Inhaled nitric oxide inhibits the release of matrix metalloproteinase-2, but not platelet activation, during extracorporeal membrane oxygenation in adult rabbits

Inflammation and lung injury in an ovine model of extracorporeal membrane oxygenation support

Extracorporeal membrane oxygenation (ECMO) is a life-saving treatment for patients with severe refractory cardiorespiratory failure. Exposure to the ECMO circuit is thought to trigger/exacerbate inflammation. Determining whether inflammation is the result of the patients' underlying pathologies or the ECMO circuit is difficult. To discern how different insults contribute to the inflammatory response, we developed an ovine model of lung injury and ECMO to investigate the impact of smoke-induced lung injury and ECMO in isolation and cumulatively on pulmonary and circulating inflammatory cells, cytokines, and tissue remodeling. Sheep receiving either smoke-induced acute lung injury (S-ALI) or sham injury were placed on veno-venous (VV) ECMO lasting either 2 or 24 h, with controls receiving conventional ventilation only. Lung tissue, bronchoalveolar fluid, and plasma were analyzed by RT-PCR, immunohistochemical staining, and zymography to assess inflammatory cells, cytokines, and matrix metalloproteinases. Pulmonary compliance decreased in sheep with S-ALI placed on ECMO with increased numbers of infiltrating neutrophils, monocytes, and alveolar macrophages compared with controls. Infiltration of neutrophils was also observed with S-ALI alone. RT-PCR studies showed higher expression of matrix metalloproteinases 2 and 9 in S-ALI plus ECMO, whereas IL-6 was elevated at 2 h. Zymography revealed higher levels of matrix metalloproteinase 2. Circulating plasma levels of IL-6 were elevated 1-2 h after commencement of ECMO alone. These data show that the inflammatory response is enhanced when a host with preexisting pulmonary injury is placed on ECMO, with increased infiltration of neutrophils and macrophages, the release of inflammatory cytokines, and upregulation of matrix metalloproteinases.

Incidence of Platelet Dysfunction by Thromboelastography-Platelet Mapping in Children Supported with ECMO: A Pilot Retrospective Study

BACKGROUND

Bleeding complications are common and decrease the odds of survival in children supported with extracorporeal membrane oxygenation (ECMO). The role of platelet dysfunction on ECMO-induced coagulopathy and resultant bleeding complications is not well understood. The primary objective of this pilot study was to determine the incidence and magnitude of platelet dysfunction according to thromboelastography (TEG(®))-platelet mapping (PM) testing.

METHODS

Retrospective chart review of children <18 years old who required ECMO at a tertiary level hospital. We collected TEG(®)-PM and conventional coagulation tests data. We also collected demographic, medications, blood products administered, and clinical outcome data. We defined severe platelet dysfunction as <50% aggregation in response to an agonist.

RESULTS

We identified 24 out of 46 children on ECMO, who had TEG(®)-PM performed during the study period. We found the incidence of severe bleeding was 42% and mortality was 54% in our study cohort. In all samples measured, severe qualitative platelet dysfunction was more common for adenosine diphosphate (ADP)-mediated aggregation (92%) compared to arachidonic acid (AA)-mediated aggregation (75%) (p = 0.001). Also, ADP-mediated percent of platelet aggregation was significant lower than AA-mediated platelet aggregation [15% (interquartile range, IQR 2.8-48) vs. 49% (IQR 22-82.5), p < 0.001]. There was no difference in kaolin-activated heparinase TEG(®) parameters between the bleeding group and the non-bleeding group. Only absolute platelet count and TEG(®)-PM had increased predictive value on receiver operating characteristics analyses for severe bleeding and mortality compared to activated clotting time.

CONCLUSION

We found frequent and severe qualitative platelet dysfunction on TEG(®)-PM testing in children on ECMO. Larger studies are needed to determine if the assessment of qualitative platelet function by TEG(®)-PM can improve prediction of bleeding complications for children on ECMO.

Prevention of ischemia/reperfusion-induced accumulation of matrix metalloproteinases in rat lung by preconditioning with nitric oxide

BACKGROUND

Pulmonary ischemia/reperfusion (I/R) injury is associated with degradation of structural proteins. Preconditioning by short-term inhalation of nitric oxide (NO) ameliorates some of the severe consequences of an I/R cycle. The aim of this study was to evaluate the effects of NO preconditioning on I/R-induced changes of matrix metalloproteinase (MMP) activity.

MATERIALS AND METHODS

Left lung in situ ischemia in rats was maintained for 1 h, followed by reperfusion for 30 min or 4 h. In the NO group, animals inhaled NO (15 ppm) for 10 min directly before ischemia. Changes of expression or activity of MMPs (MMP-2, MMP-7, MMP-9, MMP-14) and of neutrophil elastase (NE) in bronchoalveolar lavage fluid (BALF), lung tissue, and arterial plasma were analyzed by zymography and Western blotting. Western blotting was also used to detect tissue inhibitors of matrix proteases, the extracellular metalloproteinase inducer (EMMPRIN or CD147), and endostatin, a proteolytic collagen fragment.

RESULTS

Ischemia resulted in an increase of lavagable MMP activity (12.3-fold MMP-2, 8.1-fold MMP-7) at 30 min reperfusion. The activity of MMP-9 and NE in lung tissue progressively increased with time, whereas MMP-14 and MMP-2 were constant. Inhalation of NO prevented the early increase of MMP-2 and MMP-7 in BALF, but the level of MMP-9 and NE in tissue was not affected. The expression of tissue inhibitors of matrix proteases and EMMPRIN did not respond to any treatment. The release of endostatin proceeded in parallel to the level of MMPs in BALF. Significant correlations between MMP-9 and myeloperoxidase in lung tissue and between MMP-2/MMP-7 and plasma protein extravasation were found.

CONCLUSIONS

The early rise of MMP-2 and MMP-7 in BALF resulted from plasma protein extravasation, whereas MMP-9 and NE were imported into lung tissue via leukocyte invasion. The effect of NO inhalation on lavagable MMPs was secondary to the sealing of the permeability barrier.

Nitric oxide and vascular remodeling: Spotlight on the kidney

Extracellular matrix (ECM) remodeling with successive tissue fibrosis is a key feature of chronic cardiovascular diseases, including atherosclerosis and restenosis. The atherogenic changes underlying these pathologies result from chronification of an acute repair response towards injurious and inflammatory stimuli. Thereby functional tissue is replaced by excessive ECM deposition. In the kidney, impaired remodeling is a major cause of perivascular, interstitial, and glomerular fibrosis but also a common complication of chronic hypertension. Experimental evidence points to the matrix metalloproteases (MMPs) and their intrinsic inhibitors, the tissue inhibitors of MMPs as key mediators of atherogenic and fibrotic pathologies. Mechanistically, a deregulation in ECM turnover tightly correlates with an increased production and release of proinflammatory and profibrotic factors including interleukin-1beta, transforming growth factor beta, angiotensin II, and reactive oxygen species. Unlike these factors the pleiotropic messenger molecule nitric oxide (NO) by acting as the major physiological vasodilator has emerged as one of the most atheroprotective factors. However, under inflammatory conditions NO does acquire proatherogenic and profibrotic properties thereby exacerbating tissue fibrosis. In this review, the mechanisms underlying both opposing properties of NO on perivascular ECM remodeling will exemplarily be discussed for renal fibrosis with a particular focus on the MMPs and intrinsic protease inhibitors.

Platelet dysfunction in asphyxiated newborn piglets resuscitated with 21% and 100% oxygen

Hemostatic disturbances are common in asphyxiated newborns after resuscitation. We compared platelet function in hypoxic newborn piglets reoxygenated with 21% or 100% oxygen. Piglets (1-3 d, 1.5-2.1 kg) were anesthetized and acutely instrumented for hemodynamic monitoring. After stabilization, normocapnic hypoxia was induced with an inspired oxygen concentration of 10-15% for 2 h. Piglets were then resuscitated for 1 h with 21% or 100% oxygen, followed by 3 h with 21% oxygen. Platelet counts and collagen (2, 5, and 10 microg/mL)-stimulated whole blood aggregation were studied before hypoxia and at 4 h of post-hypoxia/reoxygenation. Platelet function was studied using transmission electron microscopy and by measuring plasma thromboxane B2 (TxB2) and matrix metalloproteinase (MMP)-2 and -9 levels. Control piglets were sham-operated without hypoxia/reoxygenation. The hypoxemic (PaO2 33 mm Hg) piglets developed hypotension with metabolic acidosis (pH 7.02-7.05). Upon reoxygenation, piglets recovered and blood gases gradually normalized. At 4 h reoxygenation, platelet aggregation ex vivo was impaired as evidenced by a rightward-downward shifting of the concentration-response curves. Electron microscopy showed features of platelet activation. Plasma MMP-9 but not MMP-2 activity significantly increased. Resuscitation with 100% but not 21% oxygen increased plasma TxB2 levels. Platelet counts decreased after hypoxia/reoxygenation but were not different between groups during the experiment. Resuscitation of hypoxic newborn piglets caused platelet activation with significant deterioration of platelet aggregation ex vivo and increased plasma MMP-9 levels. High oxygen concentrations may aggravate the activation of prostaglandin-thromboxane mechanistic pathway.