title: Do Resting Plasma β-Endorphin Levels Predict Responses to Opioid Analgesics?
abstract: Clinically feasible predictors of opioid analgesic responses for use in precision pain medicine protocols are needed. This study evaluated whether resting plasma β-endorphin (BE) levels predicted responses to an opioid analgesic, and whether chronic pain status or sex moderated these effects.
  
  
  
  Participants included 73 individuals with chronic low back pain (CLBP) and 88 pain-free controls, all using no daily opioid analgesics. Participants attended 2 identical laboratory sessions during which they received either intravenous morphine (0.08 mg/kg) or saline placebo, with blood samples obtained before drug administration to assay resting plasma BE levels. Once peak drug activity was achieved in each session, participants engaged in an ischemic forearm pain task (ISC) and a heat pain task. Morphine analgesic effects were derived reflecting the difference in pain outcomes between placebo and morphine conditions.
  
  
  
  In hierarchical regressions, significant Type (CLBP vs. control)×BE interactions (Ps<0.05) were noted for morphine effects on ISC tolerance, ISC intratask pain ratings, and thermal VAS unpleasantness ratings. These interactions derived primarily from associations between higher BE levels and smaller morphine effects restricted to the CLBP subgroup. All other BE-related effects, including sex interactions, for predicting morphine analgesia failed to reach statistical significance.
  
  
  
  BE was a predictor of morphine analgesia for only 3 out of 9 outcomes examined, with these effects moderated by chronic pain status but not sex. On the whole, results do not suggest that resting plasma BE levels are likely to be a clinically useful predictor of opioid analgesic responses.
authors.affiliation: *Department of Anesthesiology, Vanderbilt University School of Medicine, Nashville, TN Departments of †Behavioral Science ‡Anesthesiology, Rush University, Chicago, IL §Department of Psychology, Ohio University, Athens, OH.
authors.forename: Stephen
authors.initials: S
authors.lastname: Bruehl
authors.forename: John W
authors.initials: JW
authors.lastname: Burns
authors.forename: Rajnish
authors.initials: R
authors.lastname: Gupta
authors.forename: Asokumar
authors.initials: A
authors.lastname: Buvanendran
authors.forename: Melissa
authors.initials: M
authors.lastname: Chont
authors.forename: Daria
authors.initials: D
authors.lastname: Orlowska
authors.forename: Erik
authors.initials: E
authors.lastname: Schuster
authors.forename: Christopher R
authors.initials: CR
authors.lastname: France
mesh_terms: D000283:Administration, Intravesical; D000328:Adult; D000701:Analgesics, Opioid / Q000627:therapeutic use*; D015415:Biomarkers / Q000097:blood; D059350:Chronic Pain / Q000097:blood* / Q000188:drug therapy*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D006358:Hot Temperature; D006801:Humans; D007511:Ischemia; D017116:Low Back Pain / Q000097:blood* / Q000188:drug therapy*; D008297:Male; D009020:Morphine / Q000627:therapeutic use; D010147:Pain Measurement; D058748:Pain Perception / Q000187:drug effects; D012044:Regression Analysis; D012146:Rest; D012727:Sex Characteristics; D016896:Treatment Outcome; D001615:beta-Endorphin / Q000097:blood*
chemical_list: D000701:Analgesics, Opioid; D015415:Biomarkers; D001615:beta-Endorphin; D009020:Morphine