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Tony L. Yaksh, Ph.D.
Our group has four broad areas of ongoing investigation
1) Neuroinflammatory processes in spinal pain processing. Our group demonstrated that peripheral injury activates p38 MAPKß in spinal microglia. Blockade of this activation prevents hyperalgesia. An important question that we are addressing is how afferent transmitters such as glutamate and substance P activate spinal microglia, e.g. directly or via astrocyte or neuronal release of mediators (ATP, fractalkine and others). Definition of the expression of the relevant receptors and change in stimulation-induced phospho-p38 in spinal glia in vivo and in vitro (spinal microglia and astrocyte cultures) is an important question that can be pursued by a fellow.
2. Lipid mediators. The spinal delivery of COX isoform selective inhibitors and selective knock down of COX2 with intrathecal COX2 antisense reveal that these effects are largely mediated by a constitutively active spinal COX2 enzyme. The arachidonic acid substrate for COX arises largely form the action of PLA2 enzymes. In collaboration wit h Dr. Edward Dennis, we have shown the presence of constitutive mRNA and protein in the spinal cord for several pLA2 isoforms including group IVA calcium-dependent PLA2 (cPLA2). Block of cPLA2 by inhibitors and by cPLA knock down with intrathecal antisense will reduce evoked spinal PGE2 release and produce anti-hyperalgesia. These findings emphasize the role of constitutively active lipid cascades activated by peripheral injury and which contribute to sensitization of spinal nociceptive processing. A larger family of lipid mediators is also almost certainly relevant to these effects. Our groups have mounted a concerted effort to define the lipid release profiles in different pain states.
3. Primary afferent pharmacology.
We have an ongoing interest in the pharmacology of systems that regulate spinal C fiber terminal excitability. We use substance P receptor internalization to assess effects of pharmacological and physiological interventions on C fiber release. The spinal delivery of agents such as mu and delta opioid agonists will reduce that release. We have a systematic effort to employ this straight forward approach to define the pharmacology of the spinal terminal of the peptidergic C finer. A fellow can pursue targets to define factors such as lipid mediators and NO, which might increase or reduce terminal excitability.
4. Preclinical spinal toxicology. To move novel therapeutic agents into humans requires development of the appropriate safety data. Our department has an active preclinical spinal toxicology program. We undertake pivotal GLP studies on spinally-delivered agents. With few exceptions, preclinical safety work for all analgesics delivered spinally with a US FDA IND or NDA has been accomplished by our group (sufentanil, baclofen, Clonidine, neostigmine (cholinesterase inhibitor), slow release liposome morphine, adenosine and, most recently, ketorolac). Current work focuses on the neurotoxin sP-saporin and the synaptic release blocker botulinum toxin. A trainee can engage in these investigations, learning that process through the evaluation of kinetics/safety in large animal models.
Our work has also led us to be particularly interested in the formulation of spinal drugs. Our work suggests the possibility that some of the local toxicity may reflect upon a number of physicochemical variables, such as the formation of micelles which act as detergents at lipid membranes. A number of strategies may be useful in altering these properties and attenuating toxicity.
Selected Publications
1. Neuroinflammatory processes
Svensson CI, Fitzsimmons B, Azizi S, Powell HC, Hua XY, Yaksh TL. Spinal p38beta isoform mediates tissue injury-induced hyperalgesia and spinal sensitization. J Neurochem 92: 1508-1520, 2005.
Hua XY, Svensson CI, Matsui T, Fitzsimmons B, Yaksh TL, Webb M. Intrathecal minocycline attenuates peripheral inflammation-induced hyperalgesia by inhibiting p38 MAPK in spinal microglia. Eur J Neurosci., 22:2431-40 2005
Tang Q, Svensson CI, Fitzsimmons B, Webb M, Yaksh TL, Hua XY. Inhibition of spinal constitutive NOS-2 by 1400W attenuates tissue injury and inflammation-induced hyperalgesia and spinal p38 activation. Eur J Neurosci. 25:2964-72, 2007
2. Lipid mediators
Yaksh TL, Kokotos G, Svensson CI, Stephanos D, Kokotos CG, Fitzsimmons B, Hadjipavlou-Litnia D, Hua XY, Dennis EA. Systemic and intrathecal effects of a novel series of phospholipase A2 inhibitors on hyperalgesia and spinal prostaglandin E2 release. JPET 316:466-475, 2006.
Kim DH, Fitzsimmons B, Hefferan MP, Svensson CI, Wancewicz E, Monia BP, Hung G, Butler M, Marsala M, Hua XY, Yaksh TL. Inhibition of spinal cytosolic phospholipase A(2) expression by an antisenseoligonucleotide attenuates tissue injury-induced hyperalgesia.Neuroscience. ;154(3):1077-87, 2008.
3. Primary afferent pharmacology.
Kondo I, Marvizon JC, Song B, Salgado F, Codeluppi S, Hua XY, Yaksh TL. Inhibition by spinal mu- and delta-opioid agonists of afferent-evoked substance P release. J Neurosci 25: 3651-3660, 2005.
Khan IM, Wart CV, Singletary EA, Stanislaus S, Deerinck T, Yaksh TL, Printz, MP. Elimination of rat spinal substance P receptor bearing neurons dissociates cardiovascular and nocifensive responses to nicotinic agonists. 54:269-279, 2008
4. Spinal toxicology
Allen, JW, Mantyh PW, Horais K, Tozier N, Rogers SD, Ghilardi JR, Cizkova D, Grafe MR, Richter P, Lappi DA, Yaksh TL. Safety evaluation of Intrathecal Substance P-Saporin, a targeted neurotoxin, in dogs. Toxicol Sci. ;91:286-98, 2006
Allen JW, Horais KA, Tozier NA, Wegner K, Corbeil JA, Mattrey RF, Rossi SS, Yaksh TL. Time course and role of morphine dose and concentration in intrathecal granuloma formation in dogs: a combined magnetic resonance imaging and histopathology investigation. Anesthesiol 105:581-589, 2006
Yaksh, TL Tozier, N, Horais, KA, Malkmus, S, Rathbun, M, LaFranco, L, Eisenach, J. Toxicology profile of N-methyl-D-aspartate antagonists delivered by intrathecal infusion in the canine model. Anesthesiology;108:938-49, 2008.
Photomicrograph showing an intrathecal granulomaloma formed after the 28 day continuous infusion of high concentrations of morphine,
Xray of a rat with a chronic intrathecal cahteter connected to a subcutaneous infusion pump. tfis model permits assessment of the effects of spinally delivered drugs acutely (or chronically) on pain behavior and the biological cascades produced by nociceptive stimuli.
