FACIAL PAIN RESEARCH FOUNDATION 2014 RESEARCH PROGRESS
Compiled and submitted April, 2015 By Douglas K. Anderson, Ph.D. Eminent Scholar Professor and Chair Emeritus Department of Neuroscience, University of Florida College of Medicine, and Director of Research and Trustee, Facial Pain Research Foundation
Pain is the primary symptom causing individuals to consult their physicians resulting in pain-related health care costs exceeding $100 billion/year. Of these debilitating chronic pain conditions, trigeminal neuralgia (TN) is considered to be one of the most painful afflictions known to medical practice. TN is a disorder of the fifth cranial (trigeminal) nerve that causes episodes of intense, stabbing, electric shock-like pain in the areas of the face where the branches of the nerve are distributed – lips, eyes, nose, scalp, forehead, upper jaw, and lower jaw.
There are other neuropathic facial pain syndromes sometimes called “Atypical Trigeminal Neuralgia” which are generally characterized by a less intense, constant, dull burning or aching pain, often with occasional electric shock-like stabs. The initial treatment for neuropathic facial pain conditions is usually with anti-convulsive and/or anti-depressant drugs. Should these medications be ineffective or produce undesirable side effects, neurosurgical procedures are available (at least for TN) to relieve pressure on the nerve or to reduce nerve sensitivity. However, in many patients (particularly those in which the pain is chronic), no current treatment is effective, either permanently or in the long term.
TN is an example of neuropathic pain which is defined as pain caused by injury to or disordered functioning of the nervous system. Despite the debilitating effects chronic pain (like that of TN) has on the activities of daily living of its victims and on the economics of health care, research funding from traditional sources (i.e., federal agencies and pharmaceutical companies) that specifically target identifying the underlying causes of neuropathic pain and developing long term treatments with minimal side effects has been and continues to be very limited. Thus, for over a decade, there has been the growing realization that if there is to be any real progress in discovering the genesis of and treatment for TN, it is going to have to be accomplished with funds raised from the private sector. To this end, The Facial Pain Research Foundation (FPRF) was created in January, 2011 to provide the critical elements that are necessary and sufficient to study these facial pain conditions. Accordingly, the sole mission of the FPRF is “…to establish a well-funded translational (i.e., fundamental discovery to clinical application) research continuum that is dedicated to identifying the mechanisms underlying neuropathic facial pain and to develop novel new therapeutic strategies that will permanently stop the pain of TN and related neuropathic pain syndromes”. Since its inception a little over four years ago, the FPRF has raised approximately $2,343,710 to support four separate and distinct research projects. In funding these projects, the FPRF adhered to three criteria: (1) the projects were novel and unique; (2) the investigator(s) responsible for each project are among the leading researchers in their respective fields; and (3) all of the projects were not “cut from the same cloth”, i.e., there was significant diversification in the research strategies among the projects. The purpose of this review is to briefly summarize these four projects and some of the results that have been attained.
Investigating Protein-Lipid Interactions in Peripheral Nerve Myelin
Lucia Notterpek, Ph.D. , Professor and Chair, Department of Neuroscience, University of Florida College of Medicine
Under the general umbrella title “Investigating Protein-Lipid Interactions in Peripheral Nerve Myelin”, Dr. Notterpek continues her examination of the role of specific Schwann cell genes in the development and maintenance of myelin. Dr. Notterpek recently published the results of a potentially important study in the November 26, 2014 issue of the Journal of Neuroscience, one the world’s most respected neuroscience journals. The research detailed in this article was supported in part by the Facial Pain Research Foundation (FPRF) and Tom and Suzie Wasdin. The editors of this journal recognizing the quality of Dr. Notterpek study and of the results obtained, selected it to be the cover (featured) article for the 11/26/2014 issue.
The experiments described in Dr. Notterpek’s recent article are an example of an experimental approach from the fundamental discovery side of the research portfolio. Its relevance to the mission of the FPRF is based on the proposition that the pain of TN is thought to occur when the insulating myelin sheath of the trigeminal nerve is lost or damaged (demyelination) by the pulsations of an overlying blood vessel.
Myelin is a multi-layered membrane made up of specific lipids and proteins. Due to its molecular composition, myelin functions as an insulating material in the nervous system (NS). Myelin wraps around many axons in both the peripheral (PNS) and central (CNS) nervous systems forming the myelin sheath which is instrumental in maintaining the normal conduction velocity in nerves. Consequently, an intact myelin sheath is necessary for the proper functioning of the NS. Peripheral myelin is derived from and maintained by Schwann cells. How specific lipids and proteins are processed and maintained in these myelin-forming Schwann cells is not fully understood but is a major emphasis of Dr. Notterpek’s research program with a focus on establishing the role of a particular Schwann cell gene, peripheral myelin protein 22 (PMP22), in the development and maintenance of myelin. Specifically, the experiments described in this article were directed at assessing how cholesterol, the major lipid in myelin, interacts with PMP22 to form a stable myelin sheath. Her findings indicate that PMP22 is most likely a cholesterol binding protein that is critical for myelin stability as demonstrated by the profound myelin abnormalities seen in mice whose PMP22 has been genetically removed (i.e., PMP22 knockout mice). Also, cholesterol supplementation of cultures derived from these PMP22 knockout mice corrects these myelin abnormalities which suggests that they are directly linked with cholesterol deficiency of the plasma membrane (i.e.,the outer membrane of most cells). Dr. Notterpek’s results support the existence of a novel but until now, undiscovered role for PMP22 in the linkage of the cytoskeleton (cell’s internal structural support system) with the plasma membrane. In this scenario PMP22 newly discovered role is to regulate the cholesterol content of lipid rafts (i.e.,membrane microdomains that serve as organizing centers for the assembly of a number of molecular species). Consequently, loss of or malfunctioning PMP22 can result in unstable myelin sheaths that would be more susceptible to damage and demyelination by an overlying pulsating blood vessel like that proposed to cause TN. Thus, studies like the one performed by Dr. Notterpek and her team and published in the Journal of Neuroscience have the potential of providing critical new information regarding the subcellular mechanisms responsible for the development and maintenance of a normal, intact myelin sheath which then could open the door to the discovery of effective therapies for TN and other more wide spread demyelinating disorders of the NS such as multiple sclerosis (MS).
It is important to understand that like most biological systems, myelin and the myelin sheath are complex, multifactorial assemblies of molecular species that due to their complexity defy resolving their identity and function. Consequently, to begin to understand how these complex assemblies function they must be dissected (as much as possible) into their component parts which then can be studied in isolation devoid of influence from other molecular species. As more is learned about the individual component molecular assemblies, researchers can begin combining them to discover how they impact each other. Over time, how the myelin sheath (or any complex biological system) is structured, maintained, and functions as an entity emerges like the solving of a puzzle. With this wealth of information, the origins of malfunctions become clearer allowing cures to be sought and specific therapies designed.
Mapping Towards a Cure: Identification of Neurophysiologic Signatures of Trigeminal Neuralgia Pain
John K. Neubert, D.D.S., Ph.D., University of Florida (Project coordinator, animal modeling)
Mingzhou Ding, Ph.D., University of Florida (Human imaging)
Marcelo Febo, Ph.D., University of Florida (Animal imaging)
Robert M. Caudle, Ph.D., University of Florida (Therapeutics)
Andrew H. Ahn, M.D., Ph.D., Eli Lilly Company, IN
In 2012 a proposal entitled “A Neural Signature of TN Pain” was submitted to the FPRF by Andrew Ahn, M.D., Ph.D. who at the time of submission was an assistant professor in the Department of Neurology at the University of Florida College of Medicine (UFCOM). The FPRF supported this project whose primary goal was to acquire a neural signature or “map” of the brain in individuals with TN pain. Stated differently, Dr Ahn and his team were intent on discovering the areas of the brain that are activated in individuals experiencing TN pain. Shortly after starting this study, Dr. Ahn was recruited to the Eli Lilly Company and left UF before he could complete this project.
Fortunately, there was another recognized expert in orofacial pain with a specific emphasis on the causes of and treatments for TN on faculty at UF. John K. Neubert, D.D.S., Ph.D. is a tenured associate professor in the Department of Orthodontics at the University of Florida College of Dentistry (UFCOD). He also has an adjunct appointment in the Department of Neuroscience at the UFCOM and is on the faculty of the Evelyn F. and William L. McKnight Brain Institute of the University of Florida (MBI). Dr. Neubert is eminently qualified to be the Principal Investigator of and assume responsibility for this project. Dr. Neubert has assembled an impressive team of co-investigators and has submitted to the FPRF a proposal entitled: “Mapping Towards a Cure-Identification of Neurophysiological Signature of Trigeminal Neuralgia Pain” that not only addresses the specific aims from Dr. Ahn’s original project but also extends it in a novel new direction.
The experiments outlined in this submission are designed to study the cause of TN using a translational approach, which means determining if the neurobiology of TN in animals (rats) replicates or is very similar to the neurobiology of TN in humans. Usually this progression is done sequentially, i.e., the condition or disease is studied first in animals and then in humans. However, because of the exceptional intellectual and technical power available at the MBI, Dr. Neubert and his team will be carrying out their research project simultaneously in humans and animals. Using state of the art magnetic resonance (MR) scanners for humans, they will be looking for specific areas of the brain and spinal cord that will be activated by TN pain…so called “signature” centers of activity. They will attempt to locate these centers in individuals with TN before and after their pain has started. In a parallel study, the brain and spinal cord of rats with different types and locations of injuries of the trigeminal nerve will be imaged with a contemporary high field MR scanner to determine if signature centers of activity can be found in this species. The Phase 1 of this submission proposes to identify and compare the individual imaging patterns caused by the activation of different areas in the brain and spinal cord in both TN patients and rats. If similar imaging/activation patterns are seen in both rats and humans, then large numbers of compounds and perhaps other promising or novel therapeutic approaches can be screened (Phase 2). If the activation patterns are substantially different from each other (in both humans and rats), then it becomes necessary to image additional subjects in order to strengthen the statistical power by acquiring a larger sample size.
The importance of identifying the brainstem nerve tracts responsible for activating cortical areas in TN patients cannot be overstated. Discovery of the relevant nerve tracts provides targets for treatments that can specifically block the pain of TN and eliminate or limited unwanted side effects because the treatment can be delivered locally and not systemically. This group of investigators already has access to existing therapies that they speculate will be successful in blocking TN pain that can be tested on the rat once this animal model has been shown to be clinically relevant. This is generally the last required step in bringing treatments from the dish to the doctor.
Cell Replacement Therapy as a Treatment for Injury-Induced Neuropathic Pain
Allan Basbaum, Ph.D., FRS, Professor and Chair, Department of Anatomy, University of California San Francisco
It is well known that current treatment strategies to manage chronic pain are for the most part, unsatisfactory. However, recent studies from the laboratory of Dr. Allen Basbaum that were supported in part by the FPRF shows how cell replacement therapy might one day be used not only to quell some common types of persistent and difficult-to-treat pain, but also to cure the conditions that give rise to them.
Dr. Basbaum’s preclinical studies using mice are directed at treating neuropathic pain. As indicated earlier, neuropathic pain is purported to arise from injury to or disordered functioning of the nervous system. For example, other research has suggested that following injury, neurons in the spinal cord that normally release a pain inhibitory neurotransmitter may be lost or damaged, or neural circuitry in the CNS (central nervous system, i.e., the brain and spinal cord) may change in ways that negates signals that normally help dampen pain. This loss of mechanisms that normally reduce the transmission of pain messages to the brain can cause areas of the brain to become hyper-excitable. When the brain is in a hyper-excitable state, pain signals are enhanced and normally innocuous sensory stimuli can turn into excruciating pain.
Dr. Basbaum has taken the novel approach of transplanting immature precursor cells from the mouse brain that produce a pain inhibitory transmitter that is released into the adult mouse spinal cord in order to raise the level of inhibitory input and specifically block pain signals to the brain. A small fraction of the transplanted cells survived and matured into functioning neurons. The cells integrated into the nerve circuitry of the spinal cord, forming synapses and signaling pathways with neighboring neurons. As a result, pain hypersensitivity associated with nerve injury was almost completely eliminated. The initial studies demonstrated efficacy in a model of traumatic nerve injury-induced pain and more recently in a model of chemotherapy-induced pain. It is important to recognize that with a view to translating these findings to the human, Dr. Basbaum has initiated studies that use human embryonic stem cells that are induced to take on the properties of inhibitory neurons. These studies are performed in immunocompromised mice so that the human cells are not rejected. Dr, Basbaum is also expanding his research in an attempt to discover other “…potential treatments that might eliminate the source of neuropathic pain, and that may be much more effective than drugs that aim only to treat symptomatically the pain that results from chronic, painful conditions.” These new studies are supported by a grant from the NIH that he acquired based on the preliminary findings generated with support from the FPRF.
Finding the Genes that Predispose to Trigeminal Neuralgia
Marshall Devor, Ph.D. (Project Coordinator) Professor and Chair, Department of Cell and Animal Biology, Institute of Life Sciences, Hebrew University of Jerusalem
Kim J. Burchiel, M.D. (Phenotyping and Sample Collection) Professor and Chair, Department of Neurosurgery, Oregon Health and Science University
Ze’ev Seltzer, Ph.D. (Genomics) Professor of Pain Genetics, Faculty of Dentistry; Professor of Physiology, Faculty of Medicine, University of Toronto
Scott R. Diehl, Ph.D. (Genomics Consultant) Professor, Department of Oral Biology, Rutgers School of Dental Medicine; Professor of Health Informatics, Rutgers School of Health Related Professions, Rutgers University
Joanna Zakrzewska, M.D. (Consultant), Consultant Facial Pain , Eastman Dental Hospital, UCLH NHS Foundation Trust, London UK
The remarkable progress made in genetic analysis in the past two decades of the Human Genome Project has greatly enhanced our capacity to discover genes associated with different diseases, to reveal their function, and to develop therapeutic and/or preventive approaches precisely targeted at the specific disease. This project asks the question: Are some individuals genetically predisposed to develop TN pain? This question emanates from research which shows that although 17% of mature adults have the TN lesion (usually a vascular compression of the trigeminal nerve close to where it exits the brain) only a very small minority (0.01%) of these individuals actually experience TN pain. This disconnect between lesion and pain is an important clue pointing toward a genetic predilection for TN.
This project was conceived with the assumption that the risk for getting classical TN has a genetic basis and has as its primary objective identifying genetic mutation(s) (aka, sequence variant(s) or polymorphism(s)) associated with the development of TN pain. To achieve this objective, DNA will be collected from 500 TN patients. Analysis of the whole genome will be carried out on these patients using the latest in genetic sequencing technology and compared to matched reference controls to determine if there are candidate sequence variant(s) or polymorphism(s) present in the genome of the TN patients that are not found in the controls. Such sequence variants might cause TN pain by directly affecting the function of the proteins that these genes encode, or by altering other aspects of gene expression. Either way, assuming that genetics is indeed the basis for developing TN, there is a high probability that this project will reveal the genes and ultimately the pathophysiological mechanisms that cause the lesions to be painful. With this knowledge molecular targets for treatments that will cure the pain can be identified not only of TN but perhaps also for a variety of other facial and segmental neuropathic pain conditions.
To date, nine centers, including two international centers, are actively acquiring DNA samples via cheek swabs in patients with TN1. The members of this research team anticipate that they will achieve their original goal of having, in hand, 500 cheek swab samples by mid-summer 2015 and that all 500 samples will be sequenced and analyzed by January 1, 2016 also an original goal. Currently, DNA samples acquired from 100 professionally phenotyped TN1 patients have been sequenced and analyzed. While it is far too early to identify a gene(s) causally related to the genesis of TN pain, the sequencing procedure appears to be reliable and reproducible.
Looking ahead, this team of investigators has put forward a strong case for doubling the number of saliva samples collected from 500 to 1000. They point out that such an increase in sample size would substantially enhance the power of this study in addition to strengthening the reliability of any conclusions drawn. They project that collection of an additional 500 samples could be completed by Spring 2016.