Kappa Opioid Receptor Gene Research Articles

The impact of the OPRM1, OPRK1, DCC genes polymorphisms on the motivation for non-suicidal self-injury in young adults: a pilot study

IntroductionNon-suicidal self-injury (NSSI) – the deliberate, self-directed damage of body tissue without suicidal intent and for purposes not socially or culturally sanctioned – is a highly prevalent phenomenon in adolescents and young adults. Motivation for the NSSI is known to be heterogenous in different patients. However, biological and especially genetic markers associated with different motivation for the NSSI have not been studied to date. One of the possible candidates are mu- (OPRM1) and kappa-opioid receptor (OPRK1) genes, since opioid system is known to be involved in the NSSI. Another perspective candidate is the DCC gene, encoding the netrin 1 receptor, which plays vital part in the formation of the prefrontal cortex.ObjectivesWe conducted a pilot cross-sectional study to test the impact of the rs1779971 OPRM1, rs6473797 OPRK1 and rs8084280 DCC gene polymorphisms on the characteristics and motivations for the NSSI in young adults.Methods28 patients of European ancestry with NSSI (89,3%; n=25) women, median age (Q1-Q3) – 23 (21,25-25) years) were included in the pilot sample. The majority of the sample had a diagnosis of bipolar disorder (78,6%; n=20). Characteristics and motivation for the NSSI were measured by the Inventory of Statements about Self-Injury (ISAS). The Childhood Trauma Questionnaire (CTQ) was used to control for adverse childhood experiences, a potent environmental factor, associated with NSSI. Genotyping was performed using RT-PCR. The genetic effect was evaluated using the dominant model. For statistical analysis multiple linear regression with the presence of minor alleles, different types of childhood trauma, diagnosis, age and sex as factors and ISAS scores as dependent variables were used.ResultsMultiple linear regression showed that minor C allele of rs6473796 OPRK1 gene polymorphism was associated with an increase of the “Affect regulation” (B=2,23; CI95% [0,39–4,06]; p=0,022), “Anti-dissociation” (B=3,31; CI95% [0,18–6,44]; p=0,039) subscales of ISAS scores. Moreover, the minor T allele of the rs8082480 DCC gene polymorphism was associated with a decrease of the “Affect regulation” subscale score (B=-1,74; CI95% [-3,30 – -0,18]; p=0,032).ConclusionsTo our knowledge, this is the first study on the genetic markers of motivations for NSSI. Our pilot results showed that, controlling for diagnosis, age, sex and childhood trauma, OPRK1 and DCC gene polymorphisms may be associated with the heterogeneity of motivations for NSSI. However, these results require confirmation on the larger samples.Disclosure of InterestNone Declared

Recapitulating phenotypes of alcohol dependence via overexpression of Oprk1 in the ventral tegmental area of non-dependent TH::Cre rats

The dynorphin (DYN)/kappa-opioid receptor (KOR) system is involved in dysphoria and negative emotional states. Dysregulation of KOR function promotes maladaptive behavioral regulation during withdrawal associated with alcohol dependence. Mesolimbic dopaminergic (DA) projections from the ventral tegmental area (VTA) innervate the extended amygdala circuitry and presynaptic KORs attenuate DA in these regions leading to an excessive alcohol consumption and negative affective-like behavior, whereas mesocortical KOR-regulated DA projections have been implicated in executive function and decision-making. Thus, the neuroadaptations occurring in DYN/KOR systems are important aspects to consider for the development of personalized therapeutic solutions. Herein, we study the contribution of the VTA DA neuron Oprk1 (KOR gene) in excessive alcohol consumption, negative emotional state, and executive function. To do so, Oprk1 mRNA expression and KOR function were characterized to confirm alcohol dependence-induced dysregulation in the VTA. Then, a transgenic Cre-Lox rat model (male and female TH::Cre rats) was used to allow for conditional and inducible overexpression of Oprk1 in VTA DA neurons. The effect of this overexpression was evaluated on operant alcohol self-administration, negative emotional states, and executive function. We found that VTA Oprk1 overexpression recapitulates some phenotypes of alcohol dependence including escalated alcohol self-administration and depressive-like behavior. However, working memory performance was not impacted following VTA Oprk1 overexpression in TH::Cre rats. This supports the hypothesis that dysregulated KOR signaling within the mesolimbic DA system is an important contributor to symptoms of alcohol dependence and shows that understanding Oprk1-mediated contributions to alcohol use disorder (AUD) should be an important future goal.

RETRACTED ARTICLE: Down-regulation of kappa opioid receptor promotes ESCC proliferation, invasion and metastasis via the PDK1-AKT signaling pathway

BackgroundAs a class of the opioid receptors, the kappa opioid receptor (KOR) has been verified to be a potential biomarker and therapeutic target for human malignant tumors. However, a thorough understanding of whether KOR affects progression of esophageal squamous cell carcinoma (ESCC) is still lacking. This study focused on exploring the effect of knocking down KOR in ESCC and its underlying mechanism.MethodsBioinformatics analysis was used to compare the different expression level of OPRK1 (KOR gene) in tumor and adjacent normal tissues, and predict the relationship between KOR expression and overall survival. RNA-sequence analysis was performed to detect the altered functions and mechanisms after down regulating KOR. The in vitro and in vivo assays were used to detect the effects of down-regulated KOR on cell proliferation, migration and invasion. Substrate gel zymography and 3D cell culture assays were used to find the effect of KOR knockdown on the degradation of extracellular matrix (ECM), and immunefluorescence was performed to detect the altered cytoskeleton. Western blotting and immunohistochemistry were used to explore the underlying mechanism pathway.ResultsBioinformatics analysis revealed that the expression of OPRK1 was lower in tumor tissue than that in adjacent normal tissues, and lowered expression of KOR was associated with poorer overall survival. The in vitro assays demonstrated that down-regulation of KOR enhanced ESCC proliferation, metastasis and invasion. Western blotting revealed that down-regulation of KOR could activate PDK1-AKT signaling pathway, which actively regulated the cancer progression. Down-regulation of KOR enhanced the formation of invadopodia, secretion of matrix metalloproteinase-2 (MMP2) and rearrangement of cytoskeleton, which were positively related with the invasion of ESCC. KOR knockdown enhanced the tumor invasion and elevated the AKT phosphorylation in nude mice. The AKT kinase inhibition could reverse the effect of down-regulation of KOR.ConclusionKOR might act as a tumor suppressor in ESCC and down-regulation of KOR could enhance the ESCC tumor phenotype.Graphical abstract8saryVZK7ypoVwSXab2T6mVideo

Analyses of polymorphisms of intron 2 of OPRK1 (kappa-opioid receptor gene) in association with opioid and cocaine dependence diagnoses in an African-American population

RationaleThe dynorphin/kappa-opioid receptor (KOR) system (encoded by PDYN and OPRK1 genes respectively) is highly regulated by repeated exposure to drugs of abuse, including mu-opioid agonists and cocaine. These changes in the dynorphin/KOR system can then influence the rewarding effects of these drugs of abuse. Activation of the dynorphin/KOR system is also thought to have a role in the pro-addictive effects of stress. Recent in vitro assays showed that the OPRK1 intron 2 may function as a genomic enhancer in the regulation KOR expression, and contains a glucocorticiod-responsive sequence site. We hypothesize that SNPs in intron 2 of OPRK1 are associated with categorical opioid or cocaine dependence diagnoses, as well as with dimensional aspects of drug use (i.e., magnitude of drug exposure). MethodsThis study includes 577 subjects ≥ 18 years old, with African ancestry (AA) from the USA. They were divided into three groups: 152 control subjects, 142 persons with lifetime opioid dependence diagnosis (OD), and 283 subjects with lifetime cocaine dependence diagnosis (CD). Five SNPs (rs16918909, rs7016778, rs997917, rs6473797, rs10111937) that span 10 Kb nucleotides in intron 2 of OPRK1 were used for the association analyses. Genotyping was performed with the Smokescreen® array or sequencing of PCR-amplified DNA fragments. Association analyses for OD and CD diagnoses and the OPRK1 intron 2 alleles were carried out with Fisher’s exact test. The Kreek-McHugh-Schluger-Kellogg (KMSK) scales were used for dimensional measure of maximum exposure to specific drugs, using Mann-Whitney tests. ResultsTwo SNPs, rs997917 and rs10111937 showed point-wise significant allelic association (p < 0.05) with CD diagnosis, and rs10111937 showed a point-wise significance in association with OD. None of these single SNP associations with categorical diagnoses were significant after correction for multiple testing (pcorr > 0.05). However, significant associations of several genotype patterns (diplotypes) were found with cocaine dependence, but none for opioid dependence. The most significant genotype pattern with cocaine dependence diagnosis occurred for rs6473797 and rs10111937 (pcorr = 0.036, odds ratio = 1.92, FDR < 0.05), and survived correction for multiple testing. Dimensional analyses with KMSK scores show that persons with either rs997917 or rs10111937 variants had greater exposure to cocaine, compared to those with prototype allele (Mann-Whitney tests, point-wise). ConclusionsThis study provides additional support of potential importance of regulatory regions of intron 2 of the OPRK1 gene in development of cocaine and opioid dependence diagnoses, in a population with African-American ancestry.

Topical administration of the kappa opioid receptor agonist nalfurafine suppresses corneal neovascularization and inflammation

Corneal neovascularization (CNV) causes higher-order aberrations, corneal edema, ocular inflammation, and corneal transplant rejection, thereby decreasing visual acuity. In this study, we investigated the effects of topical administration of the kappa opioid receptor agonist nalfurafine (TRK-820) on CNV. To induce CNV, intrastromal corneal sutures were placed on the corneal stroma of BALB/c mice for 2 weeks. Nalfurafine (0.1 µg/2 μL/eye) was topically administered to the cornea once or twice daily after CNV induction. The CNV score, immune cell infiltration, and mRNA levels of angiogenic and pro-inflammatory factors in neovascularized corneas were evaluated using slit-lamp microscopy, immunohistochemistry, flow cytometry, and polymerase chain reaction. The mRNA expression of the kappa opioid receptor gene Oprk1 was significantly upregulated following CNV induction. Topical administration of nalfurafine twice daily significantly suppressed CNV and lymphangiogenesis, as well as reduced the mRNA levels of angiogenic and pro-inflammatory factors in the neovascularized corneas. Moreover, nalfurafine administration twice daily reduced the numbers of infiltrating leukocytes, neutrophils, macrophages, and interferon-γ-producing CD4+ T cells in the neovascularized corneas. In this study, we demonstrated that topical administration of nalfurafine suppressed local CNV in a mouse model along with the activation of KOR, suggesting that nalfurafine may prevent and control CNV in humans.

Intravenous Administration of Pyroglutamyl Apelin-13 Alleviates Murine Inflammatory Pain via the Kappa Opioid Receptor.

Apelin is an endogenous neuropeptide, which has wide distribution in central nervous system and peripheral tissues. Pyroglutamyl apelin-13 [(pyr)apelin-13] is the major apelin isoform in human plasma. However, the role of peripheral (pyr)apelin-13 in pain regulation is unknown. The aim of this study was to investigate the effect of the peripheral injection of (pyr)apelin-13 on inflammatory pain using the formalin test as well as to evaluate the mechanistic basis for the effect. Results showed intravenous (i.v.) injection of (pyr)apelin-13 (10, 20 mg/kg) to significantly decrease licking/biting time during the second phase of the mouse formalin test. In contrast, i.v. injection of apelin-13 had no influence on such effect. Intramuscular injection of (pyr)apelin-13 reduced licking/biting time during the second phase only at a dose of 20 mg/kg. The antinociception of i.v. (pyr)apelin-13 was antagonized by the apelin receptor (APJ, angiotensin II receptor-like 1) antagonist, apelin-13(F13A). (pyr)apelin-13 (i.v. 20 mg/kg) markedly upregulated Aplnr and Adcy2 gene expression in the prefrontal cortex, whereas Fos gene expression was downregulated. The antinociception of i.v. (pyr)apelin-13 was blocked by the opioid receptor antagonist naloxone and the specific kappa opioid receptor (KOR) antagonist nor-binaltorphimine (nor-BNI). (pyr)Apelin-13 upregulated the dynorphin and KOR gene expression and protein levels in the mouse prefrontal cortex, not in striatum. (pyr)Apelin-13 did not influence the motor behavior. Our results demonstrate that i.v. injection of (pyr)apelin-13 induces antinociception via the KOR in the inflammatory pain mouse model.

SUN-199 The Kappa Opioid Receptor (KOR)-Expressing Neurons Localize in the Ventromedial Hypothalamic Nucleus and Project to KNDy Neurons, the GnRH Pulse Generator, in Rats

KNDy neurons are named for their co-expression of three neuropeptides, kisspeptin, neurokinin B and dynorphin A (Dyn A). These cells, located in the hypothalamic arcuate nucleus (ARC), are assumed to be the generator of GnRH/LH pulses that control follicular growth, spermatogenesis and steroidogenesis. It is essential to clarify the mechanisms that regulate GnRH pulse generator to understand the reproductive functions in mammals. However, the inhibitory mechanism of GnRH pulse generator by Dyn A is unclear including the location of κ-opioid receptors (KOR; the receptor for Dyn A) in the hypothalamus. To elucidate the mechanism, we analyzed the localization and projections of KOR neurons in rats. We used a lentiviral vector that contains GFP and wheat germ agglutinin (WGA) connected with picornaviral 2A peptide, which are driven by KOR promoter, to visualize KOR neurons. This lentiviral vector was administrated into the region close to the arcuate nucleus (ARC) and ventromedial hypothalamic nucleus (VMH) in female rats. Two weeks after the injection, the rats were sacrificed to analyze the localization and projections of KOR neurons by in situ hybridization (ISH) and immunohistochemistry (IHC). GFP was strongly expressed in cells in the VMH. Double staining of KOR ISH and GFP IHC revealed that all GFP-positive cells were Oprk1 (KOR gene) positive in the VMH, demonstrating that we succeeded to obtain animals that specifically express GFP in KOR neurons. Double staining of GFP and kisspeptin IHC detected the axons of kisspeptin neurons near the cell body of GFP-positive neurons. Likewise, axons of GFP-positive neurons were observed near the Kiss1-positive cells by double staining of GFP IHC and Kiss1 (kisspeptin gene) ISH. In addition, we found axons expressing WGA in the ARC by IHC. Taken together, we found the localization of KOR neurons in the VMH and projections of KOR neurons to KNDy neurons and those of KNDy neurons to KOR neurons as well. These results suggest that KOR neurons in the VMH, which receive Dyn A signal from KNDy neurons, directly inhibit the activity of KNDy neurons. WGA-positive axons in the ARC imply the existence of unknown neurons mediating signals of KOR neurons to KNDy neurons. Our rats fluorescently labeled with KOR neurons will be useful to analyze detailed characteristics of KOR neurons, which will make major progress in elucidating the inhibitory mechanism of reproductive function.

Механизмы контроля потребления алкоголя: экспрессия генов ноцицептин/каппа-опиоидной системы в мозге крыс

Каппа-опиоидная и ноцицептиновая системы играют важную роль в модуляции функций дофаминергической системы «награды», однако их роль в механизмах формирования аддиктивного поведения до конца не ясна. Цель исследования: сравнить уровни мРНК каппа-опиоидного (OPRK1) и ноцицептинового (OPRL1) рецепторов, а также их эндогенных лигандов - препродинорфина (PDYN) и препроноцицептина (PDYN) в мозге животных с различным уровнем предпочтения алкоголя. Методы: потребление алкоголя у половозрелых крыс-самцов Wistar регистрировали с 60-го по 85-й дни жизни в модели «свободный выбор» между водой и 10% раствором этанола. Относительный уровень мРНК в структурах мозга определяли на 86-й день жизни методом ПЦР в реальном времени. Результаты: Экспрессия мРНК PDYN и PNOC в стриатуме, и OPRK1 и OPRL1 в миндалине была достоверно выше у «отвергающих», т.е. контролирующих потребление алкоголя на постоянно низком уровне животных, по сравнению с «предпочитающими», увеличившими потребление алкоголя в течение эксперимента. Заключение: более высокий уровень экспрессии генов эндогенных опиоидов PDYN и PNOC и их рецепторов в исследованных областях мозга может обусловливать меньшую гедоническую привлекательность алкоголя, играя превентивную роль и снижая риск злоупотребления алкоголем Kappa-opioidergic and nociceptinergic systems both inhibit the mesolimbic reward circuitry but their role in mechanisms of addictive behavior still is not well understood. Objective of the study was to compare expression of kappa opioid and nociceptin receptor genes (OPRK1 and OPRL1, respectively) and their endogenous ligands, preprodynorphin (PDYN) and prepronociceptin (PNOC), in the mesolimbic areas of rats with high and low voluntary alcohol consumption. Methods. Individually housed male Wistar rats were given a 25-day-long two-bottle (10% ethanol/water) free choice trial. mRNA levels were measured using the real-time polymerase chain reaction (qPCR). Results. Alcohol preferring rats progressively increased their ethanol consumption over the course of experiment while non-preferring, low-drinking animals controlled their alcohol intake near the baseline level. Alcohol non-preferring rats were identified to have significantly higher levels of PDYN and PNOC mRNA in the striatum and OPRK1 and OPRL1 mRNA in the amygdala compared to ethanol preferring animals. Conclusion. We suggested that higher levels of the “anti-reward opioid system” gene expression in mesolimbic structures may blunt the hedonic response to alcohol and thus preclude the increase in alcohol preference and uncontrolled excessive alcohol intake.

Involvement of opioid system in behavioral despair induced by social isolation stress in mice

Social isolation stress (SIS) as a type of chronic stress could induce depressive- and anxiety-like behaviors. Our study evaluates the role of opioid system on negative behavioral impacts of SIS in male NMRI mice. We investigated effects of morphine, a nonselective opioid receptor (OR) agonist, naltrexone (NLX), an OR antagonist, naltrindole (NLT), a delta opioid receptor (DOR) antagonist, SNC80, a DOR agonist, U-69593, a kappa opioid receptor (KOR) agonist, nor-Binaltorphimine, a selective KOR antagonist and cyprodime hydrochloride a selective mu opioid receptor (MOR) antagonist on depressive- and anxiety-like behaviors. Using RT-PCR we evaluated ORs gene expression in mice brain. Our findings showed that SIS induced anxiety- and depressive-like behavior in the forced swimming test, open field test, splash test and hole-board test. Moreover, administration of SNC-80 significantly mitigated anxiety- and depressive-like behaviors. NLT decreased grooming-activity in the splash test. Excitingly, administration of agents affecting KOR failed to alter the negative effects of SIS. RT-PCR demonstrated that MOR and KOR gene expression decreased in socially isolated mice; however, SIS did not affect DORs expression. Our findings suggest that SIS at least in part, probably via altering endogenous opioids particularly MORs and KORs but not DORs mediated negative impacts on behavior; also, it could be concluded that DORs might be considered as a novel target for studying depression and anxiety.

Downregulation of the neuronal opioid gene expression concomitantly with neuronal decline in dorsolateral prefrontal cortex of human alcoholics

Molecular changes in cortical areas of addicted brain may underlie cognitive impairment and loss of control over intake of addictive substances and alcohol. Prodynorphin (PDYN) gives rise to dynorphin (DYNs) opioid peptides which target kappa-opioid receptor (KOR). DYNs mediate alcohol-induced impairment of learning and memory, while KOR antagonists block excessive, compulsive-like drug and alcohol self-administration in animal models. In human brain, the DYN/KOR system may undergo adaptive changes, which along with neuronal loss, may contribute to alcohol-associated cognitive deficit. We addressed this hypothesis by comparing the expression levels and co-expression (transcriptionally coordinated) patterns of PDYN and KOR (OPRK1) genes in dorsolateral prefrontal cortex (dlPFC) between human alcoholics and controls. Postmortem brain specimens of 53 alcoholics and 55 controls were analyzed. PDYN was found to be downregulated in dlPFC of alcoholics, while OPRK1 transcription was not altered. PDYN downregulation was confined to subgroup of subjects carrying C, a high-risk allele of PDYN promoter SNP rs1997794 associated with alcoholism. Changes in PDYN expression did not depend on the decline in neuronal proportion in alcoholics, and thereby may be attributed to transcriptional adaptations in alcoholic brain. Absolute expression levels of PDYN were lower compared to those of OPRK1, suggesting that PDYN expression is a limiting factor in the DYN/KOR signaling, and that the PDYN downregulation diminishes efficacy of DYN/KOR signaling in dlPFC of human alcoholics. The overall outcome of the DYN/KOR downregulation may be disinhibition of neurotransmission, which when overactivated could contribute to formation of alcohol-related behavior.

Epigenetic regulation of the kappa opioid receptor gene by an insertion–deletion in the promoter region

Preclinical and clinical studies have demonstrated that the kappa opioid receptor (KOR) regulates reward, hedonic tone and emotions. At therapeutic level, on-going clinical trials are assessing the potential of targeting the KOR for the management of depression, anxiety disorders and substance use disorders. However, genetic polymorphisms in the KOR gene that potentially contribute to its implication in these phenotypes have been poorly studied. Here we investigated an insertion–deletion in the promoter region of KOR (rs35566036), recently associated with alcohol addiction, in a cohort of depressed subjects who died by suicide, as well as psychiatrically healthy individuals. Focusing on 3 brain regions (anterior insula, anterior cingulate cortex, and mediodorsal thalamus), we characterized the functional impact of this structural variant on the expression and patterns of DNA methylation of the KOR gene, using qPCR and targeted Bisulfite-Sequencing, respectively. While there was no significant change in the expression of KOR as a function of the insertion–deletion, or as a function of disease status in any brain region, we found that this variant strongly determines DNA methylation in KOR promoter, leading to a significant decrease in methylation levels of 8 nearby CpG dinucleotides located approximately 500 base pairs upstream the transcription start site. In addition, our results suggest a possible association between the insertion–deletion and depression; however, this result should be tested in larger populations. In sum, in this study we uncovered an epigenetic mechanism potentially contributing to KOR dysfunction in carriers of the insertion–deletion.

Association Between Genetic Polymorphisms and Pain Sensitivity in Patients with Hip Osteoarthritis.

Factors such as age, gender, and genetic polymorphisms may explain individual differences in pain phenotype. Genetic associations with pain sensitivity have previously been investigated in osteoarthritis patients, with a focus on the P2X7, TRPV1, and TACR1 genes. However, other genes may play a role as well. Osteoarthritis is a common joint disease, and many patients suffering from this disease are thought to have increased sensitivity to noxious stimuli resulting from sensitization in the nociceptive system. The aim of this study was to investigate if genetic variants of mu, kappa, and delta opioid receptor genes (OPRM1, OPRK1, and OPRD1) and the catechol-O-methyltransferase gene (COMT) influenced the pain phenotype in patients with osteoarthritis. The frequencies of 17 polymorphisms were examined. Pain sensitivity was assessed preoperatively by (1) hip rotation, (2) contact heat stimulation, (3) conditioned pain modulation effect, and (4) pressure stimulation at the tibia in both the affected and the unaffected leg. Ninety-two patients (mean age 66 years) with unilateral hip osteoarthritis were included in the study. Carriage of the OPRM1 rs589046T allele was found to be associated with increased pain ratings during hip rotation (P = 0.04) and increased conditioned pain modulation (P = 0.049). Carriage of the OPRD1 rs2234918C allele was found to be associated with an increased pain detection threshold to contact heat stimulation (P = 0.001). No other associations were found (all P > 0.05). Results from the present study suggest that, in patients with hip osteoarthritis, genetic variants in OPRM1 and OPRD1 may contribute to the pain phenotype.

How Does Stress-Induced Activation of the Kappa Opioid System Increase Addiction Risk?

How Does Stress-Induced Activation of the Kappa Opioid System Increase Addiction Risk?

Development of Functionally Selective, Small Molecule Agonists at Kappa Opioid Receptors

The kappa opioid receptor (KOR) is widely expressed in the CNS and can serve as a means to modulate pain perception, stress responses, and affective reward states. Therefore, the KOR has become a prominent drug discovery target toward treating pain, depression, and drug addiction. Agonists at KOR can promote G protein coupling and βarrestin2 recruitment as well as multiple downstream signaling pathways, including ERK1/2 MAPK activation. It has been suggested that the physiological effects of KOR activation result from different signaling cascades, with analgesia being G protein-mediated and dysphoria being mediated through βarrestin2 recruitment. Dysphoria associated with KOR activation limits the therapeutic potential in the use of KOR agonists as analgesics; therefore, it may be beneficial to develop KOR agonists that are biased toward G protein coupling and away from βarrestin2 recruitment. Here, we describe two classes of biased KOR agonists that potently activate G protein coupling but weakly recruit βarrestin2. These potent and functionally selective small molecule compounds may prove to be useful tools for refining the therapeutic potential of KOR-directed signaling in vivo.

A variant on the kappa opioid receptor gene (OPRK1) is associated with stress response and related drug craving, limbic brain activation and cocaine relapse risk

Stress increases drug craving and relapse risk. The kappa opioid receptor gene (OPRK1) mediates stress responses. Here, we examined whether the OPRK1 rs6989250 C>G affects stress-induced cocaine craving and cortisol responses, subsequent cocaine relapse risk and the neural response to stress using functional magnetic resonance imaging (fMRI) in cocaine dependence. Sixty-seven treatment-engaged, abstinent cocaine-dependent African-Americans were genotyped (CG: N=10; CC: N=57) and participated in a 3-day experiment in which they were exposed to personalized script-driven imagery of stress, drug cues and neutral scenarios, one condition per day, randomly assigned and counterbalanced across subjects. Repeated measures of craving and cortisol were obtained. The subjects were followed prospectively for 90 days to assess relapse risk. A follow-up preliminary fMRI experiment assessed neural responses to stress, drug cue and neutral conditions in matched CG (N=5) and CC (N=8) subgroups. We found greater stress-induced craving (P=0.019), higher cortisol during stress and cue relative to the neutral condition (P's<0.003), and increased cocaine relapse risk (P=0.0075) in the CG compared with the CC group. The CG relative to the CC group also showed greater activation of limbic and midbrain regions during stress and cues relative to the neutral condition with additional stress-induced activation in the right amygdala/hippocampus (P<0.05, whole-brain corrected). These results suggest that OPRK1 is associated with stress-induced craving and cortisol, hyperactive hypothalamus/thalamus–midbrain–cerebellum responses, and also associated with greater subsequent cocaine relapse risk. Future studies to replicate these findings in a larger sample size are warranted.

Polymorphisms of the Kappa Opioid Receptor and Prodynorphin Genes

Studies indicate cross-desensitization between opioid receptors (eg, kappa opioid receptor, OPRK1) and chemokine receptors (eg, CXCR4) involved in HIV infection. Whether gene variants of OPRK1 and its ligand, prodynorphin (PDYN), influence the outcome of HIV therapy was tested. Three study points, admission to the Women's Interagency HIV Study, initiation of highly active antiretroviral therapy (HAART), and the most recent visit, were chosen for analysis as crucial events in the clinical history of the HIV patients. Regression analyses of 17 variants of OPRK1 and 11 variants of PDYN with change of viral load (VL) and CD4 count between admission and initiation of HAART and initiation of HAART to the most recent visit to Women's Interagency HIV Study were performed in 598 HIV+ subjects, including African Americans, Hispanics, and Whites. Association with HIV status was done in 1009 subjects. Before HAART, greater VL decline (improvement) in carriers of PDYN IVS3+189C>T and greater increase of CD4 count (improvement) in carriers of OPRK -72C>T were found in African Americans. Also, greater increase of CD4 count in carriers of OPRK1 IVS2+7886A>G and greater decline of CD4 count (deterioration) in carriers of OPRK1 -1205G>A were found in Whites. After HAART, greater decline of VL in carriers of OPRK1 IVS2+2225G>A and greater increase of VL in carriers of OPRK1 IVS2+10658G>T and IVS2+10963A>G were found in Whites. Also, a lesser increase of CD4 count was found in Hispanic carriers of OPRK1 IVS2+2225G>A. OPRK1 and PDYN polymorphisms may alter severity of HIV infection and response to treatment.

Multigenerational effects of adolescent morphine exposure on dopamine D2 receptor function

The use and misuse of prescription opiates in adolescent populations, and in particular, adolescent female populations, has increased dramatically in the past two decades. Given the significant role that opioids play in neuroendocrine function, exposure to opiates during this critical developmental period could have significant consequences for the female, as well as her offspring. In the current set of studies, we utilized the female rat to model the transgenerational impact of adolescent opiate exposure. We examined locomotor sensitization in response to the dopamine D2/D3 receptor agonist quinpirole in the adult male progeny (F1 and F2 generations) of females exposed to morphine during adolescence. All females were drug-free for at least 3weeks prior to conception, eliminating the possibility of direct fetal exposure to morphine. Both F1 and F2 progeny of morphine-exposed females demonstrated attenuated locomotor sensitization following repeated quinpirole administration. These behavioral effects were coupled with increased quinpirole-induced corticosterone secretion and upregulated kappa opioid receptor and dopamine D2 receptor (D2R) gene expression within the nucleus accumbens. These results suggest significant modifications in response to repeated D2R activation in the progeny of females exposed to opiates during adolescence. Given the significant role that the D2R plays in psychopathology, adolescent opiate exposure could shift the vulnerability of future offspring to psychological disorders, including addiction. Moreover, that effects are also observed in the F2 generation suggests that adolescent opiate exposure can trigger transgenerational epigenetic modifications impacting systems critical for motivated behavior.

Dynorphin-Kappa Opioid Receptor Signaling Partly Mediates Estrogen Negative Feedback Effect on LH Pulses in Female Rats

Accumulating evidence suggests that the arcuate nucleus (ARC) kisspeptin/neurokinin B (NKB)/dynorphin (KNDy) neurons play a role in estrogen negative feedback action on pulsatile gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) release. The present study aimed to determine if dynorphin (Dyn) is involved in estrogen negative feedback on pulsatile GnRH/LH release. The effect of the injection of nor-binaltorphimine (nor-BNI), a kappa-opioid receptor (KOR) antagonist, into the third cerebroventricle (3V) on LH pulses was determined in ovariectomized (OVX) adult female rats with/without replacement of negative feedback levels of estradiol (low E2). The mean LH concentrations and baseline levels of LH secretion in nor-BNI-injected, low E2-treated rats were significantly higher compared with vehicle-treated controls. On the other hand, the nor-BNI treatment failed to affect any LH pulse parameters in OVX rats without low E2 treatment. These results suggest that Dyn is involved in the estrogen negative feedback regulation of pulsatile GnRH/LH release. The low E2 treatment had no significant effect on the numbers of ARC Pdyn (Dyn gene)-,Kiss1- and Tac2 (NKB gene)-expressing cells. The treatment also did not affect mRNA levels of Pdyn and Oprk1 (KOR gene) in the ARC-median eminence region, but significantly increased the ARC kisspeptin immunoreactivity. These findings suggest that the negative feedback level of estrogen suppresses kisspeptin release from the ARC KNDy neurons through an unknown mechanism without affecting the Dyn and KOR expressions in the ARC. Taken together, the present result suggests that Dyn-KOR signaling is a part of estrogen negative feedback action on GnRH/LH pulses by reducing the kisspeptin release in female rats.

Delta and kappa opioid receptor polymorphisms influence the effects of naltrexone on subjective responses to alcohol

Naltrexone, one of four FDA-approved pharmacotherapies for alcohol dependence, has shown moderate efficacy in clinical trials. Pharmacogenetic effects have been reported such that allelic variation at the gene encoding the mu-opioid receptor (OPRM1, rs1799971) predicts naltrexone-induced blunting of the positively reinforcing effects of alcohol. However, naltrexone also binds, albeit to a lesser degree, to kappa and delta opioid receptors in the brain. This alternate binding presents the possibility that single nucleotide polymorphisms (SNPs) in the kappa and delta opioid receptor (OPRK1 and OPRD1) genes may contribute to naltrexone pharmacogenetics. Therefore, the goal of this exploratory study was to re-examine data from a double-blind placebo controlled laboratory trial of naltrexone for pharmacogenetic effects at kappa and delta opioid receptor tag SNPs. Participants were 40 heavy drinkers (12 female) who underwent an intravenous alcohol challenge paradigm after receiving naltrexone (50mg) or placebo in randomized and crossover fashion. Dependent variables were self-reported alcohol-induced stimulation, sedation, and craving. Multilevel models revealed a significant Naltrexone×OPRK1 Genotype (rs997917) interaction predicting alcohol-induced sedation, such that TT homozygotes reported lower naltrexone-induced alcohol sedation as compared to carriers of the C allele. Moreover, there was a significant Naltrexone×OPRD1 Genotype (rs4654327) interaction predicting alcohol-induced stimulation and craving, such that carriers of the A allele at this locus reported greater naltrexone-induced blunting of alcohol stimulation and alcohol craving compared to GG homozygotes. These findings suggest that additional pharmacogenetic effects in the opioid receptor system may account for individual differences in response to naltrexone in the human laboratory.

Epistatic effects between variants of kappa-opioid receptor gene and A118G of mu-opioid receptor gene increase susceptibility to addiction in Indian population

Unequivocal evidence suggests contribution of κ-opioid receptor (KOR) in addiction to drugs of abuse. A study was undertaken to identify the single nucleotide polymorphisms (SNP) at selective areas of kappa opioid receptor 1 (OPRK1) gene in heroin as well as in alcohol addicts and to compare them with that in control population. The potential interaction of the identified KOR SNPs with A118G of μ opioid receptor was also investigated. Two hundred control subjects, one hundred thirty heroin and one hundred ten alcohol addicts, all male and residing in Kolkata, a city in eastern India, volunteered for the study. Exons 3 and 4 of OPRK1 and the SNP, A118G of mu opioid receptor 1 (OPRM1) in the DNA samples were genotyped by sequencing and restriction fragment length polymorphism respectively. The SNPs identified in the population were analyzed by odds ratio and its corresponding 95% confidence interval was estimated using logistic regression models. SNP-SNP interactions were also investigated. Three SNPs of OPRK1, rs16918875, rs702764 and rs963549, were identified in the population, none of which showed significant association with addiction. On the other hand, significant association was observed for A118G with heroin addiction (χ²=7.268, P=0.0264) as well as with alcoholic addition (χ²=6.626, P=0.0364). A potential SNP-SNP interaction showed that the odds of being addicted was 2.51 fold in heroin subjects [CI (95%)=1.1524 to 5.4947, P=0.0206] and 2.31 fold in alcoholics [CI (95%)=1.025 to 5.24, P=0.0433] with the OPRK1 (rs16918875) and A118G risk alleles than without either. A significant interaction was also identified between GG/AG of A118G and GG of rs702764 [O.R (95%)=2.04 (1.279 to 3.287), P=0.0029] in case of opioid population. Our study suggests that set associations of polymorphisms may be important in determining the risk profile for complex diseases such as addiction.