Host-gut microbiota interactions shape parasite infections in farmed Atlantic salmon.

Animals and their associated microbiota share long evolutionary histories. However, it is not always clear how host genotype and microbiota interact to affect phenotype. We applied a hologenomic approach to explore how host-microbiota interactions shape lifetime growth and parasite infection in farmed Atlantic salmon (Salmo salar). Multi-omics data sets were generated from the guts of 460 salmon, 82% of which were naturally infected with an intestinal cestode. A single Mycoplasma bacterial strain, MAG01, dominated the gut metagenome of large, non-parasitized fish, consistent with previous studies showing high levels of Mycoplasma in the gut microbiota of healthy salmon. While small and/or parasitized salmon also had high abundance of MAG01, we observed increased alpha diversity in these individuals, driven by increased frequency of low-abundance Vibrionaceae and other Mycoplasma species that carried known virulence genes. Colonization by one of these cestode-associated Mycoplasma strains was associated with host individual genomic variation in long non-coding RNAs. Integrating the multi-omic data sets revealed coordinated changes in the salmon gut mRNA transcriptome and metabolome that correlated with shifts in the microbiota of smaller, parasitized fish. Our results suggest that the gut microbiota of small and/or parasitized fish is in a state of dysbiosis that partly depends on the host genotype, highlighting the value of using a hologenomic approach to incorporate the microbiota into the study of host-parasite dynamics.IMPORTANCEStudying host-microbiota interactions through the perspective of the hologenome is gaining interest across all life sciences. Intestinal parasite infections are a huge burden on human and animal health; however, there are few studies investigating the role of the hologenome during parasite infections. We address this gap in the largest multi-omics fish microbiota study to date using natural cestode infection of farmed Atlantic salmon. We find a clear association between cestode infection, salmon lifetime growth, and perturbation of the salmon gut microbiota. Furthermore, we provide the first evidence that the genetic background of the host may partly determine how the gut microbiota changes during parasite-associated dysbiosis. Our study therefore highlights the value of a hologenomic approach for gaining a more in-depth understanding of parasitism.

Intestinal epigenotype of Atlantic salmon (Salmo salar) associates with tenacibaculosis and gut microbiota composition.

It remains a challenge to obtain the desired phenotypic traits in aquacultural production of Atlantic salmon, and part of the challenge might come from the effect that host-associated microorganisms have on the fish phenotype. To manipulate the microbiota towards the desired host traits, it is critical to understand the factors that shape it. The bacterial gut microbiota composition can vary greatly among fish, even when reared in the same closed system. While such microbiota differences can be linked to diseases, the molecular effect of disease on host-microbiota interactions and the potential involvement of epigenetic factors remain largely unknown. The aim of this study was to investigate the DNA methylation differences associated with a tenacibaculosis outbreak and microbiota displacement in the gut of Atlantic salmon. Using Whole Genome Bisulfite Sequencing (WGBS) of distal gut tissue from 20 salmon, we compared the genome-wide DNA methylation levels between uninfected individuals and sick fish suffering from tenacibaculosis and microbiota displacement. We discovered >19,000 differentially methylated cytosine sites, often located in differentially methylated regions, and aggregated around genes. The 68 genes connected to the most significant regions had functions related to the ulcerous disease such as epor and slc48a1a but also included prkcda and LOC106590732 whose orthologs are linked to microbiota changes in other species. Although the expression level was not analysed, our epigenetic analysis suggests specific genes potentially involved in host-microbiota interactions and more broadly it highlights the value of considering epigenetic factors in efforts to manipulate the microbiota of farmed fish.

Kinetic Modelling of [68Ga]Ga-DOTA-Siglec-9 in Porcine Osteomyelitis and Soft Tissue Infections.

BACKGROUND: [68Ga]Ga-DOTA-Siglec-9 is a positron emission tomography (PET) radioligand for vascular adhesion protein 1 (VAP-1), a protein involved in leukocyte trafficking. The tracer facilitates the imaging of inflammation and infection. Here, we studied the pharmacokinetic modelling of [68Ga]Ga-DOTA-Siglec-9 in osteomyelitis and soft tissue infections in pigs. METHODS: Eight pigs with osteomyelitis and soft tissue infections in the right hind limb were dynamically PET scanned for 60 min along with arterial blood sampling. The fraction of radioactivity in the blood accounted for by the parent tracer was evaluated with radio-high-performance liquid chromatography. One- and two-tissue compartment models were used for pharmacokinetic evaluation. Post-mortem soft tissue samples from one pig were analysed with anti-VAP-1 immunofluorescence. In each analysis, the animal's non-infected left hind limb was used as a control. RESULTS: Tracer uptake was elevated in soft tissue infections but remained low in osteomyelitis. The kinetics of [68Ga]Ga-DOTA-Siglec-9 followed a reversible 2-tissue compartment model. The tracer metabolized quickly; however, taking this into account, produced more ambiguous results. Infected soft tissue samples showed endothelial cell surface expression of the Siglec-9 receptor VAP-1. CONCLUSION: The kinetics of [68Ga]Ga-DOTA-Siglec-9 uptake in porcine soft tissue infections are best described by the 2-tissue compartment model.

Kinetic Modelling of Infection Tracers [18F]FDG, [68Ga]Ga-Citrate, [11C]Methionine, and [11C]Donepezil in a Porcine Osteomyelitis Model.

Introduction: Positron emission tomography (PET) is increasingly applied for infection imaging using [18F]FDG as tracer, but uptake is unspecific. The present study compares the kinetics of [18F]FDG and three other PET tracers with relevance for infection imaging. Methods: A juvenile porcine osteomyelitis model was used. Eleven pigs underwent PET/CT with 60-minute dynamic PET imaging of [18F]FDG, [68Ga]Ga-citrate, [11C]methionine, and/or [11C]donepezil, along with blood sampling. For infectious lesions, kinetic modelling with one- and two-tissue-compartment models was conducted for each tracer. Results: Irreversible uptake was found for [18F]FDG and [68Ga]Ga-citrate; reversible uptake was found for [11C]methionine (two-tissue model) and [11C]donepezil (one-tissue model). The uptake rate for [68Ga]Ga-citrate was slow and diffusion-limited. For the other tracers, the uptake rate was primarily determined by perfusion (flow-limited uptake). Net uptake rate for [18F]FDG and distribution volume for [11C]methionine were significantly higher for infectious lesions than for correspondingly noninfected tissue. For [11C]donepezil in pigs, labelled metabolite products appeared to be important for the analysis. Conclusions: The kinetics of the four studied tracers in infection was characterized. For clinical applications, [18F]FDG remains the first-choice PET tracer. [11C]methionine may have a potential for detecting soft tissue infections. [68Ga]Ga-citrate and [11C]donepezil were not found useful for imaging of osteomyelitis.

A multi species evaluation of the radiation dosimetry of [11C]erlotinib, the radiolabeled analog of a clinically utilized tyrosine kinase inhibitor.

INTRODUCTION: Erlotinib is a tyrosine kinase inhibitor prescribed for non-small cell lung cancer (NSCLC) patients bearing epidermal growth factor receptor mutations in the kinase domain. The objectives of this study were to (1) establish a human dosimetry profile of [11C]erlotinib and (2) assess the consistency of calculated equivalent dose across species using the same dosimetry model. METHODS: Subjects examined in this multi-species study included: a stage IIIa NSCLC patient, 3 rhesus macaque monkeys, a landrace pig, and 4 athymic nude-Fox1nu mice. [11C]erlotinib PET data of the whole body were acquired dynamically for up to 120min. Regions of interest (ROIs) were manually drawn to extract PET time activity curves (TACs) from identifiable organs. TACs were used to calculate time-integrated activity coefficients (residence times) in each ROI, which were then used to calculate the equivalent dose in OLINDA. Subject data were used to predict the equivalent dose to the organs of a 73.7kg human male. RESULTS: In three of four species, the liver was identified as the organ receiving the highest equivalent dose (critical organ). The mean equivalent doses per unit of injected activity to the liver based on human, monkey, and mouse data were 29.4µSv/MBq, 17.4±6.0µSv/MBq, and 5.27±0.25µSv/MBq, respectively. The critical organ based on the pig data was the gallbladder wall (20.4µSv/MBq) but the liver received a nearly identical equivalent dose (19.5µSv/MBq). CONCLUSIONS: (1) When designing PET studies using [11C]erlotinib, the liver should be considered the critical organ. (2) In organs receiving the greatest equivalent dose, mouse data underestimated the dose in comparison to larger species. However, the effective dose of [11C]erlotinib to the whole body of a 73.7kg man was predicted with good consistency based on mice (3.14±0.05µSv/MBq) or the larger species (3.46±0.25µSv/MBq).

Blood perfusion in osteomyelitis studied with [15O]water PET in a juvenile porcine model.

BACKGROUND: Osteomyelitis is a serious disease which can be difficult to treat despite properly instituted antibiotic therapy. This appears to be related at least partly to degraded vascularisation in the osteomyelitic (OM) lesions. Studies of perfusion in OM bones are, however, few and not quantitative. Quantitative assessment of perfusion could aid in the selection of therapy. A non-invasive, quantitative way to study perfusion is dynamic [15O]water positron emission tomography (PET). We aim to demonstrate that the method can be used for measuring perfusion in OM lesions and hypothesize that perfusion will be less elevated in OM lesions than in soft tissue (ST) infection. The study comprised 11 juvenile pigs with haematogenous osteomyelitis induced by injection of Staphylococcus aureus into the right femoral artery 1 week before scanning (in one pig, 2 weeks). The pigs were dynamically PET scanned with [15O]water to quantify blood perfusion. OM lesions (N = 17) in long bones were studied, using the left limb as reference. ST lesions (N = 8) were studied similarly. RESULTS: Perfusion was quantitatively determined. Perfusion was elevated by a factor 1.5 in OM lesions and by a factor 6 in ST lesions. CONCLUSIONS: Blood perfusion was successfully determined in pathological subacute OM lesions; average perfusion was increased compared to that in a healthy bone, but as hypothesized, the increase was less than in ST lesions, indicating that the infected bone has less perfusion reserve than the infected soft tissue.

In Alzheimer's Disease, 6-Month Treatment with GLP-1 Analog Prevents Decline of Brain Glucose Metabolism: Randomized, Placebo-Controlled, Double-Blind Clinical Trial.

In animal models, the incretin hormone GLP-1 affects Alzheimer's disease (AD). We hypothesized that treatment with GLP-1 or an analog of GLP-1 would prevent accumulation of Aß and raise, or prevent decline of, glucose metabolism (CMRglc) in AD. In this 26-week trial, we randomized 38 patients with AD to treatment with the GLP-1 analog liraglutide (n = 18), or placebo (n = 20). We measured Aß load in brain with tracer [(11)C]PIB (PIB), CMRglc with [(18)F]FDG (FDG), and cognition with the WMS-IV scale (ClinicalTrials.gov NCT01469351). The PIB binding increased significantly in temporal lobe in placebo and treatment patients (both P = 0.04), and in occipital lobe in treatment patients (P = 0.04). Regional and global increases of PIB retention did not differ between the groups (P ≥ 0.38). In placebo treated patients CMRglc declined in all regions, significantly so by the following means in precuneus (P = 0.009, 3.2 µmol/hg/min, 95% CI: 5.45; 0.92), and in parietal (P = 0.04, 2.1 µmol/hg/min, 95% CI: 4.21; 0.081), temporal (P = 0.046, 1.54 µmol/hg/min, 95% CI: 3.05; 0.030), and occipital (P = 0.009, 2.10 µmol/hg/min, 95% CI: 3.61; 0.59) lobes, and in cerebellum (P = 0.04, 1.54 µmol/hg/min, 95% CI: 3.01; 0.064). In contrast, the GLP-1 analog treatment caused a numerical but insignificant increase of CMRglc after 6 months. Cognitive scores did not change. We conclude that the GLP-1 analog treatment prevented the decline of CMRglc that signifies cognitive impairment, synaptic dysfunction, and disease evolution. We draw no firm conclusions from the Aß load or cognition measures, for which the study was underpowered.

Impact of contamination with long-lived radionuclides on PET kinetics modelling in multitracer studies.

INTRODUCTION: An important issue in multitracer studies is the separation of signals from the different radiotracers. This is especially the case when an early tracer has a long physical half-life and kinetic modelling has to be performed, because the early tracer can confer a long-lived contaminating background not only to images but also to a measured input function derived from blood samples. In this study, we examined data from a sequential multitracer infection study involving In (t1/2=2.8 days), investigating the influence on gamma counting of blood samples and on the kinetic modelling of subsequent PET tracers. Blood sample counts were corrected by recounting the samples a few days later. A more optimal choice of energy window was also explored. The effect of correction versus noncorrection was investigated using a two-tissue kinetic model with irreversible uptake (K1, k2, k3). RESULTS: K1 was least affected and k3 was most affected by the contamination, corresponding to the effect being relatively larger on the late part of the blood input function. A narrower energy window reduced the problem, but this will not be possible for all types of contaminating background. CONCLUSION: Gamma counting of blood samples can lead to a contaminating background not observed in PET imaging and this background can affect kinetic modelling. If the contaminating tracer has a much longer half-life than the foreground tracer, then the problem can be solved by late recounting of the samples.

In vivo imaging of human acetylcholinesterase density in peripheral organs using 11C-donepezil: dosimetry, biodistribution, and kinetic analyses.

UNLABELLED: Brain cholinergic function has been previously studied with PET but little effort has been devoted to imaging peripheral organs. Many disorders, including diabetes and Parkinson disease, are associated with autonomic dysfunction including parasympathetic denervation. Nonneuronal cholinergic signaling is also involved in immune responses to infections and in cancer pathogenesis. 5-(11)C-methoxy-donepezil, a noncompetitive acetylcholinesterase ligand, was previously validated for imaging cerebral levels of acetylcholinesterase. In the present study, we explored the utility of (11)C-donepezil for imaging acetylcholinesterase densities in peripheral organs, including the salivary glands, heart, stomach, intestine, pancreas, liver, and spleen. METHODS: With autoradiography, we determined binding affinities and levels of nonspecific (11)C-donepezil binding to porcine tissues. Radiation dosimetry was estimated by whole-body PET of a single human volunteer. Biodistribution and kinetic analyses of (11)C-donepezil time-activity curves were assessed with dynamic PET scans of 6 healthy human volunteers. A single pig with bacterial abscesses was PET-scanned to explore (11)C-donepezil uptake in infections. RESULTS: Autoradiography showed high (11)C-donepezil binding (dissociation constant, 6-39 nM) in pig peripheral organs with low nonspecific signal. Radiation dosimetry was favorable (effective dose, 5.2 µSv/MBq). Peripheral metabolization of (11)C-donepezil was low (>90% unchanged ligand at 60 min). Slow washout kinetics were seen in the salivary glands, heart, intestines, pancreas, and prostate. A linear correlation was seen between (11)C-donepezil volumes of distribution and standardized uptake values, suggesting that arterial blood sampling may not be necessary for modeling uptake kinetics in future (11)C-donepezil PET studies. High standardized uptake values and slow washout kinetics were seen in bacterial abscesses. CONCLUSION: (11)C-donepezil PET is suitable for imaging acetylcholinesterase densities in peripheral organs. Its uptake may potentially be quantitated with static whole-body PET scans not requiring arterial blood sampling. We also demonstrated high (11)C-donepezil binding in bacterial abscesses. We propose that (11)C-donepezil PET imaging may be able to quantify the parasympathetic innervation of organs but also detect nonneuronal cholinergic activity in infections.

Hepatic blood perfusion estimated by dynamic contrast-enhanced computed tomography in pigs: limitations of the slope method.

OBJECTIVE: The aim of this study was to determine whether dynamic contrast-enhanced computed tomography (DCE-CT) and the slope method can provide absolute measures of hepatic blood perfusion from the hepatic artery (HA) and portal vein (PV) at experimentally varied blood flow rates. MATERIALS AND METHODS: Ten anesthetized 40-kg pigs underwent DCE-CT of the liver during periods of normocapnia (normal flow), hypocapnia (decreased flow), and hypercapnia (increased flow), which were induced by adjusting the ventilation. Reference blood flows in the HA and PV were measured continuously by surgically placed ultrasound transit-time flowmeters. For each capnic condition, the DCE-CT-estimated absolute hepatic blood perfusion from the HA and PV were calculated using the slope method and compared with flowmeter-based absolute measurements of hepatic perfusions and relative errors were analyzed. RESULTS: The relative errors (mean ± SEM) of the DCE-CT based perfusion estimates were -21% ± 23% for HA and 81% ± 31% for PV during normocapnia, 9% ± 23% for HA and 92% ± 42% for PV during hypocapnia, and 64% ± 28% for HA and -2% ± 20% for PV during hypercapnia. The mean relative errors for HA were not significantly different from 0 during hypocapnia and normocapnia, and the DCE-CT slope method could detect relative changes in HA perfusion between scans. Infusion of contrast agent led to significantly increased hepatic blood perfusion, which biased the PV perfusion estimates. CONCLUSIONS: Using the DCE-CT slope method, HA perfusion estimates were accurate at low and normal flow rates, whereas PV perfusion estimates were inaccurate and imprecise. At high flow rate, both HA perfusion estimates were significantly biased.

Glucose metabolism in small subcortical structures in Parkinson's disease.

OBJECTIVES: Evidence from experimental animal models of Parkinson's disease (PD) suggests a characteristic pattern of metabolic perturbation in discrete, very small basal ganglia structures. These structures are generally too small to allow valid investigation by conventional positron emission tomography (PET) cameras. However, the high-resolution research tomograph (HRRT) PET system has a resolution of 2 mm, sufficient for the investigation of important structures such as the pallidum and thalamic subnuclei. MATERIALS AND METHODS: Using the HRRT, we performed [(18)F]-fluorodeoxyglucose (FDG) scans on 21 patients with PD and 11 age-matched controls. We employed three types of normalization: white matter, global mean, and data-driven normalization. We performed volume-of-interest analyses of small subcortical gray matter structures. Voxel-based comparisons were performed to investigate the extent of cortical hypometabolism. RESULTS: The most significant level of relative subcortical hypermetabolism was detected in the external pallidum (GPe), irrespective of normalization strategy. Hypermetabolism was suggested also in the internal pallidum, thalamic subnuclei, and the putamen. Widespread cortical hypometabolism was seen in a pattern very similar to previously reported patterns in patients with PD. CONCLUSION: The presence and extent of subcortical hypermetabolism in PD is dependent on type of normalization. However, the present findings suggest that PD, in addition to widespread cortical hypometabolism, is probably characterized by true hypermetabolism in the GPe. This finding was predicted by the animal 2-deoxyglucose autoradiography literature, in which high-magnitude hypermetabolism was also most robustly detected in the GPe.

Nucleophilic radiosynthesis of 2-[18F]fluoro-2-deoxy-D-galactose from Talose triflate and biodistribution in a porcine model.

INTRODUCTION: The galactose analogue 2-[(18)F]fluoro-2-deoxy-D-galactose (FDGal) is a promising positron emission tomography (PET) tracer for studies of regional differences in liver metabolic function and for clinical evaluation of patients with liver cirrhosis and patients undergoing treatment of liver diseases. However, there is an unmet need for routine production of FDGal from readily available starting material. In this study, we present the preparation of FDGal with high radiochemical purity and in amounts sufficient for clinical investigations from commercially available Talose triflate (1,3,4,6-tetra-O-acetyl-2-O-trifluoromethanesulfonyl-ß-D-talopyranose). In addition, the biodistribution of FDGal in the pig is presented. METHODS: FDGal was prepared by nucleophilic fluorination of Talose triflate followed by basic hydrolysis. The entire synthesis was performed using the GE TRACERlab MX 2-[(18)F]fluoro-2-deoxy-D-glucose (FDG) synthesizer and existing methods for quality control of FDG were applied. Biodistribution of FDGal was studied by successive whole-body PET recordings of two anaesthetized 37-kg pigs. RESULTS: Up to 3.7 GBq sterile, pyrogen-free and no-carrier-added FDGal was produced with a radiochemical yield of 3.8±1.2% and a radiochemical purity of 98±1% (42 productions; yield is decay corrected). The adopted quality control methods for FDG were directly applicable for FDGal. Biodistribution studies in the pig revealed the liver and the urinary bladder as critical organs in terms of radiation dose. CONCLUSION: Commercially available Talose triflate is a suitable starting material for routine productions of FDGal. The presented radiosynthesis and quality control methods allow for the production of pure, no-carrier-added FDGal in sufficient amounts for clinical PET-investigations of the liver.

Biotinylated lipid bilayer disks as model membranes for biosensor analyses.

The aim of this study was to investigate the potential of polyethylene glycol (PEG)-stabilized lipid bilayer disks as model membranes for surface plasmon resonance (SPR)-based biosensor analyses. Nanosized bilayer disks that included 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[biotinyl(polyethylene glycol)(2000)] (DSPE-PEG(2000)-biotin) were prepared and structurally characterized by cryo-transmission electron microscopy (cryo-TEM) imaging. The biotinylated disks were immobilized via streptavidin to three different types of sensor chips (CM3, CM4, and CM5) varying in their degree of carboxymethylation and thickness of the dextran matrix. The bilayer disks were found to interact with and bind stably to the streptavidin-coated sensor surfaces. As a first step toward the use of these bilayer disks as model membranes in SPR-based studies of membrane proteins, initial investigations were carried out with cyclooxygenases 1 and 2 (COX 1 and COX 2). Bilayer disks were preincubated with the respective protein and thereafter allowed to interact with the sensor surface. The signal resulting from the interaction was, in both cases, significantly enhanced as compared with the signal obtained when disks alone were injected over the surface. The results of the study suggest that bilayer disks constitute a new and promising type of model membranes for SPR-based biosensor studies.

[11C]Mirtazapine binding in depressed antidepressant nonresponders studied by PET neuroimaging.

RATIONALE: Lack of benefit from antidepressant drug therapy is a major source of human suffering, affecting at least 25% of people with major depressive disorder. We want to know whether nonresponse to antidepressants can be linked to aberrant neuroreceptor binding. OBJECTIVE: This study aims to assess the antidepressant binding in brain regions of depressed nonresponders compared with healthy controls. MATERIALS AND METHODS: Healthy volunteers and depressed subjects who had failed to benefit from at least 2 antidepressant treatments were recruited by newspaper advertisements. All subjects had received no antidepressant medication for at least 2 months before positron emission tomography (PET) that was carried out with [11C]mirtazapine. Kinetic parameters of [11C]mirtazapine were determined from PET data in selected brain regions by the simplified reference tissue model. RESULTS: Binding potentials of [11C]mirtazapine in cerebral cortical regions were lower in depressed nonresponders than in healthy controls. Removal rates of [11C]mirtazapine were higher in diencephalic regions of depressed nonresponders than in healthy controls. CONCLUSIONS: PET neuroimaging with [11C]mirtazapine showed aberrant neuroreceptor binding in brain regions of depressed subjects who had failed to benefit from treatment with antidepressant drugs.

Mannan-binding lectin deficiency modulates the humoral immune response dependent on the genetic environment.

Mannan-binding lectin (MBL) is a plasma protein implicated in innate immune defence against a broad range of microorganisms, including viruses. It is also thought that MBL plays a role in the recruitment of the specific clonal immune response. This was studied by injecting soluble hepatitis B surface antigen (HBsAg) intravenously into mice deficient in both MBL-A and MBL-C (MBL DKO mice). The MBL DKO animals on mixed genetic background (SV129EvSv x C57BL/6) produced higher antibody titres than the wild-type littermates. After primary challenge with the antigen the immunoglobulin M anti-HBsAg antibody titres were threefold higher in the MBL DKO mice than in the wild-type mice. Following the boost, the immunoglobulin G anti-HBsAg antibody titres were 10-fold higher in the MBL DKO mice, suggesting that MBL plays a role in a negative feedback regulation of adaptive immunity. However, the modulating effect of MBL was dependent on the genetic environment. The MBL DKO mice backcrossed on a C57BL/6 background showed the opposite response with the MBL DKO mice now producing fewer antibodies than the wild-type animals, whereas MBL deficiency in mice with the SV129EvSv background did not show any effect in antibody production. These findings indicate that the modifying effect of MBL on the humoral immune response is influenced by the genetic environment.

Neuroimaging of mirtazapine enantiomers in humans.

INTRODUCTION: Mirtazapine is a racemic antidepressant with a multireceptor profile. Previous studies have shown that the enantiomers of mirtazapine have different pharmacologic effects in the brain of laboratory animals. MATERIALS AND METHODS: In the present study, we used positron emission tomography (PET) and autoradiography to study effects of (R)- and (S)-[(11)C]mirtazapine in the human brain. Detailed brain imaging by PET using three methods of kinetic data analysis showed no reliable differences between regional binding potentials of (R)- and (S)-[(11)C]mirtazapine in healthy subjects. RESULTS: Autoradiographic studies carried out in whole hemispheres of human brain tissue showed, however, that (R)- and (S)-mirtazapine differ markedly as inhibitors of [(3)H]clonidine binding at alpha(2)-adrenoceptors. CONCLUSION: The multireceptor binding profiles of mirtazapine enantiomers, along with individual differences between subjects, may preclude PET neuroimaging from demonstrating reliable differences between the regional distribution and binding of (R)- and (S)-[(11)C]mirtazapine in the living human brain.

The potential application of silver and positron emission tomography for in vivo dosimetry during radiotherapy.

The possible use of silver as a material for in vivo dosimetry in radiotherapy was investigated. The investigation was carried out using a positron emission tomography (PET) scanner, two clinical accelerators and a phantom with silver implants. The phantom was irradiated several times to doses between 6 and 45 Gy. The resulting activity of positron-emitting isotopes produced in the silver by photonuclear processes was measured. It was found that the two therapeutic beams with energies of 15 MV and 18 MV would produce approximately 8344 and 7013 atoms of the radioactive isotope (106)Ag per Gy of absorbed dose per gram of silver. This demonstrates that it is possible to derive absorbed doses from the radioactivity induced in silver by radiation when measured with the PET scanner. Even though the physical basis for this method is found to be sound, its application, for instance to perform quality assurance of stereotactic radiotherapy, needs further study.

Receptor occupancy of mirtazapine determined by PET in healthy volunteers.

RATIONALE: Molecular tools are needed for assessing anti-depressant actions by positron emission tomography (PET) in the living human brain. OBJECTIVES: This study determined whether [(11)C]mirtazapine is an appropriate molecular tool for use with PET to estimate the magnitude of neuroreceptor occupancy produced by daily intake of mirtazapine. METHODS: This study used a randomised, double-blind, placebo-controlled, parallel-group, within-subject design. Eighteen healthy volunteers were PET-scanned twice with [(11)C]mirtazapine; once under baseline condition and again after receiving either placebo or mirtazapine (7.5 or 15 mg) for 5 days. We determined kinetic parameters of [(11)C]mirtazapine in brain regions by the simplified reference region method and used binding potential values to calculate receptor occupancy produced by mirtazapine. RESULTS: Serum concentrations of mirtazapine ranged from 33 to 56 nmol/l after five daily doses of 7.5 mg mirtazapine and were between 41 and 74 nmol/l after 15 mg mirtazapine. Placebo treatment failed to alter the binding potential of [(11)C]mirtazapine from baseline values, whereas daily intake of mirtazapine markedly decreased the binding potential in cortex, amygdala and hippocampus. Receptor occupancy ranged from 74 to 96% in high-binding regions of the brain after five daily doses of 7.5 mg or 15 mg mirtazapine, whereas 17-48% occupancy occurred in low-binding regions. CONCLUSIONS: [(11)C]Mirtazapine together with PET can determine the degree of receptor occupancy produced by daily doses of mirtazapine in regions of the living human brain.

T cell homing to tumors detected by 3D-coordinated positron emission tomography and magnetic resonance imaging.

A general hindrance to progress in adoptive cellular therapy is the lack of detailed knowledge of the fate of transferred cells in the body of the recipient. In this study, we present a novel technique for tracking of 124I-labeled cells in situ, which combines the high spatial resolution of magnetic resonance imaging with the high sensitivity and spatial accuracy of positron emission tomography. We have used this technique, together with determination of tissue radioactivity, flow cytometry, and microscopy, to characterize and quantitate the specific accumulation of transferred CD8+ T cells in tumor tissue in a mouse model. Transgenic CD8+ T cells, specific for the ovalbumin peptide SIINFEKL, were adoptively transferred to recipients carrying a subcutaneous tumor of the ovalbumin-expressing malignant melanoma cell line B16-OVA. The number of SIINFEKL-specific CD8+ cells in the tumor tissue was determined by flow cytometry each day for 8 consecutive days after adoptive transfer. From low levels 1 day after injection, their number gradually increased until day 5 when an average of 3.3x10(6) SIINFEKL-specific cells per gram tumor tissue was found. By applying the combined positron emission tomography/magnetic resonance imaging technique we were able to determine the position of the transferred, 124I-labeled SIINFEKL-specific T cells in 3 dimensions in recipient mice, and could demonstrate a highly significant accumulation of the 124I label in and around the subcutaneous B16-OVA tumors compared with normal tissue. Accumulation of 124I was significantly higher in B16-OVA than in B16 tumors not expressing the OVA antigen.

Evaluation of iterative reconstruction (OSEM) versus filtered back-projection for the assessment of myocardial glucose uptake and myocardial perfusion using dynamic PET.

PURPOSE: Iterative reconstruction methods based on ordered-subset expectation maximisation (OSEM) has replaced filtered backprojection (FBP) in many clinical settings owing to the superior image quality. Whether OSEM is as accurate as FBP in quantitative positron emission tomography (PET) is uncertain. We compared the accuracy of OSEM and FBP for regional myocardial (18)F-FDG uptake and (13)NH(3) perfusion measurements in cardiac PET. METHODS: Ten healthy volunteers were studied. Five underwent dynamic (18)F-FDG PET during hyperinsulinaemic-euglycaemic clamp, and five underwent (13)NH(3) perfusion measurement during rest and adenosine-induced hyperaemia. Images were reconstructed using FBP and OSEM +/- an 8-mm Gaussian post-reconstruction filter. RESULTS: Filtered and unfiltered images showed agreement between the reconstruction methods within +/-2SD in Bland-Altman plots of K (i) values. The use of a Gaussian filter resulted in a systematic underestimation of K (i) in the filtered images of 11%. The mean deviation between the reconstruction methods for both unfiltered and filtered images was 1.3%. Agreement within +/-2SD between the methods was demonstrated for perfusion rate constants up to 2.5 min(-1), corresponding to a perfusion of 3.4 ml g(-1) min(-1). The mean deviation between the two methods for unfiltered data was 2.7%, and for filtered data, 5.3%. CONCLUSION: The (18)F-FDG uptake rate constants showed excellent agreement between the two reconstruction methods. In the perfusion range up to 3.4 ml g(-1) min(-1), agreement between (13)NH(3) perfusion obtained with OSEM and FBP was acceptable. The use of OSEM for measurement of perfusion values higher than 3.4 ml g(-1) min(-1) requires further evaluation.