[Stem-cell therapy, ß-cell- and islet cell-neogenesis: possible treatments of type 1 diabetes in the future?]. / Ossejtterápia, ß-sejt- és Langerhans-sziget-neogenezis: a jövo lehetséges terápiái 1-es típusú diabetesben?

In type 1 diabetic patients perfect normoglycaemia can only be achieved by successful transplantation of the pancreas or Langerhans' islets. Surgical transplantation of the whole pancreas is an invasive operation exerting great burden on the patients. Transplantation of the islets of Langerhans does not burden the patients but the survival of the islet grafts is limited. Both interventions are hampered by the lack of donor organs. However, much of these difficulties could be overcome by the use of "artificial ß-cells" which ought to have an ultrastructure identical with that of natural ß-cells and produce and secrete insulin in a glucose dependent manner. At present three such methods are at our disposal: transformation of the ductal cells of the exocrine pancreas into ß-cells, development of ß-cells from stem-cells, and neogenesis of Langerhans' islets induced by viral delivery of transcription factors. The author summarises the experience and experimental results obtained with the use of the three methods.

Dual-modal magnetic resonance/fluorescent zinc probes for pancreatic ß-cell mass imaging.

Despite the contribution of changes in pancreatic ß-cell mass to the development of all forms of diabetes mellitus, few robust approaches currently exist to monitor these changes prospectively in vivo. Although magnetic-resonance imaging (MRI) provides a potentially useful technique, targeting MRI-active probes to the ß cell has proved challenging. Zinc ions are highly concentrated in the secretory granule, but they are relatively less abundant in the exocrine pancreas and in other tissues. We have therefore developed functional dual-modal probes based on transition-metal chelates capable of binding zinc. The first of these, Gd⋅1, binds Zn(II) directly by means of an amidoquinoline moiety (AQA), thus causing a large ratiometric Stokes shift in the fluorescence from λem =410 to 500 nm with an increase in relaxivity from r1 =4.2 up to 4.9 mM(-1) s(-1) . The probe is efficiently accumulated into secretory granules in ß-cell-derived lines and isolated islets, but more poorly by non-endocrine cells, and leads to a reduction in T1 in human islets. In vivo murine studies of Gd⋅1 have shown accumulation of the probe in the pancreas with increased signal intensity over 140 minutes.

Inside the pancreas: progress and challenges of human beta cell mass quantification.

The accurate quantification of beta cell mass in humans is one of the key challenges in understanding the role of beta cell loss and dysfunction in the pathogenesis of diabetes mellitus. Autopsy studies indicate that beta cell loss is not only a hallmark of autoimmune diabetes but also plays a pivotal role in type 2 diabetes, owing to the toxic effects of lipids, glucose and cytokines. Thus, there is an urgent need for non-invasive clinical techniques for beta cell mass quantification, which should be optimally integrated into standard diagnostic equipment in hospitals. In this issue of Diabetologia (Brom et al DOI 10.1007/s00125-014-3166-3) it is reported that single photon emission computed tomography (SPECT) data with (111)indium-labelled glucagon-like peptide-1 (GLP-1) receptor agonist exendin-3 correlate with the morphometric analysis of beta cell mass in a rat model of alloxan-induced diabetes. With this validation, the authors were able to demonstrate a significant loss of beta cell mass in C-peptide-negative type 1 diabetic patients. Thus, (111)indium-labelled exendin-3 could serve as a model tracer for future studies of larger cohorts of diabetic patients to monitor the dynamics of beta cell loss and regeneration. Despite the recent progress from SPECT imaging data there remain open questions that await clarification in the near future such as variations in GLP-1 receptor density and physiological variation of beta cell mass in relation to beta cell function. The use of GLP-1-based tracer analysis may open new clinical avenues for non-invasive quantification of beta cell mass in patients with newly diagnosed type 1 diabetes and prediabetic individuals with high titres of autoantibodies.

Non-invasive quantification of the beta cell mass by SPECT with ¹¹¹In-labelled exendin.

AIMS/HYPOTHESIS: A reliable method for in vivo quantification of pancreatic beta cell mass (BCM) could lead to further insight into the pathophysiology of diabetes. The glucagon-like peptide 1 receptor, abundantly expressed on beta cells, may be a suitable target for imaging. We investigated the potential of radiotracer imaging with the GLP-1 analogue exendin labelled with indium-111 for determination of BCM in vivo in a rodent model of beta cell loss and in patients with type 1 diabetes and healthy individuals. METHODS: The targeting of (111)In-labelled exendin was examined in a rat model of alloxan-induced beta cell loss. Rats were injected with 15 MBq (111)In-labelled exendin and single photon emission computed tomography (SPECT) acquisition was performed 1 h post injection, followed by dissection, biodistribution and ex vivo autoradiography studies of pancreatic sections. BCM was determined by morphometric analysis after staining with an anti-insulin antibody. For clinical evaluation SPECT was acquired 4, 24 and 48 h after injection of 150 MBq (111)In-labelled exendin in five patients with type 1 diabetes and five healthy individuals. The tracer uptake was determined by quantitative analysis of the SPECT images. RESULTS: In rats, (111)In-labelled exendin specifically targets the beta cells and pancreatic uptake is highly correlated with BCM. In humans, the pancreas was visible in SPECT images and the pancreatic uptake showed high interindividual variation with a substantially lower uptake in patients with type 1 diabetes. CONCLUSIONS/INTERPRETATION: These studies indicate that (111)In-labelled exendin may be suitable for non-invasive quantification of BCM. TRIAL REGISTRATION: ClinicalTrials.gov NCT01825148, EudraCT: 2012-000619-10.

Occurrence of giant focal forms of congenital hyperinsulinism with incorrect visualization by (18) F DOPA-PET/CT scanning.

CONTEXT: Congenital hyperinsulinism (CHI) is a rare disease characterized by severe hypoglycaemic episodes due to pathologically increased insulin secretion from the pancreatic beta cells. When untreated, CHI might result in irreversible brain damage and death. Currently, two major subtypes of CHI are known: a focal form, associated with local distribution of affected beta cells and a nonfocal form, affecting every single beta cell. The identification of focal forms is important, as the patients can be cured by limited surgery. (18) F DOPA-PET/CT is an established non-invasive approach to differentiate focal from nonfocal CHI. OBJECTIVE: The purpose of this study was to identify possible limitations of (18) F DOPA-PET/CT scan in patients with focal forms nonfocal CHI. DESIGN: A retrospective chart review of 32 patients (from 2008 through 2013) who underwent (18) F DOPA-PET/CT and partial pancreatectomy for focal CHI at the reference centres in Berlin, Germany and London, UK. RESULTS: In most cases (n = 29, 90·7%), (18) F DOPA-PET/CT was sufficient to localize the complete focal lesion. However, in some patients (n = 3, 9·3%), (18) F DOPA-PET/CT wrongly visualized only a small portion of the focal lesion. In this group of patients, a so-called 'giant focus' was detected in histopathological analysis during the surgery. CONCLUSIONS: Our data show that in most patients with focal CHI (18) F DOPA-PET/CT correctly predicts the size and anatomical localisation of the lesion. However, in those patients with a 'giant focal' lesion (18) F DOPA-PET/CT is unreliable for correct identification of 'giant focus' cases.

Positron emission tomography imaging of the glucagon-like peptide-1 receptor in healthy and streptozotocin-induced diabetic pigs.

PURPOSE: The glucagon-like peptide-1 receptor (GLP-1R) has been proposed as a target for molecular imaging of beta cells. The feasibility of non-invasive imaging and quantification of GLP-1R in pancreas using the positron emission tomography (PET) tracer [(68)Ga]Ga-DO3A-VS-Cys(40)-Exendin-4 in non-diabetic and streptozotocin (STZ)-induced diabetic pigs treated with insulin was investigated. METHODS: Non-diabetic (n = 4) and STZ-induced diabetic pigs (n = 3) from the same litter were examined. Development of diabetes was confirmed by blood glucose values, clinical examinations and insulin staining of pancreatic sections post mortem. Tissue perfusion in the pancreas and kidneys was evaluated by [(15)O]water PET/computed tomography (CT) scans. The in vivo receptor specificity of [(68)Ga]Ga-DO3A-VS-Cys(40)-Exendin-4 was assessed by administration of either tracer alone or by competition with 3-6.5 µg/kg of Exendin-4. Volume of distribution and occupancy in the pancreas were quantified with a single tissue compartment model. RESULTS: [(15)O]water PET/CT examinations showed reduced perfusion in the pancreas and kidneys in diabetic pigs. [(68)Ga]Ga-DO3A-VS-Cys(40)-Exendin-4 uptake in the pancreas of both non-diabetic and diabetic pigs was almost completely abolished by co-injection of unlabeled Exendin-4 peptide. [(68)Ga]Ga-DO3A-VS-Cys(40)-Exendin-4 uptake did not differ between non-diabetic and diabetic pigs. In all animals, administration of the tracer resulted in an immediate increase in the heart rate (HR). CONCLUSION: Pancreatic uptake of [(68)Ga]Ga-DO3A-VS-Cys(40)-Exendin-4 was not reduced by destruction of beta cells in STZ-induced diabetic pigs.

Derivatization of (±) dihydrotetrabenazine for copper-64 labeling towards long-lived radiotracers for PET imaging of the vesicular monoamine transporter 2.

Dihydrotetrabenazine (DTBZ) derivatized from (+) Tetrabenazine (TBZ) has been used for imaging the expression of VMAT2 when labeled with (11)C (t1/2=20.3 min) or (18)F (t1/2=110 min) in neurodegenerative diseases or pancreatic beta-cell. Because (11)C or (18)F radiolabels are only available in the proximity of a biomedical cyclotron facility, here we report our work of derivatizing (+) and (-) DTBZ using a (64)Cu-specific bifunctional chelator scaffold ((64)Cu: t1/2=12.7 h) for the preparation of long-lived VMAT2 targeted radiotracers, (64)Cu-CB-TE2A-(+)-DTBZ and (64)Cu-CB-TE2A-(-)-DTBZ. The specific VMAT2 binding affinity of (64)Cu-CB-TE2A-(+)-DTBZ measured using rat brain homogenate or porcine islets was not compromised by our chemical modifications while that of its (-) counterpart remained low as in (11)C or (18)F labeled (±) DTBZ.

Integrating genetic and imaging investigations into the clinical management of congenital hyperinsulinism.

Congenital Hyperinsulinism (CHI) is a rare but important cause of hypoglycaemia in infancy. CHI is a heterogeneous disease, but has a strong genetic basis; a number of genetic causes have been identified with CHI in about a third of individuals, chiefly in the genes that code for the ATP sensitive K(+) channels (KATP ) in the pancreatic ß-cells. Rapid KATP channel gene testing is a critical early step in the diagnostic algorithm of CHI, with paternal heterozygosity correlating with the occurrence of focal lesions. Imaging investigations to diagnose and localize solitary pancreatic foci have evolved over the last decade with (18)F-DOPA PET-CT scanning as the current diagnostic tool of choice. Although clinical management of CHI has improved significantly with the application of genetic screening and imaging investigations, much remains to be uncovered. This includes a better understanding of the molecular mechanisms for dysregulated insulin release in those patients without known genetic mutations, and the development of biomarkers that could characterize CHI, including long-term prognosis and targeted treatment planning, i.e. 'personalised medicine'. From the perspective of pancreatic imaging, it would be important to achieve greater specificity of diagnosis not only for focal lesions but also for diffuse and atypical forms of the disease.

Obstacles on the way to the clinical visualisation of beta cells: looking for the Aeneas of molecular imaging to navigate between Scylla and Charybdis.

For more than a decade, researchers have been trying to develop non-invasive imaging techniques for the in vivo measurement of viable pancreatic beta cells. However, in spite of intense research efforts, only one tracer for positron emission tomography (PET) imaging is currently under clinical evaluation. To many diabetologists it may remain unclear why the imaging world struggles to develop an effective method for non-invasive beta cell imaging (BCI), which could be useful for both research and clinical purposes. Here, we provide a concise overview of the obstacles and challenges encountered on the way to such BCI, in both native and transplanted islets. We discuss the major difficulties posed by the anatomical and cell biological features of pancreatic islets, as well as the chemical and physical limits of the main imaging modalities, with special focus on PET, SPECT and MRI. We conclude by indicating new avenues for future research in the field, based on several remarkable recent results.

Intraoperative sonography: a technique for localizing focal forms of congenital hyperinsulinism in the pancreas.

Congenital hyperinsulinism (CHI), syn. nesidioblastosis, is the most frequent cause of persistent, recurrent hypoglycemia in infancy. One third of patients show a single circumscribed focus. Enucleation of the focus and the removal of all affected ß-cells with preservation of healthy tissue is the treatment of choice. The intrapancreatic choledochus as well as the ductus pancreaticus major must remain intact. The diagnostic gold standard is 18F-DOPA-PET/CT. Intraoperative sonography is carried out to correctly visualize the focus preoperatively localized by PET/CT in situ during the operation. The enucleation of the focus was carried out 3 - 20 days after PET/CT in 5 patients at an age of 3.5 - 14 months. Intraoperative ultrasound was carried out with high-capacity devices of different manufacturers under use of broadband probes (9 - 14 MHz). The localization by intraoperative ultrasound was accurate in all 5 patients with focal CHI, with regard to the intraoperative localization as previously described by PET/CT and histology. D. choledochus and D. pancreaticus major were separated intraoperatively by ultrasound. 3 of 5 patients were cured by complete enucleation of the focus. Nevertheless, the entire intraoperative identification of the segmented focus is still problematic. Characteristic sonographic features of a CHI focus are: hypoechogenicity, variable homogeneous and inhomogenous texture, blurred, irregular limitation without capsule, filiform, lobular processes, and insular dispersal into the surrounding tissue. Intraoperative high-resolution sonography helps the pediatric surgeon to determine size, configuration and topography of a CHI focus.

Reduced pancreatic volume and beta-cell area in patients with chronic pancreatitis.

BACKGROUND & AIMS: Chronic pancreatitis (CP) often leads to the development of diabetes. To understand better this pathogenic mechanism, we investigated whether islet cell area and pancreatic volume are reduced in CP patients, islet cell turnover increases in CP patients, and islet cells are less vulnerable to apoptosis than acinar cells. METHODS: Pancreatic tissues from 43 patients with CP and 27 controls were examined by immunohistochemistry and quantitative morphometry. Pancreas volume was determined using abdominal computed tomography data. RESULTS: The pancreatic volumes were 64.9 +/- 4.3 cm(3) in CP patients and 82.3 +/- 6.7 cm(3) in controls (P = .035). beta-cell areas were 0.69% +/- 0.08% in CP patients and 0.97% +/- 0.08% in controls (P = .017), whereas alpha-cell areas did not differ between the groups (P = .47). There were no differences in the frequencies of replication among groups of alpha-cells, beta-cells, duct cells, or acinar cells nor were there differences in numbers of apoptotic alpha-cells or beta-cells between CP patients and controls. However, CP patients had an approximately 10-fold increase in numbers of apoptotic acinar cells compared with controls (P < .0001). CONCLUSIONS: Pancreatic volume was reduced by 21%, and the area comprising beta-cells was reduced by 29% in patients with CP. The lack of increased beta-cells turnover in CP patients, despite an approximately 10-fold increase in the number of apoptotic acinar cells, suggests that the damage to the pancreas is highly specific for the exocrine compartment and affects the endocrine islets to a lesser extent.

GLP-1 receptor antagonist as a potential probe for pancreatic beta-cell imaging.

We examined exendin(9-39), an antagonist of glucagon-like peptide-1 (GLP-1) receptor (GLP-1R), as a potential probe for imaging of pancreatic beta-cells. To evaluate in vitro receptor specificity, binding assay was performed using dispersed mouse islet cells. Binding assay showed competitive inhibition of [(125)I]BH-exendin(9-39) binding by non-radioactive exendin(9-39). To assess in vivo selectivity, the biodistribution was evaluated by intravenous administration of [(125)I]BH-exendin(9-39) to mice. Radioactivity of harvested pancreas reached highest levels at 60 and 120min among organs examined except lung. Pre-administration of excess non-radioactive exendin(9-39) remarkably and specifically blocked the radioactivity of pancreas. After [(125)I]BH-exendin(9-39) injection into transgenic mice with pancreatic beta-cells expressing GFP, fluorescent and radioactive signals of sections of pancreas were evaluated with an image analyzer. Imaging analysis showed that the fluorescent GFP signals and the radioactive signals were correspondingly located. Thus, the GLP-1R antagonist exendin(9-39) may serve as a useful probe for pancreatic beta-cell imaging.

11C-dihydrotetrabenazine PET of the pancreas in subjects with long-standing type 1 diabetes and in healthy controls.

UNLABELLED: Type 2 vesicular monoamine transporter (VMAT2), found in the brain, is also expressed by beta-cells of the pancreas in association with insulin. Preclinical experiments suggested that (11)C-dihydrotetrabenazine PET-measured VMAT2 binding might serve as a biomarker of beta-cell mass. We evaluated the feasibility of (11)C-dihydrotetrabenazine PET quantification of pancreatic VMAT2 binding in healthy subjects and patients with long-standing type 1 diabetes. METHODS: (11)C-Dihydrotetrabenazine PET was performed on 6 patients and 9 controls. VMAT2 binding potential (BP(ND)) was estimated voxelwise by using the renal cortex as reference tissue. As an index of total pancreatic VMAT2, the functional binding capacity (the sum of voxel BP(ND) x voxel volume) was calculated. Pancreatic BP(ND), functional binding capacity, and stimulated insulin secretion measurements were compared between groups. RESULTS: The pancreatic mean BP(ND) was decreased in patients (1.86 +/- 0.05) to 86% of control values (2.14 +/- 0.08) (P = 0.01). In controls, but not in patients, BP(ND) correlated with stimulated insulin secretion (r(2) = 0.50, P = 0.03). The average functional binding capacity was decreased by at least 40% in patients (P = 0.001). The changes in functional binding capacity and BP(ND) were less than the near-complete loss of stimulated insulin secretion observed in patients (P = 0.001). CONCLUSION: These results suggest that (11)C-dihydrotetrabenazine PET allows quantification of VMAT2 binding in the human pancreas. However, BP(ND) and functional binding capacity appear to overestimate beta-cell mass given the near-complete depletion of beta-cell mass in long-standing type 1 diabetes, which may be due to higher nonspecific binding in the pancreas than in the renal cortex.

Dual radiotracer analysis of cholinergic neuronal changes in prediabetic mouse pancreas.

BACKGROUND: Pancreatic neuronal changes associated with beta cell loss in type 1 diabetes mellitus are complex, involving, in part, parasympathetic mechanisms to compensate for preclinical hyperglycemia. The parasympathetic neurotransmitter acetylcholine (ACh) mediates insulin release via M3 muscarinic receptors on islet beta cells. The vesicular ACh transporter (VAChT) receptor has been shown to be a useful marker of cholinergic activity in vivo. The positron emission tomography (PET) radiotracer (+)-4-[(18)F]fluorobenzyltrozamicol ([(18)F]FBT) binds to the VAChT receptor on presynaptic cholinergic neurons and can be quantified by PET. The compound 4-diphenylacetoxy-N-methylpiperidine (4-DAMP), available in a tritiated form, binds to M3 muscarinic receptors on beta cells and is a potential target for assessing pancreatic beta cell mass. In this study, we investigate the feasibility of dual radiotracer analysis in identifying neurofunctional changes that may signify type 1 diabetes mellitus in its early preclinical state. METHODS: Ex vivo determinations of pancreatic uptake were performed in prediabetic nonobese diabetic mice and controls after intravenous injection of [(18)F]FBT or 4-[(3)H]DAMP. Beta cell loss in prediabetic mice was confirmed using immunohistochemical methods. RESULTS: [(18)F]FBT uptake was significantly higher in prediabetic pancreata than controls: 3.22 +/- 0.81 and 2.51 +/- 1.04, respectively (P < 0.03). 4-[(3)H]DAMP uptake was significantly lower in prediabetic pancreata than controls: 0.612 +/- 0.161 and 0.968 +/- 0.364, respectively (P = 0.01). CONCLUSIONS: These data suggest that a combination of radiotracer imaging agents that bind to neuronal elements intimately involved in insulin production may be an effective method of evaluating changes associated with early beta cell loss using PET.

A rodent model of metabolic surgery for study of type 2 diabetes and positron emission tomography scanning of beta cell mass.

BACKGROUND: Type 2 diabetes mellitus is a worldwide healthcare problem with major socioeconomic implications. Metabolic surgical procedures have been shown to improve diabetes, but the mechanism of action is poorly understood. The Goto-Kakizaki (GK) rodent is a type 2 diabetic animal model that is ideally situated for studying the effect of surgery on diabetes; however, the operative mortality is high. The aim of this study was to describe the operative technique, improvements in perioperative management, and the technique of micro-positron emission tomography (PET) scanning of the beta-cell mass in GK rodents. METHODS: A total of 53 GK rats were divided into 1 of 3 operative groups: sham, sleeve gastrectomy, and duodenojejunal bypass. A subset of animals underwent micro-PET scanning with [11C]-dihydrotetrabenazine to determine the vesicular monoamine transporter 2 binding index, an indicator of beta-cell mass. RESULTS: The 30-day mortality in the sham and sleeve gastrectomy rodents was 0; however, 2 sleeve gastrectomy rodents developed enterocutaneous fistula and 1 developed an abscess. In the duodenojejunal bypass group, the initial mortality rate was close to 90%; however, refinements in the surgical technique and perioperative management (fluids, antibiotics, pain control) lowered the mortality rate to 60%. The surgical technique is discussed in detail. [11C]-Dihydrotetrabenazine uptake in the pancreas was demonstrated on micro-PET scanning in the sham and duodenojejunal bypass rodents. CONCLUSION: Intensive medical management in the perioperative period and attention to the operative technique lowered the mortality. [11C]-Dihydrotetrabenazine micro-PET scanning is a feasible method for assessing the beta-cell mass in GK rodents and could prove to be an important modality for evaluating beta-cell performance in type 2 diabetes.

Advances in molecular imaging of pancreatic beta cells.

The development of non-invasive imaging methods for early diagnosis of beta cell associated metabolic diseases, including type 1 and type 2 diabetes (T1D and T2D), has recently drawn interest from the molecular imaging community and clinical investigators. Due to the challenges imposed by the location of the pancreas, the sparsely dispersed beta cell population within the pancreas, and the poor understanding of the pathogenesis of the diseases, clinical diagnosis of beta cell abnormalities is still limited. Current diagnostic methods are invasive, often inaccurate, and usually performed post-onset of the disease. Advances in imaging techniques for probing beta cell mass and function are needed to address this critical health care problem. A variety of imaging techniques have been tested for the assessment of pancreatic beta cell islets. Here we discuss current advances in magnetic resonance imaging (MRI), bioluminescence imaging (BLI), and nuclear imaging for the study of beta cell diseases. Spurred by early successes in nuclear imaging techniques for beta cells, especially positron emission tomography (PET), the need for beta cell specific ligands has expanded. Progress for obtaining such ligands is presented. We report our preliminary efforts of developing such a peptidic ligand for PET imaging of pancreatic beta cells.

Imaging of gene expression in live pancreatic islet cell lines using dual-isotope SPECT.

UNLABELLED: We are combining nuclear medicine with molecular biology to establish a sensitive, quantitative, and tomographic method with which to detect gene expression in pancreatic islet cells in vivo. Dual-isotope SPECT can be used to image multiple molecular events simultaneously, and coregistration of SPECT and CT images enables visualization of reporter gene expression in the correct anatomic context. We have engineered pancreatic islet cell lines for imaging with SPECT/CT after transplantation under the kidney capsule. METHODS: INS-1 832/13 and alphaTC1-6 cells were stably transfected with a herpes simplex virus type 1-thymidine kinase-green fluorescent protein (HSV1-thymidine kinase-GFP) fusion construct (tkgfp). After clonal selection, radiolabel uptake was determined by incubation with 5-(131)I-iodo-1-(2-deoxy-2-fluoro-beta-d-arabinofuranosyl)uracil ((131)I-FIAU) (alphaTC1-6 cells) or (123)I-FIAU (INS-1 832/13 cells). For the first set of in vivo experiments, SPECT was conducted after alphaTC1-6/tkgfp cells had been labeled with either (131)I-FIAU or (111)In-tropolone and transplanted under the left kidney capsule of CD1 mice. Reconstructed SPECT images were coregistered to CT. In a second study using simultaneous acquisition dual-isotope SPECT, INS-1 832/13 clone 9 cells were labeled with (111)In-tropolone before transplantation. Mice were then systemically administered (123)I-FIAU and data for both (131)I and (111)In were acquired simultaneously. RESULTS: alphaTC1-6/tkgfp cells showed a 15-fold greater uptake of (131)I-FIAU, and INS-1/tkgfp cells showed a 12-fold greater uptake of (123)I-FIAU, compared with that of wild-type cells. After transplantation under the kidney capsule, both reporter gene expression and location of cells could be visualized in vivo with dual-isotope SPECT. Immunohistochemistry confirmed the presence of glucagon- and insulin-positive cells at the site of transplantation. CONCLUSION: Dual-isotope SPECT is a promising method to detect gene expression in and location of transplanted pancreatic cells in vivo.

Efforts to develop methods for in vivo evaluation of the native beta-cell mass.

Visualization and quantification of the native beta-cell mass in vivo in humans appear to be important in the study of the natural course of diabetes, and in ongoing trials aimed at preserving beta-cell mass in patients with diabetes. This cannot be done by biopsy sampling, and therefore there is a great need for development of a non-invasive method. This article discusses the principle theoretical requirements for reaching this goal. In addition, it provides an overview of tracer probes, which have been examined as potential beta-cell mass imaging agents in the past. Finally, some future perspectives are discussed.

VMAT2 quantitation by PET as a biomarker for beta-cell mass in health and disease.

The common pathology underlying both type 1 and type 2 diabetes (T1DM and T2DM) is insufficient beta-cell mass (BCM) to meet metabolic demands. An important impediment to the more rapid evaluation of interventions for both T1DM and T2DM lack of biomarkers of pancreatic BCM. A reliable means of monitoring the mass and/or function of beta-cells would enable evaluation of the progression of diabetes as well as the monitoring of pharmacologic and other interventions. Recently, we identified a biomarker of BCM that is quantifiable by positron emission tomography (PET). PET is an imaging technique which allows for non-invasive measurements of radioligand uptake and clearance, is sensitive in the pico- to nanomolar range and of which the results can be deconvoluted into measurements of receptor concentration. For BCM estimates, we have identified VMAT2 (vesicular monoamine transporter type 2) as a biomarker and [(11)C] DTBZ (dihydrotetrabenazine) as the transporter's ligand. VMAT2 is highly expressed in beta-cells of the human pancreas relative to other cells of the endocrine and exocrine pancreas. Thus measurements of [(11)C] DTBZ in the pancreas provide an indirect measurement of BCM. Here we summarize our ongoing efforts to validate the clinical utility of this non-invasive approach to real-time BCM measurements.