Friday, April 4, 2025
4/4/2025
Mechanism and Countermeasure of Fentanyl-Induced Sudden Death - PROJECT SUMMARY Opioids were involved in 75,673 overdose deaths in 2020 in the U.S. Fentanyl, an opioid mu-receptor (MOR) agonist acting on central MORs produces analgesia, but depresses ventilation that could be lethal. Rapid intravenous injection of overdose fentanyl, particularly in Illicit use, is the deadliest. It triggers an apnea leading to sudden death within minutes in ~1/3 of adults (male > female) with ~75% of fentanyl sequestered by the lungs after injection. Naloxone is the preferable treatment for post-overdose, but not viable for the illicit FNT users who are found pulseless upon the arrival of emergency medical services. Moreover, naloxone counteracts analgesia with potentially life-threatening side effects. Central apnea, upper airway obstruction, and chest wall rigidity are assumed to be accountable for the sudden death, but the exact cause of the death and the effective countermeasure remain unknown, constituting a critical and unmet therapeutic clinical need. Bronchopulmonary C-fibers (PCFs) are the major sensory nerve endings innervating the airways and lungs and crucial in the control of respiratory rhythm. PCF stimulation could elicit central apnea and vocal closure likely by promoting release of glutamate or substance P to activate PCF 2nd-order neurons in the nucleus tractus solitarius via AMPA and neurokinin-1 receptor. We have reported that intravenous bolus injection of a low dose fentanyl triggers a PCF-mediated brief apnea, consistent with previously reported excitation of dorsal root ganglion C- neurons by MOR agonists via Gs-cAMP pathway. Our preliminary data show a triple apnea (central apnea, vocal closure and laryngeal constriction/collapse) coupled with chest wall rigidity, resulting in death within minutes in anesthetized adult rats after overdose fentanyl is rapidly injected. In this proposal, we seek to establish the first animal model of fentanyl-induced sudden death following triple apnea in awake adult rats and determine the dependency of triple apnea (death) on the gender and peripheral (especially vagal) MORs/µ1Rs (Aim 1). We will further demonstrate that fentanyl directly stimulates PCFs to evoke triple apnea by acting on MOR/µ1R and Gs- cAMP pathway, thereby promote PCF release of glutamate and SP to activate the 2nd-order neurons (Aim 2). Our pilot study has shown that intravenous injection of dermorphin (a peripherally acting MOR agonist) induces MOR internalization in vagal sensory neurons and blocks fentanyl-induced triple apnea. The β-arrestin-mediated signaling is known to be responsible for MOR desensitization/internalization. We will define that diamorphine has limited impact on baseline cardiorespiratory activity, but internalizes PCFs' MORs/µ1Rs via activation of β- arrestin-signaling to prevents the triple apnea (death) with no change in analgesia. This will present a potential safer and translational pretreatment for overdose fentanyl in clinical settings (Aim 3). A multidisciplinary approach (electrophysiology, immunohistochemistry, pharmacology and biochemistry) at systemic and cellular levels will be applied to elucidate the mechanisms underlying not only triple apnea (death) but also the lack of triple apnea after dermorphin pretreatment. The expected data will, for the first time, mechanistically reveal the key role of PCFs in generating fentanyl-induced triple apnea and provide a novel and potential countermeasure of dermorphin pretreatment to prevent/diminish the sudden death.
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