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Longitudinal mouse PET imaging is becoming increasingly popular due to the large number of transgenic and disease models available but faces challenges. These challenges are related to the small size of the mouse brain and the limited spatial resolution of microPET scanners, along with the small blood volume making arterial blood sampling challenging and impossible for longitudinal studies. The ability to extract an input function directly from the image would be useful for quantification in longitudinal small animal studies where there is no true reference region available such as TSPO imaging. Methods Using dynamic, whole-body 18 F-DPA-714 PET scans (60 min) in a mouse model of hippocampal sclerosis, we applied a factor analysis (FA) approach to extract an image-derived input function (IDIF). This mouse-specific IDIF was then used for 4D-resolution recovery and denoising (4D-RRD) that outputs a dynamic image with better spatial resolution and noise properties, and a map of the total volume of distribution (V T ) was obtained using a basis function approach in a total of 9 mice with 4 longitudinal PET scans each. We also calculated percent injected dose (%ID) with and without 4D-RRD. The V T and %ID parameters were compared to quantified ex vivo autoradiography using regional correlations of the specific binding from autoradiography against V T and %ID parameters. Results The peaks of the IDIFs were strongly correlated with the injected dose (Pearson R = 0.79). The regional correlations between the %ID estimates and autoradiography were R = 0.53 without 4D-RRD and 0.72 with 4D-RRD over all mice and scans. The regional correlations between the V T estimates and autoradiography were R = 0.66 without 4D-RRD and 0.79 with application of 4D-RRD over all mice and scans. Conclusion We present a FA approach for IDIF extraction which is robust, reproducible and can be used in quantification methods for resolution recovery, denoising and parameter estimation. We demonstrated that the proposed quantification method yields parameter estimates closer to ex vivo measurements than semi-quantitative methods such as %ID and is immune to tracer binding in tissue unlike reference tissue methods. This approach allows for accurate quantification in longitudinal PET studies in mice while avoiding repeated blood sampling.

Backgrounds & Aims As the bile acid (BA) pool composition is of major impact on liver pathophysiology, we studied its regulation by the BA receptor TGR5, promoting hepatoprotection against BA overload. Methods WT, total and hepato-specific TGR5-KO, and TGR5-overexpressing mice were used in: partial and 90% extended hepatectomies (EH) upon normal, ursodeoxycholic acid (UDCA)- or cholestyramine (CT)-enriched diet, bile duct ligation (BDL), cholic acid (1%)-enriched diet, and TGR5 agonist (RO) treatments. We thereby studied TGR5 impact on: BA pool composition, liver injury, regeneration and survival. Particular focus was made on gut microbiota (GM) and gallbladder (GB) function analysis. BA pool composition was analyzed in patients undergoing major hepatectomy. Results The TGR5-KO hyperhydrophobic BA pool was not related to BA synthesis alteration, nor to the TGR5-KO GM dysbiosis, as supported by hepatocyte-specific KO mice and cohousing experiments. The TGR5-dependent control of GB dilatation was crucial for BA pool composition, as determined by experiments including RO treatment +/− cholecystectomy. The poor TGR5-KO post-EH survival rate, related with exacerbated peribiliary necrosis and BA overload, was improved by shifting the BA pool towards a more hydrophilic composition (CT and UDCA treatments). After either BDL or CA-enriched diet +/− cholecystectomy, we found that GB dilatation had strong TGR5-dependent hepatoprotective properties. In patients, a more hydrophobic BA pool was correlated with an unfavorable outcome after hepatectomy. Conclusion BA pool composition is crucial for hepatoprotection in mice and humans. We point TGR5 as a key regulator of BA profile and thereby as a potential hepatoprotective target under BA overload conditions. Lay summary Through multiple in vivo experimental approaches in mice, together with a patients study, this work brings some new light on the relationships between biliary homeostasis, gallbladder function and liver protection. We showed that the bile acid pool composition is crucial for optimal liver repair, not only in mice but also in human patients undergoing major hepatectomy.

SummaryObjectiveMesiotemporal lobe epilepsy is the most common type of drug‐resistant partial epilepsy, with a specific history that often begins with status epilepticus due to various neurological insults followed by a silent period. During this period, before the first seizure occurs, a specific lesion develops, described as unilateral hippocampal sclerosis (HS). It is still challenging to determine which drugs, administered at which time point, will be most effective during the formation of this epileptic process. Neuroinflammation plays an important role in pathophysiological mechanisms in epilepsy, and therefore brain inflammation biomarkers such as translocator protein 18 kDa (TSPO) can be potent epilepsy biomarkers. TSPO is associated with reactive astrocytes and microglia. A unilateral intrahippocampal kainate injection mouse model can reproduce the defining features of human temporal lobe epilepsy with unilateral HS and the pattern of chronic pharmacoresistant temporal seizures. We hypothesized that longitudinal imaging using TSPO positron emission tomography (PET) with 18F‐DPA‐714 could identify optimal treatment windows in a mouse model during the formation of HS.MethodsThe model was induced into the right dorsal hippocampus of male C57/Bl6 mice. Micro‐PET/computed tomographic scanning was performed before model induction and along the development of the HS at 7 days, 14 days, 1 month, and 6 months. In vitro autoradiography and immunohistofluorescence were performed on additional mice at each time point.ResultsTSPO PET uptake reached peak at 7 days and mostly related to microglial activation, whereas after 14 days, reactive astrocytes were shown to be the main cells expressing TSPO, reflected by a continuing increased PET uptake.SignificanceTSPO‐targeted PET is a highly potent longitudinal biomarker of epilepsy and could be of interest to determine the therapeutic windows in epilepsy and to monitor response to treatment.

To identify the cells responsible for the initiation and maintenance of Hodgkin lymphoma (HL) cells, we have characterized a subpopulation of HL cells grown in vitro and in vivo with the aim of establishing a reliable and robust animal model for HL. To validate our model, we challenged the tumor cells in vivo by injecting the alkylating histone-deacetylase inhibitor, EDO-S101, a salvage regimen for HL patients, into xenografted mice. Methodology: Blood lymphocytes from 50 HL patients and seven HL cell lines were used. Immunohistochemistry, flow cytometry, and cytogenetics analyses were performed. The in vitro and in vivo effects of EDO-S101 were assessed. Results: We have successfully determined conditions for in vitro amplification and characterization of the HL L428-c subline, containing a higher proportion of CD30−/CD15− cells than the parental L428 cell line. This subline displayed excellent clonogenic potential and reliable reproducibility upon xenografting into immunodeficient NOD-SCID-gamma (−/−)(NSG) mice. Using cell sorting, we demonstrate that CD30−/CD15− subpopulations can gain the phenotype of the L428-c cell line in vitro. Moreover, the human cells recovered from the seventh week after injection of L428-c cells into NSG mice were small cells characterized by a high frequency of CD30−/CD15− cells. Cytogenetic analysis demonstrated that they were diploid and showed high telomere instability and telomerase activity. Accordingly, chromosomal instability emerged, as shown by the formation of dicentric chromosomes, ring chromosomes, and breakage/fusion/bridge cycles. Similarly, high telomerase activity and telomere instability were detected in circulating lymphocytes from HL patients. The beneficial effect of the histone-deacetylase inhibitor EDO-S101 as an anti-tumor drug validated our animal model. Conclusion: Our HL animal model requires only 103 cells and is characterized by a high survival/toxicity ratio and high reproducibility. Moreover, the cells that engraft in mice are characterized by a high frequency of small CD30−/CD15− cells exhibiting high telomerase activity and telomere dysfunction.

BACKGROUND & AIMS:Paneth cell dysfunction causes deficiencies in intestinal C-type lectins and antimicrobial peptides, which leads to dysbiosis of the intestinal microbiota, alters the mucosal barrier, and promotes development of inflammatory bowel diseases. We investigated whether transgenic (TG) expression of the human regenerating family member 3 alpha gene (REG3A) alters the fecal microbiota and affects development of colitis in mice.METHODS:We performed studies with C57BL/6 mice that express human regenerating family member 3 alpha (hREG3A) in hepatocytes, via the albumin gene promoter. In these mice, hREG3A travels via the bile to the intestinal lumen. Some mice were given dextran sodium sulfate (DSS) to induce colitis. Feces were collected from mice and the composition of the microbiota was analyzed by 16S ribosomal RNA sequencing. The fecal microbiome was also analyzed from mice that express only 1 copy of human REG3A transgene but were fed feces from control mice (not expressing hREG3A) as newborns. Mice expressing hREG3A were monitored for DSS-induced colitis after cohousing or feeding feces from control mice. Colitis was induced in another set of control and hREG3A-TG mice by administration of trinitrobenzene sulfonic acid; some mice were given intrarectal injections of the hREG3A protein. Colon tissues were collected from mice and analyzed by histology and immunohistochemistry to detect mucin 2, as well as by 16S ribosomal RNA fluorescence in situ hybridization, transcriptional analyses, and quantitative polymerase chain reaction. We measured levels of reactive oxygen species (ROS) in bacterial cultures and fecal microbiota using 2',7'-dichlorofluorescein diacetate and flow cytometry.RESULTS:The fecal microbiota of mice that express hREG3A had a significant shift in composition, compared with control mice, with enrichment of Clostridiales (Ruminococcaceae, Lachnospiraceae) and depletion of Bacteroidetes (Prevotellaceae); the TG mice developed less-severe colitis following administration of DSS than control mice, associated with preserved gut barrier integrity and reduced bacterial translocation, epithelial inflammation, and oxidative damage. A similar shift in the composition of the fecal microbiota occurred after a few months in TG mice heterozygous for REG3A that harbored a wild-type maternal microbiota at birth; these mice developed less-severe forms of colitis following DSS administration. Cohoused and germ-free mice fed feces from REG3A-TG mice and given DSS developed less-severe forms of colitis and had reduced lipopolysaccharide activation of the toll-like receptor 4 and increased survival times compared with mice not fed feces from REG3A-TG mice. REG3A TG mice developed only mild colonic inflammation after exposure to 2,4,6-trinitrobenzene sulfonic acid, compared with control mice. Control mice given intrarectal hREG3A and exposed to 2,4,6-trinitrobenzene sulfonic acid showed less colon damage and inflammation than mice not given intrarectal hREG3A. Fecal samples from REG3A-TG mice had lower levels of ROS than feces from control mice during DSS administration. Addition of hREG3A to bacterial cultures reduced levels of ROS and increased survival of oxygen-sensitive commensal bacteria (Faecalibacterium prausnitzii and Roseburia intestinalis).CONCLUSIONS:Mice with hepatocytes that express hREG3A, which travels to the intestinal lumen, are less sensitive to colitis than control mice. We found hREG3A to alter the colonic microbiota by decreasing levels of ROS. Fecal microbiota from REG3A-TG mice protect non-TG mice from induction of colitis. These findings indicate a role for reduction of oxidative stress in preserving the gut microbiota and its ability to prevent inflammation.

Purpose . We developed a new approach to visualize skin Langerhans cells by in vivo fluorescence imaging in nonhuman primates. Procedures . Macaques were intradermally injected with a monoclonal, fluorescently labeled antibody against HLA-DR molecule and were imaged for up to 5 days by fibered confocal microscopy (FCFM). Results . The network of skin Langerhans cells was visualized by in vivo fibered confocal fluorescence microscopy. Quantification of Langerhans cells revealed no changes to cell density with time. Ex vivo experiments confirmed that injected fluorescent HLA-DR antibody specifically targeted Langerhans cells in the epidermis. Conclusions . This study demonstrates the feasibility of single-cell, in vivo imaging as a noninvasive technique to track Langerhans cells in nontransgenic animals.

In vivo electroporation (EP) is used to enhance the uptake of nucleic acids and its association with DNA vaccination greatly stimulates immune responses to vaccine antigens delivered through the skin. However, the effect of EP on cutaneous cell behavior, the dynamics of immune cell recruitment and local inflammatory factors, have not been fully described. Here, we show that intradermal DNA vaccination combined with EP extends antigen expression to the epidermis and the subcutaneous skin muscle in non-human primates. In vivo fibered confocal microscopy and dynamic ex vivo imaging revealed that EP promotes the mobility of Langerhans cells (LC) and their interactions with transfected cells prior to their migration from the epidermis. At the peak of vaccine expression, we detected antigen in damaged keratinocyte areas in the epidermis and we characterized recruited immune cells in the skin, the hypodermis and the subcutaneous muscle. EP alone was sufficient to induce the production of pro-inflammatory cytokines in the skin and significantly increased local concentrations of Transforming Growth Factor (TGF)-alpha and IL-12. Our results show the kinetics of inflammatory processes in response to EP of the skin, and reveal its potential as a vaccine adjuvant.

La sclérose de l’hippocampe (SH) est fréquemment associée à une des formes résistantes aux traitements, l’épilepsie mésio-temporale. Des processus neuroinflammatoires impliquant la protéine translocatrice 18 kDa (TSPO) ont été rapportés au niveau de cette lésion à la fois chez des patients épileptiques comme dans certains modèles animaux. La TSPO à l’aide du radio-ligand [18F]DPA-714 est actuellement considérée comme un biomarqueur de processus lésionnels in vivo en imagerie TEP. L’objectif de notre étude est de valider cet outil au cours de la constitution et l’aggravation de la SH dans un modèle d’épilepsie chez la souris. Le modèle a été induit par une injection d’acide kainique dans l’hippocampe dorsal droit de souris adultes mâles C57/Bl6 (n = 19) et comparé aux contrôles (injection de sérum physiologique au même niveau ; n = 17). Les images ont été acquises avant l’injection puis à 7 jours, 2 semaines, 1 mois et 6 mois après injection sur micro-PET-CT (Inveon, Siemens), puis recalées sur un atlas IRM dans PMOD. Pour évaluer son évolution, la fixation du traceur dans les hippocampes a été normalisée par celle du cervelet. Ces résultats ont été comparés à l’autoradiographie en [18F]DPA-714 et à l’immunohistologie (Iba1/TSPO) sur des coupes de cerveaux d’autres souris euthanasiées aux différents temps correspondant à l’imagerie TEP (n = 3 pour chaque groupe de chaque temps). Comparée aux souris témoins, la fixation du DPA-714 dans les hippocampes épileptiques est plus élevée à tout moment après injection, prédominante du côté injecté. Comparé à l’état basal, le signal de la SH est maximal à 7 jours (33 % de différence, p < 0,001), diminue au fil du temps (26 % de différence, p < 0,001 à 2 semaines et 21 %, p < 0,001 à 1 mois) mais persiste même à 6 mois (15 % de différence, p = 0,007). Les résultats de la TEP au niveau des hippocampes sont confirmés par l’autoradiographie comme par immunohistologie retrouvant une surexpression de la protéine TSPO dans la microglie. Notre étude montre la faisabilité de l’imagerie TEP [18F]DPA-714 pour suivre in vivo le processus neuroinflammatoire au cours de la constitution et de l’aggravation de la SH jusqu’à 6 mois après induction du modèle. Ces résultats ouvrent la voie pour des études transgéniques et/ou de neuroprotection chez la souris. Cette étude a été soutenue par l’EU FP7 INMiND (grant agreement No. 278850).

OBJECTIVE The main limitation to the efficacy of chemotherapy for brain tumors is the restricted access to the brain because of the limited permeability of the blood-brain barrier (BBB). Previous animal studies have shown that the application of pulsed ultrasound (US), in combination with the intravenous injection of microbubbles, can temporarily disrupt the BBB to deliver drugs that normally cannot reach brain tissue. Although many previous studies have been performed with external focused US transducers, the device described in the current work emits US energy using an unfocused transducer implanted in the skull thickness. This method avoids distortion of the US energy by the skull bone and allows for simple, repetitive, and broad disruption of the BBB without the need for MRI monitoring. The purpose of the present study was to determine if the BBB can be safely and repeatedly disrupted using such an implantable unfocused US device in a primate model.METHODS An 11.5-mm-diameter, 1-MHz, planar US device was implanted via a bur hole into the skull of 3 primates (2 Papio anubis [olive] baboons and 1 Macaca fascicularis [macaque]) for 4 months. Pulsed US sonications were applied together with the simultaneous intravenous injection of sulfur hexafluoride microbubbles (SonoVue) every 2 weeks to temporarily disrupt the BBB. In each primate, a total of 7 sonications were performed with a 23.2-msec burst length (25,000 cycles) and a 1-Hz pulse repetition frequency at acoustic pressure levels of 0.6-0.8 MPa. Potential toxicity induced by repeated BBB opening was analyzed using MRI, PET, electroencephalography (EEG), somatosensory evoked potential (SSEP) monitoring, behavioral scales, and histopathological analysis.RESULTS The T1-weighted contrast-enhanced MR images acquired after each sonication exhibited a zone of hyper-signal underneath the transducer that persisted for more than 4 hours, indicating a broad region of BBB opening in the acoustic field of the implant. Positron emission tomography images with fluorine-18-labeled fluorodeoxyglucose (FDG) did not indicate any changes in the cerebral metabolism of glucose. Neither epileptic signs nor pathological central nerve conduction was observed on EEG and SSEP recordings, respectively. Behavior in all animals remained normal. Histological analysis showed no hemorrhagic processes, no petechia, and extravasation of only a few erythrocytes.CONCLUSIONS The studies performed confirm that an implantable, 1-MHz US device can be used to repeatedly open the BBB broadly in a large-animal model without inducing any acute, subacute, or chronic lesions.

Cannabinoid type 2 receptors (CB2R) have emerged as promising targets for the diagnosis and therapy of brain pathologies. However, no suitable radiotracers for accurate CB2R mapping have been found to date, limiting the investigation of the CB2 receptor expression using positron emission tomography (PET) imaging. In this work, we report the evaluation of the in vivo expression of CB2R with [11C]A-836339 PET after cerebral ischemia and in two rat models of neuroinflammation, first by intrastriatal LPS and then by AMPA injection. PET images and in vitro autoradiography showed a lack of specific [11C]A-836339 uptake in these animal models demonstrating the limitation of this radiotracer to image CB2 receptor under neuroinflammatory conditions. Further, using immunohistochemistry, the CB2 receptor displayed a modest expression increase after cerebral ischemia, LPS and AMPA models. Finally, [18F]DPA-714-PET and immunohistochemistry demonstrated decreased neuroinflammation by a selective CB2R agonist, JWH133. Taken together, these findings suggest that [11C]A-836339 is not a suitable radiotracer to monitor in vivo CB2R expression by using PET imaging. Future studies will have to investigate alternative radiotracers that could provide an accurate binding to CB2 receptors following brain inflammation.

The complementary nature of positron emission tomography (PET) and near-infrared fluorescence (NIRF) imaging makes the development of innovative multimodal PET/NIRF probes a very exciting prospect. Herein, the bioinspired design of novel platform exploiting the strength and specificity of interactions between radioactive and fluorescent biotin derivatives and an avidin core is reported. The combination of an original [18F]fluoropyridinylated-biotin derivative and commercially available fluorescent biotin derivatives (Atto-425 and Atto-680) is investigated. The in vivo distribution of such a customized platform is also reported, for the first time, in healthy rodent using PET and ex vivo fluorescence imaging.

Near-infrared (NIR) fluorescence imaging using FDA-approved indocyanine green (ICG) has been the subject of numerous studies during the past few years. It could constitute a potentially exciting new paradigm shift in veterinary oncology, especially to develop in vivo fluorescence imaging diagnostics and surgery guidance methods. The objective of this study was to evaluate the pharmacologic and toxicological characteristics in healthy beagle dogs of LipImage™ 815, a formulation made of NIR-dye-loaded lipid nanoparticles. The initial dosage for the evaluation of biodistribution was extrapolated from data in mice and then adapted to define the more adapted dose (MAD) according to the fluorescence results obtained in 5 dogs using a Fluobeam® 800 imaging device (phase 0 study). A single dose acute toxicity study was then performed (3 dogs, phase I study). Before the systemic administration of LipImage™ 815, the dogs presented a very mild residual fluorescence, particularly in the liver and kidneys. After injection, the plasma fluorescence continuously decreased, and the signal was relatively homogeneously distributed throughout the different organs, though more pronounced in the liver and to a lesser extent in the steroid-rich organs (adrenal, ovaries), intestines, lymph nodes and kidneys. A MAD of 2.0μg/kg was found. No evidence of acute or delayed general, hepatic, renal or hematologic toxicity was observed at 1-fold, 5-fold or 10-fold MAD. The results of this phase-0/phase-I study showed that an optimal dosage of LipImage™ 815 of 2.0μg/kg allowed the achievement of a fluorescence signal suitable for surgery guidance application without any acute side effects.

The effects of metoclopramide on the central nervous system (CNS) in patients suggest substantial brain distribution. Previous data suggest that metoclopramide brain kinetics may nonetheless be controlled by ATP-binding cassette (ABC) transporters expressed at the blood–brain barrier. We used 11C-metoclopramide PET imaging to elucidate the kinetic impact of transporter function on metoclopramide exposure to the brain. Methods:11C-metoclopramide transport by P-glycoprotein (P-gp; ABCB1) and the breast cancer resistance protein (BCRP; ABCG2) was tested using uptake assays in cells overexpressing P-gp and BCRP. 11C-metoclopramide brain kinetics were compared using PET in rats (n = 4–5) in the absence and presence of a pharmacologic dose of metoclopramide (3 mg/kg), with or without P-gp inhibition using intravenous tariquidar (8 mg/kg). The 11C-metoclopramide brain distribution (VT based on Logan plot analysis) and brain kinetics (2-tissue-compartment model) were characterized with either a measured or an imaged-derived input function. Plasma and brain radiometabolites were studied using radio–high-performance liquid chromatography analysis. Results:11C-metoclopramide transport was selective for P-gp over BCRP. Pharmacologic dose did not affect baseline 11C-metoclopramide brain kinetics (VT = 2.28 ± 0.32 and 2.04 ± 0.19 mL⋅cm−3 using microdose and pharmacologic dose, respectively). Tariquidar significantly enhanced microdose 11C-metoclopramide VT (7.80 ± 1.43 mL⋅cm−3) with a 4.4-fold increase in K1 (influx rate constant) and a 2.3-fold increase in binding potential (k3/k4) in the 2-tissue-compartment model. In the pharmacologic situation, P-gp inhibition significantly increased metoclopramide brain distribution (VT = 6.28 ± 0.48 mL⋅cm−3) with a 2.0-fold increase in K1 and a 2.2-fold decrease in k2 (efflux rate), with no significant impact on binding potential. In this situation, only parent 11C-metoclopramide could be detected in the brains of P-gp–inhibited rats. Conclusion:11C-metoclopramide benefits from favorable pharmacokinetic properties that offer reliable quantification of P-gp function at the blood–brain barrier in a pharmacologic situation. Using metoclopramide as a model of CNS drug, we demonstrated that P-gp function not only reduces influx but also mediates the efflux from the brain back to the blood compartment, with additional impact on brain distribution. This PET-based strategy of P-gp function investigation may provide new insight on the contribution of P-gp to the variability of response to CNS drugs between patients.

Heparan Sulfate (HS) mimetics are able to block crucial interactions of the components of the extracellular matrix in angiogenic processes and as such, represent a valuable class of original candidates for cancer therapy. Here we first report the synthesis and in vitro angiogenic inhibition properties of a conjugated, novel and rationally-designed octasaccharide-based HS mimetic. We also herein report its labeling with fluorine-18 and present the preliminary in vivo Positron Emission Tomography imaging data in rats. This constitutes one of the rare examples of labeling and in vivo evaluation of a synthetic, polysaccharide-based, macromolecule.