Slomiany A, Piotrowski E, Piotrowski J, Slomiany B L
Research Center, University of Medicine and Dentistry of New Jersey, Newark, 07103-2400, USA.
J Physiol Pharmacol. 2000 Sep;51(3):433-47.
Earlier investigations on the effect of ethanol on synthesis and posttranlational glycosylation of gastric mucus glycoprotein (mucin) revealed quantitative changes in the apoprotein assembly, glycosylation, and mucin retention on the mucosal surface (Slomiany et al.., Alcoholism: Clin. Exp. Res. 21, 417-423, 1998). To assess whether metabolic consequences of ethanol ingestion, documented in the in vitro system are also occurring in vivo the rats were subjected to 8 weeks of ethanol containing liquid diet. The retention of mucin on the surface of gastric mucosa was quantitated by measuring the binding of gastric mucin to Mucin Binding Protein (MBP) of gastric mucosa. The results were compared with those obtained with the rats subjected to pair-feeding the isocaloric-control diet. Before alcohol administration, and in two weeks' intervals thereafter, the gastric contents from the animals was collected and mucin purified. After 8 weeks of the respective diet, the animals were sacrificed and their gastric mucosa used for MBP preparation. The binding of mucin to MBP before ethanol, and after 2, 4, 6, and 8 weeks of ethanol diet was quantitated with Enzyme Linked Lectin Assay (ELLA). The study with standard mucin revealed that binding of mucin to MBP differs substantially between individual animals. The same variability in binding was observed with the individual mucin preparations collected at the onset of the experiment. However, with the progression of ethanol feeding, the mucin samples besides displaying the variable and animal-specific binding to MBP at the initiation of the experiment, also showed a dramatic decrease in binding. In five animals, after two weeks of ethanol diet, mucin binding to MBP decreased by 50%; in two animals, the drastic decrease in binding was observed in mucin collected after four weeks of alcohol feeding; and in one animal a 20% decrease in binding persisted for six weeks, and then decreased to 50% in the last collection. Also, in two animals, the mucin collected after 8 weeks of ethanol feeding retained only 6-9% of the initial binding capacity. In contrast, in pair-fed controls, the mucin binding to MBP remained the same or increased up to 20%. Results of the studies, performed on mucin of the individual animals and matching preparations of MBP, showed that each animal expresses different degree of mucin binding. Moreover, in chronic ethanol ingestion, the individual variations are accompanied by a decrease in mucin binding to MBP. Since the observed decrease in binding occurred in samples containing the same preparation of MBP, the component affected by alcohol resides on mucin. Thus, considering the in vitro impact of ethanol on generation of carbohydrate chains in Golgi, and the finding on mucin oligosaccharides-dependent mucin-MBP complex formation, we conclude that ethanol impairs the synthesis of mucin oligosaccharide structures required for binding with MBP, and the retention on gastric mucosal surfaces.
早期关于乙醇对胃黏液糖蛋白（黏蛋白）合成及翻译后糖基化作用的研究表明，载脂蛋白组装、糖基化以及黏蛋白在黏膜表面的保留存在定量变化（斯洛米亚尼等人，《酒精中毒：临床与实验研究》21卷，417 - 423页，1998年）。为评估在体外系统中记录的乙醇摄入的代谢后果在体内是否也会发生，对大鼠给予含乙醇的液体饮食8周。通过测量胃黏蛋白与胃黏膜黏蛋白结合蛋白（MBP）的结合来定量黏蛋白在胃黏膜表面的保留情况。将结果与接受等热量对照饮食配对喂养的大鼠所获结果进行比较。在给予酒精之前以及此后每隔两周，收集动物的胃内容物并纯化黏蛋白。在各自饮食8周后，处死动物并将其胃黏膜用于制备MBP。用酶联凝集素测定法（ELLA）定量乙醇饮食前以及乙醇饮食2、4、6和8周后黏蛋白与MBP的结合情况。对标准黏蛋白的研究表明，不同动物个体之间黏蛋白与MBP的结合存在显著差异。在实验开始时收集的各个黏蛋白制剂中也观察到了相同的结合变异性。然而，随着乙醇喂养的进行，黏蛋白样品除了在实验开始时显示出与MBP的可变且动物特异性结合外，还显示出结合力急剧下降。在5只动物中，乙醇饮食两周后，黏蛋白与MBP的结合下降了50%；在2只动物中，在酒精喂养四周后收集的黏蛋白中观察到结合力急剧下降；在1只动物中，结合力下降20%持续了六周，然后在最后一次收集时降至50%。此外，在2只动物中，乙醇喂养8周后收集的黏蛋白仅保留了初始结合能力的6 - 9%。相比之下，在配对喂养的对照组中，黏蛋白与MBP的结合保持不变或增加了20%。对个体动物的黏蛋白以及匹配的MBP制剂进行的研究结果表明，每只动物表达出不同程度的黏蛋白结合。此外，在慢性乙醇摄入过程中，个体差异伴随着黏蛋白与MBP结合的减少。由于在含有相同MBP制剂的样品中观察到结合力下降，受酒精影响的成分存在于黏蛋白上。因此，考虑到乙醇在体外对高尔基体中糖链生成的影响以及关于黏蛋白寡糖依赖性黏蛋白 - MBP复合物形成的发现，我们得出结论，乙醇损害了与MBP结合以及在胃黏膜表面保留所需的黏蛋白寡糖结构的合成。
