Biomedical subjects

Bernard Portha

Publications and source records attributed to Bernard Portha.

13 recordsLinked to original sources

PubMed2006

Is defective pancreatic beta-cell mass environmentally programmed in Goto-Kakizaki rat model of type 2 diabetes?: insights from crossbreeding studies during suckling period.

OBJECTIVE: The Goto-Kakizaki (GK) rat is a spontaneous model of type 2 diabetes with a well established pathological pancreatic beta-cell development. Hyperglycemia experienced during early postnatal life contributes to the programming of endocrine pancreas. We have analyzed the consequences of hyperglycemic versus euglycemic suckling period for the pancreatic beta-cell mass and the in vivo glucose tolerance and insulin secretion in 4-week-old unweaned control Wistar (W), diabetic GK, and in offspring issued from crosses between normoglycemic W and diabetic GK rats. METHODS: Mother/father crosses yielded offspring designated as follows: W/W, GK/GK, W/GK, and GK/W. In vivo glucose tolerance and insulin secretion tests were performed on males 4 weeks after birth, that is, just before weaning. Beta-cell mass was determined by immunohistochemistry and morphometry. RESULTS: Four-week-old W/GK and GK/W rats are normoglycemic, normoinsulinemic, and display a similarly small beta-cell mass. Both W/GK and GK/W rats exhibit in vivo glucose intolerance and defective insulin secretion in response to glucose. CONCLUSIONS: Our data obtained from crossbreeding studies during suckling period suggest that the defective pancreatic beta-cell mass is not environmentally programmed in the GK model of type 2 diabetes. Rather, they support the hypothesis that the beta-cell mass defect in the GK is linked to genetic determinism.

Animals↗

PubMed2006

Islet inflammation and fibrosis in a spontaneous model of type 2 diabetes, the GK rat.

The molecular pathways leading to islet fibrosis in diabetes are unknown. Therefore, we studied gene expression in islets of 4-month-old Goto-Kakizaki (GK) and Wistar control rats. Of 71 genes found to be overexpressed in GK islets, 24% belong to extracellular matrix (ECM)/cell adhesion and 34% to inflammatory/immune response families. Based on gene data, we selected several antibodies to study fibrosis development during progression of hyperglycemia by immunohistochemistry. One-month-old GK and Wistar islets appeared to be similar. Two-month-old GK islets were strongly heterogenous in terms of ECM accumulation compared with Wistar islets. GK islet vascularization, labeled by von Willebrand factor, was altered after 1 month of mild hyperglycemia. Numerous macrophages (major histocompatibility complex class II(+) and CD68(+)) and granulocytes were found in/around GK islets. These data demonstrate that marked inflammatory reaction accompanies GK islet fibrosis and suggest that islet alterations in this nonobese model of type 2 diabetes develop in a way reminiscent of microangiopathy.

Animals↗

PubMed2005

Restitution of defective glucose-stimulated insulin secretion in diabetic GK rat by acetylcholine uncovers paradoxical stimulatory effect of beta-cell muscarinic receptor activation on cAMP production.

Because acetylcholine (ACh) is a recognized potentiator of glucose-stimulated insulin release in the normal beta-cell, we have studied ACh's effect on islets of the Goto-Kakizaki (GK) rat, a spontaneous model of type 2 diabetes. We first verified that ACh was able to restore the insulin secretory glucose competence of the GK beta-cell. Then, we demonstrated that in GK islets 1) ACh elicited a first-phase insulin release at low glucose, whereas it had no effect in Wistar; 2) total phospholipase C activity, ACh-induced inositol phosphate production, and intracellular free calcium concentration ([Ca2+]i) elevation were normal; 3) ACh triggered insulin release, even in the presence of thapsigargin, which induced a reduction of the ACh-induced [Ca2+]i response (suggesting that ACh produces amplification signals that augment the efficacy of elevated [Ca2+]i on GK exocytosis); 4) inhibition of protein kinase C did not affect [Ca2+]i nor the insulin release responses to ACh; and 5) inhibition of cAMP-dependent protein kinases (PKAs), adenylyl cyclases, or cAMP generation, while not affecting the [Ca2+]i response, significantly lowered the insulinotropic response to ACh (at low and high glucose). In conclusion, ACh acts mainly through activation of the cAMP/PKA pathway to potently enhance Ca2+-stimulated insulin release in the GK beta-cell and, in doing so, normalizes its defective glucose responsiveness.

Acetylcholine↗

PubMed2005

Defective myocardial blood flow and altered function of the left ventricle in type 2 diabetic rats: a noninvasive in vivo study using perfusion and cine magnetic resonance imaging.

OBJECTIVE: In type 2 diabetes mellitus, cardiovascular complications are related to microvascular abnormalities. In this work, we aimed at characterizing in vivo myocardial blood flow and left ventricular function of the Goto-Kakizaki (GK) rat as a nonobese model of type 2 diabetes. MATERIALS AND METHODS: We performed arterial spin labeling magnetic resonance imaging (MRI) for myocardial blood flow quantification and cine MRI for functional evaluation in free-breathing isoflurane-anesthetized animals. RESULTS: Myocardial blood flow was altered in adult female GK rats compared with age-matched female Wistar rats (4.7 +/- 1.6 vs. 7.1 +/- 1.2 mL/g/min respectively, P = 0.0022). Ejection fraction was decreased in GK compared with Wistar rats (64 +/- 7 vs. 78 +/- 8% respectively, P <0.005), mainly as a result of a loss in left ventricular longitudinal contraction. CONCLUSIONS: Adult female GK rats have defective myocardial blood flow associated with altered left ventricular function. This multiparametric MRI approach in the GK rat is of particular interest for the study of type 2 diabetic cardiomyopathy.

Animals↗

PubMed2004

Protein-caloric food restriction affects insulin-like growth factor system in fetal Wistar rat.

We have previously shown that fetuses from protein-caloric undernourished pregnant rats (35% of control diet during the last week of pregnancy) at 21.5 d post coitum exhibit increased beta-cell mass. This alteration is correlated with increased insulinemia and total pancreatic insulin content, a pattern similar to that reported in infants of mild diabetic mothers. In this work, we investigated in undernourished fetuses: 1) whether availability of growth factors such as insulin, GH, and IGFs and their binding proteins (IGFBPs) could be implicated in this alteration, and 2) the beta-cell mitogenic response to IGFs in vitro. The results show that maternal undernutrition increases pancreatic IGF-I expression and islet IGF-I receptor content in undernourished fetuses, whereas hepatic IGF-I expression and serum IGF-I levels were decreased. No changes were observed in serum IGF-II, and its expression was diminished in undernourished pancreases and unchanged in the liver, compared with control fetuses. Serum levels and liver and pancreatic mRNA expression of IGFBP-1 were found to be normal in undernourished fetuses, whereas the serum concentration and abundance of IGFBP-2 mRNA in pancreas were increased. Finally, the beta-cell mitogenic response to IGFs in vitro was significantly increased in undernourished fetal islets, compared with controls. In conclusion, in undernourished fetuses the increased beta-cell mass can be related to the stimulation of replicative beta-cell response due to locally increased pancreatic IGF-I mRNA; this effect is perhaps potentiated or favored by the enhanced islet IGF-I receptor content and pancreatic IGFBP-2 gene expression.

Animals↗

PubMed2002

Comparison between D-[3-3H]- and D-[5-3H]glucose and fructose utilization in pancreatic islets from control and hereditarily diabetic rats.

The metabolism of D-glucose and/or D-fructose was investigated in pancreatic islets from control rats and hereditarily diabetic GK rats. In the case of both D-glucose and D-fructose metabolism, a preferential alteration of oxidative events was observed in islets from GK rats. The generation of 3HOH from D-[5-3H]glucose (or D-[5-3H]fructose) exceeded that from D-[3-3H]glucose (or D-[3-3H]fructose) in both control and GK rats. This difference, which is possibly attributable to a partial escape from glycolysis of tritiated dihydroxyacetone phosphate, was accentuated whenever the rate of glycolysis was decreased, e.g., in the absence of extracellular Ca(2+) or presence of exogenous D-glyceraldehyde. D-Mannoheptulose, which inhibited D-glucose metabolism, exerted only limited effects upon D-fructose metabolism. In the presence of both hexoses, the paired ratio between D-[U-14C]fructose oxidation and D-[3-3H]fructose or D-[5-3H]fructose utilization was considerably increased, this being probably attributable, in part at least, to a preferential stimulation by the aldohexose of mitochondrial oxidative events. Moreover, this coincided with the fact that D-mannoheptulose now severely inhibited the catabolism of D-[5-3H]fructose and D-[U-14C]fructose. The latter situation is consistent with both the knowledge that D-glucose augments D-fructose phosphorylation by glucokinase and the findings that D-mannoheptulose, which fails to affect D-fructose phosphorylation by fructokinase, inhibits the phosphorylation of D-fructose by glucokinase.

Animals↗

PubMed2002

Energy restriction with protein restriction increases basal metabolism and meal-induced thermogenesis in rats.

We previously observed an increased sympathetic nervous system (SNS) activity that was partly responsible for a defect in the insulin secretion response to glucose after postweaning protein-energy restriction (PER) in female rats. These results, together with other data on low-protein feeding, suggested that a low protein-to-energy ratio (P/E) in the diet could stimulate energy expenditure (EE), but direct measurements of EE have never been reported under conditions of PER. The goal of the present study was thus to quantify the changes induced by PER to body composition, the various parameters of EE, and plasma triiodothyronine levels. PER induced severe growth retardation, but the subcutaneous white and interscapular brown adipose tissue masses were preserved. Basal metabolism, meal-induced thermogenesis, and triiodothyronine levels were increased, but substrate utilization by the working muscles was unaffected. Meal-induced thermogenesis was increased by spontaneous activity in PER rats only. These results suggest that rats adapt to a low P/E in the diet by burning part of their excess nonprotein energy and storing the remaining excess in subcutaneous adipose tissue.

Animals↗

PubMed2002

Development of beta-cell mass in fetuses of rats deprived of protein and/or energy in last trimester of pregnancy.

Fetal malnutrition is now proposed as a risk factor of later obesity and type II diabetes. We previously analyzed the long-term impact of reduced protein and/or energy intake strictly limited to the last week of pregnancy in Wistar rats. Three protocols of gestational malnutrition were used: 1) low-protein isocaloric diet (5 instead of 15%) with pair feeding to the mothers receiving the control diet, 2) restricted diet (50% of control diet), and 3) low protein-restricted diet (50% of low-protein diet). Only isolated protein restriction induced a long-term beta-cell mass decrease. In the present study, we used the same protocols of food restriction to analyze their short-term impact (on day 21.5 of pregnancy) on beta-cell mass development. A 50% beta-cell mass decrease was present in the three restricted groups, but low-protein diet, either associated or not to energy restriction, increased fetal beta-cell insulin content. Among all the parameters analyzed to further explain our results, we found that the fetal plasma level of taurine was lowered by low-protein diet and was the main predictor of the fetal plasma insulin level (r = 0.63, P < 0.01). In conclusion, rat fetuses exposed to protein and/or energy restriction during the third part of pregnancy have a similar dramatic decrease in beta-cell mass, and their ability to recover beta-cell mass development retardation depends on the type of malnutrition used. Moreover, our results support the hypothesis that taurine might play an important role in fetal beta-cell mass function.

Animals↗

PubMed2002

Fetal insulin-like growth factor-2 production is impaired in the GK rat model of type 2 diabetes.

At late fetal age (21.5 days postcoitum [dpc]), GK rats present a severely reduced beta-cell mass compared with Wistar rats. This anomaly largely antedates the onset of hyperglycemia in GK rats. Thus, the beta-cell mass deficit could represent the primary defect leading to type 2 diabetes in the adult. The aim of this work was to investigate, in GK fetuses at the end of fetal age (21.5 dpc), whether impaired availability of growth factors such as insulin, growth hormone, and IGFs and their IGF binding proteins (IGFBPs) could be instrumental in this anomaly. Although it confirms that GK fetuses are hypoinsulinemic despite enhanced plasma glucose level due to maternal hyperglycemia, the present study shows for the first time that IGF-2 expression in the liver and pancreas and IGF-2 serum levels are decreased in GK fetuses. Serum level as well as liver and pancreatic mRNA expression of IGFBP-2 were found to be normal in GK fetuses, whereas serum level and liver mRNA expression of IGFBP-1 were increased. Finally, we found that the maximal beta-cell mitogenic response to IGFs in vitro is kept intact, therefore suggesting that the direct biological action of IGFs on fetal GK beta-cells is not grossly impaired. In conclusion, in GK fetuses at 21.5 dpc, the defective IGF-2 production appears to be an early landmark in the pathological sequence leading to retardation of beta-cell growth in the fetal GK rat.

Animals↗

PubMed2002

Persistent improvement of type 2 diabetes in the Goto-Kakizaki rat model by expansion of the beta-cell mass during the prediabetic period with glucagon-like peptide-1 or exendin-4.

In the Goto-Kakizaki (GK) rat, a genetic model of type 2 diabetes, the neonatal beta-cell mass deficit is considered to be the primary defect leading to basal hyperglycemia, which is detectable for the first time 3 weeks after birth. We investigated in GK females the short- and the long-term effects of a treatment with glucagon-like peptide-1 (GLP-1) or its long-acting analog exendin-4 (Ex-4) during the first postnatal week (during the prediabetic period). GK rats were treated with daily injections of glucagon-like peptide-1 (400 microg x kg(-1) x day(-1)) or Ex-4 (3 microg x kg(-1) x day(-1)) from day 2 to day 6 after birth and were evaluated against Wistar and untreated GK rats. Under these conditions, on day 7 both treatments enhanced pancreatic insulin content and total beta-cell mass by stimulating beta-cell neogenesis and regeneration. Follow-up of biological characteristics from day 7 to adult age (2 months) showed that such a GLP-1 or Ex-4 treatment exerted long-term favorable influences on beta-cell mass and glycemic control at adult age. As compared to untreated GK rats, 2-month-old treated rats exhibited significantly decreased basal plasma glucose. Their glucose-stimulated insulin secretion, in vivo after intravenous glucose load or in vitro using isolated perfused pancreas, was slightly improved. This contributed at least partly to improve the in vivo plasma glucose disappearance rate, which was found to be increased in both treated GK groups compared to the untreated GK group. These findings in the GK model indicated, for the first time, that GLP-1 or Ex-4 treatment limited to the prediabetic period delays the installation and limits the severity of type 2 diabetes. Under these conditions, GLP-1 represents a unique tool because of its beta-cell replenishing effect in spontaneously diabetic rodents. It may prove to be an invaluable agent for the prevention of human type 2 diabetes.

Age Factors↗

PubMed2002

Metabolism of D-[3-3H]glucose, D-[5-3H]glucose, D-[U-14C]glucose, D-[1-14C]glucose and D-[6-14C]glucose in pancreatic islets in an animal model of type-2 diabetes.

This study aims at exploring specific aspects of D-glucose metabolism, so far not yet investigated, in pancreatic islets from adult control rats and animals (STZ rats) injected with streptozotocin during the neonatal period. The latter animals, which represent a current model of type-2 diabetes, displayed a lower body weight, higher plasma D-glucose concentration and lower insulinogenic index than control rats. The protein, DNA and insulin content were all also lower in islets prepared from STZ, rather than control rats. In the presence of 10.0 mM D-glucose, the paired ratio between D-[U-14C]glucose oxidation and D-[5-3H]glucose utilization was also decreased in the islets from STZ rats. No significant difference between control and STZ rats was observed, however, in terms of the ratios between D-[3-3H]glucose and D-[5-3H]glucose utilization, between the generation of radioactive lactate from 14C-labelled D-glucose and tritiated D-glucose utilization and between D-[1-14C]glucose and D-[6-14C]glucose oxidation. These findings reinforce the view that the previously documented preferential impairment of the oxidative modality of glycolysis in islets from STZ rats contrasts with the absence of any major anomaly in other variables of D-glucose catabolism.

Animals↗

PubMedDate not supplied

Programmed disorders of beta-cell development and function as one cause for type 2 diabetes? The GK rat paradigm.

Now that the reduction in beta-mass has been clearly established in humans with type 2 diabetes mellitus (T2DM) 1-4, the debate focuses on the possible mechanisms responsible for decreased beta-cell number and impaired beta-cell function and their multifactorial etiology. Appropriate inbred rodent models are essential tools for identification of genes and environmental factors that increase the risk of abnormal beta-cell function and of T2DM. The information available in the Goto-Kakizaki (GK) rat, one of the best characterized animal models of spontaneous T2DM, are reviewed in such a perspective. We propose that the defective beta-cell mass and function in the GK model reflect the complex interactions of three pathogenic players: (1) several independent loci containing genes causing impaired insulin secretion; (2) gestational metabolic impairment inducing a programming of endocrine pancreas (decreased beta-cell neogenesis) which is transmitted to the next generation; and (3) secondary (acquired) loss of beta-cell differentiation due to chronic exposure to hyperglycemia (glucotoxicity). An important message is that the 'heritable' determinants of T2DM are not simply dependant on genetic factors, but probably involve transgenerational epigenetic responses.

Adult↗

PubMedDate not supplied

[Transmitted beta-cell dysfunction as a cause for type 2-diabetes].

The pathways that control insulin release and regulate pancreatic beta-cell mass are crucial on the development of type 2 diabetes mellitus. Maturity-onset diabetes of the young comprises a number of single-gene disorders affecting beta-cell development and/or function. A genetic basis for the more common forms of type 2 diabetes which affect adults in developed as well as many developing countries is less clear cut. It is also characterized by abnormal beta-cell function. Appropriate inbred rodent models are an essential tool for the identification of genes and environmental factors that increase the risk of type 2 diabetes. The informations available from studies in the Goto-Kakizaki (GK) rat are here reviewed in such a perspective. This model was obtained by selective breeding of individuals with mild glucose intolerance from a non-diabetic Wistar rat colony. Heritability of defective beta-mass and beta-cell function in GK model is proposed to reflect the complex interactions of three pathogenic players: (1) three independent loci containing genes causating impaired insulin secretion; (2) gestational metabolic (hyperglycaemic) impairment inducing a programming of endocrine pancreas (decreased beta-cell mass) which is transmitted to the next generation; (3) secondary (acquired) loss of beta-cell differentiation due to chronic exposure to hyperglycaemia (glucotoxicity). A better understanding of the mechanisms involved in the failure of beta-cell function in the GK model will lead to identification of new therapeutic targets for both the prevention and treatment of type 2 diabetes.

Adult↗