Intramicroparticle nitrogen dioxide is a bubble nucleation site leading to decompression-induced neutrophil activation and vascular injury

Abstract

Inert gases diffuse into tissues in proportion to ambient pressure, and when pressure is reduced, gas efflux forms bubbles due to the presence of gas cavitation nuclei that are predicted based on theory but have never been characterized. Decompression stress triggers elevations in number and diameter of circulating annexin V-coated microparticles (MPs) derived from vascular cells. Here we show that ∼10% MPs from wild-type (WT) but not inflammatory nitric oxide synthase-2 (iNOS) knockout (KO) mice increase in size when exposed to elevated air pressure ex vivo. This response is abrogated by a preceding exposure to hydrostatic pressure, demonstrating the presence of a preformed gas phase. These MPs have lower density than most particles, 10-fold enrichment in iNOS, and generate commensurately more reactive nitrogen species (RNS). Surprisingly, RNS only slowly diffuse from within MPs unless particles are subjected to osmotic stress or membrane cholesterol is removed. WT mice treated with iNOS inhibitor and KO mice exhibit less decompression-induced neutrophil activation and vascular leak. Contrary to injecting naïve mice with MPs from wild-type decompressed mice, injecting KO MPs triggers fewer proinflammatory events. We conclude that nitrogen dioxide is a nascent gas nucleation site synthesized in some MPs and is responsible for initiating postdecompression inflammatory injuries.

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

“…Reactive Species Generation-Neutrophil suspensions were prepared with 10 M 2,7-dihydrodichlorofluorescein-diacetate (DCF-DA) or 50 M FBBBE, and fluorescence was monitored (DCF at 492-nm excitation, 530-nm emission; FBBBE at 480-nm excitation, 512-nm emission) after incubations in PBS or PBS ϩ 100 nM DENO following the procedures described previously (36).…”

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

“…A series of studies has demonstrated that circulating microparticles (MPs), membrane-encapsulated cell fragments with diameters of 0.1 to 1 m, are elevated in animals and humans after simulated or bona fide underwater diving (14 -16, 20, 25, 26, 29). In a murine model, MPs have been shown to initiate a systemic inflammatory process postdecompression that is related to neutrophil activation (27,28,31,32).…”

“…Injuries identified in decompressed animals can be recapitulated by injecting decompression-induced MPs into naïve mice (28,31,32).…”

“…Nitration of protein tyrosine residues to form 3-nitrotyrosine by highly reactive species, such as peroxynitrite, occurs even in the presence of reduced thiols and other antioxidant scavengers (1, 7). 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).…”

Acute kidney injury caused by decompression illness successfully treated with hyperbaric oxygen therapy and temporary dialysis

“…Increasing sheared stress may lead to the release of endothelial membrane fragments, also known as microparticles (MPs), which appear to activate neutrophils and interact with the platelet membrane [9]. Increased MP levels have been observed in patients with renal diseases and have been associated with arterial and endothelial dysfunction [10].…”