The pancreatic islet: a micro-organ in control.

The islets of Langerhans constitute the endocrine pancreas which regulates blood glucose homeostasis and their dysfunction results in diabetes. Each of the pancreatic islets constitutes an entire micro-organ with intricate cell to cell interactions and that is well vascularized and innervated. An important therapeutic advantage in islet transplant is that pancreatic islets maintain their organ integrity when isolated and transplanted to patients with severe diabetes. Once transplanted, the islet micro-organs actively contribute to their own vascularization and start to function immediately. Hence, in terms of organ transplantation, the application of pancreatic islets will be a decisive clinical tool for future diabetes care (credit: Tilo Moede).

Electron Paramagnetic Resonance of Single Magnetic Moment on a Surface.

We address electron spin resonance of single magnetic moments in a tunnel junction using time-dependent electric fields and spin-polarized current. We show that the tunneling current directly depends on the local magnetic moment and that the frequency of the external electric field mixes with the characteristic Larmor frequency of the local spin. The importance of the spin-polarized current induced anisotropy fields acting on the local spin moment is, moreover, demonstrated. Our proposed model thus explains the absence of an electron spin resonance for a half integer spin, in contrast with the strong signal observed for an integer spin.

Clinical intraocular islet transplantation is not a number issue.

It is now well established that beta cell replacement through pancreatic islet transplantation results in significant improvement in the quality-of-life of type 1 diabetes (T1D) patients. This is achieved through improved control and prevention of severe drops in blood sugar levels. Islet transplant therapy is on the verge of becoming standard-of-care in the USA. Yet, as with other established transplantation therapies, there remain hurdles to overcome to bring islet transplantation to full fruition as a long-lasting therapy of T1D. One of these hurdles is establishing reliable new sites, other than the liver, where durable efficacy and survival of transplanted islets can be achieved. In this article, we discuss the anterior chamber of the eye as a new site for clinical islet transplantation in the treatment of T1D. We specifically focus on the common conceptions, and preconceptions, on the requirements of islet mass, and whether or not the anterior chamber can accommodate sufficient islets to achieve meaningful efficacy and significant impact on hyperglycemia in clinical application.

Light scattering as an intrinsic indicator for pancreatic islet cell mass and secretion.

The pancreatic islet of Langerhans is composed of endocrine cells producing and releasing hormones from secretory granules in response to various stimuli for maintenance of blood glucose homeostasis. In order to adapt to a variation in functional demands, these islets are capable of modulating their hormone secretion by increasing the number of endocrine cells as well as the functional response of individual cells. A failure in adaptive mechanisms will lead to inadequate blood glucose regulation and thereby to the development of diabetes. It is therefore necessary to develop tools for the assessment of both pancreatic islet mass and function, with the aim of understanding cellular regulatory mechanisms and factors guiding islet plasticity. Although most of the existing techniques rely on the use of artificial indicators, we present an imaging methodology based on intrinsic optical properties originating from mature insulin secretory granules within endocrine cells that reveals both pancreatic islet mass and function. We demonstrate the advantage of using this imaging strategy by monitoring in vivo scattering signal from pancreatic islets engrafted into the anterior chamber of the mouse eye, and how this versatile and noninvasive methodology permits the characterization of islet morphology and plasticity as well as hormone secretory status.

Islet inflammation in plain sight.

Although, diabetes is reaching pandemic proportions, the exact aetiology of either type 1 (T1D) or type 2 diabetes (T2D) remains to be determined. Mounting evidence, however, suggests that islet inflammation is a likely common denominator during early development of either type of the disease. In this review, we highlight some of the inflammatory mechanisms that appear to be shared between T1D and T2D, and we explore the utility of intravital imaging in the study of islet inflammation. Intravital imaging has emerged as an indispensable tool in biomedical research and a variety of in vivo imaging approaches have been developed to study pancreatic islet physiology and pathophysiology in the native environment in health and disease. However, given the scattered distribution of the islets of Langerhans within the 'sea' of the exocrine pancreas located deep within the body and the fact that the islets only constitute 1-2% of the total volume of pancreatic tissue, studying the pancreatic islet in situ has been challenging. Here, we focus on a new experimental approach that enables studying local islet inflammation with single-cell resolution in the relevant context of the in vivo environment non-invasively and longitudinally and, thereby improving our understanding of diabetes pathogenesis.

Role of T cell recruitment and chemokine-regulated intra-graft T cell motility patterns in corneal allograft rejection.

Keratoplasty is the primary treatment to cure blindness due to corneal opacification. However, immune-mediated rejection remains the leading cause of keratoplasty failure. Here, we utilize an in vivo imaging approach to monitor, track, and characterize in real-time the recruitment of GFP-labeled allo-specific activated (Bonzo) T cells during corneal allograft rejection. We show that the recruitment of effector T cells to the site of transplantation determined the fate of corneal allografts, and that local intra-graft production of CCL5 and CXCL9/10 regulated motility patterns of effector T cells in situ, and correlated with allograft rejection. We also show that different motility patterns associate with distinct in vivo phenotypes (round, elongated, and ruffled) of graft-infiltrating effector T cells with varying proportions during progression of rejection. The ruffled phenotype was characteristic of activated effectors T cells and predominated during ongoing rejection, which associated with significantly increased T cell dynamics within the allografts. Importantly, CCR5/CXCR3 blockade decreased the motility, size, and number of infiltrating T cells and significantly prolonged allograft survival. Our findings indicate that chemokines produced locally within corneal allografts play an important role in the in situ activation and dynamic behavior of infiltrating effector T cells, and may guide targeted interventions to promote graft survival.

A NATURAL BODY WINDOW TO STUDY HUMAN PANCREATIC ISLET CELL FUNCTION AND SURVIVAL.

The World Health Organization projects diabetes prevalence worldwide to be at 4.4% in 2030 compared to 2.8% in the year 2000. These alarming predictions come amid vigorous efforts in diabetes research which have failed so far to deliver effective therapies. Our incomplete understanding of the pathogenesis of diabetes is likely to contribute to the "disconnect" between our research efforts and their translation into successful therapies. Technically, studying the pathophysiology of the pancreatic islets is hindered by the anatomical location of the pancreas, which is deeply embedded in the body, and by lack of experimental tools that enable comprehensive interrogation of the pancreatic islets with sufficient resolution in the context of the natural in vivo environment non-invasively and longitudinally. Emerging evidence also indicates that challenges in successful translation of findings in animal models to the human setting are complicated by some inherent structural and functional differences between the mouse and human islets. In this review, we briefly describe the advantages and shortcomings of existing intravital imaging approaches used to study the pancreatic islet biology in vivo, and we contrast such techniques with a recently established intravital approach using pancreatic islet transplantation into the anterior chamber of the eye. We also provide a summary of recent structure-function studies in the human pancreas to reveal distinctive features of human islets compared with mouse islets. We finally touch on a recently renewed discussion of the validity of animal models in studying human health and disease, and we highlight the potential utility of "humanized" animal models in studying different aspects of human islet biology and improving our understanding of diabetes.

Non-invasive in vivo imaging of pancreatic ß-cell function and survival - a perspective.

A major problem in medical research is to translate in vitro observations into the living organism. In this perspective, we discuss ongoing efforts to non-invasively image pancreatic islets/ß-cells by techniques, such as magnetic resonance imaging and positron emission tomography, and present an experimental platform, which allows in vivo imaging of pancreatic ß-cell mass and function longitudinally and at the single-cell level. Following transplantation of pancreatic islets into the anterior chamber of the eye of mice and rats, these islets are studied by functional microscopic imaging. This imaging platform can be utilized to address fundamental aspects of pancreatic islet cell biology in vivo in health and disease. These include the dynamics of pancreatic islet vascularization, islet cell innervation, signal-transduction, change in functional ß-cell mass and immune responses. Moreover, we discuss the feasibility of studying human islet cell physiology and pathology in vivo as well as the potential of using the anterior chamber of the eye as a site for therapeutic transplantation in type 1 diabetes mellitus.

Anti-inflammatory properties of exenatide in human pancreatic islets.

Exenatide is an analog of the incretin hormone glucagon-like peptide (GLP-1) that is used for the treatment of T2D for their metabolic effects. In addition to its insulinotropic effects, exenatide increases functional islet mass and improves their survival. Improved outcomes have been reported in recent clinical islet transplantation trials for the treatment of type 1 diabetes. The purpose of this study was to investigate whether exenatide has anti-inflammatory properties in human islets. Exenatide treatment improved islet function, significantly reduced content of inflammation-related molecules (tissue factor, IFN-γ, IL-17, IL-1ß, and IL-2) and caspase 3 activation, whereas increased phosphorylation of ERK1/2, STAT3, and Akt in vitro. Immunostaining showed expression of GLP-1R in ß-cells but not in α-cells. IL-1ß colocalized with GLP-1R in ß-cells. Induction of serine proteinase inhibitor 9 (PI-9) was detected after exposure of human islets to exenatide in vitro and after transplantation into immunodeficient mice. GLP-1 induced PI-9 expression in vitro but to a lower extent than exenatide. This effect was partially blocked by the antagonist exendin-9 in vitro. As assessed by immunostaining PI-9 is mostly expressed in ß-cells but not in α-cells. In conclusion, we describe anti-inflammatory and cytoprotective properties of exenatide in human islets. Exenatide-mediated PI-9 expression, the only known granzyme B inhibitor, unveils potential immunoregulatory properties.

Molecular ecology meets remote sensing: environmental drivers to population structure of humpback dolphins in the Western Indian Ocean.

Genetic analyses of population structure can be placed in explicit environmental contexts if appropriate environmental data are available. Here, we use high-coverage and high-resolution oceanographic and genetic sequence data to assess population structure patterns and their potential environmental influences for humpback dolphins in the Western Indian Ocean. We analyzed mitochondrial DNA data from 94 dolphins from the coasts of South Africa, Mozambique, Tanzania and Oman, employing frequency-based and maximum-likelihood algorithms to assess population structure and migration patterns. The genetic data were combined with 13 years of remote sensing oceanographic data of variables known to influence cetacean dispersal and population structure. Our analyses show strong and highly significant genetic structure between all putative populations, except for those in South Africa and Mozambique. Interestingly, the oceanographic data display marked environmental heterogeneity between all sampling areas and a degree of overlap between South Africa and Mozambique. Our combined analyses therefore suggest the occurrence of genetically isolated populations of humpback dolphins in areas that are environmentally distinct. This study highlights the utility of molecular tools in combination with high-resolution and high-coverage environmental data to address questions not only pertaining to genetic population structure, but also to relevant ecological processes in marine species.

The anterior chamber of the eye as a clinical transplantation site for the treatment of diabetes: a study in a baboon model of diabetes.

AIMS/HYPOTHESIS: The aim of this study was to provide evidence that the anterior chamber of the eye serves as a novel clinical islet implantation site. METHODS: In a preclinical model, allogeneic pancreatic islets were transplanted into the anterior chamber of the eye of a baboon model for diabetes, and metabolic and ophthalmological outcomes were assessed. RESULTS: Islets readily engrafted on the iris and there was a decrease in exogenous insulin requirements due to insulin secretion from the intraocular grafts. No major adverse effects on eye structure and function could be observed during the transplantation period. CONCLUSIONS/INTERPRETATION: Our study demonstrates the long-term survival and function of allogeneic islets after transplantation into the anterior chamber of the eye. The safety and simplicity of this procedure provides support for further studies aimed at translating this technology into the clinic.

Parachuting from fixed objects: descriptive study of 106 fatal events in BASE jumping 1981-2006.

OBJECTIVE: To analyse the characteristics of fatal incidents in fixed object sport parachuting (building, antenna, span, earth (BASE) jumping) and create a basis for prevention. DESIGN: Descriptive epidemiological study. PARTICIPANTS: Data on reported fatal injury events (n = 106) worldwide in 1981-2006 retrieved from the BASE fatality list. ASSESSMENT OF RISK FACTORS: Human, equipment and environmental factors. MAIN OUTCOME MEASUREMENTS: Identification of typical fatal incident and injury mechanisms for each of the four fixed object types of BASE jumping (building, antenna, span, earth). RESULTS: Human factors included parachutist free fall instability (loss of body control before parachute deployment), free fall acrobatics and deployment failure by the parachutist. Equipment factors included pilot chute malfunction and parachute malfunction. In cliff jumping (BASE object type E), parachute opening towards the object jumped was the most frequent equipment factor. Environmental factors included poor visibility, strong or turbulent winds, cold and water. The overall annual fatality risk for all object types during the year 2002 was estimated at about one fatality per 60 participants. CONCLUSIONS: Participants in BASE jumping should target risk factors with training and technical interventions. The mechanisms described in this study should be used by rescue units to improve the management of incidents.

The imidazoline RX871024 induces death of proliferating insulin-secreting cells by activation of c-jun N-terminal kinase.

An insufficient number of insulin-producing beta-cells is a major cause of defective control of blood glucose in both type 1 and type 2 diabetes. The aim of this study was to clarify whether the insulinotropic imidazolines can affect the survival of highly proliferating insulin-secreting cells, here exemplified by the MIN6 cell line. Our data demonstrate that RX871024, but not efaroxan, triggered MIN6 cell death and potentiated death induced by a combination of the pro-inflammatory cytokines interleukin-1beta, interferon- gamma and tumor necrosis factor-alpha. These effects did not involve changes in nitric oxide production but correlated with stimulation of c-jun N-terminal kinase (JNK) activity and activation of caspases-1, -3, -8 and -9. Our results suggest that the imidazoline RX871024 causes death of highly proliferating insulin-secreting cells, putatively via augmentation of JNK activity, a finding that may impact on the possibility of using compounds of similar activity in the treatment of diabetes.

Arachidonic acid signaling is involved in the mechanism of imidazoline-induced KATP channel-independent stimulation of insulin secretion.

The mechanism by which the novel, pure glucose-dependent insulinotropic, imidazoline derivative BL11282 promotes insulin secretion in pancreatic islets has been investigated. The roles of KATP channels, alpha2-adrenoreceptors, the I1-receptor-phosphatidylcholine-specific phospholipase (PC-PLC) pathway and arachidonic acid signaling in BL11282 potentiation of insulin secretion in pancreatic islets were studied. Using SUR1(-/-) deficient mice, the previous notion that the insulinotropic activity of BL11282 is not related to its interaction with KATP channels was confirmed. Insulinotropic activity of BL11282 was not related to its effect on alpha2-adrenoreceptors, I1-imidazoline receptors or PC-PLC. BL11282 significantly increased [3H]arachidonic acid production. This effect was abolished in the presence of the iPLA2 inhibitor, bromoenol lactone. The data suggest that potentiation of glucose-induced insulin release by BL11282, which is independent of concomitant changes in cytoplasmic free Ca2+ concentration, involves release of arachidonic acid by iPLA2 and its metabolism to epoxyeicosatrienoic acids through the cytochrome P-450 pathway.

Type 1 diabetic serum interferes with pancreatic beta-cell Ca2+-handling.

The aim of this study was to clarify the frequency of patients with type 1 diabetes that have serum that increases pancreatic beta-cell cytoplasmic free Ca(2+) concentration, [Ca(2+)](i), and if such an effect is also present in serum from first-degree relatives. We also studied a possible link between the serum effect and ethnic background as well as presence of autoantibodies. Sera obtained from three different countries were investigated as follows: 82 Swedish Caucasians with newly diagnosed type 1 diabetes, 56 Americans with different duration of type 1 diabetes, 117 American first-degree relatives of type 1 diabetic patients with a mixed ethnic background and 31 Caucasian Finnish children with newly diagnosed type 1 diabetes. Changes in [Ca(2+)](i) , upon depolarization, were measured in beta-cells incubated overnight with sera from type 1 diabetic patients, first-degree relatives or healthy controls. Our data show that there is a group constituting approximately 30% of type 1 diabetic patients of different gender, age, ethnic background and duration of the disease, as well as first-degree relatives of type 1 diabetic patients, that have sera that interfere with pancreatic beta-cell Ca(2+)-handling. This effect on beta-cell [Ca(2+)](i) could not be correlated to the presence of autoantibodies. In a defined subgroup of patients with type 1 diabetes and first-degree relatives a defect Ca(2+)-handling may aggravate development of beta-cell destruction.

Single residue (K332A) substitution in Kir6.2 abolishes the stimulatory effect of long-chain acyl-CoA esters: indications for a long-chain acyl-CoA ester binding motif.

AIMS/HYPOTHESIS: The pancreatic beta cell ATP-sensitive potassium (K(ATP)) channel, composed of the pore-forming alpha subunit Kir6.2, a member of the inward rectifier K+channel family, and the regulatory beta subunit sulfonylurea receptor 1 (SUR1), a member of the ATP-binding cassette superfamily, couples the metabolic state of the cell to electrical activity. Several endogenous compounds are known to modulate K(ATP) channel activity, including ATP, ADP, phosphatidylinositol diphosphates and long-chain acyl coenzyme A (LC-CoA) esters. LC-CoA esters have been shown to interact with Kir6.2, but the mechanism and binding site(s) have yet to be identified. MATERIALS AND METHODS: Using multiple sequence alignment of known acyl-CoA ester interacting proteins, we were able to identify four conserved amino acid residues that could potentially serve as an acyl-CoA ester-binding motif. The motif was also recognised in the C-terminal region of Kir6.2 (R311-332) but not in SUR1. RESULTS: Oocytes expressing Kir6.2DeltaC26 K332A repeatedly generated K(+)currents in inside-out membrane patches that were sensitive to ATP, but were only weakly activated by 1 mumol/l palmitoyl-CoA ester. Compared with the control channel (Kir6.2DeltaC26), Kir6.2DeltaC26 K332A displayed unaltered ATP sensitivity but significantly decreased sensitivity to palmitoyl-CoA esters. Coexpression of Kir6.2DeltaC26 K332A and SUR1 revealed slightly increased activation by palmitoyl-CoA ester but significantly decreased activation by the acyl-CoA esters compared with the wild-type K(ATP) channel and Kir6.2DeltaC26+SUR1. Computational modelling, using the crystal structure of KirBac1.1, suggested that K332 is located on the intracellular domain of Kir6.2 and is accessible to intracellular modulators such as LC-CoA esters. CONCLUSIONS/INTERPRETATION: These results verify that LC-CoA esters interact at the pore-forming subunit Kir6.2, and on the basis of these data we propose an acyl-CoA ester binding motif located in the C-terminal region.

Differential protein expression in pancreatic islets after treatment with an imidazoline compound.

The effects of an imidazoline compound (BL11282) on protein expression in rat pancreatic islets were investigated with a proteomic approach. The compound increases insulin release selectively at high glucose concentrations and is therefore of interest in type 2 diabetes. Whole cell extracts from isolated drug-treated and native pancreatic rat islets were compared after separation by 2-D gel electrophoresis. Differentially expressed proteins were identified by mass spectrometry; 15 proteins were selectively up-regulated and 7 selectively down-regulated in drug-treated islets. Of special interest among the differentially expressed proteins are those involved in protein folding (Hsp60, protein disulfide isomerase, calreticulin), Ca(2+) binding (calgizzarin, calcyclin and annexin I) and metabolism or signalling (pyruvate kinase, alpha enolase and protein kinase C inhibitor 1).