title: Argon mediates protection by interleukin-8 suppression via a TLR2/TLR4/STAT3/NF-κB pathway in a model of apoptosis in neuroblastoma cells in vitro and following ischemia-reperfusion injury in rat retina in vivo.
abstract: Argon has recently come into scientific focus as a neuroprotective agent. The underlying neuroprotective mechanism remains unknown although toll-like receptors were recently suggested to play an important role. We hypothesized that TLR-associated downstream transcription factors are responsible for argon's effects, leading to anti-apoptotic and anti-inflammatory properties. Apoptosis was induced in human neuroblastoma cells. Immediately afterwards, argon treatment (75 Vol% for 2 h) was initiated. Cells were analyzed, measuring mitochondrial membrane potential, reactive-oxygen-species, annexin-V/propidium iodide staining, transcription factor phosphorylation and binding activity as well as protein and mRNA expression of interleukins. Argon's in vivo effects were analyzed by quantification of retinal ganglion cell density, mRNA expression, serum cytokine analysis and immunohistochemistry after retinal ischemia reperfusion injury (IRI) in rats. Argon diminished rotenone-induced kappa-light-chain-enhancer' of activated B-cells (NF-κB) and signal transducer and activator of transcription 3 (STAT3) but not STAT5 or cAMP-response element-binding protein (CREB) phosphorylation and DNA-binding activity. Argon treatment attenuated apoptosis by preservation of mitochondrial membrane potential and decline in reactive oxygen species (ROS) generation. NF-κB and STAT3 inhibition, as well as TLR2 and TLR4 inhibition reversed argon's effects on IL-8 mRNA expression. Argon attenuated rotenone-induced IL-8 protein and mRNA expression in vitro. Inhibition of TLR2 and 4 attenuated argon's protective effect in vivo reducing IRI driven retinal IL-8 expression. IL-8 expression was found in the retina in co-localization with Müller cells and retinal ganglion cells. Argon mediates its neuroprotective effects by TLR-mediated regulation of transcription factors NF-κB and STAT3, thus decreasing interleukin-8 expression in vitro and in vivo. These findings may open up new opportunities to effectively treat cerebral ischemia and reperfusion injury through the inhalation of argon. Argon exerts its protective effects in vitro and in vivo via toll-like receptors TLR2 and TLR4 signaling, followed by alteration of downstream enzymes. In conclusion, argon mediates its beneficial effects by suppression of STAT3 and NF-κB phosphorylation and subsequent suppression of interleukin IL-8 protein expression. These novel findings may open up opportunities for argon as a therapeutic agent, particularly in the treatment of neuronal injury. Cover image for this issue: doi: 10.1111/jnc.13334.
authors.affiliation: Department of Anesthesiology and Critical Care, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Ulbrich
authors.affiliation: Department of Anesthesiology and Critical Care, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Teresa
authors.initials: T
authors.lastname: Lerach
authors.affiliation: Eye Center, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Biermann
authors.affiliation: Department of Anesthesiology and Critical Care, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Kai B
authors.initials: KB
authors.lastname: Kaufmann
authors.affiliation: Eye Center, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Wolf A
authors.initials: WA
authors.lastname: Lagreze
authors.affiliation: Department of Anesthesiology and Critical Care, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Buerkle
authors.affiliation: Department of Anesthesiology and Critical Care, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Loop
authors.affiliation: Department of Anesthesiology and Critical Care, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany. ulrich.goebel@uniklinik-freiburg.de.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Goebel
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001128:Argon / Q000494:pharmacology*; D005260:Female; D006801:Humans; D016209:Interleukin-8 / Q000037:antagonists & inhibitors*; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D016328:NF-kappa B / Q000187:drug effects / Q000378:metabolism; D009447:Neuroblastoma / Q000188:drug therapy* / Q000473:pathology; D018696:Neuroprotective Agents / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D015427:Reperfusion Injury / Q000473:pathology / Q000517:prevention & control*; D012164:Retinal Diseases / Q000473:pathology / Q000517:prevention & control*; D050796:STAT3 Transcription Factor / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D051195:Toll-Like Receptor 2 / Q000187:drug effects / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000187:drug effects / Q000378:metabolism
chemical_list: C508606:CXCL8 protein, human; D016209:Interleukin-8; D016328:NF-kappa B; D018696:Neuroprotective Agents; D017382:Reactive Oxygen Species; D050796:STAT3 Transcription Factor; C494088:Stat3 protein, rat; C495343:Tlr2 protein, rat; C495347:Tlr4 protein, rat; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D001128:Argon
keywords: argon; interleukin 8; neuroprotection; toll like receptor; transcription factors