Arsenic methylation capacity and skin cancer.

Chronic ingestion of arsenic from drinking water is associated with the occurrence of skin cancer. To clarify the role of arsenic methylation capacity in the development of arsenic-associated skin lesions, an epidemiological case-control study was conducted in the southwestern region of Taiwan, in which 26 skin disorder patients were matched with control subjects. The objective of this study was to determine whether arsenic methylation capacity of patients with skin disorders differed from that of matched controls. Both cases and controls had been exposed to similar high concentrations of arsenic in drinking water. Results indicated that skin lesion cases had higher percents of inorganic arsenic (InAs, 13.1+/-3.7%), methylarsonic acid (MMA, 16.4+/-3.2%), lower percent of dimethylarsinic acid (DMA, 70.5+/-5.8%), and higher ratio of MMA to DMA (MMA/DMA, 0.24+/-0.06) than matched controls (InAs: 11.43+/-2.1%; MMA: 14.6+/-2.6%; DMA: 73.9+/-3.3%; MMA/ DMA: 0.20+/-0.04). Individuals with a higher percentage of MMA (>15.5%) had an odds ratio of developing skin disorder 5.5 times (95% confidence interval, 1.22-24.81) higher than those having a lower percentage of MMA. This association was not confounded by hepatitis B surface antigen, cigarette smoking, or alcohol and tea consumption. It is concluded that arsenic biotransformation including methylation capacity may have a role in the development of arsenic-induced skin disorders.

Organophosphorous pesticide exposure increases the frequency of sperm sex null aneuploidy.

It has been estimated that 4 of 1,000 live births and 35% of spontaneous abortions are aneuploid and that an important proportion of embryo and newborn aneuploidy is of paternal origin. Exposure to organophosphorous pesticides (OP) has been associated with sperm hyperploidy/polyploidy. Therefore, we aimed to assess the frequency of sperm aneuploidy (X, Y, and 18) and its relationship with urinary OP metabolites in agricultural workers. We performed multicolor fluorescence in situ hybridization on samples from nine men obtained before and during the pesticide spraying season to assess sperm aneuploidy. We measured urinary OP metabolite levels by gas-liquid chromatography. Aneuploidies were found in 0.67% of total sperm nuclei. The most frequent aneuploidy was the lack of a sexual chromosome or sex null (0.19%), followed by XY18 (0.15%) and XY18-18 (0.06%). OP metabolites detected at higher concentrations were dimethylthiophosphate, dimethyldithiophosphate, and diethylphosphate (DEP). There were no differences in average aneuploidy frequency or urinary metabolite levels between samples collected before and after exposure. However, Poisson regression analysis adjusted for age, alcohol intake, and sperm concentration showed significant associations between OP metabolite concentrations and increased frequency of sperm aneuploidies. The association was more evident between DEP and sex null, and the risk increased further during the spraying season. Thus, OP exposure could interfere with sperm chromosome segregation and increase the risk for genetic syndromes, such as Turner's. Further studies are required to assess the prevalence of spontaneous abortions, birth defects, and genetic syndromes in agricultural communities.

32P-postlabelling analysis of DNA adducts from Fischer-344 rats administered 2,4-diaminotoluene.

Using 32P-postlabelling and thin layer chromatography, DNA adduct formation by the potent animal carcinogen 2,4-diaminotoluene in Fischer-344 rats was investigated. DNA from four different organs, liver, mammary gland, kidney and lung, were examined for adducts following single administration of this compound. DNA binding was detected in all four organs, with each producing one major and two minor adduct spots on autoradiograms. The adducts induced were qualitatively identical among the different organs, but quantitative differences were observed. The two target organs of 2,4-diaminotoluene induced carcinogenesis, the liver and mammary gland produced higher adduct yields, with levels up to 30-times higher than those for the two non-target organs. Since the liver is the principal target for 2,4-diaminotoluene induced carcinogenesis, we further examined DNA adducts from this site for the effects of different doses and time points. DNA binding in liver was detected following doses as low as 4.1 mumol/kg. At the highest concentration examined (2046 mumol/kg), the level of the major adduct was 29.2 adducted nucleotides per 10(7) total nucleotides. The yields for the two minor adducts were approximately one-tenth that for the major adduct. Following a 410 mumol/kg dose, DNA adduct removal over time was examined. DNA adduct removal exhibited biphasic kinetics, with a rapid initial phase followed by a slower rate of elimination. Up to 60% of maximum adduct levels persisted after 2 weeks. DNA binding by 2,4-diaminotoluene was also compared to that by its weakly carcinogenic analog, 2,4-dinitrotoluene. The two compounds produced identical adduct patterns, suggesting that they share common metabolites and adducts. Adduct yields from 2,4-dinitrotoluene, however, were lower. The results of our studies suggest that the differences in carcinogenic potency between 2,4-diaminotoluene and 2,4-dinitrotoluene, as well as the organotropic effects of 2,4-diaminotoluene may be explained, in part, by quantitative differences in the extent of DNA adduct formation.

Comparison of DNA binding between the carcinogen 2,6-dinitrotoluene and its noncarcinogenic analog 2,6-diaminotoluene.

We used 32P-postlabelling to compare DNA binding between the potent hepatocarcinogen 2,6-dinitrotoluene and its noncarcinogenic analog 2,6-diaminotoluene. The two compounds were compared to determine whether differences in DNA binding could partly explain the differences in their carcinogenicity. Fischer-344 rats were administered 1.2 mmol/kg of a compound by single i.p. injection and examined for DNA adduct formation in the liver. Four adducts were detected following administration of 2,6-dinitrotoluene, with a total adduct yield of 13.5 adducted nucleotides per 10(7) nucleotides. Qualitatively identical adducts were also detected after treatment with the derivative 2-amino-6-nitrotoluene. Adduct yields from 2,6-dinitrotoluene were 30 times greater than from 2-amino-6-nitrotoluene. No adducts were observed following treatment with 2,6-diaminotoluene. 2,6-Dinitrotoluene and 2,6-diaminotoluene were also compared for qualitative differences in hepatotoxicity. 2,6-Dinitrotoluene produced extensive hemorrhagic necrosis in the liver, whereas no evidence of hepatocellular necrosis was detected following administration of the latter. The differences between the two compounds in both DNA binding and cytotoxicity were consistent with the differences in their carcinogenicity.

Chemical exposures of rocket-engine test-stand personnel and cancer mortality in a cohort of aerospace workers.

We conducted a retrospective cohort study of 6107 aerospace workers to examine whether exposure to chemicals--primarily hydrazine fuels--during rocket-engine fueling and testing affects cancer mortality. When conditional logistic regression analysis was applied and adjusted for confounding variables, the estimated rate ratio for lung cancer mortality, comparing exposed to unexposed workers from the same facility, ranged from 1.68 (95% confidence interval, 1.12 to 2.52) to 2.10 (95% confidence interval, 1.36 to 3.25), depending on job-duration threshold (6 or 24 months) and lag (0 to 15 years). Similar results were obtained for hemato- and lymphopoietic cancer and for bladder and kidney cancer mortality, but estimates for these cancers were imprecise. We concluded that occupational exposure to hydrazine or other chemicals associated with rocket-engine testing jobs increased the risk of dying from lung cancer, and possibly other cancers, in this population of aerospace workers; however, our results need to be replicated in other populations.

Mutagenicity studies of selected antihistamines, their metabolites and products of nitrosation.

Methapyrilene, four structurally related antihistamines, three metabolites of methapyrilene and two products of the reaction of methapyrilene with nitrite were all tested for mutagenicity to Salmonella typhimurium. The two products of the methapyrilene-nitrite reaction have also been identified as metabolites of methapyrilene. None was mutagenic alone, either with or without rat liver S-9 activation. After reaction with sodium nitrite in acetic acid solution (nitrosation), the products of five of the ten compounds were mutagenic. These compounds were methaphenilene, 2-thiophenemethanol, 2-thiophenecarboxylic acid, N-(2-pyridyl)-N'N'-dimethylethylenediamine and N-(2-thenylmethyl)-2-aminopyridine.

Approaches to addressing occupational and environmental health needs in Mexico.

The University of California, Los Angeles, has somewhat shifted the focus of its Fogarty program, taking a four-pronged approach: conducting high-level collaborative scientific research with Mexican faculty and trainees at the most advanced institutions in the country; providing training and collaborative research opportunities to faculty/students at other institutions in Mexico (primarily through training faculty who do not hold doctoral degrees); providing environmental and occupational health training to the professional community throughout Mexico; and developing short courses on special topics that provide means for greater research collaboration and skill building. The program is also working with existing institutions to develop academic programs that will enlarge the environmental and occupational health infrastructures in Mexico and Latin America.

Exposure to inhaled particulate matter activates early markers of oxidative stress, inflammation and unfolded protein response in rat striatum.

To study central nervous system airborne PM related subchronic toxicity, SD male rats were exposed for eight weeks to either coarse (32 µg/m³), fine (178 µg/m³) or ultrafine (107 µg/m³) concentrated PM or filtered air. Different brain regions (olfactory bulb, frontal cortex, striatum and hippocampus), were harvested from the rats following exposure to airborne PM. Subsequently, prooxidant (HO-1 and SOD-2), and inflammatory markers (IL-1ß and TNFα), apoptotic (caspase 3), and unfolded protein response (UPR) markers (XBP-1S and BiP), were also measured using real-time PCR. Activation of nuclear transcription factors Nrf-2 and NF-κB, associated with antioxidant and inflammation processes, respectively, were also analyzed by GSMA. Ultrafine PM increased HO-1 and SOD-2 mRNA levels in the striatum and hippocampus, in the presence of Nrf-2 activation. Also, ultrafine PM activated NF-κB and increased IL-1ß and TNFα in the striatum. Activation of UPR was observed after exposure to coarse PM through the increment of XBP-1S and BiP in the striatum, accompanied by an increase in antioxidant response markers HO-1 and SOD-2. Our results indicate that exposure to different size fractions of PM may induce physiological changes (in a neuroanatomical manner) in the central nervous system (CNS), specifically within the striatum, where inflammation, oxidative stress and UPR signals were effectively activated.

Hazard surveillance in occupational disease.

We have reviewed existing data sources available for conducting hazard surveillance. Both the NIOSH NOHS/NOES and the OSHA IMIS can have significant value for hazard surveillance that is designed both to establish priorities for various preventive strategies--including intervention, research, and planning--and to complement disease surveillance. These systems also have certain limitations that affect their overall value in these regards. We have proposed alternative hazard surveillance systems that would expand the database on actual exposures in the workplace by requiring that industry systematically conduct environmental monitoring for defined substances and then provide the data to OSHA and NIOSH for use in hazard surveillance.

Evaluation of the inhibition of glycolytic enzymes by the neurotoxicant dimethylaminopropionitrile.

The neurotoxic aminonitrile dimethylaminopropionitrile (DMAPN) inhibits the crystalline glycolytic enzymes glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and fructose-6-phosphate kinase (phosphofructokinase, PFK). Preincubation of GAPDH with the aminonitrile enhances the inhibition, indicating that the inhibition is irreversible. The overall bimolecular rate constant ki was determined to be 2.42 +/- 0.21 M-1 min-1. Dithiothreitol (DTT) partially protected the enzyme from inhibition. PFK is also inhibited by DMAPN, but the inhibition is reversible and noncompetitive with a Kl, of 2.79 X 10(-2) M. DMAPN does not inhibit lactate dehydrogenase (LDH), nor is GAPDH or PFK inhibited by 3,3'-iminodipropionitrile (IDPN).

In vitro and in vivo inhibition of lysyl oxidase by aminopropionitriles.

Inhibition of lysyl oxidase (protein-lysine 6-oxidase, EC 1.4.3.13) decreases the rate of collagen and elastin cross-link formation and produces osteolathyrism in animals. Organic nitriles, including beta-aminopropionitrile (BAPN), have been shown to irreversibly inhibit lysyl oxidase in vitro. Both BAPN and 3,3'-iminodipropionitrile (IDPN) have been shown to produce osteolathyric changes when administered to animals. To date compounds that have been reported to inhibit this enzyme possess a primary amine functional group. In this study a series of primary and substituted aminopropionitriles was studied for their ability to inhibit lysyl oxidase activity both in vitro and in vivo. Our results show that of the compounds tested, BAPN was the most potent inhibitor of the enzyme. Reversible inhibition of lysyl oxidase in vitro was found with two secondary aminonitriles, IDPN and monomethylaminopropionitrile (MMAPN). There was no inhibition of enzyme activity associated with the tertiary compound 3,3'-dimethylaminopropionitrile (DMAPN) or propionitrile, a compound lacking an amine functional group. IDPN was found to produce a slight irreversible inhibition of the enzyme both in vitro and in vivo. Pretreatment of rats with pargyline, an inhibitor of monoamine oxidase, was found to increase the inhibitory potential of BAPN (p < or = .1). Pargyline pretreatment did not alter the inhibitory potential for any of the other aminonitriles tested. These results suggest that the presence of a primary amino functional group is not a strict requirement for inhibition of lysyl oxidase. In addition, reversible and irreversible mechanisms of inhibition may be involved in the production of osteolathyric changes associated with IDPN exposure.

Comparison of DNA adduct formation between 2,4 and 2,6-dinitrotoluene by 32P-postlabelling analysis.

Using 32P-postlabelling, we examined DNA binding by 2,4 and 2,6-dinitrotoluene (DNT) in Fischer-344 rats. DNA binding between the two compounds was compared to determine if differences in adduct formation and persistence could partly explain the known isomer-specific hepatocarcinogenicity of DNTs. The differences in cytotoxicity between the two isomers were also assessed. Both 2,4 and 2,6-DNT induced adduct formation in hepatic DNA. Three distinct adducts were detected following single i.p. administration of 2,4-DNT, while the 2,6-isomer produced four different adducts. Depending on the concentration administered, the two compounds differed in their relative yields. 2,6-DNT produced a greater total adduct yield relative to the 2,4-isomer at low concentrations. Following administration of high concentrations, however, 2,4-DNT predominated. The maximum adduct levels measured were 3.0 and 1.8 adducted nucleotides per 10(6) nucleotides for 2,4 and 2,6-DNT, respectively. Substantial amounts of adducts from both compounds were found to persist over time. After 2 weeks, the mean persistence for 2,4 and 2,6-DNT induced adducts were 42% and 46%, respectively. Qualitative examination for liver toxicity showed 2,6-DNT to be more cytotoxic, inducing extensive hemorrhagic centrilobular necrosis. Rats treated with 2,4-DNT did not show any observable signs of hepatocellular necrosis. Under the conditions of this study, the differences between 2,4 and 2,6-DNT in adduct formation and persistence do not appear to be sufficient to account for their differences in carcinogenicity. The toxicity of 2,6-DNT may be a determining factor in the potent carcinogenicity observed with this compound.

Role of monoamine oxidase in aminopropionitrile-induced neurotoxicity.

Oxidation of aminopropionitriles was measured in vitro with both rat liver mitochondria and bovine plasma monoamine oxidase (MAO). The nonneurotoxic aminonitrile beta-aminopropionitrile (BAPN) was oxidized at a significantly higher rate (p less than .05) than either of the neurotoxic aminonitriles tested; 3,3'-iminodipropionitrile (IDPN) and 3,3'-dimethylaminopropionitrile (DMAPN). DMAPN was a poor substrate for both mitochondrial and plasma MAO. None of the aminonitriles tested were found to inhibit MAO activity in rat brain or liver in vivo. Inhibition of MAO activity with pargyline in vivo did not affect the pattern of IDPN- or DMAPN-induced toxicity. These results suggest that monoamine oxidase is not involved in aminonitrile-induced neurotoxicity.

Formation and removal of DNA adducts in Fischer-344 rats exposed to 2,4-diaminotoluene.

32P-Postlabeling was used to examine DNA adduct formation and removal in Fischer-344 rats exposed to the animal carcinogen 2,4-diaminotoluene (DAT). Adduct formation and persistence were compared between target (liver and mammary gland) and non-target organs (kidney and lung) to determine if possible differences could explain the observed organ specificity of DAT induced carcinogenesis. The effects of different exposure conditions on DNA adduct formation and removal were also examined by varying the concentration and frequency of compound administration. DAT produced three distinct DNA adducts. Among the organs examined, DNA binding was highest in the liver, with levels approximately 10 times greater than that of the mammary gland and up to 50 times greater than of the two nontarget sites. Despite the large differences in the initial extent of adduct formation, the persistence of adducts among sites was not significantly different. In the liver, there were dose-dependent differences in DNA adduct formation, but adduct removal following different dosages did not vary significantly. The effects of multiple administration on DNA adduct formation and removal were examined by treating rats with 5 mg/kg DAT daily for 10 consecutive days. Adduct yields from multiple treatment were greater than from a single 50 mg/kg exposure. The persistence of adducts following multiple treatment was also greater than after an equivalent single exposure. The results demonstrated organ-specific and dose-dependent differences in initial extent of DNA adduct formation, but no differences in adduct persistence. However, the results did suggest that adduct formation and persistence may change with repeated administration of DAT.

Particle bounce in a personal cascade impactor: a field evaluation.

The collection characteristics of five types of substrates (collection surfaces) used in personal cascade impactors were evaluated for particle bounce in the laboratory with lead dioxide dust, and in the field with brass pouring fume and brass grinding dust. The substrates tested were uncoated stainless steel, silicon grease-coated stainless steel, oil-saturated Millipore membrane filter, oil-saturated Teflon membrane filter and oil-saturated sintered stainless steel. The use of coated and uncoated stainless steel plates to collect lead dioxide dust produced no difference in measured mass median diameter (MMD); however, with brass grinding dust, there was a 50% decrease in measured MMD when uncoated stainless steel substrates were used, as compared with coated stainless steel substrates. Oil-saturated Millipore membrane surfaces gave consistently lower MMDs than coated stainless steel surfaces. Coated and uncoated stainless steel gave similar MMDs when used to sample brass pouring fume. Oil-saturated Teflon membrane and oil-saturated sintered metal, surfaces for which the collection efficiency is presumed to be independent of the particle loading, gave MMDs similar to those measured for grease-coated stainless steel. The implications of these comparisons are discussed. It is concluded that bounce characteristics are strongly dependent on aerosol material and the suitability of collection surfaces needs to be determined by field evaluation.

Optimized portable cordless vacuum method for sampling dry, hard surfaces for dusts.

Surface sampling in industrial/environmental hygiene is a growing field that needs validated standardized methods. There are few standard methods, one being the American Society for Testing and Materials (ASTM) method involving a portable, cordless air sampling pump. In the present work, the ASTM technique was modified to increase efficiency and versatility. A soil sample was first dried and sieved. Known weights of different sieved sizes (125 microns-180 microns, 90 microns-125 microns, and 63 microns-90 microns) were then sampled at an average flow rate of 4.0 +/- 0.2 L/min from a template of inner dimensions 10 cm by 10 cm on two different surfaces (rough and smooth). Five consecutive sampling passes were performed. For the smooth surface, the first pass efficiency for the largest particles were 45% +/- 45% (CV = 100%), and 75% +/- 20% (CV = 27%) for the smallest particles. After three passes, the efficiency independent of particle size exceeded 83 percent with a CV better than 11 percent. After five passes, the efficiency exceeded at least 85 percent with about the same precision as for three passes. The rough surface allowed higher efficiencies for the first two sampling passes. Three to five passes are recommended to achieve acceptable efficiencies for the surface loose dust/soil range 100 micrograms/cm2 to 1,500 micrograms/cm2.

Hemoglobin and DNA adduct formation in Fischer-344 rats exposed to 2,4- and 2,6-toluene diamine.

Using gas chromatography/mass spectrometry for detection of hemoglobin adducts, and 32P-postlabelling for DNA adducts, we examined macromolecular binding in Fischer-344 rats administered 2,4-or 2,6-toluene diamine (TDA). The dose-response and correlative relationship between the two macromolecules were investigated over a range of doses (0-250 mg/kg). The time course of adduct formation and removal was also examined. Both TDA isomers induced formation of hemoglobin adducts, but only the 2,4-isomer induced DNA binding. Maximum hemoglobin and DNA adduct levels were detected 24 h following administration. Both hemoglobin and DNA binding increased in a dose-dependent manner. Hemoglobin adduct clearance demonstrated a nonlinear decay, with adduct loss occurring faster than normal erythrocyte clearance. The effects of metabolic inhibitors on adduct formation were examined using piperonyl butoxide and pentachlorophenol to inhibit p450 isozymes and sulfotransferase, respectively. Microsomal enzymatic activation was critical to hemoglobin adduct formation with inhibition by piperonyl butoxide reducing adduct yields by over 90%. Sulfation did not appear to play a significant role in TDA-induced hemoglobin adduct formation.