[Labeling products of photochemical degradation of insulin with technetium (99mTc)]

Irradiation with UV light at a wavelength of 250 nm allows to convert disulphidic groups in the structure of insulin to free SH groups with high affinity to direct labelling with 99mTc. The amount of terminal SH groups depends on irradiation time. HPLC analysis revealed that while 34% of the original amount of insulin was present after 15 minutes of irradiation (approx. intensity of 500 microW.cm2), the amounts were 25%, 10%, and 2% after 30; 60, and 120 minutes, respectively. These results correlate with the amount of SH groups released by photoactivation measured using Ellman's reagent. The product of the degraded porcine insulin was labelled with 99mTc using the redox polymer RP G25 IDA under the following conditions: pH 6.8-7.9, labelling time 15 minutes, room temperature. Radiochemical purify of the labelled product was higher than 96%. Insulin and products of its degradation were evaluated by means of size exclusion chromatography (SEC). The biodistribution 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 induced diabetes.