In October 2017, the United States government declared a state of public health emergency in response to the burgeoning prescription opioid epidemic. Opioid analgesics are the gold standard of therapy for moderate to severe pain, but their clinical utility is greatly limited by analgesic tolerance – a primary driver of diminished pain control and opioid dose escalations. Integral in this process are primary afferent sensory neurons in dorsal root ganglia (DRG), the first-order components of nociceptive sensation. With surmounting evidence that morphine and other narcotics can alter gut microbial composition and promote bacterial translocation to other tissues, a question arises of whether the secondary release of bacterial products and pro-inflammatory cytokines can modulate antinociceptive tolerance development. This dissertation examines how gut bacteria depletion with antibiotics modulates the pharmacodynamic properties of chronic morphine in mice. Utilizing a “top-down” experimental approach, this is characterized at the whole-animal, single-cell, and molecular level via behavioral assays of antinociception, whole-cell patch-clamp recordings in DRG neurons, and analysis of tetrodotoxin-resistant (TTX-R) Na+ channel kinetics, respectively. Our findings collectively indicate that the gastrointestinal microbiome is an important modulator of antinociceptive tolerance development with chronic morphine administration.

Paclitaxel, vincristine, oxaliplatin, and bortezomib are cancer chemotherapy drugs with adverse effects that include chemotherapy-induced neuropathic pain (CINP) as well as depression of behavior and mood. In the clinical setting, opioids are often used concurrently with or following chemotherapy to treat pain related to the cancer or CINP, but repeated opioid exposure can also increase the risk of opioid abuse. This dissertation evaluated the effect of chemotherapy treatment on motivated behaviors and opioid reward in rats. The main findings of this evaluation are as follows: (1) Chemotherapy, at doses that produce robust and sustained mechanical hypersensitivity produce only weak or nonexistent depression of positively reinforced operant responding maintained either by electrical brain stimulation in an assay of intracranial self-stimulation or by food pellets in an assay of food-maintained responding. (2) There was no correlation between the expression of mechanical hypersensitivity and depression of motivated behaviors across individual animals, suggesting that these two effects of chemotherapy do not share common mechanisms of action. (3) Mechanical hypersensitivity, but not behavioral depression could be reversed with morphine. (4) The class of chemotherapeutic used in preclinical models is a determinant of the severity of effects on neuropathy-related endpoints and on the time course of these effects. (5) Chemotherapy does not protect against the rewarding effects of repeated morphine administration and does not alter the time course of the enhancement of reward with repeated morphine exposure. These findings suggest that administration of chemotherapy to rats induces mechanical hypersensitivity while failing to decrease behaviors dependent on mesolimbic dopamine signaling or protecting against morphine abuse-related effects. While apparent that chemotherapy can produce peripheral neuropathy, the data in this dissertation does not support the hypothesis that chemotherapy can produce behavioral depressant manifestations of chemotherapy-induced neuropathic pain (CINP) in rats.

The mechanisms that mediate the maintenance of chronic pain states are poorly understood, but elucidation of such could yield insight into how pain becomes chronic and how the process can potentially be reversed. This thesis investigated the role of ascending and descending spinal dorsal horn circuitry and interneurons in the plasticity that mediates a transition to pathological pain plasticity using hyperalgesic priming model. The results showed that, while dorsal horn neurokinin 1 receptor-positive neurons or descending serotonergic neurons mediated IL-6- and carrageenan-induced acute mechanical hypersensitivity, they were not required for PGE₂-induced mechanical hypersensitivity. In stark contrast, ablation of dopaminergic neurons did interrupt the IL-6- and carrageenan-induced mechanical hypersensitivity, but the subsequent PGE₂ injection failed to cause mechanical hypersensitivity - thereby reflecting that primed state plasticity is driven by differential mechanisms. In addition, the pharmacological antagonism of spinal dopamine D1/D5 receptors reversed priming and its agonism induced mechanical hypersensitivity exclusively in primed mice, which suggests dopaminergic control of pathological pain plasticity in a D1/D5-dependent manner. Moreover, in a primed state, changes to spinal dorsal horn GABA pharmacology were accompanied by upregulation of neuroligin 2 mRNA and protein expression. These findings 1) indicate a novel role for descending dopaminergic neurons in the maintenance of pathological pain plasticity, and 2) point to the inhibitory synaptic expression of neuroligin-2 as the spinal determinants of this type of pain plasticity.

This dissertation will present the four manuscripts I published or am ready to publish on the study of the pathophysiology of migraine headache. The first chapter will discuss the background of the current understanding of migraine pathophysiology. Chapter 2 is focused on studying how Transient receptor potential vanilloid 4 (TRPV4) might play a role in migraine headache. Chapter 3 is the study of a novel cell type: dural fibroblasts might also play an active role in migraine headache. Chapter 4 is discussing Norepinephrine's role in headache pathophysiology. Chapter 5 is studying the combined effect of Acid and ATP in the pathophysiology of migraine headache. The dissertation will end in a conclusion in Chapter 6.

Many common cancers, including breast, prostate and lung, have a predilection to metastasize to the bone, bringing not only bone destruction but severe pain. Although novel chemotherapeutic agents have increased life expectancy, patients are experiencing higher incidences of fracture, pain and drug-induced side effects; furthermore, recent findings suggest that patients are severely under-treated for their cancer pain. Strong analgesics, namely opiates, are the first-line therapy in alleviating cancer-related pain despite severe side effects including enhanced bone destruction with sustained administration. Bone resorption is primarily treated with bisphosphonates, which can bring highly undesirable side-effects including nephrotoxicity and osteonecrosis of the jaw. Thus novel therapeutics are needed to treat the pain of metastatic cancer patients. Animal models of cancer-induced bone pain (CIBP) have revealed that the neurochemistry of cancer has distinctive features from other chronic pain states. These include factors released from the cancer cells, tumor activated macrophages and increased osteoclast degredation of bone within the bone microenvironment, all acting to sensitize free nerve endings.One possibility of inhibiting cancer-mediated pain inducing factors includes agonism of the Cannabinoid 2 receptor agonists. Cannabinoid CB2 receptor-specific agonists have been shown to reduce bone loss and stimulate bone formation in a model of osteoporosis. CB2 agonists produce analgesia in both inflammatory and neuropathic pain models. Notably, mixed CB1/CB2 agonists also demonstrate a reduction in ErbB2-driven breast cancer progression. Osteolytic sarcoma within the femur produced spontaneous and touch evoked behavioral signs of pain within the tumor-bearing limb. The systemic administration of AM1241 both acutely and for 7 days significantly attenuated spontaneous and evoked pain in the inoculated limb. Sustained AM1241 significantly reduced bone loss and decreased the incidence of cancer-induced bone fractures. In addition, CB2 agonists significantly reduce breast cancer-induced bone pain, bone loss and breast cancer proliferation in part via cytokine/chemokine suppression. Studies utilized the spontaneously-occurring syngenic murine mammary cell line (66.1) implanted and sealed into the femur intramedullary space. Measurements were made of spontaneous pain, bone loss and cancer proliferation. The central and systemic administration of the CB2 agonist JWH015 for seven days significantly attenuates pain. Pharmacological characterization with cannabinoid 1 and 2 antagonists demonstrates that the effects JWH015 on pain were mediated by the CB2 receptor. We and others have found that bone induced cancer pain increases the expression of GFAP and Iba1 in the lumbar spinal cord which are markers of astrocytes and microglia respectively, compared to control animals. After administration of JWH015 (i.t), the release of spinal pro-inflammatory cytokines, IL-6 and TNFá, are reduced suggesting that modulation of glial cytokines may be one mechanism by which CB2 agonists can attenuate pain centrally. On the other hand, systemic administration of JWH015 reduces cancer-induced elevation of cytokines in the tumor microenvironment, suggesting a mechanism by which CB2 agonist is attenuating pain peripherally. Additionally, systemic administration improves bone modification, as demonstrated via micro-computed tomography and bone serum markers while decreasing femoral tumor burden. In vitro, JWH015 reduced cancer cell proliferation and other inflammatory mediators shown to promote pain, bone loss and proliferation. These results suggest CB2 agonists as a novel treatment for breast cancer-induced bone pain, where disease modifications include a reduction in bone loss, suppression of cancer growth, attenuation of severe bone-pain and increased survival without the major side effects of current therapeutic options. Another future therapeutic option for metastatic bone cancer pain may include cathepsin inhibitors. Cysteine cathepsins (B, C, F, H, K, L, O, L2/V, W, X/Z) are highly expressed in many human cancers and have been associated with poor patient prognosis. In the RIP1-Tag2 transgenic model of pancreatic cancer, mice treated with VBY-825, a reversible inhibitor of cathepsins S, B, V, L, K showed a significant reduction in tumor incidence and growth. Here we demonstrate the cathepsin inhibitor VBY-825 reduces cancer-induced pain behaviors. Additionally, tumor bearing animals treated with VBY-825 demonstrate a reduction in bone resorption, possibly mediated through a reduction in osteoclast activity. These results indicate that a cathepsin inhibitor targeting multiple cathepsins, such as VBY-825, could be a novel therapeutic for bone metastases.Part of the failure to palliate cancer pain is due to a poor understanding of the etiology of cancer pain. Preclinical studies have just begun to scratch the surface on how such cancers may interact with the bone microenvironment to result in pain and bone loss. Further studies are desperately needed at both the preclinical and clinical level to determine the unique molecular profile of cancer pain that may lead to the development of superior therapeutics for CIBP. The studies presented herein provide preclinical evidence that warrant the investigation of these compounds in the clinic as treatment for cancer-induced bone pain.

Our laboratory has previously demonstrated that experimental peripheral inflammatory pain (PIP), induced by subcutaneous plantar injection of λ-carrageenan in Sprague Dawley rats, results in increased expression and activity of the ATP-dependent efflux transporter P-glycoprotein (P-gp) that is endogenously expressed at the blood-brain barrier (BBB). Increased P-gp functional expression was associated with a significant reduction in CNS uptake of morphine and, subsequently, reduced morphine analgesic efficacy. The present study examined whether the PIP-induced increase in P-gp functional expression was due to changes in intracellular trafficking (i.e., localization of P-gp), mediated by changes in the association of P-gp and caveolin-1, a key trafficking protein. These studies also determined if the drug diclofenac, a non-steroidal antiinflammatory (NSAID) that is commonly administered in conjunction with opioids during peripheral inflammatory pain (PIP), altered or modulated P-gp functional expression providing evidence of a drug-drug interaction. Confocal microscopy and subcellular fractionation revealed that under conditions of PIP, the disassembly of high-molecular weight P-gp-containing structures result in an increase in P-gp ATPase activity and changes in the localization of P-gp. Western blot analysis demonstrated further an increase in P-gp expression in rat brain microvessels following PIP induction and also after diclofenac treatment alone in the absence of PIP. Additionally, in situ brain perfusion studies showed that both PIP and diclofenac treatment alone increased P-gp efflux activity resulting in decreased radiolabeled- morphine uptake into the brain. This concurrent administration of NSAIDs and opioids in the presence of a pathophysiological stressor (i.e., pain/inflammation) may result in clinically significant drug-drug interactions that may impair the desired pharmacologic response and analgesic effects of opioids. Such interactions can lead to significant modifications to pain management in clinical settings. Therefore: The central hypothesis of this work is that the pathophysiological stressor peripheral inflammatory pain (PIP) and the pharmacological agent diclofenac modulate P-glycoprotein functional expression at the BBB. This hypothesis may be broken down further into two parts: 1) PIP induced changes in P-gp functional expression are mediated via changes in Pgp intracellular trafficking. 2) The non-steroidal anti-inflammatory drug Diclofenac, a drug commonly used to treat pain, modulates P-gp functional expression at the BBB thus decreasing morphine uptake into the CNS.

Chronic pain is a major health problem affecting more than 1.5 billion people worldwide. Specifically, neuropathic pain and chronic post-surgical pain are debilitating clinical conditions with few efficacious treatments, warranting development of novel therapeutics. Starting with the hypothesis that dysregulated translation regulation pathways may underlie these pain states, we demonstrated that there is a major reorganization of translation machinery in the peripheral nervous system of rats and mice, including enhanced mTOR and ERK activity and increased phosphorylation of mTOR and ERK downstream targets in these persistent pain states. We also hypothesized that activators of AMP-activated protein kinase (AMPK) may represent a novel treatment avenue for the treatment of neuropathic and incision-induced pain because AMPK activators inhibit ERK and mTOR signaling, two important pathways involved in the sensitization of peripheral nociceptors. The AMP activated protein kinase (AMPK) activators, metformin, resveratrol and A769662, inhibited translation regulation signaling pathways in sensory neurons, eIF4F complex formation, nascent protein synthesis in injured nerves and sodium channel-dependent excitability of sensory neurons resulting in a resolution of neuropathic allodynia. We have further demonstrated that local injection of resveratrol, metformin or A769662 and topical application of resveratrol, a potent AMPK activator, into the hindpaw following plantar incision dose-relatedly reverses incision-mediated mechanical hypersensitivity as well as hyperalgesic priming induced by incision. In addition, co-treatment with systemic metformin and local resveratrol at individually sub-efficacious doses at the time of incision blocked acute hypersensitivity and hyperalgesic priming suggesting potential super-additive effects of combined AMPK activator use. These results highlight the importance of signaling to translation control in peripheral sensitization of nociceptors and provide further evidence for activation of AMPK as a novel treatment avenue for acute and chronic pain states.

Coronary heart disease (CHD) remains the single leading cause of natural death worldwide. Despite significant advances in the diagnosis and treatment, CHD accounts for 1 out of every 6 deaths in the United States. Myocardial infarct (MI) as a result of CHD causes irreversible damage to the heart through the loss of viable myocardial tissue. Patients surviving the initial MI are at risk of developing heart failure due to lost contractile function and adverse cardiac remodeling. Improvement in the survival rates for MI have led to an increase in the incidence of heart failure, affecting approximately 5 million people in the United States. Although treatment of heart failure has improved, the mortality rates of heart failure remain high with 1 in 5 dying within the first year of diagnosis and 50% dying within 5 years. The cost of caring for heart failure patients ranks number one in Medicare. Oxidative stress plays an important role in the etiology and pathophysiology of CHD and heart failure. The transcription factor Nrf2 is a master regulator of cellular antioxidant defense mechanisms, controlling the expression of numerous antioxidant and detoxification genes through the Antioxidant Response Element (ARE) in the promoter regions. The cytoprotective effects of Nrf2 have been demonstrated in a variety of organs and disease states; however, the role of Nrf2 in the heart and heart disease has not been defined. The work presented here defines roles of Nrf2 in limiting cardiac injury and the progression to heart failure (Chapter II), protecting cardiac myocytes from oxidative stress through the preservation of mitochondria (Chapter III), and mediating the infarct reducing effects of statins, one of the most prescribed pharmacological agent (Chapter IV). In order to investigate a role of Nrf2 in the pathology of ischemic injury in the heart, a mouse model of ischemia and myocardial infarct by occlusion of the left anterior descending coronary artery was used. Nrf2 knockout mice subjected to ischemia/reperfusion injury experienced a larger infarct size than wild-type mice. Furthermore, mice lacking Nrf2 experienced a higher mortality rate and an accelerated progression to heart failure, indicated by severely compromised contractile function and reduced cardiac output, within 10 days following an MI. Morphological examination revealed maladaptive remodeling, including myocyte hypertrophy, heart enlargement, and dilated left ventricle, in Nrf2 KO mice that was absent in WT mice. Analysis of cardiac function by echocardiogram revealed increased left ventricular mass, increased systolic volume, decreased fraction shortening, reduced ejection fraction, and decreased cardiac output in Nrf2 KO mice. Nrf2 KO mice also demonstrated expression of biomarkers of heart failure, such as expression of fetal gene program, with elevated levels of β-MHC, ANF, and BNP mRNA in the myocardium. Interestingly, a lack of immune cell infiltrate and myofibroblasts as well as a deficiency in collagen deposition were observed in the infarcted region of hearts from Nrf2 KO mice. These data indicate that Nrf2 plays an important role in protecting the myocardium from ischemic injury and the progression to heart failure. Lack of Nrf2 response results in deficiency of wound healing and instead initiation of maladaptive remodeling, leading to heart failure. Mitochondria are key sources of reactive oxygen species (ROS) generation, as well as important targets for ROS-induced cell injury. Cardiac myocytes have the highest content of mitochondria among all cell types and can be particularly susceptible to mitochondrial dysfunction due to the high metabolic demand associated with the contractile function of the heart. With cardiomyocytes (CMCs) isolated from neonatal rats and kept under tissue culture conditions, mitochondria exist in elaborated networks. Such networks were replaced by predominately individual punctate mitochondria 24 hours after exposure to a sublethal dose of H₂O₂. Mitochondrial morphology was altered with membrane swelling and disorganization of inner cristae with areas of condensation. Disrupted mitochondrial morphology was associated with a loss of membrane potential and decreased expression of mitochondrial proteins involved in the electron transport chain, such as cytochrome b and cytochrome c. Nrf2 overexpression prevented H₂O₂ from inducing morphological changes in mitochondria and the reduction of cytochrome b and cytochrome c expresssion. Although Nrf2 is known as a transcription factor regulating antioxidant and detoxification genes, Nrf2 overexpression did not significantly reduce the level of protein oxidation as measured by carbonyl formation. Instead, we found that Nrf2 localizes to the outer mitochondrial membrane, suggesting a direct role of Nrf2 in mitochondrial protection. As further evidence of a direct role in mitochondrial protection, a cell-free system of mitochondria isolated from the myocardium of Nrf2 knockout mice were more sensitive to permeability transition, an indicator of mitochondrial dysfunction. Combined, these data suggest that Nrf2 protects mitochondria from oxidant injury likely through direct interaction with mitochondria. In the clinic, statins are now commonly administered for patients experiencing MI or CHD. Statins have become mainstays in the treatment of hypercholesterolemia and atherosclerosis as inhibitors of the rate limiting enzyme in cholesterol synthesis, 3-hydroxy-3-methylglutaryl coenzyme A reductase. In addition, statins have been shown to elicit pleiotropic effects, including plaque stabilization, maintenance of endothelial function, anti-inflammatory actions, and antioxidant capabilities, independent of effects on cholesterol synthesis. Recently, these pleiotropic effects have been implicated in providing acute protection against ischemia and reperfusion injury, which has led to the use of high dose statins clinically before revascularization of an ischemic event. I have found that administration of atorvastatin in mice induced Nrf2 protein levels in the heart, brain, lung, and liver. While atorvastatin reduced infarct size following an MI in wild-type mice, this protective effect was lost in mice lacking Nrf2. Failure of atorvastatin to protect against MI in Nrf2 knockout mice indicates that Nrf2 plays a critical role in mediating the protective effects of acute statin treatment. Nrf2 induction by statins is a novel discovery. In order to understand the mechanism of such statin effect, I used an in vitro cell system, in which a variety of statins, atorvastatin, simvastatin, lovastatin, and pravastatin, were found to elevate Nrf2 protein levels. Elevation of Nrf2 by statins was independent of increased protein stability or transcriptional regulation. Instead, statins increased Nrf2 mRNA association with ribosomal complexes and induced Nrf2 protein through a translational mechanism. Recruitment of Nrf2 mRNA to ribosomes and induction of Nrf2 protein was dependent on activation of PI3 kinase. These studies provide evidence that Nrf2 plays a critical role in protecting cardiac myocytes and the heart from oxidative stress and MI. In the absence of Nrf2, mice experienced worse cardiac injury following MI and quickly advanced to heart failure. Mechanistically, this work has identified a novel role of Nrf2 in preserving mitochondrial morphology and integrity during oxidative stress through a direct interaction with the outer mitochondrial membrane. Finally, a newly defined role of Nrf2 induction by statins in mediating protection against MI by acute statin therapy indicates that modulation of Nrf2 may represent a viable pharmacological target for cardiac protection in humans.

Transmyocardial revascularization (TMR) has emerged as an additional therapeutic option for patients suffering from diffuse coronary artery disease (CAD), providing immediate angina relief. The current potential of this therapy focuses on the injection of stem cells, in order to create a synergistic angiogenic effect while increasing myocardial repair and regeneration. Although TMR procedures provide increased vascularization within the myocardium, patients suffering from ischemic cardiomyopathy may not benefit from angiogenesis alone. Therefore, the goal of introducing stem cells is to restore the functional state of a failing heart by providing stem cells with a favorable microenvironment that will enhance their engraftment. Since the therapeutic effect of stem cells is dependent on their capacity to survive and retain in the myocardium, laser therapy may provide a strategy for increasing stem cell engraftment. If so, these cells may have the potential to act as mitochondrial donors or as sources of paracrine factors, aiding in the recovery from oxidative stress and providing antioxidant reserves. Furthermore, laser therapy may also play an influential role in regulating cardiac repair and regeneration via epithelial-mesenchymal transition (EMT). By interacting with specific transcription factors TMR may provide another pathway by which it can offer reparative effects. Cumulatively, paracrine release, denervation, and angiogenesis contribute to the therapeutic benefits experienced by TMR patients, including a significant reduction in angina, with increases in myocardial perfusion and survival rates. With the addition of stem cells, these effects may be further augmented, thus providing increased symptomatic relief in patients.

Colorectal cancer is the second leading cause of cancer-related deaths in the United States and the third most common cancer in men and women. Vitamin E is a lipid soluble antioxidant that exists as eight structurally different isoforms of tocopherols and tocotrienols. Recent experimental, and molecular studies suggest that γ-tocotrienol (GT3) may be a more potent cancer-preventive form of vitamin E. 15-lipoxygenase-1 (15-LOX-1) and its product 13-S-hydroxyoctadecadienoic acid (13-S-HODE) are decreased in colon cancer cells. 15 LOX-1 is considered a tumor suppressor gene in colon carcinogenesis. Non-steroidal anti-inflammatory drug (NSAID)-induced 15-LOX-1 expression is critical to aspirin and NSAID-induced apoptosis in colorectal cancer cells. HCT-116 is a microsatellite-instability (MSI) colon cancer cell line. MSI is a marker of chemo-resistance but is associated with improved survival as compared to microsatellite-stable (MSS) colon cancers. The effects of GT3 on cytotoxicity and 15 LOX-1 expression was studied on the human colon cancer cell line HCT-116. HCT-116 colon cancer cell lines were cultured in DMEM media and dosed with increasing concentrations of GT3 (20µM-50µM). Cytotoxicity of the drugs was studied using Cell Titer Glo and MTS assays 24 hours after dosing. Cells were then plated in 6-well plates and grown for 24 hours. Cells were then dosed with 2 mL of GT3 at 20 uM at the respective time periods (2h, 4h, 6h, 12h, 16h, 24h) and lysates were harvested. Gel electrophoresis was run according to BCA protein assay from the time-dependent lysates and blots were tagged with a rabbit 15-lox antibody. Ongoing experiments include RNA PCR. RNA is being isolated at 2, 4, 6 and 12 hours. The RNA as reversed transcribed using a 15 lox 1 primer and that cDNA is being quantified using Quantitative PCR. GT3 induced cytotoxicity in MTS assay and Cell Titer Glo assay when added to HCT-116 cell line. 15 LOX 1 protein expression was found to be up-regulated in the colon cancer cell line HCT-116 when GT3 was added at 12h, 16h and 24h with the maximum expression at 16 hours. Chemotherapeutic drugs can have significant side effects. Understanding the role of GT3 on colon cancer cell lines could lead to the development of novel drugs to supplement current chemotherapy regimens and allow for lower doses of chemotherapeutic agents. Modulation of 15-LOX-1 suggests that GT3 may induce apoptosis through induction of the lipoxygenase pathway. Further experiments are under way to study the mechanism of action of GT3 on the 15 LOX-1 pathway. Since HCT-116 is a MSI- colon cancer cell line, effects of GT3 on MSS- colon cancer cell lines will also be studied.