Intermittent administration of morphine alters protein expression in rat nucleus accumbens

Functional genomic mechanisms of opioid action and opioid use disorder: a systematic review of animal models and human studies

In the past two decades, over-prescription of opioids for pain management has driven a steep increase in opioid use disorder (OUD) and death by overdose, exerting a dramatic toll on western countries. OUD is a chronic relapsing disease associated with a lifetime struggle to control drug consumption, suggesting that opioids trigger long-lasting brain adaptations, notably through functional genomic and epigenomic mechanisms. Current understanding of these processes, however, remain scarce, and have not been previously reviewed systematically. To do so, the goal of the present work was to synthesize current knowledge on genome-wide transcriptomic and epigenetic mechanisms of opioid action, in primate and rodent species. Using a prospectively registered methodology, comprehensive literature searches were completed in PubMed, Embase, and Web of Science. Of the 2709 articles identified, 73 met our inclusion criteria and were considered for qualitative analysis. Focusing on the 5 most studied nervous system structures (nucleus accumbens, frontal cortex, whole striatum, dorsal striatum, spinal cord; 44 articles), we also conducted a quantitative analysis of differentially expressed genes, in an effort to identify a putative core transcriptional signature of opioids. Only one gene, Cdkn1a, was consistently identified in eleven studies, and globally, our results unveil surprisingly low consistency across published work, even when considering most recent single-cell approaches. Analysis of sources of variability detected significant contributions from species, brain structure, duration of opioid exposure, strain, time-point of analysis, and batch effects, but not type of opioid. To go beyond those limitations, we leveraged threshold-free methods to illustrate how genome-wide comparisons may generate new findings and hypotheses. Finally, we discuss current methodological development in the field, and their implication for future research and, ultimately, better care.

Impact of Opioids on Cellular Metabolism: Implications for Metabolic Pathways Involved in Cancer

Opioid utilization for pain management is prevalent among cancer patients. There is significant evidence describing the many effects of opioids on cancer development. Despite the pivotal role of metabolic reprogramming in facilitating cancer growth and metastasis, the specific impact of opioids on crucial oncogenic metabolic pathways remains inadequately investigated. This review provides an understanding of the current research on opioid-mediated changes to cellular metabolic pathways crucial for oncogenesis, including glycolysis, the tricarboxylic acid cycle, glutaminolysis, and oxidative phosphorylation (OXPHOS). The existing literature suggests that opioids affect energy production pathways via increasing intracellular glucose levels, increasing the production of lactic acid, and reducing ATP levels through impediment of OXPHOS. Opioids modulate pathways involved in redox balance which may allow cancer cells to overcome ROS-mediated apoptotic signaling. The majority of studies have been conducted in healthy tissue with a predominant focus on neuronal cells. To comprehensively understand the impact of opioids on metabolic pathways critical to cancer progression, research must extend beyond healthy tissue and encompass patient-derived cancer tissue, allowing for a better understanding in the context of the metabolic reprogramming already undergone by cancer cells. The current literature is limited by a lack of direct experimentation exploring opioid-induced changes to cancer metabolism as they relate to tumor growth and patient outcome.

Differential Effects of Cocaine and Morphine on the Diurnal Regulation of the Mouse Nucleus Accumbens Proteome

Substance use disorders are associated with disruptions in sleep and circadian rhythms that persist during abstinence and may contribute to relapse risk. Repeated use of substances such as psychostimulants and opioids may lead to significant alterations in molecular rhythms in the nucleus accumbens (NAc), a brain region central to reward and motivation. Previous studies have identified rhythm alterations in the transcriptome of the NAc and other brain regions following the administration of psychostimulants or opioids. However, little is known about the impact of substance use on the diurnal rhythms of the proteome in the NAc. We used liquid chromatography coupled to tandem mass spectrometry-based quantitative proteomics, along with a data-independent acquisition analysis pipeline, to investigate the effects of cocaine or morphine administration on diurnal rhythms of proteome in the mouse NAc. Overall, our data reveal cocaine and morphine differentially alter diurnal rhythms of the proteome in the NAc, with largely independent differentially expressed proteins dependent on time-of-day. Pathways enriched from cocaine altered protein rhythms were primarily associated with glucocorticoid signaling and metabolism, whereas morphine was associated with neuroinflammation. Collectively, these findings are the first to characterize the diurnal regulation of the NAc proteome and demonstrate a novel relationship between the phase-dependent regulation of protein expression and the differential effects of cocaine and morphine on the NAc proteome. The proteomics data in this study are available via ProteomeXchange with identifier PXD042043.

Differential Effects of Cocaine and Morphine on the Diurnal Regulation of the Mouse Nucleus Accumbens Proteome

Substance use disorders (SUDs) are associated with disruptions in sleep and circadian rhythms that persist during abstinence and may contribute to relapse risk. Repeated use of substances such as psychostimulants and opioids may lead to significant alterations in molecular rhythms in the nucleus accumbens (NAc), a brain region central to reward and motivation. Previous studies have identified rhythm alterations in the transcriptome of the NAc and other brain regions following the administration of psychostimulants or opioids. However, little is known about the impact of substance use on the diurnal rhythms of the proteome in the NAc. We used liquid chromatography coupled to tandem mass spectrometry-based (LC-MS/MS) quantitative proteomics, along with a data-independent acquisition (DIA) analysis pipeline, to investigate the effects of cocaine or morphine administration on diurnal rhythms of proteome in the mouse NAc. Overall, our data reveals cocaine and morphine differentially alters diurnal rhythms of the proteome in the NAc, with largely independent differentially expressed proteins dependent on time-of-day. Pathways enriched from cocaine altered protein rhythms were primarily associated with glucocorticoid signaling and metabolism, whereas morphine was associated with neuroinflammation. Collectively, these findings are the first to characterize the diurnal regulation of the NAc proteome and demonstrate a novel relationship between phase-dependent regulation of protein expression and the differential effects of cocaine and morphine on the NAc proteome.

Alterations in the Proteome and Phosphoproteome Profiles of Rat Hippocampus after Six Months of Morphine Withdrawal: Comparison with the Forebrain Cortex

The knowledge about proteome changes proceeding during protracted opioid withdrawal is lacking. Therefore, the aim of this work was to analyze the spectrum of altered proteins in the rat hippocampus in comparison with the forebrain cortex after 6-month morphine withdrawal. We utilized 2D electrophoretic workflow (Pro-Q® Diamond staining and Colloidal Coomassie Blue staining) which was preceded by label-free quantification (MaxLFQ). The phosphoproteomic analysis revealed six significantly altered hippocampal (Calm1, Ywhaz, Tuba1b, Stip1, Pgk1, and Aldoa) and three cortical proteins (Tubb2a, Tuba1a, and Actb). The impact of 6-month morphine withdrawal on the changes in the proteomic profiles was higher in the hippocampus—14 proteins, only three proteins were detected in the forebrain cortex. Gene Ontology (GO) enrichment analysis of differentially expressed hippocampal proteins revealed the most enriched terms related to metabolic changes, cytoskeleton organization and response to oxidative stress. There is increasing evidence that energy metabolism plays an important role in opioid addiction. However, the way how morphine treatment and withdrawal alter energy metabolism is not fully understood. Our results indicate that the rat hippocampus is more susceptible to changes in proteome and phosphoproteome profiles induced by 6-month morphine withdrawal than is the forebrain cortex.

Proteomic analysis reveals brain Rab35 as a potential biomarker of mitragynine withdrawal in rats

Mitragyna speciosa, also known as kratom, has been used for mitigating the severity of opioid withdrawal in humans. Its main indole alkaloid, mitragynine, has been considered as a pharmacotherapy for pain conditions and opioid replacement therapy. However, at high doses, chronic mitragynine may also have an addiction potential. The effects of chronic action of mitragynine in the brain are still unknown. The present study developed a mitragynine withdrawal model in rats and used it for a proteomic analysis of mitragynine withdrawal effects. Mitragynine (30 mg/kg, i.p.) was administered daily over a period of 14 days and then withdrawn. A proteomic analysis revealed that from a total of 1524 proteins identified, 31 proteins were upregulated, and 3 proteins were downregulated in the mitragynine withdrawal model. The Rab35 protein expression increased most profoundly in the mitragynine withdrawal group as compared to vehicle group. Therefore, it is proposed that Rab35 in the brain might be considered as a potential biomarker during mitragynine withdrawal and might be valuable target protein in developing new pharmacotherapies in the future.

Impact of three-month morphine withdrawal on rat brain cortex, hippocampus, striatum and cerebellum: proteomic and phosphoproteomic studies

Opioid addiction is characterized by compulsive drug seeking and taking behavior, which is thought to result from persistent neuroadaptations. However, there is a lack of information about the changes at both the cellular and molecular levels occurring after cessation of drug administration. The aim of our study was to determine alterations of both phosphoproteome and proteome in selected brain regions of the rats (brain cortex, hippocampus, striatum, and cerebellum) 3 months after cessation of 10-day morphine treatment. Phosphoproteome profiling was performed by Pro-Q® Diamond staining. The gel-based proteomic approach accompanied by label-free quantification (MaxLFQ) was used for characterization of proteome changes. The phosphoproteomic analysis revealed the largest change in the hippocampus (14); only few altered proteins were detected in the forebrain cortex (5), striatum (4), and cerebellum (3). The change of total protein composition, determined by 2D electrophoresis followed by LFQ analysis, identified 22 proteins with significantly altered expression levels in the forebrain cortex, 19 proteins in the hippocampus, 12 in the striatum and 10 in the cerebellum. The majority of altered proteins were functionally related to energy metabolism and cytoskeleton reorganization. As the most important change we regard down-regulation of 14-3-3 proteins in rat cortex and hippocampus. Our findings indicate that i) different parts of the brain respond in a distinct manner to the protracted morphine withdrawal, ii) characterize changes of protein composition in these brain parts, and iii) enlarge the scope of evidence for adaptability and distinct neuroplasticity proceeding in the brain of drug-addicted organism.

Proteomic Data in Morphine Addiction Versus Real Protein Activity: Metabolic Enzymes

Drug dependence is an escalating problem worldwide and many efforts are being made to understand the molecular basis of addiction. The morphine model is widely used in these investigations. To date, at least 29 studies exploring the influence of morphine on mammals' proteomes have been published. Among various proteins indicated as up- or down-regulated, the expression changes of enzymes engaged in energy metabolism pathways have often been confirmed. To verify whether proteomics-indicated alterations in enzyme levels reflect changes in their activity, four enzymes: PK, MDH, Complex I, and Complex V were investigated in morphine addiction and abstinence models. After analyses of the rat brain mitochondria fraction in the model of morphine dependence, we found that one of the investigated enzymes (pyruvate kinase) showed statistically significant differences observed between morphine, control, and abstinence groups. J. Cell. Biochem. 118: 4323-4330, 2017. © 2017 Wiley Periodicals, Inc.

Morphine Regulated Synaptic Networks Revealed by Integrated Proteomics and Network Analysis

Despite its efficacy, the use of morphine for the treatment of chronic pain remains limited because of the rapid development of tolerance, dependence and ultimately addiction. These undesired effects are thought to be because of alterations in synaptic transmission and neuroplasticity within the reward circuitry including the striatum. In this study we used subcellular fractionation and quantitative proteomics combined with computational approaches to investigate the morphine-induced protein profile changes at the striatal postsynaptic density. Over 2,600 proteins were identified by mass spectrometry analysis of subcellular fractions enriched in postsynaptic density associated proteins from saline or morphine-treated striata. Among these, the levels of 34 proteins were differentially altered in response to morphine. These include proteins involved in G-protein coupled receptor signaling, regulation of transcription and translation, chaperones, and protein degradation pathways. The altered expression levels of several of these proteins was validated by Western blotting analysis. Using Genes2Fans software suite we connected the differentially expressed proteins with proteins identified within the known background protein-protein interaction network. This led to the generation of a network consisting of 116 proteins with 40 significant intermediates. To validate this, we confirmed the presence of three proteins predicted to be significant intermediates: caspase-3, receptor-interacting serine/threonine protein kinase 3 and NEDD4 (an E3-ubiquitin ligase identified as a neural precursor cell expressed developmentally down-regulated protein 4). Because this morphine-regulated network predicted alterations in proteasomal degradation, we examined the global ubiquitination state of postsynaptic density proteins and found it to be substantially altered. Together, these findings suggest a role for protein degradation and for the ubiquitin/proteasomal system in the etiology of opiate dependence and addiction.

Roles of the ubiquitin proteasome system in the effects of drugs of abuse

Because of its ability to regulate the abundance of selected proteins the ubiquitin proteasome system (UPS) plays an important role in neuronal and synaptic plasticity. As a result various stages of learning and memory depend on UPS activity. Drug addiction, another phenomenon that relies on neuroplasticity, shares molecular substrates with memory processes. However, the necessity of proteasome-dependent protein degradation for the development of addiction has been poorly studied. Here we first review evidences from the literature that drugs of abuse regulate the expression and activity of the UPS system in the brain. We then provide a list of proteins which have been shown to be targeted to the proteasome following drug treatment and could thus be involved in neuronal adaptations underlying behaviors associated with drug use and abuse. Finally we describe the few studies that addressed the need for UPS-dependent protein degradation in animal models of addiction-related behaviors.

Transient receptor potential vanilloid type 1 channel may modulate opioid reward

Transient receptor potential vanilloid type 1 (TRPV1), a nonselective cation channel, is a well-known pain-related receptor. TRPV1 involvement in morphine-induced antinociception, tolerance, and withdrawal symptoms has been previously reported. Emerging evidence indicates that TRPV1 may be related to both the cellular and behavioral effects of addictive drugs. In the present study, we investigated the role of TRPV1 in morphine reward using the conditioned place preference (CPP) paradigm in mice. Repeated morphine treatments upregulated TRPV1 expression in the dorsal striatum (DSt). Treatment with a TRPV1 agonist potentiated morphine reward, and pretreatment with TRPV1 antagonists attenuated these effects. Microinjection of a selective TRPV1 antagonist into the DSt significantly inhibited morphine-CPP. In addition, treatment with a TRPV1 antagonist suppressed morphine-induced increases in μ-opioid receptor binding, adenylyl cyclase 1 (AC1), p38 mitogen-activated protein kinase (p38 MAPK), and nuclear factor kappa B (NF-κB) expression in the DSt. Administering a p38 inhibitor not only prevented morphine-CPP, but also prevented morphine-induced NF-κB and TRPV1 activation in the DSt. Furthermore, injecting an NF-κB inhibitor significantly blocked morphine-CPP. Our findings suggest that TRPV1 in the DSt contribute to morphine reward via AC1, p38 MAPK, and NF-κB. Brain TRPV1 may serve as a novel therapeutic target to treat morphine-addictive disorders.

Effects of thienorphine on synaptic structure and synaptophysin expression in the rat nucleus accumbens

The partial opioid agonist thienorphine is currently in Phase II clinical trials in China as a candidate drug for the treatment of opioid dependence. However, its effect on synaptic plasticity in the NAc (nucleus accumbens) remains unclear. In the present study, we measured structural parameters of the synaptic interface to investigate the effect of thienorphine, morphine or a combination of both on synaptic morphology in the NAc of rats. Expression of synaptophysin was also examined. Ultrastructural observation showed that synaptic alterations were less pronounced after chronic thienorphine administration than after chronic morphine administration. Animals that received thienorphine had thinner postsynaptic densities and shorter active zones in the NAc compared with those in the saline group, but the active zone was larger, and the cleft narrower, than those in the morphine group. Furthermore, synaptophysin expression in the NAc was significantly greater after chronic administration of thienorphine, morphine, or both, than after saline. These results identified interesting differences between thienorphine and morphine in their effects on synaptic structure and synaptophysin expression in the rat NAc. Further study is deserved to investigate thienorphine as a new treatment for opioid dependence.

Proteomic analysis of post-nuclear supernatant fraction and percoll-purified membranes prepared from brain cortex of rats exposed to increasing doses of morphine

Background

Proteomic analysis was performed in post-nuclear supernatant (PNS) and Percoll-purified membranes (PM) prepared from fore brain cortex of rats exposed to increasing doses of morphine (10–50 mg/kg) for 10 days.

Results

In PNS, the 10 up (↑)- or down (↓)-regulated proteins exhibiting the largest morphine-induced change were selected, excised manually from the gel and identified by MALDI-TOF MS/MS: 1-(gi|148747414, Guanine deaminase), ↑2.5×; 2-(gi|17105370, Vacuolar-type proton ATP subunit B, brain isoform), ↑2.6×; 3-(gi|1352384, Protein disulfide-isomerase A3), ↑3.4×; 4-(gi|40254595, Dihydropyrimidinase-related protein 2), ↑3.6×; 5-(gi|149054470, N-ethylmaleimide sensitive fusion protein, isoform CRAa), ↑2.0×; 6-(gi|42476181, Malate dehydrogenase, mitochondrial precursor), ↑1.4×; 7-(gi|62653546, Glyceraldehyde-3-phosphate dehydrogenase), ↑1.6×; 8-(gi|202837, Aldolase A), ↑1.3×; 9-(gi|31542401, Creatine kinase B-type), ↓0.86×; 10-(gi|40538860, Aconitate hydratase, mitochondrial precursor), ↑1.3×. The identified proteins were of cytoplasmic (1, 4, 5, 7, 9), cell membrane (2), endoplasmic reticulum (3) and mitochondrial (6, 8, 10) origin and 9 of them were significantly increased, 1.3-3.6×. The 4 out of 9 up-regulated proteins (4, 6, 7, 10) were described as functionally related to oxidative stress; the 2 proteins participate in genesis of apoptotic cell death.

In PM, the 18 up (↑)- or down (↓)-regulated proteins were identified by LC-MS/MS and were of plasma membrane [Brain acid soluble protein, ↓2.1×; trimeric Gβ subunit, ↓2.0x], myelin membrane [MBP, ↓2.5×], cytoplasmic [Internexin, ↑5.2×; DPYL2, ↑4.9×; Ubiquitin hydrolase, ↓2.0×; 60S ribosomal protein, ↑2.7×; KCRB, ↓2.6×; Sirtuin-2, ↑2.5×; Peroxiredoxin-2, ↑2.2×; Septin-11, ↑2.2×; TERA, ↑2.1×; SYUA, ↑2.0×; Coronin-1A, ↓5.4×] and mitochondrial [Glutamate dehydrogenase 1, ↑2.7×; SCOT1, ↑2.2×; Prohibitin, ↑2.2×; Aspartate aminotransferase, ↓2.2×] origin. Surprisingly, the immunoblot analysis of the same PM resolved by 2D-ELFO indicated that the “active”, morphine-induced pool of Gβ subunits represented just a minor fraction of the total signal of Gβ which was decreased 1.2x only. The dominant signal of Gβ was unchanged.

Conclusion

Brain cortex of rats exposed to increasing doses of morphine is far from being adapted. Significant up-regulation of proteins functionally related to oxidative stress and apoptosis suggests a major change of energy metabolism resulting in the state of severe brain cell “discomfort” or even death.

Opioid-Receptor (OR) Signaling Cascades in Rat Cerebral Cortex and Model Cell Lines: the Role of Plasma Membrane Structure

Large number of extracellular signals is received by plasma membrane receptors which, upon activation, transduce information into the target cell interior via trimeric G-proteins (GPCRs) and induce activation or inhibition of adenylyl cyclase enzyme activity (AC). Receptors for opioid drugs such as morphine (μ-OR, δ-OR and κ-OR) belong to rhodopsin family of GPCRs. Our recent results indicated a specific up-regulation of AC I (8-fold) and AC II (2.5-fold) in plasma membranes (PM) isolated from rat brain cortex exposed to increasing doses of morphine (10-50 mg/kg) for 10 days. Increase of ACI and ACII represented the specific effect as the amount of ACIII-ACIX, prototypical PM marker Na, K-ATPase and trimeric G-protein α and β subunits was unchanged. The up-regulation of ACI and ACII faded away after 20 days since the last dose of morphine. Proteomic analysis of these PM indicated that the brain cortex of morphine-treated animals cannot be regarded as being adapted to this drug because significant up-regulation of proteins functionally related to oxidative stress and alteration of brain energy metabolism occurred. The number of δ-OR was increased 2-fold and their sensitivity to monovalent cations was altered. Characterization of δ-OR-G-protein coupling in model HEK293 cell line indicated high ability of lithium to support affinity of δ-OR response to agonist stimulation. Our studies of PM structure and function in context with desensitization of GPCRs action were extended by data indicating participation of cholesterol-enriched membrane domains in agonist-specific internalization of δ-OR. In HEK293 cells stably expressing δ-OR-Gi1α fusion protein, depletion of PM cholesterol was associated with the decrease in affinity of G-protein response to agonist stimulation, whereas maximum response was unchanged. Hydrophobic interior of isolated PM became more “fluid”, chaotically organized and accessible to water molecules. Validity of this conclusion was supported by the analysis of an immediate PM environment of cholesterol molecules in living δ-OR-Gi1α-HEK293 cells by fluorescent probes 22- and 25-NBD-cholesterol. The alteration of plasma membrane structure by cholesterol depletion made the membrane more hydrated. Understanding of the positive and negative feedback regulatory loops among different OR-initiated signaling cascades (µ-, δ-, and κ-OR) is crucial for understanding of the long-term mechanisms of drug addiction as the decrease in functional activity of µ-OR may be compensated by increase of δ-OR and/or κ-OR signaling.

An integrated quantitative proteomics and systems biology approach to explore synaptic protein profile changes during morphine exposure

Morphine is a classic analgesic for the treatment of chronic pain. However, its repeated use is known to produce tolerance, physical dependence, and addiction; these properties limit its long-term therapeutic use and this has led to a quest for therapeutics without these unwanted side effects. Understanding the molecular changes in response to long-term use of morphine is likely to aid in the development of novel therapeutics for the treatment of pain. Studies examining the effects of chronic morphine administration have reported alterations in gene expression, synapse morphology, and synaptic transmission implying changes in synaptic protein profile. To fully understand the changes in protein profiles, proteomic techniques have been used. Studies using two-dimensional gel electrophoresis of various brain regions combined with mass spectrometry have found alterations in the levels of a number of proteins. However, neither the changes in brain regions relevant to morphine effects nor changes in the abundance of synaptic proteins have been clearly delineated. Recent studies employing subcellular fractionation to isolate the striatal synapse, combined with quantitative proteomics and graph theory-inspired network analyses, have begun to quantify morphine-regulated changes in synaptic proteins and facilitate the generation of networks that could serve as targets for the development of novel therapeutics for the treatment of chronic pain. Thus, an integrated quantitative proteomics and systems biology approach can be useful to identify novel targets for the treatment of pain and other disorders of the brain.

Effect of Chronic Morphine Consumption on Synaptic Plasticity of Rat's Hippocampus: A Transmission Electron Microscopy Study

It is well known that the synapses undergo some changes in the brain during the course of normal life and under certain pathological or experimental circumstances. One of the main goals of numerous researchers has been to find the reasons for these structural changes. In the present study, we investigated the effects of chronic morphine consumption on synaptic plasticity, postsynaptic density thickness, and synaptic curvatures of hippocampus CA1 area of rats. So for reaching these goals, 24 N-Mary male rats were randomly divided into three groups, morphine (n = 8), placebo (n = 8), and control (n = 8) groups. In the morphine group, complex of morphine (0.1, 0.2, 0.3, and 0.4) mg/mL and in the placebo (sucrose) group complex of sucrose (% 0.3) were used for 21 days. After the end of drug treatment the animals were scarified and perfused intracardinally and finally the CA1 hippocampal samples were taken for ultrastructural studies, and then the obtained data were analyzed by SPSS and one-way analysis of variance. Our data indicated that synaptic numbers per nm(3) change significantly in morphine group compared to the other two groups (placebo and control) (P < 0.001) and also statistical analysis revealed a significant difference between groups in terms of thickness of postsynaptic density (P < 0.001) and synaptic curvature (P < 0.007). It seems that morphine dependence in rats plays a main role in the ultrastructural changes of hippocampus.

Global changes in the rat heart proteome induced by prolonged morphine treatment and withdrawal

Morphine belongs among the most commonly used opioids in medical practice due to its strong analgesic effects. However, sustained administration of morphine leads to the development of tolerance and dependence and may cause long-lasting alterations in nervous tissue. Although proteomic approaches enabled to reveal changes in multiple gene expression in the brain as a consequence of morphine treatment, there is lack of information about the effect of this drug on heart tissue. Here we studied the effect of 10-day morphine exposure and subsequent drug withdrawal (3 or 6 days) on the rat heart proteome. Using the iTRAQ technique, we identified 541 proteins in the cytosol, 595 proteins in the plasma membrane-enriched fraction and 538 proteins in the mitochondria-enriched fraction derived from the left ventricles. Altogether, the expression levels of 237 proteins were altered by morphine treatment or withdrawal. The majority of changes (58 proteins) occurred in the cytosol after a 3-day abstinence period. Significant alterations were found in the expression of heat shock proteins (HSP27, α-B crystallin, HSP70, HSP10 and HSP60), whose levels were markedly up-regulated after morphine treatment or withdrawal. Besides that morphine exposure up-regulated MAPK p38 (isoform CRA_b) which is a well-known up-stream mediator of phosphorylation and activation of HSP27 and α-B crystallin. Whereas there were no alterations in the levels of proteins involved in oxidative stress, several changes were determined in the levels of pro- and anti-apoptotic proteins. These data provide a complex view on quantitative changes in the cardiac proteome induced by morphine treatment or withdrawal and demonstrate great sensitivity of this organ to morphine.

Morphine produces immunosuppressive effects in nonhuman primates at the proteomic and cellular levels

Morphine has long been known to have immunosuppressive properties in vivo, but the molecular and immunologic changes induced by it are incompletely understood. To explore how these changes interact with lentiviral infections in vivo, animals from two nonhuman primate species (African green monkeys and pigtailed macaques) were provided morphine and studied using a systems biology approach. Biological specimens were obtained from multiple sources (e.g. lymph node, colon, cerebrospinal fluid, and peripheral blood) before and after the administration of morphine (titrated up to a maximum dose of 5 mg/kg over a period of 20 days). Cellular immune, plasma cytokine, and proteome changes were measured and morphine-induced changes in these parameters were assessed on an interorgan, interindividual, and interspecies basis. In both species, morphine was associated with decreased levels of Ki-67(+) T-cell activation but with only minimal changes in overall T-cell counts, neutrophil counts, and NK cell counts. Although changes in T-cell maturation were observed, these varied across the various tissue/fluid compartments studied. Proteomic analysis revealed a morphine-induced suppressive effect in lymph nodes, with decreased abundance of protein mediators involved in the functional categories of energy metabolism, signaling, and maintenance of cell structure. These findings have direct relevance for understanding the impact of heroin addiction and the opioids used to treat addiction as well as on the potential interplay between opioid abuse and the immunological response to an infective agent.

Proteomic analysis of the nucleus accumbens in rhesus monkeys of morphine dependence and withdrawal intervention

It has been known that the reinforcing effects and long-term consequences of morphine are closely associated with nucleus accumbens (NAc) in the brain, a key region of the mesolimbic dopamine pathway. However, the proteins involved in neuroadaptive processes and withdrawal symptom in primates of morphine dependence have not been well explored. In the present study, we performed proteomes in the NAc of rhesus monkeys of morphine dependence and withdrawal intervention with clonidine or methadone. Two-dimensional electrophoresis was used to compare changes in cytosolic protein abundance in the NAc. We found a total of 46 proteins differentially expressed, which were further identified by mass spectrometry analysis. The identified proteins can be classified into 6 classes: metabolism and mitochondrial function, synaptic transmission, cytoskeletal proteins, oxidative stress, signal transduction and protein synthesis and degradation. Importantly, we discovered 14 proteins were significantly but similarly altered after withdrawal therapy with clonidine or methadone, revealing potential pharmacological strategies or targets for the treatment of morphine addiction. Our study provides a comprehensive understanding of the neuropathophysiology associated with morphine addiction and withdrawal therapy in primate, which is helpful for the development of opiate withdrawal pharmacotherapies.

Chronic morphine alters the presynaptic protein profile: identification of novel molecular targets using proteomics and network analysis

Opiates produce significant and persistent changes in synaptic transmission; knowledge of the proteins involved in these changes may help to understand the molecular mechanisms underlying opiate dependence. Using an integrated quantitative proteomics and systems biology approach, we explored changes in the presynaptic protein profile following a paradigm of chronic morphine administration that leads to the development of dependence. For this, we isolated presynaptic fractions from the striata of rats treated with saline or escalating doses of morphine, and analyzed the proteins in these fractions using differential isotopic labeling. We identified 30 proteins that were significantly altered by morphine and integrated them into a protein-protein interaction (PPI) network representing potential morphine-regulated protein complexes. Graph theory-based analysis of this network revealed clusters of densely connected and functionally related morphine-regulated clusters of proteins. One of the clusters contained molecular chaperones thought to be involved in regulation of neurotransmission. Within this cluster, cysteine-string protein (CSP) and the heat shock protein Hsc70 were downregulated by morphine. Interestingly, Hsp90, a heat shock protein that normally interacts with CSP and Hsc70, was upregulated by morphine. Moreover, treatment with the selective Hsp90 inhibitor, geldanamycin, decreased the somatic signs of naloxone-precipitated morphine withdrawal, suggesting that Hsp90 upregulation at the presynapse plays a role in the expression of morphine dependence. Thus, integration of proteomics, network analysis, and behavioral studies has provided a greater understanding of morphine-induced alterations in synaptic composition, and identified a potential novel therapeutic target for opiate dependence.

Genes and pathways co-associated with the exposure to multiple drugs of abuse, including alcohol, amphetamine/methamphetamine, cocaine, marijuana, morphine, and/or nicotine: a review of proteomics analyses

Drug addiction is a chronic neuronal disease. In recent years, proteomics technology has been widely used to assess the protein expression in the brain tissues of both animals and humans exposed to addictive drugs. Through this approach, a large number of proteins potentially involved in the etiology of drug addictions have been identified, which provide a valuable resource to study protein function, biochemical pathways, and networks related to the molecular mechanisms underlying drug dependence. In this article, we summarize the recent application of proteomics to profiling protein expression patterns in animal or human brain tissues after the administration of alcohol, amphetamine/methamphetamine, cocaine, marijuana, morphine/heroin/butorphanol, or nicotine. From available reports, we compiled a list of 497 proteins associated with exposure to one or more addictive drugs, with 160 being related to exposure to at least two abused drugs. A number of biochemical pathways and biological processes appear to be enriched among these proteins, including synaptic transmission and signaling pathways related to neuronal functions. The data included in this work provide a summary and extension of the proteomics studies on drug addiction. Furthermore, the proteins and biological processes highlighted here may provide valuable insight into the cellular activities and biological processes in neurons in the development of drug addiction.

Insight into pain-inducing and -related gene expression: a challenge for development of novel targeted therapeutic approaches

The multidimensional issue of pain in relation to the need for efficient treatment has been the focus of extensive research. Gaining insight into the molecular mechanisms of pain and identifying specific genes and proteins as possible drug targets is strongly required considering that not all patients can be adequately treated with the currently available drugs. This up-to-date review aimed to summarize the findings of recent proteomic and genomic approaches in different types of pain to comment on their potential role in pain signaling pathways and to evaluate their possible contribution to the development of novel and possibly more targeted pain therapeutic strategies. Although pain treatment strategies have been greatly improved during the past century, no ideal targeted pain treatment has been developed. The development of modern and accurate platforms of technology for the study of genetics and physiology of pain has led to the identification of an increased number of altered genes and proteins that are involved in pain-related pathways. Through genomics and proteomics, pain-related genes and proteins, respectively, may be identified as diagnostic markers or drug targets improving therapeutic strategies. Furthermore, such molecular mediators of pain may reveal novel strategies for individualized pain management. The utilization of unique experimental approaches (through specific animal models) as well as powered genetic association studies conducted on appropriate populations is more than essential.

Proteomic research in psychiatry

Psychiatric disorders such as Alzheimer's disease, schizophrenia and mood disorders are severe and disabling conditions of largely unknown origin and poorly understood pathophysiology. An accurate diagnosis and treatment of these disorders is often complicated by their aetiological and clinical heterogeneity. In recent years proteomic technologies based on mass spectrometry have been increasingly used, especially in the search for diagnostic and prognostic biomarkers in neuropsychiatric disorders. Proteomics enable an automated high-throughput protein determination revealing expression levels, post-translational modifications and complex protein-interaction networks. In contrast to other methods such as molecular genetics, proteomics provide the opportunity to determine modifications at the protein level thereby possibly being more closely related to pathophysiological processes underlying the clinical phenomenology of specific psychiatric conditions. In this article we review the theoretical background of proteomics and its most commonly utilized techniques. Furthermore the current impact of proteomic research on diverse psychiatric diseases, such as Alzheimer's disease, schizophrenia, mood and anxiety disorders, drug abuse and autism, is discussed. Proteomic methods are expected to gain crucial significance in psychiatric research and neuropharmacology over the coming decade.

Histopathological and biochemical changes of morphine sulphate administration on the cerebellum of albino rats

In this study the long-term effects of morphine sulphate treatment (MST) on histopathological and biochemical changes in the cerebellum was assessed in albino rats. Normal saline (5ml) was given orally as placebo in the control group (n=25). Morphine groups received morphine orally at a dose level of 5mg/kg body weight day after day for 10, 20 and 30 days (n=25/group). Light microscopy revealed that the molecular layer showed vacuolation. The Purkinje cells lost their specific shaped appearance, decreased in size and numbers. The granular cells highly degenerated. Electron microscopy revealed fragmentation of the cisterns of the both types of endoplasmic reticulum, resulted in a progressive depletion of total protein contents as well as general carbohydrates in all treated groups as supported by histochemical observation. Obvious destruction of mitochondrial inner membrane and cristae mediate cell death. Also, abnormal nucleus with deformed perforated nuclear membrane and deformation of the plasma membrane with degeneration of the synapses could interpreted as a sign of necrosis. Biochemical analysis revealed that dopamine (DA) and norepinephrine (NE) were significantly decreased in four brain areas (cortex striatum, thalamus/hypothalamus, and cerebellum). In contrast, serotonin (5-HT) level was increased in these brain regions; with an exception of 5-HT on day 10 and neurotransmitter levels in the pons were unaffected. The quantitative analysis showed a significant decrease (P<0.05) in the diameter of Purkinje cells and in the thickness of both molecular and granular layers treated groups. Morphine sulphate induces may be a cell death or necrosis in the rat cerebellum and modulating neurotransmitter system. Our findings pointed out the risk of increased cerebellum damage due to long-term of morphine use.

Role of MEK-ERK pathway in morphine-induced conditioned place preference in ventral tegmental area of rats

A major goal of research on drug addiction is to develop the effective treatments to deal with the long-term behavioral disorders especially reinstatement induced by the addictive drugs such as opiates, cocaine, and cannabinoid. The molecular mechanisms underlying these substance-related disorders remain unclear so far. Here we used the model of morphine-induced conditioned place preference (CPP) in rats to mimic the progress of drug-taking, withdrawal and relapse in human. The tissue of ventral tegmental area (VTA), one of the most important brain structures associated with abused drug-related disorders, was taken and two-dimensional electrophoresis (2-DE) was performed to analyze and compare the changes of protein expression patterns during the different stages of morphine-induced CPP. First, we found that there were 80 proteins identified to be changed in the process of morphine-induced CPP. Furthermore, as the mitogen-activated protein kinase kinase 1 (MAPKK1) was increased significantly in the stages of establishment and reinstatement, we confirmed the change of activated extracellular signal-regulated kinase (ERK) by Western blotting in VTA tissue and cultured cell. The results demonstrated that the activated MEK-ERK pathway by chronic morphine treatment in VTA was involved in morphine-induced reinstatement. Moreover, inhibition of MEK-ERK pathway by infusion the MEK inhibitor U0126 in VTA blocked the establishment of morphine-induced CPP. The present study found significant changes in a group of protein expressions in VTA during morphine-induced CPP and further confirmed the role of MEK-ERK cell signaling pathway of VTA in morphine addiction.

Withdrawal from repeated administration of morphine alters histamine-induced anxiogenic effects produced by intra-ventral hippocampal microinjection

In the present study, the influence of withdrawal from repeated administration of morphine on intra-ventral hippocampal microinjection of histamine-induced anxiety-like behavior was investigated in male Wistar rats. Three days subcutaneous administration of morphine (5-10 mg/kg) followed by five days free of the drug decreased the percentage open arm time and the percentage open arm entries. Intra-ventral hippocampal administration of histamine (2.5-7.5 microg/rat) decreased percentage open arm time and percentage open arm entries. Intra-ventral hippocampal histamine-induced anxiogenic effect was reversed in animals that had previously received the three days morphine (7.5 mg/kg) followed by five days free of the drug. Intra-ventral hippocampal administration of pyrilamine (5-20 microg/rat) or ranitidine (10-40 microg/rat) decreased percentage open arm time and percentage open arm entries. Pyrilamine- or ranitidine-induced anxiogenic effect was not changed in animals that had previously received the three days morphine (7.5 mg/kg) followed by five days free of the drug. Intra-ventral hippocampal injections of clobenpropit increased percentage open arm time. The percentage open arm time and percentage open arm entries were decreased in the morphine-treated animals compared with non-morphine-treated controls. Percentage open arm entries and locomotor activity was reduced with some doses of clobenpropit. It can be concluded that the histamine system is involved in anxiety-like behavior, and repeated injections of morphine followed by five days free of the drugs interact with histamine receptor mechanism.

Mass spectrometry screening reveals peptides modulated differentially in the medial prefrontal cortex of rats with disparate initial sensitivity to cocaine

To better understand why certain individuals are more vulnerable to cocaine abuse and addiction, we identify peptide markers associated with individual variation in sensitivity to the behavioral effects of cocaine. Previous studies in rats show that low, compared to high, cocaine responders are more sensitive to cocaine-induced behavioral plasticity (sensitization), exhibit enhanced conditioning to cocaine's rewarding effects, and are more motivated to self administer cocaine. In the current study, we combine matrix-assisted laser desorption/ionization mass spectrometry with multivariate statistical methods to analyze tissue extracts from rat dorsal striatum, nucleus accumbens, and medial prefrontal cortex (mPFC) to examine trends in peptide changes that coincide with behavioral phenotype. Peptide profiles of these three regions from individual animals were characterized via mass spectrometry. Resulting mass peaks that were statistically different between these groups were identified using principal component analysis. The mass peaks were then identified in pooled samples via multistage liquid chromatography mass spectrometry. A total of 74 peptides from 28 proteins were sequenced from defined brain regions. Statistically significant changes in peak intensities for seven peptides were found in the mPFC of rats given a single injection of 10 mg/kg cocaine, with low cocaine responders showing approximately 2-fold increase in peak intensities for the acetylated N terminus peptides of stathmin and Hint 1, as well as truncated ATP synthase. These results suggest that distinct peptide profiles in the mPFC are associated with individuals that exhibit reduced sensitivity to the behavioral effects of cocaine.

The proteomic analysis of primary cortical astrocyte cell culture after morphine administration

Astrocytes are supportive cells, necessary for ensure optimal environment for neural cells functioning. They are involved in extracellular K+ level regulation and neurotransmitters removal. They are also dependent for myelination and synapses formation. They may make a contribution in signal propagation in the central nervous system, for example, through Ca2+ signaling. With the use of neonatal pure astrocyte cell culture, we investigated changes in astrocyte's proteomes under the influence of morphine. We found 10 major proteins, which show different expression between physiological cell culture and morphine treatment. With 2D gel electrophoresis and nanoLC-ESI-MS/MS, we identified proteins and characterized their potential role in morphine dependence. Observed differences were also confirmed by Western blotting. Our data suggests a role for astrocytes in the formation of the morphine dependence at the molecular level. This finding may support interpretation of causes of morphine dependence formation based only on behavioral data.

The use of neuroproteomics in drug abuse research

The number of discovery proteomic studies of drug abuse has begun to increase in recent years, facilitated by the adoption of new techniques such as 2D-DIGE and iTRAQ. For these new tools to provide the greatest insight into the neurobiology of addiction, however, it is important that the addiction field has a clear understanding of the strengths, limitations, and drug abuse-specific research factors of neuroproteomic studies. This review outlines approaches for improving animal models, protein sample quality and stability, proteome fractionation, data analysis, and data sharing to maximize the insights gained from neuroproteomic studies of drug abuse. For both the behavioral researcher interested in what proteomic study results mean, and for biochemists joining the drug abuse research field, a careful consideration of these factors is needed. Similar to genomic, transcriptomic, and epigenetic methods, appropriate use of new proteomic technologies offers the potential to provide a novel and global view of the neurobiological changes underlying drug addiction. Proteomic tools may be an enabling technology to identify key proteins involved in drug abuse behaviors, with the ultimate goal of understanding the etiology of drug abuse and identifying targets for the development of therapeutic agents.

Down-regulation of c-Cbl by morphine accounts for persistent ERK1/2 signaling in delta-opioid receptor-expressing HEK293 cells

Opioids display ligand-specific differences in the time course of ERK1/2 signaling. Whereas full agonists, like etorphine, induce only transient activation of ERK1/2, the partial agonist morphine mediates persistent stimulation of mitogenic signaling. Here we report that in stably delta-opioid receptor (DOR)-expressing HEK293 (HEK/DOR) cells, the transient nature of etorphine-induced ERK1/2 signaling is due to desensitization of epidermal growth factor (EGF) receptor-mediated activation of the Ras/Raf-1/ERK1/2 cascade. Desensitization of ERK1/2 activity by etorphine is associated with down-regulation of EGF receptors, an effect mediated by the ubiquitin ligase c-Cbl. In contrast, chronic morphine treatment failed to desensitize EGF receptors, resulting in unimpeded ERK1/2 signaling. The failure of morphine to desensitize ERK1/2 signaling is mediated by persistent activation of c-Src, which induces degradation of c-Cbl. The role of c-Src in opioid-specific ERK1/2 signaling is further demonstrated by pretreatment of the cells with PP2 and SKI-I as well as overexpression of a dominant negative c-Src mutant (c-Src(dn)) or a c-Src-resistant c-Cbl mutant (CblY3F), both of which facilitate desensitization of ERK1/2 signaling by morphine. Conversely, overexpression of c-Src as well as down-regulation of c-Cbl by small interfering RNA results in persistent etorphine-induced stimulation of ERK1/2 activity. Subcellular fractionation experiments finally attributed the ability of morphine to persistently activate c-Src to its redistribution from Triton X-100-insensitive membrane rafts to DOR and EGF receptor containing high density membrane compartments implicated in ERK1/2 signaling. These results demonstrate that agonist-specific differences in the temporal and spatial pattern of c-Src activation determine the kinetics of DOR-mediated regulation of ERK1/2 signaling.

Proteomic analysis of striatal neuronal cell cultures after morphine administration

Using primary neuronal cell culture assays, combined with 2-D gel electrophoresis and capillary LC-MS, we identified differences in proteomes between control and morphine-treated cells. Statistically significant differences were observed among 26 proteins. Nineteen of them were up-regulated, while seven were down-regulated in morphine-treated cell populations. The identified proteins belong to classes involved in energy metabolism, associated with oxidative stress, linked with protein biosynthesis, cytoskeletal ones, and chaperones. The detected proteins demand further detailed studies of their biological roles in morphine addiction. It is crucial to confirm observed processes in vivo in order to reveal the nature and importance of the biological effect of proteome changes after morphine administration. Further investigations may lead to the discovery of new proteome-based effects of morphine on living organisms.

Chronic morphine administration induces over-expression of aldolase C with reduction of CREB phosphorylation in the mouse hippocampus

In recent studies, alterations in the activity and expression of metabolic enzymes, such as those involved in glycolysis, have been detected in morphine-dependent patients and animals. Increasing evidence demonstrates that the hippocampus is an important brain region associated with morphine dependence, but the molecular events occurring in the hippocampus following chronic exposure to morphine are poorly understood. Aldolase C is the brain-specific isoform of fructose-1, 6-bisphosphate aldolase which is a glycolytic enzyme catalyzing reactions in the glycolytic, gluconeogenic, and fructose metabolic pathways. Using Western blot and immunofluorescence assays, we found the expression of aldolase C was markedly increased in the mouse hippocampus following chronic morphine treatment. Naloxone pretreatment before morphine administration suppressed withdrawal jumping, weight loss, and overexpression of aldolase C. CREB is a transcription factor regulated through phosphorylation on Ser133, which is known to play a key role in the mechanism of morphine dependence. When detecting the expression of phosphorylated CREB (p-CREB) in the mouse hippocampus using Western blot and immunohistochemistry, we found CREB phosphorylation was clearly decreased following chronic morphine treatment. Interestingly, laser-confocal microscopy showed that overexpression of aldolase C in mouse hippocampal neurons was concomitant with the decreased immunoreactivity of p-CREB. The results suggest potential links between the morphine-induced alteration of aldolase C and the regulation of CREB phosphorylation, a possible mechanism of morphine dependence.

Proteomic analysis of lung tissue of rats exposed to cigarette smoke and radon

This study examined the protein expression in lung tissues of rats exposed to radon and cigarette smoke using a proteomic approach. Male Wistar rats were exposed daily to radon at a concentration of 100,000 Bq/m(3) for 16 h, and then exposed to 20% cigarette smoke for 1 h for a period of 75 d, with the radon cumulative dose reaching 200 WLM (working level months). Proteins from rat lung tissue were separated by two-dimensional gel electrophoresis (2-DE), stained with Coomassie blue, and analyzed with ImageMaster two-dimensional (2D) platinum software. Differentially expressed proteins were analyzed by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MALDI-time of flight [TOF] MS or MALDI TOF/TOF-MS). Twenty prominent proteins that were correlated with signal transduction, metabolism, heat shock and stress, and cytoskeleton construction were identified. Some of the differential expression proteins were verified by Western blot analysis and immunohistochemical staining, and the results were consistent with 2-DE analysis. The identified proteins and peptides might be potential diagnostic markers of lung impairment induced by radon and cigarette smoke exposure.

Characterizing intercellular signaling peptides in drug addiction

Intercellular signaling peptides (SPs) coordinate the activity of cells and influence organism behavior. SPs, a chemically and structurally diverse group of compounds responsible for transferring information between neurons, are broadly involved in neural plasticity, learning and memory, as well as in drug addiction phenomena. Historically, SP discovery and characterization has tracked advances in measurement capabilities. Today, a suite of analytical technologies is available to investigate individual SPs, as well as entire intercellular signaling complements, in samples ranging from individual cells to entire organisms. Immunochemistry and in situ hybridization are commonly used for following preselected SPs. Discovery-type investigations targeting the transcriptome and proteome are accomplished using high-throughput characterization technologies such as microarrays and mass spectrometry. By integrating directed approaches with discovery approaches, multiplatform studies fill critical gaps in our knowledge of drug-induced alterations in intercellular signaling. Throughout the past 35 years, the National Institute on Drug Abuse has made significant resources available to scientists that study the mechanisms of drug addiction. The roles of SPs in the addiction process are highlighted, as are the analytical approaches used to detect and characterize them.

Psychiatric research: psychoproteomics, degradomics and systems biology

While proteomics has excelled in several disciplines in biology (cancer, injury and aging), neuroscience and psychiatryproteomic studies are still in their infancy. Several proteomic studies have been conducted in different areas of psychiatric disorders, including drug abuse (morphine, alcohol and methamphetamine) and other psychiatric disorders (depression, schizophrenia and psychosis). However, the exact cellular and molecular mechanisms underlying these conditions have not been fully investigated. Thus, one of the primary objectives of this review is to discuss psychoproteomic application in the area of psychiatric disorders, with special focus on substance- and drug-abuse research. In addition, we illustrate the potential role of degradomic utility in the area of psychiatric research and its application in establishing and identifying biomarkers relevant to neurotoxicity as a consequence of drug abuse. Finally, we will discuss the emerging role of systems biology and its current use in the field of neuroscience and its integral role in establishing a comprehensive understanding of specific brain disorders and brain function in general.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Neuroproteomics and its applications in research on nicotine and other drugs of abuse

The rapidly growing field of neuroproteomics is able to track changes in protein expression and protein modifications underlying various physiological conditions, including the neural diseases related to drug addiction. Thus, it presents great promise in characterizing protein function, biochemical pathways, and networks to understand the mechanisms underlying drug dependence. In this article, we first provide an overview of proteomics technologies and bioinformatics tools available to analyze proteomics data. Then we summarize the recent applications of proteomics to profile the protein expression pattern in animal or human brain tissues after the administration of nicotine, alcohol, amphetamine, butorphanol, cocaine, and morphine. By comparing the protein expression profiles in response to chronic nicotine exposure with those appearing in response to treatment with other drugs of abuse, we identified three biological processes that appears to be regulated by multiple drugs of abuse: energy metabolism, oxidative stress response, and protein degradation and modification. Such similarity indicates that despite the obvious differences among their chemical properties and the receptors with which they interact, different substances of abuse may cause some similar changes in cellular activities and biological processes in neurons.

Use of proteomics for the identification of novel drug targets in brain diseases

In spite of the rapid advances in the development of the new proteomic technologies, there are, to date, relatively fewer studies aiming to explore the neuronal proteome. One of the reasons is the complexity of the brain, which presents high cellular heterogeneity and a unique subcellular compartmentalization. Therefore, tissue fractionation of the brain to enrich proteins of interest will reduce the complexity of the proteomics approach leading to the production of manageable and meaningful results. In this review, general considerations and strategies of proteomics, the advantages and challenges to exploring the neuronal proteome are described and summarized. In addition, this article presents an overview of recent advances of proteomic technologies and shows that proteomics can serve as a valuable tool to globally explore the changes in brain proteome during various disease states. Understanding the molecular basis of brain function will be extremely useful in identifying novel targets for the treatment of brain diseases.