Journal of Natural Medicines

, Volume 66, Issue 3, pp 435–446 | Cite as

Withania somnifera extract attenuates stem cell factor-stimulated pigmentation in human epidermal equivalents through interruption of ERK phosphorylation within melanocytes

  • Hiroaki Nakajima
  • Katsunori Fukazawa
  • Yuki Wakabayashi
  • Kazumasa Wakamatsu
  • Genji Imokawa
Original Paper

Abstract

We previously demonstrated that mitogen-activated protein kinase (MAPK) signaling, including microphthalmia-associated transcription factor (MITF) and cAMP response element-binding protein (CREB) phosphorylation, is a major pathway involved in up-regulating melanogenesis within human melanocytes in several hyperpigmentary disorders such as UVB melanosis and lentigo senilis. Recently, a redox imbalance was shown to be closely linked to a variety of altered cellular responses in which the precise balance between levels of oxidizing and reducing equivalents that reflect the intracellular redox condition profoundly affects intracellular signaling pathways, especially the MAPK pathway. To elucidate the effects of redox balance regulation on epidermal pigmentation, we used an antioxidant-rich extract of the herb Withania somnifera to assess its effect on stem cell factor (SCF)-stimulated pigmentation in human epidermal equivalents and analyzed its biological mechanism of action. Addition of the W. somnifera extract (WSE) caused a marked reduction in SCF-stimulated pigmentation in a dose-dependent manner after 14 days of treatment, which was accompanied by a significant decrease in eumelanin content. In WSE-treated human epidermal equivalents, melanocyte-specific proteins (including tyrosinase) were significantly suppressed at the gene and protein levels by WSE. Signaling analysis with immunoblots revealed that in human melanocytes or human melanoma cells treated with WSE, there was a marked deficiency in SCF-stimulated phosphorylation of ERK, MITF and CREB, but not of Raf-1 and MEK. Since WSE had no direct inhibitory effect on tyrosinase activity and no melano-cytotoxic effect on melanocytes present in the human epidermal equivalents or on cultured human melanocytes, the sum of these findings indicates that WSE attenuates SCF-stimulated pigmentation by preferentially interrupting ERK phosphorylation within melanocytes and can serve as a therapeutic tool for SCF-associated hyperpigmentary disorders.

Keywords

Withania somnifera Melanocytes Stem cell factor MAPK Pigmentation 

Abbreviations

WSE

Withania somnifera extract

SCF

Stem cell factor

EDN1

Endothelin-1

EDNBR

Endothelin B receptor

MAPK

Mitogen-activated protein kinase

MITF

Microphthalmia-associated transcription factor

NHM

Normal human melanocytes

PKC

Protein kinase C

ROS

Reactive oxygen species

TYK

Tyrosine kinase

Tyrp1

Tyrosinase-related protein-1

Notes

Acknowledgments

We thank Dr. Hiroshi Murata of the Department of Dermatology, School of Medicine, Shinshu University for providing us with acral lentigo malignant melanoma (SM2-1) cells.

Conflict of interest

The authors have declared no conflict of interest.

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Copyright information

© The Japanese Society of Pharmacognosy and Springer 2011

Authors and Affiliations

  • Hiroaki Nakajima
    • 1
  • Katsunori Fukazawa
    • 1
  • Yuki Wakabayashi
    • 1
  • Kazumasa Wakamatsu
    • 2
  • Genji Imokawa
    • 1
  1. 1.School of Bioscience and BiotechnologyTokyo University of TechnologyHachiojiJapan
  2. 2.School of Health SciencesFujita Health UniversityToyoakeJapan

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