Simulated Reperfusion Research Articles

Pharmacological activation of mitochondrial BKCa channels protects isolated cardiomyocytes against simulated reperfusion-induced injury

The aim of this study was to find out whether opening of mitochondrial large-conductance Ca(2+)-activated potassium channels (BK(Ca)) protects cardiomyocytes against injury caused by simulated ischemia and reperfusion. This study also aimed to determine whether the protective mechanism involves signaling by reactive oxygen species (ROS) and phosphatidylinositol-3-kinase (PI3K). We used isolated ventricular myocytes, which are believed to contain no functional BK(Ca) channels in the sarcolemma. Cells were isolated from the left ventricles of adult male Wistar rats and subjected to 25-min metabolic inhibition with NaCN and 2-deoxyglucose followed by 30-min re-energization. NS11021 (0.1 μmol/L), a novel BK(Ca) channel opener, or hydrogen peroxide (2 μmol/L) added at re-energization, increased cell survival (the number of rod-shaped cells) and markedly reduced the release of lactate dehydrogenase (LDH). These cytoprotective effects of NS11021 were completely abolished by paxilline, a BK(Ca) inhibitor, or tempol, an antioxidant, but not by wortmannin, an inhibitor of PI3K. NS11021 slightly but significantly increased the fluorescence signal in 2'7'-dichlorodihydrofluorescein diacetate (DCF-DA)-loaded myocytes, indicating an increased ROS formation. The NS11021-induced ROS formation was abolished by paxilline or tempol. NS13558 (0.1 μmol/L), an inactive structural analogue of NS11021, affected neither cell survival/LDH release nor DCF-DA fluorescence. These results suggest that pharmacological activation of mitochondrial BK(Ca) channels effectively protects isolated cardiomyocytes against injury associated with simulated reperfusion. The mechanism for this form of protection requires ROS signaling, but not the activation of the PI3K pathway.

Mechanisms involved in postconditioning protection of cardiomyocytes against acute reperfusion injury

Experimental and clinical studies demonstrated that postconditioning confers protection against myocardial ischemia/reperfusion injury. However the underlying cellular mechanisms responsible for the beneficial effect of postconditioning are still poorly understood. The aim of the present study was to examine the role of cytosolic and mitochondrial Ca2+-handling. For this purpose adult rat cardiomyocytes were subjected to simulated in vitro ischemia (glucose-free hypoxia at pH6.4) followed by simulated reperfusion with a normoxic buffer (pH7.4; 2.5mmol/L glucose). Postconditioning, i.e., 2 repetitive cycles of normoxic (5s) and hypoxic (2.5min) superfusion, was applied during the first 5min of reoxygenation. Mitochondrial membrane potential (ΔΨm), cytosolic and mitochondrial Ca2+ concentrations, cytosolic pH and necrosis were analysed applying JC-1, fura-2, fura-2/manganese, BCECF and propidium iodide, respectively. Mitochondrial permeability transition pore (MPTP) opening was detected by calcein release. Hypoxic treatment led to a reduction of ΔΨm, an increase in cytosolic and mitochondrial Ca2+ concentration, and acidification of cardiomyocytes. During the first minutes of reoxygenation, ΔΨm transiently recovered, but irreversibly collapsed after 7min of reoxygenation, which was accompanied by MPTP opening. Simultaneously, mitochondrial Ca2+ increased during reperfusion and cardiomyocytes developed spontaneous cytosolic Ca2+ oscillations and severe contracture followed by necrosis after 25min of reoxygenation. In postconditioned cells, the collapse in ΔΨm as well as the leak of calcein, the increase in mitochondrial Ca2+, cytosolic Ca2+ oscillations, contracture and necrosis were significantly reduced. Furthermore postconditioning delayed cardiomyocyte pH recovery. Postconditioning by hypoxia/reoxygenation was as protective as treatment with cyclosporine A. Combining cyclosporine A and postconditioning had no additive effect. The data of the present study demonstrate that postconditioning by hypoxia/reoxygenation prevents reperfusion injury by limiting mitochondrial Ca2+ load and thus opening of the MPTP in isolated cardiomyocytes. These effects seem to be supported by postconditioning-induced delay in pH recovery and suppression of Ca2+ oscillations. This article is part of a Special Issue entitled “Calcium Signaling in Heart”.

A novel in vitro model of ischaemic preconditioning: its effect on cell viability in human skeletal muscle and a possible explanation for the ‘second window of protection’

BackgroundThe ischaemia–reperfusion (IR) injury causes significant morbidity. Ischaemic preconditioning (IPC) is a technique for limiting the effects of the IR injury. Its potential has not yet been harnessed in orthopaedics. AimsTo establish a novel in vitro IR model using a human skeletal muscle cell line. Secondly, to introduce simulated IPC to the model and examine the effect of this on cell viability. MethodsA human skeletal muscle cell line was cultured in vitro. Placing the cells in a hypoxic buffer and a closed hypoxic environment simulated ischaemia. Reversing this process simulated reperfusion. IPC was simulated by alternate cycles of ischaemia and reperfusion. Cell viability comparisons were made between control and experimental groups of cells. ResultsA reproducible in vitro IR model was established. The addition of simulated IPC is associated with increased cell death at 12 and 24h of reperfusion. Significantly greater cell survival is seen in the IPC group when measured at 72h reperfusion. ConclusionsWe hypothesise that IPC initially decreases cell number. The remaining cells are more robust. This selected cell line then expands over the course of 72h and displays greater resistance to the IR injury. This theory can help explain delayed preconditioning.

Modulation of cardiac Na+,K+-ATPase cell surface abundance by simulated ischemia-reperfusion and ouabain preconditioning

Na(+),K(+)-ATPase and cell survival were investigated in a cellular model of ischemia-reperfusion (I/R)-induced injury and protection by ouabain-induced preconditioning (OPC). Rat neonatal cardiac myocytes were subjected to 30 min of substrate and coverslip-induced ischemia followed by 30 min of simulated reperfusion. This significantly compromised cell viability as documented by lactate dehydrogenase release and Annexin V/propidium iodide staining. Total Na(+),K(+)-ATPase α(1)- and α(3)-polypeptide expression remained unchanged, but cell surface biotinylation and immunostaining studies revealed that α(1)-cell surface abundance was significantly decreased. Na(+),K(+)-ATPase-activity in crude homogenates and (86)Rb(+) transport in live cells were both significantly decreased by about 30% after I/R. OPC, induced by a 4-min exposure to 10 μM ouabain that ended 8 min before the beginning of ischemia, increased cell viability in a PKCε-dependent manner. This was comparable with the protective effect of OPC previously reported in intact heart preparations. OPC prevented I/R-induced decrease of Na(+),K(+)-ATPase activity and surface expression. This model also revealed that Na(+),K(+)-ATPase-mediated (86)Rb(+) uptake was not restored to control levels in the OPC group, suggesting that the increased viability was not conferred by an increased Na(+),K(+)-ATPase-mediated ion transport capacity at the cell membrane. Consistent with this observation, transient expression of an internalization-resistant mutant form of Na(+),K(+)-ATPase α(1) known to have increased surface abundance without increased ion transport activity successfully reduced I/R-induced cell death. These results suggest that maintenance of Na(+),K(+)-ATPase cell surface abundance is critical to myocyte survival after an ischemic attack and plays a role in OPC-induced protection. They further suggest that the protection conferred by increased surface expression of Na(+),K(+)-ATPase may be independent of ion transport.

Alpha-lipoic acid pre- and post-treatments provide protection against in vitro ischemia-reperfusion injury in cerebral endothelial cells via Akt/mTOR signaling

Alpha-lipoic acid (ALA) is an endogenous short-chain fatty acid that has beneficial protective effects against various vascular diseases. In this study, we sought to determine whether ALA could induce pre- or post-treatment protective effects against simulated ischemia and reperfusion-induced cerebral endothelial cell (CEC) injury by activating the Akt/mTOR pathway. CECs are currently considered to be an important target for ischemia therapy. Mouse brain endothelial cells (bEnd.3) and primary cultures of CECs were subjected to 6h of oxygen glucose deprivation (OGD) followed by 4h of simulated reperfusion, either alone or together with ALA administration before (pre-treatment) or immediately after (post-treatment) OGD. We found that pre-treatment administration of ALA reduced the OGD and simulated reperfusion-induced lactate dehydrogenase (LDH) release in bEnd.3 cells in a dose-dependent manner and that 1mM ALA pre- and post-treatments provided protection in both bEnd.3 cells and primary cultures of CECs. However, rapamycin, an mTOR inhibitor, was able to thoroughly abolish the protective effects of ALA. Western blotting showed that the ALA pre- and post-treatments up-regulated the phosphorylation of Akt, mTOR, S6K and 4E-BP1 in both bEnd.3 cells and primary cultures. However, after pre-treatment with rapamycin, the level of Akt phosphorylation was decreased in primary cultures of CECs but could still be restored by ALA, whereas the levels of mTOR, S6K and 4E-BP1 phosphorylation were significantly decreased and could not be restored. These results suggest that ALA pre- and post-treatments provide protective effects against simulated ischemia and reperfusion-induced CEC injury by promoting the Akt/mTOR pathway and that mTOR is required for ALA protection.

Impact of hypoxia, simulated ischemia and reperfusion in HL-1 cells on the expression of FKBP12/FKBP12.6 and intracellular calcium dynamics

AimsTo establish a cardiac cell culture model for simulated ischemia and reperfusion and in this model investigate the impact of simulated ischemia and reperfusion on expression of the calcium handling proteins FKBP12 and FKBP12.6, and intracellular calcium dynamics. MethodsHL-1 cell cultures were exposed to normoxia (as control), hypoxia, simulated ischemia (HEDA) or HEDA+reactive oxygen species (ROS) for up to 24h and after HEDA, with or without ROS, followed or not by simulated reperfusion (REPH) for 6h. Viability was analyzed with a trypan blue exclusion method. Cell lysates were analyzed with real-time PCR and Western blot (WB) for FKBP12 and FKBP12.6. Intracellular Ca2+measurements were performed using dual-wavelength ratio imaging in fura-2 loaded cells. ResultsA time-dependent drop in viability was shown after HEDA (P<0.001). Viability was not further influenced by addition of ROS or REPH. The general patterns of FKBP12 and FKBP12.6 mRNA expression showed upregulation after hypoxia, downregulation after ischemia and normalization after reperfusion, which was partially attenuated if ROS was added during HEDA. The protein contents were unaffected after hypoxia, tended to increase after ischemia and, for FKBP12.6, a further increase after reperfusion was shown. Hypoxia or HEDA, with or without REPH, resulted in a decreased amplitude of the Ca2+ peak in response to caffeine. In addition, cells subjected to HEDA for 3h or HEDA for 3h followed by 6h of REPH displayed irregular Ca2+ oscillations with a decreased frequency. ConclusionA threshold for cell survival with respect to duration of ischemia was established in our cell line model. Furthermore, we could demonstrate disturbances of calcium handling in the sarcoplasmic reticulum as well as alterations in the expressions of the calcium handling proteins FKBP12 and FKBP12.6, why this model may be suitable for further studies on ischemia and reperfusion with respect to calcium handling of the sarcoplasmic reticulum.

107 Remote ischaemic preconditioning and human atrial trabeculae in the diabetic heart

IntroductionRemote ischaemic preconditioning (RIPC) using brief cycles of upper or lower limb ischaemia and reperfusion has been reported to protect the heart against ischaemia-reperfusion injury (IRI). Previous studies suggest that...

Type 10 adenylyl cyclase mediates mitochondrial Bax translocation and apoptosis of adult rat cardiomyocytes under simulated ischaemia/reperfusion

Apoptosis of cardiomyocytes significantly contributes to the development of post-ischaemic cardiomyopathy. Although mitochondria have been suggested to play a crucial role in this process, the precise mechanisms controlling the mitochondria-dependent apoptosis in cardiomyocytes under ischaemia/reperfusion are still poorly understood. Here we aimed to analyse the role of the soluble adenylyl cyclase (sAC). Adult rat cardiomyocytes were subjected to simulated in vitro ischaemia (SI) consisting of glucose-free anoxia at pH 6.4. Apoptosis was detected by DNA laddering, chromatin condensation, and caspases cleavage. SI led to the translocation of sAC to the mitochondria and mitochondrial depolarization followed by cytochrome c release, caspase-9/-3 cleavage and apoptosis during simulated reperfusion (SR). Pharmacological inhibition of sAC during SI, but not during SR, significantly reduced the SI/SR-induced mitochondrial injury and apoptosis. Similarly, sAC knock-down mediated by an adenovirus coding for shRNA targeting sAC prevented the activation of the mitochondrial pathway of apoptosis. Analysis of the link between sAC and apoptosis revealed a sAC and protein kinase A-dependent Bax phosphorylation at Thr(167) and its translocation to mitochondria during SI, which subsequently caused mitochondrial oxygen radical formation followed by cytochrome c release and caspase-9 cleavage during SR. These results suggest a key role of sAC in SI-induced mitochondrial Bax translocation and activation of the mitochondrial pathway of apoptosis in adult cardiomyocytes.

Reversible translocation of ASK1 to a Triton-X100 insoluble cytoplasmic compartment during cardiac myocyte cell stress

ASK1 is a cellular stress-responsive MAPKKK which activates the JNK and p38 MAPK pathways that play a key role in the response of cardiac myocytes to redox stress following ischemia/reperfusion. ASK1 becomes incorporated into high-molecular weight complexes upon activation but this has not been investigated in cardiac myocytes. Here we examine the distribution of ASK1 in neonatal rat cardiomyocytes undergoing simulated ischemia and reperfusion. Simulated ischemia or redox stress in neonatal cardiac myocytes causes the translocation of ASK1 to distinct punctate cytoplasmic structures that are insoluble in Triton X-100. The translocation event is not dependent on ASK1 kinase activity, occurs subsequent to activation and is reversible upon removal of the cell stress. The structures to which ASK1 translocates in cardiac myocytes do not appear to correspond to the previously described ASK1 signalosome reported in other cell types.

Salvianolic Acid A Demonstrates Cardioprotective Effects in Rat Hearts and Cardiomyocytes After Ischemia/Reperfusion Injury

Salvianolic acid A (Sal A), the water-soluble component from the root of the Salvia miltiorrhiza plant, possesses antioxidant, antiproliferative, and antiplatelet properties. However, whether it plays a role in the protection against ischemia-reperfusion (I/R) injury in rat hearts has yet to be elucidated. In the present study, we tested cell viability, shortening amplitude, necrosis, apoptosis, and the expression levels of Akt, phosphorylated Akt, Bcl-2, Bax, and caspase-3 after 3-hour simulated ischemia and 2- or 6-hour simulated reperfusion in cardiomyocytes. We further observed the contractile function and infarct size in isolated hearts after they were subjected to global 30-minute ischemia and 120-minute reperfusion. Pretreatment with Sal A markedly increased cell viability and shortening amplitude while reducing evidence of necrosis and apoptosis in the cells. In addition, the expression of Bcl-2 was upregulated and Bax was downregulated, thereby increasing the Bcl-2/Bax ratio. Sal A inhibited the activation of caspase-3 as well. The results also showed that Sal A significantly increased phosphorylation of Akt and that this phosphorylation can be partially inhibited by phosphoinositide 3-kinase/Akt inhibitor. Furthermore, Sal A improved I/R-induced myocardial contractile function and reduced infarct size. In summary, our results showed that Sal A prevents I/R-induced myocardial damage by reducing necrosis and apoptosis in isolated rat hearts and cardiomyocytes.

Effects of simulated ischemia-reperfusion and atorvastatin on INa in rat left ventricular myocytes.

ObjectiveTo observe time dependent effects of simulated ischemia-reperfusion on transient sodium currents (INa) in rat left ventricular myocytes, and effects of atorvastatin on INa in the condition of ischemia and...

Effects of atorvastatin on transient sodium currents in rat normal/simulated ischemia/reperfusion ventricular cell

BackgroundSome clinical trials have shown statins have anti-arrhythmic effects and can improve clinical results. But its mechanism is unclear.Objectiveobserving the effects of atorvastatin on transient sodium currents in rat normal/simulated...

Mechanism of glutathione depletion during simulated ischemia-reperfusion of H9c2 cardiac myocytes

It has been reported that myocardial glutathione content is decreased during ischemia-reperfusion, but the mechanism of glutathione depletion has remained unclear. The present study tested whether osmotic stress is involved in the glutathione depletion during ischemia. Six hours of hypoxic acidosis with either high CO2 tension or low HCO3− concentration, which simulates the ischemic condition, resulted in a significant decrease of glutathione content and the glutathione depletion was prevented by hyperosmolarity. High-CO2 acidosis alone without hypoxia induced a similar degree of glutathione depletion. Intracellular pH was lowered by high-CO2 acidosis to 6.41 ± 0.03 in 15 min. Meanwhile, the cell size gradually increased and reached ∼110% in 10 min and the increased cell size was maintained for at least 30 min, which was also prevented by hyperosmolarity. Subsequent experiments observed the effects of simulated reperfusion on the glutathione content. Measured in 1 h after the hypoxic acidotic reperfusion, the glutathione content was further decreased compared to the level at the end of ischemia, which was not suppressed by increasing the osmolarity of reperfusion solution. The degree of glutathione depletion during hypoxic reperfusion with normal pH was similar to the hypoxic acidotic reperfusion group. On the other hand, normoxic reperfusion was not accompanied by further depletion of glutathione content. Based on these results, it was concluded that ischemia induces the glutathione depletion via osmotic stress, which results from intracellular acidification, and the glutathione content is further decreased during reperfusion through a mechanism other than oxygen toxicity.

P38 MAPK-dependent small HSP27 and αB-crystallin phosphorylation in regulation of myocardial function following cardioplegic arrest.

We previously demonstrated that myocardial p38 mitogen-activated protein kinase (MAPK) and heat shock protein 27 (HSP27) are phosphorylated following cardioplegic arrest in patients undergoing cardiac surgery and correlate with reduced cardiac function. The following studies were performed to determine whether inhibition of p38 MAPK and/or overexpression of nonphosphorylatable HSP27 improves cardiac function following cardioplegic arrest. Langendorff-perfused isolated rat hearts were subjected to 2 h of intermittent cold cardioplegia followed by 30 min of reperfusion. Hearts were treated with (CP+SB) or without (CP) the p38 MAPK inhibitor SB-203580 (5 μM) supplied in the cardioplegia. Sham-treated hearts served as controls. In separate experiments, isolated rat ventricular myocytes infected with either green fluorescent protein (GFP) or a nonphosphorylatable HSP27 mutant (3A-HSP27) were subjected to 3 h of cold hypoxic cardioplegia and simulated reperfusion (CP) followed by video microscopy and length change measurements. Baseline parameters of cardiac function were similar between groups [left ventricular developed pressure (LVDP), 119 ± 4.9 mmHg; positive and negative first derivatives of LV pressure (± dP/dt), 3,139 ± 245 and 2, 314 ± 110 mmHg/s]. CP resulted in reduced cardiac function (LVDP, 72.2 ± 5.8 mmHg; ± dP/dt, 2,076 ± 231 and -1,317 ± 156 mmHg/s) compared with baseline. Treatment with 5 μM SB-203580 significantly improved CP-induced cardiac function (LVDP, 101.9 ± 0 mmHg; ± dP/dt, 2,836 ± 163 and -2,108 ± 120 mmHg/s; P = 0.03, 0.01, and 0.04, CP+SB vs. CP). Inhibition of p38 MAPK significantly lowered CP-induced p38 MAPK, HSP27, and αB-crystallin (cryAB) phosphorylation. In vitro CP decreased myocyte length changes from 10.3 ± 1.5% (GFP) to 5.7 ± 0.8% (GFP+CP). Infection with 3A-HSP27 completely rescued CP-induced decreased myocyte contraction (11.1 ± 1.0%). However, infection with 3A-HSP27 did not block the endogenous HSP27 response. We conclude that inhibition of p38 MAPK and subsequent HSP27 and cryAB phosphorylation and/or overexpression of nonphosphorylatable HSP27 significantly improves cardiac performance following cardioplegic arrest. Modulation of HSP27 phosphorylation may improve myocardial stunning following cardiac surgery.

Volatile anesthetic post-treatment induces protection via inhibition of glycogen synthase kinase 3β in human neuron-like cells

Application of the volatile anesthetic isoflurane during the early phase of reperfusion reduces ischemic heart and brain injury (anesthetic post-conditioning). We hypothesize that inhibition of glycogen synthase kinase 3β (GSK3β), a protein whose activation can lead to cell death, participates in anesthetic post-conditioning-induced neuroprotection. SH-SY5Y cells, a human neuroblastoma cell line, were induced by retinoic acid to differentiate into terminal neuron-like cells. The cells were then subjected to a 1-h oxygen-glucose deprivation (OGD), a condition to simulate ischemia in vitro, and a 20-h simulated reperfusion. Isoflurane, sevoflurane or desflurane, three commonly used volatile anesthetics, were applied for 1 h during the early phase of simulated reperfusion. Cell injury was quantified by lactate dehydrogenase (LDH) release. Phospho-GSK3β at Ser9 and total GSK3β were quantified at 1 or 3 h after the OGD. OGD increased LDH release, suggesting that OGD induced cell injury. Post-treatment with isoflurane, sevoflurane or desflurane reduced this cell injury. This protection was apparent when 2% isoflurane was applied within 1 h after the onset of reperfusion. Isoflurane post-treatment also significantly increased the phosphorylation of GSK3β at Ser9 at 1 h after the OGD. GSK3β inhibitors reduced OGD and simulated reperfusion-induced LDH release. The combination of GSK3β inhibitors and isoflurane post-conditioning did not cause a greater protection than isoflurane post-conditioning alone. These results suggest that volatile anesthetic post-conditioning reduces OGD and simulated reperfusion-induced cell injury. Since phospho-GSK3β at Ser9 decreases GSK3β activity, our results suggest that volatile anesthetic post-conditioning in human neuron-like cells may be mediated by GSK3β inhibition.

Isoflurane preconditioning and postconditioning in rat hippocampal neurons

The volatile anesthetic isoflurane is capable of inducing preconditioning and postconditioning effects in the brain. However, the mechanisms for these neuroprotective effects are not fully understood. Here, we showed that rat hippocampal neuronal cultures exposed to 2% isoflurane for 30min at 24h before a 1h oxygen-glucose deprivation (OGD) and a 24h simulated reperfusion had a reduced lactate dehydrogenase release. Similarly, this OGD and simulated reperfusion-induced lactate dehydrogenase release was attenuated by exposing the neuronal cultures to 2% isoflurane for 1h at various times after the onset of the simulated reperfusion (isoflurane postconditioning). The combination of isoflurane preconditioning and postconditioning induced a better neuroprotection than either alone. Inhibition of the calcium/calmodulin-dependent protein kinase II (CaMKII), inhibition of N-methyl d-aspartate (NMDA) receptors, or activation of adenosine A2A receptors resulted in reduction of the OGD and simulated reperfusion-induced cell injury. The combination of CaMKII inhibition and isoflurane preconditioning or postconditioning did not provide better protection than CaMKII inhibition, isoflurane preconditioning, or isoflurane postconditioning alone. The combination of NMDA receptor inhibition and isoflurane postconditioning was not better than NMDA receptor inhibition or isoflurane postconditioning alone for neuroprotection. However, the combination of adenosine A2A receptor activation with either isoflurane preconditioning or isoflurane postconditioning induced a better neuroprotective effect than adenosine A2A receptor activation, isoflurane preconditioning, or isoflurane postconditioning alone. The combination of NMDA receptor inhibition and isoflurane preconditioning caused a better neuroprotective effect than NMDA receptor inhibition or isoflurane preconditioning alone. These results suggest that isoflurane preconditioning- and postconditioning-induced neuroprotection can be additive. Isoflurane preconditioning and isoflurane postconditioning may involve CaMKII inhibition, but may not involve adenosine A2A receptor activation. Inhibition of NMDA receptors may mediate the effects of isoflurane postconditioning, but not isoflurane preconditioning.

Statin post-treatment provides protection against simulated ischemia in bovine pulmonary arterial endothelial cells

Statins, inhibitors of 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase, can have protective effects in various organs. We determined whether application of statins after a detrimental insult protected endothelial cells. Bovine pulmonary arterial endothelial cells (BPAEC) were subjected to a 5-h oxygen-glucose deprivation (OGD) and a 1-h simulated reperfusion. Simvastatin or atorvastatin alone or plus mevalonate (the immediate product of the reaction mediated by HMG-CoA reductase), geranylgeranyl pyrophosphate (GGPP, a product downstream of mevalonate), Ly294002 (a protein kinase B/Akt inhibitor), U0126 [an extracellular signal-regulated kinase (ERK) pathway inhibitor] or diphenyleneiodonium [a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor] were added to cells immediately after the OGD for 1h. Simvastatin and atorvastatin dose-dependently reduced the OGD and simulated reperfusion-induced lactate dehydrogenase (LDH) release from primary BPAEC and BPAEC between passage 4 and 15. This effect was inhibited by mevalonate, GGPP and Ly294002 and was not affected by U0126. Consistent with those results, simvastatin and atorvastatin increased the expression of phospho-Akt/activated Akt, and did not change the expression of phospho-ERK/activated ERK after the OGD and simulated reperfusion. The OGD and simulated reperfusion-induced LDH release and superoxide production, as measured by the dihydroethidium fluorescent intensity, were inhibited by diphenyleneiodonium. These results suggest that statin post-treatment reduces OGD and simulated reperfusion-induced cell injury. This effect may be mediated by inhibiting HMG-CoA reductase and the subsequent inhibition of small GTPases. GTPase activation depends on GGPP generation and contributes to the formation of NADPH oxidase complex that produces superoxide. The statin post-treatment-induced protection may also involve activated Akt.

Direct evidence of chloride ion efflux in ischaemic and pharmacological preconditioning of cultured cardiomyocytes

We have previously shown that reduction of ischaemic cell swelling via enhanced cell volume regulation is a key mechanism of ischaemic preconditioning (IPC) in cardiomyocytes. We have also shown that pharmacological blockade of Cl(-) channels abolishes cardioprotection achieved by IPC in Langendorff-perfused hearts and freshly isolated cardiomyocytes, thus suggesting that Cl(-) plays a key role in IPC cardioprotection. However, direct evidence of Cl(-) channel activation resulting in transsarcolemmal Cl(-) efflux by IPC had been lacking. To address this issue, 24 h cultured rabbit cardiomyocytes were loaded with 5 mM 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ), a specific fluorescence indicator that is quenched by Cl(-) so that cellular efflux of Cl(-) results in an increase in SPQ fluorescence. After stabilization for 10 min, cardiomyocytes were preconditioned either with 10 min simulated ischaemia/10 min simulated reperfusion or with 10 min treatment with 1 microM N(6)-2-(4-aminophenyl)ethyladenosine (APNEA). IPC and APNEA significantly (P < 0.001) reduced the intracellular Cl(-) concentration ([Cl(-)](i)) to 31.9 +/- 3.2 mM (mean +/- SEM) and 32.5 +/- 2.8 mM, respectively, from an initial [Cl(-)](i) (pooled stabilization 61.5 +/- 7.1 mM). [Cl(-)](i) did not change in control (non-preconditioned) cardiomyocytes (control 58.1 +/- 1.9 mM and control + vehicle 62.6 +/- 4.9 mM, P = 0.98 and 0.99 vs. pooled pre-treatment baseline, respectively). Inhibition of Cl(-) channels with 50 microM indanyloxyacetic acid 94 completely blocked preconditioning-induced Cl(-) efflux. Thus, a net Cl(-) efflux of 29.6 and 29.0 mM was triggered by IPC and APNEA. These findings provide the first direct evidence of activation of sarcolemmal Cl(-) channels by ischaemic and pharmacological preconditioning in cardiomyocytes.

Ischemia Activates the ATF6 Branch of the Endoplasmic Reticulum Stress Response

Stresses that perturb the folding of nascent endoplasmic reticulum (ER) proteins activate the ER stress response. Upon ER stress, ER-associated ATF6 is cleaved; the resulting active cytosolic fragment of ATF6 translocates to the nucleus, binds to ER stress response elements (ERSEs), and induces genes, including the ER-targeted chaperone, GRP78. Recent studies showed that nutrient and oxygen starvation during tissue ischemia induce certain ER stress response genes, including GRP78; however, the role of ATF6 in mediating this induction has not been examined. In the current study, simulating ischemia (sI) in a primary cardiac myocyte model system caused a reduction in the level of ER-associated ATF6 with a coordinate increase of ATF6 in nuclear fractions. An ERSE in the GRP78 gene not previously shown to be required for induction by other ER stresses was found to bind ATF6 and to be critical for maximal ischemia-mediated GRP78 promoter induction. Activation of ATF6 and the GRP78 promoter, as well as grp78 mRNA accumulation during sI, were reversed upon simulated reperfusion (sI/R). Moreover, dominant-negative ATF6, or ATF6-targeted miRNA blocked sI-mediated grp78 induction, and the latter increased cardiac myocyte death upon simulated reperfusion, demonstrating critical roles for endogenous ATF6 in ischemia-mediated ER stress activation and cell survival. This is the first study to show that ATF6 is activated by ischemia but inactivated upon reperfusion, suggesting that it may play a role in the induction of ER stress response genes during ischemia that could have a preconditioning effect on cell survival during reperfusion.

In vitro modeling of nonhypoxic cold ischemia–reperfusion simulating lung transplantation

Although anoxia/reoxygenation of cultured cells has been used to model lung ischemia-reperfusion injury, this does not accurately mimic events experienced by lung cells while a lung is retrieved from a donor, stored, and transplanted. We developed an in vitro model of nonhypoxic ischemia-reperfusion injury to simulate these events. Human umbilical vein endothelial cells underwent simulated cold ischemia by replacing 37 degrees C culture media with 4 degrees C Perfadex (Vitrolife, Kungsbacka, Sweden) solution for 5 hours in 100% O(2). Culture dishes were allowed to warm to room temperature for 1 hour (implantation), and then Perfadex solution was replaced with 37 degrees C culture media (reperfusion). During cold ischemia, the human umbilical vein endothelial cell filamentous actin cytoskeleton quickly became rearranged, and gaps developed in the previously confluent monolayer occupying 20% of the surface area. Simulated reperfusion resulted in reorganization to a confluent monolayer. Development of gaps was not due to enhanced necrosis based on lactate dehydrogenase retention assay. Endothelial cytoskeletal rearrangement could account for early edema caused by ischemia-reperfusion injury with reperfusion. Mitogen-activated protein kinase and nuclear factor kappaB activation occurred with simulated reperfusion despite normoxia. Levels of the proinflammatory cytokines interleukin 6 and interleukin 8 were significantly increased in media at the end of reperfusion. Exposing human umbilical vein endothelial cells to simulated cold ischemia without hypoxia causes reversible cytoskeletal alterations, activation of inflammatory pathways, and elaboration of cytokines. Because this model accurately depicts events occurring during lung transplantation, it will be useful to explore mechanisms regulating lung cell response to this unique form of ischemia-reperfusion injury.