Structural Effect on Adjuvanticity of Saponins

Enhancing Protective Antibodies against Opioids through Antigen Display on Virus-like Particles

Opioid use disorder (OUD) has become a public health crisis, with recent significant increases in the number of deaths due to overdose. Vaccination can provide an attractive complementary strategy to combat OUD. A key for high vaccine efficacy is the induction of high levels of antibodies specific to the drug of abuse. Herein, a powerful immunogenic carrier, virus-like particle mutant bacteriophage Qβ (mQβ), has been investigated as a carrier of a small molecule hapten 6-AmHap mimicking heroin. The mQβ-6-AmHap conjugate was able to induce significantly higher levels of IgG antibodies against 6-AmHap than mice immunized with the corresponding tetanus toxoid-6-AmHap conjugate in head-to-head comparison studies in multiple strains of mice. The IgG antibody responses were persistent with high anti-6-AmHap titers 600 days after being immunized with mQβ-6-AmHap. The antibodies induced exhibited strong binding toward multiple heroin/morphine derivatives that have the potential to be abused, while binding weakly to medications used for OUD treatment and pain relief. Furthermore, vaccination effectively reduced the impacts of morphine on mice in both ambulation and antinociception assays, highlighting the translational potential of the mQβ-6-AmHap conjugate to mitigate the harmful effects of drugs of abuse.

New insights into anti-diabetes effects and molecular mechanisms of dietary saponins

Diabetes mellitus (DM) is a long-term metabolic disorder that manifests as chronic hyperglycemia and impaired insulin, bringing a heavy load on the global health care system. Considering the inevitable side effects of conventional anti-diabetic drugs, saponins-rich natural products exert promising therapeutic properties to serve as safer and more cost-effective alternatives for DM management. Herein, this review systematically summarized the research progress on the anti-diabetic properties of dietary saponins and their underlying molecular mechanisms in the past 20 years. Dietary saponins possessed the multidirectional anti-diabetic capabilities by concurrent regulation of various signaling pathways, such as IRS-1/PI3K/Akt, AMPK, Nrf2/ARE, NF-κB-NLRP3, SREBP-1c, and PPARγ, in liver, pancreas, gut, and skeletal muscle. However, the industrialization and commercialization of dietary saponin-based drugs are confronted with a significant challenge due to the low bioavailability and lack of the standardization. Hence, in-depth evaluations in pharmacological profile, function-structure interaction, drug-signal pathway interrelation are essential for developing dietary saponins-based anti-diabetic treatments in the future.

Synthesis of immunostimulatory saponins: A sweet challenge for carbohydrate chemists

Saponins are a large family of natural glycosides showing a wide range of biological activities. Current research efforts on saponins as vaccine adjuvants have been mainly focused on the development of synthetic analogs. By mimicking the immunomodulatory saponins from Quillaja saponaria (QS), less complex and readily accessible analogs have been synthesized to improve the industrial applicability and efficacy of saponins as vaccine adjuvants. Through the exploration of several structural modifications on the skeleton of QS saponins, including changes in the sugar and aglycone compositions as well as in the nature and configuration of the glycosidic bonds, structure-activity relationship (SAR) studies developed by Pr. Gin in the early 2010s were taken as a starting point for the development of a new generation of immunomodulatory candidates. In this review, the recent synthetic strategies and SAR studies of mono- and bidesmosidic QS saponins are discussed. Original concepts of vaccination including self-adjuvanticity and the development of saponin-based glycoconjugates are described. The synthesis and semi-synthesis of saponin alternatives to QS, such as Momordica saponin and onjisaponin derivatives, are also discussed in this review.

Meeting vaccine formulation challenges in an emergency setting: Towards the development of accessible vaccines

Vaccination is considered one of the most successful strategies to prevent infectious diseases. In the event of a pandemic or epidemic, the rapid development and distribution of the vaccine to the population is essential to reduce mortality, morbidity and transmission. As seen during the COVID-19 pandemic, the production and distribution of vaccines has been challenging, in particular for resource-constrained settings, essentially slowing down the process of achieving global coverage. Pricing, storage, transportation and delivery requirements of several vaccines developed in high-income countries resulted in limited access for low-and-middle income countries (LMICs). The capacity to manufacture vaccines locally would greatly improve global vaccine access. In particular, for the development of classical subunit vaccines, the access to vaccine adjuvants is a pre-requisite for more equitable access to vaccines. Vaccine adjuvants are agents required to augment or potentiate, and possibly target the specific immune response to such type of vaccine antigens. Openly accessible or locally produced vaccine adjuvants may allow for faster immunization of the global population. For local research and development of adjuvanted vaccines to expand, knowledge on vaccine formulation is of paramount importance. In this review, we aim to discuss the optimal characteristics of a vaccine developed in an emergency setting by focusing on the importance of vaccine formulation, appropriate use of adjuvants and how this may help overcome barriers for vaccine development and production in LMICs, achieve improved vaccine regimens, delivery and storage requirements.

Structure-Activity Relationship Study of Momordica Saponin II Derivatives as Vaccine Adjuvants

VSA-2 is a recently developed semisynthetic saponin immunostimulant. It is prepared by incorporating a terminal-functionalized side chain to the branched trisaccharide domain at the C3 position of Momordica saponin II (MS II) isolated from the seeds of perennial Momordica cochinchinensis Spreng. Direct comparison of VSA-2 and the clinically proven saponin adjuvant QS-21 shows that VSA-2 is comparable to QS-21 in enhancing humoral and cellular immune responses. Structure-activity relationship studies show that structural changes in the side chain have a significant impact on saponins' adjuvant activity. However, with the VSA-2 molecular framework intact, the new VSA-2 analogues with various substitution(s) at the terminal benzyl group of the side chain retain the ability of potentiating antigen-specific humoral and cellular responses.

Natural saponin and cholesterol assembled nanostructures as the promising delivery method for saponin

The application of saponins has been restricted by problems such as hemolysis, low bioavailability, and poor solubility. So it is imperative to find a strategy to deliver saponins safely and efficiently. Here, through bottom-up technique, we design and prepare two saponin-cholesterol (Cho) nano-complex: dioscin (Dio, steroid saponin)-Cho nanofibers (NFs) and escin Ia (EIa, triterpene saponin)-Cho nanoparticles (NPs). It is found that the hydrophobic force and hydrogen bonding drive the two pairs of molecules to bind in different directions (the 3β-OH of Cho face the sugar chain of EIa and the 22α-O of Dio, respectively) and finally show spherical NPs (EIa-Cho) and fibrous NFs (Dio-Cho). The equimolar saponin-Cho complex, Dio NFs and EIa NPs, reveal potent cytotoxicities against mouse breast cancer cells (4T1) in vitro. In vivo results confirm the antitumor (4T1 mice model) efficacy of PEGylation Dio NFs (10 mg/kg, i.v.) with a tumor inhibition rate of 61%, meanwhile, it does not cause extreme irritation and pain as free Dio does to mice. Moreover, compared with the free drug, the prepared nano-complex can significantly reduce hemolysis and organ toxicity. Our research reduces the toxicity of saponins while retaining their antitumor activity, providing a new strategy for the delivery of saponins.

Future Directions for the Discovery of Natural Product-Derived Immunomodulating Drugs

Drug discovery from natural sources is going through a renaissance, having spent many decades in the shadow of synthetic molecule drug discovery, despite the fact that natural product-derived compounds occupy a much greater chemical space than those created through synthetic chemistry methods. With this new era comes new possibilities, not least the novel targets that have emerged in recent times and the development of state-of-the-art technologies that can be applied to drug discovery from natural sources. Although progress has been made with some immunomodulating drugs, there remains a pressing need for new agents that can be used to treat the wide variety of conditions that arise from disruption, or over-activation, of the immune system; natural products may therefore be key in filling this gap. Recognising that, at present, there is no authoritative article that details the current state-of-the-art of the immunomodulatory activity of natural products, this in-depth review has arisen from a joint effort between the International Union of Basic and Clinical Pharmacology (IUPHAR) Natural Products and Immunopharmacology, with contributions from a Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation number of world-leading researchers in the field of natural product drug discovery, to provide a "position statement" on what natural products has to offer in the search for new immunomodulatory argents. To this end, we provide a historical look at previous discoveries of naturally occurring immunomodulators, present a picture of the current status of the field and provide insight into the future opportunities and challenges for the discovery of new drugs to treat immune-related diseases.

Effects of Wild Yam Root (Dioscorea villosa) Extract on the Gene Expression Profile of Triple-negative Breast Cancer Cells

BACKGROUND/AIM

Wild yam extract [Dioscorea villosa, (WYE)] is consistently lethal at low IC₅₀s across diverse cancer-lines in vitro. Unlike traditional anti-cancer botanicals, WYE contains detergent saponins which reduce oil-water interfacial tensions causing disintegration of lipid membranes and causing cell lysis, creating an interfering variable. Here, we evaluate WYE at sub-lethal concentrations in MDA-MB-231 triple-negative breast cancer (TNBC) cells.

MATERIALS AND METHODS

Quantification of saponins, membrane potential, lytic death and sub-lethal WYE changes in whole transcriptomic (WT) mRNA, miRNAs and biological parameters were evaluated.

RESULTS

WYE caused 346 differentially expressed genes (DEGs) out of 48,226 transcripts tested; where up-regulated DEGS reflect immune stimulation, TNF signaling, COX2, cytokine release and cholesterol/steroid biosynthesis. Down-regulated DEGs reflect losses in cell division cycle (CDC), cyclins (CCN), cyclin-dependent kinases (CDKs), centromere proteins (CENP), kinesin family members (KIFs) and polo-like kinases (PLKs), which were in alignment with biological studies.

CONCLUSION

Sub-lethal concentrations of WYE appear to evoke pro-inflammatory, steroid biosynthetic and cytostatic effects in TNBC cells.

The isolation of water-soluble natural products - challenges, strategies and perspectives

Covering period: up to 2019Water-soluble natural products constitute a relevant group of secondary metabolites notably known for presenting potent biological activities. Examples are aminoglycosides, β-lactam antibiotics, saponins of both terrestrial and marine origin, and marine toxins. Although extensively investigated in the past, particularly during the golden age of antibiotics, hydrophilic fractions have been less scrutinized during the last few decades. This review addresses the possible reasons on why water-soluble metabolites are now under investigated and describes approaches and strategies for the isolation of these natural compounds. It presents examples of several classes of hydrosoluble natural products and how they have been isolated. Novel stationary phases and chromatography techniques are also reviewed, providing a perspective towards a renaissance in the investigation of water-soluble natural products.

Natural and Synthetic Saponins as Vaccine Adjuvants

Saponin adjuvants have been extensively studied for their use in veterinary and human vaccines. Among them, QS-21 stands out owing to its unique profile of immunostimulating activity, inducing a balanced Th1/Th2 immunity, which is valuable to a broad scope of applications in combating various microbial pathogens, cancers, and other diseases. It has recently been approved for use in human vaccines as a key component of combination adjuvants, e.g., AS01b in Shingrix^® for herpes zoster. Despite its usefulness in research and clinic, the cellular and molecular mechanisms of QS-21 and other saponin adjuvants are poorly understood. Extensive efforts have been devoted to studies for understanding the mechanisms of QS-21 in different formulations and in different combinations with other adjuvants, and to medicinal chemistry studies for gaining mechanistic insights and development of practical alternatives to QS-21 that can circumvent its inherent drawbacks. In this review, we briefly summarize the current understandings of the mechanism underlying QS-21’s adjuvanticity and the encouraging results from recent structure-activity-relationship (SAR) studies.

Biological and Pharmacological Effects of Synthetic Saponins

Saponins are amphiphilic molecules consisting of carbohydrate and either triterpenoid or steroid aglycone moieties and are noted for their multiple biological activities-Fungicidal, antimicrobial, antiviral, anti-inflammatory, anticancer, antioxidant and immunomodulatory effects have all been observed. Saponins from natural sources have long been used in herbal and traditional medicines; however, the isolation of complexed saponins from nature is difficult and laborious, due to the scarce amount and structure heterogeneity. Chemical synthesis is considered a powerful tool to expand the structural diversity of saponin, leading to the discovery of promising compounds. This review focuses on recent developments in the structure optimization and biological evaluation of synthetic triterpenoid and steroid saponin derivatives. By summarizing the structure-activity relationship (SAR) results, we hope to provide the direction for future development of saponin-based bioactive compounds.

Synthetic Investigation toward QS-21 Analogues

With glycosyl o-alkynylbenzotes as donors, a highly efficient protocol to construct the challenging glycosidic linkages at C3-OH of C23-oxo oleanane triterpenoids is disclosed, on the basis of which different strategies for the highly efficient synthesis of QS-21 analogues with the west-wing trisaccharide of QS-21 have been established.