Department of Cesar; and Valledupar and Arjona, cities used as reference sites, both localized at least 100 and 200km far from the mines, respectively. Compared to Valledupar and Arjona, animals collected in close proximity to coal mining areas showed highest percentages of DNA damage for both species, evidencing that living around coal mining fields may result in an increase of DNA lesions in blood cells of rodents and reptiles. The results for micronucleus test were conflicting. Mice from Arjona had greater number of cells with micronucleus than those from the other studied locations, probably as a result of infection found by blood parasites. In summary, it was demonstrated that animals living around coal mining areas have a greater chance of having DNA damage, as measured by the comet assay, than those from sites far from the coal dust source.

Manifestation and persistence of Pig-a mutant red blood cells in C57BL/6 mice following single and split doses of N-ethyl-N-nitrosourea

Treating rats with single doses of N-ethyl-N-nitrosourea (ENU) results in a time-dependent accumulation of Pig-a-mutant phenotype peripheral red blood cells (RBCs), reaching a plateau at about 6-weeks posttreatment, with the response persisting for at least 26 weeks. In the present study, groups of 5 C57BL/6 male mice were administered single i.p. doses of up to 140 mg/kg ENU, and blood samples were collected up to 26 weeks posttreatment. The samples were analyzed by flow cytometry for the frequency of CD24-deficient (presumed Pig-a mutant) reticulocytes (RETs) and total RBCs; micronucleated RET frequencies were evaluated at 1 day posttreatment. Mean Pig-a mutant frequencies and micronucleated RET frequencies increased in a dose-responsive manner, with maximum Pig-a frequencies in RETs and RBCs observed at Week 2 and Week 4 posttreatment, respectively. Mutant frequencies in RETs and RBCs generally decreased slowly with time after reaching their maxima. In a second experiment, groups of five male C57BL/6 mice were given single i.p. injections of 8, 32, or 160 mg/kg ENU, or four weekly doses of 8 or 40 mg/kg ENU (split doses totaling 32 and 160 mg/kg, respectively). In each case the maximum RET and RBC mutant frequencies produced by the split doses were similar to but not as great as the mutant frequencies produced by the equivalent single doses. The data indicate that ENU-induced Pig-a mutant RBC frequencies accumulate in mice as they do in rats; however, mice and rats differ in the manifestation kinetics and the persistence of the responses.

Interlaboratory Pig-a gene mutation assay trial: Studies of 1,3-propane sultone with immunomagnetic enrichment of mutant erythrocytes

An international collaborative trial was established to systematically investigate the merits and limitations of a rat in vivo Pig-a gene mutation assay. The product of this gene is essential for anchoring CD59 to the plasma membrane, and mutations in this gene are identified by flow cytometric quantification of circulating erythrocytes without cell surface CD59 expression. Initial interlaboratory data from rats treated with several potent mutagens have been informative, but the time required for those flow cytometric analyses (∼20 min per sample) limited the number of cells that could be interrogated for the mutant phenotype. Thus, it was desirable to establish a new higher throughput scoring approach before expanding the trial to include weak mutagens or nongenotoxicants. An immunomagnetic column separation method that dramatically increases analysis rates was therefore developed (Dertinger et al. [2011]: Mutat Res 721:163-170). To evaluate this new method for use in the international collaborative trial, studies were conducted to determine the mutagenic response of male Sprague Dawley rats treated for 3 or 28 consecutive days with several doses of 1,3-propane sultone (1,3-PS). Pig-a mutant frequencies were measured over a period of several weeks and were supplemented with another indicator of genetic toxicity, peripheral blood micronucleated reticulocyte (MN-RET) counts. 1,3-PS was found to increase Pig-a mutation and MN-RET frequencies in both 3- and 28-day study designs. While the greatest induction of MN-RETs was observed in the 3-day study, the highest Pig-a responses were found with 28-days of treatment. Pig-a measurements were acquired in approximately one-third the time required in the original method, while the number of erythrocyte and reticulocyte equivalents analyzed per sample were increased by factors of 100 and 10, respectively. The data strongly support the value of using the immunomagnetic separation technique for enumerating Pig-a mutation frequencies. These results also demonstrate that the ongoing international trial will benefit from the inclusion of studies that are based on both acute and protracted repeat dosing schedules in conjunction with the acquisition of longitudinal data, at least until more data have been accumulated.

Biomarkers of splenic function in infants with sickle cell anemia: baseline data from the BABY HUG Trial

We evaluated spleen function in 193 children with sickle cell anemia 8 to 18 months of age by (99m)Tc sulfur-colloid liver-spleen scan and correlated results with clinical and laboratory parameters, including 2 splenic biomarkers: pitted cell counts (PIT) and quantitative Howell-Jolly bodies (HJB) enumerated by flow cytometry. Loss of splenic function began before 12 months of age in 86% of infants in association with lower total or fetal hemoglobin and higher white blood cell or reticulocyte counts, reinforcing the need for early diagnosis and diligent preventive care. PIT and HJB correlated well with each other and liver-spleen scan results. Previously described biomarker threshold values did define patients with abnormal splenic function, but our data suggest that normal spleen function is better predicted by PIT of ≤1.2% or HJB ≤55/10(6) red blood cells and absent function by PIT ≥4.5% or HJB ≥665/10(6). HJB is methodologically advantageous compared with PIT, but both are valid biomarkers of splenic function. This trial was registered at www.clinicaltrials.gov as #NCT00006400.

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.

Integration of mutation and chromosomal damage endpoints into 28-day repeat dose toxicology studies

Two endpoints of genetic toxicity, mutation at the X-linked Pig-a gene and chromosomal damage in the form of micronucleated reticulocytes (MN-RETs), were evaluated in blood samples obtained from 28-day repeat-dosing studies typical of those employed in toxicity evaluations. Male Wistar Han rats were treated at 24-h intervals on days 1 through 28 with one of five prototypical genotoxicants: N-ethyl-N-nitrosourea, 7,12-dimethyl-12-benz[a]anthracene, 4-nitroquinoline-1-oxide (4NQO), benzo(a)pyrene, and N-methyl-N-nitrosourea. Flow cytometric scoring of CD59-negative erythrocytes (indicative of glycosylphosphatidylinositol anchor deficiency and hence Pig-a mutation) was performed using blood specimens obtained on days -1, 15, 29, and 56. Blood specimens collected on days 4 and 29 were evaluated for MN-RET frequency using flow cytometry-based MicroFlow Kits. With the exception of 4NQO, each chemical induced significant increases in the frequency of MN-RETs on days 4 and 29. All five agents increased the frequency of mutant phenotype (CD59 negative) reticulocytes (RETs) and erythrocytes. Mutation responses in RETs occurred earlier than in erythrocytes and tended to peak, or nearly peak, at day 29. In contrast, the mutant phenotype erythrocyte responses were modest on day 29 and required additional time to reach their maximal value. The observed kinetics were expected based on the known turnover of RETs and erythrocytes. The data show that RETs can serve as an appropriate indicator cell population for 28-day studies. Collectively, these data suggest that blood-based genotoxicity endpoints can be effectively incorporated into routine toxicology studies, a strategy that would reduce animal usage while providing valuable genetic toxicity information within the context of other toxicological endpoints.

Pig-a mutation: kinetics in rat erythrocytes following exposure to five prototypical mutagens

An in vivo mutation assay has been developed based on flow cytometric enumeration of glycosylphosphatidylinositol (GPI) anchor-deficient rat erythrocytes. With this method, blood is incubated with anti-CD59-PE and SYTO 13 dye, and flow cytometry is used to score the frequency of CD59-negative erythrocytes. The experiments described herein were designed to define the kinetics of mutant erythrocyte appearance and disappearance from peripheral blood to support appropriate treatment and sampling designs for the assay. Wistar Han rats were treated with one of five prototypical mutagens: N-ethyl-N-nitrosourea (ENU); 7,12-dimethyl-1,2-benz[a]anthracene (DMBA); 4-nitroquinoline-1-oxide; benzo[a]pyrene; and N-methyl-N-nitrosourea. ENU and DMBA were also evaluated in Sprague Dawley rats. Animals were treated on three consecutive days (days 1-3) via oral gavage, and blood specimens were obtained on days -1, 4, 15, 30, 45, and 90 (and day 180 for ENU). A second endpoint of genotoxicity, the frequency of peripheral blood micronucleated reticulocytes, was measured on day 4. Each chemical induced micronuclei and the GPI anchor-deficient phenotype. Increased mutant cell frequencies were evident at day 15. Mutant reticulocyte frequencies remained relatively stable for some chemicals, but others peaked and then dropped significantly. The differences in kinetics observed are presumably related to the degree to which mutation occurs in hematopoietic stem cells versus more committed cells with limited self-renewal capacity. Collectively, the results suggest that enumerating GPI anchor-deficient erythrocytes is an efficient means of evaluating the in vivo mutagenic potential of chemicals. The kinetics and ease of scoring this blood-based endpoint suggest that integration into routine toxicology studies will be feasible.

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.

Inhalation of formaldehyde does not induce systemic genotoxic effects in rats

Male Fischer-344 rats were exposed to formaldehyde (FA) by inhalation for 4 weeks (6 h/day, 5 days/week). Groups of six rats each were exposed to the target concentrations of 0, 0.5, 1, 2, 6, 10 and 15 ppm. Potential systemic genotoxic effects were investigated as part of a comprehensive study on local and systemic toxic and genotoxic effects. For this purpose, peripheral blood samples were obtained by puncturing the retro-orbital venous plexus at the end of the exposure period. Blood sampling was carried out in a randomized sequence and samples were coded by sequence number to ensure blind evaluation. Blood samples were used for the comet assay, the sister chromatid exchange test (SCE test) and the micronucleus test (MNT). DNA migration in the comet assay was measured both directly and after irradiation of the blood samples with 2 Gy gamma-radiation. The latter modification of the comet assay was included to increase its sensitivity for the detection of DNA-protein cross-links (DPX). The following positive control groups were included: one group (six animals) was treated with 50mg/kg methyl methanesulfonate (MMS) once by gavage 4h before blood sampling. Another group (six animals) was treated twice orally with 10mg/kg cyclophosphamide (CP) with an interval of 24 h. The last application of CP was 24h before blood sampling. For the comet assay, four slides were analysed from each blood sample, two without and two with irradiation. From each slide, 50 randomly selected cells were measured by image analysis, and tail intensity (% tail DNA) and tail moment were evaluated. For the SCE test, blood was cultured for 56 h in the presence of BrdU (10 microg/ml for the last 35 h) and SCE were counted in 30 second-division metaphases per sample. The MNT with peripheral blood was performed according to the instructions for the micronucleus analysis kit MICROFLOW (Litron Laboratories). Approximately 20,000 cells per sample were analysed by flow cytometry and the percentage of reticulocytes with micronuclei (MN) was determined. The positive control substances induced a significant effect in the genotoxicity tests and thus demonstrated the sensitivity of the test systems. FA did not induce any significant effect in any of the genotoxicity tests performed. It can be concluded that inhalation of FA in a 28-day study with FA concentrations up to 15 ppm does not lead to systemic genotoxic effects in the blood of rats.

Reticulocyte and micronucleated reticulocyte responses to gamma irradiation: effect of age

The effect of age on the formation of radiation-induced micronucleated reticulocytes (MN-RETs) and reticulocytes (RETs) was investigated by exposing female C57BL/6J mice to graded doses of gamma rays from a (137)Cs source. Age at time of irradiation was 6, 16, or 32 weeks, and doses ranged from 0.5 to 3 Gy. A flow cytometric technique based on anti-CD71 labeling was used to measure RET and MN-RET frequencies in blood specimens collected 43 h post-irradiation. Mean RET frequencies declined in a dose-dependent manner for each age group. There was only one significant difference among the ages, that is, %RETs were not significantly reduced in the oldest animals at 0.5 Gy, whereas this dose did have a significant effect on the other age groups. MN-RET data were more complex. Age was observed to influence the baseline frequency of MN-RET, with the oldest mice exhibiting a significantly higher mean value. Each group's %MN-RETs values increased up to 1 Gy, but past this dose the frequencies plateaued or decreased. Age was observed to influence micronucleus frequency, with older mice exhibiting higher mean MN-RET values, especially at the high doses where the response was saturated (2-3 Gy). We hypothesize that these dissimilar responses can largely be explained by an age-related down-regulation of apoptosis whereby younger animals eliminate damaged bone marrow erythroid precursors with a greater efficiency compared with aged mice.

Measurement of cytogenetic damage in rodent blood with a single-laser flow cytometer

The in vivo rodent micronucleus test is widely utilized to screen chemicals for genotoxic activity. Double-strand chromosome breaks or dysfunction of the mitotic spindle apparatus can lead to micronuclei formation in dividing cells. Erythrocytes have become the target population of choice, as precursor cells are continuously dividing and micronuclei are readily observable after extrusion of nuclei. The traditional method has been to stain peripheral blood or bone marrow smears and microscopically determine the frequency of micronucleated erythrocytes. Because these events are rare, the process is tedious and time consuming. This unit describes a procedure for fixing and staining rodent peripheral blood for flow cytometric enumeration. The combination of reagents provides for differential labeling and enumeration of four subpopulations: mature erythrocytes, micronucleus-containing mature erythrocytes, young erythrocytes (reticulocytes), and micronucleus-containing young erythrocytes. Malaria-infected rodent erythrocytes, which closely mimic micronucleus-containing erythrocytes, serve as a biological standard to facilitate rational and consistent equipment calibration.

Flow cytometric analysis of micronuclei in peripheral blood reticulocytes IV: an index of chromosomal damage in the rhesus monkey (Macaca mulatta)

We report evaluation in rhesus monkeys of a flow cytometric procedure (MicroFlow) that has previously been shown to allow assessment of micronucleated reticulocytes (MN-RETs) in the peripheral blood of rats and dogs. Reticulocytes (RETs) were labeled with anti-CD71-fluorescein isothiocyanate, DNA was stained with propidium iodide using RNase treatment, and anti-CD61-phycoerythrin was used to reduce interference from platelets. Flow cytometric data were compared with microscopic scores of peripheral blood and bone marrow using standard acridine orange staining. A single iv administration of cyclophosphamide (CP, 5 mg/kg) induced an approximately 10-fold increase in blood MN-RET frequency, with the peak occurring 2 days after administration. After daily CP treatment to approximate a steady-state condition, the frequency of MN-RETs in peripheral blood was approximately 25% of that in bone marrow, indicating strong selection against MN-RETs. Nonetheless, CP-treated animals exhibited markedly elevated blood MN-RET values (2.45-3.99%, n = 3; compared to a mean baseline of 0.12%, n = 6). These measurements closely reflected the increased frequencies observed in the bone marrow compartment (Spearman correlation coefficient = 0.9856, n = 6). These data suggest that MN-RET measurements in blood are suitable for assessing chemical-induced chromosomal damage and can be readily integrated into routine toxicity tests, allowing genotoxicity data to be obtained as an integral part of toxicity evaluations. Microscopy-based scoring is challenging due to the low frequency of RETs and MN-RET in monkeys, but sufficient numbers of cells are easily scored with the flow cytometric procedure.

Reticulocyte and micronucleated reticulocyte responses to gamma irradiation: dose-response and time-course profiles measured by flow cytometry

A flow cytometric, anti-CD71-based method was used to measure peripheral blood reticulocyte and micronucleated reticulocyte frequencies in response to (137)Cs total body irradiation (TBI). In three independent experiments, groups of five female C57BL/6N mice were irradiated at graded doses up to 3 Gy, and peripheral blood specimens were collected at 43 h post-irradiation. Whereas the frequency of reticulocytes declined over the range of doses studied, micronucleated reticulocyte incidence was observed to increase in a dose-dependent manner up to 1 Gy. At doses greater than approximately 1 Gy, micronucleated reticulocyte frequencies declined with increasing exposure. These responses were highly reproducible, with significant effects on reticulocyte and micronucleated reticulocyte frequencies observed for the lowest dose studied (0.125 Gy). A time-course experiment was performed to test whether radiation-induced cell cycle delay may explain saturation of the micronucleated reticulocyte endpoint at doses >1 Gy. For this experiment, groups of four female C57BL/6N mice were exposed to 1, 1.5, or 2 Gy TBI, and blood collection occurred at 12h intervals from 43 to 115 h post-exposure. Reduced reticulocyte frequencies were observed for each dose studied, and the recovery of reticulocytes was increasingly delayed with higher radiation doses. Maximal micronucleated reticulocyte frequencies were observed at 43 or 55 h, with progressively lower values at later time points. At no time did micronucleated reticulocyte frequencies induced by 1.5 or 2 Gy significantly exceed that observed for 1 Gy at 43 h. These time-course data suggest that radiation-induced cell cycle delay cannot account for the micronucleated reticulocyte downturn phenomenon observed at doses greater than 1 Gy. An alternate hypothesis is discussed whereby apoptotic elimination of severely damaged bone marrow erythroid precursors plays a dominant role in saturating the radiation-induced micronucleated reticulocyte response observed for C57BL/6N mice.

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.

Flow Cytometric Analysis of Micronuclei in Peripheral Blood Reticulocytes III. An Efficient Method of Monitoring Chromosomal Damage in the Beagle Dog

Erythrocyte-based micronucleus tests have traditionally analyzed bone marrow because splenic filtration in most species removes micronucleated cells from peripheral blood. We have evaluated a flow cytometric method for monitoring micronucleated reticulocyte frequencies (%MN-RET) in the peripheral blood of beagle dogs treated with cyclophosphamide (CP) and have found that analysis of micronucleated reticulocytes (MN-RETs) in peripheral blood is a suitable surrogate for bone marrow analysis. The three-color flow cytometric method uses anti-CD71 labeling to identify reticulocytes and Plasmodium berghei-containing erythrocytes as a calibration standard. The spontaneous %MN-RET determined by flow cytometry was 0.31 +/- 0.09% (n = 22) for peripheral blood, compared with 0.38 +/- 0.13% (SD, n = 12) for bone marrow, and 0.27 +/- 0.08% (n = 12) for peripheral blood by microscopic scoring with acridine orange staining. The kinetics of appearance and disappearance of MN-RETs in blood were determined by collecting daily samples after iv treatment with CP. The maximum frequency occurred approximately 48 h after dosing. Frequencies of MN-RETs in peripheral blood at steady state following daily CP treatment were 55-68% of corresponding bone marrow values assessed by microscopy and 55-112% as assessed by flow cytometry. This difference is presumably due to splenic removal, which appears slightly less stringent than that previously reported for CP-treated Sprague-Dawley rats. Responses in bone marrow and peripheral blood were highly correlated and similar to or greater than those reported in mice and rats at equitoxic doses.

Comparison of flow cytometry- and microscopy-based methods for measuring micronucleated reticulocyte frequencies in rodents treated with nongenotoxic and genotoxic chemicals

The development of automated flow cytometric (FCM) methods for evaluating micronucleus (MN) frequencies in erythrocytes has great potential for improving the sensitivity, reproducibility, and throughput of the traditional in vivo rodent MN assay that uses microscopy-based methods for data collection. Although some validation studies of the FCM evaluation methods have been performed, a comprehensive comparison of these two data collection methods under routine testing conditions with a variety of compounds in multiple species has not been conducted. Therefore, to determine if FCM evaluation of MN frequencies in rodents was an acceptable alternative to traditional manual scoring methods in our laboratory, we conducted a comparative evaluation of MN-reticulocyte (MN-RET) frequencies determined by FCM- and microscopy-based scoring of peripheral blood and bone marrow samples from B6C3F1 mice and Fisher 344 rats. Four known inducers of MN (cyclophosphamide, ethyl methanesulfonate, vincristine sulfate, acrylamide) were assayed in bone marrow and peripheral blood of both mice and rats. In addition, MN-RET frequencies were measured in bone marrow (microscopy) and peripheral blood (FCM) of mice treated with five nongenotoxic chemicals (S-adenosylmethionine chloride, cefuroxime, diphenolic acid, 3-amino-6-methylphenol, pentabromodiphenyl oxide). No significant differences were observed between results obtained by the two methods in either species. These results support the use of FCM for determining MN-RET frequency in rodents after chemical exposure.

Sensitivity of the erythrocyte micronucleus assay: dependence on number of cells scored and inter-animal variability

Until recently, the in vivo erythrocyte micronucleus assay has been scored using microscopy. Because the frequency of micronucleated cells is typically low, cell counts are subject to substantial binomial counting error. Counting error, along with inter-animal variability, limit the sensitivity of this assay. Recently, flow cytometric methods have been developed for scoring micronucleated erythrocytes and these methods enable many more cells to be evaluated than is possible with microscopic scoring. Using typical spontaneous micronucleus frequencies reported in mice, rats, and dogs we calculate the counting error associated with the frequency of micronucleated reticulocytes as a function of the number of reticulocytes scored. We compare this counting error with the inter-animal variability determined by flow cytometric scoring of sufficient numbers of cells to assure that the counting error is less than the inter-animal variability, and calculate the minimum increases in micronucleus frequency that can be detected as a function of the number of cells scored. The data show that current regulatory guidelines allow low power of the test when spontaneous frequencies are low (e.g., < or =0.1%). Tables and formulas are presented that provide the necessary numbers of cells that must be scored to meet the recommendation of the International Working Group on Genotoxicity Testing that sufficient cells be scored to reduce counting error to less than the inter-animal variability, thereby maintaining a more uniform power of detection of increased micronucleus frequencies across laboratories and species.

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.

Performance of flow cytometric analysis for the micronucleus assay--a reconstruction model using serial dilutions of malaria-infected cells with normal mouse peripheral blood

To confirm the performance and statistical power of a flow cytometric method for scoring micronucleated erythrocytes, reconstruction experiments were performed. For these investigations, peripheral blood erythrocytes from untreated mice, with a micronucleated erythrocyte frequency of approximately 0.1% were combined with known quantities of Plasmodium berghei (malaria) infected mouse erythrocytes. These cells had an infected erythrocyte frequency of approximately 0.7%, and mimic the DNA content of micronuclei (MN). For an initial experiment, samples with a range of MN/malaria (Mal) content were constructed and analysed in triplicate by flow cytometry until 2000, 20,000 and 200,000 total erythrocytes were acquired. In a second experiment, each specimen was analysed in triplicate until 2000, 20,000, 200,000 and 1,000,000 erythrocytes were acquired. As expected, the sensitivity of the assay to detect small changes in rare erythrocyte sub-population frequencies was directly related to the number of cells analysed. For example, when 2000 cells were scored, increases in MN/Mal frequencies of 3.9- or 2.7-fold were detected as statistically significant. When 200,000 cells were analysed, a 1.2-fold increase was detected. These data have implications for the experimental design and interpretation of micronucleus assays that are based on automated scoring procedures, since previously unattainable numbers of cells can now be readily scored.

Flow cytometric analysis of micronucleated reticulocytes: Time- and dose-dependent response of known mutagens in mice, using multiple blood sampling

According to the current Organization of Economic Cooperation and Development (OECD) and International Committee on Harmonization (ICH) guidelines for the mammalian erythrocyte micronucleus (MN) test, analysis of peripheral blood reticulocytes (RETs) for the presence of micronuclei can be performed using flow cytometry. The MicroFlow PLUS method (Litron Laboratories, Rochester, NY) for MN analysis by flow cytometry is based on the binding of FITC-labeled antibodies to the CD71 transferrin receptor of immature RETs, on parallel RNA degradation, and on propidium iodide staining of DNA present as micronuclei. The objective of this study was to assess the sensitivity of this flow cytometry method to detect time- and dose-dependent induction of micronuclei in mouse peripheral blood RETs after treatment with nine chemical agents. Five known clastogens, two known aneugens, and two compounds previously reported to be inactive in the mouse bone marrow MN test were evaluated at three dose levels. Multiple blood sampling of the same animal before and at two time points after treatment was conducted. All known mutagens produced a dose-dependent increase in micronucleated reticulocytes (MN-RETs); the compounds previously shown to be inactive in the in vivo MN test were also negative using the present methodology. The highest frequency of MN-RETs was observed at 48 hr after treatment, except for 5-fluorouracil, which had its peak response at 72 hr. The results indicate that micronuclei can be measured by multiple blood sampling of the same animal before and after treatment without altering the sensitivity of the assay. The results confirm that the flow cytometric assessment of MN-RETs in mouse peripheral blood using MicroFlow PLUS is a sensitive method with high analysis throughput, and robust quality control.

Interlaboratory validation of a CD71-based flow cytometric method (Microflow) for the scoring of micronucleated reticulocytes in mouse peripheral blood

An interlaboratory study was performed to validate an anti-CD71/flow cytometry-based technique for enumerating micronucleated reticulocytes (MN-RETs) in mouse peripheral blood. These experiments were designed to address International Workshop on Genotoxicity Test Procedures validation criteria by evaluating the degree of correspondence between MN-RET measurements generated by flow cytometry (FCM) with those obtained using traditional microscopy-based methods. In addition to these cross-methods data, flow cytometric MN-RET measurements for each blood sample were performed at two separate sites in order to evaluate the reproducibility of data between laboratories. In these studies, groups of male CD-1 mice were treated with vehicle (saline or vegetable oil), a negative control (saline or vegetable oil), or four dose levels of five known genotoxicants (clastogens: cyclophosphamide, benzo[a]pyrene, 5-fluorouracil, methotrexate; aneugen: vincristine sulfate). Exposure occurred on 3 consecutive days via intraperitoneal injection, and blood samples were obtained approximately 24 hr after the final treatment. MN-RET frequencies were determined for each sample based on the analysis of 2,000 (microscopy) and 20,000 (FCM) reticulocytes. Regardless of the method utilized, each genotoxic agent was observed to cause statistically significant increases in the frequency of MN-RETs, and each response occurred in a dose-dependent manner. Spearman's correlation coefficient (rs) for FCM versus microscopy-based MN-RET measurements (nine experiments, 252 paired measurements) was 0.740, indicating a high degree of correspondence between methods. The rs value for all flow cytometric MN-RET measurements performed at the two independent sites was 0.857 (n = 248), suggesting that the automated method is highly transferable between laboratories. Additionally, the flow cytometric system offered advantages relative to microscopy-based scoring, including a greater number of cells analyzed, much faster analysis times, and a greater degree of objectivity. Collectively, data presented in this report suggest that the overall performance of mouse peripheral blood micronucleus tests is enhanced by the use of the flow cytometric scoring procedure.

Double staining of Plasmodium falciparum nucleic acids with hydroethidine and thiazole orange for cell cycle stage analysis by flow cytometry

BACKGROUND

Microarray analyses of stage-specific gene expression of Plasmodium falciparum require purification of RNAs from highly synchronized cultures. To date, no reliable method to control the quality of synchronization of P. falciparum cultures is available.

METHODS

A double-staining method using hydroethidine and thiazole orange for nucleic acid staining was carried out to compare by flow cytometric analysis the nucleic acid labeling of synchronized P. falciparum in cultures at different time points of the 48-h intraerythrocytic cycle.

RESULTS

With this method, we determined the quality of culture synchronization in schizont and ring stages. Nucleic acid analysis, based on thiazole orange fluorescence, clearly showed that low levels of schizonts in ring cultures results in a high contamination of ring nucleic acids by schizonts. Conversely, nucleic acids from trophozoite or schizont cultures containing ring stages did not present a significant contamination by ring nucleic acids.

CONCLUSION

The results demonstrated a very low nucleic acid content in the ring stage when compared with the high nucleic acid content of schizont-stage parasites. The rapid and reliable flow cytometric strategy using hydroethidine- and thiazole orange-stained parasite nucleic acids allows monitoring of the purity of the preparation, thus greatly improving the quality assessment of parasite cultures, a critical step to study gene expression patterns.

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.

Three-color labeling method for flow cytometric measurement of cytogenetic damage in rodent and human blood

Experiments described herein were designed to evaluate the performance characteristics of a flow cytometry-based system that scores the incidence of peripheral blood micronucleated reticulocytes (MN-RETs). These procedures represent the continued refinement of a previously reported anti-CD71-based method (Dertinger et al. [1996]: Mutat Res 371:283-292), with the following modifications: incorporation of a third fluorescent label to exclude platelets from the MN-RET region, and use of a CD71-associated fluorescence thresholding technique to increase data acquisition rates. Mouse, rat, and human blood samples were analyzed using both the previously described two-color procedure (anti-CD71-FITC and propidium iodide) and a newly developed three-color technique (which adds an antiplatelet-PE antibody). The rodent specimens were also evaluated by standard microscopy procedures (acridine orange staining). Mouse blood was collected via heart puncture of vehicle- and 5-fluorouracil-treated CD-1 mice; blood samples from saline-treated Sprague-Dawley rats were collected from the tail vein and via heart puncture. Rodent blood samples were analyzed by both the two- and three-color methods. Human blood specimens, obtained via arm venipuncture from cancer patients undergoing radiation therapy, were analyzed for MN-RETs using the two-color method. Subsequently, blood samples from a single chemotherapy patient were analyzed by both the two- and three-color methods. Finally, the chemotherapy patient blood samples and blood samples from 15 healthy volunteers were evaluated at very high densities in conjunction with a CD71-associated fluorescence thresholding technique. Results of these investigations showed that data from mouse blood analyzed by the two- and three-color procedures correlated well with microscopy data (r values = 0.917 and 0.937 for the two- and three-color methods, respectively); all three methods confirmed the genotoxicity of 5-FU. Data from rat tail vein samples showed improved reproducibility with the three-color technique, but no significant difference between the two techniques was seen with the heart puncture specimens. Human blood analyzed according to the two-color procedure produced unreliable results, as platelets and platelet aggregates impacted the rare MN-RET scoring region. The three-color technique effectively overcame this problem and produced reproducible measurements that fell within expected ranges. For human blood analyses, the high cell density/CD71-thresholding technique provided significant improvements over the low-density technique, as it allowed data acquisition to occur approximately six times faster with no loss of sensitivity.

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.