Lee Kyung-Han, Ko Bong-Ho, Paik Jin-Young, Jung Kyung-Ho, Bae Jun-Sang, Choi Joon-Young, Choe Yearn Seong, Kim Byung-Tae
Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
J Nucl Med. 2006 Mar;47(3):437-42.
123I-Metaiodobenzylguanidine (123I-MIBG) is used for lung scintigraphy to assess pulmonary endothelial cell integrity, but its processing at the cellular level has not been investigated to date. We thus characterized the mechanisms that mediate 123I-MIBG transport in pulmonary endothelial cells and investigated the effects of stimuli associated with pulmonary dysfunction.
Calf pulmonary artery endothelial (CPAE) cells were examined for 123I-MIBG uptake and efflux rates and evaluated for the presence of norepinephrine (NE) transporters by Western blotting. The specificity of 123I-MIBG uptake was investigated with inhibitors of the uptake 1 and uptake 2 transport systems. In addition, we tested the effects of hypoxia (1% O2), phorbol 12-myristate 13-acetate (PMA, a protein kinase C [PKC] activator), and NG-nitro-L-arginine methyl ester (L-NAME) (a nitric oxide synthase inhibitor) treatments on CPAE cell 123I-MIBG uptake.
CPAE cells demonstrated a time-dependent increase in 123I-MIBG uptake that reached a relative plateau (mean +/- SD) at 4 h of 375.6% +/- 5.9% the 30-min level. When the culture medium was changed after 30 min of uptake, 123I-MIBG gradually was eluted from the cells at an efflux rate of 43.8% over 2 h. Western blotting confirmed the presence of NE transporters in CPAE cells. The uptake 1 inhibitors desipramine, imipramine, and phenoxybenzamine at 50 micromol/L reduced 123I-MIBG uptake to 55.3% +/- 2.7%, 62.4% +/- 3.5%, and 48.0% +/- 2.2% control levels, respectively, whereas none of the uptake 2 inhibitors had an effect. Exposure to hypoxia resulted in a reduction in 123I-MIBG uptake to 77.5% +/- 0.2% and 50.0% +/- 3.4% control levels at 0.5 and 4 h, respectively. PMA (10 ng/mL) and L-NAME (2 nmol/L) decreased 123I-MIBG uptake to 76.7% +/- 9.0% and 86.5% +/- 5.6% control levels, respectively.
Pulmonary endothelial cells express NE transporters and actively take up 123I-MIBG through the specific uptake 1 system. Furthermore, 123I-MIBG transport can be reduced by hypoxia, PKC activation, and nitric oxide deficiency, which may contribute partly to the lower levels of lung uptake observed in diseases that compromise pulmonary endothelial cell integrity.
123I-间碘苄胍（123I-MIBG）用于肺部闪烁显像以评估肺内皮细胞完整性，但迄今为止尚未在细胞水平对其进行研究。因此，我们确定了介导123I-MIBG在肺内皮细胞中转运的机制，并研究了与肺功能障碍相关刺激的影响。
检测小牛肺动脉内皮（CPAE）细胞对123I-MIBG的摄取和流出率，并通过蛋白质印迹法评估去甲肾上腺素（NE）转运体的存在情况。用摄取1和摄取2转运系统的抑制剂研究123I-MIBG摄取的特异性。此外，我们测试了缺氧（1%O2）、佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA，一种蛋白激酶C [PKC]激活剂）和NG-硝基-L-精氨酸甲酯（L-NAME）（一种一氧化氮合酶抑制剂）处理对CPAE细胞123I-MIBG摄取的影响。
CPAE细胞对123I-MIBG的摄取呈时间依赖性增加，在4小时时达到相对平台期（平均值±标准差），为30分钟水平的375.6%±5.9%。摄取30分钟后更换培养基时，123I-MIBG以43.8%的流出率在2小时内逐渐从细胞中洗脱。蛋白质印迹法证实CPAE细胞中存在NE转运体。50μmol/L的摄取1抑制剂地昔帕明、丙咪嗪和酚苄明分别将123I-MIBG摄取降低至对照水平的55.3%±2.7%、62.4%±3.5%和48.0%±2.2%，而摄取2抑制剂均无作用。暴露于缺氧环境导致123I-MIBG摄取在0.5小时和4小时时分别降低至对照水平的77.5%±0.2%和50.0%±3.4%。PMA（10 ng/mL）和L-NAME（2 nmol/L）分别将123I-MIBG摄取降低至对照水平的76.7%±9.0%和86.5%±5.6%。
肺内皮细胞表达NE转运体，并通过特异性摄取1系统主动摄取123I-MIBG。此外，缺氧、PKC激活和一氧化氮缺乏可降低123I-MIBG转运，这可能部分解释了在损害肺内皮细胞完整性的疾病中观察到的肺部摄取水平较低的原因。
