Oxidative stress represents an imbalance between the generation of reactive oxygen and nitrogen species and the ability of antioxidant systems to decompose those products. Oxidative stress is implicated in the pathogenesis of hyperpigmentation, hypopigmentation, melanoma, and other skin diseases. Regulatory networks involving oxidative stress and related pathways are widely represented in hypopigmentation diseases, particularly vitiligo. However, there is no complete review into the role of oxidative stress in the pathogenesis of hyperpigmentation disorders, especially regarding associations involving oxidative stress and cellular signaling pathways. Here, we review oxidative and antioxidant systems, oxidative stress-induced signal transduction mechanisms, and effects of antioxidant drugs used in preclinical and clinical settings in hyperpigmentation disorders.
Summary
Down‐regulated chemerin expression has been reported to correlate with poor prognosis of several types of cancer including melanoma. All‐trans retinoic acid (atRA) is a potent inducer of chemerin, and we previously reported that atRA inhibited murine melanoma growth through enhancement of anti‐tumor T‐cell immunity. Here, we aimed to investigate whether loss of endogenous chemerin accelerated melanoma growth and whether chemerin was involved in the melanoma‐inhibitory effect of atRA. We demonstrated that chemerin was constitutively expressed in the skin, which was down‐regulated during murine melanoma growth. Rarres2−/− mice, which are deficient in chemerin, exhibited aggravated tumor growth and impaired tumor‐infiltrating natural killer (NK) cells that express CMKLR1, the functional receptor of chemerin. Topical treatment with atRA up‐regulated skin chemerin expression, which was primarily derived from dermal cells. Moreover, atRA treatment significantly enhanced tumor‐infiltrating NK cells, which was completely abrogated in Rarres2−/− mice and Cmklr1−/− mice, suggesting a dependency of NK cell recruitment on the chemerin–CMKLR1 axis in melanoma. Despite comparable melanoma growth detected in wild‐type mice and Cmklr1−/− mice, lack of CMKLR1 partially abrogated the melanoma‐inhibitory effect of atRA. This may be due to the inability to enhance tumor‐infiltrating NK cells in Cmklr1−/− mice following atRA treatment. Collectively, our study suggests that down‐regulation of chemerin could be a strategy used by cancers such as melanoma to impair anti‐tumor NK cell immunity and identifies a new anti‐tumor mechanism of atRA by up‐regulating chemerin to enhance CMKLR1‐dependent NK cell recruitment.
Post-inflammatory hyperpigmentation (PIH) is a common acquired pigmentary disorder occurring after skin inflammation or injury. Ultraviolet B irradiation could exaggerate PIH clinically due to its effect on promoting cutaneous inflammation and melanogenesis in keratinocytes and melanocytes, respectively. Solamargine (SM), a steroidal alkaloid glycoside extracted from Solanum undatum, significantly inhibits Ultraviolet B (UVB)-induced pro-inflammatory cytokines IL-1α, IL-1β, IL-8, and IFN-γ, as well as paracrine melanogenic factors ET-1, α-MSH, and bFGF in human keratinocytes. Additionally, SM significantly attenuated UVB-induced melanin synthesis in human epidermal melanocytes through down-regulation of tyrosinase activity and expression of MITF, TRP-1, TRP-2, and tyrosinase. SM exerted an anti-inflammatory effect in UVB-irradiated keratinocytes through the p38 MAPK/Nrf2/HO-1 signaling pathway. With its anti-inflammatory and whitening effect, SM may improve PIH through paracrine regulations of keratinocytes and direct action on melanocytes, making it a promising agent for PIH.
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