Prenatal exposure to nitrosatable drugs and timing of puberty in sons and daughters: A nationwide cohort study

BACKGROUND

N-nitroso compounds (NOCs) can be formed by endogenous reactions between nitrosatable drugs and nitrite. Animal studies have found that several NOCs are teratogenic, and epidemiological studies report associations between prenatal exposure to nitrosatable drugs and adverse birth outcomes. It is unknown whether prenatal exposure to nitrosatable drugs is harmful to the child's reproductive health, including pubertal development.

OBJECTIVES

We investigated whether prenatal exposure to nitrosatable drugs was associated with timing of puberty and whether nitrate, nitrite and antioxidant intake modified any association.

METHODS

The population-based Danish National Birth Cohort (DNBC) Puberty Cohort, which includes 15,819 children, was used to investigate the association between prenatal exposure to nitrosatable drugs and timing of puberty. Around gestational week 11 and gestational week 18, mothers provided information about drug use during pregnancy. The children's self-reported information on onset of pubertal milestones was collected every six months from 11 years of age and throughout puberty. To investigate potential effect modification by nitrite, nitrate and antioxidant intake, information on these factors was obtained from a food frequency questionnaire completed by the mothers in gestational week 25, and information on nitrate concentration in maternal drinking water at her residential address was obtained from monitoring data from public waterworks. Data were analysed using a multivariable regression model for interval-censored data estimating difference in months in timing of puberty between exposure groups.

RESULTS

A total of 2,715 children were prenatally exposed to nitrosatable drugs. We did not find an association between prenatal exposure to nitrosatable drugs and timing of puberty. This finding was supported by null-findings in the following sub-analyses investigating: 1. subtypes of nitrosatable drugs (secondary and tertiary amines and amides), 2. dose-dependency (duration of drug intake), 3. effect modification by maternal intake of nitrate, nitrite, and antioxidants. 4. confounding by indication.

CONCLUSIONS

Prenatal exposure to nitrosatable drugs was not associated with timing of puberty. Nitrosatable drugs are commonly used drugs in pregnancy, and further research is needed to allow firm conclusions on the potential effect of prenatal exposure to nitrosatable drugs on the child's reproductive health.

Exposure to nitrosatable drugs during pregnancy and childhood cancer: A matched case-control study in Denmark, 1996-2016

BACKGROUND

Nitrosatable drugs can be synthesized to N-nitroso compounds in human stomach. In a pregnant woman, N-nitroso compounds can be translocated to the fetus through the placenta. Maternal exposure of nitrosatable compounds during pregnancy has been associated with childhood brain tumors and leukemia. However, few studies have investigated an association between nitrosatable drug exposure during pregnancy and childhood cancer. We examined if maternal prescriptions of nitrosatable drugs received during pregnancy are associated with childhood cancer.

METHODS

A matched case-control study was conducted using Danish nationwide registry data from 1995 to 2016. Each childhood cancer case was matched with twenty-five controls. Maternal exposure of nitrosatable drugs during pregnancy was identified from the Danish National Prescription Register. A multivariable conditional logistic regression model was used to estimate adjusted odds ratios (adj.OR) with 95% confidence intervals (CI) for each childhood cancer type.

RESULTS

Maternal prescriptions of nitrosatable drugs positively associate with central nervous system tumors (adj.OR = 1.25; 95% CI = 1.04-1.51) and neuroblastoma (adj.OR = 1.96; 95% CI = 1.34-2.85) in offspring. We also observed a positive association between perinatal exposure of nitrosatable drugs and acute lymphoblastic leukemia (adj.OR = 1.31; 95% CI = 1.07-1.59), however, it appeared to be due to confounding by indication, i.e., maternal infections.

CONCLUSION

Nitrosatable drug use during pregnancy potentially increased risk of central nervous system tumors and neuroblastoma. While a positive association between maternal prescriptions of nitrosatable drugs and acute lymphoblastic leukemia should be interpreted cautiously because of confounding by indication.

Dietary N-Nitroso Compounds and Risk of Hepatocellular Carcinoma: A USA-Based Study

BACKGROUND AND AIMS

N-nitroso compounds (NOCs) are among the most potent dietary carcinogens. N-nitrosodiethylamine (NDEA), N-nitrosodimethylamine (NDMA), and N-nitrosopiperidine (NPIP) are abundant in foods and carcinogenic to the liver. We investigated the relationship between dietary NOCs and HCC risk.

APPROACH AND RESULTS

In this large, hospital-based, case-control study of 827 pathologically or radiologically confirmed HCC cases and 1,013 controls, NOC intake was calculated by linking food frequency questionnaire-derived dietary data with a comprehensive NOC concentration database. Multivariable-adjusted ORs and 95% CIs of HCC by quartiles of NOC consumption were estimated using logistic regression models, with the lowest quartile as the referent. We further investigated joint effects of consuming the highest quartile of NOCs that were associated with increased HCC risk and hepatitis, diabetes, or alcohol drinking on HCC risk. After adjustment for confounding factors, higher intake of NDEA from plant sources (ORQ4 vs. Q1  = 1.58; 95% CI = 1.03-2.41), NDMA from plant sources (ORQ4 vs. Q1  = 1.54; 95% CI = 1.01-2.34), and NPIP (ORQ4 vs. Q1  = 2.52; 95% CI = 1.62-3.94) was associated with increased HCC risk. No association was observed for nitrate or total NOC intake and HCC risk. Higher consumption of HCC-inducing NOCs and positive hepatitis virus status jointly increased the risk of developing HCC.

CONCLUSIONS

In conclusion, though some of our findings may indicate the presence of reverse causation owing to lower meat intake among cases with chronic liver diseases before HCC diagnosis, the potent dietary HCC carcinogens, NDEA, NDMA, and NPIP, and their enhanced carcinogenic effects among chronic carriers of hepatitis virus warrant further prospective investigation.

Systemic Carcinogens (N-Nitroso Compounds) and Synergistic or Additive Effects in Respiratory Carcinogenesis

Systemic carcinogens induce respiratory tract tumors in various animals species. Typical examples of systemic carcinogens are the N-nitroso compounds, which require metabolic conversion to exert their carcinogenic effect. In this review particular emphasis is put on the comparative studies performed in the same species with different nitrosamines, providing an experimental model in which is possible to examine and correlate the biochemical changes preceding the development of detectable tumors and the carcinogenic effect. In addition studies describing synergistic or additive effects in respiratory carcinogenesis are reviewed and discussed.

Prenatal Exposure to Nitrosatable Drugs, Dietary Intake of Nitrites, and Preterm Birth

Prenatal exposure to nitrosatable drugs, including secondary or tertiary amines, has been associated with preterm birth. Associations may be accentuated by higher intakes of dietary nitrites because of the increased formation of N-nitroso compounds. Using data from mothers of babies without major birth defects (controls) from the National Birth Defects Prevention Study, we examined the relationship between nitrosatable drug exposure in conjunction with dietary nitrite intake and preterm birth among 496 mothers of preterm infants and 5,398 mothers with full-term deliveries in 1997-2005. A protective association was observed with a high intake of plant nitrites (adjusted hazard ratio (AHR) = 0.72, 95% confidence interval (CI): 0.53, 0.97). Secondary amines in conjunction with high nitrite intake were associated with preterm birth during the first (AHR = 1.84, 95% CI: 1.14, 2.98), second (AHR = 1.89, 95% CI: 1.17, 3.07), and third (AHR = 2.00, 95% CI: 1.22, 3.29) trimesters. The adjusted hazard ratios for tertiary amine use in the third trimester by increasing tertiles of nitrite intake were 0.67 (95% CI: 0.35, 1.31), 1.25 (95% CI: 0.71, 2.19), and 2.02 (95% CI: 1.17, 3.49). Prenatal exposure to nitrosatable drugs, particularly secondary and tertiary amines, in conjunction with higher levels of dietary nitrite intake may increase the risk of preterm birth.

Childhood brain tumors and maternal cured meat consumption in pregnancy: differential effect by glutathione S-transferases

BACKGROUND

Some epidemiologic studies suggest that maternal consumption of cured meat during pregnancy may increase risk of brain tumors in offspring. We explored whether this possible association was modified by fetal genetic polymorphisms in genes coding for glutathione S-transferases (GSTs) that may inactivate nitroso compounds.

METHODS

We assessed six GST variants: GSTM1 null, GSTT1 null, GSTP1(I105V) (rs1695), GSTP1(A114V) (rs1138272), GSTM3*B (3-bp deletion), and GSTM3(A-63C) (rs1332018) within a population-based case-control study with data on maternal prenatal cured meat consumption (202 cases and 286 controls born in California or Washington, 1978-1990).

RESULTS

Risk of childhood brain tumor increased with increasing cured meat intake by the mother during pregnancy among children without GSTT1 [OR = 1.29; 95% confidence interval (95% CI), 1.07-1.57 for each increase in the frequency of consumption per week] or with potentially reduced GSTM3 (any -63C allele; OR = 1.14; 95% CI, 1.03-1.26), whereas no increased risk was observed among those with GSTT1 or presumably normal GSTM3 levels (interaction P = 0.01 for each).

CONCLUSIONS

Fetal ability to deactivate nitrosoureas may modify the association between childhood brain tumors and maternal prenatal consumption of cured meats.

IMPACT

These results support the hypothesis that maternal avoidance during pregnancy of sources of some nitroso compounds or their precursors may reduce risk of brain tumors in some children.

Maternal periconceptional consumption of pickled vegetables and risk of neural tube defects in offspring

BACKGROUND

Maternal exposure to nitrate, nitrite, and N-nitroso compounds from drinking water or diet has been associated with an increased risk of neural tube defects (NTDs) in some studies. Pickled vegetables contain relatively large amounts of nitrite and N-nitroso compounds. We examined the association between maternal periconceptional consumption of pickled vegetables and NTDs in Shanxi Province of northern China.

METHODS

Data were derived from a population based case-control study of major external birth defects in four counties of Shanxi Province. Participants included 519 NTDs cases identified between 2003 and 2007 and 694 healthy controls. Exposure information was collected within 1 week after delivery. Multivariable non-conditional Logistic regression model was used to estimate the adjusted odds ratio (OR) controlling for potential confounding variables.

RESULTS

The risk of NTDs was positively associated with the frequency of the consumption of pickled vegetables by the mother. Compared with pickled vegetables consumption at < 1 meal/week, the adjusted OR for consumption at 1 - 3, 4 - 6, and > 6 meals/week were 1.3 (95% confidence interval (CI): 1.0, 1.8), 1.9 (1.1, 3.2), and 3.6 (1.9, 6.9), respectively. A protective effect was found for maternal meat consumption at ≥ 1 meal/week (adjusted OR: 0.6, 95%CI: 0.4, 0.7) and egg or milk consumption at ≥ 1 meal/week (adjusted OR: 0.6, 95%CI: 0.4, 0.8).

CONCLUSION

Maternal periconceptional consumption of pickled vegetables may increase the risk for NTDs in Shanxi Province.

Human exposure to selected animal neurocarcinogens: a biomarker-based assessment and implications for brain tumor epidemiology

This review is based on the proceedings from the Second Lebow Conference, held in Chicago in 2007. The conference concentrated on developing a framework for innovative studies in the epidemiology of environmental exposures, focusing specifically on the potential relationship with brain tumors. Researchers with different perspectives, including toxicology, pharmacokinetics, and epidemiological exposure assessment, exchanged information and ideas on the use of biomarkers of exposure in molecular epidemiology studies and summarized the current knowledge on methods and approaches for biomarker-based exposure assessment. This report presents the state of science regarding biomarker-based exposure assessment of the four most common neurocarcinogens: acrylamide, 1,3-butadiene, N-nitroso compounds, and polycyclic aromatic hydrocarbons. Importantly, these chemicals are also carcinogenic in other organs; therefore, this discussion is useful for environmental epidemiologists studying all cancer types.

A review: dietary and endogenously formed N-nitroso compounds and risk of childhood brain tumors

Maternal dietary exposure to N-nitroso compounds (NOC) or to their precursors during pregnancy has been associated with risk of childhood brain tumors. Cured meat is one source of exposure to dietary NOC and their precursors. Most epidemiological studies that have examined the role of maternal consumption of cured meats during pregnancy have found a significant positive association between maternal intake of cured meat and the risk of childhood brain tumor (CBT). NOC consist of two main groups, N-nitrosamines and N-nitrosamides. The carcinogenicity profiles of NOC suggest that N-nitrosamides rather than N-nitrosamines are the compounds that may be associated with CBT and that they should be investigated more closely in epidemiological studies. We present a review of the chemical and carcinogenic properties of NOC in connection with the findings of case-control studies. This approach may be helpful in determining the essential information that must be collected in future epidemiological studies on CBT.

Dietary Nitrites and Nitrates, Nitrosatable Drugs, and Neural Tube Defects

BACKGROUND

Amine-containing (nitrosatable) drugs can react with nitrite to form N-nitroso compounds, some of which are teratogenic. Data are lacking on whether dietary intake of nitrates and nitrites modifies the association between maternal nitrosatable drug exposure and neural tube defects (NTDs) in offspring.

METHODS

We examined nitrosatable drug exposure and NTD-affected pregnancies in relation to dietary nitrite and total nitrite intake in a case-control study of Mexican American women. We interviewed 184 women with NTD-affected pregnancies and 225 women with normal live births, including questions on periconceptional drug exposures and dietary intake. For 110 study participants, nitrate was also measured in the usual source of drinking water.

RESULTS

Women who reported taking drugs classified as nitrosatable were 2.7 times more likely to have an NTD-affected pregnancy than women without this exposure (95% confidence interval [CI] = 1.4-5.3). The effect of nitrosatable drugs was observed only in women with higher intakes of dietary nitrite and total nitrite (dietary nitrite + 5% dietary nitrate). Women within the highest tertile (greater than 10.5 mg/day) of total nitrite were 7.5 times more likely to have an NTD-affected pregnancy if they took nitrosatable drugs (95% CI = 1.8-45.4). The association between nitrosatable drug exposure and NTDs was also stronger in women whose water nitrate levels were higher.

CONCLUSIONS

Findings suggest that effects of nitrosatable drug exposure on risk for neural tube defects in offspring could depend on the amounts of dietary nitrite and total nitrite intake.

A Meta-Analysis of Maternal Cured Meat Consumption during Pregnancy and the Risk of Childhood Brain Tumors

OBJECTIVE

N-Nitroso compounds (NOCs) are recognized neural carcinogens in animal models and are suspected human carcinogens. A meta-analysis was performed examining the possible association of maternal intake of cured meat (an important source of dietary NOCs) during pregnancy and the risk of pediatric brain tumors.

METHODS

Data from epidemiological studies were pooled using a general variance-based meta-analytic method employing confidence intervals described by Greenland in 1986. The outcome of interest was a summary relative risk (RR) reflecting the risk of childhood brain tumor (CBT) development associated with maternal intake of cured meats during pregnancy. Sensitivity analyses were performed when necessary to explain any observed statistical heterogeneity.

RESULTS

Seven observational studies were found that met the protocol-specified inclusion criteria. Analysis for heterogeneity demonstrated a lack of statistical heterogeneity (p = 0.59), indicating that the data could be statistically combined. Pooling data from the 6 reports containing data on maternal cured meat intake of all types yielded an RR of 1.68 (1.30- 2.17), being a statistically significant result. Analyzing CBT risk by type of cured meat ingested showed that hot dog consumption increased CBT risk by 33% (1.08-1.66), with a similar increase shown by frequent ingestion of sausage, i.e. 44%.

CONCLUSION

The data provide support for the suspected causal association between ingestion of NOCs from cured meats during pregnancy and subsequent CBT in offspring. Limitations in study design preclude definitive conclusions, but the relationship warrants exploration via additional observational and laboratory-based studies.

Etiology of pancreatic cancer, with a hypothesis concerning the role of N-nitroso compounds and excess gastric acidity

In the United States, pancreatic cancer is the fourth most frequent cause of cancer death in males as well as females, after lung, prostate or breast, and colorectal cancer. Each year, approximately 30 000 Americans are diagnosed with pancreatic cancer and about the same number die of it. Germline mutations in a few genes including p16 and BRCA2 have been implicated in a small fraction of cases, as has chronic pancreatitis. The one established risk factor for pancreatic cancer is cigarette smoking: current smokers have two to three times the risk of nonsmokers. Studies of dietary factors have not been entirely consistent but do suggest associations of higher risk with consumption of smoked or processed meats or with animal foods in general and lower risk with consumption of fruits and vegetables. Colonization by Helicobacter pylori appears to increase risk, and a history of diabetes mellitus may also increase risk. The purpose of this epidemiologic review is to consider the possibility that risk of pancreatic cancer is increased by factors associated with pancreatic N-nitrosamine or N-nitrosamide exposures and with chronic excess gastric or duodenal acidity. Host genetic variation in inflammatory cytokine mechanisms may also be involved in this process. Many features of the evidence bearing on the pathophysiology of pancreatic cancer appear to support connections with N-nitroso compounds and with gastric acidity.

Maternal prenatal exposure to nitrosatable drugs and childhood brain tumours

BACKGROUND

A compelling hypothesis was proposed that childhood brain tumours are associated with maternal exposure to N-nitroso compounds during the prenatal period. Many common drugs, such as antihistamines, aspirin, and antibiotics, are nitrosatable and depending upon the product, potentially carcinogenic. We hypothesized that maternal ingestion of certain subgroups of nitrosatable drug products during pregnancy increases the risk of brain tumour development in offspring.

METHODS

Data were collected as part of a population-based case-control study of childhood brain tumours and mothers' self-reported exposure to therapeutic drugs and dietary nitrites. Cases were enrolled from three US West Coast SEER tumour registries: Seattle-Puget sound, Los Angeles County, and the San Francisco-Oakland Bay Area. Tumours were grouped into three major histological tumour subtypes: astroglial, primitive neural ectodermal tumours, and all remaining glial tumours ('other glial'). Therapeutic drugs reported by mothers were translated into active chemical compounds and classified as secondary amines, tertiary amines, amides, or none of the three. Risk estimates were computed according to classes of nitrosatability, potential carcinogenicity, teratogenicity, and predicted end product.

RESULTS

We found no significant association between maternal use of nitrosatable drugs, either overall or within any of the nitrosatable drug classifications, and subsequent development of brain tumours in children. Nitrite consumption from cured meats was not an effect modifier. However, exposure to nitrosoephedrine during pregnancy was associated with significantly increased risk of 'other glial' tumours (OR = 3.1; 95% CI: 1.1-9.2).

CONCLUSIONS

These findings do not support an association between maternal use of nitrosatable drugs during pregnancy and brain tumour risk in offspring. While exposure to the nitrosation end product nitrosoephedrine was associated with increased risk for other glial tumours, the finding was not specific to any one type of tumour.

[Exposure level of total N-nitroso compounds in residents of high-and low-risk areas for esophageal cancer in southern]

OBJECTIVE

To assess the exposure level of total N-nitroso compounds (TNOCs) in the residents of high- and low-risk areas for esophageal cancer in southern China.

METHODS

Samples of duplicate plate diets and 12 hr overnight urine were collected from 120 male adults in each of the 2 areas, a high-risk area (Nanao county) and a low-risk area (Lufeng county) for esophageal cancer. The 240 male healthy subjects (35 - 64 years old) were selected by a 3-stage random cluster sampling procedure. Levels of TNOC, N-nitrosamino acids (NAAs) and volatile N-nitroso compounds (VNOC) in the samples were measured by Thermo Energy Analyzer.

RESULTS

The detectable rate (95%) of diet TNOC, daily dietary TNOC intake (4.25 +/- 0.84) micromol/day, 12-hr urinary TNOC excretion levels (1.76 +/- 0.23 ng/12 h) and daily dietary intake of VNOC (266 +/- 31.2 microg/day) in the high-risk area were all significantly higher than those of the low-risk area. Oesophageal cancer mortality rates were positively and significantly associated with daily dietary TNOC intake and 12-hr urinary TNOC excretion. Urinary NAAs excretion levels were not different in the two areas.

CONCLUSION

The results suggest that TNOCs may be implicated in the etiology of esophageal cancer in southern China.

West Coast study of childhood brain tumours and maternal use of hair-colouring products

The immature nervous system of the fetus is characterised by rapid cell growth and division and is particularly vulnerable to carcinogens and mutagens. Several epidemiological studies have reported an increased risk for childhood brain tumours (CBT) associated with exposure to N-nitroso compounds (NOC). Hair-colouring products (hair "dyes") that contain NOC-related aromatic amines have shown mutagenicity in vitro and carcinogenic properties in vivo. The potential public health impact of the relationship between hair dye use and carcinogenesis has prompted epidemiological research, given that a large proportion of American women have used hair dyes. A large population-based case-control study was conducted on the west coast of the USA to investigate risk factors for CBT including exposure to NOC. Eligible CBT patients (<20 years of age and diagnosed between 1984 and 1991) were identified from cancer registries in Los Angeles County, the San Francisco Bay Area in California and the Seattle area in Washington state. A total of 540 biological mothers of these children were interviewed, and 801 control subjects who were frequency matched to the CBT patients on birth year and sex were obtained using random digit dialling. Mothers were asked details about personal use of hair dyes during the index pregnancy including frequency of use, trimester of use and type of dye used. Results from age- and sex-adjusted unconditional logistic regression analyses showed no association between risk for CBT and use of hair dyes 1 month before and/or during pregnancy nor during specific trimesters. A nearly twofold increased risk for CBT was associated with single-interval use during the 1 month before pregnancy, but the confidence interval (CI) was imprecise and the estimate was not different from unity (OR = 1.9, 95% CI [0.5, 7.0]). Exclusive use of permanent dye, temporary dye or hair darkeners was not associated with risk for CBT. A twofold increased risk (OR = 2.0, 95% CI [0.83, 4.7]) was observed with exclusive use of semi-permanent dye during the month before or during pregnancy. Exclusive use of semi-permanent dye during the month before pregnancy and/or first trimester also was associated with an elevated risk for CBT, again not different from unity and with an imprecise CI (OR = 2.5, 95% CI = [0.58, 10.3]). There was no evidence of an association between risk for CBT by histological subtypes and use of hair dyes during the index pregnancy or the month before conception. Together with results from previous studies, these results provide no consistent evidence of an association between risk for CBT and use of hair dyes during pregnancy.

O6-alkylguanines, dietary N-nitroso compounds, and their precursors in gastric cancer

Several N-nitroso compounds, present in foods and beverages or formed in the stomach from their precursors, act as alkylating agents. By using a highly reliable technique (high-resolution gas chromatography-mass spectrometry with negative-ion chemical ionization and selected ion recording), we measured a series of specific O6-alkylguanines in snap-frozen paired stomach tissue samples (tumor and noninvolved mucosa) obtained at surgery from 24 gastric cancer patients identified in Florence, Italy. Samples of noninvolved mucosa had higher levels of total O6-alkylguanines and more frequently detectable levels (54%) than tumor samples (29.2%). O6-propylguanine and O6-methylguanine were the single adducts most frequently detected in noninvolved mucosa and tumor tissue, respectively. Tumor samples showed higher levels of total O6-alkylguanines in female patients (p = 0.03) and among those with a diffuse histological type (p = 0.06) or seronegative for Helicobacter pylori CagA antibodies (p = 0.06). Mean dietary nitrate intake was significantly higher in patients with detectable levels of adducts in tumor samples (p = 0.03). Estimated intakes of dimethylamine and N-nitrosodimethylamine correlated with total levels of O6-alkylguanines in noninvolved gastric mucosa. These findings, although based on a small series of cases, support a role for N-nitroso compounds from dietary sources in the etiology of gastric cancer.

Mechanisms by which garlic and allyl sulfur compounds suppress carcinogen bioactivation. Garlic and carcinogenesis

Overall, a host of studies provides compelling evidence that garlic and its organic allyl sulfur components are effective inhibitors of the cancer process. These studies reveal that the benefits of garlic are not limited to a specific species, to a particular tissue, or to a specific carcinogen. Several mechanisms are likely to account for this protection. Notable among these is a depression in nitrosamine formation and a reduction in carcinogen bioactivation. The benefits provided by garlic must be viewed as part of the entire diet, since several dietary constituents can influence the degree of protection. More than one compound is responsible for the anticancer properties associated with garlic. Future research should focus on how genetic variability and daily environmental factors influence the anticancer benefits attributed to garlic and its allyl sulfur components.

Genotoxicity of nitroso compounds and sodium dichromate in a model combining organ cultures of human nasal epithelia and the comet assay

Genotoxic effects of xenobiotics are a possible step in tumor initiation in the mucosa of the upper aerodigestive tract. Using the comet assay, detecting genotoxicity in human tissue has been restricted to single incubations in vitro, but in vivo most xenobiotics harm their target in a repetitive or chronic manner. Therefore, we propose a model, which provides repetitive incubations in human upper aerodigestive tract mucosa cultures. Samples of human inferior nasal turbinate mucosa (n = 25) were cultured according to a modified version of a technique originally described by Steinsvåg. On day 1 fresh samples and on days 7, 9 and 11 organ cultures were incubated with N-nitrosodiethylamine (NDEA), sodium dichromate (Na2Cr2O7) and N'-methyl-N-nitro-N-nitrosoguanidine (MNNG). Mucosa samples and organ cultures, respectively, underwent a modified comet assay on days 1, 7 and 11. Genotoxicity could be shown for NDEA, Na2Cr2O7 and MNNG on days 1, 7 and 11. Duration of tissue culture and repetitive incubations did not significantly influence the results for NDEA. Nevertheless, Na2Cr2O7 and MNNG caused higher genotoxic effects on cultures subjected to the comet assay on day 11. This model may help to assess genotoxic hazards posed by environmental pollutants that have a cumulative character in repetitive or chronic exposure in vivo.

Residential water source and the risk of childhood brain tumors

Gestation may represent a window of susceptibility to transplacental effects of environmental exposures, including chemicals in water. The N-nitroso compounds (NNC), a class of chemicals with demonstrated neurocarcinogenic potential, include substances detected in drinking water. We used data from a study of possible risk factors for childhood brain tumors (CBT) to investigate the association of source of residential drinking water during pregnancy and CBT occurrence among offspring. In addition, dipstick measurements were made of nitrates and nitrites in tap water for the subset of women living in the same home they had lived in during their pregnancies. Population-based CBT cases (n = 540) and controls (n = 801) were identified in three regions including Los Angeles County, and the San Francisco Bay Area of California, and the Seattle-Puget Sound area of western Washington state. Overall, we observed no increased risk of CBT in offspring associated with wells as the source of residential water. However, an increased risk of CBT [odds ratio (OR) = 2.6; 95% confidence interval (CI), = 1.3-5.2] was observed in western Washington among offspring of women who relied exclusively on well water, and a decreased risk of CBT (OR = 0.2; 95% CI, 0.1-0.8) was observed in Los Angeles County. Among the small subset of subjects for whom dipstick measurements of tap water were available, the risk of CBT associated with the presence of either measurable nitrite and/or nitrate was 1.1 (95% CI, 0.7-2.0). Given the crude measurement method employed and because measurements often were obtained years after these pregnancies occurred, the relevance of the dipstick findings is unclear. The lack of consistency in our findings related to residential water source does not support the hypothesis of increased risk related to consumption of well water; however, regional differences in well water content may exist, and the increased risk observed in western Washington deserves further evaluation.

Maternal cured meat consumption during pregnancy and risk of paediatric brain tumour in offspring: potentially harmful levels of intake

OBJECTIVE

To describe the relationship between specific levels of nitrite intake from cured meat consumption during pregnancy and the relative risk of paediatric brain tumours in the offspring.

DESIGN

Exposure data were previously collected for a population-based case-control study of paediatric brain tumours; data on nitrite content were obtained by a comprehensive literature review of surveys of residual nitrite content in cured meats published in the USA and Canada. The level of nitrite intake for each mother was predicted by year of pregnancy based on survey results. Dose-response was evaluated both categorically and continuously using polynomial and quadratic spline regression.

SETTING

The US west coast: Los Angeles County, the San Francisco-Oakland Bay Area and the Seattle-Puget Sound area.

SUBJECTS

There were 540 cases diagnosed between 1984 and 1990 at ages varying from 0 to 19 years, and 801 controls frequency-matched by geographic area, age and birth year.

RESULTS

In general, survey results suggest a trend of decreasing nitrite levels in cured meats over time. We observed a moderate increase in brain tumour risk in the offspring of mothers with relatively low levels of nitrite consumption from cured meats during pregnancy, and a two- to three-fold risk increase in offspring of mothers who consumed 3 mg day-1 nitrite from cured meats (about 125 g day-1 of cured meat consumption throughout the pregnancy).

CONCLUSIONS

A substantial risk of paediatric brain tumour appears to be associated with relatively high levels of maternal cured meat consumption during pregnancy. A more scientifically valid approach than a literature review to estimate nitrite intake from cured meats and data from a large group of highly exposed subjects would be useful in determining potentially harmful levels.

Childhood cancer in relation to cured meat intake: review of the epidemiological evidence

Over the past two decades a series of epidemiological studies have examined the relationship between consumption of cured meats during pregnancy and the subsequent risk of brain tumors, as well as other cancers, in the offspring. The research was prompted in large part by experimental investigations showing that transplacental exposure to certain N-nitroso compounds, i.e., nitrosoureas, could produce brain tumors in laboratory animals. Fourteen such epidemiological studies, 13 of which used the case-control approach, are reviewed here. Most of the studies showed no significant association between total cured meat intake and childhood cancer risk but more found positive than negative relationships. Furthermore, several studies reported significant positive associations for maternal and sometimes childhood or paternal consumption of one or more cured meats, with odds ratios of twofold or greater reported among the highest consumers. On the other hand, a correlation analysis found no positive concordance between temporal trends from the 1970s to 1990s in childhood brain cancer rates and cured meat consumption, inasmuch as cancer rates rose over time while residual nitrite levels in cured meats fell sharply. Because of the potential for bias, especially recall bias, and/or confounding, the relatively weak magnitude of the associations reported, and the inconsistency between study findings, at this time it cannot be concluded that eating cured meat has increased the risk of childhood brain cancer or any other cancers. Moreover, although N-nitroso compounds are sometimes found in cured meats or may be formed endogenously, there is no empirical evidence that eating cured meats results in human neural nitrosourea exposure. Nevertheless, the hypothesis that eating nitrite-cured meats may influence childhood and perhaps adult brain cancer cannot be dismissed. Unbiased evaluation of the hypothesis may derive from the conduct of cohort studies, where the interview-derived information on cured meat intake precedes, or is not otherwise associated with, the diagnosis of cancer.

Synergistic interaction between Helicobacter pylori gastritis and diet in gastric cancer

Infection with Helicobacter pylori increases the risk of gastric cancer. One possible mechanism is the higher likelihood of malignant transformation due to inflammatory responses in the epithelium. An alternative explanation is that these inflammatory responses induce chronic gastritis associated with decreased acidity in the stomach, which in turn increases the endogenous formation of carcinogenic N-nitroso compounds. Inflammatory responses seem to trigger two different causal pathways: one for the diffuse type of gastric cancer and the other for the intestinal type. The striking geographic variability in intestinal gastric cancer can be explained by the synergistic interaction between H. pylori infection and dietary factors, such as intake of salt and ascorbic acid. Screening and eradication of this organism, together with appropriate dietary modifications, offer promise in countries with a high prevalence of H. pylori infection and high risk of gastric cancer, but the safety of such interventions needs to be ensured.

Dose-dependent effect of dietary meat on endogenous colonic N-nitrosation

Human male volunteers were studied in a metabolic facility whilst they were fed randomized controlled diets. In eight volunteers there was a significant increase in faecal apparent total N:-nitroso compounds (ATNC) and nitrite excretion (P < 0.0001 and P = 0.046, respectively) when randomized doses of meat were increased from 0 to 60, 240 and 420 g/day over 10 day periods. Mean (+/- SE) faecal ATNC levels were 54 +/- 7 microg/day when the diets contained no meat, 52 +/- 11 microg/day when the diets contained 60 g meat/day, 159 +/- 33 microg/day with 240 g meat and 199 +/- 36 microg/day with 420 g meat. Higher concentrations of NOC were associated with longer times of transit in the gut (r = 0.55, P = 0.001) and low faecal weight (r = -0.51, P = 0.004). There was no significant decline in levels in individuals fed 420 g meat for 40 days. The exposures found on the higher meat diets were comparable with other sources of N:-nitroso compounds (NOC), such as tobacco smoke. Many NOC are known large bowel initiators and promotors in colon cancer, inducing G-->A transitions in codons 12 and 13 of K-ras. Endogenous NOC formation, combined with prolonged transit times in the gut, may explain the epidemiological associations between high meat/low fibre diets and colorectal cancer risk.

Evaluation of fecal mutagenicity and colorectal cancer risk

Colorectal cancer is one of the most common internal malignancies in Western society. The cause of this disease appears to be multifactorial and involves genetic as well as environmental aspects. The human colon is continuously exposed to a complex mixture of compounds, which is either of direct dietary origin or the result of digestive, microbial and excretory processes. In order to establish the mutagenic burden of the colorectal mucosa, analysis of specific compounds in feces is usually preferred. Alternatively, the mutagenic potency of fecal extracts has been determined, but the interpretation of these more integrative measurements is hampered by methodological shortcomings. In this review, we focus on exposure of the large bowel to five different classes of fecal mutagens that have previously been related to colorectal cancer risk. These include heterocyclic aromatic amines (HCA) and polycyclic aromatic hydrocarbons (PAH), two exogenous factors that are predominantly ingested as pyrolysis products present in food and (partially) excreted in the feces. Additionally, we discuss N-nitroso-compounds, fecapentaenes and bile acids, all fecal constituents (mainly) of endogenous origin. The mutagenic and carcinogenic potency of the above mentioned compounds as well as their presence in feces, proposed mode of action and potential role in the initiation and promotion of human colorectal cancer are discussed. The combined results from in vitro and in vivo research unequivocally demonstrate that these classes of compounds comprise potent mutagens that induce many different forms of genetic damage and that particularly bile acids and fecapentaenes may also affect the carcinogenic process by epigenetic mechanisms. Large inter-individual differences in levels of exposures have been reported, including those in a range where considerable genetic damage can be expected based on evidence from animal studies. Particularly, however, exposure profiles of PAH and N-nitroso compounds (NOC) have to be more accurately established to come to a risk evaluation. Moreover, lack of human studies and inconsistency between epidemiological data make it impossible to describe colorectal cancer risk as a result of specific exposures in quantitative terms, or even to indicate the relative importance of the mutagens discussed. Particularly, the polymorphisms of genes involved in the metabolism of heterocyclic amines are important determinants of carcinogenic risk. However, the present knowledge of gene-environment interactions with regard to colorectal cancer risk is rather limited. We expect that the introduction of DNA chip technology in colorectal cancer epidemiology will offer new opportunities to identify combinations of exposures and genetic polymorphisms that relate to increased cancer risk. This knowledge will enable us to improve epidemiological study design and statistical power in future research.

Safety of proton-pump inhibitors: the acid test

It is well established that atrophic gastritis, pernicious anaemia and partial gastrectomy are associated with an increased risk of gastric carcinoma. These conditions all result in a low acid output state. Although the mechanism of gastric carcinogenesis is not known, the model proposed by Correa has provided the most attractive explanation to date. The suggestion is that prolonged hypochlorhydria predisposes to gastric carcinoma by an increase in the production of carcinogenic N-nitroso compounds. This hypothesis has led to concerns about the safety of long-term acid suppression in the management of a variety of acid-related gastrointestinal conditions.

Endogenous N-nitroso compounds, and their precursors, present in bacon, do not initiate or promote aberrant crypt foci in the colon of rats

Processed meat intake is associated with increased risk of colorectal cancer. This association may be explained by the endogenous formation of N-nitroso compounds (NOC). The hypothesis that meat intake can increase fecal NOC levels and colon carcinogenesis was tested in 175 Fischer 344 rats. Initiation was assessed by the number of aberrant crypt foci (ACF) in the colon of rats 45 days after the start of a high-fat bacon-based diet. Promotion was assessed by the multiplicity of ACF (crypts per ACF) in rats given experimental diets for 100 days starting 7 days after an azoxymethane injection. Three promotion studies were done, each in 5 groups of 10 rats, whose diets contained 7%, 14%, or 28% fat. Tested meats were bacon, pork, chicken, and beef. Fecal and dietary NOC were assayed by thermal energy analysis. Results show that feces from rats fed bacon-based diets contained 10-20 times more NOC than feces from control rats fed a casein-based diet (all p < 0.0001 in 4 studies). In bacon-fed rats, the amount of NOC input (diet) and output (feces) was similar. Rats fed a diet based on beef, pork, or chicken meat had less fecal NOC than controls (most p < 0.01). No ACF were detected in the colon of bacon-fed uninitiated rats. After azoxymethane injection, unprocessed but cooked meat-based diets did not change the number of ACF or the ACF multiplicity compared with control rats. In contrast, the bacon-based diet consistently reduced the number of large ACF per rat and the ACF multiplicity in the three promotion studies by 12%, 17%, and 20% (all p < 0.01). Results suggest that NOC from dietary bacon would not enhance colon carcinogenesis in rats.

Sex differences in lung CYP1A1 expression and DNA adduct levels among lung cancer patients

Several epidemiological studies have indicated that female tobacco smokers may be at higher risk of lung cancer than males. In a study of lung cancer cases, we have found that female smokers had a significantly higher level of aromatic/hydrophobic DNA adducts in their nontumor lung tissue (15.39+/-9.47 adducts/10(8) nucleotides, n = 29) than male smokers (12.08+/-8.14, a = 93; P = 0.047). Females had significantly higher levels of adducts/pack-year (females 0.95+/-0.82 adducts/pack-year and males 0.46+/-0.46; P = 0.0004) and adducts/cigaret/day (females 1.48+/-1.29 and males 0.89+/-0.74, P = 0.015). By quantitative reverse transcription-PCR, it was found that female smokers exhibited a significantly higher expression level of lung CYP1A1 (494+/-334 CYP1A1 mRNA/10(6) glyceraldehyde-3-phophate dehydrogenase mRNA, n = 15) compared with males (210+/-208, n = 12; P = 0.016). Furthermore, for both sexes combined a significant correlation between CYP1A1 expression and DNA adduct level was found (r = 0.50, P = 0.009). In conclusion, the observed sex difference in aromatic/hydrophobic DNA adduct levels may at least in part be explained by different levels of CYP1A1 expression.

Natural and man-made mutagens and carcinogens in the human diet

Around 40% of human cancers may relate to dietary factors, including both exogenous and endogenous mutagens. Of exogenous factors, alcohol, certain metals and certain pesticides (both naturally produced or manufactured by the chemical industry), N-nitroso compounds, heterocyclic amines and polycyclic aromatic hydrocarbons are all probable human carcinogens. Despite current negative publicity, genetic engineering appears to be a more precise process and no more likely to lead to cancer risks than conventional breeding processes. Many traditional assessments of cancer hazard from endogenous or exogenous chemicals ignore the presence of modifying factors in the human diet. For example, dietary fat and dietary fibre probably either enhance or protect against cancer, depending upon the exact amounts and chemical nature of the fat fibre. Considerable numbers of other types of antimutagen/anticarcinogens have been identified, with varying modes of action. Additionally, there is an interaction of dietary factors with genetics. Epidemiology will always be important in assessing relative risks, but it is essential to continue developing more sensitive biomonitoring methodologies. It would be desirable to compare precise measures of individual exposure to dietary carcinogens with levels of oxidative damage and evidence of genotoxic effects in a given tissue. Such experimental approaches might be expected to lead a better understanding of the interplay between different dietary factors and also between diet, hereditary and the environment.

N-Nitroso compounds in the diet

N-Nitroso compounds were known almost 40 years ago to be present in food treated with sodium nitrite, which made fish meal hepatotoxic to animals through formation of nitrosodimethylamine (NDMA). Since that time, N-nitroso compounds have been shown in animal experiments to be the most broadly acting and the most potent group of carcinogens. The key role of nitrite and nitrogen oxides in forming N-nitroso compounds by interaction with secondary and tertiary amino compounds has led to the examination worldwide of foods for the presence of N-nitroso compounds, which have been found almost exclusively in those foods containing nitrite or which have become exposed to nitrogen oxides. Among these are cured meats, especially bacon-and especially when cooked; concentrations of 100 micrograms kg(-1) have been found or, more usually, near 10 micrograms kg(-1). This would correspond to consumption of 1 microgram of NDMA in a 100-g portion. Much higher concentrations of NDMA (but lower ones of other nitrosamines) have been found in Japanese smoked and cured fish (more than 100 micrograms kg(-1)). Beer is one source of NDMA, in which as much as 70 micrograms l(-1) has been reported in some types of German beer, although usual levels are much lower (10 or 5 micrograms l(-1)); this could mean a considerable intake for a heavy beer drinker of several liters per day. Levels of nitrosamines have been declining during the past three decades, concurrent with a lowering of the nitrite used in food and greater control of exposure of malt to nitrogen oxides in beer making. There have been declines of N-nitroso compound concentrations in many foods during the past two decades. The small amounts of nitrosamines in food are nonetheless significant because of the possibility-even likelihood-that humans are more sensitive to these carcinogens than are laboratory rodents. Although it is probable that alkylnitrosamides (which induce brain tumors in rodents) are present in cured meats and other potentially nitrosated products in spite of much searching, there has been only limited indirect evidence of their presence.

Risk of colorectal and other gastro-intestinal cancers after exposure to nitrate, nitrite and N-nitroso compounds: a follow-up study

N-nitroso compounds are potent carcinogens detected in foodstuffs. The importance of dietary nitrosamines in relation to human cancer development is, however, uncertain. We studied the relationship between intake of nitrates, nitrites and N-nitrosodimethylamine (NDMA) and risk of cancers of the gastro-intestinal tract in a cohort of 9,985 adult Finnish men and women. During a follow-up period of up to 24 years, 189 gastro-intestinal cancer cases were diagnosed in the cohort, initially free from cancer. Intake of nitrate, nitrite and NDMA were estimated, based on food-consumption data from a 1-year dietary history interview covering the total diet of the participants. A significant positive association was observed between intake of NDMA and subsequent occurrence of colorectal cancer with a relative risk (RR) between the highest and lowest quartiles of intake of 2.12 [95% confidence interval (CI) 1.04-4.33]. Of various sources of N-nitroso compounds, intake of smoked and salted fish was significantly (RR = 2.58, 95% CI 1.21-5.51) and intake of cured meat was non-significantly (RR = 1.84, 95% CI 0.98-3.47) associated with risk of colorectal cancer. No similar association was observed for intake of other fish or other meat. No significant associations were observed between NDMA intake and cancers of the head and neck combined or of the stomach or between nitrate or nitrite intake and risk of cancers of the gastro-intestinal tract. Our results are in line with the idea that N-nitroso compounds can induce colorectal cancer in humans.

N-nitroso compounds and Helicobacter pylori in the gastric remnant

AIMS AND BACKGROUND

The aims of this study were to investigate the role of N-nitroso compounds (NOC) and Helicobacter pylori (H. pylori) in gastric stump carcinogenesis.

METHODS AND STUDY DESIGN

Analyses of biochemical parameters such as pH and NOC concentration were carried out on 65 fasting gastric juice samples obtained at endoscopy from 45 patients previously submitted to partial gastrectomy for benign peptic ulcer disease (23 Billroth I, 22 Billroth II/Reichel-Polya) and 20 normal controls. Biopsy specimens were taken to determine histology and H. pylori status.

RESULTS

Significantly higher mean pH values and NOC concentrations were found in partial gastrectomies compared to normal controls. In relation to surgical methods, higher mean pH values and NOC concentrations were observed in the gastric juice of patients with Billroth II compared to Billroth I gastrectomies. Independently of the type of surgical reconstruction, higher mean NOC levels were recorded in patients with more severe histological changes and H. pylori infection.

CONCLUSIONS

All these data suggest that high levels of NOC in gastric juice and H. pylori infection could be cofactors in gastric stump carcinogenesis.

Maternal diet during pregnancy and risk of brain tumors in children

Nine studies of childhood brain tumors and maternal diet during pregnancy have focused on foods related to the N-nitroso-compound(NOC) hypothesis. An association between frequent consumption of cured meat by pregnant women and increased risk is a consistent finding in most of the studies. The data on fruit and vegetable consumption are less consistent, but suggest decreased risk. Studies that assess all aspects of maternal diet during pregnancy are needed to determine whether the observed associations remain after adjustment for other aspects of diet. Such comprehensive studies also may elucidate other dietary factors that affect the risk of brain tumors in children.

A methodological note on the selection of friends as controls

A number of issues inherent in the selection of friends as controls in case-control studies are illustrated in the light of a recent dietary study, based on hospital and friend controls. Preselection of certain characteristics of the controls by the interviewee is almost unavoidable. The choice of controls to be used in a case-control study must reflect the nature and type of hypothesis which is being tested. Advantages and drawbacks of potential control groups must be weighted against each other.

Dietary nitrosamines, heterocyclic amines, and risk of gastric cancer: a case-control study in Uruguay

To study the effects of dietary chemicals like nitrosodimethylamine and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, resulting from the cooking method of red meat, on gastric carcinogenesis, a case-control study was conducted in Uruguay, a country with areas of high rates of gastric cancer. The study involved 340 cases and 698 controls, who were interviewed between January 1993 and December 1996. Dietary nitrosodimethylamine was associated with an increased risk of gastric cancer [odds ratio (OR) = 3.6, 95% confidence interval (CI) = 2.4-5.5], whereas dietary 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (a potent mutagen derived from the frying and broiling of red meat) showed an OR of 3.9 (95% CI = 2.3-6.4). Both chemicals displayed independent effects, and its interaction followed a multiplicative model with an elevated OR of 12.7 (95% CI = 7.7-21.2). These results suggest that salted and barbecued meat, frequent items in the Uruguayan diet, and the resulting chemicals from the cooking methods of both types of meat are significantly associated with a high risk of stomach cancer.

Dietary nitrates, nitrites, and N-nitroso compounds and cancer risk: a review of the epidemiologic evidence

Experimental animal studies have shown N-nitroso compounds (NOC) to be potent carcinogens. Epidemiologic evidence of the carcinogenic potential of dietary NOC and precursor nitrates and nitrites in humans remains inconclusive with regard to the risk of stomach, brain, esophageal, and nasopharyngeal cancers. Inadequate available data could obscure a small to moderate effect of NOC.

Maternal exposure to prescription and non-prescription pharmaceuticals or drugs of abuse and risk of craniosynostosis

BACKGROUND

The pre- and peri-natal drug exposures reported by women participating in a case-control study of children in Colorado were examined for association with infant craniosynostosis.

METHODS

Mothers of case and control children underwent a standardized telephone interview and obstetric and newborn medical record review. The interview included questions on the use of prescription and non-prescription drugs, nutritional supplements, recreational and drugs of abuse. The mother's obstetric record was abstracted for information about pharmacologic agents taken before and during the antepartum period.

RESULTS

There were no statistically significant risk ratios associating craniosynostosis with prenatal exposure to hydantoin, valproic acid, or cocaine. Mothers of four case children and one control child reported specific exposure to retinoic acid. There were no statistically significant increases in the odds ratio (OR) for any suture type among children exposed to hypoxigenic agents, sympathomimetic or parasympatholytic agents, or metal-containing agents. The OR was 1.87 (lower bound of the two-sided 95% test-based confidence interval (CI): 1.08) among children with sagittal/lambdoid suture synostosis who were exposed to nitrosatable drugs chlorpheniramine, chlordiazepoxide, and nitrofurantoin compared to controls.

CONCLUSIONS

Certain nitrosatable drugs may be associated with increased risk of infant sagittal/lambdoid craniosynostosis. A possible mechanism related to ischaemia/reperfusion injury is suggested.

[Colorectal cancer: controversial role of meat consumption]

Diet is supposed to influence the colorectal cancer etiology, but the precise causative factors are yet unknown. International ecological studies show a strong correlation between meat consumption and the colorectal cancer incidence. Most case-control studies (22 of 29) show an increased risk to develop a colorectal cancer for those eating higher amounts of meat. In contrast, only 2 out of the 5 best prospective cohort studies have shown this positive association for red meat. Two studies out of 4 show an association with processed meat. Consumption of white meat or of fish is not associated with a high risk, and might even reduce the occurrence of colorectal cancer. Several plausible hypotheses concerning the link between meat and colon carcinogenesis have been suggested. They involve saturated fat, protein, iron, heterocyclic amines produced by cooking, and N-nitroso compounds. High fat diets may promote cancer because they have a high caloric content, or because they lead to increased levels of bile acids in the colonic lumen. Six experimental studies are published on the effect of meat, or meat fractions, on the colon tumor incidence in rodents initiated with chemical carcinogens. Data from these studies do not support the belief that red meat (beef) has a specific effect on intestinal carcinogenesis. Instead, diets containing beef meat (cooked or raw) decrease carcinogenesis when compared to control diets containing similar amounts of fat and protein of vegetal origin. However, high fat or high protein diets often increase carcinogenesis when compared to low fat or low protein diets. Thus, one cannot state, nor exclude, that meat promotes colorectal cancer.

N-nitroso compounds and man: sources of exposure, endogenous formation and occurrence in body fluids

Based on recent analytical data, total human exogenous exposure to N-nitrosamines is estimated to be 1.10 mumol/day; the major exposure sources are the diet (0.79 mumol/may, 80-120 micrograms/day; 72%), occupational exposure (0.15-0.30 mumol/day; 25%), cigarette smoking (0.02 mumol/day, 3.4 micrograms/day; 2%), and miscellaneous minor sources, including pharmaceutical products, cosmetics, indoor and outdoor air (0.001 mumol/day, 0.1 micrograms/day; 1%). Excretion of apparent total N-nitroso compounds (ATNC) in healthy adults is estimated to be 1.30 +/- 1.05 mumol/day in urine and between 1.56 +/- 1.56 and 3.17 +/- 2.58 mumol/day in faeces. The excretion of volatile N-nitrosamines (N-nitrosodimethylamine), and N-nitrosamine acids and their derivatives (N-nitrososarcosine, N-nitrosoproline, N-nitrosothiazolidine-4-carboxylic acid and N-nitroso-2-methylthiazoline-4-carboxylic acid) accounts for approximately 0.03% and 16.0% of urinary ATNC, respectively. 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol and its O-glucuronide conjugate, two metabolites of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone present in urine of smokers, account for 0.2% of the urinary ATNC response; < 1.5 of the excretion of currently identified N-nitroso compounds in urine. The remaining N-nitroso compounds excreted in urine and those present in faeces are still unidentified. A crude mass balance between exogenous exposure and excretion in urine and faeces indicates that 45-75% of the total human exposure to N-nitroso compounds results through in vivo formation.

Immunotoxic effects of smokeless tobacco on the accessory cell function of rat oral epithelium

Smokeless tobacco (ST) is known to adversely effect the oral mucosa, but knowledge about the influence on immune defence is limited. Few studies have investigated the effect of ST on the local immune response. In the present study, we have assessed the effect of a crude Swedish moist snuff (SS) extract, alkaloids, and nitrosamines on T-cell mitogenic response to Con A using epithelial cells, including Langerhans cells, of the rat oral mucosa as accessory cells. SS extract at a concentration of 4% reduced the T-cell proliferation by 50% (IC50 = 4%). Pretreatment of either oral epithelial cells or T-cells with SS extract also gave a significant inhibition of T-cell proliferation. This effect was not obtained following preincubation with SS components as alkaloids and different tobacco-specific nitrosamines (TSNA). None of the tested compounds were found to possess any mitogenic properties. This in vitro study showed that SS extract can evoke an immunosuppressive effect on mitogen-driven T-cell proliferation using cells from oral epithelium as accessory cells. This effect was more pronounced when SS extract was employed compared to when the single SS components were used alone.