吴小芳 万金志 钟佳胜 丁雯静
摘 要 芦荟是百合科(Liliaceae)芦荟属(Aloe)的多年生常绿肉质草本植物,因富含多种生物活性物质,是一种集医疗、保健、美容、营养于一体的重要经济植物。通过回顾芦荟的药用历史,在广泛检索文献的基础上,对目前芦荟化学成分的最新研究进展进行综述,为芦荟产品的开发利用提供参考依据,将有益于芦荟产业的发展。
关键词 芦荟;化学成分;药用植物
中图分类号 S567 文献标识码 A
Research Progress on the Chemical Constituents of Aloe
WU Xiaofang1,2, WAN Jinzhi3 *, ZHONG Jiasheng3, DING Wenjing3
1 Analysis and Testing Center, Chinese Academy of Tropical Agricultural Sciences, Haikou, Hainan, 571101, China
2 Hainan Provincial Key Laboratory of Quality and Safety for Tropical Fruits and Vegetables, Haikou, Hainan 571101, China
3 School of Pharmaceutical Sciences, Sun Yat-Sen University, Guangzhou, Guangdong, 510006, China
Abstract Aloe, a member of Asphodelaceae(Liliaceae)family, is a perennial short-stemmed succulent herb. Owing to its abundant bioactive compounds, Aloe is an important economic plant with medical treatment, health care, beauty and nutrition. On the basis of the medicinal history of Aloe and the broad literature search, the chemical compositions were introduced in the paper. These provided reference for exploiting aloe products and promoted efficiently the development of the aloe industry.
Key words Aloe; Chemical composition; Medicinal plants
doi 10.3969/j.issn.1000-2561.2015.08.030
百合科芦荟属植物,品种繁多,大约有300多种,加上其变种大约有500多种,常作为药用报道的代表性品种有库拉索芦荟(Aloe barbadensis)、好望角芦荟(A. ferox)和木立芦荟(A. arborescens),原产于非洲大陆热带沙漠及地中海沿岸地区。唐朝中期芦荟被传到中国,现在我国海南、广东、云南、福建等热带及亚热带地区均有种植。现代药理实验证明,芦荟植物中的有效部位或有效成分具有抗菌、抗炎、解热、保肝、抗癌、杀虫及免疫增强等多方面的功用,故素有“万应良药”、“家庭医生”、“不用大夫”等美称。我国芦荟的药用基础研究是在上世纪90年代开始的,而美国、德国、印度、前苏联、日本是最早进行芦荟临床应用研究的国家,其中美国进行了比较大量的基础研究和应用开发研究。芦荟以其独特的功效和广泛的用途受到人们的普遍关注,国内外对其化学成分的研究也是一大热点,因此为了进一步明确芦荟医疗、保健及美容作用的物质基础,便于芦荟产品的开发利用,笔者对芦荟植物中的化学成分研究进行了综述。
1 古籍记载
在割取芦荟叶片时,切口处会流下黄色的苦液,接触空气氧化则成黑色,凝固成一团,民间将这些苦液收集熬成稠膏经凝固后就成了“黑色的凝块”即中药芦荟,故芦荟中“芦”是黑的意思,“荟”是聚集之意[1]。《本草纲目》记载芦荟性寒、味苦、无毒,有清热解毒、明目镇心、杀虫去疳的作用,此外在数本世界闻名的古代药典中都有详细记载,如中国的《药性本草》,以及欧洲的《希腊本草》、《意大利本草》、朝鲜的《东宝医鉴》等。
2 化学成分研究进展
已知药用芦荟中含有160多种化学成分,具有药理活性和生物活性的组分也不下100种,其成分由于芦荟品种、季节、产地的不同而具有很大的差别。芦荟生物活性成分主要存在于芦荟叶片的3个独立部分:包含在纤维束细胞内的黄色汁液、凝胶和外皮[2]。叶片切口渗出的黄色汁液,主要含有蒽醌及苷类等高度活性的酚类化合物,是芦荟入药的主要活性成分;另一部分是黄色汁液渗后留下的凝胶,主要含糖类(单糖、多糖及聚合体)、蛋白质、草酸钙及纤维等[3-4];此外,芦荟叶的外皮部分主要含蒽酮、色酮等化学成分[2]。
2.1 蒽醌类化合物
芦荟大黄素是众多芦荟品种中代表性的蒽醌类化合物,其结晶是橙色针状,能促进大肠蠕动,对便秘和痔疮有特殊疗效,据报道其具有抗炎活性[5]和遗传毒性[6]。除此之外,从芦荟各品种中还发现许多其他蒽酮类化合物,如chrysophanol,nataloe-emodin,aloesaponarin I等(表1)。其结构式如下:
2.2 蒽酚类化合物
蒽酚类化合物主要存在皂角芦荟中(A. saponaria)[13],如aloesaponolⅠ、aloesaponolⅡ、aloesaponolⅢ等(表2),据报道这类化合物可能有抗肿瘤的功效[16]。其结构式如下:
2.3 蒽酮类化合物
蒽酮类化合物在芦荟有机活性成分中占主要位置,芦荟苷是最常见的蒽酮苷,我国药典指定芦荟苷作为芦荟质量控制的主要指标,其以原形到达大肠,在大肠菌作用下发挥致泻作用[20],此外还有促进酒精代谢和抗炎的作用[5,21]。除了最常见的芦荟苷,蒽酮类化合物种类很多(表3)。其结构式如下:
2.4 吡喃酮类化合物
芦荟品种中的吡喃酮类化合物含量不高,主要有芦荟宁、芦荟宁B等,其中芦荟宁是木剑芦荟中的主要成分,据报道有抗炎[5]和抑制胃酸分泌的作用[38],现已分离的芦荟吡喃酮类化合物见表4。其结构式如下:
2.5 色酮类化合物
芦荟色酮在芦荟外皮中的含量分布为:叶片近轴内表面高于叶片离轴外表面;叶片尖端高于叶片基底;叶片边缘明显高于叶片的其他部位[42]。关于芦荟色酮的药效研究国内外开展均还较少,但是芦荟科技工作者逐渐认识到存在于叶皮中的色酮所具有的生物活性更值得开发和利用,它们的基本骨架主要是5-甲基色酮衍生物及其糖苷类,目前已分离的芦荟色酮(包括本课题组分离得到的5个新色酮)见表5。其结构式如下:
2.6 萘类衍生物
据报道从芦荟中曾分离出一些萘及四氢化萘的衍生物,有plicataloside、feroxin A、feroxin B、aloveroside A、kenyaloside等,本课题组也曾分离出一个新型萘环衍生物Aloveroside B,见表6。目前此类化合物的生物活性或功效作用尚不明确。其结构式如下:
2.7 其他酚类化合物
从芦荟中曾分离出一些蒽酚酮类化合物(表7)。其结构式如下:
除此之外,还从好望角芦荟中分离到一个新的黄酮碳苷Aloeresin H[67],其他化合物见图1[68-69]。目前此类化合物的生物活性或功效作用尚不明确。其结构式如下:
2.8 糖类
芦荟凝胶干燥后所得固形物中有大约一半以上是糖类,包括多种单糖、由多种己糖以不同的比例和不同的顺序连接而成的多糖以及由多糖和蛋白质结合而成的糖蛋白[3]。单糖主要成分是甘露聚糖、阿拉伯糖、鼠李糖、木糖和半乳糖等;多糖是芦荟凝胶所含糖类中具有重要生物活性的成分,新鲜凝胶中含多糖量约为0.27%~0.5%,其成分和含量随芦荟品种和生长地区、采收季节不同而异。芦荟多糖(Acemannan,ACM)经色谱和波谱分析确定其主要成分由线性β-(1,4)-D-乙酰甘露糖基单元连接而成的聚合物,具有较好的免疫调节、抗肿瘤等功能[3,70]。
2.9 氨基酸、有机酸及酶类等其他化学成分
芦荟叶中还含有游离氨基酸,据文献报道[3]夏季芦荟叶游离氨基酸最高,包括8种人体必需氨基酸以及酒石酸、苹果酸、柠檬酸、乙酸、乳酸、丁二酸等有机酸;芦荟中已知的酶类有纤维素酶、淀粉酶、过氧化氢酶、超氧化物歧化酶(SOD)[20]等。
芦荟还含有维生素(包括Vit A、B1、B2、B6、B12、C、E等)[71];甾族类化合物包括β-谷甾醇、胆甾醇、菜油甾醇、β-麦芽固醇等[71];含有钾、钙、钠、铝、镁、铁等元素以及锌、锗、铜等微量元素[20]。这类物质主要分布在芦荟的外皮上。
3 结语
我国对芦荟的研究起于近三十年,研究较多的是芦荟作为原料或添加剂被应用于食品、保健品和化妆品等领域,但是芦荟中众多生物活性成分的化学结构与作用机理之间的相互关系还没全部研究出来,且研究较少,深度和广度都无法与国外相比。因此,对芦荟复杂多样的化学成分进行全面了解,这将为其工业化生产提供理论基础,也可作为产品质量检测技术的参考。
芦荟粗提物或芦荟胶入药能产生多种药用功效,未来从芦荟众多组分中分离纯化出更多高活性的单体化合物,用作新药品资源,具有广阔的应用前景,相信将来会有越来越多的功效明确的芦荟制品投入市场,而药用芦荟也将会给人们带来巨大的经济效益。
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