Silymarin inhibits UV radiation-induced immunosuppression through augmentation of interleukin-12 in mice

The favorable impacts of silibinin polyphenols as adjunctive therapy in reducing the complications of COVID-19: A review of research evidence and underlying mechanisms

The proceeding pandemic of coronavirus disease 2019 is the latest global challenge. Like most other infectious diseases, inflammation, oxidative stress, and immune system dysfunctions play a pivotal role in the pathogenesis of COVID-19. Furthermore, the quest of finding a potential pharmaceutical therapy for preventing and treating COVID-19 is still ongoing. Silymarin, a mixture of flavonolignans extracted from the milk thistle, has exhibited numerous therapeutic benefits. We reviewed the beneficial effects of silymarin on oxidative stress, inflammation, and the immune system, as primary factors involved in the pathogenesis of COVID-19. We searched PubMed/Medline, Web of Science, Scopus, and Science Direct databases up to April 2022 using the relevant keywords. In summary, the current review indicates that silymarin might exert therapeutic effects against COVID-19 by improving the antioxidant system, attenuating inflammatory response and respiratory distress, and enhancing immune system function. Silymarin can also bind to target proteins of SARS-CoV-2, including main protease, spike glycoprotein, and RNA-dependent RNA-polymerase, leading to the inhibition of viral replication. Although multiple lines of evidence suggest the possible promising impacts of silymarin in COVID-19, further clinical trials are encouraged.

Role of Silymarin in Cancer Treatment: Facts, Hypotheses, and Questions

The flavonoid silymarin extracted from the seeds of Sylibum marianum is a mixture of 6 flavolignan isomers. The 3 more important isomers are silybin (or silibinin), silydianin, and silychristin. Silybin is functionally the most active of these compounds. This group of flavonoids has been extensively studied and they have been used as hepato-protective substances for the mushroom Amanita phalloides intoxication and mainly chronic liver diseases such as alcoholic cirrhosis and nonalcoholic fatty liver. Hepatitis C progression is not, or slightly, modified by silymarin. Recently, it has also been proposed for SARS COVID-19 infection therapy. The biochemical and molecular mechanisms of action of these substances in cancer are subjects of ongoing research. Paradoxically, many of its identified actions such as antioxidant, promoter of ribosomal synthesis, and mitochondrial membrane stabilization, may seem protumoral at first sight, however, silymarin compounds have clear anticancer effects. Some of them are: decreasing migration through multiple targeting, decreasing hypoxia inducible factor-1α expression, inducing apoptosis in some malignant cells, and inhibiting promitotic signaling among others. Interestingly, the antitumoral activity of silymarin compounds is limited to malignant cells while the nonmalignant cells seem not to be affected. Furthermore, there is a long history of silymarin use in human diseases without toxicity after prolonged administration. The ample distribution and easy accessibility to milk thistle-the source of silymarin compounds, its over the counter availability, the fact that it is a weed, some controversial issues regarding bioavailability, and being a nutraceutical rather than a drug, has somehow led medical professionals to view its anticancer effects with skepticism. This is a fundamental reason why it never achieved bedside status in cancer treatment. However, in spite of all the antitumoral effects, silymarin actually has dual effects and in some cases such as pancreatic cancer it can promote stemness. This review deals with recent investigations to elucidate the molecular actions of this flavonoid in cancer, and to consider the possibility of repurposing it. Particular attention is dedicated to silymarin's dual role in cancer and to some controversies of its real effectiveness.

Path of Silibinin from diet to medicine: A dietary polyphenolic flavonoid having potential anti-cancer therapeutic significance

In the last few decades, targeting cancer by the use of dietary phytochemicals has gained enormous attention. The plausible reason and believe or mind set behind this fact is attributed to either lesser or no side effects of natural compounds as compared to the modern chemotherapeutics, or due to their conventional use as dietary components by mankind for thousands of years. Silibinin is a naturally derived polyphenol (a flavonolignans), possess following biochemical features; molecular formula C₂₅H₂₂O₁₀, Molar mass: 482.44 g/mol, Boiling point 793 °C, with strikingly high antioxidant and anti-tumorigenic properties. The anti-cancer properties of Silibinin are determined by a variety of cellular pathways which include induction of apoptosis, cell cycle arrest, inhibition of angiogenesis and metastasis. In addition, Silibinin controls modulation of the expression of aberrant miRNAs, inflammatory response, and synergism with existing anti-cancer drugs. Therefore, modulation of a vast array of cellular responses and homeostatic aspects makes Silibinin an attractive chemotherapeutic agent. However, like other polyphenols, the major hurdle to declare Silibinin a translational chemotherapeutic agent, is its lesser bioavailability. After summarizing the chemistry and metabolic aspects of Silibinin, this extensive review focuses on functional aspects governed by Silibinin in chemoprevention with an ultimate goal of summarizing the evidence supporting the chemopreventive potential of Silibinin and clinical trials that are currently ongoing, at a single platform.

A Green Ultrasound-Assisted Extraction Optimization of the Natural Antioxidant and Anti-Aging Flavonolignans from Milk Thistle Silybum marianum (L.) Gaertn. Fruits for Cosmetic Applications

Silybum marianum (L.) Gaertn. (aka milk thistle) constitutes the source of silymarin (SILM), a mixture of different flavonolignans and represents a unique model for their extraction. Here we report on the development and validation of an ultrasound-assisted extraction (UAE) method of S. marianum flavonolignans follow by their quantification using LC system. The optimal conditions of this UAE method were: aqueous EtOH 54.5% (v/v) as extraction solvent, with application of an ultrasound (US) frequency of 36.6 kHz during 60 min at 45 °C with a liquid to solid ratio of 25:1 mL/g dry weight (DW). Following its optimization using a full factorial design, the extraction method was validated according to international standards of the association of analytical communities (AOAC) to ensure precision and accuracy in the quantitation of each component of the SILM mixture. The efficiency of this UAE was compared with maceration protocol. Here, the optimized and validated conditions of the UAE allowed the highest extraction yields of SILM and its constituents in comparison to maceration. During UAE, the antioxidant capacity of the extracts was retained, as confirmed by the in vitro assays CUPRAC (cupric ion reducing antioxidant capacity) and inhibition of AGEs (advanced glycation end products). The skin anti-aging potential of the extract obtained by UAE was also confirmed by the strong in vitro cell-free inhibition capacity of both collagenase and elastase. To summarize, the UAE procedure presented here is a green and efficient method for the extraction and quantification of SILM and its constituents from the fruits of S. marianum, making it possible to generate extracts with attractive antioxidant and anti-aging activities for future cosmetic applications.

A significant therapeutic effect of silymarin administered alone, or in combination with chemotherapy, in experimental pulmonary tuberculosis caused by drug-sensitive or drug-resistant strains: In vitro and in vivo studies

For many years, tuberculosis (TB) has been a major public health problem worldwide. Advances for treatment and eradication have been very limited. Silymarin (Sm) is a natural product with antioxidant and hepatoprotective activities that has been proposed as a complementary medicine to reduce the liver injury produced by the conventional anti-TB chemotherapy. Sm also has immunoregulatory and microbicide properties. In this study, we determined the effect of Sm on the growth control of mycobacteria. In vitro studies showed that Sm and Silibinin (the principal active compound of Sm) have microbicidal activity against drug-sensitive and multidrug-resistant (MDR) mycobacteria, induce the production of protective cytokines from infected macrophages, and improve the growth control of mycobacteria (p ≤ 0.0001). Studies in vivo using a model of progressive pulmonary TB in BALB/c mice infected with drug-sensitive or MDR mycobacteria have shown that Sm induces significant expression of Th-1 cytokines such as IFN-γ and IL-12 as well as TNFα, which produce significant therapeutic activity when administered alone and apparently have a synergistic effect with chemotherapy. These results suggest that Sm has a bactericidal effect and can contribute to the control and establishment of a TH1 protective immune response against mycobacterial infection. Thus, it seems that this flavonoid has a promising potential as adjuvant therapy in the treatment of TB.

A Water-Soluble Microencapsulated Milk Thistle Extract as Active Ingredient for Dermal Formulations

The choice of formulation is often of crucial importance in order to obtain a pharmaceutical product for the administration of poorly soluble drugs. Recently, a new water-soluble microparticulate powder form (MTE-mp) for the oral administration of a high functionality/low solubility silymarin rich milk thistle extract (MTE) has been developed. Findings showed that extract-loaded microparticles by spray-drying were produced with high and reproducible yields and encapsulation efficiency. The in vitro dissolution and permeation rates of silymarin were dramatically improved with respect to the raw material, and also enhanced the silymarin anti-inflammatory abilities. Given these successful results, the new MTE-mp delivery system has been proposed as an active ingredient for dermal applications. The aim of this research was the design and development of two topical formulations, hydrogel and emulgel (O/W emulsion), containing the MTE-mp delivery system or MTE raw extract. All the formulations were compared to each other in terms of handling and incorporation amount of the active ingredient during the productive process. Moreover, the addition to the emulgel of lecithin (L) as enhancer of permeation was tested. The MTE-mp ingredient that resulted was stable and more-easily incorporated both in hydrogel and emulgel than raw MTE extract, obtaining the best permeation profile for MTE-mp from emulgel with the addition of L. The obtained results confirm that the MTE-mp system could be used as a stable, water-soluble, and easy-handling functional ingredient, giving the opportunity to develop new strategies for MTE delivery in health products.

Healthcare Workers Occupationally Exposed to Ionizing Radiation Exhibit Altered Levels of Inflammatory Cytokines and Redox Parameters

Studies have shown an increased risk for a variety of cancers, specifically brain cancer, in healthcare workers occupationally exposed to ionizing radiation. Although the mechanisms mediating these phenomena are not fully understood, ionizing radiation-mediated elevated levels of reactive oxygen species (ROS), oxidative DNA damage, and immune modulation are likely involved. A group of 20 radiation exposed workers and 40 sex- and age-matched non-exposed control subjects were recruited for the study. We measured superoxide (O₂•⁻) levels in whole blood of healthcare workers and all other measurements of cytokines, oxidative DNA damage, extracellular superoxide dismutase (EcSOD) activity and reduced/oxidized glutathione ratio (GSH/GSSG) in plasma. Levels of O₂•⁻ were significantly higher in radiation exposed workers compared to control. Similarly, a significant increase in the levels of interleukin (IL)-6, IL-1α and macrophage inflammatory protein (MIP)-1α in radiation exposed workers compared to control was observed, while there was no significance difference in the other 27 screened cytokines. A significant positive correlation was found between MIP-1α and O₂•⁻ levels with no correlation in either IL-6 or IL-1α. Further, a dose-dependent relationship with significant O₂•⁻ production and immune alterations in radiation exposed workers was demonstrated. There was no statistical difference between the groups in terms of oxidative DNA damage, GSH/GSSG levels, or EcSOD activity. Although the biologic significance of cytokines alterations in radiation exposed workers is unclear, further studies are needed for determining the underlying mechanism of their elevation.

Protective effects of antioxidin-RL from Odorrana livida against ultraviolet B-irradiated skin photoaging

The unavoidable daily exposure of the skin to ultraviolet (UV) B radiation is proven to have deleterious effects. The action mechanism of antioxidin-RL, an antioxidant peptide purified from skin secretions of frog Odorrana livida with amino acid sequence of AMRLTYNRPCIYAT, is well characterized by NMR titration and mutation based on ABTS⁺ scavenging activities. In order to explore the protective effects of antioxidin-RL against UVB-irradiated skin photoaging, cell uptake assay was used to detect the location of antioxidin-RL molecules serving various biological functions in the cells. The protective effects of antioxidin-RL on UVB-induced response were examined in vitro and in vivo. Results showed that antioxidin-RL successfully penetrated the cell membrane and exerted a positive effect on cell migration. It also effectively inhibited the UVB-induced excessive production of ROS and prevented oxidative damage to DNAs and proteins. Moreover, the mRNA expressions of MMP-1, VEGF, COX-2, and pro-inflammatory cytokines, such as IL-6 and TNF-α in antioxidin-RL-treated HaCaT and HSF cells were significantly down-regulated whereas those of FGF, procollagen type I and TGF-β1 up-regulated. Antioxidin-RL effectively prevented UVB-induced erythema on mouse skin, thereby inhibiting UVB-induced skin thickening and inflammation and increasing collagen deposition as demonstrated by in vivo experiments. Hence, the novel antioxidant peptide antioxidin-RL can effectively reduce UVB-induced skin reactions in vivo and in vitro, providing potential molecules against UVB-induced inflammation and photoaging.

Honokiol inhibits ultraviolet radiation-induced immunosuppression through inhibition of ultraviolet-induced inflammation and DNA hypermethylation in mouse skin

Ultraviolet (UV) radiation exposure induces immunosuppression, which contributes to the development of cutaneous malignancies. We investigated the effects of honokiol, a phytochemical found in plants of the genus Magnolia, on UVB-induced immunosuppression using contact hypersensitivity (CHS) as a model in C3H/HeN mice. Topical application of honokiol (0.5 and 1.0 mg/cm2 skin area) had a significant preventive effect on UVB-induced suppression of the CHS response. The inflammatory mediators, COX-2 and PGE2, played a key role in this effect, as indicated by honokiol inhibition of cyclooxygenase-2 (COX-2) expression and PGE2 production in the UVB-exposed skin. Honokiol application also inhibited UVB-induced DNA hypermethylation and its elevation of the levels of TET enzyme, which is responsible for DNA demethylation in UVB-exposed skin. This was consistent with the restoration of the CHS response in mice treated with the DNA demethylating agent, 5-aza-2'-deoxycytidine, after UVB exposure. There was no significant difference in the levels of inhibition of UVB-induced immunosuppression amongst mice that were treated topically with available anti-cancer drugs (imiquimod and 5-fluorouracil). This study is the first to show that honokiol has the ability to inhibit UVB-induced immunosuppression in preclinical model and, thus, has potential for use as a chemopreventive strategy for UVB radiation-induced malignancies.

Silymarin/Silybin and Chronic Liver Disease: A Marriage of Many Years

Silymarin is the extract of Silybum marianum, or milk thistle, and its major active compound is silybin, which has a remarkable biological effect. It is used in different liver disorders, particularly chronic liver diseases, cirrhosis and hepatocellular carcinoma, because of its antioxidant, anti-inflammatory and antifibrotic power. Indeed, the anti-oxidant and anti-inflammatory effect of silymarin is oriented towards the reduction of virus-related liver damages through inflammatory cascade softening and immune system modulation. It also has a direct antiviral effect associated with its intravenous administration in hepatitis C virus infection. With respect to alcohol abuse, silymarin is able to increase cellular vitality and to reduce both lipid peroxidation and cellular necrosis. Furthermore, silymarin/silybin use has important biological effects in non-alcoholic fatty liver disease. These substances antagonize the progression of non-alcoholic fatty liver disease, by intervening in various therapeutic targets: oxidative stress, insulin resistance, liver fat accumulation and mitochondrial dysfunction. Silymarin is also used in liver cirrhosis and hepatocellular carcinoma that represent common end stages of different hepatopathies by modulating different molecular patterns. Therefore, the aim of this review is to examine scientific studies concerning the effects derived from silymarin/silybin use in chronic liver diseases, cirrhosis and hepatocellular carcinoma.

Silymarin and Its Role in Chronic Diseases

Silymarin is the active constituent of Silybum marianum (milk thistle) which is a C-25 containing flavonolignan. Milk thistle has a lot of traditional values, being used as a vegetable, as salad, as bitter tonic, and as galactogogue in nursing mothers and in various ailments such as liver complications, depression, dyspepsia, spleenic congestions, varicose veins, diabetes, amenorrhea, uterine hemorrhage, and menstrual problems. In this present chapter, a comprehensive attempt has been made to discuss the potential of silymarin in chronic disorders. An insight into modulation of cellular signaling by silymarin and its implication in various disorders such as liver disorders, inflammatory disorders, cancer, neurological disorders, skin diseases, and hypercholesterolemia is being provided.

Natural products as photoprotection

The rise in solar ultraviolet radiation on the earth's surface has led to a depletion of stratospheric ozone over recent decades, thus accelerating the need to protect human skin against the harmful effects of UV radiation such as erythema, edema, hyperpigmentation, photoaging, and skin cancer. There are many different ways to protect skin against UV radiation's harmful effects. The most popular way to reduce the amount of UV radiation penetrating the skin is topical application of sunscreen products that contain UV absorbing or reflecting active molecules. Based on their protection mechanism, the active molecules in sunscreens are broadly divided into inorganic and organic agents. Inorganic sunscreens reflect and scatter UV and visible radiation, while organic sunscreens absorb UV radiation and then re-emit energy as heat or light. These synthetic molecules have limited concentration according to regulation concern. Several natural compounds with UV absorption property have been used to substitute for or to reduce the quantity of synthetic sunscreen agents. In addition to UV absorption property, most natural compounds were found to act as antioxidants, anti-inflammatory, and immunomodulatory agents, which provide further protection against the damaging effects of UV radiation exposure. Compounds derived from natural sources have gained considerable attention for use in sunscreen products and have bolstered the market trend toward natural cosmetics. This adds to the importance of there being a wide selection of active molecules in sunscreen formulations. This paper summarizes a number of natural products derived from propolis, plants, algae, and lichens that have shown potential photoprotection properties against UV radiation exposure-induced skin damage.

Silymarin alleviates bleomycin-induced pulmonary toxicity and lipid peroxidation in mice

CONTEXT

The application of bleomycin is limited due to its side effects including lung toxicity. Silymarin is a flavonoid complex isolated from milk thistle [Silybum marianum L. (Asteraceae)] which has been identified as an antioxidant and anti-inflammatory compound.

OBJECTIVE

This study evaluates the effect of silymarin on oxidative and inflammatory parameters in the lungs of mice exposed to bleomycin.

MATERIALS AND METHODS

BALB/c mice were divided into four groups of control, bleomycin (1.5 U/kg), bleomycin plus silymarin (50 and 100 mg/kg). After bleomycin administration, mice received 10 d intraperitoneal silymarin treatment. On 10th day, blood and lung samples were collected for measurement of oxidative and inflammatory factors.

RESULTS

Silymarin led to a decrease in lung lipid peroxidation (0.19 and 0.17 nmol/mg protein) in bleomycin-injected animals. Glutathione-S-transferase (GST) which was inhibited by bleomycin (32.4 nmol/min/mg protein) induced by higher dose of silymarin (41 nmol/min/mg protein). Silymarin caused an elevation in glutathione (GSH): 2.6 and 3.1 µmol/g lung compare with bleomycin-injected animals 1.8 µmol/g lung. Catalase (CAT) was increased due to high dose of silymarin (65.7 µmol/min/ml protein) compare with bleomycin treated-mice. Myeloperoxidase (MPO) which was induced due to bleomycin (p < 0.05) reduced again by high dose of silymarin (0.51 U/min/mg protein). Bleomycin led to an increase in TNF-α and interleukin-6 (IL-6) (7.9 and 11.8 pg/ml). These parameters were reduced by silymarin (p < 0.05).

CONCLUSIONS

Silymarin attenuated bleomycin induced-pulmonary toxicity. This protective effect may be due to the ability of silymarin in keeping oxidant-antioxidant balance and regulating of inflammatory mediator release.

Photoimmunology

The discipline that investigates the biologic effects of ultraviolet radiation on the immune system is called photoimmunology. Photoimmunology evolved from an interest in understanding the role of the immune system in skin cancer development and why immunosuppressed organ transplant recipients are at a greatly increased risk for cutaneous neoplasms. In addition to contributing to an understanding of the pathogenesis of nonmelanoma skin cancer, the knowledge acquired about the immunologic effects of ultraviolet radiation exposure has provided an understanding of its role in the pathogenesis of other photodermatologic diseases.

Targeting tumor microenvironment with silibinin: promise and potential for a translational cancer chemopreventive strategy

Tumor microenvironment (TME) refers to the dynamic cellular and extra-cellular components surrounding tumor cells at each stage of the carcinogenesis. TME has now emerged as an integral and inseparable part of the carcinogenesis that plays a critical role in tumor growth, angiogenesis, epithelial to mesenchymal transition (EMT), invasion, migration and metastasis. Besides its vital role in carcinogenesis, TME is also a better drug target because of its relative genetic stability with lesser probability for the development of drug-resistance. Several drugs targeting the TME (endothelial cells, macrophages, cancer-associated fibroblasts, or extra-cellular matrix) have either been approved or are in clinical trials. Recently, non-steroidal anti-inflammatory drugs targeting inflammation were reported to also prevent several cancers. These exciting developments suggest that cancer chemopreventive strategies targeting both tumor and TME would be better and effective towards preventing, retarding or reversing the process of carcinogenesis. Here, we have reviewed the effect of a well established hepatoprotective and chemopreventive agent silibinin on cellular (endothelial, fibroblast and immune cells) and non-cellular components (cytokines, growth factors, proteinases etc.) of the TME. Silibinin targets TME constituents as well as their interaction with cancer cells, thereby inhibiting tumor growth, angiogenesis, inflammation, EMT, and metastasis. Silibinin is already in clinical trials, and based upon completed studies we suggest that its chemopreventive effectiveness should be verified through its effect on biological end points in both tumor and TME. Overall, we believe that the chemopreventive strategies targeting both tumor and TME have practical and translational utility in lowering the cancer burden.

Prostaglandin E2 Promotes UV radiation-induced immune suppression through DNA hypermethylation

Exposure of mice to UV radiation results in suppression of the contact hypersensitivity (CHS) response. Here, we report that the UV-induced suppression of CHS is associated with increases in the levels of cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2), and PGE2 receptors in the exposed skin. UV radiation-induced suppression of CHS was inhibited by topical treatment of the skin with celecoxib or indomethacin (inhibitors of COX-2) or AH6809 (an EP2 antagonist). Moreover, mice deficient in COX-2 were found to be resistant to UV-induced suppression of CHS. The exposure of wild-typemice to UVB radiation resulted in DNA hypermethylation, increased DNA methyltransferase (Dnmt) activity, and elevated levels of Dnmt1, Dnmt3a, and Dnmt3b proteins in the skin, and these responses were downregulated on topical treatment of the site of exposure after irradiation with indomethacin or EP2 antagonist. Topical treatment of UVB-exposed COX-2-deficient mice with PGE2 enhanced the UVB-induced suppression of CHS as well as global DNA methylation and elevated the levels of Dnmt activity and Dnmt proteins in the skin. Intraperitoneal injection of 5-aza-2'-deoxycytidine (5-Aza-dc), a DNA demethylating agent, restored the CHS response to 2,4-dinitrofluorobenzene in UVB-exposed skin and this was associated with the reduction in global DNA methylation and Dnmt activity and reduced levels of Dnmt proteins. Furthermore, treatment with 5-Aza-dc reversed the effect of PGE2 on UV-induced suppression of CHS in COX-2-deficient mice. These findings reveal a previously unrecognized role for PGE2 in the promotion of UVB-induced immunosuppression and indicate that it is mediated through PGE2 regulation of DNA methylation.

Apigenin, a bioactive flavonoid from Lycopodium clavatum, stimulates nucleotide excision repair genes to protect skin keratinocytes from ultraviolet B-induced reactive oxygen species and DNA damage

In this study, we examined the antioxidative and the DNA protective potentials of apigenin, a flavonoid polyphenol isolated from Lycopodium clavatum, in both in-vitro (HaCaT skin keratinocytes) and in-vivo (mice) models against UV-B radiation. We used DAPI staining in UV-B-irradiated HaCaT skin keratinocytes pre-treated with and without apigenin to assess DNA damage. We also used a flow-cytometric analysis in mice exposed to UV-B radiation with or without topical application of apigenin to assess, through a comet assay, chromosomal aberrations and quanta from reactive oxygen species (ROS) generation. Data from the stability curves for the Gibb's free energy determined from a melting-temperature profile study indicated that apigenin increased the stability of calf thymus DNA. Immunofluorescence studies revealed that apigenin caused a reduction in the number of cyclobutane pyrimidine dimers (CPDs) after 24 h, the time at which the nucleotide excision repair (NER) genes were activated. Thus, apigenin accelerated reversal of UV-B-induced CPDs through up-regulation of NER genes, removal of cyclobutane rings, inhibition of ROS generation, and down-regulation of NF-κB and MAPK, thereby revealing the precise mechanism of DNA repair.

The effect of silymarin (Silybum marianum) on human skin fibroblasts in an in vitro wound healing model

CONTEXT

Silymarin, a flavonolignan from Silybum marianum (L.) Gaertn. (Asteraceae), has been reported to have antioxidant and anti-inflammatory properties. Therefore, it may be worthwhile to study the effect of silymarin on wound healing.

OBJECTIVE

To evaluate the effect of silymarin on human fibroblast cells in an in vitro model of wound healing.

MATERIALS AND METHODS

Human fibroblast cells were treated with different concentrations (4.5, 9, 18, 36 µg/mL) of silymarin. The effects of silymarin on cell viability, proliferation, collagen synthesis, and expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthetase (iNOS) were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, 5-bromo-2'-deoxy-uridine, hydroxyproline analysis and real-time PCR, respectively. The effect of silymarin on cellular antioxidant status was determined by protection against hydrogen peroxide (H₂O₂)-induced cell injury and free radical scavenging activity (ABTS assay) of the cells.

RESULTS

Results of the present study indicate that pretreatment of fibroblast cells with silymarin significantly protected cells against H₂O₂-induced injury (p < 0.05). After an 18 h treatment of cells with 36 µg/mL silymarin, total antioxidant capacity of cells significantly increased (p < 0.05). Furthermore, pretreatment of human fibroblast cells with silymarin significantly inhibited lipopolysaccharide (LPS)-induced COX-2 mRNA expression (p < 0.001). There was no significant difference in fibroblast proliferation and collagen synthesis between treatment and control groups (p > 0.05).

DISCUSSION AND CONCLUSION

Silymarin may be useful as a therapeutic agent for the treatment of cutaneous wounds through its antioxidation and anti-inflammation effects.

Silymarin inhibits ultraviolet radiation-induced immune suppression through DNA repair-dependent activation of dendritic cells and stimulation of effector T cells

Silymarin inhibits UVB-induced immunosuppression in mouse skin. To identify the molecular mechanisms underlying this effect, we used an adoptive transfer approach in which dendritic cells (DCs) from the draining lymph nodes of donor mice that had been UVB-exposed and sensitized to 2,4,-dinitrofluorobenzene (DNFB) were transferred into naïve recipient mice. The contact hypersensitivity (CHS) response of the recipient mice to DNFB was then measured. When DCs were obtained from UVB-exposed donor mice that were not treated with silymarin, the CHS response was suppressed confirming the role of DCs in the UVB-induced immunosuppression. Silymarin treatment of UVB-exposed donor mice relieved this suppression of the CHS response in the recipients. Silymarin treatment was associated with rapid repair of UVB-induced cyclobutane pyrimidine dimers (CPDs) in DCs and silymarin treatment did not prevent UV-induced immunosuppression in XPA-deficient mice which are unable to repair UV-induced DNA damage. The CHS response in mice receiving DCs from silymarin-treated UV-exposed donor mice also was associated with enhanced secretion of Th1-type cytokines and stimulation of T cells. Adoptive transfer of T cells revealed that transfer of either CD8(+) or CD4(+) cells from silymarin-treated, UVB-exposed donors resulted in enhancement of the CHS response. Cell culture study showed enhanced secretion of IL-2 and IFNγ by CD8(+) T cells, and reduced secretion of Th2 cytokines by CD4(+) T cells, obtained from silymarin-treated UVB-exposed mice. These data suggest that DNA repair-dependent functional activation of DCs, a reduction in CD4(+) regulatory T-cell activity, and stimulation of CD8(+) effector T cells contribute to silymarin-mediated inhibition of UVB-induced immunosuppression.

Pharmacotherapy of actinic keratosis: an update

INTRODUCTION

Actinic keratosis (AK) represents the initial intraepidermal manifestation of abnormal keratinocyte proliferation, with the potential of progression to squamous cell carcinoma (SCC). Few visible AKs lead to the use of lesion-directed treatments, including ablative and/or surgical procedures. Multiple and/or the suspicion of subclinical (non-visible) AKs lead to the use of field-directed therapies, including topical and ablative treatments. Predicting which AK will progress to SCC is difficult, and so all are treated. The goals of treatment are to eliminate visible AKs and to treat subclinical (non-visible) AKs, minimizing their risk of progression to invasive SCC, while pursuing good cosmesis.

AREAS COVERED

This review discusses the prevention of AKs (such as ultraviolet light avoidance, sunscreen use, protective clothing, and frequent self-examinations, in addition to chemoprevention with retinoids, eflornithine, silymarin, and others). It also covers lesion-directed treatments (e.g., cryotherapy, electrodessication and curettage, and surgery). Field-directed treatments are also mentioned (including laser resurfacing, dermabrasion, chemical peels, topical immunomodulators (imiquimod and diclofenac), topical chemotherapeutic agents (5-fluorouracil and retinoids), and photodynamic therapy). Finally, newer and investigational treatments are discussed (including ingenol mebutate).

EXPERT OPINION

There is no panacea in the treatment of AKs. The current best approach is the sequential treatment with a lesion-directed and a field-directed therapy. Several combinations seem to work well; they just need to be selected based on the evidence and adjusted to patient needs, preferences and dermatologist expertise.

Amelioration of Ochratoxin A-induced immunotoxic effects by silymarin and Vitamin E in White Leghorn cockerels

Silymarin (SL) is the bioactive extract of the plant Silybum marianum and Vitamin E (VE) is an important anti-oxidant. The present study was designed to evaluate potential ameliorative effects of SL and VE against Ochratoxin A (OTA)-induced immunotoxic effects in White Leghorn cockerels. One day-old birds were divided into 12 groups (20 birds/group) and fed basal diets amended with OTA (1.0 or 2.0 mg/kg) alone or in combination with SL (10 g/kg) and/or VE (200 mg/kg) for 42 days. Immunological in situ responses, including antibody formation against sheep red blood cells (7 and 14 days after both primary and booster injections), lymphoproliferative responses to avian tuberculin (30 days of age), and mononuclear phagocytic system function (i.e. by clearance of injected carbon particles) assay (42 days of age), were assessed. Results suggested that silymarin and Vitamin E alone or in combination ameliorated the immunotoxic effects induced by 1.0 mg OTA/kg but could not significantly impact on the effect from ingestion of 2.0 mg OTA/kg. The results of the present study suggested that both SL and VE possess an ability to ameliorate OTA-induced immunotoxicity in chicks. However, it remains to be determined whether/what SL:OTA or VE:OTA ratios are required to assure such mitigation of OTA-induced immunotoxicities.

Protective effect of curcumin, silymarin and N-acetylcysteine on antitubercular drug-induced hepatotoxicity assessed in an in vitro model

Tuberculosis (TB) is highly endemic in India. The first-line anti-TB therapy (ATT) involving isoniazid (INH), rifampicin and pyrazinamide causes hepatotoxicity in approximately 11.5% of Indian patients. Studies have shown that ATT-induced hepatotoxicity is primarily due to oxidative stress caused by the drugs and metabolites. Herbal drugs with antioxidative properties have been tested in animal studies and clinical trials for the management of hepatotoxicity. The objective of this study was to investigate the role of curcumin (CUR), silymarin (SILY) and N-acetylcysteine (N-ACET) on hepatotoxicity by ATT drugs using an in vitro model of human hepatocellular carcinoma cell line (HepG2). HepG2 cells were treated with ATT drugs alone or along with CUR, SILY or N-ACET for a 48-h duration. The cells were monitored for viability, morphology, respiring mitochondria and cell cycle. Our results suggest that the presence of hepatoprotective drugs during treatment of HepG2 cells with ATT drugs lowers the hepatotoxic effect of the latter. This is observed in terms of (a) increased cell viability, (b) healthy-looking cell morphology as revealed by phase contrast microscopy, (c) active respiring cells as observed with confocal microscopy upon staining with a mitochondrial membrane-specific dye, MitoTracker(®) Red, and reduction in the sub-G(1) peak in cell cycle analysis by flow cytometry. Our results suggest that these hepatoprotective drugs need to be further explored as potential adjuvant therapy along with ATT drugs.

The prospective role of plant products in radiotherapy of cancer: a current overview

Treatment of cancer often requires exposure to radiation, which has several limitations involving non-specific toxicity toward normal cells, reducing the efficacy of treatment. Efforts are going on to find chemical compounds which would effectively offer protection to the normal tissues after radiation exposure during radiotherapy of cancer. In this regard, plant-derived compounds might serve as “leads” to design ideal radioprotectors/radiosensitizers. This article reviews some of the recent findings on prospective medicinal plants, phytochemicals, and their analogs, based on both in vitro and in vivo tumor models especially focused with relevance to cancer radiotherapy. Also, pertinent discussion has been presented on the molecular mechanism of apoptotic death in relation to the oxidative stress in cancer cells induced by some of these plant samples and their active constituents.

Chemoprevention of melanoma

Despite advances in drug discovery programs and molecular approaches for identifying drug targets, incidence and mortality rates due to melanoma continue to rise at an alarming rate. Existing preventive strategies generally involve mole screening followed by surgical removal of the benign nevi and abnormal moles. However, due to lack of effective programs for screening and disease recurrence after surgical resection, there is a need for better chemopreventive agents. Although sunscreens have been used extensively for protecting from UV-induced melanomas, results of correlative population-based studies are controversial, with certain studies suggest increased skin cancer risk in sunscreen users. Therefore, these studies require further authentication to conclusively confirm the chemoprotective efficacy of sunscreens. This chapter reviews the current understanding regarding melanoma chemoprevention and the various strategies used to accomplish this objective.

Polyphenols: skin photoprotection and inhibition of photocarcinogenesis

Polyphenols are a large family of naturally occurring plant products and are widely distributed in plant foods, such as, fruits, vegetables, nuts, flowers, bark and seeds, etc. These polyphenols contribute to the beneficial health effects of dietary products. Clinical and epidemiological studies suggest that exposure of the skin to environmental factors/pollutants, such as solar ultraviolet (UV) radiation induce harmful effects and leads to various skin diseases including the risk of melanoma and non-melanoma skin cancers. The incidence of non-melanoma skin cancer, comprising of squamous cell carcinoma and basal cell carcinoma, is a significant public health concern world-wide. Exposure of the skin to solar UV radiation results in inflammation, oxidative stress, DNA damage, dysregulation of cellular signaling pathways and immunosuppression thereby resulting in skin cancer. The regular intake of natural plant products, especially polyphenols, which are widely present in fruits, vegetables, dry legumes and beverages have gained considerable attention as protective agents against the adverse effects of UV radiation. In this article, we first discussed the impact of polyphenols on human health based on their structure-activity relationship and bioavailability. We then discussed in detail the photoprotective effects of some selected polyphenols on UV-induced skin inflammation, proliferation, immunosuppression, DNA damage and dysregulation of important cellular signaling pathways and their implications in skin cancer management. The selected polyphenols include: green tea polyphenols, pomegranate fruit extract, grape seed proanthocyanidins, resveratrol, silymarin, genistein and delphinidin. The new information on the mechanisms of action of these polyphenols supports their potential use in skin photoprotection and prevention of photocarcinogenesis in humans.

Silymarin ameliorates cisplatin-induced hepatotoxicity in rats: histopathological and ultrastructural studies

The benefit of silymarin, a plant extract with strong antioxidant activity against hepatotoxicity induced by cisplatin in rats was investigated in this study. Cisplatin is one of the most effective chemotherapeutic drugs, yet it alone does not achieve a satisfactory therapeutic outcome and at high doses it can produce undesirable side effects. Five equal-sized groups (18 rats each) of male Sprague Dawley rats [control, vehicle; cisplatin; silymarin 2 h after cisplatin injection; and silymarin 2 h before cisplatin injection] were used. Histopathological and ultrastructural observation of livers were carried out using light and electron microscopy. Results documented that cisplatin produced behavioral, external features animal changes, as well as hazard pathological picture changes in liver where most hepatocytes appeared diminutive with vacuolated cytoplasm, sinusoids dilated and organelle disorganized. These results revealed that cisplatin may be toxic and terminates in complex liver damage. Administrations of silymarin 2 h after cisplatin, significantly increase the body weight returning it to normal, yet it failed in complete protection against the pathological alteration caused by cisplatin. Pretreatment with silymarin 2 h before cisplatin significantly decreased the pathological changes induced by cisplatin and appeared highly protective. These results suggested that silymarin possess protective effects against cisplatin hepatotoxic action in animal models. Since, no significant toxicity of silymarin is reported in human studies, this plant extract can be used as a dietary supplement by patients taking anticancerous medications and might serve as a novel combination agent with cisplatin since it plays a significant role in reducing its toxicity.

Silymarin protects epidermal keratinocytes from ultraviolet radiation-induced apoptosis and DNA damage by nucleotide excision repair mechanism

Solar ultraviolet (UV) radiation is a well recognized epidemiologic risk factor for melanoma and non-melanoma skin cancers. This observation has been linked to the accumulation of UVB radiation-induced DNA lesions in cells, and that finally lead to the development of skin cancers. Earlier, we have shown that topical treatment of skin with silymarin, a plant flavanoid from milk thistle (Silybum marianum), inhibits photocarcinogenesis in mice; however it is less understood whether chemopreventive effect of silymarin is mediated through the repair of DNA lesions in skin cells and that protect the cells from apoptosis. Here, we show that treatment of normal human epidermal keratinocytes (NHEK) with silymarin blocks UVB-induced apoptosis of NHEK in vitro. Silymarin reduces the amount of UVB radiation-induced DNA damage as demonstrated by reduced amounts of cyclobutane pyrimidine dimers (CPDs) and as measured by comet assay, and that ultimately may lead to reduced apoptosis of NHEK. The reduction of UV radiation-induced DNA damage by silymarin appears to be related with induction of nucleotide excision repair (NER) genes, because UV radiation-induced apoptosis was not blocked by silymarin in NER-deficient human fibroblasts. Cytostaining and dot-blot analysis revealed that silymarin repaired UV-induced CPDs in NER-proficient fibroblasts from a healthy individual but did not repair UV-induced CPD-positive cells in NER-deficient fibroblasts from patients suffering from xeroderma pigmentosum complementation-A disease. Similarly, immunohistochemical analysis revealed that silymarin did not reduce the number of UVB-induced sunburn/apoptotic cells in the skin of NER-deficient mice, but reduced the number of sunburn cells in their wild-type counterparts. Together, these results suggest that silymarin exert the capacity to reduce UV radiation-induced DNA damage and, thus, prevent the harmful effects of UV radiation on the genomic stability of epidermal cells.

Natural agents: cellular and molecular mechanisms of photoprotection

The skin is the largest organ of the body that produces a flexible and self-repairing barrier and protects the body from most common potentially harmful physical, environmental, and biological insults. Solar ultraviolet (UV) radiation is one of the major environmental insults to the skin and causes multi-tiered cellular and molecular events eventually leading to skin cancer. The past decade has seen a surge in the incidence of skin cancer due to changes in life style patterns that have led to a significant increase in the amount of UV radiation that people receive. Reducing excessive exposure to UV radiation is desirable; nevertheless this approach is not easy to implement. Therefore, there is an urgent need to develop novel strategies to reduce the adverse biological effects of UV radiation on the skin. A wide variety of natural agents have been reported to possess substantial skin photoprotective effects. Numerous preclinical and clinical studies have elucidated that natural agents act by several cellular and molecular mechanisms to delay or prevent skin cancer. In this review article, we have summarized and discussed some of the selected natural agents for skin photoprotection.

Proanthocyanidins inhibit UV-induced immunosuppression through IL-12-dependent stimulation of CD8+ effector T cells and inactivation of CD4+ T cells

The inhibition of UVB-induced immunosuppression by dietary grape seed proanthocyanidins (GSP) has been associated with the induction of interleukin (IL)-12 in mice, and we now confirm that GSPs do not inhibit UVB-induced immunosuppression in IL-12p40 knockout (IL-12 KO) mice and that treatment of these mice with recombinant IL-12 restores the inhibitory effect. To characterize the cell population responsible for the GSP-mediated inhibition of UVB-induced immunosuppression and the role of IL-12 in this process, we used an adoptive transfer approach. Splenocytes and draining lymph nodes were harvested from mice that had been administered dietary GSPs (0.5%-1.0%, w/w), exposed to UVB, and sensitized by the application of 2,4-dinitrofluorobenzene (DNFB) onto the UVB-exposed skin. CD8(+) and CD4(+) T cells were positively selected and transferred into naive mice that were subsequently challenged by application of DNFB on the ear skin. Naive recipients that received CD8(+) T cells from GSP-treated, UVB-irradiated donors exhibited full contact hypersensitivity (CHS) response. Naive mice that received CD4(+) suppressor T cells from GSP-treated, UVB-exposed mice could mount a CHS response after sensitization and subsequent challenge with DNFB. On culture, the CD8(+) T cells from GSP-treated, UVB-exposed mice secreted higher levels (5- to 8-fold) of Th1 cytokines than CD8(+) T cells from UVB-irradiated mice not treated with GSPs. CD4(+) T cells from GSP-treated, UVB-exposed mice secreted significantly lower levels (80%-100%) of Th2 cytokines than CD4(+) T cells from UVB-exposed mice not treated with GSPs. These data suggest that GSPs inhibit UVB-induced immunosuppression by stimulating CD8(+) effector T cells and diminishing regulatory CD4(+) T cells.

Molecular mechanisms of inhibition of photocarcinogenesis by silymarin, a phytochemical from milk thistle (Silybum marianum L. Gaertn.) (Review)

Changes in life style over the past several decades including much of the time spent outdoors and the use of tanning devices for cosmetic purposes by individuals have led to an increase in the incidence of solar ultraviolet (UV) radiation-induced skin diseases including the risk of skin cancers. Solar UV radiations are considered as the most prevalent environmental carcinogens, and chronic exposure of the skin to UV leads to squamous and basal cell carcinoma and melanoma in human population. A wide variety of phytochemicals have been reported to have substantial anti-carcinogenic activity because of their antioxidant and anti-inflammatory properties. Silymarin is one of them and extensively studied for its skin photoprotective capabilities. Silymarin, a flavanolignan, is extracted from the fruits and seeds of milk thistle (Silybum marianum L. Gaertn.), and has been shown to have chemopreventive effects against photocarcinogenesis in mouse tumor models. Topical treatment of silymarin inhibited photocarcinogenesis in mice in terms of tumor incidence, tumor multiplicity and growth of the tumors. Wide range of in vivo mechanistic studies conducted in a variety of mouse models indicated that silymarin has anti-oxidant, anti-inflammatory and immunomodulatory properties which led to the prevention of photocarcinogenesis in mice. This review summarizes and updates the photoprotective potential of silymarin with the particular emphasis on its in vivo mechanism of actions. It is suggested that silymarin may favorably supplement sunscreen protection, and may be useful for skin diseases associated with solar UV radiation-induced inflammation, oxidative stress and immunomodulatory effects.

Green tea polyphenols prevent UV-induced immunosuppression by rapid repair of DNA damage and enhancement of nucleotide excision repair genes

UV radiation-induced immunosuppression has been implicated in the development of skin cancers. Green tea polyphenols (GTP) in drinking water prevent photocarcinogenesis in the skin of mice. We studied whether GTPs in drinking water (0.1-0.5%, w/v) prevent UV-induced immunosuppression and (if so) potential mechanisms of this effect in mice. GTPs (0.2% and 0.5%, w/v) reduced UV-induced suppression of contact hypersensitivity (CHS) in response to a contact sensitizer in local (58-62% reductions; P < 0.001) and systemic (51-55% reductions; P < 0.005) models of CHS. Compared with untreated mice, GTP-treated mice (0.2%, w/v) had a reduced number of cyclobutane pyrimidine dimer-positive (CPD(+)) cells (59%; P < 0.001) in the skin, showing faster repair of UV-induced DNA damage, and had a reduced (2-fold) migration of CPD(+) cells from the skin to draining lymph nodes, which was associated with elevated levels of nucleotide excision repair (NER) genes. GTPs did not prevent UV-induced immunosuppression in NER-deficient mice but significantly prevented it in NER-proficient mice (P < 0.001); immunohistochemical analysis of CPD(+) cells indicated that GTPs reduced the numbers of UV-induced CPD(+) cells in NER-proficient mice (P < 0.001) but not in NER-deficient mice. Southwestern dot-blot analysis revealed that GTPs repaired UV-induced CPDs in xeroderma pigmentosum complementation group A (XPA)-proficient cells of a healthy person but did not in XPA-deficient cells obtained from XPA patients, indicating that a NER mechanism is involved in DNA repair. This study is the first to show a novel NER mechanism by which drinking GTPs prevents UV-induced immunosuppression and that inhibiting UV-induced immunosuppression may underlie the chemopreventive activity of GTPs against photocarcinogenesis.

Topical delivery of silymarin constituents via the skin route

AIM

Silibinin (SB), silydianin (SD), and silychristin (SC) are components of silymarin. These compounds can be used to protect the skin from oxidative stress induced by ultraviolet (UV) irradiation and treat it. To this end, the absorption of silymarin constituents via the skin was examined in the present report.

METHODS

Transport of SB, SD, and SC under the same thermodynamic activity through and into the skin and the effects of pH were studied in vitro using a Franz diffusion assembly.

RESULTS

The lipophilicity increased in the order of SC<SD<SB. Increased lipophilicity of a compound resulted in higher skin deposition but had a minor effect on permeation across the skin in the less-ionized form (pH 8). It is apparent that compounds in the less-ionized form showed higher skin uptake compared to the more-ionized form. Hyperproliferative skin produced by UVB exposure showed increased permeation of silymarin constituents in the less-ionized form, but it did not affect deposition within the skin. With in vivo topical application for 4 and 8 h, the skin deposition of SB was higher than those of SD and SC by 3.5 approximately 4.0- and 30 approximately 40-fold, respectively. The skin disruption and erythema test demonstrated that the topical application of these compounds for up to 24 h caused no apparent skin irritation.

CONCLUSION

The basic profiles of silymarin permeation via skin route were established.

Reversal of ultraviolet B-induced immunosuppression by inhibition of the extracellular signal-regulated mitogen-activated protein kinase

OBJECTIVE

Topical treatment of the specific inhibitor PD98059 (PD) for extracellular signal-regulated kinase (ERK)1/2 combined with ultraviolet B (UVB) exposure in an in vivo study was proposed to confirm the effectiveness of ERK1/2 involved in UVB-induced immunosuppression that was reversed by PD.

METHODS

Based on the mouse model of local UVB-induced immunosuppression [UVB exposure, followed by sensitization with dinitrofluorobenzene (DNFB) on the abdomen skin before challenge on the ear site], the PD was applied on the abdomen-irradiated area 1 h, immediately before and 6 h after UVB exposure, respectively. The baseline of ear thickness was measured and remeasured 24 h after the challenge of DNFB for evaluation of ear-swelling response. Histopathologically, the ear biopsies were taken for hematoxylin and eosin staining.

RESULTS

Mice that received PD post-irradiation treatment showed a statistically significant contact hypersensitivity compared with the UVB-irradiated mice (P<0.05), and paralleled with the biopsy showing a thickened epidermis with lymphocyte infiltration. Thus, the PD had abrogated the UV-induced local suppression of contact hypersensitivity.

CONCLUSION

The ERK1/2 mitogen-activated protein kinase (MAPK) pathway plays an important role in the local UVB-induced immunosuppression, and its specific inhibitor PD can arrest its function, resulting in protection against UVB-induced immunosuppression in the present in vivo study.

Silybin from Silybum Marianum Seeds Inhibits Confluent-Induced Keratinocytes Differentiation as Effectively as Retinoic Acid without Inducing Inflammatory Cytokine

Retinoic acid (RA) has been effective for improving wrinkles. However, it has also been reported that RA induces skin irritation. In this study, we explored new botanical compounds that show RA-like activity, but do not induce inflammation in vitro. Keratinocytes were maintained in a confluent condition and induced differentiation. Under this condition keratinocytes were treated with many botanical extracts and their morphological change were observed and compared with RA-treated. We found that silybin, which is a major flavonolignan from Silybum Marianum seeds, induced RA-like morphological change and prevented differentiation. We showed that silybin, like RA, reduced the expression of keratinocyte terminal differentiation markers and stimulated the expression of basement membrane component proteins. In contrast, silybin, unlike RA, did not stimulate the secretion of IL-1α, which is a skin irritation mediator. These results suggest that silybin has RA-like activity on keratinocytes and has the potential to improve winkle without inducing skin irritation.

Silibinin attenuates antigen-specific IgE production through the modulation of Th1/Th2 balance in ovalbumin-sensitized BALB/c mice

The effect of silibinin on antigen-specific antibody production and T-cell cytokine expression was investigated. BALB/c mice were either left untreated or administered daily with vehicle (VH; saline) and/or silibinin (200 or 400 mg/kg) by gavage for 3 consecutive days prior to sensitization with ovalbumin (OVA). The antibody production in the serum and T-cell-derived cytokine expression by splenocytes were determined 7 days post OVA sensitization. Our results demonstrated that the production of OVA-specific serum IgE and total IgE was significantly attenuated by silibinin treatment, whereas OVA-specific IgG(2a) was markedly enhanced. In parallel with the differential modulation of the production of IgG(2a) and IgE, treatment of OVA-sensitized mice with silibinin markedly increased and decreased the production of IFN-gamma and IL-4, respectively, by splenocytes cultured in the presence of OVA. Together, these results suggest that silibinin treatment polarizes the Th1/Th2 immune balance toward the Th1-dominant direction, which may be beneficial against IgE-mediated allergy.

Silymarin protects liver against toxic effects of anti-tuberculosis drugs in experimental animals

BACKGROUND

The first line anti-tuberculosis drugs isoniazid (INH), rifampicin (RIF) and pyrazinamide (PZA) continues to be the effective drugs in the treatment of tuberculosis, however, the use of these drugs is associated with toxic reactions in tissues, particularly in the liver, leading to hepatitis. Silymarin, a standard plant extract with strong antioxidant activity obtained from S. marianum, is known to be an effective agent for liver protection and liver regeneration. The aim of this study was to investigate the protective actions of silymarin against hepatotoxicity caused by different combinations of anti-tuberculosis drugs.

METHODS

Male Wistar albino rats weighing 250-300 g were used to form 6 study groups, each group consisting of 10 rats. Animals were treated with intra-peritoneal injection of isoniazid (50 mg/kg) and rifampicin (100 mg/kg); and intra-gastric administration of pyrazinamid (350 mg/kg) and silymarin (200 mg/kg). Hepatotoxicity was induced by a combination of drugs with INH+RIF and INH+RIF+PZA. Hepatoprotective effect of silymarin was investigated by co-administration of silymarin together with the drugs. Serum biochemical tests for liver functions and histopathological examination of livers were carried out to demonstrate the protection of liver against anti-tuberculosis drugs by silymarin.

RESULTS

Treatment of rats with INH+RIF or INH+RIF+PZA induced hepatotoxicity as evidenced by biochemical measurements: serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) activities and the levels of total bilirubin were elevated, and the levels of albumin and total protein were decreased in drugs-treated animals. Histopathological changes were also observed in livers of animals that received drugs. Simultaneous administration of silymarin significantly decreased the biochemical and histological changes induced by the drugs.

CONCLUSION

The active components of silymarin had protective effects against hepatotoxic actions of drugs used in the chemotherapy of tuberculosis in animal models. Since no significant toxicity of silymarin is reported in human studies, this plant extract can be used as a dietary supplement by patients taking anti-tuberculosis medications.

Silymarin, the antioxidant component of Silybum marianum, protects against burn-induced oxidative skin injury

BACKGROUND

Despite recent advances, severe burn is one of the most common problems faced in the emergency room. Major thermal injury induces the activation of an inflammatory cascade resulting in local tissue damage, to contribute to the development of subsequent damage of multiple organs distant from the original burn wound.

OBJECTIVE

Silymarin, the major component of milk thistle has been shown to have antioxidant properties. In the present study, we investigated the putative antioxidant effect of local or systemic silymarin treatment on burn-induced oxidative tissue injury.

METHODS

Wistar albino rats were exposed to 90 degrees C bath for 10 s to induce burn. Silymarin either locally (30 mg/kg) applied on 4 cm(2) area or locally+systemically (50 mg/kg, p.o.) was administered after the burn and repeated twice daily. Rats were decapitated 48 h after injury and blood was collected for tumor necrosis factor-alpha (TNF-alpha) and lactate dehydrogenase (LDH) activity. In skin tissue samples malondialdehyde (MDA) and glutathione (GSH) levels, myeloperoxidase (MPO) activity, and luminol-lucigenin chemiluminescense (CL) were measured in addition to the histological evaluation.

RESULTS

Burn caused a significant increase in TNF-alpha and LDH levels. MDA levels were increased and GSH levels were decreased in the skin at 48 h after-burn. Both local and systemic silymarin treatments significantly reversed these parameters. The raised MPO activity and luminol-lucigenin CL were also significantly decreased.

CONCLUSION

Results indicate that both systemic and local administration of silymarin was effective against burn-induced oxidative damage and morphological alterations in rat skin. Therefore, silymarin merits consideration as a therapeutic agent in the treatment of burns.

UV-induced immune suppression and photocarcinogenesis: chemoprevention by dietary botanical agents

Studies of immune-suppressed transplant recipients and patients with biopsy-proven skin cancer have confirmed that ultraviolet (UV) radiation-induced immune suppression is a risk factor for the development of skin cancer in humans. UV radiation suppresses the immune system in several ways. The UVB spectrum inhibits antigen presentation, induces the release of immunosuppressive cytokines, and elicits DNA damage that is a molecular trigger of UV-mediated immunosuppression. It is therefore important to elucidate the mechanisms underlying UV-induced immunosuppression as a basis for developing strategies to protect individuals from this effect and subsequent development of skin cancer. Dietary botanicals are of particular interest as they have been shown to inhibit UV-induced immune suppression and photocarcinogenesis. In this review, we summarize the most recent investigations and mechanistic studies regarding the photoprotective efficacy of selected dietary agents, including, green tea polyphenols, grape seed proanthocyanidins and silymarin. We present evidence that these chemopreventive agents prevent UVB-induced immunosuppression and photocarcinogenesis through: (i) the induction of immunoregulatory cytokine interleukin (IL)-12; (ii) IL-12-dependent DNA repair; and (iii) stimulation of cytotoxic T cells in the tumor microenvironment. The new information regarding the mechanisms of action of these agents supports their potential use as adjuncts in the prevention of photocarcinogenesis.

Interleukin-12 and photocarcinogenesis

UV radiation induces immunosuppression and inflammatory responses, as well as oxidative stress and DNA damage, in skin cells and these various effects have been implicated in melanoma and nonmelanoma skin cancers, i.e., photocarcinogenesis. The cytokine interleukin (IL)-12 has been shown to possess potent antitumor activity in a wide variety of murine tumor models. In this review, we summarize the evidence that IL-12 plays a role in preventing photocarcinogenesis, and present a model of its possible mechanisms of action. Treatment of mice with IL-12 prevents UV-induced immunosuppression in a process mediated by repair of UV-induced damaged DNA. After exposure to the photocarcinogenesis protocol, the development of UV-induced tumors is more rapid and the tumor multiplicity and tumor size are significantly greater in IL-12-deficient or knockout (KO) mice than their wild-type counterparts. IL-12-deficiency in mice enhances the proliferation potential of tumor cells, and this may be one of the reasons for the rapid growth of the tumors and their greater size. The rate of malignant transformation of UV-induced papillomas to carcinomas also is higher in the IL-12 KO mice than in their wild-type counterparts in terms of carcinoma incidence and carcinoma multiplicity. UV-induced DNA damage in the form of cyclobutane pyrimidine dimers (CPDs) and sunburn cells is lower, or repaired more rapidly, in wild-type mice than IL-12 KO mice. The IL-12-associated reduction in UV-specific CPDs is due to induction of DNA repair, and particularly enhancement of nucleotide-excision repair. We suggest that endogenous stimulation of IL-12 may protect the skin from UV-induced immunosuppression, DNA damage, and, ultimately, the risk of photocarcinogenesis. Taken together, this information suggests that augmentation of IL-12 should be considered as a strategy for the prevention and treatment of photocarcinogenesis.