A novel method of monitoring response to islet transplantation: bioluminescent imaging of an NF-kB transgenic mouse model

Aromatase-Inhibitor-Induced Musculoskeletal Inflammation Is Observed Independent of Oophorectomy in a Novel Mouse Model

Aromatase Inhibitors (AIs) block estrogen production and improve survival in patients with hormone-receptor-positive breast cancer. However, half of patients develop aromatase-inhibitor-induced arthralgia (AIIA), which is characterized by inflammation of the joints and the surrounding musculoskeletal tissue. To create a platform for future interventional strategies, our objective was to characterize a novel animal model of AIIA. Female BALB/C-Tg(NFκB-RE-luc)-Xen mice, which have a firefly luciferase NFκB reporter gene, were oophorectomized and treated with an AI (letrozole). Bioluminescent imaging showed significantly enhanced NFκB activation with AI treatment in the hind limbs. Moreover, an analysis of the knee joints and legs via MRI showed enhanced signal detection in the joint space and the surrounding tissue. Surprisingly, the responses observed with AI treatment were independent of oophorectomy, indicating that inflammation is not mediated by physiological estrogen levels. Histopathological and pro-inflammatory cytokine analyses further demonstrated the same trend, as tenosynovitis and musculoskeletal infiltrates were detected in all mice receiving AI, and serum cytokines were significantly upregulated. Human PBMCs treated with letrozole/estrogen combinations did not demonstrate an AI-specific gene expression pattern, suggesting AIIA-mediated pathogenesis through other cell types. Collectively, these data identify an AI-induced stimulation of disease pathology and suggest that AIIA pathogenesis may not be mediated by estrogen deficiency, as previously hypothesized.

Real-Time Noninvasive Bioluminescence, Ultrasound and Photoacoustic Imaging in NFκB-RE-Luc Transgenic Mice Reveal Glia Maturation Factor-Mediated Immediate and Sustained Spatio-Temporal Activation of NFκB Signaling Post-Traumatic Brain Injury in a Gender-Specific Manner

Neurotrauma especially traumatic brain injury (TBI) is the leading cause of death and disability worldwide. To improve upon the early diagnosis and develop precision-targeted therapies for TBI, it is critical to understand the underlying molecular mechanisms and signaling pathways. The transcription factor, nuclear factor kappa B (NFκB), which is ubiquitously expressed, plays a crucial role in the normal cell survival, proliferation, differentiation, function, as well as in disease states like neuroinflammation and neurodegeneration. Here, we hypothesized that real-time noninvasive bioluminescence molecular imaging allows rapid and precise monitoring of TBI-induced immediate and rapid spatio-temporal activation of NFκB signaling pathway in response to Glia maturation factor (GMF) upregulation which in turn leads to neuroinflammation and neurodegeneration post-TBI. To test and validate our hypothesis and to gain novel mechanistic insights, we subjected NFκB-RE-Luc transgenic male and female mice to TBI and performed real-time noninvasive bioluminescence imaging (BLI) as well as photoacoustic and ultrasound imaging (PAI). Our BLI data revealed that TBI leads to an immediate and sustained activation of NFκB signaling. Further, our BLI data suggest that especially in male NFκB-RE-Luc transgenic mice subjected to TBI, in addition to brain, there is widespread activation of NFκB signaling in multiple organs. However, in the case of the female NFκB-RE-Luc transgenic mice, TBI induces a very specific and localized activation of NFκB signaling in the brain. Further, our microRNA data suggest that TBI induces significant upregulation of mir-9-5p, mir-21a-5p, mir-34a-5p, mir-16-3p, as well as mir-155-5p within 24 h and these microRNAs can be successfully used as TBI-specific biomarkers. To the best of our knowledge, this is one of the first and unique study of its kind to report immediate and sustained activation of NFκB signaling post-TBI in a gender-specific manner by utilizing real-time non-invasive BLI and PAI in NFκB-RE-Luc transgenic mice. Our study will prove immensely beneficial to gain novel mechanistic insights underlying TBI, unravel novel therapeutic targets, as well as enable us to monitor in real-time the response to innovative TBI-specific precision-targeted gene and stem cell-based precision medicine.

Assessment of Polyethylene Glycol-Coated Gold Nanoparticle Toxicity and Inflammation In Vivo Using NF-κB Reporter Mice

Polyethylene glycol (PEG) coating of gold nanoparticles (AuNPs) improves AuNP distribution via blood circulation. The use of PEG-coated AuNPs was shown to result in acute injuries to the liver, kidney, and spleen, but long-term toxicity has not been well studied. In this study, we investigated reporter induction for up to 90 days in NF-κB transgenic reporter mice following intravenous injection of PEG-coated AuNPs. The results of different doses (1 and 4 μg AuNPs per gram of body weight), particle sizes (13 nm and 30 nm), and PEG surfaces (methoxyl- or carboxymethyl-PEG 5 kDa) were compared. The data showed up to 7-fold NF-κB reporter induction in mouse liver from 3 h to 7 d post PEG-AuNP injection compared to saline-injected control mice, and gradual reduction to a level similar to control by 90 days. Agglomerates of PEG-AuNPs were detected in liver Kupffer cells, but neither gross pathological abnormality in liver sections nor increased activity of liver enzymes were found at 90 days. Injection of PEG-AuNPs led to an increase in collagen in liver sections and elevated total serum cholesterol, although still within the normal range, suggesting that inflammation resulted in mild fibrosis and affected hepatic function. Administrating PEG-AuNPs inevitably results in nanoparticles entrapped in the liver; thus, further investigation is required to fully assess the long-term impacts by PEG-AuNPs on liver health.

Molecular Imaging of Stem Cells

Regenerative medicine with the use of stem cells has appeared as a potential therapeutic alternative for many disease states. Despite initial enthusiasm, there has been relatively slow transition to clinical trials. In large part, numerous questions remain regarding the viability, biology and efficacy of transplanted stem cells in the living subject. The critical issues highlighted the importance of developing tools to assess these questions. Advances in molecular biology and imaging have allowed the successful non-invasive monitoring of transplanted stem cells in the living subject. Over the years these methodologies have been updated to assess not only the viability but also the biology of transplanted stem cells. In this review, different imaging strategies to study the viability and biology of transplanted stem cells are presented. Use of these strategies will be critical as the different regenerative therapies are being tested for clinical use.

Transgenic Animal Models to Visualize Cancer-Related Cellular Processes by Bioluminescence Imaging

Preclinical animal models are valuable tools to improve treatments of malignant diseases, being an intermediate step of experimentation between cell culture and human clinical trials. Among different animal models frequently used in cancer research are mouse and, more recently, zebrafish models. Indeed, most of the cellular pathways are highly conserved between human, mouse and zebrafish, thus rendering these models very attractive. Recently, several transgenic reporter mice and zebrafishes have been generated in which the luciferase reporter gene are placed under the control of a promoter whose activity is strictly related to specific cancer cellular processes. Other mouse models have been generated by the cDNA luciferase knockin in the locus of a gene whose expression/activity has increased in cancer. Using BioLuminescence Imaging (BLI), we have now the opportunity to spatiotemporal visualize cell behaviors, among which proliferation, apoptosis, migration and immune responses, in any body district in living animal in a time frame process. We provide here a review of the available models to visualized cancer and cancer-associated events in living animals by BLI and as they have been successful in identifying new stages of early tumor progression, new interactions between different tissues and new therapeutic responsiveness.

Imaging pancreatic islet cells by positron emission tomography

It was estimated that every year more than 30000 persons in the United States - approximately 80 people per day - are diagnosed with type 1 diabetes (T1D). T1D is caused by autoimmune destruction of the pancreatic islet (β cells) cells. Islet transplantation has become a promising therapy option for T1D patients, while the lack of suitable tools is difficult to directly evaluate of the viability of the grafted islet over time. Positron emission tomography (PET) as an important non-invasive methodology providing high sensitivity and good resolution, is able to accurate detection of the disturbed biochemical processes and physiological abnormality in living organism. The successful PET imaging of islets would be able to localize the specific site where transplanted islets engraft in the liver, and to quantify the level of islets remain alive and functional over time. This information would be vital to establishing and evaluating the efficiency of pancreatic islet transplantation. Many novel imaging agents have been developed to improve the sensitivity and specificity of PET islet imaging. In this article, we summarize the latest developments in carbon-11, fluorine-18, copper-64, and gallium-68 labeled radioligands for the PET imaging of pancreatic islet cells.

Differential activation of NF-κB signaling is associated with platinum and taxane resistance in MyD88 deficient epithelial ovarian cancer cells

Development of chemoresistance is a major impediment to successful treatment of patients suffering from epithelial ovarian carcinoma (EOC). Among various molecular factors, presence of MyD88, a component of TLR-4/MyD88 mediated NF-κB signaling in EOC tumors is reported to cause intrinsic paclitaxel resistance and poor survival. However, 50-60% of EOC patients do not express MyD88 and one-third of these patients finally relapses and dies due to disease burden. The status and role of NF-κB signaling in this chemoresistant MyD88(negative) population has not been investigated so far. Using isogenic cellular matrices of cisplatin, paclitaxel and platinum-taxol resistant MyD88(negative) A2780 ovarian cancer cells expressing a NF-κB reporter sensor, we showed that enhanced NF-κB activity was required for cisplatin but not for paclitaxel resistance. Immunofluorescence and gel mobility shift assay demonstrated enhanced nuclear localization of NF-κB and subsequent binding to NF-κB response element in cisplatin resistant cells. The enhanced NF-κB activity was measurable from in vivo tumor xenografts by dual bioluminescence imaging. In contrast, paclitaxel and the platinum-taxol resistant cells showed down regulation in NF-κB activity. Intriguingly, silencing of MyD88 in cisplatin resistant and MyD88(positive) TOV21G and SKOV3 cells showed enhanced NF-κB activity after cisplatin but not after paclitaxel or platinum-taxol treatments. Our data thus suggest that NF-κB signaling is important for maintenance of cisplatin resistance but not for taxol or platinum-taxol resistance in absence of an active TLR-4/MyD88 receptor mediated cell survival pathway in epithelial ovarian carcinoma.

Effects of Mn-DPDP and manganese chloride on hemodynamics and glucose tolerance in anesthetized rats

BACKGROUND

Previous studies have demonstrated that magnetic resonance imaging may be a method of choice to visualize transplanted pancreatic islets. However, contrast agents may interfere with microcirculation and affect graft function.

PURPOSE

To evaluate the effects manganese-containing contrast media on regional blood flow and glucose tolerance.

MATERIAL AND METHODS

Anesthetized rats were injected intravenously with MnCl2 (10 µM/kg body weight) or Mn-DPDP (Teslascan™; 5 µM/kg body weight). Blood flow measurements were made with a microsphere technique 10 min later. In separate animals vascular arteriolar reactivity in isolated, perfused islets was examined. Furthermore, an intraperitoneal glucose tolerance test was performed in separate rats.

RESULTS

Glucose tolerance was unaffected by both agents. No changes in regional blood flow were seen after administration of Mn-DPDP, except for an increase in arterial liver blood flow. MnCl2 increased all blood flow values except that of the kidney. MnCl2, but not Mn-DPDP, caused a vasoconstriction in isolated rat islet arterioles but only at very high doses.

CONCLUSION

Mn-DPDP administration does not affect glucose tolerance or regional blood flow, besides an increase in arterial hepatic blood flow, and may therefore be suitable for visualization of islets.

Use of Magnetocapsules for In Vivo Visualization and Enhanced Survival of Xenogeneic HepG2 Cell Transplants

Hepatocyte transplantation is currently being considered as a new paradigm for treatment of fulminant liver failure. Xeno- and allotransplantation studies have shown considerable success but the long-term survival and immunorejection of engrafted cells needs to be further evaluated. Using novel alginate-protamine sulfate-alginate microcapsules, we have co-encapsulated luciferase-expressing HepG2 human hepatocytes with superparamagnetic iron oxide nanoparticles to create magnetocapsules that are visible on MRI as discrete hypointensities. Magnetoencapsulated cells survive and secrete albumin for at least 5 weeks in vitro. When transplanted i.p. in immunocompetent mice, encapsulated hepatocytes survive for at least 4 weeks as determined using bioluminescent imaging, which is in stark contrast to naked, unencapsulated hepatocytes, that died within several days after transplantation. However, in vivo human albumin secretion did not follow the time course of magnetoencapsulated cell survival, with plasma levels returning to baseline values already at 1 week post-transplantation. The present results demonstrate that encapsulation can dramatically prolong survival of xenotransplanted hepatocytes, leading to sustained albumin secretion with a duration that may be long enough for use as a temporary therapeutic bridge to liver transplantation.

High-resolution magnetic resonance imaging quantitatively detects individual pancreatic islets

OBJECTIVE

We studied whether manganese-enhanced high-field magnetic resonance (MR) imaging (MEHFMRI) could quantitatively detect individual islets in situ and in vivo and evaluate changes in a model of experimental diabetes.

RESEARCH DESIGN AND METHODS

Whole pancreata from untreated (n = 3), MnCl(2) and glucose-injected mice (n = 6), and mice injected with either streptozotocin (STZ; n = 4) or citrate buffer (n = 4) were imaged ex vivo for unambiguous evaluation of islets. Exteriorized pancreata of MnCl(2) and glucose-injected mice (n = 6) were imaged in vivo to directly visualize the gland and minimize movements. In all cases, MR images were acquired in a 14.1 Tesla scanner and correlated with the corresponding (immuno)histological sections.

RESULTS

In ex vivo experiments, MEHFMRI distinguished different pancreatic tissues and evaluated the relative abundance of islets in the pancreata of normoglycemic mice. MEHFMRI also detected a significant decrease in the numerical and volume density of islets in STZ-injected mice. However, in the latter measurements the loss of β-cells was undervalued under the conditions tested. The experiments on the externalized pancreata confirmed that MEHFMRI could visualize native individual islets in living, anesthetized mice.

CONCLUSIONS

Data show that MEHFMRI quantitatively visualizes individual islets in the intact mouse pancreas, both ex vivo and in vivo.

Molecular imaging: a promising tool to monitor islet transplantation

Replacement of insulin production by pancreatic islet transplantation has great potential as a therapy for type 1 diabetes mellitus. At present, the lack of an effective approach to islet grafts assessment limits the success of this treatment. The development of molecular imaging techniques has the potential to fulfill the goal of real-time noninvasive monitoring of the functional status and viability of the islet grafts. We review the application of a variety of imaging modalities for detecting endogenous and transplanted beta-cell mass. The review also explores the various molecular imaging strategies for assessing islet delivery, the metabolic effects on the islet grafts as well as detection of immunorejection. Here, we highlight the use of combined imaging and therapeutic interventions in islet transplantation and the in vivo monitoring of stem cells differentiation into insulin-producing cells.

Molecular imaging of cell therapy for gastroenterologic applications

Stem cell therapy has appeared as a possible therapeutic alternative for numerous diseases. Furthermore, cancer stem cells are a focus of significant interest as they may allow for a better understanding of the genesis of different malignancies. The ultimate goal of stem cell therapeutics is to ensure the viability and functionality of the transplanted cells. Similarly, the ultimate goal of understanding cancer stem cells is to understand how they behave in the living subject. Until recently, the efficacy of stem cell therapies has been assessed by overall organ function recovery. Understanding the behavior and biology of stem cells directly in the living subject can also lead to therapy optimization. Thus, there is a critical need for reliable and accurate methods to understand stem cell biology in vivo. Recent advances in both imaging and molecular biology have enabled transplanted stem cells to be successfully monitored in the living subject. The use of molecular imaging modalities has the capability to answer these questions and may one day be translated to patients. In this review, we will discuss the potential imaging strategies and how they can be utilized, depending on the questions that need to be answered.

In vivo imaging of transplanted islets with 64Cu-DO3A-VS-Cys40-Exendin-4 by targeting GLP-1 receptor

Glucagon-like peptide 1 receptor (GLP-1R) is highly expressed in pancreatic islets, especially on β-cells. Therefore, a properly labeled ligand that binds to GLP-1R could be used for in vivo pancreatic islet imaging. Because native GLP-1 is degraded rapidly by dipeptidyl peptidase-IV (DPP-IV), a more stable agonist of GLP-1 such as Exendin-4 is a preferred imaging agent. In this study, DO3A-VS-Cys(40)-Exendin-4 was prepared through the conjugation of DO3A-VS with Cys(40)-Exendin-4. The in vitro binding affinity of DO3A-VS-Cys(40)-Exendin-4 was evaluated in INS-1 cells, which overexpress GLP-1R. After (64)Cu labeling, biodistribution studies and microPET imaging of (64)Cu-DO3A-VS-Cys(40)-Exendin-4 were performed on both subcutaneous INS-1 tumors and islet transplantation models. The subcutaneous INS-1 tumor was clearly visualized with microPET imaging after the injection of (64)Cu-DO3A-VS-Cys(40)-Exendin-4. GLP-1R positive organs, such as pancreas and lung, showed high uptake. Tumor uptake was saturable, reduced dramatically by a 20-fold excess of unlabeled Exendin-4. In the intraportal islet transplantation models, (64)Cu-DO3A-VS-Cys(40)-Exendin-4 demonstrated almost two times higher uptake compared with normal mice. (64)Cu-DO3A-VS-Cys(40)-Exendin-4 demonstrated persistent and specific uptake in the mouse pancreas, the subcutaneous insulinoma mouse model, and the intraportal human islet transplantation mouse model. This novel PET probe may be suitable for in vivo pancreatic islets imaging in the human.

Radionuclide probes for molecular imaging of pancreatic beta-cells

Islet transplantation is a promising treatment option for patients with type 1 diabetes (T1D); however, the fate of the graft over time remains difficult to follow, due to the lack of available tools capable of monitoring graft rejection and inflammation prior to islet graft loss. Due to the challenges imposed by the location of the pancreas and the sparsely dispersed beta-cell population within the pancreas, currently, the clinical verification of beta-cell abnormalities can only be obtained indirectly via metabolic studies, which typically is not possible until after a significant deterioration in islet function has already occurred. The development of non-invasive imaging methods for the assessment of the pancreatic beta-cells, however, offers the potential for the early detection of beta-cell dysfunction prior to the clinical onset of T1D and type 2 diabetes (T2D). Ideal islet imaging agents would have an acceptable residence time in the human body, be capable of providing high-resolution images with minimal uptake in surrounding tissues (e.g., the liver), would not be toxic to islets, and would not require pre-treatment of islets prior to transplantation. A variety of currently available imaging techniques, including magnetic resonance imaging (MRI), bioluminescence imaging (BLI), and nuclear imaging have been tested for the study of beta-cell diseases. In this article, we summarize the recent advances made in nuclear imaging techniques for non-invasive imaging of pancreatic beta-cells. The use of radioactive probes for islet imaging is also discussed.

TLR4 mediates early graft failure after intraportal islet transplantation

We have previously shown that islet emboli in the portal vein block blood flow and induce local inflammatory reaction, resulting in functional loss of islet grafts following intraportal transplantation. This study was designed to test whether Toll-like receptor (TLR) activation mediates early islet graft failure. Syngeneic islet grafts were transplanted into chemically induced diabetic mice, and TLR deficient mice were used as donors and/or recipients of islet grafts. Islet viability, proinflammatory cytokines, high-mobility group box-1 (HMGB1) and NF-kappaB activation were analyzed by bioluminesce imaging (BLI), quantitative RT-PCR (qRT-PCR) and histology. Early islet graft failure was observed in mice with intraportal islet engrafts with increased proinflammatory cytokines, HMGB1 expression, NF-kappaB activation, caspase-3 and TUNEL positive cells. Deficiency of TLR4 in donor, but not in recipient, inhibited NF-kappaB activation, reduced proinflammatory cytokines and improved viability of islet grafts. Blockade of HMGB1 with anti-HMGB1 monoclonal antibody (mAb, 2g7) inhibited inflammatory reactions, as evidenced by reduced TNFalpha and IL-1ss production, and improved islet viability. We conclude that TLR4 activation mediates early graft failure following intraportal islet transplantation. Inhibition of TLR4 activation represents a novel strategy to attenuate early graft failure following intraportal islet transplantation.

Improving the procedure for detection of intrahepatic transplanted islets by magnetic resonance imaging

Islet transplantation is an effective therapy for restoring normoglycemia in type-1 diabetes, but long-term islet graft function is achieved only in a minority of cases. Noninvasive magnetic resonance imaging of pancreatic islets is an attractive option for "real-time" monitoring of graft evolution. So far, previous studies have been performed in the absence of a standardized labeling procedure and, besides a feasibility study in patients, the effectiveness and safety of various labeling approaches were tested only with high field magnets (4.7 T). In this study, we addressed: (a) standardization of a labeling procedure for human islets with clinically-approved contrast agent Endorem, (b) safety aspects of labeling related to inflammation and (c) quality of imaging both at 7 T and 1.5 T. We have highlighted that the ratio of Endorem/islet is crucial for reproducible labeling, with a ratio of 2.24 ug/IEQ, allowing successful in vivo imaging both with 1.5 T and 7.0 T magnets up to 143 days after intrahepatic transplant. With this standardized labeling procedure, labeled islets are neither inflamed nor more susceptible to inflammatory insults than unlabeled ones. This report represents an important contribution towards the development of a standardized and safe clinical protocol for the noninvasive imaging of transplanted islets in humans.

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.

CpG oligodeoxynucleotide triggers the liver inflammatory reaction and abrogates spontaneous tolerance

Liver allografts are spontaneously accepted in the liver transplantation mouse model; however, the basis for this tolerance and the conditions that abrogate spontaneous tolerance to liver allografts are incompletely understood. We examined the role of CpG oligodeoxynucleotide (ODN) in triggering the liver inflammatory reaction and allograft rejection. Bioluminescence imaging quantified the activation of nuclear transcriptional factor kappaB (NF-kappaB) at different time points post-transplantation. Intrahepatic lymphocyte subsets were analyzed by immunofluorescence assay and flow cytometry. The results showed that liver allografts survived for more than 100 days without a requirement for any immunosuppressive therapy. Donor-matched cardiac allografts were permanently accepted, whereas third-party cardiac grafts were rejected with delayed kinetics; this confirmed donor-specific tolerance. NF-kappaB activation in the liver allografts was transiently increased on day 1 and diminished by day 4; in comparison, it was elevated up to 10 days post-transplantation in the cardiac allografts. When CpG ODN was administered at a high dose (50 microg per mouse x 1) to the recipients on day 7 post-transplantation, it induced an acute liver inflammatory reaction with elevated NF-kappaB activation in both allogeneic and syngeneic liver grafts. Multiple doses of CpG ODN (10 microg per mouse x 3) elicited acute rejection of the liver allografts with significant T cell infiltration in the liver allografts, reduced T regulatory cells, and enhanced interferon gamma-producing cells in the intrahepatic infiltrating lymphocytes. These data demonstrate that CpG ODN initiates an inflammatory reaction and abrogates spontaneous tolerance in the liver transplantation mouse model. Liver Transpl 15:915-923, 2009. (c) 2009 AASLD.

Noninvasive assessment of pancreatic beta-cell function in vivo with manganese-enhanced magnetic resonance imaging

Loss of beta-cell function in type 1 and type 2 diabetes leads to metabolic dysregulation and inability to maintain normoglycemia. Noninvasive imaging of beta-cell function in vivo would therefore provide a valuable diagnostic and research tool for quantifying progression to diabetes and response to therapeutic intervention. Because manganese (Mn(2+)) is a longitudinal relaxation time (T1)-shortening magnetic resonance imaging (MRI) contrast agent that enters cells such as pancreatic beta-cells through voltage-gated calcium channels, we hypothesized that Mn(2+)-enhanced MRI of the pancreas after glucose infusion would allow for noninvasive detection of beta-cell function in vivo. To test this hypothesis, we administered glucose and saline challenges intravenously to normal mice and mice given high or low doses of streptozotocin (STZ) to induce diabetes. Serial inversion recovery MRI was subsequently performed after Mn(2+) injection to probe Mn(2+) accumulation in the pancreas. Time-intensity curves of the pancreas (normalized to the liver) fit to a sigmoid function showed a 51% increase in signal plateau height after glucose stimulation relative to saline (P < 0.01) in normal mice. In diabetic mice given a high dose of STZ, only a 9% increase in plateau signal intensity was observed after glucose challenge (P = not significant); in mice given a low dose of STZ, a 20% increase in plateau signal intensity was seen after glucose challenge (P = 0.02). Consistent with these imaging findings, the pancreatic insulin content of high- and low-dose STZ diabetic mice was reduced about 20-fold and 10-fold, respectively, compared with normal mice. We conclude that Mn(2+)-enhanced MRI demonstrates excellent potential as a means for noninvasively monitoring beta-cell function in vivo and may have the sensitivity to detect progressive decreases in function that occur in the diabetic disease process.

Imaging the pancreas: from ex vivo to non-invasive technology

While many recently published reviews have covered non-invasive nuclear imaging techniques, the aim of this review is to focus on current developments in optical imaging technologies for investigating the pancreas. Several of these modalities are being developed into non-invasive, real-time monitoring routines for pancreatic diseases. However, they also provide pre-clinical ex vivo and/or intravital tools for three-dimensional quantitative assessments of cellular and molecular events, with levels of specificity and resolution difficult to achieve with other currently available modalities.

Non-invasive detection of transplanted pancreatic islets

Type 1 diabetes (insulin-dependent, IDDM) results in immune-mediated destruction of pancreatic beta cells, which leads to a deficiency in insulin secretion and as a result, to hyperglycaemia. Keeping blood glucose levels under tight control represents the most effective way either to prevent the onset or to reduce the progression of the chronic complications of IDDM. At present, pancreatic islet transplantation is emerging as the most promising clinical modality, which can stop diabetes progression without increasing the incidence of hypoglycaemic events. Although early results of clinical trials using the Edmonton Protocol and its variations are very encouraging, it is still unclear how long the islets will survive and how often the transplantation procedure will be successful. In order to monitor transplantation efficiency and graft survival, reliable non-invasive imaging methods are critically needed. If such methods are introduced clinically, essential information regarding the location, function and viability of transplanted islets can be obtained repeatedly and non-invasively. This review will focus on the latest advancements in the field of in vivo imaging of islet transplantation and describe various islet labelling and imaging techniques. In addition, we will critically look into limitations and obstacles currently present on the way to successful clinical implementation of this approach.

Bioluminescence imaging visualizes activation of nuclear factor-kappaB in mouse cardiac transplantation

BACKGROUND

The purpose of the current study was to evaluate the role of bioluminescence imaging (BLI) in the determination of nuclear factor (NF)-kappaB activation in cardiac allograft rejection and ischemia-reperfusion injury.

METHODS

To visualize NF-kappaB activation, luciferase transgenic mice under the control of a mouse NF-kappaB promoter (NF-kappaB-Luc) were used as donors or recipients of cardiac grafts. Alternatively, NF-kappaB-Luc spleen cells were adoptively transferred into Rag2 -/- mice with or without cardiac allografts. BLI was performed posttransplantation to detect luciferase activity that represents NF-kappaB activation.

RESULTS

The results show that luciferase activity was significantly increased in the cardiac allografts when NF-kappaB-Luc mice were used as recipients as well as donors. Luciferase activity was also elevated in the wild-type cardiac allografts in Rag2 -/- mice that were transferred with NF-kappaB-Luc spleen cells. CD154 monoclonal antibody (mAb) therapy inhibited luciferase activity and induced long-term survival of cardiac allografts. toll-like receptor-9 ligand, CpG DNA, enhanced luciferase activity and abrogated tolerance induction by CD154 mAb. Luciferase activity was also increased in ischemia-reperfusion injury of the cardiac grafts.

CONCLUSION

BLI using Luc-NF-kappaB mice is a noninvasive approach to visualize the activation of NF-kappaB signaling in mouse cardiac allograft rejection and ischemia-reperfusion injury. CD154 mAb can inhibit NF-kappaB activation, which is reversed by toll-like receptor engagement.

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.

Noninvasive bioluminescence imaging in small animals

There has been a rapid growth of bioluminescence imaging applications in small animal models in recent years, propelled by the availability of instruments, analysis software, reagents, and creative approaches to apply the technology in molecular imaging. Advantages include the sensitivity of the technique as well as its efficiency, relatively low cost, and versatility. Bioluminescence imaging is accomplished by sensitive detection of light emitted following chemical reaction of the luciferase enzyme with its substrate. Most imaging systems provide 2-dimensional (2D) information in rodents, showing the locations and intensity of light emitted from the animal in pseudo-color scaling. A 3-dimensional (3D) capability for bioluminescence imaging is now available, but is more expensive and less efficient; other disadvantages include the requirement for genetically encoded luciferase, the injection of the substrate to enable light emission, and the dependence of light signal on tissue depth. All of these problems make it unlikely that the method will be extended to human studies. However, in small animal models, bioluminescence imaging is now routinely applied to serially detect the location and burden of xenografted tumors, or identify and measure the number of immune or stem cells after an adoptive transfer. Bioluminescence imaging also makes it possible to track the relative amounts and locations of bacteria, viruses, and other pathogens over time. Specialized applications of bioluminescence also follow tissue-specific luciferase expression in transgenic mice, and monitor biological processes such as signaling or protein interactions in real time. In summary, bioluminescence imaging has become an important component of biomedical research that will continue in the future.

Challenges and emerging technologies in the immunoisolation of cells and tissues

Protection of transplanted cells from the host immune system using immunoisolation technology will be important in realizing the full potential of cell-based therapeutics. Microencapsulation of cells and cell aggregates has been the most widely explored immunoisolation strategy, but widespread clinical application of this technology has been limited, in part, by inadequate transport of nutrients, deleterious innate inflammatory responses, and immune recognition of encapsulated cells via indirect antigen presentation pathways. To reduce mass transport limitations and decrease void volume, recent efforts have focused on developing conformal coatings of micron and submicron scale on individual cells or cell aggregates. Additionally, anti-inflammatory and immunomodulatory capabilities are being integrated into immunoisolation devices to generate bioactive barriers that locally modulate host responses to encapsulated cells. Continued exploration of emerging paradigms governed by the inherent challenges associated with immunoisolation will be critical to actualizing the clinical potential of cell-based therapeutics.

Noninvasive imaging of islet transplantation and rejection

Immunologic and nonimmunologic events lead to significant graft loss after islet transplantation. Unfortunately, current metabolic testing methods are inadequate to detect many of these changes, leading to a critical need for noninvasive monitoring of islet rejection. However, their small size and distribution after transplantation pose specific problems for direct islet imaging. This article reviews the relative merits of several imaging modalities for the noninvasive monitoring of islet transplantation and rejection.