Inhibition of α-melanocyte-stimulating hormone-induced melanogenesis and molecular mechanisms by polyphenol-enriched fraction of Tagetes erecta L. flower.

BACKGROUND: The pursuit for safe and efficacious skin-whitening agents has prompted a dedicated exploration of plant-derived compounds. Notably, Tagetes erecta L. flowers have been used as a medicinal extract and possessed in vitro mushroom tyrosinase activity. However, whether polyphenol-enriched fraction extracted from T. erecta L. flowers (TE) regulates melanogenesis within cellular and animal models has not yet been investigated. PURPOSE: This study aimed to investigate the effect of TE as a prospective inhibitor of melanogenesis. METHODS: Through advanced UPLC-QTof/MS analysis, the components of TE were analyzed. Anti-melanogenic effects of TE were evaluated in α-melanocyte-stimulating hormone (α-MSH)-stimulated B16F10 melanoma cells by measuring cell viability assay, extracellular and intracellular melanin biosynthesis, cyclic adenosine monophosphate (cAMP) production, and melanogenesis-related gene and protein expression. Zebrafish larvae were employed for in vivo studies, assessing both heart rate and melanogenesis. Furthermore, molecular docking analyses were employed to predict the interaction between TE components and the melanocortin 1 receptor (MC1R). Direct binding activity of TE components to MC1R was compared with [Nle4, d-Phe7]-MSH (NDP-MSH). RESULTS: TE was found to contain significant phenolic compounds such as patulitrin, quercetagetin, kaempferol, patuletin, and isorhamnetin. This study revealed that TE effectively inhibits melanin biosynthesis in both in vitro and in vivo models. This inhibition was attributed to interference of TE with the cAMP-cAMP response element-binding protein (CREB)-microphthalmia-associated transcription factor (MITF)-tyrosinase pathway, which plays a pivotal role in regulating melanogenesis. Importantly, TE exhibited the remarkable ability to curtail α-MSH-induced melanogenesis in zebrafish larvae without impacting heart rates. Molecular docking analyses predicted that the components of TE possibly interact with the melanocortin 1 receptor, suggesting their role as potential inhibitors of melanin biosynthesis. However, through the direct binding activity compared with NDP-MSH, any TE components did not directly bind to MC1R, suggesting that TE inhibits α-MSH-induced melanogenesis by inhibiting the cAMP-mediated intracellular signaling pathway. The assessment of anti-melanogenic activity, conducted both in vitro and in vivo, revealed that patulitrin and patuletin exhibited significant inhibitory effects on melanin formation, highlighting their potency as major contributors. DISCUSSION: This investigation demonstrated the considerable potential of TE as a natural remedy endowed with remarkable anti-melanogenic properties. The demonstrated capacity of TE to attenuate melanin production by modulating the cAMP-CREB-MITF-tyrosinase pathway underscores its central role in management of disorders associated with excessive pigmentation. Importantly, the implications of these findings extend to the cosmetics industry, where TE emerges as a prospective and valuable ingredient for the formulation of skin-whitening products. The elucidated interactions between TE components and MC1R not only provide insight into a potential mechanism of action but also elevate the significance of this study. In summary, this study not only contributes to our comprehension of pigmentation-related conditions but also firmly establishes TE as a secure and natural strategy for the regulation of melanin production. The innovative aspects of TE propel it into the forefront of potential interventions, marking a noteworthy advancement in the pursuit of effective and safe solutions for pigmentation disorders.

Investigating rutin as a potential transforming growth factor-ß type I receptor antagonist for the inhibition of bleomycin-induced lung fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a chronic lung condition characterized by the abnormal regulation of extracellular matrix (ECM) and epithelial-mesenchymal transition (EMT). In this study, we investigated the potential of rutin, a natural flavonoid, in attenuating transforming growth factor-ß (TGF-ß)-induced ECM regulation and EMT through the inhibition of the TGF-ß type I receptor (TßRI)-mediated suppressor of mothers against decapentaplegic (SMAD) signaling pathway. We found that non-toxic concentrations of rutin attenuated TGF-ß-induced ECM-related genes, including fibronectin, elastin, collagen 1 type 1, and TGF-ß, as well as myoblast differentiation from MRC-5 lung fibroblast cells accompanied by the downregulation of α-smooth muscle actin. Rutin also inhibited TGF-ß-induced EMT processes, such as wound healing, migration, and invasion by regulating EMT-related gene expression. Additionally, rutin attenuated bleomycin-induced lung fibrosis in mice, thus providing a potential therapeutic option for IPF. The molecular docking analyses in this study predict that rutin occludes the active site of TßRI and inhibits SMAD-mediated fibrotic signaling pathways in lung fibrosis. These findings highlight the potential of rutin as a promising anti-fibrotic prodrug for lung fibrosis and other TGF-ß-induced fibrotic and cancer-related diseases; however, further studies are required to validate its safety and effectiveness in other experimental models.

Pinostrobin Suppresses the α-Melanocyte-Stimulating Hormone-Induced Melanogenic Signaling Pathway.

Pinostrobin is a dietary flavonoid found in several plants that possesses pharmacological properties, such as anti-cancer, anti-virus, antioxidant, anti-ulcer, and anti-aromatase effects. However, it is unclear if pinostrobin exerts anti-melanogenic properties and, if so, what the underlying molecular mechanisms comprise. Therefore, we, in this study, investigated whether pinostrobin inhibits melanin biosynthesis in vitro and in vivo, as well as the potential associated mechanism. Pinostrobin reduced mushroom tyrosinase activity in vitro in a concentration-dependent manner, with an IC50 of 700 µM. Molecular docking simulations further revealed that pinostrobin forms a hydrogen bond, as well as other non-covalent interactions, between the C-type lectin-like fold and polyphenol oxidase chain, rather than the previously known copper-containing catalytic center. Additionally, pinostrobin significantly decreased α-melanocyte-stimulating hormone (α-MSH)-induced extracellular and intracellular melanin production, as well as tyrosinase activity, in B16F10 melanoma cells. More specifically, pinostrobin inhibited the α-MSH-induced melanin biosynthesis signaling pathway by suppressing the cAMP-CREB-MITF axis. In fact, pinostrobin also attenuated pigmentation in α-MSH-stimulated zebrafish larvae without causing cardiotoxicity. The findings suggest that pinostrobin effectively inhibits melanogenesis in vitro and in vivo via regulation of the cAMP-CREB-MITF axis.

A non-polar fraction of Saponaria officinalis L. acted as a TLR4/MD2 complex antagonist and inhibited TLR4/MyD88 signaling in vitro and in vivo.

Targeting Toll-like receptor 4/myeloid differentiation factor 2 (TLR4/MD2) signaling is regarded as a potential strategy for treating inflammatory diseases. Saponaria officinalis L. is rich in saponin, which include quillaic acid, gypsogenin, saponarin, and hederagenin. We evaluated the pharmacological activity of a Saponaria officinalis extract in THP-1 derived macrophages and RAW264.7 macrophages. TLR4/MyD88 complex formation and downstream signals were investigated by co-immunoprecipitation (Co-IP). In silico docking simulation was conducted to predict binding scores and perform 3D modeling of saponarin-TLR4/MD2 complex. A hexane fraction of Saponaria officinalis (SH) and fr.1 (a sub-fraction 1 of SH) inhibited mitogen-activated protein kinase (MAPK) signaling, nuclear factor kappa b (NF-κB) activity, cytokine production, and the expressions of marker genes specific for M1 polarization. The inhibitory effects of fr.1 and saponarin on TLR4/MyD88 complex formation were observed by western blotting TLR4 co-immunoprecipitated proteins. Saponarin and fr.1 markedly attenuated LPS-induced inflammatory cytokines, thus reducing mortality and morphological abnormality in zebrafish larvae. Finally, docking simulation revealed that saponarin can directly interact with TLR4/MD2 complex to inhibit downstream signalings. Our findings suggest that saponarin reduces downstream inflammatory response by disrupting TLR4/MD2 complex and blocking MyD88-dependent inflammatory signaling.

Anthocyanin-enriched polyphenols from Hibiscus syriacus L. (Malvaceae) exert anti-osteoporosis effects by inhibiting GSK-3ß and subsequently activating ß-catenin.

BACKGROUND: The bark and petal of Hibiscus syriacus L. (Malvaceae) have been used to relieve pain in traditional Korean medicine. Recently, we identified anthocyanin-enriched polyphenols from the petal of H. syriacus L. (AHs) and determined its anti-melanogenic, anti-inflammatory, and anti-oxidative properties. Nevertheless, the osteogenic potential of AHs remains unknown. PURPOSE: This study was aimed to investigating the effect of AHs on osteoblast differentiation and osteogenesis in osteoblastic cell lines and zebrafish larvae. Furthermore, we investigated whether AHs ameliorates prednisolone (PDS)-induced osteoporosis. STUDY DESIGN AND METHODS: Cell viability was assessed by cellular morphology, MTT assay, and flow cytometry analysis, and osteoblast differentiation was measured alizarin red staining, alkaline phosphatase (ALP) activity, and osteoblast-specific marker expression. Osteogenic and anti-osteoporotic effects of AHs were determined in zebrafish larvae. RESULTS: AHs enhanced calcification and ALP activity concomitant with the increased expression of osterix (OSX), runt-related transcription factor 2 (RUNX2), and ALP in MC3T3-E1 preosteoblast and MG-63 osteosarcoma cells. Additionally, AHs accelerated vertebral formation and mineralization in zebrafish larvae, concurrent with the increased expression of OSX, RUNX2a, and ALP. Furthermore, PDS-induced loss of osteogenic activity and vertebral formation were restored by treatment with AHs, accompanied by a significant recovery of calcification, ALP activity, and osteogenic marker expression. Molecular docking studies showed that 16 components in AHs fit to glucagon synthase kinase-3ß (GSK-3ß); particularly, isovitexin-4'-O-glucoside most strongly binds to the peptide backbone of GSK-3ß at GLY47(O), GLY47(N), and ASN361(O), with a binding score of -7.3. Subsequently, AHs phosphorylated GSK-3ß at SER9 (an inactive form) and released ß-catenin into the nucleus. Pretreatment with FH535, a Wnt/ß-catenin inhibitor, significantly inhibited AH-induced vertebral formation in zebrafish larvae. CONCLUSION: AHs stimulate osteogenic activities through the inhibition of GSK-3ß and subsequent activation of ß-catenin, leading to anti-osteoporosis effects.

Protective Effect of Anthocyanin-Enriched Polyphenols from Hibiscus syriacus L. (Malvaceae) against Ultraviolet B-Induced Damage.

Anthocyanin-enriched polyphenols from the flower petals of H. syriacus L. (Malvaceae, AHs) possess anti-septic shock, anti-oxidant, and anti-melanogenic properties. However, whether AHs positively or negatively regulate ultraviolet B (UVB)-mediated photoaging and photodamage remains unclear. This study aims to investigate the protective effect of AHs against UVB-induced damage. We examined the photoprotective effects of AHs on UVB-induced apoptosis, endoplasmic reticulum (ER) stress, and mitochondrial reactive oxygen species (mtROS). AHs prevented UVB irradiation-induced apoptosis of HaCaT keratinocytes by inhibiting caspase activation and ROS production. Moreover, AHs restored the survival rate and the hatchability of UVB-irradiated zebrafish larvae without any abnormalities. Furthermore, AHs inhibited UVB-induced ER stress, resulting in a decrease in mtROS production via the stabilization of the mitochondrial membrane potential. Our results indicate that AHs inhibit UVB-induced apoptosis by downregulating total cytosolic ROof cytosolic CaS and ER-mediated mitoROS production in both HaCaT keratinocytes and zebrafish larvae. These findings provide evidence for the applications of AHs to protect skin from UVB-induced photodamage.

Bisphenol A: A potential Toll-like receptor 4/myeloid differentiation factor 2 complex agonist.

In addition to endocrine disruption, bisphenol A (BPA) is known to induce inflammation through the activation of nuclear factor-κB (NF-κB). However, detailed studies on the mechanism of NF-κB activation by BPA have not been sufficiently conducted. In the present study, we observed that low concentrations of BPA (≤1 µM) upregulated the release of proinflammatory mediators, including nitric oxide (NO) and prostaglandin E2 (PGE2), as well as proinflammatory cytokines, including tumor necrosis factor (TNF)-α, interleukin (IL)-12, and IL-6. Molecular modeling predicted that BPA docked with the Toll-like receptor 4 (TLR4)/myeloid differentiation factor 2 (MD2) complex activates downstream molecules including myeloid differentiation primary response 88 (MyD88) and IL-1 receptor-associated kinase 4 (IRAK-4) and results in the upregulation of the NF-κB signaling pathway. Additionally, BPA increased morphological abnormalities and mortality in zebrafish larvae and enhanced the dispersal of macrophages and neutrophils in the whole body, thereby causing an endotoxemia-like disorder. However, a specific TLR4 inhibitor, TLR4-IN-C34, mitigated BPA-induced mortality and morphological abnormalities, which indicates that the TLR4/MD2 complex is a molecular target of BPA-induced immunotoxicity. Collectively, our results indicate that low concentrations of BPA, which is a potential agonist of the TLR4/MD2 complex, can intensify the immune response and eventually cause an endotoxemia-like disorder.

Anthocyanins isolated from Hibiscus syriacus L. attenuate lipopolysaccharide-induced inflammation and endotoxic shock by inhibiting the TLR4/MD2-mediated NF-κB signaling pathway.

BACKGROUND: Hibiscus syriacus L. has been used as a medicinal plant in many Asian countries. However, anti-inflammatory activity of H. syriacus L. remains unknown. PURPOSE: This study was aimed to investigating the anti-inflammatory effect of anthocyanin fractions from the H. syriacus L. variety Pulsae (PS) on the lipopolysaccharide (LPS)-induced inflammation and endotoxic shock. STUDY DESIGN AND METHODS: MTT assay and flow cytometry analysis were performed to determine cytotoxicity of PS. RT-PCR, western blotting, and ELISA were conducted to evaluate the expression of proinflammatory mediators and cytokines. Molecular docking study predicted the binding scores and sites of PS to TLR4/MD2 complex. Immunohistochemical assay was conducted to evaluate the binding capability of PS to TLR4/MD2 and nuclear translocation of NF-κB p65. A zebrafish endotoxic shock model was used to evaluate anti-inflammatory activity of PS in vivo. RESULTS: PS suppressed LPS-induced nitric oxide and prostaglandin E2 secretion concomitant with the downregulation of inducible nitric oxide synthase and cyclooxygenase-2 expression. Furthermore, PS inhibited the production of proinflammatory cytokines such as TNF-α, IL-6, and IL-12 in LPS-stimulated RAW 264.7 macrophages. Additionally, molecular docking data showed that PS mostly fit into the hydrophobic pocket of MD2 and bound to TLR4. In particular, apigenin-7-O-glucoside powerfully bound to MD2 and TLR4 via hydrogen bonding. Additionally, immunohistochemistry assay revealed that PS inhibited LPS-induced TLR4 dimerization or expression on the cell surface, which consequently decreased MyD88 recruitment and IRAK4 phosphorylation, resulting in the inhibition of NF-κB activity. PS also attenuated LPS-mediated mortality and abnormality in zebrafish larvae and diminished the recruitment of neutrophils and macrophages at the inflammatory site accompanied by the low levels of proinflammatory mediators and cytokines. CONCLUSION: PS might be a novel immunomodulator for the effective treatment of LPS-mediated inflammatory diseases.

GSK-3ß-Targeting Fisetin Promotes Melanogenesis in B16F10 Melanoma Cells and Zebrafish Larvae through ß-Catenin Activation.

Fisetin is found in many fruits and plants such as grapes and onions, and exerts anti-inflammatory, anti-proliferative, and anticancer activity. However, whether fisetin regulates melanogenesis has been rarely studied. Therefore, we evaluated the effects of fisetin on melanogenesis in B16F10 melanoma cell and zebrafish larvae. The current study revealed that fisetin slightly suppressed in vitro mushroom tyrosinase activity; however, molecular docking data showed that fisetin did not directly bind to mushroom tyrosinase. Unexpectedly, fisetin significantly increased intracellular and extracellular melanin production in B16F10 melanoma cells regardless of the presence or absence of α-melanocyte stimulating hormone (α-MSH). We also found that the expression of melanogenesis-related genes such as tyrosinase and microphthalmia-associated transcription factor (MITF), were highly increased 48 h after fisetin treatment. Pigmentation of zebrafish larvae by fisetin treatment also increased at the concentrations up to 200 µM and then slightly decreased at 400 µM, with no alteration in the heart rates. Molecular docking data also revealed that fisetin binds to glycogen synthase kinase-3ß (GSK-3ß). Therefore, we evaluated whether fisetin negatively regulated GSK-3ß, which subsequently activates ß-catenin, resulting in melanogenesis. As expected, fisetin increased the expression of ß-catenin, which was subsequently translocated into the nucleus. In the functional assay, FH535, a Wnt/ß-catenin inhibitor, significantly inhibited fisetin-mediated melanogenesis in zebrafish larvae. Our data suggested that fisetin inhibits GSK-3ß, which activates ß-catenin, resulting in melanogenesis through the revitalization of MITF and tyrosinase.

Fermented Oyster Extract Promotes Osteoblast Differentiation by Activating the Wnt/ß-Catenin Signaling Pathway, Leading to Bone Formation.

The Pacific oyster, Crassostrea gigas, is well-known as a nutritious food. Recently, we revealed that fermented extract of C. gigas (FO) inhibited ovariectomy-induced osteoporosis, resulting from suppression of osteoclastogenesis. However, since the beneficial effect of FO on osteogenesis is poorly understood, it was examined in mouse preosteoblast MC3T3-E1 cells, human osteosarcoma MG-63 osteoblast-like cells, and zebrafish larvae in this study. We found that FO increased mitochondrial activity from days 1 to 7; however, total cell number of MC3T3-E1 cells gradually decreased without any change in cell viability, which suggests that FO stimulates the differentiation of MC3T3-E1 cells. FO also promoted the expression of osteoblast marker genes, including runt-related transcription factor 2 (mRUNX2), alkaline phosphatase (mALP), collagen type I α1 (mCol1α1), osteocalcin (mOCN), osterix (mOSX), bone morphogenetic protein 2 (mBMP2), and mBMP4 in MC3T3-E1 cells accompanied by a significant increase in ALP activity. FO also increased nuclear translocation of RUNX2 and OSX transcription factors, ALP activity, and calcification in vitro along with the upregulated expression of osteoblast-specific marker proteins such as RUNX2, ALP, Col1α1, OCN, OSX, and BMP4. Additionally, FO enhanced bone mineralization (calcein intensity) in zebrafish larvae at 9 days post-fertilization comparable to that in the ß-glycerophosphate (GP)-treated group. All the tested osteoblast marker genes, including zRUNX2a, zRUNX2b, zALP, zCol1a1, zOCN, zBMP2, and zBMP4, were also remarkably upregulated in the zebrafish larvae in response to FO. It also promoted tail fin regeneration in adult zebrafish as same as the GP-treated groups. Furthermore, not only FO positively regulate ß-catenin expression and Wnt/ß-catenin luciferase activity, but pretreatment with a Wnt/ß-catenin inhibitor (FH535) also significantly decreased FO-mediated bone mineralization in zebrafish larvae, which indicates that FO-induced osteogenesis depends on the Wnt/ß-catenin pathway. Altogether, the current study suggests that the supplemental intake of FO has a beneficial effect on osteogenesis.

Anthocyanins from Hibiscus syriacus L. Inhibit Melanogenesis by Activating the ERK Signaling Pathway.

Hibiscus syriacus L. exhibited promising potential as a new source of food and colorants containing various anthocyanins. However, the function of anthocyanins from H. syriacus L. has not been investigated. In the current study, we evaluated whether anthocyanins from the H. syriacus L. varieties Pulsae and Paektanshim (PS and PTS) inhibit melanin biogenesis. B16F10 cells and zebrafish larvae were exposed to PS and PTS in the presence or absence of α-melanocyte-stimulating hormone (α-MSH), and melanin contents accompanied by its regulating genes and proteins were analyzed. PS and PTS moderately downregulated mushroom tyrosinase activity in vitro, but significantly decreased extracellular and intracellular melanin production in B16F10 cells, and inhibited α-MSH-induced expression of microphthalmia-associated transcription factor (MITF) and tyrosinase. PS and PTS also attenuated pigmentation in α-MSH-stimulated zebrafish larvae. Furthermore, PS and PTS activated the phosphorylation of extracellular signal-regulated kinase (ERK), whereas PD98059, a specific ERK inhibitor, completely reversed PS- and PTS-mediated anti-melanogenic activity in B16F10 cells and zebrafish larvae, which indicates that PS- and PTS-mediated anti-melanogenic activity is due to ERK activation. Moreover, chromatography data showed that PS and PTS possessed 17 identical anthocyanins as a negative regulator of ERK. These findings suggested that anthocyanins from PS and PTS inhibited melanogenesis in vitro and in vivo by activating the ERK signaling pathway.

Flumequine-Mediated Upregulation of p38 MAPK and JNK Results in Melanogenesis in B16F10 Cells and Zebrafish Larvae.

Flumequine is a well-known second generation quinolone antibiotic that induces phototoxicity. However, the effect of flumequine on skin melanogenesis is unclear. Therefore, we, for the first time, investigated whether flumequine regulates melanogenesis. The present study showed that flumequine slightly inhibited in vitro mushroom tyrosinase activity but significantly increased extracellular and intracellular melanin content in B16F10 cells and promoted the expression of microphthalmia-associated transcription factor (MITF) and tyrosinase. Additionally, flumequine remarkably increased melanin pigmentation in zebrafish larvae without any toxicity. We also found that flumequine stimulated p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK) phosphorylation; inhibition of p38 MAPK and JNK resulted in significant downregulation of extracellular and intracellular melanin content in B16F10 cells and pigmentation of zebrafish larvae accompanied with suppression of MITF and tyrosinase expression, indicating that flumequine-mediated p38 and JNK promote melanogenesis in vitro and in vivo. According to the molecular docking prediction, flumequine targeted dual-specificity MAPK phosphatase 16 (DUSP16), which is a major negative regulator of p38 MAPK and JNK. Our findings demonstrate that flumequine induces an increase in melanin content in B16F10 cells and zebrafish larvae by activating p38 MAPK and JNK. These data show the potential of flumequine for use as an anti-vitiligo agent.

Camptothecin induces mitotic arrest through Mad2-Cdc20 complex by activating the JNK-mediated Sp1 pathway.

Camptothecin (CPT) is a popular therapeutic agent that targets topoisomerase I. Our findings demonstrated that CPT-induced microtubule polymerization results in markedly increased histone H3 phosphorylation. CPT also enhanced interactions between the mitotic checkpoint proteins, Mad2 and Cdc20, and thereby increased mitotic arrest. Transient knockdown of Mad2 completely restored cell cycle progression from CPT-induced mitotic arrest, while simultaneously reduced cyclin B1 and Cdk1 expression. Moreover, we found that c-Jun N-terminal kinase (JNK) acts upstream of Sp1, which upregulates p21-mediated mitotic arrest in response to CPT; furthermore, knockdown of p21 restored cell cycle progression, while inhibition of Cdks completely restored cell cycle progression from CPT-induced mitotic arrest. We hypothesized that, during mitotic arrest in response to CPT, cell survival signaling blocks apoptosis, thereby enhancing mitotic arrest. As expected, a caspase-9 inhibitor, z-LEHD-FMK, and an autophagy inhibitor, 3-methyladenine (3 MA), significantly diminished CPT-induced mitotic arrest. On the other hand, when Mad2 was depleted, z-LEHD-FMK and 3 MA markedly increased apoptosis, and restored cell cycle progression. Taken together, these results suggest that CPT decodes the action of topoisomerase I-mediated tubulin targeting drugs, leading to mitotic arrest by upregulating Mad2 through the JNK-mediated Sp1 pathway and autophagy formation from tubulin polymerization.

Camptothecin enhances c-Myc-mediated endoplasmic reticulum stress and leads to autophagy by activating Ca2+-mediated AMPK.

Camptothecin (CPT) from Camptotheca acuminate was discovered for anticancer drugs, which targets topoisomease I. However, whether CPT regulates c-Myc expression has not been understood in endoplasmic reticulum (ER) stress and autophagy. In this study, we found that CPT enhanced c-Myc expression and that the transient knockdown of c-Myc abrogated reactive oxygen species (ROS) generation, which resulted in the accumulation of ER stress-regulating proteins, such as PERK, eIF2α, ATF4, and CHOP. Moreover, the transfection of eIF2α-targeted siRNA attenuated CPT-induced autophagy and decreased the levels of Beclin-1 and Atg7, which indicated that CPT upregulated ER stress-mediated autophagy. In addition, CPT phosphorylated AMPK in response to intracellular Ca2+ release. Ca2+ chelators, ethylene glycol tetraacetic acid and a CaMKII inhibitor, K252a, decreased CPT-induced Beclin-1 and Atg7, and downregulated AMPK phosphorylation, which suggested that CPT-induced Ca2+ release leads to the activation of autophagy through CaMKII-mediated AMPK phosphorylation. CPT also phosphorylated JNK and activated the DNA-binding activity of AP-1; furthermore, knockdown of JNK abolished the expression level of Beclin-1 and Atg7, which implied that the JNK-AP-1 pathway was a potent mediator of CPT-induced autophagy. Our findings indicated that CPT promoted c-Myc-mediated ER stress and ROS generation, which enhances autophagy via the Ca2+-AMPK and JNK-AP-1 pathways.

β-Hydroxyisovalerylshikonin promotes reactive oxygen species production in HCT116 colon cancer cells, leading to caspase-mediated apoptosis

ABSTRACT Although β-hydroxyisovalerylshikonin is suggested as a potential therapeutic agent for preventing various cancers, the underlying molecular mechanisms are not completely understood. In the present study, we investigated whether β-hydroxyisovalerylshikonin enhances apoptosis by triggering reactive oxygen species production in colon cancer HCT116 cells. β-Hydroxyisovalerylshikonin significantly inhibited the viability of HCT116 cells with maximum inhibition at 4 µM. Furthermore, treatment with β-hydroxyisovalerylshikonin subsequently increased sub-G1 cells and annexin-V+ cell population. Additionally, pretreatment with the caspase-8 inhibitor, z-IETD-fmk, and the caspase-9 inhibitor, z-LETD-fmk, significantly decreased β-hydroxyisovalerylshikonin-induced apoptosis, suggesting that β-hydroxyisovalerylshikonin promotes apoptosis through both the intrinsic and the extrinsic apoptotic pathways by activating caspase-8 and caspase-9. We also found that mitochondria played an important role in β-hydroxyisovalerylshikonin-mediated apoptosis via the intrinsic pathway. Accordingly, β-hydroxyisovalerylshikonin-induced reactive oxygen species production was evident after treatment with β-hydroxyisovalerylshikonin, and pretreatment with reactive oxygen species inhibitors, N-acetyl-L-cysteine and glutathione, significantly decreased β-hydroxyisovalerylshikonin-induced reactive oxygen species production, resulting in inhibition of apoptosis, which suggests that ROS generation is required for β-hydroxyisovalerylshikonin-mediated apoptosis. Taken together, these results demonstrated that the apoptotic effect of β-hydroxyisovalerylshikonin is enhanced in colon cancer HCT116 cells via reactive oxygen species generation and triggering of the caspase pathways, indicating that β-hydroxyisovalerylshikonin has potential as a therapeutic in the treatment of colon cancers.

TRAIL attenuates sulforaphane-mediated Nrf2 and sustains ROS generation, leading to apoptosis of TRAIL-resistant human bladder cancer cells.

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) can preferentially initiate apoptosis in malignant cells with minimal toxicity to normal cells. Unfortunately, many human cancer cells are refractory to TRAIL-induced apoptosis through many unknown mechanisms. Here, we report that TRAIL resistance can be reversed in human bladder cancer cell lines by treatment with sulforaphane (SFN), a well-known chemopreventive isothiocyanate in various cruciferous vegetables. Combined treatment with SFN and TRAIL (SFN/TRAIL) significantly induced apoptosis concomitant with activation of caspases, loss of mitochondrial membrane potential (MMP), Bid truncation, and induction of death receptor 5. Transient knockdown of Bid prevented collapse of MMP induced by SFN/TRAIL, consequently reducing apoptotic effects. Furthermore, SFN increased both the generation of reactive oxygen species (ROS) and the activation of nuclear factor erythroid 2-related factor 2 (Nrf2), which is an anti-oxidant enzyme. Interestingly, TRAIL effectively suppressed SFN-mediated nuclear translocation of Nrf2, and the period of ROS generation was more extended compared to that of treatment with SFN alone. In addition, silencing of Nrf2 increased apoptosis in cells treated with SFN/TRAIL; however, blockade of ROS generation inhibited apoptotic activity. These data suggest that SFN-induced ROS generation promotes TRAIL sensitivity and SFN can be used for the management of TRAIL-resistant cancer.