Neutrophils Generate Microparticles during Exposure to Inert Gases Due to Cytoskeletal Oxidative Stress

Abstract

Background: Microparticles are generated in vivo with exposures to high pressure gases by unclear mechanisms. Results: High inert gas pressure causes singlet oxygen formation, which initiates a cycle of actin S-nitrosylation, nitric-oxide synthase-2, and NADPH oxidase activation leading to microparticle formation. Conclusion: Inert gas-mediated oxidative stress causes microparticle production. Significance: This mechanism may initiate events leading to decompression sickness.

Factors Associated with Nitric Oxide-mediated β2 Integrin Inhibition of Neutrophils

“…NOX is a logical source for the requisite initial ROS needed to react with DENO-derived ⅐ NO to produce agents capable of S-nitrosylation. The on-going process appears to be centered on actin polymerization/turnover and inhibited by cytochalasin D. This is similar to a mechanism we reported in other studies, where S-nitrosylation drives a series of steps leading to excessive actin turnover (24,31). VASP exhibits higher affinity for S-nitrosylated sF-actin filaments (26); VASP also bundles Rac proteins in close proximity to sF-actin, and subsequent Rac activation increases actin polymerization, which leads to enhanced binding of FAK and then association of iNOS (25).…”

“…Subjects were healthy adults who had taken no medications for at least 4 days prior to phlebotomy. Blood was acquired in heparinized tubes, and neutrophils were isolated as previously described (24,31).…”

Ascorbic acid supplementation diminishes microparticle elevations and neutrophil activation following SCUBA diving

“…A subset of MPs in mice subjected to high pressure have been shown to contain nitrogen dioxide, which could react with proteins to generate nitrotyrosine (28). Nitrotyrosine is elevated in neutrophils after SCUBA diving and in isolated neutrophils exposed to elevated partial pressures of He, N 2 , or Ar (21,24).…”

“…Findings from murine studies and also several trials involving human divers have led us to hypothesize that MP production may actually occur because of high-pressure inert or ballast gas (such as nitrogen [N 2 ]) exposures, rather than being a consequence of elevations in O 2 partial pressure per se or due to decompression (20,26). Neutrophils generate MPs when exposed to elevated partial pressures of helium (He), N 2 , or argon (Ar), even when there is no elevation of O 2 partial pressure beyond that associated with ambient air (24). This occurs due to oxidative stress initiated by singlet O 2 , which is generated by collision complexes between O 2 and inert gases.…”

“…Our rationale for probing nitrotyrosine comes from more basic studies showing that intrinsic characteristics of MPs from decompressed mice, rather than merely the elevation in their number, cause vascular and neurological injuries (27,28,31,32). One component to this process pertains to augmented activity of nitric oxide synthase-2 (NOS-2 or inflammatory/inducible NOS) in cells and within MPs (24,28). A subset of MPs in mice subjected to high pressure have been shown to contain nitrogen dioxide, which could react with proteins to generate nitrotyrosine (28).…”