Hydroxyproline is a biomarker to differentiate early undistinguishable cases of osteoarthritis rather than rheumatoid arthritis.

Abstract

Background: Osteoarthritis (OA) and rheumatoid arthritis (RA) are the most frequent inflammatory diseases of the musculoskeletal system, which could not be differentiated in their early stages, and characterized by degradation of articular cartilage and impairment of joint function. Sometimes, criteria and radiography are not insufficient to distinguish early-stages of RA and OA and predict disease course, and therefor biomarkers that help clinicians to early diagnose disease are essential.

Objective: The aim of this study is to estimate serum level of Matrix metalloproteinase 3 (MMP3) and hrdroxyproline (HP) in early RA and OA patients to see if they can be used to differentiate both diseases at their early stages. 

Patients and methods: The aim of this study is to estimate serum level of Matrix metalloproteinase 3 (MMP3) and hrdroxyproline (HP) in early RA and OA patients to see if they can be used to differentiate both diseases at their early stages 

Results: We found a highly significant elevation of serum MMP3 in OA patients group compared to RA patients and control groups.  We also found a highly significant elevation  of  MMP3 in RA patients than control group,(P < 0.001). Meanwhile, we found a highly significant elevation of HP in OA patients than in RA patients and control groups, (P < 0.001), whereas there was no significant difference between HP in RA patients and control groups (P > 0.05).

Conclusion: Our results suggest that serum levels of Hydroxyproline (HP) rather than MMP3 could be used as a potential biomarker for early differentiation between osteoarthritis (OA) and rheumatoid arthritis (RA) when diagnostic criteria failed to be fulfilled.

Keywords: Metalloproteinase 3, Hydroxyproline, Osteoarthritis, Rheumatoid arthritis

Osteoarthritis (OA) is the most frequent disease of the musculoskeletal (MSK) system. OA affects millions of individuals each year. The knee is one of the most common joint involved in OA, with symptomatic knee OA has been reported in 6-10% of the adult population (1).

The diagnosis of OA is generally based on clinical and radiographical findings, which are insufficient to determine early-stage OA and predict disease course, and therefor biomarkers that help clinicians early diagnose, assess disease activity, predict prognosis and monitor response to therapy are essential (2).

On the other hand, rheumatoid arthritis (RA) is an autoimmune disease that results in a chronic, systemic inflammatory disorder that may affect many tissues and organs, but principally attacks synovial joints, leading to synovial hypertrophy and chronic joint inflammation along with extra-articular manifestations, and theorized to occur in genetically susceptible individuals (3)

The initial presenting features of early RA do not substantially differ from other inflammatory arthritis. So prior to definite diagnosis patients with early RA are usually classified as undifferentiated arthritis which difficultly can be discriminated from other inflammatory arthritis. Up to now, early RA was denoted to patients with disease duration of less than 2 years. (4) 

The degradation of articular cartilage and the impairment of joint function are characteristic findings of both Rheumatoid arthritis (RA) and osteoarthritis (OA). (5) 

The articular cartilage consists of chondrocytes and extracellular matrix (ECM). The ECM of the normal cartilage is in a state of dynamic equilibrium between synthesis and degradation of collagen. This balance is disturbed in RA and OA diseases in favor of proteolysis, which is ascribed to pathologic cartilage destruction (6) 

The Matrix metalloproteinases (MMPs) secreted from the chondrocytes are the main enzymes responsible for this destruction and collagen degradation (7,8) 

It has been suggested that MMP-3 is a marker of synovitis derived from the joint because it is produced by synovial fibroblasts of the rheumatoid joints and not by normal synovial cells.(9,10)  

Hydroxyproline is known as one of the specific amino acids of collagens, which are the substrates of MMPs. Determination of hydroxyproline provides useful information for the diagnosis and prognosis of diseases caused by disorders of the collagen metabolism (11). 

Aim of the Study

Determination of MMP3 & HP in patients with early knee osteoarthritis and early RA patients in hope to discover biomarkers that help clinicians to early diagnose, assess disease activity, predict prognosis and monitor response to therapy. 

Patients and Methods

This study was conducted on 

1. Forty (40) patients diagnosed having early knee osteoarthritis according to EULAR & Kellgren-Lawrence radiographic grading criteria. 

   
   

2. Forty (40) patients with early RA(disease duration <3yrs) : 

   
   

3. Forty (40) subjects of age and sex matched normal volunteers served as the control group. 

   
   

All patients and controls were recruited from the outpatient clinic of Rheumatology and Rehabilitation, Al Zahra University hospital. 

All participants were subjected to full history taking, full clinical musculoskeletal examination, and laboratory investigations with estimation of serum MMP3 & HP by Sandwich ELISA technique. Also they were subjected to plain x-ray of knee joints.

All OA and RA patients were selected according to Inclusion and exclusion criteria for each disease. 

RESULTS:

We found a highly significant elevation of serum MMP3 in OA patients group compared to RA patients and control groups.  We also found a highly significant elevation of MMP3 in RA patients than control group,(P < 0.001). Meanwhile, we found a highly significant elevation of HP in OA patients than in RA patients and control groups, (P < 0.001), whereas there was no significant difference between HP in RA patients and control groups (P > 0.05).

Table (1):. Demonstration of serum levels of MMP3 and HP in all groups.

DISCUSSION 

Osteoarthritis (OA) is a chronic, progressive, and degenerative osteoarthropathy, manifested in joint pain, tenderness, stiffness, joint swelling, function limitation, and joint deformity. In OA, there is excessive degradation, leading to progressive loss of matrix proteins and joint integrity (12).

 On the other hand, rheumatoid arthritis is a chronic inflammatory joint disease, which can cause cartilage and bone damage as well as disability. Early diagnosis is key to optimal therapeutic success, particularly in patients with well-characterized risk factors for poor outcomes such as high disease activity, presence of autoantibodies, and early joint damage. (3).

Many patients with early disease manifestations are not fulfilling diagnostic criteria for any of the diseases, which form a problem in prescribing and managing the disease.  Hence, we went to look for a biomarker which may facilitate early distinguishing both diseases at their early stages. 

Many studies were carried out demonstrated that serum MMP3 was elevated in OA patients than  normal subjects (13-17),  the same we found that serum levels of MMP3 were significantly elevated in knee OA patients than in normal persons. 

We also found a significant increase of MMP3 in RA patients than in normal persons. 

Thus, MMP3 could not differentiate between both diseases in early stages, although it was significantly higher In OA than RA patients.

As regards serum hydroxyproline (HP), we found a highly significant elevation of its level in OA patients than both RA and normal controls, which agrees with other researchers.(18,19) 

Meanwhile, there was no significant difference between HP serum level in RA patients and normal controls.This agrees with others who found that plasma hydroxyproline was increased 44% in early OA and 58% in other non-RA but not increased in early RA with respect to healthy controls.(20) 

CONCLUSION 

Our results suggest that serum levels of Hydroxyproline (HP) rather than MMP3 could be used as a potential biomarker for early differentiation between osteoarthritis (OA) and rheumatoid arthritis (RA) when diagnostic criteria failed to be fulfilled. 

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