PET Imaging for Oxidative Stress in Neurodegenerative Disorders Associated with Mitochondrial Dysfunction

Application of copper (I) selective ligands for PET imaging of reactive oxygen species through metabolic trapping

INTRODUCTION

Reactive oxygen species (ROS) are attractive targets for clinical PET imaging. In this study, we hypothesized that PET imaging of ROS would be possible by using chelating ligands (L) that form stable complexes with copper (I) but not with copper (II), based on metabolic trapping. Namely, when [64Cu][CuI(L)2]+ is oxidized by ROS, the oxidized complex will release [64Cu]Cu2+. Then, the released [64Cu]Cu2+ will be trapped inside the cell, resulting in PET signal depending on the redox potential of ROS. To examine the potential of this novel molecular design for ROS imaging, we synthesized copper (I) complexes with bicinchoninic acid (BCA) disodium salt and bathocuproinedisulfonic acid (BCS) disodium salt and evaluated their reactivity with several kinds of ROS. In addition, the cellular uptake of [64Cu][CuI(BCS)2]3- and the stability of [64Cu][CuI(BCS)2]3- in a biological condition were also evaluated.

METHODS

[64Cu]Cu2+ was reduced to [64Cu]Cu+ by ascorbic acid and coordinated with BCA and BCS in the acetate buffer to synthesize [64Cu][CuI(BCA)2]3- and [64Cu][CuI(BCS)2]3-. The radiochemical yields were determined by thin-layer chromatography (TLC). After [64Cu][CuI(BCS)2]3- was incubated with hydroxyl radical, lipid peroxide, superoxide, and hydrogen peroxide, the percentage of released [64Cu]Cu2+ from the parent complex was evaluated by TLC. HT-1080 human fibrosarcoma cells were treated with 0.1 % Dimethyl sulfoxide (control), imidazole ketone erastin (IKE), or IKE + ferrostatin-1 (Fer-1). Then, the uptake of [64Cu][CuI(BCS)2]3- to HT-1080 cells in each group was evaluated as %Dose/mg protein. Lastly, [64Cu][CuI(BCS)2]3- was incubated in human plasma, and its intact ratio was determined by TLC.

RESULTS

The radiochemical yield of [64Cu][CuI(BCS)2]3- (86 ± 1 %) was higher than that of [64Cu][CuI(BCA)2]3- (44 ± 3 %). [64Cu][CuI(BCA)2]3- was unstable and partially decomposed on TLC. After [64Cu][CuI(BCS)2]3- was reacted with hydroxyl radical, lipid peroxide, and superoxide, 67 ± 2 %, 44 ± 13 %, and 22 ± 3 % of total radioactivity was detected as [64Cu]Cu2+, respectively. On the other hand, the reaction with hydrogen peroxide did not significantly increase the ratio of [64Cu]Cu2+ (4 ± 1 %). These results suggest that [64Cu][CuI(BCS)2]3- could be used for detecting high-redox-potential ROS such as hydroxyl radical and lipid peroxide with high selectivity. The cellular uptake values of [64Cu][CuI(BCS)2]3- in the control, IKE, and Fer-1 group were 42 ± 2, 54 ± 2, and 47 ± 5 %Dose/mg protein (n = 3), respectively, suggesting the ROS specific uptake of [64Cu][CuI(BCS)2]3-. On the other hand, the intact ratio after the incubation of [64Cu][CuI(BCS)2]3- in human plasma was 9 ± 5 %.

CONCLUSION

PET imaging of ROS would be possible by using a copper (I) selective ligand, based on metabolic trapping. Although improvement of the membrane permeability and the stability of copper (I) complexes is required, the present results pave the way for the development of novel 64Cu-labeled complexes for PET imaging of ROS.

Arginine Supplementation in MELAS Syndrome: What Do We Know about the Mechanisms?

MELAS syndrome, characterized by mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes, represents a devastating mitochondrial disease, with the stroke-like episodes being its primary manifestation. Arginine supplementation has been used and recommended as a treatment for these acute attacks; however, insufficient evidence exists to support this treatment for MELAS. The mechanisms underlying the effect of arginine on MELAS pathophysiology remain unclear, although it is hypothesized that arginine could increase nitric oxide availability and, consequently, enhance blood supply to the brain. A more comprehensive understanding of these mechanisms is necessary to improve treatment strategies, such as dose and regimen adjustments; identify which patients could benefit the most; and establish potential markers for follow-up. This review aims to analyze the existing evidence concerning the mechanisms through which arginine supplementation impacts MELAS pathophysiology and provide the current scenario and perspectives for future investigations.

Technetium Nitrido Complexes of Tetradentate Thiosemicarbazones: Kit-Based Radiolabeling, Characterization, and In Vivo Evaluation

Bis(thiosemicarbazone) and pyridylhydrazone-thiosemicarbazone chelators have demonstrated utility in nuclear medicine. In particular, the 64Cu2+ complexes have been extensively developed for hypoxia imaging and molecular imaging of peptide and protein markers of disease. However, the chemistry and application of bis(thiosemicarbazone) and pyridylhydrazone-thiosemicarbazone chelators in combination with 99mTc, the most widely used radionuclide in nuclear medicine, is underexplored. Herein, a series of bis(thiosemicarbazone) and pyridylhydrazone-thiosemicarbazone chelators were radiolabeled with nitrido-technetium-99m in an optimized one-pot synthesis from [99mTc]TcO4-. Optimization of the radiochemical syntheses allowed for production of the complexes in >90% radiochemical conversion with apparent molar activities of 3.3-5 GBq/μmol. Competition experiments demonstrated the excellent stability of the complexes. The nitrido-technetium-99 complexes were synthesized, and the chemical identities were investigated using mass spectrometry, spectroscopy, and density functional theory calculations. Complexation of nitrido-rhenium(V) was achieved with the N4-dialkylated bis(thiosemicarbazones). Planar imaging and ex vivo biodistribution studies of the five 99mTc complexes were conducted on healthy BALB/c mice to determine in vivo behavior. The lipophilic nature of the complexes resulted in uptake of 1.6-5.7% ID g-1 in the brain at 2 min postinjection and retention of 0.4-1.7% ID g-1 at 15 min postinjection. The stability of the complexes and the biodistribution data demonstrate that these chelators are ideal platforms for future production of radiopharmaceutical candidates.

Assessment of hypoxia and oxidative-related changes in a lung-derived brain metastasis model by [64Cu][Cu(ATSM)] PET and proteomic studies

BACKGROUND

Brain metastases (BM) are the most frequent malignant brain tumors. The aim of this study was to characterize the tumor microenvironment (TME) of BM and particularly hypoxia and redox state, known to play a role in tumor growth and treatment resistance with multimodal PET and MRI imaging, immunohistochemical and proteomic approaches in a human lung cancer (H2030-BrM3)-derived BM model in rats.

RESULTS

First, in vitro studies confirmed that H2030-BrM3 cells respond to hypoxia with increasing expression of HIF-1, HIF-2 and their target genes. Proteomic analyses revealed, among expression changes, proteins associated with metabolism, oxidative stress, metal response and hypoxia signaling in particular in cortical BM. [64Cu][Cu(ATSM)] PET revealed a significant uptake by cortical BM (p < 0.01), while no uptake is observed in striatal BM 23 days after tumor implantation. Pimonidazole, HIF-1α, HIF-2α, CA-IX as well as GFAP, CTR1 and DMT1 immunostainings are positive in both BM.

CONCLUSION

Overall, [64Cu][Cu(ATSM)] imaging and proteomic results showed the presence of hypoxia and protein expression changes linked to hypoxia and oxidative stress in BM, which are more pronounced in cortical BM compared to striatal BM. Moreover, it emphasized the interest of [64Cu][Cu(ATSM)] PET to characterize TME of BM and depict inter-metastasis heterogeneity that could be useful to guide treatments.

Potential Retinal Biomarkers in Alzheimer's Disease

Alzheimer's disease (AD) represents a major diagnostic challenge, as early detection is crucial for effective intervention. This review examines the diagnostic challenges facing current AD evaluations and explores the emerging field of retinal alterations as early indicators. Recognizing the potential of the retina as a noninvasive window to the brain, we emphasize the importance of identifying retinal biomarkers in the early stages of AD. However, the examination of AD is not without its challenges, as the similarities shared with other retinal diseases introduce complexity in the search for AD-specific markers. In this review, we address the relevance of using the retina for the early diagnosis of AD and the complex challenges associated with the search for AD-specific retinal biomarkers. We provide a comprehensive overview of the current landscape and highlight avenues for progress in AD diagnosis by retinal examination.

Mitochondria and Brain Disease: A Comprehensive Review of Pathological Mechanisms and Therapeutic Opportunities

Mitochondria play a vital role in maintaining cellular energy homeostasis, regulating apoptosis, and controlling redox signaling. Dysfunction of mitochondria has been implicated in the pathogenesis of various brain diseases, including neurodegenerative disorders, stroke, and psychiatric illnesses. This review paper provides a comprehensive overview of the intricate relationship between mitochondria and brain disease, focusing on the underlying pathological mechanisms and exploring potential therapeutic opportunities. The review covers key topics such as mitochondrial DNA mutations, impaired oxidative phosphorylation, mitochondrial dynamics, calcium dysregulation, and reactive oxygen species generation in the context of brain disease. Additionally, it discusses emerging strategies targeting mitochondrial dysfunction, including mitochondrial protective agents, metabolic modulators, and gene therapy approaches. By critically analysing the existing literature and recent advancements, this review aims to enhance our understanding of the multifaceted role of mitochondria in brain disease and shed light on novel therapeutic interventions.

Physical structure of constitutional isomers influences antiproliferation activity of thiosemicarbazone-alkylthiocarbamate copper complexes

A series of hybrid thiosemicarbazone-alkylthiocarbamate copper complexes with similar electronic environments but distinct physical structures have been prepared, characterized, and evaluated for antiproliferation activity. The complexes include the constitutional isomers (1-phenylpropane-1-imine-(O-ethylthiocarbamato)-2-one-(N-methylthiosemicarbazonato))copper(II) (CuL1) and (1-phenylpropane-1-one-(N-methylthiosemicarbazonato)-2-imine-(O-ethylthiocarbamato))copper(II) (CuL2) along with (1-propane-1-imine-(O-ethylthiocarbamato)-2-one-(N-methylthiosemicarbazonato))copper(II) (CuL3). Complexes CuL1 and CuL2 differ in the positions of the pendent thiosemicarbazone (TSC) and alkylthiocarbamate (ATC) moieties on the 1-phenylpropane backbone. Complex CuL3 employs a propane backbone with the TSC in the 2-position as in CuL1. The isomer pair CuL1 and CuL2 have equivalent electronic environments with indistinguishable CuII/I potentials (E1/2 = -0.86 V vs. ferrocenium/ferrocene) and electron paramagnetic resonance (EPR) spectra (g∥ = 2.26, g⊥ = 2.08). The electronic structure of CuL3 has a similar E1/2 of -0.84 V and identical EPR parameters to CuL1, 2. Single crystal X-ray diffraction studies confirm a consistent donor environment with no substantial variation in the CuN or CuS bond distances and angles between the complexes. The antiproliferation activities of the CuL1-3 were evaluated against the lung adenocarcinoma cell line (A549) and nonmalignant lung fibroblast cell line (IMR-90) using the MTT assay. CuL1 had the highest A549 activity (A549EC50 = 0.065 μM) and selectivity (IMR-90EC50/A549EC50 = 20). The constitutional isomer CuL2 displayed decreased A549 activity (0.18 μM) and selectivity (10.6). The complex CuL3 displayed activity (0.009 μM) similar to CuL1 but with a lack of selectivity (1.0). Cellular copper loading determined by ICP-MS was consistent with the activity and selectivity trends. The complexes CuL1-3 did not induce reactive oxygen species (ROS) generation.

Circuits and Biomarkers of the Central Nervous System Relating to Astronaut Performance: Summary Report for a NASA-Sponsored Technical Interchange Meeting

Biomarkers, ranging from molecules to behavior, can be used to identify thresholds beyond which performance of mission tasks may be compromised and could potentially trigger the activation of countermeasures. Identification of homologous brain regions and/or neural circuits related to operational performance may allow for translational studies between species. Three discussion groups were directed to use operationally relevant performance tasks as a driver when identifying biomarkers and brain regions or circuits for selected constructs. Here we summarize small-group discussions in tables of circuits and biomarkers categorized by (a) sensorimotor, (b) behavioral medicine and (c) integrated approaches (e.g., physiological responses). In total, hundreds of biomarkers have been identified and are summarized herein by the respective group leads. We hope the meeting proceedings become a rich resource for NASA's Human Research Program (HRP) and the community of researchers.

Neuroinflammation and Mitochondrial Dysfunction in Parkinson's Disease: Connecting Neuroimaging with Pathophysiology

There is a pressing need for disease-modifying therapies in patients suffering from neurodegenerative diseases, including Parkinson's disease (PD). However, these disorders face unique challenges in clinical trial designs to assess the neuroprotective properties of potential drug candidates. One of these challenges relates to the often unknown individual disease mechanisms that would, however, be relevant for targeted treatment strategies. Neuroinflammation and mitochondrial dysfunction are two proposed pathophysiological hallmarks and are considered to be highly interconnected in PD. Innovative neuroimaging methods can potentially help to gain deeper insights into one's predominant disease mechanisms, can facilitate patient stratification in clinical trials, and could potentially map treatment responses. This review aims to highlight the role of neuroinflammation and mitochondrial dysfunction in patients with PD (PwPD). We will specifically introduce different neuroimaging modalities, their respective technical hurdles and challenges, and their implementation into clinical practice. We will gather preliminary evidence for their potential use in PD research and discuss opportunities for future clinical trials.

Feasibility of Renal Blood Flow Measurement Using 64Cu-ATSM PET/MRI: A Quantitative PET and MRI Study

This study aimed to evaluate the renal blood flow (RBF) in patients with chronic kidney disease (CKD) using ⁶⁴Cu(II)-diacetyl-bis(4-methylthiosemicarbazonate) (⁶⁴Cu-ATSM) for positron emission tomography (PET)/magnetic resonance imaging (MRI). We included five healthy controls (HCs) and ten patients with CKD. The estimated glomerular filtration rate (eGFR) was calculated from the serum creatinine (cr) and cystatin C (cys) levels. The estimated RBF (eRBF) was calculated using the eGFR, hematocrit, and filtration fraction. A single dose of ⁶⁴Cu-ATSM (300-400 MBq) was administered for RBF evaluation, and a 40 min dynamic PET scan was performed with simultaneous arterial spin labeling (ASL) imaging. PET-RBF images were obtained from the dynamic PET images at 3 min after injection using the image-derived input function method. The mean eRBF values calculated from various eGFR values differed significantly between the patients and HCs; both groups also differed significantly in terms of the RBF values (mL/min/100 g) measured using PET (151 ± 20 vs. 124 ± 22, p < 0.05) and ASL-MRI (172 ± 38 vs. 125 ± 30, p < 0.001). The ASL-MRI-RBF was positively correlated with the eRBFcr-cys (r = 0.858, p < 0.001). The PET-RBF was positively correlated with the eRBFcr-cys (r = 0.893, p < 0.001). The ASL-RBF was positively correlated with the PET-RBF (r = 0.849, p < 0.001). ⁶⁴Cu-ATSM PET/MRI demonstrated the reliability of PET-RBF and ASL-RBF by comparing them with eRBF. This is the first study to demonstrate that ⁶⁴Cu-ATSM-PET is useful for assessing the RBF and is well correlated with ASL-MRI.

Amyotrophic lateral sclerosis: a neurodegenerative disorder poised for successful therapeutic translation

Amyotrophic lateral sclerosis (ALS) is a devastating disease caused by degeneration of motor neurons. As with all major neurodegenerative disorders, development of disease-modifying therapies has proven challenging for multiple reasons. Nevertheless, ALS is one of the few neurodegenerative diseases for which disease-modifying therapies are approved. Significant discoveries and advances have been made in ALS preclinical models, genetics, pathology, biomarkers, imaging and clinical readouts over the last 10-15 years. At the same time, novel therapeutic paradigms are being applied in areas of high unmet medical need, including neurodegenerative disorders. These developments have evolved our knowledge base, allowing identification of targeted candidate therapies for ALS with diverse mechanisms of action. In this Review, we discuss how this advanced knowledge, aligned with new approaches, can enable effective translation of therapeutic agents from preclinical studies through to clinical benefit for patients with ALS. We anticipate that this approach in ALS will also positively impact the field of drug discovery for neurodegenerative disorders more broadly.

Neuroimaging in mitochondrial disease

The anatomic complexity of the brain in combination with its high energy demands makes this organ specifically vulnerable to defects of mitochondrial oxidative phosphorylation. Therefore, neurodegeneration is a hallmark of mitochondrial diseases. The nervous system of affected individuals typically shows selective regional vulnerability leading to distinct patterns of tissue damage. A classic example is Leigh syndrome, which causes symmetric alterations of basal ganglia and brain stem. Leigh syndrome can be caused by different genetic defects (>75 known disease genes) with variable disease onset ranging from infancy to adulthood. Other mitochondrial diseases are characterized by focal brain lesions, which is a core feature of MELAS syndrome (mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes). Apart from gray matter, also white matter can be affected by mitochondrial dysfunction. White matter lesions vary depending on the underlying genetic defect and may progress into cystic cavities. In view of the recognizable patterns of brain damage in mitochondrial diseases, neuroimaging techniques play a key role in diagnostic work-up. In the clinical setting, magnetic resonance imaging (MRI) and MR spectroscopy (MRS) are the mainstay of diagnostic work-up. Apart from visualization of brain anatomy, MRS allows the detection of metabolites such as lactate, which is of specific interest in the context of mitochondrial dysfunction. However, it is important to note that findings like symmetric basal ganglia lesions on MRI or a lactate peak on MRS are not specific, and that there is a broad range of disorders that can mimic mitochondrial diseases on neuroimaging. In this chapter, we will review the spectrum of neuroimaging findings in mitochondrial diseases and discuss important differential diagnoses. Moreover, we will give an outlook on novel biomedical imaging tools that may provide interesting insights into mitochondrial disease pathophysiology.

Oxidative stress in multiple sclerosis-Emerging imaging techniques

While conventional magnetic resonance imaging (MRI) is central to the evaluation of patients with multiple sclerosis, its role in detecting the pathophysiology underlying neurodegeneration is more limited. One of the common outcome measures for progressive multiple sclerosis trials, atrophy on brain MRI, is non-specific and reflects end-stage changes after considerable neurodegeneration has occurred. Identifying biomarkers that identify processes underlying neurodegeneration before it is irreversible and that reflect relevant neurodegenerative pathophysiology is an area of significant need. Accumulating evidence suggests that oxidative stress plays a major role in the pathogenesis of multiple neurodegenerative diseases, including multiple sclerosis. Imaging markers related to inflammation, myelination, and neuronal integrity have been areas of advancement in recent years but oxidative stress has remained an area of unrealized potential. In this article we will begin by reviewing the role of oxidative stress in the pathogenesis of multiple sclerosis. Chronic inflammation appears to be directly related to the increased production of reactive oxygen species and the effects of subsequent oxidative stress appear to be amplified by aging and accumulating disease. We will then discuss techniques in development used in the assessment of MS as well as other models of neurodegenerative disease in which oxidative stress is implicated. Multiple blood and CSF markers of oxidative stress have been evaluated in subjects with MS, but non-invasive imaging offers major upside in that it provides real-time assessment within the brain.

Rat Group IIA Secreted Phospholipase A2 Binds to Cytochrome c Oxidase and Inhibits Its Activity: A Possible Episode in the Development of Alzheimer's Disease

Alzheimer's disease (AD), a progressive form of dementia, is characterized by the increased expression of secreted phospholipase A₂ group IIA (GIIA) in the affected tissue and the dysfunction of neuronal mitochondria, similar to that induced by an orthologous GIIA from snake venom, β-neurotoxic ammodytoxin (Atx), in the motor neurons. To advance our knowledge about the role of GIIA in AD, we studied the effect of rat GIIA on the neuronal mitochondria and compared it with that of the Atx. We produced recombinant rat GIIA (rGIIA) and its enzymatically inactive mutant, rGIIA(D49S), and demonstrated that they interact with the subunit II of cytochrome c oxidase (CCOX-II) as Atx. rGIIA and rGIIA(D49S) bound to this essential constituent of the respiratory chain complex with an approximately 100-fold lower affinity than Atx; nevertheless, both rGIIA molecules potently inhibited the CCOX activity in the isolated rat mitochondria. Like Atx, rGIIA was able to reach the mitochondria in the PC12 cells from the extracellular space, independent of its enzymatic activity. Consistently, the inhibition of the CCOX activity in the intact PC12 cells and in the rat's brain tissue sections was clearly demonstrated using rGIIA(D49S). Our results show that the effects of mammalian and snake venom β-neurotoxic GIIA on the neuronal mitochondria have similar molecular backgrounds. They suggest that the elevated extracellular concentration of GIIA in the AD tissue drives the translocation of this enzyme into local neurons and their mitochondria to inhibit the activity of the CCOX in the respiratory chain. Consequently, the process of oxidative phosphorylation in the neurons is attenuated, eventually leading to their degeneration. Atx was thus revealed as a valuable molecular tool for further investigations of the role of GIIA in AD.

Resveratrol: A potential therapeutic natural polyphenol for neurodegenerative diseases associated with mitochondrial dysfunction

Most polyphenols can cross blood-brain barrier, therefore, they are widely utilized in the treatment of various neurodegenerative diseases (ND). Resveratrol, a natural polyphenol contained in blueberry, grapes, mulberry, etc., is well documented to exhibit potent neuroprotective activity against different ND by mitochondria modulation approach. Mitochondrial function impairment is the most common etiology and pathological process in various neurodegenerative disorders, viz. Alzheimer’s disease, Parkinson’s disease, Huntington’s disease and amyotrophic lateral sclerosis. Nowadays these ND associated with mitochondrial dysfunction have become a major threat to public health as well as health care systems in terms of financial burden. Currently available therapies for ND are limited to symptomatic cures and have inevitable toxic effects. Therefore, there is a strict requirement for a safe and highly effective drug treatment developed from natural compounds. The current review provides updated information about the potential of resveratrol to target mitochondria in the treatment of ND.

Ginsenoside Rg1 Ameliorates Acute Renal Ischemia/Reperfusion Injury via Upregulating AMPKα1 Expression

Acute renal ischemia/reperfusion (I/R) injury often occurs during kidney transplantation and other kidney surgeries, and the molecular mechanism involves oxidative stress. We hypothesized that ginsenoside Rg1 (Rg1), a saponin derived from ginseng, would protect the renal tissue against acute renal I/R injury by upregulating 5' adenosine monophosphate-activated protein kinase α1 (AMPKα1) expression and inhibiting oxidative stress. The models of acute anoxia/reoxygenation (A/R) damage in normal rat kidney epithelial cell lines (NRK-52E) and acute renal I/R injury in mice were constructed. The results revealed that pretreatment with 25 μM Rg1 significantly increased NRK-52E viability, decreased lactate dehydrogenase (LDH) activity and apoptosis, suppressed reactive oxygen species generation and oxidative stress, stabilized mitochondrial membrane potential and reduced mitochondria permeability transition pore openness, decreased adenosine monophosphate/adenosine triphosphate ratio, and upregulated the expression of AMPKα1, cytochrome b-c1 complex subunit 2, NADH dehydrogenase (ubiquinone) 1 beta subcomplex subunit 8, and B-cell lymphoma 2, while downregulating BCL2-associated X protein expression. The effects of Rg1 pretreatment were similar to those of pAD/Flag-AMPKα1. After acute renal I/R injury, serum creatinine, blood urea nitrogen, LDH activity, and oxidative stress in renal tissue significantly increased. Rg1 pretreatment upregulated AMPKα1 expression, which protects against acute renal I/R injury by maintaining renal function homeostasis, inhibiting oxidative stress, and reducing apoptosis. Compound C, a specific inhibitor of AMPK, reversed the effects of Rg1. In summary, Rg1 pretreatment upregulated AMPKα1 expression, inhibited oxidative stress, maintained mitochondrial function, improved energy metabolism, reduced apoptosis, and ultimately protected renal tissue against acute renal I/R injury.

Hexadentate technetium-99m bis(thiosemicarbazonato) complexes: synthesis, characterisation and biodistribution

The syntheses of non-oxido/non-nitrido bis(thiosemicarbazonato)technetium(V) complexes featuring a series of alkyl and ether substituents is presented. The bis(thiosemicarbazones) were radiolabelled with technetium-99m using an optimised one-pot synthesis from [^99mTc][TcO₄]^-. Mass spectrometry and computational chemistry data suggested a distorted trigonal prismatic coordination environment for the bis(thiosemicarbazonato)technetium(V) complexes by way of a bis(thiosemicarbazone)technetium(V)-oxido intermediate complex. The lipophilicities of the complexes were estimated using distribution ratios and three of the new complexes were investigated in mice using kinetic planar imaging and ex vivo biodistribution experiments and were compared to [^99mTc][TcO₄]^-. Modification of the technetium complexes with various lipophilic functional groups altered the biodistributions of the complexes in mice despite evidence suggesting limited stability of the complexes to biologically relevant conditions. The most hydrophilic complex had higher uptake in the kidneys compared to the most lipophilic, which had higher liver uptake, suggesting modification of the excretion pathways.

Neuroimaging Methods to Map In Vivo Changes of OXPHOS and Oxidative Stress in Neurodegenerative Disorders

Mitochondrial dysfunction is a pathophysiological hallmark of most neurodegenerative diseases. Several clinical trials targeting mitochondrial dysfunction have been performed with conflicting results. Reliable biomarkers of mitochondrial dysfunction in vivo are thus needed to optimize future clinical trial designs. This narrative review highlights various neuroimaging methods to probe mitochondrial dysfunction. We provide a general overview of the current biological understanding of mitochondrial dysfunction in degenerative brain disorders and how distinct neuroimaging methods can be employed to map disease-related changes. The reviewed methodological spectrum includes positron emission tomography, magnetic resonance, magnetic resonance spectroscopy, and near-infrared spectroscopy imaging, and how these methods can be applied to study alterations in oxidative phosphorylation and oxidative stress. We highlight the advantages and shortcomings of the different neuroimaging methods and discuss the necessary steps to use these for future research. This review stresses the importance of neuroimaging methods to gain deepened insights into mitochondrial dysfunction in vivo, its role as a critical disease mechanism in neurodegenerative diseases, the applicability for patient stratification in interventional trials, and the quantification of individual treatment responses. The in vivo assessment of mitochondrial dysfunction is a crucial prerequisite for providing individualized treatments for neurodegenerative disorders.

Cerebral Oxidative Stress in Early Alzheimer’s Disease Evaluated by 64Cu-ATSM PET/MRI: A Preliminary Study

Oxidative stress imaging using diacetyl-bis (N⁴-methylthiosemicarbazone) (Cu-ATSM) was applied to the evaluation of patients with early Alzheimer’s disease (eAD). Ten eAD patients (72 ± 9 years) and 10 age-matched healthy controls (HCs) (73 ± 9 years) participated in this study. They underwent dynamic PET/MRI using ¹¹C-PiB and ⁶⁴Cu-ATSM with multiple MRI sequences. To evaluate cerebral oxidative stress, three parameters of ⁶⁴Cu-ATSM PET were compared: standardized uptake value (SUV), tracer influx rate (K_in), and a rate constant k₃. The input functions were estimated by the image-derived input function method. The relative differences were analyzed by statistical parametric mapping (SPM) using SUV and K_in images. All eAD patients had positive and HC subjects had negative PiB accumulation, and MMSE scores were significantly different between them. The ⁶⁴Cu-ATSM accumulation tended to be higher in eAD than in HCs for both SUV and K_in. When comparing absolute values, eAD patients had a greater K_in in the posterior cingulate cortex and a greater k₃ in the hippocampus compared with lobar cortical values of HCs. In SPM analysis, eAD had an increased left operculum and decreased bilateral hippocampus and anterior cingulate cortex compared to HCs. ⁶⁴Cu-ATSM PET/MRI and tracer kinetic analysis elucidated cerebral oxidative stress in the eAD patients, particularly in the cingulate cortex and hippocampus.

Role of Oxidative Stress in Ocular Diseases Associated with Retinal Ganglion Cells Degeneration

Ocular diseases associated with retinal ganglion cell (RGC) degeneration is the most common neurodegenerative disorder that causes irreversible blindness worldwide. It is characterized by visual field defects and progressive optic nerve atrophy. The underlying pathophysiology and mechanisms of RGC degeneration in several ocular diseases remain largely unknown. RGCs are a population of central nervous system neurons, with their soma located in the retina and long axons that extend through the optic nerve to form distal terminals and connections in the brain. Because of this unique cytoarchitecture and highly compartmentalized energy demand, RGCs are highly mitochondrial-dependent for adenosine triphosphate (ATP) production. Recently, oxidative stress and mitochondrial dysfunction have been found to be the principal mechanisms in RGC degeneration as well as in other neurodegenerative disorders. Here, we review the role of oxidative stress in several ocular diseases associated with RGC degenerations, including glaucoma, hereditary optic atrophy, inflammatory optic neuritis, ischemic optic neuropathy, traumatic optic neuropathy, and drug toxicity. We also review experimental approaches using cell and animal models for research on the underlying mechanisms of RGC degeneration. Lastly, we discuss the application of antioxidants as a potential future therapy for the ocular diseases associated with RGC degenerations.

Mitochondrial dysfunction, oxidative stress, neuroinflammation, and metabolic alterations in the progression of Alzheimer's disease: A meta-analysis of in vivo magnetic resonance spectroscopy studies

Accumulating evidence demonstrates that metabolic changes in the brain associated with neuroinflammation, oxidative stress, and mitochondrial dysfunction play an important role in the pathophysiology of mild cognitive impairment (MCI) and Alzheimer's disease (AD). However, the neural signatures associated with these metabolic alterations and underlying molecular mechanisms are still elusive. Accordingly, we reviewed the literature on in vivo human brain ¹H and ³¹P-MRS studies and use meta-analyses to identify patterns of brain metabolic alterations in MCI and AD. 40 and 39 studies on MCI and AD, respectively, were classified according to brain regions. Our results indicate decreased N-acetyl aspartate and creatine but increased myo-inositol levels in both MCI and AD, decreased glutathione level in MCI as well as disrupted energy metabolism in AD. In addition, the hippocampus shows the strongest alterations in most of these metabolites. This meta-analysis also illustrates progressive metabolite alterations from MCI to AD. Taken together, it suggests that 1) neuroinflammation and oxidative stress may occur in the early stages of AD, and likely precede neuron loss in its progression; 2) the hippocampus is a sensitive region of interest for early diagnosis and monitoring the response of interventions; 3) targeting bioenergetics associated with neuroinflammation/oxidative stress is a promising approach for treating AD.

Psychological Stress as a Risk Factor for Accelerated Cellular Aging and Cognitive Decline: The Involvement of Microglia-Neuron Crosstalk

The relationship between the central nervous system (CNS) and microglia is lifelong. Microglia originate in the embryonic yolk sac during development and populate the CNS before the blood-brain barrier forms. In the CNS, they constitute a self-renewing population. Although they represent up to 10% of all brain cells, we are only beginning to understand how much brain homeostasis relies on their physiological functions. Often compared to a double-edged sword, microglia hold the potential to exert neuroprotective roles that can also exacerbate neurodegeneration once compromised. Microglia can promote synaptic growth in addition to eliminating synapses that are less active. Synaptic loss, which is considered one of the best pathological correlates of cognitive decline, is a distinctive feature of major depressive disorder (MDD) and cognitive aging. Long-term psychological stress accelerates cellular aging and predisposes to various diseases, including MDD, and cognitive decline. Among the underlying mechanisms, stress-induced neuroinflammation alters microglial interactions with the surrounding parenchymal cells and exacerbates oxidative burden and cellular damage, hence inducing changes in microglia and neurons typical of cognitive aging. Focusing on microglial interactions with neurons and their synapses, this review discusses the disrupted communication between these cells, notably involving fractalkine signaling and the triggering receptor expressed on myeloid cells (TREM). Overall, chronic stress emerges as a key player in cellular aging by altering the microglial sensome, notably via fractalkine signaling deficiency. To study cellular aging, novel positron emission tomography radiotracers for TREM and the purinergic family of receptors show interest for human study.

Imaging Biomarkers for Monitoring the Inflammatory Redox Landscape in the Brain

Inflammation is one key process in driving cellular redox homeostasis toward oxidative stress, which perpetuates inflammation. In the brain, this interplay results in a vicious cycle of cell death, the loss of neurons, and leakage of the blood–brain barrier. Hence, the neuroinflammatory response fuels the development of acute and chronic inflammatory diseases. Interrogation of the interplay between inflammation, oxidative stress, and cell death in neurological tissue in vivo is very challenging. The complexity of the underlying biological process and the fragility of the brain limit our understanding of the cause and the adequate diagnostics of neuroinflammatory diseases. In recent years, advancements in the development of molecular imaging agents addressed this limitation and enabled imaging of biomarkers of neuroinflammation in the brain. Notable redox biomarkers for imaging with positron emission tomography (PET) tracers are the 18 kDa translocator protein (TSPO) and monoamine oxygenase B (MAO–B). These findings and achievements offer the opportunity for novel diagnostic applications and therapeutic strategies. This review summarizes experimental as well as established pharmaceutical and biotechnological tools for imaging the inflammatory redox landscape in the brain, and provides a glimpse into future applications.