Data are presented as means.e.m. The CBX diastereomer 18-glycyrrhetinic acid 3-O-hemisuccinate (CBX), which we found to be selective for 11-HSD2, was also effective in reducing alcohol drinking in mice. Thus, 11-HSD inhibitors may be a promising new class of candidate alcohol abuse medications, Mps1-IN-3 and existing 11-HSD inhibitor drugs may be potentially re-purposed for alcohol abuse treatment. Introduction Alcohol remains the Mps1-IN-3 most prevalent abused substance in the United States, Mps1-IN-3 with an estimated 6.8 percent of the population aged 12 or older classified as having alcohol dependence or abuse. 1 Few pharmacotherapies for alcohol abuse are currently available, and these have shown only limited efficacy and compliance.2, 3, 4, 5 Thus, the development of more effective medications for alcohol abuse is a significant unmet medical need.6 Alcohol disrupts glucocorticoid regulation in both rodents7, 8 and humans.9, 10, 11, 12, 13 Glucocorticoids have been implicated in alcohol’s reinforcing effects,14 and activation of glucocorticoids by alcohol is involved in the escalation of alcohol intake in dependent rats and alcohol-seeking and drinking during protracted abstinence.15, 16 Both systemic and intracerebral glucocorticoid receptor antagonism with mifepristone blocked compulsive alcohol drinking in rats.13, 15, 16, 17 In humans, high adrenal sensitivity (cortisol to corticotropin ratio) in response to stress was found to correlate with greater susceptibility to relapse to heavy drinking,12 whereas glucocorticoid receptor antagonism with mifepristone significantly reduced alcohol craving and drinking.13 The effects of glucocorticoids are modulated in target cells by the activity of 11-hydroxysteroid dehydrogenase (11-HSD) isozymes acting as pre-receptors that contribute to shape the tissue-specific responsiveness to glucocorticoids.18, 19 In particular, 11-HSD1, which is usually colocalized with the glucocorticoid receptor, converts 11-keto (inert) glucocorticoids such as cortisone in humans and 11-dehydrocorticosterone in rodents, into 11-hydroxi (active) glucocorticoids such as cortisol in humans and corticosterone in rodents, respectively, to enhance the effects of glucocorticoids.18, 19 The reverse reaction by 11-HSD2 attenuates local glucocorticoid responses in some mineralocorticoid receptor (MR)-expressing cells, such as classic aldosterone-selective target tissues (distal nephron, colon, sweat gland), although Mps1-IN-3 not in others, such as several MR-expressing brain regions.20 Given the role for glucocorticoids in mediating the reinforcing effects of alcohol,14, 15 the relevance of 11-HSD to the modulating effects of glucocorticoids on alcohol drinking is unknown. Carbenoxolone (CBX, 3-hydroxy-11-oxoolean-12-en-30-oic acid 3-hemisuccinate) is a derivative of glycyrrhetinic acid, a molecule present in licorice.18, 19 CBX is a nonselective 11-HSD inhibitor21 that has long been used for the treatment of gastritis and peptic ulcer.22 In addition to its modulatory role on glucocorticoid metabolism in target tissues, CBX also inhibits gap junctional communication, at potencies several orders of magnitude higher.23 Here we tested the hypothesis that CBX and its 18 diastereomer, 18-glycyrrhetinic acid 3-O-hemisuccinate (CBX), would reduce alcohol intake in rodents because of their ability to modulate the actions of glucocorticoids. We show that these molecules are capable of reducing alcohol drinking in rodents in both baseline and excessive drinking models, and thus are promising new targets for the treatment of alcohol use disorder. We also show that CBX is a selective inhibitor of 11-HSD2 in the mouse. Materials and methods Drugs CBX, 18-glycyrrhetinic acid and 18-glycyrrhetinic were purchased from Tocris (Bristol, UK); CBX was custom synthesized from 18-glycyrrhetinic acid (Tocris). Subjects Adult male Wistar rats (Charles River, Wilmington, MA, USA), weighing 225C275?g at the beginning of the experiments, were housed in groups of two to three per cage. Adult male C57BL/6J mice (The Jackson Laboratory, Bar Harbor, ME, USA) were housed four per cage except during drinking sessions. All the rodents were housed in a temperature-controlled (22?C) vivarium on a 12?h/12?h light/dark cycle with access to food and water except during behavioral testing. Operant and limited-access drinking tests were conducted during the dark phase of the light/dark cycle. All the procedures adhered to the National Institutes of Health Guide for the Care and Use of Laboratory Animals and were approved by the Institutional Animal Care and Use Committee of The Scripps Research Institute. Rat operant self-administration Self-administration sessions were conducted in standard operant conditioning chambers (Med Associates, St. Albans, VT, USA). The rats were trained to self-administer alcohol as previously reported.15 First, the rats were given NFKBIA free-choice access to alcohol (10% w/v) and water for 1 day in their home cages to habituate them to the taste of alcohol. Second, the rats were subjected to an overnight session in the operant chambers with access to one lever (right lever) that delivered water in a fixed-ratio 1 schedule where every lever press is reinforced with delivery of 0.1?ml of solution. Food was available during this training. Third, after 1 day off, the rats were subjected to a 2?h session.