New strategy for treatment of type 2 diabetes by utilizing the regeneration of pancreatic β cell function

为探讨过氧化物酶体增殖物激活受体-γ（peroxisome proliferator-activated receptor-γ，PPARγ）激动剂吡格列酮对2型糖尿病大鼠胰岛β细胞功能改变的影响，采用吡格列酮治疗肥胖糖尿病db/db小鼠6周，观察其胰岛分泌功能和胰岛素含量的变化。此外，还检测了氧化应激标志物4-羟基-2-壬烯醛（HNE）修饰蛋白和血红素加氧酶-1在内分泌胰腺中的表达。通过吡格列酮治疗，从分离的胰岛中分泌葡萄糖诱导的胰岛素的能力和它们的胰岛素含量得到改善。吡格列酮给药db/db小鼠胰岛中氧化应激标志物的免疫染色密度显著降低。这些结果清楚地证明了吡格列酮长期治疗通过降低糖尿病状态下的加速氧化应激在体内恢复胰腺β细胞功能方面的获益。然后，利用腺病毒介导的基因转移系统，在离体胰岛细胞中过表达PPARγ，观察其对胰岛β细胞功能的直接影响。出乎意料的是，PPARγ过表达显著抑制刺激浓度葡萄糖诱导的胰岛素分泌，同时增加解偶联蛋白-2（UCP-2）的表达。因此，吡格列酮对胰岛氧化应激的保护作用似乎取决于该药物在体内其他器官或细胞中表现出的间接药理学机制，而不是其在胰腺β细胞中的直接作用。

To access the effect of the peroxisome proliferator-activated receptor-γ(PPARγ) agonist pioglitazone on altered βcell function under type 2 diabetes, obese diabetic db/db mice were treated with pioglitazone for 6weeks, and insulin secretory capacity and insulin content of isolated pancreatic islets were evaluated. In addition, the expression of oxidative stress markers, 4-hydroxy-2-nonenal (HNE) -modified protein and heme oxygenase-1, in endocrine pancreas was examined. The capacity for glucose-induced insulin secretion from isolated islets and their insulin content were improved by pioglitazone treatment. The density of immunostaining for oxidative stress markers was significantly reduced in pancreatic islets of pioglitazone-treated db/db mice. These findings clearly demonstrates the benefit of long-term treatment with pioglitazone in restoring pancreatic βcell function in vivo through the reduction of accelerated oxidative stress in the diabetic state. And then, to examine the direct effect of PPARγ on pancreatic βcell function, we overexpressed PPARγ in isolated islets in vitro by using adenovirus-mediated gene transfer system. Unexpectedly, PPARγ overexpression significantly suppressed insulin secretion induced by stimulatory concentration of glucose with concomitant increase of uncoupling protein-2(UCP-2) expression. The protection by pioglitazone against oxidative stress in pancreatic islets seems to be, therefore, dependent on the indirect pharmacological mechanism exhibited in the other organs or cells by this agent in vivo, rather than on its direct effect in pancreatic βcells.