Ethanol-induced activation of the hypothalamic-pituitary-adrenal axis in a mouse model for binge drinking: role of Ro15-4513-sensitive gamma aminobutyric acid receptors, tolerance, and relevance to humans

Dosage scaling of alcohol in binge exposure models in mice: An empirical assessment of the relationship between dose, alcohol exposure, and peak blood concentrations in humans and mice

Binge drinking is a remarkably prevalent behavior. In 2015, 27% of U.S. residents 18 years old or older reported at least one episode of binge drinking in the previous month. Rodent models for binge drinking are widely used to study the mechanisms by which alcohol causes a variety of adverse health effects in humans. Concerns have been raised that many binge-drinking studies in rodents involve alcohol doses that would be unrealistically high in humans. Allometric dosage scaling can be used to estimate the dose of a drug or chemical in mice that would be necessary to achieve similar biological effects at a realistic dose in humans. However, it has become apparent that no single allometric conversion factor is applicable for all drugs and chemicals, so it is necessary to evaluate each compound empirically. In the present study, we compared the area under the blood alcohol concentration vs. time curve (AUC) and the peak blood alcohol concentration following oral alcohol administration at various doses in mice and humans, using data from previously published studies. The results demonstrated that the oral dose of alcohol must be larger in mice (on a g of alcohol to kg of body weight basis) than in humans to achieve similar alcohol AUC values or to achieve similar peak concentrations in the blood. The dose required in mice was about 2-fold greater than the dose required in humans to achieve similar alcohol AUC and peak concentrations. The results shown here were substantially different from the average 5-12-fold difference between mice and humans calculated in previous studies using agents other than alcohol. Results shown here demonstrate that an empirical approach using data from several independent experiments provides information needed to determine the alcohol dose in mice that produces a similar level of exposure (AUC and peak concentration) as in humans. The results indicate that a single alcohol dose in the range of 5-6 g/kg, a range often used in mouse models for binge drinking, is not excessive when modeling human binge drinking. Results presented here illustrate that in mice both alcohol AUC and peak alcohol concentration correlate well with an important biological effect - activation of the hypothalamic-pituitary-adrenal axis - as indicated by increased corticosterone AUC values.

Possible Role of CRF-Hcrt Interaction in the Infralimbic Cortex in the Emergence and Maintenance of Compulsive Alcohol-Seeking Behavior

Alcohol use disorder (AUD) is a chronic, relapsing disorder that is characterized by the compulsive use of alcohol despite numerous health, social, and economic consequences. Initially, the use of alcohol is driven by positive reinforcement. Over time, however, alcohol use can take on a compulsive quality that is driven by the desire to avoid the negative consequences of abstinence, including negative affect and heightened stress/anxiety. This transition from positive reinforcement- to negative reinforcement-driven consumption involves the corticotropin-releasing factor (CRF) system, although mounting evidence now suggests that the CRF system interacts with other neural systems to ultimately produce behaviors that are symptomatic of compulsive alcohol use, such as the hypocretin (Hcrt) system. Hypocretins are produced exclusively in the hypothalamus, but Hcrt neurons project widely throughout the brain and reach regions that perform regulatory functions for numerous behavioral and physiological responses-including the infralimbic cortex (IL) of the medial prefrontal cortex (mPFC). Although the entire mPFC undergoes neuroadaptive changes following prolonged alcohol exposure, the IL appears to undergo more robust changes compared with other mPFC substructures. Evidence to date suggests that the IL is likely involved in EtOH-seeking behavior, but ambiguities with respect to the specific role of the IL in this regard make it difficult to draw definitive conclusions. Furthermore, the manner in which CRF interacts with Hcrt in this region as it pertains to alcohol-seeking behavior is largely unknown, although immunohistochemical and electrophysiological experiments have shown that CRF and Hcrt directly interact in the mPFC, suggesting that the interaction between CRF and Hcrt in the IL may be critically important for the development and subsequent maintenance of compulsive alcohol seeking. This review aims to consolidate recent literature regarding the role of the IL in alcohol-seeking behavior and to discuss evidence that supports a functional interaction between Hcrt and CRF in the IL.

Alcohol, stress hormones, and the prefrontal cortex: a proposed pathway to the dark side of addiction

Chronic exposure to alcohol produces changes in the prefrontal cortex that are thought to contribute to the development and maintenance of alcoholism. A large body of literature suggests that stress hormones play a critical role in this process. Here we review the bi-directional relationship between alcohol and stress hormones, and discuss how alcohol acutely stimulates the release of glucocorticoids and induces enduring modifications to neuroendocrine stress circuits during the transition from non-dependent drinking to alcohol dependence. We propose a pathway by which alcohol and stress hormones elicit neuroadaptive changes in prefrontal circuitry that could contribute functionally to a dampened neuroendocrine state and the increased propensity to relapse-a spiraling trajectory that could eventually lead to dependence.

Increased plasma corticosterone contributes to the development of alcoholic fatty liver in mice

Ethanol ingestion increases endogenous glucocorticoid levels in both humans and rodents. The present study aimed to define a mechanistic link between the increased glucocorticoids and alcoholic fatty liver in mice. Plasma corticosterone levels were not affected in mice on a 2-wk ethanol diet regimen but significantly increased upon 4 wk of ethanol ingestion. Accordingly, hepatic triglyceride levels were not altered after 2 wk of ethanol ingestion but were elevated at 4 wk. Based on the observation that 2 wk of ethanol ingestion did not significantly increase endogenous corticosterone levels, we administered exogenous glucocorticoids along with the 2-wk ethanol treatment to determine whether the elevated glucocorticoid contributes to the development of alcoholic fatty liver. Mice were subjected to ethanol feeding for 2 wk with or without dexamethasone administration. Hepatic triglyceride contents were not affected by either ethanol or dexamethasone alone but were significantly increased by administration of both. Microarray and protein level analyses revealed two distinct changes in hepatic lipid metabolism in mice administered with both ethanol and dexamethasone: accelerated triglyceride synthesis by diacylglycerol O-acyltransferase 2 and suppressed fatty acid β-oxidation by long-chain acyl-CoA synthetase 1, carnitine palmitoyltransferase 1a, and acyl-CoA oxidase 1. A reduction of hepatic peroxisome proliferation activator receptor-α (PPAR-α) was associated with coadministration of ethanol and dexamethasone. These findings suggest that increased glucocorticoid levels may contribute to the development of alcoholic fatty liver, at least partially, through hepatic PPAR-α inactivation.

Long-term binge and escalating ethanol exposure causes necroinflammation and fibrosis in rat liver

BACKGROUND

To investigate whether "binge" and escalating alcohol exposure in the rat influences the development of pathological liver injury.

METHODS

Time courses for the formation of eicosanoids by cyclooxygenase (COX), oxidative stress and nitrosative stress production, expression of hypoxia-inducible factor 1 (HIF-1), cytokines, hepatic tissue necroinflammation, and fibrosis were assessed in rats during 16 weeks of daily alcohol gavage.

RESULTS

In this model of binge and escalating levels of alcohol, hepatic steatosis, necrosis, and inflammation as well as fibrosis were increased over the 16-week period. The levels of COX-2, oxidative stress, nitrosative stress, HIF-1, proinflammatory mediators (tumor necrosis factor-α, interleukin 1(β) [IL-1(β) ], IL-6), and procollagen-I were increased over the 16-week period. The content of IL-10 in rat serum increased at the end of 4 and 8 weeks but decreased thereafter and was significantly decreased at 12 and 16 weeks.

CONCLUSIONS

A rat model of alcoholic liver disease (ALD) with long-term binge and escalating ethanol exposure was developed. Our data support the hypothesis that enhanced eicosanoid production by COX, oxidative stress and nitrosative stress, HIF-1, and the imbalance between pro- and anti-inflammatory cytokines plays an important role in the pathogenesis of ALD.

Patterns of immunotoxicity associated with chronic as compared with acute exposure to chemical or physical stressors and their relevance with regard to the role of stress and with regard to immunotoxicity testing

Previous studies have demonstrated that the stress response induced by some drugs and chemicals contributes in a predictable way to alteration of particular immunological parameters in mice. It has not been determined if mice can become tolerant or habituated with regard to the stress response and consequent immunological effects. Addressing this issue was the purpose of the present study. Mice were dosed daily for 28 days with atrazine, ethanol, propanil, or subjected to restraint, which are known to induce neuroendocrine stress responses and thereby to alter several immunological parameters. On day 29, a blood sample was taken and the spleen was removed for analysis of cellular phenotypes, differential cell counts (for blood), and natural killer (NK) cell activity. Corticosterone concentration at various times after dosing (or restraint) was also measured. Comparison of these results with results from previous studies with a single acute exposure revealed that the corticosterone response was almost completely absent in mice treated with ethanol, reduced in mice treated with restraint and propanil, and for atrazine the response was the same as noted for acute exposure. In most cases, the changes in immunological parameters were consistent with expectations based on these corticosterone responses. However, in a few cases (e.g., NK cell activity), it was clear that there were effects not mediated by stress. These results indicate that the nature of the stressor determines whether mice become tolerant with regard to the stress response and consequent immunological effects. This finding has practical implications for safety testing in mice.

Role of corticosterone in immunosuppressive effects of acute ethanol exposure on Toll-like receptor mediated cytokine production

Acute ethanol (EtOH) exposure causes a stress response in humans, nonhuman primates, and rodents. Previous study results indicate that the suppression of some immunological parameters by EtOH is mediated in part or completely by elevated corticosterone concentrations induced by EtOH. However, initial results suggested that corticosterone is not involved in the modulation of cytokine production by macrophages in response to polyinosinic polycytidylic acid (poly I:C). New studies were conducted to further evaluate the role of corticosterone in EtOH-mediated changes in production of interleukin-6 (IL-6), IL-10, and IL-12 in serum and peritoneal fluid in mice treated with poly I:C or lipopolysaccharide (LPS). Suppression of IL-6, but not IL-12, production by EtOH was found to be mediated by corticosterone. However, poly I:C, LPS, and EtOH all caused similar elevations of corticosterone concentrations; thus, it is not clear if EtOH is required to induce levels or durations of corticosterone needed to mediate the observed effects. The situation with IL-10 was more complicated. Inhibition of corticosterone synthesis with aminoglutethimide prevented the increase in IL-10 production caused by EtOH plus poly I:C as compared to poly I:C only. This indicates that this increase is dependent on corticosterone, but exogenous corticosterone plus poly I:C did not increase IL-10 production. Thus, EtOH and corticosterone are required. However, with LPS inhibition of corticosterone synthesis (using aminoglutethimide) or inhibition of its action (using mifepristone) further increased, or did not affect IL-10 concentrations, suggesting fundamental differences in the signaling pathways leading from poly I:C and LPS to IL-10 production.

Suppression of innate immunity by acute ethanol administration: a global perspective and a new mechanism beginning with inhibition of signaling through TLR3

Excessive consumption of ethanol (EtOH) suppresses innate immunity, but the mechanisms have not been fully delineated. The present study was conducted to determine whether EtOH suppresses TLR signaling in vivo in mice and to characterize the downstream effects of such suppression. Degradation of IL-1R-associated kinase 1 induced by a TLR3 ligand in peritoneal cells ( approximately 90% macrophages) was suppressed by EtOH. Phosphorylation of p38 kinase in peritoneal macrophages (F4/80(+)) was suppressed, as was nuclear translocation of p-c-Jun and p65 in peritoneal cells. EtOH decreased IL-6 and IL-12 (p40), but did not significantly affect IL-10 in peritoneal lavage fluid or in lysates of peritoneal cells. Changes in cytokine mRNAs (by RNase protection assay) in macrophages isolated by cell sorting or using Ficoll were generally consistent with changes in protein levels in cell lysates and peritoneal lavage fluid. Thus, suppression of TLR signaling and cytokine mRNA occurred in the same cells, and this suppression generally corresponded to changes in i.p. and intracellular cytokine concentrations. DNA microarray analysis revealed the suppression of an IFN-related amplification loop in peritoneal macrophages, associated with decreased expression of numerous innate immune effector genes (including cytokines and a chemokine also suppressed at the protein level). These results indicate that EtOH suppresses innate immunity at least in part by suppressing TLR3 signaling, suppressing an IFN-related amplification loop, and suppressing the induction of a wide range of innate effector molecules in addition to proinflammatory cytokines and chemokines.

Ethanol decreases natural killer cell activation but only minimally affects anatomical distribution after administration of polyinosinic:polycytidylic acid: role in resistance to B16F10 melanoma

BACKGROUND

Natural killer (NK) cells are critical in resistance to B16F10 lung metastases in B6C3F1 mice. Activation of NK cells by polyinosinic:polycytidylic acid (poly I:C; 0.1 mg, intraperitoneally) increases resistance to B16F10 cells. This effect is reduced after administration of ethanol (EtOH; 6 g/kg by oral gavage). The present study was conducted to determine whether decreased resistance is due to alteration of the distribution and/or the activation of NK cells.

METHODS

These parameters were measured in the spleen, lungs, and peripheral blood 4 and 12 hr after EtOH and poly I:C administration. For assessing the time after poly I:C administration during which NK cells are important in resistance to B16F10 cells, anti-NK1.1 antibody was used to deplete NK cells in vivo 48 hr before and 0, 6, 12, and 24 hr after intravenous injection of B16F10 tumor cells.

RESULTS

Depletion of NK cells at any time up to 12 hr after B16F10 administration significantly increased the number of tumor nodules in the lungs, but depletion at 24 hr had a smaller effect. Flow cytometry revealed that there was a small but significant increase in the percentage of NK cells in the lungs at 12 hr, which was not changed by EtOH. Corresponding NK cell lytic function in the lungs was increased significantly at both 4 and 12 hr by poly I:C. However, the increase was not significantly different from the naive control value at 4 hr in mice treated with poly I:C plus EtOH, indicating that EtOH decreased activation of NK cells in the lungs at 4 hr. In the spleen, no treatment significantly altered the percentage of NK cells at 4 or 12 hr. However, poly I:C significantly enhanced lytic function, and this enhancement was suppressed by EtOH (by approximately 50%). In the blood, the only significant change in NK cell percentage or lytic activity was an increase in the percentage of NK cells at 12 hr, which was equivalent in the poly I:C and the poly I:C plus EtOH groups.

CONCLUSIONS

These results demonstrate that EtOH partially abrogates the poly I:C-induced enhancement of resistance to B16F10 cells and that decreased activation of NK cells in the lungs at a critical time early in the response to poly I:C may contribute to this effect. Other parameters could also contribute, but there was little support for an important role for changes in NK cell distribution.

Brain concentrations of d-MDMA are increased after stress

RATIONALE

In the mouse but not the rat, d-3,4-methylenedioxymethamphetamine (d-MDMA) is a dopaminergic neurotoxicant. Various stressors and hypothermia protect against d-MDMA-induced neurotoxicity through unknown mechanisms, one of which could be a reduction in the distribution of d-MDMA to the brain.

OBJECTIVES

We determined striatal levels of d-MDMA in relation to body temperature in mice exposed to a neurotoxic regimen of d-MDMA in the presence or absence of various stressors.

METHODS

Female C57BL6/J mice received a neurotoxic regimen of d-MDMA (15.0 mg/kg s.c. as the base every 2 hx4) alone or in combination with manipulations with a known neuroprotective status. d-MDMA levels were determined by HPLC with fluorometric detection while rectal temperature provided core temperature status. Levels of dopamine, tyrosine hydroxylase and GFAP were used to assess neurotoxicity.

RESULTS

Restraint, ethanol co-treatment and cold stress were neuroprotective, caused hypothermia and increased striatal d-MDMA levels by 4- to 7-fold. Corticosterone treatment, as a stress mimic, did not alter striatal d-MDMA or temperature and was not protective. The protective glutamate receptor antagonist, MK-801, doubled striatal d-MDMA levels and caused hypothermia.

CONCLUSIONS

Although stress and other protective manipulations can alter the striatal concentration of d-MDMA their hypothermia-inducing properties appear a more likely determinant of their neuroprotection against the striatal dopaminergic neurotoxicity of d-MDMA.

Acute ethanol administration profoundly alters poly I:C-induced cytokine expression in mice by a mechanism that is not dependent on corticosterone

Polyinosinic polycytidylic acid (poly I:C) is an analog of double stranded RNA, which is a common replication intermediate for many viruses. It acts through a toll-like receptor (TLR3) to induce a group of cytokines that can mediate host resistance to viruses and some cancers. The effect of ethanol (EtOH) on induction of this set of cytokines has not been determined. Mice were treated with a single dose of EtOH (by gavage) at the same time as poly I:C was administered (intraperitoneally), and cytokine mRNA expression was measured by RNAse protection assay. Concentrations of IFN-alpha, IL-10, and IL-12 in the serum were measured by ELISA. A single dose of EtOH suppressed induction of mRNA for IFN-alpha, IFN-beta, IFN-gamma, IL-6, IL-9, IL-12, and IL-15. The concentrations of IFN-alpha and IL-12 in the serum were also decreased. In contrast, IL-10 was minimally induced by poly I:C alone, but it was substantially induced by poly I:C plus EtOH. Dose response and time course studies demonstrated that significant alterations of IFN-alpha, IL-10, and IL-12 expression occurred at dosages as low as 4 g/kg (a dosage previously shown to produce blood EtOH concentrations of approximately 0.2%) and that alterations persisted at least 4-6 hr after administration of EtOH. The glucocorticoid synthesis inhibitor, aminoglutethimide, diminished corticosterone levels to normal, but did not block the effects of EtOH on cytokine expression. These results demonstrate that EtOH affects the expression of poly I:C-induced cytokines and that this action is not mediated by corticosterone. These results plus previously published findings are consistent with the idea that EtOH may be a generalized suppressor of toll-like receptor signaling.

Ethanol suppresses polyinosinic:polycytidylic acid-induced activation of natural killer cells primarily by acting on natural killer cells, not through effects on other cell types

Natural killer (NK) cells can be activated in vitro and in vivo by polyinosinic:polycytidylic acid (poly I:C) through induction of type I interferons or other cytokines. Ethanol suppresses in vivo and ex vivo poly I:C activation of NK cell activity in a mouse model for binge drinking, but it is not known whether this effect is mediated by changes in NK cells or in other cell types (e.g., those that produce NK cell-activating cytokines). Splenocytes were obtained from C57BL/6 [NK cell-competent (NKc)] and C57BL/6 perforin knockout [NK cell-incompetent (NKi)] mice 6 h after administration of ethanol (6 g/kg) or vehicle (VH; dH(2)O). Cells were incubated in vitro 18 h with poly I:C (100 micro g/ml), followed by a 4-h 51Cr release assay with the use of YAC-1 target cells. Results of cell-mixing experiments involving all relevant combinations of splenocytes obtained from NKc and NKi mice treated with VH or ethanol strongly supported the suggestion that NK cells, not other cell types, are the primary target of ethanol-induced suppression of NK cell activation. For example, mixing of splenocytes obtained from ethanol-treated NKc and VH-treated NKi mice or from ethanol-treated NKc and ethanol-treated NKi mice yielded similar cytolytic function. However, mixing of splenocytes obtained from ethanol-treated NKc and VH-treated NKi mice yielded significantly less cytolytic activity than that of splenocytes from VH-treated NKc and ethanol-treated NKi mice. In addition, mixing of splenocytes obtained from VH-treated NKc and NKi mice resulted in lower cytolytic activity than when splenocytes from the NKi mice were treated with ethanol instead of with VH, demonstrating that ethanol did not decrease the function of other cell types. A strikingly similar pattern of results was observed when B6C3F1 mice, rendered NK cell deficient by administration of anti-NK 1.1 monoclonal antibody, were used instead of perforin knockout mice. These results indicate that ethanol suppresses activation of NK cells primarily by suppressing the NK cell response to poly I:C, not by acting on another cell type.

Quantitative aspects of stress-induced immunomodulation

Recent studies indicate that neuroendocrine-immune interactions can cause sufficient immunosuppression to adversely affect human health, but quantitative relationships between stress-related hormones or neurotransmitters and immune function have not been well documented. The mechanisms of stress-induced immunomodulation cannot be fully understood solely by identifying the hormones, neurotransmitters, and cytokines involved. Quantitative relationships and interactions must also be understood. Depending on the nature and duration of the stressor and the immunological parameter under investigation, stress responses can enhance, have no effect, or suppress immunological parameters. These quantitative relationships have implications with regard to safety assessment of drugs and chemicals and with regard to potential development of pharmacological interventions to ameliorate some of the immunosuppressive effects of stress. This review describes selected studies that relate the quantity and duration of exposure to stress-related neuroendocrine mediators to modulation of the immune system. These studies provide a useful starting point, but they also illustrate how much work remains to achieve a fully integrated qualitative and quantitative understanding of stress-induced immunomodulation.

Dexamethasone reverses the ethanol-induced anxiolytic effect in rats

The effects of intraperitoneal and intrahippocampal administration of the glucocorticoid dexamethasone were assessed regarding ethanol-induced anxiolysis in the elevated plus-maze in rats. Animals pretreated with systemic injections of dexamethasone (0.5, 1. 0, or 2.0 mg/kg, IP) 15 min before ethanol (1.2 g/kg, 14% w/v, IP) administration showed a significant dose-dependent attenuation of the increased percentage of frequency and time spent on open arms of the maze. However, IP dexamethasone treatment 4 h before the test had no effect. Unilateral intrahippocampal injection of dexamethasone (2 and 20 nmol in 0.5 microl) also significantly attenuated the increased exploration of the open arms induced by ethanol. The results are interpreted in terms of the modulation of the anxiolytic effects of ethanol by glucocorticoids and the possible involvement of hippocampus in this response. The rapid blockade of ethanol induced anxiolysis by dexamethasone strengthens the suggestion that a nongenomic mechanism may underlie this response.

Mechanisms of suppression of poly I:C-induced activation of NK cells by ethanol

We have previously reported that ethanol (EtOH) decreases polyinosinic-polycytidylic acid (poly I:C) and interleukin-2 (IL-2)-induced upregulation of natural killer (NK) cell lytic activity in mice. The present study was designed to determine if decreased production of or response to interferon-alpha (IFN-alpha) is involved and if this is associated with inhibited upregulation of perforin or granzyme B. Treatment of mice with poly I:C upregulated IFN-alpha and granzyme B, but not perforin, in the spleen. Administration of EtOH before poly I:C prevented the upregulation of IFN-alpha and granzyme B and decreased perforin levels. EtOH exposure in vivo rendered splenocytes less able to respond to IFN-alpha upon in vitro exposure to poly I:C. Exogenous IFN-alpha only partially prevented this decreased response. Thus, decreased production of and response to IFN-alpha as well as decreased levels of granzyme B and perforin are implicated in the diminished activation of NK cell lytic function in EtOH-treated mice.

Ethanol decreases host resistance to pulmonary metastases in a mouse model: role of natural killer cells and the ethanol-induced stress response

The present study was done to delineate cause-effect relationships between the ethanol (EtOH)-induced stress response, natural-killer (NK)-cell activity, and resistance to experimental metastases of B16F10 melanoma cells in mice. Increased numbers of metastatic nodules were noted in the lungs of mice treated with dosages of EtOH that produce peak blood levels of 0.25-0.4%. EtOH caused only a minor depletion of NK cells or NK-cell activity from the spleen or lungs of normal or B16F10-challenged mice. However, in earlier studies we have shown consistent, significant decreases in NK-cell activity (approx. 50%) in spleen preparations from EtOH-treated mice. Depletion of NK cells by a monoclonal antibody increased the number of B16F10 nodules in the lungs, confirming an important role for NK cells for resistance to B16F10 metastases. Treatment of NK-cell-depleted mice with EtOH caused no further decrease in resistance to B16F10 cells, indicating that suppression of NK-cell activity is the major mechanism by which EtOH suppresses resistance to B16F10 metastases. Adrenalectomy or a glucocorticoid antagonist partially prevented EtOH-induced increases in the number of metastatic nodules in the lungs. Administration of exogenous corticosterone increased the number of B16F10 nodules to an extent similar to that caused by EtOH. These results indicate a role for the EtOH-induced stress response in decreasing resistance to B16F10 metastases. EtOH-induced decreases in resistance to cancer have also been reported in rats. The findings of the present study support the possibility that this is a generalized phenomenon, which could occur in humans.