Saponins as Tool for Improved Targeted Tumor Therapies

Recent Advances in Steroid Discovery: Structural Diversity and Bioactivity of Marine and Terrestrial Steroids

Steroids have been pivotal in medicine and biology, with research into their therapeutic potential accelerating over the past few decades. This review examines recent steroid discoveries from marine and terrestrial sources, highlighting both novel compounds and those with newly identified biological activities. The structural diversity of these steroids contributes to their wide range of biological activity, including anticancer, antimicrobial, antidiabetic, anti-inflammatory, and immunomodulatory properties. Particular emphasis is placed on steroids derived from marine invertebrates, fungi, and medicinal plants, which have shown promising therapeutic potential. Advances in analytical techniques such as NMR spectroscopy and mass spectrometry have facilitated the identification of these compounds. These findings emphasize the growing importance of steroids in addressing pressing global health issues, particularly antibiotic resistance and cancer, where new therapeutic strategies are urgently needed. Although many newly identified steroids exhibit potent bioactivity, challenges remain in translating these findings into clinical therapies. Ongoing exploration of natural sources, along with the application of modern synthetic and computational methods, will be crucial in unlocking the full therapeutic potential of steroid-based compounds.

Pharmacological Significance, Medicinal Use, and Toxicity of Extracted and Isolated Compounds from Euphorbia Species Found in Southern Africa: A Review

This study documents the Euphorbiaceae family of plants in Southern Africa, with a focus on their traditional medicinal applications, pharmacological properties, toxicity, and active secondary metabolites. A review of the literature from scientific journals, books, dissertations, and conference papers spanning from 1962 to 2023 was conducted for 15 Euphorbia species. Recent findings indicate that specific compounds found in Euphorbia plants exhibit significant biological and pharmacological properties. However, the white sticky latex sap they contain is highly toxic, although it may also have medicinal applications. Phytochemical analyses have demonstrated that these plants exhibit beneficial effects, including antibacterial, antioxidant, antiproliferative, anticancer, anti-inflammatory, antiviral, antifungal, and anti-HIV activities. Key phytochemicals such as euphol, cycloartenol, tirucallol, and triterpenoids contribute to their therapeutic efficacy, along with various proteins like lectin and lysozyme. Despite some Euphorbiaceae species undergoing screening for medicinal compounds, many remain insufficiently examined, highlighting a critical gap in the research literature. Given their historical usage, further investigations are essential to evaluate the medicinal significance of Euphorbia species through detailed studies of isolated compounds and their pharmacokinetics and pharmacodynamics. This research will serve as a valuable resource for future inquiries into the benefits of lesser-studied Euphorbia species.

Recent advances in the anti-tumor activities of saponins through cholesterol regulation

Abnormal cholesterol metabolism has become a popular therapeutic target in cancer therapy. In recent years there has been a surge in interest in the anti-tumor activities of saponins, particularly their ability to disrupt cholesterol homeostasis in tumor cells. Cholesterol regulation by saponins is a complex process that involves multiple mechanisms. However, there are now a notable dearth of comprehensive reviews addressing their anti-tumor effects through cholesterol modulation. This review will explore the intricate mechanisms by which saponins regulate cholesterol, including modulation of synthesis, metabolism, and uptake, as well as complex formation with cholesterol. It will also outline how saponins exert their anti-cancer activities through cholesterol regulation, enhancing cytotoxicity, inhibiting tumor cell metastasis, reversing drug resistance, inducing immunotoxin macromolecule escape, and ferroptosis. This comprehensive analysis offers insights into the potential for the use of saponins anti-tumor therapies and their combinations with other drugs, advancing the understanding of their effects on cancer cells.

Advances in antitumor activity and mechanism of natural steroidal saponins: A review of advances, challenges, and future prospects

BACKGROUND

Cancer, the second leading cause of death worldwide following cardiovascular diseases, presents a formidable challenge in clinical settings due to the extensive toxic side effects associated with primary chemotherapy drugs employed for cancer treatment. Furthermore, the emergence of drug resistance against specific chemotherapeutic agents has further complicated the situation. Consequently, there exists an urgent imperative to investigate novel anticancer drugs. Steroidal saponins, a class of natural compounds, have demonstrated notable antitumor efficacy. Nonetheless, their translation into clinical applications has remained unrealized thus far. In light of this, we conducted a comprehensive systematic review elucidating the antitumor activity, underlying mechanisms, and inherent limitations of steroidal saponins. Additionally, we propose a series of strategic approaches and recommendations to augment the antitumor potential of steroidal saponin compounds, thereby offering prospective insights for their eventual clinical implementation.

PURPOSE

This review summarizes steroidal saponins' antitumor activity, mechanisms, and limitations.

METHODS

The data included in this review are sourced from authoritative databases such as PubMed, Web of Science, ScienceDirect, and others.

RESULTS

A comprehensive summary of over 40 steroidal saponin compounds with proven antitumor activity, including their applicable tumor types and structural characteristics, has been compiled. These steroidal saponins can be primarily classified into five categories: spirostanol, isospirostanol, furostanol, steroidal alkaloids, and cholestanol. The isospirostanol and cholestanol saponins are found to have more potent antitumor activity. The primary antitumor mechanisms of these saponins include tumor cell apoptosis, autophagy induction, inhibition of tumor migration, overcoming drug resistance, and cell cycle arrest. However, steroidal saponins have limitations, such as higher cytotoxicity and lower bioavailability. Furthermore, strategies to address these drawbacks have been proposed.

CONCLUSION

In summary, isospirostanol and cholestanol steroidal saponins demonstrate notable antitumor activity and different structural categories of steroidal saponins exhibit variations in their antitumor signaling pathways. However, the clinical application of steroidal saponins in cancer treatment still faces limitations, and further research and development are necessary to advance their potential in tumor therapy.

The Development and Expansion of in vivo Germline Editing Technologies in Arthropods: Receptor-Mediated Ovary Transduction of Cargo (ReMOT Control) and Beyond

In the past 20 years, sequencing technologies have led to easy access to genomic data from nonmodel organisms in all biological realms. Insect genetic manipulation, however, continues to be a challenge due to various factors, including technical and cost-related issues. Traditional techniques such as microinjection of gene-editing vectors into early stage embryos have been used for arthropod transgenesis and the discovery of Clustered regularly interspaced short palindromic repeats and CRISPR-associated protein (CRISPR-Cas) technologies allowed for targeted mutagenesis and the creation of knockouts or knock-ins in arthropods. Receptor-Mediated Ovary Transduction of Cargo (ReMOT Control) acts as an alternative to embryonic microinjections, which require expensive equipment and extensive hands-on training. ReMOT Control's main advantage is its ease of use coupled with the ability to hypothetically target any vitellogenic species, as injections are administered to the egg-laying adult rather than embryos. After its initial application in the mosquito Aedes aegypti, ReMOT Control has successfully produced mutants not only for mosquitoes but for multiple arthropod species from diverse orders, such as ticks, mites, wasps, beetles, and true bugs, and is being extended to crustaceans, demonstrating the versatility of the technique. In this review, we discuss the current state of ReMOT Control from its proof-of-concept to the advances and challenges in the application across species after 5 years since its development, including novel extensions of the technique such as direct parental (DIPA)-CRISPR.

Use of Saponinosomes from Ziziphus spina-christi as Anticancer Drug Carriers

Saponins are plant glycosides with different structures and biological activities, such as anticancer effects. Ziziphus spina-christi is a plant rich in saponin, and this compound is used to treat malignant melanoma in the present study. Nanophytosomes can be used as an advantageous nanodrug delivery system for plant extracts. The aim of this work is to use the saponin-rich fraction (SRF) from Z. spina-christi and prepare SRF-loaded nanophytosomes (saponinosomes) and observe the in vitro and in vivo effects of these carriers. First, the SRF was obtained from Z. spina-christi by a solvent-solvent fractionation method. Then, Fourier transform infrared (FTIR) analyses were performed to confirm the presence of saponins in the extracted material. Subsequently, the saponinosomes were prepared by the solvent injection method (ether injection method) using a 1:1:1 ratio of lecithin/cholesterol/SRF in the mixture. Characterization of the prepared saponinosomes was performed by FTIR, dynamic light scattering (DLS), field-emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM) analyses. In addition, a UV-vis spectrophotometer was used to determine the entrapment efficiency (EE) and in vitro release of the SRF. Finally, cell cytotoxicity of the different formulations was evaluated using a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay on both mouse melanoma cells (B16F10) and fibroblasts (L929). Using DLS, AFM, and FE-SEM analyses, the particle size was determined to be 58 ± 6 nm with a zeta potential of -32 ± 2 mV. The calculated EE was 85 ± 3%. The results of the in vitro release profile showed that 68.2% of the SRF was released from the saponinosome after 48 h. The results of the MTT assay showed that the SRF and saponinosomes have high toxicity on B16F10 melanoma cells, but saponinosomes showed a significant decrease in cytotoxicity on L929 fibroblast cells compared with that of the SRF. Our results indicate that the SRF from Z. spina-christi has anticancer activity, and the saponinosomes prepared in this work can control tumor growth, improve therapeutic efficacy, and reduce the side effects of saponins.

In addition to its endosomal escape effect, platycodin D also synergizes with ribosomal inactivation protein to induce apoptosis in hepatoma cells through AKT and MAPK signaling pathways

Efficient endosomal escape after cellular uptake is a major challenge for the clinical application of therapeutic proteins. To overcome this obstacle, several strategies have been used to help protein drugs escape from endosomes without affecting the integrity of the cell membrane. Among them, some triterpenoid saponins with special structures were used to greatly enhance the anti-tumor therapeutic effect of protein toxins. Herein, we demonstrated that platycodin D (PD), polygalacin D (PGD) and platycodin D2 (PD2) from Platycodonis Radix significantly enhanced the ability of MHBP (a type I ribosome-inactivating protein toxin MAP30 fused with a cell-penetrating peptide HBP) to induce apoptosis in hepatoma cells. Based on the results of co-localization of endocytosed EGFP-HBP with a lysosomal probe and Galectin-9 vesicle membrane damage sensor, we demonstrated that PD, PGD and PD2 have the ability to promote endosomal escape of endocytic proteins without affecting the integrity of the plasma membrane. Meanwhile, we observed that cholesterol metabolism plays an important role in the activity of PD by RNA-seq analysis and KEGG pathway enrichment analysis, and confirm that PD, PGD and PD2 enhance the anti-tumor activity of MHBP by inducing the redistribution of free cholesterol and inhibiting the activity of cathepsin B and cathepsin D. Finally, we found that PD synergized with MHBP to induce caspase-dependent apoptosis through inhibiting Akt and ERK1/2 signaling pathways and activating JNK and p38 MAPK signaling pathways. This study provides new insights into the application of PD in cancer therapy and provides efficient and promising strategies for the cytosolic delivery of therapeutic proteins.

Novel Timosaponin AIII-Based Multifunctional Liposomal Delivery System for Synergistic Therapy Against Hepatocellular Carcinoma Cancer

Introduction

As high cholesterol level has been reported to be associated with cancer cell growth and cholesterol is vulnerable to oxidation, the conventional liposomes including cholesterol in the formulation seem to be challenged. Timosaponin AIII (TAIII), as a steroid saponin from Anemarrhena asphodeloides Bunge, possesses a similar structure with cholesterol and exhibits a wide range of antitumor activities, making it possible to develop a TAIII-based liposome where TAIII could potentially stabilize the phospholipid bilayer as a substitution of cholesterol and work as a chemotherapeutic drug as well. Meanwhile, TAIII could enhance the uptake of doxorubicin hydrochloride (DOX) in human hepatocellular carcinoma (HCC) cells and exhibit synergistic effect. Thus, we designed a novel thermally sensitive multifunctional liposomal system composed of TAIII and lipids to deliver DOX for enhanced HCC treatment.

Methods

The synergistic effects of DOX and TAIII were explored on HCC cells and the tumor inhibition rate of TAIII-based liposomes carrying DOX was evaluated on both subcutaneous and orthotopic transplantation tumor models. TAIII-based multifunctional liposomes were characterized.

Results

Synergistic HCC cytotoxicity was achieved at molar ratios of 1:1, 1:2 and 1:4 of DOX/TAIII. TAIII-based liposomes carrying a low DOX dose of 2 mg/kg exhibited significantly enhanced antitumor activity than 5 mg/kg of DOX without detected cardiotoxicity on both subcutaneous and orthotopic transplantation tumor models. TAIII-based liposomes were characterized with smaller size than cholesterol liposomes but exhibited favorable stability. Mild hyperthermia generated by laser irradiation accelerated the release of DOX and TAIII from liposomes at tumor site, and cell permeability of TAIII enhanced uptake of DOX in HCC cells.

Conclusion

The innovative application of TAIII working as bilayer stabilizer and chemotherapeutic drug affords a stable multifunctional liposomal delivery system for synergistic therapy against HCC, which may be referred for the development of other types of saponins with similar property.

Magnetic Nanoparticle-Based Dianthin Targeting for Controlled Drug Release Using the Endosomal Escape Enhancer SO1861

Targeted tumor therapy can provide the basis for the inhibition of tumor growth. However, a number of toxin-based therapeutics lack efficacy because of insufficient endosomal escape after being internalized by endocytosis. To address this problem, the potential of glycosylated triterpenoids, such as SO1861, as endosomal escape enhancers (EEE) for superparamagnetic iron oxide nanoparticle (SPION)-based toxin therapy was investigated. Herein, two different SPION-based particle systems were synthesized, each selectively functionalized with either the targeted toxin, dianthin-epidermal growth factor (DiaEGF), or the EEE, SO1861. After applying both particle systems in vitro, an almost 2000-fold enhancement in tumor cell cytotoxicity compared to the monotherapy with SPION-DiaEGF and a 6.7-fold gain in specificity was observed. Thus, the required dose of the formulation was appreciably reduced, and the therapeutic window widened.

Cas9-Mediated Gene-Editing in the Malaria Mosquito Anopheles stephensi by ReMOT Control

Innovative tools are essential for advancing malaria control and depend on an understanding of molecular mechanisms governing transmission of malaria parasites by Anopheles mosquitoes. CRISPR/Cas9-based gene disruption is a powerful method to uncover underlying biology of vector-pathogen interactions and can itself form the basis of mosquito control strategies. However, embryo injection methods used to genetically manipulate mosquitoes (especially Anopheles) are difficult and inefficient, particularly for non-specialist laboratories. Here, we adapted the ReMOT Control (Receptor-mediated Ovary Transduction of Cargo) technique to deliver Cas9 ribonucleoprotein complex to adult mosquito ovaries, generating targeted and heritable mutations in the malaria vector Anopheles stephensi without injecting embryos. In Anopheles, ReMOT Control gene editing was as efficient as standard embryo injections. The application of ReMOT Control to Anopheles opens the power of CRISPR/Cas9 methods to malaria laboratories that lack the equipment or expertise to perform embryo injections and establishes the flexibility of ReMOT Control for diverse mosquito species.

Phytochemical Study on Antioxidant and Antiproliferative Activities of Moroccan Caralluma europaea Extract and Its Bioactive Compound Classes

Background

Caralluma europaea (C. europaea) is a medicinal plant used in Moroccan popular medicine. Objective of the Study. The present work was aimed at identifying the chemical composition and the antioxidant and antiproliferative activities of hydroethanolic and bioactive compound classes of C. europaea) is a medicinal plant used in Moroccan popular medicine. Materials and Methods. The chemical composition was analyzed using HPLC. The antioxidant power was determined using both DPPH and FRAP assays. The antiproliferative activity was effectuated against cancerous cells using WST-1.

Results

The chemical analysis showed the presence of bioactive constituents such as quercetin, myricetin, and hesperetin. The polyphenol and flavonoid contents were estimated at 51.42 mg GA/g and 20.06 mg EQ/g, respectively. The EC₅₀ values of FRAP assay of hydroethanolic, flavonoid, saponin, and mucilage extracts were 5.196 mg/ml, 4.537 mg/ml, 3.05 mg/ml, and 6.02 mg/ml, respectively. The obtained IC₅₀ values with the DPPH test were 1.628 mg/ml, 1.05 mg/ml, 1.94 mg/ml, and 9.674 mg/ml, respectively. Regarding MDA-MB-231, saponins were highly effective even with the lowest concentration (15.62 μg/ml). The flavonoids decreased the cell viability with IC₅₀ values of 43.62 ± 0.06 μg/ml). The flavonoids decreased the cell viability with IC₅₀ values of 43.62 ± 0.06 μg/ml). The flavonoids decreased the cell viability with IC₅₀ values of 43.62 ± 0.06 

Conclusion

The present results suggest that C. europaea) is a medicinal plant used in Moroccan popular medicine.

Gypsophila saponins enhance the cytotoxicity of etoposide in HD-MY-Z lymphoma cells

Glucuronide Oleanane-type Triterpenoid Carboxylic Acid 3,28-Bidesmosides (GOTCAB) are accumulated in Gypsophila L. roots. In the study we aimed at investigating the possible synergistic effects of Gypsophila trichotoma GOTCABs and cytostatic etoposide towards the Hodgkin lymphoma cell line HD-MY-Z. The combination effects with etoposide were evaluated using the symbolic mathematical software MAPLE. Liquid chromatography-mass spectrometry allowed the identification or tentative assignment of 28 core GOTCAB structures together with 6 monodesmosides in the root extract. Tested gypsogenin-based saponins possessed C-28 ester-bonded chain substituted with acetyl, cis/trans methoxycinnamoyl and both acetyl and sulfate groups. No cytotoxic effect was observed up to 20 μg/mL on normal mice fibroblasts (CCL-1 cell line) and lymphoma cells. Etoposide alone exerted IC₅₀ 93 μg/mL. In the presence of acetylated saponins (20 μg/mL), a strong synergism (Fa = 0.8, CI = 0.1) was observed with IC₅₀ 11 μg/mL. The combination induced apoptosis witnessed by caspase activation, elevated levels of cytosolic mono- and oligonucleosomes, and nuclear fragmentation together with discernible increase in ROS generation. The results emphasize the arabinose in the C-3 chain and acetylation pattern of the C-28 chain of the saponins as important structural features for cytotoxicity enhancing activity. Triterpenoid saponins are a valuable tool to improve the efficacy of cytostatics.

Multifunctional Silicon-Carbon Nanohybrids Simultaneously Featuring Bright Fluorescence, High Antibacterial and Wound Healing Activity

In this work, a class of multifunctional silicon-carbon nanohybrids (designated as SiCNs), which simultaneously possess aqueous dispersibility, bright fluorescence (photoluminescence quantum yield [PLQY]: ≈28%), as well as high antibacterial and wound healing activity, is presented. Taking advantage of these unique merits, cell distribution and pharmacological behavior of the SiCNs is first investigated through tracking their strong and stable fluorescence. The high bacteria inhibition ability (≈82.9% killing rate toward S. aureus) and hemostatic effects (shorten the bleeding time from ≈60 to ≈15 s) of the resultant SiCNs are then demonstrated. Moreover, the wound closure promotion activity (10% lead in wound contraction) is systematically demonstrated in vivo, which is especially suitable for wound healing applications. The results suggest the SiCNs as a new kind of high-performance multifunctional nanoagents suitable for various biological and biomedical utilizations.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

In vitro ovicidal and larvicidal activities of some saponins and flavonoids against parasitic nematodes of goats

This study assessed the anthelmintic activity of plant-derived compounds against gastrointestinal nematodes of goats using the egg hatch and larval motility assays. The compounds tested were saponins (digitonin and aescin) and their respective sapogenins (aglycones), hecogenin acetate and flavonoids (catechin, hesperidin, isocordoin and a mixture of isocordoin and cordoin). Additionally, cytotoxicity of active substances was analysed on Vero cell through 3-4,5-dimethylthiazol-2-yl,2,5diphenyltetrazolium bromide (MTT) and propidium iodide (PI) tests. Significant reduction on the egg hatching (P 90%). Nevertheless, higher cytotoxicity was observed in the MTT assay, with IC50 of 0.20 mg mL-1 (aescin) and 0.0074 mg mL-1 (digitonin). Aescin and digitonin have a pronounced in vitro anthelmintic effect and the glycone portion of these saponins plays an important role in this activity.

Selective Profiling of Saponins from Gypsophila trichotoma Wend. by HILIC Separation and HRMS Detection

INTRODUCTION

Roots of Gypsophila trichotoma Wend. (Caryophyllaceae) are rich sources of glucuronide oleanane-type triterpenoid carboxylic acid 3,28-O-bidesmosides (GOTCABs). These saponins have been reported to possess synergistic cytotoxicity in combination with type I ribosome-inactivating protein saporin.

OBJECTIVE

To develop ultra high-performance liquid chromatography - electrospray ionisation/high resolution mass spectrometry (UHPLC-ESI/HRMS) acquisition strategy for the recognition of Gypsophila GOTCAB saponins.

METHODOLOGY

A highly-selective hydrophilic interaction UHPLC method (Si-HILIC UHPLC) was developed for the separation of GOTCAB saponins from the methanol-aqueous root extract of G. trichotoma (GTR). UHPLC was coupled to an Orbitrap mass spectrometer equipped with heated electrospray ionisation (HESI) probe. ESI-HRMS and tandem mass spectrometry (MS/MS) data of the separated compounds was used for saponins structure assignment.

RESULTS

Based on the conformity of the fragmentation of 11 previously identified GTR saponins, 21 GOTCAB forming between two and four isobaric and positional isomers are identified with proposals for their structures. Tables with assignment of characteristic fragment ions and more than 10 newly identified saponins in GTR were described. Fragmentation rules for tentative identification of three major types of saponins from GTR were summarised and possible fragmentation pathways were proposed. Type I and II consisted of acylated and sulphated GOTCABs, respectively, while type III included acylated and sulphated saponins. The type II sulphated GOTCAB saponins were all previously not described.

CONCLUSIONS

The study demonstrates the potential of the coupling of highly-selective (Si)-HILIC UHPLC with HRMS and MS/MS detection for analysis and identification of triterpenoid saponins. Copyright © 2017 John Wiley & Sons, Ltd.

The Use of Plant-Derived Ribosome Inactivating Proteins in Immunotoxin Development: Past, Present and Future Generations

Ribosome inactivating proteins (RIPs) form a class of toxins that was identified over a century ago. They continue to fascinate scientists and the public due to their very high activity and long-term stability which might find useful applications in the therapeutic killing of unwanted cells but can also be used in acts of terror. We will focus our review on the canonical plant-derived RIPs which display ribosomal RNA N-glycosidase activity and irreversibly inhibit protein synthesis by cleaving the 28S ribosomal RNA of the large 60S subunit of eukaryotic ribosomes. We will place particular emphasis on therapeutic applications and the generation of immunotoxins by coupling antibodies to RIPs in an attempt to target specific cells. Several generations of immunotoxins have been developed and we will review their optimisation as well as their use and limitations in pre-clinical and clinical trials. Finally, we endeavour to provide a perspective on potential future developments for the therapeutic use of immunotoxins.

Glycosylated Triterpenoids as Endosomal Escape Enhancers in Targeted Tumor Therapies

Protein-based targeted toxins play an increasingly important role in targeted tumor therapies. In spite of their high intrinsic toxicity, their efficacy in animal models is low. A major reason for this is the limited entry of the toxin into the cytosol of the target cell, which is required to mediate the fatal effect. Target receptor bound and internalized toxins are mostly either recycled back to the cell surface or lysosomally degraded. This might explain why no antibody-targeted protein toxin has been approved for tumor therapeutic applications by the authorities to date although more than 500 targeted toxins have been developed within the last decades. To overcome the problem of insufficient endosomal escape, a number of strategies that make use of diverse chemicals, cell-penetrating or fusogenic peptides, and light-induced techniques were designed to weaken the membrane integrity of endosomes. This review focuses on glycosylated triterpenoids as endosomal escape enhancers and throws light on their structure, the mechanism of action, and on their efficacy in cell culture and animal models. Obstacles, challenges, opportunities, and future prospects are discussed.

Cytotoxic activities of naturally occurring oleanane-, ursane-, and lupane-type triterpenes on HepG2 and AGS cells

Background:

It is well known that the naturally occurring modified triterpenes in plants have a wide diversity of chemical structures and biological functions. The lupane-, oleanane-, and ursane-type triterpenes are the three major members of natural triterpenes with a wide range of biological properties. A systematic approach is necessary to review their structures and biological activities according to the backbones and the different substituents.

Objective:

Thirty lupane-(L1-7), oleanane-(O1-14), and ursane-type (U1-9) triterpenes with structural diversity were examined to evaluate their cytotoxic activities against two cancer cell lines, human hepatocellular carcinoma (HepG2) and AGS cells.

Materials and Methods:

They were isolated from Hedera helix, Juglans sinensis, and Pulsatilla koreana using a series of column chromatography methods and were treated to evaluate their cytotoxic activities against HepG2 and AGS human gastric adenocarcinoma cell. Further, two triterpenes showing the most potent activities were subjected to the apoptotic screening assay using flow cytometry.

Results:

The polar groups, such as an oxo group at C-1, a free hydroxyl at C-2, C-3, or C-23, and a carboxylic moiety at C-28, as well as the type of backbone, explicitly increased the cytotoxic activity on two cancer cells. O5 and U5 showed significantly the potent cytotoxic activity in comparison to other glycosidic triterpenes. In annexin-V/propidium iodide (PI) staining assay, the percentage of late apoptosis (annexin-V+/PI+) 12 and 24 h after treatment with O5 and U5 at 25 μM increased from 14.5% to 93.1% and from 46.4% to 49.1%, respectively, in AGS cells. The cytotoxicity induced by O5 showed a significant difference compared to U5 for 12 and 24 h.

Conclusion:

In the study, we can suggest the potent moieties which influence their cytotoxic activities against two cancer cells. The polar groups at C-1, C-2, C-3, C-23, and C-28 and the linkage of sugar moieties influenced the different cytotoxic activities.

SUMMARY

Thirty naturally occurring oleanane-, ursane-, and lupane-type triterpenes were isolated from Hedera helix, Juglans sinensis, and Pulsatilla koreana

An oxo, a free hydroxyl, a carboxylic moiety, and the types of aglycone influenced the cell cytotoxicity

Corosolic acid and α-hederin showed the most potent cytotoxicity via apoptosis.

Effects of Saponins on Lipid Metabolism: A Review of Potential Health Benefits in the Treatment of Obesity

Obesity is one of the greatest public health problems. This complex condition has reached epidemic proportions in many parts of the world, and it constitutes a risk factor for several chronic disorders, such as hypertension, cardiovascular diseases and type 2 diabetes. In the last few decades, several studies dealt with the potential effects of natural products as new safe and effective tools for body weight control. Saponins are naturally-occurring surface-active glycosides, mainly produced by plants, whose structure consists of a sugar moiety linked to a hydrophobic aglycone (a steroid or a triterpene). Many pharmacological properties have been reported for these compounds, such as anti-inflammatory, immunostimulant, hypocholesterolemic, hypoglycemic, antifungal and cytotoxic activities. The aim of this review is to provide an overview of recent studies about the anti-obesity therapeutic potential of saponins isolated from medicinal plants. Results on the in vitro and in vivo activity of this class of phytochemicals are here presented and discussed. The most interesting findings about their possible mechanism of action and their potential health benefits in the treatment of obesity are reported, as well.

Augmenting the Efficacy of Immunotoxins and Other Targeted Protein Toxins by Endosomal Escape Enhancers

The toxic moiety of almost all protein-based targeted toxins must enter the cytosol of the target cell to mediate its fatal effect. Although more than 500 targeted toxins have been investigated in the past decades, no antibody-targeted protein toxin has been approved for tumor therapeutic applications by the authorities to date. Missing efficacy can be attributed in many cases to insufficient endosomal escape and therefore subsequent lysosomal degradation of the endocytosed toxins. To overcome this drawback, many strategies have been described to weaken the membrane integrity of endosomes. This comprises the use of lysosomotropic amines, carboxylic ionophores, calcium channel antagonists, various cell-penetrating peptides of viral, bacterial, plant, animal, human and synthetic origin, other organic molecules and light-induced techniques. Although the efficacy of the targeted toxins was typically augmented in cell culture hundred or thousand fold, in exceptional cases more than million fold, the combination of several substances harbors new problems including additional side effects, loss of target specificity, difficulties to determine the therapeutic window and cell type-dependent variations. This review critically scrutinizes the chances and challenges of endosomal escape enhancers and their potential role in future developments.

Killing cancer with platycodin D through multiple mechanisms

Cancer is a multi-faceted disease comprised of a combination of genetic, epigenetic, metabolic and signalling aberrations which severely disrupt the normal homoeostasis of cell growth and death. Rational developments of highly selective drugs which specifically block only one of the signalling pathways have been associated with limited therapeutic success. Multi-targeted prevention of cancer has emerged as a new paradigm for effective anti-cancer treatment. Platycodin D, a triterpenoid saponin, is one the major active components of the roots of Platycodon grandiflorum and possesses multiple biological and pharmacological properties including, anti-nociceptive, anti-atherosclerosis, antiviral, anti-inflammatory, anti-obesity, immunoregulatory, hepatoprotective and anti-tumour activities. Recently, the anti-cancer activity of platycodin D has been extensively studied. The purpose of this review was to give our perspectives on the current status of platycodin D and discuss its anti-cancer activity and molecular mechanisms which may help the further design and conduct of pre-clinical and clinical trials to develop it successfully into a potential lead drug for oncological therapy. Platycodin D has been shown to fight cancer by inducing apoptosis, cell cycle arrest, and autophagy and inhibiting angiogenesis, invasion and metastasis by targeting multiple signalling pathways which are frequently deregulated in cancers suggesting that this multi-target activity rather than a single effect may play an important role in developing platycodin D into potential anti-cancer drug.

Membrane Disintegration Caused by the Steroid Saponin Digitonin Is Related to the Presence of Cholesterol

In the present investigation we studied the molecular mechanisms of the monodesmosidic saponin digitonin on natural and artificial membranes. We measured the hemolytic activity of digitonin on red blood cells (RBCs). Also different lipid membrane models (large unilamellar vesicles, LUVs, and giant unilamellar vesicles, GUVs) in the presence and absence of cholesterol were employed. The stability and permeability of the different vesicle systems were studied by using calcein release assay, GUVs membrane permeability assay using confocal microscopy (CM) and fluorescence correlation spectroscopy (FCS) and vesicle size measurement by dynamic light scattering (DLS). The results support the essential role of cholesterol in explaining how digitonin can disintegrate biological and artificial membranes. Digitonin induces membrane permeability or causes membrane rupturing only in the presence of cholesterol in an all-or-none mechanism. This effect depends on the concentrations of both digitonin and cholesterol. At low concentrations, digitonin induces membrane permeability while keeping the membrane intact. When digitonin is combined with other drugs, a synergistic potentiation can be observed because it facilitates their uptake.

Expression patterns, molecular markers and genetic diversity of insect-susceptible and resistant Barbarea genotypes by comparative transcriptome analysis

BACKGROUND

Barbarea vulgaris contains two genotypes: the glabrous type (G-type), which confers resistance to the diamondback moth (DBM) and other insect pests, and the pubescent type (P-type), which is susceptible to the DBM. Herein, the transcriptomes of P-type B. vulgaris before and after DBM infestation were subjected to Illumina (Solexa) pyrosequencing and comparative analysis.

RESULTS

5.0 gigabase pairs of clean nucleotides were generated. Non-redundant unigenes (33,721) were assembled and 94.1 % of them were annotated. Compared with our previous G-type transcriptome, the expression patterns of many insect responsive genes, including those related to secondary metabolism, phytohormones and transcription factors, which were significantly induced by DBM in G-type plants, were less sensitive to DBM infestation in P-type plants. The genes of the triterpenoid saponin pathway were identified in both G- and P-type plants. The upstream genes of the pathway showed similar expression patterns between the two genotypes. However, gene expression for two downstream enzymes, the glucosyl transferase (UGT73C11) and an oxidosqualene cyclase (OSC), were significantly upregulated in the P-type compared with the G-type plant. The homologous genes from P- and G-type plants were detected by BLAST unigenes with a cutoff level E-value < e(-10). 12,980 gene families containing 26,793 P-type and 36,944 G-type unigenes were shared by the two types of B. vulgaris. 38,397 single nucleotide polymorphisms (SNPs) were found in 9,452 orthologous genes between the P- and G-type plants. We also detected 5,105 simple sequence repeats (SSRs) in the B. vulgaris transcriptome, comprising mono-nucleotide-repeats (2,477; 48.5 %) and triple-nucleotide-repeats (1,590; 31.1 %). Of these, 1,657 SSRs displayed polymorphisms between the P- and G-type. Consequently, 913 SSR primer pairs were designed with a resolution of more than two nucleotides. We randomly chose 30 SSRs to detect the genetic diversity of 32 Barbarea germplasms. The distance tree showed that these accessions were clearly divided into groups, with the G-type grouping with available Western and Central European B. vulgaris accessions in contrast to the P-type accession, B. stricta and B. verna.

CONCLUSIONS

These data represent useful information for pest-resistance gene mining and for the investigation of the molecular basis of plant-pest interactions.

Pfaffosidic Fraction from Hebanthe paniculata Induces Cell Cycle Arrest and Caspase-3-Induced Apoptosis in HepG2 Cells

Hebanthe paniculata roots (formerly Pfaffia paniculata and popularly known as Brazilian ginseng) show antineoplastic, chemopreventive, and antiproliferative properties. Functional properties of these roots and their extracts are usually attributed to the pfaffosidic fraction, which is composed mainly by pfaffosides A–F. However, the therapeutic potential of this fraction in cancer cells is not yet entirely understood. This study aimed to analyze the antitumoral effects of the purified pfaffosidic fraction or saponinic fraction on the human hepatocellular carcinoma HepG2 cell line. Cellular viability, proliferation, and apoptosis were evaluated, respectively, by MTT assay, BrdU incorporation, activated caspase-3 immunocytochemistry, and DNA fragmentation assay. Cell cycle was analyzed by flow cytometry and the cell cycle-related proteins were analyzed by quantitative PCR and Western blot. The cells exposed to pfaffosidic fraction had reduced viability and cellular growth, induced G2/M at 48 h or S at 72 h arrest, and increased sub-G1 cell population via cyclin E downregulation, p27^KIP1 overexpression, and caspase-3-induced apoptosis, without affecting the DNA integrity. Antitumoral effects of pfaffosidic fraction from H. paniculata in HepG2 cells originated by multimechanisms of action might be associated with cell cycle arrest in the S phase, by CDK2 and cyclin E downregulation and p27^KIP1 overexpression, besides induction of apoptosis through caspase-3 activation.

Impact of two different saponins on the organization of model lipid membranes

Saponins, naturally occurring plant compounds are known for their biological and pharmacological activity. This activity is strongly related to the amphiphilic character of saponins that allows them to aggregate in aqueous solution and interact with membrane components. In this work, Langmuir monolayer techniques combined with polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and Brewster angle microscopy were used to study the interaction of selected saponins with lipid model membranes. Two structurally different saponins were used: digitonin and a commercial Merck Saponin. Membranes of different composition, namely, cholesterol, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine or 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) were formed at the air/water and air/saponin solution interfaces. The saponin-lipid interaction was characterized by changes in surface pressure, surface potential, surface morphology and PM-IRRAS signal. Both saponins interact with model membranes and change the physical state of membranes by perturbing the lipid acyl chain orientation. The changes in membrane fluidity were more significant upon the interaction with Merck Saponin. A higher affinity of saponins for cholesterol than phosphatidylglycerols was observed. Moreover, our results indicate that digitonin interacts strongly with cholesterol and solubilize the cholesterol monolayer at higher surface pressures. It was shown, that digitonin easily penetrate to the cholesterol monolayer and forms a hydrogen bond with the hydroxyl groups. These findings might be useful in further understanding of the saponin action at the membrane interface and of the mechanism of membrane lysis.

Cytotoxicity of the saponin TTB2 on Ewing sarcoma cells

The steroidal saponin TTB2 can be isolated from the n-BuOH extracts of Trillium tschonoskii Maxim. The aim of the present study was to observe whether this saponin exerted any cytotoxic effects on malignant sarcoma cells, and to further investigate the possible underlying molecular mechanisms. The cell viability, cell cycle arrest and phosphorylation of certain important signal molecules in the sarcoma cell line were investigated. It was found that TTB2 inhibited the growth of the Ewing sarcoma cell line and arrested cells in the G₂/M and S phases of the cell cycle in a dose- and time-dependent manner. Furthermore, the phosphorylation of extracellular signal-regulated kinase was inhibited by TTB2. In conclusion, the results showed that the saponin TTB2 isolated from T. tschonoskii Maxim exerts anticancer effects and may be a potential candidate for the development of anticancer drugs for use in the treatment of cancer.

Photochemical activation of drugs for the treatment of therapy-resistant cancers

Resistance to chemotherapy, molecular targeted therapy as well as radiation therapy is a major obstacle for cancer treatment.

Cytotoxic effects of four Caryophyllaceae species extracts on macrophage cell lines

CONTEXT

Saponins have been reported to possess antitumor properties, to inhibit angiogenesis and to induce tumor apoptosis.

OBJECTIVE

To test the possible cytotoxic effect of crude extracts from four Caryophyllaceae species including Gypsophila paniculata L., Gypsophila trichotoma Wend., Saponaria officinalis L., and Dianthus sylvestris Wulffen on cultured monocyte/macrophage cell lines.

MATERIALS AND METHODS

After acid hydrolysis of the methanol-aqueous extracts, two representative prosaponins of the Caryophyllaceae, gypsogenin 3-O-glucuronide and quillaic acid 3-O-glucuronide were purified using solid-phase extraction (SPE), then identified by ultra-performance liquid chromatography-electrospray/mass spectrometry (UPLC-ESI/MS). Cytotoxic activity of the crude extracts at concentrations ranging from 0.1 to 200 µg/ml was evaluated on rat alveolar macrophage NR8383 and human monocytic THP-1 cell lines. Apoptosis was determined by measuring caspase-3 activity.

RESULTS

Quantitative analysis by reversed-phase high-performance liquid chromatography (RP-HPLC) revealed a high content of gypsogenin 3-O-glucuronide in Gypsophila species roots (0.52-1.13% dry weight). At a concentration ≥10 µg/ml of crude extracts, a significant reduction of NR8383 and THP-1 cell lines viability was evidenced using the Trypan blue exclusion test. D. sylvestris extract exhibited the highest toxicity against THP-1 cells. Caspase-3 activation was evidenced after 4 and 24 h incubation of macrophages with 100 µg/ml of S. officinalis and G. trichotoma extracts, indicating apoptosis induction.

DISCUSSION AND CONCLUSION

Crude extracts from the assayed species revealed cytotoxic effects toward macrophage cell lines. In Gypsophila species, gypsogenin 3-O-glucuronide derivatives could be responsible for the observed cytotoxicity. Therefore, crude extract of Caryophyllaceae is worth investigating for the potential development of agents against cancer cells.

Oldhamianoside II, a new triterpenoid saponin, prevents tumor growth via inducing cell apoptosis and inhibiting angiogenesis

Oldhamianoside II is a new triterpenoid saponin that was isolated from the roots of Gypsophila oldhamiana. The present study aims to investigate the potential inhibitory activity of oldhamianoside II on tumor growth using an S180 tumor implantation mouse model. Oldhamianoside II at doses of 5.0 and 10.0 mg/kg was given with intraperitoneal injection for 10 days following subcutaneous inoculation of S180 tumor cells in anterior flank of mice. The tumor growth, the cell apoptosis, the microvessel density (MVD) in S180 tumors, the tumor cell viability, the tubular formation in vitro, and migration of tumor cells were examined. The expression of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and cyclooxygenase-2 (COX-2) was determined to analyze the associated mechanisms. The results showed that oldhamianoside II potently inhibited tumor cell viability in vitro. In addition, oldhamianoside II delayed tumor growth in anterior flank, induced S180 cell apoptosis, and reduced the MVD. Oldhamianoside II was also demonstrated to decrease the number of tubular structure and vessel formation in HUVEC cultures and chick embryo chorioallantoic membrane (CAM) model, respectively. Further study indicated that oldhamianoside II reduced the expression of VEGF, bFGF, and COX-2 in tumor sections. Moreover, oldhamianoside II inhibited the activity of migration and penetration to Matrigel of SGC7901 tumor cells in scratch wound and transwell chamber. In conclusion, our work defines oldhamianoside II, a new triterpenoid saponin, as a novel compound that can effectively inhibit S180 tumor growth, induce tumor cell apoptosis, prevent tumor angiogenesis, and inhibit cancer cell migration, suggesting that oldhamianoside II is a potential drug candidate for the treatment of cancer and for the prevention of metastasis.

Triterpene saponosides from Lysimachia ciliata differentially attenuate invasive potential of prostate cancer cells

Neither androgen ablation nor chemotherapeutic agents are effective in reducing the risk of prostate cancer progression. On the other hand, multifaceted effects of phytochemicals, such as triterpene saponins, on cancer cells have been suggested. A promising safety and tolerability profile indicate their possible application in the treatment of advanced prostate cancers. We analyzed the specificity, selectivity and versatility of desglucoanagalloside B effects on human prostate cancer cells derived from prostate cancer metastases to brain (DU-145 cells) and bone (PC-3 cells). Prominent growth arrest and apoptotic response of both cell types was observed in the presence of sub-micromolar desglucoanagalloside B concentrations. This was accompanied by cytochrome c release and caspase 3/7 activation. A relatively low cytostatic and pro-apoptotic response of cancer cells to a desglucoanagalloside B analog, anagallosaponin IV, illustrated the specificity of the effects of desglucoanagalloside B, whereas the low sensitivity of normal prostate PNT2 cells to desglucoanagalloside B showed the selectivity of its action. Inhibition of cancer cell motility was observed in the presence of both saponins, however only desglucoanagalloside B attenuated cancer cell invasive potential, predominantly through an effect on cell elastic properties. These data demonstrate the versatility of its effects on prostate cancer cells. In contrast to PNT2 cells, cancer cells tested in this study were relatively resistant to mitoxantrone. The multifaceted action of desglucoanagalloside B on basic cellular traits, crucial for prostate cancer progression, opens perspectives for elaboration of combined palliative therapies and new prostate cancer prophylaxis regimens.

Transcriptome analysis of Barbarea vulgaris infested with diamondback moth (Plutella xylostella) larvae

Background

The diamondback moth (DBM, Plutella xylostella) is a crucifer-specific pest that causes significant crop losses worldwide. Barbarea vulgaris (Brassicaceae) can resist DBM and other herbivorous insects by producing feeding-deterrent triterpenoid saponins. Plant breeders have long aimed to transfer this insect resistance to other crops. However, a lack of knowledge on the biosynthetic pathways and regulatory networks of these insecticidal saponins has hindered their practical application. A pyrosequencing-based transcriptome analysis of B. vulgaris during DBM larval feeding was performed to identify genes and gene networks responsible for saponin biosynthesis and its regulation at the genome level.

Principal Findings

Approximately 1.22, 1.19, 1.16, 1.23, 1.16, 1.20, and 2.39 giga base pairs of clean nucleotides were generated from B. vulgaris transcriptomes sampled 1, 4, 8, 12, 24, and 48 h after onset of P. xylostella feeding and from non-inoculated controls, respectively. De novo assembly using all data of the seven transcriptomes generated 39,531 unigenes. A total of 37,780 (95.57%) unigenes were annotated, 14,399 of which were assigned to one or more gene ontology terms and 19,620 of which were assigned to 126 known pathways. Expression profiles revealed 2,016–4,685 up-regulated and 557–5188 down-regulated transcripts. Secondary metabolic pathways, such as those of terpenoids, glucosinolates, and phenylpropanoids, and its related regulators were elevated. Candidate genes for the triterpene saponin pathway were found in the transcriptome. Orthological analysis of the transcriptome with four other crucifer transcriptomes identified 592 B. vulgaris-specific gene families with a P-value cutoff of 1e⁻⁵.

Conclusion

This study presents the first comprehensive transcriptome analysis of B. vulgaris subjected to a series of DBM feedings. The biosynthetic and regulatory pathways of triterpenoid saponins and other DBM deterrent metabolites in this plant were classified. The results of this study will provide useful data for future investigations on pest-resistance phytochemistry and plant breeding.

Open-chain steroidal glycosides, a diverse class of plant saponins

Saponins are an important class of plant natural products that consist of a triterpenoid or steroidal skeleton that is glycosylated by varying numbers of sugar units attached at different positions. Steroidal saponins are usually divided into two broad structural classes, namely spirostanol and furostanol saponins. A third, previously unrecognized structural class of plant saponins, the open-chain steroidal saponins, is introduced in this review; these possess an acyclic sidechain in place of the heterocyclic ring/s present in spirostanols and furostanols. Open-chain steroidal saponins are numerous and structurally diverse, with over 150 unique representatives reported from terrestrial plants. Despite this, they have to date been largely overlooked in reviews of plant natural products. This review catalogs the structural diversity of open-chain steroidal saponins isolated from terrestrial plants and discusses aspects of their structure elucidation, biological activities, biosynthesis, and distribution in the plant kingdom. It is intended that this review will provide a point of reference for those working with open-chain steroidal saponins and result in their recognition and inclusion in future reviews of plant saponins.

Targeted tumor therapy by epidermal growth factor appended toxin and purified saponin: an evaluation of toxicity and therapeutic potential in syngeneic tumor bearing mice

Targeted toxin-based therapeutics are hindered by poor intracellular uptake, limited stability and non-specific immune stimulation. To address these problems, ligand-targeted toxins in combination with low dose saponin mixtures have been adapted and tested in vivo in the past, however, undefined saponin raw mixtures are not suitable for use in clinical development. In the present work we therefore used a targeted toxin (Sap3-EGF, i.e. saporin fused to epidermal growth factor) in combination with a structurally defined isolated saponin m/z 1861 (SO-1861). In vitro evaluation confirmed a 6900-fold enhancement in the cytotoxic efficacy of Sap3-EGF against TSA-EGFR target cells. The required dose of the targeted toxin was appreciably reduced and there was a highly synergistic effect observed. An ex vivo hemolysis assay showed no or very less hemolysis up to 10 μg/mL of SO-1861. In the acute toxicity studies SO-1861 was found to be non-toxic up to a dose of 100 μg/treatment. The enzymes aspartate aminotransferase, alanine aminotransferase, and glutamate dehydrogenase did not show any statistically significant liver damage, which was further confirmed by histological examination. Additionally, creatinine was also similar to the control group thus ruling out damage to kidney. In vivo studies in a syngeneic BALB/c tumor model characterized by EGFR overexpression were done by applying 30 μg SO-1861 and 0.1 μg Sap3-EGF per treatment. A more than 90% reduction (p < 0.05) in the average tumor volume was observed by this combined therapy.

Real time monitoring of the cell viability during treatment with tumor-targeted toxins and saponins using impedance measurement

This work describes the application of an impedance-based measurement for the real time evaluation of targeted tumor therapies in cell culture (HeLa cells). We used a treatment procedure that is well established in cells and mice. Therein, tumor cells are treated with a combination of an epidermal growth factor-based targeted toxin named SE and particular plant glycosides called saponins. In the present study HeLa cells were seeded in different numbers onto interdigitated electrode structures integrated into the bottom of a 96 well plate. The cells were treated with SE in the presence and absence of the saponin SpnS-1 (isolated from Saponaria officinalis roots). The impedance was directly correlated with the viability of the cells. As expected from known end point measurements, a concentration dependent enhancement of toxicity was observed; however, with the impedance measurement we were for the first time able to trace the temporal changes of cell death during the combination treatment. This substantially added to the understanding of initial cellular mechanisms in the augmentation of the toxicity of targeted toxins by saponins and indicated the superiority of real time monitoring over end point assays. The method is less labor intensive and label-free with ease of monitoring the effects at each time point.

The endocytic uptake pathways of targeted toxins are influenced by synergistically acting Gypsophila saponins

The expression of the epidermal growth factor (EGF) receptor is upregulated in many human tumors. We developed the targeted toxin SE, consisting of the plant toxin saporin-3 and human EGF. The cytotoxic effect of SE drastically increases in a synergistic manner by a combined treatment with Saponinum album (Spn), a saponin composite from Gypsophila paniculata L. Here we analyzed which endocytic pathways are involved in the uptake of SE and which are mandatory for the Spn-mediated enhancement. We treated HER14 cells (NIH-3T3 cells transfected with human EGF receptor) with either chlorpromazine, dynasore, latrunculin A, chloroquine, bafilomycin A1 or filipin and analyzed the effect on the cytotoxicity of SE alone or in combination with Spn. We demonstrated that SE in combination with Spn enters cells via clathrin- and actin-dependent pathways and the acidification of the endosomes after endocytosis is relevant for the cytotoxicity of SE. Notably, our data suggest that SE without Spn follows a different endocytic uptake pathway. SE cytotoxicity is independent of blocking of clathrin or actin, and the decrease in endosomal pH is irrelevant for SE cytotoxicity. Furthermore, Spn has no influence on the retrograde transport. This work is important for the better understanding of the underlying mechanism of Spn-enhanced cytotoxicity and helps to describe the role of Spn better.

Synergistic interactions of saponins and monoterpenes in HeLa cells, Cos7 cells and in erythrocytes

In phytomedicine complex extracts consisting of phenolics, monoterpenes or saponins are traditionally used. It is often impossible to attribute the biological activity of an extract to one or few compounds. As an explanation of the superior activity of extracts, a synergistic effect of combinations of active compounds has been suggested. Since lipophilic monoterpenes or saponins targeting the biomembrane usually accompany polar polyphenols in phytomedical preparations, we decided to investigate their effect as single substances and in combination to gain further insight into potential synergistic effects of herbal medicine. Combinations of the monoterpenes α-pinene, thymol and menthol with the monodesmosidic saponins digitonin, aescin, glycyrrhizic acid and Quillaja saponin demonstrated strong synergistic activity. The IC(50) of haemolysis was lowered by a factor of 10-100 from 316μg/ml to 2μg/ml for aescin, 157μg/ml to 11μg/ml for Quillaja saponins and 20μg/ml to 3μg/ml for digitonin when combined with thymol. A similar significant synergistic cytotoxicity occurred both in HeLa and Cos7 cells by combining the α-pinene, thymol and menthol with the saponins. The IC(50) of glycyrrhizic acid was lowered by a factor 100 from around 300μg/ml to around 1-10μg/ml and the IC(50) of aescin, digitonin and Quillaja saponins about the factor 10. Monoterpenes and monodesmosidic saponins have a common target, the biomembrane, which is present in all animal, fungal and bacterial cells. Disturbance of membrane fluidity and permeability is the mode of action. This activity is non-specific which makes it extremely difficult for bacteria and fungi to develop resistance. This explains the overall success of these molecules as defence chemicals in the plant kingdom. The synergistic effect of combinations of saponins with monoterpenes opens a complete new field of possible applications in medicine to overcome resistance in multidrug resistant microbial and human cell.

Triterpenoids

This review covers the isolation and structure determination of triterpenoids, including squalene derivatives, protostanes, lanostanes, holostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleananes, friedelanes, ursanes, hopanes, serratanes and saponins; 278 references are cited.

Ribosome-inactivating proteins: from plant defense to tumor attack

Ribosome-inactivating proteins (RIPs) are EC3.2.32.22 N-glycosidases that recognize a universally conserved stem-loop structure in 23S/25S/28S rRNA, depurinating a single adenine (A4324 in rat) and irreversibly blocking protein translation, leading finally to cell death of intoxicated mammalian cells. Ricin, the plant RIP prototype that comprises a catalytic A subunit linked to a galactose-binding lectin B subunit to allow cell surface binding and toxin entry in most mammalian cells, shows a potency in the picomolar range. The most promising way to exploit plant RIPs as weapons against cancer cells is either by designing molecules in which the toxic domains are linked to selective tumor targeting domains or directly delivered as suicide genes for cancer gene therapy. Here, we will provide a comprehensive picture of plant RIPs and discuss successful designs and features of chimeric molecules having therapeutic potential.

Saponins as cytotoxic agents: a review

Saponins are natural glycosides which possess a wide range of pharmacological properties including cytotoxic activity. In this review, the recent studies (2005-2009) concerning the cytotoxic activity of saponins have been summarized. The correlations between the structure and the cytotoxicity of both steroid and triterpenoid saponins have been described as well as the most common mechanisms of action.

American ginseng: potential structure-function relationship in cancer chemoprevention

Ginseng has a prominent position on the list of best-selling herbal products in the world, and its main active constituents are thought to be ginsenosides. Compared with the long history of use and widespread research on Asian ginseng, studies of American ginseng are relatively limited, especially regarding cancer chemoprevention. In recent studies of American ginseng, steaming or heating altered the ginsenoside profile and thereby increased anticancer effects. Yet the ginsenoside structures and their activities have not been systematically elucidated. In this commentary, we introduce the different ginsenosides in American ginseng, both the naturally occurring compounds and those resulting from steaming or biotransformation. We briefly review American ginseng's reported anticancer effects and their mechanisms of action, and explore the possible structural-function relationship with a focus on sugar molecules, hydroxyl groups and stereoselectivity in ginsenosides. Understanding these relationships may produce insights into chemical and pharmacological approaches for enhancing the chemopreventive effects of ginsenoside and for developing novel anticancer agents.

Synergistic and additive effects of epigallocatechin gallate and digitonin on Plasmodium sporozoite survival and motility

BACKGROUND

Most medicinal plants contain a mixture of bioactive compounds, including chemicals that interact with intracellular targets and others that can act as adjuvants to facilitate absorption of polar agents across cellular membranes. However, little is known about synergistic effects between such potential drug candidates and adjuvants. To probe for such effects, we tested the green tea compound epigallocatechin gallate (EGCG) and the membrane permeabilising digitonin on Plasmodium sporozoite motility and viability.

METHODOLOGY/PRINCIPAL FINDINGS

Green fluorescent P. berghei sporozoites were imaged using a recently developed visual screening methodology. Motility and viability parameters were automatically analyzed and IC50 values were calculated, and the synergism of drug and adjuvant was assessed by the fractional inhibitory concentration index. Validating our visual screening procedure, we showed that sporozoite motility and liver cell infection is inhibited by EGCG at nontoxic concentrations. Digitonin synergistically increases the cytotoxicity of EGCG on sporozoite survival, but shows an additive effect on sporozoite motility.

CONCLUSIONS/SIGNIFICANCE

We proved the feasibility of performing highly reliable visual screens for compounds against Plasmodium sporozoites. We thereby could show an advantage of administering mixtures of plant metabolites on inhibition of cell motility and survival. Although the effective concentration of both drugs is too high for use in malaria prophylaxis, the demonstration of a synergistic effect between two plant compounds could lead to new avenues in drug discovery.