Phloxine B Phototoxicity: A Mechanistic Study Using HaCaT Keratinocytes¶

Guiding the Design of Organic Photocatalyst for PET-RAFT Polymerization: Halogenated Xanthene Dyes

By examining structurally similar halogenated xanthene dyes, this study establishes a guiding principle for resolving structure-property- performance relationships in the photocontrolled PET-RAFT polymerization system (PET-RAFT: photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer). We investigated the effect of the halogen substituents on the photophysical and electrochemical properties of the xanthene dyes acting as photocatalysts and their resultant effect on the performance of PET-RAFT polymerization. Consideration of the structure- property-performance relationships allowed design of a new xanthene photocatalyst, where its photocatalytic activity (oxygen tolerance and polymerization rate) was successfully optimized for PET-RAFT polymerization. We expect that this study will serve as a theoretical framework in broadly guiding the design of high performance photocatalysts for organic photocatalysis.

Flow mediated metal-free PET-RAFT polymerisation for upscaled and consistent polymer production

A slug flow process has been utilised in conjunction with metal-free photopolymerisation to produce well-defined polymers with outstanding consistency.

Antioxidative cellular response of lepidopteran ovarian cells to photoactivated alpha-terthienyl

Photodynamic sensitizers as useful alternative agents have been used for population control against insect pests, and the response of insect ovarian cells towards the photosensitizers is gaining attention because of the next reproduction. In this paper, antioxidative responses of lepidopteran ovarian Tn5B1-4 and Sf-21 cells to photoactivated alpha-terthienyl (PAT) are investigated. PAT shows positive inhibitory cytotoxicity on the two ovarian cells, and its inhibition on cell viability is enhanced as the concentrations are increased and the irradiation time is extended. Median inhibitory concentrations (IC₅₀) are 3.36μg/ml to Tn5B1-4 cells, and 3.15μg/ml to Sf-21 cells at 15min-UV-A irradiation 2h-dark incubation. Under 10.0μg/ml PAT exposure, 15min-UV-A irradiation excites higher ROS production than 5min-UV-A irradiation does in the ovarian cells, the maximum ROS content is about 7.1 times in Tn5B1-4 cells and 4.3 times in Sf-21 cells, and the maximum malondialdehyde levels in Tn5B1-4 and Sf-21 cells are about 1.47- and 1.36-fold higher than the control groups, respectively. Oxidative stress generated by PAT strongly decreases the activities of POD, SOD and CAT, and induces an accumulation of Tn5B1-4 cells in S phase and Sf-21 cells in G2/M phase in a concentration-dependent fashion. Apoptosis accumulation of Tn5B1-4 cells and the persistent post-irradiation cytotoxicity are further observed, indicating different antioxidative tolerance and arrest pattern of the two ovarian cells towards the cytotoxicity of PAT.

ROS mediated crosstalk between endoplasmic reticulum and mitochondria by Phloxine B under environmental UV irradiation

Phloxine B (PhB) is a most commonly used dye in cosmetic products throughout the world. It shows an absorption in visible and ultraviolet radiations. PhB was photodegraded within 4h of UV exposure. It generates reactive oxygen species (ROS) photochemically and intracellularly. Photosensitized PhB caused dose dependent cell viability reduction of human keratinocyte cell line (HaCaT) which was measured through MTT (75.4%) and NRU (77.3%) assays. It also induces cell cycle arrest and DNA damage. Photosensitized PhB induces Ca(2+) release from endoplasmic reticulum (ER). It causes the upregulation of ER stress marker genes ATF6 (1.79 fold) and CHOP (1.93 fold) at transcription levels. The similar response of ATF6 (3.6 fold) and CHOP (2.38 fold) proteins was recorded at translation levels. CHOP targeted the mitochondria and reduced the mitochondrial membrane potential analyzed through JC-1 staining. It further increases Bax/Bcl2 ratio (3.58 fold) and promotes the release of cytochrome c, finally leads to caspase-dependent apoptosis. Upregulation of APAF1 (1.79 fold) in PhB treated cells under UV B exposure supports the mitochondrial-mediated apoptotic cell death. The results support the involvement of ER and mitochondria in ROS mediated PhB phototoxicity. Therefore, the use of PhB in cosmetic products may be deleterious to users during sunlight exposure.

Evaluation of small molecule SecA inhibitors against methicillin-resistant Staphylococcus aureus

Due to the emergence and rapid spread of drug resistance in bacteria, there is an urgent need for the development of novel antimicrobials. SecA, a key component of the general bacterial secretion system required for viability and virulence, is an attractive antimicrobial target. Earlier we reported that systematical dissection of a SecA inhibitor, Rose Bengal (RB), led to the development of novel small molecule SecA inhibitors active against Escherichia coli and Bacillus subtilis. In this study, two potent RB analogs were further evaluated for activities against methicillin-resistant Staphylococcus aureus (MRSA) strains and for their mechanism of actions. These analogs showed inhibition on the ATPase activities of S. aureus SecA1 (SaSecA1) and SecA2 (SaSecA2), and inhibition of SaSecA1-dependent protein-conducting channel. Moreover, these inhibitors reduce the secretion of three toxins from S. aureus and exert potent bacteriostatic effects against three MRSA strains. Our best inhibitor SCA-50 showed potent concentration-dependent bactericidal activity against MRSA Mu50 strain and very importantly, 2-60 fold more potent inhibitory effect on MRSA Mu50 than all the commonly used antibiotics including vancomycin, which is considered the last resort option in treating MRSA-related infections. Protein pull down experiments further confirmed SaSecA1 as a target. Deletion or overexpression of NorA and MepA efflux pumps had minimal effect on the antimicrobial activities against S. aureus, indicating that the effects of SecA inhibitors were not affected by the presence of these efflux pumps. Our studies show that these small molecule analogs target SecA functions, have potent antimicrobial activities, reduce the secretion of toxins, and have the ability to overcome the effect efflux pumps, which are responsible for multi-drug resistance. Thus, targeting SecA is an attractive antimicrobial strategy against MRSA.

Development of novel in vitro photosafety assays focused on the Keap1-Nrf2-ARE pathway

Although photoallergens require UV energy for antigen formation, the subsequent immune response is considered to be the same as in ordinary skin sensitization. Therefore, in vitro tests for skin sensitization should also be applicable for photoallergy testing. In this study, we examined whether activation of the Keap1 (Kelch-like ECH-associated protein 1)-Nrf2 (nuclear factor-erythroid 2-related factor 2)-ARE (antioxidant response element) pathway could be used to assess the photoallergenic potential of chemicals, using the reporter cell line AREc32 or KeratinoSens(TM) . First, we identified an appropriate UVA irradiation dose [5 J cm(-2) irradiation in phosphate-buffered saline (PBS)] by investigating the effect of UV irradiation on ARE-dependent gene induction using untreated or 6-methylcoumarin (6-MC)-treated cells. Irradiation of well-known photoallergens under this condition increased ARE-dependent gene expression by more than 50% compared with both vehicle and non-irradiated controls. When the cut-off value for detecting photoallergens was set at 50% induction, the accuracy of predicting photoallergenic/phototoxic chemicals was 70% in AREc32 cells and 67% in KeratinoSens(TM) cells, and the specificity was 100% in each case. We designate these assays as a photo-ARE assay and photo-KeratinoSens(TM) , respectively. Our results suggest that activation of the Keap1-Nrf2-ARE pathway is an effective biomarker for evaluating both photoallergenic and phototoxic potentials. Either of the above tests might be a useful component of a battery of in vitro tests/in silico methods for predicting the photoallergenicity and phototoxicity of chemicals. Copyright © 2015 John Wiley & Sons, Ltd.

Involvement of intracellular oxidative stress-sensitive pathway in phloxine B-induced photocytotoxicity in human T lymphocytic leukemia cells

We investigated the molecular mechanisms underlying phloxine B (PhB)-induced photocytotoxicity in human T lymphocytic leukemia Jurkat cells. In addition to apoptosis-related biochemical events, photo-irradiated PhB generated intracellular reactive oxygen species (ROS), induced phosphorylation of c-Jun-N-terminal kinase (JNK) in an oxidative stress-dependent manner and up-regulated the gene expression of interferon (IFN)-γ, an inducer of diverse apoptosis-related molecules in activated T cells. PhB-induced apoptosis was significantly inhibited by N-acetyl-l-cysteine, but not by catalase, indicating that ROS generation occurred intracellularly, and by SP600125 and AG490, specific inhibitors of JNK and IFN-γ signaling, respectively, confirming their roles in the apoptotic pathway. IFN-γ up-regulation was also inhibited by SP600125, indicating that it was downstream of JNK activation. These results suggest that PhB-induced apoptosis in Jurkat cells partially involves the intracellular oxidative stress-sensitive and T cell-specific IFN-γ pathway. These data present a novel insight into the mechanisms of photocytotoxicity induced by artificial food colorants in human T lymphocytic leukemia cells.

In vitro cytotoxicity and phototoxicity study of cosmetics colorants

The aim of the work was early identification of preventable risk factors connected with the consumers usage of products of everyday use, such as cosmetics, toys and children products, and other materials intended for contact with human skin. The risk factor is represented by substances with irritation potential and subsequent possible sensitisation, resulting in negative impact on human physical and psychical health with social and societal consequences. The legislation for cosmetics, chemical substances and other products requires for hazard identification the application of alternative toxicological methods in vitro without the use of animals. For this reason we used a battery of alternative assays in vitro, based on cell cultures. Progressive methods of molecular biology, based on fluorimetry and fluorescence, were employed for identification of early morphological and functional changes on cellular level. Four colorants frequently used in cosmetics (P-WS Caramel, Chlorophyllin, Unicert Red K 7054-J and Unicert Red K 7008-J) were tested on cell line NIH3T3 (mouse fibroblast cell) and 3T3 Balb/c with/without UV irradiation (dose 5 J cm(-2)). Fluorescence methods for the study of cell damage using fluorescence probes offer results for the evaluation of cytotoxicity and cell viability of adherent cells. We detected intracellular production of ROS investigated by molecular probe CM-H(2)DCFDA, which is primarily sensitive to the increased production of hydrogen peroxide or its downstream products. Toxic effects on the cellular level were identified by viability tests using Neutral Red uptake and MTT assay, where the live cells reduce yellow soluble 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) to insoluble formazan crystals. The reaction was investigated on mitochondrial membrane of living cells and the type of cell death was determined using Apoptosis detection kit. Cytotoxicity tests revealed health risks of using Chlorophyllin and Unicert Red K 7054-J.

Hydrogen [corrected] peroxide-dependent photocytotoxicity by phloxine B, a xanthene-type food colorant

BACKGROUND

Phloxine B (PhB; 2',4',5',7'-tetrabromo-4,5,6,7-tetrachloro-fluorescein), an artificial xanthene colorant, has been used as a red coloring agent in drugs and cosmetics as well as foods in some countries. However, little effort has been devoted to the study of this colorant as a potentially useful medicinal agent.

METHODS

We investigated the daily light-induced photocytotoxicity of PhB in two human leukemia cells, HL-60 and Jurkat, and its underlying mechanisms by in vitro experiments using antioxidants. REUSLTS AND CONCLUSIONS: PhB inhibited cell proliferation more preferentially to HL-60 cells than to Jurkat cells. Co-treatment of catalase completely blocked the photocytotoxicity by PhB in HL-60 cells, whereas the effect of histidine was only partial, suggesting that hydrogen peroxide (H(2)O(2)), rather than singlet oxygen, might be a prerequisite for the PhB-induced HL-60 cell death. Actually, PhB produced a significant amount of H(2)O(2) in the media as well as in the cells in concentration- and light-dependent manners. Furthermore, methionine, a hypochlorous acid (HOCl) scavenger, also significantly attenuated the cytotoxicity in HL-60 cells, but not in Jurkat cells, indicating the involvement of myeloperoxidase (MPO)-dependent hypohalous acid formation during the photocytotoxicity. In vitro experiments revealed that halogenated tyrosine was generated from the reaction of bovine serum albumin with PhB and HL-60 cell lysate. The present findings suggested that PhB induced a differential photodynamic action in the MPO-containing leukemia cells through an H(2)O(2)-dependent mechanism.

GENERAL SIGNIFICANCE

Our findings provide new insights into the molecular mechanisms underlying the PhB-induced apoptosis and also evaluated PhB as a promising PDT agent.

Induction of keratinocyte apoptosis by photosensitizing chemicals plus UVA

BACKGROUND

The capacity of photosensitizing chemicals with ultraviolet A light (UVA) to induce apoptosis is one of the methods to assess their phototoxic and potentially photoallergic properties, since apoptotic cells may be easily presented by antigen-presenting cells.

OBJECTIVES

We examined the photoaggravated ability to induce keratinocyte apoptosis of various chemicals that are known as causative agents of photocontact dermatitis and drug photosensitivity involving photoallergic and/or phototoxic mechanisms.

METHODS

HaCaT keratinocytes were incubated with 3,3',4',5-tetrachlorosalicylanilide (TCSA), bithionol, diphenylhydramine, chlorpromazine, 6-methylcoumarin, sparfloxacin, and enoxacin at 10(-7) to 10(-4)M and irradiated with UVA at 4J/cm(2). As positive control, 8-methoxypsoralen (8-MOP) was also tested. Apoptosis and necrosis were evaluated by flow cytometric enumeration of annexin V(+) 7-AAD(-) and annexin V(+) 7-AAD(+) cells, respectively. The expression of apoptosis-related molecules, caspase-3 and poly (ADP-ribose) polymerase (PARP), was tested by flow cytometric and Western blotting analyses.

RESULTS

In a comparison with non-irradiated cells, significant apoptosis was found in TCSA, bithionol, chlorpromazine, sparfloxacin and enoxacin at 10(-4) or 10(-5)M as well as 8-MOP as assessed by both annexin V and active caspase-3 stainings, while necrosis occurred in most of these chemicals at 10(-4)M. Neither apoptosis nor necrosis was seen in diphenylhydramine or 6-methylcoumarin. PARP were activated in HaCaT cells phototreated with TCSA, bithionol and chlorpromazine.

CONCLUSIONS

We suggest that our method is useful for in vitro assessment of phototoxicity and potential photoallergenicity of chemicals.