Effects of angiotensin II and an angiotensin converting enzyme inhibitor on alcohol intake in P and NP rats

Role of aldosterone and mineralocorticoid receptor (MR) in addiction: A scoping review

Preclinical and human studies suggest a role of aldosterone and mineralocorticoid receptor (MR) in addiction. This scoping review aimed to summarize (1) the relationship between alcohol and other substance use disorders (ASUDs) and dysfunctions of the aldosterone and MR, and (2) how pharmacological manipulations of MR may affect ASUD-related outcomes. Our search in four databases (MEDLINE, Embase, Web of Science, and Cochrane Library) indicated that most studies focused on the relationship between aldosterone, MR, and alcohol (n = 30), with the rest focused on opioids (n = 5), nicotine (n = 9), and other addictive substances (n = 9). Despite some inconsistencies, the overall results suggest peripheral and central dysregulations of aldosterone and MR in several species and that these dysregulations depended on the pattern of drug exposure and genetic factors. We conclude that MR antagonism may be a promising target in ASUD, yet future studies are warranted.

The influence of chromosome 4 on high ethanol consumption and blood pressure

The Spontaneously Hypertensive Rats (SHR) strain was developed through selective breeding for high systolic blood pressure. In our laboratory, we established a congenic rat strain named SHR.Lewis-Anxrr16 (SLA16). The SLA16 rat strain is genetically identical to the SHR except for the inserted Anxrr16 region in chromosome 4. Our objective was to evaluate the influence of this genomic region on ethanol consumption and blood pressure. First, we exposed SHR and SLA16 male and female rats to ethanol consumption. Results showed that, regardless of strain, females consumed more ethanol than males during forced (10% v/v) and spontaneous ethanol consumption (SEC; 2.5-20% v/v). Then, females from both strains were used to evaluate sensitivity to ethanol. No strain differences in the loss of righting reflex were observed after ethanol treatment (3 g/kg, 20% w/v, intraperitoneal [i.p.]). But, in the triple test, female SHR rats presented lower sensitivity to the ethanol (1.2 g/kg, 14% w/v, i.p.). Surprisingly, female SHR rats also presented higher blood pressure after SEC (10% v/v). Finally, losartan treatment was effective in decreasing the blood pressure of female rats of both strains, but had specific effects on SHR ethanol consumption. Our data suggest that SLA16 female rats consume less ethanol (10%), are more sensitive to its effects, and present lower blood pressure than SHR female rats. We demonstrated that the Anxrr16 locus in chromosome 4 is a genetic candidate to explain high ethanol consumption and blood pressure, at least in females.

Pharmacotherapy for stimulant-related disorders

Stimulant-related disorders (SRD) continue to be an important public health problem for which there are presently no approved pharmacotherapies. Although behavioral interventions provide some benefit response varies. The development of novel and effective pharmacotherapies continues to be a research priority. Understanding neural mechanisms critical to the action of stimulants has helped reveal several potential pharmacotherapies that have already shown promise in controlled clinical trials. Common to some of these medications is the ability to reverse neural deficits in individuals with SRD. Results from thoroughly conducted clinical trials continue to broaden our knowledge increasing the possibility of soon developing effective pharmacotherapies for SRD.

The angiotensin-converting enzyme inhibitor perindopril treatment alters cardiovascular and subjective effects of methamphetamine in humans

A variety of medications have been assessed for their potential efficacy for the treatment of methamphetamine dependence. We conducted this study in an attempt to evaluate the potential of a novel class of medications, angiotensin-converting enzyme inhibitors, as treatments for methamphetamine dependence. All participants met the Diagnostic and Statistical Manual of Mental Disorders, fourth edition, third revision (DSM-IV-TR) criteria for methamphetamine abuse or dependence and were not seeking treatment at the time of study entry. The study was conducted using a double-blind design. Subjects received a baseline series of intravenous (IV) doses of methamphetamine (15 mg and 30 mg) and placebo. Subjects received a second identical series of methamphetamine doses 3 and 5 days after initiation of once-daily oral placebo or perindopril treatment. The dose of perindopril was 2 mg, 4mg, or 8 mg administered in the morning. Perindopril treatment was tolerated well. There were no main effects of perindopril on methamphetamine-induced changes in cardiovascular or subjective effects. There were significant perindoprilmethamphetamine interactions for diastolic blood pressure and for ratings of "Any Drug Effect", indicating inverted U dose-effect functions for these indices.

Targeting brain angiotensin and corticotrophin-releasing hormone systems interaction for the treatment of mood and alcohol use disorders

The brain renin-angiotensin system (RAS) participates importantly in the regulation of endocrine, autonomic, and behavioral response to stress. Recent data indicate that central action of AT(1) receptor antagonists can reduce anxiety symptoms in experimental animals. Furthermore, central inhibition of RAS activity decreases ethanol intake in an animal model of alcoholism. Pathological anxiety responses and the development of substance dependence are both critically mediated through corticotrophin-releasing hormone (CRH) systems, and the RAS is positioned to interact both with hypothalamic as well as extrahypothalamic CRH systems. The thesis of this paper is that the RAS is part of the neurochemical dysregulation underlying negative affective states, anxiety disorders, and ethanol dependence and that medications targeting the RAS should be considered to augment the treatment of these disorders.

Plasticity and impact of the central renin–angiotensin system during development of ethanol dependence

Pharmacological and genetic interference with the renin-angiotensin system (RAS) seems to alter voluntary ethanol consumption. However, understanding the influence of the RAS on ethanol dependence and its treatment requires modeling the neuroadaptations that occur with prolonged exposure to ethanol. Increased ethanol consumption was induced in rats through repeated cycles of intoxication and withdrawal. Expression of angiotensinogen, angiotensin-converting enzyme, and the angiotensin II receptor, AT1a, was examined by quantitative reverse transcription polymerase chain reaction. Increased ethanol consumption after a history of dependence was associated with increased angiotensinogen expression in medial prefrontal cortex but not in nucleus accumbens or amygdala. Increased angiotensinogen expression also demonstrates that the astroglia is an integral part of the plasticity underlying the development of dependence. The effects of low central RAS activity on increased ethanol consumption were investigated using either spirapril, a blood-brain barrier-penetrating inhibitor of angiotensin-converting enzyme, or transgenic rats (TGR(ASrAOGEN)680) with reduced central angiotensinogen expression. Spirapril reduced ethanol intake in dependent rats compared to controls. After induction of dependence, TGR(ASrAOGEN)680 rats had increased ethanol consumption but to a lesser degree than Wistar rats with the same history of dependence. These data suggest that the central RAS is sensitized in its modulatory control of ethanol consumption in the dependent state, but pharmacological or genetic blockade of the system appears to be insufficient to halt the progression of dependence.

Central Overexpression of Angiotensin AT1AReceptors Prevents Dopamine D2Receptor Regulation of Alcohol Consumption in Mice

BACKGROUND

While angiotensin receptors are found on the soma and terminals of dopaminergic neurons, controversy surrounds the potential role of angiotensin in alcohol consumption.

METHODS

Using a transgenic mouse with a brain-specific overexpression of angiotensin AT(1A) receptors (NSE-AT(1A) mice), we have examined the role of angiotensin in alcohol consumption and alcohol-induced regulation of the dopaminergic system.

RESULTS

The functional relevance of the overexpressed AT(1A) receptors was confirmed by an exaggerated rehydration response following 24-hour dehydration. NSE-AT(1A) mice showed a high preference for alcohol (similar to wild-type mice); yet, raclopride treatment had no effect on alcohol consumption in NSE-AT(1A) mice, while significantly reducing consumption in wild-type mice. In contrast, NSE-AT(1A) mice showed enhanced sensitivity to raclopride compared with wild types in terms of D(2) receptor up-regulation within the ventral mesencephalon. In addition, striatal D(2) receptors in NSE-AT(1A) mice were sensitive to up-regulation by chronic alcohol consumption.

CONCLUSIONS

Collectively, these data imply that while expression of angiotensin AT(1A) receptors on striatal neurons has no impact upon basal alcohol consumption or preference, AT(1A) receptors do modulate the sensitivity of dopamine D(2) receptors to regulation by alcohol and the ability of a D(2) receptor antagonist to reduce consumption.

Neutral endopeptidase and alcohol consumption, experiments in neutral endopeptidase-deficient mice

Alcohol consumption was investigated in mice which were rendered deficient in the peptide-degrading enzyme neutral endopeptidase (EC 3.4.24.11) (NEP-/-) by gene targeting and compared to alcohol consumption in corresponding wild type mice (NEP+/+). Mice were offered a free choice to drink tap water or 10% alcohol. The NEP-/- mice consumed significantly more alcohol ( approximately 42%) than the NEP+/+ mice, whereas no significant differences were observed in the total fluid consumption. The daily food consumption of alcohol naive NEP-/- animals was elevated ( approximately 29%). Furthermore, the activities of peptidases closely related to neutral endopeptidase were analysed ex vivo in several brain regions from NEP-/- and NEP+/+ mice not treated with alcohol. There was no obvious compensation for the total loss of neutral endopeptidase by the functionally related peptidases angiotensin-converting enzyme and aminopeptidase N. In vitro, the degradation of exogenously applied [Leu(5)]enkephalin was not reduced in membrane preparations of those brain regions assayed in NEP-/- mice. A small reduction in [Leu(5)]enkephalin degradation was detected in striatal membrane preparations of NEP-/- mice, if aminopeptidase N was additionally blocked by bestatin or amastatin.

Patterns of ethanol and saccharin intake in P rats under limited-access conditions

Patterns of drinking and responding for ethanol (EtOH) and saccharin (SACC) were examined in the alcohol-preferring P rat using various limited-access paradigms. Adult female P rats (n = 10-20) were given 2-h access to EtOH (10-13% v/v) and SACC (0.0125% g/v) concurrently each day, or each solution individually on alternate days. Total 2-h SACC intake was significantly greater than EtOH under both concurrent (12+/-2 vs. 7+/-0.8 ml, p<0.05) and alternate-day access (18+/-1.6 vs. 10+/-0.5 ml) conditions. Under both conditions, however, EtOH intake (over 55% of the total) in the first 15 min was significantly greater than that of SACC (<25% of total). In an operant paradigm, total responding for EtOH (124+/-29) and SACC (114+/-7) under 2-h alternate-day conditions did not differ, but 65% of total EtOH responding occurred during the first 20 min versus less than 45% for SACC (p<0.05). Increasing response requirements (FR-1 to FR-5) did not significantly alter the total number of EtOH reinforcements, but decreased the total number of SACC reinforcements by approximately 50% (p<0.05). Increasing the EtOH concentration from 15% to 35% decreased the number of reinforcements approximately 50% but did not decrease the estimated g/kg EtOH intake. Increasing the SACC concentration from 0.0125% to 0.05%, however, nearly doubled the number of reinforcements. The greater preference for EtOH versus SACC during the initial part of the access period, together with the maintenance of EtOH intake in g/kg when the response requirements and the EtOH concentration were increased, suggests that EtOH intake is motivated by pharmacological consequences. Therefore, different motivational factors appear to underlie EtOH and SACC intake of the P rat. Furthermore, the pattern of EtOH intake and responding displayed by the P rat may be the result of a "bout-" or "binge-" like loss of control under restricted EtOH access conditions.

Acetaldehyde inhibits serum aminopeptidases

Aminopeptidase A (APA)- and aminopeptidase M (APM)-like activity were assayed in Moni-Trol ES with L-alpha-aspartyl-beta-naphthylamide and L-alanyl-beta-naphthylamide, respectively. Upon preincubation of the serum with 89.4, 223.5, and 447 mM acetaldehyde at room temperature for 30 min, a reduction in 26.8%, 55.3%, and 75.8% aminopeptidase A activity was observed. Similarly, aminopeptidase M activity was reduced by 26.5% and 53.1% upon preincubation with 223.5 and 447 mM acetaldehyde. Ethanol at 84.9, 212.3, and 427.9 mM did not significantly affect the enzymic activity. Because aminopeptidase A and aminopeptidase M also degrade the pressor substance, angiotensin II, it is suggested that inhibition of aminopeptidase A- and aminopeptidase M-like activity by acetaldehyde, the product of ethanol metabolism, may lead to higher levels of circulating angiotensin II and, consequently, hypertension, in alcoholics. The hydrolysis of lysine-p-nitroanilide, an aminopeptidase B substrate, was also inhibited upon addition of acetaldehyde to Moni-Trol ES serum.

The reduction in alcohol drinking by peripherally injected angiotensin II is selectively mediated by the AT1 receptor subtype

We investigated which of the two angiotensin (ANG) receptor subtypes mediates the reduction in alcohol intake produced by peripheral injections of ANG II. Adult male Wistar rats were trained to self-administer alcohol (6% w/v) using a procedure that, by limiting access to a brief daily availability period (40 min), fosters a bout pattern of alcohol drinking and a pharmacodynamic effect. Water was continuously available. Once intake stabilized, groups received daily injections either 200 micrograms/kg ANG II SC or the control vehicle saline immediately prior to alcohol availability. Alcohol consumption was attenuated and water intake elevated in the groups receiving ANG II and was unaffected by the vehicle injections. Following this, different groups were pretreated with ascending doses (0.25, 0.5, 1.0 mg/kg) of either PD123319, the selective AT2 receptor antagonist, Sar1,Thr8-ANG II (0.25 mg/kg), the nonselective ANG II antagonist, or DuP753 (0.25, 0.5, 1.0 mg/kg), the selective AT1 receptor antagonist. Control groups received antagonist pretreatment followed by the ANG II vehicle. Neither PD123319, DuP753, or Sar1, Thr8-ANG II had any effect of their own on alcohol or water intake. Pretreatment with PD123319 did not alter the suppressive effect of ANG II on alcohol intake. DuP753 produced a dose-dependent attenuation in the suppressive effect of ANG II on alcohol intake and antagonized the dipsogenic effect of ANG II on water intake. The effect of Sar1,Thr8-ANG II was similar to that of DuP753. These findings suggest that the reduction in alcohol intake produced by ANG II is mediated through the AT1 receptor subtype.

Angiotensin converting enzyme inhibitors and alcohol abuse

Angiotensin converting enzyme plays a key role in the regulation of blood pressure and inhibitors of the enzyme are effective antihypertensive agents. An association between hypertension and alcohol abuse has long been recognized and manipulations of the renin-angiotensin system in laboratory animals has been shown to alter their consumption of ethanol. Procedures that decrease the renin-angiotensin system increase ethanol consumption. Paradoxically, inhibitors of angiotensin converting enzyme also diminish drinking. Several possible explanations for this observation have been proposed. However, observations on the relationship between stress-induced drinking and the antidipsogenic action of a fragment of adrenocorticotropic hormone suggest another possibility: angiotensin converting enzyme may be involved in the metabolism of this peptide and thereby exert an influence on drinking behavior.

Bestatin, an aminopeptidase B inhibitor, selectively reduces alcohol intake in rats

Extensive research has shown that manipulations that augment activity in the renin-angiotensin system can reduce alcohol intake. Inhibition of aminopeptidase B and M can prolong the action of angiotensin (ANG) II and ANG III by preventing their degradation. This study assessed the ability of bestatin, an aminopeptidase B and M inhibitor, to decrease alcohol intake. Bestatin produced a dose-dependent reduction in alcohol intake without altering water intake. The angiotensin antagonist Sar1Thr3-ANG II, however, did not attenuate the effect of bestatin, suggesting that the reduction in alcohol intake was mediated by a system other than the renin-angiotensin system. Bestatin (Ubenimex) is used extensively in Japan as an anticancer agent. It has a low toxicity and is readily absorbed after oral administration. Although further research is needed to uncover the mechanism of its effect, the potential of this drug as an adjunct for the treatment of alcohol abuse should be evaluated.