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M D Brendel

Publications and source records attributed to M D Brendel.

At least 19 recordsLinked to original sources
PubMed2006

[Therapy of diabetes mellitus. Pancreas transplantation, islet transplantation, stem cell and gene therapy].

The long-term normalization of glucose metabolism - a prerequisite for the prevention of secondary complications in patients with diabetes mellitus - is only possible by transplantation of a whole pancreas or a reasonable number of islets. An absolute indication for pancreas grafting is given in type 1 diabetic patients with end-stage renal disease. The 1-year survival after simultaneous kidney/pancreas transplantation is, according to the international registry, 94-100% for patients, 89-92% for kidneys and 85-87% for the pancreas. The high success rate with long lasting normalization of glucose metabolism leads to a stabilization and/or amelioration of secondary complications, to an increase in quality of life and, most importantly, to a significant reduction in mortality when compared to diabetic kidney recipients. The indications for islet transplantation are similar to those for pancreatic grafting. Islet grafting is only a minor surgical procedure, but islet isolation is difficult. The 1-year survival for the recipients is 98%, for the islets 82% and for insulin-independency 42%. There is a significant decline of islet function to 10% 5 years after transplantation. Stem cell therapy would provide a definitive treatment solution not only for patients with type 1 diabetes. So far, this therapeutic option is still at an early stage of development.

Combined Modality Therapy↗
PubMed2005

Adiponectin is functionally active in human islets but does not affect insulin secretory function or beta-cell lipoapoptosis.

CONTEXT: The adipokine adiponectin has insulin-sensitizing, antiatherogenic, and antiinflammatory properties. Mouse and human adiponectin receptor-1 and -2 have been cloned, both of which are expressed in various tissues and mediate effects of globular and full-length adiponectin. Whether adiponectin affects insulin secretion and beta-cell apoptosis and whether plasma adiponectin is associated with beta-cell function in humans is under investigation. DESIGN AND METHODS: In human islets from multiorgan donors, we investigated expression of adiponectin receptor-1 and -2. Furthermore, glucose-stimulated insulin secretion was determined by RIA. In addition, we investigated fatty acid-induced beta-cell apoptosis by terminal dUTP nick end labeling and flow-cytometric cell cycle analysis (sub-G1 formation). In humans in vivo, insulin secretory function was measured during hyperglycemic clamps in 65 normal glucose-tolerant subjects. We determined first and second phase of glucose-stimulated, glucagon-like peptide-1-stimulated, and arginine-stimulated insulin secretion. RESULTS: Adiponectin receptor-1 and -2 are expressed in human islets at the mRNA and protein level. Moreover, full-length adiponectin induces phosphorylation of acetyl coenzyme A carboxylase. However, adiponectin did not affect basal or glucose-stimulated insulin secretion or basal or fatty acid-induced beta-cell apoptosis. In vivo, fasting plasma adiponectin concentrations were not associated with glucose-stimulated first- and second-phase insulin secretion or with glucagon-like peptide-1- or arginine-stimulated insulin secretion (all P > 0.42). CONCLUSIONS: These data support a regulatory role of adiponectin in human islets; however, adiponectin does not seem to affect insulin secretion or basal/fatty acid-induced beta-cell apoptosis in humans.

Adiponectin↗
PubMed2005

The Rap-B-Raf signalling pathway is activated by glucose and glucagon-like peptide-1 in human islet cells.

AIMS/HYPOTHESIS: Glucose and glucagon-like peptide-1 have been shown to activate extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase in beta cells. We examined the contributions of the small GTPases Rap and Ras and the serine-threonine kinases B-Raf and Raf-1 to the activation of these kinases in human islet cells. METHODS: The expression of Rap, Ras, B-Raf and Raf-1 in human islets was examined by immunohistochemistry and immunoblotting. Human islets were incubated in glucose at concentrations of 2.5 and 15 mmol/l and were stimulated with 10 nmol/l glucagon-like peptide-1. The activation of ERK and Raf kinases was examined by phosphorylation-specific antibodies and immuno-complexed kinase assays. The activation of Rap and Ras was determined by pull-down assays. Stimulation of phosphoinositide 3-kinase was detected by immuno-complexed lipid kinase assays. RESULTS: Extracellular-regulated kinase and protein kinase B (a downstream target of phosphoinositide 3-kinase) were activated in islets stimulated with glucose and glucagon-like peptide-1. In these islets, the Rap-B-Raf signalling pathway was activated preferentially compared with Ras and Raf-1, and activated Rap and B-Raf mediated ERK stimulation in kinase assays in vitro. In addition, Rap rather than Ras mediated activation of phosphoinositide 3-kinase in islets stimulated with glucose and glucagon-like peptide-1. CONCLUSIONS/INTERPRETATION: In human islet cells, glucose and glucagon-like peptide-1 activate the Rap and B-Raf signalling module, which mediates ERK activation in assays in vitro. Rap also activates phosphoinositide 3-kinase, delineating central roles for Rap and B-Raf as therapeutic targets for beta cell growth in diabetes mellitus.

Cells, Cultured↗
PubMed2004

Disseminated periportal fatty degeneration after allogeneic intraportal islet transplantation in a patient with type 1 diabetes mellitus: a case report.

Insulin independence after islet transplantation has been significantly improved by using new steroid-free immunosuppressive protocols and increased islet mass. Only little is known about the influence on the morphology of the liver of intraportally transplanted islets. We describe a case of disseminated periportal fatty degeneration after allogeneic intraportal islet transplantation (ITx). A 35-year-old patient with type-1 diabetes mellitus who was suffering from repeated severe hypoglycemic episodes received two sequential intraportal islet grafts. Liver structure was normal before the first ITx, based upon ultrasound and magnetic resonance imaging (MRI). One week after the first ITx, ultrasound demonstrated normal liver morphology. Four months later, at the second ITx, we detected small, disseminated, and hypodense hepatic lesions (1 to 3 mm) by ultrasound, which were confirmed by MRI and interpreted to be fatty degenerations. Histologically we found focal drop-shaped fatty degenerations with signs of mild periportal chronic inflammation. These liver alterations without clinical symptoms or pathological liver function tests matched the predicted distribution of infused islets. Glucose metabolism markedly improved after the first ITx, namely 58.6% reduction of daily insulin requirements, 1.4% decrease in HbA1c, basal C-peptide of 0.8 to 1.3 ng/dl with no severe hypoglycemia. We interpreted these benign changes in liver morphology as reactions to a local hyperinsulinemia in the neighborhood of the transplanted islets. We hypothesized that a steroid-free immunosuppression with rapamycin and tacrolimus may have contributed to changes in the portal microenvironment.

Adult↗
PubMed2004

The role of current product release criteria for identification of human islet preparations suitable for clinical transplantation.

BACKGROUND: Alloimmunity, autoimmunity, and nonspecific inflammation are known to be potential determinants for long-term islet survival and insulin independence. Sufficient islet mass is a key determinant. But islet engraftment and posttransplant survival may also depend on functional characteristics of the graft. This study investigated the significance of current product release criteria for the transplantation outcome. METHODS: Fourty five consecutive transplanted human islet preparations and their functional outcomes were analyzed. Islet mass was determined according to standard criteria: purity by light microscopy, viability by dye exclusion and Insulin secretory response to static glucose incubation. Islet graft function was monitored for > or = 1 year. Islet function was defined as full (FF), partial (PF), or nonfunction (NF) based on serum C-peptide levels and insulin independence. RESULTS: All islet grafts displayed primary function. Islet mass [IEQ/kg BW]: 7331.3 +/- 679.7 (FF), 5821.3 +/- 546.7 (PF), 6468.6 +/- 658.5 (NF), (FF vs PF p = .032) Purity [%] 86.9 +/- 3.1 (FF), 76.0 +/- 2.87 (PF), 88.2 +/- 2.3 (NF) (FF vs PF P =.045, PF vs NF, P = 0.01). (4) Viability [%]:89.2 +/- 2 (FF), 86.2 +/- 1.7 (PF), 87.3 +/- 1.8 (NF) (ns). Stimulation index (SI): 20 +/- 6.3 (FF), 80.2 +/- 28.2 (PF), 21.6 +/- 3.5 (NF) (ns) No correlation was observed between SI and any other parameter nor between SI and C-peptide levels. Islet mass significantly correlated with C-peptide levels at 6 and 12 months after transplantation for functioning grafts. CONCLUSIONS: Stringent product release criteria allow identification of islet preparations suitable for clinical transplantation. However, currently used parameters are not predictive of long-term graft function, indicating that further refined quality assessments including apoptosis and resistance to early inflammation, are required to assess the primary engrafted islet mass.

Automation↗
PubMed2004

Can the density of native pancreatic tissue slices predict human islet isolation and purification outcome?

INTRODUCTION: With currently available technology, the outcomes of human islet isolation and purification are still inconsistent, in part due to a lack of control of the pancreas donor and the procurement conditions. Using a single donor pancreas, the critical islet mass for establishing insulin independence of approximately 5000 engrafted islet equivalents (IEQ)/kg of recipient weight can only be retrieved from about one third of isolations. The purpose of this study was to analyze whether successful islet isolation and purification outcomes might be predicted from the density of native pancreatic tissue. METHODS: Tissue slices (TS) were obtained from the neck of 9 nondistended human donor pancreata. The density of the TS was determined using gravity sedimentation in continuous density gradients under either iso-osmolar or hyperosmolar conditions. Correlation coefficients were calculated with regard to the density of isolated exocrine and endocrine tissue, donor age, body mass index (BMI), cold ischemia time (CIT), IEQ prepurification and postpurification, IEQ recovery, and purity. RESULTS: (1) There was no change in density over time for TS in 300 mOsm/kg (mean, 1.079 +/- 0.0019 g/cm(3)) (2) In 500 mOsm/kg, there was a significant increase in density from 1.086 +/- 0.0021 g/cm(3) to 1.092 +/- 0.0021 g/cm(3) over time. (3) Density of isolated exocrine and endocrine became more distinct with lower density of TS (r = -0.776; P < .05). (4) Donor age, BMI, recovery of IEQ from gradients, and number of IEQ after purification did not correlate significantly with TS density. (5) In contrast, a significant inverse correlation existed betwen TS and CIT (r = -0.829; P < .05), and between TS versus IEQ number prior to purification (r = -0.867; P < .05). CONCLUSION: No homogeneous distribution of pancreas tissue density was seen among 9 consecutive human organs. Taken together, the density of native pancreas TS is not a suitable sole predictor for successful islet isolation and purification.

Adult↗
PubMed2004

Optimization in osmolality and range of density of a continuous ficoll-sodium-diatrizoate gradient for isopycnic purification of isolated human islets.

INTRODUCTION: According to previous estimates from large animals and man, a minimum of approximately 5000 to 6000 engrafted islet equivalents (IEQ)/kg recipient weight is critical to establish insulin independence. Utilizing a single donor, this threshold yield of purified islets can be retrieved from approximately one third of all isolations. The aim of this study was to improve human islet purification by optimization of the osmolality and the density range of the continuous Ficoll-sodium-diatrizoate (FSD) gradient to facilitate consistent purities >80% of human islet preparations without considerable loss of islet yield. METHODS: Aliquots of human pancreatic digests were placed on continuous density gradients. After centrifugation, sequential aliquots were extracted for amylase and insulin to determine the relative and cumulative density distribution of endocrine and exocrine tissue. We addressed the impact of two factors: (1) osmolalities (300 to 600 mosm/kg) in the gradient of FSD covering a density range of 1.070 to 1.100 g/cm(3); and (2) density (FSD 500/1.070 to 1.100) versus density-osmolarity gradient (DO-FSD 400-530/1.080 to 1.113). RESULTS: The density of exocrine and endocrine tissue increased with rising osmolality. Differences in density of both tissues were highest at 450 and lowest at 300 and 600 mOsmol/kg. Purity and recovery were highest at 450 versus 400 or 500 mOsm/kg (NS). Exocrine but not endocrine tissue was more dense in DO-FSD than in FSD gradient (P < .05). The differences in density were 0.004 versus 0.013 g/cm(3) (P < .01), resulting in an increased islet purity and recovery. CONCLUSION: The best osmolality for the FSD 1.070 to 1.100 g/cm(3) is at 450 mOsm/kg. Using the DO-FSD may improve human islet purification allowing successful clinical islet transplantation.

Cell Count↗
PubMed2004

Diagnostic algorithm and management of immune-mediated complications associated with subcutaneous insulin therapy.

Immune mediated complications associated with subcutaneous insulin therapy such as insulin neutralizing antibodies and/or skin reactions are rare conditions since human insulin is in general use. Nevertheless, if it occurs, a stepwise diagnostic approach is essential for differential diagnosis and consecutive treatment of these complications. Here we suggest a diagnostic algorithm to deal with e.g. insulin antibody formation of the IgG and/or IgE type and/or severe skin reactions resulting in poor metabolic control and often "brittle diabetes" in affected patients. This diagnostic algorithm includes step 1: Intradermal skin testing with positive and negative controls, additives and different insulin preparations; step 2: Quantification of insulin specific IgG and IgE in the serum, and step 3: Analysis of the time dependent binding/dissociation curves of the insulin neutralizing antibodies in an ex vivo/in vitro assay to assess the clinical significance of these antibodies. Based on 158 insulin treated control subjects and four patients with typical symptoms and signs representing the spectrum of immune-mediated complications subsequent to subcutaneous insulin therapy we demonstrate that the proposed stepwise approach leads to a definite diagnosis as a prerequisite for individual and successful therapy.

Adult↗
PubMed2004

Pancreatic islet and stem cell transplantation: new strategies in cell therapy of diabetes mellitus.

Long-term studies strongly suggest that tight control of blood glucose can prevent the development and retard the progression of chronic complications of type 1 diabetes mellitus. In contrast to conventional insulin treatment, replacement of a patient's islets of Langerhans either by pancreas organ transplantation of by isolated islet transplantation is the only treatment to achieve a constant normoglycemic state and avoiding hypoglycemic episodes, a typical adverse event of multiple daily insulin injections. However, the expense of this benefit is still the need for immunosuppressive treatment of the recipient with all its potential risks. Islet cell transplantation offers the advantage of being performed as a minimally invasive procedure, in which islets can be perfused percutaneously into the liver via the portal vein. As of June 2003, 705 pancreatic islet transplants worldwide have been reported to the International Islet Transplant Registry (ITR) at our Third Medical Department, University of Giessen/Germany. Data analysis shows at 1 year after adult islet transplantation a patient survival rate of 97%, a functioning islet graft in 54% of the cases, whereas insulin independence was meanwhile achieved in 20% of the cases. However, using a novel protocol established by the Edmonton Center/Canada, the insulin independence rates have improved significantly reaching meanwhile a 50-80% level. Finally, the concept of islet cell or stem cell transplantation is most attractive since it offers many perspectives: islet cell availability could become unlimited and islet or stem cells my be transplanted without life-long immunosuppressive treatment of the recipient, just to mention 2 of them.

Animals↗
PubMed2001

Expression of complement regulatory proteins on islets of Langerhans: a comparison between human islets and islets isolated from normal and hDAF transgenic pigs.

BACKGROUND: The expression of regulators of complement activity (RCAs) on islet cells may be of great importance for protecting them against complement-mediated lysis in the immediate posttransplant period after intraportal islet transplantation. We examined porcine and human islet cells for expression of RCA. We also examined to what extent human decay accelerating factor (hDAF) is expressed on adult and fetal islet cells isolated from hDAF transgenic (TG) pigs having a high transgene expression on endothelial cells. Moreover, the susceptibility of the various types of cells to lysis in human serum and blood was investigated. METHODS: Adult human islets (n=5), normal adult and fetal porcine islets (n=9 and n=8, respectively), and islets from adult and fetal hDAF TG pigs (n=5 and n=6, respectively) were examined. With islet single-cell suspensions and flow cytometry, adult human islet cells were examined for expression of hDAF (CD55), hCD59, and human membrane cofactor protein (hMCP; CD46), while porcine islet cells were examined for expression of pCD59 and pMCP. Islet cells from hDAF TG pigs were also examined for hDAF expression. Porcine peripheral blood lymphocytes, normal and hDAF TG porcine endothelial cell lines, a human endothelial cell line, and the human cell line U937 served as controls. Islet cytotoxicity was assayed after incubation of the islet cells with fresh human serum. Furthermore, adult islets from normal control pigs and hDAF TG pigs were exposed to fresh human blood in vitro for 60 min, and the inflammatory reaction elicited was compared between the different types of islets. RESULTS: All human islet cell preparations expressed hCD59, two of five expressed hMCP, but none expressed hDAF. Porcine islet cells expressed both pCD59 and pMCP. Normal adult porcine islet cells exposed to fresh human serum resulted in 74+/-5.4% cell lysis (mean+/-SEM, n=16). In comparison, only 1.3+/-2.8% (n=20, P<0.001) of human islet cells were lysed in the human serum. One islet cell preparation from an hDAF TG pig expressed small amounts of hDAF. This preparation from hDAF TG pigs bound significantly less C3c than did normal control islets (mean fluorescence ratio 16+/-2.2 and 58+/-4.3, respectively; P=0.046) and were partially protected from cell lysis in fresh human serum (47+/-10% and 78+/-18% cell lysis, respectively; P=0.046). The other four preparations from hDAF TG pigs were negative for hDAF and were equally susceptible to lysis as normal control islets. All fetal pancreatic islet cells from hDAF TG pigs analyzed were negative for hDAF expression. When exposed to fresh human blood in vitro, adult and fetal islets from hDAF TG pigs elicited equally strong inflammatory changes as did the normal control islets. The inflammatory changes were characterized by activation of the complement and coagulation systems, resulting in islet damage with "dumping" of insulin into the blood. CONCLUSIONS: Porcine and human islet cells express species-restricted complement regulatory proteins, with the human islet cells expressing mainly hCD59. A low expression of hDAF was detected on islet cells from one of five hDAF TG pigs. These islet cells displayed reduced islet cell cytotoxicity in fresh human serum. We conclude that protection from complement-mediated lysis will be important in the context of intraportal pig-to-human islet transplantation, and expression of a human RCA on islet cells should be beneficial in this context.

Animals↗
PubMed2001

Metabolic effects of restoring partial beta-cell function after islet allotransplantation in type 1 diabetic patients.

Successful intraportal islet transplantation normalizes glucose metabolism in diabetic humans. To date, full function is not routinely achieved after islet transplantation in humans, with most grafts being characterized by only partial function. Moreover, the duration of full function is variable and cannot be sufficiently predicted with available methods. In contrast, most grafts retain partial function for a long time. We hypothesized that partial function can restore normal protein and lipid metabolism in diabetic individuals. We studied 45 diabetic patients after islet transplantation. Labeled glucose and leucine were infused to assess whole-body glucose and protein turnover in 1) 6 type 1 diabetic patients with full function after intraportal islet transplantation (FF group; C-peptide > 0.6 nmol/l; daily insulin dosage 0.03 +/- 0.02 U x kg(-1) body wt x day(-1); fasting plasma glucose < 7.7 mmol/l; HbA1c < or = 6.5%), 2) 17 patients with partial function (PF group; C-peptide > 0.16 nmol/l; insulin dosage < 0.4 U x kg(-1) body wt x day(-1)), 3) 9 patients with no function (NF group; C-peptide < 0.16 nmol/l; insulin dosage > 0.4 U x kg(-1) body wt x day(-1)), and 4) 6 patients with chronic uveitis as control subjects (CU group). Hepatic albumin synthesis was assessed in an additional five PF and five healthy volunteers by means of a primed-continuous infusion of [3,3,3-2H3]leucine. The insulin requirement was 97% lower than pretransplant levels for the FF group and 57% lower than pretransplant levels for the PF group. In the basal state, the PF group had a plasma glucose concentration slightly higher than that of the FF (P = 0.249) and CU groups (P = 0.08), but was improved with respect to the NF group (P < 0.01). Plasma leucine (101.1 +/- 5.9 micromol/l) and branched-chain amino acids (337.6 +/- 16.6 micromol/l) were similar in the PF, FF, and CU groups, and significantly lower than in the NF group (P < 0.01). During insulin infusion, the metabolic clearance rate of glucose was defective in the NF group versus in the other groups (P < 0.01). Both the basal and insulin-stimulated proteolytic and proteosynthetic rates were comparable in the PF, FF, and CU groups, but significantly higher in the NF group (P = 0.05). In addition, the PF group had a normal hepatic albumin synthesis. Plasma free fatty acid concentrations in the PF and FF groups were similar to those of the CU group, but the NF group showed a reduced insulin-dependent suppression during the clamp. We concluded that the restoration of approximately 60% of endogenous insulin secretion is capable of normalizing the alterations of protein and lipid metabolism in type 1 diabetic kidney recipients, notwithstanding chronic immunosuppressive therapy. The results of the present study indicate that "success" of islet transplantation may be best defined by a number of metabolic criteria, not just glucose concentration/metabolism alone.

Adult↗