Molecular characterization of an oxidosqualene cyclase that yields shionone, a unique tetracyclic triterpene ketone of Aster tataricus

Systematic qualitative analysis of terpenes in mastic (Pistacia lentiscus L.) extract and their fragmentations by UHPLC-Q-Orbitrap-HRMS

INTRODUCTION

Mastic is a natural resin produced by Pistacia lentiscus L. (Anacardiaceae). The beneficial properties of this resin are attributed to its triterpenes and volatile compounds.

OBJECTIVE

This study was conducted to screen and characterize the terpenes in mastic ethyl acetate extract (M-Ex).

METHODS

An ultrahigh-performance liquid chromatography coupled to quadrupole Orbitrap high-resolution mass spectrometry (UHPLC-Q-Orbitrap-HRMS) method was developed for the qualitative analysis of terpenes in M-Ex. We utilized in-house-isolated compounds as reference substance (Rs), including monoterpenes (A) with α-pinane structures, tetracyclic triterpene (B) containing tirucallane skeletons, and pentacyclic triterpene (C) belonging to olean, moronic, amyrone, and lupane types. Based on the mass spectrometric characteristics of the above compounds, and the difference in characteristic diagnostic fragment ions (DFIs) in isomeric compounds, the terpene compounds were further identified in M-Ex.

RESULTS

Out of a total of 70 compounds, including monoterpenes and tetra-, and pentacyclic triterpenes, 20 were accurately determined by Rs, retention time (RT), and DFIs. Based on the cleavage patterns summarized from the above 20 compounds and with reference to the reported literature, another 50 compounds were putatively identified. Based on our discovery, six terpenic acids with A-seco-tirucallane types and one monoterpene dimer were identified for the first time in mastic.

CONCLUSION

Our research serves not only as a foundation for the rapid identification and screening of terpene compounds in mastic but also as a supplementary basis for the identification of such compounds in other types of resins.

Functional characterization of genes related to triterpene and flavonoid biosynthesis in Cyclocarya paliurus

MAIN CONCLUSION

The oxidosqualene cyclases (OSCs) generating triterpenoid skeletons in Cyclocarya paliurus were identified for the first time, and two uridine diphosphate (UDP)-glycosyltransferases (UGTs) catalyzing the glycosylation of flavonoids were characterized. Cyclocarya paliurus, a native rare dicotyledonous plant in China, contains an abundance of triterpenoid saponins and flavonoid glycosides that exhibit valuable pharmaceutical effects in preventing hypertension, hyperlipidemia, and diabetes. However, the molecular mechanism explaining the biosynthesis of triterpenoid saponin and flavonoid glycoside in C. paliurus remains unclear. In this study, the triterpene content in different tissues and the expression pattern of genes encoding the key enzymes associated with triterpenoid saponin and flavonoid glycoside biosynthesis were studied using transcriptome and metabolome analysis. The eight upstream oxidosqualene cyclases (OSCs) involved in triterpenoid saponin biosynthesis were functionally characterized, among them CpalOSC6 catalyzed 2,3;22,23-dioxidosqualene to form 3-epicabraleadiol; CpalOSC8 cyclized 2,3-oxidosqualene to generate dammarenediol-II; CpalOSC2 and CpalOSC3 produced β-amyrin and CpalOSC4 produced cycloartenol, while CpalOSC2-CpalOSC5, CpalOSC7, and CpalOSC8 all produced lanosterol. However, no catalytic product was detected for CpalOSC1. Moreover, two downstream flavonoid uridine diphosphate (UDP)-glycosyltransferases (UGTs) (CpalUGT015 and CpalUGT100) that catalyze the last step of flavonoid glycoside biosynthesis were functionally elucidated. These results uncovered the key genes involved in the biosynthesis of triterpenoid saponins and flavonoid glycosides in C. paliurus that could be applied to produce flavonoid glycosides and key triterpenoid saponins in the future via a synthetic strategy.

Identification and Functional Characterization of Oxidosqualene Cyclases from Medicinal Plant Hoodia gordonii

Oxidosqualene cyclases (OSCs) are the key enzymes accountable for the cyclization of 2,3-oxidosqualene to varied triterpenoids and phytosterols. Hoodia gordonii (from the family Apocynaceae), a native of the Kalahari deserts of South Africa, Namibia, and Botswana, is being sold as a prevalent herbal supplement for weight loss. The appetite suppressant properties are attributed to P57AS3, an oxypregnane steroidal glycoside. At the molecular level, the enzymes involved in the biosynthesis of triterpenes and phytosterols from H. gordonii have not been previously reported. In the current study, predicted transcripts potentially encoding oxidosqualene cyclases were recognized first by searching publicly available H. gordonii RNA-seq datasets. Two OSC-like sequences were selected for functional analysis. A monofunctional OSC, designated HgOSC1 which encodes lupeol synthase, and HgOSC2, a multifunctional cycloartenol synthase forming cycloartenol and other products, were observed through recombinant enzyme studies. These studies revealed that distinct OSCs exist for triterpene formation in H. gordonii and provided opportunities for the metabolic engineering of specific precursors in producing phytosterols in this plant species.

Pharmacological Properties of Shionone: Potential Anti-Inflammatory Phytochemical against Different Diseases

Shionone is a triterpenoid that is the primary constituent of an important ancient Chinese medicine named Radix Asteris. It has emerged as an attractive candidate against different important diseases, including interstitial cystitis, colitis, cancer, Parkinson's disease, and urinary tract infections, and was found to have a protective effect on multiple organs, including the colon, kidneys, lungs, brain, and bladder. The anti-inflammation activity of shionone may be considered an important property that imparts the positive health outcomes of shionone. Important molecular targets and markers such as TNF-α, STAT3, NLRP3, and NF-κB were also found to be targeted by shionone and were verified in different diseases. This suggests the possible potential of shionone against other diseases associated with these targets. Pharmacokinetic studies also support the therapeutic potential of shionone and provide the initial track that may be pursued for its development. Yet, the compilation of the pharmacological activities of shionone and its important genes and pathway targets are absent in the existing literature, which would direct its development as a therapeutic and/or supplement. Hence, the present review provides a compilation of information concerning pharmacological activities, highlights the existing holes, and proposes a specific direction for the expansion of shionone as a therapeutic against different diseases and conditions.

Shionone Relieves Urinary Tract Infections by Removing Bacteria from Bladder Epithelial Cells

In clinical practice, urinary tract infections (UTIs) are second only to respiratory infections in terms of infectious diseases. In recent years, drug resistance of Escherichia coli (E. coli) has increased significantly. The therapeutic effects of Shionone on UTI were assessed by modelling UTI in SD rats and SV-HUC-1 cells with E. coli solution. After treatment of Shionone, the UTI rat model showed a decrease in wet weight/body weight of bladder, as well as a reduction in cellular inflammatory infiltration of bladder tissue and a decrease in urinary levels of IL-6, IL-1β, and TNF-α. In addition, the levels of proinflammatory factors were significantly reduced in a dose-dependent manner in UTI cell model treated with different doses of Shionone (5, 10, and 20 μg/kg). The results of immunofluorescence analysis in both in vivo and in vitro experiments revealed that Shionone reduced bacterial load and the number of E. coli colonies growing on the plates was greatly reduced. These results suggested that Shionone has a good therapeutic effect on UTI, achieved by reducing bacterial load in bladder epithelial cells. The data presented here provide a basis for further research into the treatment of UTI.

Biosynthetic pathways of triterpenoids and strategies to improve their Biosynthetic Efficiency

"Triterpenoids" can be considered natural products derived from the cyclization of squalene, yielding 3-deoxytriterpenes (hydrocarbons) or 3-hydroxytriterpenes. Triterpenoids are metabolites of these two classes of triterpenes, produced by the functionalization of their carbon skeleton. They can be categorized into different groups based on their structural formula/design. Triterpenoids are an important group of compounds that are widely used in the fields of pharmacology, food, and industrial biotechnology. However, inadequate synthetic methods and insufficient knowledge of the biosynthesis of triterpenoids, such as their structure, enzymatic activity, and the methods used to produce pure and active triterpenoids, are key problems that limit the production of these active metabolites. Here, we summarize the derivatives, pharmaceutical properties, and biosynthetic pathways of triterpenoids and review the enzymes involved in their biosynthetic pathway. Furthermore, we concluded the screening methods, identified the genes involved in the pathways, and highlighted the appropriate strategies used to enhance their biosynthetic production to facilitate the commercial process of triterpenoids through the synthetic biology method.

Anti-viral triterpenes: a review

Triterpenes are naturally occurring derivatives biosynthesized following the isoprene rule of Ruzicka. The triterpenes have been reported to possess a wide range of therapeutic applications including anti-viral properties. In this review, the recent studies (2010-2020) concerning the anti-viral activities of triterpenes have been summarized. The structure activity relationship studies have been described as well as brief biosynthesis of these triterpenes is discussed.

The enzymes OSC1 and CYP716A263 produce a high variety of triterpenoids in the latex of Taraxacum koksaghyz

Only very little is known about the resin composition of natural rubber from the dandelion species Taraxacum koksaghyz, thus its full characterization could provide new insights into how the isoprenoid end-products influence the physical properties of natural rubber, and this resin might be a good source of highly diverse triterpenoids. Here, we present a comprehensive analysis of the triterpenoid composition in an acetone extract and identified 13 triterpenes and triterpenoids also including the so far unknown pentacyclic compounds lup-19(21)-en-3-ol (1) and its ketone lup-19(21)-en-3-one (2). We purified single triterpenes from the acetone extract by developing a two-step HPLC system that is adapted to the structural differences of the described triterpenoids. Furthermore, we isolated six different oxidosqualene cyclases (OSCs) and two P450 enzymes, and we functionally characterized TkOSC1 and CYP716A263 in Nicotiana benthamiana and Saccharomyces cerevisiae in detail. TkOSC1 is a multifunctional OSC that was capable of synthesizing at least four of the latex-predominant pentacyclic triterpenes (taraxasterol, α-, β-amyrin and lup-19(21)-en-3-ol) while CYP716A263 oxidized pentacyclic triterpenes at the C-3 position. The identified enzymes responsible for biosynthesis and modification of pentacyclic triterpenes in T. koksaghyz latex may represent excellent tools for bioengineering approaches to produce pentacyclic triterpenes heterologously.

EVALUATION OF THE ACUTE AND SUBCHRONIC TOXICITY OF Aster tataricus L. F

BACKGROUND

Aster tataricus L. f. is used as a traditional Chinese drug to relieve cough and asthma symptoms and to eliminate phlegm. However, Aster tataricus L. f. possesses toxicity, and little systematic research has been conducted on its toxic effects in the laboratory.

METHODS AND MATERIALS

The acute group was administered 75% alcohol extract of Aster tataricus L. f. in a single dose. A subchronic toxicity study was performed via daily oral administration of Aster tataricus L. f. at a dose of 0.34 g/kg body weight in SD rats. The rats were divided into six groups: a petroleum ether extract (PEA) group, an ethyl acetate extract (EEA) group, an n-butyl alcohol extract (NEA) group, a remaining lower aqueous phases (REA) group, a 75% alcohol extract (AEA) group and a control group. Quantitative measurements of cytokines were obtained by fluorescence with a laser scanner using a Cy3 equivalent dye.

RESULTS

The LD₅₀ of the 75% alcohol extract of Aster tataricus L. f. was 15.74 g/kg bw. In the subchronic toxicity study, no significant differences were observed among groups in relative organ weights, urine traits, liver antioxidase levels, or cytokine levels. However, significant sporadic differences were observed in body weight gains, haematology indices, biochemistry values, and histopathology features in PEA, EEA group. In addition, sporadic changes in other groups in measures such as WBC, MCHC, CK, ALP, AST, ALT, LDH, T-BIL, LDL-C, HDL-C, and TC were observed.

CONCLUSION

The toxicity study showed that Aster tataricus L. f. can produce toxic effects, mainly on the liver; much less on the heart. The LD₅₀ was 15.74 g/kg BW in mice, and the subchronic toxicity study, used a dosage of 0.34 g/kg/d.BW, showed that the toxic components of Aster tataricus L. f. were mainly concentrated in the petroleum ether fraction, followed by the ethyl acetate fraction, the n-butyl alcohol fraction, the lower aqueous phase and the 75% ethanol extracts. Abbreviations: PEA, petroleum ether extract of Aster tataricus L. f.; EEA, ethyl acetate extract of Aster tataricus L. f.; NEA: n-butyl alcohol extract of Aster tataricus L. f.; REA: lower aqueous phases of Aster tataricus L. f.; AEA, 75% alcohol extract of Aster tataricus L. f.; WBC, white blood cell; RBC, red blood cell, PLT, platelet; HCT, haematocrit; MCV, mean corpuscular volume; HGB, haemoglobin; MCH, mean corpuscular haemoglobin; MCHC, mean corpuscular haemoglobin concentration; CREA, creatinine; LDH, lactate dehydrogenase; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein cholesterol; T-BIL, total bilirubin; ALT, alanine aminotransferase; ALP, alkaline phosphatase; AST, aspartate aminotransferase; TP, total protein; ALB, albumin; Glu, glucose; TC, total cholesterol; TG, triglycerides; CK, creatine kinase; GSH, Glutathione; MDA, malondialdehyde; T-SOD, total superoxide dismutase; TNF, tumour necrosis factor; IFN, interferon; MCP, monocyte chemotactic protein C.

RNAi and Homologous Over-Expression Based Functional Approaches Reveal Triterpenoid Synthase Gene-Cycloartenol Synthase Is Involved in Downstream Withanolide Biosynthesis in Withania somnifera

Withania somnifera Dunal, is one of the most commonly used medicinal plant in Ayurvedic and indigenous medicine traditionally owing to its therapeutic potential, because of major chemical constituents, withanolides. Withanolide biosynthesis requires the activities of several enzymes in vivo. Cycloartenol synthase (CAS) is an important enzyme in the withanolide biosynthetic pathway, catalyzing cyclization of 2, 3 oxidosqualene into cycloartenol. In the present study, we have cloned full-length WsCAS from Withania somnifera by homology-based PCR method. For gene function investigation, we constructed three RNAi gene-silencing constructs in backbone of RNAi vector pGSA and a full-length over-expression construct. These constructs were transformed in Agrobacterium strain GV3101 for plant transformation in W. somnifera. Molecular and metabolite analysis was performed in putative Withania transformants. The PCR and Southern blot results showed the genomic integration of these RNAi and overexpression construct(s) in Withania genome. The qRT-PCR analysis showed that the expression of WsCAS gene was considerably downregulated in stable transgenic silenced Withania lines compared with the non-transformed control and HPLC analysis showed that withanolide content was greatly reduced in silenced lines. Transgenic plants over expressing CAS gene displayed enhanced level of CAS transcript and withanolide content compared to non-transformed controls. This work is the first full proof report of functional validation of any metabolic pathway gene in W. somnifera at whole plant level as per our knowledge and it will be further useful to understand the regulatory role of different genes involved in the biosynthesis of withanolides.

P450s and UGTs: Key Players in the Structural Diversity of Triterpenoid Saponins

The recent spread of next-generation sequencing techniques has facilitated transcriptome analyses of non-model plants. As a result, many of the genes encoding enzymes related to the production of specialized metabolites have been identified. Compounds derived from 2,3-oxidosqualene (the common precursor of sterols, steroids and triterpenoids), a linear compound of 30 carbon atoms produced through the mevalonate pathway, are called triterpenes. These include essential sterols, which are structural components of biomembranes; steroids such as the plant hormones, brassinolides and the toxin in potatoes, solanine; as well as the structurally diverse triterpenoids. Triterpenoids containing one or more sugar moieties attached to triterpenoid aglycones are called triterpenoid saponins. Triterpenoid saponins have been shown to have various medicinal properties, such as anti-inflammatory, anticancerogenic and antiviral effects. This review summarizes the recent progress in gene discovery and elucidates the biochemical functions of biosynthetic enzymes in triterpenoid saponin biosynthesis. Special focus is placed on key players in generating the structural diversity of triterpenoid saponins, cytochrome P450 monooxygenases (P450s) and the UDP-dependent glycosyltransferases (UGTs). Perspectives on further gene discovery and the use of biosynthetic genes for the microbial production of plant-derived triterpenoid saponins are also discussed.

Triterpene biosynthesis in plants

The triterpenes are one of the most numerous and diverse groups of plant natural products. They are complex molecules that are, for the most part, beyond the reach of chemical synthesis. Simple triterpenes are components of surface waxes and specialized membranes and may potentially act as signaling molecules, whereas complex glycosylated triterpenes (saponins) provide protection against pathogens and pests. Simple and conjugated triterpenes have a wide range of applications in the food, health, and industrial biotechnology sectors. Here, we review recent developments in the field of triterpene biosynthesis, give an overview of the genes and enzymes that have been identified to date, and discuss strategies for discovering new triterpene biosynthetic pathways.

Astataricusones A-D and astataricusol A, five new anti-HBV shionane-type triterpenes from Aster tataricus L. f

Five new shionane-type triterpenes, astataricusones A-D (compounds 1-4) and astataricusol A (5), together with one known shionane-type triterpene 6 were obtained from the roots and rhizomes of Aster tataricus L. f. Their structures were elucidated on the basis of spectroscopic data, mainly NMR and MS data. The absolute configurations of 1 and 4 was determined by single crystal X-ray diffraction and CD analysis. Compound 2 showed inhibitory activity on HBsAg secretion with an IC50 value of 23.5 μM, while 2 and 6 showed inhibitory activities on HBeAg secretion with IC50 values of 18.6 and 40.5 μM, and cytotoxicity on HepG 2.2.15 cells with CC50 values of 172.4 and 137.7 μM, respectively. Compounds 2 and 6 also exhibited inhibitory activities on HBV DNA replication with IC50 values of 2.7 and 30.7 μM, respectively.

Molecular characterization and differential expression studies of an oxidosqualene cyclase (OSC) gene of Brahmi (Bacopa monniera)

Triterpenoid saponins are the class of secondary metabolites, synthesized via isoprenoid pathway. Oxidosqualene cyclases (OSCs) catalyzes the cyclization of 2, 3-oxidosqualene to various triterpene skeletons, the first committed step in triterpenoid biosynthesis. A full-length oxidosqualene cyclase cDNA from Bacopa monniera (BmOSC) was isolated and characterized. The open reading frame (ORF) of BmOSC consists of 2,292 bp, encoding 764 amino acid residues with an apparent molecular mass of 87.62 kDa and theoretical pI 6.21. It contained four QxxxxxW motifs, one Asp-Cys-Thr-Ala-Glu (DCTAE) motif which is highly conserved among the triterpene synthases and another MWCYCR motif involved in the formation of triterpenoid skeletons. The deduced amino acid sequence of BmOSC shares 80.5 % & 71.8 % identity and 89.7 % & 83.5 % similarity with Olea europaea mixed amyrin synthase and Panax notoginseng dammarenediol synthase respectively. Phylogenetic analysis revealed that BmOSC is closely related with other plant OSCs. Quantitative real-time PCR (qRT-PCR) data showed that BmOSC is expressed in all tissues examined with higher expression in stem and leaves as compared to roots and floral parts.