Characteristics and regulation of 123I-MIBG transport in cultured pulmonary endothelial cells.
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Lee
Kyung-Han
KH
Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. khleenm@yahoo.co.kr
Ko
Bong-Ho
BH
Paik
Jin-Young
JY
Jung
Kyung-Ho
KH
Bae
Jun-Sang
JS
Choi
Joon-Young
JY
Choe
Yearn Seong
YS
Kim
Byung-Tae
BT
D019797:3-Iodobenzylguanidine / Q000493:pharmacokinetics*; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D002417:Cattle; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000000981:diagnostic imaging* / Q000378:metabolism*; D008171:Lung Diseases / Q000000981:diagnostic imaging* / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D011651:Pulmonary Artery / Q000166:cytology / Q000000981:diagnostic imaging* / Q000378:metabolism*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics
D019275:Radiopharmaceuticals; D019797:3-Iodobenzylguanidine