The H2O2 scavenger ebselen decreases ethanol-induced locomotor stimulation in mice

Targeting NOX2 with Bivalent Small-Molecule p47phox-p22phox Inhibitors

Nicotinamide adenine dinucleotide phosphate oxidase isoform 2 (NOX2) is an enzymatic complex whose function is the regulated generation of reactive oxygen species (ROS). NOX2 activity is central to redox signaling events and antibacterial response, but excessive ROS production by NOX2 leads to oxidative stress and inflammation in a range of diseases. The protein-protein interaction between the NOX2 subunits p47phox and p22phox is essential for NOX2 activation, thus p47phox is a potential drug target. Previously, we identified 2-aminoquinoline as a fragment hit toward p47phoxSH3A-B and converted it to a bivalent small-molecule p47phox-p22phox inhibitor (Ki = 20 μM). Here, we systematically optimized the bivalent compounds by exploring linker types and positioning as well as substituents on the 2-aminoquinoline part and characterized the bivalent binding mode with biophysical methods. We identified several compounds with submicromolar binding affinities and cellular activity and thereby demonstrated that p47phox can be targeted by potent small molecules.

Mystic Acetaldehyde: The Never-Ending Story on Alcoholism

After decades of uncertainties and drawbacks, the study on the role and significance of acetaldehyde in the effects of ethanol seemed to have found its main paths. Accordingly, the effects of acetaldehyde, after its systemic or central administration and as obtained following ethanol metabolism, looked as they were extensively characterized. However, almost 5 years after this research appeared at its highest momentum, the investigations on this topic have been revitalized on at least three main directions: (1) the role and the behavioral significance of acetaldehyde in different phases of ethanol self-administration and in voluntary ethanol consumption; (2) the distinction, in the central effects of ethanol, between those arising from its non-metabolized fraction and those attributable to ethanol-derived acetaldehyde; and (3) the role of the acetaldehyde-dopamine condensation product, salsolinol. The present review article aims at presenting and discussing prospectively the most recent data accumulated following these three research pathways on this never-ending story in order to offer the most up-to-date synoptic critical view on such still unresolved and exciting topic.

S-Glutathionylation and Redox Protein Signaling in Drug Addiction

Drug addiction is a chronic relapsing disorder that comes at a high cost to individuals and society. Therefore understanding the mechanisms by which drugs exert their effects is of prime importance. Drugs of abuse increase the production of reactive oxygen and nitrogen species resulting in oxidative stress. This change in redox homeostasis increases the conjugation of glutathione to protein cysteine residues; a process called S-glutathionylation. Although traditionally regarded as a protective mechanism against irreversible protein oxidation, accumulated evidence suggests a more nuanced role for S-glutathionylation, namely as a mediator in redox-sensitive protein signaling. The reversible modification of protein thiols leading to alteration in function under different physiologic/pathologic conditions provides a mechanism whereby change in redox status can be translated into a functional response. As such, S-glutathionylation represents an understudied means of post-translational protein modification that may be important in the mechanisms underlying drug addiction. This review will discuss the evidence for S-glutathionylation as a redox-sensing mechanism and how this may be involved in the response to drug-induced oxidative stress. The function of S-glutathionylated proteins involved in neurotransmission, dendritic spine structure, and drug-induced behavioral outputs will be reviewed with specific reference to alcohol, cocaine, and heroin.

Different dose-dependent effects of ebselen in sciatic nerve ischemia-reperfusion injury in rats

Ebselen is an organoselenium compound which has strong antioxidant and anti-inflammatory effects. We investigated the neuroprotective role of ebselen pretreatment in rats with experimental sciatic nerve ischemia-reperfusion (I/R) injury. Adult male Sprague Dawley rats were divided into four groups (N = 7 in each group). Before sciatic nerve I/R was induced, ebselen was injected intraperitoneally at doses of 15 and 30 mg/kg. After a 2 h ischemia and a 3 h reperfusion period, sciatic nerve tissues were excised. Tissue levels of malondialdehyde (MDA) and nitric oxide (NO), and activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) were measured. Sciatic nerve tissues were also examined histopathologically. The 15 mg/kg dose of ebselen reduced sciatic nerve damage and apoptosis (p<0.01), levels of MDA, NO, and inducible nitric oxide synthase (iNOS) positive cells (p<0.01, p<0.05, respectively), and increased SOD, GPx, and CAT activities (p<0.001, p<0.01, p<0.05, respectively) compared with the I/R group that did not receive ebselen. Conversely, the 30 mg/kg dose of ebselen increased sciatic nerve damage, apoptosis, iNOS positive cells (p<0.01, p<0.05, p<0.001) and MDA and NO levels (p<0.05, p<0.01) and decreased SOD, GPx, and CAT activities (p<0.05) compared with the sham group. The results of this study suggest that ebselen may cause different effects depending on the dose employed. Ebselen may be protective against sciatic nerve I/R injury via antioxidant and antiapoptotic activities at a 15 mg/kg dose, conversely higher doses may cause detrimental effects.

Centrally formed acetaldehyde mediates ethanol-induced brain PKA activation

Centrally formed acetaldehyde has proven to be responsible for several psychopharmacological effects induced by ethanol. In addition, it has been suggested that the cAMP-PKA signaling transduction pathway plays an important role in the modulation of several ethanol-induced behaviors. Therefore, we hypothesized that acetaldehyde might be ultimately responsible for the activation of this intracellular pathway. We used three pharmacological agents that modify acetaldehyde activity (α-lipoic acid, aminotriazole, and d-penicillamine) to study the role of this metabolite on EtOH-induced PKA activation in mice. Our results show that the injection of α-lipoic acid, aminotriazole and d-penicillamine prior to acute EtOH administration effectively blocks the PKA-enhanced response to EtOH in the brain. These results strongly support the hypothesis of a selective release of acetaldehyde-dependent Ca(2+) as the mechanism involved in the neurobehavioral effects elicited by EtOH.

Induction of brain cytochrome P450 2E1 boosts the locomotor-stimulating effects of ethanol in mice

In the central nervous system ethanol (EtOH) is metabolized into acetaldehyde by different enzymes. Brain catalase accounts for 60% of the total production of EtOH-derived acetaldehyde, whereas cerebral cytochrome P450 2E1 (CYP 2E1) produces 20% of this metabolite. Acetaldehyde formed by the activity of central catalase has been implicated in some of the neurobehavioral properties of EtOH, yet the contribution of CYP 2E1 to the pharmacological actions of this drug has not been investigated. Here we assessed the possible participation of CYP 2E1 in the behavioral effects of EtOH. Thus, we induced CYP 2E1 activity and expression by exposing mice to chronic acetone intake (1% v/v for 10 days) and examined its consequences on the stimulating and uncoordinating effects of EtOH (0-3.2 g/kg) injected intraperitoneally. Our data showed that 24 h after withdrawal of acetone brain expression and activity of CYP 2E1 was induced. Furthermore, the locomotion produced by EtOH was boosted over the same interval of time. Locomotor stimulation produced by amphetamine or tert-butanol was unchanged by previous treatment with acetone. EtOH-induced motor impairment as evaluated in a Rota-Rod apparatus was unaffected by the preceding exposure to acetone. These results indicate that cerebral CYP 2E1 activity could contribute to the locomotor-stimulating effects of EtOH, and therefore we suggest that centrally produced acetaldehyde might be a possible mediator of some EtOH-induced pharmacological effects.

Elucidating the biological basis for the reinforcing actions of alcohol in the mesolimbic dopamine system: the role of active metabolites of alcohol

The development of successful pharmacotherapeutics for the treatment of alcoholism is predicated upon understanding the biological action of alcohol. A limitation of the alcohol research field has been examining the effects of alcohol only and ignoring the multiple biological active metabolites of alcohol. The concept that alcohol is a "pro-drug" is not new. Alcohol is readily metabolized to acetaldehyde within the brain. Acetaldehyde is a highly reactive compound that forms a number of condensation products, including salsolinol and iso-salsolinol (acetaldehyde and dopamine). Recent experiments have established that numerous metabolites of alcohol have direct CNS action, and could, in part or whole, mediate the reinforcing actions of alcohol within the mesolimbic dopamine system. The mesolimbic dopamine system originates in the ventral tegmental area (VTA) and projects to forebrain regions that include the nucleus accumbens (Acb) and the medial prefrontal cortex (mPFC) and is thought to be the neurocircuitry governing the rewarding properties of drugs of abuse. Within this neurocircuitry there is convincing evidence that; (1) biologically active metabolites of alcohol can directly or indirectly increase the activity of VTA dopamine neurons, (2) alcohol and alcohol metabolites are reinforcing within the mesolimbic dopamine system, (3) inhibiting the alcohol metabolic pathway inhibits the biological consequences of alcohol exposure, (4) alcohol consumption can be reduced by inhibiting/attenuating the alcohol metabolic pathway in the mesolimbic dopamine system, (5) alcohol metabolites can alter neurochemical levels within the mesolimbic dopamine system, and (6) alcohol interacts with alcohol metabolites to enhance the actions of both compounds. The data indicate that there is a positive relationship between alcohol and alcohol metabolites in regulating the biological consequences of consuming alcohol and the potential of alcohol use escalating to alcoholism.

Reduction in central H2O2 levels prevents voluntary ethanol intake in mice: a role for the brain catalase-H2O2 system in alcohol binge drinking

BACKGROUND

Hydrogen peroxide (H2 O2 ) is the cosubstrate used by the enzyme catalase to form Compound I (the catalase-H2 O2 system), which is the major pathway for the conversion of ethanol (EtOH) into acetaldehyde in the brain. This centrally formed acetaldehyde has been shown to be involved in some of the psychopharmacological effects induced by EtOH in rodents, including voluntary alcohol intake. It has been observed that different levels of this enzyme in the central nervous system (CNS) result in variations in the amount of EtOH consumed. This has been interpreted to mean that the brain catalase-H2 O2 system, by determining EtOH metabolism, mediates alcohol self-administration. To date, however, the role of H2 O2 in voluntary EtOH drinking has not been investigated.

METHODS

In the present study, we explored the consequence of a reduction in cerebral H2 O2 levels in volitional EtOH ingestion. With this end in mind, we injected mice of the C57BL/6J strain intraperitoneally with the H2 O2 scavengers alpha-lipoic acid (LA; 0 to 50 mg/kg) or ebselen (Ebs; 0 to 25 mg/kg) 15 or 60 minutes, respectively, prior to offering them an EtOH (10%) solution following a drinking-in-the-dark procedure. The same procedure was followed to assess the selectivity of these compounds in altering EtOH intake by presenting mice with a (0.1%) solution of saccharin. In addition, we indirectly tested the ability of LA and Ebs to reduce brain H2 O2 availability.

RESULTS

The results showed that both LA and Ebs dose-dependently reduced voluntary EtOH intake, without altering saccharin consumption. Moreover, we demonstrated that these treatments decreased the central H2 O2 levels available to catalase.

CONCLUSIONS

Therefore, we propose that the amount of H2 O2 present in the CNS, by determining brain acetaldehyde formation by the catalase-H2 O2 system, could be a factor that determines an animal's propensity to consume EtOH.

Ethanol-derived acetaldehyde: pleasure and pain of alcohol mechanism of action

Acetaldehyde (ACD), the first metabolite of ethanol (EtOH), has been implicated in several actions of alcohol, including its reinforcing effects. Previously considered an aversive compound, ACD was useful in alcoholic’s pharmacological treatment aimed at discouraging alcohol drinking. However, it has recently been shown that EtOH-derived ACD is necessary for EtOH-induced place preference and self-administration, thereby suggesting a possible involvement of ACD in EtOH motivational properties. In addition, EtOH-stimulating properties on DA neurons are prevented by pharmacological blockade of local catalase H₂O₂ system, the main metabolic step for biotransformation of EtOH into ACD within the central nervous system. It was further shown that pretreatment with thiol compounds, like L-Cysteine or D-Penicillamine, reduced EtOH and ACD-induced motivational effects, in fact preventing self-administration of both EtOH and ACD, thus suggesting a possible role for ACD as a biomarker useful in evaluating potential innovative treatments of alcohol abuse. These findings suggest a key role of ACD in the EtOH reinforcing effects. In the present paper we review the role of EtOH-derived ACD in the reinforcing effects of EtOH and the possibility that ACD may serve as a therapeutically targetable biomarker in the search for novel treatments in alcohol abuse and alcoholism.

Acquisition and reconditioning of ethanol-induced conditioned place preference in mice is blocked by the H₂O₂ scavenger alpha lipoic acid

RATIONALE

Hydrogen peroxide (H2O2) is the co-substrate used by catalase to metabolize ethanol to acetaldehyde in the brain. This centrally formed acetaldehyde has been involved in several ethanol-related behaviors.

OBJECTIVES

The present research evaluated the effect of the H2O2 scavenger, alpha lipoic acid (LA), on the acquisition and reconditioning of ethanol-induced conditioned place preference (CPP).

METHODS

Mice received pairings of a distinctive floor stimulus (CS+) associated with intraperitoneal injections of ethanol (2.5 g/kg). On alternate days, animals received pairings of a different floor stimulus (CS-) associated with saline injections. A different group of animals received pairings with the (CS-) associated with saline injections, and on alternate days they received LA (100 mg/kg) injected 30 min prior to ethanol (2.5 g/kg) administration paired with the (CS+). A preference test assessed the effect of LA on the acquisition of ethanol-induced CPP. A similar procedure was followed to study the effect of LA on the acquisition of cocaine- and morphine-induced CPP. A separate experiment evaluated the effect of LA on the reconditioning of ethanol-induced CPP. In addition, we investigated the consequence of LA administration on central H2O2 levels.

RESULTS

LA selectively blocked the acquisition of ethanol-induced CPP. Moreover, this compound impaired the reconditioning of ethanol-induced CPP. Additionally, we found that LA diminished H2O2 levels in the brain.

CONCLUSIONS

These data suggest that a decline in H2O2 availability by LA might impede the formation of brain ethanol-derived acetaldehyde by catalase, which results in an impairment of the rewarding properties of ethanol.