Proteomics on the Diagnostic Horizon: Lessons from Rheumatology

Guidelines for biomarkers in autoimmune rheumatic diseases - evidence based analysis

Autoimmune rheumatic diseases are characterised by an abnormal immune system response, complement activation, cytokines dysregulation and inflammation. In last years, despite many progresses in managing these patients, it has been shown that clinical remission is reached in less than 50% of patients and a personalised and tailored therapeutic approach is still lacking resulting in a significant gap between guidelines and real-world practice. In this context, the need for biomarkers facilitating early diagnosis and profiling those individuals at the highest risk for a poor outcome has become of crucial interest. A biomarker generally refers to a measured characteristic which may be used as an indicator of some biological state or condition. Three different types of medical biomarkers has been suggested: i. mechanistic markers; ii. clinical disease markers; iii. therapeutic markers. A combination of biomarkers from these different groups could be used for an ideal more accurate diagnosis and treatment. However, although a growing body of evidence is focused on improving biomarkers, a significant amount of this information is not integrated on standard clinical care. The overarching aim of this work was to clarify the meaning of specific biomarkers during autoimmune diseases; their possible role in confirming diagnosis, predicting outcome and suggesting specific treatments.

Axl, Ferritin, Insulin-Like Growth Factor Binding Protein 2, and Tumor Necrosis Factor Receptor Type II as Biomarkers in Systemic Lupus Erythematosus

OBJECTIVE

To evaluate the performance of 4 serum protein markers for detecting concurrent clinical activity in patients with systemic lupus erythematosus (SLE).

METHODS

Consecutive patients who fulfilled ≥4 American College of Rheumatology classification criteria for SLE and healthy controls were recruited for serologic testing of 4 protein markers identified by antibody-coated microarray screen, namely Axl, ferritin, insulin-like growth factor binding protein 2 (IGFBP-2), and tumor necrosis factor receptor type II (TNFRII). SLE disease activity was assessed by the Safety of Estrogens in Lupus Erythematosus National Assessment version of the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) and physician's global assessment (PGA). Levels of these markers were correlated with SLEDAI scores, and their sensitivity and specificity for clinical SLE activity were determined.

RESULTS

A total of 94 SLE patients (98% women, mean ± SD age 28.7 ± 9.4 years, mean ± SD disease duration 5.4 ± 5.0 years) and 49 healthy controls were studied. Fifty-two patients had clinically active SLE (defined as SLEDAI score ≥6 or having a flare). The serum concentrations of Axl, ferritin, IGFBP-2, and TNFRII were significantly higher in patients with active SLE than in those with inactive SLE or in controls. The levels of these markers correlated strongly and significantly with anti-double stranded DNA (anti-dsDNA), C3, and clinical SLEDAI and PGA scores. These markers were more specific, but less sensitive, in detecting concurrent SLE activity than elevated anti-dsDNA or depressed C3. Levels of Axl, TNFRII, and IGFBP-2, but not ferritin, could differentiate active renal from active nonrenal or inactive SLE. The specificity of Axl and IGFBP-2 for concurrent active lupus nephritis was higher than anti-dsDNA or C3.

CONCLUSION

Serum proteomic markers are potentially useful for diagnosing SLE and monitoring disease activity. The performance of Axl and IGFBP-2 in lupus nephritis should be further explored in a longitudinal cohort of SLE patients.

Proteomic toolbox for autoimmunity research

Autoimmune diseases are genetically complex and poorly understood, and may lead to clinically severe consequences including end-organ damage. Given this scenario, early biomarker discovery is becoming increasingly important for early diagnosis and treatment in these diseases. Among the different approaches tried, the application of proteomic analysis of body fluids has great potential as a non-invasive tool for early diagnosis in many different disease settings. During the past 10 years, proteomics-based approaches have made steady inroads into the study of various autoimmune diseases. In this review, we summarize the highlights of various traditional as well as novel proteomic methods, including 2D-MS/MS, multi-dimensional HPLC-MS/MS, CE-MS/MS, SELDI-TOF-MS/MS, iTRAQ and a variety of targeted antibody-based protein arrays, which have been particularly informative in the field of autoimmunity.

Proteomic diagnosis of Sjögren's syndrome

In the last few years, a growing interest has arisen in the application of proteomic analysis to rheumatic disease. Sjögren's syndrome is a systemic disease that affects exocrine glands directly, and is therefore expected to influence the composition of the whole human saliva and lachrymal fluid. Therefore, a rising number of studies have been performed in an attempt to characterize the salivary and lachrymal protein profiles of patients with Sjögren's syndrome by using a proteomic approach. This review summarizes the state of the art and the potential application of proteomics in the systematic search for diagnostic biomarkers in Sjögren's syndrome.