Kelly M. Standifer, Ph.D.
Our research goal, ultimately, is to develop alternative therapeutic options (to morphine) for the treatment of severe pain. The newest member of the opioid receptor family, nociceptin/orphanin FQ peptide receptor (NOP; also known as ORL1 and KOR3), and its endogenous agonist, nociceptin/orphanin FQ (N/OFQ), bi-directionally modulates a number of CNS and immune system functions, including (but not limited to) pain sensitivity, anxiety, cognition and monocyte chemotaxis. As one might guess, the literature is replete with papers describing two opposite effects of N/OFQ on the same endpoint. Actions of N/OFQ often vary between species, strains, sex, route of administration and time of administration. What does seem clear is that N/OFQ, through its receptor NOP, functions to modulate the system back to homeostasis. This means that baseline actions of N/OFQ in control, untreated animals is much different than its actions in animals that have experienced a trauma, stress, injury or infection… and differ between males and females that have experienced trauma, stress, injury and/or infection. Over the last 10 years, our lab has examined the role of N/OFQ/NOP in three devastating physiological conditions: traumatic brain injury (TBI), PTSD and chronic pain. We found that N/OFQ levels increase in various brain regions, CSF and/or serum over time following TBI, traumatic stress or chronic nerve injury. We hypothesize that disruption of the N/OFQ/NOP system, either in response to, or as a result of, these conditions resets the baseline. We’ve employed a variety of approaches to study receptor activity and NOP/N/OFQ expression in vitro and in vivo. This includes use of cell lines from different cell types that endogenously express NOP and/or N/OFQ, and male and female rats that express WT(+/+) or ORL1 (-/-) rats in which a single point mutation prevents NOP from being translated into protein. We found that elevated levels of N/OFQ are associated with vestibular deficits following TBI, and with allodynia following exposure to a traumatic stress. A single, acute injection of NOP antagonist within 30 min of TBI delayed the appearance of vestibular deficits, but prevented the development of oxidative damage 9 days later (Awwad et al., 2018). Similarly, administration of NOP antagonist 7 days following exposure to traumatic stress reverses persistent allodynia caused by the PTSD stress (Zhang et al., 2015). Male ORL1 (-/-) rats failed to develop allodynia following traumatic stress, but female ORL1 (-/-)rats developed allodynia at least as much as the WT females (abstract published: Standifer et al., 2017 http://www.fasebj.org/: FASEB J. 31:988.8; manuscript submission). As a result, we are investigating how sex steroids modulate N/OFQ/NOP expression, activity and nociceptive sensitivity). Cytokines such as TNFa also modulate N/OFQ expression. Our most recent grant examines changes in TNFa levels shortly after traumatic stress, and examines how blockade of TNFa actions prevents development of allodynia.
N/OFQ also has been strongly implicated in the development of morphine tolerance. Reports from several labs, including ours (Zhang et al., 2012), demonstrated that chronic morphine increased levels of N/OFQ in CSF and a number of brain regions, but that spinal NOP receptor activity differed between males and females following chronic morphine treatment. Blocking the actions of OFQ/N significantly reduced the extent to which the analgesic actions of morphine was lost with chronic morphine administration. Using human neuronal cell lines that natively express mu opioid receptors and NOP; we identified a cellular mechanism for mu opioid receptor-mediated mu and NOP receptor tolerance and cross-tolerance (Mandyam et al., 2002, 2003; Thakker and Standifer, 2002 and Ozsoy et al., 2005). Acutely, OFQ/N activates protein kinase C (PKC), which activates and translocates G protein-coupled receptor kinase 2 (GRK2) and GRK3 to the cell membrane where GRK2 can quickly desensitize the mu opioid receptor in the presence of a mu opioid against such as morphine. Tolerance induced by prolonged exposure to OFQ/N treatment (24 h or more) upregulates GRK levels. It appears that the increased availability of GRK produces the rapid tolerance and/or cross-tolerance upon challenge with an agonist. Administration of a NOP antagonist likely disrupts the GRK translocation or ‘priming’ produced by persistently elevated N/OFQ and prevents mu opioid receptor desensitization/tolerance. Therefore, we hope to understand under what conditions NOP antagonism or partial agonism may reduce chronic pain or reverse morphine tolerance.
Education & Experience
B.S. in Zoology
Duke University, Durham, NC1984
Associate Natural Science in Natural Science
St. Gregory's College, Shawnee, OK1982
University of Florida, Gainesville, FL1988
Publications & Presentations
- 1. Al Yacoub O N, Awwad H O, Zhang Y, Standifer K. Therapeutic potential of nociceptin/orphanin FQ peptide (NOP) receptor modulators for treatment of traumatic brain injury, traumatic stress, and their co-morbidities. Pharmacology & therapeutics. 2021
2. Dib P, Zhang Y, Schalo I, Durand C, Ihnat M, Gallucci R, Standifer K M. TNF-α initiates allodynia and anxiety-like symptoms in a preclinical model of PTSD and co-morbid pain. Cellular and Molecular Neurobiology . 2021; 12 : 721999
3. Standifer K M, Inturrisi C E, Foley K M, Pan Y. Understanding opioid actions, pain and analgesia: a tribute to Dr. Gavril Pasternak. Cellular and Molecular Neurobiology. In Press; 41 : 827-834
4. Zhang Y, Standifer K M. Exacerbated Headache‑Related Pain in the Single Prolonged Stress Preclinical Model of Post‑traumatic Stress Disorder. Cellular and Molecular Neurobiology . 2020
5. Awasthi V, Awwad H O, Houson H, Hedrick A, Mdzinarishvili A, Standifer K. Hemorrhagic Shock Aggravates Traumatic Brain Injury: Evidence from PET Imaging Using 18F-Fluorodeoxyglucaric Acid in a Rat Model. BRAIN INJURY. 2019; 33 : 117-118