Clinical features of hematopoietic malignancies and related disorders among benzene-exposed workers in China. Benzene Study Group

Benzene exposure-response and risk of lymphoid neoplasms in Chinese workers: A multicenter case-cohort study

BACKGROUND

While international agreement supports a causal relationship of benzene exposure with acute myeloid leukemia, there is debate about benzene and lymphoid neoplasm risks.

METHODS

In a case-cohort study with follow-up of 110 631 Chinese workers during 1972-1999, we evaluated benzene exposure-response for non-Hodgkin lymphoma (NHL), lymphoid leukemias (LL), acute lymphocytic leukemia (ALL), and total lymphoid neoplasms (LN). We estimated benzene exposures using state-of-the-art hierarchical modeling of occupational factors calibrated with historical routine measurements and evaluated cumulative exposure-response using Cox regression.

RESULTS

NHL and other specified LN were increased in exposed vs unexposed workers. However, there was no evidence of exposure-response for NHL or other specified LN. Based on a linear exposure-response, relative risks at 100 parts per million-years (RR at 100 ppm-years) for cumulative benzene exposure using a 2-year lag (exposure at least 2 years before the time at risk) were 1.05 for NHL (95 percent confidence interval (CI) = 0.97, 1.27; 32 cases), 1.11 for LL (95% CI < 0, 1.66; 12 cases), 1.21 for ALL (95% CI < 0, 3.53; 10 cases), and 1.02 for total LN (95% CI < 0, 1.16; 49 cases). No statistically significant exposure-response trends were apparent for these LN for 2 to <10-year or ≥10-year lags. NHL risks were not significantly modified by sex, age, or year at first exposure, attained age, or time since exposure.

CONCLUSION

Given the study strengths and limitations, we found little evidence of exposure-response for benzene and NHL, LL, ALL, or total LN, although NHL and other specified LN were increased in exposed vs unexposed individuals.

Benzene Exposure Response and Risk of Myeloid Neoplasms in Chinese Workers: A Multicenter Case-Cohort Study

BACKGROUND

There is international consensus that benzene exposure is causally related to acute myeloid leukemia (AML), and more recent evidence of association with myelodysplastic syndromes (MDS). However, there are uncertainties about the exposure response, particularly risks by time since exposure and age at exposure.

METHODS

In a case-cohort study in 110 631 Chinese workers followed up during 1972-1999 we evaluated combined MDS/AML (n = 44) and chronic myeloid leukemia (n = 18). We estimated benzene exposures using hierarchical modeling of occupational factors calibrated with historical routine measurements, and evaluated exposure response for cumulative exposure and average intensity using Cox regression; P values were two-sided.

RESULTS

Increased MDS/AML risk with increasing cumulative exposure in our a priori defined time window (2 to <10 years) before the time at risk was suggested (Ptrend = 08). For first exposure (within the 2 to <10-year window) before age 30 years, the exposure response was stronger (P = .004) with rate ratios of 1.12 (95% confidence interval [CI] = 0.27 to 4.29), 5.58 (95% CI = 1.65 to 19.68), and 4.50 (95% CI = 1.22 to 16.68) for cumulative exposures of more than 0 to less than 40, 40 to less than 100, and at least 100 ppm-years, respectively, compared with no exposure. There was little evidence of exposure response after at least 10 years (Ptrend = .94), regardless of age at first exposure. Average intensity results were generally similar. The risk for chronic myeloid leukemia was increased in exposed vs unexposed workers, but appeared to increase and then decrease with increasing exposure.

CONCLUSION

For myeloid neoplasms, the strongest effects were apparent for MDS/AML arising within 10 years of benzene exposure and for first exposure in the 2 to less than 10-year window before age 30 years.

Toxic effects of orally ingested oil from the Deepwater Horizon spill on laughing gulls

The explosion of the Deepwater Horizon oil rig released, millions of gallons of oil into the environment, subsequently exposing wildlife, including numerous bird species. To determine the effects of MC252 oil to species relevant to the Gulf of Mexico, studies were done examining multiple exposure scenarios and doses. In this study, laughing gulls (Leucophaeus atricilla, LAGU) were offered fish injected with MC252 oil at target doses of 5 or 10mL/kg bw per day. Dosing continued for 27 days. Of the adult, mixed-sex LAGUs used in the present study, ten of 20 oil exposed LAGUs survived to the end of the study; a total of 10 of the oil exposed LAGUs died or were euthanized within 20 days of initiation of the study. Endpoints associated with oxidative stress, hepatic total glutathione (tGSH), oxidized glutathione (GSSG) and reduced glutathione (rGSH) significantly increased as mean dose of oil increased, while the rGSH:GSSG ratio showed a non-significant negative trend with oil dose. A significant increase in 3-methyl histidine was found in oil exposed birds when compared to controls indicative of muscle wastage and may have been associated with the gross observation of diminished structural integrity in cardiac tissue. Consistent with previous oil dosing studies in birds, significant changes in liver, spleen, and kidney weight when normalized to body weight were observed. These studies indicate that mortality in response to oil dosing is relatively common and the mortality exhibited by the gulls is consistent with previous studies examining oil toxicity. Whether survival effects in the gull study were associated with weight loss, physiologic effects of oil toxicity, or a behavioral response that led the birds to reject the dosed fish is unknown.

Chemical exposures and risk of acute myeloid leukemia and myelodysplastic syndromes in a population-based study

Benzene exposure is one of the few well-established risk factors for myeloid malignancy. Exposure to other chemicals has been inconsistently associated with hematologic malignancies. We evaluated occupational and residential chemical exposures as risk factors for acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) using population-based data. AML and MDS cases were identified by the Minnesota Cancer Surveillance System. Controls were identified through the Minnesota driver's license/identification card list. Chemical exposures were measured by self-report. Unconditional logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CI). We included 265 MDS cases, 420 AML cases and 1388 controls. We observed significant associations between both MDS and AML and benzene (OR = 1.77, 95% CI 1.19, 2.63 and OR = 2.10, 95% CI 1.35, 3.28, respectively) and vinyl chlorides (OR = 2.05, 95% CI 1.15, 3.63 and OR = 2.81, 95% CI 1.14, 6.92). Exposure to soot, creosote, inks, dyes and tanning solutions and coal dust were associated with AML (range ORs = 2.68-4.03), while no association was seen between these exposures and MDS (range ORs = 0.57-1.68). Pesticides and agricultural chemicals were not significantly associated with AML or MDS. Similar results were observed in analyses stratified by sex. In addition to providing risk estimates for benzene from a population-based sample, we also identified a number of other occupational and residential chemicals that were significantly associated with AML; however, all exposures were reported by only a small percentage of cases (≤10%). While chemical exposures play a clear role in the etiology of myeloid malignancy, these exposures do not account for the majority of cases.

Temozolomide-induced myelodysplasia

A patient who had received temozolomide (TMZ) as a single agent in treatment of malignant glioma developed therapy-induced myelodysplasia (T-MDS). TMZ is an orally active imidazotetrazine which methylates guanine residues in DNA, ultimately causing single and double-strand DNA breaks leading to apoptotic cell death. TMZ does not chemically cross-link DNA and is considered a nonclassical alkylating agent, similar in structure and activity to dacarbazine. Observations on this patient, and on similarly treated others, suggest that the cumulative dose threshold (CDT) for TMZ that predisposes to T-MDS and which may potentially lead to acute myeloid leukemia (T-AML) is around 18000 to 20000 mg/sq m. Although the incidence of T-MDS and the predisposing CDT of TMZ may differ from that of other potentially leukemogenic compounds currently and formerly used as chemotherapeutic agents, all alkylating agents, including TMZ, should be considered potentially leukemogenic when administered long term.

Genetic Polymorphisms in XRCC1, APE1, ADPRT, XRCC2, and XRCC3 and Risk of Chronic Benzene Poisoning in a Chinese Occupational Population

DNA damage induced by benzene is an important mechanism of its genotoxicity that leads to chronic benzene poisoning (CBP). Therefore, genetic variation in DNA repair genes may contribute to susceptibility to CBP in the exposed population. Because benzene-induced DNA damage includes single- and double-strand breaks, we hypothesized that single-nucleotide polymorphisms in X-ray repair cross-complementing group 1 (XRCC1), apurinic/apyrimidinic endonuclease (APE1), ADP ribosyltransferase (ADPRT), X-ray repair cross-complementing group 2 (XRCC2), and X-ray repair cross-complementing group 3 (XRCC3) are associated with risk of CBP. We genotyped single-nucleotide polymorphisms at codons 194, 280, and 399 of XRCC1, codon 148 of APE1, codon 762 of ADPRT, codon 188 of XRCC2, and codon 241 of XRCC3 in 152 CBP patients and 152 healthy workers frequency matched on age and sex among those who were occupationally exposed to benzene. The genotypes were determined by PCR-RFLP technique with genomic DNA. We found that no individuals had the XRCC2 codon 188 variant alleles or Met/Met genotype of XRCC3 codon 241 in this study population. However, individuals carrying the XRCC1 194Trp allele (i.e., Arg/Trp+Trp/Trp genotypes) had a decreased risk of CBP [adjusted odds ratio (OR(adj)), 0.60; 95% confidence interval (95% CI), 0.37-0.98; P = 0.041] compared with subjects with the Arg/Arg genotype whereas individuals carrying the XRCC1 280His allele (i.e., Arg/His+His/His genotypes) had an increased risk of CBP compared with those with the Arg/Arg genotype (OR(adj), 1.91; 95% CI, 1.17-3.10; P = 0.009). The analysis of haplotypes of polymorphisms in XRCC1 showed that there was a 2.96-fold (OR, 2.96; 95% CI, 1.60-5.49; chi(2) = 12.39, P = 0.001) increased risk of CBP for subjects with alleles of XRCC1 194Arg, XRCC1 280His, and XRCC1 399Arg compared with those carrying alleles of XRCC1 194Arg, XRCC1 280Arg, and XRCC1 399Arg. Therefore, our results suggest that polymorphisms at codons 194 and 280 of XRCC1 may contribute to CBP in a Chinese occupational population.

Occupational history and exposure and the risk of adult leukemia in Shanghai

PURPOSE

Evaluation of the association of selected occupational exposures with leukemia risk.

METHODS

Population-based case-control study of 486 leukemia subjects and 502 healthy controls residing in Shanghai from 1987 to 1989. Adjusted odds ratios (OR) were calculated for the association between occupational factors and leukemia risk.

RESULTS

Significant increase in leukemia risk was observed in chemical manufacturing industry workers (OR=3.1, 95% CI=1.0-9.8). Increased risks for leukemia were observed from self-reported exposures to benzene (OR=1.7, 95% CI=1.1-2.6), radioactive materials (OR=3.7, 95% CI=1.3-10.2), synthetic fiber dust (OR=2.0, 95% CI=1.2-3.5), and toluene (OR=1.6, 95% CI=1.0-2.5). Dose-response relations of leukemia risk was observed with the duration of exposure to benzene (OR=3.3, 95% CI=1.6-6.9 for >or=15 years exposure; p for trend<0.01), radioactive materials (OR=5.2, 95% CI=1.1-24.7 for >or=15 years exposure; p for trend=0.02), paints (OR=2.3, 95% CI=1.2-4.7 for >or=15 years exposure; p for trend=0.09), and toluene (OR=2.9, 95% CI=1.3-6.7 for >or=15 years exposure; p for trend=0.02).

CONCLUSIONS

Adult leukemia risk may be associated with working in the chemical industry, and exposure to benzene, synthetic fiber dust, radioactive materials, and toluene in the study population.

Association of genetic polymorphisms in CYP2E1, MPO, NQO1, GSTM1, and GSTT1 genes with benzene poisoning

Metabolic enzymes involved in benzene activation or detoxification, including NAD(P)H, quinone oxidoreductase 1 (NQO1), cytochrome P450 2E1 (CYP2E1), myeloperoxidase (MPO), glutathione-S-transferase mu-1 (GSTM1), and glutathione-S-transferase theta-1 (GSTT1), were studied for their roles in human susceptibility to benzene poisoning. The potential interactions of these metabolic enzymes with lifestyle factors such as cigarette smoking and alcohol consumption were also explored. We studied 156 benzene-poisoning patients and 152 workers occupationally exposed to benzene in South China. Sequencing, denaturing HPLC, restriction fragment-length polymorphism, and polymerase chain reaction were used to detect polymorphisms on the promoters and complete coding regions of NQO1, CYP2E1, MPO, and the null genotypes of GSTM1 and GSTT1. Seventeen single nucleotide polymorphisms (SNPs) were identified in NQO1, CYP2E1, and MPO genes, including 6 novel SNPs in CYP2E1 and MPO. Of the subjects who smoked and drank alcohol, an 8.15-fold [95% confidence interval (CI), 1.43-46.50] and a 21.50-fold (95% CI, 2.79-165.79) increased risk of benzene poisoning, respectively, were observed among the subjects with two copies of NQO1 with a C-to-T substitution in cDNA at nucleotide 609 (c.609 C>T variation; i.e., NQO1 c.609 T/T) compared to those with the heterozygous or wild (NQO1 c.609 C/T and c.609 C/C) genotypes. Our data also indicated that individuals with CYP2E1 c.-1293 C/C and c.-1293 G/C, and NQO1 c.609 T/T, and GSTT1 null genotypes tended to be more susceptible to benzene toxicity. Our results suggest that the combined effect of polymorphisms in NQO1, CYP2E1, and GSTT1 genes and lifestyle factors might contribute to benzene poisoning.

A model for the induction of aplastic anemia by subcutaneous administration of benzene in mice

Long-term exposure to benzene vapors is associated with hematological diseases such as leukemia, lymphoma and aplastic anemia. CD(1) male mice were randomly assigned to six groups: 1B(10), 1B(15), 1B(20), 2B(10), 2B(15), and 2B(20.) 1B mice were administered 2 ml/kg (1940 mg/kg) subcutaneous injection (in the dorsal region) of benzene 5 days a week, and 2B mice were exposed 3 days a week (Monday, Wednesday and Friday) until a total of 10, 15 and 20 doses were completed. About 48 h after treatment completion, leukocyte, erythrocyte, and bone marrow cells were counted, and spleen histopathology was analyzed. 1B(15) and 1B(20) mice showed lethargy and irritability, 80% body and 42% spleen weight loss (P<0.001), while body and spleen weight loss were less severe in 2B mice (12 and 48%, respectively). After exposure to 20 benzene doses, 1B(20) and 2B(20) mice showed decreased hemoglobin concentrations, and erythrocyte, leukocyte and bone marrow cell counts (37, 34, 80 and 50%, respectively in group 1B(20); P<0.001; and 12, 48, 62 and 62%, respectively in group 2B(20)). Thrombocytopenia occurred only in group 2B. Both benzene-treatment schemes caused aplastic anemia, however, the disease was masked by spleen toxicity in group 1B. Scheme 2 allowed mice survival and caused less non-hematological effects. We establish here a reproducible and inexpensive experimental model to induce aplastic anemia in mice by subcutaneous injection of 2 ml/kg benzene, using two short-term treatment schemes.

Mortality among benzene-exposed workers in China

A large cohort of 74,828 benzene-exposed and 35,805 nonexposed workers employed between 1972 and 1987 in 12 cities in China was followed to determine mortality from all causes. Benzene-exposed study subjects were employed in a variety of occupations including coating applications, and rubber, chemical, and shoe production. Mortality was slightly increased among workers with greater cumulative exposure to benzene (ptrend < 0.05), but this excess was largely due to cancer deaths (ptrend < 0.01). Deaths due to lymphatic and hematopoietic malignancies (ptrend = 0.01) and lung cancer (ptrend = 0.01) increased with increasing cumulative exposure to benzene. Investigations continue to relate benzene exposure to specific lymphatic and hematopoietic malignancies and other causes of death.