Influência da grelina sobre o processo de estímulo-secreção de insulina in vitro em camundongos Swiss adultos hiperalimentados na lactação

O excesso ou a privação de nutrientes em períodos específicos do desenvolvimento, tais como a lactação, estimulam alterações no metabolismo celular, por exemplo. Estas modificações perpetuam-se ao longo da vida e em conseqüência tornam o organismo mais suscetível ao aparecimento de patologias na idade adulta (Programação Metabólica). Estudamos a influência da grelina na secreção de insulina em camundongos Swiss de 120 dias submetidos à hiperalimentação na lactação. Para induzir a hiperalimentação as ninhadas foram reduzidas a 3 filhotes machos por lactante no 3o dia de vida pós-natal. As ninhadas controle foram ajustadas para 9 filhotes machos por lactante. Na idade adulta os animais hiperalimentados (AH) exibiram em comparação aos animais controle (AC) um incremento de 20% no peso corporal, maior índice de Lee (1705,63 g/mm + 29,3 vs 1374,10 g/mm + 54,9; p< 0,001), elevação da gordura corporal (31,0% + 4,6 vs 21,5% + 3,6; p< 0,01), aumento da gordura retroperitoneal (0,79 g + 0,1 vs 0,44 g + 0,1; p< 0,001), hiperglicemia de jejum (151,83 mg/ dl + 8,3 vs 118,0 mg/ dl + 1,0; p< 0,001), hiperinsulinemia de jejum (54,06 UI/ml + 2,3 vs 19,28 UI/ml + 1,53; p< 0,001) e hipogrelinemia de jejum (98,64 pg/ml + 56,5 vs 201,14 pg/ml + 46,4; p< 0,05). Os AH apresentaram maior secreção de insulina in vitro em presença de glicose aos 10 minutos (209,66 UI/ml + 46,5; p< 0,05), 30 minutos (441,88 UI/ml + 30,2; p< 0,05) e 60 minutos (214,34 UI/ml + 29,8) em comparação aos AC, respectivamente 86,90 UI/ml + 9,5; 74,31 UI/ml + 7,7 vs 27,45 UI/ml + 6,1; p< 0,05. As ilhotas pancreáticas dos AH adultos demonstraram em relação aos AC diminuição do consumo de O2 (1,76 pmols O2/ s. ilhota-1 + 0,4 vs 4,85 pmols O2/ s. ilhota-1 + 1,5; p< 0,001) e elevação do conteúdo do receptor de grelina GHSR1A (3,05 % + 2,13 vs 0,95 % + 0,1; p< 0,05). A grelina acilada estimulou a secreção de insulina in vitro dos AC aos 30 minutos (controle com grelina: 208,50 UI/ml + 40,85 vs controle sem grelina: 74,31 UI/ml + 7,7; p< 0,05) e diminuiu a razão do controle respiratório (controle com grelina: 1,45 + 0,2 vs controle sem grelina: 2,51 + 0,7; p< 0,05). Nos AH, a grelina acilada elevou o conteúdo de GLUT2 nas ilhotas pancreáticas em relação aos AC (hiperalimentados com grelina: 2,07 % + 0,5 vs controle com grelina: 0,85 % + 0,4; p< 0,01); entretanto a grelina não foi capaz de estimular a secreção de insulina nestes animais. Concluímos que a hiperalimentação na lactação associou-se ao aumento da gordura corporal e elevou a secreção de insulina na fase tardia do desenvolvimento. A grelina acilada estimulou a secreção de insulina somente nos AC adultos.

Efeitos intergeracionais da obesidade materna sobre o pâncreas endócrino de camundongos C57BL/6

Objetivo: Avaliar os efeitos da obesidade materna sobre a estrutura do pâncreas e metabolismo de carboidratos no início da vida adulta, com foco na prole da primeira geração (F1) e segunda geração (F2) de progenitoras F0 alimentadas com dieta rica em gordura nos períodos pré-gestacional, durante a gestação e lactação. Métodos: Camundongos C57BL/6 do gênero feminino (F0) foram alimentadas com dieta padrão (SC) ou dieta rica em gordura (HF) durante as oito semanas que antecederam o acasalamento, durante a gestação e lactação para gerar a F1 (F1-SC e F1-HF). As proles geradas receberam dieta SC até o terceiro mês de vida. Aos três meses de idade, fêmeas F1 foram acasaladas para gerar a F2 (F2-SC e F2-HF). Apenas os machos das geração F1 e F2 foram avaliados aos 3 meses de idade. As características metabólicas foram avaliadas pela massa corporal (MC), glicemia de jejum, área sob a curva no teste oral de tolerância a glicose; análise plasmática de insulina, leptina e adiponectina; distribuição e análise morfológica do pâncreas através da imunohistoquímica e imunofluorescência. Resultados: A prole F1-HF teve aumento significativo na massa corporal e glicemia quando comparado à F1-SC. Por outro lado, as proles F2-HF e F2-SC tiveram massas corporais semelhantes. A prole F1-HF e F2-HF mostrou aumento da ingestão de energia, intolerância à glicose, hiperinsulinemia, hiperleptinemia, hipoadiponectinemia, resistência à insulina, aumento da massa pancreática, o aumento da densidade de volume de ilhotas com elevada massa de células alfa e beta, ilhotas hipertrofiadas caracterizadas por uma distribuição alterada de células alfa e beta, e fraca imunoreatividade do pâncreas homeobox duodeno-1 (PDx1). Conclusões: Uma dieta HF materna consumida durante o período pré-concepção e durante toda a gestação e lactação em camundongos promoveu programação metabólica do pâncreas endócrino com pré-disposição ao diabetes mellitus tipo 2 precoce nas proles F1 e F2 do gênero masculino, sugerindo que essas mudanças são intergeracionais.

海州湾前三岛海域栉孔扇贝生态增养殖原理与关键技术

以海州湾前三岛周围海域为研究地点，开展了栉孔扇贝岛屿生态增养殖理论和关键技术研究。调查了海区的地理、水文、水化学环境以及饵料供应能力；现场测定了栉孔扇贝的滤水率，根据扇贝实际生长情况结合水动力学因子评估了该海域的养殖容量；监测了不同养殖模式情况下栉孔扇贝的存活、生长以及污损生物附着情况；利用免疫学指标揭示了各种养殖方式下栉孔扇贝的健康状态；研究了不同水温、扇贝规格对敌害生物捕食的影响；优化了该海域栉孔扇贝的养殖模式和关键技术。主要研究结果如下： 1．查明了前三岛海域理化环境、生物资源等现状。前三岛海域水质优良，生物资源丰富，虽然饵料浓度相对较低，但是该海域海流畅通，水交换条件好，较高的流速可以弥补饵料浓度的不足，适合开展栉孔扇贝增养殖。由于各项理化因子随着时间和水深的变化而发生变化，必须根据实际情况，对养殖模式等进行相应调整，才能获得更高经济和生态效益。 2．较为系统地研究了前三岛海域深水筏式养殖栉孔扇贝生理生态学特征，评估了养殖容量。周年监测了海域的环境因子和栉孔扇贝的生长情况，利用生物沉积法，现场研究了各时期扇贝的滤食作用。结果表明：该海域养殖栉孔扇贝在当年秋、冬季和次年春季生长迅速，夏季生长相对缓慢，周年平均软组织生长速度为11.29 mg/d，平均干贝壳生长速度为48.84 mg/d，扇贝能够于次年年初达到商品规格（6cm）。不同时期栉孔扇贝的滤水率之间差异显著，滤水率随水温的升高和扇贝规格的增大而增加。利用改进的Incze等（1981）的养殖容量模型，评估了该海域养殖容量，结果表明：在现有条件下，各时期沿着海流方向适养区域长度分别为：4.0，4.6，4.7，5.1，4.5和3.2 km，平均为4.35 km。 3．揭示了不同养殖水层栉孔扇贝存活、生长以及免疫指标特征。于2007年夏、秋高温季节监测了5个不同水层（2, 5, 10, 15, 与 20 m）筏式养殖栉孔扇贝的存活、生长以及免疫指标特征。研究表明各水层栉孔扇贝成活率差异显著，其中15 m（78.0%）和20 m（86.7%）成活率要明显高于2 m（62.9%），5 m（60.8%），和10 m（66.8%）；夏季（7~9月）各水层壳高生长速度有较大差异，其中10m （205.0 μm/d）与20 m（236.9 μm/d）要显著高于2，5，和15 m，而秋季（9~11月份）20m生长速度最低，5m水层（262.9 μm/d）要显著高于其他水层；不同水层扇贝软组织生长情况与壳的生长情况类似；扇贝血淋巴SOD活性随着水深的加深而增大，15 和 20 m 养殖的栉孔扇贝ACP活性要高于其他水层，这表明深水养殖栉孔扇贝健康状态要优于浅水层。 4．比较研究了筏式和底播两种养殖方式情况下栉孔扇贝的存活、生长以及免疫指标的周年变化。结果表明夏季栉孔扇贝的生长、免疫酶活性要低于其他季节，扇贝死亡也基本集中于夏季高温季节。除了2008年春季壳高以外，筏式养殖栉孔扇贝的生长、免疫酶活性都要高于底播养殖。实验结束时筏式养殖的成活率（54.6 ± 12.3 %）要显著地低于底播养殖（86.8 ± 3.5 %）。由此可见，在夏季高温季节采取底播养殖提高成活率，然后转为筏式养殖以提高生长速度，这样可以获得更高的产量。 5．研究了日本蟳和多棘海盘车对栉孔扇贝的捕食机制。现场研究表明，成年日本蟳可以捕食壳高小于5.0 cm的栉孔扇贝，捕食强度随着水温的升高而增大，而壳高大于5.9 cm的栉孔扇贝则可以免遭日本蟳的捕食；与栉孔扇贝相比，日本蟳更倾向于捕食贻贝；室内模拟研究表明水温低于10 ℃时，日本蟳对大规格扇贝的捕食作用不明显。相同温度条件下，室内实验日本蟳的捕食强度要低于现场，但其温度系数（Q10）差别不大。室内试验表明多棘海盘车对栉孔扇贝也有很强的捕食作用。提出了提高底播栉孔扇贝成活率的方法，即选择大规格的扇贝在水温较低的秋、冬季进行底播。

Pharmacological targeting of the mitochondrial phosphatase PTPMT1.

The dual-specificity protein tyrosine phosphatases (PTPs) play integral roles in the regulation of cell signaling. There is a need for new tools to study these phosphatases, and the identification of inhibitors potentially affords not only new means for their study, but also possible therapeutics for the treatment of diseases caused by their dysregulation. However, the identification of selective inhibitors of the protein phosphatases has proven somewhat difficult. PTP localized to mitochondrion 1 (PTPMT1) is a recently discovered dual-specificity phosphatase that has been implicated in the regulation of insulin secretion. Screening of a commercially available small-molecule library yielded alexidine dihydrochloride, a dibiguanide compound, as an effective and selective inhibitor of PTPMT1 with an in vitro concentration that inhibits response by 50% of 1.08 microM. A related dibiguanide analog, chlorhexidine dihydrochloride, also significantly inhibited PTPMT1, albeit with lower potency, while a monobiguanide analog showed very weak inhibition. Treatment of isolated rat pancreatic islets with alexidine dihydrochloride resulted in a dose-dependent increase in insulin secretion, whereas treatment of a pancreatic beta-cell line with the drug affected the phosphorylation of mitochondrial proteins in a manner similar to genetic inhibition of PTPMT1. Furthermore, knockdown of PTPMT1 in rat islets rendered them insensitive to alexidine dihydrochloride treatment, providing evidence for mechanism-based activity of the inhibitor. Taken together, these studies establish alexidine dihydrochloride as an effective inhibitor of PTPMT1, both in vitro and in cells, and support the notion that PTPMT1 could serve as a pharmacological target in the treatment of type II diabetes.

Evaluation of glycated insulin in diabetic animals using immunocytochemistry and radioimmunoassay

Glycated insulin was evaluated in plasma and biological tissues of diabetic animal models by immuno. cytochemistry (ICC) and a novel radioimmunoassay. Glycated insulin circulated at 0.10 +/-0.04 ng/ml and 2.20 +/-0.14 ng/ml in lean and diabetic obese (ob/ob) mice, corresponding to 12.5 and 9.8% total plasma insulin, respectively. The concentration of glycated insulin was elevated 22-fold in obese mice compared to controls (P10 and 83 +/-4 ng/g wt (P0.17 mug/g wt). ICC revealed fluorescent positively stained cells in pancreatic islets from hydrocortisone (HC)treated diabetic rats. Fasting of HC-treated rats, resulted in 3-fold and 15-fold reductions in plasma glycated insulin (P

Metabolic and structural properties of human obestatin {1-23} and two fragment peptides

Obestatin is a peptide produced in the oxyntic mucosa of the stomach and co-localizes with ghrelin on the periphery of pancreatic islets. Several studies demonstrate that obestatin reduces food and water intake, decreases body weight gain, inhibits gastrointestinal motility, and modulates glucose-induced insulin secretion. In this study we evaluated the acute metabolic effects of human obestatin {1-23} and fragment peptides {1-10} or {11-23} in high-fat fed mice, and then investigated their solution structure by NMR spectroscopy and molecular modelling. Obestatins {1-23} and {11-23} significantly reduced food intake (86% and 90% respectively) and lowered glucose responses to feeding, whilst leaving insulin responses unchanged. No metabolic changes could be detected following the administration of obestatin (1-10). In aqueous solution none of the obestatin peptides possessed secondary structural features. However, in a 2,2,2-trifluoroethanol (TFE-d(3))-H2O solvent mixture, the structure of obestatin {1-23} was characterized by an a-helix followed by a single turn helix conformation between residues Pro(4) and Gln(15) and His(19) and Ala(22) respectively. Obestatin {1-10} showed no structural components whereas {11-23} contained an a-helix between residues Val(14) and Ser(20) in a mixed solvent. These studies are the first to elucidate the structure of human obestatin and provide clear evidence that the observed a-helical structures are critical for in vivo activity. Future structure/function studies may facilitate the design of novel therapeutic agents based on the obestatin peptide structure. (C) 2010 Elsevier Inc. All rights reserved.

N-terminal glycation of cholecystokinin-8 abolishes its insulinotropic action on clonal pancreatic B-cells

Monoglycated cholecystokinin octapeptide (Asp(1)-glucitol CCK-X) was prepared under hyperglycaemic reducing conditions and purified by reverse phase-high performance liquid chromatography. Electrospray ionisation mass spectrometry and automated Edman degradation demonstrated that CCK-8 was glycated specifically at the amino-terminal Asp(1) residue. Effects of Asp(1)-glucitol CCK-8 and CCK-8 on insulin secretion were examined using glucose-responsive clonal BRIN-BD11 cells. In acute (20 min) incubations, 10(-10) mol/l CCK-8 enhanced insulin release by 1.2-1.5-fold at 5.6-11.1 mmol/l glucose. The stimulatory effect induced by 10(-10) mom CCK-8 was abolished following glycation. At 5.6 mmol/l glucose, CCK-8 at concentrations ranging from 10(-11) to 10(-7) mol/l induced a significant 1.6-1.9-fold increase in insulin secretion. Insulin output in the presence of Asp(1)-glucitol CCK-8 over the concentration range 10(-11)-10(-7) mol/l was decreased by 21-35% compared with CCK-8, and its insulinotropic action was effectively abolished. Asp(1)-glucitol CCK-8 at 10(-8) mol/l also completely blocked the stimulatory effects of 10(-11)-10(-8) mol/l CCK-8. These data indicate that structural modification by glycation at the amino-terminal Asp(1) residue effectively abolishes and/or antagonises the insulinotropic activity of CCK-8. (C) 1999 Elsevier Science B.V. All rights reserved.

Molecular mechanisms mediating the beneficial metabolic effects of [Arg4]tigerinin-1R in mice with diet-induced obesity and insulin resistance

The frog skin host-defense peptide tigerinin-1R stimulates insulin release in vitro and improves glucose tolerance and insulin sensitivity in animal models of type 2 diabetes. This study extends these observation by investigating the molecular mechanisms of action underlying the beneficial metabolic effects of the analogue [Arg4]tigerinin-1R in mice with diet induced obesity, glucose intolerance and insulin resistance. The study also investigates the electrophysiological effects of the peptide on KATP and L-type Ca2+ channels in BRINBD11 clonal β cells. Non-fasting plasma glucose and glucagon concentrations were significantly (P<0.05) decreased and plasma insulin increased by twice daily treatment with [Arg4]tigerinin-1R (75 nmol.kg-1 body weight) for 28 days. Oral and intraperitoneal glucose tolerance were significantly (P < 0.05) improved accompanied by enhanced secretion and action of insulin. The peptide blocked KATP channels and, consistent with this, improved beta cell responses of isolated islets to a range of secretagogues. Peptide administration resulted in up-regulation of key functional genes in islets involved insulin secretion (Abcc8, Kcnj11, Cacna1c and Slc2a2) and in skeletal muscle involved with insulin action (Insr, Irs1, Pdk1, Pik3ca, and Slc2a4). These observations encourage further development of tigerinin-1R analogues for the treatment of patients with type 2 diabetes.

In vitro and in vivo insulinotropic properties of the multifunctional frog skin peptide hymenochirin-1B: a structure–activity study

Hymenochirin-1b (Hym-1B; IKLSPETKDNLKKVLKGAIKGAIAVAKMV.NH2) is a cationic, α-helical amphibian host-defense peptide with antimicrobial, anticancer, and immunomodulatory properties. This study investigates the abilities of the peptide and nine analogues containing substitutions of Pro5, Glu6, and Asp9 by either l-lysine or d-lysine to stimulate insulin release in vitro using BRIN-BD11 clonal β cells or isolated mouse islets and in vivo using mice fed a high-fat diet to produce obesity and insulin resistance. Hym-1B produced a significant and concentration-dependent increase in the rate of insulin release from BRIN-BD11 cells without cytotoxicity at concentrations up to 1 µM with a threshold concentration of 1 nM. The threshold concentrations for the analogues were: [P5K], [E6K], [D9K], [P5K, E6K] and [E6K, D9k] 0.003 nM, [E6K, D9K] and [D9k] 0.01 nM, [P5K, D9K] 0.1 nM and [E6k] 0.3 nM. All peptides displayed cytotoxicity at concentrations ≥1 µM except the [P5K] and [D9k] analogues which were non-toxic at 3 µM. The potency and maximum rate of insulin release from mouse islets produced by the [P5K] peptide were significantly greater than produced by Hym-1B. Neither Hym-1B nor the [P5K] analogue at 1 µM concentration had an effect on membrane depolarization or intracellular Ca2+. The [P5K] analogue (1 µM) produced a significant increase in cAMP concentration in BRIN-BD11 cells and stimulated GLP-1 secretion from GLUTag cells. Down-regulation of the protein kinase A pathway by overnight incubation with forskolin completely abolished the insulin-releasing effects of [P5K]hym-1B. Intraperitoneal administration of the [P5K] and [D9k] analogues (75 nmol/kg body weight) to high-fat-fed mice with insulin resistance significantly enhanced glucose tolerance with a concomitant increase in insulin secretion. We conclude that [P5K]hym-1B and [D9k]hym-1B show potential for development into anti-diabetic agents.

Interrelation entre déficits métaboliques et neuropathologie associée à la maladie d’Alzheimer chez la souris 3xTg-AD

La maladie d’Alzheimer (MA) est la maladie neurodégénérative qui cause le plus important nombre de cas de démence. On estime que près de 15% des canadiens âgés de plus de 65 ans sont atteints de la MA. Avec le vieillissement de la population, le nombre de cas augmentera de manière substantielle dans les prochaines années. À l’heure actuelle, aucun traitement ne permet de ralentir la progression de la maladie. Pour plus de 99% des cas, ses causes exactes demeurent indéterminées. Toutefois, de nombreux facteurs de risque ont été identifiés. Parmi eux, on retrouve plusieurs facteurs liés au métabolisme énergétique dont l’obésité et le diabète de type 2 (DT2). De manière intéressante, des modifications du métabolisme, telles qu’une résistance à l’insuline centrale et périphérique, sont également observées chez les patients Alzheimer. Afin de mieux comprendre l’interaction entre le DT2 et la MA, nous avons d’abord étudié les altérations métaboliques chez la souris triple transgénique (3xTg-AD), un modèle murin de la MA. Nous avons, en premier lieu, observé une intolérance au glucose qui progresse avec l’âge, qui est plus importante chez les femelles et qui semble liée à l’accumulation du peptide beta-amyloïde (Aβ) humain dans le pancréas. Ensuite, nous avons nourri cette souris avec une diète riche en gras pour vérifier l’impact d’une aggravation des déficits métaboliques sur la pathologie Alzheimer. L’aggravation de l’intolérance au glucose chez les souris 3xTg-AD semblait liée à l’atrophie des îlots de Langerhans et, en conséquence, à une réduction de la production d’insuline en réponse à l’injection de glucose. En plus de l’aggravation des déficits métaboliques, la diète riche en gras a augmenté de manière drastique l’accumulation de la forme soluble du peptide Aβ dans le cortex et a déterioré la mémoire des souris 3xTg-AD. De manière intéressante, l’élévation du peptide Aβ et les troubles de la mémoire ont été rétablis par l’administration d’une seule dose d’insuline. Aussi, nous avons observé une augmentation du peptide Aβ dans le plasma 30 minutes à la suite de l’injection d’insuline, suggérant qu’il est possible que la baisse rapide du peptide soit en partie causée par une élévation de la clairance du peptide au cerveau. Ces résultats renforcent les évidences supportant le potentiel thérapeutique de l’insuline dans le traitement de la MA. Toutefois, les résultats chez les patients mettent en lumière l’inefficacité de l’administration intranasale d’insuline chez les porteurs de l’allèle 4 du gène de l’apolipoprotéine E (APOE4). Afin de comprendre les raisons qui expliquent cette différence de réponse à l’insuline chez les porteurs de l’APOE4, nous avons injecté des souris exprimant l’APOE3 et l’APOE4 humain avec de l’insuline dans le but de vérifier l’effet central et périphérique de l’insuline chez ces animaux. Les souris APOE4 montrent une plus importante élévation de la signalisation de l’insuline au cerveau comparativement aux souris APOE3. Cette plus haute réponse est aussi associée à une élévation plus importante de la phosphorylation de la protéine tau, un marqueur neuropathologique de la MA. En somme, ces résultats suggèrent qu’il existe un cercle vicieux entre la MA et le DT2. L’administration d’insuline a un potentiel thérapeutique intéressant pour la MA, malgré des effets limités chez les patients APOE4 en raison de son impact probable sur la phosphorylation de la protéine tau.

Insulin secretion is regulated by the glucose-dependent production of islet beta cell macrophage migration inhibitory factor.

Macrophage migration inhibitory factor (MIF), originally identified as a cytokine secreted by T lymphocytes, was found recently to be both a pituitary hormone and a mediator released by immune cells in response to glucocorticoid stimulation. We report here that the insulin-secreting beta cell of the islets of Langerhans expresses MIF and that its production is regulated by glucose in a time- and concentration-dependent manner. MIF and insulin colocalize by immunocytochemistry within the secretory granules of the pancreatic islet beta cells, and once released, MIF appears to regulate insulin release in an autocrine fashion. In perifusion studies performed with isolated rat islets, immunoneutralization of MIF reduced the first and second phase of the glucose-induced insulin secretion response by 39% and 31%, respectively. Conversely, exogenously added recombinant MIF was found to potentiate insulin release. Constitutive expression of MIF antisense RNA in the insulin-secreting INS-1 cell line inhibited MIF protein synthesis and decreased significantly glucose-induced insulin release. MIF is therefore a glucose-dependent, islet cell product that regulates insulin secretion in a positive manner and may play an important role in carbohydrate metabolism.

Connexin-36 contributes to control function of insulin-producing cells.

Connexin-36 (Cx36) is a gap junction protein expressed by the insulin-producing beta-cells. We investigated the contribution of this protein in normal beta-cell function by using a viral gene transfer approach to alter Cx36 content in the insulin-producing line of INS-1E cells and rat pancreatic islets. Transcripts for Cx43, Cx45, and Cx36 were detected by reverse transcriptase-PCR in freshly isolated pancreatic islets, whereas only a transcript for Cx36 was detected in INS-1E cells. After infection with a sense viral vector, which induced de novo Cx36 expression in the Cx-defective HeLa cells we used to control the transgene expression, Western blot, immunofluorescence, and freeze-fracture analysis showed a large increase of Cx36 within INS-1E cell membranes. In contrast, after infection with an antisense vector, Cx36 content was decreased by 80%. Glucose-induced insulin release and insulin content were decreased, whether infected INS-1E cells expressed Cx36 levels that were largely higher or lower than those observed in wild-type control cells. In both cases, basal insulin secretion was unaffected. Comparable observations on basal secretion and insulin content were made in freshly isolated rat pancreatic islets. The data indicate that large changes in Cx36 alter insulin content and, at least in INS-1E cells, also affect glucose-induced insulin release.

Incrétines, sécrétion d'insuline et diabète

Nutrient ingestion triggers a complex hormonal response aimed at stimulating glucose utilization in liver, muscle and adipose tissue to minimize the raise in blood glucose levels. Insulin secretion by pancreatic beta cells plays a major role in this response. Although the beta cell secretory response is mainly controlled by blood glucose levels, gut hormones secreted in response to food intake have an important role in potentiating glucose-stimulated insulin secretion. These gluco-incretin hormones are GLP-1 (glucagon-like peptide-1) and GIP (gluco-dependent insulinotropic polypeptide). Their action on pancreatic beta cells depends on binding to specific G-coupled receptors linked to activation of the adenylyl cyclase pathway. In addition to their effect on insulin secretion both hormones also stimulate insulin production at the transcriptional and translational level and positively regulate beta cell mass. Because the glucose-dependent insulinotropic action of GLP-1 is preserved in type 2 diabetic patients, this peptide is now developed as a novel therapeutic drug for this disease.

Islet Brain 1 Protects Insulin Producing Cells against Lipotoxicity.

Chronic intake of saturated free fatty acids is associated with diabetes and may contribute to the impairment of functional beta cell mass. Mitogen activated protein kinase 8 interacting protein 1 also called islet brain 1 (IB1) is a candidate gene for diabetes that is required for beta cell survival and glucose-induced insulin secretion (GSIS). In this study we investigated whether IB1 expression is required for preserving beta cell survival and function in response to palmitate. Chronic exposure of MIN6 and isolated rat islets cells to palmitate led to reduction of the IB1 mRNA and protein content. Diminution of IB1 mRNA and protein level relied on the inducible cAMP early repressor activity and proteasome-mediated degradation, respectively. Suppression of IB1 level mimicked the harmful effects of palmitate on the beta cell survival and GSIS. Conversely, ectopic expression of IB1 counteracted the deleterious effects of palmitate on the beta cell survival and insulin secretion. These findings highlight the importance in preserving the IB1 content for protecting beta cell against lipotoxicity in diabetes.

The pancreatic islet system of the rock bass /|nby Edward Francis Squires. -- 260 St. Catharines, Ont. : [s. n.],

The endocrine pancreas of the rock bass (Ambloplites rupestris) was examined by light and electron microscopy. Two cell types with staining properties similar to mammalian A and B cells, and a third, non-staining cell type were found in the spherical pancreatic islets that were surrounded by a connective tissue capsule and embedded in two small masses of exocrine tissue. From an analysis of the ultrastructure of the A and B cells, a secretory cycle for each of these cell types was proposed. The secretory cycle of the A cell consisted of three well defined stages: (1) A cell production stage: during which A granule formation occurred in the sacs of the Golgi apparatus and the cell was characterized by the presence of numerous secretory granules, some elements of lamellar endoplasmic reticulum, and a homogeneously granular nucleus. The cytoplasm contained few distended cisternae, variable numbers of free ribosomes, microtubules and small vesicles. (2) A cell release stage: during which the release of A granules occurred and the cell usually contained several large distended cisternae and variable numbers of secretory granules. Granule release mechanisms included exocytosis, by which individual granules were released into the extracellular space after their membranes fused with the plasmalemma, and emiocytosis, by which one or more granules were released into a large cisterna whose membrane fused with the plasmalemma and formed a pore through which the cisternal contents passed out of the cell. (3) A cell reorganization stage: during which the changeover from the release stage to the production stage occurred and the reorganization of organelles and membrane structures took place. The cell contained few secretory granules and numerous small endoplasmic reticular cisternae. The cytoplasm exhibited less electron density than either of the other two stages. The A granule after formation underwent a series of morphological changes which were described in four numerically identified phases. The secretory cycle of the B cell consisred of two stages: (1) B cell production stage: during which the B granule formation occurred in the sacs of the Go1gi apparatus. The cell was characterized by an irregular outline, the presence of numerous secretory granules, and an irregularly shaped nucleus which contained variable amounts of clumped chromatin. The cytoplasm contained moderate amounts of lamellar endoplasmic reticulum studded with ribosomes, several small vesicles, and an active Go1gi apparatus. (2) B cell release stage: during which the release of B granules occurred. The cell contained a rounded nucleus with dispersed chromatin, several distended endoplasmic reticular cisternae and a variable number of secretory granules. Granule release occu~ by emiocytosis and exocytosis similar to that found for the A cell.