Influence of polyethylene terephthalate (PET) microplastic on selected active substances in the intramural neurons of the porcine duodenum

BACKGROUND

Currently, society and industry generate huge amounts of plastics worldwide. The ubiquity of microplastics is obvious, but its impact on the animal and human organism remains not fully understood. The digestive tract is one of the first barriers between pathogens and xenobiotics and a living organism. Its proper functioning is extremely important in order to maintain homeostasis. The aim of this study was to determine the effect of microplastic on enteric nervous system and histological structure of swine duodenum. The experiment was carried out on 15 sexually immature gilts, approximately 8 weeks old. The animals were randomly divided into 3 study groups (n = 5/group). The control group received empty gelatin capsules once a day for 28 days, the first research group received daily gelatin capsules with polyethylene terephthalate (PET) particles as a mixture of particles of various sizes (maximum particle size 300 µm) at a dose of 0.1 g/animal/day. The second study group received a dose ten times higher-1 g/animal/day.

RESULTS

A dose of 1 g/day/animal causes more changes in the enteric nervous system and in the histological structure of duodenum. Statistically significant differences in the expression of cocaine and amphetamine regulated transcript, galanin, neuronal nitric oxide synthase, substance P, vesicular acetylcholine transporter and vasoactive intestinal peptide between control and high dose group was noted. The histopathological changes were more frequently observed in the pigs receiving higher dose of PET.

CONCLUSION

Based on this study it may be assumed, that oral intake of microplastic might have potential negative influence on digestive tract, but it is dose-dependent.

Cholinergic Boutons are Distributed Along the Dendrites and Somata of VIP Neurons in the Inferior Colliculus

Cholinergic signaling shapes sound processing and plasticity in the inferior colliculus (IC), the midbrain hub of the central auditory system, but how cholinergic terminals contact and influence individual neuron types in the IC remains largely unknown. Using pharmacology and electrophysiology, we recently found that acetylcholine strongly excites VIP neurons, a class of glutamatergic principal neurons in the IC, by activating α3β4* nicotinic acetylcholine receptors (nAChRs). Here, we confirm and extend these results using tissue from mice of both sexes. First, we show that mRNA encoding α3 and β4 nAChR subunits is expressed in many neurons throughout the IC, including most VIP neurons, suggesting that these subunits, which are rare in the brain, are important mediators of cholinergic signaling in the IC. Next, by combining fluorescent labeling of VIP neurons and immunofluorescence against the vesicular acetylcholine transporter (VAChT), we show that individual VIP neurons in the central nucleus of the IC (ICc) are contacted by a large number of cholinergic boutons. Cholinergic boutons were distributed adjacent to the somata and along the full length of the dendritic arbors of VIP neurons, positioning cholinergic signaling to affect synaptic computations arising throughout the somatodendritic compartments of VIP neurons. In addition, cholinergic boutons were occasionally observed in close apposition to dendritic spines on VIP neurons, raising the possibility that cholinergic signaling also modulates presynaptic release onto VIP neurons. Together, these results strengthen the evidence that cholinergic signaling exerts widespread influence on auditory computations performed by VIP neurons and other neurons in the IC.

Choline acetyltransferase and vesicular acetylcholine transporter are required for metamorphosis, reproduction, and insecticide susceptibility in Tribolium castaneum

Choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT) are essential enzymes for synthesizing and transporting acetylcholine (ACh). But their functions in metamorphosis, reproduction, and the insecticide susceptibility were poorly understood in the insects. To address these issues, we identified the orthologues of chat and vacht in Tribolium castaneum. Spatiotemporal expression profiling showed Chat has the highest expression at the early adult stage, while vacht shows peak expression at the early larval stage. Both of them were highly expressed at the head of late adult. RNA interference (RNAi) of chat and vacht both led to a decrease in ACh content at the late larval stage. It is observed that chat knockdown severely affected larval development and pupal eclosion, but vacht RNAi only disrupted pupal eclosion. Further, parental RNAi of chat or vacht led to 35 % or 30 % reduction in fecundity, respectively, and knockdown of them completely inhibited egg hatchability. Further analysis has confirmed that both the reduction in fecundity and hatchability caused through the maternal specificity in T. castaneum. Moreover, the transcript levels of chat and vacht were elevated after carbofuran or dichlorvos treatment. Reduction of chat or vacht decreased the resistance to carbofuran and dichlorvos. This study provides the evidence for chat and vacht not only involved in development and reproduction of insects but also could as the potential targets of insecticides.

In vivo vesicular acetylcholine transporter density in human peripheral organs: an [18F]FEOBV PET/CT study

Background

The autonomic nervous system is frequently affected in some neurodegenerative diseases, including Parkinson’s disease and Dementia with Lewy bodies. In vivo imaging methods to visualize and quantify the peripheral cholinergic nervous system are lacking. By using [¹⁸F]FEOBV PET, we here describe the peripheral distribution of the specific cholinergic marker, vesicular acetylcholine transporters (VAChT), in human subjects. We included 15 healthy subjects aged 53–86 years for 70 min dynamic PET protocol of peripheral organs. We performed kinetic modelling of the adrenal gland, pancreas, myocardium, renal cortex, spleen, colon, and muscle using an image-derived input function from the aorta. A metabolite correction model was generated from venous blood samples. Three non-linear compartment models were tested. Additional time-activity curves from 6 to 70 min post injection were generated for prostate, thyroid, submandibular-, parotid-, and lacrimal glands.

Results

A one-tissue compartment model generated the most robust fits to the data. Total volume-of-distribution rank order was: adrenal gland > pancreas > myocardium > spleen > renal cortex > muscle > colon. We found significant linear correlations between total volumes-of-distribution and standard uptake values in most organs.

Conclusion

High [¹⁸F]FEOBV PET signal was found in structures with known cholinergic activity. We conclude that [¹⁸F]FEOBV PET is a valid tool for estimating VAChT density in human peripheral organs. Simple static images may replace kinetic modeling in some organs and significantly shorten scan duration.

Clinical Trial Registration Trial registration: NCT, NCT03554551. Registered 31 May 2018. https://clinicaltrials.gov/ct2/show/NCT03554551?term=NCT03554551&draw=2&rank=1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-022-00889-9.

In vitro characterization of [3H]VAT in cells, animal and human brain tissues for vesicular acetylcholine transporter

Vesicular acetylcholine transporter plays a crucial role in the cholinergic system, and its alterations is implicated in several neurodegenerative disorders. We recently developed a PET imaging tracer [¹⁸F]VAT to target VAChT in vivo with high affinity and selectivity. Here we report in vitro characterization of [³H]VAT, a tritiated counterpart of [¹⁸F]VAT. Using human VAChT-rich cell membrane extracts, a saturated binding curve was obtained for [³H]VAT with K_d = 6.5 nM and B_max = 22.89 pmol/mg protein. In the [³H]VAT competition-binding assay with a panel of CNS ligands, binding inhibition of [³H]VAT was observed using VAChT ligands, the K_i values ranged from 5.41 to 33.3 nM. No inhibition was detected using a panel of other CNS ligands. In vitro [³H]VAT autoradiography of rat brain sections showed strong signals in the striatum, moderate to high signals in vermis, thalamus, cortex, and hippocampus, and weak signals in cerebellum. Strong [³H]VAT ARG signals were also observed from striatal sections of normal nonhuman primates and human brains. Competitive ARG study with human striatal sections demonstrated strong ARG signals of [³H]VAT in caudate and putamen were blocked significantly by either VAChT ligand TZ659 or (-)-vesamicol, but not by the σ₁ receptor ligand Yun-122. ARG study also indicated that signal in the striatal sections from PSP human brains was lower than normal human brains. These data provide solid evidence supporting [¹⁸F]VAT as a suitable PET radiotracer for quantitative assessment of VAChT levels in vivo.

Homeostatic plasticity induced by increased acetylcholine release at the mouse neuromuscular junction

At the neuromuscular junction (NMJ), changes to the size of the postsynaptic potential induce homeostatic compensation. At the Drosophila NMJ, increased glutamate release causes a compensatory decrease in quantal content, but it is unknown if this mechanism operates at the cholinergic mammalian NMJ. We addressed this question by recording endplate potentials (EPP) and muscle contraction in 3-month and 24-month ChAT-ChR2-EYFP mice that overexpress vesicular acetylcholine transporter and release more acetylcholine per vesicle. At 3 months, the quantal content of EPPs from ChAT-ChR2-EYFP mice were not different from WT controls, however tetanic depression was greater, and quantal size during high-frequency stimulation and the size of the readily releasable pool (RRP) were decreased. At 24 months of age, quantal content was reduced in ChAT-ChR2-EYFP mice, which normalized synaptic depression despite smaller RRP. The effect of pancuronium on indirect evoked muscle twitch was not different between groups. These results indicate that an increase in the amount of acetylcholine per vesicle induces two distinct age-dependent homeostatic mechanisms compensating excessive acetylcholine release.

Effects of VAChT reduction and α7nAChR stimulation by PNU-282987 in lung inflammation in a model of chronic allergic airway inflammation

The cholinergic anti-inflammatory pathway has been shown to regulate lung inflammation and cytokine release in acute models of inflammation, mainly via α7 nicotinic receptor (α7nAChR). We aimed to evaluate the role of endogenous acetylcholine in chronic allergic airway inflammation in mice and the effects of therapeutic nAChR stimulation in this model. We first evaluated lung inflammation and remodeling on knock-down mice with 65% of vesicular acetylcholine transport (VAChT) gene reduction (KDVAChT) and wild-type(WT) controls that were subcutaneously sensitized and then inhaled with ovalbumin(OVA). We then evaluated the effects of PNU-282987(0.5-to-2mg/kg),(α7nAChR agonist) treatment in BALB/c male mice intraperitoneal sensitized and then inhaled with OVA. Another OVA-sensitized-group was treated with PNU-282987 plus Methyllycaconitine (MLA,1 mg/kg, α7nAChR antagonist) to confirm that the effects observed by PNU were due to α7nAChR. We showed that KDVAChT-OVA mice exhibit exacerbated airway inflammation when compared to WT-OVA mice. In BALB/c, PNU-282987 treatment reduced the number of eosinophils in the blood, BAL fluid, and around airways, and also decreased pulmonary levels of IL-4,IL-13,IL-17, and IgE in the serum of OVA-exposed mice. MLA pre-treatment abolished all the effects of PNU-282987. Additionally, we showed that PNU-282987 inhibited STAT3-phosphorylation and reduced SOCS3 expression in the lung. These data indicate that endogenous cholinergic tone is important to control allergic airway inflammation in a murine model. Moreover, α7nAChR is involved in the control of eosinophilic inflammation and airway remodeling, possibly via inhibition of STAT3/SOCS3 pathways. Together these data suggest that cholinergic anti-inflammatory system mainly α7nAChR should be further considered as a therapeutic target in asthma.

Deficits in the vesicular acetylcholine transporter alter lifespan and behavior in adult Drosophila melanogaster

The neurotransmitter acetylcholine (ACh) is involved in critical organismal functions that include locomotion and cognition. Importantly, alterations in the cholinergic system are a key underlying factor in cognitive defects associated with aging. One essential component of cholinergic synaptic transmission is the vesicular ACh transporter (VAChT), which regulates the packaging of ACh into synaptic vesicles for extracellular release. Mutations that cause a reduction in either protein level or activity lead to diminished locomotion ability whereas complete loss of function of VAChT is lethal. While much is known about the function of VAChT, the direct role of altered ACh release and its association with either an impairment or an enhancement of cognitive function are still not fully understood. We hypothesize that point mutations in Vacht cause age-related deficits in cholinergic-mediated behaviors such as locomotion, and learning and memory. Using Drosophila melanogaster as a model system, we have studied several mutations within Vacht and observed their effect on survivability and locomotive behavior. Here we report for the first time a weak hypomorphic Vacht allele that shows a differential effect on ACh-linked behaviors. We also demonstrate that partially rescued Vacht point mutations cause an allele-dependent deficit in lifespan and defects in locomotion ability. Moreover, using a thorough data analytics strategy to identify exploratory behavioral patterns, we introduce new paradigms for measuring locomotion-related activities that could not be revealed or detected by a simple measure of the average speed alone. Together, our data indicate a role for VAChT in the maintenance of longevity and locomotion abilities in Drosophila and we provide additional measurements of locomotion that can be useful in determining subtle changes in Vacht function on locomotion-related behaviors.

The impact of dopamine D2-like agonist/antagonist on [18F]VAT PET measurement of VAChT in the brain of nonhuman primates

Vesicular acetylcholine transporter (VAChT) is a promising target for a PET measure of cholinergic deficits which contribute to cognitive impairments. Dopamine D2-like agonists and antagonists are frequently used in the elderly and could alter cholinergic function and VAChT level. Therefore, pretreatment with dopamine D2-like drugs may interfere with PET measures using [18F]VAT, a specific VAChT radioligand. Herein, we investigated the impact of dopaminergic D2-like antagonist/agonist on VAChT level in the brain of macaques using [18F]VAT PET. PET imaging studies were carried out on macaques at baseline or pretreatment conditions. For pretreatment, animals were injected using a VAChT inhibitor (-)-vesamicol, a D2-like antagonist (-)-eticlopride, and a D2-like agonist (-)-quinpirole, separately. (-)-Vesamicol was injected at escalating doses of 0.025, 0.05, 0.125, 0.25 and 0.35 mg/kg; (-)-eticlopride was injected at escalating doses of 0.01, 0.10 and 0.30 mg/kg; (-)-quinpirole was injected at escalating doses of 0.20, 0.30, and 0.50 mg/kg. PET data showed [18F]VAT uptake declined in a dose-dependent manner by (-)-vesamicol pretreatment, demonstrating [18F]VAT uptake is sensitive to reflect the availability of VAChT binding sites. Furthermore, (-)-eticlopride increased [18F]VAT striatal uptake in a dose-dependent manner, while (-)-quinpirole decreased its uptake, suggesting striatal VAChT levels can be regulated by D2-like drug administration. Our findings confirmed [18F]VAT offers a reliable tool to in vivo assess the availability of VAChT binding sites. More importantly, PET with [18F]VAT successfully quantified the impact of dopaminergic D2-like drugs on striatal VAChT level, suggesting [18F]VAT has great potential for investigating the interaction between dopaminergic and cholinergic systems in vivo.

Decreased number of striatal cholinergic interneurons and motor deficits in dopamine receptor 2-expressing-cell-specific Dyt1 conditional knockout mice

DYT1 early-onset generalized torsion dystonia is a hereditary movement disorder characterized by abnormal postures and repeated movements. It is caused mainly by a heterozygous trinucleotide deletion in DYT1/TOR1A, coding for torsinA. The mutation may lead to a partial loss of torsinA function. Functional alterations of the basal ganglia circuits have been implicated in this disease. Striatal dopamine receptor 2 (D2R) levels are significantly decreased in DYT1 dystonia patients and in the animal models of DYT1 dystonia. D2R-expressing cells, such as the medium spiny neurons in the indirect pathway, striatal cholinergic interneurons, and dopaminergic neurons in the basal ganglia circuits, contribute to motor performance. However, the function of torsinA in these neurons and its contribution to the motor symptoms is not clear. Here, D2R-expressing-cell-specific Dyt1 conditional knockout (d2KO) mice were generated and in vivo effects of torsinA loss in the corresponding cells were examined. The Dyt1 d2KO mice showed significant reductions of striatal torsinA, acetylcholine metabolic enzymes, Tropomyosin receptor kinase A (TrkA), and cholinergic interneurons. The Dyt1 d2KO mice also showed significant reductions of striatal D2R dimers and tyrosine hydroxylase without significant alteration in striatal monoamine contents or the number of dopaminergic neurons in the substantia nigra. The Dyt1 d2KO male mice showed motor deficits in the accelerated rotarod and beam-walking tests without overt dystonic symptoms. Moreover, the Dyt1 d2KO male mice showed significant correlations between striatal monoamines and locomotion. The results suggest that torsinA in the D2R-expressing cells play a critical role in the development or survival of the striatal cholinergic interneurons, expression of striatal D2R mature form, and motor performance. Medical interventions to compensate for the loss of torsinA function in these neurons may affect the onset and symptoms of this disease.

Altered motor, anxiety-related and attentional task performance at baseline associate with multiple gene copies of the vesicular acetylcholine transporter and related protein overexpression in ChAT::Cre+ rats

Transgenic rodents expressing Cre recombinase cell specifically are used for exploring mechanisms regulating behavior, including those mediated by cholinergic signaling. However, it was recently reported that transgenic mice overexpressing a bacterial artificial chromosome containing choline acetyltransferase (ChAT) gene, for synthesizing the neurotransmitter acetylcholine, present with multiple vesicular acetylcholine transporter (VAChT) gene copies, resulting in altered cholinergic tone and accompanying behavioral abnormalities. Since ChAT::Cre+ rats, used increasingly for understanding the biological basis of CNS disorders, utilize the mouse ChAT promotor to control Cre recombinase expression, we assessed for similar genotypical and phenotypical differences in such rats compared to wild-type siblings. The rats were assessed for mouse VAChT copy number, VAChT protein expression levels and for sustained attention, response control and anxiety. Rats were also subjected to a contextual fear conditioning paradigm using an unconditional fear-inducing stimulus (electrical foot shocks), with blood samples taken at baseline, the fear acquisition phase and retention testing, for measuring blood plasma markers of hypothalamic–pituitary–adrenal gland (HPA)-axis activity. ChAT::Cre+ rats expressed multiple mouse VAChT gene copies, resulting in significantly higher VAChT protein expression, revealed anxiolytic behavior, hyperlocomotion and deficits in tasks requiring sustained attention. The HPA-axis was intact, with unaltered circulatory levels of acute stress-induced corticosterone, leptin and glucose. Our findings, therefore, reveal that in ChAT::Cre+ rats, VAChT overexpression associates with significant alterations of certain cognitive, motor and affective functions. Although highly useful as an experimental tool, it is essential to consider the potential effects of altered cholinergic transmission on baseline behavior in ChAT::Cre rats.

Radiosynthesis and evaluation of a fluorine-18 labeled radioligand targeting vesicular acetylcholine transporter

Vesicular acetylcholine transporter (VAChT) is a reliable biomarker for assessing the loss of cholinergic neurons in the brain that is associated with cognitive impairment of patients. 5-Hydrotetralin compound (±)-5-OH-VAT is potent (K_i = 4.64 ± 0.32 nM) and selective for VAChT (>1800-fold and 398-fold for σ₁ and σ₂ receptor, respectively) with favorable hydrophilicity (LogD = 1.78), while (-)-5-OH-VAT originally serves as the radiolabeling precursor of (-)-[¹⁸F]VAT, a promising VAChT radiotracer with a logD value of 2.56. To evaluate (-)-5-OH-[¹⁸F]VAT as a radiotracer for VAChT, we performed in vitro binding assay to determine the potency of the minus enantiomer (-)-5-OH-VAT and plus enantiomer (+)-5-OH-VAT, indicating that (-)-5-OH-VAT is a more potent VAChT enantiomer. Radiosynthesis of (-)-5-OH-[¹⁸F]VAT was explored using three strategies. (-)-5-OH-[¹⁸F]VAT was achieved with a good yield (24 ± 6%) and high molar activity (∼37 GBq/µmol, at the end of synthesis) using a microwave assisted two-step one-pot procedure that started with di-MOM protected nitro-containing precursor (-)-6. MicroPET studies in the brain of nonhuman primate (NHP) suggest that (-)-5-OH-[¹⁸F]VAT readily penetrated the blood brain barrier and specifically accumulated in the VAChT-enriched striatum with improved washout kinetics from striatum compared to [¹⁸F]VAT. Nevertheless, the lower target to non-target ratio may limit its use for in vivo measurement of the VAChT level in the brain.

Cholinergic imbalance in lumbar spinal cord of a rat model of multiple sclerosis

Cholinergic dysfunction in the central nervous system is an important characteristic of multiple sclerosis and experimental autoimmune encephalomyelitis (EAE). By using a rat EAE model, upregulation of vesicular acetylcholine transporter (VAChT) level in the EAE rat lumbar spinal cord was detected by western blot and immunostaining, and was associated with lymphocyte filtration and glial activation. Ex vivo and in vitro autoradiography studies with [¹⁸F]VAT, a VAChT-specific radioligand, also revealed increased tracer uptake in EAE rat lumbar spinal cord compared with shams. These studies on VAChT expression suggest central cholinergic imbalance during EAE progression.

The distribution of cholinergic neurons and their co-localization with FMRFamide, in central and peripheral neurons of the spider Cupiennius salei

The spider Cupiennius salei is a well-established model for investigating information processing in arthropod sensory systems. Immunohistochemistry has shown that several neurotransmitters exist in the C. salei nervous system, including GABA, glutamate, histamine, octopamine and FMRFamide, while electrophysiology has found functional roles for some of these transmitters. There is also evidence that acetylcholine (ACh) is present in some C. salei neurons but information about the distribution of cholinergic neurons in spider nervous systems is limited. Here, we identify C. salei genes that encode enzymes essential for cholinergic transmission: choline ACh transferase (ChAT) and vesicular ACh transporter (VAChT). We used in-situ hybridization with an mRNA probe for C. salei ChAT gene to locate somata of cholinergic neurons in the central nervous system and immunohistochemistry with antisera against ChAT and VAChT to locate these proteins in cholinergic neurons. All three markers labeled similar, mostly small neurons, plus a few mid-sized neurons, in most ganglia. In the subesophageal ganglia, labeled neurons are putative efferent, motor or interneurons but the largest motor and interneurons were unlabeled. Groups of anti-ChAT labeled small neurons also connect the optic neuropils in the spider protocerebrum. Differences in individual cell labeling intensities were common, suggesting a range of ACh expression levels. Double-labeling found a subpopulation of anti-VAChT-labeled central and mechanosensory neurons that were also immunoreactive to antiserum against FMRFamide-like peptides. Our findings suggest that ACh is an important neurotransmitter in the C. salei central and peripheral nervous systems.

Synthesis and in vitro evaluation of 5-substituted benzovesamicol analogs containing N-substituted amides as potential positron emission tomography tracers for the vesicular acetylcholine transporter

Herein, new ligands for the vesicular acetylcholine transporter (VAChT), based on a benzovesamicol scaffold, are presented. VAChT is acknowledged as a marker for cholinergic neurons and a positron emission tomography tracer for VAChT could serve as a tool for quantitative analysis of cholinergic neuronal density. With an easily accessible triflate precursor, aminocarbonylations were utilized to evaluate the chemical space around the C5 position on the tetrahydronaphthol ring. Synthesized ligands were evaluated for their affinity and selectivity for VAChT. Small, preferably aromatic, N-substituents proved to be more potent than larger substituents. Of the fifteen compounds synthesized, benzyl derivatives (±)-7i and (±)-7l had the highest affinities for VAChT. Compound (±)-7i was chosen to investigate the importance of stereochemistry for binding to VAChT and selectivity toward the σ₁ and σ₂ receptors. Enantiomeric resolution gave (+)-7i and (-)-7i, and the eutomer showed seven times better affinity. Although racemate (±)-7i was initially promising, the affinity of (-)-7i for VAChT was not better than 56.7nM which precludes further preclinical evaluation. However, the nanomolar binding together with the ready synthesis of [¹¹C]-(±)-7i shows that (-)-7i can serve as a scaffold for future optimizations to provide improved ¹¹C-labelled VAChT PET tracers.

Cholinergic PET imaging in infections and inflammation using 11C-donepezil and 18F-FEOBV

INTRODUCTION

Immune cells utilize acetylcholine as a paracrine-signaling molecule. Many white blood cells express components of the cholinergic signaling pathway, and these are up-regulated when immune cells are activated. However, in vivo molecular imaging of cholinergic signaling in the context of inflammation has not previously been investigated.

METHODS

We performed positron emission tomography (PET) using the glucose analogue 18F-FDG, and 11C-donepezil and 18F-FEOBV, markers of acetylcholinesterase and the vesicular acetylcholine transporter, respectively. Mice were inoculated subcutaneously with Staphylococcus aureus, and PET scanned at 24, 72, 120, and 144 h post-inoculation. Four pigs with post-operative abscesses were also imaged. Finally, we present initial data from human patients with infections, inflammation, and renal and lung cancer.

RESULTS

In mice, the FDG uptake in abscesses peaked at 24 h and remained stable. The 11C-donepezil and 18F-FEOBV uptake displayed progressive increase, and at 120-144 h was nearly at the FDG level. Moderate 11C-donepezil and slightly lower 18F-FEOBV uptake were seen in pig abscesses. PCR analyses suggested that the 11C-donepezil signal in inflammatory cells is derived from both acetylcholinesterase and sigma-1 receptors. In humans, very high 11C-donepezil uptake was seen in a lobar pneumonia and in peri-tumoral inflammation surrounding a non-small cell lung carcinoma, markedly superseding the 18F-FDG uptake in the inflammation. In a renal clear cell carcinoma no 11C-donepezil uptake was seen.

DISCUSSION

The time course of cholinergic tracer accumulation in murine abscesses was considerably different from 18F-FDG, demonstrating in the 11C-donepezil and 18F-FEOBV image distinct aspects of immune modulation. Preliminary data in humans strongly suggest that 11C-donepezil can exhibit more intense accumulation than 18F-FDG at sites of chronic inflammation. Cholinergic PET imaging may therefore have potential applications for basic research into cholinergic mechanisms of immune modulation, but also clinical applications for diagnosing infections, inflammatory disorders, and cancer inflammation.

Vesicular acetylcholine transporter knock down-mice are more susceptible to inflammation, c-Fos expression and sickness behavior induced by lipopolysaccharide

In addition to the well-known functions as a neurotransmitter, acetylcholine (ACh) can modulate of the immune system. Nonetheless, how endogenous ACh release inflammatory responses is still not clear. To address this question, we took advantage of an animal model with a decreased ACh release due a reduction (knockdown) in vesicular acetylcholine transporter (VAChT) expression (VAChT-KD(HOM)). These animals were challenged with lipopolysaccharide (LPS). Afterwards, we evaluated sickness behavior and quantified systemic and cerebral inflammation as well as neuronal activation in the dorsal vagal complex (DVC). VAChT-KD(HOM) mice that were injected with LPS (10mg/kg) showed increased mortality rate as compared to control mice. In line with this result, a low dose of LPS (0.1mg/kg) increased the levels of pro-inflammatory (TNF-α, IL-1β, and IL-6) and anti-inflammatory (IL-10) cytokines in the spleen and brain of VAChT-KD(HOM) mice in comparison with controls. Similarly, serum levels of TNF-α and IL-6 were increased in VAChT-KD(HOM) mice. This excessive cytokine production was completely prevented by administration of a nicotinic receptor agonist (0.4mg/kg) prior to the LPS injection. Three hours after the LPS injection, c-Fos expression increased in the DVC region of VAChT-KD(HOM) mice compared to controls. In addition, VAChT-KD(HOM) mice showed behavioral changes such as lowered locomotor and exploratory activity and reduced social interaction after the LPS challenge, when compared to control mice. Taken together, our results show that the decreased ability to release ACh exacerbates systemic and cerebral inflammation and promotes neural activation and behavioral changes induced by LPS. In conclusion, our findings support the notion that activity of cholinergic pathways, which can be modulated by VAChT expression, controls inflammatory and neural responses to LPS challenge.

Radiation dosimetry of [(18)F]VAT in nonhuman primates

Background

The objective of this study is to determine the radiation dosimetry of a novel radiotracer for vesicular acetylcholine transporter (−)-(1-((2R,3R)-8-(2-[¹⁸F]fluoro-ethoxy)-3-hydroxy-1,2,3,4-tetrahydronaphthalen-2-yl)piperidin-4-yl)(4-fluorophenyl)-methanone ([¹⁸F]VAT) based on PET imaging in nonhuman primates. [¹⁸F]VAT has potential for investigation of neurological disorders including Alzheimer’s disease, Parkinson’s disease, and dystonia.

Methods

Three macaque fascicularis (two males, one female) received 185.4–198.3 MBq [¹⁸F]VAT prior to whole-body imaging in a MicroPET-F220 scanner. Time activity curves (TACs) were created from regions of interest (ROIs) that encompassed the entire small organs or samples with the highest activity within large organs. Organ residence times were calculated based on the TACs. We then used OLINDA/EXM 1.1 to calculate human radiation dose estimates based on scaled organ residence times.

Results

Measurements from directly sampled arterial blood yielded a residence time of 0.30 h in agreement with the residence time of 0.39 h calculated from a PET-generated time activity curve measured in the left ventricle. Organ dosimetry revealed the liver as the critical organ (51.1 and 65.4 μGy/MBq) and an effective dose of 16 and 19 μSv/MBq for male and female, respectively.

Conclusions

The macaque biodistribution data showed high retention of [¹⁸F]VAT in the liver consistent with hepatobiliary clearance. These dosimetry data support that relatively safe doses of [¹⁸F]VAT can be administered to obtain imaging in humans.

Synthesis and evaluation of a new vesamicol analog o-[(11)C]methyl-trans-decalinvesamicol as a PET ligand for the vesicular acetylcholine transporter

INTRODUCTION

We focused on the vesicle acetyl choline transporter (VAChT) as target for early diagnosis of Alzheimer's diseases because the dysfunction of the cholinergic nervous system is closely associated with the symptoms of AD, such as problem in recognition, memory, and learning. Due to its low binding affinity for the sigma receptors (σ-1 and σ-2), o-methyl-trans-decalinvesamicol (OMDV) demonstrated a high binding affinity and selectivity for vesicular acetyl choline transporter (VAChT). [(11)C]OMDV was prepared and investigated the potential as a new PET ligand for VAChT imaging through in vivo evaluation.

METHOD

[(11)C]OMDV was prepared by a palladium-promoted cross-coupling reaction using [(11)C]methyl iodide, with a radiochemical yield of 60-75%, a radiochemical purity of greater than 98%, and a specific activity of 5-10 TBq/mmol 30 min after EOB. In vivo biodistribution study of [(11)C]OMDV in blood, brain regions and major organs of rats was performed at 2, 10, 30 and 60 min post-injection. In vivo blocking study and PET-CT imaging study were performed to check the binding selectivity of [(11)C]OMDV for VAChT.

RESULTS

In vivo studies demonstrated [(11)C]OMDV passage through the blood-brain barrier (BBB) and accumulation in the rat brain. The regional brain accumulation of [(11)C]OMDV was significantly inhibited by co-administration of vesamicol. In contrast, brain accumulation of [(11)C]OMDV was not significantly altered by co-administration of (+)-pentazocine, a selective σ-1 receptor ligand, or (+)-3-(3-hydroxyphenyl)-N-propylpiperidine [(+)-3-PPP], a σ-1 and σ-2 receptor ligand. PET-CT imaging revealed inhibition of [(11)C]OMDV accumulation in the brain by co-administration of vesamicol.

CONCLUSION

[(11)C]OMDV selectively binds to VAChT with high affinity in the rat brain in vivo, and that [(11)C]OMDV may be utilized in the future as a specific VAChT ligand for PET imaging.

Kinetics modeling and occupancy studies of a novel C-11 PET tracer for VAChT in nonhuman primates

INTRODUCTION

Deficits in cholinergic function have been found in the aged brain and in neurodegenerative diseases including Alzheimer's disease (AD) and Parkinson's disease (PD). The vesicular acetylcholine transporter (VAChT) is a reliable biomarker for the cholinergic system. We previously reported the initial in vitro and ex vivo characterization of (-)-[(11)C]TZ659 as a VAChT specific ligand. Here, we report the in vivo specificity, tracer kinetics, and dose-occupancy studies in the nonhuman primate brain.

METHODS

MicroPET brain imaging of (-)-[(11)C]TZ659 was performed under baseline conditions in two male macaques. Tracer kinetic modeling was carried out using a two-tissue compartment model (2TCM) and Logan plot with arterial blood input function and using a simplified reference tissue model (SRTM) and Logan plot (LoganREF) without blood input. Specificity for VAChT was demonstrated by pretreatment with (+)-pentazocine, (-)-vesamicol, or S-(-)-eticlopride. Target occupancy (Occ) was calculated following pretreatment with escalating doses of (-)-vesamicol.

RESULTS

Baseline PET imaging revealed selective retention in the striatum with rapid clearance from the cerebellar hemispheres as a reference region. Total volume of distribution (VT) values derived from both 2TCM and Logan analysis with blood input revealed ~3-fold higher levels of (-)-[(11)C]TZ659 in the striatum than the cerebellar hemispheres. Injection of (-)-vesamicol either as a blocking or displacing agent significantly reduced striatal uptake of (-)-[(11)C]TZ659. In contrast, pretreatment with the sigma-1 ligand (+)-pentazocine had no impact. Pretreatment with the S-(-)-eticlopride, a dopamine D2-like receptor antagonist, increased striatal uptake of (-)-[(11)C]TZ659. Striatal binding potential (BPND, range of 0.33-1.6 with cerebellar hemispheres as the reference region) showed good correlation (r(2)=0.97) between SRTM and LoganREF. Occupancy studies found that ~0.0057 mg/kg of (-)-vesamicol produced 50% VAChT occupancy in the striatum.

CONCLUSION

(-)-[(11)C]TZ659 demonstrated specific and reversible VAChT binding and favorable pharmacokinetic properties for assessing the density of VAChT in the living brain.

Further validation to support clinical translation of [(18)F]FTC-146 for imaging sigma-1 receptors

BACKGROUND

This study aims to further evaluate the specificity and selectivity of [(18)F]FTC-146 and obtain additional data to support its clinical translation.

METHODS

The binding of [(19)F]FTC-146 to vesicular acetylcholine transporter (VAChT) was evaluated using [(3)H]vesamicol and PC12(A123.7) cells in an in vitro binding assay. The uptake and kinetics of [(18)F]FTC-146 in S1R-knockout mice (S1R-KO) compared to wild-type (WT) littermates was assessed using dynamic positron emission tomography (PET) imaging. Ex vivo autoradiography and histology were conducted using a separate cohort of S1R-KO/WT mice, and radiation dosimetry was calculated from WT mouse data (extrapolated for human dosing). Toxicity studies in Sprague-Dawley rats were performed with a dose equivalent to 250× the anticipated clinical dose of [(19)F]FTC-146 mass.

RESULTS AND DISCUSSION

VAChT binding assay results verified that [(19)F]FTC-146 displays negligible affinity for VAChT (K i = 450 ± 80 nM) compared to S1R. PET images demonstrated significantly higher tracer uptake in WT vs. S1R-KO brain (4.57 ± 1.07 vs. 1.34 ± 0.4 %ID/g at 20-25 min, n = 4, p < 0.05). In S1R-KO mice, it was shown that rapid brain uptake and clearance 10 min post-injection, which are consistent with previous S1R-blocking studies in mice. Three- to fourfold higher tracer uptake was observed in WT relative to S1R-KO mouse brains by ex vivo autoradiography. S1R staining coincided well with the autoradiographic data in all examined brain regions (r (2) = 0.85-0.95). Biodistribution results further demonstrated high [(18)F]FTC-146 accumulation in WT relative to KO mouse brain and provided quantitative information concerning tracer uptake in S1R-rich organs (e.g., heart, lung, pancreas) for WT mice vs. age-matched S1R-KO mice. The maximum allowed dose per scan in humans as extrapolated from mouse dosimetry was 33.19 mCi (1228.03 MBq). No significant toxicity was observed even at a 250X dose of the maximum carrier mass [(19)F]FTC-146 expected to be injected for human studies.

CONCLUSIONS

Together, these data indicate that [(18)F]FTC-146 binds specifically to S1Rs and is a highly promising radiotracer ready for clinical translation to investigate S1R-related diseases.

Automated production of [¹⁸F]VAT suitable for clinical PET study of vesicular acetylcholine transporter

Automated production of a promising radiopharmaceutical (-)-(1-(8-(2-[(18)F]fluoroethoxy)-3-hydroxy-1,2,3,4-tetrahydronaphthalen-2-yl)-piperidin-4-yl)(4-fluorophenyl)methanone ([(18)F]VAT) for the vesicular acetylcholine transporter(VAChT) was achieved using a two-step procedure in a current Good Manufacturing Practices fashion. The production of [(18)F]VAT was accomplished in approximately 140 min, with radiochemical yield of ~15.0% (decay corrected), specific activity>111 GBq/µmol, radiochemical purity>99% and mass of VAT ~3.4 μg/batch (n>10). The radiopharmaceutical product meets all quality control criteria for human use, and is suitable for clinical PET studies of VAChT.

In vitro and ex vivo characterization of (-)-TZ659 as a ligand for imaging the vesicular acetylcholine transporter

The loss of cholinergic neurons and synapses relates to the severity of dementia in several neurodegenerative pathologies; and the vesicular acetylcholine transporter (VAChT) provides a reliable biomarker of cholinergic function. We recently characterized and (11)C-labeled a new VAChT inhibitor, (-)-TZ659. Here we report the in vitro and ex vivo characterization of (-)-TZ659. A stably transfected PC12(A123.7) cell line which expresses human VAChT (hVAChT) was used for the in vitro binding characterization of (-)-[(3)H]TZ659. A saturated binding curve was obtained with Kd=1.97±0.30nM and Bmax=3240±145.9fmol/mg protein. In comparison, a PC12(A123.7) cell line that expresses mutant hVAChT showed decreased binding affinity (Kd=15.94±0.28nM). Competitive binding assays using a panel of other CNS ligands showed no inhibition of (-)-[(3)H]TZ659 binding. On the other hand, binding inhibitions were observed only using VAChT inhibitors (Ki=0.20-31.35nM). An in vitro assay using rat brain homogenates showed that (-)-[(3)H]TZ659 had higher binding in striatum than in cerebellum, with a target: non-target ratio>3.46. Even higher ex vivo striatum-to-cerebellum ratios (9.56±1.11) were observed using filtered homogenates of brain tissue after rats were injected intravenously with (-)-[(11)C]TZ659. Ex vivo autoradiography of (-)-[(11)C]TZ659 confirmed high striatal uptake, with a consistently high striatum-to-cerebellum ratio (2.99±0.44). In conclusion, (-)-TZ659 demonstrated high potency and good specificity for VAChT in vitro and in vivo. These data suggest that (-)-[(11)C]TZ659 may be a promising PET tracer to image VAChT in the brain.

[(123)I]-IBVM SPECT imaging of cholinergic systems in multiple system atrophy: A specific alteration of the ponto-thalamic cholinergic pathways (Ch5-Ch6)

We evaluated in vivo the integrity of brain cholinergic pathways in Multiple System Atrophy (MSA) and the relationship between cholinergic dysfunction and motor disturbances, by measuring the vesicular acetylcholine transporter (VAChT) expression using Single Photon Emission Computed Tomography (SPECT) and [(123)I]-iodobenzovesamicol ([(123)I]-IBVM).

METHODS

Nine patients with probable MSA and 12 healthy volunteers underwent a dynamic [(123)I]-IBVM SPECT-CT scan and a magnetic resonance imaging (MRI) scan. All patients were examined with the Unified MSA Rating Scale (UMSARS; subscale I = activities of daily living (ADL), II = motor and IV = disability). CT and MRI images were used to register the dynamic SPECT image to the Montreal Neurological Institute brain template, which includes the regions of interest (ROI) of striatum and Ch1 (medial septum nucleus-hippocampus), Ch4 (nucleus basalis of Meynert-cortex) and Ch5-Ch6 (pedunculopontine and laterodorsal tegmental nuclei-thalamus) cholinergic pathways. For each ROI, pharmacokinetic modeling of regional time activity curves led to the calculation of [(123)I]-IBVM to VAChT binding potential (BPND) value, proportional to VAChT expression.

RESULTS

When compared to controls, BPND values for MSA in Ch5-Ch6 were significantly decreased in both the pedunculopontine-laterodorsal nuclei and the thalamus (p = 0.004 and p = 0.006, respectively). Additionally, thalamus BPND values were correlated with UMSARS ADL (p = 0.006), motor (p = 0.002) and disability (p = 0.02) sub-scores. UMSARS motor subscale items 13 (postural instability) and 14 (gait) were also correlated with thalamus BPND values (p = 0.04).

CONCLUSION

Ch5-Ch6 are the most affected cholinergic pathways in MSA at both cell bodies and thalamic cholinergic terminals. These results underscore the relevant role of [(123)I]-IBVM SPECT for improving our understanding of the pathophysiology in MSA.