Non-invasive detection of transplanted pancreatic islets

Magnetic resonance imaging of pancreatic islets using tissue-adhesive particles containing iron oxide nanoparticles

Post-transplantation tracking of pancreatic islets is a prerequisite for advancing cell therapy to treat type 1 diabetes. Magnetic resonance imaging (MRI) has emerged as a safe and non-invasive technique for visualizing cells in clinical applications. In this study, we proposed a novel MRI contrast agent formulation by encapsulating iron oxide nanoparticles (IONPs) in poly(lactic-co-glycolic acid) (PLGA) particles functionalized with a tissue adhesive polydopamine (PD) layer (IONP-PLGA-PD MS). Intriguingly, our particles facilitated efficient and robust labeling through a one-step process, allowing for the incorporation of a substantial amount of IONPs without detrimental impacts on the viability and functionality of pancreatic islets. The MRI signals emanating from islets labeled using our particles were found to be stable over 30 days in vitro and 60 days when transplanted under kidney capsules of diabetic mice. These results suggest that our approach provides a potential platform for monitoring the fate of pancreatic islets after transplantation.

In vivo imaging of insulin-secreting human pancreatic ductal cells using MRI reporter gene technique: A feasibility study

PURPOSE

The purpose of this study was to investigate the feasibility of in vivo imaging of human pancreatic ductal cells by OATP1B3 reporter gene under MRI.

METHODS

A human cell line (PANC-1) derived from the pancreatic ductal epithelium was used in this study. After transduction of OATP1B3, the cellular physiological functions and the ability of intracellular uptake of the MRI contrast medium (Gd-EOB-DTPA) were examined. Induced differentiation of the PANC-1 cells into hormone-secreting cells were performed to simulate pancreatic β-like cells. The hormone-secreting cells were implanted into rats and in vivo MRI was evaluated.

RESULTS

The mRNA and proteins of OATP1B3 were highly expressed. No significant change of cellular physiological functions was found after the expression. After induced differentiation, the hormone secretion capacities of the OATP1B3-expressing PANC-1 cells were confirmed. Intra-cellular uptake of Gd-EOB-DTPA was determined in vitro by inductively coupled plasma mass spectrometry and MRI. In vivo MRI of the OATP1B3-expressing xenograft revealed an increased signal intensity after contrast enhancement.

CONCLUSION

OATP1B3 can be used as a safe and feasible in vivo MRI gene reporter for human pancreatic ductal cells.

Challenges for labeling and longitudinal tracking of adoptively transferred autoreactive T lymphocytes in an experimental type-1 diabetes model

OBJECTIVE

Tracking the autoreactive T-cell migration in the pancreatic region after labeling with fluorinated nanoparticles (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-[3-(2-pyridyldithio)propionate]-perfluoro-15-crown-5-ether nanoparticles, PDP-PFCE NPs) in a diabetic murine model using ¹⁹F MRI.

MATERIALS AND METHODS

Synthesis of novel PDP-PFCE fluorine tracer was performed for in vitro labeling of T cells. Labeling conditions were optimized using different PDP-PFCE NPs concentrations. For in vivo ¹⁹F MRI, mice were longitudinally followed after adoptive transfer of activated, autoreactive, labeled T cells in NOD.SCID mice.

RESULTS

Established MR protocols were used for challenging T cell labeling to track inflammation in a model of diabetes after successful labeling of CD4+ and CD8+ T cells with PDP-PFCE NPs. However, T cells were difficult to be detected in vivo after their engraftment in animals.

DISCUSSION

We showed successful in vitro labeling of T cells using novel fluorinated liposomal nanoparticles. However, insufficient and slow accumulation of labeled T cells and subsequent T cell proliferation in the pancreatic region remains as limitations of in vivo cell imaging by ¹⁹F MRI.

Iatrogenic-related transplant injuries: the role of the interventional radiologist

As advances in surgical techniques and postoperative care continue to improve outcomes, the use of solid organ transplants as a treatment for end-stage organ disease is increasing. With the growing population of transplant patients, there is an increasing need for radiologic diagnosis and minimally invasive procedures for the management of posttransplant complications. Typical complications may be vascular or nonvascular. Vascular complications include arterial stenosis, graft thrombosis, and development of fistulae. Common nonvascular complications consist of leaks, abscess formation, and stricture development. The use of interventional radiology in the management of these problems has led to better graft survival and lower patient morbidity and mortality. An understanding of surgical techniques, postoperative anatomy, radiologic findings, and management options for complications is critical for proficient management of complex transplant cases. This article reviews these factors for kidney, liver, pancreas, islet cell, lung, and small bowel transplants.

Imaging of the β-cells of the islets of Langerhans

The major aim of this paper is to review the present status of the techniques for the non-invasive imaging and quantification of insulin-producing pancreatic islet β-cells. Emphasis is placed on both the expansion of prior work already considered in a prior review and novel achievements. Thus, the use of d-mannoheptulose analogs, hypoglycemic sulfonylureas and glinides, neural imaging agents, neuro-hormonal receptor ligands and nanoparticles is first dealt with. Thereafter, consideration is given on optical imaging technologies, the identification of new β-cells specific binding and target proteins, the functional imaging of islets transplanted into the eye anterior chamber and in vivo manganese-enhanced magnetic resonance imaging.

In vivo cell tracking via ¹⁸F-fluorodeoxyglucose labeling: a review of the preclinical and clinical applications in cell-based diagnosis and therapy

The rising interest in using functional cells for diagnosis and treatment has created an urgent need for in vivo cell-tracking techniques. Certain advanced techniques, such as those involving reporter genes or nanoparticles, are still awaiting confirmation of their safety and feasibility in human patients. Tracking cells by labeling them with (18)F-fluorodeoxyglucose, a tracer clinically used in positron emission tomography (PET), may be one way to rapidly translate some of these principles from bench to bedside. The preliminary results are exciting, although further development, optimization, and validation are required. Here, several applications of the technique are surveyed: finding inflammatory foci, targeting cancer immunotherapies, tracking transplanted islet cells, and monitoring cardiac stem cells. Advantages, limitations, and prospects of the technique are discussed. These early experiences only highlight the existing need to improve cell-labeling techniques using PET tracers. This method may finally lead to the development of effective and convenient methods for clinical cell-tracking techniques involving PET/computed tomography.

Pancreatic magnetic resonance imaging after manganese injection distinguishes type 2 diabetic and normoglycemic patients

A non-invasive method to image the mass and/or function of human pancreatic islets is needed to monitor the progression of diabetes, and the effect of therapeutic interventions. As yet, no method is available for this purpose, which could be applied to in situ human islets. Animal and in vitro studies have documented that manganese infusion could improve the magnetic resonance imaging (MRI) of the endocrine pancreas. Here, we have tested whether a similar approach could discriminate diabetic and non-diabetic patients. In vitro, human isolated islets readily incorporated manganese. In vivo, 243 manganese-enhanced magnetic resonance imaging (MEMRI) examinations were reviewed, including 41 examinations which were run on 24 patients with type 2 diabetes and 202 examinations which were run on 119 normoglycemic patients. The results show that MEMRI discriminates type 2 diabetics from non-diabetic patients, based on the signal enhancement of pancreas.

A novel method for quantitative monitoring of transplanted islets of langerhans by positive contrast magnetic resonance imaging

The Automatic Quantitative Ultrashort Echo Time imaging (AQUTE) protocol for serial MRI allows quantitative in vivo monitoring of iron labeled pancreatic islets of Langerhans transplanted into the liver, quantifying graft implantation and persistence in a rodent model. Rats (n = 14), transplanted with iron oxide loaded cells (0-4000 islet equivalents, IEQ), were imaged using a 3D radial ultrashort echo time difference technique (dUTE) on a Siemens MAGNETOM 3T clinical scanner up to 5 months postsurgery. In vivo 3D dUTE images gave positive contrast from labeled cells, suppressing liver signal and small vessels, allowing automatic quantification. Position of labeled islet clusters was consistent over time and quantification of hyperintense pixels correlated with the number of injected IEQs (R² = 0.898, p < 0.0001), and showed persistence over time (5 months posttransplantation). Automatic quantification was superior to standard imaging and manual counting methods, due to the uniform suppressed background and high contrast, resulting in significant timesavings, reproducibility and ease of quantification. Three-dimensional coverage of the whole liver in the absence of cardiac/respiratory artifact provided further improvement over conventional imaging. This imaging protocol reliably quantifies transplanted islet mass and has high translational potential to clinical studies of transplanted pancreatic islets.

Visualization of mouse pancreas architecture using MR microscopy

Pancreatic diseases, which include diabetes, pancreatitis, and pancreatic cancer, are often difficult to detect and/or stage, contributing to a reduced quality of life and lifespan for patients. Thus, there is need for a technology that can visualize tissue changes in the pancreas, improve understanding of disease progression, and facilitate earlier detection in the human population. Because of low spatial resolution, current clinical magnetic resonance imaging (MRI) at low field strength has yet to fully visualize the exocrine, endocrine, vascular, and stromal components of the pancreas. We used high field strength magnetic resonance microscopy (μMRI) to image mouse pancreas ex vivo without contrast agents at high spatial resolution. We analyzed the resulting high-resolution images using volume rendering to resolve components in the pancreas, including acini, islets, blood vessels, and extracellular matrix. Locations and dimensions of pancreatic components as seen in three-dimensional μMRI were compared with histological images, and good correspondence was found. Future longitudinal studies could expand on the use of in vivo μMRI in mouse models of pancreatic diseases. Capturing three-dimensional structural changes through μMRI could help to identify early cellular and tissue changes associated with pancreatic disease, serving as a mode of improved detection in the clinic for endocrine and exocrine pathologies.

Role of imaging in clinical islet transplantation

Islet transplantation is an innovative and effective clinical strategy for patients with type 1 diabetes whose clinical condition is inadequately managed even with the most aggressive medical treatment regimens. In islet transplantation, purified islets extracted from the pancreas of deceased donors are infused into the portal vein of the recipient liver. Engrafted islets produce insulin and thus restore euglycemia in many patients. After islet transplantation performed with the original Edmonton protocol, 80% of patients were insulin independent at 1 year and approximately 20% were insulin independent at 5 years. With more recent technical advances, 50% of patients or more maintain insulin independence 5 years after islet transplantation. The success rate with single-donor islet infusions has markedly improved over time. Even in patients who lose insulin independence, islet transplantation is considered successful because it provides improved glycemic control and a higher quality of life. Imaging plays an important role in islet transplantation and is routinely used to evaluate potential recipients, guide the transplantation process, and monitor patients for posttransplantation complications. Because of the success of islet transplantation and its increasing availability worldwide, familiarity with the role of imaging is important.

MRI as a tool to monitor islet transplantation

The development of new methods for noninvasive imaging is an area of biotechnology that is of great relevance for the diagnosis and characterization of diabetes mellitus. Noninvasive imaging can be used to study the dynamics of beta-cell mass and function; beta-cell death; vascularity, innervation and autoimmune attack of pancreatic islets; and the efficacy of islet transplantation to remedy beta-cell loss in patients with diabetes mellitus. In this Review, we focus on the application of MRI for monitoring islet transplantation and on the potential causes of islet graft failure, which are still poorly understood. Questions that have been addressed by MRI studies encompass graft longevity, and the effects of immune rejection, glucose toxic effects, and the transplanted islets' purity on graft fate. We also highlight novel technologies for simultaneous imaging and delivery of experimental therapies that aim to extend the lifespan and functionality of islet grafts. On the basis of this evidence, MRI represents a valuable platform for a thorough investigation of beta-cell function in the context of islet transplantation. State-of-the-art multimodality approaches, such as PET-MRI, can extend our current capabilities and help answer the critical questions that currently inhibit the prevention and cure of diabetes mellitus.

Noninvasive imaging of pancreatic beta cells

Noninvasive imaging and quantification of pancreatic, insulin-producing beta cells has been considered a high-priority field of investigation for the past decade. In the first review on this issue, attention was already paid to various agents for labeling beta cells, including 6-(125)I-D-glucose, (65)Zn, (3)H-glibenclamide, (3)H-mitiglinide, an (125)I-labeled mouse monoclonal antibody against beta-cell surface ganglioside(s), D-(U-(14)C)-glucose and 2-deoxy-2-(18)F-D-glucose to label glycogen accumulated in beta cells in response to sustained hyperglycemia, and, last but not least, an analog of D-mannoheptulose. This Review discusses these methods and further contributions. For instance, emphasis is placed on labeling beta cells with (11)C-dihydrotetrabenazine, which is the most advanced method at present. Attention is also drawn to the latest approaches for noninvasive imaging and functional characterization of pancreatic beta cells. None of these procedures is used in clinical practice yet.