The effect of a 2-h exposure to cigarette smoke on the metabolic activation of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in A/J mice

Differential carcinogenicity of cigarette smoke in mice exposed either transplacentally, early in life or in adulthood

Cigarette smoke (CS) plays a dominant role in the epidemiology of human cancer. However, it is difficult to reproduce its carcinogenicity in laboratory animals. Recently, we showed that CS becomes a potent carcinogen in mice when exposure starts soon after birth. In our study, we comparatively evaluated the carcinogenic response to mainstream CS in mice at different ages. Neonatal mice were exposed daily for 4 months to CS, starting within 12 hr after birth, and sacrificed at 8 months. Adult mice were exposed for the same time period (3-7 months) and sacrificed at 11 months. Other mice were exposed transplacentally or both transplacentally and early in life. A total of 351 neonatal mice and 80 adult Swiss H mice were used. With varying intensity depending on age, CS induced pulmonary emphysema, bronchial and alveolar epithelial hyperplasia, blood vessel proliferation and hemangiomas and microadenomas in lung as well as parenchymal degeneration of liver. Histopathological alterations of kidney were only observed in mice exposed to CS early in life. Lung adenomas and malignant tumors of various histopathological nature were detected in neonatally exposed mice but not in adults. Transplacental CS induced the formation of lung adenomas in the offspring 8 months after birth. Previous exposure during pregnancy attenuated CS-related alveolar epithelial hyperplasia induced after birth. In conclusion, the carcinogenic response to CS varies depending on the developmental stage. The early postnatal life and the prenatal life are particularly at risk for the later development of CS-related tumors.

Old ways, new means: tobacco industry funding of academic and private sector scientists since the Master Settlement Agreement

When, as a condition of the Master Settlement Agreement (MSA) in 1998, US tobacco companies disbanded the Council for Tobacco Research and the Center for Indoor Air Research, they lost a vital connection to scientists in academia and the private sector. The aim of this paper was to investigate two new research projects funded by US tobacco companies by analysis of internal tobacco industry documents now available at the University of California San Francisco (San Francisco, California, USA) Legacy tobacco documents library, other websites and the open scientific literature. Since the MSA, individual US tobacco companies have replaced their industry-wide collaborative granting organisations with new, individual research programmes. Philip Morris has funded a directed research project through the non-profit Life Sciences Research Office, and British American Tobacco and its US subsidiary Brown and Williamson have funded the non-profit Institute for Science and Health. Both of these organisations have downplayed or concealed their true level of involvement with the tobacco industry. Both organisations have key members with significant and long-standing financial relationships with the tobacco industry. Regulatory officials and policy makers need to be aware that the studies these groups publish may not be as independent as they seem.

Utility of the mouse dermal promotion assay in comparing the tumorigenic potential of cigarette mainstream smoke

The International Agency for Research on Cancer (IARC) has classified a number of the chemical constituents reported in cigarette mainstream smoke (MS) as carcinogens. In the international literature, 81 IARC classified carcinogens have been reported historically in MS. Cigarette smoke is a complex aerosol of minute liquid droplets (termed the particulate phase) suspended within a mixture of gases (CO(2), CO, NO(x), etc.) and semi-volatile compounds. The gases and semi-volatiles are termed the vapor phase. Due to early difficulties in inducing carcinomas in laboratory animals following inhalation exposure to MS, the mouse dermal promotion assay became the standard method of comparing the tumorigenic potential of cigarette smoke condensates (the particulate phase of MS nearly devoid of MS gases and having a significant reduction of the semi-volatile components of the vapor phase). Of the 81 IARC carcinogens reported in MS, 48 are found exclusively in the particulate phase, 29 in the vapor phase only, and four IARC carcinogens in both phases. A general comparison of the quantity and potency of the individual carcinogenic constituents of the MS vapor and particulate phases illustrates that the potential carcinogenic contribution from the vapor phase might be significant. Therefore, the mouse dermal promotion assay may not be a sensitive comparator of the tumorigenic potential of different MSs displaying a diversity of vapor phase components. However, when used in a weight-of-the-evidence approach that includes smoke chemistry, in vitro studies using whole smoke and human exposure studies evaluating both vapor and particulate phase smoke constituents, the mouse dermal promotion assay remains an important risk assessment tool as the only test that reproducibly measures the tumorigenic potential of cigarette smoke condensate.

Acute and subacute effects of tobacco alkaloids, tobacco-specific nitrosamines and phenethyl isothiocyanate on N'-nitrosonornicotine metabolism in rats

N'-Nitrosonornicotine (NNN) was the first tobacco-specific nitrosamine (TSNA) identified as carcinogen in tobacco smoke, but no data exist on in vivo interactions between NNN and other tobacco alkaloids, TSNA or phenethyl isothiocyanate (PEITC) which have been demonstrated in various studies on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Acute effects on NNN metabolism were tested in male Fischer F344 rats injected s.c. with 30nmol/kg body weight (bw) [5-(3)H]NNN either alone or simultaneously with 15mumol/kg bw nicotine, nornicotine, anatabine, or anabasine, 150mumol/kg bw cotinine, 3mumol/kg bw myosmine, or 300nmol/kg bw of either N'-nitrosoanatabine or N'-nitrosoanabasine. Another group of rats was fed a diet supplemented with PEITC at 1mumol/g diet starting 24h before NNN treatment. Within 24h more than 80% and about 10% of the radioactivity was excreted with urine and feces, respectively. Urinary metabolites were separated by reversed-phase radio-HPLC and identified by co-chromatography with UV standards. In two sets of experiments with control rats treated with NNN only, 4-hydroxy-4-(3-pyridyl)butanoic acid (hydroxy acid, 44.4/44.8%), 4-oxo-4-(3-pyridyl)butanoic acid (keto acid, 32.4/31.5%), NNN-N-oxide (5.0/3.8%), 4-(3-pyridyl)butane-1,4-diol (diol, 1.1/1.0%) and norcotinine (2.3/1.0%) were consistently detected besides unmetabolised NNN (4.7/3.3%). Co-treatment with nicotine, cotinine, nornicotine and PEITC shifted the contribution of the two major metabolites significantly in favor of hydroxy acid (108-113% of control) as compared to keto acid (86-90% of control). The same treatments also increased norcotinine (135-170% of control). These changes are consistent with a decreased metabolic activation of NNN. In subacute studies rats received NNN in drinking water for 4 weeks at a daily dose of 30 nmol/kg bw with or without nornicotine at 15 micromol/kg bw or myosmine at 3 micromol/kg bw. On the last day of the experiment all rats received [5-(3)H]NNN at 30 nmol/kg bw with a contaminated apple bite followed by collection of urine and feces for 18h. Most of the radioactivity, 87-96% of the dose, was recovered in urine and only minor amounts have been excreted in feces or persisted in blood. In urine of the NNN-control group keto acid (32.2%) and unmetabolised NNN (3.9%) were present in identical amounts as in the acute experiment whereas hydroxy acid (41.4% of total radioactivity in urine, 93% of acute NNN control) was reduced in expense of the minor NNN metabolites. Co-administration of nornicotine resulted in a small but significant rise of keto acid (107% of control) and a significant decrease in NNN-N-oxide (76% of control). After co-treatment with myosmine the increase of keto acid (104% of control) was even less but still significant whereas NNN-N-oxide and diol were significantly reduced to 72% and 79% of control, respectively. Our experiments with rats indicate significant mutual effects of some of the major tobacco alkaloids and most relevant TSNA. Further studies on the impact on smokers and the inhibitory effects of isothiocyanates are needed for a final risk assessment.

An analysis of the role of tobacco-specific nitrosamines in the carcinogenicity of tobacco smoke

Cigarette smoke is a complex mixture consisting of more than 4500 chemicals, including several tobacco-specific nitrosamines (TSNA). TSNA typically form in tobacco during the post-harvest period, with some fraction being transferred into mainstream smoke when a cigarette is burned during use. The most studied of the TSNA is 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). NNK has been shown to be carcinogenic in laboratory animals. Studies examining the carcinogenicity of NNK frequently are conducted by injecting rodents with a single dose of 2.5 to 10 mumol of pure NNK; the amount of NNK contained in all of the mainstream smoke from about 3700 to 14,800 typical U.S. cigarettes. Extrapolated to a 70-kg smoker, the carcinogenic dose of pure NNK administered to rodents would be equivalent to the amount of NNK in all of the mainstream smoke of 22 to 87 million typical U.S. cigarettes. Furthermore, extrapolating results from rodent studies based on a single injection of pure NNK to establish a causative role for NNK in the carcinogenicity of chronic tobacco smoke exposure in humans is not consistent with basic pharmacological and toxicological principles. For example, such an approach fails to consider the effect of other smoke constituents upon the toxicity of NNK. In vitro studies demonstrate that nicotine, cotinine, and aqueous cigarette "tar" extract (ACTE) all inhibit the mutagenic activity of NNK. In vivo studies reveal that the formation of pulmonary DNA adducts in mice injected with NNK is inhibited by the administration of cotinine and mainstream cigarette smoke. Cigarette smoke has been shown to modulate the metabolism of NNK, providing a mechanism for the inhibitory effects of cigarette smoke and cigarette smoke constituents on NNK-induced tumorigenesis. NNK-related pulmonary DNA adducts have not been detected in rodents exposed to cigarette smoke, nor has the toxicity of tobacco smoke or tobacco smoke condensate containing marked reductions in TSNA concentrations been shown to be reduced in any biological assay. In summary, there is no experimental evidence to suggest that reduction of TSNA will reduce the mutagenic, cytotoxic, or carcinogenic potential of tobacco smoke.

Effect of nicotine, cotinine and phenethyl isothiocyanate on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) metabolism in the Syrian golden hamster

The effect of nicotine, cotinine and phenethyl isothiocyanate (PEITC) on metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was studied in the Syrian golden hamster. Urinary metabolite profiles were determined in 24 h urine after a single subcutaneous (s.c.) administration of [5-(3)H]NNK (80 nmol/kg, s.c.). Co-administration of either a 500-fold higher dose of nicotine (40 micromol/kg, s.c.) or a 5000-fold higher dose of cotinine (400 micromol/kg, s.c.) significantly (P<0.001) reduced metabolic activation of NNK by alpha-hydroxylation to 85 and 71% of control, respectively. Co-administration of a 300-fold higher dose of PEITC (1 micromol/g diet) slightly reduced alpha-hydroxylation of NNK (94% of control). Metabolism of NNK by reduction to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) was increased by nicotine (155%), and significantly increased by cotinine (670%, P<0.001) and PEITC (219%, P<0.01). Detoxification of NNAL by glucuronidation was also increased by all three test agents. Detoxification of NNK and NNAL by N-oxidation was marginally increased by nicotine, reduced by PEITC, and significantly reduced by cotinine. The urinary metabolite profiles suggest that nicotine, which occurs in concentrations up to 30000-fold higher than NNK in mainstream cigarette smoke, and cotinine, its proximal metabolite, may have a significant protective effect against in vivo metabolic activation of NNK.