Hyperoxia elicits myocardial protection through a nuclear factor kappaB-dependent mechanism in the rat heart

An overview of hyperbaric oxygen preconditioning against ischemic stroke

Ischemic stroke (IS) has become the second leading cause of morbidity and mortality worldwide, and the prevention of IS should be given high priority. Recent studies have indicated that hyperbaric oxygen preconditioning (HBO-PC) may be a protective nonpharmacological method, but its underlying mechanisms remain poorly defined. This study comprehensively reviewed the pathophysiology of IS and revealed the underlying mechanism of HBO-PC in protection against IS. The preventive effects of HBO-PC against IS may include inducing antioxidant, anti-inflammation, and anti-apoptosis capacity; activating autophagy and immune responses; upregulating heat shock proteins, hypoxia-inducible factor-1, and erythropoietin; and exerting protective effects upon the blood-brain barrier. In addition, HBO-PC may be considered a safe and effective method to prevent IS in combination with stem cell therapy. Although the benefits of HBO-PC on IS have been widely observed in recent research, the implementation of this technique is still controversial due to regimen differences. Transferring the results to clinical application needs to be taken carefully, and screening for the optimal regimen would be a daunting task. In addition, whether we should prescribe an individualized preconditioning regimen to each stroke patient needs further exploration.

The involvement of nuclear factor-κB in astroprotection against ischemia-reperfusion injury by ischemia-preconditioned neurons

Ischemic preconditioned (IP) neurons protect astrocytes against ischemia/reperfusion (I/R)-induced injury by inhibiting oxidative stress. However, the relevant mechanisms are unknown. Based on the role of nuclear factor-κB (NF-κB) in cell survival and adaption to oxidative stress, we hypothesized that NF-κB might be associated with astroprotection induced by IP neurons via upregulation of antioxidant enzymes. Here, we investigated the effects of IP neurons on NF-κB activation, cell viability, reactive oxygen species (ROS), expression of antioxidant enzymes, erythropoietin (EPO), and tumor necrosis factor α (TNF-α), in the presence or absence of BAY11-7082 (an NF-κB inhibitor), anti-EPO, and anti-TNF-α antibodies, in astrocytes treated with or without I/R. We found that IP neurons could keep NF-κB activation at a relatively higher but beneficial level, and in turn, upregulated the activity of antioxidant enzymes and hence enhanced cell viability and reduced ROS in I/R treated astrocytes. The results collectively indicated that IP neurons are able to significantly inhibit the I/R-induced NF-κB overactivation, probably via EPO and TNF-α, being essential for IP neuron-induced astroprotection under the conditions of I/R. We concluded that NF-κB-mediated antioxidative stress is one of the mechanisms by which IP neurons protect astrocytes against I/R injury.

Preconditioning in cardiac anesthesia…… where are we?

Preconditioning, a milestone concept in the cardiovascular sciences introduced 32 years back by Murry. This concept opened a new era in the field of organ protection. To start with extensive studies done on ischemic preconditioning for myocardial protection, ischemic preconditioning is an endogenous science of cellular kinetics. Several components in signal transduction cascade have been identified but still some mechanisms not yet revealed. Anesthetic preconditioning also contributed a lot for myocardial protection and concreted the concept of preconditioning. We, with an inquisitive brain meticulously persuing newer methods of cardioprotection. Remote ischemic preconditioning (RIPC) is a brilliant example of it. RIPC can be future of cardioprotection, clinical trials and studies proved the benefits but yet to conclude the superiority of RIPC over myocardial ischemic cardioprotection. This review is an attempt to reveal this extraordinary concept with its basic cellular kinetics, methods, and recent trends.

Hemoglobin β93 Cysteine Is Not Required for Export of Nitric Oxide Bioactivity From the Red Blood Cell

BACKGROUND

Nitrosation of a conserved cysteine residue at position 93 in the hemoglobin β chain (β93C) to form S-nitroso (SNO) hemoglobin (Hb) is claimed to be essential for export of nitric oxide (NO) bioactivity by the red blood cell (RBC) to mediate hypoxic vasodilation and cardioprotection.

METHODS

To test this hypothesis, we used RBCs from mice in which the β93 cysteine had been replaced with alanine (β93A) in a number of ex vivo and in vivo models suitable for studying export of NO bioactivity.

RESULTS

In an ex vivo model of cardiac ischemia/reperfusion injury, perfusion of a mouse heart with control RBCs (β93C) pretreated with an arginase inhibitor to facilitate export of RBC NO bioactivity improved cardiac recovery after ischemia/reperfusion injury, and the response was similar with β93A RBCs. Next, when human platelets were coincubated with RBCs and then deoxygenated in the presence of nitrite, export of NO bioactivity was detected as inhibition of ADP-induced platelet activation. This effect was the same in β93C and β93A RBCs. Moreover, vascular reactivity was tested in rodent aortas in the presence of RBCs pretreated with S-nitrosocysteine or with hemolysates or purified Hb treated with authentic NO to form nitrosyl(FeII)-Hb, the proposed precursor of SNO-Hb. SNO-RBCs or NO-treated Hb induced vasorelaxation, with no differences between β93C and β93A RBCs. Finally, hypoxic microvascular vasodilation was studied in vivo with a murine dorsal skin-fold window model. Exposure to acute systemic hypoxia caused vasodilatation, and the response was similar in β93C and β93A mice.

CONCLUSIONS

RBCs clearly have the fascinating ability to export NO bioactivity, but this occurs independently of SNO formation at the β93 cysteine of Hb.

Nuclear factor kappa B in patients with a history of unstable angina: case re-opened

This study aims at assessing NF-kB activity in unstable angina (UA) patients free of symptoms after a 1 year follow-up (1YFU). Plasma oxidized low-density lipoproteins (oxLDL), circulating NF-kB, Interleukin 6 (IL-6) and Interleukin 1β (IL-1β), high-sensitivity C-reactive protein (hs-CRP), as markers of oxidative stress and inflammation and plasma double-stranded DNA (ds-DNA), as marker of Neutrophil Extracellular Traps (NETs), were measured in 23 of the previously enrolled 27 UA patients. These measurements were compared to the UA data at baseline, and then compared to the data derived from the stable angina (SA) and controls (C) enrolled in our previous study (we demonstrated that UA had higher levels of NF-kB compared to SA and C). After a 1YFU, UA patients show a significant decrease in NF-kB, IL-6, hs-CRP, oxLDL, and ds-DNA plasma levels (p < 0.001) and in IL-1β and White Blood Cells (WBC) (p < 0.005), without differences in lipid and glucose assessment. If compared to SA and C, UA after a 1YFU have higher levels of NF-kB, IL-6, ds-DNA, WBC, and oxLDL compared to C (p < 0.001), but only IL-6 is higher than SA (p < 0.001). No differences are found in lipid and glucose assessment. After a 1YFU, patients with a history of UA improve their oxidative and inflammatory status, such as the levels of circulating ds-DNA, without achieving the status of C. They become comparable to SA subjects. This study provides new insight on the multiple and apparently contradictory facets of NF-kB in UA and on its possible role as mediator in NETs' formation.

Red Blood Cells in Type 2 Diabetes Impair Cardiac Post-Ischemic Recovery Through an Arginase-Dependent Modulation of Nitric Oxide Synthase and Reactive Oxygen Species

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RBCs from mice and patients with type 2 diabetes have increased arginase activity and production of reactive oxygen species.

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RBCs from mice and patients with type 2 diabetes aggravate myocardial ischemia-reperfusion injury.

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Inhibition of arginase in RBCs from mice and patients with type 2 diabetes improves post-ischemic myocardial recovery via reduced oxidative stress.

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Inhibition of nitric oxide synthase in RBC reduces oxidative stress and restores post-ischemic myocardial functional recovery.

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These data demonstrate a novel disease mechanism by which RBC drive post-ischemic cardiac dysfunction in type 2 diabetes.

This study tested the hypothesis that red blood cell (RBC) arginase represents a potential therapeutic target in ischemia-reperfusion in type 2 diabetes. Post-ischemic cardiac recovery was impaired in hearts from db/db mice compared with wild-type hearts. RBCs from mice and patients with type 2 diabetes attenuated post-ischemic cardiac recovery of nondiabetic hearts. This impaired cardiac recovery was reversed by inhibition of RBCs arginase or nitric oxide synthase. The results suggest that RBCs from type 2 diabetics impair cardiac tolerance to ischemia-reperfusion via a pathway involving arginase activity and nitric oxide synthase-dependent oxidative stress.

In Vivo Hyperoxic Preconditioning Prevents Myocardial Infarction by Expressing Bcl-2

Preconditioning with oxidative stress has been demonstrated in vitro to stimulate the cellular adaptation to subsequent severe oxidative stress. However, it is uncertain whether this preconditioning works in vivo. In the present study, we examined in vivo the beneficial effect of oxidative preconditioning. After rats were pretreated with whole-body hyperoxygenation (100% 02 at 3 atmosphere for 20 mins, four cycles with 20-min intermission), isolated hearts were subjected to 45-min ischemia followed by 90-min reperfusion. This hyperoxic preconditioning significantly reduced infarct size, cytochrome-c release, DNA fragmentation, and terminal deoxynucleotidyl transferase-mediated dUTD nick-end labeling-positive cell frequency in the left ventricle, biphasically with an early (30-min) and a delayed (48-hr) effect after the hyperoxygenation. Mechanistically, the NF-κB activity and Bcl-2 expression were enhanced in the hearts, and a NF-κB inhibitor, pyrrolidine dithiocarbamate, abolished the Bcl-2 induction as well as the infarct-limiting effect. An antioxidant, N-acetylcysteine, and protein kinase C (PKC) inhibitors chelerythrine and Gö 6983 also blocked the preconditioning effects. These results indicate that hyperoxia induces myocardial tolerance against ischemia-reperfusion injury in association with Bcl-2 induction by NF-κB activation through reactive oxygen species and PKC-dependent signaling pathway.

Polyunsaturated fatty acid induces cardioprotection against ischemia-reperfusion through the inhibition of NF-kappaB and induction of Nrf2

The mechanistic evidence to support the cardioprotective effects of polyunsaturated fatty acids (PUFA) are controversial. The aim was to test cardioprotective mechanisms induced by PUFA supplementation against cardiac ischemia-reperfusion (IR) injury. Ten-week-old male Wistar rats (225 ± 14 g, n = 14) were divided in two groups: rats without supplementation ( n = 7) and a PUFA group, supplemented by PUFA (0.6 g/kg/day; DHA:EPA = 3:1) for eight weeks ( n = 7). Hearts were perfused with Krebs-Henseleit buffer for 20 min (control conditions); others were subjected to control conditions, 30 min of global ischemia and 120 min of reperfusion (IR group). Infarct size (IS) and left ventricular developed pressure (LVDP) were measured at 120 min of reperfusion. Oxidative stress biomarkers (TBARS, total carbonyls), antioxidant status (CAT, catalase; SOD, superoxide dismutase; GSH-Px, glutathione peroxidase activity and GSH/GSSG ratio), myeloperoxidase activity, ATP levels and nuclear transcription factor erythroid 2-related factor 2 (Nrf2) and nuclear factor kappaB (NF-κB) were determined in both experimental conditions. At the end of reperfusion, hearts supplemented with PUFA showed lower IS and a higher LVDP compared with the nonsupplemented rats. Hearts in the group supplemented with PUFA showed lower levels of oxidative stress markers and higher antioxidant activity, decreased MPO activity and NF-κB and Nrf2 activation compared with the nonsupplemented group. Cardioprotective effects of PUFA are exerted through induction of anti-inflammatory and antioxidant mechanism at tissue level.

Ω3 Supplementation and intermittent hypobaric hypoxia induce cardioprotection enhancing antioxidant mechanisms in adult rats

Intermittent hypobaric hypoxia (IH) is linked with oxidative stress, impairing cardiac function. However, early IH also activate cardio-protective mechanisms. Omega 3 fatty acids (Ω3) induce cardioprotection by reducing infarct size and reinforcing antioxidant defenses. The aim of this work was to determine the combined effects of IH and Ω3 on cardiac function; oxidative balance and inflammatory state. Twenty-eight rats were randomly divided into four groups: normobaric normoxia (N); N + Ω3 (0.3 g·kg⁻¹·day⁻¹); IH; and IH + Ω3. IH was induced by 4 intercalate periods of hypoxia (4 days)—normoxia (4 days) in a hypobaric chamber during 32 days. At the end of the exposure, hearts were mounted in a Langendorff system and subjected to 30 min of ischemia followed by 120 min of reperfusion. In addition, we determined HIF-1α and ATP levels, as well as oxidative stress by malondialdehyde and nitrotyrosine quantification. Further, the expression of the antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase was determined. NF-kappaB and myeloperoxidase levels were assessed in the hearts. Relative to N hearts, IH improved left ventricular function (Left ventricular developed pressure: N; 21.8 ± 3.4 vs. IH; 42.8 ± 7.1 mmHg; p < 0.05); reduced oxidative stress (Malondialdehyde: N; 14.4 ± 1.8 vs. IH; 7.3 ± 2.1 μmol/mg prot.; p < 0.05); and increased antioxidant enzymes expression. Supplementation with Ω3 induces similar responses as IH group. Our findings suggest that both, IH and Ω3 in an independent manner, induce functional improvement by antioxidant and anti-inflammatory mechanisms, establishing cardio-protection.

IκBβ-mediated NF-κB activation confers protection against hyperoxic lung injury

Supplemental oxygen is frequently used in an attempt to improve oxygen delivery; however, prolonged exposure results in damage to the pulmonary endothelium and epithelium. Although NF-κB has been identified as a redox-responsive transcription factor, whether NF-κB activation exacerbates or attenuates hyperoxic lung injury is unclear. We determined that sustained NF-κB activity mediated by IκBβ attenuates lung injury and prevents mortality in adult mice exposed to greater than 95% O2. Adult wild-type mice demonstrated evidence of alveolar protein leak and 100% mortality by 6 days of hyperoxic exposure, and showed NF-κB nuclear translocation that terminated after 48 hours. Furthermore, these mice showed increased expression of NF-κB-regulated proinflammatory and proapoptotic cytokines. In contrast, mice overexpressing the NF-κB inhibitory protein, IκBβ (AKBI), demonstrated significant resistance to hyperoxic lung injury, with 50% surviving through 8 days of exposure. This was associated with NF-κB nuclear translocation that persisted through 96 hours of exposure. Although induction of NF-κB-regulated proinflammatory cytokines was not different between wild-type and AKBI mice, significant up-regulation of antiapoptotic proteins (BCL-2, BCL-XL) was found exclusively in AKBI mice. We conclude that sustained NF-κB activity mediated by IκBβ protects against hyperoxic lung injury through increased expression of antiapoptotic genes.

Sustained hyperoxia-induced NF-κB activation improves survival and preserves lung development in neonatal mice

Oxygen toxicity contributes to the pathogenesis of bronchopulmonary dysplasia (BPD). Neonatal mice exposed to hyperoxia develop a simplified lung structure that resembles BPD. Sustained activation of the transcription factor NF-κB and increased expression of protective target genes attenuate hyperoxia-induced mortality in adults. However, the effect of enhancing hyperoxia-induced NF-κB activity on lung injury and development in neonatal animals is unknown. We performed this study to determine whether sustained NF-κB activation, mediated through IκBβ overexpression, preserves lung development in neonatal animals exposed to hyperoxia. Newborn wild-type (WT) and IκBβ-overexpressing (AKBI) mice were exposed to hyperoxia (>95%) or room air from day of life (DOL) 0-14, after which all animals were kept in room air. Survival curves were generated through DOL 14. Lung development was assessed using radial alveolar count (RAC) and mean linear intercept (MLI) at DOL 3 and 28 and pulmonary vessel density at DOL 28. Lung tissue was collected, and NF-κB activity was assessed using Western blot for IκB degradation and NF-κB nuclear translocation. WT mice demonstrated 80% mortality through 14 days of exposure. In contrast, AKBI mice demonstrated 60% survival. Decreased RAC, increased MLI, and pulmonary vessel density caused by hyperoxia in WT mice were significantly attenuated in AKBI mice. These findings were associated with early and sustained NF-κB activation and expression of cytoprotective target genes, including vascular endothelial growth factor receptor 2. We conclude that sustained hyperoxia-induced NF-κB activation improves neonatal survival and preserves lung development. Potentiating early NF-κB activity after hyperoxic exposure may represent a therapeutic intervention to prevent BPD.

Preconditioning mesenchymal stem cells with caspase inhibition and hyperoxia prior to hypoxia exposure increases cell proliferation

Myocardial infarction is a leading cause of mortality and morbidity worldwide. Occlusion of a coronary artery produces ischemia and myocardial necrosis that leads to left ventricular (LV) remodeling, dysfunction, and heart failure. Stem cell therapy may decrease infarct size and improve LV function; the hypoxic environment, however, following a myocardial infarction may result in apoptosis, which in turn decreases survival of transplanted stem cells. Therefore, the effects of preconditioned mesenchymal stem cells (MSC) with hyperoxia (100% oxygen), Z-VAD-FMK pan-caspase inhibitor (CI), or both in a hypoxic environment in order to mimic conditions seen in cardiac tissue post-myocardial infarction were studied in vitro. MSCs preconditioned with hyperoxia or CI significantly decreased apoptosis as suggested by TUNEL assay and Annexin V analysis using fluorescence assisted cell sorting. These effects were more profound when both, hyperoxia and CI, were used. Additionally, gene and protein expression of caspases 1, 3, 6, 7, and 9 were down-regulated significantly in MSCs preconditioned with hyperoxia, CI, or both, while the survival markers Akt1, NF-κB, and Bcl-2 were significantly increased in preconditioned MSCs. These changes ultimately resulted in a significant increase in MSC proliferation in hypoxic environment as determined by BrdU assays compared to MSCs without preconditioning. These effects may prove to be of great clinical significance when transplanting stem cells into the hypoxic myocardium of post-myocardial infarction patients in order to attenuate LV remodeling and improve LV function.

Arginase regulates red blood cell nitric oxide synthase and export of cardioprotective nitric oxide bioactivity

The theory that red blood cells (RBCs) generate and release nitric oxide (NO)-like bioactivity has gained considerable interest. However, it remains unclear whether it can be produced by endothelial NO synthase (eNOS), which is present in RBCs, and whether NO can escape scavenging by hemoglobin. The aim of this study was to test the hypothesis that arginase reciprocally controls NO formation in RBCs by competition with eNOS for their common substrate arginine and that RBC-derived NO is functionally active following arginase blockade. We show that rodent and human RBCs contain functional arginase 1 and that pharmacological inhibition of arginase increases export of eNOS-derived nitrogen oxides from RBCs under basal conditions. The functional importance was tested in an ex vivo model of myocardial ischemia-reperfusion injury. Inhibitors of arginase significantly improved postischemic functional recovery in rat hearts if administered in whole blood or with RBCs in plasma. By contrast, arginase inhibition did not improve postischemic recovery when administered with buffer solution or plasma alone. The protective effect of arginase inhibition was lost in the presence of a NOS inhibitor. Moreover, hearts from eNOS(-/-) mice were protected when the arginase inhibitor was given with blood from wild-type donors. In contrast, when hearts from wild-type mice were given blood from eNOS(-/-) mice, the arginase inhibitor failed to protect against ischemia-reperfusion. These results strongly support the notion that RBCs contain functional eNOS and release NO-like bioactivity. This process is under tight control by arginase 1 and is of functional importance during ischemia-reperfusion.

Nitric-oxide synthase-2 linkage to focal adhesion kinase in neutrophils influences enzyme activity and β2 integrin function

This investigation was to elucidate the basis for augmentation of nitric-oxide synthesis in neutrophils exposed to hyperbaric oxygen. Hyperoxia increases synthesis of reactive species leading to S-nitrosylation of β-actin, which causes temporary inhibition of β(2) integrin adherence. Impaired β(2) integrin function and actin S-nitrosylation do not occur in neutrophils from mice lacking type-2 nitric-oxide synthase (iNOS) or when incubated with 1400W, an iNOS inhibitor. Similarly, effects of hyperoxia were abrogated in cells depleted of focal adhesion kinase (FAK) by treatment with small inhibitory RNA and those exposed to a specific FAK inhibitor concurrent with hyperoxia. Nitric oxide production doubles within 10 min exposure to hyperoxia but declines to approximately half-maximum production over an additional 10 min. Elevated nitric oxide production did not occur after FAK depletion or inhibition, or when filamentous actin formation was inhibited by cytochalasin D. Intracellular content of iNOS triples over the course of a 45-min exposure to hyperoxia and iNOS dimers increase in a commensurate fashion. Confocal microscopy and immunoprecipitation demonstrated that co-localization/linkage of FAK, iNOS, and filamentous actin increased within 15 min exposure to hyperoxia but then decreased below the control level. Using isolated enzymes in ex vivo preparations an association between iNOS and filamentous actin mediated by FAK could be demonstrated and complex formation was impeded when actin was S-nitrosylated. We conclude that iNOS activity is increased by an FAK-mediated association with actin filaments but peak nitric oxide production is transient due to actin S-nitrosylation during exposure to hyperoxia.

Thioredoxin reductase linked to cytoskeleton by focal adhesion kinase reverses actin S-nitrosylation and restores neutrophil β(2) integrin function

The investigation goal was to identify mechanisms for reversal of actin S-nitrosylation in neutrophils after exposure to high oxygen partial pressures. Prior work has shown that hyperoxia causes S-nitrosylated actin (SNO-actin) formation, which mediates β(2) integrin dysfunction, and these changes can be reversed by formylmethionylleucylphenylalanine or 8-bromo-cyclic GMP. Herein we show that thioredoxin reductase (TrxR) is responsible for actin denitrosylation. Approximately 80% of cellular TrxR is localized to the cytosol, divided between the G-actin and short filamentous actin (sF-actin) fractions based on Triton solubility of cell lysates. TrxR linkage to sF-actin requires focal adhesion kinase (FAK) based on immunoprecipitation studies. S-Nitrosylation accelerates actin filament turnover (by mechanisms described previously (Thom, S. R., Bhopale, V. M., Yang, M., Bogush, M., Huang, S., and Milovanova, T. (2011) Neutrophil β(2) integrin inhibition by enhanced interactions of vasodilator stimulated phosphoprotein with S-nitrosylated actin. J. Biol. Chem. 286, 32854-32865), which causes FAK to disassociate from sF-actin. TrxR subsequently dissociates from FAK, and the physical separation from actin impedes denitrosylation. If SNO-actin is photochemically reduced with UV light or if actin filament turnover is impeded by incubations with cytochalasin D, latrunculin B, 8-bromo-cGMP, or formylmethionylleucylphenylalanine, FAK and TrxR reassociate with sF-actin and cause SNO-actin removal. FAK-TrxR association can also be demonstrated using isolated enzymes in ex vivo preparations. Uniquely, the FAK kinase domain is the site of TrxR linkage. We conclude that through its scaffold function, FAK influences TrxR activity and actin S-nitrosylation.

Hyperoxia during early reperfusion does not increase ischemia/reperfusion injury

OBJECTIVE

Oxygen is routinely administered to patients undergoing acute myocardial infarction as well as during revascularization procedures and cardiac surgery. Because reactive oxygen species are mediators of ischemia/reperfusion injury, increased oxygen availability might theoretically aggravate myocardial injury during reperfusion. We hypothesized that ventilation with a hyperoxic gas at start of reperfusion might increase ischemia/reperfusion injury.

METHODS

Rats were anesthetized with isoflurane and ventilated with 40% oxygen. The animals were subjected to 40 min of regional myocardial ischemia and 120 min of reperfusion. In the test group, rats (n=11) were ventilated with a normobaric hyperoxic gas (95% O2) during the last 10 min of ischemia and the first 10 min of reperfusion. Control rats (n=14) were ventilated with 40% O2 throughout the experiments. Due to irreversible reperfusion arrhythmias, one animal in the hyperoxia group and six animals in the control group were excluded. Hearts (n=8 in the control group and n=10 in the test group) were harvested for measurement of infarct size.

RESULTS

The incidence of lethal arrhythmias was 1/11 in the test group and 6/14 in the control group (p=0.06). Reperfusion with normobaric hyperoxia did not influence infarct size (20±8% of area at risk) compared with the normoxia group (24±8% and of area at risk), respectively (mean±SD, p>0.2).

CONCLUSION

Normobaric hyperoxia during early reperfusion did not increase ischemia/reperfusion injury.

The Effects of Prenatal Protein Restriction on β-Adrenergic Signalling of the Adult Rat Heart during Ischaemia Reperfusion

A maternal low-protein diet (MLP) fed during pregnancy leads to hypertension in adult rat offspring. Hypertension is a major risk factor for ischaemic heart disease. This study examined the capacity of hearts from MLP-exposed offspring to recover from myocardial ischaemia-reperfusion (IR) and related this to cardiac expression of β-adrenergic receptors (β-AR) and their associated G proteins. Pregnant rats were fed control (CON) or MLP diets (n = 12 each group) throughout pregnancy. When aged 6 months, hearts from offspring underwent Langendorff cannulation to assess contractile function during baseline perfusion, 30 min ischemia and 60 min reperfusion. CON male hearts demonstrated impaired recovery in left ventricular pressure (LVP) and dP/dt_max (P < 0.01) during reperfusion when compared to MLP male hearts. Maternal diet had no effect on female hearts to recover from IR. MLP males exhibited greater membrane expression of β₂-AR following reperfusion and urinary excretion of noradrenaline and dopamine was lower in MLP and CON female rats versus CON males. In conclusion, the improved cardiac recovery in MLP male offspring following IR was attributed to greater membrane expression of β₂-AR and reduced noradrenaline and dopamine levels. In contrast, females exhibiting both decreased membrane expression of β₂-AR and catecholamine levels were protected from IR injury.

Nuclear protein extraction from frozen porcine myocardium

Protocols for the extraction of nuclear proteins have been developed for cultured cells and fresh tissue, but sometimes only frozen tissue is available. We have optimized the homogenization procedure and subsequent fractionation protocol for the preparation of nuclear protein extracts from frozen porcine left ventricular (LV) tissue. This method gave a highly reproducible protein yield (6.5±0.7% of total protein; mean±SE, n=9) and a 6-fold enrichment of the nuclear marker protein B23. The nuclear protein extracts were essentially devoid of cytosolic, myofilament, and histone proteins. Compared to nuclear extracts from fresh LV tissue, some loss of nuclear proteins to the cytosolic fraction was observed. Using this method, we studied the distribution of tyrosine phosphorylated signal transducer and activator of transcription 3 (PY-STAT3) in LV tissue of animals treated with the β-agonist dobutamine. Upon treatment, PY-STAT3 increased 30.2±8.5-fold in total homogenates, but only 6.9±2.1-fold (n=4, P=0.03) in nuclear protein extracts. Of all PY-STAT3 formed, only a minor fraction appeared in the nuclear fraction. This simple and reproducible protocol yielded nuclear protein extracts that were highly enriched in nuclear proteins with almost complete removal of cytosolic and myofilament proteins. This nuclear protein extraction protocol is therefore well-suited for nuclear proteome analysis of frozen heart tissue collected in biobanks.

Neutrophil beta2 integrin inhibition by enhanced interactions of vasodilator-stimulated phosphoprotein with S-nitrosylated actin

Production of reactive species in neutrophils exposed to hyperoxia causes S-nitrosylation of β-actin, which increases formation of short actin filaments, leading to alterations in the cytoskeletal network that inhibit β(2) integrin-dependent adherence (Thom, S. R., Bhopale, V. M., Mancini, D. J., and Milovanova, T. N. (2008) J. Biol. Chem. 283, 10822-10834). In this study, we found that vasodilator-stimulated protein (VASP) exhibits high affinity for S-nitrosylated short filamentous actin, which increases actin polymerization. VASP bundles Rac1, Rac2, cyclic AMP-dependent, and cyclic GMP-dependent protein kinases in close proximity to short actin filaments, and subsequent Rac activation increases actin free barbed end formation. Using specific chemical inhibitors or reducing cell concentrations of any of these proteins with small inhibitory RNA abrogates enhanced free barbed end formation, increased actin polymerization, and β(2) integrin inhibition by hyperoxia. Alternatively, incubating neutrophils with formylmethionylleucylphenylalanine or 8-bromo-cyclic GMP activates either cyclic AMP-dependent or cyclic GMP-dependent protein kinase, respectively, outside of the short F-actin pool and phosphorylates VASP on serine 153. Phosphorylated VASP abrogates the augmented polymerization normally observed with S-nitrosylated actin, VASP binding to actin, elevated Rac activity, and elevated formation of actin free barbed ends, thus restoring normal β(2) integrin function.

Application of medical gases in the field of neurobiology

Medical gases are pharmaceutical molecules which offer solutions to a wide array of medical needs. This can range from use in burn and stroke victims to hypoxia therapy in children. More specifically however, gases such as oxygen, helium, xenon, and hydrogen have recently come under increased exploration for their potential theraputic use with various brain disease states including hypoxia-ischemia, cerebral hemorrhages, and traumatic brain injuries. As a result, this article will review the various advances in medical gas research and discuss the potential therapeutic applications and mechanisms with regards to the field of neurobiology.

Hyperoxia may be beneficial

The current practice of mechanical ventilation comprises the use of the least inspiratory O2 fraction associated with an arterial O2 tension of 55 to 80 mm Hg or an arterial hemoglobin O2 saturation of 88% to 95%. Early goal-directed therapy for septic shock, however, attempts to balance O2 delivery and demand by optimizing cardiac function and hemoglobin concentration, without making use of hyperoxia. Clearly, it has been well-established for more than a century that long-term exposure to pure O2 results in pulmonary and, under hyperbaric conditions, central nervous O2 toxicity. Nevertheless, several arguments support the use of ventilation with 100% O2 as a supportive measure during the first 12 to 24 hrs of septic shock. In contrast to patients without lung disease undergoing anesthesia, ventilation with 100% O2 does not worsen intrapulmonary shunt under conditions of hyperinflammation, particularly when low tidal volume-high positive end-expiratory pressure ventilation is used. In healthy volunteers and experimental animals, exposure to hyperoxia may cause pulmonary inflammation, enhanced oxidative stress, and tissue apoptosis. This, however, requires long-term exposure or injurious tidal volumes. In contrast, within the timeframe of a perioperative administration, direct O2 toxicity only plays a negligible role. Pure O2 ventilation induces peripheral vasoconstriction and thus may counteract shock-induced hypotension and reduce vasopressor requirements. Furthermore, in experimental animals, a redistribution of cardiac output toward the kidney and the hepato-splanchnic organs was observed. Hyperoxia not only reverses the anesthesia-related impairment of the host defense but also is an antibiotic. In fact, perioperative hyperoxia significantly reduced wound infections, and this effect was directly related to the tissue O2 tension. Therefore, we advocate mechanical ventilation with 100% O2 during the first 12 to 24 hrs of septic shock. However, controlled clinical trials are mandatory to test the safety and efficacy of this approach.

Pretreatment with hyperoxia reduces in vivo infarct size and cell death by apoptosis with an early and delayed phase of protection

OBJECTIVE

Exposure to normobaric hyperoxia protects the heart against ischemia-reperfusion injury ex vivo. In the present study, we investigated the effect of the early and late phase of hyperoxia on in vivo myocardial infarction and apoptosis.

METHODS

Rats were exposed to room air preoxygenation (O(2)≥ 95%) followed by regional ischemia (30 min) and 0, 90, 180, and 360 min of reperfusion. Hyperoxic exposure was performed for 120 min either immediately or 24h before coronary occlusion followed by 360-min reperfusion. Infarct size was evaluated by Evans blue/triphenyltetrazolium chloride staining. Apoptosis in the infarcted area was evaluated by terminal deoxy-nucleotidyl transferase-mediated deoxy uridine triphosphate (dUTP) nick end-labeling (TUNEL). Caspase 3 activity was measured by fluorometric enzyme assay, Bcl-2 and Bax protein expression assessed by western blotting and DNA laddering assessed with DNA gel electrophoresis.

RESULTS

The infarct size did not increase with increasing duration of reperfusion. However, apoptosis as evaluated by Bcl-2/Bax ratio, caspase 3 activity, and TUNEL-positive cells increased with increasing time of reperfusion. Both early and delayed pretreatment with hyperoxia reduced infarct size (p = 0.0013, p = 0.046), ameliorated ischemic arrhythmias and increased Bcl-2/Bax ratio (p = 0.015, p = 0.0159). Only hyperoxia immediately before coronary occlusion decreased caspase 3 activity (p = 0.026) and decreased TUNEL-positive staining (p = 0.046) with no visible DNA laddering.

CONCLUSIONS

Detection of myocardial apoptosis increased with prolongation of reperfusion time, as opposed to infarct detection where reperfusion was essential to detect infarction, but the infarct size did not increase with time. Pretreatment with hyperoxia significantly decreased infarct size and apoptotic cell death. Pretreatment, immediately before coronary occlusion, was most cardioprotective.

Role of nuclear factor kappaB in cardiovascular health and disease

Cardiovascular pathologies are still the primary cause of death worldwide. The molecular mechanisms behind these pathologies have not been fully elucidated. Unravelling them will bring us closer to therapeutic strategies to prevent or treat cardiovascular disease. One of the major transcription factors that has been linked to both cardiovascular health and disease is NF-kappaB (nuclear factor kappaB). The NF-kappaB family controls multiple processes, including immunity, inflammation, cell survival, differentiation and proliferation, and regulates cellular responses to stress, hypoxia, stretch and ischaemia. It is therefore not surprising that NF-kappaB has been shown to influence numerous cardiovascular diseases including atherosclerosis, myocardial ischaemia/reperfusion injury, ischaemic preconditioning, vein graft disease, cardiac hypertrophy and heart failure. The function of NF-kappaB is largely dictated by the genes that it targets for transcription and varies according to stimulus and cell type. Thus NF-kappaB has divergent functions and can protect cardiovascular tissues from injury or contribute to pathogenesis depending on the cellular and physiological context. The present review will focus on recent studies on the function of NF-kappaB in the cardiovascular system.

Activation of NF-kappaB is a critical element in the antiapoptotic effect of anesthetic preconditioning

Anesthetic preconditioning (APC), defined as brief exposure to inhalational anesthetics before cardiac ischemia-reperfusion (I/R), limits injury in both animal models and in humans. APC can result in the production of reactive oxygen species (ROS), and prior work has shown that APC can modify activation of NF-kappaB during I/R, with consequent reduction in the expression of inflammatory mediators. However, the role of NF-kappaB activation before I/R is unknown. Therefore, these experiments tested the hypothesis that APC-induced ROS results in activation of NF-kappaB before I/R, with consequent increased expression of antiapoptotic proteins such as Bcl-2 and decreased apoptosis. Experiments utilized an established perfused heart rat model of sevoflurane APC and I/R. The role of NF-kappaB was defined by a novel method of transient inhibition of the regulatory kinase IKK using the reversible inhibitor SC-514. In addition to functional measures of left ventricular developed and end-diastolic pressure, phosphorylation of IkappaBalpha and activation of NF-kappaB were measured along with cytosolic protein content of Bcl-2, release of cytochrome c, and degradation of caspase-3. APC resulted in ROS-dependent phosphorylation of IkappaBalpha and activation of NF-kappaB before I/R. APC also increased the expression of Bcl-2 before I/R. In addition to functional protection following I/R, APC resulted in lower release of cytochrome c and caspase-3 degradation. These protective effects of APC were abolished by transient inhibition of IkappaBalpha phosphorylation and NF-kappaB activation by SC-514 followed by washout. ROS-dependent activation of NF-kappaB by APC before I/R is a critical element in the protective effect of APC. APC reduces apoptosis and functional impairment by increasing Bcl-2 expression before I/R. Interventions that increase NF-kappaB activation before I/R should protect hearts from I/R injury.

Delayed cardioprotective effects of hyperoxia preconditioning prolonged by intermittent exposure

BACKGROUND

In our previous study, it was indicated that pre-exposing rats to normobaric hyperoxia could induce a late preconditioning against infarction and arrhythmia. In this study, attempts were made to know whether the intermittent pre-exposure to the same environment could prolong the late phase of hyperoxia preconditioning.

METHODS

In the first series of experiments, rats were divided into five groups; group 1 was pre-exposed to normal air (NOR) and the other groups to hyperoxic air (O(2)>95%, 120 min once a d) 12, 24, 48, and 72 h (H12, H24, H48, and H72 groups) before 30 min ischemia. In the second series of experiments, rats were pre-exposed to intermittent hyperoxic air (1, 2, or 3 consecutive d) at different times before being subjected to ischemia (H48, H2-48, H2-72, H3-72, and H3-96 groups). The infarct size was measured by triphenyltetrazolium chloride staining, and lead II of electrocardiogram recorded to monitor ischemic-induced arrhythmia.

RESULTS

Compared with NOR group, the infarct size and incidence of arrhythmia were reduced significantly in H24 and H48 groups. When the exposure periods were enhanced to 2 d, the infarct size did not decrease significantly, but the incidence of arrhythmia reduced. When the pre-exposure times were enhanced to 3 d, both the infarct size and incidence of arrhythmia decreased significantly in H3-72 group, but not in H3-96 group.

CONCLUSION

These results show that the late phase of hyperoxia preconditioning may last for more than 48 h and prolong by intermittent per-exposure to the same environment.

Hyperbaric oxygen preconditioning alleviates myocardial ischemic injury in rats

It has been shown that after ischemia-reperfusion, application of hyperbaric oxygen (HBO) reduces cardiac injury. In this study we tested the hypothesis that HBO preconditioning reduces injury to the ischemic myocardium. One hundred and eight adult male Sprague-Dawley rats (250-280 g) were randomly divided into four groups: normoxia + sham surgery (CS), normoxia + permanent occlusion of the left anterior descending (LAD) coronary artery (CMI), HBO preconditioning + sham surgery (HS), and HBO preconditioning + permanent LAD occlusion (HMI). Rats receiving HBO preconditioning were intermittently exposed to 100% O(2) at 2.5 atmosphere absolute (ATA) for 60 min, twice daily for 2 days followed by 12 hrs of recovery in room air prior to the myocardial ischemic insult induced by LAD ligation. Rats in the normoxia group were time-matched with the HBO group and maintained under normoxic conditions prior to LAD occlusion. At 3 and 7 days after LAD occlusion, heart function parameters were measured by inserting a catheter into the left ventricle, infarct size was calculated using the method of TTC staining, myocardial capillary density was determined by immunohistochemical staining with a monoclonal anti-CD(31)/PECAM-1 antibody, and VEGF protein level was determined by Western blot analysis. At 3 days after LAD ligation, the infarct size of the HMI group was significantly smaller than that of the CMI group (26 +/- 2.5% vs. 38 +/- 3%, P < 0.05). The heart function parameters including left ventricular systolic pressure (LVSP), +dP/dt(max) and -dP/dt(max) were significantly improved in the HMI group compared to the CMI group at 3 and 7 days after LAD occlusion. Capillary density and VEGF protein levels were significantly increased in the ischemic myocardium pre-exposed to HBO. We conclude that HBO preconditioning alleviates myocardial ischemia in rat model.

In vivo preconditioning with normobaric hyperoxia induces ischemic tolerance partly by triggering tumor necrosis factor-alpha converting enzyme/tumor necrosis factor-alpha/nuclear factor-kappaB

Recent studies suggest that intermittent and prolonged normobaric hyperoxia (HO) results in brain ischemic tolerance (BIT), reducing ischemic brain injury. We have attempted to determine the time course of HO-induced BIT, and to explore the putative roles of tumor necrosis factor-alpha (TNF-alpha) converting enzyme (TACE), TNF-alpha, and nuclear factor-kappaB (NF-kappaB) activation in mediating this effect. Two core experimental protocols were applied to rats (experiments 1 [E1] and 2 [E2] respectively). E1 rodents comprised six subgroups, breathing room air (RA; O(2)=21%), or 95% oxygen (HO) for 4, 8, 16 h (4RA, 8RA, 16RA and 4HO, 8HO, 16HO respectively). E2 rodents were divided into subgroups, exposed to 95% inspired HO for 4 h/day for six consecutive days (intermittent hyperoxia, InHO) or for 24 continuous hours (prolonged hyperoxia, PrHO). Each of these had a control group exposed to 21% oxygen in the same chamber. Twenty-four hours after pretreatment, each group was randomly divided to receive 60 min right middle cerebral artery occlusion (MCAO-operated), sham-operation (without MCAO), or no operation (intact). After 24 h reperfusion, neurologic deficit score (NDS), brain water content, Evans Blue extravasation (as a marker of blood-brain barrier permeability), TACE expression, serum TNF-alpha, and phosphor- kappaBalpha levels were assessed in all animals, and infarct volume in the MCAO-operated subgroups. E1: Compared with the control (RA) group, infarct volume was reduced by 58.6% and 64.4% in 16 h and 24 h respectively. NDS and Evans Blue extravasation was also reduced in 16 h and 24 h. There was no statistical difference among 4 h and 8 h. E2: Preconditioning with prolonged and intermittent HO decreased NDS, infarct volume and upregulated TACE and increased phosphor-kappaBalpha and serum TNF-alpha level significantly. Although further studies are needed to clarify the mechanisms of brain ischemic tolerance, InHO and PrHO may partly exert their effects via triggering TACE/TNF-alpha/NF-kappaB.

Actin S-nitrosylation inhibits neutrophil beta2 integrin function

The focus of this work was to elucidate the mechanism for inhibition of neutrophil beta(2) integrin adhesion molecules by hyperoxia. Results demonstrate that exposure to high oxygen partial pressures increases synthesis of reactive species derived from type 2 nitric-oxide synthase and myeloperoxidase, leading to excessive S-nitrosylation of beta-actin and possibly profilin. Hyperoxia causes S-nitrosylation of the four cysteine moieties closest to the carboxyl-terminal end of actin, which results in formation of short actin filaments. This alters actin polymerization, network formation, and intracellular distribution, as well as inhibits beta(2) integrin clustering. If neutrophils are exposed to ultraviolet light to reverse S-nitrosylation, or are incubated with N-formyl-methionyl-leucine-phenylalanine to trigger "inside-out" activation, the effects of hyperoxia are reversed. We conclude that cytoskeletal changes triggered by hyperoxia inhibit beta(2) integrin-dependent neutrophil adhesion.

Hyperoxia confers myocardial protection in mechanically ventilated rats through the generation of free radicals and opening of mitochondrial ATP-sensitive potassium channels

1. One hour exposure to hyperoxia has been shown previously to limit a subsequent ischaemia-reperfusion injury in spontaneously breathing rats. We tested the cardioprotective effect of a shorter period of hyperoxia during mechanical ventilation and the possible contribution of reactive oxygen species (ROS) and mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels. 2. Mechanically ventilated rats were exposed to normoxia (Fi O2 = 0.3) or hyperoxia (Fi O2 = 1.0) for 30 min and pH, P CO2, PO2, heart rate, airway and blood pressure were measured at baseline and after 30 min mechanical ventilation. Isolated hearts were subsequently subjected to 30 min ischaemia and 120 min reperfusion. Infarct size and left ventricular end-diastolic pressure (LVEDP), developed pressure (LVDP) and coronary flow (CF) were measured. In order to investigate the role of ROS and KATP channels within the mechanism leading to cardioprotection, the free radical scavenger N-acetylcysteine (NAC; 150 mg/kg) was infused in mechanically ventilated rats and the KATP channel blockers glibenclamide (200 mmol/L) or 5-hydroxydecanoate (10 mmol/L) were infused in isolated hearts immediately before ischaemia. 3. No differences were detected in P CO2, pH, heart rate, airway and blood pressure between the groups. However, the PO2 in hyperoxic groups was significantly higher compared with that in normoxic groups (P < 0.01). After 30 min ischaemia, we found that hyperoxic preconditioning significantly improved CF (P < 0.01), LVDP (P < 0.01) and LVEDP (P < 0.01) and reduced the extent of infarct size in the reperfused heart compared with the normoxic group (P < 0.01). When rats were pretreated either with NAC before hyperoxic ventilation or with K(ATP) channel blockers before ischaemia, myocardial protection was abolished. 4. Hyperoxic mechanical ventilation, prior to ischaemia, reduces myocardial reperfusion injury. This is likely to occur through the induction of oxidative stress, which leads to myocyte mitoKATP channel opening.

The hyperbaric oxygen preconditioning-induced brain protection is mediated by a reduction of early apoptosis after transient global cerebral ischemia

We hypothesized that the brain-protective effect of hyperbaric oxygen (HBO) preconditioning in a transient global cerebral ischemia rat model is mediated by the inhibition of early apoptosis. One hundred ten male Sprague-Dawley (SD) rats (300-350 g body weight) were allocated to the sham group and three other groups with 10 min of four-vessel occlusion, untreated or preconditioned with either 3 or 5 hyperbaric oxygenations. HBO preconditioning improved neurobehavioral scores and reduced mortality, decreased ischemic cell change, reduced the number of early apoptotic cells and hampered a conversion of early to late apoptotic alterations. HBO preconditioning reduced the immunoreactivity of phosphorylated p38 in vulnerable neurons and increased the expression of brain derived neurotrophic factor (BDNF) in early stage post-ischemia. However, preconditioning with 3 HBO treatments proved less beneficial than with 5 HBO treatments. We conclude that HBO preconditioning may be neuroprotective by reducing early apoptosis and inhibition of the conversion of early to late apoptosis, possibly through an increase in brain BDNF level and the suppression of p38 activation.

Pre-treatment with hyperoxia before coronary artery bypass grafting - effects on myocardial injury and inflammatory response

BACKGROUND

In experimental studies, exposure to hyperoxia for a limited time before ischaemia induces a low-grade systemic oxidative stress and evokes an (ischaemic) preconditioning-like effect of the myocardium. We hypothesised that hyperoxia before cardioplegia could protect the myocardium against necrosis and stunning caused by ischaemia-reperfusion.

METHODS

Forty patients undergoing coronary artery bypass grafting were randomly exposed to an oxygen fraction of 0.4 or > 0.96 in inspired air on an average of 120 min before cardioplegia. Blood for troponin I, creatine kinase-MB, lactate, glutathione and interleukin-6 was sampled from arterial and coronary sinus cannulae during 20 min of reperfusion. Additional arterial samples were drawn 60 min after declamping and in the first post-operative morning. The cardiac index and right and left ventricular stroke work indices were measured before sternotomy and up to 12 h post-operatively.

RESULTS

Troponin I, creatine kinase-MB and lactate did not differ between the groups. Hyperoxic pre-treatment had no impact on the post-operative haemodynamic indices measured with the thermodilution pulmonary artery catheter. More oxidised glutathione was released in the hyperoxia group in the first minute of reperfusion (P = 0.015). Hyperoxic pre-treatment abolished the myocardial release of interleukin-6 during 20 min of reperfusion (P = 0.021 vs. controls). In the first post-operative morning, interleukin-6 was higher in the hyperoxia group [127.0 (86.0-140.0) vs. 85.2 pg/ml (66.6-94.5 pg/ml); P = 0.016].

CONCLUSIONS

Exposure to >96% oxygen before cardioplegia did not attenuate ischaemia-reperfusion injury of the heart in patients undergoing coronary artery bypass grafting. The only potentially beneficial effect observed was the decreased transmyocardial release of interleukin-6.

Preoperative unstable angina causes venous adaptation to surgical graft injury

Ischemic preconditioning may provide a systemic organ protection, evident as the phenomenon known as remote preconditioning. Unstable angina may be a clinical analogue to ischemic preconditioning. Vein graft harvesting induces inflammation of the graft wall. We hypothesized that preoperative unstable angina preconditions vein grafts and reduces the inflammatory response to graft harvesting. Consecutive patients with stable or unstable angina undergoing open heart surgery (n = 12 in each group) were studied. Saphenous vein biopsies were collected at the start of graft harvesting, and when the last proximal anastomosis to the aorta was finished (average 112 minutes later). Gene expression of inflammatory mediators (tumor necrosis factor alpha, interleukin-1beta (IL-1beta), E-selectin (CD62E), intercellular leukocyte adhesion molecule 1, inducible nitric oxide synthase, endothelin-1) increased after surgical handling (semiquantitative RT-PCR). In vein grafts from unstable patients the increase was attenuated for Il-1beta (p < 0.004) and CD62E (p < 0.001). In stable patients the protein expression of IkappaBalpha and heat shock protein72 was reduced by surgical handling (p < 0.04), but was not influenced in unstable patients (immunoblotting). In vitro relaxation to acetylcholine was enhanced, and contractions to phenylephrine and endothelin-1 were attenuated in veins rings from unstable patients (p < 0.003). In conclusion, surgical handling of vein grafts induces inflammation of the vessel wall. This response was reduced in grafts from patients with unstable angina, indicating a possible systemic preconditioning-like effect of acute coronary syndromes.

Myocardial protection evoked by hyperoxic exposure involves signaling through nitric oxide and mitogen activated protein kinases

BACKGROUND

Hyperoxic exposure in vivo (> 95% oxygen) attenuates ischemia-reperfusion injury, but the signaling mechanisms of this cardioprotection are not fully determined. We studied a possible role of nitric oxide (NO) and mitogen activated protein kinases (MAPK) in hyperoxic protection.

METHODS

Mice (n = 7-9 in each group) were kept in normoxic or hyperoxic environments for 15 min prior to harvesting the heart and Langendorff perfusion with global ischemia (45 min) and reperfusion (60 min). Endpoints were cardiac function and infarct size. Additional hearts were collected to evaluate MAPK phosphorylation (immunoblot). The nitric oxide synthase inhibitor L-NAME, the ERK1/2 inhibitor PD98059 and the p38 MAPK inhibitor FR167653 were injected intraperitoneally before hyperoxia or normoxia.

RESULTS

Hyperoxia improved postischemic functional recovery and reduced infarct size (p < 0.05). Hyperoxic exposure caused cardiac phosphorylation of the MAPK family members p38 and ERK1/2, but not JNK. L-NAME, PD98059 and FR167653 all reduced the protection afforded by hyperoxic exposure, but did not influence performance or infarction in hearts of normoxic mice. The hyperoxia-induced phosphorylation of ERK1/2 and p38 was reduced by L-NAME and both MAPK inhibitors.

CONCLUSION

Nitric oxide triggers hyperoxic protection, and ERK1/2 and p38 MAPK are involved in signaling of protection against ischemia-reperfusion injury.

Tertiary-butyl hydroperoxide induced oxidative stress and male reproductive activity in mice: role of transcription factor NF-kappaB and testicular antioxidant enzymes

Reactive oxygen species (ROS) have been proposed as a major factor affecting male reproductive capacity. The present study has evaluated the possible role of oxidative stress during testicular pathogenesis in male mice exposed to tertiary-butyl hydroperoxide (TBHP). TBHP was administered by daily intraperitoneal injection for 2 weeks. Treatment greatly increased lipid peroxidation in the testis and led to a significant decrease in sperm concentration and motility and a reduction in litter size relative to controls. An increase in testicular mRNA abundance of redox-regulated p50 and p65 subunits of NF-kappaB was observed after TBHP treatment. Evaluation of NF-kappaB regulated antioxidant enzymes in the testis revealed an increase in superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and glutathione-S-transferase (GST) activities and corresponding mRNA abundance. These results suggest a potential role of NF-kappaB in oxidative stress mediated changes in the physiology of male reproductive system.

Optimal perioperative oxygen administration

PURPOSE OF REVIEW

During anesthesia and surgery oxygen is routinely administered to all patients. Inspired oxygen concentrations, however, vary between 30 and 100%, and oxygen is often administered in a seemingly random manner. During the last decade it has been shown in several randomized trials that perioperative supplemental oxygen administration might improve outcome after certain surgical procedures. The purpose of this review is to provide an overview about the benefits and risks of supplemental oxygen administration in the perioperative period.

RECENT FINDINGS

Supplemental oxygen improves immune function. Furthermore, 80% inspired oxygen fraction almost doubles subcutaneous tissue oxygen tension and halves the rate of postoperative wound infections. Some studies have shown that supplemental oxygen also decreases the rate of postoperative nausea and vomiting after laparoscopic and open abdominal surgical procedures. Preconditioning with oxygen might improve organ function after liver transplantation and outcome after spinal ischemic insults. Supplemental perioperative oxygen administration is not associated with clinically important side effects.

SUMMARY

Supplemental oxygen administration during the perioperative period might be a simple, inexpensive and well-tolerated treatment option to improve patient outcome. The optimal inspired oxygen concentration still needs to be evaluated.

Preharvest donor hyperoxia predicts good early graft function and longer graft survival after liver transplantation

A total of 44 donor/recipient perioperative and intraoperative variables were prospectively analyzed in 89 deceased-donor liver transplantations classified as initial good graft function (IGGF) or initial poor graft function (IPGF) according to a scoring system based on values obtained during the 1st 72 postoperative hours from the serum alanine aminotransferase (ALT) concentration, bile output, and prothrombin activity. The IGGF compared with the IPGF group showed: 1) longer graft (P = .002) and patient (P = .0004) survival; 2) at univariate analysis, a higher (mean [95% confidence interval]) preharvest donor arterial partial pressure of oxygen (PaO(2)) (152 [136-168] and 104 [91-118] mmHg, respectively; P = .0008) and arterial hemoglobin oxygen saturation (97.9 [97.2-98.7] and 96.7 [95.4-98.0]%, respectively; P = .0096), a lower percentage of donors older than 65 years (13 and 33%, respectively; P = .024), a lower percentage of donors treated with noradrenaline (16 and 41%, respectively; P = .012). At multivariate analysis, IGGF was associated positively with donor PaO(2) and negatively with donor age greater than 65 years and with donor treatment with noradrenaline. Independently from the grouping according to initial graft function, graft survival was longer when donor PaO(2) was >150 mmHg than when donor PaO(2) was < or =150 mmHg (P = .045). In conclusion, preharvest donor hyperoxia predicts IGGF and longer graft survival.

Role of tumor necrosis factor alpha and its receptor I in preconditioning by hyperoxia

Hyperoxic pretreatment (>95% O(2)) can evoke myocardial adaptation to ischemia, a method which is potentially clinically usable. We wanted to investigate the role of tumor necrosis factor alpha (TNFalpha) and its p55 receptor (receptor I) in signaling of hyperoxic adaptation to ischemia. Mice deficient for TNFalpha (TNFalpha -/-) or the TNF receptor I (TNFRI -/-) gene and their wild types were subjected to 60 minutes of hyperoxia or sham treatment. Their lungs were then collected for immunoblotting, their hearts isolated and subjected to global ischemia and reperfusion in a Langendorff system, and aortic rings mounted in organ baths for reactivity studies. Hyperoxia increased expression of TNFalpha and TNFalpha converting enzyme in pulmonary proteins from wild type mice, in which hyperoxia increased myocardial tolerance to ischemia. Post-ischemic heart function was improved and infarct size reduced in wild type mice, but not in TNFalpha -/- or TNFRI -/-. The contractile response to TNFalpha on aortic rings was attenuated by hyperoxic pretreatment and by TNFRI -/-. Thus we conclude that TNFalpha, acting through TNFRI, appears important for the protective effects of hyperoxia.

NF-kappaB protects lung epithelium against hyperoxia-induced nonapoptotic cell death-oncosis

Prolonged exposure to hyperoxia induces pulmonary epithelial cell death and acute lung injury. Although both apoptotic and nonapoptotic morphologies are observed in hyperoxic animal lungs, nonapoptotic cell death had only been recorded in transformed lung epithelium cultured in hyperoxia. To test whether the nonapoptotic characteristics in hyperoxic animal lungs are direct effects of hyperoxia, the mode of cell death was determined both morphologically and biochemically in human primary lung epithelium exposed to 95% O(2). In contrast to characteristics observed in apoptotic cells, hyperoxia induced swelling of nuclei and an increase in cell size, with no evidence for any augmentation in the levels of either caspase-3 activity or annexin V incorporation. These data suggest that hyperoxia can directly induce nonapoptotic cell death in primary lung epithelium. Although hyperoxia-induced nonapoptotic cell death was associated with NF-kappaB activation, it is unknown whether NF-kappaB activation plays any causal role in nonapoptotic cell death. This study shows that inhibition of NF-kappaB activation can accelerate hyperoxia-induced epithelial cell death in both primary and transformed lung epithelium. Corresponding to the reduced cell survival in hyperoxia, the levels of MnSOD were also low in NF-kappaB-deficient cells. These results demonstrate that NF-kappaB protects lung epithelial cells from hyperoxia-induced nonapoptotic cell death.

Hyperoxic ventilation at the critical hematocrit: effects on myocardial perfusion and function

BACKGROUND

Hemodilution reduces hematocrit (Hct) and blood oxygen content. Tissue oxygenation is mainly preserved by increased cardiac output. As myocardial O2-demands increase, coronary vasodilatation becomes necessary to increase myocardial blood flow. Myocardial ischemia occurs at a critical Hct-value (Hctcrit), with accompanying exhaustion of coronary reserve. Hyperoxic ventilation is known to both reverse peripheral tissue hypoxia at Hctcrit and also to induce coronary vasoconstriction. This study aimed to determine whether hyperoxic ventilation at Hctcrit further exacerbates myocardial ischemia and dysfunction.

METHODS

Nine anesthetized pigs ventilated on room air were hemodiluted by 1:1 exchange of blood with pentastarch (6%HES) to Hctcrit, defined as onset of myocardial ischemia (ECG changes). At Hctcrit, hyperoxic ventilation was started. Measurements were performed at baseline, at Hctcrit, and after 15 min of hyperoxic ventilation. We determined myocardial blood flow (microsphere method), arterial O2-content, subendocardial O2-delivery and myocardial function (left ventricular pressure increase).

RESULTS

At Hctcrit 7 (6;8)%, O2-content was reduced [3.7 (3.1;3.9) ml dl(-1)]. Despite a compensatory increase of myocardial blood flow [531 (449;573), ml min(-1)100 g(-1)], all pigs displayed myocardial ischemia and compromised myocardial function (P < 0.05). Hyperoxic ventilation produced increased coronary vascular resistance secondary to vasoconstriction, and reduced myocardial blood flow [426 (404;464), ml min(-1)100 g(-1); P < 0.05]. Myocardial oxygenation was found to be maintained by increased O2-content [4.4 (4.2;4.8), ml dl(-1); P < 0.05], the contribution of dissolved O2 to subendocardial O2-delivery increased (32 vs. 8%; P < 0.05), which preserved myocardial function.

CONCLUSION

Hyperoxic ventilation at Hctcrit is followed by coronary vasoconstriction and reduction of coronary blood flow. However, myocardial oxygenation and function is maintained, as increased O2-content (in particular dissolved O2) preserves myocardial oxygenation.

Biliverdin protects the functional integrity of a transplanted syngeneic small bowel

BACKGROUND & AIMS

Heme oxygenase-1 (HO-1) protects against inflammation in many disease models. By degrading heme, HO-1 generates carbon monoxide (CO), iron and biliverdin. We investigated whether biliverdin would protect rat syngeneic small intestinal transplants (SITx) against damage and, if so, by what mechanism.

METHODS

Motility was assessed by organ bath techniques. Inflammatory cytokines and mediators were assessed by RT-PCR and spectrophotometric assays. Myeloperoxidase histochemistry for neutrophils was performed in jejunal segments. Western blots were performed for biliverdin reductase and HO-1 expression. Permeability was expressed as the mucosal to serosal clearance of fluorescent dextran in everted gut sacs. NF-kappaB activation was assessed via EMSA.

RESULTS

Biliverdin significantly improved survival of recipients following SITx after prolonged intestinal ischemia (6 hours). Biliverdin treatment (1) led to a significant decrease in mRNA expression of iNOS, Cox-2, and ICAM-1 as well as the inflammatory cytokines IL-6 and IL-1beta; (2) decreased neutrophil infiltration into the jejunal muscularis; and (3) prevented SITx-induced suppression of intestinal circular muscle contractility.

CONCLUSIONS

Biliverdin administration attenuates transplantation-induced injuries to the small bowel by its anti-inflammatory action. Importantly, biliverdin enhanced recipient survival. A comparison of the mechanisms by which biliverdin exerted these salutary effects compared with inhalation of CO, which we previously showed had salutary effects, suggests that the 2 compounds (biliverdin and CO) exert their effects in part by different mechanisms. This implies that the different products of HO-1 action on heme may exert protective effects that are additive or synergistic.

Preconditioning and cardiac surgery

Preconditioning is in experimental studies the most powerful mode of cardioprotection known. The signal transduction pathways involve a variety of trigger substances, mediators, receptors, and effectors. The studies of preconditioning in cardiac surgery provide conflicting results but the majority of studies show that ischemic preconditiong is an effective adjunct to myocardial protection. However, ischemic preconditioning with repeated clamping of the aorta will never get widespread use. If the "preconditioning response" is to be exploited in cardiac surgery, targeting the underlying molecular mechanisms must provide easily applicable techniques or drugs, which are shown in large scale clinical studies to be beneficial.