Guillaume Kreutter

β cell membrane remodelling and procoagulant events occur in inflammation-driven insulin impairment: a GLP-1 receptor dependent and independent control

Inflammation and hyperglycaemia are associated with a prothrombotic state. Cell‐derived microparticles (MPs) are the conveyors of active procoagulant tissue factor (TF) and circulate at high concentration in diabetic patients. Liraglutide, a glucagon‐like peptide (GLP)‐1 analogue, is known to promote insulin secretion and β‐cell preservation. In this in vitro study, we examined the link between insulin impairment, procoagulant activity and plasma membrane remodelling, under inflammatory conditions. Rin‐m5f β‐cell function, TF activity mediated by MPs and their modulation by 1 μM liraglutide were examined in a cell cross‐talk model. Methyl‐β‐cyclodextrine (MCD), a cholesterol depletor, was used to evaluate the involvement of raft on TF activity, MP shedding and insulin secretion as well as Soluble N‐éthylmaleimide‐sensitive‐factor Attachment protein Receptor (SNARE)‐dependent exocytosis. Cytokines induced a two‐fold increase in TF activity at MP surface that was counteracted by liraglutide. Microparticles prompted TF activity on the target cells and a two‐fold decrease in insulin secretion via protein kinase A (PKA) and p38 signalling, that was also abolished by liraglutide. Large lipid raft clusters were formed in response to cytokines and liraglutide or MCD‐treated cells showed similar patterns. Cells pre‐treated by saturating concentration of the GLP‐1r antagonist exendin (9‐39), showed a partial abolishment of the liraglutide‐driven insulin secretion and liraglutide‐decreased TF activity. Measurement of caspase 3 cleavage and MP shedding confirmed the contribution of GLP‐1r‐dependent and ‐independent pathways. Our results confirm an integrative β‐cell response to GLP‐1 that targets receptor‐mediated signalling and membrane remodelling pointing at the coupling of insulin secretion and inflammation‐driven procoagulant events.

Carbidopa Effect on 18F-FDOPA Uptake in Insulinoma: from Cell Culture to microPET Imaging

Patient premedication with carbidopa seems to improve the accuracy of 6-18F-fluoro-3,4-dihydroxy-l-phenylalanine (18F-FDOPA) PET for insulinoma diagnosis. However, the risk of PET false-negative results in the presence of carbidopa is a concern. Consequently, we aimed to evaluate the effect of carbidopa on 18F-FDOPA uptake in insulinoma β-cells and an insulinoma xenograft model in mice. Methods: 18F-FDOPA in vitro accumulation was assessed in the murine β-cell line RIN-m5F. In vivo small-animal PET experiments were performed on tumor-bearing nude mice after subcutaneous injection of RIN-m5F cells. Experiments were conducted with and without carbidopa pretreatment. Results: Incubation of RIN-m5F cells with 80 μM carbidopa did not significantly affect the cellular accumulation of 18F-FDOPA. Tumor xenografts were clearly detectable by small-animal PET in all cases. Insulinoma xenografts in carbidopa-treated mice showed significantly higher 18F-FDOPA uptake than those in nontreated mice. Regardless of carbidopa premedication, the xenografts were characterized by an early increase in 18F-FDOPA uptake and then a progressive reduction over time. Conclusion: Carbidopa did not influence in vitro 18F-FDOPA accumulation in RIN-m5F cells but improved insulinoma imaging in vivo. Our findings increase current knowledge about the 18F-FDOPA uptake profile of RIN-m5F cells and a related xenograft model. To our knowledge, the present work represents the first preclinical research specifically focused on insulinomas, with potential translational implications.

Endothelial microparticles released by activated protein C protect beta cells through EPCR/PAR1 and annexin A1/FPR2 pathways in islets

Islet transplantation is associated with early ischaemia/reperfusion, localized coagulation and redox‐sensitive endothelial dysfunction. In animal models, islet cytoprotection by activated protein C (aPC) restores islet vascularization and protects graft function, suggesting that aPC triggers various lineages. aPC also prompts the release of endothelial MP that bear EPCR, its specific receptor. Microparticles (MP) are plasma membrane procoagulant vesicles, surrogate markers of stress and cellular effectors. We measured the cytoprotective effects of aPC on endothelial and insulin‐secreting Rin‐m5f β‐cells and its role in autocrine and paracrine MP‐mediated cell crosstalk under conditions of oxidative stress. MP from aPC‐treated primary endothelial (EC) or β‐cells were applied to H2O2‐treated Rin‐m5f. aPC activity was measured by enzymatic assay and ROS species by dihydroethidium. The capture of PKH26‐stained MP and the expression of EPCR were probed by fluorescence microscopy and apoptosis by flow cytometry. aPC treatment enhanced both annexin A1 (ANXA1) and PAR‐1 expression in EC and to a lesser extent in β‐cells. MP from aPC‐treated EC (eMaPC) exhibited high EPCR and annexin A1 content, protected β‐cells, restored insulin secretion and were captured by 80% of β cells in a phosphatidylserine and ANXA1‐dependent mechanism. eMP activated EPCR/PAR‐1 and ANXA1/FPR2‐dependent pathways and up‐regulated the expression of EPCR, and of FPR2/ALX, the ANXA1 receptor. Cytoprotection was confirmed in H2O2‐treated rat islets with increased viability (62% versus 48% H2O2), reduced apoptosis and preserved insulin secretion in response to glucose elevation (16 versus 5 ng/ml insulin per 10 islets). MP may prove a promising therapeutic tool in the protection of transplanted islets.

Senescence of Pancreas in Middle-Aged Rats with Normal Vascular Function

BACKGROUND In organ transplantation, particularly pancreas transplantation, donor age is a determinant factor for graft survival. Physiological aging is crucial in the progressive deterioration of organs in adulthood. We compared the senescence and function features of pancreas and vascular tissues in young rats and middle-aged rats. MATERIAL AND METHODS Islet morphology and the area of cells secreting insulin or glucagon was investigated using immunohistology in young rats (12 weeks) and middle-aged rats (52 weeks) (n=8). Senescence markers, oxidative stress (ROS), and tissue factor (TF) were measured in the rat pancreases. Circulating microparticles (MPs) were measured as surrogates of vascular cell injury. Vascular function was studied in mesenteric arterial rings. RESULTS Larger islets were twice as frequent in young rats versus middle-aged rats. In middle-aged rats there was a significant decrease of the β-cells/islet area ratio. Western blot analysis showed an increased expression of p53, p21, and p16 senescence markers (2-, 7- and 3-fold respectively) with no modification in caspase-3 activation. A 30% decrease of endothelial nitric oxide synthase (eNOS) was observed together with a 4-fold increase in TF expression. ROS formation increased significantly (2-fold) in middle-aged rats and their main source, determined by pharmacological inhibition, was NADPH oxidase and uncoupled nitric-oxide (NO) synthase. No sign of vascular injury (microparticles) or dysfunction was evidenced. CONCLUSIONS Modification in islet morphology and function were detected in middle-aged rats before any measurement of macro-vascular dysfunction. The data indicate a pancreatic senescence in the process of aging associated with uncontrolled accumulation of oxidative species that suggests a determining role of donor age in transplantation.

O-(2-18F-fluoroethyl)-l-tyrosine (18F-FET) uptake in insulinoma: first results from a xenograft mouse model and from human

INTRODUCTION Herein we have evaluated the uptake of O-(2-18F-fluoroethyl)-l-tyrosine (18F-FET) in insulinoma in comparison with those of 6-18F-fluoro-3,4-dihydroxy-l-phenylalanine (18F-FDOPA) providing first data from both murine xenograft model and one patient with proved endogenous hyperinsulinemic hypoglycemia. METHODS Dynamic 18F-FET and carbidopa-assisted 18F-FDOPA PET were performed on tumor-bearing nude mice after subcutaneous injection of RIN-m5F murine beta cells and on a 30-year-old man with type-1 multiple endocrine neoplasia and hyperinsulinemic hypoglycemia defined by a positive fasting test. RESULTS Seven and three nude mice bearing a RIN-m5F insulinoma xenograft were respectively studied by 18F-FET and 18F-FDOPA μPET. Insulinoma xenograft was detected in all the imaged animals. Xenograft was characterized by an early but moderate increase of 18F-FET uptake followed by a slight decline of uptake intensity during the 20 min dynamic acquisition. Tumoral radiotracer peak intensity and the highest tumor-to-background contrast were reached about 5 minutes after 18F-FET iv. injection (mean SUV: 1.21 ± 0.10). The biodistribution of 18F-FET and 18F-FDOPA and their dynamic tumoral uptake profile and intensity were similar. In the examined patient, 18F-FDOPA and 18F-FET PET/CT showed one concordant focal area of well-defined increased uptake in the pancreatic tail corresponding to 11 mm histologically proved insulinoma. The SUVmax tumor to liver ratio was 1.5, 1.1 for 18F-FDOPA, 1.1, 1 for 18F-FET at early (0-5 min post injection) and delayed (5-20 min post injection) PET/CT acquisition, respectively. Despite the relatively low tumoral uptake intensity, insulinoma was clearly identified due to the low background in the pancreas. At the contrary, no 18F-FDOPA or 18F-FET tumoral uptake was revealed on whole-body PET/CT images performed about 30 min after radiotracer administration. Note of worth, the dynamic uptake pattern of 18F-FET and 18F-FDOPA were similar between human insulinoma and mice xenograft tumor. CONCLUSION 18F-FET PET compared equally to 18F-FDOPA PET in a preclinical RIN-m5F murine model of insulinoma and in one patient with insulinoma-related hypoglycemia. However, in both cases, the tumoral uptake intensity was moderate and the tumor was only visible until 20 min after radiotracer injection. Hence, caution should be taken before asserting the translational relevance of our results in the clinical practices. However, the structural analogies between 18F-FET and 18F-FDOPA as well as the limited pancreatic uptake of 18F-FET in human, encourage evaluating 18F-FET as diagnostic radiotracer for insulinoma detection in further prospective studies involving large cohorts of patients.