Inert Gas Mild Pressure Action on Healthy Humans: The "IPA" Study

Abstract

The goal of this study was to evaluate inflammatory and oxidative stress responses in human subjects (9 females and 15 males) (age [29.6 ± 11.5 years old (mean ± SD)], height [172.0 ± 10.05 cm], and weight [67.8 ± 12.4 kg]) exposed to 1.45 ATA of helium (He) or nitrogen (N₂) without concurrent hyperoxia. We hypothesized that elevated gas pressures would elicit an inflammatory response concurrent with oxidative stress. Consistent with ex vivo studies, both gasses elicited neutrophil activation, small elevations in microparticles (MPs) and increases in intra-MP interleukin (IL)-1β and inflammatory nitric oxide synthase, and an increase in urinary IL-6 concurrent with a marked reduction in plasma gelsolin. Mixed responses indictive of oxidative stress, with some biomarker elevations but little change in others and a decrease in some, were observed. Overall, these results demonstrate that exposure to typical diving gasses at a mildly elevated partial pressure will initiate inflammatory responses, which may play a significant role in decompression sickness (DCS). The complex pattern of oxidative stress responses may be indicative of competing systemic reactions and sampling different body fluids.

Keywords: ROS; decompression sickness; diving; exosomes; extracellular vesicles; filamentous actin; inert gas; interleukin-1β; interleukin-6; microglia; microparticles; oxidative stress; oxyinflammation; plasma gelsolin.

Figure 1

Activation of neutrophils after inert gas exposure (N₂ grey, He Blue). Data are shown as mean ± SD expressed in % of pre-exposure values of neutrophils (identified in flow cytometer based on CD66b expression) expressing myeloperoxidase (MPO) and CD18 above threshold value as index of cell activation (one-sample t-test and unpaired t-test). (* p < 0.05; ** p < 0.01; *** p < 0.001; ns = Non-Significant.)

Figure 2

Microparticles in blood after helium or nitrogen exposure (N₂ grey, He Blue). Flow cytometry was used to evaluate MPs. Relative variations expressed in % of pre-exposure value of each that expressed proteins specific to different cells, including neutrophils (CD66b), endothelial cells (CD146), platelets (CD41a), and microglia (transmembrane protein 119, TMEM). As discussed in text, proteins expressing TSP-1 and F-actin, evaluated as those binding phalloidin, were also assessed. Data are shown as mean ± SD (* = p < 0.05; ns = non-significant; t-test vs. control, with everyone acting as its own control (one-sample t-test)).

Figure 3

IL-1B and iNOS (% of control values) (N₂ grey, He Blue). Data are shown as mean ± SD (** p < 0.01; **** p < 0.0001; ns = not significant; Wilcoxon and Mann–Whitney tests).

Figure 4

Plasma gelsolin (% of control values) (N₂ grey, He Blue). Data are shown as mean ± SD (** p < 0.01; *** p < 0.001; Wilcoxon and Mann–Whitney tests; NS = not significant).

Figure 5

Oxyinflammation % of control values (N₂ grey, He Blue). Data are shown as mean ± SD. ** p < 0.01; *** p < 0.001; ns = not significant; t-test and one-sample t-test.

Figure 6

Endothelial markers (N₂ grey, He Blue). VCAM-1. Data are shown as mean ± SD. * p < 0.05; *** p < 0.001; t-test and one-sample t-test.

Figure 7

Experimental flowchart.