Occupational exposure to diesel exhaust and lung cancer: a meta-analysis

Activation of nuclear factor kappa B by diesel exhaust particles in mouse epidermal cells through phosphatidylinositol 3-kinase/Akt signaling pathway

Diesel exhaust particles (DEP) induce intense inflammatory and allergic immune responses. The epidermal cells receive much exposure to DEP, and are an important source of pro-inflammatory cytokines and other inflammatory mediators. Transcription factors, such as nuclear factor kappa B (NF-kappaB) and activator protein 1 (AP-1), regulate the expression of these mediators. We hypothesize that the transcription factors are target of DEP action. The current study sought to determine whether DEP-activated NF-kappaB and AP-1 in a mouse epidermal cell line, JB6 P(+) cells. Using stable transfectants of JB6 P(+) cells expressing NF-kappaB or AP-1 luciferase reporter constructs, we demonstrated that exposure to DEP at a non-cytotoxic concentration significantly enhanced the transactivation of NF-kappaB, but not AP-1. Furthermore, DEP promoted phosphorylation of Akt, a substrate of phosphatidylinositol 3-kinase (PI3K), on Ser-473 and Thr-308 in a PI3K-dependent manner, and enhanced phosphorylation of down-stream p70/p85 S6 kinases (p70/p85S6K) as well as glycogen synthase kinase-3beta (GSK-3beta). Blockage of PI3K activation eliminated DEP-stimulated NF-kappaB transactivation. Although SAPK/JNK pathway was modestly activated by DEP, it was not involved in NF-kappaB transactivation. DEP had little effect on the phosphorylation of ERKs and p38 MAPK. Thus, DEP-induced transactivation of NF-kappaB is mediated by PI3K/Akt signaling pathway.

Occupation related pesticide exposure and cancer of the prostate: a meta-analysis

AIMS

To summarise recent literature on the risk of prostate cancer in pesticide related occupations, to calculate the meta-rate ratio, and to compare it to data from meta-analyses previously published.

METHODS

A meta-analysis of 22 epidemiological studies, published between 1995 and 2001, was conducted in order to pool their rate ratio estimates. Studies were summarised and evaluated for homogeneity and publication bias.

RESULTS

The meta-rate ratio estimate, based on 25 estimators of relative risk from 22 studies, was 1.13 (95% CI 1.04 to 1.22). Significant heterogeneity of rate ratios existed among the different studies. Therefore, a stratified analysis was carried out. Major sources of heterogeneity identified were geographic location, study design, and healthy worker effect. Overall, pooled risk estimates for studies derived from Europe were lower than those derived from the USA/Canada. A significant increase in rate ratio was observed for the occupation category of pesticide applicators, whereas no significant increase was observed for farmers. There was no evidence of publication bias.

CONCLUSION

This increased meta-rate ratio for prostate cancer in different pesticide related occupations, including farmers, is very similar to three, previously published, meta-rate ratios for prostate cancer in farmers calculated from studies published before 1995. Although the underlying data do not identify pesticide exposure as an independent cause for prostate cancer, the fact that an increased meta-rate ratio is again obtained points to occupational exposure to pesticides as a possible factor. Future epidemiological studies should focus, as far as possible, on reliable methods to estimate actual exposure.

Lung cancer in heavy equipment operators and truck drivers with diesel exhaust exposure in the construction industry

BACKGROUND

Several studies indicate that truck drivers have an increased risk of lung cancer, but few studies have examined lung cancer risk in heavy equipment operators. Workers in both occupations are exposed to diesel exhaust.

AIMS

To examine the incidence and mortality from lung cancer among truck drivers and among drivers of heavy vehicles.

METHODS

A computerised register of Swedish construction workers participating in health examinations between 1971 and 1992 was used. Male truck drivers (n = 6364) and drivers of heavy construction vehicles (n = 14 364) were selected as index groups; carpenters/electricians constituted the reference group (n = 119 984).

RESULTS

Operators of heavy construction equipment experienced no increased risk of lung cancer compared to risk among the carpenter/electrician referents (61 cases v 70.1 expected). However, a significant inverse trend risk with increasing use of cabins was apparent. Truck drivers had increased risks of cancer of the lung (61 cases v 47.3 expected) and prostate (124 cases v 99.7 expected), although only mortality for lung cancer was significantly increased. Comparisons with the general population showed similar results.

CONCLUSION

Results are consistent with those of previous studies suggesting that heavy equipment operators with potential exposure to diesel exhaust may have little or no increased risk of lung cancer, although the use of cabins seemed to decrease the risk of lung cancer. The results for truck drivers are also consistent with previous reports of increased lung cancer risk among truck drivers exposed to diesel exhaust, as well as recent reports linking diesel exhaust exposure to prostate cancer.

Exposure to carcinogenic polycyclic aromatic compounds and health risk assessment for diesel-exhaust exposed workers

OBJECTIVES

Workers' exposure to diesel exhaust in a bus depot, a truck repair workshop and an underground tunnel was determined by the measuring of elemental carbon (EC) and 15 carcinogenic polycyclic aromatic compounds (PACs) proposed by the US Department of Health and Human Services/National Toxicology Program (NTP). Based on these concentration data, the genotoxic PAC contribution to the diesel-exhaust particle (DEP) lung-cancer risk was calculated.

METHOD

Respirable particulate matter was collected during the summer and winter of 2001 (except for in the underground situation) and analysed by coulometry for EC and by GC-MS methods for PACs. The use of potency equivalence factors (PEFs) allowed the studied PAC concentrations to be expressed as benzo[a]pyrene equivalents (B[a]P(eq)). We then calculated the lung-cancer risk due to PACs and DEPs by multiplying the B[a]P(eq) and EC concentrations by the corresponding unit risk factor. The ratio of these two risks values has been considered as an estimate of the genotoxic contribution to the DEP cancer risk.

RESULTS

For the bus depot and truck repair workshop, exposure to EC and PACs has been shown to increase by three to six times and ten times, respectively, during winter compared to summer. This increase has been attributed mainly to a decrease in ventilation during the cold. With the PEF approach, the B[a]P(eq) concentration is five-times higher than if only benzo[ a]pyrene (B[a]P) is considered. Dibenzopyrenes contribute an important part to this increase. A simple calculation based on unit risk factors indicates that the studied PAC contribution to the total lung-cancer risk attributed to DEPs is in the range of 3-13%.

CONCLUSIONS

The 15 NTP PACs represent a small but non-negligible part of lung-cancer risk with regard to diesel exposure. From this point of view, the dibenzopyrene family are important compounds to be considered.

Diesel exhaust exposure in the Canadian railroad work environment

An investigation of occupational exposure to diesel exhaust, in terms of elemental carbon, was conducted as part of a feasibility study in the Canadian railroad industry. Both personal and area samples were collected from three major operating divisions of the railways: mechanical service, transportation, and engineering. A total of 255 elemental carbon samples have been described. The results show that all but six elemental carbon concentrations, expressed as size-selective respirable air samples taken using a 10 mm nylon cyclone, are well below the 2001 proposed American Conference of Governmental Industrial Hygienists' (ACGIH) threshold limit value (TLV) of 20 microg/m3. The concentration of diesel exhaust, expressed as elemental carbon, in the railroad industry is much lower than that in some other major industries such as mining and forklift truck operations. If the TLV is to be applicable to a broad range of workplace settings such as railroad, construction, and mining, the use of a TLV that is based on an elemental carbon measurement of size selective respirable samples, as recommended in the 2001 ACGIH proposal, would appear to be the most valid strategy for control of exposure to diesel exhaust.

Hazardous air pollutants and asthma

Asthma has a high prevalence in the United States, and persons with asthma may be at added risk from the adverse effects of hazardous air pollutants (HAPs). Complex mixtures (fine particulate matter and tobacco smoke) have been associated with respiratory symptoms and hospital admissions for asthma. The toxic ingredients of these mixtures are HAPs, but whether ambient HAP exposures can induce asthma remains unclear. Certain HAPs are occupational asthmagens, whereas others may act as adjuncts during sensitization. HAPs may exacerbate asthma because, once sensitized, individuals can respond to remarkably low concentrations, and irritants lower the bronchoconstrictive threshold to respiratory antigens. Adverse responses after ambient exposures to complex mixtures often occur at concentrations below those producing effects in controlled human exposures to a single compound. In addition, certain HAPs that have been associated with asthma in occupational settings may interact with criteria pollutants in ambient air to exacerbate asthma. Based on these observations and past experience with 188 HAPs, a list of 19 compounds that could have the highest impact on the induction or exacerbation of asthma was developed. Nine additional compounds were identified that might exacerbate asthma based on their irritancy, respirability, or ability to react with biological macromolecules. Although the ambient levels of these 28 compounds are largely unknown, estimated exposures from emissions inventories and limited air monitoring suggest that aldehydes (especially acrolein and formaldehyde) and metals (especially nickel and chromium compounds) may have possible health risk indices sufficient for additional attention. Recommendations for research are presented regarding exposure monitoring and evaluation of biologic mechanisms controlling how these substances induce and exacerbate asthma.

Allergic susceptibility associated with diesel exhaust particle exposure: clear as mud

Exposure to elevated levels of particulate air pollution from motor vehicles is frequently associated with increased morbidity and mortality from cardiovascular conditions, lung cancer, and nonmalignant respiratory illnesses (e.g., asthma, bronchitis, respiratory tract infections). It appears, however, that less attention has been paid to the potential role of road traffic fumes in the induction of allergic conditions. Laboratory studies in humans and animals have shown that particulate toxic pollutants-particularly diesel exhaust particulates-can enhance allergic inflammation and can induce allergic immune responses. Most of these immune responses are mediated by the carbon core of diesel exhaust particulates. Polyaromatic hydrocarbons (e.g., anthracene, fluoranthene, pyrene, phenanthrene) are major chemical components of diesel exhaust particulates, and they have enhanced the production of immunoglobulin E. Although several large epidemiological studies have demonstrated a strong association between exposure to motor vehicle traffic emissions and allergic symptoms and reduced lung function, the evidence for the development of allergic sensitization from diesel exhaust particulates is less abundant than for the aforementioned associations. Recent comparisons of the prevalence of hay fever, as well as positive skin-prick tests, between citizens of former West and East Germany and between Hong Kong and China civilians, have demonstrated marked differences. Crucial variations in the level of particulate air pollution from motor vehicles in these countries may account for the observed increased prevalence of atopy. Although road-traffic pollution from automobile exhausts may be a risk factor for atopic sensitization, the evidence in support of this view remains conflictive. Some investigators have reported a clear association between the prevalence of allergy and road-traffic-related air pollution, whereas such a difference was not observed in other studies. Most discrepancies have been related to important variations in study design and methodology. In addition, inasmuch as exposure to ambient particles differs substantially in worldwide urban environments, perhaps qualitative-rather than quantitative-variations in particulate air pollution at different locations account for differences in the prevalence and/or severity of respiratory allergies.

Utility of the WHO neurobehavioral core test battery in Chinese workers-a meta-analysis

We performed a meta-analysis to determine the most sensitive subtests of the WHO Neurobehavioral Core Test Battery (NCTB) when administered to Chinese workers. Extensive Chinese Biological Medical Database and MEDLINE searches, review of cited references, and discussion with other investigators were undertaken. Data were extracted from 39 eligible studies; the summary effects (effect sizes) were calculated using a fixed-effect model. Various exposure agents showed different sensitivities to the seven subtests of NCTB. For mercury-exposure, the Benton Visual Retention was the most sensitive subtest, with an effect size (95% CI) of 6.0 (4.4-7.6). For lead-exposure, the most sensitive subtests were the Pursuit Aiming II and Profile of Mood States, with effect sizes (95% CI) of 11.3 (8.3-14.3) and 10.6 (7.5-13.7), respectively. For organic solvents-exposure, Digit Span, Pursuit Aiming II, and Digit Symbol were the most sensitive subtests, with effect sizes (95- CI) of 4.7 (3.3-6.1), 4.6 (3.1-6.1), and 4.1 (2.7-5.5), respectively.

DNA adduct levels and DNA repair polymorphisms in traffic-exposed workers and a general population sample

Peripheral blood DNA adducts have been considered an acceptable surrogate for target tissues and possibly predictive of cancer risk. A group of 114 workers exposed to traffic pollution and a random sample of 100 residents were drawn from the EPIC cohort in Florence, a population recently shown to present increased DNA adduct levels (Palli et al., Int J Cancer 2000;87:444-51). DNA bulky adducts and 3 DNA repair gene polymorphisms were analyzed in peripheral leukocytes donated at enrollment, by using (32)P-postlabeling and PCR methods, respectively. Adduct levels were significantly higher for traffic workers among never smokers (p = 0.03) and light current smokers (p = 0.003). In both groups, urban residents tended to show higher levels than those living in suburban areas, and a seasonal trend emerged with adduct levels being highest in summer and lowest in winter. Traffic workers with at least 1 variant allele for XPD-Lys751Gln polymorphism had significantly higher levels in comparison to workers with 2 common alleles (p = 0.02). A multivariate analysis (after adjustment for age, season, area of residence, smoking, XPD-Lys751Gln genotype and antioxidant intake) showed a significant 2-fold association between occupational exposure and higher levels of adducts (odds ratio 2.1; 95% confidence interval 1.1-4.2), in agreement with recent pooled estimates of increased lung cancer risk for similar job titles. Our results suggest that traffic workers and the general population in Florence are exposed to high levels of genotoxic agents related to vehicle emissions. Photochemical pollution in warmer months might be responsible for the seasonal trend of genotoxic damage in this Mediterranean urbanized area.

The prevalence of asthma and heart disease in transport workers: a practice-based study

BACKGROUND

There has been widespread concern that the increasing incidence of asthma observed during the late 1980s might have arisen because of environmental pollution, and in particular vehicle pollution. The General Practice Morbidity Survey in 1991/92 (MSGP4) collected data on occupation, employment status, and smoking habit linked individually to each patient record.

OBJECTIVES

To examine whether people with occupations that have high exposure to vehicle exhaust fumes have an increased prevalence of asthma, acute respiratory infections, and ischaemic heart disease (IHD).

METHOD

Men aged 16 to 64 years were grouped by Standard Occupational Classification codes; 93,692 employed and 20,858 not-employed men were studied separately. Those with likely high occupational exposure were grouped together ('all-exposed')--the remainder occupations in corresponding chapters of the code were used as controls. We compared 12-month age and smoking standardised disease prevalence ratios for asthma, chronic obstructive pulmonary disease (COPD), acute respiratory infections (IHD), and all circulatory disorders in the all exposed and individual exposed occupations with their matching controls. Also the mean frequency of consultations per person consulting was calculated for each occupational group and disease.

RESULTS

For employed persons, the prevalence ratio (PR) for asthma in the all-exposed, (116, 95% confidence interval [95% CI] = 101-130) exceeded that for all employed persons (100); however, the difference compared with chapter-matched controls (PR = 97, 95% CI = 92-103), was not statistically significant. Results for COPD were similar. Prevalence ratios in motor mechanics, a high-exposure group, were 98 (95% CI = 70-127) 96 (95% CI = 70-123) for asthma and COPD respectively. Among the employed, prevalence ratios for IHD in all but one of the individual occupation groups examined did not differ from the average, however among those not employed the ratio in the all-exposed (PR = 152, 95% CI = 128-174) exceeded that in the controls (PR = 112, 95% CI = 104-120).

CONCLUSION

Occupational groups exposed to motor vehicle pollution have a marginally increased prevalence of asthma compared with working males generally, though not compared with occupation matched controls. This study has demonstrated a methodology for using GP data to examine occupation-related disease. This could be used in future by augmenting GP data with occupation and smoking information.

The epidemiology of lung cancer

Lung cancer continues to be the leader in cancer deaths in the United States. The incidence of lung cancer in men has slowly decreased since the late 1980s, but has just now begun to plateau in women at the end of this decade. Despite modest advances in chemotherapy for treating lung cancer, it remains a deadly disease with overall 5-yr survival rates having not increased significantly over the last 25 years, remaining at approximately 14%. Tobacco smoking causes approximately 85-90% of bronchogenic carcinoma. Environmental tobacco exposure or a second-hand smoke also may cause lung cancer in life-long non-smokers. Certain occupational agents such as arsenic, asbestos, chromium, nickel and vinyl chloride increase the relative risk for lung cancer. Smoking has an additive or multiplicative effect with some of these agents. Familial predisposition for lung cancer is an area with advancing research. Developments in molecular biology have led to growing interest in investigation of biological markers, which may increase predisposition to smoking-related carcinogenesis. Hopefully, in the future we will be able to screen for lung cancer by using specific biomarkers. Finally, dietary factors have also been proposed as potential risk modulators, with vitamins A, C and E proposed as having a protective effect. Despite the slow decline of smoking in the United States, lung cancer will likely continue its devastation for years to come.

Part VII. Air pollution: overview of sources and health effects

In this era of increasing interest about environmental contributors to illness, primary care providers may be asked by patients for guidance about air pollution. Some components of outdoor air pollution have improved in the past 30 years, but locally hazardous conditions continue to occur, especially for vulnerable subpopulations. Such groups include people with chronic cardiac and respiratory conditions, the elderly, pregnant women, and newborns. This overview discusses the sources and health effects of the primary pollutant groups--ozone, sulfur dioxide (SO2), nitrogen oxides, carbon monoxide (CO), particulates, and other air toxics. A number of Web links are provided to help clinicians and patients get up-to-date information about pollution in the areas where they live. This section concludes with a discussion of treatment and of behavioral and societal approaches to air pollution.

Oxidant stress, antioxidants and nitric oxide in traffic police of Hyderabad, India

Exposure to environmental pollutants is known to be harmful to health, in general, and to lungs in particular. In this respect, traffic police are at particular risk due to the nature of their job, since they are exposed to emissions from the vehicles. Here, we show that in the traffic police of Hyderabad city, India, the plasma levels of lipid peroxides are high, whereas the concentrations of the nitric oxide are low. In addition, the levels of various antioxidants in the RBC lysate such as catalase, superoxide dismutase and glutathione peroxidase were found to be low with no significant alteration in plasma ceruloplasmin levels. These results suggest that exposure to air pollutants, a major portion of which is due to emissions from the vehicles, can increase oxidant stress, decrease the levels of antioxidants and nitric oxide. This imbalance in the oxidant/antioxidant system may lead to lung damage and is likely to cause respiratory problems in individuals exposed to air pollution.

Outdoor air pollution and lung cancer

In the 1950s evidence of an ongoing epidemic of lung cancer in the United States and Western Europe led researchers to examine the role of outdoor air pollution, which was considered by some to be a likely cause. Although epidemiologic research quickly identified the central role of cigarette smoking in this epidemic, and despite progress in reducing outdoor air pollution in Western industrialized countries, concerns that ambient air pollution is causing lung cancer have persisted to the present day. This concern is based on the fact that known carcinogens continue to be released into outdoor air from industrial sources, power plants, and motor vehicles, and on a body of epidemiologic research that provides some evidence for an association between outdoor air pollution and lung cancer. This article reviews the epidemiologic evidence for this association and discusses the limitations of current studies for estimating the lung cancer risk in the general population. It also identifies research needs and suggests possible approaches to addressing outstanding questions.