Febrile-range hyperthermia augments reversible TNF-α-induced hyperpermeability in human microvascular lung endothelial cells

Fever commonly occurs in acute lung injury (ALI) and ALI occurs in 25% of victims of heat stroke. We have shown in mouse models of ALI that exposure to febrile-range hyperthermia (FRH), 39.5 degrees C, increases non-cardiogenic pulmonary oedema. In this study we studied the direct effects of FRH on endothelial barrier integrity using human microvascular endothelial cells (HMVEC-Ls). We analysed the effect of exposure to culture temperatures between 38.5 degrees and 41 degrees C with and without tumour necrosis factor-alpha (TNF-alpha) up to 250 U/mL for 6-24 h. We found that exposure to 2.5-250 U/mL TNF-alpha increased HMVEC-L permeability by 4.1-15.8-fold at 37 degrees C. Exposure to 39.5 degrees C alone caused variable, modest, lot-specific increases in HMVEC-L permeability, however raising culture temperature to 39.5 degrees C in the presence of TNF-alpha increased permeability an additional 1.6-4.5-fold compared with cells incubated with the same TNF-alpha concentration at 37 degrees C. Permeability occurred without measurable cytotoxicity and was reversible upon removal of TNF-alpha and reduction in temperature to 37 degrees C. Exposure to 39.5 degrees C or TNF-alpha each stimulated rapid activation of p38 and ERK but the effects were not additive. Treatment with inhibitors of ERK (U0126) or p38 (SB203580) each reduced TNF-alpha-induced permeability in 39.5 degrees C monolayers to levels in 37 degrees C cells, but did not alter TNF-alpha-induced permeability in the 37 degrees C cells. These results demonstrate that FRH directly increases paracellular pathway opening through a process that requires ERK and p38 MAPKs. A better understanding of this mechanism may provide new understanding about how fever may contribute to the pathogenesis of ALI and provide new therapeutic targets to improve clinical outcomes.