Modulation of proto-oncogene expression by polychlorinated biphenyls in 3T3-L1 cell line

Persistent organic pollutant exposure contributes to Black/White differences in leukocyte telomere length in the National Health and Nutrition Examination Survey

Despite racial disparities in diseases of aging and premature mortality, non-Hispanic Black Americans tend to have longer leukocyte telomere length (LTL), a biomarker of cellular aging, than non-Hispanic White Americans. Previous findings suggest that exposure to certain persistent organic pollutants (POPs) is both racially-patterned and associated with longer LTL. We examine whether Black/White differences in LTL are explained by differences in exposure to 15 POPs by estimating the indirect effect (IE) of self-reported race on LTL that is mediated through nine polychlorinated biphenyls (PCBs), three furans, and three dioxins, as well as their mixtures. Our study population includes 1,251 adults from the 1999-2000 and 2001-2002 cycles of the cross-sectional National Health and Nutrition Examination Survey. We characterized single-pollutant mediation effects by constructing survey-weighted linear regression models. We also implemented various approaches to quantify a global mediation effect of all POPs, including unpenalized linear regression, ridge regression, and examination of three summary exposure scores. We found support for the hypothesis that exposure to PCBs partially mediates Black/White differences in LTL. In single-pollutant models, there were significant IEs of race on LTL through six individual PCBs (118, 138, 153, 170, 180, and 187). Ridge regression (0.013, CI 0.001, 0.023; 26.0% mediated) and models examining summative exposure scores with linear combinations derived from principal components analysis (0.019, CI 0.009, 0.029; 34.8% mediated) and Toxic Equivalency Quotient (TEQ) scores (0.016, CI 0.005, 0.026; 28.8% mediated) showed significant IEs when incorporating survey weights. Exposures to individual POPs and their mixtures, which may arise from residential and occupational segregation, may help explain why Black Americans have longer LTL than their White counterparts, providing an environmental explanation for counterintuitive race differences in cellular aging.

Serum polychlorinated biphenyls and leukocyte telomere length in a highly-exposed population: The Anniston Community Health Survey

BACKGROUND

Serum polychlorinated biphenyls (PCBs) have previously been associated with longer leukocyte telomere length (LTL) in most, but not all, of the few previous studies. PCBs were produced in Anniston, Alabama from 1929 to 1971 and participants of the Anniston Community Health Survey (ACHS) were highly exposed.

OBJECTIVES

We evaluated serum levels of 35 PCBs and relative telomere length in 559 ACHS participants.

METHODS

Relative LTL was measured in DNA extracted from blood clots. We assessed PCBs individually, grouped by chlorination, and summed PCBs. We used linear regression to assess the association between each PCB metric while adjusting for pertinent covariates.

RESULTS

Serum PCBs were associated with longer LTL among white participants and the oldest age group of black participants. Among white participants, compared with those in the first quartile of sum PCBs those in the third quartile of sum PCBs had 8.09% longer relative LTL (95% CI: 1.99; 14.55) and those in the fourth had 7.58% longer relative LTL (95%CI: -0.01; 15.76) (p-quadratic=0.05). Among African American participants, serum PCBs were associated with longer relative LTL among those over age 64 only. Tests for interaction were not statistically significant.

CONCLUSIONS

We observed a non-linear positive association between serum PCBs and LTL among white participants. Serum PCBs were associated with longer LTL in the oldest age group of African Americans. This association may provide insight into the cancers previously associated with exposure to PCBs, melanoma and non-Hodgkin lymphoma, which have been associated with long LTL in previous studies.

Polychlorinated Biphenyls and Leukocyte Telomere Length: An Analysis of NHANES 1999-2002

Polychlorinated biphenyls (PCBs) induce the expression of the proto-oncogene c-myc which has a role in cellular growth and proliferation programs. The c-myc up-regulates the telomerase reverse transcriptase which adds the telomeres repeating sequences to the chromosomal ends to compensate for the progressive loss of telomeric sequence. We performed multivariate linear regression to analyze the association of PCBs, polychlorinated dibenzo-p-dioxins, and 1,2,3,4,6,7,8-heptachlorodibenzofuran with leukocyte telomere length (LTL) in the adult population (n = 2413) of the National Health and Nutrition Examination Survey 1999-2002. LTL was natural log-transformed and the results were re-transformed and presented as percent differences. Individuals in the 3rd and 4th quartiles of the sum of PCBs were associated with 8.33% (95% CI: 4.08-13.88) and 11.63% (95% CI: 6.18-17.35) longer LTLs, respectively, compared with the lowest quartile, with evidence of a dose-response relationship (p-trend < 0.01). The association of the sum PCBs with longer LTL was found in both sexes. Additionally, 1,2,3,4,6,7,8-heptachlorodibenzofuran and 1,2,3,6,7,8-hexachlorodibenzo-p-dioxin were associated with longer LTL. The age independent association between longer LTL and environmental exposures to PCBs, 1,2,3,4,6,7,8-heptachlorodibenzofuran and 1,2,3,6,7,8-hexachlorodibenzo-p-dioxin may support a role as tumor promoter of these compounds. Further studies to evaluate the effect of these compounds on LTL are needed to more fully understand the implications of our finding.

Exploring environmental causes of altered ras effects: fragmentation plus integration?

Mutations in ras genes are the most common abnormality of oncogenes in human cancer and a major example of activation by point mutation. Experimental and epidemiological studies support the notion that Ki-ras activation and expression may be chemically related. We discuss the potential role of several environmental compounds in the induction or promotion of ras mutations in humans, with a focus on exocrine pancreatic cancer, the human tumor with the highest prevalence at diagnosis of Ki-ras mutations. Organochlorine compounds, organic solvents, and coffee compounds may play an indirect role in causing Ki-ras mutations, rather than as direct inducers of the mutations. Although for some organochlorine compounds the induction of point mutations in ras oncogenes cannot be excluded, it seems more likely that the effects of these compounds are mediated through nongenomic or indirectly genotoxic mechanisms of action. Organic solvents also may act via enzymatic induction of ras mutagens or by providing a proliferation advantage to ras-mutated cell clones. In exocrine pancreatic cancer, caffeine, other coffee compounds, or other factors with which coffee drinking is associated could modulate Ki-ras activation by interfering with DNA repair, cell-cycle checkpoints, and apoptosis. Asbestos, cigarette smoking, and some dietary factors also may be involved in the initiation or the promotion of Ki-ras mutations in lung and colon cancers. Further development of the mechanistic scenarios proposed here could contribute to a meaningful integration of biological, clinical, and environmental knowledge on the causes of altered ras effects.

Proto-oncogene amplification and overexpression in cadmium-induced cell transformation

Cadmium (Cd) is an essential material used in the battery, metal-coating, and alloy industries. In addition to these industrial uses, it is also a component of cigarette smoke. Therefore, exposure to cadmium is widespread and presents a considerable health concern. Cadmium is known to be a carcinogen; however, the possible mechanism of carcinogenesis with regards to the activation and inactivation of cancer-related genes has not yet been fully elucidated. In this study, amplification, expression, and point mutation of cancer-related genes associated with Cd-induced cell transformation in BALB/c-3T3 cells were studied. Six proto-oncogenes (K-ras, c-myc, c-fos, c-jun, c-sis, and erbB), as well as the p53 tumor suppressor, were investigated for gene amplification using differential polymerase chain reaction (PCR), while the expression of the proteins produced by these genes was evaluated by Western blot analysis. Point mutations in K-ras and p53 were studied by PCR restriction fragment length polymorphism analysis and DNA sequencing. There were no point mutations observed in codons 12, 13, and 61 of K-ras or in exons 4-10 of p53 and no observed differences in the levels of any of the proteins studied. Among 10 Cd-induced transformed cell lines, significant gene amplification was found for c-myc and c-jun in 50% and 80% of the cell lines, respectively. Chromosome painting was performed to confirm that this amplification was not simply due to additional copies of the chromosomes carrying these oncogenes. In addition, reverse-transcription PCR (RT-PCR) was performed to confirm increased expression of c-myc and c-jun. These results suggest that cell transformation induced by Cd may be attributed, at least in part, to gene amplification of c-myc and c-jun and that some of the Cd-transformed cells may possess neoplastic potential resulting from genomic instability.

[Concentrations of persistent toxic compounds in the Spanish population: a puzzle without pieces and the protection of public health]

The contamination by persistent toxic compounds (PTCs) of the general population is a fact of relevance from a public health perspective. It is also relevant to health care professionals, as well as for environmental, food, industrial and economic policies. Though in Spain information on food contamination by PTCs shows large time and geographic gaps, the scarcity of data is even more severe on the concentrations that PTCs have in people: a representative study of a general healthy population living in a wide geographic area has never been conducted in the country. However, the available studies indicate that around 80-100% of the population has detectable concentrations of DDE, PCBs, hexachlorbenzene or lindane. Studies on the effects that PTCs have upon humans are extremely infrequent in Spain. Yet, the international literature suggests that some PTCs may induce significant biological and clinical effects at doses below those traditionally deemed "safe". The mechanism of action of PTCs are not restricted to endocrine disruption. Assessing the clinical and social relevance of the more subtle and long-term effects of PTCs presents interesting challenges and opportunities. Spain and other European countries lack population indicators on the impact that environmental processes have on human health. Several government levels have a role to fulfill in the monitoring of biological levels of PTCs among persons in order to assess the risks of adverse health effects. Along with over a hundred other countries. Spain will soon try to implement the Stockholm treaty on persistent organic pollutants (POPs). This constitutes a new opportunity to develop more efficient policies to control PTC residues in food, humans and the environment. As part of the treaty implementation it is necessary to launch a Report on factors that influence body concentrations of PTCs in the Spain general population.

Polychlorinated biphenyls promote 1-nitropyrene-induced lung tumorigenesis without the induction of K-ras gene mutation in A/J mice

Although the effects of polychlorinated biphenyls (PCBs) on human lung carcinogenesis are suggested from the massive PCBs poisoning that occurred in Japan designated "Yusho," the detailed molecular mechanism are unknown. 1 nitropyrene (1-NP), an ubiquitous and abundant environmental pollutant, is known to be detected in lung tissues derived from patients with lung cancer in Japan, and its relation to lung carcinogenesis is also suggested. We investigated the effects of PCBs (Kanechlor-400) on 1-NP-induced lung tumorigenesis in A/J mice. PCBs were administered intraperitoneally followed by ip injection of 1-NP. The lung lesions were examined 18 weeks after the final treatment. In the control group, no neoplastic lesions were induced in the lung. In the PCB group, preneoplastic lesions such as hyperplasia and adenoma were induced in 2/10 (20%) mice. In 1-NP group and in PCB + 1-NP group, lung lesions including adenocarcinoma were induced in 16/20 (80%) and 13/13 (100%) mice, respectively. Both the number and the size of tumors in PCB + 1-NP group were significantly greater than those in 1-NP group. K-ras gene mutation, CAA to CGA in codon 61 or GGT to GAT in codon 12, was found in either 1-NP group or PCB + 1-NP group but not in the PCB group. There was no difference in the pattern of K-ras mutation associated with the pretreatment with PCBs. These results suggest that PCBs promote 1-NP-induced lung tumorigenesis and may support, at least in part, the mechanism of the high incidence of lung cancer in patients with Yusho.

Serum concentrations of organochlorine compounds and K-ras mutations in exocrine pancreatic cancer. PANKRAS II Study Group

BACKGROUND

Organochlorine compounds such as 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane (p,p'-DDT), 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (p,p'-DDE), and some polychlorinated biphenyls (PCBs) are carcinogenic to animals and possibly also to human beings. Occupational exposure to DDT may increase the risk of pancreas cancer. The high frequency of K-ras mutations in pancreatic cancer remains unexplained. We analysed the relation between serum concentrations of selected organochlorine compounds and mutations in codon 12 of the K-ras gene in patients with exocrine pancreatic cancer.

METHODS

Cases were prospectively identified in five hospitals. Mutations in K-ras were analysed by PCR and artificial restriction fragment length polymorphism. Cases of pancreatic cancer with wild-type K-ras (n=17) were frequency matched for age and sex to cases of pancreatic cancer with a K-ras mutation (n=34, case-case study). These 51 cases were further compared with 26 hospital controls (case-control comparison). Serum organochlorine concentrations were measured by high-resolution gas chromatography with electron-capture detection and negative ion chemical ionisation mass spectrometry.

FINDINGS

Serum concentrations of p,p'-DDT were significantly higher in pancreatic cancer cases with a K-ras mutation than in cases without a mutation (odds ratio for upper tertile 8.7 [95% CI 1.6-48.5], p for trend=0.005). For p,p'-DDE the corresponding figures were 5.3 (1.1-25.2, p for trend=0.031). These estimates held after adjusting for total lipids, other covariates, and total PCBs. A specific association was observed between a glycine to valine substitution at codon 12 and both p,p'-DDT and p,p'-DDE concentrations (odds ratio 15.9, p=0.044 and odds ratio 24.1, p=0.028; respectively). A similar pattern was shown for the major di-ortho-chlorinated PCBs (congeners 138, 153, and 180), even after adjustment for p,p'-DDE, but without a specific association with spectrum. Concentrations of p,p'-DDT and p,p'-DDE were similar among wild-type cases and controls, but significantly higher for K-ras mutated cases than for controls (p<0.01).

INTERPRETATION

Organochlorine compounds such as p,p'-DDT, p,p'-DDE, and some PCBs could play a part in the pathogenesis of exocrine pancreatic cancer through modulation of K-ras activation. The results require replication, but they suggest new roles for organochlorines in the development of several cancers in human beings.