Department of Laboratory Medicine, Toho University, Tokyo, Japan.
Horm Metab Res. 2011 Jan;43(1):11-6. doi: 10.1055/s-0030-1267996. Epub 2010 Nov 15.
Smoking is a risk factor for insulin resistance and metabolic syndrome. However, mechanisms responsible for smoking-induced insulin resistance are unclear. We examined the combined effect of nicotine, a toxic substance in tobacco smoke, and palmitate in the serum physiological concentration range on tumor necrosis factor-α (TNF-α) expression and impairment of glucose uptake in C2C12 myotubes, since smokers do not have increased serum free fatty acid (FFA) concentrations with insulin resistance compared to nonsmokers. C2C12 myotubes were incubated for 24 h with nicotine (1 μmol/l) in the presence or absence of palmitate (200 μmol/l). RT-PCR and Western blotting showed increased TNF-α expression in C2C12 myotubes treated with nicotine in the presence of palmitate. Furthermore, stimulation with nicotine in the presence of palmitate enhanced the production of reactive oxygen species (ROS) and activated the protein kinase C-nuclear factor-κB (PKC-NF-κB) pathway, as detected by dihydroethidium staining and Western blotting, respectively. Consequently, the translocation of GLUT4 to the plasma membrane as well as insulin-stimulated Akt phosphorylation was impaired, and glucose uptake to the myocytes was blocked. In addition, the production of ROS was suppressed by 4-hydroxy-TEMPO, and inhibition of GLUT4 translocation to the plasma membrane was canceled. These results suggest that in C2C12 myotubes, nicotine in the presence of palmitate enhanced the production of ROS and the expression of TNF-α through the PKC-NF-κB pathway; suppressed GLUT4 translocation to the plasma membrane; and impaired glucose uptake to cells. This pathway represents a possible mechanism by which smoking induces insulin resistance in the body.
吸烟是胰岛素抵抗和代谢综合征的一个风险因素。然而，导致吸烟引起的胰岛素抵抗的确切机制尚不清楚。我们研究了尼古丁（烟草烟雾中的有毒物质）和血清生理浓度范围内的棕榈酸酯对 C2C12 肌管中肿瘤坏死因子-α（TNF-α）表达和葡萄糖摄取的损伤的联合作用，因为与不吸烟者相比，吸烟者的血清游离脂肪酸（FFA）浓度没有增加。将 C2C12 肌管在存在或不存在棕榈酸酯（200 μmol/l）的情况下用尼古丁（1 μmol/l）孵育 24 小时。RT-PCR 和 Western blot 显示，在存在棕榈酸酯的情况下，尼古丁处理的 C2C12 肌管中 TNF-α表达增加。此外，通过二氢乙啶染色和 Western blot 分别检测到，在存在棕榈酸酯的情况下，尼古丁刺激增强了活性氧（ROS）的产生并激活了蛋白激酶 C-核因子-κB（PKC-NF-κB）通路。因此，GLUT4 向质膜的易位以及胰岛素刺激的 Akt 磷酸化受到损害，肌细胞的葡萄糖摄取受阻。此外，4-羟基-TEMPO 抑制 ROS 的产生，并取消 GLUT4 向质膜的易位。这些结果表明，在 C2C12 肌管中，尼古丁在棕榈酸酯存在的情况下，通过 PKC-NF-κB 通路增强 ROS 的产生和 TNF-α的表达；抑制 GLUT4 向质膜的易位；并损害细胞的葡萄糖摄取。该通路可能代表了吸烟导致机体胰岛素抵抗的一种机制。
