title: Tyrosinase activity of Greyia flanaganii (Bolus) constituents.
abstract: Hyper-pigmentation of the skin is a common problem that is prevalent in middle aged and elderly people. It is caused by over production of melanin. Tyrosinase is known to be the key enzyme in melanin production. Ethanolic extract of Greyia flanaganii leaves showed significant (P<0.05) antityrosinase activity exhibiting the IC₅₀ of 32.62 μg/ml. The total extract was further investigated for its toxicity and effect on melanin production by melanocytes cells, and showed significant inhibition (P<0.05) (20%) of melanin production at 6.25 μg/ml and low levels of cytotoxicity (IC₅₀<400 μg/ml). The amount of antioxidants necessary to decrease the initial DPPH absorbance by 50% (EC₅₀) by the total ethanolic extract was found to be 22.01 μg/ml. The effect of G. flanaganii against acne causing bacteria, Propionibacterium acnes, was investigated using microdilution assay. The MIC of the extract of G. flanaganii was found to be 250 μg/ml. Bioassay-guided fractionation led to the isolation of (3S)-4-hydroxyphenethyl 3-hydroxy-5-phenylpentanoate (1), 2',4',6'-trihydroxydihydrochalcone (2), 2',6',4-trihydroxy-4'-methoxydihydrochalcone (3), 2',6'-dihydroxy-4'-methoxydihydrochalcone (4), 5,7-dihydroxyflavanone [(2S)-pinocembrin] (5), 2',6'-dihydroxy-4',4-dimethoxy dihydrochalcone (6) and (2R,3R)-3,5,7-trihydroxy-3-O-acetylflavanone (7). The isolated compounds were tested for their antioxidant, cytotoxicity, tyrosinase inhibition and antibacterial activities. Compound 2 exhibited significant (P<0.05) antityrosinase activity exhibiting the IC₅₀ of 69.15 μM. The isolated compounds showed low toxicity of the cells with reduction of melanin content of the cells. All compounds tested showed good radical scavenging activity. These data indicates that G. flanaganii extract and its isolated phenolic constituents could be possible skin lightening agents.
authors.affiliation: Department of Plant Science, University of Pretoria, Pretoria 0002, South Africa.
authors.forename: M B
authors.initials: MB
authors.lastname: Mapunya
authors.forename: A A
authors.initials: AA
authors.lastname: Hussein
authors.forename: B
authors.initials: B
authors.lastname: Rodriguez
authors.forename: N
authors.initials: N
authors.lastname: Lall
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000975:Antioxidants / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D047188:Chalcones / Q000494:pharmacology*; D005591:Chemical Fractionation; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology; D019684:Magnoliopsida / Q000737:chemistry*; D008543:Melanins / Q000378:metabolism*; D008544:Melanocytes / Q000187:drug effects; D051379:Mice; D008826:Microbial Sensitivity Tests; D015394:Molecular Structure; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors* / Q000737:chemistry; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*; D011425:Propionibacterium acnes / Q000187:drug effects
chemical_list: C424502:2',6'-dihydroxy-4'-methoxydihydrochalcone; D000900:Anti-Bacterial Agents; D000975:Antioxidants; D047188:Chalcones; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D008543:Melanins; D010936:Plant Extracts; C424503:asebogenin; D014442:Monophenol Monooxygenase