The effect of adhesion molecule blockade on pulmonary reperfusion injury

Novel Strategies for Endothelial Preservation in Lung Transplant Ischemia-Reperfusion Injury

Lung ischemia reperfusion (IR) injury inevitably occurs during lung transplantation. The pulmonary endothelium is the primary target of IR injury that potentially results in severe pulmonary dysfunction. Over the last decades, various molecules, receptors, and signaling pathways were identified in order to develop treatment strategies for the preservation of the pulmonary endothelium against IR injury. We here review the latest and most promising therapeutic strategies for the protection of the endothelium against IR injury. These include the stabilization of the endothelial glycocalyx, inhibition of endothelial autophagy, inhibition of adhesion molecules, targeting of angiotensin-converting enzyme, and traditional viral and novel non-viral gene transfer approaches. Though some of these strategies proved to be promising in experimental studies, very few of these treatment concepts made the transfer into clinical application. This dilemma underscores the need for more experimental evidence for the translation into clinical studies to invent therapeutic concepts against IR injury-mediated endothelial damage.

Inhibitory effects of kaempferol-3-O-sophoroside on HMGB1-mediated proinflammatory responses

High mobility group box 1 (HMGB1) protein is secreted by activated cells of the innate immune system and/or released by injured tissues and necrotic cells; HMGB1 up-regulates proinflammatory cytokines in several inflammatory diseases. Kaempferol-3-O-sophoroside (KP) was isolated from the leaves of cultivated mountain ginseng. KP has antitumor, antioxidative, antiallergic and antidiabetic activities, but the effects of KP on HMGB1-mediated proinflammatory responses have not been studied. In this study, we monitored the effect of KP on the lipopolysaccharide (LPS)-mediated release of HMGB1 and the HMGB1-mediated modulation of proinflammatory responses in human endothelial cells. We found that KP potently inhibited the release of HMGB1 by LPS and inhibited LPS- or HMGB1-mediated barrier permeability and expression of cell adhesion molecules. Further studies revealed that KP inhibited cell surface receptor of HMGB1, toll-like receptor (TLR) 2/4, but not the receptor for advanced glycation end products (RAGE). Collectively, these results suggest that KP possesses anti-inflammatory responses against HMGB1-mediated proinflammatory responses, thereby endorsing its usefulness as a therapy for vascular inflammatory diseases.

Small interfering RNA efficiently suppresses adhesion molecule expression on pulmonary microvascular endothelium

Background. Adhesion molecules are known to influence postoperative organ function, they are hardly involved in the inflammatory response following the ischemia-reperfusion injury. We sought to investigate the potency of small interfering RNAs to suppress adhesion molecule expression in human pulmonary microvascular endothelial cells. Methods. Human lung microvascular endothelial cells were transfected with specific siRNA followed by a stimulation of the cells with an inflammatory cytokine. Adhesion molecule expression was determined by FACS-analysis, and reduction of intracellular mRNA was determined by qRT-PCR. Furthermore, the attachment of isolated neutrophils on the endothelial layer was determined after siRNA transfection. Results. In summary, siRNA transfection significantly decreased the percentage positive cells in a single cocktail transfection of each adhesion molecule investigated. Adhering neutrophils were diminished as well. Conclusion. siRNA might be a promising tool for the effective suppression of adhesion molecule expression on pulmonary microvascular cells, potentially minimizing leukocyte-endothelial depending interactions of a pulmonary allograft.

Pressure-induced leukocyte margination in lung postcapillary venules

Although pressure elevation in lung postcapillary venules increases endothelial P-selectin expression, the extent to which P-selectin causes lung leukocyte margination remains controversial. To address this issue, we optically viewed postcapillary venules of the isolated blood-perfused rat lung by real-time fluorescence imaging. To determine leukocyte margination in single postcapillary venules, we quantified the fluorescence of leukocytes labeled in situ with rhodamine 6G (R6G). Although baseline fluorescence was sparse, a 10-min pressure elevation by 10 cmH(2)O markedly increased R6G fluorescence. Both stopping blood flow during pressure elevation and eliminating leukocytes from the perfusion blocked the fluorescence increase, affirming that these fluorescence responses were attributable to pressure-induced leukocyte margination. A P-selectin-blocking MAb and the L- and P-selectin blocker fucoidin each inhibited the fluorescence increase, indicating that P-selectin was critical for inducing margination. Time-dependent imaging of blood-borne fluorescent beads revealed reduction of plasma velocity during pressure elevation. After pressure returned to baseline, a similar reduction of plasma velocity, established by manually decreasing the perfusion rate, prolonged margination. Our findings show that in lung postcapillary venules, the decrease in plasma velocity critically determines pressure-induced leukocyte margination.

Early expression of adhesion molecules after lung transplantation: evidence for a role of aggregated P-selectin-positive platelets in human primary graft failure

BACKGROUND

Primary graft failure (PGF) secondary to ischemia-reperfusion injury is the main cause of death in the first month after lung transplantation. The aim of this study was to identify early cellular and immunologic events associated with PGF in human lung transplants.

METHODS

Induction of P-selectin, E-selectin and intercellular adhesion molecule-1 (ICAM-1) and evaluation of leukocytes and platelets accumulation were investigated in 18 post-reperfusion surgical specimens of lung allografts by an immunohistochemical technique.

RESULTS

Selectins were restricted to the venular plexus after reperfusion as in the normal lung, whereas ICAM-1 was induced in all cases on alveolar capillaries. Numerous polymorphonuclear cells (18 of 18 cases) and aggregated platelets (7 of 18 cases) were identified along the venular plexus after reperfusion. Compared with the other patients, those with aggregated P-selectin-positive platelets were characterized by a longer duration of mechanical ventilation (p < 0.01), a lower PaO2/FiO2 ratio (p < 0.01) and the presence of radiologic edema (p < 0.05) within the first 3 post-operative days.

CONCLUSIONS

We showed in the reperfused lung a distinct expression of adhesion molecules on venous and capillary pulmonary endothelia that may influence the role of leukocytes and platelets during the early course of transplantation. Furthermore, the knowledge of an association between the presence of P-selectin-positive platelet aggregates and PGF criteria might have implications for graft management and therapeutic strategies.

Up-regulation of endothelial nitric oxide synthase inhibits pulmonary leukocyte migration following lung ischemia-reperfusion in mice

Endogenous nitric oxide (NO) is known to modulate post-ischemic inflammatory response in various organs. However, the role of nitric oxide synthase isoforms (NOS) in mediating pulmonary post-ischemic inflammatory response is poorly understood. We therefore studied post-ischemic endothelial adhesion molecule expression and leukocyte migration in endothelial NOS knockout (eNOS-KO) mice subjected to pulmonary ischemia and reperfusion in vivo. Under anesthesia and mechanical ventilation, the left pulmonary hilum in wild-type (WT) and eNOS-KO mice was clamped for 1 hour, followed by reperfusion for up to 24 hours. In WT mice, we observed a selective up-regulation of both eNOS mRNA and protein in lung tissue, while inducible NOS (iNOS) and neuronal NOS (nNOS) remained unchanged. Survival in eNOS-KO mice was reduced due to severe pulmonary edema, underlining an increased susceptibility to ischemia-reperfusion (I/R) injury. Interstitial tissue infiltration by CD18- and CD11a-positive white blood cells as well as lung tissue water content peaked at 5 hours of reperfusion and were found significantly higher than in WT mice. Enhanced leukocyte-endothelial interaction was associated with pronounced up-regulation of vascular cell adhesion molecule (VCAM) in eNOS-KO mice during post-ischemic reperfusion. We conclude that eNOS attenuates post-ischemic inflammatory injury to the lung most probably via inhibition of endothelial adhesion molecule expression.

Adhesion molecules as therapeutic targets for autoimmune diseases and transplant rejection

Inflammatory disorders such as autoimmune diseases and graft rejection are mediated by activated leukocytes, particularly T lymphocytes, which penetrate the inflamed tissue and perpetuate or amplify the immune reaction. In an unstimulated state, leukocytes do not readily adhere to the vascular endothelium. However, inflammatory signals induce the expression of proteins on the endothelial cell surface that promote the adhesion and extravasation of activated immune cells from the circulation into the underlying tissues. Key among these molecules are P- and E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on the endothelial cells, and their respective counter receptors, P-selectin glycoprotein ligand-1 (PSGL-1), leukocyte function-associated antigen-1 (LFA-1) and very late antigen-4 (VLA-4), on the leukocytes. In vitro blockade of these molecules inhibits the adhesion of leukocytes. In many cases there is attenuation of leukocyte activation as well. Adhesion blockade in animal models prevents or ameliorates graft rejection and disease severity in autoimmune models. Clinical studies with humanised monoclonal antibodies which interfere with LFA-1/ICAM-1 or VLA-4/VCAM-1 interactions have shown significant efficacy and good safety profiles in autoimmune disease, including psoriasis, multiple sclerosis and inflammatory bowel disease. Thus, adhesion blockade is emerging as a useful therapeutic strategy in several inflammatory settings.