Memantine Alleviates Acute Lung Injury Via Inhibiting Macrophage Pyroptosis

ABSTRACT

Acute lung injury (ALI) is caused by direct pulmonary insults and indirect systemic inflammatory responses that result from conditions such as sepsis and trauma. Alveolar macrophages are the main and critical leukocytes in the airspace, and through the synthesis and release of various inflammatory mediators critically influence the development of ALI following infection and non-infectious stimuli. There is increasing recognition that inflammation and cell death reciprocally affect each other, which forms an auto-amplification loop of these two factors, and in turn, exaggerates inflammation. Therefore, pharmacological manipulation of alveolar macrophage death signals may serve as a logical therapeutic strategy for ALI. In this study, we demonstrate that memantine, a N-methyl-D-aspartic acid receptor (NMDAR) antagonist, through suppressing Ca2+ influx and subsequent ASC oligomerization inhibits macrophage Nlrp3 inflammasome activation and pyroptosis, therefore, alleviates ALI in septic mice. This finding explores a novel application of memantine, an FDA already approved medication, in the treatment of ALI, which is currently lacking effective therapy.

Divergent Effects of the N-Methyl-D-Aspartate Receptor Antagonist Kynurenic Acid and the Synthetic Analog SZR-72 on Microcirculatory and Mitochondrial Dysfunction in Experimental Sepsis

Introduction: Sepsis is a dysregulated host response to infection with macro- and microhemodynamic deterioration. Kynurenic acid (KYNA) is a metabolite of the kynurenine pathway of tryptophan catabolism with pleiotropic cell-protective effects under pro-inflammatory conditions. Our aim was to investigate whether exogenously administered KYNA or the synthetic analog SZR-72 affects the microcirculation and mitochondrial function in a clinically relevant rodent model of intraabdominal sepsis.

Methods: Male Sprague–Dawley rats (n = 8/group) were subjected to fecal peritonitis (0.6 g kg⁻¹ feces ip) or a sham operation. Septic animals were treated with sterile saline or received ip KYNA or SZR-72 (160 μmol kg⁻¹ each) 16 and 22 h after induction. Invasive monitoring was performed on anesthetized animals to evaluate respiratory, cardiovascular, renal, hepatic and metabolic dysfunctions (PaO₂/FiO₂ ratio, mean arterial pressure, urea, AST/ALT ratio and lactate levels, respectively) based on the Rat Organ Failure Assessment (ROFA) score. The ratio of perfused vessels (PPV) of the ileal serosa was quantified with the intravital imaging technique. Complex I- and II-linked (CI; CII) oxidative phosphorylation capacities (OXPHOS) and mitochondrial membrane potential (ΔΨmt) were evaluated by High-Resolution FluoRespirometry (O2k, Oroboros, Austria) in liver biopsies. Plasma endothelin-1 (ET-1), IL-6, intestinal nitrotyrosine (NT) and xanthine oxidoreductase (XOR) activities were measured as inflammatory markers.

Results: Sepsis was characterized by an increased ROFA score (5.3 ± 1.3 vs. 1.3 ± 0.7), increased ET-1, IL-6, NT and XOR levels, and decreased serosal PPV (65 ± 12% vs. 87 ± 7%), ΔΨmt and CI–CII-linked OXPHOS (73 ± 16 vs. 158 ± 14, and 189 ± 67 vs. 328 ± 81, respectively) as compared to controls. Both KYNA and SZR-72 reduced systemic inflammatory activation; KYNA treatment decreased serosal perfusion heterogeneity, restored PPV (85 ± 11%) and complex II-linked OXPHOS (307 ± 38), whereas SZR-72 improved both CI- and CII-linked OXPHOS (CI: 117 ± 18; CII: 445 ± 107) without effects on PPV 24 h after sepsis induction.

Conclusion: Treatment with SZR-72 directly modulates mitochondrial respiration, leading to improved conversion of ADP to ATP, while administration of KYNA restores microcirculatory dysfunction. The results suggest that microcirculatory and mitochondrial resuscitation with KYNA or the synthetic analog SZR-72 might be an appropriate supportive tool in sepsis therapy.

Anti-NMDA Receptor Autoantibody Is an Independent Predictor of Hospital Mortality but Not Brain Dysfunction in Septic Patients

The presence of autoantibodies against neuronal cell surface or synaptic proteins and their relationship to autoimmune encephalitis have recently been characterized. These autoantibodies have been also reported in other pathologic conditions; however, their role during sepsis is not known. This study detected the presence of autoantibodies against neuronal cell surface or synaptic proteins in the serum of septic patients and determined their relationship to the occurrence of brain dysfunction and mortality. This prospective, observational cohort study was performed in four Brazilian intensive care units (ICUs). Sixty patients with community-acquired severe sepsis or septic shock admitted to the ICU were included. Blood samples were collected from patients within 24 h of ICU admission. Antibodies to six neuronal proteins were assessed, including glutamate receptors (types NMDA, AMPA1, and AMPA2); voltage-gated potassium channel complex (VGKC) proteins, leucine-rich glioma-inactivated protein 1 (LGI1), and contactin-associated protein-2 (Caspr2), as well as the GABAB1 receptor. There was no independent association between any of the measured autoantibodies and the occurrence of brain dysfunction (delirium or coma). However, there was an independent and significant relationship between anti-NMDAR fluorescence intensity and hospital mortality. In conclusion, anti-NMDAR was independently associated with hospital mortality but none of the measured antibodies were associated with brain dysfunction in septic patients.

Targeted Metabolomics Identifies Pharmacodynamic Biomarkers for BIO 300 Mitigation of Radiation-Induced Lung Injury

PURPOSE

Biomarkers serve a number of purposes during drug development including defining the natural history of injury/disease, serving as a secondary endpoint or trigger for intervention, and/or aiding in the selection of an effective dose in humans. BIO 300 is a patent-protected pharmaceutical formulation of nanoparticles of synthetic genistein being developed by Humanetics Corporation. The primary goal of this metabolomic discovery experiment was to identify biomarkers that correlate with radiation-induced lung injury and BIO 300 efficacy for mitigating tissue damage based upon the primary endpoint of survival.

METHODS

High-throughput targeted metabolomics of lung tissue from male C57L/J mice exposed to 12.5 Gy whole thorax lung irradiation, treated daily with 400 mg/kg BIO 300 for either 2 weeks or 6 weeks starting 24 h post radiation exposure, were assayed at 180 d post-radiation to identify potential biomarkers.

RESULTS

A panel of lung metabolites that are responsive to radiation and able to distinguish an efficacious treatment schedule of BIO 300 from a non-efficacious treatment schedule in terms of 180 d survival were identified.

CONCLUSIONS

These metabolites represent potential biomarkers that could be further validated for use in drug development of BIO 300 and in the translation of dose from animal to human.

Dramatic increases in blood glutamate concentrations are closely related to traumatic brain injury-induced acute lung injury

Traumatic brain injury-induced acute lung injury (TBI-ALI) is a serious complication after brain injury for which predictive factors are lacking. In this study, we found significantly elevated blood glutamate concentrations in patients with TBI or multiple peripheral trauma (MPT), and patients with more severe injuries showed higher blood glutamate concentrations and longer durations of elevated levels. Although the increase in amplitude was similar between the two groups, the duration was longer in the patients with TBI. There were no significant differences in blood glutamate concentrations in the patients with MPT with regard to ALI status, but the blood glutamate levels were significantly higher in the patients with TBI-ALI than in those without ALI. Moreover, compared to patients without ALI, patients with TBI showed a clearly enhanced inflammatory response that was closely correlated with the blood glutamate levels. The blood glutamate concentration was also found to be a risk factor (adjusted odds ratio, 2.229; 95% CI, 1.082–2.634) and was a better predictor of TBI-ALI than the Glasgow Coma Scale (GCS) score. These results indicated that dramatically increased blood glutamate concentrations were closely related to the occurrence of TBI-ALI and could be used as a predictive marker for “at-risk” patients.

Tumor necrosis factor regulates NMDA receptor-mediated airway smooth muscle contractile function and airway responsiveness

We have shown that N-methyl-d-aspartate receptors (NMDA-Rs) are receptor-operated calcium entry channels in human airway smooth muscle (HASM) during contraction. Tumor necrosis factor (TNF) augments smooth muscle contractility by influencing pathways that regulate intracellular calcium flux and can alter NMDA-R expression and activity in cortical neurons and glial cells. We hypothesized that NMDA-R-mediated Ca(2+) and contractile responses of ASM can be altered by inflammatory mediators, including TNF. In cultured HASM cells, we assessed TNF (10 ng/ml, 48 h) effect on NMDA-R subunit abundance by quantitative PCR, confocal imaging, and immunoblotting. We observed dose- and time-dependent changes in NMDA-R composition: increased obligatory NR1 subunit expression and altered regulatory NR2 and inhibitory NR3 subunits. Measuring intracellular Ca(2+) flux in Fura-2-loaded HASM cultures, we observed that TNF exposure enhanced cytosolic Ca(2+) mobilization and changed the temporal pattern of Ca(2+) flux in individual myocytes induced by NMDA, an NMDA-R selective analog of glutamate. We measured airway responses to NMDA in murine thin-cut lung slices (TCLS) from allergen-naive animals and observed significant airway contraction. However, NMDA acted as a bronchodilator in TCLS from house dust mice-challenged mice and in allergen-naive TCLS subjected to TNF exposure. All contractile or bronchodilator responses were blocked by a selective NMDA-R antagonist, (2R)-amino-5-phosphonopentanoate, and bronchodilator responses were prevented by N(G)-nitro-l-arginine methyl ester (nitric oxide synthase inhibitor) or indomethacin (cyclooxygenase inhibitor). Collectively, we show that TNF augments NMDA-R-mediated Ca(2+) mobilization in HASM cells, whereas in multicellular TCLSs allergic inflammation and TNF exposure leads to NMDA-R-mediated bronchodilation. These findings reveal the unique contribution of ionotrophic NMDA-R to airway hyperreactivity.

Glutamate in peripheral organs: Biology and pharmacology

Glutamate is a versatile molecule existing in both the central nervous system and peripheral organs. Previous studies have mainly focussed on the biological effect of glutamate in the brain. Recently, abundant evidence has demonstrated that glutamate also participates in the regulation of physiopathological functions in peripheral tissues, including the lung, kidney, liver, heart, stomach and immune system, where the glutamate/glutamate receptor/glutamate transporter system plays an important role in the pathogenesis of certain diseases, such as myocardial ischaemia/reperfusion injury and acute gastric mucosa injury. All these findings provide new insight into the biology and pharmacology of glutamate and suggest a potential therapeutic role of glutamate in non-neurological diseases.

Influence of glutathione-S-transferase (GST) inhibition on lung epithelial cell injury: role of oxidative stress and metabolism

Oxidant-mediated tissue injury is key to the pathogenesis of acute lung injury. Glutathione- S-transferases (GSTs) are important detoxifying enzymes that catalyze the conjugation of glutathione with toxic oxidant compounds and are associated with acute and chronic inflammatory lung diseases. We hypothesized that attenuation of cellular GST enzymes would augment intracellular oxidative and metabolic stress and induce lung cell injury. Treatment of murine lung epithelial cells with GST inhibitors, ethacrynic acid (EA), and caffeic acid compromised lung epithelial cell viability in a concentration-dependent manner. These inhibitors also potentiated cell injury induced by hydrogen peroxide (H2O2), tert-butyl-hydroperoxide, and hypoxia and reoxygenation (HR). SiRNA-mediated attenuation of GST-π but not GST-μ expression reduced cell viability and significantly enhanced stress (H2O2/HR)-induced injury. GST inhibitors also induced intracellular oxidative stress (measured by dihydrorhodamine 123 and dichlorofluorescein fluorescence), caused alterations in overall intracellular redox status (as evidenced by NAD+/NADH ratios), and increased protein carbonyl formation. Furthermore, the antioxidant N-acetylcysteine completely prevented EA-induced oxidative stress and cytotoxicity. Whereas EA had no effect on mitochondrial energetics, it significantly altered cellular metabolic profile. To explore the physiological impact of these cellular events, we used an ex vivo mouse-isolated perfused lung model. Supplementation of perfusate with EA markedly affected lung mechanics and significantly increased lung permeability. The results of our combined genetic, pharmacological, and metabolic studies on multiple platforms suggest the importance of GST enzymes, specifically GST-π, in the cellular and whole lung response to acute oxidative and metabolic stress. These may have important clinical implications.

NMDA Receptor Antagonist Attenuates Bleomycin-Induced Acute Lung Injury

Background

Glutamate is a major neurotransmitter in the central nervous system (CNS). Large amount of glutamate can overstimulate N-methyl-D-aspartate receptor (NMDAR), causing neuronal injury and death. Recently, NMDAR has been reported to be found in the lungs. The aim of this study is to examine the effects of memantine, a NMDAR channel blocker, on bleomycin-induced lung injury mice.

Methods

C57BL/6 mice were intratracheally injected with bleomycin (BLM) to induce lung injury. Mice were randomized to receive saline, memantine (Me), BLM, BLM plus Me. Lungs and BALF were harvested on day 3 or 7 for further evaluation.

Results

BLM caused leukocyte infiltration, pulmonary edema and increase in cytokines, and imposed significant oxidative stress (MDA as a marker) in lungs. Memantine significantly mitigated the oxidative stress, lung inflammatory response and acute lung injury caused by BLM. Moreover, activation of NMDAR enhances CD11b expression on neutrophils.

Conclusions

Memantine mitigates oxidative stress, lung inflammatory response and acute lung injury in BLM challenged mice.

NMDA receptors mediate contractile responses in human airway smooth muscle cells

Human airway smooth muscle (HASM) exhibits enhanced contractility in asthma. Inflammation is associated with airway hypercontractility, but factors that underpin these features are not fully elucidated. Glutamate toxicity associated with increased plasma glutamate concentrations was observed in airway inflammation, suggesting that multisubunit glutamate receptors, N-methyl-d-aspartate receptors (NMDA-R) contribute to airway hyperreactivity. We tested the hypothesis that HASM expresses NMDA-R subunits that can form functional receptors to mediate contractile responses to specific extracellular ligands. In cultured HASM cells, we measured NMDA-R subunit mRNA and protein abundance by quantitative PCR, immunoblotting, flow cytometry, and epifluorescence immunocytochemistry. We measured mRNA for a number of NMDA-R subunits, including the obligatory NR1 subunit, which we confirmed to be present as a protein. In vitro and ex vivo functional NMDA-R activation in HASM cells was measured using intracellular calcium flux (fura-2 AM), collagen gel contraction assays, and murine thin-cut lung slices (TCLS). NMDA, a pharmacological glutamate analog, induced cytosolic calcium mobilization in cultured HASM cells. We detected three different temporal patterns of calcium response, suggesting the presence of heterogeneous myocyte subpopulations. NMDA-R activation also induced airway contraction in murine TCLS and soft collagen gels seeded with HASM cells. Responses in cells, lung slices, and collagen gels were mediated by NMDA-R, as they could be blocked by (2R)-amino-5-phosphonopentanoate, a specific NMDA-R inhibitor. In summary, we reveal the presence of NMDA-R in HASM that mediate contractile responses via glutamatergic mechanisms. These findings suggest that accumulation of glutamate-like ligands for NMDA-R associated with airway inflammation contributes directly to airway hyperreactivity.

Experimental lung injury promotes alterations in energy metabolism and respiratory mechanics in the lungs of rats: prevention by exercise

In the present study we investigated the effects of lung injury on energy metabolism (succinate dehydrogenase, complex II, cytochrome c oxidase, and ATP levels), respiratory mechanics (dynamic and static compliance, elastance and respiratory system resistance) in the lungs of rats, as well as on phospholipids in bronchoalveolar lavage fluid. The protective effect of physical exercise on the alterations caused by lung injury, including lung edema was also evaluated. Wistar rats were submitted to 2 months of physical exercise. After this period the lung injury was induced by intratracheal instillation of lipopolysaccharide. Adult Wistar rats were submitted to 2 months of physical exercise and after this period the lung injury was induced by intratracheal instillation of lipopolysaccharide in dose 100 μg/100 g body weight. The sham group received isotonic saline instillation. Twelve hours after the injury was performed the respiratory mechanical and after the rats were decapitated and samples were collected. The rats subjected to lung injury presented a decrease in activities of the enzymes of the electron transport chain and ATP levels in lung, as well as the formation of pulmonary edema. A decreased lung dynamic and static compliance, as well as an increase in respiratory system resistance, and a decrease in phospholipids content were observed. Physical exercise was able to totally prevent the decrease in succinate dehydrogenase and complex II activities and the formation of pulmonary edema. It also partially prevented the increase in respiratory system resistance, but did not prevent the decrease in dynamic and static compliance, as well as in phospholipids content. These findings suggest that the mitochondrial dysfunction may be one of the important contributors to lung damage and that physical exercise may be beneficial in this pathology, although it did not prevent all changes present in lung injury.

The N-methyl-d-aspartic acid receptor antagonist memantine ameliorates and delays the development of arthritis by enhancing regulatory T cells

The neuroendocrine impact on rheumatoid arthritis is not yet fully described although numerous neurotransmitters are shown to act as inflammatory modulators. One of these is the excitatory transmitter glutamate (Glu). In this study, the influence of the Glu receptor (GluR)-mediated effects on collagen-induced arthritis (CIA) was investigated. CIA was induced in DBA/1 mice by immunization with chicken collagen type II (CII). Mice were exposed to the following GluR antagonists: group 1, the N-methyl-D-aspartic acid (NMDA) receptor channel blocker memantine; group 2, the metabotropic GluR antagonist AIDA, and group 3, the excitatory amino acid receptor antagonist kynurenic acid (KA). Arthritis was evaluated clinically and histologically and compared to PBS-treated controls. The effects of treatment on T cell populations and the levels of anti-CII and anti-citrullinated peptide antibodies were evaluated. Memantine treatment significantly improved the course of CIA, reducing synovitis (p = 0.007) and the frequency of erosions (p = 0.007). Memantine treatment up-regulated the expression of Foxp3 in spleen CD4+ T cells followed by an increase in CD4+CD25+ regulatory T cells. The other GluR antagonists, AIDA and KA, had no effect on CIA. These results demonstrate that blockade of the NMDA receptor channel with memantine delays and attenuates the development of arthritis, probably by promoting the development of regulatory T lymphocytes.