Molecular Imaging of Inflammatory Arthritis and Related Disorders

In vivo multimodal imaging of hyaluronan-mediated inflammatory response in articular cartilage

OBJECTIVE

One driving factor in the progression to posttraumatic osteoarthritis (PTOA) is the perpetuation of the inflammatory response to injury into chronic inflammation. Molecular imaging offers many opportunities to complement the sensitivity of current imaging modalities with molecular specificity. The goal of this study was to develop and characterize agents to image hyaluronan (HA)-mediated inflammatory signaling.

DESIGN

We developed optical (Cy5.5-P15-1) and magnetic resonance contrast agents (Gd-DOTA-P15-1) based in a hyaluronan-binding peptide (P15-1) that has shown anti-inflammatory effects on human chondrocytes, and validated them in vitro and in vivo in two animal models of PTOA.

RESULTS

In vitro studies with a near infrared (NIR) Cy5.5-P15-1 imaging agent showed a fast and stable localization of Cy5.5-P15-1 on chondrocytes, but not in synovial cells. In vivo NIR showed significantly higher retention of imaging agent in PTOA knees between 12 and 72 h (n = 8, Cohen's d > 2 after 24 h). NIR fluorescence accumulation correlated with histologic severity in cartilage and meniscus (ρ between 0.37 and 0.57, P < 0.001). By using in vivo magnetic resonance imaging with a Gd-DOTA-P15-1 contrast agent in 12 rats, we detected a significant decrease of T1 on injured knees in all cartilage plates at 48 h (-15%, 95%-confidence interval (CI) = [-18%,-11%]) while no change was observed in the controls (-2%, 95%-CI = [-5%,+1%]).

CONCLUSIONS

This study provides the first in vivo evidence that hyaluronan-related inflammatory response in cartilage after injury is a common finding. Beyond P15-1, we have demonstrated that molecular imaging can provide a versatile technology to investigate and phenotype PTOA pathogenesis, as well as study therapeutic interventions.

Correlation Between Diagnostic Imaging Findings of Sacroiliitis and Inflammation Parameters

Objectives Sacroiliitis is an inflammation of the sacroiliac joints. Diagnostic imaging has a very important role in the diagnosis of sacroiliac involvement in the disease process. In addition, laboratory parameters can also be useful for the detection of inflammation. This study aims to investigate the relationship between active sacroiliitis and subclinical inflammation parameters in patients who underwent MRI and 99mTc-methylene diphosphonate (MDP) bone scintigraphy.

Material and Methods This study includes 65 patients with suspected spondyloarthritis (SpA). Patients who had a sacroiliac MRI, a 99mTc-MDP bone scintigraphy and a complete blood count (CBC) within 3 months were reviewed retrospectively. Sacroiliac joints were evaluated bilaterally by using bone scintigraphy and MRI. Blood inflammation parameters were further assessed regarding evidence of probable sacroiliitis.

Results Significant differences were reported between MRI groups for sacroiliac indices (SII) (p=0.003), neutrophil-to-lymphocyte ratio (NLR) (p=0.008), C-reactive protein (CRP) (p = 0.037), and white blood cell (WBC) count (p=0.031). A significant correlation was found between active sacroiliitis and SII (p=0.001), CRP (p=0.000), erythrocyte sedimentation rate (ESR) (p=0.000), and NLR (p=0.001). Based on the ROC curve analysis, SII was found to have a sensitivity of 64.3% and specificity of 69.8%; NLR was found to have a sensitivity of 64.3% and specificity of 73.3% for diagnosing active sacroiliitis.

Conclusions Subclinical inflammation indices obtained from CBC and, particularly, NLR may contribute to disease activity assessment like acute-phase reactants. However, this needs to be confirmed in further studies.

Molecular Imaging of Infection: The First 50 Years

Despite significant advances in the understanding of microorganisms and an increased availability of antimicrobial therapy, infection remains a major cause of morbidity and mortality. The diagnosis can be challenging and imaging studies often are used for confirmation and localization. For nearly 50 years, molecular imaging agents have played an important role in the diagnosis of infection. Gallium-67 citrate was perhaps the first molecular imaging agent used for diagnosing and localizing infection. Poor imaging characteristics, along with a lack of specificity, and the long (usually 48-72 hours) interval between administration and imaging motivated investigators to search for alternatives. Currently the role of ⁶⁷Ga is limited to differentiating acute tubular necrosis from interstitial nephritis and as an alternative to ¹⁸F-FDG for indications, such as sarcoid, spondylodiscitis, and fever of unknown origin, when the latter is not available. The development, in the mid-1970s, of techniques for radiolabeling leukocytes that subsequently migrate to foci of infection was a significant advance and labeled leukocyte imaging still has a preeminent role in molecular imaging of infection. There are significant disadvantages to in-vitro labeled leukocyte imaging. Efforts devoted to developing in-vivo leukocyte labeling methods, however, met with only limited success. Over the past 20 years ¹⁸F-FDG has established itself as the molecular imaging agent of choice for fever of unknown origin, vasculitis, sarcoid, and spondylodiscitis. As useful as these agents are, their uptake is based on the host response to infection, not infection itself. Previous attempts at developing infection specific agents, including radiolabeled antibiotics, antibiotics, and vitamins like biotin were limited by poor results and/or limited availability and so investigators continue to focus on developing infection specific molecular imaging agents. Initial results with radiolabeled nucleoside analogs, sugars, and amino acids, and a renewed interest in radiolabeled antibiotics for both diagnosis and monitoring treatment are exciting and hold great promise for the future.

Diagnostic Performance of 18F-FDG PET/CT in Infectious and Inflammatory Diseases according to Published Meta-Analyses

Purpose

To date, several meta-analyses have reported data about the diagnostic performance of ¹⁸F-FDG PET/CT in infectious and inflammatory diseases. This article aims to summarize the published evidence-based data about the diagnostic performance of ¹⁸F-FDG PET/CT in this setting.

Methods

A comprehensive computer literature search of meta-analyses published in PubMed/MEDLINE and Cochrane library database from January 2009 through December 2018 and regarding the diagnostic performance of ¹⁸F-FDG PET/CT in infectious and inflammatory diseases was carried out. This combination of key words was used: (i) “PET” OR “positron emission tomography” OR “FDG” OR “fluorodeoxyglucose” AND (ii) meta-analysis. Only records on inflammatory or infectious diseases were selected.

Results

The diagnostic performance of ¹⁸F-FDG PET/CT in detecting inflammatory and infectious diseases has been summarized taking into account 36 meta-analyses published in the literature. Evidence-based data demonstrated good diagnostic performance of ¹⁸F-FDG PET/CT for several inflammatory and infectious diseases, in particular cardiovascular infectious and inflammatory diseases and some musculoskeletal infections.

Conclusions

Evidence-based data about the diagnostic performance of ¹⁸F-FDG PET/CT in infectious and inflammatory diseases are increasing, with good diagnostic performance of this imaging method for some indications. More prospective multicenter studies and cost-effective analyses are warranted.

Role of miR-9-5p in preventing peripheral neuropathy in patients with rheumatoid arthritis by targeting REST/miR-132 pathway

MicroRNAs (miRNAs) are found to play a key role in neural cell differentiation, peripheral nerve injury, and rheumatoid arthritis (RA). However, no study has yet been conducted highlighting their role in RA-induced peripheral neuropathy. Here, we investigated the role of miRNAs in RA-induced peripheral neuropathy. Levels of six miRNAs were detected in serum collected from 15 patients with RA and peripheral neuropathy and 16 patients with RA. In vitro, Schwann cells were treated with 0.1 ng/mL IL-6 and 20 ng/mL TNF-α. The expression level of miR-9-5p and its association with the repressor element-1 silencing transcription factor (REST) were investigated. The roles of miR-9-5p and REST in Schwann cell injury were examined after transfection of miR-9-5p mimics or REST siRNA. In patients with RA and peripheral neuropathy, serum miR-9-5p was significantly downregulated when compared with RA. In IL-6- and TNF-α-stimulated Schwann cells, apoptosis was induced, while the cell viability and level of miR-9-5p were inhibited. A significantly negative correlation was observed between miR-9-5p and REST. Transfection of miR-9-5p mimics and REST siRNA significantly reversed the inhibition of cell viability and induction of apoptosis caused by IL-6 and TNF-α. In addition, overexpression of miR-9-5p upregulated the expression of miR-132, miRNA targeting E1A binding protein EP300 (EEP300), phosphatase and tensin homolog (PTEN) and forkhead box O3 (FOXO3). These results showed that Schwann cells were protected by miR-9-5p from inflammatory damage by targeting REST/miR-132 pathway, which could provide new targets for treatment of RA-induced peripheral neuropathy.