Effects of oxygen status on Hypoxia Inducible Factor 1-α. A pilot proof of principle study.

Oxygen is a widely used therapeutically agent for maintaining adequate tissue
oxygen levels in modern medicine. Low oxygen levels (hypoxia) can result in
inadequate tissue oxygenation, which can, when all compensation mechanisms fail
or are exhausted, result in organ failure. On the other hand, prolonged
hyperoxia can be toxic as well; probably due to formation of reactive oxygen
species (ROS). Recent in vitro and animal studies have established that oxygen
status and the innate immune system are intimately linked.
Hypoxia can exert pro-inflammatory effects, mainly through hypoxia-inducible
factor (HIF) of which HIF1α is the most studied, and conversely, inflammation
can induce an intracellular hypoxic state due to increased oxygen demand.
On the other hand, hyperoxia is related to immune suppression, as in animal
studies, hyperoxia has been shown to attenuate systemic inflammation and
improve survival in inflammatory conditions. However, hyperoxia-induced
immunosuppression renders animals increased vulnerable to pathogens. In
clinical studies, there is conflicting evidence on the effect of hyperoxia on
prevention of surgical site infections, with some reporting a 50% reduction in
the incidence of surgical site infections using 80% oxygen, while others report
a 100% increased incidence of surgical site infections when using an FiO2 of
80%.
Taken together, permissive hypoxia or hyperoxia may be a cheap,
non-pharmacological, non-invasive treatment modality to modulate the innate
immune response in a wide variety of inflammatory conditions, such as sepsis.
For instance, dampening innate immunity could be beneficial in the early
hyperinflammatory phase of sepsis, while stimulation of the innate immune
response could represent a novel treatment option to reverse sepsis-induced
immunoparalysis, a hyporesponsive state of the immune system frequently
encountered in patients after hyperinflammation has waned. However, up till
now, most of this evidence has been obtained in in vitro and animal studies,
and precise effects of hypoxia and hyperoxia on kinetics of HIF1α, ROS, and
innate immunity have only been sparsely studied. Therefore, in the present
study we wish to investigate the effect of hypoxia and hyperoxia on the
kinetics of HIF1α and ROS as well as measures of innate immunity in healthy
volunteers.

The primary objective of the study is to determine the effects of hyperoxia and
hypoxia in healthy volunteers on kinetics of HIF1α mRNA in circulating
leukocytes. Secondary objectives are to determine the effects of hyperoxia and
hypoxia on HIF1α protein and aHIF mRNA expression in circulating leukocytes,
the induction of ROS, phagocytic function of circulating leukocytes, ex vivo
stimulation of leukocyten with diverse inflammator stimuli, the release of
inflammatory cytokines, basic hemodynamic and ventilatory parameters, and to
evaluate their effects on tissue oxygenation, measured by near infrared
spectrometry.

A parallel, randomized study in healthy male volunteers. The subjects will be
randomized to hypoxia or hyperoxia.

In the hypoxia group: the subjects will breathe an individualized mix of
nitrogen and room air for three-and-a-half hours using an air-tight respiratory
helmet. The gas mixture will be adjusted to achieve a saturation of 80-85%. In
the hyperoxia group, subjects will breathe 100% oxygen for three-and-a-half
hours using the same respiratory helmet used in the hypoxia group.

All subjects will visit the hospital for a screening visit in which a medical
interview and physical examination will be carried out (30 minutes). At the
screening visit and the day after the experiment blood will be obtained by
venapuncture. During the experimental day, subjects will receive an arterial
line, placed under local anaesthesia. Furthermore, a venous cannula will be
placed for the administration of fluids. The subjects will be exposed to
hypoxia or hyperoxia for 3 hours, and will be monitored for 5.5 hour after
cessation of hypoxia or hyperoxia. There is a large body of scientific work
with induction of hypoxia in healthy human subjects; minor side effects as
nausea, headache and light-headedness have been reported after six hours of
hypoxia, making the chance of these side effects occurring in the present study
(3 hours of hypoxia) very low. There are no reports of damage or discomfort of
exposure to hyperoxia. The subjects will wear a respiratory helmet that is
approved for regular patient care. A physician or nurse will be present in the
experiment room at all times, and subjects will be continuously monitored. In
total, approximately 350 ml blood will be drawn during the study, which is
comparable to previous experiments, and has never resulted in adverse events.
Subjects will not benefit directly from participation to the study. A subject
fee is provided.