Detailed Mechanisms Underlying Neutrophil Bactericidal Activity against Streptococcus pneumoniae.

Neutrophils are an essential cellular component of innate immunity and control bacterial infections through a combination of intracellular and extracellular killing methods. Although the importance of neutrophils has been established, the exact methods used to handle particular bacterial challenges and the efficiency of bacterial killing remain not well understood. In this study, we addressed how neutrophils eliminate Streptococcus pneumoniae (Spn), a leading cause of community acquired and post-influenza bacterial pneumonia. We analyzed killing methods with variable bacterial:neutrophil concentrations and following priming with PAM3CSK4 (P3CSK), an agonist for Toll-like-receptor 2 (TLR2). Our results show that murine neutrophils display surprisingly weak bactericidal activity against Spn, employing a predominantly extracellular mode of killing at lower concentrations of bacteria, whereas challenges with higher bacterial numbers induce both extracellular and intracellular elimination modes but require TLR2 activation. TLR2 activation increased reactive oxygen species (ROS) and neutrophil extracellular trap (NET) formation in response to Spn. Despite this, supernatants from P3CSK-stimulated neutrophils failed to independently alter bacterial replication. Our study reveals that unstimulated neutrophils are capable of eliminating bacteria only at lower concentrations via extracellular killing methods, whereas TLR2 activation primes neutrophil-mediated killing using both intracellular and extracellular methods under higher bacterial burdens.

Heterogeneity of neutrophils and inflammatory responses in patients with COVID-19 and healthy controls.

Severe respiratory viral infections, including SARS-CoV-2, have resulted in high mortality rates despite corticosteroids and other immunomodulatory therapies. Despite recognition of the pathogenic role of neutrophils, in-depth analyses of this cell population have been limited, due to technical challenges of working with neutrophils. We undertook an unbiased, detailed analysis of neutrophil responses in adult patients with COVID-19 and healthy controls, to determine whether distinct neutrophil phenotypes could be identified during infections compared to the healthy state. Single-cell RNA sequencing analysis of peripheral blood neutrophils from hospitalized patients with mild or severe COVID-19 disease and healthy controls revealed distinct mature neutrophil subpopulations, with relative proportions linked to disease severity. Disruption of predicted cell-cell interactions, activated oxidative phosphorylation genes, and downregulated antiviral and host defense pathway genes were observed in neutrophils obtained during severe compared to mild infections. Our findings suggest that during severe infections, there is a loss of normal regulatory neutrophil phenotypes seen in healthy subjects, coupled with the dropout of appropriate cellular interactions. Given that neutrophils are the most abundant circulating leukocytes with highly pathogenic potential, current immunotherapies for severe infections may be optimized by determining whether they aid in restoring an appropriate balance of neutrophil subpopulations.

Neutrophils drive pulmonary vascular leakage in MHV-1 infection of susceptible A/J mice.

Background: Lung inflammation, neutrophil infiltration, and pulmonary vascular leakage are pathological hallmarks of acute respiratory distress syndrome (ARDS) which can lethally complicate respiratory viral infections. Despite similar comorbidities, however, infections in some patients may be asymptomatic while others develop ARDS as seen with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections for example. Methods: In this study, we infected resistant C57BL/6 and susceptible A/J strains of mice with pulmonary administration of murine hepatitis virus strain 1 (MHV-1) to determine mechanisms underlying susceptibility to pulmonary vascular leakage in a respiratory coronavirus infection model. Results: A/J animals displayed increased lung injury parameters, pulmonary neutrophil influx, and deficient recruitment of other leukocytes early in the infection. Moreover, under basal conditions, A/J neutrophils overexpressed primary granule protein genes for myeloperoxidase and multiple serine proteases. During infection, myeloperoxidase and elastase protein were released in the bronchoalveolar spaces at higher concentrations compared to C57BL/6 mice. In contrast, genes from other granule types were not differentially expressed between these 2 strains. We found that depletion of neutrophils led to mitigation of lung injury in infected A/J mice while having no effect in the C57BL/6 mice, demonstrating that an altered neutrophil phenotype and recruitment profile is a major driver of lung immunopathology in susceptible mice. Conclusions: These results suggest that host susceptibility to pulmonary coronaviral infections may be governed in part by underlying differences in neutrophil phenotypes, which can vary between mice strains, through mechanisms involving primary granule proteins as mediators of neutrophil-driven lung injury.

Respiratory Viral Infection-Induced Microbiome Alterations and Secondary Bacterial Pneumonia.

Influenza and other respiratory viral infections are the most common type of acute respiratory infection. Viral infections predispose patients to secondary bacterial infections, which often have a more severe clinical course. The mechanisms underlying post-viral bacterial infections are complex, and include multifactorial processes mediated by interactions between viruses, bacteria, and the host immune system. Studies over the past 15 years have demonstrated that unique microbial communities reside on the mucosal surfaces of the gastrointestinal tract and the respiratory tract, which have both direct and indirect effects on host defense against viral infections. In addition, antiviral immune responses induced by acute respiratory infections such as influenza are associated with changes in microbial composition and function ("dysbiosis") in the respiratory and gastrointestinal tract, which in turn may alter subsequent immune function against secondary bacterial infection or alter the dynamics of inter-microbial interactions, thereby enhancing the proliferation of potentially pathogenic bacterial species. In this review, we summarize the literature on the interactions between host microbial communities and host defense, and how influenza, and other acute respiratory viral infections disrupt these interactions, thereby contributing to the pathogenesis of secondary bacterial infections.

Lack of the P2X7 receptor protects against AMD-like defects and microparticle accumulation in a chronic oxidative stress-induced mouse model of AMD.

The P2X7 receptor (P2X7R) is an ATP-gated ion channel that is a key player in oxidative stress under pathological conditions. The P2X7R is expressed in the retinal pigmented epithelium (RPE) and neural retina. Chronic oxidative stress contributes to the pathogenesis of age-related macular degeneration (AMD). Mice lacking Cu, Zn superoxide dismutase (Sod1) developed chronic oxidative stress as well as AMD-like features, but whether the P2X7R plays a causative role in oxidative stress-induced AMD is unknown. Thus, the main purpose of this study was to test if concurrent knockout (KO) of P2X7R could block AMD-like defects seen in Sod1 KO mice. Using multiple approaches, we demonstrate that Sod1 KO causes AMD-like defects, including positive staining for oxidative stress markers, 3-nitrotyrosine and carboxymethyl lysine, thinning of the RPE and retina, thickening of Bruch's membrane, presence of basal laminar and linear deposits, RPE barrier disruption and accumulation of microglia/macrophages. Moreover, we find that Sod1 KO mice accumulate more microparticles (MPs) within RPE/choroid tissues. Concurrent KO of the P2X7R protects against AMD-like defects and MP accumulation in Sod1 KO mice. Together, we show for the first time, that deficiency of P2X7R prevents in vivo oxidative stress-induced accumulation of MPs and AMD-like defects. This work could potentially lead to novel therapies for AMD and other oxidative stress-driven diseases.

N-Acetylcysteine Amide Protects Against Oxidative Stress-Induced Microparticle Release From Human Retinal Pigment Epithelial Cells.

PURPOSE: Oxidative stress is a major factor involved in retinal pigment epithelium (RPE) apoptosis that underlies AMD. Drusen, extracellular lipid- and protein-containing deposits, are strongly associated with the development of AMD. Cell-derived microparticles (MPs) are small membrane-bound vesicles shed from cells. The purpose of this study was to determine if oxidative stress drives MP release from RPE cells, to assess whether these MPs carry membrane complement regulatory proteins (mCRPs: CD46, CD55, and CD59), and to evaluate the effects of a thiol antioxidant on oxidative stress-induced MP release. METHODS: Retinal pigment epithelium cells isolated from human donor eyes were cultured and treated with hydrogen peroxide (H2O2) to induce oxidative stress. Isolated MPs were fixed for transmission electron microscopy or processed for component analysis by flow cytometry, Western blot analysis, and confocal microscopy. RESULTS: Transmission electron microscopy showed that MPs ranged in diameter from 100 to 1000 nm. H2O2 treatment led to time- and dose-dependent elevations in MPs with externalized phosphatidylserine and phosphatidylethanolamine, known markers of MPs. These increases were strongly correlated to RPE apoptosis. Oxidative stress significantly increased the release of mCRP-positive MPs, which were prevented by a thiol antioxidant, N-acetylcysteine amide (NACA). CONCLUSIONS: This is the first evidence that oxidative stress induces cultured human RPE cells to release MPs that carry mCRPs on their surface. The levels of released MPs are strongly correlated with RPE apoptosis. N-acetylcysteine amide prevents oxidative stress-induced effects. Our findings indicate that oxidative stress reduces mCRPs on the RPE surface through releasing MPs.

Dendritic nanoconjugates for intracellular delivery of neutral oligonucleotides.

Dendrimer-based gene delivery has been constrained by intrinsic toxicity and suboptimal nanostructure. Conjugation of neutral morpholino oligonucleotides (ONs) with PAMAM dendrimers resulted in neutral, uniform, and ultra-small (∼10 nm) nanoconjugates. The nanoconjugates dramatically enhanced cellular delivery of the ONs in cancer cells. After release from the dendrimer in the cytosol, the ONs produced potent functional activity without causing significant cytotoxicity. When carrying an apoptosis-promoting ON, the nanoconjugates produced cancer cell killing directly. Thus, the dendritic nanoconjugates may provide an effective tool for delivering ONs to tumors and other diseased tissues.

Angiotensin-(1-7) prevents angiotensin II-induced fibrosis in cremaster microvessels.

OBJECTIVE: The effect of the heptapeptide hormone Ang-(1-7) on microvascular fibrosis in rats with Ang II-induced hypertension was investigated, since vascular fibrosis/remodeling plays a prominent role in hypertension-induced end-organ damage and Ang-(1-7) inhibits vascular growth and fibrosis. METHODS: Fibrosis of cremaster microvessels was studied in male Lewis rats infused with Ang II and/or Ang-(1-7). RESULTS: Ang II elevated systolic blood pressure by approximately 40 mmHg, while blood pressure was not changed by Ang-(1-7). Ang II increased perivascular fibrosis surrounding 20-50 µm arterioles as well as interstitial fibrosis; coadministration of Ang-(1-7) prevented the increases in fibrosis. The fibrotic factor CTGF and phospho-Smad 2/3, which upregulates CTGF, were increased by Ang II; this effect was prevented by coadministration of Ang-(1-7). Although TGF-ß phosphorylates Smad 2/3, TGF-ß was no different among treatment groups. In contrast, Ang II increased the MAP kinase phospho-ERK1/2, which also phosphorylates Smad; p-ERK was reduced by Ang-(1-7). Ang-(1-7), in the presence or absence of Ang II, upregulated the MAP kinase phosphatase DUSP1. CONCLUSIONS: These results suggest that Ang-(1-7) increases DUSP1 to reduce MAP kinase/Smad/CTGF signaling and decrease fibrosis in resistance arterioles, to attenuate end-organ damage associated with chronic hypertension.

Tumor cell-targeted delivery of nanoconjugated oligonucleotides in composite spheroids.

Standard tissue culture has often been a poor model for predicting the efficacy of anti-cancer agents including oligonucleotides. In contrast to the simplicity of monolayer tissue cultures, a tumor mass includes tightly packed tumor cells, tortuous blood vessels, high levels of extracellular matrix, and stromal cells that support the tumor. These complexities pose a challenge for delivering therapeutic agents throughout the tumor, with many drugs limited to cells proximal to the vasculature. Multicellular tumor spheroids are superior to traditional monolayer cell culture for the assessment of cancer drug delivery, since they possess many of the characteristics of metastatic tumor foci. However, homogeneous spheroids comprised solely of tumor cells do not account for some of the key aspects of metastatic tumors, particularly the interaction with host cells such as fibroblasts. Further, homogeneous culture does not allow for the assessment of targeted delivery to tumor versus host cells. Here we have evaluated delivery of targeted and untargeted oligonucleotide nanoconjugates and of oligonucleotide polyplexes in both homogeneous and composite tumor spheroids. We find that inclusion of fibroblasts in the spheroids reduces delivery efficacy of the polyplexes. In contrast, targeted multivalent RGD-oligonucleotide nanoconjugates were able to effectively discriminate between melanoma cells and fibroblasts, thus providing tumor-selective uptake and pharmacological effects.

Multicellular tumor spheroids as a model for assessing delivery of oligonucleotides in three dimensions.

Oligonucleotides have shown promise in selectively manipulating gene expression in vitro, but that success has not translated to the clinic for cancer therapy. A potential reason for this is that cells behave differently in monolayer than in the three-dimensional tumor, resulting in limited penetration and distribution of oligonucleotides in the tumor. This may be especially true when oligonucleotides are associated with nanocarriers such as lipoplexes and polyplexes, commonly used delivery vehicles for oligonucleotides. The multicellular tumor spheroid (MCTS), a three-dimensional model that closely resembles small avascular tumors and micrometastases, has been utilized as an intermediate between monolayer culture and in vivo studies for the screening of small-molecule drugs. However, spheroids have been little used for the study of various oligonucleotide delivery formulations. Here, we have evaluated the uptake and efficacy of splice-switching antisense oligonucleotides using various delivery modalities in two- and three-dimensional culture models. We find that the size of the delivery agent dramatically influences penetration into the spheroid and thus the biological effect of the oligonucleotides. We hypothesize that the MCTS model will prove to be a useful tool in the future development of oligonucleotide delivery formulations.Molecular Therapy-Nucleic Acids (2014) 3, e153; doi:10.1038/mtna.2014.5; published online 11 March 2014.

Cellular uptake and intracellular trafficking of oligonucleotides: implications for oligonucleotide pharmacology.

One of the major constraints on the therapeutic use of oligonucleotides is inefficient delivery to their sites of action in the cytosol or nucleus. Recently it has become evident that the pathways of cellular uptake and intracellular trafficking of oligonucleotides can strongly influence their pharmacological actions. Here we provide background information on the basic processes of endocytosis and trafficking and then review recent literature on targeted delivery and subcellular trafficking of oligonucleotides in that context. A variety of approaches including molecular scale ligand-oligonucleotide conjugates, ligand-targeted nanocarriers, and the use of small molecules to enhance oligonucleotide effects are discussed.

Conjugation with receptor-targeted histidine-rich peptides enhances the pharmacological effectiveness of antisense oligonucleotides.

Ineffective delivery to intracellular sites of action is one of the key limitations to the use of antisense and siRNA oligonucleotides as therapeutic agents. Here, we describe molecular scale antisense oligonucleotide conjugates that bind selectively to a cell surface receptor, are internalized, and then partially escape from nonproductive endosomal locations to reach their sites of action in the nucleus. Peptides that include bombesin sequences for receptor targeting and a run of histidine residues for endosomal disruption were covalently linked to a splice switching antisense oligonucleotide. The conjugates were tested for their ability to correct splicing and up-regulate expression of a luciferase reporter in prostate cancer cells that express the bombesin receptor. We found that trivalent conjugates that included both the targeting sequence and several histidine residues were substantially more effective than conjugates containing only the bombesin or histidine moieties. This demonstrates the potential of creating molecular scale oligonucleotide conjugates with both targeting and endosome escape capabilities.

Albumin-based nanoconjugates for targeted delivery of therapeutic oligonucleotides.

Nanoparticle-based delivery has become an important strategy to advance siRNA and antisense oligonucleotides into clinical reality. However, limited biodistribution of nanoparticles and the toxicity of some nanocarriers restrict the wider application of this strategy. To address these issues we aimed to construct oligonucleotide delivery systems which are non-cytotoxic and smaller than typical nanoparticles. Thus, a morpholino oligonucleotide was conjugated to a tumor-targeting RGD peptide, and then, multiple RGD-oligo conjugates were linked to a single molecule of human serum albumin via a reductively responsive linkage. The resultant nanoconjugates showed uniform and monodispersed size distribution with a diameter of 13 nm. A single nanoconjugate molecule contains 15 oligonucleotides as well as 15 targeting ligands on the surface of albumin. The nanoparticle demonstrated 61-fold enhancement in receptor-specific cellular delivery of oligonucleotides in integrin-expressing tumor cells compared to the non-targeted control nanoconjugates and were able to robustly enhance functional activity of the oligonucleotide at low nanomolar concentrations without causing cytotoxicity. Due to their small size, the targeted nanoconjugates could penetrate deeply and distribute throughout 3-D tumor spheroids, whereas the conventional nanoparticles with sizes over 300 nm could only deliver to the cells on the surface of the tumor spheroids. As a result of their greater cellular delivery, smaller size, and lack of cytotoxicity compared to conventional nanoparticles, the multivalent nanoconjugates may provide an effective tool for targeting oligonucleotides to tumors and other diseased tissues.

The small molecule Retro-1 enhances the pharmacological actions of antisense and splice switching oligonucleotides.

The attainment of strong pharmacological effects with oligonucleotides is hampered by inefficient access of these molecules to their sites of action in the cytosol or nucleus. Attempts to address this problem with lipid or polymeric delivery systems have been only partially successful. Here, we describe a novel alternative approach involving the use of a non-toxic small molecule to enhance the pharmacological effects of oligonucleotides. The compound Retro-1 was discovered in a screen for small molecules that reduce the actions of bacterial toxins and has been shown to block the retrograde trafficking pathway. We demonstrate that Retro-1 can also substantially enhance the effectiveness of antisense and splice switching oligonucleotides in cell culture. This effect occurs at the level of intracellular trafficking or processing and is correlated with increased oligonucleotide accumulation in the nucleus but does not involve the perturbation of lysosomal compartments. We also show that Retro-1 can alter the effectiveness of splice switching oligonucleotides in the in vivo setting. These observations indicate that it is possible to enhance the pharmacological actions of oligonucleotides using non-toxic and non-lysosomotropic small molecule adjuncts.

Vasodilation in response to the GPR30 agonist G-1 is not different from estradiol in the mRen2.Lewis female rat.

Our studies in the mRen2.Lewis female rat, an angiotensin II- and estrogen-dependent model of hypertension, revealed that chronic activation of estrogen receptor GPR30 markedly reduces blood pressure in ovariectomized females. The present studies measured acute vasodilation to the selective GPR30 agonist G-1 and 17-ß-estradiol (10(-9)-10(-5.5) M) in isolated aortic rings and mesenteric arteries from intact mRen2.Lewis females. Maximal relaxation was greater in mesenteric vessels versus the aorta for both G-1 (47% ± 8% vs 80% ± 5% of phenylephrine preconstriction, P < 0.001) and estradiol (42% ± 7% vs 83% ± 4% of phenylephrine preconstriction, P < 0.001). The GPR30 antagonist G15 attenuated the response to both estradiol and G-1. Removal of the endothelium or pretreatment with Nitro-L-arginine methyl ester (L-NAME) partially attenuated vasorelaxation. Responses were not altered in mesenteric vessels from ovariectomized females. Immunohistochemical analysis revealed GPR30 expression in mesenteric endothelial and smooth muscle cells, and smooth muscle expression was confirmed in cultured cells. We conclude that estradiol-induced relaxation in conduit and resistance vessels from mRen2.Lewis females may be mediated by the novel estrogen receptor GPR30. The direct vasodilatory response of G-1 in resistance vessels presents one mechanism for the reduction in blood pressure induced by chronic G-1 administration.