Modulation of benzo[a]pyrene-induced covalent DNA modifications in adult and fetal mouse tissues by gestation stage

Morinda citrifolia (noni) reduces cancer risk in current smokers by decreasing aromatic DNA adducts

Quantitative determination of aromatic DNA adducts in peripheral blood lymphocytes (PBLs) of current smokers is an useful surrogate biomarker for the evaluation of environmental carcinogen exposure or chemopreventive intervention. In this study, we examined the impact of Tahitian Noni Juice (TNJ) on the aromatic DNA adducts of PBLs, before and after a 1-mo intervention, using (32)P postlabeling assay. Of 283 enrolled, 203 smokers completed the trial. Aromatic DNA adducts levels in all participants were significantly reduced by 44.9% (P < 0.001) after drinking 1 to 4 oz of TNJ for 1 mo. Dose-dependent analyses of aromatic DNA adduct levels showed reductions of 49.7% (P < 0.001) in the 1-oz TNJ group and 37.6% (P < 0.001) in the 4-oz TNJ group. Gender-specific analyses resulted in no significant differences in the 4-oz TNJ groups. Interestingly, the 1-oz TNJ group showed a reduction of 43.1% (P < 0.001) in females compared with 56.1% (P < 0.001) in males. The results suggest that drinking 1 to 4 oz of TNJ daily may reduce the cancer risk in heavy cigarette smokers by blocking carcinogen-DNA binding or excising DNA adducts from genomic DNA.

Alterations in CD4+, CD8+, Vgamma3, Vgammadelta, and/or Valpha betaT-lymphocyte expression in lymphoid tissues of progeny after in utero exposure to benzo(alpha)pyrene

That benzo alpha)pyrene (Balpha P) decreases both humoral and cell-mediated immunity, and leads to increases in progeny tumor development after in utero insult, suggests that T- and B-lymphocytes are made defective in exposed offspring. In the study here, C3H mice were injected once with Balpha P (150 microg/g BW) at day 12 of pregnancy and progeny lymphoid tissues were excised during gestation (day 18; GD18) or at 1 or 6 weeks post-partum. The isolated lymphoid cells were analyzed by flow cytometry/immunofluorescence or assessed for function. In Balpha P-exposed fetuses, thymic Thy1(+) cell levels were decreased (relative to levels in organs of corn oil-exposed dam progeny). In addition, for up to 6 weeks post-birth, CD4(+)CD8(+) (double positive; DP) cells were virtually absent and levels of CD4(-)CD8(-) (double negative; DN) cells were consistently at epsilon 90%. With regard to single positive (SP) cells, CD4(+) cell levels were also decreased in tissues at GD18 up through 6 weeks post-birth; CD8(+) cell levels were increased, but only in pups at 1-week and 6-weeks post-birth. In 1-week-old progeny, spleen CD8(+) cell levels were quantitatively unchanged, though CD4(+) levels were reduced 2-4-fold and CD4(-)CD8(-) DN levels significantly increased. With respect to TCRs, fetal levels of thymic CD3Vgamma(3)(+) and CD3Vgamma delta(+) cells were decreased; levels of CD3Valphabeta cells were only slightly depressed. The latter results contrast sharply with a strong reduction in CD3Valphabeta cells in the fetal livers of Balpha P-exposed progeny. Interestingly, these livers also strongly evidenced a presence of BalphaP-7,8-dihydrodiol-9,10-epoxide metabolite. When assessed for any change in function, the CD4(+), Thy1(+) cells isolated from Balpha P-exposed progeny tissues responded weakly (relative to controls) to ConA and in an allogeneic MLR. Taken in totality, the results here strengthen our original hypothesis that BalphaP can create a favorable milieu for tumor growth progression in progeny of exposed mothers by affecting development of sufficient numbers of functional lymphocytes in the offspring.

Presence of CD4(+) SP and DP (gammadelta, alphabeta) T-Cells Expressing BPDE-DNA Adducts in Progeny of Mouse Dams Exposed to Benzo(alpha) pyrene at Mid-Gestation

After one exposure of C3H/HeJ pregnant females (at mid-gestation) to B(alpha) P (at 150 mu g/g BW), their progeny evidenced suppression of both humoral and cell-mediated immunity, as well as quantitative deficiencies in the levels of Lyt1(+) and Lyt2(+)cells, and CD4(+) CD8(+), V(gamma 3)(+), V(gamma delta)(+), and V(alpha beta)(+)T-cells. We hypothesized that these conditions could be a result, in part, of covalent binding of BPDE to DNA within these cells. To test this, antiserum to BPDE-DNA was generated in rabbits; after multiple purification steps, an anti-BPDE-DNA (rendered approximately 99.5% specific for BPDE-DNA and did not react with free BPDE or DNA antigens at dilutions even of < 1:50) antiserum was isolated. Flow cytometry and immunofluorescence analyses showed the adduct was present in CD4(+) cells of progeny fetal and in both post-natal thymus and spleen tissues. Using a [(32)P]-post-labelling method, adduct was also detected in samples of fetal liver during the period from Day 15 to 18 gestation. Surprisingly, it was found that thymus cells from B(alpha)P-exposed mice not exhibiting the adduct could severely suppress allogeneic mixed lymphocyte responses, while those in which the adduct was detected caused had a more pronounced suppression. We suspect from the findings here that the presence of BPDE-DNA adducts in T-cells contributes to, but is not necessarily the causa sola for, the immunosuppression that develops in the offspring of pregnant mothers who are exposed to B(alpha)P (among many other agents) via smoking, ingestion, or inhalation of environmental pollution.

Assessment of interactions between PAH exposure and genetic polymorphisms on PAH-DNA adducts in African American, Dominican, and Caucasian mothers and newborns

Polycyclic aromatic hydrocarbons (PAH) are widespread pollutants commonly found in air, food, and drinking water. Benzo[a]pyrene is a well-studied representative PAH found in air from fossil fuel combustion and a transplacental carcinogen experimentally. PAHs bind covalently to DNA to form DNA adducts, an indicator of DNA damage, and an informative biomarker of potential cancer risk. Associations between PAH-DNA adduct levels and both cancer risk and developmental deficits have been seen in previous experimental and epidemiologic studies. Several genes have been shown to play an important role in the metabolic activation or detoxification of PAHs, including the cytochrome P450 genes CYP1A1 and CYP1B1 and the glutathione S-transferase (GST) genes GSTM1, and GSTT2. Genetic variation in these genes could influence susceptibility to adverse effects of PAHs in polluted air. Here, we have explored interactions between prenatal PAH exposure and 17 polymorphisms in these genes (rs2198843, rs1456432, rs4646903, rs4646421, rs2606345, rs7495708, rs2472299, rs162549, rs1056837, rs1056836, rs162560, rs10012, rs2617266, rs2719, rs1622002, rs140194, and gene deletion GSTM1-02) and haplotypes on PAH-DNA adducts in cord blood of 547 newborns and in maternal blood of 806 mothers from three different self-described ethnic groups: African Americans, Dominicans, and Caucasians. PAHs were measured by personal air monitoring of mothers during pregnancy. Significant interactions (p < 0.05) were observed between certain genetic polymorphisms and CYP1A1 haplotype and PAHs in mothers and their newborns in the three ethnic groups. However, with our limited sample size, the current findings are suggestive only, warranting further study.

Environmental genotoxicants/carcinogens and childhood cancer: Bridgeable gaps in scientific knowledge

Cancer in children is a major concern in many countries. An important question is whether these childhood cancers are caused by something, or are just tragic random events. Causation of at least some children's cancers is suggested by direct and indirect evidence, including epidemiological data, and animal studies that predict early life sensitivity of humans to carcinogenic effects. Candidate risk factors include genotoxic agents (chemicals and radiation), but also diet/nutrition, and infectious agents/immune responses. With regard to likelihood of risks posed by genotoxicants, there are pros and cons. The biological properties of fetuses and infants are consistent with sensitivity to preneoplastic genotoxic damage. Recent studies of genetic polymorphisms in carcinogen-metabolizing enzymes confirm a role for chemicals. On the other hand, in numerous epidemiological studies, associations between childhood cancers and exposure to genotoxicants, including tobacco smoke, have been weak and hard to reproduce. Possibly, sensitive genetic or ontogenetic subpopulations, and/or co-exposure situations need to be discovered to allow identification of susceptible individuals and their risk factors. Among the critical knowledge gaps needing to be bridged to aid in this effort include detailed tissue and cellular ontogeny of carcinogen metabolism and DNA repair enzymes, and associations of polymorphisms in DNA repair enzymes with childhood cancers. Perinatal bioassays in animals of specific environmental candidates, for example, benzene, could help guide epidemiology. Genetically engineered animal models could be useful for identification of chemical effects on specific genes. Investigations of interactions between factors may be key to understanding risk. Finally, fathers and newborn infants should receive more attention as especially sensitive targets.

DNA damage from polycyclic aromatic hydrocarbons measured by benzo[a]pyrene-DNA adducts in mothers and newborns from Northern Manhattan, the World Trade Center Area, Poland, and China

Polycyclic aromatic hydrocarbons (PAH), of which benzo[a]pyrene is a representative member, are combustion-related environmental pollutants and include known carcinogens. Laboratory animal studies indicate that the dose of PAHs to the fetus is on the order of a 10th that to the mother and that there is heightened susceptibility to PAH-induced carcinogenesis during the fetal and infancy periods. Carcinogen-DNA adducts, a measure of procarcinogenic genetic damage, are considered a biomarker of increased cancer risk. Here we compare the levels of benzo[a]pyrene-DNA adducts as a proxy for PAH-DNA damage measured in maternal blood and newborn cord blood obtained at delivery in four different populations of mothers (total of 867) and newborns (total of 822), representing a 30-fold range of exposure to ambient PAHs. The populations include residents in Northern Manhattan, participants in a study of the effects of the World Trade Center disaster, residents in Krakow, Poland, and residents in Tongliang, China. Mean adduct concentrations in both maternal and cord blood and the proportion of samples with detectable adducts, increased across the populations [Northern Manhattan < World Trade Center (WTC) < Krakow < Tongliang], consistent with the trend in estimated ambient exposure to PAHs (P < 0.001). For mothers, the means in the respective populations were Northern Manhattan (0.21 adducts per 10(8) nucleotides), WTC (0.23 adducts per 10(8) nucleotides), Krakow (0.28 adducts per 10(8) nucleotides), Tongliang (0.31 adducts per 10(8) nucleotides); the corresponding means in the newborns were Northern Manhattan (0.23), WTC (0.24), Krakow (0.29), Tongliang (0.31). The percentage of mothers with detectable levels of adducts in the respective populations were Northern Manhattan (36.8%), WTC (57.5%), Krakow (72.9%), Tongliang (73.4%); the corresponding percentages among the newborns were Northern Manhattan (42.4%), WTC (60.6%), Krakow (71.1%), Tongliang (79.5%). Despite the estimated 10-fold lower PAH dose to the fetus based on laboratory animal experiments, the adduct levels in the newborns were similar to or higher than in the mothers. This study suggests that the fetus may be 10-fold more susceptible to DNA damage than the mother and that in utero exposure to polycyclic aromatic hydrocarbons may disproportionately increase carcinogenic risk. The data support preventive policies to limit PAH exposure to pregnant women and children.

Biomarkers in maternal and newborn blood indicate heightened fetal susceptibility to procarcinogenic DNA damage

Polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]pyrene (BaP) are widespread air contaminants released by transportation vehicles, power generation, and other combustion sources. Experimental evidence indicates that the developing fetus is more susceptible than the adult to carcinogenic effects of PAHs, although laboratory studies in rodents suggest that the dose to fetal tissues is an order of magnitude lower than that to maternal tissues. To assess fetal versus adult susceptibility to PAHs and environmental tobacco smoke (ETS), we compared carcinogen-DNA adducts (a biomarker associated with increased cancer risk) and cotinine (a biomarker of tobacco smoke exposure) in paired blood samples collected from mothers and newborns in New York City. We enrolled 265 nonsmoker African-American and Latina mother-newborn pairs in New York City between 1997 and 2001 (estimated average ambient air BaP concentrations < 0.5 ng/m3). Despite the estimated 10-fold lower fetal dose, mean levels of BaP-DNA adducts as determined by high-performance liquid chromatography-fluorescence were comparable in paired New York City newborn and maternal samples (0.24 adducts per 10(8) nucleotides, 45% of newborns with detectable adducts vs. 0.22 per 10(8) nucleotides, 41% of mothers with detectable adducts). However, by the Wilcoxon signed-rank test, the levels in newborns were higher (p = 0.02). Mean cotinine was higher in newborns than in mothers (1.7 ng/mL, 47% detectable vs. 1.28 ng/mL, 44% detectable). Consistent with our prior study in a Caucasian Polish population, these results indicate increased susceptibility of the fetus to DNA damage and reduced ability to clear ETS constituents. The findings have implications for risk assessment, given the need to protect children as a sensitive subset of the population.

Transplacental lung carcinogenesis: molecular mechanisms and pathogenesis

A wide variety of studies in both animal models and human populations have demonstrated age-related differences in the susceptibility of the developing organism to environmentally prevalent toxicants. While this differential susceptibility has been clearly established, the mechanistic basis for these age-related differences is still poorly understood. The developing fetus utilizes many of the same metabolic and signaling pathways as adult organisms in responding to environmental agents. However, it is becoming increasingly evident that the fetus is not a "little adult" and exhibits unique biochemical responses and gene expression profiles to chemical and physical agents. Because of the rapid growth and developmental changes that occur during gestation, the fetus represents a particularly challenging research subject as a result of the dynamic alterations that occur in gene expression pathways as gene systems are activated or repressed during specific stages of development. Thus, an understanding of the mechanism(s) that render the developing organism more or less susceptible to specific carcinogenic agents is crucial for both regulatory decisions regarding the determination of safe levels of toxic chemicals released into the environment and also for determining the effects of therapeutic compounds in younger age groups and pregnant women. Concentrating on studies from the author's laboratory, this review will highlight recent research on the molecular pathogenesis of transplacentally induced tumors. While focusing on the lung, other animal models and recent human epidemiological studies will also be discussed to contrast similarities and differences in the developing and adult organisms in terms of responses to toxic chemicals, including metabolism of environmentally prevalent toxicants and alterations in gene systems at the molecular level.

Detection of DNA adducts in developing CD4+ CD8+ thymocytes and splenocytes following in utero exposure to benzo[a]pyrene

Environmental carcinogen exposure may play an important role in the incidence of cancer in children. In addition to environmental pollutants, maternal smoking during pregnancy may be a contributing factor. Major carcinogenic components of cigarette smoke and other combustion by-products in the environment include polycyclic aromatic hydrocarbons (PAH). Mouse offspring exposed during midpregnancy to the PAH, benzo[a]pyrene (B[a]P), show significant deficiencies in their immune functions, observed in late gestation which persist for at least 18 months. Tumor incidences in these progeny are 8 to 10-fold higher than in controls. We have demonstrated a significant reduction in thymocytes (CD4+ CD8+, CD4+ CD8+ Vbeta8+, CD4+ CD8+ Vgamma2+) from newborn and splenocytes (CD4+ CD8+) from 1-week-old mouse progeny exposed to B[a]P in utero. To investigate possible causes of the observed T cell reduction, we analyzed the thymocytes and splenocytes from progeny and maternal tissues for the presence of B[a]P-DNA adducts. Adducts were detected in maternal, placental and offspring lymphoid tissues at day 19 of gestation, at birth and 1-wk after birth. The presence of B[a]P-DNA adducts in immature T cells may, in part, explain the previously observed T cell immunosuppression and tumor susceptibility in mice exposed to B[a]P in utero. The effects of DNA lesions on progeny T cells may include interference with normal T-cell development. These results provide a possible explanation for the relationship between maternal smoking during pregnancy and childhood carcinogenesis.

Immunomodulation in progeny from thymectomized primiparous mice exposed to benzo(a)pyrene during mid-pregnancy

Previous studies have shown that Benzo(a)pyrene (B(a)P3) given to non-thymectomized (NTX) female mice alters expression of T cell subsets and suppresses cell mediated immunity (CMI) and humoral immunity (HI) in the progeny. Thus, maternal exposure to B(a)P may influence changes in progeny immune status. To understand how maternal cellular and humoral factors influence embryonic development of progeny immunity, adult female mice were thymectomized (TX) at 6 weeks, mated and injected with 150 microg B(a)P)/g body weight at 12 days of pregnancy. After B(a)P exposure, the following studies were performed: (A) Maternal reproductive capacity and survival rate of progeny; (B) Detection of T cells in progeny thymus; (C) Functional characteristics of progeny thymus or spleen. Maternal thymectomy and B(a)P exposure reduced average litter size by 40%. Serological sensitivity of thymus cells with anti-Thyl + complement occurred at a higher dilution of mAb in progeny from TX mothers exposed to B(a)P, suggesting that B(a)P-thymectomy led to increased sensitivity of developing thymocytes to mAb plus complement. Progeny from TX mothers exposed to B(a)P showed enhanced thymic CMI, but suppressed splenic CMI and HI. Thus, thymectomy prevents CMI immunosuppression by B(a)P, while HI is still suppressed. These results indicate that the maternal thymus is necessary for incurring the effect of B(a)P on progeny CMI.

Maternal exposure to benzo[a]pyrene alters development of T lymphocytes in offspring

Childhood cancer has been increasing significantly over the past two decades in the United States, suggesting that environmental exposures may be playing a causative role. One such cause may be maternal smoking during pregnancy. Suspected carcinogens in cigarette smoke and environmental pollution include N-nitrosamines and polycyclic aromatic hydrocarbons, which may be several micrograms per exposure. Previously, we have shown that mouse progeny of mothers exposed to benzo[a]pyrene (B[a]P) during midpregnancy had abnormalities in their humoral and cell-mediated immune response. Immunodeficiency was detectable during gestation, at one week after birth and persisted for 18 months. Tumor incidences in progeny were eight to 10-fold higher than in controls. The present study compared frequencies of CD4+, CD8+, V gamma 2+, and V beta 8+ T cells in progeny following in utero exposure to B[a]P. The significant reduction in newborn CD4+CD8+, CD4+CD8+V beta 8+ thymocytes and CD4+ splenocytes from 1-week-old progeny, suggests that B[a]P induces abnormal changes in developing T cells. These early alterations may lead to postnatal T cell suppression, thus providing a more suitable environment for the growth of tumors later in life. These results suggest that developmental immunosuppression mediated by B[a]P may play a critical role in the relationship between maternal exposures and childhood carcinogenesis.

Effect of glutathione modulation of the distribution and transplacental uptake of 2-[14C]-chloroacetonitrile (CAN) quantitative whole-body autoradiographic study in pregnant mice

Chloroacetonitrile (CAN), a drinking water disinfectant by-product, has mutagenic and carcinogenic properties. CAN is known to deplete glutathione (GSH), and previous studies reported an enhanced molecular interaction of CAN after GSH depletion in the uterine and fetal tissues of mice. The present report may help to understand the potential mechanisms involved in such molecular interactions by examining the disposition, transplacental uptake and covalent interaction of the chemical in normal and GSH depleted pregnant mice (at 13th day of gestation). Both normal and GSH depleted (by administration of Diethylmaleate (DEM), 0.6 mL/kg, i.p.) pregnant mice were given an equitoxic i.v. dose of 2-[14C]-CAN(333 microCi/kg equivalent to 77 mg/kg). Animals were processed for whole-body autoradiography (WBA) at 1, 8 and 24 hr after treatment. Tissue distribution of radioactivity in the autoradiographs was quantitated using computer aided image analysis. With few exceptions, a rapid high uptake (at 1 hr) of radioactivity was observed in all major maternal (liver, lung, urinary bladder, gastrointestinal mucosa, cerebellum, uterine luminal fluid) and fetal (liver, brain) organs of both normal and GSH depleted mice. This pattern of distribution was observed, with lesser intensity, at 8 hr following treatment. At a later time period (24 hr), there was a significant higher retention and covalent interaction of radioactivity in GSH depleted mouse tissues especially in the liver as compared to normal mouse. This study suggests that 2-[14C]-CAN and/or its metabolites are capable of crossing the placental barrier. The observed higher uptake and retention of the radioactivity in the maternal liver, kidney, cerebellum, nasal turbinates and fetal liver may pose toxicity of the chemical to these organs. The increased covalent interaction of radioactivty in GSH depleted mice liver may indicate the potential utilization of GSH pathway by this organ in the detoxication of CAN derived metabolites and thus exerting hepatotoxicity.

Age-dependent change of metabolic capacity and genotoxic injury in rat intestine

The ontogeny of intestinal phase I and II xenobiotic metabolising enzymes and influence on susceptibility to genotoxic injury, are unclear. This study assessed expression of cytochrome P450 monooxygenases (CYP1A, CYP2B, CYP2C, CYP3A, CYP4A), glutathione-S-transferase (GSTA1/2, GSTA3, GSTA4, AND GSTM1), and uridine diphosphate glucuronosyl transferase (UGT) in rat intestine, between fetal life and maturity. Enzyme induction and DNA adduct formation were assessed after 3-methylcholanthrene (MC) exposure. Untreated rat intestine expressed CYP2B, GSTA1/2, GSTA4 and UGT at all stages of maturation, although CYP2B and GSTA1/2 increased in postnatal life. MC induced new expression of CYP1A, GSTA3 and enhanced expression of GSTA1/2 and UGT. Age-dependent differences of enzyme induction and DNA adduct formation between pre- and postnatal intestine and during postnatal maturation, were observed. Rat intestinal epithelium shows variable competence for MC metabolism and sustains disparate levels of DNA adducts during pre- and postnatal development.

Absence of formation of benzo[a]pyrene/DNA adducts in the cuttlefish (Sepia officinalis, Mollusca: Cephalopoda)

Benzo[a]pyrene (B[a]P) injected intramuscularly into the base of the arms of cuttlefish was released continuously from the injection site and removed from the organism. Only a portion of the compound accumulated in the body. Twenty-four hr after its injection, 75% of B[a]P applied in olive oil was removed from the cuttlefish, and 1.2% was found in the body outside the head, the site of injection. If the carcinogen was dissolved in dimethylformamide, the removal of B[a]P was slower, so that only 18% of the injected B[a]P was removed from the organism and 0.36% accumulated in the body outside the head 24 hr after injection. The high level of B[a]P in gills and hemolymph 4 hr after injection and the kinetics of the decrease of its concentration with time indicate that these two organs could be involved in the excretion of B[a]P from the body. The B[a]P/DNA adducts characteristic for vertebrates could not be demonstrated in gills, skin, brain, hepatopancreas, and lymphocytes of the cuttlefish 24 hr after injection of B[a]P. The dose of the carcinogen injected into the cuttlefish was 2-4 times higher than the dose resulting in the formation of a high level of B[a]P/DNA adducts in the vertebrates. A different metabolism of B[a]P in the tissue of cephalopods, compared to vertebrates, could be less favorable to the process leading to malignant transformation and could explain the absence from the literature of reports of tumors in cephalopods.

Effect of glutathione modulation on molecular interaction of [14C]-chloroacetonitrile with maternal and fetal DNA in mice

Binding of haloacetonitriles or their reactive metabolites to macromolecules of fetal tissue may be responsible for reproductive toxicity. To investigate the role of glutathione (GSH) in the metabolism and reproductive toxicity of haloacetonitriles, irreversible interaction of chloroacetonitrile (CAN) with maternal uterine and fetal DNA was assessed in a time course study among normal and among glutathione-depleted mice treated with [2-14C]-CAN. GSH was depleted in maternal and fetal tissues by treating of animals with diethylmaleate (DEM) 1 h before [2-14C]-CAN administration. Maternal urinary excretion of thiocyanate was 5 times higher in glutathione-depleted mice than in controls. At 8 and 24 h following [2-14C]-CAN administration, total radioactivity uptake in maternal uterine tissue, amniotic fluid, and fetal tissue was higher in glutathione-depleted mice than in control. Also the interaction of CAN or its reactive metabolites with maternal uterine DNA was enhanced following glutathione depletion. At 24 h after treatment, the covalent binding to DNA in fetal tissue was significantly increased in glutathione depleted mice (205% of control). The magnitude of interaction of CAN in fetal DNA was about 4 times higher than that in uterine DNA. The time course study in either maternal uterine or fetal DNA revealed elevated and persistent levels of covalent binding of [ C]-CAN to DNA at 72 h after treatment. Enhancement of the molecular interaction of CAN in maternal and fetal DNA following GSH depletion indicates an important role for GSH in CAN metabolism.