Exposure to traffic exhausts and oxidative DNA damage

AIMS

To assess the relations between exposure to traffic exhausts and indicators of oxidative DNA damage among highway toll station workers.

METHODS

Cross-sectional study of 47 female highway toll station workers exposed to traffic exhausts and 27 female office workers as a reference group. Exposure assessment was based on average and cumulative traffic density and a biomarker of exposure, urinary 1-hydroxypyrene-glucuronide (1-OHPG). Urinary 8-hydroxydeoxyguanosine (8-OHdG) was used as a biomarker of oxidative DNA damage. Plasma nitric oxide (NO) was measured as an indicator of oxidative stress related to traffic exhaust exposure.

RESULTS

The mean concentration of urinary 8-OHdG was substantially higher among the exposed non-smokers (13.6 microg/g creatinine) compared with the reference non-smokers (7.3 microg/g creatinine; difference 6.3, 95% CI 3.0 to 9.6). The mean concentration of NO among the exposed (48.0 micromol/l) was also higher compared with the reference non-smokers (37.6 micromol/l; difference 10.4, 95% CI -0.4 to 21.2). In linear regression adjusting for confounding, a change in log(8-OHdG) was statistically significantly related to a unit change in log(1-OHPG) (beta = 0.372, 95% CI 0.081 to 0.663).

CONCLUSIONS

Results indicate that exposure to traffic exhausts increases oxidative DNA damage. Urinary 8-OHdG is a promising biomarker of traffic exhaust induced oxidative stress.

Golestan cohort study of oesophageal cancer: feasibility and first results

To investigate the incidence of oesophageal cancer (EC) in the Golestan province of North-East Iran, we invited 1349 rural and urban inhabitants of Golestan province aged 35–80 to undergo extensive lifestyle interviews and to provide biological samples. The interview was repeated on a subset of 130 participants to assess reliability of questionnaire and medical information. Temperature at which tea was consumed was measured on two occasions by 110 subjects. Samples of rice, wheat and sorghum were tested for fumonisin contamination. An active follow-up was carried out after 6 and 12 months. A total of 1057 subjects (610 women and 447 men) participated in this feasibility study (78.4% participation rate). Cigarette smoking, opium and alcohol use were reported by 163 (13.8%), 93 (8.8%) and 39 (3.7%) subjects, respectively. Tobacco smoking was correlated with urinary cotinine (κ=0.74). Most questionnaire data had κ >0.7 in repeat measurements; tea temperature measurement was reliable (κ=0.71). No fumonisins were detected in the samples analysed. During the follow-up six subjects were lost (0.6%), two subjects developed EC (one dead, one alive); in all, 13 subjects died (with cause of death known for 11, 84.6%). Conducting a cohort study in Golestan is feasible with reliable information obtained for suspected risk factors; participants can be followed up for EC incidence and mortality.

Concentration of 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) in urine and alkali-hydrolyzed urine after consumption of charbroiled beef

Heterocyclic amines (HAs) and polycyclic aromatic hydrocarbons are carcinogenic products formed during the cooking of meat at moderate to high temperatures. We have previously shown that the urinary concentration of 1-hydroxypyrene-glucuronide, a metabolite of pyrene, increased significantly in ten subjects who had ingested charbroiled ground beef. We now report the time course and interindividual variation of 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) concentration in the urine samples from these ten subjects. PhIP concentration was determined in both untreated and alkali-hydrolyzed urine to obtain estimates of the proportion of conjugated PhIP metabolites in each subject. PhIP was measured by gas chromatography-negative ion chemical ionization-mass spectrometry after derivatization with pentafluorobenzyl bromide. Ten healthy non-smoking males consumed identical amounts of broiled beef on five consecutive days. The morning after the first day of broiled beef consumption, urinary concentration of PhIP increased 14-38 fold above mean pre-feed concentration of PhIP in individual alkali-hydrolyzed urine samples. Following cessation of broiled beef consumption, urinary PhIP concentration declined to near pre-feed levels within 48-72 hrs. The ratio of total alkali-labile PhIP metabolites to unmetabolized PhIP varied by about 2.7-fold among subjects, ranging from 18:1 to 48:1, suggesting that interindividual differences in PhIP metabolism occur and can be detected by this method. This study of urinary PhIP following ingestion of meat cooked by charbroiling, that contains both HAs and polycyclic aromatic hydrocarbons, extends previous studies of ingestion of pan-fried meat that contains primarily HAs. The results indicate that significant amounts of PhIP are bioavailable from ingestion of charbroiled ground beef and that measurement of proportions of alkali-labile PhIP metabolites and parent PhIP in human urine may yield information on individual metabolism of ingested PhIP.

COMT genotype, micronutrients in the folate metabolic pathway and breast cancer risk

Catechol-O-methyltransferase (COMT) catalyzes the O-methylation of catechol estrogens (CEs), using S-adenosylmethionine (SAM) as a methyl donor. Several studies have indicated that the val108met COMT polymorphism, which results in a 3-4-fold decrease in activity, is associated with increased breast cancer risk. Folate, whose intake levels have also been associated with breast cancer risk, and other micronutrients in the folate metabolic pathway influence levels of SAM and S-adenosylhomocysteine (SAH), a COMT inhibitor generated by the demethylation of SAM. Because these micronutrients have been shown to alter SAM and SAH levels, we hypothesized that they could also affect COMT-catalyzed CE methylation. Although measurements of SAM and SAH were not initially collected, a secondary analysis of data from two nested case-control studies was performed to examine whether serum levels of folate, vitamin B12 (B12), pyridoxal 5'-phosphate (PLP), cysteine and homocysteine, in conjunction with COMT genotype, were associated with breast cancer risk. COMT(HH) (high activity COMT homozygote) breast cancer cases had statistically significantly lower levels of homocysteine (P = 0.05) and cysteine (P = 0.04) and higher levels of PLP (P = 0.02) than COMT(HH) controls. In contrast, COMT(LL) (low activity COMT homozygote) cases had higher levels of homocysteine than COMT(LL) controls (P = 0.05). No associations were seen between B12, COMT genotype, and breast cancer risk. An increasing number of COMT(L) alleles was significantly associated with increased breast cancer risk in women with below median levels of folate (P(trend) = 0.05) or above median levels of homocysteine (P(trend) = 0.02). These findings are consistent with a role for certain folate pathway micronutrients in mediating the association between COMT genotype and breast cancer risk.

Effect of photoreactivating light on UV radiation-induced alterations in human skin

BACKGROUND/AIMS

Photoreactivating light (PRL) after ultraviolet radiation (UVR) exposure causes photoreversal of cyclobutane pyrimidine dimers through the activation of photolyase. Although photoreversal has been demonstrated in the "three kingdoms of life," its existence in man remains controversial. We sought evidence for photoreversal in man.

METHODS AND RESULTS

Seven subjects were spot-irradiated at two sites with 4 minimal erythema doses (MED) of solar-simulating UVR. Of the two sites, one was then immediately exposed to a PRL source. Epidermal biopsies were taken immediately after exposure. No significant difference in the quantity of pyrimidine dimers was detected comparing the "UVR only" site to the "UVR, PRL-exposed" site. Biopsies were repeated 24 h later and no significant difference in p53 protein expression or dendritic cell number was detected. However, the "UVR, PRL-exposed" site showed a greater reduction in pyrimidine dimer quantity.

CONCLUSIONS

We found no evidence for a direct effect of PRL causing photoreversal of UVR-induced pyrimidine dimers in man. Our results do, however, suggest that some indirect effect of PRL may enhance pyrimidine dimer repair in the 24-h period following UVR exposure.

Development of aflatoxin B(1)-lysine adduct monoclonal antibody for human exposure studies

Mouse monoclonal antibodies were developed against a synthetic aflatoxin B(1) (AFB)-lysine-cationized bovine serum albumin conjugate. The isotype of one of these antibodies, IIA4B3, has been classified as immunoglobulin G1(lambda). The affinity and specificity of IIA4B3 were further characterized by a competitive radioimmunoassay. The affinities of IIA4B3 for AFB and its associated adducts and metabolites are ranked as follows: AFB-lysine > 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl formamido)-9-hydroxy-AFB > AFB = 8,9-dihydro-8-(N(7)-guanyl)-9-hydroxy-AFB > aflatoxin M(1) > aflatoxin Q(1). IIA4B3 had about a 10-fold higher affinity for binding to AFB-lysine adduct than to AFB when (3)H-AFB-lysine was used as the tracer. The concentration for 50% inhibition for AFB-lysine was 0.610 pmol; that for AFB was 6.85 pmol. IIA4B3 had affinities at least sevenfold and twofold higher than those of 2B11, a previously developed antibody against parent AFB, for the major aflatoxin-DNA adducts 8,9-dihydro-8-(N(7)-guanyl)-9-hydroxy-AFB and 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl formamido)-9-hydroxy-AFB, respectively. An analytical method based on a competitive radioimmunoassay with IIA4B3 and (3)H-AFB-lysine was validated with a limit of detection of 10 fmol of AFB-lysine adduct. The method has been applied to the measurement of AFB-albumin adduct levels in human serum samples collected from the residents of areas at high risk for liver cancer.

Associations of lead exposure and dose measures with erythrocyte protein kinase C activity in 212 current Korean lead workers

Lead can replace calcium in enzyme assays that measure protein kinase C activity and lead activates protein kinase C in human erythrocytes after exposure to lead in vitro. To examine the relevance of these observations to lead exposure in humans, we studied the associations of lead found in blood or tibia with activation of protein kinase C in erythrocytes isolated from workers in the lead industry. We examined erythrocytes among 212 lead workers, with a mean (+/-SD) age of 39.1 (10.0) years and exposure duration of 8.1 (6.5) years and measured protein kinase C activation by an in vitro back-phosphorylation assay. After adjustment for potential confounding factors (age and sex), tibia lead and exposure duration were significantly associated with erythrocyte protein kinase C activation (both p values < 0.05). No associations were observed between protein kinase C activation and blood-lead or zinc-protoporphyrin levels. These findings suggest that human exposure to lead results in activation of erythrocyte protein kinase C, which may be directly relevant to the neurotoxicity of lead.

Relationship between the Val158Met polymorphism of catechol O-methyl transferase and breast cancer

A case-control study was performed to assess the potential influence of catechol O-methyl transferase (COMT) genotype on the risk of breast cancer in Korean women. One hundred and sixty-three histologically confirmed incident breast cancer cases and 163 age- and menopausal status-matched control individuals with no present or previous history of cancer were selected as study subjects. COMT genetic polymorphism was determined by gel electrophoresis after NlaIII enzyme digestion of amplified DNA. Odds ratios and 95% confidence intervals were estimated by unconditional logistic regression after adjustment for known or suspected risk factors of breast cancer. Women with at least one COMT lower enzyme activity associated allele (COMT-L) were at elevated risk for breast cancer (OR = 1.7, 95% CI = 1.04-2.78) compared with those homozygous for high enzyme activity associated COMT-H alleles. Among women with low (> or = 23.1) body mass index the COMT-L allele containing genotypes posed a marginally significant increased risk of breast cancer compared to the COMT-HH genotype (OR = 1.8, 95% CI = 0.95-3.48). Women with at least one COMT-L allele who had experienced a full-term pregnancy when aged over 30 years or were nulliparous had 2.7-fold increased risk; however, this increase did not reach statistical significance (OR = 2.7, 95% CI = 0.64-11.35). Furthermore, never-drinking and never-smoking women with at least one COMT-L allele were at increased risk of breast cancer compared to those with COMT-HH genotype with ORs of 2.0 (95% CI = 1.23-3.38) and 1.7 (95% CI = 1.04-2.62), respectively. These results are consistent with studies showing that COMT genotype of lower enzyme activity might be related to increase in risk of breast cancer, and extend this finding to Korean women.

Alcohol consumption, glutathione S-transferase M1 and T1 genetic polymorphisms and breast cancer risk

To evaluate the potential association between GSTM1 and GSTT1 genotypes and development of breast cancer, a hospital based case-control study was conducted in a South Korean study population consisting of 189 histologically confirmed incident breast cancer cases and their 189 age-matched control subjects with no present or previous history of cancer. A multiplex polymerase chain reaction method was used for the genotyping analyses and statistical evaluations were performed by unconditional logistic regression model. The GSTM1 null genotype was significantly associated with breast cancer risk in premenopausal women [odds ratio (OR) = 2.0, 95% confidence interval (CI) = 1-3.7], but not in the postmenopausal women (OR = 0.9, 95% CI = 0.5-1.9), nor in all women grouped together (OR = 1.3, 95% CI = 0.8-1.1). The GSTT1 null genotype posed a similar risk of breast cancer with an OR of 1.6 (95% CI = 1.0-2.5) for the total breast cancer group, OR of 1.7 (95% CI = 0.9-3.2) for pre-menopausal women, and OR of 1.3 (95% CI = 0.6-2.8) for post-menopausal women. The breast cancer risk associated with concurrent lack of both GSTM1 and GSTT1 genes was 2.2 (95% CI = 1.1-4.5), and the risk increased as the number of null genotype increased (P for trend = 0.03). When the data were stratified by the known risk factors of breast cancer, a significant interaction was observed between the GSTM1 genotypes and alcohol consumption (P for interaction = 0.03). An especially remarkable risk of breast cancer was observed for alcohol-consuming premenopausal women lacking both the GSTM1 and GSTT1 genes (OR = 5.3, 95% CI = 1.0-27.8) compared to those with both of the genes. Our findings thus suggest a novel gene-environment interaction which plays an important role in the individual susceptibility to breast cancer. p6

Phage display of ScFv peptides recognizing the thymidine(6-4)thymidine photoproduct

Solar ultraviolet (UV) radiation induces DNA photoproducts in skin cells and is the predominant cause of human skin cancers. To understand human susceptibility to skin cancer and to facilitate the development of prevention measures, highly specific reagents to detect and quantitate UV-induced DNA adducts in human skin will be needed. One approach towards this end is the use of monoclonal antibody-based molecular dosimetry methods. To facilitate the development of photoproduct-specific antibody reagents we have: (i) cloned and sequenced a single chain variable fragment (ScFv) gene coding for one such high affinity monoclonal antibody, [alpha]UVssDNA-1 (mAb C3B6), recognizing the thymidine(6-4)thymidine photoproduct; (ii) expressed and displayed the cloned ScFv gene on the surface of phage; (iii) selected functional recombinant phage by panning; (iv) purified the ScFv peptide; (v) shown that the purified ScFv peptide binds to UV-irradiated polythymidylic acid but not unirradiated polythymidylic acid. This is the first demonstration of the use of phage display to select a ScFv recognizing DNA damage. In addition, this is the initial step towards immortalizing the antibody gene for genetic manipulation, structure-function studies and application to human investigations.

An automated, handheld biosensor for aflatoxin

A new immunoaffinity fluorometric biosensor has been developed for detecting and quantifying aflatoxins, a family of potent fungi-produced carcinogens that are commonly found in a variety of agriculture products. They have also been cited as a biological agent under weapons development. The handheld, self-contained biosensor is fully automatic, highly sensitive, quick, quantitative, and requires no special storage. Approximately 100 measurements can be made before refurbishment is required, and concentrations from 0.1 parts per billion (ppb) to 50 ppb can be determined in <2 min with a 1 ml sample volume. The device operates on the principles of immunoaffinity for specificity and fluorescence for a quantitative assay. The analytic procedure is flexible so that other chemical and biological analytes could be detected with minor modifications to the current device. Advances in electro-optical components, electronics, and miniaturized fluidics were combined to produce this reliable, small, and versatile instrument.

Comparison of three analytical methods for 1-hydroxypyrene glucuronide in urine after non-occupational exposure to polycyclic aromatic hydrocarbons

Urinary pyrene metabolites, 1-OHP and 1-OHPG, have been used as biomarkers for the assessment of occupational and environmental exposure to PAHs. This study compares the sensitivity and applicability of the different analytical methods of 1-OHPG for human biomonitoring of low level exposure to PAHs. Three analytical methods were compared: (1) HPLC method from that reported by Singh et al. (Singh, R., Tucek, M., Maxa, K., Tenglerova, J., Weyand, E.H., 1995. A rapid and simple method for the analysis of 1-hydroxypyrene glucuronide: a potential biomarker for polycyclic aromatic hydrocarbon exposure. Carcinogenesis 16, 2909-2915); (2) IAC-SFS method: the rapid and simple assay using IAC purification using monoclonal antibody specific for PAH-DNA adduct and PAH metabolites and SFS quantitation; and (3) IAC-HPLC method: IAC and HPLC separation and quantitation. The correlation between the IAC-SFS method, HPLC method, and the IAC-SFS method was determined in 20 first year-grade junior high school students (age 12-13) from Yochon, Korea who participated in a nationwide survey for the environmental disease surveillance projects in Korea. Chromatograms obtained by the IAC purification and HPLC quantitation method were clear with no interfering peaks adjacent to 1-OHPG, thus 1-OHPG could be easily quantitated. However, the HPLC method produced chromatogram profiles with many interfering peaks adjacent to 1-OHPG peak. The concentrations of 1-OHPG in 20 urine samples were similar when analyzed by all three analytical methods. The correlation coefficient between the IAC-HPLC and IAC-SFS methods was 0.915, and between the IAC-HPLC and HPLC methods was 0.844, and between the IAC-SFS and HPLC methods was 0.805. The analytical methods for 1-OHPG compared in this study showed a good correlation with one another. These results suggest that any of the methods can be applied to human biomonitoring of PAH exposure. However, SFS quantitation after IAC purification is rapid and simple because this method does not need HPLC separation of 1-OHPG.

Serum concentrations of organochlorine compounds and the subsequent development of breast cancer

A nested case-control study was conducted to examine the association between serum concentrations of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), the primary metabolite of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), and polychlorinated biphenyls (PCBs) and the development of breast cancer up to 20 years later. Cases (n = 346) and controls (n = 346) were selected from cohorts of women who donated blood in 1974, 1989, or both, and were matched on age, race, menopausal status, and month and year of blood donation. Analyses were stratified by cohort participation because median DDE and PCB concentrations among the controls were 59 and 147% higher in 1974 than 1989, respectively. Median concentrations of DDE were lower among cases than controls in both time periods [11.7% lower in 1974 (P = 0.06) and 8.6% lower in 1989 (P = 0.41)]. Median concentrations of PCBs were similar among cases and controls [P = 0.21 for 1974 and P = 0.37 for 1989 (Wilcoxon signed rank test)]. The risk of developing breast cancer among women with the highest concentrations of DDE was roughly half that among women with the lowest concentrations, whether based on concentrations in 1974 [odds ratio (OR), 0.50; 95% confidence interval (CI), 0.27-0.89; P(trend) = 0.02] or in 1989 (OR, 0.53; 95% CI, 0.24-1.17; P(trend) = 0.08). The associations between circulating concentrations of PCBs and breast cancer were less pronounced but still in the same direction (1974: OR, 0.68; 95% CI, 0.36-12.9; P(trend) = 0.2; and 1989: OR, 0.73; 95% CI, 0.37-1.46; P(trend) = 0.6). Adjustment for family history of breast cancer, body mass index, age at menarche or first birth, and months of lactation did not materially alter these associations. These associations remained consistent regardless of lactation history and length of the follow-up interval, with the strongest inverse association observed among women diagnosed 16-20 years after blood drawing. Results from this prospective, community-based nested case-control study are reassuring. Even after 20 years of follow-up, exposure to relatively high concentrations of DDE or PCBs showed no evidence of contributing to an increased risk of breast cancer.

Plasma 5-aminolevulinic acid concentration and lead exposure in children

The relationship between concentration of 5-aminolevulinic acid in plasma (ALAP) and other biomarkers of lead exposure and effect was investigated in lead-exposed children. We measured ALAP by chemical derivatization and high-performance liquid chromatography with fluorescence detection. The study population consisted of 103 children: 78 from a referral clinic for children with lead poisoning and 25 from a general pediatric clinic. Blood lead concentration (PbB), age, and ALAP were higher in lead clinic subjects than in general clinic subjects. ALAP was significantly correlated with PbB (Spearman r=0.38, P=0.0007) and free erythrocyte protoporphyrin concentration (r=0.41, P=0.0002) in lead clinic subjects. PbB was a significant predictor of ALAP (P=0.0001) by multiple linear regression in all subjects. The average PbB in the 3- to 12-month period prior to blood collection correlated with ALAP to the same degree that current PbB correlated with ALAP. Possible associations between ALAP and adverse health outcomes, particularly neurobehavioral effects, should be investigated in children to assess the predictive value of ALAP for these endpoints.

Genotyping by mass spectrometric analysis of short DNA fragments

A method has been developed to produce small DNA fragments from PCR products for analysis of defined DNA variations by mass spectrometry. The genomic region to be analyzed is PCR-amplified with primers containing a sequence for the type IIS restriction endonuclease Bpml. Bpml digestion of the resultant PCR products yields fragments as small as seven bases, which are then analyzed by electrospray ionization mass spectrometry. The approach was validated using seven different variants within the APC tumor suppressor gene, in which a perfect correlation was obtained with DNA sequencing. Both the sense and antisense strands were analyzed independently, and several variants can be analyzed simultaneously. These results provide the basis for a generally applicable and highly accurate method that directly queries the mass of variant DNA sequences.

Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by human cytochrome P4501A1, P4501A2 and P4501B1

While the metabolic activation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by N-hydroxylation has been well documented, the relative roles of the human cytochrome P450 (CYP) enzymes that catalyze this reaction have not been established. Previous studies indicated that the mutagenic activation product, 2-hydroxyamino-PhIP (N2-OH-PhIP), is produced primarily by CYP1A2, and to a lesser extent by CYP1A1. We recently reported that human CYP1B1 also produces N2-OH-PhIP (Carcinogenesis, 18, 1793-1798, 1997). In the present study, we examined PhIP metabolism by microsomes containing recombinant human CYP1A1, 1A2 or 1B1 expressed in Sf9 insect cells and compared the kinetic values for PhIP metabolite formation. PhIP metabolites were analyzed by high pressure liquid chromatography with fluorescence and absorbance detection. Vmax values for N2-OH-PhIP formation were 90, 16 and 0.2 nmol/min/nmol P450, and the apparent Km values were 79, 5.1 and 4.5 microM for human CYP1A2, 1A1 and 1B1, respectively. The non-mutagenic metabolite, 4'-hydroxy-PhIP, was also formed by all three CYP enzymes with Vmax values of 1.5, 7.8 and 0.3 nmol/ min/nmol P450 and apparent Km values of 43, 8.2 and 2.2 microM for human CYP1A2, 1A1 and 1B1, respectively. Although the Vmax for N2-OH-PhIP production was highest for CYP1A2, the catalytic efficiency (Vmax/Km) of CYP1A1 was greater than that of CYP1A2. These results suggest that, for humans, extrahepatic CYP1A1 may be more important than previously thought for the metabolic activation of the dietary carcinogen PhIP.

Association between CYP17 polymorphisms and the development of breast cancer

A nested case-control study was conducted to determine whether a genetic polymorphism in the CYP17 gene, which encodes for an enzyme that mediates steroid hormone metabolism, was associated with an increased risk of breast cancer. No association was found between the presence of an A2 allele and the subsequent development of breast cancer [A1/A2 odds ratio, 0.61 (95% confidence interval, 0.33-1.14); A2/A2 odds ratio, 0.89 (95% confidence interval, 0.41-1.95)]. No significant association was observed with risk factors presumed to be surrogates for endogenous estrogen exposure, nor was there an association observed with the stage of disease at diagnosis. Genotype frequencies in this Caucasian population were similar to those reported for African-American, Asian, and Latino women. Additional studies of larger size are needed to achieve a consensus regarding the relevance of CYP17 genotypes to the risk of developing breast cancer.

Urinary 5-aminolevulinic acid (ALA) adjusted by creatinine: a surrogate for plasma ALA?

5-Aminolevulinic acid (ALA) is the first intermediate substrate in the heme synthetic pathway and is the substrate of aminolevulinic acid dehydratase (ALAD, porphobilinogen synthase). Because lead effectively inhibits ALAD activity, resulting in accumulation of ALA in urine and blood, urinary ALA (ALAU) has been used as a biomarker for lead exposure or early biologic effect of lead. Intraindividual variation in urinary excretion of ALA requires the use of 24-hour urine samples or adjustment of single urine samples by other normalizing variables, such as urinary creatinine concentration. Previous studies of ALAU concentration have used various adjustment methods; however, few have compared creatinine-adjusted ALAU concentration with ALA concentration in plasma (ALAP) from subjects with low (< 30 micrograms/dL) to moderate (< 60 micrograms/dL) levels of blood lead. To determine if creatinine-adjusted ALAU is associated with ALAP, we measured ALAU, ALAP, and urinary creatinine in 65 Korean lead workers with blood lead concentrations in the range of 14-60 micrograms/dL. ALAU, ALAU/creatinine, or ALAU/log creatinine all correlated with ALAP. However, ALAU/creatinine correlated more closely with ALAP based on Spearman's r (rs = 0.40, P, = 0.0009), supporting the use of ALA/creatinine in single urine samples as a surrogate for ALAP.

Metabolism of benzo[a]pyrene and benzo[a]pyrene-7,8-diol by human cytochrome P450 1B1

Benzo[a]pyrene (B[a]P), a ubiquitous environmental, tobacco and dietary carcinogen, has been implicated in human cancer etiology. The role of human cytochrome P450 1B1 in the metabolism of B[a]P is poorly understood. Using microsomal preparations of human P450 1A1, 1A2 and 1B1 expressed in baculovirus-infected insect cells, as well as human and rat P450 1B1 expressed in yeast, we have determined the metabolism of B[a]P, with and without the addition of exogenous epoxide hydrolase, and B[a]P-7,8-dihydrodiol (7,8-diol), each substrate at a concentration of 10 microM. HPLC analysis detected eight major metabolites of B[a]P and four metabolites of the 7,8-diol. The results of these studies indicate that cytochrome P450 1B1 carries out metabolism of B[a]P along the pathway to the postulated ultimate carcinogen, the diol epoxide 2, at rates much higher than P450 1A2 but less than P450 1A1. The rates of formation of the 7,8-diol metabolite in incubations with epoxide hydrolase are 0.17 and 0.38 nmol/min/nmol P450 for human P450 1B1 and 1A1, respectively, and undetectable for 1A2. The rates of total tetrol metabolite formation from the 7,8-diol, which are indicative of diol epoxide formation, are 0.60, 0.43 and 2.58 nmol/min/nmol P450 for 1B1, 1A2 and 1A1 respectively. In agreement with other reports of rat P450 1B1 activity, our data show this rat enzyme to be very active for B[a]P and 7,8-diol, with rates higher than human P450 1B1. In addition to the established role of P450 1A1 in B[a]P metabolism, P450 1B1 may significantly contribute to B[a]P and 7,8-diol metabolism and carcinogenesis in rodent tumor models and in humans.

Post-exposure treatment with isoproterenol attenuates pulmonary edema in phosgene-exposed rabbits

This study investigated the post-treatment effect of isoproterenol (ISO) on pulmonary parameters in rabbits whole-body-exposed to a lethal dose of the toxic gas phosgene. Phosgene is widely used in industry as a chemical intermediate for the production of plastics, drugs and polyurethane products. The results of this study are from five study groups: 10-min perfused baseline; uninjured controls exposed to air; phosgene-exposed; phosgene-exposed isoproterenol-treated intravascularly and intratracheally (ISO i.v.+i.t.); and phosgene-exposed isoproterenol-treated intratracheally (ISO i.t.). Treatment with ISO was administered as either a continuous intravascular infusion (24 microg min(-1)) from the beginning to end of perfusion (i.v.) and a 24-microg intratracheal bolus (i.t.) or just an i.t. bolus immediately prior to the start of perfusion. Rabbits of 2.5-3 kg were exposed to a cumulative dose of phosgene to attain a concentration x time exposure-effect of 1500 ppm x min. Lungs were isolated in situ and perfused 50-60 min after the start of exposure with Krebs-Henseleit buffer at 40 ml min(-1). Pulmonary artery pressure (Ppa), tracheal pressure (Pt) and lung weight gain (lwg) were continuously measured. Leukotrienes (LT) C4/D4/E4 were measured in the perfusate every 20 min during perfusion. At the immediate conclusion of the experiment, lung tissue was frozen in liquid N2 and analyzed for glutathione (GSH) and cyclic 3',5'-adenosine monophosphate (cAMP). Post-treatment with ISO by either i.v.+i.t. or i.t. routes 50+ min after phosgene exposure significantly lowered Ppa, Pt and lwg. Phosgene-exposed rabbits post-treated with ISO i.t. had significantly higher levels of reduced GSH (3 +/- 0.4 nmol mg(-1) protein), GSH/GSSG ratios (3.3 +/- 0.6 nmol mg(-1) protein) and percentage of total as reduced GSH (75 +/- 2.5%) compared with phosgene-exposed rabbits: 1.9 +/- 0.3, 2 +/- 0.3 and 58 +/- 6.3%, respectively. The ISO (i.v.+i.t.) post-treatment route significantly increased reduced GSH (6.2 +/- 1.7 nmol mg(-1) protein), GSH/GSSG ratio (5.9 +/- 0.8 nmol mg(-1) protein) and percentage of total as reduced GSH (85 +/- 1.7%) when compared to the phosgene-only group. The ISO i.t. and ISO i.v.+i.t. treatments significantly reduced perfusate LTC4/D4/E4 150 min after the start of exposure by 90% and 48%, respectively. These data suggest that protective mechanisms for ISO involve reduced vascular pressure, decreased LTC4/D4/E4-mediated pulmonary capillary permeability and a favorable lung tissue redox state compared with untreated phosgene-exposed rabbits.

Association between glutathione S-transferase M1, P1, and T1 genetic polymorphisms and development of breast cancer

BACKGROUND

Glutathione S-transferases (GSTs) are encoded by a superfamily of genes and play a role in the detoxification of potential carcinogens. In a nested case-control study, we investigated associations between genetic variability in specific GST genes (GSTM1, GSTT1, and GSTP1) and susceptibility to breast cancer.

METHODS

In 1989, a total of 32 898 individuals donated blood samples to a research specimen bank established in Washington County, MD. Genotypes of blood specimen DNA were determined for 110 of 115 women with incident cases of breast cancer diagnosed during the period from 1990 through 1995 and up to 113 of 115 control subjects. Associations between specific genotypes and the development of breast cancer were examined by use of logistic regression to calculate odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

The GSTM1 homozygous null genotype was associated with an increased risk of developing breast cancer (OR = 2.10; 95% CI = 1.22-3.64), principally due to an association with postmenopausal breast cancer (OR = 2.50; 95% CI = 1.34-4.65). For GSTP1, the data were suggestive of a trend of increasing risk with higher numbers of codon 105 valine alleles (compared with isoleucine alleles); a 1.97-fold increased risk of breast cancer (95% CI = 0.77-5.02) was associated with valine/valine homozygosity. The risk of breast cancer associated with the GSTT1 homozygous null genotype was 1.50 (95 % CI = 0.76-2.95). The risk of breast cancer increased as the number of putative high-risk genotypes increased (P for trend <.001) (OR = 3.77; 95% CI = 1.10-12.88 for a combined genotype of GSTM1 null, GSTT1 null, and either GSTP1 valine heterozygosity or GSTP1 valine homozygosity).

CONCLUSIONS

Our findings suggest that genetic variability in members of the GST gene family may be associated with an increased susceptibility to breast cancer.

Induction and localization of cytochrome P450 1B1 (CYP1B1) protein in the livers of TCDD-treated rats: detection using polyclonal antibodies raised to histidine-tagged fusion proteins produced and purified from bacteria

Knowledge of the response of cytochrome P450 1B1 (CYP1B1) to exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in both humans and rodents is limited. To improve the analysis of CYP1 proteins, specific CYP1B1 and CYP1A1 polypeptides were expressed as hexahistidine-tagged fusion proteins in Escherichia coli, purified to homogeneity and used to produce polyclonal antibodies in rabbits. Immunoblot analyses showed that these antibodies were specific and sensitive, detecting both the human and rat forms of the respective isozymes and exhibiting negligible cross-reactivity between the two known CYP1 subfamilies. We show that CYP1B1, CYP1A1 and CYP1A2 protein levels were induced in the livers of female Sprague-Dawley rats following either acute (single dose of 25 microg TCDD/kg) or chronic (125 ng TCDD/kg/day for 30 weeks) exposure to TCDD. CYP1B1 protein exhibited a dose-response to TCDD that was different from those of CYP1A1 and CYP1A2. CYP1B1 induction appeared to be less sensitive to TCDD exposure, with induction occurring at higher doses of TCDD than that required for induction of CYP1A1 or CYP1A2. Immunohistochemical analysis showed that in animals chronically exposed to TCDD (35 ng/kg/day for 30 weeks), CYP1B1 was induced only in centrilobular hepatocytes, a pattern of expression similar to that of CYP1A1 and CYP1A2. These observations of cellular co-localization of the CYP1 cytochromes in livers of TCDD-treated rats and apparent differences in both protein amounts and dose-response are indicative of both common and unique regulation of CYP1 induction.

An association between the allele coding for a low activity variant of catechol-O-methyltransferase and the risk for breast cancer

Mounting evidence suggests that catechol metabolites of estradiol may contribute to the development of estrogen-induced cancers. O-Methylation, catalyzed by catechol-O-methyltransferase (COMT), inactivates catechol estrogens. COMT is polymorphic in the human population, with 25% of Caucasians being homozygous for a low activity allele of the enzyme (COMT(LL)). We hypothesized that low activity COMT may be a risk factor for human breast cancer and designed a PCR-based RFLP assay to determine COMT genotype in a cohort of 112 matched, nested case-control samples. In the total study population, the odds ratios for the association of breast cancer risk with COMT(HL) and COMT(LL) genotypes were 1.30 [confidence interval (CI), 0.66-2.58] and 1.45 (CI, 0.69-3.07), respectively. Postmenopausal COMT(LL) women had a greater than 2-fold increased risk of developing breast cancer [odds ratio (OR), 2.18; CI, 0.93-5.11]. The association of COMT(LL) with the development of postmenopausal breast cancer was stronger and statistically significant in those women with a body mass index >24.47 kg/m2 (OR, 3.58; CI, 1.07-11.98). When COMT(LL) was combined with either glutathione S-transferase (GST) M1 null or with GSTP1 Ile-105-Val/Val-105-Val (intermediate/low activity, respectively) genotypes, the risk for developing postmenopausal breast cancer was also significantly increased. Our findings suggest that the allele encoding low activity COMT may be an important contributor to the postmenopausal development of breast cancer in certain women.

Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human cytochrome P4501B1

Cytochrome P4501B1 (CYP1B1) is the most recently identified member of the dioxin-inducible CYP1 family. CYP1B1 is constitutively expressed in most human tissues, including colon and breast, and can activate numerous chemically diverse carcinogens. We evaluated the metabolism of the dietary heterocyclic amine carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by microsomes from yeast expressing the human CYP1B1 protein. PhIP metabolites were analysed by HPLC with fluorescence and absorbance detection. We found that human CYP1B1 metabolizes PhIP to three products: N2-OH-PhIP, a mutagenic activation product; 4'-OH-PhIP, a detoxification product; and 2-OH-PhIP, the mutagenic potential of which is unknown. Metabolite identity was confirmed by co-elution with authentic standards and synchronous fluorescence spectroscopy. The identity of the 2-OH-PhIP standard was additionally confirmed by mass spectrometry. Kinetic studies of the formation of N2-OH-PhIP, 4'-OH-PhIP and 2-OH-PhIP by CYP1B1 indicated apparent Km values of 5.7 +/- 1.3, 2.2 +/- 0.5 and 1.3 +/- 0.2 microM, respectively. Apparent turnover rates were 0.40 +/- 0.03, 0.93 +/- 0.02 and 0.04 +/- 0.00 nmol product/min nmol P450, respectively. At saturating levels of substrate, CYP1B1-mediated formation of the non-mutagenic metabolite 4'-OH-PhIP was favored two-fold over that of the mutagenic metabolite, N2-OH-PhIP and >10-fold over that of 2-OH-PhIP. The formation of N2-OH-PhIP, a potent mutagen implicated in the etiology of human colon and breast cancer, indicates that CYP1B1 may play an important role in PhIP-mediated carcinogenesis.

A nested case-control study of non-Hodgkin lymphoma and serum organochlorine residues

BACKGROUND

The steady worldwide increase in the incidence of non-Hodgkin lymphoma during the past few decades remains mostly unexplained. Several studies suggest that there may be an association between the agricultural use of the organochlorine 1,1,1-trichloro-2,2'bis(p-chlorophenyl)ethane (DDT) and increased risk of non-Hodgkin lymphoma. We have investigated the association between risk of non-Hodgkin lymphoma and body burden of selected organochlorines in the general population in a nested case-control study.

METHODS

We measured prediagnostic serum concentrations of DDT, its metabolites, and other organochlorines, including polychlorinated biphenyls (PCBs), in 74 cases of non-Hodgkin lymphoma and 147 matched controls identified from a prospective cohort of 25,802 adults, established in 1974 in Washington County, Maryland, USA. We report results for total lipid-corrected serum concentrations of DDT and total PCBs.

FINDINGS

There was a strong dose-response relation between quartiles of total lipid-corrected serum PCB concentrations and risk of non-Hodgkin lymphoma overall (odds ratios by quartile: 1.0; 1.3 [95% CI 0.5-3.3]; 2.8 [1.1-7.6]); and 4.5 [1.7-12.0]; p for trend = 0.0008) and separately in men and in women. There was also evidence suggesting that seropositivity for the Epstein-Barr virus early antigen potentiated the effects of serum PCBs. By contrast, total lipid-corrected serum concentrations of DDT were not associated with risk of non-Hodgkin lymphoma.

INTERPRETATION

These results should be regarded as hypothesis-generating. Before causal inferences can be made about exposure to PCBs and increased risk of non-Hodgkin lymphoma, our findings require replication and the biological plausibility of the association needs further investigation.

Aminolevulinic acid dehydratase genotype mediates plasma levels of the neurotoxin, 5-aminolevulinic acid, in lead-exposed workers

The first intermediate substrate in the heme synthetic pathway, 5-aminolevulinic acid (ALA), is neurotoxic in animal models and may be responsible for some of the adverse neurologic outcomes in lead poisoning and porphyria in adult humans. ALA is a substrate for the enzyme aminolevulinic acid dehydratase (ALAD; EC 4.2.1.24), which is encoded by the ALAD gene containing 2 co-dominant alleles, 1 and 2. We measured plasma ALA (ALAP) and urinary ALA (ALAU) in 65 Korean lead workers, of whom 44 were homozygous for ALADI (ALAD1-1 genotype) and 21 were heterozygous for ALAD (ALAD1-2 genotype). ALAP in subjects with the ALAD1-1 genotype was significantly higher than in those with the ALAD1-2 genotype (Wilcoxon rank sum test, P = 0.01). No difference between ALAD genotypes was found for age, zinc protoporphyrin (ZPP), blood lead levels (PbB), ALAU, or ALAU adjusted for creatinine. ALAP was significantly correlated with ZPP (Spearman's r = 0.38, P = 0.002) and with PbB (r = 0.34, P = 0.006), and marginally with employment duration (r = 0.22, P = 0.08). ALAP remained significantly elevated (P = 0.032) in ALAD1-1 subjects after adjustment for PbB and age by multiple linear regression. These results suggest that ALAD1-1 subjects respond differently and may be more susceptible than ALAD1-2 subjects to the ALA-mediated neurotoxic effects of lead.

Postexposure treatment with aminophylline protects against phosgene-induced acute lung injury

Pretreatment with aminophylline has been shown to protect against various types of acute lung injury. Mechanisms responsible for protection are multifactorial but are thought to involve upregulation of cAMP. While previous studies focused on pretreatment, the present investigation examined post-treatment in rabbits following exposure to a lethal dose of the oxidant gas phosgene. Rabbits, 2-3 kg, were exposed to a cumulative dose of phosgene to attain a c x t exposure effect of 1500 ppm.min. Lungs were isolated in situ and perfused for 90-100 min after exposure with Krebs-Henseleit buffer at 40 mL/min. Pulmonary artery pressure (Ppa), tracheal pressure (Pt), and lung weight gain (lwg) were measured continuously. Leukotrienes C4/D4/E4 were measured in the perfusate every 20 min during perfusion. At the immediate conclusion of the experiment, lung tissue was frozen in liquid N2 and analyzed for reduced GSH, GSSG, cAMP, and lipid peroxidation (TBARS). Post-treatment with aminophylline 80-90 min after exposure significantly lowered Ppa, Pt, and lwg. Aminophylline significantly reduced TBARS and perfusate LTC4/D4/E4, and prevented phosgene-induced decreases in lung tissue cAMP. These data suggest that protective mechanisms observed with aminophylline involve decreased LTC4/D4/E4-mediated pulmonary capillary permeability and attenuated lipid peroxidation. Direct antipermeability effects of cAMP on cellular contraction may also be important in protection against phosgene-induced lung injury.

Schistosoma mansoni: the immune response against cercarial glycocalyx

Schistosoma mansoni cercarial glycocalyx was separated and purified by Sephacryl-300 SR. It was found to stimulate the humoral immune response in mice injected with it. Antiglycoalyx antibodies raised in CD/1 mice were found to be cytotoxic to schistosomula in vitro. But conversely, no protective effect was demonstrated in vivo. Eosinophil-mediated cytotoxicity was found to have no effector function in the murine immune response against schistosomes. A monoclonal antiglycocalyx IgM was prepared during our study. It was found to have no cytotoxic effect on schistosomules in vitro. However, it was found to have an inhibitory activity blocking the cytotoxic effect of other antiglycocalyx isotypes in the immune mouse. The contradiction between the result of antiglycocalyx antibody-mediated cytotoxicity obtained in vivo and that obtained in vitro is in itself revealing and suggests that the effect is crucially dependent upon factors as yet poorly understood.

Multicollinearity may lead to artificial interaction: an example from a cross sectional study of biomarkers

Collinearity is the situation which arises in multiple regression when some or all of the explanatory variables are so highly correlated with one another that it becomes very difficult, if not impossible, to disentangle their influences and obtain a reasonably precise estimate of their effects. Suppressor variable is one of the extreme situations of collinearity that one variable can substantially increase the multiple correlation when combined with a variable that is only modestly correlated with the response variable. In this study, we describe the process by which we disentangled and discovered multicollinearity and its consequences, namely artificial interaction, using the data from cross-sectional quantification of several biomarkers. We showed how the collinearity between one biomarker (blood lead level) and another (urinary trans, trans-muconic acid) and their interaction (blood lead level* urinary trans, trans-muconic acid) can lead to the observed artificial interaction on the third biomarker (urinary 5-aminolevulinic acid).

Multicollinearity may lead to artificial interaction: an example from a cross sectional study of biomarkers

Collinearity is the situation which arises in multiple regression when some or all of the explanatory variables are so highly correlated with one another that it becomes very difficult, if not impossible, to disentangle their influences and obtain a reasonably precise estimate of their effects. Suppressor variable is one of the extreme situations of collinearity that one variable can substantially increase the multiple correlation when combined with a variable that is only modestly correlated with the response variable. In this study, we describe the process by which we disentangled and discovered multicollinearity and its consequences, namely artificial interaction, using the data from cross-sectional quantification of several biomarkers. We showed how the collinearity between one biomarker (blood lead level) and another (urinary trans, trans-muconic acid) and their interaction (blood lead level* urinary trans, trans-muconic acid) can lead to the observed artificial interaction on the third biomarker (urinary 5-aminolevulinic acid).

Oxidation of xenobiotics by recombinant human cytochrome P450 1B1

Human cytochrome P450 (P450) 1B1 (CYP1B1) has recently been shown to be an important enzyme in the activation of diverse procarcinogens such as arylarenes, nitroarenes, and arylamines to reactive metabolites that cause DNA damage in the cells. However, it is not known whether this P450 enzyme also plays roles in the oxidation of certain drugs or model substrates commonly used in P450 assays. We examined the substrate oxidation activities of recombinant human CYP1B1 in yeast microsomes and compared these activities with those catalyzed by reconstituted systems containing recombinant CYP1A1 and CYP1A2 which were isolated from membranes of Escherichia coli in which respective cDNAs have been expressed. Catalytic activities towards some of the model substrates of other human P450 enzymes including CYP2A6, 2C9, 2C19, 2D6, 2E1, and 3A4 were also determined and compared. CYP1B1 catalyzed benzo[a]pyrene 3-hydroxylation at rates lower than those of CYP1A1 but higher than those of CYP1A2. The activity towards 7-ethoxyresorufin O-deethylation catalyzed by CYP1B1 was about one-tenth of that of CYP1A1, but the Km values were lower for CYP1B1 than those for CYP1A1 and CYP1A2. CYP1B1 was also able to catalyze the oxidation of theophylline and caffeine, two prototypic substrates for CYP1A2. CYP1B1 did not oxidize other typical P450 substrates such as coumarin, tolbutamide, S-mephenytoin, chlorzoxazone, nifedipine, and testosterone, while low rates of oxidation of bufuralol and 7-ethoxycoumarin were found for CYP1B1. These results indicate that CYP1B1 has catalytic activities overlapping CYP1A1 and CYP1A2 with respect to the oxidation of drugs and model P450 substrates, although the relative catalytic roles in these three P450 enzymes differ depending upon the substrates examined. A distinct marker activity of CYP1B1 has not been identified.

delta-Aminolevulinic acid dehydratase genotype modifies four hour urinary lead excretion after oral administration of dimercaptosuccinic acid

OBJECTIVES

Previous research suggests that binding of lead by delta-aminolevulinic acid dehydratase (ALAD) may vary by ALAD genotype. This hypothesis was tested by examining whether ALAD genotype modifies urinary lead excretion (DMSA chelatable lead) after oral administration of dimercaptosuccinic acid (DMSA).

METHODS

57 South Korean lead battery manufacturing workers were given 5 mg/kg oral DMSA and urine was collected for four hours. Male workers were randomly selected from two ALAD genotype strata (ALAD1-1, ALAD1-2) from among all current workers in the two plants (n = 290). Subjects with ALAD1-1 (n = 38) were frequency matched with subjects with ALAD1-2 (n = 19) on duration of employment in the lead industry. Blood lead, zinc protoporphyrin, and plasma aminolevulinic acid concentrations, as well as ALAD genotype, duration of exposure, current tobacco use, and weight were examined as predictors or effect modifiers of levels of DMSA chelatable lead.

RESULTS

Blood lead concentrations ranged from 11 to 53 micrograms/dl, with a mean (SD) of 25.4 (10.2) micrograms/dl. After 5 mg/kg DMSA orally, the workers excreted a mean (SD) 85.4 (45.0) micrograms lead during a four hour urine collection (range 16.5-184.1 micrograms). After controlling for blood lead concentrations, duration of exposure, current tobacco use, and body weight, subjects with ALAD1-2 excreted, on average, 24 micrograms less lead during the four hour urine collection than did subjects with ALAD1-1 (P = 0.05). ALAD genotype seemed to modify the relation between plasma delta-aminolevulinic acid (ALA) and DMSA chelatable lead. Workers with ALAD1-2 excreted more lead, after being given DMSA, with increasing plasma ALA than did workers with ALAD1-1 (P value for interaction = 0.01).

CONCLUSIONS

DMSA chelatable lead may partly reflect the stores of bioavailable lead, and the current data indicate that subjects with ALAD1-2 have lower stores than those with ALAD1-1. These data provide further evidence that the ALAD genotype modifies the toxicokinetics of lead-for example, by differential binding of current lead stores or by differences in long-term retention and deposition of lead.

Intratracheal administration of DBcAMP attenuates edema formation in phosgene-induced acute lung injury

Phosgene, a toxic gas widely used as an industrial chemical intermediate, is known to cause life-threatening latent noncardiogenic pulmonary edema. Mechanisms related to its toxicity appear to involve lipoxygenase mediators of arachidonic acid (AA) and can be inhibited by pretreatment with drugs that increase adenosine 3',5'-cyclic monophosphate (cAMP). In the present study, we used the isolated buffer-perfused rabbit lung model to investigate the mechanisms by which cAMP protects against phosgene-induced lung injury. Posttreatment with dibutyryl cAMP (DBcAMP) was given 60-85 min after exposure by an intravascular or intratracheal route. Lung weight gain (LWG) was measured continuously. AA metabolites leukotriene (LT) C4, LTD4, and LTE4 and 6-ketoprostaglandin F1 alpha were measured in the perfusate at 70, 90, 110, 130, and 150 min after exposure. Tissue malondialdehyde and reduced and oxidized glutathione were analyzed 150 min postexposure. Compared with measurements in the lungs of rabbits exposed to phosgene alone, posttreatment with DBcAMP significantly reduced LWG, pulmonary arterial pressure, and inhibited the release of LTC4, LTD4, and LTE4. Intratracheal administration of DBcAMP was more effective than intravascular administration in reducing LWG. Posttreatment also decreased MDA and protected against glutathione oxidation observed with phosgene exposure. We conclude that phosgene causes marked glutathione oxidation, lipid peroxidation, release of AA mediators, and increases LWG. Posttreatment with DBcAMP attenuates these effects, not only by previously described inhibition of pulmonary endothelial or epithelial cell contraction but also by inhibition of AA-mediator production and a novel antioxidant effect.

The impact of glutathione s-transferase M1 and cytochrome P450 1A1 genotypes on white-blood-cell polycyclic aromatic hydrocarbon-DNA adduct levels in humans

Carcinogenic polycyclic aromatic hydrocarbons (PAHs) form DNA adducts via a complex metabolic activation pathway that includes cytochrome P450 (CYP) 1A1, whereas intermediate metabolites can be detoxified by conjugation through pathways including glutathione s-transferase M1 (GSTM1). PAH-DNA adducts can be measured in peripheral white blood cells (WBCs) and should reflect the net effect of competing activation and detoxification pathways and DNA repair as well as exposure. We have previously shown that WBC PAH-DNA adducts measured by an enzyme-linked immunosorbent assay (ELISA) were associated with recent, frequent consumption of charbroiled food among 47 nonsmoking wildland fire-fighters who provided two blood samples 8 wk apart. In the investigation reported here, which was performed in the same population, we measured the association between the GSTM1 null genotype, which results in loss of enzyme activity, and PAH-DNA adduct levels, hypothesizing that subjects with this genotype would have higher levels of DNA adducts because of their decreased ability to detoxify PAH metabolites. However, PAH-DNA adduct levels were nonsignificantly lower in subjects with the GSTM1 null genotype (n = 28) compared with other subjects (n = 19) (median 0.04 fmol/microgram DNA vs 0.07 fmol/microgram DNA, respectively, P = 0.45, Wilcoxon rank-sum test). Adduct levels were also lower in the nine subjects heterozygous or homozygous for the CYP1A1 exon 7 polymorphism (which codes for a valine rather than isoleucine and is thought to be associated with greater CYP1A1 activity) compared with the 38 wild-type subjects (P = 0.12). In the entire group, there was a positive association between consuming charbroiled food and PAH-DNA adduct formation (r = 0.24, P = 0.02, Spearman rank-order correlation). This association was weaker in the subgroup of subjects with the GSTM1 null genotype (r = 0.03, P = 0.84) and stronger among the remaining subjects (r = 0.57, P = 0.0002). These results suggest that the GSTM1 null genotype and CYP1A1 exon 7 polymorphism are not associated with increased susceptibility for PAH-DNA adduct formation in peripheral WBCs measured by ELISA in nonsmoking populations.

Association of exposure to polycyclic aromatic hydrocarbons (estimated from job category) with concentration of 1-hydroxypyrene glucuronide in urine from workers at a steel plant

OBJECTIVES

Increased risk of lung cancer has been associated with employment in the steel industry. This association is thought to be due in part to increased concentrations of polycyclic aromatic hydrocarbons (PAHs) in air found in this work environment. Measurement of PAH metabolites in human urine provides a means of assessing individual internal dose of PAHs. This study examined the relative contribution of occupation and smoking to urinary concentration of 1-hydroxypyrene glucuronide (1-OHPG) among a group of workers at a steel plant.

METHODS

Concentrations of 1-OHPG in urine from 44 workers with jobs associated with increased air concentrations of PAHs and 40 workers with jobs with low or no exposure to PAHs were measured. 20 workers in each group were not current smokers. Urinary 1-OHPG was measured by synchronous fluorescence spectroscopy after immunoaffinity chromatography specific for PAH metabolites.

RESULTS

Mean (SEM) urinary 1-OHPG concentration was 2.16 (0.42) pmol/ml urine among the 44 occupationally exposed workers compared with 0.38 (0.05) among the 40 workers with no or low exposure (P < 0.0001). Mean urinary 1-OHPG concentration was 1.82 (0.41) pmol/ml urine among the 44 current smokers compared with 0.75 (0.20) among the 40 non-smokers (P < 0.005). Mean 1-OHPG concentrations in non-smokers were 0.26 (n = 20), 0.70 (n = 15), and 2.84 pmol/ml urine (n = 5) for strata of exposure to PAHs (no or low, mid, and high) based on job category; the corresponding values in smokers were 0.55 (n = 20), 0.94 (n = 12), and 4.91 pmol/ml (n = 12), respectively. Multiple linear regression showed significant differences between subjects in different PAH exposure with increased concentrations of 1-OHPG in urine. Amounts of foods containing PAHs ingested by this group of workers were relatively low and did not contribute significantly to urinary 1-OHPG concentrations.

CONCLUSIONS

These results indicate that 1-OHPG is a common urinary metabolite in people with recent occupational exposure to PAHs and is associated with both job category and estimated stratum of PAH exposure.

Interindividual differences in the concentration of 1-hydroxypyrene-glucuronide in urine and polycyclic aromatic hydrocarbon-DNA adducts in peripheral white blood cells after charbroiled beef consumption

Biological markers of internal dose and macromolecular dose from PAHs provide a potential means of assessing environmental exposure to PAHs through inhalation, ingestion and percutaneous absorption. In this study we examined the time course and interindividual variation of 1-hydroxypyrene-glucuronide (1-OHP-gluc) excretion in urine and PAH-DNA adduct formation in peripheral white blood cells (WBCs) after charbroiled (CB) beef consumption. As a marker of internal dose, 1-OHP-gluc was measured in human urine using immunoaffinity chromatography and synchronous fluorescence spectroscopy. PAH-DNA adducts were measured in WBCs by enzyme-linked immunosorbent assay (ELISA) in order to assess macromolecular dose. Ten healthy non-smoking males consumed identical amounts of CB beef on five consecutive days. Multiple blood and urine samples were collected before, during, and after the feeding period. The morning after the first day of CB beef consumption, individual urinary concentrations of 1-OHP-gluc increased 10- to 80-fold (range: 2.0-16.6 pmol/ml urine) above pre-feed baseline concentrations (0.23 +/- 0.11 pmol/ml) in the 10 subjects. 1-OHP-gluc concentration decreased to near baseline levels by 24-72 h after CB beef consumption ended. In contrast, PAH-DNA adducts in WBCs increased markedly in only four of 10 subjects during or after CB beef consumption. Significant interindividual variation was observed for both urinary 1-OHP-gluc concentration (P < 0.001 by Kruskal-Wallis) and PAH-DNA adduct levels (P < 0.005) during the feeding period. The mean urinary 1-OHP-gluc concentration for each subject during and immediately after (days 2-8) the feeding period was significantly correlated with their mean PAH-DNA adduct level in WBCs during the same time period (Spearman r = 0.79, P < 0.01). Evidence of segregation of the subjects into separate response groups based on level of urinary 1-OHP-gluc was observed, suggesting that discrete determinants may regulate the absorption, metabolism and/or excretion of ingested pyrene.

Protective effects of N-acetylcysteine treatment after phosgene exposure in rabbits

We examined the effects of treatment with N-acetylcysteine (NAC) on pulmonary edema formation in isolated perfused rabbit lungs following in vivo phosgene exposure. This study focused on posttreatment intratracheal administration of NAC after exposure. Rabbits, 2 to 3 kg, were exposed to a cumulative dose of phosgene to attain a concentration x time exposure effect of 1,500 ppm/min. Lungs were perfused with Krebs-Henseleit buffer at 40 ml/min from 70 to 150 min after exposure. Pulmonary artery pressure (Ppa), tracheal pressure (Pt), and the rate of lung weight gain (LWG) were measured continuously. Perfusate concentration of peptide leukotrienes LTC4, D4, and E4 were measured every 20 min during perfusion. At the conclusion of the experiment, lung tissue was analyzed for reduced and oxidized glutathione (GSH and GSSG) and lipid peroxidation (thiobarbituric acid-reactive substances, TBARS). Exposure to phosgene significantly increased Pt, LWG, LTC4, D4, and E4, TBARS, and GSSG over time compared with controls. Compared with phosgene, intratracheal NAC lowered Ppa, LWG, LTC4, D4, and E4, TBARS, and GSSG. We conclude that NAC protected against phosgene-induced lung injury by acting as an antioxidant by maintaining protective levels of glutathione, reducing both lipid peroxidation and production of arachidonic acid metabolites.

Biomarkers for assessing environmental exposure to carcinogens in the diet

The major sources of human exposure to environmental carcinogens are through inhalation, ingestion, and percutaneous absorption. Food-borne carcinogens constitute the primary source of ingested carcinogens. Epidemiological analyses indicate that 20-50% of all human cancer is due to dietary causes, unfortunately, few specific etiologic agents have been identified. The use of chemical-specific molecular biomarkers in studies of several classes of carcinogens to which humans are exposed through the ingestion of food may provide the necessary data to identify these etiologic agents. These molecular biological markers can be classified into several categories: markers of exposure reflecting dose of toxic agents, markers of effect indicating a biological response to an exposure, and markers of susceptibility providing information about the inherent sensitivity of an individual to the toxic agent. By definition some of these markers are chemical-agent specific, such as a carcinogen-DNA or carcinogen-protein adduct, whereas others are biological process-specific such as the altered expression of a gene. In the future, information obtained from studies of molecular biomarkers in humans and experimental animals can be used for a range of public health applications from primary and secondary prevention to the design of clinical therapies. Aflatoxins have been extensively studied with validated biomarkers, and, currently, dietary polycyclic aromatic hydrocarbons (PAH) and heterocyclic amines (HA) derived from cooking meats and other staples are being intensively investigated. This article reviews some of the recent information on aflatoxins and describes future potential of PAH and HA biomarkers.

Enhanced photoproduct repair: its role in the DNA damage-resistance phenotype of human malignant melanoma cells

A fundamental issue in understanding melanoma is to seek the basis for the cellular resistance to DNA damaging agents, which is manifested in vivo as pronounced tumor resistance to therapeutic agents. The published consensus on melanoma has been that exaggerated postreplication recovery (PRR), rather than excision repair, underlies the unusual damage-resistance phenotype. We examined the resistance to the model DNA damaging agent, UV-C, of subclones derived from a human metastatic melanoma cell line. The clones essentially fall into two groups: one with normal and the other with enhanced resistance. We exploited this range to investigate the interrelationships between replication, transcription, and repair of DNA after UV irradiation. Subclones resistant to UV killing were indeed found to possess enhanced rates of PRR and were coresistant to cisplatin. However, we now report an overall elevation of photoproduct repair in both melanoma groups compared to nonmelanoma controls and conclude that this accounts for the resistant melanoma phenotype, including that of enhanced PRR. Repair enhancement may explain chemoresistance, while loss of efficiency of certain functions, such as PRR, due to the intrinsic genetic lability of tumor cells, may generate the class of melanoma subclones exhibiting only normal resistance.

Identification of 1-hydroxypyrene glucuronide as a major pyrene metabolite in human urine by synchronous fluorescence spectroscopy and gas chromatography-mass spectrometry

Humans are exposed to polycyclic aromatic hydrocarbons (PAHs) from various occupational, environmental, medicinal and dietary sources. The measurement of specific PAH metabolites, particularly 1-hydroxypyrene, in human urine treated with deconjugating enzymes (e.g. beta-glucuronidase) has been extensively used as a means of assessing recent exposure to PAHs. We have examined pyrene metabolites in human urine prior to enzymatic deconjugation in order to determine the relative proportions of conjugated and unconjugated pyrene metabolites. The analytical method utilized immunoaffinity chromatography, high performance liquid chromatography (HPLC) and the complementary techniques of synchronous fluorescence spectroscopy (SFS) and gas chromatography-mass spectrometry (GC-MS) to measure pyrene-containing metabolites. SFS analysis of immunoaffinity-purified urine samples showed fluorescence spectra characteristic of the pyrene moiety (using wavelength differences of 34 nm, 54 nm and 102 nm). These spectra are produced by several PAHs containing the pyrene moiety. HPLC analysis with fluorescence detection indicated that the major fluorescent metabolite in immunoaffinity-purified urine was much more polar than simple hydroxylated metabolites of pyrene (1-hydroxypyrene) or benzo[a]pyrene (benzo[a]pyrene-diols or -tetrols). Following digestion with beta-glucuronidase, this metabolite co-chromatographed with authentic 1-hydroxypyrene and exhibited fluorescence spectra characteristic of 1-hydroxypyrene, suggesting that the major metabolite was a glucuronide conjugate of 1-hydroxypyrene. This was subsequently confirmed by GC-MS analysis of trimethylsilyl derivatives of the major metabolite; both 1-hydroxypyrene and glucuronic acid were detected independently as derivatized products. Since 1-hydroxypyrene glucuronide is approximately 5-fold more fluorescent than 1-hydroxypyrene, it may provide a more sensitive biomarker for assessing exposure to pyrene in mixtures of PAHs.

Methodologies for measuring carcinogen adducts in humans

In summary, although some of the more optimistic aspirations for human biomonitoring studies envisaged a decade ago have not been realized thus far, some considerable advances have been made. The examples cited above indicate that the feasibility of biomonitoring has been clearly established. In addition, they demonstrate the need for preliminary biomarker testing and validation through transitional studies prior to their field application. In the next decade of research into carcinogen adducts in humans, continued improvements in the reproducibility and specificity of assays for DNA adducts will be needed. Perhaps the increasing use of hybrid methodologies to concentrate adducts followed by specific chemical analyses will allow such adducts to be monitored more precisely. Of course, further basic research into the mechanisms of carcinogenesis will allow the measurement of specific novel markers which are more closely tied to the disease endpoint than adducts. The development of new assays for determining metabolic phenotypes and genotypes relevant to carcinogenesis should improve our estimates of susceptibility (46-48). Such new approaches along with the sustained improvement of current assays will allow molecular approaches to continue to enrich cancer epidemiology in the future.

Increased sensitivity for determination of polycyclic aromatic hydrocarbon-DNA adducts in human DNA samples by dissociation-enhanced lanthanide fluoroimmunoassay (DELFIA)

A competitive enzyme-linked immunosorbent assay (ELISA), the most frequently used immunoassay for the determination of polycyclic aromatic hydrocarbon-DNA adducts in human tissues, has been modified to achieve approximately a 6-fold increase in sensitivity. The new assay, a competitive dissociation-enhanced lanthanide fluoroimmunoassay (DELFIA) has utilized the same rabbit antiserum as the ELISA, antiserum elicited against DNA modified with benzo[a]pyrene. However, the alkaline phosphatase conjugate has been replaced with a biotin-europium-labeled streptavidin signal amplification system, and the release of europium into the solution forms a highly fluorescent chelate complex that is measured by time-resolved fluorometry. The DELFIA has achieved a 5- to 6-fold increase in sensitivity for measurement of DNA samples modified in vitro with benzo[a]pyrene, for cultured cells exposed to radiolabeled benzo[a]pyrene, and for human samples from occupationally exposed workers. The assay has been validated by comparison of adduct levels determined by DELFIA, ELISA, and radioactivity in DNA from mouse keratinocytes exposed to radiolabeled benzo[a]pyrene. Human lymphocyte DNA samples from 104 Hungarian aluminum plant workers were assayed by ELISA and compared to blood cell DNA samples from 69 Italian coke oven workers assayed by DELFIA. The standard curves demonstrated that the limit of detection of 4.0 adducts in 10(8) nucleotides for polycyclic aromatic hydrocarbon-DNA adducts by ELISA, using 35 micrograms of DNA/microtiter plate well, has been decreased to 1.3 adducts in 10(8) nucleotides by DELFIA, using 20 micrograms of DNA/microtiter well. If 35 micrograms of DNA were used in the DELFIA, the calculated detection limit would be 0.7 adducts in 10(8) nucleotides.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of occupation and diet to white blood cell polycyclic aromatic hydrocarbon-DNA adducts in wildland firefighters

Wildland (forest) firefighters are exposed to a wide range of carcinogenic polycyclic aromatic hydrocarbons (PAH) in forest fire smoke. PAH undergo metabolic activation and can subsequently bind to DNA. In this study, we investigated the association between occupational and dietary PAH exposures and the formation of WBC PAH-DNA adducts in a population of wildland firefighters. An enzyme-linked immunosorbent assay using an antiserum elicited against benzo(a)pyrene-modified DNA was used to measure PAH-DNA adducts in WBC obtained from 47 California firefighters at two time points, early and late in the 1988 forest fire season. PAH-DNA adduct levels were not associated with cumulative hours of recent firefighting activity. However, firefighters who consumed charbroiled food within the previous week had elevated PAH-DNA adduct levels, which were related to frequency of charbroiled food intake. These findings suggest that dietary sources of PAH contribute to PAH-DNA adduct levels in peripheral WBC and should be evaluated when using this assay to assess occupational and environmental PAH exposure.

Antibodies to carcinogen-DNA adducts in mice chronically exposed to polycyclic aromatic hydrocarbons

Antibodies specific for polycyclic aromatic hydrocarbon (PAH)-DNA adducts have previously been reported in human sera. In this study, we examined the association between mixed PAH exposure and PAH-DNA adduct specific antibodies in BALB/c mice. Mice were treated either by i.p. injection or by intragastric (i.g.) intubation with a mixture of seven different PAHs [benzo(a)pyrene (BP), benz(a)anthracene (BA), fluoranthene (FA), dibenz(a,h)anthracene (DBA), 3-methyl-cholanthrene (MC), chrysene (Ch), benzo(b)fluoranthene (BF)] at three doses (0, 15, 150 micrograms of each PAH) twice a week for 8 weeks. Sera were screened by direct ELISA for antibodies recognizing DNA modified by diolepoxides or epoxides of each PAH injected. In i.p. treated mice, the sera were slightly more reactive to DNAs modified with diolepoxides of BP, BA, or Ch or an epoxide of DBA than to unmodified DNA. In i.g. treated mice, the sera were more reactive to DNAs modified with diolepoxides of BA or BF than to unmodified DNA. For some PAHs, a dose-response effect was observed between sera reactivity to PAH metabolites and the dose of PAH administered. However, there was considerable variation in the immune responses among individual mice within each treatment group. When tested by competitive ELISA, none of the sera could discriminate between modified and unmodified DNA. This animal study suggests that an assessment of previous carcinogen exposure by measuring DNA adduct-specific antibodies requires further validation prior to its application to the human monitoring of carcinogen exposure.

Detection of metabolites of polycyclic aromatic hydrocarbons in human urine

A non-invasive assay has been developed for the recovery of r-7,t-8,t-9,c-10-tetrahydroxy-7,8,9,10-tetrahydrobenzo[alpha]-pyrene (BP-7,10/8,9-tetrol) from human urine. This tetrol is excreted as a metabolite of benzo[alpha]pyrene (BP) in a process catalyzed by cytochrome P450 enzymes and epoxide hydrolases. Urine was hydrolysed to release activated benzo[alpha]-pyrene-diol-epoxides covalently bound to macromolecular species or conjugated tetrols. The relatively non-polar organic molecules from urine hydrolysates were collected on octadecasilane chromatography columns (Sep-Paks). Materials eluted in solvent (80% CH3OH), were further purified on immunoaffinity columns with antibodies raised against anti-N2-[10(7,8,9-trihydroxy-7,8,9,10-tetrahydrobenzo [alpha]pyrenyl)]-guanosine. HPLC was then used to isolate BP-7,10/8,9-tetrol, which was quantitated by synchronous fluorescence spectroscopy (SFS). This assay detected 0.24-3.12 pmol BP-7,10/8,9-tetrol per ml urine (limit of detection 0.01 pmol/ml, given 10 ml urine), in four study subjects. Reproducibility was assessed by adding tritium labeled BP-7,10/8,9-tetrol (1500 fmol) to a urine sample previously identified to contain the tetrol at levels below the limit of detection of the fluorescence assay; a recovery of > 30% of the added radioactivity was achieved (510 +/- 64 fmol, mean +/- SD, n = 3). Because HPLC alone was not sufficient to isolate materials for quantitation by SFS directly from human urine, immunoaffinity chromatography was found to be a necessary preparatory step in BP-7,10/8,9-tetrol isolation. These data demonstrate the presence of tetrahydrotetrol metabolites of BP in human urine and suggest that measurement of BP-7,10/8,9-tetrol and other polycyclic aromatic hydrocarbon-tetrols may prove to be valuable dosimeters of human internal exposure to polycyclic aromatic hydrocarbons.

Association of PAH-DNA adducts in peripheral white blood cells with dietary exposure to polyaromatic hydrocarbons

Previous investigations suggest that dietary sources of polycyclic aromatic hydrocarbons (PAHs) contribute to the PAH-DNA adduct load in peripheral white blood cells (WBCs). In the current study, we measured PAH-DNA adducts by enzyme-linked immunosorbent assay in WBCs obtained from 47 California wildland (forest) firefighters at two time points (early and late) during an active forest fire season. PAH-DNA adduct levels were not associated with recent firefighting activity, but were positively associated with frequency of charbroiled food consumption in the previous 2 weeks. In addition, adduct levels declined with time since last ingestion of charbroiled food. These studies indicate that recent consumption of charbroiled food contributes to the PAH-DNA adduct load in peripheral WBCs.

Biomarkers of carcinogen exposure and cancer risk in a coke plant

To evaluate the association between an indicator of carcinogen exposure (peripheral blood leukocyte DNA adducts of polycyclic aromatic hydrocarbons) and an early indicator of neoplastic transformation (sputum epithelial cell membrane antigens binding by monoclonal antibodies against small cell lung cancer and against nonsmall cell lung cancer), a survey of 350 coke-oven workers and 100 unexposed workers was planned. This paper reports a pilot investigation on a subgroup of 23 coke-oven workers and 8 unexposed controls. A "gas regulator" worker with positive tumor antigen binding was identified. Results show that smokers, subjects with decreased pulmonary function (forced expiratory volume in 1 sec/forced vital capacity% < 80), and those with morphological dysplasia of sputum cells have higher levels of DNA adducts. The gas regulators showed the highest values for adducts; however, no significant difference of adduct levels was found between the coke-oven group and unexposed controls.

ras gene activation and aberrant expression of keratin K13 in ultraviolet B radiation-induced epidermal neoplasias of mouse skin

Both papillomas and squamous cell carcinomas (SCC) induced in mouse epidermis by initiation with 7,12-dimethylbenz[a]anthracene (DMBA) and promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA) exhibit aberrant expression of a type I keratin, K13, that is normally characteristic of terminal differentiation of internal stratified epithelia. There is evidence that the aberrant expression of K13 depends on the presence of an activated ras gene in mouse epidermal keratinocytes (Sutter et al., Mol Carcinog 4:467-476, 1991). To assess the general validity of this hypothesis, we investigated both aberrant K13 expression and activation of each of the three members of the ras gene family in epidermal tumors induced in four different mouse strains (SKH-1 hr, SENCAR, BALB/c, and C3H/He) by chronic irradiation with ultraviolet (UV) B. The tumor collection comprised nine papillomas and 30 well or poorly differentiated SCC. Aberrant K13 expression occurred in only five of 39 tumors and was restricted to SCC of both types. This indicates that aberrant K13 expression in UV-induced epidermal tumors was intrinsically different from that in chemically induced tumors. Polymerase chain reaction analysis of the tumors for different point mutations in codons 12, 13, and 61 of the Ha-ras and Ki-ras genes and in codon 61 of the N-ras gene revealed that only one of the well differentiated tumors from a SKH-1 hr mouse exhibited a GGA-->GAA mutation in codon 12 of the Ha-ras gene. Although this tumor was also positive for aberrant K13 expression, such a correlation could not be made for the remaining K13-expressing tumors. This indicates that the activation of one of the members of the ras gene family is not a general prerequisite for the aberrant expression of K13 in mouse epidermal keratinocytes.