Measurement of glucose concentrations in rats: differences between glucose meter and plasma laboratory results

Measurements of basal d-glucose transport through GLUT1 across the intact plasma membrane of isolated segments from single fast- and slow-twitch skeletal muscle fibres of rat

Aim

To develop a method for direct measurement of the fluorescent d‐glucose analogue 2‐NBDG transport across the plasma membrane of single skeletal muscle fibres and derive the theoretical framework for determining the kinetic parameters for d‐glucose transport under basal conditions.

Methods

A novel method is described for measuring free 2‐NBDG transport across plasma membrane of single rat muscle fibres at rest. The 2‐NBDG uptake was >90% suppressed by 100 µM cytochalasin B in both fast‐twitch and slow‐twitch fibres, indicating that the 2‐NBDG transport is GLUT‐mediated. Fibres were identified as fast‐twitch or slow‐twitch based on the differential sensitivity of their contractile apparatus to Sr²⁺.

Results

The time course of 2‐NBDG uptake in the presence of 50 µM 2‐NBDG follows a one‐phase exponential plateau curve and is faster in fast‐twitch (rate constant 0.053 ± 0.0024 s^‐1) than in slow‐twitch fibres (rate constant 0.031 ± 0.0021 s^‐1). The rate constants were markedly reduced in the presence of 20 mM d‐glucose to 0.0082 ± 0.0004 s^‐1 and 0.0056 ± 0.0002 s^‐1 in fast‐twitch and slow‐twitch fibres respectively. 2‐NBDG transport was asymmetric, consistent with GLUT1 being the major functional GLUT isoform transporting 2‐NBDG in muscle fibres at rest. The parameters describing the transport kinetics for both 2‐NBDG and d‐glucose (dissociation constants, Michaelis–Menten constants, maximal rates of uptake and outflow) were calculated from the measurements made with 2‐NBDG.

Conclusion

Free 2‐NBDG and d‐glucose transport across the plasma membrane of single rat muscle fibres at rest is fast, conclusively showing that the rate‐limiting step in d‐glucose uptake in skeletal muscle is not necessarily the GLUT‐mediated transport of d‐glucose.

Practical Considerations when Using Mouse Models of Diabetes

Mouse models of diabetes are important tools used in preclinical diabetes research. However, when working with these models, it is important to consider factors that could influence experimental outcome. This is particularly important given the wide variety of models available, each with specific characteristics that could be influenced by extrinsic or intrinsic factors. Blood glucose concentrations, a commonly used and valid endpoint in these models, are particularly susceptible to manipulation by these factors. These include potential effects of intrinsic factors such as strain, sex, and age and extrinsic factors such as husbandry practices and experimental protocols. These variables should therefore be taken into consideration when the model is chosen and the experiments are designed. This chapter outlines common variables that can impact the phenotype of a model, as well as describes the methods used for assessing onset of diabetes and monitoring diabetic mice.

Evaluation of the appropriateness of using glucometers for measuring the blood glucose levels in mice

Glucometers are also widely used in diabetes research conducted using animal models. However, the appropriateness of measuring blood glucose levels using glucometers in animal models remains unclear. In this study, we evaluated the consistency between the blood glucose levels measured by 11 models of glucometers and plasma glucose levels measured by a laboratory biochemical test in blood samples collected by retro-orbital sinus puncture or tail-tip amputation. In both blood samples obtained by retro-orbital sinus puncture and those obtained by tail-tip amputation, 10 of the 11 models of glucometers yielded higher glucose values, while 1 yielded lower glucose values, than the plasma glucose values yielded by the laboratory test, the differences being in direct proportion to the plasma glucose values. Most glucometers recorded higher blood glucose levels after glucose loading and lower blood glucose levels after insulin loading in retro-orbital sinus blood as compared to tail vein blood. Our data suggest that the blood glucose levels measured by glucometers in mice tended to be higher than the plasma glucose levels yielded by the biochemical test under the hyperglycemic state, and that differences in the measured levels were observed according to the blood collection method depending on the glycemia status.

Protective unfolded protein response in human pancreatic beta cells transplanted into mice

BACKGROUND

There is great interest about the possible contribution of ER stress to the apoptosis of pancreatic beta cells in the diabetic state and with islet transplantation.

METHODS AND FINDINGS

Expression of genes involved in ER stress were examined in beta cell enriched tissue obtained with laser capture microdissection (LCM) from frozen sections of pancreases obtained from non-diabetic subjects at surgery and from human islets transplanted into ICR-SCID mice for 4 wk. Because mice have higher glucose levels than humans, the transplanted beta cells were exposed to mild hyperglycemia and the abnormal environment of the transplant site. RNA was extracted from the LCM specimens, amplified and then subjected to microarray analysis. The transplanted beta cells showed an unfolded protein response (UPR). There was activation of many genes of the IRE-1 pathway that provide protection against the deleterious effects of ER stress, increased expression of ER chaperones and ERAD (ER-associated protein degradation) proteins. The other two arms of ER stress, PERK and ATF-6, had many down regulated genes. Downregulation of EIF2A could protect by inhibiting protein synthesis. Two genes known to contribute to apoptosis, CHOP and JNK, were downregulated.

CONCLUSIONS

Human beta cells in a transplant site had UPR changes in gene expression that protect against the proapoptotic effects of unfolded proteins.

Performance of the Ascensia ENTRUST glucose meter for determination of blood glucose concentration in rats

BACKGROUND

The Ascensia ENTRUST blood glucose meter is intended for self-monitoring of blood glucose by diabetic patients. Use of such a glucometer would minimize blood volume requirements for the measurement of glucose in small laboratory animals.

OBJECTIVE

The purpose of this study was to assess the performance of the Ascensia ENTRUST for measuring glucose in whole blood from Wistar rats by evaluating the effect of anticoagulant and sample processing delay and comparing normalized results with plasma glucose concentration.

METHODS

Blood samples were collected from the retroorbital sinus of 30 male Wistar rats with a wide range of blood glucose concentrations. Glucose concentration was measured with the Ascensia ENTRUST in nonheparinized (NH) and heparinized samples immediately after collection (Hep-0) and in heparinized samples after a 15 min delay at 23-28 degrees C (Hep-15). Heparinized samples were centrifuged and glucose concentration was determined in plasma using an automated chemistry analyzer. Results were compared to assess the effect of anticoagulant (NH vs Hep-0) and time (Hep 0 vs Hep 15), and to compare normalized Hep-15 results with plasma glucose concentration.

RESULTS

Glucose concentration was not significantly different between NH and Hep-0 samples. Glucose concentration was lower in Hep-15 (77+/-36.9 mg/dL) than Hep-0 (88+/-39.7 mg/dL) samples, but the difference was not significant. With normalization, Hep-15 glucose concentration correlated well (r>or=.98) with plasma glucose concentration but was lower by 6.0+/-16.7 mg/dL, with a positive bias at low glucose concentrations and a negative bias at high concentrations.

CONCLUSION

The Ascensia ENTRUST may be adequate for repeated blood glucose measurements in rats, but its results do not accurately predict plasma glucose concentrations measured by an automated clinical chemistry analyzer.

Pancreatic endoderm derived from human embryonic stem cells generates glucose-responsive insulin-secreting cells in vivo

Development of a cell therapy for diabetes would be greatly aided by a renewable supply of human beta-cells. Here we show that pancreatic endoderm derived from human embryonic stem (hES) cells efficiently generates glucose-responsive endocrine cells after implantation into mice. Upon glucose stimulation of the implanted mice, human insulin and C-peptide are detected in sera at levels similar to those of mice transplanted with approximately 3,000 human islets. Moreover, the insulin-expressing cells generated after engraftment exhibit many properties of functional beta-cells, including expression of critical beta-cell transcription factors, appropriate processing of proinsulin and the presence of mature endocrine secretory granules. Finally, in a test of therapeutic potential, we demonstrate that implantation of hES cell-derived pancreatic endoderm protects against streptozotocin-induced hyperglycemia. Together, these data provide definitive evidence that hES cells are competent to generate glucose-responsive, insulin-secreting cells.

Changes in gene expression in beta cells after islet isolation and transplantation using laser-capture microdissection

AIMS/HYPOTHESIS

The process of islet isolation can cause chemical and mechanical injury to beta cells. In addition, hyperglycaemia after islet transplantation can compromise beta cell function. The aim of this experiment was to evaluate changes in gene expression in endogenous islets using laser-capture microdissection (LCM).

MATERIALS AND METHODS

Islets from B6AF1 mice were studied in situ in the pancreas as well as those freshly isolated or cultured for 24 h. Fresh islets were transplanted under the kidney capsule of syngeneic diabetic (streptozocin-induced) and non-diabetic mice. Frozen sections from all the samples were prepared for LCM to obtain beta cell-enriched tissue; RNA was extracted and amplified using T7 polymerase. RT-PCR was used to assess expression of selected genes critical for beta cell function (Ins, Ipf1 [previously known as Pdx1], Slc2a2 [previously known as GLUT2] and Ldha) and the stress response (Hmox1 [previously known as HO-1], Gpx1, Tnfaip3 [previously known as A20] and Fas). Immunostaining was also performed.

RESULTS

In freshly isolated and cultured islets, insulin and Ipf1 mRNA levels were decreased by 40% (compared with islets in situ), while stress genes were upregulated. Comparison between in situ pancreatic islets and engrafted beta cells of cured mice showed declines in Ipf1 expression.

CONCLUSIONS/INTERPRETATION

Our experiment, the first report to investigate changes in gene expression in endogenous islets using LCM, indicate that beta cells following islet isolation and residing in a foreign graft environment have decreased expression of genes involved in insulin production and increased expression of stress genes. Our data suggest that an islet graft, even in successful transplantation, may be different from endogenous islets in gene expression.

Exercise induces hypoglycemia in rats with islet transplantation

Recently, islet transplantation in patients with type 1 diabetes has had greater success than in the past, but the important question of whether the kinetics of islet secretion are able to accommodate the metabolic demands of special conditions such as exercise remains unanswered. Syngeneic rat islets (4,000 islet equivalents/rat) were transplanted into the liver, kidney, and peritoneal cavity (encapsulated or nonencapsulated) of rats with streptozocin-induced diabetes. Normoglycemic transplanted rats and age-matched controls were subjected to 30 min of moderate exercise on a treadmill 5 weeks after transplantation. Although control rats maintained near normoglycemia during and after exercise, the rats with islet transplants had significantly lower blood glucose levels. For the rats with islets in the liver, increased C-peptide levels were found at 30 min (790 +/- 125 and 1,450 +/- 250 pmol/l at 0 and 30 min, respectively; P < 0.01), whereas a decrease was found in controls and in rats with islets transplanted into the peritoneal cavity or under the kidney capsule. Moreover, increased glucagon levels were found after exercise in the rats with islets transplanted into the liver (62 +/- 6, 165 +/- 29, 155 +/- 27, and 97 +/- 13 pg/ml at 0, 30, 60, and 90 min, respectively; P < 0.05), whereas no changes in glucagon levels were observed in controls. In conclusion, moderate exercise caused hypoglycemia in rats with islet transplants in different sites including liver, kidney, and peritoneal cavity. C-peptide and glucagon responses to exercise were very different in rats with transplanted islets compared with controls. This islet dysfunction led to exercise-induced hypoglycemia.

Importance of hyperglycemia on the primary function of allogeneic islet transplants

BACKGROUND

Hyperglycemia has been shown to influence primary function of islet isografts. In this study, we investigated the influence of hyperglycemia on primary function of allogeneic islets transplanted into spontaneously diabetic recipients (NOD) or streptozotocin-induced diabetic mice (BALB/c).

METHODS

Mice with moderate, severe, or very severe hyperglycemia underwent transplantation with a marginal number of islets (350 into BALB/c mice and 700 into NOD mice). To prevent the alloimmune response, we used blockade of CD28:B7 and CD40L:CD40 costimulatory signaling pathways to determine the effect of hyperglycemia alone. Blood glucose levels of the mice were monitored after transplantation, and the grafts were assessed morphologically.

RESULTS

Transplantation of allogeneic islets into moderately hyperglycemic BALB/c mice or severely diabetic NOD mice normalized the blood glucose levels in all mice within 3 days after transplantation, demonstrating the primary function of the graft. However, primary nonfunction was observed in all animals when islet transplantation was performed into severely diabetic BALB/c mice or very severely diabetic NOD mice. When mice were treated with costimulation blockade, reversal of diabetes was observed in severely diabetic BALB/c mice 15 days after transplantation, showing that the islets could adapt to the environment and function. However, transplantation of islets into NOD mice with very severe diabetes treated with costimulation blockade did not reverse diabetes, showing that even in the absence of alloimmune responses and given an adaptation period, the islets could not function.

CONCLUSIONS

This study demonstrates that severe hyperglycemia impairs islet allograft function in BALB/c and NOD mice and that successful islet allotransplantation depends on the degree of hyperglycemia in the recipient.

Altering dietary protein type and quantity reduces urinary albumin excretion without affecting plasma glucose concentrations in BKS.cg-m +Lepr db/+Lepr db (db/db) mice

Protein restriction is used conventionally in the prevention and treatment of diabetic nephropathy. Recently, the use of soy protein instead of animal protein has been postulated as a new preventive and treatment option. The aim of this study was to determine the qualitative and quantitative effects of dietary protein on biomarkers of diabetic nephropathy in a Type 2 diabetes mellitus mouse model (BKS.cg-m +Lepr(db)/+Lepr(db) mice). Diabetic (+Lepr(db)/+Lepr(db)) and control (m+/m+) mice (n = 24/group) consumed one of four different diets ad libitum [20% casein, 20% soy protein, 12% casein or 12% soy protein (energy-based percentages)] from 35 +/- 4 d of age until termination (184-217 d of age). Blood and urine were collected throughout the study to measure biomarkers of diabetes and diabetic nephropathy. Kidney tissue was collected at the end of the study for weight. In diabetic mice, a 20% casein diet increased urinary albumin excretion to macroalbuminuric levels, whereas a 20% soy protein diet led to no major changes in urinary albumin excretion. Low protein diets (12%), independently of protein type, decreased urinary albumin excretion to low microalbuminuric levels. There were no significant differences in plasma glucose concentrations. These findings show lower urinary albumin excretion when a soy protein diet or a low casein diet is fed, suggesting a delay in the progression of diabetic nephropathy.

Effects of dual angiotensin-converting enzyme and neutral endopeptidase 24-11 chronic inhibition by mixanpril on insulin sensitivity in lean and obese Zucker rats

The aim of this study was to examine the effects of chronic (8-day) oral treatment with the dual angiotensin-converting enzyme (ACE) and neutral endopeptidase 24-11 (NEP) inhibitor mixanpril (25 mg/kg twice a day), compared with the ACE inhibitor captopril (25 mg/kg twice a day), on whole body insulin-mediated glucose disposal in young (10-week) and old (19-week) obese Zucker rats (ZOs). Moreover, the effects of chronic mixanpril administration on femoral blood flow at rest and during an insulin infusion were assessed. In the young ZOs, mixanpril decreased the glucose response during an IV glucose tolerance test more effectively than did captopril (-49 and -30%, respectively, p < 0.05). Incremental glucose area under the curve in mixanpril-treated ZOs was then no longer different from that observed in vehicle-treated lean rats (1,592 +/- 175 and 1, 470 +/- 104 mg/dl x min, respectively). The beneficial effects resulting from mixanpril or captopril administration were observed in ZOs but not in lean littermates. In the old ZOs, mixanpril induced higher glucose infusion rates to maintain euglycemia than did captopril during a hyperinsulinemic euglycemic clamp test (+92 and +35%, respectively, p < 0.001). However, the glucose infusion rates in mixanpril-treated ZOs remained much lower than that observed in vehicle-treated lean rats (9.4 +/- 0.7 mg/kg/min vs 28.6 +/- 1.0 mg/kg/min, p < 0.001). Mixanpril did not affect resting femoral vascular bed hemodynamics but restored the femoral blood flow response to insulin infusion. In conclusion, in ZOs, chronic dual ACE/NEP inhibition improves whole body insulin-mediated glucose disposal more effectively than does ACE inhibition alone. This beneficial effect seems to be restricted to conditions of insulin resistance and not directly linked to the improvement in the femoral blood flow response to insulin.

Long-term treatment with dipeptidyl peptidase IV inhibitor improves hepatic and peripheral insulin sensitivity in the VDF Zucker rat: a euglycemic-hyperinsulinemic clamp study

Upon release into circulation, the potent insulin secretagogues glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are rapidly cleaved and inactivated by the enzyme dipeptidyl peptidase IV (DP IV). Long-term administration of specific DP IV inhibitors, so as to enhance circulating active GIP and GLP-1 levels, has been shown to improve glucose tolerance and beta-cell glucose responsiveness and to reduce hyperinsulinemia in the Vancouver diabetic fatty (VDF) rat model of type 2 diabetes. Using the VDF model, the current study was undertaken to examine the effects of long-term DP IV inhibitor treatment on insulin sensitivity. Euglycemic-hyperinsulinemic clamps were performed on two sets of conscious VDF rats treated with or without the DP IV inhibitor P32/98 (20 mg. kg(-1). day(-1) for 12 weeks). The protocol consisted of three sequential 90-min periods with insulin infusion rates of 0, 5, and 15 mU. kg(-1). min(-1) and included a constant infusion of [ (3)H]glucose for measure of hepatic and peripheral insulin sensitivity. Relative to untreated littermates, the treated animals showed a left shift in the sensitivity of hepatic glucose output to insulin (average reduction approximately 6 micro mol. kg(-1). min(-1)) and a marked gain in peripheral responsiveness to insulin, with glucose disposal rates increasing 105 and 216% in response to the two insulin steps (versus 2 and 46% in controls). These results provide the first demonstration of improved hepatic and peripheral insulin sensitivity after DP IV inhibitor therapy, and coupled with apparent improvements in beta-cell function, they offer strong support for the utility of these compounds in the treatment of diabetes.

Genetic regulation of metabolic pathways in beta-cells disrupted by hyperglycemia

In models of type 2 diabetes the expression of beta-cell genes is altered, but these changes have not fully explained the impairment in beta-cell function. We hypothesized that changes in beta-cell phenotype and global alterations in both carbohydrate and lipid pathways are likely to contribute to secretory abnormalities. Therefore, expression of genes involved in carbohydrate and lipid metabolism were analyzed in islets 4 weeks after 85-95% partial pancreatectomy (Px) when beta-cells have impaired glucose-induced insulin secretion and ATP synthesis. Px rats after 1 week developed mild to severe hyperglycemia that was stable for the next 3 weeks, whereas neither plasma triglyceride, non-esterified fatty acid, or islet triglyceride levels were altered. Expression of peroxisome proliferator-activated receptors (PPARs), with several target genes, were reciprocally regulated; PPARalpha was markedly reduced even at low level hyperglycemia, whereas PPARgamma was progressively increased with increasing hyperglycemia. Uncoupling protein 2 (UCP-2) was increased as were other genes barely expressed in sham islets including lactate dehydrogenase-A (LDH-A), lactate (monocarboxylate) transporters, glucose-6-phosphatase, fructose-1,6-bisphosphatase, 12-lipoxygenase, and cyclooxygenase 2. On the other hand, the expression of beta-cell-associated genes, insulin, and GLUT2 were decreased. Treating Px rats with phlorizin normalized hyperglycemia without effecting plasma fatty acids and reversed the changes in gene expression implicating the importance of hyperglycemia per se in the loss of beta-cell phenotype. In addition, parallel changes were observed in beta-cell-enriched tissue dissected by laser capture microdissection from the central core of islets. In conclusion, chronic hyperglycemia leads to a critical loss of beta-cell differentiation with altered expression of genes involved in multiple metabolic pathways diversionary to normal beta-cell glucose metabolism. This global maladaptation in gene expression at the time of increased secretory demand may contribute to the beta-cell dysfunction found in diabetes.

Increased expression of antioxidant and antiapoptotic genes in islets that may contribute to beta-cell survival during chronic hyperglycemia

Hypertrophy is one mechanism of pancreatic beta-cell growth and is seen as an important compensatory response to insulin resistance. We hypothesized that the induction of protective genes contributes to the survival of enlarged (hypertrophied) beta-cells. Here, we evaluated changes in stress gene expression that accompany beta-cell hypertrophy in islets from hyperglycemic rats 4 weeks after partial pancreatectomy (Px). A variety of protective genes were upregulated, with markedly increased expression of the antioxidant genes heme oxygenase-1 and glutathione peroxidase and the antiapoptotic gene A20. Cu/Zn-superoxide dismutase (SOD) and Mn-SOD were modestly induced, and Bcl-2 was modestly reduced; however, several other stress genes (catalase, heat shock protein 70, and p53) were unaltered. The increases in mRNA levels corresponded to the degree of hyperglycemia and were reversed in Px rats by 2-week treatment with phlorizin (treatment that normalized hyperglycemia), strongly suggesting the specificity of hyperglycemia in eliciting the response. Hyperglycemia in Px rats also led to activation of nuclear factor-kappaB in islets. The profound change in beta-cell phenotype of hyperglycemic Px rats resulted in a reduced sensitivity to the beta-cell toxin streptozotocin. Sensitivity to the toxin was restored, along with the beta-cell phenotype, in islets from phlorizin-treated Px rats. Furthermore, beta-cells of Px rats were not vulnerable to apoptosis when further challenged in vivo with dexamethasone, which increases insulin resistance. In conclusion, beta-cell adaptation to chronic hyperglycemia and, hence, increased insulin demand is accompanied by the induction of protective stress genes that may contribute to the survival of hypertrophied beta-cells.

Porcine neonatal pancreatic cell clusters in tissue culture: benefits of serum and immobilization in alginate hydrogel

Porcine neonatal pancreatic cell clusters (NPCCs) may be a suitable source of insulin producing tissue for transplantation in diabetic patients. The possible beneficial effect of serum on maturation of NPCCs in vitro is difficult to achieve because of cell clumping, which can be avoided by immobilization in alginate hydrogel matrix. Collagenase treated pancreata, cultured for 4 days, formed NPCCs that were embedded in alginate cross-linked with CaCl2 and cultured in modified Ham's F10 medium with 10% fetal calf serum (FCS) for 10 days. NPCCs cultured as suspension in F10+ with 0.5% bovine serum albumin or with 10% FCS were used as control. To prevent the aggregation when cultured with serum, NPCCs were kept as a very diluted suspension. At the beginning and end of the culture, samples were taken for insulin and DNA content and immunostained for beta and non-beta cells. The culture of NPCCs immobilized in alginate resulted with 3-fold increase in insulin content and 9-fold increase in insulin/DNA ratio. Histology revealed evident increase of number of insulin- and other hormone-positive cells compared with the control. Even though 2 weeks in culture resulted in impaired glucose-induced insulin release, the amount of insulin secreted by clusters cultured in the presence of serum was 4-fold higher than in serum-free conditions. After transplantation, NPCCs retrieved from alginate reversed hyperglycemia similarly to NPCCs cultured in standard conditions. In conclusion, this study shows the feasibility of in vitro immobilization of NPCCs in alginate three-dimensional matrix, allowing cell clusters to be cultured at least two times higher density compared with culture in suspension.

Acute effect of the dual angiotensin-converting enzyme and neutral endopeptidase 24-11 inhibitor mixanpril on insulin sensitivity in obese Zucker rat

The aim of this study was to determine whether acute dual angiotensin-converting enzyme (ACE)/neutral endopeptidase 24-11 (NEP) inhibition could improve whole body insulin-mediated glucose disposal (IMGD) more than ACE inhibition alone and whether this effect was mediated by the kinin-nitric oxide (NO) pathway activation. We therefore compared in anaesthetized obese (fa/fa) Zucker rats (ZOs) the effects of captopril (2 mg kg(-1), i.v.+2 mg kg(-1) h(-1)), retrothiorphan (25 mg kg(-1), i.v. +25 mg kg(-1) h(-1)), a selective NEP inhibitor, and mixanpril (25 mg kg(-1), i.v. +25 mg kg(-1) h(-1)), a dual ACE/NEP inhibitor, on IMGD using hyperinsulinaemic euglycaemic clamp technique. The role of the kinin-NO pathway in the effects of mixanpril was tested using a bradykinin B2 receptor antagonist (Hoe-140, 300 microg kg(-1)) and a NO-synthase inhibitor (N(omega)-nitro-L-arginine methyl ester, L-NAME, 10 mg kg(-1) i.v. +10 mg kg(-1) h(-1)) as pretreatments. Insulin sensitivity index (ISI) was lower in ZO controls than in lean littermates. Increases in ISI were observed in captopril- and retrothiorphan-treated ZOs. In mixanpril-treated ZOs, ISI was further increased, compared to captopril- and retrothiorphan-treated ZOs. In ZOs, Hoe-140 and L-NAME alone did not significantly alter and slightly reduced the ISI respectively. Hoe-140 and L-NAME markedly inhibited the ISI improvement induced by mixanpril. These results show that in obese insulin-resistant Zucker rats, under acute conditions, NEP or ACE inhibition can improve IMGD and that dual ACE/NEP inhibition improves IMGD more effectively than does either single inhibition. This effect is linked to an increased activation of the kinin-NO pathway.

Differentiation and expansion of beta cell mass in porcine neonatal pancreatic cell clusters transplanted into nude mice

Neonatal porcine pancreas has considerable capacity for growth and differentiation, making it an attractive potential source of islet tissue for xenotransplantation. Pancreases from 1-3-day-old newborn pigs were digested with collagenase and cultured for 8 days. The resulting cellular aggregates are called porcine neonatal pancreatic cell clusters (NPCCs). The mean yield of NPCCs from a newborn pig was 28,200 +/- 1700 islet equivalents. Cytokeratin 7 (CK7) was used as a marker for the immunostaining of pancreatic duct cells. In neonatal pancreas, 18% of the insulin-positive cells co-stained for CK7, thus being protodifferentiated. NPCCs also contained protodifferentiated cells; insulin/PP and insulin/somatostatin co-stained cells were more common than insulin/glucagon cells. Between 1 and 8 days of culture, the DNA content of the NPCCs fell to 16% and the insulin content to 33% of the starting value, mainly due to the preferential loss of exocrine cells. Transplantation of 2000 or 4000 NPCCs into diabetic nude mice typically normalized glucose values in 10-20 weeks. Mice with successful grafts had lower fasting blood glucose levels than normal mice and accelerated glucose clearance after an i.p. glucose load. The starting NPCCs consisted of 17% insulin-staining cells, but the grafts of mice with reversed diabetes consisted of 94% beta cells, with some co-stained for CK7, indicating that the grafts still contained immature cells. The mass of insulin-producing cells rose from 0.22 +/- 0.08 mg 1 week after transplantation to 4.34 +/- 0.27 mg in mice sacrificed at 27-35 weeks. In summary, NPCCs contain mostly islet precursor cells, which when transplanted into nude mice undergo striking differentiation and beta cell expansion.