X-ray 3D imaging-based microunderstanding of granular mixtures: Stiffness enhancement by adding small fractions of soft particles.

This research focuses on performing ultrasound propagation measurements and micro-X-ray computed tomography (µXRCT) imaging on prestressed granular packings prepared with biphasic mixtures of monodisperse glass and rubber particles at different compositions/fractions. Ultrasound experiments employing piezoelectric transducers, mounted in an oedometric cell (complementing earlier triaxial cell experiments), are used to excite and detect longitudinal ultrasound waves through randomly prepared mixtures of monodisperse stiff/soft particles. While the fraction of the soft particles is increasing linearly from zero, the effective macroscopic stiffness of the granular packings transits nonlinearly and nonmonotonically toward the soft limit, remarkably via an interesting stiffer regime for small rubber fractions between 0.1 ≲ ν ≲ 0.2. The contact network of dense packings, as accessed from µXRCT, plays a key role in understanding this phenomenon, considering the structure of the network, the chain length, the grain contacts, and the particle coordination. While the maximum stiffness is due to surprisingly shortened chains, the sudden drop in elastic stiffness of the mixture packings, at ν ≈ 0.4, is associated with chains of particles that include both glass and rubber particles (soft chains); for ν ≲ 0.3, the dominant chains include only glass particles (hard chains). At the drop, ν ≈ 0.4, the coordination number of glass and rubber networks is approximately four and three, respectively, i.e., neither of the networks are jammed, and the chains need to include particles from another species to propagate information.

Characterization of flame-generated C10 to C 160 polycyclic aromatic hydrocarbons by atmospheric-pressure chemical ionization mass spectrometry with liquid introduction via heated nebulizer interface.

Complex mixtures of polycyclic aromatic hydrocarbons (PAHs) generated from fuel-rich combustion of ethylene-naphthalene mixtures in a jet-stirred-plug-flow reactor were chemically characterized by combined mass spectrometric techniques to yield product composition data that cover the molecular mass region from simple PAHs (naphthalene, 128 u) to large molecules comparable in molecular size (1792 u) to nanoparticles of soot. Two techniques based on atmospheric-pressure chemical ionization mass spectrometry (APCI-MS) were investigated: (1) APCI-MS combined with high-performance liquid chromatography through a heated nebulizer interface was found suitable for PAHs up to C36 (448 u). (2) For the characterization of larger PAHs beyond C36, direct liquid introduction (DLI) of sample into an atmospheric-pressure chemical ionization mass spectrometer through a heated nebulizer gave protonated molecular ions for PAHs over the m/z 400-2000 range. Although unequivocal elemental composition information is unattainable from the unit-resolution DLI/APCI-MS data, by starting with structural data from identified C16 to C32 PAHs, and applying PAH molecular growth principles, it was possible to generate PAH molecular maps from the DLI/APCI-MS data from which values for the elemental composition could be derived for all major peaks.

Acetylator phenotype, aminobiphenyl-hemoglobin adduct levels, and bladder cancer risk in white, black, and Asian men in Los Angeles, California.

BACKGROUND: There is a large body of epidemiologic and experimental data that have identified a number of arylamines as human bladder carcinogens. Metabolic activation is required to biotransform these arylamines into their carcinogenic forms, and N-hydroxylation, which is catalyzed by the hepatic cytochrome P4501A2 isoenzyme, is generally viewed as the first critical step. On the other hand, the N-acetylation reaction, catalyzed by the hepatic N-acetyltransferase enzyme, represents a detoxification pathway for such compounds. The N-acetyltransferase enzyme is coded by a single gene displaying two phenotypes, slow and rapid acetylators. In the United States, cigarette smoking is a major cause of bladder cancer in men, and carcinogenic arylamines present in cigarette smoke are believed to be responsible for inducing bladder cancer in smokers. PURPOSE: Our purpose was to test the differences in three ethnic/racial groups for the prevalence of acetylator phenotypes and to ascertain whether slow acetylators actually have higher levels of activated arylamines in comparison with rapid acetylators. METHODS: One hundred thirty-three male residents of Los Angeles County who were either white, black, or Asian (Chinese or Japanese) and over the age of 35 years were assessed for their acetylator phenotype and levels of 3- and 4-aminobiphenyl (ABP) hemoglobin adducts. Subjects were either lifetime nonsmokers (n = 72) or current cigarette smokers of varying intensity (n = 61). RESULTS: The proportion of slow acetylators was highest among whites (54%), intermediate among blacks (34%), and lowest among Asians (14%). Similarly, geometric mean levels of both 3- and 4-ABP-hemoglobin adducts were highest in whites (1.80 and 49.2 pg/g hemoglobin [Hb], respectively), intermediate in blacks (1.54 and 38.5 pg/g Hb), and lowest in Asians (0.73 and 36.0 pg/g Hb). As expected, cigarette smokers had significantly higher mean levels of both 3- and 4-ABP-hemoglobin adducts relative to nonsmokers, and the levels increased with the number of cigarettes smoked per day (P < .0005 for both adducts). Slow acetylators consistently exhibited higher mean levels of ABP-hemoglobin adducts relative to rapid acetylators, independent of race and level of smoking. CONCLUSION: The present cross-sectional survey supports acetylation phenotype as an important determinant of bladder cancer risk and a possible major factor in the varying bladder cancer risk among whites, blacks, and Asians.

Characterization of various classes of protein adducts.

Analysis of the types of protein adducts formed by chemical carcinogens indicate that adducts may be categorized into various classes according to the nature of the carcinogen as well as the amino acid with which they react. Tryptophan(214) of serum albumin was previously shown to react specifically with N-sulfonyloxy-N-acetyl-4-aminobiphenyl. The same residue is now shown to also react with the sulfate esters of N-hydroxy-N-acetyl-2-aminofluorene and N-hydroxy-N,N'-diacetylbenzidine. Thus, Trp-214 appears to be a binding site for a variety of activated N-aryl hydroxamic acids. Epoxides and diol epoxides derived from polynuclear aromatic hydrocarbons alkylate carboxylic groups in hemoglobin and serum albumin. Because the esters formed are readily hydrolyzed to dihydrodiols and tetrahydrotetrols which can be determined by GC-MS, it is possible to analyze for a wide range of polyaromatic hydrocarbon (PAH) epoxide adducts. With this approach it was shown that human subjects experiencing exposure to ambient levels of environmental PAH do take up and metabolize chrysene and benzo[a]pyrene. Feral, bottom-dwelling fish inhabiting contaminated waters were also examined. Globin adducts containing certain dihydroxy groups such as those arising in anti-diol epoxide adducts were concentrated by boronate affinity chromatography and further analyzed by HPLC with diode-array UV/visible detection. Four compounds were detected that exhibited spectra characteristic of a polynuclear chromophore. Two of these appeared to be isomers. Further instrumental analysis is needed to elucidate the structure of these unknown putative adducts.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between environmental tobacco smoke exposure and carcinogen-hemoglobin adduct levels in nonsmokers.

BACKGROUND: A potent bladder carcinogen for workers in the dye industry, 4-aminobiphenyl (4-ABP), is present in environmental tobacco smoke and has been shown to bond covalently with hemoglobin. PURPOSE: The goal of this study was to examine the relationship between exposure to environmental tobacco smoke and levels of 4-ABP-hemoglobin adducts in nonsmoking pregnant women and to compare adduct levels in those women with levels in smoking pregnant women. METHODS: A questionnaire on smoking and exposure to environmental tobacco smoke was administered to 15 pregnant women who smoked cigarettes and 40 who did not smoke. Exposure was quantified for 1 week with a personal diary and by air sampling with a monitor worn by each woman. The monitor collected nicotine by passive diffusion to a filter treated with sodium bisulfate, and the deposit on the filter was analyzed by gas chromatography. Aliquots of maternal blood and cord blood collected during delivery were analyzed for 4-ABP-hemoglobin adducts by gas chromatography with negative ion chemical ionization mass spectrometry. RESULTS: The mean adduct level in smokers (184 pg of 4-ABP per gram of hemoglobin) was substantially higher than that in nonsmokers (22 pg/g). This difference was statistically significant. Among nonsmokers, the levels of 4-ABP adducts increased significantly with increasing environmental tobacco smoke level (P = .009). Those in the lowest exposure category (< 0.5 micrograms/m3 weekly average nicotine) had median 4-ABP-hemoglobin adduct levels of 15 pg of 4-ABP per gram of hemoglobin, while those in the highest exposure category (> or = 2.0 micrograms/m3) had median levels of 26 pg/g. Nonsmokers in this study had a median adduct level of 20 pg/g, and smokers had a median level of 143 pg/g. CONCLUSIONS: 4-ABP-hemoglobin adduct levels in nonsmokers were 14% of the levels in smokers, which is consistent with findings of 20% in two other studies. Nonsmokers may receive a nontrivial dose of carcinogens from environmental tobacco smoke proportional to their exposure to environmental tobacco smoke. IMPLICATION: The relationship between environmental tobacco smoke exposure and 4-ABP-hemoglobin adduct levels supports epidemiologic evidence that environmental tobacco smoke is carcinogenic to passive smokers.

Mutagenic decomposition products of nitrosated 4-chloroindoles.

4-Chloro-6-methoxyindole, a constituent of fava beans, forms a potent direct-acting mutagen, 4-chloro-6-methoxy-2-hydroxy-1-nitrosoindolin-3-one oxime, when nitrosated. In order to better understand the properties of this mutagen, we have studied a readily-available analog, 4-chloro-2-hydroxy-1-nitrosoindolin-3-one oxime, prepared by nitrosation of 4-chloroindole. This analog is also mutagenic, and both mutagens decompose rapidly at neutral or higher pH to yield in each case a new, less potent mutagen which then reacts further to form a nonmutagenic final product. The two products arising from 4-chloro-2-hydroxy-1-nitrosoindolin-3-one oxime, on the basis of comparison of spectroscopic and chromatographic evidence with that from authentic standards, are 4-chloro-N-nitrosodioxindole and 4-chloroisatin; those arising from 4-chloro-6-methoxy-2-hydroxy-1-nitrosoindolin-3-one oxime appear to be the corresponding 6-methoxy analogs. The interplay of these pathways with respect to net biological activity, especially under gastric conditions, remains to be described.

Measurement of 4-aminobiphenyl-hemoglobin adducts in lung cancer cases and controls.

Hemoglobin adducts of the activated carcinogenic aromatic amine 4-aminobiphenyl have been measured in a case-control study of lung cancer. Data obtained for lung cancer cases are compared to those obtained for controls that consisted of patients with either chronic obstructive pulmonary disease or non-pulmonary cancers. Both simple and multivariate analysis found a positive association of 4-aminobiphenyl-hemoglobin adducts with the quantity of tobacco smoked as determined by either urine cotinine or questionnaire data. No association was found between 4-aminobiphenyl-hemoglobin adducts and cancer diagnosis, and adduct levels were not related to remote tobacco use, i.e., total pack years of smoking. There was no association between the levels of adducts detected and the ability of an individual to metabolize debrisoquine (debrisoquine metabolic phenotype, CYP2D6). Whereas 4-aminobiphenyl-hemoglobin adduct levels reflected recent tobacco smoking, they were not correlated with lung cancer risk.

4-Aminobiphenyl hemoglobin adducts in fetuses exposed to the tobacco smoke carcinogen in utero.

Maternal-fetal exchange of a potent tobacco-related human carcinogen, 4-aminobiphenyl, was studied in smoking (n = 14) and nonsmoking (n = 38) pregnant women. N-Hydroxy-4-aminobiphenyl, the active metabolite of 4-aminobiphenyl, forms chemical addition products (adducts) with hemoglobin. Levels of 4-aminobiphenyl hemoglobin adducts were measured in maternal-fetal paired blood samples obtained from smoking and nonsmoking women during labor and delivery. Carcinogen-hemoglobin adducts were detected in all maternal and fetal blood samples. Levels of such adducts were significantly higher (P less than .001) in maternal and fetal blood samples from smokers: the mean 4-aminobiphenyl hemoglobin adduct level was 92 +/- 54 pg/g of hemoglobin in blood samples from fetuses of smokers, and 17 +/- 13 pg/g of hemoglobin in blood samples from fetuses of nonsmokers; the mean maternal 4-aminobiphenyl hemoglobin adduct level was 183 +/- 108 pg/g of hemoglobin in smokers, and 22 +/- 8 pg/g of hemoglobin in nonsmokers. Fetal carcinogen-adduct levels were consistently lower than maternal levels: the mean maternal to fetal ratio was 2.4 +/- 1.1 in smokers and 1.9 +/- .98 in nonsmokers. Fetal 4-aminobiphenyl hemoglobin adduct levels were strongly associated (correlation coefficient [r2] = .51, P = .002) with maternal 4-aminobiphenyl hemoglobin adduct levels when paired samples from smoking mothers were analyzed. A measure of third-trimester tobacco smoke exposure based on number of cigarettes smoked per day, amount of each cigarette smoked, and depth of inhalation was associated (r2 = .59, P = .029) with maternal 4-aminobiphenyl levels but not with fetal 4-aminobiphenyl levels. This study demonstrates that a potent tobacco-related carcinogen, 4-aminobiphenyl, or its active metabolite, N-hydroxy-4-aminobiphenyl, crosses the human placenta and binds to fetal hemoglobin in concentrations that are significantly higher in smokers than in nonsmokers.