Age-dependent changes of cerebral copper metabolism in Atp7b -/- knockout mouse model of Wilson's disease by [64Cu]CuCl2-PET/CT

Atp7b-dependent choroid plexus dysfunction causes transient copper deficit and metabolic changes in the developing mouse brain

Copper (Cu) has a multifaceted role in brain development, function, and metabolism. Two homologous Cu transporters, Atp7a (Menkes disease protein) and Atp7b (Wilson disease protein), maintain Cu homeostasis in the tissue. Atp7a mediates Cu entry into the brain and activates Cu-dependent enzymes, whereas the role of Atp7b is less clear. We show that during postnatal development Atp7b is necessary for normal morphology and function of choroid plexus (ChPl). Inactivation of Atp7b causes reorganization of ChPl' cytoskeleton and cell-cell contacts, loss of Slc31a1 from the apical membrane, and a decrease in the length and number of microvilli and cilia. In ChPl lacking Atp7b, Atp7a is upregulated but remains intracellular, which limits Cu transport into the brain and results in significant Cu deficit, which is reversed only in older animals. Cu deficiency is associated with down-regulation of Atp7a in locus coeruleus and catecholamine imbalance, despite normal expression of dopamine-β-hydroxylase. In addition, there are notable changes in the brain lipidome, which can be attributed to inhibition of diacylglyceride-to-phosphatidylethanolamine conversion. These results identify the new role for Atp7b in developing brain and identify metabolic changes that could be exacerbated by Cu chelation therapy.

High value of 64Cu as a tool to evaluate the restoration of physiological copper excretion after gene therapy in Wilson's disease

Wilson’s disease (WD) is an inherited disorder of copper metabolism associated with mutations in ATP7B gene. We have shown that the administration of an adeno-associated vector (AAV) encoding a mini version of human ATP7B (VTX-801) provides long-term correction of copper metabolism in a murine WD model. In preparation of a future clinical trial, we have evaluated by positron emission tomography (PET) the value of ⁶⁴Cu biodistribution, excretion pattern, and blood kinetics as pharmacodynamic biomarkers of VTX-801 effects. Six-week-old WD mice were injected intravenously with increasing doses of VTX-801 and 3 weeks or 3 months later with [⁶⁴Cu]CuCl₂. Untreated WD and wild-type (WT) mice were included as controls. Control WD mice showed increased hepatic ⁶⁴Cu retention, reduced fecal excretion of the radiotracer, and altered ⁶⁴Cu blood kinetics (BK) compared with WT mice. VTX-801 treatment in WD mice resulted in a significant reduction of hepatic ⁶⁴Cu accumulation, the restoration of fecal ⁶⁴Cu excretion, and the correction of ⁶⁴Cu BK. This study showed that VTX-801 restores physiological copper metabolism in WD mice, confirming the mechanism of action of VTX-801, and demonstrated the translational potential of [⁶⁴Cu]CuCl₂-PET to explore VTX-801 pharmacodynamics in a minimally invasive and sensitive manner in WD patients.

Non-invasive radionuclide imaging of trace metal trafficking in health and disease: "PET metallomics"

Several specific metallic elements must be present in the human body to maintain health and function. Maintaining the correct quantity (from trace to bulk) and location at the cell and tissue level is essential. The study of the biological role of metals has become known as metallomics. While quantities of metals in cells and tissues can be readily measured in biopsy and autopsy samples by destructive analytical techniques, their trafficking and its role in health and disease are poorly understood. Molecular imaging with radionuclides - positron emission tomography (PET) and single photon emission computed tomography (SPECT) - is emerging as a means to non-invasively study the acute trafficking of essential metals between organs, non-invasively and in real time, in health and disease. PET scanners are increasingly widely available in hospitals, and methods for producing radionuclides of some of the key essential metals are developing fast. This review summarises recent developments in radionuclide imaging technology that permit such investigations, describes the radiological and physicochemical properties of key radioisotopes of essential trace metals and useful analogues, and introduces current and potential future applications in preclinical and clinical investigations to study the biology of essential trace metals in health and disease.

Alteration of neuroinflammation detected by 18F-GE180 PET imaging in place-conditioned rats with morphine withdrawal

BACKGROUND

Accumulating evidence indicates that neuroinflammation (NI) significantly contributes to drug addiction, but the conversion of NI after drug withdrawal is not clear. Here, we conducted ¹⁸F-flutriciclamide (GE180) positron emission tomography (PET) imaging to investigate the conversion of NI during drug withdrawal and conditioning-induced aversion by measuring the change in microglial activation with ¹⁸F-GE180.

METHODS

Twelve male adult Sprague-Dawley rats were subjected to morphine withdrawal by the administration of naloxone, and six of them were used to model conditioned place aversion (CPA). ¹⁸F-GE180 PET imaging was performed for 11 rats on the last day of the morphine treatment phase and for 10 rats on the response assessment phase of the behavior conditioning procedure. A ¹⁸F-GE180 template was established for spatial normalization of each individual image, and the differential ¹⁸F-GE180 uptakes between the drug withdrawal (DW) group and the drug addiction (DA) group, the CPA group and the DA group, and the CPA group and the DW group were compared by a voxel-wise two-sample t test using SPM8.

RESULTS

Both the DW group and the CPA group spent less time in the conditioning cage during the post-test phase compared with the pretest phase, but only the difference in the CPA group was significant (63.2 ± 34.6 vs. - 159.53 ± 22.02, P < 0.005). Compared with the DA group, the uptake of ¹⁸F-GE180 increased mainly in the hippocampus, visual cortex, thalamus and midbrain regions and decreased mainly in the sensory-related cortices after the administration of naloxone in both the DW and CPA groups. Increased ¹⁸F-GE180 uptake was only observed in the mesolimbic regions after conditioned aversion compared with the DW group.

CONCLUSION

In morphine-dependent rats, Neuroinflammation (NI) became more severe in the addiction-involved brain regions but remitted in the sensory-related brain regions after the administration of naloxone, and this NI induced by withdrawal was further aggravated after conditioned aversion formation thus may help to consolidate the withdrawal memory.

Providing multicolor plasmonic patterns with graphene quantum dots functionalized d-penicillamine for visual recognition of V(V), Cu (II), and Fe(III): Colorimetric fingerprints of GQDs-DPA for discriminating ions in human urine samples

In this study, a novel fluorescent probe (graphene quantum dots functionalized d-penicillamine [GQDs-DPA]) was developed for the selective identification of Cu²⁺ , V⁵⁺ , and Fe³⁺ among 26 types of metal ions, which considerably quench the fluorescence intensity of GQD. So, GQDs-DPA was applied as a simple fluorescent probe for facile metal ions recognition in standard solution. The proposed DPA-GQD supported amino acids respond to Cu²⁺ , V⁵⁺ , and Fe³⁺ , with high sensitivity. The intensity of the fluorescence histogram of this probe significantly diminished in exposure to metal ions such as Cu(II), V(V), and Fe(III). Moreover, a microfluidic paper-based device (μPAD) was fabricated through a facile and cost-effective protocol. Cu²⁺ , V⁵⁺ , and Fe³⁺ can be selectively recognized by GQDs-DPA using μPAD by naked eye. Also, GQDs-DPA exhibits a linear response for the detection of ions in concentrations ranging from 0.01 to 1 ppm, with a low limit of quantification of 0.01 ppm in standards samples. The boosted color uniformity, low instrumental needs of the stamp, and disposability of μPADs enable the application of the proposed device for commercial applications in environmental science and technology.

Across the spectrum: integrating multidimensional metal analytics for in situ metallomic imaging

To know how much of a metal species is in a particular location within a biological context at any given time is essential for understanding the intricate roles of metals in biology and is the fundamental question upon which the field of metallomics was born. Simply put, seeing is powerful. With the combination of spectroscopy and microscopy, we can now see metals within complex biological matrices complemented by information about associated molecules and their structures. With the addition of mass spectrometry and particle beam based techniques, the field of view grows to cover greater sensitivities and spatial resolutions, addressing structural, functional and quantitative metallomic questions from the atomic level to whole body processes. In this perspective, I present a paradigm shift in the way we relate to and integrate current and developing metallomic analytics, highlighting both familiar and perhaps less well-known state of the art techniques for in situ metallomic imaging, specific biological applications, and their use in correlative studies. There is a genuine need to abandon scientific silos and, through the establishment of a metallomic scientific platform for further development of multidimensional analytics for in situ metallomic imaging, we have an incredible opportunity to enhance the field of metallomics and demonstrate how discovery research can be done more effectively.

Maturation of topological organization of brain networks in male adolescent rats: A longitudinal FDG-PET study

Recent studies have found developmental alterations of the brain during the adolescent period. However, maturation-related changes of the topological properties in brain networks are unexplored so far. We therefore used fluoro-d-glucose positron emission tomography (FDG PET) to explore the maturation-related topological metabolic changes in brain networks from adolescence to adulthood with a longitudinal study in rats (male, n = 6), followed by a graph theoretical analysis. Our results showed reduced normalization characteristic path length and increased small world index of brain networks. Specifically, we found that relative to adulthood, in the adolescent stage rats had significantly increased nodal centrality in right entorhinal cortex, left frontal association cortex, and cerebellum, areas relating to memory, executive function and higher cognitive control and motor control; and significantly reduced nodal centrality in left superior colliculus and left retrosplenial cortex. These findings suggest that moving from adolescence to adulthood, networks of the brain mature accompanied by reassignment of hub regions to increase network efficiency. These results provide an animal model of brain network maturation from adolescence to adulthood which are relevant for understanding of development of psychiatric disorders during adolescence or transition from adolescence to adulthood.

Decreased striatal vesicular monoamine transporter 2 (VMAT2) expression in a type 1 diabetic rat model: A longitudinal study using micro-PET/CT

AIMS

Diabetes mellitus is a risk factor for Parkinson's disease. These diseases share similar pathogenic pathways, such as mitochondrial dysfunction, inflammation, and altered metabolism. Despite these similarities, the pathogenic relationship between these two diseases is unclear. [¹⁸F]FP-(+)-DTBZ is a promising radiotracer targeting VMAT2, which has been used to measure β-cell mass and to diagnose Parkinson's disease. The aim of this study was to examine the effect of type 1 diabetes on VMAT2 expression in the striatum using [¹⁸F]FP-(+)-DTBZ.

MATERIALS AND METHODS

A longitudinal study of type 1 diabetic rats was established by intraperitoneally injecting male Wistar rats with streptozotocin. Rats injected with saline were used as the control group. Glucose level, body weight, and [¹⁸F]FP-(+)-DTBZ uptake in the striatum and pancreas were evaluated at 0.5, 1, 4, 6 and 12 months after STZ or saline injection.

RESULTS

At one-half month post-STZ injection, the glucose levels in these rats increased and then returned to a normal level at 6 months. Along with increased glucose levels, body weight was also decreased significantly and returned slowly to a normal level. β-Cell mass and striatal [¹⁸F]FP-(+)-DTBZ uptake were impaired significantly at 2 weeks post-STZ injection in type 1 diabetic rats and returned to a normal level at 6 and 4 months post-STZ injection.

CONCLUSIONS

Due to increased glucose levels and decreased β-cell mass, decreased [¹⁸F]FP-(+)-DTBZ uptake in the striatum was observed in type 1 diabetic rats. Decreased BCM and increased glucose levels were correlated with VMAT2 expression in the striatum which indicated DM is a risk factor for PD.

Copper-64: a real theranostic agent

Ongoing studies of physiological and pathological processes have led to a corresponding need for new radiopharmaceuticals, especially when studies are limited by the absence of a particular radiolabeled target. Thus, the development of new radioactive tracers is highly relevant and can represent a significant contribution to efforts to elucidate important phenomena in biology. Currently, theranostics represents a new frontier in the fields of medicine and nuclear medicine, with the same compound being used for both diagnosis and treatment. In the human body, copper (Cu) is the third most abundant metal and it plays a crucial role in many biological functions. Correspondingly, in various acquired and inherited pathological conditions, such as cancer and Alzheimer’s disease, alterations in Cu levels have been found. Moreover, a wide spectrum of neurodegenerative disorders are associated with higher or lower levels of Cu, as well as inappropriately bound or distributed levels of Cu in the brain. In human cells, the membrane protein, hCtr1, binds Cu in its Cu(I) oxidation state in an energy-dependent manner. Copper-64 (⁶⁴Cu) is a cyclotron-produced radionuclide that has exhibited physical properties that are complementary for diagnosis and/or therapeutic purposes. To date, very few reports have described the clinical development of ⁶⁴Cu as a radiotracer for cancer imaging. In this review, we highlight recent insights in our understanding and use of ⁶⁴CuCl₂ as a theranostic agent for various types of tumors. To the best of our knowledge, no adverse effects or clinically observable pharmacological effects have been described for ⁶⁴CuCl₂ in the literature. Thus, ⁶⁴Cu represents a revolutionary radiopharmaceutical for positron emission tomography imaging and opens a new era in the theranostic field.

Insights into Trace Metal Metabolism in Health and Disease from PET: "PET Metallomics"

Essential trace metals such as copper, zinc, iron, and manganese perform critical functions in cellular and physiologic processes including catalytic, regulatory, and signaling roles. Disturbed metal homeostasis is associated with the pathogenesis of diseases such as dementia, cancer, and inherited metabolic abnormalities. Intracellular pathways involving essential metals have been extensively studied but whole-body fluxes and transport between different compartments remain poorly understood. The growing availability of PET scanners and positron-emitting isotopes of key essential metals, particularly 64Cu, 63Zn, and 52Mn, provide new tools with which to study these processes in vivo. This review highlights opportunities that now present themselves, exemplified by studies of copper metabolism that are in the vanguard of a new research front in molecular imaging: "PET metallomics."

Radiopharmaceuticals for Assessment of Altered Metabolism and Biometal Fluxes in Brain Aging and Alzheimer's Disease with Positron Emission Tomography

Aging is a risk factor for Alzheimer's disease (AD). There are changes of brain metabolism and biometal fluxes due to brain aging, which may play a role in pathogenesis of AD. Positron emission tomography (PET) is a versatile tool for tracking alteration of metabolism and biometal fluxes due to brain aging and AD. Age-dependent changes in cerebral glucose metabolism can be tracked with PET using 2-deoxy-2-[18F]-fluoro-D-glucose (18F-FDG), a radiolabeled glucose analogue, as a radiotracer. Based on different patterns of altered cerebral glucose metabolism, 18F-FDG PET was clinically used for differential diagnosis of AD and Frontotemporal dementia (FTD). There are continued efforts to develop additional radiopharmaceuticals or radiotracers for assessment of age-dependent changes of various metabolic pathways and biometal fluxes due to brain aging and AD with PET. Elucidation of age-dependent changes of brain metabolism and altered biometal fluxes is not only significant for a better mechanistic understanding of brain aging and the pathophysiology of AD, but also significant for identification of new targets for the prevention, early diagnosis, and treatment of AD.

Alteration of Copper Fluxes in Brain Aging: A Longitudinal Study in Rodent Using 64CuCl2-PET/CT

Brain aging is associated with changes of various metabolic pathways. Copper is required for brain development and function, but little is known about changes in copper metabolism during brain aging. The objective of this study was to investigate alteration of copper fluxes in the aging mouse brain with positron emission tomography/computed tomography using ⁶⁴CuCl₂ as a radiotracer (⁶⁴CuCl₂-PET/CT). A longitudinal study was conducted in C57BL/6 mice (n = 5) to measure age-dependent brain and whole-body changes of ⁶⁴Cu radioactivity using PET/CT after oral administration of ⁶⁴CuCl₂ as a radiotracer. Cerebral ⁶⁴Cu uptake at 13 months of age (0.17 ± 0.05 %ID/g) was higher than the cerebral ⁶⁴Cu uptake at 5 months of age (0.11 ± 0.06 %ID/g, p < 0.001), followed by decrease to (0.14 ± 0.04 %ID/g, p = 0.02) at 26 months of age. In contrast, cerebral ¹⁸F-FDG uptake was highest at 5 months of age (7.8 ± 1.2 %ID/g) and decreased to similar values at 12 (5.2 ± 1.1 %ID/g, p < 0.001) and 22 (5.6 ± 1.1 %ID/g, p < 0.001) months of age. The findings demonstrated alteration of copper fluxes associated with brain aging and the time course of brain changes in copper fluxes differed from changes in brain glucose metabolism across time, suggesting independent underlying physiological processes. Hence, age-dependent changes of cerebral copper fluxes might represent a novel metabolic biomarker for assessment of human brain aging process with PET/CT using ⁶⁴CuCl₂ as a radiotracer.