Chronic oxycodone induces integrated stress response in rat brain

Abstract

BackgroundOxycodone is an opioid that is prescribed to treat multiple types of pain, especially when other opioids are ineffective. Unfortunately, similar to other opioids, repetitive oxycodone administration has the potential to lead to development of analgesic tolerance, withdrawal, and addiction. Studies demonstrate that chronic opioid exposure, including oxycodone, alters gene expression profiles and that these changes contribute to opioid-induced analgesic effect, tolerance and dependence. However, very little is known about opioids altering the translational machinery of the central nervous system. Considering that opioids induce clinically significant levels of hypoxia, increase intracellular Ca2+ levels, and induce the production of nitric oxide and extracellular glutamate transmission, we hypothesize that opioids also trigger a defensive mechanism called the integrated stress response (ISR). The key event in the ISR activation, regardless of the trigger, is phosphorylation of translation initiation factor 2 alpha (eIF2α), which modulates expression and translational activation of specific mRNAs important for adaptation to stress. To test this hypothesis, we used an animal model in which female rats were orally gavaged with 15 mg/kg of oxycodone every 24 h for 30 days.ResultsWe demonstrated increased levels of hsp70 and BiP expression as well as phosphorylation of eIF2α in various rat brain areas after oxycodone administration. Polysomal analysis indicated oxycodone-induced translational stimulation of ATF4 and PDGFRα mRNAs, which have previously been shown to depend on the eIF2α kinase activation. Moreover, using breast adenocarcinoma MCF7 cells, which are known to express the μ-opioid receptor, we observed induction of the ISR pathway after one 24-h treatment with oxycodone.ConclusionsThe combined in vivo and in vitro data suggest that prolonged opioid treatment induces the integrated stress response in the central nervous system; it modulates translational machinery in favor of specific mRNA and this may contribute to the drug-induced changes in neuronal plasticity.

Brain-Derived Extracellular Vesicle microRNA Signatures Associated with In Utero and Postnatal Oxycodone Exposure

“…Recent studies coupled to high-throughput technologies have further provided new insights into the molecular underpinnings associated with chronic oxy dependency. These include alterations in genes associated with the integrated stress response in the brain [41], induction of apoptotic signaling in neurons by promoting demyelination [39], alterations in reward-related genes [42], axon guidance molecules [42], inflammation/immune-related genes [43], neurotransmitter receptor genes [44] as well as expression of synaptic plasticity genes [45], including key sex-specific neuroplasticity-related genes [46]. miRNAs represent a class of noncoding RNAs that critically regulate gene expression by binding to the 3 UTR of target transcripts, thus blocking their translation.…”

Carbonyl-protein content increases in brain and blood of female rats after chronic oxycodone treatment

“…Ours and other studies have shown that chronic opioid administration is associated with activation of the pro-apoptotic signaling and neuronal degeneration in animal models [5][6][7][8][9]. In our current study, we analyzed carbonyl content in brain and blood/plasma samples from the same animals that have been used to evaluate oxidative and neurodegenerative effect of oxycodone reported in [5,10]. We demonstrated increased levels of protein carbonylation in rat cortex and also accumulation of Triton ™ X-100 insoluble carbonyl-protein aggregates in blood plasma of animals treated with oxycodone, indicating a systemic degenerative process.…”

“…In this study, we have used tissue samples from female 60 day-old Sprague-Dawley rats that have been reported in our previous studies [5,10]. Briefly, randomly assigned animals were gavaged with vehicle water or with 15 mg/ kg oxycodone (Mallinckrodt Inc., St. Louis MO) in a volume of 1.0 ml/kg every 24 h for 30 days.…”

“…Briefly, randomly assigned animals were gavaged with vehicle water or with 15 mg/ kg oxycodone (Mallinckrodt Inc., St. Louis MO) in a volume of 1.0 ml/kg every 24 h for 30 days. Lack of toxicity and efficient anti-nociceptive effect of this oxycodone scheme treatment were assessed by daily weight measurement and by the hot plate tests, respectively, as it is described in [5,10]. We investigated tissues from twelve water and twenty oxycodone treated rats using from four sets of littermates.…”

“…The western blot analysis was performed as it is described in [5,10]. Briefly, to analyse the expression of proteins in blood, equal amounts of total protein were loaded on a 12% or 4-12% NuPAGE ® Novex ® Bis-Tris Gel (Invitrogen).…”