Minimally invasive treatment of left main coronary artery thrombosis in a young patient with COVID-19.

COVID-19 has been associated with cardiovascular events. This case demonstrates severe left main coronary artery thrombosis with distal embolisation in a young male patient admitted with COVID-19 who developed ST-elevation myocardial infarction. The patient was treated with thrombus aspiration combined with aggressive anticoagulant treatment, which yielded complete resolution of the thrombus. Left main thrombus represents a life-threatening coronary event and is most often associated with atherosclerotic plaque rupture. In this case, however, we suspect that COVID-19-related intimal inflammation and hypercoagulopathy might be the causal mechanism of thrombus formation. Revascularisation with coronary artery bypass grafting or percutaneous coronary intervention is the standard treatment of left main thrombosis. However, due to the patient's young age and lack of significant atherosclerotic disease burden, we used a conservative medical treatment strategy using potent antithrombotic therapy.

Migraine-Associated Mutation in the Na,K-ATPase Leads to Disturbances in Cardiac Metabolism and Reduced Cardiac Function.

Background Mutations in ATP1A2 gene encoding the Na,K-ATPase α2 isoform are associated with familial hemiplegic migraine type 2. Migraine with aura is a known risk factor for heart disease. The Na,K-ATPase is important for cardiac function, but its role for heart disease remains unknown. We hypothesized that ATP1A2 is a susceptibility gene for heart disease and aimed to assess the underlying disease mechanism. Methods and Results Mice heterozygous for the familial hemiplegic migraine type 2-associated G301R mutation in the Atp1a2 gene (α2+/G301R mice) and matching wild-type controls were compared. Reduced expression of the Na,K-ATPase α2 isoform and increased expression of the α1 isoform were observed in hearts from α2+/G301R mice (Western blot). Left ventricular dilation and reduced ejection fraction were shown in hearts from 8-month-old α2+/G301R mice (cardiac magnetic resonance imaging), and this was associated with reduced nocturnal blood pressure (radiotelemetry). Cardiac function and blood pressure of 3-month-old α2+/G301R mice were similar to wild-type mice. Amplified Na,K-ATPase-dependent Src kinase/Ras/Erk1/2 (p44/42 mitogen-activated protein kinase) signaling was observed in hearts from 8-month-old α2+/G301R mice, and this was associated with mitochondrial uncoupling (respirometry), increased oxidative stress (malondialdehyde measurements), and a heart failure-associated metabolic shift (hyperpolarized magnetic resonance). Mitochondrial membrane potential (5,5´,6,6´-tetrachloro-1,1´,3,3´-tetraethylbenzimidazolocarbocyanine iodide dye assay) and mitochondrial ultrastructure (transmission electron microscopy) were similar between the groups. Proteomics of heart tissue further suggested amplified Src/Ras/Erk1/2 signaling and increased oxidative stress and provided the molecular basis for systolic dysfunction in 8-month-old α2+/G301R mice. Conclusions Our findings suggest that ATP1A2 mutation leads to disturbed cardiac metabolism and reduced cardiac function mediated via Na,K-ATPase-dependent reactive oxygen species signaling through the Src/Ras/Erk1/2 pathway.

Myocardial subcellular glycogen distribution and sarcoplasmic reticulum Ca2+ handling: effects of ischaemia, reperfusion and ischaemic preconditioning.

Ischaemic preconditioning (IPC) protects against myocardial ischaemia-reperfusion injury. The metabolic and ionic effects of IPC remain to be clarified in detail. We aimed to investigate the effect of IPC (2 times 5 min ischaemia) on the subcellular distribution of glycogen and Ca2+-uptake and leakiness by the sarcoplasmic reticulum (SR) in response to ischaemia-reperfusion in cardiomyocytes of isolated perfused rat hearts (Wistar rats, 335 ± 25 g). As estimated by quantitative transmission electron microscopy, the pre-ischaemic contribution [%, mean (95% CI)] of three sub-fractions of glycogen relative to total glycogen was 50 (39:61) as subsarcolemmal, 41 (31:50) as intermyofibrillar, and 9 (5:13) as intramyofibrillar glycogen. After 25 min of ischaemia, the relative contribution (%) of subsarcolemmal glycogen decreased to 39 (32:47) in control hearts (Con) and to 38 (31:45) in IPC. After 15 min reperfusion the contribution of subsarcolemmal glycogen was restored to pre-ischaemic levels in IPC hearts, but not in Con hearts. IPC increased the left ventricular developed pressure following ischaemia-reperfusion compared with Con. In saponin-skinned cardiomyocyte bundles, ischaemia reduced the SR Ca2+-uptake rate, with no effect of IPC. However, IPC reduced a SR Ca2+-leakage at pre-ischaemia, after ischaemia and during reperfusion. In conclusion, subsarcolemmal glycogen was preferentially utilised during sustained myocardial ischaemia. IPC improved left ventricular function reflecting reduced ischaemia-reperfusion injury, mediated a re-distribution of glycogen towards a preferential storage within the subsarcolemmal space during reperfusion, and lowered SR Ca2+-leakage. Under the present conditions, we found no temporal associations between alterations in glycogen localisation and SR Ca2+ kinetics.

Impact of Administration Time and Kv7 Subchannels on the Cardioprotective Efficacy of Kv7 Channel Inhibition.

PURPOSE: The mechanism of cardioprotection by Kv7.1-5 (KCNQ1-5) channels inhibition by XE991 is unclear. We examined the impact of administration time on the cardioprotective efficacy of XE991, the involvement of key pro-survival kinases, and the importance of the Kv7 subchannels. METHODS: Isolated perfused rat hearts were divided into five groups: 1) vehicle, 2) pre-, 3) post- or 4) pre- and post-ischemic administration of XE991 or 5) chromanol 293B (Kv7.1 inhibitor) followed by infarct size quantification. HL-1 cells undergoing simulated ischemia/reperfusion were exposed to either a) vehicle, b) pre-, c) per-, d) post-ischemic administration of XE991 or pre-, per- and post-ischemic administration of e) XE991, f) Chromanol 293B or g) HMR1556 (Kv7.1 inhibitor). HL-1 cell injury was evaluated by propidium iodide/Hoechst staining. Pro-survival kinase activation of Akt, Erk and STAT3 in XE991-mediated HL-1 cell protection was evaluated using phosphokinase inhibitors. Kv7 subtype expression was examined by RT-PCR and qPCR. RESULTS: XE991, but not Chromanol 293B, reduced infarct size and improved hemodynamic recovery in all isolated heart groups. XE991 protected HL-1 cells when administered during simulated ischemia. Minor activation of the survival kinases was observed in cells exposed to XE991 but pharmacological inhibition of kinase activation did not reduce XE991-mediated protection. Kv7 subchannels 1-5 were all present in rat hearts but predominately Kv7.1 and Kv7.4 were present in HL-1 cells and selective Kv7.1 did not reduce ischemia/reperfusion injury. CONCLUSION: The cardioprotective efficacy of XE991 seems to depend on its presence during ischemia and early reperfusion and do not rely on RISK (p-Akt and p-Erk) and SAFE (p-STAT3) pathway activation. The protective effect of XE991 seems mainly mediated through the Kv7.4 subchannel.

Cardioprotective effect of succinate dehydrogenase inhibition in rat hearts and human myocardium with and without diabetes mellitus.

Ischemia reperfusion (IR) injury may be attenuated through succinate dehydrogenase (SDH) inhibition by dimethyl malonate (DiMAL). Whether SDH inhibition yields protection in diabetic individuals and translates into human cardiac tissue remain unknown. In isolated perfused hearts from 24 weeks old male Zucker diabetic fatty (ZDF) and age matched non-diabetic control rats and atrial trabeculae from patients with and without diabetes, we compared infarct size, contractile force recovery and mitochondrial function. The cardioprotective effect of a 10 minutes DiMAL administration prior to global ischemia and ischemic preconditioning (IPC) was evaluated. In non-diabetic hearts exposed to IR, DiMAL 0.1 mM reduced infarct size compared to IR (55 ± 7% vs. 69 ± 6%, p < 0.05). Mitochondrial respiration was reduced by DiMAL 0.6 mM compared to sham and DiMAL 0.1 mM (p < 0.05). In diabetic hearts an increased concentration of DiMAL (0.6 mM) was required for protection compared to IR (64 ± 13% vs. 79 ± 8%, p < 0.05). Mitochondrial function remained unchanged. In trabeculae from humans without diabetes, IPC and DiMAL improved contractile force recovery compared to IR (43 ± 12% and 43 ± 13% vs. 23 ± 13%, p < 0.05) but in patients with diabetes only IPC provided protection compared to IR (51 ± 15% vs. 21 ± 8%, p < 0.05). Neither IPC nor DiMAL modulated mitochondrial respiration in patients. Cardioprotection by SDH inhibition is possible in human tissue, but depends on diabetes status. The narrow therapeutic range and discrepancy in respiration between experimental and human studies may limit clinical translation.

Impact of hyperglycemia on myocardial ischemia-reperfusion susceptibility and ischemic preconditioning in hearts from rats with type 2 diabetes.

BACKGROUND: The mechanisms underlying increased mortality in patients with diabetes and admission hyperglycemia after an acute coronary syndrome may involve reduced capacity for cardioprotection. We investigated the impact of hyperglycemia on exogenously activated cardioprotection by ischemic preconditioning (IPC) in hearts from rats with type 2 diabetes mellitus (T2DM) that were endogenously cardioprotected by an inherent mechanism, and the involvement of myocardial glucose uptake (MGU) and myocardial O-linked ß-N-acetylglucosamine (O-GlcNAc). METHODS AND RESULTS: In isolated, perfused rat hearts subjected to ischemia-reperfusion, infarct size (IS) was overall larger during hyper- ([Glucose] = 22 mmol/L]) than normoglycemia ([Glucose] = 11 mmol/L]) (p < 0.001). IS was smaller in 12-week old Zucker diabetic fatty rats with recent onset T2DM (fa/fa) than in rats without T2DM (fa/+) (n = 8 in each group) both during hyperglycemia (p < 0.05) and normoglycemia (p < 0.05). IPC (2 × 5 min cycles) reduced IS during normo- (p < 0.01 for both groups) but not during hyperglycemia independently of the presence of T2DM. During hyperglycemia, an intensified IPC stimulus (4 × 5 min cycles) reduced IS only in hearts from animals with T2DM (p < 0.05). IPC increased MGU and O-GlcNAc levels during reperfusion in animals with and without T2DM at normoglycemia (MGU: p < 0.05, O-GlcNAc: p < 0.01 for both groups) but not during hyperglycemia. Intensified IPC at hyperglycemia increased MGU (p < 0.05) and O-GlcNAc levels (p < 0.05) only in hearts from animals with T2DM. CONCLUSION: While the effect of IPC is reduced during hyperglycemia in rats without T2DM, endogenous cardioprotection in animals with T2DM is not influenced by hyperglycemia and the capacity for exogenous cardioprotection by IPC is preserved. MGU and O-GlcNAc levels are increased by exogenously induced cardioprotection by IPC but not by endogenous cardioprotection in animals with T2DM reflecting different underlying mechanisms by exogenous and endogenous cardioprotection.

Influence of long-term treatment with glyceryl trinitrate on remote ischemic conditioning.

Remote ischemic conditioning (RIC) protects against sustained myocardial ischemia. Because of overlapping mechanisms, this protection may be altered by glyceryl trinitrate (GTN), which is commonly used in the treatment of patients with chronic ischemic heart disease. We investigated whether long-term GTN treatment modifies the protection by RIC in the rat myocardium and human endothelium. We studied infarct size (IS) in rat hearts subjected to global ischemia-reperfusion (I/R) in vitro and endothelial function in healthy volunteers subjected to I/R of the upper arm. In addition to allocated treatment, rats were coadministered with reactive oxygen species (ROS) or nitric oxide (NO) scavengers. Rats and humans were randomized to 1) control, 2) RIC, 3) GTN, and 4) GTN + RIC. In protocols 3 and 4, rats and humans underwent long-term GTN treatment for 7 consecutive days, applied subcutaneously or 2 h daily transdermally. In rats, RIC and long-term GTN treatment reduced mean IS (18 ± 12%, P = 0.007 and 15 ± 5%, P = 0.002) compared with control (35 ± 13%). RIC and long-term GTN treatment in combination did not reduce IS (29 ± 12%, P = 0.55 vs. control). ROS and NO scavengers both attenuated IS reduction by RIC and long-term GTN treatment. In humans, I/R reduced endothelial function ( P = 0.01 vs. baseline). Separately, RIC and long-term GTN prevented the reduction in endothelial function caused by I/R; given in combination, prevention was lost. RIC and long-term GTN treatment both protect against rat myocardial and human endothelial I/R injury through ROS and NO-dependent mechanisms. However, when given in combination, RIC and long-term GTN treatment fail to confer protection. NEW & NOTEWORTHY Remote ischemic conditioning (RIC) and long-term glyceryl trinitrate (GTN) treatment protect against ischemia-reperfusion injury in both human endothelium and rat myocardium. However, combined application of RIC and long-term GTN treatment abolishes the individual protective effects of RIC and GTN treatment on ischemia-reperfusion injury, suggesting an interaction of clinical importance.

Effects of hypoglycemia on myocardial susceptibility to ischemia-reperfusion injury and preconditioning in hearts from rats with and without type 2 diabetes.

BACKGROUND: Hypoglycemia is associated with increased mortality rate in patients with diabetes. The underlying mechanisms may involve reduced myocardial tolerance to ischemia and reperfusion (IR) or reduced capacity for ischemic preconditioning (IPC). As IPC is associated with increased myocardial glucose uptake (MGU) during reperfusion, cardioprotection is linked to glucose metabolism possibly by O-linked ß-N-acetylglucosamine (O-GlcNAc). We aimed to investigate the impact of hypoglycemia in hearts from animals with diabetes on myocardial IR tolerance, on the efficacy of IPC and whether modulations of MGU and O-GlcNAc levels are involved in the underlying mechanisms. METHODS: In a Langendorff model using diabetic ZDF (fa/fa) and non-diabetic (fa/+) rats (n = 6-7 in each group) infarct size (IS) was evaluated after 40 min of global ischemia and 120 min reperfusion during hypoglycemia [(glucose) = 3 mmol/l] and normoglycemia [(glucose) = 11 mmol/l]. Myocardial glucose uptake and O-GlcNAc levels were evaluated during reperfusion. IPC was induced by 2 × 5 min of global ischemia prior to index ischemia. RESULTS: IS increased in hearts from animals with (p < 0.01) and without (p < 0.01) diabetes during hypoglycemia compared to normoglycemia. IPC reduced IS during normoglycemia in both animals with (p < 0.01) and without (p < 0.01) diabetes. During hypoglycemia, however, IPC only reduced IS in hearts from animals with diabetes (p < 0.05). IPC increased MGU during reperfusion and O-GlcNAc levels in animals with diabetes during hypo- (MGU: p < 0.05, O-GlcNAc: p < 0.05) and normoglycemia (MGU: p < 0.01, O-GlcNAc: p < 0.05) and in animals without diabetes only during normoglycemia (MGU: p < 0.05, O-GlcNAc: p < 0.01). CONCLUSIONS: Hypoglycemia increases myocardial susceptibility to IR injury in hearts from animals with and without diabetes. In contrast to hearts from animals without diabetes, the hearts from animals with diabetes are amenable to cardioprotection during hypoglycemia. In parallel with IPC induced cardioprotection, MGU and O-GlcNAc levels increase suggesting that increased MGU and O-GlcNAc levels are involved in the mechanisms of IPC.

Assessing Selenium, Manganese, and Iodine Status in Pediatric Patients Receiving Parenteral Nutrition.

BACKGROUND: Pediatric patients who are receiving parenteral nutrition (PN) unsupplemented with trace minerals can become deficient. Due to shortages in trace mineral products and the 2004 American Society for Parenteral and Enteral Nutrition report stating that individualized trace element supplementation may be warranted, a review was conducted concerning the trace minerals selenium (Se), manganese (Mn), and iodine (I). METHOD: A retrospective review of pediatric patients receiving PN that contained Se and Mn was conducted to determine if a difference existed between them and patients receiving PN without Se and Mn. Statistical analysis was done to assess a difference between trace mineral levels and the time to deficiency between supplemented and unsupplemented patients. Unsupplemented I patients had urine I levels assessed to determine deficiencies in patients receiving PN. RESULTS: Plasma Se levels were measured at a mean of 20 days for supplemented patients (n = 131) and 19 days for nonsupplemented patients (n = 57) with no difference between groups ( P = .2973). Plasma Mn levels were measured at a mean of 28 days, showing no statistical difference ( P = .721). Of the 177 nonsupplemented I patients, 74% demonstrated I deficiencies without supplementation. CONCLUSIONS: Time to the development of a Se, Mn, or I deficiency is important to guide supplementation of exclusive PN in children when trace mineral products are short in supply. Our retrospective experience supports assessment of the trace minerals Se at 21 days and Mn at 30 days. It also suggests that some pediatric patients receiving PN are deficient in I.

Untargeted metabolomics reveals a mild impact of remote ischemic conditioning on the plasma metabolome and α-hydroxybutyrate as a possible cardioprotective factor and biomarker of tissue ischemia.

INTRODUCTION: Remote ischemic conditioning (RIC) is a maneuver by which short non-lethal ischemic events are applied on distant organs or limbs to reduce ischemia and reperfusion injuries caused by e.g. myocardial infarct. Although intensively investigated, the specific mechanism of this protective phenomenon remains incompletely understood and in particular, knowledge on the role of small metabolites is scarce. OBJECTIVES: In this study, we aimed to study perturbations in the plasma metabolome following RIC and gain insight into metabolic changes by the intervention as well as to identify potential novel cardio-protective metabolites. METHODS: Blood plasma samples from ten healthy males were collected prior to and after RIC and tested for bioactivity in a HL-1 based cellular model of ischemia-reperfusion damage. Following this, the plasma was analyzed using untargeted LC-qTOF-MS and regulated metabolites were identified using univariate and multivariate statistical analysis. Results were finally verified in a second plasma study from the same group of volunteers and by testing a metabolite ester in the HL-1 cell model. RESULTS: The analysis revealed a moderate impact on the plasma metabolome following RIC. One metabolite, α-hydroxybutyrate (AHB) however, stood out as highly significantly upregulated after RIC. AHB might be a novel and more sensitive plasma-biomarker of transient tissue ischemia than lactate. Importantly, it was also found that a cell permeable AHB precursor protects cardiomyocytes from ischemia-reperfusion damage. CONCLUSION: Untargeted metabolomics analysis of plasma following RIC has led to insight into metabolism during RIC and revealed a possible novel metabolite of relevance to ischemic-reperfusion damage.

Effect of paroxetine on left ventricular remodeling in an in vivo rat model of myocardial infarction.

Left ventricular (LV) remodeling following a myocardial infarction (MI) involves formation of reactive oxygen species (ROS). Paroxetine, a selective serotonin reuptake inhibitor, has an antioxidant effect in the vascular wall. We investigated whether paroxetine reduces myocardial ROS formation and LV remodeling following a MI. In a total of 32 Wistar rats, MI was induced by a 30-min ligation of the left anterior descending artery followed by 7- or 28-day reperfusion. During the 28 days of reperfusion, LV remodeling was evaluated by magnetic resonance imaging (MRI) and echocardiography (n = 20). After 28 days of reperfusion, the susceptibility to ventricular tachycardia was evaluated prior to sacrifice and histological assessment of myocyte cross-sectional area, fibrosis, and presence of myofibroblasts. Myocardial ROS formation was measured with dihydroethidium after 7 days of reperfusion in separate groups (n = 12). Diastolic LV volume, evaluated by MRI (417 ± 60 vs. 511 ± 64 µL, p < 0.05), and echocardiography (515 ± 80 vs. 596 ± 83 µL, p < 0.05) as well as diastolic LV internal diameter evaluated with echocardiography (7.2 ± 0.6 vs. 8.1 ± 0.7 mm, p < 0.05) were lower in the paroxetine group than in controls. Furthermore, myocyte cross-sectional area was reduced in the paroxetine group compared with controls (277 ± 26 vs. 354 ± 23 mm3, p < 0.05) and ROS formation was reduced in the remote myocardium (0.415 ± 0.19 normalized to controls, p < 0.05). However, no differences in the presence of fibrosis or myofibroblasts were observed. Finally, paroxetine reduced the susceptibility to ventricular tachycardia (induced in 2/11 vs. 6/8 rats, p < 0.05). Paroxetine treatment following MI decreases LV remodeling and susceptibility to arrhythmias, probably by reducing ROS formation.

Inotropic Effects of Prostacyclins on the Right Ventricle Are Abolished in Isolated Rat Hearts With Right-Ventricular Hypertrophy and Failure.

BACKGROUND: Prostacyclin mimetics are vasodilatory agents used in the treatment of pulmonary arterial hypertension. The direct effects of prostanoids on right-ventricular (RV) function are unknown. We aimed to investigate the direct effects of prostacyclin mimetics on RV function in hearts with and without RV hypertrophy and failure. METHODS: Wistar rats were subjected to pulmonary trunk banding to induce compensated RV hypertrophy (n = 32) or manifest RV failure (n = 32). Rats without banding served as healthy controls (n = 30). The hearts were excised and perfused in a Langendorff system and subjected to iloprost, treprostinil, epoprostenol, or MRE-269 in increasing concentrations. The effect on RV function was evaluated using a balloon-tipped catheter inserted into the right ventricle. RESULTS: In control hearts, iloprost, treprostinil, and MRE-269 improved RV function. The effect was, however, absent in hearts with RV hypertrophy and failure. Treprostinil and MRE-269 even impaired RV function in hearts with manifest RV failure. CONCLUSIONS: Iloprost, treprostinil, and MRE-269 improved RV function in the healthy rat heart. RV hypertrophy abolished the positive inotropic effect, and in the failing right ventricle, MRE-269 and treprostinil impaired RV function. This may be related to changes in prostanoid receptor expression and reduced coronary flow reserve in the hypertrophic and failing right ventricle.

sGC-cGMP-PKG pathway stimulation protects the healthy but not the failing right ventricle of rats against ischemia and reperfusion injury.

BACKGROUND: To investigate whether modulation of the sGC-cGMP-PKG pathway protects against ischemia and reperfusion injury in the healthy and the failing right ventricle (RV). METHODS: Hearts from male Wistar rats with a healthy RV (n=39) or a hypertrophic and failing RV induced by pulmonary trunk banding (n=57) were isolated and perfused in a pressure-controlled modified Langendorff setup. The isolated hearts were randomized to control, ischemic preconditioning (IPC, 2×5min of global ischemia), a phosphodiesterase-5 (PDE5) inhibitor vardenafil (66nM) alone and in combination with a cGMP-dependent protein kinase (PKG) blocker KT 5823 (1µM). Failing hearts were exposed to the same protocols and to soluble guanylate cyclase stimulation/activation, and phosphodiesterase 9 inhibition. All interventions were followed by 40min of global ischemia and 120min of reperfusion. The effects on the RV were evaluated by measurement of the infarct size/area-at-risk ratio (IS/AAR). RESULTS: In healthy hearts, IPC and pharmacological preconditioning with vardenafil reduced RV infarct size. PKG blockade by KT-5823 did not alter infarct size per se but abolished the cardioprotective effect of vardenafil. In the hypertrophic and failing hearts, none of the conditioning strategies altered RV infarct size. CONCLUSION: PDE-5 inhibition by vardenafil protects the healthy right ventricle against ischemia and reperfusion injury by a PKG dependent mechanism. Neither ischemic preconditioning nor pharmacologic stimulation of the sGC-cGMP-PKG pathway induces cardioprotection in the hypertrophic and failing RV.

Inhibition of KV7 Channels Protects the Rat Heart against Myocardial Ischemia and Reperfusion Injury.

The voltage-gated KV7 (KCNQ) potassium channels are activated by ischemia and involved in hypoxic vasodilatation. We investigated the effect of KV7 channel modulation on cardiac ischemia and reperfusion injury and its interaction with cardioprotection by ischemic preconditioning (IPC). Reverse-transcription polymerase chain reaction revealed expression of KV7.1, KV7.4, and KV7.5 in the left anterior descending rat coronary artery and all KV7 subtypes (KV7.1-KV7.5) in the left and right ventricles of the heart. Isolated hearts were subjected to no-flow global ischemia and reperfusion with and without IPC. Infarct size was quantified by 2,3,5-triphenyltetrazolium chloride staining. Two blockers of KV7 channels, XE991 [10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone] (10 µM) and linopirdine (10 µM), reduced infarct size and exerted additive infarct reduction to IPC. An opener of KV7 channels, flupirtine (10 µM) abolished infarct size reduction by IPC. Hemodynamics were measured using a catheter inserted in the left ventricle and postischemic left ventricular recovery improved in accordance with reduction of infarct size and deteriorated with increased infarct size. XE991 (10 µM) reduced coronary flow in the reperfusion phase and inhibited vasodilatation in isolated small branches of the left anterior descending coronary artery during both simulated ischemia and reoxygenation. KV7 channels are expressed in rat coronary arteries and myocardium. Inhibition of KV7 channels exerts cardioprotection and opening of KV7 channels abrogates cardioprotection by IPC. Although safety issues should be further addressed, our findings suggest a potential role for KV7 blockers in the treatment of ischemia-reperfusion injury.

The remote ischemic preconditioning algorithm: effect of number of cycles, cycle duration and effector organ mass on efficacy of protection.

Remote ischemic preconditioning (rIPC), induced by cycles of transient limb ischemia and reperfusion (IR), is cardioprotective. The optimal rIPC-algorithm is not established. We investigated the effect of cycle numbers and ischemia duration within each rIPC-cycle and the influence of effector organ mass on the efficacy of cardioprotection. Furthermore, the duration of the early phase of protection by rIPC was investigated. Using a tourniquet tightened at the inguinal level, we subjected C57Bl/6NTac mice to intermittent hind-limb ischemia and reperfusion. The rIPC-protocols consisted of (I) two, four, six or eight cycles, (II) 2, 5 or 10 min of ischemia in each cycle, (III) single or two hind-limb occlusions and (IV) 0.5, 1.5, 2.0 or 2.5 h intervals from rIPC to index cardiac ischemia. All rIPC algorithms were followed by 5 min of reperfusion. The hearts were subsequently exposed to 25 min of global ischemia and 60 min of reperfusion in an ex vivo Langendorff model. Cardioprotection was evaluated by infarct size and post-ischemic hemodynamic recovery. Four to six rIPC cycles yielded significant cardioprotection with no further protection by eight cycles. Ischemic cycles lasting 2 min offered the same protection as cycles of 5 min ischemia, whereas prolonged cycles lasting 10 min abrogated protection. One and two hind-limb preconditioning were equally protective. In our mouse model, the duration of protection by rIPC was 1.5 h. These findings indicate that the number and duration of cycles rather than the tissue mass exposed to rIPC determines the efficacy of rIPC.

Frequent biomarker analysis in the isolated perfused heart reveals two distinct phases of reperfusion injury.

BACKGROUND: Reperfusion injury and its modulation are incompletely characterized. The purpose of the present study was to characterize the dynamics of reperfusion injury by portraying the temporal release of lactate dehydrogenase (LDH) during ischemia-reperfusion injury in an isolated heart model. METHODS: We studied infarct size and LDH release in the following groups: I) Effect of reperfusion length was evaluated in 79 rats subjected to 40 minute ischemia and 60, 90, 120 or 180 minute reperfusion and a) ischemic preconditioning (IPC) or b) No IPC (control). II) LDH release kinetics was studied in 6 rats subjected to calcium-paradox to verify the applicability of LDH as a dynamic marker of cellular injury. III) Ischemia-reperfusion injury modification was studied in 36 rats subjected to: a) ischemic postconditioning, b) prolonged ischemia, c) Reperfusion Injury Salvage Kinase (RISK) pathway inhibition with wortmannin in IPC hearts, d) RISK activation with insulin or e) mitochondrial permeability transition pore (mPTP) inhibition with cyclosporine A. RESULTS: Infarct size increased from 60 to 180 minute reperfusion in control hearts. LDH was released in two separate peaks from 2 to 20 and 30 to 120 min of reperfusion. IPC attenuated both peaks. Postconditioning and agents known to modify reperfusion injury attenuated the second peak. CONCLUSIONS: Frequent measurement of myocardial ischemia markers for 120 min of reperfusion allows identification of two phases of reperfusion injury that are affected by cardioprotective stimuli. The second phase contributes significantly to final infarct size, which is modifiable and a potential target for cardioprotective interventions.

Ischemic preconditioning increases myocardial O-GlcNAc glycosylation.

OBJECTIVES: Through the hexosamine biosynthetic pathway (HBP) proteins are modified by O-linked-ß-N-acetylglucosamine (O-GlcNAc), which acts as a stress sensor. Augmentation of O-GlcNAc confers cardioprotection against ischemia- reperfusion injury, but its role in ischemic preconditioning (IPC) is unknown. Azaserine and alloxan are unspecific blockers of the HBP and have been used to block the cardioprotective effects of O-GlcNAc. We hypothesized that IPC reduces infarct size and increases O-GlcNAc levels in hearts subjected to ischemia-reperfusion injury, and that these effects could be blocked by azaserine and alloxan. DESIGN: Isolated rat hearts subjected to 40 min global ischemia and 120 min reperfusion were randomized to control, IPC, IPC + azaserine or alloxan, or control + azaserine or alloxan. The effects on infarct size, hemodynamic recovery, myocardial O-GlcNAc levels, and HBP enzyme activities were determined. RESULTS: IPC reduced infarct size, increased O-GlcNAc levels, O-GlcNAc-transferase levels, and O-GlcNAc-transferase activity. Azaserine and alloxan did not block the effect of IPC on O-GlcNAc levels and O-GlcNAc-transferase activity. CONCLUSIONS: IPC increased O-GlcNAc levels though increased O-GlcNAc-transferase expression and activity. Azaserine and alloxan failed to block these effects presumably due to poor specificity and sensitivity of the blockers, and IPC-mediated cardioprotection may therefore still be dependent on O-GlcNAc.

Remote ischemic conditioning: the cardiologist's perspective.

Early and successful restoration of myocardial reperfusion following an ischemic event is the most effective strategy to reduce final infarct size and improve clinical outcome. However, revascularization per se may induce further myocardial damage by myocardial ischemia-reperfusion injury and worsen clinical outcome. Therefore, new therapeutic strategies are required to protect the myocardium against ischemia-reperfusion injury in patients with coronary artery disease. Remote ischemic conditioning (RIC) by brief nonlethal episodes of ischemia and reperfusion to an organ or tissue remote from the heart activates innate cardioprotective mechanisms. The discovery that RIC can be performed noninvasively using a blood pressure cuff on the upper arm to induce brief episodes of limb ischemia and reperfusion has facilitated the translation of RIC into the clinical arena. Whereas some trials have shown contradictory results, recently published proof-of-concept clinical studies have reported encouraging results with RIC. Large-scale multicenter clinical trials are needed to establish the role of RIC in the current clinical practice. At present, the use of RIC in acute coronary syndromes seems particularly attractive due to its potential in-ambulance application and apparent dramatic reduction in infarct size in the patients with the largest infarcts. Cardiac arrest and stroke represent ischemia-reperfusion disorders where RIC has further potential to improve outcome beyond rapid revascularization alone.