Effects of helium on inflammatory and oxidative stress-induced endothelial cell damage

•Helium does not reduce the increase of adhesion molecules after TNF-α stimulation.•Helium increases caspase-3 containing microparticles after TNF-α stimulation.•Helium is not inert and affects the number and content of released microparticles.•Helium in combination with H2O2-stimulation resulted in increased cell death.

Helium induces preconditioning in human endothelium protecting against postischemic endothelial dysfunction. Circulating endothelial microparticles are markers of endothelial dysfunction derived in response to injury. Another noble gas, xenon, protected human umbilical vein endothelial cells (HUVEC) against inflammatory stress in vitro. We hypothesised that helium protects the endothelium in vitro against inflammatory and oxidative stress. HUVEC were isolated from fresh umbilical cords and grown upon confluence. Cells were subjected to starving medium for 12 h before the experiment and treated for either 3×5 min or 1×30 min with helium (5% CO2, 25% O2, 70% He) or control gas (5% CO2, 25% O2, 70% N2) in a specialised gas chamber. Subsequently, cells were stimulated with TNF-α (40 ng/ml for 24 h or 10 ng/ml for 2 h) or H2O2 (500 μM for 2 h) or left untreated. Adhesion molecule expression was analysed using real-time quantitative polymerase chain reaction. Caspase-3 expression and viability of the cells was measured by flowcytometry. Microparticles were investigated by nanoparticle tracking analysis. Helium had no effect on adhesion molecule expression after TNF-α stimulation but in combination with oxidative stress decreased cell viability (68.9±1.3% and 58±1.9%) compared to control. Helium further increased TNF-α induced release of caspase-3 containing particles compared to TNF-α alone (6.4×106±1.1×106 and 2.9×106±0.7×106, respectively). Prolonged exposure of helium increased microparticle formation (2.4×109±0.5×109) compared to control (1.7×109±0.2×109).Summarized, helium increases inflammatory and oxidative stress-induced endothelial damage and is thus not biologically inert. A possible noxious effects on the cellular level causing alterations in microparticle formation both in number and content should be acknowledged.