Detection of keratan sulfate by immunological methods in commercial chondroitin sulfate preparations

Chondroitin sulfate (CS), a well known nutraceutical, and keratan sulfate (KS) are glycosaminoglycans involved in the structure of cartilage proteoglycan, aggrecan. Since CS is extracted from cartilage, there may be a possibility that purified CS is contaminated with small amount of KS. A total of 15 samples, including four samples of CS as laboratory reagents, one sample of CS as a food additive and ten samples of dietary supplements containing CS were examined to detect KS in these samples by using immunodiffusion and enzyme-linked immunosorbent assay (ELISA) with anti-KS monoclonal antibody (IgM). With the exception of three samples of CS as laboratory reagents, all samples were found to contain varying amounts of KS. It was concluded that both the immunodiffusion, a quick one-step method, and ELISA for quantification, are reliable methods to detect KS contamination in CS products.