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Marked suppression by salicylate of the augmented proteoglycan synthesis in osteoarthritic cartilage.

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83
MARKED SUPPRESSION BY SALICYLATE OF THE
AUGMENTED PROTEOGLYCAN
SYNTHESIS IN OSTEOARTHRITIC CARTILAGE
MARSHALL J. PALMOSKI. ROBERT A. COLYER, and KENNETH D. BRANDT
In osteoarthritis a net increase in proteoglycan
synthesis has been noted until the disease is far advanced and presumably reflects an attempt by the
chondrocyte to repair the defect in the cartilage matrix.
Because salicylates are the agents most commonly employed in treatment of osteoarthritis and because we recently showed that IO-’M sodium salicylate (i.e., approximately 20 mg%) suppresses proteoglycan synthesis
in normal canine knee cartilage in vitro, we have studied
the effects of this compound on osteoarthritic knee cartilage from dogs whose anterior cruciate ligament had
been transected 9 weeks previously. The data indicated
that the augmented synthesis of glycosaminoglycans in
the degenerating cartilage was suppressed to a much
greater degree by IO-’M sodium salicylate than the
lower level of glycosaminoglycan synthesis in control
cartilage from the contralateral knee of the same animal. Uptake of ‘‘C-acetylsalicylic acid was increased
about 35% in osteoarthritic cartilage, suggesting that
the drug permeated it more readily than normal cartilage. The salicylate-induced suppression of proteoglycan synthesis in the osteoarthritic cartilage was
From the Departments of Medicine and Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, Indiana.
Supported in part by N I H grant #5S07 R R 05371,
NIAMDD grant #AM 20582, and awards from the Arthritis Foundation and the Grace M. Showalter Trust.
Marshall J. Palmoski, PhD: Assistant Professor of Medicine;
Rohert A. Colyer, MD: Assistant Professor of Orthopaedic Surgery;
Kenneth D. Brandt, MD: Professor of Medicine and Chief, Rheumatology Division, Indiana University School of Medicine.
Address reprint requests to Marshall J. Palmoski, PhD,
Rheumatology Division, Indiana University School of Medicine, 1 100
W. Michigan Street, Indianapolis, Indiana 46223.
Submitted for publication May 7, 1979; accepted in revised
form August 10, 1979.
Arthritis and Rheumatism, Vol. 23, No. 1 (January 1980)
not accompanied by reversal of the defect in proteoglycan aggregation or by improvement in the (presumed) defect in proteoglycan-collagen interaction in
the matrix, as reflected by the abnormally high proportion of 3sS-proteoglycanspresent in the culture medium.
The extracellular matrix of normal articular cartilage is constituted principally of two species of macromolecules--collagen and proteoglycans (PGs). The latter, which have average molecular weights of 1-2 x lo6
daltons (I), possess a high fixed negative charge density,
which renders them highly hydrophilic (2). There is evidence that the PG content of joint cartilage accounts for
its elasticity and ability to resist compression (3), while
the collagen confers tensile strength (4).In normal articular cartilage the proteoglycans exist chiefly in very
large aggregates, in which many individual PGs are
noncovalently associated with hyaluronic acid in a linkage stabilized by tissue glycoproteins (5). The role of aggregation is unknown but it may, by facilitating formation of macromolecular structures of enormous size
(Swzoo= 60-70) (6), help constrain the PGs within the
collagen network of the tissue.
In osteoarthritis (OA) the articular cartilage matrix is deficient. Its content of proteoglycans is subnormal and its compressive stiffness is diminished (7).
This loss of PGs, at least in the earlier stages of the disease, occurs despite an increase in net synthesis of PGs
(which presumably reflects an attempt by the chondrocytes to “repair” the lesion) (S), suggesting an accelerated rate of PG breakdown. A defect in PG aggregation
(9,lO) and an increase in water content (1 1) of the articular cartilage commonly occur in the initial stages of
osteoarthritis. The increased water content, which may
PALMOSKI ET AL
84
be of fundamental importance, can be accounted for by
enlargement of the molecular domains of the PGs,
which are presumably less constrained than normal by
the collagen network (12).
It is notable that salicylates, the drugs most commonly employed in treatment of this disease, inhibit
synthesis of glycosaminoglycans (GAGS) (13,14). We
recently reported that sodium salicylate (SodSal), when
introduced into the culture medium at a concentration
of 10-3M(which is readily achieved in the serum of patients treated with salicylates for rheumatic disease), reduced PG synthesis in cultures of normal adult canine
articular cartilage by about 30%, but had no effect on
PG catabolism or aggregation (15).
The symptomatic relief produced by salicylates
in many patients with osteoarthritis may be attributed
to the analgesic and/or antiinflammatory properties of
these agents. Do these drugs have other effects on the
disease, which might result from a direct action on articular cartilage, e.g., on PG catabolism or aggregation, or
on the stability of PG-collagen interactions? The answer
is not clear at this time. Aspirin has been reported to inhibit the cartilage degeneration occurring from superficial scarification (16) or prolonged joint compression
(17) in rabbits, and to reduce the prevalence of degenerative changes in cartilage of human beings suffering recurrent dislocation of the patella (1 8). However, the cartilage degeneration in C57 black mice, which are
genetically predisposed to OA, has been shown to be
aggravated by administration of salicylates (19).
Clearly, more information is needed about the
effects of salicylates on normal and osteoarthritic cartilage. The present study examines the effect of SodSal on
articular cartilage from dogs who had undergone transection of their anterior cruciate ligament. This surgical
procedure produces instability of the knee and leads
predictably to the morphologic and biochemical
changes of OA (20). Our data indicate that the inhibition of net PG synthesis produced by SodSal in the degenerating cartilage is more marked than that produced
by the drug in normal cartilage, while the PG aggregation defect and the greater than normal extractability of
PGs from the matrix, which are integral features of the
disease, are not improved by the drug.
MATERIALS AND METHODS
Surgical procedure. Five adult mongrel dogs were
anesthetized with intravenous sodium pentothal, after which
the left knee was shaved and scrubbed with Betadine antiseptic soap. Its joint capsule was opened through a short
oblique anteromedial incision and the anterior cruciate ligament was transected with a scalpel, with care taken to avoid
damage to the articular cartilage. The capsule was closed with
2-0 chromic sutures and the skin with interrupted 4-0 nylon.
Two dogs underwent sham operations i.e., the joint capsule
was opened, the anterior cruciate ligament was identified but
not transected, and the capsule and skin were closed as above.
Postoperatively all animals were allowed to ambulate freely in
pens large enough to allow walking. All dogs bore weight on
the operated limb by the third day after surgery. None developed a wound infection.
Tissues and culture conditions. Nine weeks postoperatively the dogs whose anterior cruciate ligaments had
been transected (dogs 1-5) were killed with an overdose of sodium pentothal. The sham-operated dogs were killed in the
same fashion 7 weeks (dog S1) and 12 weeks (dog S2) after
surgery. Immediately after killing, both knees were opened
aseptically. The distal femurs were removed with a bone saw
and representative full-thickness samples of the articular cartilage, including a portion of the underlying subchondral
bone, were obtained with a Craig biopsy needle for histologic
study. Other portions (approximately 10 mg) were taken for
determination of dry weight and uronic acid content, while
the remainder of the cartilage from the distal weight-bearing
portions of the femoral condyles of each joint (approximately
200 mg) was shaved into slices less than 0.5 mm thick, with
the tissue from the operated knee and contralateral control
knee of each dog cultured separately. Approximately 50 mg of
cartilage were incubated for 24 hours at 37OC under 5%
C02:95%air in 10 ml of medium consisting of Ham's F-12 nutrient mixture, pH 7.4, (containing approximately 5 X 10-6M
inorganic SO,); fetal calf serum (10%); streptomycin (50 pg/
ml); penicillin (50 units/ml) and no SodSal or 10-3M SodSal.
At the end of the incubation period the medium was removed
with a pasteur pipette and replaced with fresh medium containing Na25S0, (20 pCi/ml) (New England Nuclear Corp.,
Boston, Massachusetts) and the same concentration of SodSal. The incubation was then continued for an additional 8
hours.
The medium was then decanted and the cartilage
washed with cold saline. Medium and wash were combined
and dialyzed for 48 hours at 4°C against 200 volumes of
0.05M sodium acetate, pH 6.8, in Spectrapor No. 3 dialysis
tubing (Spectrum Medical Industries, Inc.; Los Angeles, California), which has a molecular weight cutoff of approximately
3,500 daltons. The tubing was rinsed with distilled water and
the retentate and rinses were combined.
Extraction of PGs from the cartilage. The washed cartilage slices were stirred for 48 hours at 4OC in 10 ml of 4M
guanidinium hydrochloride (GuHC1) in 0.05M sodium acetate, pH 5.8, containing the protease inhibitors ethylenediaminetetraacetic acid (O.OlM), 6-aminohexanoic acid (0. lM),
and benzamidine hydrochloride (0.OSM) (21). The extract was
filtered, the residue was washed with fresh 4M GuHC1, and
filtrate and washings were combined and dialyzed against
0.05M sodium acetate, pH 6.8, as above.
After extraction with 4M GuHCl the cartilage residue
was suspended in 0.2M borate, pH 8.0, containing 0.02M calcium chloride and pronase (Calbiochem; San Diego, California) (1 mg enzyme/50 mg cartilage wet weight). The tissue
SALICYLATE SUPPRESSION OF PG SYNTHESIS
was digested under toluene for 24 hours at 55"C, after which
the small amount of tissue remaining was removed by centrifugation. The supernatant was dialyzed overnight at 4°C
against distilled water and aliquots (0.1 ml) of the dialyzed
samples of the medium recovered at the end of the incubation
period, the 4M GuHCl extract and the pronase digest were
added to Ready-Solve HP 60 (Beckman Instruments, Inc., Irvine, California) and counted in a Beckman liquid scintillation spectrometer. Results (cpm) were adjusted for differences
in wet weight of the cartilage.
Isolation of PGs. After dialysis of the 4M GuHCl extract, PG aggregates were isolated and purified by cesium
chloride equilibrium density gradient centrifugation under associative conditions in the presence of 0.4M GuHCl, according to the method of Hascall and Sajdera (22). Fractions from
the bottom 2/5 of the density gradient (h 2 1.76 gm/ml) were
combined and dialyzed exhaustively at 4°C against 0.05M sodium acetate, pH 6.9, to yield fraction AGU.
Digestion of fraction AGuwith hyaluronic acid /31-+3
hydrolase. Aliquots (2 ml) of fraction AGuwere made 0.1M
with respect to citric acid a n d 0.2M with respect to
Na,HPO, ' 7 H,O. After the pH was adjusted to 5.6, 1.5 pg of
hyaluronic acid /?l -+ 3 hydrolase (Biotrics, Inc., Arlington,
Massachusetts) were added in 5 equal portions over a 5 hour
incubation period at 37°C (23). Sepharose 2B chromatographs
of the proteoglycans before and after incubation were compared. The specificity of the enzyme for hyaluronic acid was
confirmed by its failure to alter the elution profile of disaggregated 35Sproteoglycans after they had been treated as
described in the previous section.
Determination of net GAG synthesis. To assess the effect of SodSal on GAG synthesis, triplicate samples (approximately 15 mg each) of cartilage from control and operated
limbs of each dog were incubated for 16 hours in 5 ml of medium (see above) containing no SodSal or 10-3M SodSal.
Na,35S0, (20 pCi/ml) was then added and the incubation was
continued for an additional 8 hours after which the medium
was decanted and the tissues were washed with cold saline.
The medium and wash were combined and dialyzed against
distilled water at 4"C, and the tissue was digested with pronase as above. Net GAG synthesis was determined from the
sum of the nondialyzable '%04
radioactivities of the medium
and the pronase digest.
''C-acetylsalicylic acid uptake by the cartilage. In one
set of experiments triplicate samples of cartilage from the unstable and control knees of Dog 4 and Dog 5 were each incubated as above in medium containing lOP3Macetylsalicylic
acid plus 2 pCi/ml of acetylsalicylic acid, ~arboxyl-'~C
(New
England Nuclear Corp., Boston, Massachusetts). At the end of
the incubation period the medium was removed with a pasteur pipette and the tissues were washed with three 5 ml aliquots of fresh unlabeled medium. The cartilage was digested
with pronase as above and 0. Iml aliquots of the digests were
counted in a liquid scintillation spectrometer, with the results
(cpm) adjusted for differences in the wet weight of the cartilage.
Gel chromatography. Samples (0.5 ml) of proteoglycans in 0.5M sodium acetate, pH 6.9, were applied to a
column (95 X 1.0 cm) of Sepharose 2B (Pharmacia Fine
Chemicals, Piscataway, New Jersey) and eluted with the ace-
85
tate buffer at a rate of 2 ml/hour. The radioactivity ( 3 5 S 0 , ) of
1 ml effluent fractions was determined and the partition coefficients (Kav)of PG samples were calculated from the formula:
K,, = (V, - V,)/(V, - VJ. V, was taken as the peak fraction
in the elution diagram, V, as the void volume, and V, as the
total column volume.
Analytical methods. To determine water content, portions of the cartilage (approximately 10 mg) were placed in
two changes of acetone for 48 hours and dried to constant
weight in vacuo at 80°C. The dried cartilage was digested
with pronase as above, after which the GAGS were isolated by
precipitation with 9-aminoacridine hydrochloride and converted to their sodium salts with Bio-Rad AG-50 (Na+) (24).
The resin was removed by filtration and the uronic acid content of the filtrate was determined by the method of Bitter and
Muir (25).
Histologic examination. Histologic sections (6p) of the
samples of articular cartilage and subchondral bone obtained
with the Craig biopsy needles from the central portion of the
medial condyle were examined microscopically after staining
with Safranin-0-fast green (26).
RESULTS
Gross and histologic observations. Articular cartilage from the control knee of every animal was white,
glistening, and smooth, with an intact surface. No osteophytes were noted. Safranin-0 staining of the matrix
was normal and intense, and cell distribution was normal, with only one chondrocyte per lacuna. The tidemark was intact in every case.
The femoral condyles of the knees, which had
been rendered unstable by previous cruciate ligament
transection, exhibited apparently normal cartilage over
the weight-bearing areas, with no evidence of softening,
pitting, or discoloration. Surface fibrillation was noted
only in the sample from Dog 3 (Table 1). In contrast to
the controls, marginal osteophytes were apparent in
every case. All samples of articular cartilage from the
operated knees showed a diminution in intensity of Safranin-0 staining when compared to cartilage from the
control knees (Table 1). Chondrocyte clusters, containing up to 5 cells per lacuna, were seen near the tidemark
in all sections obtained from the unstable knees, although the tidemark was intact in all cases.
Water and uronic acid content of the cartilage.
Water constituted 66.2-79.3% of the total weight of the
articular cartilage from the control knees (mean, 69.5%),
while uronic acid represented 5.0-6.8% of the dry
weight (mean, 5.7%). In every case cartilage from the
unstable knee showed a higher water content and lower
uronic acid content than that from the control knee of
the same animal (Table 1). The increase in water content ranged from 3.34.1% (mean, 3.6%) of the tissue
PALMOSKI ET AL
86
Table 1. Osteoarthritic changes in knee cartilage of dogs whose anterior cruciate ligament had been
transected 9 weeks previously
Knee from
which cartilage
was obtained
Safranin-0 staining
Fibrillation
Dog 1
Control
Operated
Normal
Moderate reduction
-
-
+
+
-
66.2
10.3
5.2
3.4
Dog 2
Control
Operated
Normal
Slight reduction
-
-
-
13.5
16.9
5.0
4.1
Dog 3
Control
Operated
Normal
Severe reduction
-
-
-
63.8
61.4
5.8
2.9
Dog 4
Control
Operated
Normal
Slight reduction
-
-
-
64.4
68.2
5.1
4.1
Dog 5
Control
Operated
Normal
Slight reduction
-
-
-
19.3
82.6
6.8
5.9
Animal
+
Chondrocyte
cluster
+
+
+
+
Osteophytes
+
+
+
+
Uronic
Water
acid
content* content?
* Percent of tissue wet weight.
t Percent of tissue dry weight.
wet weight. The uronic acid content of cartilage from
the unstable knees ranged from 2.9-5.9% of the tissue
dry weight (mean, 4.2%) which represented an average
decrease in uronic acid content of about 25%, with a
maximum decrease of 50% (Dog 3), in comparison with
the control cartilage (Table 1).
GAG metabolism. Based on nondialyzable "S radioactivity measured after pronase digestion of the cartilage, plus that contained in the culture medium, the
amount of newly synthesized GAGS in articular cartilage from the unstable knees was greater (164-308%)
than that in cartilage from control knees (Table 2). SodSal lO-'M invariably reduced GAG synthesis in control
cartilage (range, 21-55%; mean, 40.4%) (Table 2). In
osteoarthritic cartilage the augmented (baseline) level of
GAG synthesis was reduced by SodSal in every case.
Notably, except for the experiment with cartilage from
Dog 1, the SodSal-induced inhibition of GAG synthesis
(40-99%) in the osteoarthritic cartilage was much
greater than that in control cartilage from the same animal (Table 2).
Salicylate uptake by the tissue. In experiments
in which cartilage from Dogs 4 and 5 was incubated
with 14C-acetylsalicylic
acid, uptake of the radionuclide
by degenerating cartilage from the unstable knee was
35% and 37% greater, respectively, than that by cartilage from control knees of these animals (Table 3).
Extractability of PGs from the cartilage. There
was no effect from lO-'M SodSal on the distribution of
"S PGs between the culture medium, 4M GuHCl ex-
tract, and pronase digest of the cartilage (Table 4). In
every case the proportion of total 3sSPGs contained in
the medium after incubation of cartilage from the unstable knee was greater than that in the medium of cultures of control cartilage. Thus, some 7.9-13% of the total nondialyzable 3sS radioactivity was recovered in
medium of the control cultures and 13.2-23.7% in medium of cultures of the degenerating cartilage.
In all cases the majority of the '%O, proteoglycans were extracted with 4M GuHCl (Table 4),
and fraction AGuaccounted for about 70-80% of the total nondialyzable radioactivity in the 4M GuHCl extracts of control and osteoarthritic cartilage. SodSal did
not alter the distribution of 35SPGs between the medium, 4M GuHCl extract, and the pronase digest in cultures of normal or osteoarthritic cartilage, nor the proportion of total "S PG radioactivity in the 4M GuHCl
extract which was recovered in fraction AGu.
PG aggregation. The proteoglycans in fraction
AGu from control cartilage were markedly heterogeneous in hydrodynamic size and some 23-38% eluted
in the void volume on Sepharose 2B chromatography.
The K,, of those PGs from fraction A,, of control cartilage which were small enough to be retarded by the gel
ranged from 0.20-0.49 (Table 5). In every case the retarded peak was symmetrical, broad, and smooth.
In contrast to this finding, proteoglycans in fraction AGufrom the degenerating cartilage contained no
material sufficiently large in hydrodynamic size to elute
in the Sepharose 2B void volume. The K,,'s of the PGs
SALICYLATE SUPPRESSION OF PG SYNTHESIS
87
Table 2. Effect of sodium salicylate (SodSal) on %04incorporation into glycosaminoglycans (GAGS)*
in knee cartilage of dogs 9 weeks after transection of anterior cruciate ligament
% inhibition
’3 incorporation
35Scpm x 10-~/10
Source of
cartilage
Dog I
Dog 2
Dog 3
Culture conditions
mg wet
weight of cartilage
Control
Control SodSal
Operated
Operated SodSal
+
+
229.5 f 15.6
129.2 f 3.0
377.2 f 17.0
226.6 f 10.5
164
Control
Control + SodSal
Operated
Operated + SodSal
193.9 f 10.0
87.2 f 6.6
403.3 f 24.3
100.8 f 7.1
208
Control
Control + SodSal
Operated
Operated SodSal
221.6 f 12.5
106.4 f 2.3
683.6 f 21.9
7.4 f 0.3
308
Control
Control + SodSal
Operated
Operated SodSal
264.7 f 17.5
209.8 f 7.2
481.1 f 19.8
182.1 f 5.8
182
Control
Control + SodSal
Operated
Operated SodSal
272.7 f 8.7
191.7 f 8.4
479.0 f 24.5
198.6 f 9.5
176
+
Dog 4
+
Dog 5
into GAGs
in cartilage
from unstable
kneet
+
of 35s
incorporation
into GAGs
produced by
IO-’M SodSal
44
40
55
7s
52
99
21
62
30
59
* Nondialyzable 35Scpms in culture medium plus pronase digests of triplicate samples f one standard
error.
t Percent of central knee, in absence of SodSal.
retarded by the gel were somewhat larger than the K,,’s
of analagous PGs from control cartilage of these animals, indicating that they tended to be smaller than normal in hydrodynamic size. Sepharose 2B elution profiles of fraction AGufrom the osteoarthritic and control
cartilage were wholly unaffected by the presence of
SodSal in the culture medium (Table 5).
Treatment with hyaluronic acid pl+3 hydrolase
abolished the Sepharose 2B void volume peaks in all
Table 3. Uptake of I4C acetylsalicylic acid by normal and osteoarthritic canine knee cartilage
Animal
Dog 4
Dog 5
Knee from
which cartilage
was obtained
I4C cpm/lo
mg wet weight
of cartilage*
14Ccpm
incorporation,
% of control
Control
Operated
11,184 f 671
15,088 -+ 603
135
Control
Operated
9,624 f 485
13,209 f 748
137
-
-
* Results represent the mean f one standard error of triplicate samples.
A,, samples from control cartilage but had no effect on
the chromatographs of AGufrom osteoarthritic cartilage,
suggesting that the PGs in the latter fraction did not exist as aggregates in association with hyaluronic acid.
Characterization of knee cartilage from dogs undergoing sham operation. Cartilage from the control
and sham-operated joints of Dogs S1 and S2 appeared
grossly normal, and histologic sections stained with Safranin-0 showed no abnormality (Table 6). The water
content of the cartilage from the sham-operated limbs
was similar to that from the control knees (Dog S1
73.3%, 12.9% respectively; Dog S2 74.9%, 75.2% respectively, of tissue wet weight), and no appreciable difference was observed between the uronic acid contents of
the cartilage from the control and sham-operated knees
(Table 6).
incorporation into GAGs by cartilage from
the operated joints of these dogs was 103% and 98% of
controls, respectively. No difference was noted between
the average hydrodynamic size of the PGs in fraction
AGufrom the sham-operated knees and that of the AGu
PALMOSKI ET AL
88
Table 4. Effect of sodium salicylate (SodSal) on distribution of 35Sproteoglycans* between culture medium, 4M GuHCl extract, and pronase digest of normal and osteoarthritic canine knee cartilage
No SodSal
Animal
Knee from
which cartilage
was obtained
10-3M SodSal
% distribution of total cpm
Medium 4M GuHCl
Pronase
digest
% distribution of total cpm
Medium 4M GuHCl
Pronase
digest
Dog I
Control
Operated
13.0
23.7
56.0
59.8
31.0
16.5
13.0
21.3
60.2
59.0
26.8
19.7
Dog 2
Control
Operated
8.3
19.3
65.7
61.5
26.0
19.2
10.8
20.8
58.3
62.2
30.9
17.0
Dog 3
Control
Operated
9.1
22.2
66.4
44.8
24.5
33.0
7.0
21.1
60.2
47.9
32.8
31.0
Dog 4
Control
Operated
11.1
21.1
66.3
56.5
22.6
22.4
9.2
20.2
69.3
57.9
21.5
19.9
Dog 5
Control
Operated
7.9
13.2
56.7
51.4
35.4
35.4
8.4
14.5
57.9
48.2
33.7
37.3
* Nondialyzable
"S radioactivity.
from the controls. In all cases about 30% of the "S-PGs
eluted in the Sepharose 2B void volume. Digestion with
hyaluronic acid pl+3 hydrolase eliminated the void
volume peaks of fraction A,".
the cartilage of the operated knees in the present study
can be attributed to the consequences of knee instability, rather than to the trauma of the operative procedure.
The cartilage from the knee that did not undergo
DISCUSSION
The experimental model of osteoarthritis emplayed here has been studied extensively by us and produces the structural. biochemical, and metabolic
changes that occur in the spontaneously occurring form
of the disease (20). The model is similar to that described by Pond and Nuki (27), except that in our studies an arthrotomy is performed and the anterior cruciate
ligament is transected under direct vision, whereas in
the Pond-Nuki model the ligament is cut by a blind stab
wound. Our own attempts at blind sectioning of the ligament have occasionally resulted in laceration of articular cartilage and/or incomplete transection of the ligament. Since arthrotomy itself could conceivably
produce some degenerative changes in cartilage, we
have examined knee cartilage from dogs undergoing
sham operations, in which arthrotomy was performed
and the joint capsule closed without transection of the
ligament. At a postoperative interval relevant to the
present study (7-12 weeks) the cartilage in these shamoperated dogs was morphologically, metabolically, and
biochemically normal (Table 6), so that the changes in
Table 5. Effect of sodium salicylate (SodSal) on the Sepharose 2B
elution profiles of proteoglycans extracted with 4M GuHCl from canine knee cartilage 9 weeks after sectioning of anterior cruciate ligament
No SodSal
Animal
Knee from
which cartilage
was obtajned
Fraction A,,
10-3M SodSal
Fraction A,,
Dog I
Control
Operated
23
0
0.20
0.30
22
0
0.24
0.30
Dog2
Control
Operated
32
0
0.35
0.56
35
0
0.38
0.57
Dog3
Control
Operated
30
0
0.45
0.58
28
0
0.42
0.55
Dog4
Control
Operated
38
0
0.49
0.44
40
0
0.47
0.47
Control
Operated
25
0
0.38
0.49
28
0
0.35
0.47
Dog 5
* Percent of 35S-proteoglycans eluting in the Sepharose 2B void
volume.
t Partition coefficient of 35S-proteoglycansretarded by Sepharose
2B.
SALICYLATE SUPPRESSION OF PG SYNTHESIS
89
Table 6. Characterization of knee cartilage from dogs undergoing sham operation
Animal
Dog S I
Dog S2
Interval
between
shamKnee from
operation
which cartilage
and
was obtained
sacrifice
Safranin-0
staining
Fibrillation
Osteophytes
-
-
-
-
-
-
-
-
Control
Operated
7
Normal
Normal
Control
Operated
12
Normal
Normal
Water
Uronic acid
content,
content,
35S cpm,*
% of tissue
% of
% of
wet weight dry weight
control
12.9
13.3
4.5
4.1
75.2
74.9
5.3
5. I
-
I03
-
98
Sepharose 2B
chromatography
of fraction AGu
%Vat
k,,, Vr*
29
30
0.20
0.20
25
28
0.32
0.34
* Nondialyzable ”S in culture medium plus pronase digests. Results represent analyses of triplicate samples. Standard error was less than 6% in
each case.
t Percent of 35S-proteoglycanseluting in the Sepharose 2B void volume.
Partition coefficient of 35S-proteoglycanswhich were retarded by Sepharose 2B.
*
surgery may not have been “normal,” since it was presumably subjected to excessive loading because of the
instability induced in the opposite limb. Indeed, we
found that some decrease in PG aggregation occurred in
cartilage from the left knee of dogs when the right hind
limb was immobilized in a cast for several weeks (28).
However, in the present study, PGs from the unoperated limb were aggregated and the tissue appeared histologically and histochemically normal.
The histologic changes in the cartilage of the unstable knee, i.e. the decrease in Safranin-0 staining,
clustering of chondrocytes and, in one case, fibrillation
(Table l), as well as the osteophytes, are typical of
osteoarthritis (29). The increase in cartilage water (1 l),
decrease in uronic acid content (8,11,26), and the decrease in PG aggregation, which was indicated by Sepharose 2B chromatography (9, lo), are also characteristic
of this disease. A decrease in PG aggregation has also
recently been demonstrated by differential ultracentrifugation in this animal model of OA (30,31). The observed increase in net GAG synthesis in cartilage from
the unstable knee is also a well recognized feature of the
earlier stages of osteoarthritis (8) and may reflect attempts by the cartilage cells to replenish the deficit in
matrix proteoglycans.
The concentration of SodSal chosen in the present study, 10-3M, corresponds to a therapeutic concentration of approximately 20 mg% and is readily
achieved in human serum and synovial fluid (32). Our
results are significant insofar as they show that at this
reasonable concentration the drug-induced inhibition of
GAG synthesis in OA Cartilage was appreciably greater
than that in normal cartilage. It is possible that this difference resulted from a greater penetration of salicylate
into the diseased cartilage, whose matrix integrity had
been altered (as indicated, e.g., by the increased loss of
PGs into the medium). This possibility is strengthened
by the evidence that uptake of ’‘C-acetylsalicylic acid
by osteoarthritic cartilage was greater than that by control cartilage from the same animal. Indeed, cartilage
from the unstable knee of Dog 3, which showed the
most severe histologic and histochemical abnormalities
in the series (Table l), exhibited the greatest degree of
salicylate-induced inhibition of GAG synthesis (99%
suppression).
Although SodSal inhibited net GAG synthesis, it
did not reverse the defect in PG aggregation in the
osteoarthritic cartilage or improve the organizational integrity of the matrix. Thus, the abnormally high proportion of proteoglycans present in the culture medium after incubation of cartilage from the unstable joints was
not diminished by inclusion of SodSal in the cultures.
The present studies provide no information concerning
whether cartilage breakdown in osteoarthritis is altered
by SodSal. The cartilage activity of acid and neutral
proteases, which degrade PGs, is greater in OA cartilage
than in normal (33,34) so that if the drug inhibited release of enzymes or suppressed their activity, it could
have a beneficial effect that might counterbalance its
suppression of GAG synthesis.
The present studies also do not deal with the
basis for the salicylate-induced suppression of GAG
synthesis in normal and osteoarthritic cartilage. This
may, however, be due to inhibition of enzymes involved
in the early stages of GAG synthesis, which has been
demonstrated at the salicylate concentration employed
in the present study (35). Finally, it must be emphasized
that the results reported here represent data from short-
PALMOSKI ET AL
90
term in vitro experiments. T h e effects of salicylate on
normal and osteoarthritic cartilage in vivo, if any, remain to be clarified. Studies aimed at clarifying this
point are in progress in this laboratory.
14.
ACKNOWLEDGMENTS
We are grateful to Janet Anderson and Jeffrey Wilson
for technical assistance and to Margaret Britner for secretarial
support.
15.
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Rheumatoid Arthritis: Advances in Therapy and Pathophysiology
The New Mexico Chapter of the Arthritis Foundation will hold its Thirteenth Annual Arthritis Symposium, “Rheumatoid Arthritis: Advances in Therapy and Pathophysiology,” March 14 and 15,
1980 at the Airport Marina Hotel in Albuquerque.
Registration fee is $50 advance, $60 after March 1. For more information write Arthritis Foundation, PO Box 8022, Albuquerque, New Mexico 87198, or call (505) 265-1545.
Romanian Conference of Rheumatology
The Third Romanian Conference of Rheumatology will be held in Bucharest May 2 2 and 23,
1980. lmmunopathologic mechanisms, antiinflammatory drugs, and medico-surgical rehabilitation will be some of the subjects covered.
The official languages of the conference will be Romanian, English, French, and Russian. Registration fee for U.S. participants is $50.00.
For more information, contact Dr. I. Stroescu, General Secretary, The Union Societies of Medical
Sciences, Romanian Society of Rheumatology, Progresului Str. 8, Bucharest 70754, Romania.
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