99mTc-insulin: labeling, biodistribution and scintiimaging in animals

Porcine insulin was labeled with 99mTc by direct tin reduction. More than 95% labeling efficiency was obtained on paper chromatography in saline and methyl ethyl ketone. The stability of the labeled compound was confirmed by paper chromatography at 3 h post-labeling and by human serum albumin (HSA) challenge. PAGE pattern indicated no change in the electrophoretic behavior and the molecular size of insulin after the labeling procedure. Biodistribution in rats shows that kidney took up the maximum amount of 99mTc-insulin; maxima being maintained throughout 24 h post-injection. Liver and intestine were the other organs with significant uptake; the rest localizing little or negligible radioactivity. Most of the radioactivity was excreted via the renal pathway into urine. Scintiimages conformed to the biodistribution data. The results of this study present the potential of 99mTc-labeling of insulin by a simple method.