Development of a dermal TLR4 challenge in healthy volunteers.

Inflammation is a response to damaged tissue and/or pathogens resulting a
release of cytokines and subsequent cellular activation. Although inflammation
is in principle a healthy process, in some cases an excessive and/or poorly
regulated inflammatory response can be harmful to the host, which is the case
in many inflammatory disorders.

Toll-like receptors belongs to the family of pattern recognition receptors
(PRRs). These highly conserved receptors recognize pathogen-associated
molecular patterns (PAMPs) and danger associated molecular patterns (DAMPs).
Upon recognition PRRs induce the activation of a strong inflammatory response
and thereby kick starting the innate immune response. Toll-like receptor 4
(TLR4) is able to recognize several exogenous ligands of which
lipopolysaccharides (LPS) found on gram-negative bacteria is best known
(Molteni et al. 2016).

Systemic LPS administration in humans is a widely used, safe and well tolerated
method to study a controlled systemic inflammatory response (Andreasen et al.
2008, Van Poelgeest et al. 2018). This inflammatory response offers a platform
for the investigation of pharmacodynamic and potentially clinically significant
effects in early drug development. The disadvantage of a systemic LPS challenge
is that it is relatively burdensome for the volunteer, and that it cannot be
repeated over time. A local LPS challenge model could be an interesting drug
development tool, since it would allow repeated or multiple LPS stimulations
over time within one volunteer. However, a local dermal response to LPS in
healthy humans has only been studied once (Basran et al. 2013). Their interest
was mainly in neutrophil recruitment, therefore a more in depth
characterization of the TLR4 response to LPS in human skin is still lacking.

In 2016 Motwani et al. presented a challenge model in which they injected
UV-killed E. coli (a Gram-negative bacterium and thus containing LPS)
intradermally in healthy volunteers. Although UV-killed E. coli led to a strong
but transient local inflammatory response, the downside is that E. coli
contains multiple different PAMPs, which makes the subsequent inflammatory
response less specific.
Specific knowledge on the TLR4 response in human skin is of interest because
TLR4 signaling is indicated in several skin diseases such as psoriasis and acne
vulgaris.

The aim of this study is to characterize the inflammatory response upon
intradermal LPS injection in healthy volunteers. By doing so we create a
challenge model that temporarily induces skin inflammation via a specific
pathway which enables future application as proof-of-pharmacology or drug
profiling in drug developmental programs.

To characterize the response to intradermal LPS by:
- Clinical measures
- Biophysical measures
- Imaging
- Molecular and cellular responses
- Routine safety measures

A saline controlled, interventional study to characterize the inflammatory
response to intradermal LPS in healthy volunteers.

LPS, purified lipopolysaccharide prepared from Escherichia Coli: 113: H10:K
negative (U.S. Standard Reference Endotoxin)

No medical benefit can be expected from this study for the participating
subjects.
Risk assessment
Expected adverse events related to LPS administration
Intravenous administration of LPS can lead to influenza-like symptoms (e.g.
chills, headache, eye sensitivity to light, nausea, myalgia and arthralgia),
increase in core temperature and pulse rate, and decline in mean arterial
pressure. Most symptoms are dose-related and resolve within 2-6 hours.
(Andreasen et al., 2008). As with any study involving administration of
exogenous substance, rare side effects cannot be excluded beforehand. Reports
of a decrease in cardiac contractility have been made following administration
of 4 ng/kg bodyweight (Suffredini et al., 1989), but were temporary and were
resolved after 8 to 12 hours. Noteworthy, CHDR has extensive experience with
both in vivo and ex vivo LPS challenges (Dillingh et al., 2014; Monnet et al.,
2017; van Poelgeest et al., 2018) and will not administer a LPS dosage of more
than 0.5 ng/kg - 0.8 ng/kg (based on body weight of 50 kg - 80 kg), thereby
minimizing the chance of stated adverse events ever happening Basran et al.
have administered up to 45 ng LPS divided over 3 intradermal injections and
this led a localized painless erythema, and no adverse effects deemed to be
related to systemic LPS exposure were observed. A related study by Gilroy et
al. used UV-killed E. coli to induce an intradermal inflammatory response. This
inflammatory response peaked at 4-6 hours and subsided over a period of
approximately 48 hours. In this current study the LPS challenge will provide a
safer and more controlled alternative when compared to the UV-killed E. coli
challenge.

Expected adverse events related to the suction blister device
During the study suction blisters will be induced on the LPS and saline
injected skin. The suction blister device (NP-4, Electric Diversities,
Maryland, USA) is widely used in dermatological research settings. Using
negative pressure (up to 8 in/Hg) a 10mm diameter blister is formed in
approximately 60 to 90 minutes. The blister formation process is not painful.
Once the blister is formed the roof is pierced with a needle and the blister
fluid is aspirated, after which the blister is dressed with a small gauze. Rare
complications of a the blister include infection and post inflammatory
hyperpigmentation. To minimize the risk of post inflammatory hyperpigmentation
Fitzpatrick skin types 4-6 are excluded.