In vivo molecular imaging of experimental joint inflammation by combined (18)F-FDG positron emission tomography and computed tomography

The relationship between right atrial wall inflammation and poor prognosis of atrial fibrillation based on 18F-FDG positron emission tomography/computed tomography

Background

Atrial fibrillation (AF) has been identified to increase stroke risk, even after oral anticoagulants (OACs), and the recurrence rate is high after radiofrequency catheter ablation (RFCA). Inflammation is an essential factor in the occurrence and persistence of AF. 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) is an established molecular imaging modality to detect local inflammation. We aimed to investigate the relationship between atrial inflammatory activity and poor prognosis of AF based on 18F-FDG PET/CT.

Methods

A total of 204 AF patients including 75 with paroxysmal AF (ParAF) and 129 with persistent AF (PerAF) who underwent PET/CT before treatment were enrolled in this prospective cohort study. Clinical data, electrocardiograph (ECG), echocardiography, and cardiac 18F-FDG uptake were collected. Follow-up information was obtained from patient clinical case notes or telephone reviews, with the starting point being the time of PET/CT scan. The follow-up deadline was either the date of AF recurrence after RFCA, new-onset stroke, or May 2023. Cox proportional hazards regression models were used to identify predictors of poor prognosis and hazard ratios (HRs) with 95% confidence intervals (CIs) was calculated.

Results

Median follow-up time was 29 months [interquartile range (IQR), 22-36 months]. Poor prognosis occurred in 52 patients (25.5%), including 34 new-onset stroke patients and 18 recrudescence after RFCA. The poor prognosis group had higher congestive heart failure, hypertension, age ≥75 years (doubled), diabetes mellitus, prior stroke or transient ischemic attack (TIA) or thromboembolism (doubled), vascular disease, age 65-74 years, sex category (female) (CHA2DS2-VASc) score [3.0 (IQR, 1.0-3.75) vs. 2.0 (IQR, 1.0-3.0), P=0.01], right atrial (RA) wall maximum standardized uptake value (SUVmax) (4.13±1.82 vs. 3.74±1.58, P=0.04), higher percentage of PerAF [39 (75.0%) vs. 90 (59.2%), P=0.04], left atrial (LA) enlargement [45 (86.5%) vs. 104 (68.4%), P=0.01], and RA wall positive FDG uptake [40 (76.9%) vs. 79 (52.0%), P=0.002] compared with the non-poor prognosis group. Univariate and multivariate Cox proportional hazard regression analysis concluded that only CHA2DS2-VASc score (HR, 1.29; 95% CI: 1.06-1.57; P=0.01) and RA wall positive FDG uptake (HR, 2.68; 95% CI: 1.10-6.50; P=0.03) were significantly associated with poor prognosis.

Conclusions

RA wall FDG positive uptake based on PET/CT is tightly related to AF recurrence after RFCA or new-onset stroke after antiarrhythmic and anticoagulation treatment.

Right atrial wall inflammation detected by 18F-FDG PET/CT may be significantly associated with persistent atrial fibrillation: a prospective case-control study

AIM

Atrial fibrillation (AF) is a progressive disease from paroxysmal to persistent, and persistent AF (PerAF) had worse prognosis. AF has potential link with inflammation, but it is not clear whether PerAF or paroxysmal AF (ParAF) is more closely related to inflammation. On the basis of inhibiting myocardial physiological uptake, 18F-fluorodeoxyglucosepositron emission tomography/computed tomography (18F-FDG PET/CT) is an established imaging modality to detect cardiac inflammation. We aimed to decipher the association between AF and atrial inflammatory activity by 18F-FDG PET/CT.

METHODS

Thirty-five PerAF patients were compared to age and sex matched ParAF group with baseline 18F-FDG PET/CT scans prior to radiofrequency catheter ablation (RFCA) in the prospective case-control study. High-fat and low-carbohydrate diet and prolonged fast (HFLC+Fast) was applied to all AF patients before PET/CT. Then 22 AF patients with positive right atrial (RA) wall FDG uptake (HFLC+Fast) were randomly selected and underwent HFLC+Fast+heparin the next day. The CHA2DS2-VASc score was calculated to evaluate the risk of stroke. Clinical data, ECG, echocardiography, and atrial 18F-FDG uptake were compared.

RESULTS

PerAF patients had significantly higher probability of RA wall positive FDG uptake and higher SUVmax than ParAF group [91.4% VS. 28.6%, P < 0.001; SUVmax: 4.10(3.20-4.90) VS. 2.60(2.40-3.10), P < 0.001]. Multivariate logistic regression analyses demonstrated that RA wall SUVmax was the independent influencing factor of PerAF (OR = 1.80, 95%CI 1.02-3.18, P = 0.04). In 22 AF patients with RA wall positive FDG uptake (HFLC+Fast), the "HFLC+Fast+Heparin" method did not significantly change RA wall FDG uptake evaluated by either quantitative analysis or visual analysis. High CHA2DS2-VASc score group had higher RA wall 18F-FDG uptake [3.35 (2.70, 4.50) vs, 2.8 (2.4, 3.1) P = 0.01].

CONCLUSIONS

RA wall FDG positive uptake was present mainly in PerAF. A higher RA wall 18F-FDG uptake was an independent influencing factor of PerAF. RA wall FDG uptake based on 18F-FDG PET/CT may indicate pathological inflammation.

TRIAL REGISTRATION

http://www.chictr.org.cn , ChiCTR2000038288.

The Value of 18F-FDG PET/MRI in Detecting Lumbar Radiculopathy for Selective Percutaneous Endoscopic Discectomy: a Case Report

Magnetic resonance imaging (MRI) is the most popular imaging modality for investigating intervertebral disc herniation. However, it has a high chance for identifying incidental findings that are morphologically or structurally abnormal but not responsible for patients' symptoms. Although a previous study suggested that 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) may help identify neuroinflammation in lumbar radiculopathy, there is currently no direct evidence obtained from surgery. Here, we describe the case of a 32-year-old man with low back pain and right leg paresthesia for 7 months. MRI demonstrated disc herniation at the L3-L4, L4-L5 and L5-S1 levels, causing bilateral L5 and left S1 root compression. 18F-FDG PET/MRI demonstrated increased 18F-FDG uptake at the right L5 root, which was compatible with the patient's symptoms. Transforaminal percutaneous endoscopic lumbar discectomy (PELD) was performed. Intraoperative images revealed a swollen nerve root at the right L5 after removal of the herniated disc. After surgery, the patient experienced immediate pain relief and had no recurrence at the 6-month follow-up. When performing PELD in patients with multilevel radiculopathy identified on MRI, the use of 18F-FDG PET/MRI can help in accurate localization of the symptomatic roots and minimize surgical incision and soft-tissue injury.

Review on risk factors, classification, and treatment of sternal wound infection

Sternal wound infection (SWI) is the most common complication of the median sternal incision. The treatment time is long, and the reconstruction is difficult, which causes challenges for surgeons. Plastic surgeons were often involved too late in such clinical scenarios when previous empirical treatments failed and the wound damage was relatively serious. Accurate diagnosis and risk factors against sternal wound infection need to be in focus. Classification of different types of sternotomy complications post-cardiac surgery is important for specific categorization and management. Not familiar with this kind of special and complex wound, objectively increasing the difficulty of wound reconstruction. The purpose of this comprehensive review is to review the literature, introduce various SWI risk factors related to wound nonunion, various classification characteristics, advantages and disadvantages of various wound reconstruction strategies, to help clinicians understand the pathophysiological characteristics of the disease and choose a better treatment method.

Right Atrial Fluorodeoxyglucose Uptake Is a Risk Factor for Stroke and Improves Prediction of Stroke Above the CHA2DS2-VASc Score in Patients With Atrial Fibrillation

Background

Atrial fibrillation (AF) is a common arrhythmia, and its most severe and dreaded complication is stroke. The CHA2DS2-VASc score is currently recommended for stroke risk assessment in AF. We aimed to explore the relationship between atrial FDG uptake and stroke and whether atrial FDG uptake could provide incremental value above the CHA2DS2-VAS score to predict stroke in AF by 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT).

Materials and Methods

From September 2017 to December 2020, we retrospectively enrolled 230 patients (115 with AF and 115 without AF as the non-AF group, matched for the date of PET/CT examination and the basic characteristics of the patient) who underwent 18F-FDG PET/CT due to tumor screening or preoperative staging after prolonged fasting and followed up for at least 12 months from the date of PET/CT examination; the endpoint event is the occurrence of stroke. We visually and quantitatively analyzed 18F-FDG uptake in the right and left atria (RA/LA), right and left atrial appendage (RAA/LAA), right and left ventricle (RV/LV), and collected clinical features. In addition, according to the endpoint event (stroke), the enrolled population was divided into the stroke group and non-stroke group, and relevant clinical features and atrial FDG uptake indicators of the two groups were analyzed. Univariate and multivariate Cox regression analyzes were used to analyze the risk factors of stroke events. The Kaplan–Meier survival curve of atrial FDG uptake was drawn, and the log-rank method was used to compare the differences in the survival curves of the two groups. Receiver operating characteristic (ROC) curves were used to examine the discriminatory power of atrial FDG uptake in predicting stroke and determine whether the addition of atrial FDG uptake improves predictive value beyond the CHA2DS2-VASc score for stroke.

Results

In the AF group, more than half of patients had RA FDG uptake and one-fifth had LA FDG uptake, while one patient had RA FDG uptake and two patients had LA FDG uptake in the non-AF group. In quantitative analysis, the maximum standardized uptake value (SUVmax) of the RA and LA in the AF group was significantly higher than that of the non-AF group (all P &lt; 0.001). We followed up the patients for 28 ± 10 months, and finally, 31 patients had stroke. In the stroke group, atrial fibrillation, RA SUVmax, RAA SUVmax, LAA SUVmax, age ≥ 75 years, and left atrial dilation were significantly higher than those of the non-stroke group (all P &lt; 0.05). Multivariate Cox regression analysis showed that high RA SUVmax (RA SUVmax ≥ 2.62) was an independent risk factor for stroke (HR = 4.264, 95% CI 1.368–13.293, P = 0.012). By using the log-rank test, patients with high RA SUVmax had a significantly higher incidence of stroke compared with patients with low RA SUVmax (P &lt; 0.001). Addition of high RA SUVmax to the CHA2DS2-VASc score could predict stroke more effectively, with a larger AUC 0.790 (P &lt; 0.001).

Conclusion

This study found a significant correlation between atrial FDG uptake and AF, especially in RA. Meanwhile, RA FDG uptake is an independent risk factor for stroke, and patients with high RA SUVmax have a significantly higher risk of stroke. Moreover, RA FDG uptake improves prediction of stroke above the CHA2DS2-VASc score in patients with AF.

Preclinical evaluation and pilot clinical study of [18F]AlF-NOTA-FAPI-04 for PET imaging of rheumatoid arthritis

PURPOSE

Fibroblast-like synoviocytes (FLSs) are key effector cells in the inflamed joints of patients with rheumatoid arthritis (RA). Previous studies have suggested that fibroblast activation protein (FAP) is highly expressed in RA-derived FLSs and is a specific marker of activated RA FLSs. In this study, we developed aluminum-[¹⁸F]-labeled 1,4,7-triazacyclononane-N,N',N″-triacetic acid-conjugated FAP inhibitor 04 ([¹⁸F]AlF-NOTA-FAPI-04) to image RA-FLSs in vitro and arthritic joints in collagen-induced arthritis (CIA) mice and RA patients.

METHODS

RA FLSs and NIH3T3 cells transfected with FAP were used to perform in vitro-binding studies. Biodistribution was conducted in normal DBA1 mice. Collagen-induced arthritis (CIA) models with different arthritis scores were subjected to [¹⁸F]AlF-NOTA-FAPI-04 and ¹⁸F-FDG PET imaging. Histological examinations were performed to evaluate FAP expression and Cy3 dye-labeled FAPI-04(Cy3-FAPI-04) uptake. Blocking studies with excess unlabeled FAPI-04 in CIA mice and NIH3T3 xenografts in immunocompromised mice were used to evaluate the binding specificity of [¹⁸F]AlF-NOTA-FAPI-04. Additionally, [¹⁸F]AlF-NOTA-FAPI-04 PET imaging was performed on two RA patients.

RESULTS

The binding of [¹⁸F]AlF-NOTA-FAPI-04 increased significantly in RA FLSs and NIH3T3 cells overexpressing FAP compared to their parental controls (^FAP-GFP-NIH3T3 vs. ^GFP-NIH3T3, 2.40 ± 0.078 vs. 0.297 ± 0.05% AD/10⁵ cells; RA FLSs vs. OA FLSs, 1.54 ± 0.064 vs. 0.343 ± 0.056% AD/10⁵ cells). Compared to ¹⁸F-FDG imaging, [18F]AlF-NOTA-FAPI-04 showed high uptake in inflamed joints in the early stage of arthritis, which was positively correlated with the arthritic scores (Pearson r=0.834, P<0.001). In addition, the binding of [¹⁸F]AlF-NOTA-FAPI-04 to cells with high FAP expression and the uptake of [¹⁸F]AlF-NOTA-FAPI-04 in arthritic joints both could be blocked by excessive unlabeled FAPI-04. Fluorescent staining showed that the intensity of Cy3-FAPI-04 binding to FAP increased accordingly as the expression of FAP protein increased in cells and tissue sections. Furthermore, the uptake of [¹⁸F]AlF-NOTA-FAPI-04 in ^FAP-GFP-NIH3T3 xenografts was significantly higher than that in ^GFP-NIH3T3 xenograft (35.44 ± 4.27 vs 7.92 ± 1.83% ID/mL). Finally, [¹⁸F]AlF-NOTA-FAPI-04 PET/CT imaging in RA patients revealed nonphysiologically high tracer uptake in the synovium of arthritic joints.

CONCLUSION

[¹⁸F]AlF-NOTA-FAPI-04 is a promising radiotracer for imaging RA FLSs and could potentially complement the current noninvasive diagnostic parameters.

Lactate Production Precedes Inflammatory Cell Recruitment in Arthritic Ankles: an Imaging Study

PURPOSE

Inflammation is involved in many disease processes. However, accurate imaging tools permitting diagnosis and characterization of inflammation are still missing. As inflamed tissues exhibit a high rate of glycolysis, pyruvate metabolism may offer a unique approach to follow the inflammatory response and disease progression. Therefore, the aim of the study was to follow metabolic changes and recruitment of inflammatory cells after onset of inflammation in arthritic ankles using hyperpolarized 1-13C-pyruvate magnetic resonance spectroscopy (MRS) and 19F magnetic resonance imaging (MRI), respectively.

PROCEDURE

Experimental rheumatoid arthritis (RA) was induced by intraperitoneal injection of glucose-6-phosphate-isomerase-specific antibodies (GPI) containing serum. To monitor pyruvate metabolism, the transformation of hyperpolarized 1-13C-pyruvate into hyperpolarized 1-13C-lactate was followed using MRS. To track phagocytic immune cell homing, we intravenously injected a perfluorocarbon emulsion 48 h before imaging. The animals were scanned at days 1, 3, or 6 after GPI-serum injection to examine the different stages of arthritic inflammation. Finally, to confirm the pyruvate metabolic activity and the link to inflammatory cell recruitment, we conducted hematoxylin-eosin histopathology and monocarboxylase transporter (MCT-1) immune histochemistry (IHC) of inflamed ankles.

RESULTS

Hyperpolarized 1-13C-pyruvate MRS revealed a high rate of lactate production immediately at day 1 after GPI-serum transfer, which remained elevated during the progression of the disease, while 19F-MRI exhibited a gradual recruitment of phagocytic immune cells in arthritic ankles, which correlated well with the course of ankle swelling. Histopathology and IHC revealed that MCT-1 was expressed in regions with inflammatory cell recruitment, confirming the metabolic shift identified in arthritic ankles.

CONCLUSIONS

Our study demonstrated the presence of a very early metabolic shift in arthritic joints independent of phagocytic immune cell recruitment. Thus, hyperpolarized 1-13C-pyruvate represents a promising tracer to monitor acute arthritic joint inflammation, even with minor ankle swelling. Furthermore, translated to the clinics, these methods add a detailed characterization of disease status and could substantially support patient stratification and therapy monitoring.

Multimodal [18 F]FDG PET/CT Is a Direct Readout for Inflammatory Bone Repair: A Longitudinal Study in TNFα Transgenic Mice

In rheumatoid arthritis (RA), chronic joint inflammation leading to bone and cartilage damage is the major cause of functional impairment. Whereas reduction of synovitis and blockade of joint damage can be successfully achieved by disease modifying antirheumatic therapies, bone repair upon therapeutic interventions has only been rarely reported. The aim of this study was to use fluorodeoxyglucose ([¹⁸ F]FDG) and [¹⁸ F]fluoride µPET/CT imaging to monitor systemic inflammatory and destructive bone remodeling processes as well as potential bone repair in an established mouse model of chronic inflammatory, erosive polyarthritis. Therefore, human tumor necrosis factor transgenic (hTNFtg) mice were treated with infliximab, an anti-TNF antibody, for 4 weeks. Before and after treatment period, mice received either [¹⁸ F]FDG, for detecting inflammatory processes, or [¹⁸ F]fluoride, for monitoring bone remodeling processes, for PET scans followed by CT scans. Standardized uptake values (SUV_mean ) were analyzed in various joints and histopathological signs of arthritis, joint damage, and repair were assessed. Longitudinal PET/CT scans revealed a significant decrease in [¹⁸ F]FDG SUVs in affected joints demonstrating complete remission of inflammatory processes due to TNF blockade. In contrast, [¹⁸ F]fluoride SUVs could not discriminate between different severities of bone damage in hTNFtg mice. Repeated in vivo CT images proved a structural reversal of preexisting bone erosions after anti-TNF therapy. Accordingly, histological analysis showed complete resolution of synovial inflammation and healing of bone at sites of former bone erosion. We conclude that in vivo multimodal [¹⁸ F]FDG µPET/CT imaging allows to quantify and monitor inflammation-mediated bone damage and reveals not only reversal of synovitis but also bone repair upon TNF blockade in experimental arthritis. © 2019 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals, Inc.

Acellular Dermal Matrix Mistaken as Recurrence of Malignancy Following Surgery on Positron Emission Tomography/Computed Tomography: A Case Report

OBJECTIVES

To report a rare clinical presentation of an acellular dermal matrix (ADM) used during lateral temporal bone resection mimicking recurrence of cancer of external auditory canal (EAC) on positron emission tomography/computed tomography (PET/CT) 9 months after surgery.

METHODS

Case report and literature review.

RESULTS

A 71-year-old woman underwent lateral temporal bone resection 9 months earlier for management of squamous cell carcinoma of the EAC. She exhibited recurrence of the tumor on ¹⁸F-FDG PET/CT with an intense uptake value (SUV_max 12.8) at the operated site. Exploration was conducted as the location of the lesion was unfavorable to perform biopsy. However, histopathologic evaluation revealed that the lesion was the ADM implanted during surgery.

CONCLUSIONS

Care should be taken when using an ADM during malignant tumor surgery if the site of surgery is not conducive for fine needle aspiration or biopsy.

Preclinical Multimodal Molecular Imaging Using 18F-FDG PET/CT and MRI in a Phase I Study of a Knee Osteoarthritis in In Vivo Canine Model

The aim of this study was to use a multimodal molecular imaging approach to serially assess regional metabolic changes in the knee in an in vivo anterior cruciate ligament transection (ACLT) canine model of osteoarthritis (OA). Five canine underwent ACLT in one knee and the contralateral knee served as uninjured control. Prior, 3, 6, and 12 weeks post-ACLT, the dogs underwent ¹⁸F-fluoro-d-glucose (¹⁸F-FDG) positron emission tomography (PET)/computed tomography (CT) and magnetic resonance imaging (MRI). The MRI was coregistered with the PET/CT, and 3-dimensional regions of interest (ROIs) were traced manually and maximum standardized uptake values (SUV_max) were evaluated. ¹⁸F-fluoro-d-glucose SUV_max in the ACLT knee ROIs was significantly higher compared to the uninjured contralateral knees at 3, 6, and 12 weeks. Higher ¹⁸F-FDG uptake observed in ACLT knees compared to the uninjured knees reflects greater metabolic changes in the injured knees over time. Knee ¹⁸F-FDG uptake in an in vivo ACLT canine model using combined PET/CT and MRI demonstrated to be highly sensitive in the detection of metabolic alterations in osseous and nonosteochondral structures comprising the knee joint. ¹⁸F-fluoro-d-glucose appeared to be a capable potential imaging biomarker for early human knee OA diagnosis, prognosis, and management.

Development of an Ultra High Resolution PET Scanner for Imaging Rodent Paws: PawPET

A positron emission tomography (PET) scanner with submillimeter spatial resolution, capable of in vivo imaging of murine extremities was built based on two dual ended readout, hybrid depth of interaction (DOI) PET detectors. Each was composed of a 36 × 36 array of 0.43 mm × 0.43 mm × 8 mm unpolished lutetium oxyorthosilicate crystals separated by a 50 μm white diffuse reflector. The array was coupled to a position-sensing photomultiplier tube at one end and to an avalanche photodiode at the other end. The detector characterization included crystal identification accuracy, DOI, energy, and timing resolution measurements. The scanner was characterized in terms of its spatial resolution and its sensitivity and mouse images were acquired of a mouse paw injected with 18-F-NaF. Out of the 36 × 36 crystals only 33 × 33 crystals were identified. The coincidence timing, DOI, and energy resolution of the scanner was measured to be 2.8 ns, 1.4 mm, and 27%, respectively. The scanner's spatial resolution was measured with a line source and determined from an ordered subsets expectation maximization reconstruction to be 0.56 mm. The sensitivity of the scanner was measured to be 0.6% at the center of the field of view.

Anti-inflammatory effects of ursolic acid-3-acetate on human synovial fibroblasts and a murine model of rheumatoid arthritis

Ursolic acid (UA), a pentacyclic triterpenoid, is a common natural substance known to be effective in the treatment of inflammation, oxidative stress, and ulcers in arthritis. This study examined the effects of ursolic acid-3-acetate (UAA), a derivative of UA, on rheumatoid arthritis (RA) and verified the underlying mechanism of action by using a type-II collagen-induced arthritis (CIA) mice model and tumor necrosis factor (TNF)-α-stimulated RA synovial fibroblasts. The oral administration of UAA showed a decrease in clinical arthritis symptoms, paw thickness, histologic and radiologic changes, and serum IgG1 and IgG2a levels. UAA administration reduced Th1/Th17 phenotype CD4+ T lymphocyte expansion and inflammatory cytokine production in draining lymph nodes. In addition, UAA effectively reduced the expression and production of inflammatory mediators, including cytokines and matrix metalloproteinase-1/3 in the knee joint tissue and RA synovial fibroblasts, through the downregulation of IKKα/β, ΙκBα, and nuclear factor-κB. Our findings showed that UAA modulated helper T cell immune responses and matrix-degrading enzymes. The effects of UAA were comparable with those of the positive control drug, dexamethasone. In summary, all the evidence presented in this paper suggest that UAA could be a therapeutic candidate for the treatment of RA.

In vivo imaging of Lyme arthritis in mice by [18F]fluorodeoxyglucose positron emission tomography/computed tomography

OBJECTIVE

Lyme borreliosis (LB) is a tick-borne infectious disease caused by Borrelia burgdorferi spirochaetes, which are able to disseminate from the tick-bite site to distant organs. Mouse models are widely used to study LB and especially Lyme arthritis (LA), but only a few whole-animal in vivo imaging studies on the pathogenesis of B. burgdorferi infection in mice have been published so far. The existing imaging techniques have their drawbacks and, therefore, novel tools to complement the array of available LB imaging methodologies are needed.

METHOD

The applicability of positron emission tomography combined with computed tomography (PET/CT) imaging was evaluated as a method to monitor LB and especially LA in the C3H/HeN mouse model infected with wild-type B. burgdorferi N40 bacteria. The imaging results were compared with the traditional LA analysis methods, such as tibiotarsal joint swelling and histopathological assessment of joint inflammation.

RESULTS

PET/CT imaging provided high-resolution images with quantitative information on the spatial and temporal distribution of the [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) tracer in B. burgdorferi-infected mice. The [¹⁸F]FDG accumulated in the affected joints and activated lymph nodes of infected mice, while the tracer signal could not be visualized in these organs in uninfected control animals. Importantly, in vivo PET/CT imaging data were in agreement with the histopathological scoring of inflammation of mouse joints.

CONCLUSION

PET/CT imaging with [¹⁸F]FDG is a reliable method to longitudinally monitor the development and progression of B. burgdorferi infection-induced inflammation in vivo in mouse joints.

Automated Quantification of Early Bone Alterations and Pathological Bone Turnover in Experimental Arthritis by in vivo PET/CT Imaging

The assessment of bone damage is required to evaluate disease severity and treatment efficacy both in arthritis patients and in experimental arthritis models. Today there is still a lack of in vivo methods that enable the quantification of arthritic processes at an early stage of the disease. We performed longitudinal in vivo imaging with [¹⁸F]-fluoride PET/CT before and after experimental arthritis onset for diseased and control DBA/1 mice and assessed arthritis progression by clinical scoring, tracer uptake studies and bone volume as well as surface roughness measurements. Arthritic animals showed significantly increased tracer uptake in the paws compared to non-diseased controls. Automated CT image analysis revealed increased bone surface roughness already in the earliest stage of the disease. Moreover, we observed clear differences between endosteal and periosteal sites of cortical bone regarding surface roughness. This study shows that in vivo PET/CT imaging is a favorable method to study arthritic processes, enabling the quantification of different aspects of the disease like pathological bone turnover and bone alteration. Especially the evaluation of bone surface roughness is sensitive to early pathological changes and can be applied to study the dynamics of bone erosion at different sites of the bones in an automated fashion.

Quantification of arthritic bone degradation by analysis of 3D micro-computed tomography data

The use of animal models of arthritis is a key component in the evaluation of therapeutic strategies against the human disease rheumatoid arthritis (RA). Here we present quantitative measurements of bone degradation characterised by the cortical bone profile using glucose-6-phosphate isomerase (G6PI) induced arthritis. We applied micro-computed tomography (μCT) during three arthritis experiments and one control experiment to image the metatarsals of the hind paws and to investigate the effect of experimental arthritis on their cortical bone profile. For measurements of the cortical profile we automatically identified slices that are orthogonal to individual metatarsals, thereby making the measurements independent of animal placement in the scanner. We measured the average cortical thickness index (CTI) of the metatarsals, as well as the thickness changes along the metatarsal. In this study we introduced the cortical thickness gradient (CTG) as a new measure and we investigated how arthritis affects this measure. We found that in general both CTI and CTG are able to quantify arthritic progression, whilst CTG was found to be the more sensitive measure.

In-vivo quantitative assessment of the therapeutic response in a mouse model of collagen-induced arthritis using 18 F-fluorodeoxyglucose positron emission tomography

Mouse collagen-induced arthritis (CIA) is the most commonly used animal model to investigate underlying pathogenesis of autoimmune arthritis and to demonstrate the therapeutic efficacy of novel drugs in autoimmune arthritis. The conventional read-outs of CIA are clinical score and histopathology, which have several limitations, including (i) subjected to observer bias; and (ii) longitudinal therapeutic efficacy of a new drug cannot be determined. Thus, a robust, non-invasive, in-vivo drug screening tool is currently an unmet need. Here we have assessed the utility of ¹⁸ F-fluorodeoxyglucose positron emission tomography (¹⁸ F-FDG) as an in-vivo screening tool for anti-inflammatory drugs using the mouse CIA model. The radiotracer ¹⁸ F-FDG and a PET scanner were employed to monitor CIA disease activity before and after murine anti-tumour necrosis factor (TNF)-α antibody (CNTO5048) therapy in the mouse CIA model. Radiotracer concentration was derived from PET images for individual limb joints and on a per-limb basis, and Spearman's correlation coefficient (ρ) was determined with clinical score and histology of the affected limbs. CNTO5048 improved arthritis efficiently, as evidenced by clinical score and histopathology. PET showed an increased uptake of ¹⁸ F-FDG with the progression of the disease and a significant decrease in the post-treatment group. ¹⁸ F-FDG uptake patterns showed a strong correlation with clinical score (ρ = 0·71, P < 0·05) and histopathology (ρ = 0·76, P < 0·05). This study demonstrates the potential of ¹⁸ F-FDG PET as a tool for in-vivo drug screening for inflammatory arthritis and to monitor the therapeutic effects in a longitudinal setting.

Pilot study on 18 F-FDG PET/CT for detection of inflammatory changes in blood-induced knee arthropathy in a rabbit model

RATIONALE

¹⁸ F-FDG-PET/CT has a potential role in the early detection of haemophilic arthritis, at a time when treatment may still avoid further joint degeneration. The purposes of this pilot study were to determine the ability of ¹⁸ F-FDG-PET/CT to detect inflammatory changes associated with blood-induced arthropathy in knees of a rabbit model.

METHODS

Ten juvenile rabbits were imaged at baseline and weeks 5 and 17 post intraarticular autologous blood injections (ABI). Five rabbits in group 1 (G1) had ABI into the same knee joint every 2 weeks (total, eight injections). Five rabbits in group 2 (G2) had only two injections into the same knee, at weeks 5 and 17. Images were assessed visually and semi-quantitatively by measuring maximal standardized uptake values (SUVmax) and standardized uptake ratio (SUR = SUVmax in affected knee/SUVmax in non-affected knee).

RESULTS

More rabbits in G1 than G2 presented with positive chronic inflammatory synovial scores at week 17. Mean iron staining scores in injected knees were greater for G1 than for G2 (P = 0.049). No increased uptake was identified in the injected knees in any of the rabbits at baseline or at week 5. At week 17, all G1 rabbits demonstrated increased uptake in their affected knees with higher mean SUVmax (1.5) than normal knees (1.0) (P < 0.02). None of the G2 rabbits showed asymmetric increased uptake. The SUR of G1 was higher at week 17 compared to baseline (P < 0.01) and week 5 (P < 0.01). The SUR at week 17 was higher for G1 than for G2 (1.13) rabbits (P < 0.01).

CONCLUSION

¹⁸ F-FDG-PET is able to detect the inflammatory changes associated with haemophilic arthropathy in this experimental model.

Advances in PET Detection of the Antitumor T Cell Response

Positron emission tomography (PET) is a powerful noninvasive imaging technique able to measure distinct biological processes in vivo by administration of a radiolabeled probe. Whole-body measurements track the probe accumulation providing a means to measure biological changes such as metabolism, cell location, or tumor burden. PET can also be applied to both preclinical and clinical studies providing three-dimensional information. For immunotherapies (in particular understanding T cell responses), PET can be utilized for spatial and longitudinal tracking of T lymphocytes. Although PET has been utilized clinically for over 30 years, the recent development of additional PET radiotracers have dramatically expanded the use of PET to detect endogenous or adoptively transferred T cells in vivo. Novel probes have identified changes in T cell quantity, location, and function. This has enabled investigators to track T cells outside of the circulation and in hematopoietic organs such as spleen, lymph nodes, and bone marrow, or within tumors. In this review, we cover advances in PET detection of the antitumor T cell response and areas of focus for future studies.

Radiation Dosimetry Study of [(89)Zr]rituximab Tracer for Clinical Translation of B cell NHL Imaging using Positron Emission Tomography

PURPOSE

We evaluated the dosimetry of [(89)Zr]rituximab, an anti-CD20 immunoPET tracer to image B cell non-Hodgkin's lymphoma (NHL) using a humanized transgenic mouse model that expresses human CD20 transgenic mice (huCD20TM).

PROCEDURES

Rituximab was conjugated to desferrioxamine (Df) for radiolabeling of Zirconium-89. [(89)Zr]rituximab (2.8 ± 0.2 MBq) was tail vein-injected into huCD20T mice. Positron emission tomography (PET)/CT imaging was performed on the two groups of mice (blocking = 2 mg/kg pre-dose of rituximab and non-blocking; n = 5) at eight time points (1, 4, 24, 48, 72, 96, 120, and 168 h) post injection.

RESULTS

The novel [(89)Zr]rituximab PET tracer had good immunoreactivity, was stable in human serum, and was able to specifically target human CD20 in mice. The human equivalents of highest dose (mean ± SD) organs with and without pre-dose are liver (345 ± 284 μSv/MBq) and spleen (1165 ± 149 μSv/MBq), respectively.

CONCLUSIONS

Dosimetry of the human patient whole-body dose was found to be 145 MBq per annum, and the patient dose-limiting organ will be the liver (with rituximab pre-dose blocking) and spleen for non-blocking. The [(89)Zr]rituximab (t½ = 78.4 h) imaging of B cell NHL patients could permit the observation of targeting lesions in NHL patients over an extended period due to longer half-life as compared to the [(64)Cu] rituximab (t½ = 12.7 h).

Oleanolic acid acetate inhibits rheumatoid arthritis by modulating T cell immune responses and matrix-degrading enzymes

Rheumatoid arthritis (RA) is a chronic autoimmune disease associated with a combination of synovium joint inflammation, synovium hyperplasia, and destruction of cartilage and bone. Oleanolic acid acetate (OAA), a compound isolated from Vigna angularis, has been known to possess pharmacological activities, including anti-inflammation and anti-bone destruction. In this study, we investigated the effects of OAA on RA and the underlying mechanisms of action by using a type-II collagen-induced arthritis (CIA) mouse model and tumor necrosis factor (TNF)-α-stimulated RA synovial fibroblasts. Oral administration of OAA decreased the clinical arthritis symptoms, paw thickness, histologic and radiologic changes, and serum total and anti-type II collagen IgG, IgG1, and IgG2a levels. OAA administration reduced Th1/Th17 phenotype CD4(+) T lymphocyte expansions and inflammatory cytokine productions in T cell activated draining lymph nodes and spleen. OAA reduced the expression and production of inflammatory mediators, such as cytokines and matrix metalloproteinase (MMP)-1/3, in the ankle joint tissue and RA synovial fibroblasts by down-regulating Akt, mitogen-activated protein kinases, and nuclear factor-κB. Our results clearly support that OAA plays a therapeutic role in RA pathogenesis by modulating helper T cell immune responses and matrix-degrading enzymes. The immunosuppressive effects of OAA were comparable to dexamethasone and ketoprofen. We provide evidences that OAA could be a potential therapeutic candidate for RA.

In vivo optical imaging of matrix metalloproteinase activity detects acute and chronic contact hypersensitivity reactions and enables monitoring of the antiinflammatory effects of N-acetylcysteine

The aim of this study was to determine whether the severity of contact hypersensitivity reactions (CHSRs) can be observed by noninvasive in vivo optical imaging of matrix metalloproteinase (MMP) activity and whether this is an appropriate tool for monitoring an antiinflammatory effect. Acute and chronic CHSRs were elicited by application of a 1% trinitrochlorobenzene (TNCB) solution for up to five times on the right ear of TNCB-sensitized mice. N-Acetylcysteine (NAC)-treated and sham-treated mice were monitored by measuring ear swelling and optical imaging of MMP activity. In addition, we performed hematoxylin-eosin staining and CD31 immunohistochemistry for histopathologic analysis of the antiinflammatory effects of NAC. The ear thickness and the MMP activity increased in line with the increasing severity of the CHSR. MMP activity was enhanced 2.5- to 2.7-fold during acute CHSR and 3.1- to 4.1-fold during chronic CHSR. NAC suppressed ear swelling and MMP signal intensity in mice with acute and chronic CHSR. During chronic CHSR, the vessel density was significantly reduced in ear sections derived from NAC-treated compared to sham-treated mice. In vivo optical imaging of MMP activity measures acute and chronic CHSR and is useful to monitor antiinflammatory effects.

(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.

FDG PET/CT in infection and inflammation--current and emerging clinical applications

Integrated positron emission tomography/computed tomography (PET/CT) with the glucose analogue, 2-[(18)F]-fluoro-2-deoxy-d-glucose (FDG), is an evolving hybrid imaging technique in the evaluation of an important and diverse group of pathological conditions, which are characterised by infection and aseptic inflammation. With a rapidly expanding body of evidence, it is being increasingly recognised that, in addition to its established role in oncological imaging, FDG PET/CT also has clinical utility in suspected infection and inflammation. The technique can identify the source of infection or inflammation in a timely fashion ahead of morphological changes on conventional anatomical imaging techniques, such as computed tomography (CT) and magnetic resonance imaging (MRI), map the extent and severity of disease, identify sites for tissue sampling, and assess therapy response. FDG PET/CT exhibits distinct advantages over traditional radionuclide imaging techniques in terms of shorter duration of examination, higher spatial resolution, non-invasive nature of acquisition, ability to perform quantitative analyses, and the provision of a synergistic combination of functional and anatomical imaging. With the use of illustrative clinico-radiological cases, this article discusses the current and emerging evidence for the use of FDG PET/CT in a broad spectrum of disorders, such as fever of unknown origin, sarcoidosis, large vessel vasculitis, musculoskeletal infections, joint prosthesis or implant-related complications, human immunodeficiency virus (HIV)-related infections, and miscellaneous indications, such as IgG4-related systemic disease. It will also briefly summarise the role of more novel tracers such as FDG-labelled leukocytes and gallium-68 PET tracers in this arena.

Immuno-PET and Immuno-SPECT of Rheumatoid Arthritis with Radiolabeled Anti-Fibroblast Activation Protein Antibody Correlates with Severity of Arthritis

One of the most prominent cell populations playing a role in rheumatoid arthritis (RA) is activated fibroblast-like synoviocytes. Among many other proteins, fibroblast-like synoviocytes dominantly express fibroblast activation protein (FAP). Because of the high expression of FAP in arthritic joints, radioimmunoimaging of activated fibroblasts with anti-FAP antibodies might be an attractive noninvasive imaging tool in RA.

METHODS

SPECT and PET with (111)In- and (89)Zr-labeled anti-FAP antibody 28H1 was performed in mice with CIA. The radioactivity uptake in joints was quantified and correlated with arthritis score.

RESULTS

Both (111)In-28H1 and (89)Zr-28H1 showed high uptake in inflamed joints, being 3-fold higher than that of the irrelevant isotype-matched control antibody DP47GS, clearly indicating specific accumulation of 28H1. Uptake of (111)In-28H1 ranged from 2.2 percentage injected dose per gram (%ID/g) in noninflamed joints to 32.1 %ID/g in severely inflamed joints. DP47GS accumulation ranged from 1.6 %ID/g in noninflamed tissue to 12.0 %ID/g in severely inflamed joints. Uptake of 28H1 in inflamed joints correlated with arthritis score (Spearman ρ, 0.69; P < 0.0001) and increased with severity of arthritis.

CONCLUSION

SPECT/CT imaging with the anti-FAP antibody (111)In-28H1 specifically visualized arthritic joints with high resolution, and tracer accumulation correlated with the severity of the inflammation in murine experimental arthritis. Background uptake of the radiolabeled antibody was low, resulting in excellent image quality. (89)Zr-28H1 was less favorable for RA imaging because of an elevated bone uptake of (89)Zr. Future studies will focus on the potential role of 28H1 as a tool to monitor therapy response early on.

18 F-Fluoride positron emission tomography/computed tomography for noninvasive in vivo quantification of pathophysiological bone metabolism in experimental murine arthritis

Introduction

Evaluation of disease severity in experimental models of rheumatoid arthritis is inevitably associated with assessment of structural bone damage. A noninvasive imaging technology allowing objective quantification of pathophysiological alterations of bone structure in rodents could substantially extend the methods used to date in preclinical arthritis research for staging of autoimmune disease severity or efficacy of therapeutical intervention. Sodium ¹⁸ F-fluoride (¹⁸ F-NaF) is a bone-seeking tracer well-suited for molecular imaging. Therefore, we systematically examined the use of ¹⁸ F-NaF positron emission tomography/computed tomography (PET/CT) in mice with glucose-6-phosphate isomerase (G6PI)–induced arthritis for quantification of pathological bone metabolism.

Methods

F-fluoride was injected into mice before disease onset and at various time points of progressing experimental arthritis. Radioisotope accumulation in joints in the fore- and hindpaws was analyzed by PET measurements. For validation of bone metabolism quantified by ¹⁸ F-fluoride PET, bone surface parameters of high-resolution μCT measurements were used.

Results

Before clinical arthritis onset, no distinct accumulation of ¹⁸ F-fluoride was detectable in the fore- and hindlimbs of mice immunized with G6PI. In the course of experimental autoimmune disease, ¹⁸ F-fluoride bone uptake was increased at sites of enhanced bone metabolism caused by pathophysiological processes of autoimmune disease. Moreover, ¹⁸ F-fluoride signaling at different stages of G6PI-induced arthritis was significantly correlated with the degree of bone destruction. CT enabled identification of exact localization of ¹⁸ F-fluoride signaling in bone and soft tissue.

Conclusions

The results of this study suggest that small-animal PET/CT using ¹⁸ F-fluoride as a tracer is a feasible method for quantitative assessment of pathophysiological bone metabolism in experimental arthritis. Furthermore, the possibility to perform repeated noninvasive measurements in vivo allows longitudinal study of therapeutical intervention monitoring.

In vivo quantification of mouse autoimmune arthritis by PET/CT

AIM

To quantify the progression and severity of mouse collagen-induced arthritis (CIA) using an in vivo imaging tool, (18) F-fluorodeoxyglucose ((18) F-FDG) PET/CT and validate it against gold standard 'histopathological' evaluation.

METHOD

The PET radiotracer (18) F-FDG, a marker for glucose metabolism, was injected in mice at different stages of CIA and the radiotracer distribution was imaged using a PET scanner. A sequential CT scan provided correlated anatomy. Radiotracer concentration was derived from PET/CT images for individual limb joints and on a per-limb basis at different stages of the disease. The imaging outcomes were subjected to correlation analysis with concurrently measured clinical and histological score.

RESULTS

Clinical and histological score, and hence disease severity, showed a strong linear correlation (r(2)  = 0.71, P = 0.001 and r(2)  = 0.87, P < 0.001, respectively) with radiotracer concentration measured from PET/CT during the progression of CIA.

CONCLUSIONS

The strong positive correlation of the (18) F-FDG PET/CT findings with the histopathological evaluation at different stages of the disease suggest the potential of this imaging tool for the non-invasive assessment of progression and severity in mouse autoimmune arthritis. Thus, in preclinical studies, (18) F-FDG PET/CT can be considered as a non-invasive tool to develop novel therapies of inflammatory arthritis.

Molecular imaging of rheumatoid arthritis: emerging markers, tools, and techniques

Early diagnosis and effective monitoring of rheumatoid arthritis (RA) are important for a positive outcome. Instant treatment often results in faster reduction of inflammation and, as a consequence, less structural damage. Anatomical imaging techniques have been in use for a long time, facilitating diagnosis and monitoring of RA. However, mere imaging of anatomical structures provides little information on the processes preceding changes in synovial tissue, cartilage, and bone. Molecular imaging might facilitate more effective diagnosis and monitoring in addition to providing new information on the disease pathogenesis. A limiting factor in the development of new molecular imaging techniques is the availability of suitable probes. Here, we review which cells and molecules can be targeted in the RA joint and discuss the advances that have been made in imaging of arthritis with a focus on such molecular targets as folate receptor, F4/80, macrophage mannose receptor, E-selectin, intercellular adhesion molecule-1, phosphatidylserine, and matrix metalloproteinases. In addition, we discuss a new tool that is being introduced in the field, namely the use of nanobodies as tracers. Finally, we describe additional molecules displaying specific features in joint inflammation and propose these as potential new molecular imaging targets, more specifically receptor activator of nuclear factor κB and its ligand, chemokine receptors, vascular cell adhesion molecule-1, αVβ₃ integrin, P2X7 receptor, suppression of tumorigenicity 2, dendritic cell-specific transmembrane protein, and osteoclast-stimulatory transmembrane protein.

Rational development of radiopharmaceuticals for HIV-1

The global battle against HIV-1 would benefit from a sensitive and specific radiopharmaceutical to localize HIV-infected cells. Ideally, this probe would be able to identify latently infected host cells containing replication competent HIV sequences. Clinical and research applications would include assessment of reservoirs, informing clinical management by facilitating assessment of burden of infection in different compartments, monitoring disease progression and monitoring response to therapy. A "rational" development approach could facilitate efficient identification of an appropriate targeted radiopharmaceutical. Rational development starts with understanding characteristics of the disease that can be effectively targeted and then engineering radiopharmaceuticals to hone in on an appropriate target, which in the case of HIV-1 (HIV) might be an HIV-specific product on or in the host cell, a differentially expressed gene product, an integrated DNA sequence specific enzymatic activity, part of the inflammatory response, or a combination of these. This is different from the current approach that starts with a radiopharmaceutical for a target associated with a disease, mostly from autopsy studies, without a strong rationale for the potential to impact patient care. At present, no targeted therapies are available for HIV latency, although a number of approaches are under study. Here we discuss requirements for a radiopharmaceutical useful in strategies targeting persistently infected cells. The radiopharmaceutical for HIV should be developed based on HIV biology, studied in an animal model and then in humans, and ultimately used in clinical and research settings.

Molecular imaging with macrophage CRIg-targeting nanobodies for early and preclinical diagnosis in a mouse model of rheumatoid arthritis

An accurate and noninvasive tracer able to detect molecular events underlying the development of rheumatoid arthritis (RA) would be useful for RA diagnosis and drug efficacy assessment. A complement receptor of the Ig superfamily (CRIg) is expressed on synovial macrophages of RA patients, making it an interesting target for molecular imaging of RA. We aim to develop a radiotracer for the visualization of CRIg in a mouse model for RA using radiolabeled single-domain variable antibody VHH fragments (Nanobodies).

METHODS

Quantitative polymerase chain reaction was used to locate CRIg expression in mice with collagen-induced arthritis (CIA). A Nanobody, NbV4m119, was generated to specifically target CRIg. Flow cytometry, phosphorimaging, and confocal microscopy were used to confirm NbVm119 binding to CRIg-positive cells. SPECT (SPECT/CT) was used to image arthritic lesions in the inflamed paws of 29 mice using (99m)Tc-NbV4m119 Nanobody.

RESULTS

CRIg is constitutively expressed in the liver and was found to be upregulated in synovial tissues of CIA mice. SPECT/CT imaging revealed that (99m)Tc-NbV4m119 specifically targeted CRIg-positive liver macrophages in naïve wild-type but not in CRIg(-/-) (CRIg knockout) mice. In CIA mice, (99m)Tc-NbV4m119 accumulation in arthritic lesions increased according to the severity of the inflammation. In the knees of mice with CIA, (99m)Tc-NbV4m119 was found to accumulate even before the onset of macroscopic clinical symptoms.

CONCLUSION

SPECT/CT imaging with (99m)Tc-NbV4m119 visualizes joint inflammation in CIA. Furthermore, imaging could predict which mice will develop clinical symptoms during CIA. Consequently, imaging of joint inflammation with CRIg-specific Nanobodies offers perspectives for clinical applications in RA patients.

[¹⁸F]DPA-714 as a biomarker for positron emission tomography imaging of rheumatoid arthritis in an animal model

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic disease, affecting 0.5 to 1% of adults in industrialized countries, in which systemic inflammation and synovitis drive joint destruction. [¹⁸F]DPA-714 is a specific tracer of the 18 kDa translocator protein (TSPO), which is overexpressed on activated macrophages, and proposed as a biomarker of neuroinflammation. Today, diagnosis of patients with early inflammatory arthritis is limited by poor sensitivity and specificity. The present study aims to investigate the potential of [¹⁸F]DPA-714 to monitor in vivo inflammatory processes at a preclinical stage via positron emission tomography (PET).

METHODS

RA was induced in Dark Agouti rats by subcutaneous injection of inactivated Mycobacterium tuberculosis. Development of arthritis clinical signs was investigated daily and the severity of the disease evaluated. Animals were imaged at the peak of inflammation using [¹⁸F]DPA-714 and a small-animal PET-CT tomograph.

RESULTS

The first clinical signs appeared at 10 days post-injection, with a peak of inflammation at 20 days. At this time, PET-analyses showed a clear uptake of [¹⁸F]DPA-714 in swollen ankles, with mean values of 0.52 ± 0.18% injected dose (ID/cc) for treated (n = 11) and 0.19 ± 0.09 for non-treated (n = 6) rats. A good correlation between [¹⁸F]DPA-714's uptake and swelling was also found. Immunohistochemistry showed an enhanced TSPO expression in hind paws, mainly co-localized with the macrophages specific antigen CD68 expressing cells.

CONCLUSION

These preliminary results demonstrate that the TSPO 18 kDa specific radioligand [¹⁸F]DPA-714 is adapted for the study and follow-up of inflammation linked to RA in our experimental model, suggesting also a strong potential for clinical imaging of peripheral inflammation.

Evaluation of 89Zr-rituximab tracer by Cerenkov luminescence imaging and correlation with PET in a humanized transgenic mouse model to image NHL

PURPOSE

This research aimed to study the use of Cerenkov luminescence imaging (CLI) for non-Hodgkin's lymphoma (NHL) using 89Zr-rituximab positron emission tomography (PET) tracer with a humanized transgenic mouse model that expresses human CD20 and the correlation of CLI with PET.

PROCEDURES

Zr-rituximab (2.6 MBq) was tail vein-injected into transgenic mice that express the human CD20 on their B cells (huCD20TM). One group (n=3) received 2 mg/kg pre-dose (blocking) of cold rituximab 2 h prior to tracer; a second group (n=3) had no pre-dose (non-blocking). CLI was performed using a cooled charge-coupled device optical imager. We also performed PET imaging and ex vivo studies in order to confirm the in vivo CLI results. At each time point (4, 24, 48, 72, and 96 h), two groups of mice were imaged in vivo and ex vivo with CLI and PET, and at 96 h, organs were measured by gamma counter.

RESULTS

huCD20 transgenic mice injected with 89Zr-rituximab demonstrated a high-contrast CLI image compared to mice blocked with a cold dose. At various time points of 4-96 h post-radiotracer injection, the in vivo CLI signal intensity showed specific uptake in the spleen where B cells reside and, hence, the huCD20 biomarker is present at very high levels. The time-activity curve of dose decay-corrected CLI intensity and percent injected dose per gram of tissue of PET uptake in the spleen were increased over the time period (4-96 h). At 96 h, the 89Zr-rituximab uptake ratio (non-blocking vs blocking) counted (mean±standard deviation) for the spleen was 1.5±0.6 for CLI and 1.9±0.3 for PET. Furthermore, spleen uptake measurements (non-blocking and blocking of all time points) of CLI vs PET showed good correlation (R2=0.85 and slope=0.576), which also confirmed the corresponding correlations parameter value (R2=0.834 and slope=0.47) obtained for ex vivo measurements.

CONCLUSIONS

CLI and PET of huCD20 transgenic mice injected with 89Zr-rituximab demonstrated that the tracer was able to target huCD20-expressing B cells. The in vivo and ex vivo tracer uptake corresponding to the CLI radiance intensity from the spleen is in good agreement with PET. In this report, we have validated the use of CLI with PET for NHL imaging in huCD20TM.

Amelioration of experimental arthritis by stroke-induced immunosuppression is independent of Treg cell function

Objectives

Clinical evidence suggests that neurological lesions can protect from arthritis. Acute cerebral ischaemia induces severe immunosuppression, resulting in enhanced susceptibility to infections. We aimed to determine if stroke-induced immunosuppression can ameliorate arthritis and to delineate the immunological mechanisms involved.

Methods

Unilateral cerebral ischaemia was induced in mice by occlusion of one middle cerebral artery (MCAO) at different time points after induction of G6PI-induced arthritis in mice. Clinical and histological signs of arthritis were assessed. Regulatory T cells were specifically depleted by injection of diphtheria toxin into transgenic DEREG mice. Immunological correlates of MCAO were determined by flow cytometry and serological methods.

Results

MCAO reduced the clinical and histological signs of arthritis significantly. To be effective, stroke had to be induced during the induction phase or the early clinical stage of arthritis. MCAO induced a global loss of leucocytes. Despite the reduced absolute number of lymphocytes, the functional differentiation of T helper cells into Th1/17 cells and the production of autoantibodies were unimpaired. Depletion experiments showed that regulatory T cells were dispensable for the protective effect of MCAO.

Conclusions

MCAO ameliorates arthritis. The correlate of protection from arthritis is not the reduction of a particular pathogenic leucocyte subset or the preferential expansion or emergence of a protective cell population but the global reduction of leucocytes during arthritis.

PET imaging of inflammation biomarkers

Inflammation plays a significant role in many disease processes. Development in molecular imaging in recent years provides new insight into the diagnosis and treatment evaluation of various inflammatory diseases and diseases involving inflammatory process. Positron emission tomography using (18)F-FDG has been successfully applied in clinical oncology and neurology and in the inflammation realm. In addition to glucose metabolism, a variety of targets for inflammation imaging are being discovered and utilized, some of which are considered superior to FDG for imaging inflammation. This review summarizes the potential inflammation imaging targets and corresponding PET tracers, and the applications of PET in major inflammatory diseases and tumor associated inflammation. Also, the current attempt in differentiating inflammation from tumor using PET is also discussed.

SPECT imaging of joint inflammation with Nanobodies targeting the macrophage mannose receptor in a mouse model for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease occurring in approximately 1% of the worldwide population. The disease primarily affects the joints, where inflammatory cells, such as macrophages, invade the synovium and cause cartilage and bone destruction. Currently, it is difficult to efficiently diagnose and monitor early-stage RA. In this study, we investigated whether SPECT/micro-CT imaging with (99m)Tc-labeled Nanobodies directed against the macrophage mannose receptor (MMR) is a useful tool for monitoring and quantifying joint inflammation in collagen-induced arthritis (CIA), a mouse model for RA. The expression of MMR was analyzed on macrophages and osteoclasts generated in vitro and in cells obtained from various organs from mice with CIA.

METHODS

CIA was induced in DBA/1 mice by injection of collagen type II in complete Freund adjuvant, and cell suspensions from the inflamed joints and other organs were obtained. Macrophages and osteoclasts were generated in vitro from bone marrow cells. Expression of MMR was quantified by quantitative polymerase chain reaction and flow cytometry with specific Nanobodies and conventional antibodies. SPECT/micro-CT imaging was performed with (99m)Tc-labeled MMR and control Nanobodies.

RESULTS

MMR was highly expressed on macrophages and to a lesser extent on osteoclasts generated in vitro. In mice with CIA, MMR expression was detected on cells from the bone marrow, lymph nodes, and spleen. In synovial fluid of arthritic joints, MMR was expressed on CD11b(+)F4/80(+) macrophages. On in vivo SPECT/micro-CT imaging with consecutive injections of MMR and control Nanobodies, a strong MMR signal was seen in the knees, ankles, and toes of arthritic mice. Quantification of the SPECT imaging confirmed the specificity of the MMR signal in inflamed joints as compared with the control Nanobody. Dissection of the paws revealed an additional significant MMR signal in nonarthritic paws of affected mice (i.e., mice displaying symptoms of arthritis in other paws).

CONCLUSION

Our data show that MMR is expressed on macrophages in vitro and in vivo in synovial fluid of inflamed paws, whereas expression is relatively low in other tissues. The use of Nanobodies against MMR in SPECT/micro-CT imaging generates the possibility to track inflammatory cells in vivo in arthritic joints.

In vivo imaging of cell proliferation enables the detection of the extent of experimental rheumatoid arthritis by 3'-deoxy-3'-18f-fluorothymidine and small-animal PET

The aim of this work was to study the feasibility of measuring cell proliferation noninvasively in vivo during different stages of experimental arthritis using the PET proliferation tracer 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT).

METHODS

We injected mice with serum containing glucose-6-phosphate-isomerase-specific antibodies to induce experimental arthritis, and we injected control mice with control serum. Animals injected with (18)F-FLT 1, 3, 6, and 8 d after the onset of disease were analyzed in vivo by PET, PET/CT, or PET/MR imaging followed by autoradiography analysis. The (18)F-FLT uptake in the ankles and forepaws was quantified on the basis of the PET images by drawing standardized regions of interest. To correlate the in vivo PET data with cell proliferation, we performed Ki-67 immunohistochemistry of diseased and healthy joints at the corresponding time points.

RESULTS

Analysis of the different stages of arthritic joint disease revealed enhanced (18)F-FLT uptake in arthritic ankles (2.2 ± 0.2 percentage injected dose per gram [%ID/g]) and forepaws (2.1 ± 0.3 %ID/g), compared with healthy ankles (1.4 ± 0.3 %ID/g) and forepaws (1.5 ± 0.5 %ID/g), as early as 1 d after the glucose-6-phosphate-isomerase serum injection, a time point characterized by clear histologic signs of arthritis but only slight ankle swelling. The (18)F-FLT uptake in the ankles (3.5 ± 0.3 %ID/g) reached the maximum observed level at day 8. Ki-67 immunohistochemical staining of the arthritic ankles and forepaws revealed a strong correlation with the in vivo (18)F-FLT PET data. PET/CT and PET/MR imaging measurements enabled us to identify whether the (18)F-FLT uptake was located in the bone or the soft tissue.

CONCLUSION

Noninvasive in vivo measurement of cell proliferation in experimental arthritis using (18)F-FLT PET is a promising tool to investigate the extent of arthritic joint inflammation.

PBEF/NAMPT/visfatin: a promising drug target for treating rheumatoid arthritis?

NAMPT, also known as pre-B-cell colony-enhancing factor and visfatin, has been proposed to be involved in preventing apoptosis in cancer cells and, as such, has received a great deal of attention in recent years and stimulated the development to specific inhibitors for treating cancer. The role of NAMPT inhibitors as potential therapeutic agents for other diseases has not been studied extensively. Here, we describe their applicability for treating rheumatoid arthritis. We summarize current knowledge of NAMPT expression in healthy and diseased tissues, thereafter, we focus on pathological mechanisms relevant to rheumatoid arthritis that involve the NAMPT pathway and review the current status of NAMPT inhibitors being evaluated in clinical trials.

Development of a novel long-lived immunoPET tracer for monitoring lymphoma therapy in a humanized transgenic mouse model

Positron emission tomography (PET) is an attractive imaging tool to localize and quantify tracer biodistribution. ImmunoPET with an intact mAb typically requires two to four days to achieve optimized tumor-to-normal ratios. Thus, a positron emitter with a half-life of two to four days such as zirconium-89 [(89)Zr] (t1/2: 78.4 h) is ideal. We have developed an antibody-based, long-lived immunoPET tracer (89)Zr-Desferrioxamine-p-SCN (Df-Bz-NCS)-rituximab (Zr-iPET) to image tumor for longer durations in a humanized CD20-expressing transgenic mouse model. To optimize the radiolabeling efficiency of (89)Zr with Df-Bz-rituximab, multiple radiolabelings were performed. Radiochemical yield, purity, immunoreactivity, and stability assays were carried out to characterize the Zr-iPET for chemical and biological integrity. This tracer was used to image transgenic mice that express the human CD20 on their B cells (huCD20TM). Each huCD20TM mouse received a 7.4 MBq/dose. One group (n = 3) received a 2 mg/kg predose (blocking) of cold rituximab 2 h prior to (89)Zr-iPET; the other group (n = 3) had no predose (nonblocking). Small animal PET/CT was used to image mice at 1, 4, 24, 48, 72, and 120 h. Quality assurance of the (89)Zr-iPET demonstrated NCS-Bz-Df: antibody ratio (c/a: 1.5 ± 0.31), specific activity (0.44-1.64 TBq/mol), radiochemical yield (>70%), and purity (>98%). The Zr-iPET immunoreactivity was >80%. At 120 h, Zr-iPET uptake (% ID/g) as mean ± STD for blocking and nonblocking groups in spleen was 3.2 ± 0.1% and 83.3 ± 2.0% (p value <0.0013.). Liver uptake was 1.32 ± 0.05% and 0.61 ± 0.001% (p value <0.0128) for blocking and nonblocking, respectively. The small animal PET/CT image shows the spleen specific uptake of Zr-iPET in mice at 120 h after tracer injection. Compared to the liver, the spleen specific uptake of Zr-iPET is very high due to the expression of huCD20. We optimized the radiolabeling efficiency of (89)Zr with Df-Bz-rituximab. These radioimmunoconjugate lots were stable up to 5 days in serum in vitro. The present study showed that (89)Zr is well-suited for mAbs to image cancer over an extended period of time (up to 5 days).

A shift from cell cultures to creatures: in vivo imaging of small animals in experimental regenerative medicine

Although the use of small animals for in vivo experimentation has been widespread, only recently has there been easy availability of techniques that allow noninvasive in vivo imaging of small animals. Because these techniques allow the same individual subject to be followed longitudinally throughout the duration of an experiment, their use is rapidly changing the way small animals are employed in the laboratory. In this review, we focus on six imaging modalities that are increasingly employed for small animal in vivo imaging: optical imaging (OI), magnetic resonance imaging (MRI), computed tomography (CT), single-photon emission tomography (SPECT), ultrasound (US), and positron-emission tomography (PET). Each modality allows for the noninvasive tracking of cells and cell products in vivo. In addition, multimodality imaging, combining two or more of these techniques, has also been increasingly employed to overcome the limitations of each independent technique. After reviewing these available imaging modalities, we detail their experimental application, exemplified by the emerging field of regenerative medicine, referring to publications whose conclusions would otherwise be difficult to support without the availability of in vivo imaging.