F E AT U R E
E-cig Aerosol Versus Smoke
Chemical analyses clearly show that
e-cigarette vapour is much simpler than
cigarette smoke, but what does this
mean in terms of biological impact? This
can be tested in the laboratory using cellbased tests. For example: an irritancy
test that uses a 3-D model of human lung
tissue (Fig 4) can be used to examine
the impact of aerosol versus smoke; and
Fig 4: 3D reconstructed human lung tissue model
Picture Credit: MatTek Corporation , Cilia (α-tubulin, red),
Tight Junctions (e-cadherin, green), Nuclei (DAPI, blue)
there is a ‘scratch test’ that examines
a tissue’s ability to repair itself (when
scratched) after exposure to e-cigarette
aerosol and cigarette smoke (Fig 5).
The irritancy test uses a unique
combination of systems to mimic vaping
and smoking. A smoking robot is used to
‘smoke’ or ‘vape’ to produce an aerosol
and a commercially available 3-D human
airway tissue model (EpiAirwayTM) is
exposed to the aerosol. A dye is used to
observe the impact of aerosol exposure
on the cells. Viable cells have an enzyme
that breaks down the dye so that it
changes from purple to yellow. Healthy
cells will therefore appear more yellow in
colour than non-viable cells.
This test has been used to test the
irritant potential of cigarette smoke and
e-cigarette vapour from two commercially
available e-cigarettes on human airway
tissue. The results show that exposure to
cigarette smoke for 6 hours causes near
complete death of human airway cells
in this test. In contrast, despite hours of
aggressive and continuous exposure, the
impact of the e-cigarette vapour on the
airway tissue was found to be similar to
that of air7.
Another test is the ‘scratch test’ or
‘wound-healing assay’. The basic steps
involve creating a ‘scratch’ in a single
layer of cells and capturing the images
at the beginning and at regular intervals
as cells move to close the scratch. The
impact of different substances on the
rate of wound closure can be measured
and compared, for example between
e-cigarette aerosol and cigarette smoke.
The scratch mimics natural wear and
tear in the cardiovascular system.
The test is designed to examine the
impact of smoke or vapour on the cells
ability to repair. In the human body, a
reduced ability to repair could lead to
blood vessel damage and eventually
cardiovascular disease.
This test was used to compare the effect
of e-cigarette vapour on wound healing
compared to cigarette smoke. When
the cells were exposed to smoke, they
appeared to lose their sense of direction
and position relevant to other cells, with
the result that they appeared ‘confused’
and could not find their way across
the gap – the wound did not close. By
contrast, when the cells were exposed
to e-cigarette vapour, the cells quickly
closed the gap in much the same way as
they do when exposed only to air8.
Real World Testing
Lab tests can be used to study the
products to determine whether the
aerosol from e-cigarettes contain fewer
toxicants than cigarette smoke and
Fig 5: A: Complete inhibition of wound healin g after
exposure to cigarette smoke B: Uninhibited wound
closure after exposure to e-cigarette aerosol
Despite hours of aggressive
and continuous exposure,
the impact of the e-cigarette
vapour on the airway tissue
was found to be similar to
that of air7.
to compare the biological impact of
e-cigarette aerosol on human tissue
models. Clinical testing with real
consumers is needed to determine
whether reductions in toxicants seen in
the lab translate into reductions in human
exposure, and whether these reductions
will make any difference to a person’s
individual risk when using new products
like e-cigarettes over a sustained period
of time. And finally real-world testing
is required to determine the impact of
e-cigarette use on population risk. In the
clinic, chemicals called biomarkers of
exposure, which can be found in blood,
saliva, and urine, can be measured
to determine a person’s exposure
to certain toxicants. A biomarker of
exposure can be the toxicant itself
or its metabolic breakdown product
– the higher the level of biomarkers,
the higher the exposure. A person’s
individual risk may be indicated by the
presence of certain other compounds
or physiological signs directly related to
smoking-related diseases. For example,
cholesterol levels can be monitored to
give an indication of an individual’s likely
cardi¬ovascular health.
Finally, the testing moves into ‘realworld’ use, to determine what impact
using a new product like e-cigarettes
has on population risk, in comparison to
cigarette smoking. The lab-based tests
and clinical assessment enable us to
understand the potential of e-cigarettes
to reduce risk. But, the impact of
e-cigarette usage and uptake by
consumers must be calculated in order
to assess their potential to reduce risk
at a population level. This assessment
framework will help build the required
evidence base needed to demonstrate
that novel tobacco and nicotine products
can deliver a net population health gain
in comparison to cigarette smoking.
References
1. WHO Report on the Global Tobacco Epidemic 2008. mPower report [http://www.who.int/tobacco/mpower/mpower_report_full_2008.pdf] 2. JAMA. Vol 311(2), 2014. Smoking Prevalence and
Cigarette Consumption in 187 Countries, 1980-2012. Marie Ng et al. p183-192doi:10.1001/jama.2013.284692. 3. E-cigarettes: an evidence update. A report commissioned by Public Health England,
2015; [https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/457102/Ecigarettes_an_evidence_update_A_report_commissioned_by_Public_Health_England_FINAL.pdf,
accessed 22nd October 2015] 4. Recent Advances in Tobacco Science: The scientific basis of harm reduction and the risk continuum Vol 41, 2015. A framework for the biological assessment of
reduced risk tobacco and nicotine products. F Lowe, IM Fearon, OM Camarcho, E Minet and J Murphy, p 51-8 5. BMC Public Health. Vol 13, 2013. A single-blinded, single-centre, controlled study in
healthy adult smokers to identify the effects of a reduced toxicant prototype cigarette on biomarkers of exposure and of biological effect versus commercial cigarettes Shepperd, C. et al. p690
6. A framework for the assessment of reduced risk tobacco and nicotine products, 69th Tobacco Science Research Conference, 2015 Keynote Lecture #2 C. Proctor, et al.
7. Toxicol in vitro., Development of an in-vitro cytotoxicity model for aerosol exposure using 3D reconstructed human airway tissue; application for assessment of e-cigarette aerosol. Vol 29, 2015 L
Neilson et al., p856-863
42 ISSUE 03 VAPOUROUND MAGAZINE