Serum Keratan Sulfate Levels in Marathon Runners M. B. E. Sweet1, I. Jakim1 , A. Coelho1 , P. J. Becker2, E. J.-M A. Thonar3 Bone and Joint Research Unit, University of the Witwatersrand, Johannesburg, South Africa institute for Biostatistics, South African Medical Research Council 3Departments of Biochemistry and Medicine, Rush Medical College, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois, U. S. A.
M. B. E. Sweet, I. Jakim, A. Coelho, P. J. Becker and E. J.-M. A. Thonar, Serum Keratan Sulfate Levels in Marathon Runners. Tnt J Sports Med, Vol 13, No 4,pp348—3SO, 1992.
Accepted after revision: January 6, 1992
The effect of strenuous joint loading on the metabolism of articular cartilage in man is not known. The development of a non-invasive immunoassay for the assessment of the catabolism of cartilage aggrecan has enabled us to quantify keratan sulfate (KS), a component of aggrecan, in the serum of fifteen male marathon runners. Serum KS was measured by an ELISA before and immediately after a marathon (42 km), as well as 48 hours after the completion of the race. The mean level at rest was similar to those previ-
ously reported for another population of age-matched males. There was no statistically significant difference in
the serum level of KS at the three different readings. Further, there was no correlation between age, height, weight and performance time, and the serum level of KS at any of the three different times. We conclude that marathon running by carefully trained runners causes neither a transient nor a sustained increase in proteoglycan catabolism in articular cartilage.
bilization cause a marked suppession of both the anabolic and catabolic phases of the metabolism of this proteoglycan.
In contrast, the effects of increased joint loading on cartilage have received limited attention: running has been shown to cause a decrease in the proteoglycan content of articular cartilage in some experimental animals (14). In other studies, this appeared to cause no change (15) or an increase in proteoglycan content (4, 7, 8, 10). These conflicting results are probably due to the type of animal used, possible pre-existing joint anomalies, the age and weight, and most importantly, the experimental model studied. Keratan sulfate is a major component of aggrecan, the major type of proteoglycan in cartilage. These highly anionic aggrecan macromolecules are entrapped at high con-
centrations within the collagen framework, and are responsible for the ability of cartilage to undergo reversible deformation. KS is present in serum on aggrecan fragments and can be measured by a very sensitive ELISA. Numerous studies have provided support for the contention (11) that the level of antigenic KS in serum reflects the rate at which aggrecan is turned over in cartilage; these were reviewed in a recent manuscript (13). The rationale for this contention is based in part on the fact that most of the KS in the body is present in car-
tilages (hyaline, fibrous and elastic); although KS has now been detected in some other tissues such as tendon and cornea,
and body fluids, it is found in these at much lower concentrations (13). In normal adults, the level of serum KS is very
constant with time (13). It shows no diurnal variation and fluctuates little from day to day, strongly suggesting that the me-
Keratan sulfate, articular cartilage, exercise, cartilage catabolism
tabolism of KS is at a stable equilibrium. The non-invasive ELISA has proved useful to measure changes in the rate of catabolism of cartilage aggrecan following drug treatment or ex-
perimentally-induced depletion of aggrecan in a single joint Infroduction
Reduced loading, restricted movement and
Road running has become a popular recreational activity. It is important to find out if this has any influence on cartilage matrix integrity, structure, metabolism and biomechanical properties. In this report, we provide evidence that marathon running by carefully trained runners has no measurable effect on the catabolism of aggrecan in car-
immobilization, all leading to a reduction in cyclic compres-
sion forces, have been shown to be accompanied by diminished synthesis of aggrecan in articular cartilage (1, 3, 5, 16). This leads to moderate to severe depletion of aggrecan, the cartilage-specific proteoglycan which gives this tissue many of its functional properties. Prolonged inactivity due to bed rest
leads to a fall in the serum level of keratan sulfate (KS), a marker of the rate of catabolism of cartilage aggrecan in man (9). These findings strongly suggest that inactivity and immomt. J. Sports Med. 13(1992)348—350 Georg Thieme Verlag StuttgartNew York
Materials and Methods
Subjects Fifteen male marathon runners, aged 24 to 44
years (mean standard deviation (SD) = 31.8 57 years)
Downloaded by: National University of Singapore. Copyrighted material.
mt. J. Sports Med. 13(1992) 349
Serum Keratan Sulfate Levels in Marathon Runners
volunteered to participate in the study. The mean height SD
was 171.4± 5.8 cm (range 165 to 182 cm) and the mean weight±SD was 63.1±6.0 kg (range 62 to 85 kg). All had
the subjects had used any steroids or non-steroidal anti-inflammatory agents for at least six months prior to the event.
350 300 250
All 15 subjects participated in a marathon race
of 42 km. The mean performance time was 2:52 21 mm (range 2:22 to 3:30). Ten ml of venous blood was taken 30 minutes before the race (Time I). Subsequent blood samples were taken within 15 to 30 minutes of the completion of the
50 1 T1
race (Time II), and 48 hours later (Time III). Serum was sepa-
ratedwithinl hourandstoredat— 70 °C.
Enzyme-linked Immunosorbent Assay (ELISA)for the quantification of KS The ELISA method, using the monoclonal antibody ET-4-A-4 which recognizes a highly sulfated epitope found specifically on KS, has been described previously (11, 13). The concentration of KS was determined using a standard curve drawn from the identical analysis of bovine articular cartilage monomeric aggrecan. The concentration of KS in this aggrecan preparation was calculated using an international standard of KS purified from human costal cartilage (a gift from Drs. M. B. Mathews and A. L. Horwitz, The University of Chicago, Chicago, U. S. A).
Statistical Analysis Possible relationships between the different serum KS values and the other variables were investigated by correlation analysis. In addition, serum KS values at Times I, II and III were compared by analysis of variance for repeated measurements.
Mean serum KS SD prior to the race was 224.3 69.3 ng/ml. Immediately after the race the mean was
223.3 ng/ml SD 62.7; 48 hours later the mean was ng/ml. The difference between these values did 221.5 not reach statistical significance.
There was no correlation between resting
Fig. 1 Serum levels of keratan sulfate (KS) before and after running a marathon. Levels of the fifteen runners are given as ng KS/mI at rest before the race (Ti), immediately after the marathon (T2), and 48 hours later (T3).
ment in the biochemical and biomechanical properties of cartilage. This is particularly so where training has been gradually
increased (8, 10). The structure of proteoglycan alters: the ratio of KS to chondroitin sulfate rises and the extractability of
proteoglycan diminishes, features compatible with maturation of cartilage (8, 10). However, long periods of high intensity running have been reported to cause cartilage fibrillation in canine cartilage (14); this degenerative state is associated with the production of smaller aggrecan monomers and a reduced ability of the latter to form aggregates with hyaluronate (6, 14).
Little or no work has been done on the effect of joint loading on the rate of catabolism of proteoglycans in articular cartilage. The level of aggrecan fragments in two synovial fluid samples taken from the same knee joint before and 30 —60 mm after a soccer game or running for 1 h were very sim-
ilar, suggesting that these activities do not cause a transient rise
in the rate of catabolism of aggrecan in articular cartilage within that joint (2). The results presented in this paper suggest that running a marathon race following a prolonged period of careful and regular training causes neither a transient nor a sustained increase in the serum level of KS, and by implication causes no increase in the rate of degradation of proteoglycans in articular cartilage. Recent studies have demonstrated that fragments produced by the injection of a small amount of chy-
mopapain in a rabbit knee joint can be detected in blood
Jogging and long-distance running have be-
within 30 mm: the level of serum KS reaches a peak between 24 h and 48 h, decreasing progressively thereafter (13, 17). The movement of the fragments from cartilage to blood is thus relatively slow; in contrast, once they arrive in the blood, the fragments are eliminated relatively rapidly (half-life < 60 mm) (13). The absence of any change in the serum level of KS 48 h after the marathon thus suggests that no significant increase in the rate of catabolism of aggrecan occurred as a consequence of the intense loading which the articular surfaces sustained during the run.
come popular recreational activities. The long term effects of running on articular cartilage in man are not known. Moderate levels of physical training are known to lead to an improve-
Interestingly, the mean serum level of KS in this group of experienced marathon runners, prior to the run,
serum KS levels (Time I) and age (p = 0.53), height (p = 0.55)
or weight (p 0.62). In addition, no correlation was observed between resting serum KS and the distance run during weekly training (p = 0.87). There was no correlation between performance time and serum KS levels immediately after the race (p = 0.23) or 48 hours after the race (p = 0.22). Discussion
Downloaded by: National University of Singapore. Copyrighted material.
participated in regular distance running for many years, taking part in an average of 5 marathons a year. They trained between 3 and 4 times a week, over a mean distance of 88.6 15.8 km (range 55 to 102 km). All subjects were in good general health; in particular none had any joint disease or anomaly. None of
M. B. E. Sweet, I. Jakim, A. Coelho, P. J. Becker, E. J.-M. A. Thonar
was very similar to the mean levels of age-matched groups of
normal volunteers [251 ng/mlj (12) or male hospitalized
patients [234 ng/ml] (11). This strongly suggests that
marathon running does not over the long term cause a significant increase in the rate of catabolism of cartilage proteogly-
cans. A marathon race could reasonably be described as a strenuous activity. Where the borderline with exaggerated
Pachman L. M., Glickman P., Katz R., Huff J., Kuettner K. E.: Quantification of keratan sulfate in blood as a marker of cartilage
vigorous activity lies, has not yet been established. Acknowledgements This work was supported by the South African Medical Research Council and by grants 1-P50-AR39239 and AG-04736 from the National Institutes of Health.
Caterson B., Lowther D. A.: Change in the metabolism of the proteoglycans from sheep articular cartilage in response to mechanical stress. Biochim BiophysActa 540:412—422, 1978. Dahlberg L., Roos H., Ekblom B., Celsing F., Lohmander L. S.: Proteoglycan epitope in knee joint fluid after exercise (abstract). Ort/iop Res Soc Trans 16: 334, 1991.
Eronen I., Videman T., Friman C., Michaelson J.-E.: Glycosaminoglycan metabolism in experimental osteoarthritis
of keratan sulfate in blood as a marker of cartilage catabolism. J RheumatolSuppl 14: 23—24, 1987. Thonar E. J.-M. A., Williams J. M., Maldonado B. A., Lenz M. E., Schnitzer T. J., Campion G. V., Kuettner K. E., Sweet M. B. E.: Serum keratan sulfate concentration as a measure of the catabolism of cartilage proteoglycans. In: Monoclonal Antibodies, Cytokines, and Arthritis. Mediators of Inflammation and Therapy. KressinaT. F. (ed). Marcel Dekker, NewYork, pp 373—398. Vason N.: Effects of physical stress on the synthesis and degradation of cartilage matrix. Connect TissueRes 12:49—48, 1983. Videman T., Eronen I., Candolin T.: Effects of motion load
Environ Health (Suppl 3)5:56—67, 1979. Williams J., Brandt K. D.: Immobilization ameliorates chemically-induced articular cartilage damage. Arthritis Rheum 27: 208— 216, 1984. Williams J. M., Downey C., Thonar E. J.-M. A.: Increase in levels
and thickness of articular cartilage in the knee joint of young
of serum keratan sulfate following cartilage proteoglycan de-
beagle dogs.J OrthopRes 6: 188—195, 1988.
gradation in the rabbit knee joint. Arthritis Rheum 31: 557—560, 1988.
Olah E. H., Kostenszky K. S.: Effect of loading and prednisolone treatment on the glycosaminoglycan content of articular cartilage in dogs. ScandJRheumatol5: 49—2, 1976. Palmoski M. J., Brandt K. D.: Running inhibits the reversal of atrophic changes in canine knee cartilage after removal of cast. ArthritisRheum 24: 1329—1337, 1981.
Saamanen A.-M., Tammi M,, Kiviranta I., Jurvelin J., Helminen
H. J.: Moderate running increased but strenuous running prevented elevation of proteoglycan content in canine articular car8
catabolism. Arthritis Rheum 28: 1367—1376, 1985. Thonar F. J.-M. A., Schnitzer T. J., Kuettner K. E.: Quantification
changes on tendon tissues and articular cartilage: a biochemical and scanning electron microscopic study in rabbits. ScandJ Work
caused by immobilization: Acta Orthop Scand 49: 329— 334, 1978.
Kiviranta 1., Tammi M., Jurvelin J., Saamanen A.-M., Helminen H. J.: Moderate running exercise augments glycosaminoglycans
Sweet M. B. E., Jakim I., Coelho A., Becker P. J., Thonar E. J.-M. A.: Serum keratan sulphate levels during prolonged rest. SAfrMed J, in press. Tammi M., Saamanen A.-M., Jauhiainen A., Malminen 0., Kiviranta I., Helminen H. J.: Proteoglycan alterations in rabbit knee articular cartilage following physical exercise and immobilization. Connect Tissue Res 11:45—55, 1983. Thonar E. J.-M. A., Lenz, M. E., Klinworth G. K., Caterson B.,
tilage (abstract). ScandJRheumatol(Suppl) 50:45, 1986. Saamanen A.-M., Tammi M., Kiviranta I., Helminen H. J.: Running exercise as a modulator ofproteoglycan matrix in the articular cartilage of young rabbits. IntfSports Med 9: 127—133, 1988.
ProfessorM B. E. Sweet Department of Orthopaedic Surgery Medical School 7 York Road Parktown 2193 South Africa
Downloaded by: National University of Singapore. Copyrighted material.
350 mt. J. Sports Med. 13(1992)