Optical imaging of experimental arthritis using allogenic leukocytes labeled with a near-infrared fluorescent probe
The purpose of this study was to assess the feasibility of inflammation detection in an antigen-induced arthritis model using fluorescent leukocytes and optical imaging.
Antigen-mediated monoarthritis was induced in the right knee of 12 Sprague-Dawley rats. Six rats remained untreated and six rats were treated with cortisone. All rats received ex vivo fluorescent-labeled rat leukocytes. Optical images of both knees were acquired before and at 5 min, 1 h, 4 h, and 24 h after cell injection. Images were evaluated qualitatively and quantitatively by calculating signal intensity ratios between the right arthritic (A) and contralateral normal (N) knee. A/N ratios were tested for significant differences between baseline values and values after cell injection using a paired t test as well as between the untreated and cortisone-treated group using an unpaired t test. Synovial specimens were processed and evaluated for labeled cells with fluorescence microscopy.
At 4 h and 24 h p.i., the A/N ratios of untreated arthritic knees showed a significant signal increase compared with baseline values (p<0.05) and a significant difference compared with A/N ratios of cortisone-treated animals (p<0.05). Fluorescent microscopy confirmed the presence of labeled cells in the arthritic synovium.
Inflammation in antigen-induced arthritis can be detected with ex vivo labeled allogenic leukocytes and optical imaging.
Available from: Gerald Brandacher
- "Other investigators have proposed using fluorescence imaging to visualize inflammation. Rodent leukocytes and macrophages have been labeled with non-clinically approved dyes and injected systemically to image induced inflammation in animal models [10–12]. Despite toxicity, radiolabelling currently provides the most clinically relevant option. "
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ABSTRACT: Distinguishing cutaneous infection from sterile inflammation is a diagnostic challenge and currently relies upon subjective interpretation of clinical parameters, microbiological data, and nonspecific imaging. Assessing characteristic variations in leukocytic infiltration may provide more specific information. In this study, we demonstrate that homing of systemically administered monocytes tagged using indocyanine green (ICG), an FDA-approved near infrared dye, may be assessed non-invasively using clinically-applicable laser angiography systems to investigate cutaneous inflammatory processes. RAW 264.7 mouse monocytes co-incubated with ICG fluoresce brightly in the near infrared range. In vitro, the loaded cells retained the ability to chemotax toward monocyte chemotactic protein-1. Following intravascular injection of loaded cells into BALB/c mice with induced sterile inflammation (Complete Freund's Adjuvant inoculation) or infection (Group A Streptococcus inoculation) of the hind limb, non-invasive whole animal imaging revealed local fluorescence at the inoculation site. There was significantly higher fluorescence of the inoculation site in the infection model than in the inflammation model as early as 2 hours after injection (p<0.05). Microscopic examination of bacterial inoculation site tissue revealed points of near infrared fluorescence, suggesting the presence of ICG-loaded cells. Development of a non-invasive technique to rapidly image inflammatory states without radiation may lead to new tools to distinguish infectious conditions from sterile inflammatory conditions at the bedside.
Available from: Wolfgang Hartung
- "The major drawback of FOI is the limited tissue penetration of light; however, as inflammatory arthopathies typically affect the small joints of the hands and feet, this is not necessarily a significant limitation for this imaging method . Under various experimental conditions, FOI proved to correspond to synovitis [17,18,20-24]. In those experiments, early hyperemia of inflamed joints could be diagnosed by recording scattering and absorption patterns of light transmitted through inflamed finger joints. "
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ABSTRACT: To prospectively evaluate quantitative assessment of fluorescence optical imaging (FOI) for differentiation of synovitic from non-synovitic joints in patients suffering from rheumatoid arthritis (RA).
FOI of the hands was performed in patients with active RA, and a stratified quantitative fluorescence readout (FLRO) of 3 phases (1-120 s; 121-240 s; 241-360 s) was generated for 5 individual joints of the clinical predominant hand (carpal joint, metacarpophalangeal and proximal interphalangeal joints of digits II & III). To dissect the effect of the overall perfusion of the hand from the perfusion due to synovitis, a fluorescence ratio (FLRA) was additionally calculated, dividing each FLRO by the readout of the eponychium of digit II. The mean FLRO and FLRA were compared between joints with absent vs. present synovitis determined by clinical examination, grayscale, color Doppler ultrasonography, or magnetic resonance imaging (MRI).
The analysis for 90 individual joints from 18 patients yielded FLRO ranging from 4.4 to 49.0 × 10(3), and FLRAs ranging from 0.37 to 2.27. Overall, the analyses based on the FLRA revealed a higher discrimination than the analyses related to the FLRO, demonstrating most significant differences in phases 2 and 3. A sensitivity of 26/39 (67%) and a specificity of 31/40 (77%) were calculated for FLRA of phase 3 using a cut-off value of more than 1.2 to detect MRI-confirmed synovitis with FOI.
FOI has a potential for visualizing synovitis in subjects with RA. For adequate FOI interpretation, quantitative analysis should be based on the novel FLRA calculated for phases 2 and 3.
Available from: PubMed Central
- "This increase was greater than that obtained following injection of free dye. Another study has examined in vivo fluorescent signal returned from allogeneic leukocytes that were labelled ex vivo with fluorescent dye and re-injected into arthritic mice . Steroid reduced the signal intensity obtained; however, the degree of quantitative analysis was hampered by a relatively small change in signal intensity compared to the background signal. "
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ABSTRACT: Novel molecular imaging techniques are at the forefront of both preclinical and clinical imaging strategies. They have significant potential to offer visualisation and quantification of molecular and cellular changes in health and disease. This will help to shed light on pathobiology and underlying disease processes and provide further information about the mechanisms of action of novel therapeutic strategies. This review explores currently available molecular imaging techniques that are available for preclinical studies with a focus on optical imaging techniques and discusses how current and future advances will enable translation into the clinic for patients with arthritis.
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