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Human rheumatoid arthritic cartilage and its neutral proteoglycan-degrading proteases. The effects of antirheumatic drugs

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HUMAN RHEUMATOID ARTHRITIC CARTILAGE
AND ITS NEUTRAL PROTEOGLYCAN-DEGRADING
PROTEASES
The Effects of Antirheumatic Drugs
JOHANNE MARTEL-PELLETIER, JEAN-MARIE CLOUTIER, DAVID S. HOWELL, and
JEAN-PIERRE PELLETIER
+
Measurements were made of the neutral proteoglycan-digesting protease activity in the cartilage matrix
breakdown observed in the rheumatoid arthritic process. Normal knee (tibia1 plateau) cartilage specimens
were obtained from 7 fresh cadavers and 29 cartilage
specimens were obtained from 23 patients diagnosed as
having rheumatoid arthritis (RA). The total neutral
metalloproteoglycan-degrading enzyme (NMPE) activity in RA cartilages exhibited roughly an eightfold elevation over that of control subjects. The active form of the
NMPE for diseased cartilage was higher than that
observed for normal cartilage, but was not statistically
different. A very low level of activity was detected .for
serine proteases and no variation was observed between
normal and diseased cartilages. Data obtained from RA
cartilages were also analyzed with respect to the relationship between enzyme activities and the patients’
medications. Four groups of patients were then selected
according to their drug treatments: S
G patients
received steroid and gold therapy; S patients received
steroids only; NS NG patients did not receive steroid
or gold therapy; G patients received gold therapy alone.
The total NMPE activity for each of these groups
remained at a very high level. The active enzyme activity
measured in S G and S patients was decreased to a
level not different from that of normal controls. Specimens from NS NG patients presented a significantly
higher level of the active form of the enzyme ( P < 0.05)
when compared with either normal controls, S G, or
S patients. No significant difference was noted in the
level of serine protease activity between the RA cartilage
and normal cartilage. These data strongly support the
role of NMPE in the destruction of RA cartilage.
Steroids, whether alone or associated with gold compounds, are able to suppress the activity of the active
form of the NMPE.
Presented in part at the 30th Annual Scientific Meeting of
the Orthopedic Research Society, Atlanta, GA, February 1984.
From the Department of Medicine and Surgery, University
of Montreal, Notre Dame and St. Luc Hospitals, Montreal, Canada
and the Department of Medicine, University of Miami, School of
Medicine, Miami, Florida.
Supported by a grant from the Medical Research Council of
Canada.
Johanne Martel-Pelletier, PhD: Assistant Professor of
Medicine, Notre Dame Hospital, University of Montreal, School of
Medicine: Jean-Marie Cloutier, MD: Professor of Surgery, St. Luc
Hospital, University of Montreal, School of Medicine; David S .
Howell, MD: Professor of Medicine, University of Miami, School of
Medicine; Jean-Pierre Pelletier, MD: Assistant Professor of Medicine, Notre Dame Hospital, University of Montreal, School of
Medicine.
Address reprint requests to J . Martel-Pelletier, PhD, Unit6
des Maladies Rhumatismales, HBpital Notre-Dame, 1560 est, rue
Sherbrooke, Montreal, Quebec, Canada H2L 4K8.
Submitted for publication May 21, 1984; accepted in revised
form October 11. 1984.
Cartilage destruction is a major characteristic of
rheumatoid arthritis (RA). The mechanism involved
seems to be. a degradation of the cartilage matrix
components by a number of proteolytic enzymes that
are found in one or more cellular elements of the
diseased joint (1). Although some of the enzymes have
been partially characterized, their cellular origins and
individual roles in the pathogenic sequence of cartilage
degradation have not yet been established.
Chondrocytes have the capacity to degrade
their own matrix probably via the synthesis of proteolytic enzymes (2-5). Some of these enzymes hydrolyse
peptides which are bound in the core protein of the
proteoglycan (PG) subunits. A mechanism, independent of the direct diffusion of degrading enzyme into
the cartilage matrix, and one which includes the partic-
Arthritis and Rheumatism, Vol. 28, No. 4 (April 1985)
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MARTEL-PELLETIER ET AL
ipation of chondrocytes, has been found (6-8). I t was
demonstrated that cartilage matrix degradation, mediated by chondrocytes, can be enhanced by a soluble
factor. This factor is released from the inflamed synovial membrane of rheumatoid joints. Moreover, this
increased degradation can be inhibited by hydrocortisone-related compounds (9).
Neutral proteoglycanases have been found in
cartilage tissue. For instance, neutral metalloproteases, capable of degrading proteoglycans, have been
described and identified in human articular cartilage
(10,ll). W e have recently demonstrated that human
osteoarthritic cartilage contains neutral metalloproteoglycan-degrading enzymes (NMPE) (5). T h e activity of these enzymes was directly correlated with many
parameters of the disease severity. This study focused
attention on the quantitative net neutral protease activity in the cartilage matrix during the rheumatoid
arthritic process in humans. T h e relationship between
neutral enzyme activity and the medication taken by
these patients was also investigated.
There was an observable increase in the level of
NMPE activity, especially when RA cartilages were
compared with normal human articular cartilages. RA
patients treated with steroids were found to have a
significantly lower level of the active form of the
metalloenzymes. T h e possible significance of this finding and its helpfulness in understanding the matrix
destruction that occurs in rheumatoid cartilage is
outlined.
PATIENTS AND METHODS
Chemicals. The chemicals used were either American
Chemical Society certified or were the best grade commercially available. Phenylmethylsulfonyl fluoride (PMS-F) was
purchased from Sigma Chemical Co., St. Louis, MO;
p-aminophenylmercuric acetate (APMA), cetylpyridinium
chloride (CPC), and carbazole from Eastman Kodak, Rochester, NY.
Patients and tissue preparation. The subjects studied
were patients from both St. Luc and Notre Dame Hospitals,
Montreal, Quebec, Canada. All were classified as having
either definite or classic rheumatoid arthritis determined by
the established criteria of the American Rheumatism Association (12). Although the indications for surgical intervention
were not uniform from a clinical and biochemical evaluation,
at the time of surgery, all patients had active synovitis in the
joint under study.
Twenty-nine tibial plateaus from 23 patients (18
female, 5 male, mean age 62, range 44-80), were obtained at
the time of surgery for total knee replacement. Previous
medications were documented. Therapy consisted of 1 or
more of the basic treatments for rheumatoid arthritis, i.e., 1)
therapeutic doses (ranging from moderate to high) of nonsteroidal antiinflammatory drugs (NSAIDs), 2) steroids (predni-
sone) in a daily dosage of 5 to 10 mg taken orally, and/or 31
gold salts (sodium aurothiomalate) as a standard course, i.e..
weekly injections of 50 mg intramuscularly for 20 weeks.
followed by 50 mg every 2-4 weeks for an indefinite period.
None of the patients had received any other type of treatment (chloroquine, D-penicillamine, immunosuppressive
agents, levamisole) for RA in the preceding 6 months.
Patients had, in the past, used I or more antirheumatic
drugs, but only those drugs in use at the time of hospitalization and those used for at least 6 months previously are
listed.
We grouped the RA patients according to their
previous medication. Because all 23 patients were taking
nonsteroidal antiinflammatory compounds, these drugs were
not used as a variable. Cartilage specimens from RA patients
were then divided into 4 broad groups-S + G: patients who
were receiving steroid and gold therapies, 8 specimens from
7 female patients; S: patients who underwent steroid therapy
solely, 10 specimens from 7 patients (5 female, 2 male); NS
+ NG: patients who received neither steroid nor gold
compounds, i.e., they were receiving a support therapy
of nonsteroidal antiinflammatory drugs only, 8 specimens from 6 patients (5 female, 1 male); G: patients who
received only gold salts, 3 specimens from 3 patients ( 1
female, 2 male). Caution should be used in interpreting the
statistical accuracy of the results from group G: because gold
compounds are seldom used alone in the treatment of RA
patients, this group had only 3 such specimens. The accuracy of the statistical data on 3 specimens may or may not be
relevant. Therefore, these results are mentioned only in the
text.
Immediately after the resection of the knee the
specimens were kept on ice, washed with cold physiologic
saline solution, scraped with a policeman, and dissected.
The cartilage tissue from the tibial surfaces was shaved from
the bone with a scalpel. Care was taken to remove the
cartilage sections in areas away from the invading pannus
tissue. Histologic experiments showed no evidence of invading pannus nor of any surface-adhering inflammatory cells.
The diced cartilage was weighed, frozen, and stored at
-80°C until further use.
Normal control cartilages from 7 age-matched patients were obtained from the knee joint at autopsy, within
12 hours of death. Cartilage that appeared macroscopically
normal and was without any evidence of fibrillation was
chosen. Samples were taken from the same site previously
described for RA specimens.
Enzyme assay. The neutral proteoglycan-degrading
protease assay was described in detail in an earlier study ( 5 ) .
In summary, the cartilage tissue was homogenized in 7
volumes of Tris buffer (Tris-HCI 50 mM, CaClz 10 mM, NaCl
150 mM, NaN3 0.02% weight/volume and gentamycin 40 c ~ g
[Schering Corp.]) at pH 7.4 and incubated at 37°C for 42
hours. Aliquots subjected to incubation were first submitted
to either: (a) APMA (1 mM); (b) APMA ( I mM) plus ophenanthroline (5 mM); (c) no addition; (d) o-phenanthroline
( 5 mM); or (e) APMA ( 1 mM), o-phenanthroline (5 mM) plus
PMS-F (1 mM).
To determine any possible interference of the serine
proteases with the level of the active metalloenzymes by an
in vitro activation, we conducted the following test. We
repeated the experiment, already knowing that the NMPE
407
NEUTRAL PG DEGRADATION IN RA
Table 2.
(active form) activity was high, but this time we added PMSF (1mW under conditions c and d stated above. N o change
in the level of the active form was noted.
After the incubation period, proteolytic activity was
quantitated via the degradative products released from the
endogenous PG. The quantification method uses the precipitation of PG with CPC at a final concentration of 1.7%. This
was followed by the release of the PG-digested products with
trichloroacetic acid. in solution, at a final concentration of
9%. The degradation of these PG was quantitated by their
uronic acid content (13) analyzed in the last supernatant. A
unit of PG-degrading enzyme activity was defined as the
release of I pg of uronic acid per hour. All homogenates
subjected to the above-described conditions were assayed in
this manner. The activity was expressed in unitsigm (wet
weight) of cartilage.
PG-degrading enzyme activity was calculated for the
following: 1 ) total NMPE-the digestion found in group a
minus that found 'in group b , 2) active NMPE-group c
difference between
minus group d , 3) latent NMPE-the
total and active forms, and 4) serine proteases-group b
minus group c. All activities were corrected for non-enzymatic release of the proteoglycans. This was done under a
42-hour test period at 4°C.
Analytic study of the whole cartilage and the PGdigested products of NMPE. DN,4 determination was made
on each cartilage sample using the method of Bonting and
Jones (14). The DNA unit used was pgimg wet weight of
cartilage. Uronic acid measurement was carried out on a
whole cartilage sample (10 mg wet weight) and was used as
an index of PG content. Too little tissue was left for further
quantification using any other parameter.
Statistical analysis. Mean values and standard errors
of the resulting data were calculated for both patient and
control samples. To test the equality of means, an analysis of
variance was performed. When significant P values, <0.05,
were obtained in any combination of the groups studied, a
Scheffe's multiple comparison (15) was done to assess which
group(s) was (were 1 responsible for the significant difference.
No. of specimens
Totdl NMPEt
Rheumatoid
arthritis
subiects
uatients
7
29
9.95
1.68
0.48
No. of specimens
Uronic acid, F g h g
wet weight
7
3.82 2 0.23t
*
*
*
-
RA subgroups*
RA
29
1.80
2
0.1.5
<O.OOl
S + G
S
NS
8
1.80 t 0.24
10
2.34 +- 0.31
1.31
<0.001
<0.001
+ NG
8
2
0.15
<O.OOl
rheumatoid arthritis; S + G = patients receiving steroid and gold therapies; S = patients
receiving steroid therapy; NS + NG = patients who received neither steroid nor gold compounds.
t Values expressed as mean t SEM.
$ Probability values were calculated by analysis of variance followed by Scheffe's procedure
comparing the values for the RA specimens with those from normal tissues. When RA specimens from
subgroups were compared with one another, no significant difference was noted.
* RA
=
2
2
1.14
0.40
0.17
<0.003
NS
NS
were consistent with the findings published by other
authors (16). The uronic acid content of t h e cartilage of
the diseased joints was significantly lower (P< 0.001)
than that of the controls. This reduction was greater in
groups where the patients received NSAlDs a l o n e ,
compared with the 2 groups of patients (S + G and S)
treated with steroids. The uronic acid v a l u e for patients receiving gold compound alone (G) was lower
(1.14 ? 0.08) than t h a t of the control values. Rheumatoid cartilage samples showed a lower DNA c o n t e n t
(0.47 ? 0.02 p g h g wet weight; mean t SEM) than the
normal c o n t r o l s (0.54 0.04), but no statistical difference could be noted between these 2 s e t s of data. The
treatment applied did not seem to affect the D N A
c o n t e n t , with values roughly in the same r a n g e , i.e., S
+ G, 0.46 -+ 0.05; S, 0.45 0.03; NS + NG, 0.48 5
0.04; G, 0.53 0.12.
Neutral protease activity. Table 2 illustrates the
trend of the neutral enzyme activity in normal and
r h e u m a t o i d arthritic cartilages. T h e major neutral enzyme activity a p p e a r e d in t h e category of rnetalloproteases, i.e., activated by APMA (1 m M ) and inhibited
by o-phenanthroline ( 5 mM). A very low level of serine
Uronic acid content
Normal
subjects
+_
P*
* Probability values were calculated by the analysis of variance
followed by Scheffe's procedure comparing the values for the
rheumatoid arthritis specimens with those from normal tissues. NS
= not significant.
t Enzyme activity was measured as described in Patients and
Methods after 42 hours incubation at 37"C, and expressed as units/
gm of cartilage (wet weight).
$ Values expressed as mean t SEM.
Biochemical data. Table 1 shows t h e PG c o n t e n t
(expressed as uronic acid) in t h e diseased cartilage
compared w i t h that of normal controls. These results
PS
Normal
1.16 t 0.37$
0.10 ? 0.10
0.36 ? 0.18
Active NMPE
Serine motease
RESULTS
Table 1 .
Neutral metalloproteoglycan-degradingprotease (NMPE)
activity
408
MARTEL-PELLETIER ET AL
protease activity was recorded in our cartilage specimens.
The patients with diseased cartilage exhibited a
very high level of total NMPE activity. The mean
value of all patients with arthritic disease was significantly increased over the mean value of the control
group ( P < 0.003). One should particularly note the
level of the active form of the NMPE. Thus, the RA
cartilage samples showed a higher mean value (1.68 t
0.40) than that noted for normal cartilage (0.10 t 0. lo),
but the analysis of variance showed no significant
difference ( P < 0.07). Serine proteases showed an
insignificant difference in activity between normal
subjects and diseased specimens. Similar serine levels
were noted for both RA specimens and normal controls.
For comparison purposes, the data obtained in
this study were divided into 4 groups, each specifying
an individual drug therapy. Figure 1 presents the
distribution of the total NMPE activity of RA carti-
'"1
It I
12
4i
N
8
10
S+G
I
SI
8
NS+NG
I
Figure 1. Total neutral metalloproteoglycan4egrading enzyme aci = normal controls
tivity in human articular cartilage specimens. l
ccrossline column); S + G = patients receiving steroid and gold
therapies; S = patients receiving steroid therapy; NS + NG =
patients receiving nonsteroidal antiinflammatory compounds. The
assay is described in Patients and Methods. Enzyme activity is
expressed as unitsigm of cartilage (wet weight). Results are given as
the mean t SEM. The number of tissue specimens is indicated in
the lower part of each column. Using analysis of variance and
subsequent Scheffe's multiple comparison, there are two subsets: N
and ( S + G , S, NS + NG), statistically different at P < 0.05.
t
4
EL
3
c
U
4
u i
f
N
t
1
T
rh
1
7
N
L
S+G
10
8
-
SI
NS+NG
Figure 2. Neutral metalloproteoglycan4egrading enzyme activity
in human articular cartilage specimens. Results are given as the
SEM. The number of tissue specimens is indicated in the
mean
lower part of each column (except N column; number shown above
column). Using analysis of variance and subsequent Scheffe's
multiple comparison, there are two subsets: (N. S + G . S ) and NS +
NG, statistically different at P < 0.05. See Figure 1 for definitions.
*
lages (divided into 3 broad groups) and that of normal
control cartilages. Total NMPE activity was high in
every RA group and did not seem influenced by
different therapies. All RA groups presented similar
amounts of enzyme. The multiple comparison procedure showed the 4 RA groups as a subset, which was
significantly different from the normal control group.
The total NMPE activity of group G also presented a
higher level (7.56 t 4.09) than the one found for the
control group.
Figure 2 illustrates the level of the active form
of the NMPE for the 4 groups. In contrast to the total
NMPE activity, the level of the active form showed a
wide variation with respect to the different medications. Our results revealed that patients receiving
steroids along with gold (S + G; 0.27 t 0.15) or those
receiving steroids alone (S; 0.60 k 0.29) formed a
subset. This subset had a significantly lower level of
activity observed than that noted from group NS +
NG, which was comparatively high (4.0 t 0.85) (Figure 2). The values of group G (2.36 ? 1.41) were in the
same range as those of group NS + NG. Cartilage
from patients taking steroids showed about the same
level of NMPE activity as that found in normal cartilage. No significant difference was recorded among
groups S + G , S, and normal subjects. However,
NEUTRAL PG DEGRADATION IN RA
E>
1-
F
V
4
Yi
5 0.5
N
S+G
h
S
NS+NG
Figure 3. Serine protease activity in human articular cartilage specimens. Results are given as the mean % SEM. The number of tissue
specimens is indicated in the lower part of each column. Using
analysis of variance and subsequent Scheffe’s multiple comparison,
there was no statistical difference between any of the groups listed.
See Figure 1 for definitions.
group NS + NG showed a significant increase in
active enzyme activity, especially when the group was
compared with the normal controls.
Serine proteases had a low level of activity.
This was observed not only in normal controls (0.36 -+
0.18) but also in RA cartilages, regardless of the
treatment (Figure 3 ) . Although an increase in activity
was seen in group S, statistically it was not different
from any of the other 3 groups studied. The mean
value for group G was 0.23 0 . 2 3 .
*
DISCUSSION
The operative mechanism in the process of
irreversible cartilage damage in inflammatory arthritis
is largely unknown. Generalized damage of the rheumatoid cartilage includes a “thinning” of the cartilage,
a dramatic decrease of metachromatic proteoglycans,
and a degradation of surface collagen. PG loss appears
in the early stages of the disease and even precedes
collagenolysis ( I ) . Several enzymatic mechanisms,
such as those dependent on synovial fluid proteases of
diverse origin and the enzymes which come from the
inflammatory synovium, pannus cells, or chondro-
409
cytes, have been considered to play a role in cartilage
degradation.
In chronic inflammatory arthritis, an obvious
source of proteolytic enzymes is their release from the
inflammatory cells present in the synovial fluid. Therefore, the enzyme diffusion into the cartilage might be
responsible for the matrix degradation. Some of these
enzymes, such as leukocyte elastase, have been found
in the synovial fluid in rabbit models of arthritis (17).
The presence of enzyme inhibitors (a,-antitrypsin and
a2-macroglobulins) in the synovial fluid is responsible
for the inactivation of these neutral enzymes. Neutral
proteases capable of degrading PG have been isolated
from mononuclear cells (18). Again, most of this
activity is inactivated by the same enzyme inhibitors.
Both the breakdown of matrix components and
the progressive cartilage erosion brought about by
rheumatoid pannus have been reported by many authors (19,20). However, cartilage degradation due
solely to an enzymatic invasion from the pannus area
is unlikely. Erosion has also been seen on the free
surface of the cartilage, which is some distance from
the synovium (6,19). lt has been proposed that chondrocytes participate in these erosions by destroying
their own matrix (6). The histologic observation of the
early collagen degradation and of the loss of matrix
proteoglycans around the chondrocytes ( 2 I ) , analyzed
in RA cartilage, adds some credence to the hypothesis
that matrix degradation may be mediated by these
cells.
The primary stimulus that activates chondrocytes in the diseased cartilage is not known. It seems
that self-propagating cartilage damage must be attributed to endogenous enzyme activation. It has been
demonstrated that synovial factors and the factors
derived from mononuclear cells and from macrophages stimulated the chondrocytes to either degrade
their own matrices or to secrete proteases (22-24).
It is likely that PG breakdown occurs by a
proteolytic action on the core protein. This protein is
readily destroyed by many proteases. There are only a
few enzymes, isolated from articular cartilage or chondrocytes in culture, to which one can attribute the PG
degradation. Muirden et a1 (25) found an increased
amount of cathepsin D in the cartilage of patients with
rheumatoid arthritis. However, it is unlikely that those
acid proteases had an important role in extracellular
rather than intracellular digestion, since the pH of the
cartilage matrix lies in the neutral range. Hembry et a1
(26) have performed experiments in which they demonstrated that the proteolytic action of cathepsin D
was limited to the intrachondrocytic degradation of
410
proteoglycans in lysosomes. Therefore neutral proteases seem the most likely candidates responsible for
the loss of matrix proteoglycans in the injured joint.
Our results have clearly demonstrated that human RA cartilage contains a substantial amount of
neutral proteases, which are capable of degrading PG.
The total NMPE in rheumatoid cartilage was enhanced
8-9 times over that of normal controls (Table 2). Our
findings are in accordance with previous reports that
suggested the major fraction of neutral protease activit y found in articular cartilage does respond to metalloprotease inhibitors (27). The total NMPE activity
present in these RA cartilages was not affected by the
patients’ medication (steroid and/or gold salts). Although there was a slight decrease in total NMPE
when steroids and gold agents were used in combination, one could not correlate the combination with a
further suppression of this enzyme activity. If, as
previously reported, the cartilage breakdown and
possibly the synthesis of proteolytic enzymes by chondrocytes are under the control of stimulating factors in
RA tissue (22-24), there are at least 2 possible explanations for the apparent lack of suppression of total
NMPE in patients receiving either steroids or steroids
in conjunction with gold.
One explanation may be that even though the
cartilage specimens used came from 23 different patients, the patients themselves had at least 2 features in
common. They all had long-standing rheumatoid arthritis and all, technically speaking, had had unsuccessful results with medical therapy. That is, the
patients needed surgery because of either their lack of
therapeutic response to or an inadequate dosage in
their medication.
The second explanation can be related to the
fact that steroids inhibit the synthesis and/or the
release of chondrocytic-activating factor(s) (9). It has
also been postulated that there is a direct chondrocytic
inhibition of the synovial factor(s) action (28). As yet,
little is known about this mechanism in vivo. The
above observations were based on in vitro experiments and the response was visible at very high drug
concentrations. It is therefore possible that the therapeutic level was not enough to suppress the release
and/or action of the activating factor(s) in our study.
These two explanations may be operative; however,
they may play only a small role in regard to the entire
degenerative process of this disease.
The NMPE detected in tissues or in cell cultures occurred mostly as latent enzymes, which could
be activated by trypsin or mercurial compounds. We
have previously reported the presence in human OA
MARTEL-PELLETIER ET AL
cartilage of NMPE in both latent and active forms (5).
In addition to the prominent increase in total NMPE
activity, rheumatoid cartilage exhibited an increase in
the active enzyme level-especially so in the specimens taken from patients receiving NSAIDs only (NS
+ NG, Figure 2). This quantitatively high increase in
the enzyme activity level can be relevant in the
degradative process.
It has not yet been established how the latent
enzyme is activated in vivo. The latency could be
explained by the presence of a pro-enzyme (zymogen),
which in turn causes a proteolytic cleavage to yield the
active form (29). Activation of neutral metallopyoteases, from a latent to an active form, may be affected
by a number of proteinases of which the serine type
seems the most likely candidate. Despite the fact that
serine proteases show a clear capacity to activate
synovial collagenase (30), there is no evidence that
they activate the NMPE in the RA matrix cartilage. So
far, in our assay, we have been unable to demonstrate
an in vitro, serine enzyme activation of the NMPE.
In this study, only trace amounts of serine
proteases were found in normal and RA cartilages
(Table 2). The various medications received had no
significant effect on the serine level (Figure 3). Even if
the chondrocytic production of plasminogen activator
has been shown to be stimulated by a substance that is
isolated from cultured synovium (31), there is little
evidence to prove that chondrocytes actually initiate
in vivo protease activity. Recently, Vater et a1 (32)
have reported that latent collagenase can be activated
by a protein called procollagenase activator. Even if
purely speculative at this stage, it is possible tbat a
similar mechanism might be responsible for activating
the NMPE in RA cartilage.
The present study emphasized the steroid-induced suppression of the active NMPE activity. Our
data demonstrated that active NMPE activity was
altered to a normal level in groups S + G and S (Figure
2). This was, moreover, paralleled by a less severe
depletion of the uronic acid content in these specimens
(Table 1). However, with this observation, we are not
excluding the possibility that the combination of steroid, gold, and NSAIDs affects NMPE activity. It is
possible that the predominant effect of these steroids
operates on the activation step. It has been shown that
activators, such as the plasminogen activator, are
inhibited by steroid agents (33). On the other hand,
McGuire et a1 (34) have suggested that the steroidinduced reduction of matrix degradation is due to an
increased concentration of free endogenous inhibitors.
Our data do not allow us to determine which hypothe-
NEUTRAL PG DEGRADATION IN RA
sis is correct, nor whether activators or inhibitors are
likely to play a significant role in the progressive tissue
damage of RA. However, the suppressive effect of
steroid compounds on the active enzyme activity
confirms the reported protective effect that low steroid
doses seem to have on RA cartilage breakdown (35).
This may also explain the beneficial effect that low
prednisone doses have on hand/wrist erosions in RA
patients (36).
Nevertheless, the fact that total NMPE is enhanced in RA cartilage and that the active form is
significantly increased in the degradative RA (NSAID
group), may be relevant in explaining the disease
process. The effect of steroids on the active form of
the NMPE gives us an additional insight in determining the possible mechanism of action of these drugs.
ACKNOWLEDGMENTS
The authors thank Dr. R. Vauclair, Head of the
Department of Pathology, Notre Dame Hospital, for supplying the postmortem specimens. The technical assistance of
W. Nedwetsky and F. Mineau and the assistance of D.
Fournier in preparing the manuscript are greatly appreciated.
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3. Sapolsky AI, Malemud CJ, Norby DP, Moskowitz RW,
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