Van H Tran’s research while affiliated with The University of Sydney and other places

Prenylated and hydroxyprenylated piceatannol, resveratrol and pinosylvin derivatives were isolated from resin produced by three Australian Lepidosperma Labill. species (Cyperaceae). From L. congestum R.Br. one known compound, 3′,5′-bis-prenyl-E-resveratrol, and five undescribed compounds were isolated, 3′-O-prenyl-5′-prenyl-E-piceatannol, 5′,6′-bis-prenyl-E-piceatannol, 5′-prenyl-E-piceatannol, 3′,5′-bis(3-hydroxy-3-methylbutyl)-E-resveratrol and 3′,5′-bis-E-hydroxyprenyl-E-resveratrol. From L. gunnii Boeckeler one undescribed compound was isolated, 3′-E-hydroxyprenyl-5′-Z-hydroxyprenyl-E-resveratrol. From L. laterale R.Br. six undescribed compounds were isolated, 3-O-prenyl-E-pinosylvin, 3-O-Z-hydroxyprenyl-E-pinosylvin, 3′-Z-hydroxyprenyl-E-resveratrol, 3-O-Z-hydroxyprenyl-E-resveratrol, 3-O-Z-hydroxyprenyl-4′-O-methyl-E-resveratrol, and 3-O-prenyl-3′-δ,δ′-dihydroxyprenyl-E-resveratrol. Compounds, including a reference compound 3-O-prenyl-3′-O-methyl-E-piceatannol, were screened in an assay for melatoninergic binding to MT1 and MT2 receptors and binding to QR2/MT3 enzyme, and for inhibition of QR2/MT3 in a functional assay. Strong binding was observed for 3-O-Z-hydroxyprenyl-E-resveratrol with a Ki of 0.022 nM and the strongest inhibition of QR2/MT3 observed was for the reference compound, 3-O-prenyl-3′-O-methyl-E-piceatannol, with an inhibition of 61% at 1 μM and 95% at 10 μM. The three most active binders and inhibitors of QR2/MT3 were found to have a common substructure corresponding to 3-O-prenylresveratrol.

The endemic Australian plants Lepidosperma sp. Flinders Chase (Cyperaceae), Lepidosperma viscidum (Cyperaceae) and Dodonaea humilis (Sapindaceae) were found to be the botanical origin of three propolis types found on Kangaroo Island identified by TLC and ¹H NMR matching of propolis and plant resin analytical profiles. Resin samples extracted from the plant, Lepidosperma sp. Flinders Chase, were chromatographically fractionated to give: methyl 3-phenyl-2-(E-cinnamoyloxy)propanoate (1), 3-(E-8-methoxy-8-oxo-3,7-dimethyloct-2-enyl)-4-hydroxy-E-cinnamic acid (2), 3-(E-6,7-dihydroxy-3,7-dimethyloct-2-enyl)-4-hydroxy-E-cinnamic acid (3), previously undescribed; and the known stilbenes, 2-prenyl-3,5-dihydroxy-E-stilbene (6) and 2-prenyl-3-methoxy-5-hydroxy-E-stilbene (7). The resin from L. viscidum gave: 5′-(E-4-hydroxy-3-methylbut-2-enyl)-4,2′,4′-trihydroxydihydrochalcone (4); 5′-(E-4-hydroxy-3-methylbut-2-enyl)-4′-methoxy-4,2′-dihydroxydihydrochalcone (5), previously undescribed; and three known flavanones, farrerol (8), 5,7,3′,5′-tetrahydroxy-6,8-dimethylflavanone (9) and 5,7,3′,5′-tetrahydroxy-6-methylflavanone (10). The major constituent in the propolis identified as being sourced from D. humilis was identified as 6,8-diprenyl-5,7,3′,4′-tetrahydroxyflavanone (11), a known compound identified in several unrelated plant species.

Propolis samples from Kangaroo Island, South Australia, were investigated for chemical constituents using high-field nuclear magnetic resonance spectral profiling. A type of propolis was found containing a high proportion of prenylated hydroxystilbenes. Subsequently, the botanical origin of this type of propolis was identified using a beehive propolis depletion method and analysis of flora. Ligurian honey bees, Apis mellifera ligustica Spinola, were found to produce propolis from resin exuded by the Australian native sedge plant Lepidosperma sp. Montebello (Cyperaceae). The plants, commonly known as sword sedge, were found to have resin that matched with the propolis samples identified as the most abundant propolis type on the island containing C- and O-prenylated tetrahydroxystilbenes (pTHOS) in addition to a small amount of prenylated p-coumarate. The isolation of five pTHOS not previously characterized are reported: (E)-4-(3-methyl-2-buten-1-yl)-3,4′,5-trihydroxy-3′-methoxystilbene, (E)-2,4-bis(3-methyl-2-buten-1-yl)-3,3′,4′,5-tetrahydroxystilbene, (E)-2-(3-methyl-2-buten-1-yl)-3-(3-methyl-2-butenyloxy)-3′,4′,5-trihydroxystilbene, (E)-2,6-bis(3-methyl-2-buten-1-yl)-3,3′,5,5′-tetrahydroxystilbene and (E)-2,6-bis(3-methyl-2-buten-1-yl)-3,4′,5-trihydroxy-3′-methoxystilbene. A National Cancer Institute 60 human cell line anticancer screen of three of these compounds showed growth inhibitory activity. The large Australasian genus Lepidosperma is identified as a valuable resource for the isolation of substances with medicinal potential.

Lepidosperma (Cyperaceae, Schoeneae) is a morphologically distinct genus but often taxonomically difficult at the species level. The L. viscidum complex is widespread through eastern Australia and may contain up to 10 undescribed, cryptic species. More corroborating characters are needed. Discovery of compounds with medicinal potential from the resin of these plants has led to recognition of a clear relationship between resin chemotype and plant morphotype. We investigate resin chemistry as a taxonomic tool, compare with morphological, anatomical and molecular (ETS and matK) data sources, and assess its potential application across the genus and family. Novel use of resin chemistry provides an additional and excellent line of evidence for systematics, may be less subjective than morphological and anatomical data, and is cheaper than genetic analysis. Resin chemical analysis has potential further application for taxonomy and identification within Lepidosperma and other groups in Cyperaceae.

Insulin resistance is a core component of metabolic syndrome and usually precedes the development of type 2 diabetes mellitus. We have examined the preventative effect of an ethanol extract of ginger (Zingiber officinale, Zingiberaceae) on insulin resistance in a high-fat, high-carbohydrate (HFHC) diet-fed rat model of metabolic syndrome. The HFHC control rats displayed severe insulin resistance, whilst rats treated with ginger extract (200 mg/kg) during HFHC diet feeding showed a significant improvement of insulin sensitivity using the Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) after 10 weeks (P < 0.01). An in vitro mechanistic study showed that (S)-[6]-gingerol, the major pungent phenolic principle in ginger, dose-dependently (from 50 to150 μM) increased AMPK α-subunit phosphorylation in L6 skeletal muscle cells. This was accompanied by a time-dependent marked increment of PGC-1α mRNA expression and mitochondrial content in L6 skeletal muscle cells. These results suggest that the protection from HFHC diet-induced insulin resistance by ginger is likely associated with the increased capacity of energy metabolism by its major active component (S)-[6]-gingerol. This article is protected by copyright. All rights reserved.

Purpose: The aim of this study was to investigate the mechanism of (S)-[6]-gingerol in promoting glucose uptake in L6 skeletal muscle cells. Methods: The effect of (S)-[6]-gingerol on glucose uptake in L6 myotubes was examined using 2-[1,2-3H]-deoxy-D-glucose. Intracellular Ca2+ concentration was measured using Fluo-4. Phosphorylation of AMPKα was determined by Western blotting analysis. Results: (S)-[6]-Gingerol time-dependently enhanced glucose uptake in L6 myotubes. (S)-[6]-Gingerol elevated intracellular Ca2+ concentration and subsequently induced a dose- and time-dependent enhancement of threonine172 phosphorylated AMPKα in L6 myotubes via modulation by Ca2+/calmodulin-dependent protein kinase kinase. Conclusion: The results indicated that (S)-[6]-gingerol increased glucose uptake in L6 skeletal muscle cells by activating AMPK. (S)-[6]-gingerol, a major component of Zingiber officinale, may have potential for development as an antidiabetic agent.

(S)-[6]-Gingerol is under investigation for a variety of therapeutic uses. Transforming growth factor (TGF)-β stimulates proteoglycan synthesis, leading to increased binding of low-density lipoproteins, which is the initiating step in atherosclerosis. We evaluated the effects of (S)-[6]-gingerol on these TGF-β-mediated proteoglycan changes to explore its potential as an anti-atherosclerotic agent. Purified (S)-[6]-gingerol was assessed for its effects on proteoglycan synthesis by [(35) S]-sulfate incorporation into glycosaminoglycan chains and [(35) S]-Met/Cys incorporation into proteoglycans and total proteins in human vascular smooth muscle cells. Biglycan level was assessed by real-time quantitative polymerase chain reactions and the effects of (S)-[6]-gingerol on TGF-β signalling by assessment of the phosphorylation of Smads and Akt by western blotting. (S)-[6]-Gingerol concentration-dependently inhibited TGF-β-stimulated proteoglycan core protein synthesis, and this was not secondary to inhibition of total protein synthesis. (S)-[6]-Gingerol inhibited biglycan mRNA expression. (S)-[6]-Gingerol did not inhibit TGF-β-stimulated glycosaminoglycan hyperelongation or phosphorylation of Smad 2, in either the carboxy terminal or linker region, or Akt phosphorylation. The activity of (S)-[6]-gingerol to inhibit TGF-β-stimulated biglycan synthesis suggests a potential role for ginger in the prevention of atherosclerosis or other lipid-binding diseases. The signalling studies indicate a novel site of action of (S)-[6]-gingerol in inhibiting TGF-β responses.

Synthesis of the naturally occurred C- and O-prenylated tetrahydroxystilbenes and O-prenylated cinnamates was carried out by decarbonylative Heck reaction and selenium dioxide catalysed oxidation, respectively. In the decarbonylative Heck synthetic route, fusion of benzoyl chloride and styrene derivatives was catalysed by an N-heterocyclic carbene system generated in situ by palladium acetate and 1,3-bis(2,6-diisopropylphenyl)imidazolinium chloride to form a E-tetrahydroxystilbene derivative. Formation of allyl ether was subsequently carried out by reaction of the deprotected OH in the A phenyl ring of the stilbene with 3,3-dimethylallyl bromide and a base (sodium hydride) to form O-prenylated tetrahydroxystilbene derivatives. [1,5]-Rearrangement of the isoprenyl unit from O- to C-position in the A ring was carried out at elevated temperature in the presence of magnesium silicate (Florisil) to form the corresponding C-prenylated tetrahydroxystilbene. Formation of O-prenylated cinnamate was first carried out by base catalysed allyl ether formation between 3,3-dimethylallyl bromide and hydroxycinnamic acid methyl ester. The methyl group of the isoprenyl unit was subsequently oxidized using selenium dioxide to form a terminal hydroxyl group. The prenylated tetrahydroxystilbenes and cinnamate synthesized in this study were novel derivatives of piceatannol and methyl 4-(3'-methylbut-2'-enyloxy)cinnamate isolated from propolis in Kangaroo Island, South Australia. The synthetic compounds were tested against K562 cancer cells and potent growth inhibitory activity was observed for E-1-[5-hydroxy-3-methoxy-2-(3-methyl-2-butenyl)phenyl]-2-[4-hydroxy-3-methoxyphenyl]ethene, IC50 = 0.10 μM.

Introduction. Hepatic inflammation underlies the pathogenesis of chronic diseases such as insulin resistance and type 2 diabetes mellitus. S-[6]-Gingerol has been shown to have anti-inflammatory properties. Important inflammatory mediators of interleukins include nuclear factor κ B (NF κ B) and cyclooxygenase 2 (COX2). We now explore the mechanism of anti-inflammatory effects of S-[6]-gingerol in liver cells. Methods. HuH7 cells were stimulated with IL1β to establish an in vitro hepatic inflammatory model. Results. S-[6]-Gingerol attenuated IL1β-induced inflammation and oxidative stress in HuH7 cells, as evidenced by decreasing mRNA levels of inflammatory factor IL6, IL8, and SAA1, suppression of ROS generation, and increasing mRNA levels of DHCR24. In addition, S-[6]-gingerol reduced IL1β-induced COX2 upregulation as well as NF κ B activity. Similar to the protective effects of S-[6]-gingerol, both NS-398 (a selective COX2 inhibitor) and PDTC (a selective NF κ B inhibitor) suppressed mRNA levels of IL6, IL8, and SAA1. Importantly, PDTC attenuated IL1β-induced overexpression of COX2. Of particular note, the protective effect of S-[6]-gingerol against the IL1β-induced inflammatory response was similar to that of BHT, an ROS scavenger. Conclusions. The findings of this study demonstrate that S-[6]-gingerol protects HuH7 cells against IL1β-induced inflammatory insults through inhibition of the ROS/NF κ B/COX2 pathway.