Background:Glioblastoma multiforme (GBM) is an aggressive brain tumor with abysmal prognosis because cancer cell growth in the tumor microenvironment (TME) is orchestrated by complex interplay between aerobic glycolysis (AG) and endothelial dysfunction (ED). AG acidifies extracellular pH (pHe) to promote tumor invasion and suppress immune response, whereas ED leads to leaky blood vessels which hampers perfusion and stimulates hypoxia. Since metabolism generates heat and perfusion removes heat, we hypothesized that temperature could reflect both metabolic and vascular reprogramming in the TME mediated by AG and ED. Methods:We used multiple magnetic resonance methods and bioheat modeling to dissect temperature contributions from metabolic and vascular sources in rat gliomas. Results:Upregulated AG in the TME results from enhanced glycolysis (∼4.2× higher) and reduced glucose oxidation (∼4.8× lower), which leads to more acidic pHe (6.9 ± 0.1 vs 7.3 ± 0.1). Since TME is hypoperfused (∼40% lower) and glycolysis is less exothermic compared to glucose oxidation, simulations predict a cooler TME as in vivo measurements clearly demonstrate (0.5-1.5 °C). Moreover, temperature and pHe are correlated both inside and outside the TME for untreated and treated rats (r > 0.6). Conclusions:Since TME is more glycolytic, acidic, hypoperfused, and cooler than neighboring milieu, thermal mapping can represent combined effects of AG and ED for early GBM detection and therapy optimization.

Extracellular acidosis is a biologically important feature of the tumor microenvironment in the liver, promoting immune evasion, angiogenesis, and resistance to therapy, and representing a mechanistically important and potentially targetable axis in liver cancer. Imaging extracellular pH (pHe) at high resolution is needed to better understand the immuno-metabolic interplay, especially at the transition regions between the tumor core, tumor margin, and background liver, which is critical for any pharmacological or image-guided intervention. Yet, there is a paucity of imaging techniques capable of providing pHe mapping at high resolution. Here, we demonstrate high-resolution pHe imaging in a mouse Hepa1-6 liver tumor model using 1H Biosensor Imaging of Redundant Deviation in Shifts (BIRDS) with REduced Spherical Encoding with GAussian Weighting (RESEGAW). Eight tumor-bearing C57BL/6J mice were used to demonstrate pHe imaging with RESEGAW using the macrocyclic agent TmDOTP5- at 0.6 mm isotropic resolution on a 9.4 T scanner, which was validated using 31P-MRSI with 3-aminopropylphosphonate (3-APP). pHe imaging with 1H-BIRDS-RESEGAW consistently showed acidic tumor regions (pHe = 6.77 ± 0.14) relative to adjacent normal liver (pHe = 7.14 ± 0.07). Mean pHe values measured by 31P-MRSI with 3-APP and 1H-BIRDS-RESEGAW with TmDOTP5- show no significant differences in tumors (pHe = 6.81 ± 0.13) and normal liver (pHe = 7.14 ± 0.06). Voxelwise comparison after co-registration of 31P-MRSI with 3-APP to 1H-BIRDS-RESEGAW using Bland-Altman analysis demonstrated excellent agreement between the two methods, with minimal mean bias (-0.005 pH units) and variance of less than 0.1 pH units. These results demonstrate the feasibility and quantitative reliability of 1H-BIRDS-RESEGAW for imaging extracellular acidosis in liver tumors at submillimeter resolution, establishing a technical foundation for studying the immuno-metabolic interplay in liver cancer and its response to therapy.

Background: Alzheimer’s disease (AD) is a progressive neurodegenerative disorder marked by memory loss and cognitive decline, reflecting widespread brain dysfunction across multiple neural systems. Early detection of pathological changes is critical for enabling timely intervention, improved management, and better therapeutic outcomes. Methods: Using non-transgenic AD rats (Samaritan) and sham rats (Long–Evans), we explored structural and functional differences with multimodal MRI and multi-unit activity (MUA). Results: Diffusion tensor imaging (DTI) revealed no significant changes in mean diffusivity of water, but AD-related microstructural alterations of fractional anisotropy were confined to subcortical regions with cortical areas and white matter tracts remaining intact. We used functional MRI (fMRI) with blood oxygenation level-dependent (BOLD) contrast in rest-state (R-fMRI) and task-based (T-fMRI) paradigms. R-fMRI revealed much stronger functional connectivity in subcortical vs. cortical areas in AD rats, implicating AD-related functional changes in subcortical areas in agreement with DTI data. T-fMRI with sensory stimulation revealed reproducible fMRI responses in both groups; however, AD rats exhibited reduced BOLD response amplitude and spatial activation extent, which was accompanied by attenuated stimulus-evoked MUA responses. These suggest that attenuated evoked BOLD response reflects diminished neuronal activity in AD, rather than impaired neurovascular and/or neurometabolic coupling. Conclusions: Together these findings suggest that AD-induced anatomical and functional changes in subcortical areas are related to altered cortical responses, highlighting multimodal MRI as a sensitive tool for early AD-related brain changes.

Background & Aims: Increasing enthusiasm around integrating locoregional therapy with systemic immunotherapy in primary liver cancer underscores the need for non-invasive imaging biomarkers. In this study, we aimed to establish advanced molecular MRI tools for monitoring T-cell responses to cryoablation in murine models, distinguishing between immunologically "hot" and "cold" hepatocellular carcinoma (HCC). Methods: Immunocompetent 7-10-week-old C57BL/6J and BALB/cJ mice (n = 18 each) received carbon tetrachloride for 12 weeks to induce cirrhosis. Intrinsically immunogenic Hepa1-6 ("hot") and non-immunogenic TiB75 ("cold") cells were orthotopically implanted into C57BL/6 or BALB/c mice, respectively, to generate focal HCC lesions. After one week, animals were randomly assigned to (A) partial cryoablation (pCryo) (1.2 mm cryoprobe, -40 degrees C) or (B) no treatment (n = 8 per group and tumor type). Gadolinium 160 (Gd-160)-labeled CD8(+) antibody was administered intravenously either 1 week after tumor induction (control) or 1-week post (pCryo) (treatment). T1-weighted MRI scans were performed using a 9.4 T MRI scanner. Radiological-pathological correlation included imaging mass cytometry and immunohistochemistry. Results: pCryo-treated Hepa1-6 tumors displayed peritumoral ring enhancement on T1-weighted MRI with Gd-160-CD8, correlating with imaging mass cytometry signal patterns. Untreated Hepa1-6 tumors lacked such enhancement. Radiological-pathological correlation confirmed significantly increased tumor-infiltrating CD8(+) T lymphocytes in pCryo Hepa1-6 tumors compared with untreated tumors (p <0.001), and a stronger local response compared with systemic lymph nodes (p = 0.0415). Increased T-lymphocyte infiltration was not observed in TiB75 tumors, as indicated by MRI and histopathology. Conclusion: pCryo induced increased T-cell infiltration in Hepa1-6 tumors compared to TiB75 tumors. T1-weighted MRI, following Gd-160-CD8 antibody administration, reproducibly detected the ablation-induced changes. These findings encourage further investigation of MRI-based molecular imaging biomarkers to assess immune responses to local tumor therapies. (c) 2024 The Authors. Published by Elsevier B.V. on behalf of European Association for the Study of the Liver (EASL). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Leukemia Inhibitory Factor (LIF) is an injury-induced cytokine that peaks 48 hours after a traumatic brain injury (TBI). Juvenile LIF haplodeficient mice exhibit desynchronized glial responses, increased neurodegeneration, decreased axonal conductivity and behavioral deficits after a concussive head injury. Given the necessity of LIF during the acute recovery phase after injury, we hypothesized that intranasal LIF (IN-LIF) treatment would prevent neurodegeneration when administered during the chronic recovery period from a mild TBI (mTBI). Young adult male CD1 mice were subjected to a midline, closed-head frontal cortex injury using a flat metal impactor with a 3mm tip to induce a mTBI. In the 6-8 weeks post-mTBI, known to precede axonal atrophy in this mTBI model, two doses of 40 ng and 100 ng of LIF were administered twice daily, 5 days/week for two consecutive weeks. Sensorimotor functions were assessed at 4 and 8 weeks post mTBI, followed by ex-vivo brain magnetic resonance imaging at 9.4T and histopathology. mTBI mice showed sensorimotor deficits at 4 weeks, which worsened by 8 weeks post-injury. IN-LIF treatment prevented the progressive sensorimotor loss seen in the vehicle-treated controls. Increased mean diffusivity and decreased fractional anisotropy were observed in the corpus callosum and prefrontal cortex of mTBI brains. In a dose-dependent manner, IN-LIF prevented the mTBI-induced mean diffusivity increase and fractional anisotropy decrease. Histologically, there was significantly less astrogliosis, microgliosis and axonal injury in the IN-LIF treated mice vs. controls. These results support the therapeutic potential of IN-LIF to reduce delayed neurodegeneration and improve neurological outcomes after mTBIs.

Solid tumors, including hepatocellular carcinoma (HCC), arises most often in cirrhotic livers, where immune exclusion and metabolic reprogramming drive extracellular acidosis (the "Warburg effect") and create an immunosuppressive tumor microenvironment (TME). This study applied a non-invasive MR Spectroscopic Imaging method called Biosensor Imaging of Redundant Deviation in Shifts (BIRDS) to quantify extracellular pH (pHe) dynamics in a mouse model of cirrhosis-associated HCC. Forty-two Mdr2-/- mice received chronic carbon tetrachloride (CCl4), inducing cirrhosis and HCC, confirmed by contrast-enhanced MR and histology. BIRDS revealed significantly lower tumor pHe in untreated tumors (6.78 ± 0.3) compared with liver parenchyma (7.17 ± 0.02). Cryoablation induced tumor pHe normalization (7.08 ± 0.03), coinciding with downregulation of metabolic markers and increased T-cell and macrophage infiltration. These results demonstrate that BIRDS enables non-invasive monitoring of the metabolic and immunologic response to cryoablation in HCC within cirrhotic livers. Cryoablation-induced re-normalization of tumor acidity, coupled with enhanced immune activity, suggests a favorable therapeutic outcome and establishes pHe imaging as a tool for assessing treatment efficacy in acidic TMEs.

Caloric restriction and methionine restriction-driven enhanced lifespan and healthspan induces 'browning' of white adipose tissue, a metabolic response that increases heat production to defend core body temperature. However, how specific dietary amino acids control adipose thermogenesis is unknown. Here, we identified that weight loss induced by caloric restriction in humans reduces thiol-containing sulfur amino acid cysteine in white adipose tissue. Systemic cysteine depletion in mice causes lethal weight loss with increased fat utilization and browning of adipocytes that is rescued upon restoration of cysteine in diet. Mechanistically, cysteine-restriction-induced adipose browning and weight loss requires sympathetic nervous system-derived noradrenaline signalling via β3-adrenergic-receptors that is independent of FGF21 and UCP1. In obese mice, cysteine deprivation induced rapid adipose browning, increased energy expenditure leading to 30% weight loss and reversed metabolic inflammation. These findings establish that cysteine is essential for organismal metabolism as removal of cysteine in the host triggers adipose browning and rapid weight loss.

Traumatic spinal cord injury (SCI) is a devastating neurologic condition lacking effective prognostic and treatment methods. PET imaging of synaptic vesicle glycoprotein 2A (SV2A) has been used in measuring synapse changes. We explore the feasibility of using [18F]SynVesT-1 PET to detect the synaptic changes in a rat model of SCI. Methods: [18F]SynVesT-1 PET scans were performed on rats with T7 moderate contusion injury (n = 9) and sham controls (n = 7) on day 1 and days 9-11 after injury. The simplified reference region method 2 was used to compute the distribution volume ratios (DVRs) for the spinal cord (SC) and the brain, with the cervical cord and brain stem as the reference region, respectively. The averaged SUV ratio 30-60 min after injection was calculated as an alternative outcome measure. Diffusion tensor imaging (DTI) was used to evaluate axonal changes on post mortem SCs. Western blotting, immunohistochemical staining, and immunofluorescence staining were used to confirm the imaging results. Results: [18F]SynVesT-1 showed the highest uptake in the cervical SC. Notably, the DVR at the injury epicenter in SCI rats showed a 61% decrease on day 1 and a 53% decrease on days 9-11, compared with sham controls. The changes in SUV ratio 30-60 min after injection were consistent with the changes in DVR. The fiber damage in the epicenter was identified by DTI, and the loss of SV2A was confirmed by immunohistochemical staining and Western blotting. Further, the amygdala, limbic insular cortex, and cerebellum were found to be significantly affected by the SCI on day 1 by PET. The DTI analysis revealed fiber damage in the internal capsule and somatosensory cortex. Conclusion: [18F]SynVesT-1 PET effectively identified synapse loss in the contusion SCI rat model. The quantification of synaptic density through SV2A PET presents a promising objective metric for evaluating novel therapeutics for SCI.

ABSTRACTCellular metabolism is inextricably linked to transmembrane levels of proton (H+), sodium (Na+), and potassium (K+) ions. Although reduced sodium‐potassium pump (Na+‐K+ ATPase) activity in tumors directly disturbs transmembrane Na+ and K+ levels, this dysfunction is a result of upregulated aerobic glycolysis generating excessive cytosolic H+ (and lactate) which are extruded to acidify the interstitial space. These oncogene‐directed metabolic changes, affecting intracellular Na+ and H+, can be further exacerbated by upregulation of ion exchangers/transporters. As Na+/H+ imbalances impact tumor invasion, chromosomal rearrangements, proliferation rate, angiogenesis, and immune function, measuring interstitial H+ (H+o) or pH (pHo) and interstitial Na+ (Na+o) could provide unique insights into cancer hallmarks. We obtained proton (1H) and sodium (23Na) magnetic resonance spectroscopic imaging (MRSI) data to map pHo and Na+o in a human‐derived glioblastoma model (U87) in vivo with sorafenib (protein kinase inhibitor) treatment and a placebo. In U87 tumors, sorafenib slowed tumor growth compared to placebo and restored transmembrane H+ and Na+ levels. Placebo tumors maintained an interstitial space that was less salty and more acidic, similar to naive U87 tumors, implying a proliferative state. However, sorafenib‐treated tumors had interstitial space that became more salty and less acidic, comparable to normal tissue. Importantly, these interstitial ionic changes occurred prior to tumor growth changes. These results imply that glioblastoma therapies, which may perturb transmembrane ions by different mechanisms (e.g., ion pumping, exchange, and/or transport), can be tracked by merging 1H with 23Na MRSI to measure treatment effectiveness.

Extracellular acidosis in relation to intracellular milieu is a unique feature of the tumor microenvironment. The difference between intracellular pH (pHi) and extracellular pH (pHe) is much larger in tumors than normal tissue. Measuring the transmembrane pH gradient (ΔpH=pHi–pHe) could provide a tool for assessing tumor aggressiveness, monitoring treatment efficacy, guiding localized drug delivery, and understanding tumor responsiveness. This work establishes transmembrane pH gradient imaging in brain tumors. We observed a significantly higher transmembrane pH gradient in RG2 tumors compared to normal brain. Decreasing transmembrane pH gradient may serve as a functional biomarker for positive therapeutic outcome.

Noninvasive extracellular pH (pH e ) mapping with Biosensor Imaging of Redundant Deviation in Shifts (BIRDS) using MR spectroscopic imaging (MRSI) has been demonstrated on 3T clinical MR scanners at 8 × 8 × 10  mm 3 spatial resolution and applied to study various liver cancer treatments. Although pH e imaging at higher resolution can be achieved by extending the acquisition time, a postprocessing method to increase the resolution is preferable, to minimize the duration spent by the subject in the MR scanner. In this work, we propose to improve the spatial resolution of pH e mapping with BIRDS by incorporating anatomical information in the form of multiparametric MRI and using an unsupervised deep-learning technique, Deep Image Prior (DIP). Specifically, we used high-resolution T 1 , T 2 , and diffusion-weighted imaging (DWI) MR images of rabbits with VX2 liver tumors as inputs to a U-Net architecture to provide anatomical information. U-Net parameters were optimized to minimize the difference between the output super-resolution image and the experimentally acquired low-resolution pH e image using the mean-absolute error. In this way, the super-resolution pH e image would be consistent with both anatomical MR images and the low-resolution pH e measurement from the scanner. The method was developed based on data from 49 rabbits implanted with VX2 liver tumors. For evaluation, we also acquired high-resolution pH e images from two rabbits, which were used as ground truth. The results indicate a good match between the spatial characteristics of the super-resolution images and the high-resolution ground truth, supported by the low pixelwise absolute error.

A unique feature of the tumor microenvironment is extracellular acidosis in relation to intracellular milieu. Metabolic reprogramming in tumors results in overproduction of H+ ions (and lactate), which are extruded from the cells to support tumor survival and progression. As a result, the transmembrane pH gradient (ΔpH), representing the difference between intracellular pH (pHi) and extracellular pH (pHe), is posited to be larger in tumors compared with normal tissue. Controlling the transmembrane pH difference has promise as a potential therapeutic target in cancer as it plays an important role in regulating drug delivery into cells. The current study shows successful development of an MRI/MRSI-based technique that provides ΔpH imaging at submillimeter resolution. We applied this technique to image ΔpH in rat brains with RG2 and U87 gliomas, as well as in mouse brains with GL261 gliomas. pHi was measured with Amine and Amide Concentration-Independent Detection (AACID), while pHe was measured with Biosensor Imaging of Redundant Deviation in Shifts (BIRDS). The results indicate that pHi was slightly higher in tumors (7.40-7.43 in rats, 7.39-7.47 in mice) compared with normal brain (7.30-7.38 in rats, 7.32-7.36 in mice), while pHe was significantly lower in tumors (6.62-6.76 in rats, 6.74-6.84 in mice) compared with normal tissue (7.17-7.22 in rats, 7.20-7.21 in mice). As a result, ΔpH was higher in tumors (0.64-0.81 in rats, 0.62-0.65 in mice) compared with normal brain (0.13-0.16 in rats, 0.13-0.16 in mice). This work establishes an MRI/MRSI-based platform for ΔpH imaging at submillimeter resolution in gliomas.

Background: Image-guided tumor ablation is the first-line therapy for early-stage hepatocellular carcinoma (HCC), with ongoing investigations into its combination with immunotherapies. Matrix metalloproteinase (MMP) inhibition demonstrates immunomodulatory potential and reduces HCC tumor growth when combined with ablative treatment. Purpose: To evaluate the effect of incomplete cryoablation with or without MMP inhibition on the local immune response in residual tumors in a murine HCC model. Materials and Methods: Sixty 8- to 10-week-old female BALB/c mice underwent HCC induction with use of orthotopic implantation of syngeneic Tib-75 cells. After 7 days, mice with a single lesion were randomized into treatment groups: (a) no treatment, (b) MMP inhibitor, (c) incomplete cryoablation, and (d) incomplete cryoablation and MMP inhibitor. Macrophage and T-cell subsets were assessed in tissue samples with use of immunohistochemistry and immunofluorescence (cell averages calculated using five 1-mu m2 fields of view [FOVs]). C -X -C motif chemokine receptor type 3 (CXCR3)- and interferon gamma (IFN gamma)- positive T cells were assessed using flow cytometry. Groups were compared using unpaired Student t tests, one-way analysis of variance with Tukey correction, and the Kruskal-Wallis test with Dunn correction. Results: Mice treated with incomplete cryoablation (n = 6) showed greater infiltration of CD206+ tumor-associated macrophages (mean, 1.52 cells per FOV vs 0.64 cells per FOV; P = .03) and MMP9-expressing cells (mean, 0.89 cells per FOV vs 0.11 cells per FOV; P = .03) compared with untreated controls (n = 6). Incomplete cryoablation with MMP inhibition (n = 6) versus without (n = 6) led to greater CD8+ T-cell (mean, 15.8% vs 8.29%; P = .04), CXCR3+CD8+ T-cell (mean, 11.64% vs 8.47%; P = .004), and IFN gamma+CD8+ T-cell infiltration (mean, 11.58% vs 5.18%; P = .02). Conclusion: In a mouse model of HCC, incomplete cryoablation and systemic MMP inhibition showed increased cytotoxic CD8+ T-cell infiltration into the residual tumor compared with either treatment alone.

Paramagnetic complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA4-) derivatives have shown potential for molecular imaging with magnetic resonance. DOTA-tetraglycinate (DOTA-4AmC4-) coordinated with lanthanide metal ions (Ln3+) demonstrates pH/temperature sensing with Biosensor Imaging of Redundant Deviation in Shifts (BIRDS) and Chemical Exchange Saturation Transfer (CEST), respectively, detecting nonexchangeable (e.g., -CHy, where 3 ≥ y ≥ 1) and exchangeable (e.g., -OH or -NHx, where 2 ≥ x ≥ 1) protons. Herein, we report paramagnetic complexes of divalent transition-metal ions (M2+ = Fe2+, Co2+, Ni2+) with DOTA-4AmC4- that endow a unique amide proton (-NH) moiety for pH/temperature sensing. Crystallographic data reveal that DOTA-4AmC4- coordinates with M2+ through oxygen and nitrogen donor atoms, ranging in coordination numbers from 8-coordinate in Fe(II)DOTA-4AmC2-, 7-coordinate in Co(II)DOTA-4AmC2-, and 6-coordinate in Ni(II)DOTA-4AmC2-. The -CHy protons in M(II)DOTA-4AmC2- displayed modest pH/temperature sensitivities, but -NH protons exhibited higher intensity, suggesting prominent BIRDS properties. The pH sensitivity was the highest for Ni(II)DOTA-4AmC2- (1.42 ppm/pH), followed by Co(II)DOTA-4AmC2- (0.21 ppm/pH) and Fe(II)DOTA-4AmC2- (0.16 ppm/pH), whereas temperature sensitivities were comparable (i.e., 0.22, 0.13, and 0.17 ppm/°C, respectively). The CEST image contrast for -NH in M(II)DOTA-4AmC2- was much weaker compared to that of Ln(III)DOTA-4AmC-. Given its high pH sensitivity and low cytotoxicity, Ni(II)DOTA-4AmC2- shows promise for use in preclinical BIRDS-based pH imaging.

Apolipoprotein ε4 (APOE4) carriers develop brain metabolic dysfunctions decades before the onset of Alzheimer’s disease (AD). A goal of the study is to identify if rapamycin, an inhibitor for the mammalian target of rapamycin (mTOR) inhibitor, would enhance synaptic and mitochondrial function in asymptomatic mice with human APOE4 gene (E4FAD) before they showed metabolic deficits. A second goal is to determine whether there may be genetic-dependent responses to rapamycin when compared to mice with human APOE3 alleles (E3FAD), a neutral AD genetic risk factor. We fed asymptomatic E4FAD and E3FAD mice with control or rapamycin diets for 16 weeks from starting from 3 months of age. Neuronal mitochondrial oxidative metabolism and excitatory neurotransmission rates were measured using in vivo 1H-[13C] proton-observed carbon-edited magnetic resonance spectroscopy, and isolated mitochondrial bioenergetic measurements using Seahorse. We found that rapamycin enhanced neuronal mitochondrial function, glutamate-glutamine cycling, and TCA cycle rates in the asymptomatic E4FAD mice. In contrast, rapamycin enhances glycolysis, non-neuronal activities, and inhibitory neurotransmission of the E3FAD mice. These findings indicate that rapamycin might be able to mitigate the risk for AD by enhancing brain metabolic functions for cognitively intact APOE4 carriers, and the responses to rapamycin are varied by APOE genotypes. Consideration of precision medicine may be needed for future rapamycin therapeutics.

The authors have requested that this preprint be removed from Research Square.

PURPOSE:To establish molecular magnetic resonance (MR) imaging instruments for in vivo characterization of the immune response to hepatic radiofrequency (RF) ablation using cell-specific immunoprobes. MATERIALS AND METHODS:Seventy-two C57BL/6 wild-type mice underwent standardized hepatic RF ablation (70 °C for 5 minutes) to generate a coagulation area measuring 6-7 mm in diameter. CD68+ macrophage periablational infiltration was characterized with immunohistochemistry 24 hours, 72 hours, 7 days, and 14 days after ablation (n = 24). Twenty-one mice were subjected to a dose-escalation study with either 10, 15, 30, or 60 mg/kg of rhodamine-labeled superparamagnetic iron oxide nanoparticles (SPIONs) or 2.4, 1.2, or 0.6 mg/kg of gadolinium-160 (160Gd)-labeled CD68 antibody for assessment of the optimal in vivo dose of contrast agent. MR imaging experiments included 9 mice, each receiving 10-mg/kg SPIONs to visualize phagocytes using T2∗-weighted imaging in a horizontal-bore 9.4-T MR imaging scanner, 160Gd-CD68 for T1-weighted MR imaging of macrophages, or 0.1-mmol/kg intravenous gadoterate (control group). Radiological-pathological correlation included Prussian blue staining, rhodamine immunofluorescence, imaging mass cytometry, and immunohistochemistry. RESULTS:RF ablation-induced periablational infiltration (206.92 μm ± 12.2) of CD68+ macrophages peaked at 7 days after ablation (P < .01) compared with the untreated lobe. T2∗-weighted MR imaging with SPION contrast demonstrated curvilinear T2∗ signal in the transitional zone (TZ) (186 μm ± 16.9), corresponsing to Iron Prussian blue staining. T1-weighted MR imaging with 160Gd-CD68 antibody showed curvilinear signal in the TZ (164 μm ± 3.6) corresponding to imaging mass cytometry. CONCLUSIONS:Both SPION-enhanced T2∗-weighted and 160Gd-enhanced T1-weighted MR imaging allow for in vivo monitoring of macrophages after RF ablation, demonstrating the feasibility of this model to investigate local immune responses.

Introduction An inactivating mutation in the histidine decarboxylase gene (Hdc) has been identified as a rare but high-penetrance genetic cause of Tourette syndrome (TS). TS is a neurodevelopmental syndrome characterized by recurrent motor and vocal tics; it is accompanied by structural and functional abnormalities in the cortico-basal ganglia circuitry. Hdc, which is expressed both in the posterior hypothalamus and peripherally, encodes an enzyme required for the biosynthesis of histamine. Hdc knockout mice (Hdc-KO) functionally recapitulate this mutation and exhibit behavioral and neurochemical abnormalities that parallel those seen in patients with TS. Materials and methods We performed exploratory RNA-seq to identify pathological alterations in several brain regions in Hdc-KO mice. Findings were corroborated with RNA and protein quantification, immunohistochemistry, and ex vivo brain imaging using MRI. Results Exploratory RNA-Seq analysis revealed, unexpectedly, that genes associated with oligodendrocytes and with myelin production are upregulated in the dorsal striatum of these mice. This was confirmed by qPCR, immunostaining, and immunoblotting. These results suggest an abnormality in myelination in the striatum. To test this in an intact mouse brain, we performed whole-brain ex vivo diffusion tensor imaging (DTI), which revealed reduced fractional anisotropy (FA) in the dorsal striatum. Discussion While the DTI literature in individuals with TS is sparse, these results are consistent with findings of disrupted descending cortical projections in patients with tics. The Hdc-KO model may represent a powerful system in which to examine the developmental mechanisms underlying this abnormality.