Sirolimus toxicity and vascular endothelial growth factor release from islet and renal cell lines

Safety Evaluation of Oral Sirolimus in the Treatment of Childhood Diseases: A Systematic Review

Background: Sirolimus, a mammalian target of rapamycin inhibitor, has been widely used in pediatric patients, but the safety of sirolimus in pediatric patients has not been well determined. Objective: The objective of this study was to systematically evaluate prospective studies reporting the safety of sirolimus in the treatment of childhood diseases. Methods: The following data were extracted in a standardized manner: study design, demographic characteristics, intervention, and safety outcomes. Results: In total, 9 studies were included, encompassing 575 patients who received oral sirolimus for at least 6 months. Various adverse events occurred. The most common adverse event was oral mucositis (8.2%, 95% CI: 0.054 to 0.110). Through comparative analysis of the subgroups based on the targeted concentration range, we discovered that many adverse events were significantly higher in the high concentration group (≥10 ng/mL) than in the low concentration group (<10 ng/mL) (p < 0.01). More interestingly, we found that oral mucositis was more frequently reported in children with vascular anomalies than tuberous sclerosis complex. Conclusions: This study shows that oral sirolimus in the treatment of childhood diseases is safe and reliable. However, sirolimus treatment in the pediatric population should be strictly monitored to reduce the occurrence of serious or fatal adverse events.

The potential role of multifunctional human amniotic epithelial cells in pancreatic islet transplantation

Pancreatic islet cell transplantation has proven efficacy as a treatment for type 1 diabetes mellitus, chiefly in individuals who are refractory to conventional insulin replacement therapy. At present its clinical use is restricted, firstly by the limited access to suitable donor organs but also due to factors associated with the current clinical transplant procedure which inadvertently impair the long-term functionality of the islet graft. Of note, the physical, biochemical, inflammatory, and immunological stresses to which islets are subjected, either during pretransplant processing or following implantation are detrimental to their sustained viability, necessitating repeated islet infusions to attain adequate glucose control. Progressive decline in functional beta (β)-cell mass leads to graft failure and the eventual re-instatement of exogenous insulin treatment. Strategies which protect and/or preserve optimal islet function in the peri-transplant period would improve clinical outcomes. Human amniotic epithelial cells (HAEC) exhibit both pluripotency and immune-privilege and are ideally suited for use in replacement and regenerative therapies. The HAEC secretome exhibits trophic, anti-inflammatory, and immunomodulatory properties of relevance to islet graft survival. Facilitated by β-cell supportive 3D cell culture systems, HAEC may be integrated with islets bringing them into close spatial arrangement where they may exert paracrine influences that support β-cell function, reduce hypoxia-induced islet injury, and alter islet alloreactivity. The present review details the potential of multifunctional HAEC in the context of islet transplantation, with a focus on the innate capabilities that may counter adverse events associated with the current clinical transplant protocol to achieve long-term islet graft function.

Engineering the vasculature for islet transplantation

The microvasculature in the pancreatic islet is highly specialized for glucose sensing and insulin secretion. Although pancreatic islet transplantation is a potentially life-changing treatment for patients with insulin-dependent diabetes, a lack of blood perfusion reduces viability and function of newly transplanted tissues. Functional vasculature around an implant is not only necessary for the supply of oxygen and nutrients but also required for rapid insulin release kinetics and removal of metabolic waste. Inadequate vascularization is particularly a challenge in islet encapsulation. Selectively permeable membranes increase the barrier to diffusion and often elicit a foreign body reaction including a fibrotic capsule that is not well vascularized. Therefore, approaches that aid in the rapid formation of a mature and robust vasculature in close proximity to the transplanted cells are crucial for successful islet transplantation or other cellular therapies. In this paper, we review various strategies to engineer vasculature for islet transplantation. We consider properties of materials (both synthetic and naturally derived), prevascularization, local release of proangiogenic factors, and co-transplantation of vascular cells that have all been harnessed to increase vasculature. We then discuss the various other challenges in engineering mature, long-term functional and clinically viable vasculature as well as some emerging technologies developed to address them. The benefits of physiological glucose control for patients and the healthcare system demand vigorous pursuit of solutions to cell transplant challenges. STATEMENT OF SIGNIFICANCE: Insulin-dependent diabetes affects more than 1.25 million people in the United States alone. Pancreatic islets secrete insulin and other endocrine hormones that control glucose to normal levels. During preparation for transplantation, the specialized islet blood vessel supply is lost. Furthermore, in the case of cell encapsulation, cells are protected within a device, further limiting delivery of nutrients and absorption of hormones. To overcome these issues, this review considers methods to rapidly vascularize sites and implants through material properties, pre-vascularization, delivery of growth factors, or co-transplantation of vessel supporting cells. Other challenges and emerging technologies are also discussed. Proper vascular growth is a significant component of successful islet transplantation, a treatment that can provide life-changing benefits to patients.

Oxygenation of the Intraportally Transplanted Pancreatic Islet

Intraportal islet transplantation (IT) is not widely utilized as a treatment for type 1 diabetes. Oxygenation of the intraportally transplanted islet has not been studied extensively. We present a diffusion-reaction model that predicts the presence of an anoxic core and a larger partly functional core within intraportally transplanted islets. Four variables were studied: islet diameter, islet fractional viability, external oxygen partial pressure (P) (in surrounding portal blood), and presence or absence of a thrombus on the islet surface. Results indicate that an islet with average size and fractional viability exhibits an anoxic volume fraction (AVF) of 14% and a function loss of 72% at a low external P. Thrombus formation increased AVF to 30% and function loss to 92%, suggesting that the effect of thrombosis may be substantial. External P and islet diameter accounted for the greatest overall impact on AVF and loss of function. At our institutions, large human alloislets (>200 μm diameter) account for ~20% of total islet number but ~70% of total islet volume; since most of the total transplanted islet volume is accounted for by large islets, most of the intraportal islet cells are likely to be anoxic and not fully functional.

Sirolimus-eluting dextran and polyglutamic acid hybrid coatings on AZ31 for stent applications

Magnesium (Mg)-based cardiovascular stents are promising candidate as the next generation of novel stents. Clinical studies have revealed encouraging outcomes, but late restenosis and thrombogenesis still largely exist. Blood and vascular biocompatible coatings with drug-eluting features could be the solution to such problems.

OBJECTIVE

This study was to investigate the feasibility of a three-layer hybrid coating on Mg alloy AZ31 with sirolimus-eluting feature for cardiovascular stent application.

MATERIALS AND METHODS

The first and third layers were low molecular weight dextran loaded with sirolimus, and the second layer was polyglutamic acid (PGA) to control sirolimus release. The hybrid coating was verified by scanning electron microscope (SEM). DC polarization and immersion tests were used to evaluate corrosion rate of the materials. Indirect cell viability and cell proliferation tests were performed by culturing cells with extract solutions of AZ31 samples. Blood compatibility was assessed using hemolysis assay.

RESULTS

Coated samples had an enhanced corrosion resistance than that of uncoated controls, more PGA slower corrosion. Sirolimus had a burst release for the initial ∼3 days and then a slower release until reached a plateau. The PGA thickness was able to control the sirolimus release, the thicker of PGA the slower release. The overall cell viability was extract concentration-dependent, and improved by the hybrid coatings. Cell proliferation was correlated to coating thickness and was inhibited by sirolimus. In addition, all coated AZ31 samples were non-hemolytic.

CONCLUSION

Results demonstrated that such a three-layer hybrid coating may be useful to improve the vascular biocompatibility of Mg stent materials.

Five-year follow-up of patients with type 1 diabetes transplanted with allogeneic islets: the UIC experience

This report summarizes a 5-year phase 1/2 allogeneic islet transplantation clinical trial conducted at the University of Illinois at Chicago (UIC). Ten patients were enrolled in this single center, open label, and prospective trial in which patients received 1-3 transplants. The first four subjects underwent islet transplantation with the Edmonton immunosuppressive regimen and the remaining six subjects received the UIC immunosuppressive protocol (Edmonton plus etanercept and exenatide). All 10 patients achieved insulin independence after 1-3 transplants. At 5 years of follow-up, 6 of the initial 10 patients were free of exogenous insulin. During the follow-up period, 7 of the 10 patients maintained positive C-peptide levels and a composite hypoglycemic score of 0. Most patients maintained HbA1c levels <6.0 % (42.1 mmol/mol) and a significantly improved β-score. In conclusion, this study demonstrated long-term islet graft function without using T cell depleting induction, with an encouraging outcome that includes 60 % of patients remaining insulin independent after 5 years of initial transplantation.

Assessment of tissue-engineered islet graft viability by fluorine magnetic resonance spectroscopy

INTRODUCTION

Despite significant progress in the last decade, islet transplantation remains an experimental therapy for a limited number of patients with type 1 diabetes. Tissue-engineered approaches may provide promising alternatives to the current clinical protocol and would benefit greatly from concurrent development of graft quality assessment techniques. This study was designed to evaluate whether viability of tissue-engineered islet grafts can be assessed using fluorine magnetic resonance spectroscopy ((19)F-MRS), by the noninvasive measurement of oxygen partial pressure (pO(2)) and the subsequent calculation of islet oxygen consumption rate (OCR).

METHODS

Scaffolds composed of porcine plasma were seeded with human islets and perfluorodecalin. Each graft was covered with the same volume of culture media in a Petri dish. Four scaffolds were seeded with various numbers (0-8000) of islet equivalents (IE) aliquoted from the same preparation. After randomizing run order, grafts were examined by (19)F-MRS at 37°C using a 5T spectrometer and a single-loop surface coil placed underneath. A standard inversion recovery sequence was used to obtain characteristic (19)F spin-lattice relaxation times (T1), which were converted to steady-state average pO(2) estimates using a previously determined linear calibration (R(2) = 1.000). Each condition was assessed using replicate (19)F-MRS measurements (n = 6-8).

RESULTS

Grafts exhibited IE dose-dependent increases in T1 and decreases in pO(2) estimates. From the difference between scaffold pO(2) estimates and ambient pO(2), the islet preparation OCR was calculated to be 95 ± 12 (mean ± standard error of the mean) nmol/(min·mg DNA) using theoretical modeling. This value compared well with OCR values measured using established methods for human islet preparations.

CONCLUSIONS

(19)F-MRS can be used for noninvasive pre- and possibly posttransplant assessment of tissue-engineered islet graft viability by estimating the amount of viable, oxygen-consuming tissue in a scaffold.

Pre-transplant signal induction for vascularisation in human islets

Human islet transplant success is partially impaired by slow revascularisation. Our study investigated the potential for rotational cell culture (RC) of human islets combined with thiazolidinedione (TZD) stimulation of peroxisome proliferator-activated receptor gamma (PPARγ) to upregulate vascular endothelial growth factor (VEGF) expression in the islets. Four groups of human islets were studied: static culture (SC) with and without 25 mmol/L TZD and RC with and without 25 mmol/L TZD. These were assessed for insulin secretion and soluble VEGF-A release. Both proteins were quantified by enzyme-linked immunosorbent assay (ELISA), supported with qualitative immunofluorescence staining. RC + TZD increased insulin secretion by >20% (p < 0.05-0.001) in response to 16.7 mmol/L glucose and 16.7 mmol/L glucose + 10 mmol/L theophylline (G + T). This effect was seen at all time intervals compared with SC and without addition of TZD. Soluble VEGF-A release was significantly augmented by RC and TZD exposure with an increased effect of >30% (p < 0.001) at 72 h under both SC and RC conditions. RC supplemented with a TZD enhances and prolongs the release of insulin and soluble VEGF-A by isolated human islets.

Mizoribine as sole immunosuppressive agent in islet xenotransplantation models: a candidate immunosuppressant causing no adverse effects on islets

Mizoribine (MZ) inhibits the differentiation and proliferation of helper T and B cells after antigen recognition by suppressing the purine biosynthesis pathway and nucleic acid synthesis. MZ has been used in kidney transplantation, but distinct data are unavailable for islet transplantation. The present study investigated the efficacy of MZ for islet xenotransplantation. Immunosuppressive effects of MZ were determined by mixed lymphocyte reaction (MLR) assay in vitro. Toxicities for Wistar rat islets were determined by adenosine triphosphate (ATP) contents of islets during 3-day culture and stimulation index in response to glucose after culture. Immunosuppressive effects in vivo were tested in a Wistar-to-B6 islet xenotransplantation model. MZ was administered continuously for 28 days subcutaneously or intramuscularly. MZ inhibited MLR response by approximately 50% at 0.1 μg/ml. ATP contents decreased with MZ >100 μg/ml, while stimulation index was maintained. Continuous infusion of MZ at 10 mg/kg maintained blood concentrations at 0.13-0.19 μg/ml, while intramuscular injection of MZ at 100 mg/kg/day (peak 520 μg/ml at 1 h postinjection) resulted in below measurable levels (<0.03 μg/ml) within 24 h. Graft survival was significantly prolonged following continuous infusion of 10 mg/kg/day compared to controls (31.0 ± 9.5 vs. 13.2 ± 5.2 days; p = 0.002). Furthermore, animals with intramuscular injection at doses of 3.2, 10, or 100 mg/kg/day showed significantly longer graft survival (20.0 ± 7.5, 22.0 ± 7.31, and 24.5 ± 8.1 days, respectively; p < 0.05 each). Histological examination showed significant suppression of lymphocyte infiltration by MZ administration. MZ showed immunosuppressive effects in an experimental islet xenotransplantation model without adverse effects on endocrine function of islet grafts.

Implication of mitochondrial cytoprotection in human islet isolation and transplantation

Islet transplantation is a promising therapy for type 1 diabetes mellitus; however, success rates in achieving both short- and long-term insulin independence are not consistent, due in part to inconsistent islet quality and quantity caused by the complex nature and multistep process of islet isolation and transplantation. Since the introduction of the Edmonton Protocol in 2000, more attention has been placed on preserving mitochondrial function as increasing evidences suggest that impaired mitochondrial integrity can adversely affect clinical outcomes. Some recent studies have demonstrated that it is possible to achieve islet cytoprotection by maintaining mitochondrial function and subsequently to improve islet transplantation outcomes. However, the benefits of mitoprotection in many cases are controversial and the underlying mechanisms are unclear. This article summarizes the recent progress associated with mitochondrial cytoprotection in each step of the islet isolation and transplantation process, as well as islet potency and viability assays based on the measurement of mitochondrial integrity. In addition, we briefly discuss immunosuppression side effects on islet graft function and how transplant site selection affects islet engraftment and clinical outcomes.

Encapsulated islets transplantation: Past, present and future

Islet transplantation could become an ideal treatment for severe diabetes to prevent hypoglycemia shock and irreversible diabetic complications, once some of the major and unresolved obstacles are overcome, including limited donor supplies and side effects caused by permanent immunosuppressant use. Approximately 30 years ago, some groups succeeded in improving the blood glucose of diabetic animals by transplanting encapsulated islets with semi-permeable membranes consisting of polymer. A semi-permeable membrane protects both the inner islets from mechanical stress and the recipient's immune system (both cellular and humoral immunities), while allowing bidirectional diffusion of nutrients, oxygen, glucose, hormones and wastes, i.e., immune-isolation. This device, which enables immune-isolation, is called encapsulated islets or bio-artificial pancreas. Encapsulation with a semi-permeable membrane can provide some advantages: (1) this device protects transplanted cells from the recipient's immunity even if the xenogeneic islets (from large animals such as pig) or insulin-producing cells are derived from cells that have the potential for differentiation (some kinds of stem cells). In other words, the encapsulation technique can resolve the problem of limited donor supplies; and (2) encapsulation can reduce or prevent chronic administration of immunosuppressants and, therefore, important side effects otherwise induced by immunosuppressants. And now, many novel encapsulated islet systems have been developed and are being prepared for testing in a clinical setting.

Rapamycin causes upregulation of autophagy and impairs islets function both in vitro and in vivo

Autophagy is a lysosomal degradation process of redundant or faulty cell components in normal cells. However, certain diseases are associated with dysfunctional autophagy. Rapamycin, a major immunosuppressant used in islet transplantation, is an inhibitor of mammalian target of rapamycin and is known to cause induction of autophagy. The objective of this study was to evaluate the in vitro and in vivo effects of rapamycin on pancreatic β cells. Rapamycin induced upregulation of autophagy in both cultured isolated islets and pancreatic β cells of green fluorescent protein-microtubule-associated protein 1 light chain 3 transgenic mice. Rapamycin reduced the viability of isolated β cells and down-regulated their insulin function, both in vitro and in vivo. In addition, rapamycin increased the percentages of apoptotic β cells and dead cells in both isolated and in vivo intact islets. Treatment with 3-methyladenine, an inhibitor of autophagy, abrogated the effects of rapamycin and restored β-cell function in both in vitro experiments and animal experiments. We conclude that rapamycin-induced islet dysfunction is mediated through upregulation of autophagy, with associated downregulation of insulin production and apoptosis of β cells. The results also showed that the use of an autophagy inhibitor abrogated these effects and promoted islet function and survival. The study findings suggest that targeting the autophagy pathway could be beneficial in promoting islet graft survival after transplantation.

AEB071 (sotrastaurin) does not exhibit toxic effects on human islets in vitro, nor after transplantation into immunodeficient mice

AEB071 (AEB, sotrastaurin), a specific inhibitor of protein kinase C, reduces T-lymphocyte activation and cytokine release. AEB delays islet allograft rejection in rats and prevents rejection when combined with cyclosporine. Since many immunosuppressive agents have toxic effects on the function of transplanted islets, we investigated whether this was also the case with AEB. Human islets were transplanted into Rag-knockout mice randomly assigned to vehicle control, AEB or sirolimus treatment groups. Non-fasting blood glucose levels, body weight and glucose tolerance was measured in recipients. In a separate experiment, human islets were cultured in the presence of AEB and assayed for glucose dependent insulin secretion and level of β-cell apoptosis. Eighty-six percent of the AEB-treated recipients achieved normoglycemia following transplant (compared with none in sirolimus-treated group, p < 0.05). AEB-treated recipients exhibited similar glucose homeostasis as vehicle-treated controls, which was better than in sirolimus-treated recipients. Human islets cultured with AEB showed similar rates of β-cell apoptosis (p = 0.98 by one-way ANOVA) and glucose stimulated insulin secretion (p = 0.15) as those cultured with vehicle. These results suggest that AEB is not associated with toxic effects on islet engraftment or function. AEB appears to be an appropriate immunosuppressive candidate for clinical trials in islet transplantation.

Neuroprotective, immunosuppressant and antineoplastic properties of mTOR inhibitors: current and emerging therapeutic options

The acronym mTOR defines a family of serine-threonine protein kinase called mammalian target of rapamycin. The major role of these kinases in the cell is to merge extracellular instructions with information about cellular metabolic resources and to control the rate of anabolic and catabolic processes accordingly. In mammalian cells mTOR is present in two distinct heteromeric protein complexes commonly referred to as mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), involved in the control of a wide variety of cellular processes. It has been recently reported that compounds acting modulating mTOR activity, beside mediating the well recognized processes exploited in the anticancer and immunosuppressant effects, are provided with neuroprotective properties. In fact, mTOR is involved in the mechanism of PI3K/Akt-induced upregulation of glutamate transporter 1, GLT1, that is linked to several neuronal disorders such as stroke, Alzheimer's disease, and amyotrophic lateral sclerosis. Furthermore, in adult brain mTOR is crucial for numerous physiological processes such as synaptic plasticity, learning, memory, and brain control of food uptake. Moreover, the activation of mTOR pathway is involved in neuronal development, dendrite development and spine morphogenesis.

Rotational co-culture of clonal β-cells with endothelial cells: effect of PPAR-γ agonism in vitro on insulin and VEGF secretion

AIM

Delayed graft revascularization impedes the success of human islet transplantation. This study utilized rotational co-culture of insulin secreting β-cells with human umbilical vein endothelial cells (HUVECs) and a peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist to promote insulin and vascular endothelial growth factor (VEGF) secretory function.

METHODS

Clonal BRIN-BD11 (D11) cells were maintained in static culture (SC) and rotational culture (RC) ± HUVEC and ± the TZD (thiazolidinedione) rosiglitazone (10 mmol/l) as a specific PPAR-γ agonist. HUVECs were cultured in SC and RC ± D11 and ± TZD. D11 insulin secretion was induced by static incubation with low glucose (1.67 mmol/l), high glucose (16.7 mmol/l) and high glucose with 10 mmol/l theophylline (G+T) and assessed by enzyme-linked immunosorbent assay (ELISA). HUVEC proliferation was determined by ATP luminescence, whereas VEGF secretion was quantified by ELISA. Co-cultured cells were characterized by immunostaining for insulin and CD31.

RESULTS

D11 SC and RC showed enhanced insulin secretion in response to 16.7 mmol/l and G+T (p < 0.01); without significant alteration by the TZD. Co-culture with HUVEC in SC and RC also increased D11 insulin secretion when challenged with 16.7 mmol/l and G+T (p < 0.01), and this was slightly enhanced by the TZD. The presence of HUVEC increased D11 SC and RC insulin secretion in response to high glucose and G+T, respectively (p < 0.01). Addition of the TZD increased SC and RC HUVEC ATP content (p < 0.01) and VEGF production (p < 0.01) in the presence and absence of D11 cells.

CONCLUSIONS

Rotational co-culture of insulin secreting cells with endothelial cells, and exposure to a PPAR-γ agonist may improve the prospects for graft revascularization and function after implantation.

Mammalian target of rapamycin and diabetes: what does the current evidence tell us?

New-onset diabetes mellitus after transplantation (NODAT) is a serious complication in organ transplantation; not only does it enhance the risk of graft dysfunction, it also increases cardiovascular morbidity and mortality. The mammalian target of rapamycin (mTOR) is regulated independently by insulin, amino acids, and energy sufficiency. It integrates signal from growth factors, hormones, nutrients, and cellular energy levels to regulate protein translation and cell growth, proliferation, and survival. In addition, mTOR generates an inhibitory feedback loop on insulin receptor substrate (IRS) proteins. Therefore, it was suggested that mTOR might link nutrient excess with both obesity and insulin resistance. In this review, we summarize the role of mTOR and its inhibitor sirolimus (SRL) on chronic hyperglycemia and insulin resistance in beta cells, adipose tissue, liver, and muscle. We further hypothesize, based on data from the literature and generated in our laboratory, that SRL could counteract the development of NODAT in stable glucose homeostasis due to its positive effects on insulin-stimulated glucose uptake, whereas in conditions that require an adaptive beta cell proliferation (such as pregnancy and weight increase), the administration of SRL might have effects that would promote the development of NODAT. Therefore, it seems crucial for patient outcome to consider these potentially contrasting effects of SRL.

Long-term treatment of sirolimus but not cyclosporine ameliorates diabetic nephropathy in the rat

BACKGROUND

Not just de novo induction of diabetes mellitus, but also the progression of diabetic nephropathy may be enhanced under immunosuppressive therapy after organ transplantation. We evaluated whether sirolimus (SRL) or cyclosporine A (CsA) therapy would be a superior immunosuppressant in streptozotocin-induced diabetic nephropathy.

METHODS

Diabetes was induced by intravenous injection of streptozotozin (60 mg/kg body weight) in 26 male Sprague-Dawley rats. Eight days after diabetes induction, animals were divided into three groups, which were treated with placebo (n=8), SRL (n=9), or CsA (n=9). Six nondiabetic placebo-treated rats were included as controls.

RESULTS

After 19 weeks of diabetes, SRL significantly decreased fibrosis as assessed by periodic acid Schiff staining and by specific extracellular matrix proteins such as fibronectin and laminin at messenger RNA and protein level compared with the diabetic placebo group. SRL ameliorated renal inflammation, glomerular hypertrophy, and podocyte loss as indicated by morphometric and immunohistological analysis. SRL lowered expression and activity of glomerular transforming growth factor-beta1/2 and vascular endothelial growth factor, all of which are considered central cytokines in the pathogenesis of diabetic nephropathy. In contrast, calcineurin phosphatase inhibition through CsA did not ameliorate any of the features of diabetic nephropathy compared with placebo treatment but slightly aggravated glomerular fibrosis without affecting transforming growth factor-beta1/2 or vascular endothelial growth factor.

CONCLUSION

Compared with CsA, SRL by anti-inflammatory, antifibrotic, and podocyte-protective effects clearly seems to be the superior treatment of prevention or amelioration of diabetic nephropathy in the rat.

Local expression of B7-H4 by recombinant adenovirus transduction in mouse islets prolongs allograft survival

BACKGROUND

Allogeneic pancreatic islet transplantation has the potential to cure type 1 diabetes. One of the barriers to islet transplantation is the alloreactive T-cell response between donors and recipients. Costimulatory molecules, which play a major role in the regulation of the immune response to antigens during graft rejection, may be used to inhibit allograft destruction. B7-H4 is one such member in the costimulatory family, which has established negative regulatory function of T-cell responses.

METHODS

To determine whether local expression of B7-H4 protein can protect beta cells from damage in islet allotransplantation, we have constructed a recombinant adenovirus expressing a B7-H4 complementary deoxyribonucleic acid (Ad-B7-H4). To study the in vivo effects of B7-H4 expression on islet graft survival, adenovirus-transduced islets from donor Balb/c mice were transplanted into streptozotocin-diabetic C57BL/6 mice (n=12).

RESULTS

Expression of B7-H4 in islets by Ad-B7-H4 transduction at an optimized condition did not inhibit glucose-stimulated insulin secretion of the treated islets. The recipient mice transplanted with Ad-B7-H4-transduced islets established euglycemia for a longer time (mean 56.5 days), compared with control mice transplanted with Ad-LacZ-transduced islets (mean 14.5 days, [n=12, P<0.001]). Splenocytes isolated from the recipients of Ad-B7-H4-transduced islets showed hyporesponsiveness to alloantigenic stimulation, compared with control recipients. CD45 and insulin staining of the graft transplanted with Ad-B7-H4-transduced islets indicated the preservation of beta cells and decrease of infiltrating immune cells.

CONCLUSIONS

Local expression of B7-H4 prolongs islet allograft survival in vivo, suggesting translational potential for beta-cell replacement with reduced immune injury.

Tracking intrahepatically transplanted islets labeled with Feridex-polyethyleneimine complex using a clinical 3.0-T magnetic resonance imaging scanner

OBJECTIVES

To evaluate the images acquired with a clinical 3.0-T magnetic resonance imaging machine as the quantification of transplanted and surviving islets in vivo.

METHODS

Polyethyleneimine (PEI) was introduced to increase the labeling efficiency of Feridex, a dextran-coated superparamagnetic iron oxide. Allogeneic (Lewis-to-Wistar) and syngeneic (Wistar-to-Wistar) intraheptatic islet transplantations were performed to study the relationship among magnetic resonance imaging, metabolic monitoring, and pathological examination.

RESULTS

After receiving Feridex-PEI-labeled islets, dark voids could be observed in the livers of both groups, accompanied with a significant decrease in liver/muscle intensity ratio from 1.25 +/- 0.03 to 1.09 +/- 0.05 (P < 0.01). One week after transplantation, islet grafts were rejected in the allogeneic group. Rapid disappearance of dark voids and a significant increase of liver/muscle ratio were observed. No islet grafts could be found in the paraffin sections of livers by that time. Meanwhile, in the syngeneic group, islet grafts survived indefinitely. Dark voids persisted and low liver/muscle ratios retained. The fact that the dark voids represented the labeled islets was confirmed by combined staining of insulin activity and Prussian blue.

CONCLUSIONS

Either spot counting or signal intensity measurement provides a perfect quantification of transplanted and surviving islets in vivo. Feridex-PEI provides an effective and safe way to label islets.

Stable renal function after islet transplantation: importance of patient selection and aggressive clinical management

BACKGROUND

Proteinuria development and decrease in glomerular filtration rate (GFR) have been observed after successful islet transplantation. The aim of this study was to determine clinical, laboratory, and immunosuppressant-related factors associated with kidney dysfunction in islet transplant recipients.

METHODS

A retrospective cohort study was conducted in 35 subjects submitted to pancreatic islet transplantation for treatment of unstable type 1 diabetes mellitus. Demographic, anthropometrical, and laboratory data, as well as immunosuppressive and antihypertensive therapy were recorded. Kidney function was assessed by albuminuria and estimated GFR (eGFR), calculated by modification of diet in renal disease formula.

RESULTS

Age was the only independent risk factor for low eGFR (<60 mL/min/1.73 m2) (odds ratio [OR]=1.78 [1.22-2.61]). Low-density lipoprotein cholesterol (OR=2.90 [1.37-6.12]) and previous microalbuminuria (OR=6.42 [1.42-29.11]) were risk factors for transient macroalbuminuria. Interestingly, tacrolimus was a protective factor for macroalbuminuria (OR=0.12 [0.06-0.26]). Six of 30 (20%) normoalbuminuric subjects at baseline progressed to microalbuminuria. No subject developed sustained macroalbuminuria. Surprisingly, overall eGFR remained stable during follow-up (before transplant: 74.0+/-2.0; during immunosuppressive therapy: 75.4+/-2.8; and after withdrawal: 76.3+/-5.3 mL/min/1.73 m2; P>0.05). Even subjects with low eGFR and microalbuminuria at baseline (n=10) maintained stable values posttransplantation (61.13+/-3.25 mL/min/1.73 m2 vs. 63.32+/-4.36 mL/min/1.73 m2, P=0.500).

CONCLUSIONS

Kidney function remained stable after islet transplantation alone. The unchanged kidney function found in this sample may be attributed to healthier kidney status at baseline and possibly to prompt treatment of modifiable risk factors. Aggressive treatment of risk factors for nephropathy, such as blood pressure, low-density lipoprotein cholesterol, and careful tacrolimus levels monitorization, should be part of islet transplant recipient care.

Rapamycin inhibits growth factor-induced cell cycle regulation in pancreatic beta cells

A progressive decline in islet function is a major obstacle to success of islet transplantation. The cause of this decline is islet function is unclear, but immunosuppressive agents may contribute. Insulin-like growth factor-I (IGF-I) and betacellulin are important for islet cell survival and/or proliferation. In the present study, we performed studies of IGF-I and betacellulin on progression of islet cells through the cell cycle and the impact of immunosuppressive agents. Treatment of INS-1 cells for 24 hours with 20 ng/mL betacellulin or 50 ng/mL IGF-1 increased cells in S phase by ~2-fold. Treatment of INS-1 cells with IGF-I or betacellulin also increased cyclin D1 expression and nuclear exclusion of the cyclindependent kinase inhibitors p21(Cip1) and p27(Kip1). In INS-1 cells and islets, betacellulin- and IGF-I increased the increase in p70(s6 kinase) phosphorylation stimulated by betacellulin- and IGF-I in INS-1 cells. Rapamycin also inhibited betacellulin- and IGF-I IN IGF-1 cells. Rapamycin also inhibited betacellulin- and IGF-I-induced entry of cells into S phase and 5'-Bromo-2'-deoxyuridine incorporation as well as the effect of betacellulin and IGF-I on cyclin D1 expression and nuclear exclusion of p21(Cip1) and p(27Kip1). Together, these data suggest that the effect of betacellulin and IGF-I on islet cell growth and proliferation is mediated, in part, via signaling through mammalian target of rapamycin. As rapamycin is used to treat islet transplant recipients, these results suggest that rapamycin could have deleterious effects on islet proliferation and function over time.

mTOR regulates expression of slit diaphragm proteins and cytoskeleton structure in podocytes

The immunosuppressive mammalian target of rapamycin (mTOR) inhibitors can cause proteinuria, especially in kidney and heart transplanted patients. Podocytes play a major role in establishing the selective permeability of the blood-urine filtration barrier. Damage of these cells leads to proteinuria, a hallmark of most glomerular diseases. Interestingly, podocyte damage and focal segmental glomerulosclerosis can occur after treatment with an mTOR inhibitor in some transplant patients. To investigate the mechanisms of mTOR inhibitor-induced podocyte damage, we analyzed the effect of rapamycin on mTOR signaling and cellular function in human podocytes. We found that prolonged rapamycin treatment reduced the expression of total mTOR, which correlates with diminished levels of mTOR phosphorylation at Ser(2448) and Ser(2481). In addition, treatment with rapamycin reduced rictor expression and mTORC2 formation, resulting in a reduced phosphorylation of protein kinase B at Ser(473). The expression level of the slit-diaphragm proteins nephrin and transient receptor potential cation channel 6 as well as the cytoskeletal adaptor protein Nck significantly decreased. Moreover, rapamycin reduced cell adhesion and cell motility, which was accompanied by an enhanced formation of dot-like actin-rich structures. Our data provide new molecular insights explaining which pathways and molecules are affected in podocytes by an imbalanced mTOR function because of rapamycin treatment.

Rapamycin in islet transplantation: friend or foe?

The Edmonton protocol was undoubtedly a major step forward in the history of islet transplantation. Its immunosuppression regimen was largely based on the mTOR inhibitor rapamycin (sirolimus), which remains the most frequently used immunosuppressive drug in clinical islet transplant protocols. As time reveals the somewhat disappointing long-term results achieved with the Edmonton protocol, a number of publications have appeared addressing the potential beneficial or deleterious role of rapamycin on islet cell engraftment, function survival and regeneration, as well as on its side-effects in human subjects. This paper reviews the sometimes contradictory evidence on the impact of rapamycin in islet transplantation.

Differential effects of rapamycin in anti-GBM glomerulonephritis

The immunosuppressive mammalian target of rapamycin inhibitor rapamycin is widely used in solid-organ transplantation, but the effect of rapamycin on kidney disease is controversial. This study evaluated the effect of rapamycin in the autologous phase of anti-glomerular basement membrane (anti-GBM) glomerulonephritis. Disease was induced by preimmunizing the animals with rabbit IgG 5 d before administration of rabbit anti-mouse GBM antiserum. When rapamycin was started on the day of immunization (group 1), mice were protected from glomerulonephritis, suggested by a dramatic decrease in albuminuria, influx of inflammatory cells, and Th1-cytokine expression in the kidneys. Activation of T cells and production of autologous mouse anti-rabbit IgG were also significantly reduced in rapamycin-treated animals. In contrast, when rapamycin was started 14 d after immunization (group 2), mice had a significant increase in albuminuria and renal infiltration of inflammatory cells compared with vehicle-treated animals, and there were no differences in T and B cell responses. A significant decrease in vascular endothelial growth factor-A and an increase in IL-6 were detected in kidneys of these rapamycin-treated mice. In conclusion, rapamycin has the potential to significantly reduce the B and T cell responses and thereby protect from glomerulonephritis when administered early in disease. Once disease is established, however, rapamycin seems to worsen glomerulonephritis by disturbing the endothelial cell/vascular endothelial growth factor system in the kidney.

Rapamycin impairs in vivo proliferation of islet beta-cells

BACKGROUND

Progressive graft dysfunction is commonly observed in recipients of islet allografts treated with high doses of rapamycin. This study aimed at evaluating the effect of rapamycin on pancreatic islet cell proliferation in vivo.

METHODS

The murine pregnancy model was utilized, since a high rate of beta-cell proliferation occurs in a well-defined time frame. Rapamycin (0.2 mg/kg/day) was given to C57BL/6 mice for 5-7 days starting on day 7.5 of pregnancy. Cell proliferation was evaluated by detection of bromodeoxyuridine incorporation by immunohistochemistry.

RESULTS

Pregnancy led to increased beta-cell proliferation and islet yield with skewing in islet size distribution as well as higher pancreatic insulin content, when compared to that of nonpregnant females. These effects of pregnancy on beta-cell proliferation and mass were significantly blunted by rapamycin treatment. Minimal effect of rapamycin was observed on islet function both in vivo and in vitro. Rapamycin treatment of islets in vitro resulted in reduced p70s6k phosphorylation, which was paralleled by increased ERK1/2 phosphorylation.

CONCLUSIONS

Rapamycin treatment reduces the rate of beta-cell proliferation in vivo. This phenomenon may contribute to impair beta-cell renewal in transplanted patients and to the progressive dysfunction observed in islet graft recipients.