Proteomic Profile Analysis of Synovial Fluid in Patients With Anterior Cruciate Ligament Tears

Periostin Is a Biomarker for Anterior Shoulder Instability: Proteomic Analysis of Synovial Fluid

BACKGROUND

The incremental biological changes in the synovial microenvironment of the shoulder in acute and chronic instability that may contribute to joint degeneration are poorly understood. Proteomic analysis of synovial fluid in patients with shoulder instability may improve our understanding of proteins that are shed into shoulder synovial fluid after an injury.

HYPOTHESIS

Injury-specific factors such as the direction of instability and the severity of glenoid and humeral bone loss are associated with the proteome of synovial fluid in patients with shoulder instability.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Synovial fluid lavage samples were compared between patients with anterior (n = 12) and posterior (n = 8) instability and those without instability (n = 5). Synovial proteins were identified with liquid chromatography-tandem mass spectrometry. Orthogonal validation of protein targets found to be significant on tandem mass spectrometry was performed in a separate set of prospective patients with Western blotting. Data were processed and analyzed, and P values were adjusted with the Benjamini-Hochberg method for multiple comparisons.

RESULTS

A total of 25 patients were included. Tandem mass spectrometry identified 720 protein groups in synovial fluid of patients with shoulder instability. There were 4 synovial proteins that were significantly expressed in patients with anterior instability relative to posterior instability: periostin (POSTN) (adjusted P value = .03; log fold change [logFc] = 4.7), transforming growth factor beta-induced protein ig-h3 (adjusted P value = .05; logFc = 1.7), collagen type VI alpha-3 chain (adjusted P value = .04; logFc = 2.6), and coagulation factor V (adjusted P value = .04; logFc = -3.3). Among these targets, POSTN showed a moderate correlation with the Hill-Sachs lesion size (r = 0.7). Prospective validation with Western blotting confirmed a significantly higher level of POSTN in synovial fluid of patients with anterior instability (P = .00025; logFc = 5.1).

CONCLUSION

Proteomic analysis enriched our understanding of proteins that were secreted into shoulder synovial fluid of patients with shoulder instability. The identification of POSTN, a proinflammatory catabolic protein involved with tissue remodeling and repair, as a significant target in anterior shoulder instability is a novel finding. Therefore, further study is warranted to determine the role that POSTN may play in the progression of bone loss and posttraumatic osteoarthritis.

CLINICAL RELEVANCE

Proteomic analysis of synovial fluid in patients with shoulder instability improved our understanding of this abnormality after an injury.

Evidence of Bacterial Metabolism in Synovial Fluid of Patients With Graft Failure After Anterior Cruciate Ligament Reconstruction: A Microbiological Comparison of Primary Anterior Cruciate Ligament and Hamstring Tendon Autograft Ruptures

PURPOSE

To investigate whether the bacterial presence in a primary ruptured native anterior cruciate ligament (ACL) differs from that in a ruptured hamstrings ACL autograft and whether low-grade infections cumulatively can be detected in the case of graft failure.

METHODS

In a retrospective case-control study with prospectively collected data, synovial fluid aspirates and tissue samples of failed ACL grafts were examined for evidence of bacterial colonization and compared to samples of the native ACL in primary ACL reconstruction (ACLR) using microbiological culture, 16S rRNA-PCR and histopathological examination. Furthermore, synovial fluid aspiration was investigated for possible future biomarkers for a low-grade infection.

RESULTS

A total of 112 consecutive patients undergoing primary ACLR without history of previous surgeries to the affected knee (n = 59) and revision ACLR after reconstruction with a hamstring tendon autograft (n = 53) were recruited from one center. No patient had a history or showed clinical signs of infection. A total of 389 samples were analyzed by culture. Bacteria were detected in 9.4% of patients with a graft rupture (n = 5/53) compared to 3.4% of patients with a primary ACL rupture (n = 2/59) showing no statistical difference (P = .192). One patient with a "true" low-grade infection was found in our study population, resulting in a prevalence of 1.9% (1/53) in the graft group. The percentage of polymorphonuclear leukocytes (PMN%) as a highly sensitive marker for joint infections was significantly higher in aspirated synovial fluid of graft ruptures (27% ± 3% vs 20% ± 4%; P = .032), as well as glucose levels were significantly lower (83 mg/dL ± 2 mg/dL vs 88 mg/dL ± 2 mg/dL; P = .042).

CONCLUSIONS

Synovial fluid obtained before revision ACLR showed a higher percentage of polymorphonuclear leukocytes and lower glucose levels compared with primary ACLR, suggesting bacterial metabolism and demonstrating that the intra-articular milieu changes significantly after ACLR. Tissue samples of ACL grafts revealed a low-grade infection in one case, although overall cultivable bacterial presence did not differ significantly when compared to samples of a native ACL.

LEVEL OF EVIDENCE

Level III, retrospective case-control study.

Synovial Fluid Proteomics From Serial Aspirations of ACL-Injured Knees Identifies Candidate Biomarkers

BACKGROUND

Anterior cruciate ligament (ACL) tears often result in knee effusion and an increased risk for developing knee osteoarthritis (OA) in the long run. The molecular profile of these effusions could be informative regarding initial steps in the development of posttraumatic OA after an ACL tear.

HYPOTHESIS

The proteomics of knee synovial fluid changes over time after ACL injury.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Synovial fluid was collected from patients with an acute traumatic ACL tear presenting to the office for evaluation (18.31 ± 19.07 days from injury) (aspiration 1) and again at the time of surgery (35.41 ± 58.15 days after aspiration 1 (aspiration 2). High-resolution liquid chromatography mass spectrometry was used to assess the quantitative protein profile of synovial fluid, and differences in protein profile between the 2 aspirations were determined computationally.

RESULTS

A total of 58 synovial fluid samples collected from 29 patients (12 male, 17 female; 12 isolated ACL tear, 17 combined ACL and meniscal tear) with a mean age and body mass index of 27.01 ± 12.78 years and 26.30 ± 4.93, respectively, underwent unbiased proteomics analysis. The levels of 130 proteins in the synovial fluid changed over time (87 high, 43 low). Proteins of interest that were significantly higher in aspiration 2 included CRIP1, S100A11, PLS3, POSTN, and VIM, which represent catabolic/inflammatory activities in the joint. Proteins with a known role in chondroprotection and joint homeostasis such as CHI3L2 (YKL-39), TNFAIP6/TSG6, DEFA1, SPP1, and CILP were lower in aspiration 2.

CONCLUSION

Synovial fluid from knees with ACL tears exhibits an increased burden of inflammatory (catabolic) proteins relevant to OA with reduced levels of chondroprotective (anabolic) proteins.

CLINICAL RELEVANCE

This study identified a set of novel proteins that provide new biological insights into the aftermath of ACL tears. Elevated inflammation and decreased chondroprotection could represent initial disruption of homeostasis, potentially initiating the development of OA. Longitudinal follow-up and mechanistic studies are necessary to assess the functional role of these proteins in the joint. Ultimately, these investigations could lead to better approaches to predict and possibly improve patient outcomes.

Osteoarthritis as an Umbrella Term for Different Subsets of Humans Undergoing Joint Degeneration: The Need to Address the Differences to Develop Effective Conservative Treatments and Prevention Strategies

Osteoarthritis (OA) of joints such as the knee and hip are very prevalent, and the number of individuals affected is expected to continue to rise. Currently, conservative treatments after OA diagnosis consist of a series of increasingly invasive interventions as the degeneration and pain increase, leading very often to joint replacement surgery. Most interventions are focused on alleviating pain, and there are no interventions currently available that stop and reverse OA-associated joint damage. For many decades OA was considered a disease of cartilage, but it is now considered a disease of the whole multi-tissue joint. As pain is the usual presenting symptom, for most patients, it is not known when the disease process was initiated and what the basis was for the initiation. The exception is post-traumatic OA which results from an overt injury to the joint that elevates the risk for OA development. This scenario leads to very long wait lists for joint replacement surgery in many jurisdictions. One aspect of why progress has been so slow in addressing the needs of patients is that OA has been used as an umbrella term that does not recognize that joint degeneration may arise from a variety of mechanistic causes that likely need separate analysis to identify interventions unique to each subtype (post-traumatic, metabolic, post-menopausal, growth and maturation associated). A second aspect of the slow pace of progress is that the bulk of research in the area is focused on post-traumatic OA (PTOA) in preclinical models that likely are not clearly relevant to human OA. That is, only ~12% of human OA is due to PTOA, but the bulk of studies investigate PTOA in rodents. Thus, much of the research community is failing the patient population affected by OA. A third aspect is that conservative treatment platforms are not specific to each OA subset, nor are they integrated into a coherent fashion for most patients. This review will discuss the literature relevant to the issues mentioned above and propose some of the directions that will be required going forward to enhance the impact of the research enterprise to affect patient outcomes.