rheumatoid arthritis ( ra ) is characterised by a progressive , erosive polyarthritis , resulting in immune - mediated joint destruction and eventual disability.components of the immunoinflammatory response include acute phase proteins , auto - reactive t cells , b cells , and their respective inflammatory mediators .
the consequence is a self - perpetuating chronic inflammatory response involving a complex interplay between infiltrating inflammatory cells and the structural cells of the synovial joint [ 1 , 2 ] .   
matrix metalloproteinase-3 ( mmp-3 ) is produced predominantly by chondrocytes and synovial fibroblasts and is found in high concentrations in the synovial fluid , with elevated levels also found in the serum of ra patients .
mmp-3 production is upregulated by the proinflammatory cytokines il-1 , tnf , ifn  , and il-17a , as well as by serum amyloid a ( saa ) , an acute phase reactant , with counter - regulatory inhibition from il-4 and il-13 [ 410 ] . cytokine / saa - driven production of mmp-3 in the rheumatoid joint appears to be a key mediator of cartilage destruction , while bone resorption is facilitated by mmp-3-mediated removal of the outer osteoid layer , enabling attachment of osteoclasts to the underlying bone .
moreover , mmp-3 mediates the proteolytic activation of pro - mmp-9 released from both inflammatory and structural cells . aside from its role in promoting the recruitment of neutrophils , monocytes , t cells , and osteoclasts
, mmp-9 promotes the release of membrane - bound vascular endothelial growth factor ( vegf ) , thereby contributing to angiogenesis and disease progression .   with respect to its diagnostic and prognostic potential , elevated serum concentrations of mmp-3 , while having no specificity for ra , have been found in many [ 1321 ] , but not all [ 2225 ] , studies to correlate with disease severity and response to chemotherapy .
however , the global interrelationships of mmp-3 with proven genetic markers of disease susceptibility , such as the shared epitope ( se ) , as well as with other systemic biomarkers such as autoantibodies , cytokines , cartilage breakdown products , and the acute phase reactants crp and saa in particular , have not been well characterised .  
crp and saa are synthesised in the liver in response to proinflammatory cytokines such as tnf , il-1 , and il-6 .
monocytes / macrophages , endothelial cells , synovial fibroblasts , and chondrocytes can also produce saa .
unlike crp , saa is also locally expressed and accumulates in inflamed tissue with histological studies demonstrating expression of saa in the perivascular and lining layer of ra synovial tissue , in regions of leukocyte recruitment and angiogenesis , especially at the cartilage pannus junction .
saa is apparently a more sensitive marker of inflammation in ra than crp , with the saa / crp ratio , possibly being of more significance .
saa augments the inflammatory response in a cytokine - like fashion by attracting monocytes / macrophages , leukocytes and t lymphocytes , while promoting neutrophil survival and endothelial activation and stimulating the production of the proinflammatory mediators tnf , il-1 , il-6 , il-8 , and il-17 , thus initiating an amplifying loop .
exposure of synovial fibroblasts and chondrocytes to saa promotes mmp-3 mediated adhesion molecule expression , as well as phagocytosis and chemotaxis of monocytes and neutrophils , thereby contributing to synovial inflammation , hyperplasia , angiogenesis , and joint destruction .
saa has also been implicated in the pathogenesis of atherosclerosis and premature cardiovascular disease , an important aspect in the management of patients with ra , thus making it a potential target for therapy to control both ra and its complications .  
the objectives of the current study were to assess the relationships between circulating mmp-3 and ( i ) se ; ( ii ) biomarkers of inflammation and cartilage degradation ; ( iii ) disease activity and radiographic changes in comparison with crp and saa in a cohort of predominantly black female south africans with early disease - modifying antirheumatic drugs ( dmard ) naive ra .
baseline data was reviewed from 128 patients who were part of the gauteng rheumatoid arthritis trial ( great ) , a prospective study of early dmard naive ra patients [ 2729 ] .
patients were recruited from the rheumatology clinics of two tertiary hospitals , chris hani baragwanath hospital and steve biko academic hospital , attached to the universities of the witwatersrand and pretoria , south africa , respectively , and the study was approved by the research ethics committees of the faculties of health sciences of both institutions .  
demographic data , duration of symptoms , education level , medication history , clinical assessment including 28 joint count , and the presence of extra - articular involvement were recorded , as was disease activity measured according to the health questionnaire disability index ( haq - di ) and simplified disease activity index ( sdai ) , and have been described in detail elsewhere for this cohort of patients [ 2729 ] .  
radiographs of the hands and feet were scored according to the modified larsen score . in each case , 32 joint areas were scored : 8 pip ( proximal interphalangeal ) , 2 thumb ip ( interphalangeal ) , 10 mcp ( metacarpophalangeal ) , 4 areas in each wrist , and 8 mtp ( metatarsophalangeal ) joints .
venous blood was collected as described previously , followed by prompt separation of serum and storage at minus 20c until analysed .  
these were assayed using nephelometric , immunofluorimetric , and multiplex suspension bead array procedures as previously described , while haemoglobin concentrations and erythrocyte sedimentation rates were measured using standard haematological procedures .  
serum concentrations of mmp-3 were measured using the quantikine total mmp-3 immunoassay ( elisa ) according to the instructions supplied by the manufacturer ( r & d systems , minneapolis , mn , usa ) and the results expressed as nanograms ( ng)/ml serum .
serum levels were measured in healthy controls ( 15 females and 10 males , age range 2464 ) .  
serum levels were measured using the kamiya human comp elisa system ( kamiya biomedical company , seattle , wa , usa ) and the results expressed as micrograms / ml .
this was performed as described previously using high - resolution reverse sequence - specific oligonucleotide probes and luminex technology , with classification as se or non - se genotypes according to the method of tezenas du montcel et al .
[ 30 , 31 ] .   descriptive statistics of continuous variables were done by using a measure of central tendency ( mean or median ) and a measure of variability ( standard deviation or range ) .
frequencies and percentages were used to describe categorical variables of the nominal or ordinal scales .
cytokine data were not normally distributed , and therefore the spearman 's pairwise correlations were used to find the strength of each cytokine , demographics with mmp-3 and comp , and between themselves .
a p value of < 0.05 was considered statistically significant , while , in the case of the cytokines , a p value of < 0.003 following correction for multiple comparisons was used .
statistical analysis was done using stata version 12.0 ( stata corporation , college station , tx , usa ) .
as seen in table 1 , the majority of patients were middle - aged black females , with a mean disease duration of almost 12 months .
patients had high disease activity as reflected by a mean das of 6.28 and moderate to high functional disability .
erosions were seen in 52% , and the mean larsen score was 22.4 ( 12.7 ) .  
serum mmp-3 levels were significantly ( p < 0.0001 ) higher in the ra patients relative to the healthy control subjects . using cut - off values of 18  ng / ml and 1.99  g / ml for mmp-3 and comp , respectively ( based on the mean values for the healthy control subjects + 2 standard deviations ) , the mean mmp-3 and comp values for the control groups compared favourably with previous studies of 46 and 291 healthy controls respectively [ 32 , 33 ] .
the respective frequencies of elevated mmp-3 and comp levels for the ra patients were 56.25% and 34.6% ( table 1 ) .  
correlations that achieved statistical significance are shown in table 2 , which demonstrates associations of serum mmp-3 with sdai , crp , saa , rf and comp .
there were no statistically significant associations of mmp-3 with haq - di , tender joint count , nodules , erosions , larsen score or acpa .  
we have previously reported that the circulating cytokine / chemokine / growth factor concentrations in this cohort of ra patients are significantly higher than in healthy control subjects . in the current study , circulating mmp-3
was found to correlate positively and significantly with il-6 , il-8 , il-12 , ifn- , and vegf ( r values 0.270.33 , p values <
0.0030.0001 ) , the strongest correlations being observed with il-8 > il-6 > ifn- and vegf ( table 3 ) .  
comp correlated positively and significantly with rf ( r = 0.23 , p < 0.006 ) , but not with any of the clinical indices or other inflammatory biomarkers . a weak positive correlation between comp and smoking history ( ever smoked )
subgroup analysis revealed no differences in mmp-3 , saa , crp , or comp levels in risk allele negative or positive patients .  
given the key role of saa in activating the synthesis of mmp-3 by synovial chondrocytes and fibroblasts [ 9 , 34 ] , correlations of this acute phase reactant , as well as those of crp , with clinical and traditional noncytokine indices of disease activity were determined and these are shown in table 4 .
correlations included evaluation of the saa / crp ratio , but this did not reveal any significant associations ( data not shown ) .
both acute phase proteins , especially crp , were found to have stronger associations with disease activity in early ra than mmp-3 .
consistent with data from other studies finding elevated mmp-3 levels in 62%80% of patients [ 14 , 35 ] , mmp-3 levels were found to be elevated in 56.25% of our patients .
although no correlations with se were detected , mmp-3 was found to correlate significantly with measures of disease activity , specifically sdai , esr , crp , and saa .
in addition to these , correlations with predominantly proinflammatory cytokines , especially il-8 , il-6 , ifn , and vegf ( table 3 ) , were also observed .
in a study of 144 patients with ra showed significant correlations with il-8 , il-1 and crp , the strongest correlation being with crp ( r = 0.601 , p < 0.001 ) . a smaller study by ribbens et al . in 20 patients with
ra showed correlations of mmp-3 and disease activity score ( das ) , crp , and il-6 level .   
few studies have examined serum levels of mmp-3 in a dmard nave early ra cohort of predominantly black females , exploring the associations with clinical parameters of disease activity , acute phase response , se , and a wide range of cytokines , chemokines , and growth factors .  
recent developments in the management of ra are aimed at rapid disease control , as well as early introduction of efficient therapies , which makes the search for useful biomarkers such as mmp-3 important .
this contention is underscored by an interest in the development of an automated serum detection procedure for mmp-3 and the recent introduction of a commercially available multibiomarker disease activity ( mbda ) test .
the mbda test includes mmp-3 in the quantitative assessment of disease activity , having shown significant correlations with das 28-crp ( auroc  =  0.77 ; p < 0.001 for seropositive patients and auroc  =  0.70 ; p < 0.001 for seronegative patients ) .   in the current study , the levels of circulating saa
, a mediator of synthesis of mmp-3 , as well as those of crp , were found to be elevated in 74.4% and 76.1% of patients , respectively , and correlated significantly with measures of disease activity , as described in previous studies , some of which suggest that saa is a more sensitive marker in ra than crp .
however , this was not confirmed in the current study , with crp being equivalent or slightly superior to saa as a marker of disease activity in early ra . because saa is also locally released and expressed in the synovial tissue
, we reasoned that the saa / crp ratio may be a more accurate index of disease activity than the individual biomarkers .
with regard to poor prognostic markers , such as the presence of nodules , erosive disease , and the larsen score , correlations with crp and saa , but not with mmp-3 , were evident .
no associations of saa or crp with the se risk alleles or comp were observed .  
importantly , the correlations of both crp and saa with sdai were considerably stronger than those of mmp-3 with sdai , demonstrating that measurement of either of these acute phase reactants , but preferably crp , is probably the best serological determinant of disease activity in early ra .  
cartilage destruction is one of the consequences of uncontrolled synovial proliferation , with serum levels of cartilage degradation products such as comp having been shown to be associated with ra disease activity and future radiological damage . in the current study , comp levels were elevated in 34.6% of patients compared to other studies showing percentage of elevated comp levels ranging from 41% to 67% [ 38 , 39 ] .
comp was found to correlate weakly with smoking history ( ever smoked ) , rf , and mmp-3 , but no correlations were found with measures of disease activity as reflected in some previous studies which described correlations with crp , das , esr , and rheumatoid nodules .
mmp-3 is an important effector of cartilage metabolism ; hence , the correlation with comp is not surprising .
although no correlations between comp and radiographic changes were found , this may simply reflect increased cartilage turnover rather than destruction in early disease .  
the correlation of mmp-3 with comp and lack thereof with the acute phase reactants studied may suggest that mmp-3 is a better biomarker to predict disease progression ; thus , combining measurement of crp with that of mmp-3 may be a useful strategy predict disease progression .   in conclusion ,
the most significant and original findings of the current study are ( i ) elevated levels of circulating mmp-3 , which may identify a subset of ra patients likely to develop severe disease , are significantly associated with sdai , proinflammatory cytokines , and most strongly with crp and saa ; ( ii ) crp and saa are more strongly correlated with disease activity in early ra than mmp-3 ; ( iii ) measurement of either crp or saa in combination with mmp-3 on presentation may be useful in the assessment of disease activity and prediction of progression in early ra .
 matrix metalloproteinase-3 ( mmp-3 ) is involved in the immunopathogenesis of rheumatoid arthritis ( ra ) , but little is known about its relationship to genetic susceptibility and biomarkers of disease activity , especially acute phase reactants in early ra . 
 mmp-3 was measured by elisa in serum samples of 128 disease - modifying , drug - nave patients and analysed in relation to shared epitope genotype , a range of circulating chemokines / cytokines , acute phase reactants , autoantibodies , cartilage oligomeric protein ( comp ) , and the simplified disease activity index ( sdai ) . 
 mmp-3 was elevated > 1.86  ng / ml in 56.25% of patients ( p < 0.0001 ) , correlated with several biomarkers , notably il-8 , il-6 , ifn  , vegf and comp ( r values = 0.220.33 , p < 0.0140.0001 ) and with crp and saa levels ( r = 0.40 and 0.41 , resp . , p < 0.0000 ) and sdai ( r = 0.29 , p < 0.0001 ) , but not with erosions or nodulosis . 
 however , the correlations of crp and saa with sdai were stronger ( respective values of 0.63 and 0.54 , p < 0.001 for both ) . 
 comp correlated with smoking , rf , and mmp-3 . 
 
 mmp-3 is significantly associated with disease activity , inflammatory mediators and cartilage breakdown , making it a potential biomarker of disease severity , but seemingly less useful than crp and saa as a biomarker of disease activity in early ra . 
1. Introduction
2. Patients and Methods
3. Results
4. Discussion