Suppression of heavy drinking and alcohol seeking by a selective ALDH-2 inhibitor

Declinol, a Complex Containing Kudzu, Bitter Herbs (Gentian, Tangerine Peel) and Bupleurum, Significantly Reduced Alcohol Use Disorders Identification Test (AUDIT) Scores in Moderate to Heavy Drinkers: A Pilot Study

It is well established that inherited human aldehyde dehydrogenase 2 (ALDH-2) deficiency reduces the risk for alcoholism. Kudzu plants and extracts have been used for 1,000 years in traditional Chinese medicine to treat alcoholism. Kudzu contains daidzin, which inhibits ALDH-2 and suppresses heavy drinking in rodents. Decreased drinking due to ALDH-2 inhibition is attributed to aversive properties of acetaldehyde accumulated during alcohol consumption. However not all of the anti-alcohol properties of diadzin are due to inhibition of ALDH-2. This is in agreement with our earlier work showing significant interaction effects of both pyrozole (ALDH-2 inhibitor) and methyl-pyrozole (non-inhibitor) and ethanol's depressant effects. Moreover, it has been suggested that selective ALDH 2 inhibitors reduce craving for alcohol by increasing dopamine in the nucleus accumbens (NAc). In addition there is significant evidence related to the role of the genetics of bitter receptors (TAS2R) and its stimulation as an aversive mechanism against alcohol intake. The inclusion of bitters such as Gentian & Tangerine Peel in Declinol provides stimulation of gut TAS2R receptors which is potentially synergistic with the effects of Kudzu. Finally the addition of Radix Bupleuri in the Declinol formula may have some protective benefits not only in terms of ethanol induced liver toxicity but neurochemical actions involving endorphins, dopamine and epinephrine. With this information as a rationale, we report herein that this combination significantly reduced Alcohol Use Disorders Identification Test (AUDIT) scores administered to ten heavy drinkers (M=8, F=2; 43.2 ± 14.6 years) attending a recovery program. Specifically, from the pre-post comparison of the AUD scores, it was found that the score of every participant decreased after the intervention which ranged from 1 to 31. The decrease in the scores was found to be statistically significant with the p-value of 0.00298 (two-sided paired test; p-value = 0.00149 for one-sided test). Albeit this being a small pilot, we are encouraged about these significant results, and caution any interpretation until larger controlled studies are executed.

Signaling pathways mediating alcohol effects

Ethanol's effects on intracellular signaling pathways contribute to acute effects of ethanol as well as to neuroadaptive responses to repeated ethanol exposure. In this chapter we review recent discoveries that demonstrate how ethanol alters signaling pathways involving several receptor tyrosine kinases and intracellular tyrosine and serine-threonine kinases, with consequences for regulation of cell surface receptor function, gene expression, protein translation, neuronal excitability and animal behavior. We also describe recent work that demonstrates a key role for ethanol in regulating the function of scaffolding proteins that organize signaling complexes into functional units. Finally, we review recent exciting studies demonstrating ethanol modulation of DNA and histone modification and the expression of microRNAs, indicating epigenetic mechanisms by which ethanol regulates neuronal gene expression and addictive behaviors.

Animal models for medications development targeting alcohol abuse using selectively bred rat lines: neurobiological and pharmacological validity

The purpose of this review paper is to present evidence that rat animal models of alcoholism provide an ideal platform for developing and screening medications that target alcohol abuse and dependence. The focus is on the 5 oldest international rat lines that have been selectively bred for a high alcohol-consumption phenotype. The behavioral and neurochemical phenotypes of these rat lines are reviewed and placed in the context of the clinical literature. The paper presents behavioral models for assessing the efficacy of pharmaceuticals for the treatment of alcohol abuse and dependence in rodents, with particular emphasis on rats. Drugs that have been tested for their effectiveness in reducing alcohol/ethanol consumption and/or self-administration by these rat lines and their putative site of action are summarized. The paper also presents some current and future directions for developing pharmacological treatments targeting alcohol abuse and dependence.

Effects of Puerariae Radix Extract on Endotoxin Receptors and TNF-α Expression Induced by Gut-Derived Endotoxin in Chronic Alcoholic Liver Injury

Kudzu (Pueraria lobata) is one of the earliest medicinal plants used to treat alcohol abuse in traditional Chinese medicine for more than a millennium. However, little is known about its effects on chronic alcoholic liver injury. Therefore, the present study observed the effects of puerariae radix extract (RPE) on chronic alcoholic liver injury as well as Kupffer cells (KCs) activation to release tumor necrosis factor alpha (TNF-α) induced by gut-derived endotoxin in rats and macrophage cell line. RPE was observed to alleviate the pathological changes and lipids deposition in liver tissues as well as the serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and hepatic gamma-glutamyl transpeptidase (GGT) activity. Meanwhile, RPE inhibited KCs activation and subsequent hepatic TNF-α expression and downregulated the protein expression of endotoxin receptors, lipopolysaccharide binding protein (LBP), CD14, Toll-like receptor (TLR) 2, and TLR4 in chronic alcohol intake rats. Furthermore, an in vitro study showed that RPE inhibited the expression of TNF-α and endotoxin receptors, CD14 and TLR4, induced by LPS in RAW264.7 cells. In summary, this study demonstrated that RPE mitigated liver damage and lipid deposition induced by chronic alcohol intake in rats, as well as TNF-α release, protein expression of endotoxin receptors in vivo or in vitro.

Aldehyde dehydrogenase inhibitors: a comprehensive review of the pharmacology, mechanism of action, substrate specificity, and clinical application

Aldehyde dehydrogenases (ALDHs) belong to a superfamily of enzymes that play a key role in the metabolism of aldehydes of both endogenous and exogenous derivation. The human ALDH superfamily comprises 19 isozymes that possess important physiological and toxicological functions. The ALDH1A subfamily plays a pivotal role in embryogenesis and development by mediating retinoic acid signaling. ALDH2, as a key enzyme that oxidizes acetaldehyde, is crucial for alcohol metabolism. ALDH1A1 and ALDH3A1 are lens and corneal crystallins, which are essential elements of the cellular defense mechanism against ultraviolet radiation-induced damage in ocular tissues. Many ALDH isozymes are important in oxidizing reactive aldehydes derived from lipid peroxidation and thereby help maintain cellular homeostasis. Increased expression and activity of ALDH isozymes have been reported in various human cancers and are associated with cancer relapse. As a direct consequence of their significant physiological and toxicological roles, inhibitors of the ALDH enzymes have been developed to treat human diseases. This review summarizes known ALDH inhibitors, their mechanisms of action, isozyme selectivity, potency, and clinical uses. The purpose of this review is to 1) establish the current status of pharmacological inhibition of the ALDHs, 2) provide a rationale for the continued development of ALDH isozyme-selective inhibitors, and 3) identify the challenges and potential therapeutic rewards associated with the creation of such agents.

Recent advances in the discovery and preclinical testing of novel compounds for the prevention and/or treatment of alcohol use disorders

Alcohol abuse and dependence have a staggering socioeconomic impact, yet current therapeutic strategies are largely inadequate to treat these disorders. Thus, the development of new strategies that can effectively prevent alcohol use disorders (AUDs) is of paramount importance. Currently approved medications attempt to deter alcohol intake by blocking ethanol metabolism or by targeting the neurochemical systems downstream of the cascades leading to craving and dependence. Unfortunately, these medications have provided only limited success as indicated by the continued high rates of alcohol abuse and alcoholism. The lack of currently available effective treatment strategies is highlighted by the urgent call by the NIAAA to find new and paradigm-changing therapeutics to either prevent or treat alcohol-related problems. This mini-review highlights recent findings from 4 laboratories with a focus on compounds that have the potential to be novel therapeutic agents that can be developed for the prevention and/or treatment of AUDs.

Traditional Chinese Medicine for Treatment of Alcoholism: From Ancient to Modern

Alcohol has long been used as a daily beverage in China and around the world. It is a medicinal substance with various biological activities. In fact, alcohol has played an important role in the development of traditional Chinese medicine (TCM), within which it is considered as the earliest exhilarant and anaesthetic. Yet, as a substance with great potency of misuse and addiction, the consumption of alcohol can lead to serious damage to individual health and the society. Over the past 20 years, alcohol abuse or alcoholism has become an increasing social problem in China along with the rapid economic development. China, the country of origin for TCM, has accumulated abundant clinical experience in the treatment of alcoholism with its ancient medicine. In the present research, we have summarized clinical and primary studies concerning various remedies of TCM for alcohol abuse, including herbal components (such as Kudzu/Pueraria Lobata, Pediculus melo, Hypericumpperforatum L.), decoctions and acupuncture.

Identification of aldehyde dehydrogenase 1A1 modulators using virtual screening

The highly similar aldehyde dehydrogenase isozymes (ALDH1A1 and ALDH2) have been implicated in the metabolism of toxic biogenic aldehydes such as 3,4-dihydroxyphenylacetaldehyde (DOPAL) and 4-hydroxy-2E-nonenal. We report the down-regulation of ALDH1A1 mRNA found in substantia nigra tissue of human Parkinson's disease (PD) samples using the Genome-Wide SpliceArray(™) (GWSA(™)) technology. Since DOPAL can rapidly inactivate ALDH1A1 in vitro, we set up a DOPAL-induced ALDH1A1 inactivation assay and used this assay to demonstrate that Alda-1, a compound originally identified as an activator of ALDH2, can also activate ALDH1A1. We carried out a virtual screening of 19,943 compounds and the top 21 hits from this screen were tested in the DOPAL inactivation assay with ALDH1A1 which led to identification of an activator as well as two inhibitors among these hits. These findings represent an attractive starting point for developing higher potency activator compounds that may have utility in restoring the metabolism of DOPAL in PD.

Dihydromyricetin as a novel anti-alcohol intoxication medication

Alcohol use disorders (AUDs) constitute the most common form of substance abuse. The development of AUDs involves repeated alcohol use leading to tolerance, alcohol withdrawal syndrome, and physical and psychological dependence, with loss of ability to control excessive drinking. Currently there is no effective therapeutic agent for AUDs without major side effects. Dihydromyricetin (DHM; 1 mg/kg, i.p. injection), a flavonoid component of herbal medicines, counteracted acute alcohol (EtOH) intoxication, and also withdrawal signs in rats including tolerance, increased anxiety, and seizure susceptibility; DHM greatly reduced EtOH consumption in an intermittent voluntary EtOH intake paradigm in rats. GABA(A) receptors (GABA(A)Rs) are major targets of acute and chronic EtOH actions on the brain. At the cellular levels, DHM (1 μM) antagonized both acute EtOH-induced potentiation of GABA(A)Rs and EtOH exposure/withdrawal-induced GABA(A)R plasticity, including alterations in responsiveness of extrasynaptic and postsynaptic GABA(A)Rs to acute EtOH and, most importantly, increases in GABA(A)R α4 subunit expression in hippocampus and cultured neurons. DHM anti-alcohol effects on both behavior and CNS neurons were antagonized by flumazenil (10 mg/kg in vivo; 10 μM in vitro), the benzodiazepine (BZ) antagonist. DHM competitively inhibited BZ-site [(3)H]flunitrazepam binding (IC(50), 4.36 μM), suggesting DHM interaction with EtOH involves the BZ sites on GABA(A)Rs. In summary, we determined DHM anti-alcoholic effects on animal models and determined a major molecular target and cellular mechanism of DHM for counteracting alcohol intoxication and dependence. We demonstrated pharmacological properties of DHM consistent with those expected to underlie successful medical treatment of AUDs; therefore DHM is a therapeutic candidate.

Novel therapeutic strategies for alcohol and drug addiction: focus on GABA, ion channels and transcranial magnetic stimulation

Drug addiction represents a major social problem where addicts and alcoholics continue to seek and take drugs despite adverse social, personal, emotional, and legal consequences. A number of pharmacological compounds have been tested in human addicts with the goal of reducing the level or frequency of intake, but these pharmacotherapies have often been of only moderate efficacy or act in a sub-population of humans. Thus, there is a tremendous need for new therapeutic interventions to treat addiction. Here, we review recent interesting studies focusing on gamma-aminobutyric acid receptors, voltage-gated ion channels, and transcranial magnetic stimulation. Some of these treatments show considerable promise to reduce addictive behaviors, or the early clinical studies or pre-clinical rationale suggest that a promising avenue could be developed. Thus, it is likely that within a decade or so, we could have important new and effective treatments to achieve the goal of reducing the burden of human addiction and alcoholism.

Discovery of a novel class of covalent inhibitor for aldehyde dehydrogenases

Human aldehyde dehydrogenases (ALDHs) comprise a family of 17 homologous enzymes that metabolize different biogenic and exogenic aldehydes. To date, there are relatively few general ALDH inhibitors that can be used to probe the contribution of this class of enzymes to particular metabolic pathways. Here, we report the discovery of a general class of ALDH inhibitors with a common mechanism of action. The combined data from kinetic studies, mass spectrometric measurements, and crystallographic analyses demonstrate that these inhibitors undergo an enzyme-mediated β-elimination reaction generating a vinyl ketone intermediate that covalently modifies the active site cysteine residue present in these enzymes. The studies described here can provide the basis for rational approach to design ALDH isoenzyme-specific inhibitors as research tools and perhaps as drugs, to address diseases such as cancer where increased ALDH activity is associated with a cellular phenotype.

An optimized method for the measurement of acetaldehyde by high-performance liquid chromatography

BACKGROUND

Acetaldehyde is produced during ethanol metabolism predominantly in the liver by alcohol dehydrogenase and rapidly eliminated by oxidation to acetate via aldehyde dehydrogenase. Assessment of circulating acetaldehyde levels in biological matrices is performed by headspace gas chromatography and reverse phase high-performance liquid chromatography (RP-HPLC).

METHODS

We have developed an optimized method for the measurement of acetaldehyde by RP-HPLC in hepatoma cell culture medium, blood, and plasma. After sample deproteinization, acetaldehyde was derivatized with 2,4-dinitrophenylhydrazine (DNPH). The reaction was optimized for pH, amount of derivatization reagent, time, and temperature. Extraction methods of the acetaldehyde-hydrazone (AcH-DNP) stable derivative and product stability studies were carried out. Acetaldehyde was identified by its retention time in comparison with AcH-DNP standard, using a new chromatography gradient program, and quantitated based on external reference standards and standard addition calibration curves in the presence and absence of ethanol.

RESULTS

Derivatization of acetaldehyde was performed at pH 4.0 with an 80-fold molar excess of DNPH. The reaction was completed in 40 minutes at ambient temperature, and the product was stable for 2 days. A clear separation of AcH-DNP from DNPH was obtained with a new 11-minute chromatography program. Acetaldehyde detection was linear up to 80 μM. The recovery of acetaldehyde was >88% in culture media and >78% in plasma. We quantitatively determined the ethanol-derived acetaldehyde in hepatoma cells, rat blood and plasma with a detection limit around 3 μM. The accuracy of the method was <9% for intraday and <15% for interday measurements, in small volume (70 μl) plasma sampling.

CONCLUSIONS

An optimized method for the quantitative determination of acetaldehyde in biological systems was developed using derivatization with DNPH, followed by a short RP-HPLC separation of AcH-DNP. The method has an extended linear range, is reproducible and applicable to small-volume sampling of culture media and biological fluids.

Discovery of novel regulators of aldehyde dehydrogenase isoenzymes

Over the past three years we have been involved in high-throughput screening in an effort to discover novel small molecular modulators of aldehyde dehydrogenase (ALDH) activity. In particular, we have been interested in both the activation and inhibition of the three commonly studied isoenzymes, ALDH1A1, ALDH2 and ALDH3A1, as their distinct, yet overlapping substrate specificities, present a particularly difficult challenge for inhibitor discovery and design. Activation of ALDH2 has been shown to benefit cardiovascular outcome following periods of ischemia and renewed interest in specific inhibition of ALDH2 has application for alcohol aversion therapy, and more recently, in cocaine addiction. In contrast, inhibition of either ALDH1A1 or ALDH3A1 has application in cancer treatments where the isoenzymes are commonly over-expressed and serve as markers for cancer stem cells. We are taking two distinct approaches for these screens: in vitro enzyme activity screens using chemical libraries and virtual computational screens using the structures of the target enzymes as filters for identifying potential inhibitors, followed by in vitro testing of their ability to inhibit their intended targets. We have identified selective inhibitors of each of these three isoenzymes with inhibition constants in the high nanomolar to low micromolar range from these screening procedures. Together, these inhibitors provide proof for concept that selective inhibition of these broad specificity general detoxication enzymes through small molecule discovery and design is possible.

Medications for unhealthy alcohol use: across the spectrum

The prevalence of unidentified or untreated unhealthy alcohol use remains high. With the advent of pharmacotherapy and models of counseling appropriate for use in primary care settings as well as in specialty care, clinicians have new tools to manage the range of alcohol problems across the spectrum of health care settings. By extending treatment to primary care, many people who do not currently receive specialty care may have increased access to treatment. In addition, primary care providers, by virtue of their ongoing relationship with patients, may be able to provide continuing treatment over time. Extending the spectrum of care to hazardous drinkers who may not be alcohol dependent could result in earlier intervention and reduce the consequences of excessive drinking.

Inhibition of aldehyde dehydrogenase-2 suppresses cocaine seeking by generating THP, a cocaine use-dependent inhibitor of dopamine synthesis

There is no effective treatment for cocaine addiction despite extensive knowledge of the neurobiology of drug addiction. Here we show that a selective aldehyde dehydrogenase-2 (ALDH-2) inhibitor, ALDH2i, suppresses cocaine self-administration in rats and prevents cocaine- or cue-induced reinstatement in a rat model of cocaine relapse-like behavior. We also identify a molecular mechanism by which ALDH-2 inhibition reduces cocaine-seeking behavior: increases in tetrahydropapaveroline (THP) formation due to inhibition of ALDH-2 decrease cocaine-stimulated dopamine production and release in vitro and in vivo. Cocaine increases extracellular dopamine concentration, which activates dopamine D2 autoreceptors to stimulate cAMP-dependent protein kinase A (PKA) and protein kinase C (PKC) in primary ventral tegmental area (VTA) neurons. PKA and PKC phosphorylate and activate tyrosine hydroxylase, further increasing dopamine synthesis in a positive-feedback loop. Monoamine oxidase converts dopamine to 3,4-dihydroxyphenylacetaldehyde (DOPAL), a substrate for ALDH-2. Inhibition of ALDH-2 enables DOPAL to condense with dopamine to form THP in VTA neurons. THP selectively inhibits phosphorylated (activated) tyrosine hydroxylase to reduce dopamine production via negative-feedback signaling. Reducing cocaine- and craving-associated increases in dopamine release seems to account for the effectiveness of ALDH2i in suppressing cocaine-seeking behavior. Selective inhibition of ALDH-2 may have therapeutic potential for treating human cocaine addiction and preventing relapse.

Emerging drugs to treat alcoholism

IMPORTANCE OF THE FIELD

Alcoholism is a widespread disorder with substantial mortality and negative treatment outcomes. To date, few medications have been found to reduce relapse rates or drinking in alcohol-dependent patients.

AREAS COVERED IN THIS REVIEW

This review focuses on drugs that have been clinically tested for the treatment of alcohol dependence in clinical trials, pilot trials or which are considered to have a clinical perspective. For this purpose, a detailed Medline search was conducted on this issue. Although the neurochemical basis of alcoholism and the neuronal circuitry mediating its psychotropic effects have been explored in great detail in recent years, few drugs have emerged for the treatment of alcohol dependence, also because pharmaceutical companies have only a limited interest in this area of research. Acamprosate and the opioid antagonist naltrexone have been found to be effective, although data are mixed. A depot formula of naltrexone and the alternate opioid antagonist nalmefene have been studied in clinical trials and will presumably be introduced in the markets soon. Other emerging drugs are topiramate, novel acetaldehyde dehydrogenase (ALDH) inhibitors, baclofen, a combination therapy of gababentin and flumazenil and drugs targeting the cortitropin-releasing factor/neuropeptide Y mediated stress axis.

WHAT THE READER WILL GAIN

Insights on the neurochemical basis of alcohol dependence and possible targets of medications.

TAKE HOME MESSAGE

Acamprosate, naltrexone and the ALDH inhibitor disulfiram are proven medications for the treatment of alcohol dependence with modest efficacy. Novel alternate medications, a depot formulation of the opioid antagonist naltrexone and another oral opioid antagonist, nalmefene, are available now with good evidence for clinical efficacy. Novel ALDH inhibitors, antiepileptic drugs such as topiramate and drugs targeting the stress axis are currently among the most promising emerging drugs.

Genetic and environmental influences on ethanol consumption: perspectives from preclinical research

BACKGROUND

Alcohol use disorders (abuse and dependence, AUD) are multifactorial phenomena, depending on the interplay of environmental and genetic variables.

METHOD

This review describes current developments in animal research that may help (a) develop gene therapies for the treatment of alcoholism, (b) understand the permissive role of stress on ethanol intake, and (c) elucidate why exposure to ethanol early in life is associated with a greater risk of AUD.

RESULTS

The polymorphisms found in liver alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) affect the elimination of ethanol and the susceptibility to ethanol intake. A highly active ADH protects against alcoholism, an effect related to a presteady state burst in arterial acetaldehyde. Social stressors, such as repeated early maternal separation or social defeat, exert a permissive effect on ethanol intake, perhaps by altering the normal development of the hypothalamic-pituitary-adrenal axis. Ethanol exposure during gestation, infancy, or adolescence increases the likelihood of AUD later in life. Early perception of ethanol's positive and negative (anti-anxiety) reinforcing effects may play a role in this phenomenon.

CONCLUSIONS

The review underscores the advantages of using preclinical animal models of AUD and highlights points of intersection between the topics to help design a more integrated approach for the study of alcohol-related problems.

Supervised disulfiram in relapse prevention in alcohol-dependent patients suffering from comorbid borderline personality disorder--a case series

AIMS

Disulfiram is widely used to prevent alcoholic relapse. However, due to the intended adverse reaction with ethanol, some believe that its use is dangerous for patients with personality disorders or psychiatric comorbidities because of their increased risk of impulsivity or suicidal behaviour. We examined the safety and efficacy in relapse prevention of a series of alcoholics with borderline personality disorder (BPD).

METHODS

Case history study of patients diagnosed with BPD, prescribed disulfiram in a dose of 1.5-2.5 g/week, supervised by a physician in up to three brief contacts per week.

RESULTS

Two out of eight patients remained completely abstinent during the supervised disulfiram therapy over a mean period of 9.25 months. Adherence to treatment was 18.44 +/- 21.78 months. The first relapse occurred after 1.38 +/- 1.41 months. The cumulated time of abstinence was 16.88 +/- 20.48 months. The overall tolerability was considered to be high; dizziness and fatigue appeared in all patients at the beginning of the therapy but did not persist. No serious adverse events or ethanol-disulfiram interactions were observed. No suicidal behaviour was reported.

CONCLUSIONS

Although case observations should be interpreted with caution, supervised disulfiram seems to deserve further investigation in patients with comorbid BPD, for whom it appears to help prevent alcoholic relapse.

A selective ALDH-2 inhibitor reduces anxiety in rats

CVT-10216 is a highly selective, reversible inhibitor of ALDH-2 that reduces excessive alcohol drinking. Anxiety plays a role in alcoholism. The present study asks whether CVT-10216 has anxiolytic properties, as reflected in social interaction behavior in four unrelated rodent models: endogenous anxiety-like behavior in naïve Fawn-Hooded rats, repeated alcohol-withdrawal-induced anxiety, restraint stress-induced anxiety and drug-induced anxiety. CVT-10216 counteracted anxiety in all models except that produced by the 5-HT(2C) agonist, mCPP. CVT-10216 exhibited both acute and prophylactic inhibitions of repeated alcohol-withdrawal-induced anxiety. Importantly, anxiogenic behavior induced by the benzodiazepine receptor inverse agonist, DMCM, was counteracted dose-dependently by CVT-10216. Thus, a non-addictive selective inhibitor of ALDH-2 has both anxiolytic and antidipsotropic properties, which may be dependent, in part on the involvement of the GABA-benzodiazepine system.