Increased frequency of chromosome translocations in airline pilots with long-term flying experience.

BACKGROUND: Chromosome translocations are an established biomarker of cumulative exposure to external ionising radiation. Airline pilots are exposed to cosmic ionising radiation, but few flight crew studies have examined translocations in relation to flight experience. METHODS: We determined the frequency of translocations in the peripheral blood lymphocytes of 83 airline pilots and 50 comparison subjects (mean age 47 and 46 years, respectively). Translocations were scored in an average of 1039 cell equivalents (CE) per subject using fluorescence in situ hybridisation (FISH) whole chromosome painting and expressed per 100 CE. Negative binomial regression models were used to assess the relationship between translocation frequency and exposure status and flight years, adjusting for age, diagnostic x ray procedures, and military flying. RESULTS: There was no significant difference in the adjusted mean translocation frequency of pilots and comparison subjects (0.37 (SE 0.04) vs 0.38 (SE 0.06) translocations/100 CE, respectively). However, among pilots, the adjusted translocation frequency was significantly associated with flight years (p = 0.01) with rate ratios of 1.06 (95% CI 1.01 to 1.11) and 1.81 (95% CI 1.16 to 2.82) for a 1- and 10-year incremental increase in flight years, respectively. The adjusted rate ratio for pilots in the highest compared to the lowest quartile of flight years was 2.59 (95% CI 1.26 to 5.33). CONCLUSIONS: Our data suggests that pilots with long-term flying experience may be exposed to biologically significant doses of ionising radiation. Epidemiological studies with longer follow-up of larger cohorts of pilots with a wide range of radiation exposure levels are needed to clarify the relationship between cosmic radiation exposure and cancer risk.

The relationship between genotype and chromosome aberration frequencies in a normal adult population.

Cancer susceptibility differences may be attributed in part to genetic variation in genes involved in metabolism of environmental procarcinogens. Increased risks for some cancers have been linked to polymorphisms in certain phase I and II genes, and have been associated with genomic instability and chromosomal aberrations. Aberration frequencies in general, and stable aberration frequencies (translocations and insertions) in particular, are used as biomarkers for disease. Thus, knowledge of the genetic factors that influence the frequency of stable aberrations in a normal population is important for cancer risk determination. In this work, genotypes for a number of xenobiotic enzymes (CYPIA1, CYP2D6, GSTM1, GSTT1, GSTP1, NAT1, NAT2 and epoxide hydrolase) and stable aberration frequencies were determined for 65 normal individuals aged 19-77 years. The population was divided at age 60 years for analysis because there was a significant difference in stable aberration frequencies between these groups. Subjects with low levels (0-66th percentile) of stable aberrations were compared to those with high levels (67th percentile and above). Of all the genotypes studied, only NAT2 showed a notable difference between the high and the low stable aberration groups in the percentage of polymorphisms observed, and this was seen only in the older subjects group. All individuals in the older-high stable aberration group were NAT2 rapid acetylator smokers. NAT2 slow acetylator smokers had significantly lower stable aberration frequencies compared to the NAT2 rapid acetylator smokers. Following previous work showing an increased risk of cancer associated with high levels of aberrations (above the 66th percentile), we hypothesize that smokers with the NAT2 rapid acetylator genotype may be at an increased risk for cancer.

Role of maternal exposures and newborn genotypes on newborn chromosome aberration frequencies.

Maternal exposures may induce chromosome damage and birth defects in the fetus. Polymorphic variation in genes coding for enzymes involved in metabolic activation and detoxification of environmental procarcinogens may account for some of the differences in chromosome aberration frequencies in newborns. In this study, 40 mothers completed questionnaires regarding exposures they received during their pregnancy. Umbilical cord blood samples were analyzed for chromosome aberrations. An average of 1020 metaphase cell equivalents (equal to 1020 G-banded cells) were examined from each newborn. In 26 of the newborns, genotyping analysis was performed for genes functioning in metabolic activation and detoxification (cytochrome P450 genes: CYP2D6 and CYP1A1, and phase II genes: NAT1, NAT2, GSTT1, GSTM1, GSTP1, and epoxide hydrolase). A significant association between the CYP1A1 MspI polymorphism and chromosome aberration frequencies was observed in the newborns (p=0.02), with heterozygotes showing higher aberration frequencies than the wild type homozygotes. Some large differences in chromosome aberration frequencies for other genotypes were also noted, but these were not statistically significant. Exposure to tobacco smoke in utero also appeared to increase translocation frequencies. The mean frequency of translocations per 100 cell equivalents from newborns of mothers who smoked during pregnancy was significantly higher than that of newborns whose mothers did not smoke (0.21 vs. 0.11, respectively, p=0.045).

Corticosteroid treatment for idiopathic facial nerve paralysis: a meta-analysis.

OBJECTIVE: A meta-analysis was designed to evaluate facial recovery in patients with complete idiopathic facial nerve paralysis (IFNP) by comparing outcomes of those treated with corticosteroid therapy with outcomes of those treated with placebo or no treatment. STUDY DESIGN: Meta-analysis of prospective trials evaluating corticosteroid therapy for idiopathic facial nerve paralysis. METHODS: A protocol was followed outlining methods for trial selection, data extraction, and statistical analysis. A MEDLINE search of the English language literature was performed to identify clinical trials evaluating steroid treatment of IFNP. Three independent observers used an eight-point analysis to determine inclusion criteria. Data analysis was limited to individuals with clinically complete IFNP. The endpoints measured were clinically complete or incomplete facial motor recovery. Effect magnitude and significance were evaluated by calculating the rate difference and Fisher's Exact Test P value. Pooled analysis was performed with a random effects model. RESULTS: Forty-seven trials were identified. Of those, 27 were prospective and 20 retrospective. Three prospective trials met the inclusion criteria Tests of heterogeneity indicate the trial with the smallest sample size (RD = -0.19; 95% CI, -0.58-0.20), to be an outlier. It was excluded from the final analysis. Analyses of data from the remaining two studies indicate corticosteroid treatment improves complete facial motor recovery for individuals with complete IFNP. Rate difference demonstrates a 17% (990% CI, 0.01-0.32) improvement in clinically complete recovery for the treatment group based on the random effects model. CONCLUSIONS: Corticosteroid treatment provides a clinically and statistically significant improvement in recovery of function in complete IFNP.

Lifetime persistence and clonality of chromosome aberrations in the peripheral blood of mice acutely exposed to ionizing radiation.

As the measurement of chromosomal translocations increases in popularity for quantifying prior radiation exposure, information on the possible decline of these "stable" aberrations over time is urgently needed. We report here information about the persistence of radiation-induced chromosome aberrations in vivo over the life span of a rodent. Female C57BL/6 mice were given a single whole-body acute exposure of 0, 1, 2, 3 or 4 Gy (137)Cs gamma rays at 8 weeks of age. Chromosome aberrations were analyzed from peripheral blood samples at various intervals between 1 day and 21 months after exposure. Aberrations were detected by painting chromosomes 2 and 8. Translocations decreased dramatically during the first 3 months after irradiation, beyond which time the frequencies remained relatively constant out to 1 year, when the effects of aging and clonal expansion became significant. Both reciprocal and nonreciprocal translocations increased with age in the unexposed control animals and were involved in clones. As expected of unstable aberrations, dicentrics decreased rapidly after exposure and reached baseline levels within 3 months. These results indicate that the persistence of translocations induced by ionizing radiation is complicated by aging and clonal expansion and that these factors must be considered when quantifying translocations at long times after exposure. These results have implications for biological dosimetry in human populations.

Estimation of the target stem-cell population size in chronic myeloid leukemogenesis.

Estimation of the number of hematopoietic stem cells capable of causing chronic myeloid leukemia (CML) is relevant to the development of biologically based risk models of radiation-induced CML. Through a comparison of the age structure of CML incidence data from the Surveillance, Epidemiology, and End Results (SEER) Program and the age structure of chromosomal translocations found in healthy subjects, the number of CML target stem cells is estimated for individuals above 20 years of age. The estimation involves three steps. First, CML incidence among adults is fit to an exponentially increasing function of age. Next, assuming a relatively short waiting time distribution between BCR-ABL induction and the appearance of CML, an exponential age function with rate constants fixed to the values found for CML is fitted to the translocation data. Finally, assuming that translocations are equally likely to occur between any two points in the genome, the parameter estimates found in the first two steps are used to estimate the number of target stem cells for CML. The population-averaged estimates of this number are found to be 1.86x10(8) for men and 1.21x10(8) for women; the 95% confidence intervals of these estimates are (1.34x10(8), 2. 50x10(8)) and (0.84x10(8), 1.83x10(8)), respectively.

Mouse phosphoinositide 3-kinase p110alpha gene: cloning, structural organization, and localization to chromosome 3 band B.

Phosphoinositide 3-Kinases (PI3-Kinases) are a family of dual specificity enzymes with a unique lipid kinase activity toward the D-3 position of the inositol ring of phosphoinositides and a less well characterized serine/threonine protein kinase activity. Class IA PI3-Kinases comprise a 110-120 kDa catalytic subunit (usually termed p110) and an 85 kDa or 50 to 55 kDa regulatory subunit (often called p85). cDNAs for three mammalian Class IA PI3-Kinase catalytic subunits designated p110alpha, p110beta, and p110delta have been cloned from several species. A YAC clone for the human p110alpha gene has also been cloned and mapped to chromosome 3q26.3. However, structural organization for any of the PI3-Kinase p110alpha genes has not been reported. Here, we report the cloning, structural organization, and chromosomal localization of the mouse PI3-Kinase p110alpha gene. The translated portion of the mouse p110alpha gene is encoded by 19 exons that span at least 24 kb. Dual color fluorescence in situ hybridization (FISH) was performed to determine the chromosomal localization of the mouse PI3-Kinase p110alpha gene. FISH results and DAPI banding demonstrated localization of the p110alpha gene to band B on mouse chromosome 3, a region syntenic with human chromosome 3q26.3.

A transgene insertion creating a heritable chromosome deletion mouse model of Prader-Willi and angelman syndromes.

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) result from the loss of function of imprinted genes in human chromosome 15q11-q13. The central part of mouse chromosome 7 is homologous to human 15q11-q13, with conservation of both gene order and imprinted features. We report here the characterization of a transgene insertion (Epstein-Barr virus Latent Membrane Protein 2A, LMP2A) into mouse chromosome 7C, which has resulted in mouse models for PWS and AS dependent on the sex of the transmitting parent. Epigenotype (allelic expression and DNA methylation) and fluorescence in situ hybridization analyses indicate that the transgene-induced mutation has generated a complete deletion of the PWS/AS-homologous region but has not deleted flanking loci. Because the intact chromosome 7, opposite the deleted homolog, maintains the correct imprint in somatic cells of PWS and AS mice and establishes the correct imprint in male and female germ cells of AS mice, homologous association and replication asynchrony are not part of the imprinting mechanism. This heritable-deletion mouse model will be particularly useful for the identification of the etiological genes and mechanisms, phenotypic basis, and investigation of therapeutic approaches for PWS.

Frequency of spontaneous chromosome aberrations in mice: effects of age.

In this paper, we present data on chromosome aberration frequencies in mice which served as unexposed controls in a variety of radiation and chemical toxicology experiments conducted in our laboratory in recent years. All chromosome aberration data were obtained by chromosome painting. In peripheral blood lymphocytes from 102 animals, the frequencies of translocations and insertions increased significantly with age. No increase with age was seen for dicentrics or acentric fragments. When the data were analyzed by strain, the age-related increase in translocation frequencies was observed only in the 71 homozygous C57BL/6 mice and not in any of the three heterozygous strains. Very few aberrations of any type were observed in 62 bone marrow samples, and no effect of age was seen for any aberration type in this tissue. These results are similar to those observed in unexposed humans, and suggest that the increase in translocations is not the result of accumulated damage from chronic 'background' environmental exposures but instead may be due to biological processes associated with aging.

Chronic ingestion of clastogens by mice and the frequency of chromosome aberrations.

Environmental exposure to mutagens is believed to play a significant role in human carcinogenesis. Determination of the in vivo effects of a single mutagen is best done in laboratory animals because humans are exposed to a variety of mutagens both in their diet and in the rest of their environment. In this study, C57BL/6N female mice were used to analyze the effect on chromosomes of chronic ingestion of a mutagen dissolved in drinking water. Cyclophosphamide (CP) or urethane (ethyl carbamate, EC) were dissolved in sterile drinking water at concentrations of 0, 32, 64, and 96 ppm or 0, 5,000, 10,000, and 15,000 ppm, respectively. All exposures began at 8 weeks of age and continued through the 20th week unless terminated earlier due to toxicity. Body weights and water consumption were measured weekly. Blood and bone marrow were taken from approximately five mice per exposure group at 4, 8, and 12 weeks from the start of exposure. All mice remaining after 12 weeks received drinking water without any carcinogen for an additional 6 weeks to determine if induced aberrations persisted. Chromosome translocations, measured by painting, were not induced in blood or bone marrow cells at any time point for either chemical. However, both carcinogens induced significant increases in micronucleated normochromatic erythrocytes, indicating that the carcinogens reached the tissues examined in these experiments. These results indicate that chronic exposure of mice to chemical carcinogens induces chromosome breakage measurable by micronuclei. However, the breakage and reunion necessary to see chromosome exchanges such as translocations were not observed in this study.

The accumulation of chromosome aberrations and Dlb-1 mutations in mice with highly fractionated exposure to gamma radiation.

The dichotomy between the doses at which experimental measurements of genetic effects can be made and the doses to which people are exposed is often different by two or more orders of magnitude. This presents a significant problem when determining the effects of low doses of radiation or chemicals. The solution has usually involved extrapolating the data by curve-fitting or by applying theoretical considerations. Both approaches are unsatisfactory due to uncertainties of the assumptions used in each process. The alternative solution has been to increase the sample size enormously at the lower doses. This is impractical beyond a certain point due to the variation in the spontaneous frequency and the need to quadruple the sample size for a doubling of precision. The development of new methods for measuring stable genetic effects, however, permits a simple and effective approach to this problem: if the genetic events being detected have no effect on survival, i.e., are selectively neutral, then the effects of multiple independent treatments will be additive. If the independent treatments are identical, then the effect of each is easily calculated by dividing the total effect by the number of treatments. Here we report a limited test of this approach using mice. Chromosome aberrations induced in lymphocytes and Dlb-1 mutations induced in the small intestine were measured after daily doses of 0.64, 1.85 or 5.5 cGy 137Cs gamma rays administered for 21, 42 or 63 days. The dose response curve for chromosome translocations obtained in this way, combined with the data from single larger acute doses, shows no evidence for a threshold over a 500-fold dose range. Dlb-1 mutations were increased at each dose and time but the results do not permit reliable extrapolations. The results suggest that translocations might be useful for quantifying the effect of doses below 0.05 cGy and that the effect of dose rate and dose fractionation at much lower doses than reported here could be investigated.

Chromosome aberrations induced in mice by chronic feeding of 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ).

Dietary intake of mutagenic compounds is considered to be an important factor for the induction of some human cancers. Highly mutagenic compounds are known to be formed in meat during the cooking process. Since the discovery of such compounds, many studies have been conducted to evaluate their carcinogenic potential. One of the most mutagenic compounds formed in the cooking of meat is 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ). The recent development of mouse chromosome painting probes expand the capability of evaluating these food mutagens as potential clastogens in vivo. In this paper, we demonstrate the induction of chromosome aberrations in mice chronically exposed to MeIQ in their diet. CDF1 female mice were fed 400 ppm MeIQ beginning at 7 wk of age. At 76 wk of age, five control and eight exposed mice were euthanized. Blood and bone marrow cells were obtained and arrested in metaphase. Whole chromosome painting probes were used for fluorescence in situ hybridization of metaphase cells from blood and bone marrow. MeIQ-exposed mice were found to have a twofold increase in translocations and a 16-fold increase in fragments in their peripheral blood compared with controls. No aberrations were observed in the bone marrow. All organs were examined for the presence of tumours and routine histopathological analysis was performed on all organs as well as any tissue with macroscopic abnormalities. Forestomach and/or liver tumours developed in all but one of the mice fed MeIQ, but no such tumours were observed in the control mice. These data indicate that MeIQ is clastogenic and carcinogenic in vivo.

Persistence of radiation-induced translocations in human peripheral blood determined by chromosome painting.

We have investigated the persistence of translocations and other types of chromosome damage with time using human peripheral blood acutely exposed in vitro to 137Cs gamma rays at doses ranging from 0.5 to 4 Gy. Freshly drawn blood from one donor was irradiated and metaphase chromosomes were prepared 2 to 7 days after exposure. Chromosomes 1, 2 and 4 were painted red-orange and chromosomes 3, 5 and 6 were painted green by fluorescence in situ hybridization (FISH) using "semi-directly" labeled whole-chromosome painting probes. This type of labeling combines direct and indirect labeling and showed significant advantages over both these other methods. All types of structural chromosome aberrations were classified by the Protocol for Aberration Identification and Nomenclature Terminology (PAINT) system. The yields of dicentric chromosomes, acentric fragments and ring chromosomes diminished with time as expected. Translocations exhibited greater persistence but showed a clear and statistically significant reduction in frequency at all doses. The mathematical model suggested that the translocation frequencies would reach a plateau of approximately 4, 15, 51, 106 and 179 translocations per 100 cell equivalents after irradiation with 0.5, 1, 2, 3 and 4 Gy, respectively. When translocations were classified by the conventional system, an analysis of the distribution of translocations and dicentrics per cell indicated that both types of exchanges were Poisson-distributed 48 h postirradiation. However, cells bearing translocations have a higher possibility of having dicentrics than cells without translocations. These findings suggest that dicentrics may contribute to a decline of translocation frequencies with time, and that some translocations are not completely persistent. The results obtained here using human blood exposed in vitro may influence the use of translocations as a retrospective biodosimeter of exposure to ionizing radiation in humans.

Molecular analysis of ERCC2 mutations in the repair deficient hamster mutants UVL-1 and V-H1.

The cDNA sequence of the Chinese hamster ERCC2 nucleotide excision repair and transcription gene from the UVL-1 Chinese hamster ovary (CHO) mutant cell line and the V-H1 Chinese hamster V79 mutant line was analyzed. ERCC2 encodes a presumed ATP-dependent DNA helicase and is single copy in CHO lines due to the structural hemizygosity of chromosome 9. Both UVL-1 and V-H1 have intermediate levels of (6-4) photoproduct repair but are as highly UV sensitive as the group 2 mutants that have no detectable repair. Deficiency in cyclobutane dimer removal has also been shown for V-H1. In UVL-1, a single base substitution resulting in an Arg75-->Trp substitution in helicase domain Ia was identified. The equivalent amino acid position is also Arg in the human, mouse, Xiphophorus maculatus, Saccharomyces cerevisiae, and Schizosaccharomyces pombe homologs. In V-H1, a single base substitution resulting in a Thr46-->Ile substitution in helicase domain I (the ATP-binding domain) was identified in both alleles. The equivalent amino acid position is also Thr in the five homologs. Analysis of three V-H1 partial revertants revealed that they still have the original V-H1 mutation in both alleles, indicating that these are second site reversion events. Site-specific mutagenesis was used to introduce the Thr46-->Ile, Arg75-->Trp, and Lys48-->Arg (helicase domain I) mutations into a hamster ERCC2 expression plasmid. These plasmids each failed to confer UV resistance to group 2 mutant cells, further demonstrating that the changes identified are the causative mutations in V-H1 and UVL-1. Correlations between specific mutations, biochemical activities, and repair phenotype are discussed.

Biological dosimetry of radiation workers at the Sellafield nuclear facility.

The British Nuclear Fuels plc facility at Sellafield performs a range of nuclear-related activities. The site has been in operation since 1950 and has, in general, employed a stable work force, many of whom have accumulated relatively high occupational exposures to ionizing radiation. This paper compares the physical dosimetry with two biological end points for evaluating radiation exposure: fluorescence in situ hybridization with whole-chromosome painting probes to quantify stable chromosome aberrations (translocations and insertions), and glycophorin A (GPA) analysis of variant erythrocytes. For the cytogenetic analyses, 81 workers were evaluated in five dose categories, including 23 with minimal radiation exposure (< or = 50 mSv) and 58 with exposures ranging from 173 to 1108 mSv, all but 3 being > 500 mSv. In a univariate analysis, the mean stable chromosome aberration frequencies showed a significant increase with dose category (P = 0.032), and with cumulative dose when dose is treated as a continuous variable (P = 0.015). The slope of the dose response for stable aberrations is 0.79 +/- 0.22 aberrations per 100 cells per sievert (adjusted for smoking status), which is less than that observed among atomic bomb survivors, and suggests a dose and dose-rate effectiveness factor for chronic exposure of about 6. Analyses of the data for GPA N/O and N/N variants from 36 workers revealed no correlation with dose. Neither was there a correlation between the frequencies of N/O GPA variants and stable aberrations, although a weak negative association was observed between N/N variant frequency and stable aberrations (r = -0.38, P = 0.05). These results provide clear evidence for the accumulation of stable aberrations under conditions of chronic occupational exposure to ionizing radiation and show that stable chromosome aberrations are a more sensitive indicator for chronic radiation exposure than GPA variants. In comparison with human studies of brief exposure, chronic low-dose exposures appear substantially less effective for producing somatic effects as reflected by stable chromosome aberrations.

The persistence of aberrations in mice induced by gamma radiation as measured by chromosome painting.

Fluorescence in situ hybridization, or chromosome painting, has become an invaluable tool in the cytogenetic evaluation of historical or chronic exposure because it can be used to detect stable genetic damage, such as translocations, which persist through cell division, quickly and easily. The recent development of chromosome-specific composite DNA probes for the mouse has allowed the use of chromosome painting in this commonly used animal model. In order to measure the persistence of radiation-induced translocations, C57BL/6 female mice were given a whole body acute dose of 0, 1, 2, 3 or 4 Gy 137Cs gamma rays at 8 weeks of age. Metaphase chromosomes from both peripheral blood and bone marrow cells were obtained from four mice in each dose group at 1, 8, 15 and 30 days post-irradiation. Chromosomes 2 and 8 were painted, while the remaining chromosomes were counterstained with propidium iodide. DAPI counterstain was used to differentiate between translocations and dicentrics because it brightly labels the centromeric heterochromatin. The equivalent of 100 cells from each tissue was scored from each mouse. The results show that the percentage of reciprocal translocations, at least at doses of 3 Gy or lower, did not decrease with time in either tissue. In contrast, the frequency of non-reciprocal translocations induced by doses of 3 Gy or lower, remained unchanged in the peripheral blood, but decreased after a week in the bone marrow, then remained constant. An increase in these two types of aberration was observed between 15 and 30 days in the bone marrow and may have been due to clonal expansion. Dicentrics decreased with time in both tissues, almost none remained in the bone marrow after 8 days. These data suggest that reciprocal translocations are persistent and will serve as an effective biodosimeter for radiation exposure.

Cytogenetic results from a chronic feeding study of MeIQx in mice.

The primary food mutagens found in cooked meat are the heterocyclic aromatic amines, including 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx). High dose, acute exposures of MeIQx produce hepatic tumours in some mouse and rat strains. By assaying chromosome damage it may be possible to correlate aberrations with exposure to a mutagen. Whole chromosome painting by fluorescence in situ hybridization allows the rapid screening of metaphase chromosomes for rearrangements. This technique was applied to female mice (C57BL/6) chronically fed 100-400 ppms MeIQx for up to 6 months. Two tissues, blood and bone marrow, were screened with multicolour whole chromosome painting probes (1,2,3 and 8). The mice showed no outward signs of toxicity at any dose and very few chromosome aberrations were observed. A slight but significant increase in sister chromatid exchanges (SCE) was seen at 400 ppm in blood at 6 months. When MeIQx was removed from the diet for 1 month there was an apparent decline in SCEs only for animals previously given the 400 ppm diet.

Cytogenetic analysis of mice chronically fed the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5b]pyridine.

The cytogenetic effects in mice chronically fed the heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5b]pyridine (PhIP) were evaluated by chromosome painting, micronucleated normochromatic erythrocytes (MN NCEs) and sister chromatid exchanges (SCEs). PhIP and numerous other heterocyclic amines have been isolated from cooked foods, and many have been found to be carcinogenic in laboratory rodents. Female C57BL/6N mice were chronically fed a diet containing 0, 100, 250 or 400 ppm of PhIP beginning at 8 weeks of age. Peripheral blood and bone marrow were taken from 5 mice per treatment group at 1, 4 and 6 months from the start of exposure. PhIP was removed from the diet for a final month of the experiment, at which time blood was taken from the remaining animals. Chromosome-specific composite DNA probes for mouse chromosomes 2 and 8 were hybridized to metaphase cells from each tissue. The 1- and 4-month time points showed no statistically significant difference between the control and exposed mice for either tissue in chromosome aberration frequencies. Both MN NCEs and SCEs were analyzed at a single time point during exposure (4 months for MN NCEs and 6 months for SCEs) and again 1 month after removing PhIP from the diet. MN NCEs in the peripheral blood showed a statistically significant dose response, with all values decreasing significantly 1 month after removing PhIP from the diet. SCE frequencies in the peripheral blood showed an approximate doubling compared to control mice, and decreased to control levels 1 month after removing PhIP from the diet. SCE frequencies in the bone marrow of exposed mice showed no difference from the control animals. These results show that chronic ingestion of PhIP by female C57BL/6 mice does not produce persistent cytogenetic damage as visualized by chromosome aberrations, MN NCEs or SCEs.

The effects of age and lifestyle factors on the accumulation of cytogenetic damage as measured by chromosome painting.

Individual responses to the aging process are variable and are affected by genetic as well as environmental factors. Fluorescent in situ hybridization with whole chromosome probes ('chromosome painting') provides an efficient approach for detecting structural chromosome aberrations in human lymphocytes. This rapid and sensitive technique is an effective tool for quantifying chronic exposure to environmental agents which may result in an accumulation of cytogenetic damage with age. We have applied this technology to a normal, putatively unexposed, population to document the relationship between age and the accumulation of cytogenetic damage, as well as to establish a baseline frequency of stable aberrations. Using probes for chromosomes 1, 2 and 4 simultaneously, the equivalent of 1000 metaphases was scored for stable and unstable aberrations from each of 91 subjects ranging in age from newborns (umbilical cord bloods; n = 14) to adults aged 19 to 79 years. Each subject (or one parent of each newborn) completed an extensive questionnaire to identify possible lifestyle factors that may influence the frequency of cytogenetic damage. Our findings show a significant increase in stable aberrations (translocations and insertions) with age (p < 0.0001). We also observed age-related increases with dicentrics (p < 0.0001) and acentric fragments (p < 0.0001). Relative to the frequencies observed in cord bloods, the frequencies of stable aberrations, dicentrics, and acentric fragments in adults aged 50 and over were elevated 10.6-fold, 3.3-fold, and 2.9-fold, respectively. Nine variables other than age are significantly associated with the frequency of stable aberrations; these are: smoking (two variables), consumption of diet drinks and/or diet sweeteners (4 variables), exposure to asbestos or coal products (1 variable each), and having a previous major illness (1 variable). Newborns whose mothers smoked during pregnancy had a 1.5-fold increase in stable aberrations (p = 0.029). Repeat samples from a subset of the adults indicate that for most subjects there is little change in individual translocation frequencies over a period of two to three years. These results support the hypothesis that stable chromosome aberrations show a greater accumulation with age than do unstable aberrations and suggest that lifestyle factors contribute to the accumulation of cytogenetic damage.

Otoacoustic emissions: an emerging diagnostic tool.

Otoacoustic emissions are acoustic signals detectable in the external auditory canal that reflect the state of health of the cochlea. Transiently-evoked otoacoustic emissions and distortion-project otoacoustic emissions are two types of otoacoustic emissions currently under investigation as well as in limited clinical use. These objective tests of cochlear function add significantly to the armamentarium currently in place for the evaluation of hearing. The clinical use of these diagnostic tools will likely increase dramatically in the coming years. The following review provides a basis for understanding the nature and clinical utility of otoacoustic emissions.