LABELING OF HIGH-MOLECULAR-WEIGHT HYALURONAN WITH I-125 TYROSINE - STUDIES IN-VITRO AND IN-VIVO IN THE RAT

Studies on the metabolism of the polysaccharide hyaluronan has previously been hampered by the lack of radioactive hyaluronan of high molecular weight (MW) and high specific activity. In the present study I-125-tyrosine (T)-labelled hyaluronan was produced after CNBr-activation of the polysaccharide. A specific activity of approximately 0.1 MBq mu g(-1) was achieved using 100 mu g of 0.5 x 10(6) Da hyaluronan labelled for 2 h with 18 MBq I-125. The I-125-T-hyaluronan kept a high MW-profile upon gel filtration chromatography and was found to be cleared from the circulation with the kinetics and organ distribution reported for biosynthetically labelled hyaluronan of high MW. The I-125-labelled polysaccharide is also taken up by liver endothelial cells both in vivo and in vitro, indicating that the labelling does not interfere with the binding to specific cell-surface receptors found on these cells. The intracellular degradation is slower than that earlier reported for biosynthetically labelled hyaluronan and seems to be halted at the level of low MW oligo- or mono-saccharides that eventually leave the organism via the urine. Scintigraphic images of rats after intravenous injection of I-125-T-hyaluronan showed rapid uptake in the liver and a redistribution of radioactivity from liver to urine with time. Our results indicate that the I-125-T-hyaluronan is suitable for studies of hyaluronan-metabolism in a number of ways. The gamma emitters I-125 and I-131 are easy to monitor and can be used also for in vivo 3D-imaging using single photon emission computer tomography.