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G Reach

Publications and source records attributed to G Reach.

At least 37 records · Page 2Linked to original sources
PubMed1999

Cryopreservation of specific pathogen-free (SPF) pig islet cells: effect of culture time before cryopreservation and after thawing.

UNLABELLED: The aim of this study was to determine the optimal conditions (effect of culture time before and after cryopreservation) for cryopreservation of specific pathogen-free pig islet cells. METHODS: (1) Glucose-induced insulin secretion by fresh islet cells cultured for 10 days was compared to that by islet cells cryopreserved 7 days after isolation and cultured 3 days after thawing. (2) Islet cells were cryopreserved 1, 7, or 14 days after isolation and cultured 3, 7, 14, or 21 days after thawing. Islet cell number, insulin content, and insulin response under perifusion tests were investigated. RESULTS: (1) Insulin response by cryopreserved islet cells was identical to that by fresh islet cells (basal/stimulation index: 2. 13 +/- 0.19 vs 2.17 +/- 0.16, n = 4, NS), although the amount of secreted insulin was reduced by 40% (area under the curve: 2136 +/- 198 pM/10(4) cells/180 min vs 3564 +/- 636 pM/10(4) cells/180 min, P = 0.104). (2) Cell number 6 days after thawing was reduced by 54, 40, and 63% when cryopreservations were carried out at D1, D7, and D14. (3) Insulin content in cultured or cryopreserved islet cells increased between 7 and 14 days of culture. (4) Whatever the culture time before and after cryopreservation, insulin secretion in response to glucose was maintained. The insulin release was the highest for islet cells cryopreserved 14 days after isolation and cultured 14 days after thawing (stimulation index: 6.19 +/- 2.68). CONCLUSIONS: SPF pig islet cells remained functional after cryopreservation in polyethylene glycol and it may be important to culture islet cells over 14 days before and after cryopreservation.

Animals↗
PubMed1999

Long-term exposure of isolated rat islets of Langerhans to supraphysiologic glucose concentrations decreases insulin mRNA levels.

Chronic hyperglycemia has been postulated to contribute to beta-cell dysfunction in type 2 diabetic patients. A deleterious effect of prolonged exposure to high glucose concentrations on insulin gene expression has been demonstrated in insulin-secreting cell lines. This study was designed to investigate in isolated rat islets the effects of long-term exposure to supraphysiologic glucose concentrations on insulin, GLUT2, and glucokinase gene expression. The acute effects of glucose on gene expression were investigated by culturing rat islets in 2.8 or 16.7 mmol/L glucose for 24 hours. Insulin, GLUT2, and glucokinase mRNA levels were assessed by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). As expected, glucose acutely increased relative insulin and GLUT2 mRNA levels by 2.8- +/- 0.5-fold (n = 5, P < .005) and 1.8- +/- 0.3-fold (n = 5, P < .05), respectively, but had no effect on glucokinase gene expression (1.1- +/- 0.1-fold increase, n = 4, NS). These results validate the use of semiquantitative RT-PCR to detect changes in gene expression in rat islets. Islets were then cultured in 5.6 or 16.7 mmol/L glucose for 2, 4, or 6 weeks. Relative insulin mRNA levels were higher in islets cultured in high glucose after 2 weeks (1.8+/-0.1 v 1.0+/-0.1, n = 4, P < .05), identical after 4 weeks (0.9+/-0.1 v 1.00+/-0.2, n = 4, NS), and significantly lower after 6 weeks (0.6+/-0.1 v 1.0+/-0.2, n = 6, P < .05). Relative GLUT2 mRNA levels were higher in islets cultured in high glucose after 2 weeks (1.7+/-0.2 v 1.0+/-0.2, n = 3, P < .05) and then identical in both groups after 4 weeks (1.0+/-0.1 v 1.0+/-0.1, n = 3, NS) and 6 weeks (1.0+/-0.2 v 1.0+/-0.1, n = 6, NS). Relative glucokinase mRNA levels were identical under both culture conditions at 2 (1.4+/-0.4 v 1.0+/-0.2, n = 3, NS), 4 (0.8+/-0.5 v 1.0+/-0.3, n = 3, NS), and 6 (0.9+/-0.2 v 1.0+/-0.1, n = 6, NS) weeks. These results indicate that a 6-week exposure of rat islets to supraphysiologic glucose concentrations decreases insulin mRNA levels without affecting GLUT2 and glucokinase gene expression. We conclude that the phenomenon of glucose toxicity decreasing insulin gene expression is not restricted to transformed cells, and might provide insight into the mechanisms by which chronic hyperglycemia adversely affects beta-cell function.

Animals↗
PubMed1999

[Possible consequences on the follow up of type 2 diabetic patients of a recent modification of a glycosylated hemoglobin assay].

Glycated hemoglobin assay is considered as the gold standard for the follow-up of diabetic patients, and the assay must now be calibrated on the results of the method used in the DCCT study. It is considered as appropriate to intensify the therapy of type 2 diabetic patients when two consecutive values higher than 8% are observed. We present herein a case report illustrating the possible consequences on the follow up of type 2 diabetic patients of a recent significant modification, not reported elsewhere, aimed to eliminate a bias vs the DCCT method of a system, DCA 2000, largely used to determine HbA1c level in diabetic patients: before this modification, the DCA 2000 method underestimated the glycated hemoglobin level by 0.5% for a 8% value. Such is no more the case.

Adult↗
PubMed1998

Continuous glucose monitoring in the free-moving rat.

The aim of this work was to set up an experimental model of glycemic fluctuations for assessing in the conscious freely moving rat, the performance of a continuous glucose-monitoring system, using a pocket-calculator-size electronic control unit and a miniaturized subcutaneous glucose sensor. The well-known triphasic glycemic pattern following streptozotocin injection (initial peak and secondary hypoglycemia preceding the establishment of permanent hyperglycemia) was used as a way to obtain spontaneous changes in blood glucose level over a wide concentration range. This report demonstrates that streptozotocin injection produced highly reproducible changes in the current generated by the sensor: an initial peak and a secondary nadir, during which blood sampling provided the evidence of hyperglycemia associated with immunoreactive hypoinsulinemia, and of hypoglycemia associated with hyperinsulinemia, respectively. This reproducible experimental model should be valuable for the assessment of a continuous glucose-monitoring system.

Animals↗
PubMed1998

[Use of islet cells in cell therapy].

Insulin dependent diabetes mellitus is a common disease affecting 1.5 million patients in Europe. It is currently treated by multiple injections of insulin associated with blood glucose self monitoring. The goal of the treatment is to obtain near normal glucose concentration, in order to prevent the later complications (retinopathy, nephropathy, neuropathy, macroangiopathy) of the disease--which may be severe--while avoiding severe hypoglycaemia. Although diabetes therapy has improved enormously in the last few decades, intensive research is currently aimed at replacing not only the missing hormone but also the cells which normally produce insulin in the pancreas. Transplantation of insulin secreting cells as a treatment of diabetes mellitus therefore has a special significance among other applications of cell therapy, since it deals with a disease which already has an efficient therapy. The aim of this article is the discussion of the objectives and the hopes in this field.

Cell- and Tissue-Based Therapy↗
PubMed1998

Glucose-insulin kinetics of a bioartificial pancreas made of an AN69 hydrogel hollow fiber containing porcine islets and implanted in diabetic mice.

The goal of this study was to determine whether porcine islets encapsulated in hollow fibers made of AN69 copolymer can correct hyperglycemia in diabetic mice and provide normal tolerance to a glucose challenge. In vitro perifusion of hollow fibers demonstrated the rapid kinetics of insulin release in response to glucose. Two fibers containing islets were transplanted into the peritoneal cavity of each of 17 streptozotocin induced diabetic mice. In 11 mice, diabetes was reversed within 3 days with plasma glucose levels decreasing from 19.7 +/- 0.9 (mean +/- SEM) before implantation to 10.9 +/- 0.8 mmol/L. Intraperitoneal glucose tolerance tests were performed in transplanted (n = 7), nondiabetic (n = 15), and diabetic mice (n = 6). A normal glucose pattern was observed in the transplanted diabetic mice. This was achieved in the presence of plasma insulin levels lower than those observed in control nondiabetic mice, suggesting the presence of a state of hypersensitivity to insulin, which was demonstrated in this model by exogenous insulin tolerance tests. In conclusion, encapsulation of islets suspended in ultraculture medium in biocompatible membranes of AN69 can provide xenograft survival, and complete normalization of glucose tolerance can be achieved.

Acrylic Resins↗
PubMed1998

Inhibition of insulin secretion by leptin in normal rodent islets of Langerhans.

The recently discovered adipose cell-specific hormone called leptin decreases food intake and increases energy expenditure in rodents through a pathway involving hypothalamic leptin receptors, OB-R. In addition, leptin decreases insulin circulating levels independent of the reduction in food intake. Whether or not the hormone has a direct effect on pancreatic beta-cells is not clear, because previous in vitro studies have led to controversial results depending on the animal model used. The present study was designed to investigate the effects of leptin in islets of Langerhans isolated from normal rodents. Three isoforms of the leptin receptor, OB-Ra, b, and f, were detected by RT-PCR analysis of total RNA from rat islets. In static incubations, leptin (10 ng/ml) did not alter basal insulin secretion nor insulin secretion stimulated by glucose alone, potassium chloride, or ketoisocaproic acid. In contrast, insulin secretion stimulated by glucose + 3-isobutyl 1-methylxanthine (IBMX) was inhibited by 34 +/- 15% (n = 4, P < 0.05). This was further substantiated in perifusion experiments, in which leptin decreased by 31 +/- 3% (n = 5, P < 0.01) glucose + IBMX-stimulated insulin release. Similarly, in mouse islets a significant inhibitory effect of leptin (-31 +/- 4%, n = 6, P < 0.05) was observed only on glucose + IBMX-stimulated insulin secretion, with no effect of the hormone on basal nor glucose-stimulated secretion. Finally, leptin was totally inefficient in islets isolated from obese fa/fa rats, which bear a mutation in OB-R. These results suggest that, in normal rodent islets, leptin specifically inhibits IBMX-potentiated glucose-induced insulin secretion, through a direct effect involving at least one of the three isoforms of OB-R expressed in islets.

1-Methyl-3-isobutylxanthine↗
PubMed1998

Perifusion analysis of insulin secretion from specific pathogen-free large-white pig islets shows satisfactory functional characteristics for xenografts in humans.

Though the pig appears to be the islet donor of choice for grafts in diabetic patients, there may be a risk of transmission of infectious agents. In this context, we adopted a strategy of islet isolation from pigs raised and killed in specific pathogen-free (SPF) conditions as a minimum with regard to the concept of quality assurance. Accordingly, the present study investigated the function of SPF pig islets to determine whether they react qualitatively and quantitatively to nutriments, hormones and neuromediators with which they would be confronted in man and could therefore provide effective regulation during physiologic or physiopathologic situations. beta cells from 18 Large-White SPF pigs were functionally intact after 7 days in culture. Insulin stimulation indexes (SI) of 3.1 +/- 0.2, 2.2 +/- 0.1, and 4.4 +/- 0.3 were found respectively for 30 mmol/l K+, 100 mumol/l tolbutamide and 10 mmol/l theophylline. Basal insulin secretion (72.2 +/- 7.6 muU/min) had already increased significantly (p < 0.001) with 5.5 mmol/l glucose (184.2 +/- 25.5 muU/min, SI: 2.5 +/- 0.6), indicating that the threshold stimulatory concentration was comparable to that of human islets. Insulin secretion increased in a glucose dose-dependent manner (p < 0.001): SI: 3.1 +/- 0.3 and 3.6 +/- 0.2 with 11.0 mmol/l and 22.0 mmol/l glucose, which showed a satisfactory magnitude with reference to human islets. Even the subtle phenomenon of "glucose memory" was apparent in these pig islets. Arginine stimulated (p < 0.001) insulin secretion dose-dependently (SI: 2.2 +/- 0.3 with 5 mmol/l and 2.9 +/- 0.2 with 10 mmol/l). The ketone body beta-hydroxybutyrate (10 mmol/l) also induced insulin secretion (SI: 4.3 +/- 0.3). Insulin release was stimulated by 4 mumol/l gastric inhibitory peptide, revealing sensitivity to the hormonal enteroinsular axis, and by 2 mumol/l glucagon. Parasympathetic cholinergic influence was studied using 500 mumol/l carbamylcholine, which increased insulin secretion. The influence of orthosympathetic control and of stress situations was also studied. As in human islet response, epinephrine and the alpha 2-agonist clonidine (50 mumol/l) inhibited insulin secretion. Finally pre-culture of islets may be beneficial for graft outcome, provided that no deterioration in islet function occurs. A prolonged 21-day culture of SPF pig islets showed no decrease in insulin response to glucose, arginine and potassium, even with an unaltered threshold stimulatory glucose concentration. Thus, Large-White SPF pigs and the application of our isolation procedure provided islets with functional characteristics reproducibly compatible with potential utilisation for effective regulation of glycaemia under physiologic and physiopathologic situations in humans.

Animals↗
PubMed1998

Does leptin regulate insulin secretion?

The hormone leptin secreted by adipocytes plays a major role in body weight homeostasis. Its main target is the hypothalamus, but it also affects several peripheral tissues directly. The direct effect of leptin on insulin secretion by pancreatic beta cells has been investigated in several studies, though with controversial results. Interpretation of these data must take into account the animal model and the leptin concentrations used. Experiments carried out on islets from ob/ob mice harbouring a mutation in the leptin gene are not representative of the leptin effect in normal animals because ob/ob islets are very sensitive to the hormone and show altered regulation of insulin secretion. In normal rodent islets, physiological concentrations of leptin seem to inhibit insulin secretion only when the islets are maximally stimulated with high concentrations of glucose associated with secretion potentiators. Several isoforms of the leptin receptor are expressed in pancreatic beta cells. Indirect experimental evidence suggests that leptin signalling in islets requires the long isoform of the receptor. The molecular mechanisms underlying the effect of leptin on insulin secretion are unknown. Our hypothesis is that physiological concentrations of leptin in normal rodents do not affect the direct pathway (coupling a rise in glucose concentration to insulin secretion) but modulate a potentiation of glucose-induced insulin secretion involving cyclic AMP or phospholipase C/protein kinase C activation.

Adipocytes↗
PubMed1998

Long-term culture of free or encapsulated islets isolated from specific pathogen-free (SPF) pigs.

As the risk of recipient contamination is a limiting factor for xenotransplantation, the use of specific pathogen-free (SPF) pigs is mandatory. This study investigated the long-term culture of SPF pig islets and evaluated their insulin production when encapsulated in AN69 hollow fibres. Insulin secretion was studied after 3 weeks (n = 10), 2 months (n = 8) and 3 months (n = 3) by 45-min incubation in the presence of 2.8, 5.5, 11 and 16.5mM glucose. Although a decrease in the amount of secreted insulin occurred (1385 +/- 421 and 4323 +/- 1068 microns U/ml at 3 weeks for 2.8 and 16.5 mM glucose respectively; 702 +/- 261 and 2397 +/- 1047 microU/ml at 2 months; 59 +/- 23 and 154 +/- 34 microU/ml at 3 months), glucose-dependent insulin secretion was observed in all cases, i.e. stimulation indices of 8.1 +/- 3.1 (p < 0.05 vs the presence of 5.5 mM glucose) at 3 weeks, 3.3 +/- 1.1 at 2 months and 3.0 +/- 0.7 at 3 months. The insulin secretion of encapsulated SPF pig islets, cultured for 1 or 3 weeks, was evaluated under perifusion conditions using a stimulus of 10mM glucose plus 5.5 mM theophylline. Glucose stimulation resulted in a significant two-fold increase in insulin secretion (p < 0.05), which was maintained over culture time. These results indicate that SPF-isolated islets remained functional when cultured for several weeks either as free or encapsulated islets, although the magnitude of insulin secretion decreased dramatically after three months of culture.

Animals↗
PubMed1997

A user-friendly method for calibrating a subcutaneous glucose sensor-based hypoglycaemic alarm.

A crucial step in developing a glucose monitoring system using a subcutaneous implanted glucose sensor is the transformation of the sensor signal (a current) into an estimation of a blood glucose concentration. We have developed an Electronic Control Unit (ECU) able to recognize, before and after a glucose load, that the sensor current presents a plateau, thus triggering an alarm asking for blood glucose determination. The system, fed with these results, subsequently transforms the current into an estimation of glucose concentration by linear extrapolation based on the sensor sensitivity and the background current computed from the two sets of current and glycaemia values (two-point calibration). In addition, the system is able to trigger an alarm when this estimation decreases below a threshold that can be set by the user. This system was evaluated in experiments performed in 12 normal rats. The quality of the calibration was assessed by comparing, by error grid analysis, the data displayed on the liquid-crystal display of the ECU to concomitant plasma glucose concentration determined at frequent intervals, 65 +/- 6 and 26 +/- 5% of the values were in zones A (good) and B (acceptable estimation) of the grid, respectively. The system was set to trigger an alarm when the estimation of glucose concentration decreased below 70 mg/dl. Following an insulin administration, the alarm was triggered when the system displayed a 64 +/- 2 mg/dl glucose concentration. The concomitant plasma glucose concentration was 59 +/- 5 mg/dl (NS). In conclusion, this work validates experimentally the new, user-friendly method for calibrating the glucose sensor integrated into the ECU, based on an automatic detection of plateaus. The quality of the sensor calibration performed with this procedure is compatible with the appropriate functioning of this continuous glucose monitoring system, which was demonstrated by its ability to detect mild hypoglycaemia following insulin injection.

Animals↗
PubMed1997

Reversal of diabetes in non-obese diabetic mice by xenografts of porcine islets entrapped in hollow fibres composed of polyacrylonitrile-sodium methallylsulphonate copolymer.

Intraperitoneal xenografting of islets immunoprotected by semipermeable membranes is a potential method of avoiding rejection by reversal of diabetes without immunosuppression. In this preliminary study, a xenograft of porcine islets, immunoprotected in semipermeable hollow fibres composed of a hydrogel of a polyacrylonitrile-sodium methallylsulphonate copolymer (AN 69), was used to reverse autoimmune insulin-dependent diabetes mellitus (IDDM) in the NOD mouse. A diabetic state was maintained in all 46 NOD mice which received transplants of empty fibres. Transplantation of encapsulated islets reversed the diabetic state in 37% (18/54) of the recipients. In these mice, nonfasting blood glucose concentration decreased within 24 h. Glycaemia was kept below the diabetic control range and the initial pretransplant value for 6 weeks. Recipient NOD mice suffered from the severe insulitis characteristic of clinical diabetes, confirming that reversal of the hyperglycaemic state was due solely to the xenografts. Pretransplant glycaemia was slightly (p < 0.05) higher in mice which remained diabetic after grafts of fibre-containing islets than in animals which experienced reversal of hyperglycaemia after transplantation) for the peritoneal cavity of recipients which had returned to normoglycaemia after grafting with islet-containing fibres. In all 4 cases, the islets responded to glucose during a perifusion assay. In 2 out of 4 grafts removed from mice which remained hyperglycaemic after grafting with islet-containing fibres (11, 13, 15 and 27 days after transplantation), no basal or stimulated insulin secretion was detectable. Histological sections of a total of 75 fibres retrieved from the peritoneal cavities of recipient NOD mice showed surrounding inflammation, with adherent cells, neovascularisation and fibrotic reaction. These preliminary results are promising for the continued development of this bioartificial pancreas for xenogeneic islet transplantation since they demonstrate that xenogeneic islets can survive in the autoimmune environment of the NOD mouse with spontaneous diabetes mimicking human IDDM).

Acrylic Resins↗
PubMed1997

Bioartificial pancreas containing porcine islets of Langerhans implanted in low-dose streptozotocin-induced diabetic mice: effect of encapsulation medium.

Two encapsulation culture media without animal serum were compared for development of a bioartificial pancreas. Porcine islets were suspended in Hams F10 medium supplemented with 2% Ultroser (US) or in Ultraculture medium (UC) and encapsulated in hollow fibres composed of AN69 copolymer. The function of encapsulated islets was assessed by intraperitoneal transplantation of two fibres in streptozotocin-induced diabetic mice. In both groups of transplanted mice (US, n = 26; UC, n = 18), a significant decrease in plasma glucose concentration was observed three days after fibre implantation (from 21.9 +/- to 14.4 +/- 0.8 mmol/l for US fibres and from 22.7 +/- 0.8 to 13.3 +/- 1.3 mmol/l for US fibres and from 22.7 +/- 0.8 to 13.3 +/- 1.3 mmol/l for UC fibres). Graft survival 17 days after implantation was 61% for mice with UC fibres and 35% for those with US fibres (P = 0.0001). Intramuscular glucose tolerance tests were performed in these animals (US, n = 5; UC, n = 10), and a normal glucose pattern was observed in both groups of transplanted mice. The results show that a complete normalisation of blood glucose and glucose tolerance can be achieved by implantation of a bioartificial pancreas. Moreover, UC appears to be a more suitable encapsulation culture medium for porcine islets in vivo.

Acrylic Resins↗
PubMed1997

Extreme insulin resistance: clinical management by external subcutaneous insulin infusion.

Management of very high insulin requirements in rare extreme insulin resistance syndromes is difficult and poorly documented. We report a case of a type B insulin-resistant patient requiring approximately 10,000 units of insulin per day, i.e. beyond the possibilities of current insulin formulations and delivery devices. Only the Panomat C10 portable pump model (Disetronic) and U500 Humulin (Lilly) allowed the required rate of 400 units per hour to be attained only when the reservoir was changed twice daily and the site and catheter were changed once daily. Three months after discharge, the patient was in good general and local condition, but with only fair diabetes control (glycated haemoglobin 9.5%).

Adult↗
PubMed1997

Minimisation of microbial contamination for potential islet xenografts using specific pathogen-free pigs and a protected environment during tissue preparation.

One major risk of islet xenotransplantation is transmission of infections. We thus compared microbial contamination during preparation of islets from 4 pigs conventionally breeded and slaughtered or 8 specific pathogen free (SPF) pigs, and different environmental conditions during pancreas excision. Pancreas harvested in a slaughterhouse (for conventional pigs) or in a protected autopsy room (for SPF pigs) were soaked in betadine solution and submitted to enzymatic digestion with collagenase. Islets were purified on histopaque gradient with a COBE 2991 processor. For each step of the process, a 10 ml aliquot was harvested and microbial contamination was analysed. For all animals, contamination of livers, which were not soaked in betadine solution, was also examined. Analysis of livers from the 4 conventional pigs showed polymicrobial contaminations (1,122 +/- 841 CFU/mg) with several species of Staphylococcus, Streptococcus, Bacillus and Enterobacteriaceae. For these conventional pigs, soaking of pancreas in betadine solution and presence of antibiotics in all media decreased the pancreatic contamination compared to hepatic contamination, but were unable to suppress it, as transport solution and crude suspension obtained after the digestion step with collagenase showed persistent contamination (9.7 +/- 2.4 and 10.5 +/- 4 CFU/ml, respectively). After islet purification by histopaque gradient, no medium remained contaminated. During analysis of the 8 SPF pigs, no liver exhibited contamination. Analysis of medium from each preparation step showed complete absence of contamination for 7 pancreases. Only one contamination with Staphylococcus simulans was observed for one pancreas in transport solution (6 CFU/ml), and persisted in digestion medium (16 CFU/ml). Finally, all purified suspensions were completely sterile. In conclusion, breeding conditions of pig islet donors, and controlled environment for pancreas excision, considerably influence the risk of microbial contamination. In order to limit the risk, SPF pigs are a suitable and compulsory source of islets.

Animals↗
PubMed1996

Use of a subcutaneous glucose sensor to detect decreases in glucose concentration prior to observation in blood.

The development of a hypoglycemic alarm system using a subcutaneous glucose sensor implies that a decrease in blood glucose is rapidly followed by a decrease in the signal generated by the sensor. In a first set of experiments the linearity and the kinetics of the response of sensors implanted in the subcutaneous tissue of normal rats were investigated during a progressive increase in plasma glucose concentration: the sensitivities determined between 5 and 10 mM and between 10 and 15 mM were not significantly different, and a 5-10 min delay in the sensor's response was observed. In a second set of experiments, performed in diabetic rats, the kinetics of the decrease in subcutaneous glucose concentration following insulin administration was monitored during a decrease in plasma glucose level, from 15 to 3 mmol/L. During the 20 first min following insulin administration, the sensor monitored glucose concentration in subcutaneous tissue with no lag time. Subsequently, the decrease in the estimation of subcutaneous glucose concentration preceded that of plasma glucose. This phenomenon was not observed when the same sensors were investigated in vitro during a similar decrease in glucose concentration and may be due to a mechanism occurring in vivo, such as the effect of insulin on glucose transfer from the interstitial space to the cells surrounding the sensor. It reinforces the interest of the use of implantable glucose sensors as a part of a hypoglycemic alarm.

Scintillation Counting↗
PubMed1996

Xenografts of porcine islets immunoprotected in hollow fibres reduce the incidence of diabetes in non-obese diabetic mice.

Non-obese diabetic (NOD) mice develop an autoimmune disease with a long prodromal period and constitute a model for investigating the prevention of human insulin-dependent diabetes mellitus. Since insulin injected prophylactically has been shown to reduce incidence of diabetes in NOD mice, we tested a new strategy consisting of prophylactic xenografts of porcine pancreatic islets immunoprotected in semipermeable hollow fibres. Female NOD mice were transplanted twice (at 60 and 180 days of age) with islet-containing or empty fibres. Within the group grafted with protected islets, the incidence of diabetes was reduced (37 vs 75%; p < 0.01), the onset of disease was delayed (p < 0.02), and the severity of lymphocytic inflammation of endogenous islets was reduced (p < 0.02). When already diabetic mice were not taken into account for analysis, blood glucose level was slightly lower in those grafted with islet-containing fibres (p < 0.04). Graft function was also evidenced by HPLC separation of porcine insulin in NOD sera. Histological and perifusion studies of fibres retrieved from recipients confirmed immunoprotection. During co-transfer, T splenocytes from mice grafted with islet-containing fibres were able to reduce the capacity of T cells from diabetic donors to adoptively transfer the disease (p < 0.01). Antigens for islet-cell autoantibodies (ICA) in pancreata from both groups were compared by immunofluorescence with the same ICA-positive human sera to ensure that differences were due to antigen quantitative changes. These antigens, which could serve as an index of a possibly more extensive antigen beta-cell rest, were decreased (p < 0.01) in mice grafted with protected islets. Reduction of diabetes and insulitis following early islet transplantation may thus be due to generation of cellular mechanisms that actively suppress disease, and possibly in part to a decrease in antigens which make beta cells less vulnerable to autoimmune aggression. These effects can be obtained with xenogeneic islets protected in hollow fibres, thereby eliminating the need for immunosuppression. Based on the concept of prophylactic insulin therapy, this form of insulin administration offers a controlled means of delivering insulin to meet the physiological needs of recipients.

Aging↗