Clinical evaluation of optical spectral transmission imaging for detection of disease activity in rheumatoid arthritis.

OBJECTIVE: To investigate the performance and factors of influence of optical spectral transmission (OST) imaging as a new technique for measuring joint inflammation in rheumatoid arthritis (RA). METHOD: OST was performed in 24 RA patients and 37 controls. Mann-Whitney U-test was used to assess differences in OST score between RA patients and controls. Receiver operating characteristics (ROC), linear regression and generalized estimating equations analysis were used to assess the discriminative capability of OST and the association of OST score with clinical disease parameters, ultrasound, radiographic features and cardiovascular risk parameters. RESULTS: Median OST score was higher in RA patients than in controls [16.9 (interquartile range 12.77-19.7) vs 12.11 (10.32-14.93)]. At patient level, OST score was moderately associated with ultrasound [beta 0.38 (95% CI 0.16-0.60), p = 0.001] and clinical disease activity [28-joint Disease Activity Score-C-reactive protein beta 0.30 (95% CI 0.04- 0.57), p = 0.024] in RA patients. In controls, male sex, high body mass index, and hypertension were associated with higher OST scores, while these associations were absent in RA. At joint level, the area under the ROC curve for OST score, with ultrasound or clinical swelling as reference, ranged from 0.63 to 0.70. Joint-space narrowing and malalignment were associated with higher OST joint scores, and subchondral sclerosis with lower scores. CONCLUSION: OST provides an objective measure of synovitis and correlates moderately with other examined disease activity assessment tools. Clinical patient characteristics must be considered when interpreting the results.

Development of a simple standardized scoring system for assessing large vessel vasculitis by 18F-FDG PET-CT and differentiation from atherosclerosis.

PURPOSE: This study is to develop a structured approach to distinguishing large-artery vasculitis from atherosclerosis using 18-fluorodeoxyglucose positron emission tomography combined with low-dose computed tomography (FDG PET/CT). METHODS: FDG PET/CT images of 60 patients were evaluated, 30 having biopsy-proven giant cell arteritis (GCA; the most common form of large-artery vasculitis), and 30 with severe atherosclerosis. Images were evaluated by 12 nuclear medicine physicians using 5 criteria: FDG uptake pattern (intensity, distribution, circularity), the degree of calcification, and co-localization of calcifications with FDG-uptake. Criteria that passed agreement, and reliability tests were subsequently analysed for accuracy using receiver operator curve (ROC) analyses. Criteria that showed discriminative ability were then combined in a multi-component scoring system. Both initial and final 'gestalt' conclusion were also reported by observers before and after detailed examination of the images. RESULTS: Agreement and reliability analyses disqualified 3 of the 5 criteria, leaving only FDG uptake intensity compared to liver uptake and arterial wall calcification for potential use in a scoring system. ROC analysis showed an area under the curve (AUC) of 0.90 (95%CI 0.87-0.92) for FDG uptake intensity. Degree of calcification showed poor discriminative ability on its own (AUC of 0.62; 95%CI 0.58-0.66). When combining presence of calcification with FDG uptake intensity into a 6-tiered scoring system, the AUC remained similar at 0.91 (95%CI 0.88-0.93). After exclusion of cases with arterial prostheses, the AUC increased to 0.93 (95%CI 0.91-0.95). The accuracy of the 'gestalt' conclusion was initially 89% (95%CI 86-91%) and increased to 93% (95%CI 91-95%) after detailed image examination. CONCLUSION: Standardised assessment of arterial wall FDG uptake intensity, preferably combined with assessment of arterial calcifications into a scoring method, enables accurate, but not perfect, distinction between large artery vasculitis and atherosclerosis.

Does a short course of etanercept influence disease progression and radiographic changes in patients suspected of non-radiographic axial spondyloarthritis? Three -years follow- up of a placebo-controlled trial.

OBJECTIVE: To study the long-term effect of 16 weeks of etanercept treatment on disease activity and radiographic changes in patients with suspected non-radiographic axial spondyloarthritis (nr-axSpA). METHOD: Eighty patients with inflammatory back pain and suspected nr-axSpA, with a Bath Ankylosing Disease Activity Index (BASDAI) ≥ 4, received etanercept (n = 40) 25 mg twice weekly or placebo (n = 40) for 16 weeks. They were followed without treatment restrictions after 24 weeks, for up to 3 years. Comparisons were made between patients who received etanercept or placebo in the first period, and changes in BASDAI, Ankylosing Spondylitis Disease Activity Score (ASDAS), Bath Ankylosing Spondylitis Metrology Index (BASMI), function, and radiographic changes in the spine [according to the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS)] and sacroiliac joints (Bath Ankylosing Spondylitis Radiology Index (BASRI). RESULTS: After 3 years of follow-up, 84% of the patients were diagnosed with SpA, predominantly axSpA. Biological treatment was started after 24 weeks in 30% of patients. Disease activity scores after 3 years did not reveal significant differences between the initial randomization groups in mean BASDAI scores (mean difference 0.9, 95% CI -1.1;0.7, p = 0.6) and ASDAS (mean ASDAS 0.3, 95% CI 0.6;3.1, p = 0.5). BASMI and function scores remained stable over 3 years. No differences in radiographic changes of the sacroiliac joints or spine were observed over 3 years between the two groups. CONCLUSION: A short course of etanercept in patients with suspected nr-axSpA did not affect disease activity, the chance of biological treatment, or radiographic progression after 3 years of follow-up.

Imaging disease activity of rheumatoid arthritis by macrophage targeting using second generation translocator protein positron emission tomography tracers.

BACKGROUND: Positron emission tomography (PET) imaging of macrophages using the translocator protein (TSPO) tracer (R)-[11C]PK11195 has shown the promise to image rheumatoid arthritis (RA). To further improve TSPO PET for RA imaging, second generation TSPO tracers [11C]DPA-713 and [18F]DPA-714 have recently been evaluated pre-clinically showing better imaging characteristics. OBJECTIVE: A clinical proof of concept study to evaluate [11C]DPA-713 and [18F]DPA-714 to visualize arthritis in RA patients. METHODS: RA patients (n = 13) with at least two active hand joints were included. PET/CT scans of the hands were obtained after injection of [18F]DPA-714, [11C]DPA-713 and/or (R)-[11C]PK11195 (max. 2 tracers pp). Standardized uptake values (SUVs) and target-to-background (T/B) ratios were determined. Imaging data of the 3 different tracers were compared by pooled post-hoc testing, and by a head to head comparison. RESULTS: Clinically active arthritis was present in 110 hand joints (2-17 pp). Arthritic joints were visualized with both [11C]DPA-713 and [18F]DPA-714. Visual tracer uptake corresponded with clinical signs of arthritis in 80% of the joints. Mean absolute uptake in PET-positive joints was significantly higher for [11C]DPA-713 than for [18F]DPA-714, the latter being not significantly different from (R)-[11C]PK11195 uptake. Background uptake was lower for both DPA tracers compared with that of (R)-[11C]PK11195. Higher absolute uptake and lower background resulted in two-fold higher T/B ratios for [11C]DPA-713. CONCLUSIONS: [11C]DPA-713 and [18F]DPA-714 visualize arthritic joints in active RA patients and most optimal arthritis imaging results were obtained for [11C]DPA-713. Second generation TSPO macrophage PET provides new opportunities for both early diagnosis and therapy monitoring of RA.

Extracranial giant cell arteritis: A narrative review.

A systematic literature search was performed to summarise current knowledge on extracranial giant cell arteritis (GCA), i.e. large-artery involvement in patients with or without clinically apparent temporal arteritis (cranial GCA). Extracranial GCA is increasingly recognised, both in patients with cranial GCA and with solitary extracranial GCA, due to increased awareness among physicians and development of modern imaging modalities. The literature on the pathogenesis and histopathology of extracranial GCA is scarce. It is considered to be similar to cranial GCA. Patients with solitary extracranial GCA often present with non-specific signs and symptoms, although vascular manifestations, mostly secondary to stenosis, may occur. Due to the non-specific clinical presentation and low sensitivity of temporal artery biopsies, extracranial GCA is usually diagnosed by imaging. 18F-FDG-PET, MRI, CT angiography and ultrasound are used for this purpose. At present, the optimal diagnostic strategy is undetermined. The choice for a particular modality can be guided by the clinical scenario that raises suspicion of extracranial GCA, in addition to local availability and expertise. Extracranial complications in GCA consist of aortic aneurysm or dissection (mainly the ascending aorta), aortic arch syndrome, arm claudication and posterior stroke (although this is technically a cranial complication, it often results from stenosis of the vertebrobasilar arteries). Mortality is generally not increased in patients with GCA. Treatment of patients with solitary extracranial and those with extracranial and cranial GCA has been debated in the recent literature. In general, the same strategy is applied as in patients with temporal arteritis, although criteria regarding who to treat are unclear. Surgical procedures may be indicated, in which case optimal medical treatment prior to surgery is important.

Large-vessel vasculitis: interobserver agreement and diagnostic accuracy of 18F-FDG-PET/CT.

INTRODUCTION: (18)F-FDG-PET visualises inflammation. Both atherosclerosis and giant cell arteritis cause vascular inflammation, but distinguishing the two may be difficult. The goal of this study was to assess interobserver agreement and diagnostic accuracy of (18)F-FDG-PET for the detection of large artery involvement in giant cell arteritis (GCA). METHODS: 31 (18)F-FDG-PET/CT scans were selected from 2 databases. Four observers assessed vascular wall (18)F-FDG uptake, initially without and subsequently with predefined observer criteria (i.e., vascular wall (18)F-FDG uptake compared to liver or femoral artery (18)F-FDG uptake). External validation was performed by two additional observers. Sensitivity and specificity of (18)F-FDG-PET were determined by comparing scan results to a consensus diagnosis. RESULTS: The highest interobserver agreement (kappa: 0.96 in initial study and 0.79 in external validation) was observed when vascular wall (18)F-FDG uptake higher than liver uptake was used as a diagnostic criterion, although agreement was also good without predefined criteria (kappa: 0.68 and 0.85). Sensitivity and specificity were comparable for these methods. The criterion of vascular wall (18)F-FDG uptake equal to liver (18)F-FDG uptake had low specificity. CONCLUSION: Standardization of image assessment for vascular wall (18)F-FDG uptake promotes observer agreement, enables comparative studies, and does not appear to result in loss of diagnostic accuracy compared to nonstandardized assessment.

Present role of positron emission tomography in the diagnosis and monitoring of peripheral inflammatory arthritis: a systematic review.

OBJECTIVE: To determine the current status of positron emission tomography (PET) as a tool for diagnosis and monitoring of peripheral inflammatory arthritis (IA). METHODS: For conducting this systematic review, the PubMed (Medline), Embase, and Cochrane Library databases were searched until December 31, 2012. Studies of PET for diagnosis and/or therapy monitoring of peripheral IA were included. Data were summarized qualitatively using best evidence synthesis. RESULTS: Eighteen articles met our inclusion criteria. The majority of studies were feasibility studies with varying methods applied. All studies demonstrated that PET visualized IA with high sensitivity, corresponding to clinical assessments. PET outcome of clinically active IA also matched that of ultrasound and magnetic resonance imaging. PET differentiates from other modalities by (quantitative) imaging of molecular sites in the synovium. The first studies reporting on the potential clinical applications of PET to image subclinical synovitis in preclinical RA and during therapy have been published. The results are promising, but the number and study populations of these studies are still limited. CONCLUSION: Thus far, a limited number of PET studies addressing IA imaging have been published. The PET modality seems to offer highly sensitive and potentially specific imaging of IA at the (quantitative) molecular level. Clinical application studies for early diagnostics and therapy monitoring are arising, but these topics should be further explored in future studies with larger cohorts. For integration in clinical practice, aspects such as radiation burden and cost-effectiveness should also be taken into account.

Arthritis development in patients with arthralgia is strongly associated with anti-citrullinated protein antibody status: a prospective cohort study.

BACKGROUND: Anti-citrullinated protein antibodies (ACPA) are associated with increased risk for rheumatoid arthritis. OBJECTIVE: To investigate the effect of the presence and levels of ACPA on arthritis development in patients with arthralgia. METHODS: Patients with arthralgia positive for ACPA or IgM rheumatoid factor (IgM-RF) were tested for the shared epitope (SE) and were prospectively followed up for at least 12 months. Absence of clinical arthritis at inclusion and arthritis development during follow-up were independently confirmed by two investigators. Cox regression hazard analyses were used to calculate hazard ratios (HRs) for arthritis development. RESULTS: 147 patients with arthralgia were included (50 ACPA positive, 52 IgM-RF positive and 45 positive for both antibodies). After a median follow-up of 28 months (interquartile range (IQR) 19-39), 29 patients developed arthritis in a median of 4 (IQR 3-6) joints and 26 (90%) of these were ACPA positive. The presence of ACPA (HR = 6.0; 95% confidence interval (95% CI) 1.8 to 19.8; p = 0.004), but not of IgM-RF (HR = 1.4, 95% CI 0.6 to 3.1) nor the SE (HR = 1.5, 95% CI 0.7 to 3.0), was associated with arthritis development. Within the group of ACPA-positive patients, the risk for arthritis was enhanced by the presence of IgM-RF (HR = 3.0; 95% CI 1.4 to 6.9; p = 0.01) and high ACPA levels (HR = 1.7; 95% CI 1.1 to 2.5; p = 0.008), but not the SE (HR = 1.0; 95% CI 0.5 to 2.1; p = 1.0). CONCLUSION: In patients with arthralgia the presence of ACPA (but not of IgM-RF or SE) predicts arthritis development. The risk in ACPA-positive patients may be further increased by the concomitant presence of IgM-RF or high levels of ACPA.

Quantification of (R)-[11C]PK11195 binding in rheumatoid arthritis.

PURPOSE: Rheumatoid arthritis (RA) involves migration of macrophages into inflamed areas. (R)-[(11)C]PK11195 binds to peripheral benzodiazepine receptors, expressed on macrophages, and may be used to quantify inflammation using positron emission tomography (PET). This study evaluated methods for the quantification of (R)-[(11)C]PK11195 binding in the knee joints of RA patients. METHODS: Data from six patients with RA were analysed. Dynamic PET scans were acquired in 3-D mode following (R)-[(11)C]PK11195 injection. During scanning arterial radioactivity concentrations were measured to determine the plasma (R)-[(11)C]PK11195 concentrations. Data were analysed using irreversible and reversible one-tissue and two-tissue compartment models and input functions with various types of metabolite correction. Model preferences according to the Akaike information criterion (AIC) and correlations between measures were evaluated. Correlations between distribution volume (V(d)) and standardized uptake values (SUV) were evaluated. RESULTS: AIC indicated optimal performance for a one-tissue reversible compartment model including blood volume. High correlations were observed between V(d) obtained using different input functions (R(2)=0.80-1.00) and between V(d) obtained with one- and two-tissue reversible compartment models (R(2)=0.75-0.94). A high correlation was observed between optimal V(d) and SUV after injection (R(2)=0.73). CONCLUSION: (R)-[(11)C]PK11195 kinetics in the knee were best described by a reversible single-tissue compartment model including blood volume. Applying metabolite corrections did not increase sensitivity. Due to the high correlation with V(d), SUV is a practical alternative for clinical use.

[The formation of infliximab and anti-infliximab immune complexes as an explanation for non-responding to infliximab treatment of rheumatoid arthritis: observational study in 4 patients]. / Het ontstaan van immuuncomplexen van infliximab en anti-infliximab als een verklaring voor het falen van infliximabtherapie bij reumatoïde artritis: observationeel onderzoek bij 4 patiënten.

OBJECTIVE: To investigate the in vivo mechanism of non-responding to infliximab treatment of patients with rheumatoid arthritis (RA) and the role of anti-infliximab antibodies by using radiolabeled infliximab. DESIGN: Descriptive and comparative study. METHOD: Two responding and two non-responding RA patients were infused with radiolabeled infliximab. Subsequently imaging investigations and serum analysis were performed at set times. RESULTS: The scintigrams showed that the labelled infliximab was mainly present in the blood until 24 h after infusion. There was a trend of faster blood clearance and higher liver and spleen uptake of 99mTc-infliximab in one non-responding patient. Labelled infliximab was taken up by inflamed joints. The anti-infliximab level was high (1008 and 1641 U/ml) in the non-responders and low or not detectable in the responders. Sucrose gradients of serum revealed antibody complexes in both non-responders. Various sizes of antibody complexes, including very large ones, were observed in one non-responder who developed a serious infusion reaction. CONCLUSION: Infliximab-anti-infliximab immune complexes were found to form in RA non-responders due to the presence of significant quantities of anti-infliximab. This finding may partly explain the failure of the infliximab treatment.

2-Deoxy-2-[F-18]fluoro-D-glucose joint uptake on positron emission tomography images: rheumatoid arthritis versus osteoarthritis.

PURPOSE: Previous positron emission tomography (PET) studies have shown increased 2-deoxy-2-[18F]fluoro-D-glucose (FDG) uptake in joints of patients with osteoarthritis (OA) and inflamed joints of patients with rheumatoid arthritis (RA). This study compares FDG uptake in joints of RA and OA patients and FDG-uptake with clinical signs of inflammation. PROCEDURES: FDG-PET scans of hands and wrists were performed in patients with RA and primary OA. PET data were compared with clinical data. RESULTS: 29% of RA joints and 6% of OA joints showed elevated FDG-uptake. The level of uptake in PET-positive OA joints was not significantly different from that in RA joints. The majority of PET results of RA joints corresponded with clinical findings. Clinical synovitis was found some OA joints with FDG-uptake. CONCLUSIONS: FDG-uptake was observed in the majority of clinically inflamed RA joints and in a few OA joints with no significant difference in uptake level. The latter may be due to secondary synovitis.

Imaging and serum analysis of immune complex formation of radiolabelled infliximab and anti-infliximab in responders and non-responders to therapy for rheumatoid arthritis.

BACKGROUND: Many patients with rheumatoid arthritis are currently successfully treated with infliximab (anti-tumour necrosis factor); however, about 30% of the patients do not respond to infliximab. One of the postulated hypotheses of not responding is the fast clearance of infliximab due to the development of infliximab-anti-infliximab complexes. OBJECTIVE: To investigate the in vivo mechanism of not responding and the role of human anti-chimeric antibodies (HACAs) by using radiolabelled infliximab. METHODS: Two responding and two non-responding patients with rheumatoid arthritis, infused with radiolabelled infliximab, were investigated by both imaging and serum analysis. RESULTS: Images showed predominant presence of infliximab in blood up to 24 h, with a trend of faster blood clearance and of higher liver/spleen uptake in a non-responding patient. Clinically inflamed joints showed uptake of the drug. The HACA level in the non-responders was high (1641 and 1008 U/ml), but low or not detectable in responders. Sucrose gradients of serum showed antibody complexes in both non-responders. Various sizes of antibody complexes, including very large ones, were observed in a non-responder who developed a serious infusion reaction. CONCLUSION: Formation of infliximab-anti-infliximab complexes were found in non-responders due to the presence of large amounts of HACA. This finding, supported by both imaging and serum analysis data, may explain failure of infliximab treatment.

Radiolabelled interleukin-1 receptor antagonist for detection of synovitis in patients with rheumatoid arthritis.

OBJECTIVES: To investigate the distribution of radiolabelled interleukin-1 receptor antagonist (IL-1ra) in patients with rheumatoid arthritis (RA) and to assess whether this cytokine is suitable for scintigraphic visualization of synovitis. METHODS: In patients with active RA, scintigraphy was performed after a single i. v. dose of [(123)I]IL-1ra. Clearance and organ distribution of radiolabelled IL-1ra were studied. To assess whether radiolabelled IL-1ra targets the synovial IL-1 receptors, the scintigraphic images obtained with IL-1ra were compared with those obtained by the use of a non-specific control agent. In addition, autoradiography was performed in mice with antigen-induced arthritis that were injected with either radiolabelled IL-1ra or a size-matched, non-receptor-binding protein. RESULTS: Radiolabelled IL-1ra allowed clear visualization of inflamed joints. Specificity in the detection of synovitis was high, whereas a number of painful and swollen joints were not visualized by scintigraphy. The procedure was well tolerated and [(123)I]IL-1ra was rapidly cleared from the circulation (t(1/2)alpha 11 min, t(1/2)beta 612 min) and excreted mainly in the urine. The definition of synovial contours by IL-1ra scintigraphy was not better than that observed with a non-specific agent. Although radiolabelled IL-1ra retained its affinity for IL-1 receptors, no binding to synovium was observed by autoradiography. CONCLUSIONS: Radiolabelled IL-1ra allows the visualization of synovitis in patients with RA. However, neither the imaging nor the autoradiographic studies indicate that joint accumulation of radiolabelled IL-1ra is due to specific IL-1 receptor targeting. IL-1ra has proved its therapeutic value in RA, but with the dose schedule in this study it does not behave as a specific radiopharmaceutical that is suitable for scintigraphic detection of inflammation.

Radiolabeled interleukin-8: specific scintigraphic detection of infection within a few hours.

UNLABELLED: Several small receptor-binding agents have been tested for imaging of infection and inflammation. The potential of chemotactic peptides and of interleukins is promising and superior to that of conventional agents. In this study, we investigated the potential of interleukin-8 (IL-8) to image infection in rabbits. METHODS: IL-8 was labeled with 123I using the Bolton-Hunter method. Twenty-fours hours after induction of Escherichia coli abscesses in the left thigh muscle, rabbits were injected intravenously with 18.5 MBq 123I-IL-8. Gamma camera images were obtained at 5 min and at 1, 4, and 8 h after injection. Biodistribution was determined 8 h after injection. RESULTS: 123I-IL-8 rapidly cleared from the blood. Accumulation of 123I-IL-8 in the abscess was visible as early as 1 h after injection. The highest abscess uptake was obtained 4 h after injection (2.6+/-0.2 percentage injected dose [%ID]), whereas 123I-IL-8 rapidly cleared from all other tissues. This resulted in increases in abscess-to-background ratios to 13.0+/-0.7 (8 h after injection), as determined by quantification of the images. In tissue biodistribution (8 h after injection), the abscess uptake was 0.057+/-0.011 %ID/g with abscess-to-contralateral muscle ratios of 114.7+/-23.0. The radioiodination method clearly affected the in vivo biodistribution of IL-8 because IL-8 iodinated using the lodo-Gen method cleared significantly slower from the blood and most other organs, resulting in poor visualization of the abscess. CONCLUSION: The superior characteristics of IL-8 radioiodinated using the Bolton-Hunter method--i.e., high abscess uptake and rapid background clearance within a few hours--make IL-8 a promising agent to image infection and inflammation.

The kinetics of radiolabelled interleukin-8 in infection and sterile inflammation.

Radiolabelled interleukin-8 (IL-8) is a promising agent for the imaging of infection and inflammation. Several experiments were performed to explore further the imaging potential of radiolabelled IL-8. IL-8 was radioiodinated via the Bolton-Hunter method. Rabbits with focal infection (Escherichia coli, Staphylococcus aureus) or sterile inflammation (zymosan) were injected intravenously with 18.5 MBq (0.5 mCi) of 123I-IL-8. In separate studies, rabbits were injected intravenously with 111In-granulocytes with or without 125I-IL-8. Gamma camera images were obtained at 5 min, 1, 4 and 8 h post-injection (p.i.). Biodistribution was determined at 8 h p.i. In all models, the biodistribution of 123I-IL-8 was characterized by rapid blood clearance and high uptake in infection and sterile inflammation. All foci could be clearly visualized within 4 h p.i. Ex vivo abscess-to-contralateral muscle ratios increased to 114.7+/-23.0 (E. coli), 52.3+/-24.5 (S. aureus) and 49.8+/-8.3 (zymosan) at 8 h p.i. In the circulation, most 123I-IL-8 was bound to erythrocytes. The abscess uptake of 125I-IL-8 reached high levels despite reduced migration of granulocytes towards the site of infection due to the anti-inflammatory activity of intravenously injected IL-8. IL-8 could be injected without induction of neutropenia at a dosage of 2 ng kg(-1). In conclusion, the characteristics of radiolabelled IL-8 for imaging of infection and sterile inflammation are highly encouraging and warrant further optimization for clinical application.

Scintigraphic detection of infection and inflammation: new developments with special emphasis on receptor interaction.

Various conventional radiopharmaceuticals are currently available for scintigraphic imaging of infection and inflammation. Although a wide variety of infectious and inflammatory foci can be detected with these agents, several disadvantages limit their application. These limitations have stimulated the search for new radiopharmaceuticals. In the past decade a new class of radiopharmaceuticals has emerged: radiolabelled receptor-specific small proteins and peptides. These proteins and peptides are naturally occurring inflammatory mediators which specifically bind to receptors abundantly present in the area of inflammation. In addition, owing to their small size, they rapidly clear from all non-target tissues. This paper provides an overview of these newly developed agents, focussing on imaging characteristics and in vivo uptake mechanisms.

Imaging of infection in rabbits with radioiodinated interleukin-1 (alpha and beta), its receptor antagonist and a chemotactic peptide: a comparative study.

Previous studies have reported the favourable characteristics of chemotactic peptides and interleukins for imaging of infection and inflammation. In the present study, the potential of two species of interleukin 1 (IL-1), IL-1alpha and IL-1beta, the IL-1 receptor antagonist (IL-1ra) and the synthetic chemotactic peptide N-formyl-methionyl-leucyl-phenylalanyl-lysine (fMLFK) were directly compared in a rabbit model of infection. IL-1alpha, IL-1beta, IL-1ra and fMLFK were labelled with iodine-123 according to the Bolton-Hunter method. Twenty-four hours after induction of Escherichia coli abscesses in the left thigh muscle, rabbits were injected intravenously with 0.5 mCi of 123I-labelled agent. Gamma camera images were obtained at 5 min and 1, 4, 8 and 20 h p.i. Biodistribution was determined at 20 h p.i. Although all agents rapidly cleared from the blood, at 20 h p.i. blood levels and the levels in most organs of 123I-fMLFK were significantly lower than those of the other three agents (P<0.05). The abscesses were clearly visualized with all agents from 4 h p.i. onwards. After 1 h p.i., the abscess uptake of 123I-IL-1beta was significantly higher than that of the other agents (P<0.05), with the highest uptake observed at 8 h p.i. (1.3%+/-0.3%). After 20 h p.i., the highest abscess-to-contralateral muscle ratios were obtained with 123I-IL-1beta, i.e. 39.0+/-11.5 vs 18.7+/-5.4, 18.1+/-2.3 and 29. 9+/-7.0 for 123I-IL-1alpha, 123I-IL-1ra and 123I-fMLFK, respectively. In conclusion, all agents localized in the infectious focus. The potential of radiolabelled IL-1beta for imaging of infection was better than that of the other agents: higher absolute uptake in the infection and higher abscess-to-contralateral muscle ratios were obtained. The observation of localization of radiolabelled IL-1ra in infection was important since this protein can be administered to humans without any side-effects.

In vivo expression of interleukin-1 receptors during various experimentally induced inflammatory conditions.

Systemically administered interleukin-1 (IL-1) has been shown to preferentially bind to IL-1 receptors (IL-1Rs) in inflammation. Using radiolabeled IL-1alpha and molecular methods to assess gene expression for these receptors, the in vivo behavior of these receptors was investigated in a number of experimental inflammatory conditions. The uptake of 125I-labeled IL-1alpha in inflammatory foci significantly correlated with the mRNA expression for the type I and type II IL-1Rs (P < .05). Type II IL-1R mRNA showed a greater increase in expression than type I IL-1R mRNA. In neutropenic mice, inflammatory lesions, which are devoid of granulocytes, significantly lower 125I-labeled IL-1alpha uptake (P < .001), and type II IL-1R mRNA expression (P < .005) was found. Thus, there is strong up-regulation of IL-1Rs at sites of focal inflammation. Of interest, this mainly involved the type II IL-1R on granulocytes, which is not involved in signal transduction.

Technetium-99m-labeled chemotactic peptides in acute infection and sterile inflammation.

UNLABELLED: Chemotactic peptides have been proposed as vehicles to image infection and inflammation. Previous studies have shown high uptake at the site of infection soon after injection, most likely because of specific binding to receptors on locally present leukocytes. To investigate this hypothesis, the in vivo behavior of a synthetic chemotactic peptide was compared to a control peptide of similar molecular weight with low receptor binding affinity. In addition, the potential to target to different infections and sterile inflammation was tested. METHODS: Twenty-four hours after induction of Escherichia coli, Staphylococcus aureus and zymosan abscesses, rabbits were i.v. injected with either 1 mCi of 99mTc-labeled formyl-methionyl-leucyl-phenylalanyl-lysine-hydrazinonicotinamid e (99mTc-fMLFK-HYNIC) or 99mTc-labeled hydrazinonicotinamide-methionyl-leucyl-phenylalanyl-OMe (99mTc-HYNIC-MLFOMe, control peptide). Gamma camera images were obtained at 5 min and 1, 4, 8 and 20 hr postinjection. Biodistribution was determined at 20 hr postinjection. RESULTS: The blood clearances of 99mTc-fMLFK-HYNIC and 99mTc-HYNIC-MLFOMe were similar. With time, 99mTc-fMLFK-HYNIC was retained in the abscess (E. coli), whereas the control agent 99mTc-HYNIC-MLFOMe was cleared from the abscess (0.049 +/- 0.011 versus 0.005 +/- 0.0003% 1D/g at 20 hr postinjection; p < 0.0005). Abscess-to-contralateral muscle ratios of 99mTc-fMLFK-HYNIC rose to 36.8 +/- 4.3 at 20 hr postinjection. E. coli, S. aureus and zymosan abscesses were clearly visualized from 4 hr postinjection onward. Abscess-to-background ratios increased to values varying from 4.4 +/- 0.2 (zymosan) to 7.1 +/- 0.6 (S. aureus) at 20 hr postinjection. The uptake in S. aureus and zymosan abscesses did not differ significantly from the uptake in E. coli abscesses. CONCLUSIONS: fMLFK-HYNIC is retained in both acute infection and sterile inflammation by means of specific receptor binding if sufficient cellular infiltration is present.