Rapid superoxide production by endothelial cells and their injury upon reperfusion

Acid sphingomyelinase inhibition induces cerebral angiogenesis post-ischemia/reperfusion in an oxidative stress-dependent way and promotes endothelial survival by regulating mitochondrial metabolism

Acid sphingomyelinase (ASM) inhibitors are widely used for the treatment of post-stroke depression. They promote neurological recovery in animal stroke models via neurorestorative effects. In a previous study, we found that antidepressants including amitriptyline, fluoxetine, and desipramine increase cerebral angiogenesis post-ischemia/reperfusion (I/R) in an ASM-dependent way. To elucidate the underlying mechanisms, we investigated the effects of the functional ASM inhibitor amitriptyline in two models of I/R injury, that is, in human cerebral microvascular endothelial hCMEC/D3 cells exposed to oxygen-glucose deprivation and in mice exposed to middle cerebral artery occlusion (MCAO). In addition to our earlier studies, we now show that amitriptyline increased mitochondrial reactive oxygen species (ROS) formation in hCMEC/D3 cells and increased ROS formation in the vascular compartment of MCAO mice. ROS formation was instrumental for amitriptyline's angiogenic effects. ROS formation did not result in excessive endothelial injury. Instead, amitriptyline induced a profound metabolic reprogramming of endothelial cells that comprised reduced endothelial proliferation, reduced mitochondrial energy metabolism, reduced endoplasmic reticulum stress, increased autophagy/mitophagy, stimulation of antioxidant responses and inhibition of apoptotic cell death. Specifically, the antioxidant heme oxygenase-1, which was upregulated by amitriptyline, mediated amitriptyline's angiogenic effects. Thus, heme oxygenase-1 knockdown severely compromised angiogenesis and abolished amitriptyline's angiogenic responses. Our data demonstrate that ASM inhibition reregulates a complex network of metabolic and mitochondrial responses post-I/R that contribute to cerebral angiogenesis without compromising endothelial survival.

Selenocompounds and Sepsis: Redox Bypass Hypothesis for Early Diagnosis and Treatment: Part A-Early Acute Phase of Sepsis: An Extraordinary Redox Situation (Leukocyte/Endothelium Interaction Leading to Endothelial Damage)

Significance: Sepsis is a health disaster. In sepsis, an initial, beneficial local immune response against infection evolves rapidly into a generalized, dysregulated response or a state of chaos, leading to multiple organ failure. Use of life-sustaining supportive therapies creates an unnatural condition, enabling the complex cascades of the sepsis response to develop in patients who would otherwise die. Multiple attempts to control sepsis at an early stage have been unsuccessful. Recent Advances: Major events in early sepsis include activation and binding of leukocytes and endothelial cells in the microcirculation, damage of the endothelial surface layer (ESL), and a decrease in the plasma concentration of the antioxidant enzyme, selenoprotein-P. These events induce an increase in intracellular redox potential and lymphocyte apoptosis, whereas apoptosis is delayed in monocytes and neutrophils. They also induce endothelial mitochondrial and cell damage. Critical Issues: Neutrophil production increases dramatically, and aggressive immature forms are released. Leukocyte cross talk with other leukocytes and with damaged endothelial cells amplifies the inflammatory response. The release of large quantities of reactive oxygen, halogen, and nitrogen species as a result of the leukocyte respiratory burst, endothelial mitochondrial damage, and ischemia/reperfusion processes, along with the marked decrease in selenoprotein-P concentrations, leads to peroxynitrite damage of the ESL, reducing flow and damaging the endothelial barrier. Future Directions: Endothelial barrier damage by activated leukocytes is a time-sensitive event in sepsis, occurring within hours and representing the first step toward organ failure and death. Reducing or stopping this event is necessary before irreversible damage occurs.

Pathophysiological and histomorphological evaluation of polyacryloylmorpholine vs polyethylene glycol modified superoxide dismutase in a rat model of ischaemia/reperfusion injury

Twenty Wistar rats were divided into two groups. Both underwent acute ischaemia followed by reperfusion of the left hind limb. The first group was a control group while the second was treated with PAcM-SOD. The survival percentage of the limb after 10 days was 30% for the first group and 70% for the second. Neither linear regression nor correlation were found between groups as far as the survival percentage of the limb after 10 days and reperfusion pmO2 data were concerned. After ten days the histomorphological analysis was significant regarding the fibre diameter and the percentage of central located nuclei in the specimens of PAcM-SOD treated limbs compared to normal limbs, but not when compared to the muscular fibres of the control group. Comparing these results with others obtained with native SOD and monomethoxypoly (ethylene glycol) modified SOD (mPEG-SOD) used in the same experimental model, we can conclude that the clinical and morphological results were better using mPEG-SOD, and that PAcM-SOD does have a protective effect on ischaemic muscle damage, although it is not as effective as mPEG-SOD in preventing ischaemia/reperfusion injury.

Oxidative stress augments chemoreflex sensitivity in rats exposed to chronic intermittent hypoxia

Chronic exposure to intermittent hypoxia (CIH) elicits plasticity of the carotid sinus and phrenic nerves via reactive oxygen species (ROS). To determine whether CIH-induced alterations in ventilation, metabolism, and heart rate are also dependent on ROS, we measured responses to acute hypoxia in conscious rats after 14 and 21 d of either CIH or normoxia (NORM), with or without concomitant administration of allopurinol (xanthine oxidase inhibitor), combined allopurinol plus losartan (angiotensin II type 1 receptor antagonist), or apocynin (NADPH oxidase inhibitor). Carotid body nitrotyrosine production was measured by immunohistochemistry. CIH produced an increase in the ventilatory response to acute hypoxia that was virtually eliminated by all three pharmacologic interventions. CIH caused a robust increase in carotid body nitrotyrosine production that was greatly attenuated by allopurinol plus losartan and by apocynin but unaffected by allopurinol. CIH caused a decrease in metabolic rate and a reduction in hypoxic bradycardia. Both of these effects were prevented by allopurinol, allopurinol plus losartan, and apocynin.

Simulating obstructive sleep apnea patients' oxygenation characteristics into a mouse model of cyclical intermittent hypoxia

Mouse models of cyclical intermittent hypoxia (CIH) are used to study the consequences of both hypoxia and oxidative stress in obstructive sleep apnea (OSA). Whether or not a mouse model of CIH that simulates OSA patients' oxygenation characteristics would translate into improved patient care remains unanswered. First we identified oxygenation characteristics using the desaturation and resaturation time in 47 OSA subjects from the Molecular Signatures of Obstructive Sleep Apnea Cohort (MSOSA). We observe that a cycle of intermittent hypoxia is not sinusoidal; specifically, desaturation time increases in an almost linear relationship to the degree of hypoxia (nadir), whereas resaturation time is somewhat constant (∼15 s), irrespective of the nadir. Second, we modified the Hycon mouse model of CIH to accommodate a 15-s resaturation time. Using this modified CIH model, we explored whether a short resaturation schedule (15 s), which includes the characteristics of OSA patients, had a different effect on levels of oxidative stress (i.e., urinary 8,12-iso-iPF2α-VI levels) compared with sham and a long resaturation schedule (90 s), a schedule that is not uncommon in rodent models of CIH. Results suggest that shorter resaturation time may result in a higher level of 8,12-iso-iPF2α-VI compared with long resaturation or sham conditions. Therefore, simulating the rodent model of CIH to reflect this and other OSA patients' oxygenation characteristics may be worthy of consideration to better understand the effects of hypoxia, oxidative stress, and their interactions.

Ophiopogonin D prevents H2O2-induced injury in primary human umbilical vein endothelial cells

AIM OF THE STUDY

Vessel endothelium injury caused by reactive oxygen species (ROS) including H(2)O(2) plays a critical role in the pathogenesis of cardiovascular disorders. Therefore, drug targeting ROS elimination has highly clinical values in cardiovascular therapy. The plant of Radix Ophiopogon japonicus is a traditional Chinese herbal medicine that has been commonly used for prevention and treatment of cardiovascular diseases for a long history. However, the effective component mediating its beneficial effects remains unknown. In the present study, we investigated the action of Ophiopogonin D (OP-D), one of the most bioactive components of Radix Ophiopogon japonicus, in an endothelial injury model induced by H(2)O(2).

MATERIALS AND METHODS

Primarily cultured human umbilical vein endothelial cells (HUVECs) were pretreated with increased doses of OP-D overnight and then challenged with H(2)O(2). The protective effects of OP-D against H(2)O(2) were evaluated.

RESULTS

We found that OP-D inhibited mRNA levels of antioxidant, inflammatory and apoptotic genes in a dose-dependent manner in HUVECs. H(2)O(2)-induced lipid peroxidation and protein carbonylation were reduced by OP-D pretreatment. Mitochondrial ROS generation and cell apoptosis were also attenuated in OP-D pretreated cells. In addition, OP-D restored cellular total antioxidative capacity and inhibited the release of inflammatory cytokines. Furthermore, OP-D suppressed the enzymatic activity of catalase, HO-1, and caspases. Finally, OP-D blocked activation of NF-kappaB and ERK signaling cascades.

CONCLUSION

Our findings provide the first evidence that OP-D plays a protective role as an effective antioxidant in H(2)O(2)-induced endothelial injury. Ophiopogonin D can be therefore developed as a novel drug for the therapy of cardiovascular disorders.

Vitamin C: update on physiology and pharmacology

Although ascorbic acid is an important water-soluble antioxidant and enzyme cofactor in plants and animals, humans and some other species do not synthesize ascorbate due to the lack of the enzyme catalyzing the final step of the biosynthetic pathway, and for them it has become a vitamin. This review focuses on the role of ascorbate in various hydroxylation reactions and in the redox homeostasis of subcellular compartments including mitochondria and endoplasmic reticulum. Recently discovered functions of ascorbate in nucleic acid and histone dealkylation and proteoglycan deglycanation are also summarized. These new findings might delineate a role for ascorbate in the modulation of both pro- and anti-carcinogenic mechanisms. Recent advances and perspectives in therapeutic applications are also reviewed. On the basis of new and earlier observations, the advantages of the lost ability to synthesize ascorbate are pondered. The increasing knowledge of the functions of ascorbate and of its molecular sites of action can mechanistically substantiate a place for ascorbate in the treatment of various diseases.

Salvianolic acid B inhibits hydrogen peroxide-induced endothelial cell apoptosis through regulating PI3K/Akt signaling

Background

Salvianolic acid B (Sal B) is one of the most bioactive components of Salvia miltiorrhiza, a traditional Chinese herbal medicine that has been commonly used for prevention and treatment of cerebrovascular disorders. However, the mechanism responsible for such protective effects remains largely unknown. It has been considered that cerebral endothelium apoptosis caused by reactive oxygen species including hydrogen peroxide (H₂O₂) is implicated in the pathogenesis of cerebrovascular disorders.

Methodology and Principal Findings

By examining the effect of Sal B on H₂O₂-induced apoptosis in rat cerebral microvascular endothelial cells (rCMECs), we found that Sal B pretreatment significantly attenuated H₂O₂-induced apoptosis in rCMECs. We next examined the signaling cascade(s) involved in Sal B-mediated anti-apoptotic effects. We showed that H₂O₂ induces rCMECs apoptosis mainly through the PI3K/ERK pathway, since a PI3K inhibitor (LY294002) blocked ERK activation caused by H₂O₂ and a specific inhibitor of MEK (U0126) protected cells from apoptosis. On the other hand, blockage of the PI3K/Akt pathway abrogated the protective effect conferred by Sal B and potentated H₂O₂-induced apoptosis, suggesting that Sal B prevents H₂O₂-induced apoptosis predominantly through the PI3K/Akt (upstream of ERK) pathway.

Significance

Our findings provide the first evidence that H₂O₂ induces rCMECs apoptosis via the PI3K/MEK/ERK pathway and that Sal B protects rCMECs against H₂O₂-induced apoptosis through the PI3K/Akt/Raf/MEK/ERK pathway.

In vitro effects of reactive oxygen metabolites, with and without flunixin meglumine, on equine colonic mucosa

OBJECTIVE

To determine effects of reactive oxygen metabolites (ROMs), with and without flunixin meglumine, on equine right ventral colon (RVC) in vitro.

ANIMALS

18 healthy horses and ponies.

PROCEDURES

In 3 groups of 6 animals each, short-circuit current and conductance were measured in RVC mucosa in Ussing chambers. The 3 groups received physiologic saline (0.9% NaCl) solution, IV, 10 minutes before euthanasia and tissue incubation in Krebs-Ringer-bicarbonate (KRB) solution; flunixin meglumine (1.1 mg/kg, IV) 10 minutes before euthanasia and tissue incubation in KRB solution; or physiologic saline solution, IV, 10 minutes before euthanasia and incubation in KRB solution with 2.7 x 10(5)M flunixin meglumine. Incubation conditions included control (no addition) and ROM systems, including addition of 1 mM xanthine and 80 mU of xanthine oxidase (to produce the superoxide radical), 1 mM H(2)O(2), and 1 mM H(2)O(2) and 0.5 mM ferrous sulfate (to produce the hydroxyl radical).

RESULTS

All ROMs that were added or generated significantly increased the short-circuit current except in tissues coincubated with flunixin meglumine, and they induced mild epithelial vacuolation and apoptosis, but did not disrupt the epithelium nor change conductance, lactate dehydrogenase release, or [(3)H]mannitol flux.

CONCLUSIONS AND CLINICAL RELEVANCE

Responses to ROMs could be attributed to increased chloride secretion and inhibited neutral NaCl absorption in equine RVC, possibly by stimulating prostaglandin production. The ROMs examined under conditions of this study could play a role in prostaglandin-mediated colonic secretion in horses with enterocolitis without causing direct mucosal injury.

Coronary Artery Bypass Grafting Ameliorates the Decreased Plasma Adiponectin Level in Atherosclerotic Patients

Adiponectin functions as an anti-inflammatory and anti-atherogenic factor, and the decreased plasma adiponectin is a risk factor for coronary disease. The aim of this study was to determine the changes in plasma levels of adiponectin, a potential parameter for atherosclerosis, in patients underwent surgical revascularization. We included forty patients with atherosclerosis (age, 58 +/- 9 years; body mass index [BMI] 26.93 +/- 2.3 kg/m(2)) undergoing coronary artery bypass grafting (CABG). Control group consisted of 40 healthy volunteers, matched for age, gender and BMI (age, 56 +/- 6 years; BMI, 26.78 +/- 2.3 kg/m(2)). We measured various parameters, including high sensitive C-reactive protein (hsCRP), homeostasis model assessment-insulin resistance (HOMA-IR) indexes, and adiponectin. The baseline profile of the patients before CABG showed higher levels of serum hsCRP (13.15 +/- 2.40 mg/l vs 3.97 +/- 1.07 mg/l) and HOMA-IR (1.86 +/- 0.30 vs 1.26 +/- 0.33) and lower plasma adiponectin levels (7.02 +/- 2.01 microg/ml vs 25.46 +/- 3.9 microg/ml), compared to controls (p < 0.001 for each parameter). Plasma adiponectin level was increased one month after CABG from the baseline level to 8.67 +/- 2.05 microg/ml(p < 0.001), although the level was still lower than the control value. Thus, postoperative adiponectin level might be helpful for evaluating the progression of atherosclerosis. Moreover, CABG significantly decreased hsCRP to 7.25 +/- 1.89 mg/l and HOMA-IR to 1.59 +/- 0.33, although these levels were higher than the controls. These results suggest that CABG decreases the cardiac risk factors in atherosclerotic patients.

ERK promotes hydrogen peroxide-induced apoptosis through caspase-3 activation and inhibition of Akt in renal epithelial cells

Reactive oxygen species, including hydrogen peroxide (H(2)O(2)), are generated during ischemia-reperfusion and are critically involved in acute renal failure. The present studies examined the role of the extracellular signal-regulated kinase (ERK) pathway in H(2)O(2)-induced renal proximal tubular cells (RPTC) apoptosis. Exposure of RPTC to 1 mM H(2)O(2) resulted in apoptosis and activation of ERK1/2 and Akt. Pretreatment with the specific MEK inhibitors, U0126 and PD98059, or adenoviral infection with a construct that encodes a negative mutant of MEK1, protected cells against H(2)O(2)-induced apoptosis. In contrast, expression of constitutively active MEK1 enhanced H(2)O(2)-induced apoptosis. H(2)O(2) induced activation of caspase-3 and phosphorylation of histone H2B at serine 14, a posttranslational modification required for nuclear condensation, which also were blocked by ERK1/2 inhibition. Furthermore, blockade of ERK1/2 resulted in an increase in Akt phosphorylation and blockade of Akt potentiated apoptosis and diminished the protective effect conferred by ERK inhibition in H(2)O(2)-treated cells. Although Z-DEVD-FMK, a caspase-3 inhibitor, was able to inhibit histone H2B phosphorylation and apoptosis, it did not affect ERK1/2 phosphorylation. We suggest that ERK elicits apoptosis in epithelial cells by activating caspase-3 and inhibiting Akt pathways and elicits nuclear condensation through caspase-3 and histone H2B phosophorylation during oxidant injury.

Abrupt reoxygenation following hypoxia reduces electrical coupling between endothelial cells of wild-type but not connexin40 null mice in oxidant- and PKA-dependent manner

Although electrical coupling along the arteriolar endothelium is central in arteriolar conducted response and in control of vascular resistance, little is known about the pathophysiological effect of hypoxia and reoxygenation (H/R) on this coupling. We examined this effect in a monolayer of cultured microvascular endothelial cells (ECs) derived from wild-type (WT) or connexin (Cx)40-/- mice (Cx40 is a key gap junction protein in ECs). To assess electrical coupling, we used a current injection technique and Bessel function model to compute the monolayer intercellular resistance. Hypoxia (0.1% O2, 1 h) followed by abrupt reoxygenation (5-90 min) reduced coupling (i.e., increased resistance) in WT but not in Cx40-/- monolayer. H/R increased superoxide production and reduced protein kinase A (PKA) activity in both monolayers. Activation of PKA by 8-bromo-cAMP prevented the reduction in coupling. Preloading of the WT monolayer with the antioxidant ascorbate prevented reductions in both PKA activity and cell coupling. Inhibition of PKA with 6-22 amide during normoxia mimicked the reduction in coupling. Finally, hypoxia followed by slow reoxygenation caused no change in superoxide level, PKA activity, or coupling. Using intravital microscopy, we assessed the physiological relevance of these findings in terms of KCl-induced conducted vasoconstriction in arterioles of WT mouse cremaster muscle in vivo. Ischemia (1 h) followed by abrupt reperfusion (15-30 min) reduced conduction. 8-bromo-cAMP prevented this reduction, while 6-22 amide mimicked this reduction in control nonischemic arterioles. We propose that abrupt reoxygenation reduces interendothelial electrical coupling via oxidant- and PKA-dependent signaling that targets Cx40. We suggest that this mechanism contributes to compromised arteriolar function after H/R.

Hypoxia/reoxygenation reduces microvascular endothelial cell coupling by a tyrosine and MAP kinase dependent pathway

Communication of electrical signals along the microvascular endothelium plays a key role in integrating microvascular function required for local regulation of blood flow. The aim of the present study was to examine the effect of a short-term hypoxia (0.1% O(2), 1 h) plus reoxygenation (H/R) on electrical coupling in cultured monolayers of microvascular endothelial cells (rat skeletal muscle origin). To assess coupling, we used a current injection technique and a Bessel function model to compute the intercellular resistance (an inverse measure of coupling) and cell membrane resistivity (a measure of resistance to current leakage across the cell membrane). H/R resulted in rapid (within 4 min after reoxygenation) and sustained (up to 100 min) reduction in intercellular coupling, but it did not alter membrane resistivity. H/R did not alter gap junction protein connexin 43 expression nor its tyrosine phosphorylation as determined by immunoblot and immunoprecipitation analyses. Inhibition of mitochondrial respiration (1 mM NaCN) did not mimic the effect of H/R. However, pre-treatment of monolayers with tyrphostin A48 (1.5 microM), PP2 (10 nM) (tyrosine kinase inhibitors), U 0126 (20 microM), and PD 98059 (5 microM) (MEK1/2 inhibitors) inhibited the H/R-induced reduction in coupling. These results indicate that endothelial cell coupling was reduced quickly after reoxygenation, via activation of a tyrosine and MAP kinase dependent pathway. We predict that a short-term H/R can rapidly compromise microvascular function in terms of reduced cellular communication along the vascular wall.

Hypoxia-reoxygenation-induced mitochondrial damage and apoptosis in human endothelial cells are inhibited by vitamin C

Hypoxia and hypoxia-reperfusion (H-R) play important roles in human pathophysiology because they occur in clinical conditions such as circulatory shock, myocardial ischemia, stroke, and organ transplantation. Reintroduction of oxygen to hypoxic cells during reperfusion causes an increase in generation of reactive oxygen species (ROS), which can alter cell signaling, and cause damage to lipids, proteins, and DNA leading to ischemia-reperfusion injury. Since vitamin C is a potent antioxidant and quenches ROS, we investigated the role of intracellular ascorbic acid (iAA) in endothelial cells undergoing hypoxia-reperfusion. Intracellular AA protected human endothelial cells from H-R-induced apoptosis. Intracellular AA also prevents loss of mitochondrial membrane potential and the release of cytochrome C and activation of caspase-9 and caspase-3 during H-R. Additionally, inhibition of caspase-9 activation prevented H-R-induced apoptosis, suggesting a mitochondrial site of initiation of apoptosis. We found that H-R induced an increase in ROS in endothelial cells that was abrogated in the presence of iAA. Our results indicate that vitamin C prevents hypoxia and H-R-induced damage to human endothelium.

The evaluation of the protective action of antioxidants on small intestine of rabbits experimentally injured by ischemia and reperfusion

PURPOSE

The aim of this study was to ascertain the possibility of diminishing ischemia-reperfusion injury by intravenous application of the chosen antioxidants: vitamin C, mannitol, and N-acetylcysteine.

METHODS

The study was performed on New Zealand Red male rabbits, which were divided into 6 groups of 8. In group 1, 5 segments of the small intestine were taken for histopathologic examination (normal intestine). In group 2, segments of the small intestine were taken for histopathologic examination after 3 hours of closure of the superior mesenteric artery (ischemic intestine). In group 3, after 3 hours of closure of the superior mesenteric artery, 1 hour of reperfusion took place. In this group, blood flow in the superior mesenteric artery was measured within the first 30 minutes, and segments of the small intestine were taken for histopathologic examination after 60 minutes of the reperfusion. In groups 4, 5, and 6 the procedure was similar to that in group 3, but additionally the rabbits were given antioxidants intravenously: in group 4, vitamin C, 250 mg/kg; in group 5, 20% mannitol, 3 mL/kg; and in group 6, N-acetylcysteine, 100 mg/kg.

RESULTS

All the chosen antioxidants had a beneficial influence on the blood flow in the superior mesenteric artery. The blood flow in the groups with antioxidants after 30 minutes of the reperfusion was 53% to 57% of initial values compared with 27% of initial values in group 3. In histopathologic evaluation, protective action of the antioxidants was seen in the groups with vitamin C and mannitol.

CONCLUSIONS

Application of the chosen antioxidants reduces injury of the rabbit small intestine caused by reperfusion after 3 hours of closure of the superior mesenteric artery.

Cytoprotection against ischemia-induced DNA cleavages and cell injuries in the rat liver by pro-vitamin C via hydrolytic conversion into ascorbate

To search a regimen for prevention of post-ischemic reperfusional (I/R) injuries, I/R in the liver was induced by 30-min clamping and subsequent unfastening of the portal vein of a rat, which underwent previous i.v. administration with ascorbic acid (Asc) of 1 mg/kg or the autooxidation-resistant pro-vitamin C, 2-O-alpha-D-glucosylated Asc (Asc2G) or 2-O-phosphorylated Asc (Asc2P) of 1 mg Asc equivalent/kg from the viewpoint of utilization of antioxidants that can promptly scavenge I/R-derived reactive oxygen species. The administration with Asc, Asc2P or Asc2G prevented some features of hepatic I/R injuries such as release of hepatic marker enzymes GOT and GPT into the blood vessel, cellular degenerative symptoms including vacuolation and cell fragmentation, and nuclear DNA strand cleavage as detected by TUNEL staining. The preventive effects on I/R injuries were in the order: Asc2G > Asc2P >> Asc. This order of preventive degrees of three anti-oxidants is partly attributable to proper efficiency of conversion to vitamin C and stability in blood stream; Asc2P was moderately converted to a free monoanion form of Asc in human serum, but, in rat serum, so efficiently converted to Asc as to undergo the resultant oxidative decomposition before reaching the liver, whereas Asc2G underwent scarce conversion to Asc in human serum but moderate conversion in rat serum, suggesting that Asc2P might be less cytoprotective against I/R injury than Asc2G in the rat liver in a way different from the human liver. In contrast Asc was so susceptible to autooxidation as to be rapidly decomposed in either rat or human serum. The concentrations of ascorbyl radicals (AscR) in serum were unchanged during I/R for sham-operated rats, but appreciably diminished time-dependently for I/R-operated rats as shown by ESR spectra. A marked increase in serum AscR occurred in rats receiving Asc, Asc2G or Asc2P, but it was time-dependently restored down to the pre-ischemic level of AscR in I/R-operated rats more rapidly than in sham-operated rats. Thus, hepatic I/R injuries were shown to be prevented more markedly by Asc2G or Asc2P than by Asc, which is attributable to efficiencies of both vitamin C conversion and subsequent AscR retention.

Effects of recombinant human superoxide dismutase during reoxygenation with 21% or 100% oxygen after cerebral asphyxia in newborn piglets

OBJECTIVE

Superoxide radicals (O2-) are generated during reoxygenation following asphyxia, possibly more when higher concentrations of O2 are used during resuscitation. Superoxide dismutase (SOD) is an antioxidant enzyme, which scavenges O2-. We tested the hypothesis that a single intravenous dose of recombinant human Cu,Zn SOD (rhSOD) could influence microcirculation and biochemical markers of asphyxia in piglets reoxygenated with 21% or 100% O2 after combined cerebral hypoxemia-ischemia-hypercapnia.

METHODS

Anesthetized newborn piglets were randomized to asphyxia (n = 40) or control (n = 3). Asphyxia was induced by ventilation with 8% O2, adding CO2, and temporary occlusion of both common carotid arteries. After 20 min, 16 piglets received rhSOD 5 mg/kg intravenously and reoxygenation with 21% O2 (rhSOD, 21%; n = 8) or 100% O2 (rhSOD, 100%; n = 8), and 24 piglets received saline and reoxygenation with 21% O2 (21%, n = 13) or 100% O2 (100%, n = 11). The cortical microcirculation was assessed by laser Doppler flowmetry, and glutamate in the striatum and hypoxanthine in the cortex were measured by in vivo microdialysis.

RESULTS AND CONCLUSION

rhSOD peaked in plasma after 5 min. No rhSOD was detected in brain tissue. There were no significant differences between rhSOD and non-rhSOD groups in any measured variable.

Bcl-2 prevents hypoxia/reoxygenation-induced cell death through suppressed generation of reactive oxygen species and upregulation of Bcl-2 proteins

The function of bcl-2 in preventing cell death is well known, but the mechanisms whereby bcl-2 functions are not well characterized. One mechanism whereby bcl-2 is thought to function is by alleviating the effects of oxidative stress upon the cell. To examine whether Bcl-2 can protect cells against oxidative injury resulting from post-hypoxic reoxygenation (H/R), we subjected rat fibroblasts Rat-1 and their bcl-2 transfectants b5 to hypoxia (5% CO2, 95% N2) followed by reoxygenation (5% CO2, 95% air). The bcl-2 transfectants exhibited the cell viability superior to that of their parent non-transfectants upon treatment with reoxygenation after 24-, 48-, or 72-h hypoxia, but not upon normoxic serum-deprivation or upon serum-supplied hypoxic treatment alone. Thus bcl-2 transfection can prevent cell death of some types, which occurred during H/R but yet not appreciably until termination of hypoxia. The time-sequential events of H/R-induced cell death were shown to be executed via (1) reactive oxygen species (ROS) production at 1-12 h after H/R, (2) activation of caspases-1 and -3, at 1-3 h and 3-6 h after H/R, respectively, and (3) loss of mitochondrial membrane potential (DeltaPsi) at 3-12 h after H/R. These cell death-associated events were prevented entirely except caspase-1 activation by bcl-2 transfection, and were preceded by Bcl-2 upregulation which was executed as early as at 0-1 h after H/R for the bcl-2 transfectants but not their non-transfected counterpart cells. Thus upregulation of Bcl-2 proteins may play a role in prevention of H/R-induced diminishment of cell viability, but may be executed not yet during hypoxia itself and be actually operated as promptly as ready to go immediately after beginning of H/R, resulting in cytoprotection through blockage of either ROS generation, caspase-3 activation, or DeltaPsi decline.

Cytoprotection by pro-vitamin C against ischemic injuries in perfused rat heart together with differential activation of MAP kinase family

The cardiac muscle cells are known to be killed by ischemia-reperfusion (I/R) treatment that produce reactive oxygen species (ROS). We analyzed the function of the autooxidation-resistant pro-vitamin C, 2-O-alpha-D-glucosylated derivative (Asc2G) of ascorbic acid (Asc), in protecting against I/R injury of the heart in rat. The serum release of the intracellular enzyme CPK due to I/R injury decreased upon injection with Asc2G. Out of the mitogen-activated protein (MAP) kinase family members, MAP kinase and JNK underwent the down-regulation in contrast to up-regulation of p38 compared with the I/R-treated control in the absence of Asc2G. These data suggest important roles for differential activation of the MAP kinase family in cytoprotection against I/R injury by Asc2G.

Protective effect of antioxidants on pulmonary endothelial function after cardiopulmonary bypass

OBJECTIVES

Pulmonary endothelium-dependent vasodilation is impaired after cardiopulmonary bypass. One explanation might be the generation of reactive oxygen species during the period without flow in the pulmonary artery. The aim of the current study was to investigate if treatment with antioxidants could improve pulmonary endothelial function after cardiopulmonary bypass and influence the blood oxidative status.

DESIGN

A prospective, randomized, double-blind study.

SETTING

The operating room, intensive care unit, and the biochemistry laboratory in University Hospitals.

PARTICIPANTS

Patients scheduled for cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

Treatment with vitamin E, vitamin C, allopurinol, and acetylcysteine (n = 12) or placebo (n = 10).

MEASUREMENTS AND MAIN RESULTS

The pulmonary reactivity to an infusion of acetylcholine and markers of oxidative stress in blood were measured before and after cardiopulmonary bypass. Sixteen control patients received saline instead of acetylcholine. Before surgery the pulmonary vascular resistance index decreased during infusion of acetylcholine by 24% and 21% in the treatment and placebo groups. After surgery the decrease was 20% and 8%, respectively, (p = 0.422 and p = 0.026) compared with preoperative response. Pulmonary vasodilation induced by acetylcholine was better maintained in the group treated with antioxidants (p = 0.048). In the treatment group, the blood concentrations of early intermediates of lipid peroxidation were higher, but not that of the end products. Glutathione and oxidized glutathione increased after cardiopulmonary bypass in the treatment group.

CONCLUSION

The better maintained endothelium-dependent vasodilation after cardiopulmonary bypass in the treatment group indicated that antioxidant therapy reduced endothelial dysfunction.

Reactive oxygen species mediate endotoxin-induced human dermal endothelial NF-kappaB activation

BACKGROUND

Microvascular endothelial cell "activation" by endotoxin is an early and critical phenomenon underlying organ dysfunction related to sepsis. Dermal endothelial cells contribute to many of the manifestations of septic shock, such as cutaneous interstitial edema and loss of peripheral vasomotor regulation. Human dermal endothelial cell activation by endotoxin (lipopolysaccharide [LPS]) is characterized by the generation of reactive oxygen species (ROS) that enhance nuclear translocation of the transcription factor kappa-B (NF-kappaB).

METHODS

We tested our hypothesis by stimulating human dermal microvascular endothelial cells (HMEC.1) with endotoxin and assaying for endothelial generation of ROS and nuclear translocation of NF-kappaB subunits. HMEC.1 cultures were treated individually with LPS, hydrogen peroxide, or xanthine, xanthine oxidase, and ferrous sulfate (xanthine/XO/Fe(2+)). Nuclear proteins were isolated and consensus sequence binding was assessed by electrophoretic mobility shift assay (EMSA). 2',7'-Dichlorofluorescin diacetate and confocal microscopy were used to examine ROS production in LPS-stimulated HMEC.1.

RESULTS

Nuclear translocation of the p65/p50 NF-kappaB heterodimer was detectable 30 min after stimulation with LPS alone or the xanthine/XO/Fe(2+) combination, but not with hydrogen peroxide. Antioxidant N-acetylcysteine (NAC) inhibited LPS-stimulated ROS production in HMEC.1. Antioxidant prior to or simultaneously with LPS exposure, but not following LPS, also prevented NF-kappaB activation. NAC was ineffective at inhibiting NF-kappaB translocation at increased LPS concentrations.

CONCLUSIONS

Dermal endothelial cells, a microvascular cell type that may contribute to the systemic response to blood-borne endotoxemia, generate ROS in the absence of other inflammatory cells. These LPS-activated endothelial cells, in turn, rapidly translocate transcription factor NF-kappaB to cell nuclei, a process regulated in part by intracellular ROS.

Cardiac surgery: myocardial energy balance, antioxidant status and endothelial function after ischemia-reperfusion

Myocardial and endothelial damage is still a widely debated problem during the ischemia-reperfusion sequence in heart surgery. We evaluated myocardial purine metabolites, antioxidant defense mechanisms, oxidative status and endothelial dysfunction markers in 14 patients undergoing coronary artery by-pass graft (CABG). Heart biopsies were taken before aortic cross-clamping (t1), before clamp removal (t2) and 30 min after reperfusion (t3); perchloric extracts of the tissue were analyzed for glutathione, NAD, nucleotide nucleoside and base content by capillary electrophoresis (CE). In plasma samples from the coronary sinus we evaluated: nitrate and nitrite concentrations by CE, plasma glutathione peroxidase (plGPx) by ELISA, endothelin-1 (ET-1) by RIA and reactive oxygen metabolites (ROM) by colorimetric assay. During the ischemic period (t2) we observed a reduction in cellular NAD and GSH levels, as well as nitrate, nitrite and plGPx. ATP and GTP levels decreased and their catabolic products AMP, GMP, IMP, adenosine, inosine and hypoxanthine accumulated. The energy charge, ATP/ADP ratio, and nucleotide/(nucleoside + base) ratios decreased. At t3, levels of plasma ET-1 increased and monophosphate nucleotides tended to return to basal values. The energy charge did not increase but the nucleotide/(nucleoside + nucleobase) ratio recovered to some extent. Levels of nitrates plus nitrites continued to decrease. No significant variation in ROM levels was observed. Our data indicate that oxidative stress and endothelial damage are major events during CABG, overwhelming the scavenging capacity of the myocyte and preventing restoration of the normal energy balance for 30 min after reperfusion. The AMP deaminase pathway leading to IMP production is active during ischemia and adenosine is not the main compound derived from ATP break-down in the human heart. The possible role of extracorporeal circulation is also discussed.

Ischemia-reperfusion injury of retinal endothelium by cyclooxygenase- and xanthine oxidase-derived superoxide

The formation of reactive oxygen species (ROS) may be important in the pathogenesis of microvascular dysfunction and injury in ischemic retinopathies. The authors hypothesized that retinal endothelial cells can generate injurious levels of superoxide radical in response to ischemia/reperfusion, that endothelial xanthine oxidase and cyclooxygenase are important enzymatic sources of superoxide radical under these conditions, and that superoxide scavengers and inhibitors of these enzymes can protect endothelium from ischemic injury. The authors used confluent cultures of mouse retinal endothelial cells (MREC) subjected to exogenously generated superoxide or simulated ischemia-reperfusion to test these hypotheses. Cell injury was assessed biochemically by lactate dehydrogenase release into the culture medium. MREC were injured in a duration-dependent fashion by exposure to the superoxide-generating mix of hypoxanthine and xanthine oxidase. Increasing periods of oxygen and glucose deprivation (OGD) for 5-9 hr followed by replenishment of substrates for 2 hr led to progressive increases in endothelial cell injury; a significant proportion of the injury occurred during the period of substrate replenishment. Significant MREC protection was achieved by the superoxide scavengers SOD (1000 U ml(-1)) and a carboxylic acid derivative of carboxyfullerene (10 microM), the xanthine oxidase inhibitors oxypurinol (100 microM) and diphenyleneiodonium (DPI) (100 n M), and the cyclooxygenase inhibitors indomethacin (300 microM) and ibuprofen (300 microM). It is concluded that MREC are vulnerable to auto-oxidative injury by superoxide radical generated following a period of OGD. Both xanthine oxidase- and cyclooxygenase-dependent pathways are important enzymatic sources of superoxide formation in this setting. These enzymes and the ROS produced from their activity may be viable therapeutic targets to reduce microvascular dysfunction and injury in ischemic retinopathies.

Ebselen suppresses late airway responses and airway inflammation in guinea pigs

Although ebselen, a seleno-organic compound, inhibits inflammation in various animal models, its efficacy as an anti-asthma drug remains to be clarified. In this study, we investigated the inhibitory effect of ebselen on a guinea pig asthma model. Ebselen was orally administered at dosages of 1-20 mg/kg 2 h before an ovalbumin (OA) challenge, and then airway responses, airway inflammation, the generation of superoxide, H(2)O(2), and nitrotyrosine, and the induction of inducible nitric oxide synthase (iNOS) were evaluated. Sensitized animals challenged with OA aerosol showed dual airflow limitations, i.e., immediate and late airway responses (IAR and LAR). Ebselen significantly inhibited LAR at dosages greater than 10 mg/kg, but did not inhibit IAR at any dosage. Bronchoalveolar lavage (BAL) examination showed that airway inflammation was significantly suppressed by ebselen at 10 mg/kg. The generation of superoxide and H(2)O(2) occurred on endothelial cells of LAR bronchi, and was inhibited by 10 mg/kg of ebselen. Superoxide generation was inhibited by diphenyleneiodonium chloride (DPI), a NAD(P)H oxidase inhibitor, but not by allopurinol, a xanthine oxidase inhibitor. Immunoreactivities for iNOS and nitrotyrosine were also observed on endothelial cells of LAR bronchi and were abolished in ebselen-treated animals. The present findings suggest that ebselen can be applied as a new therapeutic agent for asthma. The possible mechanisms by which ebselen inhibits LAR likely involve suppression of oxidant formation and iNOS induction in endothelial cells.

Changes of endothelial nitric oxide synthase level and activity during endothelial cell proliferation

The goal of this study was to investigate the effect of endothelial cell proliferation on the expression and activity of endothelial nitric oxide synthase (eNOS). Bovine atrial endothelial cells (BAtEC) were studied between day 1 and 6 after seeding. During this period the number of cells in S-phase decreased progressively, while cell number and protein content increased, reaching a maximum at confluence (day 4). Expression of eNOS (determined by ELISA) and eNOS activity (determined by L-arginine to L-citrulline conversion) increased with culture duration with a maximum at confluence. Nitric oxide (*NO) release from BAtEC was determined after stimulation with Ca2+ ionophore A23187 (10 microM, 30 min) by .NO chemiluminescence in the absence of a chemical reduction system. Total *NO release (measured in the presence of 100 U/ml superoxide dismutase) did not change with state of cell proliferation/growth, whereas "bioavailable" *NO (measured in the absence of superoxide dismutase) was low in highly proliferating BAtEC. Relative eNOS activity (.NO and L-citrulline production per eNOS protein) was highest in proliferating BAtEC. The novel finding of this study is that the specific eNOS activity is upregulated in proliferating BAtEC and downregulated in quiescent BAtEC. The amount of "bioavailable" *NO is determined by eNOS activity and *NO inactivation (probably by superoxide), both high in proliferating BAtEC.

Thermal injury alters endothelial vasoconstrictor and vasodilator response to endotoxin

BACKGROUND

The unique location of the endothelium makes it vulnerable to injury from circulating factors created at remote wounds. In this study, we examined the effect of a sequential burn and lipopolysaccharide (LPS) challenge on endothelial function in vitro.

METHODS

Human umbilical vein endothelial cells treated with 20% human serum isolated from burn patients (>40% total burn surface area) at 2 and 24 hours postinjury. Cultures were subsequently treated with Escherichia coli LPS:0111:B4 (0.10-100ng/mL). Endothelin-1 (ET-1), 6-ketoPGF1a, and NO2/NO3 were detected by using specific enzyme immunoassays.

RESULTS

Burn serum did not alter endothelial ET-1, PGI2, or NO secretion compared with Control serum. LPS significantly enhanced 6-ketoPGF1a (54,242+/-14,466 pg/10(6) cells) and NO2/ NO3 (723+/-210 microM) secretion, but not ET-1 compared with Control serum alone (3,878+/-963 and 219+/-110). Burn serum pretreatment significantly enhanced the ET-1 response to LPS (303+/-36 pg/10(6) cells vs. 193+/-47). The 6-ketoPGF1a (16,509+/-3,785) and NO2/NO3 (354+/-98) responses to Burn/LPS were significantly diminished compared with Control/LPS. Although this level of 6-ketoPGF1a was elevated compared with Control alone (7,518+/-2,299), NO2/NO3 was unchanged (significance at p < 0.05).

CONCLUSION

Thermal injury may prime remote endothelium and alter the response to a septic focus with an enhanced vasoconstrictor (ET-1) and diminished vasodilator (PGI2/NO) response, a situation that may contribute to postburn distal organ injury.

Immunohistochemical detection of oxidative DNA damage induced by ischemia-reperfusion insults in gerbil hippocampus in vivo

There is much evidence to suggest that ischemic injury occurs during the reperfusion phase of ischemia-reperfusion insults, and that the injury may be due to reactive-oxygen-species (ROS)-mediated oxidative events, including lipid peroxidation and DNA damage. However, oxidative DNA damage has until now not been examined in situ. In the present study, we report for the first time observation of cell type- and region-specific oxidative DNA damages in 5 min transient ischemic model by immunohistochemical methods, using monoclonal antibody against 8-hydroxy-2'-deoxyguanosine (8-OHdG), an oxidative DNA product. The cell types containing 8-OHdG immunoreactivity were neurons, glia and endothelial cells in the hippocampus. The 8-OHdG immunoreactivity was present in the nucleus but not the cytoplasm of these cells. The level of 8-OHdG in CA1 increased significantly (P<0.05) at the end of 30 min after ischemia, but there was no increase within CA2 and CA3 areas. The 8-OHdG levels in the hippocampus increased significantly (about fourfold) after 3 h of reperfusion and remained significantly (P<0.01) elevated for at least 12 h. At 4 days after ischemia, 8-OHdG levels in the CA2 and CA3 areas decreased to levels of the sham without neuronal loss, while disappearance of 8-OHdG immunoreactivity in the CA1 coincided with neuronal death in this area. These findings strongly suggest that ischemia-induced DNA damage evolves temporally and spatially, and that oxidative DNA damage may be involved in delayed neuronal death in the CA1 region.

Effects of glutathione depletion on oxidant-induced endothelial cell injury

Ischemia-reperfusion produces edema in vivo by disrupting endothelial cell junctional integrity. A cultured rat pulmonary artery endothelial cell (RPAEC) model was used to analyze the effects of oxidants and ischemic plasma in vitro. RPAEC cultures were treated with ischemic human plasma from transverse rectus abdominis musculocutaneous (TRAM) flaps following mastectomy or with an equal quantity of nonischemic plasma taken peripherally. Endothelial cells treated with ischemic plasma rounded and formed gaps within 5 min, then ruffled and blebbed after 10 min. Cultures treated with human nonischemic plasma had no gross morphological changes. Additionally, cultures treated with human ischemic plasma demonstrated an increase in diffusion rate of 125I-albumin across monolayers while monolayers treated with human nonischemic plasma had no increase in diffusion rate. RPAEC monolayers were treated with malic acid diethyl ester (DEM) or L-buthionine-[S, R]-sulfoximine (BSO) to decrease cellular stores of glutathione before exposure to oxidant stress. Cultures depleted of cellular glutathione stores were significantly (P < 0.05) more susceptible to 50 microM H2O2 than controls, as determined by an increase in diffusion rate of 125I-albumin across monolayers. To determine if ischemic plasma effects were mediated by oxidants, cultures were depleted of glutathione by DEM or BSO pretreatment before exposure to plasma from the ischemic hind limbs of Sprague-Dawley rats. Glutathione-depleted RPAEC monolayers were significantly (P < 0.05) and substantially (2-3 X) more susceptible to the effects of ischemic plasma than were cultures with normal glutathione levels. Glutathione depletion had no effect on cultures treated with an equal amount of nonischemic plasma from sham-operated rats. These data strongly suggest that ischemic plasma in the absence of any cellular component are able to induce an oxidant injury in endothelial cells and thereby compromise junctional integrity.

Reperfusion induces sublethal endothelial injury

BACKGROUND

Endothelial cells are pivotal in regulating thrombosis and hemostasis. In this study, we sought to characterize endothelial dysfunction and endothelial cell injury in vitro after hypoxia/reoxygenation.

MATERIALS AND METHODS

Cultured human umbilical vein endothelial cells (ECs) were exposed to 120 min of hypoxia followed by reoxygenation. The release of thrombomodulin (TM) and the production of prostaglandin I2 (PGI2) were measured. Endothelial cell injury in hypoxia/reoxygenation was measured by two assays, the Fura-2 release assay and the 51chromium (51Cr) release assay.

RESULTS

TM release from ECs during normoxic incubation was undetectable, while it was slightly increased during hypoxic incubation. After reoxygenation, the release of TM increased, and it became significantly higher at 120 min after reoxygenation compared with hypoxic incubation. The production of PGI2 significantly decreased during hypoxic incubation and further decreased within 30 min after reoxygenation, but returned to normoxic levels at 120 min after reoxygenation. In the Fura-2 release assay, a rapid and significantly greater release of Fura-2 was observed in hypoxia/reoxygenation compared with hypoxic incubation. In the 51Cr release assay which demonstrates cell death, 51Cr release did not increase in hypoxia/reoxygenation.

CONCLUSIONS

The present study suggests that 120 min of hypoxia/reoxygenation induces endothelial dysfunction of ECs but does not cause cell death.

Exercise-induced acute renal failure in a girl with renal hypouricemia

A 10-year-old Japanese girl developed acute renal failure following a 100-meter dash during physical training at school. After the run, she experienced intense pain in the loins with nausea and vomiting lasting more than 12 h. On the following morning, she was found to have mild proteinuria and acute renal failure (ARF). Serum creatinine and blood urea nitrogen were elevated, but the serum uric acid level was normal (3.1 mg/dL). With recovery of renal function over the ensuing days, hypouricemia (0.6 mg/dL) became evident in the patient. Although the pathophysiological association between renal hypouricemia and ARF is not known, oxygen free radicals have been implicated in the pathogenesis for ischemic-reperfusion ARF. Superoxide production by neutrophils stimulated by N-formyl methionine leucyl-phenylalanine was normal in the patient both before and following exercise. Pyrazinamide and probenecid tests were undertaken on both the patient and her parents, who had borderline hypouricemia, to determine their renal tubular handling of uric acid. Results showed that the patient and her mother had a subtotal reabsorption defect, while the father had defective postsecretory uric acid reabsorption.

Blood radicals: reactive nitrogen species, reactive oxygen species, transition metal ions, and the vascular system

Free radicals, such as superoxide, hydroxyl and nitric oxide, and other "reactive species", such as hydrogen peroxide, hypochlorous acid and peroxynitrite, are formed in vivo. Some of these molecules, e.g. superoxide and nitric oxide, can be physiologically useful, but they can also cause damage under certain circumstances. Excess production of reactive oxygen or nitrogen species (ROS, RNS), their production in inappropriate relative amounts (especially superoxide and NO) or deficiencies in antioxidant defences may result in pathological stress to cells and tissues. This oxidative stress can have multiple effects. It can induce defence systems, and render tissues more resistant to subsequent insult. If oxidative stress is excessive or if defence and repair responses are inadequate, cell injury can be caused by such mechanisms as oxidative damage to essential proteins, lipid peroxidation, DNA strand breakage and base modification, and rises in the concentration of intracellular "free" Ca(2+). Considerable evidence supports the view that oxidative damage involving both ROS and RNS is an important contributor to the development of atherosclerosis. Peroxynitrite (derived by reaction of superoxide with nitric oxide) and transition metal ions (perhaps released by injury to the vessel wall) may contribute to lipid peroxidation in atherosclerotic lesions.