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BACKGROUND: Mediating glucose absorption in the small intestine and renal clearance, sodium glucose cotransporters (SGLTs) have emerged as an attractive therapeutic target in diabetic patients. A substantial fraction of patients, however, only achieve inadequate glycemic control. Thus, we aimed to assess the potential of the SGLT-targeting PET radiotracer alpha-methyl-4-deoxy-4-[18F]fluoro-D-glucopyranoside ([18F]Me4FDG) as a noninvasive intestinal and renal biomarker of SGLT-mediated glucose transport. METHODS: We investigated healthy rats using a dedicated small animal PET system. Dynamic imaging was conducted after administration of the reference radiotracer 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG), or the SGLT-targeting agent, [18F]Me4FDG either directly into the digestive tract (for assessing intestinal absorption) or via the tail vein (for evaluating kidney excretion). To confirm the specificity of [18F]Me4FDG and responsiveness to treatment, a subset of animals was also pretreated with the SGLT inhibitor phlorizin. In this regard, an intraintestinal route of administration was used to assess tracer absorption in the digestive tract, while for renal assessment, phlorizin was injected intravenously (IV). RESULTS: Serving as reference, intestinal administration of [18F]FDG led to slow absorption with retention of 89.2 ± 3.5% of administered radioactivity at 15 min. [18F]Me4FDG, however, was rapidly absorbed into the blood and cleared from the intestine within 15 min, leading to markedly lower tracer retention of 18.5 ± 1.2% (P < 0.0001). Intraintestinal phlorizin led to marked increase of [18F]Me4FDG uptake (15 min, 99.9 ± 4.7%; P < 0.0001 vs. untreated controls), supporting the notion that this PET agent can measure adequate SGLT inhibition in the digestive tract. In the kidneys, radiotracer was also sensitive to SGLT inhibition. After IV injection, [18F]Me4FDG reabsorption in the renal cortex was significantly suppressed by phlorizin when compared to untreated animals (%ID/g at 60 min, 0.42 ± 0.10 vs. untreated controls, 1.20 ± 0.03; P < 0.0001). CONCLUSION: As a noninvasive read-out of the concurrent SGLT expression in both the digestive tract and the renal cortex, [18F]Me4FDG PET may serve as a surrogate marker for treatment response to SGLT inhibition. As such, [18F]Me4FDG may enable improvement in glycemic control in diabetes by PET-based monitoring strategies.

DOI： 10.1155/2022/4635171

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BACKGROUND: Equipped with two stationary detectors, a large bore collimator for medium-sized animals has been recently introduced for dedicated preclinical single-photon emission computed tomography (SPECT) imaging. We aimed to evaluate the basic performance of the system using phantoms and healthy rabbits. METHODS: A general-purpose medium-sized animal (GP-MSA) collimator with 135 mm bore diameter and thirty-three holes of 2.5 mm diameter was installed on an ultrahigh-resolution scanner equipped with two large stationary detectors (U-SPECT5-E/CT). The sensitivity and uniformity were investigated using a point source and a cylinder phantom containing 99mTc-pertechnetate, respectively. Uniformity (in %) was derived using volumes of interest (VOIs) on images of the cylinder phantom and calculated as [(maximum count - minimum count)/(maximum count + minimum count) × 100], with lower values of % indicating superior performance. The spatial resolution and contrast-to-noise ratios (CNRs) were evaluated with images of a hot-rod Derenzo phantom using different activity concentrations. Feasibility of in vivo SPECT imaging was finally confirmed by rabbit imaging with the most commonly used clinical myocardial perfusion SPECT agent [99mTc]Tc-sestamibi (dynamic acquisition with a scan time of 5 min). RESULTS: In the performance evaluation, a sensitivity of 790 cps/MBq, a spatial resolution with the hot-rod phantom of 2.5 mm, and a uniformity of 39.2% were achieved. The CNRs of the rod size 2.5 mm were 1.37, 1.24, 1.20, and 0.85 for activity concentration of 29.2, 1.0, 0.5, and 0.1 MBq/mL, respectively. Dynamic SPECT imaging in rabbits allowed to visualize most of the thorax and to generate time-activity curves of the left myocardial wall and ventricular cavity. CONCLUSION: Preclinical U-SPECT5-E/CT equipped with a large bore collimator demonstrated adequate sensitivity and resolution for in vivo rabbit imaging. Along with its unique features of SPECT molecular functional imaging is a superior collimator technology that is applicable to medium-sized animal models and thus may promote translational research for diagnostic purposes and development of novel therapeutics.

DOI： 10.1155/2022/9810097

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Background: Radiolabeled agents that are substrates for the norepinephrine transporter (NET) can be used to quantify cardiac sympathetic nervous conditions and have been demonstrated to identify high-risk congestive heart failure (HF) patients prone to arrhythmic events. We aimed to fully characterize the kinetic profile of the novel 18F-labeled NET probe AF78 for PET imaging of the cardiac sympathetic nervous system (SNS) among various species. Methods:18F-AF78 was compared to norepinephrine (NE) and established SNS radiotracers by employing in vitro cell assays, followed by an in vivo PET imaging approach with healthy rats, rabbits and nonhuman primates (NHPs). Additionally, chase protocols were performed in NHPs with NET inhibitor desipramine (DMI) and the NE releasing stimulator tyramine (TYR) to investigate retention kinetics in cardiac SNS. Results: Relative to other SNS radiotracers, 18F-AF78 showed higher transport affinity via NET in a cell-based competitive uptake assay (IC50 0.42 ± 0.14 µM), almost identical to that of NE (IC50, 0.50 ± 0.16 µM, n.s.). In rabbits and NHPs, initial cardiac uptake was significantly reduced by NET inhibition. Furthermore, cardiac tracer retention was not affected by a DMI chase protocol but was markedly reduced by intermittent TYR chase, thereby suggesting that 18F-AF78 is stored and can be released via the synaptic vesicular turnover process. Computational modeling hypothesized the formation of a T-shaped π-π stacking at the binding site, suggesting a rationale for the high affinity of 18F-AF78. Conclusion:18F-AF78 demonstrated high in vitro NET affinity and advantageous in vivo radiotracer kinetics across various species, indicating that 18F-AF78 is an SNS imaging agent with strong potential to guide specific interventions in cardiovascular medicine.

DOI： 10.7150/thno.63205

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PURPOSE: A neuropathological hallmark of Alzheimer's disease (AD) is the presence of amyloid-β (Aβ) plaques in the brain, which are observed in a significant number of cognitively normal, older adults as well. In AD, butyrylcholinesterase (BChE) becomes associated with Aβ aggregates, making it a promising target for imaging probes to support diagnosis of AD. In this study, we present the synthesis, radiochemistry, in vitro and preliminary ex and in vivo investigations of a selective, reversible BChE inhibitor as PET-tracer for evaluation as an AD diagnostic. PROCEDURES: Radiolabeling of the inhibitor was achieved by fluorination of a respective tosylated precursor using K[18F]. IC50 values of the fluorinated compound were obtained in a colorimetric assay using recombinant, human (h) BChE. Dissociation constants were determined by measuring hBChE activity in the presence of different concentrations of inhibitor. RESULTS: Radiofluorination of the tosylate precursor gave the desired radiotracer in an average radiochemical yield of 20 ± 3 %. Identity and > 95.5 % radiochemical purity were confirmed by HPLC and TLC autoradiography. The inhibitory potency determined in Ellman's assay gave an IC50 value of 118.3 ± 19.6 nM. Dissociation constants measured in kinetic experiments revealed lower affinity of the inhibitor for binding to the acylated enzyme (K2 = 68.0 nM) in comparison to the free enzyme (K1 = 32.9 nM). CONCLUSIONS: The reversibly acting, selective radiotracer is synthetically easily accessible and retains promising activity and binding potential on hBChE. Radiosynthesis with 18F labeling of tosylates was feasible in a reasonable time frame and good radiochemical yield.

DOI： 10.1007/s11307-021-01584-2

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The enzyme butyrylcholinesterase (BChE) represents a promising target for imaging probes to potentially enable early diagnosis of neurodegenerative diseases like Alzheimer's disease (AD) and to monitor disease progression in some forms of cancer. In this study, we present the design, facile synthesis, in vitro and preliminary ex vivo and in vivo evaluation of a morpholine-based, selective inhibitor of human BChE as a positron emission tomography (PET) tracer with a pseudo-irreversible binding mode. We demonstrate a novel protecting group strategy for 18 F radiolabeling of carbamate precursors and show that the inhibitory potency as well as kinetic properties of our unlabeled reference compound were retained in comparison to the parent compound. In particular, the prolonged duration of enzyme inhibition of such a morpholinocarbamate motivated us to design a PET tracer, possibly enabling a precise mapping of BChE distribution.

DOI： 10.1002/cmdc.202000942

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OBJECTIVES: This study is aimed at investigating the impact of frame numbers in preclinical electrocardiogram- (ECG-) gated 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) on systolic and diastolic left ventricular (LV) parameters in rats. METHODS: 18F-FDG PET imaging using a dedicated small animal PET system with list mode data acquisition and continuous ECG recording was performed in diabetic and control rats. The list-mode data was sorted and reconstructed with different numbers of frames (4, 8, 12, and 16) per cardiac cycle into tomographic images. Using an automatic ventricular edge detection software, left ventricular (LV) functional parameters, including ejection fraction (EF), end-diastolic (EDV), and end-systolic volume (ESV), were calculated. Diastolic variables (time to peak filling (TPF), first third mean filling rate (1/3 FR), and peak filling rate (PFR)) were also assessed. RESULTS: Significant differences in multiple parameters were observed among the reconstructions with different frames per cardiac cycle. EDV significantly increased by numbers of frames (353.8 ± 57.7 μl∗, 380.8 ± 57.2 μl∗, 398.0 ± 63.1 μl∗, and 444.8 ± 75.3 μl at 4, 8, 12, and 16 frames, respectively; ∗ P < 0.0001 vs. 16 frames), while systolic (EF) and diastolic (TPF, 1/3 FR and PFR) parameters were not significantly different between 12 and 16 frames. In addition, significant differences between diabetic and control animals in 1/3 FR and PFR in 16 frames per cardiac cycle were observed (P < 0.005), but not for 4, 8, and 12 frames. CONCLUSIONS: Using ECG-gated PET in rats, measurements of cardiac function are significantly affected by the frames per cardiac cycle. Therefore, if you are going to compare those functional parameters, a consistent number of frames should be used.

DOI： 10.1155/2021/4629459

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>
We aimed to investigate the image quality of the U-SPECT5/CT E-Class a micro single-photon emission computed tomography (SPECT) system with two large stationary detectors for visualization of rat hearts and bones using clinically available ^99mTc-labelled tracers. Sensitivity, spatial resolution, uniformity and contrast-to-noise ratio (CNR) of the small-animal SPECT scanner were investigated in phantom studies using an ultra-high-resolution rat and mouse multi-pinhole collimator (UHR-RM). Point source, hot-rod, and uniform phantoms with ^99mTc-solution were scanned for high-count performance assessment and count levels equal to animal scans, respectively. Reconstruction was performed using the similarity-regulated ordered-subsets expectation maximization (SROSEM) algorithm with Gaussian smoothing. Rats were injected with ~ 100 MBq [^99mTc]Tc-MIBI or ~ 150 MBq [^99mTc]Tc-HMDP and received multi-frame micro-SPECT imaging after tracer distribution. Animal scans were reconstructed for three different acquisition times and post-processed with different sized Gaussian filters. Following reconstruction, CNR was calculated and image quality evaluated by three independent readers on a five-point scale from 1 = “very poor” to 5 = “very good”. Point source sensitivity was 567 cps/MBq and radioactive rods as small as 1.2 mm were resolved with the UHR-RM collimator. Collimator-dependent uniformity was 55.5%. Phantom CNR improved with increasing rod size, filter size and activity concentration. Left ventricle and bone structures were successfully visualized in rat experiments. Image quality was strongly affected by the extent of post-filtering, whereas scan time did not have substantial influence on visual assessment. Good image quality was achieved for resolution range greater than 1.8 mm in bone and 2.8 mm in heart. The recently introduced small animal SPECT system with two stationary detectors and UHR-RM collimator is capable to provide excellent image quality in heart and bone scans in a rat using standardized reconstruction parameters and appropriate post-filtering. However, there are still challenges in achieving maximum system resolution in the sub-millimeter range with in vivo settings under limited injection dose and acquisition time.

DOI： 10.1038/s41598-020-75696-0

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Other Link： http://www.nature.com/articles/s41598-020-75696-0

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DOI： 10.1016/j.jcmg.2019.05.018

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PURPOSE: Taking full advantage of positron emission tomography (PET) technology, fluorine-18-labelled radiotracers targeting norepinephrine transporter (NET) have potential applications in the diagnosis and assessment of cardiac sympathetic nerve conditions as well as the delineation of neuroendocrine tumours. However, to date, none have been used clinically. Drawbacks of currently reported radiotracers include suboptimal kinetics and challenging radiolabelling procedures. PROCEDURES: We developed a novel fluorine-18-labelled radiotracer targeting NET, AF78, with efficient one-step radiolabelling based on the phenethylguanidine structure. Radiosynthesis of AF78 was undertaken, followed by validation in cell uptake studies, autoradiography, and in vivo imaging in rats. RESULTS: [18F]AF78 was successfully synthesized with 27.9 ± 3.1 % radiochemical yield, > 97 % radiochemical purity and > 53.8 GBq/mmol molar activity. Cell uptake studies demonstrated essentially identical affinity for NET as norepinephrine and meta-iodobenzylgaunidine. Both ex vivo autoradiography and in vivo imaging in rats showed homogeneous and specific cardiac uptake. CONCLUSIONS: The new PET radiotracer [18F]AF78 demonstrated high affinity for NET and favourable biodistribution in rats. A structure-activity relationship between radiotracer structures and affinity for NET was revealed, which may serve as the basis for the further design of NET targeting radiotracers with favourable features.

DOI： 10.1007/s11307-019-01407-5

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We aimed to explore the impact of ageing on 11C-hydroxyephedrine (11C-HED) uptake in the healthy rat heart in a longitudinal setting. To investigate a potential cold mass effect, the influence of specific activity on cardiac 11C-HED uptake was evaluated: 11C-HED was synthesized by N-methylation of (-)-metaraminol as the free base (radiochemical purity >95%) and a wide range of specific activities (0.2-141.9 GBq/μmol) were prepared. 11C-HED (48.7 ± 9.7MBq, ranged 0.2-60.4 μg/kg cold mass) was injected in healthy Wistar Rats. Dynamic 23-frame PET images were obtained over 30 min. Time activity curves were generated for the blood input function and myocardial tissue. Cardiac 11C-HED retention index (%/min) was calculated as myocardial tissue activity at 20-30 min divided by the integral of the blood activity curves. Additionally, the impact of ageing on myocardial 11C-HED uptake was investigated longitudinally by PET studies at different ages of healthy Wistar Rats. A dose-dependent reduction of cardiac 11C-HED uptake was observed: The estimated retention index as a marker of norepinephrine function decreased at a lower specific activity (higher amount of cold mass). This observed high affinity of 11C-HED to the neural norepinephrine transporter triggered a subsequent study: In a longitudinal setting, the 11C-HED retention index decreased with increasing age. An age-related decline of cardiac sympathetic innervation could be demonstrated. The herein observed cold mass effect might increase in succeeding scans and therefore, 11C-HED microPET studies should be planned with extreme caution if one single radiosynthesis is scheduled for multiple animals.

DOI： 10.1038/s41598-018-29509-0

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Background: 18F-N-[3-bromo-4-(3-fluoro-propoxy)-benzyl]-guanidine (18F-LMI1195) is a new class of PET tracer designed for sympathetic nervous imaging of the heart. The favorable image quality with high and specific neural uptake has been previously demonstrated in animals and humans, but intracellular behavior is not yet fully understood. The aim of the present study is to verify whether it is taken up in storage vesicles and released in company with vesicle turnover. Results: Both vesicle-rich (PC12) and vesicle-poor (SK-N-SH) norepinephrine-expressing cell lines were used for in vitro tracer uptake studies. After 2 h of 18F-LMI1195 preloading into both cell lines, effects of stimulants for storage vesicle turnover (high concentration KCl (100 mM) or reserpine treatment) were measured at 10, 20, and 30 min. 131I-meta-iodobenzylguanidine (131I-MIBG) served as a reference. Both high concentration KCl and reserpine enhanced 18F-LMI1195 washout from PC12 cells, while tracer retention remained stable in the SK-N-SH cells. After 30 min of treatment, 18F-LMI1195 releasing index (percentage of tracer released from cells) from vesicle-rich PC12 cells achieved significant differences compared to cells without treatment condition. In contrast, such effect could not be observed using vesicle-poor SK-N-SH cell lines. Similar tracer kinetics after KCl or reserpine treatment were also observed using 131I-MIBG. In case of KCl exposure, Ca2+-free buffer with the calcium chelator, ethylenediaminetetracetic acid (EDTA), could suppress the tracer washout from PC12 cells. This finding is consistent with the tracer release being mediated by Ca2+ influx resulting from membrane depolarization. Conclusions: Analogous to 131I-MIBG, the current in vitro tracer uptake study confirmed that 18F-LMI1195 is also stored in vesicles in PC12 cells and released along with vesicle turnover. Understanding the basic kinetics of 18F-LMI1195 at a subcellular level is important for the design of clinical imaging protocols and imaging interpretation.

DOI： 10.1186/s13550-018-0365-9

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Authorship：Lead author   Language：English   Publisher：SOC NUCLEAR MEDICINE INC  

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER IRELAND LTD  

Coronary flow reserve (CFR), defined as the ratio of maximum coronary flow increase from baseline resting blood flow, is one of the most sensitive parameters to detect early signs of coronary arteriosclerosis at the microvascular level. Myocardial perfusion PET is a well-established technology for CFR measurement, however, availability is still limited. The aim of this study is to introduce and validate myocardial flow reserve measurement by myocardial perfusion SPECT.
Methods: Myocardial perfusion SPECT at rest and ATP stress (0.16 mg/Kg/min) was performed in 10 patients with known coronary artery disease. Immediately after the injection of Tc-99m sestamibi (MIBI), left ventricular (LV) dynamic planar angiographic data were obtained for 90s. Coronary flow reserve index as measured by MIBI SPECT (CFRMIBI) was calculated as follows: CFRMIBI = Cm(s)Sbm(b) / Cm(b)Sbm(s), where subscripts (b, s,) Cm, and Sbm indicate baseline, during stress, myocardial counts with MIBI SPECT, and integral of LV counts with first pass angiography, respectively. Additionally, standard stress/rest O-15-water PET to estimate CFR was performed in all patients as standard of reference.
Results: CFRMIBI increased in conjunction with CFR, but underestimated blood flow at high flow rates. The relationship between CFRMIBI (Y) and CFRPET (X) was well fitted as follows: Y = 1.40x(1-exp(1.79/x)) (r = 0.84).
Conclusions: The index of CFRMIBI reflects the CFR by O-15-water PET but underestimates flow at high flows, maybe as a reflection of pharmacokinetic limitations of MIBI. (C) 2016 Elsevier Ireland Ltd. All rights reserved.

DOI： 10.1016/j.ijcard.2016.07.183

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Transformation with large DNA molecules enables multiple genes to be introduced into plants simultaneously to produce transgenic plants with complex phenotypes. In this study, a large DNA fragment (ca. 100 kb) containing a set of Aegilops tauschii hardness genes was introduced into rice plants using a novel transformation method, called bioactive beads-mediated transformation. Nine transgenic rice plants were obtained and the presence of transgenes in the rice genome was confirmed by PCR and FISH analyses. The results suggested that multiple transgenes were successfully integrated in all transgenic plants. The expression of one of the transgenes, puroindoline b, was confirmed at the mRNA and protein levels in the T(2) generation. Our study clearly demonstrates that the bioactive bead method is capable of producing transgenic rice plants carrying large DNA fragments. This method will facilitate the production of useful transgenic plants by introducing multiple genes simultaneously.

DOI： 10.1007/s00299-009-0678-2

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