Islet transplantation as a treatment for diabetes - a work in progress

Effects of mycophenolate mofetil vs cyclosporine administration on graft survival and function after islet allotransplantation in diabetic rats

AIM: To develop an experimental model of islet allotran-splantation in diabetic rats and to determine the positive or adverse effects of MMF as a single agent.

METHODS: Thirty-six male Wistar rats and 18 male Lewis rats were used as recipients and donors respectively. Diabetes was induced by the use of streptozotocin (60 mg/kg) intraperitoneally. Unpurified islets were isolated using the collagenase digestion technique and transplanted into the splenic parenchyma. The recipients were randomly assigned to one of the following three groups: group A (control group) had no immunosuppression; group B received cyclosporine (CsA) (5 mg/kg); group C received mycophenolate mofetil (MMF) (20 mg/kg). The animals were killed on the 12^th d. Blood and grafted tissues were obtained for laboratory and histological assessment.

RESULTS: Median allograft survival was significantly higher in the two therapy groups than that in the controls (10 and 12 d for CsA and MMF respectively vs 0 d for the control group, P<0.01). No difference in allograft survival between the CsA and MMF groups was found. However, MMF had less renal and hepatic toxicity and allowed weight gain.

CONCLUSION: Monotherapy with MMF for immunosu-ppression was safe in an experimental model of islet allotransplantation and was equally effective with cyclosporine, with less toxicity.

Assessment of pancreatic islet mass after islet transplantation using in vivo bioluminescence imaging

BACKGROUND

Pancreatic islet transplantation is an emerging therapy for type 1 diabetes, but it is difficult to assess islets after transplantation and thus to design interventions to improve islet survival.

METHODS

To image and quantify islets, the authors transplanted luciferase-expressing murine or human islets (by adenovirus-mediated gene transfer) into the liver or beneath the renal capsule of immunodeficient mice and quantified the in vivo bioluminescence imaging (BLI) of mice using a cooled charge-coupled device camera and digital photon-counting image analysis. To account for variables that are independent of islet mass such as transplant site, animal positioning, and wound healing, the BLI of transplanted islets was calibrated against measurement of luminescence of an implanted bead emitting a constant light intensity.

RESULTS

BLI of mice bearing islet transplants was seen in the expected anatomic location, was stable for more than 8 weeks after transplantation, and correlated with the number of islets transplanted into the liver or kidney. BLI of the luminescent bead and of transplanted islets in the kidney was approximately four times greater than when transplanted in the liver, indicating that photon emission is dependent on optical absorption of generated light and thus light source location.

CONCLUSION

In vivo BLI allows for quantitative, serial measurements of pancreatic islet mass after transplantation and should be useful in assessing interventions to sustain or increase islet survival of transplanted islets.

A perspective on pancreatic stem/progenitor cells

The prevalence of both type 1 and type 2 diabetes mellitus is increasing throughout the world along with the ensuant morbidity and early mortality because of premature microvascular and macrovascular disease. Current insulin and drug therapies control diabetes, but do not cure it. Cell-based therapies offer the possibilities of a permanent cure for diabetes. Recently, success in the transplantation of pancreatic islets in the livers of type 1 diabetics has afforded the opportunity for a potential cure. However, the severe shortage of donor islets for transplantation limits the usefulness of this therapy. One approach is to exploit the use of stem cells, either embryo-derived or adult tissue-derived, as substrates to create islet tissue suitable for transplantation. Cells isolated from embryo blastocysts and from adult pancreas, liver, and bone marrow can be expanded extensively in vitro and differentiated into islet-like clusters that produce insulin, and, in some instances, can achieve glycemic control when transplanted into streptozotocin-induced diabetic mice. It is, now, also possible to envision the direct systemic administration of stem cells that would home in on and regenerate injured islets, or to administer stem cell stimulators that would enhance endogenous pancreatic stem cells to expand and differentiate into functional, insulin-producing beta-cells. This perspective discusses the potential applications of cellular medicines, in the new discipline of regenerative medicine, to achieve a cure for diabetes.

Embryonic stem cells and islet replacement in diabetes mellitus

Transplantation of functional islets of Langerhans may emerge as a useful therapy for some patients with type 1 diabetes mellitus (DM), but donor islet shortages motivate the search for new sources of transplantable islets. Pluripotent embryonic stem (ES) cells are expandable in culture and have the potential to give rise to all cell types in the body. The recent isolation of pluripotent ES cells from humans has generated excitement over the possibility of engineering glucose-responsive islet replacement tissue from these cells in large quantities. In this study, we review the recent advances in generating insulin-producing cells (IPC) from mouse and human ES (hES) cells.

Toxin-based selection of insulin-producing cells with improved defense properties for islet cell transplantation

Insulin-producing pancreatic beta-cells are known to be extremely susceptible to destruction, primarily by autoimmune mechanisms, infectious agents, and by chemical toxins that cause overt type I diabetes. As development of highly protected insulin-producing cells would be important for successful cell therapy of diabetic patients, gene transfection technique was utilized by several investigators in order to improve the defense properties of transplanted cells. In this article, we summarize other approaches based on a selection strategy that has been developed in our laboratory and by other research groups that engineer pancreatic beta-cells to provide protection against diabetogenic toxins (streptozotocin and alloxan), oxidative stress and cytokines. Selection strategies based on acute repeated or long-term continuous treatment of cell lines with cytotoxic agents have resulted in the selection of highly resistant cell subpopulations. We discuss possible involvement of different expression of cytoprotective genes in the selection of cell subpopulations, which demonstrate a broad spectrum of resistance. Importantly, toxin-based selection did not impair functional activity of the cells as it was shown in vitro. In addition, selected cells preserved their improved metabolic characteristics following encapsulation in alginate and subsequent implantation in diabetic animals. Identifying the mechanisms through which cell defense properties act will help clarify the process responsible for beta-cell regeneration in type I diabetes patients. Such knowledge might be useful in developing strategies focusing on the regeneration of beta-cell resistant populations.

Parasympathetic innervation and function of endocrine pancreas requires the glial cell line-derived factor family receptor alpha2 (GFRalpha2)

Vagal parasympathetic input to the islets of Langerhans is a regulator of islet hormone secretion, but factors promoting parasympathetic islet innervation are unknown. Neurturin signaling via glial cell line-derived neurotrophic factor family receptor alpha2 (GFRalpha2) has been demonstrated to be essential for the development of subsets of parasympathetic and enteric neurons. Here, we show that the parasympathetic nerve fibers and glial cells within and around the islets express GFRalpha2 and that islet parasympathetic innervation in GFRalpha2 knockout (KO) mice is reduced profoundly. In wild-type mice, neuroglucopenic stress produced a robust increase in plasma levels of islet hormones. In the GFRalpha2-KO mice, however, pancreatic polypeptide and insulin responses were completely lost and glucagon response was markedly impaired. Islet morphology and sympathetic innervation, as well as basal secretions of the islet hormones, were unaffected. Moreover, a glucose tolerance test failed to reveal differences between the genotypes, indicating that direct glucose-stimulated insulin secretion was not affected by GFRalpha2 deficiency. These results show that GFRalpha2 signaling is needed for development of the parasympathetic islet innervation that is critical for vagally induced hormone secretion. The GFRalpha2-KO mouse represents a useful model to study the role of parasympathetic innervation of the endocrine pancreas in glucose homeostasis.

Pancreas Islet Transplantation in Patients With Type 1 Diabetes Mellitus After Kidney Transplantation

Diabetic patients with end-stage renal disease have a high mortality rate. A combined kidney-pancreas transplant is associated with greater life expectancy. Pancreas islet transplantation is an alternative involving a lower degree of morbidity. We present two patients, of 41 and 37 years of age, with a long history of diabetes mellitus (C-peptide negative), both with a previous kidney transplant, who had been treated with 22 and 28 U of insulin/d, respectively. Both patients had frequent episodes of unawareness hypoglycemia. Pancreatic islets were infused to a total of 7809 and 19,180 IE/kg, respectively. Basal posttransplant C peptide levels were 2.9 and 1.3 ng/mL. After the implant, one patient required occasional doses of insulin, and the other patient more than 50% reduced dose. After the first implant neither patient had any episodes of unawareness hypoglycemia. HbA1c at 4 months were 6.2% and 6.9%. There were no transplant-related complications.

PDX-1/VP16 fusion protein, together with NeuroD or Ngn3, markedly induces insulin gene transcription and ameliorates glucose tolerance

Diabetes is the most prevalent and serious metabolic disease, and the number of diabetic patients worldwide is increasing. The reduction of insulin biosynthesis in pancreatic beta-cells is closely associated with the onset and progression of diabetes, and thus it is important to search for ways to induce insulin-producing cells in non-beta-cells. In this study, we showed that a modified form of the pancreatic and duodenal homeobox factor 1 (PDX-1) carrying the VP16 transcriptional activation domain (PDX-1/VP16) markedly increases insulin biosynthesis and induces various pancreas-related factors in the liver, especially in the presence of NeuroD or neurogenin 3 (Ngn3). Furthermore, in streptozotocin-induced diabetic mice, PDX-1/VP16 overexpression, together with NeuroD or Ngn3, drastically ameliorated glucose tolerance. Thus PDX-1/VP16 expression, together with NeuroD or Ngn3, markedly induces insulin gene transcription and ameliorates glucose tolerance. This approach warrants further investigation and may have utility in the treatment of diabetes.

La necesaria coordinación del trasplante de páncreas, islotes y riñón en España

We describe the historical background and current situation of pancreatic and islet cell transplantations in Spain and other countries, as well as their relationship with replacement therapy in chronic renal failure in diabetic kidney transplant recipients. Emphasis is placed on the improved results achieved in the last decade, the increased demand for these techniques and the need for highly efficient organization of these transplantations to optimize the available resources, which are clearly limited in terms of both donation and finances. The process initiated by the National Transplantation Organization (NTO) to coordinate all these activities and the preparation of a consensus document endorsed by all the professional bodies involved is described.

A crucial role of MafA as a novel therapeutic target for diabetes

MafA, a recently isolated pancreatic beta-cell-specific transcription factor, is a potent activator of insulin gene transcription. In this study, we show that MafA overexpression, together with PDX-1 (pancreatic and duodenal homeobox factor-1) and NeuroD, markedly increases insulin gene expression in the liver. Consequently, substantial amounts of insulin protein were induced by such combination. Furthermore, in streptozotocin-induced diabetic mice, MafA overexpression in the liver, together with PDX-1 and NeuroD, dramatically ameliorated glucose tolerance, while combination of PDX-1 and NeuroD was much less effective. These results suggest a crucial role of MafA as a novel therapeutic target for diabetes.

Psychosocial aspects of xenotransplantation: Survey in adolescent recipients of porcine islet cells

INTRODUCTION

Transplantation is a process with several psychosocial challenges. Regarding the case of xenotransplantation, the perceived similarity between humans and pigs may be stressful. Adjustment disorders have been reported among transplantation recipients. We sought to assess the psychosocial aspects of xenotransplantation among porcine islet-cell recipients and their efforts to adapt themselves to this condition.

MATERIAL AND METHODS

Ten insulin-dependent diabetes mellitus patients aged 14.58 +/- 7.93 who received porcine islet-cells were included. The bioartificial steel/fibrous tissue chamber method was used. All patients and their relatives were interviewed about their expectations, overall functioning, and experiences. The quality of life, enjoyment, and satisfaction scale and the hospital anxiety and depression scales were used. A 1-year follow-up was done.

RESULTS

Their motivation was centered on autonomy; there were no troubles regarding the graft origin. Xenotransplantation was perceived with pragmatism, seeing pigs as an unlimited resource. The patients with best outcomes also had the greatest improvements in several quality of life areas (QOL) while the medium responders had fewer QOL improvements. The nonresponders experienced mainly frustration. Parents' concerns were not related to their children's health but to their recently gained autonomy.

CONCLUSIONS

In addition to enthusiasm, the perception of animals as an unlimited source of organs may affect patient compliance; in this group, xenotransplantation was seen as using as a long-lasting drug, with chamber walls considered as a physical, immunologic, and, in certain manner, a psychological barrier.

Mortality assessment for pancreas transplants

We determined and compared the mortality of pancreas transplant recipients and of patients on the pancreas waiting lists by using United Network for Organ Sharing (UNOS) and International Pancreas Transplant Registry (IPTR) data. From January 1, 1995, through May 31, 2003, a total of 12,478 patients were listed for a simultaneous pancreas-kidney (SPK) transplant; 2942 for a pancreas after (previous) kidney transplant (PAK); and 1207 for a pancreas transplant alone (PTA). In this retrospective observational cohort study, patients with multiple listings at different transplant centers and patients who changed transplant centers were counted only once. The Social Security Death Master File (SSDMF) and the UNOS kidney transplant database were used to update mortality information. By univariate analyses, 4-year patient survival rates on the waiting lists (vs. post-transplant), in the SPK category, were 58.7% (vs. 90.3%); in the PAK category, 81.7% (vs. 88.3%); and in the PTA category, 87.3% (vs. 90.5%). Up to one-third of recipient deaths after post-transplant day 90 were not related to the transplant procedure itself. Multivariate analyses showed that the overall mortality in all three categories was not increased after transplantation (for SPK recipients only, it was significantly decreased). In summary, the mortality for solitary pancreas transplant recipients is not higher than for wait-listed patients.

Pancreatic islet transplantation

Islet transplantation offers hope to many patients with diabetes, who envision a life free of glucose checks and insulin injections. What are the barriers to its widespread implementation?

Selection of diabetic patients for islet transplantation. A single-center experience

OBJECTIVE

Since the Edmonton protocol, islet transplantation (IT) offers the prospect of adequate glycemic control with no major surgical risk. In our single-center experience of IT, we studied the recruitment of eligible diabetic patients.

METHODS

Between 1998 and 2002, we screened 79 diabetic patients that were divided into 2 groups according to their renal status: 41 were not receiving dialysis (ND) while 38 were receiving ongoing dialysis (D).

RESULTS

In the ND group, 20 patients initiated the contact with our team, 8 patients were recruited during hospitalization for very poor glycemic imbalance, and 13 were referred by their diabetologist. 14/41 (34%) patients were ineligible for IT either because of very good glycemic balance, detectable C-peptide (C-p), kidney or liver problems, or plans for future pregnancy. 16/41 (39%) did not wish to proceed, 7 of whom were more interested by a pump. 11/41 (27%) were eligible, among which 8 are currently being assessed, 1 is on the waiting list and 2 have been transplanted. In the D group, 17/38 (45%) had a detectable C-p and received a kidney graft alone. Among the remaining 21 C-p negative diabetic patients, 3 were not eligible for kidney transplantation mainly for psychological reasons, and 4 were enlisted for kidney+pancreas transplantation. The remaining 14 C-p negative patients were kidney-transplanted. Among them, 6 were not eligible for IT, mainly for lack of motivation, slightly positive C-p stimulation tests, obesity, cancer, or increased creatininemia. The remaining 8/14 C-p negative kidney-engrafted patients were enlisted for IT. 3 had secondary failure with the pre-Edmonton immunosuppressive (IS) protocol. Five have been transplanted with the Edmonton-like IS regimen.

CONCLUSION

Twenty-five per cent of the 79 patients for whom islet transplantation was considered underwent pregraft assessment and 12% (10 patients, 8 kidney-transplanted and 2 islet alone) of the 79 have been transplanted. The main eligibility criteria were undetectable Cpeptide, normal kidney function, average weight, glycemic imbalance, hypoglycemia unawareness, and glycemic brittleness.

Factors Influencing Quantification of in Vivo Bioluminescence Imaging: Application to Assessment of Pancreatic Islet Transplants

The aim of this study is to determine and characterize factors influencing in vivo bioluminescence imaging (BLI) and apply them to the specific application of imaging transplanted pancreatic islets. Noninvasive quantitative assessment of transplanted pancreatic islets poses a formidable challenge. Murine pancreatic islets expressing firefly luciferase were transplanted under the renal capsule or into the portal vein of nonobese diabetic-severe combined immunodeficiency mice and the bioluminescence was quantified with a cooled charge coupled device camera and digital photon image analysis. The important, but often neglected, effects of wound healing, mouse positioning, and transplantation site on bioluminescence measurements were investigated by imaging a constant emission, isotropic light-emitting bead (lambda = 600) implanted at the renal or hepatic site. The renal beads emitted nearly four times more light than hepatic beads with a smaller spot size, indicating that light absorption and scatter are greatly influenced by the transplant site and must be accounted for in BLI measurements. Detected luminescence decreased with increasing angle between the mouse surface normal and optical axis. By defining imaging parameters such as postsurgical effects, animal positioning, and light attenuation as a function of transplant site, this study develops BLI as a useful imaging modality for quantitative assessment of islets post-transplantation.

Risks and side effects of islet transplantation

Islet transplantation can deliver stable glycemic control, relief from recurrent severe hypoglycemia, and insulin independence. Accessing the portal vein via the percutaneous hepatic approach carries the risk of bleeding, and the infusion of islets a risk of portal vein thrombosis. In the long term, common minor problems with immunosuppression are mouth ulcers, diarrhea, and acne. Longer-term risks include malignancy and serious infection, both rare to date in clinical islet transplantation. Sensitization to donor antigens may also occur. The long-term diabetes complications may stabilize, but of this aspect little is known to date. In the short term, there may be some elevation of serum cholesterol and blood pressure, in some patients there has been a decline in renal function, and in a few, acute retinal bleeds. For most, improvement in glucose control with resolution of glycemic lability and hypoglycemia has been a net benefit.

Transplantation as a therapeutic option for diabetic nephropathy

Diabetic nephropathy affects both type 1 and type 2 diabetic patients with a frequency of 20-30%. The first sign is microalbuminuria within a range of 30-300 mg/24h, frequently evolving towards frank proteinuria and renal failure. Tight glucose control, control of arterial hypertension with the use of ACEi or ARB can retard progression. Once renal failure is established, kidney transplantation can be considered for type 1 and type 2 diabetic patients. Quality of life and survival are improved with this procedure. In type 1 diabetes, simultaneous grafting of a kidney and pancreas considerably improves quality of life and diabetic complications. Surgical and infectious complications are sporadic drawbacks of this procedure. Pancreas transplantation alone (PTA) remains controversial, since a retrospective study in 2003 by Venstrom concluded that survival for PTA patients is worse than for comparable patients remaining on the waiting list. PTA can be considered for type 1 diabetic patients without advanced renal failure with severe and frequent metabolic instability (hypoglycaemia, ketoacidosis). Islet transplantation is still an experimental but promising procedure in highly selected patients, avoiding major abdominal surgery.