Microvascular Research 55, 146–152 (1998) Article No. MR982068 Indocyanine Green: Physicochemical Factors Affecting Its Fluorescence in Vivo Serge Mordon,* ,1 Jean Marie Devoisselle,² Sylvie Soulie-Begu,² and Thomas Desmettre* * INSERM JE2084, Pavillon Vancostenobel, Lille University Hospital, 59037 Lille Cedex, France; and †Laboratoire de Technique Pharmaceutique Industrielle, UFR des Sciences Pharmaceutiques, 34060 Montpellier, France Received June 19, 1997 This study reinvestigates the spectral properties of ICG amphiphilic properties of ICG are consistent with fixa- tion of some ICG molecules on sites other than plasmatic (Indocyanine green) in vivo, the role of quenching, and the possibility of an interaction of ICG with blood com- proteins after injection. The process of fixation of ICG molecules on surface components or within the vascular ponents and/or vessel walls. ICG quenching as a function of concentration was studied by spectrophotometry on endothelium could be due to a change in the microenvi- ronment of some ICG molecules.  1998 Academic Press whole blood samples from golden hamsters. Fluores- cence ICG characteristics were evaluated by front-face Key Words: indocyanine green; fluorescence; proteins; blood; quenching. fluorometry. In vivo, fluorescence measurements were performed on the femoral artery of golden hamsters. In vitro, on whole blood samples, fluorescence intensity is INTRODUCTION modified by ICG quenching as concentration increases above 80 mg/ml. The maximum fluorescence peak is not affected and remains centered at 832 nm. The in vivo Fluorescein angiography is an established and im- measurements display a similar fluorescence intensity portant diagnostic method in ophthalmology and in shape, which is affected only by ICG concentrations. capillary microscopy for the study of several human However, the maximum fluorescence emission peak is microangiopathies (Bollinger et al., 1991). In gastroen- modified significantly with time. Between 0 and 120 min, terology, this method has been proposed for studying four phases can be distinguished in which a wavelength blood vessels of the stomach, the intestine, and the co- shift from 826 to 835 nm is observed. The wavelength lon since tissue perfusion plays an important role in shift with change in fluorescence intensity observed in several diseases. For example, progressive reduction in vivo could be due to a localization of ICG molecules in neoterminal ilea blood flow after ileocolonic resection sites more hydrophobic than serum proteins. It is possi- for Crohn’s disease may accompany recurrence of this ble to hypothesize the presence of an endothelium- disease (Angerson et al., 1993). Our group has already bound form with a specific fluorescence spectrum. The proposed a fluorescence endoscopic imaging technique using fluorescein sodium to study the anastomotic re- 1 To whom correspondence should be addressed at INSERM currence of Crohn’s disease (Maunoury et al., 1996). In (French National Institute of Health and Medical Research), JE2084 that study, we showed that blood flow was increased Pavillon Vancostenobel, Lille University Hospital, 59037 Lille Cedex, France. Fax: /33 (0) 320 446 708. E-mail: mordon@lille.inserm.fr. in early-stage disease and reduced in late-stage disease 0026-2862/98 $25.00 Copyright  1998 by Academic Press All rights of reproduction in any form reserved. 146