Group VIB Ca(2+)-independent phospholipase A(2γ) is associated with acute lung injury following trauma and hemorrhagic shock

Vagus nerve stimulation modulates arachidonic acid production in the mesenteric lymph following intestinal ischemia-reperfusion injury

BACKGROUND

Inflammatory lipid mediators in mesenteric lymph (ML), including arachidonic acid (AA), are considered to play an important role in the pathogenesis of multiple-organ dysfunction after hemorrhagic shock. A previous study suggested that vagus nerve stimulation (VNS) could relieve shock-induced gut injury and abrogate ML toxicity, resulting in the prevention of multiple-organ dysfunction. However, the detailed mechanism of VNS in lymph toxicity remains unclear. The study aimed to investigate the relationship between VNS and inflammatory lipid mediators in ML.

METHODS

Male Sprague-Dawley rats underwent laparotomy and superior mesenteric artery obstruction (SMAO) for 60 minutes to induce intestinal ischemia followed by reperfusion and observation. The ML duct was cannulated, and ML samples were obtained both before and after SMAO. The distal ileum was removed at the end of the observation period. In one group of animals, VNS was performed from 10 minutes before 10 minutes after SMAO (5 V, 0.5 Hz). Liquid chromatography-electrospray ionization-tandem mass spectrometry analysis of AA was performed for each ML sample. The biological activity of ML was examined using a monocyte nuclear factor κ-light-chain-enhancer of activated B cells activation assay. Western blotting of phospholipase A2 group IIA (PLA2-IIA) was also performed for ML and ileum samples.

RESULTS

Vagus nerve stimulation relieved the SMAO-induced histological gut injury. The concentration of AA and level of nuclear factor κ-light-chain-enhancer of activated B cells activation in ML increased significantly after SMAO, whereas VNS prevented these responses. Western blotting showed PLA2-IIA expression in the ML and ileum after SMAO; however, the appearance of PLA2-IIA band was remarkably decreased in the samples from VNS-treated animals.

CONCLUSION

The results suggested that VNS could relieve gut injury induced by SMAO and decrease the production of AA in ML by altering PLA2-IIA expression in the gut and ML.

The role of mesenteric lymph exosomal lipid mediators following intestinal ischemia-reperfusion injury on activation of inflammation

BACKGROUND

Intestinal ischemia caused by hemorrhagic shock is known to induce systemic inflammatory responses. Previous studies have shown that mesenteric lymph (ML) plays a crucial role in gut-mediated inflammation. Lipid mediators, such as lysophosphatidylcholines (LPCs), which contain polyunsaturated fatty acids (PUFAs), are present in the postshock ML. Exosomes are also present in the ML and act as transcellular carriers of lipids; however, their role in postshock systemic inflammation has not been revealed. Here, we aimed to identify changes in lipid mediators in ML exosomes after intestinal ischemia.

METHODS

Male Sprague-Dawley rats underwent laparotomy, followed by ML duct cannulation. Animals were subjected to 60 minutes of intestinal ischemia by superior mesenteric artery clamping, followed by 120 minutes of reperfusion. Mesenteric lymph was obtained before and after intestinal ischemia, and exosomes were isolated from ML by ultracentrifugation. The biological activity of ML exosomes was determined using the monocyte nuclear factor κB (NF-κB) activation assay. Lipids of ML exosomes were extracted and quantified by liquid chromatography/electrospray ionization mass spectrometry.

RESULTS

Mesenteric lymph exosome-induced NF-κB activation significantly increased after intestinal ischemia, and lipid analysis revealed a significant increase in the concentration of PUFA-containing LPCs. In addition, PUFA-containing LPCs also induced NF-κB activation.

CONCLUSION

Our results suggest that biologically active lipid mediators in ML exosomes may be involved in the inflammatory response after intestinal ischemia.

Exosomes in postshock mesenteric lymph are key mediators of acute lung injury triggering the macrophage activation via Toll-like receptor 4

Acute lung injury (ALI) is a common cause of morbidity in patients after severe injury due to dysregulated inflammation, which is believed to be driven by gut-derived inflammatory mediators carried via mesenteric lymph (ML). We have previously demonstrated that nano-sized extracellular vesicles, called exosomes, secreted into ML after trauma/hemorrhagic shock (T/HS) have the potential to activate immune cells in vitro Here, we assess the function of ML exosomes in the development of T/HS-induced ALI and the role of TLR4 in the ML exosome-mediated inflammatory response. ML exosomes isolated from rats subjected to T/HS stimulated NF-κB activation and caused proinflammatory cytokine production in alveolar macrophages. In vivo experiments revealed that intravenous injection of exosomes harvested after T/HS, but not before shock, caused recruitment of inflammatory cells in the lung, increased vascular permeability, and induced histologic ALI in naive mice. The exosome-depleted supernatant of ML had no effect on in vitro and in vivo inflammatory responses. We also demonstrated that both pharmacologic inhibition and genetic knockout of TLR4 completely abolished ML exosome-induced cytokine production in macrophages. Thus, our findings define the critical role of exosomes secreted into ML as a critical mediator of T/HS-induced ALI through macrophage TLR4 activation.-Kojima, M., Gimenes-Junior, J. A., Chan, T. W., Eliceiri, B. P., Baird, A., Costantini, T. W., Coimbra, R. Exosomes in postshock mesenteric lymph are key mediators of acute lung injury triggering the macrophage activation via Toll-like receptor 4.

Exosomes, not protein or lipids, in mesenteric lymph activate inflammation: Unlocking the mystery of post-shock multiple organ failure

BACKGROUND

Previous studies have shown that mesenteric lymph (ML) has a crucial role in driving the systemic inflammatory response after trauma/hemorrhagic shock (T/HS). The specific mediators in the ML that contribute to its biological activity remain unclear despite decades of study. Exosomes are extracellular vesicles that are shed into body fluids such as serum and urine that can mediate intercellular communication. We hypothesized that exosomes are present in the ML after trauma/shock and are responsible for the biological activity of ML.

METHODS

Male rats underwent cannulation of the vessels and mesenteric lymph duct. T/HS was induced by laparotomy and 60 minutes of HS (mean arterial pressure, 35 mmHg), followed by resuscitation. The ML was collected during three distinct time periods (pre-shock, shock, and resuscitation phase) and subsequently separated into exosome and supernatant fractions. Exosomes were characterized by electron microscope, nanoparticle tracking analysis, and immunoblotting. The biological activity of exosomes and supernatant of ML were characterized using a monocyte NF-κB reporter assay and by measuring macrophage intracellular TNF-α production.

RESULTS

Exosomes were identified in ML by size and expression of the exosome markers CD63 and HSP70. The number of exosomes present in the ML was 2-fold increased during shock and 4-fold decreased in resuscitation phase compared to pre-shock. However, biological activity of exosomes isolated during the resuscitation phase was markedly increased and caused an 8-fold increase in monocyte NF-κB activation compared to supernatant. Macrophage TNF-α production was also increased after exposure to exosomes harvested in the resuscitation phase. The ML supernatant fraction had no effect on TNF-α production during any phase.

CONCLUSIONS

Our findings show that exosomes, and not the liquid fraction of ML, are the major component triggering inflammatory responses in monocytes and macrophages after experimental T/HS.

Biosynthesis of oxidized lipid mediators via lipoprotein-associated phospholipase A2 hydrolysis of extracellular cardiolipin induces endothelial toxicity

We (66) have previously described an NSAID-insensitive intramitochondrial biosynthetic pathway involving oxidation of the polyunsaturated mitochondrial phospholipid, cardiolipin (CL), followed by hydrolysis [by calcium-independent mitochondrial calcium-independent phospholipase A2-γ (iPLA2γ)] of oxidized CL (CLox), leading to the formation of lysoCL and oxygenated octadecadienoic metabolites. We now describe a model system utilizing oxidative lipidomics/mass spectrometry and bioassays on cultured bovine pulmonary artery endothelial cells (BPAECs) to assess the impact of CLox that we show, in vivo, can be released to the extracellular space and may be hydrolyzed by lipoprotein-associated PLA2 (Lp-PLA2). Chemically oxidized liposomes containing bovine heart CL produced multiple oxygenated species. Addition of Lp-PLA2 hydrolyzed CLox and produced (oxygenated) monolysoCL and dilysoCL and oxidized octadecadienoic metabolites including 9- and 13-hydroxyoctadecadienoic (HODE) acids. CLox caused BPAEC necrosis that was exacerbated by Lp-PLA2 Lower doses of nonlethal CLox increased permeability of BPAEC monolayers. This effect was exacerbated by Lp-PLA2 and partially mimicked by authentic monolysoCL or 9- or 13-HODE. Control mice plasma contained virtually no detectable CLox; in contrast, 4 h after Pseudomonas aeruginosa (P. aeruginosa) infection, 34 ± 8 mol% (n = 6; P < 0.02) of circulating CL was oxidized. In addition, molar percentage of monolysoCL increased twofold after P. aeruginosa in a subgroup analyzed for these changes. Collectively, these studies suggest an important role for 1) oxidation of CL in proinflammatory environments and 2) possible hydrolysis of CLox in extracellular spaces producing lysoCL and oxidized octadecadienoic acid metabolites that may lead to impairment of pulmonary endothelial barrier function and necrosis.

Novel role of group VIB Ca2+-independent phospholipase A2γ in leukocyte-endothelial cell interactions: An intravital microscopic study in rat mesentery

BACKGROUND

Phospholipase A2 (PLA2) is associated with a variety of inflammatory processes related to polymorphonuclear neutrophil (PMN)-endothelial cell interactions. However, the cellular and molecular mechanisms underlying the interactions and the causative isoform(s) of PLA2 remain elusive. In addition, we recently showed that calcium-independent PLA2γ (iPLA2γ), but not cytosolic PLA2 (cPLA2), is responsible for the cytotoxic functions of human PMN including respiratory bursts, degranulation, and chemotaxis. We therefore hypothesized that iPLA2γ is a prerequisite for the PMN recruitment cascade into the site of inflammation. The aim of this study was to elucidate the roles of the three major phospholipases A2, iPLA2, cPLA2 and secretory PLA2, in leukocyte rolling and adherence and in the surface expression of β2-integrins in vivo and in vitro in response to well-defined stimuli.

METHODS

Male Wistar rats were pretreated with PLA2 inhibitors selective for iPLA2β, iPLA2γ, cPLA2, or secretory PLA2. Leukocyte rolling/adherence in the mesenteric venules superfused with platelet-activating factor (PAF) were quantified by intravital microscopy. Furthermore, isolated human PMNs or whole blood were incubated with each PLA2 inhibitor and then activated with formyl-methionyl-leucyl-phenylalanine (fMLP) or PAF. PMN adherence was assessed by counting cells bound to purified fibrinogen, and the surface expression of lymphocyte function-associated antigen 1 and macrophage antigen 1 (Mac-1) was measured by flow cytometry.

RESULTS

The iPLA2γ-specific inhibitor almost completely inhibited the fMLP/PAF-induced leukocyte adherence in vivo and in vitro and also decreased the fMLP/PAF-stimulated surface expression of Mac-1 by 60% and 95%, respectively. In contrast, the other inhibitors did not affect these cellular functions.

CONCLUSION

iPLA2γ seems to be involved in leukocyte/PMN adherence in vivo and in vitro as well as in the up-regulation of Mac-1 in vitro in response to PAF/fMLP. This enzyme is therefore likely to be a major regulator in the PMN recruitment cascade.

Discrete roles of intracellular phospholipases A2 in human neutrophil cytotoxicity

BACKGROUND

The role of calcium-independent phospholipase A2 (iPLA2), a component of the three major PLA2 families, in acute/chronic inflammatory processes remains elusive. Previous investigations have documented iPLA2-mediated respiratory burst of neutrophils (PMNs); however, the causative isoform of iPLA2 is unidentified. We also demonstrated that the iPLA2γ-specific inhibitor attenuates trauma/hemorrhagic shock-induced lung injury. Therefore, iPLA2γ may be implicated in acute inflammation. In addition, arachidonic acid (AA), which is primarily produced by cytosolic PLA2 (cPLA2), is known to display PMN cytotoxicity, although the relationship between AA and the cytotoxic function is still being debated on. We therefore hypothesized that iPLA2γ regulates PMN cytotoxicity via AA-independent signaling pathways. The study aim was to distinguish the role of intracellular phospholipases A2, iPLA2, and cPLA2, in human PMN cytotoxicity and explore the possibility of the presence of signaling molecule(s) other than AA.

METHODS

Isolated human PMNs were incubated with the PLA2 inhibitor selective for iPLA2β, iPLA2γ, or cPLA2 and then activated with formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol 12-myristate 13-acetate (PMA). Superoxide production was assayed according to the superoxide dismutase-inhibitable cytochrome c reduction method, and the degree of elastase release was measured using a p-nitroanilide-conjugated elastase-specific substrate. In addition, chemotaxis toward platelet activating factor/fMLP was determined with a modified Boyden chamber system.

RESULTS

The iPLA2γ-specific inhibitor reduced the fMLP/PMA-stimulated superoxide generation by 90% and 30%, respectively; in addition, the inhibitor completely blocked the fMLP/PMA-activated elastase release. However, the cPLA2-specific inhibitor did not abrogate these effects to any degree at all concentrations. Likewise, the inhibitor for iPLA2γ, but not iPLA2β or cPLA2, completely inhibited the platelet activating factor/fMLP-induced chemotaxis.

CONCLUSION

iPLA2 is involved in extracellular reactive oxygen species production, elastase release, and chemotaxis in response to well-defined stimuli. In addition, the ineffectiveness of the cPLA2 inhibitor suggests that AA may not be relevant to these cytotoxic functions.