Ian Webb

Glycogen Synthase Kinase-3 Inactivation Is Not Required for Ischemic Preconditioning or Postconditioning in the Mouse

The inactivation of glycogen synthase kinase-3β (GSK-3β) is proposed as the event integrating protective pathways initiated by preconditioning and other interventions. The inactivation of GSK-3 is thought to decrease the probability of opening of the mitochondrial permeability transition pore. The aim of this study was to verify the role of GSK-3 using a targeted mouse line lacking the critical N-terminal serine within GSK-3β (Ser9) and the highly homologous GSK-3α (Ser21), which when phosphorylated results in kinase inactivation. Postconditioning with 10 cycles of 5 seconds of reperfusion/5 seconds of ischemia and preconditioning with 6 cycles of 4 minutes of ischemia/6 minutes of reperfusion, similarly reduced infarction of the isolated perfused mouse heart in response to 30 minutes of global ischemia and 120 minutes of reperfusion. Preconditioning caused noticeable inactivating phosphorylation of GSK-3. However, both preconditioning and postconditioning still protected hearts of homozygous GSK-3 double knockin mice. Moreover, direct pharmacological inhibition of GSK-3 catalytic activity with structurally diverse inhibitors before or after ischemia failed to recapitulate conditioning protection. Nonetheless, cyclosporin A, a direct mitochondrial permeability transition pore inhibitor, reduced infarction in hearts from both wild-type and homozygous GSK-3 double knockin mice. Furthermore, in adult cardiac myocytes from GSK-3 double knockin mice, insulin exposure was still as effective as cyclosporin A in delaying mitochondrial permeability transition pore opening. Our results, which include a novel genetic approach, suggest that the inhibition of GSK-3 is unlikely to be the key determinant of cardioprotective signaling in either preconditioning or postconditioning in the mouse.

First-Pass Contrast-Enhanced Myocardial Perfusion MRI in Mice on a 3-T Clinical MR Scanner

First‐pass contrast‐enhanced myocardial perfusion MRI in rodents has so far not been possible due to the temporal and spatial resolution requirements. We developed a new first‐pass perfusion MR method for rodent imaging on a clinical 3.0‐T scanner (Philips Healthcare, Best, The Netherlands) that employed 10‐fold k‐space and time domain undersampling with constrained image reconstruction, using temporal basis sets (k‐t principle component analysis) to achieve a spatial resolution of 0.2 × 0.2 × 1.5mm3 and an acquisition window of 43 msec. The method was successfully tested in five healthy and four infarcted mice (C57BL/6J) at heart rates of 495.1 ± 45.8 beats/min. Signal‐intensity‐time profiles showed a percentage myocardial signal increase of 141.3 ± 38.9% in normal mice, compared with 44.7 ± 32.4% in infarcted segments. Mean myocardial blood flow by Fermi function for constrained deconvolution in control mice was 7.3 ± 1.5 mL/g/min, comparable to published literature, with no significant differences between three myocardial segments. In infarcted segments, myocardial blood flow was significantly reduced to 1.2 ± 0.8 mL/g/min (P < 0.01). This is the first report of first‐pass myocardial perfusion MR in a mouse model on a clinical 3‐T MR scanner and using a k‐t undersampling method. Data were acquired on a 3‐T scanner, using an approach similar to clinical acquisition protocols, thus facilitating translation of imaging findings between rodent and human studies. Magn Reson Med, 2010.

Constitutive glycogen synthase kinase-3α/β activity protects against chronic β-adrenergic remodelling of the heart

Aims Glycogen synthase kinase 3 (GSK-3) signalling is implicated in the growth of the heart during development and in response to stress. However, its precise role remains unclear. We set out to characterize developmental growth and response to chronic isoproterenol (ISO) stress in knockin (KI) mice lacking the critical N-terminal serines, 21 of GSK-3α and 9 of GSK-3β respectively, required for inactivation by upstream kinases. Methods and results Between 5 and 15 weeks, KI mice grew more rapidly, but normalized heart weight and contractile performance were similar to wild-type (WT) mice. Isolated hearts of both genotypes responded comparably to acute ISO infusion with increases in heart rate and contractility. In WT mice, chronic subcutaneous ISO infusion over 14 days resulted in cardiac hypertrophy, interstitial fibrosis, and impaired contractility, accompanied by foetal gene reactivation. These effects were all significantly attenuated in KI mice. Indeed, ISO-treated KI hearts demonstrated reversible physiological remodelling traits with increased stroke volume and a preserved contractile response to acute adrenergic stimulation. Furthermore, simultaneous pharmacological inhibition of GSK-3 in KI mice treated with chronic subcutaneous ISO recapitulated the adverse remodelling phenotype seen in WT hearts. Conclusion Expression of inactivation-resistant GSK-3α/β does not affect eutrophic myocardial growth but protects against pathological hypertrophy induced by chronic adrenergic stimulation, maintaining cardiac function and attenuating interstitial fibrosis. Accordingly, strategies to prevent phosphorylation of Ser-21/9, and consequent inactivation of GSK-3α/β, may enable a sustained cardiac response to chronic β-agonist stimulation while preventing pathological remodelling.

A prospective study of the impact of serial troponin measurements on the diagnosis of myocardial infarction and hospital and six-month mortality in patients admitted to ICU with non-cardiac diagnoses

IntroductionTroponin T (cTnT) elevation is common in patients in the Intensive Care Unit (ICU) and associated with morbidity and mortality. Our aim was to determine the epidemiology of raised cTnT levels and contemporaneous electrocardiogram (ECG) changes suggesting myocardial infarction (MI) in ICU patients admitted for non-cardiac reasons.MethodscTnT and ECGs were recorded daily during week 1 and on alternate days during week 2 until discharge from ICU or death. ECGs were interpreted independently for the presence of ischaemic changes. Patients were classified into four groups: (i) definite MI (cTnT ≥15 ng/L and contemporaneous changes of MI on ECG), (ii) possible MI (cTnT ≥15 ng/L and contemporaneous ischaemic changes on ECG), (iii) troponin rise alone (cTnT ≥15 ng/L), or (iv) normal. Medical notes were screened independently by two ICU clinicians for evidence that the clinical teams had considered a cardiac event.ResultsData from 144 patients were analysed (42% female; mean age 61.9 (SD 16.9)). A total of 121 patients (84%) had at least one cTnT level ≥15 ng/L. A total of 20 patients (14%) had a definite MI, 27% had a possible MI, 43% had a cTNT rise without contemporaneous ECG changes, and 16% had no cTNT rise. ICU, hospital and 180-day mortality was significantly higher in patients with a definite or possible MI.Only 20% of definite MIs were recognised by the clinical team. There was no significant difference in mortality between recognised and non-recognised events.At the time of cTNT rise, 100 patients (70%) were septic and 58% were on vasopressors. Patients who were septic when cTNT was elevated had an ICU mortality of 28% compared to 9% in patients without sepsis. ICU mortality of patients who were on vasopressors at the time of cTnT elevation was 37% compared to 1.7% in patients not on vasopressors.ConclusionsThe majority of critically ill patients (84%) had a cTnT rise and 41% met criteria for a possible or definite MI of whom only 20% were recognised clinically. Mortality up to 180 days was higher in patients with a cTnT rise.

Does left ventricular function continue to influence mortality following contemporary percutaneous coronary intervention

BackgroundLeft ventricular (LV) dysfunction was associated with adverse outcome after percutaneous coronary intervention (PCI) in the balloon-angioplasty and bare-metal stent era. Technological advances have reduced complications after PCI. The impact of left ventricular ejection fraction (LVEF) on outcomes in current clinical practice is unknown, with commonly used risk stratification models not consistently incorporating preprocedural LVEF. MethodsA total of 2328 consecutive patients undergoing PCI in a single centre between April 2005 and July 2009 were analysed. Patients were eligible if LVEF had been categorized before PCI as good (LVEF ≥50%), moderate (LVEF 30–49%) or poor (LVEF <30%). Those in cardiogenic shock were excluded. Mortality data were tracked using the UK Office of National statistics database. Logistic regression analysis was used to predict the risk of mortality at 30-day and long-term follow-up. ResultsOverall all-cause mortality was 1.0% at 30 days and 5% at long-term follow-up. Kaplan–Meier analysis revealed an early divergence in survival curves according to LVEF. Mortality rates stratified by LVEF category were 0.4, 1.3 and 6.3% at 30 days and 3.3, 5.7 and 12.0% in the long term (2.2±1.1 years) (P<0.0001). Multiple regression analysis confirmed that impaired LVEF (⩽50%) independently predicts 30-day [hazard ratio 4.20 (confidence interval 2.50–7.04), P=0.001] and long-term all-cause mortality [hazard ratio 1.67 (1.28–2.19), P=0.001]. ConclusionLV impairment remains a strong predictor of early and late mortality after PCI. LV function assessment is integral in risk stratification and patient optimization and should be recommended, wherever feasible, before PCI.

Myocardial stress remodelling after regional infarction is independent of glycogen synthase kinase-3 inactivation

Phosphorylation and inactivation of glycogen synthase kinase 3 (GSK-3) is observed in the failing heart induced by chronic pharmacological stress and aortic banding. Constitutive kinase activity attenuates pathological remodelling, suggesting an obligatory role in stress signalling. However, this has been challenged by recent data whereby conditional GSK-3β deletion has been shown to protect against post-infarct remodelling. Here, we set out to determine the chronic remodelling response to infarction in hearts of GSK-3α/βAla21/9 knockin (KI) mice encoding constitutively active GSK-3 isoforms. At 4 weeks after infarction there were significant increases in normalised heart weight and left ventricular (LV) muscle volume compared to sham in both KI and wild type animals. This was associated with an increase in LV cavity dimensions and remote LV wall thickness. Hypertrophy in both genotypes resulted in marked contractile impairment on both invasive and non-invasive interrogation. Increased phosphorylation of GSK-3β, but not GSK-3α, was demonstrated at 1 week after infarction and remained elevated at 4 weeks compared to sham-treated hearts. In conclusion, GSK-3β phosphorylation and inactivation occurs with, but is not an obligatory signalling event in, chronic post-infarct remodelling in the mouse heart. This highlights the heterogeneity of pathological hypertrophy and the divergent role of GSK-3 signalling in chronic myocardial stress.

Lizard Spit and Reperfusion Injury

Although the incidence of ST-segment elevation myocardial infarction (STEMI) is declining in industrialized nations, there are still an estimated 500,000 events annually in the U.S. ([1][1]). Furthermore, the in-hospital mortality is 6% to 7%, and over 15% of survivors to discharge experience a

Myocardial infarction on the ICU: can we do better?

Myocardial infarction remains a major cause of death despite contemporary therapeutic strategies. Diagnosis in the intensive care unit is challenging, but is essential to target therapy accurately. In this issue of Critical Care Lim and colleagues present the results of a prospective non-interventional screening study for acute myocardial infarction in patients admitted to the intensive care unit. Myocardial infarction is observed to occur frequently, often without being clinically apparent, with a high associated mortality. Such approaches may facilitate accurate diagnosis of myocardial infarction in this setting, hence opening the way to improved therapy.

Images in InterventionA Calcific, Undilatable Stenosis: Lithoplasty, a New Tool in the Box?

A 69-year-old man with established coronary artery disease and left ventricular dysfunction (ejection fraction, 40%) with typical Canadian Cardiovascular Society class III angina underwent percutaneous coronary intervention (PCI) for severe diffuse calcific disease in the right coronary artery ([

An unusual case of pericardial effusion in a diabetic patient.

![Figure][1] A 49-year-old man presented acutely in low-output shock related to a large pericardial effusion. His past medical history was notable for longstanding depression and type II diabetes mellitus. Emergency pericardiocentesis was performed with the removal of 700 ml of heavy blood-