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Biomedical subjects

R G Bretzel

Publications and source records attributed to R G Bretzel.

At least 181 records · Page 10Linked to original sources
PubMed1993

Lymphoid activation by micro- and macroencapsulated islets during mixed lymphocyte islet culture.

We have recently demonstrated long-lasting normoglycaemia after transplantation of barium alginate microencapsulated rat and porcine islets. Nevertheless the transplantation results obtained with different microencapsulation techniques have been controversial. Little is known about possible immune interactions between host and encapsulated islet. This study demonstrates in vitro stimulation of lymphoid cells by encapsulated islets that is similar to that of unencapsulated islets. This stimulation was reduced by a 4-day culture with unencapsulated islets only. After macroencapsulation of islets in hollow fibres a stimulatory effect was also observed, but this was less pronounced than after microencapsulation. Empty microcapsules as well as macrocapsules induced lymphoid proliferation as a result of mitogenic impurities in the encapsulation materials themselves. In the same donor-recipient combination in which we have shown successful transplantation, we found activation of the sensibilization arm of the immune system. This suggests that microencapsulation results in protection of the transplanted islets from the action of the effector arm. This lymphoid activation could be triggered by the mitogeniticity of the encapsulation material itself. In the case of alginates these mitogenic factors could not be abolished by culture (i.e. dialysis).

Alginates↗
PubMed1993

Rat pancreatic islet pretreatment with anti-MHC class II monoclonal antibodies and culture: in vitro MLIC test response does not predict islet allograft survival.

Antigen presenting cells (APC) expressing MHC class II antigens have been attributed with stimulatory capacity for initiating islet allograft rejection (direct pathway). Therefore, we evaluated the effect of pretreating isolated islets with different monoclonal antibodies against MHC class II antigens and complement, with and without culture at 22 degrees C or 37 degrees C, on MHC class II antigen expression, on the allogeneic proliferative response in the mixed lymphocyte islet culture (MLIC) and on islet allograft survival in adult rats. Experiments were performed in two different strain combinations incompatible for MHC class II antigens and either incompatible or compatible for MHC class I antigens, in order to elucidate further the impact of class I antigens on islet allograft rejection. In terms of class II antigen suppression, pretreatment with anti-MHC class II antibodies together with complement and a 5-day (37 degrees C) culture period proved most effective. After this procedure 92.7% of the islets of LEW rats and 91.1% of the islets of LEW.1WR2 rats were negative for MHC class II antigens, as demonstrated by indirect immunofluorescence. Transfer of successfully pretreated islets to a MLIC in vitro test system provoked a significantly reduced allogeneic T-cell proliferative response in the case of additional MHC class I disparity (ratio 1.3 vs 4.7) and a response as low as that of a syngeneic setting when stimulator islets and allogeneic responder lymphocytes shared MHC class I antigens (ratio 1.0 vs 1.6).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Nephroprotective effects of nitrendipine in hypertensive type I and type II diabetic patients.

Hypertension is significantly involved in the progression of diabetic nephropathy and in the development of end stage renal disease in both type I and type II diabetes mellitus. We have investigated whether long-term monotherapy with a calcium antagonist, nitrendipine, prevents the development of overt diabetic nephropathy in type I and type II diabetic patients with mild to moderate hypertension and persistent microalbuminuria (ie, incipient nephropathy). After a 4-week run-in and washout period, respectively, 25 patients met the inclusion criteria. Twenty-two patients (six with type I and 16 with type II diabetes) completed the 12-month study. Twelve months of treatment with nitrendipine resulted in a significant reduction in systolic blood pressure in patients with type I (157.5 +/- 8.1 mm Hg v 135.8 +/- 4.2 mm Hg, P < 0.05) and type II (163.1 +/- 4.3 mm Hg v 135.9 +/- 3.6 mm Hg, P < 0.001) diabetes. A significant reduction also was seen in diastolic blood pressure (91.7 +/- 1.7 mm Hg v 79.2 +/- 3.5 mm Hg in type I diabetic patients, P < 0.01; 94.7 +/- 1.4 mm Hg v 78.1 +/- 1.5 mm Hg in type II diabetic patients, P < 0.001). A significant reduction in albuminuria was associated with the blood pressure reduction in both type I (57.8 +/- 11.9 mg/24 hr v 24.9 +/- 5.9 mg/24 hr, -57%) and type II (134.6 +/- 20.7 mg/24 hr v 70.3 +/- 16.8 mg/24 hr, -48%) diabetic patients. The mean glomerular filtration rate increased by 21% (112 +/- 12 mL/min v 135 +/- 14 mL/min) and by 23% (106 +/- 12 mL/min v 130 +/- 14 mL/min) in type I and type II diabetic patients, respectively. No significant changes were found in renal plasma flow rates or in serum concentrations of beta 2-microglobulin. With the exception of a significant (P < 0.05) reduction in hemoglobin A1 concentration in type II diabetic patients after 3 months of treatment with nitrendipine, fasting blood glucose, hemoglobin A1, residual beta-cell function (C-peptide levels), total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, and body mass index remained essentially unchanged during follow-up. These findings suggest that 12 months of monotherapy with the dihydropyridine-type calcium antagonist nitrendipine reduced albuminuria and increased the lowered glomerular filtration rate without adverse effects on glucose and lipid control.(ABSTRACT TRUNCATED AT 400 WORDS)

Albuminuria↗
PubMed1993

Transplantation of free and microencapsulated islets in rats: evidence for the requirement of an increased islet mass for transplantation into the peritoneal site.

Microencapsulation of islets of Langerhans may avoid the necessity of a permanent immunosuppressive drug therapy and opens up new perspectives for xenotransplantation in the treatment of insulin dependent diabetes. In a mouse model we recently showed long-term normoglycemia after microencapsulated xenotransplantation. Since the acceptance of mice to any kind of foreign material is quite high we assume that the rat model better reflects the situation of higher mammalians or even humans. Due to the volume of the transplanted material (i.e. islets+alginate-capsule) only the peritoneal cavity can be used up to now. The quantity of islets necessary to normalize the non-fasting blood glucose level was much higher than expected and free transplants needed even a higher amount of islets than encapsulated ones (3000 encapsulated vs. 2 x 3000 non-encapsulated). Transplantation beneath the kidney capsule was successful with only 1200-1500 islets per rat proving the metabolic potency of the islets. Implantation of empty capsules did not alter the diabetic state. We conclude that the alginate matrix may act as a "spacer" creating a distance between the consuments of a lacking substrate esp. oxygen in an unfavourable environment and perhaps protect it from unspecific mediators released during the postoperative period. Our findings underline the necessity for smaller capsules that would enable us to use other transplantation sites.

Animals↗
PubMed1993

Islet transplantation inhibits diabetic retinopathy in the sucrose-fed diabetic Cohen rat.

PURPOSE: To study the effect of islet transplantation on the development of diabetic retinopathy in the sucrose-fed diabetic Cohen rat, a useful experimental model of accelerated microvascular disease. METHODS: Syngeneic transplantation of collagenase-ficoll isolated islets by intraportal injection was performed either after 6 weeks or after 12 weeks of diabetes, i.e., before or after the first morphologic retinal changes, respectively. Retinal digest preparations were examined using quantitative morphologic parameters. RESULTS: After 26 weeks of diabetes, characteristic features of background retinopathy such as a 5% increase in capillary endothelial cells, a 27% pericyte dropout, acellular occluded vessels and, occasionally, microaneurysms developed in untreated animals. Islet transplantation performed after 6 weeks of diabetes completely prevented endothelial cell proliferation and diminished pericyte loss (2950 +/- 140 vs 2390 +/- 40 in diabetic controls, P < 0.01). A significant increase in acellular occluded capillaries persisted (31 +/- 14 vs 8 +/- 2 in NC; P < 0.01). Islet transplantation after 12 weeks of diabetes, i.e., after established pericyte loss, only partially restored capillary cell composition and did not prevent retinal vessel occlusion. These findings indicate that the beneficial effect of islet transplantation on diabetic retinopathy is limited to a time very early in the evolution of this process. CONCLUSIONS: These data suggest that irreversible changes induced by antecedent hyperglycemia play a central role in the progressive development of diabetic retinopathy.

Animals↗
PubMed1992

Production of mitogen-contamination free alginates with variable ratios of mannuronic acid to guluronic acid by free flow electrophoresis.

Commercial alginates consisting of variable homopolymeric regions of beta-D-mannuronic acid and alpha-L-guluronic acid, interspaced with regions of alternating blocks, are potent stimulators of macrophages and lymphocytes. Therefore, inflammatory reactions and fibrotic overgrowth of the beads result if Langerhans islets are encapsulated in raw alginate hydrogel beads (cross-linked with divalent cations). The result is random failure of the islets some time after transplantation. Analysis of raw alginates by using free flow electrophoresis demonstrated that commercial alginates contained at least 10-20 fractions (characterized by different electrophoretic mobilities) which showed mitogenic activity. These fractions could be quantitatively separated from the alginic acids by free flow electrophoresis on a preparative scale. The purified alginates cross-linked with Ca2+ ions exhibited no mitogenic reactions as proved by an in vitro assay. In addition, examination of purified Ba2+ alginate beads implanted intraperitoneally in rats or mice for three weeks showed no fibrotic overgrowth in contrast to implants made from unpurified alginate.

Alginates↗
PubMed1992

Antibodies to the M(r) 64,000 (64K) protein in islet cell antibody positive non-diabetic individuals indicate high risk for impaired beta-cell function.

A prospective study of a normal childhood population identified 44 islet cell antibody positive individuals. These subjects were typed for HLA DR and DQ alleles and investigated for the presence of antibodies to the M(r) 64,000 (64K) islet cell antigen, complement-fixing islet cell antibodies and radiobinding insulin autoantibodies to determine their potency in detecting subjects with impaired Beta-cell function. At initial testing 64K antibodies were found in six of 44 islet cell antibody positive subjects (13.6%). The same sera were also positive for complement-fixing islet cell antibodies and five of them had insulin autoantibodies. During the follow-up at 18 months, islet cell antibodies remained detectable in 50% of the subjects studied. In all six cases who were originally positive, 64K antibodies were persistently detectable, whereas complement-fixing islet cell antibodies became negative in two of six and insulin autoantibodies in one of five individuals. HLA DR4 (p less than 0.005) and absence of asparic acid (Asp) at position 57 of the HLA DQ beta chain (p less than 0.05) were significantly increased in subjects with 64K antibodies compared with control subjects. Of 40 individuals tested in the intravenous glucose tolerance test, three had a first phase insulin response below the first percentile of normal control subjects. Two children developed Type 1 (insulin-dependent) diabetes mellitus after 18 and 26 months, respectively. Each of these subjects was non-Asp homozygous and had persistent islet cell and 64K antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Alginate coating of islets of Langerhans: in vitro studies on a new method for microencapsulation for immuno-isolated transplantation.

Immuno-isolated transplantation offers the attractive prospect of being able to transplant xenogeneic islets without immunosuppression. This study introduces a completely new method of coating single islets using a homogeneous alginate membrane approximately 10 microns thick. During glucose challenge (perifusion and static incubation) encapsulated islets show the same pattern and quantity of insulin release as non-encapsulated controls. This encapsulation method markedly reduces the amount of transplanted material by reducing the size of the capsule. It is suggested that encapsulated islets may be transplanted into sites such as the renal capsule or omentum or even by intraportal injection into the liver.

Alginates↗
PubMed1992

A comparative study of antigen expression by skin and pancreas in the prediabetic and diabetic state of the BB rat.

Type 1, insulin-dependent diabetes mellitus is an autoimmune disease with destruction of beta-cells in islets of Langerhans by activated (antigen-positive) infiltrating mononuclear cells accompanied by serological immune phenomena. The pathological mechanism has not yet been clarified in detail, and some inversion in the proportion of epidermal antigen expression has recently been described in spontaneous diabetes. The BB rat is one of the animal models most closely resembling human type 1 diabetes of autoimmune origin. We compared the class I and class II antigen expression in the islets of Langerhans and in the skin of spontaneously diabetic (BBD) and normoglycaemic (BBND) BB rats in the prediabetic, diabetic and non-diabetic states. Class I and class II antigen expression increased significantly in the islets of BBD rats from prediabetes to diabetes and compared with non-diabetic controls. In the same period, the dermal antigen expression (class I and class II) did not decrease and was not lower in BBD than in BBND animals. These results do not support a loss of activated (antigen-positive) dermal cells at the onset of diabetes in the BB rat and do not show a clear correlation with the antigen expression in infiltrated islets of Langerhans.

Aging↗
PubMed1992

Prevention of recurrent autoimmune diabetes in the BB rat by islet transplantation under the renal capsule.

Pancreatic islet grafts transplanted into subjects with spontaneous autoimmune diabetes are threatened by two immune responses, allograft rejection and the recurrence of autoimmune insulitis. To examine the recurrent autoimmune response to transplanted islets it is necessary to exclude islet allograft rejection. The BB rat is a unique model of spontaneous diabetes with clinical and pathological characteristics identical or similar to those found in human insulin dependent diabetes mellitus (IDDM). In this study we demonstrate permanent acceptance of histocompatible islet grafts in chemically induced diabetes and a lack of intracolony tissue antigen rejection in our BB rat colony. Therefore the vigorous destruction of transplanted BB islets in the liver of spontaneously diabetic BB rats is due to recurrence of diabetes. This recurrence can be prevented by transplantation of islets under the renal capsule. This may be important for clinical application in IDDM, particularly with regard to host and donor tissue matching.

Animals↗
PubMed1992

[Experimental and clinical islets transplantation. Current status].

25 years have passed since the first enzymatic isolation of islets of Langerhans from the rat pancreas. During this period of time, it could be demonstrated that transplantation of syngeneic islets intraportally into streptozoticin-treated diabetic recipients (rat, mouse) does not only guarantee long term normoglycemia but inhibits also typical late complications of the disease. Allogeneic islets, however, exhibit strong immunogenicity (rejection within a few days) which can be overcome by various immunomodulating in vitro measures of the islets before transplantation. Isolated islets have been successfully transplanted also in larger animals as dogs and pigs, when transplanted in an autologous or allogeneic system. In human diabetes the success rate of islet transplantation up to now is low and cannot be compared with the results in experimental diabetes. The reasons are manyfold: islet damage due to long ischemia time, low number of islets, low purity, lack of diagnostic markers which indicate rejection, autoimmune destruction. The fact that in the meantime a few patients remain insulin independent after a single islet transplant with the maximum of 2 years indicates however that this method in principle may serve as a tool for the treatment of diabetes. This is underlined by several advantages compared to pancreatic organ transplantation as low risk of the procedure for the recipient and the possibility of repeated transplantation. In addition, in the future xenotransplantation of (porcine) islets might be feasible.

Animals↗
PubMed1992

Islet transplantation: clinical and experimental.

Experimental diabetes in rodents has been successfully treated by implantation of isolated islets using a syngenic system (Lewis rats). It is possible to reverse all diabetic symptoms of the animals and to prevent late complications in kidney, eye and nervous system. Although isolated islets are highly immunogenic in an allogenic system immuno-alteration techniques have been developed and succeeded in longterm survival after culture at low temperature (24 degrees C), UV-irradiation, cryopreservation, pretreatment with Ia-antibodies etc. Islet transplantation in larger animals and in man up to now has been less successful. Although in a few studies longterm survival of canine islets has been observed, other groups were less successful using dogs and pigs in auto- or allo-transplantation. In man there are reports from various institutions during the last fifteen years using adult or fetal islet material. Only in a few instances the patients came off insulin for some weeks or months. The reasons for this failure are probably manifold: low number of islets, impurity, long ischemia time before isolation, transplantation to inappropriate sites, impairment of engraftment in longterm diabetic recipients and recurrence of autoimmunity in transplanted islets. Further studies are necessary to overcome these barriers. Recent observations using a higher number of islets (> 500,000) and new immunosuppressive drugs (FK506) seem to be promising.

Animals↗