Imoto Hirofumi, Sasaki Nobuhiro, Iwase Masanori, Nakamura Udai, Oku Miwako, Sonoki Kazuo, Uchizono Yuji, Iida Mitsuo
Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan.
Endocrinology. 2008 Nov;149(11):5391-400. doi: 10.1210/en.2008-0186. Epub 2008 Jul 10.
Pancreatic islets express the superoxide-producing nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system, but its role remains unknown. To address this, we studied the mechanisms of impaired insulin secretion induced by diphenyleneiodium (DPI), an NADPH oxidase inhibitor. We investigated the effects of DPI on glucose- and nonfuel-stimulated insulin secretion, islet glucose metabolism, and intracellular Ca2+ concentration ([Ca2+]i) dynamics in rat islets and beta-cell line RINm5F cells. DPI did not affect insulin secretion at 3.3 mm glucose but totally suppressed insulin secretion stimulated by 16.7 mm glucose (percentage of control, 9.2 +/- 1.2%; P <0.001). DPI also inhibited insulin release by high K+-induced membrane depolarization (percentage of control, 36.0 +/- 5.3%; P <0.01) and protein kinase C activation (percentage of control, 30.2 +/- 10.6% in the presence of extracellular Ca2+, P <0.01; percentage of control, 42.0 +/- 4.7% in the absence of extracellular Ca2+, P <0.01). However, DPI had no effect on mastoparan-induced insulin secretion at 3.3 and 16.7 mm glucose under Ca2+-free conditions. DPI significantly suppressed islet glucose oxidation and ATP content through its known inhibitory action on complex I in the mitochondrial respiratory chain. On the other hand, DPI altered [Ca2+]i dynamics in response to high glucose and membrane depolarization, and DPI per se dose-dependently increased [Ca2+]i. The DPI-induced [Ca2+]i rise was associated with a transient increase in insulin secretion and was attenuated by removal of extracellular Ca2+, by L-type voltage-dependent Ca2+ channel blockers, by mitochondrial inhibitors, or by addition of 0.1 or 1.0 microm H2O2 exogenously. Our results showed that DPI impairment of insulin secretion involved altered Ca2+ signaling, suggesting that NADPH oxidase may modulate Ca2+ signaling in beta-cells.
胰岛表达产生超氧化物的烟酰胺腺嘌呤二核苷酸磷酸（NADPH）氧化酶系统，但其作用尚不清楚。为了解决这个问题，我们研究了NADPH氧化酶抑制剂二苯碘鎓（DPI）诱导胰岛素分泌受损的机制。我们研究了DPI对大鼠胰岛和β细胞系RINm5F细胞中葡萄糖和非燃料刺激的胰岛素分泌、胰岛葡萄糖代谢以及细胞内Ca2+浓度（[Ca2+]i）动态变化的影响。DPI在3.3 mmol/L葡萄糖浓度下不影响胰岛素分泌，但完全抑制16.7 mmol/L葡萄糖刺激的胰岛素分泌（相对于对照组的百分比为9.2±1.2%；P<0.001）。DPI还抑制高钾诱导的膜去极化引起的胰岛素释放（相对于对照组的百分比为36.0±5.3%；P<0.01）以及蛋白激酶C激活引起的胰岛素释放（在存在细胞外Ca2+的情况下相对于对照组的百分比为30.2±10.6%，P<0.01；在不存在细胞外Ca2+的情况下相对于对照组的百分比为42.0±4.7%，P<0.01）。然而，在无Ca2+条件下，DPI对3.3和16.7 mmol/L葡萄糖浓度下蜂毒肽诱导的胰岛素分泌没有影响。DPI通过其对线粒体呼吸链中复合物I的已知抑制作用，显著抑制胰岛葡萄糖氧化和ATP含量。另一方面，DPI改变了对高葡萄糖和膜去极化的[Ca2+]i动态变化，并且DPI本身剂量依赖性地增加[Ca2+]i。DPI诱导的[Ca2+]i升高与胰岛素分泌的短暂增加相关，并且通过去除细胞外Ca2+、L型电压依赖性Ca2+通道阻滞剂、线粒体抑制剂或外源性添加0.1或1.0 μmol H2O2而减弱。我们的结果表明，DPI对胰岛素分泌的损害涉及Ca2+信号的改变，提示NADPH氧化酶可能调节β细胞中的Ca2+信号。
