Urinary excretion of glycosaminoglycans in horses: Changes with age, training, and osteoarthritis

The aim of the current study was to investigate if the urinary glycosaminoglycans reflect the changes that occur in cartilages with age, training, and osteoarthritis in horses. The glycosaminoglycans were extracted by ion exchange chromatography from urine samples of 90 sedentary and athletic horses of different ages and genders, with or without osteoarthritis. The main urinary glycosaminoglycans in horses are chondroitin sulfate, dermatan sulfate, and heparan sulfate. A marked decrease occurred with age. Trace amounts of keratan sulfate were detected by immunochemical methods, and its concentration increased linearly with age. Athletes excreted fewer glycosaminoglycans in the urine than age-matched sedentary horses (including keratan sulfate), and sedentary horses with osteoarthritis excreted fewer total glycosaminoglycans, but more keratan sulfate, than their healthy counterparts. The chondroitin sulfate excreted in the urine by foals contained a low 6-sulfated disaccharide/4-sulfated disaccharide (Di6S/Di4S) ratio, as compared with adults and aged horses. Low Di6S/Di4S ratios were also found in the chondroitin sulfate excreted by healthy racehorses and by horses with osteoarthritis. Our data show clear correlations between urinary glycosaminoglycans in horses and age, physical exercise, and osteoarthritis. The combination of qualitative, quantitative, and structural analyses of these compounds may be useful for the diagnosis and follow-up of osteoarthritis in horses.