Another focus of the clinical research for this Collaboration involves our hypothesis that microglial cells become activated in critical brain nuclei creating a form of neuroinflammation, which affects normal function of multiple brain nuclei including those in the brainstem, during the development of the ME/CFS disease.
Specifically, microglial activation or neuroinflammation involves a M1 (proinflammatory) phenotype of microglia in brain stem nuclei and this inflammatory phenotype, as demonstrated by its genomic and proteomic characteristics, is causally related to the neurological symptoms associated with many, if not most, of those seen in ME/CFS patients. There are two other states or phenotypes for microglial cells (macrophages). These are M0 (resting) and M2 (repair) phenotypes, which also have characteristic genomic and proteomic features, and these phenotypes are not inflammatory.
Much of this microglial activation can be attributed to both vagus nerve afferent signals as well as key components of vagal efferent signals. There are a multitude of nuclei within the dorsal region of the brainstem but those involved with autonomic regulation representing vagal afferent and efferent signals are shown to the right taken from reference (1). They are the Edinger-Westfal nucleus (EW), periaqueductal grey (PAG), Nucleus cuneiformis (NCF), Nucleus ambiguus (NAmb), Area postrema (AP), and Dorsal motor nucleus of the vagal nerve (DMV) to only mention a few. This clinical research by the Collaboration takes advantage of two world class magnetic resonance imaging (MRI) and positron emission technology (PET) centers at MGH - The Athinoula A. Martinos Center for Biomedical Imaging and The Gordon Center for Medical Imaging.
These facilities offer outstanding opportunities to spatially localize microglial activation as well as highly related metabolic phenomena consistent with this hypothesis. Since these imaging studies will be in comparable patients or in some instances, in the same highly phenotyped ME/CFS patients, correlations can be made with the intent to identify biomarkers and suggest drug targets for use in the development of therapeutics for ME/CFS.
There is ample evidence that low grade inflammation is present in ME/CFS patients at all times when the disease is active and this inflammation might be very significant during periods of flares. This peripheral inflammation can either be spread directly to the central nervous system (CNS) via porous portions of the blood brain barrier or it might be detected by the vagus nerve afferent system and transmitted to the CNS indirectly. Either way, it is easy to understand the possibility that a CNS form of neuroinflammation is also likely present in ME/CFS in the form of activated microglial cells, which are the macrophages in the CNS.
This possibility was first directly demonstrated by a 2014 study by Nakatomi utilizing 11C-(R)-PK11195 to identify a translocator protein (TSPO) that is thought to be expressed in microglial cells when activated to an M1 (proinflammatory) phenotype as shown to the right (2). This study has significant shortcomings that reduces its reliability and limits its contribution to the subtle details about microglial activation in ME/CFS as identified in a publication by VanElzakker (3).
First, it is a small study of nine patients and ten controls. Second, normally the image is “registered” relative to the cerebral cortex, however, the brainstem’s orientation relative to the cortex varies significantly among individuals as shown to the right (4). Third, the arterial concentration of the PET tracer was modeled and normalized to the cerebellum because no arterial line was placed. This significantly compromises accuracy.
Fourth, the PET tracer is a first generation ligand with some ambiguity in specificity and second generation tracers have greatly improved on this specificity problem.
These shortcomings can be easily addressed using a second generation tracer (11C-PBR28), an arterial line, registration on the brain stem using a cranial dual MR-PET instrument in a somewhat larger patient population and will greatly improve the spatial localization of the microglial activation states within the brainstem. Many of these studies are in alignment with those of Jarred Younger at the University of Alabama.
Given the frequent involvement of neurotropic pathogens during symptom onset and given the profundity of frequent neurological and "sickness" symptoms including autonomic dysfunction, brain fog, sensory sensitivity, and pain, a significant focus of both ME/CFS and Post-Treatment Lyme Disease (PTLD) research should involve the brain. We hypothesize that glial signaling is activated along the neuro-immune axis, and that this state contributes to symptom maintenance.
Two neuro-imaging studies, headed by Dr. Michael VanElzakker, are currently ongoing at the The Athinoula A. Martinos Center for Biomedical Imaging. One study examines the neural basis of PEM using functional magnetic resonance imaging (fMRI). and the second study investigates the link between neuro-inflammation and in both ME/CFS and PTLD using a dual magnetic resonance and positron emission tomography (MR-PET) instrumentation. Both of these projects are currently funded by private donations.
Because many immune molecules and cells do not easily diffuse passively across the blood-brain barrier (BBB), the brain has specific strategies for sensing immune system activation. One key mechanism involves the vagus nerve, which we believe may be a central system in ME/CFS (5). Both the afferent (sensory, toward the brain) and the efferent (motor, toward the body) vagus nerve may be essential to ME/CFS symptom expression.
Chemoreceptors on the afferent vagus nerve are capable of detecting a local cytokine response, even when the cytokines are not circulating at sufficient enough levels to be detected in peripheral blood (3). This process triggers a "mirror response" of glial cell activation on the brain side of the BBB, which we believe may be central to subjective symptoms. Perhaps more importantly, in addition to being activated by afferent vagus signaling, glia can be directly activated by multiple factors including sensing pathogens or microbial products, physical injury or compression, or sensing damaged "self" cells. Furthermore, glial activation in the brainstem where the vagus nerve enters the central nervous system is also likely to disrupt appropriate efferent vagus nerve function and possibly contribute to autonomic symptoms including postural tachycardia, gastro-intestinal immotility, and temperature regulation dysfunction.
Imaging of Neuro-inflammation
The dual MR-PET study is intended to better understand the role of neuro-inflammation in ME/CFS and PTLD. The resident immune cells of the brain (microglia) enter a state of activation when they detect pathogens, pathogen products, or damaged cells. This activation is a key component of neuro-inflammation. Upon activation, microglia produce a protein (translocator protein or TSPO). This protein is detectable by PET imaging using the PBR28 radioligand, which binds to TSPO.
PBR28 is an experimental radioligand that is not available in most hospitals and universities. Importantly, access to a dual MR-PET instrument will allow concurrent structural and functional MRI scanning during the PET scan and allow the discovery of correlations between PBR28 signal and the current, more widely available data. This study will also investigate hypotheses related to cognitive "brain fog" by having patients perform a mental task, called the multi-source interference task (MSIT) during the scan. The MSIT engages the anterior mid-cingulate cortex (aMCC), which is a structure that is key to maintenance of attention, and it also is particularly sensitive to inflammation. Our techniques will allow the aMCC to be measured in several ways, both when activated and during the resting state. The study will be performed on a well-characterized group of ME/CFS and PTLD patients compared to matched healthy controls.
The fMRI study examines the neural mechanisms of PEM, which is a worsening of symptoms following exertion. Our experimental PEM trigger is an invasive cardiopulmonary exercise test (iCPET) supervised by Dr. David Systrom at the BWH. Patient volunteers are scanned during their baseline symptom severity and again 24 to 72 hours following the iCPET, which should coincide with their anticipated maximum flare of PEM. By comparing baseline and PEM data, it is hoped that a better understanding of mechanisms resulting the exaggeration of symptoms.
Both scans involve patients at rest as well as during breath-hold and cold challenges. During the studies, several peripheral physiology measurements to use as fMRI signal correlates (heart rate, respiration, oxygen saturation, and partial pressures of carbon dioxide and oxygen) are collected. These correlates allow additional assessment of brain vascular function. Simultaneously, magnetic resonance spectroscopy (MRS) sequences will allow measurement of metabolite concentrations in the brain.
The resources at the MGH for these studies are extraordinary for neuroimaging. The Martinos Center at MGH is the major hub for biomedical imaging and home to 120 HMS faculty and hundreds of researchers for high quality dual MR-PET brain imaging of ME/CFS patients. We also will take advantage of The Gordon Center at MGH, which has been a leading center in PET for more than 60 years.
Participation In The Studies
These are also complex studies. For these MGH and BWH studies in ME/CFS patients, one of these studies (fMRI study to evaluate brain metabolism during PEM) is currently open for enrollment. The second study (MRI/PET dual instrument study to localize the regions of microglial activation in ME/CFS) is currently under review by the MGH/Partners Harvard Institutional Review Board with enrollment not yet possible.
Over the course of time, various projects will be involved in open enrollment and others pending to open enrollment and others that have closed and are under analysis. This becomes a very fluid process and it is our intent to develop a separate portion of this website to announce opportunities for any potential patient volunteers to be updated readily for any currently enrolling studies within the ME/CFS Collaboration. Any patients with interest can register and participate as well as provide any feedback regarding their experience.
- Sclocco R, Beissner F, Bianciaardi M, Polimeni JR, Napadow V. Challenges and opportunities for brainstem neuroimaging with ultrahigh field MRI. Neuroimage 2018 168:412-26 (doi:10.1016/j.neuroimage.2017.02.-52).
- Nakatomi Y, Mizuno, K, Ishii A, et al. Neuroinflammation in Patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis: An 11C-(R)-PK11195 PET Study. J Nucl Med 2014; 55:945–950 (DOI: 10.2967/jnumed.113.131045).
- VanElzakker MB, Brumfield SA, Paula S. Lara Mejia, PS. Neuroinflammation and Cytokines in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): A Critical Review of Research Methods. Front Neurol 9:Article1033, 1/10/2019, (DOI:10.3389/fneur.2018.01033).
- Napadow V, Dhond R, Kennedy D, Hui KKS, Makrisb N. Automated brainstem co-registration (ABC) for MRI. NeuroImage 2006 32:1113–1119.
- VanElzakker MB. Chronic Fatigue Syndrome from Vagus Nerve Infection: a Psychoneuroimmunological Hypothesis. Med Hypothesis 2013. 81(3):414-23.