Altered levels of basal cortisol in healthy subjects with a 118G allele in exon 1 of the Mu opioid receptor gene

Genetic Vulnerability to Opioid Addiction

Opioid addiction, also referred to as opioid use disorder, continues to be a devastating problem throughout the world. Familial relation and twin studies have revealed opioid addiction, like other addictive diseases, to be profoundly influenced by genetics. Genetics studies of opioid addiction have affirmed the importance of genetics contributors in susceptibility to develop opioid addiction, and also have important implications on treatment for opioid addiction. But the complexity of the interactions of multiple genetic variants across diverse genes, as well as substantial differences in allelic frequencies across populations, thus far limits the predictive value of individual genetics variants.

The μ-opioid receptor gene A118G polymorphism is associated with insecure attachment in children with disruptive mood regulation disorder and their mothers

BACKGROUND

The A118G single nucleotide polymorphism (SNP) of the μ-opioid receptor gene, with high expression of the A allele and low expression of the G allele, has been associated with emotional/behavioral dysregulation and depressive disorders and is recognized as a mediator of affiliative behavior. No study has thus far investigated this SNP in school-age children with disruptive mood regulation disorder (DMDD). This study compared a sample of healthy children and their mothers with a sample of children with DMDD and their mothers, evaluating whether insecure attachment and psychopathological symptoms are associated with A allele- or G allele-carrying mothers and children and whether caregiving capacities are associated with A allele- or G allele-carrying mothers.

METHODS

For evaluation of their psychopathological symptoms and attachment styles, mothers filled out the CBCL/6-18, the SCL-90-R, and the ECR. To evaluate the types of relationship children were experiencing with their mothers, children filled out the ECR-revised child version and the PBI. Genotypic analyses were conducted on DNA samples obtained by buccal swabbing from children and mothers.

RESULTS

An insecure attachment style was more frequent in mothers and children carrying the G allele (G/G + A/G genotypes). In the clinical sample, G allele-carrying children scored higher than homozygous A/A ones on the subscales of Withdrawal and Conduct Problems. G-carrying mothers showed higher interpersonal sensitivity, depression, hostility, and paranoid ideation and provided less care than A/A mothers.

CONCLUSIONS

This study offers new insights into the associations between the A118G SNP of the μ-opioid receptor gene and emotional/behavioral functioning, attachment style in children, and psychopathology and caregiving ability in mothers.

Disaggregating physiological components of cortisol output: A novel approach to cortisol analysis in a clinical sample - A proof-of-principle study

Although childhood adversity (CA) increases risk for subsequent mental illnesses, developmental mechanisms underpinning this association remain unclear. The hypothalamic-pituitary-adrenal axis (HPAA) is one candidate system potentially linking CA with psychopathology. However, determining developmental effects of CA on HPAA output and differentiating these from effects of current illness has proven difficult. Different aspects of HPAA output are governed by differentiable physiological mechanisms. Disaggregating HPAA output according to its biological components (baseline tonic cortisol, background diurnal variation, phasic stress response) may improve precision of associations with CA and/or psychopathology. In a novel proof-of-principle investigation we test whether different predictors, CA (distal risk factor) and current depressive symptoms, show distinct associations with dissociable HPAA components. A clinical group (aged 16-25) at high-risk for developing severe psychopathology (n = 20) were compared to age and sex matched healthy controls (n = 21). Cortisol was measured at waking (x4), following stress induction (x8), and during a time-environment-matched non-stress condition. Using piecewise multilevel modeling, stress responses were disaggregated into increase and decrease, while controlling for waking cortisol, background diurnal output and confounding variables. Elevated waking cortisol was specifically associated with higher CA scores. Higher non-stress cortisol was specifically associated with higher depressive scores. Following stress induction, depressive symptoms attenuated cortisol increase, whilst CA attenuated cortisol decrease. The results support a differential HPAA dysregulation hypothesis where physiologically dissociable components of HPAA output are differentially associated with distal (CA) or proximal (depressive symptoms) predictors. This proof-of-principle study demonstrates that future cortisol analyses need to disaggregate biologically independent mechanisms of HPAA output.

Oprm1 A112G, a single nucleotide polymorphism, alters expression of stress-responsive genes in multiple brain regions in male and female mice

BACKGROUND

OPRM1 A118G, a functional human mu-opioid receptor (MOR) polymorphism, is associated with drug dependence and altered stress responsivity in humans as well as altered MOR signaling. MOR signaling can regulate many cellular processes, including gene expression, and many of the long-term, stable effects of drugs and stress may stem from changes in gene expression in diverse brain regions. A mouse model bearing an equivalent polymorphism (Oprm1 A112G) was previously generated and studied. Mice homozygous for the G112 allele show differences in opioid- and stress-related phenotypes.

APPROACH

The current study examines the expression of 24 genes related to drug and stress responsivity in the caudoputamen, nucleus accumbens, hypothalamus, hippocampus, and amygdala of drug-naïve, stress-minimized, male and female mice homozygous for either the G112 variant allele or the wild-type A112 allele.

RESULTS

We detected nominal genotype-dependent changes in gene expression of multiple genes. We also detected nominal sex-dependent as well as sex-by-genotype interaction effects on gene expression. Of these, four genotype-dependent differences survived correction for multiple testing: Avp and Gal in the hypothalamus and Oprl1 and Cnr1 in the hippocampus.

CONCLUSIONS

Changes in the regulation of these genes by mu-opioid receptors encoded by the G112 allele may be involved in some of the behavioral and molecular consequences of this polymorphism observed in mice.

Cortisol Stress Response in Men and Women Modulated Differentially by the Mu-Opioid Receptor Gene Polymorphism OPRM1 A118G

Differences in stress reactivity may affect long-term health outcomes, but there is little information on how these differences arise. The stress axis is regulated by, in part, the endogenous opioid, beta-endorphin, acting on mu-opioid receptors. Persons carrying one or two copies of the G allele of the mu-opioid receptor gene (OPRM1 A118G) may have higher receptor binding for beta-endorphin compared with AA homozygotes that may contribute to individual differences in cortisol reactivity to stress, leading to a relative blunting of cortisol stress reactivity in G allele genotypes. We measured cortisol in 251 young adults (69 GA/GG vs 182 AA genotypes) exposed to mental arithmetic plus public speaking stress relative to a resting control day. Women had smaller cortisol responses than men (F=10.2, p=0.002), and women with GA or GG genotypes (N=39) had an absence of cortisol response relative to AA carriers (N=110) (F=18.4, p<0.0001). Male genotypes had no such difference in response (F=0.29). Cortisol response following mu-opioid receptor blockade using naltrexone in 119 of these subjects unmasked a greater tonic opioid inhibition of cortisol secretion in women (N=64), consistent with their blunted stress reactivity. Compared with men, women may have cortisol stress responses that are more heavily regulated by endogenous opioid mechanisms, and the OPRM1 GA/GG genotypes may affect females differentially relative to males. Diminished cortisol responses to stress may have consequences for health behaviors in women with GA/GG genotypes.

Genetics of opiate addiction

Addiction to MOP-r agonists such as heroin (and also addiction to prescription opioids) has reemerged as an epidemic in the twenty first century, causing massive morbidity. Understanding the genetics contributing to susceptibility to this disease is crucial for the identification of novel therapeutic targets, and also for discovery of genetic markers which would indicate relative protection or vulnerability from addiction, and relative responsiveness to pharmacotherapy. This information could thus eventually inform clinical practice. In this review, we focus primarily on association studies of heroin and opiate addiction, and further describe the studies which have been replicated in this field, and are thus more likely to be useful for translational efforts.

Subjective health complaints in patients with lumbar radicular pain and disc herniation are associated with a sex - OPRM1 A118G polymorphism interaction: a prospective 1-year observational study

Background

Earlier observations show that development of persistent pain may be associated with the genetic variability in the gene encoding for the μ-opioid receptor 1, the OPRM1 A118G (rs1799971). The aim of this study was to investigate the association between OPRM1 genotype and subjective health complaints in patients with radicular pain and disc herniation.

Methods

A prospective, 1-year observational study was conducted at a hospital back clinic, including 118 Caucasian patients with lumbar radicular pain and MRI confirmed disc herniation. Single nucleotide polymorphism genotyping regarding the OPRM1 A118G was performed. The data of individuals with AA versus AG or GG were analysed separately by linear mixed models. The Subjective Health Complaints Inventory (0-81) including 27 common complaints experienced the previous month on a scale from not at all (0) to severe (3) was used as outcome. Pain, prior duration of leg pain, age, smoking status, and lumbar disc surgery were considered as covariates.

Results

In total 23 of 118 patients were carriers of the OPRM1 G-allele. All patients except female carriers of the G-allele reported a decrease in pain from baseline to 1 year. Female carriers of the G-allele reported significantly higher subjective health complaints score during the study time span than male carriers of the G-allele when controlling for pain and pain duration.

Conclusion

The present data indicate that, when controlling for pain intensity and duration, subjective health complaints are associated with a sex - OPRM1 A118G polymorphism interaction in patients with radicular pain.

Analysis of acute pain scores and skin conductance measurements in infants

BACKGROUND

Skin conductance (SC) has been previously used to measure acute post-operative pain in adults and older children (>1year old).We have investigated the ability of SC to predict the severity of post-operative pain scores in the exclusively infant population.

METHODS

Infants (ages 6-12months) scheduled for elective surgery were recruited for the study. Data for behavioral pain scores and SC values - frequency of electrodermal responses per second (EDR/s), peak and basal levels, were recorded in the post-anesthesia care unit (PACU). Blood samples were collected for genomic studies, including single nucleotide polymorphisms (SNP) in morphine opioid receptor (MOR) A118G and the catechol-O-methyltransferase (COMT) G1947A genes.

RESULTS

31 infants, mean age 8.9months (±1.9); mean weight 8.5kg (±1.1) were included in the final study analysis. With every 0.1 unit increase in peak values noted on SC, the odds of higher pain scores were found to be 5% greater (p=0.03). For predictability of moderate to severe pain, the area under the curve, sensitivity and specificity were 0.64, 90.9% and 51.4% respectively for peak values and 0.66, 54.5% and 79.4% respectively for EDR/s values. Genotyping performed in 16 out of 31 infants demonstrated that the carriers of MOR 118G allele had consistently higher basal SC values in the PACU.

CONCLUSION

Peak SC values may serve as indicators of unmitigated pain. Further studies are needed to fully investigate the effect of MOR A118G SNP on the post operative pain scores and SC values in the larger infant population in order to validate both the clinical significance of the skin conductance for routine pain assessment in infants and the observed genetic effect.

Mu-opioid receptor A118G polymorphism in healthy volunteers affects hypothalamic-pituitary-adrenal axis adrenocorticotropic hormone stress response to metyrapone

The mu-opioid receptor encoded by the gene OPRM1 plays a primary role in opiate, alcohol, cocaine and nicotine addiction. Studies using opioid antagonists demonstrate that the mu-opioid receptor (MOP-r) also mediates the hypothalamic-pituitary-adrenal (HPA) axis stress response. A common polymorphism in exon one of the MOP-r gene, A118G, has been shown to significantly alter receptor function and MOP-r gene expression; therefore, this variant likely affects HPA-axis responsivity. In the current study, we have investigated whether the presence of the 118AG variant genotype affects HPA axis responsivity to the stressor metyrapone, which transiently blocks glucocorticoid production in the adrenal cortex. Forty-eight normal and healthy volunteers (32 men, 16 women) were studied, among whom nine men and seven women had the 118AG genotype. The 118G allele blunted the adrenocorticotropic hormone (ACTH) response to metyrapone. Although there was no difference in basal levels of ACTH, subjects with the 118AG genotype had a more modest rise and resultant significantly lower ACTH levels than those with the prototype 118AA at the 8-hour time point (P < 0.02). We found no significant difference between genders. These findings suggest a relatively greater tonic inhibition at hypothalamic-pituitary sites through the mu-opioid receptor and relatively less cyclical glucocorticoid inhibition in subjects with the 118G allele.

Pain intensity the first year after lumbar disc herniation is associated with the A118G polymorphism in the opioid receptor mu 1 gene: evidence of a sex and genotype interaction

Earlier studies have shown that the single nucleotide polymorphism (SNP) A118G (rs1799971) in the opioid receptor mu 1 (OPRM1) gene may affect pain sensitivity. In the present study we investigated whether the A118G SNP could predict clinical outcome regarding progression of pain intensity and disability in patients with low back pain and sciatica after lumbar disc herniation. Patients (n = 258) with lumbar disc herniation and sciatic pain, all European-Caucasian, were recruited from two hospitals in Norway. Pain and disability were rated on a visual analog scale (VAS), by McGill Sensory Questionnaire and by Oswestry Disability Index (ODI) over a 12 months period. The data revealed a significant interaction between sex and A118G genotype regarding the pain intensity during the 12 months (VAS, p = 0.002; McGill, p = 0.021; ODI, p = 0.205, repeated-measures ANOVA). We found that */G women had a slower recovery rate than the */G men. Actually, the */G women had 2.3 times as much pain as the */G men 12 months after the disc herniation (VAS, p = 0.043, one-way ANOVA; p = 0.035, Tukey HSD). In contrast, the A/A women and A/A men seemed to have almost exactly the same recovery rate. The present data suggest that OPRM1 G allele increases the pain intensity in women, but has a protective effect in men the first year after disc herniation.

The genetics of the opioid system and specific drug addictions

Addiction to drugs is a chronic, relapsing brain disease that has major medical, social, and economic complications. It has been established that genetic factors contribute to the vulnerability to develop drug addiction and to the effectiveness of its treatment. Identification of these factors may increase our understanding of the disorders, help in the development of new treatments and advance personalized medicine. In this review, we will describe the genetics of the major genes of the opioid system (opioid receptors and their endogenous ligands) in connection to addiction to opioids, cocaine, alcohol and methamphetamines. Particular emphasis is given to association and functional studies of specific variants. We will provide information on the sample populations and the size of each study, as well as a list of the variants implicated in association with addiction-related phenotypes, and with the effectiveness of pharmacotherapy for addiction.

μ-Opioid receptor gene A118G polymorphism predicts survival in patients with breast cancer

BACKGROUND

Preclinical studies suggest that opioids may promote tumor growth. Genetic polymorphisms have been shown to affect opioid receptor function and to modify the clinical effects of morphine. In this study we assessed the association between six common polymorphisms in the μ-opioid receptor gene, including the well known A118G polymorphism, and breast cancer survival.

METHODS

A total of 2,039 women ages 23-74 yr (38% African-American, 62% European-American, 55% postmenopausal) diagnosed with breast cancer between 1993-2001 were followed through 2006. Genotyping was performed using the TaqMan platform (Applied Biosystems Inc., Foster City, CA). Kaplan-Meier curves, log-rank tests, and Cox proportional hazard models were used to examine the association between each genotype and survival.

RESULTS

After Bonferroni correction for multiple testing, patient genotype at A118G was associated with breast cancer-specific mortality at 10 yr. Women with one or more copies of the G allele had decreased breast cancer-specific mortality (P < 0.001). This association was limited to invasive cases only; effect size appeared to increase with clinical stage. Cox regression model adjusted for age and ethnicity also showed decreased mortality in A/G and G/G genotypes compared with A/A genotype (hazard ratio = 0.57 [0.38, 0.85] and 0.32 [0.22, 0.49], respectively; P = 0.006).

CONCLUSIONS

These results suggest that opioid pathways may be involved in tumor growth. Further studies examining the association between genetic variants influencing opioid system function and cancer survival are warranted.

Association of polymorphisms of the mu opioid receptor gene with the severity of HIV infection and response to HIV treatment

BACKGROUND

Mu opioid receptor (OPRM1) ligands may alter expression of chemokines and chemokine receptors involved in penetration of human immunodeficiency virus (HIV) type 1 into the cell. We suggest that OPRM1 variants may affect the pathophysiology of HIV infection.

METHODS

DNA samples from 1031 eligible African Americans, Hispanics, and whites from the Women's Interagency HIV Study (WIHS) who were alive as of April 2006 were analyzed. We performed regression analysis of association of 18 OPRM1 variants with a change of viral load and CD4 cell count during 2 periods: between admission to WIHS and the start of highly active antiretroviral therapy (HAART) (interval X) and between the start of HAART and the most recent WIHS visit (interval Y), and examined the association of these variants with HIV status.

RESULTS

Regardless of genotype, a significant decrease in viral load during interval X was found for each ethnicity. Whites with allele G of the functional polymorphism 118A > G (reference sequence rs1799971) showed a smaller decrease in viral load; those bearing minor alleles IVS1 + 1050A, IVS1 + 14123A, and IVS2 + 31A showed a larger decrease in viral load over interval X (0.01 < P < .05). Hispanics with the same alleles showed a greater increase in CD4 cell count over interval Y (0.01 < P < .05). We found an association between OPRM1 variants and HIV status in African Americans and whites.

CONCLUSIONS

OPRM1 polymorphisms may alter the severity of HIV infection before and after HAART.

Micro Opioid Receptor A118G Polymorphism and Post-Operative Pain: Opioids' Effects on Heterozigous Patients

The Single-Nucleotide-Polymorphism (SNP) 118A>G in the μ-1 Opioid Receptor gene (OPRM1) is associated with a decrease in the analgesic effects of opioids. The aim of this study is to assess whether 118A>G polymorphism could influence the analgesic response to opioid-based postoperative pain (POP) therapy. The study consisted of two parts: section α, observational, included 199 subjects undergoing scheduled surgical procedures with pain management standardized on surgery invasiveness and on expected level of postoperative pain; section β, randomized, included 41 women undergoing scheduled caesarean delivery with continuous intra-operative epidural anesthesia and post-operative analgesia (CEA). In both sections, POP was measured over 48 h (T6h-T24h-T48h) by the visual analogue scale (VAS). In section β we also tested the responsiveness of hypothalamic-pituitary-adrenal axis (HPA) expressed by Cortisol levels. In section α, with cluster analysis, subjects were analyzed according to their genotype: a group (#1) of 34 patients reporting VAS score >3 at every time lapse was identified and included only A118G carriers, while wild-type (A118A - absence of 118A>G polymorphism) patients were unevenly distributed between those with cluster #2 (VAS score <3 at every study steps) and those with cluster #3 (VAS score progressively reducing from T6h). In section (3, A118G carriers receiving epidural sufentanil had the lowest VAS scores at T24h; also in these patients, Cortisol levels remained more stable, with a mild decrease at T6h. This study shows that the OPRM1 118A>G polymorphism affects postoperative pain response in heterozygous patients: they have a different postoperative pain response than patients with wild-type genes, which may affect the efficacy of the analgesic therapy.

Extreme marginalization: addiction and other mental health disorders, stigma, and imprisonment

Major well-defined medical problems that are, in part, the unfortunate outcome of a negative social environment may include specific addictive diseases and other mental health disorders, in particular the affective disorders of anxiety, depression, social phobia, and posttraumatic stress syndrome. This overview touches on the topic of extreme marginalization associated with addiction and other mental health disorders, along with arrest, imprisonment, and parole. All of these are characterized by a lasting stigma that hauntingly continues to affect each person suffering from any of these problems.

Child μ-opioid receptor gene variant influences parent-child relations

Variation in the μ-opioid receptor gene has been associated with early social behavior in mice and rhesus macaques. The current study tested whether the functional OPRM1 A118G predicted various indices of social relations in children. The sample included 226 subjects of self-reported European ancestry (44% female; mean age 13.6, SD=2.2) who were part of a larger representative study of children aged 9-17 years in rural North Carolina. Multiple aspects of recent (past 3 months) parent-child relationship were assessed using the Child and Adolescent Psychiatric Assessment. Parent problems were coded based upon a lifetime history of mental health problems, substance abuse, or criminality. Child genotype interacted with parent behavior such that there were no genotype differences for those with low levels of parent problems; however, when a history of parent problems was reported, the G allele carriers had more enjoyment of parent-child interactions (mean ratio (MR)=3.5, 95% CI=1.6, 8.0) and fewer arguments (MR=3.1, 95% CI=1.1, 8.9). These findings suggest a role for the OPRM1 gene in the genetic architecture of social relations in humans. In summary, a variant in the μ-opioid receptor gene (118G) was associated with improved parent-child relations, but only in the context of a significant disruption in parental functioning.

Human behavioral pharmacology, past, present, and future: symposium presented at the 50th annual meeting of the Behavioral Pharmacology Society

A symposium held at the 50th annual meeting of the Behavioral Pharmacology Society in May 2007 reviewed progress in the human behavioral pharmacology of drug abuse. Studies on drug self-administration in humans are reviewed that assessed reinforcing and subjective effects of drugs of abuse. The close parallels observed between studies in humans and laboratory animals using similar behavioral techniques have broadened our understanding of the complex nature of the pharmacological and behavioral factors controlling drug self-administration. The symposium also addressed the role that individual differences, such as sex, personality, and genotype play in determining the extent of self-administration of illicit drugs in human populations. Knowledge of how these factors influence human drug self-administration has helped validate similar differences observed in laboratory animals. In recognition that drug self-administration is but one of many choices available in the lives of humans, the symposium addressed the ways in which choice behavior can be studied in humans. These choice studies in human drug abusers have opened up new and exciting avenues of research in laboratory animals. Finally, the symposium reviewed behavioral pharmacology studies conducted in drug abuse treatment settings and the therapeutic benefits that have emerged from these studies.

OPRM1 SNP (A118G): involvement in disease development, treatment response, and animal models

Endogenous opioids acting at mu-opioid receptors mediate many biological functions. Pharmacological intervention at these receptors has greatly aided in the treatment of acute and chronic pain, in addition to other uses. However, the development of tolerance and dependence has made it difficult to adequately prescribe these therapeutics. A common single nucleotide polymorphism (SNP), A118G, in the mu-opioid receptor gene can affect opioid function and, consequently, has been suggested to contribute to individual variability in pain management and drug addiction. Investigation into the role of A118G in human disease and treatment response has generated a large number of association studies across various disease states as well as physiological responses. However, characterizing the functional consequences of this SNP and establishing if it causes or contributes to disease phenotypes have been significant challenges. In this manuscript, we will review a number of association studies as well as investigations of the functional impact of this gene variant. In addition, we will describe a novel mouse model that was generated to recapitulate this SNP in mice. Evaluation of models that incorporate known human genetic variants into a tractable system, like the mouse, will facilitate the understanding of discrete contributions of SNPs to human disease.

Acute HPA axis response to naltrexone differs in female vs. male smokers

BACKGROUND

Both opioid antagonist administration and cigarette smoking acutely increase hypothalamic-pituitary-adrenal (HPA) axis activity as measured by adrenocorticotropic hormone (ACTH) and cortisol levels. However, male and female smokers may differ in their response to the opioid antagonist naltrexone, which may be partially mediated by sex differences in HPA axis function. Smokers, as a group, have frequently been shown to have HPA axis dysfunction, which may have relevance to the course and maintenance of nicotine dependence. The purpose of this study was to examine possible sex differences in HPA axis function by comparing stress-hormone response to naltrexone within healthy male and female smokers. Additionally, exploratory analyses compared the combined effects of naltrexone and cigarette smoking on hormonal responsivity between the sexes.

METHOD

Thirty-eight healthy smokers (22 men) were tested in two separate morning sessions after 12h of smoking abstinence. For women, self-reports of menstrual cycle information were obtained prior to each session (date of last menstruation, cycle length, reproductive phase, etc.). Each participant received 50mg naltrexone or placebo capsule (in random order) and plasma levels of ACTH and cortisol were assessed at regular intervals for several hours. A subgroup of 12 participants underwent a similar, additional session in which they smoked a single cigarette three hours after naltrexone administration.

RESULTS

Naltrexone significantly increased ACTH and cortisol levels in women, but not men (DrugxSexxTime, p<0.05). A post hoc analysis suggested that women at an estimated 'high estrogen' phase had a greater cortisol response (DrugxEstrogen level, p<0.05) than those at an estimated 'low estrogen' phase. Exploratory analyses showed that smoking a single cigarette potentiated naltrexone-induced increases in ACTH (p<0.05) and cortisol (p<0.01) in all participants.

CONCLUSION

The findings support the hypothesis that women are more sensitive to opioid antagonism at the level of the HPA axis. Although further studies are needed to examine mechanisms underlying these responses, both results may have clinical implications for the use of naltrexone as a treatment for nicotine dependence.

Pharmacotherapy in the treatment of addiction: methadone

Methadone maintenance treatment (MMT) is the most widely available pharmacotherapy for opioid addiction and has been shown to be an effective and safe treatment over a period of 40 years. Although women comprise approximately 40% of clients currently being treated in MMT programs, comparatively little research geared specifically toward this group has been published. This article begins with an overview of neurobiological studies on opioid addiction, including a discussion of gender differences, followed by a review of the pharmacology of methadone. The authors then examine the particular needs and differences of women being treated in MMTs, including co-dependence with other substances, women's health issues, and psychosocial needs unique to this population. Research shows that women have different substance abuse treatment needs in comparison to their male counterparts. One New York City MMT program that has attempted to address these differences is highlighted.

Search for genetic markers and functional variants involved in the development of opiate and cocaine addiction and treatment

Addiction to opiates and illicit use of psychostimulants is a chronic, relapsing brain disease that, if left untreated, can cause major medical, social, and economic problems. This article reviews recent progress in studies of association of gene variants with vulnerability to develop opiate and cocaine addictions, focusing primarily on genes of the opioid and monoaminergic systems. In addition, we provide the first evidence of a cis-acting polymorphism and a functional haplotype in the PDYN gene, of significantly higher DNA methylation rate of the OPRM1 gene in the lymphocytes of heroin addicts, and significant differences in genotype frequencies of three single-nucleotide polymorphisms of the P-glycoprotein gene (ABCB1) between "higher" and "lower" methadone doses in methadone-maintained patients. In genomewide and multigene association studies, we found association of several new genes and new variants of known genes with heroin addiction. Finally, we describe the development and application of a novel technique: molecular haplotyping for studies in genetics of drug addiction.

Drug-induced and genetic alterations in stress-responsive systems: Implications for specific addictive diseases

From the earliest work in our laboratory, we hypothesized, and with studies conducted in both clinical research and animal models, we have shown that drugs of abuse, administered or self-administered, on a chronic basis, profoundly alter stress-responsive systems. Alterations of expression of specific genes involved in stress responsivity, with increases or decreases in mRNA levels, receptor, and neuropeptide levels, and resultant changes in hormone levels, have been documented to occur after chronic intermittent exposure to heroin, morphine, other opiates, cocaine, other stimulants, and alcohol in animal models and in human molecular genetics. The best studied of the stress-responsive systems in humans and mammalian species in general is undoubtedly the HPA axis. In addition, there are stress-responsive systems in other parts in the brain itself, and some of these include components of the HPA axis, such as CRF and CRF receptors, along with POMC gene and gene products. Several other stress-responsive systems are known to influence the HPA axis, such as the vasopressin-vasopressin receptor system. Orexin-hypocretin, acting at its receptors, may effect changes which suggest that it should be properly categorized as a stress-responsive system. However, less is known about the interactions and connectivity of some of these different neuropeptide and receptor systems, and in particular, about the possible connectivity of fast-acting (e.g., glutamate and GABA) and slow-acting (including dopamine, serotonin, and norepinephrine) neurotransmitters with each of these stress-responsive components and the resultant impact, especially in the setting of chronic exposure to drugs of abuse. Several of these stress-responsive systems and components, primarily based on our laboratory-based and human molecular genetics research of addictive diseases, will be briefly discussed in this review.

Association of polymorphism in the human mu-opioid receptor OPRM1 gene with proinflammatory cytokine levels and health perception

Recent studies in psychoneuroimmunology have indicated that proinflammatory cytokines cause several diseases and behaviors that overlap symptomatically with depression. It is known that the endogenous opioid peptide beta-endorphin regulates proinflammatory cytokine secretion from peripheral immune cells via mu-opioid receptor-dependent mechanisms. Therefore, it is possible that the functional polymorphism of the mu-opioid receptor gene (OPRM1, SNP: A118G) influences peripheral circulating proinflammatory cytokine levels and the health-related quality of life (QOL) even in healthy populations. In this study, we compared the serum concentrations of several proinflammatory cytokines (interleukin-2 (IL-2), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma)) and the health-related QOL between OPRM1 genotypes. Interestingly, serum concentrations of IL-6, TNF-alpha, and IFN-gamma were significantly lower and the general health score was significantly higher in carriers of the G allele, who show a strong binding of beta-endorphin to the mu-opioid receptor as compared to individuals without the G allele. Correlation analysis indicated that the general health score was negatively correlated with the IL-6 serum concentration. These results suggest that the sensitive endogenous opioid system in carriers of the G allele may suppress proinflammatory cytokine secretion from peripheral immune cells; consequently, it may influence the health perception.

Genetic susceptibility to heroin addiction: a candidate gene association study

Heroin addiction is a chronic complex disease with a substantial genetic contribution. This study was designed to identify genetic variants that are associated with susceptibility to develop heroin addiction by analyzing 1350 variants in 130 candidate genes. All subjects had Caucasian ancestry. The sample consisted of 412 former severe heroin addicts in methadone treatment, and 184 healthy controls with no history of drug abuse. Nine variants, in six genes, showed the lowest nominal P values in the association tests (P < 0.01). These variants were in noncoding regions of the genes encoding the mu (OPRM1; rs510769 and rs3778151), kappa (OPRK1; rs6473797) and delta (OPRD1; rs2236861, rs2236857 and rs3766951) opioid receptors; the neuropeptide galanin (GAL; rs694066); the serotonin receptor subtype 3B (HTR3B; rs3758987) and the casein kinase 1 isoform epsilon (CSNK1E; rs1534891). Several haplotypes and multilocus genotype patterns showed nominally significant associations (e.g. OPRM1; P = 0.0006 and CSNK1E; P = 0.0007). Analysis of a combined effect of OPRM1 and OPRD1 showed that rs510769 and rs2236861 increase the risk of heroin addiction (P = 0.0005). None of these associations remained significant after adjustment for multiple testing. This study suggests the involvement of several genes and variants in heroin addiction, which is worthy of future study.

Bidirectional translational research: Progress in understanding addictive diseases

The focus of this review is primarily on recent developments in bidirectional translational research on the addictions, within the Laboratory of the Biology of Addictive Diseases at The Rockefeller University. This review is subdivided into major interacting aspects, including (a) Investigation of neurobiological and molecular adaptations (e.g., in genes for the opioid receptors or endogenous neuropeptides) in response to cocaine or opiates, administered under laboratory conditions modeling chronic patterns of human self-exposure (e.g., chronic escalating "binge"). (b) The impact of such drug exposure on the hypothalamic-pituitary-adrenal (HPA) axis and interacting neuropeptidergic systems (e.g., opioid, orexin and vasopressin). (c) Molecular genetic association studies using candidate gene and whole genome approaches, to define particular systems involved in vulnerability to develop specific addictions, and response to pharmacotherapy. (d) Neuroendocrine challenge studies in normal volunteers and current addictive disease patients along with former addicts in treatment, to investigate differential pharmacodynamics and responsiveness of molecular targets, in particular those also investigated in the experimental and molecular genetic approaches as described above.

Effects of gender and cigarette smoking on reactivity to psychological and pharmacological stress provocation

We examined the influence of gender and smoking status on reactivity in two human laboratory stress paradigms. Participants were 46 (21 men, 25 women) healthy individuals who completed the Trier Social Stress Task (i.e., performed speech and math calculations in front of an audience) and a pharmacological stress provocation (i.e., administration of corticotrophin releasing hormone (CRH)) after an overnight hospital stay. Approximately half (53%) of the participants were smokers. Cortisol, adrenocorticotrophin hormone (ACTH), physiologic measures (heart rate, blood pressure), and subjective stress were assessed at baseline and at several time points post-task. Men demonstrated higher baseline ACTH and blood pressure as compared to women; however, ACTH and blood pressure responses were more pronounced in women. Women smokers evidenced a more blunted cortisol response as compared to non-smoking women, whereas smoking status did not affect the cortisol response in men. Finally, there was a more robust cardiovascular and subjective response to the Trier as compared to the CRH. Although preliminary, the findings suggest that women may be more sensitive than men to the impact of cigarette smoking on cortisol response. In addition, there is some evidence for a more robust neuroendocrine and physiologic response to acute laboratory stress in women as compared to men.

Role of a functional human gene polymorphism in stress responsivity and addictions

Over the past decade, enormous progress has been made in both the technical approaches and the scientific information available for studying the human genome. Therefore, increasingly, scientists have begun to address not just single-gene disorders but complex disorders. The limiting factor in most of such studies remains appropriate, well-focused detailed phenotyping of the complex disorders under study, with careful ascertainment of subjects with the specific disorder, as well as healthy control subjects.

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).

Perspectives on current directions in the neurobiology of addiction disorders relevant to genetic risk factors

There is a significant heritability of drug addiction disorders, but potential genes that may underlie such vulnerability have not been clearly identified. Common neurobiological candidates for drug abuse include genes related to dopamine, opioid neuropeptide, and glutamate transmission that play important roles in drug reward and inhibitory control. This article provides an overview of genetic polymorphisms linked to these neurobiological systems, particularly in relation to psychostimulant- and opioid-addiction vulnerability.