DCE-MRI of Brain Fluid Barriers: In Vivo Water Cycling at the Human Choroid Plexus

Cerebral small vessel disease and glymphatic system dysfunction in multiple sclerosis: A narrative review

As the multiple sclerosis (MS) population ages, the prevalence of vascular comorbidities increases, potentially accelerating disease progression and brain atrophy. Recent studies highlight the prevalence of cerebral small vessel disease (CSVD) in MS, suggesting a potential link between vascular comorbidities and accelerated disability. CSVD affects the brain's small vessels, often leading to identifiable markers on MRI such as enlarged perivascular spaces (EPVS). EPVS are increasingly recognized also in MS and have been associated with vascular comorbidities, lower percentage of MS-specific perivenular lesions, brain atrophy and aging. The exact sequence of event leading to MRI visible EPVS is yet to be determined, but an impaired perivascular brain fluid drainage appears a possible physiopathological explanation for EPVS in both CSVD and MS. In this context, a dysfunction of the brain fluid clearance system - also known as "glymphatic system" - appears associated in MS to aging, neuroinflammation, and vascular dysfunction. Advanced imaging techniques show an impaired glymphatic function in both MS and CSVD. Additionally, lifestyle factors such as physical exercise, diet, and sleep quality appear to influence glymphatic function, potentially revealing novel therapeutic strategies to mitigate microangiopathy and neuroinflammation in MS. This review underscores the potential role of glymphatic dysfunction in the complex and not-yet elucidated interplay between neuroinflammation and CSVD in MS.

Imaging of brain barrier inflammation and brain fluid drainage in human neurological diseases

The intricate relationship between the central nervous system (CNS) and the immune system plays a crucial role in the pathogenesis of various neurological diseases. Understanding the interactions among the immunopathological processes at the brain borders is essential for advancing our knowledge of disease mechanisms and developing novel diagnostic and therapeutic approaches. In this review, we explore the emerging role of neuroimaging in providing valuable insights into brain barrier inflammation and brain fluid drainage in human neurological diseases. Neuroimaging techniques have enabled us not only to visualize and assess brain structures, but also to study the dynamics of the CNS in health and disease in vivo. By analyzing imaging findings, we can gain a deeper understanding of the immunopathology observed at the brain-immune interface barriers, which serve as critical gatekeepers that regulate immune cell trafficking, cytokine release, and clearance of waste products from the brain. This review explores the integration of neuroimaging data with immunopathological findings, providing valuable insights into brain barrier integrity and immune responses in neurological diseases. Such integration may lead to the development of novel diagnostic markers and targeted therapeutic approaches that can benefit patients with neurological disorders.

Choroid plexuses at the interface of peripheral immunity and tissue repair in multiple sclerosis

PURPOSE OF REVIEW

Choroid plexuses (ChPs) are key actors of the blood-to-cerebrospinal-fluid barrier and serve as brain immune checkpoint. The past years have seen a regain of interest about their potential involvement in the physiopathology of neuroinflammatory disorders like multiple sclerosis (MS). This article offers an overview of the recent findings on ChP alterations in MS, with a focus on the imaging tools able to detect these abnormalities and on their involvement in inflammation, tissue damage and repair.

RECENT FINDINGS

On MRI, ChPs are enlarged in people with MS (PwMS) versus healthy individuals. This size increase is an early event, already detected in presymptomatic and pediatric MS. Enlargement of ChPs is linked to local inflammatory infiltrates, and their dysfunction selectively impacts periventricular damage, larger ChPs predicting the expansion of chronic active lesions, smoldering inflammation and remyelination failure in tissues surrounding the ventricles. ChP volumetry may add value for the prediction of disease activity and disability worsening.

SUMMARY

ChP imaging metrics are emerging as possible biomarkers of neuroinflammation and repair failure in MS. Future works combining multimodal imaging techniques should provide a more refined characterization of ChP functional changes, their link with tissue damage, blood to cerebrospinal-fluid barrier dysfunction and fluid trafficking in MS.

A year in review: brain barriers and brain fluids research in 2022

This aim of this editorial is to highlight progress made in brain barrier and brain fluid research in 2022. It covers studies on the blood-brain, blood-retina and blood-CSF barriers (choroid plexus and meninges), signaling within the neurovascular unit and elements of the brain fluid systems. It further discusses how brain barriers and brain fluid systems are impacted in CNS diseases, their role in disease progression and progress being made in treating such diseases.

Metabolic activity diffusion imaging (MADI): II. Noninvasive, high-resolution human brain mapping of sodium pump flux and cell metrics

We introduce a new ¹ H₂ O magnetic resonance approach: metabolic activity diffusion imaging (MADI). Numerical diffusion-weighted imaging decay simulations characterized by the mean cellular water efflux (unidirectional) rate constant (k_io ), mean cell volume (V), and cell number density (ρ) are produced from Monte Carlo random walks in virtual stochastically sized/shaped cell ensembles. Because of active steady-state trans-membrane water cycling (AWC), k_io reflects the cytolemmal Na⁺ , K⁺ ATPase (NKA) homeostatic cellular metabolic rate (^c MR_NKA ). A digital 3D "library" contains thousands of simulated single diffusion-encoded (SDE) decays. Library entries match well with disparate, animal, and human experimental SDE decays. The V and ρ values are consistent with estimates from pertinent in vitro cytometric and ex vivo histopathological literature: in vivo V and ρ values were previously unavailable. The library allows noniterative pixel-by-pixel experimental SDE decay library matchings that can be used to advantage. They yield proof-of-concept MADI parametric mappings of the awake, resting human brain. These reflect the tissue morphology seen in conventional MRI. While V is larger in gray matter (GM) than in white matter (WM), the reverse is true for ρ. Many brain structures have k_io values too large for current, invasive methods. For example, the median WM k_io is 22s^-1 ; likely reflecting mostly exchange within myelin. The k_io •V product map displays brain tissue ^c MR_NKA variation. The GM activity correlates, quantitatively and qualitatively, with the analogous resting-state brain ¹⁸ FDG-PET tissue glucose consumption rate (^t MR_glucose ) map; but noninvasively, with higher spatial resolution, and no pharmacokinetic requirement. The cortex, thalamus, putamen, and caudate exhibit elevated metabolic activity. MADI accuracy and precision are assessed. The results are contextualized with literature overall homeostatic brain glucose consumption and ATP production/consumption measures. The MADI/PET results suggest different GM and WM metabolic pathways. Preliminary human prostate results are also presented.

Neuroimaging is the new "spatial omic": multi-omic approaches to neuro-inflammation and immuno-thrombosis in acute ischemic stroke

Ischemic stroke (IS) is the leading cause of acquired disability and the second leading cause of dementia and mortality. Current treatments for IS are primarily focused on revascularization of the occluded artery. However, only 10% of patients are eligible for revascularization and 50% of revascularized patients remain disabled at 3 months. Accumulating evidence highlight the prognostic significance of the neuro- and thrombo-inflammatory response after IS. However, several randomized trials of promising immunosuppressive or immunomodulatory drugs failed to show positive results. Insufficient understanding of inter-patient variability in the cellular, functional, and spatial organization of the inflammatory response to IS likely contributed to the failure to translate preclinical findings into successful clinical trials. The inflammatory response to IS involves complex interactions between neuronal, glial, and immune cell subsets across multiple immunological compartments, including the blood-brain barrier, the meningeal lymphatic vessels, the choroid plexus, and the skull bone marrow. Here, we review the neuro- and thrombo-inflammatory responses to IS. We discuss how clinical imaging and single-cell omic technologies have refined our understanding of the spatial organization of pathobiological processes driving clinical outcomes in patients with an IS. We also introduce recent developments in machine learning statistical methods for the integration of multi-omic data (biological and radiological) to identify patient-specific inflammatory states predictive of IS clinical outcomes.