Improvement and prediction of the extraction parameters of lupeol and stigmasterol metabolites of Melia azedarach with response surface methodology.

BACKGROUND: Melia azedarach is known as a medicinal plant that has wide biological activities such as analgesic, antibacterial, and antifungal effects and is used to treat a wide range of diseases such as diarrhea, malaria, and various skin diseases. However, optimizing the extraction of valuable secondary metabolites of M. azedarach using alternative extraction methods has not been investigated. This research aims to develop an effective, fast, and environmentally friendly extraction method using Ultrasound-assisted extraction, methanol and temperature to optimize the extraction of two secondary metabolites, lupeol and stigmasterol, from young roots of M. azedarach using the response surface methodology. METHODS: Box-behnken design was applied to optimize different factors (solvent, temperature, and ultrasonication time). The amounts of lupeol and stigmasterol in the root of M. azedarach were detected by the HPLC-DAD. The required time for the analysis of each sample by the HPLC-DAD system was considered to be 8 min. RESULTS: The results indicated that the highest amount of lupeol (7.82 mg/g DW) and stigmasterol (6.76 mg/g DW) was obtained using 50% methanol at 45 °C and ultrasonication for 30 min, and 50% methanol in 35 °C, and ultrasonication for 30 min, respectively. Using the response surface methodology, the predicted conditions for lupeol and stigmasterol from root of M. azedarach were as follows; lupeol: 100% methanol, temperature 45 °C and ultrasonication time 40 min (14.540 mg/g DW) and stigmasterol 43.75% methanol, temperature 34.4 °C and ultrasonication time 25.3 min (5.832 mg/g DW). CONCLUSIONS: The results showed that the amount of secondary metabolites lupeol and stigmasterol in the root of M. azedarach could be improved by optimizing the extraction process utilizing response surface methodology.

Combinatorial Metabolic Engineering for Improving Betulinic Acid Biosynthesis in Saccharomyces cerevisiae.

Betulinic acid (BA) is a lupane-type triterpenoid with potent anticancer and anti-HIV activities. Its great potential in clinical applications necessitates the development of an efficient strategy for BA synthesis. This study attempted to achieve efficient BA biosynthesis in Saccharomyces cerevisiae using systematic metabolic engineering strategies. First, a de novo BA biosynthesis pathway in S. cerevisiae was constructed, which yielded a titer of 14.01 ± 0.21 mg/L. Then, by enhancing the BA synthesis pathway and dynamic inhibition of the competitive pathway, a greater proportion of the metabolic flow was directed toward BA synthesis, achieving a titer of 88.07 ± 5.83 mg/L. Next, acetyl-CoA and NADPH supply was enhanced, which increased the BA titer to 166.43 ± 1.83 mg/L. Finally, another BA synthesis pathway in the peroxisome was constructed. Dual regulation of the peroxisome and cytoplasmic metabolism increased the BA titer to 210.88 ± 4.76 mg/L. Following fed-batch fermentation process modification, the BA titer reached 682.29 ± 8.16 mg/L. Overall, this work offers a guide for building microbial cell factories that are capable of producing terpenoids with efficiency.

Plant In Vitro Culture Factories for Pentacyclic Triterpenoid Production.

Pentacyclic triterpenoids are a diverse subclass of naturally occurring terpenes with various biological activities and applications. These compounds are broadly distributed in natural plant resources, but their low abundance and the slow growth cycle of plants pose challenges to their extraction and production. The biosynthesis of pentacyclic triterpenoids occurs through two main pathways, the mevalonic acid (MVA) pathway and the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway, which involve several enzymes and modifications. Plant in vitro cultures, including elicited and hairy root cultures, have emerged as an effective and sustainable system for pentacyclic triterpenoid production, circumventing the limitations associated with natural plant resources. Bioreactor systems and controlling key parameters, such as media composition, temperature, light quality, and elicitor treatments, have been optimized to enhance the production and characterization of specific pentacyclic triterpenoids. These systems offer a promising bioprocessing tool for producing pentacyclic triterpenoids characterized by a low carbon footprint and a sustainable source of these compounds for various industrial applications.

Activation of NRF2 by celastrol increases antioxidant functions and prevents the progression of osteoarthritis in mice.

Excessive oxidative stress impairs cartilage matrix metabolism balance, significantly contributing to osteoarthritis (OA) development. Celastrol (CSL), a drug derived from Tripterygium wilfordii, has recognized applications in the treatment of cancer and immune system disorders, yet its antioxidative stress mechanisms in OA remain underexplored. This study aimed to substantiate CSL's chondroprotective effects and unravel its underlying mechanisms. We investigated CSL's impact on chondrocytes under both normal and inflammatory conditions. In vitro, CSL mitigated interleukin (IL)-1ß-induced activation of proteinases and promoted cartilage extracellular matrix (ECM) synthesis. In vivo, intra-articular injection of CSL ameliorated cartilage degeneration and mitigated subchondral bone lesions in OA mice. Mechanistically, it was found that inhibiting nuclear factor erythroid 2-related factor 2 (NRF2) abrogated CSL-mediated antioxidative functions and exacerbated the progression of OA. This study is the first to elucidate the role of CSL in the treatment of OA through the activation of NRF2, offering a novel therapeutic avenue for arthritis therapy.

Chromosome-level genome assembly of Prunella vulgaris L. provides insights into pentacyclic triterpenoid biosynthesis.

Prunella vulgaris is one of the bestselling and widely used medicinal herbs. It is recorded as an ace medicine for cleansing and protecting the liver in Chinese Pharmacopoeia and has been used as the main constitutions of many herbal tea formulas in China for centuries. It is also a traditional folk medicine in Europe and other countries of Asia. Pentacyclic triterpenoids are a major class of bioactive compounds produced in P. vulgaris. However, their biosynthetic mechanism remains to be elucidated. Here, we report a chromosome-level reference genome of P. vulgaris using an approach combining Illumina, ONT, and Hi-C technologies. It is 671.95 Mb in size with a scaffold N50 of 49.10 Mb and a complete BUSCO of 98.45%. About 98.31% of the sequence was anchored into 14 pseudochromosomes. Comparative genome analysis revealed a recent WGD in P. vulgaris. Genome-wide analysis identified 35 932 protein-coding genes (PCGs), of which 59 encode enzymes involved in 2,3-oxidosqualene biosynthesis. In addition, 10 PvOSC, 358 PvCYP, and 177 PvUGT genes were identified, of which five PvOSCs, 25 PvCYPs, and 9 PvUGTs were predicted to be involved in the biosynthesis of pentacyclic triterpenoids. Biochemical activity assay of PvOSC2, PvOSC4, and PvOSC6 recombinant proteins showed that they were mixed amyrin synthase (MAS), lupeol synthase (LUS), and ß-amyrin synthase (BAS), respectively. The results provide a solid foundation for further elucidating the biosynthetic mechanism of pentacyclic triterpenoids in P. vulgaris.

Betulinic acid inhibits the proliferation of human laryngeal carcinoma cells through reactive oxygen species-mediate mitochondrial apoptotic pathway.

Betulinic acid (BA), a natural pentacyclic triterpene, was extracted from the white birch tree, Triphyophyllum peltatum and the jujube tree. In a variety of human cancer cell lines, this substance displays anticancer properties. In this study, we examined how BA works to inhibit human laryngeal cancer growth. We discovered that BA minimally exhibited cytotoxicity in normal cells (human normal cell line GES-1), while remarkably inhibiting viability of AMC-HN-8, TU212, HEp-2 and M4e cells in a concentration-dependent manner. In AMC-HN-8 cancer cells, BA induced apoptosis, activated caspase-3/9/PARP, significantly reduced mitochondrial membrane potential (MMP), increased the expression of cytochrome C in the cytoplasm, transported Bax to the mitochondria, increased the production of reactive oxygen species (ROS), and the ROS scavenger N-acetylcysteine can reduce apoptosis. All data showed that BA triggered apoptosis via the mitochondrial pathway, in which ROS production was likely involved. The findings support the development of BA as a viable drug for the treatment of human laryngeal carcinoma.

[Research progress of celastrol on the prevention and treatment of metabolic associated fatty liver disease].

Metabolic associated fatty liver disease (MAFLD) is a liver disease with hepatocyte steatosis caused by metabolic disorders, which is closely related to obesity, diabetes, metabolic dysfunction, and other factors. Its pathological process changes from simple steatosis, liver inflammation to non-alcoholic steatohepatitis (NASH), and then leads to liver fibrosis, cirrhosis, and liver cancer. At present, no specific therapeutics are available for treatment of MAFLD targeting its etiology. Celastrol is the main active component of the traditional Chinese medicine Celastrus orbiculatus Thunb. In recent years, it has been found that celastrol shows important medicinal value in regulating lipid metabolism, reducing fat and weight, and protecting liver, and then ameliorates MAFLD. This article reviews the related research progress of celastrol in the prevention and treatment of MAFLD, so as to provide a reference for the comprehensive development and utilization of celastrol.

Radical Scavenging, Anti-Inflammatory, and Hepatoprotective Activities of Pentacyclic Triterpene isolated from Rosa webbiana.

INTRODUCTION: Rosa webbiana (RW) Wall Ex. Royle is used in traditional medicine in Pakistan for the treatment of several diseases including jaundice. To date, only neuroprotective potential of the plant has been evaluated. OBJECTIVE: The current study was designed to isolate bioactive compound(s) and investigate its possible radical scavenging, anti-inflammatory and hepatoprotective activities. METHODS: Column chromatography was done to isolate compounds from the chloroform fraction of RW. The compound was characterized by mass spectrometry, 1H-NMR, and 2D-NMR spectroscopy. Radical scavenging activity was assessed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydrogen peroxide (H2O2) assays, while anti-inflammatory potential was evaluated via xylene-induced ear edema and carrageenan-induced paw edema models. For hepatoprotection, CCl4-induced model in mice was used. RESULTS: A triterpene compound (3α, 21ß-dihydroxy-olean-12-ene) was isolated from RW fruits (ARW1). The compound exhibited DPPH and H2O2 scavenging activities 61 ± 1.31% and 66 ± 0.48% respectively at 500 µg/ml. ARW1 (at 50 mg/kg) exhibited 62.9 ± 0.15% inhibition of xylene-induced ear edema and 66.6 ± 0.17% carrageenan-induced paw edema in mice. In CCl4-induced hepatotoxic mice, ARW1 significantly countered elevation in alanine transaminase (ALT), alkaline phosphatase (ALP), total bilirubin (T.B), and reduction in total protein (T.P) levels. Liver histomorphological study supported the serum biochemical profile for hepatoprotection. Moreover, ARW1 significantly attenuated the toxic changes in body and liver weight induced by CCl4. CONCLUSION: The compound ARW1 exhibited anti-radical, anti-inflammatory and hepatoprotective effects. The anti-inflammatory and hepatoprotective activities may be attributed to anti-oxidant potential of the compound.

Asiatic acid increased locomotor and head width by inducing brain-derived neurotrophic factor in intrauterine hypoxia-exposed zebrafish.

Background: Hypoxia ischemia leads to abnormal behavior and growth. Prenatal hypoxia also decreases brain adaptive potential, which can cause fatal effects such as cell death. Asiatic acid (AA) in Centella asiatica is a neuroprotector through antioxidant and anti-inflammatory activities. Aim: This study aimed to analyze the effect of AA as a neuroprotector against hypoxia during intrauterine development on locomotor activity, head width, and brain-derived neurotrophic factor (BDNF) expression. Methods: The true experimental laboratory research used a posttest control-only design. Zebrafish embryos (Danio rerio) aged 0-2 dpf (days postfertilization) were exposed to hypoxia with oxygen levels reaching 1.5 mg/l. Then, AA was administered at successive concentrations, namely, 0.36, 0.72, and 1.45 µg/ml, at 2 hpf (hours postfertilization), 3, 6, and 9 dpf. Head width, velocity activity, and BDNF expression were observed. Results: Intrauterine hypoxia significantly decreased head width, velocity rate, and BDNF expression (<0.001). Administration of AA at all concentrations and age 9 dpf to zebrafish larvae with intrauterine hypoxia exposure increased head width ( p < 0.0001), velocity (p < 0.05), and relative mRNA expression of BDNF (p < 0.05). Conclusion: AA is potentially neuroprotective to the brain in zebrafish larvae exposed to hypoxia during intrauterine development.

Combination Therapy with Resveratrol and Celastrol Using Folic Acid-Functionalized Exosomes Enhances the Therapeutic Efficacy of Sepsis.

Overactivated macrophages are a prominent feature of many inflammatory and autoimmune diseases, including sepsis. Attention and regulation of macrophages activity is of great significance for sepsis treatment. Herein, this study shows that folic acid-functionalized exosomes accumulate in the lung of septic mice and specifically target inflammatory macrophages. Therefore, FA-functionalized exosomes co-loaded with resveratrol (an anti-inflammatory polyphenol) and celastrol (an immunosuppressive pentacyclic triterpenoid; FA-Exo/R+C), which exhibit powerful anti-inflammatory and immunosuppressive activities against LPS-stimulated macrophages in vitro by regulating NF-κB and ERK1/2 signaling pathways, are designed. Encouraged by these positive data, the efficacy of FA-Exo/R+C is systematically investigated in an LPS-induced mouse sepsis model. FA-Exo/R+C shows striking therapeutic benefits in terms of attenuated cytokine storm, reduced acute lung injury, and increased survival of septic mice by inhibiting the inflammation and proliferation of proinflammatory M1 macrophages. Importantly, multiple administrations of FA-Exo/R+C significantly enhance and prolong the protective effect, and resist rechallenge to LPS. Collectively, the strategy of co-delivering drugs combination through functionalized exosomes offers a new avenue for sepsis treatment.

Discovery of Novel Pentacyclic Triterpene Acid Amide Derivatives as Excellent Antimicrobial Agents Dependent on Generation of Reactive Oxygen Species.

Developing new agricultural bactericides is a feasible strategy for stopping the increase in the resistance of plant pathogenic bacteria. Some pentacyclic triterpene acid derivatives were elaborately designed and synthesized. In particular, compound A22 exhibited the best antimicrobial activity against Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas axonopodis pv. citri (Xac) with EC50 values of 3.34 and 3.30 mg L-1, respectively. The antimicrobial mechanism showed that the compound A22 induced excessive production and accumulation of reactive oxygen species (ROS) in Xoo cells, leading to a decrease in superoxide dismutase and catalase enzyme activities and an increase in malondialdehyde content. A22 also produced increases in Xoo cell membrane permeability and eventual cell death. In addition, in vivo experiments showed that A22 at 200 mg L-1 exhibited protective activity against rice bacterial blight (50.44%) and citrus canker disease (84.37%). Therefore, this study provides a paradigm for the agricultural application of pentacyclic triterpene acid.

Enhanced acetate utilization for value-added chemicals production in Yarrowia lipolytica by integration of metabolic engineering and microbial electrosynthesis.

The limited supply of reducing power restricts the efficient utilization of acetate in Yarrowia lipolytica. Here, microbial electrosynthesis (MES) system, enabling direct conversion of inward electrons to NAD(P)H, was used to improve the production of fatty alcohols from acetate based on pathway engineering. First, the conversion efficiency of acetate to acetyl-CoA was reinforced by heterogenous expression of ackA-pta genes. Second, a small amount of glucose was used as cosubstrate to activate the pentose phosphate pathway and promote intracellular reducing cofactors synthesis. Third, through the employment of MES system, the final fatty alcohols production of the engineered strain YLFL-11 reached 83.8 mg/g dry cell weight (DCW), which was 6.17-fold higher than the initial production of YLFL-2 in shake flask. Furthermore, these strategies were also applied for the elevation of lupeol and betulinic acid synthesis from acetate in Y. lipolytica, demonstrating that our work provides a practical solution for cofactor supply and the assimilation of inferior carbon sources.

Natural products of pentacyclic triterpenoids: from discovery to heterologous biosynthesis.

Covering: up to 2022Pentacyclic triterpenoids are important natural bioactive substances that are widely present in plants and fungi. They have significant medicinal efficacy, play an important role in reducing blood glucose and protecting the liver, and have anti-inflammatory, anti-oxidation, anti-fatigue, anti-viral, and anti-cancer activities. Pentacyclic triterpenoids are derived from the isoprenoid biosynthetic pathway, which generates common precursors of triterpenes and steroids, followed by cyclization with oxidosqualene cyclases (OSCs) and decoration via cytochrome P450 monooxygenases (CYP450s) and glycosyltransferases (GTs). Many biosynthetic pathways of triterpenoid saponins have been elucidated by studying their metabolic regulation network through the use of multiomics and identifying their functional genes. Unfortunately, natural resources of pentacyclic triterpenoids are limited due to their low content in plant tissues and the long growth cycle of plants. Based on the understanding of their biosynthetic pathway and transcriptional regulation, plant bioreactors and microbial cell factories are emerging as alternative means for the synthesis of desired triterpenoid saponins. The rapid development of synthetic biology, metabolic engineering, and fermentation technology has broadened channels for the accumulation of pentacyclic triterpenoid saponins. In this review, we summarize the classification, distribution, structural characteristics, and bioactivity of pentacyclic triterpenoids. We further discuss the biosynthetic pathways of pentacyclic triterpenoids and involved transcriptional regulation. Moreover, the recent progress and characteristics of heterologous biosynthesis in plants and microbial cell factories are discussed comparatively. Finally, we propose potential strategies to improve the accumulation of triterpenoid saponins, thereby providing a guide for their future biomanufacturing.

Celastrol acts as a new histone deacetylase inhibitor to inhibit colorectal cancer cell growth via regulating macrophage polarity.

The tumorigenesis and progression of colorectal cancer are closely related to the tumor microenvironment, especially inflammatory response. Inhibitors of histone deacetylase (HDAC) have been reported as epigenetic regulators of the immune system to treat cancer and inflammatory diseases and our results demonstrated that Celastrol could act as a new HDAC inhibitor. Considering macrophages as important members of the tumor microenvironment, we further found that Celastrol could influence the polarization of macrophages to inhibit colorectal cancer cell growth. Specially, we used the supernatant of HCT116 and SW480 cells to induce Ana-1 cells in vitro and chose the spontaneous colorectal cancer model APCmin/+ mice as an animal model to validate in vivo. The results indicated that Celastrol could reverse the polarization of macrophages from M2 to M1 through impacting the colorectal tumor microenvironment both in vitro and in vivo. Furthermore, using bioinformatics analysis, we found that Celastrol might mechanistically polarize the macrophages through MAPK signaling pathway. In conclusion, our findings identified that Celastrol as a new HDAC inhibitor and suggested that Celastrol could modulate macrophage polarization, thus inhibiting colorectal cancer growth, which may provide some novel therapeutic strategies for colorectal cancer.

Research progress of celastrol on the prevention and treatment of metabolic associated fatty liver disease / 生理学报

Metabolic associated fatty liver disease (MAFLD) is a liver disease with hepatocyte steatosis caused by metabolic disorders, which is closely related to obesity, diabetes, metabolic dysfunction, and other factors. Its pathological process changes from simple steatosis, liver inflammation to non-alcoholic steatohepatitis (NASH), and then leads to liver fibrosis, cirrhosis, and liver cancer. At present, no specific therapeutics are available for treatment of MAFLD targeting its etiology. Celastrol is the main active component of the traditional Chinese medicine Celastrus orbiculatus Thunb. In recent years, it has been found that celastrol shows important medicinal value in regulating lipid metabolism, reducing fat and weight, and protecting liver, and then ameliorates MAFLD. This article reviews the related research progress of celastrol in the prevention and treatment of MAFLD, so as to provide a reference for the comprehensive development and utilization of celastrol.

Pentacyclic triterpenes modulate farnesoid X receptor expression in colonic epithelial cells: Implications for colonic secretory function.

The nuclear bile acid receptor, farnesoid X receptor (FXR), is an important regulator of intestinal and metabolic function. Previous studies suggest that pentacyclic triterpenes (PCTs), a class of plant-derived bioactive phytochemical, can modulate FXR activity and may therefore offer therapeutic benefits. Here, we investigated the effects of a prototypical PCT, hederagenin (HG), on FXR expression, activity, and antisecretory actions in colonic epithelial cells. T84 cells and murine enteroid-derived monolayers were employed to assess HG effects on FXR expression and activity in colonic epithelia. We measured mRNA levels by qRT-PCR and protein by ELISA and immunoblotting. Transepithelial Cl- secretion was assessed as changes in short circuit current in Ussing chambers. We determined HG treatment (5-10 µM) alone did not induce FXR activation but significantly increased expression of the receptor, both in T84 cells and murine enteroid-derived monolayers. This effect was accompanied by enhanced FXR activity, as assessed by FGF-15/19 induction in response to the synthetic, GW4064, or natural FXR agonist, chenodeoxycholic acid. Effects of HG on FXR expression and activity were mimicked by another PCT, oleanolic acid. Furthermore, we found FXR-induced downregulation of cystic fibrosis transmembrane conductance regulator Cl- channels and inhibition of transepithelial Cl- secretion were enhanced in HG-treated cells. These data demonstrate that dietary PCTs have the capacity to modulate FXR expression, activity, and antisecretory actions in colonic epithelial cells. Based on these data, we propose that plants rich in PCTs, or extracts thereof, have excellent potential for development as a new class of "FXR-targeted nutraceuticals".

Additional effects of simultaneous treatment with C14-Cblin and celastrol on the clinorotation-induced rat L6 myotube atrophy.

Two novel reagents, N-myristoylated Cbl-b inhibitory peptide (C14-Cblin) and celastrol, a quinone methide triterpene, are reported to be effective in preventing myotube atrophy. The combined effects of C14-Cblin and celastrol on rat L6 myotubes atrophy induced by 3D-clinorotation, a simulated microgravity model, was investigated in the present study. We first examined their effects on expression in atrogenes. Increase in MAFbx1/atrogin-1 and MuRF-1 by 3D-clinorotation was significantly suppressed by treatment with C14-Cblin or celastrol, but there was no additive effect of simultaneous treatment. However, celastrol significantly suppressed the upregulation of Cbl-b and HSP70 by 3D-clinorotation. Whereas 3D-clinorotation decreased the protein level of IRS-1 in L6 myotubes, C14-Cblin and celastrol inhibited the degradation of IRS-1. C14-Cblin and celastrol promoted the phosphorylation of FOXO3a even in microgravity condition. Simultaneous administration of C14-Cblin and celastrol had shown little additive effect in reversing the impairment of IGF-1 signaling by 3D-clinorotation. While 3D-clinorotation-induced marked oxidative stress in L6 myotubes, celastrol suppressed 3D-clinorotation-induced ROS production. Finally, the C14-Cblin and celastrol-treated groups were inhibited decrease in L6 myotube diameter and increased the protein content of slow-twitch MyHC cultured under 3D-clinorotation. The simultaneous treatment of C14-Cblin and celastrol additively prevented 3D-clinorotation-induced myotube atrophy than single treatment. J. Med. Invest. 69 : 127-134, February, 2022.

Mitochondria-targeted polymer-celastrol conjugate with enhanced anticancer efficacy.

Celastrol, a natural triterpene extracted from traditional Chinese medicine, shows anticancer effects on various cancer cells. However, its poor water-solubility, short plasma half-life, and high systemic toxicity impede its applications in vivo, necessitating a stable drug delivery system to overcome these critical drawbacks. We present here a block copolymer, poly(2-(N-oxide-N,N-dimethylamino)ethyl methacrylate)-block-poly(2-hydroxyethyl methacrylate) (OPDMA-HEMA), as the carrier for celastrol delivery. The amphiphilic polymer-celastrol conjugate can self-assemble into nanoparticles in aqueous solutions. The OPDMA outer shell confers the nanoparticles with improved pharmacokinetics and efficient mitochondria targeting capacity, and profoundly potentiates celastrol's induction of immunogenic cell death, which collectively contribute to the enhanced therapeutic effects of celastrol in vivo. This mitochondria-targeted polymer-celastrol conjugate may promise the applications of celastrol in cancer treatment.

A comprehensive study of celastrol metabolism in vivo and in vitro using ultra-high-performance liquid chromatography coupled with hybrid triple quadrupole time-of-flight mass spectrometry.

Celastrol has attracted great attention owing to its anti-arthritis, antioxidant, and anticancer activities. Nevertheless, its metabolism in vivo (rats) and in vitro (rat liver microsomes and intestinal flora) has not been comprehensively characterized. In this study, ultra-high-performance liquid chromatography coupled with hybrid triple quadrupole time-of-flight mass spectrometry was used as a rapid and sensitive approach for studying the metabolism of celastrol in vivo and in vitro. A total of 43 metabolites were identified and characterized. These include 26 metabolites in vivo, and 28 metabolites in vitro (nine metabolites in rat liver microsomes and 24 metabolites in rat intestinal flora). Additionally, the celastrol-biotransformation capacity of the intestinal tract was confirmed to exceed that of the liver. Furthermore, the metabolic profile of celastrol is summarised. The information obtained from this study may provide a basis for understanding the pharmacological mechanisms of celastrol and will be beneficial for clinical applications.

Probing the functions of friedelane-type triterpene cyclases from four celastrol-producing plants.

Triterpenes are among the most diverse plant natural products, and their diversity is closely related to various triterpene skeletons catalyzed by different 2,3-oxidosqualene cyclases (OSCs). Celastrol, a friedelane-type triterpene with significant bioactivities, is specifically distributed in higher plants, such as Celastraceae species. Friedelin is an important precursor for the biosynthesis of celastrol, and it is synthesized through the cyclization of 2,3-oxidosqualene, with the highest number of rearrangements being catalyzed by friedelane-type triterpene cyclases. However, the molecular mechanisms underlying the catalysis of friedelin production by friedelane-type triterpene cyclases have not yet been fully elucidated. In this study, transcriptome data of four celastrol-producing plants from Celastraceae were used to identify a total of 21 putative OSCs. Through functional characterization, the friedelane-type triterpene cyclases were separately verified in the four plants. Analysis of the selection pressure showed that purifying selection acted on these OSCs, and the friedelane-type triterpene cyclases may undergo weaker selective restriction during evolution. Molecular docking and site-directed mutagenesis revealed that changes in some amino acids that are unique to friedelane-type triterpene cyclases may lead to variations in catalytic specificity or efficiency, thereby affecting the synthesis of friedelin. Our research explored the functional diversity of triterpene synthases from a multispecies perspective. It also provides some references for further research on the relative mechanisms of friedelin biosynthesis.