Pilot study on the effect of prophylactic versus therapeutic treatment with coal tar and vaseline lanette ointment on the skin barrier repair mechanisms in absence of a chronic inflammatory component.

Atopic dermatitis (AD) is characterized by a skin barrier disturbance often
caused by loss-of-function mutation in the Filaggrin (FLG) gene. Mutations in
the FLG gene lead to a diminished protein expression and are the main risk
factor for developing AD. Improvement of the skin barrier is considered an
important therapeutic strategy. One of the possibilities for such a treatment
is the topical application of coal tar. The use of coal tar for skin diseases
was first described by Hippocrates and despite the more than 2000 years of use,
its mechanism of action remained unidentified until the recent study of our
department. We showed that coal tar activates the aryl hydrocarbon receptor
(AHR) in skin and thereby induces the expression of important skin barrier
proteins and dampens the inflammatory process. This study was an important
first step in unraveling the mechanism of action of this ancient therapy. The
paradigm that FLG expression is a measure of skin barrier function and that the
lack of FLG is causally related to skin barrier dysfunction is under debate.
The question remains whether the induction of FLG by coal tar actually leads to
an improved skin barrier function in vivo, or that other mechanisms are causing
the therapeutic efficacy of coal tar in AD.

To study if the induction of skin barrier proteins, like FLG, by coal tar leads
to an improved skin barrier repair and function in the absence of a chronic
inflammatory component.

Vehicle-controlled intervention pilot study

Healthy volunteers are asked to apply coal tar ointment or the vehicle
(petrolatum) on defined skin areas of the lower back during four days.

Healthy volunteers visit our clinic three times in seven days time. During four
days they will apply locally the ointments on their skin of the lower back.
Visits will take between 45 and 120 minutes. During the visits we take
non-invasive skin barrier measurements. This will cause no harm or discomfort
to the volunteers. The tapestripping procedure is also non-invasive with
minimal discomfort. A total of four skin biopsies will be taken (4mm in
diameter) under local anesthesia. Skin biopsies of this size do not require
stitches and heal without any complications, leaving only a little scar. We
will exclude people who are known to develop hypertrophic scars. The expected
risks of study are therefore negligible.