Mrg Receptors and Analgesia

Three manuscripts published in 2014:

1) Zhe Li, Shao-Qiu He, Qian Xu, Fei Yang, Vinod Tiwari, Qin Liu, Zongxiang Tang, Liang Han, Yu-Xia Chu, Yun Wang, Niyada Hin, Takashi Tsukamoto, Barbara Slusher, Xiaowei Guan, Feng Wei, Srinivasa N. Raja, Xinzhong Dong and Yun Guan: Activation of MrgC receptor inhibits N-type calcium channels in small-diameter primary sensory neurons in mice. Pain. 2014; 155(8):1613-21

2) Shao-Qiu He, Zhe Li, Yu-Xia Chu, Liang Han, Qian Xu, Man Li, Fei Yang, Qin Liu, Zongxiang Tang, Yun Wang, Niyada Hin, Takashi Tsukamoto, Barbara Slusher, Vinod Tiwari, Ronen Shechter, Feng Wei, Srinivasa N. Raja, Xinzhong Dong, Yun Guan: MrgC agonism at central terminals of primary sensory neurons inhibits neuropathic pain. Pain. 2014;155(3):534-44.

3) Shao-Qiu He, Liang Han, Zhe Li, Qian Xu, Vinod Tiwari, Fei Yang, Xiaowei Guan, Yun Wang, Srinivasa N. Raja, Xinzhong Dong and Yun Guan: Temporal changes in MrgC expression after spinal nerve injury. Neuroscience. 2014; 261:43-51

Patients who suffer neuropathic pain are often the most challenging to treat. Major analgesics (e.g, opioids) bind to receptors that are expressed throughout the central nervous system, resulting in potential adverse effects and perceived risks of abuse that may limit their clinical use. Identifying novel molecular targets on primary nociceptive sensory neurons may offer an opportunity for pain-selective treatment. We recently discovered that Mas-related G-protein-coupled receptor subtype C (MrgC) receptors, which are specifically expressed in small-diameter primary sensory neurons, may be a novel selective target for the treatment of pathological pain. Investigating the role of MrgC in pain has been hampered by a lack of tools to examine its expression and function. We generated an MrgC-specific antibody and a dipeptide MrgC-selective agonist (JHU58) for use in functional analysis. In 2014, we published a series of papers to establish the roles of MrgC in neuropathic pain. Firstly, we provide multiple lines of evidence that activation of MrgC receptors at the central terminals of afferent sensory neurons constitutes a novel and powerful pain inhibitory mechanism in different animal models of neuropathic pain. Secondly, we showed that changes in MrgC expression after nerve injury differ temporally in injured and uninjured DRG neurons, and upregulation of MrgC expression in uninjured DRG may be an essential adaptive component that affects the temporal resolution of the chronic pain state. Finally, we revealed for the first time that an MrgC agonist selectively and dose-dependently inhibits N-type HVA calcium channels in native nociceptive DRG neurons, which then lead to attenuation of both miniature and the evoked excitatory postsynaptic currents in spinal dorsal horn neurons. Further, MrgC activation leads to the inhibition of HVA calcium channels through phospholipase C- and Gβγ-dependent mechanisms. MrgC shares substantial genetic homogeneity with human MrgX1. Therefore, our findings suggest that intrathecally delivered MrgX1 receptor agonists, which are currently being synthesized at Brain Science Institute-JHU, may function as a new class of analgesics to treat intractable pain in humans. Notably, we also developed novel transgenic mice that express MrgX1 under the endogenous MrgC promoter, which offers an opportunity to examine the functions of the human receptor in animal pain models. Because of its highly specific expression in nociceptors, activation of MrgX1 may offer an opportunity for developing a pain-specific treatment with minimal foreseeable side effects.

Level of Sedation and Surgical Outcomes

Manuscript published in 2014

1) Charles H. Brown IV, Andrew S. Azman, Allan Gottschalk, Simon C. Mears and Frederick E. Sieber. Sedation depth during spinal anesthesia and survival in elderly patients undergoing hip fracture repair Anesth Analg. 2014;118(5):977-80.

Low intraoperative bispectral index (BIS) values have been associated with increased mortality in several studies, although this finding has not been confirmed universally. Because few randomized trials of BIS-targeted anesthesia have been reported, it is unclear whether low BIS values are simply a marker of poor prognosis, or whether targeting anesthetic management based on BIS monitoring could reduce mortality. Therefore, between 2005 and 2008, we randomized patients undergoing surgical repair of a hip fracture under spinal anesthesia to light sedation (BIS>80) compared to deep sedation (BIS~50). We reported results of this trial previously (2), which demonstrated a 50% reduction in postoperative delirium in the light versus deep sedation group. Subsequent to this trial, conflicting evidence emerged that low intraoperative BIS values might be associated with increased long-term mortality. To specifically address this question, we conducted a follow-up survival analysis of patients enrolled in the original trial, with the hypothesis that light sedation compared to deep sedation would reduce 1-year and long-term mortality, particularly among patients with serious comorbidity. We also hypothesized that the association between light sedation during spinal anesthesia and decreased mortality would be mediated by reduced delirium incidence. We found that among all patients in the trial, mortality was equivalent across sedation groups. However, among patients with serious comorbidities (Charlson score >4), 1-year mortality was reduced in the light (22.2%) vs. deep (43.6%) sedation group (Hazard Ratio [HR], 0.43; 95% CI, 0.19–0.97; P=0.04) during spinal anesthesia. Similarly, among patients with Charlson score >6, 1-year mortality was reduced in the light (28.6%) vs. deep (52.6%) sedation group (HR 0.33; 95%CI 0.12–0.94; P=0.04) during spinal anesthesia. Reduction in postoperative delirium was not a mediator between depth of sedation and mortality. This study was limited because of small sample size, lack of knowledge of cause of death, post-hoc analysis, and limitation to a specific surgery. However, light sedation during repair of hip fracture under spinal anesthesia may reduce mortality in patients with high comorbidity scores. Further research on reduced mortality following light sedation during spinal anesthesia is needed. (Please also see the accompanying editorials on this work in the same issue of Anesthesia & Analgesia).

2) Sieber F, Zakriya K Gottschalk A, Blute M-R, Lee HB, Rosenberg PB, Mears SC. Sedation depth during spinal anesthesia and the development of postoperative delirium in elderly patients undergoing hip fracture repair. Mayo Clin Proc 2010;85(1):18-26.

Targeting Arginase for Vascular Health

Manuscript published in 2014

1) Deepesh Pandey, Anil Bhunia, Young Jun Oh, Fumin Chang, Yehudit Bergman, Jae Hyung Kim, Janna Serbo, Tatiana N. Boronina, Robert N. Cole, Jennifer Van Eyk, Alan T. Remaley, Dan E. Berkowitz, Lewis H. Romer. OxLDL triggers retrograde translocation of arginase2 in aortic endothelial cells via ROCK and mitochondrial processing peptidase. Circ Res 2014;115(4):450-9

Arginase is an important negative regulator of endothelial Nitric Oxide Synthase (eNOS) because of its competition for the common substrate L-arginine. Arginase upregulation contributes to the pathobiology of vascular diseases, including atherosclerosis, erectile dysfunction, and pulmonary and systemic hypertension. Oxidized LDL-mediated injury to endothelium causes 2 distinct events that contribute to increased Arginase 2 (Arg2): a decreased check on Arg2 transcription by histone deacetylase 2 (HDAC2) (2,3); and a rapid increase in Arg2 activity (1). In the second event, oxidized LDL triggers rapid Arg2 translocation from endothelial mitochondria (where it is confined in the quiescent state) to the cytosol. This process requires the lectin-like oxidized LDL receptor-1 receptor, Rho kinase, and mitochondrial processing peptidase. Arg2 translocation leads to eNOS uncoupling, decreased NO production, and impaired endothelial-dependent vasorelaxation. Finally, Arg2-/- mice bred on an ApoE-/- background exhibit enhanced eNOS function, improved endothelium-mediated vasoreactivity, and reduced plaque load. These findings suggest a novel mechanism for rapid Arg2 activation in response to endothelial injury and reveal a signaling pathway by which a single gene product with an unambiguous mitochondrial targeting sequence undergoes dual compartmentalization (1)(Please also see the accompanying editorial on this work in the same issue of Circulation Research).

2) Deepesh Pandey, Gautam Sikka, Yehudit Bergman, Jae Hyung Kim, Sungwoo Ryoo, Lewis H. Romer, Dan E. Berkowitz. Transcriptional regulation of endothelial arginase 2 by histone deacetylase 2. Arteriosclerosis Thrombosis and Vascular Biology. 2014 Jul; 34(7): 1556-66.

3)Deepesh Pandey, Daijiro Hori, Jae Hyung Kim, Dan E. Berkowitz, Lewis H. Romer. NEDDylation promotes endothelial dysfunction: A role for HDAC2. Journal of Molecular and Cellular Cardiology. Accepted January 26, 2015.

Hypoxia-induced mitogenic factor (FIZZ1/RELMα) and Pulmonary Hypertension

Manuscript published in 2014

1) Kazuyo Yamaji-Kegan, Eiki Takimoto, Ailan Zhang, Noah C. Weiner, Lucas W. Meuchel, Alan E. Berger, Chris Cheadle, and Roger A. Johns. Hypoxia-induced mitogenic factor (FIZZ1/RELMα) induces endothelial cell apoptosis and subsequent interleukin-4-dependent pulmonary hypertension. Am J Physiol Lung Cell Mol Physiol. 2014;306(12):L1090-103

Pulmonary hypertension (PH) is a devastating disease of the pulmonary vasculature that is characterized by enhanced inflammation, vasoconstriction, and remodeling of small pulmonary arteries. It is a fatal disease that is usually diagnosed at a late stage as it progresses toward congestive heart failure and death. Its prevalence worldwide is estimated at 20-25 million. Current therapies are primarily palliative in nature, and none significantly prolong life. Our group has discovered that hypoxia-induced mitogenic factor (HIMF, also known as FIZZ1 or Resistin-Like Molecule [RELM]α) is critically involved in the vascular remodeling and cardiac dysfunction seen in animal and human pulmonary arterial hypertension (PH) (2-4). Inhibition of this pathway by adeno-associated virus (AAV) shRNA against HIMF or knockout of HIMF prevents the development of hypoxia-induced PH (2). We also have found that human homologues of this protein, human (h)Resistin and hRELMβ, are upregulated in the lung hypertrophic vasculature, plexiform lesions, and myofibroblasts of patients with idiopathic pulmonary arterial hypertension and scleroderma-associated PH (3). In the highlighted manuscript (1), we report that intravenous administration of mouse HIMF causes early lung vascular inflammation and subsequent PH development in mice in a manner dependent on the T-helper 2 cytokine interleukin-4. We also demonstrate that mouse HIMF and hResistin induce endothelial cell (EC) activation and apoptosis. These apoptotic ECs lead to the production of growth factors that stimulate pulmonary arterial smooth muscle cell (SMC) proliferation. Thus, an EC apoptosis-SMC growth loop could result in the progression of pulmonary vascular remodeling in PH. Moreover, these proteins could serve as potential biomarkers and therapeutic targets for the disease.

2) Angelini DJ, Su Q, Yamaji-Kegan K, Fan C, Skinner JT, Champion HC, Crow MT, Johns RA. Hypoxia-induced mitogenic factor (HIMF/FIZZ1/RELMalpha) induces the vascular and hemodynamic changes of pulmonary hypertension. American Journal of Physiology 2009;296:L582-93.

3) Angelini DJ, Su Q, Yamaji-Kegan K, Fan C, Teng X, Hassoun PM, Yang SC, Champion HC, Tuder RM, Johns RA. Resistin-like molecule-beta in scleroderma-associated pulmonary hypertension. American Journal of Respiratory Cell and Molecular Biology 2009;41:553-61.

4) Yamaji-Kegan K, Su Q, Angelini DJ, Myers AC, Cheadle C, Johns RA. Hypoxia-induced mitogenic factor (HIMF/FIZZ1/RELMalpha) increases lung inflammation and activates pulmonary microvascular endothelial cells via an IL-4-dependent mechanism. Journal of Immunology 2010;185:5539-48.

Effective Treatment for Spinal Pain

Manuscript published in 2014

1) Steven P Cohen, Salim Hayek, Yevgeny Semenov, Paul F. Pasquina, Ronald L White, Elias Veizi, Julie H. Huang, Connie Kurihara, Zirong Zhao, Kevin B Guthmiller, Scott R. Griffith, Aubrey V. Verdun, David M. Giampetro, Yakov Vorobeychik. Epidural steroid injections, conservative treatment, or combination treatment for cervical radicular pain: a multicenter, randomized, comparative-effectiveness study. Anesthesiology. 2014 Nov;121(5):1045-55.

Spinal pain is the leading cause of disability in the world, with low back pain ranking 1st and neck pain 4th. Among the different types of ‘spinal’ pain, approximately 40% can be classified as neuropathic, which is often due to spinal stenosis or radiculopathy from a herniated disc. There are several non-surgical treatments for neuropathic spinal pain. Epidural steroid injections (ESI) are the most commonly performed pain medicine procedures in the world, with over 9 million being done each year in the United States. Gabapentin (Neurontin) and nortriptyline (Pamelor) are considered to be first-line pharmacological treatments for neuropathic pain in all published guidelines. Yet, these treatments are effective in only a subset of patients, and there is no consensus as to a treatment algorithm. To date, no studies have compared different first-line treatments for spinal pain, and none have compared any treatments for neck pain. In this 6-center randomized, 3-arm comparative-effectiveness study that included military treatment facilities, VA hospitals and academic teaching hospitals, 169 patients with cervical radicular pain were randomized to receive up to 3 ESI as needed, conservative treatment consisting of nortriptyline and/ or gabapentin plus physical therapy, or combination treatment composed of ESI and conservative treatment. The first follow-up visit was at 1-month after treatment was initiated, with those experiencing a positive outcome being followed at 3-months and 6-months post-treatment. For the primary outcome measure, radicular arm pain at 1-month, 0-10 numerical rating scale pain scores were 3.5 (95% CI 2.8, 4.2) in the combination group, 4.2 (CI 2.8, 4.2) in ESI patients, and 4.3 (CI 2.8, 4.2) in individuals treated conservatively (p=0.26). Combination group patients experienced a mean reduction of -3.1 (95% CI -3.8, -2.3) in average arm pain at 1-month vs. -1.8 (CI -2.5, -1.2) in the conservative group and -2.0 (CI -2.7, -1.3) in ESI patients (p=0.035). For neck pain, a mean reduction of -2.2 (95% CI -3.0, -1.5) was noted in combination patients vs. -1.2 (CI -1.9, -0.5) in conservative group patients and -1.1 (CI -1.8, -0.4) in those who received ESI; p=0.064). 3-months post-treatment, 56.9% of patients treated with combination therapy experienced a positive outcome vs. 26.8% in the conservative group and 36.7% in ESI patients (p=0.006). Although mixed, these results suggest that combination treatment using an interdisciplinary approach might afford the best outcomes for treating neuropathic spinal pain. ESI and conservative therapy might provide additive or complementary effects because they work via different mechanisms of action. A second possibility is that ESI provide excellent short-term pain relief and functional improvement, providing a window of opportunity with which physical therapy can reinforce the benefits. An alternative explanation is that those subjects who received combination therapy may have experienced a greater placebo response rate than those who received unimodal therapy, as their expectations for success were higher. (Please also see the accompanying editorial on this work in the same issue of Anesthesiology)