Hong-Brown L Q, Frost R A, Lang C H
Department of Cellular and Molecular Physiology, Pennsylvania State College of Medicine, Hershey, Pennsylvania 17033, USA.
Alcohol Clin Exp Res. 2001 Sep;25(9):1373-82.
Acute and chronic alcohol intoxication decreases skeletal muscle protein synthesis under in vivo conditions. We investigated whether ethanol (EtOH) and its major metabolites, acetaldehyde and acetate, can directly modulate protein balance under in vitro conditions.
Human myocytes were incubated with different doses of EtOH for varying periods of time (i.e., 4-72 hr). Alternatively, cells were incubated with acetaldehyde, acetate, insulin, insulin-like growth factor-I (IGF-I), or with a combination of EtOH plus insulin or IGF-I. Rates of protein synthesis or degradation were determined by 35S-methionine/cysteine incorporation into or release from cellular protein.
A significant, 15% to 20%, decrease in basal protein synthesis was observed after 24 hr, but not at earlier time points, in response to 80 mM EtOH. Incubation of myocytes for 72 hr decreased synthesis in cells incubated with EtOH ranging between 60 and 120 mM. The ability of IGF-I or insulin to stimulate protein synthesis was impaired by 30% and 60%, respectively, in cells incubated with 80 mM EtOH for 72 hr. Exposure of cells to 200 microM acetaldehyde or 5 mM Na-acetate also decreased basal protein synthesis. In contrast, neither EtOH, acetaldehyde, nor acetate altered the basal rate of protein degradation. However, EtOH completely impaired the ability of insulin and IGF-I to inhibit proteolysis. Finally, EtOH did not impair IGF-I receptor autophosphorylation, but inhibited the ability of insulin to phosphorylate its own receptor. EtOH also did not alter the number of insulin or IGF-I receptors or the formation of insulin/IGF-I hybrid receptors.
We have demonstrated that EtOH can directly inhibit muscle protein synthesis under in vitro conditions. Neither EtOH nor its metabolites altered basal protein degradation, although EtOH did compromise the ability of both insulin and IGF-I to slow proteolysis. This impairment seems to be mediated by different defects in signal transduction.
急性和慢性酒精中毒会降低体内条件下骨骼肌蛋白质的合成。我们研究了乙醇（EtOH）及其主要代谢产物乙醛和乙酸盐在体外条件下是否能直接调节蛋白质平衡。
将人肌细胞与不同剂量的EtOH孵育不同时间（即4 - 72小时）。或者，将细胞与乙醛、乙酸盐、胰岛素、胰岛素样生长因子-I（IGF-I）孵育，或与EtOH加胰岛素或IGF-I的组合孵育。通过35S-甲硫氨酸/半胱氨酸掺入细胞蛋白质或从细胞蛋白质中释放来测定蛋白质合成或降解的速率。
在80 mM EtOH作用下，24小时后基础蛋白质合成显著下降15%至20%，但在更早的时间点未出现这种情况。将肌细胞孵育72小时，在60至120 mM的EtOH作用下，细胞内合成减少。在与80 mM EtOH孵育72小时的细胞中，IGF-I或胰岛素刺激蛋白质合成的能力分别受损30%和60%。细胞暴露于200 microM乙醛或5 mM乙酸钠也会降低基础蛋白质合成。相比之下，EtOH、乙醛或乙酸盐均未改变基础蛋白质降解速率。然而，EtOH完全损害了胰岛素和IGF-I抑制蛋白水解的能力。最后，EtOH并未损害IGF-I受体的自身磷酸化，但抑制了胰岛素使其自身受体磷酸化的能力。EtOH也未改变胰岛素或IGF-I受体的数量或胰岛素/IGF-I杂合受体的形成。
我们已经证明，EtOH在体外条件下可直接抑制肌肉蛋白质合成。EtOH及其代谢产物均未改变基础蛋白质降解，尽管EtOH确实损害了胰岛素和IGF-I减缓蛋白水解的能力。这种损害似乎是由信号转导中的不同缺陷介导的。
