Tobacco-specific nitrosamines, an important group of carcinogens in tobacco and tobacco smoke

Tobacco-specific nitrosamines are a group of carcinogens that are present in tobacco and tobacco smoke. They are formed from nicotine and related tobacco alkaloids. Two of the nicotine-derived nitrosamines, NNK and NNN, are strong carcinogens in laboratory animals. They can induce tumors both locally and systemically. The induction of oral cavity tumors by a mixture of NNK and NNN, and the organospecificity of NNK for the lung are particularly noteworthy. The amounts of NNK and NNN in tobacco and tobacco smoke are high enough that their total estimated doses to long-term snuff-dippers or smokers are similar in magnitude to the total doses required to produce cancer in laboratory animals. These exposures thus represent an unacceptable risk to tobacco consumers, and possibly to non-smokers exposed for years to environmental tobacco smoke. The permission of such high levels of carcinogens in consumer products used by millions of people represents a major legislative failure. Indeed, the levels of tobacco-specific nitrosamines in tobacco are thousands of times higher than the amounts of other nitrosamines in consumer products that are regulated by government authorities. Although the role of tobacco-specific nitrosamines as causative factors in tobacco-related human cancers cannot be assessed with certainty because of the complexity of tobacco and tobacco smoke, several lines of evidence strongly indicate that they have a major role, especially in the causation of oral cancer in snuff-dippers. Epidemiologic studies have demonstrated that snuff-dipping causes oral cancer. NNK and NNN are quantitatively the most prevalent known carcinogens in snuff, and they induce oral tumors when applied to the rat oral cavity. A role for NNK in the induction of lung cancer by tobacco smoke is likely because of its organospecificity for the lung. Tobacco-specific nitrosamines may also be involved in the etiology of tobacco-related cancers of the esophagus, nasal cavity, and pancreas. Because they are derived from nicotine, and therefore should be associated only with tobacco, tobacco smoke and other nicotine-containing products, tobacco-specific nitrosamines as well as their metabolites and macromolecular adducts should be ideal markers for assessing human exposure to, and metabolic activation of, tobacco smoke carcinogens. Ongoing research has demonstrated the formation of globin and DNA adducts of NNK and NNN in experimental animals. Sensitive methods for the detection and quantitation of these adducts in humans would provide an approach to assessing individual risk for tobacco-related cancers.(ABSTRACT TRUNCATED AT 400 WORDS)

Screening of tobacco smoke constituents for mutagenicity using the Ames' test

To clarify the mutagenic activity of individual smoke components, 239 compounds, representative of the gaseous and semivolatile phases of tobacco smoke, were assayed for mutagenicity towards 4 histidine-requiring mutants of Salmonella typhimurium (TA 98, TA 100, TA 1535 and TA 1537). All compounds were tested qualitatively both with and without metabolic activation using a liver fraction (S-9) from Aroclor 1254 or methylcholanthrene induced rats. Without S-9, only 2,3-dimethylindole and 2,3,5-trimethylindole showed mutagenic activity that was not enhanced by the metabolic activation system. 2,6-Diaminotoluene and coronene, which like the above compounds are not documented carcinogens were found to be mutagenic for strain TA 98 with S-9. Mutagenic activity was also observed for the previously known mutagens benz[a]pyrene, chrysene, benz[a]-anthracene, perylene and beta-naphthylamine, on exposure to strains TA 98 and/or TA 100 with S-9.

Relation of nicotine yield of cigarettes to blood nicotine concentrations in smokers

Blood nicotine and carboxyhaemoglobin (COHb) concentrations were studied in 330 smokers (206 women and 124 men). Blood nicotine concentrations in individual smokers varied from 25 to 444 nmol/l (4 to 72 ng/ml). The average concentration, 203 nmol/l (33 ng/ml), was the same in the men and the women, although cigarette consumption was higher in the men. Despite large differences in nicotine yield, there was no relation between blood nicotine concentration and the type of cigarette smoked: smokers of plain, untipped cigarettes (1.9 mg nicotine), cigarettes with unventilated filters (1.3 mg nicotine), and cigarettes with ventilated filters (0.8 mg nicotine) had similar blood nicotine concentrations. Cigarette consumption was also similar in these three groups. The correlation between blood nicotine concentration and nicotine yield of cigarette, though significant, was low (0.21, p < 0.001), showing that the nicotine yield of the cigarettes accounted for only 4.4% of the variation in blood nicotine concentrations. Similarly, the low correlation of 0.30 between COHb concentration and cigarette consumption suggests that cigarette consumption accounted for only 9% of the variation in the amount of smoke taken into the smokers' lungs. These results suggest that the assumed health advantage of switching to lower-tar and lower-nicotine cigarettes may be largely offset by the tendency of smokers to compensate by increasing inhalation. The findings of epidemiological studies showing lower risks with filter-tipped cigarettes may be attributable to other factors such as biases in the samples and changes in the quality and carcinogenicity of tobacco tar, rather than to reduced tar intake.

Smokers of low-yield cigarettes do not consume less nicotine

Advertisements suggest that smokers of cigarettes low in nicotine are exposed to less nicotine and tar. Nicotine yields are measured with smoking machines, but machines do not smoke cigarettes as people do. We therefore measured the actual nicotine content of commercial cigarettes with different nicotine and tar yields as determined with smoking machines, and also measured actual nicotine intake as indicated by blood concentrations of its metabolite, cotinine, in 272 subjects smoking various brands of cigarettes. We found that low-yield cigarette tobacco did not contain less nicotine; in fact, the nicotine concentration in tobacco inversely correlated (r = -0.53, P less than 0.05) with the concentration measured by smoking machines. Blood cotinine concentrations correlated with the number of cigarettes smoked per day but not with the nicotine yield measured by smoking machines. Only 3.8 to 5.0 per cent of total variance in blood cotinine was contributed by nicotine yield. We conclude that smokers of low-nicotine cigarettes do not consume less nicotine.

Expired air carbon monoxide and serum thiocyanate as objective measures of cigarette exposure

Expired air carbon monoxide (CO) and serum thiocyanate (SCN) were used to asses exposure to cigarettes in 139 middle-aged men. Subjects who reported smoking cigarettes generally had CO levels exceeding 8ppm and SCN levels exceeding 100umol/L; non-smokers had lower levels. For both tests the mean concentration among men smoking more than one pack daily was three times that of non-smokers. The is a high correlation between the two tests (r=.571 for smokers), an association that was largely independent of the smaller correlations between either test and reported smoking frequency (r=.476 for CO; r=.479 for SCN). The ability to distinguish between individuals who reported "typical" smoking habits and non-smokers was best when the CO and SCN analyses were used together to take advantage of their separate sources of variance; it was 99 per cent when the two tests were mutually concordant (91 per cent of cases). The CO and SCN measurements allowed 16 individuals who reported light smoking habits to be categorized into high and low presumptive tobacco exposure groups. The two tests are inexpensive and suitable for use in epidemiologic and health care delivery programs.

Ethyl carbamate: analytical methodology, occurrence, formation, biological activity and risk assessment

Ethyl carbamate (EC) is a genotoxic compound in vitro and in vivo, it binds covalently to DNA and is an animal carcinogen. Today, EC is mainly found as a natural trace constituent in different alcoholic beverages and in fermented food items. Data on analytical methodology and the levels of EC in different food items are summarized and the daily burden of humans is estimated. Under normal dietary habits excluding alcoholic beverages, the unavoidable daily intake is 10-20 ng/kg b.w. On the basis of the evaluation of all toxicity data and its mode of action a conventional risk assessment of EC indicates that this level represents a negligible lifetime cancer risk (less than 0.0001%). Individual habits may greatly enhance the risk. Regular drinking of table wine (500 ml/day) would increase the risk up to 5 times, regular drinking of stone-fruit distillates (20-40 ml/day) would raise the calculated hypothetical tumor risk to near 0.01%. Human exposure to carcinogenic compounds should be as low as reasonably achievable. In order to take reliable measures to reduce EC levels in beverages and foods, it is crucial to know the mode of its formation. For its natural formation the presence of ethanol is absolutely required. In stone-fruit distillates hydrogen cyanide together with photochemically active substances are crucial to form EC. The main part of EC is formed after the distillation involving photochemical reactions. In wine (and probably bread) significant EC formation seems to depend on heat treatment. While in distillates hydrogen cyanide is the most important single precursor, in wine different carbamyl compounds, mainly urea, seem to be involved in EC formation. Despite this apparent difference a common EC formation pathway is discussed for all alcoholic beverages by assuming cyanic-/isocyanic acid as an important ultimate reactant with ethanol. Some ideas are presented as to the possible course of future work.

Low-tar medium-nicotine cigarettes: a new approach to safer smoking

The logic of expecting people who cannot stop smoking to switch to cigarettes that have hardly any nicotine is questionable. Tar and nicotine yields of cigarettes available in Britain today correlate 0-93, and further reduction of tar intake is limited by the reluctance of smokers to tolerate similar reductions in nicotine. A new approach would be to aim at lowering tar yields of cigarettes from the present average of 18 mg to around 6 mg but maintaining nicotine yields at around 1-0 to 1-2 mg, which would be acceptable to most smokers. This approach requires that emphasis be placed on tar: nicotine ratios as well as on the absolute yields. These ratios for brands on sale in Britain today average 14-2 and range from 9-6 to 20-8. They provide an additional guide for comparing the relative harmfulness of different brands. For example, 35% of cigarette smokers in Britain smoke either Embassy Filter or Players No 6 Filter; by changing to John Player Carlton King Size they could reduce their tar intake by more than 20% without having to suffer any nicotine deprivation.

The reemergence of smokeless tobacco

Smokeless tobacco (snuff and chewing tobacco) is reemerging as a popular form of tobacco, particularly among male adolescents. In different regions of the United States, from 8 to 36 percent of male high-school students are regular users. The use of smokeless tobacco has been shown to cause oral-pharyngeal cancer. The strongest link is with cancers of the cheek and gum. White mucosal lesions (leukoplakia) are found in 18 to 64 percent of users, often at the site where the tobacco was held. Other associations have been suggested for cancers of the esophagus, larynx, and pancreas. Nitrosamines, found in high concentrations in smokeless tobacco, most likely have a role in its carcinogenicity. Other health problems include periodontal disease, acute elevations of blood pressure, and dependence. In early 1986, after action at the state level, Congress enacted a federal law requiring health-warning labels on packages of smokeless tobacco and a ban on electronic advertising. Other regulatory measures under consideration include raising state and federal excise taxes, tightening controls on advertising, and prohibiting sales to minors. In view of the recent growth of this problem, policy makers are taking the opportunity to intervene with preventive measures to protect a new generation of tobacco users.

Sequence complexity of nuclear and polysomal RNA in leaves of the tobacco plant

The first measurements are reported of the sequence complexity of nuclear and polysomal RNA contained within the cells of a higher plant. Polysomal RNA from tobacco leaves was prepared by a procedure which minimized contamination with nuclear RNA. Hybridization of 3H-cDNA complementary to polysomal poly(A) RNA with an excess of tobacco DNA indicated that greater than 95% of the poly(A) mRNA was transcribed from single-copy sequences. RNA excess hybridization reactions with polysomal poly(A) RNA and 3H-cDNA revealed the presence of three abundance classes in the poly(A) mRNA. The best least-squares solution indicated that these classes comprise 9, 52, and 39% of the poly (A) mRNA and contain sequences present an average of 4500, 340 and 17 times per cell. Hybridization reactions containing an excess of nuclear or total polysomal RNA and 3H-single-copy DNA indicated the complexity of these RNA populations to be 1.19 X 10(8) nucleotides (nuclear) and 3.33 X 10(7) nucleotides (polysomal). Thus only 28% of the nuclear RNA sequence diversity (27,000 average-sized mRNA sequences) is respresented in leaf polysomes. These results suggest that there is a general similarity in the basic transcriptional processes of metaphytan and metazoan cells.

Quantitative analysis of the hydrogen peroxide formed in aqueous cigarette tar extracts

We have established, for the first time, a reliable method to quantitate hydrogen peroxide (H2O2) generated in aqueous extracts of cigarette smoke tar. The aqueous tar extract was passed through a short reverse-phase column and its H2O2 concentration determined by differential pulse polarography using an automatic reference subtraction system. The H2O2 concentration increased with aging, pH and temperature; the presence of superoxide dismutase lead to lower H2O2 concentrations. This method was applied to many kinds of research and commercial cigarettes. With a few exceptions, the amount of H2O2 formed after a fixed time from each cigarette smoke was proportional to its tar yield.

Puffing frequency and nicotine intake in cigarette smokers

The smoking behaviour of 36 subjects smoking cigarettes with different filter retention efficiencies for nicotine was studied. Subjects were observed while performing various tasks on a driving simulator and also during a resting period after the tasks. Smokers of cigarettes with high-retention filters took more frequent puffs and obtained nearly the same amount of nicotine as smokers of cigarettes with low-retention filters, both while performing the tasks and during the resting period. Smokers of both types of cigarettes took significantly more puffs and obtained more nicotine per unit time during the resting period than during the tasks. The results are compatible with the possibility that smokers automatically adjust the nicotine dose obtained from a cigarette to some "optimum" level which may vary with different activities.

Detection of mutagenic activity in cigarette smoke condensates

The Salmonella typhimurium microsomal test system for mutagenic activity was successfully used to detect the presence of mutagenic compounds in the smoke condensates of several types of cigarettes. The condensates were shown to contain compounds which could cause frameshift mutations when activated by microsomal enzymes. An analysis of fractions of smoke condensate revealed that the detected mutagenic activity was distributed in several of the fractions. Most of the activity of the whole condensate was in basic fractions and in a weakly acidic fraction. Condensates from cigarettes treated with magnesium nitrate differed from other condensates in two respects. They contained frameshift mutagens which did not require microsomal activation and mutagens which could cause base-pair substitution mutations. Although the detection system usually employs rat liver microsomal preparations, a rat lung microsomal preparation was also found to be capable of converting smoke condensates and known chemical carcinogens into mutagenic forms.

Crystalline fraction I protein: preparation in large yield

Abolut 1 milligram of twice-recrystallized fraction I protein of constant specific ribulose diphosphate carboxylase activity per gram of leaves (fresh weight) has been obtained from each of seven different species of Nicotiana and 14 reciprocal, interspecific F(1) hybrids. Crystals are produced from honmogenates that have only been centrifuged to remove particulate matter.

Cadmium exposure from smoking cigarettes: variations with time and country where purchased

Cadmium has been determined in 26 brands of cigarettes purchased in eight different countries throughout the world and in 16 different samples of cigarettes produced in Sweden between 1918 and 1968. In addition the amount of cadmium released from smoking one cigarette to the particulate phase collected from a smoking simulation machine, corresponding to the amount actually inhaled by a smoker, has been determined. The cadmium concentration in different brands of cigarettes ranged from 0.19 to 3.0 micrograms Cd/g dry wt, with a general tendency toward lower values in cigarettes from developing countries. No systematic change in the cadmium concentration of cigarettes with time could be revealed. The amount of cadmium inhaled from smoking one cigarette containing about 1.7 microgram Cd was estimated to be 0.14 to 0.19 microgram, corresponding to about 10% of the total cadmium content in the cigarette.

The effects of the anti-smoking campaign on cigarette consumption

The impact of the anti-smoking campaign on the consumption of cigarettes is measured by fitting cigarette demand functions to pre-campaign dat, projecting "ahead" as if the campaign had not occurred, and then comparing these predictions with realized consumption. The analysis suggests that major "events" in the campaign (e.g., the Surgeon General's Report) caused immediate though transitory decreases of 4 to 5 per cent in annual per capita consumption. However, the cumulative effect of persistent publicity supported by other public policies, has been substantial: in the absence of the campaign, per capita consumption likely would have exceeded its actual 1975 value by 20 to 30 per cent. This is a conservative indication of the effectiveness of the campaign, for it ignores other potentially important and desirable behavior changes, such as the shift to low "tar" and nicotine cigarettes.

Quantum efficiency and antenna size of photosystems II alpha, II beta and I in tobacco chloroplasts

Reaction center concentrations were determined in chloroplasts of tobacco, cv John William's Broadleaf, and its mutants Su/su and Su/su var. Aurea. Quantum yields of the primary reactions of Photosystems I, II alpha and II beta (Melis, A. and Homann, P.H. (1975) Photochem. Photobiol. 21, 431--437) were obtained by measurement of their rate constants and the absorbed energy, under conditions where all three photosystems operated simultaneously and produced almost irreversibly a single charge separation. The concentrations and reaction rates of the photosystems were different in chloroplasts from the wild type and the mutants, but in chloroplasts of each type of plant used essentially all quanta absorbed by chlorophyll caused a charge separation in PS I, PS II alpha or PS II beta. since the quantum efficiency of each photosystem was close to one, kinetic differences between the photosystems and between different kinds of chloroplasts were only due to differences in antenna size. From the rate constants the number of chlorophyll molecules in the antenna of each photosystem could be calculated. It is argued that PS II alpha and PS II beta must be different, independent structures.

Cholesteryl ester accumulation in macrophages incubated with low density lipoprotein pretreated with cigarette smoke extract

Although cigarette smoking is one of the major risk factors for atherosclerosis and coronary heart disease, the precise mechanisms of its adverse effects have not been fully elucidated. We incubated low density lipoprotein (LDL) with cigarette smoke (CS) extract and examined the incorporation of the lipoprotein by macrophages in vitro. When incubated with macrophages, LDL pretreated with CS extract (100 micrograms/ml) stimulated cholesteryl [14C]oleate synthesis approximately equal to 12.5-fold that with unmodified LDL and transformed macrophages to cells rich in lipid droplets positively stained with oil red O. Enhancement in cholesteryl ester synthesis was dependent on the concentration of CS-modified LDL and exhibited saturation kinetics. When subjected to electrophoreses, CS-modified LDL migrated to a more anionic position than did unmodified LDL and showed extensive fragmentation of apolipoprotein B. This LDL modification depended upon the incubation time and concentration of the CS extract. Superoxide dismutase inhibited modification of LDL by 52%, suggesting that superoxide anion is, at least in part, involved. These results suggest that CS extract alters LDL into a form recognized and incorporated by macrophages. Such modification if it occurs in vivo, could explain the increased incidence of atherosclerosis and coronary heart disease in smokers.

Cigarettes as a source of some trace and heavy metals and pesticides in man

Trace and heavy metal and pesticide contents of different tobacco brands sold in Finland during 1920 to 1984 were determined by atomic absorption spectroscopy and gas chromatography-mass spectrometry with the purpose of investigating the variation in contents over time. In addition, the following were studied: the effect of commercial filters in cigarettes in preventing the inhalation of metals, the transfer of metals and pesticides to the mainstream smoke; and the correlation between the cadmium content of adipose tissue of smokers and their smoking habits. No differences were found in trace and heavy metal contents of different brands and packs from different decades. The pesticide residues in tobacco have followed the pattern of their use in the tobacco plantation. The dichlorodiphenyltrichloroethane (DDT) content of tobacco has decreased during the past 20 yr to about 1/200 of the peak value, i.e., from 34.5 to 0.17 micrograms/g. Cigarette filters significantly prevent the inhalation of cadmium, lead, magnesium, and iron. The mean content of cadmium in fat tissue of male smokers was four times that of non-smokers. The difference was statistically significant.

Electrophoretic and spectrophotometric studies of chlorophyll-protein complexes from tobacco chloroplasts. Isolation of a light harvesting pigment protein complex with a molecular weight of 70,000

Abstract— …After a short‐term solubilization with sodium dodecyl sulphate, chloroplast membranes of tobacco were separated by polyacrylamide gel electrophoresis into three chlorophyll‐protein complexes. In addition to the two major complexes termed I and IIc corresponding respectively to P700 chlorophyll a‐protein and light‐harvesting chlorophyll a/b‐protein described by Thornber (1975), a relatively stable complex termed IIa has been observed. This new complex has an apparent molecular weight of 70,000 daltons and possesses Chl a and b.

Complexes I, IIa and IIC have been isolated and precise spectroscopic analyses have been performed. Fourth derivative analyses of low temperature absorption spectra suggest that complex IIa seems more representative than IIC of chlorophyll a forms present in intact thylakoid membranes.

Moreover, the electrophoretic study reveals that CPI and CPII are composed of only one polypeptidic subunit with respective molecular weights of 68,000 and 24,000 daltons.

Gaschromatographic determination of polycyclic aromatic hydrocarbons, aza-arenes, aromatic amines in the particle and vapor phase of mainstream and sidestream smoke of cigarettes

The present arrangement collects particles and semivolatiles of main- and sidestream smoke and allows a recovery of the trapped substances nearly quantitatively and without impurities. The fractionation procedure allows to separate various groups of carcinogens such as PAH, aza-arenes and aromatic amines for analytical and biological studies. Sidestream smoke contains ten times more polycyclic aromatic hydrocarbons (PAH) compared with mainstream smoke. This holds also true for aza-arenes and amines. PAH of the gaseous phases include only 1% of the particle-bound PAH.