Labelling of high molecular weight hyaluronan with125I-tyrosine: studiesin vitro andin 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 study¹²⁵I-tyrosine (T)-labelled hyaluronan was produced after CNBr-activation of the polysaccharide. A specific activity of approximately 0.1 MBq µg^–1 was achieved using 100 µg of 0.5×10⁶ Da hyaluronan labelled for 2 h with 18 MBq¹²⁵I. The¹²⁵I-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. The¹²⁵I-labelled polysaccharide is also taken up by liver endothelial cells bothin vivo andin 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 of¹²⁵I-T-hyaluronan showed rapid uptake in the liver and a redistribution of radioactivity from liver to urine with time. Our results indicate that the¹²⁵I-T-hyaluronan is suitable for studies of hyaluronan-metabolism in a number of ways. The gamma emitters¹²⁵I and¹³¹I are easy to monitor and can be used also forin vivo 3D-imaging using single photon emission computer tomography.Abbreviations CNBr cyanogen bromide - T-HA tyrosine-labelled hyaluronan