Investigation of the effects of different Onosma L. (Boraginaceae) species on tyrosinase inhibition

In this study, the tyrosinase enzyme inhibitory effect of five different species belonging to the genus Onosma L. (Boraginaceae) was investigated to determine their potential for use in anti-hyperpigmentation treatment. Plant materials used in the study are endemic O. papillosa Riedl, endemic O. discedens Hausskn. ex Bornm. endemic O. erzincanica Binzet & Eren, O. rascheyana Boiss., and O. alborosea Fisch. & C.A.Mey. ssp. alborosea var. alborosea taxa. First, the aerial parts of each species were mechanically ground and dispersed in methanol, and after the maceration method was applied, it was then filtered with filter paper. The solutions were taken to the evaporator and the solvent was removed at low temperature (<40°C). Wet extracts were lyophilized to obtain dry extracts and stored for use in experiments. Firstly, the total phenolic compounds, flavonoids and flavonol contents in the extracts were investigated. In order to determine the antioxidant activities of the extracts, DPPH, NO and SO radical scavenging effects and CUPRAC copper reducing capacity experiments were carried out. In order to determine the tyrosinase inhibitory effect of the extracts, the effects of species and concentration were investigated by using L-DOPA as a substrate. Finally, cytotoxicity experiments with MTT test were performed on mouse embryonic fibroblast (3T3) cell line in order to investigate the effects of extracts on cell viability. The obtained results showed that all Onosma species have tyrosinase inhibitory effect and antioxidant activity. In addition, the cytotoxicity values of the species at low concentrations (≤ 500µg/mL) are at acceptable levels.