Abnormal changes in skin color cause great problems in beauty, and seriously impair the quality of life. Dyschromatosis can be largely divided into hyperpigmentation and hypopigmentation. Hyperpigmentation with darkening of skin color due to excessive pigmentation is one of the major skin problems frequently occur, especially in East Asia, including Korea. So a variety of whitening agents have been used over the years. However, to this day, hyperpigmentation treatment is still difficult and often the results of the treatment are not good. Ginseng Panax ginseng C.A. Meyer is one of the representative medicinal plants that have been widely used in East Asian regions including our country for a long time. In addition to the well-known actions such as immunosuppression, neural protection, antioxidant and anti-cancer activations, recently some studies results have shown that extracts, powders or some ingredients of ginseng can inhibit melanin production in vivo or in vitro, attracting people’s attention. In this review, we summarize the whitening effects and their mechanism reported to date for ginseng and its representative ingredient, ginsenoside, and then anticipate its potential as new skin whitening agents in the future.
Main ingredients of ginseng
Korean ginseng, Panax ginseng C.A. Meyer has been traditionally used in East Asia for thousands of years. It has been not only administered orally to treat a variety of diseases including diabetes, hypertension, liver and kidney dysfunction, mental illnesses and menopausal diseases, but also used topically to treat wounds and reduce skin inflammation . Over the past several decades, the fact that ginseng extracts are effective in immune regulation [2,3], neuroprotection [4,5], antioxidant activity , antitumor activity , and liver protection activity  has been proven by outcomes. Ginseng contains various active ingredients together with ginsenosides, polysaccharides, peptides, and fatty acids [9,10]. Among these active ingredients, ginsenoside is known to be a key active ingredient that plays a central role in the pharmacological efficacy of ginseng, and numerous ginsenosides have been found to date .
Ginsenosides are largely divided into two groups according to the carbon- centered structure: the Dammarane group and the Oleanane group. The Dammarane group, to which most ginsenosides belong, is divided into two main groups (Protopanaxadiol, PPD group and Protopanaxatriol, PPT groups) due to differences in carbohydrate parts . In addition to ginsenoside, ginseng contains various ingredients such as phenolic compounds, alcohols, ginsenoyne, polyacetylenes, sesquiterpenes, methoxypyrazine, alkylpyrazine derivatives, panasinsanols and β-caboline. And active studies have also been performed on the efficacy of these components [13,14].
Changes of components and efficacy according to processing methods: White ginseng and Red ginseng
White ginseng and red ginseng are produced by traditional ginseng processing. White ginseng is made by peeling off the ginseng roots and drying them. Red ginseng is made by steaming fresh ginseng roots and drying them. Both white ginseng and red ginseng showed immune regulatory activity [15, 16], antiinflammatory activity , antioxidant activity , and atopy improvement effect . In particular, red ginseng has been reported to show more distinct pharmacological activities in some aspects than white ginseng [20-22].
The difference in biological activity between red ginseng and white ginseng is thought to be due to the chemical change of ginsenoside during steaming process . The steaming process converts the original ginsenosides into partially deglycosylated derivatives . What is remarkable is that although ginsenosides show a variety of biological activities, their absorption rate is very low when orally administered to human in the original form. Ginsenosides are metabolized by intestinal bacteria in the human digestive tract and their metabolites are absorbed [25, 26]. Therefore, the pharmacological efficacy of ginsenoside is closely related to the biotransformation process by human intestinal bacteria . For this reason, fermentation methods have been utilized to increase oral absorption and bioavailability of ginsenosides. Current study results have shown that it is necessary to convert ginsenosides to deglycosylated ginsenosides in order to increase the effect of ginseng in vivo .
Pathogenesis of hyperpigmentation
Abnormal changes of skin color cause cosmetic problems and seriously impair the quality of life. Dyschromatosis can be largely divided into 2 types. Hyperpigmentation is a symptom that darkens the skin due to excessive pigmentation. Especially in Korea, it is one of the major skin problems commonly found in people in the Fitzpatrick skin type classification III (yellow) and IV (brownish yellow) -V (dark brown), . The skin symptoms related to hyperpimentation include melasma, lentigines, nevus, freckles, and inflammatory pigmentation that occur after skin inflammatory diseases such as acne, eczema, contact dermatitis, and atopic dermatitis . On the other hand, hypopigmentation is a symptom that skin color is abnormally brightened due to insufficient pigmentation .
Skin color is determined by various factors such as melanin content in skin, hemoglobin-oxygen binding state of blood in capillary vessels, carotenoid content, moisture content, and the state of organization of collagen fibers in the dermis. Among these factors, melanin is a determination factor of skin color . Therefore, a precise understanding about mechanisms related to melanogenesis is very important for the development of effective skin whitening agents. Melanogenesis is a complex biochemical reaction pathway controlled by a complex regulatory mechanism . Melanogenesis occurs in specialized organelles called melanosomes, which contain several enzymes involved in melanin production in melanocytes. The difference in skin colors is related to the size, number, type, and distribution of melanosomes. On the other hand, melanocyte’s density is relatively constant even among people with different skin colors .
Tyrosinase acts as a major regulating enzyme of melanin production. However, in addition, tyrosinase-related protein TRP-1, dopachrome tautomerase DCT/TRP2, melanosomal matrix proteins PM17 and MART-1, etc. play important roles in melanogenesis control . The genes of tyrosinase, TRP-1 and DCT commonly contain the micropthalmia-associated transcription factor, MITF, binding site. And MITF plays an important role in regulation of melanogenesis process . Protein kinase C, cAMP and Nitric oxideNO are also involved in the regulation of melanogenesis . Various endogenous and exogenous factors such as estrogen and ultraviolet light also affect melanin production. These endogenous/ exogenous factors act directly on melanocytes or indirectly through peripheral skin cells . Within the actual skin tissue, melanocytes, keratinocytes, dermal fibroblasts, and other skin cells are closely communicating with each other through direct contact with secretory signaling factors cells . In particular, the interaction between keratinocytes and melanocytes is known to be crucial for regulation of melanin production . Keratinocytes regulate the growth and activity of melanocytes with various soluble factors and cell adhesion molecules [39, 40]. At the same time, not only keratinocytes but also activated melanocytes secrete various signaling factors that act on the skin’s immune cells [41, 42]. These signaling factors include various inflammatory cytokines and chemokines such as Interleukin; IL-6, -8-10, Tumor necrosis factor TNF-α, Transforming growth factor TGF-β, Catecholamines, Eicosanoids, Serotonin, α-Melanocyte stimulating factor α-MSH and NO [41, 42]. In order to regulate the melanin production process and improve skin dyschromatosis, Hydroquinone, Arbutin, Tretinoin, Kojic acid, Azelaic acid, N-acetylglucosamine, Niacinamide, Linoleic acid, Ellagic acid, Methimazole, Dicarboxylic acid, Soy extract, Licorice extract, Rucinol, Glycolic acid, Vitamin C and derivatives are used alone or in combination [29, 31]. However, until now, many attempts to improve hyperpigmentation by applying whitening products to the skin often fail to produce satisfactory results.
Effects of ginseng ingredients on the major factors of melanogenesis process
Ginseng is one of the most widely used medicinal plants in traditional oriental medicine, and has been used for thousands of years to improve the overall condition of the skin and treat various diseases. However, relatively recently the efficacy of ginseng on the skin has begun to be illustrated. Many researchers have reported that ginseng extract, powder or some ingredients can inhibit melanogenesis in vitro and in vivo. One of these studies has performed human clinical trials on Korean female patients with melasma by orally administering them with red ginseng powder for 24 weeks .
As a result, the Melasma area and severity index MASI score, a scale for measuring melasma, decreased, and the Melasma quality of life scale, MELASQoL, a measure of quality of life of melasma patients, was improved in 91% of patients. Pigmentation and erythema levels were also reduced, and 74% of patients showed overall symptom improvement as assessed by patients and researchers . However, most studies investigating the inhibitory effect of ginseng on melanogenesis were carried out using tyrosinase purified in vitro or immortalized melanin cell lines. For example, melanin content and tyrosinase activity were reduced in Melan-a cell studies following the treatment with ethanol extract of ginseng seeds . Apart from studies using crude ginseng extracts or powders, many studies have tested the efficacy of specific ingredients of ginseng. Several studies have reported that some of the ginsenoside components showed inhibitory activity on melanogenesis alone.
Aglycone of ginsenoside Rh4, one of the ingredients isolated from red ginseng, inhibited melanogenesis in the B16 melanoma cell line, which is probably related to the protein kinase A pathway [45, 46]. Ginsenoside Rh4 significantly reduced melanin content and tyrosinase activity in the B16 melanoma cell line stimulated with α-MSH and Forskolin. In addition, ginsenoside Rh4 reduced the levels of cAMP and cAMP response factor binding protein, suggesting that the expression of MITF and tyrosinase were inhibited . Ginsenoside Rb1 also reduced melanogenesis by inhibiting tyrosinase activity in B16 melanoma cell lines stimulated with α-MSH . However, ginsenoside is not the only one that shows the inhibitory effect on melanin production, among ginseng ingredients. The crude methanol extract of fresh P. ginseng leaves showed inhibitory activity against mushroom tyrosinase. Among them, p-coumaric acid was identified as a major tyrosinase inhibitor . The p-coumaric acid inhibited melanogenesis in the B16F10 melanoma cell line stimulated with α-MSH, which seems to interfere with melanin production due to structural similarity with tyrosine . Interestingly, p-coumaric acid was weaker in its inhibitory power against mushroom tyrosinase than Kojic acid and arbutin. However, it showed stronger inhibitory effects against tyrosinase of human or mouse . In addition, p-coumaric acid strongly inhibited melanogenesis in human epidermal melanocytes exposed to UVB . The cinnamic acid, one of the main ingredients of Cinnamomum cassia Blume, is also found in the roots and seeds of ginseng [51, 52]. The cinnamic acid has shown an inhibitory effect on the purified mushroom tyrosinase [53, 54], and reduced melanin production and tyrosinase activity and expression in Melan-a cell lines . The cinnamic acid also showed pigment- reducing activity in the Brown Guinea pig’s skin tanned by UVB exposure . This pharmacological action of ginsenosides is closely related to biotransformation by human intestinal bacteria . When comparing red ginseng and red ginseng fermented with Lactobacillus brevis, there was no significant difference in total ginsenoside contents. However, the contents of the ginsenoside metabolites in fermented red ginseng were higher than those in normal red ginseng . Furthermore, in the test using mushroom tyrosinase, tyrosinase inhibitory activity of fermented red ginseng extract was stronger than that of red ginseng extract .
Effects of ginseng ingredients on factors indirectly involved in melanogenesis
However, the effect of ginseng on NO production remains still unclear. Some studies have reported that ginseng reduces NO production. Sun ginseng, a new type of ginseng product manufactured by steaming and drying at high temperature, inhibits inducible Nitric oxide synthase, iNOS, mRNA synthesis in human keratin cell line HaCaT cells and human dermal fibroblasts, thereby attenuates cell damage caused by UVB and NO production . It is also important to remember that human skin tissue is not solely composed of melanocytes, keratinocytes, and fibroblasts. In the dermal tissues, a large number of immune cells such as Langerhans cells which are epidermal specific dendritic cells, macrophages, mast
cells, and T cells are actively acting. It is not surprising that ginsenosides can improve the reactivity of skin immune cells because the immune activation action of ginsenoside is already widely known through numerous studies. Actually, a significant whitening effect was observed when cream containing 0.1% ginsenoside F1 (the metabolite of ginsenoside Rg1) was applied to artificially tanned human skin . Ginsenoside F1 did not directly inhibit the expression of tyrosinase or DCT in the primary cultured human melanocytes, but increased IL-13 production when cultured γδ T cells isolated from human epidermis was treated with ginsenoside F1. IL-13 visually brightened the color of human epidermal melanocytes, and decreases the amount of mRNA expression and protein of tyrosinase and DCT at the same time . These findings suggest that ginsenoside can indirectly regulate melanogenesis through its effects on skin immune cells.
As previously mentioned, several recent studies have reported that extracts, powders or some ingredients of ginseng inhibit melanogenesis in vivo or in vitro. The fundamental mechanism that allows ginseng and its ingredients to inhibit melanogenesis are as follows: First, it directly inhibits key enzymes involved in melanogenesis itself (Tyrosinase and DCT), transcription factors (MITF, NF-κB), or signaling pathways (protein kinase A pathway and protein kinase C pathway). Second, it promotes the production of signaling elements that inhibit melanin production or inhibit melanin production. Second, it inhibits the production of signaling factors that induce or promote the production of signaling factors that inhibit melanogenesis. Figure 3 shows the summary of study results reported so far on the effects of ginseng and its ingredients on the melanogenesis process. In conclusion, although some part of skin whitening effects of ginseng remains unknown, recent studies have strongly suggested that ginseng and its ingredients, especially ginsenoside, could be a candidate substance for a new skin whitening agent.