Left Atrial Glucose Metabolism Evaluation by 18F-FDG-PET in Persistent Atrial Fibrillation and in Sinus Rhythm.

The role of atrial metabolism alterations for initiation and atrial fibrillation (AF) persistence remains poorly understood. Therefore, we evaluated left atrial glucose metabolism by nicotinic acid derivative stimulated 18-fluorodeoxyglucose positron emission tomography in 36 patients with persistent AF undergoing catheter ablation before and 3 months after return to sinus rhythm and compared values against healthy controls. Under identical hemodynamics and metabolic conditions, and although left ventricular FDG uptake remained unchanged, patients in persistent AF presented significantly higher total left atrial and left atrial appendage uptake, which decreased significantly after return to sinus rhythm, despite improvement of passive and active atrial contractile function. These findings support a role of altered glucose metabolism and metabolic wasting underlying the pathophysiology of persistent AF.

Overexpression of AMP-activated protein kinase or protein kinase D prevents lipid-induced insulin resistance in cardiomyocytes.

During lipid oversupply, the heart becomes insulin resistant, as exemplified by defective insulin-stimulated glucose uptake, and will develop diastolic dysfunction. In the healthy heart, not only insulin, but also increased contractile activity stimulates glucose uptake. Upon increased contraction both AMP-activated protein kinase (AMPK) and protein kinase D (PKD) are activated, and mediate the stimulation of glucose uptake into cardiomyocytes. Therefore, each of these kinases is a potential therapeutic target in the diabetic heart because they may serve to bypass defective insulin-stimulated glucose uptake. To test the preventive potential of these kinases against loss of insulin-stimulated glucose uptake, AMPK or PKD were adenovirally overexpressed in primary cultures of insulin resistant cardiomyocytes for assaying substrate uptake, insulin responsiveness and lipid accumulation. To induce insulin resistance and lipid loading, rat primary cardiomyocytes were cultured in the presence of high insulin (100 nM; HI) or high palmitate (palmitate/BSA: 3/1; HP). HI and HP each reduced insulin responsiveness, and increased basal palmitate uptake and lipid storage. Overexpression of each of the kinases prevented loss of insulin-stimulated glucose uptake. Overexpression of AMPK also prevented loss of insulin signaling in HI- and HP-cultured cardiomyocytes, but did not prevent lipid accumulation. In contrast, overexpression of PKD prevented lipid accumulation, but not loss of insulin signaling in HI- and HP-cultured cardiomyocytes. In conclusion, AMPK and PKD prevent loss of insulin-stimulated glucose uptake into cardiomyocytes cultured under insulin resistance-inducing conditions through different mechanisms. This article is part of a Special Issue entitled "Focus on Cardiac Metabolism".

Role of the ductal transcription factors HNF6 and Sox9 in pancreatic acinar-to-ductal metaplasia.

OBJECTIVE: Growing evidence suggests that a phenotypic switch converting pancreatic acinar cells to duct-like cells can lead to pancreatic intraepithelial neoplasia and eventually to invasive pancreatic ductal adenocarcinoma. Histologically, the onset of this switch is characterised by the co-expression of acinar and ductal markers in acini, a lesion called acinar-to-ductal metaplasia (ADM). The transcriptional regulators required to initiate ADM are unknown, but need to be identified to characterise the regulatory networks that drive ADM. In this study, the role of the ductal transcription factors hepatocyte nuclear factor 6 (HNF6, also known as Onecut1) and SRY-related HMG box factor 9 (Sox9) in ADM was investigated. DESIGN: Expression of HNF6 and Sox9 was measured by immunostaining in normal and diseased human pancreas. The function of the factors was tested in cultured cells and in mouse models of ADM by a combination of gain and loss of function experiments. RESULTS: Expression of HNF6 and Sox9 was ectopically induced in acinar cells in human ADM as well as in mouse models of ADM. HNF6 and, to a lesser extent, Sox9 were required for repression of acinar genes, for modulation of ADM-associated changes in cell polarity and for activation of ductal genes in metaplastic acinar cells. CONCLUSIONS: HNF6 and Sox9 are new biomarkers of ADM and constitute candidate targets for preventive treatment in cases when ADM may lead to cancer. This work also shows that ectopic activation of transcription factors may underlie metaplastic processes occurring in other organs.

Cardiac atrial metabolism quantitative assessment with analog and digital time of flight-PET/computed tomography.

BACKGROUND: Evaluation of left atrium (LA) remodeling is becoming increasingly relevant in understanding several pathological cardiac conditions. 18 F-FDG-PET/computed tomography (CT), the current gold standard for metabolic evaluation of the left ventricle, could be extended to LA using the latest PET technologies. We sought to perform a phantom study to optimize the reconstruction algorithm in this context. METHODS: The liver, heart cavity and walls of an anthropomorphic phantom were filled with typical patient 18 F-FDG activity concentrations. Acquisitions were performed on an analog and on a digital TOF-PET/CT, and reconstructed with and without resolution recovery (RR). The Richardson-Lucy RR method was used, either through a third-party software or through the PET/CT manufacturer algorithm. Activity recoveries in the atria and ventricles and signal-to-noise ratios were evaluated to identify the best reconstruction and RR parameters. The same methodology was applied on a patient cardiac study. RESULTS: Analog PET/CT with the third-party RR cannot improve the activity recovery without markedly degrading the image quality. For the digital PET/CT, the optimal algorithm was the manufacturer RR reconstruction using four iterations and 15 subsets combined with five RR iterations. This reconstruction improved the LA activity recovery from 58% to 70% while preserving images of diagnostic quality. Similar results were obtained for the patient study. CONCLUSION: The digital TOF-PET/CT with the identified optimal reconstruction can be used to quantitatively analyze the LA uptake in 18 F-FDG cardiac studies while still preserving image reading quality. This may lead to more precise cardiovascular disease status evaluation, especially when atria are concerned.

Extramedullary Hematopoiesis in Treated Diffuse Large B-Cell Lymphoma of Bone.

ABSTRACT: A 65-year-old man with a history of diffuse large B-cell bone lymphoma of the right radius underwent an interim FDG PET/CT after 2 cycles of chemotherapy. Besides a complete metabolic response on the primary site, images revealed a hypermetabolic nodule in the posterior mediastinum, not present on the initial images. The metabolic activity of the nodule was similar to that of the reactive bone marrow and disappeared, concomitantly to the normalization of the medullar signal on the posttreatment images. The similarity and synchronous metabolic activity evolution in the nodule and bone marrow indicate extramedullary hematopoiesis.

Prediction of Left Atrial Fibrosis and Success of Catheter Ablation by Speckle Tracking Echocardiography in Patients Imaged in Persistent Atrial Fibrillation.

Background: Non-invasive evaluation of left atrial structural and functional remodeling should be considered in all patients with persistent atrial fibrillation (AF) to optimal management. Speckle tracking echocardiography (STE) has been shown to predict AF recurrence after catheter ablation; however in most studies, patients had paroxysmal AF, and STE was performed while patients were in sinus rhythm. Aim: The aim of this study was to evaluate the ability of STE parameters acquired during persistent AF to assess atrial fibrosis measured by low voltage area, and to predict maintenance of sinus rhythm of catheter ablation. Methods: A total of 94 patients (69 men, 65 ± 9 years) with persistent AF prospectively underwent measurement of Global Peak Atrial Longitudinal Strain (GPALS), indexed LA Volume (LAVI), E/e' ratio, and LA stiffness index (the ratio of E/e' to GPALS) by STE prior to catheter ablation, while in AF. Low-voltage area (LVA) was assessed by electro-anatomical mapping and categorized into absent, moderate (>0 to <15%), and high (≥15%) atrial extent. AF recurrence was evaluated after 3 months of blanking. Results: Multivariable regression showed that LAVI, GPALS, and LA stiffness independently predicted LVA extent after correcting for age, glomerular filtration rate, and CHA2DS2-VASc score. Of all the parameters, LA stiffness index had the highest diagnostic accuracy (AUC 0.85), allowing using a cut-off value ≥0.7 to predict moderate or high LVA with 88% sensitivity and 47% specificity, respectively. In multivariable Cox analysis, both GPALS and LA stiffness were able to significantly improve the c statistic to predict AF recurrence (n = 40 over 9 months FU) over CHARGE-AF (p < 0.001 for GPALS and p = 0.01 for LA stiffness) or CHA2DS2-VASc score (p < 0.001 for GPALS and p = 0.02 for LA stiffness). GPALS and LA stiffness also improved the net reclassification index (NRI) over the CHARGE-AF index (NRI 0.67, 95% CI [0.33-1.13] for GPALS and NRI 0.73, 95% CI [0.12-0.91] for LA stiffness, respectively), and over the CHA2DS2-VASc score (NRI 0.43, 95% CI [-0.14 to 0.69] for GPALS and NRI 0.52, 95% CI [0.10-0.84], respectively) for LA stiffness to predict AF recurrence at 9 months. Conclusion: STE parameters acquired during AF allow prediction of LVA extent and AF recurrence in patients with persistent AF undergoing catheter ablation. Therefore, STE could be a valuable approach to select candidates for catheter ablation.

Effects of granulocyte-colony-stimulating factor on progenitor cell mobilization and heart perfusion and function in normal mice.

BACKGROUND AIMS: Mobilization of stem cells and progenitor cells from the bone marrow (BM) into the peripheral blood (PB) by granulocyte-colony-stimulating factor (G-CSF) is being investigated for cardiac regeneration in ischemic heart disease. However, hematopoietic (HPC), mesenchymal (MPC) and endothelial (EPC) progenitor mobilization have not been optimized and the effect of G-CSF on myocardial perfusion and cardiac function in a normal heart has never been studied. METHODS: Normal mice were injected daily for 1-10 days with subcutaneous recombinant human G-CSF. PB and BM were evaluated for HPC and EPC by flow cytometry and HPC and MPC by hematopoietic (CFU-GM) and mesenchymal (CFU-F) colony assays. Echocardiography, microSPECT imaging, cardiac catheterization and immunohistochemistry were performed in mice treated for 10 days. RESULTS: HPC and CFU-GM in PB peaked after 2 days, CFU-F after 4 days and EPC after 3 days. Thereafter, while HPC temporally decreased before showing a second peak, EPC remained detectable only at low levels. In BM, hematopoietic stem cells (HSC) and CFU-GM did not increase much overall but peaked twice on days 2 and 7. EPC (peak on day 7) production increased in the BM, but CFU-F formation declined considerably after day 2. G-CSF enhanced myocardial perfusion and vascularization but impaired hemodynamic performance of the heart through apparently increased ventricular wall rigidity. CONCLUSIONS: G-CSF induces the mobilization of HPC, EPC and CFU-F progenitors in PB according to very different patterns, and has a significant impact on perfusion and function of the normal heart.

A sarcoidosis-lymphoma syndrome revealed by hypopituitarism.

SUMMARY: A 26-year-old woman presented with persistent headache and tiredness. Biological investigations disclosed a moderate inflammatory syndrome, low PTH-hypercalcemia and complete anterior hypopituitarism. A magnetic resonance imaging (MRI) of the pituitary gland was performed and revealed a symmetric enlargement with a heterogeneous signal. Ophthalmological examination showed an asymptomatic bilateral anterior and posterior uveitis, and a diagnosis of pituitary sarcoidosis was suspected. As the localization of lymphadenopathies on the fused whole-body FDG-PET/computerized tomography (CT) was not evoking a sarcoidosis in first instance, an excisional biopsy of a left supraclavicular adenopathy was performed showing classic nodular sclerosis Hodgkin's lymphoma (HL). A diagnostic transsphenoidal biopsy of the pituitary gland was proposed for accurate staging of the HL and surprisingly revealed typical granulomatous inflammation secondary to sarcoidosis, leading to the diagnosis of a sarcoidosis-lymphoma syndrome. The co-existence of these diseases constitutes a diagnostic challenge and we emphasize the necessity of exact staging of disease in order to prescribe adequate treatment. LEARNING POINTS: The possibility of a sarcoidosis-lymphoma syndrome, although rare, should be kept in mind during evaluation for lymphadenopathies. In the case of such association, lymphoma usually occurs after sarcoidosis. However, sarcoidosis and lymphoma can be detected simultaneously and development of sarcoidosis in a patient with previous lymphoma has also been reported. An accurate diagnosis of the disease and the respective organ involvements, including biopsy, is necessary in order to prescribe adequate treatment.

Comparison between adenoviral and retroviral vectors for the transduction of the thymidine kinase PET reporter gene in rat mesenchymal stem cells.

UNLABELLED: Mesenchymal stem cells (MSCs) are a promising cell line for the treatment of ischemic heart disease. To evaluate the success of their transplantation into living animals, noninvasive imaging techniques that are able to track the distribution and fate of those cells would be useful. The aim of this study was to investigate the feasibility of infecting rat MSCs with adenoviruses and retroviruses carrying the herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene; to compare the level of transgene expression induced by the 2 viral vectors; to evaluate the effects of viral transduction on cell phenotype, viability, proliferation rates, and differentiation capabilities; and to test the possibility of noninvasively imaging transduced MSCs using 9-(4-18F-fluoro-3-[hydroxymethyl]butyl)guanine (18F-FHBG) and small-animal PET after their transplantation into living rats. METHODS: We infected rat bone marrow MSCs with adenoviruses carrying the HSV1 mutant tk (Ad-HSV1-sr39tk) PET reporter gene (PRG) or with a retroviral construct expressing the wild-type HSV1-tk PRG. The efficacy and intensity of HSV1-sr39tk and HSV1-tk gene expression were determined by a direct comparison of [8-3H]-penciclovir ([8-3H]-PCV) cell uptake in both infected MSC populations and noninfected control MSCs. Small-animal PET studies were performed on living rats after an intramuscular injection of infected MSCs. The MSCs either have been incubated in advance with 18F-FHBG or they were administered and 18F-FHBG was thereafter intravenously administered [corrected] RESULTS: Both adenoviral and retroviral vectors can be used to introduce the tk PRG in MSCs. Neither adenovirus nor retrovirus infections significantly modify MSC phenotype, viability, proliferation, and differentiation capabilities. No significant 3H-PCV uptake was observed in noninfected MSCs. By contrast, after both adenoviral and retroviral infections, the infected MSC populations exhibited a similar, significantly higher, 3H-PCV accumulation. Small-animal PET images showed intense activity within the transplanted regions irrespective of the infected MSC population used. CONCLUSION: Our results demonstrate the feasibility of infecting MSCs with adenoviruses and retroviruses expressing the HSV1-tk PRG and suggest that infected MSCs can be noninvasively imaged with 18F-FHBG and small-animal PET after their transplantation into living animals.

Flow-function relationships in chronic left-ventricular ischemic dysfunction: Impact of the transmurality of infarction.

BACKGROUND: We examined flow-function relationships in humans with chronic coronary artery disease (CAD) in relation to the transmural extent of necrosis, aiming to distinguish the various pathophysiologic conditions that cause chronic ischemic dysfunction, ie, chronic hibernation (perfusion-contraction match) from chronic stunning (perfusion-contraction mismatch). METHODS AND RESULTS: Twenty-two patients (18 men, 61 +/- 13 years) with CAD and chronic contractile dysfunction (ejection fraction, 26% +/- 13%) and 6 volunteers underwent tagged and gadolinium (Gd)-DTPA contrast-enhanced magnetic resonance imaging as well as (13)NH(3)-positron emission tomography. The relationship between regional circumferential shortening strain (ECC), transmural necrosis, and absolute transmural myocardial perfusion (MBF) was examined quantitatively in dysfunctional segments (<10% ECC). Noninfarcted (<25% transmurality), dysfunctional myocardium presented a perfusion-contraction mismatch, as indicated by a 72% reduction (to -5% +/- 4% shortening) of ECC, versus only a 12% (to 63 +/- 20 mL/min/100 g) reduction of transmural MBF. With increasing amounts of necrosis, reductions between perfusion versus contraction became increasingly matched, ie, dysfunctional segments with a greater than 75% transmural extent of necrosis had a 57% reduction of MBF (to 30 +/- 17 mL/min/100 g), for a similar severe reduction of 80% of ECC (to -3% +/- 3% shortening). CONCLUSIONS: Noninfarcted, dysfunctional human myocardium mostly presents with a perfusion-contraction mismatch, consistent with stunning. By contrast, dysfunctional myocardium presenting with a perfusion-contraction match is always associated with significant amounts of necrosis.

Biodistribution of Liver-Derived Mesenchymal Stem Cells After Peripheral Injection in a Hemophilia A Patient.

BACKGROUND: With the exception of liver transplantation, there is no cure for hemophilia, which is currently managed by preemptive replacement therapy. Liver-derived stem cells are in clinical development for inborn and acquired liver diseases and could represent a curative treatment for hemophilia A. The liver is a major factor VIII (FVIII) synthesis site, and mesenchymal stem cells have been shown to control joint bleeding in animal models of hemophilia. Adult-derived human liver stem cells (ADHLSCs) have mesenchymal characteristics and have been shown able to engraft in and repopulate both animal and human livers. Thus, the objectives were to evaluate the potency of ADHLSCs to control bleeding in a hemophilia A patient and assess the biodistribution of the cells after intravenous injection. METHODS: A patient suffering from hemophilia A was injected with repeated doses of ADHLSCs via a peripheral vein (35 million In-oxine-labeled cells, followed by 125 million cells the next day, and 3 infusions of 250 million cells every 2 weeks thereafter; total infusion period, 50 days). RESULTS: After cell therapy, we found a temporary (15 weeks) decrease in the patient's FVIII requirements and severe bleeding complications, despite a lack of increase in circulating FVIII. The cells were safely administered to the patient via a peripheral vein. Biodistribution analysis revealed an initial temporary entrapment of the cells in the lungs, followed by homing to the liver and to a joint afflicted with hemarthrosis. CONCLUSION: These results suggest the potential use of ADHLSCs in the treatment of hemophilia A.

Head-to-Head Comparison of Inflammation and Neovascularization in Human Carotid Plaques: Implications for the Imaging of Vulnerable Plaques.

BACKGROUND: Inflammation and intraplaque neovascularization are acknowledged to be 2 features of plaque vulnerability, although their temporal expression and their respective value in predicting clinical events are poorly understood. To determine their respective temporal associations, we conducted a comprehensive assessment of inflammation and intraplaque neovascularization in the carotid plaque of symptomatic and asymptomatic patients. METHODS AND RESULTS: Thirty patients with severe carotid stenosis underwent 18F-fluorodeoxyglucose-positron emission tomography/computed tomographic imaging. Plaque 18F-fluorodeoxyglucose-uptake, indicative of inflammation, was measured by calculating the target:background ratio. The presence of intraplaque neovascularization during contrast-enhanced ultrasound was judged semiquantitatively; low-grade contrast enhancement (CE) suggested its absence, and high-grade CE, the presence of neovascularization. Carotid surgery was performed 1.6±1.8 days after completing both imaging modalities in all patients, and the presence of macrophages and neovessels was quantified by immunohistochemistry. We identified a significant correlation between the target:background ratio and macrophage quantification (R=0.78; P<0.001). The number of vessels was also significantly higher in carotid plaque with high-CE (P<0.001). Surprisingly, immunohistochemistry showed that high-CE and vessel number were neither associated with an elevated target:background ratio (P=0.28 and P=0.60, respectively) nor macrophage infiltration (P=0.59 and P=0.40, respectively). Finally, macrophage infiltration and target:background ratio were higher in the carotid plaque of symptomatic patients (P=0.021 and P=0.05, respectively), whereas CE grade and the presence of neovessels were not. CONCLUSIONS: Inflammation and intraplaque neovascularization are not systematically associated in carotid plaques, suggesting a temporal separation between the 2 processes. Inflammation seems more pronounced when symptoms are present. These data highlight the challenges that face any imaging strategy designed to assess plaque vulnerability.

Attenuation-corrected 99mTc-MIBI SPECT in overweight patients with chronic ischaemic dysfunction: a comparison to NH3 PET and implications for the diagnosis of myocardial viability.

OBJECTIVE: We determined the value of attenuation correction (AC) of myocardial perfusion estimation with (99m)Tc-MIBI SPECT in overweight patients by comparison of uncorrected (filtered back-projection (FBP) and corrected (an iterative algorithm with a measured attenuation coefficients map (FL-AC)) (99m)Tc-MIBI relative uptake to perfusion data obtained in the same patients with NH3 PET. In addition, the impact of attenuation correction for the assessment of myocardial viability with (99m)Tc-MIBI SPECT was determined using FDG PET as the reference method. METHODS: Thirty consecutive overweight patients (BMI=28+/-4) with left ventricular dysfunction underwent a resting (99m)Tc-MIBI SPECT and a PET study (NH3 and FDG). (99m)Tc-MIBI SPECT scans were reconstructed without attenuation correction (FBP) and with attenuation correction (FL-AC). The left ventricle was divided into 16 segments, in which the relative uptake was quantified using circumferential profiles. A relative uptake > or = 60% was considered consistent with viable myocardium for FDG and MIBI. RESULTS: The absolute difference between (99m)Tc-MIBI SPECT and NH3 PET uptakes was less pronounced in the inferior (12+/-10% vs. 17+/-12%, P<0.001), anteroseptal (12+/-11% vs. 16+/-12%, P=0.009) and septal (15+/-12% vs. 18+/-14%, P=0.003) regions (FL-AC vs. FBP, respectively). The sensitivity of MIBI for diagnosing myocardial viability increased from 83 to 100% (P=0.034), without loss in specificity. CONCLUSION: Attenuation correction improves myocardial perfusion estimation by (99m)Tc-MIBI SPECT in the inferior, anteroseptal and septal regions and increases its sensitivity for the diagnosis of myocardial viability.

αVß3 integrin-targeted microSPECT/CT imaging of inflamed atherosclerotic plaques in mice.

BACKGROUND: αVß3-integrin is expressed by activated endothelial cells and macrophages in atherosclerotic plaques and may represent a valuable marker of high-risk plaques. We evaluated (99m)Tc-maraciclatide, an integrin-specific tracer, for imaging vascular inflammation in atherosclerotic lesions in mice. METHODS: Apolipoprotein E-negative (ApoE(-/-)) mice on a Western diet (n = 10) and normally fed adult C57BL/6 control mice (n = 4) were injected with (99m)Tc-maraciclatide (51.8 ± 3.7 MBq). A blocking peptide was infused in three ApoE(-/-) mice; this condition served as another control. After 90 min, the animals were imaged via single-photon emission computed tomography (SPECT). While maintained in the same position, the mice were transferred to computed tomography (CT) to obtain contrast-enhanced images of the aortic arch. Images from both modalities were fused, and signal was quantified in the aortic arch and in the vena cava for subtraction of blood-pool activity. The aorta was carefully dissected after imaging for gamma counting, autoradiography, and histology. RESULTS: Tracer uptake was significantly higher in ApoE(-/-) mice than in both groups of control mice (1.56 ± 0.33 vs. 0.82 ± 0.24 vs. 0.98 ± 0.11, respectively; P = 0.006). Furthermore, higher tracer activity was detected via gamma counting in the aorta of hypercholesterolemic mice than in both groups of control mice (1.52 ± 0.43 vs. 0.78 ± 0.19 vs. 0.47 ± 0.31 (99m)Tc-maraciclatide %ID/g, respectively; P = 0.018). Autoradiography showed significantly higher tracer uptake in the atherosclerotic aorta than in the control aorta (P = 0.026). Finally, in the atherosclerotic aorta, immunostaining indicated that the integrin signal came predominantly from macrophages and was correlated with the macrophage CD68 immunomarker (r = 0.73). CONCLUSIONS: (99m)Tc-maraciclatide allows in vivo detection of inflamed atherosclerotic plaques in mice and may represent a non-invasive approach for identifying high-risk plaques in patients.

Assessment of the physiologic significance of coronary disease with dipyridamole real-time myocardial contrast echocardiography. Comparison with technetium-99m sestamibi single-photon emission computed tomography and quantitative coronary angiography.

OBJECTIVES: The purposes of this study were to test whether quantitative real-time myocardial contrast echocardiography (RT-MCE) can detect coronary disease during pharmacologic stress and to compare this approach with single-photon emission computed tomography (SPECT). BACKGROUND: Assessing myocardial perfusion during stress is important for the diagnosis and risk stratification of patients with coronary disease. METHOD: Thirty-five patients referred for coronary angiography underwent RT-MCE and technetium-99m methoxyisobutylisonitrile (MIBI) SPECT at baseline and after 0.84 mg/kg dipyridamole. The modalities of RT-MCE and SPECT were analyzed both qualitatively and quantitatively. For this purpose, myocardial flow reserve was calculated from microbubble replenishment curves, and regional MIBI uptake was measured on circumferential profiles. Segments and vascular territories were categorized into five groups with increasing stenosis severity by quantitative coronary angiography. RESULTS: With dipyridamole, beta and A x beta increased in all but the highest stenosis severity group. The increase in beta and A x beta was significantly lower in territories supplied by stenotic arteries than in those supplied by arteries with <50% stenosis. Graded decreases in beta and A x beta reserves were noted with increasing stenosis severity. Using the cutoff value of 2.00 for beta reserve, quantitative RT-MCE correctly identified 97% of the territories supplied by significant stenoses and 82% of those supplied by normal arteries. In contrast, quantitative SPECT correctly identified only 71% of the territories supplied by significant stenoses and 81% of those supplied by normal arteries. CONCLUSIONS: This study shows that RT-MCE, with dipyridamole, can define the presence and severity of coronary disease in a manner that compares favorably with quantitative SPECT.

Reverse redistribution on exercise-redistribution (201)Tl SPECT in chronic ischemic dysfunction: predictive of functional outcome after revascularization?

UNLABELLED: This study analyzed the incidence and clinical significance of reverse redistribution (RR) on stress-redistribution (201)Tl SPECT studies in patients with poor left ventricular function and tested the hypothesis that the RR phenomenon could be caused by artifacts. METHODS: Seventy-three consecutive patients with chronic coronary artery disease and left ventricular dysfunction (ejection fraction, 36% +/- 12%) who underwent exercise-redistribution-reinjection (201)Tl SPECT before myocardial revascularization were included. Recovery of left ventricular systolic function was assessed with 2-dimensional echocardiography performed before and 5.5 +/- 2.5 mo after revascularization. RR was determined visually and confirmed quantitatively as a > or = 10% decrease in (201)Tl uptake on the circumferential profiles. The left ventricle was divided in 16 segments for (201)Tl uptake and wall motion analyses. RESULTS: RR was present in 39 of 1,168 segments (3.3%) and in 18 of 73 patients (25%). Before revascularization, regional wall motion was normal in 26 of 39 RR segments (67%), hypokinetic in 7 of 39 (18%), and akinetic in 6 of 39 (15%). Eight percent of all dysfunctional segments (13/167) of RR patients presented RR. After revascularization, 60 of 167 dysfunctional segments (36%) improved function by > or = 1 grade, among which 8 (13%) displayed RR on (201)Tl SPECT before revascularization. Segments with RR improved function more frequently than those without RR (62% vs. 34%; P = 0.05). Using a threshold for segmental (201)Tl uptake of >54%, the accuracy of (201)Tl reinjection to detect functional improvement in RR segments after revascularization was 77% (10/13). Artifactually induced RR was also excluded in all but 1 case because no increased activity of the pixel used for normalization could be found on redistribution images relative to that of the stress images. CONCLUSION: These data suggest that in patients with chronic left ventricular ischemic dysfunction, RR on exercise-redistribution (201)Tl SPECT is not an artifact and occurs rarely in normally functioning and in dysfunctional myocardium. In the latter, RR is frequently associated with myocardial viability as shown by functional recovery after revascularization. However, the presence or absence of RR in dysfunctional segments seems to be of little clinical relevance.

Role of AMP-activated protein kinase in regulating hypoxic survival and proliferation of mesenchymal stem cells.

AIMS: Mesenchymal stem cells (MSCs) are widely used for cell therapy, particularly for the treatment of ischaemic heart disease. Mechanisms underlying control of their metabolism and proliferation capacity, critical elements for their survival and differentiation, have not been fully characterized. AMP-activated protein kinase (AMPK) is a key regulator known to metabolically protect cardiomyocytes against ischaemic injuries and, more generally, to inhibit cell proliferation. We hypothesized that AMPK plays a role in control of MSC metabolism and proliferation. METHODS AND RESULTS: MSCs isolated from murine bone marrow exclusively expressed the AMPKα1 catalytic subunit. In contrast to cardiomyocytes, a chronic exposure of MSCs to hypoxia failed to induce cell death despite the absence of AMPK activation. This hypoxic tolerance was the consequence of a preference of MSC towards glycolytic metabolism independently of oxygen availability and AMPK signalling. On the other hand, A-769662, a well-characterized AMPK activator, was able to induce a robust and sustained AMPK activation. We showed that A-769662-induced AMPK activation inhibited MSC proliferation. Proliferation was not arrested in MSCs derived from AMPKα1-knockout mice, providing genetic evidence that AMPK is essential for this process. Among AMPK downstream targets proposed to regulate cell proliferation, we showed that neither the p70 ribosomal S6 protein kinase/eukaryotic elongation factor 2-dependent protein synthesis pathway nor p21 was involved, whereas p27 expression was increased by A-769662. Silencing p27 expression partially prevented the A-769662-dependent inhibition of MSC proliferation. CONCLUSION: MSCs resist hypoxia independently of AMPK whereas chronic AMPK activation inhibits MSC proliferation, p27 being involved in this regulation.

Myocardial infarct size quantification in mice by SPECT using a novel algorithm independent of a normal perfusion database.

BACKGROUND: There is a growing interest in developing non-invasive imaging techniques permitting infarct size (IS) measurements in mice. The aim of this study was to validate the high-resolution rodent Linoview single photon emission computed tomography (SPECT) system for non-invasive measurements of IS in mice by using a novel algorithm independent of a normal database, in comparison with histology. METHODS: Eleven mice underwent a left coronary artery ligature. Seven days later, animals were imaged on the SPECT 2h30 after injection of 173 ± 27 MBq of Tc-99m-sestamibi. Mice were subsequently killed, and their hearts were excised for IS determination with triphenyltetrazolium chloride (TTC) staining. SPECT images were reconstructed using the expectation maximization maximum likelihood algorithm, and the IS was calculated using a novel algorithm applied on the 20-segment polar map provided by the commercially available QPS software (Cedars-Sinai Medical Center, CA, USA). This original method is attractive by the fact that it does not require the implementation of a normal perfusion database. RESULTS: Reconstructed images allowed a clear delineation of the left ventricles borders in all mice. No significant difference was found between mean IS determined by SPECT and by TTC staining [37.9 ± 17.5% vs 35.6 ± 17.2%, respectively (P = 0.10)]. Linear regression analysis showed an excellent correlation between IS measured on the SPECT images and IS obtained with TTC staining (y = 0.95x + 0.03 (r = 0.97; P < 0.0001)), without bias, as demonstrated by the Bland-Altman plot. CONCLUSION: Our results demonstrate the accuracy of the method for the measurement of myocardial IS in mice with the Linoview SPECT system.