Chronic pain and opioid use disorders (OUD) are burgeoning interrelated epidemics. There is a major public health need to investigate modifiable risk factors and elucidate the pathophysiology of these poorly understood disorders so that novel therapies and prevention efforts can be developed. Sleep disturbances, especially insomnia and sleep apnea are highly prevalent, treatable and increasingly recognized as risk factors for both chronic pain and OUD. It is not known, however, whether sleep disturbance causally alters mechanisms that contribute to OUD risk. Sleep disruption impairs endogenous pain inhibition; a phenomenon associated with descending neural pathways that are linked to both the analgesic efficacy and rewarding properties mu-opioid receptor (MOR) agonists. This suggests that cerebral MOR dysregulation may be a shared neurobiological mechanism by which sleep disturbance causally increases risk for chronic pain and OUD. Direct interrogation of cerebral MOR availability, however, has yet to be undertaken after experimental sleep deprivation in humans. Based on preclinical data and our preliminary studies, we hypothesize that sleep continuity disruption (SCD) and/or sleep fragmentation (SF), two sleep patterns commonly observed in both chronic pain and OUD, will alter cerebral MOR availability in descending pain inhibitory and reward processing pathways. We further hypothesize that these forms of sleep disruption will increase OUD risk by reducing opioid analgesic efficacy and/or enhancing standard abuse liability measures. We propose a parallel group experiment that will randomize 100 healthy subjects to two nights of either experimental: 1) SCD (frank, prolonged, nightly awakenings with curtailed sleep duration, a pattern associated with insomnia); 2) SF (multiple, frequent, non- waking arousals with preserved sleep duration, a pattern observed in sleep apnea); or 3) undisturbed sleep (US). Subjects will then complete two [11C]Carfentanil PET brain imaging scans (resting to measure basal MOR binding potential (BP) and during pain to quantify endogenous opioid release). We will then use a placebo- controlled, cumulative dose paradigm to evaluate the analgesic efficacy and abuse liability of the prototypic MOR agonist, hydromorphone. Analgesic efficacy and abuse liability will be evaluated using quantitative sensory testing and standard procedures.
We aim to: 1) evaluate whether experimental SCD and/or SF alter resting or pain-evoked MOR BP in brain regions associated with pain inhibition; 2) examine whether SCD and/or SF alters the analgesic response and abuse liability profile of hydromorphone; and 3) determine whether MOR BPs in brain regions of interest are associated with hydromorphone analgesia and abuse liability. We will also evaluate the extent to which associations differ by sleep condition or sex. Establishing whether common and treatable forms of sleep disturbance directly alter cerebral MOR availability, opioid analgesia and abuse liability will transform the understanding of how sleep disturbance is a risk factor for OUD and chronic pain and lead to novel prevention efforts and changes in pain management practice.
Chronic pain and opioid use disorder are, respectively, leading causes of disability and accidental death in the US; there is a public health imperative to identify modifiable risk factors so that these inter-related problems can be better understood and prevented. Sleep disturbance is a common and highly treatable risk factor for both chronic pain and OUD and we hypothesize that sleep disturbance increases risk for pain and OUD by dysregulating brain mu-opioid receptor (MOR) signaling. To answer this question, we will conduct a randomized controlled experiment in healthy individuals, testing the effects of two common sleep disruption patterns experience by the majority of individuals with chronic pain and OUD (insomnia pattern and sleep apnea pattern) on: 1) brain imaging measures of MOR signaling, and 2) the analgesic response and abuse liability profile of hydromorphone, a prototypical opiate drug.
