Myeloperoxidase-targeted imaging of active inflammatory lesions in murine experimental autoimmune encephalomyelitis

Microglial suppression by myeloperoxidase inhibitor does not delay neurodegeneration in a mouse model of progressive multiple sclerosis

Drugs able to efficiently counteract the progression of multiple sclerosis (MS) are still an unmet need. Numerous preclinical evidence indicates that reactive oxygen-generating enzyme myeloperoxidase (MPO), expressed by neutrophils and microglia, might play a key role in neurodegenerative disorders. Then, the MPO inhibition has been evaluated in clinical trials in Parkinson's and multiple system atrophy patients, and a clinical trial for the treatment of amyotrophic lateral sclerosis is underway. The effects of MPO inhibition on MS patients have not yet been explored. In the present study, by adopting the NOD mouse model of progressive MS (PMS), we evaluated the pharmacological effects of the MPO inhibitor verdiperstat (also known as AZD3241) on functional, immune, and mitochondrial parameters during disease evolution. We found that daily treatment with verdiperstat did not affect the pattern of progression as well as survival, despite its ability to reduce mitochondrial reactive oxygen species and microglia activation in the spinal cord of immunized mice. Remarkably, verdiperstat did not affect adaptive immunity, neutrophils invasion as well as mitochondrial derangement in the spinal cords of immunized mice. Data suggest that microglia suppression is not sufficient to prevent disease evolution, corroborating the hypothesis that immune-independent components drive neurodegeneration in progressive MS.

Rational Design of Mono-Substituted Gd-DOTA as Highly Stable and Efficient MRI Contrast Agents for Hepatobiliary and Inflammation Imaging

Hepatobiliary-specific magnetic resonance imaging contrast agents (MRI CAs) play a crucial role in the early diagnosis of hepatocellular carcinoma (HCC). However, only two acyclic CAs, Gd-BOPTA and Gd-EOB-DTPA, exhibit unfavorable kinetic inertness. Our study focused on the development of superior stable innovative macrocyclic CAs. By introducing a lipophilic benzyloxy group (OBn) into the H4DOTA ring (Gd-L1), we achieved significant enhancement in kinetic inertness. In vivo experiments in mice demonstrated that 40% of the dosage was distributed to the liver at 5 min, providing sustained hepatic enhancement for over 35 min. We also developed an MPO-responsive MRI CA (Gd-L3), which can participate in the "peroxidase cycle" as the substrate, generating oligomers with a 3.8-fold increase in relaxivity, and selectively enhance the lesion in an acute gout mouse model. Overall, our work represents a significant advancement in the field of hepatic and inflammatory MRI, offering promising avenues for early diagnosis and improved imaging outcomes.

Basic Science of Neuroinflammation and Involvement of the Inflammatory Response in Disorders of the Nervous System

Neuroinflammation is a key immune response observed in many neurologic diseases. Although an appropriate immune response can be beneficial, aberrant activation of this response recruits excessive proinflammatory cells to cause damage. Because the central nervous system is separated from the periphery by the blood-brain barrier (BBB) that creates an immune-privileged site, it has its own unique immune cells and immune response. Moreover, neuroinflammation can compromise the BBB causing an influx of peripheral immune cells and factors. Recent advances have brought a deeper understanding of neuroinflammation that can be leveraged to develop more potent therapies and improve patient selection.

Myeloperoxidase Gene Deletion Causes Drastic Microbiome Shifts in Mice and Does Not Mitigate Dextran Sodium Sulphate-Induced Colitis

Neutrophil-myeloperoxidase (MPO) is a heme-containing peroxidase which produces excess amounts of hypochlorous acid during inflammation. While pharmacological MPO inhibition mitigates all indices of experimental colitis, no studies have corroborated the role of MPO using knockout (KO) models. Therefore, we investigated MPO deficient mice in a murine model of colitis. Wild type (Wt) and MPO-deficient mice were treated with dextran sodium sulphate (DSS) in a chronic model of experimental colitis with three acute cycles of DSS-induced colitis over 63 days, emulating IBD relapse and remission cycles. Mice were immunologically profiled at the gut muscoa and the faecal microbiome was assessed via 16S rRNA amplicon sequencing. Contrary to previous pharmacological antagonist studies targeting MPO, MPO-deficient mice showed no protection from experimental colitis during cyclical DSS-challenge. We are the first to report drastic faecal microbiota shifts in MPO-deficient mice, showing a significantly different microbiome profile on Day 1 of treatment, with a similar shift and distinction on Day 29 (half-way point), via qualitative and quantitative descriptions of phylogenetic distances. Herein, we provide the first evidence of substantial microbiome shifts in MPO-deficiency, which may influence disease progression. Our findings have significant implications for the utility of MPO-KO mice in investigating disease models.

Myeloperoxidase-Sensitive Magnetic Resonance Imaging Assesses Inflammatory Activation State in Experimental Mouse Acute Gout

BACKGROUND

A novel myeloperoxidase-activatable manganese-based (MPO-Mn) MRI probe may enable the activation state of inflammatory foci to be detected and monitored noninvasively.

PURPOSE

To evaluate the inflammatory response in a mouse model of acute gout using MPO as an imaging biomarker and a potential therapeutic target.

STUDY TYPE

Prospective.

ANIMAL MODEL

A total of 40 male Swiss mice with monosodium urate crystals induced acute gout.

FIELD STRENGTH/SEQUENCE

A 3.0 T/T1-weighted imaging with 2D fast spoiled gradient recalled echo and T2-weighted imaging with fast recovery fast spin-echo sequences.

ASSESSMENT

The difference in contrast-to-noise ratio between left hind limb (lesion) and right hind limb (internal reference) (ΔCNR), and normalized signal-to-noise ratio (nSNR) on the right hind limb were calculated and compared. The expression level and activity of myeloperoxidase (MPO) were analyzed using western blotting and spectrophotometric quantitation activity assay. MPO-positive cell infiltration and lesion volume were evaluated using immunofluorescence staining and T2-weighted images, respectively.

STATISTICAL TESTS

Student's t test. A P-value less than 0.05 was considered to be statistically significant.

RESULTS

MPO-Mn resulted in a significantly higher ΔCNR than Gd-DTPA (22.54 ± 1.86 vs. 13.90 ± 2.22) but lower nSNR on the reference right hind limb (1.08 ± 0.07 vs. 1.21 ± 0.08). Compared to the nontreatment group, MPO-inhibition resulted in a significantly reduced contrast enhancement at the lesion (17.81 ± 1.58 vs. 22.96 ± 3.12), which was consistent with a remission of the inflammatory response, as evidenced by a substantial reduction of lesion volume (0.55 ± 0.16 mm3 /g vs. 1.14 ± 0.15 mm3 /g), myeloperoxidase expression level (0.98 ± 0.09 vs. 1.48 ± 0.19) and activity (0.75 ± 0.12 vs. 1.12 ± 0.07), and inflammatory cell recruitment.

DATA CONCLUSION

MPO-Mn MRI has potential to evaluate the activation state of inflammatory foci in the experimental model of acute gout.

EVIDENCE LEVEL

1.

TECHNICAL EFFICACY

Stage 1.

Optimizing animal models of autoimmune encephalitis using active immunization

Background and objectives

Encephalitis is a devastating neurologic disorder with high morbidity and mortality. Autoimmune causes are roughly as common as infectious ones. N-methyl-D-aspartic acid receptor (NMDAR) encephalitis (NMDARE), characterized by serum and/or spinal fluid NMDAR antibodies, is the most common form of autoimmune encephalitis (AE). A translational rodent NMDARE model would allow for pathophysiologic studies of AE, leading to advances in the diagnosis and treatment of this debilitating neuropsychiatric disorder. The main objective of this work was to identify optimal active immunization conditions for NMDARE in mice.

Methods

Female C57BL/6J mice aged 8 weeks old were injected subcutaneously with an emulsion of complete Freund's adjuvant, killed and dessicated Mycobacterium tuberculosis, and a 30 amino acid peptide flanking the NMDAR GluN1 subunit N368/G369 residue targeted by NMDARE patients' antibodies. Three different induction methods were examined using subcutaneous injection of the peptide emulsion mixture into mice in 1) the ventral surface, 2) the dorsal surface, or 3) the dorsal surface with reimmunization at 4 and 8 weeks (boosted). Mice were bled biweekly and sacrificed at 2, 4, 6, 8, and 14 weeks. Serum and CSF NMDAR antibody titer, mouse behavior, hippocampal cell surface and postsynaptic NMDAR cluster density, and brain immune cell entry and cytokine content were examined.

Results

All immunized mice produced serum and CSF NMDAR antibodies, which peaked at 6 weeks in the serum and at 6 (ventral and dorsal boosted) or 8 weeks (dorsal unboosted) post-immunization in the CSF, and demonstrated decreased hippocampal NMDAR cluster density by 6 weeks post-immunization. In contrast to dorsally-immunized mice, ventrally-induced mice displayed a translationally-relevant phenotype including memory deficits and depressive behavior, changes in cerebral cytokines, and entry of T-cells into the brain at the 4-week timepoint. A similar phenotype of memory dysfunction and anxiety was seen in dorsally-immunized mice only when they were serially boosted, which also resulted in higher antibody titers.

Discussion

Our study revealed induction method-dependent differences in active immunization mouse models of NMDARE disease. A novel ventrally-induced NMDARE model demonstrated characteristics of AE earlier compared to dorsally-induced animals and is likely suitable for most short-term studies. However, boosting and improving the durability of the immune response might be preferred in prolonged longitudinal studies.

The role of neutrophils in the dysfunction of central nervous system barriers

Leukocyte migration into the central nervous system (CNS) represents a central process in the development of neurological diseases with a detrimental inflammatory component. Infiltrating neutrophils have been detected inside the brain of patients with several neuroinflammatory disorders, including stroke, multiple sclerosis and Alzheimer’s disease. During inflammatory responses, these highly reactive innate immune cells can rapidly extravasate and release a plethora of pro-inflammatory and cytotoxic factors, potentially inducing significant collateral tissue damage. Indeed, several studies have shown that neutrophils promote blood-brain barrier damage and increased vascular permeability during neuroinflammatory diseases. Recent studies have shown that neutrophils migrate into the meninges and choroid plexus, suggesting these cells can also damage the blood-cerebrospinal fluid barrier (BCSFB). In this review, we discuss the emerging role of neutrophils in the dysfunction of brain barriers across different neuroinflammatory conditions and describe the molecular basis and cellular interplays involved in neutrophil-mediated injury of the CNS borders.

Myeloperoxidase as a Marker to Differentiate Mouse Monocyte/Macrophage Subsets

Macrophages are present in every tissue in the body and play essential roles in homeostasis and host defense against microorganisms. Some tissue macrophages derive from the yolk sac/fetal liver that populate tissues for life. Other tissue macrophages derive from monocytes that differentiate in the bone marrow and circulate through tissues via the blood and lymphatics. Circulating monocytes are very plastic and differentiate into macrophages with specialized functions upon entering tissues. Specialized monocyte/macrophage subsets have been difficult to differentiate based on cell surface markers. Here, using a combination of "pan" monocyte/macrophage markers and flow cytometry, we asked whether myeloperoxidase (MPO) could be used as a marker of pro-inflammatory monocyte/macrophage subsets. MPO is of interest because of its potent microbicidal activity. In wild-type SPF housed mice, we found that MPO⁺ monocytes/macrophages were present in peripheral blood, spleen, small and large intestines, and mesenteric lymph nodes, but not the central nervous system. Only monocytes/macrophages that expressed cell surface F4/80 and/or Ly6C co-expressed MPO with the highest expression in F4/80^HiLy6C^Hi subsets regardless of tissue. These cumulative data indicate that MPO expression can be used as an additional marker to differentiate between monocyte/macrophage subsets with pro-inflammatory and microbicidal activity in a variety of tissues.

Opportunities for Molecular Imaging in Multiple Sclerosis Management: Linking Probe to Treatment

Imaging has been a critical component of multiple sclerosis (MS) management for nearly 40 years. The visual information derived from structural MRI, that is, signs of blood-brain barrier disruption, inflammation and demyelination, and brain and spinal cord atrophy, are the primary metrics used to evaluate therapeutic efficacy in MS. The development of targeted imaging probes has expanded our ability to evaluate and monitor MS and its therapies at the molecular level. Most molecular imaging probes evaluated for MS applications are small molecules initially developed for PET, nearly half of which are derived from U.S. Food and Drug Administration-approved drugs and those currently undergoing clinical trials. Superparamagnetic and fluorinated particles have been used for tracking circulating immune cells (in situ labeling) and immunosuppressive or remyelinating therapeutic stem cells (ex vivo labeling) clinically using proton (hydrogen 1 [¹H]) and preclinically using fluorine 19 MRI. Translocator protein PET and ¹H MR spectroscopy have been demonstrated to complement imaging metrics from structural (gadolinium-enhanced) MRI in nine and six trials for MS disease-modifying therapies, respectively. Still, despite multiple demonstrations of the utility of molecular imaging probes to evaluate the target location and to elucidate the mechanisms of disease-modifying therapies for MS applications, their use has been sparse in both preclinical and clinical settings.

Molecular immuno-imaging improves tumor detection in head and neck cancer

Detection and accurate delineation of tumor is important for the management of head and neck squamous cell carcinoma (HNSCC) but is challenging with current imaging techniques. In this study, we evaluated whether molecular immuno-imaging targeting myeloperoxidase (MPO) activity, an oxidative enzyme secreted by many myeloid innate immune cells, would be superior in detecting tumor extent compared to conventional contrast agent (DTPA-Gd) in a carcinogen-induced immunocompetent HNSCC murine model and corroborated in human surgical specimens. In C57BL/6 mice given 4-nitroquinoline-N-oxide (4-NQO), there was increased MPO activity in the head and neck region as detected by luminol bioluminescence compared to that of the control group. On magnetic resonance imaging, the mean enhancing volume detected by the MPO-targeting agent (MPO-Gd) was higher than that by the conventional agent DTPA-Gd. The tumor volume detected by MPO-Gd strongly correlated with tumor size on histology, and higher MPO-Gd signal corresponded to larger tumor size found by imaging and histology. On the contrary, the tumor volume detected by DTPA-Gd did not correlate as well with tumor size on histology. Importantly, MPO-Gd imaging detected areas not visualized with DTPA-Gd imaging that were confirmed histopathologically to represent early tumor. In human specimens, MPO was similarly associated with tumors, especially at the tumor margins. Thus, molecular immuno-imaging targeting MPO not only detects oxidative immune response in HNSCC, but can better detect and delineate tumor extent than nonselective imaging agents. Thus, our findings revealed that MPO imaging could improve tumor resection as well as be a useful imaging biomarker for tumor progression, and potentially improve clinical management of HNSCC once translated.

D-Mannose Slows Glioma Growth by Modulating Myeloperoxidase Activity

Host immune response in the tumor microenvironment plays key roles in tumorigenesis. We hypothesized that D-mannose, a simple sugar with anti-inflammatory properties, could decrease oxidative stress and slow glioma progression. Using a glioma stem cell model in immunocompetent mice, we induced gliomas in the brain and tracked MPO activity in vivo with and without D-mannose treatment. As expected, we found that D-mannose treatment decreased the number of MPO+ cells and slowed glioma progression compared to PBS-treated control animals with gliomas. Unexpectedly, instead of decreasing MPO activity, D-mannose increased MPO activity in vivo, revealing that D-mannose boosted the MPO activity per MPO+ cell. On the other hand, D-glucose had no effect on MPO activity. To better understand this effect, we examined the effect of D-mannose on bone marrow-derived myeloid cells. We found that D-mannose modulated MPO activity via two mechanisms: directly via N-glycosylation of MPO, which boosted the MPO activity of each molecule, and indirectly by increasing H2O2 production, the main substrate for MPO. This increased host immune response acted to reduce tumor size, suggesting that increasing MPO activity such as through D-mannose administration may be a potential new therapeutic direction for glioma treatment.

d-mannose suppresses oxidative response and blocks phagocytosis in experimental neuroinflammation

Inflammation drives the pathology of many neurological diseases. d-mannose has been found to exert an antiinflammatory effect in peripheral diseases, but its effects on neuroinflammation and inflammatory cells in the central nervous system have not been studied. We aimed to determine the effects of d-mannose on key macrophage/microglial functions-oxidative stress and phagocytosis. In murine experimental autoimmune encephalomyelitis (EAE), we found d-mannose improved EAE symptoms compared to phosphate-buffered saline (PBS)-control mice, while other monosaccharides did not. Multiagent molecular MRI performed to assess oxidative stress (targeting myeloperoxidase [MPO] using MPO-bis-5-hydroxytryptamide diethylenetriaminepentaacetate gadolinium [Gd]) and phagocytosis (using cross-linked iron oxide [CLIO] nanoparticles) in vivo revealed that d-mannose-treated mice had smaller total MPO-Gd+ areas than those of PBS-control mice, consistent with decreased MPO-mediated oxidative stress. Interestingly, d-mannose-treated mice exhibited markedly smaller CLIO+ areas and much less T2 shortening effect in the CLIO+ lesions compared to PBS-control mice, revealing that d-mannose partially blocked phagocytosis. In vitro experiments with different monosaccharides further confirmed that only d-mannose treatment blocked macrophage phagocytosis in a dose-dependent manner. As phagocytosis of myelin debris has been known to increase inflammation, decreasing phagocytosis could result in decreased activation of proinflammatory macrophages. Indeed, compared to PBS-control EAE mice, d-mannose-treated EAE mice exhibited significantly fewer infiltrating macrophages/activated microglia, among which proinflammatory macrophages/microglia were greatly reduced while antiinflammatory macrophages/microglia increased. By uncovering that d-mannose diminishes the proinflammatory response and boosts the antiinflammatory response, our findings suggest that d-mannose, an over-the-counter supplement with a high safety profile, may be a low-cost treatment option for neuroinflammatory diseases such as multiple sclerosis.

Acting centrally or peripherally: A renewed interest in the central nervous system penetration of disease-modifying drugs in multiple sclerosis

With the recent approval of cladribine tablets, siponimod and ozanimod, there has been a renewed interest into the extent to which these current generation disease-modifying therapies (DMTs) are able to cross into the central nervous system (CNS), and how this penetration of the blood-brain barrier (BBB) may influence their ability to treat multiple sclerosis (MS). The integrity of the CNS is maintained by the BBB, blood-cerebrospinal fluid barrier, and the arachnoid barrier, which all play an important role in preserving the immunological environment and homeostasis within the CNS. The integrity of the BBB decreases during the course of MS, with a putative temporal relationship to disease worsening. Furthermore, it is currently considered that progression of the disease is mediated mainly by resident cells of the CNS. The existing literature provides evidence to show that some of the current generation DMTs for MS are able to penetrate the CNS and potentially exert direct effects on CNS-resident cells, in particular the CNS-penetrating prodrugs cladribine and fingolimod, and other sphingosine-1 phosphate receptor modulators; siponimod and ozanimod. Other current generation DMTs appear to be restricted to the periphery due to their high molecular weight or physicochemical properties. As more effective brain penetrant therapies are developed for the treatment of MS, there is a need to understand whether the potential for direct effects within the CNS are of significance, and whether this brings additional benefits over and above treatment effects mediated in the periphery. In turn, this will require an improved understanding of the structure and function of the BBB, the role it plays in MS and subsequent treatments. This narrative review summarizes the data supporting the biological plausibility of a potential benefit from therapeutic molecules entering the CNS, and discusses the potential significance in the current and future treatment of MS.

Highly Efficient Activatable MRI Probe to Sense Myeloperoxidase Activity

Myeloperoxidase (MPO) is a key component of innate immunity but can damage tissues when secreted abnormally. We developed a new generation of a highly efficient MPO-activatable MRI probe (heMAMP) to report MPO activity. heMAMP has improved Gd stability compared to bis-5-HT-Gd-DTPA (MPO-Gd) and demonstrates no significant cytotoxicity. Importantly, heMAMP is more efficiently activated by MPO compared to MPO-Gd, 5HT-DOTA(Gd), and 5HT-DOTAGA-Gd. Molecular docking simulations revealed that heMAMP has increased rigidity via hydrogen bonding intramolecularly and improved binding affinity to the active site of MPO. In animals with subcutaneous inflammation, activated heMAMP showed a 2-3-fold increased contrast-to-noise ratio (CNR) compared to activated MPO-Gd and 4-10 times higher CNR compared to conventional DOTA-Gd. This increased efficacy was further confirmed in a model of unstable atherosclerotic plaque where heMAMP demonstrated a comparable signal increase and responsiveness to MPO inhibition at a 3-fold lower dosage compared to MPO-Gd, further underscoring heMAMP as a potential translational candidate.

Ethanol exacerbates manganese-induced oxidative/nitrosative stress, pro-inflammatory cytokines, nuclear factor-κB activation, and apoptosis induction in rat cerebellar cortex

Manganese (Mn) exposure is causing public health concerns as well as heavy alcohol consumption. This study investigates the mechanisms of neurotoxicity associated with Mn and ethanol (EtOH) exposure in the rat cerebellar cortex. Experimental animals received 30 mg/kg of Mn alone, 5 g/kg of EtOH alone, co-exposed with 30 mg/kg of Mn and 1.25 or 5 g/kg EtOH, while control animals received water by oral gavage for 35 days. Subsequently, alterations in the neuronal morphology of the cerebellar cortex, oxidative/nitrosative stress, acetylcholinesterase (AChE) activity, neuro-inflammation and protein expression of p53, BAX, caspase-3, and BCL-2 were investigated. The results indicate that Mn alone and EtOH alone induce neuronal alterations in the cerebellar cortex, decrease glutathione level and antioxidant enzyme activities, along with an increase in AChE activity, lipid peroxidation, and hydrogen peroxide generation. Mn alone and EtOH alone also increased neuro-inflammatory markers, namely nitric oxide, myeloperoxidase activity, interleukin-1β, tumor necrosis factor-α, and nuclear factor-κB (NF-κB) levels in the cerebellar cortex. Immunohistochemistry analysis further revealed that exposure of Mn alone and EtOH alone increases the protein expression of cyclooxygenase-2, BAX, p53, and caspase-3 and decrease BCL-2 in the rat cerebellar cortex. Furthermore, the results indicated that Mn co-exposure with EtOH at 1.25 and 5 g/kg EtOH significantly (p ≤ .05) increases the toxicity in the cerebellum when compared with the toxicity of Mn or EtOH alone. Taken together, co-exposure of Mn and EtOH exacerbates neuronal alterations, oxidative/nitrosative stress, AChE activity, pro-inflammatory cytokines, NF-κB signal transcription, and apoptosis induction in the rat cerebellar cortex.

Quantifying phagosomal HOCl at single immune-cell resolution

Neutralization of pathogens by phagocytic immune cells requires the biogenesis of a compartmentalized hotspot of reactive species called the phagosome. One of these reactive species is hypochlorous acid (HOCl), produced by the enzyme myeloperoxidase (MPO) after the phagosome fuses with the lysosome. Mapping HOCl during phagosome maturation can report on pathogen killing and offer insights into regulation of MPO activity, mechanisms of resistance and host-pathogen interactions. However, this has been difficult because of a lack of a suitable method to chemically map a transient organelle with pH fluctuations like the phagosome. Here, we detail a protocol for quantifying HOCl dynamics in phagosomes using a fluorescent DNA-based reporter. Compared to traditional methods of visualizing HOCl or measuring MPO activity, this method offers sub-cellular spatial resolution and the capacity to assay HOCl production with single cell resolution.

Nitric oxide debilitates the neuropathogenic schistosome Trichobilharzia regenti in mice, partly by inhibiting its vital peptidases

Background

Avian schistosomes, the causative agents of human cercarial dermatitis (or swimmer’s itch), die in mammals but the mechanisms responsible for parasite elimination are unknown. Here we examined the role of reactive nitrogen species, nitric oxide (NO) and peroxynitrite, in the immune response of mice experimentally infected with Trichobilharzia regenti, a model species of avian schistosomes remarkable for its neuropathogenicity.

Methods

Inducible NO synthase (iNOS) was localized by immunohistochemistry in the skin and the spinal cord of mice infected by T. regenti. The impact of iNOS inhibition by aminoguanidine on parasite burden and growth was then evaluated in vivo. The vulnerability of T. regenti schistosomula to NO and peroxynitrite was assessed in vitro by viability assays and electron microscopy. Additionally, the effect of NO on the activity of T. regenti peptidases was tested using a fluorogenic substrate.

Results

iNOS was detected around the parasites in the epidermis 8 h post-infection and also in the spinal cord 3 days post-infection (dpi). Inhibition of iNOS resulted in slower parasite growth 3 dpi, but the opposite effect was observed 7 dpi. At the latter time point, moderately increased parasite burden was also noticed in the spinal cord. In vitro, NO did not impair the parasites, but inhibited the activity of T. regenti cathepsins B1.1 and B2, the peptidases essential for parasite migration and digestion. Peroxynitrite severely damaged the surface tegument of the parasites and decreased their viability in vitro, but rather did not participate in parasite clearance in vivo.

Conclusions

Reactive nitrogen species, specifically NO, do not directly kill T. regenti in mice. NO promotes the parasite growth soon after penetration (3 dpi), but prevents it later (7 dpi) when also suspends the parasite migration in the CNS. NO-related disruption of the parasite proteolytic machinery is partly responsible for this effect.

Roles of Reconstituted High-Density Lipoprotein Nanoparticles in Cardiovascular Disease: A New Paradigm for Drug Discovery

Epidemiological results revealed that there is an inverse correlation between high-density lipoprotein (HDL) cholesterol levels and risks of atherosclerotic cardiovascular disease (ASCVD). Mounting evidence supports that HDLs are atheroprotective, therefore, many therapeutic approaches have been developed to increase HDL cholesterol (HDL-C) levels. Nevertheless, HDL-raising therapies, such as cholesteryl ester transfer protein (CETP) inhibitors, failed to ameliorate cardiovascular outcomes in clinical trials, thereby casting doubt on the treatment of cardiovascular disease (CVD) by increasing HDL-C levels. Therefore, HDL-targeted interventional studies were shifted to increasing the number of HDL particles capable of promoting ATP-binding cassette transporter A1 (ABCA1)-mediated cholesterol efflux. One such approach was the development of reconstituted HDL (rHDL) particles that promote ABCA1-mediated cholesterol efflux from lipid-enriched macrophages. Here, we explore the manipulation of rHDL nanoparticles as a strategy for the treatment of CVD. In addition, we discuss technological capabilities and the challenge of relating preclinical in vivo mice research to clinical studies. Finally, by drawing lessons from developing rHDL nanoparticles, we also incorporate the viabilities and advantages of the development of a molecular imaging probe with HDL nanoparticles when applied to ASCVD, as well as gaps in technology and knowledge required for putting the HDL-targeted therapeutics into full gear.

A versatile imaging platform with fluorescence and CT imaging capabilities that detects myeloperoxidase activity and inflammation at different scales

Aberrant innate immune response drives the pathophysiology of many diseases. Myeloperoxidase (MPO) is a highly oxidative enzyme secreted by activated myeloid pro-inflammatory immune cells such as neutrophils and macrophages, and is a key mediator of the damaging innate immune response. Current technologies for detecting MPO activity in living organisms are sparse and suffer from any combination of low specificity, low tissue penetration, or low spatial resolution. We describe a versatile imaging platform to detect MPO activity using an activatable construct conjugated to a biotin moiety (MPO-activatable biotinylated sensor, MABS) that allows monitoring the innate immune response and its modulation at different scales and settings.

Methods:We designed and synthesized MABS that contains MPO-specific and biotin moieties, and validated its specificity and sensitivity combining with streptavidin-labeled fluorescent agent and gold nanoparticles imaging in vitro and in vivo in multiple mouse models of inflammation and infection, including Matrigel implant, dermatitis, cellulitis, cerebritis and complete Fraud's adjuvant (CFA)-induced inflammation.

Results: MABS MPO imaging non-invasively detected varying MPO concentrations, MPO inhibition, and MPO deficiency in vivo with high sensitivity and specificity. MABS can be used to obtain not only a fluorescence imaging agent, but also a CT imaging agent, conferring molecular activity information to a structural imaging modality. Importantly, using this method on tissue-sections, we found that MPO enzymatic activity does not always co-localize with MPO protein detected with conventional techniques (e.g., immunohistochemistry), underscoring the importance of monitoring enzymatic activity.

Conclusion:By choosing from different available secondary probes, MABS can be used to create systems suitable to investigate and image MPO activity at different scales and settings.

Monitoring diffuse injury during disease progression in experimental autoimmune encephalomyelitis with on resonance variable delay multiple pulse (onVDMP) CEST MRI

Multiple sclerosis (MS) is an autoimmune disorder that targets myelin proteins and results in extensive damage in the central nervous system in the form of focal lesions as well as diffuse molecular changes. Lesions are currently detected using T1-weighted, T2-weighted, and gadolinium-enhanced magnetic resonance imaging (MRI); however, monitoring such lesions has been shown to be a poor predictor of disease progression. Chemical exchange saturation transfer (CEST) MRI is sensitive to many of the biomolecules in the central nervous system altered in MS that cannot be detected using conventional MRI. We monitored disease progression in an experimental autoimmune encephalomyelitis (EAE) model of MS using on resonance variable delay multiple pulse (onVDMP) CEST MRI. Alterations in onVDMP signal were observed in regions responsible for hindlimb function throughout the central nervous system. Histological analysis revealed glial activation in areas highlighted in onVDMP CEST MRI. onVDMP signal changes in the 3rd ventricle preceded paralysis onset that could not be observed with conventional MRI techniques. Hence, the onVDMP CEST MRI signal has potential as a novel imaging biomarker and predictor of disease progression in MS.

Myeloperoxidase Molecular MRI Reveals Synergistic Combination Therapy in Murine Experimental Autoimmune Neuroinflammation

Background Despite advances in immunomodulatory agents, most current therapies for multiple sclerosis target lymphocytes or lymphocytic function. However, therapy response may be less than optimal due to demyelination and axonal damage caused by myeloid cells. Purpose To determine if myeloperoxidase (MPO) molecular MRI can evaluate whether combination therapy targeting both lymphoid and myeloid inflammation can improve autoimmune neuroinflammation compared with either drug alone, even at suboptimal doses. Materials and Methods Four groups of 94 female mice (8-10 weeks old) were induced with experimental autoimmune encephalomyelitis (EAE) from August 2, 2016, to March 30, 2018, and divided into saline control (n = 22), 4-aminobenzoic acid hydrazide (ABAH) therapy group (n = 19), glatiramer acetate (GA) therapy group (n = 22), and combination therapy group (n = 31). Mice were administered suboptimal doses of ABAH, an irreversible inhibitor of MPO; GA, a first-line multiple sclerosis drug; both ABAH and GA; or saline (control). Mice were imaged with bis-5-hydroxytryptamide-diethylenetriaminepentaacetate gadolinium (hereafter, MPO-Gd) MRI. One-way analysis of variance, two-way analysis of variance, Kurskal-Wallis, and log-rank tests were used. P < .05 was considered to indicate statistical significance. Results The combination-treated group showed delayed disease onset (day 11.3 vs day 9.8 for ABAH, day 10.4 for GA, day 9.9 for control; P < .05) and reduced disease severity (clinical score during the acute exacerbation period of 1.8 vs 3.8 for ABAH, 3.1 for GA, 3.9 for control; P < .05). The combination-treated group demonstrated fewer MPO-positive lesions (30.2 vs 73.7 for ABAH, 64.8 for GA, 67.2 for control; P < .05), smaller MPO-positive lesion volume (16.7 mm3 vs 65.2 mm3 for ABAH, 69.9 mm3 for GA, 66.0 mm3 for control; P < .05), and lower intensity of MPO-Gd lesion activation ratio (0.7 vs 1.9 for ABAH, 3.2 for GA, 2.3 for control; P < .05). Reduced disease severity in the combination group was confirmed at histopathologic analysis, where MPO expression (1779 vs 2673 for ABAH, 2898 for GA; P < .05) and demyelination (5.3% vs 9.0% for ABAH, 10.6% for GA; P < .05) were ameliorated. Conclusion Myeloperoxidase molecular MRI can track the treatment response from immunomodulatory drugs even if the drug does not directly target myeloperoxidase, and establishes that combination therapy targeting both myeloid and lymphocytic inflammation is effective for murine autoimmune neuroinflammation, even at suboptimal doses. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Walczak in this issue.

Bioluminescence Imaging of Inflammation in Vivo Based on Bioluminescence and Fluorescence Resonance Energy Transfer Using Nanobubble Ultrasound Contrast Agent

Inflammation is an immunological response involved in various inflammatory disorders ranging from neurodegenerative diseases to cancers. Luminol has been reported to detect myeloperoxidase (MPO) activity in an inflamed area through a light-emitting reaction. However, this method is limited by low tissue penetration and poor spatial resolution. Here, we fabricated a nanobubble (NB) doped with two tandem lipophilic dyes, red-shifting luminol-emitted blue light to near-infrared region through a process integrating bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET). This BRET-FRET process caused a 24-fold increase in detectable luminescence emission over luminol alone in an inflammation model induced by lipopolysaccharide. In addition, the echogenicity of the BRET-FRET NBs also enables perfused tissue microvasculature to be delineated by contrast-enhanced ultrasound imaging with high spatial resolution. Compared with commercially available ultrasound contrast agent, the BRET-FRET NBs exhibited comparable contrast-enhancing capability but much smaller size and higher concentration. This bioluminescence/ultrasound dual-modal contrast agent was then successfully applied for imaging of an animal model of breast cancer. Furthermore, biosafety experiments revealed that multi-injection of luminol and NBs did not induce any observable abnormality. By integrating the advantages of bioluminescence imaging and ultrasound imaging, this BRET-FRET system may have the potential to address a critical need of inflammation imaging.

A transgenic zebrafish line for in vivo visualisation of neutrophil myeloperoxidase

The neutrophil enzyme myeloperoxidase (MPO) is a major enzyme made by neutrophils to generate antimicrobial and immunomodulatory compounds, notably hypochlorous acid (HOCl), amplifying their capacity for destroying pathogens and regulating inflammation. Despite its roles in innate immunity, the importance of MPO in preventing infection is unclear, as individuals with MPO deficiency are asymptomatic with the exception of an increased risk of candidiasis. Dysregulation of MPO activity is also linked with inflammatory conditions such as atherosclerosis, emphasising a need to understand the roles of the enzyme in greater detail. Consequently, new tools for investigating granular dynamics in vivo can provide useful insights into how MPO localises within neutrophils, aiding understanding of its role in preventing and exacerbating disease. The zebrafish is a powerful model for investigating the immune system in vivo, as it is genetically tractable, and optically transparent. To visualise MPO activity within zebrafish neutrophils, we created a genetic construct that expresses human MPO as a fusion protein with a C-terminal fluorescent tag, driven by the neutrophil-specific promoter lyz. After introducing the construct into the zebrafish genome by Tol2 transgenesis, we established the Tg(lyz:Hsa.MPO-mEmerald,cmlc2:EGFP)sh496 line, and confirmed transgene expression in zebrafish neutrophils. We observed localisation of MPO-mEmerald within a subcellular location resembling neutrophil granules, mirroring MPO in human neutrophils. In Spotless (mpxNL144) larvae-which express a non-functional zebrafish myeloperoxidase-the MPO-mEmerald transgene does not disrupt neutrophil migration to sites of infection or inflammation, suggesting that it is a suitable line for the study of neutrophil granule function. We present a new transgenic line that can be used to investigate neutrophil granule dynamics in vivo without disrupting neutrophil behaviour, with potential applications in studying processing and maturation of MPO during development.

Inhibition of myeloperoxidase by N-acetyl lysyltyrosylcysteine amide reduces experimental autoimmune encephalomyelitis-induced injury and promotes oligodendrocyte regeneration and neurogenesis in a murine model of progressive multiple sclerosis

It is known that oxidative stress produced by proinflammatory myeloid cells plays an important role in demyelination and neuronal injury in progressive multiple sclerosis (MS). Myeloperoxidase (MPO) is a pro-oxidative enzyme released from myeloid cells during inflammation. It has been shown that MPO-dependent oxidative stress plays important roles in inducing tissue injury in many inflammatory diseases. In this report, we treated NOD experimental autoimmune encephalomyelitis (EAE) mice, a murine model of progressive MS, with N-acetyl lysyltyrosylcysteine amide (KYC), a novel specific MPO inhibitor. Our data showed that KYC treatment not only attenuated MPO-mediated oxidative stress but also reduced demyelination and axonal injury in NOD EAE mice. More importantly, we found that KYC treatment increased oligodendrocyte regeneration and neurogenesis in NOD EAE mice. Taken together, our data suggests that targeting MPO should be a good therapeutic approach for reducing oxidative injury and preserving neuronal function in progressive MS patients.

Nrf2/ARE Pathway Modulation by Dietary Energy Regulation in Neurological Disorders

Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates the expression of an array of enzymes with important detoxifying and antioxidant functions. Current findings support the role of high levels of oxidative stress in the pathogenesis of neurological disorders. Given the central role played by Nrf2 in counteracting oxidative damage, a number of studies have targeted the modulation of this transcription factor in order to confer neuroprotection. Nrf2 activity is tightly regulated by oxidative stress and energy-based stimuli. Thus, many dietary interventions based on energy intake regulation, such as dietary energy restriction (DER) or high-fat diet (HFD), modulate Nrf2 with consequences for a variety of cellular processes that affect brain health. DER, by either restricting calorie intake or meal frequency, activates Nrf2 thereby triggering its protective effects, whilst HFD inhibit this pathway, thereby exacerbating oxidative stress. Consequently, DER protocols can be valuable strategies in the management of central nervous system (CNS) disorders. Herein, we review current knowledge of the role of Nrf2 signaling in neurological diseases, namely Alzheimer’s disease, Parkinson’s disease, multiple sclerosis and cerebral ischemia, as well as the potential of energy intake regulation in the management of Nrf2 signaling.

A DNA-based fluorescent reporter maps HOCl production in the maturing phagosome

Phagocytes destroy pathogens by trapping them in a transient organelle called the phagosome, where they are bombarded with reactive oxygen species (ROS) and reactive nitrogen species (RNS). Imaging reactive species within the phagosome would directly reveal the chemical dynamics underlying pathogen destruction. Here we introduce a fluorescent, DNA-based combination reporter, cHOClate, which simultaneously images hypochlorous acid (HOCl) and pH quantitatively. Using cHOClate targeted to phagosomes in live cells, we successfully map phagosomal production of a specific ROS, HOCl, as a function of phagosome maturation. We found that phagosomal acidification was gradual in macrophages and upon completion, HOCl was released in a burst. This revealed that phagosome-lysosome fusion was essential not only for phagosome acidification, but also for providing the chloride necessary for myeloperoxidase activity. This method can be expanded to image several kinds of ROS and RNS and be readily applied to identify how resistant pathogens evade phagosomal killing.

MRI of Iron Oxide Nanoparticles and Myeloperoxidase Activity Links Inflammation to Brain Edema in Experimental Cerebral Malaria

Purpose To investigate the association of inflammation and brain edema in a cerebral malaria (CM) mouse model with a combination of bis-5-hydroxy-tryptamide-diethylenetriaminepentaacetate gadolinium, referred to as MPO-Gd, and cross-linked iron oxide nanoparticle (CLIO-NP) imaging. Materials and Methods Female wild-type (n = 23) and myeloperoxidase (MPO) knock-out (n = 5) mice were infected with the Plasmodium berghei ANKA strain from May 2016 to July 2018. Seven healthy mice served as control animals. At a Rapid Murine Coma and Behavioral Scale (RMCBS) score of less than 15, mice underwent MRI at 9.4 T and received gadodiamide, MPO-Gd, or CLIO-NPs. T1-weighted MRI was used to assess MPO activity, and T2*-weighted MRI was used to track CLIO-NPs. Immunofluorescent staining and flow cytometric analyses characterized CLIO-NPs, MPO, endothelial cells, and leukocytes. An unpaired, two-tailed Student t test was used to compare groups; Spearman correlation analysis was used to determine the relationship of imaging parameters to clinical severity. Results MPO-Gd enhancement occurred in inflammatory CM hotspots (olfactory bulb > rostral migratory stream > brainstem > cortex, P < .05 for all regions compared with control mice; mean olfactory bulb signal intensity ratio: 1.40 ± 0.07 vs 0.96 ± 0.01, P < .01). The enhancement was reduced in MPO knockout mice (mean signal intensity ratio at 60 minutes: 1.13 ± 0.04 vs 1.40 ± 0.07 in CM, P < .05). Blood-brain barrier compromise was suggested by parenchymal gadolinium enhancement, leukocyte recruitment, and endothelial activation. CLIO-NPs accumulated mainly intravascularly and at the vascular endothelium. CLIO-NPs were also found in the choroid plexus, indicating inflammation of the ventricular system. Blood-cerebrospinal fluid barrier breakdown showed correlation with brain swelling (r²: 0.55, P < .01) and RMCBS score (r²: 0.75, P < .001). Conclusion Iron oxide nanoparticle imaging showed strong inflammatory involvement of the microvasculature in a murine model of cerebral malaria. Furthermore, bis-5-hydroxy-tryptamide-diethylenetriaminepentaacetate gadolinium imaging depicted parenchymal and intraventricular inflammation. This combined molecular imaging approach links vascular inflammation to breakdown of the blood-brain barrier and blood-cerebrospinal fluid barrier that correlate with global brain edema and disease severity. © RSNA, 2018 Online supplemental material is available for this article. See also the editorial by Kiessling in this issue.

Serum myeloperoxidase concentrations for outcome prediction in acute intracerebral hemorrhage

BACKGROUND

Oxidative stress is related to brain injury after spontaneous intracerebral hemorrhage (ICH). Myeloperoxidase (MPO) is a potent oxidizing enzyme. We tested the hypothesis that serum MPO concentrations are increased after ICH and they correlate with stroke severity and outcome.

METHODS

Serum MPO concentrations were measured in 128 ICH patients and 128 controls. Odds ratios of dependent variables, including early neurological deterioration, hematoma growth, 1-week mortality, 6-month mortality, 6-month unfavorable outcome (modified Rankin Scale score > 2) and 6-month overall survival, were calculated and adjusted for age, sex, hematoma volume, National Institutes of Health Stroke Scale (NIHSS) score and vascular risk factors.

RESULTS

As compared to the controls, the patients had significantly increased serum MPO concentrations. MPO concentrations of the ICH patients were strongly correlated with hematoma volume and NIHSS scores. Serum MPO were independently associated with the above-mentioned study points. Its area under receiver operating characteristic curve was equivalent to those of hematoma volume and NIHSS score. Moreover, serum MPO significantly improved the discriminatory ability of hematoma and NIHSS in predicting 6-month mortality and unfavorable outcome.

CONCLUSIONS

Serum MPO concentrations rise in ICH patients and there is a correlation between MPO concentrations and severity or prognosis.

Inflammation in CNS neurodegenerative diseases

Neurodegenerative diseases, the leading cause of morbidity and disability, are gaining increased attention as they impose a considerable socioeconomic impact, due in part to the ageing community. Neuronal damage is a pathological hallmark of Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, Huntington's disease, spinocerebellar ataxia and multiple sclerosis, although such damage is also observed following neurotropic viral infections, stroke, genetic white matter diseases and paraneoplastic disorders. Despite the different aetiologies, for example, infections, genetic mutations, trauma and protein aggregations, neuronal damage is frequently associated with chronic activation of an innate immune response in the CNS. The growing awareness that the immune system is inextricably involved in shaping the brain during development as well as mediating damage, but also regeneration and repair, has stimulated therapeutic approaches to modulate the immune system in neurodegenerative diseases. Here, we review the current understanding of how astrocytes and microglia, as well as neurons and oligodendrocytes, shape the neuroimmune response during development, and how aberrant responses that arise due to genetic or environmental triggers may predispose the CNS to neurodegenerative diseases. We discuss the known interactions between the peripheral immune system and the brain, and review the current concepts on how immune cells enter and leave the CNS. A better understanding of neuroimmune interactions during development and disease will be key to further manipulating these responses and the development of effective therapies to improve quality of life, and reduce the impact of neuroinflammatory and degenerative diseases.

Microglial Phenotypes and Functions in Multiple Sclerosis

Microglia are the resident immune cells that constantly survey the central nervous system. They can adapt to their environment and respond to injury or insult by altering their morphology, phenotype, and functions. It has long been debated whether microglial activation is detrimental or beneficial in multiple sclerosis (MS). Recently, the two opposing yet connected roles of microglial activation have been described with the aid of novel microglial markers, RNA profiling, and in vivo models. In this review, microglial phenotypes and functions in the context of MS will be discussed with evidence from both human pathological studies, in vitro and in vivo models. Microglial functional diversity-phagocytosis, antigen presentation, immunomodulation, support, and repair-will also be examined in detail. In addition, this review discusses the emerging evidence for microglia-related targets as biomarkers and therapeutic targets for MS.

Myeloperoxidase: A new player in autoimmunity

Myeloperoxidase (MPO) is the most toxic enzyme found in the azurophilic granules of neutrophils. MPO utilizes H2O2 to generate hypochlorous acid (HClO) and other reactive moieties, which kill pathogens during infections. In contrast, in the setting of sterile inflammation, MPO and MPO-derived oxidants are thought to be pathogenic, promoting inflammation and causing tissue damage. In contrast, evidence also exists that MPO can limit the extent of immune responses. Elevated MPO levels and activity are observed in a number of autoimmune diseases including in the central nervous system (CNS) of multiple sclerosis (MS) and the joints of rheumatoid arthritis (RA) patients. A pathogenic role for MPO in driving autoimmune inflammation was demonstrated using mouse models. Mechanisms whereby MPO is thought to contribute to disease pathogenesis include tuning of adaptive immune responses and/or the induction of vascular permeability.

Interrogating Metabolism in Brain Cancer

This article reviews existing and emerging techniques of interrogating metabolism in brain cancer from well-established proton magnetic resonance spectroscopy to the promising hyperpolarized metabolic imaging and chemical exchange saturation transfer and emerging techniques of imaging inflammation. Some of these techniques are at an early stage of development and clinical trials are in progress in patients to establish the clinical efficacy. It is likely that in vivo metabolomics and metabolic imaging is the next frontier in brain cancer diagnosis and assessing therapeutic efficacy; with the combined knowledge of genomics and proteomics a complete understanding of tumorigenesis in brain might be achieved.

The neuroprotective effect of mesenchymal stem cells on an experimentally induced model for multiple sclerosis in mice

Multiple sclerosis (MS) is a chronic autoimmune demyelinating neurodegenerative central nervous system disorder. The aim of the present study was to investigate the prophylactic effect exerted by the one-time intraperitoneal injection of mesenchymal stem cells (MSCs) 1 × 10⁶ and 14-day intraperitoneal injection of methylprednisolone (MP) 40 mg/kg in an experimental autoimmune encephalomyelitis (EAE). EAE was induced by intradermal injection of rat spinal cord homogenate with complete Freund's adjuvant in Swiss mice. Results of MSCs and MP-treated mice showed a significantly milder disease and fewer clinical scores compared to control mice. They suppressed tumor necrosis factor-alpha and myeloperoxidase and increased interleukin 10, whereas thiobarbituric acid reactive substances and nitric oxide brain contents were reduced to comparable levels between treatment groups. Brain content of GSH was significantly higher in MSCs-treated mice than control mice. It is evident that MSCs have relevant prophylactic effect in an animal model of MS and might represent a valuable tool for stem cell based therapy in MS.

Molecular MR Imaging of Myeloperoxidase Distinguishes Steatosis from Steatohepatitis in Nonalcoholic Fatty Liver Disease

Purpose To test whether MPO-Gd, an activatable molecular magnetic resonance (MR) imaging agent specific for myeloperoxidase (MPO) activity, could detect MPO activity in nonalcoholic steatohepatitis (NASH) mouse models and human liver biopsy samples. Materials and Methods In this study, 20 leptin receptor-deficient and three MPO knockout mice were injected with endotoxin (lipopolysaccharide) or fed a methionine and choline-deficient (MCD) diet to induce experimental NASH and underwent MR imaging with MPO-Gd. Saline-injected and control diet-fed leptin receptor-deficient mice were used as respective controls. MPO protein and activity measurements and histologic analyses were performed. Eleven human liver biopsy samples underwent MPO-Gd-enhanced MR imaging ex vivo and subsequent histologic evaluation. Results were compared with Student t test or Mann-Whitney U test. Results With endotoxin, a significantly increased contrast-to-noise ratio (CNR) was found compared with sham (mean CNR, 1.81 [95% confidence interval {CI}: 1.53, 2.10] vs 1.02 [95% CI: 0.89, 1.14]; P = .03) at MPO-Gd MR imaging. In the diet-induced NASH model, an increased CNR was also found compared with sham mice (mean CNR, 1.33 [95% CI: 1.27, 1.40] vs 0.98 [95% CI: 0.83, 1.12]; P = .008). Conversely, CNR remained at baseline in NASH mice imaged with gadopentetate dimeglumine and in MPO knockout NASH mice with MPO-Gd, which proves specificity of MPO-Gd. Ex vivo molecular MR imaging of liver biopsy samples from NASH and control patients confirmed results from animal studies (mean CNR for NASH vs control patients, 2.61 [95% CI: 1.48, 3.74] vs 1.29 [95% CI: 1.06, 1.52]; P = .004). Conclusion MPO-Gd showed elevated MPO activity in NAFLD mouse models and human liver biopsy samples. ^© RSNA, 2017 Online supplemental material is available for this article. An earlier incorrect version of this article appeared online. This article was corrected on April 6, 2017.

In vivo nanoparticle imaging of innate immune cells can serve as a marker of disease severity in a model of multiple sclerosis

Innate immune cells play a key role in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis (EAE). Current clinical imaging is restricted to visualizing secondary effects of inflammation, such as gliosis and blood-brain barrier disruption. Advanced molecular imaging, such as iron oxide nanoparticle imaging, can allow direct imaging of cellular and molecular activity, but the exact cell types that phagocytose nanoparticles in vivo and how phagocytic activity relates to disease severity is not well understood. In this study we used MRI to map inflammatory infiltrates using high-field MRI and fluorescently labeled cross-linked iron oxide nanoparticles for cell tracking. We confirmed nanoparticle uptake and MR detectability ex vivo. Using in vivo MRI, we identified extensive nanoparticle signal in the cerebellar white matter and circumscribed cortical gray matter lesions that developed during the disease course (4.6-fold increase of nanoparticle accumulation in EAE compared with healthy controls, P < 0.001). Nanoparticles showed good cellular specificity for innate immune cells in vivo, labeling activated microglia, infiltrating macrophages, and neutrophils, whereas there was only sparse uptake by adaptive immune cells. Importantly, nanoparticle signal correlated better with clinical disease than conventional gadolinium (Gd) imaging (r, 0.83 for nanoparticles vs. 0.71 for Gd-imaging, P < 0.001). We validated our approach using the Food and Drug Administration-approved iron oxide nanoparticle ferumoxytol. Our results show that noninvasive molecular imaging of innate immune responses can serve as an imaging biomarker of disease activity in autoimmune-mediated neuroinflammation with potential clinical applications in a wide range of inflammatory diseases.

Myeloperoxidase Inhibition Increases Neurogenesis after Ischemic Stroke

The relationship between inflammation and neurogenesis in stroke is currently not well understood. Focal ischemia enhances cell proliferation and neurogenesis in the neurogenic regions, including the subventricular zone (SVZ), dentate gyrus, as well as the non-neurogenic striatum, and cortex in the ischemic hemisphere. Myeloperoxidase (MPO) is a potent oxidizing enzyme secreted during inflammation by activated leukocytes, and its enzymatic activity is highly elevated after stroke. In this study, we investigated whether the inhibition of MPO activity by a specific irreversible inhibitor, 4-aminobenzoic acid hydrazide (ABAH) (MPO-/- mice) can increase neurogenesis after transient middle cerebral artery occlusion in mice. ABAH administration increased the number of proliferating bromodeoxyuridine (BrdU)-positive cells expressing markers for neural stems cells, astrocytes, neuroprogenitor cells (Nestin), and neuroblasts (doublecortin) in the ischemic SVZ, anterior SVZ, striatum, and cortex. MPO inhibition also increased levels of brain-derived neurotrophic factor, phosphorylation of cAMP response element-binding protein (Ser133), acetylated H3, and NeuN to promote neurogenesis in the ischemic SVZ. ABAH treatment also increased chemokine CXC receptor 4 expression in the ischemic SVZ. MPO-deficient mice treated with vehicle or ABAH both showed similar effects on the number of BrdU+ cells in the ischemic hemisphere, demonstrating that ABAH is specific to MPO. Taken together, our results underscore a detrimental role of MPO activity to postischemia neurogenesis and that a strategy to inhibit MPO activity can increase cell proliferation and improve neurogenesis after ischemic stroke.

Spinal Cord Inflammation: Molecular Imaging after Thoracic Aortic Ischemia Reperfusion Injury

Purpose To evaluate whether noninvasive molecular imaging technologies targeting myeloperoxidase (MPO) can reveal early inflammation associated with spinal cord injury after thoracic aortic ischemia-reperfusion (TAR) in mice. Materials and Methods The study was approved by the institutional animal care and use committee. C57BL6 mice that were 8-10 weeks old underwent TAR (n = 55) or sham (n = 26) surgery. Magnetic resonance (MR) imaging (n = 6) or single photon emission computed tomography (SPECT)/computed tomography (CT) (n = 15) studies targeting MPO activity were performed after intravenous injection of MPO sensors (bis-5-hydroxytryptamide-tetraazacyclododecane [HT]-diethyneletriaminepentaacetic acid [DTPA]-gadolinium or indium 111-bis-5-HT-DTPA, respectively). Immunohistochemistry and flow cytometry were used to identify myeloid cells and neuronal loss. Proinflammatory cytokines, keratinocyte chemoattractant (KC), and interleukin 6 (IL-6) were measured with enzyme-linked immunosorbent assay. Statistical analyses were performed by using nonparametric tests and the Pearson correlation coefficient. P < .05 was considered to indicate a significant difference. Results Myeloid cells infiltrated into the injured cord at 6 and 24 hours after TAR. MR imaging confirmed the presence of ischemic lesions associated with mild MPO-mediated enhancement in the thoracolumbar spine at 24 hours compared with the sham procedure. SPECT/CT imaging of MPO activity showed marked MPO-sensor retention at 6 hours (P = .003) that continued to increase at 24 hours after TAR (P = .0001). The number of motor neurons decreased substantially at 24 hours after TAR (P < .01), which correlated inversely with in vivo inflammatory changes detected at molecular imaging (r = 0.64, P = .0099). MPO was primarily secreted by neutrophils, followed by lymphocyte antigen 6 complex^high monocytes and/or macrophages. There were corresponding increased levels of proinflammatory cytokines KC (P = .0001) and IL-6 (P = .0001) that mirrored changes in MPO activity. Conclusion MPO is a suitable imaging biomarker for identifying and tracking inflammatory damage in the spinal cord after TAR in a mouse model. ^© RSNA, 2016 Online supplemental material is available for this article.

Myeloperoxidase: Bridging the gap in neurodegeneration

Neurodegenerative conditions present a group of complex disease pathologies mostly due to unknown aetiology resulting in neuronal death and permanent neurological disability. Any undesirable stress to the brain, disrupts homeostatic balance, through a remarkable convergence of pathophysiological changes and immune dysregulation. The crosstalk between inflammatory and oxidative mechanisms results in the release of neurotoxic mediators apparently spearheaded by myeloperoxidase derived from activated microglia, astrocytes, neurons as well as peripheral inflammatory cells. These isolated entities combinedly have the potential to flare up and contribute significantly to neuropathology and disease progression. Recent, clinicopathological evidence support the association of myeloperoxidase and its cytotoxic product, hypochlorous acid in a plethora of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, Multiple sclerosis, Stroke, Epilepsy etc. But the biochemical and mechanistic insights into myeloperoxidase mediated neuroinflammation and neuronal death is still an uncharted territory. The current review outlines the emerging recognition of myeloperoxidase in neurodegeneration, which may offer novel therapeutic and diagnostic targets for neurodegenerative disorders.

Inhibition of myeloperoxidase oxidant production by N-acetyl lysyltyrosylcysteine amide reduces brain damage in a murine model of stroke

BACKGROUND

Oxidative stress plays an important and causal role in the mechanisms by which ischemia/reperfusion (I/R) injury increases brain damage after stroke. Accordingly, reducing oxidative stress has been proposed as a therapeutic strategy for limiting damage in the brain after stroke. Myeloperoxidase (MPO) is a highly potent oxidative enzyme that is capable of inducing both oxidative and nitrosative stress in vivo.

METHODS

To determine if and the extent to which MPO-generated oxidants contribute to brain I/R injury, we treated mice subjected to middle cerebral artery occlusion (MCAO) with N-acetyl lysyltyrosylcysteine amide (KYC), a novel, specific and non-toxic inhibitor of MPO. Behavioral testing, ischemic damage, blood-brain-barrier disruption, apoptosis, neutrophils infiltration, microglia/macrophage activation, and MPO oxidation were analyzed within a 7-day period after MCAO.

RESULTS

Our studies show that KYC treatment significantly reduces neurological severity scores, infarct size, IgG extravasation, neutrophil infiltration, loss of neurons, apoptosis, and microglia/macrophage activation in the brains of MCAO mice. Immunofluorescence studies show that KYC treatment reduces the formation of chlorotyrosine (ClTyr), a fingerprint biomarker of MPO oxidation, nitrotyrosine (NO2Tyr), and 4-hydroxynonenal (4HNE) in MCAO mice. All oxidative products colocalized with MPO in the infarcted brains, suggesting that MPO-generated oxidants are involved in forming the oxidative products.

CONCLUSIONS

MPO-generated oxidants play detrimental roles in causing brain damage after stroke which is effectively reduced by KYC.

Albumin and multiple sclerosis

Leakage of the blood-brain barrier (BBB) is a common pathological feature in multiple sclerosis (MS). Following a breach of the BBB, albumin, the most abundant protein in plasma, gains access to CNS tissue where it is exposed to an inflammatory milieu and tissue damage, e.g., demyelination. Once in the CNS, albumin can participate in protective mechanisms. For example, due to its high concentration and molecular properties, albumin becomes a target for oxidation and nitration reactions. Furthermore, albumin binds metals and heme thereby limiting their ability to produce reactive oxygen and reactive nitrogen species. Albumin also has the potential to worsen disease. Similar to pathogenic processes that occur during epilepsy, extravasated albumin could induce the expression of proinflammatory cytokines and affect the ability of astrocytes to maintain potassium homeostasis thereby possibly making neurons more vulnerable to glutamate exicitotoxicity, which is thought to be a pathogenic mechanism in MS. The albumin quotient, albumin in cerebrospinal fluid (CSF)/albumin in serum, is used as a measure of blood-CSF barrier dysfunction in MS, but it may be inaccurate since albumin levels in the CSF can be influenced by multiple factors including: 1) albumin becomes proteolytically cleaved during disease, 2) extravasated albumin is taken up by macrophages, microglia, and astrocytes, and 3) the location of BBB damage affects the entry of extravasated albumin into ventricular CSF. A discussion of the roles that albumin performs during MS is put forth.

Methods for measuring myeloperoxidase activity toward assessing inhibitor efficacy in living systems

Myeloperoxidase aids in clearance of microbes by generation of peroxidase-mediated oxidants that kill leukocyte-engulfed pathogens. In this review, we will examine 1) strategies for in vitro evaluation of myeloperoxidase function and its inhibition, 2) ways to monitor generation of certain oxidant species during inflammation, and 3) how these methods can be used to approximate the total polymorphonuclear neutrophil chemotaxis following insult. Several optical imaging probes are designed to target reactive oxygen and nitrogen species during polymorphonuclear neutrophil inflammatory burst following injury. Here, we review the following 1) the broad effect of myeloperoxidase on normal physiology, 2) the difference between myeloperoxidase and other peroxidases, 3) the current optical probes available for use as surrogates for direct measures of myeloperoxidase-derived oxidants, and 4) the range of preclinical options for imaging myeloperoxidase accumulation at sites of inflammation in mice. We also stress the advantages and drawbacks of each of these methods, the pharmacokinetic considerations that may limit probe use to strictly cell cultures for some reactive oxygen and nitrogen species, rather than in vivo utility as indicators of myeloperoxidase function. Taken together, our review should shed light on the fundamental rational behind these techniques for measuring myeloperoxidase activity and polymorphonuclear neutrophil response after injury toward developing safe myeloperoxidase inhibitors as potential therapy for chronic obstructive pulmonary disease and rheumatoid arthritis.

Assessment of electrophile damage in a human brain endothelial cell line utilizing a clickable alkyne analog of 2-chlorohexadecanal

Peripheral leukocytes aggravate brain damage by releasing cytotoxic mediators that compromise blood-brain barrier function. One of the oxidants released by activated leukocytes is hypochlorous acid (HOCl) that is formed via the myeloperoxidase-H2O2-chloride system. The reaction of HOCl with the endogenous plasmalogen pool of brain endothelial cells results in the generation of 2-chlorohexadecanal (2-ClHDA), a toxic, lipid-derived electrophile that induces blood-brain barrier dysfunction in vivo. Here, we synthesized an alkynyl-analog of 2-ClHDA, 2-chlorohexadec-15-yn-1-al (2-ClHDyA) to identify potential protein targets in the human brain endothelial cell line hCMEC/D3. Similar to 2-ClHDA, 2-ClHDyA administration reduced cell viability/metabolic activity, induced processing of pro-caspase-3 and PARP, and led to endothelial barrier dysfunction at low micromolar concentrations. Protein-2-ClHDyA adducts were fluorescently labeled with tetramethylrhodamine azide (N3-TAMRA) by 1,3-dipolar cycloaddition in situ, which unveiled a preferential accumulation of 2-ClHDyA adducts in mitochondria, the Golgi, endoplasmic reticulum, and endosomes. Thirty-three proteins that are subject to 2-ClHDyA-modification in hCMEC/D3 cells were identified by mass spectrometry. Identified proteins include cytoskeletal components that are central to tight junction patterning, metabolic enzymes, induction of the oxidative stress response, and electrophile damage to the caveolar/endosomal Rab machinery. A subset of the targets was validated by a combination of N3-TAMRA click chemistry and specific antibodies by fluorescence microscopy. This novel alkyne analog is a valuable chemical tool to identify cellular organelles and protein targets of 2-ClHDA-mediated damage in settings where myeloperoxidase-derived oxidants may play a disease-propagating role.

Gelsolin decreases actin toxicity and inflammation in murine multiple sclerosis

Gelsolin is the fourth most abundant protein in the body and its depletion in the blood has been found in multiple sclerosis (MS) patients. How gelsolin affects the MS brain has not been studied. We found that while the secreted form of gelsolin (pGSN) decreased in the blood of experimental autoimmune encephalomyelitis (EAE) mice, pGSN concentration increased in the EAE brain. Recombinant human pGSN (rhp-GSN) decreased extracellular actin and myeloperoxidase activity in the brain, resulting in reduced disease activity and less severe clinical disease, suggesting that gelsolin could be a potential therapeutic target for MS.

Protective effect of ginsenoside Rb1 on integrity of blood-brain barrier following cerebral ischemia

Ginsenosides, the major bioactive compounds in ginseng root, have been found to have antioxidant, immunomodulatory, and anti-inflammatory activities. In the present study, we sought to investigate whether and how ginsenoside Rb1 (GS-Rb1), the most abundant ginsenoside, can protect blood-brain barrier (BBB) integrity following cerebral ischemia in middle cerebral artery occlusion (MCAO) animal model. ICR mice underwent MCAO and received GS-Rb1 by intraperitoneal injection at 3 h after reperfusion. We evaluated infarction, neurological scores, brain edema, Evans blue (EB) extravasation, and tight junction protein expression at 48 h after MCAO. We further examined whether GS-Rb1 protected BBB integrity by suppressing post-ischemic inflammation-induced activity of matrix metalloproteinase-9 (MMP-9) and nicotinamide adenine dinucleotide phosphate oxidase (NOX). First, GS-Rb1 decreased infarction and improved neurological deficits in MCAO animals. In addition, GS-Rb1 reduced EB extravasation and brain edema and preserved expression of tight junction proteins in the ischemic brain. Moreover, GS-Rb1 inhibited expression of pro-inflammatory factors including nitric oxide synthase and IL-1β, but increased expression of anti-inflammatory markers arginase 1 and IL-10 in the ischemic brain. Consistently, GS-Rb1 attenuated ischemia-induced expression and activity of MMP9. Finally, GS-Rb1 reduced NOX-4 mRNA expression and NOX activity in ischemic brain. These results suggest that GS-Rb1 protects loss of BBB integrity in ischemic stroke by suppressing neuroinflammation induction of MMP-9 and NOX4-derived free radicals, and indicate its potential for treating brain injuries, such as ischemia and stroke.