Enhanced bioactivity of silybin B methylation products

Current mechanistic insights into Withaferin A: a promising potential adjuvant anticancer agent from Withania somnifera

Cancer remains a global health challenge, with drug resistance and disease recurrence posing significant obstacles despite advances in immunotherapy and targeted treatments. This has driven interest in natural products as sources of novel anticancer agents. Withania somnifera (Ashwagandha), a well-regarded plant in Ayurvedic medicine, is noted for its various therapeutic properties, including anticancer effects. Among its bioactive compounds, Withaferin A (WFA), a steroidal lactone, has shown notable promise in reducing inflammation, angiogenesis, and tumor proliferation with minimal toxicity. This review examines the anticancer properties of WFA, with a focus on its mechanisms of action, therapeutic efficacy, and safety profile across various cancer types. A comprehensive literature review was conducted, compiling data from in vitro and in vivo studies that investigate WFA's impact on cancer hallmarks, including apoptosis induction, angiogenesis reduction, and metastasis inhibition. Key molecular interactions with NFκB, STAT, HSP90, estrogen receptors, p53, and TGFβ pathways are highlighted. Findings indicate that WFA exhibits significant anticancer activity by modulating critical signaling pathways and inducing apoptosis with minimal adverse effects. In preclinical models, WFA demonstrated therapeutic potential across multiple cancers, such as breast, colon, prostate, ovarian, lung, and brain cancers. WFA represents a promising candidate for future cancer therapies, particularly as a natural adjuvant that could enhance treatment efficacy with low toxicity. Further clinical trials are needed to explore WFA's full potential and confirm its safety in human oncology.

Silybin and its congeners: from traditional medicine to molecular effects

Covering: 2015 up to 2022 (Feb)Silymarin, an extract of milk thistle (Silybum marianum) fruits, has been used in various medicinal applications since ancient times. A major component of silymarin is the flavonolignan silybin and its relatives isosilybin, silychristin, silydianin, 2,3-dehydrosilybin, and some others. Except for silydianin, they occur in nature as two stereomers. This review focuses on recent developments in chemistry, biosynthesis, modern advanced analytical methods, and transformations of flavonolignans specifically reflecting their chirality. Recently described chemotypes of S. marianum, but also the newest findings regarding the pharmacokinetics, hepatoprotective, antiviral, neuroprotective, and cardioprotective activity, modulation of endocrine functions, modulation of multidrug resistance, and safety of flavonolignans are discussed. A growing number of studies show that the respective diastereomers of flavonolignans have significantly different activities in anisotropic biological systems. Moreover, it is now clear that flavonolignans do not act as antioxidants in vivo, but as specific ligands of biological targets and therefore their chirality is crucial. Many controversies often arise, mainly due to the non-standard composition of this phytopreparation, the use of various undefined mixtures, the misattribution of silymarin vs. silybin, and also the failure to consider the chemistry of the respective components of silymarin.

Structure-activity relationships reveal a 2-furoyloxychalcone as a potent cytotoxic and apoptosis inducer for human U-937 and HL-60 leukaemia cells

Synthetic flavonoids with new substitution patterns have attracted attention as potential anticancer drugs. Here, twelve chalcones were synthesized and their antiproliferative activities against five human tumour cells were evaluated. This series of chalcone derivatives was characterized by the presence of an additional aromatic or heterocyclic ring linked by an ether, in the case of a benzyl radical, or an ester or amide functional group in the case of a furoyl radical. In addition, the influence on cytotoxicity by the presence of one or three methoxy groups or a 2,4-dimethoxy-3-methyl system on the B ring of the chalcone scaffold was also explored. The results revealed that the most cytotoxic chalcones contain a furoyl substituent linked by an ester or an amide through the 2'-hydroxy or the 2'-amino group of the A ring of the chalcone skeleton, with IC₅₀ values between 0.2 ± 0.1 μM and 1.3 ± 0.1 μM against human leukaemia cells. The synthetic chalcone 2'-furoyloxy-4-methoxychalcone (FMC) was, at least, ten-fold more potent than the antineoplastic agent etoposide against U-937 cells and displayed less cytotoxicity against human peripheral blood mononuclear cells. Treatment of U-937 and HL-60 cells with FMC induced cell cycle arrest at the G₂-M phase, an increase in the percentage of sub-G₁ and annexin-V positive cells, the release of mitochondrial cytochrome c, activation of caspase and poly(ADP-ribose) polymerase cleavage. In addition, it inhibited tubulin polymerization in vitro in a concentration dependent manner. Cell death triggered by this chalcone was decreased by the pan-caspase inhibitor z-VAD-fmk and was dependent of the generation of reactive oxygen species. We conclude that this furoyloxychalcone may be useful in the development of a potential anti-leukaemia strategy.

Discovery of Potent Glucokinase and PPARγ Dual-Target Agonists through an Innovative Scheme for Regioselective Modification of Silybin

Glucokinase (GK) and PPARγ are important targets for antidiabetic use. Silybin is one of the major active ingredients of Silybum marianum. The regioselective modification of the five hydroxyl groups in the silybin structure has always been a challenge. In this study, we found that silybin was an agonist of GK and PPARγ. A novel synthesis scheme of silybin derivatives was designed, and a series of novel silybin derivatives has been synthesized. The derivative 8d showed relatively strong activation activity for GK and PPARγ in enzyme activity and transactivation assays (GK activation fold: 1.86; PPARγ transactivation activation percentage: 90.32%). This research suggests that silybin and its derivatives could be used as novel GK and PPARγ dual-target agonists.

3-O-Carbamoyl-5,7,20-O-trimethylsilybins: Synthesis and Preliminary Antiproliferative Evaluation

To search for novel androgen receptor (AR) modulators for the potential treatment of castration-resistant prostate cancer (CRPC), naturally occurring silibinin was sought after as a lead compound because it possesses a moderate potency towards AR-positive prostate cancer cells and its chemical scaffold is dissimilar to all currently marketed AR antagonists. On the basis of the structure-activity relationships that we have explored, this study aims to incorporate carbamoyl groups to the alcoholic hydroxyl groups of silibinin to improve its capability in selectively suppressing AR-positive prostate cancer cell proliferation together with water solubility. To this end, a feasible approach was developed to regioselectively introduce a carbamoyl group to the secondary alcoholic hydroxyl group at C-3 without causing the undesired oxidation at C2-C3, providing an avenue for achieving 3-O-carbamoyl-5,7,20-O-trimethylsilybins. The application of the synthetic method can be extended to the synthesis of 3-O-carbamoyl-3',4',5,7-O-tetramethyltaxifolins. The antiproliferative potency of 5,7,20-O-trimethylsilybin and its nine 3-carbamoyl derivatives were assessed in an AR-positive LNCaP prostate cancer cell line and two AR-null prostate cancer cell lines (PC-3 and DU145). Our preliminary bioassay data imply that 5,7,20-O-trimethylsilybin and four 3-O-carbamoyl-5,7,20-O-trimethylsilybins emerge as very promising lead compounds due to the fact that they can selectively suppress AR-positive LNCaP cell proliferation. The IC50 values of these five 5,7,20-O-trimethylsilybins against the LNCaP cells fall into the range of 0.11-0.83 µM, which exhibit up to 660 times greater in vitro antiproliferative potency than silibinin. Our findings suggest that carbamoylated 5,7,20-O-trimethylsilybins could serve as a natural product-based scaffold for new antiandrogens for lethal castration-resistant prostate cancer.

Chirality Matters: Biological Activity of Optically Pure Silybin and Its Congeners

This review focuses on the specific biological effects of optically pure silymarin flavo-nolignans, mainly silybins A and B, isosilybins A and B, silychristins A and B, and their 2,3-dehydro derivatives. The chirality of these flavonolignans is also discussed in terms of their analysis, preparative separation and chemical reactions. We demonstrated the specific activities of the respective diastereomers of flavonolignans and also the enantiomers of their 2,3-dehydro derivatives in the 3D anisotropic systems typically represented by biological systems. In vivo, silymarin flavonolignans do not act as redox antioxidants, but they play a role as specific ligands of biological targets, according to the "lock-and-key" concept. Estrogenic, antidiabetic, anticancer, antiviral, and antiparasitic effects have been demonstrated in optically pure flavonolignans. Potential application of pure flavonolignans has also been shown in cardiovascular and neurological diseases. Inhibition of drug-metabolizing enzymes and modulation of multidrug resistance activity by these compounds are discussed in detail. The future of "silymarin applications" lies in the use of optically pure components that can be applied directly or used as valuable lead structures, and in the exploration of their true molecular effects.

Exploring the Multifaceted Therapeutic Potential of Withaferin A and Its Derivatives

Withaferin A (WA), a manifold studied, C28-steroidal lactone withanolide found in Withania somnifera. Given its unique beneficial effects, it has gathered attention in the era of modern science. Cancer, being considered a "hopeless case and the leading cause of death worldwide, and the available conventional therapies have many lacunae in the form of side effects. The poly pharmaceutical natural compound, WA treatment, displayed attenuation of various cancer hallmarks by altering oxidative stress, promoting apoptosis, and autophagy, inhibiting cell proliferation, reducing angiogenesis, and metastasis progression. The cellular proteins associated with antitumor pathways were also discussed. WA structural modifications attack multiple signal transduction pathways and enhance the therapeutic outcomes in various diseases. Moreover, it has shown validated pharmacological effects against multiple neurodegenerative diseases by inhibiting acetylcholesterinases and butyrylcholinesterases enzyme activity, antidiabetic activity by upregulating adiponectin and preventing the phosphorylation of peroxisome proliferator-activated receptors (PPARγ), cardioprotective activity by AMP-activated protein kinase (AMPK) activation and suppressing mitochondrial apoptosis. The current review is an extensive survey of various WA associated disease targets, its pharmacokinetics, synergistic combination, modifications, and biological activities.

Effect of herbs for treating coronary heart disease on the CYP450 enzyme system and transporters

The incidence and mortality of coronary heart disease (CHD) continue to increase every year in China. It has become a serious public health concern, threatening people's health. The combination of herbs and drugs has become a common mode of treatment for various chronic diseases such as CHD and chronic lung disease. Clinical studies have shown that the combination of herbs and drugs can bring more clinical benefits in the treatment of CHD. However, safety issues caused by the interaction between herbs and drugs deserve attention. Recent findings indicate that many herbs and their active ingredients can affect the activities of cytochrome P450 enzyme system (CYP450s) and transporters related to drug metabolism, thus changing the metabolic process of combined drugs, leading to an increase or a decrease in plasma drug concentrations, finally increasing the uncertainty of clinical efficacy and the possibility of adverse events. This review aimed to discuss in detail the effect of herbs on CYP450s and/or transporters in the treatment of CHD and the potential herb-drugs interaction, thus providing the basis for the clinical rational combination of drugs.

23-O-Substituted-2,3-Dehydrosilybins Selectively Suppress Androgen Receptor-Positive LNCaP Prostate Cancer Cell Proliferation

As part of our ongoing project to search for natural product-based antiandrogens, nine derivatives of 2,3-dehydrosilybin have been synthesized for the evaluation of its antiproliferative activity in an androgen receptor-positive prostate cancer cell model. Specifically, 3,5,7,20- O-tetramethyl-2,3-dehydrosilybin was synthesized through two approaches, and eight 23- O-substituted-3,5,7,20- O-tetramethyl-2,3-dehydrosilybins were achieved from 3,5,7,20- O-tetramethyl-2,3-dehydrosilybin. The antiproliferative potency of 3,5,7,20- O-tetramethyl-2,3-dehydrosilybin and its eight derivatives were assessed in an androgen receptor (AR)-positive LNCaP prostate cancer cell line, as well as in two AR-negative (PC-3 and DU145) prostate cancer cell models as a comparison. Our WST cell proliferation assay data indicate 3,5,7,20- O-tetramethyl-2,3-dehydrosilybin and most of its 23- O-substituents can selectively inhibit AR-positive LNCaP prostate cancer cell proliferation. Our data suggest that 3,5,7,20- O-tetramethyl-2,3-dehydrosilibins could serve as a natural product-based scaffold for new antiandrogens for lethal castration-resistant prostate cancer.

The synthetic flavanone 6-methoxy-2-(naphthalen-1-yl)chroman-4-one induces apoptosis and activation of the MAPK pathway in human U-937 leukaemia cells

Synthetic flavonoids containing a naphthalene ring have attracted attention as potential cytotoxic compounds. Here, we synthesized ten chalcones and their corresponding flavanones and evaluated their antiproliferative activity against the human tumour cell line U-937. This series of chalcone derivatives was characterized by the presence of a naphthalene ring which was kept unaltered- and attached to the β carbon of the 1-phenyl-2-propen-1-one framework. The structure-activity relationship of these chalcone derivatives and their corresponding cyclic compounds was investigated by the introduction of different substituents (methyl, methoxy, benzyloxy, chlorine) or by varying the position of the methoxy or benzyloxy groups on the A ring. The results revealed that both the chalcone containing the methoxy group at 5' position of the A ring as well as its corresponding flavanone [6-methoxy-2-(naphthalen-1-yl)chroman-4-one] were the most cytotoxic compounds, with IC₅₀ values of 2.8 ± 0.2 and 1.3 ± 0.2 μM, respectively, against U-937 cells. This synthetic flavanone was as cytotoxic as the antitumor etoposide in U-937 cells and displayed strong cytotoxicity against additional human leukaemia cell lines, including HL-60, MOLT-3 and NALM-6. Human peripheral blood mononuclear cells were more resistant than leukaemia cells to the cytotoxic effects of the flavanone. Treatment of U-937 cells with this compound induced G₂-M cell cycle arrest, an increase in sub-G₁ ratio and annexin-V positive cells, mitochondrial cytochrome c release, caspase activation and poly(ADP-ribose)polymerase processing. Apoptosis induction triggered by this flavonoid was blocked by overexpression of the anti-apoptotic protein Bcl-2. This flavanone induces phosphorylation of p38 mitogen-activated protein kinases, extracellular-signal regulated kinases and c-jun N-terminal kinases/stress-activated protein kinases (JNK/SAPK) following different kinetics. Moreover, cell death was attenuated by the inhibition of mitogen-activated extracellular kinases and JNK/SAPK and was independent of reactive oxygen species generation.

2, 3-Dihydro-3β-methoxy Withaferin-A Lacks Anti-Metastasis Potency: Bioinformatics and Experimental Evidences

Withaferin-A is a withanolide, predominantly present in Ashwagandha (Withania somnifera). It has been shown to possess anticancer activity in a variety of human cancer cells in vitro and in vivo. Molecular mechanism of such cytotoxicity has not yet been completely understood. Withaferin-A and Withanone were earlier shown to activate p53 tumor suppressor and oxidative stress pathways in cancer cells. 2,3-dihydro-3β-methoxy analogue of Withaferin-A (3βmWi-A) was shown to lack cytotoxicity and well tolerated at higher concentrations. It, on the other hand, protected normal cells against oxidative, chemical and UV stresses through induction of anti-stress and pro-survival signaling. We, in the present study, investigated the effect of Wi-A and 3βmWi-A on cell migration and metastasis signaling. Whereas Wi-A binds to vimentin and heterogeneous nuclear ribonucleoprotein K (hnRNP-K) with high efficacy and downregulates its effector proteins, MMPs and VEGF, involved in cancer cell metastasis, 3βmWi-A was ineffective. Consistently, Wi-A, and not 3βmWi-A, caused reduction in cytoskeleton proteins (Vimentin, N-Cadherin) and active protease (u-PA) that are essential for three key steps of cancer cell metastasis (EMT, increase in cell migration and invasion).

O-Aminoalkyl-O-Trimethyl-2,3-Dehydrosilybins: Synthesis and In Vitro Effects Towards Prostate Cancer Cells

As part of our ongoing silybin project, this study aims to introduce a basic nitrogen-containing group to 7-OH of 3,5,20-O-trimethyl-2,3-dehydrosilybin or 3-OH of 5,7,20-O-trimethyl-2,3-dehydrosilybin via an appropriate linker for in vitro evaluation as potential anti-prostate cancer agents. The synthetic approaches to 7-O-substituted-3,5,20-O-trimethyl-2,3-dehydrosilybins through a five-step procedure and to 3-O-substituted-5,7,20-O-trimethyl-2,3- dehydrosilybins via a four-step transformation have been developed. Thirty-two nitrogen-containing derivatives of silybin have been achieved through these synthetic methods for the evaluation of their antiproliferative activities towards both androgen-sensitive (LNCaP) and androgen-insensitive prostate cancer cell lines (PC-3 and DU145) using the WST-1 cell proliferation assay. These derivatives exhibited greater in vitro antiproliferative potency than silibinin. Among them, 11, 29, 31, 37, and 40 were identified as five optimal derivatives with IC₅₀ values in the range of 1.40⁻3.06 µM, representing a 17- to 52-fold improvement in potency compared to silibinin. All these five optimal derivatives can arrest the PC-3 cell cycle in the G₀/G₁ phase and promote PC-3 cell apoptosis. Derivatives 11, 37, and 40 are more effective than 29 and 31 in activating PC-3 cell apoptosis.

Cancer chemoprevention through dietary flavonoids: what's limiting?

Flavonoids are polyphenols that are found in numerous edible plant species. Data obtained from preclinical and clinical studies suggest that specific flavonoids are chemo-preventive and cytotoxic against various cancers via a multitude of mechanisms. However, the clinical use of flavonoids is limited due to challenges associated with their effective use, including (1) the isolation and purification of flavonoids from their natural resources; (2) demonstration of the effects of flavonoids in reducing the risk of certain cancer, in tandem with the cost and time needed for epidemiological studies, and (3) numerous pharmacokinetic challenges (e.g., bioavailability, drug–drug interactions, and metabolic instability). Currently, numerous approaches are being used to surmount some of these challenges, thereby increasing the likelihood of flavonoids being used as chemo-preventive drugs in the clinic. In this review, we summarize the most important challenges and efforts that are being made to surmount these challenges.

Antihyperlipidemic and hepatoprotective effects of Gardenin A in cellular and high fat diet fed rodent models

The gum of Gardenia resinifera Roth., is one of the important drugs used in the Indian system of medicine and a source of unique polymethoxylated flavones. This study was aimed to evaluate the antihyperlipidemic and anti-NAFLD effects of Gardenin A (Gar-A) from G. resinifera gum using in vitro and in vivo models. Gar-A was isolated from G. resinifera gum and was identified on the basis of the physical and spectral data. Toxicity of Gar-A to HepG2 cells was evaluated using MTT assay. The ability of Gar-A to reduce steatosis was assessed using oleate-palmitate induced HepG2 cell lines by estimating the lipid levels by ORO staining and by estimating the intracellular triglyceride content. Effect of Gar-A on amelioration of lipotoxicity was measured by estimating the LDH levels. The doses for in vivo experiments were fixed by Irwin test, between 50 and 100 mg/kg concentrations, through oral route. The acute antihyperlipidemic effect of Gar-A was assessed in Triton WR-1339 induced hyperlipidemic animals. The chronic antihyperlipidemic and anti-NAFLD effects of Gar-A were evaluated in HFD fed rats. In vitro experiments with HepG2 cell line indicated that the cells treated with Gar-A did not show any significant reduction in the viability up to 70 μg/mL concentration. Steatotic HepG2 cells treated with Gar-A showed a significant reduction in lipid accumulation at 2.5-10 μg/mL concentrations. In triton induced hyperlipidemic rats, the treatment significantly reduced the lipid levels at the synthesis phase. The treatment with Gar-A to the HFD fed animals significantly lowered the steatosis and transaminase levels. The other biochemical parameters such as TC, TG, LDL-c, ALP and ACP were also decreased significantly. Treatment with Gar-A significantly lowered the hyperlipidemia and fat accumulation in the liver; detailed molecular investigations are necessary to establish the antihyperlipidemic and hepatoprotective potentials of Gar-A.

Talarolutins A-D: Meroterpenoids from an endophytic fungal isolate of Talaromyces minioluteus

Four meroterpenoids [talarolutins A-D] and one known compound [purpurquinone A] were characterized from an endophytic fungal isolate of Talaromyces minioluteus (G413), which was obtained from the leaves of the medicinal plant milk thistle [Silybum marianum (L.) Gaertn. (Asteraceae)]. The structures of talarolutins A-D were determined by the analysis of various NMR and MS techniques. The relative and absolute configuration of talarolutin A was determined by X-ray diffraction analysis. A combination of NOESY data and comparisons of ECD spectra were employed to assign the relative and absolute configuration of the other analogs. Talarolutins B-D were tested for cytotoxicity against human prostate carcinoma (PC-3) cell line, antimicrobial activity, and induction of quinone reductase; no notable bioactivity was observed in any assay.

Silibinin derivatives as anti-prostate cancer agents: Synthesis and cell-based evaluations

This study aims to systematically explore the alkylation effect of 7-OH in silibinin and 2,3-dehydrosilibinin on the antiproliferative potency toward three prostate cancer cell lines. Eight 7-O-alkylsilibinins, eight 7-O-alkyl-2,3-dehydrosilibinins, and eight 3,7-O-dialkyl-2,3-dehydrosilibinins have been synthesized from commercially available silibinin for the in vitro cell-based evaluation. The WST-1 cell proliferation assay indicates that nineteen out of twenty-four silibinin derivatives have significantly improved antiproliferative potency when compared with silibinin. 7-O-Methylsilibinin (2) and 7-O-ethylsilibinin (3) have been identified as the most potent compounds with 98- and 123-fold enhanced potency against LNCaP human androgen-dependent prostate cancer cell line. Among 2,3-dehydrosilibinin derivatives, 7-O-methyl-2,3-dehydrosilibinin (10) and 7-O-ethyl-2,3-dehydrosilibinin (11) have been identified as the optimal compounds with the highest potency towards both androgen-dependent LNCaP and androgen-independent PC-3 prostate cancer cell lines. 7-O-Ethyl-2,3-dehydrosilibinin (11) was demonstrated to arrest PC-3 cell cycle at the G0/G1 phase and to induce PC-3 cell apoptosis. The findings in this study suggest that antiproliferative potency of silibinin and 2,3-dehydrosilibinin can be appreciably enhanced through suitable chemical modifications on the phenolic hydroxyl group at C-7 and that introduction of a chemical moiety with the potential to improve bioavailability through a linker to 7-OH in silibinin and 2,3-dehydrosilibinin would be a feasible strategy for the development of silibinin derivatives as anti-prostate cancer agents.

Chemoenzymatic Synthesis, Characterization, and Scale-Up of Milk Thistle Flavonolignan Glucuronides

Plant-based therapeutics, including herbal products, continue to represent a growing facet of the contemporary health care market. Mechanistic descriptions of the pharmacokinetics and pharmacodynamics of constituents composing these products remain nascent, particularly for metabolites produced following herbal product ingestion. Generation and characterization of authentic metabolite standards are essential to improve the quantitative mechanistic understanding of herbal product disposition in both in vitro and in vivo systems. Using the model herbal product, milk thistle, the objective of this work was to biosynthesize multimilligram quantities of glucuronides of select constituents (flavonolignans) to fill multiple knowledge gaps in the understanding of herbal product disposition and action. A partnership between clinical pharmacology and natural products chemistry expertise was leveraged to optimize reaction conditions for efficient glucuronide formation and evaluate alternate enzyme and reagent sources to improve cost effectiveness. Optimized reaction conditions used at least one-fourth the amount of microsomal protein (from bovine liver) and cofactor (UDP glucuronic acid) compared with typical conditions using human-derived subcellular fractions, providing substantial cost savings. Glucuronidation was flavonolignan-dependent. Silybin A, silybin B, isosilybin A, and isosilybin B generated five, four, four, and three monoglucuronides, respectively. Large-scale synthesis (40 mg of starting material) generated three glucuronides of silybin A: silybin A-7-O-β-D-glucuronide (15.7 mg), silybin A-5-O-β-D-glucuronide (1.6 mg), and silybin A-4´´-O-β-D-glucuronide (11.1 mg). This optimized, cost-efficient method lays the foundation for a systematic approach to synthesize and characterize herbal product constituent glucuronides, enabling an improved understanding of mechanisms underlying herbal product disposition and action.

Chemistry of silybin

Silybin, a secondary metabolite isolated from the seeds of the blessed milk thistle (Silybum marianum) was discovered as the first member of a new family of natural compounds called flavonolignans in 1959. Over the years it has received the research attention of many organic chemists. This research has resulted in a number of semisynthetic derivatives prepared in an effort to modulate and better target the biological activities of silybin or to improve its physical properties, such as its solubility. A fundamental breakthrough in silybin chemistry was the determination of the absolute configurations of silybin A and silybin B, and the development of methods for their separation. This review covers articles dealing with silybin chemistry and also summarizes all the derivatives prepared.

Flavonolignans from Aspergillus iizukae, a fungal endophyte of milk thistle (Silybum marianum)

Silybin A (1), silybin B (2), and isosilybin A (3), three of the seven flavonolignans that constitute silymarin, an extract of the fruits of milk thistle (Silybum marianum), were detected for the first time from a fungal endophyte, Aspergillus iizukae, isolated from the surface-sterilized leaves of S. marianum. The flavonolignans were identified using a UPLC-PDA-HRMS-MS/MS method by matching retention times, HRMS, and MS/MS data with authentic reference compounds. Attenuation of flavonolignan production was observed following successive subculturing of the original flavonolignan-producing culture, as is often the case with endophytes that produce plant-based secondary metabolites. However, production of 1 and 2 resumed when attenuated spores were harvested from cultures grown on a medium to which autoclaved leaves of S. marianum were added. The cycle of attenuation followed by resumed biosynthesis of these flavonolignans was replicated in triplicate.

Biotransformation on the flavonolignan constituents of Silybi Fructus by an intestinal bacterial strain Eubacterium limosum ZL-II

Eubacterium limosum ZL-II is an anaerobic bacterium with demethylated activity, which was isolated from human intestinal bacteria in our previous work. In this study, the flavonolignan constituents of Silybi Fructus were biotransformed by E. limosum(1) ZL-II, producing four new transformation products - demethylisosilybin B (T1), demethylisosilybin A (T2), demethylsilybin B (T3) and demethylsilybin A (T4), among which T1 and T2 were new compounds. Their chemical structures were identified by ESI-TOF/MS, (1)H NMR, (13)C NMR, HMBC and CD spectroscopic data. The bioassay results showed that the transformation products T1-T4 exhibited significant inhibitory activities on Alzheimer's amyloid-β 42 (Aβ42(2)) aggregation with IC50 values at 7.49 μM-10.46 μM, which were comparable with that of the positive control (epigallocatechin gallate, EGCG(3), at 9.01 μM) and much lower than those of their parent compounds (at not less than 145.10 μM). The method of biotransformation by E. limosum ZL-II explored a way to develop the new and active lead compounds in Alzheimer's disease from Silybi Fructus. However, the transformation products T1-T4 exhibited decreased inhibitory activities against human tumor cell lines comparing with their parent compounds.

Review article: management of chronic hepatitis C in patients with contraindications to anti-viral therapy

BACKGROUND

There are patients with chronic hepatitis C who are not eligible for the current interferon-based therapies or refuse to be treated due to secondary effects.

AIM

To provide information on alternative treatments for the management of these patients.

METHODS

A PubMed search was performed to identify relevant literature. Search terms included hepatitis C virus, anti-inflammatory treatment, antioxidant, natural products and alternative treatment, alone or in combination. Additional publications were identified using the references cited by primary and review articles.

RESULTS

Several approaches, such as iron depletion (phlebotomy), treatment with ursodeoxycholic acid or glycyrrhizin, have anti-inflammatory and/or anti-fibrotic effects. Life interventions like weight loss, exercise and coffee consumption are associated with a biochemical improvement. Other alternatives (ribavirin monotherapy, amantadine, silibinin, vitamin supplementation, etc.) do not have any beneficial effect or need to be tested in larger clinical studies.

CONCLUSION

There are therapeutic strategies and lifestyle interventions that can be used to improve liver damage in patients with chronic hepatitis C who cannot receive or refuse interferon-based treatments.

Mechanistic study of the biomimetic synthesis of flavonolignan diastereoisomers in milk thistle

The mechanism for the biomimetic synthesis of flavonolignan diastereoisomers in milk thistle is proposed to proceed by single-electron oxidation of coniferyl alcohol, subsequent reaction with one of the oxygen atoms of taxifolin's catechol moiety, and finally, further oxidation to form four of the major components of silymarin: silybin A, silybin B, isosilybin A, and isosilybin B. This mechanism is significantly different from a previously proposed process that involves the coupling of two independently formed radicals.

Semisynthesis, cytotoxicity, antiviral activity, and drug interaction liability of 7-O-methylated analogues of flavonolignans from milk thistle

Silymarin, an extract of the seeds of milk thistle (Silybum marianum), is used as an herbal remedy, particularly for hepatoprotection. The main chemical constituents in silymarin are seven flavonolignans. Recent studies explored the non-selective methylation of one flavonolignan, silybin B, and then tested those analogues for cytotoxicity and inhibition of both cytochrome P450 (CYP) 2C9 activity in human liver microsomes and hepatitis C virus infection in a human hepatoma (Huh7.5.1) cell line. In general, enhanced bioactivity was observed with the analogues. To further probe the biological consequences of methylation of the seven major flavonolignans, a series of 7-O-methylflavonolignans were generated. Optimization of the reaction conditions permitted selective methylation at the phenol in the 7-position in the presence of each metabolite's 4-5 other phenolic and/or alcoholic positions without the use of protecting groups. These 7-O-methylated analogues, in parallel with the corresponding parent compounds, were evaluated for cytotoxicity against Huh7.5.1 cells; in all cases the monomethylated analogues were more cytotoxic than the parent compounds. Moreover, parent compounds that were relatively non-toxic and inactive or weak inhibitors of hepatitis C virus infection had enhanced cytotoxicity and anti-HCV activity upon 7-O-methylation. Also, the compounds were tested for inhibition of major drug metabolizing enzymes (CYP2C9, CYP3A4/5, UDP-glucuronsyltransferases) in pooled human liver or intestinal microsomes. Methylation of flavonolignans differentially modified inhibitory potency, with compounds demonstrating both increased and decreased potency depending upon the compound tested and the enzyme system investigated. In total, these data indicated that monomethylation modulates the cytotoxic, antiviral, and drug interaction potential of silymarin flavonolignans.