Significant levels of oxidants are generated by isolated cardiomyocytes during ischemia prior to reperfusion

Intracellular pH regulates superoxide production by the macula densa

We hypothesized that elevated macula densa intracellular pH (pH(i)) during tubuloglomerular feedback enhances O(2)(-) production from NAD(P)H oxidase. Microdissected thick ascending limbs from rabbits with intact macula densa were cannulated and perfused with physiological saline. When luminal NaCl was switched from 10 to 80 mM, O(2)(-) production increased from 0.53 +/- 0.09 to 2.62 +/- 0.54 U/min (P < 0.01). To determine whether inhibiting the Na/H exchanger blocks O(2)(-) production, we used dimethyl amiloride (DMA) to block Na/H exchange. In the presence of DMA, O(2)(-) production induced by NaCl was blunted by 40%. To study the effect of pH(i) on O(2)(-) in intact macula densa cells, we measured O(2)(-) while pH(i) was changed by adjusting luminal pH. When the macula densa was perfused with 80 mM NaCl and the pH of the perfusate was switched to 6.8, 7.4, and 8.0, O(2)(-) production was significantly enhanced, but not at 10 mM NaCl. To ascertain the source of O(2)(-), we used the NAD(P)H oxidase inhibitor apocynin. In the presence of apocynin (10(-5) M), O(2)(-) production induced by elevating pH(i) was blocked. Finally, we measured the optimum pH for O(2)(-) production by the macula densa and found optimum extracellular pH is at 7.7 and optimum pH(i) is approximately 8 for O(2)(-) production. We found that elevated pH(i) enhances O(2)(-) production from NAD(P)H oxidase induced by increasing luminal NaCl when the lumen is perfused with 80 mM NaCl, not 10 mM, and O(2)(-) production is pH sensitive, with an optimum pH(i) of 8.

Analysis of calcium ion homeostasis and mitochondrial function in cerebellar granule cells of adult CaV 2.1 calcium ion channel mutant mice

CaV 2.1 voltage-gated calcium channels (VGCC) are highly expressed by cerebellar neurons, and their dysfunction is linked to human disorders including familial hemiplegic migraine, episodic ataxia type 2 and spinocerebellar ataxia type 6. Altered calcium homeostasis, due to dysfunctional Ca(V 2.1 VGCC can severely affect mitochondrial function, eventually leading to neuronal cell death. We study leaner and tottering mice, which carry autosomal recessive mutations in the gene coding for the alpha 1A pore-forming subunit of CaV 2.1 VGCC. Both leaner and tottering mice exhibit cerebellar ataxia and epilepsy. Excessive leaner cerebellar granule cell (CGC) death starts soon after postnatal day 10, but it is not known whether the degree of CGC cell death observed in adult leaner mice is significantly different from wild type mice. We used Fluoro-Jade and TUNEL staining to quantify apoptotic cell death in leaner and wild type CGC. We investigated calcium homeostasis, mitochondrial function and generation of reactive oxygen species (ROS) in isolated CGC, using indicator dyes Fura-2AM, TMRM and CMH2DCFDA, respectively. We observed a small but significant increase in number of apoptotic adult leaner CGC. Calcium homeostasis and mitochondrial function also were altered in leaner CGC. However, no significant differences in ROS levels were observed. It is possible that CGC death in leaner mice may be related to mitochondrial dysfunction but may not be directly related to decreased basal intracellular calcium.

Inorganic arsenic activates reduced NADPH oxidase in human primary macrophages through a Rho kinase/p38 kinase pathway

Inorganic arsenic is an immunotoxic environmental contaminant to which millions of humans are chronically exposed. We recently demonstrated that human primary macrophages constituted a critical target for arsenic trioxide (As(2)O(3)), an inorganic trivalent form. To specify the effects of arsenic on macrophage phenotype, we investigated in the present study whether As(2)O(3) could regulate the activity of NADPH oxidase, a major superoxide-generating enzymatic system in human phagocytes. Our results show that superoxide levels were significantly increased in a time-dependent manner in blood monocyte-derived macrophages treated with 1 muM As(2)O(3) for 72 h. Concomitantly, As(2)O(3) induced phosphorylation and membrane translocation of the NADPH oxidase subunit p47(phox) and it also increased translocation of Rac1 and p67(phox). Apocynin, a selective inhibitor of NADPH oxidases, prevented both p47(phox) translocation and superoxide production. NADPH oxidase activation was preceded by phosphorylation of p38-kinase in As(2)O(3)-treated macrophages. The p38-kinase inhibitor SB-203580 prevented phosphorylation and translocation of p47(phox) and subsequent superoxide production. Pretreatment of macrophages with the Rho-kinase inhibitor Y-27632 was found to mimic inhibitory effects of SB-203580 and to prevent As(2)O(3)-induced phosphorylation of p38 kinase. Treatment with As(2)O(3) also resulted in an increased secretion of the proinflammatory chemokine CCL18 that was fully inhibited by both apocynin and SB-203580. Taken together, our results demonstrate that As(2)O(3) induced a marked activation of NADPH oxidase in human macrophages, likely through stimulation of a Rho-kinase/p38-kinase pathway, and which may contribute to some of the deleterious effects of inorganic arsenic on macrophage phenotype.

Cardiolipin as an oxidative target in cardiac mitochondria in the aged rat

The aged heart sustains greater injury during ischemia (ISC) and reperfusion (REP) compared to the adult heart. In the Fischer 344 (F344) rat, aging decreases oxidative phosphorylation and complex III activity increasing the production of reactive oxygen species in interfibrillar mitochondria (IFM) located among the myofibrils. In the isolated, perfused 24 month old elderly F344 rat heart 25 min of stop-flow ISC causes additional damage to complex III, further decreasing the rate of oxidative phosphorylation. We did not observe further progressive mitochondrial damage during REP. We next asked if ISC or REP increased oxidative damage within mitochondria of the aged heart. Cardiolipin (CL) is a phospholipid unique to mitochondria consisting predominantly of four linoleic acid residues (C18:2). Following ISC and REP in the aged heart, there is a new CL species containing three oxygen atoms added to one linoleic residue. ISC alone was sufficient to generate this new oxidized molecular species of CL. Based upon oxidative damage to CL, complex III activity, and oxidative phosphorylation, mitochondrial damage thus occurs in the aged heart mainly during ISC, rather than during REP. Mitochondrial damage during ischemia sets the stage for mitochondrial-driven cardiomyocyte injury during reperfusion in the aged heart.

Baicalein protects chicken embryonic cardiomyocyte against hypoxia-reoxygenation injury via mu- and delta- but not kappa-opioid receptor signaling

Baicalein, a pure compound derived from Scutellaria baicalensis Georgi, protected cells from lethal damage in an ischemia-reperfusion model. This study was aimed to investigate the role of opioid receptors in mediating cardioprotection by baicalein against hypoxia-reoxygenation injury. By using chick cardiomyocyte as in vitro model, baicalein was added to the perfusate during 1 h-hypoxia followed by 1 h-reoxygenation. Cell viability was assessed by propidium iodide uptake, while apoptosis was assessed by TUNEL and Hoechst 33342 staining. The expression of opioid receptors mRNA in chicken embryonic myocardium was determined by RT-PCR. Opioid receptor antagonists, protein kinase C inhibitors, and KATP channel blockers were used to determine the presumed signal transduction pathways. The results showed that baicalein (0.1 approximately 5 microM) concentration dependently reduced hypoxia-reoxygenation-induced myocardial death and apoptosis. The cardioprotective effect of baicalein (1 microM) was blocked by pretreatment of nonspecific opioid receptor antagonist (naloxone), opioid mu-receptor (beta-funaltrexamine) and delta-receptor (7-Benzylidenenaltrexone) antagonists, protein kinase C inhibitors (H7 and chelerythrine), and KATP channel blockers (glibenclamide and 5-hydroxydecanoate). Finally, RT-PCR analysis successfully demonstrated the presence of opioid receptors mRNA in chicken embryonic cardiomyocytes. We conclude that the cardioprotective effect of baicalein is mediated via mu-, delta- but not kappa-opioid receptor and their related signal transduction pathways, such as protein kinase C and the KATP channel.

Effect of diazoxide on flavoprotein oxidation and reactive oxygen species generation during ischemia-reperfusion: a study on Langendorff-perfused rat hearts using optic fibers

This study analyzed the oxidant generation during ischemia-reperfusion protocols of Langendorff-perfused rat hearts, preconditioned with a mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) opener (i.e., diazoxide). The autofluorescence of mitochondrial flavoproteins, and that of the total NAD(P)H pool on the one hand and the fluorescence of dyes sensitive to H(2)O(2) or O(2)(*-) [i.e., the dihydrodichlorofluoroscein (H(2)DCF) and dihydroethidine (DHE), respectively] on the other, were noninvasively measured at the surface of the left ventricular wall by means of optic fibers. Isolated perfused rat hearts were subjected to an ischemia-reperfusion protocol. Opening mitoK(ATP) with diazoxide (100 microM) 1) improved the recovery of the rate-pressure product after reperfusion (72 +/- 2 vs. 16.8 +/- 2.5% of baseline value in control group, P < 0.01), and 2) attenuated the oxidant generation during both ischemic (-46 +/- 5% H(2)DCF oxidation and -40 +/- 3% DHE oxidation vs. control group, P < 0.01) and reperfusion (-26 +/- 2% H(2)DCF oxidation and -23 +/- 2% DHE oxidation vs. control group, P < 0.01) periods. All of these effects were abolished by coperfusion of 5-hydroxydecanoic acid (500 microM), a mitoK(ATP) blocker. During the preconditioning phase, diazoxide induced a transient, reversible, and 5-hydroxydecanoic acid-sensitive flavoprotein and H(2)DCF (but not DHE) oxidation. In conclusion, the diazoxide-mediated cardioprotection is supported by a moderate H(2)O(2) production during the preconditioning phase and a strong decrease in oxidant generation during the subsequent ischemic and reperfusion phases.

Biliverdin reductase mediates hypoxia-induced EMT via PI3-kinase and Akt

Chronic hypoxia in the renal parenchyma is thought to induce epithelial-to-mesenchymal transition (EMT), leading to fibrogenesis and ultimately end-stage renal failure. Biliverdin reductase, recently identified as a serine/threonine/tyrosine kinase that may activate phosphatidylinositol 3-kinase (PI3K) and Akt, is upregulated in response to reactive oxygen species that may accompany hypoxia. We investigated this potential role of biliverdin reductase in hypoxia-induced renal tubular EMT. Expression of biliverdin reductase was upregulated in a human proximal tubule cell line (HK-2) cultured in hypoxic conditions (1% O2), and this was accompanied by reduced expression of E-cadherin and increased expression of the mesenchymal marker vimentin. Inhibiting PI3K reversed these changes, consistent with EMT. In normoxic conditions, overexpression of biliverdin reductase promoted similar characteristics of EMT, which were also reversed by inhibiting PI3K. Furthermore, using small interfering RNA (siRNA) to knockdown biliverdin reductase, we demonstrated that the enzyme associates with phosphorylated Akt and mediates the hypoxia-induced EMT phenotype. In vivo, expression of biliverdin reductase increased in the tubular epithelia of 5/6-nephrectomized rats, and immunohistochemistry of serial sections demonstrated similar localization of phosphorylated Akt and biliverdin reductase. In conclusion, biliverdin reductase mediates hypoxia-induced EMT through a PI3K/Akt-dependent pathway.

Stimulation of mitochondrial biogenesis and autophagy by lipopolysaccharide in the neonatal rat cardiomyocyte protects against programmed cell death

Adult rat cardiomyocytes in culture respond to sub-lethal doses of lipopolysaccharides (LPS) by activation of pathways including the production of TNF-alpha and increased apoptosis. We and others have demonstrated a protective phenotype for neonatal rat cardiomyocytes to LPS. Concentrations of LPS far exceeding those necessary to induce TNF-alpha release do not induce apoptosis in the neonatal cells, although these cells are fully capable or inducing apoptosis in response to multiple other stimuli. In neonatal cells, we demonstrate that LPS treatment leads to a loss of mitochondrial membrane potential (Deltapsi) which is temporally associated with an increase in the level of uncoupling protein 3 (UCP3). Cells remain viable with no measurable increase in apoptotic or necrotic cell death. Many markers of mitochondrial biogenesis are also activated. LPS treatment stimulates an increase in the (i) transcription of mitochondrial transcription factor A (Tfam), (ii) nuclear accumulation of redox-sensitive nuclear respiratory factor 1 (NRF-1), and (iii) expression of peroxisome proliferator-activated receptor gamma co-activator 1 (PGC-1). We also observed that LPS increased intracellular autophagy. Autophagy was assessed by monitoring the levels of a mammalian protein specifically associated with autophagosomes, microtubule-associated light chain 3 (LC3). Furthermore, inhibition of autophagy in the presence of LPS stimulates markers of apoptosis. Our data suggest that the protective response of neonatal cells to LPS is multi-faceted at the level of the mitochondrion. Viable cells replace dysfunctional mitochondria by mitochondrial biogenesis and the extent of the damage limited by the rapid removal of damaged organelles by the stimulation of autophagy.

In vivo reactive oxygen species production induced by ischemia in muscle arterioles of mice: involvement of xanthine oxidase and mitochondria

Reactive oxygen species (ROS) participate in tissue injury after ischemia-reperfusion. Their implication in leukocyte adherence and increase in permeability at the venular side of the microcirculation have been reported, but very little is known about ROS production in arterioles. The objective of this work was to evaluate, in the arteriole wall in vivo, the temporal changes in superoxide anion production during ischemia and reperfusion and to identify the source of this production. Mouse cremaster muscle was exposed to 1 h of ischemia followed by 30 min of reperfusion, and superoxide anion production was assessed by a fluorescent probe, i.e., intracellular dihydroethidium oxidation. During ischemia, we found a significant increase in dihydroethidium oxidation; however, we observed no additional increase in fluorescence during the subsequent reperfusion. This phenomenon was significantly inhibited by pretreatment with superoxide dismutase. Allopurinol (xanthine oxidase inhibitor) or stigmatellin [Q(o)-site (oriented toward the intermembrane space) inhibitor of mitochondrial complex III] or simultaneous administration of these two inhibitors significantly reduced superoxide production during ischemia to 80%, 88%, and 72%, respectively, of that measured in the untreated ischemia-reperfusion group. By contrast, no significant inhibition was found when NADPH oxidase was inhibited by apocynin or when mitochondrial complex I or complex II was inhibited by rotenone or thenoyltrifluoroacetone. A significant increase in ROS was found with antimycin A [Q(i)-site (located in the inner membrane and facing the mitochondrial matrix) inhibitor of mitochondrial complex III]. We conclude that a significant increase in ROS production occurs during ischemia in the arteriolar wall. This increased production involves both a cytoplasmic source (i.e., xanthine oxidase) and the mitochondrial complex III at the Q(o) site.

Reactive oxygen species and fatigue-induced prolonged low-frequency force depression in skeletal muscle fibres of rats, mice and SOD2 overexpressing mice

Skeletal muscle often shows a delayed force recovery after fatiguing stimulation, especially at low stimulation frequencies. In this study we focus on the role of reactive oxygen species (ROS) in this fatigue-induced prolonged low-frequency force depression. Intact, single muscle fibres were dissected from flexor digitorum brevis (FDB) muscles of rats and wild-type and superoxide dismutase 2 (SOD2) overexpressing mice. Force and myoplasmic free [Ca(2+)] ([Ca(2+)](i)) were measured. Fibres were stimulated at different frequencies before and 30 min after fatigue induced by repeated tetani. The results show a marked force decrease at low stimulation frequencies 30 min after fatiguing stimulation in all fibres. This decrease was associated with reduced tetanic [Ca(2+)](i) in wild-type mouse fibres, whereas rat fibres and mouse SOD2 overexpressing fibres instead displayed a decreased myofibrillar Ca(2+) sensitivity. The SOD activity was approximately 50% lower in wild-type mouse than in rat FDB muscles. Myoplasmic ROS increased during repeated tetanic stimulation in rat fibres but not in wild-type mouse fibres. The decreased Ca(2+) sensitivity in rat fibres could be partially reversed by application of the reducing agent dithiothreitol, whereas the decrease in tetanic [Ca(2+)](i) in wild-type mouse fibres was not affected by dithiothreitol or the antioxidant N-acetylcysteine. In conclusion, we describe two different causes of fatigue-induced prolonged low-frequency force depression, which correlate to differences in SOD activity and ROS metabolism. These findings may have clinical implications since ROS-mediated impairments in myofibrillar function can be counteracted by reductants and antioxidants, whereas changes in SR Ca(2+) handling appear more resistant to interventions.

Hydrogen peroxide and superoxide anion production during acetic acid-induced yeast programmed cell death

Hydrogen peroxide production in yeast cells undergoing programmed cell death in response to acetic acid occurred in the majority of live cells 15 min after death induction and was no longer detectable after 60 min. Superoxide anion production was found later, 60 and 90 min after death induction when cells viability was 60 and 30%, respectively. In cells protected from death due to acid stress adaptation neither hydrogen peroxide nor superoxide anion could be observed after acetic acid treatment. The early production of hydrogen peroxide in cells in which survival was 100% could play a major role in acetic acid-induced programmed cell death signaling. Superoxide anion is assumed to be generated in cells already en route to acetic acid-induced programmed cell death.

Rapid non-invasive external cooling to induce mild therapeutic hypothermia in adult human-sized swine

AIM OF THE STUDY

Mild therapeutic hypothermia is a promising new therapy for patients resuscitated from cardiac arrest. Early and fast induction of hypothermia seems to be crucial for best results. The aim of the study was to investigate the feasibility and safety of a new surface cooling method using cold metal plates.

SUBJECTS AND METHODS

Twelve adult human-sized swine (79+/-9 kg) were cooled from 38 to 33 degrees C brain temperature. The skin surface was covered with -20 degrees C metal plates (M), as compared to ice packs, alcohol rubs, and fans used in a control group (C). Each method was tested during spontaneous circulation and, after re-warming, during cardiac arrest. Temperatures were recorded continuously. Data are given as mean+/-standard deviation or as median (interquartile range), if not normally distributed. Comparisons between the treatment groups were performed with the independent samples t-test, or the Mann-Whitney rank-sum test.

RESULTS

During spontaneous circulation, cooling rates were 9.3+/-1.4 degrees C/h (M), and 6.1+/-1.4 degrees C/h (C) (p=0.003); no skin lesions were observed. During cardiac arrest, cooling rates were 4.1 degrees C/h (1.8-4.8) (M), and 3.7 degrees C/h (3.1-5.3) (C) (p=0.9); no skin lesions were observed.

CONCLUSION

Cooling with cold metal plates was an effective method for rapid induction of mild therapeutic hypothermia in adult human-sized swine during spontaneous circulation, without any signs of skin damage. This new surface-cooling device, independent of energy supply during use, should be further investigated.

p66(ShcA) and oxidative stress modulate myogenic differentiation and skeletal muscle regeneration after hind limb ischemia

Oxidative stress plays a pivotal role in ischemic injury, and p66(ShcA)ko mice exhibit both lower oxidative stress and decreased tissue damage following hind limb ischemia. Thus, it was investigated whether tissue regeneration following acute hind limb ischemia was altered in p66(ShcA)ko mice. Upon femoral artery dissection, muscle regeneration started earlier and was completed faster than in wild-type (WT) control. Moreover, faster regeneration was associated with decreased oxidative stress. Unlike ischemia, cardiotoxin injury induced similar skeletal muscle damage in both genotypes. However, p66(ShcA)ko mice regenerated faster, in agreement with the regenerative advantage upon ischemia. Since no difference between p66(ShcA)wt and knock-out (ko) mice was found in blood perfusion recovery after ischemia, satellite cells (SCs), a resident population of myogenic progenitors, were examined. Similar SCs numbers were present in WT and ko mice. However, in vitro cultured p66(ShcA)ko SCs displayed lower oxidative stress levels and higher proliferation rate and differentiated faster than WT. Furthermore, when exposed to sublethal H(2)O(2) doses, p66(ShcA)ko SCs were resistant to H(2)O(2)-induced inhibition of differentiation. Finally, myogenic conversion induced by MyoD overexpression was more efficient in p66(ShcA)ko fibroblasts compared with WT. The present work demonstrates that oxidative stress and p66(ShcA) play a crucial role in the regenerative pathways activated by acute ischemia.

Nitric oxide during ischemia attenuates oxidant stress and cell death during ischemia and reperfusion in cardiomyocytes

Nitric oxide (NO) has been implicated as a cardioprotective agent during ischemia/reperfusion (I/R), but the mechanism of protection is unknown. Oxidant stress contributes to cell death in I/R, so we tested whether NO protects by attenuating oxidant stress. Cardiomyocytes and murine embryonic fibroblasts were administered NO (10-1200 nM) during simulated ischemia, and cell death was assessed during reperfusion without NO. In each case, NO abrogated cell death during reperfusion. Cells overexpressing endothelial NO synthase (NOS) exhibited a similar protection, which was abolished by the NOS inhibitor N(omega)-nitro-l-arginine methyl ester. Protection was not mediated by guanylate cyclase or the mitochondrial K(ATP) channel, as inhibitors of these systems failed to abolish protection. NO did not prevent decreases in mitochondrial potential, but cells protected with NO demonstrated recovery of potential at reperfusion. Measurements using C11-BODIPY reveal that NO attenuates lipid peroxidation during ischemia and reperfusion. Measurements of oxidant stress using the ratiometric redox sensor HSP-FRET demonstrate that NO attenuates protein oxidation during ischemia. These findings reveal that physiological levels of NO during ischemia can attenuate oxidant stress both during ischemia and during reperfusion. This response is associated with a remarkable attenuation of cell death, suggesting that ischemic cell death may be a regulated event.

Altering CO2 during reperfusion of ischemic cardiomyocytes modifies mitochondrial oxidant injury

OBJECTIVE

Acute changes in tissue CO2 and pH during reperfusion of the ischemic heart may affect ischemia/reperfusion injury. We tested whether gradual vs. acute decreases in CO2 after cardiomyocyte ischemia affect reperfusion oxidants and injury.

DESIGN

Comparative laboratory investigation.

SETTING

Institutional laboratory.

SUBJECTS

Embryonic chick cardiomyocytes.

INTERVENTIONS

Microscope fields of approximately 500 chick cardiomyocytes were monitored throughout 1 hr of simulated ischemia (PO2 of 3-5 torr, PCO2 of 144 torr, pH 6.8), followed by 3 hrs of reperfusion (PO2 of 149 torr, PCO2 of 36 torr, pH 7.4), and compared with cells reperfused with relative hypercarbia (PCO2 of 71 torr, pH 6.8) or hypocarbia (PCO2 of 7 torr, pH 7.9).

MEASUREMENTS AND MAIN RESULTS

The measured outcomes included cell viability (via propidium iodide) and oxidant generation (reactive oxygen species via 2',7'-dichlorofluorescin oxidation and nitric oxide [NO] via 4,5-diaminofluorescein diacetate oxidation). Compared with normocarbic reperfusion, hypercarbia significantly reduced cell death from 54.8% +/- 4.0% to 26.3% +/- 2.8% (p < .001), significantly decreased reperfusion reactive oxygen species (p < .05), and increased NO at a later phase of reperfusion (p < .01). The NO synthase inhibitor N-nitro-L-arginine methyl ester (200 microM) reversed this oxidant attenuation (p < .05), NO increase (p < .05), and the cardioprotection conferred by hypercarbic reperfusion (increasing death to 54.3% +/- 6.0% [p < .05]). Conversely, hypocarbic reperfusion increased cell death to 80.4% +/- 4.5% (p < .01). It also increased reactive oxygen species by almost two-fold (p = .052), without affecting the NO level thereafter. Increased reactive oxygen species was attenuated by the mitochondrial complex III inhibitor stigmatellin (20 nM) when given at reperfusion (p < .05). Cell death also decreased from 85.9% +/- 4.5% to 52.2% +/- 6.5% (p < .01). The nicotinamide adenine dinucleotide phosphate oxidase inhibitor apocynin (300 microM) had no effect on reperfusion reactive oxygen species.

CONCLUSIONS

Altering CO2 content during reperfusion can significantly affect myocardial postresuscitation injury, in part by modifying mitochondrial oxidants and NO synthase-induced NO production.

Ischemic preconditioning does not protect via blockade of electron transport

Ischemic preconditioning (IPC) before sustained ischemia decreases myocardial infarct size mediated in part via protection of cardiac mitochondria. Reversible blockade of electron transport at complex I immediately before sustained ischemia also preserves mitochondrial respiration and decreases infarct size. We proposed that IPC would attenuate electron transport from complex I as a potential effector mechanism of cardioprotection. Isolated, Langendorff-perfused rat hearts underwent IPC (3 cycles of 5-min 37°C global ischemia and 5-min reperfusion) or were perfused for 40 min without ischemia as controls. Subsarcolemmal (SSM) and interfibrillar (IFM) populations of mitochondria were isolated. IPC did not decrease ADP-stimulated respiration measured in intact mitochondria using substrates that donate reducing equivalents to complex I. Maximally expressed complex I activity measured as rotenone-sensitive NADH:ubiquinone oxidoreductase in detergent-solubilized mitochondria was also unaffected by IPC. Thus the protection of IPC does not occur as a consequence of a partial decrease in complex I activity leading to a decrease in integrated respiration through complex I. IPC and blockade of electron transport both converge on mitochondria as effectors of cardioprotection; however, each modulates mitochondrial metabolism during ischemia by different mechanisms to achieve cardioprotection.

(6R)-5,6,7,8-tetrahydro-L-biopterin and its stereoisomer prevent ischemia reperfusion injury in human forearm

OBJECTIVE

6R-5,6,7,8-tetrahydro-L-biopterin (6R-BH4) is a cofactor for endothelial nitric oxide synthase but also has antioxidant properties. Its stereo-isomer 6S-5,6,7,8-tetrahydro-L-biopterin (6S-BH4) and structurally similar pterin 6R,S-5,6,7,8-tetrahydro-D-neopterin (NH4) are also antioxidants but have no cofactor function. When endothelial nitric oxide synthase is 6R-BH4-deplete, it synthesizes superoxide rather than nitric oxide. Reduced nitric oxide bioavailability by interaction with reactive oxygen species is implicated in endothelial dysfunction (ED). 6R-BH4 corrects ED in animal models of ischemia reperfusion injury (IRI) and in patients with cardiovascular risks. It is uncertain whether the effect of exogenous 6R-BH4 on ED is through its cofactor or antioxidant action.

METHODS AND RESULTS

In healthy volunteers, forearm blood flow was measured by venous occlusion plethysmography during intra-arterial infusion of the endothelium-dependent vasodilator acetylcholine, or the endothelium-independent vasodilator glyceryl trinitrate, before and after IRI. IRI reduced plasma total antioxidant status (P=0.03) and impaired vasodilatation to acetylcholine (P=0.01), but not to glyceryl trinitrate (P=0.3). Intra-arterial infusion of 6R-BH4, 6S-BH4 and NH4 at approximately equimolar concentrations prevented IRI.

CONCLUSION

IRI causes ED associated with increased oxidative stress that is prevented by 6R-BH4, 6S-BH4, and NH4, an effect mediated perhaps by an antioxidant rather than cofactor function. Regardless of mechanism, 6R-BH4, 6S-BH4, or NH4 may reduce tissue injury during clinical IRI syndromes.

Oxidant stress during simulated ischemia primes cardiomyocytes for cell death during reperfusion

Ischemia-reperfusion injury induces oxidant stress, and the burst of reactive oxygen species (ROS) production after reperfusion of ischemic myocardium is sufficient to induce cell death. Mitochondrial oxidant production may begin during ischemia prior to reperfusion because reducing equivalents accumulate and promote superoxide production. We utilized a ratiometric redox-sensitive protein sensor (heat shock protein 33 fluorescence resonance energy transfer (HSP-FRET)) to assess oxidant stress in cardiomyocytes during simulated ischemia. HSP-FRET consists of the cyan and yellow fluorescent protein fluorophores linked by the cysteine-containing regulatory domain from bacterial HSP-33. During ischemia, ROS-mediated oxidation of HSP-FRET was observed, along with a decrease in cellular reduced glutathione levels. These findings were corroborated by measurements using redox-sensitive green fluorescent protein, another protein thiol ratiometric sensor, which became 93% oxidized by the end of simulated ischemia. However, cell death did not occur during ischemia, indicating that this oxidant stress is not sufficient to induce death before reperfusion. However, interventions that attenuate ischemic oxidant stress, including antioxidants or scavengers of residual O(2) that attenuate/prevent ROS generation during ischemia, abrogated cell death during simulated reperfusion. These findings reveal that, in isolated cardiomyocytes, sublethal H(2)O(2) generation during simulated ischemia regulates cell death during simulated reperfusion, which is mediated by the reperfusion oxidant burst.

Increased poly(ADP-ribose) polymerase activity during porcine hemorrhagic shock is transient and predictive of mortality

AIM OF THE STUDY

The aim of our study was to compare poly(ADP-ribose) polymerase (PARP) activity levels in a porcine model of hemorrhagic shock and resuscitation.

MATERIALS AND METHODS

We designed a prospective, comparative randomized survival study of hemorrhagic shock using 20 male Yorkshire-Landrace pigs (15-25 kg). In 16 pigs after splenectomy, we induced hemorrhagic shock to a mean arterial pressure of 50 mm Hg ( approximately 35% bleed). Pigs were randomized to receive normotensive resuscitation (SBP 90 mm Hg), mild hypotensive resuscitation (SBP 80 mm Hg), moderate hypotensive resuscitation (SBP 65 mm Hg), or no resuscitation (n=4 in each group). We also included a group of sham animals that were instrumented and had a splenectomy but not bled (n=4). Muscle and liver biopsies were taken prior to hemorrhage, after 45 min of shock, and 8, 24, and 48 h after resuscitation. PARP activity levels in biopsies were measured using chemical quantitation of NAD+.

RESULTS

Irrespective of our resuscitation strategy or outcome, both muscle and liver PARP activity levels rose after 45 min of shock and then returned to baseline. Excluding our control animals, PARP activity levels were significantly higher during shock in non-survivors compared to survivors.

CONCLUSIONS

In our model of porcine hemorrhagic shock, PARP activity levels increased during hemorrhagic shock. However, this increase in PARP activity levels was transient as they returned to baseline regardless of resuscitation strategy. Interestingly, PARP activity levels were significantly higher during hemorrhagic shock in non-survivors compared to survivors. These findings suggest that PARP activity may be a part of initial pathways leading from hemorrhagic shock to death.

Potential role and mechanisms of subcellular remodeling in cardiac dysfunction due to ischemic heart disease

Several studies have revealed varying degrees of changes in sarcoplasmic reticular and myofibrillar activities, protein content, gene expression and intracellular Ca-handling during cardiac dysfunction due to ischemia-reperfusion (I/R); however, relatively little is known about the sarcolemmal and mitochondrial alterations, as well as their mechanisms in the I/R hearts. Because I/R is associated with oxidative stress and intracellular Ca-overload, it has been indicated that changes in subcellular activities, protein content and gene expression due to I/R are related to both oxidative stress and Ca-overload. Intracellular Ca-overload appears to induce changes in subcellular activities, protein contents and gene expression (subcellular remodeling) by activation of proteases and phospholipases, as well as by affecting the genetic apparatus, whereas oxidative stress is considered to cause oxidation of functional groups of different subcellular proteins in addition to modifying the genetic machinery. Ischemic preconditioning, which is known to depress the development of both intracellular Ca-overload and oxidative stress due to I/R, was observed to attenuate the I/R-induced subcellular remodeling and improve cardiac performance. It is suggested that a combination therapy with antioxidants and interventions, which reduce the development of intracellular Ca-overload, may improve cardiac function by preventing or attenuating the occurrence of subcellular remodeling due to ischemic heart disease. It is proposed that defects in the activities of subcellular organelles may serve as underlying mechanisms for I/R-induced cardiac dysfunction under acute conditions, whereas subcellular remodeling due to alterations in gene expression may explain the impaired cardiac performance under chronic conditions of I/R.

Redox control of calcium channels: from mechanisms to therapeutic opportunities

Calcium plays an integral role in cellular function. It is a well-recognized second messenger necessary for signaling cellular responses, but in excessive amounts can be deleterious to function, causing cell death. The main route by which calcium enters the cytoplasm is either from the extracellular compartment or internal addistores via calcium channels. There is good evidence that calcium channels can respond to pharmacological compounds that reduce or oxidize thiol groups on the channel protein. In addition, reactive oxygen species such as hydrogen peroxide and superoxide that can mediate oxidative pathology also mediate changes in channel function via alterations of thiol groups. This review looks at the structure and function of calcium channels, the evidence that changes in cellular redox state mediate changes in channel function, and the role of redox modification of channels in disease processes. Understanding how redox modification of the channel protein alters channel structure and function is providing leads for the design of therapeutic interventions that target oxidative stress responses.

Comparative effects of flavonoids on oxidant scavenging and ischemia-reperfusion injury in cardiomyocytes

Since flavonoids scavenge reactive oxygen species, they may potentially protect against ischemia/reperfusion injury. This study compared the scavenging capacity of specific flavonoids towards different reactive oxygen species. Whether the differential oxidant scavenging capacity correlated with their protective efficacy in ischemia/reperfusion injury of cardiomyocytes was determined. The free radical scavenging capacity of five flavonoids (wogonin, baicalin, baicalein, catechin and procyanidin B2) was analyzed using electron spin resonance spectrometry for 3 radicals: 1,1-diphenyl-2picrylhydrazyl (DPPH), superoxide and hydroxyl radical. A well-established chick cardiomyocyte model of ischemia (1 h)/reperfusion (3 h) was used to evaluate flavonoid-induced protection against ischemia/reperfusion injury in chronic treatment (pretreated 72 h and treated through ischemia/reperfusion) and acute treatment protocols (during ischemia/reperfusion or only at reperfusion). The cell viability was assessed by propidium iodide. The DPPH scavenging was most significant with catechin, followed by procyanidin B2, baicalein, baicalin, and wogonin. The superoxide scavenging was, similarly, most significant with catechin, followed by baicalein, procyanidin B2, and baicalin. For hydroxyl radical, only baicalein showed a significant scavenging capacity (>50% reduction in ESR signal). For the cardiomyocyte studies, all flavonoids but wogonin showed protection against ischemia/reperfusion injury in the chronic treatment protocol. When flavonoids were administered only during ischemia/reperfusion, baicalein, procyanidin B2, and catechin significantly reduced cell death. If flavonoids were administered just at reperfusion, only baicalein and procyanidin B2 had protective effects, and the efficacy was less. Flavonoids possess specific but differential radical scavenging capacity, which, in conjunction with the timing of treatment, affects their protective efficacy in cardiomyocytes exposed to ischemia/reperfusion.

Reactive oxygen species are essential for autophagy and specifically regulate the activity of Atg4

Autophagy is a major catabolic pathway by which eukaryotic cells degrade and recycle macromolecules and organelles. This pathway is activated under environmental stress conditions, during development and in various pathological situations. In this study, we describe the role of reactive oxygen species (ROS) as signaling molecules in starvation-induced autophagy. We show that starvation stimulates formation of ROS, specifically H(2)O(2). These oxidative conditions are essential for autophagy, as treatment with antioxidative agents abolished the formation of autophagosomes and the consequent degradation of proteins. Furthermore, we identify the cysteine protease HsAtg4 as a direct target for oxidation by H(2)O(2), and specify a cysteine residue located near the HsAtg4 catalytic site as a critical for this regulation. Expression of this regulatory mutant prevented the formation of autophagosomes in cells, thus providing a molecular mechanism for redox regulation of the autophagic process.

Effect of a short-term diet and exercise intervention in youth on atherosclerotic risk factors

Early stages of atherosclerosis are commonly noted in youth. The present study was designed to examine the effects of lifestyle modification in 19 overweight children (age 8-17) who were placed on a high-fiber, low-fat diet in a 2-week residential program where food was provided ad libitum and daily exercise (2-2.5h) was performed. In each subject, pre- and post-intervention fasting blood was drawn to measure serum lipids, oxidative stress marker 8-isoprostaglandin F2alpha (8-iso-PGF2alpha) and generating enzyme myeloperoxidase (MPO), soluble intracellular adhesion molecule (sICAM)-1 and sE-selectin as indicators of endothelial activation, the inflammatory protein C-reactive protein (CRP) and total matrix metalloproteinase-9 (MMP-9). Using subject sera and human aortic endothelial cell (HAEC) culture systems, monocyte chemotactic protein-1 (MCP-1) production, as well as nitric oxide (NO), superoxide and hydrogen peroxide production were measured in vitro by fluorometric detection. After 2 weeks, significant reductions (p<0.05) in all serum lipids (except HDL cholesterol), 8-iso-PGF2alpha, MPO, sICAM-1, sE-selectin, CRP, MMP-9, and cellular MCP-1 production were noted. Additionally, there was a significant decrease in cultured, serum-stimulated HAEC production of superoxide and hydrogen peroxide, and a concomitant increase in NO production (all p<0.01), These results indicate amelioration of several traditional as well as novel factors associated with atherosclerosis after lifestyle modification, even in youth without documented disease.

Toxic effects of cobalt in primary cultures of mouse astrocytes

Cobalt is suspected to cause memory deficit in humans and was reported to induce neurotoxicity in animal models. We have studied the effects of cobalt in primary cultures of mouse astrocytes. CoCl(2) (0.2-0.8mM) caused dose-dependent ATP depletion, apoptosis (cell shrinkage, phosphatidylserine externalization and chromatin rearrangements) and secondary necrosis. The mitochondria appeared to be a main target of cobalt toxicity, as shown by the loss of mitochondrial membrane potential (DeltaPsi(m)) and release from the mitochondria of apoptogenic factors, e.g. apoptosis inducing factor (AIF). Pre-treatment with bongkrekic acid reduced ATP depletion, implicating the involvement of the mitochondrial permeability transition (MPT) pore. Cobalt increased the generation of oxygen radicals, but antioxidants did not prevent toxicity. There was also an impaired response to ATP stimulation, evaluated as a lower raise in intracellular calcium. Similarly to hypoxia and dymethyloxallyl glycine (DMOG), cobalt triggered stabilization of the alpha-subunit of hypoxia-inducible factor HIF-1 (HIF-1alpha). This early event was followed by an increased expression of HIF-1 regulated genes, e.g. stress protein HO-1, pro-apoptotic factor Nip3 and iNOS. Although all of the three stimuli activated the HIF-1alpha pathway and decreased ATP levels, the downstream effects were different. DMOG only inhibited cell proliferation, whereas the other two conditions caused cell death by apoptosis and necrosis. This points to cobalt and hypoxia not only inducing HIF-1alpha regulated genes but also affecting similarly other cellular functions, including metabolism.

Hypoxia-induced reactive oxygen species formation in skeletal muscle

The existence of hypoxia-induced reactive oxygen species (ROS) production remains controversial. However, numerous observations with a variety of methods and in many cells and tissue types are supportive of this idea. Skeletal muscle appears to behave much like heart in that in the early stages of hypoxia there is a transient elevation in ROS, whereas in chronic exposure to very severe hypoxia there is evidence of ongoing oxidative stress. Important remaining questions that are addressed in this review include the following. Are there levels of PO2 in skeletal muscle, typical of physiological or mildly pathophysiological conditions, that are low enough to induce significant ROS production? Does the ROS associated with muscle contractile activity reflect imbalances in oxygen uptake and demand that drive the cell to a more reduced state? What are the possible molecular mechanisms by which ROS may be elevated in hypoxic skeletal muscle? Is the production of ROS in hypoxia of physiological significance, both with respect to cell signaling pathways promoting cell function and with respect to damaging effects of long-term exposure? Discussion of these and other topics leads to general conclusions that hypoxia-induced ROS may be a normal physiological response to imbalance in oxygen supply and demand or environmental stress and may play a yet undefined role in normal response mechanisms to these stimuli. However, in chronic and extreme hypoxic exposure, muscles may fail to maintain a normal redox homeostasis, resulting in cell injury or dysfunction.

ROS scavenging before 27 degrees C ischemia protects hearts and reduces mitochondrial ROS, Ca2+ overload, and changes in redox state

We have shown that cold perfusion of hearts generates reactive oxygen and nitrogen species (ROS/RNS). In this study, we determined 1) whether ROS scavenging only during cold perfusion before global ischemia improves mitochondrial and myocardial function, and 2) which ROS leads to compromised cardiac function during ischemia and reperfusion (I/R) injury. Using fluorescence spectrophotometry, we monitored redox balance (NADH and FAD), O(2)(*-) levels and mitochondrial Ca(2+) (m[Ca(2+)]) at the left ventricular wall in 120 guinea pig isolated hearts divided into control (Con), MnTBAP (a superoxide dismutase 2 mimetic), MnTBAP (M) + catalase (C) + glutathione (G) (MCG), C+G (CG), and N(G)-nitro-L-arginine methyl ester (L-NAME; a nitric oxide synthase inhibitor) groups. After an initial period of warm perfusion, hearts were treated with drugs before and after at 27 degrees C. Drugs were washed out before 2 h at 27 degrees C ischemia and 2 h at 37 degrees C reperfusion. We found that on reperfusion the MnTBAP group had the worst functional recovery and largest infarction with the highest m[Ca(2+)], most oxidized redox state and increased ROS levels. The MCG group had the best recovery, the smallest infarction, the lowest ROS level, the lowest m[Ca(2+)], and the most reduced redox state. CG and L-NAME groups gave results intermediate to those of the MnTBAP and MCG groups. Our results indicate that the scavenging of cold-induced O(2)(*-) species to less toxic downstream products additionally protects during and after cold I/R by preserving mitochondrial function. Because MnTBAP treatment showed the worst functional return along with poor preservation of mitochondrial bioenergetics, accumulation of H(2)O(2) and/or hydroxyl radicals during cold perfusion may be involved in compromised function during subsequent cold I/R injury.

Sarcoplasmic ATP-sensitive potassium channel blocker HMR1098 protects the ischemic heart: implication of calcium, complex I, reactive oxygen species and mitochondrial ATP-sensitive potassium channel

The aim of this study was to investigate the effects of HMR1098, a selective blocker of sarcolemmal ATP-sensitive potassium channel (sarcK(ATP)), in Langendorff-perfused rat hearts submitted to ischemia and reperfusion. The recovery of heart hemodynamic and mitochondrial function, studied on skinned fibers, was analyzed after 30-min global ischemia followed by 20-min reperfusion. Infarct size was quantified on a regional ischemia model after 2-h reperfusion. We report that the perfusion of 10 microM HMR1098 before ischemia, delays the onset of ischemic contracture, improves recovery of cardiac function upon reperfusion, preserves the mitochondrial architecture, and finally decreases infarct size. This HMR1098-induced cardioprotection is prevented by 1 mM 2-mercaptopropionylglycine, an antioxidant, and by 100 nM nifedipine, an L-type calcium channel blocker. Concomitantly, it is shown that HMR1098 perfusion induces (i) a transient and specific inhibition of the respiratory chain complex I and, (ii) an increase in the averaged intracellular calcium concentration probed by the in situ measurement of indo-1 fluorescence. Finally, all the beneficial effects of HMR1098 were strongly inhibited by 5-hydroxydecanoate and abolished by glibenclamide, two mitoK(ATP) blockers. This study demonstrates that the HMR1098-induced cardioprotection occurs indirectly through extracellular calcium influx, respiratory chain complex inhibition, reactive oxygen species production and mitoK(ATP) opening. Taken together, these data suggest that a functional interaction between sarcK(ATP) and mitoK(ATP) exists in isolated rat heart ischemia model, which is mediated by extracellular calcium influx.

Hypothermia-induced cardioprotection using extended ischemia and early reperfusion cooling

Optimal timing of therapeutic hypothermia for cardiac ischemia is unknown. Our prior work suggests that ischemia with rapid reperfusion (I/R) in cardiomyocytes can be more damaging than prolonged ischemia alone. Also, these cardiomyocytes demonstrate protein kinase C (PKC) activation and nitric oxide (NO) signaling that confer protection against I/R injury. Thus we hypothesized that hypothermia will protect most using extended ischemia and early reperfusion cooling and is mediated via PKC and NO synthase (NOS). Chick cardiomyocytes were exposed to an established model of 1-h ischemia/3-h reperfusion, and the same field of initially contracting cells was monitored for viability and NO generation. Normothermic I/R resulted in 49.7 +/- 3.4% cell death. Hypothermia induction to 25 degrees C was most protective (14.3 +/- 0.6% death, P < 0.001 vs. I/R control) when instituted during extended ischemia and early reperfusion, compared with induction after reperfusion (22.4 +/- 2.9% death). Protection was completely lost if onset of cooling was delayed by 15 min of reperfusion (45.0 +/- 8.2% death). Extended ischemia/early reperfusion cooling was associated with increased and sustained NO generation at reperfusion and decreased caspase-3 activation. The NOS inhibitor N(omega)-nitro-L-arginine methyl ester (200 microM) reversed these changes and abrogated hypothermia protection. In addition, the PKCepsilon inhibitor myr-PKCepsilon v1-2 (5 microM) also reversed NO production and hypothermia protection. In conclusion, therapeutic hypothermia initiated during extended ischemia/early reperfusion optimally protects cardiomyocytes from I/R injury. Such protection appears to be mediated by increased NO generation via activation of protein kinase Cepsilon; nitric oxide synthase.

beta(1) Receptors protect the renal afferent arteriole of angiotensin-infused rabbits from norepinephrine-induced oxidative stress

Renal afferent arterioles (Aff) from angiotensin II (AngII)-infused rabbits have enhanced contractions to AngII that are normalized by tempol (superoxide dismutase mimetic), whereas contractions to norepinephrine (NE) are normal and unaffected by tempol. Tested was the hypothesis that beta-receptor stimulation with NE prevents enhanced reactivity and superoxide generation. Preconstricted Aff from AngII- or vehicle-infused rabbits were perfused at physiologic pressure. Aff from vehicle-infused rabbits had strong, endothelium-independent relaxations to dobutamine (beta(1)-receptor agonist; 78 +/- 6%; P < 0.0001; mean +/- SD) but only weak relaxations to salbutamol (beta(2)-receptor agonist; 13 +/- 3%; P < 0.05) or BRL-37,344 (beta(3)-receptor agonist; 14 +/- 3%; P < 0.05). Contractions to NE were similar in Aff from vehicle- and AngII-infused rabbits (-36 +/- 5 versus -34 +/- 3%; NS) and were unaffected by tempol (-32 +/- 4%; NS). In contrast, phenylephrine contractions (alpha(1) agonist) were enhanced in Aff from AngII-infused rabbits (-59 +/- 6 versus -46 +/- 4%; P < 0.05) and normalized by tempol. NE contractions in Aff from AngII-infused rabbits (-34 +/- 4%) were enhanced (P < 0.01) by propranolol (nonselective beta antagonist; -53 +/- 6%), CGP-20,712A (selective beta(1)-receptor antagonist; -61 +/- 9%), or Rp-cAMP (competitive inhibitor of cAMP; -56 +/- 4%); were normalized by tempol; but were unaffected by ICI-118,551 (selective beta(2)-receptor antagonist) or SR-59,230A (selective beta(3)-receptor antagonist). Superoxide generation in Aff from AngII-infused rabbits that were assessed from ethidium:dihydroethidium was enhanced by addition of CGP-20,712A to NE but was normalized by tempol. Aff have robust alpha(1)-receptor contraction and beta(1)-receptor dilation. NE elicits beta(1) signaling via cAMP that moderates oxidative stress and contractions in Aff from AngII-infused rabbits.

Reactive oxygen species mediate central cardiorespiratory network responses to acute intermittent hypoxia

Although oxidative stress and reactive oxygen species generation is typically associated with localized neuronal injury, reactive oxygen species have also recently been shown to act as a physiological signal in neuronal plasticity. Here we define an essential role for reactive oxygen species as a critical stimulus for cardiorespiratory reflex responses to acute episodic hypoxia in the brain stem. To examine central cardiorespiratory responses to episodic hypoxia, we used an in vitro medullary slice that allows simultaneous examination of rhythmic respiratory-related activity and synaptic neurotransmission to cardioinhibitory vagal neurons. We show that whereas continuous hypoxia does not stimulate excitatory neurotransmission to cardioinhibitory vagal neurons, acute intermittent hypoxia of equivalent duration incrementally recruits an inspiratory-evoked excitatory neurotransmission to cardioinhibitory vagal neurons during intermittent hypoxia. This recruitment was dependent on the generation of reactive oxygen species. Further, we demonstrate that reactive oxygen species are incrementally generated in glutamatergic neurons in the ventrolateral medulla during intermittent hypoxia. These results suggest a neurochemical basis for the pronounced bradycardia that protects the heart against injury during intermittent hypoxia and demonstrates a novel role of reactive oxygen species in the brain stem.

Modulation of glucose transport in skeletal muscle by reactive oxygen species

Glucose transport is an essential physiological process that is characteristic of all eukaryotic cells, including skeletal muscle. In skeletal muscle, glucose transport is mediated by the GLUT-4 protein under conditions of increased carbohydrate utilization. The three major physiological stimuli of glucose transport in muscle are insulin, exercise/contraction, and hypoxia. Here, the role of reactive oxygen species (ROS) in modulating glucose transport in skeletal muscle is reviewed. Convincing evidence for ROS involvement in insulin- and hypoxia-mediated transport in muscle is lacking. Recent experiments, based on pharmacological and genetic approaches, support a role for ROS in contraction-mediated glucose transport. During contraction, endogenously produced ROS appear to mediate their effects on glucose transport via AMP-activated protein kinase.

Increased toxicity by transforming growth factor-beta 1 in liver cells overexpressing CYP2E1

Ethanol treatment causes an increase in expression of TGF-beta1 and CYP2E1 in the centrilobular area. Alcoholic liver disease is usually initiated in the centrilobular region of the liver. We hypothesized that the combination of TGF-beta1 and CYP2E1 produces increased oxidative stress and liver cell toxicity. To test this possibility, we studied the effects of TGF-beta1 on the viability of HepG2 E47 cells that express human CYP2E1, and C34 HepG2 cells, which do not express CYP2E1. E47 cells underwent greater growth inhibition and enhanced apoptosis after TGF-beta1 treatment, as compared to the C34 cells. There was an enhanced production of reactive oxygen species (ROS) and a decline in reduced glutathione (GSH) levels in the TGF-beta1-treated E47 cells and the enhanced cell death could be prevented by antioxidants. The CYP2E1 inhibitor diallyl sulfide prevented the potentiated cell death in E47 cells validating the role of CYP2E1. Mitochondrial membrane potential declined in the TGF-beta1-treated E47 cells, prior to developing toxicity, and cell death could be prevented by trifluoperazine, an inhibitor of the mitochondrial membrane permeability transition. TGF-beta1 also produced a loss of cell viability in hepatocytes from pyrazole-treated rats with elevated levels of CYP2E1, compared to control hepatocytes. In conclusion, increased toxic interactions by TGF-beta1 plus CYP2E1 can occur by a mechanism involving increased production of intracellular ROS and depletion of GSH, resulting in mitochondrial membrane damage and loss of membrane potential, followed by apoptosis. Potentiation of TGF-beta1-induced cell death by CYP2E1 may contribute to mechanisms of alcohol-induced liver disease.

Iron enhances endothelial cell activation in response to Cytomegalovirus or Chlamydia pneumoniae infection

BACKGROUND

Chronic inflammation has been implemented in the pathogenesis of inflammatory diseases like atherosclerosis. Several pathogens like Chlamydia pneumoniae (Cp) and cytomegalovirus (CMV) result in inflammation and thereby are potentially artherogenic. Those infections could trigger endothelial activation, the starting point of the atherogenic inflammatory cascade. Considering the role of iron in a wide range of infection processes, the presence of iron may complicate infection-mediated endothelial activation.

MATERIALS AND METHODS

Endothelial intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and endothelial selectin (E-selectin) expression were measured using flow cytometry, as an indication of endothelial activation. Cytotoxicity was monitored using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Immunostaining was applied to measure Cp and CMV infectivity to endothelial cells.

RESULTS

An increased number of infected endothelial cells in a monolayer population leads to a raised expression of adhesion molecules of the whole cell population, suggesting paracrine interactions. Iron additively up-regulated Cp-induced VCAM-1 expression, whereas synergistically potentiated Cp-induced ICAM-1 expression. Together with CMV, iron also enhanced ICAM-1 and VCAM-1 expression. These iron effects were observed without modulation of the initial infectivity of both microorganisms. Moreover, the effects of iron could be reversed by intracellular iron chelation or radical scavenging, conforming modulating effects of iron on endothelial activation after infections.

CONCLUSIONS

Endothelial response towards chronic infections depends on intracellular iron levels. Iron status in populations positive for Cp or CMV infections should be considered as a potential determinant for the development of atherosclerosis.

Increased expression of stress proteins in the surf clam Donax variabilis following hydrogen sulfide exposure

Endogenous free radical production and resulting oxidative damage may result from exposure to hypoxia, hyperoxia, or hydrogen sulfide. Previous investigations of sulfide-induced oxidative damage have produced conflicting results, perhaps because these studies utilized species presumably adapted to sulfide. We examined the effects of sulfide, hypoxia and hyperoxia on the surf clam Donax variabilis to test whether these stressors induce a cellular response to oxidative stress. These clams inhabit high-energy sandy beaches and are unlikely to have specific adaptations to these stressors. In duplicate flow-through experiments performed in fall and spring, clams were exposed to normoxia (22 kPa P(O(2))), hypoxia (10 kPa), hyperoxia (37 kPa), or sulfide with normoxia ( approximately 100 mumol L(-1), 22 kPa respectively) for 24 h. We quantified whole-animal expression of three antioxidants (Cu/Zn and Mn superoxide dismutases, glutathione peroxidase), a lipid peroxidation marker (4-hydroxy-2E-nonenol-adducted protein), a DNA repair enzyme (OGG1-m), four heat shock proteins (small Hsp, Hsp60, Hsp70, and mitochondrial Hsp70), ubiquitin, and actin. Clams exposed to sulfide showed upregulation of the greatest number of stress proteins and the pattern was consistent with a cellular response to oxidative stress. Furthermore, there was a marked seasonality, with greater stress protein expression in clams from the spring.

Modulation of electron transport protects cardiac mitochondria and decreases myocardial injury during ischemia and reperfusion

Mitochondria are increasingly recognized as lynchpins in the evolution of cardiac injury during ischemia and reperfusion. This review addresses the emerging concept that modulation of mitochondrial respiration during and immediately following an episode of ischemia can attenuate the extent of myocardial injury. The blockade of electron transport and the partial uncoupling of respiration are two mechanisms whereby manipulation of mitochondrial metabolism during ischemia decreases cardiac injury. Although protection by inhibition of electron transport or uncoupling of respiration initially appears to be counterintuitive, the continuation of mitochondrial oxidative phosphorylation in the pathological milieu of ischemia generates reactive oxygen species, mitochondrial calcium overload, and the release of cytochrome c. The initial target of these deleterious mitochondrial-driven processes is the mitochondria themselves. Consequences to the cardiomyocyte, in turn, include oxidative damage, the onset of mitochondrial permeability transition, and activation of apoptotic cascades, all favoring cardiomyocyte death. Ischemia-induced mitochondrial damage carried forward into reperfusion further amplifies these mechanisms of mitochondrial-driven myocyte injury. Interruption of mitochondrial respiration during early reperfusion by pharmacologic blockade of electron transport or even recurrent hypoxia or brief ischemia paradoxically decreases cardiac injury. It increasingly appears that the cardioprotective paradigms of ischemic preconditioning and postconditioning utilize modulation of mitochondrial oxidative metabolism as a key effector mechanism. The initially counterintuitive approach to inhibit mitochondrial respiration provides a new cardioprotective paradigm to decrease cellular injury during both ischemia and reperfusion.

Effect of a diet and exercise intervention on oxidative stress, inflammation and monocyte adhesion in diabetic men

Diabetes increases the risk of coronary artery disease. We examined the effects of lifestyle modification on key contributing factors to atherogenesis, including oxidative stress, inflammation and cell adhesion. Diabetic men (N=13) were placed on a high-fiber, low-fat diet in a 3-week residential program where food was provided ad libitum and daily aerobic exercise was performed. In each subject, pre- and post-intervention fasting blood was drawn for circulating levels of serum lipids, glucose and insulin, oxidative stress marker 8-isoprostaglandin F2alpha (8-iso-PGF2alpha), the inflammatory protein C-reactive protein (CRP), and soluble intracellular adhesion molecule (sICAM)-1 and sE-selectin as indicators of endothelial activation. Using subject sera and human aortic endothelial cell (HAEC) culture systems, serum-induced monocyte adhesion, ICAM-1, vascular cell adhesion molecule-1 (VCAM-1) and cell surface abundance, and monocyte chemotactic protein-1 (MCP-1) production were determined. Nitric oxide (NO), superoxide, and hydrogen peroxide production were measured in vitro by fluorometric detection. After 3 weeks, significant reductions (p<0.05) in BMI, all serum lipids including total cholesterol (pre: 188.9+/-10.1 mg/dL versus post: 146.3+/-3.8 mg/dL) and low-density lipoprotein (103.1+/-10.2 mg/dL versus 76.4+/-4.3 mg/dL), fasting serum glucose (157.5+/-10.1 mg/dL versus 126.7+/-8.7 mg/dL), insulin (33.8+/-4.0 microU/ml versus 23.8+/-3.4 microU/ml), homeostasis model assessment for insulin resistance, 8-iso-PGF2alpha, CRP, sICAM-1, and sE-selectin were noted. In vitro, serum-stimulated monocyte adhesion, cellular ICAM-1 and VCAM-1 expression (p<0.05), and fluorometric detection of superoxide and hydrogen peroxide production decreased, while a concomitant increase in NO production was noted (all p<0.01). A combination of diet and exercise ameliorates oxidative stress, inflammation, and monocyte-endothelial interaction. Intensive lifestyle modification may improve novel CAD risk factors in men with diabetes.

Inhibition of phospholipase C-γ1augments the decrease in cardiomyocyte viability by H2O2

The present study was conducted to examine the role of a major cardiac phospholipase C (PLC) isozyme, PLC-γ1, in cardiomyocytes during oxidative stress. Left ventricular cardiomyocytes were isolated by collagenase digestion from adult male Sprague-Dawley rats (250–300 g) and treated with 20, 50, and 100 μM H2O2for 15 min. A concentration-dependent (up to 50 μM) increase in the mRNA level and membrane protein content of PLC-γ1was observed with H2O2treatment. Furthermore, PLC-γ1was activated in response to H2O2, as revealed by an increase in the phosphorylation of its tyrosine residues. There was a marked increase in the phosphorylation of the antiapoptotic protein Bcl-2 by H2O2; this change was attenuated by a PLC inhibitor, U-73122. Although both protein kinase C (PKC)-δ and -ε protein contents were increased in the cardiomyocyte membrane fraction in response to H2O2, PKC-ε activation, unlike PKC-δ, was attenuated by U-73122 (2 μM). Inhibition of PKC-ε with inhibitory peptide (0.1 μM) prevented Bcl-2 phosphorylation. Moreover, different concentrations (0.05, 0.1, and 0.2 μM) of this peptide augmented the decrease in cardiomyocyte viability in response to H2O2. In addition, a decrease in cardiomyocyte viability, as assessed by trypan blue exclusion, due to H2O2was also seen when cells were pretreated with U-73122 and was as a result of increased apoptosis. It is therefore suggested that PLC-γ1may play a role in cardiomyocyte survival during oxidative stress via PKC-ε and phosphorylation of Bcl-2.

Protection by 6-aminonicotinamide against oxidative stress in cardiac cells

Oxidative stress at the time of reperfusion is a major aspect of ischemia-reperfusion injury in heart as well as in other organs. There is a continuing interest in development of pharmacological approaches to alleviate this injury. 6-Aminonicotinamide (6AN) has been shown to diminish myocardial necrosis following global ischemia in an isolated rat heart, apparently by limiting the oxidative injury component. We therefore explored the antioxidative potential of 6AN in a model using H9C2(2-1) rat cardiac myoblasts exposed to H2O2 stress. Dependent on the specific protocol, 6AN pretreatment for 6-23 h resulted in a strongly increased cell survival: from 11% to 16% in untreated cells to 56-75% following 6AN treatment. This 6AN-mediated protection was associated with a modest increase (up to 55%) of the cytosolic free Ca2+, and was blocked by ryanodine, but not by verapamil or nifedipine. The protective effect of 6AN was associated with a decrease in total cell content of the reduced glutathione (GSH) by 15-44%, indicative of an oxidative shift in the GSH/GSSG system redox potential. We propose that this redox shift caused an increased Ca2+ leak through ryanodine receptors, reflecting their known sensitivity to redox modulation. In turn, this Ca2+ redistribution appeared to trigger a state of an enhanced antioxidative resistance, somewhat analogous to the phenomenon of Ca2+ preconditioning. Similar to some of the cases of Ca2+ preconditioning, this protected state involved the activity of Ca2+ -independent, but not of Ca2+ -dependent, isoform(s) of protein kinase C.

Dynamic responses of single cardiomyocytes to graded ischemia studied by oxygen clamp in on-chip picochambers

Single mouse cardiomyocytes were exposed to defined ischemia. We designed chambers on glass chips with a volume of 192 pL (picochambers). After a picochamber was loaded with a single cardiomyocyte, P(O2) in the picochamber was equilibrated with that in the headspace, where it was controlled in the critical range between <0.2 and 10 mm Hg. Because the extracellular fluid volume in a picochamber was restricted, these conditions are close to tissue ischemia. Responses of the sarcolemmal K(ATP)-channel current (I(KATP)), the production of reactive oxygen species (ROS), and the mitochondrial membrane potential (delta psi) of single cardiomyocytes to graded ischemia and, in particular, to rapid changes of the ischemic grade by defined oxygen steps were studied. The results show that I(KATP) is readily activated during ischemia and that the grade of ischemia tightly controls the amplitude of I(KATP). Furthermore, maximal ischemia-induced I(KATP) was similar when it followed either reoxygenation or reperfusion, suggesting that there is no major autocrine modulation of maximal I(KATP) during ischemia. A P(O2) staircase from <0.2 to 10 mm Hg increased the ROS signal, starting already at a P(O2) of approximately 0.3 mm Hg. With a similar P(O2) staircase, delta psi first hyperpolarized and then, above 1 mm Hg, depolarized. The depolarizing response of delta psi at a P(O2) of >1 mm Hg could be blocked by increasing the antioxidant defense with glutathione-monoethyl ester. It is concluded that in an ischemic cardiomyocyte I(KATP) is essentially controlled by Po(2) and that at low P(O2) delta psi is balanced by oxygen-induced hyperpolarization and ROS-induced depolarization.

Effects of various oxidants and antioxidants on the p38-MAPK signalling pathway in the perfused amphibian heart

We investigated the effects of different antioxidants such as L-ascorbic acid, catalase, and superoxide dismutase (SOD), on the p38-MAPK activation induced by oxidative stress in the isolated perfused amphibian heart. Oxidative stress was exemplified by perfusing hearts with 30 microM H(2)O(2) for 5 min or with the enzymatic system of xanthine/xanthine oxidase (200 microM/10 mU/ml, respectively) for 10 min. H(2)O(2)-induced activation of p38-MAPK (7.04 +/- 0.20-fold relative to control values) was totally attenuated by L-ascorbic acid (100 microM) or catalase (150 U/ml). These results were confirmed by immunohistochemical studies in which the phosphorylated form of p38-MAPK was localised in the perinuclear region and dispersedly in the cytoplasm of the ventricular cells during H(2)O(2) treatment, a pattern that was abolished by catalase or L-ascorbic acid. p38-MAPK was also activated (2.34 +/- 0.17-fold) by perfusing amphibian hearts with the reactive oxygen species (ROS)-generating system of xanthine/xanthine oxidase and this activation sustained in the presence of 150 U/ml catalase (2.16 +/- 0.26-fold), 50 U/ml SOD (2.02 +/- 0.07) or 100 microM L-ascorbic acid (2.18 +/- 0.10), but was suppressed by the combination of 150 U/ml catalase and 50 U/ml SOD. Finally, our studies showed that xanthine/xanthine oxidase induced the phosphorylation of the potent p38-MAPK substrates MAPKAPK2 (3.14 +/- 0.27-fold) and HSP27 (5.32 +/- 0.83-fold), which are implicated in cell protection, and this activation was reduced by the simultaneous use of catalase and SOD.

Oxidative balance and immunodetection of antioxidant enzymes in the hepatopancreas of the crabChasmagnathus granulatasubjected to anoxia and reoxygenation

The present study shows the activities and concentrations of the antioxidant enzymes superoxide dismutase (SOD) and glutathione S-transferase (GST) in the hepatopancreas of the crab Chasmagnathus granulata (Dana, 1851) (Decapoda, Brachyura) when exposed to periods of anoxia (8 h) and aerobic recovery (20 and 40 min post anoxia). Exposure to anoxia did not cause any change in the activities of the enzymes analyzed. The activities of these enzymes did not change with a decrease in environmental oxygen concentration. During reoxygenation, enzyme activities returned to control levels. The concentrations and activities of SOD and GST presented different response profiles. Exposure to anoxia caused increased lipoperoxidation (conjugated dienes and thiobarbituric acid reactive substances), whereas aerobic recovery reduced lipoperoxidation. The results of this study showed that C. granulata adjusts its antioxidant defense systems in an attempt to reduce and (or) avoid damage resulting from the reintroduction of oxygen.

Effect of a short-term diet and exercise intervention on oxidative stress, inflammation, MMP-9, and monocyte chemotactic activity in men with metabolic syndrome factors

The present study was designed to examine the effects of lifestyle modification on key contributing factors to atherogenesis, including oxidative stress, inflammation, chemotaxis, and cell adhesion. Obese men ( n = 31), 15 of whom had metabolic syndrome, were placed on a high-fiber, low-fat diet in a 3-wk residential program where food was provided ad libitum and daily aerobic exercise was performed. In each subject, pre- and postintervention fasting blood was drawn for circulating levels of serum lipids, glucose and insulin (for estimation of insulin sensitivity), oxidative stress-generating enzyme myeloperoxidase and marker 8-isoprostaglandin F2α, the inflammatory protein C-reactive protein, soluble ICAM-1 as an indicator of endothelial activation, sP-selectin as a marker of platelet activation, the chemokine macrophage inflammatory protein-1α, and total matrix metalloproteinase-9. Using subject sera and human aortic endothelial cell culture systems, we measured VCAM-1 cell surface abundance and monocyte chemotactic protein-1, nitric oxide, superoxide, and hydrogen peroxide production in vitro by fluorometric detection. Also determined in vitro was serum-induced, monocyte adhesion and monocyte chemotactic activity. After 3 wk, significant reductions ( P < 0.05) in body mass index, all serum lipids and lipid ratios, fasting glucose, insulin, homeostasis model assessment for insulin resistance, myeloperoxidase, 8-isoprostaglandin F2α, C-reactive protein, soluble ICAM-1, soluble P-selectin, macrophage inflammatory protein-1α, and matrix metalloproteinase-9 were noted. In vitro, serum-stimulated cellular VCAM-1 expression, monocyte chemotactic protein-1 production, and fluorometric detection of superoxide and hydrogen peroxide production decreased, whereas a concomitant increase in NO production was noted (all P < 0.01). Additionally, both monocyte adhesion ( P < 0.05) and MCA ( P < 0.01) decreased. Nine of 15 were no longer positive for metabolic syndrome postintervention. Intensive lifestyle modification may ameliorate novel coronary artery disease risk factors in men with metabolic syndrome factors before reversal of obesity.

Physiopathology of the embryonic heart (with special emphasis on hypoxia and reoxygenation)

The adaptative response of the developing heart to adverse intrauterine environment such as reduced O2 delivery can result in alteration of gene expression with short- and long-term consequences including adult cardiovascular diseases. The tolerance of the developing heart of acute or chronic oxygen deprivation, its capacity to recover during reperfusion and the mechanisms involved in reoxygenation injury are still under debate. Indeed, the pattern of response of the immature myocardium to hypoxia-reoxygenation differs from that of the adult. This review deals with the structural and metabolic characteristics of the embryonic heart and the functional consequences of hypoxia and reoxygenation. The relative contribution of calcium and sodium overload, pH disturbances and oxidant stress to the hypoxia-induced cardiac dysfunction is examined, as well as various cellular signaling pathways (e.g. MAP kinases) involved in cell survival or death. In the context of the recent advances in developmental cardiology and fetal cardiac surgery, a better understanding of the physiopathology of the stressed developing heart is required.

Antioxidant effects of ginsenoside Re in cardiomyocytes

We have previously demonstrated that American ginseng berry extract exhibited significant protection against oxidant-mediated injury in cardiomyocytes. To extend this work, we sought to investigate the antioxidant effects of Re, a protopanaxatriols-type and single chemical integrant present in American ginseng berry extract, using the same chick cardiomyocyte model of oxidant injury as well as ESR spectroscopy in a cell-free chemical system. In cells exposed to 2 h of H2O2 (0.5 mM), pretreatment with Re (0.05, 0.1, or 0.5 mg/ml for 2 h) significantly attenuated 2',7'-dichlorofluorescein (DCF) fluorescence by 51% (from 1345+/-67 to 658+/-46 a.u., P<0.001), and remarkably reduced cell death (from 51.5+/-3.0% to 11.8+/-1.5%, P<0.001, compared to the control). Similar results were also observed in cells exposed to antimycin A (100 microM), a mitochondrial electron transport chain site III inhibitor which increases endogenous oxidative stress. In the ESR study, however, Re failed to reduce the formation of the superoxide/DMPO adduct and DPPH radicals. These results suggest that ginsenoside Re functions as an antioxidant, protecting cardiomyocytes from oxidant injury induced by both exogenous and endogenous oxidants, and that its protective effects may be mostly attributed to scavenging H2O2 and hydroxyl radicals.

β2-adrenergic agonist protects human endothelial cells from hypoxia/reoxygenation injury in vitro

OBJECTIVE

Circulatory shock results in hypoxia/reoxygenation processes that lead to the release of reactive oxygen species, endothelial injury, and multiple organ failure. Previous data suggest that beta2-adrenergic agonists prevent endothelial dysfunction. The study aimed at determining whether the beta2-adrenergic agonist formoterol protects endothelial cells against hypoxia/reoxygenation injury in vitro.

DESIGN

Prospective controlled trial.

SETTING

University hospital research laboratory.

SUBJECTS

Cultured human umbilical vein endothelial cells (HUVECs).

INTERVENTIONS

Confluent HUVECs were sealed in a flow-through chamber mounted on an inverted microscope and perfused with a constant flow of Krebs medium. After 1 hr of equilibration, HUVECs underwent 2 hrs of hypoxia and 1 hr of reoxygenation. Cell death at the end of reoxygenation and reactive oxygen species formation were assessed with fluorescent probes propidium iodide and 2',7'-dichlorodihydrofluorescein diacetate, respectively. The effects of the beta2-adrenergic agonist formoterol, the beta2-adrenergic antagonist ICI 118,551 and the nitric oxide synthase inhibitor L-NNA were investigated. Statistical analysis was performed with analysis of variance followed by post hoc Fisher's test.

MEASUREMENTS AND MAIN RESULTS

Hypoxia/reoxygenation increased cell death (hypoxia/reoxygenation 29 +/- 4% vs. control 1 +/- 5%, p < .05) and endothelial reactive oxygen species production (hypoxia/reoxygenation 126 +/- 4% vs. control 108 +/- 4%, p < .05). Formoterol reduced cell death in a concentration-dependent manner (EC95 = 10 mol/L) and reduced endothelial reactive oxygen species production (hypoxia/reoxygenation + formoterol EC95 109 +/- 4% vs. hypoxia/reoxygenation 126 +/- 4%, p < .05). When added to formoterol EC95, ICI 118,551 and L-NNA abolished the formoterol-induced cell protection and reduced reactive oxygen species production.

CONCLUSIONS

These results indicate that formoterol reduces endothelial cell death and reactive oxygen species production in this in vitro hypoxia/reoxygenation model. These effects are beta2-adrenergic specific and are partially mediated by nitric oxide synthase.