Simultaneous determination of NNK and its seven metabolites in rabbit blood by hydrophilic interaction liquid chromatography–tandem mass spectrometry

Brain distribution and metabolic profiling of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in rats investigated by UHPLC-HRMS/MS following peripheral administration

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is known to be a tobacco-specific N-nitrosamine and has peripheral carcinogenic properties. It can also induce oxidative stress, glial cell activation, and neuronal damage in the brain. However, the distribution and metabolic characteristics of NNK in the central nervous system are still unclear. Here, a sensitive and effective UHPLC-HRMS/MS method was established to identify and investigate the metabolites of NNK and their distribution in the rat brain. In addition, the pharmacokinetic profiles were simultaneously investigated via blood-brain synchronous microdialysis. NNK and its seven metabolites were well quantified in the hippocampus, cortex, striatum, olfactory bulb, brain stem, cerebellum, and other regions of rat brain after peripheral exposure (5 mg/kg, i.p.). The average content of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in all brain regions was at least threefold higher than that of NNK, indicating a rapid carbonyl reduction of NNK in the brain. Lower concentrations of pyridine N-oxidation products in the cortex, olfactory bulb, hippocampus, and striatum might be related to the poor detoxification ability in these regions. Compared to α-methyl hydroxylation, NNK and NNAL were more inclined to the α-methylene hydroxylation pathway. Synchronous pharmacokinetic results indicated that the metabolic activity of NNK in the brain was different from that in the blood. The mean α-hydroxylation ratio in the brain and blood was 0.037 and 0.161, respectively, which indicated poor metabolic activity of NNK in the central nervous system.

90-day nose-only inhalation toxicity study of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in Sprague-Dawley rats

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is one of the key tobacco-specific nitrosamines that plays an important role in human lung carcinogenesis. Repeated dose inhalation toxicity data on NNK, particularly relevant to cigarette smoking, however, is surprisingly limited. Hence, there is a lack of direct information available on the carcinogenic and potential non-carcinogenic effects of NNK via inhalational route exposure. In the present study, the subchronic inhalation toxicity of NNK was evaluated in Sprague Dawley rats. Both sexes (9-10 weeks age; 23 rats/sex/group) were exposed by nose-only inhalation to air, vehicle control (75% propylene glycol), or 0.2, 0.8, 3.2, or 7.8 mg/kg body weight (BW)/day of NNK (NNK aerosol concentrations: 0, 0, 0.0066, 0.026, 0.11, or 0.26 mg/L air) for 1 h/day for 90 consecutive days. Toxicity was evaluated by assessing body weights; food consumption; clinical pathology; histopathology; organ weights; blood, urine, and tissue levels of NNK, its major metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and their glucuronides (reported as total NNK, tNNK, and total NNAL, tNNAL, respectively); tissue levels of the DNA adduct O6-methylguanine; blood and bone marrow micronucleus (MN) frequency; and bone marrow DNA strand breaks (comet assay). The results showed that NNK exposure caused multiple significant adverse effects, with the most sensitive endpoint being non-neoplastic lesions in the nose. Although the genotoxic biomarker O6-methylguanine was detected, genotoxicity from NNK exposure was negative in the MN and comet assays. The Lowest-Observed-Adverse-Effect-Level (LOAEL) was 0.8 mg/kg BW/day or 0.026 mg/L air of NNK for 1 h/day for both sexes. The No-Observed-Adverse-Effect-Level (NOAEL) was 0.2 mg/kg BW/day or 0.0066 mg/L air of NNK for 1 h/day for both sexes. The results of this study provide new information relevant to assessing the human exposure hazard of NNK.

Toxicokinetic and Genotoxicity Study of NNK in Male Sprague Dawley Rats Following Nose-Only Inhalation Exposure, Intraperitoneal Injection, and Oral Gavage

The tobacco-specific nitrosamine NNK [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone] is found in tobacco products and tobacco smoke. NNK is a potent genotoxin and human lung carcinogen; however, there are limited inhalation data for the toxicokinetics (TK) and genotoxicity of NNK in vivo. In the present study, a single dose of 5 × 10-5, 5 × 10-3, 0.1, or 50 mg/kg body weight (BW) of NNK, 75% propylene glycol (vehicle control), or air (sham control) was administered to male Sprague-Dawley (SD) rats (9-10 weeks age) via nose-only inhalation (INH) exposure for 1 h. For comparison, the same doses of NNK were administered to male SD rats via intraperitoneal injection (IP) and oral gavage (PO). Plasma, urine, and tissue specimens were collected at designated time points and analyzed for levels of NNK and its major metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and tissue levels of DNA adduct O6-methylguanine by LC/MS/MS. TK data analysis was performed using a non-linear regression program. For the genotoxicity subgroup, tissues were collected at 3 h post-dosing for comet assay analysis. Overall, the TK data indicated that NNK was rapidly absorbed and metabolized extensively to NNAL after NNK administration via the three routes. The IP route had the greatest systemic exposure to NNK. NNK metabolism to NNAL appeared to be more efficient via INH than IP or PO. NNK induced significant increases in DNA damage in multiple tissues via the three routes. The results of this study provide new information and understanding of the TK and genotoxicity of NNK.

14-Day Nose-Only Inhalation Toxicity and Haber's Rule Study of NNK in Sprague-Dawley Rats

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is one of the key tobacco-specific nitrosamines that plays an important role in human lung carcinogenesis. However, repeated inhalation toxicity data on NNK, which is more directly relevant to cigarette smoking, are currently limited. In the present study, the subacute inhalation toxicity of NNK was evaluated in Sprague Dawley rats. Both sexes (9-10 weeks age; 16 rats/sex/group) were exposed by nose-only inhalation to air, vehicle control (75% propylene glycol), or 0.8, 3.2, 12.5, or 50 mg/kg body weight (BW)/day of NNK (NNK aerosol concentrations: 0, 0, 0.03, 0.11, 0.41, or 1.65 mg/L air) for 1 hour/day for 14 consecutive days. Toxicity was evaluated by assessing body and organ weights; food consumption; clinical pathology; histopathology observations; blood, urine, and tissue levels of NNK, its major metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and their glucuronides (reported as total NNK, tNNK, and total NNAL, tNNAL, respectively); O6-methylguanine DNA adduct formation; and blood and bone marrow micronucleus frequency. Whether the subacute inhalation toxicity of NNK followed Haber's Rule was also determined using additional animals exposed 4 hours/day. The results showed that NNK exposure caused multiple significant adverse effects, with the most sensitive endpoint being non-neoplastic histopathological lesions in the nose. The lowest-observed-adverse-effect level (LOAEL) was 0.8 mg/kg BW/day or 0.03 mg/L air for 1 hour/day for both sexes. An assessment of Haber's Rule indicated that 14-day inhalation exposure to the same dose at a lower concentration of NNK aerosol for a longer time (4 hours daily) resulted in greater adverse effects than exposure to a higher concentration of NNK aerosol for a shorter time (1 hour daily).

Toxic compounds from tobacco in placenta samples analyzed by UPLC-QTOF-MS

Polycyclic aromatic hydrocarbons (PAHs), tobacco-specific nitrosamines (TSNAs) and aromatic amines are carcinogens present in cigarette smoke. These compounds are distributed in the human body and they could be transferred to the foetus during the pregnancy. Placenta is the main barrier to these toxic compounds and its study is the objective of this work. A method based on solid-phase extraction (SPE) with ultra-performance liquid chromatography-tandem quadrupole-time-of-flight mass spectrometry (UPLC-QTOF-MS) has been examined and optimized for the analysis of 9 target analytes (4 tobacco-specific nitrosamines and some of their metabolites, 3 aromatic amines, nicotine and cotinine) in 26 placenta samples from smoking and non-smoking women. Limits of detection (LODs) were in the range of 3-27ng/g of placenta. Nicotine, cotinine, N-nitrosoanatabine (NAT) and 4-(methylnitrosamino)-1- (3-pyridyl)-1-butanone (NNK) metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) were detected in the placenta samples of smoking woman. Nicotine was detected in 3 out of 8 placentas from smoking women, always below the limit of quantification (88ng/g). This could be expected, as the half-life of nicotine in the body is limited to about 0.5-3h. Cotinine, the main metabolite from nicotine, was detected in all placentas from smoking women at concentrations between 17.2 and 61.8ng/g, reaching the highest values for those women that smoked the highest number of cigarettes. NAT and NNAL were detected in all placentas from smoking women, always below the limit of quantification (40ng/g and 33ng/g respectively).

Effects of 8-methoxypsoralen on the metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in mice

8-Methoxypsoralen (8-MOP) is a well established drug in the treatment of various skin diseases. Pretreatment of mice with 8-MOP before administration of 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) significantly reduced the incidence of NNK-induced tumor. The present study was designed to evaluate the in vivo effects of 8-MOP on the bioactivation of NNK in mice. Decrease in the α-hydroxylation of NNK in mouse blood and tissues was observed as the most pronounced effect of 8-MOP. The catalytic property of cytochrome P450 2A5 (CYP2A5) enzyme in mice was determined by the coumarin 7-hydroxylation reaction, suggesting that 8-MOP produced remarkable inhibition on CYP2A5 in female C57BL/6 mice. These results implied that 8-MOP could prevent NNK-induced mutagenesis and tumorigenesis in mice through the inhibition of NNK α-hydroxylation, which may be achieved through the effect of 8-MOP on the bioactivities of CYP2A5.

Simultaneous determination of NNK and its metabolites in mouse tissue for evaluating the effects of chronic alcohol consumption on the metabolism of NNK in mouse liver and lung

A hydrophilic-interaction liquid chromatography-tandem mass spectrometry (HILIC-MS-MS) method was developed for the determination of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and its metabolites in mouse liver and lung. The limits of detection of all analytes were in the range 0.017-0.057 ng mL(-1), and recovery ranged from 88.4-119.8 % with intra and inter-day precision in the range 0.89-6.03 % and 1.01-6.97 %, respectively. This simple and accurate method was used to evaluate the effect of chronic alcohol consumption on NNK bioactivation in mouse tissue. Time-course curves for NNK and its metabolites were generated, and the areas under the curves (AUCs) were compared. It was found that target tissues of NNK carcinogenesis in C57BL/6 mice contained high levels of α-hydroxylation metabolites of NNK and its carbonyl reduction metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL). The most pronounced effect of alcohol was to enhance α-hydroxylation of NNK in mouse lung and liver, which suggests that chronic alcohol consumption may increase the risk of carcinogenicity associated with NNK in mice.