Tempol modulates the leukocyte response to inflammatory stimuli and attenuates endotoxin-induced sickness behaviour in mice.

Background and aims: Lipopolysaccharide (LPS), an endotoxin, is a component of the outer membrane of Gram-negative bacteria that is able to activate the peripheral immune system, leading to changes in signalling pathways that act locally and systemically to achieve adaptive responses. Sickness behaviour is a motivational state in response to endotoxin exposure and includes depressed activity and a reduction of exploratory behaviour, potentially reorganising organism priorities to cope with infectious diseases. We hypothesised that 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) modulates the leukocyte response to endotoxins and decreases LPS-induced sickness behaviour in mice.Methods: The effects of Tempol on LPS-induced peritonitis and the respiratory burst of neutrophils primed with LPS and triggered by phorbol 12-myristate-13-acetate (PMA) were evaluated. To evaluate the effects of Tempol on sickness behaviour, the mice were submitted to an open field and forced swim tests.Results: Tempol (50-100 μM/106 cells) decreased the respiratory burst of LPS-primed and PMA-stimulated neutrophils in vitro. In vivo, this nitroxide (30 and 100 mg/kg body weight) inhibited leukocyte migration to the peritoneal cavity after LPS administration in mice. Moreover, Tempol pretreatment (30 and 100 mg/kg body weight) before LPS administration also attenuated sickness behavioural changes.Conclusions: Together, these findings shed light on the mechanisms underlying the anti-inflammatory potential and confirm the therapeutic potential of nitroxides.