Binding Properties of Indocyanine Green in Human Blood

Purpose: Binding properties of indocyanine green (ICG) to human plasma proteins were identified using electrophoresis and a fundus video system.

Methods: Blood samples were obtained from three healthy volunteers after intravenous administration of ICG. The resulting plasma samples were fractionated by agarose gel immunoelectrophoresis and polyacrylamide gel DISC electrophoresis. In the former, antisera, anti-apolipoprotein (Apo)-A, and anti-Apo-B antibodies were used to identify all classes of plasma proteins, high-density lipoprotein (HDL), and low-density lipoprotein (LDL), respectively. In the latter method, plasma samples could be separated into chylomicron, very low-density lipoprotein, LDL, and HDL. The electrophoretic pattern obtained by each method was observed with an ICG fundus video system. Furthermore, we studied the affinity of ICG for lipids that were common molecular components of HDL and LDL. Four kinds of ICG solutions mixed with phospholipid, free cholesterol, esterified cholesterol, and triacylglycerol were observed with the ICG fundus video system.

Results: Both electrophoretic studies showed that ICG bound intensely to HDL and moderately to LDL, and only the solution with phospholipid fluoresced brightly when observed with the ICG fundus video system.

Conclusions: These findings indicated low vascular or tissue permeability of ICG, which is caused by the larger molecular size of HDL and LDL. Also noted was that the ICG fluorescence observed in the angiogram may be equivalent to the hemodynamics of HDL alone or in combination with LDL in the bloodstream. This biochemical consideration may be a basis for the further understanding of ICG angiography.