A dose-response analysis and quantitative assessment of lung cancer risk and occupational cadmium exposure

Prevalence of Self-Reported Voice Concerns and Associated Risk Markers in a Nonclinical Sample of Military Service Members

INTRODUCTION

Difficult communication environments are common in military settings, and effective voice use can be critical to mission success. This study aimed to estimate the prevalence of self-reported voice disorders among U.S. military service members and to identify factors that contribute to their voice concerns.

METHOD

A nonclinical sample of 4,123 active-duty service members was recruited across Department of Defense hearing conservation clinics. During their required annual hearing evaluation, volunteers provided responses to voice-related questions including a slightly adapted version of the Voice Handicap Index-10 (VHI-10) as part of a larger survey about communication issues. Changepoint detection was applied to age and years of service to explore cohort effects in the reporting of voice concerns. Logistic regression analyses examined multiple available factors related to communication to identify factors associated with abnormal results on the VHI-10.

RESULTS

Among the respondents, 41% reported experiencing vocal hoarseness or fatigue at least several times per year, and 8.2% (n = 336) scored above the recommended abnormal cut-point value of 11 on the VHI-10. Factors independently associated with the greatest risk for self-reported voice concerns were sex (female), cadmium exposure, vocal demands (the need for a strong, clear voice), and auditory health measures (frequency of experiencing temporary threshold shifts; self-reported hearing difficulties).

CONCLUSIONS

Based on self-reported voice concerns and false negative rates reported in the literature, the prevalence of dysphonia in a large sample of active-duty service members is estimated to be 11.7%, which is higher than that in the general population. Certain predictors for voice concerns were expected based on previous literature, like female sex and voice use, but frequency of temporary threshold shifts and exposure to cadmium were surprising. The strong link between voice and auditory problems has particular implications regarding the need for effective communication in high-noise military and other occupational environments.

Cadmium Monitoring at the Workplace: Effectiveness of a Combination of Air- and Biomonitoring

Inhalation exposure to cadmium at the workplace has been associated with an increased risk of lung cancer and non-cancer respiratory effects. To ensure levels of cadmium remain below effect levels, air quality is monitored and regulations specifying an air limit value are implemented. The EU Carcinogens and Mutagens Directive of 2019 recommended values for the inhalable fraction and the respirable fraction but the latter only for a transitional period. Cadmium exposure has also been associated with systemic effects, following its storage in the kidneys and due to its long half-life. The accumulation of cadmium occurs via different exposure routes and from different sources, including workplace dust and fumes, food, and smoking. Biomonitoring (in blood, urine) has been identified as the most appropriate method to follow up cumulative exposure and total cadmium body burden, as it conveniently reflects intakes by all routes. However, it is not systematically implemented. This paper has a double objective: first, proposing a possible limit value for the respirable fraction, using an approach integrating epidemiological data. Secondly, demonstrating that the implementation of both air and biological limit values is key to protecting workers' health in occupational settings. The paper summarizes the current knowledge on cadmium health effects and how biomarkers reflect those. It presents an approach to derive a respirable value, using recent human data, and describes how the combination of air monitoring and biomonitoring is applied by the EU industry to protect the workforce. While a respirable fraction value helps protect workers against local respiratory adverse health effects, air monitoring alone is not sufficient to protect workers against systemic effects of cadmium. Therefore, complementary biomonitoring and the implementation of a biological limit value is recommended.

Early Cardiovascular Risk in E-cigarette Users: the Potential Role of Metals

PURPOSE OF REVIEW

Electronic cigarettes (e-cigs) are a source of metals. Epidemiologic and experimental evidence support that metals are toxic to the cardiovascular system. Little is known, however, about the role that e-cig metals may play as toxicants for the possible cardiovascular effects of e-cig use. The goal of this narrative review is to summarize the evidence on e-cig use and metal exposure and on e-cig use and cardiovascular toxicity and discuss the research needs.

RECENT FINDINGS

In vitro studies show cytotoxicity and increased oxidative stress in myocardial cells and vascular endothelial cells exposed to e-liquids and e-cig aerosols, with effects partially reversed with antioxidant treatment. There is some evidence that the heating coil plays a role in cell toxicity. Mice exposed to e-cigs for several weeks showed higher levels of oxidative stress, inflammation, platelet activation, and thrombogenesis. Cross-over clinical experiments show e-cig use alters nitric oxide-mediated flow-mediated dilation, endothelial progenitor cells, and arterial stiffness. Cross-sectional evidence from large nationally representative samples in the USA support that e-cig use is associated with self-reported myocardial infarction. Smaller studies found associations of e-cig use with higher oxidized low-density protein and heart variability compared to healthy controls. Numerous studies have measured elevated levels of toxic metals in e-cig aerosols including lead, nickel, chromium, and manganese. Arsenic has been measured in some e-liquids. Several of these metals are well known to be cardiotoxic. Numerous studies show that e-cigs are a source of cardiotoxic metals. Experimental studies (in vitro, in vivo, and clinical studies) show acute toxicity of e-cigs to the vascular system. Studies of long-term toxicity in animals and humans are missing. Longitudinal studies with repeated measures of metal exposure and subclinical cardiovascular outcomes (e.g., coronary artery calcification) could contribute to determine the long-term cardiovascular effects of e-cigs and the potential role of metals in those effects.

Cadmium induces A549 cell migration and invasion by activating ERK

Cadmium (Cd) is an established carcinogen that is involved in the progression of lung cancer. However, the mechanisms underlying this Cd-induced process have yet to be fully elucidated. The present study explored the potential roles of phosphorylated (p)-ERK in the Cd-induced migration and invasion of lung cancer cells. An MTT assay was performed to evaluate cell viability whilst western blot analysis and reverse transcription-quantitative PCR were used to detect the expression of protein and mRNA, respectively. Migration and invasion assays were performed to assess cell migratory and invasive abilities. The results demonstrated that exposure to Cd increased the expression of p-ERK in A549 cells. Cd also enhanced the migration and invasion of A549 cells, which could be blocked via U0126 treatment (an inhibitor of mitogen activated protein kinase). In addition, it was identified that Cd-induced expression of matrix metalloproteinases 2 mRNA was mediated by p-ERK. In conclusion, the present findings indicated that Cd induced A549 cell migration and invasion by activating ERK, and it was hypothesized that p-ERK could serve as a target in the clinical treatment of Cd-induced lung cancer.

Effect of dietary patterns on the blood/urine concentration of the selected toxic metals (Cd, Hg, Pb) in Korean children

This study was aimed to examine the association the blood/urinary concentration of toxic metal (Hg, Pb, and Cd) with children's dietary patterns. This cross-sectional study included 1026 school children aged 8-17 years. Dietary patterns were defined using factor loading scores for 108 foods from a Semi-Quantitative Food Frequency Questionnaire. A high blood Hg level was found in boys with a high score in the 'fish' pattern (p = 0.02), and in girls with a high score in 'fruit' pattern (p = 0.04). The concentration of Pb was related to the 'imprudent' pattern in high school boys (p = 0.02). The effect of the 'vegetable' pattern on high excretion of urinary Cd was observed in low grade elementary (p = 0.04) and middle school students (p < 0.0001), and the effect of the 'fruit' pattern on the urinary Cd was observed in high grade elementary school students (p = 0.02). This study suggests that the concentration of selected toxic metals in blood/urine could be affected by children's dietary pattern.

Effects of urban coarse particles inhalation on oxidative and inflammatory parameters in the mouse lung and colon

Background

Air pollution is a recognized aggravating factor for pulmonary diseases and has notably deleterious effects on asthma, bronchitis and pneumonia. Recent studies suggest that air pollution may also cause adverse effects in the gastrointestinal tract. Accumulating experimental evidence shows that immune responses in the pulmonary and intestinal mucosae are closely interrelated, and that gut-lung crosstalk controls pathophysiological processes such as responses to cigarette smoke and influenza virus infection. Our first aim was to collect urban coarse particulate matter (PM) and to characterize them for elemental content, gastric bioaccessibility, and oxidative potential; our second aim was to determine the short-term effects of urban coarse PM inhalation on pulmonary and colonic mucosae in mice, and to test the hypothesis that the well-known antioxidant N-acetyl-L-cysteine (NAC) reverses the effects of PM inhalation.

Results

The collected PM had classical features of urban particles and possessed oxidative potential partly attributable to their metal fraction. Bioaccessibility study confirmed the high solubility of some metals at the gastric level. Male mice were exposed to urban coarse PM in a ventilated inhalation chamber for 15 days at a concentration relevant to episodic elevation peak of air pollution. Coarse PM inhalation induced systemic oxidative stress, recruited immune cells to the lung, and increased cytokine levels in the lung and colon. Concomitant oral administration of NAC reversed all the observed effects relative to the inhalation of coarse PM.

Conclusions

Coarse PM-induced low-grade inflammation in the lung and colon is mediated by oxidative stress and deserves more investigation as potentiating factor for inflammatory diseases.

Electronic supplementary material

The online version of this article (10.1186/s12989-017-0227-z) contains supplementary material, which is available to authorized users.

Is Urinary Cadmium a Biomarker of Long-term Exposure in Humans? A Review

Cadmium is a naturally-occurring element, and humans are exposed from cigarettes, food, and industrial sources. Following exposure, cadmium accumulates in the kidney and is slowly released into the urine, usually proportionally to the levels found in the kidneys. Cadmium levels in a single spot urine sample have been considered indicative of long-term exposure to cadmium; however, such a potentially exceptional biomarker requires careful scrutiny. In this review, we report good to excellent temporal stability of urinary cadmium (intraclass correlation coefficient 0.66-0.81) regardless of spot urine or first morning void sampling. Factors such as changes in smoking habits and diseases characterized by increased excretion of proteins may produce short-term changes in urinary cadmium levels. We recommend that epidemiologists use this powerful biomarker in prospective studies stratified by smoking status, along with thoughtful consideration of additional factors that can influence renal physiology and cadmium excretion.

Characterization of a cadmium resistance Lactococcus lactis subsp. lactis strain by antioxidant assays and proteome profiles methods

Heavy metal contamination poses a major threat to the environment and human health for their potential toxicity and non-biodegradable properties. At present, some probiotics bacteria are reported to have great potential to eliminate heavy metals from food and water. In this study, resistance properties of a newly isolated Lactococcus lactis subsp. lactis for cadmium were studied by antioxidant assays and proteomics analysis. Antioxidant capacity of this strain was significantly activated under cadmium stress indicated by Fenton reaction, DPPH assay, SOD assay and GSH assay. Intracellular antioxidant enzyme systems, such as superoxide dismutase, glutathione reductase and catalase were suggested to play vital roles in the activated antioxidant capacity. The up-regulated cadA was associated with the activated P-type ATPases that plays an important role in cadmium resistance. Proteomics analysis identified 12 over-expressed proteins under 50mg/L cadmium stress and these proteins are abundant in oxidative stress response and energy metabolism regulation, which were considered as consequences as cadmium resistance of the strain. Thus, the probiotics Lactococcus lactis subsp. lactis may resist cadmium stress through antioxidant approach and enhanced energy metabolism. The food grade lactis strain may be applied in metal decontamination in environment and food/feed.

Fluorescence detection of intracellular cadmium with Leadmium Green

Leadmium Green is a commercially available, small molecule, fluorescent probe advertised as a detector of free intracellular cadmium (Cd(2+)) and lead (Pb(2+)). Leadmium Green has been used in various paradigms, such as tracking Cd(2+) sequestration in plant cells, heavy metal export in protozoa, and Pb(2+) absorption by vascular endothelial cells. However very little information is available regarding its affinity and selectivity for Cd(2+), Pb(2+), and other metals. We evaluated the in vitro selectivity of Leadmium Green using spectrofluorimetry. Consistent with manufacturer's claims, Leadmium Green was sensitive to Cd(2+) (KD ~600 nM) and also Pb(2+) (KD ~9.0 nM) in a concentration-dependent manner, and furthermore proved insensitive to Ca(2+), Co(2+), Mn(2+) and Ni(2+). Leadmium Green also responded to Zn(2+) with a KD of ~82 nM. Using fluorescence microscopy, we evaluated Leadmium Green in live mouse hippocampal HT22 cells. We demonstrated that Leadmium Green detected ionophore-mediated acute elevations of Cd(2+) or Zn(2+) in a concentration-dependent manner. However, the maximum fluorescence produced by ionophore-delivered Zn(2+) was much less than that produced by Cd(2+). When tested in a model of oxidant-induced liberation of endogenous Zn(2+), Leadmium Green responded weakly. We conclude that Leadmium Green is an effective probe for monitoring intracellular Cd(2+), particularly in models where Cd(2+) accumulates rapidly, and when concomitant fluctuations of intracellular Zn(2+) are minimal.

Urinary Cadmium and Risk of Invasive Breast Cancer in the Women's Health Initiative

Cadmium is a widespread heavy metal pollutant that may act as an exogenous estrogenic hormone. Environmental cadmium exposure has been associated with risk of breast cancer in retrospective studies. We prospectively assessed the relationship between cadmium exposure, evaluated by creatinine-normalized urinary cadmium concentration, and invasive breast cancer among 12,701 postmenopausal women aged ≥50 years in a Women's Health Initiative study of bone mineral density. After a median of 13.2 years of follow-up (1993-2010), 508 cases of invasive breast cancer and 1,050 comparison women were identified for a case-cohort analysis. Multivariable Cox regression was used to calculate hazard ratios and 95% confidence intervals. Risk of breast cancer was not associated with urinary cadmium parameterized either in quartiles (comparing highest quartile with lowest, hazard ratio = 0.80, 95% confidence interval: 0.56, 1.14; P for trend = 0.20) or as a log-transformed continuous variable (per 2-fold higher urinary cadmium concentration, hazard ratio = 0.94, 95% confidence interval: 0.86, 1.03). We did not observe an association between urinary cadmium and breast cancer risk in any subgroup examined, including never smokers and women with body mass index (weight (kg)/height (m)(2)) less than 25. Results were consistent in both estrogen receptor-positive and estrogen receptor-negative tumors. Our results do not support the hypothesis that environmental cadmium exposure is associated with risk of postmenopausal breast cancer.

Cadmium accumulation in leaves of leafy vegetables

Leafy vegetables have a relatively high potential for Cd uptake and translocation, and are thus considered Cd accumulators. For this reason, leaves and roots of lettuce (Lactuca sativa L.) and endive (Cichorium endivia L.) plants, grown on different agricultural soils in Campania region (southern Italy), subjected to different fertilisation treatments (unfertilisation, compost amendment and mineral fertilisation), were analysed for Cd concentrations. Moreover, to clarify if the highest concentrations found are linked to older and inedible or to younger and edible leaves, external and internal endive leaves were separately analysed. All the leafy vegetables analysed showed on average 2-fold higher Cd concentrations in leaves than in roots. Leaf Cd concentrations in both lettuce and endive plants significantly differed among fertilisation treatments, with values highest in the plants grown on mineral fertilised soils. Apart from the soil fertilisation treatments, however, Cd leaf concentrations were often higher (up to 4-fold) than the threshold deduced by the EU 420/2011 Regulation, although the plants grew on unpolluted soils. Anyway, external leaves of endive plants showed significantly higher concentrations than internal leaves (in some cases the values were 3-fold higher), partly reassuring on the consumption of the younger leaves. Moreover, this study points out two major drawbacks in the Italian and European regulatory frameworks: (1) metal concentration (as total and/or available fraction) limits in agricultural soils are lacking; (2) metal concentration thresholds (currently existing only for Cd and Pb in crops) reported in the EU 420/2011 Regulation, expressed on the fresh weight basis rather than on the dry weight basis, appear not suitable.

Cadmium exposure and risk of pancreatic cancer: a meta-analysis of prospective cohort studies and case-control studies among individuals without occupational exposure history

Pancreatic cancer is one of the most deadly types of cancer for both genders. Classified as a human carcinogen, cadmium has been related to diverse cancers. However, the association between cadmium exposure and the risk of pancreatic cancer is still unclear. We quantitatively reviewed the observational studies on the association of cadmium exposure with pancreatic cancer risk among individuals without occupational exposure history published through July 2014 in PubMed by using a fixed-effect model. Four prospective cohort studies (112,934 participants with 335 events) and two case-control studies (177 cases and 539 controls) were identified. The summarized relative risk (RR) with a 95% confidence interval (CI) was 2.05 (95% CI = 1.58-2.66), comparing the highest to the lowest category of cadmium exposure. This positive association persisted in men (RR = 1.78, 95% CI = 1.04-3.05) but not in women (RR = 1.02, 95% CI = 0.63-1.65). Further research is needed to provide more solid evidence on the association of cadmium exposure with pancreatic cancer risk and to elucidate the underlying biological mechanism of the potential gender difference.

Calcium homeostasis disruption - a bridge connecting cadmium-induced apoptosis, autophagy and tumorigenesis

Calcium and cadmium are divalent metals and have similar chemical properties. Both can enter cells through, albeit different, channels, or through protein-dependent permeation. However, cadmium disturbs the calcium homeostasis by inhibiting calcium channels and/or related proteins. Cadmium can also alter membrane phospholipid concentrations, and so induce a calcium homeostasis disorder. The altered calcium homeostasis induced by cadmium results in cell apoptosis, autophagy or tumorigenesis. In this review, calcium homeostasis disruption is summarized as a bridge connecting cadmium-induced apoptosis, autophagy, and tumorigenesis.

Cadmium status among pediatric cancer patients in Egypt

Cadmium (Cd) is a toxic, nonessential, and bio-accumulating heavy metal widely used in industry. Several studies have suggested a positive association between Cd exposure and risks of several cancers. However, data from general population, especially children are sparse.In the current cross-sectional case-control study, we aimed to assess the association between Cd exposure, as expressed by Cd body status (blood, urine, scalp hair, and nails) and cancer among Egyptian children. Three hundred and fifty pediatric cancer cases aged 3 to 14-years old were enrolled in our study. Their body Cd levels were evaluated using Atomic Absorption Spectrophometer and were compared with Cd levels of 350 healthy children.Significantly higher Cd levels (blood, urine, scalp hair, and nails) were documented in cancer cases when compared with control (P < 0.001). Such difference was still detected when comparing each malignant type separately, with controls. Tobacco smoke exposure, rural residence, and low socioeconomic status were reported more frequently among cases than comparisons.Positive association between Cd exposure and pediatric malignancy may be present.

Dietary cadmium exposure and risk of breast, endometrial, and ovarian cancer in the Women's Health Initiative

BACKGROUND

In vitro and animal data suggest that cadmium, a heavy metal that contaminates some foods and tobacco plants, is an estrogenic endocrine disruptor. Elevated estrogen exposure is associated with breast, endometrial, and ovarian cancer risk.

OBJECTIVES

We examined the association between dietary cadmium intake and risk of these cancers in the large, well-characterized Women's Health Initiative (WHI).

METHODS

A total of 155,069 postmenopausal women, 50-79 years of age, who were enrolled in the WHI clinical trials or observational study, participated in this study. We estimated dietary cadmium consumption by combining baseline food frequency questionnaire responses with U.S. Food and Drug Administration data on food cadmium content. Participants reported incident invasive breast, endometrial, or ovarian cancer, and WHI centrally adjudicated all cases through August 2009. We applied Cox regression to estimate adjusted hazard ratios (HRs) and 95% CIs for each cancer, comparing quintiles of energy-adjusted dietary cadmium intake.

RESULTS

Over an average of 10.5 years, 6,658 invasive breast cancers, 1,198 endometrial cancers, and 735 ovarian cancers were reported. We observed no statistically significant associations between dietary cadmium and risk of any of these cancers after adjustment for potential confounders including total dietary energy intake. Results did not differ in any subgroup of women examined.

CONCLUSIONS

We found little evidence that dietary cadmium is a risk factor for breast, endometrial, or ovarian cancers in postmenopausal women. Misclassification in dietary cadmium assessment may have attenuated observed associations.

Concentrations and potential health risks of metals in lip products

BACKGROUND

Metal content in lip products has been an issue of concern.

OBJECTIVES

We measured lead and eight other metals in a convenience sample of 32 lip products used by young Asian women in Oakland, California, and assessed potential health risks related to estimated intakes of these metals.

METHODS

We analyzed lip products by inductively coupled plasma optical emission spectrometry and used previous estimates of lip product usage rates to determine daily oral intakes. We derived acceptable daily intakes (ADIs) based on information used to determine public health goals for exposure, and compared ADIs with estimated intakes to assess potential risks.

RESULTS

Most of the tested lip products contained high concentrations of titanium and aluminum. All examined products had detectable manganese. Lead was detected in 24 products (75%), with an average concentration of 0.36 ± 0.39 ppm, including one sample with 1.32 ppm. When used at the estimated average daily rate, estimated intakes were > 20% of ADIs derived for aluminum, cadmium, chromium, and manganese. In addition, average daily use of 10 products tested would result in chromium intake exceeding our estimated ADI for chromium. For high rates of product use (above the 95th percentile), the percentages of samples with estimated metal intakes exceeding ADIs were 3% for aluminum, 68% for chromium, and 22% for manganese. Estimated intakes of lead were < 20% of ADIs for average and high use.

CONCLUSIONS

Cosmetics safety should be assessed not only by the presence of hazardous contents, but also by comparing estimated exposures with health-based standards. In addition to lead, metals such as aluminum, cadmium, chromium, and manganese require further investigation.

Dietary cadmium and risk of invasive postmenopausal breast cancer in the VITAL cohort

PURPOSE

The aim of the study was to estimate the association between dietary intake of cadmium, a carcinogenic heavy metal, and risk of invasive postmenopausal breast cancer.

METHODS

Study subjects were 30,543 postmenopausal women in the VITamins And Lifestyle (VITAL) cohort who completed a food frequency questionnaire (FFQ) at baseline (2000-2002). Dietary cadmium consumption was estimated by combining FFQ responses with US Food and Drug Administration data on food cadmium content. Incidence of invasive breast cancer was ascertained through linkage of the cohort to the western Washington Surveillance, Epidemiology, and End Results cancer registry through 31 December 2009. Cox regression was applied to estimate adjusted hazard ratios (aHRs) and 95 % confidence intervals (CIs) for breast cancer with increasing dietary cadmium intake, adjusted for total energy intake, smoking history, consumption of vegetables, potatoes, and whole grains, multivitamin use, education, race, body mass index, physical activity, age at first birth, postmenopausal hormone use, and mammography.

RESULTS

Vegetables and grains together contributed an average of 66 % of estimated dietary cadmium. During a mean of 7.5 years of follow-up, 1,026 invasive postmenopausal breast cancers were identified. Among 899 cases with complete covariate information, no evidence of an association between dietary cadmium intake and breast cancer risk was observed (aHR (95 % CI), highest to lowest quartile cadmium: 1.00 (0.72-1.41), p (trend) = 0.95). No evidence was found for interactions between dietary cadmium and breast cancer risk factors, smoking habits, or total intake of calcium, iron, or zinc from diet, supplements, and multivitamins.

CONCLUSIONS

This study does not support the hypothesis that dietary cadmium intake is a risk factor for breast cancer. However, non-differential measurement error in the estimate of cadmium intake is likely the most important factor that could have obscured an association.

Cadmium and lung cancer mortality accounting for simultaneous arsenic exposure

OBJECTIVES

Prior investigations identified an association between airborne cadmium and lung cancer but questions remain regarding confounding by arsenic, a well-established lung carcinogen.

METHODS

A cadmium smelter population exhibiting excess lung cancer was re-analysed using a retrospective exposure assessment for arsenic (As), updated mortality (1940-2002), a revised cadmium (Cd) exposure matrix and improved work history information.

RESULTS

Cumulative exposure metrics for both cadmium and arsenic were strongly associated making estimation of their independent effects difficult. Standardised mortality ratios (SMRs) were modelled with Poisson regression with the contribution of arsenic to lung cancer risk constrained by exposure-response estimates previously reported. The results demonstrate (1) a statistically significant effect of Cd independent of As (SMR=3.2 for 10 mg-year/m(3) Cd, p=0.012), (2) a substantial healthy worker effect for lung cancer (for unexposed workers, SMR=0.69) and (3) a large deficit in lung cancer mortality among Hispanic workers (SMR=0.27, p=0.009), known to have low lung cancer rates. A supralinear dose-rate effect was observed (contribution to risk with increasing exposure intensity has declining positive slope). Lung cancer mortality was somewhat better predicted using a cadmium burden metric with a half-life of about 20-25 years.

CONCLUSIONS

These findings support an independent effect for cadmium in risk of lung cancer mortality. 1/1000 excess lifetime risk of lung cancer death is predicted from an airborne exposure of about 2.4 μg/m(3) Cd.

Epigenetic Contributions to the Relationship between Cancer and Dietary Intake of Nutrients, Bioactive Food Components, and Environmental Toxicants

Epigenetics is the study of heritable changes in gene expression that occur without a change in DNA sequence. Cancer is a multistep process derived from combinational crosstalk between genetic alterations and epigenetic influences through various environmental factors. The observation that epigenetic changes are reversible makes them an attractive target for cancer prevention. Until recently, there have been difficulties studying epigenetic mechanisms in interactions between dietary factors and environmental toxicants. The development of the field of cancer epigenetics during the past decade has been advanced rapidly by genome-wide technologies - which initially employed microarrays but increasingly are using high-throughput sequencing - which helped to improve the quality of the analysis, increase the capacity of sample throughput, and reduce the cost of assays. It is particularly true for applications of cancer epigenetics in epidemiologic studies that examine the relationship among diet, epigenetics, and cancer because of the issues of tissue heterogeneity, the often limiting amount of DNA samples, and the significant cost of the analyses. This review offers an overview of the state of the science in nutrition, environmental toxicants, epigenetics, and cancer to stimulate further exploration of this important and developing area of science. Additional epidemiologic research is needed to clarify the relationship between these complex epigenetic mechanisms and cancer.

Occupational exposure to metal compounds and lung cancer. Results from a multi-center case-control study in Central/Eastern Europe and UK

PURPOSE

To study the association between occupational exposure to metals including chromium, cadmium, nickel, and arsenic compounds, within a population-based study design, while adjusting for confounding factors.

METHODS

A population-based lung cancer case-control study in Central/Eastern Europe and UK was conducted in 1998-2003, including 2,853 cases and 3,104 controls. Exposure to 70 occupational agents was assessed by local expert-teams for all subjects. Odds ratios (OR) for exposure to dust and fumes/mist of chromium, nickel, cadmium, arsenic, as well as inorganic pigment dust and inorganic acid mist, were adjusting for smoking, age, center, sex, and exposure to other occupational agents including the metals under study.

RESULTS

Exposure to arsenic (prevalence = 1.4%) was associated with an increased lung cancer risk ((OR) 1.65, 95% confidence interval (95% CI):1.05-2.58). For chromium dust (prevalence = 4.8%, OR: 1.25, 95% CI: 0.95-1.65), a linear upward trend for duration and cumulative exposure was observed. A weak association was observed for exposure to cadmium fumes (prevalence = 1.8%, OR: 1.19, 95% CI: 0.77-1.82), which was strongest for the highest category of cumulative exposure (OR: 2.04, 95% CI: 1.07-3.90). No increased risk was observed for inorganic acid mist, inorganic pigment dust, or nickel, after adjustment for other metals. An independent effect of nickel cannot be excluded, due to its collinearity with chromium exposure.

CONCLUSIONS

Occupational exposure to metals is an important risk factor for lung cancer. Although the strongest risk was observed for arsenic, exposure to chromium dust was most important in terms of attributable risk due to its high prevalence.

Association between six environmental chemicals and lung cancer incidence in the United States

BACKGROUND

An increased risk of lung cancer has been observed at exposure to certain industrial chemicals in occupational settings; however, less is known about their carcinogenic potential to the general population when those agents are released into the environment.

METHODS

We used the Toxics Release Inventory (TRI) database and Surveillance, Epidemiology, and End Results (SEER) data to conduct an ecological study at the county level. We used multiple linear regression to assess the association of age-adjusted lung cancer incidence with the quantities of on-site air and water releases of six selected industrial chemicals including arsenic, 1,3 butadiene, cadmium, chromium, formaldehyde, and nickel after controlling for other risk variables.

RESULTS

Overall, we observed a significantly increased risk of lung cancer incidence associated with releases of chromium, formaldehyde, and nickel. The links were present for both males and females. Significant effects were present in nonmetropolitan but not metropolitan counties. Releases of arsenic, 1,3 butadiene, and cadmium were reported by small numbers of facilities, and no relationships to lung cancer incidence were detected.

CONCLUSIONS

Our results suggest that environmental exposure to chromium, formaldehyde, and nickel from TRI sites may increase population risk of lung cancer. These findings need to be confirmed in individual-level studies, but in congruence with the precautionary principle in environmental science, support prudent efforts to limit release of these agents into the environment.

Possible association between nickel and chromium and oral cancer: a case-control study in central Taiwan

Oral cancer is one of the most common cancers in Taiwan. Changhua County, in central Taiwan, has an extremely high prevalence of oral cancer, along with a high concentration of metal-related industries and soil metal contamination. The aim of this study was to clarify the possible association between metals and oral cancer within this specific area. This study recruited 101 oral cancer patients and 104 controls from the Changhua Christian Hospital. All subjects completed a questionnaire that asked about demographic information; cigarette, alcohol, and betel quid use; and environmental and occupational exposure history. Blood samples were collected and tested for metal concentrations with inductively coupled plasma mass spectrometry. A multiple logistic regression model illustrated that oral cancer was significantly associated with the blood levels of nickel and chromium (both with P<0.0001) after controlling for potential confounders. This study suggested a potential role of these two metals in the mechanism of oral cancer development.

Sublethal levels of cadmium down-regulate the gene expression of DNA mismatch recognition protein MutS homolog 6 (MSH6) in zebrafish (Danio rerio) embryos

MutS homolog 6 (MSH6) is the major mismatch contacting component of the MSH2-MSH6 heterodimeric complex (MutSα) that mediates DNA mismatch repair (MMR) of simple mispairs and small insertion-deletion loops in eukaryotes. This study examined the potential of cadmium (Cd) to disturb the gene expression of MSH6 in vertebrates using zebrafish (Danio rerio) embryo as a model organism. Semiquantitative RT-PCR indicated that msh2 and msh6 expressions were suppressed in embryos at 1h post fertilization (hpf), then drastically up-regulated in 2 hpf embryos and actively expressed in 3-25 hpf embryos. In the presence of a constitutive β-actin expression, exposure of 1 hpf embryos to sublethal concentrations of CdCl(2) at 0.5-3 μM for 4 or 9h caused a time and concentration-dependent down-regulation of msh6 transcription. Cd failed to inhibit msh2 transcription except at 3 μM, reflecting the higher sensitivity of msh6 than msh2 transcription to Cd. Whole mount in situ hybridization showed a wide distribution of msh6 transcripts in the front body portions of 10 hpf embryos and Cd-induced a general suppression of msh6 expression in zebrafish tissues. Cd-induced down-regulation of msh6 transcription paralleled with reduced levels of MSH6 protein synthesis and MSH6-mediated G-T mismatch binding activities identified by band shift assay using recombinant zebrafish MSH6 and an anti-human MSH6 antibody. Our results revealed the inhibition of Cd on MSH6 expression at both mRNA and protein levels and this mechanism may play a role in Cd genotoxicity.

Assessment of cadmium genotoxicity in peripheral blood and bone marrow tissues of male Wistar rats

In this study, Cadmium (Cd) genotoxicity was investigated in both bone marrow and peripheral blood treatment using rat micronucleus technique as genotoxicity test at acute and chronic treatment in the same animals. This study evaluated the frequency of micronuclei in the peripheral blood and bone marrow of male rats treated with unique cadmium dose (15 mg/kg. body w/day) by gavage for 60 days and acute treatment for 24 h, respectively. Mitomycin C (MMC) 2 mg/kg body wt was used as a positive control. This study shows that cadmium chloride treatment significantly induced the frequency of micronucleus in polychromatic erythrocytes in both tibia bone marrow and peripheral blood (p < 0.001, p < 0.01, respectively). This increase in micronucleus frequency shows that cadmium has a genotoxic effect on bone marrow and peripheral blood at this level. Also, in order to determine cytotoxicity in bone marrow and peripheral blood, the ratio of polychromatic erythrocytes to normochromatic erythrocytes was calculated in bone marrow and peripheral blood. Cd treatment decreased this ratio in only bone marrow. The results of this study demonstrate that Cd has both toxic and genotoxic potential in bone marrow and only genotoxic potential in peripheral blood. There is a significant difference between the control group and exposed group, including acute and chronic treatment for blood Cd level (p < 0.001). No significant difference was found between acute and chronic exposure group (p > 0.05).

Lung cancer mortality in arsenic-exposed workers from a cadmium recovery plant

BACKGROUND

There is evidence that arsenic is a late-stage human lung carcinogen.

AIMS

To investigate lung cancer risks in a cohort of cadmium recovery workers in relation to period from ceasing exposure to arsenic.

METHODS

The mortality experience (1940-2001) of a cohort of 625 male workers from a US cadmium recovery plant was compared with expectations based on US national mortality rates.

RESULTS

There was a statistically significant (P < 0.05) negative trend in lung cancer standardized mortality ratios in relation to period from ceasing arsenic exposure.

CONCLUSIONS

The findings are consistent with the hypothesis that arsenic is a late-stage human carcinogen.

Lung cancer and exposure to metals: the epidemiological evidence

Exposure to metallic compounds is ubiquitous, with its widespread use in industry and its presence, mostly in trace amounts, in the environment. This paper reviews the epidemiologic evidence of the relation between lung cancer and exposure to metallic compounds by building on and updating the corresponding International Agency for Research on Cancer (IARC) assessments. Given that most of the well-identified human populations with given metal exposure are in occupational settings, this review is mostly based on results in occupational epidemiology. The epidemiological evidence is shortly reviewed for accepted carcinogens: chromium, nickel, beryllium, cadmium, arsenic, and silicon, highlighting what is still unclear. We then review in more detail metals for which the evidence is less clear: lead, titanium, iron, and cobalt. There is scarce evidence for the human carcinogenicity of titanium. Exposure to titanium dioxide is associated with lung cancer excesses in one large study, but this excess may be due to confounders. The evidence for lead is contradictory. The lung cancer risk is presented as a function of a post hoc exposure ranking but no dose-response relationship is found. A weak but consistent lung cancer excess in many populations exposed to iron oxides but it is not possible to state on causality. Finally the evidence in the hard metal industry is presented, which suggests a possible carcinogenic effect of cobalt in presence of tungsten carbide. A short discussion presents the limitations of epidemiology in assessing the carcinogenicity of metals.

Environmental and occupational risk factors for lung cancer

Lung cancer is the world's leading cause of cancer death. It is primarily due to the inhalation of carcinogens and highly accessible to prevention by diminishing exposures to lung carcinogens. Most important will be the complete cessation of exposure to cigarette smoke (first and second hand) and to asbestos. Two environmental exposures--radon in homes and arsenic in drinking water--cannot be totally avoided, but people in certain geographical regions would greatly benefit from a reduction in exposure magnitude. And last but not least, workers all over the world deserve that preventive measures at the workplace are observed with regard to exposures, such as arsenic, beryllium, bis-chloromethyl ether (BCME), cadmium, chromium, polycyclic aromatic hydrocarbons (PAHs), and nickel.

Determination of cadmium in whole blood and scalp hair samples of Pakistani male lung cancer patients by electrothermal atomic absorption spectrometer

A large number of epidemiologic studies have been undertaken to identify potential risk factors for cancer, amongst which the association with cadmium has received considerable attention. There is compelling evidence in support of positive associations between cadmium and risk of lung cancer. In present study we measured the concentration of Cd in whole blood and scalp hair samples of 120 male lung cancer patients (smokers) and 150 controls or referents (smokers and nonsmokers) from different cities of Pakistan. Both referents and patients were of same age group (ranged 40-70 years), socio-economic status, localities and dietary habits. The scalp hair and whole blood samples were oxidized by 65% nitric acid: 30% hydrogen peroxide (2:1) ratio in microwave oven. To check the validity of the proposed method, a conventional wet acid digestion method was used to obtain total Cd concentration in certified samples of human hair BCR 397 and Clincheck control-lyophilized human whole blood. All digests were analyzed for Cd concentration by electrothermal atomic absorption spectrometer (ETAAS). The results of this study showed that the average Cd concentration was higher in the blood and scalp hair of lung cancer patients at different stages as compared to controls (p<001). The smoker referents have high level of Cd in both biological samples as compared to nonsmoker subjects. These results illustrate that the patients who continued smoking after confirmed diagnosis of lung cancer have 34.2-67.26 and 22.4-57.3% more Cd in blood samples and scalp hair than lung cancer patients who cease smoking. This study is compelling evidence in support of positive associations between cadmium, cigarette smoking and lung cancer risk.

Cause-specific mortality and cancer incidence rates in relation to urinary beta2-microglobulin: 23-year follow-up study in a cadmium-polluted area

A longitudinal study was performed to investigate the associations of exposure to environmental cadmium (Cd) with cause-specific mortality and cancer incidence rates. The study population comprised 275 adults living in a Cd-polluted area, Nagasaki Prefecture, Japan. The follow-up period extended from 1982 to 2005 for the analysis of cancer mortality, and from 1985 to 2002 for the analysis of cancer incidence. In the study area, the daily Cd intake from foods had decreased after 1980-1983 because of the restoration of Cd-polluted rice fields. The mortality rate among those with urinary beta2-microglobulin (U-beta2M)>/=1000 microg/g creatinine was significantly higher than that of the Japanese population for death from causes other than cancer, but not for cancers (177 at the 95% confidence interval [CI] 94-303). From analysis within the Cd-polluted area, the age-adjusted rate ratio of cancer deaths associated with increased U-beta2M was 2.58 (95% CI 1.25-5.36). The incidence rate of cancer among those with U-beta2M>/=1000 microg/g creatinine was 1.38 (95% CI 0.69-2.47) times that of the regional reference rate. Within the Cd-polluted area, the age-adjusted rate ratio of developing cancer associated with high U-beta2M was 1.79 (95% CI 0.84-3.82). In summary, there was a significant association between U-beta2M excretion and cancer mortality. However, there was neither a significantly increased standardized incidence ratio of cancer, nor significant relationship between U-beta2M and cancer incidence rate, though the point estimates were higher than unity. Continued follow-up and investigation of a larger cohort may be required before drawing a conclusion for the association between exposure to environmental Cd and cancer risk.

Trace elements and cancer risk: a review of the epidemiologic evidence

Worldwide, there are more than 10 million new cancer cases each year, and cancer is the cause of approximately 12% of all deaths. Given this, a large number of epidemiologic studies have been undertaken to identify potential risk factors for cancer, amongst which the association with trace elements has received considerable attention. Trace elements, such as selenium, zinc, arsenic, cadmium, and nickel, are found naturally in the environment, and human exposure derives from a variety of sources, including air, drinking water, and food. Trace elements are of particular interest given that the levels of exposure to them are potentially modifiable. In this review, we focus largely on the association between each of the trace elements noted above and risk of cancers of the lung, breast, colorectum, prostate, urinary bladder, and stomach. Overall, the evidence currently available appears to support an inverse association between selenium exposure and prostate cancer risk, and possibly also a reduction in risk with respect to lung cancer, although additional prospective studies are needed. There is also limited evidence for an inverse association between zinc and breast cancer, and again, prospective studies are needed to confirm this. Most studies have reported no association between selenium and risk of breast, colorectal, and stomach cancer, and between zinc and prostate cancer risk. There is compelling evidence in support of positive associations between arsenic and risk of both lung and bladder cancers, and between cadmium and lung cancer risk.

Quantifying potential health impacts of cadmium in cigarettes on smoker risk of lung cancer: a portfolio-of-mechanisms approach

This article introduces an approach to estimating the uncertain potential effects on lung cancer risk of removing a particular constituent, cadmium (Cd), from cigarette smoke, given the useful but incomplete scientific information available about its modes of action. The approach considers normal cell proliferation; DNA repair inhibition in normal cells affected by initiating events; proliferation, promotion, and progression of initiated cells; and death or sparing of initiated and malignant cells as they are further transformed to become fully tumorigenic. Rather than estimating unmeasured model parameters by curve fitting to epidemiological or animal experimental tumor data, we attempt rough estimates of parameters based on their biological interpretations and comparison to corresponding genetic polymorphism data. The resulting parameter estimates are admittedly uncertain and approximate, but they suggest a portfolio approach to estimating impacts of removing Cd that gives usefully robust conclusions. This approach views Cd as creating a portfolio of uncertain health impacts that can be expressed as biologically independent relative risk factors having clear mechanistic interpretations. Because Cd can act through many distinct biological mechanisms, it appears likely (subjective probability greater than 40%) that removing Cd from cigarette smoke would reduce smoker risks of lung cancer by at least 10%, although it is possible (consistent with what is known) that the true effect could be much larger or smaller. Conservative estimates and assumptions made in this calculation suggest that the true impact could be greater for some smokers. This conclusion appears to be robust to many scientific uncertainties about Cd and smoking effects.

Molecular mechanisms of cadmium induced mutagenicity

Cadmium is a human carcinogen of worldwide concern because it accumulates in the environment due to its extremely long half-life. Its compounds are classified as human carcinogens by several regulatory agencies. Cadmium affects cell proliferation, differentiation, apoptosis and other cellular activities and can cause numerous molecular lesions that would be relevant to carcinogenesis. For a long time cadmium has been considered as a non-genotoxic carcinogen, as it is only weakly mutagenic in bacterial and mammalian cell test systems. Recently, we presented evidence that when assayed in a test system, in which both intragenic and multilocus mutations can be detected, cadmium acts as a strong mutagen which induces predominantly multilocus deletions. In this review, we discuss two mechanisms that play an important role in cadmium mutagenicity: (i) induction of reactive oxygen species (ROS); and (ii) inhibition of DNA repair. Experimental evidence suggests that cadmium at low, for environmental exposure relevant concentrations, induces mutations by inducing oxidative DNA damage and that it decreases genetic stability by inhibiting the repair of endogenous and exogenous DNA lesions, which in turn increase the probability of mutations and consequently cancer initiation by this metal.

Eukaryotic Translation Initiation Factor 4E Is a Cellular Target for Toxicity and Death Due to Exposure to Cadmium Chloride

Whether translation initiation factor 4E (eIF4E), the mRNA cap binding and rate-limiting factor required for translation, is a target for cytotoxicity and cell death induced by cadmium, a human carcinogen, was investigated. Exposure of human cell lines, HCT15, PLC/PR/5, HeLa, and Chang, to cadmium chloride resulted in cytotoxicity and cell death, and this was associated with a significant decrease in eIF4E protein levels. Similarly, specific silencing of the expression of the eIF4E gene, caused by a small interfering RNA, resulted in significant cytotoxicity and cell death. On the other hand, overexpression of the eIF4E gene was protective against the cadmium-induced cytotoxicity and cell death. Further studies revealed the absence of alterations in the eIF4E mRNA level in the cadmium-treated cells despite their decreased eIF4E protein level. In addition, exposure of cells to cadmium resulted in enhanced ubiquitination of eIF4E protein while inhibitors of proteasome activity reversed the cadmium-induced decrease of eIF4E protein. Exposure of cells to cadmium, as well as the specific silencing of eIF4E gene, also resulted in decreased cellular levels of cyclin D1, a critical cell cycle and growth regulating gene, suggesting that the observed inhibition of cyclin D1 gene expression in the cadmium-treated cells is most likely due to decreased cellular level of eIF4E. Taken together, our results demonstrate that the exposure of cells to cadmium chloride resulted in cytotoxicity and cell death due to enhanced ubiquitination and consequent proteolysis of eIF4E protein, which in turn diminished cellular levels of critical genes such as cyclin D1.

The effect of pH, time and dietary source of cadmium on the bioaccessibility and adsorption of cadmium to/from lettuce (Lactuca sativa L. cv. Ostinata)

This study evaluated the influence of three variables in the effectiveness of an in vitro digestion protocol used to determine bioaccessibility of cadmium from the diet. The percentage of solubilized metal was measured in relation to digestion time, pH of each digestion phase and the dietary source of the metal in the diet. Because it would be convenient to add the metal to the diet before digestion instead of growing contaminated vegetables, the importance of metal incorporation in the plant in comparison to amendment through foliar spraying was also studied. From our results we conclude that the dietary source of metal in the protocols tested doesn't seem to be a significant factor when comparing the lettuce sprayed with cadmium with the lettuce that had cadmium incorporated in it, although the difference was barely significant (P=0.057). Time affects the digestion in different ways depending on the dietary source of cadmium. pH is a relevant factor in both intestinal and gastric phases and should be taken into consideration when analyzing the results from in vitro digestions. Since the intestinal phase in our experiments decreased the amount of cadmium solubilized during the digestion, we investigated the effect of pH on the adsorption of this metal to lettuce and found that there is an increased binding of cadmium at pH values above 3. Therefore we suggest that part of the reduction in bioaccessibility following intestinal digestion could be explained by an increase in adsorption of metal to the plant material at higher pH values.

A practical guide to dose-response analyses and risk assessment in occupational epidemiology

Dose-response modeling in occupational epidemiology is usually motivated by questions of causal inference (eg, is there a monotonic increase of risk with increasing exposure?) or risk assessment (eg, how much excess risk exists at any given level of exposure?). We focus on several approaches to dose-response in occupational cohort studies. Categorical analyses are useful for detecting the shape of dose-response. However, they depend on the number and location of cutpoints and result in step functions rather than smooth curves. Restricted cubic splines and penalized splines are useful parametric techniques that provide smooth curves. Although splines can complement categorical analyses, they do not provide interpretable parameters. The shapes of these curves will depend on the degree of "smoothing" chosen by the analyst. We recommend combining categorical analyses and some type of smoother, with the goal of developing a reasonably simple parametric model. A simple parametric model should serve as the goal of dose-response analyses because (1) most "true" exposure response curves in nature may be reasonably simple, (2) a simple parametric model is easily communicated and used by others, and (3) a simple parametric model is the best tool for risk assessors and regulators seeking to estimate individual excess risks per unit of exposure. We discuss these issues and others, including whether the best model is always the one that fits the best, reasons to prefer a linear model for risk in the low-exposure region when conducting risk assessment, and common methods of calculating excess lifetime risk at a given exposure from epidemiologic results (eg, from rate ratios). Points are illustrated using data from a study of dioxin and cancer.

Lung cancer mortality in UK nickel-cadmium battery workers, 1947-2000

AIMS

To investigate mortality from lung cancer in nickel-cadmium battery workers in relation to cumulative exposure to cadmium hydroxide.

METHODS

The mortality of a cohort of 926 male workers from a factory engaged in the manufacture of nickel-cadmium batteries in the West Midlands of England was investigated for the period 1947-2000. All subjects were first employed at the plant in the period 1947-75 and employed for a minimum period of 12 months. Work histories were available for the period 1947-86; the factory closed down in 1992. Two analytical approaches were used, indirect standardisation and Poisson regression.

RESULTS

Based on serial mortality rates for the general population of England and Wales, significantly increased mortality was shown for cancers of the pharynx (observed (Obs) 4, expected (Exp) 0.7, standardised mortality ratio (SMR) 559, p<0.05), non-malignant diseases of the respiratory system (Obs 61, Exp 43.0, SMR 142, p<0.05), and non-malignant diseases of the genitourinary system (Obs 10, Exp 4.1, SMR 243, p<0.05). Non-significantly increased SMRs were shown for lung cancer (Obs 45, Exp 40.7, SMR 111) and cancer of the prostate (Obs 9, Exp 7.5, SMR 116). Estimated cumulative cadmium exposures were not related to risks of lung cancer or risks of chronic obstructive pulmonary diseases, even when exposure histories were lagged first by 10, then by 20 years.

CONCLUSIONS

The study findings do not support the hypotheses that cadmium compounds are human lung carcinogens.

Molecular and cellular mechanisms of cadmium carcinogenesis

Cadmium is a heavy metal, which is widely used in industry, affecting human health through occupational and environmental exposure. In mammals, it exerts multiple toxic effects and has been classified as a human carcinogen by the International Agency for Research on Cancer. Cadmium affects cell proliferation, differentiation, apoptosis and other cellular activities. Cd2+ does not catalyze Fenton-type reactions because it does not accept or donate electrons under physiological conditions, and it is only weakly genotoxic. Hence, indirect mechanisms are implicated in the carcinogenicity of cadmium. In this review multiple mechanisms are discussed, such as modulation of gene expression and signal transduction, interference with enzymes of the cellular antioxidant system and generation of reactive oxygen species (ROS), inhibition of DNA repair and DNA methylation, role in apoptosis and disruption of E-cadherin-mediated cell-cell adhesion. Cadmium affects both gene transcription and translation. The major mechanisms of gene induction by cadmium known so far are modulation of cellular signal transduction pathways by enhancement of protein phosphorylation and activation of transcription and translation factors. Cadmium interferes with antioxidant defense mechanisms and stimulates the production of reactive oxygen species, which may act as signaling molecules in the induction of gene expression and apoptosis. The inhibition of DNA repair processes by cadmium represents a mechanism by which cadmium enhances the genotoxicity of other agents and may contribute to the tumor initiation by this metal. The disruption of E-cadherin-mediated cell-cell adhesion by cadmium probably further stimulates the development of tumors. It becomes clear that there exist multiple mechanisms which contribute to the carcinogenicity of cadmium, although the relative weights of these contributions are difficult to estimate.

Cadmium, lung and prostate cancer: a systematic review of recent epidemiological data

Cadmium (Cd) and its compounds were classified as "carcinogenic to humans (Group 1)" by IARC in 1993. The observation of an increased number of lung cancers in a U.S. cohort of cadmium-exposed workers and the finding of tumors in animals exposed to various cadmium compounds apparently played an important role in this assessment. Since this evaluation, several cohorts of cadmium exposed workers have been updated and some additional data regarding environmental exposure to cadmium and cancer risk have been published. The main purpose of this systematic review was to examine whether inclusion of the studies that were not available for the 1993 evaluation might change the overall assessment of the carcinogenic potential of cadmium compounds. A second objective was to examine whether the recent studies are qualitatively better than the older ones and whether they should receive more weight in this assessment. A third issue was to investigate whether a competing effect between nonmalignant respiratory disease (NMRD) and lung cancer may have affected the results for lung cancer in occupationally exposed cohorts. Overall, considering the results of the most recent studies does not suggest that the effect of cadmium on lung cancer increases with improvement of the study design but points to a lower relative risk in the groups exposed to cadmium in the absence of arsenic and nickel. No evidence was found to support the hypothesis that NMRD represents a competing cause of death reducing the mortality from lung cancer. The association between cadmium exposure and prostate cancer was not confirmed in the latest available updates. Studies in environmentally exposed populations do not indicate an increased relative risk of cancer.

Low-Dose Cadmium Exposure Reduces Human Prostate Cell Transformation in Culture and Up-Regulates Metallothionein and MT-1G mRNA

Chronic low-level exposure to environmental toxins, including cadmium (Cd), is a growing problem in the industrialized world. One promising strategy for protection from these toxins is the use of low-dose exposure of environmental chemicals to induce cell tolerance and recovery, a phenomenon known as "protective hormesis". Hormetic [low-dose stimulatory] effects occur in a variety of systems and with a number of chemicals. Cd is a potent carcinogen in rodents and has also been linked to human lung and prostate cancers. In the present study, we have evaluated the protective effects of low and ultra-low dose, long-term Cd exposure in the normal human prostate cells, RWPE-1. Cells were exposed to low and ultra-low doses (0, 0 (S(-36)), 10(-6), 10(-7), 10(-18), 10(-21), 10(-32), or 10(-36)M) of Cd for 20 weeks followed by treatment with 10(-5)M Cd for another 8 weeks. Continuous exposure of RWPE-1 cells to 10(-5)M Cd results in malignant transformation. However, cells pretreated with low and ultra-low doses of Cd had delayed transformation compared with controls. In addition, the number of transformed cell mounds was lower in pretreated cells indicating that low and ultra-low dose exposure had protective effects against high-dose Cd induced carcinogenesis. The expression of metallothionein (MT), the primary Cd detoxification protein, was induced by low-dose exposure to Cd and maintained during the 20 weeks. In addition, MT-1G mRNA was up-regulated 2- to 3-fold by low-dose and ultralow-dose Cd exposures and may be the mechanism of protective hormesis in this model. MT-1G mRNA might also serve as a biological indicator of very low-dose environmental Cd exposure.

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.