Effect of cigarette smoke on the mutagenic activation of various carcinogens in hamster

Interplay between smoking-induced genotoxicity and altered signaling in pancreatic carcinogenesis

Despite continuous research efforts directed at early diagnosis and treatment of pancreatic cancer (PC), the status of patients affected by this deadly malignancy remains dismal. Its notoriety with regard to lack of early diagnosis and resistance to the current chemotherapeutics is due to accumulating signaling abnormalities. Hoarding experimental and epidemiological evidences have established a direct correlation between cigarette smoking and PC risk. The cancer initiating/promoting nature of cigarette smoke can be attributed to its various constituents including nicotine, which is the major psychoactive component, and several other toxic constituents, such as nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, and polycyclic aromatic hydrocarbons. These predominant smoke-constituents initiate a series of oncogenic events facilitating epigenetic alterations, self-sufficiency in growth signals, evasion of apoptosis, sustained angiogenesis, and metastasis. A better understanding of the molecular mechanisms underpinning these events is crucial for the prevention and therapeutic intervention against PC. This review presents various interconnected signal transduction cascades, the smoking-mediated genotoxicity, and genetic polymorphisms influencing the susceptibility for smoking-mediated PC development by modulating pivotal biological aspects such as cell defense/tumor suppression, inflammation, DNA repair, as well as tobacco-carcinogen metabolization. Additionally, it provides a large perspective toward tumor biology and the therapeutic approaches against PC by targeting one or several steps of smoking-mediated signaling cascades.

Genotoxicity of 10 cigarette smoke condensates in four test systems: comparisons between assays and condensates

The particulate fraction of cigarette smoke, cigarette smoke condensate (CSC), is genotoxic in many short-term in vitro tests and is carcinogenic in rodents. However, no study has evaluated a series of CSCs prepared from a diverse set of cigarettes and produced with different smoking machine regimens in several short-term genotoxicity tests. Here we report on the genotoxicity of 10 CSCs prepared from commercial cigarettes that ranged from ultra-low tar per cigarette (< or =6.5 mg) to full flavor (>14.5 mg) as determined by the Federal Trade Commission (FTC) smoking regimen, a reference cigarette blended to be representative of a U.S. FTC-regimen low-tar cigarette, and experimental cigarettes constructed of single tobacco types. CSCs were tested in the presence of rat liver S9 in the Salmonella plate-incorporation assay using frameshift strains TA98 and YG1041; in micronucleus and comet assays in L5178Y/Tk(+/-) 7.3.2C mouse lymphoma cells, and in CHO-K(1) cells for chromosome aberrations. All 10 CSCs were mutagenic in both strains of Salmonella, and the rank order of their mutagenic potencies was similar. Their mutagenic potencies in Salmonella spanned 7-fold when expressed as rev/mug CSC but 158-fold when expressed as rev/mg nicotine; the range of genotoxic potencies of the CSCs in the other assays was similar regardless of how the data were expressed. All 10 CSCs induced micronuclei with a 3-fold range in their potency. All but one CSC induced DNA damage over a 20-fold range, and all but one CSC induced chromosome aberrations over a 4-fold range. There was no relation among the genotoxic potencies of the CSCs across the assays, and a qualitative advantage of the addition of the other assays to the Salmonella assay was not supported by our findings. Although consideration of nicotine levels may improve the relevance of the quantitative data obtained in the Salmonella and possibly comet assays, compensatory smoking habits and other factors may make the data from the assays used here have qualitative but not quantitative value in assessing risk of cigarette types and cigarette smoking to human health.

Chronic pancreatic inflammation induced by environmental tobacco smoke inhalation in rats

OBJECTIVE

Despite a strong epidemiological association between cigarette smoking and pancreatic diseases, such as pancreatic cancer and chronic pancreatitis, the effects of long-term cigarette smoke inhalation on the pancreas have not been clearly determined. In the present study, we investigated the effect of cigarette smoke inhalation on the pancreas.

METHODS

Thirty-six female Sprague Dawley rats were exposed to two different doses of environmental tobacco smoke averaging 100 mg or 160 mg/m3 total suspended particulate matter (TSP) per m3 for 70 min twice a day for 12 wk. The animals were sacrificed and examined for the effects of tobacco smoke exposure on pancreatic morphology and function.

RESULTS

In 58% (7/12) of the animals, exposure to 160 mg/m3 TSP cigarette smoke induced a chronic pancreatic inflammatory process with fibrosis and scarring of pancreatic acinar structures. Animals with fibrotic alterations showed an induction of pancreatic pro-collagen 1 gene expression, and the infiltration of immune cells was accompanied by the expression of the inflammatory mediators MIP-1alpha, IL-1beta, and TGF-beta in 33% (4/12) of the animals. Acinar cell stress was manifested by a significant up-regulation of pancreatitis-associated protein expression (PAP) in smoke-exposed animals (smoke-exposed 6,932 +/- 1,236 vs control 3,608 +/- 305, p < 0.05). Possibly contributing to the morphological damage to the exocrine pancreas, the inhalation of cigarette smoke induced trypsinogen and chymotrypsinogen gene expression and, furthermore, reduced pancreatic enzyme content.

CONCLUSIONS

This study provides experimental evidence of morphological pancreatic damage induced by the inhalation of cigarette smoke, which is likely to be mediated by alterations of acinar cell function.

Genotoxicity of tobacco smoke and tobacco smoke condensate: a review

This report reviews the literature on the genotoxicity of mainstream tobacco smoke and cigarette smoke condensate (CSC) published since 1985. CSC is genotoxic in nearly all systems in which it has been tested, with the base/neutral fractions being the most mutagenic. In rodents, cigarette smoke induces sister chromatid exchanges (SCEs) and micronuclei in bone marrow and lung cells. In humans, newborns of smoking mothers have elevated frequencies of HPRT mutants, translocations, and DNA strand breaks. Sperm of smokers have elevated frequencies of aneuploidy, DNA adducts, strand breaks, and oxidative damage. Smoking also produces mutagenic cervical mucus, micronuclei in cervical epithelial cells, and genotoxic amniotic fluid. These data suggest that tobacco smoke may be a human germ-cell mutagen. Tobacco smoke produces mutagenic urine, and it is a human somatic-cell mutagen, producing HPRT mutations, SCEs, microsatellite instability, and DNA damage in a variety of tissues. Of the 11 organ sites at which smoking causes cancer in humans, smoking-associated genotoxic effects have been found in all eight that have been examined thus far: oral/nasal, esophagus, pharynx/larynx, lung, pancreas, myeoloid organs, bladder/ureter, uterine cervix. Lung tumors of smokers contain a high frequency and unique spectrum of TP53 and KRAS mutations, reflective of the PAH (and possibly other) compounds in the smoke. Further studies are needed to clarify the modulation of the genotoxicity of tobacco smoke by various genetic polymorphisms. These data support a model of tobacco smoke carcinogenesis in which the components of tobacco smoke induce mutations that accumulate in a field of tissue that, through selection, drive the carcinogenic process. Most of the data reviewed here are from studies of human smokers. Thus, their relevance to humans cannot be denied, and their explanatory powers not easily dismissed. Tobacco smoke is now the most extreme example of a systemic human mutagen.

Possibility of the involvement of 9H-pyrido[3,4-b]indole (norharman) in carcinogenesis via inhibition of cytochrome P450-related activities and intercalation to DNA

This study investigated the inhibitory effect of 9H-pyrido[3,4-b]indole (norharman), one of the naturally occurring beta-carbolines, on cytochrome P450 (CYP)-related activities and the relationship between its inhibitory effect, its intercalation to DNA, and its comutagenic effect. Norharman reduced the mutagenicities of heterocyclic amines (HCAs) containing 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1), aflatoxin B1, benzo[a]pyrene (BP), and some nitrosamines in the presence of 10 microl liver S9 (20.9 microg protein/ml) from polychlorinated biphenyl-treated rats. Norharman inhibited microsomal CYP-related enzyme activities and CO-binding to the CYP heme (50% inhibitory concentration (IC50), 0.07-6.4 microg/ml). It also inhibited the formation of 3-hydroxyamino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (N-OH-Glu-P-1) and was a noncompetitive-inhibitor of CYP1A-related activities, while it enhanced the direct mutagenicity of N-OH-Glu-P-1 (50% effective concentration, 25.0 microg/ml) and inhibited topo I activity (IC50, 31.0 microg/ml). In the presence of norharman, S9 up to 100 microl incrementally enhanced the mutagenicities of HCAs, BP and dimethylnitrosamine. These data clarified that norharman acts as an inhibitor of the CYP-mediated biotransformation of Glu-P-1 via inhibition of O2-binding to CYP heme, and its inhibition of CYP enzymes occurs at much lower concentration than that for its intercalation to DNA. It is indicated that norharman's inhibitory effect on CYP results in the inhibition of excess metabolism by S9 and this is more likely the mechanism for comutagenic action than the intercalation. Norharman's inhibition of CYP and its enhancement of the N-OH-Glu-P-1 mutagenicity suggest that beta-carbolines modulate chemical carcinogenesis by controlling the xenobiotic metabolism and by intercalating to DNA.

Enhancement by cigarette smoke exposure of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline-induced rat hepatocarcinogenesis in close association with elevation of hepatic CYP1A2

The modifying effects of cigarette smoke (CS) exposure on a heterocyclic amine (HCA) 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx)-induced carcinogenesis were investigated in male F344 rats. Groups 1 and 2 were fed MeIQx at a dose of 300 ppm, and simultaneously received CS and sham smoke (SS) for 16 weeks, respectively. Groups 3 - 5 were given the MeIQx diet for 4 weeks, and simultaneously exposed to CS for 4 weeks (group 3), exposed to CS for 12 weeks after the MeIQx treatment (group 4) or received SS for 16 weeks (group 5). Groups 6 and 7 were fed basal diet and respectively received CS and SS for 16 weeks. In terms of the mean number or area, the development of glutathione S-transferase placental form-positive (GST-P(+)) liver cell foci was significantly (P < 0.01) greater in group 1 than in group 2. The mean number of colonic aberrant crypt foci (ACFs) per animal was increased by continuous CS exposure regardless of MeIQx feeding, the differences between groups 4 and 5 (P < 0.05), and between groups 6 and 7 (P < 0.05) being significant. Immunoblot analysis confirmed that the hepatic CYP1A2 level in group 6 was remarkably increased as compared to that in group 7. In addition, liver S9 from rats in group 6 consistently increased the mutagenic activities of six HCAs including MeIQx as compared to those in group 7. Thus, our results clearly indicate that CS enhances hepatocarcinogenesis when given in the initiation phase via increasing intensity of metabolic activation for MeIQx and possibly colon carcinogenesis when given in the post-initiation phase in rats induced by MeIQx.

Effect of cigarette smoke on the mutagenic activation of environmental carcinogens by rodent liver

In order to assess the effect of cigarette smoke (CS) on metabolic enzymes, male hamsters and rats were exposed for two weeks to smoke produced in a Hamburg type II smoking machine. The livers were then used for Ames liquid incubation and western immunoblot assays. Mutagenic activities of seven heterocyclic amines (HCAs) in Salmonella typhimurium TA98 in the presence of rat or hamster liver S9 were elevated up to 3.7 times above controls (including sham smoke control). Enhancement of mutagenic activities of PhIP and aflatoxin B(1) was observed only in CS-exposed hamster, whereas no significant alteration of mutagenicity was observed with 2-aminofluorene, benzo[a]pyrene, and 3'-hydroxymethyl-N, N-dimethyl-4-aminoazobenzene in strain TA98 or with six N-nitrosodialkylamines in strain TA100. 7,8-Benzoflavone and/or furafylline considerably inhibited the mutagenic activation of IQ and Trp-P-1 in the presence of liver S9 from untreated hamsters and sham smoke- or CS-exposed hamsters and rats, indicating the predominant involvement of hamster cytochrome P450 (CYP) 1A enzymes in the metabolic activation of HCAs. In addition, the data suggest that CS-exposure may selectively induce hepatic CYP1A1/1A2 isoforms. Western immunoblot analyses of liver microsomes using anti-rat CYP antibodies revealed that CS-exposure increased the levels of hamster CYP1A2 (3.9-fold) and rat CYP1A2 (3.0-fold) and CYP1A1, without significant change in the levels of CYP2E1 and CYP2B and 3A isoforms in each species. The presently observed selective induction of HCA activation and CYP isozymes due to CS supports the idea that CS may contribute to enhancing effects on initiation by carcinogens which are metabolically activated by hepatic CYP1A1/1A2. In conjunction with results observed for smokers, the present findings indicate that the hamster is a good animal for studies with CS, and that cigarette smoking in combination with intake of heating protein-rich foods as a life style may markedly contribute to the human carcinogenesis by HCAs.