Molecular imaging: novel tools in visualizing rheumatoid arthritis

Total-Body PET Imaging of Musculoskeletal Disorders

Imaging of musculoskeletal disorders, including arthritis, infection, osteoporosis, sarcopenia, and malignancies, is often limited when using conventional modalities such as radiography, computed tomography (CT), and MR imaging. As a result of recent advances in Positron Emission Tomography (PET) instrumentation, total-body PET/CT offers a longer axial field-of-view, higher geometric sensitivity, and higher spatial resolution compared with standard PET systems. This article discusses the potential applications of total-body PET/CT imaging in the assessment of musculoskeletal disorders.

Molecular imaging of the urokinase plasminogen activator receptor: opportunities beyond cancer

The urokinase plasminogen activator receptor (uPAR) plays a multifaceted role in almost any process where migration of cells and tissue-remodeling is involved such as inflammation, but also in diseases as arthritis and cancer. Normally, uPAR is absent in healthy tissues. By its carefully orchestrated interaction with the protease urokinase plasminogen activator and its inhibitor (plasminogen activator inhibitor-1), uPAR localizes a cascade of proteolytic activities, enabling (patho)physiologic cell migration. Moreover, via the interaction with a broad range of cell membrane proteins, like vitronectin and various integrins, uPAR plays a significant, but not yet completely understood, role in differentiation and proliferation of cells, affecting also disease progression. The implications of these processes, either for diagnostics or therapeutics, have received much attention in oncology, but only limited beyond. Nonetheless, the role of uPAR in different diseases provides ample opportunity to exploit new applications for targeting. Especially in the fields of oncology, cardiology, rheumatology, neurology, and infectious diseases, uPAR-targeted molecular imaging could offer insights for new directions in diagnosis, surveillance, or treatment options.

Immuno-Imaging to Predict Treatment Response in Infection, Inflammation and Oncology

Background: Molecular nuclear medicine plays a pivotal role for diagnosis in a preclinical phase, in genetically susceptible patients, for radio-guided surgery, for disease relapse evaluation, and for therapy decision-making and follow-up. This is possible thanks to the development of new radiopharmaceuticals to target specific biomarkers of infection, inflammation and tumour immunology. Methods: In this review, we describe the use of specific radiopharmaceuticals for infectious and inflammatory diseases with the aim of fast and accurate diagnosis and treatment follow-up. Furthermore, we focus on specific oncological indications with an emphasis on tumour immunology and visualizing the tumour environment. Results: Molecular nuclear medicine imaging techniques get a foothold in the diagnosis of a variety of infectious and inflammatory diseases, such as bacterial and fungal infections, rheumatoid arthritis, and large vessel vasculitis, but also for treatment response in cancer immunotherapy. Conclusion: Several specific radiopharmaceuticals can be used to improve diagnosis and staging, but also for therapy decision-making and follow-up in infectious, inflammatory and oncological diseases where immune cells are involved. The identification of these cell subpopulations by nuclear medicine techniques would provide personalized medicine for these patients, avoiding side effects and improving therapeutic approaches.

Cat's whiskers (Orthosiphon stamineus) tea modulates arthritis pathogenesis via the angiogenesis and inflammatory cascade

Background

Orthosiphon stamineus is used traditionally to treat gout, arthritis, and inflammatory related conditions. The in vitro anti-inflammatory effects of the plant have been scientifically investigated. The goal of the present study was to evaluate the potential of the 50% ethanol extract of O. stamineus (EOS) to treat rheumatoid arthritis.

Methods

Anti-arthritic activity was assessed using the in vitro heat denaturation test and the (FCA)-induced arthritis model. Efficacy was assessed by measurements of paw edema and granulation, X-ray radiography, fluorescence molecular tomography (FMT), and histological evaluation. Levels of (TNF-α), interleukin-1 (IL-1), and (COX-1 and COX-2) were analyzed in vitro in lipopolysaccharide (LPS)-stimulated human macrophage (U937). TNF-α and IL-1 levels in the serum samples of arthritic rats were also measured using an ELISA kit.

Results

Treatment with EOS resulted in dose-dependent inhibition of paw edema in acute and chronic models of inflammation. It also inhibited significantly the production of TNF-α, IL-1 COX-1, and COX-2 in the LPS-stimulated U937 macrophages. EOS significantly suppressed FCA-induced paw edema as well as the serum levels of TNF-α and IL-1. X-rays of the synovial joint of the hind leg showed considerable improvement in joint integrity and recovery of tibia-talus bones from degeneration and osteoporotic lesions. Histology of proximal interphalangeal joints of EOS-treated animals showed obvious protection of cartilage and soft tissue. Finally, FMT analysis strongly supported the anti-arthritic effect of EOS. EOS had high phenolic and total flavonoid content as well as strong antioxidant activity.

Conclusions

Results illustrated that the anti-arthritic properties of O. stamineus could be beneficial for prevention and management of rheumatoid arthritis and other chronic inflammatory disorders.

Graphical abstract

Illustration of the Anti- arthritis efficacy of Orthosiphon Stamineus standardized extract.

Cardiovascular magnetic resonance in rheumatology: Current status and recommendations for use

Targeted therapies in connective tissue diseases (CTDs) have led to improvements of disease-associated outcomes, but life expectancy remains lower compared to general population due to emerging co-morbidities, particularly due to excess cardiovascular risk. Cardiovascular magnetic resonance (CMR) is a noninvasive imaging technique which can provide detailed information about multiple cardiovascular pathologies without using ionizing radiation. CMR is considered the reference standard for quantitative evaluation of left and right ventricular volumes, mass and function, cardiac tissue characterization and assessment of thoracic vessels; it may also be used for the quantitative assessment of myocardial blood flow with high spatial resolution and for the evaluation of the proximal coronary arteries. These applications are of particular interest in CTDs, because of the potential of serious and variable involvement of the cardiovascular system during their course. The International Consensus Group on CMR in Rheumatology was formed in January 2012 aiming to achieve consensus among CMR and rheumatology experts in developing initial recommendations on the current state-of-the-art use of CMR in CTDs. The present report outlines the recommendations of the participating CMR and rheumatology experts with regards to: (a) indications for use of CMR in rheumatoid arthritis, the spondyloarthropathies, systemic lupus erythematosus, vasculitis of small, medium and large vessels, myositis, sarcoidosis (SRC), and scleroderma (SSc); (b) CMR protocols, terminology for reporting CMR and diagnostic CMR criteria for assessment and quantification of cardiovascular involvement in CTDs; and (c) a research agenda for the further development of this evolving field.

(18)F-FDG and (18)F-NaF PET/CT demonstrate coupling of inflammation and accelerated bone turnover in rheumatoid arthritis

OBJECTIVE

To compare the findings in rheumatoid arthritis (RA)-affected joints between (18)F-fluorodeoxyglucose (FDG) and (18)F-fluoride (NaF) positron emission tomography (PET)/computed tomography (CT).

METHODS

We enrolled twelve RA patients who started a new biologic agent (naïve 9 and switch 3). At entry, both hands were examined by (18)F-FDG PET/CT, (18)F-NaF PET/CT, and X-ray. Intensity of PET signals was determined by standardized uptake value max (SUVmax) in metacarpophalangeal (MCP), proximal interphalangeal (PIP), and ulnar, medial, and radial regions of the wrists. Hand X-rays were evaluated according to the Genant-modified Sharp score at baseline and 6 months.

RESULTS

Both (18)F-FDG and (18)F-NaF accumulated in RA-affected joints. The SUVmax of (18)F-FDG correlated with that of (18)F-NaF in individual joints (r = 0.65), though detail distribution was different between two tracers. (18)F-NaF and (18)F-FDG signals were mainly located in the bone and the surrounding soft tissues, respectively. The sum of SUVmax of (18)F-NaF correlated with disease activity score in 28 joint (DAS28), modified health assessment questionnaire (MHAQ), and radiographic progression. (18)F-FDG and (18)F-NaF signals were associated with the presence of erosions, particularly progressive ones.

CONCLUSION

Our data show that both (18)F-FDG and (18)F-NaF PET signals were associated with RA-affected joints, especially those with ongoing erosive changes.

Current imaging techniques in rheumatology: MRI, scintigraphy and PET

The first-line imaging technique for diagnosis inflammation in musculo-skeletal organs in rheumatoid arthritis (RA) is planar X-ray examination, which was for many years the first and the only single tool for RA diagnostics and response evaluation. Today, in the era of more aggressive RA treatment, ultrasound examination (US) and magnetic resonance imaging (MRI) are also frequently used. US is used to detect early signs of inflammation within the soft tissue. MRI allows to assess the soft tissue and bone marrow involvement in case of inflammation and/or infection. MRI is capable of detecting more inflammatory lesions and erosions than US, X-ray, or CT. Standard scintigraphy plays a crucial role, and data from positron emission tomography (PET) are also promising. These functional imaging techniques are used in detection of inflammation and/or infection in case of ambiguous results being obtained by other techniques or at other clinics. In patients with RA, scintigraphy plays a key role in the differential diagnosis of hip, knee, etc. endoprosthesis disorders, including mechanical or septic loosening.

Detection of active matrix metalloproteinase-3 in serum and fibroblast-like synoviocytes of collagen-induced arthritis mice

The activity of rheumatoid arthritis (RA) correlates with the expression of proteases. Among several proteases, matrix metalloproteinase-3 (MMP-3) is one of the biological markers used to diagnose RA. The active form of MMP-3 is a key enzyme involved in RA-associated destruction of cartilage and bone. Thus, detection of active MMP-3 in serum or in vivo is very important for early diagnosis of RA. In this study, a soluble MMP-3 probe was prepared to monitor RA progression by detecting expression of active MMP-3 in collagen-induced arthritis (CIA) mice in vivo in both serum and fibroblast-like synoviocytes (FLSs). The MMP-3 probe exhibited strong sensitivity to MMP-3 and moderate sensitivity to MMP-7 at nanomolecular concentrations, but was not sensitive to other MMPs such as MMP-2, MMP-9, and MMP-13. In an optical imaging study, the MMP-3 probe produced early and strong NIR fluorescence signals prior to observation of erythema and swelling in CIA mice. The MMP-3 probe was able to rapidly and selectively detect and monitor active MMP-3 in diluted serum from CIA mice. Furthermore, histological data demonstrated that activated FLSs in arthritic knee joints expressed active MMP-3. Together, our results demonstrated that the MMP-3 probe may be useful for detecting active MMP-3 for diagnosis of RA. More importantly, the MMP-3 probe was able to detect active MMP-3 in diluted serum with high sensitivity. Therefore, the MMP-3 probe developed in this study may be a very promising probe, useful as a biomarker for early detection and diagnosis of RA.

Tracking rheumatic disease through imaging

This review recounts the historical, current, and future involvement of radiology and imaging in the diagnosis, management, and follow-up of patients with various rheumatic conditions. Radiographs are the mainstay of imaging patients with rheumatic conditions, although magnetic resonance imaging and ultrasonography are routinely used for early diagnosis of disease. Computed tomography remains useful in evaluating the extent of involvement of inflammatory spondyloarthropathies that classically involve the axial skeleton and sacroiliac joints. Molecular imaging has begun to play an innovative role in evaluating patients with arthritis, aiming to identify disease earlier and provide greater specificity.

Identification of the optimal therapeutic antibody for fluorescent imaging of cutaneous squamous cell carcinoma

Intraoperative, real-time fluorescence imaging may significantly improve tumor visualization and resection and postoperatively, in pathological assessment. To this end, we sought to determine the optimal FDA approved therapeutic monoclonal antibody for optical imaging of human cutaneous squamous cell carcinoma (cSCC). A near-infrared (NIR) fluorescent probe (IRDye800) was covalently linked to bevacizumab, panitumumab or tocilizumab and injected systemically into immunodeficient mice bearing either cutaneous tumor cell lines (SCC13) or cutaneous human tumor explants. Tumors were then imaged and resected under fluorescent guidance with the SPY, an FDA-approved intraoperative imaging system, and the Pearl Impulse small animal imaging system. All fluorescently labeled antibodies delineated normal tissue from tumor in SCC13 xenografts based on tumor-to-background (TBR) ratios. The conjugated antibodies produced TBRs of 1.2-2 using SPY and 1.6-3.6 using Pearl; in comparison, isotype control antibody IgG-IRDye produced TBRs of 1.0 (SPY) and 0.98 (Pearl). Comparison between antibodies revealed them to be roughly equivalent for imaging purposes with both the SPY and Pearl (p = 0.89 SPY, p = 0.99 Pearl; one way ANOVA). Human tumor explants were also imaged and tumor detection was highest with panitumumab-IRDye800 when using the SPY (TBR 3.0) and Pearl (TBR 4.0). These data suggest that FDA approved antibodies may be clinically used for intraoperative detection of cSCC.

Visualizing arthritic inflammation and therapeutic response by fluorine-19 magnetic resonance imaging (19F MRI)

Background

Non-invasive imaging of inflammation to measure the progression of autoimmune diseases, such as rheumatoid arthritis (RA), and to monitor responses to therapy is critically needed. V-Sense, a perfluorocarbon (PFC) contrast agent that preferentially labels inflammatory cells, which are then recruited out of systemic circulation to sites of inflammation, enables detection by ¹⁹F MRI. With no ¹⁹F background in the host, detection is highly-specific and can act as a proxy biomarker of the degree of inflammation present.

Methods

Collagen-induced arthritis in rats, a model with many similarities to human RA, was used to study the ability of the PFC contrast agent to reveal the accumulation of inflammation over time using ¹⁹F MRI. Disease progression in the rat hind limbs was monitored by caliper measurements and ¹⁹F MRI on days 15, 22 and 29, including the height of clinically symptomatic disease. Naïve rats served as controls. The capacity of the PFC contrast agent and ¹⁹F MRI to assess the effectiveness of therapy was studied in a cohort of rats administered oral prednisolone on days 14 to 28.

Results

Quantification of ¹⁹F signal measured by MRI in affected limbs was linearly correlated with disease severity. In animals with progressive disease, increases in ¹⁹F signal reflected the ongoing recruitment of inflammatory cells to the site, while no increase in ¹⁹F signal was observed in animals receiving treatment which resulted in clinical resolution of disease.

Conclusion

These results indicate that ¹⁹F MRI may be used to quantitatively and qualitatively evaluate longitudinal responses to a therapeutic regimen, while additionally revealing the recruitment of monocytic cells involved in the inflammatory process to the anatomical site. This study may support the use of ¹⁹F MRI to clinically quantify and monitor the severity of inflammation, and to assess the effectiveness of treatments in RA and other diseases with an inflammatory component.

Assessment of collagen-induced arthritis using cyanine 5.5 conjugated with hydrophobically modified glycol chitosan nanoparticles: correlation with 18F-fluorodeoxyglucose positron emission tomography data

OBJECTIVE

To evaluate the potential and correlation between near-infrared fluorescence (NIRF) imaging using cyanine 5.5 conjugated with hydrophobically modified glycol chitosan nanoparticles (HGC-Cy5.5) and (18)F-fluorodeoxyglucose-positron emission tomography ((18)F-FDG-PET) imaging of collagen-induced arthritis (CIA).

MATERIALS AND METHODS

We used 10 CIA and 3 normal mice. Nine days after the injecting collagen twice, microPET imaging was performed 40 minutes after the intravenous injection of 9.3 MBq (18)F-FDG in 200 µL PBS. One day later, NIRF imaging was performed two hours after the intravenous injection of HGC-cy5.5 (5 mg/kg). We assessed the correlation between these two modalities in the knees and ankles of CIA mice.

RESULTS

The mean standardized uptake values of (18)F-FDG for knees and ankles were 1.68 ± 0.76 and 0.79 ± 0.71, respectively, for CIA mice; and 0.57 ± 0.17 and 0.54 ± 0.20 respectively for control mice. From the NIRF images, the total photon counts per 30 mm(2) for knees and ankles were 2.32 ± 1.54 × 10(5) and 2.75 ± 1.51 × 10(5), respectively, for CIA mice, and 1.22 ± 0.27 × 10(5) and 0.88 ± 0.24 × 10(5), respectively, for control mice. These two modalities showed a moderate correlation for knees (r = 0.604, p = 0.005) and ankles (r = 0.464, p = 0.039). Moreover, both HGC-Cy5.5 (p = 0.002) and (18)F-FDG-PET (p = 0.005) imaging also showed statistically significant differences between CIA and normal mice.

CONCLUSION

NIRF imaging using HGC-Cy5.5 was moderately correlated with (18)F-FDG-PET imaging in the CIA model. As such, HGC-Cy5.5 imaging can be used for the early detection of rheumatoid arthritis.

Early diagnosis of arthritis in mice with collagen-induced arthritis, using a fluorogenic matrix metalloproteinase 3-specific polymeric probe

OBJECTIVE

Early treatment based on an early diagnosis of rheumatoid arthritis (RA) could halt progression of the disease, but early diagnosis is often difficult. Matrix metalloproteinase 3 (MMP-3) is thought to be particularly important in the pathogenesis of RA. The aim of this study was to investigate whether an MMP-3-specific polymeric probe could be used for early diagnosis and for visualizing the progression of arthritis, using a near-infrared fluorescence (NIRF) imaging system.

METHODS

The MMP-3-specific polymeric probe was developed by conjugating NIRF dye, MMP substrate peptide, and dark quencher to self-assembled chitosan nanoparticles. One hour after intravenous administration of the probe, fluorescent images of mice with collagen-induced arthritis at different stages of disease development were obtained. The correlation between the fluorescence recovered in in vivo imaging when using an MMP-3-specific polymeric probe and up-regulated MMP-3 activity in the joint tissues was evaluated by Western blotting and immunohistochemical staining. Histologic analysis and micro-computed tomography (micro-CT) were also used to assess arthritis progression.

RESULTS

A significantly higher NIRF signal was recovered from arthritic joints compared with normal joints at 14 days after the first immunization, before any erythema or swelling could be observed with the naked eye or any erosion was detected by histologic analysis or micro-CT. The results of immunohistochemical analysis and Western blotting confirmed that the fluorescence recovered in the in vivo imaging was related to up-regulated MMP-3 activity in the joint tissues.

CONCLUSION

An MMP-3-specific polymeric probe provided clear early diagnosis of arthritis and visualization of arthritis progression using an NIRF imaging system. This approach could be used for early diagnosis and for monitoring drug and surgical therapies in individual cases.

Imaging in arthritis: quantifying effects of therapeutic intervention using MRI and molecular imaging

Modern imaging techniques are becoming increasingly important in assessing the course of arthritis and in permitting measurement of response to treatment as part of the follow-up of patients. They include ultrasonography (US), MRI, PET/CT, and biofluorescence. In patients with rheumatoid arthritis, clinical evaluation is significantly less sensitive than either US or MRI in detecting synovitis. As a result, imaging is a useful alternative to achieving proper assessment of disease activity. The different areas in which the new imaging techniques could help practicing rheumatologists and internal physicians include the following: early and differential diagnosis of arthritis, evaluation of disease activity, prognosis, assessment of treatment efficacy, assessment of remission, and evaluation of subclinical disease. MRI is probably the best imaging method to study disease activity in RA, because it can study all the joints with similar efficacy, has been sufficiently standardised, and yields data on inflammation that can be quantified. Different methods, developed to score synovitis activity, are increasingly used in clinical trials. The main application of PET/CT in rheumatology is the diagnosis and follow-up of large vessel vasculitis. More recently, also RA disease activity has been evaluated, allowing a panoramic view of the patient. Molecular imaging studies molecular and cellular processes in intact living organisms in a non-invasive fashion. In fluorescence, dyes, that emit light upon excitation by a light source and are read by a camera, can be used to show inflamed areas where neoangiogenesis, vasodilatation, and increased vessel permeability are present. These dyes can be coupled with different compounds including antibodies and drugs.

Detection of rheumatoid arthritis by evaluation of normalized variances of fluorescence time correlation functions

Fluorescence imaging using the dye indocyanine green as a contrast agent was investigated in a prospective clinical study for the detection of rheumatoid arthritis. Normalized variances of correlated time series of fluorescence intensities describing the bolus kinetics of the contrast agent in certain regions of interest were analyzed to differentiate healthy from inflamed finger joints. These values are determined using a robust, parameter-free algorithm. We found that the normalized variance of correlation functions improves the differentiation between healthy joints of volunteers and joints with rheumatoid arthritis of patients by about 10% compared to, e.g., ratios of areas under the curves of raw data.

Optical image-guided surgery--where do we stand?

In cancer surgery, intra-operative assessment of the tumor-free margin, which is critical for the prognosis of the patient, relies on the visual appearance and palpation of the tumor. Optical imaging techniques provide real-time visualization of the tumor, warranting intra-operative image-guided surgery. Within this field, imaging in the near-infrared light spectrum offers two essential advantages: increased tissue penetration of light and an increased signal-to-background-ratio of contrast agents. In this article, we review the various techniques, contrast agents, and camera systems that are currently used for image-guided surgery. Furthermore, we provide an overview of the wide range of molecular contrast agents targeting specific hallmarks of cancer and we describe perspectives on its future use in cancer surgery.

Recommendations for an update of 2003 European regulatory requirements for registration of drugs to be used in the treatment of RA

Since 2003, the European Medicines Agency (EMA) document, 'Points to consider on clinical investigation of medicinal products other than NSAIDs (nonsteroidal anti-inflammatory drugs) for the treatment of rheumatoid arthritis' has provided guidance for the clinical development of both biologic and non-biologic disease-modifying antirheumatic drugs (DMARDs). In the last few years, several new products have been developed or are in development for the treatment of RA, which offer significant efficacy with regard to disease control, including prevention of structural damage and disability. Concurrently, novel insights have been gained with respect to the assessment of disease activity, joint damage and disability. New treatment strategies have been established which relate to early therapy, tight control and rapid switching of medication. Accordingly, several new EULAR/ACR recommendations have been or are being developed. Several important additions and changes are needed in the 2003 guidance to incorporate the current scientific knowledge into clinical trial design for the development of future products. Under the auspices of the Group for the Respect of Ethics and Excellence in Science (GREES), a group of experts in the field of RA and clinical trial design met to provide a consensus recommendation for an update to the 2003 EMA guidance document.

In vivo fluorescence imaging of E-selectin: quantitative detection of endothelial activation in a mouse model of arthritis

OBJECTIVE

In vivo optical imaging can delineate at the macroscopic level processes that are occurring at the cellular and molecular levels. E-selectin, a leukocyte adhesion molecule expressed on endothelium, is induced by tumor necrosis factor α (TNFα) and other cytokines involved in the pathogenesis of rheumatoid arthritis (RA). Collagen-induced arthritis (CIA) in mice is widely used to study the disease mechanisms and identify new treatments for RA. The purpose of this study was to demonstrate E-selectin-targeted fluorescence imaging in vivo in a mouse model of paw edema generated by local injection of TNFα as well as in mice with CIA.

METHODS

Animals with either CIA or TNFα-induced paw edema were injected with anti-E-selectin or control antibodies labeled with a DyLight 750-nm near-infrared (NIR) probe. In vivo imaging studies were undertaken using an NIR optical imaging system, and images were coregistered with plain radiographic images.

RESULTS

The mean fluorescence intensity measured over the time-course of TNFα-induced edema demonstrated a 1.97-fold increase (P<0.001) in signal in inflamed paws at 8 hours following injection of anti-E-selectin antibody, as compared to that in the isotype control. In the CIA model, a 2.34-fold increase in E-selectin-targeted signal was demonstrated (P<0.01). Furthermore, significant E-selectin-targeted signal was observed in the paws of animals immunized with collagen that did not display overt signs of arthritis.

CONCLUSION

E-selectin-targeted fluorescence in vivo imaging is a quantifiable method of detecting endothelial activation in arthritis and can potentially be applied to the quantification of disease and the investigation of the effects of new therapies. Importantly, this approach may also be useful for the detection of subclinical disease in RA.

Potential targets for molecular imaging of apoptosis resistance in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers, which is mainly a concern in Southeast Asia. Apoptosis resistance in HCC is one of the significant factors for hepatocarcinogenesis and tumour progression. Recent advances of apoptosis resistance mechanisms in HCC could serve as potential targets for molecular imaging, which would be of considerable value to explore the molecular processes involved in HCC progression and to evaluate responses of certain anti-HCC therapies. Disruptions in the balance of anti-apoptotic and pro-apoptotic processes have been found to be involved in apoptosis resistance in HCC. Loss of response to death receptors, transformation of growth factor-β induced apoptosis, upregulation of anti-apoptotic Bcl-2 subgroup, as well as downregulation of pro-apoptotic Bax subgroup and BH3-only subgroup, are associated with apoptosis resistance in HCC. Mutation of p53 gene, dysregulation of NF-κB and survivin are also of interest because of their contribution to HCC development. In this review, the aim is to identify potential targets for molecular imaging of apoptosis resistance in HCC.

Non-invasive surface-stripping for epifluorescence small animal imaging

Non-invasive near-infrared fluorescence (NIRF) imaging is a powerful tool to study pathophysiology in a wide variety of animal disease models including brain diseases. However, especially in NIRF imaging of the brain or other deeper laying target sites, background fluorescence emitted from the scalp or superficial blood vessels can impede the detection of fluorescence in deeper tissue. Here, we introduce an effective method to reduce the impact of fluorescence from superficial layers. The approach uses excitation light at two different wavelengths generating two images with different depth sensitivities followed by an adapted subtraction algorithm. This technique leads to significant enhancement of the contrast and the detectability of fluorochromes located in deep tissue layers in tissue simulating phantoms and murine models with stroke.

Molecular MR imaging for visualizing ICAM-1 expression in the inflamed synovium of collagen-induced arthritic mice

Objective

To determine the utility of intercellular adhesion molecule (ICAM)-1 antibody-conjugated gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA-anti-ICAM-1) as a targeted contrast agent for the molecular magnetic resonance imaging (MRI) in collagen-induced arthritis (CIA).

Materials and Methods

Three groups of mice were used: non-arthritic normal, CIA mice in both the early inflammatory and chronic destructive phases. The MR images of knee joints were obtained before and after injection of Gd-DTPA-anti-ICAM-1, Gd-DTPA, and Gd-DTPA-Immunoglobulin G (Ig G) and were analyzed quantitatively. The patterns of enhancement on the MR images were compared with the histological and immunohistochemical ICAM-1 staining.

Results

The images obtained after injection of Gd-DTPA-anti-ICAM-1 displayed gradually increasing signal enhancement from the moment following injection (mean ± standard deviation [SD]: 424.3 ± 35.2, n = 3) to 24 hours (532 ± 11.3), rather than on pre-enhanced images (293 ± 37.6) in the early inflammatory phase of CIA mice. However, signal enhancement by Gd-DTPA and Gd-DTPA-IgG disappeared after 80 minutes and 24 hours, respectively. In addition, no significant enhancement was seen in the chronic destructive phase of CIA mice, even though they also showed inflammatory changes on T2-weighted MR images. ICAM-1 expression was demonstrated in the endothelium and proliferating synovium of the early inflammatory phase of CIA mice, but not in the chronic destructive phase.

Conclusion

Molecular MRI with Gd-DTPA-anti-ICAM-1 displays specific images targeted to ICAM-1 that is expressed in the inflamed synovium of CIA. This novel tool may be useful for the early diagnosis and differentiation of the various stages of rheumatoid arthritis.

Optical imaging of vascular pathophysiology

Pathophysiological processes in the vascular system are the major cause of mortality and disease. Atherosclerosis, an inflammatory process in arterial walls, can lead to formation of plaques, whose rupture can lead to thrombus formation, obstruction of vessels (thrombosis), reduction of the blood flow (ischemia), cell death in the tissue fed by the occluded vessel, and depending on the affected vessel, to myocardial infarction or stroke. Imaging techniques enabling visualization of the biological processes involved in this scenario are therefore highly desirable. In recent years, a number of reporter agents and reporter systems have been developed to visualize these processes using different imaging modalities including nuclear imaging techniques, such as positron emission tomography or single photon emission computed tomography, magnetic resonance imaging, and ultrasound. This article comprises a brief overview of optical imaging techniques, such as fluorescence imaging and bioluminescence imaging for the visualization of vascular pathophysiology.

Molecular scintigraphic imaging using 99mTc-transferrin is useful for early detection of synovial inflammation of collagen-induced arthritis mouse

Transferrin receptor (TfR) is highly expressed on rapidly dividing inflammatory cells, but not in nonproliferating cells. We investigated whether scintigraphic imaging using 99mTechnetium-radiolabeled transferrin (99mTc-Tf) is useful for early detection of synovial inflammation of collagen-induced arthritis (CIA) mouse. 99mTc-Tf conjugate was synthesized to target the TfR in inflamed synovium. 99mTc-Tf scintigraphic images were obtained in nonarthritic normal mouse and advanced phase of CIA mouse. 99mTc-Tf and 99mTc-methylenediphosphonate (99mTc-MDP) bone scintigraphic images were obtained in same early phase of CIA mouse. Western blot analysis, hematoxylin & eosin (H&E), and immunohistochemical staining were performed to determine development of arthritis and expression of TfR. Image analyses revealed that the uptake of 99mTc-Tf in inflamed joints of advanced phase of CIA mouse was markedly higher than those by normal nonarthritic mouse. 99mTc-Tf scintigraphy also showed higher uptake in knee joint prior to significant joint swelling in early phase of CIA mouse but 99mTc-MDP bone scintigraphy does not. These scintigraphic findings are well correlated with the results of Western blot, H&E and immunohistochemical analysis. In conclusion, TfR can be used as a specific target for molecular imaging in CIA mouse, and 99mTc-Tf scintigraphy detects synovial inflammation prior to significant clinical findings in CIA mouse.

Correlation between joint [F-18] FDG PET uptake and synovial TNF-α concentration: A study with two rabbit models of acute inflammatory arthritis

The objective of this study was to verify that the [F-18]FDG PET synovial uptake is correlated with the synovial fluid (SF) TNF-alpha concentration. Two rabbit models of acute inflammatory arthritis induced by human interleukin-8 and lipopolysaccharide were used. Modified standard uptake values (MSUVs) obtained from PET images of the animals were compared with results of SF TNF-alpha measurements. Statistically significant correlations were found between the MSUVs and the SF TNF-alpha ratios. An equation to estimate the TNF-alpha ratio from a MSUV was also derived.

Established rheumatoid arthritis – new imaging modalities

New imaging modalities are assuming an increasingly important role in the investigation and management of rheumatoid arthritis. It is now possible to obtain information about all tissues within the joint in three dimensions using tomographic techniques such as magnetic resonance imaging (MRI) and high-resolution computerized tomography. Erosions are very clearly depicted using these modalities and MRI also allows imaging of soft tissues with assessment of joint inflammation. High-resolution ultrasound is a convenient clinical technique for the assessment of erosions, synovitis and tenosynovitis in real-time and facilitates diagnostic and therapeutic interventions such as joint aspiration and injection. Exciting experimental modalities are also being developed with the potential to provide not just morphological but functional imaging. Techniques such as positron emission tomography (PET) and single photon emission tomography (SPECT) can reveal actively metabolizing bone and the proliferation of synovial cells via radioactive labeling. Bioluminescence and fluorescence reflectance imaging are other approaches that allow imaging, and potentially the delivery of therapeutic agents, at a molecular level.