Ethanol suppression of the hypothalamic proopiomelanocortin level and the splenic NK cell cytolytic activity is associated with a reduction in the expression of proinflammatory cytokines but not anti-inflammatory cytokines in neuroendocrine and immune cells.

BACKGROUND: Immune signals activate a network of cytokines in the central nervous system (CNS) that in turn causes release of neurotransmitters and hormones to modulate immune cell functions. We have recently shown that hypothalamic beta-endorphin neurons, via inhibition of the sympathetic neuronal activity, activate natural killer (NK) cell function in the spleen, and this communication is disrupted following chronic ethanol administration. Beta-endorphin neuronal function is known to be regulated by various proinflammatory and anti-inflammatory cytokines. The effects of ethanol on the proinflammatory and anti-inflammatory cytokines known to control beta-endorphin neuronal and NK cell functions during immune challenges have not been determined.

METHODS: In the present study, we evaluated the effects of chronic ethanol consumption on the basal and lipopolysaccharide (LPS)-activated NK cells' functions in the spleen, the beta-endorphin peptide precursor proopiomelanocortin (POMC) gene expression in the arcuate nucleus (ARC) of the hypothalamus, and mRNA levels of proinflammatory cytokines interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), and anti-inflammatory cytokines IL-6 and IL-10 in the spleen and in the ARC. Male rats were ad libitum fed rat chow (ad lib-fed), pair-fed an isocaloric liquid diet, or fed an ethanol-containing liquid diet, and each was treated with LPS (100 microg/kg body weight). After 2 hours, splenocytes and ARC tissues were isolated and used for this study. Splenocytes were used to determine mRNA levels of IL-1beta, TNF-alpha, IL-6, IL-10, granzyme B, and perforin using the real-time RT-PCR assays. Splenocytes were also used to determine the cytolytic activity using a standard 4-hour (51)Cr release assay against YAC-1 lymphoma target cells. Arcuate nuclei were used to determine IL-1beta, TNF-alpha, IL-6, IL-10, and POMC mRNA levels using real-time RT-PCR assays.

RESULTS: The results demonstrate that ethanol feeding via a liquid diet for 2 weeks suppressed both basal and LPS-stimulated NK cell cytolytic functions and the levels of cytotoxicity-regulatory perforin and granzyme B mRNAs in the spleen. Ethanol feeding reduced the basal and LPS-stimulated levels of POMC mRNA in the ARC. Ethanol also impaired LPS-induced levels of IL-1beta and TNF-alpha mRNAs both in the spleen and in the ARC. In contrast, ethanol feeding did not cause any significant changes in basal and the LPS-stimulated expression of IL-6 and IL-10 mRNAs in the spleen and of IL-6 mRNA levels in the ARC. These results indicate that ethanol suppression of hypothalamic POMC levels and splenic NK cell functions is associated with a reduced expression of proinflammatory cytokines in neuroendocrine and immune cells.