Intraoperative ultrasound examination is useful for monitoring transplanted islets: a case report

A Gelatin Hydrogel Nonwoven Fabric Combined With Adipose Tissue-Derived Stem Cells Enhances Subcutaneous Islet Engraftment

Subcutaneous islet transplantation is a promising treatment for severe diabetes; however, poor engraftment hinders its prevalence. We previously revealed that a gelatin hydrogel nonwoven fabric (GHNF) markedly improved subcutaneous islet engraftment. We herein investigated whether the addition of adipose tissue-derived stem cells (ADSCs) to GHNF affected the outcome. A silicone spacer sandwiched between two GHNFs with (AG group) or without (GHNF group) ADSCs, or a silicone spacer alone (Silicone group) was implanted into the subcutaneous space of healthy mice at 6 weeks before transplantation, then diabetes was induced 7 days before transplantation. Syngeneic islets were transplanted into the pretreated space. Intraportal transplantation (IPO group) was also performed to compare the transplant efficiency. Blood glucose, intraperitoneal glucose tolerance, immunohistochemistry, and inflammatory mediators were evaluated. The results in the subcutaneous transplantation were compared using the Silicone group as a control. The results of the IPO group were also compared with those of the AG group. The AG group showed significantly better blood glucose changes than the Silicone and the IPO groups. The cure rate of AG group (72.7%) was the highest among the groups (GHNF; 40.0%, IPO; 40.0%, Silicone; 0%). The number of vWF-positive vessels in the subcutaneous space of the AG group was significantly higher than that in other groups before transplantation (P < 0.01). Lectin angiography also showed that the same results (P < 0.05). According to the results of the ADSCs tracing, ADSCs did not exist at the transplant site (6 weeks after implantation). The positive rates for laminin and collagen III constructed around the transplanted islets did not differ among groups. Inflammatory mediators were higher in the Silicone group, followed by the AG and GHNF groups. Pretreatment using bioabsorbable scaffolds combined with ADSCs enhanced neovascularization in subcutaneous space, and subcutaneous islet transplantation using GHNF with ADSCs was superior to intraportal islet transplantation.

A gelatin hydrogel nonwoven fabric improves outcomes of subcutaneous islet transplantation

Subcutaneous islet transplantation is a promising treatment for severe diabetes; however, poor engraftment hinders its prevalence. We previously reported that a recombinant peptide (RCP) enhances subcutaneous islet engraftment. However, it is impractical for clinical use because RCP must be removed when transplanting islets. We herein investigated whether a novel bioabsorbable gelatin hydrogel nonwoven fabric (GHNF) could improve subcutaneous islet engraftment. A silicon spacer with or without GHNF was implanted into the subcutaneous space of diabetic mice. Syngeneic islets were transplanted into the pretreated space or intraportally (Ipo group). Blood glucose, intraperitoneal glucose tolerance, immunohistochemistry, CT angiography and gene expression were evaluated. The cure rate and glucose tolerance of the GHNF group were significantly better than in the control and Ipo groups (p < 0.01, p < 0.05, respectively). In the GHNF group, a limited increase of vWF-positive vessels was detected in the islet capsule, whereas laminin (p < 0.05), collagen III and IV were considerably enhanced. TaqMan arrays revealed a significant upregulation of 19 target genes (including insulin-like growth factor-2) in the pretreated space. GHNF markedly improved the subcutaneous islet transplantation outcomes, likely due to ECM compensation and protection of islet function by various growth factors, rather than enhanced neovascularization.

Ideal Duration of Pretreatment Using a Gelatin Hydrogel Nonwoven Fabric Prior to Subcutaneous Islet Transplantation

Subcutaneous islet transplantation is a promising treatment for severe diabetes; however, poor engraftment hinders its prevalence. We previously revealed that a gelatin hydrogel nonwoven fabric (GHNF) markedly improved subcutaneous islet engraftment in comparison with intraportal islet transplantation. We herein investigated whether the duration of pretreatment using GHNF affected the outcome of subcutaneous islet transplantation. A silicone spacer with GHNF was implanted into the subcutaneous space of healthy mice at 2, 4, 6, or 8 weeks before transplantation, and then diabetes was induced 7 days before transplantation. Syngeneic islets were transplanted into the pretreated space. Blood glucose, intraperitoneal glucose tolerance, immunohistochemistry, inflammatory mediators, and gene expression were evaluated. The 6-week group showed significantly better blood glucose changes than the other groups (P < 0.05). The cure rate of the 6-week group (60.0%) was the highest among the groups (2-week = 0%, 4-week = 50.0%, 8-week = 15.4%). The number of von Willebrand factor (vWF)-positive vessels in the 6-week group was significantly higher than in the other groups at pre-islet and post-islet transplantation (P < 0.01 [vs 2-and 4-week groups] and P < 0.05 [vs all other groups], respectively). Notably, this beneficial effect was also observed when GHNF was implanted into diabetic mice injected with streptozotocin 7 days before GHNF implantation. The positive rates for laminin, collagen III, and collagen IV increased as the duration of pretreatment became longer and were significantly higher in the 8-week group (P < 0.01). Inflammatory mediators, including interleukin (IL)-1b, granulocyte colony-stimulating factor (G-CSF), and interferon (IFN)-γ, were gradually downregulated according to the duration of GHNF pretreatment and re-elevated in the 8-week group. Taken together, the duration of GHNF pretreatment apparently had an impact on the outcomes of subcutaneous islet transplantation, and 6 weeks appeared to be the ideal duration. Islet graft revascularization, extracellular matrix compensation of the islet capsule, and the inflammatory status at the subcutaneous space would be crucial factors for successful subcutaneous islet transplantation.

Development of a novel method for measuring tissue oxygen pressure to improve the hypoxic condition in subcutaneous islet transplantation

Subcutaneous tissue is a promising site for islet transplantation, but poor engraftment, due to hypoxia and low vascularity, hinders its prevalence. However, oxygen partial pressure (pO₂) of the subcutaneous space (SC) and other sites were reported to be equivalent in several previous reports. This contradiction may be based on accidental puncture to the indwelling micro-vessels in target tissues. We therefore developed a novel optical sensor system, instead of a conventional Clark-type needle probe, for measuring tissue pO₂ and found that pO₂ of the SC was extremely low in comparison to other sites. To verify the utility of this method, we transplanted syngeneic rat islets subcutaneously into diabetic recipients under several oxygenation conditions using an oxygen delivery device, then performed pO₂ measurement, glucose tolerance, and immunohistochemistry. The optical sensor system was validated by correlating the pO₂ values with the transplanted islet function. Interestingly, this novel technique revealed that islet viability estimated by ATP/DNA assay reduced to less than 75% by hypoxic condition at the SC, indicating that islet engraftment may substantially improve if the pO₂ levels reach those of the renal subcapsular space. Further refinements for a hypoxic condition using the present technique may contribute to improving the efficiency of subcutaneous islet transplantation.

In Vivo Imaging of Pancreatic Islet Grafts in Diabetes Treatment

Transplantation of pancreatic islets has potential to offer life-long blood glucose management in type I diabetes and severe type II diabetes without the need of exogenous insulin administration. However, islet cell therapy suffers from autoimmune and allogeneic rejection as well as non-immune related factors. Non-invasive techniques to monitor and evaluate the fate of cell implants in vivo are essential to understand the underlying causes of graft failure, and hence to improve the precision and efficacy of islet therapy. This review describes how imaging technology has been employed to interrogate the distribution, number or volume, viability, and function of islet implants in vivo. To date, fluorescence imaging, PET, SPECT, BLI, MRI, MPI, and ultrasonography are the many imaging modalities being developed to fulfill this endeavor. We outline here the advantages, limitations, and clinical utility of each particular imaging approach.

Current Progress and Perspective: Clinical Imaging of Islet Transplantation

Islet transplantation has great potential as a cure for type 1 diabetes. At present; the lack of a clinically validated non-invasive imaging method to track islet grafts limits the success of this treatment. Some major clinical imaging modalities and various molecular probes, which have been studied for non-invasive monitoring of transplanted islets, could potentially fulfill the goal of understanding pathophysiology of the functional status and viability of the islet grafts. In this current review, we summarize the recent clinical studies of a variety of imaging modalities and molecular probes for non-invasive imaging of transplanted beta cell mass. This review also includes discussions on in vivo detection of endogenous beta cell mass using clinical imaging modalities and various molecular probes, which will be useful for longitudinally detecting the status of islet transplantation in Type 1 diabetic patients. For the conclusion and perspectives, we highlight the applications of multimodality and novel imaging methods in islet transplantation.

Islet Transplantation Imaging in vivo

Although islet transplantation plays an effective and powerful role in the treatment of diabetes, a large amount of islet grafts are lost at an early stage due to instant blood-mediated inflammatory reactions, immune rejection, and β-cell toxicity resulting from immunosuppressive agents. Timely intervention based on the viability and function of the transplanted islets at an early stage is crucial. Various islet transplantation imaging techniques are available for monitoring the conditions of post-transplanted islets. Due to the development of various imaging modalities and the continuous study of contrast agents, non-invasive islet transplantation imaging in vivo has made great progress. The tracing and functional evaluation of transplanted islets in vivo have thus become possible. However, most studies on contrast agent and imaging modalities are limited to animal experiments, and long-term toxicity and stability need further evaluation. Accordingly, the clinical application of the current achievements still requires a large amount of effort. In this review, we discuss the contrast agents for MRI, SPECT/PET, BLI/FI, US, MPI, PAI, and multimodal imaging. We further summarize the advantages and limitations of various molecular imaging methods.

Real-Time, Intraoperative Doppler/Ultrasound Monitoring of Islet Infusion During Total Pancreatectomy With Islet Autotransplant: A First Report

Chronic pancreatitis (CP), secondary to a wide variety of etiologies, is a progressive and irreversible disease. Initially, CP is managed with endoscopic interventions, long-term analgesia for its associated chronic abdominal pain syndrome and pancreatic enzyme replacement for exocrine dysfunction. As the disease advances, pancreatic drainage procedures and partial resections are considered, but they leave diseased tissue behind and usually result in short-term relief only. Total pancreatectomy alone is widely viewed as a last resort treatment option because it causes brittle diabetes mellitus. However, total pancreatectomy with islet autotransplantation (TPIAT) can prevent the development of diabetes and cure the chronic pain syndrome. One serious, albeit rare, complication of TPIAT is (partial) portal vein thrombosis. Its incidence is probably about 5%. To prevent the occurrence of portal vein thrombosis, we propose herein, and have successfully performed, continuous real-time Doppler ultrasonography during the islet infusion to study portal vein and intrahepatic flow patterns, as well as changes in Doppler signals. Flow and signal changes may allow for timely adjustment of the infusion rate, before a marked increase in portal vein pressure is noted and decrease the risk of portal vein thrombosis.

A Trimodal Imaging Platform for Tracking Viable Transplanted Pancreatic Islets In Vivo: F-19 MR, Fluorescence, and Bioluminescence Imaging

PURPOSE

Combining specific and quantitative F-19 magnetic resonance imaging (MRI) with sensitive and convenient optical imaging provides complementary information about the distribution and viability of transplanted pancreatic islet grafts. In this study, pancreatic islets (PIs) were labeled with positively charged multimodal nanoparticles based on poly(lactic-co-glycolic acid) (PLGA-NPs) with encapsulated perfluoro-15-crown-5-ether and the near-infrared fluorescent dye indocyanine green.

PROCEDURES

One thousand and three thousand bioluminescent PIs were transplanted into subcutaneous artificial scaffolds, which served as an alternative transplant site. The grafts were monitored using in vivo F-19 MR, fluorescence, and bioluminescence imaging in healthy rats for 2 weeks.

RESULTS

Transplanted PIs were unambiguously localized in the scaffolds by F-19 MRI throughout the whole experiment. Fluorescence was detected in the first 4 days after transplantation only. Importantly, in vivo bioluminescence correlated with the F-19 MRI signal.

CONCLUSIONS

We developed a trimodal imaging platform for in vivo examination of transplanted PIs. Fluorescence imaging revealed instability of the fluorescent dye and its limited applicability for longitudinal in vivo studies. A correlation between the bioluminescence signal and the F-19 MRI signal indicated the fast clearance of PLGA-NPs from the transplantation site after cell death, which addresses a major issue with intracellular imaging labels. Therefore, the proposed PLGA-NP platform is reliable for reflecting the status of transplanted PIs in vivo.

Magnetic particle imaging of islet transplantation in the liver and under the kidney capsule in mouse models

Background

Islet transplantation (Tx) represents the most promising therapy to restore normoglycemia in type 1 diabetes (T1D) patients to date. As significant islet loss has been observed after the procedure, there is an urgent need for developing strategies for monitoring transplanted islet grafts. In this report we describe for the first time the application of magnetic particle imaging (MPI) for monitoring transplanted islets in the liver and under the kidney capsule in experimental animals.

Methods

Pancreatic islets isolated from Papio hamadryas were labeled with superparamagnetic iron oxides (SPIOs) and used for either islet phantoms or Tx in the liver or under the kidney capsule of NOD scid mice. MPI was used to image and quantify islet phantoms and islet transplanted experimental animals post-mortem at 1 and 14 days after Tx. Magnetic resonance imaging (MRI) was used to confirm the presence of labeled islets in the liver and under the kidney capsule 1 day after Tx.

Results

MPI of labeled islet phantoms confirmed linear correlation between the number of islets and the MPI signal (R²=0.988). Post-mortem MPI performed on day 1 after Tx showed high signal contrast in the liver and under the kidney capsule. Quantitation of the signal supports islet loss over time, which is normally observed 2 weeks after Tx. No MPI signal was observed in control animals. In vivo MRI confirmed the presence of labeled islets/islet clusters in liver parenchyma and under the kidney capsule one day after Tx.

Conclusions

Here we demonstrate that MPI can be used for quantitative detection of labeled pancreatic islets in the liver and under the kidney capsule of experimental animals. We believe that MPI, a modality with no depth attenuation and zero background tissue signal could be a suitable method for imaging transplanted islet grafts.

In Vivo Imaging of Transplanted Pancreatic Islets

The beta-cells in the islets of Langerhans in the pancreas secrete insulin and play an important role in glucose homeostasis. Diabetes, characterized by hyperglycemia, results from an absolute or a relative deficiency of the pancreatic beta-cell mass. Islet transplantation has been considered to be a useful therapeutic approach, but it is largely unsuccessful because most of the transplanted islets are lost in the early stage of transplantation. To evaluate the efficacy of intervention methods for the improvement of islet survival, monitoring of the functional islet mass is needed. Various techniques to image and track transplanted islets have been investigated to assess islets after transplantation. In this review, recent progresses in imaging methods to visualize islets are discussed.

Enhanced ultrasonography using a nano/microbubble contrast agent for islet transplantation

Recent basic and clinical studies have assessed the use of highly sensitive imaging modalities for visualizing transplanted islets. We investigated the utility of enhanced ultrasonography, combined with fluorescent acoustic liposome nano/microbubbles (FALs), for evaluating angiogenesis and the endocrine function of transplanted islets. BALB/c mice were classified into three groups: Diabetic mice that underwent syngeneic islet transplantation into the subrenal capsule and achieved normoglycemia (Tx group); those that failed to achieve normoglycemia (Tx-DM group); and those not receiving any treatment (DM group). Mice were examined by FAL-enhanced high frequency ultrasonography. The echogenicity of the islets increased rapidly within the first minute after injection of FALs and remained at a higher level in the Tx group, while small increases were observed in the other two groups. In histological assessments, fluorescently stained erythrocytes could be seen in and around the transplanted islets, indicating that the transplanted islets were enhanced by infusion of FALs via vessel networks between the engrafted islets and tissue. Furthermore, the echogenicity correlated significantly with endocrine parameters, including blood glucose (BG), serum insulin, and the BG change in the glucose tolerance test. In conclusion, the echogenicity of the islets under FAS-enhanced ultrasonosonography correlated with the endocrine status of transplanted islets.

Imaging of transplanted islets by positron emission tomography, magnetic resonance imaging, and ultrasonography

While islet transplantation is considered a useful therapeutic option for severe diabetes mellitus (DM), the outcome of this treatment remains unsatisfactory. This is largely due to the damage and loss of islets in the early transplant stage. Thus, it is important to monitor the condition of the transplanted islets, so that a treatment can be selected to rescue the islets from damage if needed. Recently, numerous trials have been performed to investigate the efficacy of different imaging modalities for visualizing transplanted islets. Positron emission tomography (PET) and magnetic resonance imaging (MRI) are the most commonly used imaging modalities for this purpose. Some groups, including ours, have also tried to visualize transplanted islets by ultrasonography (US). In this review article, we discuss the recent progress in islet imaging.