Opioid induces increased DNA damage in prefrontal cortex and nucleus accumbens

The impact of opioids on the hallmarks of ageing

Opioids rank among the most hazardous substances of abuse, leading to opioid use disorders (which greatly diminish life quality) and contributing to the highest drug-related mortality rates. Nonetheless, both the therapeutic and recreational use of opioids is escalating globally. Interestingly, chronic opioid users often exhibit signs consistent with accelerated ageing, suggesting that they likely interfere with well-characterized ageing mechanisms (e.g., telomere shortening, epigenetic changes, mitochondrial dysfunction, cellular senescence). Here, we review the most recent advances regarding the impact of opioids on well-characterized hallmarks of ageing, to ascertain a potential association between opioid use and accelerated ageing. Our findings indicate that there is accumulating evidence supporting a close association between the use of opioids and the early onset of some ageing hallmarks, namely mitochondrial dysfunction, genomic instability, or telomere shortening. However, there is still limited data available regarding how opioids specifically impact other ageing hallmarks, like nutrient sensing, cellular senescence, or loss of proteostasis. Taking into consideration the high prevalence of opioid use, strengthening the understanding of the mechanisms underlying opioids' impact on ageing assumes utmost relevance, both in terms of improving risk assessment, as well as to help researchers and clinicians prevent or mitigate these effects in clinical settings.

Sex-specific Concordance of Striatal Transcriptional Signatures of Opioid Addiction in Human and Rodent Brains

Opioid use disorder (OUD) has emerged as a severe, ongoing public health emergency. Current, frontline addiction treatment strategies fail to produce lasting abstinence in most users. This underscores the lasting effects of chronic opioid exposure and emphasizes the need to understand the molecular mechanisms of drug seeking and taking, but also how those alterations persist through acute and protracted withdrawal. Here, we used RNA sequencing in post-mortem human tissue from males (n=10) and females (n=10) with OUD and age and sex-matched comparison subjects. We compared molecular alterations in the nucleus accumbens (NAc) and dorsolateral prefrontal cortex (DLPFC) between humans with OUD and rodent models across distinct stages of opioid use and withdrawal (acute and prolonged) using differential gene expression and network-based approaches. We found that the molecular signature in the NAc of females with OUD mirrored effects seen in the NAc of female mice at all stages of exposure. Conversely, males with OUD showed strong overlap in expression profile with rats in acute withdrawal. Co-expression networks involved in post-transcriptional modification of RNA and epigenetic modification of chromatin state. This study provides fundamental insight into the converging molecular pathways altered by opioids across species. Further, this work helps to disentangle which alterations observed in humans with OUD are driven by acute drug exposure and which alterations are consequences of chronic exposure.

A Novel Role for the Histone Demethylase JMJD3 in Mediating Heroin-Induced Relapse-Like Behaviors

BACKGROUND

Epigenetic changes that lead to long-term neuroadaptations following opioid exposure are not well understood. We examined how histone demethylase JMJD3 in the nucleus accumbens (NAc) influences heroin seeking after abstinence from self-administration.

METHODS

Male Sprague Dawley rats were trained to self-administer heroin. Western blotting and quantitative polymerase chain reaction were performed to quantify JMJD3 and bone morphogenetic protein (BMP) pathway expression in the NAc (n = 7-11/group). Pharmacological inhibitors or viral expression vectors were microinfused into the NAc to manipulate JMJD3 or the BMP pathway member SMAD1 (n = 9-11/group). The RiboTag capture method (n = 3-5/group) and viral vectors (n = 7-8/group) were used in male transgenic rats to identify the contributions of D1- and D2-expressing medium spiny neurons in the NAc. Drug seeking was tested by cue-induced response previously paired with drug infusion.

RESULTS

Levels of JMJD3 and phosphorylated SMAD1/5 in the NAc were increased after 14 days of abstinence from heroin self-administration. Pharmacological and virus-mediated inhibition of JMJD3 or the BMP pathway attenuated cue-induced seeking. Pharmacological inhibition of BMP signaling reduced JMJD3 expression and H3K27me3 levels. JMJD3 bidirectionally affected seeking: expression of the wild-type increased cue-induced seeking whereas expression of a catalytic dead mutant decreased it. JMJD3 expression was increased in D2+ but not D1+ medium spiny neurons. Expression of the mutant JMJD3 in D2+ neurons was sufficient to decrease cue-induced heroin seeking.

CONCLUSIONS

JMJD3 mediates persistent cellular and behavioral adaptations that underlie heroin relapse, and this activity is regulated by the BMP pathway.

The impact of chronic fentanyl administration on the cerebral cortex in mice: Molecular and histological effects

PURPOSE

Fentanyl, a fully synthetic opioid, is widely used for severe pain management and has a huge abuse potential for its psychostimulant effects. Unlike other opioids, the neurotoxic effects of chronic fentanyl administration are still unclear. In particular, little is known about its effect on the cerebral cortex. The current study aims to test the chronic toxicity of fentanyl in the mice model.

METHODS

Adult male Balb/c mice were chronically treated with low (0.05 mg/kg, i.p) and high (0.1 mg/kg, i.p) doses of fentanyl for 5 consecutive weeks, and various neurotoxic parameters, including apoptosis, oxidative stress, and neuroinflammatory response were assessed in the cortex. Potential histological as well as neurochemical changes were also evaluated.

RESULTS

The results of this study show that chronic fentanyl administration induced intense levels of apoptosis, oxidative stress, and neuroinflammation in the cerebral cortex. These findings were found to be correlated with histopathological characteristics of neural degeneration and white matter injury. Moreover, fentanyl administration was found to reduce the expression of both NMDA receptor subunits and dopamine receptors and elevate the level of epidermal growth factor (EGF).

CONCLUSION

Fentanyl administration induced neurotoxic effects in the mouse cerebral cortex that could be primarily mediated by the evoked oxidative-inflammatory response. The altered expression of NMDA receptors, dopamine receptors, and EGF suggests the pernicious effects of fentanyl addiction that may end in the development of toxic psychosis.

Single nuclei transcriptomics in human and non-human primate striatum in opioid use disorder

In brain, the striatum is a heterogenous region involved in reward and goal-directed behaviors. Striatal dysfunction is linked to psychiatric disorders, including opioid use disorder (OUD). Striatal subregions are divided based on neuroanatomy, each with unique roles in OUD. In OUD, the dorsal striatum is involved in altered reward processing, formation of habits, and development of negative affect during withdrawal. Using single nuclei RNA-sequencing, we identified both canonical (e.g., dopamine receptor subtype) and less abundant cell populations (e.g., interneurons) in human dorsal striatum. Pathways related to neurodegeneration, interferon response, and DNA damage were significantly enriched in striatal neurons of individuals with OUD. DNA damage markers were also elevated in striatal neurons of opioid-exposed rhesus macaques. Sex-specific molecular differences in glial cell subtypes associated with chronic stress were found in OUD, particularly female individuals. Together, we describe different cell types in human dorsal striatum and identify cell type-specific alterations in OUD.

Drug addiction and treatment: An epigenetic perspective

Drug addiction is a complex disease affected by numerous genetic and environmental factors. Brain regions in reward pathway, neuronal adaptations, genetic and epigenetic interactions causing transcriptional enhancement or repression of multiple genes induce different addiction phenotypes for varying duration. Addictive drug use causes epigenetic alterations and similarly epigenetic changes induced by environment can promote addiction. Epigenetic mechanisms include DNA methylation and post-translational modifications like methylation, acetylation, phosphorylation, ubiquitylation, sumoylation, dopaminylation and crotonylation of histones, and ADP-ribosylation. Non-coding RNAs also induce epigenetic changes. This review discusses these above areas and stresses the need for exploring epidrugs as a treatment alternative and adjunct, considering the limited success of current addiction treatment strategies. Epigenome editing complexes have lately been effective in eukaryotic systems. Targeted DNA cleavage techniques such as CRISPR-Cas9 system, CRISPR-dCas9 complexes, transcription activator-like effector nucleases (TALENs) and zinc-finger nucleases (ZFNs) have been exploited as targeted DNA recognition or anchoring platforms, fused with epigenetic writer or eraser proteins and delivered by transfection or transduction methods. Efficacy of epidrugs is seen in various neuropsychiatric conditions and initial results in addiction treatment involving model organisms are remarkable. Epidrugs present a promising alternative treatment for addiction.