Circulating Retinol-Binding Protein 4 as a Possible Biomarker of Treatment Response for Ankylosing Spondylitis: An Array-Based Comparative Study

The Hepatokine RBP4 Links Metabolic Diseases to Articular Inflammation

OBJECTIVES

This study investigates the role of retinol binding protein 4 (RBP4) in an articular context. RBP4, a vitamin A transporter, is linked to various metabolic diseases.

METHODS

Synovial fluid RBP4 levels were assessed in crystalline arthritis (CA) patients using ELISA. RBP4's impact on articular cell types was analysed in vitro through RT-PCR and flow cytometry. Proteomic analysis was conducted on primary human osteoarthritis chondrocytes (hOACs).

RESULTS

Synovial fluid RBP4 concentrations in CA patients correlated positively with glucose levels and negatively with synovial leukocyte count and were elevated in hypertensive patients. In vitro, these RBP4 concentrations activated neutrophils, induced the expression of inflammatory factors in hOACs as well as synoviocytes, and triggered proteomic changes consistent with inflammation. Moreover, they increased catabolism and decreased anabolism, mitochondrial dysfunction, and glycolysis promotion. Both in silico and in vitro experiments suggested that RBP4 acts through TLR4.

CONCLUSIONS

This study identifies relevant RBP4 concentrations in CA patients' synovial fluids, linking them to hypertensive patients with a metabolic disruption. Evidence is provided that RBP4 acts as a DAMP at these concentrations, inducing robust inflammatory, catabolic, chemotactic, and metabolic responses in chondrocytes, synoviocytes, and neutrophils. These effects may explain RBP4-related metabolic diseases' contribution to joint destruction in various rheumatic conditions like CA.

Measurement of pre-treatment inflammatory cytokine levels is valuable for prediction of treatment efficacy to tumor necrosis factor inhibitor in axial spondyloarthritis patients

Aim

To evaluate the correlation of inflammatory cytokines with the treatment response to tumor necrosis factor inhibitor (TNFi) in axial spondyloarthritis (axSpA) patients.

Methods

This study enrolled 86 axSpA patients and 20 healthy controls (HCs). Inflammatory cytokines including tumor necrosis factor‐α (TNF‐α), interleukin (IL)‐1β, IL‐6, IL‐12, IL‐17A, IL‐21, IL‐23, and IL‐32 were determined in serum samples of axSpA patients before treatment and in HCs after enrollment. All patients received 40 mg adalimumab every 2 weeks for 12 weeks; meanwhile, ASAS40 (40 criteria of the Assessment by the SpondyloArthritis International Society) response rates were evaluated at weeks 2, 4, 8, and 12.

Results

Most inflammatory cytokines were elevated in axSpA patients compared with HCs (all P < 0.05) except for IL‐32 (P = 0.101). In axSpA patients, ASAS40 response rates were 0%, 19.5%, 34.5%, 47.1%, and 56.3% at weeks 0, 2, 4, 8, and 12, respectively. Baseline [interquartile range] IL‐6 (47.3 [32.5‐53.4] pg/mL vs 31.7 [23.0‐50.9] pg/mL, P = 0.005) and IL‐17A (127.9 [90.7‐149.5] pg/mL vs 96.6 [56.1‐112.6] pg/mL, P < 0.001) were higher in axSpA patients with ASAS40 response compared with those without ASAS40 response, while baseline TNF‐α, IL‐1β, IL‐12, IL‐21, IL‐23, and IL‐32 were not different between them (all P > 0.050). Multivariate logistic regression analysis disclosed that baseline IL‐17A (P = 0.037), C‐reactive protein (P = 0.012), and history of TNF inhibitor (P = 0.029) were independently associated with ASAS40 response. Furthermore, baseline IL‐17A, C‐reactive protein, history of TNFi, and their combination had an acceptable to good ability for predicting ASAS40 response.

Conclusion

Measurement of pre‐treatment inflammatory cytokine levels is valuable for predicting treatment efficacy of TNFi in axSpA patients.

Leukemia inhibitory factor is dysregulated in ankylosing spondylitis and contributes to bone formation

AIM

Ankylosing spondylitis (AS) is a chronic inflammatory disease. However, the key inflammatory cytokines disrupted in this disease are not well defined. In this study, we performed protein array and multiple protein quantification to investigate the differentially expressed cytokines in plasma between AS patients and healthy subjects.

METHOD

In the discovery cohort, 5 AS patients who never underwent biologic therapy and 5 gender- and age-matched healthy subjects were enrolled in the protein array analysis. Another 40 AS patients and 20 healthy participants were recruited in the validation stage. In addition, the messenger RNA and protein levels of osteogenesis-related genes were quantified in hFOB1.19 cells in an in vitro osteoblast model.

RESULTS

Of the 318 cytokines found to be differentially expressed by protein array, leukemia inhibitor factor (LIF) was significantly increased in AS patients as compared to controls. The "signaling by interleukins" pathway was the most enriched pathway in AS patients, and "signaling by interleukins"-related cytokines, including LIF, interleukin (IL)-6, IL-23, and IL-31, were significantly differentially expressed in the validation stage. Additionally, we correlated the expression of LIF with C-reactive protein (CRP) and inflammation of magnetic resonance imaging lesions in the spine (MRI-SPINE) in AS patients. We further analyzed the effects of LIF in hFOB cells and found that LIF promoted the growth factor receptor-bound protein 2 / phospho-extracellular signal-regulated kinase / runt-related transcription factor 2 / alkaline phosphatase pathway at the protein level and activated several osteogenesis-related genes (RUNX2 and BGLAP).

CONCLUSION

LIF was increased in the plasma of AS patients as compared with healthy subjects and significantly correlated with inflammation indices (CRP and MRI-SPINE) in AS patients. Thus, LIF may play a critical role in the pathogenesis of AS via promoting osteogenic differentiation.

Serum Amyloid A in Inflammatory Rheumatic Diseases: A Compendious Review of a Renowned Biomarker

Serum amyloid A (SAA) is an acute phase protein with a significant importance for patients with inflammatory rheumatic diseases (IRD). The central role of SAA in pathogenesis of IRD has been confirmed by recent discoveries, including its involvement in the activation of the inflammasome cascade and recruitment of interleukin 17 producing T helper cells. Clinical utility of SAA in IRD was originally evaluated nearly half a century ago. From the first findings, it was clear that SAA could be used for evaluating disease severity and monitoring disease activity in patients with rheumatoid arthritis and secondary amyloidosis. However, cost-effective and more easily applicable markers, such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), overwhelmed its use in clinical practice. In the light of emerging evidences, SAA has been discerned as a more sensitive biomarker in a wide spectrum of IRD, especially in case of subclinical inflammation. Furthermore, a growing number of studies are confirming the advantages of SAA over many other biomarkers in predicting and monitoring response to biological immunotherapy in IRD patients. Arising scientific discoveries regarding the role of SAA, as well as delineating SAA and its isoforms as the most sensitive biomarkers in various IRD by recently developing proteomic techniques are encouraging the revival of its clinical use. Finally, the most recent findings have shown that SAA is a biomarker of severe Coronavirus disease 2019 (COVID-19). The aim of this review is to discuss the SAA-involving immune system network with emphasis on mechanisms relevant for IRD, as well as usefulness of SAA as a biomarker in various IRD. Therefore, over a hundred original papers were collected through an extensive PubMed and Scopus databases search. These recently arising insights will hopefully lead to a better management of IRD patients and might even inspire the development of new therapeutic strategies with SAA as a target.