Attenuation of pulmonary injury by an inhaled MMP inhibitor in the endotoxin lung injury model

Effect of low-dose hydrocortisone and inhaled nitric oxide on inflammatory mediators and local pulmonary metalloproteinases activity in LPS-induced sepsis in piglets

Hospital mortality in sepsis varies between 30-45%. It has been shown that administration of inhaled nitric oxide (iNO) and intravenous corticosteroid in a porcine endotoxemia model attenuated the systemic inflammatory response. We explored the anti-inflammatory effect of a double-treatment strategy (iNO + low-dose steroid) on the lungs in a long-term porcine endotoxic shock model. As metalloproteinases (MMPs) are involved in the initiation of multiple organ dysfunction in septic shock, we evaluated the influence of this combination therapy on MMP2 and MMP9 activity and proIL-1β maturation. A shock-like condition was established in 23 animals by continuous infusion of E. coli lipopolysaccharide (LPS) for 10 h. Then the animals were observed for 10 h. Twelve pigs received iNO and hydrocortisone (iNO treatment started 3 h after the initial LPS infusion and continued until the end of the experiment). Eleven pigs were controls. Pigs treated with iNO and hydrocortisone displayed less inflammatory infiltrates in the lungs than the controls and a lower level of IL-1β. The proMMP2 was significantly decreased in the iNO and hydrocortisone group. The amount of an active MMP9 (~ 60 kDa) was decreased in the iNO and hydrocortisone group. Total gelatinolytic activity was lower in the iNO and hydrocortisone group. Reduced MMP activity was accompanied by a 2.5-fold decrease of the active IL-1β form (17 kDa) in the pulmonary tissue of iNO combined with hydrocortisone exposed pigs. We demonstrated that in a porcine endotoxemia model the NO inhalation combined with intravenous hydrocortisone led to the attenuation of the inflammatory cascade induced by bacterial LPS. The decrease in pulmonary MMPs activities was accompanied by reduced proIL-1β processing.

Blocking RAGE expression after injury reduces inflammation in mouse model of acute lung injury

BACKGROUND

Receptor for Advanced Glycated Endproducts (RAGE) plays a major role in the inflammatory response to infectious and toxin induced acute lung injury. We tested the hypothesis that a RAGE blocking antibody when administered after the onset of injury can reduce lung inflammation compared to control antibody.

METHODS

Male and female C57BL/6 (WT) mice were used. Forty-six received lipopolysaccharide (LPS) and 26 PBS by nasal instillation on day one, repeated on day three. On day 2, 36 mice receiving LPS were divided into two groups of 18, one treated with 200 μg of non-immune isotype control IgG and the second group treated with 200 μg of anti-RAGE Ab, each dose divided between IV and IP. Ten of the 46 were not treated. On day 4, before euthanasia, mice were injected with fluorescein isothiocyanate (FITC) labelled albumen. BALF and serum samples were collected as well as lung tissue for immunohistochemistry (IHC). BALF was analyzed for cell (leukocyte) counts, for FITC BALF/serum ratios indicating pulmonary vascular leak, and for cytokines/chemokines using bead based multiplex assays. Quantitative IHC was performed for MPO and RAGE.

RESULTS

Ten LPS mice showed minimal inflammation by all measures indicating poor delivery of LPS and were excluded from analysis leaving n = 11 in the LPS + IgG group and n = 12 in the LPS + anti-RAGE group. BALF cell counts were low in the PBS administered mice (4.9 ± 2.1 × 10⁵/ml) and high in the LPS injured untreated mice (109 ± 34) and in the LPS + IgG mice (91 ± 54) while in comparison, LPS + anti-RAGE ab mice counts were significantly lower (51.3 ± 18 vs. LPS + IgG, P = 0.03). The BALF/serum FITC ratios were lower for the LPS + anti-RAGE mice than for the LPS + IgG mice indicating less capillary leakiness. Quantitative IHC RAGE staining was lower in the LPS + anti-RAGE ab mice than in the LPS + IgG treated mice (P = 0.02).

CONCLUSIONS

These results describe a four-day LPS protocol to sustain lung injury and allow for treatment and suggests that treatment aimed at blocking RAGE when given after onset of injury can reduce lung inflammation.

Vitamin D protects silica particles induced lung injury by promoting macrophage polarization in a KLF4-STAT6 manner

Silicosis is one of the severest occupational diseases worldwide, manifesting as infiltration of inflammatory cells, excessive secretion of pro-inflammatory mediators and pulmonary diffuse fibrosis. Macrophages polarization to M2 is one of the major strategies that attenuates inflammatory response. Our previous study found that vitamin D could protect against silica-induced lung injury by damping the secretion of pro-inflammatory cytokines. Here we further identified that vitamin D attenuated silica particles-induced lung inflammation by regulating macrophage polarization in a KLF4-STAT6 manner. Myeloid-specific Stat6 knockout (cKO) mice were generated for in vivo studies. Primary macrophages purified from bronchoalveolar lavage fluid (BALF) of wildtype or Stat6 cKO mice and differentiated THP-1 cells were used for in vitro studies. Vitamin D was found to promote alveolar macrophage polarizing to M2 phenotype through the STAT6 signaling pathway, as demonstrated by worse lung inflammation and ablated protection of vitamin D in silica particles-instilled Stat6 cKO mice. Mechanismly, vitamin D upregulated KLF4 expression in the alveolar macrophage, which synergistically activated STAT6. Additionally, KLF4 was found to upregulate macrophages autophagy, which protected them from silica particles-induced oxidative stress and cell apoptosis. The protective effects of vitamin D were dismissed by silencing KLF4. Our study demonstrates the potential mechanism of vitamin D-mediated macrophage polarization and reveals the therapeutic application of vitamin D in inflammatory disease.

A potential new pathway for heparin treatment of sepsis-induced lung injury: inhibition of pulmonary endothelial cell pyroptosis by blocking hMGB1-LPS-induced caspase-11 activation

Sepsis is a significant cause of mortality in critically ill patients. Acute lung injury (ALI) is a leading cause of death in these patients. Endothelial cells exposed to the bacterial endotoxin lipopolysaccharide (LPS) can progress into pyroptosis, a programmed lysis of cell death triggered by inflammatory caspases. It is characterized by lytic cell death induced by the binding of intracellular LPS to caspases 4/5 in human cells and caspase-11 in mouse cells. In mice,caspase-11-dependent pyroptosis plays an important role in endotoxemia. HMGB1 released into the plasma binds to LPS and is internalized into lysosomes in endothelial cells via the advanced glycation end product receptor. In the acidic lysosomal environment, HMGB1 permeates the phospholipid bilayer, which is followed by the leakage of LPS into the cytoplasm and the activation of caspase-11. Heparin is an anticoagulant widely applied in the treatment of thrombotic disease. Previous studies have found that heparin could block caspase-11-dependent inflammatory reactions, decrease sepsis-related mortality, and reduce ALI, independent of its anticoagulant activity. Heparin or modified heparin with no anticoagulant property could inhibit the alarmin HMGB1-LPS interactions, minimize LPS entry into the cytoplasm, and thus blocking caspase-11 activation. Heparin has been studied in septic ALI, but the regulatory mechanism of pulmonary endothelial cell pyroptosis is still unclear. In this paper, we discuss the potential novel role of heparin in the treatment of septic ALI from the unique mechanism of pulmonary endothelial cell pyroptosis.