Distinctive Roles and Mechanisms of Human Neutrophil Peptides in Experimental Sepsis and Acute Respiratory Distress Syndrome

Human Neutrophil Defensins Disrupt Liver Interendothelial Junctions and Aggravate Sepsis

Human neutrophil peptides 1-3 (HNP1-3), also known as human α-defensins, are the most abundant neutrophil granule proteins. The genes that encode HNP1-3, DEFA1/DEFA3, exhibit extensive copy number variations, which correlate well with their protein levels. Human and mouse studies have shown that increased copy numbers of DEFA1/DEFA3 worsen sepsis outcomes. Additionally, high concentrations of HNP1-3 in body fluids have been reported in patients with sepsis. However, direct evidence for the pathogenic role of HNP1-3 proteins during sepsis progression is lacking. In current study, sepsis was induced by means of cecal puncture and ligation. Various doses of HNP-1 (low dose with 0.5 mg/kg body weight and high dose with 10 mg/kg body weight) or phosphate buffer saline were intraperitoneally administered to mice at six hours after sepsis onset. Survival rate was monitored, and vascular permeability, endothelial cell pyroptosis, and immunofluorescence of endothelial adherens junction protein vascular endothelial-cadherin were evaluated. The administration of a high dose of HNP-1 after sepsis onset led to increased mortality, more severe liver injury, and increased vascular permeability in the liver and mesentery. The injection of high dose of HNP-1 did not directly induce liver endothelial cell death but destroyed interendothelial junctions in the liver. Moreover, genetic deficiency of nucleotide-binding oligomerization domain-like receptor protein-3 or caspase-1 abrogated the high mortality and disrupted liver interendothelial junctions caused by high dose of HNP-1 during sepsis. This study directly demonstrates that neutrophil defensins play a key role in regulating endothelial stability during sepsis development.

Antioxidants as Therapeutic Agents in Acute Respiratory Distress Syndrome (ARDS) Treatment-From Mice to Men

Acute respiratory distress syndrome (ARDS) is a major cause of patient mortality in intensive care units (ICUs) worldwide. Considering that no causative treatment but only symptomatic care is available, it is obvious that there is a high unmet medical need for a new therapeutic concept. One reason for a missing etiologic therapy strategy is the multifactorial origin of ARDS, which leads to a large heterogeneity of patients. This review summarizes the various kinds of ARDS onset with a special focus on the role of reactive oxygen species (ROS), which are generally linked to ARDS development and progression. Taking a closer look at the data which already have been established in mouse models, this review finally proposes the translation of these results on successful antioxidant use in a personalized approach to the ICU patient as a potential adjuvant to standard ARDS treatment.

Therapeutic targeting of neutrophil exocytosis

Dysregulation of neutrophil activation causes disease in humans. Neither global inhibition of neutrophil functions nor neutrophil depletion provides safe and/or effective therapeutic approaches. The role of neutrophil granule exocytosis in multiple steps leading to recruitment and cell injury led each of our laboratories to develop molecular inhibitors that interfere with specific molecular regulators of secretion. This review summarizes neutrophil granule formation and contents, the role granule cargo plays in neutrophil functional responses and neutrophil-mediated diseases, and the mechanisms of granule release that provide the rationale for development of our exocytosis inhibitors. We present evidence for the inhibition of granule exocytosis in vitro and in vivo by those inhibitors and summarize animal data indicating that inhibition of neutrophil exocytosis is a viable therapeutic strategy.

Modulation of Human Neutrophil Peptides on P. aeruginosa Killing, Epithelial Cell Inflammation and Mesenchymal Stromal Cell Secretome Profiles

Objective

Neutrophil infiltration and release of the abundant human neutrophil peptides (HNP) are a common clinical feature in critically ill patients. We tested a hypothesis that different cell types respond to HNP differently in lung microenvironment that may influence the host responses.

Methods

Plasma concentrations of HNP were measured in healthy volunteers and patients with sepsis. Cells including the bacteria P. aeruginosa, human lung epithelial cells and mesenchymal stromal cells (MSCs) were exposed to various concentrations of HNP. Bacterial killing, epithelial cell inflammation, MSC adhesion and behaviours were examined after HNP stimulation.

Results

Incubation of P. aeruginosa or stimulation of human lung epithelial cells with HNP resulted in bacterial killing or IL-8 production at a dose of 50 μg/mL, while MSC adhesion and alternations of secretome profiles took place after HNP stimulation at a dose of 10 μg/mL. The secretome profile changes were characterized by increased release of the IL-6 family members such as C-reactive protein (CRP), leukemia inhibitory factor (LIF) and interleukin (IL-11), and first apoptosis signal (FAS) and platelet-derived growth factor-AA as compared to a vehicle control group.

Conclusion

Stimulation of MSCs with HNP resulted in changes of secretome profiles at 5-fold lower concentration than that required for bacterial killing and lung epithelial inflammation. This undisclosed risk factor of HNP in lung environment should be taken into consideration when MSCs are applied as cell therapy in inflammatory lung diseases.

Dual effects of human neutrophil peptides in a mouse model of pneumonia and ventilator-induced lung injury

BACKGROUND

Pneumonia is a major cause of high morbidity and mortality in critically illness, and frequently requires support with mechanical ventilation. The latter can lead to ventilator-induced lung injury characterized by neutrophil infiltration. The cationic human neutrophil peptides (HNP) stored in neutrophils can kill microorganisms, but excessive amount of HNP released during phagocytosis may contribute to inflammatory responses and worsen lung injury. Based on our previous work, we hypothesized that blocking the cell surface purinergic receptor P2Y₆ will attenuate the HNP-induced inflammatory responses while maintaining their antimicrobial activity in pneumonia followed by mechanical ventilation.

METHODS

Plasma HNP levels were measured in patients with pneumonia who received mechanical ventilation and in healthy volunteers. FVB littermate control and HNP transgenic (HNP⁺) mice were randomized to receive P. aeruginosa intranasally. The P2Y₆ antagonist (MRS2578) or vehicle control was given after P. aeruginosa instillation. Additional mice underwent mechanical ventilation at either low pressure (LP) or high pressure (HP) ventilation 48 h after pneumonia, and were observed for 24 h.

RESULTS

Plasma HNP concentration increased in patients with pneumonia as compared to healthy subjects. The bacterial counts in the bronchoalveolar lavage fluid (BALF) were lower in HNP⁺ mice than in FVB mice 72 h after P. aeruginosa instillation. However, upon receiving HP ventilation, HNP⁺ mice had higher levels of cytokines and chemokines in BALF than FVB mice. These inflammatory responses were attenuated by the treatment with MRS2578 that did not affect the microbial effects of HNP.

CONCLUSIONS

HNP exerted dual effects by exhibiting antimicrobial activity in pneumonia alone condition while enhancing inflammatory responses in pneumonia followed by HP mechanical ventilation. Blocking P2Y₆ can attenuate the inflammation without affecting the antibacterial property of HNP. The P2Y₆ receptor may be a novel therapeutic target in attenuation of the leukocyte-mediated excessive host responses in inflammatory lung diseases.