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Biomedical subjects

R G Bretzel

Publications and source records attributed to R G Bretzel.

At least 199 records · Page 11Linked to original sources
PubMed1991

The effect of pancreatic islet transplantation on experimental diabetic neuropathy.

Quantitative light and electronmicroscopical morphometric techniques were used to determine the effect of pancreatic islet transplantation on experimental diabetic neuropathy. Groups of STZ-diabetic rats were given islet transplants at 3 weeks after diabetes onset (prevention) and at 6 months after diabetes onset (reversal). Comparisons were made with onset controls, age-matched non-diabetic controls and untreated diabetic controls 6 months later (n = 8 for all groups). Euglycaemia and normal levels of glycosylated haemoglobin were achieved in both groups of diabetics after islet transplantation. Loss of body weight in diabetic animals was prevented by early islet transplantation, but was only partially reversed following delayed islet transplantation. Normal growth of myelinated fibres and axons during development was retarded in untreated diabetics, but was normal in rats given islet transplants soon after the onset of diabetes (cross-sectional perimeter and area). Diabetics transplanted with islets after a delay had myelinated fibres and axons with diminished calibre. Teased fibre preparations of nerves from diabetics which had received islet transplants showed no excess of abnormalities. This study has shown that the development of certain structural abnormalities of peripheral nerve fibres is prevented in diabetic rats which receive transplants of islets of Langerhans soon after the onset of diabetes. However, once established abnormal fibre morphology can not be completely ameliorated merely by achieving and sustaining euglycaemia through delayed islet transplantation.

Animals↗
PubMed1991

Islet transplantation in experimental diabetes of the rat. XIII. Cryopreservation reduces MHC class II but not class I antigens of rat pancreatic islets.

Pretreatment of islet allografts prior to transplantation may reduce islet immunogenicity and prolong graft acceptance. We have studied the MHC antigen reducing effect of cryopreservation onto rat pancreatic islets performing indirect immunofluorescence tests and peroxidase-anti-peroxidase staining (PAP). Three different freezing programs were used. Program A: 0.5 degrees C/min to -35 degrees C and 1 degree C/min from -35 to -100 degrees C. Program B: 2 degrees C/min to -35 degrees C and 6 degrees C/min from -35 to -100 degrees C. Program C: 0.25 degrees C/min to -40 degrees C. Cryopreservation clearly reduced the number of class II antigen positive cells per islet in all cases. Program A was most effective with 45.5% of class II antigen negative islets compared to 6.4% of class II antigen negative fresh islets as shown by indirect immunofluorescence. The class II antigen reducing effect of cryopreservation proved to be permanent and not only temporary. Reduced class II antigen expression of cryopreserved islets could not be reestablished by incubation of the islets with rat IFN. A combination of cryopreservation followed by a 10 day culture period proved to be most effective with 85.6% of class II antigen negative islets. In contrast, we could not show any effect of cryopreservation on class I antigen expression. Viability of the cryopreserved rat islets was shown in-vitro by glucose stimulated insulin secretion.

Animals↗
PubMed1991

Pretreatment of rat pancreatic islets with MHC I-A monoclonal antibody: in-vitro and in-vivo effects on islet antigenicity.

Pancreatic islet allografts are rejected very rapidly due to their high immunogenicity. Several attempts have been made to reduce the immunogenicity prior to transplantation. We treated islets with MHC Ia (class II) antigen monoclonal antibody and complement in order to lyse Ia antigen bearing cells within the islets. This treatment caused a distinct reduction of Ia antigen positive cells, which was demonstrated by indirect immunofluorescence tests. A total depletion of the Ia antigens, however, could not be achieved. As a second in-vitro test to evaluate the effect of the antibody treatment a mixed lymphocyte islet culture (MLIC) was performed. The partial Ia antigen reduction provoked a significantly reduced but not completely suppressed allogenic T-cell response. Antibody treatment did neither impair the morphological integrity nor the function of the islets as could be demonstrated by syngenic transplantation of islets pretreated by antibodies in the same way. After allotransplantation of antibody-pretreated islets across a major histocompatibility barrier into non immunosuppressed rats, however, there was no significant prolongation of the graft survival. Thus, a partial reduction of the number of the Ia antigen positive cells within the islets is not sufficient for the prevention of allograft rejection.

Animals↗
PubMed1991

Persistent reversal of diabetes by transplantation of fetal pig proislets into nude mice.

Facing the limited availability of human adult and fetal pancreases, fetal pig proislets (pancreatic islet precursors) were investigated in view of several inherent advantages. Six litters of fetuses of mean +/- SE gestational age 75 +/- 3 days were obtained from commercially available farm pigs. Pancreatic tissue was gently digested with collagenase, then a 10-day culture was performed. During culture, fetal proislets showed no insulin response to glucose alone but a significant response to glucose plus theophylline. The insulin content per microgram of DNA in the cultured proislets continuously increased. Histological examination by immunoperoxidase staining showed that, apart from single insulin- and glucagon-positive cells, there were no discrete islets in the pancreatic tissue and the cultured proislets. Diabetes was induced with streptozocin (STZ) in eight nude mice 3-4 wk after proislet transplantation and in another eight nude mice without transplantation. During the initial week, blood glucose levels of mice in both groups increased rapidly. The mean +/- SE peak value of blood glucose levels in the transplanted group was 20.4 +/- 2.0 mM and was 20.1 +/- 1.3 mM in the group without transplantation. Simultaneously, body weight decreased from 29.5 +/- 0.7 to 21.5 +/- 0.9 g and from 27.9 +/- 0.7 to 19 +/- 1 g in the groups, respectively. Afterward, blood glucose levels of mice in the transplanted group gradually decreased, and normoglycemia was achieved in all mice within 50 +/- 13 days after injection of STZ, i.e., 74 +/- 13 days after transplantation. The group without transplantation persistently maintained blood glucose levels greater than 16.7 mM.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Light- and electron-microscopic studies on isolated bovine islets of Langerhans.

While several recent studies have focussed on the critical assessment of yield, purity and function of isolated islets, fine-structural investigations of isolated islets have been the subject of only a few studies. After intraductal injection of collagenase solution, the distended bovine pancreata were processed in a continuous digestion-filtration device, after which the purification of the islet suspension was accomplished by density gradient centrifugation. Purified islets were then prepared for light- and transmission electron-microscopic analysis. In semithin sections, no evidence of either connective tissue or exocrine tissue surrounding isolated islets was found. Endocrine cells exhibiting cytoplasmic granules were packed in clusters varying in size. In ultrathin sections, A-cells containing numerous secretory granules were distinctive; their cytoplasm contained conspicuous formations of rough endoplasmatic reticulum and juxtanuclear Golgi complexes. In the B-cells, the Golgi complexes were also prominent; these elements, however, were poor in endoplasmic reticulum and displayed characteristic B-cell granules surrounded by a halo. A few ultrastructurally heterogeneous cells were scattered among the identified cellular elements.

Animals↗
PubMed1991

[Islet transplantation in the treatment of diabetes mellitus: the challenges to the transplant of rejection and recurrent autoimmunity].

The success of islet transplantation for therapy of spontaneous diabetes mellitus depends on two immune responses of the recipient. The rejection of foreign tissue plays a major role in islet transplantation and can successfully be prevented by different immunomodulation in animals. In spontaneous diabetes the islet transplant can also be destroyed by the recurrent autoimmune insulitis. We describe, in which experiments recurrence occurred. We also demonstrate the influence of the donor-host combination on the immune attack and the possibilities to prevent the destruction of transplanted islets in animals. An outlook on the clinical situation is given.

Autoimmunity↗
PubMed1990

Effects of ganglioside (Cronassial) treatment on MHC Ia antigen expression and allograft survival of pancreatic islets in diabetic rats.

Streptozotocin-diabetic BdII rats were treated daily with 20 mg/kg body weight gangliosides for ten days beginning two days before transplantation. This treatment did not prolong allograft survival of untreated Lewis islets. Culture treatment of isolated Lewis islets with gangliosides (100 micrograms/ml in RPMI 1640) for one day resulted in a significant reduction of MHC Ia antigen positive cells but not of class I antigens within the islets. Transplantation of the ganglioside pretreated islets into non-immunosuppressed BdII recipients prolonged allograft survival to 12 days only in one of five animals.

Animals↗