Valproate and acetyl-L-carnitine prevent methamphetamine-induced behavioral sensitization in mice

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.

Epigenetic Regulatory Dynamics in Models of Methamphetamine-Use Disorder

Methamphetamine (METH)-use disorder (MUD) is a very serious, potentially lethal, biopsychosocial disease. Exposure to METH causes long-term changes to brain regions involved in reward processing and motivation, leading vulnerable individuals to engage in pathological drug-seeking and drug-taking behavior that can remain a lifelong struggle. It is crucial to elucidate underlying mechanisms by which exposure to METH leads to molecular neuroadaptive changes at transcriptional and translational levels. Changes in gene expression are controlled by post-translational modifications via chromatin remodeling. This review article focuses on the brain-region specific combinatorial or distinct epigenetic modifications that lead to METH-induced changes in gene expression.

Evidence for Modulation of Substance Use Disorders by the Gut Microbiome: Hidden in Plain Sight

The gut microbiome modulates neurochemical function and behavior and has been implicated in numerous central nervous system (CNS) diseases, including developmental, neurodegenerative, and psychiatric disorders. Substance use disorders (SUDs) remain a serious threat to the public well-being, yet gut microbiome involvement in drug abuse has received very little attention. Studies of the mechanisms underlying SUDs have naturally focused on CNS reward circuits. However, a significant body of research has accumulated over the past decade that has unwittingly provided strong support for gut microbiome participation in drug reward. β-Lactam antibiotics have been employed to increase glutamate transporter expression to reverse relapse-induced release of glutamate. Sodium butyrate has been used as a histone deacetylase inhibitor to prevent drug-induced epigenetic alterations. High-fat diets have been used to alter drug reward because of the extensive overlap of the circuitry mediating them. This review article casts these approaches in a different light and makes a compelling case for gut microbiome modulation of SUDs. Few factors alter the structure and composition of the gut microbiome more than antibiotics and a high-fat diet, and butyrate is an endogenous product of bacterial fermentation. Drugs such as cocaine, alcohol, opiates, and psychostimulants also modify the gut microbiome. Therefore, their effects must be viewed on a complex background of cotreatment-induced dysbiosis. Consideration of the gut microbiome in SUDs should have the beneficial effects of expanding the understanding of SUDs and aiding in the design of new therapies based on opposing the effects of abused drugs on the host's commensal bacterial community. SIGNIFICANCE STATEMENT: Proposed mechanisms underlying substance use disorders fail to acknowledge the impact of drugs of abuse on the gut microbiome. β-Lactam antibiotics, sodium butyrate, and high-fat diets are used to modify drug seeking and reward, overlooking the notable capacity of these treatments to alter the gut microbiome. This review aims to stimulate research on substance abuse-gut microbiome interactions by illustrating how drugs of abuse share with antibiotics, sodium butyrate, and fat-laden diets the ability to modify the host microbial community.

Sodium butyrate modulates a methamphetamine-induced conditioned place preference

Previous studies demonstrated that histone acetylation modulated the transcription of associated gene expression and thus contributed to the persistence of addictive behaviors and neuroplasticity. Nonetheless, the roles of histone acetylation in distinct phases of methamphetamine (METH)-induced conditioned place preference (CPP) remain unclear. The current study examines the effects of the histone deacetylases (HDACs) inhibitor sodium butyrate (NaB) on the acquisition, extinction, and reinstatement of METH-induced CPP in mice. Our results showed that 1 mg/kg METH induced CPP in mice after four conditioning sessions. METH-induced CPP was extinguished after three extinction training sessions and could be triggered by the same dose (1 mg/kg) of METH on the reinstatement test day. Meanwhile, NaB (400 mg/kg) per se had no effect on the natural preference of mice, but injections of NaB during the conditioning and extinction phases facilitated the acquisition and extinction of METH-induced CPP, respectively. Additionally, although the effect of a single NaB injection prior to the trigger of CPP reinstatement was not observed, repeated NaB injections during the extinction phase totally blocked the reinstatement of METH-induced CPP. Taken together, our results suggested a specific effect of histone acetylation on modulating distinct phases of METH-induced CPP and that treatment of NaB during the extinction phase not only produced beneficial effects on eliminating already established CPP but also blocked the reinstatement of METH-induced CPP. © 2016 Wiley Periodicals, Inc.

Epigenetic landscape of amphetamine and methamphetamine addiction in rodents

Amphetamine and methamphetamine addiction is described by specific behavioral alterations, suggesting long-lasting changes in gene and protein expression within specific brain subregions involved in the reward circuitry. Given the persistence of the addiction phenotype at both behavioral and transcriptional levels, several studies have been conducted to elucidate the epigenetic landscape associated with persistent effects of drug use on the mammalian brain. This review discusses recent advances in our comprehension of epigenetic mechanisms underlying amphetamine- or methamphetamine-induced behavioral, transcriptional, and synaptic plasticity. Accumulating evidence demonstrated that drug exposure induces major epigenetic modifications-histone acetylation and methylation, DNA methylation-in a very complex manner. In rare instances, however, the regulation of a specific target gene can be correlated to both epigenetic alterations and behavioral abnormalities. Work is now needed to clarify and validate an epigenetic model of addiction to amphetamines. Investigations that include genome-wide approaches will accelerate the speed of discovery in the field of addiction.

Experimental evidence for the involvement of PDLIM5 in mood disorders in hetero knockout mice

Background

Reports indicate that PDLIM5 is involved in mood disorders. The PDLIM5 (PDZ and LIM domain 5) gene has been genetically associated with mood disorders; it’s expression is upregulated in the postmortem brains of patients with bipolar disorder and downregulated in the peripheral lymphocytes of patients with major depression. Acute and chronic methamphetamine (METH) administration may model mania and the evolution of mania into psychotic mania or schizophrenia-like behavioral changes, respectively.

Methods

To address whether the downregulation of PDLIM5 protects against manic symptoms and cause susceptibility to depressive symptoms, we evaluated the effects of reduced Pdlim5 levels on acute and chronic METH-induced locomotor hyperactivity, prepulse inhibition, and forced swimming by using Pdlim5 hetero knockout (KO) mice.

Results

The homozygous KO of Pdlim5 is embryonic lethal. The effects of METH administration on locomotor hyperactivity and the impairment of prepulse inhibition were lower in Pdlim5 hetero KO mice than in wild-type mice. The transient inhibition of PDLIM5 (achieved by blocking the translocation of protein kinase C epsilon before the METH challenge) had a similar effect on behavior. Pdlim5 hetero KO mice showed increased immobility time in the forced swimming test, which was diminished after the chronic administration of imipramine. Chronic METH treatment increased, whereas chronic haloperidol treatment decreased, Pdlim5 mRNA levels in the prefrontal cortex. Imipramine increased Pdlim5 mRNA levels in the hippocampus.

Conclusion

These findings are partially compatible with reported observations in humans, indicating that PDLIM5 is involved in psychiatric disorders, including mood disorders.

Effects of sodium butyrate on methamphetamine-sensitized locomotor activity

Neuroadaptations associated with behavioral sensitization induced by repeated exposure to methamphetamine (MA) appear to be involved in compulsive drug pursuit and use. Increased histone acetylation, an epigenetic effect resulting in altered gene expression, may promote sensitized responses to psychostimulants. The role of histone acetylation in the expression and acquisition of MA-induced locomotor sensitization was examined by measuring the effect of histone deacetylase inhibition by sodium butyrate (NaB). For the effect on expression, mice were treated repeatedly with MA (10 days of 2mg/kg MA) or saline (10 days), and then vehicle or NaB (630 mg/kg, intraperitoneally) was administered 30 min prior to MA challenge and locomotor response was measured. NaB treatment increased the locomotor response to MA in both acutely MA treated and sensitized animals. For acquisition, NaB was administered 30 min prior to each MA exposure (10 days of 1 or 2mg/kg), but not prior to the MA challenge test. Treatment with NaB during the sensitization acquisition period significantly increased locomotor activation by MA in sensitized mice only. NaB alone did not significantly alter locomotor activity. Acute NaB or MA, but not the combination, increased striatal acetylation at histone H4. Repeated treatment with MA, but not NaB or MA plus NaB, increased striatal acetylation at histone H3. Although increased histone acetylation may alter the expression of genes involved in acute locomotor response to MA and in the acquisition of MA-induced sensitization, results for acetylation at H3 and H4 showed little correspondence with behavior.

Methamphetamine disrupts blood-brain barrier function by induction of oxidative stress in brain endothelial cells

Methamphetamine (METH), a potent stimulant with strong euphoric properties, has a high abuse liability and long-lasting neurotoxic effects. Recent studies in animal models have indicated that METH can induce impairment of the blood-brain barrier (BBB), thus suggesting that some of the neurotoxic effects resulting from METH abuse could be the outcome of barrier disruption. In this study, we provide evidence that METH alters BBB function through direct effects on endothelial cells and explore possible underlying mechanisms leading to endothelial injury. We report that METH increases BBB permeability in vivo, and exposure of primary human brain microvascular endothelial cells (BMVEC) to METH diminishes the tightness of BMVEC monolayers in a dose- and time-dependent manner by decreasing the expression of cell membrane-associated tight junction (TJ) proteins. These changes were accompanied by the enhanced production of reactive oxygen species, increased monocyte migration across METH-treated endothelial monolayers, and activation of myosin light chain kinase (MLCK) in BMVEC. Antioxidant treatment attenuated or completely reversed all tested aspects of METH-induced BBB dysfunction. Our data suggest that BBB injury is caused by METH-mediated oxidative stress, which activates MLCK and negatively affects the TJ complex. These observations provide a basis for antioxidant protection against brain endothelial injury caused by METH exposure.