Myricetin inhibits Akt survival signaling and induces Bad-mediated apoptosis in a low dose ultraviolet (UV)-B-irradiated HaCaT human immortalized keratinocytes

Honey Phytochemicals: Bioactive Agents With Therapeutic Potential for Dermatological Disorders

Honey has been reported to have a range of biological activities including antimicrobial, immunomodulatory, and wound healing effects. Indeed, medical-grade honey is currently used in hospitals for the clinical management of wound infections. Honey is also of scientific interest for its therapeutic effects on other dermatological disorders such as atopic dermatitis, rosacea, and skin cancer. Recent studies have uncovered that honey contains a range of phytochemicals including flavonoids, dicarboxylic acids, coumarins, and phenolic acids. In this review, PubMed was used to search the scientific literature on the biological properties of honey phytochemicals in relation to dermatological disorders and to evaluate their potential as bioactive agents, drugs, or cosmeceuticals for the treatment of skin disease. The review revealed that phytochemicals found in honey have antimicrobial, anti-inflammatory, antiaging, antioxidant, anticancer, depigmenting, photoprotective, wound healing, and skin barrier enhancing properties. Although further high-quality studies are required to establish clinical efficacy, these findings suggest that honey phytochemicals may have the potential to be used as bioactive agents for the management of a range of dermatological disorders including wounds, psoriasis, atopic dermatitis, vitiligo, rosacea, and skin cancer.

Myricetin-induced suicidal erythrocyte death

BACKGROUND

Myricetin, a type of flavonol commonly found in fruits and herbs, has demonstrated anticancer properties by triggering the process of apoptosis or programmed cell death in tumor cells. Despite the absence of mitochondria and nuclei, erythrocytes can undergo programmed cell death, also known as eryptosis.This process is characterized by cell shrinkage, externalization of phosphatidylserine (PS) on the cell membrane, and the formation of membrane blebs. The signaling of eryptosis involves Ca²⁺ influx, the formation of reactive oxygen species (ROS), and the accumulation of cell surface ceramide. The present study explored the effects of myricetin on eryptosis.

METHODS AND RESULTS

Human erythrocytes were exposed to various concentrations of myricetin (2-8 µM) for 24 h. Flow cytometry was used to assess the markers of eryptosis, including PS exposure, cellular volume, cytosolic Ca²⁺ concentration, and ceramide accumulation. In addition, the levels of intracellular ROS were measured using the 2',7'-dichlorofluorescin diacetate (DCFDA) assay. The myricetin-treated (8 µM) erythrocytes significantly increased Annexin-positive cells, Fluo-3 fluorescence intensity, DCF fluorescence intensity, and the accumulation of ceramide. The impact of myricetin on the binding of annexin-V was significantly reduced, but not completely eliminated, by the nominal removal of extracellular Ca²⁺.

CONCLUSION

Myricetin triggers eryptosis, which is accompanied and, at least in part, caused by Ca²⁺ influx, oxidative stress and increase of ceramide abundance.

Potential Role of Phytochemical Extract from Saffron in Development of Functional Foods and Protection of Brain-Related Disorders

The present review is designed to measure the effects of saffron extract in functional foods and its pharmacological properties against various disorders. Saffron is a traditional medicinal plant used as a food additive. The stigma of saffron has bioactive compounds such as safranal, crocin, crocetin, picrocrocin, kaempferol, and flavonoid. These bioactive compounds can be extracted using conventional (maceration, solvent extraction, soxhlet extraction, and vapor or hydrodistillation) and novel techniques (emulsion liquid membrane extraction, ultrasound-assisted extraction, enzyme-associated extraction, pulsed electric field extraction, microwave-assisted extraction, and supercritical fluid extraction). Saffron is used as a functional ingredient, natural colorant, shelf-life enhancer, and fortifying agent in developing different food products. The demand for saffron has been increasing in the pharma industry due to its protection against cardiovascular and Alzheimer disease and its antioxidant, anti-inflammatory, antitumor, and antidepressant properties. Conclusively, the phytochemical compounds of saffron improve the nutrition value of products and protect humans against various disorders.

Repurposing Natural Dietary Flavonoids in the Modulation of Cancer Tumorigenesis: Decrypting the Molecular Targets of Naringenin, Hesperetin and Myricetin

In the past few years flavonoids have been gaining more attention regarding their (still un) exploited anticancer properties. Flavonoids are natural compounds present in fruits, vegetables, and seeds, meaning that they are already present in the daily life of every person, with a described broad-spectrum of pharmacological activities, including anticancer, anti-inflammatory and antioxidant. In the present review we discuss the anticancer activity of three important flavonoids - myricetin (MYR) (flavanol group), hesperetin (HESP) and naringenin (NAR) (flavanone group). Although some mechanisms underlying their activities remain still unclear, they can act as potential inhibitors of key tumorigenic signaling pathways, such as PI3K/Akt/mTOR, p38 MAPK and NF-κB. Simultaneously, they can reset the levels of pro-apoptotic proteins that belong to the Bcl-2 and caspase family and decrease the intracellular levels of ROS and pro-inflammatory cytokines, such as TNF-α, IL-1β and IL-6. Together with their synergetic effect they have the potential to become key elements in the prevention and/or treatment of several types of cancer, with the major improvement to the patient life quality, due to their non-existent toxicity.

Effect of Green Tea Supplementation on Antioxidant Status in Adults: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

It is well-established that green tea supplementation has antioxidant properties. However, whether green tea supplementation leads to oxidative stress reduction remains unclear, as clinical investigations on this subject have yielded inconsistent outcomes. Consequently, we aimed to determine the effects of green tea supplementation on oxidative stress in adults. A systematic search of English language publications up to 21 August 2021 was carried out in PubMed, Scopus, Embase, and ISI Web of Science, utilizing pertinent keywords. These searches included randomized controlled trials (RCTs) evaluating the relationship between green tea supplementation, malondialdehyde (MDA), and total antioxidant capacity (TAC) in adults. A random-effects model was used to estimate the weighted mean difference (WMD) and 95% confidence intervals (95% CI). Meta-regression and non-linear dose-response analyses were performed to investigate the association between the dosage of green tea (mg/day) and the duration of the intervention (weeks) with pooled effect size. Sixteen RCTs with seventeen arms including 760 participants met the inclusion criteria. Our results indicated that green tea supplementation had significant effects on TAC (weighted mean difference [WMD]: 0.20 mmol/L; 95% CI: 0.09, 0.30, p < 0.001) and significant heterogeneity between studies (I² = 98.6%, p < 0.001), which was largely related to gender and body mass index (BMI). Subgroup analysis in TAC identified a significant relationship except with low dose supplementation and obese individuals. No relationship between MDA and green tea supplementation was observed in any subgroups; however, meta-regression analysis revealed a linear inverse association between the dosage and significant change in MDA (r = −2117.18, p = 0.017). Our outcomes suggest that green tea supplementation improves TAC and affects MDA based on the dose of the intervention in adults. Future RCTs with longer durations are needed to expand our findings.

Epigallocatechin gallate protects the human lens epithelial cell survival against UVB irradiation through AIF/endo G signalling pathways in vitro

OBJECTIVE

Oxidative stress has been recognised as an important mediator of apoptosis in lens epithelial cells. It also plays an important role in the pathogenesis of cataracts. It is reported that (-)-Epigallocatechin gallate (EGCG), the most abundant component in green tea, exhibits potent antioxidant activity against oxidative stress. This study aimed to investigate the protective effect of EGCG against Ultraviolet B (UVB) induced apoptotic death and the underlying mechanism in human lens epithelial cells (HLECs).

METHODS

HLECs were exposed to various concentrations of EGCG under UVB (30 mJ/cm²), and cell viability was monitored by the MTT assay. Next, mitochondrial membrane potential (Δψm), reactive oxygen species (ROS) and apoptosis were detected by flow cytometry. Meanwhile, the total antioxigenic capacity (T-AOC) was determined by enzyme standard instrument, and the expression of apoptosis inducing factor (AIF) and endonuclease G (Endo G) was measured by quantitative PCR (Q-PCR) and western blotting, respectively. Moreover, the localisation of AIF and Endo G within cells was further detected by confocal optical microscopy.

RESULTS

The results indicated that EGCG could enhance the cell viability and protect against cell apoptosis caused by UVB irradiation in HLECs. EGCG could also decrease the UVB-induced generation of ROS and collapse of Δψm, increase the T-AOC level. In addition, EGCG could also inhibit the UVB-stimulated increase of AIF and Endo G expression at mRNA and protein levels and ameliorate the UVB-induced mitochondria-nuclear translocation of AIF and Endo G.

CONCLUSIONS

UVB irradiation could damage HLECs viability, while EGCG exhibits antioxidant effect and inhibits UVB-induced apoptosis in HLECs through AIF/Endo G signalling pathways. Our findings reveal the underlying mechanism of EGCG against UVB-induced oxidative stress in HLECs.

Antimicrobial evaluation of myricetin derivatives containing benzimidazole skeleton against plant pathogens

A series of novel myricetin derivatives containing benzimidazole skeleton were constructed. The structure of compound 4g was further corroborated via X-ray single crystal diffractometer. The antimicrobial bioassays showed that all compounds exhibited potent inhibitory activities against Xanthomonas axonopodis pv. Citri (Xac), Ralstonia solanacearum (Rs) and Xanthomonas oryzae pv. Oryzae (Xoo) in vitro. Significantly, compound 4q showed the best inhibitory activities against Xoo, with the EC₅₀ value of 8.2 μg/mL, which was better than thiodiazole copper (83.1 μg/mL) and bismerthiazol (60.1 μg/mL). In vivo experimental studies showed that compound 4q can treat rice bacterial leaf blight at 200 μg/mL, and the corresponding curative and protection efficiencies were 45.2 and 48.6%, respectively. Meanwhile, the antimicrobial mechanism of the compounds 4l and 4q were investigated through scanning electron microscopy (SEM). Studies showed that compounds 4l or 4q can cause deformation or rupture of Rs or Xoo cell membrane. These results indicated that novel benzimidazole-containing myricetin derivatives can be used as a potential antibacterial reagent.

Multiple signaling pathways converge on proapoptotic protein BAD to promote survival of melanocytes

Melanocyte survival is mediated by diverse signaling pathways. However, the molecular mechanisms they use and molecules that they target are incompletely understood. Here, we show that melanocyte survival is mediated by diverse, nonredundant signaling pathways, including ERK1/2, AKT, PKA, and PKC. Each of these pathways is exerting prosurvival effects by phosphorylating the BAD. While Ser112-BAD phosphorylation is regulated by pERK, pPKA and pPKC, Ser136 and Ser155 phosphorylation are exclusively controlled by pAKT and pPKA, respectively. Inhibition of these pathways individually resulted in only modest apoptosis; however, most significant apoptosis, as a result of BAD dephosphorylation, was seen when all pathways were inhibited concurrently. BAD phosphorylation was essential for survival of melanocytes as cells expressing phosphorylation-deficient BAD were not rescued by any of the identified pathway. Furthermore, melanocytes became insensitive to kinase inhibitor-induced apoptosis when BAD expression was knocked down by BAD-shRNA. Overexpression of BAD in melanocytes stimulated faster apoptosis in response to kinase inhibitors. Taken together, our results show that BAD is acting as a convergence point for diverse survival pathways in melanocytes. Understanding the molecular mechanisms of melanocyte survival provides fundamental new insights into physiological mechanisms involved in the development of various melanocyte pathologies such as melanoma and vitiligo.

Flavonoids as Epigenetic Modulators for Prostate Cancer Prevention

Prostate cancer (PCa) is a multifactorial disease with an unclear etiology. Due to its high prevalence, long latency, and slow progression, PCa is an ideal target for chemoprevention strategies. Many research studies have highlighted the positive effects of natural flavonoids on chronic diseases, including PCa. Different classes of dietary flavonoids exhibit anti-oxidative, anti-inflammatory, anti-mutagenic, anti-aging, cardioprotective, anti-viral/bacterial and anti-carcinogenic properties. We overviewed the most recent evidence of the antitumoral effects exerted by dietary flavonoids, with a special focus on their epigenetic action in PCa. Epigenetic alterations have been identified as key initiating events in several kinds of cancer. Many dietary flavonoids have been found to reverse DNA aberrations that promote neoplastic transformation, particularly for PCa. The epigenetic targets of the actions of flavonoids include oncogenes and tumor suppressor genes, indirectly controlled through the regulation of epigenetic enzymes such as DNA methyltransferase (DNMT), histone acetyltransferase (HAT), and histone deacetylase (HDAC). In addition, flavonoids were found capable of restoring miRNA and lncRNA expression that is altered during diseases. The optimization of the use of flavonoids as natural epigenetic modulators for chemoprevention and as a possible treatment of PCa and other kinds of cancers could represent a promising and valid strategy to inhibit carcinogenesis and fight cancer.

Anti-tumor effects and associated molecular mechanisms of myricetin

Myricetin (3, 5, 7, 3', 4', 5'-hexahydroxyflavone) is a natural flavonol compound found in a large variety of plants, including berries, oranges, grapes, herbs, teas, and wine. In the last decade, a convergence of evidence has demonstrated that myricetin has good biological activity as an anti-tumor, anti-inflammatory, and anti-oxidation agent. In studies involving various types of cancer cells, myricetin has been shown to suppress cancer cell invasion and metastasis, to induce cell cycle arrest and apoptosis of cancer cells, and to inhibit their proliferation. These findings have raised interest in myricetin as a potential tumor inhibitor in human patients. In this review, evidence of myricetin's anti-tumor activity and its underlying molecular mechanisms published in the last decade are summarized.

Myricetin Suppresses the Propagation of Hepatocellular Carcinoma via Down-Regulating Expression of YAP

Myricetin is a naturally occurring flavonoid with protective effects against a variety of cancers. However, the molecular mechanism of myricetin against hepatocellular carcinoma (HCC) has still not been fully elucidated. Previous studies have indicated that YAP is essential for cancer initiation and progression. However, whether YAP contributes to the anti-cancer effects of myricetin remains unclear. Herein, we aimed to investigate the effect of myricetin on HCC, and identify the underlying mechanisms. We report that myricetin induced apoptosis and proliferation inhibition in HepG2 and Huh-7 cells. Myricetin inhibited expression of YAP by promoting its phosphorylation and subsequent degradation. Myricetin inhibited YAP expression by stimulating kinase activation of LATS1/2. Knockdown expression of LATS1/2 by shRNA attenuated myricetin-induced phosphorylation and degradation of YAP. Furthermore, myricetin sensitized HCC cells to cisplatin treatment through inhibiting YAP and its target genes, both in vitro and in vivo. The identification of the LATS1/2-YAP pathway as a target of myricetin may help with the design of novel strategies for human HCC prevention and therapy.

Inhibition of suilysin activity and inflammation by myricetin attenuates Streptococcus suis virulence

Streptococcus suis (S. suis) is a gram-positive, zoonotic pathogenic bacterium that poses a serious threat to the pig industry and human health. This globally distributed pathogen can cause multiple diseases and fatal infections in both humans and animals. Suilysin (SLY) is an important extracellular secreted toxin regarded as an essential S. suis capsular type 2 (SS2) virulence factor and plays a key role in the infection and cytotoxicity of SS2. In addition, an excessive inflammatory response is also a serious hazard caused by SS2 infection. In this study, we demonstrated that the natural compound myricetin can inhibit the hemolytic activity of SLY and is effective at reducing the production of the inflammatory cytokines TNF-α and IL-1β and reducing inflammation by downregulating the activation of P38. In addition, myricetin could effectively treat SS2 infections in vitro and in vivo. These findings may aid in the development of promising therapeutic candidates for treating SS2 infections.

Protective effects of anthocyanin against apoptosis and oxidative stress induced by arsanilic acid in DF-1 cells

Anthocyanin is a natural plant pigment that acts as an antioxidant and scavenges free radicals. This study aimed to investigate the potential protective role of nightshade anthocyanin (NA), a natural flavonoid compound, against the arsanilic acid (ASA)-induced cell death of DF-1 cells. DF-1 cells were initially exposed to ASA, and then NA was applied to the treated cells. Cell viability, intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and apoptosis were examined. Results showed that NA inhibited the ASA-induced decrease in cell viability, increase in ROS, and loss of MMP in DF-1 cells. Moreover, caspase-3 activation was inhibited by ASA supplementation and NA attenuated the ASA-induced increase in the percentage of apoptotic cells. In summary, our study suggested that NA can enhance ASA-induced cytotoxicity and apoptosis, thereby providing a basis for the molecular mechanisms of NA-mediated protection.

Flavonoids in Cancer and Apoptosis

Cancer is the second leading cause of death globally. Although, there are many different approaches to cancer treatment, they are often painful due to adverse side effects and are sometimes ineffective due to increasing resistance to classical anti-cancer drugs or radiation therapy. Targeting delayed/inhibited apoptosis is a major approach in cancer treatment and a highly active area of research. Plant derived natural compounds are of major interest due to their high bioavailability, safety, minimal side effects and, most importantly, cost effectiveness. Flavonoids have gained importance as anti-cancer agents and have shown great potential as cytotoxic anti-cancer agents promoting apoptosis in cancer cells. In this review, a summary of flavonoids and their effectiveness in cancer treatment targeting apoptosis has been discussed.

The protective effect of some Thai plants and their bioactive compounds in UV light-induced skin carcinogenesis

Skin cancer, represents a major public health concern. While the vast majority is non-melanoma skin cancers, melanomas are mostly responsible for mortality. Solar UVB radiation is mutagenic and carcinogenic. It is primarily responsible for both non-melanoma and melanoma skin cancers via excessive production of reactive oxygen species (ROS), which mediate changes in inflammation and immunity, and have been implicated in all three stages of skin cancer development. Due to their regulatory role in numerous functions of cells, signaling pathways are targets for chemoprevention. The current standards in melanoma therapy are targeted and combination therapies, which, albeit prolong survival responses, are still prone to development of drug resistance. To this extent, drugs of natural origin continue to spark great interest. Thailand has a rich biodiversity of indigenous flora, which have traditionally been used to treat a variety of pathologies. The active components in plant extracts that have medicinal properties, termed 'bioactive compounds,' are efficient chemopreventive agents due to their antioxidant, antimutagenic, anticarcinogenic, and carcinogen detoxification properties. Thai plants and their bioactive compounds have shown protective effects on UV light-induced skin cancer in different experimental models. This warrants further in vivo investigations and translation to clinical studies to determine efficacy and safety, for use as lead compounds in targeted/combination therapy or adjuvant therapy with existing regimes. Coupled with a strategy for prevention, this offers a promising outlook for protection against photocarcinogenesis.

Myricetin Inhibits Angiogenesis by Inducing Apoptosis and Suppressing PI3K/Akt/mTOR Signaling in Endothelial Cells

Background

Myricetin has been shown to possess potential antiangiogenic effects in endothelial cells. However, the underlying mechanisms are not fully understood. Therefore, we evaluated its antiangiogenic effects in human umbilical vascular endothelial cells (HUVECs).

Methods

HUVECs were cultured in endothelial cell growth medium-2 to induce proliferation and angiogenesis and treated with different doses of myricetin (0.25, 0.5, and 1 μM) for 24 hours. Cell proliferation was analyzed by the MTT and lactate dehydrogenase release assays; angiogenesis was determined by the tube formation assay. In addition, cell signaling pathways related to angiogenesis were investigated by Western blotting.

Results

Myricetin induced apoptosis and procaspase-3 cleavage though the induction of reactive oxygen species (ROS). It significantly inhibited cell migration, tube formation, and PI3K/Akt/mTOR signaling in HUVECs.

Conclusions

Myricetin exerts antiangiogenic effects by inducing ROS-mediated apoptosis and inhibiting PI3K/Akt/mTOR signaling in HUVECs.

The role of lipid raft translocation of prohibitin in regulation of Akt and Raf-protected apoptosis of HaCaT cells upon ultraviolet B irradiation

Prohibitin (PHB) plays a role in regulation of ultraviolet B light (UVB)-induced apoptosis of human keratinocytes, HaCaT cells. The regulatory function of PHB appears to be associated with its lipid raft translocation. However, the detailed mechanism for PHB-mediated apoptosis of these keratinocytes upon UVB irradiation is not clear. In this report, we determined the role of lipid raft translocation of PHB in regulation of UVB-induced apoptosis. Our data show that upon UVB irradiation PHB is translocated from the non-raft membrane to the lipid rafts, which is correlated with a release of both Akt and Raf from membrane. Overexpression of Akt and/or Raf impedes UVB-induced lipid raft translocation of PHB. Immunoprecipitation analysis indicates that UVB alters the interactions among PHB, Akt, and Raf. Reduced expression of PHB leads to a decreased phosphorylation of Akt and ERK, as well as a decreased activity of Akt, and increased apoptosis of the cells upon UVB irradiation. These results suggest that PHB regulates UVB-induced apoptosis of keratinocytes via a mechanism that involves detachment from Akt and Raf on the plasma membrane, and sequential lipid raft translocation.

Development of a pharmaceutical cocrystal with solution crystallization technology: Preparation, characterization, and evaluation of myricetin-proline cocrystals

Myricetin shows low oral bioavailability (<10%) in rats due to poor aqueous solubility, although it has demonstrated various pharmacological activities such as those related to anticancer, anti-diabetes, and hepatic protection. To overcome this issue, in this study, pharmaceutical cocrystals were designed to efficiently deliver myricetin by oral administration. A 1:2 stoichiometric cocrystal of myricetin with proline was prepared successfully by solution crystallization based on the ternary phase diagram (TPD) principle, and it is presented as a new sphericity-like crystalline phase characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). The formation of myricetin-proline cocrystals was a spontaneous and exothermic process, probably due to the supramolecular interactions between themselves, which were determined by Fourier transform-infrared spectroscopy (FT-IR). Consequently, the dissolution efficiency of myricetin from cocrystals was increased 7.69-fold compared with that of coarse myricetin, and the oral bioavailability of myricetin cocrystals in rats was enhanced by approximately 3.03 times compared with that of pure myricetin. The present study provides useful information for the potential application of cocrystal technology for water-insoluble drugs, especially flavonoid compounds.

Myricetin: A Dietary Molecule with Diverse Biological Activities

Myricetin is a common plant-derived flavonoid and is well recognised for its nutraceuticals value. It is one of the key ingredients of various foods and beverages. The compound exhibits a wide range of activities that include strong anti-oxidant, anticancer, antidiabetic and anti-inflammatory activities. It displays several activities that are related to the central nervous system and numerous studies have suggested that the compound may be beneficial to protect against diseases such as Parkinson's and Alzheimer's. The use of myricetin as a preserving agent to extend the shelf life of foods containing oils and fats is attributed to the compound's ability to protect lipids against oxidation. A detailed search of existing literature revealed that there is currently no comprehensive review available on this important molecule. Hence, the present work includes the history, synthesis, pharmaceutical applications and toxicity studies of myricetin. This report also highlights structure-activity relationships and mechanisms of action for various biological activities.

Anticancer effect of SZC017, a novel derivative of oleanolic acid, on human gastric cancer cells

Oleanolic acid (OA) and its several derivatives possess chemopreventive and chemotherapeutic functions against a series of cancer types. Many chemotherapeutic compounds are effective in improving the quality of life and prolonging the survival of patients with gastric cancer, therefore progress in the treatment of gastric cancer, especially the anticancer effects of OA derivatives must be achieved. The inhibitory effect of SZC017, a newly synthesized derivative of OA, on cell viability was determined by MTT assay. Furthermore, flow cytometry, transmission electron microscopy, and western blot analysis revealed that the inhibition of cell viability by OA was mediated by triggering the intrinsic apoptosis of gastric cancer cells, and inducing S phase arrest of SGC7901 cells. Mechanistically, SZC017 was effective against gastric cancer cells via inhibiting Akt/NF‑κB signaling and topoisomerase I and IIα proteins. Taken together, our data indicate that SZC017 may be a potential chemotherapeutic agent against gastric cancer cells.

SZC017, a novel oleanolic acid derivative, induces apoptosis and autophagy in human breast cancer cells

Oleanolic acid (OA) and its derivatives such as 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO), CDDO-Me, and CDDO-Im show potent anticancer function. In this study, we elucidated the anticancer effect of SZC017, a novel OA derivative and identified the mechanisms by which SZC017 induces MCF-7 cell death. We found that SZC017 effectively decreased the cell viability of these breast cancer cells, but was less toxic to MCF10A mammary epithelial cells. Mechanisms underlying the inhibition of cell viability are apoptosis, autophagy induction, and G0/G1 phase arrest. SZC017 treatment suppressed the levels of Akt, phosphorylated-Akt (p-Akt), p-IκBα, total p65, and total p-p65, in addition to p-p65 in both the cytoplasm and nucleus. Furthermore, the inhibition of p65 nuclear translocation was confirmed by immunofluorescence staining. Cell viability was increased after pretreatment with chloroquine, an inhibitor of autophagy, whereas the level of procaspase-3 was significantly decreased. A concentration-dependent increase in the intracellular reactive oxygen species (ROS) level was observed in both MCF-7 and MDA-MB-231 cells. Additionally, pretreatment with N-acetyl-L-cysteine (NAC), a ROS scavenger, increased cell viability and the expression of Akt and procaspase-3, but decreased the ratio of LC3-II/I. These data show that SZC017 is an effectively selective anticancer agent against breast cancer cells, highlighting the potential use of this derivative as a breast cancer therapeutic agent.

Molecular mechanisms underlying anticancer effects of myricetin

Dietary guidelines published in the past two decades have acknowledged the beneficial effects of myricetin, an important and common type of herbal flavonoid, against several human diseases such as inflammation, cardiovascular pathologies, and cancer. An increasing number of studies have shown the beneficial effects of myricetin against different types of cancer by modifying several cancer hallmarks including aberrant cell proliferation, signaling pathways, apoptosis, angiogenesis, and tumor metastasis. Most importantly, myricetin interacts with oncoproteins such as protein kinase B (PKB) (Akt), Fyn, MEK1, and JAK1-STAT3 (Janus kinase-signal transducer and activator of transcription 3), and it attenuates the neoplastic transformation of cancer cells. In addition, myricetin exerts antimitotic effects by targeting the overexpression of cyclin-dependent kinase 1 (CDK1) in liver cancer. Moreover, it also targets the mitochondria and promotes different kinds of cell death in various cancer cells. In the present paper, a critical review of the available literature is presented to identify the molecular targets underlying the anticancer effects of myricetin.

The Protecting Effect of Deoxyschisandrin and Schisandrin B on HaCaT Cells against UVB-Induced Damage

Schisandra chinensis is a traditional Chinese medicine that has multiple biological activities, including antioxidant, anticancer, tonic, and anti-aging effects. Deoxyschisandrin (SA) and schisandrin B (SB), the two major lignans isolated from S. chinensis, exert high antioxidant activities in vitro and in vivo by scavenging free radicals, such as reactive oxygen species (ROS). Ultraviolet B-ray (UVB) radiation induces the production of ROS and DNA damage, which eventually leads to cell death by apoptosis. However, it is unknown whether SA or SB protects cells against UVB-induced cellular DNA damage. Our study showed that both SA and SB effectively protected HaCaT cells from UVB-induced cell death by antagonizing UVB-mediated production of ROS and induction of DNA damage. Our results showed that both SA and SB significantly prevented UVB-induced loss of cell viability using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assays. Dichloro-dihydro-fluorescein diacetate (DCFH-DA) assays showed that the production of ROS following UVB exposure was inhibited by treatment with SA and SB. Moreover, SA and SB decreased the UVB-induced DNA damage in HaCaT cells by comet assays. In addition, SA and SB also prevented UVB-induced cell apoptosis and the cleavage of caspase-3, caspase-8 and caspase-9. In a word, our results imply that the antioxidants SA and SB could protect cells from UVB-induced cell damage via scavenging ROS.

Myricetin suppresses lipoteichoic acid-induced interleukin-1β and cyclooxygenase-2 expression in human gingival fibroblasts

Periodontitis is an inflammatory disease affecting the connective tissue and supporting bone surrounding the teeth. In periodontitis, human gingival fibroblasts (HGFs) synthesize IL-1β, causing a progressive inflammatory response. Flavones demonstrate a variety of biological activity: among others, they possess anti-inflammatory properties. Myricetin is a flavone with a strong anti-inflammatory activity. The objective of this study was to evaluate the effect of the flavonoid myricetin on HGFs under inflammatory conditions induced by lipoteichoic acid (LTA). the effect of myricetin on HGFs was assessed by measuring cell viability, signaling pathways and IL-1β expression and synthesis. It was found that, over time, myricetin did not affect cell viability. However, it inhibited activation of p38 and extracellular-signal-regulated kinase-1/2 in LTA-treated HGFs and also blocked IκB degradation and cyclooxygenase-2 and prostaglandin E2 synthesis and expression. These findings suggest that myricetin has therapeutic effects in the form of controlling LTA-induced inflammatory responses.

New Enlightenment of Skin Cancer Chemoprevention through Phytochemicals: In Vitro and In Vivo Studies and the Underlying Mechanisms

Skin cancer is still a major cause of morbidity and mortality worldwide. Skin overexposure to ultraviolet irradiations, chemicals, and several viruses has a capability to cause severe skin-related disorders including immunosuppression and skin cancer. These factors act in sequence at various steps of skin carcinogenesis via initiation, promotion, and/or progression. These days cancer chemoprevention is recognized as the most hopeful and novel approach to prevent, inhibit, or reverse the processes of carcinogenesis by intervention with natural products. Phytochemicals have antioxidant, antimutagenic, anticarcinogenic, and carcinogen detoxification capabilities thereby considered as efficient chemopreventive agents. Considerable efforts have been done to identify the phytochemicals which may possibly act on one or several molecular targets that modulate cellular processes such as inflammation, immunity, cell cycle progression, and apoptosis. Till date several phytochemicals in the light of chemoprevention have been studied by using suitable skin carcinogenic in vitro and in vivo models and proven as beneficial for prevention of skin cancer. This revision presents a comprehensive knowledge and the main molecular mechanisms of actions of various phytochemicals in the chemoprevention of skin cancer.

Curcumin-loaded nanoparticles enhance apoptotic cell death of U2OS human osteosarcoma cells through the Akt-Bad signaling pathway

Curcumin has potential anticancer activity and has been shown to be involved in several signaling pathways including differentiation and apoptosis. Our previous study showed that water-soluble PLGA curcumin nanoparticles (Cur-NPs) triggered apoptotic cell death through regulation of the function of MDR1 and the production of reactive oxygen species (ROS) in cisplatin-resistant human oral cancer CAR cells. In this study, we investigated the anti-proliferative effects of Cur-NPs on human osteosarcoma U2OS cells. The morphology of Cur-NPs showed spherical shape by TEM analysis. The encapsulation efficiency of curcumin in Cur-NPs prepared by single emulsion was 90.5 ± 3.0%. Our results demonstrated that the curcumin fragments on the mass spectrum of Cur-NPs and the peaks of curcumin standard could be found on the Cur-NPs spectrum by 1H-NMR spectra analysis. Cur-NPs induced anti-proliferative effects and apoptosis in U2OS cells. Compared to the untreated U2OS cells, more detectable amount of Cur-NPs was found inside the treated U2OS cells. Cur-NPs induced DNA fragmentation and apoptotic bodies in U2OS cells. Both the activity and the expression levels of caspases-3/-7 and caspase-9 were elevated in the treated U2OS cells. Cur-NPs upregulated the protein expression levels of cleaved caspase-3/caspase-9, cytochrome c, Apaf-1 and Bad and downregulated the protein expression level of p-Akt in U2OS cells. These results suggest Cur-NPs are effective in enhancing apoptosis in human osteosarcoma cells and thus could provide potential for cancer therapeutics.

Antiproliferative and apoptotic effects of spanish honeys

Background:

Current evidence supports that consumption of polyphenols has beneficial effects against numerous diseases mostly associated with their antioxidant activity. Honey is a good source of antioxidants since it contains a great variety of phenolic compounds.

Objective:

The main objective of this work was to investigate the antiproliferative and apoptotic effects of three crude commercial honeys of different floral origin (heather, rosemary and polyfloral honey) from Madrid Autonomic Community (Spain) as well as of an artificial honey in human peripheral blood promyelocytic leukemia cells (HL-60).

Material and Methods:

HL-60 cells were cultured in the presence of honeys at various concentrations for up to 72 hours and the percentage of cell viability was evaluated by MTT assay. Apoptotic cells were identified by chromatin condensation and flow cytometry analysis. ROS production was determined using 2´,7´-dichlorodihydrofluorescein diacetate (H₂DCFDA).

Results:

The three types of crude commercial honey induced apoptosis in a concentration and time dependent-manner. In addition, honeys with the higher phenolic content, heather and polyfloral, were the most effective to induce apoptosis in HL-60 cells. However, honeys did not generate reactive oxygen species (ROS) and N-acetyl-L-cysteine (NAC) could not block honeys-induced apoptosis in HL-60 cells.

Conclusion:

These data support that honeys induced apoptosis in HL-60 cells through a ROS-independent cell death pathway. Moreover, our findings indicate that the antiproliferative and apoptotic effects of honey varied according to the floral origin and the phenolic content.

Rhamnetin and cirsiliol induce radiosensitization and inhibition of epithelial-mesenchymal transition (EMT) by miR-34a-mediated suppression of Notch-1 expression in non-small cell lung cancer cell lines

Radioresistance is a major cause of decreasing the efficiency of radiotherapy for non-small cell lung cancer (NSCLC). To understand the radioresistance mechanisms in NSCLC, we focused on the radiation-induced Notch-1 signaling pathway involved in critical cell fate decisions by modulating cell proliferation. In this study, we investigated the use of Notch-1-regulating flavonoid compounds as novel therapeutic drugs to regulate radiosensitivity in NSCLC cells, NCI-H1299 and NCI-H460, with different levels of radioresistance. Rhamnetin and cirsiliol were selected as candidate Notch-1-regulating radiosensitizers based on the results of assay screening for activity and pharmacological properties. Treatment with rhamnetin or cirsiliol reduced the proliferation of NSCLC cells through the suppression of radiation-induced Notch-1 expression. Indeed, rhamnetin and cirsiliol increased the expression of tumor-suppressive microRNA, miR-34a, in a p53-dependent manner, leading to inhibition of Notch-1 expression. Consequently, reduced Notch-1 expression promoted apoptosis through significant down-regulation of the nuclear factor-κB pathway, resulting in a radiosensitizing effect on NSCLC cells. Irradiation-induced epithelial-mesenchymal transition was also notably attenuated in the presence of rhamnetin and cirsiliol. Moreover, an in vivo xenograft mouse model confirmed the radiosensitizing and epithelial-mesenchymal transition inhibition effects of rhamnetin and cirsiliol we observed in vitro. In these mice, tumor volume was significantly reduced by combinational treatment with irradiation and rhamnetin or cirsiliol compared with irradiation alone. Taken together, our findings provided evidence that rhamnetin and cirsiliol can act as promising radiosensitizers that enhance the radiotherapeutic efficacy by inhibiting radiation-induced Notch-1 signaling associated with radioresistance possibly via miR-34a-mediated pathways.

Identification of quercitrin as an inhibitor of the p90 S6 ribosomal kinase (RSK): structure of its complex with the N-terminal domain of RSK2 at 1.8 Å resolution

Members of the RSK family of kinases constitute attractive targets for drug design, but a lack of structural information regarding the mechanism of selective inhibitors impedes progress in this field. The crystal structure of the N-terminal kinase domain (residues 45-346) of mouse RSK2, or RSK2(NTKD), has recently been described in complex with one of only two known selective inhibitors, a rare naturally occurring flavonol glycoside, kaempferol 3-O-(3'',4''-di-O-acetyl-α-L-rhamnopyranoside), known as SL0101. Based on this structure, it was hypothesized that quercitrin (quercetin 3-O-α-L-rhamnopyranoside), a related but ubiquitous and inexpensive compound, might also act as an RSK inhibitor. Here, it is demonstrated that quercitrin binds to RSK2(NTKD) with a dissociation constant (K(d)) of 5.8 µM as determined by isothermal titration calorimetry, and a crystal structure of the binary complex at 1.8 Å resolution is reported. The crystal structure reveals a very similar mode of binding to that recently reported for SL0101. Closer inspection shows a number of small but significant differences that explain the slightly higher K(d) for quercitrin compared with SL0101. It is also shown that quercitrin can effectively substitute for SL0101 in a biological assay, in which it significantly suppresses the contractile force in rabbit pulmonary artery smooth muscle in response to Ca(2+).

PIM1 kinase inhibitors induce radiosensitization in non-small cell lung cancer cells

Radiotherapy plays a critical role in the treatment of non-small cell lung cancer (NSCLC). However, radioresistance is a major barrier against increasing the efficiency of radiotherapy for NSCLC. To understand the mechanisms underlying NSCLC radioresistance, we previously focused on the potential involvement of PIM1, PRAS40, FOXO3a, 14-3-3, and protein phosphatases. Among these proteins, PIM1 functioned as an oncogene and was found to act as a crucial mediator in radioresistant NSCLC cells. Therefore, we investigated the use of PIM1-specific inhibitors as novel therapeutic drugs to regulate radiosensitivity in NSCLC. After structure-based drug selection, SGI-1776, ETP-45299, and tryptanthrin were selected as candidates of PIM1 inhibitors that act as radiosensitizers. With irradiation, these drugs inhibited only PIM1 kinase activity without affecting PIM1 mRNA/protein levels or cellular localization. When PIM1 kinase activity was suppressed by these inhibitors, PRAS40 was not phosphorylated. Consequently, unphosphorylated PRAS40 did not form trimeric complexes with 14-3-3 and FOXO3a, leading to increased nuclear localization of FOXO3a. Nuclear FOXO3a promoted the expression of pro-apoptotic proteins such as Bim and FasL, resulting in a radiosensitizing effect on radioresistant NSCLC cells. Moreover, an in vivo xenograft mouse model confirmed this radiosensitizing effect induced by PIM1 inhibitors. In these model systems, tumor volume was significantly reduced by a combinational treatment with irradiation and PIM1 inhibitors compared to irradiation alone. Taken together, our findings provided evidence that PIM1-specific inhibitors, SGI-1776, ETP-45299, and tryptanthrin, can act as novel radiosensitizers to enhance the efficacy of radiotherapy by inhibiting irradiation-induced signaling pathway associated with radioresistance.

Myricetin attenuates lipopolysaccharide-stimulated activation of mouse bone marrow-derived dendritic cells through suppression of IKK/NF-κB and MAPK signalling pathways

BACKGROUND

Myricetin is a naturally occurring flavonoid that is found in many fruits, vegetables, teas and medicinal herbs. It has been demonstrated to have anti-inflammatory properties, but, to date, no studies have described the immunomodulatory effects of myricetin on the functions of dendritic cells (DCs). The aim of this study was to evaluate the potential for myricetin to modulate lipopolysaccharide (LPS)-stimulated activation of mouse bone marrow-derived DCs.

RESULTS

Our experimental data showed that treatment with myricetin up to 10 µg mL(-1) does not cause cytotoxicity in cells. Myricetin significantly decreased the secretion of tumour necrosis factor-α, interleukin-6 and interleukin-12p70 by LPS-stimulated DCs. The expression of LPS-induced major histocompatibility class II, CD40 and CD86 on DCs was also inhibited by myricetin, and the endocytic and migratory capacity of LPS-stimulated DCs was blocked by myricentin. In addition, LPS-stimulated DC-elicited allogeneic T-cell proliferation was reduced by myricetin. Moreover, our results confirmed that myricetin attenuates the responses of LPS-stimulated activation of DCs via suppression of IκB kinase/nuclear factor-κB and mitogen-activated protein kinase-dependent pathways.

CONCLUSION

Myricetin has novel immunopharmacological activity, and modulation of DCs by myricetin may be an attractive strategy for the treatment of inflammatory and autoimmune disorders, and for transplantation.

Insights into the inhibition of the p90 ribosomal S6 kinase (RSK) by the flavonol glycoside SL0101 from the 1.5 Å crystal structure of the N-terminal domain of RSK2 with bound inhibitor

The p90 ribosomal S6 family of kinases (RSK) are potential drug targets, due to their involvement in cancer and other pathologies. There are currently only two known selective inhibitors of RSK, but the basis for selectivity is not known. One of these inhibitors is a naturally occurring kaempferol-α-L-diacetylrhamnoside, SL0101. Here, we report the crystal structure of the complex of the N-terminal kinase domain of the RSK2 isoform with SL0101 at 1.5 Å resolution. The refined atomic model reveals unprecedented structural reorganization of the protein moiety, as compared to the nucleotide-bound form. The entire N-lobe, the hinge region, and the αD-helix undergo dramatic conformational changes resulting in a rearrangement of the nucleotide binding site with concomitant formation of a highly hydrophobic pocket spatially suited to accommodate SL0101. These unexpected results will be invaluable in further optimization of the SL0101 scaffold as a promising lead for a novel class of kinase inhibitors.

The UVA and aqueous stability of flavonoids is dependent on B-ring substitution

Flavonols such as kaempferol and quercetin are believed to provide protection against ultraviolet (UV)-induced damage to plants. Recent in vitro studies have examined the ability of flavonols to protect against UV-induced damage to mammalian cells. Stability of flavonols in cell culture media, however, has been problematic, especially for quercetin, one of the most widely studied flavonols. As part of our investigations into the potential for flavonols to protect skin against UV-induced damage, we have determined the stability of a series of flavonols that differ only in the number of substituents on the B-ring. We measured the stability of these flavonols over time to UVA radiation, Dulbecco's modified Eagle's medium (DMEM), and Dulbecco's phosphate-buffered saline (DPBS) using high performance liquid chromatography with UV detection (HPLC-UV). The identification of the breakdown products of flavonols was accomplished by using a hybrid quadrupole linear ion trap mass spectrometer coupled with liquid chromatography. Tandem mass spectrometric analysis (MS/MS) of flavonol photoproducts was confirmed by comparing with the known standard samples. We have determined that flavonol stability decreases with increasing B-ring substitution, suggesting that future investigation of potential photoprotective flavonols will need to be cognizant of this trend.

Linkage of cardiac gene expression profiles and ETS2 with lifespan variability in rats

Longevity variability is a common feature of aging in mammals, but the mechanisms responsible for this remain largely unknown. Using microarray datasets coupled with prediction analysis of microarrays (PAM), we identified a set of 252 cardiac transcripts predictive of relative lifespan in Wistar and Fisher 344 rats. Prediction analysis of microarrays 'tests' of rat heart transcriptomes from a third longer lived Fisher × Norway Brown rat strain validated the predictive value of this gene subset. The expression patterns of these genes were highly conserved, and corresponding promoter regions were employed to identify common cis-elements and trans-activating factors implicated in their control. Specifically, four transcription factors (Max, Ets2, Erg, and Msx2) present in heart displayed longevity-dependent, strain-independent changes in abundance, but only ETS2 had an expression profile that directly correlated with the relative lifespan gene set. In heart, ETS2 was prevalent in cardiomyocytes (CMs) and showed a high degree of myocyte-to-myocyte variability predominantly in adult rat hearts prior to the exponential increase in the rate of mortality. Exclusively in this group, elevated ETS2 significantly overlapped with TUNEL staining in heart myocytes. In response to sympathetic stimuli, ETS2 is also up-regulated, and functionally, adenovirus-mediated over-expression of ETS2 promotes apoptosis-inducing factor-mediated, caspase-independent programmed necrosis exclusively in CMs that can be fully inhibited by the PARP-1 inhibitor DPQ. We conclude that variations in ETS2 abundance in hearts of adult rodents and the associated loss of CMs contribute at least partially, to the longevity variability observed during normal aging of rats through activation of programmed necrosis.

Myricetin is a potent chemopreventive phytochemical in skin carcinogenesis

Myricetin is a widely distributed flavonol that is found in many plants, including tea, berries, fruits, vegetables, and medicinal herbs. Abundant sources provide interesting insights into the multiple mechanisms by which myricetin mediates chemopreventive effects on skin cancer. Myricetin strongly inhibited tumor promoter-induced neoplastic cell transformation by inhibiting MEK, JAK1, Akt, and MKK4 kinase activity directly. In a mouse skin model, myricetin attenuated the ultraviolet B (UVB)-induced COX-2 expression and skin tumor formation by regulating Fyn. Myricetin-mediated inactivation of Akt in the UVB response plays a role in regulating UVB-induced carcinogenesis. Recently, myricetin was found to inhibit UVB-induced angiogenesis by targeting PI3-K in an SKH-1 hairless mouse skin tumorigenesis model. Raf kinase is a critical target for myricetin in inhibiting the UVB-induced formation of wrinkles and suppression of type I procollagen and collagen levels in mouse skin. Accumulated data suggest that myricetin acts as a promising agent for the chemoprevention of skin cancer.

Selective apoptotic effects of piceatannol and myricetin in human cancer cells

Numerous studies have shown the potential of dietary polyphenols as anticarcinogenic agents. The aim of the present study was to evaluate the apoptotic effects of piceatannol and myricetin, naturally occurring polyphenols in red wine, alone or in combination, in two human cell lines: HL-60 (leukemia) and HepG2 (hepatoma). Apoptotic cells were identified by chromatin condensation, poly(ADP-ribose) polymerase cleavage and flow cytometry analysis. Results from TUNEL assay showed that piceatannol or myricetin alone induced apoptotic cell death in a concentration- and time-dependent manners in HL-60 cells. Furthermore, in combined treatment the percentage of apoptotic HL-60 cells was significantly higher. Nevertheless, the percentage of TUNEL positive HepG2 cells only was significant after piceatannol treatment and in combined treatment was even lower than in cells treated with piceatannol alone. Moreover, we also studied the relative reactive oxygen species (ROS) production. Our results indicate that apoptosis induced by piceatannol or myricetin occurs through an ROS-independent cell death pathway. In conclusion, piceatannol and myricetin synergistically induced apoptosis in HL-60 cells but not in HepG2 cells. These findings suggest that the potential anticarcinogenic properties of dietary polyphenols depend largely on the cell line used. The relevance of these data needs to be verified in human epidemiological studies.

PIM1-activated PRAS40 regulates radioresistance in non-small cell lung cancer cells through interplay with FOXO3a, 14-3-3 and protein phosphatases

Resistance of cancer cells to ionizing radiation plays an important role in the clinical setting of lung cancer treatment. To date, however, the exact molecular mechanism of radiosensitivity has not been well explained. In this study, we compared radioresistance in two types of non-small cell lung cancer (NSCLC) cells, NCI-H460 and A549, and investigated the signaling pathways that confer radioresistance. In radioresistant cells, exposure to radiation led to overexpression of PIM1 and reduction of protein phosphatases (PP2A and PP5), which induced translocation of PIM1 into the nucleus. Increased nuclear PIM1 phosphorylated PRAS40. Consequently, pPRAS40 made a trimeric complex with 14-3-3 and AKT-activated pFOXO3a, which then moved rapidly to the cytoplasm. Cytoplasmic retention of FOXO3a was associated with downregulation of proapoptotic genes and possibly radioresistance. On the other hand, no suppressive effect of radiation on protein phosphatases was detected and, concomitantly, protein phosphatases downregulated PIM1 in radiosensitive cells. In this setting, PIM1-activated pPRAS40, AKT-activated pFOXO3a, and their complex formation with 14-3-3 could be key regulators of the radiation-induced radioresistance in NSCLC cells.

Plant polyphenols differentially modulate inflammatory responses of human keratinocytes by interfering with activation of transcription factors NFκB and AhR and EGFR-ERK pathway

Molecular mechanisms underlying modulation of inflammatory responses in primary human keratinocytes by plant polyphenols (PPs), namely the glycosylated phenylpropanoid verbascoside, the stilbenoid resveratrol and its glycoside polydatin, and the flavonoid quercetin and its glycoside rutin were evaluated. As non-lethal stimuli, the prototypic ligand for epidermal growth factor receptor (EGFR) transforming growth factor alpha (TGFalpha), the combination of tumor necrosis factor (TNFalpha) and interferon (IFNgamma) (T/I), UVA+UVB irradiation, and bacterial lipopolysaccharide (LPS) were used. We demonstrated differential modulation of inflammatory responses in keratinocytes at signal transduction, gene transcription, and protein synthesis levels as a function of PP chemical structure, the pro-inflammatory trigger used, and PP interaction with intracellular detoxifying systems. The PPs remarkably inhibited constitutive, LPS- and T/I-induced but not TGFalpha-induced ERK phosphorylation. They also suppressed NFkappaB activation by LPS and T/I. Verbascoside and quercetin invariably impaired EGFR phosphorylation and UV-associated aryl hydrocarbon receptor (AhR)-mediated signaling, while rutin, polydatin and resveratrol did not affect EGFR phosphorylation and further activated AhR machinery in UV-exposed keratinocytes. In general, PPs down-regulated gene expression of pro-inflammatory cytokines/enzymes, except significant up-regulation of IL-8 observed under stimulation with TGFalpha. Both spontaneous and T/I-induced release of IL-8 and IP-10 was suppressed, although 50μM resveratrol and polydatin up-regulated IL-8. At this concentration, resveratrol activated both gene expression and de novo synthesis of IL-8 and AhR-mediated mechanisms were involved. We conclude that PPs differentially modulate the inflammatory response of human keratinocytes through distinct signal transduction pathways, including AhR and EGFR.