Lai-King Sy

Timosaponin A-III induces autophagy preceding mitochondria-mediated apoptosis in hela cancer cells

Timosaponin A-III (TAIII), a saponin isolated from the rhizome of Anemarrhena asphodeloides, exhibits potent cytotoxicity and has the potential to be developed as an anticancer agent. Here, we provide evidence that TAIII induces autophagy in HeLa cells followed by apoptotic cell death. TAIII-induced autophagy was morphologically characterized by the formation of membrane-bound autophagic vacuoles recognizable at the ultrastructural level. TAIII-treated cells expressing green fluorescent protein (GFP)-labeled microtubule-associated protein 1 light chain 3 (LC3) displayed punctate fluorescence indicative of LC3 recruitment to the autophagosome. This was associated with the conversion of LC3-I (the cytosolic form) into LC3-II (the lipidated form located on the autophagosome membrane). TAIII treatment also induced mitochondrial dysfunction involving overproduction of reactive oxygen species and reduction of mitochondrial membrane potential accompanied by induction of mitochondrial permeability transition. Prolonged exposure to TAIII resulted in cytochrome c release and caspase-3 activation, events that signified the onset of apoptotic cell death. TAIII-induced autophagy preceded apoptosis, as evidenced by early autophagic vacuole formation, GFP-LC3 translocation, and LC3-II increase in the absence of caspase-3 cleavage. Notably, TAIII-mediated apoptotic cell death was potentiated by treatment with autophagy inhibitor 3-methyladenine or small interfering RNA against the autophagic gene beclin 1. These findings suggest that TAIII-elicited autophagic response plays a protective role that impedes the eventual cell death. In terms of structure-activity relationship, the sugar chain in TAIII is indispensable to the drug action, as the sugar-lacking aglycone sarsasapogenin did not induce autophagy and exhibited weaker cytotoxicity.

The mechanism of the spontaneous autoxidation of dihydroartemisinic acid

Abstract Dihydroartemisinic acid undergoes slow spontaneous autoxidation to artemisinin and other natural products, which have been reported from the medicinal plant Artemisia annua. The mechanism of this complex transformation is shown to involve four steps: (i) initial reaction of the Δ4,5-double bond of dihydroartemisinic acid with molecular oxygen, (ii) Hock cleavage of the resulting tertiary allylic hydroperoxide; (iii) oxygenation of the enol product from Hock cleavage; and (iv) cyclization of the resulting vicinal hydroperoxyl-aldehyde to the 1,2,4-trioxane system of artemisinin.

Terpenoids from the seeds of Artemisia annua

Fourteen sesquiterpenes, three monoterpenes and one diterpene natural product have been isolated from the seeds of Artemisia annua. The possible biogenesis of some of these natural products are discussed by reference to recently reported experimental results for the autoxidation of dihydroartemisinic acid and other terpenoids from Artemisia annua.

Coniferaldehyde derivatives from tissue culture of Artemisia annua and Tanacetum parthenium

Plant tissue cultures of both Artemisia annua and Tanacetum parthenium were found to produce the novel compound (2-glyceryl)-O-coniferaldehyde as the major constituent. Cultures of A. annua produced several other coniferaldehyde derivatives, including the novel (2-propenal)-O-coniferaldehyde and the unusual neolignan balanophonin. None of the cinnamaldehyde derivatives have been reported previously from the parent plants.

A novel endoperoxide and related sesquiterpenes from Artemisia annua which are possibly derived from allylic hydroperoxides

Abstract Seven novel cadinane sesquiterpenes, including the seven-membered endoperoxide lactone arteannuin H (1), two six-membered lactones arteannuins I (4) and J (5), three five-membered lactones arteannuins K-M (6–8) and a keto acid arteannuin N (9) have been isolated from the dried leaves of Artemisia annua in addition to the known compounds dihydroartemisinic acid (27), dihydroarteannuin B (24) and dihydro-epi-deoxyarteannuin B (22). It is proposed that these novel sesquiterpenes are biogenetically related to dihydroartemisinic acid via intermediate secondary and tertiary allylic hydroperoxides.

Phytochemistry of Illicium dunnianum and the systematic position of the illiciaceae

Detailed chemical investigation of a dichloromethane extract of Illicium dunnianum yielded six phenylpropanoids (two of which, 1-[(3-methylbut-2-enyl)oxy]-2-methoxy-4-(prop-1-en-3-ol)benzene and 1,2-(methylenedioxy)-4-(propan-1,2-diol)benzene, were novel), five known neolignans, three known cycloartane triterpenes and a novel ring-A cleaved cycloartane, 3,4-seco-(24Z)-cycloart-4(28),24-diene-3,26-dioic acid 3-methyl ester. The significance of these chemical findings is assessed in the context of the historical debate concerning the systematic position and phylogenetic relationships of the genus.

Three sesquiterpenes from Artemisia annua

The dried leaves of Artemisia annua, collected from Sichuan Province in Southern China, have yielded an unusual cadinane sesquiterpene oxygenated at the 7-position and a novel eudesmane sesquiterpene, in addition to several known sesquiterpenes and flavanoids.

Oxygenated bisabolanes from Alpinia densibracteata

Seven novel oxygenated bisabolane sesquiterpenes and four oxygenated menthane monoterpenes have been isolated from the dichloromethane extract of Alpinia densibracteata in addition to known bisabolanes and menthanes. The structures of these compounds were established by NMR spectroscopy and by some chemical transformations.

The role of the 12-carboxylic acid group in the spontaneous autoxidation of dihydroartemisinic acid

Abstract Three of the four steps in the slow spontaneous autoxidation of dihydroartemisinic acid to artemisinin (‘ene-type’ reaction of molecular oxygen with the Δ4,5 double bond, Hock cleavage of the resulting tertiary allylic hydroperoxide, oxygenation of the enol product from Hock cleavage and cyclization of the resulting vicinal hydroperoxyl-aldehyde to the 1,2,4-trioxane system of artemisinin) are shown to be assisted by the proximity of the 12-carboxylic acid functional group in dihydroartemisinic acid to the functional groups participating in these reactions.

Syntheses of dihydroartemisinic acid and dihydro-epi-deoxyarteannuin B incorporating a stable isotope label at the 15-position for studies into the biosynthesis of artemisinin

Abstract [15-13C2H3]-Dihydroartemisinic acid (3a) and [15-13CH3]-dihydro-epi-deoxyarteannuin B (7b), intended for evaluation in vivo as biosynthetic precursors to artemisinin, have been obtained from a reconstructive synthesis. The decalenone acid 8 from acid degradation of artemisinin (1) serves as a common intermediate: following addition of labeled methyl Grignard reagent to 8, either labeled precursor can be prepared in good yield by varying the work-up conditions employed. It is shown that both compounds are prone to autoxidation on storage and that the products of such oxidation and subsequent rearrangement reactions might be confused with bona fide metabolites when using these labeled precursors in feeding experiments designed to determine the biosynthetic route to artemisinin in Artemisia annua.