Department of Rheumatology, University of Newcastle upon Tyne and 1Department of Rheumatology, Freeman Hospital, Newcastle Hospitals NHS Trust, UK.
Correspondence to: A. Myers, Musculoskeletal Unit, Freeman Hospital, High Heaton, Newcastle upon Tyne, NE7 7DN, UK. E-mail: andrea.myers{at}ncl.ac.uk
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Abstract |
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Methods. MMP-1 and TIMP-1 serum levels were determined by enzyme-linked immunosorbent assay (ELISA) in (a) index cases with PsA (subtype: RA n = 43, distal interphalangeal disease n = 2, oligoarticular n = 15, spondyloarthropathy n = 9, enthesitis n = 1), (b) siblings with PsA, (c) siblings with psoriasis (Ps), (d) unaffected siblings and (e) local controls. Patients with Ps were divided according to the onset of disease: type I disease, onset before age 40 yr and type II, onset after age 40 yr.
Results. MMP-1 and TIMP-1 levels were significantly increased in both the index cases and the group including all siblings compared with the controls (P < 0.0001). There was no statistical difference in MMP-1 or TIMP-1 levels between index cases and their siblings. There was no difference in serum MMP-1 level between the different subtypes (Moll and Wright) of PsA, but there was an increased level of serum TIMP-1 in patients with rheumatoid pattern (P = 0.05). In the index cases there were increased levels of TIMP-1 in type II onset psoriasis (P = 0.03) but no difference in MMP-1 levels.
Conclusion. MMP-1 and TIMP-1 serum levels are elevated in PsA. This is greatest in RA pattern PsA. These levels were also elevated in unaffected siblings suggesting that genetic factors may be important. TIMP-1 levels were elevated in psoriasis alone, more so in late onset psoriasis, suggesting that the pathological processes of early and late onset psoriasis may be different.
KEY WORDS: Psoriatic arthritis, Matrix metalloproteinases, Tissue inhibitor metalloproteinases, Psoriasis.
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Introduction |
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Matrix metalloproteinases are involved in a wide variety of normal physiological processes including the turnover of connective tissue matrix during growth and development. They are also implicated in the destruction of joint tissue such that raised levels are found in rheumatoid synovial fluid, in synovial tissue at the cartilagepannus junction from rheumatoid joints and in animal models of arthritis [1]. Stromelysin-1 (MMP-3) is raised in rheumatoid arthritis (RA) and is able to degrade proteoglycan and activate proenzyme forms of MMP including MMP-1 [2, 3]. It has been widely studied in RA [47] and it is found in RA cartilage [8], synovium [9], synovial fluid [10] and serum [11, 12]. MMP-1 and MMP-8 have been reported at elevated levels in RA synovial fluid [10, 13], whilst only MMP-1 has been found at elevated levels in RA serum [11, 12]. Recently metalloproteinases have been looked for in the synovium of individuals with PsA [1416], but very little work exists on serum measurements of these enzymes [17].
All connective tissue cells produce endogenous tissue inhibitors of metalloproteinases (TIMPs) which bind tightly to active MMPs in a 1:1 ratio [1]. This family of small polypeptide inhibitors plays an important role in controlling tissue breakdown by blocking MMP activity. The equilibrium between local concentrations of active MMPs and TIMPs determines the extent of connective tissue turnover. TIMP-1 is produced by a variety of cells and is found in many human body fluids with the exception of normal urine [18]. This suggests that TIMP-1 is an essential protein in humans. The TIMPs are differentially regulated, which may explain why there are several proteins performing the same regulatory function. Serum TIMP-1 levels correlate with inflammatory markers in RA [19], but TIMP-1 has not previously been examined in PsA.
Psoriasis is a chronic inflammatory dermatosis and is associated with abnormal keratinocyte proliferation and infiltration of inflammatory cells into the dermis and epidermis. Keratinocytes express high levels of transforming growth factor (TGF-) [20], interleukin 8 (IL-8) [21], IL-6 [22] and IL-1 [23].
Although the pathogenesis of psoriasis remains unclear, there are several features that suggest an immunologically mediated process characterized by T cells infiltrating into the epidermis. Large numbers of activated T lymphocytes and neutrophil granulocytes are found in the epidermis. Activation of keratinocytes seems to play a major role in the disease, which is in part mediated by lymphokines secreted from T cells. It has been shown that interferon- can lead to the expression of human leucocyte antigen (HLA) class II molecules, intercellular adhesion molecule (ICAM)-1, and
-IP-10 in lesional keratinocytes [24].
In psoriasis it has been shown that the majority of epidermal T lymphocytes found in psoriatic lesions produce interferon- and no or very little IL-4, indicating that these cells belong to the TH1 subset [25]. Moreover, these cells produce high amounts of IL-2 but little or no IL-10 or tumour necrosis factor-
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IL-2 is an inflammatory cytokine that is also found in RA. The amount of IL-2 present in the synovial fluid of patients with RA is low compared with other cytokines. It is present in nearly all RA fluids but absent from fluids from patients with osteoarthritis [26]. Anti-cytokine therapy for RA targets inflammatory cytokines, such as TNF- and IL-1. Unfortunately, when treatment ceases, disease activity can increase once again. A recent placebo-controlled trial in RA of an anti-IL-2 agent (DAB486 IL-2) has revealed a modest improvement in disease activity [27].
We have measured serum MMP-1 and TIMP-1 levels in patients with PsA and compared this with sibling and local controls. Serum levels in sibling controls will enable us to determine whether these enzymes are associated with PsA or whether they are genetically determined.
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Patients and methods |
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Serum samples were collected from (a) index cases with PsA (subtype: RA n = 43, distal interphalangeal disease (DIP) n = 2, oligoarticular n = 15, spondyloarthropathy n = 9, enthesitis n = 1), (b) siblings with PsA (n = 15), (c) siblings with psoriasis (Ps) (n = 21), (d) unaffected siblings (n = 67) and (e) local healthy blood donor controls (n = 98). Table 1 illustrates the demographics of the subjects included in the study.
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Laboratory analysis
Total MMP-1 assay. The enzyme-linked immunosorbent assay (ELISA) measures both proenzyme and active enzyme. The limit of detection of this assay was 5 ng/ml. The technique used has been slightly modified from that previously published [11]. Plates were coated with 2 mg/ml RRU-CL1 antibody and samples diluted in protein diluent (phosphate-buffered saline containing 0.1% Tween and 0.5 mg/ml bovine serum albumin). All other conditions and times were identical to the original protocols.
Total TIMP-1 assay. The ELISA used measures free and bound TIMP-1, and was performed using a method previously reported [30].
Statistical analysis
Data were analysed using the statistical software package Arcus Biostat version 1.1 in conjunction with Microsoft Excel. Because the patients serum levels of MMP-1 and TIMP-1 did not follow a Gaussian distribution, results are given as median values with the interquartile range. Differences between median scores were analysed with the non-parametric MannWhitney U-test and for comparisons between different study groups we used the KruskalWallis one-way analysis of variance.
Ethical approval was obtained from Newcastle and North Tyneside Joint Ethics Committee.
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Results |
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We compared the serum levels of MMP-1 and TIMP-1 in our PsA and sibling populations with local control data (Figs 1 and 2). MMP-1 and TIMP-1 levels were significantly increased in both the index cases and the group including all siblings (irrespective of presence of psoriasis) compared with the controls (P < 0.0001). Using the MannWhitney test there was no statistical difference between the index cases (all of whom had PsA) and the siblings, or between siblings with or without psoriasis. There was no difference in levels of either MMP-1 or TIMP-1 between male and female patients. Also there was no correlation with the markers of inflammation, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP).
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When our data were analysed according to the age of onset of psoriasis in index cases (type I onset <40 yr, type II onset >40 yr), we found no difference in MMP-1 levels but a significant increase in TIMP-1 levels in type II disease (n = 15, P = 0.03) (Fig. 3) compared with type I disease (n = 56). A plot of patients ages vs MMP-1 or TIMP-1 showed no correlation. There was no difference in either MMP-1 or TIMP-1 levels and type of psoriasis in the sibling cohort.
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Discussion |
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There was a trend for those patients with rheumatoid pattern PsA or a DIP pattern of joint involvement to have increased MMP-1 levels, but this did not achieve statistical significance. A larger study is required to confirm or refute this observation. We were unable to demonstrate differences between the remaining subtypes of PsA. However, there was a significantly increased level of serum TIMP-1 in patients with rheumatoid pattern disease (P = 0.05). These findings were consistent irrespective of the disease classification used [28, 31]. TIMP-1 levels in patients with RA are known to correlate with disease activity (CRP and ESR) [19, 32], therefore this increased serum level in patients with rheumatoid pattern PsA may be a reflection of the number of joints affected (by definition, patients with rheumatoid pattern PsA have more joints involved, therefore more chance of active synovitis than other PsA subtypes).
Our data reveal significantly increased levels of MMP-1 and TIMP-1 in siblings with psoriasis alone compared with controls (P < 0.0001). There was no difference in metalloproteinase levels between the patterns of skin involvement of psoriasis in index cases or siblings, however there was a significant increase in TIMP-1 levels in type II onset psoriasis (onset age >40 yr). We have shown that, as in patients with RA [13, 19], MMP-1 and TIMP-1 levels in patients with PsA do not correlate with age, therefore this observation that TIMP-1 levels are increased in type II onset psoriasis suggests a link with cutaneous psoriasis and warrants further investigation. If psoriatic lesions are known to be inflammatory and plaque cells are producing cytokines, then it is possible that metalloproteinases are induced and therefore also playing a role in the pathogenesis of psoriasis.
In conclusion, our results show increased levels of MMP-1 and TIMP-1 in index cases with PsA and in their siblings compared with controls. We also found increased levels of TIMP-1 in subjects with rheumatoid pattern PsA, but this needs validating in a larger study. Finally, we also demonstrated increased levels of TIMP-1 in type II onset psoriasis. Metalloproteinases are known to play an important role in the pathogenesis of rheumatoid arthritis; this study has suggested that there is a difference between the disease subtypes of psoriatic arthritis and types of psoriasis, which warrants further work.
The authors have declared no conflicts of interest.
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References |
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