Double dissociation of inhibitory effects between the hippocampal TET1 and TET3 in the acquisition of morphine self-administration in rats

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.

DNA Epigenetics in Addiction Susceptibility

Addiction is a chronically relapsing neuropsychiatric disease that occurs in some, but not all, individuals who use substances of abuse. Relatively little is known about the mechanisms which contribute to individual differences in susceptibility to addiction. Neural gene expression regulation underlies the pathogenesis of addiction, which is mediated by epigenetic mechanisms, such as DNA modifications. A growing body of work has demonstrated distinct DNA epigenetic signatures in brain reward regions that may be associated with addiction susceptibility. Furthermore, factors that influence addiction susceptibility are also known to have a DNA epigenetic basis. In the present review, we discuss the notion that addiction susceptibility has an underlying DNA epigenetic basis. We focus on major phenotypes of addiction susceptibility and review evidence of cell type-specific, time dependent, and sex biased effects of drug use. We highlight the role of DNA epigenetics in these diverse processes and propose its contribution to addiction susceptibility differences. Given the prevalence and lack of effective treatments for addiction, elucidating the DNA epigenetic mechanism of addiction vulnerability may represent an expeditious approach to relieving the addiction disease burden.

Sex dependent alteration of epigenetic marks after chronic morphine treatment in mice organs

Epigenetic marks may be also affected by several factors, such as age, lifestyle, early life experiences and exposure to chemicals or drugs, such as opioids. Previous studies have focused on how morphine epigenetically regulates different regions of the brain that are implicated in tolerance, dependence and other psychiatric disorders more related to the physio-pathological effects of opioids. Nevertheless, a significant knowledge gap remains regarding the effect of chronic treatment on other organs and biological systems. Therefore, the aim of this work is to increase our knowledge about the impact of chronic morphine exposure on DNA methylation and histone modification levels in each of the organs of male and female model mice in vivo. Our results reveal, for the first time, that chronic morphine treatment induced changes in DNA methylation/hydroxymethylation and histone modification in-vivo at the systemic level, revealing a potential physiological effect on the regulation of gene expression. Notably, morphine-induced epigenetic modification occurs in a sex-dependent manner, revealing the existence of different underlying mechanisms of epigenetic modification in male and female mice.

Global DNA methylation levels in white blood cells of patients with chronic heroin use disorder. A prospective study

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Opioid abstinence for 21 days does not affect global DNA methylation levels in white blood cells.

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All participants in the study completed a 21-day “dry” detoxification program.

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Findings do not rule out the possibility of site-specific methylation changes.

Background

Increasing scientific evidence shows the significant role of epigenetic mechanisms in drug use disorder, abstinence and relapse. Studies on human subjects are limited compared to those on animals, for various reasons such as poly-substance abuse, high drop-out rate and technical difficulties.

Objectives

Our goal was to evaluate whether a monitored abstinence period of 21 days could induce changes in global DNA methylation in chronic heroin users.

Method

In the current study, we present data on global DNA methylation on a set of 18 male patients with chronic heroin use disorder, carefully selected based on inclusion and exclusion criteria, who were hospitalized and closely monitored during a 21-day detoxification program, one of the few where no opioid agonist is administered. The participants were sampled twice, once upon enrolment to the program and once upon completion.

Results

According to our results, no difference in global DNA methylation was detected between samples collected upon enrolment and samples collected upon completion of the program.

Conclusion

The findings of this study do not rule out the possibility that the 21-day abstinence period was not long enough to observe changes in global DNA methylation, or that abstinence induced site-specific methylation changes (but not global changes), that certainly merit further evaluation.