Chronic Ethanol Inhibits NK Cell Cytolytic Activity: Role of Opioid Peptide β-Endorphin

Abstract

The role of β-endorphin (β-EP) in ethanol-altered NK cell cytolytic activity is studied using male Fischer-344 rats as an animal model. Ethanol was administered for 1, 2, 3, or 4 wk in a liquid diet containing 8.7% ethanol (v/v), which means that 37% of the total calories were derived from ethanol. Rats treated with ethanol for 1 wk showed an increase in hypothalamic and plasma levels of immunoreactive (IR)-β-EP, but displayed no significant effect on NK cell activity determined by 51Cr release assay, as compared with those in pair-fed and ad libitum-fed animals. However, animals treated with ethanol for 2, 3, or 4 wk showed decreased hypothalamic and plasma levels of IR-β-EP and decreased splenic NK cell activity. No significant decrease in the number of splenocytes and NK cells or in the percentage of NK cells was seen until after 3 and 4 wk of ethanol treatment. Exposure in vitro of splenic lymphocytes obtained from control animals to various concentrations of β-EP increased NK cell activity. The opiate antagonist naltrexone blocked the β-EP-stimulated effect. The in vitro NK cell response to β-EP was reduced in the splenocytes obtained from animals treated with ethanol for 2 wk, but not in those obtained from animals treated with ethanol for 1 wk as compared with those in control animals. Additionally, β-EP administration into the paraventricular nucleus of the hypothalamus stimulated NK cell cytolytic activity, whereas the opiate blocker administration reduced NK cell activity. The NK cell responses to paraventricular nucleus β-EP were reduced in the animals treated with ethanol for 2 wk. These data provide evidence for the first time that ethanol inhibits NK cell cytolytic activity, possibly by reducing β-EP-regulated splenic NK cell function.

Circadian Rhythms of Granzyme B, Perforin, IFN-γ, and NK Cell Cytolytic Activity in the Spleen: Effects of Chronic Ethanol

“…Glucocorticoids, prolactin, melatonin, pro-opiomelanocortinderived peptides and catecholamines are all substances that are released in a circadian fashion and have been proven to affect NK cell function (20, 38 -41). We have previously shown the strong influence of the opioid ␤-endorphin on NK cytolytic activity (20,34). We have found recently that pro-opiomelanocortin transcript levels in the hypothalamic arcuate nucleus follow a circadian pattern that correlates with the circadian rhythm in NK activity (42).…”

“…McNulty et al (30) did not find significant changes of NK cell numbers during the day either. Our previous work demonstrated that 2-wk alcohol treatment does not produce a significant change in the total splenocyte number, percentage of NK cells, or in NK cell numbers in the spleen (20). Other authors have also concluded that ethanol minimally affects the anatomical distribution of NK cells (33).…”

“…To assess NK activity, standard 4-h 51 Cr release assays were performed as described previously (20). Briefly, splenocytes were isolated from fresh spleen tissues and then challenged to 51 Cr-labeled YAC-1 lymphoma cells.…”

“…There is a strong association between ethanol consumption and both increased cancer risk and infection morbidity (18,19). We have recently shown how chronic ethanol reduces granzyme B, perforin, and NK cell cytolytic activity (20,21), however, there is no report showing a direct influence of ethanol on the circadian rhythm of NK cells. Our aim was to test whether NK cell function follows a circadian rhythm and, if so, to analyze the effect of chronic ethanol consumption.…”

Circadian Oscillations of Clock Genes, Cytolytic Factors, and Cytokines in Rat NK Cells

“…Spleens were individually processed as previously described (29) to obtain homogeneous splenocyte suspensions in RPMI 1640 (Invitrogen Life Technologies). RBCs and granulocytes were separated by centrifugation (30 min at 400 ϫ g) with Histopaque 1083 (Sigma-Aldrich).…”