Selene Capitanio

Detection of significant coronary artery disease by noninvasive anatomical and functional imaging.

Background—The choice of imaging techniques in patients with suspected coronary artery disease (CAD) varies between countries, regions, and hospitals. This prospective, multicenter, comparative effectiveness study was designed to assess the relative accuracy of commonly used imaging techniques for identifying patients with significant CAD. Methods and Results—A total of 475 patients with stable chest pain and intermediate likelihood of CAD underwent coronary computed tomographic angiography and stress myocardial perfusion imaging by single photon emission computed tomography or positron emission tomography, and ventricular wall motion imaging by stress echocardiography or cardiac magnetic resonance. If ≥1 test was abnormal, patients underwent invasive coronary angiography. Significant CAD was defined by invasive coronary angiography as >50% stenosis of the left main stem, >70% stenosis in a major coronary vessel, or 30% to 70% stenosis with fractional flow reserve ⩽0.8. Significant CAD was present in 29% of patients. In a patient-based analysis, coronary computed tomographic angiography had the highest diagnostic accuracy, the area under the receiver operating characteristics curve being 0.91 (95% confidence interval, 0.88–0.94), sensitivity being 91%, and specificity being 92%. Myocardial perfusion imaging had good diagnostic accuracy (area under the curve, 0.74; confidence interval, 0.69–0.78), sensitivity 74%, and specificity 73%. Wall motion imaging had similar accuracy (area under the curve, 0.70; confidence interval, 0.65–0.75) but lower sensitivity (49%, P<0.001) and higher specificity (92%, P<0.001). The diagnostic accuracy of myocardial perfusion imaging and wall motion imaging were lower than that of coronary computed tomographic angiography (P<0.001). Conclusions—In a multicenter European population of patients with stable chest pain and low prevalence of CAD, coronary computed tomographic angiography is more accurate than noninvasive functional testing for detecting significant CAD defined invasively. Clinical Trial Registration—URL: http://www.clinicaltrials.gov. Unique identifier: NCT00979199.

Direct inhibition of hexokinase activity by metformin at least partially impairs glucose metabolism and tumor growth in experimental breast cancer

Emerging evidence suggests that metformin, a widely used anti-diabetic drug, may be useful in the prevention and treatment of different cancers. In the present study, we demonstrate that metformin directly inhibits the enzymatic function of hexokinase (HK) I and II in a cell line of triple-negative breast cancer (MDA-MB-231). The inhibition is selective for these isoforms, as documented by experiments with purified HK I and II as well as with cell lysates. Measurements of 18F-fluoro-deoxyglycose uptake document that it is dose- and time-dependent and powerful enough to virtually abolish glucose consumption despite unchanged availability of membrane glucose transporters. The profound energetic imbalance activates phosphorylation and is subsequently followed by cell death. More importantly, the “in vivo” relevance of this effect is confirmed by studies of orthotopic xenografts of MDA-MB-231 cells in athymic (nu/nu) mice. Administration of high drug doses after tumor development caused an evident tumor necrosis in a time as short as 48 h. On the other hand, 1 mo metformin treatment markedly reduced cancer glucose consumption and growth. Taken together, our results strongly suggest that HK inhibition contributes to metformin therapeutic and preventive potential in breast cancer.

Multicentre multi-device hybrid imaging study of coronary artery disease: results from the EValuation of INtegrated Cardiac Imaging for the Detection and Characterization of Ischaemic Heart Disease (EVINCI) hybrid imaging population

AIMS Hybrid imaging provides a non-invasive assessment of coronary anatomy and myocardial perfusion. We sought to evaluate the added clinical value of hybrid imaging in a multi-centre multi-vendor setting. METHODS AND RESULTS Fourteen centres enrolled 252 patients with stable angina and intermediate (20-90%) pre-test likelihood of coronary artery disease (CAD) who underwent myocardial perfusion scintigraphy (MPS), CT coronary angiography (CTCA), and quantitative coronary angiography (QCA) with fractional flow reserve (FFR). Hybrid MPS/CTCA images were obtained by 3D image fusion. Blinded core-lab analyses were performed for CTCA, MPS, QCA and hybrid datasets. Hemodynamically significant CAD was ruled-in non-invasively in the presence of a matched finding (myocardial perfusion defect co-localized with stenosed coronary artery) and ruled-out with normal findings (both CTCA and MPS normal). Overall prevalence of significant CAD on QCA (>70% stenosis or 30-70% with FFR≤0.80) was 37%. Of 1004 pathological myocardial segments on MPS, 246 (25%) were reclassified from their standard coronary distribution to another territory by hybrid imaging. In this respect, in 45/252 (18%) patients, hybrid imaging reassigned an entire perfusion defect to another coronary territory, changing the final diagnosis in 42% of the cases. Hybrid imaging allowed non-invasive CAD rule-out in 41%, and rule-in in 24% of patients, with a negative and positive predictive value of 88% and 87%, respectively. CONCLUSION In patients at intermediate risk of CAD, hybrid imaging allows non-invasive co-localization of myocardial perfusion defects and subtending coronary arteries, impacting clinical decision-making in almost one every five subjects.

Metformin Temporal and Localized Effects on Gut Glucose Metabolism Assessed Using 18F-FDG PET in Mice

In the course of metformin treatment, staging abdominal cancer lesions with 18F-FDG PET images is often hindered by the presence of a high bowel radioactivity. The present study aimed to verify the mechanism underlying this phenomenon. Methods: Fifty-three mice were submitted to dynamic acquisitions of 18F-FDG kinetics under fasting conditions. Three small-animal PET scans were obtained over a 4-mo study period. The animals were subdivided into 4 groups according to the following metformin administration protocol: group 1, untreated mice (n = 15); group 2, mice exposed to metformin treatment (750 mg/kg/d) for the 48 h before each PET study (pulsed, n = 10); group 3, mice treated for the whole study period (prolonged, n = 10); and group 4, mice in which prolonged treatment was interrupted 48 h before PET (interrupted, n = 8). The rate constant of 18F-FDG uptake was estimated by Patlak analysis. At the end of the study, the ileum and colon were harvested, washed, and counted ex vivo. Two further groups, of 5 animals each, were included to evaluate the effect of prolonged metformin treatment on phosphorylated adenosine monophosphate (AMP)–activated protein kinase (pAMPK) form and gene expression for thioredoxin-interacting protein (TXNIP). Results: Pulsed treatment did not modify gut tracer retention with respect to the untreated group. Conversely, prolonged treatment induced a progressive increase in 18F-FDG uptake that selectively involved the colonic wall, without any significant contamination of bowel content. This effect persisted after a complete drug washout in the interrupted group. These responses were paralleled by increased pAMPK availability and by reduced expression of TXNIP messenger RNA in colonic enterocytes exposed to prolonged metformin treatment. Conclusion: Metformin causes a selective increase in colonic 18F-FDG uptake. This effect appears after a relatively long period of treatment and persists soon after drug washout. Accordingly, the increased bowel glucose metabolism reflects a biologic response to chronic metformin treatment characterized by increased levels of pAMPK and reduced levels of TXNIP.

Divergent targets of glycolysis and oxidative phosphorylation result in additive effects of metformin and starvation in colon and breast cancer.

Emerging evidence demonstrates that targeting energy metabolism is a promising strategy to fight cancer. Here we show that combining metformin and short-term starvation markedly impairs metabolism and growth of colon and breast cancer. The impairment in glycolytic flux caused by starvation is enhanced by metformin through its interference with hexokinase II activity, as documented by measurement of 18F-fluorodeoxyglycose uptake. Oxidative phosphorylation is additively compromised by combined treatment: metformin virtually abolishes Complex I function; starvation determines an uncoupled status of OXPHOS and amplifies the activity of respiratory Complexes II and IV thus combining a massive ATP depletion with a significant increase in reactive oxygen species. More importantly, the combined treatment profoundly impairs cancer glucose metabolism and virtually abolishes lesion growth in experimental models of breast and colon carcinoma. Our results strongly suggest that energy metabolism is a promising target to reduce cancer progression.

123I-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl) nortropane single photon emission computed tomography and 123I-metaiodobenzylguanidine myocardial scintigraphy in differentiating dementia with lewy bodies from other dementias: A comparative study

To compare the diagnostic value of striatal 123I‐2β‐carbomethoxy‐3β‐(4‐iodophenyl)‐N‐(3‐fluoropropyl) nortropane (123I‐FP‐CIT) single photon emission computed tomography (SPECT) and 123I‐metaiodobenzylguanidine (123I‐MIBG) myocardial scintigraphy in differentiating dementia with Lewy bodies (DLB) from other dementia types.

Resting metabolic connectivity in Alzheimer's disease

Metabolic connectivity analysis of resting 18F-FDG PET is based on the assumption that brain regions whose metabolism is significantly correlated at rest are functionally associated and that the strength of the association is proportional to the magnitude of the correlation coefficient. Therefore, this method could be used to evaluate connectivity networks independently on the basis of performance in specific tasks. Published studies have provided evidence that metabolic connectivity substantially overlaps underlying anatomical pathways and depends on the location of the analyzed regions, but is not influenced by their size. The present review focuses on the methods and meaning of resting inter-regional correlation analysis of cerebral metabolic rate of glucose consumption in Alzheimer’s disease. Accordingly, we describe the evolution of analytical tools from the correlation with a single region of interest to a voxel-based statistical parametric mapping-based approach. We also discuss the pathophysiological implications of metabolic connectivity studies both for Alzheimer-related disconnection syndrome and for default-mode network impairment and compensation mechanisms.

Intrabone Transplant of Cord Blood Stem Cells Establishes a Local Engraftment Store: A Functional PET/FDG Study

Background. Despite advancements in comprehension of molecular mechanisms governing bone marrow (BM) homing of hematopoietic stem cells, cord blood transplant (CBT) suffers from a slow rate of hematopoietic recovery. Intrabone (IB) injection has been proposed as a method able to improve speed of BM engraftment with respect to conventional IV protocols. However, the mechanisms underlying this benefit are largely unknown. Aim. To verify whether IB-CBT determines a local engraftment able to predict the reconstitution of recipient hematopoiesis. Design and Methods. Twenty-one patients with hematologic malignancies received IB injection into both iliac crests of 3.2 ± 0.68 ∗ 107/kg cord blood cells. One month following IB-CBT, PET-CT imaging was performed. Maximal standardized uptake values (SUVs) were assessed in BM of both iliac crests and in all lumbar vertebrae. Results. Maximal SUV within iliac crests was higher than in lumbar vertebrae (4.1 ± 1.7 versus 3.2 ± 0.7, resp., P = 0.01). However, metabolic activity in these two different BM districts was significantly correlated (r = 0.7, P < 0.001). Moreover, FDG uptake values within the injection site closely predicted platelet recovery 100 days after IB-CBT (r = 0.72, P < 0.01). Conclusions. The metabolic activity of injected BM predicts the subsequent rate of hematopoietic recovery after IB-CBT, suggesting a pivotal role of the local engraftment in the reconstitution of recipient hematopoiesis.

Metformin and cancer: Technical and clinical implications for FDG-PET imaging

Metformin is the most widely used hypoglycemic agent. Besides its conventional indications, increasing evidence demonstrate a potential efficacy of this biguanide as an anticancer drug. Possible mechanisms of actions seem to be independent from its hypoglycemic effect and seem to involve the interference with key pathways in cellular proliferation and glycolysis. To date, many clinical trials implying the use of metformin in cancer treatment are on-going. The increasing use of (18)F-2-fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET) in cancer evaluation raises a number of questions about the possible interference of the biguanide on FDG distribution. In particular, the interferences exerted by metformin on AMP-activated protein kinase pathway (the cellular energy sensor), on insulin levels and on Hexokinase could potentially have repercussion on glucose handling and thus on FDG distribution. A better comprehension of the impact of metformin on FDG uptake is needed in order to optimize the use of PET in this setting. This evaluation would be useful to ameliorate scans interpretation in diabetic patients under chronic metformin treatment and to critically interpret images in the context of clinical trials. Furthermore, collecting prospective data in this setting would help to verify whether FDG-PET could be a valid tool to appreciate the anticancer effect of this new therapeutic approach.

A new compartmental method for the analysis of liver FDG kinetics in small animal models

BackgroundCompartmental analysis is a standard method to quantify metabolic processes using fluorodeoxyglucose-positron emission tomography (FDG-PET). For liver studies, this analysis is complex due to the hepatocyte capability to dephosphorylate and release glucose and FDG into the blood. Moreover, a tracer is supplied to the liver by both the hepatic artery and the portal vein, which is not visible in PET images. This study developed an innovative computational approach accounting for the reversible nature of FDG in the liver and directly computing the portal vein tracer concentration by means of gut radioactivity measurements.MethodsTwenty-one mice were subdivided into three groups: the control group ‘CTR’ (n = 7) received no treatment, the short-term starvation group ‘STS’ (n = 7) was submitted to food deprivation with free access to water within 48 h before imaging, and the metformin group ‘MTF’ (n = 7) was treated with metformin (750 mg/Kg per day) for 1 month. All mice underwent a dynamic micro-PET study for 50 min after an 18F-FDG injection. The compartmental analysis considered two FDG pools (phosphorylated and free) in both the gut and liver. A tracer was carried into the liver by the hepatic artery and the portal vein, and tracer delivery from the gut was considered as the sole input for portal vein tracer concentration. Accordingly, both the liver and gut were characterized by two compartments and two exchange coefficients. Each one of the two two-compartment models was mathematically described by a system of differential equations, and data optimization was performed by applying a Newton algorithm to the inverse problems associated to these differential systems.ResultsAll rate constants were stable in each group. The tracer coefficient from the free to the metabolized compartment in the liver was increased by STS, while it was unaltered by MTF. By contrast, the tracer coefficient from the metabolized to the free compartment was reduced by MTF and increased by STS.ConclusionsData demonstrated that our method was able to analyze FDG kinetics under pharmacological or pathophysiological stimulation, quantifying the fraction of the tracer trapped in the liver or dephosphorylated and released into the bloodstream.