Patent Publication Number: US-2010108083-A1

Title: Use of means for trapping co2 in a filter for preventing inflammation, cancer and cardiovascular diseases in a subject exposed to tobacco smoke

Description:
The present invention relates to a filter composition comprising means for trapping CO 2  for preventing inflammation, cancer and/or cardiovascular diseases in a subject exposed to tobacco smoke. 
     It relates more particularly to a cigarette filter designed for selectively adsorbing CO 2  from the gases resulting from the burning of tobacco, inhaled by a smoker or by a subject exposed to tobacco smoke. 
     It is well known that smoking is the cause of a large number of cases of lung and throat cancers. In fact, the burning of tobacco in a cigarette, a cigar or a pipe gives rise to smoke that contains numerous chemical substances originating from the tobacco leaf, or that form by chemical reaction when tobacco is consumed. Some of these substances are classed as being carcinogenic or mutagenic, and in fact are involved in the development of tumours in the throat or in the lungs. 
     Moreover, the major role of tobacco in the incidence of myocardial infarction and of coronary artery diseases has been known for many years [Ambrose J A et al., The pathophysiology of cigarette smoking and cardiovascular diseases: an update (2004)  J Am Coll Cardiol . May 19; 43(10):1731-7]. However, the action mechanisms involved in these diseases are still largely unknown. 
     Tobacco smoke, in its main, primary stream, i.e. as inhaled directly by a smoker when the latter activates the combustion of tobacco, via a cigarette or by means of a pipe, is an aerosol composed of a gas phase and a particulate phase. 
     The particulate phase comprises particles with diameter between 0.1 and 1 μm, which, owing to their small size, reach the pulmonary alveoli. These particles often contain toxic organic products which are precipitated on contact with the alveolar membranes and form deposits that are not easily eliminated by the body (tars) or which dissolve in the cytoplasm of the cells, forming free radicals which react with various cellular constituents (mutagenic, cytotoxic etc.). 
     The most basic cigarette filters are generally constituted of a filter composition comprising entangled cellulose fibres, with the primary aim of retaining the fine particles. 
     The gas phase, constituted to 80% by nitrogen and oxygen from the atmospheric air, includes from 12 to 15% of carbon dioxide (CO 2 ), 3 to 6% of carbon monoxide (CO), 0.1 to 0.2% of hydrogen cyanide (CHN) and 1 to 3% of various volatile organic compounds and in particular nitrogen oxides (NOx) [Norman, V. An overview of the vapor phase, semi volatile and non volatile components of cigarette smoke (1997)  Recent Advances in Tobacco Science,  3:28-58]. 
     The amounts of gas are expressed here as molar percentage relative to the total gases constituting the gas phase. The nitrogen oxides form free radicals that are very irritant and can notably cause asthma attacks. Hydrogen cyanide and carbon monoxide display great affinity for erythrocytes, which transport the oxygen in the blood, and can cause anaemias, or even asphyxia. 
     In an attempt to limit the inhalation by the smoker of these three gases that are deemed harmful, various types of cigarette filters have been developed, notably filter compositions comprising catalysts in the form of nanometre-size metallic particles (WO 2004/110186) attached to the surface of porous structures such as zeolites, active carbon or silica beads. These porous structures can offer a large area of contact with these gases, so that in the presence of the catalysts, the gases are converted to carbon dioxide (CO 2 ) by oxidation. Accordingly, the porous structures or silica gels are treated with a solution of catalysts before they are incorporated in the cigarette filters. 
     The existing filters of this type therefore have the aim of removing carbon monoxide, nitrogen oxides and hydrogen cyanide, which are regarded as harmful, by converting them to CO 2  by oxidation. In fact, CO 2  is regarded in the literature as a gas that has no known effect on smokers&#39; health. 
     However, as a result of experiments conducted on mice, and described below, the present inventors demonstrated, surprisingly, that CO 2  induces an inflammatory reaction in the lungs. In fact they found a very significant increase in expression of the proteins β-catenin and NF-κBp65, in the lung tissues of mice that had inhaled air with a CO 2  content above 10% (without a decrease in the proportion of oxygen). This increase, which reflects an inflammatory state of the pulmonary cells, was not found in mice inhaling atmospheric air, i.e. air containing less than 2% CO 2  (Example 1 presented below). The inventors also showed that the inflammation found in the mice could be eliminated partially or even completely by selectively trapping the CO 2  contained in tobacco smoke by means of a filter that includes a solution of potassium hydroxide (KOH) (Example 2 presented below). 
     It therefore appears that, contrary to what has been assumed to date in the literature, CO 2  released by the combustion of tobacco has a significant role in inflammation of the epithelial tissues of the respiratory tract, such as those of the throat and of the lungs. 
     Moreover, since cancers of the respiratory tract, such as those of the throat and of the lungs, are correlated with the number of cigarettes smoked, as well as with the number of years during which an individual is exposed to tobacco smoke, it is assumed that inflammation of the tissues precedes the appearance of tumours in a great many cancer cases [Schwartz L. et al. Cancer: the role of extracellular disease.  Med Hypotheses . (2002) 58(4):340-61]. Thus, inflammation of the respiratory tract associated with CO 2  is regarded by the inventors, owing to its wide occurrence, as a phenomenon with a determining role in the initiation of tobacco-linked cancers, equally, or even more, than the presence of the numerous carcinogenic substances contained in tobacco smoke. 
     Medically, moreover, it is recognized that chronic inflammation of tissues promotes the appearance of pulmonary fibroses and the development of cancers. 
     In the blood vessels, the inflammatory mechanisms are very similar to those responsible for the inflammation observed in the pulmonary alveoli in response to cigarette smoke. Furthermore, the inflammatory response to cigarette smoke (notably secretion of interleukin-6 and TNF-alpha, recruitment of leukocytes) demonstrated by the inventors is also a major factor in the development of atherosclerosis, as well as cardiovascular events. 
     Thus, CO 2 -related inflammation of the arteries is regarded by the inventors, in view of its frequency, as a phenomenon with a determining role in the initiation of tobacco-related cardiovascular events, equally, or even more, than the presence of the numerous toxic substances contained in tobacco smoke. 
     It is in fact medically recognized that chronic inflammation of the vessel wall promotes the appearance of atheromatous plaques and the development of cardiovascular diseases. 
     In order to overcome these risks, the inventors propose, via the present application, incorporating in air filters, and notably cigarette filters, means for reducing the proportion of CO 2  resulting from the combustion of tobacco. These means can be implemented in large filters, such as those for ventilating public places, or in smaller filters, such as cigarette filters. 
     The invention relates more particularly to fixed or detachable cigarette filters that can contain such means. 
     “Fixed filter” means a disposable filter such as those that are inserted in the end of cigarettes by the manufacturer during their manufacture. 
     “Detachable filter” means a filter that can be used several times and which, according to a preferred aspect, can be cleaned or regenerated. 
    
    
     
         FIG. 1  presents a graph in which the ordinate shows the Penh index measured by plethysmography on Balb c/ mice used in the experiment described in Example 1, and the abscissa shows the successive injections of CO 2  (5, 10 and 15%) carried out every two minutes in the air inhaled by said mice. 
         FIG. 2  shows two diagrams. These diagrams compare the relative concentration of the protein p-catenin and of the protein NF-κB p65 in cellular extracts from the lungs of mice sacrificed after inhalation of air containing 15% CO 2  for 10 minutes and of control mice that inhaled atmospheric air. 
         FIG. 3  presents four graphs showing, as a function of time, the concentrations of CO 2  or of O 2  in mmHg measured in the chambers in which the experiments described in Example 2 were carried out. The respective concentrations of CO 2  and of O 2  are measured at the outlet from the cigarette in graphs  3 A and  3 C, and at the outlet from the filtration column in graphs  3 B and  3 D. The measurements were performed in four situations: ♦(control/H 2 O): control air filtered by the column containing water, ▪(control/KOH): control air filtered by the column containing potassium hydroxide, ▴(smoke/H 2 O): cigarette smoke filtered by the column containing water, X (smoke/KOH): cigarette smoke filtered by the column containing potassium hydroxide. 
         FIG. 4  presents a diagram showing the number of cells producing the protein RANTES (SFC for Spot Forming Cells, ELISPOT technique) in a well containing 2×10 5  pulmonary cells from mice sacrificed after inhalation of air or cigarette smoke for 38 minutes. The four situations summarized in the commentary of the aforementioned  FIG. 3  are shown. 
         FIG. 5  presents a diagram showing the number of cells producing the protein IL-6 (SFC for Spot Forming Cells, ELISPOT technique) in a well containing 2×10 5  pulmonary cells from mice sacrificed after inhalation of air or cigarette smoke for 38 minutes. The four situations summarized in the aforementioned commentary of  FIG. 3  are shown. 
         FIG. 6  presents a diagram showing the concentration of chemokine MIP-2 (ELISA technique), in the medium after 20-hour culture of cells isolated from the lungs of mice sacrificed after inhalation of air or cigarette smoke for 38 minutes. The four situations summarized above in the commentary of  FIG. 3  are shown. 
         FIG. 7  presents a diagram showing the concentration of TNF-alpha (ELISA technique), in the medium after 20-hour culture of cells isolated from the lungs of mice sacrificed after inhalation of air or cigarette smoke for 38 minutes. The four situations summarized above in the commentary of  FIG. 3  are shown. 
         FIG. 8  presents a diagram showing the activity of the proteins NF-κB p65 in cellular extracts from the lungs of mice sacrificed after inhalation of air or cigarette smoke for 38 minutes. The four situations summarized above in the commentary of  FIG. 3  are shown. 
         FIG. 9  presents a diagram showing the activity of phosphatase PP2A in cellular extracts from the lungs of mice sacrificed after inhalation of air or cigarette smoke for 38 minutes. The four situations summarized above in the commentary of  FIG. 3  are shown. 
     
    
    
     The present invention therefore relates to the use of means for trapping CO 2  in a cigarette filter to reduce the proportion of CO 2  inhaled by a smoker resulting from the combustion of tobacco. 
     It relates more particularly to the use of one or more of these means for trapping CO 2  for the preparation of a filter intended for preventing cancer or inflammation and/or cardiovascular diseases in a subject exposed to tobacco smoke. 
     “Trapping” means any means for immobilizing CO 2  on a molecular support or its conversion to another chemical entity. 
     Preferably, said means make it possible to trap at least 20% of the CO 2  that would be inhaled by the smoker, more preferably at least 40% and even more preferably at least 60% of the CO 2  that would be inhaled by the smoker. The amounts of CO 2  trapped are expressed here relative to the amount of CO 2  present in the gas phase resulting from the combustion of tobacco. 
     The amount of CO 2  trapped is expressed here as a percentage of the (molar) amount of CO 2  relative to the total amount of CO 2  present in the gas phase resulting from the combustion of tobacco, in its main, primary stream, in a cigarette without filter. This calculation results from comparison of measurements taken by means of an analytical cigarette-smoking machine in the presence and in the absence of the means for trapping CO 2  incorporated in the cigarette or in the filter, according to a standard method that complies with current specifications (The standardized conditions are defined in Standard 3308 of the International Standards Organization (ISO) with the title: “Routine analytical cigarette-smoking machine”). 
     The means envisaged according to the invention are preferably means for adsorption of CO 2 . 
     They make it possible to reduce or limit the proportion of CO 2  that would be inhaled by the smoker. 
     These means, as such, are known by a person skilled in the art and have been used in fields of application unrelated to cigarette filters. 
     The means of the invention can be combined with other filtering means to limit the emission of particles or of toxic gases other than CO 2 . 
     These means, as well as the structure of the cigarette filters are well known by a person skilled in the art [Davis D. L. and Nielsen M. T. eds. (1999) Tobacco: Production, Chemistry and Technology, Blackwell Science]. 
     Another subject of the invention is a filter composition comprising a trapping means as defined above for preventing inflammation and/or cancer and/or cardiovascular diseases in a subject exposed to tobacco smoke. 
     “Filter composition” means any mixture of solid and liquid materials having the effect of forming a filter, i.e. a structure capable of retaining solid particles and/or of trapping molecules in gaseous form, such as CO 2 . 
     A preferred means for trapping CO 2  is a means for adsorption of CO 2 . 
     A means for adsorption of CO 2  that is preferred according to the invention is active carbon. Active carbon can be manufactured for example from carbonized coconut shells. This material produces a carbon with a strong granular structure, reducing the formation of dust. It is “activated” by treatment with superheated steam at 800-1000° C., which has the effect of very significantly increasing the porosity of the carbon, thus giving a specific surface between 500 and 3500 m 2 /g, generally between 500 and 1500 m 2 /g. 
     An active carbon according to the invention is for example that marketed by Sud Chemie (Lenbachplatz 6, 80333 Munich, Germany) which is able to adsorb about 4 mol of CO 2  per kg of active carbon at 22° C., 250 psi in the presence of 15% CO 2 , 82% N 2  and 3% O 2  and H 2 O, 19 cc/min, or the active carbon sold under the trademark MAXSORB® by Kansai Coke Chemicals Co. Ltd. [Otowa, T. et al. Production and adsorption characteristics of MAXSORB: high-surface-area active carbon.(1993)  Active carbon and carbon molecular sieves  7(4):241-245]. 
     A filter composition according to the invention preferably comprises a cigarette filter. 
     A cigarette filter according to the invention generally contains between 0.1 and 3 g and preferably between 0.2 and 2 g of an active carbon according to the invention. 
     Another preferred means of adsorption of CO 2  according to the invention comprises the use of zeolites. The zeolites are hydrated aluminosilicates, of natural origin (volcanic rock) or synthetic origin. Their chemical structure is a complex crystal lattice, having numerous cavities containing water molecules and positively-charged ions (notably K +  and Ca 2+ ). 
     Once the water has been removed by heating, the cavities can be occupied by chemical compounds depending on the size of the molecules and their polarity, such as molecules of CO 2 . 
     Zeolites that are preferred according to the invention are high-aluminium zeolites, i.e. for which the silicon/aluminium ratio in the crystal is between 1 and 5, preferably between 2 and 5, and more preferably between 3 and 5. 
     The high-sodium zeolites are also preferred. These types of zeolites have in fact shown a higher capacity for adsorption of CO 2 . 
     The zeolites, for example those of type 4A and 5A, i.e. zeolites generally having pores between 0.3 nm and 0.8 nm, preferably between 0.4 and 0.7 nm and more preferably between 0.5 and 0.7 nm are particularly suitable, as well as those with a crystal structure of type X, i.e. hexagonal, such as zeolites 13X. 
     The company Zeochem AG markets a zeolite 13X that is particularly useful for this purpose, which is capable of adsorbing about 6-7 mol of CO 2  per kg of zeolite 13X at 22° C., 250 psi, in the presence of 15% CO 2 , 82% N 2  and 3% O 2  and H 2 O, 19 cc/min. Another type of zeolite that can be used for the adsorption of CO 2  is Siliporite®, marketed by the company CECA, used notably in an oxygen concentrator, the MEDOX (Medical Oxygen Concentrator). 
     A cigarette filter that is preferred according to the invention generally contains between 0.1 and 3 g, preferably between 0.2 and 2 g of a zeolite according to the invention. According to a preferred aspect of the invention the zeolites can be treated beforehand with polar solutions, for example solutions of an amine or ether compound, in order to increase their adsorption capacity as stated in U.S. Pat. No. 6,908,497. 
     A means for adsorption of CO 2  that is preferred according to the invention comprises the use of MOFs (Metal-Organic Frameworks). The MOFs are crystalline materials of low density constituted of units of zinc and of oxygen joined together by organic molecules such as 1,4-benzenedicarboxylate [Yaghi, O.,  Science,  295:469]. Their crystal structure is such that gas molecules can even be stored inside the crystal lattice. MOFs are easily synthesized and certain adaptations to the composition of the organic chains are possible so that the crystal structure is provided with chemical groups that allow interactions with the gas molecules that are to be adsorbed. It is also possible to alter the size of the crystal by modifying the organic chains to provide an optimum size for the adsorption of CO 2  molecules. According to the invention, the MOF used is more particularly selected from the following: MOF-177, IRMOF-1, IRMOF-6, IRMOF-3, IRMOF-11, Cu 3 (BTC) 2 , MOF-74 and MOF-505 [Millward A. R. et al. (2005) Metal-organic frameworks with exceptionally High Capacity for storage of carbon dioxide at room temperature,  J. Am. Chem. Soc.,  127:17998-999]. 
     A cigarette filter that is preferred according to the invention generally contains between 0.1 and 3 g, preferably between 0.2 and 2 g of MOF. 
     The various means described above that can be used according to the invention for trapping and more particularly for adsorbing CO 2  are generally incorporated in cellulose acetate filters in the form of a transverse segment a few millimetres thick to provide maximum trapping of the gas stream inhaled by the smoker. Alternatively, these means can be dispersed uniformly in the filter or according to a concentration gradient in the same direction as this stream or in the opposite direction. 
     A cigarette filter according to the invention more generally comprises means for adsorption of CO 2  that can trap at least 20%, preferably at least 40% and more preferably at least 60% of the proportion of CO 2  resulting from the combustion of tobacco inhaled by a smoker. 
     The invention also relates to a cigarette comprising a filter as defined previously. 
     The invention also relates to a method of filtering cigarette smoke, characterized in that it includes a stage comprising selective trapping of the CO 2  resulting from the combustion of tobacco by means of a filter composition according to the invention, notably before the gases arising from said combustion are inhaled by the smoker. 
     In said method, the CO 2  can be trapped by a means for adsorption of CO 2  as defined previously. 
     The use of a means for trapping CO 2  in a filter or a cigarette, as defined previously, aims more particularly to limit the risks of inflammation, of cancer and/or of cardiovascular diseases of a subject exposed to tobacco smoke, and more particularly inflammation and cancer of the respiratory tract, in particular of the lungs or of the throat. 
     With regard to cardiovascular diseases, the invention aims more particularly to prevent atherosclerosis and its consequences. 
     The present invention thus relates to a method of preventing inflammation, cancer, and/or cardiovascular diseases, characterized in that it restricts the proportion of CO 2  inhaled by a subject, more particularly by a smoker. This method aims more particularly to prevent cancer or inflammation of the respiratory tract, as well as cardiovascular diseases in a subject exposed to tobacco smoke. More particularly said method uses one or more of the means of trapping CO 2  as defined previously for the preparation of a filter or of a filter composition according to the invention. 
     The examples given below are for the purpose of illustrating the principles of the invention without limiting the scope of protection requested. 
     EXAMPLE 1 
     Demonstration of an Inflammatory Effect of CO 2  on the Pulmonary Cells 
     1/ BALB/c mice were placed in a closed chamber in which the proportion of CO 2 , at constant proportion of oxygen, was raised artificially to 2 (atmospheric air control), 5, 10 and 15% by injection of CO 2  into the chamber every other minute. At each of these concentrations, non-invasive functional testing was carried out on the mice by plethysmography, according to the technique described by Hamelmann et al. (1997)  Am J Respir Crit Care Med  156: 766-775). This technique involves assessing the respiratory distress of the mice by determining the Penh (enhanced pause) value. The Penh value is a parameter that notably makes it possible to measure the ratio of the expiratory and inspiratory amplitude and thus evaluate the extent of asthma attacks, i.e. the inflammatory state of the bronchi and bronchioles owing to a reduction in diameter of the latter (respiratory resistance). 
     The results obtained are presented in the graph in  FIG. 1 . It follows from this experiment that the Penh value increases when the proportion of CO 2  increases. This value is doubled when the proportion of CO 2  changes from 10 to 15%, reaching a level that is 6 times higher than the control. Thus, a mean proportion of CO 2  of 13%, equivalent to that resulting from the combustion of tobacco, has a considerable effect on the respiratory system, causing inflammation. 
     2/After keeping the mice for 10 minutes in the chambers at the various concentrations of CO 2  stated above, the mice were sacrificed (one hour after the start of the experiment) in order to determine the proteins β-catenin and NF-κBp65 in the nucleus of their pulmonary cells. 
     The protein β-catenin is a transcription factor that acts on the cell cycle, and is implicated notably in cellular proliferation and in lung cancer [Lim J. H. (2006)  Cancer Res;  66(22): 10677-82]. 
     The protein NF-κBp65 is a transcription factor in the NF-κBfamily, contributing to the activation of a great many oncogenes and genes implicated in the inflammatory response [Nishikori, M. (2005)  J. Clin. Exp. Hemathopathol.  45(1):15-18]. 
     These two proteins are recognized markers of inflammation and of cancer. They were determined on the basis of optical density using specialized kits. β-Catenin was determined by ELISA (Catenin Enzyme Immunoassay Kit, Assay designs, Ann Arbor, Mich.) following the manufacturer&#39;s instructions. The protein NF-κB p65 was determined by another ELISA assay (TrasAM NF-κB p65 nuclear DNA based ELISA, Active Motif, Rixensart, Belgium) following the manufacturer&#39;s instructions. The values obtained, presented in the diagram in  FIG. 2 , are expressed relative to the total amount of proteins extracted from the cell nucleus. 
     The increase in the concentration of the proteins β-catenin and NF-κB p65 in the nucleus reflects a state of inflammation or of deregulation of the cells, which is directly attributable to the increase in CO 2  concentration. 
     EXAMPLE 2 
     Demonstration of an Inflammatory Response in Mice Specifically Linked to the CO 2  Contained in Cigarette Smoke 
     The following experiment involved causing mice to inhale cigarette smoke in which most of the CO 2  had been trapped selectively. The CO 2  was trapped selectively by reaction with a solution of potassium hydroxide (CO 2 +H 2 O⇄H 2 CO 3 ; H 2 CO 3 +2KOH⇄K 2 CO 2 +2H 2 O). A solution of water serves as negative control. For this, cigarette smoke was brought into contact with the water or the potassium hydroxide by passing through a filtration column containing these solutions. 
     The set-up employed for the experiment comprises: a suction pump specially adapted for consuming cigarettes. The smoke thus obtained is sent to a 250-ml sealed chamber, which is connected to a second chamber with a capacity of 1600 ml via a column which is half-filled with a 1M KOH solution or with distilled water at pH=7. A pair of sensors for taking measurements of the concentration of O 2  and of CO 2  are arranged inside each chamber. The measurements were taken every minute for 38 minutes, and the results obtained are shown in  FIG. 3 . The KOH solution ensures a considerable decrease in the concentration of CO 2  present in cigarette smoke, which decreases by 50 to 70% (see  FIG. 3 ) without significantly altering the concentration of oxygen. 
     The experiment was conducted on BALB/c mice aged from 6 to 7 weeks under in vivo conditions. The number of mice used was 32 males, divided into four groups of eight. The mice were placed in the second chamber of the set-up (1600-ml chamber) and they breathed either air (control group) or cigarette smoke that had passed through the connecting column between the two chambers containing either distilled water or a 1M KOH solution. Each experiment lasted 38 minutes, or typically the equivalent of the consumption of 5 cigarettes by a smoker. 
     The mice were sacrificed after inhalation of air for 38 minutes in the four situations described above (see also the commentary of  FIG. 3 ) and the lungs were removed immediately for analysis. 
     The lungs were analysed in order to measure the activity or the secretion of six proteins that are known markers of inflammation. Some of these proteins are also known to be markers of certain cancers and atherosclerosis (NE-κB, PP2A). These proteins are as follows: RANTES, IL-6, TNF-alpha, MIP-2, PP2A and NE-κB p65. The three first proteins belong to the cytokine family. MIP-2 is a chemokine secreted by macrophages which permits recruitment of neutrophils. PP2A is a phosphatase known for its role in the induction of apoptosis by inhibition or activation of the pro- or anti-apoptotic pathways. Deregulation of its activity is linked to cancers, in particular lung cancer [Van Hoof C. and Goris J. PP2A fulfills its promises as tumour suppressor: which subunits are important? (2004)  Cancer Cell  5(2)105-61]. Finally, NF-κB p65 is a transcription factor, which plays an important role in the activation of genes of proteins involved in inflammatory reactions, for example TNF-alpha. This protein is notably implicated in atherosclerosis [Valen G. et al. Nuclear factor kappa-B and the heart. (2001)  J. Am. Coll. Cardiol.  38(2):307-14]. Measurements of activity or of relative concentration of these proteins were performed using the following commercial kits: Mouse TNF-alpha/TNFSF1A DuoSet (ELISA assay for the concentration of TNF-alpha); Mouse CXCL2/MIP-2 DuoSet (ELISA assay for the concentration of MIP-2), Mouse CCL5/RANTES ELISpot Kit (ELISpot assay for the secretion of RANTES); Mouse IL-6 ELISpot Kit (ELISpot assay for the secretion of IL-6), all from R&amp;D Systems (Minneapolis, Minn., USA). 
     The results obtained are presented in  FIGS. 4 to 9 . These results show that when the concentration of CO 2  in cigarette smoke is reduced, the inflammation of pulmonary cells is less, based on the markers that were analysed. Accordingly, tobacco smoke would be less irritant and likely to cause cancers of the respiratory tract and cardiovascular diseases if a significant proportion of the CO 2  present in tobacco smoke were to be removed.