侯秋莉,楊振國,丁 偉,2,張永強,2*
1西南大學植物保護學院2西南大學農藥研究所,重慶400716
東莨菪內酯(scopoletin)又稱東莨菪素、莨菪亭、莨菪酚,是一種重要的香豆素類化合物,其化學名稱為7-羥基-6 甲氧基香豆素(化學結構式見圖1)。其在氯仿或乙酸中的結晶體為淺黃色或白色針狀,熔點為205~207 ℃[1],易溶于氯仿、熱乙醇、熱乙酸、N-甲基吡咯烷酮、二甲基亞砜等高極性有機溶劑中,微溶于水,其溶液在365 nm 的紫外光下顯示藍色熒光[2]。由于東莨菪內酯的良好殺螨活性,全國農藥標準化技術委員會于2012 年正式將其通用名稱定為“甲氧香螨酯”(農標字2012 第005號)。
圖1 東莨菪內酯化學結構式Fig.1 Chemical structural formula of scopoletin
植物受到外界生物及非生物不良環(huán)境的刺激后,會產生一些次生代謝物抵御干擾。東莨菪內酯是植物體內的一種重要的酚類植物抗毒素,當植物受到病原菌、害蟲或其他植物及環(huán)境變化等因素的干擾時,能夠大量合成和累積東莨菪內酯,用于防御不良因素的干擾。東莨菪內酯存在于多個科的110000 余種[3,4]植物中,主要分布于菊科(Asteraceae)、旋花科(Convolvulaceae)、十字花科(Cruciferae)、杜鵑花科(Ericaceae)、大戟科(Euphorbiaceae)、豆科(Fabaceae)、楝科(Meliaceae)、桑科(Moraceae)、茜草科(Rubiaceae)、蕓香科(Rutaceae)、茄科(Solanaceae)、傘形科(Umbelliferae)等多個科的多種植物中,其中在黃花蒿(Artemisia annua)莖葉、茵陳蒿(A. capillaris)葉、丁公藤(Erycibe obtusifolia)莖、擬南芥(Arabidopsis thaliana)全株、諾麗(Morinda citrifolia)果實、苦楝(Melia azedarach)種子等多種植物中的含量相對較高。因此,東莨菪內酯也被賦予了多種藥理活性以及殺蟲、抗菌殺菌、殺螨、化感等農用生物活性?,F(xiàn)就近年來國內外對東莨菪內酯這一天然活性化合物的生物活性研究進展進行綜述。
東莨菪內酯的抗腫瘤活性一直備受醫(yī)學界的關注,狗骨柴(Tricalysia dubia)[5]、紅果小蕓木(Micromelum minutum)[6]、黃花蒿[7]等植物中具有較強細胞毒素活性的物質即為東莨菪內酯。目前報道較多的是東莨菪內酯對前列腺癌PC3 細胞以及T 淋巴瘤細胞的抗腫瘤活性[8,9]。東莨菪內酯能阻斷腫瘤細胞血管內皮生長因子受體-2 的自身磷酸化及下游信號通路,抑制纖維母細胞生長因子(FGF-2)及細胞外信號調節(jié)激酶(ERK1/2)的活性,從而使腫瘤細胞血管生成受阻,抑制原發(fā)腫瘤細胞的生長和轉移,并誘導腫瘤細胞凋亡[10]。研究表明,東莨菪內酯的抗腫瘤活性位點主要為C-6 的酚羥基和C-7 的甲氧基,對其C-6 的酚羥基引入烷氧基后,其衍生物對乳腺癌細胞MCF-7 和MDA-MB231 及結腸癌HT-29 的抑制活性比東莨菪內酯提高10 余倍[11,12]。此外,其4-烷氧基衍生物也具有顯著地細胞毒素活性[13]。目前,Khuda-Bukhsh 等[14]研制了東莨菪內酯聚合物納米膠囊,可增強人體黑色素腫瘤細胞A375 對東莨菪內酯的吸收和利用,顯著提高其抗腫瘤活性。
東莨菪內酯能夠調節(jié)Fe3+與活性氧(ROS)螯合,減弱及清除ROS 產生,從而表現(xiàn)出調節(jié)心血管疾病的作用[15]。高甘油三酯血癥是重要的心血管疾病,其中脂蛋白脂酶(LPL)是重要的致病因素,而東莨菪內酯具有提高LPL 活性的作用,從而表現(xiàn)出治療高甘油三酯血癥的作用,其機制是在通過增加LPL 的mRNA 的合成,從而增加了LPL[16]。此外,在心血管疾病方面,東莨菪內酯具有誘導人體骨髓性白血病細胞的凋亡,并激活細胞核因子κB 及抗血小板凝聚的作用[17]。Olivera 等[18]報道,東莨菪內酯具有抑制大鼠離體主動脈環(huán)收縮的作用,很可能緩解動脈粥樣硬化所導致的心肌缺血。
Ca2+在痙攣中具有重要的作用,東莨菪內酯可調控Ca2+平衡而具有解痙攣活性[19]。0.1 μM 東莨菪內酯能顯著激活紅細胞膜的Ca2+-ATP 酶和Mg2+-ATP 酶,0. 25 μM 東莨菪內酯能顯著激活Na+-K+-ATP 酶,可有效調節(jié)機體的離子平衡[20],且對GH4C1細胞誘導的Ca2+上調抑制率為15.2%,即東莨菪內酯具有調節(jié)Ca2+平衡的作用[21]。Oliveira 等[22]發(fā)現(xiàn)東莨菪內酯能有效抑制苯腎上腺素的活性,增強肌鈣蛋白與Ca2+的親和力,從而起到解痙攣的作用。
東莨菪內酯是藥用植物藏藥雪蓮(Saussurea involucrata)[23]、紫花前胡(Angelica decursiva)[24]、月桂(Litsea guatemalensis)[25]等抗炎和鎮(zhèn)痛的主要活性物質。東莨菪內酯主要通過抑制一氧化氮(NO)合酶和環(huán)氧化酶(COX-2)的活性,抑制炎癥過程中產生的NO 對機體的危害[26]。Mahattanadul 等[27]的東莨菪內酯對小鼠反流性食管炎和慢性胃潰瘍的調控作用研究也證明了這一點。中藥丁公藤注射液的主要活藥理活性物質為東莨菪內酯,臨床上用于治療風濕性關節(jié)炎。研究表明,東莨菪內酯可降低大鼠的關節(jié)炎指數,減少滑膜組織中血管的生成[28]。此外,東莨菪內酯能夠競爭性的抑制高尿酸血癥小鼠中黃嘌呤氧化酶的活性,減少尿酸的產生,進而對抗由高尿酸血癥引起的痛風性關節(jié)炎[29]。
含有東莨菪內酯的藥用植物對肝炎、肝硬化及肝臟損傷具有良好的保護作用[30]。Chang 等[31]發(fā)現(xiàn)芙蓉菊(C. chinensis)水提取物對CCl4致?lián)p的小鼠肝臟具有顯著地保護和治療作用的活性物質為東莨菪內酯;Han 等[32]報道在膽汁導管結扎的小鼠模型中,東莨菪內酯使淤膽型肝纖維化變弱,保護肝臟的功能;Yin 等[33]發(fā)現(xiàn)刺天茄(S.indicum)種子提取物中具有抗乙型肝炎病毒及細胞毒素活性的活性成分為東莨菪內酯;Noh 等[34]報道日本栗(Castanea crenata)內殼提取物含有東莨菪內酯,其對乙醇誘導慢性氧化效應的小鼠肝臟細胞具有較強的保護作用,可抑制乙醇誘導產生的氧化酶(CAT、SOD、GPx、GR)活性。另外,日本栗內殼提取物對飼喂高脂肪的小鼠的肝脂質沉著癥也具有較強地抑制作用[35]。
東莨菪內酯是一種有效的天然乙酰膽堿酯酶抑制劑[3],在老年性癡呆癥模型小鼠中,東莨菪內酯可抑制大腦海馬體突觸體的AChE 作用于煙堿乙酰膽堿受體,促進乙酰膽堿的釋放,提高了老年性癡呆癥患者的學習和記憶能力[4,36]。東莨菪內酯及其衍生物對AChE 的抑制作用,主要通過C-6 和C-7 上的的官能團作用于AChE 的Trp286、Tyr124、Tyr341和Phe295 等氨基酸殘基而發(fā)揮抑制活性[37]。此外,諾麗果的果實富含東莨菪內酯,其氯仿提取物對乙酰膽堿酯酶的抑制活性最強,對莨菪堿導致小鼠記憶損失的保護作用,且提取物與東莨菪內酯對小鼠的行為、生物化學及大腦血液流動的影響相似[38]。
東莨菪內酯還具有其他藥理活性,例如東莨菪內酯具有降溫作用,能顯著地降低正?;顒蛹彝眉坝纱竽c桿菌內毒素致熱的家兔的體溫[39];東莨菪內酯可通過抑制酪氨酸酶活性,進而抑制黑色素的合成,具有美白功能;東莨菪內酯的乙酰膽堿酯酶抑制作用,在臨床上有應用于縮瞳和降眼壓[40]。
東莨菪內酯的藥動力學研究主要集中在大鼠腸道、體胃的吸收和滲透方面。在大鼠體內,東莨菪內酯口服吸收快,在10 min 左右即可達峰,口服后血漿半衰期t1/2=(14.1 ±0.6)min。東莨菪素在大鼠胃中2 h 的吸收百分率為76.3l%,在結腸、十二指腸、回腸、空腸的吸收率分別為46.25%,40.54%,38.21%,32.77%;不同質量濃度、pH 值對東莨菪素在大鼠全腸道的吸收沒有顯著性影響,藥物的吸收呈一級動力學過程,吸收機制主要為被動擴散,這與體外試驗相一致;東莨菪素在胃腸道均有較好的吸收[41]。Galkin 等[42]通過Caco-2 模型對香豆素類口服藥物的膜透性和細胞毒性進行了評估,結果表明該類藥物的有很好的滲透性,在腸道內的吸收較好,但又不只局限于吸收,對線粒體功能也有一定影響。
東莨菪內酯對昆蟲的生物活性主要表現(xiàn)為拒食、抑制生長、觸殺、胃毒等方面,其中在拒食和抑制生長的研究較多。Leszcynski 等[43]發(fā)現(xiàn)小麥葉中東莨菪內酯等甲氧基酚類化合物對麥長管蚜(Sitobion avenae)具有顯著的拒食活性。據此,有學者將小麥低溫馴化后,使得小麥葉中東莨菪內酯等酚類化合物的含量顯著提高,表現(xiàn)出良好的抗蟲和抗病性[44]。甘薯(Ipomoea batatas)塊根富含東莨菪內酯,對小菜蛾(Plutella xylostella)幼蟲具有顯著地生長抑制作用和胃毒作用[45],其塊根被金針蟲(Conoderus spp.和Systena elongata)、玉米根蟲(Diabrotica balteata)、甘薯跳甲(Chaetocnema confinis)、白蠐螬(Phyllophaga spp.)等地下害蟲的危害率與其東莨菪內酯的含量呈負相關關系[46]。Vera 等[47]報道了含200 μg/g 的東莨菪內酯飼料對草地夜蛾(Spodoptera frugiperda)幼蟲的選擇性拒食率為61%;源于黃花蒿的東莨菪內酯與人工飼料混合對塵污燈蛾(Spilarctia oblique)幼蟲具有明顯的拒食和抑制生長作用,東莨菪內酯(>100 μg/g)對塵污燈蛾幼蟲的生物活性與印楝素(50 μg/g)無顯著性差異[48]。
東莨菪內酯不僅對同翅目、鞘翅目及鱗翅目的昆蟲具有拒食及抑制生長作用,其對等翅目和雙翅目的昆蟲也具有拒食及毒殺活性。Adfa 等[49]發(fā)現(xiàn)東莨菪內酯對臺灣乳白蟻(Coptotermes formosanus)表現(xiàn)出顯著的拒食活性,同時發(fā)現(xiàn),其抗白蟻的活性位點主要為C-6 和C-7 的烷氧基。據此,Adfa 等[50]將香豆素修飾為6-烷氧基香豆素和7-烷氧基香豆素,且不飽和烷氧基及環(huán)烷氧基能顯著提高抗白蟻活性。Tunón 等[51]發(fā)現(xiàn)南木蒿(A. abrotanum)的細枝和葉的甲苯提取物對埃及伊蚊(Aedes aegypti)具有顯著地驅避活性,其提取物中主要含有東莨菪內酯和香豆素。此外,東莨菪內酯為諾麗果葉甲醇提取物主要活性物質,提取物對斯氏按蚊(Anopheles stephensi)、致倦庫蚊(Culex quinquefasciatus)及埃及伊蚊幼蟲具有顯著地觸殺活性[52]。
東莨菪內酯對植食性螨類的生物活性研究起始于黃花蒿殺螨活性的研究,張永強等[53]系統(tǒng)研究了黃花蒿不同月份及其不同部位的不同溶劑提取物對朱砂葉螨(Tetranychus cinnabarinus)的觸殺活性,結果表明:黃花蒿七月份葉的丙酮提取物中東莨菪內酯含量最高,對朱砂葉螨的LC50值(48h)為0.105 mg/mL,并且對柑桔全爪螨(Panonychus citri)和酢漿草巖螨(Petrobia harti)也表現(xiàn)出強烈的觸殺活性,對朱砂葉螨還具有一定的產卵抑制活性[54]。Tunón 等[51]發(fā)現(xiàn)南木蒿地上部分乙醇提取物主要為東莨菪內酯和香豆素,對蓖子硬蜱(Ixodes ricinus)有較好的驅避作用。
東莨菪內酯的殺螨活性具有明顯的溫度效應和亞致死效應,其對朱砂葉螨雌成螨的最佳毒力溫度為23.2 ℃,在亞致死劑量下能使朱砂葉螨種群的發(fā)育和繁殖速率降低,且不易產生抗藥性[55,56],原因可能與東莨菪內酯對朱砂葉螨的多靶標作用機理有關[56]。東莨菪內酯處理朱砂葉螨后,能夠顯著抑制螨體內超過氧化物岐化酶(superoxide dismutase,SOD)和過氧化物酶(peroxidase,POD);對過氧化氫酶(catalase,CAT)、羧酸酯酶(carboxylesterase,CarE)和谷胱甘肽S-轉移酶(gultathione S transferases,GSTs)表現(xiàn)為激活作用;對螨體的神經系統(tǒng)靶標——乙酰膽堿酯酶(acetylcholinesterase,AChE)、單胺氧化酶(monoamine oxidase,MAO)、Na+-K+-ATP 酶及Ca2+-Mg2+-ATP 酶的酶活性也表現(xiàn)為抑制作用,并推測東莨菪內酯可能是一種神經毒劑[53,57]。
植物在受到病原菌或外來物質的刺激時,可誘導合成更多的東莨菪內酯,提高其抵抗能力[58]。2,4-D[59]、茉莉酸甲酯[60]、細胞分裂素[61]、阿氟曼鏈霉菌(Streptomyces scabiei)及其毒素thaxtomin A[62]等均可誘導煙草細胞中東莨菪內酯的含量增加,提高其抗菌活性。源于疫酶根腐病(Phytophthora megasperma)的無致病性糖蛋白也能誘導煙葉中東莨菪內酯含量的增加,顯著增強煙株對煙草花葉病毒(TMV)的抗性[63]。東莨菪內酯在煙草中的抗菌活性需要通過轉化為東莨菪苷,才能有效發(fā)揮作用[64],此過程需要煙草葡萄糖基轉移酶(TOGTs)的協(xié)助,其主要調控基因是Togt1 和Togt2,且基因的表達受水楊酸(SA)信號系統(tǒng)的調控[65,66]。但過度使東莨菪內酯轉化為東莨菪苷,對煙草的組織也是有害的[67]。此外,核黃素(維生素B2)也能誘導煙草細胞中東莨菪內酯的合成,其作用機理不屬于水楊酸信號系統(tǒng)控制,而是依賴于磷脂酶C (PLC)和磷脂酶D (PLD)的表達[68]。
東莨菪內酯也是巴西橡膠樹(Hevea brasiliensis)的一種重要植物抗毒素,棕櫚疫霉分泌蛋白質激發(fā)子elicitin 可誘導橡膠樹葉東莨菪內酯的累積,能有效提高其對橡膠南美葉疫病菌(Microcyclus ulei)等的抗性[69]。
東莨菪內酯不僅可提高植物的抗菌作用,也具有殺菌或抑菌作用。0.5 mg/mL 的東莨菪內酯能夠完全抑制煙草灰霉病菌的孢子萌發(fā)和菌絲生長[70];東莨菪內酯(>0.4 mg/mL)能有效抑制腐皮鐮刀菌(Fusarium solani)、尖孢鐮刀菌(F.oxysporum)、根霉病菌(Rhizopus stolonifer)和焦腐病菌(Lasiodiplodia theobromae)的菌絲生長[45]。東莨菪內酯對梭形桿菌(F.fusiformis)、半裸鐮刀菌(F.semitectum)和鏈格胞菌(Alternaria alternata)也具有顯著的抑制作用[71]。此外,東莨菪內酯對蘋果擴展青霉(Penicillium expansum)及其擴展青霉素的累積具有良好的控制作用[72];對侵染白榆(Ulmus pumila)的長喙殼科真菌Ophiostoma ulmi 具有抑制孢子萌發(fā)和菌絲生長的活性[73]。Carpinella 等[74]將東莨菪內酯分別與代森鋅和萎銹靈復配,可有效減少兩者的用量,顯著提高了對鐮刀菌(F.verticillioides)的抑制效果。
香豆素類化合物可作用于植物的細胞膜,致使胞內離子平衡紊亂、激素變化、代謝異常等,從而擾亂植物的平衡和光合作用,調控植物的生長[75]。Kim 等[76]發(fā)現(xiàn)東莨菪內酯是多種入侵植物的化感物質。在多種雜草中,東莨菪內酯也發(fā)揮著化感作用的特性[77]。
東莨菪內酯可調節(jié)禾本科植物燕麥(Avena sativa)和梯牧草(Phleum pratense)幼苗根的生長,且高濃度表現(xiàn)為抑制作用,而低濃度則表現(xiàn)為促進作用,其調控作用主要作用于根尖,使根尖分生組織壞死,分泌黑色物質堵塞導管,進而調控植物的生長[78,79],其作用機理主要是保護吲哚乙酸(IAA)免受吲哚乙酸氧化酶的氧化作用,使生長點IAA 含量過高[80]。此外,東莨菪內酯(>0.019 mg/mL)也能顯著抑制紅根莧(Amaranthus palmeri)和芥菜(Brassica juncea)根的生長,且破壞細胞胚植[81]。另外,東莨菪內酯對雙子葉植物的幼苗根抑制較弱,但對葉的抑制作用也較為顯著,其化感活性主要通過調節(jié)植物體內的相關酶系和氣孔的開度,影響其光合作用,從而調節(jié)植物的生長[82,83]。
東莨菪內酯存在于多個科的多種植物體內,其臨床應用十分廣泛,但是其研究主要集中在藥理學方面,藥動力學方面的研究報道較少。在農業(yè)應用上,東莨菪內酯對多種農業(yè)害蟲及害螨具有作用方式多樣性和作用靶標多樣性的特點,能夠減緩或者避免抗藥性的產生,具有很好的開發(fā)利用價值。但是,現(xiàn)階段對東莨菪內酯的研究還不是很深入,其殺蟲殺螨作用機理尚不清楚,而且目前還沒有一個成熟的劑型可以應用于實際生產。因此,要實現(xiàn)東莨菪內酯這一植物源物質的實際應用價值,首先,在醫(yī)學上需要對其藥動力學進行進一步的研究;第二,在農業(yè)應用上,需明確東莨菪內酯的殺蟲殺螨作用機理,以期發(fā)現(xiàn)新的作用靶標,減緩抗性的產生;第三,研究東莨菪內酯的毒力與藥劑本身、受體生理代謝、環(huán)境條件等多方面因素的關系,為制劑的研發(fā)和有效利用提供理論依據。
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