Traditional medicine and plant-derived compounds have a long history of use across various cultures, valued for their medicinal properties. These natural remedies are increasingly popular due to their accessibility, cost-effectiveness, and perceived safety compared to synthetic pharmaceutical products. One area where natural remedies are being explored is in the treatment of epidermal hyperpigmentation disorders.
Skin hyperpigmentation disorders, such as melasma, are characterized by excessive melanin production. Melanin, a pigment synthesized by tyrosinase in melanocytes, determines skin, eye, and hair color and protects against UV radiation. Dysregulation of tyrosinase activity leads to excessive melanin, causing conditions like melasma, solar melanosis, and acne scars. Melasma, specifically, is a chronic, disfiguring condition often associated with negative emotional and mental health impacts. Existing treatments for hypermelanosis are often limited by issues such as high recurrence rates, toxicity, low stability, poor skin penetration, and reduced efficacy. The current combination therapy approach for melasma can sometimes lead to skin irritation and inflammation, which may aggravate vascular complexities.
In the rural areas of KwaZulu-Natal and Eastern Cape Provinces in South Africa, women have traditionally used bark extracts from Cassipourea flanaganii, C. malosana, and C. gummiflua for skin lightening and sun protection. Recognizing the potential of these traditionally used plants, this study aimed to investigate their anti-tyrosinase and antioxidant activities to scientifically validate their traditional use and identify potential lead compounds for treating skin hyperpigmentation.
Methods
The study involved collecting stem bark from Cassipourea flanaganii, C. malosana, and C. gummiflua in South Africa. Methanolic bark extracts were prepared. In vitro assessments included determining total polyphenol, flavonol, and flavanol content, as well as evaluating antioxidant capacity using FRAP, DPPH, and TEAC assays. Anti-tyrosinase activity was evaluated using IC50 values with kojic acid as a control. Computational studies involved in silico screening of identified Cassipourea metabolites for drug-likeness, pharmacokinetics, and toxicity, followed by molecular docking and molecular dynamics simulations against tyrosinase. Statistical analyses, including ANOVA and post-hoc tests, were used to compare the activities of the extracts.
Key Findings
• Traditional Use: The bark extracts of C. flanaganii, C. malosana, and C. gummiflua are traditionally used by women in rural KwaZulu-Natal and Eastern Cape provinces of South Africa for skin lightening and sun protection.
• Antioxidant Activity: C. gummiflua extract exhibited the highest total polyphenol and flavanol content compared to the other two species. This correlated with superior antioxidant activity as measured by FRAP, DPPH, and TEAC assays, with C. gummiflua showing the highest activity in all three tests.
• Anti-Tyrosinase Activity: All three extracts showed tyrosinase inhibitory activity. C. flanaganii demonstrated the most potent anti-tyrosinase activity with the lowest IC50 value (37.10 µg/mL), although statistical analysis showed no significant difference in inhibitory activity among the three species extracts. Inhibition was concentration-dependent.
• Isolated Compound (7-methoxygeranin A): The study successfully isolated 7-methoxygeranin A from C. malosana. This compound showed lower anti-tyrosinase activity (IC50: 45.16 µg/mL) compared to the C. flanaganii extract. 7-methoxygeranin A is known for its antioxidant effects and potential skin health benefits, but its lower anti-tyrosinase activity compared to the crude extract suggested other potent metabolites might be present.
• In Silico Lead Identification: In silico screening for drug-likeness identified afzelechin, emodin 6,8-dimethyl ether, hexose, tricin, and ellisinin A as top-ranked compounds with favorable oral bioavailability properties (zero Lipinski Rule of 5 violations). Notably, 7-methoxygeranin A was not among these top-ranked compounds due to pharmacokinetic concerns.
• Molecular Dynamics Simulations: Molecular dynamics simulations identified emodin 6,8-dimethyl ether as the most promising lead compound among the top-ranked metabolites. It showed the lowest binding free energy (ΔG<sub>bind</sub>: −39.88 kcal/mol), suggesting a strong binding affinity to tyrosinase. Emodin 6,8-dimethyl ether demonstrated significant stability and prolonged residence at the tyrosinase active site throughout the 150 ns simulation, interacting with key catalytic residues.
This research supports the traditional use of Cassipourea species as natural skin lighteners and photoprotective agents, validating their anti-tyrosinase and antioxidant properties through in vitro evaluations. The study’s novelty lies in its combined in vitro investigation and in silico identification of potential lead compounds from these traditionally used plants.
While C. flanaganii extract showed the most potent anti-tyrosinase activity in vitro, C. gummiflua displayed the highest antioxidant potential, highlighting different strengths among the species. The isolated compound 7-methoxygeranin A, known for its antioxidant effects, showed lower anti-tyrosinase activity than the crude extracts, suggesting other active components are present.
The in silico analysis was crucial in identifying emodin 6,8-dimethyl ether as a highly promising lead compound for skin lightening applications. Its strong binding affinity and stable interaction with tyrosinase, as demonstrated by molecular dynamics simulations, are critical for enzyme inactivation and regulation of skin pigmentation.
The findings have significant future implications for developing natural skin lighteners and enhanced photoprotection approaches. These plant extracts and identified compounds could potentially offer safer alternatives to current synthetic agents. Furthermore, the research validates indigenous knowledge and promotes potential economic opportunities for local communities through sustainable harvesting. However, further in vitro and in vivo studies are highly recommended to confirm the anti-tyrosinase activity of emodin 6,8-dimethyl ether. Additionally, future research should explore the pharmacokinetics, safety, and efficacy of these compounds in clinical settings, and further investigate the mechanism and optimal use of compounds like 7-methoxygeranin A.
Link to the study: https://tinyurl.com/yfxktnrn
