Abstract
Oenothera laciniata Hill is a perennial herb traditionally used to alleviate inflammatory complications. This study investigated the antioxidant and anti-melanogenic activities of O. laciniata. The methanolic extract (OLM) of O. laciniata and its different fractions, including ethyl acetate (OLEF), n-butanol (OLBF), and water (OLWF) fractions, were prepared. Antioxidant activities were evaluated by total phenolic content, the radical-scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH•), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+•), and superoxide anion (O2−•), reducing capacity, and metal chelating ability. OLM and its fractions exhibited potent antioxidant activity in these in vitro assays, with a correlation between radical-scavenging activity and total phenolic content. OLM and its fractions inhibited the mushroom tyrosinase activity superior to the reference control, ascorbic acid. In B16-F10 melanoma cells, OLM and its fractions significantly decreased melanin production and tyrosinase activity. Mechanistic investigations revealed that OLM and its fractions inhibited tyrosinase and TRP-2 expressions via downregulating MITF and phosphorylated CREB and differentially inducing ERK or JNK phosphorylation. Additionally, OLM and its fractions caused no significant cytotoxicity towards B16-F10 or skin fibroblast cells at concentrations used in these cellular assays. These findings demonstrated the potential of O. laciniata extracts as the ideal skin protective agent with dual antioxidant and anti-melanogenic activities.
Highlights
Melanogenesis is a physiological process by which melanocytes produce melanin pigment and the primary determinant of skin color [1]
Fatty acids and steroids were obtained in OLEF (Supplementary Figure S2), phenolic compounds and tannins/sugars were obtained in OLBF (Supplementary Figure S3), and tannins/sugars were obtained in OLWF (Supplementary Figure S4)
OLWF (IC50 = 80.5 ± 0.9 μg/mL) and OLBF (IC50 = 84.8 ± 0.6 μg/mL) were the most active ones, with about twofold of inhibitory effects than ascorbic acid (IC50 = 162.4 ± 11.3 μg/mL). These results demonstrated that O. laciniata. The methanolic extract (OLM) and its different soluble fractions possessed anti-tyrosinase activity, and the rank order of efficacy inhibiting mushroom tyrosinase activity was OLWF ≈ OLBF > OLM > OLEF
Summary
Melanogenesis is a physiological process by which melanocytes produce melanin pigment and the primary determinant of skin color [1]. Melanin pigment is one of the major defense mechanisms of human skin against deleterious effects of ultraviolet (UV) radiation [2]. Excessive UV exposure usually causes the generation of intracellular reactive oxygen species (ROS) and oxidative stresses, one of the inducing factors for melanin synthesis and skin damage [3,4]. Apart from UV light exposure, various extrinsic and intrinsic factors, such as hormonal changes, inflammation, and age, trigger the biosynthesis of melanin in humans [5,6]. Depigmenting agents with additional antioxidant effects that ensure a downregulation of melanogenesis and a decrease in the melanin content are of significant value in cosmetic and pharmaceutical uses
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