Institute of Agricultural and Nutritional Sciences, Biofunctionality of Secondary Plant Compounds, Martin-Luther-University Halle-Wittenberg, Weinbergweg 22, 06120, Halle/Saale, Germany.
Eur J Nutr. 2020 Feb;59(1):137-150. doi: 10.1007/s00394-019-01894-w. Epub 2019 Feb 1.
Hibiscus sabdariffa L. is commonly used as an ingredient for herbal teas and food supplements. Several studies demonstrated the beneficial effects of Hibiscus sabdariffa L. extracts (HSE); however, the bioactive components and their mode of action still remain unclear. Caenorhabditis elegans (C. elegans) was used to study health-related effects and the underlying molecular mechanisms of HSE in this model organism as well as effects of hydroxycitric acid (HCA), a main compound of HSE, and its structural analogue isocitric acid (ICA).
Survival and locomotion were detected by touch-provoked movement. Thermotolerance was analysed using the nucleic acid stain SYTOX green, and intracellular ROS accumulation was measured via oxidation of HDCF. Localisation of the transcription factors DAF-16 and SKN-1 was analysed in transgenic strains (DAF-16::GFP, SKN-1::GFP). The involvement of DAF-16 and SKN-1 was further investigated using loss-of-function strains as well as gene silencing by feeding RNAi-inducing bacteria. Protection against amyloid-β toxicity was analysed using a transgenic strain with an inducible expression of human amyloid-β peptides in body wall muscle cells (paralysis assay).
HSE treatment resulted in a prominent extension of lifespan (up to 24%) and a reduction of the age-dependent decline in locomotion. HCA, a main compound of HSE increased lifespan too, but to a lesser extent (6%) while ICA was not effective. HSE and HCA did not modulate resistance against thermal stress conditions and did not exert antioxidative effects: HSE rather increased intracellular ROS levels, suggesting a pro-oxidative effect of the extract in vivo. HSE and HCA increased the nuclear localisation of the pivotal transcription factors DAF-16 and SKN-1 indicating an activation of these factors. Consistent with this result, lifespan prolongation by HSE was dependent on both transcription factors. In addition to the positive effect on lifespan, HSE treatment also elicited a (strong) protection against amyloid-ß induced toxicity in C. elegans in a DAF-16- and SKN-1-dependent manner.
Our results demonstrate that HSE increases lifespan and protects against amyloid-β toxicity in the model organism C. elegans. These effects were mediated, at least in parts via modulation of pathways leading to activation/nuclear localisation of DAF-16 and SKN-1. Since HCA, a main component of HSE causes only minor effects, additional bioactive compounds like flavonoids or anthocyanins as well as synergistic effects of these compounds should be investigated.
洛神花（Hibiscus sabdariffa L.）常用于草本茶和食品补充剂。几项研究表明，洛神花提取物（HSE）具有有益作用。然而，其生物活性成分及其作用方式仍不清楚。秀丽隐杆线虫（Caenorhabditis elegans，C. elegans）被用于研究 HSE 在该模式生物中的健康相关作用及其潜在的分子机制，以及 HSE 的主要化合物羟基柠檬酸（HCA）及其结构类似物异柠檬酸（ICA）的作用。
通过触摸诱发运动检测生存和运动。使用核酸染料 SYTOX 绿分析耐热性，并通过 HDCF 氧化测量细胞内 ROS 积累。通过转(transgenic)基因株（DAF-16::GFP、SKN-1::GFP）分析转录因子 DAF-16 和 SKN-1 的定位。通过使用功能丧失菌株以及通过喂食 RNAi 诱导细菌进行基因沉默，进一步研究 DAF-16 和 SKN-1 的参与情况。使用诱导表达于体壁肌肉细胞的人淀粉样β肽的转基因株（瘫痪测定）分析对淀粉样β毒性的保护作用。
HSE 处理导致寿命显著延长（高达 24%），并减少了随年龄增长而下降的运动能力。HSE 的主要化合物 HCA 也延长了寿命，但程度较小（6%），而 ICA 则没有效果。HSE 和 HCA 均未调节对热应激条件的抵抗力，也没有发挥抗氧化作用：HSE 反而增加了细胞内 ROS 水平，表明提取物在体内具有促氧化作用。HSE 和 HCA 增加了关键转录因子 DAF-16 和 SKN-1 的核定位，表明这些因子的激活。与这一结果一致，HSE 延长寿命依赖于这两个转录因子。除了对寿命的积极影响外，HSE 处理还以 DAF-16 和 SKN-1 依赖的方式引发对秀丽隐杆线虫中淀粉样β诱导毒性的强烈保护作用。
我们的研究结果表明，HSE 可延长秀丽隐杆线虫模型生物的寿命并保护其免受淀粉样β毒性的侵害。这些作用至少部分通过调节导致 DAF-16 和 SKN-1 激活/核定位的途径来介导。由于 HSE 的主要成分 HCA 仅引起较小的作用，因此应该研究其他生物活性化合物，如类黄酮或花青素，以及这些化合物的协同作用。
