The vagus nerve can reflexively attenuate the innate immune response via binding of the vagal
neurotransmitter acetylcholine (ACh) to the α7 nicotinic
ACh receptor (α7nAChR). We recently reported potent anti-inflammatory effects of the α7nAChR agonist
GTS-21 in human leukocytes. In the present work, we investigated the anti-inflammatory effects of
GTS-21 on the innate immune response during experimental human
endotoxemia. We performed a double-blind placebo-controlled pilot study in 14 healthy nonsmoking male volunteers. Subjects received 150 mg
GTS-21 (n = 7) or placebo (n = 7) orally three times per day during 3 days before
endotoxin administration and on the day of the human
endotoxemia experiment. This
GTS-21 dosage scheme is the highest reported to be safe in humans. Subsequently, subjects were i.v. administered 2 ng/kg
endotoxin (LPS derived from Escherichia coli O:113). Serial blood withdrawals were performed to determine
GTS-21 plasma concentrations and inflammatory mediators. Plasma concentrations of
GTS-21 and its active metabolite 4-OH-GTS-21 were highly variable between subjects. LPS administration resulted in a transient inflammatory response. There were no differences in the LPS-induced
cytokine response between the GTS-21- and placebo-treated groups. However, within the GTS-21-treated group, higher
GTS-21 plasma concentrations correlated with lower levels of TNF-α (r = -0.78, P = 0.03),
IL-6 (r = -0.76, P = 0.04), and
IL-1RA (r = -0.86, P = 0.01), but not
IL-10 (r = -0.35, P = 0.25). In conclusion, although higher
GTS-21 plasma concentrations significantly correlated with lower
cytokine levels, the highest dose tested to be safe in humans did not result in significant differences in inflammatory mediators between the GTS-21- and placebo-treated groups.