Fataccioli V, Andraud E, Gentil M, French S W, Rouach H
Laboratory of Biomedical Research on Alcoholism, Univ. René Descartes, Paris, France.
Hepatology. 1999 Jan;29(1):14-20. doi: 10.1002/hep.510290106.
We previously reported that ethanol elicits an increased protein oxidation in the liver of rats receiving chronic ethanol by continuous intragastric infusion (Tsukamoto-French method). This accumulation of oxidized proteins could result from a decrease in the cytosolic proteolysis, related specifically to alkaline protease and its major components, the proteasomes. Because several studies suggest that intracellular proteolysis depends on the severity of oxidative stress, we investigated the cytosolic proteolytic activity under two chronic ethanol treatment paradigms associated with varying degrees of oxidative stress. For 4 weeks, male rats received chronic ethanol by continuous intragastric infusion or by oral administration (10% ethanol ad libitum as sole drinking fluid). A significant decrease was evident for alkaline protease activity as well as for sodium dodecyl sulfate (SDS)-activated latent 20S proteasome (chymotrypsine-like [ChT-L] and peptidylglutamyl peptide hydrolase [PGPH] activities) in the liver of rats receiving ethanol by continuous intragastric infusion. Free radical production and related processes appeared to be contributing events in proteolysis inhibition, because phenethyl isothiocyanate (PIC), an inhibitor of cytochrome P4502E1 (CYP2E1), reduced the inhibition of the ethanol-related ChT-L activity. Moreover, the lipid peroxidation level was inversely correlated with ChT-L activity. In contrast, no such changes were observed in ChT-L and PGPH activities or in cellular free radical targets following the oral ad libitum consumption of 10% ethanol. It appears, thus, that only the alcohol treatment paradigm associated with an overt oxidative stress produced a significant inhibition of the proteasome activity. The mechanisms of proteasome inhibition could involve the formation of an endogenous inhibitor such as protein aggregates or aldehyde-derivative peptides. Whatever the mechanism, the inhibition of cytosolic proteolysis and the subsequent accumulation of damaged proteins may be involved in the oxidatively challenged alcoholic livers and play a pathogenic role in experimental alcoholic liver disease.
我们之前报道过，通过持续胃内输注（筑本-弗伦奇法）给予大鼠慢性乙醇时，乙醇会引发大鼠肝脏中蛋白质氧化增加。氧化蛋白质的这种积累可能是由于胞质蛋白水解减少所致，这与碱性蛋白酶及其主要成分蛋白酶体密切相关。由于多项研究表明细胞内蛋白水解取决于氧化应激的严重程度，我们研究了在两种与不同程度氧化应激相关的慢性乙醇处理模式下的胞质蛋白水解活性。雄性大鼠连续4周通过持续胃内输注或口服给予慢性乙醇（10%乙醇任其自由饮用作为唯一的饮用水）。通过持续胃内输注给予乙醇的大鼠肝脏中，碱性蛋白酶活性以及十二烷基硫酸钠（SDS）激活的潜在20S蛋白酶体（类胰凝乳蛋白酶样[ChT-L]和肽基谷氨酰肽水解酶[PGPH]活性）明显降低。自由基产生及相关过程似乎是蛋白水解抑制的促成因素，因为细胞色素P4502E1（CYP2E1）的抑制剂苯乙基异硫氰酸酯（PIC）减少了乙醇相关ChT-L活性的抑制。此外，脂质过氧化水平与ChT-L活性呈负相关。相比之下，自由饮用10%乙醇后，ChT-L和PGPH活性或细胞自由基靶点未观察到此类变化。因此，似乎只有与明显氧化应激相关的酒精处理模式会对蛋白酶体活性产生显著抑制。蛋白酶体抑制的机制可能涉及内源性抑制剂的形成，如蛋白质聚集体或醛衍生肽。无论机制如何，胞质蛋白水解的抑制以及随后受损蛋白质的积累可能参与了氧化应激状态下的酒精性肝脏，并在实验性酒精性肝病中起致病作用。
