Probiotic mixture decreases DNA adduct formation in colonic epithelium induced by the food mutagen 2-amino-9H-pyrido[2,3-b]indole in a human-flora associated mouse model.

Consumption of probiotic bacteria such as bifidobacteria has been shown to reduce the risk of colon cancer in animal models. However, the composition and metabolic activities of the intestinal flora of experimental animals are significantly different from those of humans. The aim of the study was to examine whether the probiotic mixture, which consisted of Streptococcus faecalis, Clostridium butyricum and Bacillus mesentericus, could decrease DNA adduct formation induced by 2-amino-9H-pyrido[2,3-b]indole (2-amino-alpha-carboline; AAC) in the colonic epithelium of a human-flora-associated (HFA) mouse model. Ten HFA mice were divided into a control group (n=4) and a probiotic group (n=6). The control group was administered AAC for 3 days and sacrificed 24 h after the last dose. The probiotic group was administered the probiotic mixture for 2 weeks prior to the administration of AAC. Analysis of DNA adducts with the 32P-high-performance liquid chromatography method was performed on stomach, jejunum and colonic epithelium, representing direct exposure sites of AAC, and colon wall, liver and kidney, representing indirect exposure sites. The mean level of the DNA adducts in the colonic epithelium of the probiotic group was significantly lower than that of control group, while the mean levels at the other sites did not differ significantly between the groups. The results indicated that the probiotic mixture could decrease the DNA adduct formation in the colonic epithelium induced by AAC.

Formation of DNA adducts from oil-derived products analyzed by 32P-HPLC.

The aim of this study was to investigate the genotoxic potential of DNA adducts and to compare DNA adduct levels and patterns in petroleum vacuum distillates, coal tar distillate, bitumen fume condensates, and related substances that have a wide range of boiling temperatures. An in vitro assay was used for DNA adduct analysis with human and rat S-9 liver extract metabolic activation followed by 32P-postlabeling and 32P-high-performance liquid chromatography (32p-HPLC). For petroleum distillates originating from one crude oil there was a correlation between in vitro DNA adduct formation and mutagenic index, which showed an increase with a distillation temperature of 250 degrees C and a peak around a distillation point of approximately 400 degrees C. At higher temperatures, the genotoxicity (DNA adducts and mutagenicity) rapidly declined to very low levels. Different petroleum products showed a more than 100-fold range in DNA adduct formation, with severely hydrotreated base oil and bitumen fume condensates being lowest. Coal tar distillates showed ten times higher levels of DNA adduct formation than the most potent petroleum distillate. A clustered DNA adduct pattern was seen over a wide distillation range after metabolic activation with liver extracts of rat or human origin. These clusters were eluted in a region where alkylated aromatic hydrocarbons could be expected. The DNA adduct patterns were similar for base oil and bitumen fume condensates, whereas coal tar distillates had a wider retention time range of the DNA adducts formed. Reference substances were tested in the same in vitro assay. Two- and three-ringed nonalkylated aromatics were rather low in genotoxicity, but some of the three- to four-ringed alkylated aromatics were very potent inducers of DNA adducts. Compounds with an amino functional group showed a 270-fold higher level of DNA adduct formation than the same structures with a nitro functional group. The most potent DNA adduct inducers of the 16 substances tested were, in increasing order, 9,10-dimethylanthracene, 7,12-dimethylbenz[a]anthracene and 9-vinylanthracene. Metabolic activation with human and rat liver extracts gave rise to the same DNA adduct clusters. When bioactivation with material from different human individuals was used, there was a significant correlation between the CYP 1A1 activity and the capacity to form DNA adducts. This pattern was also confirmed using the CYP 1A1 inhibitor ellipticine. The 32P-HPLC method was shown to be sensitive and reproducible, and it had the capacity to separate DNA adduct-forming substances when applied to a great variety of petroleum products.

32P-postlabeling high-performance liquid chromatography (32P-HPLC) adapted for analysis of 8-hydroxy-2'-deoxyguanosine.

8-Hydroxy-2'-deoxyguanosine (8-OH-dG) is a promutagenic lesion in DNA caused by reactive oxygen species. It normally exists at a level of 0.1-1 per 10(5) 2'-deoxyguanosines (dG). To analyze the lesion in easily obtainable biological samples, a very sensitive analytical method is required. The method should also handle the problem with potential oxidation of dG to 8-OH-dG during workup and analysis. 32P-postlabeling high-performance liquid chromatography (32P-HPLC) is an analytical method previously used to analyze lipophilic DNA adducts at levels as low as 1 per 10(9) normal nucleotides when analyzing microgram amounts of DNA. This method was adapted for analysis of 8-OH-dG. The aim was to develop an analytical method that provided a high sensitivity and good reproducibility, prevented oxidation of dG present in samples to 8-OH-dG, was capable of analyzing DNA from very small samples and still offered high sample throughput and ease of use. In analysis of calf thymus DNA, the method had a detection limit of 0.1 8-OH-dG per 10(5) dG when 1 microgram of DNA was used. The standard deviation of repeated analyses of the same sample was +/-10% and the result corresponded well with the established analytical method using HPLC with electrochemical detection. 32P-HPLC is sensitive enough to enable analysis of low levels of 8-OH-dG in biological samples such as small volumes of blood, needle biopsies and tissue swabs. It also substantially reduces oxidation of dG to 8-OH-dG during sample workup and analysis.

Methodological considerations and factors affecting 8-hydroxy-2-deoxyguanosine analysis.

Oxidative stress is related to a number of diseases due to the formation of reactive oxygen species (ROS). There are also several substances found in the occupational environment or as life style related situations that generates ROS. A stable biomarker for oxidative stress on DNA is 8-hydroxy-2'-deoxyguanosine (8-OH-dG). A potential problem in the work-up and analysis of 8-OH-dG is oxidation of dG with false high levels as a result of analysis. This paper summarizes and discusses some of the critical moments in terms of auto-oxidation. The removal of transition metals, low temperatures, absence of isotopes (or 2'-deoxyguanosine) and incubation times are all important factors. Removal of oxygen is complicated while the problem is reduced if a nitroxide (TEMPO) is added during work-up. Certain reducing agents and enzymes could be critical if added during work-up. The application of the 32p-HPLC method to analyze 8-OH-dG is discussed. The 32P-HPLC method is suitable for 8-OH-dG analysis and avoids several factors that oxidizes dG by removal of dG before addition of isotopes. Factors of crucial importance (columns, eluents, gradients and detection of 32p) for the analysis of 8-OH-dG are commented upon and certain recommendations are made to make it possible to apply the 32P-HPLC methodology for this type of analysis.

32P-Postlabeling high-performance liquid chromatographic improvements to characterize DNA adduct stereoisomers from benzo[a]pyrene and benzo[c]phenanthrene, and to separate DNA adducts from 7,12-dimethylbenz[a]anthracene.

Single compounds can generate complex DNA adduct patterns by reactions through different pathways, with different target nucleotides and through different configurations of the products. DNA adduct analysis by 32P-HPLC was improved by adding an isocratic plateau in an otherwise linear gradient, thereby enhancing resolution of predictable retention time intervals. This enhanced 32P-HPLC technique was used to analyze and at least partly resolve 14 out of 16 available benzo[c]phenanthrene deoxyadenosine and deoxyguanosine adduct standards, 8 out of 8 available benzo[a]pyrene deoxyadenosine and deoxyguanosine adduct standards, and 51 peaks from 7,12-dimethylbenz[a]anthracene-calf thymus DNA reaction products. The same type of gradient modifications could be used to enhance resolution in analyses of other complex DNA adduct mixtures, e.g., in vivo in humans.

32-P-HPLC analysis of DNA adducts formed in vitro and in vivo by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 2-amino-3,4,8-trimethyl-3H-imidazo[4,5-f]quinoxaline, utilizing an improved adduct enrichment procedure.

DNA adducts of 2-amino-1 methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,4,8-trimethyl-3H-imidazo[4,5-f]quinoxaline (4,8-diMeIQx), synthesized in vitro with calf thymus DNA and formed in vivo in the male Wistar rat, were enriched from digested DNA by butanol extraction before 32P-postlabeling. The recovery after butanol enrichment was 79% and 32% for in vitro modified PhIP- and 4,8-diMeIQx-DNA adducts, respectively. Crude postlabeling mixtures were chromatographically separated by high-performance liquid chromatography with on-line 32P-detection (32P-HPLC). The major PhIP- and 4,8-diMeIQx-DNA adducts formed in vitro cochromatographed with the respective pdGp-C8 adduct standard. 32P-HPLC was also used to separate hydrolysates of in vitro formed PhIP-DNA and 4,8-diMeIQx-DNA that had been 32P-postlabeled under ATP-deficient conditions. The adduct recovery of the ATP-deficient method relative to the improved butanol enrichment procedure was 29% and 59% for total PhIP-DNA and 4,8-diMeIQx-DNA adducts, respectively. Simplified DNA adduct patterns were obtained when the postlabeling mixtures were incubated with nuclease P1, suggesting incomplete DNA hydrolysis. After nuclease P1 treatment, the major DNA adducts of PhIP and 4,8-diMeIQx formed in vitro cochromatographed with the respective pdG-C8 adduct standard. In vivo PhIP formed what appeared to be multiple DNA adducts; however, after nuclease P1 treatment the PhIP-associated peaks were concentrated into a single peak cochromatographing with pdG-C8-PhIP, 4,8-diMeIQx formed multiple DNA adducts in vivo. Nuclease P1 treatment resulted in two 4,8-diMeIQx related peaks, one cochromatographing with pdG-C8-4,8-diMeIQx. The second peak remains unidentified. The improved workup procedures in combination with the high resolution and reproducibility of the 32P-HPLC system should be useful for characterization of PhIP- and 4,8-diMeIQx-DNA adducts in DNA modified by complex mixtures.

Seasonal variation of DNA adduct pattern in human lymphocytes analyzed by 32P-HPLC.

32P-HPLC is a recently published method to generate DNA adduct profiles after exposure to a complex of genotoxic substances. The low detection limit enables characterization of individual DNA adducts in the general population. The 32P-HPLC method was applied to human lymphocytes and granulocytes from Silesia, a polluted industrial region in the south of Poland. Human samples were collected at the end of winter and summer to investigate the seasonal influence on DNA adduct formation. In lymphocytes a strong seasonal variation was seen in total DNA adducts, with winter values exceeding the summer values by 7.33 +/- 3.56 times. Granulocytes did not show any seasonal variation. In winter-collected lymphocytes the DNA adduct levels were 21.4 +/- 16.6/10(8) normal nucleotides (NN) while the summer values were 2.96 +/- 2.46/10(8) NN. Granulocytes had 8.06 +/- 7.76 and 9.59 +/- 6.19 DNA adducts/10(8) NN during winter and summer respectively. The lymphocyte DNA adduct profile consisted of at least 16 individual or clusters of DNA adducts. All 16 had a clear winter influence, with a winter:summer ratio of 1.6-15.3, indicating exposure to a complex mixture of genotoxic substances. The DNA adducts analyzed in human lymphocytes had retention times similar to DNA adducts generated by polycyclic aromatic hydrocarbons. The suggested candidates for DNA adducts displayed a similar seasonal variation in airborne particles to that found in DNA adducts in lymphocytes of humans living in the area. This is the first application of the 32P-HPLC method to analysis of DNA adducts in human tissues.

Improvements in the analytical method for 8-hydroxydeoxyguanosine in nuclear DNA.

Modifications at two points in the sequence of 8-hydroxy-2'-deoxyguanosine (8-OH-dG) analysis have contributed to a more accurate and simplified determination of 8-OH-dG in DNA. The first was an improvement in the detection limit for 8-OH-dG in high-performance liquid chromatography analysis and the second was a pronase digestion and ethanol precipitation method (pronase/ethanol method) for DNA isolation which could minimize artificial formation of 8-OH-dG. Since the changes in background current from electrochemical detection are regularly periodical, it was possible to reduce this background change by connecting a pressure damper, degassing the eluent before use and finally subtracting its theoretical function. After this background correction, the detection limit for 8-OH-dG was improved one order of magnitude, from 20 fmol (5.68 pg) to 1.76 fmol (0.5 pg). Therefore, 0.005 8-OH-dG/10(5) dG can be detected from 50 micrograms DNA. This improvement will allow the analysis of small samples, tissues from needle biopsies, < 5 ml whole blood, etc., and will contribute to the accuracy of 8-OH-dG measurements. The pronase/ethanol method resulted in lower levels of 8-OH-dG than the phenol method in analyses of both rat liver and calf thymus DNA, even after 6 h incubation at 45 degrees C. The level obtained by the pronase/ethanol method with butylated hydroxytoluene was approximately equal to or lower than the 8-OH-dG levels reported in normal rat liver. The pronase/ethanol method for DNA isolation can replace the phenol or other methods in 8-OH-dG analysis. This method also omits the use of highly toxic organic solvents.

32P-HPLC suitable for characterization of DNA adducts formed in vitro by polycyclic aromatic hydrocarbons and derivatives.

Analysis of DNA adducts demands both high sensitivity and good resolution. A high-performance liquid chromatography method for 32P-postlabeled DNA adducts (32P-HPLC) was used to investigate DNA adduct formation from 38 polycyclic hydrocarbons and biphenyls in vitro. The 32P-HPLC method proved to be useful for separation, detection and characterization of DNA adducts from most of the substances. The in vitro method used to form the DNA adducts, with calf thymus DNA, nucleotide 3'-phosphates and metabolic activation through S-9 liver homogenate, gave poor quantitative reproducibility. However, the results showed that the 32P-HPLC method was suitable for characterizing DNA adducts from many substances. From 35 of the tested substances 365 DNA and nucleotide 3'-phosphate adducts were detected and characterized concerning retention times. Of the adducts, 171 were detected in DNA and 39 of them from five substances were characterized concerning target nucleotides. The retention time library built can be used in future analyses of DNA with complex patterns of DNA adducts.

Intestinal microflora enhances formation of DNA adducts following administration of 2-NF and 2-AAF.

2-Nitrofluorene (NF) is found in the environment mainly due to incomplete combustion, as in vehicles. The major class of metabolites in vivo in rats after oral administration is the reduced and acetylated metabolites, e.g. derivatives of 2-acetylaminofluorene (AAF). The intestinal microflora reduces the nitro function to an amine which is further metabolized via acetylation and hydroxylations. In this study, NF and AAF were orally administered to germ-free and conventional rats with the aim of studying DNA adduct formation in different tissues with the 32P-post-labelling assay. Chromatographic detection was performed with TLC and on-line 32P detection after HPLC separation of DNA adducts. The major (95%) DNA adduct formed was dG-C8-AF for both NF and AAF. The potency to form DNA adducts successively declined with the combinations conventional/AAF, germ-free/AAF, conventional/NF and germ-free/NF. The DNA adduct dG-C8-AF was detected in all four tissues that were analysed, e.g. liver, kidney, lung and heart. The presence of intestinal microflora enhanced the formation of DNA adducts in the tissues studied.

Lack of initiating capacity of the genotoxic air pollutant 2-nitrofluorene in the mouse skin two-stage carcinogenesis system.

2-Nitrofluorene (NF) is a potent genotoxic substance found in environments where incomplete combustion takes place. NF is a mutagen and a carcinogen in animal models. NF or 7,12-dimethylbenz[a]anthracene (DMBA) was administered once topically to female SENCAR mice followed by promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA) in two different studies. TPA (2-5 micrograms) was administered twice a week for 13 or 19 weeks after initiation of DMBA (5-10 micrograms) or NF (50-1500 micrograms). DMBA administration (positive control) resulted in the formation of many papillomas, which were seen from week 8-9 after initiation. The negative controls administered acetone only were free of tumours. NF administration did not result in papilloma formation, even at high initiating doses of NF combined with a dose of TPA causing a systemic toxic effect in terms of a significant reduced body weight. The mechanism behind the absence of papilloma formation after administration of genotoxic and carcinogenic NF remains to be investigated.

Optimization of an HPLC method for analyses of 32P-postlabeled DNA adducts.

A further development of an HPLC method to analyze 32P-postlabeled DNA adducts is presented. The method is based on on-line detection of 32P radioactivity after separation by reversed-phase chromatography. The method has an advantage in that the postlabeling mixture can be injected directly into the HPLC system without any prior purification, with the background radioactivity on a low level. The analysis includes the whole range of substances from orthophosphate to non-polar DNA adducts, which makes it possible to analyze normal nucleotides and ATP together with DNA adducts. The analytical system has a high reproducibility and separates complex mixtures of DNA adducts. The slightly lower sensitivity compared to the TLC method is compensated for by the possibility of injecting large amounts of DNA into the system without affecting the analytical properties. The system can be applied to different DNA adducts as well as complex mixtures of DNA adducts.

DNA adduct formation after oral administration of 2-nitrofluorene and N-acetyl-2-aminofluorene, analyzed by 32P-TLC and 32P-HPLC.

DNA adducts have been detected in laboratory animals after exposure to carcinogens as well as in human populations with known or suspected risk of developing cancer. Examples are smokers, coke and aluminium workers, urban citizens and roofers. The formation of DNA adducts is an early event in carcinogenesis which can be used for measuring target dose and as a biomarker for genotoxic risk. A method of analyzing 32P-postlabelled DNA adducts on reverse HPLC with on-line detection of 32P has been developed. The method permits direct injection of the 32P-postlabeling mixture into the analytical system without prior purification with background radioactivity on a low level. The method can be used in parallel with TLC analyses of 32P-postlabelled DNA adducts to improve the analytical capacity. The time for analysis of a typical single sample by HPLC and TLC is 30-60 min and 6-24 h respectively. A high (2 M) salt concentration in the HPLC eluent reduces the 32P background considerably. Also the peak tailing was substantially diminished, giving an ability to separate DNA adducts equal to or better than the TLC method. The method has been applied to 2-nitrofluorene (NF), a carcinogenic air pollutant, and N-acetyl-2-aminofluorene (AAF), a model carcinogen which is also a metabolite of NF. A number of DNA adducts are formed in the livers of rats. After oral administration of AAF and NF, DNA adducts in the liver have been characterized as dG-C8-AF and dG-C8-AAF. The major DNA adduct found in both NF- and AAF-administered animals was dG-C8-AF. The described HPLC method can, with minor adjustments, generally be used to analyze 32P-postlabelled DNA adducts.