Genes in drug abuse

Non-coding RNA in alcohol use disorder by affecting synaptic plasticity

Alcohol use disorder (AUD) is one of the most serious public health problems worldwide. AUD is a complex disorder, and there is ample evidence that genetic predisposition is critical to its development. Recent studies have shown that genetic predisposition leads to the onset of AUD, and alcohol metabolism can affect epigenetic inheritance, which in turn affects synaptic plasticity, alters brain function, and leads to more severe addictive behaviors. Non-coding RNAs (ncRNAs), especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), play an important role in alcohol addiction. This paper reviews the regulatory role of ncRNAs. ncRNAs are involved in enzyme and neurotransmitter reaction systems during alcohol use disorder. Alcohol consumption regulates the expression of ncRNAs that mediate epigenetic modification and synaptic plasticity, which play an important role in the development of chronic AUD. ncRNAs may be used not only as predictors of therapeutic responses but also as therapeutic targets of AUD. Chronic alcoholism is more likely to lead to neuroimmune disorders, including permanent brain dysfunction. AUD induced by long-term alcoholism greatly alters the expression of genes in the human genome, especially the expression of ncRNAs. Alcohol can cause a series of pathological changes by interfering with gene expression, such as through disordered miRNA-mRNA expression networks, epigenetic modifications, disordered metabolism, and even synaptic remodeling. ncRNAs are involved in the transition from moderate drinking to alcohol dependence.

Society and its influences on drug use among young individuals in Tehran, Iran

Illicit Drug use poses a substantial public health problem around the world, mainly affecting young people. Current estimates suggest that Iran has the highest rate of opium addiction per capita in the world. It has been suggested that multiple elements contribute to the process of drug use. The aim of this study is to explore the probable components in the society that might play a role in the initiation of drug use among young adults. The study is qualitative in nature. Twenty four in-depth interviews were conducted with drug-using young men (n = 10) and women (n = 10) and their family members (n = 4). Based on our data analysis, developing a pro-drug attitude, conformist attitude of society toward treating youth and young individuals, and having weak approach toward prevention were identified as important determinants of substance use. We recommend the need for early intervention, especially for at-risk communities. The results of this research suggest that dealing with a major problem such as drug use needs a comprehensive assessment of the context in which young people live and use substances. According to our findings, exploring young drug users experiences is not only important but also useful for policy makers to develop more effective prevention and intervention programs.

More aroused, less fatigued: fatty acid amide hydrolase gene polymorphisms influence acute response to amphetamine

Amphetamine is a stimulant drug that enhances attention and feelings of alertness. Amphetamine's effects are known to be modulated by endogenous cannabinoids, which are degraded by the enzyme fatty acid amide hydrolase (FAAH). In this study we investigated inter-individual differences in mood response to amphetamine in relation to four polymorphisms in the FAAH gene, including the FAAH missense variant rs324420C --> A (Pro129Thr), which was previously found to be associated with street drug use and addictive traits. One hundred and fifty-nine healthy Caucasian volunteers participated in a three-session, double-blind crossover study receiving either placebo or oral d-amphetamine (10 and 20 mg). Associations between individual genotypes and levels of self-reported Arousal (Profile of Mood States) after d-amphetamine ingestion were investigated using two-way ANOVAs/ANCOVAs. Association analyses for haplotypes were performed using the adaptive permutation approach implemented in PLINK. Genotypes at rs3766246 and rs2295633 were significantly associated with increased ratings of Arousal (p<0.05) and Fatigue (p<0.01) after the 10-mg dose. Fatigue levels were also found to be associated with the haplotypes CCC and TAT formed from rs3766246, rs324420, and rs2295633 (p<0.05). These data suggest that the endocannabinoid system influences variation in subjective response to amphetamine. This has important implications for understanding the role of endogenous cannabinoids in response to amphetamine, studies of poly-substance abuse, and understanding the genetic determinants of inter-individual differences in stimulant effects and risk of abuse.

The housekeeping gene (GA3PDH) and the long interspersed nuclear element (LINE) in the blood and organs of rats treated with cocaine

Housekeeping genes are necessary for maintenance of the vital activity of the cells of any phylum of organisms. Transposons or mobile genetic elements are eurysynusic in nature. Thus, the role of these and other genes in the pathogenesis of many diseases and of drug addiction in particular is being investigated. The goal of the work is to determine the influence of cocaine on the activity of GA3PDH and on a representative of the LINE family (L1Rn) in plasma, and in a pellet of blood cells, and in the organs of rats. Gene expression was evaluated by RT-PCR. The GA3PDH (452-bp fragment) was predictably found in plasma, in a pellet of blood cells, and in organs. Its quantity in plasma was greater in the experimental groups than in the control. In a pellet of blood cells and in organs, the GA3PDH activity between the different groups of animals essentially did not differ. The L1Rn fragment (319 bp) in plasma was not found. The expression of L1Rn was much higher in a pellet of blood cells and in organs of experimental animals. These experiments have shown the presence of GA3PDH in the plasma of the controls and an increase in quantity in the plasma of experimental animals. The activation of LINE in a pellet of blood cells of rats and in organs under the influence of cocaine has been demonstrated. Apparently, a recruitment phenomenon of housekeeping genes and transposons is possible in the pathogenesis of drug addiction.

Mu-opioid receptor activation induces transcriptional plasticity in the central extended amygdala

Addiction develops from the gradual adaptation of the brain to chronic drug exposure, and involves genetic reprogramming of neuronal function. The central extended amygdala (EAc) is a network formed by the central amygdala and the bed nucleus of the stria terminalis. This key site controls drug craving and seeking behaviors, and has not been investigated at the gene regulation level. We used Affymetrix microarrays to analyze transcriptional activity in the murine EAc, with a focus on mu-opioid receptor-associated events because these receptors mediate drug reward and dependence. We identified 132 genes whose expression is regulated by a chronic escalating morphine regimen in the EAc from wild-type but not mu-opioid receptor knockout mice. These modifications are mostly EAc-specific. Gene ontology analysis reveals an overrepresentation of neurogenesis, cell growth and signaling protein categories. A separate quantitative PCR analysis of genes in the last of these groups confirms the dysregulation of both orphan (Gpr88) and known (DrD1A, Adora2A, Cnr1, Grm5, Gpr6) G protein-coupled receptors, scaffolding (PSD95, Homer1) and signaling (Sgk, Cap1) proteins, and neuropeptides (CCK, galanin). These transcriptional modifications do not occur following a single morphine injection, and hence result from long-term adaptation to excessive mu receptor activation. Proteins encoded by these genes are classically associated with spine modules function in other brain areas, and therefore our data suggest a remodeling of EAc circuits at sites where glutamatergic and monoaminergic afferences interact. Together, mu receptor-dependent genes identified in this study potentially contribute to drug-induced neural plasticity, and provide a unique molecular repertoire towards understanding drug craving and relapse.

Norepinephrine transporter gene variation modulates acute response to D-amphetamine

BACKGROUND

Individual differences in subjective responses to stimulant drugs such as amphetamine may influence risk of abuse as well as clinical-treatment response to these drugs. Because the effects of amphetamine are mediated in part by the norepinephrine transporter (SLC6A2), we examined interindividual differences in mood response to amphetamine in relation to SLC6A2 gene polymorphisms.

METHODS

Ninety-nine healthy volunteers participated in three sessions in which they randomly received either placebo or D-amphetamine (10 mg or 20 mg) under double-blind conditions. Every subject completed self-report measures on subjective effects (Profile of Mood States). Afterward, all individuals were genotyped for eight SLC6A2 gene polymorphisms. Individual genotypes and haplotypes were investigated.

RESULTS

The intronic 36001C/C (rs47958) genotype was associated with increases in positive mood and elation after 20 mg of D-amphetamine. Positive mood and elation levels were also found to be associated with the haplotype GCC formed from 28257G/C (rs36017), 28323C/T (rs2270935), and 36001A/C (rs47958). These findings remained significant after adjustment for multiple testing.

CONCLUSIONS

Polymorphisms in the SLC6A2 gene were associated with mood responses to D-amphetamine. If confirmed, this observation may contribute to a better understanding of interindividual variations in the clinical response to amphetamine and in the risk of becoming addicted to amphetamine.

Modified 'Joyce model' of opioid dependence/withdrawal

By comprehensive and detailed measurement of the time course of withdrawal signs in rats, Joyce et al. (J. Theo. Biol. 240:531-537, 2006) recently provided a creative quantitative model of the onset of drug dependence based on the requirement of protein synthesis. Because the initial model fit the data imperfectly over the full time course, those authors postulated that additional features would be needed. We report excellent fit of the data (R(2)=0.96) by adding: (1) a transient early phase, and (2) a delay in the buildup of protein.

Modeling the onset of drug dependence: A consideration of the requirement for protein synthesis

It has been proposed, with some supporting evidence, that development of opiate tolerance and dependence requires protein synthesis. However, a quantitative, biologically based model within which to analyse and support the data has been lacking. Utilizing such a framework or model, we recently compared the time course of onset of opiate dependence in laboratory animals, with the mathematical time course of general changes in protein levels. Not only did the time course of onset of dependence parallel the time course of increasing levels of a protein, but also the half-life of the putative protein required by the model was very similar to those of many brain proteins. In this study, we have more extensively tested the model by producing and examining a much more detailed and surprisingly complex time course of the onset of dependence. Applying the protein synthesis time course model to the data suggested the presence of two distinct components of dependence, an early transient component and a later long-lasting component. These components appear to correspond to acute and chronic dependence, respectively. The protein synthesis hypothesis more readily applies to the chronic dependence portion. Because consideration of the model can generate components that correspond to accepted and well-known components of dependence, both the utility of the model as well as the hypothesis that opiate dependence at least partially requires protein synthesis are supported. It is also possible that individual components of the withdrawal syndrome have individual and unique rate limiting mechanisms. In any case, time course analysis may be helpful in revealing underlying mechanisms of change.

New ideas on the origin of L-dopa-induced dyskinesias: age, genes and neural plasticity

More than 50% of Parkinson's disease (PD) patients treated with L-dopa develop L-dopa-induced dyskinesias (LIDs) in the long term. Some patients exhibit severe dyskinesias soon after starting low doses of L-dopa, whereas other patients remain free of this disabling complication despite treatment with L-dopa. Avoiding or delaying the appearance of LIDs is one of the main objectives of the management of PD. Plasticity of the brain to adapt to a progressive disease, together with a non-physiological treatment strategy, might be the key physiopathological element that underlies LIDs. Neural plasticity varies among patients according to age and genetics. Thus, I propose that this variation explains the observed differences in the occurrence of LIDs in PD patients. Furthermore, I suggest that denervation and L-dopa treatment act as modulating and triggering factors of LIDs, respectively. In this article, the practical implications of these ideas and the role of pharmacogenetics in PD treatment are discussed. Treatment decisions are likely to rely on this information, challenging the relevance of current 'hot' debates about how to start treatment in PD.

Bioinformatics models in drug abuse and Neuro-AIDS: Using and developing databases

The magnitude of the problems of drug abuse and Neuro-AIDS warrants the development of novel approaches for testing hypotheses in diagnosis and treatment ranging from cell culture models to developing databases. In this study, cultured neurons were treated with/without HIV-TAT, ENV, or cocaine in a 2x2x2 expression study design. RNA was purified, labeled, and expression data were produced and analyzed using ANOVA. Thus, we identified 35 genes that were significantly expressed across treatment conditions. A diagram is presented showing examples of molecular relationships involving a significantly expressed gene in the current study (SOX2). Also, we use this information to discuss examples of gene expression interactions as a means to portray significance and complexity of gene expression studies in Drug Abuse and Neuro-AIDS. Furthermore, we discuss here that critical interactions remain undetected, which may be unravelled by developing robust database systems containing large datasets and gleaned information from collaborating scientists . Hence, we are developing a public domain database we named The Agora database , that will served as a shared infrastructure to query, deposit, and review information related to drug abuse and dementias including Neuro-AIDS. A workflow of this database is also outlined in this paper.

Long-term gene expression in the nucleus accumbens following heroin administration is subregion-specific and depends on the nature of drug administration

Repeated exposure to addictive drugs results in long-lasting neuroadaptations in the brain, especially in the mesocorticolimbic system. Within this system, the nucleus accumbens (NAc) plays a major integrative role. As such, the NAc has been shown to be a target of short- and long-lasting drug-induced neuroadaptations at the levels of neurotransmission and cellular morphology. The long-lasting neuroadaptations might depend critically on alterations in gene expression. Recently, we obtained a set of transcripts by means of subtractive hybridization, of which the expression was decreased in the rat NAc shell after long-term extinction of intravenous heroin self-administration. Interestingly, the majority of these transcripts were also down-regulated upon long-term extinction of cocaine self-administration. Using the yoked-control operant paradigm, it was shown that non-contingent administration of these drugs resulted in a totally different gene expression profile. However, in the rat NAc core, both self-administration and non-contingent heroin administration induced a qualitatively similar expression profile. Hence, cognitive processes associated with drug self-administration seem to direct the long-term genomic responses in the NAc shell, whereas the NAc core might primarily mediate the persistent pharmacological effects of addictive drugs (including Pavlovian conditioning).

Microarray studies of psychostimulant-induced changes in gene expression

Alterations in the expression of multiple genes in many brain regions are likely to contribute to psychostimulant-induced behaviours. Microarray technology provides a powerful tool for the simultaneous interrogation of gene expression levels of a large number of genes. Several recent experimental studies, reviewed here, demonstrate the power, limitations and progress of microarray technology in the field of psychostimulant addiction. These studies vary in the paradigms of cocaine or amphetamine administration, drug doses, route and also mode of administration, duration of treatment, animal species, brain regions studied and time of tissue collection after final drug administration. The studies also utilize different microarray platforms and statistical techniques for analysis of differentially expressed genes. These variables influence substantially the results of these studies. It is clear that current microarray techniques cannot detect small changes reliably in gene expression of genes with low expression levels, including functionally significant changes in components of major neurotransmission systems such as glutamate, dopamine, opioid and GABA receptors, especially those that may occur after chronic drug administration or drug withdrawal. However, the microarray studies reviewed here showed cocaine- or amphetamine-induced alterations in the expression of numerous genes involved in the modulation of neuronal growth, cytoskeletal structures, synaptogenesis, signal transduction, apoptosis and cell metabolism. Application of laser capture microdissection and single-cell cDNA amplification may greatly enhance microarray studies of gene expression profiling. The combination of rapidly evolving microarray technology with established methods of neuroscience, molecular biology and genetics, as well as appropriate behavioural models of drug reinforcement, may provide a productive approach for delineating the neurobiological underpinnings of drug responses that lead to addiction.

Genetics and drug use as a complex phenotype

Drug use is a complex behavior influenced by multiple biological, family, and sociocultural factors. The concurrent use/misuse of multiple drugs is often seen and drug use also co-occurs with other psychiatric conditions. Behavior and molecular genetic studies support an important posited role of genes in drug use. This posited genetic risk does not appear to be conferred by one or two major genes manifesting large effects, but rather by a number of genes manifesting smaller effects. Genetic factors explain, on average, only about half of the total variability in drug use, with the remaining variability influenced by environmental factors. Also, genetic risk may be differentially expressed in the presence vs. absence of particular environmental conditions. Thus, investigation of environmental factors and their interaction with genetic risk is a necessary component of genetic research. While the full potential of genetic investigations for the prevention of drug misuse has yet to be realized, an example of the impact of risk factor modification under various conditions of gene-environment interaction is provided, and the implications for use of genetic information in drug-misuse prevention are discussed. The multifactorial nature of drug use necessitates coordinated investigation from multiple disciplines and timely dissemination of scientific findings. In addition, this work demands adherence to the highest standards of confidentiality and ethical use of genetic information to best inform future prevention efforts.

Is the onset of psychoactive drug effects compatible with a protein-synthesis mechanism?

While many have suggested that protein synthesis may mediate the action of antipsychotic drugs, it is difficult to test. In this math modeling study it is found that the time course of action of the drugs are compatible with a protein-synthesis model and, furthermore, that the half-lives required by the model are indeed found in relevant proteins in the brain.

Repeated cocaine self-administration causes multiple changes in rat frontal cortex gene expression

Repeated cocaine administration produces changes in gene expression that are thought to contribute to the behavioral alterations observed with cocaine abuse. This study focuses on gene expression changes in the frontal cortex, a component of reinforcement, sensory, associative, and executive circuitries. Changes in frontal cortex gene expression after repeated cocaine self-administration may lead to changes in the behaviors associated with this brain region. Rats self-administered cocaine for 10 days in a continuous access, discrete trial paradigm (averaging 100 mg/kg/day) and were examined for changes in relative frontal cortex mRNA abundance by cDNA hybridization arrays. Among the changes observed following array analysis, increased nerve-growth-factor-induced B (NGFI-B), adenylyl cyclase type VIII (AC VIII), and reduced cysteine-rich protein 2 (CRP2) mRNA were confirmed by quantitative RT-PCR. These changes share commonalities and exhibit differences with previous reports of gene expression changes in the frontal cortex after noncontingent cocaine administration.

Drug dependence: neuropharmacology and management

This overview has attempted to highlight the brain regions associated with reward, and the pathways and neurotransmitters responsible for communication between these regions. Work conducted in this field has shown that stimulants and opioids, despite interactions with different receptor types and different neurotransmitter reuptake transporters, appear to share a common action on brain reward pathways. Their effects on these pathways (the distinct brain regions making up the mesocorticolimbic dopaminergic system) are predominantly mediated through changes in dopamine neurotransmission, and compounds aimed at selectively modulating these effects may form the basis of drugs to treat addiction. Other transmitters such as GABA, acetylcholine and serotonin inevitably have a role to play in reward, although at present the exact nature of their effects remains unclear. Diverging from manipulating the CNS directly as a management strategy for dependence, it might be possible to exploit the immune system to prevent administered psychostimulants penetrating the brain, but antibody saturation and specificity are problematic.

Addiction and the brain: the neurobiology of compulsion and its persistence

People take addictive drugs to elevate mood, but with repeated use these drugs produce serious unwanted effects, which can include tolerance to some drug effects, sensitization to others, and an adapted state - dependence - which sets the stage for withdrawal symptoms when drug use stops. The most serious consequence of repetitive drug taking, however, is addiction: a persistent state in which compulsive drug use escapes control, even when serious negative consequences ensue. Addiction is characterized by a long-lasting risk of relapse, which is often initiated by exposure to drug-related cues. Substantial progress has been made in understanding the molecular and cellular mechanisms of tolerance, dependence and withdrawal, but as yet we understand little of the neural substrates of compulsive drug use and its remarkable persistence. Here we review evidence for the possibility that compulsion and its persistence are based on a pathological usurpation of molecular mechanisms that are normally involved in memory.

Slow onset of CNS drugs: can changes in protein concentration account for the delay?

A 'protein regulation hypothesis' might explain the delay in reaching a maximal clinical effect, exhibited by some antipsychotic and addicting drugs. It also suggests that crucial 'effector' proteins that mediate the actions of these drugs might have half-lives of days to weeks. In this article, the rate of onset of some antipsychotic and addicting drugs will be examined and a model will be used to test if a change in the concentration of a given protein(s) could cause the drug-induced effects. This hypothesis uses a model where protein concentrations are determined by a zero-order synthesis rate and a first-order degradation rate. The model in its simplest form produces an exponential increase (or decrease) in protein concentrations over time, but reasonable extensions of the model can account for more complex mechanisms that allow for delayed time-courses and contributions of multiple proteins to the clinical effect.