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Abstract
BACKGROUND Opinions differ on the relationship between tar level and risk of smoking-related disease. However, except for lung cancer, few reviews have evaluated the epidemiological evidence. Here the relationship of tar level to risk of the four main smoking-related diseases is considered. METHODS Papers comparing risk of lung cancer, COPD, heart disease or stroke in smokers of lower and higher tar yield cigarettes were identified from reviews and searches, relative risk estimates being extracted comparing the lowest and highest tar groups. Meta-analyses investigated heterogeneity by various study characteristics. RESULTS Twenty-six studies were identified, nine of prospective design and 17 case-control. Two studies grouped cigarettes by nicotine rather than tar. Seventeen studies gave results for lung cancer, 16 for heart disease, five for stroke and four for COPD. Preferring relative risks adjusted for daily amount smoked, where adjusted and unadjusted estimates were available, combined estimates for lowest versus highest tar (or nicotine) groups were 0.78 (95% confidence interval 0.70-0.88) for lung cancer, 0.86 (0.81-0.91) for heart disease, 0.77 (0.62-0.95) for stroke and 0.81 (0.65-1.02) for COPD. Lower risks were generally evident in subgroups by publication period, gender, study design, location and extent of confounder adjustment. Estimates were similar preferring data unadjusted for amount smoked or excluding nicotine-based estimates. CONCLUSIONS Despite evidence that smokers substantially compensate for reduced cigarette yields, the results clearly show lower risks in lower tar smokers. Limitations of the evidence are discussed, but seem unlikely to affect this conclusion.
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Affiliation(s)
- Peter N Lee
- a P.N. Lee Statistics and Computing Ltd , Sutton , Surrey , UK
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Lee PN, Fry JS, Hamling JS. Investigation into the risk of ultra-low tar cigarettes and lung cancer. Regul Toxicol Pharmacol 2017; 89:112-117. [DOI: 10.1016/j.yrtph.2017.07.023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Revised: 07/21/2017] [Accepted: 07/23/2017] [Indexed: 01/06/2023]
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Lee PN, Gosney JR. The effect of time changes in diagnosing lung cancer type on its recorded distribution, with particular reference to adenocarcinoma. Regul Toxicol Pharmacol 2016; 81:322-333. [DOI: 10.1016/j.yrtph.2016.09.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Revised: 09/19/2016] [Accepted: 09/20/2016] [Indexed: 02/06/2023]
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4
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Lee PN, Forey BA, Coombs KJ, Lipowicz PJ, Appleton S. Time trends in never smokers in the relative frequency of the different histological types of lung cancer, in particular adenocarcinoma. Regul Toxicol Pharmacol 2016; 74:12-22. [DOI: 10.1016/j.yrtph.2015.11.016] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Revised: 11/12/2015] [Accepted: 11/23/2015] [Indexed: 02/07/2023]
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5
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Fry JS, Lee PN, Forey BA, Coombs KJ. Is the shape of the decline in risk following quitting smoking similar for squamous cell carcinoma and adenocarcinoma of the lung? A quantitative review using the negative exponential model. Regul Toxicol Pharmacol 2015; 72:49-57. [DOI: 10.1016/j.yrtph.2015.02.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 02/12/2015] [Accepted: 02/13/2015] [Indexed: 01/20/2023]
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6
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Scherer G, Lee PN. Smoking behaviour and compensation: A review of the literature with meta-analysis. Regul Toxicol Pharmacol 2014; 70:615-28. [DOI: 10.1016/j.yrtph.2014.09.008] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Revised: 09/15/2014] [Accepted: 09/16/2014] [Indexed: 11/28/2022]
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Lee PN. The effect of reducing the number of cigarettes smoked on risk of lung cancer, COPD, cardiovascular disease and FEV1 – A review. Regul Toxicol Pharmacol 2013; 67:372-81. [DOI: 10.1016/j.yrtph.2013.08.016] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 08/23/2013] [Accepted: 08/26/2013] [Indexed: 01/31/2023]
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Lee PN, Forey BA. Indirectly estimated absolute lung cancer mortality rates by smoking status and histological type based on a systematic review. BMC Cancer 2013; 13:189. [PMID: 23570286 PMCID: PMC3639928 DOI: 10.1186/1471-2407-13-189] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2012] [Accepted: 03/10/2013] [Indexed: 01/30/2023] Open
Abstract
Background National smoking-specific lung cancer mortality rates are unavailable, and studies presenting estimates are limited, particularly by histology. This hinders interpretation. We attempted to rectify this by deriving estimates indirectly, combining data from national rates and epidemiological studies. Methods We estimated study-specific absolute mortality rates and variances by histology and smoking habit (never/ever/current/former) based on relative risk estimates derived from studies published in the 20th century, coupled with WHO mortality data for age 70–74 for the relevant country and period. Studies with populations grossly unrepresentative nationally were excluded. 70–74 was chosen based on analyses of large cohort studies presenting rates by smoking and age. Variations by sex, period and region were assessed by meta-analysis and meta-regression. Results 148 studies provided estimates (Europe 59, America 54, China 22, other Asia 13), 54 providing estimates by histology (squamous cell carcinoma, adenocarcinoma). For all smoking habits and lung cancer types, mortality rates were higher in males, the excess less evident for never smokers. Never smoker rates were clearly highest in China, and showed some increasing time trend, particularly for adenocarcinoma. Ever smoker rates were higher in parts of Europe and America than in China, with the time trend very clear, especially for adenocarcinoma. Variations by time trend and continent were clear for current smokers (rates being higher in Europe and America than Asia), but less clear for former smokers. Models involving continent and trend explained much variability, but non-linearity was sometimes seen (with rates lower in 1991–99 than 1981–90), and there was regional variation within continent (with rates in Europe often high in UK and low in Scandinavia, and higher in North than South America). Conclusions The indirect method may be questioned, because of variations in definition of smoking and lung cancer type in the epidemiological database, changes over time in diagnosis of lung cancer types, lack of national representativeness of some studies, and regional variation in smoking misclassification. However, the results seem consistent with the literature, and provide additional information on variability by time and region, including evidence of a rise in never smoker adenocarcinoma rates relative to squamous cell carcinoma rates.
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Affiliation(s)
- Peter N Lee
- P N Lee Statistics and Computing Ltd, Sutton, Surrey, UK.
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9
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Towards the validation of a lung tumorigenesis model with mainstream cigarette smoke inhalation using the A/J mouse. Toxicology 2013; 305:49-64. [DOI: 10.1016/j.tox.2013.01.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Revised: 01/11/2013] [Accepted: 01/16/2013] [Indexed: 11/17/2022]
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Lee PN, Forey BA, Coombs KJ. Systematic review with meta-analysis of the epidemiological evidence in the 1900s relating smoking to lung cancer. BMC Cancer 2012; 12:385. [PMID: 22943444 PMCID: PMC3505152 DOI: 10.1186/1471-2407-12-385] [Citation(s) in RCA: 180] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Accepted: 07/18/2012] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND Smoking is a known lung cancer cause, but no detailed quantitative systematic review exists. We summarize evidence for various indices. METHODS Papers published before 2000 describing epidemiological studies involving 100+ lung cancer cases were obtained from Medline and other sources. Studies were classified as principal, or subsidiary where cases overlapped with principal studies. Data were extracted on design, exposures, histological types and confounder adjustment. RRs/ORs and 95% CIs were extracted for ever, current and ex smoking of cigarettes, pipes and cigars and indices of cigarette type and dose-response. Meta-analyses and meta-regressions investigated how relationships varied by study and RR characteristics, mainly for outcomes exactly or closely equivalent to all lung cancer, squamous cell carcinoma ("squamous") and adenocarcinoma ("adeno"). RESULTS 287 studies (20 subsidiary) were identified. Although RR estimates were markedly heterogeneous, the meta-analyses demonstrated a relationship of smoking with lung cancer risk, clearly seen for ever smoking (random-effects RR 5.50, CI 5.07-5.96) current smoking (8.43, 7.63-9.31), ex smoking (4.30, 3.93-4.71) and pipe/cigar only smoking (2.92, 2.38-3.57). It was stronger for squamous (current smoking RR 16.91, 13.14-21.76) than adeno (4.21, 3.32-5.34), and evident in both sexes (RRs somewhat higher in males), all continents (RRs highest for North America and lowest for Asia, particularly China), and both study types (RRs higher for prospective studies). Relationships were somewhat stronger in later starting and larger studies. RR estimates were similar in cigarette only and mixed smokers, and similar in smokers of pipes/cigars only, pipes only and cigars only. Exceptionally no increase in adeno risk was seen for pipe/cigar only smokers (0.93, 0.62-1.40). RRs were unrelated to mentholation, and higher for non-filter and handrolled cigarettes. RRs increased with amount smoked, duration, earlier starting age, tar level and fraction smoked and decreased with time quit. Relationships were strongest for small and squamous cell, intermediate for large cell and weakest for adenocarcinoma. Covariate-adjustment little affected RR estimates. CONCLUSIONS The association of lung cancer with smoking is strong, evident for all lung cancer types, dose-related and insensitive to covariate-adjustment. This emphasises the causal nature of the relationship. Our results quantify the relationships more precisely than previously.
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Affiliation(s)
- Peter N Lee
- P N Lee Statistics and Computing Ltd, Sutton, Surrey, United Kingdom
| | - Barbara A Forey
- P N Lee Statistics and Computing Ltd, Sutton, Surrey, United Kingdom
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11
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Schwartz L, Guais A, Chaumet-Riffaud P, Grévillot G, Sasco AJ, Molina TJ, Mohammad A. Carbon dioxide is largely responsible for the acute inflammatory effects of tobacco smoke. Inhal Toxicol 2011; 22:543-51. [PMID: 20387988 DOI: 10.3109/08958370903555909] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Tobacco smoking is responsible for a vast array of diseases, particularly chronic bronchitis and lung cancer. It is still unclear which constituent(s) of the smoke is responsible for its toxicity. The authors decided to focus on carbon dioxide, since its level of concentration in mainstream cigarette smoke is about 200 times higher than in the atmosphere. The authors previously demonstrated that inhalation of carbon dioxide concentrations above 5% has a deleterious effect on lungs. In this study, the authors assessed the inflammatory potential of carbon dioxide contained in cigarette smoke. Mice were exposed to cigarette smoke containing a high or reduced CO(2) level by filtration through a potassium hydroxyde solution. The inflammatory response was evaluated by histological analysis, protein phosphatase 2 A (PP2A) and nuclear factor (NF)-kappaB activation, and proinflammatory cytokine secretion measurements. The data show that the toxicity of cigarette smoke may be largely due to its high level of CO(2). Pulmonary injuries consequent to tobacco smoke inhalation observed by histology were greatly diminished when CO(2) was removed. Cigarette smoke exposure causes an inflammatory response characterized by PP2A and NF-kappaB activation followed by proinflammatory cytokine secretion. This inflammatory response was reduced when the cigarette smoke was filtered through a potassium hydroxide column, and reestablished when CO(2) was injected downstream from the filtration column.Given that there is an extensive literature linking a chronic inflammatory response to the major smoking-related diseases, these data suggest that carbon dioxide may play a key role in the causation of these diseases by tobacco smoking.
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Affiliation(s)
- Laurent Schwartz
- Service de Radiothérapie, AP-HP Hôpital Pitié-Salpétrière, boulevard de l'Hôpital, Paris, France.
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Hatsukami DK, Hanson K, Briggs A, Parascandola M, Genkinger JM, O'Connor R, Shields PG. Clinical trials methods for evaluation of potential reduced exposure products. Cancer Epidemiol Biomarkers Prev 2009; 18:3143-95. [PMID: 19959672 PMCID: PMC2799338 DOI: 10.1158/1055-9965.epi-09-0654] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Potential reduced exposure products (PREPs) to tobacco toxicants may have promise in reducing tobacco-related morbidity or mortality or may promote greater harm to individuals or the population. Critical to determining the risks or benefits from these products are valid human clinical trial PREP assessment methods. Such an assessment involves determining the effects of these products on biomarkers of exposure and effect, which serve as proxies for harm, and assessing the potential for consumer uptake and abuse of the product. This article identifies critical methodologic issues associated with PREP assessments, reviews the methods that have been used to assess PREPs, and describes the strengths and limitations of these methods. Additionally, recommendations are provided for clinical trial PREP assessment methods and future research directions in this area based on this review and on the deliberations from a National Cancer Institute sponsored Clinical Trials PREP Methods Workshop.
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Affiliation(s)
- Dorothy K Hatsukami
- University of Minnesota Tobacco Use Research Center, Minneapolis, 55414, USA.
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Yoon SH, Paek YJ, Yoo SH, Cho JJ, Song HJ, Park KH, Chang HM, Ban JH. Relationship between Brand Nicotine Yield of Cigarettes and Urine Cotinine Level in Male Smokers. Korean J Fam Med 2009. [DOI: 10.4082/kjfm.2009.30.9.703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Affiliation(s)
- Sang Ho Yoon
- Department of Family Medicine, Hallym University College of Medicine, Hallym Sacred Heart Hospital, Anyang, Korea
| | - Yu Jin Paek
- Department of Family Medicine, Hallym University College of Medicine, Hallym Sacred Heart Hospital, Anyang, Korea
| | - Sang Ho Yoo
- Department of Family Medicine, Hallym University College of Medicine, Hallym Sacred Heart Hospital, Anyang, Korea
| | - Jung Jin Cho
- Department of Family Medicine, Hallym University College of Medicine, Hallym Sacred Heart Hospital, Anyang, Korea
| | - Hong Ji Song
- Department of Family Medicine, Hallym University College of Medicine, Hallym Sacred Heart Hospital, Anyang, Korea
| | - Kyung Hee Park
- Department of Family Medicine, Hallym University College of Medicine, Hallym Sacred Heart Hospital, Anyang, Korea
| | - Hye Mi Chang
- Department of Family Medicine, Hallym University College of Medicine, Hallym Sacred Heart Hospital, Anyang, Korea
| | - Jin Hwa Ban
- Department of Family Medicine, Hallym University College of Medicine, Hallym Sacred Heart Hospital, Anyang, Korea
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Peters J, Mengersen K. Selective reporting of adjusted estimates in observational epidemiology studies: reasons and implications for meta-analyses. Eval Health Prof 2008; 31:370-89. [PMID: 19000980 DOI: 10.1177/0163278708324438] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
For meta-analyses of observational epidemiology studies, unadjusted and adjusted study estimates are often extracted. However, there is evidence of selective reporting of adjusted study estimates. We investigate adjustment reporting bias, examining the reasons why some studies do not contribute an adjusted estimate to a meta-analysis. Ten published meta-analyses were re-analysed to assess evidence of adjustment reporting bias and over 100 primary studies were read to investigate why they did not contribute an adjusted estimate to a meta-analysis. Selective reporting of adjusted estimates may lead to a bias in some meta-analyses when adjusted study estimates are not reported because univariate analyses indicated a non-significant effect. We recommend that unadjusted and adjusted study estimates be extracted for a meta-analysis. If adjusted estimates cannot be obtained, the reasons for this should be investigated and sensitivity analyses could be used to assess the impact of this on the meta-analysis.
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Affiliation(s)
- Jaime Peters
- School of Mathematical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane QLD 4001, Australia.
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Zhu K, Moriarty C, Caplan LS, Levine RS. Cigarette smoking and primary liver cancer: a population-based case-control study in US men. Cancer Causes Control 2007; 18:315-21. [PMID: 17294291 DOI: 10.1007/s10552-006-0105-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2006] [Accepted: 12/11/2006] [Indexed: 01/02/2023]
Abstract
OBJECTIVE Using the case-control data from the Selected Cancers Study, the authors assessed whether cigarette smoking increases the risk of primary liver cancer in the US. METHODS Cases were men who were pathologically diagnosed with primary liver cancer during 1984-1988, were 31-59 years old, and lived in the areas covered by eight US cancer registries (n=168). Controls were men without a history of primary liver cancer who were selected by random-digit telephone dialing (n=1910). RESULTS Relative to non-smokers, the risks of liver cancer were 1.85 (95% confidence interval (CI), 1.05-3.25) and 1.49 (95% CI, 0.83-2.68) for former and current smokers, respectively. The adjusted odds ratio (OR) estimates were 0.96, 1.43, 1.80, and 1.87 for smoking for less than 15, 15-24, 25-34 and 35 or more years, respectively (p for trend=0.039). The OR estimates were 1.41 (95% CI, 0.74-2.68), 1.67 (95% CI, 0.93-2.98), and 1.83 (95% CI, 0.89-3.76) for less than 1, 1-2, and 2 or more packs smoked per day (p for trend=0.068). CONCLUSIONS Cigarette smoking may be a factor that contributes somewhat to the occurrence of primary liver cancer among men in the United States, a country with low risk of liver cancer.
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Affiliation(s)
- Kangmin Zhu
- US Military Cancer Institute, Walter Reed Army Medical Center, 6900 Georgia Avenue, NW, Building 1, Suite A-109, Washington, DC 20307-5001, USA.
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Lee PN, Forey BA, Gori GB. Do reductions in the tar and nicotine yields of cigarettes help to explain recent reductions in lung cancer rates in young men and women in the United States? Inhal Toxicol 2006; 18:365-88. [PMID: 16513594 DOI: 10.1080/08958370500516101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Between 1985 and 2000, lung cancer rates in U.S. men and women aged 35-54 yr have declined. To investigate whether these declines can adequately be explained by changes in smoking prevalence, consumption, and duration, or if changes in tar and nicotine yields also contributed, two model-fitting approaches were used. Both approaches used individual person National Health Interview Survey data on smoking prevalence, age of starting and time of quitting, and national estimates of consumption per smoker and yields. Both approaches compared observed rates (by sex and age) relative to 1985, with those predicted after successively including various smoking variables into the model, making varying allowance for compensation for reduced yield. Approach A was simpler, based on mean smoking statistics estimated separately for current and former smokers. Approach B used the multistage model and individual smoking histories to estimate risk. Both approaches showed observed declines in risk were (except for men aged 35-39 yr) clearly greater than predicted based only on prevalence, consumption, and duration. Including yield generally improved the fit. At younger ages, models assuming substantial compensation (consistent with evidence from studies relating nicotine yield and intake) fitted well, but at age 50-54 yr in both sexes and age 45-49 yr in women, the decline was better fitted by models assuming little compensation. The conclusions were not sensitive to the precise parameter values assumed in the modeling. Interpretation is not straightforward, but the findings suggest declines in yields have contributed to the recent declines in rates in young U.S. men and women.
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Affiliation(s)
- Peter N Lee
- P. N. Lee Statistics and Computing Ltd, Sutton, Surrey, United Kingdom.
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Sassen AW, Richter E, Semmler MP, Harréus UA, Gamarra F, Kleinsasser NH. Genotoxicity of nicotine in mini-organ cultures of human upper aerodigestive tract epithelia. Toxicol Sci 2005; 88:134-41. [PMID: 16120750 DOI: 10.1093/toxsci/kfi297] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The direct role of nicotine in tobacco carcinogenesis is still controversial. Recently, DNA damage by nicotine has been demonstrated in isolated human tonsillar tissue cells. Presently, these effects were investigated using mini-organ cultures (MOC) of human nasal epithelia. Intact MOC were repeatedly exposed to 2 and 4 mM nicotine for 1 h on culture days 7, 9, and 11. N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG) served as a positive control. DNA damage was examined by Comet assay either directly after exposure or following a 24-h recovery period. Cell viability was not reduced by any treatment. On day 7, 1 h exposure to 2 and 4 mM nicotine caused a significant dose-dependent 3.3- and 5.6-fold increase in DNA damage compared to solvent controls. Although there was no evidence of significant repair within 24 h recovery, DNA damage was not further increased by nicotine on days 9 and 11. After double and triple exposure to 4 mM nicotine a significant reduction in DNA damage following 24 h recovery was observed. In contrast, treatment with MNNG resulted in a highly significant and cumulative increase in DNA migration up to 110-fold compared to controls. During recovery periods, MNNG-induced DNA damage was significantly repaired, leading to a 1.5- to 1.8-fold reduction in DNA migration within 24 h. These results confirm genotoxic effects of nicotine on human nasal epithelia. Further studies are needed to explain the lack of cumulative DNA-damaging effects of nicotine and the absence of significant DNA repair. These studies should include a battery of assays with multiple end points.
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Affiliation(s)
- Andrea W Sassen
- Otolaryngology-Head and Neck Surgery, University of Regensburg, Germany
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Kleinsasser NH, Sassen AW, Semmler MP, Harréus UA, Licht AK, Richter E. The tobacco alkaloid nicotine demonstrates genotoxicity in human tonsillar tissue and lymphocytes. Toxicol Sci 2005; 86:309-17. [PMID: 15858221 DOI: 10.1093/toxsci/kfi186] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Recent studies suggest a direct contribution of nicotine, the addictive component of tobacco and tobacco smoke, to human carcinogenesis. To assess the genotoxicity of nicotine, the DNA-damaging effect on human lymphocytes and target cells from lymphatic tissue of the palatine tonsils from 10 healthy patients was tested with the alkaline single-cell microgel electrophoresis (Comet) assay. The degree of DNA migration, a measure of possible DNA single strand breaks, alkali labile sites, and incomplete excision repair sites, was expressed as the Olive tail moment, the percentage of DNA in the tail, and the tail length. One hour exposure to nicotine at 0.125, 0.25, 0.5, 1, 2, and 4 mM induced a statistically significant dose-dependent increase of DNA migration up to 3.8-fold and 3.2-fold in tonsillar cells and lymphocytes, respectively. The lowest concentration eliciting significant DNA damage was 0.5 mM nicotine. The genotoxic effect was confirmed in a second series of experiments using nicotine of high purity from two different suppliers. There were no significant differences between the two series, excluding artifacts from the source of nicotine. Finally, DNA damage by nicotine was compared in cells incubated in medium strictly adjusted to neutral pH, with non-adjusted medium becoming alkaline with increasing nicotine concentrations. Again no differences in DNA migration were observed. The data indicate that nicotine expresses significant direct genotoxic effects in human target cells in vitro. However, no differences in DNA damage were observed in cells from smokers and nonsmokers incubated without nicotine. The lack of higher DNA damage in smokers compared to nonsmokers could be a question of nicotine dose, rapid DNA repair, or interactions with other smoke constituents. These results require further investigations on the contribution of nicotine to tobacco carcinogenesis.
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Affiliation(s)
- Norbert H Kleinsasser
- Department of Otolaryngology-Head and Neck Surgery, University of Regensburg, D-93053 Regensburg, Germany.
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