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Biomedical subjects

G Pozza

Publications and source records attributed to G Pozza.

At least 37 records · Page 2Linked to original sources
PubMed2000

Modulation of humoral islet autoimmunity by pancreas allotransplantation influences allograft outcome in patients with type 1 diabetes.

Pancreas transplantation in patients with type 1 diabetes presents allogeneic beta-cell autoantigens to the immune system long after the initial beta-cell destruction that leads to diabetes has occurred. The aims of this study were to determine whether re-exposure to beta-cell autoantigen through transplantation affect the humoral autoimmune response and whether its modulation correlates with graft outcome. Antibodies to the major autoantigens GAD (GADA) and protein tyrosine phosphatase IA-2 (IA-2A) were measured before and after transplantation in patients with type 1 diabetes who received pancreas and kidney allografts. In the 110 cases studied, pancreas graft survival was not significantly associated with the presence of GADA or IA-2A before transplantation. In the 75 patients with sequential follow-up samples up to 11.2 years after transplantation, autoantibodies were persistently undetectable in 44 cases (59%) and remained at stable detectable levels in 13 cases (17%). Substantial changes in antibody levels were found in 18 cases (24%), of which 13 cases (17%) had declining levels and 5 cases (7%) had marked increments after transplantation. Rising GADA and IA-2A levels in these five patients were predominantly of the IgG1 subclass, with progressive spreading of epitope reactivity. Pancreas graft function was lost 0.7-2.3 years after rising autoantibody levels in four of these five patients, and a significantly lower pancreas graft survival was found in patients with major rises in either GADA or IA-2A levels (P < 0.0001 vs. the remainder) and in patients having persistently high levels of IA-2A (P = 0.002 vs. stable antibody-negative patients). Kidney graft survival was not associated with islet autoantibody status. In conclusion, a minority of patients receiving pancreas allografts under generalized immunosuppression show a stimulation of islet autoantibody reactivity characteristic of that found in preclinical type 1 diabetes, which is almost invariably followed by graft function failure and resumption of insulin therapy.

Adult↗
PubMed2000

Reversal of left ventricular diastolic dysfunction after kidney-pancreas transplantation in type 1 diabetic uremic patients.

OBJECTIVE: Diastolic function is frequently impaired in diabetic patients. Our aim was to evaluate the effects of glycometabolic control achieved by pancreas transplantation on left ventricular function in uremic type 1 diabetic patients. RESEARCH DESIGN AND METHODS: Left ventricular systolic and diastolic functions were evaluated using radionuclide ventriculography in 42 kidney-pancreas transplant patients and 26 kidney-alone recipients who had similar clinical characteristics before transplantation. Patients were grouped according to 6, 24, and 48 months of follow-up. Control subjects consisted of 20 type 1 diabetic patients. RESULTS: The left ventricular ejection fraction was normal in all of the patients. However, kidney-pancreas transplant patients with 4 years of graft function had a higher ejection fraction (75.7 +/- 1.8%) than kidney-alone patients with 4 years of graft function (65.3 +/- 2.8%, P = 0.02) and type 1 diabetic patients (61.3 +/- 3.7%, P = 0.004). In patients with 4 years of graft function, normal diastolic parameters were evident in kidney-pancreas but not in kidney-alone or in type 1 diabetic patients (peak filling rate: 4.46 +/- 0.15 end diastolic volume (EDV)/s in kidney-pancreas patients vs. 2.73 +/- 0.24 EDV/s [P < 0.01] and 3.39 +/- 0.30 EDV/s [P < 0.01] in kidney-alone and type 1 diabetic patients, respectively; time-to-peak filling rate: 141.9 +/- 7.8 ms in kidney-alone patients vs. 209.4 +/- 13.5 ms in kidney-alone patients [P < 0.01]; peak filling rate/peak ejection rate ratio: 1.10 +/- 0.04 in kidney-pancreas patients vs. 0.81 +/- 0.08 in kidney-alone patients [P < 0.01]). A significant reduction in diastolic dysfunction rate was observed only in kidney-pancreas patients. CONCLUSIONS: Kidney-pancreas transplantation results in complete insulin independence, a better glycometabolic pattern and blood pressure control, an improvement of left ventricular function, and a reversal of diastolic dysfunction.

Adult↗
PubMed1999

Endothelial and metabolic characteristics of patients with angina and angiographically normal coronary arteries: comparison with subjects with insulin resistance syndrome and normal controls.

OBJECTIVES: This study was performed to characterize the endothelial and metabolic alterations of patients with angina and angiographically normal coronary arteries ("cardiac" syndrome X [CSX]) compared with subjects with insulin resistance syndrome ("metabolic" syndrome X [MSX]) and normal controls. BACKGROUND: Previous studies have found high endothelin-1 levels, impaired endothelium-dependent vasodilation and insulin resistance in patients with angina pectoris and angiographically normal coronary arteries. On the other hand, subjects with insulin resistance syndrome have shown high endothelin-1 levels. METHODS: Thirty-five subjects were studied: 13 patients with angina pectoris and angiographically normal coronary arteries (CSX group); 9 subjects with insulin resistance syndrome (MSX group) and 13 normal controls. All subjects received an acute intravenous bolus of insulin (0.1 U/kg) combined with a euglycemic clamp and forearm indirect calorimetry. Endothelin-1 levels, nitrite/nitrate (NOx) levels, end products of nitric oxide metabolism, glucose infusion rates (index of insulin sensitivity) and their incremental areas (deltaAUCs [area under curves]) were measured during this period. RESULTS: Basal endothelin-1 levels were higher in CSX and MSX groups than in normal controls (8.19 +/- 0.46 and 6.97 +/- 0.88 vs. 3.67 +/- 0.99 pg/ml; p < 0.01), while basal NOx levels were significantly higher in MSX group than in CSX and normal controls (36.5 +/- 4.0 vs. 24.2 +/- 3.3 and 26.8 +/- 3.2 mol/liter, p < 0.05). After insulin administration, the deltaAUCs of NOx (p < 0.05) were lower in CSX group than in MSX and normal controls, and the deltaAUCs of endothelin-1 were lower in group CSX than in normal controls. Glucose infusion rate was significantly lower in CSX and MSx groups than in normal controls (p < 0.01), suggesting that in both CSX and MSX groups insulin resistance is present. A positive correlation was found between the deltaAUCs of nitric oxide and the AUCs of glucose infusion rate. CONCLUSIONS: Blunted nitric oxide and endothelin responsiveness to intravenously infused insulin is a typical feature of patients with angina pectoris and angiographically normal coronary arteries and may contribute to the microvascular dysfunction observed in these subjects.

Calorimetry, Indirect↗
PubMed1999

Effects of cryopreservation on in vitro and in vivo long-term function of human islets.

BACKGROUND: The possibility of performing transplantation several days after explant seems to be a peculiarity of islet grafts, and the opportunity to cryopreserve human islets may permit an indefinite period for modulating the recipient immune system. The aim of the present study was the evaluation of in vitro and in vivo functional properties of cryopreserved human islets. METHODS: We used six consecutive human islet preparations not suitable for an immediate transplantation in diabetic patients because the limited islet mass separated. The in vitro function of cryo and fresh islets was studied by determination of insulin and glucagon secretion in response to such classical stimuli as glucose (16.7 mM), glucose (16.7 mM) + 3-isobutyl-1-methylxanthine (0.1 mM), arginine (10 mM), and tolbutamide (100 microM). In vivo islet function was assessed through intravenous glucose tolerance tests performed at 15, 30, 60, and 90 days after transplantation of 1000 hand-picked fresh or cryopreserved islets in nude mice. RESULTS: Basal secretion of true insulin was significantly higher in cryopreserved islets than in fresh ones. The response of cryopreserved islets to arginine and glucose + isobutyl-1-methylxanthine seemed partially impaired. Proinsulin-like molecule secretion seemed higher in cryopreserved than in fresh islets in response to all secretagogues used, and the difference was statistically significant for arginine. The capacity of human cryopreserved islets to maintain a correct metabolic control in diabetic nude mice was progressively lost in 3 months. CONCLUSIONS: These findings showed that cryopreservation affects the function of isolated human islets, maintaining in vivo function for a limited period of time.

1-Methyl-3-isobutylxanthine↗
PubMed1999

Reversal of diabetes in mice by implantation of human fibroblasts genetically engineered to release mature human insulin.

Autoimmune destruction of pancreatic beta cells in type I, insulin-dependent diabetes mellitus (IDDM) results in the loss of endogenous insulin secretion, which is incompletely replaced by exogenous insulin administration. The functional restoration provided by allogeneic beta-cell transplantation is limited by adverse effects of immunosuppression. To pursue an insulin replacement therapy based on autologous, engineered human non-beta cells, we generated a retroviral vector encoding a genetically modified human proinsulin, cleavable to insulin in non-beta cells, and a human nonfunctional cell surface marker. Here we report that this vector efficiently transduced primary human cells, inducing the synthesis of a modified proinsulin that was processed and released as mature insulin. This retrovirally derived insulin displayed in vitro biological activity, specifically binding to and phosphorylation of the insulin receptor, comparable to human insulin. In vivo, the transplantation of insulin-producing fibroblasts reverted hyperglycemia in a murine model of diabetes, whereas proinsulin-producing cells were ineffective. These results support the possibility of developing insulin production machinery in human non-beta cells for gene therapy of IDDM.

Animals↗
PubMed1999

Insulin and intracellular calcium responsiveness to glucagon-like peptide-1 and pituitary adenylate cyclase-activating peptide by dispersed adult porcine islet cells.

BACKGROUND: There is a great need to learn more about porcine islet physiology because porcine islets represent a promising source of xenogeneic tissue for beta-cell replacement therapy in humans. METHODS: We evaluated the effects of two important physiological regulators of insulin secretion, glucagon-like peptide-1 (GLP-1) and pituitary adenylate cyclase-activating peptide (PACAP), on insulin release and intracellular calcium ([Ca++]i) by adult porcine islet cells. RESULTS: Exposure to GLP-1 and PACAP significantly potentiated glucose-induced insulin release and improved the sensitivity to glucose as a secretagogue. About 70% of cells stimulated with 20 mmol/L glucose alone showed an increase in [Ca++]i, whereas the addition of GLP-1 and PACAP induced [Ca++]i increases in 86% and 93% of cells, respectively. CONCLUSIONS: The good insulin and [Ca++]i responsiveness of porcine islet cells to both GLP-1 and PACAP provides an additional proof of their suitability for transplantation.

Animals↗
PubMed1999

Insulin secretory patterns and blood glucose homeostasis after islet allotransplantation in IDDM patients: comparison with segmental- or whole-pancreas transplanted patients through a long term longitudinal study.

IDDM patients undergoing islet, segmental pancreas or whole pancreas allotransplantation were studied at regular intervals after surgery (3-6 months, 1, 2, 3 and 4 years) to evaluate glycometabolic control (24 h metabolic profile, OGTT) and serum free insulin response to insulinogenic stimuli (arginine, IVGTT). Patients received the same immunosuppressive therapy, based on cyclosporin, steroids and azathioprine. Islet transplanted patients showed: 1) an early peak of insulin secretion after arginine, that was maintained up to 4 years; 2) an early, but low peak of insulin secretion after IVGTT, which was lost at 3 years, despite evidence that islets were still functioning (insulin independence with normal HbAlc levels); 3) a diabetic-like response to OGTT at 3 months, which improved at 2 years (IGT response); 4) fasting euglycemia with mild and reversible post-prandial hyperglycemia during the 24 h metabolic profile, which was maintained for up to 2 years. Insulin secretory patterns of islet transplanted patients were similar to segmental pancreas transplanted patients, and lower than whole pancreas transplanted patients. The reduced beta cell mass transplanted and the functional denervation of the transplanted islets seem to be the major determinants of this behaviour.

Adult↗
PubMed1999

Indications for clinical islet transplantation today and in the forseeable future--the diabetologist's point of view.

The treatment of patients with type 1 diabetes mellitus has to focus on short-term and long-term risks of the disease which means to avoid hyperglycemic or hypoglycemic coma as well as late complications. As we know from the DCCT study metabolic control substantially lowers the risk for retinopathy, nephropathy and neuropathy. We also know, that keeping the blood glucose in a nearly normal range inevitably is connected with a marked increase of severe hypoglycemia, an event which occurs more frequently when normoglycemia has been reached and the further slow decline of blood glucose is not recognized by the patient (autonomous neuropathy, hypoglycemia unawareness of other origin, long duration of diabetes etc.). Furthermore, counterregulatory hormones as glucagon and epinephrine may be lacking due to diminished or even lost alpha cells within the islets and as recently observed due to fibrosis of the adrenal medulla in long-term diabetes. The consequences of severe hypoglycemia are manifold: in the actual situation of unconsciousness the risk of heavy injuries and as long-term consequences irreversible brain damage may occur. Finally, the effort of the patient to reach normoglycemia includes the burden of an intensive blood glucose self-control day by day. This broad scenario of all the achievements and of all the problems connected with an intensified insulin treatment has to be regarded when the indication for an islet transplant will be discussed. From our point of view as clinicians it seems adequate not to give definite recommendations but to express our considerations for islet transplantation in patients with type 1 diabetes mellitus with the following list (table 1). It must be clearly stated, that at present transplantation of isolated islets by no means can serve as a treatment for a larger number of patients and this may hold through also for the foreseeable future. In this context, also the many contraindications should be summarized (table 2). Consequently we have to deal with several questions and problems which can be subdivided into those regarding the possible benefit for the patients from an islet graft (full success = insulin independence, partial success = lower exogenous insulin requirement due to additional endogenous insulin, measured by C-peptide levels, more stable glucose metabolism) and those regarding possible side effects (primary risk of implantation, threat for rejection of the primarily transplanted kidney). Furthermore, one may ask for risks when islets are transplanted alone (ITA). We therefore will address the following areas: 1. Simultaneous islet and kidney transplants 2. Islet transplants after kidney transplantation alone (IAK) 3. Islet transplantation after pancreas transplantation failure (P-failure) 4. Defect hypoglycemia counterregulation--life threatening hypoglycemia unawareness as indication for islet transplantation? 5. Autonomous cardiac neuropathy as indication for islet transplantation? 6. Significant clinical problems with exogenous insulin therapy as indication for islet transplantation?

Contraindications↗
PubMed1999

Human proinsulin production in primary rat hepatocytes after retroviral vector gene transfer.

The development of autologous somatic cells, engineered for the synthesis and release of human insulin under physiological stimuli, would certainly represent a major breakthrough in the therapy of insulin-dependent diabetes mellitus. We generated a retroviral vector containing the human proinsulin cDNA and the gene coding for the human nerve growth factor receptor for quantitative analysis of transduced cells. Primary rat hepatocytes were selected as target cells because of the constitutive expression of the pancreatic beta-cell glucose transporter GLUT-2 and the glycolitic enzyme glucokinase. Appropriate conditions for culture and retroviral transduction are described. The highest transduction efficiency, evaluated as percentage of LNGFr expressing cells was obtained by repeated infection cycles (40+/-10%). Human proinsulin accumulated in the culture medium of transduced rat hepatocytes (mean+/-SD): 18.1+/-7.9 (range 8.7-36.4) ng/24h/10(6) cells. Primary rat hepatocytes can be efficiently transduced by a retroviral vector and the de novo synthesis of human proinsulin can be induced. Primary cultured hepatocytes represent an useful model to test retroviral constructs engineered for the glucose-inducible expression of insulin under the control of liver-specific promoters.

Animals↗
PubMed1999

Efficacy and safety of acarbose in the treatment of Type 1 diabetes mellitus: a placebo-controlled, double-blind, multicentre study.

AIMS: The aim of the study was to evaluate the efficacy and safety of acarbose in patients with Type 1 diabetes mellitus (DM). METHODS: A multicentre double-blind, randomized, placebo-controlled study was performed. After a 6-week run-in, 121 patients were randomized to acarbose or placebo and to high- or low-fibre diet for 24 weeks. Acarbose dose was 50 mg t.d.s. for the first 2 weeks and 100 mg t.d.s. for the subsequent weeks. RESULTS: At the end of 24 weeks of treatment the intention to treat analysis showed that acarbose compared with placebo decreased 2 h postprandial plasma glucose levels (12.23 +/- 0.83 vs. 14.93 +/- 0.87 mmol/l; F = 6.1, P < 0.02) (least square means +/- SEM). No significant effect of acarbose was recorded on HbA1c or on the number of hypoglycaemic episodes. The effect of acarbose on blood glucose control was not influenced by the amount of carbohydrate and/or fibre intake. The incidence of adverse events were 75% and 39% in acarbose and placebo groups, respectively; they were mild and confined to the gastrointestinal tract. CONCLUSIONS: The use of acarbose in combination with insulin reduces postprandial plasma glucose levels in Type 1 diabetic patients who are not satisfactorily controlled with insulin alone but without significant effect on HbA1c.

Acarbose↗
PubMed1999

Mechanisms of coordination of Ca2+ signals in pancreatic islet cells.

Within pancreatic islet cells, rhythmic changes in the cytosolic Ca2+ concentration have been reported to occur in response to stimulatory glucose concentrations and to be synchronous with pulsatile release of insulin. We explored the possible mechanisms responsible for Ca2+ signal propagation within islet cells, with particular regard to gap junction communication, the pathway widely credited with being responsible for coordination of the secretory activity. Using fura-2 imaging, we found that multiple mechanisms control Ca2+ signaling in pancreatic islet cells. Gap junction blockade by 18 alpha-glycyrrhetinic acid greatly restricted the propagation of Ca2+ waves induced by mechanical stimulation of cells but affected neither Ca2+ signals nor insulin secretion elicited by glucose elevation. The source of Ca2+ elevation was also different under the two experimental conditions, the first being sustained by release from inner stores and the second by nifedipine-sensitive Ca2+ influx. Furthermore, glucose-induced Ca2+ waves were able to propagate across cell-free clefts, indicating that diffusible factors can control Ca2+ signal coordination. Our results provide evidence that multiple mechanisms of Ca2+ signaling operate in beta-cells and that gap junctions are not required for intercellular Ca2+ wave propagation or insulin secretion in response to glucose.

Animals↗
PubMed1999

Intramyocellular triglyceride content is a determinant of in vivo insulin resistance in humans: a 1H-13C nuclear magnetic resonance spectroscopy assessment in offspring of type 2 diabetic parents.

Insulin resistance is the best prediction factor for the clinical onset of type 2 diabetes. It was suggested that intramuscular triglyceride store may be a primary pathogenic factor for its development. To test this hypothesis, 14 young lean offspring of type 2 diabetic parents, a model of in vivo insulin resistance with increased risk to develop diabetes, and 14 healthy subjects matched for anthropomorphic parameters and life habits were studied with 1) euglycemic-hyperinsulinemic clamp to assess whole body insulin sensitivity, 2) localized 1H nuclear magnetic resonance (NMR) spectroscopy of the soleus (higher content of fiber type I, insulin sensitive) and tibialis anterior (higher content of fiber type IIb, less insulin sensitive) muscles to assess intramyocellular triglyceride content, 3) 13C NMR of the calf subcutaneous adipose tissue to assess composition in saturated/unsaturated carbons of triglyceride fatty acid chains, and 4) dual X-ray energy absorption to assess body composition. Offspring of diabetic parents, notwithstanding normal fat content and distribution, were characterized by insulin resistance and increased intramyocellular triglyceride content in the soleus (P < 0.01) but not in the tibialis anterior (P = 0.19), but showed a normal content of saturated/unsaturated carbons in the fatty acid chain of subcutaneous adipocytes. Stepwise regression analysis selected intramyocellular triglyceride soleus content and plasma free fatty acid levels as the main predictors of whole body insulin sensitivity. In conclusion, 1H and 13C NMR spectroscopy revealed intramyocellular abnormalities of lipid metabolism associated with whole body insulin resistance in subjects at high risk of developing diabetes, and might be useful tools for noninvasively monitoring these alterations in diabetes and prediabetic states.

Adult↗
PubMed1998

Independence of dimethylamiloride-sensitive Li+ efflux pathways and Na+-Li+ countertransport in human erythrocytes.

The in vivo function of the erythrocyte Na+-Li+ countertransport (SLC) is unknown. Whether SLC may reflect an operational mode of the widespread Na+-H+ exchanger (NHE) or may otherwise be expression of an independent membrane transport, remains presently unclear. We explored the presence of 5-(N,N-dimethyl)-amiloride (DMA)-sensitive Li+ pathways in human erythrocytes where the activity of the Na+ pump, Na+-K+ cotransport and anion exchange were suitably inhibited. A total of 0.02 mM DMA had no effect on SLC as expected, but gave a significant inhibition of Li+ efflux into both Na+ and Na+-free media. This DMA-sensitive Li+ pathway, but not SLC, was significantly enhanced by hyperosmolar cell shrinkage, which is a characteristic feature of NHE. In conclusion, DMA-sensitive Li+ pathways, possibly mediated by NHE, are present in erythrocytes and coexist with the DMA-insensitive, SLC. This finding supports the notion that SLC is independent of amiloride-sensitive NHE.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗