Anand Preetha, Kunnumakkara Ajaikumar B, Harikumar Kuzhuvelil B, Ahn Kwang Seok, Badmaev Vladimir, Aggarwal Bharat B
Department of Experimental Therapeutics, Cytokine Research Laboratory, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
Cancer Res. 2008 Nov 1;68(21):8861-70. doi: 10.1158/0008-5472.CAN-08-1902.
Picroliv, an iridoid glycoside derived from the plant Picrorhiza kurroa, is used traditionally to treat fever, asthma, hepatitis, and other inflammatory conditions. However, the exact mechanism of its therapeutic action is still unknown. Because nuclear factor-kappaB (NF-kappaB) activation plays a major role in inflammation and carcinogenesis, we postulated that picroliv must interfere with this pathway by inhibiting the activation of NF-kappaB-mediated signal cascade. Electrophoretic mobility shift assay showed that pretreatment with picroliv abrogated tumor necrosis factor (TNF)-induced activation of NF-kappaB. The glycoside also inhibited NF-kappaB activated by carcinogenic and inflammatory agents, such as cigarette smoke condensate, phorbol 12-myristate 13-acetate, okadaic acid, hydrogen peroxide, lipopolysaccharide, and epidermal growth factor. When examined for the mechanism of action, we found that picroliv inhibited activation of IkappaBalpha kinase, leading to inhibition of phosphorylation and degradation of IkappaBalpha. It also inhibited phosphorylation and nuclear translocation of p65. Further studies revealed that picroliv directly inhibits the binding of p65 to DNA, which was reversed by the treatment with reducing agents, suggesting a role for a cysteine residue in interaction with picroliv. Mutation of Cys(38) in p65 to serine abolished this effect of picroliv. NF-kappaB inhibition by picroliv leads to suppression of NF-kappaB-regulated proteins, including those linked with cell survival (inhibitor of apoptosis protein 1, Bcl-2, Bcl-xL, survivin, and TNF receptor-associated factor 2), proliferation (cyclin D1 and cyclooxygenase-2), angiogenesis (vascular endothelial growth factor), and invasion (intercellular adhesion molecule-1 and matrix metalloproteinase-9). Suppression of these proteins enhanced apoptosis induced by TNF. Overall, our results show that picroliv inhibits the NF-kappaB activation pathway, which may explain its anti-inflammatory and anticarcinogenic effects.
苦味叶下珠素是一种从植物胡黄连中提取的环烯醚萜苷，传统上用于治疗发热、哮喘、肝炎及其他炎症性疾病。然而，其治疗作用的确切机制尚不清楚。由于核因子-κB（NF-κB）激活在炎症和致癌过程中起主要作用，我们推测苦味叶下珠素必定通过抑制NF-κB介导的信号级联反应激活来干扰这一途径。电泳迁移率变动分析表明，苦味叶下珠素预处理可消除肿瘤坏死因子（TNF）诱导的NF-κB激活。该苷还抑制由致癌剂和炎症剂激活的NF-κB，如香烟烟雾浓缩物、佛波酯12-肉豆蔻酸酯13-乙酸酯、冈田酸、过氧化氢、脂多糖和表皮生长因子。在研究其作用机制时，我们发现苦味叶下珠素抑制IκBα激酶的激活，导致IκBα的磷酸化和降解受到抑制。它还抑制p65的磷酸化和核转位。进一步研究表明，苦味叶下珠素直接抑制p65与DNA的结合，用还原剂处理可逆转这种结合，提示半胱氨酸残基在与苦味叶下珠素相互作用中起作用。p65中Cys(38)突变为丝氨酸消除了苦味叶下珠素的这种作用。苦味叶下珠素对NF-κB的抑制导致NF-κB调节蛋白的抑制，包括那些与细胞存活（凋亡抑制蛋白1、Bcl-2、Bcl-xL、存活素和TNF受体相关因子2）、增殖（细胞周期蛋白D1和环氧化酶-2）、血管生成（血管内皮生长因子）和侵袭（细胞间黏附分子-1和基质金属蛋白酶-9）相关的蛋白。这些蛋白的抑制增强了TNF诱导的细胞凋亡。总体而言，我们的结果表明苦味叶下珠素抑制NF-κB激活途径，这可能解释了其抗炎和抗癌作用。
