Photoprotection by dietary phenolics against melanogenesis induced by UVA through Nrf2-dependent antioxidant responses
Authors: Thanyawan Pluemsamran
Saowalak Limsaengurai
Uraiwan Panich
Anyamanee Chaiprasongsuk
Tasanee Onkoksoong
Journal: Redox Biology (2016)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: Antioxidant; Melanogenesis; Nuclear factor E2-related factor 2 (Nrf2); Phenolics; Ultraviolet A.
Affiliations: Department of Pharmacology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand., Department of Pharmacology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand. Electronic address: .

Abstract:  Dietary phenolics may play a protective role in UV-mediated skin pigmentation through their antioxidant and UV-absorbing actions. In this study, we investigated whether genetic silencing of Nrf2, regulating the transcription of antioxidant genes, affected melanogenesis in primary human epidermal melanocytes (HEMn) and B16F10 melanoma cells subjected to UVA (8J/cm(2)) exposure. Then, we explored the antimelanogenic actions of phenolics; caffeic acid (CA) and ferulic acid (FA) providing partial UVA protection; quercetin (QU) and rutin (RU) providing strong UVA protection and; avobenzone (AV), an efficient UVA filter, in association with modulation of Nrf2-mediated antioxidant defenses in response to UVA insults in B16F10 cells. Upon oxidative insults, Nrf2 silencing promoted melanogenesis in both HEMn and B16F10 cells irradiated with UVA. Stimulation of melanogenesis by UVA correlated with increased ROS and oxidative DNA damage (8-OHdG), GSH depletion as well as a transient downregulation of Nrf2 nuclear translocation and of Nrf2-ARE signaling in B16F10 cells. All test compounds exerted antimelanogenic effects with respect to their abilities to reverse UVA-mediated oxidative damage as well as downregulation of Nrf2 activity and its target antioxidants (GCLC, GST and NQO1) in B16F10 cells. In conclusion, defective Nrf2 may promote melanogenesis under UVA irradiation through oxidative stress mechanisms. Compounds with antioxidant and/or UVA absorption properties could protect against UVA-induced melanogenesis through indirect regulatory effect on Nrf2-ARE pathway. 

Retracted: No

PubPeer comments:
 Figure 2E appears to have some repeating features, although dimensions differ. Could the authors please provide the original data? *** Closeup ![file] *** ![file] , 
 We appreciate your comments. Please find the uncropped image of Western Blotting for tyrosinase protein in QU- and AV-treated groups (Fig. 2E). The samples including control no UV, UVA treated group and each compound (QU or AV)-treated groups were loaded on the same blot in an experiment. The same images for the protein in control no UV and UV-treated groups were used to compare the tyrosinase expression between each treatment and control groups because the images from the same blot (please see uncropped blot below) should be used to compare the protein expression between groups in the same experiment. The images are split into two separate figures because the tyrosinase protein expression in control no UV, UV-treated groups could be clearly compared to that in the cells treated with each compound. The images showing the tyrosinase affected by each compound and the quantitative data (bar graphs) displayed together should also be clear to readers. ![file] Kind regards, Uraiwan , 
 #2 Thank you, that makes sense and Iu2019m sorry I didnu2019t understand. The lack of a splice line in a 2016 paper was what confused me. Likewise in Supplemental Figure 1, there appears to be a differential splice also not identified. Could the authors kindly also comment on this one? *** False color ![file] *** Original ![file] *** ![file] , 
 #3 We appreciate your kind comments. We didn t intend that figures of Western blot images would confuse readers. In Supplementary Figure 1, the untranfected control sample was loaded in different blot but in the same experiment so the image for this control group from the same experiment was used to compare the level of Nrf2 between the untransfected control and transfected cells. Kind regards, Uraiwan , 
 #4 Thank you again for your response. Perhaps you should consider contacting the journal to see if your representations here meet their standards for publication. Currently they read: **Image manipulations.** All Western blots should be presented with molecular weights noted, replicated, quantified and with statistical analysis. Cropping of the image is acceptable but must be clearly indicated. Merging images together to give the appearance of one image is not acceptable. The method of normalization to total protein, or where appropriate, a loading control (e.g. cell signaling studies) should be explicitly stated in the text. Images may be subjected to analysis for manipulation prior to publication and authors may be requested to provide copies of the original data , 
 #5 We appreciate your constructive comments and the suggestion that help us improve our works concerning the appropriate way of presenting image data. ,