The study of flavonolignan association patterns in fruits of diverging Silybum marianum (L.) Gaertn. chemotypes provides new insights into the silymarin biosynthetic pathway

One-step sustainable extraction of Silymarin compounds of wild Algerian milk thistle (Silybum marianum) seeds using Gas Expanded Liquids

This work reports the application of Gas Expanded Liquid (GXL) extraction to concentrate the flavonolignan fraction (silymarin) and taxifolin from Silybum marianum seeds, which have proven to be highly valuable health-promoting compounds. GXL using green solvents was used to isolate silymarin with the objective of replacing conventional methods. In one hand, the effect of different compositions of solvents, aqueous ethanol (20%, 50% or 80% (v/v)) at different CO2/liquid (25, 50 and 75%) ratios, on the GXL extraction was investigated. The obtained extracts have been chemically and functionally characterized by means of UHPLC-ESI-MS/MS (triple quadrupole) and in-vitro assays such as anti-inflammatory, anti-cholinergic and antioxidant. Results revealed that the operating conditions influenced the extraction yield, the total phenolic content and the presence of the target compounds. The best obtained yield was 55.97% using a ternary mixture of solvents composed of CO2:EtOH:H2O (25:60:15) at 40 °C and 9 MPa in 160 min. Furthermore, the results showed that obtained extracts had significant antioxidant and anti-inflammatory activities (with best IC50 value of 8.80 µg/mL and 28.52 µg/mL, respectively) but a moderate anti-cholinesterase activity (with best IC50 value of 125.09 µg/mL). Otherwise, the concentration of silymarin compounds in extract can go up to 59.6% using the present one-step extraction method without further purification, being silybinA+B the predominant identified compound, achieving value of 545.73 (mg silymarin/g of extract). The obtained results demonstrate the exceptional potential of GXL to extract high-added values molecules under sustainable conditions from different matrices.

MS-FINDER Assisted in Understanding the Profile of Flavonoids in Temporal Dimension during the Fermentation of Pu-erh Tea

Flavonoid represents a significant class of secondary metabolites in Pu-erh tea with benefits to human health. For a rapid and complete discovery of such compounds, we established a data mining workflow that integrates software MS-DIAL, MS-FINDER, and molecular networking analysis. As a result, 181 flavonoids were tentatively annotated including 22 first found in Pu-erh tea, and two of them were potentially new molecules. The dynamic alteration of these flavonoids during Pu-erh fermentation was further investigated. They all showed a trend of first increasing and then decreasing. Moreover, statistical analysis showed that the first to third pile turnings of the fermentation process had a greater impact on the changes of flavonoids. Partial metabolic pathways were proposed. This study provides a quick and automatic strategy for flavonoid profiling. The temporal dimension of flavonoids during fermentation may serve as a theoretical basis for Pu-erh tea manufacturing technology and study on substance foundation.

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.

Silymarin ameliorates the disordered glucose metabolism of mice with diet-induced obesity by activating the hepatic SIRT1 pathway

Obesity-induced insulin resistance is the principal cause of type 2 diabetes worldwide. The use of natural products for the treatment of diabetes is increasingly attracting attention. Silymarin (SLM) is a flavonolignan compound that has been shown to have promise for the treatment of diabetes. In the present study, we aimed to investigate the mechanisms underlying its therapeutic effects. C57BL/6 mice were fed a high-fat diet (HFD) for 12 weeks and then orally administered SLM (30 mg/kg) daily for 1 month. The effects of SLM were also investigated in HepG2 cells that had been rendered insulin resistant by palmitic acid (PA) treatment. SLM ameliorated the dyslipidemia, hepatic steatosis, and insulin resistance of the HFD-fed mice. HFD-feeding and PA treatment reduced the expression of sirtuin-1 (SIRT1) in the livers of the mice and in HepG2 cells, respectively. SLM increased the phosphorylation of AKT and FOXO1, and reduced the level of FOXO1 acetylation in PA-treated cells. However, SIRT1 knockdown by RNA interference reduced these effects of SLM. Moreover, the results of molecular dynamic simulation and in vitro activity assays indicated that SLM may directly bind to SIRT1 and increase its enzymatic activity. These findings suggest that hepatic SIRT1 may be an important pharmacological target of SLM and mediate effects on insulin resistance and gluconeogenesis, which may underlie its anti-diabetic activity.

In Silybum marianum Italian wild populations the variability of silymarin profiles results from the combination of only two stable chemotypes

Silybum marianum (L.) Gaertn. is an important medicinal plant belonging to Mediterranean flora. The medicinal properties of the species are mainly due to silymarin, a combination of different flavonolignans contained in the fruit. As for silymarin, so far a wide variability of possible S. marianum chemotypes has been described. In the present study the flavonolignan profile of 40 different S. marianum wild accessions was analysed at both population and single plant level, further extending the analysis to progenies derived from crosses between parental lines with different chemotypes. The results of this work indicate that S. marianum wild populations can be composed either of individuals with the same chemotype, or heterogeneous mixtures of individuals characterized by different chemotypes. Only three chemotypes (A, B and C) have been identified among Italian wild populations. Based on data collected we furthermore propose that chemotype C is the result of the hybridization between A and B chemotypes. If assessed at single plant level, chemotypes are extremely stable therefore evidencing a strong genetic control of silymarin biosynthetic pathway. Chemotypes A and B are present in all the analysed regions and no clear correlation between chemotypes and geographic features has been found. In conclusion, this work provides a general procedure for the characterization of different and stable chemotypes, for a deeper understanding of silymarin biosynthetic pathway, and in order to implement S. marianum breeding programmes aiming to improve silymarin quality.

Gene Expression Analysis and Metabolite Profiling of Silymarin Biosynthesis during Milk Thistle (Silybum marianum (L.) Gaertn.) Fruit Ripening

Mature fruits (i.e., achenes) of milk thistle (Silybum marianum (L.) Gaertn., Asteraceae) accumulate high amounts of silymarin (SILM), a complex mixture of bioactive flavonolignans deriving from taxifolin. Their biological activities in relation with human health promotion and disease prevention are well described. However, the conditions of their biosynthesis in planta are still obscure. To fill this gap, fruit development stages were first precisely defined to study the accumulation kinetics of SILM constituents during fruit ripening. The accumulation profiles of the SILM components during fruit maturation were determined using the LC-MS analysis of these defined developmental phases. The kinetics of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and peroxidase (POX) activities suggest in situ biosynthesis of SILM from l-Phenylalanine during fruit maturation rather than a transport of precursors to the achene. In particular, in contrast to laccase activity, POX activity was associated with the accumulation of silymarin, thus indicating a possible preferential involvement of peroxidase(s) in the oxidative coupling step leading to flavonolignans. Reference genes have been identified, selected and validated to allow accurate gene expression profiling of candidate biosynthetic genes (PAL, CAD, CHS, F3H, F3'H and POX) related to SILM accumulation. Gene expression profiles were correlated with SILM accumulation kinetic and preferential location in pericarp during S. marianum fruit maturation, reaching maximum biosynthesis when desiccation occurs, thus reinforcing the hypothesis of an in situ biosynthesis. This observation led us to consider the involvement of abscisic acid (ABA), a key phytohormone in the control of fruit ripening process. ABA accumulation timing and location during milk thistle fruit ripening appeared in line with a potential regulation of the SLIM accumulation. A possible transcriptional regulation of SILM biosynthesis by ABA was supported by the presence of ABA-responsive cis-acting elements in the promoter regions of the SILM biosynthetic genes studied. These results pave the way for a better understanding of the biosynthetic regulation of SILM during the maturation of S. marianum fruit and offer important insights to better control the production of these medicinally important compounds.

Linear regression analysis of silychristin A, silybin A and silybin B contents in Silybum marianum

Quantitative correlations between the contents of the flavonolignans silychristin A and silybins A/B provide biosynthetic clues that support a pathway in which one mesomeric form of a taxifolin radical is undergoing an oxidative coupling with a coniferyl alcohol radical. The flavonolignan content and patterns reported in the literature for 53 samples, representing populations of the Silybum marianum plant growing in different parts of the world, were subject to a meta-analysis. Linear regression analyses were carried out on these data sets, and a mathematical model was derived that predicts the content of silychristin A relative to the metabolomic pattern of its congeners. The validity of the model was verified by applying it to test samples. This approach could potentially become a tool to enhance the understanding of both the relative composition of the silymarin complex and the biosynthetic pathways that underlie its formation.

Formulation of Nanomicelles to Improve the Solubility and the Oral Absorption of Silymarin

Two novel nanomicellar formulations were developed to improve the poor aqueous solubility and the oral absorption of silymarin. Polymeric nanomicelles made of Soluplus and mixed nanomicelles combining Soluplus with d-α-tocopherol polyethylene glycol 1000 succinate (vitamin E TPGS) were prepared using the thin film method. Physicochemical parameters were investigated, in particular the average diameter, the homogeneity (expressed as polydispersity index), the zeta potential, the morphology, the encapsulation efficiency, the drug loading, the critical micellar concentration and the cloud point. The sizes of ~60 nm, the narrow size distribution (polydispersity index ≤0.1) and the encapsulation efficiency >92% indicated the high affinity between silymarin and the core of the nanomicelles. Solubility studies demonstrated that the solubility of silymarin increased by ~6-fold when loaded into nanomicelles. Furthermore, the physical and chemical parameters of SLM-loaded formulations stored at room temperature and in refrigerated conditions (4 °C) were monitored over three months. In vitro stability and release studies in media miming the physiological conditions were also performed. In addition, both formulations did not alter the antioxidant properties of silymarin as evidenced by the 1,1-Diphenyl-2-picrylhydrazyl radical (DPPH) assay. The potential of the nanomicelles to increase the intestinal absorption of silymarin was firstly investigated by the parallel artificial membrane permeability assay. Subsequently, transport studies employing Caco-2 cell line demonstrated that mixed nanomicelles statistically enhanced the permeability of silymarin compared to polymeric nanomicelles and unformulated extract. Finally, the uptake studies indicated that both nanomicellar formulations entered into Caco-2 cells via energy-dependent mechanisms.

Localization of phenolic compounds in the fruits of Silybum marianum characterized by different silymarin chemotype and altered colour

Silybum marianum (L.) Gaertn (Asteraceae) is a valuable medicinal plant utilized for silymarin production. However, only fragmentary and contradictory information about silymarin localization within S. marianum fruit are available. In this work, a twofold research approach was adopted in order to investigate the distribution and quantification of silymarin and of other phenolic compounds within the different fruit regions (pericarp, seed integument, cotyledon). Two S. marianum wild accessions with contrasting silymarin chemotype (A and B) and a mutant line (C) with an altered fruit colour were analysed. Fruits of Cynara cardunculus were studied as a reference. Firstly, the fruit morpho-anatomy was reviewed by means of light microscopy digital imaging and, secondly, a comprehensive histolocalization of the different classes of polyphenols within the fruit was carried out. The experimental evidences confirmed that silymarin, and its precursor taxifolin, are only accumulated in the seed integuments. The dark colour of fully-ripened fruits is due to the accumulation of condensed tannins in the pericarp subepidermal cell layer. On the contrary, the studied mutant line shows reduced condensed tannin content that probably result from impairment at the level of flavonoid biosynthetic pathway. Condensed tannins content is comparatively low in S. marianum fruits and very low in the identified mutant line. This could represent an advantage for the possible employment of S. marianum fruits and of silymarin extraction by-products in the feed and food sector.

Differential accumulation of silymarin induced by exposure of Silybum marianum L. callus cultures to several spectres of monochromatic lights

Silybum marianum L. (Milk thistle) is one of the most extensively studied medicinal herbs with well-known hepatoprotective activity. Light is considered as a key abiotic elicitor influencing several physiological processes in plants, including the biosynthesis of secondary metabolites. In this study, we investigated the influence of light quality on morphological and biochemical aspects in in vitro grown leaf-derived callus cultures of S. marianum. Combination of 6-benzylaminopurine (BAP 2.5 mg/L) and α-naphthalene acetic acid (NAA 1.0 mg/L) resulted in optimum callogenic response (97%) when placed under cool-white light with 16 h light and 8 h dark. Red light significantly increased the total phenolic content (TPC), total flavonoid content (TFC), antioxidant and superoxide dismutase (SOD) activities while highest peroxidase (POD) activity was recorded for the dark grown cultures, followed by green light grown cultures. HPLC analysis revealed enhanced total silymarin content under red light (18.67 mg/g DW), which was almost double than control (9.17 mg/g DW). Individually, the level of silychristin, isosilychristin, silydianin, silybin A and silybin B were found greatest under red light, whereas green spectrum resulted in highest accumulation of isosilybin A and isosilybin B. Conversely, the amount of taxifolin was found maximum under continuous white light (0.480 mg/g DW) which was almost 8-fold greater than control (0.063 mg/g DW). A positive correlation was found between the TPC, TFC and antioxidant activities. This study will assist in comprehending the influence of light quality on production of valuable secondary metabolites in in vitro cultures of S. marianum L.

Lower glycemic indices and lipid profile among type 2 diabetes mellitus patients who received novel dose of Silybum marianum (L.) Gaertn. (silymarin) extract supplement: A Triple-blinded randomized controlled clinical trial

OBJECTIVE

This randomized clinical trial was conducted to evaluate the effects of silymarin supplementation on glycemic indices and serum lipid profile in type 2 diabetes mellitus (T2DM) patients.

METHODS

40 T2DM patients (twenty male and twenty female), 25-50 years of age and on stable medication, were recruited for the present paralleled, randomized, triple-blinded, placebo-controlled clinical trial. The participants were randomly assigned to the silymarin or placebo groups, in which the patients either received 140 mg of silymarin, thrice daily (n = 20) or placebo (n = 20) for 45 days. Anthropometric and dietary intake data were collected at the baseline and end of the trial. Fasting blood samples were collected, and glycemic indices and lipid profile were determined at baseline, as well as the end of the study.

RESULTS

Silymarin supplementation led to significant reduction in fasting blood sugar, serum insulin, homeostatic model assessment for insulin resistance, serum triglyceride and triglyceride to high-density lipoprotein cholesterol ratio as compared to the placebo, by 11.01, 14.35, 25.92, 23.7 and 27.67% respectively. There was significant increase in high-density lipoprotein cholesterol levels and quantitative insulin sensitivity check index in the silymarin group as compared to the placebo group, by 6.88 and 5.64% respectively, (p < 0.05). Total cholesterol and low-density lipoprotein cholesterol concentrations significantly decreased in the silymarin group as compared to the baseline, by 7.93 (p = 0.001) and 7.15% (p = 0.02), respectively.

CONCLUSION

Silymarin supplementation may improve the glycemic indices and lipid profiles of T2DM patients. More studies are needed to validate the adjunct use of silymarin for metabolic control of T2DM patients.

Single Laboratory Validation of a Quantitative Core Shell-Based LC Separation for the Evaluation of Silymarin Variability and Associated Antioxidant Activity of Pakistani Ecotypes of Milk Thistle (Silybum Marianum L.)

Fruits of Silybum marianum (L.) Gaernt are the main source of taxifolin derived flavonolignans. Together, these molecules constitute a mixture called silymarin with many useful applications for cosmetic and pharmaceutic industries. Here, a validated method for the separation of the silymarin constituents has been developed to ensure precision and accuracy in their quantification. Each compound was separated with a high reproducibility. Precision and repeatability of the quantification method were validated according to the AOAC recommendations. The method was then applied to study the natural variability of wild accessions of S. marianum. Analysis of the variation in the fruits composition of these 12 accessions from Pakistan evidenced a huge natural diversity. Correlation analysis suggested a synergistic action of the different flavonolignans to reach the maximal antioxidant activity, as determined by cupric ion reducing antioxidant capacity (CUPRAC) and ferric reducing antioxidant power (FRAP) assays. Principal component analysis (PCA) separated the 12 accessions into three distinct groups that were differing from their silymarin contents, whereas hierarchical clustering analysis (HCA) evidenced strong variations in their silymarin composition, leading to the identification of new silybin-rich chemotypes. These results proved that the present method allows for an efficient separation and quantification of the main flavonolignans with potent antioxidant activities.