Effect of Pretreatment with Alcohol on Subsequent Endocrine and Immune Responses in the Adult Male Rat

Role of hypothalamic corticotropin-releasing factor in mediating alcohol-induced activation of the rat hypothalamic-pituitary-adrenal axis

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis through brain-based mechanisms in which endogenous corticotropin-releasing factor (CRF) plays a major role. This review first discusses the evidence for this role, as well as the possible importance of intermediates such as vasopressin, nitric oxide and catecholamines. We then illustrate the long-term influence exerted by alcohol on the HPA axis, such as the ability of a first exposure to this drug during adolescence, to permanently blunt neuroendocrine responses to subsequent exposure of the drug. In view of the role played by CRF in addiction, it is likely that a better understanding of the mechanisms through which this drug stimulates the HPA axis may lead to the development of new therapies used in the treatment of alcohol abuse, including clinically relevant CRF antagonists.

Adolescent alcohol exposure alters the central brain circuits known to regulate the stress response

Adolescent alcohol exposure (AAE) may exert long-term effects on the adult brain. Here, we tested the hypothesis that the brain regions affected include the rat hypothalamic-pituitary-adrenal (HPA) axis. Specifically, we examined the consequences of AAE [postnatal days (PND) 28-42] on the HPA axis-related brain circuitry of male rats challenged with an intragastric (ig) administration of alcohol in young adulthood (PND 61-62). Adolescent rats were exposed to alcohol vapors, while controls did not receive the drug. The mean blood alcohol level in adolescence on PND 40 was 212.8±5.7 mg %. Using immunohistochemistry and in situ hybridization procedures, we measured signals for c-fos and corticotropin releasing factor (CRF) in the paraventricular nucleus (PVN) of the hypothalamus, as well as signals for c-fos and phenylethanolamine N-methyltransferase (PNMT) in the adrenergic brain stem regions (C1 and C2). PVN CRF mRNA expression was significantly blunted in AAE rats tested at PND 61-62, compared to their controls. These animals also displayed a significant increase in the mean number of PNMT-ir cells/brain stem section in the C2 area. Collectively, these results suggest that exposure to alcohol vapors during adolescence exerts long-term effects on the ability of the PVN to mount a response to an acute alcohol administration in young adulthood, possibly mediated by medullary catecholamine input to the PVN.

Acute ethanol treatment modulates Toll-like receptor-4 association with lipid rafts

BACKGROUND

Alcohol, a substance that is most frequently abused, suppresses innate immune responses to microbial pathogens. The host senses pathogens via Toll-like receptors (TLRs). Recent studies indicate that alcohol affects TLR signaling.

METHODS

Here, we hypothesized that acute alcohol treatment may interfere with early steps of membrane-associated TLR2 and TLR4 signaling at the level of lipid rafts. Human monocytes and Chinese hamster ovary (CHO) cells, transfected with human TLR2, TLR4, or CD14, were stimulated with peptidoglycan (PGN, TLR2 ligand) or lipopolysaccharide (LPS, TLR4 ligand) with or without alcohol (50 mM) and analyzed for cytokine production (enzyme-linked immunosorbent assay), nuclear factor-kappaB (NF-kappaB) activation (electrophoretic mobility shift assay), membrane fluidity (fluorescent pyrene eximer formation), and partition of cellular membrane into cholesterol-rich, detergent-resistant domains (DRMs; Western blot).

RESULTS

We determined that both TLR2 and TLR4 were located outside the rafts; flotillin, a DRM marker, was resident in the rafts, while CD14 was equally distributed in and outside the rafts in a steady-state condition. PGN forced TLR2 to migrate into DRMs. Engagement of TLR4 and CD14 with LPS induced their migration into the rafts. Alcohol prevented TLR4 partitioning; however, it did not affect TLR2 migration into the rafts. Furthermore, alcohol downregulated TLR4-induced, but not TLR2-induced, NF-kappaB activation and cytokine production in monocytes. We found that alcohol increased membrane fluidity and depleted cellular cholesterol in CHO cells without affecting cell viability.

CONCLUSIONS

These data demonstrate for the first time that alcohol disturbs TLR4 and CD14 association with lipid rafts. We propose that alcohol-induced effects on lipid rafts may contribute to modulation of TLR4-CD14-triggered early cellular responses.

Alcoholism and neuro-immune-endocrine interactions: physiochemical aspects

The role of alcohol consumption and alcoholism as an addiction in regulating the chemistry of the brain and its physiology has gained a backlog of interest over the past few decades. Besides the notion that alcohol acts as a brain depressant, the molecular mechanisms and neuronal interactions are not well understood. Emerging evidence implicates alcohol as a neurochemical messenger that influences a cross talk amongst the nervous, immune, and endocrine systems. Specifically, alcohol acts as a crucial regulator of the hypothalamic-pituitary-adrenal (HPA) axis, thereby modulating the release of hormones, particularly adrenocorticotropic hormone (ACTH) and corticosterone (CORT). It is the aim of this review, therefore, to investigate current concepts on how alcohol, particularly ethanol, and alcoholism affect neuro-immune-endocrine neurochemical interactions via the regulation of the HPA axis, taking into consideration bio-behavioral and physiochemical aspects.

Prolonged exposure to intermittent alcohol vapors decreases the ACTH as well as hypothalamic nitric oxide and cytokine responses to endotoxemia

BACKGROUND

Prolonged exposure to alcohol blunts the response of the hypothalamic-pituitary-adrenal (HPA) axis to various stressors, including the systemic injection of a lipopolysaccharide (LPS). We previously showed that decreased synthesis of the hypothalamic peptides corticotropin-releasing factor (CRF) and vasopressin (VP) played a central role in this phenomenon. However, the mechanisms that lead to decreased hypothalamic neuronal activity have not been identified. In the present work, we tested the hypothesis that alcohol decreased signals that are elicited by LPS and that stimulate hypothalamic CRF and VP synthesis, namely nitric oxide (NO) and the proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6).

METHODS

Adult male rats were exposed to intermittent (5 hr/day) alcohol vapors for 5 days. Control animals were kept in comparable chambers but not exposed to the vapors. On day 6, the animals received an injection of LPS through permanent indwelling intravenous cannulae. The dependent variables were plasma ACTH levels measured by IRMA (immunoradiometric assay); pituitary and hypothalamic TNF-alpha and IL-6 mRNA levels measured by RNase protection assay; basal activity of neuronal NO synthase measured by conversion of [14C]arginine to [14C]citrulline, the constitutive enzyme that synthesizes NO and modulates the influence of this gas on LPS-induced HPA axis activity; and basal and LPS-induced levels of citrulline (an index of NO formation) in the hypothalamus, measured by immunocytochemistry.

RESULTS

After injection with LPS, rats that were pretreated with alcohol exhibited a significantly (p < 0.01) decreased release of ACTH, compared with controls. There was no difference in basal NO synthase activity or hypothalamic citrulline levels. In contrast, LPS-induced hypothalamic citrulline levels were significantly (p < 0.01) lower in alcohol-exposed rats, as were pituitary TNF-alpha and IL-6 transcripts. In the hypothalamus, the TNF-alpha but not IL-6 response to LPS was also reduced.

CONCLUSIONS

These results indicate that prolonged exposure to alcohol decreases the ACTH, hypothalamic NO and TNF-alpha, and pituitary TNF-alpha and IL-6 responses to LPS. This suggests that altered NO and proinflammatory cytokine levels in the brain may modulate the inhibitory influence exerted by alcohol on the HPA axis response to endotoxemia.

Decreased proopiomelanocortin mRNA in lymphocytes of chronic alcoholics after intravenous human corticotropin releasing factor injection

BACKGROUND

Alcohol abuse may involve an altered neuroendocrine response that mediates lymphocyte-derived proopiomelanocortin (POMC) production and inflammation. We investigated POMC messenger RNA (mRNA) expression in human lymphocytes ex vivo and their relation to plasma ACTH and immunoreactive beta-endorphin (IR-beta-EP) after intravenous injection of human corticotropin releasing factor (hCRF) in chronic alcoholics (n = 12) and nonalcoholics (n = 12) before surgery. Lipopolysaccharide-stimulated interleukin (IL)-1 receptor antagonist (IL-1 Ra) as a marker for chronic inflammation was determined.

METHODS

Chronic alcohol abuse was diagnosed according to DSM-IV criteria and alcohol consumption >60 g/day. A reverse transcription-polymerase chain reaction method with total RNA and subsequent solid phase minisequencing was used to quantify lymphocytic POMC mRNA after intravenous hCRF injection. Plasma ACTH, cortisol, and lipopolysaccharide-stimulated IL-1 Ra of monocytes were measured by enzyme-linked immunosorbent assay, and plasma IR-beta-EP was measured by using radioimmunoassay.

RESULTS

Baseline values of POMC mRNA content in lymphocytes and IL-1 Ra of chronic alcoholics were significantly increased compared with nonalcoholics (p < 0.01). Thirty minutes after intravenous hCRF injection, a significant increase of lymphocytic POMC mRNA was measured (p < 0.05) in nonalcoholics, whereas in chronic alcoholics a significant decrease was observed (p < 0.05).

CONCLUSIONS

Chronic alcoholic patients had an altered neuroendocrine immune axis before intravenous hCRF administration and were not able to adjust to intravenous CRF injection by increasing lymphocytic POMC mRNA expression.

Long-term influence of an initial exposure to alcohol on the rat hypothalamic-pituitary axis

OBJECTIVE

We have previously shown that adult male rats injected with alcohol daily for 3 consecutive days displayed a significantly blunted ACTH to a second alcohol injection, given 3 to 7 days later. The purpose of the present work was to determine the maximum duration over which the ACTH response remained blunted after an initial alcohol treatment.

METHODS

Male rats were exposed to alcohol (intragastrically or via vapors for 4 hr) on three consecutive days, starting when they were 22 (group A), 34 (group B), or 50 days old (group C). Control animals were injected with the vehicle intragastrically or kept in chambers through which normal air was circulated. At 60 days of age, the animals were injected with the vehicle or alcohol (4.5 g/kg intragastrically) to determine whether the initial treatment had long-term consequences on the ACTH response to a second alcohol challenge.

RESULTS

Rats of group C, pretreated with alcohol via intragastric injections or vapors, all exhibited a blunted ACTH response to the second acute alcohol challenge. In contrast, the second alcohol challenge only attenuated ACTH responses in rats of group B that had received intragastric injections, but not vapors. Group A showed a comparable response to acute intragastric alcohol injection at 60 days of age regardless of whether they had been preexposed to the drug. This was not due to a lack of neuroendocrine response because alcohol vapors significantly increased plasma ACTH levels and up-regulated paraventricular nucleus neuronal activity regardless of the age at which it was initially administered.

CONCLUSIONS

Repeated (daily for 3 consecutive days) administration of alcohol by the gastric route induces a long-lasting (up to 24 days) but not permanent blunting of the ACTH response to a second (acute) alcohol challenge. The fact that alcohol delivered by inhalation only caused a relatively brief (</=8 days) decrease in the ability of a second intragastric alcohol challenge to release ACTH suggests that the mode of alcohol delivery influences its long-term consequences.

Alcohol, injury, and cellular immunity

It is widely accepted that alcohol exposure is a causative factor in the occurrence of burn or other traumatic injury. It is less well known that individuals who have consumed alcohol before sustaining an injury suffer from increased morbidity and mortality compared with the morbidity and mortality of non-alcohol-consuming subjects with similar injuries. Complications due to bacterial infection are the most common burn sequelae in injured patients and are frequently associated with depressed immunity. Independently, alcohol exposure and injury have been shown to influence cellular immunity negatively. These changes in immunity are closely linked to injury- or alcohol-induced alterations in the cytokine milieu in both clinical studies and animal models. Not surprisingly, the combination of insult of alcohol exposure and burn injury results in immune suppression that is greater in magnitude and duration compared with either insult alone. The combined effects of alcohol and injury on immunity have been examined in a limited number of studies. However, results of these studies support the suggestion that altered cytokine production is an integral part of the immune dysregulation and increased mortality that is observed. In particular, the increased presence of macrophage-derived mediators observed after burn or alcohol exposure alone seems to be synergistically increased in a combined injury model. Although more research is needed, it is likely that therapeutic modalities that include manipulation of cytokine networks to boost cellular immunity may improve outcome for patients who sustain injuries subsequent to consuming alcohol.

Ovariectomy has minimal effects on neuroadaptations associated with ethanol dependence in female rats

We previously found gender selective alterations in gene expression for GABA(A) and NMDA receptors associated with the development of ethanol dependence. Males and females have a differing hormonal environment, including steroid hormone derivatives (neuroactive steroids) that exert effects at GABA(A) and NMDA receptors. Therefore, we explored whether the removal of ovarian steroids would alter gender differences in response to chronic ethanol exposure. We found that ovariectomy reduced ethanol drinking levels by 15%, comparable to earlier observations between intact female and male rats. However, investigation of the effects of chronic ethanol exposure on intact versus ovariectomized female rats uncovered few differences in chronic ethanol-induced alterations in selected GABA(A) or NMDA receptor subunit peptide levels. In general, findings for both groups of females were similar to previous observations. There was no reduction in GABA(A) receptor alpha1 subunit levels in cerebral cortex in either intact or ovariectomized female rats, in contrast to the significant reduction observed in male rats. In addition, both intact and ovariectomized female rats had increased levels of the NMDA NR1 subunit in cerebral cortex and hypothalamus, but not in hippocampus, whereas ethanol dependent male rats displayed significant increases in the NR1 subunit only in hippocampus. Radioligand binding analysis with [35S]TBPS found no differences in modulation of the GABA(A) receptor by neuroactive steroids between ethanol dependent male, intact female or ovariectomized female rats. Seizure susceptibility was not different between intact or ovariectomized female rats during ethanol withdrawal. We did observe differential effects on brain allopregnanolone and plasma corticosterone levels between ethanol dependent intact and ovariectomized female rats, suggesting that ovarian steroids influence HPA axis adaptations to prolonged ethanol exposure. Overall, these data suggest that ovarian steroids do not significantly impact the gender selective alterations of GABA(A) and NMDA receptors associated with ethanol dependence.