Thomas Albert Perfetti

IARC carcinogens reported in cigarette mainstream smoke and their calculated log P values.

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 International Agency for Research on Cancer (IARC) has classified a number of the chemical constituents reported in cigarette mainstream smoke (MS) as carcinogens. Previously, we published a series of historical reviews reporting that 11 IARC Group 1 (known human), nine Group 2A (probable human) and 48 Group 2B (possible human) carcinogens have been observed in MS. Here, we expand the list of IARC classified carcinogens from 68 to 81 compounds (11 Group 1, 14 Group 2A and 56 Group 2B) reported in MS. A number of the IARC compounds reported in MS are found in the vapor phase including three Group 1, eight Group 2A and 18 Group 2B constituents. Several IARC MS compounds are found in both the vapor and particulate phases including two in Group 1, one in Group 2A and one in Group 2B. Forty-eight IARC MS carcinogens are found in the particulate phase only. Lipophilicity, as determined by the base 10 logarithm of the calculated octanol-water partition coefficient and denoted as Clog P, is reported for each of the 71 non-metallic MS IARC carcinogens. Clog P correlates with a number of biological activities including in vitro mutagenicity and carcinogenicity in rodents, and in the absence of any additional toxicological or epidemiological data, a high log P compound is more likely to be carcinogenic than a low log P compound.

Perspectives on Pulmonary Inflammation and Lung Cancer Risk in Cigarette Smokers

Cigarette mainstream smoke (MSS) inhaled by smokers is a complex aerosol composed of minute liquid droplets suspended within a mixture of combustion gases (CO, CO2, NOx, etc.) and semivolatile compounds. The minute liquid droplets represent the particulate or “tar” phase, while the combustion gases and semivolatiles comprise the vapor phase. For historical and technical reasons, the vast majority of studies on the carcinogenicity of MSS have focused on the particulate phase. The particulate phase is mutagenic and cytotoxic in vitro, proinflammatory, and promotes tumor formation in animal models. In addition to cytotoxic compounds found in the particulate phase, the vapor phase of MSS contains a number of cytotoxic constituents including reactive aldehydes and carbonyls capable of damaging cells and inducing pulmonary inflammation. A large body of evidence suggests that smoking-induced pulmonary inflammation may play an important role in increasing lung cancer risk in smokers. Use of aspirin and nonsteroidal anti-inflammatory drugs is associated with reduced cancer development in animal models and lower lung cancer rates in smokers. A number of benign nonpulmonary and pulmonary diseases characterized by chronic inflammation increase the risk of cancer at the affected site in the absence of chemical exposure. Animal models displaying tumorigenic responses following exposure to either whole smoke or smoke fractions show elevated rates of cellular proliferation. A relationship between pulmonary inflammation and lung cancer is mechanistically plausible because inflammatory cells secrete activated oxygen species, inflammatory mediators, and proteolytic enzymes that can both damage DNA and lead to increases in reparative cell proliferation rates.

Effect of pyrolysis temperature on the mutagenicity of tobacco smoke condensate.

Tobacco smoke aerosols with fewer mutagens in the particulate fraction may present reduced risk to the smoker. The objective of this study was to test the hypothesis that the temperature at which tobacco is pyrolyzed or combusted can affect the mutagenicity of the particulate fraction of the smoke aerosol. Tobacco smoke aerosol was generated under precisely controlled temperature conditions from 250 to 550 degrees C by heating compressed tobacco tablets in air. The tobacco aerosols generated had a cigarette smoke-like appearance and aroma. The tobacco smoke aerosol was passed through a Cambridge filter pad to collect the particulate fraction, termed the smoke condensate. Although condensates of tobacco smoke and whole cigarette mainstream smoke share many of the same chemical components, there are physical and chemical differences between the two complex mixtures. The condensates from smoke aerosols prepared at different temperatures were assayed in the Ames Salmonella microsome test with metabolic activation by rat liver S9 using tester strains TA98 and TA100. Tobacco smoke condensates were not detectably mutagenic in strain TA98 when the tobacco smoke aerosol was generated at temperatures below 400 degrees C. Above 400 degrees C, condensates were mutagenic in strain TA98. Similarly, condensates prepared from tobacco smoke aerosols generated at temperatures below 475 degrees C were not detectably mutagenic in strain TA100. In contrast, tobacco tablets heated to temperatures of 475 degrees C or greater generated smoke aerosol that was detectably mutagenic as measured in TA100. Therefore, heating and pyrolyzing tobacco at temperatures below those found in tobacco burning cigarettes reduces the mutagenicity of the smoke condensate. Highly mutagenic heterocyclic amines derived from the pyrolysis of tobacco leaf protein may be important contributors to the high temperature production of tobacco smoke Ames Salmonella mutagens. The relevance of these findings regarding cancer risk in humans is difficult to assess because of the lack of a direct correlation between mutagenicity in the Ames Salmonella test and carcinogenicity.

The composition of cigarette smoke : A catalogue of the polycyclic aromatic hydrocarbons

Abstract Classified as toxicants in many of the substances to which humans are exposed are the polycyclic aromatic hydrocarbons (PAHs). Such exposures include air pollutants from a variety of sources, foodstuffs and beverages, and tobacco smoke. Since the early 1950s, the composition of the latter has been more completely defined than that of any other consumer product. Nearly 4800 components have been identified in tobacco smoke and among these are over 500 PAHs either completely or partially identified. Because of the tumorigenicity of many PAHs, much research has been conducted in attempts to define the relationship between the PAH structures and their specific tumorigenicities in laboratory animals. None of the theories to date completely answers all the questions. As a prelude to an attempt to develop a more reasonable PAH structure-tumorigenicity relationship, the PAHs completely or partially identified in cigarette smoke have been catalogued. In the catalogue, they are categorized as bicyclic, tricyclic, tetracyclic, etc. with each group subdivided into all-benzenoid PAHs and cyclopentanoid-benzenoid PAHs. Another tabulation includes the PAHs considered in several previous studies on structure-tumorigenicity relationships, studies that dealt primarily with all-benzenoid PAHs.

Percutaneous penetration enhancers in cigarette mainstream smoke

Percutaneous penetration enhancers (PPEs) are chemicals used to enhance the transdermal delivery of drugs. Fifty-eight of the approximately 150 PPEs used for the transdermal delivery of drugs have been reported in cigarette mainstream smoke (MS). MS 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 many of the semi-volatiles are termed the vapor phase. Twenty-nine of the 58 PPEs have been identified in MS vapor phase, 15 in the particulate phase and 14 in both the vapor and particulate phases. There is a tendency for MS PPEs to be hydrophobic, with 40 of the 58 compounds (69%) being either hydrophobic or strongly hydrophobic, and only 24% being hydrophilic. Many of the 4800 known constituents of MS are hydrophilic and would not be expected to readily cross cell membranes or penetrate tissue when delivered as single compounds. The in vivo effect on biological activity of the juxtaposition within the cigarette smoke aerosol of the large number of hydrophilic constituents with the 58 PPEs is currently unknown. As an initial step in understanding this potential complex interaction, the 58 PPEs in MS have been identified and a number of molecular parameters related to the ability to penetrate tissue have been calculated, including MS concentration, measured and calculated base ten logarithm of the octanol-water partition coefficient (Mlog P and Clog P), molecular volume (MgVol) and calculated molar refractivity (CMR).

The Chemical Components Identified in Tobacco and Tobacco Smoke Prior to 1954: A Chronology of Classical Chemistry

Abstract Because of the excellent fractionation and identification technologies developed during the early-1950s, the compositions of tobacco and tobacco smoke, both classified as highly complex mixtures, have been defined more completely than the composition of any other highly complex commercial product such as coffee. By year-end 1953, the many years of research by scientists using classical chemical techniques to define the composition of tobacco and its smoke provided meaningful information on the nature of over 300 tobacco components and fewer than 100 tobacco smoke components. Those involved in the pre-1954 research not only provided the cornerstone of our knowledge of the two compositions but also deserve the gratitude of their successors for the early information generated on tobacco and its smoke. This article is our tribute to those researchers who generated much meaningful knowledge on the composition of tobacco and tobacco smoke prior to 1954 despite the now known fractionation and analytical limitations of the so-called classical chemical techniques. It also notes the similarity of some of the early and more recent research results obtained on the chemical and biological properties of smoke condensate and several of its components from tobacco with those obtained by Roffo in the 1930s on a destructive distillate of tobacco.

The Composition of Cigarette Smoke: A Chronology of the Studies of Four Polycyclic Aromatic Hydrocarbons*

Abstract Among the polycyclic aromatic hydrocarbons (PAHs), a major class of identified cigarette mainstream smoke (MSS) components, are several shown to be tumorigenic in laboratory animals and suspect as possible tumorigens to humans. To date, nearly 540 PAHs have been completely or partially identified in tobacco smoke [Rodgman and Perfetti (1)]. A detailed chronology is presented of studies on four much discussed PAHs identified in tobacco smoke, namely, benz[a]anthracene (B[a]A), its 7,12-dimethyl derivative (DMB[a]A), dibenz[a, h]anthracene (DB[a, h]A), and benzo[a]pyrene (B[a]P). Of the four, DMB[a]A, DB[a, h]A, and B[a]P are considered to be potently tumorigenic on mouse skin painting and subcutaneous injection. Opinions on the tumorigenicity of B[a]A to mouse skin vary. DMB[a]A is frequently used in tumorigenicity studies as an initiator. Examination of the number of tobacco smoke-related citations listed for these four PAHs reveals the enormous effort devoted since the early 1950s to B[a]P vs. the other three. An annotated chronology from 1886 to date describes the tobacco smoke-related research pertinent to these four PAHs, their discovery, isolation and/or identification, quantitation, and contribution to the observed biological activity of MSS or cigarette smoke condensate (CSC). Much of the major literature on these four PAHs in tobacco smoke is presented in order to permit the reader to decide whether the current evidence is sufficient to classify them as a health risk to smokers. There has certainly been a tremendous effort by researchers to learn about these PAHs over the past several decades. Each of these PAHs when tested individually has been shown to possess the following biological properties: 1) Mutagenicity in certain bacterial situations, 2) tumorigenicity in certain animal species, to varying degrees under various administration modes, and 3) a threshold limit below which no tumorigenesis occurs. For more than five decades, it has been known that some of the PAHs, when co-administered in pairs of a potent tumorigen plus a non-tumorigen or weak tumorigen, show inhibitory effects on the tumorigenicity of the most potent, e.g., B[a]A plus DB[a, h]A; B[a]A plus B[a]P; anthracene plus DB[a, h]A. Over the period studied, some regulatory agencies considered these tobacco smoke PAHs to be serious health concerns, others did not. With respect to cigarette MSS, certainly the ‘danger is in the dose’ for any MSS component tested singularly to be tumorigenic. But is the level of any of these MSS PAHs high enough to be of concern to smokers? The information herein presented indicates that over the last five decades the following has occurred: 1) The per cigarette yields of these four PAHs have decreased substantially, 2) compared to CSC or Federal Trade Commission (FTC) ‘tar’, their per cigarette yields have also decreased to a point that they may be below any significance biologically, and 3) the specific tumorigenicity in mouse skin-painting studies of the CSC has decreased. These are the three criteria originally proposed to define the ‘less hazardous’ cigarette. Actually, criterion 1) was first directed only at B[a]P. Previous studies highlighted the concern that some regulatory bodies had in attempting to understand why lung cancer and other forms of cancer seemed more prevalent in smokers. But cigarette smoking alone could not reconcile the evidence. Social, ethnic, environmental, and economic factors are also very important in understanding the entire biological effect. In fact, the level of B[a]P in CSC could only explain about 2% of its specific tumorigenicity observed in skin-painted mice and the combination of the levels of all the known tumorigenic PAHs in CSC could only explain about 3% of its tumorigenicity. Despite an 18-month study in the late 1950s, the search for a ‘supercarcinogen’ in MSS and CSC to explain the observed biological effects was unsuccessful. In addition, the exceptional study on MSS PAHs by United States Department of Agriculture (USDA) personnel in the 1970s indicated no ‘supercarcinogen’ was present. Only recently has the concept of complex mixtures in relation to the understanding of the complexity of carcinogenesis taken hold. Perhaps the reason why MSS is less tumorigenic than expected in humans is because of the presence of other MSS components that inhibit or prevent tumorigenesis. For example, it is well known that MSS contains numerous anticarcinogens present in quantities significantly greater than those of the PAHs of concern. When one reviews the history of these four PAHs in MSS or CSC it is clear that many unanswered questions remain.

Improving the ACGIH threshold limit value (TLV) process

The intent of this manuscript is to elucidate needed improvements in American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) deliberations. More broadly, irreproducibility and bias adversely impact the collection, interpretation, statistical analysis, presentation, and reporting of results in many fields. In 2012, Begley and Ellis reported that scientists at Amgen had attempted to confirm published findings related to research topics of possible interest to Amgen. Fifty-three papers were deemed “landmark” studies. The authors were “shocked” when scientific findings were confirmed in only 6 (11%) cases. Many studies have confirmed that the peer-reviewed literature in biomedicine is in the midst of an irreproducibility crisis. Compounding the irreproducibility crisis is the existence of a significant bias against the publication of negative results. In the toxicology setting, negative toxicity test results are infrequently published as compared with reports that a chemical possesses a particular toxicity in a given test. Despite these deficiencies, the ACGIH states that “…the TLV®-CS Committee preferably relies on published, peer reviewed literature available in the public domain.” The primarily academic studies published in the peer-reviewed literature upon which ACGIH relies to determine TLVs rarely report raw data not already statistically transformed that are thus incalculable. In contrast, consideration of unpublished studies funded by industry, the vast majority of which are good laboratory practice-conducted contract lab studies, is only acceptable to ACGIH if the data owner provides the raw data to third parties upon request. This asymmetry in both the source of data emphasized, and inability to independently statistically analyze findings reported in the published academic literature, introduces a strong skew toward reliance on unverifiable although published measurements in the TLV process. Since Occupational Safety and Health Administration (OSHA) recommends that workplaces rely on ACGIH TLVs and National Institute for Occupational Safety and Health recommended exposure limits rather than older OSHA permissible exposure limit values to optimize worker safety, ACGIH should adopt a more transparent and science-based process.

Comparison of carcinogenicity predictions by the Oncologic expert system with NTP 2-year rodent study tumorigenicity results

The degree of correlation between tumors predicted by OncoLogic™ (Oncologic) and the actual formation of tumors as observed in the National Toxicology Program (NTP) 2-year rodent studies is lower for “justification reports” that incorporate historical data than for “data reports” that do not. The correlation between the ordinal ranking of the observed carcinogenicity of parent NTP chemicals and the predicted “level of carcinogenicity concern” from the justification reports obtained from Oncologic is poor (r = 0.56). Similarly, the correlation between the ordinal ranking of the carcinogenicity of metabolites from parent NTP chemicals and the predicted “level of carcinogenicity concern” from the justification report obtained from Oncologic is also poor (r = 0.43). In contrast, the correlation between the ordinal ranking of the observed carcinogenicity of parent NTP chemicals and the predicted level of carcinogenicity concern from the data reports obtained from Oncologic is comparatively better (r = 0.75). The correlation between the ordinal ranking of the carcinogenicity of metabolites from parent NTP chemicals and the predicted “level of carcinogenicity concern” from the data reports generated from Oncologic is also comparatively good (r = 0.68). The level of correlation between the ordinal tumorigenicity ranks of parent chemicals and between the ordinal tumorigenicity ranks of chemicals reported to induce liver tumors in the National Center for Toxicological Research liver cancer database was also investigated. There was a higher degree of correlation seen for Oncologic “data reports” as compared with Oncologic “justification reports.” Incorporation of additional information via “justification reports” weakens the predictive power of Oncologic.

Tumor site concordance and genetic toxicology test correlations in NTP 2-year gavage, drinking water, dermal, and intraperitoneal injection studies:

The National Toxicology Program has conducted 594, 2-year studies exposing various strains of rats and mice via different routes of exposure. In the current study, we analyze the results from 108 chemicals tested in 106, 2-year studies conducted by exposing F334/N rats and B6C3F1 mice via gavage. An additional 18, 2-year gavage studies have been conducted in Osborne–Mendel rats and B6C3F1 mice on 19 different chemicals. We analyze the results from 23 chemicals tested in 21, 2-year studies conducted by exposing F334/N rats and B6C3F1 mice via drinking water; 18 chemicals tested in 18, 2-year studies conducted by exposing F334/N rats and B6C3F1 mice via dermal application; and 11 chemicals tested in 11, 2-year studies conducted by exposing F334/N rats and B6C3F1 mice via intraperitoneal injection. The results from these 174 studies are analyzed and discussed separately. The neoplasticity of each chemical was analyzed for tumor incidence by species–sex category, tumor site concordance across species, and tumor site concordance across sex within species. When available the Ames Salmonella mutagenicity assay results, and any results from a test for genotoxicity other than the Ames test, were correlated with the neoplasticity results. Tumor site concordance across sex within species is generally higher than tumor site concordance across species. In addition, the high degree of variability of Ames test results suggests that historical Ames test data are less reliable than recent results conducted under good laboratory practices and employing Organization for Economic Cooperation and Development protocols relevant to the physicochemical characteristics of the test chemical.