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Rationale: The severe acute respiratory syndrome coronavirus 2/coronavirus disease 2019 pandemic has highlighted the serious unmet need for effective therapies that reduce acute respiratory distress syndrome (ARDS) mortality. We explored whether extracellular nicotinamide phosphoribosyltransferase (eNAMPT), a ligand for Toll-like receptor (TLR)4 and a master regulator of innate immunity and inflammation, is a potential ARDS therapeutic target., Methods: Wild-type C57BL/6J or endothelial cell (EC)-c NAMPT -/- knockout mice (targeted EC NAMPT deletion) were exposed to either a lipopolysaccharide (LPS)-induced ("one-hit") or a combined LPS/ventilator ("two-hit")-induced acute inflammatory lung injury model. A NAMPT-specific monoclonal antibody (mAb) imaging probe ( 99m Tc-ProNamptor) was used to detect NAMPT expression in lung tissues. Either an eNAMPT-neutralising goat polyclonal antibody (pAb) or a humanised monoclonal antibody (ALT-100 mAb) were used in vitro and in vivo ., Results: Immunohistochemical, biochemical and imaging studies validated time-dependent increases in NAMPT lung tissue expression in both pre-clinical ARDS models. Intravenous delivery of either eNAMPT-neutralising pAb or mAb significantly attenuated inflammatory lung injury (haematoxylin and eosin staining, bronchoalveolar lavage (BAL) protein, BAL polymorphonuclear cells, plasma interleukin-6) in both pre-clinical models. In vitro human lung EC studies demonstrated eNAMPT-neutralising antibodies (pAb, mAb) to strongly abrogate eNAMPT-induced TLR4 pathway activation and EC barrier disruption. In vivo studies in wild-type and EC-c NAMPT -/- mice confirmed a highly significant contribution of EC-derived NAMPT to the severity of inflammatory lung injury in both pre-clinical ARDS models., Conclusions: These findings highlight both the role of EC-derived eNAMPT and the potential for biologic targeting of the eNAMPT/TLR4 inflammatory pathway. In combination with predictive eNAMPT biomarker and NAMPT genotyping assays, this offers the opportunity to identify high-risk ARDS subjects for delivery of personalised medicine., Competing Interests: Conflict of interest: H. Quijada has nothing to disclose. Conflict of interest: T. Bermudez has nothing to disclose. Conflict of interest: C.L. Kempf has nothing to disclose. Conflict of interest: D.G. Valera has nothing to disclose. Conflict of interest: A.N. Garcia has nothing to disclose. Conflict of interest: S.M. Camp has nothing to disclose. Conflict of interest: J.H. Song has nothing to disclose. Conflict of interest: E. Franco has nothing to disclose. Conflict of interest: J.K. Burt has nothing to disclose. Conflict of interest: B. Sun has nothing to disclose. Conflict of interest: J.B. Mascarenhas has nothing to disclose. Conflict of interest: K. Burns has nothing to disclose. Conflict of interest: A. Gaber has nothing to disclose. Conflict of interest: R.C. Oita has nothing to disclose. Conflict of interest: V. Reyes Hernon has nothing to disclose. Conflict of interest: C. Barber has nothing to disclose. Conflict of interest: L. Moreno-Vinasco has nothing to disclose. Conflict of interest: X. Sun has nothing to disclose. Conflict of interest: A.E. Cress has nothing to disclose. Conflict of interest: D. Martin has investments in Aqualung, outside the submitted work. Conflict of interest: Z. Liu has nothing to disclose. Conflict of interest: A.A. Desai reports grants from NIH R01 (HL136603) and consultancy for Novartis, outside the submitted work. Conflict of interest: V. Natarajan has nothing to disclose. Conflict of interest: J.R. Jacobson has nothing to disclose. Conflict of interest: S.M. Dudek has nothing to disclose. Conflict of interest: C. Bime has nothing to disclose. Conflict of interest: S. Sammani has nothing to disclose. Conflict of interest: J.G.N. Garcia reports grants and non-financial support (provision of research materials) from Aqualung Therapeutics, Corp., during the conduct of the study; grants and personal fees from Aqualung Therapeutics, Corp., outside the submitted work; and has a US Patent No. 9,409,983 issued., (Copyright ©ERS 2021.)

Despite an encouraging outcome of antioxidant therapy in animal models of acute lung injury, effective antioxidant agents for clinical application remain to be developed. The present study investigated the effect of pre-treatment with amifostine, a thiol antioxidant compound, on lung endothelial barrier dysfunction induced by Gram-negative bacteria wall-lipopolysaccharide (LPS). Endothelial permeability was monitored by changes in transendothelial electrical resistance. Cytoskeletal remodelling and reactive oxygen species (ROS) production was examined by immunofluorescence. Cell signalling was assessed by Western blot. Measurements of Evans blue extravasation, cell count and protein content in bronchoalveolar lavage fluid were used as in vivo parameters of lung vascular permeability. Hydrogen peroxide, LPS and interleukin-6 caused cytoskeletal reorganisation and increased permeability in the pulmonary endothelial cells, reflecting endothelial barrier dysfunction. These disruptive effects were inhibited by pre-treatment with amifostine and linked to the amifostine-mediated abrogation of ROS production and redox-sensitive signalling cascades, including p38, extracellular signal regulated kinase 1/2, mitogen-activated protein kinases and the nuclear factor-kappaB pathway. In vivo, concurrent amifostine administration inhibited LPS-induced oxidative stress and p38 mitogen-activated protein kinase activation, which was associated with reduced vascular leak and neutrophil recruitment to the lungs. The present study demonstrates, for the first time, protective effects of amifostine against lipopolysaccharide-induced lung vascular leak in vitro and in animal models of lipopolysaccharide-induced acute lung injury.