| These
organotypic models of human tissue consist of normal, human-derived,
epidermal keratinocytes, that have been cultured to form a
multi-layered, highly differentiated (three-dimensional) model
of the human epidermis with functional stratum corneum, stratum
granulosum, stratum spinosum and basal cell layers.
Organotypic:
Closely resembling the normal morphology
of the target tissue
SPL offer two tissue models - the SkinEthic
Human Reconstituted Epidermal Model (HRE - SkinEthic
Laboratories, Nice, France) and the EpidermTM EPI-200 Epidermal
Tissue Model from MatTek Corporation (Ashland, MA, USA). Test substances
are applied to the culture surface for exposure periods of
three and 60 minutes. Corrosive substances are identified
by their ability to produce a decrease in cell viability below
a threshold level, as determined using the MTT dye reduction
assay.
MTT reduction assay:
A test in which a water soluble
yellow dye is converted to insoluble purple-coloured formazan
within viable cells
 The
SkinEthic HRE and EpidermTM
models have undergone formal validation and are acceptable
methods for determination of skin corrosivity potential in
accordance with OECD Test Guideline 431 “In
Vitro Skin
Corrosion: Human Skin Model Test” (adopted 6 May 2004)
and Method B.41 of Annex V to Directive 67/548/EEC (Council
Directive 2000/33/EEC).
(Pictured Right SkinEthic
- Human reconstituted human epidermis removed from the polycarbonate
substrate)
OECD TG 431 defines general functional and performance criteria
for new skin or epidermal models used in the context of the
guideline. To demonstrate that this concept works, SPL participated
in an inter-laboratory blind validation exercise, together
with ZEBET and BASF of Germany, using the SkinEthic
HRE model. The 12 reference chemicals specified in
OECD TG 431 were evaluated in each laboratory. Data on reproducibility
between laboratories, as well as predictions obtained, were
recently presented at the 43rd Society of Toxicology meeting
held at Baltimore, USA. Results obtained with SkinEthic
HRE were reproducible, both within and between laboratories,
and over time. The protocol was applicable to testing a  diverse
group of chemicals (both liquids and solids), including organic
acids and bases, neutral organics, inorganic acids and bases,
electrophiles and phenols.
Concordance between the in vitro prediction of skin corrosivity
potential obtained with SkinEthic
HRE, and in vitro predictions obtained with the accepted
tests of OECD TG 431 were excellent. The test was able to
distinguish between corrosive and non-corrosive chemicals
for all of the chemical types studied. |
This
ex vivo test is used to assess the skin corrosivity of a test
substance following topical application to the epidermal surface
of skin discs taken from a single rat. The method is conducted
in accordance with OECD Test Guideline 430 “In
Vitro Skin
Corrosion: Transcutaneous Electrical Resistance Test”
and Method B40 of Annex V to Directive 67/548/EEC (Council Directive
2000/33/EEC). The contact period between the test substance
and epidermis is 24 hours. Corrosive materials are identified
by their ability to produce a loss of normal stratum corneum
integrity and barrier function, which is measured as a reduction
in the TER below a threshold level of 5 kilo Ohms. A dye-binding
step can be conducted with surfactants and neutral organics
in order to reduce false positives obtained specifically with
these types of chemical.
The
Corrositex™ continuous time monitor assay is a standardised,
quantitative in vitro assay that is used to evaluate skin
corrosivity. The time taken for the test substance to ‘break
through’ a calibrated biobarrier (hydrated collagen
matrix) and produce a colour change in a chemical detection
system (an aqueous pH indicator solution) is recorded. The
result is compared to a classification chart to determine
corrosivity potential.