Immunomodulatory effects and structure-activity relationship of botanical pentacyclic triterpenes: A review

Immunomodulatory effects of epiphytic Loranthus micranthus leaf extracts collected from two host plants: Psidium guajava and Parkia biglobosa

BACKGROUND

Immunological abnormalities are implicated in the pathogenesis of many chronic diseases. Due to the drug-related adverse effects of currently available orthodox immunomodulators, natural immunomodulators are being looked upon as potential agents to replace them in therapeutic regimens. This research aimed to investigate the immunomodulatory potential of L. micranthus extracts epiphytic on Psidium guajava (LMPGE) and Parkia biglobosa (LMPBE).

METHODS

Phytochemical screening and acute toxicity testing were carried out to identify the phytoconstituents and safety profiles of the extracts. The extracts' innate and adaptive immunomodulatory potentials were determined in experimental animals using in vivo leucocyte mobilization, delayed-type hypersensitivity (DTH) response, hemagglutination antibody titre, and cyclophosphamide-induced myelosuppression models. Levamisole was used as the standard drug throughout the study.

RESULTS

Compared to LMPBE, LMPGE contained significantly (p <  0.05) more tannins, cyanogenic glycosides, saponins, reducing sugars, glycosides, flavonoids, and alkaloids. Furthermore, the groups treated with the extracts had a significant (p <  0.05) increase in the total number of leucocytes, neutrophils, basophils, and antibody titers relative to the untreated control. In the same way, the treatment raised TLC in cyclophosphamide-intoxicated rats, with 250 mg/kg b. w. of LMPGE and LMPBE recording 9712.50 ± 178.00 and 8000.00 ± 105.00 ×  109 /L, respectively, compared to 3425.00 ± 2 5.00 × 109 /L in the untreated group. Overall, LMPGE was more effective.

CONCLUSIONS

The findings from this study suggest that L. micranthus epiphytic in Psidium guajava and Parkia biglobosa has possible immune stimulating potential.

Dynamic metabolites: A bridge between plants and microbes

Plant metabolites have a great influence on soil microbiomes. Although few studies provided insights into plant-microbe interactions, we still know very little about how plants recruit their microbiome. Here, we discuss the dynamic progress that typical metabolites shape microbes by a variety of factors, such as physiographic factors, cultivar factors, phylogeny factors, and environmental stress. Several kinds of metabolites have been reviewed, including plant primary metabolites (PPMs), phytohormones, and plant secondary metabolites (PSMs). The microbes assembled by plant metabolites in return exert beneficial effects on plants, which have been widely applied in agriculture. What's more, we point out existing problems and future research directions, such as unclear mechanisms, few species, simple parts, and ignorance of absolute abundance. This review may inspire readers to study plant-metabolite-microbe interactions in the future.

Bioactivity of the Genus Turnera: A Review of the Last 10 Years

Turnera is a genus of plants whose biological activity has been widely studied. The importance of this genus, particularly Turnera diffusa, as a source of treatment for various conditions is evidenced by the large number of new studies that have evaluated its biological activity. Accordingly, the objective of this review was to compile the information published in the last ten years concerning the biological activities reported for Turnera spp. The present work includes 92 publications that evaluate 29 bioactivities and toxicological and genotoxic information on five species of this genus. Among the pharmacological effects reported, the antioxidant, hepatoprotective, neuroprotective, hypoglycemic, and aphrodisiac activities seem more promising. Phytochemicals and standardized plant extracts could offer alternative therapeutic remedies for various diseases. Although several flavonoids, cyanogenic glycosides, monoterpenoids, triterpenoids, and fatty acids have been isolated for Turnera plants, future research should focus on the identification of the main active principles responsible for these pharmacological activities, as well as to perform clinical trials to support the laboratory results.

Characterization of the horse chestnut genome reveals the evolution of aescin and aesculin biosynthesis

Horse chestnut (Aesculus chinensis) is an important medicinal tree that contains various bioactive compounds, such as aescin, barrigenol-type triterpenoid saponins (BAT), and aesculin, a glycosylated coumarin. Herein, we report a 470.02 Mb genome assembly and characterize an Aesculus-specific whole-genome duplication event, which leads to the formation and duplication of two triterpenoid biosynthesis-related gene clusters (BGCs). We also show that AcOCS6, AcCYP716A278, AcCYP716A275, and AcCSL1 genes within these two BGCs along with a seed-specific expressed AcBAHD6 are responsible for the formation of aescin. Furthermore, we identify seven Aesculus-originated coumarin glycoside biosynthetic genes and achieve the de novo synthesis of aesculin in E. coli. Collinearity analysis shows that the collinear BGC segments can be traced back to early-diverging angiosperms, and the essential gene-encoding enzymes necessary for BAT biosynthesis are recruited before the splitting of Aesculus, Acer, and Xanthoceras. These findings provide insight on the evolution of gene clusters associated with medicinal tree metabolites.

Plants and Plant-Derived Molecules as Natural Immunomodulators

Background. Nowadays, the immunomodulatory properties of plants have been studied extensively with greater interest due to increasing awareness and combating the severity of immunomodulatory diseases. Scope and Approach. This paper highlights the efficacy of the available literature evidence on natural immunomodulators of plant origin and synthetic ones. In addition, several aspects of plants and their phytoconstituents responsible for immunomodulation have been discussed. Moreover, this review also discusses the mechanism involved in immunomodulation. Key Findings. One hundred fifty medicinal immunomodulatory plants are currently identified to find novel immunomodulatory drugs. Of these plants, the plant family Asteraceae also takes the first rank by offering 18 plant species (12%). Similarly of the plants studied so far, 40% belong to the Asteraceae family. Echinacea purpurea of this family is most known for its immunostimulating activity. The most prominent immune-active bioactive molecules are polyphenols, terpenoids, and alkaloids. Also, eight plant bioactive immunomodulators were checked for clinical trials and found in the market. These are six immunosuppressants, resveratrol, epigallocatechin-3-gallate, quercetin, colchicine, capsaicin, and andrographolide, and two immunostimulants, curcumin and genistein. Nowadays, there are a lot of polyherbal traditional medicinal products sold in the market and claimed to their immunomodulators. However, much work is still needed to find more active immunomodulatory agents. The mechanism by which immunomodulatory medicinal plant exert their effect is through the induction of cytokines and phagocyte cells and the inhibition of iNOS, PGE, and COX-2 synthesis.

Protective effect of soloxolone derivatives in carrageenan- and LPS-driven acute inflammation: Pharmacological profiling and their effects on key inflammation-related processes

The anti-inflammatory potential of three cyanoenone-containing triterpenoids, including soloxolone methyl (SM), soloxolone (S) and its novel derivative bearing at the C-30 amidoxime moiety (SAO), was studied in murine models of acute inflammation. It was found that the compounds effectively suppressed the development of carrageenan-induced paw edema and peritonitis as well as lipopolysaccharide (LPS)-driven acute lung injury (ALI) with therapeutic outcomes comparable with that of the reference drugs indomethacin and dexamethasone. Non-immunogenic carrageenan-stimulated inflammation was more sensitive to the transformation of C-30 of SM compared with immunogenic LPS-induced inflammation: the anti-inflammatory properties of the studied compounds against carrageenan-induced paw edema and peritonitis decreased in the order of SAO > S > > SM, whereas the efficiency of these triterpenoids against LPS-driven ALI was similar (SAO ≈ S ≈ SM). Further studies demonstrated that soloxolone derivatives significantly inhibited a range of immune-related processes, including granulocyte influx and the expression of key pro-inflammatory cytokines and chemokines in the inflamed sites as well as the functional activity of macrophages. Moreover, SM was found to prevent inflammation-associated apoptosis of A549 pneumocytes and effectively inhibited the protease activity of thrombin (IC₅₀ = 10.3 µM) tightly associated with rodent inflammatome. Taken together, our findings demonstrate that soloxolone derivatives can be considered as novel promising anti-inflammatory drug candidates with multi-targeted mechanism of action.

Integrated transcriptome and proteome analyses reveal candidate genes for ginsenoside biosynthesis in Panax japonicus C. A. Meyer

Panax japonicus C. A. Meyer is a plant of the Araliaceae family, and its rhizomes can be used as dietary supplements. It is extremely rich in bioactive components ginsenosides with benefits to human health. However, the underlying mechanisms of ginsenosides biosynthesis in Panax japonicus remains poorly understood. Therefore, a comprehensive analysis of the metabolites, transcriptome, and proteome was conducted to investigate ginsenoside metabolism of Panax japonicus. Here, three types of ginsenosides were found to exhibited tissue-specific distribution using the liquid chromatography-mass spectrometry method. Next, differentially expressed gene analysis revealed that transcript levels of ginsenosides biosynthetic genes have significant differences between differential samples. In addition, correlation analysis showed that the ginsenosides content was closely related to the expression level of 29 cytochrome P450s and 92 Uridine diphosphate-glycosyltransferases. Finally, phylogenetic analysis was performed for the target proteins to conduct preliminary studies on their functions and classification. This study provides insight into the dynamic changes and biosynthetic pathway of ginsenosides and offers valuable information on the metabolic regulation of Panax japonicus.

Edible pentacyclic triterpenes: A review of their sources, bioactivities, bioavailability, self-assembly behavior, and emerging applications as functional delivery vehicles

Edible pentacyclic triterpenes (PTs) are a group of nutraceutical ingredients commonly distributed in human diets. Existing evidence has proven that they have various biological functions, including anticancer, antioxidant, anti-inflammatory and hypoglycemic activities, making them as "functional factor" for a long time. However, their properties of strong hydrophobicity, poor permeability, poor absorption, and rapid metabolism result in low oral bioavailability, which dramatically hinders their efficacy for use. Recently, free PTs have successively been found to self-assemble or co-assemble into self-contained nanostructures with enhanced water dispersibility and oral bioavailability, which seems to be an efficient processing method for increased oral efficacy. Of particular interest, formulating them into nanostructures can also be introduced as functional delivery carriers for bioactive compounds or drugs with various advantages, such as improved stability, controlled release, enhanced oral bioavailability, synergistic bioactivity, and targeted delivery. This review systematically summarized the chemical structures, plant sources, bioactivities, absorption, metabolism, and oral bioavailability of PTs. Notably, we emphasized their self-assembly properties and emerging role as functional delivery carriers for nutrients, suggesting that PT nanostructures are not only efficient oral forms when introduced into foods but also functional delivery materials for nutrients to expand their commercial food applications.

Ursolic acid alleviates tetrandrine-induced hepatotoxicity by competitively binding to the substrate-binding site of glutathione S-transferases

BACKGROUND

Tetrandrine (TET), a bisbenzylisoquinoline alkaloid isolated from Stephania tetrandra S. Moore, is the only approved medicine in China for silicosis. However, TET-induced hepatotoxicity has raised safety concerns. The underlying toxic targets and mechanism induced by TET remain unclear; there are no targeted detoxification strategies developed for TET-induced hepatotoxicity. Ursolic acid (UA), a pentacyclic triterpene with liver protective effects, may have detoxification effects on TET-induced hepatotoxicity.

PURPOSE

This study aims to explore toxic targets and mechanism of TET and present UA as a potential targeted therapy for alleviating TET-induced hepatotoxicity.

METHODS

A TET-induced liver-injury model was established to evaluate TET toxicity and the potential UA detoxification effect. Alkenyl-modified TET and UA probes were designed to identify potential liver targets. Pharmacological and molecular biology methods were used to explore the underlying toxicity/detoxification mechanism.

RESULTS

TET induced liver injury by covalently binding to the substrate-binding pocket (H-site) of glutathione S-transferases (GSTs) and inhibiting GST activity. The covalent binding led to toxic metabolite accumulation and caused redox imbalance and liver injury. UA protected the liver from TET-induced damage by competitively binding to the GST H-site.

CONCLUSION

The mechanism of TET-induced hepatotoxicity is related to irreversible binding with the GST H-site and GST-activity inhibition. UA, a natural antidote, competed with TET on H-site binding and reversed the redox imbalance. This study revealed the hepatotoxic mechanism of TET and provided a targeted detoxifying agent, UA, to alleviate hepatotoxicity caused by GST inhibition.

State-of-the-Art and Opportunities for Bioactive Pentacyclic Triterpenes from Native Mexican Plants

Native Mexican plants are a wide source of bioactive compounds such as pentacyclic triterpenes. Pentacyclic triterpenes biosynthesized through the mevalonate (MVA) and the 2-C-methyl-D-erythritol-phosphate (MEP) metabolic pathways are highlighted by their diverse biological activity. Compounds belonging to the oleanane, ursane, and lupane groups have been identified in about 33 Mexican plants, located geographically in the southwest of Mexico. The works addressing these findings have reported 45 compounds that mainly show antimicrobial activity, followed by anti-inflammatory, cytotoxic, anxiolytic, hypoglycemic, and growth-stimulating or allelopathic activities. Extraction by maceration and Soxhlet with organic solvents and consecutive chromatography of silica gel have been used for their whole or partial purification. Nanoparticles and nanoemulsions are the vehicles used in Mexican formulations for drug delivery of the pentacyclic triterpenes until now. Sustainable extraction, formulation, regulation, isolation, characterization, and bioassay facilities are areas of opportunity in pentacyclic triterpenes research in Mexico while the presence of plant and human resources and traditional knowledge are strengths. The present review discusses the generalities of the pentacyclic triterpene (definition, biogenic classification, and biosynthesis), a summary of the last two decades of research on the compounds identified and their evaluated bioactivity, the generalities about the extraction and purification methods used, drug delivery aspects, and a critical analysis of the advantages and limitations of research carried out in this way.

Synthesis and Structural Characterization of a New 1,2,3-Triazole Derivative of Pentacyclic Triterpene

The new 30-substituted triazole derivative of 3,28-O,O′-diacetylbetulin was obtained in the copper(I) catalyzed azide-alkyne cycloaddition (CuAAC). The title compound was characterized by NMR, IR, HR-MS, and X-ray diffraction techniques. The X-ray diffraction study showed that the 1,2,3-triazole derivative crystallizes in the orthorhombic space group P212121, Z = 4, and unit cell parameters are as follows a = 9.4860(10) Å, b = 13.9440(2) Å, and c = 30.2347(4) Å. The molecular packing is stabilized by intermolecular hydrogen interactions C-H…O. The Hirshfeld surface analysis showed the presence of the O…H interactions with a percentage of the 16.5% in the total Hirshfeld area. The MEP analysis showed that the nucleophilic regions are located near the oxygen atoms of the acyl and carbonyl groups of betulin moiety and the sulfur atom in the triazole linker. The HOMO and LUMO orbitals are located near the triazole moiety. The obtained results indicated that this new betulin derivative is more reactive with electrophilic than nucleophilic molecules.

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.

Phytomolecules Repurposed as Covid-19 Inhibitors: Opportunity and Challenges

The SARS-CoV-2 virus has spread worldwide to cause a full blown pandemic since 2020. To date, several promising synthetic therapeutics are repurposed and vaccines through different stages of clinical trials were approved and being administered, but still the efficacy of the drugs and vaccines are yet to be decoded. This article highlights the importance of traditional medicinal plants and the phytomolecules derived from them, which possess in vitro antiviral and anti-CoV properties and further explores their potential as inhibitors to molecular targets of SARS-CoV-2 that were evaluated by in silico approaches. Botanicals in traditional medicinal systems have been investigated for anti-SARS-CoV-2 activity through in silico and in vitro studies. However, information linking structure of phytomolecules to their antiviral activity is limited. Most phytomolecules with anti-CoV activity were studied for inhibition of the human ACE2 receptor through which the virus enters host cells, and non-structural proteins 3CLpro and PLpro. Although the proteases are ideal anti-CoV targets, information on plant-based inhibitors for the CoV structural proteins, e.g., spike, envelope, membrane, nucleocapsid required further investigations. In absence of scientific evaluations through in vitro and biocompatibility studies, plant-based antivirals fall short as treatment options. Plant-based anti-SARS-CoV-2 therapeutics can be promising alternatives to their synthetic counterparts as they are economical and bear fewer chances of toxicity, side effects, and viral resistance. Our review could provide a systematic overview of the potential phytomolecules which can be repurposed and subjected to further modes of experimental evaluation to qualify for use in treatment and prophylaxis of SARS-CoV-2 infections.

Anticancer Potential of Betulonic Acid Derivatives

Clinical trials have evidenced that several natural compounds, belonging to the phytochemical classes of alkaloids, terpenes, phenols and flavonoids, are effective for the management of various types of cancer. Latest research has proven that natural products and their semisynthetic variants may serve as a starting point for new drug candidates with a diversity of biological and pharmacological activities, designed to improve bioavailability, overcome cellular resistance, and enhance therapeutic efficacy. This review was designed to bring an update regarding the anticancer potential of betulonic acid and its semisynthetic derivatives. Chemical derivative structures of betulonic acid including amide, thiol, and piperidine groups, exert an amplification of the in vitro anticancer potential of betulonic acid. With the need for more mechanistic and in vivo data, some derivatives of betulonic acids may represent promising anticancer agents.