Characteristics of an adenylate cyclase enhancing factor from mouse pancreatic islet cytosol

Summary The role of cytosolic components in the regulation of mouse pancreatic islet adenylate cyclase activity was studied. Addition of mouse islet cytosol (27000 g supernatant of mouse islet sonicate), devoid of adenylate cyclase activity itself, increased adenylate cyclase activity by 93±17% (n = 9) in the 27000 g total particulate fraction of mouse islets. Addition of GTP stimulated adenylate cyclase activity by 91±11% (n = 13) or to the same degree as cytosol. Like GTP, the substance causing the enhancing activity of the cytosol was found to be dialysable, resistant to heat, sensitive to charcoal treatment and alkaline phosphatase and insensitive to digestion with trypsin. However, in contrast to the stimulation by GTP, the stimulation by cytosol was not inhibited by guanosine 5-0-(2-thiodiphosphate), and furthermore, the effects of cytosol and GTP were additive. Neither NAD nor phosphoenolpyruvate stimulated adenylate cyclase activity. The cytosolic factor did not confer sensitivity towards glucose, Ca²⁺ or Ca²⁺-calmodulin on adenylate cyclase. The results demonstrate that mouse pancreatic islets contain a phosphocompound (or several compounds) distinct from GTP and capable of markedly stimulating adenylate cyclase. The identity of the compound and its physiological significance remain to be established.     

Pancreatic islets and their roles in metabolic programming

Experimental and epidemiologic data have confirmed that undernutrition or overnutrition during critical periods of life can result in metabolic dysfunction, leading to the development of obesity, hypertension, and type 2 diabetes, later in life. These studies have contributed to the concept of the developmental origins of health and disease (DOHaD), which involves metabolic programming patterns. Beyond the earlier phases of development, puberty can be an additional period of plasticity, during which any insult can lead to changes in metabolism. Impaired brain development, associated with imbalanced autonomous nervous system activity due to metabolic programming, is pivotal to the creation of pathophysiology. Excess glucocorticoid exposure, due to hypothalamic–pituitary–adrenal axis deregulation, is also involved in malprogramming in early life. Additionally, the pancreatic islets appear to play a decisive role in the setup and maintenance of these metabolic dysfunctions as key targets of metabolic programming, and epigenetic mechanisms may underlie these changes. Moreover, studies have indicated the possibility that deprogramming renders the islets able to recover their functioning after malprogramming. In this review, we discuss the key roles of the pancreatic islets as targets of malprogramming; however, we also discuss their roles as important targets for the treatment and prevention of metabolic diseases.     

Isolated pancreatic islets of the rat: An immunohistochemical and morphometric study

Although there is a recent increase in the use of the isolated pancreatic islets of the rat in the transplantation and functional studies, there has been no detailed quantitative assessment on the size and cellular constituents of islets after the isolation procedure. The present work was undertaken to study the size classes of the isolated islets and the morphometry of their cellular populations. Islets of the rat pancreas were isolated by using the intraductal collagenase digestion technique, the most commonly used procedure for the isolation of pancreatic islets. Different endocrine cells of the isolated islets were stained by immunoperoxidase staining techniques. The distribution of the cellular constituents of the isolated islets was similar to that of the intact islets of the normal pancreas; A, D, and PP cells were peripherally arranged around the centrally located B cells. However, morphometric quantitative study showed that the percent volume and percent number of A, D, and PP cells of the isolated islets were lower than those of the corresponding intact ones. Further, the mean true diameter of the isolated islets was lower than that of the intact ones. These data indicate loss of islet cells during the process of isolation. Most of the lost cells were from the periphery of islets. This may provide an explanation for the incomplete metabolic control and recurrence of hyperglycemia encountered after isolated islet transplantation in the treatment of diabetes mellitus. It seems that further refinements of the isolation techniques are necessary to obtain islet tissue with total cellular integrity, before a complete success in transplantation could be achieved. © 1993 Wiley-Liss, Inc.     

免疫抑制剂对人胰岛细胞的毒性作用

目的 探讨临床常用免疫抑制剂对人胰岛细胞的直接毒性作用.方法 应用体外分离纯化后培养的人胰岛细胞,以刺激系数和丫啶橙/碘丙啶染色为效应指标,检验低、中、高不同浓度免疫抑制剂对人胰岛细胞的直接毒性作用.结果 体外培养3天后,低浓度免疫抑制剂未表现出胰岛毒性作用;中浓度免疫抑制剂对胰岛的毒性不同,以他克莫司为重;高浓度免疫抑制剂有较强的胰岛毒性.结论 免疫抑制剂对人胰岛细胞直接毒性作用与浓度相关,选择低胰岛毒性免疫抑制方案有助于提高胰岛移植成功率.     

组织培养对乳胰B细胞功能和形态的影响

本文报道了不同培养时间对乳胰组织培养后胰岛活性的影响。通过对各组培养液胰岛素含量的测定和使用免疫组化与显微图象分析技术对 B 细胞内胰岛素的定性和定量观察表明,新鲜乳胰碎片行短期组织培养(2～8天),可获得良好的效果。     

Abnormal insulin secretion and glucose metabolism in pancreatic islets from the spontaneously diabetic GK rat

Summary Insulin secretion and islet glucose metabolism were compared in pancreatic islets isolated from GK/Wistar (GK) rats with spontaneous Type 2 (non-insulin-dependent) diabetes mellitus and control Wistar rats. Islet insulin content was 24.5±3.1 U/ng islet DNA in GK rats and 28.8±2.5 U/ng islet DNA in control rats, with a mean (±SEM) islet DNA content of 17.3±1.7 and 26.5±3.4 ng (p < 0.05), respectively. Basal insulin secretion at 3.3 mmol/l glucose was 0.19±0.03 · ng islet DNA^–1· h^–1 in GK rat islets and 0.40±0.07 in control islets. Glucose (16.7 mmol/l) stimulated insulin release in GK rat islets only two-fold while in control islets five-fold. Glucose utilization at 16.7 mmol/l glucose, as measured by the formation of ³H₂O from [5-³ H]glucose, was 2.4 times higher in GK rat islets (3.1±0.7 pmol · ng islet DNA^–1 · h^–1) than in control islets (1.3±0.1 pmol · ng islet DNA^–1 · h^–1; p<0.05). In contrast, glucose oxidation, estimated as the production of ¹⁴CO₂ from [U-¹⁴C]glucose, was similar in both types of islets and corresponded to 15±2 and 30±3 % (p<0.001) of total glucose phosphorylated in GK and control islets, respectively. Glucose cycling, i. e. the rate of dephosphorylation of the total amount of glucose phosphorylated, (determined as production of labelled glucose from islets incubated with ³H₂O) was 16.4±3.4% in GK rat and 6.4±1.0% in control islets, respectively (p<0.01). We conclude that insulin secretion stimulated by glucose is markedly impaired in GK rat islets. Glucose metabolism is also altered in GK rat islets, with diminished ratio between oxidation and utilization of glucose, and increased glucose cycling, suggesting links between impaired glucose-induced insulin release and abnormal glucose metabolism.     

原代分离的大鼠胰岛细胞对葡萄糖刺激胰岛素分泌的反应性研究

目的:研究原代分离的大鼠胰岛对葡萄糖刺激的胰岛素分泌反应性。方法:胶原酶原位灌注法分离大鼠胰岛,在含0.5%BSA、5.5或11.1mmol/L葡萄糖的培养基中培养不同时间后,用含0.2%BSA、3.3mmol/L葡萄糖的KRB缓冲液预培养胰岛30min,分别换入含不同浓度葡萄糖KRB缓冲液,培养1h,收集上清,RIA法测定胰岛素浓度。结果:大鼠胰岛过夜培养后,在基础(3.3mmol/L)和高浓度(16.7mmol/L)葡萄糖条件下胰岛素分泌量分别为(12.4±3.2)和(45.2±4.2)μU/ml/10islets/h;5.5mmol/L和11.1mmol/L葡萄糖浓度下培养12h和20h后,胰岛对葡萄糖的反应性均明显高于16.7mmol/L和22.5mmol/L葡萄糖组(P<0.05);体外培养5d后,对高糖的反应性为(4.28±0.67)倍。结论:原代分离的大鼠胰岛可在(1～5)d内保持对葡萄糖的反应性。     

胰岛α细胞培养上清液对INS-1细胞胰岛素释放与合成的影响

在培养的INS 1细胞中 ,分别加入不同比例的胰岛α细胞培养上清液 (以下简称上清液 ) ,在不同浓度葡萄糖的刺激下 ,分别孵育不同时间 ,用放射免疫法测定INS 1细胞培养基中的胰岛素含量。在 2 0mmol L葡萄糖浓度下 ,不同刺激时间 ,不同浓度的上清液刺激INS 1细胞分泌的胰岛素显著高于 0 %上清液 (以下简称对照组 ,P <0 0 5或0 0 1 )。在 0、1 85mmol L葡萄糖刺激时 ,不同浓度的上清液对INS 1细胞的胰岛素分泌无明显作用 ,而在 5 6、1 6 7和 5 0mmol L葡萄糖刺激时 ,不同浓度的上清液刺激INS 1细胞分泌的胰岛素显著高于对照组 (P <0 0 5或 0 0 1 )。RT PCR结果显示 ,在 1 6 7mmol L葡萄糖刺激 4、1 2和 2 4h后 ,30 %上清液对INS 1细胞胰岛素mRNA水平均无明显影响。提示胰岛α细胞培养上清液对糖刺激的INS 1细胞的胰岛素分泌有促进作用 ,但不影响胰岛素的生物合成     

Glycosylphosphatidylinositol-specific phospholipase D immunoreactivity is present in islet amyloid in type 2 diabetes

Numerous apolipoproteins associate with amyloid plaques. A minor high-density lipoprotein-associated protein, glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD), has recently been described by the authors and others. Since GPI-PLD is synthesized by, and secreted from, pancreatic islet beta cells, the present study examined the hypothesis that GPI-PLD associates with islet amyloid. GPI-PLD immunoreactivity was examined in pancreatic tissues from type 2 diabetic and non-diabetic humans. GPI-PLD binding to heparan sulphate proteoglycan was determined in the absence or presence of heparan sulphate or heparin. Fibril formation from human islet amyloid polypeptide was determined in the absence or presence of GPI-PLD. In non-diabetics, GPI-PLD immunoreactivity was present and co-localized with insulin, as opposed to co-localizing with amyloid in diabetics. No immunoreactivity for apolipoprotein A-I was present in islet cells or islet amyloid. Heparan sulphate proteoglycan, which is commonly present in most amyloid, bound GPI-PLD in vitro. GPI-PLD inhibited the formation of amyloid fibrils from synthetic islet amyloid polypeptide in vitro. GPI-PLD is therefore present in islet amyloid and appears to derive from local production from islets. This localization likely derives from interaction between GPI-PLD and heparan sulphate proteoglycan. Since GPI-PLD also inhibited islet amyloid polypeptide fibril formation in vitro, it is concluded that GPI-PLD may play a role in islet amyloid formation in type 2 diabetes.