Effects of hypoxia-reoxygenation on microvascular endothelial function in the rat hippocampal slice

The effects of normoxic versus hyperoxic cardiopulmonary bypass on oxidative stress and inflammatory response in cyanotic pediatric patients undergoing open cardiac surgery: a randomized controlled trial

OBJECTIVES

This study investigates the effects of controlled reoxygenation cardiopulmonary bypass on oxidative stress, inflammatory response, and organ function in children undergoing repair of cyanotic congenital heart defects.

METHODS

Sixty-seven cyanotic patients (median age 15 months, interquartile range 6-49 months) undergoing corrective cardiac surgery were randomized to receive either controlled normoxic (50-0 mm Hg; n = 35) or hyperoxic (150-180 mm Hg; n = 32) cardiopulmonary bypass. Troponin I and 8-isoprostane, C3a, interleukins 6, 8, and 10, cortisol, protein S100, and alpha-glutamate transferase were measured preoperatively and 10 and 30 minutes after starting bypass, on removal of the aortic crossclamp, and 12 and 24 hours thereafter.

RESULTS

Overall, troponin I and 8-isoprostane levels were lower in the controlled normoxic group (-29%, 95% CI -48% to -3%, P = .03, and -26%, 95% CI -44% to -2%, P = .03, respectively). Protein S100 release was also lower in the normoxic group 10 minutes after starting bypass (-26%, 95% CI -40% to -9%, P = .005) and 10 minutes after aortic crossclamp removal (-23%, 95% CI -38% to -3%, P = .02, respectively), but similar at other time points in the two groups (P >or= .17). The alpha-glutamate transferase release was significantly lower in the normoxic group 10 minutes after aortic crossclamp removal (-28%, 95% CI -44% to -9%, P = .006, respectively) but was similar at other times (P >or= .11). Release of C3a, interleukins 6, 8, and 10, and cortisol was similar in the two groups throughout (P >or= .15).

CONCLUSION

Controlled reoxygenation on starting cardiopulmonary bypass is associated with reduced myocardial damage, oxidative stress, and cerebral and hepatic injury compared with hyperoxic bypass and similar whole body inflammatory and stress response in cyanotic children undergoing open cardiac surgery.

Microcirculation and oxidative stress

The microcirculation is a complex and integrated system, transporting oxygen and nutrients to the cells. The key component of this system is the endothelium, contributing to the local balance between pro and anti-inflammatory mediators, hemostatic balance, as well as vascular permeability and cell proliferation. A constant shear stress maintains vascular endothelium homeostasis while perturbed shear stress leads to changes in secretion of vasodilator and vasoconstrictor agents. Increased oxidative stress is a major pathogenetic mechanism of endothelial dysfunction by decreasing NO bioavailability, promoting inflammation and participating in activation of intracellular signals cascade, so influencing ion channels activation, signal transduction pathways, cytoskeleton remodelling, intercellular communication and ultimately gene expression. Targeting the microvascular inflammation and oxidative stress is a fascinating approach for novel therapies in order to decrease morbidity and mortality of chronic and acute diseases.

Molecular physiology of preconditioning-induced brain tolerance to ischemia

Ischemic tolerance describes the adaptive biological response of cells and organs that is initiated by preconditioning (i.e., exposure to stressor of mild severity) and the associated period during which their resistance to ischemia is markedly increased. This topic is attracting much attention because preconditioning-induced ischemic tolerance is an effective experimental probe to understand how the brain protects itself. This review is focused on the molecular and related functional changes that are associated with, and may contribute to, brain ischemic tolerance. When the tolerant brain is subjected to ischemia, the resulting insult severity (i.e., residual blood flow, disruption of cellular transmembrane gradients) appears to be the same as in the naive brain, but the ensuing lesion is substantially reduced. This suggests that the adaptive changes in the tolerant brain may be primarily directed against postischemic and delayed processes that contribute to ischemic damage, but adaptive changes that are beneficial during the subsequent test insult cannot be ruled out. It has become clear that multiple effectors contribute to ischemic tolerance, including: 1) activation of fundamental cellular defense mechanisms such as antioxidant systems, heat shock proteins, and cell death/survival determinants; 2) responses at tissue level, especially reduced inflammatory responsiveness; and 3) a shift of the neuronal excitatory/inhibitory balance toward inhibition. Accordingly, an improved knowledge of preconditioning/ischemic tolerance should help us to identify neuroprotective strategies that are similar in nature to combination therapy, hence potentially capable of suppressing the multiple, parallel pathophysiological events that cause ischemic brain damage.

Vascular dysfunction in ischemia-reperfusion injury

Microvascular dysfunction mediates many of the local and systemic consequences of ischemic-reperfusion (I/R) injury, with a spectrum of changes specific to arterioles, capillaries, and venules. This review discusses the specific changes in the endothelium during I/R injury; describes the differential responses of the various levels of the vasculature including arterioles, capillaries, and venules; and explores mechanisms for remote organ injury. Vascular dysfunction is largely a consequence of changes in the endothelial cells themselves, affecting the integrity of barrier function, cytokine and adhesion molecule expression, and vascular tone. The bioavailability of nitric oxide, an important mediator of vasodilation, is profoundly decreased during the reperfusion period, resulting in impaired vasodilation of arterioles. Release of inflammatory mediators and increased expression of adhesion molecules initiate inflammatory and coagulation cascades that culminate in the occlusion of capillaries, known as the "no-reflow''" phenomenon. In postcapillary venules, the recruitment and transmigration of leukocytes further compromise the integrity of the endothelial barrier and increase the oxidative burden, resulting in leakage and tissue edema. I/R injury can have significant and untoward consequences beyond the affected tissue, with such conditions as systemic inflammatory response syndrome. This review highlights recent progress in understanding of the varied phenomena of vascular dysfunction in I/R injury and some promising advances in the understanding and application of ischemic preconditioning and other potential therapies.

Hypoxia-reoxygenation contributes to increased frequency of venous thromboembolism in air travellers

Commercial air travel is widespread, with close to 2 billion people traveling each year. The association between venous thromboembolism (VTE) and confined sitting has been established and a correlation between the distance traveled and its incidence had been documented. Most studies underscore stasis caused by immobility as the cause of VTE and ignore the possible contribution of additional factors including coagulation and the blood vessel wall. Recent studies indicate that hypobaric hypoxia may contribute to blood vessel wall alteration and activation of coagulation. We suggest that air travel associated hypobaric hypoxia may lead to endothelial injury and initiation of a pro-coagulatory response, effects which are augmented by the reoxygenation upon landing, thus culminating in thrombosis. Prevention of air travel associated hypoxia and reoxygenation injury may decrease the incidence of flight associated VTE.

Cerebral endothelial cell apoptosis after ischemia-reperfusion: role of PARP activation and AIF translocation

Cerebral ischemia-reperfusion leads to vascular dysfunction characterized by endothelial cell injury or death. In the present study, we used an in vitro model to elucidate mechanisms of human brain microvascular endothelial cell (HBMEC) injury after episodic ischemia-reperfusion. Near-confluent HBMEC cultures were exposed to intermittent hypoxia-reoxygenation (HX/RO) and, at different recovery time points, cell viability was assessed by the MTT assay, apoptotic death by fluorescence microscopy of terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL)-positive cells, and nuclear translocation of apoptosis-inducing factor (AIF) and cleavage of poly(ADP-ribose) polymerase-1 (PARP-1) by immunoblotting of subcellular fractions. Reductions in HBMEC viability were proportional to the number of HX/RO cycles, and not the total duration of hypoxia. Using four cycles of 1-h HX with 1 h of intervening normoxic RO, cell viability was reduced 30% to 40% between 12 and 48 h. Treatment with the PARP-1 inhibitors 3-aminobenzamide or 4-amino-1,8-naphthalimide during the insult improved HBMEC viability at 24 h after insult, and resulted in dose-dependent reductions in TUNEL-positivity at 16 h after insult, but not if these treatments were delayed by 4 h. HX/RO-induced increases in nuclear AIF translocation, as well as PARP-1 cleavage, were also reduced dose-dependently at 4 h after insult by the inhibitors. The caspase inhibitor z-VAD-fmk blocked PARP-1 cleavage, but did not affect AIF translocation and was only modestly cytoprotective. These findings indicate that PARP-1 activation and a PARP-1-dependent, caspase-independent, nuclear translocation of AIF contribute to apoptotic cerebral endothelial cell death after ischemia-reperfusion, underscoring the potential for ischemic microvascular protection by inhibiting PARP activation or preventing AIF translocation.