Bogdan Catargi

Comparative evaluation of conventional and dynamic magnetic resonance imaging of the pituitary gland for the diagnosis of Cushing's disease.

The ability of MRI to detect pituitary ACTH‐secreting adenomas in patients with Cushings disease is limited. Owing to different dynamics of contrast enhancement between adenomas and normal pituitary tissue, it has been suggested that obtaining images within seconds after gadolinium (Gad) injection using dynamic procedures increases the sensitivity of MRI in the detection of pituitary microadenomas. The objective of this study was to compare the ability of conventional magnetic resonance imaging (CMRI) and dynamic MRI (DMRI) to detect ACTH‐secreting pituitary adenomas.

Glucose-responsive microgels with a core–shell structure

New multiresponsive core-shell microgels have been synthesized, with a thermoresponsive core and a glucose-responsive shell, made respectively of poly(N-isopropylacrylamide) (pNIPAM) and pNIPAM-co-acrylamidophenylboronic acid (pNIPAM-co-APBA). The structure of the particles was elucidated by means of dynamic light scattering. Their thermal properties were investigated and compared to those of the core alone. Without glucose, the hydrophobic shell prevented the core from swelling in a certain temperature range where the shell was shown to be collapsed. This core compression vanished upon glucose addition, when the shell became hydrophilic and swelled. Therefore, the extent of core swelling was regulated by two processes: its own internal stimulus, i.e. temperature, and shell compression, which is proportional to glucose concentration, even at physiological salinity. The concept was applied to a selected chemical composition. Core-shell microgels with a response to glucose at physiological pH were obtained and used to encapsulate insulin. Insulin release was shown to be regulated by the presence of glucose.

Photochemical crosslinking of hyaluronic acid confined in nanoemulsions: towards nanogels with a controlled structure

We present the preparation of nanogels made of hyaluronic acid (HA) with a well-controlled structure. To this end, HA precursors with polymerizable methacrylate groups (HA-MA) were confined within water-in-oil nanoemulsion droplets as nanoreactors and further photopolymerized under UV. Particular attention was paid to the preparation of a stable nanoemulsion template with a homogeneous droplet size. Upon UV irradiation of the emulsion containing HA-MA, crosslinked HA-MA particles with a well-defined size were obtained. Moreover, by varying the photopolymerization conditions, i.e. the number of received photons, we could control the conversion rate of the polymerization, as proved by 1H-NMR. Nanogels with controlled cross-linking densities were thus obtained. Not only could their crosslinking densities be controlled by the number of incident photons, but also by the degree of methacrylation (DM) of HA-MA derivatives. In addition, the swelling properties of the nanogels depended on external factors, showing their pH and ionic strength responsiveness. We show that these structures were highly biocompatible, stable under storage and enzymatically biodegradable, which opens the route for their application as drug delivery systems. Finally, insulin was loaded in the nanogels and its pH-dependent release was demonstrated. This versatile method of nanogel preparation, which can be applied to every type of hydrophilic precursor, offers a potential synthetic route to design other types of fully biocompatible drug delivery systems.

Readily prepared dynamic hydrogels by combining phenyl boronic acid- and maltose-modified anionic polysaccharides at neutral pH.

Dynamic covalent hydrogels are facilely prepared from biocompatible polysaccharides in physiological conditions by the formation of phenylboronate ester cross-links. This is based on the simple mixing of carboxylate-containing polysaccharides (i.e., hyaluronic acid or carboxymethylcellulose) modified with phenylboronic acid and maltose moieties according to mild coupling reactions performed in aqueous solution. The formation of dynamic networks based on reversible boronic-ester cross-links is demonstrated by analyzing their rheological behavior. This study shows that these gels can adapt their structure in response to chemical stimuli such as variations in pH or addition of glucose and self-heal.

Differential Photoluminescent and Electrochemiluminescent Behavior for Resonance Energy Transfer Processes in Thermoresponsive Microgels.

Stimuli-responsive microgels with redox and luminescent resonance energy transfer (LRET) properties are reported. Poly(N-isopropylacrylamide) microgels are functionalized simultaneously with two models dyes: a derivative of tris(bipyridine) ruthenium complex and cyanine 5. Both moieties are chosen as a pair of luminophores with a spectral overlap for resonance energy transfer, where the ruthenium complex acts as a donor and the cyanine an acceptor. The effect of the temperature on the efficiency of the LRET of the microgels has been investigated and compared using either photoluminescence (PL) or electrochemiluminescence (ECL) as the excitation process. In PL, the synthesized microgels exhibit resonance energy transfer regardless of the swelling degree of the microgels. The transfer efficiency is a function of the donor-acceptor distance and can be tuned either by the swell-collapse phase transition or by the dye content in the microgel network. In ECL, the microgels emit light only at the wavelength of the ruthenium complex because the resonance energy transfer does not occur. Indeed, even within the microgel matrix, the cyanine dye is oxidized at the potential required for ECL generation, which impairs its emitting properties. Thus, both excitation channels (i.e., PL and ECL) show differential behavior for the resonance energy transfer processes.

Non‐invasive long‐term and real‐time analysis of endocrine cells on micro‐electrode arrays

•  Pancreatic islet cells are required for glucose homeostasis and their dysfunction leads to diabetes mellitus. •  The electrical activity of these cells is regulated by nutrients as well as hormones and this provides the first integrative read‐out reflecting their function. •  Non‐invasive recording of their electrical activity and its analysis in real time would provide the possibility of long‐term and repetitive investigations or testing of multiple drugs. •  Combining electrophysiology and microelectronics, we now demonstrate such an approach with multiple (up to 60) electrodes and including on‐line signal analysis on the two major cell types present in islets, α‐ and β‐cells. •  This method should be applicable to other endocrine cells and may serve in the long‐run as the basis for a novel biosensor.

Biosensors in Diabetes : How to get the most out of evolution and transpose it into a signal.

The increase in diabetes is a major threat to health and economic development in the 21st century, as stated by the United Nations Millennium Development Goals. In 2013, 380 million people worldwide had diabetes, and almost 600 million are expected to have it by 2035. Diabetes is the major cause of nontraumatic amputation and blindness in developed countries. It is also an expensive disease. In the United States, one in five dollars for health care is spent on diabetes. Net losses in national income from diabetes amount to hundreds of billions of international dollars in China and India. Clearly, novel therapies are required.

Sealing hyaluronic acid microgels with oppositely-charged polypeptides: A simple strategy for packaging hydrophilic drugs with on-demand release

A simple route to deliver on demand hydrosoluble molecules such as peptides, packaged in biocompatible and biodegradable microgels, is presented. Hyaluronic acid hydrogel particles with a controlled structure are prepared using a microfluidic approach. Their porosity and their rigidity can be tuned by changing the crosslinking density. These negatively-charged polyelectrolytes interact strongly with positively-charged linear peptides such as poly-l-lysine (PLL). Their interactions induce microgel deswelling and inhibit microgel enzymatic degradability by hyaluronidase. While small PLL penetrate the whole volume of the microgel, PLL larger than the mesh size of the network remain confined at its periphery. They make a complexed layer with reduced pore size, which insulates the microgel inner core from the outer medium. Consequently, enzymatic degradation of the matrix is fully inhibited and non-affinity hydrophilic species can be trapped in the core. Indeed, negatively-charged or small neutral peptides, without interactions with the network, usually diffuse freely across the network. By simple addition of large PLL, they are packaged in the core and can be released on demand, upon introduction of an enzyme that degrades selectively the capping agent. Single polyelectrolyte layer appears as a simple generic method to coat hydrogel-based materials of various scales for encapsulation and controlled delivery of hydrosoluble molecules.

Indications for islet or pancreatic transplantation: Statement of the TREPID working group on behalf of the Société francophone du diabète (SFD), Société francaise d’endocrinologie (SFE), Société francophone de transplantation (SFT) and Société française de néphrologie – dialyse – transplantation (SFNDT)

While either pancreas or pancreatic islet transplantation can restore endogenous insulin secretion in patients with diabetes, no beta-cell replacement strategies are recommended in the literature. For this reason, the aim of this national expert panel statement is to provide information on the different kinds of beta-cell replacement, their benefit-risk ratios and indications for each type of transplantation, according to type of diabetes, its control and association with end-stage renal disease. Allotransplantation requires immunosuppression, a risk that should be weighed against the risks of poor glycaemic control, diabetic lability and severe hypoglycaemia, especially in cases of unawareness. Pancreas transplantation is associated with improvement in diabetic micro- and macro-angiopathy, but has the associated morbidity of major surgery. Islet transplantation is a minimally invasive radiological or mini-surgical procedure involving infusion of purified islets via the hepatic portal vein, but needs to be repeated two or three times to achieve insulin independence and long-term functionality. Simultaneous pancreas-kidney and pancreas after kidney transplantations should be proposed for kidney recipients with type 1 diabetes with no surgical, especially cardiovascular, contraindications. In cases of high surgical risk, islet after or simultaneously with kidney transplantation may be proposed. Pancreas, or more often islet, transplantation alone is appropriate for non-uraemic patients with labile diabetes. Various factors influencing the therapeutic strategy are also detailed in this report.

O51 Diaβchip : un nouveau biosenseur hybride de l’état physiologique des îlots de Langerhans et de la demande en insuline

Introduction Les ilots pancreatiques generent une activite electrique en reponse aux variations glycemiques et hormonales. Nous avons publie une nouvelle approche pour etudier ces signaux electriques de facon non-invasive sur Multielectrode Arrays (MEA). Nous developpons actuellement un capteur bioelectronique dedie (i) au criblage pharmaco-toxicologique, (ii) au controlequalite pre-transplantation des ilots, (iii) a l’amelioration des algorithmes de senseurs et, a long terme, au pilotage de pompes a insuline. Il est donc crucial de definir des parametres d’analyse refletant l’etat physiologique des ilots et appropries pour un traitement on-chip en temps-reel. Materiels et methodes Des ilots de souris cultives pendant 2–4 jours sur des MEA ont ete enregistres avec un amplificateur MEA1060-Inv-BC (MCS). Nous avons developpe des algorithmes pour separer les signaux en analyse offline. Une implantation d’analyse en temps-reel sur cartes electroniques est en cours. Resultats L’analyse a permis de separer les signaux rapides (potentiels d’action) des signaux lents, et de quantifier trois parametres d’interet : frequence instantanee et plateau-fraction des potentiels d’action, et frequence moyenne des ondes lentes. Ces parametres presentent une dose-dependance au glucose pour des concentrations croissantes et decroissantes avec un phenomene d’hysteresis. De plus, on constate un effet du GLP-1 pour des concentrations picomolaires. Le systeme electronique actuel permet d’ores et deja un traitement en tempsreel des potentiels d’action. Discussion Les trois parametres choisis sont pertinents du point de vue physiologique et pour le developpement du biocapteur. Leur combinaison assure robustesse et reactivite, et devrait permettre de determiner dynamiquement la demande en insuline. La sensibilite differentielle des ilots envers augmentation et diminution des taux de glucose pourrait refleter un demarrage rapide lors de l’hyperglycemie et un frein de protection contre l’hypoglycemie, ce qui contribue favorablement aux caracteristiques d’un biosenseur. Un systeme electronique embarque est en developpement pour l’analyse online des signaux rapides et des signaux lents.