Inhibitory effects of Sargassum polycystum on tyrosinase activity and melanin formation in B16F10 murine melanoma cells.

ETHNOPHARMACOLOGICAL RELEVANCE: Sargassum polycystum, a type of brown seaweed, has been used for the treatment of skin-related disorders in traditional medicine. AIM OF THE STUDY: The aim of the present study is to investigate the antimelanogenesis effect of Sargassum polycystum extracts by cell-free mushroom tyrosinase assay followed by cell viability assay, cellular tyrosinase assay and melanin content assay using B16F10 murine melanoma cells. MATERIALS AND METHODS: Sargassum polycystum was extracted with 95% ethanol and further fractionated with hexane, ethyl acetate and water. The ethanolic crude extract and its fractionated extracts were tested for their potential to act as antimelanogenesis or skin-whitening agents by their abilities to inhibit tyrosinase activity in the cell-free mushroom tyrosinase assay and cellular tyrosinase derived from melanin-forming B16F10 murine melanoma cells. The tyrosinase inhibitory activity was correlated to the inhibition of melanin production in α-MSH-stimulated and unstimulated B16F10 cells. RESULTS: Sargassum polycystum ethanolic extract and its fractions had little or no inhibitory effect on mushroom tyrosinase activity. However, when tested on cellular tyrosinase, the ethanolic extract and its non-polar fraction, hexane fraction (SPHF), showed significant inhibition of cellular tyrosinase activity. In parallel to its cellular tyrosinase inhibitory activity, SPHF was also able to inhibit basal and α-MSH-stimulated melanin production in B16F10 cells. CONCLUSIONS: Our findings showed that (i) cellular tyrosinase assay is more reliable than mushroom tyrosinase assay in the initial testing of potential antimelanogenesis agents and, (ii) SPHF inhibited melanogenesis by inhibiting cellular tyrosinase activity. SPHF may be useful for treating hyperpigmentation and as a skin-whitening agent in cosmetics industry.

Constituents of the roots and stems of Aristolochia mollissima.

Five new sesquiterpenes, mandolins R (1), S (2), U (3), W (4), and X (5), together with 39 known compounds, were isolated from the dried roots and stems of Aristolochia mollissima. Their structures were determined by spectroscopic methods.

Constituents from the stem and root of Aristolochia kaempferi.

Three new phenanthrene derivatives, aristoliukine-C, aristofolin-E and aristolochic acid-Ia methyl ester, and one new sesquiterpene, madolin-P, together with 58 known compounds were isolated from the stem and root of Aristolochia kaempferi. The structures of these compounds were determined by spectral analysis. The cytotoxicity and antiplatelet activity of the isolated compounds are also discussed.

The constituents of the root and stem of Aristolochia heterophylla Hemsl.

Seven new compounds, sodium aristolochate-VII (1), aristolactam-CIV (2), madolin-I (3), -J (4), -K (5), -L (6) and -M (7) together with 71 known compounds were isolated and characterized from the fresh root and stem of Aristolochia heterophylla Hemsl. Their structures were determined by spectral methods. Compound 8 was revised as aromadendrane-4beta, 10beta-diol by spectral data and single-crystal X-ray analysis.

Sesquiterpene esters of aristolochic acid from the root and stem of Aristolochia heterophylla.

Three novel sesquiterpene esters of aristolochic acid, aristoloterpenate-II (2), -III (3), and-IV (4), together with known aristoloterpenate-I (1), were isolated and characterized from the root and stem of Aristolochia heterophylla. Their structures were elucidated by spectroscopic methods. The absolute configuration of these compounds at C-4' was determined as R by circular dichroic studies. These compounds showed cytotoxicity against hepatoma G2, 2, 2, 15 cells.

Naphthoquinone esters from the root of Rhinacanthus nasutus.

Reinvestigation of the root of Rhinacanthus nasutus afforded, in addition to rhinacanthin-A to -D reported previously, two new dimethyldihydropyranonaphthoquinone esters (5, 6) and eight new 2-hydroxy-1,4-naphthoquinone esters (7-14) were isolated. The stereochemistry of rhinacanthin-A was determined as the R configuration. Compounds rhinacanthin-G to -N, belong to a class of 2-hydroxy-3-(3-hydroxy-2,2-dimethylpropyl)-1,4-naphthoquinone esters, and so far have been isolated only in this plant. Their biosynthesis is also discussed.

Regulation of hypothalamic neuropeptide-Y neurons by growth hormone in the rat.

GH is thought to exert a short-loop feedback action on the hypothalamic somatostatin- and GH-releasing hormone (GHRH)-containing neurons. The direct actions of GH are mediated through GH receptors. In the male rat, few GHRH-containing neurons in the arcuate nucleus (ARC) appear to express the GH receptor messenger RNA (mRNA); however, some unidentified neurons near GHRH neurons do. Recent evidence suggests that neuropeptide-Y (NPY)-containing neurons, which are located near GHRH neurons in the ARC, are targets for GH action because treatment of rats with GH induces c-fos expression in these cells. We conducted two experiments to test the hypothesis that GH acts on NPY neurons in the ARC. First, we performed double-label in situ hybridization to determine whether NPY neurons in the ARC express GH receptor mRNA. Second, we investigated the possibility that GH regulates NPY mRNA expression by using in situ hybridization to compare ARC NPY mRNA levels among groups of normal (n = 7), hypophysectomized (n = 7), and hypophysectomized/rGH-treated (1.5 mg rat GH over 3 days; n = 6) rats. We found that most of the NPY-containing neurons in the ARC expressed GH receptor mRNA, whereas hypothalamic NPY neurons residing outside of the ARC did not. Furthermore, hypophysectomy significantly decreased NPY mRNA levels, and GH treatment restored the levels to those of the intact animals. We conclude that GH regulates the activity of NPY neurons in the ARC by a direct action on GH receptors that are expressed by NPY neurons. Whether the action of GH on NPY neurons in the ARC is related to the feedback control of GH secretion or some other physiological function remains to be determined.