Nitric oxide : An ally in extracorporeal circulation?

Many complications associated with heart surgery are due to the negative effects of extracorporeal circulation (ECC). Some of these complications may be attributed to ECC-induced activation of inflammation and coagulation pathways. The inflammatory reaction may be caused by the interaction of blood components with air and the artificial surfaces of the ECC, from substances produced due to ischaemia-reperfusion injury of the heart and lungs, and from increased release of endotoxin from ischemic intestines. Staphylococcus aureus (S. aureus) infections are the leading cause of respiratory, skin and soft tissue, and bloodstream infections. Nitric oxide (NO) is a gaseous signaling molecule involved in many physiological and pathological processes. The role of NO in infection and inflammation is complex. NO may contribute to morbidity by acting as a vasodilator, myocardial depressant, and cytotoxic mediator. On the other hand, NO may have a salutary role through microvascular, cytoprotective, immunoregulatory, and antimicrobial properties. A simulated extracorporeal circulation (SECC) model is a closed circuit, including a roller pump, an oxygenator, a venous reservoir and polyvinyl chloride (PVC) tubing, where human blood is circulated. The SECC model allows studies of the blood and its components, without any influence from other organ systems. The aim of this work was to investigate NO effects during SECC and in S. aureus infection. Study I. Human blood was circulated through SECC during 3 hours, and leukocyte granule release was studied. Results indicated that NO addition during SECC is pro-inflammatory by stimulating leukocyte activation and granule release, and has no effect on oxygen free radical production and interleukin release. Study II. Investigating the effect of NO on S. aureus growth in whole blood during 180 min SECC, results showed a 6.2 fold growth in the presence of NO. Results indicated that by stimulating the expression of inducible lactate dehydrogenase, specific to S. aureus, NO may improve S. aureus resistance to oxidative stress, giving the pathogen a survival advantage. Study III. In an in vitro system of SECC, we measured glyceryl trinitrate (GTN) induced changes in leukocyte activation in whole blood caused by S. aureus infestation, as well as the effect of GTN on S. aureus growth. Results indicated that GTN does not affect S. aureus growth during SECC and has no effect on SECC-induced leukocyte activation. Study IV. Whole blood concentrations of selected leukocyte adhesion molecules, complement system components and myeloperoxidase were measured in an in vitro system of SECC. Results indicated that SECC induces the increased expression of some leukocyte markers and that GTN addition significantly reduces the expression of some leukocyte activation markers