Islet transplantation for the cure of diabetes

Fetal Islet Cell Transplants: Promises and Limits of the Experience in the Eastern Countries

The fetal pancreas is a potential source of islet ceils for transplantation. Despite marked advances in experimental islet grafting over the past two decades, successful clinical fetal transplantation seems to be very rare. The possible reasons for the failure of this transplantation are discussed. The review summarizes the development of a method for the isolation of fetal tissue, and the factor influencing the growth and differentiation of isolated fetal islets prior to and after transplantation. Finally, a brief overview is given of the status of clinical human pancreatic transplantation and a possible key to successful grafting.

Cell transplantation in liver-directed gene therapy

Somatic cell gene therapy is a new field of biomedical research that encompasses a variety of traditional basic research and clinical disciplines. This new approach to therapeutics has the potential to prevent, treat, or cure a variety of inherited and acquired diseases. Two divergent strategies of hepatocyte transplantation are being employed in animal models and clinical trials in an attempt to correct genetic deficiencies. Allogeneic hepatocyte transplantation has two main advantages over autologous cell transplantation. First, invasive surgical procedures are not required in the recipient. Second, allogeneic cells can be administered repetitively, so that multiple harvests are not necessary. The major drawbacks to allogeneic hepatocyte transplants are rejection and the risks of immunosuppression. Although there is no clinical experience with the treatment of genetic disease by allogeneic hepatocyte transplantation, a variety of animal models have been characterized, including the Gunn rat (UDP-glucuronosyl transferase deficient), the Nagase analbuminemic rat, and the Watanabe heritable hyperlipidemic rabbit (LDL receptor deficient). The use of genetically corrected autologous cells represents a different and more elegant approach to the correction of inherited disease. A segment of liver is harvested from the affected individual. Recombinant retroviruses are used to transduce normal genes--with a variety of promoter/enhancer constructs--into the patients own hepatocytes. The genetically corrected hepatocytes are then transplanted back into the patient. This approach, known as ex vivo gene therapy, eliminates the risk of rejection and the need for immunosuppression. The safety and efficacy of this approach has been proven in a variety of preclinical animals models, including Watanabe rabbits, dogs, and Papio spp. A clinical trial for the treatment of familial hypercholesterolemia is currently in progress. A number of approaches for the reintroduction of hepatocytes into the recipient have been proposed, including catheter-mediated delivery into the inferior mesenteric vein, the umbilical vein, or into the spleen. Candidate diseases, which are likely to result in the first clinical trials include familial hypercholesterolemia, ornithine transcarbamylase deficiency, Crigler-Najjar syndrome, alpha 1-antitrypsin deficiency, and phenylketonuria.

Integration of new embryonic nephrons into the kidney

The current report summarizes our experiments exploring the feasibility of creating a chimeric kidney, that is, an organ constituted by cells derived from more than one fertilized ovum. The overall strategy has been to obtain donor renal tissue from avian and murine embryos and to implant this into the host avian mesonephric mesoderm or into the cortex of murine neonatal kidney. In both models, donor cells were distinguished from the host by the presence of characteristic nuclear or cytoplasmic markers. Examination of quail to chick transplants showed the tandem development of mesonephric tissue in the form of bilobed organ. In the mouse chimeric kidney, examined 2 to 4 weeks postnatally, transplanted metanephric tissue grew and developed glomeruli, proximal tubules, and cords of cells, which extended into the medulla of the host kidney. Before death, intravenous FITC-dextran was administered to the host mouse. Some transplanted tubules were connected to filtering glomeruli, as judged by the presence of fluorescein within their lumens. These experimental models provide novel means with which to study nephrogenesis in vivo. Finally, if the embryonic donor tissue could be genetically engineered before implantation, the prospect of "nephron therapy" arises, in which altered implanted nephrons could deliver therapeutically useful molecules into the urine or kidney interstitium.

Update of pancreatic transplantation

Pancreatic transplantation for the treatment of diabetes mellitus in man has proved increasingly successful. Between December 1966 and August 1990 2735 pancreas transplants from 141 institutions were reported to the International Pancreas Transplant Registry. For the period 1986 to 1989 the one year graft survival rate in 1,200 patients was almost 70%, a significant improvement over the preceding five years. The commonest techniques for the diversion of pancreatic secretions are bladder drainage, intestinal drainage and duct occlusion with synthetic polymers. The survival rate of pancreas grafts is significantly higher in recipients of simultaneous pancreas and kidney transplants than in recipients of pancreas transplants after kidney transplants and transplants of the pancreas alone. For this reason pancreas transplantation is mainly indicated as an adjunct to kidney transplantation, when the patient must be given immunosuppressive treatment in any case. A steady decline in the rate of technical failures and of serious adverse reactions as a result of immunosuppressive treatment will undoubtedly widen the present indications. In most recipients of a pancreas graft the blood glucose and hemoglobin A1c levels become normal or near normal. No convincing evidence of an ameliorating effect on microangiopathic and neuropathic complications has been obtained so far. On the other hand, it is established that pancreas transplantation may prevent the development of glomerular lesions in a simultaneously grafted kidney. Previously, transplantation of pancreas islets in man has not been successful. In 1990, however, in several insulin-dependent, diabetic subjects the intraportal transplantation of islets isolated from cadaver pancreas resulted in significant insulin production, and, in a few patients, it was possible to stop insulin treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypothesis: insulin is responsible for the vascular complications of diabetes

It is proposed that the systemic hyperinsulinemia and hepatic portal hypoinsulinemia that occurs with conventional injectable preparations of insulin currently used in the treatment of patients with diabetes mellitus is largely responsible for the morbidity associated with this disease. Epidemiological evidence and animal experimentation strongly support systemic hyperinsulinemia as a major factor in genesis of atherosclerosis in diabetic patients. In addition, in vitro studies demonstrate a direct effect of insulin on endothelial cell and arterial smooth muscle proliferation. On the other hand, inadequate hepatic delivery of insulin is associated with overproduction of renal vasoregulatory factors leading to glomerular hyperfiltration and ultimately to glomerulosclerosis and its clinical endpoint--end-stage renal disease. In the absence of widespread success of pancreatic and islet-cell transplantation as a means to deliver insulin physiologically into the hepatic portal circulation, methods must be devised and perfected to accomplish such delivery using approaches such as orally administering insulin in intestinal-enzyme protected capsules. Until such methods of delivery are available for safe and widespread use, one should abandon the illusory goal of rigid glucose control in favor of methods that reduce insulin requirement. Along these lines, dietary restriction and aerobic exercise should be the major life style changes advised for diabetic patients. Reduction of glomerular hyperfiltration in diabetic patients can be promoted with the use of low protein diets and/or angiotensin converting enzyme inhibitors.

Creation of a functioning chimeric mammalian kidney

The possibility of adding new nephrons to the mammalian kidney was studied. Embryonic metanephric tissue was implanted into the renal cortex of neonatal mice less than 24 hours old, and the development of the chimeric kidney was followed over the following two to four weeks. Donor tissue was obtained from the homozygous beige mouse and a mouse line transgenic for the beta-globin gene, which provided distinct cellular and nuclear markers which were used to distinguish donor from recipient nephrons. Differentiation and growth of donor nephrons occurred in the host kidney and included vascularized glomeruli, mature proximal tubules, and tubular extensions into the renal medulla. Glomerular filtration was demonstrable in donor nephrons using FITC-dextran as a marker of filtration into the proximal tubules. Transplantation of metanephric tissue into adult mouse kidneys did not lead to glomerular or tubular differentiation. This study demonstrates the feasibility of adding functioning nephrons to mammalian kidneys in species in which there is ongoing nephrogenesis post-natally.

Adverse effects of cyclosporine on islet growth and differentiation

In light of recent evidence that cyclosporine (CsA) inhibits growth of the exocrine pancreas, we decided to examine the effects of cyclosporine in a hamster model of islet cell proliferation and differentiation induced by partial pancreatic duct obstruction (PPDO), in which the growth of pancreatic endocrine tissue is mediated by production of an islet cell growth factor (ICGF) contained in a cytosolic extract of pancreas. In Part I of this study, extract was prepared from PPDO pancreas, from PPDO pancreas in animals treated with CsA (20 mg/kg ip daily for 10 days), and from pancreas in control animals. Data obtained from an in vivo bioassay confirmed that administration of the extract derived from PPDO and PPDO + CsA animals increased pancreatic organ weight significantly by 10 and 17%, respectively, compared to control. Similarly, total pancreatic DNA content was increased significantly by 25 and 41%, respectively. In Part II of the study, the direct effect of CsA on islet cell proliferation and differentiation induced by PPDO was examined. The number of islets per square millimeter and the uptake of tritiated thymidine by islet cells (%) were increased significantly in PPDO animals (2.4 +/- 0.1 and 0.56 +/- 0.06) compared to those in PPDO + CsA animals (1.2 +/- 0.1 and 0.24 +/- 0.01) and to those in controls (1.1 +/- 0.0 and 0.22 +/- 0.07). It is concluded from the data in Part I that CsA does not inhibit ICGF production, but the results of Part II suggest that CsA acts to block ICGF activity.(ABSTRACT TRUNCATED AT 250 WORDS)