Flavonoid Silibinin Research Articles

Human Monocyte-Derived Dendritic Cells Are the Pharmacological Target of the Immunosuppressant Flavonoid Silibinin.

Silibinin, a natural polyphenolic flavonoid, is known to possess anti-inflammatory, anticancer, antioxidant, and immunomodulatory properties. However, the effects of Silibinin on the maturation and immunostimulatory functions of human dendritic cells (DC) remain to be elucidated. In this study, we have attempted to ascertain whether Silibinin influences the maturation, cytokine production, and antigen-presenting capacity of human monocyte-derived DC. We show that Silibinin significantly suppresses the upregulation of costimulatory and MHC molecules in LPS-stimulated mature DC and inhibits lipopolysaccharide (LPS)-induced interleukin (IL)-12, IL-23, and TNF-α production. Furthermore, Silibinin impairs the proliferation response of the allogenic memory CD4 T lymphocytes elicited by LPS-matured DC and their Th1/Th17 profile. These findings demonstrate that Silibinin displays immunosuppressive activity by inhibiting the maturation and activation of human DC and support its potential application of adjuvant therapy in the treatment of autoimmune diseases.

A review of biologically active flavonoids as inducers of autophagy and apoptosis in neoplastic cells and as cytoprotective agents in non‐neoplastic cells

Phytochemicals are a diverse group of compounds found in various fruits, vegetables, nuts, and legumes. Many phytochemicals have been observed to possess health benefits. Some have been found to be chemoprotective or can act as chemotherapeutics by inducing autophagy, apoptosis, or otherwise regulating the cell cycle. Many also act as potent antioxidants. Flavonoids are a subclass of bioactive phytochemicals consisting of two phenolic benzene rings, joined together by a heterocyclic pyran or pyrone. It has been observed in multiple studies that there is a correlation between diets rich in flavonoids and a reduction in cancer levels, heart disease, neurodegenerative diseases, and other pathologies. As foods containing flavonoids are widely consumed, and their mechanisms of action are still only partially understood, this review was compiled to compare the effects and mechanisms of action of some of the most widely characterized and publicized flavonoids. The flavonoids silibinin, quercetin, isorhamnetin, luteolin, curcumin genkwanin, and acacetin, together with flavonoid extracts from papaw and Tephroseris kirilowii (Turcz) Holub, a member of the Daisy family, were found to be potent regulators of the cell cycle. The decision to overview these specific flavonoids was based on their therapeutic effects, and/or their potential effects. The sparsity of data comparing these flavonoids was also a key consideration. These flavonoids all modulated to some extent the pathways of autophagy and/or apoptosis and regulated the cell cycle, inflammation, and free radical levels. This explains why they are protective of healthy or moderately damaged cells, but toxic to neoplastic or pre-cancerous cells.

Silibinin downregulates the expression of the Th1 and Th17 profiles by modulation of STATs and transcription factors in pregnant women with preeclampsia

Preeclampsia (PE) is a multifactorial disease that is characterized by inflammation. Some of the factors responsible for this inflammation are the cells of the innate and adaptive immune systems and their interactions. The use of natural products, such as silibinin (SB), can contribute to the control of this inflammation and gestational success. The present study evaluated whether the flavonoid SB has an in vitro immunomodulatory effect on the signal transducers and transcription activators (STATs) signaling pathway and transcription factors of CD4+ T cell subsets obtained from preeclamptic and normotensive (NT) pregnant women. Peripheral blood mononuclear cells (PBMCs) from 18 preeclamptic and 18 NT pregnant women were cultured with and without SB to analyze the expression of STATs and transcription factors by flow cytometry, and cytokines were measured in the culture supernatant by ELISA. The results showed that treating cells with SB decreased STAT1/ STAT4/T-bet and STAT3/RORγt, which characteristic of Th1 and Th17 inflammatory profiles, as well as increased STAT6/GATA-3 and STAT5/FoxP3 of anti-inflammatory and regulatory profiles, respectively. In addition, PBMCs from preeclamptic women treated with SB released lower concentrations of inflammatory cytokines and higher levels of IL-10 and TGF-β. Therefore, SB plays an immunomodulatory role on CD4+ T cell subsets in PE, leading to the downregulation of inflammatory profiles and upregulation of anti-inflammatory and regulatory profiles. More studies are necessary to better understand the modulation of CD4+ T cell subsets by the JAK/STAT and NF-κB pathways in this gestational pathology.

Silibinin treatment protects human skin cells from UVB injury through upregulation of estrogen receptors

Ultraviolet B (UVB) from the sunlight is a major environmental cause for human skin damages, inducing cell death, inflammation, senescence and even carcinogenesis. The natural flavonoid silibinin, clinically used as liver protectant, has protective effects against UVB-caused skin injury in vivo and in vitro. Silibinin is often classified as a phytoestrogen, because it modulates the activation of estrogen receptors (ERs). However, whether silibinin's estrogenic effect contributes to the skin protection against UVB injury remains to be elucidated. The issue was explored in this study by using the human foreskin dermal fibroblasts (HFF) and human non-malignant immortalized keratinocytes (HaCaT). In HFF, pre-treatment with silibinin rescued UVB-irradiated cells from apoptosis. Interestingly, silibinin increased the whole cellular and nuclear levels of ERα and ERβ in UVB-irradiated cells. Activation of ERs by treatment with estradiol elevated the cell survival and reduced apoptosis in UVB-treated cells. ERα agonist increased cell survival, while its antagonist decreased it. ERβ agonist also increased cell survival, but the antagonist had no effect on cell survival. Transfection of the cells with the small interfering RNAs (si-RNAs) to ERα or ERβ diminished the protective effect of silibinin on UVB-irradiated cells. In UVB-treated HaCaT cells, both ERα and ERβ were increased by silibinin treatment. Inhibition of activation and expression of ERα or ERβ by specific antagonists and si-RNAs, respectively, reduced cell survival in UVB-treated HaCaT cells regardless of silibinin treatment. Taken together, it is summarized that silibinin up-regulates both ERα and ERβ pathways in UVB-treated dermal HFF cells and epidermal HaCaT cells, leading to protection of skin from UVB-damage.

Natural flavonoid silibinin promotes the migration and myogenic differentiation of murine C2C12 myoblasts via modulation of ROS generation and down-regulation of estrogen receptor α expression.

Skeletal muscle regeneration is a complex process, involving the proliferation, migration, and differentiation of myoblasts. Recent studies suggest that some natural flavanones stimulate myogenesis. However, the effect of plant estrogen, silibinin, on the regulation of myoblast behaviors is unclarified. In this study, we investigated the effects of silibinin on immortalized murine myoblast C2C12 in the aspects of proliferation, migration, differentiation along with underlying mechanisms. The results show that silibinin at concentrations below 50μM enhanced the migration and differentiation of C2C12 cells, but had no effect on cell proliferation. Silibinin significantly promoted the production of ROS, which appeared to play important roles in the migration and differentiation of the myoblasts. Interestingly, among ROS, the superoxide anion and hydroxyl radical were associated with the migration, whereas hydrogen peroxide contributed to the myogenic differentiation. We used ER agonist and antagonist to explore whether estrogen receptors (ERs), which are affected by silibinin treatment in the silibinin-enhanced C2C12 migration and differentiation. Migration was independent of ERs, whereas the differentiation was associated with decreased ERα activity. In summary, silibinin treatment increases ROS levels, leading to the promotion of migration and myogenic differentiation. Negative regulation ERα of differentiation but not of migration may suggest that ERα represses hydrogen peroxide generation. The effect of silibinin on myoblast migration and differentiation suggests that silibinin may have therapeutic benefits for muscle regeneration.

301 Association between Hair Proliferation and Flavonoid Silibinin in Human Dermal Papilla Cells

Silibinin is a secondary metabolite derived from Silybum marianum. Silibinin had been used as a hepatoprotective substance for more than 2,000 years in Europe. A number of studies have revealed the efficacy of silibinin as an antioxidant preventing skin damages, but there is a lack of study on the hair inductive property of silibinin. Thus, we assess the effectiveness of silibinin as a therapeutic candidate for alopecia using three-dimensional cultured human dermal papilla cells. In this study, cultured human dermal papilla cells were seeded into 96-well round-bottom microplate to make the unified spheres. After the spheres were treated with silibinin for 48 hours, the size of cultured human dermal papilla cells was calculated using phase-contrast microscopy. To assess the cell growth effect, AKT protein levels were evaluated using western blotting. Using luciferase reporter assay, the activity of Wnt/β-catenin signaling pathways associated with hair proliferation was analyzed. Quantative real time polimerase chain reaction assay was performed to evaluate upregulation of the signiture genes such as VCAN, FGF7, BMP2 and ALPL. The results of our study revealed silibinin increases the diameter of three-dimensional cultured human dermal papilla cells and elevates AKT protein levels. And Wnt/β-catenin signaling pathway was activated remarkably in silibinin treated spheres. In addition, signature genes of human dermal papill cell such as VCAN, FGF7, BMP2, and ALPL were upregulated by silibinin treatment. In conclusion, silibinin enhances the signaling pathway related to hair proliferation. Our study suggests silibinin could be a successful therapeutic agent for alopecia.

Flavonoids inhibit chronically exposed arsenic-induced proliferation and malignant transformation of HaCaT cells.

Apart from exposure to UV-radiation, studies show relationship between skin cancer and chronic ingestion of arsenic through drinking water. Chemopreventive strategies could help in reducing the toxic effects of arsenic and arsenic-induced skin cancer. Cytotoxicity of arsenic on human skin keratinocytes HaCaT cells was evaluated using MTT and trypan blue assays. Arsenic-induced malignant transformant HaCaT cells were selected through soft agar colony assay. Cell cycle progression was analyzed through FACS. The expressions of genes modulated by arsenic were studied through RT-PCR. The lower concentrations (0.1-0.5μmol/L) of arsenic were non-toxic and transformed HaCaT cells on chronic exposure, and also enhanced the cell proliferation. Silibinin and fisetin reduced the arsenic-induced cell proliferation and malignant transformation. A slight increase in G2-M phase cell population was also observed. The anti-proliferation effects of flavonoids on HaCaT transformants were further enhanced when combined with gamma radiation. Chronic and acute exposure to arsenic modulated the expression of transformation-associated genes including Bcl-2A1, IGFL-1, Rab31, and TNC in HaCaT cells. Chronic exposure to lower arsenic concentrations caused malignant transformation of skin keratinocytes and that effect was attenuated by flavonoids silibinin and fisetin. Thus, chemoprevention could reduce arsenic-caused detrimental effects on skin cells.

Anti‑proliferative activity of epigallocatechin‑3‑gallate and silibinin on soft tissue sarcoma cells.

Disseminated soft tissue sarcomas (STS) present a therapeutic dilemma. The first-line cytostatic doxorubicin demonstrates a response rate of 30% and is not suitable for elderly patients with underlying cardiac disease, due to its cardiotoxicity. Well-tolerated alternative treatment options, particularly in palliative situations, are rare. Therefore, the present study assessed the anti-proliferative effects of the natural compounds epigallocatechin-3-gallate (EGCG), silibinin and noscapine on STS cells. A total of eight different human STS cell lines were used in the study: Fibrosarcoma (HT1080), liposarcoma (SW872, T778 and MLS-402), synovial sarcoma (SW982, SYO1 and 1273) and pleomorphic sarcoma (U2197). Cell proliferation and viability were analysed by 5-bromo-2′-deoxyuridine and MTT assays and real-time cell analysis (RTCA). RTCA indicated that noscapine did not exhibit any inhibitory effects. By contrast, EGCG decreased proliferation and viability of all cell lines except for the 1273 synovial sarcoma cell line. Silibinin exhibited anti-proliferative effects on all synovial sarcoma, liposarcoma and fibrosarcoma cell lines. Liposarcoma cell lines responded particularly well to EGCG while synovial sarcoma cell lines were more sensitive to silibinin. In conclusion, the green tea polyphenol EGCG and the natural flavonoid silibinin from milk thistle suppressed the proliferation and viability of liposarcoma, synovial sarcoma and fibrosarcoma cells. These compounds are therefore potential candidates as mild therapeutic options for patients that are not suitable for doxorubicin-based chemotherapy and require palliative treatment. The findings from the present study provide evidence to support in vivo trials assessing the effect of these natural compounds on solid sarcomas.

Beneficial effects of the naturally occurring flavonoid silibinin on the prostate cancer microenvironment: role of monocyte chemotactic protein-1 and immune cell recruitment.

Tumor microenvironment plays an essential role in prostate carcinogenesis and offers novel opportunities to prevent and treat prostate cancer (PCA). Here, we investigated the ability of cancer-associated fibroblasts (CAFs) to promote PCA progression, and silibinin efficacy to target this response. We collected conditioned media from CAFs treated with vehicle or silibinin, and labeled as control conditioned media (CCM) or silibinin-treatment conditioned media (SBCM), respectively. Next, we characterized the effect of CCM and SBCM treatment in several PCA cell lines (RWPE-1, WPE-1 NA-22, WPE-1 NB-14 and PC3). Result showed that compared with SBCM, CCM significantly reduces E-cadherin expression and increases invasiveness and clonogenicity in PCA cells. Further molecular studies identified monocyte chemotactic protein-1 (MCP-1) as the key component of CCM that promotes PCA invasiveness, whereas silibinin treatment strongly reduced MCP-1 expression in CAFs by inhibiting the DNA-binding activity of MCP-1 transcriptional regulators-nuclear factor-kappaB and AP-1. In vivo, silibinin feeding (200mg/kg body weight) strongly reduced TRAMPC1 allografts growth (by 68%) in syngeneic C57Bl/6 mice. TRAMPC1 tumor analysis showed that silibinin reduced MCP-1 and CAFs' biomarkers (fibroblast activation protein, α-smooth muscle actin, transforming growth factor beta 2, vimentin etc.) and significantly modulated the recruitment of immune cells in the tumor microenvironment. Similar inhibitory effects of silibinin on MCP-1 and immune cells recruitment were also observed in TRAMP PCA tissues with reported silibinin efficacy. Overall, our data suggest that silibinin can target CAF-mediated invasiveness in PCA by inhibiting MCP-1 secretion. This, in turn, was associated with a reduction in immune cell recruitment in vivo along with a marked reduction in tumor growth.

Silibinin prevents dopaminergic neuronal loss in a mouse model of Parkinson's disease via mitochondrial stabilization.

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by the selective loss of dopaminergic neurons in the nigrostriatal pathway. The lipophile 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can cross the blood-brain barrier and is subsequently metabolized into toxic1-methyl-4-phenylpyridine (MPP(+) ), which causes mitochondrial dysfunction and the selective cell death of dopaminergic neurons. The present article reports the neuroprotective effects of silibinin in a murine MPTP model of PD. The flavonoid silibinin is the major active constituent of silymarin, an extract of milk thistle seeds, and is known to have hepatoprotective, anticancer, antioxidative, and neuroprotective effects. In the present study, silibinin effectively attenuated motor deficit and dopaminergic neuronal loss caused by MPTP. Furthermore, in vitro study confirmed that silibinin protects primary cultured neurons against MPP(+) -induced cell death and mitochondrial membrane disruption. The findings of the present study indicate that silibinin has neuroprotective effects in MPTP-induced models of PD rather than antioxidative or anti-inflammatory effects and that the neuroprotection afforded might be mediated by the stabilization of mitochondrial membrane potential. Furthermore, these findings suggest that silibinin protects mitochondria in MPTP-induced PD models and that it offers a starting point for the development of treatments that ameliorate the symptoms of PD.

Abstract 2452: Silibinin inhibits lipid metabolism by primarily targeting the master regulator sterol response element binding protein 1 (SREBP1) in prostate cancer cells

Abstract Aberrant lipid metabolism is a major factor in growth, progression and invasion/metastasis of prostate tumors. Prostate cancer (PCa) cells are unique in terms of their low glycolytic rate and weak expression of glucose transporters. Concomitantly, PCa cells overexpress fatty acid synthase (FASN) which is considered a metabolic oncogene. As glucose consumption is not elevated in PCa, a metabolic switch to lipogenesis and fatty acid oxidation provides energy and cellular building blocks for abnormal cell growth and proliferation. In the present study, we evaluated the effect and related molecular mechanisms of a natural flavonoid silibinin in inhibiting lipid metabolism in PCa cells. Results showed that silibinin (30-90 µM) inhibited lipid and cholesterol accumulation specifically in human prostate carcinoma LNCaP and DU145 cells but not in non-neoplastic prostate epithelial PWR-1E cells. This inhibition by silibinin was mediated via a decrease in the expression of key enzymes regulating fatty acid and cholesterol synthesis including FASN, acetyl CoA carboxylase, acetyl CoA synthetase and HMG CoA reductase. Since most of these lipogenic enzymes are transcriptionally controlled by SREBP, we next analyzed the effect of silibinin on this master transcriptional regulator of lipogenesis. Silibinin inhibited SREBP1 (as well as SREBP2) protein expression without affecting its mRNA level in PCa cells suggesting a post-translational mode of regulation. SREBP1 activation involves proteolytic cleavage of precursor protein (125 kDa), generating a 68 kDa fragment that translocates to the nucleus and binds to sterol response element on target genes. Confocal and Immunoblot analyses confirmed that silibinin inhibited the proteolytic cleavage and subsequent nuclear translocation of SREBP1. Importantly, silibinin activated AMPK that phosphorylates SREBP1 (at Ser-372 site) inhibiting its nuclear translocation and transcriptional activity. Moreover, AMPK inhibition, through Compound C, reversed silibinin-mediated inhibition of nuclear SREBP1 and lipid accumulation. The central role of SREBP1 in silibinin-mediated effects on lipid accumulation and cell growth inhibition was also established by using a specific synthetic SREBP inhibitor, fatostatin. Parallely, we also observed that silibinin attenuates fatty acid uptake through down regulating LDL receptor expression. Furthermore, silibinin also significantly reduced AMACR (α-methylacyl-CoA racemase) expression in PCa cells, suggesting that it could also negatively regulate fatty acid oxidation. Overall, we found that silibinin targets SREBP1 and metabolically starves PCa cells by reducing de novo lipogenesis and lipolysis leading to a strong growth inhibition. Considering the critical role of lipid metabolism in prostate carcinogenesis, non-toxic silibinin could be useful in PCa prevention and treatment. Citation Format: Dhanya K. Nambiar, Gagan Deep, Rana P. Singh, Chapla Agarwal, Rajesh Agarwal. Silibinin inhibits lipid metabolism by primarily targeting the master regulator sterol response element binding protein 1 (SREBP1) in prostate cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2452. doi:10.1158/1538-7445.AM2014-2452

Silibinin inhibits fibronectin induced motility, invasiveness and survival in human prostate carcinoma PC3 cells via targeting integrin signaling

Prostate cancer (PCA) is the 2nd leading cause of cancer-related deaths among men in the United States. Preventing or inhibiting metastasis-related events through non-toxic agents could be a useful approach for lowering high mortality among PCA patients. We have earlier reported that natural flavonoid silibinin possesses strong anti-metastatic efficacy against PCA however, mechanism/s of its action still remains largely unknown. One of the major events during metastasis is the replacement of cell–cell interaction with integrins-based cell–matrix interaction that controls motility, invasiveness and survival of cancer cells. Accordingly, here we examined silibinin effect on advanced human PCA PC3 cells’ interaction with extracellular matrix component fibronectin. Silibinin (50–200μM) treatment significantly decreased the fibronectin (5μg/ml)-induced motile morphology via targeting actin cytoskeleton organization in PC3 cells. Silibinin also decreased the fibronectin-induced cell proliferation and motility but significantly increased cell death in PC3 cells. Silibinin also inhibited the PC3 cells invasiveness in Transwell invasion assays with fibronectin or cancer associated fibroblasts (CAFs) serving as chemoattractant. Importantly, PC3-luc cells cultured on fibronectin showed rapid dissemination and localized in lungs following tail vein injection in athymic male nude mice; however, in silibinin-treated PC3-luc cells, dissemination and lung localization was largely compromised. Molecular analyses revealed that silibinin treatment modulated the fibronectin-induced expression of integrins (α5, αV, β1 and β3), actin-remodeling (FAK, Src, GTPases, ARP2 and cortactin), apoptosis (cPARP and cleaved caspase 3), EMT (E-cadherin and β-catenin), and cell survival (survivin and Akt) related signaling molecules in PC3 cells. Furthermore, PC3-xenograft tissue analyses confirmed the inhibitory effect of silibinin on fibronectin and integrins expression. Together, these results showed that silibinin targets PCA cells’ interaction with fibronectin and inhibits their motility, invasiveness and survival; thus further supporting silibinin use in PCA intervention including its metastatic progression.

The binding of silibinin to ERp57

The flavonoid silibinin is known to intervene in many cellular processes involved in a variety of pathologies, thus appearing a promising therapeutic tool. The molecular mechanisms responsible for these activities, however, have not been clearly defined, and although some of its interactions with proteins have been identified, the relative affinities are often too low to appear relevant in vivo. Here we describe the interaction of silibinin with the protein disulfide isomerase ERp57, characterized by a submicromolar dissociation constant. This interaction enhances the formation of a ERp57/REF-1 complex, and furthermore appears to affect the intracellular distribution of ERp57. This protein is involved in signaling pathways which are also affected by silibinin. This suggests that the ERp57–silibinin interaction might explain at least some of the biological effects caused by the flavonoid.

Antiproliferative and apoptosis-inducing activity of an oxidovanadium(IV) complex with the flavonoid silibinin against osteosarcoma cells

Flavonoids are a large family of polyphenolic compounds synthesized by plants. They display interesting biological effects mainly related to their antioxidant properties. On the other hand, vanadium compounds also exhibit different biological and pharmacological effects in cell culture and in animal models. Since coordination of ligands to metals can improve or change the pharmacological properties, we report herein, for the first time, a detailed study of the mechanisms of action of an oxidovanadium(IV) complex with the flavonoid silibinin, Na2[VO(silibinin)2]·6H2O (VOsil), in a model of the human osteosarcoma derived cell line MG-63. The complex inhibited the viability of osteosarcoma cells in a dose-dependent manner with a greater potency than that of silibinin and oxidovanadium(IV) (p < 0.01), demonstrating the benefit of complexation. Cytotoxicity and genotoxicity studies also showed a concentration effect for VOsil. The increase in the levels of reactive oxygen species and the decrease of the ratio of the amount of reduced glutathione to the amount of oxidized glutathione were involved in the deleterious effects of the complex. Besides, the complex caused cell cycle arrest and activated caspase 3, triggering apoptosis as determined by flow cytometry. As a whole, these results show the main mechanisms of the deleterious effects of VOsil in the osteosarcoma cell line, demonstrating that this complex is a promising compound for cancer treatments.

Effects of Single Oral Doses of Flavonoids on Absorption and Tissue Distribution of Orally Administered Doses of Trace Elements in Rats

Many flavonoids have the capacity to modulate the activity of drug metabolizing enzymes and transporters, thus raising the potential for alterations in the pharmacokinetics of drugs and other essential elements. The present study evaluates the effect of single supraphysiological orally administered doses of silibinin, epigallocatechin gallate (EGCG), quercetin and rutin on the absorption and tissue distribution of orally administered doses of the trace elements zinc copper and iron in rats. Thirty rats were allocated into 5 groups treated as follow: 1<SUP>st</SUP> group treated with olive oil, served as control; the other 4 groups were administered orally single doses of either silibinin, EPGC, quercetin or rutin, after 2 hr a solution contains sulphate salts of zinc, copper and iron was administered orally. The animals were sacrificed, blood samples, tissues of brain, kidney and liver were obtained for evaluation of the plasma and tissues concentrations of Zn, Cu and Fe using atomic absorption spectrometry. All four flavonoids decreased serum and tissues concentrations of the trace elements compared with control. In conclusion, concomitant administration of single doses of Zn, Cu and Fe with supra-physiological doses of the flavonoids silibinin, EGCG, quercetin and rutin significantly decreases serum and tissue levels of these trace elements.

Silibinin protects murine fibroblast L929 cells from UVB‐induced apoptosis through the simultaneous inhibition of ATM‐p53 pathway and autophagy

Ultraviolet B (UVB) is a major cause of skin inflammation, leading to skin damage. Our previous in vivo study revealed that a natural flavonoid silibinin had marked anti-inflammatory effect on UVB-exposed murine skin. UVB exposure caused reduced autophagy in epidermis while it promoted autophagy in dermis. Nevertheless, silibinin inhibited the inflammatory flux in the skin epidermis as well as dermis through the modulation of autophagy. In order to elucidate the underlying protective mechanisms of silibinin for UVB damage on skin, separate studies on epidermis and dermis are helpful. Derived from the normal tissue of the mouse, L929 cells are capable of representing some characteristics of dermal cells. UVB irradiation caused L929 cell apoptosis in a time- and dose-dependent manner. Ataxia-telangiectasia-mutated (ATM) protein and p53 were activated to cause cell apoptosis, accompanying upregulation of the autophagic flux. The pharmacological inhibition of ATM, p53 and autophagy or the transfection with autophagy-associated protein-targeted small interfering RNAs showed that the UVB-activated ATM-p53 axis and autophagy formed a positive feedback loop, which synergistically promoted cell apoptosis. Silibinin treatment simultaneously repressed the activation of ATM-p53 and autophagy and thereby protected UVB-irradiated L929 cells from apoptotic death.

Molecular Mechanisms of Silibinin-Mediated Cancer Chemoprevention with Major Emphasis on Prostate Cancer

Despite advances in early detection, prostate cancer remains the second highest cancer mortality in American men, and even successful interventions are associated with enormous health care costs as well as prolonged deleterious effects on quality of patient life. Prostate cancer chemoprevention is one potential avenue to alleviate these burdens. It is a regime whereby long-term treatments are intended to prevent or arrest cancer development, in contrast to more direct intervention upon disease diagnosis. Based on this intention, cancer chemoprevention generally focuses on the use of nontoxic chemical agents which are well-tolerated for prolonged usage that is necessary to address prostate cancer's multistage and lengthy period of progression. One such nontoxic natural agent is the flavonoid silibinin, derived from the milk thistle plant (Silybum marianum), which has ancient medicinal usage and potent antioxidant activity. Based on these properties, silibinin has been investigated in a host of cancer models where it exhibits broad-spectrum efficacy against cancer progression both in vitro and in vivo without noticeable toxicity. Specifically in prostate cancer models, silibinin has shown the ability to modulate cell signaling, proliferation, apoptosis, epithelial to mesenchymal transition, invasion, metastasis, and angiogenesis, which taken together provides strong support for silibinin as a candidate prostate cancer chemopreventive agent.

Silibinin inhibits VEGF secretion and age‐related macular degeneration in a hypoxia‐dependent manner through the PI‐3 kinase/Akt/mTOR pathway

Hypoxia-mediated neovascularization plays an important role in age-related macular degeneration (AMD). There are few animal models or effective treatments for AMD. Here, we investigated the effects of the flavonoid silibinin on hypoxia-induced angiogenesis in a rat AMD model. Retinal pigmented epithelial (RPE) cells were subjected to hypoxia in vitro and the effects of silibinin on activation of key hypoxia-induced pathways were examined by elucidating the hypoxia-inducible factor-1 alpha (HIF-1α) protein level by Western blot. A rat model of AMD was developed by intravitreal injection of VEGF in Brown Norway rats, with or without concomitant exposure of animals to hypoxia. Animals were treated with oral silibinin starting at day 7 post-VEGF injection and AMD changes were followed by fluorescein angiography on days 14 and 28 post-injection. Silibinin pretreatment of RPE cells increased proline hydroxylase-2 expression, inhibited HIF-1α subunit accumulation, and inhibited VEGF secretion. Silibinin-induced HIF-1α and VEGF down-regulation required suppression of hypoxia-induced phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (mTOR) pathway. In the rat model of AMD, silibinin administration prevented VEGF- and VEGF plus hypoxia-induced retinal oedema and neovascularization. The effects of silibinin, both in vitro and in vivo, support its potential as a therapeutic for the prevention of neovascular AMD.

Glycine Pretreatment Ameliorates Liver Injury After Partial Hepatectomy in the Rat

ABSTRACTBackground: Living donor liver transplantation subjects the donor to a major hepatectomy. Pharmacological or nutritive protection of the liver during the procedure is desirable to ensure that the remnant is able to maintain sufficient function. The aim of our study was to analyze the effects of pretreatments with α-tocopherol (vitamin E), the flavonoid silibinin and/or the amino acid L-glycine on the donor in a rat model. Methods: Male Wistar rats were pretreated with L-glycine (5%% in chow, 5 days), α-tocopherol (100 mg/kg body weight by gavage, 3 days) and/or silibinin (100 mg/kg body weight, i.p., 5 days). Thereafter, 90%% partial hepatectomy was performed without portal vein clamping. Results: Glycine pretreatment markedly decreased transaminase release (AST, 12 hr: glycine 1292 ± 192 U/L, control 2311 ± 556 U/L, p < .05; ALT, 12 hr: glycine 1013 ± 278 U/L, control 2038 ± 500 U/L, p < .05), serum ALP activity and serum bilirubin levels (p < .05). Prothrombin time was reduced, and histologically, liver injury was also decreased in the glycine group. Silibinin pretreatment was less advantageous and pretreatment with α-tocopherol at this very high dose showed some adverse effects. Combined, i.e., triple pretreatment was less advantageous than glycine alone. Liver resection induced HIF-1α accumulation and HIF-1α accumulation was also decreased by glycine pretreatment. Conclusion: The decrease of liver injury and improvement of liver function after pretreatment with glycine suggests that glycine pretreatment might be beneficial for living liver donors as well as for patients subjected to partial hepatectomy for other reasons.

Inhibitory effects of xanthohumol from hops (Humulus lupulus L.) on human hepatocellular carcinoma cell lines

Xanthohumol is one of the main flavonoids in hop extracts and in beer. Very few investigations of xanthohumol have studied hepatocellular carcinoma. In this study, the inhibitory effects of xanthohumol on human hepatocellular carcinoma cell lines were investigated. The IC(50) values of xanthohumol for two hepatocellular carcinoma cell lines and one normal hepatocyte cell line were 108, 166 and 211 microm, respectively. Normal murine hepatocyte cell line had more resistance to xanthohumol than hepatocellular carcinoma cell lines. Besides, the inhibitory effects of xanthohumol on human hepatocellular carcinoma cell lines were attributed to apoptosis as indicated in the results of flow cytometry, fluorescent nuclear staining and electrophoresis of oligonucleosomal DNA fragments. Hop xanthohumol was more efficient in the growth inhibition of hepatocellular carcinoma cell lines than the flavonoids silibinin and naringin from thistle and citrus. It was shown for the first time that xanthohumol from hops effectively inhibits proliferation of human hepatocellular carcinoma cells in vitro.