APLAR Journal of Rheumatology 2005; 8: 213–219

©Asia Pacific League of Associations for Rheumatology

Blackwell Publishing, Ltd.ORIGINAL ARTICLEMMP in RA

Serum matrix metalloproteinase activity relating to cartilage destruction in rheumatoid arthritisTatsuya TAKEMURA,1 Katsuaki KANBE,2 Kimihiko TAKEUCHI,1 Kazuhiko INOUE2 and Kenji TAKAGISHI1

1Department of Orthopaedic Surgery, Gunma University, School of Medicine, Gunma and 2Department of Orthopaedic Surgery, Tokyo Women’s Medical University/Daini Hospital, Tokyo, Japan

AbstractAims: The aim of this study was to determine which matrix metalloproteinases (MMPs) are involved with C-reactive protein (CRP) and which stage of rheumatoid arthritis (RA) correlated with MMP-9 or MMP-13 level.

Methods: In the present clinical trial, we analysed MMP-9 activity and MMP-13 activity in 53 RA patients. Weexamined the presence of MMP-9 and MMP-13 in the synovium tissue and articular cartilage in RA patientsby immunohistochemistry. In addition, we compared these factors and clinical Steinbrocker staging.

Results: We found that MMP-9 in blood serum correlates significantly with CRP. MMP-13 also correlates withCRP but the coefficiency with CRP is much higher in MMP-9 (r = 0.6694) than in MMP-13 (r = 0.4037). MMP-9 and MMP-13 did not correlated with rheumatoid factor (RF). MMP-9 level is increased in stages II and IIIin RA. On the other hand, MMP-13 is increased in stages III and IV. Our results indicated that early stage RAshows high MMP-9 release in serum while late stage RA shows high MMP-13 release.

Conclusion: MMP-9 activity may correlate with synovium proliferation with vascularization, and serum MMP-13 activity may correlate with the grade of joint destruction in rheumatoid arthritis.

Key words: MMP-13, MMP-9, rheumatoid arthritis.

INTRODUCTION

C-reactive protein (CRP) is used for the detection ofgeneral inflammation in rheumatoid arthritis (RA).1

High CRP indicates RA disease activity. However, highCRP is not an indicator of joint destruction in RA.Many matrix metalloproteinases (MMPs) are foundin the blood serum of RA patients.2 But there is nodescription in the literature of which MMP is actuallycorrelated with CRP or the joint destruction associatedwith RA. We investigated MMP-9 and MMP-13 which

are important in understanding RA development. Weanalysed the correlation between CRP and MMP-9 andMMP-13, and between rheumaoid factor (RF) andMMP-9 and MMP-13 in order to investigate the func-tion of MMPs in the development of RA.

In RA patients, arthroscopy often reveals synovialproliferation.3–6 However, we do not know the mecha-nism by which synovial proliferation leads to cartilagedestruction. Clinically, patients with slight RA havebeen shown to gain relief from pain and ameliorationof other symptoms.3 A method for determining thestage of RA through the use of serum factor has not yetbeen developed. Though X-ray examination of the jointcan reveal atrophy, narrowing of the joint space, boneerosion, pseudocysts, and joint destruction with anky-losis, determination of the developmental stage of RA

Correspondence: Katsuaki Kanbe, Department of Orthopaedic Surgery, Tokyo Women’s Medical University/Daini Hospital, 2-1-10 Nishioku, Arakawa, Tokyo 116–8567, Japan.Email: kanbeor@dnh.twmu.ac.jp

T. Takemura et al.

214 APLAR Journal of Rheumatology 2005; 8: 213–219

also still depends on X-ray analysis. Many kinds ofMMPs are produced by the synovium in joints of RApatients, yet the pattern of MMP increase during eachstage of RA development has not been established. Ourhypothesis is that MMP-9 and MMP-13 can be used asmarkers to determine the stage of RA. To test thishypothesis, we analysed MMP-9 and MMP-13 levels inRA patients, and studied their relationship with thestage of RA.

PATIENTS AND METHODSComparison of MMP-9 activity and MMP-13 activity concentrations in the blood sera of RA patientsFifty-three outpatients with RA seen at the Departmentof Orthopaedic Surgery, Gunma University Hospital,Gunma, Japan, were studied. Diagnosis of the patientswith RA was based on the American College of Rheu-matology 1987 revised criteria.7 The average diseaseduration of RA was 7.5 years (range, 1.2−12.2 years).All the patients with RA were treated with non-steroidanti-inflammatory drugs (NSAIDs). Thirty-five patientsalso received low-dose steroid treatment (prednisolone,maximum 10 mg/day). Twenty-three of these were alsotreated with disease-modifying antirheumatic drugsincluding bucillamine, auranofin, sulfasalazine, andmizoribine, while 11 patients received methotrexate, eitheralone or in combination with prednisolone. The 53patients included eight men and 45 women, with a meanage of 58 years (range, 17−80 years). The 53 patientsincluded 16 in stage I, 17 in stage II, 14 in stage III, and16 in stage IV according to the Steinbrocker staging ofRA.8 The same patients included 15 in grade I, 18 ingrade II, 17 in grade III, and 13 in grade IV accordingto the Larsen grade of RA. We assessed wrist X-raysby three different doctors and classified those patientsaccoding to the Larsen grade.9 In order to analyse thecorreration between MMP-9 or MMP-13 and RA dis-ease activity, we measured MMP-9 activity and MMP-13activity from blood serum centrifuged at 2500 g for10 min in order to remove cells and debris and storedthe samples in a freezer at −80°C until analysis. Theconcentrations of MMP-9 activity and MMP-13 activitywere quantified by a double-antibody sandwich enzymelinked immunosorbent assay (ELISA) according to themanufacturer’s instructions (Biotrak; Amersham Bio-science, Piscataway, NJ). We compared the concentrationof MMP-9 and MMP-13 in 41 osteoarthritis patientsto RA patients to confirm if these facors were specificto RA.

Detection of MMP-9 and MMP-13 in synovial tissue by immunohistochemistryFor immunofluorescence staining, synovial tissue andarticular cartilage were fixed at room temperature with4% paraformaldehyde then embedded in paraffin. Each5 µm slice was mounted on a glass slide and washed insequence, with 100% xylen, 95% ethanol, 90% ethanol,70% ethanol, and phosphate-buffered saline (PBS) toremove paraffin. Slides were then washed with PBS andincubated with primary antibodies. Antihuman MMP-9 and MMP-13 monoclonal antibodies (R & D Systems,Inc. Minneapolis, MN) and a secondary antibody withconjugates (Jackson ImmunoResearch, West Grove, PA)were used. Slides were washed and mounted in 95%glycerol in PBS. We used a histofine kit according tothe manufacturer’s protocol and took pictures using amicroscope from Nikon.

Statistical analysisSpearman’s rank correlation coefficient test was usedto analyse the coefficiency between MMPs and CRP orRF. Mann–Whitney U-tests were used to compare theincrease of MMPs to stage I, respectively. P-values ofless than 0.01 were considered significant.

RESULTSThe relationship between MMP-9 or MMP-13 and CRP, ESR or RF in blood serum of RA patientsMMP-9 correlated significantly with CRP (r = 0.6694,P < 0.01) (Fig. 1). MMP-9 correlated significantly withMMP-13 (r = 0.5087, P < 0.01) (Fig. 2). MMP-9 had asignificantly high coefficient with CRP (r = 0.6390, P <0.01) (Fig. 3). MMP-9 did not correlate with RF

Figure 1 The relationship between serum C-reactive protein(CRP) and erythrocyte sedimentation rate (ESR) in rheumatoidarthritis (RA).

MMP in RA

APLAR Journal of Rheumatology 2005; 8: 213–219 215

(r = 0.01, P = 0.28) (Fig. 4). MMP-13 correlated signifi-cantly with CRP (r = 0.4037, P < 0.01) (Fig. 5), though itdid not correlate with RF (r = 0.3079, P = 0.12) (Fig. 6).The mean concentrations of MMP-9 activity and MMP-13 in blood serum from RA patients were 54.7 and25.4 ng/mL, respectively. The mean concentrations ofCRP, erythrocyte sedimentation rate (ESR), and RFwere 2.21, 58.5, and 238, respectively. Therefore, serumMMP-9 activity, rather than MMP-13 activity, is corre-lated with CRP. This indicates that MMP-9 is moresensitive to inflammation with CRP in RA.

Comparison of MMP-9 and MMP-13 according to clinical stagingMMP-9 increased significantly in stage II and stage IIIcompared with stage I (Fig. 7), while MMP-13 increasedsignificantly in Steinbrocker’s stage III and stage IVcompared with stage I (Fig. 7). Several patients under-went arthroscopic synovectomy in stage II and stage IIIor tyrosine kinase activity in stage IV in RA. This findingindicates that synovium proliferation with vasculariza-

tion in stages II and III is much higher than in stage IV.Therefore, serum MMP-9 activity is correlated with syn-ovium proliferation in the early stage and serum MMP-13 activity is correlated with joint destruction in the

Figure 2 The relationship between serum MMP-9 and MMP-13 (matrix metalloproteinase) in rheumatoid arthritis (RA).

Figure 3 The relationship between serum MMP-9 and CRP(matrix metalloproteinase) in rheumatoid arthritis (RA).

Figure 4 The relationship between serum MMP-9 (matrixmetalloproteinase) and rheumatoid factor (RF) in rheumatoidarthritis (RA).

Figure 5 The relationship between serum MMP-13 (matrixmetalloproteinase) and C-reactive protein (CRP) in rheumatoidarthritis (RA).

Figure 6 The relationship between serum MMP-13 (matrixmetalloproteinase) and rheumatoid arthritis (RA) in rheumatoidarthritis (RA).

T. Takemura et al.

216 APLAR Journal of Rheumatology 2005; 8: 213–219

late stage of RA. We detected the average MMP-9 were32 ± 0.5, 67 ± 0.7, 43 ± 0.5 and 35 ± 0.3 ng/dL inLarcen’s grade I, II, III and IV, respectively. We alsodetected the average MMP-13 were 45 ± 0.5, 56 ± 0.7,115 ± 1.8 and 97 ± 1.2 ng/dL in Larcen’s grade I, II, IIIand IV, respectively. MMP-9 in grade II was significantlyincreased over grade IV (P < 0.01). MMP-13 in grade IIIand IV was significantly increased over grade II (P < 0.01).

Immunohistochemical detection of MMP-9 and MMP-13 in synovial tissue of RA (Fig. 8)MMP-9 positivity was detected in epithelial cells of bloodvessels and macrophages in synovial tissues of RApatients. MMP-9 was expressed in local areas aroundblood vessels. On the other hand, MMP-13 was positiv-ity detected in almost all areas in the synovium, suchas synovial tissue and epithelial cells or lymphocytes in

Figure 7 MMP-9 and MMP-13 (matrix metalloproteinase)increases in each stage of the Steinbrocker staging of rheumatoidarthritis (RA). * and ** show significantly higher MMP-9 andMMP-13 increases over stage I, respectively.

Figure 8 Immunohistochemical examination of MMP-9 and MMP-13 (matrix metalloproteinase) in synovium in stage III andarticular cartilage in stage III of the Steinbrocker staging of rheumatoid arthritis (RA). Arrow is positive for MMP-9 and MMP-13.

MMP in RA

APLAR Journal of Rheumatology 2005; 8: 213–219 217

blood vessels. MMP-13 expression is much strongerthan MMP-9 throughout the synovial tissue of RA.In articular cartilage, both MMP-9 and MMP-13 wereexpressed in chondrocytes with MMP-13 being expressedat a slightly higher level than MMP-9. Therefore, MMP-13 may play a major role in the destruction of jointcartilage and it is possible that MMP-9 and MMP-13 isreleased from cartilage to joint fluid and blood serumafter cartilage breakdown.

DISCUSSION

Cartilage destruction is a major cause of joint dysfunc-tion, and is followed by impairment due to pain, a lossof range of motion, swelling, and low patient activity.Synovium is thought to be a key part of the catabolicpathway in the destruction of joint cartilage in RApatients.10 The synovium produces many kinds of MMPs,such as MMP-12, 3, 8, 9, and 13.2 MMP-1 and MMP-3are produced by cells of the synovial lining, and MMP-2 is produced by stromal cells in the synovial sublininglayer. On the other hand, MMP-8 and MMP-9 aresecreted by neutrophils, and MMP-9 is also producedby macrophages and synovial cells.11,12 In addition, theexpression of those MMPs in chondrocytes has alsobeen confirmed.13

Rheumatoid synovitis is charactererized by an invasiveand tissue-destructive infiltrate of lymphocytes, macro-phages and synoviocytes.10 MMPs and tissue inhibitorsof metalloproteinases (TIMPs) produced by these cellsare important in the remodeling of the articular tissuesin RA.14,15 It has been reported that the serum concen-trations of MMP-1, MMP-3, and MMP-9 were higher inRA patients than in osteoarthritis patients.16 These threeMMPs dominated in the serum of RA patients withfollicular synovitis compared with those with diffusesynovitis.14

Total joint replacement results in the total resectionof cartilage and synovium at the joint. It is reportedthat in RA patients the plasma MMP-3 and the MMP-3/TIMP ratio decreased after total joint replacement,whereas CRP and ESR did not change.15 Therefore, CRPand ESR reflect systemic inflammation; however, plasmaMMP-3 and the MMP-3/TIMP-1 ratio may reflectinflammation and degeneration of the affected joint.15

MMP-13 has been suggested to play a major role inthe pathogenesis of tissue destruction in rheumatoidarthritis.17 MMP-13 mRNA (messenger ribonucleic acid)and enzyme protein were found in the pannocytes inthe pannus hard-tissue junction.10 MMP-13 or collagenase-3 has not been found in any trauma samples, but was

found in almost all rheumatoid samples.2 This is inaccordance with earlier observations, which demon-strate MMP-13 enzyme protein in immunohistochem-ical staining in RA to a much higher extent than itwas found in osteoarthritis, and that the expression ofMMP-13 seems to correlate with degree of inflamma-tion.17,18 Interleukin 1-β (IL1β) and tumor necrosisfactor-α (TNFα) induce fibroblasts to synthesize andsecrete MMP-13.19 It seems therefore that inflammatorycytokines have a central role in arthritis, that is, IL1βand TNFα, induce MMP-13 gene transcription andexpression in the RA synovial membrane. Severalcytokines including chemokine are also related to car-tilage breakdown in RA.20,21 Those catabolic pathwaysthrough joint fluid may also play a major role in jointdestruction in RA.

MMP-13 is able to break down type II collagen aswell as types IX and X collagen.22–25 MMP-13 can alsobreak down aggrecan as well as type IV collagen.22,24,26

MMP-13 is expressed to a greater degree in synoviumin RA patients than in OA patients.17 Because IL1β andTNFα can produce MMP-13 from synovium, MMP-13in RA is much higher than OA.27–30 We chose to focuson MMP-9 and MMP-13 because it has been reportedthat MMP-1, MMP-9 and MMP-13 play major roles inproducing joint destruction enzymes in joint fluid.31,32

It has been reported that MMP-1, MMP-3, MMP-9, andMMP-13 have coefficiency with CRP and ESR in theclinical course of RA.33–35 However, the relationshipbetween Steinblocker staging and MMP-9 or MMP-13has not been described. In the present data, we foundthat MMP-9 increased at stage II and stage III. Thisindicates that MMP-9 is associated with synovial prolif-eration as well as systemic inflammation with vascular-ization in the early stage of RA. In late stage RA suchas stage IV, there is almost no joint space with jointdestruction or ankylosis and there is no space to prolif-erate synovium any more, rather than in the early stageof RA where there is enough joint space. We also foundthat MMP-13 increased in stage III and stage IV.However, MMP-13 also correlated with CRP in regardto inflammation, and in late stage RA and also is moresignificantly released in serum from cartilage throughjoint fluid as well as synovium. We also found the cor-relation between MMP-13 and Larsen’s grading to bemore significant. This data supports the hypothesis thatjoint destruction may be involved in MMP-13. WhileCRP is a good marker of inflammation, it is only oneof the parameters to measure RA disease activity. Amore appropriate tool should be the disease activityscore (DAS). However, data on DAS scores are not

T. Takemura et al.

218 APLAR Journal of Rheumatology 2005; 8: 213–219

available. Future studies should address this. Howeverwidely Steinbrocker’s criteria is generally accepted forevaluating a patient’s functional outcome, it is not asensitive marker for clinical severity or the degree ofjoint destruction in RA.

In summary, MMP-9 may reflect inflammation, whileMMP-13 may be more important in the later stage ofRA. We found that MMP-9 was much more sensitive toCRP than was MMP-13 in the serum from RA patients.This means that MMP-9 may be also clinically useful todetect inflammation as well as CRP in RA. While higherlevels of MMP-9 are found in patients with earlierSteinbrocker’s stage than those at a later stage, there isconsiderable overlap. Measurements of MMP-13 activ-ity, that is, MMP-13 is not exclusively found in patientswith late Steinbrocker stages of functional class, but notclass I and II patients. However, MMP-13 expression ofimmunohistochemical studies is greater than that ofMMP-9 in rheumatoid synovial tissues and furtherstudies are needed to confirm their specific role in caus-ing inflammation and joint destruction.

REFERENCES

1 Fearon U, Reece R, Smith J, Emery P, Veale DJ (1999)Synovial cytokine and growth factor regulation of MMPs/TIMPs: implications for erosions and angiogenesis inearly rheumatoid and psoriatic arthritis patients. Ann N YAcad Sci 878, 619–21.

2 Konttinen YT, Ainola M, Valleala H, et al. (1999) Analysisof 16 different matrix metalloproteinases (MMP-1 toMMP-20) in the synovial membrane: different profiles intrauma and rheumatoid arthritis. Ann Rheum Dis 58, 691–7.

3 Altmann RD, Gray R (1983) Diagnostic and therapeuticuses of the arthroscope in rheumatoid arthritis andosteoarthritis. Am J Med 75, 50–5.

4 Roch-Bras F, Daures JP, Legouffe MC, Sany J, Combe B(2002) Treatment of chronic knee synovitis with arthro-scopic synovectomy: long-term results. J Reumatol 29,1171–5.

5 Horiuchi K, Momohara S, Tomatsu T, Inoue K, Toyama Y(2002) Arthroscopic synovectomy of the elbow inrheumatoid arthritis. J Bone Joint Surg Am 84, 342–7.

6 Matsui N, Moriya H, Kitahara H (1979) The use ofarthroscopy for follow-up in knee joint surgery. OrthopClin North Am 10, 697–708.

7 Arnett FC, Edworthy SM, Bloch DA, et al. (1988) TheAmerican Rheumatism Association 1987 revised criteriafor the classification of rheumatoid arthritis. ArthritisRheum 31, 315–24.

8 Steinbrocker O, Traeger CH, Battermann RC (1949)Therapeutic criteria in rheumatoid arthritis. JAMA 140,659–62.

9 Larsen A (1995) How to apply Larsen score in evaluatingradiographs of rheumatoid arthritis in long-term studies.J Rheumatol 22, 1974–5.

10 Konttinen YT, Salo T, Hanemaaijer R, et al. (1999) Colla-genase-3 (MMP-13) and its active in rheumatoid arthritis:localization in the pannus-hard tissue junction andinhibition by alendronate. Matrix Biol 18, 401–12.

11 Yoshihara Y, Nakamura H, Obata K, et al. (2000) Matrixmetalloproteases and tissue inhibitors of metalloproteasesin synovial fluids from patients with rheumatoid arthritisor osteoarthritis. Ann Rheum Dis 59, 455–61.

12 Fraser A, Fearon U, Reece R, Emery P, Veale DJ (2001) MatrixMetalloproteinase 9, apoptosis, and vascular morphologyin early arthritis. Arthritis Rheumatism 44, 2024–8.

13 Moldovan F, Pelletier JP, Hambor J, Cloutier JM, Martel-Pelletier J (1997) Collagenase-3 (matrixmetalloprotease 13)is preferentially localized in the deep layer of humanarthritic cartilage in situ: in vitro mimicking effect bytransforming growth factor beta. Arthritis Rheum 40,1653–61.

14 Klimiuk PA, Sierakowski S, Latosiewicz R, Cylwik B,Skowronski J, Chwiecko J (2002) Serum matrix metallo-proteinases and tissue inhibitors of metalloproteinases indifferent histological variants of rheumatoid synovitis.Rheumatology 41, 78–87.

15 Omura K, Takahashi M, Omura T, et al. (2002) Changesin the concentration of plasma matrix metalloproteinase(MMPs) and tissue inhibitor of metalloproteinases-1(TIMP-1) after total joint replacement in patients witharthritis. Clin Rheumatol 21, 488–92.

16 Ishiguro N, Ito T, Oguchi T, et al. (2001) Relationships ofmatrix metalloproteinases and their inhibitors to cartilageproteoglycan and collagen turnover and inflammation asrevealed by analyses of synovial fluids from patients withrheumatoid arthritis. Arthritis Rheum 44, 2503–11.

17 Lindy O, Kontiinen YT, Sorsa T, Santavirta S, Ceponis A,López-Otin C (1997) Matrix metalloproteinase 13 (colla-genase 3) in human rheumatoid synovium. ArthritisRheum 40, 1391–9.

18 Imai S, Konttinen YT, Jumppanen M, et al. (1998) Highlevel of expression of colagenase-3 (MMP-13) in patho-logical condition associated to a forein body reaction.J Bone Joint Surg 80, 701–10.

19 Uria JA, Stahle-Backdahl M, Seiki M, Fueyo A, López-Otín C(1997) Regulation of collagenase-3 expression in humanbreast carcinomas is mediated by stromal–epitherial cellinteraction. Cancer Res 57, 4882–8.

20 Kanbe K, Takagishi K, Chen Q (2002) Stimulation ofmatrix metalloprotease 3 release from human chondro-cytes by the interaction of stromal cell-derived factor 1and CXC chemokine receptor 4. Arthritis Rheum 46,130–7.

21 Katsche KJ Jr, Rottman JB, Ruth JH, et al. (2001) Differentialexpression of chemokine receptors on peripheral blood,synovial fluid, and synovial tissue monocytes/macrophagesin rheumatoid arthritis. Arthritis Rheum 44, 1022–32.

MMP in RA

APLAR Journal of Rheumatology 2005; 8: 213–219 219

22 Knäuper V, López-Otin C, Smith B, Knight G, Murphy G(1996) Biochemical characterization of human colla-genase-3. J Biol Chem 271, 1544–50.

23 Mitchell PG, Magna HA, Reeves LM, et al. (1996) Cloning,expression, and type II collagenolytic activity of matrixmetalloproteinase-13 from human osteoarthritic cartilage.J Clin Invest 97, 761–8.

24 Billinghurst RC, Dahlberg L, Ionescu M, et al. (1997)Enhanced cleavage of type II collagen by collagenasein osteoarthritic articular cartilage. J Clin Invest 99, 1534–45.

25 Knäuper V, Cowell S, Smith B, et al. (1997) The role ofthe C-terminal domain of human collagenase-3 (MMP-13)in the activation of procollagenase-3, substrate specificityand tissue inhibitor of metalloproteinase interaction.J Biol Chem 272, 7608–16.

26 Fosang AJ, Last K, Knäuper V, Murphy G, Neame PJ(1996) Degradation of cartilage aggrecan by collagenase-3(MMP-13). FEBS Lett 380, 17–20.

27 Reboul P, Pelletier JP, Tardif G, et al. (1996) The newcollagenase, collagenase-3, is expressed and synthesizedby human chondrocytes but not by synoviocytes. J ClinInvest 97, 2011–9.

28 MacNaul KL, Chartrain N, Lark M, Tocci MJ, Hutchinson NI(1990) Discoordinate expression of stromelysin, colla-genase, and tissue inhibitor of metalloproteinase-1 inrheumatoid human synovial fibroblast. J Biol Chem 265,17238–45.

29 Gearing AJ, Beckett P, Christodoulou M, et al. (1994)Processing of tumor necrosis factor-α precursor bymetalloproteinases. Nature 370, 555–7.

30 Itoh A, Mukaiyama A, Itoh Y, et al. (1996) Degradation ofinterleukin 1 by matrix metalloproteinases. J Biol Chem271, 14657–60.

31 Maeda S, Sawai T, Uzuki M, et al. (1995) Determinationof interstitial collagenase (MMP-1) in patients withrheumatoid arthritis. Ann Rheum Dis 54, 970–5.

32 Ahrens D, Koch AE, Pope RM, Stein-Picarella M, Niedbala MJ(1996) Expression of matrix metalloproteinase 9 (96-kdgelatinase B) in human rheumatoid arthritis. ArthrritisRheum 39, 1576–87.

33 Keyszer G, Lambiri I, Nagel R, et al. (1999) Circulatinglevels of matrix metalloproteinases MMP-3 and MMP-1,tissue inhibitor of metalloproteinases 1 (TIMP-1), andMMP-1/TIMP-1 complex in rheumatic disease. Correla-tion with clinical activity of rheumatoid arthritis versusother surrogate markers. J Rheumatol 26, 251–8.

34 Goldbach-Mansky R, Lee JM, Hoxworth JM, et al. (2000)Active synovial matrix metalloproteinase-2 is associatedwith radiographic erosions in patients with early synovitis.Arthritis Res 2, 145–53.

35 Westhoff CS, Freudiger D, Petrow P, et al. (1999) Charac-terization of collagenase 3 (matrix metaloproteinase 13)messenger RNA expression in the synovial membrane andsynovial fibroblasts of patients with rheumatoid arthritis.Arthritis Rheum 42, 1517–27.