CAS No. 76014-81-8
Metabolite of 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone, NNK (a tobacco-specific N-nitrosamine)
4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is a metabolite of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which belongs to a group of chemicals termed tobacco-specific N-nitrosamines (TSNA). As the name implies, TSNA are found only in tobacco and products derived from tobacco (Hecht and Hoffman 1988). TSNA are chemically related to nicotine and other tobacco alkaloids, and they are present particularly in tobacco leaves. The TSNA content of tobacco varies depending upon soil conditions, agricultural practices, fertilizer use, and tobacco manufacturing processes (IARC, 2007). The largest amounts of TSNA are formed during tobacco curing and processing after harvesting, and additional amounts are formed when tobacco is smoked. In general, the levels of TSNA are greater in smokeless tobacco than in tobacco used in cigarettes and produced in mainstream tobacco smoke (IARC, 2007). Human exposure occurs by use of smokeless tobacco products (e.g., snuff, chewing tobacco, etc.), and by inhaling tobacco smoke during the process of active smoking or as a result of passive exposure to ambient tobacco smoke (referred to as second hand smoke, SHS, or environmental tobacco smoke). Considerably lower levels of TSNA have been detected in second hand or sidestream smoke, as in poorly ventilated rooms where heavy smoking occurred. The small amounts of N-nitrosamines that may occur in food and non-food products are several orders of magnitude lower than the content of tobacco and tobacco smoke (Hecht and Hoffman, 1988). Measurement of TSNA and their metabolites in humans provides biomarkers of exposure to carcinogens that are specific to tobacco.
NNK has no commercial use (IARC, 2007). It forms in tobacco by the reaction of nicotine with nitrite that may be naturally occurring or added during processing. NNK is released into the environment when tobacco is burned, but environmental fate has not been well characterized (HSDB, 2010). Inhalation or dermal exposure may occur in workers involved in NNK production or use. General population exposure occurs largely through inhalation of tobacco smoke, either active smoking or SHS exposure, and through ingestion of NNK in smokeless tobacco products. There is no evidence that absorption of nicotine from a patch, lozenge, or gum can lead to production of NNK in the human body (Hecht, 1998).
In the body, NNK undergoes metabolic activation and is metabolized largely (about 95%) to NNAL (IARC, 2007; Stepanov et al., 2008). Both chemicals are procarcinogens that require metabolic activation to react with DNA and other cellular molecules (IARC, 2007). NNAL is slowly eliminated in urine with an elimination half-life of 18-45 days (Goniewicz et al., 2009; Hecht et al., 1999) and can be detected for months after smoking cessation. Transplacental transfer of NNK and/or NNAL has been demonstrated by measuring urinary NNAL in newborn babies (Lackmann et al., 1999).
NNK was mutagenic in in vitro assays, including bacteria, rodent fibroblasts, and human lymphoblastoid cells (IARC, 2007). Cytotoxicity has been documented in in vitro mammalian liver and pancreatic cells (IARC, 2007). NNK carcinogenesis is thought to involve metabolic activation and formation of DNA adducts (Hecht, 1998). NNK appeared to be a lung-specific carcinogen in several animal species, primarily producing adenocarcinomas, independent of the route of administration (Hecht, 1998). NNK-induced tumors also were produced in the nasal cavity, liver, and pancreas in experimental animals (IARC, 2007). NNAL produced lung tumors in mice, and when given prenatally to mice, resulted in lung or liver tumors in the offspring (Anderson et al., 1989). Studies using animal and human cells demonstrated metabolic activation of NNK and NNAL and the formation of DNA adducts, suggesting that the mechanism of human lung cancer may be similar to that seen in experimental animals (Hecht, 1998; Richter et al., 2009).
NNAL has been extensively studied as a carcinogen biomarker of tobacco use and SHS exposure. NNAL has been detected in urine and blood of smokers (Carmella et al., 2005) and smokeless tobacco users, and in urine of individuals with SHS exposure (IARC, 2007). In general, urinary NNAL levels were well correlated with either serum or urinary cotinine levels. In smokers, NNAL levels were also correlated with the number of cigarettes smoked (Kavvadias et al., 2009; Xia et al., 2010). In non-smokers, NNAL levels were also correlated with the amount of SHS exposure (Bernert et al., 2009). In a study of nonsmokers with chronic obstructive pulmonary disease, more severe symptoms were reported when urinary NNAL levels were higher, indicative of greater SHS exposure (Eisner et al., 2009). In a case-control study, levels of NNAL measured in serum collected prospectively were associated with increased lung cancer risk (Church et al., 2009). Non-smoking women living with a partner who smoked cigarettes had urinary NNAL levels that were about 5% of the levels in their smoking partners, a percentage similar (1-2%) to that for lung cancer risk in non-smokers with SHS exposure compared to smokers (Anderson et al., 2001).
IARC considers NNK to be a human carcinogen, and NNAL is an animal carcinogen (IARC, 2007). NTP (2005) determined that NNK is reasonably anticipated to be a human carcinogen.
Urinary levels of NNAL reflect use of one or more smokeless tobacco products or exposure to tobacco smoke via active smoking or from SHS exposure. From NHANES 2007-2008 to 2009-2010, urine NNAL appeared to decline slightly among all groups of non-smokers except for non-Hispanic blacks (CDC, 2012). Total urinary NNAL was detectable above the limit of detection (0.6 pg/mL) in 55% of NHANES 2007-2008 participants aged six years and older, and in 41.2% of the nonsmokers (Bernert et al., 2010). Compared to non-smokers, defined as participants with serum cotinine <10 ng/mL, the 75th and 95th percentile NNAL levels in smokers were about 75 and 200 times higher, respectively (Bernert et al., 2010). For a subgroup of more highly exposed nonsmokers, defined as participants with serum cotinine 0.1 to less than 10 ng/mL, the geometric mean of 5.56 (CI, 4.8-6.4) pg/mL was similar to levels reported in studies of adults exposed to SHS (Anderson et al., 2001 and 2003; Bernert et al., 2010; Tulunay et al., 2005). Within this subgroup, non-Hispanic whites had slightly higher urinary NNAL levels than either non-Hispanic blacks or Mexican Americans. No differences were apparent between levels in males and females, but among the age groups, the highest geometric mean NNAL level was in children aged 6-11 years (Bernert et al., 2010). In contrast to nonsmokers, urinary NNAL levels in smokers in NHANES 2007-2008, demonstrated gender and racial/ethnic differences. The adjusted geometric mean (95% CI) NNAL levels were highest in females, 353 (324-384) pg/mL and non-Hispanic whites, 336 (298-379) pg/mL. Urinary NNAL levels were significantly correlated with levels of serum cotinine, urine creatinine, and the number of cigarettes per day smoked but not to the menthol type of the cigarette (Xia et al., 2011). In the U.S. population, urinary total NNAL levels were approximately 50-150 times higher in smokers compared with non-smokers (Bernert et al., 2010; Xia et al., 2011). Urinary NNAL levels in U.S. smokers appear to be similar to levels reported in smaller studies of smokers (Breland et al., 2003; Byrd and Ogden, 2003; Carmella et al., 2002).
Variability in urinary NNAL levels may be due to TSNA content of the smoked product, the frequency and intensity of smoking, and such individual factors as age and genetics (Ashley et al., 2010; Herstgaard et al., 2008; Lubin et al., 2007). Total urinary NNAL levels reported from studies of U.S. smokers varied widely, but typically, average levels ranged from 200-600+ pg/mL or pg/mg creatinine (Breland et al., 2003; Carmella et al., 2002; Church et al., 2010; Hecht et al., 1999 and 2002; Hertsgaard et al., 2008; Muscat et al., 2009; Stepanov et al., 2007). Consistent with the lower NNK levels of most cigarettes from outside the U.S., lower urinary NNAL levels, often less than 200 pg/mL were reported in smokers from countries other than the U.S. (Ashley et al., 2010; Calapai et al, 2009; Morin et al., 2010; Yuan et al., 2009).
Nonsmokers with SHS exposure typically had urinary NNAL levels below 10 pg/mL (Anderson et al., 2001; Carmella et al., 2003; Hecht et al., 1999 and 2007), but higher levels were reported following exposure under controlled conditions (Bernert et al., 2009). Studies in infants and young children suggest that they may be susceptible to inhaling large doses of SHS, as evidenced by high urinary levels of total NNAL. Children exposed to SHS in the home had average urinary NNAL levels ranging from 10-30 pg/ml, about 2-3 times higher than those reported in SHS-exposed adults (Hecht et al., 2001 and 2006; Lackmann et al., 1999). Notably higher urinary NNAL levels, averaging 29.3 pg/mL (95% CI 17.3-41.8) were found in newborns of mothers who smoked during pregnancy (Lackmann et al., 1999).
Urinary total NNAL levels are similar or slightly higher in users of smokeless tobacco products compared to active smokers, indicative of the higher levels of TSNA and NNK that may be present in smokeless tobacco. Small studies of snuff dippers and chewing tobacco users reported average NNAL levels of approximately 850 pg/mL and 600-900 pg/mg creatinine (Carmella et al., 2002 and 2003; Hatsukami et al., 2004; Hecht et al., 2002; Kresty et al., 1996; Lemmonds et al., 2005). Possibly the highest urinary NNAL levels, averaging more than 250,000 pg/mL, were measured in several Sudanese users of "toombak", a paste of tobacco and sodium bicarbonate that is held in the mouth like snuff (Murphy et al., 1994).
Biomonitoring studies of urinary NNAL provide physicians and public health officials with reference values so that they can determine whether people have been exposed to higher levels of NNK from SHS and tobacco than are found in the general population. Biomonitoring data can also help scientists plan and conduct research about exposure to NNK and its health effects.
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