Skin hyperpigmentation disorders, such as melasma, freckles, and solar lentigines, are associated with elevated activity of the enzyme tyrosinase, which plays a central role in melanin biosynthesis. Topical application of tyrosinase inhibitors is a key strategy for preventing or treating various forms of skin hyperpigmentation. Additionally, oxidative stress factors often aggravate the pigmentation process. Essential oils (EOs) represent a natural source of diverse phytoconstituents that may offer health-promoting effects, including antioxidative and anti-tyrosinase properties, potentially suppressing excessive melanin production and protecting skin cells from oxidative stress. Acorus calamus L. and Juniperus communis L. plants have been traditionally utilized in phytotherapy, both individually and in combination, for various applications, including topical ones. However, the biological and pharmacological effects of the EOs derived specifically from A. calamus rhizomes (EOA) and J. communis cone-berries (EOJ) remain largely unexplored. This study aimed to address this gap by evaluating the chemical composition, anti-tyrosinase activity, and antioxidant potential of both EOA and EOJ, as well as investigating the effects of their mixtures.
Methods
The study utilized dried rhizomes of Acorus calamus and cone-berries of Juniperus communis obtained from a local herbal store. The essential oils were extracted from the ground plant materials using the hydrodistillation method with a Clevenger-type apparatus. The chemical composition of the extracted EOs was analyzed using gas chromatography–mass spectrometry (GC-MS). Anti-tyrosinase potential was assessed using a commercial screening assay kit, while antioxidant capacity was determined using DPPH• and ABTS•+ free radical scavenging assays. Mixtures of EOA and EOJ were also prepared at various volume ratios (1:1, 1:2, and 2:1) and tested for both anti-tyrosinase and antioxidant activities.
Key Findings
- Chemical Composition: GC-MS analysis identified 48 chemical compounds in EOA and 81 in EOJ. The major constituents of EOA were sesquiterpenoids, including acorenone (18.1%), preisocalamendiol (12.0%), shyobunone (7.5%), and isoshyobunone (5.7%), with the phenylpropanoid β-asarone also present (4.2%). The predominant compound in EOJ was α-pinene (22%), a monoterpene. Other notable compounds in EOJ included caryophyllene oxide, p-cymene, β-myrcene, terpinen-4-ol, and spathulenol (ranging from 3.1% to 3.7%). The study identified an acorenone-rich chemotype for EOA and an α-pinene-rich chemotype for EOJ.
- Anti-Tyrosinase Activity: Both individual EOs demonstrated dose-dependent anti-tyrosinase activity. At concentrations of 50 µg/mL and higher, EOA exhibited a 2–10% greater inhibitory effect than EOJ at the same concentrations. However, at the lowest tested concentration (5 µg/mL), EOA stimulated tyrosinase activity (approx. 7% increase), while EOJ showed inhibition (approx. 3%). Mixtures of EOA and EOJ exhibited enhanced tyrosinase inhibition compared to the individual oils. The mixture with a 1:1 volume ratio of EOA to EOJ showed the highest inhibition (approx. 30%). Combination Index (CI) values indicated synergistic or near-additive interactions for all tested mixture ratios (1:1, 1:2, 2:1).
- Antioxidant Potential: Both individual EOs showed progressively higher antioxidant activity with increasing concentration against DPPH• and ABTS•+ radicals. EOJ consistently exhibited stronger antioxidative potential than EOA. The IC50 values for EOA were 216.5 µg/mL (DPPH) and 45.0 µg/mL (ABTS), while for EOJ they were 85.4 µg/mL (DPPH) and 14.2 µg/mL (ABTS), indicating EOJ was more potent. Mixtures of the two EOs also showed antioxidant activity. At the highest concentration tested (1 mg/mL), the 1:2 (EOA:EOJ) mixture exhibited the greatest antioxidant activity (90–92% inhibition) against both radicals. CI values revealed synergistic interactions for antioxidant activity against both DPPH and ABTS radicals across all tested mixture ratios, with the 1:2 ratio showing the most pronounced synergism, particularly in the ABTS assay. Antioxidant potential was generally higher when assessed using the ABTS method compared to the DPPH method.
This study provides evidence that essential oils derived from Acorus calamus rhizomes (acorenone-rich chemotype) and Juniperus communis cone-berries (α-pinene-rich chemotype) possess significant antioxidant capacity and effectively inhibit tyrosinase activity. Notably, this is the first report specifically demonstrating the anti-tyrosinase activity of EOs isolated from A. calamus and J. communis, both individually and as mixtures, and also the first information on the antioxidant effects of their mixtures. The findings indicate that combining EOA and EOJ can lead to enhanced anti-tyrosinase and antioxidant effects through synergistic or near-additive interactions, depending on the ratio. The differing results at low EOA concentrations (stimulation of tyrosinase) warrant particular attention. The research highlights the potential of these EOs as natural ingredients for skincare, especially for issues related to hyperpigmentation and oxidative stress. Future implications include the recommendation for additional research to evaluate these activities in human cell lines and in vivo models to determine optimal concentrations and confirm efficacy and safety. Furthermore, cytotoxicity and genotoxicity screening of both individual and combined EOs is a crucial next step.
Link to the study: https://www.mdpi.com/1420-3049/30/11/2417
