Terms of Reference
Two in vitro methods
developed to assess skin
corrosivity of chemicals, the
"Rat skin Trancutaneous
Electrical Resistance
(TER)test" and the "EPISKIN
test" have been validated by
ESAC (ECVAM Scientific Advisory
Committee).
The Scientific Committee
on Cosmetic Products and
Non-Food Products (SCCNFP) has
been requested by DG III to
advise the Commission on the
applicability of the methods to
the safety assessment of
chemicals used as cosmetic
ingredients.
1- Background
The European Centre for
the Validation of Alternative
Methods (ECVAM) has conducted
in 1996-1997 a validation study
of in vitro tests developed to
assess skin corrosivity of
chemicals. This study was a
follow-up to a pre-validation
study of tests developed for
replacing the in vivo Draize
skin corrosivity test in
rabbits.
The main objectives of
the validation study, as
defined by the sponsors and the
management team before the
study began, were :
(a) to identify tests
capable of discriminating
corrosives (C) from non
corrosive (NC) for selected
groups of chemicals (e.g.
organic acids, phenols) and/or
all chemicals (single chemical
entities only);
(b) to determine whether
the tests could identify
correctly known R35 (UN packing
group I) and R34 (UN packing
groups II & III) chemicals.
2- Organisation of the
study
The study was
coordinated from ECVAM. A
Management Team (MT) was
constituted by four
representatives of « lead
laboratories », each of them
being responsible for one of
the four tests being evaluated.
The tests selected for
inclusion in the validation
study were the rat
transcutaneous electrical
resistance (TER) test,
CorrositexTM, the Skin2TM
ZK1350 corrosivity test, and
EpiskinTM. Each test was
conducted in three different
laboratories, according to
principles, criteria and
procedures previously defined
by ECVAM. Prediction models for
each of the four tests were
defined in the test protocols.
Coordination /MT
/Laboratories
Sixty chemicals were
selected by an independent
Chemicals Selection
Sub-Committee, and distributed
coded to the participating
laboratories. These included
organic acids (6C/5NC), organic
bases (7C/3NC), neutral
organics (9NC), phenols
(2C/3NC), inorganic acids
(6C/1NC), inorganic bases
(2C/2NC), inorganic salts
(1C/2NC), electrophiles
(3C/5NC), and soaps/surfactants
(3NC). The selection is fully
described in a publication
(Ref. 1); the main criterion
for including chemicals in the
test set was that the
corrosivity classifications
were based on unequivocal
animal data.
The results obtained
were analysed by statistician
experts. The classifications of
the corrosivity potential of
the test chemicals, as derived
from the in vitro data obtained
in the three laboratories
conducting the test, were
compared to the in vivo
classifications independently
assigned to the chemicals
before the blind trial, to
yield sensitivity, specificity,
predictivity and accuracy of
the test.
3- Main results
The full details of the
validation study have been
published (Ref. 2). Two tests,
with a good reproductibility
within and between test
laboratories, proved applicable
to the testing of a diverse
group of chemicals : the TER
test and Episkin.
In the TER test, test
materials are applied for 2 to
24 hours to the epidermal
surface of skin discs taken
from the pelts of humanely
killed young rats, and
corrosive chemicals are
identified by their ability to
produce a loss of normal
stratum corneum integrity,
which is measured as a
reduction of the inherent
transcutaneous electrical
resistance (below a
predetermined threshold level).
Episkin is a
tri-dimensional human skin
model with a reconstructed
epidermis and a functional
stratum corneum. When utilised
in corrosivity testing,
application of test chemicals
to the surface of the skin for
3, 60 and 240 min, is followed
by an assessment of cell
viability.
Sensitivity,
specificity, predictivity and
accuracy in distinguishing
corrosive from non corrosive
chemicals were very high for
both tests: 88, 72, 72, 79 and
83, 80, 77, 81 % respectively
for the TER test and Episkin.
In addition, Episkin was also
able to distinguish between
known R35 (UN packing group I)
and R34 (UN packing groups II
& III) chemicals
4- Opinion of the SCCNFP
ECVAM Scientific
Advisory Committee (ESAC),
which had been fully informed
of the progression of the
validation procedure, reviewed
the final results and
unanimously endorsed a
statement that the rat skin TER
test is scientifically
validated for use as a
replacement for the animal test
for distinguishing between
corrosive and non corrosive
chemicals, and that Episkin is
scientifically validated as a
replacement for the animal
test, and that these tests are
ready for regulatory
acceptance.
Sixty chemicals were
used for the validation of
these two methodologies; twenty
of them are used as cosmetic
ingredients, according to the
"European inventory and common
nomenclature of ingredients
employed in cosmetic products"
(Ref. 3).
SCCNFP reviewed
publications from the
validation study and ESAC
statements, and propose that
these two methods could be
applied to the safety
assessment of chemicals used as
cosmetic ingredients.
A cosmetic ingredient or
mixture of ingredients can be
corrosive per se. When
corrosivity cannot be excluded,
testing for irritancy on
animals or humans should be
preceeded by a corrosivity test
using one of these two
validated in vitro
methodologies.
5- References
1- Barratt M.D. &
al. Toxicology in Vitro (1998)
12, 471-482
2- Barratt M.D. &
al. Toxicology in vitro (1998)
12, 483-524
3- Commission Decision
96/335 EC of 8 May 1996
establishing an inventory and a
common nomenclature of
ingredients employed in
cosmetic products J.O. L 132 of
1 June 1996