Abstract

Plants rich in antioxidant substances may be useful for preventing skin aging. Pomegranates, containing flavonoids and other polyphenolic compounds, are widely consumed due to their beneficial properties. We examined the underlying mechanisms of dried pomegranate concentrate powder (PCP) on melanin synthesis in B16F10 melanoma cells. The antioxidant effects of PCP were determined by measuring free radical scavenging capacity and transcript levels of antioxidant enzymes. To explore the inhibitory effects of PCP on melanin synthesis, we measured tyrosinase activity and melanin content in α-melanocyte stimulating hormone (α-MSH)-stimulated B16F10 cells. In addition, the levels of tyrosinase-related protein-1 (TRP-1), TRP-2, tyrosinase, and microphthalmia-associated transcription factor (MITF) expression were determined by Western blotting. Changes in the phosphorylation status of protein kinase A (PKA), cAMP response element-binding protein (CREB), mitogen-activated protein kinases (MAPKs), phosphatidylinositol 3-kinase (PI3K), serine/threonine kinase Akt, and glycogen kinase 3β (GSK3β) were also examined. The free radical scavenging activity of PCP increased in a dose-dependent manner. In PCP-treated B16F10 cells, transcript levels of glutathione peroxidase-1 (GPx-1) were increased compared with α-MSH-stimulated cells. In addition, PCP led to the down-regulation of phospho-p38, phospho-PKA, phospho-CREB, phospho-GSK3β, MITF, and TRP-1 compared with α-MSH-stimulated B16F10 cells. We believe this effect may be associated with PCP activity, which leads to the inhibition of melanin production and tyrosinase activity. These results suggest that PCP decreases tyrosinase activity and melanin production via inactivation of the p38 and PKA signaling pathways, and subsequently decreases phosphorylation of CREB, MITF, and melanogenic enzymes. These observations provided new insights on the molecular mechanisms of the skin-whitening property of PCP.

Highlights

  • Melanin, a pigment produced by epidermal melanocytes, is the main determinant of skin color and contributes to protection against ultraviolet (UV) irradiation [1]

  • Values are expressed as the means ± standard deviation (SD) from three independent experiments

  • Mitogen-activated protein kinases (MAPKs) play pivotal roles in the regulation of melanogenesis, we examined protein levels of p-protein kinase A (PKA), p-cAMP response element binding protein (CREB), p-JNK, p-p38, p-extracellular response kinase (ERK), p-PI3K, p-AKT, and p-GSK3β in α-melanocyte stimulating hormone (α-MSH)-stimulated B16F10 cells to further demonstrate the effects of pomegranate concentrate powder (PCP) on melanogenesis

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Summary

Introduction

A pigment produced by epidermal melanocytes, is the main determinant of skin color and contributes to protection against ultraviolet (UV) irradiation [1]. Melanogenesis is a complex process involving tyrosinase and tyrosinase-related proteins (TRPs). Tyrosinase and TRPs are controlled by microphthalmia-associated transcription factor (MITF) in melanocytes. Melanin synthesis is regulated by the transduction of several signals that play important functions in the process of melanogenesis. Thereafter, PKA leads to the phosphorylation of cAMP response element binding protein (CREB), and the phosphorylation of CREB has been found to activate MITF transcription [6,7]. Mitogen-activated protein kinases (MAPKs), p38, extracellular response kinase (ERK), and c-Jun N-terminal (JNK) are important factors in melanogenesis. Recent studies have reported that p38 MAPK is involved in MITF regulation [8]. Activation of the p38 MAPK signaling pathway increases the transcription of tyrosinase, which activates melanin synthesis [9,10]

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