Autoimmune Encephalitides

Synthesis of [11C]BIIB104, an α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic-Acid-Positive Allosteric Modulator, and Evaluation of the Bio-Distribution in Non-Human Primate Brains Using Positron Emission Tomography

The aim of this study was to measure the brain penetrance and kinetics of BIIB104, a first-in-class AMPA receptor potentiator developed for cognitive impairment associated with schizophrenia. It was recently halted in phase 2 clinical development, and there are a lack of tools to directly measure AMPA receptor engagement. To achieve this, the drug candidate was radiolabeled with carbon-11, and its brain penetrance and kinetics were measured in non-human primates via dynamic PET scans. Radiolabeling was achieved through a three-step nucleophilic [11C]cyanation reaction in one pot, resulting in the high radioactivity and radiochemical purity (>99%) of [11C]BIIB104. The study found that [11C]BIIB104 entered the non-human primate brains at 4-5% ID at peak, with a homogeneous distribution. However, a mild regional heterogeneity was observed in the thalamus. The lack of conclusive evidence for a change in regional values after BIIB104 dosing suggests that any specific binding component of BIIB104 is negligible compared to the free and non-specific components in the living brain. Overall, the study demonstrated high brain uptake with minor variability in [11C]BIIB104 distribution across various brain regions, its kinetics were consistent with those of passive diffusion, and the dominating components were the free concentration and non-specific binding. This information is valuable for understanding the potential effects and mechanisms of BIIB104 in the brain.

Evaluation of thiadiazine-based PET radioligands for imaging the AMPA receptor

As a subclass of ionotropic glutamate receptors (iGluRs), α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA) receptors have been implicated in various neurological disorders and neurodegenerative diseases. To further our understanding of AMPA receptor-related disorders in the central nervous system (CNS), it is important to be able to image and quantify AMPA receptors in vivo. In this study, we identified a novel F-containing AMPA positive allosteric modulator (PAM) 6 as a potential lead compound. Molecular docking studies and CNS PET multi-parameter optimization (MPO) analysis were used to predict the absorption, distribution, metabolism, and excretion (ADME) characteristics of 6 as a PET probe. The resulting PET probe, [18F]6 (codename [18F]AMPA-2109), was successfully radiolabeled and demonstrated excellent blood-brain barrier (BBB) permeability and high brain uptake in rodents and non-human primates. However, [18F]6 did not show substantial specific binding in the rodent or non-human primate brain. Further medicinal chemistry efforts are necessary to improve specific binding, and our work may serve as a starting point for the design of novel 18F-labeled AMPA receptor-targeted PET radioligands aimed for clinical translation.

Primary central nervous system vasculitis and headache: Ten themes

PURPOSE OF REVIEW

The primary central nervous system (CNS) vasculitides refers to clinicopathologic disorders that share the histopathology of inflammation of cerebral or spinal blood vessels. Unrecognized and therefore untreated, vasculitis of the CNS results in irreversible injury and disability making these disorders of paramount importance to clinicians.

RECENT FINDINGS

Headache is an important clue to vasculitic involvement of CNS vessels. CNS vasculitis can be primary, in which only intracranial or spinal vessels are involved in the inflammatory process, or secondary to another known disorder with overlapping systemic involvement. The suspicion of vasculitis based on the history, clinical examination, and laboratory studies warrants prompt evaluation and treatment to prevent cerebral ischemia or infarction.

SUMMARY

Primary CNS vasculitides can be diagnosed with certainty after intensive evaluation that includes tissue confirmation whenever possible. As in its systemic counterparts, clinicians must choose from among the available immune modulating, suppressive, and targeted immunotherapies to induce and maintain remission status and prevent relapse, tempered by anticipated medication adverse effects.

Adult and childhood vasculitis

Vasculitis refers to heterogeneous clinicopathologic disorders that share the histopathology of inflammation of blood vessels. Unrecognized and therefore untreated, vasculitis of the nervous system leads to pervasive injury and disability, making this a disorder of paramount importance to all clinicians. There has been remarkable progress in the pathogenesis, diagnosis, and treatment of primary CNS and PNS vasculitides, predicated on achievement in primary systemic forms. Primary neurological vasculitides can be diagnosed with assurance after intensive evaluation that incudes tissue confirmation whenever possible. Clinicians must choose from among the available immune modulating, suppressive, and targeted immunotherapies to induce and maintain remission status and prevent relapse, unfortunately without the benefit of RCTs, and tempered by the recognition of anticipated medication side effects. It may be said that efforts to define a disease are attempts to understand the very concept of the disease. This has been especially evident in systemic and neurological disorders associated with vasculitis. For the past 100 years, since the first description of granulomatous angiitis of the brain, the CNS vasculitides have captured the attention of generations of clinical investigators around the globe to reach a better understanding of vasculitides involving the central and peripheral nervous system. Since that time it has become increasingly evident that this will necessitate an international collaborative effort.

Pediatric neuropsychiatric disorders with motor and nonmotor phenomena

The concept of pediatric autoimmune neuropsychiatric disorders associated with group A beta-hemolytic streptococcus (PANDAS) has become seminal since first introduced more than two decades ago. At the time of this writing, most neurologists, pediatricians, psychiatrists, and general pediatricians will probably have heard of this association or treated an affected child with PANDAS. The concept of an acute-onset, and typically self-limited, postinfectious autoimmune neuropsychiatric disorder resembling PANDAS manifesting vocal and motor tics and obsessive-compulsive disorder has broadened to other putative microbes and related endogenous and exogenous disease triggers. These disorders with common features of hypometabolism in the medial temporal lobe and hippocampus in brain 18fluorodeoxyglucose positron emission tomography fused to magnetic resonance imaging (FDG PET-MRI), form a spectrum: with the neuropsychiatric disorder Tourette syndrome and PANDAS with its well-defined etiopathogenesis at one end, and pediatric abrupt-onset neuropsychiatric syndrome (PANS), alone or associated with specific bacterial and viral pathogens, at the other end. The designation of PANS in the absence of a specific trigger, as an exclusionary diagnosis, reflects the current problem in nosology.

Autoimmune Encephalitis: NMDA Receptor Encephalitis as an Example of Translational Neuroscience

Autoimmune encephalitis (AE) is a group of disorders causing synaptic receptor dysfunction with a broad range of neurological symptoms that has been historically difficult to differentiate clinically. Today, AE represents an excellent example of the rapid determination of the cause of a disease and the ability to identify potential treatments using relatively simple basic science techniques of investigation. Of the number of autoimmune encephalitides identified thus far, one of the best examples of the impact of basic science studies on disease management is NMDA receptor mediated autoimmune encephalitis (NMDAr-AE). In this review, we will provide an overview of the epidemiology of NMDAr-AE, clinical features and treatments, and the basic science tools and techniques that were used to identify the cause, correlate symptoms to underlying pathophysiology, and to understand the mechanism of disease pathology.