Table 1.
Major Characteristics of the 53 Included Studies
| Study | Year | City, Country |
Study Type | Tissue Type | Comparison to cigarette smoke | Sample, Participant, or Animal | Duration of Exposure | Methodology | Site | Flavors Examined (if stated) |
E-Cigarette Components (if stated) |
Oxford Level of Evidence | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Oral Cavity | |||||||||||||
| Ji EH, et al12 | 2016 | Multi-national (USA, China) | Basic Science | Human | No | Oral keratinocyte cell line | 24 hours of e-cigarette aerosol exposure | ATP assay, GSH assay, qPCR | Oral mucosa | Not stated | PG/VG + Nicotine + Flavor | 5 | |
| Franco T, et al13 | 2016 | Magna Graecia, Italy | Clinical | Human | Yes | Buccal mucosa scrape biopsy from 23 cigarette smokers, 22 e-cigarette users, and 20 non-smokers | Not stated | Exfoliative cytology, Optical microscopy | Buccal mucosa | Not stated | Not stated | 2b | |
| Ganapathy V et al14 | 2017 | Multi-national (USA, India) | Basic Science | Human | Yes | Dysplastic oral keratinocyte cell line (POE9n), Oral SCCa cell line (UM-SCC-1) | 1, 10, or 100 puffs/5 L, 1 hour/day, every other day for 2 weeks of e-cigarette aerosol condensate exposure | q-PADDA assay, ELISA, MTT assay, TAC assay, DCFDA assay, RT-PCR, Western Blot | Oral mucosa | Traditional, Desert Sands | PG/VG +/− Nicotine + Flavor | 5 | |
| Tommasi S, et. al.15 | 2019 | Los Angeles, CA, USA | Clinical | Human | Yes | Buccal mucosa scrape biopsy from 42 e-cigarette users, 24 cigarette smokers, and 27 non-smokers | Not stated | RNA-sequencing, qRT-PCR, IPA | Buccal mucosa | Not stated | Not stated | 2b | |
| Iskander AR, et al16 | 2019 | Multi-national (Switzerland, USA) | Basic Science | Human | Yes | Organotypic buccal epithelial cultures (MatTek) | 28 minutes of e-cigarette aerosol exposure | Histopathology, Multiplex immunoassay, qRT-PCR, IPA | Buccal mucosa | Not stated | PG/Glycerol +/− Nicotine +/− Flavor | 5 | |
| Ureña JF, et al17 | 2020 | University Park, PA, USA | Basic Science | Human | No | Oral SCCa cell line (SCC-25) | 45 total puffs of 4 seconds duration of e-cigarette aerosol exposure | MTT assay, Immunofluorescence | Oral mucosa, Gingiva | Lava Flow, Very Cool, Hawaiian Pog, American Patriots | PG/VG +/− Nicotine + Flavor | 5 | |
| Tsai KYF, et al18 | 2020 | Provo, UT, USA | Basic Science | Human | No | Oral SCCa cell line (Ca9-22), Tongue SCCa cell line (CAL-27) | 24 hours of e-liquid exposure | Real-Time Cell Invasion, Immunofluorescence, ELISA | Oral mucosa, Tongue | Red Hot, Green Apple | PG/VG +/− Nicotine + Flavor | 5 | |
| Pop AM, et. al.19 | 2021 | Tirgu Mures, Romania | Clinical | Human | Yes | Buccal mucosa scrape biopsy from 25 cigarette smokers, 23 e-cigarette users and 20 non-smokers | ≥ 12 months of daily e-cigarette use | Exfoliative cytology, Optical microscopy | Buccal mucosa | Not stated | Not stated | 2b | |
| Guo J, et. al.20 | 2021 | Minneapolis, MN, USA | Clinical | Human | Yes | Buccal mucosa scrape biopsy from 35 non-smokers, 30 cigarette smokers, and 30 e-cigarette users | ≥ 3 months of daily e-cigarette use; ≥ 12 months of daily cigarette use | LC-NSI-HRMS/MS | Buccal mucosa | Not stated | Not stated | 2b | |
| Muqawwi et al21 | 2021 | Bandung, Indonesia | Clinical | Human | Yes | Buccal mucosa scrape biopsy from 20 non-smokers, 20 cigarette smokers, and 15 e-cigarette users | ≥ 12 months of e-cigarette use | Micronucleus assay | Buccal mucosa | Not stated | Not stated | 2b | |
| Tellez CS, et al22 | 2021 | Multi-national (USA, Japan) | Basic Science | Human | Yes | 3 immortalized oral epithelial cell lines | 20 minutes of e-cigarette aerosol exposure | Neutral red uptake assay, ROS-Glo assay, TBARS assay, Alkaline comet assay, Micronuclei assay | Oral mucosa | Arctic Blast, Blue Pucker, Jamestown, Love Potion, Mardi Gras, Midnight Splash, Port Royale, Tobacco Row, Tortuga, Uptown | PG/VG +/− Nicotine +/− Flavor | 5 | |
| Schwarzmeier LAT, et. al.23 | 2021 | Sao Jose dos Campos, Brazil | Clinical | Human | Yes | Oral cavity scrape biopsy from 20 e-cigarette users, 22 current cigarette smokers, 22 former cigarette smokers, and 27 non-smokers | ≥ 5 months of e-cigarette use | Exfoliative cytology, Optical microscopy | Lateral tongue, floor of mouth | Not stated | Not stated | 2b | |
| Hamad S, et. al.24 | 2021 | Chapel Hill, NC, USA | Clinical | Human | No | Buccal mucosa scrape biopsy from 3 healthy e-cigarette users | ≥ 2 months of daily e-cigarette use; Scripted vaping of 20 puffs over 20 minutes | qRT-PCR, IPA | Buccal mucosa | Not stated | PG/VG + Nicotine | 2b | |
| Cátala-Valentín AR, et al25 | 2022 | Orlando, FL, USA | Basic Science | Human | No | Oral epithelial cell line (OKF6) | 30 minutes of e-cigarette condensate exposure | EdU cell proliferation assay, Biofilm measurement, ELISA, qRT-PCR, Immunofluorescence | Oral mucosa | None | PG/VG +/− Nicotine | 5 | |
| Marinucci L et al26 | 2022 | Perugia, Italy | Basic Science | Human | Yes | Oral keratinocyte cell line (PSC-200-01) | 24 hours of e-cigarette aerosol condensate exposure | MTT assay, Scanning electron microscopy, Scratch assay, Flow cytometry, qRT-PCR | Oral mucosa | Tobacco | PG/VG + Nicotine + Flavor | 5 | |
| Cheng G et al27 | 2022 | Minneapolis, MN, USA | Clinical | Human | Yes | Buccal mucosa scrape biopsy from 8 cigarette smokers, 20 e-cigarette users and 20 non-smokers | ≥ 3 months of 4 days/week of e-cigarette use; ≥ 12 months of daily cigarette use | LC-NSI-HRMS/MS | Buccal mucosa | Not stated | Not stated | 2b | |
| Robin H et al28 | 2022 | South Jordan, UT, USA | Basic Science | Human | No | Oral SCCa cell line (Ca9-22), Tongue SCCa cell line (CAL-27) | 6 hours of e-cigarette aerosol condensate exposure | ELISA, Western Blot, Real time cell invasion | Oral mucosa | Red Hot, Green Apple | PG/VG +/− Nicotine + Flavor | 5 | |
| Reeve G et al29 | 2022 | New York, NY, USA | Clinical | Human | No | Non-smokers and e-cigarette users | Active e-cigarette users | Histopathology, Transcriptomics | Oral mucosa | Not stated | Not stated | 2b | |
| Mandour D et al30 | 2023 | Zagazig, Egypt | Basic Science | Murine | No | 30 adult male albino rats | 1 hour/day, 5 days/week, for 4 weeks of e-cigarette aerosol exposure | ELISA, Histopathology, Immunohistochemistry | Submandibular gland | Not stated | VG/PG + Nicotine + Flavor | 5 | |
| Elmahdi F et al31 | 2023 | Madinah, Saudi Arabia | Clinical | Human | No | Buccal mucosa scape biopsy from 250 non-smokers, 250 e-cigarette users | ≥ 6 months of daily e-cigarette use | Papanicolaou staining, Immunohistochemistry | Buccal mucosa | Not stated | Not stated | 2b | |
| Tommasi S et al32 | 2023 | Los Angeles, CA, USA | Clinical | Human | Yes | Oral mucosa scrape biopsy from 24 non-smokers, 24 e-cigarette users, 24 cigarette smokers | ≥ 3x week for 6 months of e-cigarette use; ≥ 3x week for 12 months of cigarette use | LA-QPCR | Oral epithelium | Fruit, Sweet, Mint/Menthol, Tobacco | VG/PG + Nicotine + Flavor | 2b | |
| de Lima JM, et al33 | 2023 | Multi-national (Brazil, Canada) | Basic Science | HumanMurine | No | Human oral mucosal keratinocyte and tongue epithelial cell lines, human tongue SCCa cell lines (CAL-27, HSC3), and mouse oral cancer cell line (AT84) | 7, 24, or 48 hours of e-liquid exposure | MTT assay, Colony formation assay, Wound healing migration assay, Cell invasion assay, Western Blot, qRT-PCR, Immunocytochemistry | Oral mucosa, Tongue | Not stated | PG/Glycerine + Nicotine + Flavor | 5 | |
| Oropharynx | |||||||||||||
| Welz C, et. al.34 | 2016 | Munich, Germany | Basic Science | Human | No | Primary oropharyngeal epithelial cells from healthy adult donors | 24 hours of e-liquid exposure | MTT assay, Alkaline microgel electrophoresis | Oropharynx mucosa | Apple. Cherry, Tobacco | PG/VG + Nicotine + Flavor | 5 | |
| Nasal Cavity/Nasopharynx | |||||||||||||
| Martin EM, et. al.35 | 2016 | Chapel Hill, NC, USA | Clinical | Human | Yes | Nasal biopsy and lavage fluid from 13 non-smokers, 14 cigarette smokers, 12 e-cigarette users | ≥ 6 months of e-cigarette use | Liquid chromatography tandem mass spectrometry, Nanostring based gene expression analysis, IPA, ELISA | Nasal mucosa, Nasal lavage fluid | Not stated | Not stated | 2b | |
| Kumral TL, et. al.36 | 2016 | Istanbul, Turkey | Clinical | Human | No | 72 current smokers in cessation clinic randomized to e-cigarette smoking group (n=42) or non e-cigarette group (n=30). | ≥ 5 years of daily cigarette use | Mucociliary clearance (via saccharin transit time), SNOT-22 | Nasal epithelium | Not stated | Not stated | 2b | |
| Carson JL, et al.37 | 2017 | Chapel Hill, NC, USA | Basic Science | Human | Yes | Primary nasal epithelial cells from healthy non-smoking adults | 20 consecutive e-cigarette “puffs” | Electron microscopy, Nitric oxide production, Ciliary beat frequency | Nasal epithelium | Tobacco | PG/VG + Nicotine + Flavor | 5 | |
| Miyashita L et al38 | 2018 | Multi-national (UK, South Africa) | Basic Science | Human, Murine | No | 11 adult vaping males; Primary nasal epithelial cells from a healthy never-smoking, never-vaping adult; Female CD1 mice | ≥ 1 week of e-cigarette use; 2x/day of e-cigarette aerosol condensate exposure | Immunostaining, Flow cytometry, Adhesion assay, Miles and Misra method | Nasal epithelium | Not stated | PG/VG +/− Nicotine + Flavor | 5 | |
| Jabba S et al39 | 2020 | Durham, NC, USA | Basic Science | Human | No | Primary nasal epithelial cells (PromoCell) | 24 hours of e-liquid flavor exposure | LIVE/DEAD Viability/Cytotoxicity assay | Nasal epithelium | Benzaldehyde, Vanillin | PG + Flavor | 5 | |
| Rouabhia M, et al40 | 2020 | Quebec, Canada | Basic Science | Human | Yes | Primary nasal epithelial cells from healthy non-smoking adults | 15 minutes, 2x/day, for 3 days of e-cigarette aerosol exposure | Tryptan blue exclusion assay, LDH assay, MTT assay, Ki67 immunostaining, ELISA assay | Nasal epithelium | Smooth Canadian Tobacco | PG/VG +/− Nicotine + Flavor | 5 | |
| Rebuli ME, et al41 | 2021 | Chapel Hill, NC, USA | Clinical | Human | Yes | Nasal lavage and epithelial lining fluid from 20 non-smokers, 14 cigarette smokers, and 15 e-cigarette users | Not stated | Viral load, NanoString nCounter, qRT-PCR, ELISA, Influenza-specific IgA quantification | Nasal epithelial-lining fluid, Nasal lavage fluid, Nasal mucosa | Not stated | Not stated | 2b | |
| Escobar YN et al42 | 2021 | Chapel Hill, NC, USA | Basic Science | Human | No | Primary nasal epithelial cells from adult smokers and nonsmokers |
20 consecutive e-cigarette “puffs” each of 4 secs duration | Western blot, ELISA | Nasal epithelium | None | PG/VG +/− Nicotine | 5 | |
| Kwak S et al43 | 2021 | Daegu, Republic of Korea | Basic Science | Human | No | Primary nasal epithelial cells (Epithelix) | 24 hours of Glyoxal or Methylglyoxal exposure | WST-1 assay, Western blot, ELISA | Nasal epithelium | None | Glyoxal or Methylglyoxal | 5 | |
| Hinds D et al44 | 2022 | Iowa City, IA, USA | Basic Science | Murine | No | Male golden Syrian Hamsters | 2 hours/day for 2 days of e-cigarette aerosol exposure | Histopathology, qRT-PCR | Nasal epithelium | None | PG/VG +/− Nicotine | 5 | |
| Karey E et al45 | 2022 | Chapel Hill, NC, USA | Clinical | Human | Yes | Nasal epithelial lining fluid from 37 never-smokers, 16 cigarette smokers, and 20 e-cigarette users | E-cigarette or cigarette use within last 7 days | ELISA | Nasal epithelial lining fluid | Not stated | Not stated | 2b | |
| Pozuelos et al46 | 2022 | Riverside, CA, USA | Clinical | Human | Yes | Nasal biopsy from 3 never-smokers, 3 cigarette smokers, and 3 e-cigarette users | Active e-cigarette or cigarette use | RNA sequencing, Gene Ontology, IPA | Nasal epithelium | Not stated | Not stated | 2b | |
| Nicholas BD, et. Al.47 | 2022 | Syracuse, NY, USA | Basic Science | Murine | No | Male and female BALB/cJ mice | 15 minutes, 3x/day for 5 days/week for 8 weeks of e-cigarette aerosol exposure | Histopathology | Eustachian tube mucosa | Tobacco | PG/VG + Flavor | 5 | |
| Larynx | |||||||||||||
| Salturk Z, et al.48 | 2015 | Istanbul, Turkey | Basic Science | Murine | No | Female Wistar albino rats | 1 hour/day for 4 weeks of e-cigarette aerosol exposure | Histopathology, Ki67 immunostaining | Vocal fold epithelium | None | PG/VG + Nicotine | 5 | |
| Ha TN, et. Al.49 | 2019 | Houston, TX, USA | Basic Science | Murine | Yes | C57BL/6 mice | 31 minutes/day, 5 days/week for 16 weeks of e-cigarette aerosol exposure | ELISA | Larynx | None | PG/VG +/− Nicotine | 5 | |
| Hassan NH, et al50 | 2022 | Zagazig, Egypt | Basic Science | Murine | No | Adult male Wistar albino rats | 1 hour/day, 5 days/week for 4 weeks of e-cigarette aerosol exposure | Histopathology, Ki67 and p53 immunostaining, MDA and TAC levels, Transmission electron microscopy | Larynx | Not stated | PG/VG + Nicotine + Flavor | 5 | |
| Martinez JD, et al.51 | 2022 | Palo Alto, CA, USA | Basic Science | Human | Yes | Immortalized vocal fold fibroblast cell line | 24 hours of e-cigarette condensate exposure | MTT assay, qRT-PCR, Immunofluorescence | Vocal fold epithelium | None | PG/VG +/− Nicotine | 5 | |
| Easwaran M et al52 | 2023 | Stanford, CA, USA | Basic Science | Murine | No | Male C57BL6/J mice | 2 hour/day for 1, 5, and 10 days of e-cigarette aerosol exposure | Histopathology, Immunohistochemistry, immunofluorescence, Scanning electron microscopy | Larynx | Mint, Mango | PG/VG + Nicotine + Flavor | 5 | |
| Trachea | |||||||||||||
| Wu Q et al53 | 2014 | Denver, CO, USA | Basic Science | Human | No | Primary tracheobronchial epithelial cells | 24 or 48 hours of e-liquid exposure | LDH assay, ELISA, qRT-PCR | Trachea | Tobacco | PG/VG +/− Nicotine | 5 | |
| El-Merhie et al54 | 2021 | Borstel, Germnay | Basic Science | Drosophilia melanogaster | No | L3 larvae | 2 min, every hour x 8 sessions of e-cigarette aerosol exposure | Stereomicroscope, NeuronJ | Trachea | None | PG/VG + Nicotine | 5 | |
| Multi-site | |||||||||||||
| Manyanga J, et al55 | 2021 | Oklahoma City, OK, USA | Basic Science | Human | Yes | Floor of mouth SCCa cell line (UM-SCC-1), Tongue SCCa cell line (WSU-HN6), and Pharyngeal SCCa cell line (WSU-HN30) | 48 hours of e-cigarette condensate exposure | Tryptan blue exclusion assay, MTT assay, qRT-PCR, Western Blot | Tongue, Floor of mouth, and Pharynx | Not stated | PG/VG +/− Nicotine | 5 | |
| Werley MS, et al56 | 2016 | Richmond, VA USA | Basic Science | Murine | No | Male and female Sprague-Dawley rats | 16, 48, or 160 minutes/day for 13 weeks of e-cigarette aerosol exposure | Histopathology | Nasal epithelium, Larynx | Not stated | PG/VG +/− Nicotine +/− Flavor | 5 | |
| Phillips B, et al57 | 2017 | Multi-national (Singapore, Germany, Switzerland) | Basic Science | Murine | No | Male and female Sprague-Dawley rats | 6 hours/day, 5 days/week for 13 weeks of e-cigarette aerosol exposure | Histopathology, DNA microarray, Proteomics | Nasal epithelium, Larynx | None | PG/VG +/−Nicotine | 5 | |
| Lee KM, et al58 | 2018 | Multi-national (Switzerland, USA) | Basic Science | Murine | Yes | Female C57BL/6 mice | 4 hours/day for 13 days of e-cigarette aerosol exposure | Histopathology | Nasal epithelium, Larynx, trachea | Not stated | PG/VG + Nicotine +/− Flavor | 5 | |
| Ho J, et al59 | 2020 | Multi-national (Singapore, Switzerland) | Basic Science | Murine | No | Male and female Sprague-Dawley rats | 6 hours/day, 5 days/week for 13 weeks of e-cigarette aerosol exposure | Histopathology, DNA microarray | Nasal epithelium, Larynx | Not stated | PG/VG +/− Nicotine +/− Flavor | 5 | |
| Ni F, et. al.60 | 2020 | Baltimore, MD, USA | Basic Science | Murine | No | Male and female C57BL/6 mice | 30 minutes of e-cigarette aerosol exposure | Immunohistochemistry, Event-related potential recordings | Nasal epithelium, Trachea | Vanilla, Menthol, Cinnamon | PG/VG + Nicotine + Flavor | 5 | |
| Wong ET et al61 | 2021 | Multi-national (Singapore, Switzerland, USA, Germany) | Basic Science | Murine | Yes | Female ApoE−/− mice | 3 hours/day, 5 days/week for 6 months of e-cigarette aerosol exposure | Histopathology, Transcriptomics | Nasal epithelium, Larynx, Trachea | Not stated | PG/VG +/− Nicotine +/− Flavor | 5 | |
| Kim M et al62 | 2022 | Kansas City, KS, USA | Clinical & Basic Science | Human, Sheep | No | Primary nasal epithelial cells and epithelial lining fluid from healthy non-smoking adults; Tracheal secretions from adult female sheep | Humans vaped 80 puffs/day for 8 days; Sheeps exposed to 80 puffs/day for 5 days of e-cigarette aerosols | Nasal ion transport assay, ELISA | Nasal epithelium, Nasal epithelial lining fluid, Tracheal secretions | None | VG +/− PG | 2b | |
| Wong ET, et al63 | 2022 | Multi-national (Singapore, Switzerland, USA) | Basic Science | Murine | Yes | Male and female A/J mice | 6 hours/day for 5 weeks of e-cigarette aerosol exposure | Histopathology | Nasal epithelium, Larynx, Trachea | Not stated |
PG/VG + Nicotine +/− Flavor | 5 | |
| Desai R et al64 | 2023 | Multi-national (USA, Greece) | Basic Science | Murine | Yes | Male and female Sprague-Dawley rats | 6 hours/day, 5 days/week for 90 days of e-cigarette aerosol exposure | Histopathology | Nasal epithelium, Larynx, Trachea | Virginia Tobacco, Menthol | PG/VG + Nicotine + Flavor | 5 | |
Abbreviations: ATP, Adenosine; GSH, Glutathione; qPCR, quantitative polymerase chain reaction, PG, propylene glycol; VG, vegetable glycerin; SCCa, squamous cell carcinoma; q-PADDA, quantitative primer-anchored DNA damage detection assay; ELISA, enzyme-linked immunosorbent assay; MTT, 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide; TAC, total antioxidant capacity; DCFDA, 2’,7’–dichlorofluorescin diacetate; qRT-PCR, reverse transcription quantitative polymerase chain reaction; IPA, Ingenuity Pathway Analysis; LC-NSI-HRMS/MS, Liquid Chromatography-Nanoelectrospray Ionization-High-Resolution Tandem Mass Spectrometry; ROS, reactive oxidative species; TBARS, Thiobarbituric Acid Reactive Substances; EdU, 5-ethynyl-2’-deoxyuridine; LA-QPCR, long-amplicon quantitative polymerase chain reaction; SNOT-22, Sino-nasal Outcome Test; LDH, lactatae dehydrogenase; WST-1, Water-soluble tetrazolium salt-1, MDA, malondialdehyde