99m Tc-Labelled Product of Photochemical Degradation of Insulin

Overview

Irradiation with UV light at a wavelength of 250 nm allows to convert disulphidic groups in thestructure of insulin to free SH groups with high affinity to direct labelling with 99m Tc. The amountof terminal SH groups depends on irradiation time. HPLC analysis revealed that while 34% of theoriginal amount of insulin was present after 15 minutes of irradiation (approx. intensity of500 mW.cm 2 ), the amounts were 25%, 10%, and 2% after 30; 60, and 120 minutes, respectively. Theseresults correlate with the amount of SH groups released by photoactivation measured using Ellman’sreagent. The product of the degraded porcine insulin was labelled with 99m Tc using the redox polymerRP G25 IDA under the following conditions: pH 6.8–7.9, labelling time 15 minutes, room tempera-ture. Radiochemical purify of the labelled product was higher than 96 %. Insulin and products ofits degradation were evaluated by means of size exclusion chromatography (SEC). The biodistribu-tion of the labelled substances in laboratory animals showed activity mostly in the kidneys and liver.No specific biodistribution of the labelled products was observed in rats with experimentally induceddiabetes.

Key words:
insulin – redox polymer – technetium(99mTc) – radioassay – biodistribution