Corbett JA, McDaniel ML
Department of Pathology, Washington University School of Medicine, St. Louis, Missouri, 63110
Methods. 1996 Aug;10(1):21-30. doi: 10.1006/meth.1996.0074.
Insulin-dependent diabetes mellitus is an autoimmune disease characterized by the selective destruction of insulin-secreting beta cells found in islets of Langerhans. The biochemical mechanisms associated with beta-cell destruction have remained elusive. Cytokines, released from T lymphocytes, macrophages, and monocytes during islet insulitis, have been implicated as effector molecules that participate in beta-cell death. Recently, cytokine-induced expression of inducible nitric oxide synthase (iNOS) and production of nitric oxide by beta cells has been suggested as one potential mechanism associated with beta-cell destruction. Treatment of rat islets with interleukin 1 (IL-1) results in a potent inhibition of insulin secretion followed by islet destruction. The inhibitory and destructive effects of this cytokine on islet function are completely prevented by the inhibition of iNOS enzymatic activity. Islets contain a heterogeneous population of both endocrine and nonendocrine cells including a low level of resident tissue macrophages ( approximately0.5% of all islet cells). The intraislet macrophage appears to one cellular source of IL-1. Activation of resident islet macrophages results in both the expression of iNOS and the release of IL-1. Intraislet macrophage production of nitric oxide (in the absence of IL-1) does not modulate beta-cell function; however, macrophage release of IL-1 and IL-1-induced iNOS expression by beta cells results in a potent inhibition of beta-cell function. These findings support a role for nitric oxide as a potential mediator of cytokine-induced inhibition of beta-cell function and implicate the intraislet macrophage as one cellular source of IL-1. Direct support for a role of nitric oxide in the development of diabetes includes the ability of inhibitors of iNOS to prevent or delay the development of this disease condition in animal models. Important to these studies has been the identification of selective inhibitors of iNOS. Many inhibitors of nitric oxide synthase have been developed; however, few selective inhibitors for the individual isoforms of NOS (inducible, endothelial, neuronal) have been described. Aminoguanidine has been identified as one of the first iNOS selective inhibitors. Aminoguanidine is over 50-fold more effective at inhibiting the enzymatic activity of iNOS than endothelial or neuronal NOS. The effects of aminoguanidine on the development of diabetes in the nonobese diabetic mouse using an adoptive transfer protocol has been evaluated. Aminoguanidine delays the onset of diabetes in this animal model by 7-10 days. These studies, which provide in vivo evidence implicating a role for nitric oxide in the development of autoimmune diabetes, also support the use of selective inhibitors of iNOS for the attenuation of disease conditions associated with the expression of iNOS and an increased production of nitric oxide.
胰岛素依赖型糖尿病是一种自身免疫性疾病，其特征是胰岛中分泌胰岛素的β细胞被选择性破坏。与β细胞破坏相关的生化机制一直难以捉摸。在胰岛炎期间，T淋巴细胞、巨噬细胞和单核细胞释放的细胞因子被认为是参与β细胞死亡的效应分子。最近，细胞因子诱导的诱导型一氧化氮合酶（iNOS）表达以及β细胞产生一氧化氮被认为是与β细胞破坏相关的一种潜在机制。用白细胞介素1（IL-1）处理大鼠胰岛会导致胰岛素分泌受到强烈抑制，随后胰岛被破坏。通过抑制iNOS酶活性，这种细胞因子对胰岛功能的抑制和破坏作用可被完全阻止。胰岛包含内分泌和非内分泌细胞的异质群体，包括低水平的驻留组织巨噬细胞（约占所有胰岛细胞的0.5%）。胰岛内巨噬细胞似乎是IL-1的一个细胞来源。驻留胰岛巨噬细胞的激活会导致iNOS的表达以及IL-1的释放。胰岛内巨噬细胞产生一氧化氮（在没有IL-1的情况下）不会调节β细胞功能；然而，巨噬细胞释放IL-1以及β细胞中IL-1诱导的iNOS表达会导致β细胞功能受到强烈抑制。这些发现支持一氧化氮作为细胞因子诱导的β细胞功能抑制的潜在介质的作用，并表明胰岛内巨噬细胞是IL-1的一个细胞来源。一氧化氮在糖尿病发展中作用的直接证据包括iNOS抑制剂在动物模型中预防或延迟这种疾病状态发展的能力。这些研究的重要之处在于鉴定了iNOS的选择性抑制剂。已经开发了许多一氧化氮合酶抑制剂；然而，针对NOS（诱导型、内皮型、神经元型）各个同工型的选择性抑制剂很少被描述。氨基胍已被确定为首批iNOS选择性抑制剂之一。氨基胍抑制iNOS酶活性的效果比内皮型或神经元型NOS高出50多倍。已使用过继转移方案评估了氨基胍对非肥胖糖尿病小鼠糖尿病发展的影响。氨基胍使该动物模型中的糖尿病发病延迟7至10天。这些研究提供了体内证据，表明一氧化氮在自身免疫性糖尿病的发展中起作用，也支持使用iNOS选择性抑制剂来减轻与iNOS表达增加和一氧化氮产生增加相关的疾病状态。
