Clinical and biochemical studies support smokeless tobacco's carcinogenic potential in the human oral cavity

In 2007, the International Agency for Research on Cancer presented compelling evidence that linked smokeless tobacco use to the development of human oral cancer. Although these findings imply vigorous local carcinogen metabolism, little is known about levels and distribution of phase I, II, and III (drug egress) enzymes in human oral mucosa. In this study here, we integrated clinical data, and imaging and histopathologic analyses of an oral squamous cell carcinoma that arose at the site of smokeless tobacco quid placement in a patient. Immunoblot and immunohistochemical (IHC) analyses were used to identify tumor and normal human oral mucosal smokeless tobacco-associated metabolic activation and detoxification enzymes. Human oral epithelium contains every known phase I enzyme associated with nitrosamine oxidative bioactivation with approximately 2-fold interdonor differences in protein levels. Previous studies have confirmed approximately 3.5-fold interdonor variations in intraepithelial phase II enzymes. Unlike the superficially located enzymes in nonreplicating esophageal surface epithelium, IHC studies confirmed that oral mucosal nitrosamine metabolizing enzymes reside in the basilar and suprabasilar region, which notably is the site of ongoing keratinocyte DNA replication. Clearly, variations in product composition, nitrosamine metabolism, and exposure duration will modulate clinical outcomes. The data presented here form a coherent picture consistent with the abundant experimental data that link tobacco-specific nitrosamines to human oral cancer.

Dietary sources of N-nitroso compounds and bladder cancer risk: findings from the Los Angeles bladder cancer study

N-Nitroso compounds (NOCs) have been proposed as possible bladder carcinogens. The main sources of exogenous exposure to NOCs are cigarette smoke and diet, particularly processed (i.e., nitrite-treated) meats. Perhaps more importantly, NOCs can be formed endogenously from dietary precursors such as nitrate, nitrite and amines. Heme has been shown to increase endogenous nitrosation. We examined the role of dietary sources of NOCs and NOC precursors as potential bladder cancer risk factors using data from the Los Angeles Bladder Cancer Study, a population-based case-control study. Dietary and demographic information was collected from 1,660 bladder cancer cases and 1,586 controls via a structured questionnaire. Intake of liver and of salami/pastrami/corned beef, were both statistically significantly associated with risk of bladder cancer in this study, particularly among nonsmokers. Heme intake was also statistically significantly associated with risk of bladder cancer among nonsmokers only. When considering NOC precursors, risk was consistently higher among subjects with concurrent high intake of nitrate and high intake of the different meats (sources of amines and nitrosamines). Results of this study are consistent with a role of dietary sources of NOC precursors from processed meats in bladder cancer risk, suggesting consumption of meats with high amine and heme content such as salami and liver as a risk factor for bladder cancer. In addition, any effect of consuming these meats may be greater when accompanied by high nitrate intake.

Formation and speciation of nine haloacetamides, an emerging class of nitrogenous DBPs, during chlorination or chloramination

Haloacetamides (HAcAms) are an emerging class of nitrogenous disinfection by-products (N-DBPs) of health concern. However, there are very limited data on the formation and speciation of the nine bromine- and chlorine-containing haloacetamides (HAcAm9). In the study, their formation and speciation during chlor(am)ination were investigated for a group of waters with a range of specific ultraviolet absorbance at 254 nm (SUVA₂₅₄), dissolved organic nitrogen (DON), and bromide levels. The waters that were the least impacted by anthropogenic pollution had the lowest DON levels, the highest ratios of dissolved organic carbon (DOC) to DON, and exhibited the least HAcAm9 formation. DON/DOC may act as an indicator of HAcAm yields during chlorination. HAcAm9 exhibited more formation during chloramination in the low-SUVA waters with no bromide, relative to high-SUVA waters with bromide. The selected waters all formed primarily dihalogenated (di-) HAcAms, followed by trihalogenated (tri-) species and, to a much lesser extent, monohalogenated (mono-) HAcAms. Di-HAcAm formation had similar trends as that of HAcAm9; whereas chloramination formed more mono- and less tri-HAcAms than chlorination. Bromine utilization factors and bromine incorporation factor increased with decreasing and increasing bromide during either chlorination or chloramination, and bromine was easier to incorporate into tri-HAcAms during chloramination than chlorination.

Atrazine and nitrate in public drinking water supplies and non-hodgkin lymphoma in nebraska, USA

A secondary analysis of 1999-2002 Nebraska case-control data was conducted to assess the risk of non-Hodgkin lymphoma (NHL) associated with exposure to nitrate- and atrazine-contaminated drinking water. Water chemistry data were collected and weighted by well contribution and proximity of residence to water supply, followed by logistic regression to determine odds ratios (OR) and 95% confidence intervals (CI). We found no association between NHL risk and exposure to drinking water containing atrazine or nitrate alone. Risk associated with the interaction of nitrate and atrazine in drinking water was elevated (OR, 2.5; CI, 1.0-6.2). Risk of indolent B-cell lymphoma was higher than risk of aggressive B-cell lymphoma (indolent: OR, 3.5; CI, 1.0-11.6 vs. aggressive: OR, 1.9; CI, 0.6-5.58). This increased risk may be due to in vivo formation and subsequent metabolism of N-nitrosoatrazine. A larger study is warranted to confirm our findings.

Mechanisms for nicotine in the development and progression of gastrointestinal cancers

Long-term smoking is major risk factor for a variety of cancers, including those of the gastrointestinal (GI) tract. Historically, nicotine and its derivatives are well known for their role in addiction, and have more recently been documented for their carcinogenic role in a number of human cancers. The cellular and molecular pathways activated by nicotine mimic physiological and environmental carcinogenesis in cancers throughout the GI tract potentiating cancer growth and/or inducing the formation of cancer on their own. Thus, it is important to unlock the carcinogenic mechanisms induced by nicotine in these systems, and underscore nicotine's potential as an environmental hazard. This review outlines the specific pathways demonstrated to mediate nicotine's carcinogenic mechanism in the GI tract. The abundance of cell and animal evidence calls for increased epidemiologic and case-control evaluation of nicotine's role in cancer.

Carcinogenic tobacco-specific N-nitrosamines in US cigarettes: three decades of remarkable neglect by the tobacco industry

BACKGROUND

Modification of tobacco curing methods and other changes in cigarette manufacturing techniques could substantially reduce the levels of tobacco-specific nitrosamines (TSNA), a group of potent carcinogens, in cigarette smoke. In 1999, two major US cigarette manufacturers stated their intent to move towards using tobaccos low in TSNA. There is no information available on current TSNA levels in tobacco of various cigarettes available in the US, particularly in the newer varieties introduced over the past decade.

METHODS

Seventeen brands of cigarettes were purchased in April of 2010 from retail stores in Minnesota. TSNA levels were measured in the tobacco filler and smoke of these cigarettes.

RESULTS

In all brands, the sum of two potent carcinogenic TSNA--4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N'-nitrosonornicotine--in cigarette filler averaged 2.54 (± 1.05) μg/g tobacco. This value is virtually identical to the sum of these two carcinogens reported for the tobacco of a US filtered cigarette in 1979. TSNA levels in smoke positively correlated with those in tobacco filler of the same cigarettes.

CONCLUSION

We found no indication that any meaningful attempt was made to reduce or at least control TSNA levels in the new varieties of the popular brands Marlboro and Camel introduced over the last decade. In light of the recently granted regulatory authority to the FDA over tobacco products, regulation of TSNA levels in cigarette tobacco should be strongly considered to reduce the levels of these potent carcinogens in cigarette smoke.

Is neurodegenerative disease a long-latency response to early-life genotoxin exposure?

Western Pacific amyotrophic lateral sclerosis and parkinsonism-dementia complex, a disappearing neurodegenerative disease linked to use of the neurotoxic cycad plant for food and/or medicine, is intensively studied because the neuropathology (tauopathy) is similar to that of Alzheimer's disease. Cycads contain neurotoxic and genotoxic principles, notably cycasin and methylazoxymethanol, the latter sharing chemical relations with nitrosamines, which are derived from nitrates and nitrites in preserved meats and fertilizers, and also used in the rubber and leather industries. This review includes new data that influence understanding of the neurobiological actions of cycad and related genotoxins and the putative mechanisms by which they might trigger neurodegenerative disease.

Distinguishing the common components of oil- and water-based metalworking fluids for assessment of cancer incidence risk in autoworkers

BACKGROUND

Metalworking fluids (MWF)--straight, soluble, and synthetic--have overlapping components. We derived constituent-based metrics of polycyclic aromatic hydrocarbons (PAHs), water-based MWF, biocides, and nitrosamines to account for this overlap and examined their relations with cancer incidence.

METHODS

An autoworkers cohort of 30,000 was followed for cancer incidence. Hazard ratios were estimated for each cancer and cumulative exposure (lagged) to each new metric; soluble MWF contributed variably to several metrics with weight k = 0-1.

RESULTS

For most cancer sites, the constituent-based metrics resulted in stronger exposure-disease associations than the MWF classes alone. Laryngeal and bladder cancer were most strongly associated with PAH (k = 0). Protective effects for stomach and lung cancer were observed with biocide, a component that may be a surrogate for endotoxin.

CONCLUSIONS

Our findings provide support and clarification of possible etiologies for previous positive associations and provide support for distinguishing exposure from oil- and water-based MWF in epidemiologic studies.

Role of CYP2E1 gene polymorphisms association with hepatitis risk in Northeast India

AIM

To investigate hepatitis virus, genetic and environmental factors, and their interactions in predisposing patients to liver diseases in Northeast India.

METHODS

A total of 104 jaundice patients and 124 community controls were included. Serological analysis was performed by routine enzyme-linked immunosorbent assay, and nucleic acid testing for hepatitis viruses was done by polymerase chain reaction (PCR), followed by PCR direct sequencing for viral genotyping. Cytochrome P450 2E1 (CYP2E1) polymorphism was studied by PCR-restriction fragment length polymorphism. Nitrite and volatile nitrosamines in indigenous foods consumed routinely by the Northeast Indian ethnic population were estimated by Griess's reagent and GC-MS, respectively.

RESULTS

Hepatitis A virus (HAV) infection was predominantly prevalent (36.5%) in our cohort, followed by hepatitis B virus (HBV), hepatitis E virus (HEV) and hepatitis C virus. HBV genotype D and HEV genotype 1 were the most dominant. CYP2E1 c1/c2 genotype frequency was comparatively higher in alcoholic (P < 0.0001, OR = 30.5) and cryptogenic (P = 0.014, OR = 8.714) patients, and was associated with significantly higher hepatitis risk (P = 0.0.007, OR = 6.489). Mutant C allele of Cyp2E1 DraI frequency was comparatively higher in HAV (P = 0.006), alcoholic (P = 0.003) and cryptogenic (P = 0.014) cases, and was associated with overall hepatitis risk (P = 0.026, OR = 5.083). Indigenous foods, Gundruk, Kharoli, betel leaf and nuts were found to have the highest nitrite content.

CONCLUSION

Apart from viral factors, CYP2E1 polymorphism might be associated with increased risk of liver diseases in Northeast India. Indigenous foods that contain nitrite and nitrosamine might be an associated risk factor.

Phenotypic CYP2A6 variation and the risk of pancreatic cancer

OBJECTIVE

Cytochrome P450 2A6 (CYP2A6) is an important metabolic enzyme capable of activating several procarcinogens, including dietary and tobacco-specific nitrosamines, which have been linked to pancreatic cancer. Positive associations between high CYP2A6 activity and lung and colorectal cancers have been reported. This is the first investigation of CYP2A6 activity and pancreatic cancer.

DESIGN

In this case-control study of cancer of the exocrine pancreas, phenotypic CYP2A6 activity was measured using a ratio of urinary caffeine metabolites. Demographic, smoking, dietary and medical information were obtained by questionnaire. CYP2A6 phenotype, which is not influenced by smoking status, was measured for 90 cases and 470 controls.

RESULTS

When modeled as a continuous variable, and adjusted for age, sex, race, education, current smoking status and chronic pancreatitis, the odds ratio (OR) per one unit of the natural log of the CYP2A6 ratio was 1.52 (95% confidence interval, CI: 1.09-2.12). In an adjusted categorical analysis, subjects in the uppermost quartile (based on controls) of CYP2A6 activity, when compared to the lower three quartiles, carried an 80% greater risk of pancreatic cancer (OR=1.80; 95% CI: 1.07-3.02).

CONCLUSIONS

High levels of CYP2A6 activity, as measured by a caffeine phenotyping assay, were positively associated with pancreatic cancer in this casecontrol study among a Midwestern U.S. population.

The consequences of the unregulated cigarette

This article considers changes in cigarette design in relation to the concept of "dose", drawing attention to the observation that there is not one smoking related epidemic of lung cancer, but at least two. Squamous carcinoma is declining in parallel with smoking prevalence while adenocarcinoma is increasing in the face of declining smoking prevalence. It is concluded that the adenocarcinoma epidemic is unnecessary and is due substantially to cigarette design changes, including increases in tobacco specific nitrosamines, manipulation of droplet size and ventilated filters. The need for regulation of smoke constituents is emphasised.

Cellular targets and mechanisms of nitros(yl)ation: an insight into their nature and kinetics in vivo

There is mounting evidence that the established paradigm of nitric oxide (NO) biochemistry, from formation through NO synthases, over interaction with soluble guanylyl cyclase, to eventual disposal as nitrite/nitrate, represents only part of a richer chemistry through which NO elicits biological signaling. Additional pathways have been suggested that include interaction of NO-derived metabolites with thiols and metals to form S-nitrosothiols (RSNOs) and metal nitrosyls. Despite the overwhelming attention paid in this regard to RSNOs, little is known about the stability of these species, their significance outside the circulation, and whether other nitros(yl)ation products are of equal importance. We here show that N-nitrosation and heme-nitrosylation are indeed as ubiquitous as S-nitrosation in vivo and that the products of these reactions are constitutively present throughout the organ system. Our study further reveals that all NO-derived products are highly dynamic, have fairly short lifetimes, and are linked to tissue oxygenation and redox state. Experimental evidence further suggests that nitroso formation occurs substantially by means of oxidative nitrosylation rather than NO autoxidation, explaining why S-nitrosation can compete effectively with nitrosylation. Moreover, tissue nitrite can serve as a significant extravascular pool of NO during brief periods of hypoxia, and tissue nitrate/nitrite ratios can serve as indicators of the balance between local oxidative and nitrosative stress. These findings vastly expand our understanding of the fate of NO in vivo and provide a framework for further exploration of the significance of nitrosative events in redox sensing and signaling. The findings also raise the intriguing possibility that N-nitrosation is directly involved in the modulation of protein function.

Fish sauce and gastric cancer: an ecological study in Fujian Province, China

AIM: To explore the relationship between consumption of fish sauce and the risk of gastric cancer in Fujian Province.

METHODS: An ecological study was carried out. A total of 11000 subjects from 55 townships were randomly selected from 10 counties within Fujian Province. All subjects were local residents who had been living in Fujian Province for more than 20 years, within the age group of 45-74 years. Trained interviewers conducted face-to-face interviews with a standardized questionnaire, which covered the frequency and amount of food intake, dietary habit, tobacco and alcohol consumption and history of chronic gastric diseases. Univariate and multivariate analyses were performed using Epi-info and SAS statistical packages, respectively.

RESULTS: A significant correlation between monthly consumption of fish sauce and mortality of gastric cancer was found. Pearson’s coefficient of correlation was statistically significant with r = 0.7356 for males, r = 0.5246 for females (P < 0.01). In the multivariate analysis, consumption of fish sauce still showed an association with the risk of gastric cancer. No significant positive correlation between esophagus cancer, liver cancer, colon cancer and consumption of fish sauce were observed.

CONCLUSION: Long-term intake of fish sauce may be related to high mortality of gastric cancer. Consumption of fish sauce might be one of important and unique etiologic factors of gastric cancer in Fujian Province. Further studies are needed to confirm this ecological study.

The induction of bladder tumors in F344 rats by intravesicular administration of some nitrosamines

Three nitrosamines, metabolically related and formed in vivo from the bladder carcinogen nitrosomethyl-n-octylamine, were administered to groups of 12 female F344 rats by intraurethral instillation twice a week for 30 weeks. All three compounds induced tumors in the urinary bladder. Nitrosomethyl-2-oxopropylamine at 10 mg/ml was the most potent, causing death of half of the animals with tumors at 43 weeks, following a total dose of 1.0 mmol; most of the rats also had tumors of the nasal mucosa, and there were some tumors of the kidney and kidney pelvis. Nitrosomethyl-2-hydroxypropylamine at 10 mg/ml (total dose 1.0 mmol) was much less effective, the median week of death being 83 weeks. In addition to bladder tumors, this group had tumors of the nasal mucosa, esophagus, and kidney. Nitrosomethyl-3-carboxypropylamine at 75 mg/ml and a total dose of 6.2 mmol per rat induced a high incidence of bladder tumors and tumors of the kidney pelvis, but not tumors of the nasal mucosa; the median week of death for this group was 55 weeks. It is concluded that nitrosomethyl-n-alkylamines that induce bladder tumors by oral administration to rats are metabolized to nitrosomethyl-3-carboxypropylamine, which is excreted in the urine and further metabolized to nitrosomethyl-2-oxopropylamine, the proximate bladder carcinogen.