Proteoglycan extraction of sized cartilage particles

The relationship between cartilage thickness and proteoglycan extractability was examined. Bovine nasal cartilage slices (20, 100, and 500 micron thicknesses) were extracted with low-ionic-strength buffer and 4 M guanidine hydrochloride. The extractability of proteoglycans with both solutions depended on slice thickness. Thinner slices yielded greater amounts of proteoglycans. Sixty-three percent of the total cartilage uronic acid was extracted from 20-micron cartilage slices with low-ionic-strength buffer while only 7% was extracted for 500-micron slices. Each fivefold increase in cartilage surface area led to a threefold increase in uronic acid extraction with low-ionic-strength buffer. Extraction of proteoglycan aggregates was directly proportional to the cartilage surface area whereas extraction of non-aggregated proteoglycans, per surface area, increased with increasing cartilage thickness. These data are consistent with the hypothesis that proteoglycan aggregates are extracted mainly from the cartilage surface while non-aggregated proteoglycans diffuse from deep within the cartilage. Extraction with low-ionic-strength buffer occurred in two phases. There was an initial rapid loss of proteoglycans in which 1/3 to 1/2 of all proteoglycans eluting over 6 days were extracted during the first 30 min. Subsequent extraction was much slower with decreasing amounts extracted on each consecutive day. The initial rapid loss of proteoglycans was probably due to the steep osmotic-pressure gradient existing when the cartilage was placed in the low-ionic-strength buffer.