Perceptions, intentions, and actual use of a consumer nicotine gum.

BACKGROUND: Little is known about perceptions, use intentions, and behaviors of adults regarding nicotine gum that is marketed and regulated as a consumer product rather than as a medicinal nicotine replacement therapy (NRT). METHODS: Survey data were collected from a Qualtrics online panel (N = 1000) of adults who had never used a consumer nicotine gum, recruited based on smoking behavior, and from current and former purchasers of one commercially available nicotine gum product (LUCY Chew and Park), recruited via emails to a customer database (N = 500). In addition to descriptive cross-sectional analyses, logistic regression was used to estimate the probability of intent to try and of product appeal among these different groups. RESULTS: Among online panel respondents, individuals who smoked with and without plans to quit showed high intention to try the product (odds ratios 15.6 [95% CI 9.3, 27.6] and 9.8 [95% CI 5.8, 17.3] respectively, compared to people who formerly smoked) and persons who had never smoked showed low intentions to try. These results stood regardless of flavor. Among current and former purchasers of the study product, 43.4% of persons who had smoked cigarettes regularly indicated they were motivated to try the product "to help me quit smoking." Only 0.6% of young adult consumers of the nicotine gum (aged 21-30) had not tried tobacco products previously. CONCLUSIONS: Consumer nicotine gum does not appear to attract those who have never used a tobacco product and the results for young adults suggest minimal appeal to youth. The study product was used primarily by individuals who currently smoke and/or use e-cigarettes but who wished to quit or reduce consumption. These results suggest that a consumer nicotine gum may reduce harm by substituting for higher-risk products such as combustible cigarettes.

Behavioral intentions assessment of a disposable e-cigarette among adult current, former, and non-smokers in the United States.

Modeling the public health effects of e-cigarettes requires estimates of the likelihood that different individuals and population subgroups will start using e-cigarettes and subsequently transition to and from combustible cigarette use. To begin to generate input values for modeling efforts, this study assessed adults' behavioral intentions in relation to a disposable e-cigarette, "BIDI® Stick." An online questionnaire assessed intentions to try and use a BIDI® Stick regularly in 11 flavor variants among United States (U.S.) nationally representative samples of adult (21+ years) non-smokers (n = 2284), current smokers (n = 2391), former smokers (n = 2241), and young adult (21-24 years) non-smokers (n = 1140) of combustible cigarettes following exposure to product information and images. Current smokers rated their intentions to use a BIDI® Stick to partially or completely replace cigarettes. Positive intention to try a BIDI® Stick at least once was, for each flavor variant, highest among current smokers (22.4%-28.1%), lower among former smokers (6.0%-9.7%) and non-smokers (3.4%-5.2%), and lowest among never-smokers (1.0%-2.4%). Among current smokers, former smokers, and non-smokers, trial and regular use intentions were lowest among e-cigarette non-users and e-cigarette never-users. Approximately 23.6% of current smokers reported an intention to use a BIDI® Stick in at least one flavor to completely switch from cigarettes and/or to reduce cigarette consumption. Low trial and regular use intentions suggest that U.S. adults who do not currently smoke cigarettes and/or use e-cigarettes are unlikely to initiate use of the BIDI® Stick e-cigarette. Trial and regular use intentions are highest among adults who currently smoke cigarettes and/or use e-cigarettes. A moderate proportion of current smokers may try using a BIDI® Stick e-cigarette as a partial or complete replacement for combustible cigarettes.

A comprehensive physiologically based pharmacokinetic (PBPK) model for nicotine in humans from using nicotine-containing products with different routes of exposure.

Physiologically based pharmacokinetic (PBPK) modeling can be a useful tool for characterizing nicotine pharmacokinetics (PK) from use of tobacco products. We expand a previously published PBPK model to simulate a nicotine PK profile, following single or multiple use of various tobacco products [cigarettes, smokeless tobacco, and electronic nicotine delivery systems, or a nicotine inhaler (NICOTROL)] The uptake route in the model was designed to allow for three uptake compartments: buccal cavity (BC), upper respiratory tract (URT) (conducting and transitional airways) and lower respiratory tract (alveolar region). Within each region, the model includes product-specific descriptions of the flux of nicotine into plasma, as well as the flux of nicotine from the BC and URT to the gastrointestinal tract. These descriptions are based on regional deposition and diffusion models of nicotine into plasma, which depends on the product type. Regional deposition flux combined with regional differences in physiological parameters (e.g., blood perfusion ratio and tissue thickness) play a key role in the product-specific PK profile of nicotine. The current model describes the slower flux of nicotine into plasma across the BC and URT, as well as the rapid flux known to occur in the alveolar region. Overall, the addition of the BC and respiratory tract compartments to the nicotine model provided simulation results that are comparable to the nicotine time-course plasma concentrations reported from clinical studies for the four product categories simulated.

A lower impact of an acute exposure to electronic cigarette aerosols than to cigarette smoke in human organotypic buccal and small airway cultures was demonstrated using systems toxicology assessment.

In the context of tobacco harm-reduction strategy, the potential reduced impact of electronic cigarette (EC) exposure should be evaluated relative to the impact of cigarette smoke exposure. We conducted a series of in vitro studies to compare the biological impact of an acute exposure to aerosols of "test mix" (flavors, nicotine, and humectants), "base" (nicotine and humectants), and "carrier" (humectants) formulations using MarkTen® EC devices with the impact of exposure to smoke of 3R4F reference cigarettes, at a matching puff number, using human organotypic air-liquid interface buccal and small airway cultures. We measured the concentrations of nicotine and carbonyls deposited in the exposure chamber after each exposure experiment. The deposited carbonyl concentrations were used as representative measures to assess the reduced exposure to potentially toxic volatile substances. We followed a systems toxicology approach whereby functional biological endpoints, such as histopathology and ciliary beating frequency, were complemented by multiplex and omics assays to measure secreted inflammatory proteins and whole-genome transcriptomes, respectively. Among the endpoints analyzed, the only parameters that showed a significant response to EC exposure were secretion of proteins and whole-genome transcriptomes. Based on the multiplex and omics analyzes, the cellular responses to EC aerosol exposure were tissue type-specific; however, those alterations were much smaller than those following cigarette smoke exposure, even when the EC aerosol exposure under the testing conditions resulted in a deposited nicotine concentration approximately 200 times that in saliva of EC users.

An evaluation of electronic cigarette formulations and aerosols for harmful and potentially harmful constituents (HPHCs) typically derived from combustion.

U.S. FDA draft guidance recommends reporting quantities of designated harmful and potentially harmful constituents (HPHCs) in e-cigarette e-liquids and aerosols. The HPHC list comprises potential matrix-related compounds, flavors, nicotine, tobacco-related impurities, leachables, thermal degradation products, and combustion-related compounds. E-cigarettes contain trace levels of many of these constituents due to tobacco-derived nicotine and thermal degradation. However, combustion-related HPHCs are not likely to be found due to the relatively low operating temperatures of most e-cigarettes. The purpose of this work was to use highly sensitive, selective, and validated analytical methods to determine if these combustion-related HPHCs (three aromatic amines, five volatile organic compounds, and the polycyclic aromatic hydrocarbon benzo[a]pyrene) are detectable in commercial refill e-liquids, reference e-cigarette e-liquids, and aerosols generated from rechargeable e-cigarettes with disposable cartridges (often referred to as "cig-a-likes"). In addition, the transfer efficiency of these constituents from e-liquid to aerosol was evaluated when these HPHCs were added to the e-liquids prior to aerosol formation. This work demonstrates that combustion-related HPHCs are not present at measurable levels in the commercial and reference e-liquids or e-cigarette aerosols tested. Additionally, when combustion-related HPHCs are added to the e-liquids, they transfer to the aerosol with transfer efficiencies ranging from 49% to 99%.

Biological changes in C57BL/6 mice following 3 weeks of inhalation exposure to cigarette smoke or e-vapor aerosols.

We compared early biological changes in mice after inhalation exposures to cigarette smoke or e-vapor aerosols (MarkTen® cartridge with Carrier, Test-1, or Test-2 formulations; 4% nicotine). Female C57BL/6 mice were exposed to 3R4F cigarette smoke or e-vapor aerosols by nose-only inhalation for up to 4 hours/day, 5 days/week, for 3 weeks. The 3R4F and e-vapor exposures were set to match the target nose port aerosol nicotine concentration (∼41 µg/L). Only the 3R4F group showed postexposure clinical signs such as tremors and lethargy. At necropsy, the 3R4F group had significant increases in lung weight and changes in bronchoalveolar lavage parameters, as well as microscopic findings in the respiratory tract. The e-vapor groups had minimal microscopic changes, including squamous metaplasia in laryngeal epiglottis, and histiocytic infiltrates in the lung (Test-2 group only). The 3R4F group had a higher incidence and severity of microscopic findings compared to any e-vapor group. Transcriptomic analysis also showed that the 3R4F group had the highest number of differentially expressed genes compared to Sham Control. Among e-vapor groups, Test-2 group had more differentially expressed genes but the magnitude of gene expression-based network perturbations in all e-vapor groups was ∼94% less than the 3R4F group. On proteome analysis in the lung, differentially regulated proteins were detected in the 3R4F group only. In conclusion, 3-weeks of 3R4F exposure induced molecular and microscopic changes associated with smoking-related diseases in the respiratory tract, while e-vapor exposures showed substantially reduced biological activities.

Toxicological assessment of a prototype e-cigaret device and three flavor formulations: a 90-day inhalation study in rats.

A prototype electronic cigaret device and three formulations were evaluated in a 90-day rat inhalation study followed by a 42-day recovery period. Animals were randomly assigned to groups for exposure to low-, mid- and high-dose levels of aerosols composed of vehicle (glycerin and propylene glycol mixture); vehicle and 2.0% nicotine; or vehicle, 2.0% nicotine and flavor mixture. Daily targeted aerosol total particulate matter (TPM) doses of 3.2, 9.6 and 32.0 mg/kg/day were achieved by exposure to 1 mg/L aerosol for 16, 48 and 160 min, respectively. Pre-study evaluations included indirect ophthalmoscopy, virology and bacteriological screening. Body weights, clinical observations and food consumption were monitored weekly. Plasma nicotine and cotinine and carboxyhemoglobin levels were measured at days 28 and 90. After days 28, 56 and 90, lung function measurements were obtained. Biological endpoints after 90-day exposure and 42-day recovery period included clinical pathology, urinalysis, bronchoalveolar fluid (BALF) analysis, necropsy and histopathology. Treatment-related effects following 90 days of exposure included changes in body weight, food consumption and respiratory rate. Dose-related decreases in thymus and spleen weights, and increased BALF lactate dehydrogenase, total protein, alveolar macrophages, neutrophils and lung weights were observed. Histopathology evaluations revealed sporadic increases in nasal section 1-4 epithelial hyperplasia and vacuolization. Following the recovery period, effects in the nose and BALF were persistent while other effects were resolved. The no observed effect level based upon body weight decreases is considered to be the mid-dose level for each formulation, equivalent to a daily TPM exposure dose of approximately 9.6 mg/kg/day.

Characterization of potential impurities and degradation products in electronic cigarette formulations and aerosols.

E-cigarettes are gaining popularity in the U.S. as well as in other global markets. Currently, limited published analytical data characterizing e-cigarette formulations (e-liquids) and aerosols exist. While FDA has not published a harmful and potentially harmful constituent (HPHC) list for e-cigarettes, the HPHC list for currently regulated tobacco products may be useful to analytically characterize e-cigarette aerosols. For example, most e-cigarette formulations contain propylene glycol and glycerin, which may produce aldehydes when heated. In addition, nicotine-related chemicals have been previously reported as potential e-cigarette formulation impurities. This study determined e-liquid formulation impurities and potentially harmful chemicals in aerosols of select commercial MarkTen(®) e-cigarettes manufactured by NuMark LLC. The potential hazard of the identified formulation impurities and aerosol chemicals was also estimated. E-cigarettes were machine puffed (4-s duration, 55-mL volume, 30-s intervals) to battery exhaustion to maximize aerosol collection. Aerosols analyzed for carbonyls were collected in 20-puff increments to account for analyte instability. Tobacco specific nitrosamines were measured at levels observed in pharmaceutical grade nicotine. Nicotine-related impurities in the e-cigarette formulations were below the identification and qualification thresholds proposed in ICH Guideline Q3B(R2). Levels of potentially harmful chemicals detected in the aerosols were determined to be below published occupational exposure limits.

A comprehensive evaluation of selected components and processes used in the manufacture of cigarettes: approach and overview.

CONTEXT: In addition to tobacco and cigarette ingredients, there are many non-tobacco components and processes used to manufacture commercial cigarettes. Proposed cigarette components and manufacturing process changes were evaluated using a tiered toxicological testing program. OBJECTIVE: The toxicological testing and evaluation of proposed changes to selected non-tobacco cigarette components and manufacturing processes are described in this special report. MATERIALS AND METHODS: Selected non-tobacco cigarette components and manufacturing processes were evaluated using experimental and control cigarettes. These experimental cigarettes were evaluated using mainstream smoke chemistry, bacterial mutagenicity and cytotoxicity assays. In some evaluations, 90-day nose-only mainstream smoke inhalation studies using rats were performed. RESULTS: Some proposed design changes were not implemented, or limitations on their use were established. Most study results, however, were similar to those previously reported in the scientific literature for design changes in cigarette construction. CONCLUSION: The studies reported in the series of publication demonstrate that our testing approach is feasible for evaluation of cigarette component and manufacturing process changes.

A comprehensive toxicological evaluation of three adhesives using experimental cigarettes.

CONTEXT: Adhesives are used in several different manufacturing operations in the production of cigarettes. The use of new, "high-speed-manufacture" adhesives (e.g. vinyl acetate based) could affect the smoke chemistry and toxicology of cigarettes, compared with older "low-speed-manufacture" adhesives (e.g. starch based). OBJECTIVE: This study was conducted to determine whether the inclusion of different levels of three adhesives (ethylene vinyl acetate, polyvinyl acetate and starch) in experimental cigarettes results in different smoke chemistry and toxicological responses in in vitro and in vivo assays. MATERIALS AND METHODS: A battery of tests (analytical chemistry, in vitro and in vivo assays) was used to compare the chemistry and toxicology of smoke from experimental cigarettes made with different combinations of the three adhesives. Varying levels of the different side-seam adhesives, as well as the transfer of adhesives from packaging materials, were tested. RESULTS: There were differences in some mainstream cigarette smoke constituents as a function of the level of adhesive added to experimental cigarettes and between the tested adhesives. None of these differences translated into statistically significant differences in the in vitro or in vivo assays. CONCLUSION: The use of newer "high-speed-manufacture" vinyl acetate-based adhesives in cigarettes does not produce toxicological profiles that prevent the adhesives from replacing the older "low-speed-manufacture" adhesives (such as starch).

A comprehensive evaluation of the toxicology of experimental cigarettes manufactured with banded papers.

CONTEXT: To comply with state requirements, cigarette manufacturers have added low-permeability bands to the cigarette paper. These bands can extinguish the cigarette when it is no longer being puffed by a smoker. OBJECTIVE: This study was conducted to evaluate the toxicology resulting from the addition of different types of bands to experimental cigarettes. MATERIALS AND METHODS: A battery of assays that are typically used in toxicology studies with cigarette smoke, namely smoke chemistry, in vitro mutagenicity and cytotoxicity, and inhalation studies with rats, were used to evaluate different band characteristics added to cigarette paper. RESULTS: Although differences in the amount of band material was associated with an increase in some metals measured in mainstream tobacco smoke, it was not dose responsive to any band design parameter (base paper permeability, band width, band spacing, band chalk amount, or citrate). Occasional, minor differences were produced by the different types of bands; overall, there was no increased toxicity. CONCLUSION: Although there were increases and decreases in some mainstream smoke constituents, the in vitro and in vivo testing performed demonstrated that low-permeability bands on cigarettes do not modify the toxicity of smoke inhaled by smokers.

A comprehensive evaluation of the toxicology of experimental, non-filtered cigarettes manufactured with different circumferences.

CONTEXT: Historical work indicates that cigarette circumference may affect the toxicological profile of experimental cigarettes. OBJECTIVE: Studies were conducted to examine the effect of different cigarette circumferences on (1) selected mainstream smoke constituents including concentrations of tobacco specific nitrosamines (TSNA) in smoke and (2) mutagenicity and cytotoxicity of cigarette smoke condensate. MATERIALS AND METHODS: Analytical chemistry, Salmonella mutagenicity and cytotoxicity assays were used to evaluate the composition and biological activity of mainstream smoke from experimental, non-filtered cigarettes manufactured with four different circumferences (17.0-27.1 mm). RESULTS: Most smoke constituents, including TSNA, decreased with decreasing cigarette circumference; however, amounts of hydrogen cyanide increased in a non-circumference dependent manner. Mutagenicity and cytotoxicity also decreased slightly with decreasing cigarette circumference. CONCLUSION: Cigarette circumference may have a minor role in the toxicological profile of experimental cigarettes, with a so-far-unidentified mechanism.

Discriminatory power of standard toxicity assays used to evaluate ingredients added to cigarettes.

A tiered approach for testing ingredients in a cigarette matrix was developed and includes chemical-analytical testing and a standard battery of biological toxicity assays. These assays were adapted for comparative evaluation of mainstream smoke from experimental cigarettes with or without ingredients at various inclusion levels. This adaptation to test cigarette mainstream smoke may impact assay response. Since it is difficult to a priori determine discriminatory power, it was evaluated using a large experimental dataset from a multi-year program of cigarette ingredient testing performed at two separate laboratories. A statistical method, minimum detectable difference (MDD), was used as a measure of assay discriminatory power. MDD of cigarette smoke constituents ranged from 6% to 29% of the average. Salmonella mutagenicity and cytotoxicity test MDDs ranged from 20% to 81% and 18% to 49%, respectively. Body weight gain in 90-day nose-only inhalation studies yielded an MDD of 30-40%. Histopathological findings with severity scores between 0.5 and 1.5 had the lowest MDDs of 23% and higher. In general, discriminatory power decreased with increasing biological complexity and toxicological relevance of the assay. Beyond statistical analysis, however, a weight-of-the-evidence analysis by experienced researchers is required for toxicological assessment of a cigarette ingredient.

Chemical analysis of cigarette smoke particulate generated in the MSB-01 in vitro whole smoke exposure system.

Cigarette mainstream smoke (MS) is a dynamic aerosol consisting of a gas-vapor phase and a particulate phase. In recent years, novel in vitro whole smoke exposure systems have been developed to expose cells directly to whole MS. One such system is the Burghart Mimic Smoker-01 (MSB-01). Our previous data using the MSB-01 indicated that a 50 +/- 10% loss of particulate matter occurred prior to MS delivery into the exposure chamber. Additionally, a change in aerosol particle diameter was also measured, suggesting that the chemical composition of MS might be changing within the system. In this study, we have expanded on our previous work and compared the particulate phase chemical composition of undiluted and diluted MS generated by the instrument and that of the MS delivered into the exposure chamber. The average percent delivery of cigarette smoke condensate (CSC) detected for all the measured chemical constituents was 35 +/- 13% for undiluted MS and 23 +/- 8% for 1:1 diluted MS. The data also indicate that under our experimental conditions, incomplete mixing of the freshly generated MS occurs during its dilution by the system. Taken together, the data presented here show that significant chemical changes occur between the generation of MS by the system and its delivery into the exposure chamber. This indicates that due to the dynamic nature of cigarette smoke, it is important to characterize the exposure conditions in order to gain the best insight and accurately correlate exposure with biological endpoints.

Cigarette smoke extract induced protein phosphorylation changes in human microvascular endothelial cells in vitro.

Phosphorylation is the most widely studied posttranslational modification (PTM) and is an important regulatory mechanism used during cellular responses to external stimuli. The kinases and phosphatases that regulate protein phosphorylation are known to be affected in many human diseases. Cigarette smoking causes cardiovascular disease (CVD). Endothelial cells play a pivotal role in CVD initiation and development; however, there have been limited investigations of the specific signaling cascades and protein phosphorylations activated by cigarette smoke in endothelial cells. The purpose of this research was to better understand the differential protein phosphorylation in endothelial cells stimulated with extracts of cigarette smoke total particulate matter (CS-TPM) in vitro. Human microvascular endothelial cells were exposed in vitro to CS-TPM at concentrations that were shown to cause endothelial cell dysfunction. The phosphorylated proteins were isolated using phosphoprotein-specific chromatography, followed by enzymatic digestion and nano-flow capillary liquid chromatography (ncap-LC) coupled to high resolution mass spectrometry. This study putatively identified 94 proteins in human microvascular endothelial cells that were differentially bound to a phosphoprotein-specific chromatography column following exposure to CS-TPM suggesting differential phosphorylation. Pathway analysis has also been conducted and confirmations of several observations have been made using immunoaffinity-based techniques (e.g., Western blotting).

Characterization of a whole smoke in vitro exposure system (Burghart Mimic Smoker-01).

In vitro systems are frequently used to study mechanisms of mainstream cigarette smoke (MS)-induced lung injury. Traditional methods of exposure involve the capture of MS particulate phase with filter pads or bubbling MS through phosphate buffered saline (PBS) or cell culture medium. Although useful for in vitro experiments, these exposure methods may fail to capture potential interactions between the gas and particulate phases. To better understand the effect of MS on the human airway, in vitro whole smoke exposure systems that utilize freshly generated whole smoke are needed. Here we report the characterization of a new in vitro whole smoke exposure system (Burghart Mimic Smoker-01 (MSB-01)). This system uses a smoke distribution manifold to simultaneously deliver MS to each well of a 96-well plate. Intraday and interday variations for particulate matter deposition were less than 5% and 13% respectively. Cytotoxicity measurements using lung epithelial BEAS-2B cells indicate variations in calculated EC(50) (half maximal effective concentration) values of 13% intraday and 20% interday. Smoke particulate losses and changes in particle size distribution were also analyzed. The data indicate that 45-50% of the MS generated at the smoking ports is lost within the system prior to delivery into the exposure chamber; however, no changes in particle size distribution were detected throughout the system. Overall, the MSB-01 reproducibly delivered mainstream cigarette smoke in a dose dependent manner across the multiwell plate. The MSB-01 is a high throughput system capable of exposing cells to both the MS particulate and gas/vapor phases simultaneously.

Characterization of the mouse bronchoalveolar lavage proteome by micro-capillary LC-FTICR mass spectrometry.

Bronchoalveolar lavage fluid (BALF) contains proteins derived from various pulmonary cell types, secretions and blood. As the characterization of the BALF proteome will be instrumental in establishing potential biomarkers of pathophysiology in the lungs, the objective of this study was to contribute to the comprehensive collection of Mus musculus BALF proteins using high resolution and highly sensitive micro-capillary liquid chromatography (microLC) combined with state-of-the-art high resolution mass spectrometry (MS). BALF was collected from ICR and C57BL/6 male mice exposed to nose-only inhalation to either air or cigarette smoke. The tandem mass spectra were analyzed by SEQUEST for peptide identifications with the subsequent application of accurate mass and time tags resulting in the identification of 1797 peptides with high confidence by high resolution MS. These peptides covered 959 individual proteins constituting the largest collection of BALF proteins to date. High throughput monitoring profiles of this extensive collection of BALF proteins will facilitate the discovery and validation of biomarkers that would elucidate pathogenic or adaptive responses of the lungs upon toxic insults.

Pulmonary inflammation in mice exposed to mainstream cigarette smoke.

Male C57Bl/6 (C57) and ICR mice were exposed by nose-only inhalation to mainstream cigarette smoke (MS) from 2R4F reference cigarettes, at concentrations of 75, 250, and 600 microg of total particulate matter (TPM) per liter, for up to 6 mo. Respiratory-tract tissue (nose, larynx, and lung), blood, and bronchoalveolar lavage fluid (BALF) samples were collected and analyzed at several time points. Blood samples were analyzed for biomarkers of exposure (COHb and nicotine). BALF was analyzed for biomarkers of cell injury, inflammation, oxidative stress, enzyme activity, and cytokines. Blood COHb and plasma nicotine concentrations increased in a dose-dependent manner, confirming smoke exposure. Mild emphysema was observed following 28 wk of exposure. Macrophage accumulation and inflammatory infiltrates were observed around the alveolar ducts and adjacent vasculature. There was an approximately 13% increase in mean linear intercept (Lm) only in ICR mice exposed to 600 microg/L TPM. There were no significant changes in biomarkers of oxidative stress secondary to smoke exposures; however, 8-isoprostane significantly increased following the 13-wk post-inhalation period. BALF macrophage and neutrophil counts were rapidly and consistently elevated, while lymphocyte counts gradually increased over time. MS-induced inflammatory responses observed in this study are comparable to changes reported in chronic smokers, supporting the role of chronic inflammation in the pathogenesis of emphysema. However, mild emphysema in minimal numbers of mice suggests that MS exposure concentration and/or duration in the current study were not sufficient to induce a definitive emphysema phenotype.