Endotoxemia-induced inflammation and the effect on the human brain

INTRODUCTION: Effects of systemic inflammation on cerebral function are not clear, as both inflammation-induced encephalopathy as well as stress-hormone mediated alertness have been described. METHODS: Experimental endotoxemia (2 ng/kg Escherichia coli lipopolysaccharide [LPS]) was induced in 15 subjects, whereas 10 served as controls. Cytokines (TNF-α, IL-6, IL1-RA and IL-10), cortisol, brain specific proteins (BSP), electroencephalography (EEG) and cognitive function tests (CFTs) were determined. RESULTS: Following LPS infusion, circulating pro- and anti-inflammatory cytokines, and cortisol increased (P < 0.0001). BSP changes stayed within the normal range, in which neuron specific enolase (NSE) and S100-β changed significantly. Except in one subject with a mild encephalopathic episode, without cognitive dysfunction, endotoxemia induced no clinically relevant EEG changes. Quantitative EEG analysis showed a higher state of alertness detected by changes in the central region, and peak frequency in the occipital region. Improved CFTs during endotoxemia was found to be due to a practice effect as CFTs improved to the same extent in the reference group. Cortisol significantly correlated with a higher state of alertness detected on the EEG. Increased IL-10 and the decreased NSE both correlated with improvement of working memory and with psychomotor speed capacity. No other significant correlations between cytokines, cortisol, EEG, CFT and BSP were found. CONCLUSIONS: Short-term systemic inflammation does not provoke or explain the occurrence of septic encephalopathy, but primarily results in an inflammation-mediated increase in cortisol and alertness. TRIAL REGISTRATION: NCT00513110.