The excretion and degradation of chondroitin 4-sulphate administered to guinea pigs as free chondroitin sulphate and as proteoglycan

Abstract

The excretion and degradation was studied of 35S-labelled 4-chondroitin sulphate injected into guinea pigs in the form of proteoglycan isolated from cartilage and in the form of free chondroitin 4-sulphate prepared from the same proteoglycan by proteolysis. When the proteoglycan was injected there was a delay of about 15–20min before significant amounts or radioactivity were excreted, whereas after injection of chondroitin 4-sulphate a considerable amount of radioactivity was excreted within 10min and a much higher proportion of the radioactive dose was excreted in 1h or 24h compared with the proteoglycan. In both cases, however, a major part of the radioactivity was not excreted even in 24h. Sterile conditions were used to collect the radioactive material directly from the bladder. When chondroitin 4-sulphate was injected, the molecular sizes of injected and excreted materials were similar, as assessed by gel chromatography on Sephadex G-200, whereas when proteoglycan was injected the molecular size of the excreted labelled material was similar to that of the chondroitin 4-sulphate chains in the original proteoglycan. In neither case did the size of the excreted labelled material change with time over 1h, and low-molecular-weight labelled material was virtually absent. In contrast, when urine was collected for 24h without preservative the labelled material in it was extensively degraded after either the proteoglycan or chondroitin 4-sulphate had been given. Chondroitin 4-sulphate became similarly degraded when incubated with non-sterile urine, but not when the urine was passed through a bacterial filter, suggesting that degradation was caused by contaminating micro-organisms in the experiments in which urine was collected for 24 h. It is concluded that chondroitin 4-sulphate chains of about 18000 molecular weight can be excreted readily as such, whereas intact proteoglycans must be degraded to free glycosaminoglycans first, although both are taken up by the tissues more rapidly than they are excreted.