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.