Emerging evidence links glial activation, particularly microglia, to Alzheimer's disease (AD) progression. While TSPO PET (positron emission tomography) imaging detects neuroinflammation, its limitations drive interest in alternative targets like the P2X7 receptor. Myelin loss, potentially tied to chronic inflammation, is increasingly recognized as a key hallmark in AD, though the timing and relationship between neuroinflammation and demyelination remain poorly understood. We conducted a longitudinal PET study from 4 to 22 months of age in TgF344-AD rats and wild-type controls to assess neuroinflammation with [18F]JNJ-64413739 (P2X7R) and [18F]DPA-714 (TSPO) only at 22 months, alongside myelin content using [18F]Florbetaben. Diffusion tensor imaging (DTI) was used to study variations on myelin structure in old AD and WT rats. In vitro studies, including autoradiography, immunofluorescence and staining were used to support the in vivo results. [18F]JNJ-64413739 PET showed increased P2X7 receptor expression in AD and control animals over time, while [18F]DPA-714 PET showed significant differences between groups at 22 months. [18F]Florbetaben PET showed different uptake in white matter rich areas between groups with observed demyelination in AD rats at 20 months in the brain stem, supported by diffusional MRI findings. In our study, P2X7R overexpression was attributed to aging rather than genotype effects, and no link was found to the observed demyelination in AD rats. Conversely, increased TSPO neuroinflammation in TgF344-AD rats correlated with myelin loss and the reported cognitive decline in this model. Our results support the use of the TgF344-AD model to study early AD pathology, focusing on neuroinflammation and white matter integrity.

Self-sufficient heterogeneous biocatalysts (ssHBs), in which enzymes and cofactors are coimmobilized on the same support, provide in situ cofactor regeneration and reduce operating costs. However, the underlying mechanisms remain poorly understood. Here, we present a theoretical model for ssHBs consisting of NAD(P)H-dependent dehydrogenases immobilized on porous agarose-based materials with cofactors coimmobilized through electrostatic interactions via a cationic polymer coating. This model links enzyme activity to cofactor-polymer binding thermodynamics and demonstrates that ssHBs obey the Sabatier principle, where maximum catalytic efficiency is achieved at an intermediate binding strength. Adjustment of pH and ionic strength modulates this interaction, and the resulting activity exhibits the predicted volcano plot. Depending on the reaction conditions, electrostatic complexation is influenced, resulting in the formation of a dense, liquid-like phase inside the particles. Our study directly confirms the Sabatier principle in ssHBs and highlights the crucial role of cofactor binding thermodynamics in optimizing biocatalysis for chemical applications.

ABSTRACTBackgroundMultiple sclerosis (MS) is a chronic demyelinating disease characterized by autoimmune attacks on myelin sheaths. Its deleterious effects may be reversed by remyelination, a process that restores the integrity of myelin sheaths and, consequently, neuronal function. However, the functional implications of demyelination and remyelination in MS, as well as the potential impact of therapeutic interventions, remain incompletely understood. We used noninvasive longitudinal resting‐state functional magnetic resonance imaging in a cuprizone murine model of demyelination to investigate these unsolved questions.MethodsThree groups of (n = 6) animals were studied. A control group was fed with standard food for 5 weeks while two treatment groups (cuprizone and clemastine) suffered progressive demyelination by feeding them with 2% cuprizone. At Week 5 (W5), all animals returned to the standard diet and studied for another 5‐week period to compare controls vs spontaneous (cuprizone group) vs clemastine‐aided (clemastine group) remyelination group. Group clemastine was treated with this antihistaminic (oral gavage) during the remyelination period (Weeks 5–10). Anatomical magnetic resonance imaging (T2w‐MRI) and resting state functional MRI (rs‐FMRI) studies were conducted on weeks W0, W2, W5 (maximal demyelination) W7 and W10 (remyelination). MRI images were processed with the FMRIB Software Library, involving seed‐free functional imaging and seed‐based correlation. This study uses the t‐test and the D'Agostino–Pearson normality test to make an assessment.ResultsThe principal findings of our research include: (1) cuprizone‐treated animals suffer an initial phase of elevated connectivity at Week 2 with respect to controls, transitioning to reduced connectivity at Week 5; (2) different temporal trajectories across brain regions, reflecting varying susceptibility to demyelination; (3) while spontaneous remyelination normalizes connectivity in most networks at Week 10 (5 weeks after ceasing cuprizone intoxication), the thalamocortical axis exhibits lasting disruption even 6 months after normalization of diet; and (4) on the contrary, clemastine‐aided remyelination re‐establishes normal thalamocortical connectivity at 6 months after demyelination.ConclusionThis approach provides insights into the dynamic processes of demyelination and remyelination, informing the development of more effective interventions for MS.

Here we use magnetic resonance imaging to study the impact of marathon running on brain structure in humans. We show that the signal for myelin water fraction—a surrogate of myelin content—is substantially reduced upon marathon running in specific brain regions involved in motor coordination and sensory and emotional integration, but recovers within two months. These findings suggest that brain myelin content is temporarily and reversibly diminished by severe exercise, a finding consistent with recent evidence from rodent studies that suggest that myelin lipids may act as glial energy reserves in extreme metabolic conditions. Using magnetic resonance imaging on marathon runners, Ramos-Cabrer, Cabrera-Zubizarreta et al. report that the signal detected as a surrogate of myelin content is significantly reduced after exercise, but fully recovered within two months.

Adenosine A 2 receptors (A 2 ARs) have shown promising therapeutic properties despite their controversial role in modulating stroke outcome. However, the temporal evolution of cerebral A 2 ARs density after cerebral ischemia and its subsequent neuroinflammatory response have been scarcely explored. In this study, the expression of A 2 ARs after transient middle cerebral artery occlusion (MCAO) was evaluated in rats by positron emission tomography (PET) with [ 11 C]SCH442416 and immunohistochemistry (IHC). In addition, the role of A 2 ARs in stroke inflammation with pharmacological modulation was assessed with magnetic resonance imaging (MRI), PET imaging with [ 18 F]DPA-714 (TSPO), IHC, western-blot, and autoradiography. After cerebral ischemia, [ 11 C]SCH442416 and IHC revealed neural expression of A 2 ARs in the striatum in healthy brains, followed by a binding decrease at day 1 and a subsequent significant increase at day 3 after ischemia in microglia and infiltrated leukocytes. Furthermore, activation of A 2 ARs with the agonist CGS-21680 resulted in a reduction in stroke volume, along with an increase in TSPO expression in immune cells in the striatum. Our results provide novel evidence on A 2 ARs density dynamics after cerebral ischemia that might guide the therapeutic management of stroke by modulating adenosine receptors.

The energy cost of neuronal activity is mainly sustained by glucose 1,2 . However, in an apparent paradox, neurons only weakly metabolize glucose through glycolysis 3,4,5,6 , a circumstance that can be accounted for by the constant degradation of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (Pfkfb3) 3,7,8 , a key glycolysis-promoting enzyme. To evaluate the in vivo physiological significance of this hypo-glycolytic metabolism, here we genetically engineered mice with their neurons transformed into active glycolytic cells through Pfkfb3 expression. In vivo molecular, biochemical, and metabolic flux analyses of these neurons revealed an accumulation of anomalous mitochondria, complex I disassembly, bioenergetic deficiency and mitochondrial redox stress. Notably, glycolysis-mediated NAD + reduction impaired sirtuin-dependent autophagy. Furthermore, these mice displayed cognitive decline and a metabolic syndrome that was mimicked by confining Pfkfb3 expression to hypothalamic neurons. Neuron-specific genetic ablation of mitochondrial redox stress corrected these alterations. Thus, the weak glycolytic nature of neurons is required to sustain higher-order organismal functions.

Hyperglycemia has been linked to worsening outcomes after subarachnoid hemorrhage (SAH). Nevertheless, the mechanisms involved in the pathogenesis of SAH have been scarcely evaluated so far. The role of hyperglycemia was assessed in an experimental model of SAH by T2 weighted, dynamic contrast-enhanced magnetic resonance imaging (T2W and DCE-MRI), [18F]BR-351 PET imaging and immunohistochemistry. Measures included the volume of bleeding, the extent of cerebral infarction and brain edema, blood brain barrier disruption (BBBd), neutrophil infiltration and matrix metalloprotease (MMP) activation. The neurofunctional outcome, neurodegeneration and myelinization were also investigated. The induction of hyperglycemia increased mortality, the size of the ischemic lesion, brain edema, neurodegeneration and worsened neurological outcome during the first 3 days after SAH in rats. In addition, these results show for the first time the exacerbating effect of hyperglycemia on in vivo MMP activation, Intercellular Adhesion Molecule 1 (ICAM-1) expression and neutrophil infiltration together with increased BBBd, bleeding volume and fibrinogen accumulation at days 1 and 3 after SAH. Notably, these data provide valuable insight into the detrimental effect of hyperglycemia on early BBB damage mediated by neutrophil infiltration and MMP activation that could explain the worse prognosis in SAH.

Magnetic resonance imaging (MRI) is a valuable tool for studying brain structure and function in animal and clinical studies. With the growth of public MRI repositories, access to data has finally become easier. However, filtering large datasets for potential poor-quality outliers can be a challenge. We present AIDAqc, a machine-learning-assisted automated Python-based command-line tool for small animal MRI quality assessment. Quality control features include signal-to-noise ratio (SNR), temporal SNR, and motion. All features are automatically calculated and no regions of interest are needed. Automated outlier detection for a given dataset combines the interquartile range and the machine-learning methods one-class support vector machine, isolation forest, local outlier factor, and elliptic envelope. To evaluate the reliability of individual quality control metrics, a simulation of noise (Gaussian, salt and pepper, speckle) and motion was performed. In outlier detection, single scans with induced artifacts were successfully identified by AIDAqc. AIDAqc was challenged in a large heterogeneous dataset collected from 19 international laboratories, including data from mice, rats, rabbits, hamsters, and gerbils, obtained with different hardware and at different field strengths. The results show that the manual inter-rater agreement (mean Fleiss Kappa score 0.17) is low when identifying poor-quality data. A direct comparison of AIDAqc results, therefore, showed only low-to-moderate concordance. In a manual post hoc validation of AIDAqc output, precision was high (>70%). The outlier data can have a significant impact on further postprocessing, as shown in representative functional and structural connectivity analysis. In summary, this pipeline optimized for small animal MRI provides researchers with a valuable tool to efficiently and effectively assess the quality of their MRI data, which is essential for improved reliability and reproducibility.

Compulsivity is considered a transdiagnostic dimension in obsessive-compulsive and related disorders, characterized by heterogeneous cognitive and behavioral phenotypes associated with abnormalities in cortico-striatal-thalamic-cortical circuitry. The present study investigated the structural morphology of white and gray matter in rats selected for low- (LD) and high- (HD) compulsive drinking behavior on a schedule-induced polydipsia (SIP) task. Regional brain morphology was assessed using ex-vivo high-resolution magnetic resonance imaging (MRI). Voxel-based morphometry of segmented MRI images revealed larger white matter volumes in anterior commissure and corpus callosum of HD rats compared with LD rats. HD rats also showed significantly larger regional volumes of dorsolateral orbitofrontal cortex, striatum, amygdala, hippocampus, midbrain, sub-thalamic nucleus, and cerebellum. By contrast, the medial prefrontal cortex was significantly smaller in HD rats compared with LD rats with no significant group differences in whole brain, ventricular, or cerebrospinal fluid volumes. These findings show that limbic cortico-basal ganglia structures implicated in impulse control disorders are distinct in rats that are vulnerable to develop compulsive behavior. Such abnormalities may be relevant to the etiology of compulsive disorders in humans.

AbstractRecent evidence suggests that myelin lipids may act as glial energy reserves when glucose is lacking, a hypothesis yet to be solidly proven. Hereby, we examined the effects of running a marathon on the myelin content by MRI. Our findings show that marathon runners undergo widespread robust myelin decrease at completion of the effort. This reduction involves white and gray matter, and includes primary motor and sensory cortical areas and pathways, as well as the entire corpus callosum and internal capsule. Notably, myelin levels partially recover within two weeks after the marathon. These results reveal that myelin use and replenishment is an unprecedented form of metabolic plasticity aimed to maintain brain function during extreme conditions.One-Sentence SummaryBrain myelin usage during strenuous exercise and recovery thereafter

Cyanidin 3-O-glucoside (CND) is a frequently-used anthocyanin that has excellent antioxidant properties but a limited bioavailability in bloodstream. Complexation of CND with alginate can improve its therapeutic outcome. Here we have studied the complexation of CND with alginate under a range of pH values from 2.5 to 5. CND is positively charged at low pH, and becomes neutral, and then negatively charged as pH increases. CND/alginate complexation was studied by dynamic light scattering, transmission electron microscopy, small angle X-ray scattering, STEM, UV-Vis spectroscopy and circular dichroism (CD). CND/alginate complexes at pH 4.0 and 5.0 form chiral fibres with a fractal structure. At these pH values, CD spectra show very intense bands, which are inverted compared with free CND. Complexation at lower pH results in disordered polymer structures and CD spectra show the same features as for CND in solution. Molecular dynamics simulations suggest the formation of parallel CND dimers through complexation with alginate at pH 3.0, while at pH 4.0 CND dimers form in a cross like arrangement

Abstract Recent evidence suggests that myelin lipids may act as glial energy reserves when glucose is lacking, a hypothesis yet to be solidly proven. Hereby, we examined the effects of running a marathon on myelin content by MRI. Our findings show that marathon runners undergo widespread robust myelin decrease at completion of the effort. This reduction involves white and gray matter and includes primary motor and sensory cortical areas and pathways, as well as the entire corpus callosum and internal capsule. Notably, myelin levels partially recover within two weeks after the marathon. These results reveal that myelin use and replenishment is an unprecedented form of metabolic plasticity aimed at maintaining brain function during extreme conditions.

The development of imaging technologies allowing noninvasive observation through solid bodies has represented a breakthrough in medical diagnosis, facilitating the comprehension of biomolecular events underlying disease and the development of more efficient therapeutic approaches. Some of the traditional limitations of these techniques are nowadays fading away thanks to the combination of imaging with nanotechnology, allowing the development of novel functional biomaterials that increase the sensitivity of detection, enable sensitivity to specific targets, and facilitate the combination of therapeutic and diagnostic functions (theragnosis) with molecular platforms functioning simultaneously as imaging probes and drug delivery carriers. The design of such functional biomaterials requires a comprehensive understanding of the principles that govern the generation of signal and modulation of contrast for a given imaging modality to exploit its capabilities to the maximal level. In this sense, magnetic resonance imaging (MRI) is a technique that presents a complex relationship between the detected signal and the physical-chemical properties of its sourcing matter, allowing the generation of multiple image contrasts. Thus, while magnetic resonance imaging is a highly versatile imaging modality, it requires specific knowledge of its physical principles to take advantage of all of its possibilities. This work reviews the origin of the image signal and contrast in MRI and the concepts of relaxometry and MRI contrast agents.

Ex vivo models for the noninvasive study of myelin-related diseases represent an essential tool to understand the mechanisms of diseases and develop therapies against them. Herein, we assessed the potential of multimodal imaging traceable myelin-targeting liposomes to quantify myelin in organotypic cultures. Methods: MRI testing was used to image mouse cerebellar tissue sections and organotypic cultures. Demyelination was induced by lysolecithin treatment. Myelin-targeting liposomes were synthetized and characterized, and their capacity to quantify myelin was tested by fluorescence imaging. Results: Imaging of freshly excised tissue sections ranging from 300 µm to 1 mm in thickness was achieved with good contrast between white (WM) and gray matter (GM) using T2w MRI. The typical loss of stiffness, WM structures, and thickness of organotypic cultures required the use of diffusion-weighted methods. Designed myelin-targeting liposomes allowed for semiquantitative detection by fluorescence, but the specificity for myelin was not consistent between assays due to the unspecific binding of liposomes. Conclusions: With respect to the sensitivity, imaging of brain tissue sections and organotypic cultures by MRI is feasible, and myelin-targeting nanosystems are a promising solution to quantify myelin ex vivo. With respect to specificity, fine tuning of the probe is required. Lipid-based systems may not be suitable for this goal, due to unspecific binding to tissues.

Fluorinated nanoparticles have increasing applications, but they are still challenging to prepare, especially in the case of water-soluble fluorinated nanoparticles. Herein, a fluorine labeling strategy is presented that is based on the conjugation of custom-made small fluorinated building blocks, obtained by simple synthetic transformations, with carboxylated gold nanoparticles through a convenient phase-transfer process. The synthesis of four fluorinated building blocks with different chemical shifts in 19F nuclear magnetic resonance and varied functionalities is reported, along with their conjugation onto nanoparticles. Fluorinated nanoparticles of small core size obtained by this conjugation methodology and by direct synthesis presented high transverse relaxation times (T2) ranging from 518 to 1030 ms, and a large number of equivalent fluorine atoms per nanoparticle (340-1260 fluorine atoms), which made them potential candidates for 19F magnetic resonance related applications. Finally, nontargeted fluorinated nanoparticles were probed by performing in vivo 19F magnetic resonance spectroscopy (19F MRS) in mice. Nanoparticles were detected at both 1 and 2 h after being injected. 19F MRI images were also acquired after either intravenous or subcutaneous injection. Their fate was studied by analyzing the gold content in tissues by ICP-MS. Thus, the present work provides a general fluorination strategy for nanoparticles and shows the potential use of small fluorinated nanoparticles in magnetic-resonance-related applications.