Differences in the nature and kinetics of the ethanol-related circulating cytotoxic proteins in normal subjects and patients with alcohol-induced cirrhosis

Ethanol metabolism by macrophages: possible role in organ damage

Macrophages and hepatocytes oxidize ethanol to acetate in vitro at comparable rates but by different biochemical pathways. Ethanol metabolism by macrophages is largely ADH-independent and mainly based on cytochrome P450 and on the extracellular release of superoxide anion radicals. There is also evidence that during ethanol metabolism, macrophages release more acetaldehyde extracellularly than hepatocytes; the high concentrations of acetaldehyde around macrophages may damage surrounding tissue cells. Some of this acetaldehyde forms unstable cytotoxic complexes with serum albumin and with erythrocytes. The superoxide anion radicals released by macrophages may not only oxidize ethanol to acetaldehyde but also react with and damage cells in their immediate vicinity. After exposure to ethanol, macrophage-depleted rodents show markedly reduced levels of cytotoxic acetaldehyde-albumin complexes in the blood and reduced levels of hydroxyethyl radicals in the bile compared to control animals, indicating that the generation of such potentially pathogenic molecules is, to a large extent, dependent on macrophage activity. Macrophage-depleted animals also show less early liver damage than control animals. The reduction in ethanol-induced liver damage in macrophage-depleted mice and rats may be due to a reduction or elimination of the generation of various Kupffer-cell-derived hepatotoxic substances, including acetaldehyde and reactive oxygen radicals, in such animals. These data suggest that ethanol metabolism by tissue macrophages may play an important role in mediating ethanol-related tissue damage.

Differences in the serum levels of acetaldehyde and cytotoxic acetaldehyde-albumin complexes after the consumption of red and white wine: in vitro effects of flavonoids, vitamin E, and other dietary antioxidants on cytotoxic complexes

After the consumption of ethanol, acetaldehyde levels increase in the serum, and the serum develops a nondialyzable cytotoxic activity caused by the formation of unstable acetaldehyde-albumin complexes. The concentration of acetaldehyde in the serum and the cytotoxic activity in serum albumin 8.5 hr after six healthy volunteers began to drink 94 g of ethanol were significantly less when the ethanol was consumed as red wine than as white wine. The serum acetaldehyde was measured by a fluorigenic HPLC assay, and the cytotoxic activity in albumin was determined using two different assays based on dissimilar endpoints: (1) detachment of adherent A9 cells and (2) impairment of the ability of A9 cells to reduce tetrazolium. When serum obtained from five other healthy volunteers after the consumption of white wine was incubated at 37 degrees C for 3 hr with a number of dietary antioxidants at a concentration of 100 mumol/liter, the cytotoxicity of the albumin was markedly reduced. The antioxidants studied consisted of six flavonoids (kaempherol, fisetin, quercetin catechin, taxifolin, and coumarin) and three nonflavonoids (salicylic acid, tannic acid, and alpha-tocopherol). In the cases of alpha-tocopherol, a statistically significant reduction of cytotoxicity was observed at a concentration of 10 mumol/liter. In addition, the cytotoxicity of artificially prepared acetaldehyde-albumin complexes was significantly reduced when such complexes were incubated with 50 to 100 mumol/liter of kaempherol, fisetin, quercetin, coumarin or salicylic acid, or 10 mumol/liter of alpha-tocopherol at 37 degrees C for 3 hr. Evidently, in vitro, flavonoid and nonflavonoid dietary constituents reduce the amount of unstable acetaldehyde-albumin complexes found in both postalcohol serum and in artificially produced acetaldehyde-albumin complexes. The difference in the amount of unstable acetaldehyde-albumin complexes found in serum after the consumption of red and white wine may therefore be caused by the higher concentration of antioxidants, including flavonoids, in red wine than in white wine. Because acetaldehyde and acetaldehyde-albumin complexes have been implicated in the pathogenesis of alcohol-mediated tissue damage, these data suggest that dietary antioxidants may influence the biological consequences of excess alcohol consumption.

Acetaldehyde-serum protein adducts inhibit interleukin-2 secretion in concanavalin A-stimulated murine splenocytes: a potential common pathway for ethanol-induced immunomodulation

Variable immunobiological changes occur with alcohol consumption. Previous studies have shown that acetaldehyde forms stable adducts with serum proteins, including albumin. These adducts are elevated in persons and animals consuming ethanol. We examined the effect of serum protein-acetaldehyde adducts formed with fetal bovine serum (FBS) on concanavalin A-stimulated murine splenocytes. Interleukin-2 (IL-2) secretion and IL-2 receptor (IL-2R) expression were determined as a function of the effect of the acetaldehyde-protein adduct(s). FBS was incubated with acetaldehyde (500, 100, 50, 25, 10, and 0 microM) for 1 hr at 37 degrees C. Excess acetaldehyde was removed by ultrafiltration using a 500 molecular weight cut-off membrane in 3 volumes. Free as well as bound acetaldehyde was quantified using fluorigenic HPLC before and after incubation. Recovered acetaldehyde correlated with the amount added (r2 = 0.996). Splenocytes were cultured for 48 hr in complete medium containing 5% acetaldehyde-treated and 5% untreated FBS with 4 micrograms/ml concanavalin A. Although cell viability was unchanged, acetaldehyde-treated FBS mixed with native FBS decreased IL-2 secretion in a dose-dependent manner. The percentage of cells expressing IL-2R was reduced only at the highest acetaldehyde-FBS dose. Therefore, immunological effects ascribed to ethanol may result in part from the toxic properties of acetaldehyde-protein adducts on IL-2 secretion.

Macrophages are a major source of acetaldehyde in circulating acetaldehyde-albumin complexes formed after exposure of mice to ethanol

C57BL mice were depleted of macrophages by an intravenous injection of liposome-encapsulated dichloromethylene diphosphonate (DCMDP), and control mice were uninjected or injected with empty liposomes. One day after injection, a proportion of the DCMDP-treated and control mice was continuously exposed to ethanol vapor for 4 days. Albumin fractions were separated from the sera of both ethanol-unexposed and ethanol-exposed animals and tested for cytotoxicity against a monolayer of A9 cells using two indicators of cytotoxicity: detachment of adherent cells and a decrease in the ability of cells to reduce tetrazolium. The results show that, in mice exposed to ethanol, macrophages are a major source of the acetaldehyde in circulating cytotoxic acetaldehyde-albumin complexes and presumably also of free acetaldehyde.

In vivo effects of vitamin C on the cytotoxicity of post-ethanol serum

The consumption of alcohol is followed by the development in the serum of a non-dialysable cytotoxic activity against A9 cells. This cytotoxicity has been previously shown to reside mainly in unstable acetaldehyde-albumin complexes from which cytotoxic acetaldehyde molecules can be transferred to target cells. The cytotoxicity developing in serum albumin 8 hr after seven healthy volunteers drank 84 g ethanol over 45 min was abolished when the same volunteers were pre-treated with 1 g vitamin C daily for 3 days prior to alcohol consumption. The cytotoxicity was measured against A9 cells using two different indicators: (i) detachment of adherent cells and (ii) a decrease in the ability of cells to reduce tetrazolium. These data suggest that the administration of vitamin C may be useful in limiting those aspects of alcohol toxicity mediated by circulating acetaldehyde.