The effect of Aspalathus linearis (Burm.f.) R.Dahlgren and its compounds on tyrosinase and melanogenesis.

Pigmentation, a process controlled by melanogenesis, plays a vital role in protecting the skin against harmful ultraviolet rays. The level of protection is compromised in case of hypopigmentation. This study aimed to evaluate an Aspalathus linearis extract, fractions and phytoconstituents, for their efficacy on melanogenesis stimulation. Fifteen compounds were kinetically assessed against tyrosinase; the rate-limiting enzyme of melanogenesis. Aspalathin and catechin significantly (p value < 0.001) increased the enzymatic rate, showing 50% stimulatory effects at 119.70 ± 2.06 µg/mL and 143.30 ± 2.74 µg/mL, respectively, by acting as subversive substrates. Five compounds inhibited the enzyme's activity, of which four exhibited competitive inhibition. To investigate the molecular interactions between the compounds and the active site, molecular docking was done, using tyrosinase (PBD: 2Y9X) and tyrosinase related protein 1 (PBD: 5M8P). All the compounds docked successfully with acceptable docking scores. Further quantitative structure-activity relationship analysis identified potential functional groups, linked to the specific activity. The crude extract, its fractions, and compounds exhibited low antiproliferative activity with 50% cell viability at concentrations higher than 100 µg/mL. Finally, both aspalathin and catechin exhibited a significant increase (4.5%) in melanin production at 119.82 µg/mL and 76.92 µg/mL, respectively. This is the first report of A. linearis' compounds on skin re-pigmentation.

Sideritis Perfoliata (Subsp. Perfoliata) Nutritive Value and Its Potential Medicinal Properties.

Sideritis perfoliata L. subsp. perfoliata is an endemic species of the Eastern Mediterranean region with several uses in traditional medicine. The present study aims to explore the unknown properties of S. perfoliata investigating the nutritional content as well as the antioxidant, anticancer, antituberculosis, antiwrinkle, anti-acne, hyper/hypo-pigmentation and antibacterial activities. Mineral content, nutritional value, the composition and antioxidant properties of the essential oil, the antityrosinase, the antibacterial activity and anti-elastase potential of the extract, were evaluated. The antiproliferative activity of S. perfoliata against cervical cancer (HeLa), human melanoma (UCT-Mel-1), human hepatocellular carcinoma (HepG2) and human epidermoid carcinoma (A431) was investigated. Cytotoxic effects on normal human keratinocyte (HaCat) and kidney epithelial (Vero) cell lines were also determined. Sideritis perfoliata exhibited high nutritional value of proteins and minerals (K, P, Mg, Fe, Zn, Cu). The most abundant components of the essential oil were found to be α-pinene, ß-phelladrene, valeranone, ß-pinene and sabinene. The ethanolic extract of S. perfoliata displayed moderate antioxidant potential and antibacterial activity against Prevotella intermedia. Noteworthy elastase and moderate anticancer potential against the human liver cancer cell line (HepG2) was observed with IC50 values of 57.18 ± 3.22 µg/mL and 64.27 ± 2.04 µg/mL respectively. The noteworthy in vitro activity of S. perfoliata could be due to the presence of flavonoids and phenols in the leaves, having high nutritional value. Sideritis perfoliata could potentially be useful to reduce the appearance of wrinkles and for the treatment of liver cancer. The moderate antibacterial, antioxidant and elastase activity of the plant can be linked to the traditional use of S. perfoliata for the treatment of wounds and inflammation.

Isolation of Flavonoids and Flavonoid Glycosides from Myrsine africana and Their Inhibitory Activities against Mushroom Tyrosinase.

Bioassay-guided fractionation of the methanol extract of the shoots of Myrsine africana led to the isolation of the new compound myricetin 3-O-(2″,4″-di-O-acetyl)-α-l-rhamnopyranoside (9) and 11 known compounds. The known compounds quercetin 3-O-(3″,4″-di-O-acetyl)-α-l-rhamnopyranoside (8), rutin (10), quercetin 3-O-α-l-rhamnopyranoside (11), and myricetin 3-O-α-l-rhamnopyranoside (12) are reported for the first time from the methanol extract of the shoots of M. africana. Compounds 10 and 12 showed significant inhibition of tyrosinase with 50% inhibition (IC50 values) of the enzyme at 0.13 ± 0.003 and 0.12 ± 0.002 mM, respectively, which was supported by the docking fitness scores obtained through molecular docking analysis. In addition, compounds 1-12 displayed significant antioxidant activity with IC50 values ranging 1.90 to 3.90 µM.