The effects of different vasopressors on the innate immune response during experimental human endotoxemia, a pilot proof-of-principle study

Septic shock is a major medical challenge associated with a high mortality rate
and increasing incidence. Massive release of pro-inflammatory mediators result
in hemodynamic instability, coagulation disorders and multiple organ
dysfunction. Previous strategies have aimed to treat sepsis by inhibition of
pro-inflammatory mediators, however, most of these approaches have failed. This
might be due to the fact that the majority of septic patients do not succumb to
the initial pro-inflammatory *hit*, but die at a later time-point in a
pronounced immunosuppressive state. This so-called *immunoparalysis*, which
renders patients extremely vulnerable to secondary infections, results from the
triggering of counter-regulatory anti-inflammatory pathways along with the
pro-inflammatory response. Immunoparalysis is increasingly being recognized as
the overriding immune dysfunction during sepsis. As a consequence, preservation
of immune function should be a pillar in current treatment strategies for
septic patients.

Noradrenaline is a catecholamine and is the cornerstone treatment for the
improvement of hemodynamic parameters and organ perfusion in septic shock.
However, catecholamines exert profound immunomodulatory effects which have
mainly been studied for adrenaline. It has been shown that adrenaline
profoundly inhibits LPS-induced production of TNF-α, and enhances production of
anti-inflammatory IL-10 in vitro, as well as in animal and human models of
inflammation. Furthermore, we have recently shown that endogenously increased
production of adrenalin in humans potently dampens the inflammatory response,
again through increased production of the anti-inflammatory cytokine IL-10.
The effects of noradrenaline, a potent α-adrenergic agonist which has β
affinity as well, on the immune system are far less studied: no in vivo (animal
or human) studies have been performed to date. Nevertheless, in vitro studies
have shown that noradrenaline inhibits LPS-induced pro-inflammatory cytokine
production as potently as adrenaline.

Considering the important role of immunoparalysis in patients with septic shock
and the anti-inflammatory effects of catecholamines, it is vital to review
current vasopressor management. Therefore the immunomodulatory effects of
noradrenaline in humans in vivo warrantinvestigation. Furthermore, effects on
the immune system of viable vasopressor alternatives for the treatment of
septic patients, namely phenylephrine and vasopressin, need to be established
in humans in vivo to evaluate whether they could represent non- or less
immunosuppressive alternatives.

Our primary objective is to investigate whether noradrenaline exerts
immunomodulatory effects in humans in vivo during experimental human
endotoxemia. This will be determined by comparing plasma levels of various pro-
and anti-inflammatory cytokines between the group that receives noradrenaline
infusion and the group that receives placebo (0.9% NaCl) infusion.

A randomized single-blind placebo-controlled study in healthy human volunteers
during experimental endotoxemia.
In this study we will enrol 40 subjects. There will be four groups, all will
undergo experimental endotoxemia combined with infusion of noradrenaline,
phenylephrine, vasopressin, or placebo.

Study groups:
1. The noradrenaline group: a group of 10 subjects that will receive
noradrenaline 0.05 µg/kg/min infusion for 5 hours, starting 60 minutes before
the endotoxemia experiment.

2. The phenylephrine group: a group of 10 subjects that will receive
phenylephrine 0.5 µg/kg/min infusion for 5 hours, starting 60 minutes before
the endotoxemia experiment.

3. The vasopressin group: a group of 10 subjects that will receive vasopressin
0.04 IU/min infusion for 5 hours, starting 60 minutes before the endotoxemia
experiment

4. The placebo group: a group of 10 subjects that will receive NaCL 0.9%
infusion for 5 hours, starting 60 minutes before the endotoxemia experiment.

Two hours before LPS administration, subjects will be admitted to the research
unit of the Intensive Care department. A venous cathether (fossa cubiti) will
be placed. Furthermore, an arterial catheter (brachial artery) will be inserted
after local anaesthesia using lidocaïne 2%. One hour prior to LPS
administration, subjects will receive a continuous infusion of noradrenaline,
phenylephrine, vasopressin, or placebo (for dosages, see study design) for 5
hours. At T=0, 2 ng/kg LPS will be administered intravenously. Subjects will be
monitored for 8 hours after LPS administration, after which catheters will be
removed and subjects can return home.

All subjects will visit the hospital for an initial screening visit in which a
medical interview and physical examination will be carried out (60 minutes). At
the screening visit blood will be collected.

Subjects will undergo experimental endotoxemia. Volunteers will be admitted and
monitored on the research unit of our intensive care unit for 10 hours and
receive an arterial line to facilitate blood pressure monitoring and blood
sampling. Furthermore, a venous cannula will be placed for the administration
of vasopressors, fluids and LPS.
Noradrenaline, phenylephrine and vasopressin can in theory induce hypertension
when administered to normotensive subjects (ie. healthy volunteers). However,
extensive research has been performed administering these drugs in healthy
volunteers showing no serious adverse events, no malignant hypertension and no
long term effects. Furthermore, vasopressors have been administered in numerous
trials to healthy volunteers in low dosages for short periodes of time over
normal venous canulas, showing nog local side effects.

The administration of LPS induces flu-like symptoms for approximately 4-6 hrs.
This model of systemic inflammation has been applied for 10 years in our
department and thousands of subjects in various research centres in the world
have participated in experimental endotoxemia trials. During the endotoxemia
experiment day, subjects will be under constant supervision of an experienced
intensivist with continuous monitoring of blood pressure (intra-arterially) and
heart rate (ECG). The endotoxemia protocol and associated risks are identical
to earlier endotoxemia studies performed in our institute. Furthermore,
randomization will be carried out in a manner guaranteeing that LPS will not be
administered to more than one person with the same intervention on one day. In
total, a maximum of 350 ml blood will be drawn during the study, which is
comparable to previous studies and never resulted in adverse events. Subjects
will not benefit directly from participation to the study. A subject fee is
provided