Secondary metabolites of genus Astragalus: Structure and biological activity

Potent telomerase activators from a novel sapogenin via biotransformation utilizing Camarosporium laburnicola, an endophytic fungus

BACKGROUND

Cycloartane-type triterpenoids possess important biological activities, including immunostimulant, wound healing, and telomerase activation. Biotransformation is one of the derivatization strategies of natural products to improve their bioactivities. Endophytic fungi have attracted attention in biotransformation studies because of their ability to perform modifications in complex structures with a high degree of stereospecificity.

RESULTS

This study focuses on biotransformation studies on cyclocephagenol (1), a novel cycloartane-type sapogenin from Astragalus species, and its 12-hydroxy derivatives (2 and 3) to obtain new telomerase activators. Since the hTERT protein levels of cyclocephagenol (1) and its 12-hydroxy derivatives (2 and 3) on HEKn cells were found to be notable, biotransformation studies were carried out on cyclocephagenol and its 12-hydroxy derivatives using Camarosporium laburnicola, an endophytic fungus isolated from Astragalus angustifolius. Later, immunoblotting and PCR-based ELISA assay were used to screen starting compounds and biotransformation products for their effects on hTERT protein levels and telomerase activation. All compounds showed improved telomerase activation compared to the control group.

CONCLUSIONS

As a result of biotransformation studies, seven new metabolites were obtained and characterized, verifying the potential of C. laburnicola as a biocatalyst. Additionally, the bioactivity results showed that this endophytic biocatalyst is unique in transforming the metabolites of its host to afford potent telomerase activators.

Overexpression of chalcone isomerase A gene in Astragalus trigonus for stimulating apigenin

Apigenin is one of the most studied flavonoids and is widely distributed in the plant kingdom. Apigenin exerts important antioxidant, antibacterial, antifungal, antitumor activities, and anti-inflammatory effects in neurological or cardiovascular disease. Chalcone isomerase A (chiA) is an important enzyme of the flavonoid biosynthesis pathway. In order to enhance the apigenin production, the petunia chi A gene was transformed for Astragalus trigonus. Bialaphos survived plants were screened by PCR, dot blot hybridization and RT-PCR analysis. Also, jasmonic acid, salicylic acid, chitosan and yeast extract were tested to evaluate their capacity to work as elicitors for apigenin. Results showed that yeast extract was the best elicitor for induction of apigenin with an increase of 3.458 and 3.9 fold of the control for calli and cell suspension culture, respectively. Transformed cell suspension showed high apigenin content with a 20.17 fold increase compared to the control and 6.88 fold more than the yeast extract treatment. While, transformed T1 calli derived expressing chiA gene produced apigenin 4.2 fold more than the yeast extract treatment. It can be concluded that the highest accumulation of apigenin was obtained with chiA transgenic cell suspension system and it can be utilized to enhancement apigenin production in Astragalus trigonus.

Hyphenated LC-ABTS•+ and LC-DAD-HRMS for simultaneous analysis and identification of antioxidant compounds in Astragalus emarginatus Labill. extracts

The compounds in leaf and stem extracts of Astragalus emarginatus Labill. (AEL), a plant species used in traditional Lebanese medicine, were investigated for antioxidant properties. First, the activity of various extracts was assessed using the Trolox equivalent antioxidant capacity, oxygen radical absorption capacity, and 2,2-diphenyl-1-picryl-hydrazyl-hydrate assays. The extract obtained using 30% ethanol showed the greatest activity. The antioxidant compounds in this extract were screened using a hyphenated high-performance liquid chromatography-2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonate) radical (ABTS^·+) system before being separated by ultra-high-performance liquid chromatography and identified using high-resolution mass spectrometry and ultra-violet-visible diode array detection. Approximately 40 compounds were identified. Hydroxycinnamates (caffeic, ferulic, and p-coumaric acid derivatives) and flavonoids (quercetin, luteolin, apigenin, and isorhamnetin derivatives) were the two main categories of the identified compounds. The active compounds were identified as caffeic acid derivatives and quercetin glycosides. In addition, the catechol moiety was shown to be key to antioxidant activity. This study showed that AEL is a source of natural antioxidants, which may explain its medicinal use.

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Antioxidant activity of 30% ethanol extract from Astragalus emarginatus Labill was shown by an on-line HPLC-ABTS ^•+ assay.

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Caffeic acid derivatives and quercetin glycosides were responsible for antioxidant activity.

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Approximately forty compounds were tentatively identified using UHPLC-DAD-HRMS.

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Structure-activity investigations showed that the catechol moiety is central to the detected antioxidant activity.

Antiproliferative and antitumour activity of saponins from Astragalus glycyphyllos on myeloid Graffi tumour

ETHNOPHARMACOLOGICAL RELEVANCE

Astragalus glycyphyllos L. has been extensively used in Bulgarian folk medicine as an antihypertensive, diuretic, anti-inflammatory, anti-tumour, in cases of cardiac insufficiency, renal inflammation, calculosis, etc. AIM OF THE STUDY: To evaluate the possible in vitro/in vivo anti-proliferative/anti-tumour activity of a purified saponins' mixture (PSM) obtained from the plant.

MATERIALS AND METHODS

Viability and proliferative activity of the Graffi myeloid tumour cells was assessed by MTT test. The morphological alterations were visualized and analysed by fluorescent microscopy after intravital double staining. An in vivo model of Graffi tumour bearing hamsters was used to examine the influence of PSM on transplantability, tumour growth, survival and mortality as well as to observe pathomorphological changes.

RESULTS

Graffi tumour cells were sensitive to purified saponins' mixture after 24 and 48 h treatment. The treatment induced a statistically significant decrease of the viability/proliferation of the Graffi tumour cells. These effects were concentration- and time-dependent. Fluorescent microscopy studies showed that these antiproliferative effects were connected to the induction of apoptosis. The in vivo study showed the presence of a stromal component, single mononuclear cells in the stroma. Multiple incorrect mitotic figures were observed in the tumour tissue from the control group. Well-formed stroma with accumulation of mononuclear cells and mitotic cells were found in the group, treated with PSM. The tumour weight was decreased in the group, treated with PMS.

CONCLUSION

The results indicate that PSM exhibited in vitro/in vivo antiproliferative/anti-tumour effects.

Phytochemistry and cardiovascular protective effects of Huang-Qi (Astragali Radix)

Huang-Qi (Astragali Radix) is an herbal tonic widely used in China and many other countries. It is derived from the roots of Astragalus membranaceus and A. membranaceus var. mongholicus and shows potent cardiovascular protective effects. In this article, we comprehensively reviewed 189 small molecules isolated from the two Astragalus species and discussed the interspecies chemical differences. Moreover, we summarized the pharmacological activities and mechanisms of action of Huang-Qi and its major bioactive compounds for the treatment of cardiovascular diseases. This review covers 171 references published between February 1983 and March 2020.

Characterization of astragaloside I-IV based on the separation of HPTLC from Pleurotus ostreatus cultivated with Astragalus

In this study, total saponins were extracted from Pleurotus ostreatus cultivated with Astragalus as one of organic culture substrates. High Performance Thin Layer Chromatography (HPTLC) assay showed total saponins could be separated effectively, and four kinds of spots were identified as AG I, AG II, AG III, and AG IV, respectively. FTIR spectra based on HPTLC separation assay showed the saponin characteristic groups including -OH, C-H, C=O, and the glycoside linkaged to sapogenin group C-O-C, suggesting the four kinds of spots belonged to cycloartane-type triterpene saponins. The primary mass spectra of precursor ion (HPTLC-ESI-MS) assay further proved the main composition of four kinds of spots was AG I-IV, respectively. Physical properties, including the detection of specific rotation and melting point, revealed the separation of high-purity saponin monomer by HPTLC. HPTLC-dual wavelength spectrodensitometric method detection showed that content of astragaloside I-IV was ranged from 0.2 to 0.5 mg/g, and the total astragalosides contents attained to 1.397 mg/g, indicating P. ostreatus could bioaccumulate astragalosides from Astragalus. These results demonstrated the characterization of astragalosides based on the separation of HPTLC was effective, and supported to consider astragalosides-enriched P. ostreatus as functional edible fungus for food and medical applications. PRACTICAL APPLICATION: Currently, the consumption of enriched foods has become common and continues to increase due to urgent demanding for foods with high nutritional value. Pleurotus ostreatus is a functional edible fungus, which not only can produce secondary metabolites, but can enrich bioactive ingredients. Astragalosides have a wide range of biological activities, especially currently being tested as cardioprotective agent. In this study, P. ostreatus was cultivated through adding Astragalus into culture substrates, which realized massive enrichment of astragalosides. Astragalosides-enriched P. ostreatus as functional edible fungus could be extensively used in food and medical areas, especially for the prevention of cardiovascular diseases.

A review of traditional uses, phytochemistry and pharmacology of the genus Indigofera

ETHNOPHARMACOLOGICAL RELEVANCE

Indigofera is the third-largest genus in the family of Fabaceae, with approximately 750 species. It is distributed across all tropical regions. Indigofera species are widely employed in traditional medicine all around the world, against many ailments. Thus, based on these medicinal properties, various investigations have been undertaken in order to appraise the pharmacological activities and the chemical composition of these species. A recent paper provides a summary of the phytochemistry and pharmacology of the genus Indigofera. Consequently, this review is a continuation of this previous study by updating some data and adding information about the phylogeny and traditional uses of the genus.

AIM OF THE STUDY

To provide an overview of the phylogeny, traditional uses, phytochemistry, pharmacology and toxicity of the genus Indigofera, and to identify the remaining gaps and thus supply a basis for further investigations.

MATERIALS AND METHODS

A review of the literature was performed by consulting scientific databases such as 'ScienceDirect', 'PubMed', 'Google Scholar' and 'SpringerLink' and using the keyword Indigofera.

RESULTS

Over 60 Indigofera species are reported in traditional medicine. The uses depend on the country and the species, but similarities have been noticed. Indeed, treatments of gastrointestinal disorders, inflammatory conditions and pain, skin ailments, and respiratory and infectious diseases are recurring. Phytochemical studies have led to the identification of more than 200 compounds, notably flavonoids and terpenoids. Many pharmacological activities have been demonstrated, particularly antimicrobial, cytotoxic and anti-inflammatory activities, and thus allowed to assert most of the traditional uses of the genus. Some active compounds have been isolated and have shown remarkable therapeutic potential, like the alkaloid indirubin, which is currently being clinically trialed.

CONCLUSIONS

The data on the genus Indigofera are extensive, but gaps still remain. Indeed, some promising species have not been assessed for their phytochemistry and/or pharmacology and thus remain unexplored. Moreover, relatively few active compounds have been isolated and tested for their biological activity, and studies to explain their mechanism of action are nearly inexistent. Furthermore, some pharmacological studies have inappropriate methodologies that make the results difficult to interpret. Consequently, further in-depth and relevant research is required to supplement the knowledge on this wide-ranging genus and to confirm its reported therapeutic potential.

Flavonoid Glycosides from Endemic Bulgarian Astragalus aitosensis (Ivanisch.)

Astragalus is a very interesting plant genus, well-known for its content of flavonoids, triterpenes and polysaccharides. Its secondary metabolites are described as biologically active compounds showing several activities, e.g., immunomodulating, antibacterial, antiviral and hepatoprotective. This inspired us to analyze the Bulgarian endemic A. aitosensis (Ivanisch.) to obtain deeper information about its phenolic components. We used extensive chromatographic separation of A. aitosensis extract to obtain seven phenolic compounds (1-7), which were identified using combined LC-MS and NMR spectral studies. The 1D and 2D NMR analyses and HR-MS allowed us to resolve the structures of known compounds 5-7 as isorhamnetin-3-O-robinobioside, isorhamnetin-3-O-(2,6-di-O-α-rhamno-pyranosyl-β-galactopyranoside), and alangiflavoside, respectively, and further comparison of these spectral data with available literature helped us with structural analysis of newly described flavonoid glycosides 1-4. These were described in plant source for the first time.

Mineral and Phytochemical Profiles and Antioxidant Activity of Herbal Material from Two Temperate Astragalus Species

Only a few species of the large Astragalus genus, widely used for medicinal purposes, have been thoroughly studied for phytochemical composition. The aim of our research was to investigate the rarely studied species A. glycyphyllos L. and A. cicer L. for the distribution of mineral elements and phytochemicals in whole plants at two growth stages and in morphological fractions. We also investigated the capacity of the plant extracts to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and to chelate ferrous ions. Chemical composition and antioxidant properties depended on species, maturity, and plant part. Herbal material of A. glycyphyllos was richer in Fe, total phenolics, and flavonoids, whereas extracts of A. cicer showed a higher antioxidant activity. Young plants had more isoflavones, showed greater quenching of DPPH radicals, and exhibited better mineral profiles than flowering plants. Among plant parts, leaves were the most valuable plant material according to most characteristics investigated. Isoflavone concentration in flowers was lower than in leaves and stems. None of the Astragalus samples contained detectable amounts of the alkaloid swainsonine. The study demonstrates the potential of plant material from two Astragalus species as a valuable source of iron, phenolic substances including isoflavones, free-radical scavengers, and Fe²⁺ chelators for pharmaceutical use.

Unusual alkaloids of the highland species Astragalus cryptanthus Wedd. (Fabaceae)

Two unusual caprolactam alkaloids, 3-(dimethylamino)hexahydro-2H-azepin-2-one and 3-(methylamino)-hexahydro-2H-azepin-2-one, were isolated from the aerial parts of Astragalus cryptanthus Wedd.; their structures were unambiguously determined based on data from extensive 1D and 2D NMR, GC-MS and FT-IR spectroscopic analyses. This is the first report of this alkaloid type in the genus Astragalus.

Bioactive fractions from the pasture legume Biserrula pelecinus L. have an anti-methanogenic effect against key rumen methanogens

Methanogenic archaea (methanogens) are common inhabitants of the mammalian intestinal tract. In ruminants, they are responsible for producing abundant amounts of methane during digestion of food, but selected bioactive plants and compounds may inhibit this activity. Recently, we have identified that, Biserrula pelecinus L. (biserrula) is one such plant and the current study investigated the specific anti-methanogenic activity of the plant. Bioassay-guided extraction and fractionation, coupled with in vitro fermentation batch culture were used to select the most bioactive fractions of biserrula. The four fractions were then tested against five species of methanogens grown in pure culture. Fraction bioactivity was assessed by measuring methane production and amplification of the methanogen mcrA gene. Treatments that showed bioactivity were subcultured in fresh broth without the bioactive fraction to distinguish between static and cidal effects. All four fractions were active against pure cultures, but the F2 fraction was the most consistent inhibitor of both methane production and cell growth, affecting four species of methanogens and also producing equivocal-cidal effects on the methanogens. Other fractions had selective activity affecting only some methanogens, or reducing either methane production or methanogenic cell growth. In conclusion, the anti-methanogenic activity of biserrula can be linked to compounds contained in selected bioactive fractions, with the F2 fraction strongly affecting key rumen methanogens. Further study is required to identify the specific plant compounds in biserrula that are responsible for the anti-methanogenic activity. These findings will help devise novel strategies to control methanogen populations and activity in the rumen, and consequently contribute in reducing greenhouse gas emissions from ruminants.

Flavonoids from the Genus Astragalus: Phytochemistry and Biological Activity

Flavonoids, the most common plant polyphenols are widely distributed in every species and possess a broad range of pharmacological activities. The genus Astragalus is the largest in the Fabaceae family with more than 2,500 species spread. They are known to contain different metabolites such as flavonoids, saponins, and polysaccharides. Plants from the genus have been used in the traditional medicine of many countries for centuries. This paper is focused on the large group of flavonoid compounds. Details on structure as well as information about the pharmacological properties of flavonoids, isolated from Astragalus species have been discussed. This review is based on publications until the first half of 2014 and includes also the results from our phytochemical investigations of the genus.

Experimental liver protection of n-butanolic extract of Astragalus monspessulanus L. on carbon tetrachloride model of toxicity in rat

OBJECTIVE

To investigate the hepatoprotective potential of n-butanolic extract of Astragalus monspessulanus L. (EAM) against in-vitro/in-vivo carbon tetrachloride (CCl4)-induced liver damage in rats. Silymarin was used as a positive control.

METHODS AND RESULTS

The in-vitro experiments were carried out in primary isolated rat hepatocytes first incubated with CCl4 (86 µmol/l). Hepatic injury was discerned by a decrease in cell viability and cell glutathione (GSH) levels, an increase in lactate dehydrogenase leakage into the medium, and an elevation in malondialdehyde (MDA) quantity. Cell pre-incubation with EAM (1 µg/ml and 10 µg/ml) significantly ameliorated the CCl4-induced liver damage. In-vivo rats were challenged orally with CCl4 (10% solution in olive oil) alone and after 7 days pre-treatment with EAM (100 mg/kg body weight per day, oral gavage). CCl4 damage was judged by an increased production of MDA, depletion of cell GSH, and a decrease in cell antioxidant defense system. EAM pre-treatment normalizes the activities of the antioxidant enzymes and the levels of GSH and MDA. These data are supported by the histopathological examination.

CONCLUSION

These results indicate that EAM has a similar significant protective effect, in vitro and in vivo, against CCl4 induced hepatotoxicity in rat as silymarin.This may be due to its antioxidant and membrane stabilizing properties.

Evaluation of the immunomodulatory properties in mice and in vitro anti-inflammatory activity of cycloartane type saponins from Astragalus species

ETHNOPHARMACOLOGICAL RELEVANCE

Astragalus roots are used to treat leukemia and for their wound healing properties in Southeast Anatolia-Turkey.

MATERIALS AND METHODS

In vivo studies to investigate the effects of two Astragalus saponins were carried out on the immune response cytokines by using six to eight weeks old male Swiss albino mice. The production of IL-1β, TGF-1β, TNF-α, IL-2, IL-4 and IFN-γ cytokines was determined by ELISA. The spleen and lymph nodes, isolated from the mice subjects, were analyzed to realize induction of the surface antigen productions for IL-2Rα (CD25) and CD69. In addition, their effects on the targets of inflammation such as NF κB, iNOS and NAG-1 were investigated in cell-based assays.

RESULTS

The results suggested that AST VII and Mac B had positive effect on Th1 cytokine release (IL-2 and IFN-γ), and suppression on Th2 cytokine production (IL-4). The immunohistochemical results exhibited induction of both IL-Rα (CD25) and CD69 surface receptors justifying the Th1 cytokine release. The compounds did not affect NF-κB or NAG-1 activity but iNOS activity was inhibited by Mac B with an IC(50) of 156 μg/ml.

CONCLUSIONS

The results show that Ast VII and Mac B create powerful immunoregulatory effects without the stimulation of inflammatory cytokines in mice, and have no significant effect on the inflammatory cellular targets in vitro.

Composition of volatile organic compounds in flowers of Astragalus sahendi

A hydrodistillation sampling method, coupled to gas chromatography-mass spectrometry, was used in monitoring the volatile organic compounds in flowers of Astragalus sahendi. Accordingly, a total of 48 compounds were recognised, which were united by their terpenoid or aliphatic skeletons and low molecular weight. Above all, the significant presence of some insect-favoured terpenoid compounds, such as farnesol, cis- and trans-geraniol, alpha-bisabolol, nerolidol isomer, alpha-terpineol, alpha-terpinolene and thymol was significant. These findings confer a better understanding of pollination processes in the giant genus Astragalus. Furthermore, the results add to an increasing quantity of data corroborating the ecologic and evolutionary correlation between the floral bioactive compounds of plant species and their special types of pollinators.

Effect of purified saponin mixture from Astragalus corniculatus on enzyme- and non-enzyme-induced lipid peroxidation in liver microsomes from spontaneously hypertensive rats and normotensive rats

The aim of the following study was to evaluate the effect of a purified saponin mixture (PSM), isolated from Astragalus corniculatus Bieb. (Fabaceae), on enzyme-induced and non-enzyme-induced lipid peroxidation (LPO), in liver microsomes from spontaneously hypertensive rats (SHRs) - strain Okamoto Aoki, as compared to normotensive Wistar rats (NTRs). The enzyme-induced lipid peroxidation was performed by incubating rat liver microsomes with carbonetetrachloride (CCl(4)) in the presence of NADPH. In nonenzyme-induced LPO, the microsomes were incubated with a solution of iron sulphate and ascorbinic acid (Fe(2+)/AA). The effect of PSM (196.5 microg/ml) was assessed at 20 minutes' incubation time. MDA, a product of LPO, was measured spectrophotometrically. The results of our study showed that the initial MDA quantity in SHRs was significantly higher, than in NTRs. The incubation of the microsomes from both strains with PSM (196.5 microg/ml), resulted in significant reduction of MDA level, by 25% in SHRs. In NTRs, the formation of MDA was unchanged. In enzyme-induced LPO model, PSM significantly decreased the formation of MDA, by 55% in NTRs and by 35% in SHRs, compared to the respective control groups. In the model of non-enzyme induced LPO, PSM significantly decreased the formation of MDA by 95% in NTRs and practically restored it to the control level. The MDA quantity in SHR's microsomes was reduced by 25%. According to the results of this experiment we could conclude that PSM, isolated from Astragalus corniculatus, shows antioxidant activity both in SHRs and NTRs and the effect in NTRs is more pronounced.

Immunorestoration and augmentation of mitogen lymphocyte response in Graffi tumor bearing hamsters by purified saponin mixture from Astragalus corniculatus

Investigations on the effect of purified saponin mixture (PSM) obtained from the aerial parts of Astragalus corniculatus Bieb. (Fabaceae) on mitogen response of the spleen cells in Graffi tumor bearing (GTBH) and healthy hamsters were reported. The saponin mixture in a doses of 50mg/kg b.w. was injected i.p. 4 times starting simultaneously with implantation of tumor cells. Stimulation indices to phytohemagglutinine (PHA) and lipopolysaccharide (LPS) of lymphocytes in spleens of tumor bearing hamsters (TBH) were significantly decreased during the whole period of the observation. It was established that PSM stimulated the functions of spleen cells in Graffi-TBH, resulting in increased mitogen response to PHA and LPS. The stimulation was better expressed in healthy PSM-treated hamsters. The proliferation response of spleen lymphocytes to PSM was also found. PSM did not change the in vitro proliferation ability of Graffi tumor cells. The results obtained proved the immunostimulating and immunorestorating activity of PSM on the T- and B-spleen cells in healthy and GTBH hamsters, as well as the proliferative response of it to PSM.

Triterpenoids

This review covers the isolation and structure determination of triterpenoids including squalene derivatives, lanostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleannes, friedelanes, ursanes, hopanes, isomalabaricanes and saponins. The literature from January to December 2002 is reviewed and 221 references are used.