Accumulation of radiolabelled low molecular peptides and proteins in experimental inflammation

This study focuses on evaluating accumulation of the low molecular peptides and proteins labelled with 99mTc in rat inflammatory/infection foci. Peptides (human leukocyte dialysate, HLD; thymosin fraction 5, TF5; aprotinin, APT), and proteins (human IgG, HIG) were labelled with 99mTc using redox polymer. The labelling efficiency was evaluated using paper, TLC and/or column chromatography. Biodistribution of labelled substances was evaluated in rats with Staphylococcus aureus infection or with sterile kaolin suspension inflammation 24 h after abscess induction. Accumulation of 99mTc activity was determinated both by external gamma camera imaging and by counting dissected tissues 4 h after administration. The evaluated peptides and proteins show high labelling efficiency (99mTc-HLD > 98%, 99mTc-TF5 > 95%, 99mTc-APT > 98%, 99mTc-HIG > 95%). Usage of redox polymer for labelling increases the stability of 99mTc-labelled substances. The labelling efficiency stays nearly the same (95-98%) after 8 h at least. In experimentally induced inflammation the amount of 99mTc-peptides and 99mTc-HIG activity accumulated is 2.5-6.5 and 5.3-10.6 times higher than in a control tissue. When comparing two types of model inflammations (kaolin- and Staphylococcus-induced ones), the values measured with 99mTc-peptides are more than double than those of kaolin suspension inflammation. The studied low molecular peptides labelled with 99mTc allow rapid localisation of infection foci. 99mTc labelled HIG proved useful for detection of infections and inflammatory lesions.