British Journal of Rheumatology 1992;31:583-591
CARTILAGE OLIGOMERIC MATRIX PROTEIN: A NOVEL MARKER OF CARTILAGE TURNOVER DETECTABLE IN SYNOVIAL FLUID AND BLOOD BY T. SAXNE* AND D. HEINEGARDt * Department of Rheumatology, Lund University Hospital and t Department of Physiological Chemistry, Lund University, Lund, Sweden
KEY WORDS:
Cartilage matrix, Noncollagenous protein. Rheumatoid arthritis, Proteoglycans.
in synovial fluid and serum. The protein fragments released into these fluids have also been characterized by sodium dodecylsulphate-polyacrylamide gel electrophoresis, transfer blot, and immunostaining. We also report the release from cartilage of the protein in inflammatory and degenerative joint diseases.
SEVERAL non-collagenous proteins have over recent years been identified in the extracellular matrix of cartilage (for review see [1]). These proteins show different distributions among cartilages. The 148 kDa protein (cartilage matrix protein) for instance, is abundant in tracheal cartilage, but is not found in mature articular cartilage [2]. This and other proteins are only found in cartilage, e.g. the C-terminal propeptide of type II collagen, chondrocalcin. Others have a wider tissue distribution and are present in many connective tissues, e.g. fibromodulin and decorin [1]. Little is known of the functions of most of these proteins. However, it has recently been shown that fibromodulin and decorin both bind to type I and type II collagen in vitro and inhibit collagen fibrillogenesis [3]. The two proteins appear to bind to different sites along the collagen molecule [3]. The cartilage oligomeric matrix protein (COMP) is a protein recently isolated from cartilage [4]. It resembles a protein described by Fife and Brandt [5,6]. The protein could be identiifed in cartilage from several species, but not in non-cartilaginous tissue using immunoassay [4]. The highest amounts, 1% of the wet weight, are found in articular cartilage [4,7]. It consists of five subunits with an apparent /vf of around 100 kDa each [4]. The protein contains small amounts of chondrotin sulphate and thus appears to represent a proteoglycan [4]. The function of this protein is unknown. In this report we describe an enzyme-linked immunosorbent assay (ELIS A) for the quantification of COMP
MATERIALS AND METHODS Preparation of antigen The protein was purified from bovine articular cartilage as described [4]. Briefly, powderized articular cartilage was extracted with 4 M guanidine-HCl, 0.05 M sodium acetate, pH 5.8, also containing a mixture of protease inhibitors and /V-ethylmaleimide. Proteins were separated from proteoglycans by CsCl density gradient centrifugation and the top fraction was used for subsequent purification. The first step was chromatography on Sephadex G-200 eluted with 4 M guanidine-HCl. The material recovered from the void volume peak contained the protein and was chromatographed on a DEAE-cellulose column eluted with a sodium chloride gradient in 7 M urea. A major fraction which eluted at high ionic strength was shown to contain COMP. The protein was further purified by affinity chromatography on heparin-Sepharose to remove traces of fibronectin. An identical approach was used to isolate and partially purify the protein from human femoral head cartilage. Preparation of antibody Antibodies against the purified bovine protein were raised in a rabbit as described [4]. The antibodies were purified by passage through an affinity column containing insolubilized bovine plasma fibronectin
Submitted 6 September; revised version accepted 24 November 1991. Correspondence to T. Saxne, Department of Rheumatology, Lund University Hospital, S-221 85 Lund, Sweden.
© 1992 British Society for Rheumatology
0263-7103/92/090583 + 09 $08.00/0 583
Downloaded from http://rheumatology.oxfordjournals.org/ by guest on January 26, 2015
SUMMARY Cartilage oligomeric matrix protein (COMP) is a tissue specific non-collagenous matrix protein. We have developed an enzyme-linked immunosorbent assay for the detection of this protein in synovial fluid and serum. The protein has been quantified in these fluids in patients with rheumatoid arthritis (RA), reactive arthritis, juvenile chronic arthritis, osteoarthritis and in sera of control subjects. The protein was detectable in all fluids and the synovial fluid levels were always higher than in serum in paired samples. The highest knee joint synovial fluid levels were found in reactive arthritis patients and the lowest in RA patients with advanced destruction of the knee joint. However, the relative synovial fluid content of COMP was higher in these RA patients than in patients with advanced osteoarthritis. In patients with longstanding reactive synovitis the concentrations decreased. This decrease, however, was less marked than for proteoglycan concentrations. The serum concentrations were low in patients with juvenile chronic arthritis and in patients with RA with advanced cartilage destruction of the studied knee joint. In the other groups serum levels did not differ between groups or from controls.
BRITISH JOURNAL OF RHEUMATOLOGY VOL. XXXI NO. 9
584
(Extraco AB, Klippan, Sweden) to remove traces of antibodies reacting with fibronectin. The specificity of the antiserum was checked by Western blotting of a bovine articular cartilage extract.
ELISA for proteoglycans The core protein of the large, aggregating proteoglycan or fragments thereof was measured by a previously described ELISA [9,10]. The polyclonal antibodies
1.0
1.0
0.5
0.5
in !
->-//
i
0 " 0.158
0.312
0.625
1.2S
2.5
(Cone of COMP r«f•rsnea, pg/m0 1/8OO 1/4O0 1/2OO 1/10O (Muttons of synovial fluid sample*)
1/50
'0.312 0.625 1.25 (Cone of COMP ref*r«nc«, |tg/mO 1/100 1/50 1/25 (Muttons of ssnrni samptes)
2.5 1/10
FIG. 1.—Inhibition curves produced by dilutions of synovial fluids (left) and serum (right) from three patients with rheumatoid arthritis (O) and dilutions of a standard ( • ) of partially purified human cartilage oligomeric matrix protein (COMP).
Downloaded from http://rheumatology.oxfordjournals.org/ by guest on January 26, 2015
ELISA for human COMP The assay was developed according to the basic principles of immunoassay [8,9]. Human COMP was coated to gamma irradiated polystyrene microtitre plates (Nunc immunoplate I, Nunc, Roskilde, Denmark) at 0.1 ug/ml in 4 M guanidinium hydrochloride, 0.05 M sodium carbonate, pH 10.0, for 24 h at room temperature. After rinsing with 0.15 M sodium chloride, 0.05% (w/v) Tween 20 the plates were aftercoated with 2 mg/ml bovine serum albumin (Serva, Fine Biochemicals, Heidelberg, Germany) in phosphate buffered saline, pH 7.4, for 1 h to minimize nonspecific binding. Samples of synovial fluid/serum or standards were dissolved in 0.8% (w/v) SDS, 0.1 M sodium chloride, 0.05 M sodium phosphate, pH 7.4, and added to an appropriate dilution of an equal volume of antiserum in 4% Triton X-100, 0.01 M sodium phosphate, pH 7.4. The analysis was performed with the protein solubilized as a sodium dodecylsulphate (SDS) complex, necessary to solubilize the protein and to dissociate the protein from any interaction with
other proteins in the fluid analysed. After preincubation for 24 h at room temperature this mixture was added to the coated wells of the microtitre plate. After incubation for 1 h the plate was rinsed. A dilution of swine anti-rabbit IgG conjugated with alkaline phosphatase (Orion Diagnostica, Helsinki, Finland) in 0.1 M sodium chloride, 0.05 M sodium phosphate and bovine serum albumin 2 mg/ml, pH 7.4, was added to detect bound antibodies. After incubation for 1 h at room temperature the plate was rinsed. Enzyme substrate, 1 mg/ml para-nitrophenyl phosphate in 1 M diethanolamine, pH 9.8, containing 0.5 HIM MgCl2, was added and the absorbance at 405 nm was read immediately and after 1 h in a Multiscan filter photometer (Labsystem, Stockholm, Sweden). The increase in absorbance was used for calculations. A standard curve using different concentrations (0.156-2.5 ug/ml) of human COMP was included in each microtitre plate. All samples were analysed in triplicate, and the mean value was used for calculations.
SAXNE AND HEINEGARD: CARTILAGE OLIGOMERIC MATRIX PROTEIN
585
SDS-polyacrylamide gel electrophoresis, electrophoretic transfer and immunostaining Cell free synovial fluid (200 ul) was chromatographed through a 500 ul column of Blue Sepharose CL-6B (Pharmacia Fine Chemicals, Uppsala, Sweden) and then through a 250 ul column of Protein A Sepharose CL-4B (Pharmacia Fine Chemicals, Uppsala, Sweden) to remove excessive albumin and immunoglobulins, respectively. These synovial fluid samples were electrophoresed on 4-16% gradient polyacrylamide gels [11]. Proteins were passively transferred to nitrocellulose by diffusion [12]. The proteins reacting with antibodies to COMP were detected after transfer to the nitrocellulose by incubation first with antibody against COMP and subsequent demonstration of bound IgG with a swine anti-rabbit IgG peroxidase conjugate (Dakopatts, Copenhagen, Denmark).
400-
1
1 200-
BS
"5A"
FIG. 2.—Synovial fluid concentrations of cartilage oligomeric matrix protein (COMP) in patients with rheumatoid arthritis with well preserved knee joints (RA, Larsen grade 0-1, n=20) and rheumatoid arthritis with severe knee joint damage (RA, Larsen grade 4-5, n=23), reactive arthritis (ReA, n=20), juvenile chronic arthritis (JCA, n=21) and osteoarthritis (OA, n=20). Trie horizontal bars indicate the median of each group.
preferentially recognize epitopes in the chondroitin sulphate rich region (Heinegard, Saxne, unpublished).
TABLE I CHARACTERISTICS OF PATIENTS AND CONTROLS IN WHOM CONCENTRATIONS OF COMP WERE DETERMINED*
Diagnosis Rheumatoid arthritis (Larsen 0-1) (n=20) Rheumatoid arthritis (Larsen 4—5) ("=23) Osteoarthritis («=20) Reactive arthritis («=20) Juvenile chronic arthritis (n^23) Blood donors (II=20)
Healthy children (n=29)
Age (years)
Female/male
60 (34-71)
14/6
63 (35-79)
16/7
Disease duration (years)
Synovitis duration (months)
ESR(mm/h)
2
(0.5CM0)
0.75 (0.25-1)
(7-117)
11 (1-60)
3 (0.5-6)
(30-124)
—
44
6/14
6 (2-15) 0.08 (0.01-20) 4 (0.25-18) —
(20-65) 5 (1-20)
14/15
—
73
12/8
(62-88) 39 (23-55)
5/15
12
16/7
(5-20)
0.25 (0.03-1)
45
64
9 (5-24) 33 (6-75)
4
22
(0.25-12)
(2-75)
— —
—
'Except for number of females/number of males, values are medians (ranges). ESR, erythrocyte sedimentation rate (Westergren). The Larsen index grades radiographic joint damage on a 6-gTade scale, where 5 denotes the most severe lesions.
Downloaded from http://rheumatology.oxfordjournals.org/ by guest on January 26, 2015
RA
(laraa* grada 0-1)(Lar»an frada 4-s>
Collection of synovialfluidsand blood Paired samples of knee joint synovial fluid and blood from patients with RA, reactive arthritis, juvenile chronic arthritis (JCA) and osteoarthritis (OA) were analysed. The RA specimens were chosen from the banks of fluids collected during a 6-year period and were selected only by the degree of radiographic joint damage, to obtain one group of patients with well preserved joints (Larsen index 0-1) and one group with advanced changes (Larsen index 4-5) [13]. The samples from reactive arthritis patients were chosen at random from the bank offluids.Eight reactive arthritis patients with a duration of synovitis more than 2 months were selected from the bank of fluids and studied separately. The JCA patients were those described in a previous report [14], and these fluids were obtained at arthroscopy. Samples from patients with OA of the knee joint were obtained from the Department of Orthopaedic Surgery, Malmo General Hospital.
BRITISH JOURNAL OF RHEUMATOLOGY VOL. XXXI NO. 9
586
TABLE II SYNOVIAL FLUID AND SERUM CONCENTRATIONS OF COMP IN PATIENTS WITH JOINT DISEASES AND IN BLOOD DONORS
Rheumatoid arthritis (Larsen 0-1) Rheumatoid arthritis (Larsen 4-5) Osteoarthritis Reactive arthritis Juvenile chronic arthritis Blood donors Healthy children
Synovial fluid (ug/ml)
Serum (ug/ml)
85(32-172)
11.5(6.8-19.3)
57(38-85)
7.6(4.9-10.7)
104(75-454) 172(82-376) 86(46-142) — —
10.6(4.3-18.0) 9.5(6.3-18.0) 7.3(4.5-10.8) 11.3(7.3-17.5) 10.3(5.2-13.4)
Values are medians (ranges).
Proteoglycans
COMP
Proteoglycan conc/COMP cone — p
CARTILAGE OLIGOMERIC MATRIX PROTEIN: A NOVEL MARKER OF CARTILAGE TURNOVER DETECTABLE IN SYNOVIAL FLUID AND BLOOD BY T. SAXNE* AND D. HEINEGARDt * Department of Rheumatology, Lund University Hospital and t Department of Physiological Chemistry, Lund University, Lund, Sweden
KEY WORDS:
Cartilage matrix, Noncollagenous protein. Rheumatoid arthritis, Proteoglycans.
in synovial fluid and serum. The protein fragments released into these fluids have also been characterized by sodium dodecylsulphate-polyacrylamide gel electrophoresis, transfer blot, and immunostaining. We also report the release from cartilage of the protein in inflammatory and degenerative joint diseases.
SEVERAL non-collagenous proteins have over recent years been identified in the extracellular matrix of cartilage (for review see [1]). These proteins show different distributions among cartilages. The 148 kDa protein (cartilage matrix protein) for instance, is abundant in tracheal cartilage, but is not found in mature articular cartilage [2]. This and other proteins are only found in cartilage, e.g. the C-terminal propeptide of type II collagen, chondrocalcin. Others have a wider tissue distribution and are present in many connective tissues, e.g. fibromodulin and decorin [1]. Little is known of the functions of most of these proteins. However, it has recently been shown that fibromodulin and decorin both bind to type I and type II collagen in vitro and inhibit collagen fibrillogenesis [3]. The two proteins appear to bind to different sites along the collagen molecule [3]. The cartilage oligomeric matrix protein (COMP) is a protein recently isolated from cartilage [4]. It resembles a protein described by Fife and Brandt [5,6]. The protein could be identiifed in cartilage from several species, but not in non-cartilaginous tissue using immunoassay [4]. The highest amounts, 1% of the wet weight, are found in articular cartilage [4,7]. It consists of five subunits with an apparent /vf of around 100 kDa each [4]. The protein contains small amounts of chondrotin sulphate and thus appears to represent a proteoglycan [4]. The function of this protein is unknown. In this report we describe an enzyme-linked immunosorbent assay (ELIS A) for the quantification of COMP
MATERIALS AND METHODS Preparation of antigen The protein was purified from bovine articular cartilage as described [4]. Briefly, powderized articular cartilage was extracted with 4 M guanidine-HCl, 0.05 M sodium acetate, pH 5.8, also containing a mixture of protease inhibitors and /V-ethylmaleimide. Proteins were separated from proteoglycans by CsCl density gradient centrifugation and the top fraction was used for subsequent purification. The first step was chromatography on Sephadex G-200 eluted with 4 M guanidine-HCl. The material recovered from the void volume peak contained the protein and was chromatographed on a DEAE-cellulose column eluted with a sodium chloride gradient in 7 M urea. A major fraction which eluted at high ionic strength was shown to contain COMP. The protein was further purified by affinity chromatography on heparin-Sepharose to remove traces of fibronectin. An identical approach was used to isolate and partially purify the protein from human femoral head cartilage. Preparation of antibody Antibodies against the purified bovine protein were raised in a rabbit as described [4]. The antibodies were purified by passage through an affinity column containing insolubilized bovine plasma fibronectin
Submitted 6 September; revised version accepted 24 November 1991. Correspondence to T. Saxne, Department of Rheumatology, Lund University Hospital, S-221 85 Lund, Sweden.
© 1992 British Society for Rheumatology
0263-7103/92/090583 + 09 $08.00/0 583
Downloaded from http://rheumatology.oxfordjournals.org/ by guest on January 26, 2015
SUMMARY Cartilage oligomeric matrix protein (COMP) is a tissue specific non-collagenous matrix protein. We have developed an enzyme-linked immunosorbent assay for the detection of this protein in synovial fluid and serum. The protein has been quantified in these fluids in patients with rheumatoid arthritis (RA), reactive arthritis, juvenile chronic arthritis, osteoarthritis and in sera of control subjects. The protein was detectable in all fluids and the synovial fluid levels were always higher than in serum in paired samples. The highest knee joint synovial fluid levels were found in reactive arthritis patients and the lowest in RA patients with advanced destruction of the knee joint. However, the relative synovial fluid content of COMP was higher in these RA patients than in patients with advanced osteoarthritis. In patients with longstanding reactive synovitis the concentrations decreased. This decrease, however, was less marked than for proteoglycan concentrations. The serum concentrations were low in patients with juvenile chronic arthritis and in patients with RA with advanced cartilage destruction of the studied knee joint. In the other groups serum levels did not differ between groups or from controls.
BRITISH JOURNAL OF RHEUMATOLOGY VOL. XXXI NO. 9
584
(Extraco AB, Klippan, Sweden) to remove traces of antibodies reacting with fibronectin. The specificity of the antiserum was checked by Western blotting of a bovine articular cartilage extract.
ELISA for proteoglycans The core protein of the large, aggregating proteoglycan or fragments thereof was measured by a previously described ELISA [9,10]. The polyclonal antibodies
1.0
1.0
0.5
0.5
in !
->-//
i
0 " 0.158
0.312
0.625
1.2S
2.5
(Cone of COMP r«f•rsnea, pg/m0 1/8OO 1/4O0 1/2OO 1/10O (Muttons of synovial fluid sample*)
1/50
'0.312 0.625 1.25 (Cone of COMP ref*r«nc«, |tg/mO 1/100 1/50 1/25 (Muttons of ssnrni samptes)
2.5 1/10
FIG. 1.—Inhibition curves produced by dilutions of synovial fluids (left) and serum (right) from three patients with rheumatoid arthritis (O) and dilutions of a standard ( • ) of partially purified human cartilage oligomeric matrix protein (COMP).
Downloaded from http://rheumatology.oxfordjournals.org/ by guest on January 26, 2015
ELISA for human COMP The assay was developed according to the basic principles of immunoassay [8,9]. Human COMP was coated to gamma irradiated polystyrene microtitre plates (Nunc immunoplate I, Nunc, Roskilde, Denmark) at 0.1 ug/ml in 4 M guanidinium hydrochloride, 0.05 M sodium carbonate, pH 10.0, for 24 h at room temperature. After rinsing with 0.15 M sodium chloride, 0.05% (w/v) Tween 20 the plates were aftercoated with 2 mg/ml bovine serum albumin (Serva, Fine Biochemicals, Heidelberg, Germany) in phosphate buffered saline, pH 7.4, for 1 h to minimize nonspecific binding. Samples of synovial fluid/serum or standards were dissolved in 0.8% (w/v) SDS, 0.1 M sodium chloride, 0.05 M sodium phosphate, pH 7.4, and added to an appropriate dilution of an equal volume of antiserum in 4% Triton X-100, 0.01 M sodium phosphate, pH 7.4. The analysis was performed with the protein solubilized as a sodium dodecylsulphate (SDS) complex, necessary to solubilize the protein and to dissociate the protein from any interaction with
other proteins in the fluid analysed. After preincubation for 24 h at room temperature this mixture was added to the coated wells of the microtitre plate. After incubation for 1 h the plate was rinsed. A dilution of swine anti-rabbit IgG conjugated with alkaline phosphatase (Orion Diagnostica, Helsinki, Finland) in 0.1 M sodium chloride, 0.05 M sodium phosphate and bovine serum albumin 2 mg/ml, pH 7.4, was added to detect bound antibodies. After incubation for 1 h at room temperature the plate was rinsed. Enzyme substrate, 1 mg/ml para-nitrophenyl phosphate in 1 M diethanolamine, pH 9.8, containing 0.5 HIM MgCl2, was added and the absorbance at 405 nm was read immediately and after 1 h in a Multiscan filter photometer (Labsystem, Stockholm, Sweden). The increase in absorbance was used for calculations. A standard curve using different concentrations (0.156-2.5 ug/ml) of human COMP was included in each microtitre plate. All samples were analysed in triplicate, and the mean value was used for calculations.
SAXNE AND HEINEGARD: CARTILAGE OLIGOMERIC MATRIX PROTEIN
585
SDS-polyacrylamide gel electrophoresis, electrophoretic transfer and immunostaining Cell free synovial fluid (200 ul) was chromatographed through a 500 ul column of Blue Sepharose CL-6B (Pharmacia Fine Chemicals, Uppsala, Sweden) and then through a 250 ul column of Protein A Sepharose CL-4B (Pharmacia Fine Chemicals, Uppsala, Sweden) to remove excessive albumin and immunoglobulins, respectively. These synovial fluid samples were electrophoresed on 4-16% gradient polyacrylamide gels [11]. Proteins were passively transferred to nitrocellulose by diffusion [12]. The proteins reacting with antibodies to COMP were detected after transfer to the nitrocellulose by incubation first with antibody against COMP and subsequent demonstration of bound IgG with a swine anti-rabbit IgG peroxidase conjugate (Dakopatts, Copenhagen, Denmark).
400-
1
1 200-
BS
"5A"
FIG. 2.—Synovial fluid concentrations of cartilage oligomeric matrix protein (COMP) in patients with rheumatoid arthritis with well preserved knee joints (RA, Larsen grade 0-1, n=20) and rheumatoid arthritis with severe knee joint damage (RA, Larsen grade 4-5, n=23), reactive arthritis (ReA, n=20), juvenile chronic arthritis (JCA, n=21) and osteoarthritis (OA, n=20). Trie horizontal bars indicate the median of each group.
preferentially recognize epitopes in the chondroitin sulphate rich region (Heinegard, Saxne, unpublished).
TABLE I CHARACTERISTICS OF PATIENTS AND CONTROLS IN WHOM CONCENTRATIONS OF COMP WERE DETERMINED*
Diagnosis Rheumatoid arthritis (Larsen 0-1) (n=20) Rheumatoid arthritis (Larsen 4—5) ("=23) Osteoarthritis («=20) Reactive arthritis («=20) Juvenile chronic arthritis (n^23) Blood donors (II=20)
Healthy children (n=29)
Age (years)
Female/male
60 (34-71)
14/6
63 (35-79)
16/7
Disease duration (years)
Synovitis duration (months)
ESR(mm/h)
2
(0.5CM0)
0.75 (0.25-1)
(7-117)
11 (1-60)
3 (0.5-6)
(30-124)
—
44
6/14
6 (2-15) 0.08 (0.01-20) 4 (0.25-18) —
(20-65) 5 (1-20)
14/15
—
73
12/8
(62-88) 39 (23-55)
5/15
12
16/7
(5-20)
0.25 (0.03-1)
45
64
9 (5-24) 33 (6-75)
4
22
(0.25-12)
(2-75)
— —
—
'Except for number of females/number of males, values are medians (ranges). ESR, erythrocyte sedimentation rate (Westergren). The Larsen index grades radiographic joint damage on a 6-gTade scale, where 5 denotes the most severe lesions.
Downloaded from http://rheumatology.oxfordjournals.org/ by guest on January 26, 2015
RA
(laraa* grada 0-1)(Lar»an frada 4-s>
Collection of synovialfluidsand blood Paired samples of knee joint synovial fluid and blood from patients with RA, reactive arthritis, juvenile chronic arthritis (JCA) and osteoarthritis (OA) were analysed. The RA specimens were chosen from the banks of fluids collected during a 6-year period and were selected only by the degree of radiographic joint damage, to obtain one group of patients with well preserved joints (Larsen index 0-1) and one group with advanced changes (Larsen index 4-5) [13]. The samples from reactive arthritis patients were chosen at random from the bank offluids.Eight reactive arthritis patients with a duration of synovitis more than 2 months were selected from the bank of fluids and studied separately. The JCA patients were those described in a previous report [14], and these fluids were obtained at arthroscopy. Samples from patients with OA of the knee joint were obtained from the Department of Orthopaedic Surgery, Malmo General Hospital.
BRITISH JOURNAL OF RHEUMATOLOGY VOL. XXXI NO. 9
586
TABLE II SYNOVIAL FLUID AND SERUM CONCENTRATIONS OF COMP IN PATIENTS WITH JOINT DISEASES AND IN BLOOD DONORS
Rheumatoid arthritis (Larsen 0-1) Rheumatoid arthritis (Larsen 4-5) Osteoarthritis Reactive arthritis Juvenile chronic arthritis Blood donors Healthy children
Synovial fluid (ug/ml)
Serum (ug/ml)
85(32-172)
11.5(6.8-19.3)
57(38-85)
7.6(4.9-10.7)
104(75-454) 172(82-376) 86(46-142) — —
10.6(4.3-18.0) 9.5(6.3-18.0) 7.3(4.5-10.8) 11.3(7.3-17.5) 10.3(5.2-13.4)
Values are medians (ranges).
Proteoglycans
COMP
Proteoglycan conc/COMP cone — p
