4-(Phenylsulfanyl) Butan-2-One Attenuates the Inflammatory Response Induced by Amyloid-β Oligomers in Retinal Pigment Epithelium Cells
Authors: Supin Chompoopong
Zhi-Hong Wen
Shun-Ping Huang
Peeraporn Varinthra
Ingrid Y Liu
Journal: Marine Drugs (2020)
Discipline: PHARMACOLOGY & TOXICOLOGY
Keywords: 4-(Phenylsulfanyl) Butan-2-One; amyloid-β; coral; inflammatory responses; retinal pigment epithelium cells.
Affiliations: Institute of Medical Sciences, Tzu Chi University, Hualien 970, Taiwan., Department of Molecular Biology and Human Genetics, Tzu Chi University, Hualien 970, Taiwan., Department of Anatomy, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand., Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung 804, Taiwan.

Abstract:  Age-related macular degeneration (AMD) is a progressive eye disease that causes irreversible impairment of central vision, and effective treatment is not yet available. Extracellular accumulation of amyloid-beta (Aβ) in drusen that lie under the retinal pigment epithelium (RPE) has been reported as one of the early signs of AMD and was found in more than 60% of Alzheimer's disease (AD) patients. Extracellular deposition of Aβ can induce the expression of inflammatory cytokines such as IL-1β, TNF-α, COX-2, and iNOS in RPE cells. Thus, finding a compound that can effectively reduce the inflammatory response may help the treatment of AMD. In this research, we investigated the anti-inflammatory effect of the coral-derived compound 4-(phenylsulfanyl) butan-2-one (4-PSB-2) on Aβ1-42 oligomer (oAβ1-42) added to the human adult retinal pigment epithelial cell line (ARPE-19). Our results demonstrated that 4-PSB-2 can decrease the elevated expressions of TNF-α, COX-2, and iNOS via NF-κB signaling in ARPE-19 cells treated with oAβ1-42 without causing any cytotoxicity or notable side effects. This study suggests that 4-PSB-2 is a promising drug candidate for attenuation of AMD. 

Retracted: No

PubPeer comments:
 1. Abstract: ....... In this research, we investigated the anti-inflammatory effect of the coral-derived compound 4-(phenylsulfanyl) butan-2-one (4-PSB-2) on ............ . However, 4-(phenylsulfanyl) butan-2-one (4-PSB-2) was not derived from the corals, this compound was produced in the chemical laboratory solely by chemical reactions. 2. In third paragraph of 1. Introduction, it was claimed that  The compound 4-(phenylsulfanyl) butan-2-one (4-PSB-2), modified from dihydroaustrasulfone alcohol, is synthetic precursor of soft coral (Cladiella australis)-derived natural compound, austrasulfone.  However, the compound 4-(phenylsulfanyl) butan-2-one has not ever been found to be modified from dihydroaustrasulfone alcohol, otherwise please provide the related references. 3.The compound 4-(phenylsulfanyl) butan-2-one can not be the synthetic precursor of austrasulfone. The phenyl group of 4-(phenylsulfanyl) butan-2-one has the difficulty to be converted to the vinyl group of austrasulfone. , 
 Our responses, which have been sent to the journal editor, are as follows: Response to comment 1: The synthesis of compound 4-(phenylsulfanyl) butan-2-one (4-PSB-2) had been published previously by Wu et al. in 2015. In the introduction section of this paper, the 4-PSB-2 compound is mentioned as follows: u201cTwo chemical constituents, austrasulfone and dihydroaustrasulfone alcohol, of Formosan soft coral Cladiella australis show significant in vitro anti-inflammatory activity. In this study, we continued to screen compounds with skin whitening properties and favorable safety profiles from a series of sulfur-containing compounds that are structurally related to the marine natural product, austrasulfone, which has a four-carbon carbonyl group and an unsaturated phenyl group (similar to the vinyl group for sp2 hybridization) attached to sulfur. 4-(phenylsulfanyl)butan-2-one was found to be a safer and more effective ingredient than traditionally used agents for cosmetic and medical applications.u201d In the Abstract section of the same paper: u201cIn this study, we screened compounds with skin whitening properties and favorable safety profiles from a series of marine related natural products, which were isolated from Formosan soft coral Cladiella australis. Our results indicated that 4-(phenylsulfanyl)butan-2-one could successfully inhibit pigment generation process--------u201c. In the introduction section of our study published in MarineDrugs (Mar. Drugs 2021, 19, 1. https: dx.doi.org 10.3390 md19010001), we cited the reference published by Chien et al. in 2016 (ref #25) regarding this 4-PSB-2 compound. According to the last paragraph in the Introduction section, Chien et al. described that u201cAustrasulfone, a bioactive substance isolated from the Formosan soft coral Cladiella australis, exhibits potent neuroprotective effects against the 6-OHDA-induced neurotoxicity in neuroblastoma SH-SY5Y cells (Wen et al., 2010). Dihydroaustrasulfone alcohol, the synthetic precursor of austrasulfone, not only exhibited anti-inflammatory activity in vitro, but also showed potent therapeutic potential in the treatment of inflammatory-related diseases (Wen et al., 2010). In order to easily pass through the cell membrane, the polar hydroxyl group (-OH) of hydroxylated sulfone was replaced with benzene ring in a straightforward synthesis to yield the compound 4-(Phenylsulfanyl)butane-2-one (4-PSB-2).u201d Thus, we describe 4-PSB-2 as a coral-derived compound. Response to comments 2 and 3: In the Introduction section, we wrote: u201cThe compound 4-(phenylsulfanyl) butan-2-one (4-PSB-2), modified from dihydroaustrasulfone alcohol, is synthetic precursor of soft coral (Cladiella australis)-derived natural compound, austrasulfone.u201d The synthetic precursor refers to dihydroaustrasulfone alcohol. To be precise, this sentence should be: u201cThe compound 4-(phenylsulfanyl) butan-2-one (4-PSB-2) is modified from dihydroaustrasulfone alcohol, a synthetic precursor of soft coral (Cladiella australis)-derived natural compound, austrasulfone. -------[25] (Chien et al., 2016)u201d Wording of this sentence would not change the results and conclusion of this study. References: Wen, Z.H.; Chao, C.H.; Wu, M.H.; Sheu, J.H. A neuroprotective sulfone of marine origin and the in vivo anti-inflammatory activity of an analogue. Eur. J. Med. Chem. 2010, 45, 5998u20136004 Wu SY, Wang HM, Wen YS, Liu W, Li PH, Chiu CC, Chen PC, Huang CY, Sheu JH, Wen ZH. 4-(Phenylsulfanyl)butan-2-One Suppresses Melanin Synthesis and Melanosome Maturation In Vitro and In Vivo. Int. J. Mol. Sci. 2015, 16, 20240-20257; doi:10.3390 ijms160920240 Chien, J.Y.; Sheu, J.H.; Wen, Z.H.; Tsai, R.K.; Huang, S.P. Neuroprotective effect of 4-(phenylsulfanyl)butan-2-one on optic nerve crush model in rats. Exp. Eye Res. 2016, 143, 148u2013157 , 
 All fatty acids and terpenoids have a portion of similar partial structures as those discovered from soft corals and sponges, however , one can not simply consider these compounds as the soft coral- or sponges-derived compounds. Also, not all compounds with a structurally similar fundtional group(s) can be freely derived to others. Dihydrosulfone alcohol could be converted to austrasulfone, but asutrasulfone has the difficulty to be derived from 4-(PSB-2). , 
 In lines 3-5, page 8, a description about the chemical structures and bioactivity between 4-PSB-2 and BAY 11-7082 was found as below indicated. Besides, the chemical structure of 4-PSB-2 is similar to BAY 11-7082, which also shows anti-inflammatory effects via NF-u03baB signaling [41]. Thus, the two compounds probably repress the inflammatory response via a similar mechanism. However, the phenyl, sulfanyl, saturated ethylene (CH2CH2), and acetyl (CH3CO) groups of 4-PSB-2 were changed to 4-methylphenyl, unsaturated acetylene (CHCH) ,and nitrile groups of BAY 11-7082, respectively. The chemical structures of 4-PSB-2 and BAY 11-7082 should be in significant difference. , 
 Figure 3 ![file] Figure 4 ![file] The Beta-Actin seems similar, just different exposure , 
 Both of beta actin are different membranes but same exposure time at 3 minutes. ![file] , 
 Both of beta actin are from different membranes with the same exposure time for 3 minutes. ![file] , 
 ![file] Is this really from the same membrane? If yes, the gel running was so bad because the band became larger on the lower size. ![file] What is this on the end of the lane? is that also a sample? if that also a sample, why there is no beta actin band showing? , 
 #8 ![file] 1.tAnyone experienced in performing the western blot would know that this is the marker lane. 2.tThe journal reviewers did not question the authoru2019s western blot quality. However, the authors would be happy to discuss with the commenter regarding this study if he she submits his her comment to the journal. 3.tThe authors are ready to provide original gels and data to the journal editor upon request. Corresponding author: Ingrid Y Liu , 
 The following statement might need to clarified. 4.3. Preparation of 4-PSB-2 Solution and Treatment In this study, 4-PSB-2 was provided by the Research Center of National Research Program for Biopharmaceuticals, Taiwan, and its structure is shown in Figure 1D. To verify the cytotoxicity of 4-PSB-2, it was dissolved in DMSO and medium to final concentrations of 1, 25, 50, 100, and 200 u00b5M. 1. What medium was used together with DMSO to prepare the solution of 4-PSB-2? 2. This article mainly investigated the anti-inflammatory effect of 4-PSB-2 toward the elevated expressions of TNF-u03b1, COX-2, and iNOS via NF-u03baB signaling in ARPE-19 cells treated with oAu03b21-42, not only for verification of the cytotoxicity of 4-PSB-2 which seems to be not the subject of this research. , 
 Please see the following content in page 3.  2.2. 4-PSB-2 Increased Cell Viability in ARPE-19 Cells To examine the cytotoxic effect of 4-PSB-2 (Figure 1D) on ARPE-19 cells, we first applied five different concentrations of 4-PSB-2 (1, 25, 50, 100, and 200 u00b5M) to ARPE-19 cell cultures for 24 h, and we used the MTT assay to measure cell viability. Results of the MTT analysis indicated that 4-PSB-2 did not cause toxicity in ARPE-19 cells; on the other hand,25 u00b5M of 4-PBS-2 significantly enhanced cell viability (F(5,28) = 6.818, p 0.001; Figure 1E). However, the above statements are inconsistent with those shown in Figure 4E as at 100 u00b5M 4-PSB-2 could reduce the growth of ARPE-19 cells to around 92%, and further significantly inhibit the growth of the cells to about 55% at 200 u00b5M. ,