The diet-derived short chain fatty acid propionate improves beta-cell function in humans and stimulates insulin secretion from human islets in vitro

Aims: Diet-derived short chain fatty acids (SCFAs) improve glucose homeostasis in vivo, but the role of individual SCFAs and their mechanisms of action have not been defined. This study evaluated the effects of increasing colonic delivery of the SCFA propionate on β-cell function in humans and the direct effects of propionate on isolated human islets in vitro. Materials and Methods: For 24 weeks human subjects ingested an inulin-propionate ester that delivers propionate to the colon. Acute insulin, GLP-1 and non-esterified fatty acid (NEFA) levels were quantified pre- and post-supplementation in response to a mixed meal test. Expression of the SCFA receptor FFAR2 in human islets was determined by western blotting and immunohistochemistry. Dynamic insulin secretion from perifused human islets was quantified by radioimmunoassay and islet apoptosis was determined by quantification of caspase 3/7 activities. Results: Colonic propionate delivery in vivo was associated with improved β-cell function with increased insulin secretion that was independent of changes in GLP-1 levels. Human islet β-cells expressed FFAR2 and propionate potentiated dynamic glucose-stimulated insulin secretion in vitro, an effect that was dependent on signalling via protein kinase C. Propionate also protected human islets from apoptosis induced by the NEFA sodium palmitate and inflammatory cytokines. Conclusions: Our results indicate that propionate has beneficial effects on β-cell function in vivo, and in vitro analyses demonstrated that it has direct effects to potentiate glucose-stimulated insulin release and maintain β-cell mass through inhibition of apoptosis. These observations support ingestion of propiogenic dietary fibres to maintain healthy glucose homeostasis

Mechanisms of RA action in steroidogenic tissues and pro-apoptotic effects of combined treatment of breast tumoral cell lines with 9-cis retinoic acid and rosiglitazione

Dottorato di Ricerca in: Cellular Biochemistry and Drug Activity in Oncology, Ciclo XXII,a.a. 2008-2009Vitamin A (Retinol) plays a central role in many essential biological processes such as vision, immunity, reproduction, growth, development, control of cellular proliferation and differentiation. The main active forms of retinol, not primary involved in vision, are alltrans retinoic acid and 9-cis retinoic acid, both able to act at nuclear level by binding their receptors RAR and RXR and modulating many physiological processes. However, the nuclear action of vitamin A derivatives is not the only mechanism of retinoic acid (RA) acting on cells. RA is able to modify covalently proteins via a post-translational modification, named retinoylation that has been shown to occur at physiological concentration on pre-existing proteins and localized mainly in the mitochondrial compartment. The present study has been focused on the non genomic action of RA on steroidogenic tissues, testes and adrenal glands, giving further details on the ability of RA to influence protein activity and therefore cell physiology. In particular RA effects on mitochondria from the adrenal glands and the 2-oxoglutarate carrier protein from testes and TM-3 Leydig cell line were studied, providing new data on the peculiarity of steroidogenic tissues to incorporate RA at dietary levels and demonstrating how the shuttling of reducing equivalent across the mitochondrial membrane is influenced by RA treatment. Looking for the biochemical mechanism of RA action on the Adenine Nucleotide Translocator, that exchanges ATP for ADP between mitochondria and cytosol, for the first time, it was possible to demonstrate how the activity of this carrier protein is positively modulated by the Coenzyme A, a fundamental component of the retynoilating buffer. At pharmacological levels, retinoids are also active compounds in the treatment of cancer due to the capability to promote cell differentiation and their pro-apoptotic activity. In this latter concern, the mechanisms of nutriceutical concentration of 9-cis RA, together with nanomolar concentration of the selective PPARγ ligand, rosiglitazone, to promote apoptosis in breast cancer cell lines, have been investigated. The data lay the basis for a potential use of the combined therapy with low doses of both BRL and 9-cis RA as novel therapeutic tool particularly for breast cancer patients who develop resistance to antiestrogen therapyUniversity of Calabri

Dynamic Profiling of Insulin Secretion and ATP Generation in Isolated Human and Mouse Islets Reveals Differential Glucose Sensitivity

Background/Aims: Rodent islets are often used for basic science research but they do not always recapitulate signalling events in human islets. This study evaluated the glucose-dependent responses of human and mouse islets in terms of dynamic insulin secretion, metabolic coupling and the role of glucose transporters. Methods: Glucose-induced insulin secretion from isolated mouse and human islets was profiled by perifusion and islet ATP levels were measured by chemoluminescence assay. Glucose transporter expression was determined by qPCR and western blotting. Results: Human islets show a left-shifted glucose concentration-insulin secretion profile compared to mouse islets. These data are consistent with glucose transporter expression, with human islets expressing mainly GLUT1 and GLUT3, and GLUT2 being the predominant transporter in mouse islets. Using the GLUT1 inhibitor STF-31 we unveiled an important role for GLUT1 for differences in glucose-induced insulin secretion profiles observed between the two species. Conclusion: The high affinity of GLUT1/3 for glucose reflects the left-shifted glucose-induced insulin secretory response of human islets and the impairment of insulin secretion from human islets after STF-31 treatment indicates an important role for GLUT1 in human islet stimulus-secretion coupling. Our data provide further insight into key differences between insulin secretion regulation in mouse and human islets

APT070 (Mirococept), a membrane-localizing C3 convertase inhibitor, attenuates early human islet allograft damage in vitro and in vivo in a humanized mouse model

BACKGROUND AND PURPOSE: A major obstacle to islet cell transplantation is the early loss of transplanted islets resulting from the instant blood‐mediated inflammation reaction (IBMIR). The activation of complement pathways plays a central role in IBMIR. The aim of this study was to test the inhibitory effect of “painting” human islets with APT070, a membrane‐localizing C3 convertase inhibitor, on inflammation evoked by exposure to human serum in vitro and by transplantation in vivo in a humanized diabetic mouse model. EXPERIMENTAL APPROACH: In vitro, human islets pre‐incubated with APT070 were exposed to allogeneic whole blood. In vivo, similarly treated islets were transplanted underneath the kidney capsule of streptozotocin‐induced diabetic NOD‐SCID IL2rγ(−/−) mice that had been reconstituted with human CD34(+) stem cells. Complement activation and islet hormone content were assayed using enzyme‐linked immunosorbent assays. Supernatants and sera were assayed for cytokines using cytometric beads array. Morphology of the islets incubated with human serum in vitro and in graft‐bearing kidney were evaluated using immunofluorescence staining. KEY RESULTS: Pre‐incubation with APT070 decreased C‐peptide release and iC3b production in vitro, with diminished deposition of C4d and C5b‐9 in islets embedded in blood clots. In vivo, the APT070‐treated islets maintained intact structure and showed less infiltration of inflammatory cells than untreated islets. The pretreatments also significantly reduced pro‐inflammatory cytokines in supernatants and sera. CONCLUSIONS AND IMPLICATIONS: Pre‐treatment of islets with APT070 could reduce intra‐islet inflammation with accompanying preservation of insulin secretion by beta cells. APT070 could be as a potential therapeutic tool in islet transplantation