Integrative And Molecular Studies Of Pain And Pain Contr

Dental &Craniofacial Research

Investigators

Linked publications & trials

Abstract

Summary: Our research program addresses basic molecular and physiological processes of nociceptive transmission in the central nervous system and new, effective ways to treat intractable pain. The molecular research is performed using animal and in vitro cell-based models. We concentrate on primary afferent pain-sensing neurons located in dorsal root ganglion (DRG) that innervate the skin and deep tissues and their connections in the dorsal spinal cord, which is the first site of synaptic information processing for pain. Our research has identified the DRG and spinal cord as loci of neuronal plasticity and altered gene expression in persistent pain states. The regulation of transduction of physical pain stimuli is also under investigation using cloned thermal and chemo-responsive ion channels ectopically expressed in heterologous cell systems and naturally expressed in primary cultures of dorsal root ganglion. Our goals are (1) to understand the molecular and cell biological mechanisms of acute and chronic pain at these two basic levels of the nervous system and (2) to use this knowledge to devise new treatments for pain. Clinical Treatment Research:We address the new treatment goal in a translational research and human clinical trials program to evaluate new analgesic treatments for severe pain. The main approach is based on our studies of the molecular mechanisms of pain transduction through the vanilloid receptor 1 (TRPV1). This molecule is a heat-sensitive calcium/sodium ion channel and converts painful heat into nerve action potentials by opening the channel and depolarizing pain-sensing nerve terminals. Channel opening is also stimulated by capsaicin which is a vanilloid chemical and the active ingredient in hot pepper and. We use a very potent vanilloid analog to prop open the channel causing death of a specific class of pain-sensing neuron. We have established an inter-institute working group with NIDA's Division of Pharmaco-Therapeutics and Medical Consequences of Drug Abuse to bring the treatment to human clinical trial. The working group consists of experts on medical, neurobiological, toxicological, chemical and formulation issues as well as anesthesiologists, pharmacologists and pathologists from our group. We have also established mechanisms for obtaining the natural product from which the active drug is extracted and procedures for isolation purification and formulation of the drug product compliant with Food and Drug Administration (FDA) regulations. We are presently finalizing the toxicology study, the Investigational New Drug Application with the FDA and the Human Clinical Protocol with the NCI's IRB. This may be a very effective approach to control of certain types of chronic pain especially those associated with cancer, arthritis and tempro-mandibular joint disorders, trigeminal neuralgia and chronic neuropathic pain problems. Based on the above, we have submitted a new protocol to examine the use of vanilloid agonist-induced nerve terminal inactivation to treat burning mouth syndrome and pain components mucositis in human oro-facial pain patients. This is a reversible treatment that produces a calcium overload and thereby targets only the nerve endings. Clinical Pain Mechanisms: Certain chronic pain problems, such as neuropathic pain in the body or the oro-facial region, do not have good animals models, one of these is a neuropathic pain problem now referred to as Chronic Regional Pain Syndrome (CRPS). We have established a clinical protocol to study patients CRPS using proteomic analyses of serum and analysis of serum for presence of antibodies to peripheral nerve components. If there is some success we can expand the analyses to several other cohorts of chronic pain patients to establish whether the underlying mechanisms are generalize or specific to these types of nerve injury-induced neuropathies. Basic Pain Mechanisms: Underlying the translational studies are our investigations of molecular regulation in chronic pain and mechanisms of pain transduction in peripheral nerve endings. We have addressed the question of molecular plasticity, in part, by using subtraction cloning, differential hybridization, gene arrays, and neurobehavioral measurements. These studies represent a systematic attempt to understand pain at the first three steps in the pathway beginning with injured peripheral tissue, the DRG and the dorsal spinal cord. Our studies reveal the dynamic modulation of gene expression at all three steps in a more complex fashion than previously hypothesized. We have examined novel molecules as well as neuropeptide, cytokine and chemokine expression and identified prominent roles for new key molecules with distinct combinatorial patterns. In addition to pain, these studies fundamentally explore the molecular basis of synaptic plasticity. We hypothesize modularity in neuronal responses to new levels of synaptic or pharmacological input (e.g. learning, neurological disorders, drug abuse). The "generic" alterations are combined with modulation of tissue-specific genes to meet the demands generated by the new level of stimulation. This will lead to a deeper understanding of molecular mechanisms that trigger and sustain chronic pain and possibly other chronic disorders of the nervous system.