Introduction

Polyphenols are constituents of a large family of naturally occurring plant products found in dry legumes, honey, red wine, chocolate, green tea, milk thistle, and numerous fruits and vegetables1. Polyphenols are widely recognized for their antioxidant, anti-inflammatory, immunomodulatory, and anti-carcinogenic properties2. Numerous in vivo animal studies have confirmed the anti-photocarcinogenic potential of dietary polyphenols3,4. Xanthones are a class of polyphenolic compounds that are frequently found in plants and have been demonstrated to possess extensive biological and pharmacological activities5,6. Mangosteen (Garcinia mangostana Linn) is a tree that is indigenous to Southeast Asia, and its pericarps have been employed as traditional medicine7. Phytochemical studies have demonstrated that mangosteens contain a variety of xanthones, which exhibit various biological activities, including anti-inflammatory, anti-bacterial, and anti-cancer effects8,9. α-mangostin is the most abundant xanthone in the mangosteen pericarp, and the mangosteen rind, leaves, and bark have been used as folk medicine for thousands of years10,11. α-mangostin exhibits various effects, including anti-inflammatory and antioxidant properties, induction of apoptosis, and inhibition of tumor invasion and metastasis. Numerous studies have been conducted on the use of α-mangostin for anti-cancer, anti-inflammatory and other aspects both domestically and internationally12,13.

Many chemical ingredients are employed in botanical sunscreens, such as flavonoids, hesperidin, diosmin, anthraquinones, aloe-emodin, rhein, emodin, minerals, SOD, vitamins C and E, and β-carotene14. The mechanisms underlying their effects involve TY inhibition, maturation, and enhancement of its degradation, microphthalmia-associated transcription factor (MITF) inhibition, downregulation of MC1R activity, interference with melanosome maturation and transfer, melanocyte loss, desquamation and chemical peeling15,16.

Interestingly, MITF can regulate diverse biological processes in pigment cells by activating the expression of its downstream genes17,18. In an earlier investigation, we screened MITF regulators from a small molecule compound library containing over 20000 lipophilic compounds for topical application. α-Mangostin, a significant xanthone isolated from the pericarp of mangosteen, was discovered to exhibit the best depigmentation activity among skin-lightening agents19,20. Xanthones can potentially target various cellular proteins due to their relatively rigid chemical structures and lipophilic properties10,21.

Our previous research demonstrated that α-mangostin exhibits limited anti-proliferation activity against human primary melanocytes at concentrations of up to 10 µM19. We determined that α-mangostin possesses skin-lightening and anti-pigmentation properties that could be used to treat melasma, post-inflammatory hyperpigmentation, solar lentigo, and other conditions. In addition, we discovered that MITF can be regulated by retinoic acid receptors (RAR) and its associated proteins18,19. In the current study, we assessed the depigmentation effect of α-mangostin on MITF and pigmentation-related genes. We also investigated its effects on UV-B or FSK-induced hyperpigmentation in cultured skin to explore the underlying mechanisms.

Materials and methods

Materials

A-Mangostin (Sigma, CAS NO.6147-11-1), PTU (David. Fisher’s lab, US), FSK (Sigma, CAS NO.66575-29-9), ATRA(RA, All-Trans Retinoic Acid) (Sigma, CAS NO.302-79-4), MM 11253 (Aladdin, M275863), NAC (David. Fisher’s lab, US), RIPA Lysis Buffered Solution(Medium)(Aladdin, R301900), PMSF (Aladdin, P408676), PhosSTOP™ (Sigma, PHOSS-RO), Roche cOmplete™ (Sigma, 11836170001), BCA Protein Quantification (Sigma, 71285-M), Protein SDS PAGE Loading Buffered Solution (Aladdin, S301935), Transcriptor One Step RT-PCR Kit (Sigma, TOSRTRO), Enhanced Chemiluminescence Kit (ECL, Pierce, Rockford, IL, USA), NuPAGE® Novex Bis-Tris Gels (BioRed, USA), PBS (Aladdin, P743267), DMEM/F12 (Aladdin, D755875), Trypsin-Chymotrypsin (Aladdin, T118254), 6-well plates (Corning, Tewksbury, MA, USA).

Human melanoma cell lines culture

B16F10 cells (ATCC, CRL-6475) were grown in Dulbecco’s modified Eagle medium (DMEM; fetal calf serum, 10%; penicillin, 100 000 U/L; streptomycin sulfate, 100 mg/L; Life Technologies, Grand Island, NY, USA). Cells were incubated at 37 ℃ in a 5% CO2 humidified incubator and passaged at 2 × 104 cells/mL every three days until near-confluent monolayers were obtained. Cells were free of mycoplasma contamination.

Human skin culture

Human skin was obtained from surgeries performed at the plastic surgery department of Wuhan Union Hospital. Informed consent and approval of the Medical Ethics Committee of Tongji Medical College, Huazhong University of Science and Technology were obtained. The skin was superficially disinfected and degreased using 70% ethanol, then 5 cm punch biopsies were performed. Biopsies were immediately transferred to a six-well cell culture plate containing semi-solid medium (SFM; fetal calf serum, 10%; penicillin, 100 000 U/L; streptomycin sulfate, 100 mg/L; EGF; 2% agarose; Life Technologies, Grand Island, NY, USA) with the epidermal side facing upwards. The dermis was in contact with the semi-solid medium, while the epidermis was exposed to air. Ex vivo cultures were incubated at 37 ℃ in a 5% CO2 humidified incubator.

Treatment of melanoma cells and human skin

Cultured skin: Cultured human skin was subjected to an exfoliator (David. Fisher’s lab, US) to remove the stratum corneum. The pigmentation inhibitor (PTU; David. Fisher’s lab, US) and pigmentation inducer (Forskolin, FSK) were dissolved in dimethylsulfoxide (DMSO) and added it directly to the surface of cultured skin at the concentration to be measured. In addition to UVB radiation (2000 mJ/cm2) given every day, the experimental group was given different concentrations of α-mangostin (50 µM, 100 µM), the control group was given PTU (10 mM), FSK (80 mM), skin not affected by drugs served as a control. The skin pigmentation of each group was observed seven days after treatment.

Hair follicles from cultured skin: Hair follicles (HFs) were removed from cultured skin and soaked in tissue preservation solution after removal of adipose and dermal tissue. Except for the blank control group, HFs were added with 2% H2O2 to simulate the oxidative stress environment. The experimental group was added with different concentrations of α-mangostin (10 µM, 40 µM), the positive control compound (NAC 40 µM) from Dr. David Fisher’s laboratory, the group not affected by drugs served as a control. The levels of pigmentation and ROS were recorded at 2 h and 24 h after treatment.

The B16F10 cells: The B16F10 cell line (purchased from Wuhan Procell Company, ATCC® CRL-6475™) was cultured in DMEM (fetal calf serum, 10%; penicillin, 100 000 U/L; streptomycin sulfate, 100 mg/L; Life Technologies, Grand Island, NY, USA). The pigmentation inhibitor (PTU; David. Fisher’s lab, US), pigmentation inducer (Forskolin, FSK), ATRA(RA, All-Trans Retinoic Acid) and RA antagonist(MM 11253) were dissolved in dimethylsulfoxide (DMSO) and added directly to the culture medium of melanoma cells at the concentrations that were to be tested. B16F10 cells were plated at a density of 1 mL/well in 6-well plates (Corning, Tewksbury, MA, USA) on day 1 and subsequently incubated at 37 ℃ for 48 h. The cells were starved in fresh DMEM growth media without FBS overnight on day 3. On the fourth day, 1 µL of different concentrations of α-mangostin(0.5 µM, 5 µM), FSK (5 µM), RA (0.5 µM, 5 µM), MM (5 µM) were added and incubated for 8 h.

Cell lysis and protein extraction

B16F10 cells were cultured to 80% confluence, followed by removal of the medium and two washes with pre-cooled PBS (without Ca²⁺/Mg²⁺). Trypsin (containing EDTA) was added to digest for 2 min, and the cells were collected by centrifugation (1000 × g, 5 min, 4 ℃). For lysis, cell pellets (1 × 106 cells) were resuspended in 100 µL of RIPA lysis buffer [50 mM Tris-HCl (pH 7.4), 150 mM NaCl, 1% NP-40, 0.5% sodium deoxycholate, 0.1% SDS] supplemented with freshly prepared 1 mM phenylmethylsulfonyl fluoride (PMSF), 1× protease inhibitor cocktail (Roche cOmplete™), and 1× phosphatase inhibitor cocktail (PhosSTOP™). The mixture was incubated on ice for 30 min with intermittent vortexing (10 s every 5 min). To fragment genomic DNA and reduce viscosity, lysates were sonicated on ice using three 5-second pulses at 10% amplitude. Cellular debris was removed by centrifugation at 12,000 × g for 15 min at 4 °C, and the clarified supernatants were transferred to fresh tubes. Protein concentrations were quantified using a bicinchoninic acid (BCA) assay kit and normalized to a uniform concentration (e.g., 2 µg/µL). Samples were then mixed with 5× SDS loading buffer (containing β-mercaptoethanol), denatured by boiling at 95 °C for 5 min, and storage at −80 °C until further analysis.

Western blotting

Western blotting analysis was performed according to previous studies. Protein was loaded onto 4%–12% NuPAGE® Novex Bis-Tris Gels (BioRed, USA) and transferred onto polyvinylidene difluoride membranes. The following primary antibodies were employed: anti-MITF, anti-tyrosinase, anti-RARα, retinoid x receptors (RXR)α, anti-tyrosinase-related proteins (TYRP1), anti-beta-actin, and anti-tubulin (Cell Signaling Technology). The membrane was incubated in the first antibodies and then with either anti-rabbit (1: 5000) or anti-mouse (1: 5000) secondary antibodies after blocking nonspecific binding with 5% BSA in tris-buffered saline and tween 20 (0.1%) for 1 h at room temperature. B16F10 cells were treated with varying concentrations of α-mangostin, RA, or their combination for 8 h. The expression levels of MITF, TYR, TYRP1, RARα, and RXRα were detected by Western blotting. Protein bands were visualized with an enhanced chemiluminescence kit (ECL, Pierce, Rockford, IL, USA).

RT-PCR of MITF relative expression

B16F10 cells were treated with varying concentrations of α-mangostin, FSK (10 µM), RA (0.5 µM), MM 11253 (5 µM) or their combination for 3 or 8 h. Total RNA was extracted from treated or vehicle-treated cells using an Transcriptor One Step RT-PCR Kit. The RNAs were PCR amplified using specific primers for MITF. The primers used were MITF forward (5’-CTGATCTGGTGAATCGGATC-3’ nt 1051 to 1070), MITF reverse (5’-TCCTGA AGAAGAGAGGGAGC-3’ nt 1422 to 1441). The 18 S primer, which served as an internal standard, was obtained from Life Technologies.

Melanin content analysis

For human skin explants, melanin levels were quantified using a modified NaOH solubilization method. Briefly, following treatment, the explants were thoroughly rinsed, homogenized, and dissolved in 1 N NaOH at 80 °C for 1 h. The resulting homogenate was centrifuged, and the absorbance of the supernatant was measured spectrophotometrically at 405 nm. The melanin content was determined by comparing the absorbance values to a standard curve of synthetic melanin and was normalized to the tissue weight of each explant. Image analysis for melanin quantification was performed using ImageJ software (Version 1.53k, National Institutes of Health, USA; available at: https://imagej.nih.gov/ij/).

Statistical and computational analysis

The significance of the differences between the experimental conditions was determined using Student’s t-test for unpaired observations.

Results

Effects of α-mangostin on the UVB-induced hyperpigmentation of cultured skin

Epidermal melanin has important evolutionary and physiological implications, particularly for bared skins. Significantly, a high melanin content (racial pigmentation) protects the skin against UV-induced skin damage through its optical and chemical filtering properties22,23,24. Cultured skin was administered different concentrations of α-mangostin (50 µM, 100 µM), 10 mM PTU (a pigmentation inhibitor), 80 mM FSK (a pigment inducer), and UVB radiation (2000 mJ/cm2) daily. As depicted in Fig. 1A, significant melanin production was observed in the cultured skin after 7 days of treatment. As illustrated in Fig. 1B, the melanin pigmentation in the cultured skin was analyzed using ImageJ. The findings revealed that PTU (10 mM) neutralized and FSK (80 mM) enhanced melanin production in UVB-irradiated skin, respectively. Meanwhile, α-mangostin-treated skin demonstrated a dose-dependent reduction in pigmentation induced by UVB radiation.

Fig. 1
figure 1

α-Mangostin neutralizes melanogenesis induced by UVB radiation. Cultured skin was treated with different concentrations of α-mangostin (100, 50, and 25 µM) and UVB radiation (2000 mJ/cm2) daily. UVB radiation-induced hyperpigmentation in the vehicle (DMSO) treated skin. PTU (10 mM) or FSK (80 mM) neutralized or increased the melanogenesis in UVB radiation-treated skin. Compared to these controls, cultured skin treated with α-mangostin was absolved from hyperpigmentation induced by UVB radiation in a dose-dependent manner. B. Analysis of the amount of melanin pigmentation in cultured skin through Image J. Schemes follow the same formatting.

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Effects of α-mangostin on hydrogen peroxide (H2O2)-induced hyperpigmentation on follicles

An increasing body of evidence suggests that H2O2 activates melanogenesis-related proteins, including cAMP-responsive element-binding protein (CREB), MITF, and TYR). It has been reported that H2O2 induces phosphorylation of CREB; p-CREB can promote MITF expression and regulate mitochondrial gene expression, thereby supporting melanogenesis in melanocytes25. UV radiation also strongly influences skin melanogenesis in epidermal cells through an oxidative stress pathway involving the generation of reactive oxygen species (ROS), including H2O2. Oxidative stress was induced in follicles to confirm the effect of α-mangostin. Pigmented melanoblasts in bulge areas were examined under bright field microscopy with or without genotoxic stress (2% H2O2) (Fig. 2A). We found that NAC (40 µM), a positive control compound from Dr. David Fisher’s lab, inhibited H2O2-induced pigmentation (P < 0.05). 10 µM α-mangostin combined with H2O2 treatment exhibited the same rate of pigment production as the untreated blank control. Increasing the concentration of α-mangostin to 40 µM further reduced melanin content. Therefore, the study demonstrated that as the concentration of α-mangostin increases, the inhibitory effect on pigment production also increases (Fig. 2B). Immunofluorescence microscopy of ROS/DAPI-stained cells for H2O2-induced ROS and the corresponding image gray analysis (using ImageJ) demonstrated that α-mangostin reduced ROS expression in a dose-dependent manner in hair follicles (Figs. 2C-D).

Fig. 2
figure 2

α-Mangostin neutralizes melanogenesis induced by H2O2. Cultured individual follicles were treated with different concentrations of α-mangostin with or without genotoxic stress (2% H2O2). Pigmented melanoblasts in bulge areas were examined under bright field microscopy. For example, blank control without H2O2 treatment, H2O2 treatment, and H2O2 with a positive control compound from Dr. David Fisher’s lab. Pigments were circled in red. B. Paired T-test demonstrates that the pigment-suppressive effects were much stronger with higher concentrations of α-mangostin. The error bar denotes the standard error of the mean (SEM). C. Representative immunofluorescence microscopic images of cells-stained ROS/DAPI for H2O2 induced ROS. Pigments are cycled in red. D. Image analysis-based ROS expression. ROS levels were evaluated under microscopy presented in panel C. n = 7, **P < 0.01, indicating a statistically significant difference between 2% H2O2 and α-mangostin (10 µM) + 2% H2O2 treatment.

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Depigmentation effect of α-mangostin on melanogenesis-related proteins

MITF is vital for regulating melanocyte function, including development, differentiation, and survival, and regulates the TYRPs gene, which encodes the main regulatory enzyme of melanogenesis, tyrosinase18,26. To identify the specific inhibitory effect of α-mangostin on melanogenesis, we analyzed the expression of proteins involved in the regulation of melanin synthesis in B16F10 cells. After treating B16F10 cells with various concentrations of α-mangostin (0.5 µM, 5 µM), we conducted Western blotting on pigment-related genes TYR and TYRP1. Additionally, we utilized ImageJ software to perform grayscale analysis on the protein bands. The findings revealed that α-mangostin decreased the expression of TYR and TYRP1 in a dose-dependent manner (refer to Fig. 3A). To further validate the impact of α-mangostin on MITF expression, we treated B16F10 cells with 5 µM FSK, 5 µM α-mangostin, and a combination of 5 µM FSK and 5 µM α-mangostin, respectively, with the DMSO group serving as the control. Following this, we assessed the expression level of MITF using Western blotting, and our results indicated that α-mangostin not only diminished the expression of MITF but also hindered the upregulation of MITF expression induced by FSK (Fig. 3B-C).

Fig. 3
figure 3

α-Mangostin modulates the expression of melanogenesis-related proteins. (A) B16F10 cells were treated with different concentrations of α-mangostin (5 µM, 0.5 µM). Typical WB images and summary analysis revealed that TYR and TYRP1 expression levels were decreased by 5 µM α-mangostin. *p < 0.05, **p < 0.01,***p < 0.001 (n = 3).The three bands in (A) are from the same gel. (B,C) Combination for 8 h, MITF protein and mRNA expression were strongly induced by 10 µM FSK, and their induction could be neutralized by α-mangostin. *p < 0.05, **p < 0.01, ***p < 0.001 (n = 3). All images in (A) are from different parts of the same gel. See Supplementary Fig. 1 for the original gel image; All images in (B) are from the same gel.

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α-Mangostin can reduce the expression of MITF by disrupting the formation of RAR/RXR heterodimers

Our previous research has shown that MITF can be regulated by RAR and its related proteins18,19. In addition, RA has been identified as a potential inducer of melanocyte maturation, as it can promote melanin production in melanocytes27. The results of this study (Fig. 4A-B) clearly showed that retinoic acid (RA) significantly increased the expression of MITF at the RNA and protein levels. More importantly, we found that α-mangostin can effectively neutralize the upregulation of MITF expression induced by RA (Fig. 4A-B). This neutralizing effect is more significant when α-mangostin is combined with RA antagonist (MM 11253), manifested as a synergistic inhibition of MITF expression (Fig. 4B). These results strongly indicate that α-mangostin interferes with the regulatory effect of the RA signaling pathway on MITF.

Fig. 4
figure 4

α-Mangostin modulates MITF expression. (A) Representative pictures and statistical chart for the western blot of MITF. B16F10 cells were treated with different concentrations of α-mangostin (5 µM, 0.5 µM), RA (5 µM, 0.5 µM) or their combination for 8 h, MITF expression level was induced by 5µM RA, and this induction effect could be neutralized by α-mangostin. *p < 0.05, **p < 0.01, ***p < 0.001 (n = 3). (B) B16F10 cells were treated with α-mangostin (5 µM), RA (5 µM), MM (5 µM) or their combination for 8 h, MITF mRNA expression was induced by 5µM RA, and this induction effect could be neutralized by α-mangostin. Moreover, α-mangostin combined with a RAR antagonist, MM, could synergistically decrease the RNA expression level of MITF. (C) B16F10 cells were treated with α-mangostin (5 µM), RA (5 µM) or their combination for 8 h, the proteins expression of total RXRα and RARα were significantly induced by α-mangostin. *p < 0.05, **p < 0.01, ***p < 0.001 (n = 3). All images in (A) and (C) are from different parts of the same gel. See Supplementary Fig. 2 for the original image of gel.

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In order to further investigate the target of α-mangostin, we analyzed the expression of RXR and RAR (Fig. 4C). Compared with the DMSO blank control group and the RA treatment group alone, α-mangostin treatment significantly increased the total RXR and RAR protein content in cells (Fig. 4C). This phenomenon suggests that α-mangostin may disrupt the formation of RAR/RXR heterodimers. RAR/RXR heterodimers are the main form of transcriptional regulation by nuclear receptors, which bind to specific DNA sequences (RARE or RXRE) to regulate the expression of downstream genes (such as MITF)28,29,30. The decrease in heterodimer formation may lead to the accumulation of free monomeric receptors (RXR and RAR) in cells, thereby explaining the increase in their total protein levels (Fig. 4C). This is consistent with the known mechanism that when the ability of RXR to heterodimerize with other receptors (such as RAR) decreases, its monomer levels may increase28.

Figure 5 further integrates our findings and proposes a possible pathway model for the regulation of MITF by α-mangostin. The transcriptional regulation of MITF involves multiple upstream signaling pathways, including the MAPK and PI3K pathways (Fig. 5). Key kinases in these pathways, such as Ras downstream effectors, can phosphorylate RXR28. Phosphorylation modification can significantly alter the function of nuclear receptors, including affecting their binding ability to ligands, DNA, and co regulatory proteins28. Our data (Fig. 4C) suggests that α-mangostin may reduce the ability of RXR to participate in the formation of functional RAR/RXR heterodimers by enhancing the phosphorylation state of RXR (possibly through activation of Ras-PI3K or related pathways) (Fig. 5). The formation of RAR/RXR heterodimers decreased, resulting in their inability to effectively bind to the RARE/RXRE elements in the MITF gene promoter region (Fig. 5), ultimately inhibiting RA induced MITF transcriptional activation (Fig. 4A-B). Therefore, α-mangostin effectively blocks the key regulatory role of the RA signaling pathway on melanin production by interfering with the formation of RAR/RXR heterodimers and their binding ability to the MITF promoter. This targeted intervention on the formation of nuclear receptor complexes is an important molecular mechanism by which α-mangostin inhibits MITF expression and melanin production.

Fig. 5
figure 5

The promising pathway. The regulation of MITF is complex, with multiple upstream pathways converging on MITF; MAPK and PI3K pathways(represented by the right and left routes respectively) have some known transcription factors that bind to the MITF promoter and regulate its transcription. These two pathways act on the RXRα and increase its phosphorylation, which can block the formation of RAR/RXR heterodimers that bind specific DNA sequences in RARE or RXRE on MITF. Retinoic Acid (RA, ATRA) binds and activates members of the RARα family. α-Mangostin can increase the expression of total RXR and RAR and, conversely, inhibit the formation of RAR/RXR heterodimers, which may be linked to the phosphorylation levels of RXR.

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Discussion

Here we demonstrate that α-mangostin attenuates UVB and FSK induced hyper pigmentation through MITF suppression in human skin explants, hair follicle melanoblasts, and B16F10 cells. Previously, we screened MITF regulators from a small molecule compound library containing over 20000 lipophilic compounds for topical application. High-throughput technology was employed to screen hypo-pigmenting agents, which encompassed transmission of keratinocyte signals to the melanocyte pigment machinery and determined the actual melanin content. α-Mangostin is one of the most promising inhibitors in Sp-1 and Melan-A co-culture assay, exhibiting the best depigmentation performance among the skin-lightening agents31,32. Although in our previous research, the α-mangostin did not exhibit strong anti-cell proliferation effects, we hypothesized that it could target MITF-mediated pigmentation pathways.

We confirmed that α-mangostin could inhibit hyperpigmentation in cultured skin induced by UVB and in follicles under oxidative stress. Subsequently, we discovered that α-mangostin could suppress MITF overexpression and downregulated pigmentation-related genes in melanocytes induced by FSK.

RA represents natural and synthetic analogs of vitamin A or ATRA, which can bind and activate nuclear RR33. ATRA is the most biologically active RA, and the skin is one of the primary production sites34,35. The human epidermis contains up to five times more RXR protein (90% RXR-α) than RAR. Typically, these receptors are usually paired and form RAR/RXR heterodimers that bind specific DNA sequences, known as the RA responsive elements (RARE or RXRE)29,30. Our findings indicated that MITF expression increased following stimulation by RA, which suggested RXR and RAR regulated it. Moreover, α-mangostin interfered with the formation of RAR/RXR heterodimers, resulting in RXR and RAR levels increased after treatment with α-mangostin. Accordingly, the targeting of RXR and RAR is a potential mechanism of α-mangostin.

In summary, our experiments substantiated that α-mangostin can inhibit melanogenesis by regulating the MITF and protecting it from damage induced by oxidative stress pathways. In addition, this effect disrupts the formation of RAR/RXR heterodimers, which interferes with their regulatory effect on MITF. This experiment revealed the potential use of α-mangostin as an anti-melanogenesis compound that could be incorporated into sunscreens as a whitening active ingredient.

In addition, certain limitations of this study need to be addressed. Firstly, our experiments mainly relied on in vitro cell models (B16F10) and ex vivo human skin models. Although these models can effectively control variables and elucidate preliminary mechanisms, they cannot fully simulate the complex physiological environment and systemic responses within the human body. Secondly, the dose-response analysis range of α-mangostin in this study was relatively limited, and its optimal effective concentration and potential toxicity window in the human body still need to be further determined. Finally, this study did not conduct in vivo experiments (such as animal models) to verify the depigmenting effect and long-term safety of α-mangostin. These limitations suggest that future research should focus on in vivo validation, explore a broader dose-response relationship, and conduct formulation studies to optimize its skin permeability and stability, laying the foundation for subsequent clinical translation.

Conclusion

This study confirms that α-mangostin, a natural flavonoid derived from mangosteen, can effectively inhibit UV-B and oxidative stress-induced melanogenesis in in vitro and ex vivo models. Its mechanism of action is twofold: on the one hand, it downregulates the expression of the key transcription factor MITF and its regulated pigment-related genes such as TYR and TYRP1 by interfering with the formation of RAR/RXR heterodimers; on the other hand, it mitigates the promoting effect of oxidative stress (e.g., H₂O₂-induced) on the pigmentation process. These findings highlight the potential of α-mangostin as a safe, multi-targeted natural skin depigmenting agent. However, further research is still required in the future, such as conducting in vivo validation, dosage optimization, and comprehensive safety assessments, to facilitate its translation into clinical applications. This study lays a theoretical foundation for the development of safe and effective natural whitening agents and also provides a new perspective for research on the molecular mechanisms regulating pigmentation.