title: Select steroid hormone glucuronide metabolites can cause toll-like receptor 4 activation and enhanced pain.
abstract: We have recently shown that several classes of glucuronide metabolites, including the morphine metabolite morphine-3-glucuronide and the ethanol metabolite ethyl glucuronide, cause toll like receptor 4 (TLR4)-dependent signaling in vitro and enhanced pain in vivo. Steroid hormones, including estrogens and corticosterone, are also metabolized through glucuronidation. Here we demonstrate that in silico docking predicts that corticosterone, corticosterone-21-glucuronide, estradiol, estradiol-3-glucuronide and estradiol-17-glucuronide all dock with the MD-2 component of the TLR4 receptor complex. In addition to each docking with MD-2, the docking of each was altered by pre-docking with (+)-naloxone, a TLR4 signaling inhibitor. As agonist versus antagonist activity cannot be determined from these in silico interactions, an in vitro study was undertaken to clarify which of these compounds can act in an agonist fashion. Studies using a cell line transfected with TLR4, necessary co-signaling molecules, and a reporter gene revealed that only estradiol-3-glucuronide and estradiol-17-glucuronide increased reporter gene product, indicative of TLR4 agonism. Finally, in in vivo studies, each of the 5 drugs was injected intrathecally at equimolar doses. In keeping with the in vitro results, only estradiol-3-glucuronide and estradiol-17-glucuronide caused enhanced pain. For both compounds, pain enhancement was blocked by the TLR4 antagonist lipopolysaccharide from Rhodobacter sphaeroides, evidence for the involvement in TLR4 in the resultant pain enhancement. These findings have implications for several chronic pain conditions, including migraine and temporomandibular joint disorder, in which pain episodes are more likely in cycling females when estradiol is decreasing and estradiol metabolites are at their highest.
authors.affiliation: Department of Psychology and Neuroscience, University of Colorado at Boulder, Boulder, CO, USA. Electronic address: susannah.lewis@colorado.edu.
authors.forename: Susannah S
authors.initials: SS
authors.lastname: Lewis
authors.affiliation: Discipline of Physiology, School of Medical Sciences, University of Adelaide, Adelaide, South Australia, Australia.
authors.forename: Mark R
authors.initials: MR
authors.lastname: Hutchinson
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO, USA.
authors.forename: Morin M
authors.initials: MM
authors.lastname: Frick
authors.affiliation: Department of Psychology and Neuroscience, University of Colorado at Boulder, Boulder, CO, USA.
authors.forename: Yingning
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Psychology and Neuroscience, University of Colorado at Boulder, Boulder, CO, USA.
authors.forename: Steven F
authors.initials: SF
authors.lastname: Maier
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO, USA.
authors.forename: Tarek
authors.initials: T
authors.lastname: Sammakia
authors.affiliation: Chemical Biology Research Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism National Institutes of Health, Rockville, MD, USA.
authors.forename: Kenner C
authors.initials: KC
authors.lastname: Rice
authors.affiliation: Department of Psychology and Neuroscience, University of Colorado at Boulder, Boulder, CO, USA.
authors.forename: Linda R
authors.initials: LR
authors.lastname: Watkins
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D003345:Corticosterone / Q000378:metabolism; D004958:Estradiol / Q000031:analogs & derivatives / Q000378:metabolism; D020719:Glucuronides / Q000378:metabolism*; D012739:Gonadal Steroid Hormones / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D006930:Hyperalgesia / Q000209:etiology / Q000378:metabolism; D008297:Male; D062105:Molecular Docking Simulation; D009270:Naloxone / Q000494:pharmacology; D010146:Pain / Q000209:etiology / Q000378:metabolism*; D010812:Physical Stimulation; D017207:Rats, Sprague-Dawley; D051197:Toll-Like Receptor 4 / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D020719:Glucuronides; D012739:Gonadal Steroid Hormones; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D009270:Naloxone; D004958:Estradiol; D000469:Alkaline Phosphatase; D003345:Corticosterone
keywords: (+)-Naloxone; Corticosterone; Corticosterone-21-glucuronide; Estradiol; Estradiol-17-glucuronide; Estradiol-3-glucuronide; TLR4