stilbenes and galangin

The leaves of the Japanese Alnus sieboldiana have been extracted with n-hexane and then with methanol. A bioactivity-guided approach based on MTT assay for growth inhibition and quantitative real-time PCR for TNF-α inhibitory activity was taken to identify the active compounds in EtOAc soluble fraction of the methanol extract. From this active fraction, seven compounds have been isolated and four compounds (pinosylvin, galangin, quercetin and methyl gallate) have been examined for their dose-response effect on the viability of A549 cells and on TNF-α inhibitory activity. Based on MTT assay, all of the four examined compounds inhibit growth of human lung cancer cells. Among four tested compounds only galangin (3,5,7-trihydroxyflavone) significantly inhibited TNF-α gene expression in A549 cells (IC₅₀ = 94 μM). Taken together, this finding suggests that galangin may be useful in cancer prevention.

Topics: Alnus; Anticarcinogenic Agents; Antineoplastic Agents, Phytogenic; Cell Line, Tumor; Dose-Response Relationship, Drug; Flavonoids; Gallic Acid; Humans; Lung Neoplasms; Phytotherapy; Plant Extracts; Plant Leaves; Quercetin; Stilbenes; Tumor Necrosis Factor-alpha

Plant polyphenols like flavonoids and hydroxystilbens have been found to possess radical scavenging/antioxidative activity, especially when studied in cell-free systems. A positive effect in such assays, however, does not necessarily indicate a protective activity against deleterious effects of oxidative stress in intact cells. In fact it has been shown that polyphenols can act as anti-oxidants as well as pro-oxidants. The aim of the present study was to investigate whether and with what potency selected polyphenols are able to inhibit cellular radical generation in C6 cells and whether they can induce oxidative stress themselves. Cumene hydroperoxide (CHP) was used as a model to induce radical generation which was measured by means of a fluorometric 2',7'-dichlorodihydro-fluorescein assay. CHP-induced, time and concentration dependent, a manifold increase of DCF fluorescence indicating intracellular radical generation. This process was inhibited by all the flavonoids and the hydroxystilben resveratrol, at low micromolar concentrations. The most potent compounds, luteolin and galangin, already at concentrations of 5 to 10 microM nearly completely abolished the radical generation in the presence of 500 microM CHP. The following ranking of anti-oxidative potency was obtained: luteolingalangin>kaempferol>quercetin>resveratrolgenisteintaxifolin. This ranking is completely different from that obtained by means of a trolox equivalent antioxidant capacity (TEAC) assay in a cell-free system, thus putting the biological relevance of the latter in question. Remarkably, one compound induced oxidative stress itself, namely genistein. This flavonoid inhibited the cellular radical generation in the presence of CHP while it significantly enhanced it in the absence of the peroxide.

Topics: Astrocytoma; Benzene Derivatives; Brain Neoplasms; Dose-Response Relationship, Drug; Flavonoids; Free Radical Scavengers; Free Radicals; Genistein; Luteolin; Oxidants; Oxidative Stress; Phenols; Plant Extracts; Polyphenols; Resveratrol; Stilbenes

Forty-two flavonoids and a stilbene (pinosylvin) were identified in the leaf exudates of 11 temperate species of Nothofagus from South America, Australia and New Zealand. The flavonoid profiles demonstrate significant taxonomic value at the subgeneric level. Most species of subgenus Fuscospora are characterized by the presence of pinosylvin, galangin and galangin methyl ethers. Kaempferol-type flavonols are abundant in subgenus Lophozonia while these flavonols are largely absent from species of subgenus Fuscospora. The flavonoid patterns are largely in agreement with a recent subgeneric classification of Nothofagus.

Topics: Cluster Analysis; Flavonoids; Magnoliopsida; Phylogeny; Plant Leaves; Species Specificity; Stilbenes