Department of Food Science and Nutrition, Hallym University, Chuncheon, Republic of Korea.
J Med Food. 2009 Oct;12(5):952-8. doi: 10.1089/jmf.2009.0056.
Conjugated linoleic acid (CLA), which is naturally present in a variety of foods such as milk fat and the meat of ruminant animals, has been demonstrated to exert chemoprotective effects in several tissues in experimental animals. CLA is a collective term, which denotes one or more positional and geometric isomers of octadecadienoic acid, with cis-9,trans-11 (c9t11) and trans-10,cis-12 CLA (t10c12) being the principal isomers in commercial preparations. We observed previously that physiological levels of CLA inhibited HT-29 cell growth, and the growth inhibitory effects of CLA were attributed to the effect of t10c12, but not c9t11. In the present study, we assessed the mechanisms by which physiological levels of CLA and t10c12 induce apoptosis in HT-29 cells. HT-29 cells were cultured for 3 days in serum-free medium in the presence of various concentrations of CLA (0-20 micromol/L) or t10c12 (0-4 micromol/L). Addition of CLA or t10c12 to culture medium resulted in a dose-dependent increase in the numbers of apoptotic cells. The results of western blot analysis of total cell lysates showed that CLA and t10c12 increased the levels of cleaved caspase-9, caspase-3, and poly(ADP-ribose) polymerase but did not alter the levels of Bcl-2 family member proteins. However, these fatty acids were shown to increase the translocation of Bad and Bax to the mitochondria, increase mitochondrial membrane permeability, and induce the release of cytochrome c and Smac/Diablo from the mitochondria. In addition, CLA and t10c12 diminished Akt content and Akt phosphorylation. These findings indicate that physiological levels of t10c12 induce apoptosis in HT-29 colon cancer cells, which is mediated via mitochondrion-mediated events associated with a decline in Akt activity, an increase in the translocation of the pro-apototic Bad and Bax to the mitochondria, and the subsequent disruption of normal mitochondrial membrane potential.
共轭亚油酸（CLA）天然存在于多种食物中，如牛奶脂肪和反刍动物的肉，已被证明在实验动物的几种组织中具有化学保护作用。CLA 是一个统称，它表示十八碳二烯酸的一种或多种位置和几何异构体，其中顺式-9，反式-11（c9t11）和反式-10，顺式-12（t10c12）是商业制剂中的主要异构体。我们之前观察到生理水平的 CLA 抑制 HT-29 细胞生长，CLA 的生长抑制作用归因于 t10c12 的作用，而不是 c9t11。在本研究中，我们评估了生理水平的 CLA 和 t10c12 诱导 HT-29 细胞凋亡的机制。将 HT-29 细胞在无血清培养基中培养 3 天，存在不同浓度的 CLA（0-20 μmol/L）或 t10c12（0-4 μmol/L）。向培养基中添加 CLA 或 t10c12 会导致凋亡细胞数量呈剂量依赖性增加。总细胞裂解物的 Western blot 分析结果表明，CLA 和 t10c12 增加了 cleaved caspase-9、caspase-3 和聚（ADP-核糖）聚合酶的水平，但不改变 Bcl-2 家族蛋白的水平。然而，这些脂肪酸被证明增加了 Bad 和 Bax 向线粒体的易位，增加了线粒体膜的通透性，并诱导了细胞色素 c 和 Smac/Diablo 从线粒体中的释放。此外，CLA 和 t10c12 减少了 Akt 含量和 Akt 磷酸化。这些发现表明，生理水平的 t10c12 诱导 HT-29 结肠癌细胞凋亡，这是通过与 Akt 活性下降、促凋亡 Bad 和 Bax 向线粒体易位增加以及随后破坏正常线粒体膜电位相关的线粒体介导事件介导的。
