Selenium Pretreatment for Mitigation of Ischemia/Reperfusion Injury in Cardiovascular Surgery: Influence on Acute Organ Damage and Inflammatory Response.

Ischemia/reperfusion injury (IRI) contributes to morbidity and mortality after cardiovascular surgery requiring cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA). Multi-organ damage is associated with substantial decreases of blood selenium (Se) levels in patients undergoing cardiac surgery with CPB. We compared the influence of a dietary surplus of Se and pretreatment with ebselen, a mimic of the selenoenzyme glutathione peroxidase, on IRI-induced tissue damage and inflammation. Male Wistar rats were fed either a Se-adequate diet containing 0.3 ppm Se or supplemented with 1 ppm Se (as sodium selenite) for 5 weeks. Two other groups of Se-adequate rats received intraperitoneal injection of ebselen (30 mg/kg) or DMSO (solvent control) before surgery. The animals were connected to a heart-lung-machine and underwent 45 min of global ischemia during circulatory arrest at 16 °C, followed by re-warming and reperfusion. Selenite and ebselen suppressed IRI-induced leukocytosis and the increase in plasma levels of tissue damage markers (AST, ALT, LDH, troponin) during surgery but did not prevent the induction of proinflammatory cytokines (IL-6, TNF-α). Both Se compounds affected phosphorylation and expression of proteins related to stress response and inflammation: Ebselen increased phosphorylation of STAT3 transcription factor in the heart and decreased phosphorylation of ERK1/2 MAP kinases in the lungs. Selenite decreased ERK1/2 phosphorylation and HSP-70 expression in the heart. Pretreatment with selenite or ebselen protected against acute IRI-induced tissue damage during CPB and DHCA. Potential implications of their different actions with regard to molecular stress markers on the recovery after surgery represent promising targets for further investigation.

A cardiopulmonary bypass with deep hypothermic circulatory arrest rat model for the investigation of the systemic inflammation response and induced organ damage.

BACKGROUND: Cardiopulmonary bypass (CPB) is a commonly used technique in cardiac surgery. CPB is however associated with a strong induction of systemic inflammatory response syndrome (SIRS) which in conjunction with ischemia and reperfusion may lead to multiple organ failure. The aim of the study was to establish and characterize a CPB rat model incorporating deep hypothermic circulatory arrest with a specific focus on the extent of the inflammatory reactions and organ damage as a groundwork for novel therapeutics against SIRS and I/R induced organ injury. MATERIALS AND METHODS: Male Wistar rats (n = 6) were cannulated for CPB, connected to a heart-lung-machine (HLM) and cooled to a temperature of 16°C before they underwent 45 minutes of deep hypothermic circulatory arrest with global ischaemia. Arrest was followed by rewarming and 60 minutes of reperfusion. Haemodynamic and vital parameters were recorded throughout the CPB procedure. Only animals displaying sinus rhythm throughout reperfusion were utilized for analysis. Rats were euthanized and tissue samples were harvested. Blood gas analysis was performed and blood samples were taken. Induction of organ damage was examined by analysis of protein levels and phosphorylation status of kinases and stress proteins. Results were compared to animals (n = 6) which did not undergo CPB. RESULTS: CPB induced leucocytosis and an increase of interleukin-6 and TNF-α plasma values indicating an inflammatory response. Markers of tissue damage and dysfunction, such as troponin T, creatinine and AST were elevated. Phosphorylation of STAT3 was induced in all examined organs. Activation of MAPK and induction of heat shock proteins occurred in an organ-specific manner with most pronounced effects in heart, lungs and kidneys. CONCLUSIONS: The presented CPB rat model shows the induction of SIRS and activation of specific signalling cascades. SIRS seems not to be provoked during DHCA and is elicited mainly during reperfusion. This model might be suitable to test the efficacy of therapeutics applied in major heart surgery with and without DHCA.

Selenoprotein P protects endothelial cells from oxidative damage by stimulation of glutathione peroxidase expression and activity.

A major fraction of the essential trace element selenium circulating in human blood plasma is present as selenoprotein P (SeP). As SeP associates with endothelial membranes, the participation of SeP in selenium-mediated protection against oxidative damage was investigated, using the human endothelial cell line Ea.hy926 as a model system. Hepatocyte-derived SeP prevented tert-butylhydroperoxide (t-BHP)-induced oxidative cell death of Ea.hy926 cells in a similar manner as did sodium selenite, counteracting a t-BHP-induced loss of cellular membrane integrity. Protection was detected after at least 10 h of SeP supplementation and it peaked at 24 h. SeP time-dependently stimulated the expression of cytosolic glutathione peroxidase (cGPx) and increased the enzymatic activities of glutathione peroxidase (GPx) and thioredoxin reductase (TR). The cGPx inhibitor mercaptosuccinate as well as the gamma-glutamylcysteine synthetase inhibitor buthionine sulfoximine counteracted the SeP-mediated protection, while the TR inhibitors cisplatin and auranofin had no effect. The presented data suggest that selenium supplementation by SeP prevents oxidative damage of human endothelial cells by restoring expression and enzymatic activity of GPx.

Involvement of selenoprotein P in protection of human astrocytes from oxidative damage.

Selenoprotein P (SeP) is a highly glycosylated, selenium-rich plasma protein. Aside from its role as selenium carrier protein, an antioxidative function of SeP has been suggested. Astrocytes, which detoxify reactive oxygen species in the brain, were described as potential target cells of SeP. We investigated the expression of SeP in human astrocytes and its involvement in the protection of these cells against tert-butyl hydroperoxide (t-BHP)-induced oxidative damage. We show that primary human astrocytes and the human astrocytoma cell line MOG-G-CCM express SeP as an unglycosylated protein, which is not secreted. SeP expression in astrocytes is constitutive. Preincubation of astrocytes with hepatocyte-derived SeP mimicks the protective effect of low-molecular-weight selenocompounds such as sodium selenite or selenomethionine against oxidative damage, shielding astrocytes from t-BHP-induced cytotoxicity. Selenium supplementation of astrocytes counteracts oxidative stress via an increase in expression and activity of the selenoenzyme cytosolic glutathione peroxidase (cGPx). Furthermore, specific downregulation of SeP expression by small interfering RNA decreases cell viability of human astrocytes and makes them more susceptible to t-BHP-induced cytotoxicity. Our results implicate an antioxidant activity of constitutively expressed SeP in selenium-deficient astrocytes, while during adequate selenium supply the enhanced protection against oxidative stress is exerted by cGPx.