International Commission for Protection Against Environmental Mutagens and Carcinogens. Working paper no. 3. Somatic mutant frequency, mutation rates and mutational spectra in the human population in vivo

Cancer incidence trends in New York State and associations with common population-level exposures 2010-2018: an ecological study

The impact of common environmental exposures in combinations with socioeconomic and lifestyle factors on cancer development, particularly for young adults, remains understudied. Here, we leveraged environmental and cancer incidence data collected in New York State at the county level to examine the association between 31 exposures and 10 common cancers (i.e., lung and bronchus, thyroid, colorectal, kidney and renal pelvis, melanoma, non-Hodgkin lymphoma, and leukemia for both sexes; corpus uteri and female breast cancer; prostate cancer), for three age groups (25-49, 50-69, and 70-84 year-olds). For each cancer, we stratified by age group and sex, and applied regression models to examine the associations with multiple exposures simultaneously. The models included 642,013 incident cancer cases during 2010-2018 and found risk factors consistent with previous reports (e.g., smoking and physical inactivity). Models also found positive associations between ambient air pollutants (ozone and PM2.5) and prostate cancer, female breast cancer, and melanoma of the skin across multiple population strata. Additionally, the models were able to better explain the variation in cancer incidence data among 25-49 year-olds than the two older age groups. These findings support the impact of common environmental exposures on cancer development, particularly for younger age groups.

Molecular characterization of hypoxanthine guanine phosphoribosyltransferase mutant T cells in human blood: The concept of surrogate selection for immunologically relevant cells

Somatic cell gene mutations arise in vivo due to replication errors during DNA synthesis occurring spontaneously during normal DNA synthesis or as a result of replication on a DNA template damaged by endogenous or exogenous mutagens. In principle, changes in the frequencies of mutant cells in vivo in humans reflect changes in exposures to exogenous or endogenous DNA damaging insults, other factors being equal. It is becoming increasingly evident however, that somatic mutations in humans have a far greater range of interpretations. For example, mutations in lymphocytes provide invaluable probes for in vivo cellular and molecular processes, providing identification of clonal amplifications of these cells in autoimmune and infectious diseases, transplantation recipients, paroxysmal nocturnal hemoglobinuria (PNH), and cancer. The assay for mutations of the X-chromosomal hypoxanthine guanine phosphoribosyltransferase (HPRT) gene has gained popular acceptance for this purpose since viable mutant cells can be recovered for molecular and other analyses. Although the major application of the HPRT T cell assay remains human population monitoring, the enrichment of activated T cells in the mutant fraction in individuals with ongoing immunological processes has demonstrated the utility of surrogate selection, a method that uses somatic mutation as a surrogate marker for the in vivo T cell proliferation that underlies immunological processes to investigate clinical disorders with immunological features. Studies encompassing a wide range of clinical conditions are reviewed. Despite the historical importance of the HPRT mutation system in validating surrogate selection, there are now additional mutational and other methods for identifying immunologically active T cells. These methods are reviewed and provide insights for strategies to extend surrogate selection in future studies.

Characterization of integration frequency and insertion sites of adenovirus DNA into mouse liver genomic DNA following intravenous injection

While generally referred to as "non-integrating" vectors, adenovirus vectors have the potential to integrate into host DNA via random, illegitimate (nonhomologous) recombination. The present study provides a quantitative assessment of the potential integration frequency of adenovirus 5 (Ad5)-based vectors following intravenous injection in mice, a common route of administration in gene therapy applications particularly for transgene expression in liver. We examined the uptake level and persistence in liver of first generation (FG) and helper-dependent (HD) Ad5 vectors containing the mouse leptin transgene. As expected, the persistence of the HD vector was markedly higher than that of the FG vector. For both vectors, the majority of the vector DNA remained extrachromosomal and predominantly in the form of episomal monomers. However, using a quantitative gel-purification-based integration assay, a portion of the detectable vector was found to be associated with high molecular weight (HMW) genomic DNA, indicating potential integration with a frequency of up to ~44 and 7000 integration events per μg cellular genomic DNA (or ~0.0003 and 0.05 integrations per cell, respectively) for the FG and HD Ad5 vectors, respectively, following intravenous injection of 1 × 10¹¹ virus particles. To confirm integration occurred (versus residual episomal vector DNA co-purifying with genomic DNA), we characterized nine independent integration events using Repeat-Anchored Integration Capture (RAIC) PCR. Sequencing of the insertion sites suggests that both of the vectors integrate randomly, but within short segments of homology between the vector breakpoint and the insertion site. Eight of the nine integrations were in intergenic DNA and one was within an intron. These findings represent the first quantitative assessment and characterization of Ad5 vector integration following intravenous administration in vivo in wild-type mice.

Mutagenicity monitoring in humans: Global versus specific origin of mutations

An underappreciated aspect of human mutagenicity biomonitoring is tissue specificity reflected in different assays, especially those that measure events that can only occur in developing bone marrow (BM) cells. Reviewed here are 9 currently-employed human mutagenicity biomonitoring assays. Several assays measure chromosome-level events in circulating T-lymphocytes (T-cells), i.e., traditional analyses of aberrations, translocation studies involving chromosome painting and fluorescence in situ hybridization (FISH) and determinations of micronuclei (MN). Other T-cell assays measure gene mutations. i.e., hypoxanthine-guanine phosphoriboslytransferase (HPRT) and phosphoribosylinositol glycan class A (PIGA). In addition to the T-cell assays, also reviewed are those assays that measure events in peripheral blood cells that necessarily arose in BM cells, i.e., MN in reticulocytes; glycophorin A (GPA) gene mutations in red blood cells (RBCs), and PIGA gene mutations in RBC or granulocytes. This review considers only cell culture- or cytometry-based assays to describe endpoints measured, methods, optimal sampling times, and sample summaries of typical quantitative and qualitative results. However, to achieve its intended focus on the target cells where events occur, kinetics of the cells of peripheral blood that derive at some point from precursor cells are reviewed to identify body sites and tissues where the genotoxic events originate. Kinetics indicate that in normal adults, measured events in T-cells afford global assessments of in vivo mutagenicity but are not specific for BM effects. Therefore, an agent's capacity for inducing mutations in BM cells cannot be reliably inferred from T-cell assays as the magnitude of effect in BM, if any, is unknown. By contrast, chromosome or gene level mutations measured in RBCs/reticulocytes or granulocytes must originate in BM cells, i.e. in RBC or granulocyte precursors, thereby making them specific indicators for effects in BM. Assays of mutations arising directly in BM cells may quantitatively reflect the mutagenicity of potential leukemogenic agents.

PIG-A gene mutation as a genotoxicity biomarker in human population studies: An investigation in lead-exposed workers

The rodent Pig-a gene mutation assay has demonstrated remarkable sensitivity in identifying in vivo mutagens, while much less is known about the value of the human PIG-A assay for risk assessment. To obtain more evidence of its potential as a predictive biomarker for carcinogen exposure, we investigated PIG-A mutant frequencies (MFs), along with performing the Comet assay and micronucleus (MN) test, in 267 workers occupationally exposed to lead. Multivariate Poisson regression showed that total red blood cell PIG-A MFs were significantly higher in lead-exposed workers (10.90 ± 10.7 × 10^-6 ) than in a general population that we studied previously (5.25 ± 3.6 × 10^-6 ) (p < .0001). In contrast, there was no increase in lymphocyte MN frequency or in DNA damage as measured by percentage comet tail intensity in whole blood cells. Current year worker blood lead levels (BLL), an exposure biomarker, were elevated (232.6 ± 104.6 μg/L, median: 225.4 μg/L); a cumulative blood lead index (CBLI) also was calculated based on a combination of current and historical worker BLL data. Chi-square testing indicated that PIG-A MFs were significantly related to CBLI (p = .0249), but independent of current year BLL (p = .4276). However, % comet tail intensity and MN frequencies were better associated with current year BLL than CBLI. This study indicates that the PIG-A assay could serve as biomarker to detect the genotoxic effects of lead exposure and demonstrates that a battery of genotoxicity biomarkers having mechanistic complementarity may be useful for comprehensively monitoring human carcinogenic risk.

Exploring Genetic Outcomes as Frailty Biomarkers

Frailty has emerged as a reliable measure of the aging process. Because the early detection of frailty is crucial to prevent or even revert it, the use of biomarkers would allow an earlier and more objective identification of frail individuals. To improve the understanding of the biological features associated with frailty as well as to explore different biomarkers for its early identification, several genetic outcomes-mutagenicity, different types of genetic damage, and cellular repair capacity-were analyzed in a population of older adults classified into frail, prefrail, and nonfrail. Besides, influence of clinical parameters-nutritional status and cognitive status-was evaluated. No association of mutation rate or primary DNA damage with frailty was observed. However, DNA repair capacity showed a nonsignificant tendency to decrease with frailty, and persistent levels of phosphorylated H2AX, as indicative of DNA breakage, increased progressively with frailty severity. These results support the possible use of H2AX phosphorylation to provide information regarding frailty severity. Further investigation is necessary to determine the consistency of the current findings in different populations and larger sample sizes, to eventually standardize biomarkers to be used in clinics, and to fully understand the influence of cognitive impairment.

Cell division rates decrease with age, providing a potential explanation for the age-dependent deceleration in cancer incidence

A new evaluation of previously published data suggested to us that the accumulation of mutations might slow, rather than increase, as individuals age. To explain this unexpected finding, we hypothesized that normal stem cell division rates might decrease as we age. To test this hypothesis, we evaluated cell division rates in the epithelium of human colonic, duodenal, esophageal, and posterior ethmoid sinonasal tissues. In all 4 tissues, there was a significant decrease in cell division rates with age. In contrast, cell division rates did not decrease in the colon of aged mice, and only small decreases were observed in their small intestine or esophagus. These results have important implications for understanding the relationship between normal stem cells, aging, and cancer. Moreover, they provide a plausible explanation for the enigmatic age-dependent deceleration in cancer incidence in very old humans but not in mice.

A population study using the human erythrocyte PIG-A assay

Erythrocyte-based PIG-A assay is sensitive and reliable in detecting exposure to mutagenetic agents in animal studies, but there are few data from human populations. In this study, we employed a method for detecting CD59 phenotypic variants, resulting from mutation in the PIG-A gene, in human red blood cells (RBCs), and determined the CD59-deficient RBC (RBC^CD59- ) frequencies in 217 subjects from general population. The majority of subjects had a relatively low mutant frequencies (MFs) (average, 5.25 ± 3.6 × 10^-6 , median, 4.38 × 10^-6 , for all subjects), but with males having a significantly greater MFs (5.97 ± 4.0 × 10^-6 ) than females (4.19 ± 2.5 ×10^-6 ). There was no correlation between MFs and age. In addition, MFs showed no difference between smoker and nonsmoker, and also no association with smoke duration in male subjects. However, there was a significant correlation between cigarette-pack-years which indicated that the MF was only slightly elevated with the increase of cigarette-pack-years. Moreover, intraindividual variations were investigated in three volunteer subjects over 300 days, and the MFs were relatively stable and repeatable. Furthermore, a pilot study by using white blood cell (WBC) assay based on labeling with FLAER was performed in volunteer subjects. The MFs of FLAER-deficient WBC (WBC^FLAER- ) and RBC^CD59- were consistently elevated in two subjects. Our findings provide baseline data that will be helpful in designing further studies using the PIG-A assay to monitor the genotoxic effects of carcinogens in human populations. Environ. Mol. Mutagen. 57:589-604, 2016. © 2016 Wiley Periodicals, Inc.

Genome-wide quantification of rare somatic mutations in normal human tissues using massively parallel sequencing

We present the bottleneck sequencing system (BotSeqS), a next-generation sequencing method that simultaneously quantifies rare somatic point mutations across the mitochondrial and nuclear genomes. BotSeqS combines molecular barcoding with a simple dilution step immediately before library amplification. We use BotSeqS to show age- and tissue-dependent accumulations of rare mutations and demonstrate that somatic mutational burden in normal human tissues can vary by several orders of magnitude, depending on biologic and environmental factors. We further show major differences between the mutational patterns of the mitochondrial and nuclear genomes in normal tissues. Lastly, the mutation spectra of normal tissues were different from each other, but similar to those of the cancers that arose in them. This technology can provide insights into the number and nature of genetic alterations in normal tissues and can be used to address a variety of fundamental questions about the genomes of diseased tissues.

Jaundice, phototherapy and DNA damage in full-term neonates

OBJECTIVE

Phototherapy is the standard therapeutic approach for neonatal hyperbilirubinemia. Oxidative effects of phototherapy may have potential harms, including DNA damage. Unconjugated bilirubin (UCB) might also possess antigenotoxic potential. Intensive phototherapy is more efficacious than conventional phototherapy in treating hyperbilirubinemia. This study aimed to assess the impact of hyperbilirubinemia and the two different types of phototherapy on DNA damage in peripheral blood mononuclear cells of neonates.

STUDY DESIGN

The study was conducted on term neonates with non-hemolytic hyperbilirubinemia and control healthy neonates. Genotoxicity was assessed using single-cell gel electrophoresis (Comet assay) in peripheral mononuclear cells. Blood samples were obtained at enrollment in all infants and after intensive or conventional phototherapy in jaundiced infants.

RESULT

DNA damage did not significantly differ between jaundiced and non-jaundiced neonates (11.4±8.7 and 10.9±8.3 arbitrary units (AU), respectively, P=0.58). It increased significantly after exposure to phototherapy compared with prephototherapy values (45.6±14.7 vs 11.4±8.7 AU, respectively, P<0.001). The duration of phototherapy correlated positively with markers of DNA damage (r=0.86, P<0.001); however, the intensity of used light did not significantly impact genotoxicity.

CONCLUSION

Hyperbilirubinemia does not influence DNA damage, whereas both conventional and intensive phototherapy are associated with DNA damage in term infants with hyperbilirubinemia.

Increased DNA damage and oxidative stress among silver jewelry workers

Silver has long been valued as a precious metal, and it is used to make ornaments, jewelry, high-value tableware, utensils, and currency coins. Human exposures to silver and silver compounds can occur oral, dermal, or by inhalation. In this study, we investigated genotoxic and oxidative effects of silver exposure among silver jewelry workers. DNA damage in peripheral mononuclear leukocytes was measured by using the comet assay. Serum total antioxidative status (TAS), total oxidative status (TOS), total thiol contents, and ceruloplasmin levels were measured by using colorimetric methods among silver jewelry workers. Moreover, oxidative stress index (OSI) was calculated. Results were compared with non-exposed healthy subjects. The mean values of mononuclear leukocyte DNA damage were significantly higher than control subjects (p < 0.001). Serum TOS, OSI, and ceruloplasmin levels were also found to be higher in silver particles exposed group than those of non-exposed group (p < 0.001, p < 0.001, p < 0.01, respectively). However, serum TAS levels and total thiol contents of silver exposed group were found significantly lower (p < 0.05, p < 0.001, respectively). Exposure to silver particles among silver jewelry workers caused oxidative stress and accumulation of severe DNA damage.

Influence of hyperbilirubinemia and phototherapy on markers of genotoxicity and apoptosis in full-term infants

Concerns of possible genotoxic effects of hyperbilirubinemia and phototherapy were raised from experimental and observational studies in neonates. This study aimed to assess the impact of hyperbilirubinemia and phototherapy on DNA damage and apoptosis in peripheral blood lymphocytes in healthy full-term infants. This study was conducted in the Children's Hospital, Mansoura University. Patients enrolled in this study were classified into three groups (each with 45 full-term infants): group 1 was composed of infants with hyperbilirubinemia requiring phototherapy, group 2 infants with physiological jaundice not requiring phototherapy, and group 3 infants without clinical jaundice. All enrolled infants were subjected to assessment of DNA damage and apoptosis in peripheral blood lymphocytes, using the comet assay and P53 by flow cytometry, consecutively. In group 1, measurements were done twice, before starting phototherapy and just before its discontinuation. DNA damage was not significantly different in the three groups, but it significantly increased after exposure to phototherapy compared to pre-phototherapy levels. There was no significant difference in P53 level in the three groups; however, it significantly increased after exposure to phototherapy. There were significant positive correlations between the duration of phototherapy and markers of DNA damage and apoptosis.

CONCLUSIONS

Hyperbilirubinemia does not influence DNA damage and apoptosis, whereas phototherapy causes DNA damage and induces apoptosis in peripheral blood lymphocytes of full-term infants.

Flow cytometric quantification of mutant T cells with altered expression of the T-cell receptor: detecting somatic mutants in humans and mice

Spontaneously generated mutant T cells defective in T-cell receptor (TCR) gene expression are detectable at the frequency of 2×10(-4) in vivo, and the mutant fractions are dose dependently increased by exposure to genotoxic agents such as ionizing radiation. Mutant cells with altered expression of TCRα or -β among CD4(+) T cells can be detected as CD3(-)/CD4(+) cells by two-color flow cytometry using anti-CD3 and anti-CD4 monoclonal antibodies labeled with different fluorescent dyes, because incomplete TCRαβ/CD3 complexes cannot be transported to the cellular membrane. This flow cytometric mutation assay can be applied to CD4(+) T cells from human peripheral blood and mouse spleen. Methods for both preparation of target cells and detection of the mutant cells are described.

Measuring genome instability in aging - a mini-review

BACKGROUND

There is mounting evidence for an age-dependent accumulation of somatic mutations as a result of the inherent imperfection of DNA replication and repair. A possible age-related decline in genome maintenance systems may exacerbate this age-related loss of genome integrity. A review of the current methods of mutation detection is timely in view of the lack of insight as to the magnitude of somatic mutation accumulation, the types of mutations that accumulate, and their functional consequences.

OBJECTIVE

In this paper we review the current methods for measuring genome instability in organisms during aging or in relation to life span.

METHODS

The review is based on established and novel concepts from the existing literature, with some examples from our own laboratory.

RESULTS

Studies using cytogenetic assays and endogenous or transgenic mutation reporter assays provide strong evidence for age-related increases of different types of mutations in animals and humans during aging. This increase in DNA mutations is tissue-specific and also differs between species.

CONCLUSION

Today, our knowledge of somatic mutation profiles in aging is mainly derived from cytogenetics and the use of endogenous and transgenic mutation reporter assays. The emergence of new approaches, most notably massively parallel sequencing, will give us deeper insight into the nature of spontaneous genome instability and its possible causal relationship to aging and age-related disease.

Oxidation of 8-oxo-7,8-dihydro-2'-deoxyguanosine by oxyl radicals produced by photolysis of azo compounds

Oxidative damage to 8-oxo-7,8-dihydroguanine (8-oxoG) bases initiated by photolysis of the water-soluble radical generator 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) has been investigated by laser kinetic spectroscopy. In neutral oxygenated aqueous solutions, 355 nm photolysis of AAPH initiates efficient one-electron oxidation of the 8-oxodG nucleosides directly monitored by the appearance of the 8-oxodG(*+)/8-oxodG(-H)* radicals at 325 nm. The reaction kinetics consist of a mechanism that includes the transformation of the 2-amidinoprop-2-peroxyl radicals (ROO*) derived from photolysis of AAPH to more reactive 2-amidinoprop-2-oxyl radicals (RO*), which directly react with the 8-oxoG bases. The major pathways for the formation of end products of 8-oxoG oxidation include the combination of the 8-oxodG(*+)/8-oxodG(-H)* radicals with superoxide (O(2)(*-)) and ROO* radicals in approximately 1:1 ratios, as demonstrated by experiments with Cu,Zn superoxide dismutase, to form dehydroguanidinohydantoin (Gh(ox)) derivatives. This mechanism was confirmed by analysis of the end products produced by the oxidation of two substrates: (1) the 8-oxoG derivative 2',3',5'-tri-O-acetyl-7,8-dihydroguanosine (tri-O-Ac-8-oxoG) and (2) the 5'-d(CCATC[8-oxoG]CTACC) sequence. The major products isolated by HPLC and identified by mass spectrometry methods were the tri-O-Ac-Gh(ox) and 5'-d(CCATC[Gh(ox)]CTACC products.

Increased DNA damage and oxidative stress in chickens with natural Marek's disease

Oxidative stress contributes to the accumulation of genomic abnormalities, prevents cellular apoptosis, and also mediates immunosuppression resulting in tumor formation. Marek's Disease provides excellent opportunities for the study of herpesvirus-induced tumors both in experimental- and natural conditions. The aim of this study was to examine the effects of Marek's Disease (MD) on basal levels of DNA strand breaks and on the oxidative-antioxidative status of chickens with MD. White-Lohmann hens-fifteen infected with Marek's Disease Virus (MDV) and fifteen healthy-of same age and sex were included in this study. MD infection was diagnosed via clinical signs, gross- and micro-pathological findings and also by detection of viral antigens in feather follicle epithelium by the indirect immunoperoxidase method. Compared with healthy controls, DNA damage was greater and levels of malondialdehyde (MDA) and plasma protein carbonyl (PCO), and plasma concentration of nitric oxide metabolites (NOx) higher in the MD group. Furthermore, total antioxidant activities (AOAs) were found lowered and glutathione (GSH) levels reduced in the MD group compared to the control group. Significantly positive correlation was found between DNA damage, MDA, PCO, and NOx in the MD group. DNA strand breaks were found negatively associated with AOA and GSH concentrations in the MD group. Our results demonstrated that oxidative stress markers and DNA damage substantially increased in chickens with MD, which indicated that increased DNA damage levels might be related to the increased oxidative stress and reduced antioxidant activity.

Styrene Metabolism, Genotoxicity, and Potential Carcinogenicity

This report reviews styrene biotransformation, including minor metabolic routes, and relates metabolism to the genotoxic effects and possible styrene-related carcinogenicity. Styrene is shown to require metabolic activation in order to become notably genotoxic and styrene 7,8-oxide is shown to contribute quantitatively by far the most (in humans more than 95%) to the genotoxicity of styrene, while minor ring oxidation products are also shown to contribute to local toxicities, especially in the respiratory system. Individual susceptibility depending on metabolism polymorphisms and individual DNA repair capacity as well as the dependence of the nonlinearity of the dose-response relationships in the species in question and the consequences for risk evaluation are analyzd.

Studies of thioguanine-resistant lymphocytes induced by in vivo irradiation of mice

The frequency of Hprt-deficient lymphocytes in mice after in vivo gamma irradiation, has been found to vary as a function of time elapsed after exposure and irradiation dose. The frequency of mutant lymphocytes in spleen was determined using an in vitro, clonogenic assay for thioguanine-resistant T-lymphocytes. Mice were exposed to single doses of 0-400 cGy from cesium-137 or to eight daily doses of 50 cGy. The time to maximum-induced mutant frequency was 3 weeks. The dose response was strikingly curvilinear at 3-5 weeks after irradiation, but less precisely defined for 10-53 weeks after exposure, being fit by either linear or quadratic dependence. Three weeks after eight daily 50 cGy exposures, mutant frequency was elevated above controls and mice exposed to 50 cGy (which were not distinct from the nonirradiated controls), but only 17% in that of mice given a single 400 cGy fraction. This fractionation effect and the curvilinearity of the early dose-response curve suggested that saturation of repair increased the yield of mutations at higher acute doses. The decline of spleen mutant frequency in mice observed between 5 and 10 weeks after irradiation may reflect selection against some mutants. The marked variation of mutant frequency, as a function of time after irradiation and of dose rate, emphasize the need to evaluate these variables carefully and consistently in future studies.

Elevated levels of somatic mutation in a manifesting BRCA1 mutation carrier

Homozygous loss of activity at the breast cancerpredisposing genes BRCA1 and BRCA2 (FANCD1) confers increased susceptibility to DNA double strand breaks, but this genotype occurs only in the tumor itself, following loss of heterozygosity at one of these loci. Thus, if these genes play a role in tumor etiology as opposed to tumor progression, they must manifest a heterozygous phenotype at the cellular level. To investigate the potential consequences of somatic heterozygosity for a BRCA1 mutation demonstrably associated with breast carcinogenesis on background somatic mutational burden, we applied the two standard assays of in vivo human somatic mutation to blood samples from a manifesting carrier of the Q1200X mutation in BRCA1 whose tumor was uniquely ascertained through an MRI screening study. The patient had an allele-loss mutation frequency of 19.4 x 10(-6) at the autosomal GPA locus in erythrocytes and 17.1 x 10(-6) at the X-linked HPRT locus in lymphocytes. Both of these mutation frequencies are significantly higher than expected from age-matched disease-free controls (P < 0.05). Mutation at the HPRT locus was similarly elevated in lymphoblastoid cell lines established from three other BRCA1 mutation carriers with breast cancer. Our patient's GPA mutation frequency is below the level established for diagnosis of homozygous Fanconi anemia patients, but consistent with data from obligate heterozygotes. The increased HPRT mutation frequency is more reminiscent of data from patients with xeroderma pigmentosum, a disease characterized by UV sensitivity and deficiency in the nucleotide excision pathway of DNA repair. Therefore, this BRCA1-associated breast cancer patient manifests a unique phenotype of increased background mutagenesis that likely contributed to the development of her disease independent of loss of heterozygosity at the susceptibility locus.

The L84F polymorphism in the O6-Methylguanine-DNA-Methyltransferase (MGMT) gene is associated with increased hypoxanthine phosphoribosyltransferase (HPRT) mutant frequency in lymphocytes of tobacco smokers

OBJECTIVES

O-methylguanine-DNA-methyltransferase (MGMT) is a crucial DNA repair protein that removes DNA adducts formed by alkylating mutagens. Several coding single nucleotide polymorphisms (cSNPs) in the MGMT gene have been reported. Their biological significance, however, is not known.

METHODS

We used a newly modified cloning HPRT mutant lymphocyte assay to test the hypothesis that inheritance of the L84F and I143V coding single nucleotide polymorphism in the MGMT gene is associated with increases in HPRT mutant frequency in lymphocytes of individuals exposed to alkylating agents. In addition, we expanded and sequenced 109 mutant clones to test the hypothesis that the mutation spectrum would shift to a larger percentage of base substitutions and G-->A transition mutations in cells with L84F and I143 V coding single nucleotide polymorphisms.

RESULTS

We observed no significant effect for the I143 V coding single nucleotide polymorphism on mutant frequency. In contrast, we observed a significant increase in mutant frequency (P<0.01) in lymphocytes from smokers with the 84F coding single nucleotide polymorphism compared with smokers homozygous for the referent L84 wild-type allele. A multiple regression analysis indicated that the mutant frequency increased significantly as a function of the 84F coding single nucleotide polymorphism and smoking, according to the model; mutant frequency (x10)=0.90+0.618 (84F polymorphism)+0.46 (smoking) with R=0.22. Mutation spectra analysis revealed an apparent increase, which was short of statistical significance (P=0.08), in base substitutions in cells with the 84F polymorphism.

CONCLUSIONS

These new data suggest that the 84F coding single nucleotide polymorphism may alter the phenotype of the MGMT protein, resulting in suboptimal repair of O-methylguanine lesions after exposure to alkylating agents.

Mechanisms of Disease: hydrogen peroxide, DNA damage and mutagenesis in the development of thyroid tumors

Somatic mutations can be identified in two-thirds of papillary and follicular thyroid carcinomas and 'hot' thyroid nodules, whereas equivalent mutations relevant for benign 'cold' thyroid nodules are unknown. This Review summarizes current knowledge about early molecular conditions for nodular and tumor transformation in the thyroid gland. We reconstruct a line of events that could explain the predominant neoplastic character (i.e. originating from a single mutated cell) of thyroid nodular lesions. This process might be triggered by the oxidative nature of thyroid hormone synthesis or additional oxidative stress caused by iodine deficiency or smoking. If the antioxidant defense is not effective, this oxidative stress can cause DNA damage followed by an increase in the spontaneous mutation rate, which is a platform for tumor genesis. The hallmark of thyroid physiology--H2O2 production during hormone synthesis--is therefore very likely to be the ultimate cause of frequent mutagenesis in the thyroid gland. DNA damage and mutagenesis could provide the basis for the frequent nodular transformation of endemic goiters.

Parental age at delivery and incidence of breast cancer: a prospective cohort study

BACKGROUND

Studies on parental age at delivery in relation to breast cancer risk have had mixed results, but prospective data are limited. No study has explored the associations with subtypes of breast cancer defined by hormonal receptor status.

METHODS

109,773 women in the Nurses' Health Study were followed from 1976 to 2002. We used Cox proportional hazards model to examine the association between parental age at delivery and daughters' risk of breast cancer.

RESULTS

6,827 incident cases of invasive breast cancer occurred in this cohort during 2,581,098 person-years. Adjusting for other early life exposures and family history of breast cancer, the hazard ratio for breast cancer in women born to mothers aged 21-25, 26-30, 31-35, and > or =36 years was, respectively, 1.08 (95% CI: 0.99-1.18), 1.12 (95% CI: 1.03-1.23), 1.17 (95% CI: 1.06-1.29), and 1.12 (95% CI: 1.01-1.25), compared to women born to mothers aged < or =20 years (P for trend = 0.008). Similarly, advanced paternal age was associated with increased incidence of breast cancer (P for trend = 0.03), but the association disappeared when conditioning on maternal age. The positive association between maternal age and incidence of breast cancer was stronger for estrogen receptor-positive and progesterone receptor-positive tumors (P for trend = 0.003) than for tumors with both receptors negative (P for trend = 0.78), and was more consistent among postmenopausal women, women without a family history and women who were first born.

CONCLUSION

Our findings support a modest positive association between maternal age and daughter's risk of breast cancer, possibly mediated by hormonal factors.

Use of genotypic selection to detect P53 codon 273 CGT>CTT transversion: application to an occupationally exposed population

CGT>CTT transversion in codon 273 of the P53 tumor-suppressor gene is one of the major mutations detected in human tumors. Within an epidemiological framework, we investigated the use of a genotypic selection method to measure this point mutation. The allele-specific polymerase chain reaction (AS-PCR) that was developed was able to detect 10 mutant copies of the gene among a total of 5 x 10(5) wild-type copies. We used this assay to detect CGT>CTT transversions in buccal cell DNA of production workers (n=76) from a viscose factory exposed to carbon disulfide (amongst other pollutants) and in the DNA of non-exposed office workers (n=67). The mutation appeared more frequently in the exposed than in the non-exposed worker who were smokers. The results of the study indicate that occupational exposure results in a significant increase in P53 CGT>CTT transversions and more especially identified occupational exposure in combination with smoking as a significant risk factor for the mutation. We conclude that AS-PCR of the P53 273rd codon transversions is a suitable technique for studying the effects of occupational exposure.

Deoxyribonucleic acid damage and spontaneous mutagenesis in the thyroid gland of rats and mice

Thyroid tumors are a frequent finding not only in iodine-deficient regions. They are predominantly characterized by somatic genetic changes (e.g. point mutations or rearrangements). Because slow thyroid proliferation is a apparent contradiction to a high frequency of tumor initiation, we characterized mutational events in thyroid. First we studied the frequency of certain base exchanges in somatic TSH receptor (TSHR) mutations and determined the spontaneous mutation rate in thyroid and liver. Then we applied different protocols of the comet assay to quantify genomic DNA damage and conducted immunohistochemistry for 8-oxoguanine as a molecular marker for oxidative stress. Among 184 somatic mutations of the human TSHR found in thyroid tumors, C-->T transitions had a unexpectedly high frequency (>32%). The mutation rate in thyroid is 8-10 times higher than in other organs. The comet assay detected increased levels of oxidized pyrimidine (2- to 3-fold) and purine (2- to 4-fold) in thyroid, compared with liver and lung, and a 1.6-fold increase of oxidized purine, compared with spleen. Immunohistochemistry revealed high levels of 8-oxoguanine in thyroid epithelial cells. We have shown a strikingly high mutation rate in the thyroid. Furthermore, results of the comet assay as well as immunohistochemistry suggest that oxidative DNA modifications are a likely cause of the higher mutation rate. It is possible that free radicals resulting from reactive oxygen species in the thyroid generate mutations more frequently. This is also supported by the spectrum of somatic mutations in the TSHR because more frequent base changes could stem from oxidized base adducts that we detected in the comet assay and with immunohistochemistry.

The Delayed Manifestation of T-Cell Receptor (TCR) Variants in X-Irradiated Mice Depends onTrp53Status

The influence of Trp53 on the radiation-induced elevation of T-cell receptor (TCR) variant fractions was examined in splenic T lymphocytes of Trp53-proficient and -deficient mice. Wild-type Trp53+/+, heterozygous Trp53+/- and null Trp53-/- mice were exposed to 3 Gy of X rays at 8 weeks of age. The fraction of TCR-defective variants was measured at various times after irradiation. Initially, the TCR variant fraction increased rapidly and reached its maximum level at 9 days after irradiation before decreasing gradually. In Trp53+/+ and Trp53+/- mice, the TCR variant fraction fell to normal background levels at 16 and 20 weeks of age, respectively. In contrast, the TCR variant fraction of Trp53-/- mice failed to decrease to background levels during the observation period. Baseline levels were then maintained for approximately 60 weeks in the Trp53+/+ mice and approximately 40 weeks in the Trp53+/- mice. After the long flat period, a significant re-increase in the fraction of TCR variants was found after 72 weeks of age in the irradiated Trp53+/+ mice and after 44 weeks of age in the irradiated Trp53+/- mice. Measurement of the fraction of apoptotic cells in the spleen and thymus 4 h after X irradiation at these ages in Trp53+/+ and Trp53+/- mice demonstrated a reduction in apoptosis in the irradiated mice compared to the nonirradiated mice. This suggests that the delayed increase in TCR variants after irradiation is due to a reduction in Trp53-dependent apoptosis.

Depleted uranium exposure and health effects in Gulf War veterans

Health effects stemming from depleted uranium (DU) exposure in a cohort of Gulf War veterans who were in or on US Army vehicles hit by friendly fire involving DU munitions are being carefully monitored through the Baltimore Veterans Affairs (VA) DU Follow-Up Program initiated in 1993. DU exposure in this cohort has been directly measured using inductively coupled plasma-mass spectrometer (ICP-MS) isotopic analysis for DU in urine specimens. Soldiers with embedded DU fragments continue to excrete elevated concentrations of U in their urine, documenting ongoing systemic exposure to U released from their fragments. Biennial surveillance visits provide a detailed health assessment that includes basic clinical measures and surveillance for early changes in kidney function, an expected target organ for U. Tests also include measurements of genotoxicity and neuroendocrine, neurocognitive and reproductive function. With the exception of the elevated urine U excretion, no clinically significant expected U-related health effects have been identified to date. Subtle changes in renal function and genotoxicity markers in veterans with urine U concentrations greater than 0.1 microg(-1) creatinine, however, indicate the need for continued surveillance of these DU-exposed veterans.

Microsatellite instability (MSI) increases with age in normal somatic cells

Small pool PCR (SP-PCR) is a sensitive method for the detection and quantification of microsatellite instability (MSI) in somatic cells. Here we propose that mutant microsatellite fragments accumulate with age in normal somatic cells and that this increase in MSI can be quantified by SP-PCR. MSI at 6 microsatellite loci was determined by SP-PCR in PBL DNA from 17 "normal" blood bank donors. These individuals varied in age from 20 to 67 y/o. MSI phenotypes were plotted against age in a regression analyses. A positive slope indicated a correlation between age and MSI phenotype (p=0.0006). The mean weighted average mutant frequencies across all loci for all individuals in the age groups (0.009 for 20-30 y/o; 0.019 for 35-50 y/o; 0.034 for 60-70 y/o) were also significantly different from each other (p<0.01). A baseline for increases of MSI with age in human somatic cells was therefore begun and the effectiveness of SP-PCR to evaluate low, but significant, levels of MSI, established.

In vitro studies of the genotoxicity of ionizing radiation in human G(0) T lymphocytes

In an effort to mimic human in vivo exposures to ionizing irradiation, G(0) phase T lymphocytes from human peripheral blood samples were utilized for in vitro studies of the genotoxic effects of (137)Cs low-LET irradiation and (222)Rn high-LET irradiation. Both types of radiation induced mutations in the HPRT gene in a dose-dependent manner, with a mutant frequency (MF) = 4.28 + 1.34x + 7.51x(2) for (137)Cs (R(2) = 0.95) and MF = 4.81 + 0.67x for (222)Rn (R(2) = 0.51). Post (137)Cs irradiation incubation in the presence of cytosine arabinoside, a reversible inhibitor of DNA repair, caused an increase in the MF over irradiation alone, consistent with a misrepair mechanism being involved in the mutagenicity of low-LET irradiation. The spectrum of (137)Cs irradiation-induced mutation displayed an increase in macro-deletions (in particular total gene deletions) and rearrangement events, some of which were further defined by either chromosome painting or direct DNA sequencing. The spectrum of (222)Rn irradiation-induced mutation was characterized by an increase in small alterations, especially multiple single base deletions/substitutions and micro-deletions. These studies define the specific response of human peripheral blood T cells to ionizing irradiation in vitro and form a basis for evaluating the genotoxic effects of human in vivo exposure.

Increased DNA damage in patients with chronic obstructive pulmonary disease who had once smoked or been exposed to biomass

OBJECTIVE

Chronic obstructive pulmonary disease (COPD) is a slowly progressive condition characterised by poorly reversible airflow limitation associated with an abnormal inflammatory response of the lung. The main causal factors of COPD are chronic oxidative stress as a result of long-term smoking, use of biomass fuels, and air pollution. In this study, basal levels of DNA strand breaks were investigated together with some additional oxidative markers implicating oxidative damage on the other biomolecules such as proteins and lipids in patients with COPD who were exposed to smoking and biomass.

MATERIAL AND METHODS

We detected DNA strand breaks in peripheral blood mononuclear leukocytes by using a Single Cell Gel Electrophoresis (also called Comet Assay), plasma protein carbonyl (PC) content by using Reznick and Parker's spectrophotometric method, and lipid peroxidation by measurement of malondialdehyde (MDA) as indexes of oxidative stress in 47 patients with smoking-related COPD and 25 patients with biomass-related COPD and 36 age-and-sex matched control participants.

RESULTS

The mean values of DNA strand breaks, MDA and protein carbonyl levels were significantly higher in smoking- and biomass-related COPD groups than in the control group (ANOVA P<0.001, <0.05 and <0.05, respectively). DNA damage levels were also higher in smoking-related COPD group than in biomass-related COPD group (P<0.05). There was a positive relationship between DNA damage and MDA levels in smoking-related COPD group (P<0.05).

CONCLUSION

Oxidative stress markers and DNA damage were strongly increased in both patient groups with smoking- and biomass-related COPD. However, DNA is more affected in smoking-related COPD patients than in biomass-related COPD. These data indicate that cigarette smoking is a more significant DNA damaging risk factor than biomass smoke.

Association between Cigarette Smoking and Hypoxanthine Guanine Phosphoribosyltransferase Activity

The aim of this study was to investigate the association between smoking behavior and hypoxanthine guanine phosphoribosyltransferase (HGPRT) activity. A cross-sectional study was performed of 82 men, including 38 non-smokers and 44 smokers. Inosine monophosphate (IMP), the product of HGPRT (used as the index of activity), was measured in peripheral blood mononuclear cells using high-performance liquid chromatography. The factors potentially associated with HGPRT activity included age, glutamyl oxaloacetic transaminase, glutamyl pyruvic transaminase, cholesterol, uric acid, triglycerides, creatinine, body mass index, gout, systolic blood pressure, diastolic blood pressure, alcohol consumption, and cigarette smoking. Mean HGPRT activity was 7.05 +/- 3.44 nmol/10(6) viable cells/hour for all participants, and was significantly lower for smokers than for non-smokers (6.24 +/- 3.40 vs 7.98 +/- 3.28 nmol/10(6) viable cells/hour; p = 0.02). In addition, as the number of smoked cigarettes increased, the HGPRT activity decreased (p < 0.05). The age at onset of cigarette smoking showed a positive correlation with HGPRT activity after adjusting for smoking duration, serum uric acid, and cigarettes smoked per year using a multiple regression model (p < 0.001). We concluded that the greater the number of cigarettes smoked, the lower the HGPRT activity, and that HGPRT activity was higher in smokers who had started smoking later.

II. Cationic Lipid-Formulated Plasmid DNA-Based Bacillus anthracis Vaccine: Evaluation of Plasmid DNA Persistence and Integration Potential

Several formulated plasmid DNA (pDNA)-based vaccines are being evaluated for safety and efficacy in healthy human subjects. A safety concern for any vaccine that contains genetic material, be it whole organism, live-attenuated, or gene-based, is the potential for integration into genomic DNA (gDNA). To address this concern, a preclinical pDNA persistence/integration study was conducted in rabbits to determine the level of pDNA in muscle 2, 28, and 64 days after intramuscular injection of DMRIE:DOPE-formulated pDNAs encoding Bacillus anthracis detoxified LF and PA proteins (VCL-AB01 vaccine). Total DNA was extracted from day 64 muscle tissue and fractionated by column agarose gel electrophoresis (CAGE). Plasmid copy number (PCN) in muscle 64 days after injection (geometric mean, 2808 PCN/microg of total DNA or 150,000 diploid genomes) was determined by quantitative polymerase chain reaction. Analysis of total DNA from five VCLAB01- injected rabbits revealed that two of five samples had no detectable PCN in the high molecular weight fraction after one round of CAGE, two samples had PCN under the lower limit of quantitation, and the remaining sample had 123 PCN/microg. All PCN in the latter sample cleared after an additional round of CAGE. It appears, therefore, that persisting PCN fractionate as low molecular weight material and are most likely not integrated into gDNA. Even if the worst-case assumption is made that the highest PCN found associated with gDNA represented covalently integrated pDNA inserts, the frequency of mutation would still be 500-fold lower than the autosomal spontaneous mutation rate.

I. Poloxamer-Formulated Plasmid DNA-Based Human Cytomegalovirus Vaccine: Evaluation of Plasmid DNA Biodistribution/Persistence and Integration

Preclinical studies were conducted in mice and rabbits to evaluate biodistribution/persistence and potential integration of plasmid DNA (pDNA) after intramuscular administration of a poloxamer-formulated pDNAbased vaccine, VCL-CT01, encoding gB, pp65, and IE1 human cytomegalovirus (hCMV) immunogens. Tissue distribution in mice vaccinated with VCL-CT01 was compared with that in mice vaccinated with a phosphate- buffered saline (PBS)-formulated control pDNA vaccine. Residual pDNA copy number (PCN), in selected tissues collected on days 3, 30, and 60 after vaccination, was measured by quantitative polymerase chain reaction. In VCL-CT01-vaccinated mice and in control pDNA-vaccinated mice, pDNA was below the limit of detection by day 60 in all tissues except the injection site. Clearance of pDNA from the injection site was slower in VCL-CT01-vaccinated mice compared with PBS-pDNA-vaccinated mice. An integration study was conducted in rabbits to determine whether pDNA integration into the genome of the vaccinated animal contributed to pDNA persistence. Residual pDNA in VCL-CT01-injected rabbit muscle collected 60 days after vaccination (geometric mean of 1085 PCN/microg total DNA) was comparable to that observed in VCL-CT01- injected mouse muscle (geometric mean of 1471 PCN/microg total DNA) collected at the same time point. pDNA integration was not detectable by column agarose gel electrophoresis despite the persistence of pDNA at the injection site 60 days after vaccination. Therefore the risk of genomic integration of hCMV pDNA formulated with poloxamer was considered negligible.

Biological monitoring and surveillance results of Gulf War I veterans exposed to depleted uranium

OBJECTIVE

To relate medical surveillance outcomes to uranium biomonitoring results in a group of depleted uranium (DU)-exposed, Gulf War I veterans.

METHODS

Thirty-two veterans of Gulf War I who were victims of 'friendly fire' involving DU weapons, in whom exposure assessment can accurately be measured, had urine uranium concentrations determined using ICP-MS technology. Clinical laboratory parameters were measured and related to urine uranium concentrations. Data were examined by stratifying the cohort into a low U group, <0.10 mug/g creatinine versus a high U group, >/=0.10 mug/g creatinine and assessing differences between groups.

RESULTS

Over a decade after first exposure, soldiers possessing embedded DU fragments continue to excrete elevated concentrations of uranium in urine. No clinically significant uranium related health effects were observed in blood count, blood chemistries including renal markers, neuropsychological measures, and semen quality or genotoxicity measures. Markers of early changes in renal glomerular and tubular function were not statistically different between groups; however, genotoxicity measures continue to show subtle, mixed results.

CONCLUSION

Persistent urine uranium elevations continue to be observed more than 12 years since first exposure. Despite this, renal and other clinical abnormalities were not observed, likely due to the 'relatively' low uranium burden in this cohort compared to historical uranium-exposed occupational groups. Continuing surveillance is indicated, however, due to the on-going nature of the exposure. These results are an important finding in light of the on-going controversy regarding health effects observed in soldiers of the Gulf War and other conflicts, whose uranium exposure assessment is unable to be accurately determined.

Increased DNA damage and oxidative stress in patients with cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) is a chronic infectious and granulomatous disease caused by the Leishmania parasite that invades the skin. Reactive oxygen and nitrogen species (ROS and RNS) produced during an inflammatory response are an important part of host-defense strategies of organisms to kill the parasite. However, it is not well known whether these intermediates cause DNA damage in CL patients. We investigated the effect of Leishmania infection on basal levels of DNA strand breaks and on the oxidative/anti-oxidative status of patients with CL, and compared the data with those of healthy subjects. Twenty-five CL patients and 19 age- and sex-matched control subjects were enrolled in the study. We used the single-cell gel electrophoresis (also called comet assay) to measure DNA strand breaks in peripheral blood mononuclear leukocytes. Plasma protein carbonyl (PC), malondialdehyde (MDA) and total peroxide (TP) concentrations were measured to determine oxidative status and total anti-oxidative response (TAR) in plasma was measured to determine anti-oxidative status. The mean values of DNA damage and MDA and TP concentrations were significantly higher in CL patients than in the control group (p<0.001, p<0.01 and p<0.001, respectively). PC levels were also higher in patients, but this was not statistically significant (p>0.05). There was a significantly positive correlation between plasma MDA and DNA damage (r=0.524, p<0.01), and a negative correlation between TAR and TP levels (r=-0.790, p<0.001) in the patient group. These findings support the notion that ROS and RNS produced by the organism as a defense strategy may amplify the leishmanicidal activity in patients with CL. However, these intermediates not only cause the killing of the parasite but also induce oxidative damage in non-infected cells. Therefore, these patients must be treated urgently to counteract the oxidative DNA damage.

Qualitatively and quantitatively similar effects of active and passive maternal tobacco smoke exposure on in utero mutagenesis at the HPRT locus

BACKGROUND

Induced mutagenesis in utero is likely to have life-long repercussions for the exposed fetus, affecting survival, birth weight and susceptibility to both childhood and adult-onset diseases, such as cancer. In the general population, such exposures are likely to be a consequence of the lifestyle choices of the parents, with exposure to tobacco smoke one of the most pervasive and easily documented. Previous studies attempting to establish a direct link between active smoking and levels of somatic mutation have largely discounted the effects of passive or secondary exposure, and have produced contradictory results.

METHODS

Data from three studies of possible smoking effects on in utero mutagenesis at the HPRT locus were compiled and reanalyzed, alone and in combination. Where possible, passive exposure to environmental tobacco smoke was considered as a separate category of exposure, rather than being included in the non-smoking controls. Molecular spectra from these studies were reanalyzed after adjustment for reported mutation frequencies from the individual studies and the entire data set.

RESULTS

A series of related studies on mutation at the X-linked HPRT locus in human newborn cord blood samples has led to the novel conclusion that only passive maternal exposure to tobacco mutagens has a significant effect on the developing baby. We performed a pooled analysis of the complete data from these studies, at the levels of both induced mutation frequency and the resulting mutational spectrum.

CONCLUSION

Our analysis reveals a more commonsensical, yet no less cautionary result: both active maternal smoking and secondary maternal exposure produce quantitatively and qualitatively indistinguishable increases in fetal HPRT mutation. Further, it appears that this effect is not perceptibly ameliorated if the mother adjusts her behavior (i.e. stops smoking) when pregnancy is confirmed, although this conclusion may also be affected by continued passive exposure.

Somatic mutant frequency at the HPRT locus in children associated with a pediatric cancer cluster linked to exposure to two superfund sites

The somatic mutant frequency (Mf) of the hypoxanthine phosphoribosyl transferase (HPRT) gene has been widely used as a biomarker for the genotoxic effects of exposure but few studies have found an association with environmental exposures. We measured background Mfs in 49 current and former residents of Dover Township, New Jersey, who were exposed during childhood to industrially contaminated drinking water. The exposed subjects were the siblings of children who developed cancer after residing in Dover Township, where the incidence of childhood cancer has been elevated since 1979. Mfs from this exposed group were compared to Mfs in 43 age-matched, presumably unexposed residents of neighboring communities with no known water contamination and no increased cancer incidence. Statistical comparisons were based on the natural logarithm of Mf (lnMF). The mean Mf for the exposed group did not differ significantly from the unexposed group (3.90 x 10(-6) vs. 5.06 x 10(-6); P = 0.135), but unselected cloning efficiencies were higher in the exposed group (0.55 vs. 0.45; P = 0.005). After adjustment for cloning efficiency, lnMf values were very similar in both groups and age-related increases were comparable to those previously observed in healthy children. The results suggest that HPRT Mf may not be a sensitive biomarker for the genotoxic effects of environmental exposures in children, particularly when substantial time has elapsed since exposure.

HPRT mutations, TCR gene rearrangements, and HTLV-1 integration sites define in vivo T-cell clonal lineages

HPRT mutations in vivo in human T-lymphocytes are useful probes for mechanistic investigations. Molecular analyses of isolated mutants reveal their underlying mutational changes as well as the T-cell receptor (TCR) gene rearrangements present in the cells in question. The latter provide temporal reference points for other perturbations in the in vivo clones as well as evidence of clonal relationships among mutant isolates. Immunological studies and investigations of genomic instability have benefited from such analyses. A method is presented describing a T-cell lineage analysis in a patient with HTLV-1 infection. Lineage reconstruction of an in vivo proliferating HPRT mutant clone allows timing of the integration event to a postthymic differentiated cell prior to the occurrence of HPRT mutations.

A comparison of somatic mutational spectra in healthy study populations from Russia, Sweden and USA

A comparison of mutation spectra at the hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene of peripheral blood T-lymphocytes may provide an insight into the aetiology of somatic mutation contributing to carcinogenesis and other diseases. To increase the knowledge of mutation spectra in healthy people, we have analysed HPRT mutant T-cells of 50 healthy Russians originally recruited as controls in a study involving Chernobyl clean-up workers [I.M. Jones, H.Galick, P.Kato et al. (2002) Radiat. Res., 158, 424-442]. Reverse transcriptase-polymerase chain reactions and DNA sequencing identified 161 independent mutations among 176 thioguanine-resistant mutants. Forty mutations affected splicing mechanisms and 27 deletions or insertions of 1-60 nt were identified. Ninety-four single base substitutions were identified, including 62 different mutations at 55 different nucleotide positions, of which 19 had not been reported previously in human T-cells. Comparison of this base substitution spectrum with mutation spectra in a USA [K.J.Burkhart-Schultz, C.L. Thompson and I.M. Jones (1996) Carcinogenesis, 17, 1871-1883] and two Swedish populations [A.Podlutsky, A.-M.Osterholm, S.-M.Hou, A. Hofmaier and B. Lambert (1998) Carcinogenesis, 19, 557-566; A.Podlutsky, S.M.Hou, F.Nyberg, G. Pershagen and B. Lambert (1999) Mutat. Res., 431, 325-39] revealed similarity in the type, frequency and distribution of mutations in the four spectra, consistent with aetiologies inherent in human metabolism. There were 15-19 identical mutations in the three pairwise comparisons of Russian with USA and Swedish spectra. Intriguingly, there were 21 mutations unique to the Russian spectrum, and comparison by the Monte Carlo method of W.T. Adams and T.R. Skopek [(1987) J. Mol. Biol., 194, 391-396] indicated that the Russian spectrum was different from both Swedish spectra (P = 0.007, 0.002), but not different from the USA spectrum (P = 0.07) when Bonferroni correction for multiple comparisons was made (P < 0.008 required for significance). Age and smoking did not account for these differences. Other factors causing mutational differences need to be explored.

Genotoxicity of tobacco smoke and tobacco smoke condensate: a review

This report reviews the literature on the genotoxicity of mainstream tobacco smoke and cigarette smoke condensate (CSC) published since 1985. CSC is genotoxic in nearly all systems in which it has been tested, with the base/neutral fractions being the most mutagenic. In rodents, cigarette smoke induces sister chromatid exchanges (SCEs) and micronuclei in bone marrow and lung cells. In humans, newborns of smoking mothers have elevated frequencies of HPRT mutants, translocations, and DNA strand breaks. Sperm of smokers have elevated frequencies of aneuploidy, DNA adducts, strand breaks, and oxidative damage. Smoking also produces mutagenic cervical mucus, micronuclei in cervical epithelial cells, and genotoxic amniotic fluid. These data suggest that tobacco smoke may be a human germ-cell mutagen. Tobacco smoke produces mutagenic urine, and it is a human somatic-cell mutagen, producing HPRT mutations, SCEs, microsatellite instability, and DNA damage in a variety of tissues. Of the 11 organ sites at which smoking causes cancer in humans, smoking-associated genotoxic effects have been found in all eight that have been examined thus far: oral/nasal, esophagus, pharynx/larynx, lung, pancreas, myeoloid organs, bladder/ureter, uterine cervix. Lung tumors of smokers contain a high frequency and unique spectrum of TP53 and KRAS mutations, reflective of the PAH (and possibly other) compounds in the smoke. Further studies are needed to clarify the modulation of the genotoxicity of tobacco smoke by various genetic polymorphisms. These data support a model of tobacco smoke carcinogenesis in which the components of tobacco smoke induce mutations that accumulate in a field of tissue that, through selection, drive the carcinogenic process. Most of the data reviewed here are from studies of human smokers. Thus, their relevance to humans cannot be denied, and their explanatory powers not easily dismissed. Tobacco smoke is now the most extreme example of a systemic human mutagen.

Use of whole blood directly for single-cell gel electrophoresis (comet) assay in vivo and white blood cells for in vitro assay

The present study investigated the use of whole blood from humans and rats directly for single-cell gel electrophoresis (comet) assay. As little as 20 microl of whole blood was sufficient for comet assay, and the comet images obtained from whole blood were not different from those obtained from isolated lymphocytes. The DNA remained intact up to 4 h at 4 degrees C after isolation and had no observable strand breakage, when whole blood was cryopreserved (at -80 degrees C) in 10% pre-cooled DMSO up to 60 days. To demonstrate that the whole-blood technique could be applied to in vivo studies, we injected rats with a known carcinogen Fe/NTA and measured DNA strand breaks in whole blood in comparison with isolated lymphocytes. We showed that Fe/NTA injection resulted in similar extent of DNA strand breakage in both whole blood and lymphocytes, indicating that whole-blood method can be used for in vivo genotoxic studies. One disadvantage of the whole-blood technique is that whole blood cannot be used for in vitro studies because of the interferences from red blood cell (RBC) components. However, this problem can be overcome by prior hemolysis of RBCs and a brief centrifugation to obtain white blood cells (WBCs), which can then be used for in vitro incubation with genotoxic compounds before comet assay. Overall, this whole-blood technique for comet assay is expected to provide a simple, rapid, and cost-effective alternative for the existing comet assay using isolated lymphocytes in situations such as when time and cost are limiting factors.

Studies on the HPRT mutant frequency in T lymphocytes from healthy Indian male population as a function of age and smoking

Mutant frequency at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene in the peripheral blood lymphocytes obtained from 44 healthy individuals (23 non-smokers and 21 smokers) of an Indian male population was studied using T-lymphocyte cloning assay. It was found that lnMF increased with age at a rate of 2.5% per year (P <0.001). Blood samples from smokers showed a significant (P <0.037) increase in HPRT mutant frequency (MF) (10.43 +/- 4.74 x 10(-6)) as compared to that obtained from non-smokers (7.69 +/- 3.69 x 10(-6)). This study also showed a significant (P <0.027) inverse correlation between lnMF and non-selected cloning efficiency (CE). However, with respect to age no variation was observed in cloning efficiency. The results obtained in this study showed a good comparison with those reported in different populations of the world.

Structural and functional analysis of mutations at the human hypoxanthine phosphoribosyl transferase (HPRT1) locus

Hypoxanthine phosphoribosyl transferase (HPRT, also known as HGPRT) is an often-used genetic marker in eukaryotic cells. The gene is conserved from bacteria to human, with retained catalytic activity, although substrate specificity may have changed, and the enzyme is essential in malaria-causing protozoans. Inherited mutations in the human HPRT1 gene result in three different phenotypes: Lesch-Nyhan syndrome (LNS or LND), LND variants, and HPRT-related hyperuricemia (HRH). In cultured cells, loss of HPRT activity gives rise to 6-thioguanine (6-TG) resistance. In general, cells from LND patients are also 6-TG resistant, whereas cells from HRH patients are not, with some interesting exceptions. Using modeling methods, we have studied the correlation between the mutable and nonmutated amino acid residues on one hand, and sequence conservation and predicted phenotypic effects on the other hand. Our results demonstrate that most of the mutations are explainable by the predicted effect on protein structure and function. They are also consistent with sequence conservation. Moreover, the mutational profiles of TG-resistant cells and LND overlap to a great extent, while most of the mutations in HRH are unique to that condition. We have also noticed a strong correlation between mutations in the tetramer interfaces and observed phenotypes, suggesting a functional role for a tetramer transition during catalysis.