Dose-response relationship in tobacco-related cancers of bladder and lung: A biochemical interpretation

GRADE GUIDANCE 38: Updated guidance for rating up certainty of evidence due to a dose-response gradient

INTRODUCTION

This updated guidance from the Grading of Recommendations Assessment, Development, and Evaluation addresses rating up certainty of evidence due to a dose-response gradient (DRG) observed in synthesis of intervention and exposure studies.

STUDY DESIGN AND SETTING

This guidance was developed using iterative discussions and consensus in multiple meetings and was presented to attendees of the Grading of Recommendations Assessment, Development, and Evaluation Working Group meeting for feedback in November 2022 and for final approval in May 2023.

RESULTS

The guidance consists of two steps. The first is to determine whether the DRG is credible. We describe five items for assessing credibility: a) is DRG identified using a proper analytical approach; b) is confounding the cause of the DRG; c) is there serious concern about ecological bias; d) is the DRG consistent across studies; and e) is there indirect evidence supporting the DRG. The first two of these items are the most critical. If the DRG was judged to be credible, then the second step is to apply the DRG domain and consider rating up, but only by one level due to the concern about residual confounding.

CONCLUSION

Systematic review authors should only rate up certainty in evidence when a DRG is deemed credible.

Protective actions of nuclear factor erythroid 2-related factor 2 (NRF2) and downstream pathways against environmental stressors

Environmental risk factors, including noise, air pollution, chemical agents, ultraviolet radiation (UVR) and mental stress have a considerable impact on human health. Oxidative stress and inflammation are key players in molecular pathomechanisms of environmental pollution and risk factors. In this review, we delineate the impact of environmental risk factors and the protective actions of the nuclear factor erythroid 2-related factor 2 (NRF2) in connection to oxidative stress and inflammation. We focus on well-established studies that demonstrate the protective actions of NRF2 and its downstream pathways against different environmental stressors. State-of-the-art mechanistic considerations on NRF2 signaling are discussed in detail, e.g. classical concepts like KEAP1 oxidation/electrophilic modification, NRF2 ubiquitination and degradation. Specific focus is also laid on NRF2-dependent heme oxygenase-1 induction with detailed presentation of the protective down-stream pathways of heme oxygenase-1, including interaction with BACH1 system. The significant impact of all environmental stressors on the circadian rhythm and the interactions of NRF2 with the circadian clock will also be considered here. A broad range of NRF2 activators is discussed in relation to environmental stressor-induced health side effects, thereby suggesting promising new mitigation strategies (e.g. by nutraceuticals) to fight the negative effects of the environment on our health.

The association of rs710886 in lncRNA PCAT1 with bladder cancer risk in a Chinese population

OBJECTIVE

The long noncoding RNA PCAT1 is an important gene involved in urinary tumors. In this study, we aimed to explore the association between polymorphisms in PCAT1 and bladder cancer susceptibility.

METHODS

A two-stage case-control study was conducted to assess the association between four tagging SNPs (i.e., rs4871771, rs1902432, rs16901904 and rs710886) and bladder cancer risk. Odds ratios (ORs) and their 95% confidence intervals (CIs) were calculated with unconditional univariate and multivariate logistic regression.

RESULTS

At the first stage of discovery, we identified that SNP rs710886A>G was significantly associated with bladder cancer risk (OR=0.86, 95% CI=0.74-0.99, P=0.046). At the following stage of validation, individuals with GG genotype were found to have a significant reduction in bladder cancer risk compared with those carrying AA genotype (adjusted OR=0.83, 95% CI=0.74-0.93, P=0.001). Furthermore, stratified analyses showed that protective effect of rs710886 was more pronounced in subgroup of age>60 and never smoking, and had little to do with sex. Besides, rs710886 was identified as an eQTL for PCAT1. G allele was consistent with lower PCAT1 expression.

CONCLUSION

This study indicates that genetic variants in lncRNA PCAT1 were associated with bladder cancer susceptibility and the SNP rs710886 may act as a potential biomarker for bladder cancer risk.

Bulky DNA Adducts, Tobacco Smoking, Genetic Susceptibility, and Lung Cancer Risk

The generation of bulky DNA adducts consists of conjugates formed between large reactive electrophiles and DNA-binding sites. The term "bulky DNA adducts" comes from early experiments that employed a ³²P-DNA postlabeling approach. This technique has long been used to elucidate the association between adducts and carcinogen exposure in tobacco smoke studies and assess the predictive value of adducts in cancer risk. Molecular data showed increased DNA adducts in respiratory tracts of smokers vs nonsmokers. Experimental studies and meta-analysis demonstrated that the relationship between adducts and carcinogens was linear at low doses, but reached steady state at high exposure, possibly due to metabolic and DNA repair pathway saturation and increased apoptosis. Polymorphisms of metabolic and DNA repair genes can increase the effects of environmental factors and confer greater likelihood of adduct formation. Nevertheless, the central question remains as to whether bulky adducts cause human cancer. If so, lowering them would reduce cancer incidence. Pooled and meta-analysis has shown that smokers with increased adducts have increased risk of lung cancer. Adduct excess in smokers, especially in prospective longitudinal studies, supports their use as biomarkers predictive of lung cancer.

Modifiable risk factors for the prevention of bladder cancer: a systematic review of meta-analyses

Each year, 430,000 people are diagnosed with bladder cancer. Due to the high recurrence rate of the disease, primary prevention is paramount. Therefore, we reviewed all meta-analyses on modifiable risk factors of primary bladder cancer. PubMed, Embase and Cochrane database were systematically searched for meta-analyses on modifiable risk factors published between 1995 and 2015. When appropriate, meta-analyses (MA) were combined in meta-meta-analysis (MMA). If not, the most comprehensive MA was selected based on the number of primary studies included. Probability of causation was calculated for individual factors and a subset of lifestyle factors combined. Of 1496 articles identified, 5 were combined in MMA and 21 were most comprehensive on a single risk factor. Statistically significant associations were found for current (RR 3.14) or former (RR 1.83) cigarette smoking, pipe (RR 1.9) or cigar (RR 2.3) smoking, antioxidant supplementation (RR 1.52), obesity (RR 1.10), higher physical activity levels (RR 0.86), higher body levels of selenium (RR 0.61) and vitamin D (RR 0.75), and higher intakes of: processed meat (RR 1.22), vitamin A (RR 0.82), vitamin E (RR 0.82), folate (RR 0.84), fruit (RR 0.77), vegetables (RR 0.83), citrus fruit (RR 0.85), and cruciferous vegetables (RR 0.84). Finally, three occupations with the highest risk were tobacco workers (RR 1.72), dye workers (RR 1.58), and chimney sweeps (RR 1.53). The probability of causation for individual factors ranged from 4 to 68 %. The combined probability of causation was 81.8 %. Modification of lifestyle and occupational exposures can considerably reduce the bladder cancer burden. While smoking remains one of the key risk factors, also several diet-related and occupational factors are very relevant.

Attenuation of exposure-response rate ratios at higher exposures: a simulation study focusing on frailty and measurement error

BACKGROUND

Positive exposure-response trends for rate ratios (RRs) often diminish at higher exposures. Depletion of susceptibles with higher exposure and increased measurement error at higher exposures are possible reasons.

METHODS

We conducted simulations to investigate attenuation under various assumptions about susceptibility to exposure effects and measurement error, considering a hypothetical occupational cohort, using an excess relative risk model. We simulated an occupational cohort in which entry occurred over time. The metric of interest was cumulative exposure, which had a strong linear effect (RR = 4 for mean exposure), maximizing potential depletion. Measurement error of both classical and Berkson types was also simulated, increasing with increasing exposure. We conducted 100 simulations per scenario, each with 25,000 subjects enrolled from years 1940 to 2010, followed through 2010.

RESULTS

With less than 100% susceptibility to exposure (a requirement for depletion), there was only modest evidence of depletion of susceptibles with increasing cumulative exposure distributed normally. There was correspondingly little attenuation of RRs, and linear exposure-response models fit well. Adding classical measurement error to cumulative exposure, increasing with increasing exposure, resulted in some modest attenuation. Using log normal instead of normally distributed cumulative exposure also resulted in some attenuation.

CONCLUSIONS

Strong attenuation of relatively strong linear exposure-response trends using cumulative exposure, with relatively common disease and heterogeneous susceptibility, does not appear likely due to depletion of susceptibles. Strong attenuation seems more likely to be due to other mechanisms.

Genetic susceptibility, residential radon, and lung cancer in a radon prone area

INTRODUCTION

Radon exposure has been classified as the second cause of lung cancer, after tobacco, and the first in never smokers. GSTM1 and GSTT1 genes deletion increase the risk of lung cancer. We aim to know whether the risk of lung cancer because of residential radon is modulated by these genetic polymorphisms.

METHODS

Hospital-based, case-control study where cases had confirmed lung cancer. Cases and controls did not have previous neoplasm and were older than 30. Controls attended hospital for noncomplex surgery. We analyzed the results for the whole sample and separately for never/light smokers and moderate/heavy smokers.

RESULTS

Seven-hundred and ninety-two participants were analyzed. GSTM1 and GSTT1 deletion conferred an odds ratio (OR) of 1.38 (95% confidence interval [CI] 0.93-2.04) and 1.13 (95% CI 0.70-1.82), respectively. Individuals with GSTM1 present and residential radon concentrations higher than 148 Bq/m had an OR of 1.48 (95% CI 0.73-3.00), whereas those with GSTM1 deleted had an OR of 2.64 (95% CI 1.18-5.91) when compared with participants with GSTM1 present and radon concentrations below 50 Bq/m3. Similar results were observed for GSTT1 deletion. These results were basically the same for the moderate/heavy smokers' subgroup.

CONCLUSIONS

The absence of GSTM1 and GSTT1 genes increases the risk of lung cancer because of radon exposure. These genes might modulate the carcinogenic pathway of alpha radiation. Further studies are warranted analyzing this association in never smokers.

Nrf2: friend and foe in preventing cigarette smoking-dependent lung disease

Chronic exposure to cigarette smoke (CS) generally confronts cellular defense systems with one of the strongest known environmental challenges. In particular, the continuous exposure of tissues of the respiratory tract to abundant concentrations of radicals; volatile compounds of the gas phase, mainly reactive oxygen and nitrogen species; and CS condensate deposits trigger a pleiotropic adaptive response, generally aimed at restoring tissue homeostasis. As documented by numerous studies published over the past decade, a hallmark of this defense system is the activation of the transcription factor NF-E2-related factor 2 (Nrf2), which, consequent to its established role as master regulator of the cellular antioxidant response, has been shown to orchestrate the first line of defense against cell- and tissue-damaging components present in CS. The key to CS-dependent Nrf2 activation is assumed to be based on the long-known phenomenon of a general strong sulfhydryl (-SH) reactivity inherent to CS. This chemical trait is virtually predestined to be sensitized by the major route leading to Nrf2 activation, characterized by its dependence on the interaction of electrophiles with specific cysteine residues inherited by Nrf2's negative cytosolic regulator Keap1 (Kelch-like ECH-associated protein 1). In addition, other pathways involving CS-activated protein kinases implicated in the upstream regulation of Nrf2, such as protein kinase C, represent an alternative/complementary mechanism of CS-induced Nrf2 activation. Because of the outstanding function of the Nrf2-Keap1 axis in defending cells and tissues against oxidant and chemical stress, either directly or indirectly via cross-talking with other defense pathways, changes in the Nrf2 or Keap1 genotype have long been associated with disease development. In terms of the two major smoking-related diseases of the lung, that is, emphysema and lung cancer, a fully functional Nrf2 genotype seems to be necessary, although not sufficient by itself, to protect the smoker from acquiring emphysema. Contrasting with this protective role, however, Nrf2 function may be potentially fatal in smoking-related lung tumorigenesis: as concluded from recent clinical investigations, lung tumor tissues harbor increased mutation or, alternatively, aberrant expression rates in either the KEAP1 or the NRF2 gene, generally resulting in constitutive Nrf2 activation, suggesting that "abuse" of Nrf2 function is an advantageous strategy of the (developing) tumor to protect itself against oxidative stress in general. On the basis of the fundamental significance of the Nrf2 pathway in smoking-dependent disease development, several attempts have been described for dietary and pharmacological intervention, the majority of which are intended to activate Nrf2 aiming at emphysema prevention. The intention of this review is to compile and discuss the various aspects of CS-Nrf2/Keap1 interaction in terms of mechanism, disease development, and chemoprevention.

Association of secondhand smoke exposures with DNA methylation in bladder carcinomas

BACKGROUND

The association between secondhand smoke (SHS) exposure and bladder cancer is inconclusive. Epigenetic alterations in bladder tumors have been linked to primary cigarette smoking and could add to the biological plausibility of an association between SHS exposure and bladder cancer.

HYPOTHESIS

SHS exposure is associated with DNA methylation in bladder tumors.

METHODS

Using an array-based approach, we profiled DNA methylation from never smoking cases of incident bladder cancer. Analyses examined associations between individual loci's methylation with SHS variables (exposure in adulthood, childhood, occupationally, and total exposure). A canonical pathway analysis was used to find pathways significantly associated with each SHS exposure type.

RESULTS

There is a trend toward increased methylation of numerous CpG loci with increasing exposure to adulthood, occupational, and total SHS. Discrete associations between methylation extent of several CpG loci and SHS exposures demonstrated significantly increased methylation of these loci across all types of SHS exposure. CpGs with SHS-related methylation alterations were associated with genes in pathways involved in carcinogenesis, immune modulation, and immune signaling.

INTERPRETATION

Exposures to SHS in adulthood, childhood, occupationally, and in total are each significantly associated with changes in DNA methylation of several CpG loci in bladder tumors, adding biological plausibility to SHS as a risk factor for bladder cancer.

Environmental tobacco smoke in relation to bladder cancer risk--the Shanghai bladder cancer study [corrected]

BACKGROUND

Environmental tobacco smoke (ETS) contains tobacco carcinogens. Hepatic cytochrome P450 (CYP) 1A2 and N-acetyltransferase (NAT2) are important isoenzymes in activation and detoxification, respectively, of tobacco carcinogens. Data on ETS and bladder cancer risk are sparse.

METHODS

We examined the effects of ETS alone and combined with NAT2/CYP1A2 on bladder cancer risk among lifelong-nonsmokers in a case-control study involving 195 patients and 261 controls in Shanghai, China. A comprehensive history of ETS exposure was determined through in-person interviews while CYP1A2 and NAT2 phenotypes by a caffeine-based urinary assay.

RESULTS

ETS exposure was related to an overall statistically nonsignificant 38% increased bladder cancer risk. The risk increased with increasing number of cigarettes smoked by household members or number of hours per day at workplace where coworkers smoked. Compared with no ETS exposure, subjects living with smoking parents during childhood had an OR of 2.43 (95% CI = 0.99-5.96) for bladder cancer. When all ETS sources were combined, the risk increased with increasing total ETS score (P(trend) = 0.03). The OR for high versus nil ETS exposure was 3.00 (95% CI = 1.24-7.26). The increased risk with ETS was mainly seen among individuals possessing a CYP1A2 high efficiency and/or a NAT2 slow acetylation phenotype (P(trend) = 0.04).

CONCLUSIONS

ETS was associated with an increased bladder cancer risk for lifelong-nonsmokers. The association was stronger for people possessing the at-risk phenotypes of CYP1A2 and/or NAT2.

IMPACT

Reducing exposure to ETS for children and genetically more susceptible individuals could be more effective for bladder cancer prevention.

The impact of new research technologies on our understanding of environmental causes of disease: the concept of clinical vulnerability

In spite of decades of epidemiological research, the etiology and causal patterns for many common diseases, such as breast and colon cancer or neurodegenerative diseases, are still largely unknown. Such chronic diseases are likely to have an environmental origin. However, "environmental" risks have been often elusive in epidemiological studies. This is a conundrum for current epidemiological research. On the other side, the relative contribution of genes to chronic diseases, as emerging from GWAS, seems to be modest (15-50% increase in disease risk). What is yet to be explored extensively is a model of disease based on long-term effects of low doses of environmental exposures, incorporating both genetic and acquired susceptibility ("clinical vulnerability"), and the cumulative effects of different exposures. Such a disease model would be compatible with the weak associations found by GWAS and the still elusive role of many (low-level) environmental exposures. We also propose that the introduction of "-omic" high-throughput technologies, such as transcriptomics, proteomics and metabolomics, may provide, in the next years, powerful tools to investigate early effects of environmental exposures and understand the etiology of common diseases better, according to the "clinical vulnerability model". The development of "-omics", in spite of current limitations and lack of sound validation, could greatly contribute to the elucidation of the disease model we propose.

Using time-dependent covariate analysis to elucidate the relation of smoking history to Warthin's tumor risk

The authors aimed to elucidate the relation of the time-dependent smoking history parameters--age at smoking initiation and smoking intensity, duration, and latency--to the risk of Warthin's tumor, a benign tumor of the salivary gland for which cigarette smoking is a strong risk factor. They studied 117 cases of Warthin's tumor and 336 matched controls included in an Israeli nationwide case-control study of parotid gland tumors conducted from 2002 to 2003 by using the Cox regression model with time-dependent covariates, with age as the time axis. When current age and smoking duration were included in the statistical model, the authors show that the coefficient of a latency variable does not represent latency as such, but a balancing of the effects of age at initiation and time since cessation. They found a strong positive linear effect of duration of smoking, together with a positive nonlinear effect of intensity that levels off at higher intensities, and a negative effect of latency from 25 years onward. The latter finding implies that the effect of time since cessation dominates the effect of age at initiation, with risk decreasing sharply after smoking cessation. The relation of smoking variables to Warthin's tumor agrees with the patterns reported for lung cancer.

Common genetic variations of the cytochrome P450 1A1 gene and risk of hepatocellular carcinoma in a Chinese population

Cytochrome P450 1A1 is a major enzyme in the bioactivation of exogenous procarcinogens of hepatocellular carcinoma (HCC). However, the contribution of common genetic variants in CYP1A1 to the HCC risk in Chinese populations has not been thoroughly investigated. In this study, we examined the association between HCC and four selected tagging single nucleotide polymorphisms (SNPs) of CYP1A1, and the risk of CYP1A1 haplotypes/diplotypes in 1006 pathologically confirmed HCC patients and 1015 cancer-free controls, from a Han Chinese population. Haplotypes/diplotypes were constructed from observed genotypes using the Haplo.Stats program. Relative risk was estimated by using multivariable logistic regression method. To summarise, we detected an increased HCC risk in rs4646421 variant carriers (OR 1.30, 95% CI 1.05-1.61) and rs2198843 variant carriers (OR 1.33, 95% CI 1.05-1.69), and a reduced risk of HCC (OR 0.70. 95% CI 0.52-0.94) associated with homozygote carriers of rs4886605 variant. These association signals were also observed in non-smokers with rs4646421 (OR 1.56, 95% CI 1.16-2.08) and rs4886605 (OR 0.61, 95% CI 0.40-0.91). Compared to the most common CYP1A1 haplotype CCAG, the haplotype TTGC conferred an increased risk of HCC (OR 1.26, 95% CI 1.04-1.52). Similarly, the TTGC/TTGC diplotype conferred an increased risk of HCC compared with diplotype CCAG/CCAG (OR 2.06, 95% CI 1.23-3.45, P=0.006). Interestingly, the diplotype TTAC/CCAG also conferred an increased risk of HCC (OR 1.76, 95% CI 1.22-2.54, P=0.003). Our results suggested that common genetic variants in CYP1A1 may modulate the risk of developing HCC in the study population, particularly in non-smokers. However, our findings need to be validated in at least one independent study of Han Chinese population.

Mycoplasma pneumoniae infection and environmental tobacco smoke inhibit lung glutathione adaptive responses and increase oxidative stress

Chronic cigarette smoking evokes a lung glutathione (GSH) adaptive response that results in elevated GSH levels in the lung epithelial lining fluid (ELF). Currently, little is known about how the lung regulates or maintains steady-state levels of ELF GSH. Pathogens such as Mycoplasma pneumoniae can exacerbate airway inflammation and oxidative stress. The present study examined whether M. pneumoniae infections synergize with environmental tobacco smoke (ETS) to disrupt lung GSH adaptive responses. Mice were exposed separately and in combination to ETS and M. pneumoniae for 16 weeks. ETS exposure resulted in a doubling of ELF GSH levels, which was blocked in the M. pneumoniae-exposed mice. In addition, the ETS-plus-M. pneumoniae-exposed mice had elevated levels of oxidized glutathione (GSSG), resulting in a dramatic change in the ELF redox state that corresponded with an increase in lung tissue DNA oxidation. Similar findings were observed in human lung epithelial cells in vitro. Cells exposed separately or in combination to cigarette smoke extract and M. pneumoniae for 48 h had elevated apical levels of GSH compared to control cells, and these increases were blocked by M. pneumoniae and were also associated with increased cellular DNA oxidation. Further studies showed that M. pneumoniae exposure blocked ETS-induced increases in GSH reductase, an enzyme that recycles GSSG back to GSH, both in vitro and in vivo. These studies suggest that M. pneumoniae infection synergizes with ETS and suppresses the lung's ability to respond appropriately to environmental challenges leading to enhanced oxidative stress.

Practical use of investigations in patients with hematuria

OBJECTIVE

The majority of patients with microscopic hematuria undergo a complete evaluation resulting in negative findings. The outcome of patients with hematuria was analyzed in an effort to optimize the use of investigations.

PATIENTS AND METHODS

The records for 404 patients who presented with hematuria were reviewed. Data were collected on demographics, type of hematuria, investigations, and final diagnosis.

RESULTS

The hematuria was microscopic in 140 patients (35%) and gross in 264 patients (65%). In gross hematuria patients, 10% had urinary tract tumors and 12% had calculi. All patients with genitourinary tumors and 87% of patients with calculi had gross hematuria and/or > or =5 RBCs/HPF (red blood cells per high-power microscopic field) on urinalysis. The sensitivity and specificity were 94% and 6% for the dipstick urine test, 37% and 71% for urine cytology, 92% and 93% for computed tomography (CT), 50% and 95% for ultrasound scans, and 38% and 90% for intravenous pyelography, respectively. Logistic regression analysis showed that age and number of RBCs/HPF in the urinalyses were the only significant factors predicting genitourinary cancer. In patients < or =40 years old, there was one patient with malignancy and seven patients with stones. In older patients, there were 31 patients with malignancy and 32 patients with stones.

CONCLUSIONS

Patients with <5 RBCs/HPF on three urinalyses are unlikely to have significant pathology and could possibly be followed up conservatively. Patients < or =40 years of age should have a noncontrast CT or ultrasound study if they present with microscopic hematuria, and a cystoscopy should be added if gross hematuria exists. In older patients, a pre- and postcontrast CT and a cystoscopy should be performed.

The Association of a Tobacco-Specific Biomarker and Cigarette Consumption and Its Dependence on Host Characteristics

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent carcinogen, which can be characterized by urinary concentrations of the metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-butanol (NNAL) and its glucuronide. Using baseline data in current smokers from four clinical trials, we examine the associations of urinary cotinine with CPD and of total NNAL with cotinine and the modification of these associations by several host factors. There was a linear relationship between ln(cotinine) and ln(CPD) within categories of the Fagerstrom Test of Nicotine Dependence and of age. The increasing trend was significantly smaller for subjects with high and very high nicotine addiction and for older subjects and larger in females than males. The regression of ln(total NNAL/cotinine) on ln(cotinine) declined linearly, suggesting reduced NNK uptake per unit cotinine with increasing cotinine. The decline in trend was greater in subjects with increased CPD, with greater nicotine addiction, and at older ages and was smaller in females, although gender differences were small. Variations in the ratio with host characteristics were generally similar to a recent epidemiologic analysis of effect modification of the association between lung cancer and cigarette smoking.

Effect of delivered dosage of cigarette smoke toxins on the levels of urinary biomarkers of exposure

Urinary metabolites of tobacco smoke toxins are often used as biomarkers for the evaluation of active and passive exposure to cigarette smoke toxins. In a study of healthy smokers, we investigated concentrations of urinary biomarkers in relation to concentrations of selected toxins in mainstream cigarette smoke as determined by machine smoking of cigarettes in a manner that mimics an individual's smoking behavior (topography). Concentrations of nicotine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, and benzo(a)pyrene, in mainstream smoke determined under human smoking conditions, and their urinary metabolites cotinine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol, and 1-hydroxypyrene were established for 257 individuals who smoked low-yield (0.1-0.8 mg Federal Trade Commission nicotine/cigarette; mean, 0.66; n = 87), medium-yield (0.9-1.2 mg nicotine/cigarette; mean, 1.1; n = 109), and high-yield cigarettes (nicotine, >1.3 mg nicotine/cigarette; mean, 1.41; n = 61). Levels of urinary metabolites expressed per unit of delivered parent compounds decreased with increased smoke emissions. In smokers of low-, medium-, and high-yield cigarettes, the respective cotinine (ng/mg creatinine)-to-nicotine (mg/d) ratios were 89.4, 77.8, and 57.1 (low versus high; P = 0.06); the 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (pmol/mg creatinine)-to-4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (ng/d) ratios were 0.81, 0.55, and 0.57 (low versus high; P = 0.05); and the 1-hydroxypyrene (pg/mg creatinine)-to-benzo(a)pyrene (ng/d) ratios were 1.55, 1.13, and 0.97 (low versus high; P = 0.008). Similarly, means of cotinine per unit of delivered nicotine in smokers who consumed <20 cigarettes per day was 3.5-fold higher than in those who smoked >20 cigarettes per day. Likewise, a negative correlation was observed between cotinine-to-nicotine ratios and delivered doses of nicotine in subgroups of smokers who used the identical brand of cigarette, namely a filter tip-vented Marlboro (r = -0.59), which is a popular brand among Euro-Americans, and Newport (r = -0.37), a menthol-flavored cigarette without filter tip vents that is preferred by African-Americans. Thus, the intensity of the exposures significantly affects the levels of urinary biomarkers of exposure and should be taken into account in the evaluation of human exposure to cigarette smoke toxins.

Genetic susceptibility according to three metabolic pathways in cancers of the lung and bladder and in myeloid leukemias in nonsmokers

BACKGROUND

We chose a set of candidate single nucleotide polymorphisms (SNPs) to investigate gene-environment interactions in three types of cancer that have been related to air pollution (lung, bladder and myeloid leukemia).

PATIENTS AND METHODS

The study has been conducted as a nested case-control study within the European Prospective Investigation into Cancer and Nutrition cohort (409 cancer cases and 757 matched controls). We included never and ex-smokers. SNPs were in genes involved in oxidative stress, phase I metabolizing genes, phase II metabolizing genes and methylenetetrahydrofolate reductase (MTHFR).

RESULTS

The most notable findings are: GSTM1 deletion and bladder cancer risk [odds ratio (OR) = 1.60; 95% confidence interval 1.00-2.56]; CYP1A1 and leukemia (2.22, 1.33-3.70; heterozygotes); CYP1B1 and leukemia (0.47, 0.27-0.84; homozygotes); MnSOD and leukemia (1.91, 1.08-3.38; homozygotes) and NQO1 and lung cancer (8.03, 1.73-37.3; homozygotes). Other statistically significant associations were found in subgroups defined by smoking habits (never or ex-smokers), environmental tobacco smoke or gender, with no obvious pattern. When gene variants were organized according to the three main pathways, the emerging picture was of a strong involvement of combined phase I enzymes in leukemia, with an OR of 5 (1.63-15.4) for those having three or more variant alleles. The association was considerably stronger for leukemias arising before the age of 55.

Cigarette smoking and risk of lung cancer in Korean men: the Seoul Male Cancer Cohort Study

Lung cancer is the leading cause of cancer deaths in Korea. The aim of this study was to estimate lung cancer risk of cigarette smoking in Korean men by a 10-yr follow-up prospective cohort study using the primary databases. The number of subjects was 14,272 men, who had full information of smoking habits among participants in the Seoul Male Cancer Cohort Study (SMCC). Total 125,053 person-years were calculated by determining the number of days from the start of followup, January 1, 1993, until the date of lung cancer diagnosis, death from another cause, or the end of follow-up, December 31, 2002, followed by converting the number of days to years. The information of outcome was obtained by the database of Korea Central Cancer Registry, Seoul Regional Cancer Registry, and Korea Statistical Office. The relative risk (RR) and its 95% confidence interval (CI) values of smoking were calculated using Cox proportional hazards regression stratified on potential confounders. During the follow-up periods, 78 cases of lung cancer occurred. The cigarette smoking is the major risk factor and increases the 4.18-fold risk of lung cancer in Korean men. In order to control lung cancer, intervention of quitting smoking is needed.

Does occupational exposure to PAHs, diesel and aromatic amines interact with smoking and metabolic genetic polymorphisms to increase the risk on bladder cancer?; The Belgian case control study on bladder cancer risk

To investigate the association between occupational exposure to polycyclic aromatic hydrocarbons, aromatic amines and diesel and bladder cancer risk and the modification by smoking and metabolic polymorphisms, have we recruited 200 cases and 385 population controls. The adjusted OR of bladder cancer was 5.75 (95%CI 2.09-15.83) comparing the highest tertile of the cumulative probability of occupational exposure to aromatic amines with no occupational exposure. A possible interaction between occupational exposures to aromatic amines and smoking was found. The increased ORs of GSTM1, GSTT1, NAT2 and SULT1A1 among those ever occupational exposed was explored by estimating the false-positive report probability. We confirm that occupational exposure to aromatic amines is associated with an increase in bladder cancer risk.

Hemoglobin adducts of the human bladder carcinogen o-toluidine after treatment with the local anesthetic prilocaine

Prilocaine, a widely used local anesthetic, is metabolized to o-toluidine which is classified as human carcinogen. We aimed to assess the impact of prilocaine-treatment on hemoglobin adducts from o-toluidine. Blood samples were obtained before and 24h after receiving prilocaine local anesthesia (Xylonest, 100mg) from 20 head and neck surgery patients and 6 healthy volunteers. Hemoglobin adducts of o-toluidine and 4-aminobiphenyl were determined by gas chromatography/mass spectrometry. Hemoglobin adducts of o-toluidine were significantly increased 24h after 100mg prilocaine-treatment by 21.6+/-12.8ng/g hemoglobin (mean+/-S.D., N=26; P<0.0001). This corresponds to a 6-360-fold increase of o-toluidine adduct levels in 25 patients from 0.54+/-0.95ng/g before treatment to 22.0+/-13.2ng/g 24h after surgery (mean+/-S.D.). Because of an extremely high background level the increase was only 1.6-fold in one patient (40.9ng/g before and 64.4ng/g 24h after prilocaine injection). Current smoking had no influence on background values and on the increase of o-toluidine adducts. No treatment-related differences were seen in mean hemoglobin adduct levels of 4-aminobiphenyl which were significantly higher in smokers, 0.149+/-0.096ng/g (mean+/-S.D., N=8) as compared to nonsmokers 0.036+/-0.035ng/g (mean+/-S.D., N=16; P<0.01). In conclusion, prilocaine anesthesia leads to a massive increase of hemoglobin adducts of the carcinogenic arylamine o-toluidine. This implies a carcinogenic risk which should be taken into account in preventive hazard minimization.

Radon, secondhand smoke, glutathione-S-transferase M1 and lung cancer among women

Tobacco smoke and ionizing radiation induce oxidative stress by transmitting or generating reactive oxygen species (ROS). We hypothesized that glutathione-S-transferase M1 (GSTM1) null homozygotes would have decreased ability to neutralize ROS that might increase their susceptibility to lung cancer. A case-only design was used with lung cancer cases pooled from 3 previously completed case-control studies using archival tissue samples from 270 lung cancer cases to genotype GSTM1. Radon concentrations were measured with long-term alpha-track radon detectors. Secondhand smoke (SHS) was measured with questionnaires and interviews. Unconditional logistic regression was used to calculate the interaction odds ratios (OR) and 95% confidence intervals (95% CI). Radon concentrations >121 Bq m(-3) were associated with a >3-fold interaction OR (OR = 3.41; 95% CI = 1.10, 10.61) for GSTM1 null homozygotes compared to GSTM1 carriers; the linear trend was significant (p trend = 0.03). The SHS and GSTM1 interaction OR was also elevated (OR = 2.28; 95% CI = 1.15-4.51) among never-smokers. This may be the first study to provide evidence of a GSTM1 and radon interaction in risk of lung cancer. Additionally, these findings support the hypothesis that radon and SHS promote neoplasia through shared elements of a common pathway.

Cigarette smoking and lung cancer: modeling total exposure and intensity

Investigators typically analyze cigarette smoking using smoking duration and intensity (number of cigarettes smoked per day) as risk factors. However, odds ratios (OR) for categories of intensity either adjusted for, or jointly with, duration of smoking may be distorted by differences in total pack-years of exposure to cigarette smoke. To study effects of intensity, we apply a linear excess OR model to compare total exposure delivered at low intensity for a long period of time with an equal total exposure delivered at high intensity for a short period of time to data from a large case-control study of lung cancer. The excess OR per pack-year increases with intensity for subjects who smoke < or =20 cigarettes per day and decreases with intensity for subjects who smoke >20 cigarettes per day. The intensity patterns are homogeneous by histologic type of lung cancer, suggesting that observed differences in risks by histologic type are related to total smoking exposure or smoking duration and not smoking intensity. At lower smoking intensities, there is an "exposure enhancement" effect such that for equal total exposure, the excess OR per pack-year increases with intensity. At higher smoking intensities, there is a "reduced potency" or "wasted exposure" effect such that for equal total exposure, the excess OR per pack-year decreases with intensity (i.e., smoking at a lower intensity for longer duration is more deleterious than smoking at a higher intensity for shorter duration).

Dose effects in gene environment interaction: an enzyme kinetics based approach

There have been many observations of different forms of the effect of dose in toxicological and pharmacological research into gene environment interactions. In one form, the effect of genetic variation is seen to be more potent at lower doses, while in the other, the genetic variant has a stronger effect at higher doses of exposure. The application of principles of classical enzyme kinetics to this problem has led to a hypothesis that for any gain of function polymorphism, a low exposure gene (LEG) or low dose effect will always be observed, while for any loss of function polymorphism, the high exposure gene (HEG) effect will always be seen. Furthermore the dose effect is found to be independent of any effects on Vmax, but is related to effects on Km of the gene product. The hypothesis is derived from the Michaelis-Menten equation, and if supported by experimental evidence, could lead to important implications for drug dosage and toxicological risk analysis in the context of individual differences in genetic profiles.

N-acetyltransferase 2 genetic polymorphism: effects of carcinogen and haplotype on urinary bladder cancer risk

A role for the N-acetyltransferase 2 (NAT2) genetic polymorphism in cancer risk has been the subject of numerous studies. Although comprehensive reviews of the NAT2 acetylation polymorphism have been published elsewhere, the objective of this paper is to briefly highlight some important features of the NAT2 acetylation polymorphism that are not universally accepted to better understand the role of NAT2 polymorphism in carcinogenic risk assessment. NAT2 slow acetylator phenotype(s) infer a consistent and robust increase in urinary bladder cancer risk following exposures to aromatic amine carcinogens. However, identification of specific carcinogens is important as the effect of NAT2 polymorphism on urinary bladder cancer differs dramatically between monoarylamines and diarylamines. Misclassifications of carcinogen exposure and NAT2 genotype/phenotype confound evidence for a real biological effect. Functional understanding of the effects of NAT2 genetic polymorphisms on metabolism and genotoxicity, tissue-specific expression and the elucidation of the molecular mechanisms responsible are critical for the interpretation of previous and future human molecular epidemiology investigations into the role of NAT2 polymorphism on cancer risk. Although associations have been reported for various cancers, this paper focuses on urinary bladder cancer, a cancer in which a role for NAT2 polymorphism was first proposed and for which evidence is accumulating that the effect is biologically significant with important public health implications.

GSTM1 and CYP1A1 polymorphisms, tobacco, air pollution, and lung cancer: a study in rural Thailand

OBJECTIVES

The Lampang Province is situated in the northern region of Thailand. Incidence rates of lung cancer are high for Asian standards, particularly in women. This study was conducted to quantify the risk of lung cancer associated with exposures prevalent in the area and to investigate possible interactions with genetic susceptibility. The presence of several large open-cast coal mines from 1955 close to electricity-generating plants was a particular focus of concern.

METHODS

Two-hundred and eleven cases of primary lung cancers diagnosed in 1993 to 1995 and residents in the province were recruited at the Lampang Provincial Hospital (main referral center for treatment of the disease). Two sets of controls, frequency-matched to the cases by sex and age, were recruited (a) from the resident population (202 interviewed) and (b) from patients admitted to the hospital for diseases predominantly unrelated to tobacco smoking (211 interviewed). Sociodemographic information, complete residential history, and characteristics of the household (place of cooking, cooking fuel, and heating fuels), occupational history, and history of tobacco smoking were obtained by interview. Cases and controls ( approximately 50% of the population-based series) provided a blood sample. A point source air pollution exposure index was calculated for each village/township reported in residential histories based on the linear distance from the Mae Moh Center (the area of the electricity-generating plants), the year-specific gaseous (SO(2) and NO(2)) or total suspended particulate emissions from the Mae Moh Power Plant, and the percentage of wind from the center. Odds ratios (OR) for the disease associated with categorical variables were estimated within unconditional logistic regression. Extraction of genomic DNA and genotyping of variants in CYP1A1 and GSTM1 were conducted to assess the extent of modification of risk by these genes that are involved in the metabolism of polycyclic aromatic hydrocarbons, a common component of the exposures.

RESULTS

Overall, there was no evidence of relevant differences in the socioeconomic level of the three groups. The two control sets were similar with respect to lifelong tobacco habit and were subsequently pooled in analyses. Never-smokers were 7% of men and 33% of women. Smoking of local traditional products unfiltered and high in tar content is a common habit in the rural female population. ORs associated with smoking increased with duration of the habit and average daily amount, being 4.9 [95% confidence interval (95% CI), 2.5-9.7] for smokers of > or =7 cigarettes/d and 3.3 (95% CI, 1.7-6.2) for duration of 41 years or longer compared with nonsmokers. Smoking of local products was associated with an independent OR of 3.1 (95% CI, 1.7-5.6) adjusted for lifelong cumulative amount of tobacco smoked. Although most smokers had the habit for at least 16 years, the daily consumption was low compared with Western standards. Other potential sources of exposure to lung carcinogens (emission from the power-generating plants and domestic burning of coal and wood for cooking and heating) were not associated with increased risk of lung cancer. None of the three polymorphisms examined increased the risk of lung cancer or modified the risk associated with tobacco smoking.

CONCLUSION

In this rural population, 96% of male and 64% of female lung cancer incidence were explained by tobacco smoking. None of the potential sources of air pollution deriving from the combustion of coal and wood, or polymorphisms in the CYP1A1 gene or deletion of the GSTM1 had an effect on the risk of lung cancer, either together or separately.

Animal models and their limitations: On the problem of high-to-low dose extrapolations following inhalation exposures

Inhalation of complex mixtures such as combustion aerosols constitutes a parallel and simultaneous exposure of two distinctively different barriers to the body; the alveolar type I cells and the rest of the airway air/blood barrier, mainly the epithelium of the conducting airways. Exposure of the type I epithelium to most solutes leads to a rapid passage into the systemic circulation, and activation/deactivation of toxicants will take place mostly in the liver. Because of the huge metabolizing capacity of the liver, the dose-response of this component of an inhalation exposure is likely to be close to linear over larger exposure intervals. In contrast, exposures of the epithelium in the conducting airways lead to a slower passage, and in the case of semi-volatile solutes of high lipophilicities, a much slower passage into the systemic circulation. The result is a highly elevated concentration in the epithelium of the conducting airways during absorption, which may either lead directly to a localized toxicity, or, provide substrate for activating enzymes present in the airway mucosa. However, because of a limited capacity of the airway epithelium in this region both to dissolve sparingly soluble inhalants and to metabolize such solutes, the local dose response is likely to saturate at rather low exposure levels. One important consequence of local saturation in the epithelium of the conducting airways, is that inhalation exposures of laboratory animals conducted at elevated concentrations and limited time spans, may underestimate the risk in humans chronically exposed at relatively low concentrations. The phenomenon could be relevant in the etiology of lung cancer as well as inflammatory airway disease, where semi-volatile organic toxicants are suspected to contribute significantly.

CYP1A1 polymorphisms and risk of lung cancer in non-smoking Chinese women: influence of environmental tobacco smoke exposure and GSTM1/T1 genetic variation

OBJECTIVE

We examined whether polymorphisms of CYP1A1, which plays a role in the metabolic activation of polycyclic aromatic hydrocarbons (PAHs), confer an increased risk of lung cancer in lifetime non-smoking Chinese women.

METHODS

A total of 126 incident lung cancer cases, of which 87.7 were pathologically confirmed, and 162 age-matched hospital controls were included. CYP1A1 MspI and Ile(462)Val polymorphisms were genotyped and tested for association with this disease.

RESULTS

An elevated risk of lung cancer was observed among individuals with the MspI CC (OR=1.7, 95 CI=0.9-3.3) and Ile(462)Val ValVal genotypes (OR=2.8, 95 CI=1.1-7.6). After stratifying by environmental tobacco smoke (ETS) exposure, the risk of lung cancer associated with both polymorphisms was higher among individuals with lower exposure to ETS, compared with those who reported at least weekly exposure. Individuals with the MspI CC genotype showed a two-fold higher risk of lung cancer if they were also null for either GSTM1 or T1 (OR=2.3, 95CI=1.0-5.0 and OR=2.7, 95 CI=1.1-6.9, respectively, compared to other genotype combinations combined).

CONCLUSIONS

CYP1A1 is a susceptibility gene for lung cancer among non-smoking Asian women and this association can be influenced by ETS exposure and genetic variation at GST genes.

Human glutathion S-transferase A1 polymorphism and susceptibility to urothelial cancer in the Japanese population

GSTA1 has been reported to be most efficient in detoxifying N-acetoxy PhIP. In this study, 341 Japanese urothelial cancer patients and 457 healthy controls were compared for frequencies of GSTA1 genotype. We present the first evidence of an association between GSTA1*B (-567G, -69T, -52A) and urothelial cancer among never smokers. The frequency of GSTA1 *A/*B or *B/*B genotype was 24.3% in urothelial cancer cases, compared with 21.2% in the control groups (OR=1.22; 95%CI 0.87-1.72) after adjustment for age, gender and smoking status. But among never smokers, the GSTA1 *A/*B or *B/*B genotype was significantly higher in urothelial cancer cases (31.2%) compared with the controls (19.9%) (OR=1.73; 95%CI 1.01-2.97). This study suggests that exposure to food-derived PhIP could be one of the risk factors in the incidence of urothelial cancer in never smokers.

Genetic polymorphisms in CYP1B1, GSTA1, NQO1 and NAT2 and the risk of lung cancer

In a population-based case-cohort study, we have investigated the occurrence of lung cancer in relation to polymorphisms in the phase I gene cytochrome P450 1B1 and in the phase II genes glutathione S-transferase A1, NAD(P)H quinone oxidoreductase and N-acetyltransferase 2 (NAT2). Among 54,220 cohort members, 265 lung cancer cases were identified and a sub-cohort comprising 272 individuals was used for comparison. No overall associations were found between the polymorphisms and risk of lung cancer. The NAT2 fast acetylator genotype seemed to be protective against lung cancer in light smokers (< or =20 cigarettes/day) and not among heavy smokers (>20 cigarettes/day).

The effect of benzo(a)pyrene on porcine urinary bladder epithelial cells analyzed for the expression of selected genes and cellular toxicological endpoints

Consumption of tobacco products is the most relevant risk factor for the development of bladder cancer beside occupational contributions. In order to investigate mechanisms of tobacco smoke components in bladder carcinogenesis we have introduced a primary epithelial cell culture system derived from porcine urinary bladder as a suitable representative for the corresponding human tissue under physiological conditions. Two independent readouts were selected as markers for genotoxic events. Changes in the expression level of several toxicologically relevant genes should serve as indicators for early response, while classical genotoxic endpoints monitored manifested damages. Here, we present the first results of our study with benzo(a)pyrene (BaP) as a member of polycyclic aromatic hydrocarbons (PAHs) found in tobacco smoke. Cells treated with BaP show a dramatic increase in the expression of CYP1A1 that appears to be both indicator of and contributor for BaP toxicity. Genes coding for other proteins relevant in xenobiotic metabolism, signal transduction or tumor suppression show moderate effects or no enhancement of their expression levels. Comet assay and micronucleus test did show a significant, dose-dependent increase in DNA damages or aberrations after cell division. While these effects are conforming to the response at the mRNA expression level, they are less pronounced and require rather higher dosages of the chemical.

Individual susceptibility to carcinogens

The contribution of polymorphisms in carcinogen metabolizing genes to overall cancer rates may vary widely between groups with differing allele frequencies and with varying levels of carcinogenic exposure. Their effects are modified by interactions with each other and with other genes, particularly those involved in DNA repair. Studies on the combined effects of particular polymorphisms on colorectal and other cancers, and also on intermediate markers such as DNA adduct formation, are discussed. Such susceptibility genes are of considerable scientific interest, but do not confer high enough risks to be clinically relevant.