Naltrexone selectively elevates GABAergic neuroactive steroid levels in heavy drinkers with the Asp40 allele of the OPRM1 gene: a pilot investigation

The role of neurosteroids in posttraumatic stress disorder and alcohol use disorder: A review of 10 years of clinical literature and treatment implications

Rates of alcohol use disorder (AUD) are increasing in men and women and there are high rates of concurrent posttraumatic stress disorder (PTSD) and AUD. AUD and PTSD synergistically increase symptomatology and negatively affect treatment outcomes; however, there are very limited pharmacological treatments for PTSD/AUD. Neurosteroids have been implicated in the underlying neurobiological mechanisms of both PTSD and AUD and may be a target for treatment development. This review details the past ten years of research on pregnenolone, progesterone, allopregnanolone, pregnanolone, estradiol, testosterone and dehydroepiandrosterone/dehydroepiandrosterone-sulfate (DHEA/DHEA-S) in the context of PTSD and AUD, including examination of trauma/alcohol-related variables, such as stress-reactivity. Emerging evidence that exogenous pregnenolone, progesterone, and allopregnanolone may be promising, novel interventions is also discussed. Specific emphasis is placed on examining the application of sex as a biological variable in this body of literature, given that women are more susceptible to both PTSD diagnoses and stress-related alcohol consumption.

Sex differences in progestogen- and androgen-derived neurosteroids in vulnerability to alcohol and stress-related disorders

Stress and trauma exposure disturbs stress regulation systems and thus increases the vulnerability for stress-related disorders which are characterized by negative affect, including major depressive disorder, anxiety disorders and posttraumatic stress disorder. Similarly, stress and trauma exposure results in increased vulnerability to problematic alcohol use and alcohol use disorder, especially among women, who are more likely to drink to cope with negative affect than their male counterparts. Given these associations, the relationship between stress-related disorders and alcohol use is generally stronger among women leading to complex comorbidities across these disorders and alcohol misuse. This review highlights the therapeutic potential for progestogen- and androgen-derived neurosteroids, which affect both stress- and alcohol-related disorders, to target the overlapping symptoms related to negative affect. This article is part of the special issue on 'Vulnerabilities to Substance Abuse.'

Availability of Medications for the Treatment of Alcohol and Opioid Use Disorder in the USA

Despite high mortality rates due to opioid overdose and excessive alcohol consumption, medications for the treatment of alcohol and opioid use disorder have not been widely used in the USA. This paper provides an overview of the literature on the availability of alcohol and opioid used disorder medications in the specialty substance use disorder treatment system, other treatment settings and systems, and among providers with a federal waiver to prescribe buprenorphine. We also present the most current data on the availability of alcohol and opioid use disorder medications in the USA. These estimates show steady growth in availability of opioid use disorder medications over the past decade and a decline in availability of alcohol use disorder medications. However, overall use of medications in the USA remains low. In 2017, only 16.3% of specialty treatment programs offered any single medication for alcohol use disorder treatment and 35.5% offered any single medication for opioid use disorder treatment. Availability of buprenorphine-waivered providers has increased significantly since 2002. However, geographic disparities in access to buprenorphine remain. Some of the most promising strategies to increase availability of alcohol and opioid use disorder medications include the following: incorporating substance use disorder training in healthcare education programs, educating the substance use disorder workforce about the benefits of medication treatment, reducing stigma surrounding the use of medications, implementing medications in primary care settings, implementing integrated care models, revising regulations on methadone and buprenorphine, improving health insurance coverage of medications, and developing novel medications for the treatment of substance use disorder.

Divergent neuroactive steroid responses to stress and ethanol in rat and mouse strains: relevance for human studies

RATIONALE

Neuroactive steroids are endogenous or synthetic steroids that rapidly alter neuronal excitability via membrane receptors, primarily γ-aminobutyric acid type A (GABAA) receptors. Neuroactive steroids regulate many physiological processes including hypothalamic-pituitary-adrenal (HPA) axis function, ovarian cycle, pregnancy, aging, and reward. Moreover, alterations in neuroactive steroid synthesis are implicated in several neuropsychiatric disorders.

OBJECTIVES

This review will summarize the pharmacological properties and physiological regulation of neuroactive steroids, with a particular focus on divergent neuroactive steroid responses to stress and ethanol in rats, mice, and humans.

RESULTS

GABAergic neuroactive steroids exert a homeostatic regulation of the HPA axis in rats and humans, whereby the increase in neuroactive steroid levels following acute stress counteracts HPA axis hyperactivity and restores homeostasis. In contrast, in C57BL/6J mice, acute stress decreases neurosteroidogenesis and neuroactive steroids exert paradoxical excitatory effects upon the HPA axis. Rats, mice, and humans also differ in the neuroactive steroid responses to ethanol. Genetic variation in neurosteroidogenesis may explain the different neuroactive steroid responses to stress or ethanol.

CONCLUSIONS

Rats and mouse strains show divergent effects of stress and ethanol on neuroactive steroids in both plasma and brain. The study of genetic variation in the various processes that determine neuroactive steroids levels as well as their effects on cell signaling may underlie these differences and may play a relevant role for the potential therapeutic benefits of neuroactive steroids.

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.

Pharmacogenetically driven treatments for alcoholism: are we there yet?

Pharmacogenetic analyses of treatments for alcohol dependence attempt to predict treatment response and side-effect risk for specific medications. We review the literature on pharmacogenetics relevant to alcohol dependence treatment, and describe state-of-the-art methods of pharmacogenetic research in this area. Two main pharmacogenetic study designs predominate: challenge studies and treatment-trial analyses. Medications studied include US FDA-approved naltrexone and acamprosate, both indicated for treating alcohol dependence, as well as several investigational (and off-label) treatments such as sertraline, olanzapine and ondansetron. The best-studied functional genetic variant relevant to alcoholism treatment is rs1799971, a single-nucleotide polymorphism in exon 1 of the OPRM1 gene that encodes the μ-opioid receptor. Evidence from clinical trials suggests that the presence of the variant G allele of rs1799971 may predict better treatment response to opioid receptor antagonists such as naltrexone. Evidence from clinical trials also suggests that several medications interact pharmacogenetically with variation in genes that encode proteins involved in dopaminergic and serotonergic neurotransmission. Variation in the DRD4 gene, which encodes the dopamine D(4) receptor, may predict better response to naltrexone and olanzapine. A polymorphism in the serotonin transporter gene SLC6A4 promoter region appears related to differential treatment response to sertraline depending on the subject's age of onset of alcoholism. Genetic variation in SLC6A4 may also be associated with better treatment response to ondansetron. Initial pharmacogenetic efforts in alcohol research have identified functional variants with potential clinical utility, but more research is needed to further elucidate the mechanism of these pharmacogenetic interactions and their moderators in order to translate them into clinical practice.

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.

The role of the Asn40Asp polymorphism of the mu opioid receptor gene (OPRM1) on alcoholism etiology and treatment: a critical review

The endogenous opioid system has been implicated in the pathophysiology of alcoholism as it modulates the neurobehavioral effects of alcohol. A variant in the mu opioid receptor gene (OPRM1), the Asn40Asp polymorphism, has received attention as a functional variant that may influence a host of behavioral phenotypes for alcoholism as well as clinical response to opioid antagonists. This paper will review converging lines of evidence on the effect of the Asn40Asp SNP on alcoholism phenotypes, including: (i) genetic association studies; (ii) behavioral studies of alcoholism; (iii) neuroimaging studies; (iv) pharmacogenetic studies and clinical trials; and (v) preclinical animal studies. Together, these lines of research seek to elucidate the effects of this functional polymorphism on alcoholism etiology and treatment response.

Pharmacogenetics of naltrexone in asian americans: a randomized placebo-controlled laboratory study

Recent clinical and laboratory studies have shown that the effects of naltrexone for alcoholism may be moderated by the Asn40Asp single-nucleotide polymorphism (SNP) of the μ-opioid receptor gene (OPRM1). Allele frequencies for this polymorphism, however, have been shown to vary substantially as a function of ethnic background, such that individuals of Asian descent are more likely to carry the minor (Asp40) allele. The objective of this study is to test the naltrexone pharmacogenetic effects of the Asn40Asp SNP in a sample of Asian Americans. This study consists of a double-blinded, randomized, placebo-controlled laboratory trial of naltrexone. Participants (n=35, 10 females; 13 Asn40Asn and 22 Asp40 carriers) were non-treatment-seeking heavy drinkers recruited from the community. After taking naltrexone or placebo, participants completed an intravenous alcohol administration session. The primary outcome measures were subjective intoxication and alcohol craving. Results suggested that Asp40 carriers experienced greater alcohol-induced sedation, subjective intoxication, and lower alcohol craving on naltrexone, as compared to placebo, and to Asn40 homozygotes. There results were maintained when controlling for ALDH2 (rs671) and ADH1B (rs1229984) markers and when examining the three levels of OPRM1 genotype, thereby supporting an OPRM1 gene dose response. These findings provide a much-needed extension of previous studies of naltrexone pharmacogenetics to individuals of Asian descent, an ethnic group more likely to express the minor allele putatively associated with improved biobehavioral and clinical response to this medication. These findings help further delineate the biobehavioral mechanisms of naltrexone and its pharmacogenetics.

Chronic ethanol exposure produces tolerance to elevations in neuroactive steroids: mechanisms and reversal by exogenous ACTH

Acute ethanol administration increases potent GABAergic neuroactive steroids, specifically (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP) and (3α,5α)-3,21-dihydroxypregnan-20-one. In addition, neuroactive steroids contribute to ethanol actions. Chronic ethanol exposure results in tolerance to many effects of ethanol, including ethanol-induced increases in neuroactive steroid levels. To determine the mechanisms of tolerance to ethanol-induced increases in neuroactive steroids, we investigated critical signaling molecules that are required for acute ethanol effects. Male Sprague-Dawley rats were administered ethanol via liquid diet for 2 weeks and steroid levels, adrenocorticotrophic hormone (ACTH) and adrenal steroidogenic acute regulatory (StAR) protein expression were measured. Chronic ethanol exposure elicits tolerance to ethanol-induced elevation of serum ACTH and the steroids pregnenolone and progesterone. Surprisingly, chronic ethanol exposure does not result in tolerance to ethanol-induced increases in adrenal StAR protein. However, ethanol-induced StAR phosphorylation is decreased when compared to acute ethanol administration. A separate group of rats exposed to chronic ethanol diet were subsequently challenged with ethanol (2 g/kg) and exhibited a blunted elevation of serum ACTH and progesterone as well as cerebral cortical and hippocampal 3α,5α-THP. Administration of ACTH with the ethanol challenge restored the elevation of serum ACTH and progesterone as well as cerebral cortical 3α,5α-THP levels to those observed in ethanol-naïve rats. Thus, chronic ethanol exposure disrupts ACTH release, which results in tolerance to ethanol-induced increases in neuroactive steroid levels. Loss of the ethanol-induced increases in neuroactive steroids may contribute to behavioral tolerance to ethanol and influence the progression towards alcoholism.