Hepatic metabolism and biliary excretion of silymarin flavonolignans in isolated perfused rat livers: role of multidrug resistance-associated protein 2 (Abcc2)

Dietary silymarin improves performance by altering hepatic lipid metabolism and cecal microbiota function and its metabolites in late laying hens

BACKGROUND

Liver lipid dysregulation is one of the major factors in the decline of production performance in late-stage laying hens. Silymarin (SIL), a natural flavonolignan extracted from milk thistle, is known for its hepatoprotective and lipid-lowering properties in humans. This study evaluates whether SIL can provide similar benefits to late-stage laying hens. A total of 480 68-week-old Lohmann Pink laying hens were randomly assigned into 5 groups, each group consisting of 6 replicates with 16 hens each. The birds received a basal diet either without silymarin (control) or supplemented with silymarin at concentrations of 250, 500, 750, or 1,000 mg/kg (SIL250, SIL500, SIL750, SIL1000) over a 12-week period.

RESULTS

The CON group exhibited a significant decline in laying rates from weeks 9 to 12 compared to the initial 4 weeks (P = 0.042), while SIL supplementation maintained consistent laying rates throughout the study (P > 0.05). Notably, the SIL500 and SIL750 groups showed higher average egg weight than the CON group during weeks 5 to 8 (P = 0.049). The SIL750 group had a significantly higher average daily feed intake across the study period (P < 0.05), and the SIL500 group saw a marked decrease in the feed-to-egg ratio from weeks 5 to 8 (P = 0.003). Furthermore, the SIL500 group demonstrated significant reductions in serum ALT and AST levels (P < 0.05) and a significant decrease in serum triglycerides and total cholesterol at week 12 with increasing doses of SIL (P < 0.05). SIL also positively influenced liver enzyme expression (FASN, ACC, Apo-VLDL II, FXR, and CYP7A1; P < 0.05) and altered the cecal microbiota composition, enhancing species linked to secondary bile acid synthesis. Targeted metabolomics identified 9 metabolites predominantly involved in thiamin metabolism that were significantly different in the SIL groups (P < 0.05).

CONCLUSIONS

Our study demonstrated that dietary SIL supplementation could ameliorate egg production rate in late stage laying hens, mechanistically, this effect was via improving hepatic lipid metabolism and cecal microbiota function to achieve. Revealed the potentially of SIL as a feed supplementation to regulate hepatic lipid metabolism dysregulation. Overall, dietary 500 mg/kg SIL had the best effects.

Pharmaceutical prospects of Silymarin for the treatment of neurological patients: an updated insight

Background

Silymarin is a polyphenolic flavonoid complex extricated from dried fruits and seeds of the plant Silybum marianum L. Chemically, it is a mixture of flavonolignan complexes consisting of silybin, isosilybin, silychristin, silydianin, a minor quantity of taxifolin, and other polyphenolic compounds, which possess different bio medicinal values.

Purpose

This review critically looks into the current status, pharmaceutical prospects and limitations of the clinical application of Silymarin for treating neurological disorders. In particular, Silymarin's medicinal properties and molecular mechanisms are focused on providing a better-compiled understanding helpful in its neuro-pharmacological or therapeutic aspects.

Methods

This review was compiled by the literature search done using three databases, i.e., PubMed (Medline), EMBASE and Science Direct, up to January 2023, using the keywords-Silymarin, neurological disorders, cognitive disorders, Type 2 Diabetes, pharmaceutical prospects and treatment. Then, potentially relevant publications and studies (matching the eligible criteria) were retrieved and selected to explain in this review using PRISMA 2020 (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) study flow chart.

Result

Since its discovery, it has been widely studied as a hepatoprotective drug for various liver disorders. However, in the last 10-15 years, several research studies have shown its putative neuroprotective nature against various brain disorders, including psychiatric, neurodegenerative, cognitive, metabolic and other neurological disorders. The main underlying neuroprotective mechanisms in preventing and curing such disorders are the antioxidant, anti-inflammatory, anti-apoptotic, pro-neurotrophic and pro-estrogenic nature of the bioactive molecules.

Conclusion

This review provides a lucid summary of the well-studied neuroprotective effects of Silymarin, its underlying molecular mechanisms and current limitations for its usage during neurological disorders. Finally, we have suggested a future course of action for developing it as a novel herbal drug for the treatment of brain diseases.

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.

Systematic review of pharmacokinetics and potential pharmacokinetic interactions of flavonolignans from silymarin

Silymarin is an extract from the seeds (fruits) of Silybum marianum that contains flavonolignans and flavonoids. Although it is frequently used as a hepatoprotective agent, its application remains somewhat debatable, in particular, due to the low oral bioavailability of flavonolignans. Moreover, there are claims of its potential interactions with concomitantly used drugs. This review aims at a systematic summary and critical assessment of known information on the pharmacokinetics of particular silymarin flavonolignans. There are two known major reasons for poor systemic oral bioavailability of flavonolignans: (1) rapid conjugation in intestinal cells or the liver and (2) efflux of parent flavonolignans or formed conjugates back to the lumen of the gastrointestinal tract by intestinal cells and rapid excretion by the liver into the bile. The metabolism of phase I appears to play a minor role, in contrast to extensive conjugation and indeed the unconjugated flavonolignans reach low plasma levels after common doses. Only about 1%-5% of the administered dose is eliminated by the kidneys. Many in vitro studies tested the inhibitory potential of silymarin and its components toward different enzymes and transporters involved in the absorption, metabolism, and excretion of xenobiotics. In most cases, effective concentrations are too high to be relevant under real biological conditions. Most human studies showed no silymarin-drug interactions explainable by these suggested interferences. More interactions were found in animal studies, likely due to the much higher doses administered.

Hepatic organic anion transporting polypeptides mediate disposition of milk thistle flavonolignans and pharmacokinetic silymarin-drug interactions

Silybum marianum (L.) Gaertn. (Asteraceae), commonly known as milk thistle, is a botanical natural product used to self-treat multiple diseases such as Type 2 diabetes mellitus and nonalcoholic steatohepatitis (NASH). An extract from milk thistle seeds (achenes), termed silymarin, is comprised primarily of several flavonolignans. Systemic concentrations of these flavonolignans can influence the potential biologic effects of silymarin and the risk for pharmacokinetic silymarin-drug interactions. The aims of this research were to determine the roles of organic anion transporting polypeptides (OATPs/Oatps) in silymarin flavonolignan disposition and in pharmacokinetic silymarin-drug interactions. The seven major flavonolignans from silymarin were determined to be substrates for OATP1B1, OATP1B3, and OATP2B1. Sprague Dawley rats were fed either a control diet or a NASH-inducing diet and administered pitavastatin (OATP/Oatp probe substrate), followed by silymarin via oral gavage. Decreased protein expression of Oatp1b2 and Oatp1a4 in NASH animals increased flavonolignan area under the plasma concentration-time curve (AUC) and maximum plasma concentration. The combination of silymarin inhibition of Oatps and NASH-associated decrease in Oatp expression caused an additive increase in plasma pitavastatin AUC in the animals. These data indicate that OATPs/Oatps contribute to flavonolignan cellular uptake and mediate the interaction between silymarin and NASH on pitavastatin systemic exposure.

Flavolignans from Silymarin as Nrf2 Bioactivators and Their Therapeutic Applications

Silymarin (SM) is a mixture of flavolignans extracted from the seeds of species derived from Silybum marianum, commonly known as milk thistle or St. Mary'sthistle. These species have been widely used in the treatment of liver disorders in traditional medicine since ancient times. Several properties had been attributed to the major SM flavolignans components, identified as silybin, isosilybin, silychristin, isosilychristin, and silydianin. Previous research reported antioxidant and protective activities, which are probably related to the activation of the nuclear factor erythroid 2 (NFE2)-related factor 2 (Nrf2), known as a master regulator of the cytoprotector response. Nrf2 is a redox-sensitive nuclear transcription factor able to induce the downstream-associated genes. The disruption of Nrf2 signaling has been associated with different pathological conditions. Some identified phytochemicals from SM had shown to participate in the Nrf2 signaling pathway; in particular, they have been suggested as activators that disrupt interactions in the Keap1-Nrf2 system, but also as antioxidants or with additional actions regarding Nrf2 regulation. Thus, the study of these molecules makes them appear attractive as novel targets for the treatment or prevention of several diseases.

Metabolism and Pharmacokinetics of Phytochemicals in the Human Body

Background:

Phytochemicals are obtained from various plants and used for the treatment of diseases as both traditional and modern medicines. Poor bioavailability of phytochemicals is a major concern in applying phytochemicals as a therapeutic agent. It is, therefore, necessary to understand the metabolism and pharmacokinetics of phytochemicals for its implication as a therapeutic agent.

Methods:

Articles on the metabolism of phytochemicals from the PubMed database. The articles were classified into the digestion, absorption, metabolism, excretion, toxicity, and bioavailability of phytochemicals and the effect of gut microbiota on the metabolism of phytochemicals.

Results:

The metabolism of each phytochemical is largely dependent on the individual's digestive ability, membrane transporters, metabolizing enzymes and gut microbiota. Further, the form of the phytochemical and genetic make-up of the individual greatly influences the metabolism of phytochemicals.

Conclusion:

The metabolism of phytochemicals is mostly depended on the form of phytochemicals and individualspecific variations in the metabolism of phytochemicals. Understanding the metabolism and pharmacokinetics of phytochemicals might help in applying plant-based medicines for the treatment of various diseases.

Biotransformation of Silymarin Flavonolignans by Human Fecal Microbiota

Flavonolignans occur typically in Silybum marianum (milk thistle) fruit extract, silymarin, which contains silybin, isosilybin, silychristin, silydianin, and their 2,3-dehydroderivatives, together with other minor flavonoids and a polymeric phenolic fraction. Biotransformation of individual silymarin components by human microbiota was studied ex vivo, using batch incubations inoculated by fecal slurry. Samples at selected time points were analyzed by ultrahigh-performance liquid chromatography equipped with mass spectrometry. The initial experiment using a concentration of 200 mg/L showed that flavonolignans are resistant to the metabolic action of intestinal microbiota. At the lower concentration of 10 mg/L, biotransformation of flavonolignans was much slower than that of taxifolin, which was completely degraded after 16 h. While silybin, isosilybin, and 2,3-dehydrosilybin underwent mostly demethylation, silychristin was predominantly reduced. Silydianin, 2,3-dehydrosilychristin and 2,3-dehydrosilydianin were reduced, as well, and decarbonylation and cysteine conjugation proceeded. No low-molecular-weight phenolic metabolites were detected for any of the compounds tested. Strong inter-individual differences in the biotransformation profile were observed among the four fecal-material donors. In conclusion, the flavonolignans, especially at higher (pharmacological) doses, are relatively resistant to biotransformation by gut microbiota, which, however, depends strongly on the individual structures of these isomeric compounds, but also on the stool donor.

Metabolism, Transport and Drug-Drug Interactions of Silymarin

Silymarin, the extract of milk thistle, and its major active flavonolignan silybin, are common products widely used in the phytotherapy of liver diseases. They also have promising effects in protecting the pancreas, kidney, myocardium, and the central nervous system. However, inconsistent results are noted in the different clinical studies due to the low bioavailability of silymarin. Extensive studies were conducted to explore the metabolism and transport of silymarin/silybin as well as the impact of its consumption on the pharmacokinetics of other clinical drugs. Here, we aimed to summarize and highlight the current knowledge of the metabolism and transport of silymarin. It was concluded that the major efflux transporters of silybin are multidrug resistance-associated protein (MRP2) and breast cancer resistance protein (BCRP) based on results from the transporter-overexpressing cell lines and MRP2-deficient (TR-) rats. Nevertheless, compounds that inhibit the efflux transporters MRP2 and BCRP can enhance the absorption and activity of silybin. Although silymarin does inhibit certain drug-metabolizing enzymes and drug transporters, such effects are unlikely to manifest in clinical settings. Overall, silymarin is a safe and well-tolerated phytomedicine.

Nanotherapeutic silibinin: An insight of phytomedicine in healthcare reformation

Most of the herbal origin drugs possess water insoluble active constituents which lower the bioavailability and increase systemic clearance after administration of repeated or higher dose of drug. Silymarin is extracted from the seeds and fruits of milk thistle plant Silybum marianum which consists of main biologically active component as silibinin. However, the clinical applications of silibinin show some limitations due to low aqueous solubility, poor penetration into the epithelial cells of intestine, high metabolism and rapid systemic elimination. But nanotechnology-based drug delivery system explores great potential for phytochemicals to enhance the aqueous solubility and bioavailability of BCS class II and IV drugs, improve stability and modify the pharmacological activity. This review focuses on the therapeutic properties of silibinin and discusses the benefits, challenges and applications of silibinin nanoformulations. Such nanotherapeutic system as a regular medicine will be an attractive approach to reduce the adverse events and toxicities of current therapies.

Altered Expression and Function of Hepatic Transporters in a Rodent Model of Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common form of inherited polycystic kidney disease (PKD) and is a leading cause of kidney failure. Fluid-filled cysts develop in the kidneys of patients with ADPKD, and cysts often form in their liver and other organs. Previous data have shown that bile acids are increased in the liver of polycystic kidney (PCK) rats, a rodent model of PKD; these changes may be associated with alterations in liver transporter expression and function. However, the impact of PKD on hepatic transporters has not been characterized. Therefore, this preclinical study was designed to investigate hepatic transporter expression and function in PCK compared with wild-type (WT) Sprague-Dawley rats. Transporter gene expression was measured by quantitative polymerase chain reaction, and protein levels were quantified by Western blot and liquid chromatography-tandem mass spectroscopy (LC-MS/MS)-based proteomic analysis in rat livers. Transporter function was assessed in isolated perfused livers (IPLs), and biliary and hepatic total glutathione content was measured. Protein expression of Mrp2 and Oatp1a4 was decreased 3.0-fold and 2.9-fold, respectively, in PCK rat livers based on Western blot analysis. Proteomic analysis confirmed a decrease in Mrp2 and a decrease in Oatp1a1 expression (PCK/WT ratios, 0.368 ± 0.098 and 0.563 ± 0.038, respectively; mean ± S.D.). The biliary excretion of 5(6)-carboxy-2',7'-dichlorofluorescein, a substrate of Oatp1a1, Mrp2, and Mrp3, was decreased 28-fold in PCK compared with WT rat IPLs. Total glutathione was significantly reduced in the bile of PCK rats. Differences in hepatic transporter expression and function may contribute to altered disposition of Mrp2 and Oatp substrates in PKD.

Silymarin as a flavonoid-type P-glycoprotein inhibitor with impact on the pharmacokinetics of carbamazepine, oxcarbazepine and phenytoin in rats

P-glycoprotein (P-gp) is an efflux transporter involved in drug-resistant epilepsy and some flavonoids have been targeted as effective P-gp inhibitors. Herein, we assessed the impact of silymarin on the pharmacokinetics of three antiepileptic drugs (AEDs) in rats. Animals were pretreated with silymarin, verapamil (positive control) or vehicle (negative control) 1 h before AEDs administration (carbamazepine (25 mg/kg), oxcarbazepine (OXC) (50 mg/kg), or phenytoin (100 mg/kg)). Multiple blood samples were collected after AED dosing, and a non-compartmental analysis was performed. An independent study was also conducted to investigate the effects of silymarin on the OXC plasma-to-brain distribution. Silymarin altered the pharmacokinetics of OXC, increasing its peak plasma concentration by 50% and its extent of systemic exposure by 41%, which had also impact on brain drug concentrations. These findings support that the co-administration of silymarin and OXC should continue to be explored as a strategy to reverse the pharmacoresistance in epilepsy.

Piperine enhances the bioavailability of silybin via inhibition of efflux transporters BCRP and MRP2

BACKGROUND

Although silybin serves as a well-known hepatoprotective agent with prominent anti-inflammatory, anti-oxidant and anti-fibrotic activities, its low bioavailability limits its application in the treatment of chronic liver diseases. However, novel formulation products with increased solubility were not sufficient to achieve pharmacologically meaningful concentrations of silybin in the clinical studies even used at high dosage.

HYPOTHESIS/PURPOSE

We hypothesized that inhibiting efflux transporter(s) and/or glucuronidation by piperine might enhance the bioavailability and efficacy of silybin.

METHODS

Pharmacokinetics of silybin given alone or in-combination with piperine was determined by a validated LC-MS method. A CCl₄ induced rat model of liver injury was prepared and verified for comparing the effects of silybin and combination treatment. To investigate the underlying mechanism, the inhibition effects of piperine on transportation of silybin were performed in Caco-2 and transfected MDCKII cell lines as well as sandwich-cultured rat hepatocytes (SCH). Human liver microsomes incubation was used for exploring the modulation effects of piperine on the phase-2 metabolism of silybin.

RESULTS

In the present study, we demonstrated for the first time that piperine as a bioenhancer increased the bioavailability of silybin (146%- 181%), contributing to a boosted therapeutic effect in CCl₄-induced acute liver-injury rat model. The underlying mechanisms involved that piperine enhanced the absorption of silybin by inhibiting the efflux transporters including MRP2 and BCRP but not MDR1 in Caco-2 and transfected MDCKII cell lines. Moreover, piperine could inhibit the biliary excretion of silybin and conjugated metabolites in sandwich-cultured rat hepatocytes. Notably, we found that piperine did not affect the phase-2 metabolism of silybin.

CONCLUSION

Efflux transporters play an important role in the pharmacokinetic behavior of flavolignans, and modulating these transporters by bioenhancer such as piperine could enhance the in vivo absorption of silybin, leading to more effective treatments.

Altered Hepatobiliary Disposition of Tolvaptan and Selected Tolvaptan Metabolites in a Rodent Model of Polycystic Kidney Disease

Tolvaptan, a vasopressin V₂-receptor antagonist, has demonstrated efficacy in slowing kidney function decline in patients with autosomal dominant polycystic kidney disease (ADPKD). In the pivotal clinical trial, the incidence of elevated liver enzymes was higher in patients receiving tolvaptan compared with placebo. Adjudication by a panel of expert hepatologists concluded a causal link of tolvaptan to liver injury in patients with ADPKD. An ex situ isolated perfused liver (IPL) study of tolvaptan disposition was undertaken in a rodent model of ADPKD, the polycystic kidney (PCK) rat (n = 5), and compared with wild-type (WT) Sprague-Dawley rats (n = 6). Livers were perfused with tolvaptan, followed by a tolvaptan-free washout phase. Total recovery (mean ± S.D. percentage of dose; PCK vs. WT) of tolvaptan and two metabolites, DM-4103 and DM-4107, quantified by liquid chromatography-tandem mass spectroscopy, was 58.14% ± 24.72% vs. 43.40% ± 18.11% in liver, 20.10% ± 9.15% vs. 21.17% ± 12.51% in outflow perfusate, and 0.08% ± 0.01% vs. 0.39% ± 0.32% in bile. DM-4103 recovery (mean ± S.D. percentage of dose) was decreased in PCK vs. WT bile (<0.01% ± <0.01% vs. 0.02% ± 0.01%; P = 0.0037), and DM-4107 recovery was increased in PCK vs. WT outflow perfusate (1.60% ± 0.57% vs. 0.43% ± 0.29%; P = 0.0017). A pharmacokinetic compartmental model assuming first-order processes was developed to describe the rate vs. time profiles of tolvaptan and DM-4103 + DM-4107 in rat IPLs. The model-derived estimate of tolvaptan's biliary clearance was significantly decreased in PCK compared with WT IPLs. The model predicted greater hepatocellular concentrations of tolvaptan and DM-4103 + DM-4107 in PCK compared with WT IPLs. Increased hepatocellular exposure to tolvaptan and metabolites may contribute to the hepatotoxicity in patients with ADPKD treated with tolvaptan.

3-Amino-5-pyridin-3-yl-1,2,4-triazole, a novel fluorescence probe for trace analysis of silymarin in bulk material, pharmaceutical dosage forms and human plasma: Further insights on reaction mechanism using computational molecular modeling and NMR spectroscopy

A rapid, highly sensitive and roubst spectrofluorimetric method was developed for trace analysis of silymarin (SLM) in active pharmaceutical ingredient (API), pharmaceutical preparations and human plasma. The proposed method is based on reaction of SLM with a novel reagent; 3-amino-5-pyridin-3-yl-1,2,4-triazole (3-APT); in the presence of 0.04 M sodium hydroxide. The formed fluorescent product was formed within 5 min and was measured at 504 nm after excitation at 390 nm. All reaction parameters were optimized and the proposed method was validated according to ICH guidelines. The developed method was linearly correlated at the concentration range of 0.05-8 μg mL^-1 with good correlation coefficient 0.9993, limit of detection 10.79 ng mL^-1 and limit of quantitation 32.71 ng mL^-1. The relative standard deviations %RSD values were 1.59-2.69% and 1.47-2.62% in case of intra- and inter-day precision, respectively. Computational molecular modeling and NMR spectroscopy were used to identify the reaction mechanism between SLM and 3-APT. The proposed method was employed for determination of SLM in API or bulk material, pharmaceutical capsules and sachets. Further, the method was sensitive enough to be applied for analysis of the free (unconjugated) SLM flavonolignans in human plasma samples.

Baicalein Enhances the Oral Bioavailability and Hepatoprotective Effects of Silybin Through the Inhibition of Efflux Transporters BCRP and MRP2

Although hepatoprotective properties of silybin are well documented, the clinical therapeutic efficacy is limited by its low bioavailability due to absorption rates, extensive phase II metabolism, and biliary excretion. As our previous study indicated that metabolic enzymes may have limited effects on the pharmacokinetic (PK) behavior of silymarin, here, we intended to increase the oral bioavailability and bio-efficacy of silybin through the inhibition of active efflux. In Caco-2 and transfected MDCKII cell models, flavone baicalein significantly inhibited the efflux of silybin as a BCRP and MRP2 inhibitor. In addition, baicalein reduced the biliary excretion index (BEI) and biliary clearance of silybin conjugates in the sandwich-cultured rat hepatocyte (SCH) model, indicating the inhibition of baicalein in biliary excretion of conjugated silybin metabolites. PK study demonstrated that baicalein significantly increased the area under the curve (AUC) and C_max of silybin and its conjugates, suggesting enhanced absorption in vivo. Moreover, coadministration of silybin with baicalein boosted the liver protective, antioxidant, and anti-inflammatory effects of silybin in the carbon tetrachloride (CCl₄)-induced liver injury model in comparison with silybin given alone. In summary, efflux transporters play a critical role in the low bioavailability of silybin, while inhibition of breast cancer resistance protein (BCRP) and multi-drug resistance protein 2 (MRP2) by baicalein can significantly increase the absorption and bio-efficacy of silybin, which provides a new combination therapeutic approach for the treatment of chronic liver diseases.

Sulfated Metabolites of Flavonolignans and 2,3-Dehydroflavonolignans: Preparation and Properties

Silymarin, an extract from milk thistle (Silybum marianum) fruits, is consumed in various food supplements. The metabolism of silymarin flavonolignans in mammals is complex, the exact structure of their metabolites still remains partly unclear and standards are not commercially available. This work is focused on the preparation of sulfated metabolites of silymarin flavonolignans. Sulfated flavonolignans were prepared using aryl sulfotransferase from Desulfitobacterium hafniense and p-nitrophenyl sulfate as a sulfate donor and characterized by high-resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR). Their 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and N,N-dimethyl-p-phenylenediamine (DMPD) radical scavenging; ferric (FRAP) and Folin⁻Ciocalteu reagent (FCR) reducing activity; anti-lipoperoxidant potential; and effect on the nuclear erythroid 2-related factor 2 (Nrf2) signaling pathway were examined. Pure silybin A 20-O-sulfate, silybin B 20-O-sulfate, 2,3-dehydrosilybin-20-O-sulfate, 2,3-dehydrosilybin-7,20-di-O-sulfate, silychristin-19-O-sulfate, 2,3-dehydrosilychristin-19-O-sulfate, and silydianin-19-O-sulfate were prepared and fully characterized. Sulfated 2,3-dehydroderivatives were more active in FCR and FRAP assays than the parent compounds, and remaining sulfates were less active chemoprotectants. The sulfated flavonolignans obtained can be now used as authentic standards for in vivo metabolic experiments and for further research on their biological activity.

Metabolism of flavonolignans in human hepatocytes

This study examined the in vitro biotransformation of eight structurally related flavonolignans, namely silybin, 2,3-dehydrosilybin, silychristin, 2,3-dehydrosilychristin, silydianin, 2,3-dehydrosilydianin, isosilybin A and isosilybin B. The metabolic transformations were performed using primary cultures of human hepatocytes and recombinant human cytochromes P450 (CYPs 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1 and 3A4). The metabolites produced were analyzed by ultra-performance liquid chromatography coupled with tandem mass spectrometry. We found that each of the tested compounds was metabolized in vitro by one or more CYP enzymes, which catalyzed O-demethylation, hydroxylation, hydrogenation and dehydrogenation reactions. In human hepatocytes, silybin, 2,3-dehydrosilybin, silychristin, 2,3-dehydrosilychristin, and isosilybins A and B were directly conjugated by sulfation or glucuronidation. Moreover, isosilybin A was also converted to a methyl derivative, while isosilybin B was hydroxylated and methylated. Silydianin and 2,3-dehydrosilydianin were found to undergo hydrogenation and/or glucuronidation. In addition, 2,3-dehydrosilydianin was found to be metabolically the least stable flavonolignan in human hepatocytes, and its main metabolite was a cleavage product corresponding to a loss of CO. We conclude that the hepatic biotransformation of flavonolignans primarily involves the phase II conjugation reactions, however in some cases the phase I reactions may also occur. These results are highly relevant for research focused on flavonolignan metabolism and pharmacology.

The effects of dietary and herbal phytochemicals on drug transporters

Membrane transporter proteins (the ABC transporters and SLC transporters) play pivotal roles in drug absorption and disposition, and thus determine their efficacy and safety. Accumulating evidence suggests that the expression and activity of these transporters may be modulated by various phytochemicals (PCs) found in diets rich in plants and herbs. PC absorption and disposition are also subject to the function of membrane transporter and drug metabolizing enzymes. PC-drug interactions may involve multiple major drug transporters (and metabolizing enzymes) in the body, leading to alterations in the pharmacokinetics of substrate drugs, and thus their efficacy and toxicity. This review summarizes the reported in vitro and in vivo interactions between common dietary PCs and the major drug transporters. The oral absorption, distribution into pharmacological sanctuaries and excretion of substrate drugs and PCs are considered, along with their possible interactions with the ABC and SLC transporters which influence these processes.

Milk Thistle Constituents Inhibit Raloxifene Intestinal Glucuronidation: A Potential Clinically Relevant Natural Product-Drug Interaction

Women at high risk of developing breast cancer are prescribed selective estrogen response modulators, including raloxifene, as chemoprevention. Patients often seek complementary and alternative treatment modalities, including herbal products, to supplement prescribed medications. Milk thistle preparations, including silibinin and silymarin, are top-selling herbal products that may be consumed by women taking raloxifene, which undergoes extensive first-pass glucuronidation in the intestine. Key constituents in milk thistle, flavonolignans, were previously shown to be potent inhibitors of intestinal UDP-glucuronosyl transferases (UGTs), with IC50s ≤ 10 μM. Taken together, milk thistle preparations may perpetrate unwanted interactions with raloxifene. The objective of this work was to evaluate the inhibitory effects of individual milk thistle constituents on the intestinal glucuronidation of raloxifene using human intestinal microsomes and human embryonic kidney cell lysates overexpressing UGT1A1, UGT1A8, and UGT1A10, isoforms highly expressed in the intestine that are critical to raloxifene clearance. The flavonolignans silybin A and silybin B were potent inhibitors of both raloxifene 4'- and 6-glucuronidation in all enzyme systems. The Kis (human intestinal microsomes, 27-66 µM; UGT1A1, 3.2-8.3 µM; UGT1A8, 19-73 µM; and UGT1A10, 65-120 µM) encompassed reported intestinal tissue concentrations (20-310 µM), prompting prediction of clinical interaction risk using a mechanistic static model. Silibinin and silymarin were predicted to increase raloxifene systemic exposure by 4- to 5-fold, indicating high interaction risk that merits further evaluation. This systematic investigation of the potential interaction between a widely used herbal product and chemopreventive agent underscores the importance of understanding natural product-drug interactions in the context of cancer prevention.

Hepatocellular organic anion-transporting polypeptides (OATPs) and multidrug resistance-associated protein 2 (MRP2) are inhibited by silibinin

Silibinin has been reported to be a promising compound for hepatitis C treatment of nonresponders to standard treatment. Although administered silibinin is well tolerated, increased serum bilirubin levels have been observed during high-dose i.v. silibinin therapy. The mechanism of silibinin-induced hyperbilirubinemia in humans, however, has not been identified so far. The aim of this study was to investigate the effect of silibinin on hepatocellular uptake and efflux transport systems for organic anions to elucidate the cause of silibinin-induced hyperbilirubinemia. Therefore, the effect of silibinin on transport activity of the hepatocellular uptake transporters organic anion-transporting polypeptides (OATPs) OATP1B1, OATP1B3, and OATP2B1, as well as Na(+)-taurocholate cotransporting polypeptide (NTCP) and of the efflux transporters multidrug resistance-associated protein 2 (MRP2) and bile-salt export pump (BSEP) was studied. The effect of silibinin on OATPs and NTCP function was studied in stable transfected Chinese hamster ovary cells using the radiolabeled model substrates estrone-3-sulfate and dehydroepiandrosteronesulfate for OATPs and taurocholate for NTCP. Interaction of silibinin with MRP2 and BSEP was measured in vesicles isolated from Sf21 or Sf9 insect cells expressing these transporters using either estradiol-17β-glucuronide or taurocholate as substrates. OATP1B1, OATP1B3, and OATP2B1 were inhibited by silibinin, with OATP1B1 being inhibited by (a) complex mechanism(s). An inhibitory effect was also seen for MRP2. In contrast, the bile acid transporters NTCP and BSEP were not affected by silibinin. We concluded that silibinin-induced hyperbilirubinemia may be caused by an inhibition of the bilirubin-transporting OATPs and the efflux-transporter MRP2.

Enzymatic preparation of silybin phase II metabolites: sulfation using aryl sulfotransferase from rat liver

Aryl sulfotransferase IV (AstIV) from rat liver was overexpressed in Escherichia coli and purified to homogeneity. Using the produced mammalian liver enzyme, sulfation-the Phase II conjugation reaction-of optically pure silybin diastereoisomers (silybin A and B) was tested. As a result, silybin B was sulfated yielding 20-O-silybin B sulfate, whereas silybin A was completely resistant to the sulfation reaction. Milligram-scale sulfation of silybin B was optimized employing resting E. coli cells producing AstIV, thus avoiding the use of expensive 3'-phosphoadenosine-5'-phosphate cofactor and laborious enzyme purification. Using this approach, we were able to reach 48 % conversion of silybin B into its 20-sulfate within 24 h. The sulfated product was isolated by solid phase extraction and its structure was characterized by HRMS and NMR. Sulfation reaction of silybin appeared strictly stereoselective; only silybin B was sulfated by AstIV.

Dramatic increase in hepatic and biliary curcumin exposure by modulation of its elimination pathway in rats

OBJECTIVES

Curcumin, a major component of the food spice turmeric (Curcuma longa), has multiple beneficial effects on diseases of the liver and bile duct. We have investigated whether modulation of the curcumin elimination pathway could increase its hepatic and biliary exposure in rats.

METHODS

Probenecid, an inhibitor of the metabolism and biliary excretion of curcumin, was used as a modulator. After intravenous administration of curcumin at a dose of 18 mg/kg/h without (control) or with co-infusion of probenecid (230 mg/kg/h) in rats, the pharmacokinetic parameters of curcumin were estimated.

KEY FINDINGS

Coadministration of probenecid significantly increased the total area under the plasma (1.88-fold) and bile (6.73-fold) concentration-time curves from 0 to 80 min of curcumin relative to those in the controls. The tissue-to-plasma concentration ratio in the liver was also dramatically increased (69.3-fold) by probenecid. These results may be attributed to the dual inhibitory effects of probenecid, to a greater extent, on metabolism via glucuronidation, and to a lesser extent, on the biliary excretion of curcumin via the multidrug resistance-associated protein 2.

CONCLUSIONS

The probenecid-mediated increase in hepatic and biliary exposure of curcumin suggested that the use of combination drug regimens involving curcumin and modulators of elimination may be an innovative approach for the therapeutic use of curcumin.

The toxicity and pathology of selected dietary herbal medicines

Toxicity studies were conducted by the National Toxicology Program (NTP) to provide information on the potential for toxicity from long-term use of commonly used herbal medicines. Here, we review the findings from these NTP toxicology/carcinogenesis 2-year rodent studies of 7 commonly used herbs. In these studies, the individual herb or herbal product was administered to F344/N rats and B6C3F1 mice by oral administration for up to 2 years. The spectrum of carcinogenic responses ranged from no or equivocal evidence for carcinogenic activity (ginseng, milk thistle, and turmeric oleoresin) to a liver tumor response (ginkgo, goldenseal, kava), thyroid tumor response (ginkgo), or an intestinal tumor response (Aloe vera whole leaf nondecolorized extract). Different mechanisms may be involved in the occurrence of liver (ginkgo, goldenseal, and kava kava) and gastrointestinal toxicity (turmeric oleoresin and Aloe vera whole leaf nondecolorized extract), while the toxic lesion is the same. The results from these hazard identification toxicity/carcinogenesis studies along with those from ongoing National Institute of Health clinical trials of herbal medicines provide more complete information on the risks and benefits from herbal medicine use in the general population.

Mutual interactions between flavonoids and enzymatic and transporter elements responsible for flavonoid disposition via phase II metabolic pathways

Flavonoids, existing mainly as glycosides in nature, have multiple "claimed" beneficial effects in humans. Flavonoids are extensively metabolized in enterocytes and hepatocytes by phase II enzymes such as UGTs and SULTs to form glucuronides and sulfates, respectively. These glucuronides and sulfates are subsequently excreted via ABC transporters (e.g., MRP2 or BCRP). Therefore, it is the interplay between phase II enzymes and efflux transporters that affects the disposition of flavonoids and leads to the low bioavailability of flavonoid aglycones. Flavonoids can also serve as chemical regulators that affect the activity or expression levels of phase II enzymes including UGTs, SULTs and GSTs, and transporters including P-gp, MRP2, BCRP, OATP and OAT. In general, flavonoids may exert the inhibitory or inductive effects on the phase II enzymes and transporters via multiple mechanisms that may involve different nuclear receptors. Since flavonoids may affect the metabolic pathways shared by many important clinical drugs, drug-flavonoid interaction is becoming an increasingly important concern. This review article focused on the disposition of flavonoids and effects of flavonoids on relevant enzymes (e.g. UGTs and SULTs) and transporters (e.g. MRP2 and BCRP) involved in the interplay between phase II enzymes and efflux transporters. The effects of flavonoids on other metabolic enzymes (e.g. GSTs) or transporters (e.g. P-gp, OATP and OAT) are also addressed but that is not the emphasis of this review.

Effect of silymarin (milk thistle) on liver disease in patients with chronic hepatitis C unsuccessfully treated with interferon therapy: a randomized controlled trial

CONTEXT

The botanical product silymarin, an extract of milk thistle, is commonly used by patients to treat chronic liver disease, despite scant and conflicting evidence of its efficacy.

OBJECTIVE

To determine the effect of silymarin on liver disease activity in patients with chronic hepatitis C virus (HCV) infection unsuccessfully treated with interferon-based therapy.

DESIGN, SETTING, AND PARTICIPANTS

Multicenter, double-blind, placebo-controlled trial conducted at 4 medical centers in the United States. Participants included 154 persons with chronic HCV infection and serum alanine aminotransferase (ALT) levels of 65 U/L or greater who were previously unsuccessfully treated with interferon-based therapy. Enrollment began in May 2008 and was completed in May 2010, with the last follow-up visit completed in March 2011.

INTERVENTION

Participants were randomly assigned to receive 420-mg silymarin, 700-mg silymarin, or matching placebo administered 3 times per day for 24 weeks.

MAIN OUTCOME MEASURES

The primary outcome measure was serum ALT level of 45 U/L or less (considered within the normal range) or less than 65 U/L, provided this was at least a 50% decline from baseline values. Secondary outcomes included changes in ALT levels, HCV RNA levels, and quality-of-life measures.

RESULTS

After 24 weeks of treatment, only 2 participants in each treatment group (P ≥ .99) met the primary outcome measure (3.8% [95% CI, 0.5% to 13.2%] for placebo, 4.0% [95% CI, 0.5% to 13.7%] for 420-mg silymarin, and 3.8% [95% CI, 0.5% to 13.2%] for 700-mg silymarin). The mean decline in serum ALT activity at the end of treatment did not differ significantly (P = .75) across the 3 treatment groups (mean decline, -4.3 [95% CI, -17.3 to 8.7] U/L for placebo, -14.4 [95% CI, -41.6 to 12.7] U/L for 420-mg silymarin, -11.3 [95% CI, -27.9 to 5.4] U/L for 700-mg silymarin); there likewise were no significant differences in HCV RNA levels (mean change, 0.07 [95% CI, -0.05 to 0.18] log10 IU/mL for placebo, -0.03 [95% CI, -0.18 to 0.12] log10 IU/mL for 420-mg silymarin, 0.04 [95% CI, -0.08 to 0.16] log10 IU/mL for 700-mg silymarin; P = .54) or quality-of-life measures. The adverse event profile of silymarin was comparable with that of placebo.

CONCLUSION

Higher than customary doses of silymarin did not significantly reduce serum ALT levels more than placebo in participants with chronic HCV infection unsuccessfully treated with interferon-based therapy.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00680342.

Differences in the disposition of silymarin between patients with nonalcoholic fatty liver disease and chronic hepatitis C

Silymarin, derived from the milk thistle plant Silybum marianum and widely used for self-treatment of liver diseases, is composed of six major flavonolignans including silybin A and silybin B, which are the predominant flavonolignans quantified in human plasma. The single- and multiple-dose pharmacokinetics of silymarin flavonolignans were examined in patients with nonalcoholic fatty liver disease (NAFLD) or hepatitis C virus (HCV) to determine whether the disposition of silymarin and therefore its potential efficacy vary among liver disease populations. Cohorts of eight subjects with noncirrhotic liver disease were randomized 3:1 to oral silymarin or placebo (280 or 560 mg) every 8 h for 7 days. Forty-eight-hour blood sampling was conducted after the first and final doses. In general, plasma concentrations of silybin A and silybin B were higher, whereas concentrations of conjugates were lower in NAFLD compared with HCV. After adjustment of the area under plasma concentration-time curve from 0 to 8 h (AUC(0-8 h)) for weight and dose, only silybin B and silybin B conjugates differed significantly between disease types. For NAFLD, the adjusted mean AUC(0-8 h) was higher for silybin B (p < 0.05) but lower for silybin B conjugates (p < 0.05) compared with that for HCV. At the 280-mg dose, steady-state plasma concentrations of silybin B conjugates for NAFLD subjects were characterized by 46% lower AUC(0-8 h) (p < 0.05) and 42% lower C(max) (p < 0.05) compared with HCV subjects. Evidence of enterohepatic cycling of flavonolignans was only observed in NAFLD subjects. In summary, the efficacy of silymarin may be more readily observed in NAFLD patients because of their higher flavonolignan plasma concentrations and more extensive enterohepatic cycling compared with those in HCV patients.

Silybin and the liver: From basic research to clinical practice

Herbal products are increasingly used, mainly in chronic liver disease. Extracts of milk thistle, Silymarin and silybin, are the most prescribed natural compounds, with different indications, but with no definitive results in terms of clinical efficacy. This review analyzes the available studies on the effects of the purified product silybin, both as a free and a conjugated molecule, on liver cells or on experimentally induced liver damage, and in patients with liver disease. We searched PUBMED for articles pertaining to the in vitro and in vivo effects of silybin, its antifibrotic, anti-inflammatory, and antioxidant properties, as well as its metabolic effects, combined with the authors’ own knowledge of the literature. Results indicate that the bioavailability of silybin phytosome is higher than that of silymarin and is less influenced by liver damage; silybin does not show significant interactions with other drugs and at doses < 10 g/d has no significant side effects. Experimental studies have clearly demonstrated the antifibrotic, antioxidant and metabolic effects of silybin; previous human studies were insufficient for confirming the clinical efficacy in chronic liver disease, while ongoing clinical trials are promising. On the basis of literature data, silybin seems a promising drug for chronic liver disease.

Biological analysis of herbal medicines used for the treatment of liver diseases

Herbal medicines have been used to treat liver disorders for thousands of years in the East and have now become a promising therapy internationally for pathological liver conditions. Biological analysis of hepatoprotective herbs is an important issue from the pharmacokinetic perspective in developing new therapeutic managements for liver disease. The biological analysis focuses on the pretreatment methods, separation and quantification of herbal medicines in biological samples. We have compiled and discuss the biological analytical method of six herbal medicines for liver protection containing Silybum marianum(silymarin), Glycyrrhiza glabra, Scutellaria baicalensis, Schisandra chinensis, Salvia miltiorrhiza and Astragalus membranaceus. This review provides a convenient reference for researchers to reduce time-consuming method optimization.

"Silymarin", a promising pharmacological agent for treatment of diseases

Widespread use of herbal drugs because of their protective effects on different organs toxicity has been shown in many studies. These protective effects have been illustrated in the fields of nephrotoxicity, hepatotoxicity, viral hepatitis, cancer, in vitro fertilization, neurotoxicity, depression, lung diseases, prostate diseases etc. Silymarin has cytoprotection activities due to its antioxidant activity and radical scavenging. The possible known mechanisms of action of silymarin protection are blockade and adjustment of cell transporters, p-glycoprotein, estrogenic and nuclear receptors. Moreover, silymarin anti-inflammatory effects through reduction of TNF-α, protective effects on erythrocyte lysis and cisplatin-induced acute nephrotoxicity have been indicated in some studies. Silymarin has also inhibited apoptosis and follicular development in patients undergoing IVF. Basis on such data, silymarin can be served as a novel medication in complementary medicine.

ABCC2/Abcc2: a multispecific transporter with dominant excretory functions

ABCC2/Abcc2 (MRP2/Mrp2) is expressed at major physiological barriers, such as the canalicular membrane of liver cells, kidney proximal tubule epithelial cells, enterocytes of the small and large intestine, and syncytiotrophoblast of the placenta. ABCC2/Abcc2 always localizes in the apical membranes. Although ABCC2/Abcc2 transports a variety of amphiphilic anions that belong to different classes of molecules, such as endogenous compounds (e.g., bilirubin-glucuronides), drugs, toxic chemicals, nutraceuticals, and their conjugates, it displays a preference for phase II conjugates. Phenotypically, the most obvious consequence of mutations in ABCC2 that lead to Dubin-Johnson syndrome is conjugate hyperbilirubinemia. ABCC2/Abcc2 harbors multiple binding sites and displays complex transport kinetics.

Silymarin ascending multiple oral dosing phase I study in noncirrhotic patients with chronic hepatitis C

Silymarin, derived from the milk thistle plant Silybum marianum, is widely used for self-treatment of liver diseases, including hepatitis C virus (HCV), and its antiviral activity has been demonstrated in vitro and in HCV patients administered an intravenous formulation of the major silymarin flavonolignans, silybin A and silybin B. The safety and dose-exposure relationships of higher than customary oral doses of silymarin and its acute effects on serum HCV RNA were evaluated in noncirrhotic HCV patients. Four cohorts of 8 patients with well-compensated, chronic noncirrhotic HCV who failed interferon-based therapy were randomized 3:1 to silymarin or placebo. Oral doses of 140, 280, 560, or 700 mg silymarin were administered every 8 hours for 7 days. Steady-state exposures for silybin A and silybin B increased 11-fold and 38-fold, respectively, with a 5-fold increase in dose, suggesting nonlinear pharmacokinetics. No drug-related adverse events were reported, and no clinically meaningful reductions from baseline serum transaminases or HCV RNA titer were observed. Oral doses of silymarin up to 2.1 g per day were safe and well tolerated. The nonlinear pharmacokinetics of silybin A and silybin B suggests low bioavailability associated with customary doses of silymarin may be overcome with doses above 700 mg.