Use of metaiodobenzylguanidine (MIBG) in pneumology

Norepinephrine (NE) is one of the many biologically active substances that are metabolized by the lung. The norepinephrine uptake in the lung has been widely investigated in animal studies in order to detect abnormalities of the endothelial cells. 131I- or 123I-labelled metaiodobenzylguanidine (MIBG) is a radioactive tracer that shares several metabolic pathways with NE; it has been used instead NE or both in animal and in human studies for the same purposes. It has been definitely demonstrated that MIBG lung uptake following intravenous administration is a reliable marker of minimal endothelial cell lesions and it allows one to investigate several conditions involving damage to the lung vasculature such as adult respiratory distress syndrome, post-actinic lung fibrosis or chemotherapic lung toxicity. MIBG could also potentially be used as a tracer of the neuroadrenergic system of the airways, once it has been deposited in the whole branches of the bronchial tree. With this in mind we evaluated the feasibility of the administration of MIBG in radioaerosol form. We first performed a chromatographic study on [123I]MIBG aliquots aerosolized for variable lengths of time (2-30 minutes). Radiochemical purity was always over 96%, thus demonstrating that aerosolization does not significantly modify the stability of the tracer. We then compared both the lung clearance curves and the scintigraphic images in two groups of normal subjects who respectively underwent [123I]MIBG and 99mTc-DTPA radioaerosol dynamic scintigraphy. We found that MIBG clearance to be significantly lower than that of DTPA (135 +/- 32 minutes versus 69 +/- 27 minutes, p < 0.01), probably due to its being trapped in the adrenergic nerve endings of the airways. The pulmonary distribution of both tracers was homogeneous, as demonstrated by the correspondence of the values for the aerosol penetration index in both groups of subjects. Such results warrant further research and pharmacologic tests.