Bradykinin suppresses alcohol intake and plays a role in the suppression produced by an ACE inhibitor

Voluntary exposure to a toxin: the genetic influence on ethanol consumption

Ethyl alcohol is a toxin that, when consumed at high levels, produces organ damage and death. One way to prevent or ameliorate this damage in humans is to reduce the exposure of organs to alcohol by reducing alcohol ingestion. Both the propensity to consume large volumes of alcohol and the susceptibility of human organs to alcohol-induced damage exhibit a strong genetic influence. We have developed an integrative genetic/genomic approach to identify transcriptional networks that predispose complex traits, including propensity for alcohol consumption and propensity for alcohol-induced organ damage. In our approach, the phenotype is assessed in a panel of recombinant inbred (RI) rat strains, and quantitative trait locus (QTL) analysis is performed. Transcriptome data from tissues/organs of naïve RI rat strains are used to identify transcriptional networks using Weighted Gene Coexpression Network Analysis (WGCNA). Correlation of the first principal component of transcriptional coexpression modules with the phenotype across the rat strains, and overlap of QTLs for the phenotype and the QTLs for the coexpression modules (module eigengene QTL) provide the criteria for identification of the functionally related groups of genes that contribute to the phenotype (candidate modules). While we previously identified a brain transcriptional module whose QTL overlapped with a QTL for levels of alcohol consumption in HXB/BXH RI rat strains and 12 selected rat lines, this module did not account for all of the genetic variation in alcohol consumption. Our search for QTL overlap and correlation of coexpression modules with phenotype can, however, be applied to any organ in which the transcriptome has been measured, and this represents a holistic approach in the search for genetic contributors to complex traits. Previous work has implicated liver/brain interactions, particularly involving inflammatory/immune processes, as influencing alcohol consumption levels. We have now analyzed the liver transcriptome of the HXB/BXH RI rat panel in relation to the behavioral trait of alcohol consumption. We used RNA-Seq and microarray data to construct liver transcriptional networks, and identified a liver candidate transcriptional coexpression module that explained 24% of the genetic variance in voluntary alcohol consumption. The transcripts in this module focus attention on liver secretory products that influence inflammatory and immune signaling pathways. We propose that these liver secretory products can interact with brain mechanisms that affect alcohol consumption, and targeting these pathways provides a potential approach to reducing high levels of alcohol intake and also protecting the integrity of the liver and other organs.

The effects of polymorphisms in genes from the renin-angiotensin, bradykinin, and fibrinolytic systems on plasma t-PA and PAI-1 levels are dependent on environmental context

Thrombosis is a key factor in the pathophysiology of cardiovascular disease. Important biochemical constituents of the fibrinolytic system, affecting thrombosis, include tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1). Both t-PA and PAI-1 are determined by multiple genetic and environmental factors. We aimed to investigate whether the effects of polymorphism in genes from the renin-angiotensin, bradykinin, and fibrinolytic systems on t-PA or PAI-1 levels are dependent on environmental factors in a large population-based sample from the PREVEND study in Groningen, The Netherlands (n = 2,527). We found strong evidence (P <or= 0.02) for interaction effects of polymorphisms from the bradykinin receptor (BDKRB2) gene and alcohol consumption on t-PA in females and males and on PAI-1 in males. Only suggestive evidence (P <or= 0.10) was present for an interaction effect of the BDKRB2 gene and alcohol consumption on PAI-1 levels in females. Another consistent finding was evidence for an interaction between bradykinin receptor (BDKRB2) gene polymorphisms and body size as measured by body mass index and/or waist-hip-ratio. For each gender and for both t-PA and PAI-1 there was at least one BDKRB2-body size combination that exhibited suggestive (P <or= 0.10), significant (P <or= 0.04) and/or strong evidence (P <or= 0.02) for interaction. In conclusion, the genetic architecture of t-PA and PAI-1 is dependent on the environmental context such as body size and alcohol use. The present study emphasizes the importance of including environmental factors in genetic analyses to fully comprehend the genetic architecture of a specific trait.

Central angiotensin II controls alcohol consumption via its AT1 receptor

Pharmacological and genetic manipulations of the renin-angiotensin system (RAS) have been found to alter the voluntary consumption of alcohol. Here we characterize the role of central angiotensin II (Ang II) in alcohol intake first by using transgenic rats that express an antisense RNA against angiotensinogen and consequently have reduced Ang II levels exclusively in the central nervous system [TGR(ASrAOGEN)680]. These rats consumed markedly less alcohol in comparison to their wild-type controls. Second, Spirapril, an inhibitor of the angiotensin-converting enzyme (ACE), which passes the blood-brain barrier, did not influence the alcohol consumption in the TGR(ASrAOGEN)680, but it significantly reduced alcohol intake in wild-type rats. Studies in knockout mice indicated that the central effect of Ang II on alcohol consumption is mediated by the angiotensin receptor AT1 whereas the AT2 receptor and the bradykinin B2 receptor are not involved. Furthermore, the dopamine concentration in the ventral tegmental area (VTA) is markedly reduced in rats with low central Ang II, strengthening our hypothesis of a role of dopaminergic transmission in Ang II-controlled alcohol preference. Our results indicate that a distinct drug-mediated control of the central RAS could be a promising therapy for alcohol disease.

Role of angiotensin II and the subfornical organ in the pharmacological actions of ethanol

AIMS

The current study was designed to evaluate if angiotensin II mediates the hypothermic effects of ethanol, and to determine if the effects of angiotensin are mediated centrally. We also tested the hypothesis that the subfornical organ (SFO) is a site responsible for the alterations in body temperature and aerial righting reflex mediated by ethanol and for the modulation of ethanol consumption in rats.

METHODS

Male Sprague-Dawley rats were used in a series of experiments to evaluate the role of both peripheral and central administration of losartan, a selective angiotensin type 1 receptor antagonist on ethanol-induced hypothermia. Subsequent studies were undertaken in SFO-lesioned rats to evaluate the effects of SFO-lesion on alcohol intake, the thermal response to alcohol and angiotensin, and the aerial righting reflex.

RESULTS

Selective antagonism of the angiotensin II type 1 receptor, administered either peripherally or centrally, attenuated not only the fall in colonic temperature but also attenuated the transient rise in tail skin temperature that was associated with administration of ethanol. The thermal responses to both angiotensin and ethanol were similarly attenuated in SFO-lesioned rats. Likewise the aerial righting reflex, which has previously been shown to be impaired by losartan treatment, was also significantly attenuated in SFO-lesioned animals. Alcohol intake, as determined by a 48 h, two-bottle preference test also revealed that SFO-lesioned animals consumed significantly less alcohol (ethanolic beer) than did controls.

CONCLUSION

Collectively, the results demonstrate that ethanol-induced temperature responses are mediated by the renin-angiotensin system and that this interaction is mediated centrally. In addition, the results demonstrate that the SFO is a site that mediates several neurobiological effects of ethanol, possibly via the renin-angiotensin system.

The effect of bradykinin on the oxidative state of rats with acute hyperglycaemia

Many clinical and experimental studies have established the beneficial effect of kinins in hypertension, heart failure and ischaemia-reperfusion syndrome, but little attention has been given to the role of kinins in hyperglycaemic conditions. The purpose of the present study was to determine the influence of bradykinin on the levels of glucose, insulin, malondialdehyde and hydrogen peroxide, as well as antioxidative enzyme activity in rats with streptozotocin (STZ)-induced acute hyperglycaemia. In STZ-induced hyperglycaemic rats the levels of glucose, hydrogen peroxide and malondialdehyde were increased by 256% (from 6.0+/-0.3 to 21.4+/-1.3 mmol/l, P<0.001), 33% (from 1.9+/-0.1 to 5.6+/-0.3 mmol H(2)O(2)/ml, P<0.001) and 19% (from 3.7+/-0.3 to 4.9+/-0.2 nmol/l, P<0.001) respectively. The activity of superoxide dismutase, catalase and glutathione peroxidase and the level of insulin were decreased by 46% (from 1367+/-73 to 737+/-59 U/g Hb, P<0.001), 36% (from 2.3+/-0.3 to 1.4+/-0.1 U Bergmayera/g Hb, P<0.001), 31% (from 236+/-19 to 163+/-24 U/g Hb, P<0.001) and 91% (from 47.5+/-1.7 to 2.4+/-0.5 mU/l, P<0.001) respectively in rats treated with streptozotocin. The administration of bradykinin caused the decrease in glucose, hydrogen peroxide and malondi-aldehyde levels by 38% (from 21.4+/-1.3 to 13.3+/-1.0 mmol/l, P<0.001), 37% (from 5.6+/-0.3 to 4.3+/-0.2 mmol H2O2/ml, P<0.001), 39% (from 4.9+/-0.2 to 3.0+/-0.2 nmol/l, P<0.001) respectively and the increase in insulin level and superoxide dismutase, catalase and glutathione peroxidase activity by 62% (from 2.4+/-0.5 to 4.0+/-0.4 mU/l, P<0.001), 23% (from 736.8+/-58.5 to 906.7+/-47.8 U/g Hb, P<0.001), 23% (from 1.4+/-0.1 to 1.9+/-0.1 U Bergmayera/g Hb, P<0.01) and 19% (from 163.1+/-23.6 to 202.3+/-11.7 U/g Hb, P<0.001) respectively in rats with hyperglycaemia. Thus, bradykinin is able to reduce oxidative stress in hyperglycaemic conditions.

Intracerebroventricular infusion of angiotensin II increases water and ethanol intake in rats

The influence of prolonged ingestion of ethanol on stimulation of water or ethanol intake by intracerebroventricular infusion of ANG II was evaluated in rats. Animals were maintained for 5-6 mo with either 10% ethanol solution or water as their only source of fluid. In both groups of rats, infusion of ANG II caused a large increase in water intake (7-fold) and a lesser increase in 10% ethanol intake (2-fold). The effect of ANG II on the volume of ethanol solution ingested, however, was inversely related to the concentration of the ethanol solution. As the concentration of ethanol solution was decreased, frequency and duration of drinking bouts increased. The intake of sweetened 10% ethanol solution or commercially produced wine during infusion of ANG II was similar to the intake of 10% ethanol and not related to taste preference. In conclusion, chronic consumption of ethanol solution did not appear to adversely effect ANG II stimulation of water intake. The intake of ethanol solution during infusion of ANG II was inhibited by a direct effect of ingested ethanol and/or by indirect effect from metabolized ethanol.

Bradykinin-induced water intake and brain fos-like immunoreactivity in rats

We have previously shown that peripheral injection of bradykinin in combination with the kininase II inhibitor, captopril, to rats produces a robust water intake. We now extend this observation to another kininase II inhibitor, enalapril. Water intake increases with dose of dose of bradykinin, but has an inverted U-shaped relationship with dose of kininase II inhibitor. The induced water intake is completely blocked by peripheral administration of the bradykinin antagonist, Hoe 140, and is partly attenuated by peripheral injection of an angiotensin (Ang) II receptor antagonist, losartan. Relative to captopril alone, the combination of captopril and bradykinin greatly elevated plasma renin activity, but did not reduce blood pressure. We further show that, while either bradykinin or enalapril alone induce little or no Fos-like immunoreactivity in areas of the brain related to fluid balance, their combination induces staining in many cells in the supraoptic and paraventricular magnocellular nuclei, as well as along the lamina terminalis. These data suggest that bradykinin may have a role in regulation of fluid balance, partly mediated through Ang II.

Increased alcohol consumption in weight-reduced rats is modulated by the renin-angiotensin system

Weight reduction and food restriction increase the self-administration of alcohol and other drugs of abuse, but the underlying physiological mechanisms have not been identified. Because weight reduction alters angiotensin (ANG) II activity, and ANG II is known to modulate alcohol intake, ANG II may play a role in the enhanced alcohol consumption of food-deprived weight-reduced rats and in the drop in alcohol intake when these rats are refed. Two groups of rats were reduced to and maintained at 80% of their free feeding weights and offered daily 40 min access to a 6% (w/v) alcohol solution and water. Water was available ad lib. After alcohol intake stabilized, one group was given daily injections of the angiotensin converting enzyme inhibitor captopril (5.0 mg/kg) for 6 days while the other group received the saline vehicle. Following this, each group continued to receive either captopril or vehicle injections but was returned to ad lib feeding. Captopril did not alter alcohol intake when the rats were food-deprived and weight-reduced, but did significantly attenuate the decline in alcohol consumption compared to the vehicle group when both groups were refed and regaining weight. These findings suggest that the increase in alcohol intake with food restriction and its decline following refeeding are, in part, related to changes in ANG II activity.

New drugs for the treatment of experimental alcoholism

This article presents a current overview of the efforts to suppress pharmacologically the craving, dependence, or other factors associated with the self-selection of alcohol in an experimental animal. The contemporary status of the pharmacotherapy of experimental alcoholism similarly is described for different animal models of alcohol drinking. An evaluation is presented of several classes of drug for their efficacy in ameliorating the volitional ingestion of alcohol in the presence of an alternative fluid. Currently, two main experimental animal models of alcoholism are being used in this endeavor: (a) genetic lines or substrains of high alcohol preferring or high drinking rats; and (b) strains of nondrinking or low alcohol preferring rats which are induced chemically to prefer alcohol. Because of technical, methodological, and other issues surrounding the procedures used to assess the efficacy of a drug in reducing alcohol intake, several of the newer findings remain controversial. For example, serious side effects on the intake of food, caloric regulation, motor activity, or other functions would preclude the clinical utility of the drug. However, several drugs which affect monoaminergic neurons as well as opioid systems in the brain now seem to offer promise as agents which do possess clinical benefits. Two of these drugs, FG5606 (amperozide) and FG 5893 are essentially "antialcoholic" or anticraving and are without any significant side effects on cerebral mechanisms responsible for hunger, caloric intake, motor activity, or other physiological process. Amperozide, a 5-HT2 receptor antagonist with dopamine releasing properties, is particularly notable because of its irreversible nature in attenuating alcohol preference for months after its administration. It is concluded that future pharmacological research on presently available and newly developed compounds will provide exciting opportunities to the clinician who can utilize a particular drug as an adjunctive tool in the therapeutic treatment of the alcoholic individual.

The reduction in alcohol intake produced by enalapril is not attenuated by centrally administered angiotensin inhibitors

Angiotensin-converting enzyme (ACE) inhibitors, which prevent the conversion of angiotensin I to angiotensin II, reduce alcohol intake when injected peripherally. The mechanism by which ACE inhibitors produce this effect on alcohol intake is unknown. A rise in the biosynthesis of angiotensin II in the periphery is known to reduce alcohol intake. In this experiment, we examine the possibility that the reduction in alcohol intake produced by an ACE inhibitor, enalapril, is mediated by a rise in angiotensin II in the brain. Enalapril, 20 mg/kg, injected intraperitoneally, produced a 40% reduction in alcohol intake. This reduction was not attenuated by the concurrent administration into the lateral ventricle of either the ACE inhibitors captopril or ceranapril (1, 10, or 25 micrograms), or the angiotensin II receptor antagonist Sar1-Thr8-Angiotensin II (5 micrograms). These findings suggest that the ACE inhibitors do not reduce alcohol intake by raising angiotensin II in the brain.

Adrenalectomy does not modify the suppressive effect of angiotensin II on voluntary ethanol drinking in rats

Enhancement of activity in the renin-angiotensin system reduces voluntary ethanol consumption in rats. Because angiotensin II, which is a major bioactive component of the renin-angiotensin system, stimulates the release of aldosterone, aldosterone may play a role in the reduction of ethanol intake by angiotensin II. The present study examined ethanol drinking in a group of rats that was bilaterally adrenalectomized and incapable of producing aldosterone, and in a sham group that underwent similar surgery except that the adrenal glands were left intact. Rats were maintained on ad libitum food, water and 1.5% saline solution in their home cages. Access to ethanol (6% weight/volume) was restricted to a daily 40 min period and was always offered as a choice in conjunction with water. Adrenalectomy did not alter the effect of angiotensin II on ethanol intake as subcutaneous injections of angiotensin II (400 micrograms/kg) significantly reduced ethanol intake to the same degree in both the adrenalectomized and sham groups. In the next phase, daily subcutaneous injections of aldosterone (100 micrograms/kg) reduced the home cage intake of 1.5% saline in the adrenalectomized group indicating that this dose of aldosterone was biologically active. These aldosterone injections did not affect ethanol intake in either the adrenalectomized or sham groups. Under the present conditions of testing aldosterone does not appear to play a role in the angiotensin II-induced reduction of ethanol consumption.