Heng Yen Khong

Malaysianol B, an oligostilbenoid derivative from Dryobalanops lanceolata

A new oligostilbenoid tetramer, malaysianol B (1), was isolated from the acetone extract of the stem bark of Dryobalanops lanceolata along with seven oligostilbenoids tetramers; hopeaphenol (2), stenophyllol A (3), nepalensinol B (4), vaticanol B (5) and C (6), upunaphenol D (7), and flexuosol A (8). The structures of the isolated compounds were established on the basis of their spectroscopic data evidence. The antibacterial activity of the isolated compounds was evaluated using resazurin microtitre-plate assay.

The pyranoxanthone inophyllin A induces oxidative stress mediated-apoptosis in Jurkat T lymphoblastic leukemia cells☆

Inophyllin A (INO-A), a pyranoxanthone isolated from the roots of Calophyllum inophyllum represents a new xanthone with potential chemotherapeutic activity. In this study, the molecular mechanism of INO-A-induced cell death was investigated in Jurkat T lymphoblastic leukemia cells. Assessment of phosphatidylserine exposure confirmed apoptosis as the primary mode of cell death in INO-A-treated Jurkat cells. INO-A treatment for only 30 min resulted in a significant increase of tail moment which suggests that DNA damage is an early apoptotic signal. Further flow cytometric assessment of the superoxide anion level confirmed that INO-A induced DNA damage was mediated with a concomitant generation of reactive oxygen species (ROS). Investigation on the thiols revealed an early decrease of free thiols in 30 min after 50 μM INO-A treatment. Using tetramethylrhodamine ethyl ester, a potentiometric dye, the loss of mitochondrial membrane potential (MPP) was observed in INO-A-treated cells as early as 30 min. The INO-A-induced apoptosis progressed with the simultaneous activation of caspases-2 and -9 which then led to the processing of caspase-3. Taken together, these data demonstrate that INO-A induced early oxidative stress, DNA damage and loss of MMP which subsequently led to the activation of an intrinsic pathway of apoptosis in Jurkat cells.

Antioxidant, Anti-Inflammatory, and Cytotoxic Activities of Garcinia nervosa (Clusiaceae)

In our continuing interest on Sarawak Garcinia species, we carried out the evaluation of antioxidant, anti-inflammatory and cytotoxic activities on the methanolic extracts of Garcinia nervosa. The extracts were prepared from its air-dried grounded leaves and barks. The evaluation of antioxidant activities was done using the (2,2-diphenyl-1-picrylhydrazyl) DPPH radical scavenging assay and the result showed high radical scavenging activities. Meanwhile, the anti-inflammatory evaluation was performed using the lipoxygenase assay, hyaluronidase assay, and xanthine oxidase assay which showed, both of these extracts exhibited high anti-inflammatory properties. The lipoxygenase assay showed a high inhibition of enzyme activity for the barks extracts and a moderate enzyme activity for the leaves extracts. However, there were low inhibitions for both extracts in the hyaluronidase assay and only the barks extracts exhibited moderate antigout properties in the xanthine oxidase assay. For the cytotoxic assay, the extracts exhibited positive responses against the three cancer cell lines, the HeLa cell lines, MCF-7 cell lines, and HT-29 cell lines. Thus, Garcinia nervosa contains high antioxidativeand anti-inflammation properties, which have great potential in the development of pharmaceutical and dermatological products.

Resveratrol oligomers from the tree bark of Shorea accuminatissima: Their properties and significance

This study was aimed to isolate and structure elucidate the resveratrol oligomers from the acetone extract of the tree bark of S. accuminatissima. Five resveratrol oligomers, namely vaticanol-A, davidiol-A, α-viniferin, hopeaphenol and hemsleyanol-D have been isolated for the first time from this plant. The structures of these compounds were established based on the spectroscopic data evidence, including UV, IR, 1H NMR, and 13C NMR spectra, and compared to their reported data. Hopeaphenol showed cytotoxicity and strongly inhibited murine leukemia P-388 cells.