Endothelial cells inhibit receptor-mediated superoxide anion production by human polymorphonuclear leukocytes via a soluble inhibitor

Acute lung injury results from failure of neutrophil de-priming: a new hypothesis

Neutrophils are the most abundant circulating white cell in humans and play a crucial role in the innate immune response. Accumulation and activation of neutrophils, together with delayed clearance, have been shown to be a key event in the pathogenesis of acute lung injury. Previously, it has been proposed that there is substantial pooling of neutrophils within the pulmonary vasculature, even under physiological conditions, making the lung especially vulnerable to neutrophil-mediated tissue injury. However, more recent evidence suggests that only primed neutrophils accumulate in the pulmonary vasculature. This article examines the evidence for these two opposing views and proposes a new two-step model for the recruitment of neutrophils into the lung. Firstly, neutrophils that become primed, by exposure to a range of inflammatory mediators or physicochemical perturbations, become shape changed and stiff because of alterations in their cytoskeleton, and as a result, accumulate within the pulmonary circulation. In the absence of further stimuli, the healthy pulmonary vasculature is able to selectively retained these primed cells, allow them to 'de-prime' and be released back into the circulation in a quiescent, state. If this pulmonary 'de-priming' mechanism fails, or a second insult occurs, such as ventilator-associated barotrauma, which causes loss of alveolar integrity, primed neutrophils migrate from the pulmonary vasculature into the interstitial space with resultant lung injury. This canonical 'two step' model highlights the importance of neutrophil priming in the genesis of lung injury and the importance of adopting strategies to minimise alveolar injury.

A(2A) adenosine receptor: a novel therapeutic target in renal disease

Present strategies in the treatment of inflammatory renal injury have focused on developing agents that specifically target individual mechanisms thought to contribute toward the pathogenesis of the disease. Such an approach is hindered by redundancies in the inflammatory cascade, rendering intervention suboptimal. The A(2A) adenosine receptor (A(2A)-AR) is a member of the family of guanine nucleotide binding proteins and has become a focus of major interest primarily because of its ability to broadly inactivate the inflammatory cascade. This review summarizes our present knowledge regarding the molecular biology and pharmacology of A(2A)-ARs as well as the physiological effects of activation of A(2A)-ARs in the kidney. We also review our recent experience in targeting this receptor subtype in abrogating the inflammatory cascade in ischemia-reperfusion injury.

Enhanced protection from renal ischemia-reperfusion [correction of ischemia:reperfusion] injury with A(2A)-adenosine receptor activation and PDE 4 inhibition

BACKGROUND

We previously demonstrated in rats and mice that agonists of A(2A)-adenosine receptors (A(2A)-ARs) reduce renal injury following ischemia-reperfusion. We now extend these studies and examine the effects of ATL-146e (formerly DWH-146e), an A(2A)-AR agonist, and rolipram, a type IV phosphodiesterase (PDE 4) inhibitor, on murine renal injury following ischemia-reperfusion.

METHODS

C57BL/6 mice were treated with rolipram, ATL-146e, or both compounds combined and were subjected to renal ischemia for 32 minutes and reperfusion for 24 to 48 hours. In vitro studies were performed on suspended and adhering human neutrophils.

RESULTS

Continuous delivery of rolipram or ATL-146e during reperfusion reduced renal injury in a dose-dependent manner. Maximal protection was observed when ATL-146e was infused for six hours during reperfusion. Elevated plasma creatinine and myeloperoxidase activity produced by ischemia-reperfusion were reduced by rolipram (0.1 ng/kg/min) and ATL-146e (10 ng/kg/min) by up to approximately 60% and 70%, respectively. Co-infusion of both compounds produced a maximum reduction of plasma creatinine of approximately 90% and myeloperoxidase activity. In vitro studies on suspended and adhering human neutrophils demonstrated that selective stimulation of A(2A)-ARs by ATL-146e increased cAMP accumulation, reduced oxidative activity of activated neutrophils, and decreased activated neutrophil adherence. These responses were potentiated by rolipram.

CONCLUSIONS

We conclude that the combined infusion of ATL-146e and rolipram leads to enhanced renal tissue protection from ischemia-reperfusion by mechanisms that may include reduced neutrophil adherence/recruitment and release of reactive oxygen species.

A(2A) adenosine receptor-mediated inhibition of renal injury and neutrophil adhesion

We sought to determine the mechanisms responsible for the reduced renal tissue injury by agonists of A(2A) adenosine receptors (A(2A)-ARs) in models of ischemia-reperfusion (I/R) injury. DWH-146e, a selective A(2A)-AR agonist, was administered subcutaneously to Sprague-Dawley rats and C57BL/6 mice via osmotic minipumps, and animals were subjected to I/R. I/R led to an increase in plasma creatinine and kidney neutrophil infiltration. Infusion of DWH-146e at 10 ng. kg(-1). min(-1) produced a 70% reduction in plasma creatinine as well as a decrease in neutrophil density in outer medulla and cortex and myeloperoxidase activity in the reperfused kidney. Myeloperoxidase activity in kidney correlated with the degree of renal injury. P-selectin and intercellular adhesion molecule 1 (ICAM-1) immunoreactivity were most prominent in endothelial cells of peritubular capillaries and interlobular arteries of cortex and outer and inner medulla of vehicle-treated mice whose kidneys were subjected to I/R. DWH-146e treatment led to a pronounced decrease in P-selectin- and ICAM-1-like immunoreactivity. These data are consistent with our hypothesis that A(2A)-AR agonists limit I/R injury due to an inhibitory effect on neutrophil adhesion.

Endothelial cells upregulate eosinophil superoxide generation via VCAM-1 expression

BACKGROUND

In vitro eosinophil (EOS) adhesion to recombinant human (rh)-vascular cell adhesion molecule (VCAM)-1 stimulates superoxide anion (O2-) generation and enhances formyl-methionyl-leucyl phenylalanine (FMLP)-activated O2- generation. Therefore, EOS adhesion via VLA-4 to VCAM-1 expressed on endothelium may be instrumental in the selective recruitment and function of EOS in airway inflammation.

OBJECTIVE

We hypothesized that EOS interaction with endothelial cells expressing VCAM-1 will undergo an enhancement in inflammatory function.

METHODS

To determine this possibility, human umbilical vein endothelial cells (HUVEC) were stimulated with either a combination of interleukin (IL)-4 and tumour necrosis factor (TNF)-alpha (100 pM) or medium alone for 24 h; the expression of adhesion proteins on HUVEC and their effect on EOS O2- generation was subsequently determined.

RESULTS

As determined by both enzyme-linked immunosorbent assay and flow cytometry, IL-4 and TNFalpha acted synergistically to induce VCAM-1 expression on HUVEC. Treating HUVEC with IL-4/TNFalpha also increased EOS adhesion and primed subsequent FMLP (0.1 microM) activated EOS O2- generation. Although EOS adhesion was partially inhibited by both antialpha4 and antibeta2 monoclonal antibodies (MoAbs), O2- generation was completely inhibited by either antialpha4 integrin MoAb (HP1/2) or anti-VCAM MoAb (BBIG-V1). Furthermore, enhanced O2- generation, but not adhesion, associated with IL-4 + TNFalpha-treatment of HUVEC was inhibited when EOS were treated with the platelet activating factor (PAF)-antagonist WEB 2086 (20 microM), thus suggesting an involvement of PAF in priming EOS. However, paraformaldehyde fixation of IL-4/TFN-alpha treated HUVEC did not significantly alter EOS function.

CONCLUSIONS

These results suggest EOS adhesion to endothelial cells via an VLA-4/VCAM-1 interaction may be important in the development of the function of this cell. Furthermore, our results suggest that modulation of EOS function involves two priming factors: EOS adhesion to HUVEC expressing VCAM-1 and PAF.

Release of a leukocyte activation inhibitor by staurosporine-treated pulmonary artery endothelial cells

Bovine pulmonary arterial endothelial cells (BPAE) treated with the protein kinase C (PKC) inhibitor staurosporine inhibited O-2. generation by neutrophils exposed to phorbol myristate acetate (PMA) but did not affect O-2. generated enzymatically by xanthine/xanthine oxidase (X/XO). Similar results were obtained with conditioned medium from staurosporine-pretreated BPAE. The inhibitory effects of staurosporine-treated BPAE on O-2. generation were not altered by the superoxide dismutase inhibitor diethylcarbamazine. This BPAE-derived inhibitor was continuously released from staurosporine-pretreated BPAE for at least 5 h. The exact nature of the inhibitor remains unknown, but it appears to be a positively charged molecule with molecular weight <10,000. Treatment of either BPAE or neutrophils with staurosporine or conditioned medium from staurosporine-treated BPAE prevented the neutrophil-mediated decrease in endothelium-bound angiotensin-converting enzyme activity and cytotoxicity in BPAE. In contrast, staurosporine potentiated the H2O2- and X/XO-mediated endothelial cytotoxicity. These data suggest that staurosporine-treated endothelial cells release a soluble factor that inhibits neutrophil activation and protects endothelial cells from neutrophil-mediated injury.

Mechanisms of biomaterial-induced superoxide release by neutrophils

Biomaterial-centered infection is an important cause of the failure of prosthetic implants and organs. Because neutrophils mediate host defense against infection, the effect of biomaterials on neutrophil superoxide release and the mechanism of that effect were investigated using three materials commonly employed in surgical practice. The graft materials were expanded polytetrafluorethylene (PTFE), polyurethane and woven dacron. Polystyrene, a commonly used laboratory support vessel, was also studied. Both polystyrene and polyurethane were activating, but serum inhibitable, whereas PTFE was nonactivating, and woven dacron was not activating unless serum was present. The signaling mechanisms used by these materials demonstrated time and material dependency. Pertussis toxin inhibition of G protein-dependent activation had little or no effect on biomaterial induced activation, whereas FMLP-induced activation of the same biomaterial-associated cells was inhibited. Protein kinase C inhibition with staurosporine greatly inhibited polystyrene-induced activation, but had only a partial effect with polyurethane and even less effect with the activation associated with serum-treated woven dacron. These studies demonstrated that biomaterial contact-induced neutrophil activation differed from that described for cells in suspension, and showed that activation mechanisms on one material cannot be extrapolated to mechanisms on other materials.

Effect of prostaglandin E1 on chemiluminescence response and adherence of human polymorphonuclear leukocytes to human cultured endothelial cells of prostaglandin E1 treated polytraumatized patients

We investigated the effect of prostaglandin E1 on human polymorphonuclear leukocytes, in vivo. Polymorphonuclear leukocytes of a prostaglandin E1 and placebo study group were harvested and their function, as production of oxygen-derived metabolites and adherence to human cultured endothelial cells, was compared. Additionally, data obtained from polymorphonuclear leukocytes of a prostaglandin E1 and placebo group were compared with data obtained from polymorphonuclear leukocytes from 28 blood donors, who served as a control group. Production of oxygen-derived metabolites by polymorphonuclear leukocytes during contact with endothelial cells was measured by chemiluminescence. Chemiluminescence was significantly (p < 0.01) increased in the placebo group in comparison to the control group decreasing to values of control group after 6 d (post-trauma). Chemiluminescence response was not significantly suppressed in patients treated with prostaglandin E1 in comparison to the placebo group. Adherence of polymorphonuclear leukocytes (placebo group) to endothelial cells was significantly increased (p < 0.01) within the first 6d post-trauma. Following day 6, values were in the same range as values for the control group. Adherence was not significantly suppressed in patients treated with prostaglandin E1 in comparison to the placebo group. In conclusion, prostaglandin E1 at a dose of 20 ng/kg bw/min does not influence production of oxygen-derived metabolites and adherence in polytraumatized patients in comparison to a placebo group. Additionally, production of oxygen-derived metabolites by polymorphonuclear leukocytes in response to endothelial cells is shown and it is evident that endothelial cells might influence production of oxygen derived metabolites by polymorphonuclear leukocytes.