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

Pharmacokinetic analysis of nicotine and its metabolites (cotinine and trans-3'-hydroxycotinine) in male Sprague-Dawley rats following nose-only inhalation, oral gavage, and intravenous infusion of nicotine

Nicotine is an alkaloid found in tobacco. Human exposure to nicotine primarily occurs through the use of tobacco products. To date, limited nicotine pharmacokinetic data in animals have been reported. This study exposed male Sprague-Dawley rats to vehicle (and/or air) or 4 doses of nicotine via nose-only inhalation (INH), oral gavage (PO), and intravenous (IV) infusion. Plasma, 6 tissues (brain, heart, lung, liver, kidney, and muscle), and urine were collected at multiple timepoints from 5 min to 48 h post-dose. The concentrations of nicotine, cotinine, and trans-3'-hydroxycotinine (3-OH-cotinine) were determined, and the pharmacokinetic profiles were compared among the 4 doses for each route. The results indicated that after single nicotine dose, nicotine bioavailability was 53% via PO. Across all the administration routes and doses, nicotine was quickly distributed to all 6 tissues; kidney had the highest nicotine and cotinine levels, and the lung had the highest 3-OH-cotinine levels; nicotine was metabolized extensively to cotinine and cotinine was metabolized to a lesser extent to 3-OH-cotinine; the elimination of plasma nicotine, cotinine, and 3-OH-cotinine followed first-order kinetics; plasma nicotine had a shorter half-life than cotinine or 3-OH-cotinine; the half-lives of plasma nicotine, cotinine, and 3-OH-cotinine were dose- and route-independent; and nicotine and cotinine were major urinary excretions followed by 3-OH-cotinine. Nicotine, cotinine, and 3-OH-cotinine levels in plasma, tissues, and urine exhibited dose-dependent increases. These study findings improve our understanding of the pharmacokinetics of nicotine, cotinine, and 3-OH-cotinine across different routes of exposure.

An update on the formation in tobacco, toxicity and carcinogenicity of N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

The tobacco-specific nitrosamines N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are considered 'carcinogenic to humans' by the International Agency for Research on Cancer (IARC) and are believed to be important in the carcinogenic effects of both smokeless tobacco and combusted tobacco products. This short review focuses on the results of recent studies on the formation of NNN and NNK in tobacco, and their carcinogenicity and toxicity in laboratory animals. New mechanistic insights are presented regarding the role of dissimilatory nitrate reductases in certain microorganisms involved in the conversion of nitrate to nitrite that leads to the formation of NNN and NNK during curing and processing of tobacco. Carcinogenicity studies of the enantiomers of the major NNK metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and the enantiomers of NNN are reviewed. Recent toxicity studies of inhaled NNK and co-administration studies of NNK with formaldehyde, acetaldehyde, acrolein and CO2, all of which occur in high concentrations in cigarette smoke, are discussed.

Proteome derangement in malignant epithelial cells and its stroma following exposure to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

Discovering novel changes in the proteome of malignant lung epithelial cells and/or the tumor-microenvironment is paramount for diagnostic, prognostic, and/or therapy development. A time-dependent 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced mouse lung tumor model was used to screen the proteome of lung tumors. NNK-transformed human lung epithelial BEAS-2B cells were then established to evaluate the epithelial cell-specific protein changes. A duration-dependent increase of tumor burden was observed in NNK-treated mice, 2/12 (17%), 8/12 (67%), 9/12 (75%), and 10/10 (100%) at weeks 8, 12, 16, and 20 after the NNK exposure, respectively. A total of 25 differentially expressed proteins (≥ twofold change), predominantly structural, signaling, and metabolic proteins, were detected by two-dimensional difference gel electrophoresis and identified by mass spectrometry. Calregulin, ezrin, histamine releasing factor (HRF), and inorganic pyrophosphatase 1 (PPA1) exhibited changes and were further confirmed via immunoblotting. In addition, immunohistochemistry (IHC) analysis indicated upregulated E-cadherin and decreased vimentin expression in epithelial cells of tumor tissues. Acquisition of a neoplastic phenotype in NNK-transformed BEAS-2B cells was demonstrated by enhanced wound closure and increased anchorage independent colony formation. In transformed BEAS-2B cells, protein expression of E-cadherin, ezrin, and PPA1 (but not calregulin and HRF) was upregulated, as was observed in tumor tissues IHC staining using mouse lung tumor tissues further revealed that HRF upregulation was not lung epithelial cell specific. Altogether, tumorigenesis after NNK exposure may be initiated by protein dysregulation in lung epithelial cells together with proteome derangement derived from other cell types existing in the tumor-microenvironment.