Time course of the inflammatory and oxidative stress response to pulmonary infection in mice

Antibacterial, anti-biofilm and in vivo activities of the antimicrobial peptides P5 and P6.2

Cationic antimicrobial peptides (AMPs) are short linear amino acid sequences, which display antimicrobial activity against a wide range of bacterial species. They are promising novel antimicrobials since they have shown bactericidal effects against multiresistant bacteria. Their amphiphilic structure with hydrophobic and cationic regions drives their interaction with anionic bacterial cytoplasmic membranes, which leads to their disruption. In this work two synthetic designed AMPs, P5 and P6.2, which have been previously analyzed in their ability to interact with bacterial or eukaryotic membranes, were evaluated in their anti-biofilm and in vivo antibacterial activity. In a first step, a time-kill kinetic assay against P. aeruginosa and S. aureus and a curve for hemolytic activity were performed in order to determine the killing rate and the possible undesirable toxic effect, respectively, for both peptides. The biofilm inhibitory activity was quantified at sub MIC concentrations of the peptides and the results showed that P5 displayed antibiofilm activity on both strains while P6.2 only on S. aureus. Scanning electron microscopy (SEM) of bacteria treated with peptides at their MIC revealed protruding blisters on Gam-negative P. aeruginosa strain, but almost no visible surface alteration on Gram-positive S. aureus. These micrographs highlighted different manifestations of the membrane-disrupting activity that these kinds of peptides possess. Finally, both peptides were analyzed in vivo, in the lungs of neutropenic mice previously instilled with P. aeruginosa. Mice lungs were surgically extracted and bacteria and pro-inflammatory cytokines (IL-β, IL-6 and TNF-α) were quantified by colony forming units and ELISA, respectively. Results showed that instillation of the peptides produced a significant decrease in the number of living bacteria in the lungs, concomitant with a decrease in pro-inflammatory cytokines. Overall, the results presented here suggest that these two new peptides could be good candidates for future drug development for anti-biofilm and anti-infective therapy.

Adipose-derived stem cells attenuate pulmonary microvascular hyperpermeability after smoke inhalation

Background

Pulmonary edema is a hallmark of acute respiratory distress syndrome (ARDS). Smoke inhalation causes ARDS, thus significantly increasing the mortality of burn patients. Adipose-derived stem cells (ASCs) exert potent anti-inflammatory properties. The goal of the present study was to test the safety and ecfficacy of ASCs, in a well-characterized clinically relevant ovine model of ARDS.

Methods

Female sheep were surgically prepared. ARDS was induced by cooled cotton smoke inhalation. Following injury, sheep were ventilated, resuscitated with lactated Ringer’s solution, and cardiopulmonary hemodynamics were monitored for 48 hours in a conscious state. Pulmonary microvascular hyper-permeability was assessed by measuring lung lymph flow, extravascular lung water content, protein content in plasma and lung lymph fluid. Sheep were randomly allocated to two groups: 1) ASCs: infused with 200 million of ASCs in 200mL of PlasmaLyteA starting 1 hours post-injury, n = 5; 2) control, treated with 200mL of PlasmaLyteA in a similar pattern, n = 5.

Results

Lung lymph flow increased 9-fold in control sheep as compared to baseline. Protein in the plasma was significantly decreased, while it was increased in the lung lymph. The treatment with ASCs significantly attenuated these changes. Treatment with ASCs almost led to the reversal of increased pulmonary vascular permeability and lung water content. Pulmonary gas exchange was significantly improved by ASCs. Infusion of the ASCs did not negatively affect pulmonary artery pressure and other hemodynamic variables.

Conclusions

ASCs infusion was well tolerated. The results suggest that intravenous ASCs modulate pulmonary microvascular hyper-permeability and prevent the onset of ARDS in our experimental model.

Infections: A Possible Risk Factor for Type 2 Diabetes

Diabetes mellitus is one of the biggest challenges to human health globally, with an estimated 95% of the global diabetic population having type 2 diabetes. Classical causes for type 2 diabetes, such as genetics and obesity, do not account for the high incidence of the disease. Recent data suggest that infections may precipitate insulin resistance via multiple mechanisms, such as the proinflammatory cytokine response, the acute-phase response, and the alteration of the nutrient status. Even pathogen products, such as lipopolysaccharide and peptidoglycans, can be diabetogenic. Therefore, we argue that infections that are known to contribute to insulin resistance should be considered as risk factors for type 2 diabetes.

Dimethylarginine dimethylaminohydrolase II overexpression attenuates LPS-mediated lung leak in acute lung injury

Acute lung injury (ALI) is a severe hypoxemic respiratory insufficiency associated with lung leak, diffuse alveolar damage, inflammation, and loss of lung function. Decreased dimethylaminohydrolase (DDAH) activity and increases in asymmetric dimethylarginine (ADMA), together with exaggerated oxidative/nitrative stress, contributes to the development of ALI in mice exposed to LPS. Whether restoring DDAH function and suppressing ADMA levels can effectively ameliorate vascular hyperpermeability and lung injury in ALI is unknown, and was the focus of this study. In human lung microvascular endothelial cells, DDAH II overexpression prevented the LPS-dependent increase in ADMA, superoxide, peroxynitrite, and protein nitration. DDAH II also attenuated the endothelial barrier disruption associated with LPS exposure. Similarly, in vivo, we demonstrated that the targeted overexpression of DDAH II in the pulmonary vasculature significantly inhibited the accumulation of ADMA and the subsequent increase in oxidative/nitrative stress in the lungs of mice exposed to LPS. In addition, augmenting pulmonary DDAH II activity before LPS exposure reduced lung vascular leak and lung injury and restored lung function when DDAH activity was increased after injury. Together, these data suggest that enhancing DDAH II activity may prove a useful adjuvant therapy to treat patients with ALI.