Radiosynthesis of the norepinephrine transporter tracer [F-18]NS12137 via copper-mediated F-18-labelling

[F-18]NS12137 (exo-3-[(6-[F-18]fluoro-2-pyridyl)oxy]8-azabicyclo[3.2.1]octane) is a highly selective norepinephrine transporter (NET) tracer. NETs are responsible for the reuptake of norepinephrine and dopamine and are linked to several neurodegenerative and neuropsychiatric disorders. The aim of this study was to develop a copper-mediated F-18-fluorination method for the production of [F-18]NS12137 with straightforward synthesis conditions and high radiochemical yield and molar activity. [F-18]NS12137 was produced in two steps. Radiofluorination of [F-18]NS12137 was performed via a copper-mediated pathway starting with a stannane precursor and using [F-18]F- as the source of the fluorine-18 isotope. Deprotection was performed via acid hydrolysis. The radiofluorination reaction was nearly quantitative as was the deprotection based on HPLC analysis. The radiochemical yield of the synthesis was 15.1 +/- 0.5%. Molar activity of [F-18]NS12137 was up to 300 GBq/mu mol. The synthesis procedure is straightforward and can easily be automated and adapted for clinical production

Study of the Effect of Reconstruction Parameters for Myocardial Perfusion Imaging in PET With a Novel Flow Phantom

Myocardial perfusion imaging (MPI) with positron emission tomography (PET) allows quantitative temporal measurements of the radioactive tracer distribution in tissue. The quantification for myocardial blood flow (MBF) is conducted with kinetic modeling of the image-derived time-activity curves (TACs) allowing derivation for MBF in units of mL/min per gram of tissue. The ordered-subset expectation maximization (OSEM) reconstruction algorithm with time-of-flight (TOF) and point spread function (PSF) modeling is now routinely employed in cardiac imaging. However, the varying counting statistics of the MPI measurements conducted with short-lived tracers present a challenge for the PET image reconstruction methods. Thus, the effect of the reconstruction methods on the flow quantification needs to be evaluated in a standardized manner. Recently, a novel PET flow phantom modeling the MBF has been developed for investigation of the standardization of the MBF measurements. In this study, the effect of the reconstruction parameters on the image-derived flow values against a known reference flow of the flow phantom was studied with [O-15]H2O. The effects were studied by comparison of TACs and relative errors of the image-derived flow values with respect to the phantom-derived reference flow value using 5 repeated PET scans with fixed acquisition parameters using a digital Discovery MI PET/CT system. The reconstruction methods applied were OSEM using both TOF and PSF (OSEM-TOF-PSF) with several matrix sizes (128 x 128, 192 x 192, 256 x 256, 384 x 384), Gaussian filter sizes (4, 8 mm) and OSEM without TOF and PSF (OSEM), with TOF (OSEM-TOF) and with PSF (OSEM-PSF) in addition to recently introduced regularized reconstruction method based on Bayesian-penalized maximum likelihood (Q.Clear). Between repeated measurements, the image-derived flow values showed high repeatability with a SD less than 2 mL/min as well as high accuracy with the maximum error of 7% with respect to the reference flow for all reconstructions. Overall, reconstruction settings had only a small impact on the resulting flow values. In conclusion, due to the small differences detected, any of the implemented reconstruction algorithms on the system can be applied in MPI studies for accurate flow quantification

Automated GMP production and long-term experience in radiosynthesis of CB(1)tracer [F-18]FMPEP-d(2)

Here, we describe the development of an in-house-built device for the fully automated multistep synthesis of the cannabinoid CB(1)receptor imaging tracer (3R,5R)-5-(3-([F-18]fluoromethoxy-d(2))phenyl)-3-(((R)-1-phenylethyl)amino)-1-(4-(trifluoromethyl)phenyl)pyrrolidin-2-one ([F-18]FMPEP-d(2)), following good manufacturing practices. The device is interfaced to a HPLC and a sterile filtration unit in a clean room hot cell. The synthesis involves the nucleophilic(18)F-fluorination of an alkylating agent and its GC purification, the subsequent(18)F-fluoroalkylation of a precursor molecule, the semipreparative HPLC purification of the(18)F-fluoroalkylated product, and its formulation for injection. We have optimized the duration and temperature of the(18)F-fluoroalkylation reaction and addressed the radiochemical stability of the formulated product. During the past 5 years (2013-2018), we have performed a total of 149 syntheses for clinical use with a 90% success rate. The activity yield of the formulated product has been 1.0 +/- 0.4 GBq starting from 11 +/- 2 GBq and the molar activity 600 +/- 300 GBq/mu mol at the end of synthesis

Novel effects of the gastrointestinal hormone secretin on cardiac metabolism and renal function

The cardiac benefits of gastrointestinal hormones have been of interest in recent years. The aim of this study was to explore the myocardial and renal effects of the gastrointestinal hormone secretin in the GUTBAT trial (NCT03290846). A placebo-controlled crossover study was conducted on 15 healthy males in fasting conditions, where subjects were blinded to the intervention. Myocardial glucose uptake was measured with [F-18]2-fluoro-2-deoxy-o-glucose ([F-18]FDG) positron emission tomography. Kidney function was measured with [F-18]FDG renal clearance and estimated glomerular filtration rate (eGFR). Secretin increased myocardial glucose uptake compared with placebo (secretin vs. placebo, means +/- SD, 15.5 +/- 7.4 vs. 9.7 +/- 4.9 gmol/100 g/min, 95% confidence interval (CI) [2.2, 9.4], P = 0.004). Secretin also increased [F-18]FDG renal clearance (44.5 +/- 5.4 vs. 39.5 8.5 mL/min, 95%CI [1.9, 8.1], P = 0.004), and eGFR was significantly increased from baseline after secretin, compared with placebo (17.8 +/- 9.8 vs. 6.0 +/- 5.2 Delta mL/min/1.73 m(2),( ) 95%CI [6.0, 17.6], P = 0.001). Our results implicate that secretin increases heart work and renal filtration, making it an interesting drug candidate for future studies in heart and kidney failure. NEW & NOTEWORTHY Secretin increases myocardial glucose uptake compared with placebo, supporting a previously proposed inotropic effect. Secretin also increased renal filtration rate.Peer reviewe

Assessment of a digital and an analog PET/CT system for accurate myocardial perfusion imaging with a flow phantom

In Myocardial Perfusion Imaging (MPI) with Positron Emission Tomography/Computed Tomography (PET/CT) systems, accurate quantification is essential. We assessed flow quantification accuracy over various injected activities using a flow phantom.Methods The study was performed on the digital 4-ring Discovery MI (DMI-20) and analog Discovery 690 (D690) PET/CT systems, using 325-1257 MBq of [O-15]H2O. PET performance and flow quantification accuracy were assessed in terms of count-rates, dead-time factors (DTF), scatter fractions (SF), time-activity curves (TACs), areas-under-the-curves (AUCs) and flow values.Results On DMI-20, prompts of 12.8 Mcps, DTF of 2.06 and SF of 46.1% were measured with 1257 MBq of activity. On the D690, prompts of 6.85 Mcps, DTF of 1.57 and SF of 32.5% were measured with 1230 MBq of activity. AUC values were linear over all activities. Mean wash-in flow error was - 9% for both systems whereas wash-out flow error was - 5% and - 6% for DMI-20 and D690. With the highest activity, wash-out flow error was - 12% and - 7% for the DMI-20 and D690.Conclusion DMI-20 and D690 preserved accurate flow quantification over all injected activities, with maximum error of - 12%. In the future, flow quantification accuracy over the activities and count-rates evaluated in this study should be assessed

Cool-water immersion reduces postexercise quadriceps femoris muscle perfusion more than cold-water immersion

Purpose The muscle perfusion response to postexercise cold-water immersion (CWI) is not well understood. We examined the effects of graded postexercise CWI upon global and regional quadriceps femoris muscle perfusion using positron emission tomography and [15O]H2O. Methods Using a matched-group design, 30 healthy men performed cycle ergometer exercise at 70% VO2peak to a core body temperature of 38°C, followed by either 10 min of CWI at 8°C, 22°C, or seated rest (control). Quadriceps muscle perfusion; thigh and calf cutaneous vascular conductance; intestinal, muscle, and local skin temperatures; thermal comfort; mean arterial pressure; and heart rate were assessed at preexercise, postexercise, and after CWI. Results Global quadriceps perfusion was reduced beyond the predefined minimal clinically relevant threshold (0.75 mL per 100 g·min-1) in 22°C water versus control (difference (95% confidence interval (CI)), -2.5 (-3.9 to -1.1) mL per 100 g·min-1). Clinically relevant decreases in muscle perfusion were observed in the rectus femoris (-2.0 (-3.0 to -1.0) mL per 100 g·min-1) and vastus lateralis (-3.5 (-4.9 to -2.0) mL per 100 g·min-1) in 8°C water, and in the vastus lateralis (-3.3 (-4.8 to -1.9) mL per 100 g·min-1) in 22°C water versus control. The mean effects for vastus intermedius and vastus medialis perfusion were not clinically relevant. Clinically relevant decreases in thigh and calf cutaneous vascular conductance were observed in both cooling conditions. Conclusions The present findings revealed that less noxious CWI (22°C) promoted clinically relevant postexercise decreases in global quadriceps muscle perfusion, whereas noxious cooling (8°C) elicited no effect

Cool-Water Immersion Reduces Post-Exercise Quadriceps Femoris Muscle Perfusion more than Cold-Water Immersion

Purpose: The muscle perfusion response to post-exercise cold water immersion (CWI) is not well understood. We examined the effects of graded post-exercise CWI upon global and regional quadriceps femoris muscle perfusion using positron emission tomography (PET) and [15O]H2O.Methods: Using a matched-group design, 30 healthy men performed cycle ergometer exercise at 70% V[Combining Dot Above]O2peak to a core body temperature of 38 °C, followed by either 10 min of CWI at 8 °C, 22 °C or seated rest (control). Quadriceps muscle perfusion, thigh and calf cutaneous vascular conductance (CVC), intestinal, muscle, and local skin temperatures, thermal comfort, mean arterial pressure, and heart rate were assessed at pre-, post-exercise and following CWI.Results: Global quadriceps perfusion was reduced beyond the pre-defined minimal clinically relevant threshold (0.75 mL·100 g·min-1) in 22 °C water versus control (difference [95% confidence interval (CI)]: -2.5 mL·100 g·min-1 [-3.9 to -1.1]). Clinically relevant decreases in muscle perfusion were observed in the rectus femoris (-2.0 mL·100 g·min-1 [-3.0 to -1.0]) and vastus lateralis (VL; -3.5 mL·100 g·min-1 [-4.9 to -2.0]) in 8 °C water, and in the vastus lateralis (-3.3 mL·100 g·min-1 [-4.8 to -1.9]) in 22 °C water versus control. The mean effects for vastus intermedius and vastus medialis perfusion were not clinically relevant. Clinically relevant decreases in thigh and calf CVC were observed in both cooling conditions.Conclusions: The present findings revealed that less noxious CWI (22 °C) promoted clinically relevant post-exercise decreases in global quadriceps muscle perfusion whereas noxious cooling (8 °C) elicited no effect.</p

Obesity risk is associated with brain glucose uptake and insulin resistance

Objective: To investigate whether alterations in brain glucose uptake (BGU), insulin action in the brain-liver axis and whole-body insulin sensitivity occur in young adults in pre-obese state.Methods: Healthy males with either high risk (HR; n = 19) or low risk (LR; n = 22) for developing obesity were studied with [18F]fluoro-d-glucose ([18F]FDG)-positron emission tomography during hyperinsulinemic-euglycemic clamp. Obesity risk was assessed according to BMI, physical activity and parental overweight/obesity and type 2 diabetes. Brain, skeletal muscle, brown adipose tissue (BAT), visceral adipose tissue (VAT) and abdominal and femoral s.c. adipose tissue (SAT) glucose uptake (GU) rates were measured. Endogenous glucose production (EGP) was calculated by subtracting the exogenous glucose infusion rate from the rate of disappearance of [18F]FDG. BGU was analyzed using statistical parametric mapping, and peripheral tissue activity was determined using Carimas Software imaging processing platform.Results: BGU was higher in the HR vs LR group and correlated inversely with whole-body insulin sensitivity (M value) in the HR group but not in the LR group. Insulin-suppressed EGP did not differ between the groups but correlated positively with BGU in the whole population, and the correlation was driven by the HR group. Skeletal muscle, BAT, VAT, abdominal and femoral SAT GU were lower in the HR group as compared to the LR group. Muscle GU correlated negatively with BGU in the HR group but not in the LR group.Conclusion: Increased BGU, alterations in insulin action in the brain-liver axis and decreased whole-body insulin sensitivity occur early in pre-obese state.</p

A Computational and Experimental Study of the Regulatory Mechanisms of the Complement System

The complement system is key to innate immunity and its activation is necessary for the clearance of bacteria and apoptotic cells. However, insufficient or excessive complement activation will lead to immune-related diseases. It is so far unknown how the complement activity is up- or down- regulated and what the associated pathophysiological mechanisms are. To quantitatively understand the modulatory mechanisms of the complement system, we built a computational model involving the enhancement and suppression mechanisms that regulate complement activity. Our model consists of a large system of Ordinary Differential Equations (ODEs) accompanied by a dynamic Bayesian network as a probabilistic approximation of the ODE dynamics. Applying Bayesian inference techniques, this approximation was used to perform parameter estimation and sensitivity analysis. Our combined computational and experimental study showed that the antimicrobial response is sensitive to changes in pH and calcium levels, which determines the strength of the crosstalk between CRP and L-ficolin. Our study also revealed differential regulatory effects of C4BP. While C4BP delays but does not decrease the classical complement activation, it attenuates but does not significantly delay the lectin pathway activation. We also found that the major inhibitory role of C4BP is to facilitate the decay of C3 convertase. In summary, the present work elucidates the regulatory mechanisms of the complement system and demonstrates how the bio-pathway machinery maintains the balance between activation and inhibition. The insights we have gained could contribute to the development of therapies targeting the complement system.Singapore. Ministry of Education (Grant T208B3109)Singapore. Agency for Science, Technology and Research (BMRC 08/1/21/19/574)Singapore-MIT Alliance (Computational and Systems Biology Flagship Project)Swedish Research Counci