Tumor necrosis factor-alpha internalization and degradation by isolated hepatocytes of rats exposed to ethanol.

Internalization and degradation of human recombinant [125I]TNF-alpha was studied in hepatocytes isolated from rats exposed to ethanol (EtOH) either acutely (i.p. injection, 2.2 g kg(-1) b.wt.) or chronically (14-16 weeks of EtOH feeding in liquid diet). Both acute and chronic EtOH exposure diminished cytokine binding to the cell-surface receptors. In the acute group, EtOH increased internalization of the cytokine, accelerated its disappearance from the cell surface, and markedly reduced its conversion into acid-soluble 125I-containing compounds. In the chronic group, EtOH did not markedly affect these parameters. Internalization and degradation of the cytokine in the chronic group was much lower than in the acute group. It is concluded that EtOH interferes not only with the cytokine binding to the cell-surface receptors, as demonstrated in previous studies, but also with postbinding events, such as internalization and intracellular degradation of TNF-alpha. Possible mechanisms of action of EtOH are discussed.

Effect of chronic alcohol consumption by rats on tumor necrosis factor-alpha and interleukin-6 clearance in vivo and by the isolated, perfused liver.

The effects of chronic (16-week) alcohol consumption by rats on [125I] tumor necrosis factor (TNF)-alpha and [125I]interleukin (IL)-6 plasma clearance and organ distribution in vivo and uptake and metabolism by the isolated, perfused liver were studied. Alcohol was administered to rats in a liquid diet for 16 weeks, and caused a decreased (48%) plasma clearance rate of IL-6 and converted the plasma clearance kinetics of the cytokine from a biphasic exponential in normal rats to a monophasic exponential decay. Alcohol feeding significantly increased (101%) plasma clearance of TNF-alpha, which followed a biphasic exponential decay and decreased the T1/2 for both the alpha (67%) and beta (76%) elimination components. The distribution of both cytokines in trichloroacetic acid precipitable and non-precipitable fractions of liver, spleen, stomach, small intestine (ileum), lung, kidney, and blood was also studied. The only effect of alcohol treatment was a significant decrease in IL-6 uptake and metabolism by the small intestine. Perfused livers, isolated from alcohol-fed rats, took up and metabolized larger amounts of IL-6 than did livers isolated from pair-fed rats. TNF-alpha uptake and metabolism by the isolated, perfused liver were not affected by chronic alcohol consumption. Regardless of the animal treatment, the isolated perfused liver took up and metabolized significantly larger (17-fold) amounts of TNF-alpha than IL-6, in spite of identical concentrations of cytokines (6 nM) in the perfusion medium. The data presented in this study along with our previous results demonstrating the effects of alcohol consumption on TNF-alpha and IL-6 receptors on various liver cells suggest that the effects of chronic alcohol treatment on cytokine clearance cannot be ascribed to changes in the receptors for the two cytokines. Also, no correlation was found between the effects of alcohol treatment on plasma cytokine clearance and uptake and metabolism of cytokines by the isolated, perfused liver. Experimental data and theoretical considerations suggest that cytokine receptor recycling may play an important role in mediating alcohol effects on cytokine clearance.

Interleukin-6 tumor necrosis factor-alpha clearance and metabolism in vivo and by the isolated, perfused liver in the rat: effect of acute alcohol administration.

Plasma clearance and organ distribution of intravenously injected human recombinant [125I]interleukin (IL)-6 and [125I]tumor necrosis factor (TNF)-alpha were studied in male rats, 2 hr after intravenous alcohol (ethanol) administration (single dose, 2.2 g.kg-1 body weight). Also, the rate of uptake and degradation of the two cytokines by the isolated, perfused rat liver was studied in the absence or in the presence of ethanol (35 mM) in the perfusate. Acute ethanol administration significantly increased plasma clearance rate for both cytokines (36% and 72%, for IL-6 and TNF-alpha, respectively), decreased the t1/2 alpha (30% and 11%, for IL-6 and TNF-alpha, respectively), abolished the slow (beta)-phase component for TNF-alpha, and increased t1/2 beta for IL-6 (31%). Although alcohol did not affect organ distribution of TNF-alpha, it increased the IL-6 content in the liver, kidney, and blood. IL-6 uptake rate by the isolated, perfused rat liver was 2-fold higher than TNF-alpha uptake, whereas the rate of degradation was larger for TNF-alpha than for IL-6, despite the fact that both cytokines were presented to the liver at the same concentration (6 nM). Ethanol addition to the perfusate (35 mM, final concentration) significantly increased TNF-alpha uptake (24%), without affecting IL-6 uptake or the degradation rate of either cytokine. Also, the kinetics of degradation by the isolated, perfused rat liver was linear for TNF-alpha, but exponential for IL-6. Data presented in this study demonstrate that: (1) acute alcohol consumption can alter the kinetic behavior of IL-6 and TNF-alpha in the bloodstream, mainly by accelerating their clearance which, in turn, may counteract the outcome of cytokine secretion and delivery to the blood; and (2) short exposure of liver to ethanol levels commonly seen in humans after binge drinking may alter its capacity to take up cytokines.

Effect of acute and chronic alcohol administration to rats on the expression of interleukin-6 cell-surface receptors of hepatic parenchymal and nonparenchymal cells.

Rats were treated with alcohol either acutely (continuous, 7-hr intravenous infusion; blood alcohol levels approximately 35 mM) or chronically (liquid diet, 12-14 weeks). Three hr before killing, the animals received Gram-negative bacterial lipopolysaccharide (LPS) or saline. Hepatocytes, Kupffer cells, and liver sinusoidal endothelial cells were isolated by liver collagenase perfusion and centrifugal elutriation, and used for measurements of recombinant human [125I]interleukin-6 binding. Dissociation constant (Kd) and the amount of cell-surface receptors (Bmax) were measured on whole cells, at 4 degrees C. Two binding sites were detected on all three cell types: high-affinity (Kd1, from 20 to 125 pM) and low-affinity (Kd2, from 0.2 to 2 nM), with low Bmax (Bmax, from 0.4 to 12 fmol/10(6) cells) and high Bmax (Bmax2, from 10 to 210 fmol/10(6) cells). Hepatocytes displayed an 8-fold higher binding capacity for high-affinity sites (Bmax1) than the other two cell types. Acute ethanol treatment induced the following significant changes in the binding parameters: a decrease in Kd1 for hepatocytes and Kupffer cells, an increase in Bmax2 for hepatocytes, and a decrease in Bmax1 for Kupffer cells. Although the control (nonalcoholic) liquid diet per se completely suppressed the high-affinity binding sites, alcohol-containing diet induced only one change: a significant increase in Kd2 for hepatocytes. No changes in the binding parameters were seen after LPS administration to the chronically treated group. In the acute group, LPS mimicked alcohol action on hepatocyte binding parameters. Alcohol blunted LPS effects.(ABSTRACT TRUNCATED AT 250 WORDS)