D
Cytotoxicity Tables
This appendix contains summary tables (Tables D-1, D-2, and D-3) of in vitro studies in which cytotoxicity is assessed.
Reference | Exposure: Aerosol (A), Extracts (X), E-liquid (L) | Humectant Only as an Exposure | Nicotine Only as an Exposure | Combustible Tobacco Cigarette Smoke as a Control | Compares Flavors | Cell or Tissue Type Used and Comments |
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Aufderheide and Emura, 2017 | A | 10004 |
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Bahl et al., 2012 | L | ✔ | ✔ | ✔ |
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Barber et al., 2016 | X | ✔ | ✔ |
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Behar et al., 2014 | L | ✔ | ✔ | ✔ |
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Behar et al., 2016 | L and A | ✔ | ✔ |
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Bharadwaja et al., 2017 | L and A |
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Cervellati et al., 2014 | A | ✔ | ✔ |
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Reference | Exposure: Aerosol (A), Extracts (X), E-liquid (L) | Humectant Only as an Exposure | Nicotine Only as an Exposure | Combustible Tobacco Cigarette Smoke as a Control | Compares Flavors | Cell or Tissue Type Used and Comments |
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Farsalinos et al., 2013 | A | ✔ | ✔ | ✔ | ✔ |
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Husari et al., 2016 | X | ✔ |
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Leigh et al., 2016 | A | ✔ | ✔ | ✔ | ✔ |
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Lerner et al., 2015 | A | ✔ | ✔ | ✔ | ✔ |
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Lerner et al., 2016 | A |
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Misra et al., 2014 | X | ✔ | ✔ |
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Neilson et al., 2015 | A | ✔ |
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goblet cells, ciliated cells with actively beating cilia, basal cells, and club cells (Clara). However, cells were obtained from a single donor and therefore may not be representative of responses from a heterogeneous population (e.g., polymorphisms, ethnicities, sex-related factors). |
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Romagna et al., 2013 | L | ✔ | ✔ |
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Sancilio et al., 2016 | L | ✔ |
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Sancilio et al., 2017 | L | ✔ |
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Scheffler et al., 2015a | A | ✔ | ✔ |
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Reference | Exposure: Aerosol (A), Extracts (X), E-liquid (L) | Humectant Only as an Exposure | Nicotine Only as an Exposure | Combustible Tobacco Cigarette Smoke as a Control | Compares Flavors | Cell or Tissue Type Used and Comments |
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Scheffler et al., 2015b | A | ✔ | ✔ | ✔ |
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Welz et al., 2016 | L | ✔ |
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Willershausen et al., 2014 | L | ✔ | ✔ | ✔ |
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Wu et al., 2014 | L | ✔ |
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Yu et al., 2016 | X | ✔ |
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NOTE: hESC = human embryonic stem cell; HFL1 = human fetal lung fibroblast; HGF = human gingival fibroblast; HNSCC = head and neck squamous cell carcinoma; HPdLF = human periodontal ligament fibroblast; hPF = human pulmonary fibroblast; hTBE = human tracheobronchial epithelial; HUVEC = human umbilical vein endothelial cell; mNSC = mouse neural stem cell; NHBE = normal human bronchial epithelial.
Reference | Test Agent(s) | Cell or Tissue Type Used | Dose and Time Course | Assay Employed |
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Aufderheide and Emura, 2017 |
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Bahl et al., 2012 |
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Barber et al., 2016 |
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Behar et al., 2014 |
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Reference | Test Agent(s) | Cell or Tissue Type Used | Dose and Time Course | Assay Employed |
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Behar et al., 2016 |
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Bharadwaja et al., 2017 |
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Cervellati et al., 2014 |
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Reference | Test Agent(s) | Cell or Tissue Type Used | Dose and Time Course | Assay Employed |
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Farsalinos et al., 2013 |
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Husari et al., 2016 |
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Reference | Test Agent(s) | Cell or Tissue Type Used | Dose and Time Course | Assay Employed |
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Leigh et al., 2016 |
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Reference | Test Agent(s) | Cell or Tissue Type Used | Dose and Time Course | Assay Employed |
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Lerner et al., 2015 |
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Lerner et al., 2016 |
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Misra et al., 2014 |
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Reference | Test Agent(s) | Cell or Tissue Type Used | Dose and Time Course | Assay Employed |
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Neilson et al., 2015 |
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Romagna et al., 2013 |
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glycerol USP, 8.11% water, 0.8% nicotine USP, and < 0.5% flavorings |
3.12% for 24 hours at 37ºC |
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Sancilio et al., 2016 |
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Reference | Test Agent(s) | Cell or Tissue Type Used | Dose and Time Course | Assay Employed |
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Sancilio et al., 2017 |
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Scheffler et al., 2015a |
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Reference | Test Agent(s) | Cell or Tissue Type Used | Dose and Time Course | Assay Employed |
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Scheffler et al., 2015b |
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Welz et al., 2016 |
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Willershausen et al., 2014 |
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Wu et al., 2014 |
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Reference | Test Agent(s) | Cell or Tissue Type Used | Dose and Time Course | Assay Employed |
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Yu et al., 2016 |
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NOTE: 2-MOCA = 2-methoxycinnamaldehyde; CSE = cigarette smoke extract; DAPI = 4’,6-diamidino-2-phenylindole; GC/MS = gas chromatography/mass spectrometry; hESC = human embryonic stem cell; HFL1 = human fetal lung fibroblast; HGF = human gingival fibroblast; HNSCC = head and neck squamous cell carcinoma; HPdLF = human periodontal ligament fibroblast; hPF = human pulmonary fibroblast; HRV = human rhinovirus; hTBE = human tracheobronchial epithelial; HUVEC = human umbilical vein endothelial cell; LDH = lactate dehydrogenase; mNSC = mouse neural stem cell; MTT = 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; NHBE = normal human bronchial epithelial; PG = propylene glycol; TEM = transmission electron microscopy.
TABLE D-3 Summary of Results from In Vitro Studies of E-Cigarettes Assessing Cytotoxicity
Reference | Results and Observations |
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Aufderheide and Emura, 2017 | Cultures exposed to both mainstream combustible tobacco cigarette smoke and e-liquid aerosol showed a clear reduction in mucus production and cilia bearing, but the effect was weaker for the aerosol than for the smoke. |
Bahl et al., 2012 | The MTT assay showed effects of refill solutions on cell survival that ranged from no evidence of cytotoxicity to high levels of toxicity. |
Cinnamon Ceylon had the strongest effects and was the only sample that was cytotoxic for all three cell types. Fifteen refill samples were moderately cytotoxic to hESC, and in general, mNSC responded similarly to these samples. In general, hESC were more sensitive than hPF, but Freedom Smoke menthol arctic and Global Smoke caramel produced stronger cytotoxic effects on hPF than on the other two cells. | |
The humectants (PG and glycerol) were non-cytotoxic for all cell types. Five butterscotch- or caramel-flavored samples were also non-cytotoxic at the highest dose tested. | |
The relevance of exposure to refill liquid (as compared with aerosols) in cytotoxicity studies is a concern. | |
Barber et al., 2016 | Most of the exposure conditions resulted in significant effects on cell density. There was also a slight reduction in viability, independent of nicotine concentration or the exact formulation of the extract. Authors observed a significant decrease in metabolic activity for cells that were exposed to combustible tobacco cigarette smoke or e-cigarette aerosol extracts, independent of the formulation of the extract. Exposure to pure nicotine did not alter endothelial cell metabolic activity. |
Results showed significant increase in the deposition of C1q and C5b9, and in C3b to a lesser extent. There were no changes in C4d. | |
Behar et al., 2014 | The study established NOAELs of 0.03% for hESC and 0.01% for hPF; hESC was more sensitive than hPF. |
Of 4 chemical additives tested, CAD and 2-MOCA were the most cytotoxic, producing similar IC50 for both hESC and hPF cells. By contrast, dipropylene glycol and vanillin were the least cytotoxic, and their IC50 were higher than a user would likely experience. |
Reference | Results and Observations |
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Behar et al., 2016 | In the 48-hour MTT assay, hESC (embryonic stem cells) were more sensitive to cinnamon Ceylon and cinnamaldehyde aerosols than hPF and A549 (respiratory) cells. By contrast, hESC tolerated short-term exposure to cinnamaldehyde for a longer time (8 hours) than hPF (2 hours). |
Cytoskeletal structure disruption (e.g., depolymerization of actin microfilaments and microtubules) was observed for both hESC and hPF exposed to cinnamaldehyde at MTT NOAEL and IC50 concentrations. | |
Bharadwaja et al., 2017 | Following exposure to e-liquids and e-cigarette aerosol at various concentrations, bioluminescent recombinant bacterial cells (as biosensors) showed dose-dependent and stress-specific responses. Interestingly, cells exposed to e-liquid showed greater inhibition of bioluminescence at high concentrations, which declined dose-dependently with dilutions, whereas cells exposed to e-cigarette aerosols showed the opposite effect, with bioluminescence increasing in a dose-dependent manner with exposure to decreasing concentrations of e-cigarette aerosol. These changes in bioluminescence expression indicate potential cellular damage, such as DNA damage, oxidative stress, ion homeostasis, and membrane damage. Both e-liquid and aerosol exposure resulted in cellular damage, but e-cigarette aerosol exposure showed damage without significant growth inhibition. |
Results of the DNA fragmentation assay showed considerable DNA breaks at high doses of e-liquid exposure, compared with lower doses (which showed partial DNA fragmentation) and controls. |
Reference | Results and Observations |
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Cervellati et al., 2014 | Exposure to e-cigarette aerosol with humectants only (no flavorings or nicotine) resulted in no change in either cell viability or LDH release over 24 hours. Exposure to e-cigarette aerosol with flavoring caused significant progressive loss of viability and increased LDH release in both cell types. E-cigarette aerosol with both flavoring and nicotine caused rapid (50 minutes) and marked loss in viability and enhanced LDH release. This is similar to effects of combustible tobacco cigarette smoke exposure, which caused an early (6 hours) and progressive decrease in cell viability and increased LDH release. The authors observed a similar trend during the different time points in both cell lines, but keratinocytes appeared more susceptible to combustible tobacco cigarette smoke–induced toxicity after 24 hours. |
The morphology of the cells exposed to combustible tobacco cigarette smoke shows clear signs of cellular damage and presence of vacuoles. By contrast, cells treated with e-cigarette aerosol with humectants only (no flavors or nicotine), remained intact with the same ultrastructural aspect of control cells, even 24 hours after treatment. In cells exposed to e-cigarette with flavors, an increase in vacuolization and alteration of cytoplasmic membrane was observed. The degeneration of intracellular organelles was more pronounced after exposure to e-cigarette aerosols with flavors and nicotine, especially in HaCaT cells, which showed a marked vacuolization consequent to the expansion of the mitochondria and the endoplasmic reticulum. | |
Results suggest that e-liquid and/or aerosol components contain some pro-inflammatory stimuli leading to a change in the secretome pattern depending on the cells lines employed. Fluctuations in cytokine release after other e-cigarette and combustible tobacco cigarette smoke exposures were also observed, but interpreting these effects was possible due to subsequent cell death. |
Reference | Results and Observations |
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Farsalinos et al., 2013 | Of 20 samples tested, 4 samples exhibited a cytotoxic effect in the 3.7-V experiments: |
Cinnamon cookies flavor was slightly cytotoxic at the highest extract concentration, while both samples of El Toro cigarillos and El Toro puros were cytotoxic at both 100% and 50% extract concentrations. | |
The range of myocardial cell survival for all e-cigarette samples at 3.7 V was 89.7%–112.1% at 6.25%, 90.6%–115.3% at 12.5%, 81.0%–106.6% at 25%, 7.4%–106.8% at 50%, and 2.2%–110.8% at 100% extract concentration. The “base” sample was not cytotoxic at any extract concentration. | |
Combustible tobacco cigarette smoke extract was significantly cytotoxic at concentrations above 6.25%, with viability rates being 76.9 ± 2.0% at 6.25%, 38.2 ± 0.6% at 12.5%, 3.082 ± 0.2% at 25%, 5.2 ± 0.8% at 50%, and 3.9 ± 0.2% at 100% extract concentration. | |
The absolute mean difference in viability between 3.7-V and 4.5-V experiments was 7.1 ± 4.1% at 6.25%, 5.0 ± 5.3% at 12.5%, 4.2 ± 4.8% at 25%, 5.0 ± 3.8% at 50%, and 17.0 ± 12.2% at 100% extract concentration. Only the difference at 6.25% extract concentration was statistically significant (p = 0.039). None of the 4 samples was considered cytotoxic. | |
IC50 could be determined only for combustible tobacco cigarette smoke extract and for El Toro cigarrillos and El Toro puros, since for every other e-cigarette sample, viability was higher than 50% at all extract concentrations. | |
The lowest NOAEL and IC50 were observed in combustible tobacco cigarette smoke extract. | |
Husari et al., 2016 | Combustible tobacco cigarette smoke total particulate matter extract at concentrations of 2 mg/ml and higher attenuated cellular growth and triggered cell death. Similar effects only occurred from exposure to e-cigarette total particulate matter extract at concentrations of 64 mg/ml. |
Reference | Results and Observations |
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Leigh et al., 2016 | Effects of e-cigarette aerosols on toxicity to bronchial epithelial cells differed significantly. Flavors have a significant and differential effect on toxicity: e-cigarette aerosols with menthol, coffee, and strawberry flavors significantly reduced cell viability and metabolic activity compared to air controls. E-cigarette aerosols with coffee and strawberry flavors also significantly increased cytokine levels compared to both air controls and reference combustible tobacco cigarettes. |
No significant differences (p < 0.05) in metabolic activity and cell viability were observed between the e-cigarette aerosols with various nicotine concentrations and the air control, or among the varying nicotine concentrations when compared against each other. However, significant differences (p < 0.05) were found between the various nicotine concentrations and combustible tobacco cigarette smoke. Of note, metabolic activity of exposed cells was measured by neutral red uptake assay, but the definition of this endpoint is not clear because neutral red assay is a quantitative estimation of the number of viable cells in culture. | |
With respect to cytokine release, compared with air controls, exposure to aerosol with 18 mg/ml nicotine resulted in significant decreases in IL-1β, CXCL1, and CXCL2, while exposure to aerosol with 24 mg/ml nicotine resulted in significantly increased IL-6. IL-1β and CXCL2 levels were also significantly decreased between 18 mg/ml nicotine aerosol and the reference combustible tobacco cigarette. Significant differences were observed among aerosols with variable nicotine concentrations for IL-1β, IL-6, CXCL1, and CXCL2. | |
Exposure of H292 cells to e-cigarette humectant-only aerosols significantly decreased cell viability (p < 0.05) compared to air controls, but toxic effects were significantly less than from exposure to combustible tobacco cigarette smoke. Effects of humectant aerosols on cell metabolic activity differed significantly, decreasing significantly in cells exposed to PG/glycerol and glycerol-only aerosols, but not to PG-only compared with air controls. With respect to cytokine release, all tested cytokines increased significantly except CXCL1 and CXCL10 in cells exposed to PG-only compared with air controls. | |
Aerosol from the 4.0-V and 4.8-V devices significantly decreased (p < 0.05) metabolic activity and cell viability compared with the air control. Aerosol generated with the 3.3-V device was not different than air and significantly less toxic than combustible tobacco cigarette smoke (p < 0.05). Aerosol generated with the device at the highest (4.8-V) setting significantly increased all tested cytokines compared with air controls. |
Reference | Results and Observations |
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Lerner et al., 2015 | Fibroblasts cultured with e-liquid or combustible tobacco CSE exhibited a reduction in the number of cells per count area. Many of the treated cells were enlarged and vacuolarized, and this effect was greater in CSE-treated cells and cells treated with 5% e-liquids. Compared to control cells, e-liquid and CSE-treated cells showed morphological changes—enlarged cells and spindle formation. Morphological changes were similar in cells exposed to e-liquid without nicotine added to cells at 1% concentration and 1% PG. In contrast, fibroblasts cultured in 1% e-liquid with nicotine resulted in morphological changes that resemble cells treated with 1% CSE. |
Lung fibroblast viability following treatments with 2.5% PG, glycerol, or commercial e-liquids was not significantly different than control after 24 hours (% viability in means ± SD; control: 90.53 ± 5.34, PG: 88.40 ± 2.99, glycerol: 91.97 ± 6.23, Ecto American tobacco flavor 0 mg nicotine: 92.7 ± 2.55, Ecto American tobacco flavor 24 mg nicotine: 78.57 ± 6.67, p > 0.05). | |
Exposure to humectants only (PG, glycerol) elicited no significant increase in release of IL-8 compared with the control group (15.9 ± 12.02 pg/ml) after 24-hour treatment. Of the four commercially available e-liquids, only cinnamon roll-flavored e-liquid stimulated a significant increase in IL-8 secretion (458.14 ± 26.20 pg/ml). IL-8 and IL-6 secretion at 16 hours post-exposure was significantly higher for cells exposed to e-cigarette aerosols than air controls for each exposure time period. The release of IL-6 into culture media was dose dependent. IL-6 secretion was significantly higher after 10-minute exposure than 5-minute exposure. The IL-8 levels were all significantly increased in cells exposed to e-cigarette aerosol compared with the air controls. | |
In cells exposed to e-cigarette aerosols, small but significant increases in fluorescence were observed. | |
Reference | Results and Observations |
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Lerner et al., 2016 | Results showed a small but significant reduction in the amount of mtROS present after 20 minutes of aerosol exposure compared to 10- or 15-minute exposures. |
The level of ARE-inducible Nqo1 expression increased for the 10- and 20-minute exposure sessions. Similarly, 10 minutes of exposure of HFL-1 to e-cigarette aerosol increased average Nqo1 levels when total cellular proteins were collected 18 hours following the exposures. | |
After 24 hours, the level of mtROS in cells treated with the copper metal nanoparticles increased significantly. | |
E-cigarette aerosol-exposed cells exhibited Complex IV sensitivity as observed by decreased levels of COX-2 (MTCO2) subunit in cell lysates collected 18 hours after aerosol exposure. A reduced level of Complex I NDUFB8 subunit in addition to reduced COX-2 was observed in cell lysates harvested 90 minutes after exposure. | |
5-minute aerosol exposure did not produce any difference in DNA fragmentation, whereas, 10- and 15-minute exposures resulted in significant increases in DNA fragmentation compared to air control groups. However, as the exposure duration increased, the likelihood for DNA damage increased in the air control group as well. | |
10-minute aerosol exposure resulted in increased IL-6 secretion (45.70 pg/ml) at 18 hours post-e-cigarette exposure, compared with IL-6 levels (7.34 pg/ml) from the air control group. IL-8 levels (28.02 pg/ml) also increased compared with the air control group (16.42 pg/ml). | |
Misra et al., 2014 | No cytotoxicity was observed for any of the e-liquids tested up to their respective highest sample doses. |
E-liquid exposure resulted in greater IL-8 release at high doses (6.9–13.8 mg/ml). Any IL-8 release from blu MM e-liquid treatments that were significant when compared with IL-8 release from exposure to combustible tobacco cigarettes occurred at doses approximately 42-fold higher than the combustible tobacco cigarettes. |
Reference | Results and Observations |
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Neilson et al., 2015 | Tissue cell viability following combustible tobacco cigarette smoke exposure was reduced in a time- and dose-dependent manner from 100% to 12% viability after 6 hours of exposure, relative to untreated controls. Exposure of EpiAirway™ tissue to either variety of e-cigarette did not reduce tissue viability relative to untreated control tissues. Thus, an ET50 for e-cigarette aerosol could not be calculated. No statistical difference in viability was seen between NJOY bold or NJOY menthol and diluting air controls. |
A dose-dependent decrease in cell viability was seen following incremental hourly exposures to cigarette smoke for up to 6 hours, resulting in reductions of around 90% at the highest dose. By contrast, the two e-cigarettes did not cause cytotoxic effects under any of the test conditions, despite a much larger puff volume and exposure frequency in the e-cigarette machine smoking regime. | |
Romagna et al., 2013 | From the 21 samples examined, only the coffee-flavored e-liquid exhibited a cytotoxic effect, and this only at the highest extract concentration. For this sample, the viability rate was 114.5 ± 2.0% at 3.125%, 112.2 ± 3.6% at 6.25%, 101.5 ± 3.1% at 12.5%, 92.0 ± 8.9% at 25%, 85.9 ± 11.8% at 50%, and 51.0 ± 2.6% at 100% extract concentration. Combustible tobacco cigarette smoke extract exhibited significant cytotoxicity at extract concentrations greater than 12.5%. For the majority of e-liquids (13 of 21), viability was not statistically different between extract concentrations. Thus, NOAEL for these samples was defined as 100% concentration. None of the 12 tobacco-flavored e-cigarette liquids tested were associated with a statistically significant difference in fibroblast viability. |
Reference | Results and Observations |
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Sancilio et al., 2016 | E-liquid exposure resulted in reduced metabolic activity in a time- and dose-dependent manner in HGFs. For e-liquids both with and without nicotine at 5 mg/ml and 2 mg/ml concentrations, the metabolic activity was reduced up to 20% of the control. |
There were no significant changes in apoptosis in the treated HGFs compared with untreated cells. After 48 hours, cell viability decreased in all the experimental conditions (about 60% versus about 85% in the controls), with a higher range in the 1-N sample (35.85% of viable cells). | |
The reactive oxygen species production showed a peak after 24 hours of treatment compared with untreated controls (771.6 [nicotine], 798.6 [warmed nicotine], 458.9 [no nicotine], and 687.6 [warmed, no nicotine] versus 200 [untreated]). In the nicotine-free fluid-treated HGFs, the ROS production was lower than in the other experimental conditions. However, effects were seen after 48 hours (540.7 nicotine-free versus 271.1 untreated), whereas the other samples showed no significant changes compared with the control after 48 hours. | |
Bax protein expression did not appear to be affected after 6 hours of exposure, but after 24 hours, it was higher in the e-liquid–exposed conditions than in the control sample (1.485-fold increase [nicotine], 1.605-fold increase [warmed nicotine], 1.490-fold increase [no nicotine], and 1.405-fold increase [warmed no nicotine] on the untreated samples). After 48 hours, Bax expression in the nicotine, warmed nicotine, and nicotine-free conditions remained higher than in the untreated HGFs (1.735-, 1.695-, and 1.385-fold increase on the untreated samples, respectively) while in the warmed e-liquid without nicotine, the increase was close to onefold. | |
Sancilio et al., 2017 | E-liquids with nicotine exerted cytotoxicity as demonstrated by the increased levels of LDH, in parallel to the presence of numerous vacuoles in the cytoplasm, as well as a decrease in collagen I production and an augmented LC3 II expression. Autophagic vesicles and an increased number of pro-collagen I molecules were present in the cytoplasm of fibroblasts exposed to nicotine-free fluids. In the same samples, the time-dependent activation of the lysosomal compartment with no changes in LC3 expression was detected. |
Reference | Results and Observations |
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Scheffler et al., 2015a | Primary NHBE48 cells were the most sensitive, responding to e-liquid aerosol exposure with a decrease in viability up to 60% and 52% compared to clean air-exposed cells. In comparison, combustible tobacco cigarette mainstream smoke–exposed cells showed only 7% viability of clean air–exposed cells. Immortalized CL-1548 cells are less sensitive to e-liquid aerosol (75% and 70% viability) and combustible tobacco cigarette smoke exposure (10% viability) compared to primary NHBE48 cells, but are still significantly more sensitive than A549 cells (88% viability for e-liquid aerosol, 21% for mainstream smoke exposure). In all cell types, no significant differences were seen after exposure to nicotine-containing and nicotine-free aerosol. |
The oxidative stress level is elevated in CL-1548 cells compared to A549 cells, but lower than those of primary NHBE48 cells. | |
Scheffler et al., 2015b | The authors found toxicological effects of e-cigarette aerosol and the humectant-only substances, whereas the nicotine concentration did not have an effect on cell viability. The viability of combustible tobacco cigarette mainstream smoke–exposed cells was 4.5–8 times lower and the oxidative stress levels 4.5–5 times higher than those of e-cigarette aerosol–exposed cells, depending on the donor. |
Welz et al., 2016 | Both fruit- and tobacco-flavored extracts were cytotoxic to oropharyngeal tissue, but fruit-flavored liquids showed a higher toxicity than tobacco-flavored ones. Additionally, incubation of mucosal tissue cultures with fruit-flavored extracts showed DNA fragmentation, but no serious DNA damage was seen in tissue cultures incubated in tobacco-flavored extracts. |
Reference | Results and Observations |
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Willershausen et al., 2014 | Starting at 24 hours, the highest reduction in the proliferation was observed for the treatment with menthol-flavored liquids, which was the only statistically significant reduction as compared to control cells. |
After an incubation time of 48 hours with the menthol-flavored liquid, the difference in comparison both to the control cells and the nicotine-treated cells was highly statistically significant (p < 0.001). Hazelnut flavor or lime flavor only caused a slight not statistically significant reduction of the proliferation rates at 48 hours. After 96 hours of incubation this strong growth-reducing effect of the menthol-flavored liquids persisted and was still statistically significant. | |
In comparison to the untreated cells, incubation with hazelnut-flavored (p < 0.024), lime-flavored (p < 0.009), or menthol-flavored liquids (p < 0.001) led to a statistically significant reduction of ATP detection. | |
The untreated human periodontal ligament fibroblasts and those incubated for 24 hours with PG showed good proliferation. Those incubated with nicotine-, hazelnut-, or lime-flavored liquids showed a slight growth reduction, while incubation with the menthol-flavored liquid produced a strong growth inhibition. The inhibitory effect of menthol flavor exposure on the fibroblast cells was especially noticeable in the migration assay. Only the menthol-flavored liquid caused a highly statistically significant reduction (p < 0.001) of cell migration after 72 hours in comparison to the control cells as well as to the cells treated with nicotine. | |
Wu et al., 2014 | Within the physiological nicotine range, e-liquid exposure did not cause noticeable cytotoxicity at either 24 or 48 hours. |
Exposure to e-liquid without nicotine increased IL-6 protein levels in a dose-dependent manner at both 24 and 48 hours. Addition of nicotine to e-liquid only marginally enhanced the IL-6 levels. | |
Cells exposed to tobacco-flavored e-liquid (without or with nicotine) had higher levels of HRV load than unexposed cells at both 6 and 24 hours. Compared with e-liquid without nicotine, the addition of nicotine into e-liquid either did not alter (at 6 hours) or slightly increased (at 24 hours, p = 0.05) HRV load. HRV infection significantly increased IL-6 production at both 6 and 24 hours in cells that were pre-exposed to the control (medium alone) or e-liquid with and without nicotine. |
Reference | Results and Observations |
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Yu et al., 2016 | E-cigarette exposure without nicotine induced a 10-fold increase in cell death, while e-cigarette exposure with nicotine induced a 10-fold increase compared with controls. |
UMSCC10B showed a statistically significant increased accumulation of arrest in G1, and HN30 showed an increase in G2, both independently of e-cigarette nicotine content. | |
A stepwise decrease in colony count and decreased survival was observed with increasing e-cigarette doses in both brands, independently of nicotine content. After exposure to 0.5% v/v nicotine-free e-cigarette aerosol, greater than a twofold decrease in survival was seen in all cell lines. |
NOTE: 2-MOCA = 2-methoxycinnamaldehyde; CSE = cigarette smoke extract; hESC = human embryonic stem cell; HFL1 = human fetal lung fibroblast; HGF = human gingival fibroblast; HNSCC = head and neck squamous cell carcinoma; HPdLF = human periodontal ligament fibroblast; hPF = human pulmonary fibroblast; HRV = human rhinovirus; hTBE = human tracheobronchial epithelial; HUVEC = human umbilical vein endothelial cell; LDH = lactate dehydrogenase; mNSC = mouse neural stem cell; MTT = 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; NHBE = normal human bronchial epithelial; NOAEL = no observed adverse effect level; PG = propylene glycol.
REFERENCES
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Behar, R. Z., B. Davis, Y. Wang, V. Bahl, S. Lin, and P. Talbot. 2014. Identification of toxicants in cinnamon-flavored electronic cigarette refill fluids. Toxicology in Vitro 28(2):198–208.
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