Polyionic fluorescent bioconjugates as tracer agents for continuous monitoring of renal function

Fluorescein dye covalently attached to anionic and cationic carriers of molecular weight 0.5 to 30 kDa were prepared and evaluated as potential fluorescent tracer agents for monitoring real-time dynamic renal function. These fluorescein bioconjugates were generally prepared by the reaction of fluorescein isothiocyanate with the desired polypeptides. The mode of clearance from the blood, and the clearance rate, is substantially altered in these conjugated compounds with respect to the dye alone. For example, the blood clearance of fluorescein is known to be through both the hepatic and renal systems, while several of the newly synthesized anionic fluorescein bioconjugates exhibit renal clearance only. Increasing the number of anionic residues in such compounds yields an increase in the renal clearance rate until a lower limit (saturation value) is reached. Thus, an optimum fluorescent renal tracer agent with respect to clearance rate and chain length can be identified. More lipophilic anionic conjugates clear at slower rates, and are not exclusively renal. In contrast, fluorescein bioconjugates composed of cationic carriers do not clear from the blood within the time frame of measurement.