{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,7]],"date-time":"2026-10-07T18:32:35Z","timestamp":1791397955869,"version":"4.3.3"},"reference-count":52,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2014,5,12]],"date-time":"2014-05-12T00:00:00Z","timestamp":1399852800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>Few anti-pigmenting agents have been designed and developed according to their known hyperpigmentation mechanisms and corresponding intracellular signaling cascades. Most anti-pigmenting agents developed so far are mechanistically involved in the interruption of constitutional melanogenic mechanisms by which skin color is maintained  at a normal and unstimulated level. Thus, owing to the difficulty of confining topical application to a specific hyperpigmented skin area, potent anti-pigmenting agents capable of attenuating the natural unstimulated pigmentation process have the risk of leading to hypopigmentation. Since intracellular signaling pathways within melanocytes do not function substantially in maintaining normal skin color and are activated only by environmental stimuli such as UV radiation, specifically down-regulating the activation of melanogenesis to the constitutive level would be an appropriate strategy to develop new potent anti-pigmenting agents with a low risk of hypopigmentation. In this article, we review the hyperpigmentation mechanisms and intracellular signaling pathways that lead to the stimulation of melanogenesis. We also discuss a screening and evaluation system to select candidates for new anti-melanogenic substances by focusing on inhibitors of endothelin-1 or stem cell factor-triggered intracellular signaling cascades. From this viewpoint, we show that extracts of the herbs Withania somnifera and Melia toosendan and the natural chemicals Withaferin A and Astaxanthin are new candidates for potent anti-pigmenting substances that avoid the risk of hypopigmentation.<\/jats:p>","DOI":"10.3390\/ijms15058293","type":"journal-article","created":{"date-parts":[[2014,5,12]],"date-time":"2014-05-12T11:42:27Z","timestamp":1399894947000},"page":"8293-8315","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":62,"title":["Inhibitors of Intracellular Signaling Pathways that  Lead to Stimulated Epidermal Pigmentation:  Perspective of Anti-Pigmenting Agents"],"prefix":"10.3390","volume":"15","author":[{"given":"Genji","family":"Imokawa","sequence":"first","affiliation":[{"name":"Research Institute for Biological Functions, Chubu University, 1200 Matsumoto, Kasugai,  Aichi 487-8501, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Koichi","family":"Ishida","sequence":"additional","affiliation":[{"name":"Global R&D-Skin Beauty, Kao Corporation, Tokyo 103-8210, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2014,5,12]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"962","DOI":"10.1016\/j.bbagen.2012.03.018","article-title":"Evaluation of in vitro and in vivo anti-melanogenic activity of a newly synthesized strong tyrosinase inhibitor (E)-3-(2,4-dihydroxybenzylidene) pyrrolidine-2,5-dione (3-DBP)","volume":"1820","author":"Chung","year":"2012","journal-title":"Biochim. Biophys. Acta"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1312","DOI":"10.1016\/S0022-2275(20)33493-3","article-title":"Possible involvement of proteolytic degradation of tyrosinase in the regulatory effect of fatty acids on melanogenesis","volume":"40","author":"Ando","year":"1999","journal-title":"J. Lipid Res"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"587","DOI":"10.1046\/j.1523-1747.2001.01291.x","article-title":"An alternative approach to depigmentation by soybean extracts via inhibition of the PAR-2 pathway","volume":"116","author":"Paine","year":"2001","journal-title":"J. Investig. Dermatol"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"18352","DOI":"10.1016\/S0021-9258(18)55277-7","article-title":"Effects of endothelins on signal transduction and proliferation in human melanocytes","volume":"266","author":"Yada","year":"1991","journal-title":"J. Biol. Chem"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"24675","DOI":"10.1016\/S0021-9258(18)35817-4","article-title":"Endothelins secreted from human keratinocytes are intrinsic mitogens for human melanocytes","volume":"267","author":"Imokawa","year":"1992","journal-title":"J. Biol. Chem"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"32","DOI":"10.1111\/1523-1747.ep12312500","article-title":"Endothelin-1 as a new melanogen: Coordinated expression of its gene and the tyrosinase gene in UVB-exposed human epidermis","volume":"105","author":"Imokawa","year":"1995","journal-title":"J. Investig. Dermatol"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"305","DOI":"10.1042\/bj3140305","article-title":"Signaling mechanisms of endothelin-induced mitogenesis and melanogenesis in human melanocytes","volume":"314","author":"Imokawa","year":"1996","journal-title":"Biochem. J"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"218","DOI":"10.1111\/j.1600-0749.1997.tb00488.x","article-title":"The role of endothelin-1 in epidermal hyperpigmentation and signaling mechanisms of mitogenesis and melanogenesis","volume":"10","author":"Imokawa","year":"1997","journal-title":"Pigment Cell Res"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"578","DOI":"10.1046\/j.1523-1747.2001.01290.x","article-title":"The paracrine role of stem cell factor\/c-kit signaling in the activation of human melanocytes in ultraviolet B-induced pigmentation","volume":"116","author":"Hachiya","year":"2001","journal-title":"J. Investig. Dermatol"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"5395","DOI":"10.1074\/jbc.M105874200","article-title":"Biochemical characterization of endothelin-converting enzyme-1\u03b1 in cultured skin-derived cells and its postulated role in the stimulation of melanogenesis in human epidermis","volume":"277","author":"Hachiya","year":"2002","journal-title":"J. Biol. Chem"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"2099","DOI":"10.1016\/S0002-9440(10)63260-9","article-title":"Biphasic expression of two paracrine melanogenic cytokines, stem cell factor and endothelin-1, in ultraviolet B-induced human melanogenesis","volume":"65","author":"Hachiya","year":"2004","journal-title":"Am. J. Pathol"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"571","DOI":"10.1046\/j.1523-1747.2001.01296.x","article-title":"The role of the epidermal endothelin cascade in the hyperpigmentation mechanism of lentigo senilis","volume":"116","author":"Kadono","year":"2001","journal-title":"J. Investig. Dermatol"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1256","DOI":"10.1111\/j.0022-202X.2004.22503.x","article-title":"The epidermal stem cell factor is over-expressed in lentigo senilis: Implication for the mechanism of hyperpigmentation","volume":"122","author":"Hattori","year":"2004","journal-title":"J. Investig. Dermatol"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"1094","DOI":"10.1111\/j.1365-2133.2006.07179.x","article-title":"The dermal stem cell factor and c-kit are overexpressed in melasma","volume":"154","author":"Kang","year":"2006","journal-title":"Br. J. Dermatol"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1235","DOI":"10.1042\/bj3301235","article-title":"Biological characterization of human fibroblast-derived mitogenic factors for human melanocytes","volume":"330","author":"Imokawa","year":"1998","journal-title":"Biochem. J"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"130","DOI":"10.1016\/0167-4889(96)00063-8","article-title":"Production and release of proopiomelanocortin (POMC) derived peptides by human melanocytes and keratinocytes in culture: Regulation by ultraviolet B","volume":"1313","author":"Chakraborty","year":"1996","journal-title":"Biochim. Biophys. Acta"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"2258","DOI":"10.1172\/JCI117224","article-title":"Proopiomelanocortin-derived peptides are synthesized and released by human keratinocytes","volume":"93","author":"Schauer","year":"1994","journal-title":"J. Clin. Investig"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"1789","DOI":"10.1073\/pnas.92.5.1789","article-title":"Mitogenic and melanogenic stimulation of normal human melanocytes by melanotropic peptides","volume":"92","author":"Swope","year":"1995","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1627","DOI":"10.1210\/endo.137.5.8612494","article-title":"Binding of melanotropic hormones to the melanocortin receptor MC1R on human melanocytes stimulates proliferation and melanogenesis","volume":"137","author":"Suzuki","year":"1996","journal-title":"Endocrinology"},{"key":"ref_20","first-page":"43","article-title":"Hyperpigmentation mechanisms involved in UVB-melanosis and solar lentigo and clinical effects of Chamomira ET extract on the pigmentation","volume":"98","author":"Kawashima","year":"2005","journal-title":"Mon. Book Derma"},{"key":"ref_21","first-page":"716","article-title":"Differentiation of epidermal melanocytes by UVB irradiation in tail skin of mouse (C57BL\/6J mice-aa\/ee, recessive yellow) with mutation of melanocortin receptor","volume":"106","author":"Kobayashi","year":"1996","journal-title":"Jpn. J. Dermatol"},{"key":"ref_22","first-page":"917","article-title":"Paracrine interaction between UVB-exposed human keratinocytes and human melanocytes in co-culture system with cell insert leading to an increased expression of tyrosinase and its blockade by Witherferin A","volume":"25","author":"Niwano","year":"2012","journal-title":"Pigment Cell Melanoma Res"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"249","DOI":"10.1038\/364249a0","article-title":"Protein kinase C\u03b1 activates RAF-1 by direct phosphorylation","volume":"364","author":"Kolch","year":"1993","journal-title":"Nature"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"790","DOI":"10.1128\/MCB.18.2.790","article-title":"Activation of the mitogen-activated protein kinase\/extracellular signal-regulated kinase pathway by conventional, novel, and atypical protein kinase C isotypes","volume":"18","author":"Schonwasser","year":"1998","journal-title":"Mol. Cell. Biol"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2137","DOI":"10.1093\/emboj\/18.8.2137","article-title":"Serine and tyrosine phosphorylations cooperate in Raf-1, but not B-Raf activation","volume":"18","author":"Mason","year":"1999","journal-title":"EMBO J"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"109","DOI":"10.1126\/science.280.5360.109","article-title":"Requirement of Ras-GTP-Raf complexes for activation of Raf-1 by protein kinase C","volume":"280","author":"Marais","year":"1998","journal-title":"Science"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"33321","DOI":"10.1074\/jbc.M004346200","article-title":"Intracellular signaling mechanisms leading to synergistic effects of endothelin-1 and stem cell factor on proliferation of cultured human melanocytes: Cross-talk via trans-activation of the tyrosine kinase c-kit receptor","volume":"275","author":"Imokawa","year":"2000","journal-title":"J. Biol. Chem"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1155","DOI":"10.1096\/fj.07-9080com","article-title":"Epistatic connections between MITF and endothelin signaling in Waardenburg syndrome and other pigmentary disorders","volume":"22","author":"Nishimura","year":"2008","journal-title":"FASEB J"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"4121","DOI":"10.1002\/j.1460-2075.1991.tb04989.x","article-title":"Activation of the human c-kit product by ligand-induced dimerization mediates circular actin reorganization and chemotaxis","volume":"10","author":"Siegbahn","year":"1991","journal-title":"EMBO J"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"21463","DOI":"10.1016\/S0021-9258(20)80558-4","article-title":"Multiple cytokines induce the tyrosine phosphorylation of Shc and its association with Grb2 in hemopoietic cells","volume":"268","author":"Cutler","year":"1993","journal-title":"J. Biol. Chem"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"5546","DOI":"10.1038\/sj.onc.1202929","article-title":"Phosphorylation of Shc by Src family kinases is necessary for stem cell factor receptor\/c-kit mediated activation of the Ras\/MAP kinase pathway and c-fos induction","volume":"18","author":"Lennartsson","year":"1999","journal-title":"Oncogene"},{"key":"ref_32","first-page":"6926","article-title":"Multiple cytokines stimulate the binding of a common 145-kilodalton protein to Shc at the Grb2 recognition site of Shc","volume":"14","author":"Liu","year":"1994","journal-title":"Mol. Cell. Biol"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"241","DOI":"10.1007\/s11010-011-0823-4","article-title":"Regulation of melanocyte pivotal transcription factor MITF by some other transcription factors","volume":"354","author":"Wan","year":"2011","journal-title":"Mol. Cell. Biochem"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1007\/s004390000328","article-title":"Transcription factor hierarchy in Waardenburg syndrome: Regulation of MITF expression by SOX10 and PAX3","volume":"107","author":"Potterf","year":"2000","journal-title":"Hum. Genet"},{"key":"ref_35","first-page":"7996","article-title":"Melanocyte-specific expression of the human tyrosinase promoter: Activation by the microphthalmia gene product and role of the initiator","volume":"14","author":"Bentley","year":"1994","journal-title":"Mol. Cell. Biol"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"657","DOI":"10.1006\/bbrc.1999.0400","article-title":"Role of microphthalmia transcription factor in regulation of melanocyte differentiation marker TRP-1","volume":"256","author":"Fang","year":"1999","journal-title":"Biochem. Biophys. Res. Commun"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"333","DOI":"10.1016\/S0002-9440(10)63657-7","article-title":"MLANA\/MART1 and SILV\/PMEL17\/GP100 are transcriptionally regulated by MITF in melanocytes and melanoma","volume":"163","author":"Du","year":"2003","journal-title":"Am. J. Pathol"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"283","DOI":"10.1007\/s00403-009-1007-x","article-title":"A single UVB exposure increases the expression of functional KIT in human melanocytes by up-regulating MITF expression through the phosphorylation of p38\/CREB","volume":"302","author":"Mizutani","year":"2010","journal-title":"Arch. Dermatol. Res"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"263","DOI":"10.1007\/s00403-011-1143-y","article-title":"An extract of Melia toosendan attenuates endothelin-1-stimulated pigmentation in human epidermal equivalents through the interruption of PKC activity within melanocytes","volume":"303","author":"Nakajima","year":"2011","journal-title":"Arch. Dermatol. Res"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"435","DOI":"10.1007\/s11418-011-0604-0","article-title":"WSE attenuates stem cell factor-stimulated pigmentation in human epidermal equivalent through interruption of ERK phosphorylation within melanocytes","volume":"66","author":"Nakajima","year":"2012","journal-title":"J. Nat. Med"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"1398","DOI":"10.1002\/ptr.3552","article-title":"An extract of Withania somnifera attenuates endothelin-1-stimulated pigmentation in human epidermal equivalents through the interruption of PKC activity within melanocytes","volume":"25","author":"Nakajima","year":"2011","journal-title":"Phytother. Res"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"803","DOI":"10.1007\/s00403-012-1248-y","article-title":"Abrogating effect of a xanthophyll carotenoid astaxanthin on the stem cell factor-induced stimulation of human epidermal pigmentation","volume":"304","author":"Nakajima","year":"2012","journal-title":"Arch. Dermatol. Res"},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"27","DOI":"10.1016\/S0378-8741(99)00065-3","article-title":"Studies on immunomodulatory activity of Withania somnifera (Ashwagandha) extract in experimental immune inflammation","volume":"67","author":"Agarwal","year":"1999","journal-title":"J. Ethnopharmacol"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"39","DOI":"10.1023\/B:MCBI.0000026051.16803.03","article-title":"Cardioprotection from ischemia and reperfusion injury by Withania somnifera: A hemodynamic, biochemical and histopathological assessment","volume":"260","author":"Gupta","year":"2004","journal-title":"Mol. Cell. Biochem"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"137","DOI":"10.1191\/0960327105ht509oa","article-title":"Neuroprotective effects of Withania somnifera on 6-hydroxydopamine induced Parkisonism in rats","volume":"24","author":"Ahmad","year":"2005","journal-title":"Hum. Exp. Toxicol"},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"229","DOI":"10.1016\/j.phymed.2003.07.012","article-title":"Antibacterial efficacy of Withania somnifera (Ashwagandha) an indigenous medicinal plant against experimental murine salmonellosis","volume":"12","author":"Owais","year":"2005","journal-title":"Phytomedicine"},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"406","DOI":"10.1016\/j.vph.2006.01.015","article-title":"Immunomodulatory role of Withania somnifera root powder on experimental induced inflammation: An in vivo and in vitro study","volume":"44","author":"Rasool","year":"2006","journal-title":"Vascul. Pharmacol"},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"905","DOI":"10.1002\/ptr.2180","article-title":"Withania somnifera inhibits NF-\u03baB and AP-1 transcription factors in human peripheral blood and synovial fluid mononuclear cells","volume":"21","author":"Singh","year":"2007","journal-title":"Phytother. Res"},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"1434","DOI":"10.1158\/1535-7163.MCT-06-0096","article-title":"Withanolides potentiate apoptosis, inhibit invasion, and abolish osteoclastogenesis through suppression of nuclear factor-\u03baB (NF-\u03baB) activation and NF-\u03baB-regulated gene expression","volume":"5","author":"Ichikawa","year":"2006","journal-title":"Mol. Cancer Ther"},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"4253","DOI":"10.1074\/jbc.M606728200","article-title":"Withaferin A strongly elicits I\u03baB kinase \u03b2 hyperphosphorylation concomitant with potent inhibition of its kinase activity","volume":"282","author":"Kaileh","year":"2007","journal-title":"J. Biol. Chem"},{"key":"ref_51","first-page":"177","article-title":"Genomic analysis highlights the role of the JAK-STAT signaling in the anti-proliferative","volume":"7","author":"Aalinkeel","year":"2010","journal-title":"Altern. Med"},{"key":"ref_52","first-page":"E5","article-title":"Withaferin A attenuates SCF-stimulated pigmentation in human epidermal equivalents by interrupting c-KIT activation within human melanocytes","volume":"26","author":"Terazawa","year":"2013","journal-title":"Pigment Cell Melanoma Res"}],"container-title":["International Journal of Molecular Sciences"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1422-0067\/15\/5\/8293\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T21:11:16Z","timestamp":1760217076000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1422-0067\/15\/5\/8293"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2014,5,12]]},"references-count":52,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2014,5]]}},"alternative-id":["ijms15058293"],"URL":"https:\/\/doi.org\/10.3390\/ijms15058293","relation":{},"ISSN":["1422-0067"],"issn-type":[{"value":"1422-0067","type":"electronic"}],"subject":[],"published":{"date-parts":[[2014,5,12]]}}}