Influx Constant Research Articles

The value of net influx constant based on FDG PET/CT dynamic imaging in the differential diagnosis of metastatic from non-metastatic lymph nodes in lung cancer.

This study aims to evaluate the value of the dynamic and static quantitative metabolic parameters derived from 18F-fluorodeoxyglucose (FDG)-positron emission tomography/CT (PET/CT) in the differential diagnosis of metastatic from non-metastatic lymph nodes (LNs) in lung cancer and to validate them based on the results of a previous study. One hundred and twenty-one patients with lung nodules or masses detected on chest CT scan underwent 18F-FDG PET/CT dynamic + static imaging with informed consent. A retrospective collection of 126 LNs in 37 patients with lung cancer was pathologically confirmed. Static image analysis parameters include LN-SUVmax and LN-SUVmax/primary tumor SUVmax (LN-SUVmax/PT-SUVmax). Dynamic metabolic parameters including the net influx rate (Ki) and the surrogate of perfusion (K1) and of each LN were obtained by applying the irreversible two-tissue compartment model using in-house Matlab software. Ki/K1 was then calculated as a separate marker. Based on the pathological findings, we divided into a metastatic group and a non-metastatic group. The χ2 test was used to evaluate the agreement of the individual and combined diagnosis of each metabolic parameter with the gold standard. The receiver-operating characteristic (ROC) analysis was performed for each parameter to determine the diagnostic efficacy in differentiating non-metastatic from metastatic LNs with high FDG-avid. P < 0.05 was considered statistically significant. Among the 126 FDG-avid LNs confirmed by pathology, 70 LNs were metastatic, and 56 LNs were non-metastatic. For ROC analysis, in separate assays, the dynamic metabolic parameter Ki [sensitivity (SEN) of 84.30%, specificity (SPE) of 94.60%, accuracy of 88.89%, and AUC of 0.895] had a better diagnostic value than the static metabolic parameter SUVmax (SEN of 82.90%, SPE of 62.50%, accuracy of 74.60%, and AUC of 0.727) in differentiating between metastatic from non-metastatic LNs groups, respectively. In the combined diagnosis group, the combined SUVmax + Ki diagnosis had a better diagnostic value in the differential diagnosis of metastatic from non-metastatic LNs, with SEN, SPE, accuracy, and AUC of 84.3%, 94.6%, 88.89%, and 0.907, respectively. When the cutoff value of Ki was 0.022ml/g/min, it had a high diagnostic value in the differential diagnosis between metastasis and non-metastasis in FDG-avid LNs of lung cancer, especially in improving the specificity. The combination of SUVmax and Ki is expected to be a reliable metabolic parameter for N-staging of lung cancer.

Valine and nonessential amino acids affect bidirectional transport rates of leucine and isoleucine in bovine mammary epithelial cells

A more complete understanding of the mechanisms controlling AA transport in mammary glands of dairy cattle will help identify solutions to increase nitrogen feeding efficiency on farms. It was hypothesized that Ala, Gln, and Gly (NEAAG), which are actively transported into cells and exchanged for all branched-chain AA (BCAA), may stimulate transport of BCAA, and that Val may antagonize transport of the other BCAA due to transporter competition. Thus, we evaluated the effects of varying concentrations of NEAAG and Val on transport and metabolism of the BCAA Ala, Met, Phe, and Thr by bovine mammary epithelial cells. Primary cultures of bovine mammary epithelial cells were assigned to treatments of low (70% of mean in vivo plasma concentrations of lactating dairy cows) and high (200%) concentrations of Val and NEAAG (LVal and LNEAAG, HVal and HNEAAG, respectively) in a 2 × 2 factorial design. Cells were preloaded with treatment media containing [15N]-labeled AA for 24 h. The [15N]-labeled media were replaced with treatment media containing [13C]-labeled AA. Media and cells were harvested from plates at 0, 0.5, 1, 5, 15, 30, 60, and 240 min after application of the [13C]-labeled AA and assessed for [15N]- and [13C]-AA label concentrations. The data were used to derive transport, transamination, irreversible loss, and protein-synthesis fluxes. All Val fluxes, except synthesis of rapidly exchanging tissue protein, increased with the HVal treatment. Interestingly, the rapidly exchanging tissue protein, transamination, and irreversible-loss rate constants decreased with HVal, indicating that the significant flux increases were primarily driven by mass action with the cells resisting the flux increases by downregulating activity. However, the decreases could also reflect saturation of processes that would drive down the mass-action rate constants. This is supported by decreases in the same rate constants for Ile and Leu with HVal. This could be due to either competition for shared transamination and oxidation reactions or a reduction in enzymatic activity. Also, NEAAG did not affect Val fluxes, but influx and efflux rate constants increased for both Val and Leu with HNEAAG, indicating an activating substrate effect. Overall, AA transport rates generally responded concordantly with extracellular concentrations, indicating the transporters are not substrate-saturated within the in vivo range. However, BCAA transamination and oxidation enzymes may be approaching saturation within in vivo ranges. In addition, System L transport activity appeared to be stimulated by as much as 75% with high intracellular concentrations of Ala, Gln, and Gly. High concentrations of Val antagonized transport activity of Ile and Leu by 68% and 15%, respectively, indicating competitive inhibition, but this was only observable at HNEAAG concentrations. The exchange transporters of System L transport 8 of the essential AA that make up approximately 40% of milk protein, so better understanding this transporter is an important step for increased efficiency.

Brain perfusion estimation by Tikhonov model-free deconvolution in a long axial field of view PET/CT scanner exploring five different PET tracers

PurposeNew total-body PET scanners with a long axial field of view (LAFOV) allow for higher temporal resolution due to higher sensitivity, which facilitates perfusion estimation by model-free deconvolution. Fundamental tracer kinetic theory predicts that perfusion can be estimated for all tracers despite their different fates given sufficiently high temporal resolution of 1 s or better, bypassing the need for compartment modelling. The aim of this study was to investigate whether brain perfusion could be estimated using model-free Tikhonov generalized deconvolution for five different PET tracers, [15O]H2O, [11C]PIB, [18F]FE-PE2I, [18F]FDG and [18F]FET. To our knowledge, this is the first example of a general model-free approach to estimate cerebral blood flow (CBF) from PET data.MethodsTwenty-five patients underwent dynamic LAFOV PET scanning (Siemens, Quadra). PET images were reconstructed with an isotropic voxel resolution of 1.65 mm3. Time framing was 40 × 1 s during bolus passage followed by increasing framing up to 60 min. AIF was obtained from the descending aorta. Both voxel- and region-based calculations of perfusion in the thalamus were performed using the Tikhonov method. The residue impulse response function was used to estimate the extraction fraction of tracer leakage across the blood–brain barrier.ResultsCBF ranged from 37 to 69 mL blood min−1 100 mL of tissue−1 in the thalamus. Voxelwise calculation of CBF resulted in CBF maps in the physiologically normal range. The extraction fractions of [15O]H2O, [18F]FE-PE2I, [11C]PIB, [18F]FDG and [18F]FET in the thalamus were 0.95, 0.78, 0.62, 0.19 and 0.03, respectively.ConclusionThe high temporal resolution and sensitivity associated with LAFOV PET scanners allow for noninvasive perfusion estimation of multiple tracers. The method provides an estimation of the residue impulse response function, from which the fate of the tracer can be studied, including the extraction fraction, influx constant, volume of distribution and transit time distribution, providing detailed physiological insight into normal and pathologic tissue.

Enhanced Extraction of Blood and Tissue Time-Activity Curves in Cardiac Mouse FDG PET Imaging by Means of Constrained Nonnegative Matrix Factorization.

We propose an enhanced method to accurately retrieve time-activity curves (TACs) of blood and tissue from dynamic 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) positron emission tomography (PET) cardiac images of mice. The method is noninvasive and consists of using a constrained nonnegative matrix factorization algorithm (CNMF) applied to the matrix (A) containing the intensity values of the voxels of the left ventricle (LV) PET image. CNMF factorizes A into nonnegative matrices H and W, respectively, representing the physiological factors (blood and tissue) and their associated weights, by minimizing an extended cost function. We verified our method on 32 C57BL/6 mice, 14 of them with acute myocardial infarction (AMI). With CNMF, we could break down the mouse LV into myocardial and blood pool images. Their corresponding TACs were used in kinetic modeling to readily determine the [18F]FDG influx constant (Ki) required to compute the myocardial metabolic rate of glucose. The calculated Ki values using CNMF for the heart of control mice were in good agreement with those published in the literature. Significant differences in Ki values for the heart of control and AMI mice were found using CNMF. The values of the elements of W agreed well with the LV structural changes induced by ligation of the left coronary artery. CNMF was compared with the recently published method based on robust unmixing of dynamic sequences using regions of interest (RUDUR). A clear improvement of signal separation was observed with CNMF compared to the RUDUR method.

Early Diagnosis of Murine Sepsis-Associated Encephalopathy Using Dynamic PET/CT Imaging and Multiparametric MRI.

Early diagnosis of sepsis-associated encephalopathy (SAE) is essential for the treatment and prognosis of septic patients. Static PET and MRI have shown promise for early diagnosis, while pharmacokinetic parameters from dynamic PET may provide better quantification for SAE. This study aims to compare the performance of dynamic 2-deoxy-2-[18F]fluoro-D-glucose ([18F]F-FDG) PET and multiparametric MRI in early imaging SAE with a view to providing guidance for the early diagnosis of SAE. Dynamic [18F]F-FDG-PET/CT scans and multiparametric MRI were performed in SAE mice induced by LPS. Standardized uptake value (SUV) was measured in static scan images and [18F]F-FDG pharmacokinetic parameters were analyzed with two-tissue compartment model and Patlak plot. MRI relative signal intensity (rT1) derived from T1-weighted images (pre and post contrast) and 4 parameters originating from diffusion-weighted data were measured. Both SUV and dephosphorylation rate constant (k4) increased in SAE model as early as 6h post sepsis induction, while k4 increased with the relative value (SAE/normal) significantly stronger than that of SUV. Moreover, the net influx constant (Ki) showed significant decrease in SAE as early as 6h compared with normal mice. Increased signal intensity was identified in T1-weighted contrast enhanced images and rT1 value increased at 12h post induction. Diffusion tensor imaging (DTI) revealed fractional anisotropy (FA) decreased at 12h and 24h in external capsule (ec) and declined axial diffusivity (AD) was shown in white matter at 24h. The dynamic PET (k4) was more sensitive than static PET (SUV) for early diagnosis of SAE and declined Ki was firstly found in murine SAE, which indicated the advantage of dynamic PET/CT in early detection and differential diagnosis of SAE. While MRI has a higher soft tissue resolution than PET/CT and can classify more subtle brain areas, the comprehensive utilization of the two modalities is helpful for managing SAE.

Blood-brain barrier permeability changes in the first year after alemtuzumab treatment predict 2-year outcomes in relapsing-remitting multiple sclerosis

BackgroundIn relapsing-remitting multiple sclerosis (RRMS), early disease control reduces the risk of permanent disability. The blood–brain barrier (BBB) is compromised in MS, and its permeability is a potential biomarker. ObjectiveTo investigate BBB permeability measured by MRI as a marker of alemtuzumab efficacy. MethodsPatients with RRMS initiating alemtuzumab treatment were recruited prospectively. BBB permeability was assessed as the Patlak-derived influx constant (Ki) by dynamic contrast-enhanced MRI before and 6, 12, and 18 months after the first course of alemtuzumab. No Evidence of Disease Activity-3 (NEDA-3) status was ascertained two years after treatment initiation. ResultsPatients who maintained NEDA-3 status at two years (n = 7) had a larger decrease in Ki between baseline and six months (-0.029 ml/100 g/min [CI -0.005 − -0.053]) and between baseline and 12 months in normal appearing white matter (0.043 [CI 0.022 – -0.065]), than those who experienced disease activity (n = 8). ROC curve analysis of the Ki change between baseline and 12 months in NAWM predicted a loss of NEDA status at 2 years with 86% sensitivity and 86% specificity (AUC 0.98, p = 0.002). ConclusionBBB permeability predicted alemtuzumab efficacy at two years, indicating that BBB permeability is a biomarker of treatment response in RRMS.

Target occupancy study and whole-body dosimetry with a MAGL PET ligand [11C]PF-06809247 in non-human primates

BackgroundMonoacylglycerol lipase (MAGL) is a key serine hydrolase which terminates endocannabinoid signaling and regulates arachidonic acid driven inflammatory responses within the central nervous system. To develop [11C]PF-06809247 into a clinically usable MAGL positron emission tomography (PET) radioligand, we assessed the occupancy of MAGL by an inhibitor in the non-human primate (NHP) brain. Additionally, we measured the whole-body distribution of [11C]PF-06809247 in NHP and estimated human effective radiation doses.MethodsSeven cynomolgus monkeys were enrolled for brain PET measurements. Two PET measurements along with arterial blood sampling were performed in each NHP: one baseline and one pretreatment condition with intravenous administration of PF-06818883, a pro-drug of a selective MAGL inhibitor (total of seven doses between 0.01 and 1.27 mg/kg). Kinetic parameters K1, k2 and k3 were estimated by a two tissue compartment (2TC) model using metabolite corrected plasma radioactivity as the input function. k4 was set as 0 according to the irreversible binding of [11C]PF-06809247. Ki by 2TC and Patlak analysis were calculated as the influx constant. The target occupancy was calculated using Ki at baseline and pretreatment conditions. Two cynomolgus monkeys were enrolled for whole-body PET measurements. Estimates of the absorbed radiation dose in humans were calculated with OLINDA/EXM 1.1 using the adult male reference model.ResultsRadioactivity retention was decreased in all brain regions following pretreatment with PF-06818883. Occupancy was measured as 25.4–100.5% in a dose dependent manner. Whole-body PET showed high radioactivity uptake values in the liver, small intestine, kidney, and brain. The effective dose of [11C]PF-06809247 was calculated as 4.3 μSv/MBq.Conclusions[11C]PF-06809247 is a promising PET ligand for further studies of MAGL in the human brain.

Cerebral [18F]-FDOPA Uptake in Autism Spectrum Disorder and Its Association with Autistic Traits.

Dopaminergic signaling is believed to be related to autistic traits. We conducted an exploratory 3,4-dihydroxy-6-[18F]-fluoro-L-phenylalanine positron emission tomography/computed tomography ([18F]-FDOPA PET/CT) study, to examine cerebral [18F]-FDOPA influx constant (kicer min−1), reflecting predominantly striatal dopamine synthesis capacity and a mixed monoaminergic innervation in extrastriatal neurons, in 44 adults diagnosed with autism spectrum disorder (ASD) and 22 controls, aged 18 to 30 years. Autistic traits were assessed with the Autism Spectrum Quotient (AQ). Region-of-interest and voxel-based analyses showed no statistically significant differences in kicer between autistic adults and controls. In autistic adults, striatal kicer was significantly, negatively associated with AQ attention to detail subscale scores, although Bayesian analyses did not support this finding. In conclusion, among autistic adults, specific autistic traits can be associated with reduced striatal dopamine synthesis capacity. However, replication of this finding is necessary.

PET Imaging of brain muscarinic receptors with 18F-Fluorobenzyl-Dexetimide: A first in human study

M1 and M4 muscarinic receptor (mAChR) agonists are under development for the treatment of schizophrenia, Alzheimer's and Parkinson's disease. We performed first-in-human PET imaging of mAChR with 18F-Fluorobenzyl-Dexetimide (FDEX) in 10 healthy participants (29.4±4.3yrs). Four underwent dynamic brain scanning for 240 min, and then six underwent static brain scans at 120 and 160-min post injection of 250 MBq of FDEX. Gjedde-Patlak graphical analysis was applied to determine the influx constant (Ki). Regional tissue ratios (SUVR) were calculated using the cerebellar cortex as the reference region. No adverse events were observed. The tracer showed good brain entry (∼4.2% ID at 5 min) but irreversible distribution kinetics over four hours in regions of high mAChR. Binding was consistent with the distribution of mAChR receptors with striatum > cortex > hippocampus >> thalamus >>> cerebellum with low variance in regional binding between subjects. Ki was 0.42±0.04 in the putamen, 0.27±0.01 in frontal cortex, 0.25±0.02 in the hippocampus and 0.10±0.01 in the thalamus. SUVR at 120 and 240 min. were highly correlated with these Ki values with R2 of 0.91 and 0.99 respectively. FDEX yields high quality brain images with uptake in the known distribution of mAChR with remarkably little variance between normal subjects.

In Vivo Induction of P-Glycoprotein Function can be Measured with [18F]MC225 and PET.

P-Glycoprotein (P-gp) is an efflux pump located at the blood–brain barrier (BBB) that contributes to the protection of the central nervous system by transporting neurotoxic compounds out of the brain. A decline in P-gp function has been related to the pathogenesis of neurodegenerative diseases. P-gp inducers can increase the P-gp function and are considered as potential candidates for the treatment of such disorders. The P-gp inducer MC111 increased P-gp expression and function in SW480 human colon adenocarcinoma and colo-320 cells, respectively. Our study aims to evaluate the P-gp inducing effect of MC111 in the whole brain in vivo, using the P-gp tracer [18F]MC225 and positron emission tomography (PET). Eighteen Wistar rats were treated with either vehicle solution, 4.5 mg/kg of MC111 (low-dose group), or 6 mg/kg of MC111 (high-dose group). Animals underwent a 60 min dynamic PET scan with arterial-blood sampling, 24 h after treatment with the inducer. Data were analyzed using the 1-tissue-compartment model and metabolite-corrected plasma as the input function. Model parameters such as the influx constant (K1) and volume of distribution (VT) were calculated, which reflect the in vivo P-gp function. P-gp and pregnane xenobiotic receptor (PXR) expression levels of the whole brain were assessed using western blot. The administration of MC111 decreased K1 and VT of [18F]MC225 in the whole brain and all of the selected brain regions. In the high-dose group, whole-brain K1 was decreased by 34% (K1-high-dose = 0.20 ± 0.02 vs K1-control = 0.30 ± 0.02; p < 0.001) and in the low-dose group by 7% (K1-low-dose = 0.28 ± 0.02 vs K1-control = 0.30 ± 0.02; p = 0.42) compared to controls. Whole-brain VT was decreased by 25% in the high-dose group (VT-high-dose = 5.92 ± 0.41 vs VT-control = 7.82 ± 0.38; p < 0.001) and by 6% in the low-dose group (VT-low-dose = 7.35 ± 0.38 vs VT-control = 7.82 ± 0.37; p = 0.38) compared to controls. k2 values did not vary after treatment. The treatment did not affect the metabolism of [18F]MC225. Western blot studies using the whole-brain tissue did not detect changes in the P-gp expression, however, preliminary results using isolated brain capillaries found an increasing trend up to 37% in treated rats. The decrease in K1 and VT values after treatment with the inducer indicates an increase in the P-gp functionality at the BBB of treated rats. Moreover, preliminary results using brain endothelial cells also sustained the increase in the P-gp expression. In conclusion, the results verify that MC111 induces P-gp expression and function at the BBB in rats. An increasing trend regarding the P-gp expression levels is found using western blot and an increased P-gp function is confirmed with [18F]MC225 and PET.

Manganese-enhanced T1 mapping to quantify myocardial viability: validation with 18F-fluorodeoxyglucose positron emission tomography

Gadolinium chelates are widely used in cardiovascular magnetic resonance imaging (MRI) as passive intravascular and extracellular space markers. Manganese, a biologically active paramagnetic calcium analogue, provides novel intracellular myocardial tissue characterisation. We previously showed manganese-enhanced MRI (MEMRI) more accurately quantifies myocardial infarction than gadolinium delayed-enhancement MRI (DEMRI). Here, we evaluated the potential of MEMRI to assess myocardial viability compared to gold-standard 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) viability. Coronary artery ligation surgery was performed in male Sprague-Dawley rats (n = 13) followed by dual MEMRI and 18F-FDG PET imaging at 10–12 weeks. MEMRI was achieved with unchelated (EVP1001-1) or chelated (mangafodipir) manganese. T1 mapping MRI was followed by 18F-FDG micro-PET, with tissue taken for histological correlation. MEMRI and PET demonstrated good agreement with histology but native T1 underestimated infarct size. Quantification of viability by MEMRI, PET and MTC were similar, irrespective of manganese agent. MEMRI showed superior agreement with PET than native T1. MEMRI showed excellent agreement with PET and MTC viability. Myocardial MEMRI T1 correlated with 18F-FDG standard uptake values and influx constant but not native T1. Our findings indicate that MEMRI identifies and quantifies myocardial viability and has major potential for clinical application in myocardial disease and regenerative therapies.

Increase in P-glycoprotein levels in the blood-brain barrier of partial portal vein ligation /chronic hyperammonemia rats is medicated by ammonia/reactive oxygen species/ERK1/2 activation: In vitro and in vivo studies

Liver failure altered P-glycoprotein (P-gp) function and expression at blood-brain barrier (BBB), partly owing to hyperammonemia. We aimed to examine the effects of partial portal vein ligation (PVL) plus chronic hyperammonemia (CHA) on P-gp function and expression at rat BBB. Experimental rats included sham-operation (SH), PVL, CHA and PVL+CHA. The PVL+CHA rats were developed by ammonia-containing diet for 2 weeks after operation. The brain-to-plasma concentration ratios (Kp) and apparent unidirectional influx constants (Kin) of rhodamine123 and sodium fluorescein were measured to assess function of P-gp and BBB integrity, respectively. Human cerebral microvascular endothelial cells (HCMEC/D3) were used to assess effects of ammonia on P-gp expression and function. It was found that PVL+CHA significantly decreased Kp and Kin of rhodamine123 without affecting brain distribution of fluorescein. The P-gp expressions in membrane protein in cortex and hippocampus were significantly increased in CHA and PVL +CHA rats, especially in PVL + CHA rats, while remarkably increased phosphorylated ERK1/2 was only found in PVL +CHA rats. Expressions of tight junction proteins claudin-5 and occluding in rat brain remained unchanged. In vitro data showed that NH4Cl increased reactive oxygen species, membrane expression and function of P-gp as well as phosphorylated ERK1/2 levels in HCMEC/D3. The NH4Cl-induced alterations were reversed by reactive oxygen species scavenger N-acetylcysteine and ERK1/2 inhibitor U0126. In conclusion, PVL+CHA increased function and membrane translocation of P-gp at rat BBB partly via ammonia. Reactive oxygen species/ERK1/2 pathway activation may be one of the reasons that ammonia upregulated P-gp expression and function at BBB.

Applying dynamic contrast enhanced MSOT imaging to intratumoral pharmacokinetic modeling

Examining the dynamics of an agent in the tumor microenvironment can offer critical insights to the influx rate and accumulation of the agent. Intratumoral kinetic characterization in the in vivo setting can further elicudate distribution patterns and tumor microenvironment.Dynamic contrast-enhanced Multispectral Optoacoustic Tomographic imaging (DCE-MSOT) acquires serial MSOT images with the administration of an exogenous contrast agent over time. We tracked the dynamics of a tumor-targeted contrast agent, HypoxiSense 680 (HS680), in breast xenograft mouse models using MSOT. Arterial input function (AIF) approach with MSOT imaging allowed for tracking HS680 dynamics within the mouse. The optoacoustic signal for HS680 was quantified using the ROI function in the ViewMSOT software. A two-compartment pharmacokinetics (PK) model constructed in MATLAB to fit rate parameters. The contrast influx (kin) and outflux (kout) rate constants predicted are kin = 1.96 × 10−2 s-1 and kout = 9.5 × 10-3 s-1 (R = 0.9945).

P-Glycoprotein (ABCB1) Inhibits the Influx and Increases the Efflux of 11C-Metoclopramide Across the Blood-Brain Barrier: A PET Study on Nonhuman Primates.

PET imaging using radiolabeled avid substrates of the ATP-binding cassette (ABC) transporter P-glycoprotein (ABCB1) has convincingly revealed the role of this major efflux transporter in limiting the influx of its substrates from blood into the brain across the blood-brain barrier (BBB). Many drugs, such as metoclopramide, are weak ABCB1 substrates and distribute into the brain even when ABCB1 is fully functional. In this study, we used kinetic modeling and validated simplified methods to highlight and quantify the impact of ABCB1 on the BBB influx and efflux of 11C-metoclopramide, as a model of a weak ABCB1 substrate, in nonhuman primates. Methods: The regional brain kinetics of a tracer dose of 11C-metoclopramide (298 ± 44 MBq) were assessed in baboons using PET without (n = 4) or with (n = 4) intravenous coinfusion of the ABCB1 inhibitor tariquidar (4 mg/kg/h). Metabolite-corrected arterial input functions were generated to estimate the regional volume of distribution (VT), as well as the influx (K1) and efflux (k2) rate constants, using a 1-tissue-compartment model. Modeling outcome parameters were correlated with image-derived parameters, that is, areas under the regional time-activity curves (AUCs) from 0 to 30 min and from 30 to 60 min (SUV⋅min) and the elimination slope (kE; min-1) from 30 to 60 min. Results: Tariquidar significantly increased the brain distribution of 11C-metoclopramide (VT = 4.3 ± 0.5 mL/cm3 and 8.7 ± 0.5 mL/cm3 for baseline and ABCB1 inhibition conditions, respectively, P < 0.001), with a 1.28-fold increase in K1 (P < 0.05) and a 1.64-fold decrease in k2 (P < 0.001). The effect of tariquidar was homogeneous across different brain regions. The parameters most sensitive to ABCB1 inhibition were VT (2.02-fold increase) and AUC from 30 to 60 min (2.02-fold increase). VT correlated significantly (P < 0.0001) with AUC from 30 to 60 min (r2 = 0.95), with AUC from 0 to 30 min (r2 = 0.87), and with kE (r2 = 0.62). Conclusion:11C-metoclopramide PET imaging revealed the relative importance of both the influx hindrance and the efflux enhancement components of ABCB1 in a relevant model of the human BBB. The overall impact of ABCB1 on drug delivery to the brain can be noninvasively estimated from image-derived outcome parameters without the need for an arterial input function.

S181. THE STATE OR TRAIT COMPONENT OF DOPAMINE AND GLUTAMATE DYSFUNCTION IN THE RISK FOR PSYCHOSIS: AN IN VIVO MULTIMODAL IMAGING STUDY OF INDIVIDUALS WITH 22Q11.2 DELETION

BackgroundDopaminergic and glutamatergic dysregulation are among the leading hypotheses for schizophrenia. Previous in vivo imaging studies have shown that increased striatal presynaptic dopamine synthesis capacity (DSC) predates the onset of psychosis and is associated with symptom severity. Recent meta-analysis in magnetic resonance spectroscopy studies in schizophrenia reported increased levels of glutamate and glutamine (Glx) in basal ganglia and medial frontal cortex in clinical high-risk groups for psychosis. Despite the evidence of alterations in both dopamine and glutamate in schizophrenia, the degree to which these alterations are trait markers linked to genetic risk for psychosis or reflects state changes is not clear from previous studies. Over the last fifteen years, it has been well established that 22q11 deletion is one of the most important genetic risk factors for the development of schizophrenia. Individuals with 22q11 deletion are at increased genetic risk for psychosis, reaching a prevalence 30% for psychotic disorder. The aims of our study were to investigate dopaminergic and glutamatergic function in individuals with 22q11.2 deletion.MethodsParticipants underwent 18F DOPA PET, MRI, as well as clinical measures.21 individuals with 22q11 deletion (14 females and 7 males, age (mean, SD): 26.1(7.72)) and 26 healthy volunteers (15 females and 11 males, age (mean, SD): 26.12(4.28)) took part in the 18F DOPA PET. Standardised ROIs was defined in the striatum, including limbic, associative and sensorimotor sub-regions, and the reference region, defined according to previous study. The ROI atlas was normalised to each individual PET dynamic image. A Patlak analysis was applied to calculate influx constants (Ki values) for the whole striatal ROI relative to uptake in the cerebellar reference region (Kicer [min-1]).In addition, 17 individuals with 22q11 deletion (11 females and 6 males, age (mean, SD): 26.39(7.7)) and 30 healthy controls (17 females and 13 males, age (mean, SD): 27.17(4.8)) had MRI. 1H-MRS voxels were placed on the anterior cingulate cortex and left striatum. Spectra were analyzed using LC Model version 6.3-1L. Poorly fitted metabolite peaks (Cramer–Rao minimum variance bounds >20% as reported by LC Model) were excluded from further analysis.ResultsDSC in the whole striatum was significantly increased in the individuals with 22q11 deletion compared to healthy controls (mean (Kicer [min-1] =0.0143; SD=0.001; mean Kicer [min-1] = 0.0127; SD=0.001, respectively; effect size (Cohen’s d= 1.47, p< 0.000). In addition, no difference was found between groups in Glx levels in anterior cingulate cortex (individuals with 22q11 deletion; mean=19.85; SD=3.17, healthy controls; mean= 21.04; SD=3.91) and left striatum (individuals with 22q11 deletion; mean=11.45; SD=2.88, healthy controls; mean=11.6;SD=2.74)(t(44) =-1.065; p=0.29, t(42)=-0.172;p=0.86, respectively).Psychopathology scales were not correlated with either dopaminergic or glutamatergic function in the group of 22q11 deletion.DiscussionOur findings provide evidence that dopamine synthesis capacity has a strong trait component and glutamatergic dysfunction may be most likely associated with disease status. Future studies with longitudinal design are warranted to further investigate the role of dopamine and glutamate in individuals with 22q11 deletion. Moreover, there is a clear need for studies utilizing higher field resonance strength and appropriate radiotracers to investigate glutamatergic function in this population. These will be crucial steps towards the development of new treatments, that can be applied in early stages of illness.

Comparison of three-parameter kinetic model analysis to standard Patlak\u2019s analysis in 18F-FDG PET imaging of lung cancer patients

BackgroundPatlak’s graphical analysis can provide tracer net influx constant (Ki) with limitation of assuming irreversible tracer trapping, that is, release rate constant (kb) set to zero. We compared linear Patlak’s analysis to non-linear three-compartment three-parameter kinetic model analysis (3P-KMA) providing Ki, kb, and fraction of free 18F-FDG in blood and interstitial volume (Vb).MethodsDynamic PET data of 21 lung cancer patients were retrospectively analyzed, yielding for each patient an 18F-FDG input function (IF) and a tissue time-activity curve. The former was fitted with a three-exponentially decreasing function, and the latter was fitted with an analytical formula involving the fitted IF data (11 data points, ranging 7.5–57.5 min post-injection). Bland-Altman analysis was used for Ki comparison between Patlak’s analysis and 3P-KMA. Additionally, a three-compartment five-parameter KMA (5P-KMA) was implemented for comparison with Patlak’s analysis and 3P-KMA.ResultsWe found that 3P-KMA Ki was significantly greater than Patlak’s Ki over the whole patient series, + 6.0% on average, with limits of agreement of ± 17.1% (95% confidence). Excluding 8 out of 21 patients with kb > 0 deleted this difference. A strong correlation was found between Ki ratio (=3P-KMA/Patlak) and kb (R = 0.801; P < 0.001). No significant difference in Ki was found between 3P-KMA versus 5P-KMA, and between 5P-KMA versus Patlak’s analysis, with limits of agreement of ± 23.0 and ± 31.7% (95% confidence), respectively.ConclusionsComparison between 3P-KMA and Patlak’s analysis significantly showed that the latter underestimates Ki because it arbitrarily set kb to zero: the greater the kb value, the greater the Ki underestimation. This underestimation was not revealed when comparing 5P-KMA and Patlak’s analysis. We suggest that further studies are warranted to investigate the 3P-KMA efficiency in various tissues showing greater 18F-FDG trapping reversibility than lung cancer lesions.

Diagnostic value of quantitative assessment of cardiac 18F-fluoro-2-deoxyglucose uptake in suspected cardiac sarcoidosis.

The identification of cardiac sarcoidosis is challenging as there is no gold standard consensually admitted for its diagnosis. The aim of this study was to evaluate the diagnostic value of the assessment of cardiac dynamic 18F-fluoro-2-deoxyglucose positron emission tomography (18F-FDG PET/CT) and net influx constant (Ki) in patients suspected of cardiac sarcoidosis. Data obtained from 30 biopsy-proven sarcoidosis patients suspected of cardiac sarcoidosis who underwent a 50-min list-mode cardiac dynamic 18F-FDG PET/CT after a 24h high-fat and low-carbohydrate diet were analyzed. A normalized coefficient of variation of quantitative glucose influx constant, calculated as the ratio: standard deviation of the segmental Ki (min-1)/global Ki (min-1) was determined using a validated software (Carimas® 2.4, Turku PET Centre). Cardiac sarcoidosis was diagnosed according to the Japanese Ministry of Health and Welfare criteria. Receiving operating curve analysis was performed to determine sensitivity and specificity of cardiac dynamic 18F-FDG PET/CT analysis to diagnose cardiac sarcoidosis. Six out of 30 patients (20%) were diagnosed as having cardiac sarcoidosis. Myocardial glucose metabolism was significantly heterogeneous in patients with cardiac sarcoidosis who showed significantly higher normalized coefficient of variation values compared to patients without cardiac sarcoidosis (0.513 ± 0.175 vs. 0.205 ± 0.081; p = 0.0007). Using ROC curve analysis, we found a cut-off value of 0.38 for the diagnosis of cardiac sarcoidosis with a sensitivity of 100% and a specificity of 91%. Our results suggest that quantitative analysis of cardiac dynamic 18F-FDG PET/CT could be a useful tool for the diagnosis of cardiac sarcoidosis.

In vivo PET imaging with [(18)F]FDG to explain improved glucose uptake in an apolipoprotein A-I treated mouse model of diabetes.

Type 2 diabetes is characterised by decreased HDL levels, as well as the level of apolipoprotein A-I (apoA-I), the main apolipoprotein of HDLs. Pharmacological elevation of HDL and apoA-I levels is associated with improved glycaemic control in patients with type 2 diabetes. This is partly due to improved glucose uptake in skeletal muscle. This study used kinetic modelling to investigate the impact of increasing plasma apoA-I levels on the metabolism of glucose in the db/db mouse model. Treatment of db/db mice with apoA-I for 2h significantly improved both glucose tolerance (AUC 2574 ± 70mmol/l × min vs 2927 ± 137mmol/l × min, for apoA-I and PBS, respectively; p < 0.05) and insulin sensitivity (AUC 388.8 ± 23.8mmol/l × min vs 194.1 ± 19.6mmol/l × min, for apoA-I and PBS, respectively; p < 0.001). ApoA-I treatment also increased glucose uptake by skeletal muscle in both an insulin-dependent and insulin-independent manner as evidenced by increased uptake of fludeoxyglucose ([(18)F]FDG) from plasma into gastrocnemius muscle in apoA-I treated mice, both in the absence and presence of insulin. Kinetic modelling revealed an enhanced rate of insulin-mediated glucose phosphorylation (k 3) in apoA-I treated mice (3.5 ± 1.1 × 10(-2) min(-1) vs 2.3 ± 0.7 × 10(-2) min(-1), for apoA-I and PBS, respectively; p < 0.05) and an increased influx constant (3.7 ± 0.6 × 10(-3) ml min(-1) g(-1) vs 2.0 ± 0.3 × 10(-3) ml min(-1) g(-1), for apoA-I and PBS, respectively; p < 0.05). Treatment of L6 rat skeletal muscle cells with apoA-I for 2h indicated that increased hexokinase activity mediated the increased rate of glucose phosphorylation. These findings indicate that apoA-I improves glucose disposal in db/db mice by improving insulin sensitivity and enhancing glucose phosphorylation.

Blood-brain barrier transport kinetics of the neuromedin peptides NMU, NMN, NMB and NT

The neuromedin peptides are peripherally and centrally produced, but until now, it is generally believed that they only function as locally acting compounds without any quantitative knowledge about their blood-brain barrier (BBB) passage. Here, we characterize the transport kinetics of four neuromedins (NMU, NMN, NMB and NT) across the BBB, as well as their metabolization profile, and evaluate if they can act as endocrine hormones.Using the in vivo mouse model, multiple time regression (MTR), capillary depletion (CD) and brain efflux studies were performed. Data was fitted using linear (NMU, NT and NMB) or biphasic modeling (NMU and NMN). Three of the four investigated peptides, i.e. NMU, NT and NMN, showed a significant influx into the brain with unidirectional influx rate constants of 1.31 and 0.75 μL/(g × min) for NMU and NT respectively and initial influx constants (K1) of 72.14 and 7.55 μL/(g × min) and net influx constants (K) of 1.28 and 1.36 × 10−16 μL/(g×min) for NMU and NMN respectively. The influx of NMB was negligible. Only NMN and NT showed a significant efflux out of the brain with an efflux constant (kout) of 0.042 min−1 and 0.053 min−1 respectively.Our results indicate that locally produced neuromedin peptides and/or fragments can be transported through the whole body, including passing the BBB, and taken up by different organs/tissues, supporting the idea that the neuromedins could have a much bigger role in the regulation of biological processes than currently assumed.

Positron emission tomography imaging of human colon cancer xenografts in mice with [18F]fluorothymidine after TAS-102 treatment.

TAS-102 is an orally administered anticancer agent composed of α,α,α-trifluorothymidine (FTD) and thymidine phosphorylase inhibitor (TPI). This study assessed 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) uptake after TAS-102 administration. The human colorectal carcinoma cell lines HCT116, HT29, HCT8 and SW620 were exposed to FTD for 2h, further incubated for 0, 2 and 24h, and assayed for [(3)H]FLT uptake, nucleoside transport, thymidine kinase 1 (TK1) expression and TK1 activity. Static and 2-hdynamic [(18)F]FLT positron emission tomography (PET) was performed in mice bearing HT29 or SW620 tumours orally administered with vehicle or TAS-102. FTD decreased the viability of all cell lines, whereas increased [(3)H]FLT uptake (P<0.05). Increased nucleoside transport and/or TK1 expression were observed 24h after FTD, but not in 0-2h. Static [(18)F]FLT PET in mice bearing HT29 tumours showed accumulation of [(18)F]FLT in tumours 1h (day 1) after TAS-102. Two-hour dynamic PET in mice bearing SW620 tumours showed increased influx constant and volume of distribution of phosphorylated [(18)F]FLT on days 1 and 8 (P<0.05) after TAS-102 with decreased dephosphorylation on day 1 (P<0.001). Ex vivo studies showed that SW620 tumours after TAS-102 had higher TK1 expression than those with vehicle on days 8 and 15. TAS-102 administration induces an increase in [(18)F]FLT uptake. Mechanisms may involve decreased dephosphorylation of [(18)F]FLT phosphate early after TAS-102 administration. Increased TK1 expression and/or nucleoside transporter may be related to increased [(18)F]FLT uptake at a later time. [(18)F]FLT PET has a potential to assess the pharmacodynamics of TAS-102 in cancer patients.