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Lecture Notes - Course Skin Sensitization


After understanding the processes that happen in our body during skin sensitization, the targeting of alternative test methods becomes clearer.

Scheme of Adverse Outcome Pathway - Skin Sensitization


It has been shown that skin sensitizers activate the ARE-pathway (=antioxidant response
element). An activation of the pathway protects a cell from oxidative-induced stress. How
does this work?

First of all – oxidative stress can have many causes for example UV-light which can itself
cause the build-up of reactive oxygen species (ROS). To avoid the interaction of reactive
molecules with cell proteins or DNA our body produces more metabolizing enzymes to
eliminate the substance.

As we already know, skin sensitizers can activate the pathway too. The induction of
enzymes is what we can finally measure in our test method via Luciferase Genes.

Small electrophilic substances can bind to Keap1 which is the sensor protein of the
pathway. Now Nrf2 can dissociate from Keap1 which it was bound to. Nrf2 is a
transcription factor that causes the transcription of ARE-dependent genes which are
coding detoxifying enzymes.


Luciferases are enzymes that catalyze a reaction which causes light. Bioanalytically they
are used as so called “Reporter Genes”. We are able to insert the luciferase-gene behind a
certain promotor region on our DNA. If the gene is induced – for example because of a skin
sensitizer – we can measure the amount of expressed genes by measuring the power of
the light.


Keratinosens/ ARE-dependent pathway:
Link to pdf from Eurofins.

Eurofins provides different analytic testing services for clients all around the globe. In this abstract
they informed about the KeratinoSens as an alternative test method and gave the reader some
extra information about the Nrf2-ARE-dependent pathway for better understanding.

The role of transcription factor NrF2 in skin cells metabolism

the article informes about the role of transcriptional factor Nrf2 in skin cells metabolism. In the
beginning it gives a short summary on how skin cells react to oxidative stress and explains the role
of the Nrf2-ARE-dependent pathway.

Luciferase genes:
The wikipedia article explains why Luciferase genes can be used as a biochemical marker in analytics and
helps understanding the evaluation of KeratinoSens.

Mutual Acceptance of data

In 1981 the OECD established the principle of Mutual Acceptance of Data, which states that…

“the test data generated in any member country in accordance with OECD Test Guidelines and Principles of Good Laboratory Practice (GLP) shall be accepted in other member countries for assessment purposes and other uses relating to the protection of human health and the environment”.

This principle has various advantages like saving huge amounts of money and less animal-testing.



Guidance document on Good In Vitro Method Practice (GIVIMP)

This is a lexicon, written by the OECD to explain important terms such as “mutual acceptance of data” (MAD), which is an important principle to reduce animal testing worldwide.
Link to OECD website

On this webpage the OECD gives more information on the benefits of MAD, the criteria and the conditions for taking part. // intermediate