Helium Influences Caveolae Numbers in Left Ventricular Endothelial Cells and Alters Metabolic Profile in Mice

Abstract

BackgroundMyocardial ischemia and reperfusion (I/R) injury is a major cause of morbidity and mortality. IR injury leads to calcium overload, increased oxidative stress, mitochondrial dysfunction and ultimately apoptosis. Helium, an inert gas, causes cardioprotection potentially through secretion of cellular factors into serum. This study aimed to elucidate the protective potential of helium conditioned serum, the metabolite content of serum, and the impact of helium on endothelial cell ultrastructure. We hypothesized that helium induces the release of circulating factors to mediate conditioning and impacts endothelial cell ultrastructure.Materials and methodsMice were exposed to 70% helium/30% oxygen or 30% oxygen in air. Serum was harvested at 30 min, 4 hrs and 24 hrs after gas exposure (n=7/group). In addition, mice (n=4/group) were prepared and fixed for transmission electron microscopy. High magnification images (11000×) of left ventricular tissue were analyzed for the amount of caveolae in endothelial cells and myocytes. Serum from exposed mice was analyzed for metabolites of primary metabolism and complex lipids by mass spectrometry. Metabolites were categorized by physiologic pathways and multivariate analysis was used to determine interaction between helium and recover time.ResultsEndothelial cell caveolae number was increased at 30 min and 24 hrs post exposure in the helium group by 39% (p < 0.01, C: 3.5 ± 0.2, n=83 images; He: 4.8 ± 0.3 caveolae/mm, n=67 as mean ± SEM) and 18% (p < 0.05, C: 4.3 ± 0.3, n=72; He: 5.3 ± 0.3 caveolae/mm, n=61), respectively. No differences were observed in myocyte caveolae formation. Interaction of time and drug showed a trend for oxidative phosphorylation (p= 0.097) and galactose metabolism pathway (p= 0.0798). An overall drug effect between the different time points was observed for biotin metabolism (p < 0.05). The metabolites of the two pathways, valine/leucine/isoleucine and pantothenate/CoA biosynthesis showed a trend towards a drug effect (p=0.053; p=0.057 respectively). Three pathways were significantly changed in the 4 hrs group and in the 24 hrs group biosynthesis of unsaturated fatty acids was influenced. In addition three cardioprotective ceramides were significantly upregulated by helium (p < 0.05).ConclusionHelium exposure altered endothelial cell ultrastructure by inducing the formation of caveolae and induced secretion of factors resulting in different metabolic profiles of primary metabolism and complex lipids. Such changes in cell ultrastructure and metabolite secretion may be key to the conditioning effects induced by helium.