Interaction of holothurian triterpene glycoside with biomembranes of mouse immune cells

Holothurian triterpene glycoside cucumarioside A2-2 induces macrophages activation and polarization in cancer immunotherapy

BACKGROUND

Despite intensive developments of adoptive T cell and NK cell therapies, the efficacy against solid tumors remains elusive. Our study demonstrates that macrophage-based cell therapy could be a potent therapeutic option against solid tumors.

METHODS

To this end, we determine the effect of a natural triterpene glycoside, cucumarioside A2-2 (CA2-2), on the polarization of mouse macrophages into the M1 phenotype, and explore the antitumor activity of the polarized macrophage. The polarization of CA2-2-pretreated macrophages was analyzed by flow cytometry and confocal imaging. The anti-cancer activity of CA2-2 macrophages was evaluated against 4T1 breast cancer cells and EAC cells in vitro and syngeneic mouse model in vivo.

RESULTS

Incubation of murine macrophages with CA2-2 led to polarization into the M1 phenotype, and the CA2-2-pretreated macrophages could selectively target and kill various types of cancer in vitro. Notably, loading near-infrared (NIR) fluorochrome-labeled nanoparticles, MnMEIO-mPEG-CyTE777, into macrophages substantiated that M1 macrophages can target and penetrate tumor tissues in vivo efficiently.

CONCLUSION

In this study, CA2-2-polarized M1 macrophages significantly attenuated tumor growth and prolonged mice survival in the syngeneic mouse models. Therefore, ex vivo CA2-2 activation of mouse macrophages can serve as a useful model for subsequent antitumor cellular immunotherapy developments.

Immunomodulatory properties of triterpenes

The immune system is one of the main defence mechanisms of the human body. Inadequacy of this system or immunodeficiency results in increased risk of infections and tumours, whereas over-activation of the immune system causes allergic or autoimmune disorders. A well-balanced immune system is important for protection and for alleviation of these diseases. There is a growing interest to maintain a well-balanced immune system, especially after the Covid-19 pandemic. Many biological extracts, as well as natural products, have become popular due to their wide array of immunomodulatory effects and influence on the immune system. Triterpenes, one of the secondary metabolite groups of medicinal plants, exhibit immunomodulatory properties by various mechanisms. Different triterpenes, including components of commonly consumed plants, can promote some protection and alleviation of disease symptoms linked with immune responses and thus enhance overall well-being. This review aims to highlight the efficacy of triterpenes in light of the available literature evidence regarding the immunomodulatory properties of triterpenes. We have reviewed widely investigated immunomodulatory triterpenes; oleanolic acid, glycyrrhizin, glycyrrhetinic acid, pristimerin, ursolic acid, boswellic acid, celastrol, lupeol, betulin, betulinic acid, ganoderic acid, cucumarioside, and astragalosides which have important immunoregulatory properties. In spite of many preclinical and clinical trials were conducted on triterpenes related to their immunoregulatory actions, current studies have several limitations. Therefore, especially more clinical studies with optimal design is essential.

Sulfated Glycosides from the Sea Cucumbers Block Ca2+ Flow in Murine Neuroblastoma Cells

Recently the ability of triterpene glycosides from sea cucumbers to interact with purinergic receptors of P2X family on the membranes of immune cells enhancing the reversible ATP-dependent Ca2+ intake and therefore modulating (stimulating) the receptor's activity was discovered. As a result the activation of cellular immunity on the organism level was observed. Purinergic receptors are associated with a series of important functions in normal and pathophysiology, thus the searching of its new modulators (both stimulants and blockers) seems to be very important medical and scientific task. The cytotoxic activity of four triterpene glycosides isolated from different species of sea cucumbers: liouvilloside A (1) from Pseudocolochirus violaceus, fallaxoside D1 (2) from Cucumaria fallax and magnumosides C3 (3) and C4 (4) from Massinium (=Neothynidium) magnum against neuroblastoma Neuro 2A cells was tested. The glycosides 1 and 4 were the most cytotoxic in the series (EC50 5.0 μM and 21.5 μM, correspondingly). Moreover, non-cytotoxic concentration (1 μM) of these compounds inhibited ATP-dependent Ca2+ intake into the Neuro 2A cells, containing P2X7 receptors on the surface, by 53 and 47%, correspondingly. The ability of sea cucumbers triterpene glycosides to block the purinergic receptors in vitro is first discovered.

Saponins from Sea Cucumber and Their Biological Activities

Sea cucumbers, belonging to the phylum Echinodermata, have been valued for centuries as a nutritious and functional food with various bioactivities. Sea cucumbers can produce highly active substances, notably saponins, the main secondary metabolites, which are the basis of their chemical defense. The saponins are mostly triterpene glycosides with triterpenes or steroid in aglycone, which possess multiple biological properties including antitumor, hypolipidemic activity, improvement of nonalcoholic fatty liver, inhibition of fat accumulation, antihyperuricemia, promotion of bone marrow hematopoiesis, antihypertension, etc. Sea cucumber saponins have received attention due to their rich sources, low toxicity, high efficiency, and few side effects. This review summarizes current research on the structure and activities of sea cucumber saponins based on the physiological and pharmacological activities from source, experimental models, efficacy, and mechanisms, which may provide a valuable reference for the development of sea cucumber saponins.

Cucumarioside A₂-2 Causes Macrophage Activation in Mouse Spleen

The immunomodulatory effect of triterpene glycoside cucumarioside A₂-2 (CA₂-2), isolated from the Far Eastern sea cucumber Cucumaria japonica, was compared with lipopolysaccharide (LPS) on mouse spleen. It has been shown that the intraperitoneal (i.p.) glycoside administration leads to increased spleen macrophage activating markers iba-1, IL-1β, iNOs, ROS and NO formation, with additional change of macrophage phenotype to M1. The mass spectrometry profiles of peptide/protein were obtained using MALDI-TOF-MS on the different parts of spleen sections isolated by laser mircodissection techniques. It was found that i.p. stimulation of animals with CA₂-2 leads to marked changes in the intensity of the characteristic peaks of spleen peptides/proteins, primarily in red pulp.

Glycosides from edible sea cucumbers stimulate macrophages via purinergic receptors

Since ancient times, edible sea cucumbers have been considered a jewel of the seabed and used in Asian folk medicine for stimulation of resistance against different diseases. However, the power of this sea food has not been established on a molecular level. A particular group of triterpene glycosides was found to be characteristic metabolites of the animals, responsible for this biological action. Using one of them, cucumarioside A₂-2 (CA₂-2) from the edible Cucumaria japonica species as an example as well as inhibitory analysis, patch-clamp on single macrophages, small interfering RNA technique, immunoblotting, SPR analysis, computer modeling and other methods, we demonstrate low doses of CA₂-2 specifically to interact with P2X receptors (predominantly P2X4) on membranes of mature macrophages, enhancing the reversible ATP-dependent Ca²⁺ intake and recovering Ca²⁺ transport at inactivation of these receptors. As result, interaction of glycosides of this type with P2X receptors leads to activation of cellular immunity.

In vitroAnticancer Activities of Some Triterpene Glycosides from Holothurians of Cucumariidae, Stichopodidae, Psolidae, Holothuriidae and Synaptidae families

Triterpene glycosides isolated from holothurians are natural products known to possess cytotoxic properties against cancer cells. However, their anticancer prophylactic activity has not been studied sufficiently. The anticancer prophylactic, cytotoxic, and pro-apoptotic properties of 18 triterpene glycosides, as well as their effects on the transcriptional activities of activator protein-1 (AP-1) and nuclear factor-κB (NF-κB), were examined using methods that included EGF-induced JB6 Cl41 P+ cell transforation in soft agar, flow cytometry, MTS assessment of cell viability, and a luciferase activity assay. The compounds inhibited EGF-induced neoplastic JB6 Cl41 P+ cell transforation in soft agar and caused apoptosis and necrosis of human HL-60 and THP-1 leukemia cells. AP-1 and NF-κB were involved in the cellular response to the treatment by the compounds. Conclusion: glycosides isolated from holothurians of Cucumariidae, Stichopodidae, Psolidae, Holothuriidae and Synaptidae families have potential for development as new antitumor agents and as instruments to study AP-1 and NF-κB.

Acetylated Triterpene Glycosides and Their Biological Activity from Holothuroidea Reported in the Past Six Decades

Sea cucumbers have been valued for many centuries as a tonic and functional food, dietary delicacies and important ingredients of traditional medicine in many Asian countries. An assortment of bioactive compounds has been described in sea cucumbers. The most important and abundant secondary metabolites from sea cucumbers are triterpene glycosides (saponins). Due to the wide range of their potential biological activities, these natural compounds have gained attention and this has led to their emergence as high value compounds with extended application in nutraceutical, cosmeceutical, medicinal and pharmaceutical products. They are characterized by bearing a wide spectrum of structures, such as sulfated, non-sulfated and acetylated glycosides. Over 700 triterpene glycosides have been reported from the Holothuroidea in which more than 145 are decorated with an acetoxy group having 38 different aglycones. The majority of sea cucumber triterpene glycosides are of the holostane type containing a C18 (20) lactone group and either Δ(7(8)) or Δ(9(11)) double bond in their genins. The acetoxy group is mainly connected to the C-16, C-22, C-23 and/or C-25 of their aglycone. Apparently, the presence of an acetoxy group, particularly at C-16 of the aglycone, plays a significant role in the bioactivity; including induction of caspase, apoptosis, cytotoxicity, anticancer, antifungal and antibacterial activities of these compounds. This manuscript highlights the structure of acetylated saponins, their biological activity, and their structure-activity relationships.

Cucumarioside A2-2 causes changes in the morphology and proliferative activity in mouse spleen

The immunomodulatory effect of triterpene glycoside cucumarioside A2-2 (CA2-2), isolated from the Far Eastern sea cucumber Cucumaria japonica, on the mouse spleen was investigated in comparison with lipopolysaccharide (LPS). It has been shown that the intraperitoneal (i.p.) glycoside administration did not influence on splenic weights, while the statistically significant increase in splenic weight was observed after LPS administration. Changes in the ratio of red to white pulp after CA2-2 or LPS administration were observed. The proportion of splenic white pulp after glycoside or LPS administration increased by up to 34% and 36%, respectively. A detailed study of the distribution of the РСNA (Proliferating Cell Nuclear Antigen) marker showed that the proliferative activity in the white pulp under CA2-2 and LPS influence increased 2.07 and 2.24 times, respectively. The localization of PCNA-positive nuclei in the white pulp region, as well as their dimensional characteristics, suggests that a large proportion of the proliferating cell population consisted of B cells. The mass spectrometry profiles of spleen peptide/protein homogenate were obtained using the MALDI-TOF-MS (Matrix -Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry) approach. It was found that i.p. stimulation of animals with CA2-2 or LPS leads to marked changes in the intensity of revealed characteristic peaks of peptides/proteins after exposure to immunostimulants.

Biological and taxonomic perspective of triterpenoid glycosides of sea cucumbers of the family Holothuriidae (Echinodermata, Holothuroidea)

Since the discovery of saponins in sea cucumbers, more than 150 triterpene glycosides have been described for the class Holothuroidea. The family Holothuriidae has been increasingly studied in search for these compounds. With many species awaiting recognition and formal description this family currently consists of five genera and the systematics at the species-level taxonomy is, however, not yet fully understood. We provide a bibliographic review of the triterpene glycosides that has been reported within the Holothuriidae and analyzed the relationship of certain compounds with the presence of Cuvierian tubules. We found 40 species belonging to four genera and 121 compounds. Holothurin A and B are the most common saponins for Actinopyga, Holothuria, and Pearsonothuria. The genus Bohadschia presents mainly bivittoside C and D. Actinopyga has only sulfated saponins mainly oxidized, Bohadschia non-sulfated ones mainly non-oxidized, Holothuria and Pearsonothuria contain both types of compounds, mainly oxidized. Within the genus Holothuria, the subgenus Panningothuria only has non-sulfated saponins. The presence of sulfated and non-sulfated compounds seemingly relates to the expellability or the absence of Cuvierian tubules and the temporal or permanent concealing habits of the species. Our study concludes that better insights into the systematic distribution of saponins in Holothuriidae will only be possible if the identifications of the investigated species are confirmed by a taxonomist, especially in this group wherein cryptic species and variation between life-history stages are common and yet poorly understood. Understanding of saponin distribution within the Holothuriidae would also benefit from a stabilization of triterpene glycoside nomenclature.

Relationships between chemical structures and functions of triterpene glycosides isolated from sea cucumbers

Many marine triterpene glycosides have in vitro and in vivo activities with very low toxicity, suggesting that they are suitable agents for the prevention and treatment of different diseases, particularly cancer. However, the molecular mechanisms of action of natural marine compounds in cancer, immune, and other various cells are not fully known. This review focuses on the structural characteristics of marine triterpene glycosides and how these affect their biological activities and molecular mechanisms. In particular, the membranotropic and membranolytic activities of frondoside A and cucumariosides from sea cucumbers and their ability to induce cytotoxicity and apoptosis have been discussed, with a focus on structure-activity relationships. In addition, the structural characteristics and antitumor effects of stichoposide C and stichoposide D have been reviewed along with underlying their molecular mechanisms.

Inhibition of Tumor Cells Multidrug Resistance by Cucumarioside A2-2, Frondoside A and their Complexes with Cholesterol

In non-cytotoxic concentrations, frondoside A (1) from the sea cucumber Cucumaria okhotensis and cucumarioside A2-2 (2) from C. japonica, as well as their complexes with cholesterol block the activity of membrane transport P-glycoprotein in cells of the ascite form of mouse Ehrlich carcinoma. They prevent in this way an efflux of fluorescent probe Calcein from the cells. Since the blocking of P-glycoprotein activity results in decrease of multidrug resistance, these glycosides and their complexes with cholesterol may be considered as potential inhibitors of multidrug resistance of tumor cells.