Bioactive saponins and glycosides. VII. On the hypoglycemic principles from the root cortex of Aralia elata Seem.: structure related hypoglycemic activity of oleanolic acid oligoglycoside

New biofunctional effects of oleanane-type triterpene saponins

In the current review, we describe the novel biofunctional effects of oleanane-type triterpene saponins, including elatosides, momordins, senegasaponins, camelliasaponins, and escins, obtained from Aralia elata (bark, root cortex, young shoot), Kochia scoparia (fruit), Polygala senega var. latifolia (roots), Camellia japonica (seeds), and Aesculus hippocastanum (seeds), considering the following biofunctional activities: (1) inhibitory effects on elevated levels of blood alcohol and glucose in alcohol and glucose-loaded rats, respectively, (2) inhibitory effects on gastric emptying in rats and mice, (3) accelerative effects on gastrointestinal transit in mice, and (4) protective effects against gastric mucosal lesions in rats. In addition, we describe (5) suppressive effects of the extract and chakasaponins from Camellia sinensis (flower buds) on obesity based on inhibition of food intake in mice. The active saponins were classified into the following three types: (1) olean-12-en-28-oic acid 3-O-monodesmoside, (2) olean-12-ene 3,28-O-acylated bisdesmoside, and (3) acylated polyhydroxyolean-12-ene 3-O-monodesmoside. Furthermore, common modes of action, such as involvements of capsaicin-sensitive nerves, endogenous NO and PGs, and possibly sympathetic nerves, as well as common structural requirements, were observed. Based on our findings, a common mechanism of action might mediate the pharmacological effects of active saponins. It should be noted that the gastrointestinal tract is an important action site of saponins, and the role of the saponins in the gastrointestinal tract should be carefully considered.

Traditional uses, phytochemistry, pharmacology, toxicity and quality control of medicinal genus Aralia: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Aralia, which belongs to Araliaceae family, is mainly distributed in Asia, such as China, Japan and South Korea. It has a long medicinal history and is widely used in the treatment of various diseases, such as hepatitis, rheumatoid arthritis, bruises, lumps and carbuncles.

AIM OF THE STUDY

The purpose of this review is to systematically evaluate the traditional uses, phytochemistry, pharmacology, toxicity and quality control of main medicinal plants of Aralia, discusses the application of ethnic medicine, modern scientific research and the relationship between them, and put forward some suggestions to promote the further development and utilization of Aralia.

MATERIALS AND METHODS

The relevant information on Aralia was collected through electronic databases (PubMed, Web of Science, Science Direct, Springer, CNKI and Wanfang), Chinese herbal classics, Ph.D. and M.Sc. dissertations, Chinese Pharmacopoeia. Plant names were verified by "The Plant List" (http://www.theplantlist.org). The literature cited in this review can be traced back to 1878 to 2021.

RESULTS

More than 290 chemical constituents have been isolated from the genus Aralia, including triterpenoid saponins, terpenoids, organic acids, flavonoids, polyacetylenes, phenylpropanoids and other constituents. Pharmacological studies have shown that the extracts and compounds of Aralia have a wide range of pharmacological activities, including anti-inflammation, analgesic, anti-tumor, liver protection, protection of cardiovascular and nervous system, regulating substance metabolism, antibacterial, antiviral and antioxidation.

CONCLUSIONS

The genus Aralia is not only an excellent traditional herbal medicine, but also a source of bioactive molecules with good application prospects. However, the structure-activity relationship, in vivo activity and action mechanism of its bioactive components need to be further studied. In addition, more toxicological and quality control studies are essential to evaluate the efficacy and safety of Aralia as medicine.

Saponin toxicity as key player in plant defense against pathogens

Microbial pathogens attack every plant tissue, including leaves, roots, shoots, and flowers during all growth stages. Thus, they cause several diseases resulting in a plant's failure or loss of the whole crop in severe cases. To combat the pathogens attack, plants produce some biologically active toxic compounds known as saponins. The saponins are secondary metabolic compounds produced in healthy plants with potential anti-pathogenic activity and serve as potential chemical barriers against pathogens. Saponins are classified into two major groups the steroidal and terpenoid saponins. Here, we reported the significance of saponin toxins in the war against insect pests, fungal, and bacterial pathogens. Saponins are present in both cultivated (chilies, spinach, soybean, quinoa, onion, oat, tea, etc.) and wild plant species. As they are natural toxic constituents of plant defense, breeders and plant researchers aiming to boost plant imm unity should focus on transferring these compounds in cash crops.

Hypoglycemic property of triterpenoid saponin PFS isolated from Polyscias fruticosa leaves

This paper evaluated the inhibitory effect of 3-O-[β-d-glucopyranosyl-(1→4)-β-d-glucuronopyranosyl] oleanolic acid 28-O-β-d-glucopyranosyl ester (PFS), a major saponin isolated from Polyscias fruticosa leaves, on α-amylase and α-glucosidase, and its potential for reducing the postprandial blood glucose level in mice. In enzyme inhibition assays, PFS strongly inhibited porcine pancreas α-amylase and yeast α-glucosidase. Using the Lineweaver-Burk equation, we found that PFS inhibited porcine pancreas α-amylase in a mixed noncompetitive mode, and yeast α-glucosidase via noncompetitive inhibition. In the sucrose tolerance test, PFS at 100 mg/kg body weight significantly decreased the postprandial blood glucose level in mice fed a high-sucrose diet. These findings suggest that P. fruticosa leaves and their major saponin PFS can be used to prevent and treat diabetes and its complications.

Chronic Alcohol Exposure Induced Neuroapoptosis: Diminishing Effect of Ethyl Acetate Fraction from Aralia elata

An ethyl acetate fraction from Aralia elata (AEEF) was investigated to confirm its neuronal cell protective effect on ethanol-induced cytotoxicity in MC-IXC cells and its ameliorating effect on neurodegeneration in chronic alcohol-induced mice. The neuroprotective effect was examined by methylthiazolyldiphenyl-tetrazolium bromide (MTT) and 2',7'-dichlorodihydrofluorescein diacetate (DCF-DA) assays. As a result, AEEF reduced alcohol-induced cytotoxicity and oxidative stress. To evaluate the improvement of learning, memory ability, and spatial cognition, Y-maze, passive avoidance, and Morris water maze tests were conducted. The AEEF groups showed an alleviation of the decrease in cognitive function in alcohol-treated mice. Then, malondialdehyde (MDA) levels and the superoxide dismutase (SOD) content were measured to evaluate the antioxidant effect of AEEF in the brain tissue. Treatment with AEEF showed a considerable ameliorating effect on biomarkers such as SOD and MDA content in alcohol-induced mice. To assess the cerebral cholinergic system involved in neuronal signaling, acetylcholinesterase (AChE) activity and acetylcholine (ACh) content were measured. The AEEF groups showed increased ACh levels and decreased AChE activities. In addition, AEEF prevented alcohol-induced neuronal apoptosis via improvement of mitochondrial activity, including reactive oxygen species levels, mitochondrial membrane potential, and adenosine triphosphate content. AEEF inhibited apoptotic signals by regulating phosphorylated c-Jun N-terminal kinases (p-JNK), phosphorylated protein kinase B (p-Akt), Bcl-2-associated X protein (BAX), and phosphorylated Tau (p-Tau). Finally, the bioactive compounds of AEEF were identified as caffeoylquinic acid (CQA), 3,5-dicaffeoylquinic acid (3,5-diCQA), and chikusetsusaponin IVa using the UPLC-Q-TOF-MS system.

Oleanane-Type Saponins from the Roots of Ligulariopsis shichuana and Their α-Glucosidase Inhibitory Activities

Five new oleanane-type saponins, named ligushicosides A-E, and three known oleanane-type saponins were isolated from the roots of Ligulariopsis shichuana. Their structures were established by a combination of spectroscopic techniques, including 1D and 2D NMR and high resolution electrospray ionization mass spectroscopy (HR-ESI-MS). Furthermore, all isolates were evaluated for their yeast α-glucosidase inhibitory effects and exhibited potent inhibition against α-glucosidase, while compounds 1 and 2 showed excellent inhibitory activities. The 3-O-glycoside moiety in oleanane-type saponin is important for the α-glucosidase inhibitory effects.

Aralia elata var. mandshurica (Rupr. & Maxim.) J.Wen: An overview of pharmacological studies

PURPOSE

Aralia elata var. mandshurica (Rupr. & Maxim.) J.Wen syn. A. mandshurica Rupr. & Maxim is evaluated for its medicinal application. The aim of this study is to analyze pharmacological studies on A. elata var. mandshurica published until December 2015.

METHODS

The information regarding the chemistry, safety, effectiveness, and pharmacological and clinical effects of A. elata was systematically collected from the scientific literature through library catalogs; online services such as E-library.ru, Medline/PubMed, Scopus, Web of Science, and Google Scholar.

RESULTS

A. elata is often considered an example of a medicinal plant used in Chinese, Korean, and Japanese traditional medicine. However, the contemporary applications of Aralia in officinal medicine result primarily from a large number of pharmacological and clinical investigations carried out in the former USSR in the mid-20th century. Since the 1950s, medicinal preparations from radices of A. elata and radices of A. mandshurica have secured an established position within Russian/USSR medicine as evidenced by the inclusion of the drug in recent editions of the National Pharmacopoeia of the USSR and in the Register of Medicinal Preparations of Russia. Pharmacological studies on animals have shown that Aralia increases physical working capacity and affords a stress-protective effect against a broad spectrum of harmful factors including cold stress, immobilization, UV irradiation, and low air pressure. The phytoadaptogen exerts an effect on the central nervous, reproductive, immune, respiratory, and gastrointestinal systems; the metabolic syndrome including hypolipidemic and antidiabetic effects; and blood coagulation. Together with general properties of adaptogens, Aralia has its own specificity, which manifests in cardioprotective and antiarrhythmic activities. Studies on isolated organs, cells, and enzymes have revealed that Aralia preparations exhibit antioxidant activities and enhance sarcoplasmic reticulum Ca²⁺-ATPase activity, inhibit endoplasmic reticulum stress-associated apoptosis markers (GRP78, CHOP, Caspase-12, and JNK), and increase phosphorylation of STAT3 and Bcl2/Bax ratio; they also show cytotoxic activities against some tumor cell lines; affect NF-κB and PPARs activities; and regulate biosynthesis of pro-inflammatory cytokines and inflammation-related protein expression, tissue respiration, and oxygen consumption. In healthy subjects, Aralia increases mental performance, working capacity, and endurance of movement. Numerous clinical trials have shown the efficiency of Aralia preparations in patients with traumatic brain injury (accompanied with asthenic syndrome and neurotic reactions, depression, neurasthenia, and psychasthenia), neurological diseases (accompanied with astheno-depressive and astheno-hypochondriasis syndromes), myasthenia syndrome (accompanied with chronic post-influenza arachnoiditis), and arterial hypotension. Aralia tincture and "Saparal" are useful as antiviral remedies. Radioprotective properties of Aralia have been reported in pregnant women. Synergistic antiobesity effect was reported for the combination of A. mandshurica and Engelhardtia chrysolepis extracts and antidiabetic effect for the combination of Aralia and glipizide. Promising stress-relieving effects of Aralia are reported for professionals whose work requires a high level of attention. Its proposed ability to moderate stress-induced damage and dysfunction in the cardiovascular tissue might make Aralia the adaptogen of choice among patients with higher risk for cardiovascular diseases. Because Aralia extract administration appears to affect plasma glucose level and hepatic lipid accumulation and ameliorate hyperinsulinemia, it might also provide benefits and be the adaptogen of choice for patients with obesity and diabetes.

CONCLUSION

This review describes the considerable diversity of pharmacological effects of A. elata reported in numerous studies carried out in the former USSR and other countries, which have been confirmed over >47 years of use of the plant as an official medicinal remedy. The knowledge discussed in this review can be applied to the expansion of the use of this high-value plant in the pharmacotherapy of European and other countries and for the further discovery of new drugs based on the secondary metabolites of this plant. Modern approaches in mechanisms of action, including a study of gene expression profiling, suggest the most up-to-date challenges for the future research of Aralia.

Natural Triterpenoids for the Treatment of Diabetes Mellitus: A Review

Triterpenoids, an important group of secondary metabolites, are widely distributed in nature. Many triterpenoids have been found with potential therapeutic effect against diabetes mellitus. However, the use of triterpenoids for the treatment of diabetes has not been systematically discussed previously. This review summarized the anti-diabetic activity of natural triterpenoids reported since the late 1980s with the emphasis on the molecular mechanisms.

α-Amylase andα-Glucosidase Inhibitory Saponins fromPolyscias fruticosaLeaves

Three bisdesmosidic saponins 3-O-[β-D-glucopyranosyl-(1→4)-β-D-glucuronopyranosyl] oleanolic acid 28-O-β-D-glucopyranosyl ester (1), polyscioside D (2), and 3-O-{β-D-glucopyranosyl-(1→2)-[β-D-glucopyranosyl-(1→4)]-β-D-glucuronopyranosyl}oleanolic acid 28-O-β-D-glucopyranosyl-(1→2)-β-D-galactopyranosyl ester (3) were isolated from a methanol extract ofPolyscias fruticosa(L.) Harms leaves. Compound1was obtained as a main constituent and compound3was reported for the first time and named as polyscioside I. Saponin1inhibited porcine pancreasα-amylase and yeastα-glucosidase activities while2and3were inactive. Synergistic inhibitory effect onα-amylase was observed from the combination of low concentrations of1and acarbose. The findings suggest the use ofP. fruticosaand its major saponin1for the prevention and treatment of diabetes and its complications.

Medicinal plants of the Russian Pharmacopoeia; their history and applications

ETHNOPHARMACOLOGICAL RELEVANCE

Due to the location of Russia between West and East, Russian phytotherapy has accumulated and adopted approaches that originated in European and Asian traditional medicine. Phytotherapy is an official and separate branch of medicine in Russia; thus, herbal medicinal preparations are considered official medicaments. The aim of the present review is to summarize and critically appraise data concerning plants used in Russian medicine. This review describes the history of herbal medicine in Russia, the current situation and the pharmacological effects of specific plants in the Russian Pharmacopoeia that are not included in the European Pharmacopoeia.

MATERIALS AND METHODS

Based on the State Pharmacopoeia of the USSR (11(th) edition), we selected plant species that have not yet been adopted in Western and Central Europe (e.g., selected for inclusion in the European Pharmacopoeia) and systematically searched the scientific literature for data using library catalogs, the online service E-library.ru, and databases such as Medline/Pubmed, Scopus, and the Web of Science regarding species, effectiveness, pharmacological effects, and safety.

RESULTS

The Russian Federation follows the State Pharmacopoeia of the USSR (11(th) edition), which contains 83 individual plant monographs. Fifty-one of these plants are also found in the European Pharmacopoeia and have been well studied, but 32 plants are found only in the Pharmacopoeia of the USSR. Many articles about these medicinal plants were never translated in English, and much of the information collected by Russian scientists has never been made available to the international community. Such knowledge can be applied in future studies aimed at a safe, evidence-based use of traditional Russian medicinal plants in European and global phytopharmacotherapy as well as for the discovery of novel leads for drug development.

CONCLUSION

The review highlights the therapeutic potential of these Russian phytopharmaceuticals but also highlights cases where concern has been raised about product safety and tolerability, which would aid in supporting their safe use.

Inhibition of Increases in Blood Glucose and Serum Neutral Fat byMomordica charantiaSaponin Fraction

Focusing on a functional component of Momordica charantia, saponin, we investigated its effects on serum glucose and neutral fat levels. Saponin was extracted as a butanol-soluble fraction (saponin fraction) from hot blast-dried Momordica charantia powder. The disaccharidase-inhibitory activity and the pancreatic lipase-inhibitory activity of the saponin fraction were measured, and in vivo sugar- and lipid-loading tests were performed. The saponin fraction inhibited disaccharidase activity and elevation of the blood glucose level after sucrose loading. The fraction also markedly inhibited pancreatic lipase activity and elevation of the serum neutral fat level after corn oil loading. Based on these findings, the main active component related to the anti-diabetic effect of Momordica charantia is present in the butanol fraction, and it may be saponin. The blood glucose and serum neutral fat-lowering effects of Momordica charantia were closely associated with its inhibitory activity against disaccharidase and pancreatic lipase.

Antioxidation and antiglycation of Fagopyrum tataricum ethanol extract

Fagopyrum tataricum is used for the treatment of type 2 diabetes mellitus in Taiwan. The aim of this study was to evaluate the inhibitory effects of 75 % ethanol extract of buckwheat (EEB) and rutin on carbohydrate-metabolized enzymes, including α-amylase and α-glucosidase, which are related to hyperglycemia. The rutin dosage (40 μg/mL) was equivalent to that of EEB (200 μg/mL). In addition, the antioxidant and antiglycation activities of EEB and rutin were investigated. Results showed that both EEB and rutin exerted free radical (DPPH and ABTS) scavenging activity. They also attenuated protein glycation to lower the generation of advanced glycation end-products (AGEs) through the suppression of fructosamine and α-dicarbonyl compounds. Moreover, EEB and rutin also inhibited α-amylase and α-glucosidase activity. Taken together, these findings suggest that EEB and rutin may reduce oxidative stress, AGEs formation, and carbohydrate-metabolized enzymes hence EEB may use as protection agent in diabetic patients.

Oleanane-triterpenoids from Panax stipuleanatus inhibit NF-κB

In continuation of our research to find biological components from Panax stipuleanatus, four oleanane-type triterpenes (12 to 15) were isolated successively. Fifteen oleanane-type saponins (1 to 15) were evaluated for nuclear factor (NF)-κB activity using a luciferase reporter gene assay in HepG2 cells. Compounds 6 to 11 inhibited NF-κB, with IC₅₀ values between 3.1 to 18.9 μM. The effects on inducible nitric oxide synthase and cyclooxygenase-2 by compounds 8, 10, and 11 were also examined using reverse transcription-polymerase chain reaction. Three compounds (8, 10, and 11) inhibited NF-κB activity by reducing the concentration of inflammatory factors in HepG2 cells.

Potent spermicidal effect of oleanolic acid 3-beta-D-glucuronide, an active principle isolated from the plant Sesbania sesban Merrill

BACKGROUND

The spermicidal activity of oleanolic acid 3-β-D-glucuronide (OAG), an active principle isolated from root extracts of Sesbania sesban, was evaluated.

STUDY DESIGN

Under the Sander-Cramer test criteria, the sperm-immobilizing activity of OAG was studied using highly motile rat sperm. Sperm mortality and membrane integrity were assessed by supravital staining, hypo-osmotic swelling (HOS), transmission electron microscopy (TEM) and sperm membrane lipid peroxidation (LPO). In vitro microbicidal potential and hemolytic index of OAG were examined in Lactobacillus culture and rat red blood corpuscles (RBCs), respectively. Post-intravaginal OAG application, the in vivo contraceptive efficacy was evaluated in rats. Ames test determined the carcinogenic potential of OAG.

RESULTS

The minimum effective concentration (MEC) of OAG was 50 mcg/mL. More than 97% of the OAG-treated sperm lost their HOS responsiveness in a dose-dependent manner. TEM and LPO revealed that OAG affected the sperm membrane integrity. OAG declined fertility to zero, was nonmutagenic and was not harmful to lactobacillus.

CONCLUSION

OAG has significant spermicidal activity that may be explored further.

Isolation and tandem mass fragmentations of an anti-inflammatory compound from Aralia elata

One-step isolation of a saponin from Aralia elata was undertaken using high-speed countercurrent chromatography coupled with evaporative light scattering detection. A triterpenoid saponin, elatoside F, was purified with 96.8% purity using a two-phase-system comprising chloroform-methanol-water-isopropanol. The yield was 35.0 mg from 348.2 mg of the enriched saponin fraction. In vitro anti-inflammatory study demonstrated that elatoside F inhibited lipopolysaccharide-induced nitric oxide production, as well as nuclear factor kappaB activation, in a dose-dependent manner. Two types of mass ionization technique were compared on elatoside F to investigate characteristic fragmentation patterns. MALDI-TOF tandem mass spectrometric fragmentation patterns of sodiated ions provided structural information on glycosidic cleavages and on extensive cross-ring cleavages. Electrospray ionization multiple-stage tandem mass fragmentation of both sodiated and lithiated ions could provide information on glycosidic cleavages. All observed tandem mass fragmentation spectra provided valuable elatoside F structural information when unknown samples from crude extracts are under screening by mass spectrometry.

Oleanolic acid and related derivatives as medicinally important compounds

Oleanolic acid has been isolated from chloroform extract of Olea ferruginea Royle after removal of organic bases and free acids. The literature survey revealed it to be biologically very important. In this review the biological significance of oleanolic acid and its derivatives has been discussed. The aim of this review is to update current knowledge on oleanolic acid and its natural and semisynthetic analogs, focussing on its cytotoxic, antitumer, antioxidant, anti-inflamatory, anti-HIV, acetyl cholinesterase, alpha-glucosidase, antimicrobial, hepatoprotective, anti-inflammatory, antipruritic, spasmolytic activity, anti-angiogenic, antiallergic, antiviral and immunomodulatory activities. We present in this review, for the first time, a compilation of the most relevant scientific papers and technical reports of the chemical, pre-clinical and clinical research on the properties of oleanolic acid and its derivatives.

Water extract of Aralia elata prevents cataractogenesis in vitro and in vivo

The water extract of Aralia elata (Aralia extract) has been used in Korean traditional medicine to treat diabetes mellitus. Here, we investigated the aldose reductase inhibitory activity, antioxidant activity and anticataract capacity of Aralia extract using various experimental systems. To determine its aldose reductase inhibitory activity and its antioxidant effect, we used rat lens homogenates. Rat lens cultures and a rat model were used to observe anticataract activity. The resulting IC50 value of Aralia extract in vitro as an aldose reductase inhibitor was 11.3 microg/ml and as an antioxidant was 25.1 microg/ml. Rat lenses in media containing 20 mM xylose developed a distinctly opaque ring in 9h, and treatment with Aralia extract at a concentration of 1mg/ml lowered lens opacity by 36.4 and 31.3% after 24 and 48 h, respectively. In vivo experiments were performed with streptozotocin (STZ) induced diabetic rats. The diabetic control animals developed cataracts at 11 weeks after STZ injection, while oral Aralia extract administered at 300 and 600 mg/kg body weight for 11 weeks reduced cataract formation by 15 and 12%, respectively. The present study shows that Aralia extract inhibits aldose reductase and acts in vitro as an antioxidant, and suggests that these activities have a preventive effect on cataractogenesis in xylose containing lens organ cultures and in in vivo in STZ induced diabetic rats.

Araloside A, an Antiulcer Constituent from the Root Bark of Aralia elata

Araloside A, a potent inhibitor of gastric lesion and ulcer formation in rats, was isolated from the root bark of Aralia elata through a bioassay-guided separation procedure. The compound exhibited significant reduction of HCl.ethanol-induced gastric lesions and aspirin-induced gastric ulcers at oral doses of 50 and 100 mg/kg, respectively. These activities are comparable to those of cimetidine.

Saponins and Other Constituents from the Leaves of Aralia elata

A new triterpenoid saponin, together with five known saponins, were isolated from the nonpolar n-hexane fraction of the leaves of Aralia elata. The structure of the new saponin, durupcoside C, was elucidated as hederagenin 3-O-beta-D-glucopyranosyl(1-->3)-beta-D-glucopyranosyl(1-->3)-alpha-L-arabinopyranoside on the basis of spectroscopic analysis. The known saponins were characterized as 3-O-alpha-L-rhamnopyranosyl(1-->2)-alpha-L-arabinopyranosyl hederagenin 28-O-beta-D-xylopyranosyl(1-->6)-beta-D-glucopyranosyl ester, hederagenin 3-O-beta-D-glucopyranosyl(1-->3)-alpha-L-rhamnopyranosyl(1-->2)-alpha-L-arabinopyranoside, oleanolic acid 3-O-beta-D-glucopyranosyl(1-->3)-alpha-L-rhamnopyranosyl(1-->2)-alpha-L-arabinopyranoside, hederagenin 3-O-alpha-L-rhamnopyranosyl(1-->2)-alpha-L-arabinopyranoside (alpha-hederin), and hederagenin 3-O-beta-D-glucopyranosyl(1-->3)-alpha-L-arabinopyranoside (collinsonidin). In addition, two known lipids, Arisaema glyceride 3 and ceramide mixtures were also isolated and characterized. Collinsonidin and two known lipids were isolated for the first time from this plant.

Structural requirements of flavonoids and related compounds for aldose reductase inhibitory activity

The methanolic extracts of several natural medicines and medicinal foodstuffs were found to show an inhibitory effect on rat lens aldose reductase. In most cases, flavonoids were isolated as the active constituents by bioassay-guided separation, and among them, quercitrin (IC(50)=0.15 microM), guaijaverin (0.18 microM), and desmanthin-1 (0.082 microM) exhibited potent inhibitory activity. Desmanthin-1 showed the most potent activity, which was equivalent to that of a commercial synthetic aldose reductase inhibitor, epalrestat (0.072 microM). In order to clarify the structural requirements of flavonoids for aldose reductase inhibitory activity, various flavonoids and related compounds were examined. The results suggested the following structural requirements of flavonoid: 1) the flavones and flavonols having the 7-hydroxyl and/or catechol moiety at the B ring (the 3',4'-dihydroxyl moiety) exhibit the strong activity; 2) the 5-hydroxyl moiety does not affect the activity; 3) the 3-hydroxyl and 7-O-glucosyl moieties reduce the activity; 4) the 2-3 double bond enhances the activity; 5) the flavones and flavonols having the catechol moiety at the B ring exhibit stronger activity than those having the pyrogallol moiety (the 3',4',5'-trihydroxyl moiety).

Absolute stereostructure of potent alpha-glucosidase inhibitor, Salacinol, with unique thiosugar sulfonium sulfate inner salt structure from Salacia reticulata

A most potent alpha-glucosidase inhibitor named salacinol has been isolated from an antidiabetic Ayurvedic traditional medicine, Salacia reticulata WIGHT, through bioassay-guided separation. The absolute stereostructure of salacinol was determined on the basis of chemical and physicochemical evidence, which included the alkaline degradation of salacinol to 1-deoxy-4-thio-D-arabinofuranose and the X-ray crystallographic analysis, to be the unique spiro-like configuration of the inner salt comprised of 1-deoxy-4-thio-D-arabinofuranosyl sulfonium cation and 1'-deoxy-D-erythrosyl-3'-sulfate anion. Salacinol showed potent inhibitory activities on several alpha-glucosidases, such as maltase, sucrase, and isomaltase, and the inhibitory effects on serum glucose levels in maltose- and sucrose-loaded rats (in vivo) were found to be more potent than that of acarbose, a commercial alpha-glucosidase inhibitor.

Medicinal flowers. III. Marigold. (1): hypoglycemic, gastric emptying inhibitory, and gastroprotective principles and new oleanane-type triterpene oligoglycosides, calendasaponins A, B, C, and D, from Egyptian Calendula officinalis

The methanolic extract and its 1-butanol-soluble fraction from the flowers of Calendula officinalis were found to show a hypoglycemic effect, inhibitory activity of gastric emptying, and gastroprotective effect. From the 1-butanol-soluble fraction, four new triterpene oligoglycosides, calendasaponins A, B, C, and D, were isolated, together with eight known saponins, seven known flavonol glycosides, and a known sesquiterpene glucoside. Their structures were elucidated on the basis of chemical and physicochemical evidence. The principal saponin constituents, glycosides A, B, C, D, and F, exhibited potent inhibitory effects on an increase in serum glucose levels in glucose-loaded rats, gastric emptying in mice, and ethanol- and indomethacin-induced gastric lesions in rats. Some structure-activity relationships are discussed.

The bioactivity of saponins: triterpenoid and steroidal glycosides

Triterpenoid and steroidal glycosides, referred to collectively as saponins, are bioactive compounds present naturally in many plants. They have considerable potential as pharmaceutical and/or nutraceutical agents in natural or synthetic form. Saponins, from a variety of sources, have been shown to have hypocholesterolemic, anti-coagulant, anticarcinogenic, hepatoprotective, hypoglycemic, immunomodulatory, neuroprotective, anti-inflammatory and anti-oxidant activity. This paper reviews saponin research of the last decade, focussing on developments in understanding their mechanism of action and structure-activity relationships. Virtually all of this work has used animal and in vitro models. To date there are very few human data.

Five saponins from the root bark of Aralia elata

Five saponins, 3-O-[beta-D-glucopyranosyl (1-->2)-[beta-D-glucopyranosyl (1-->3)]-beta-D-glucopyranosyl]-oleanolic acid 28-O-beta-D-glucopyranosyl ester (aralia-saponin V), 3-O-[beta-D-glucopyranosyl (1-->2)-[beta-D-glucopyranosyl (1-->3)]-beta-D-glucopyranosyl]-echinocystic acid 28-O-beta-D-glucopyranosyl ester (aralia-saponin VI), 3-O-beta-D-glucopyranosyl (1-->2)-[beta-D-glucopyranosyl (1-->3)]-beta-D-glucopyranosyl]-hederagenin 28-O-beta-D-glucopyranosyl ester (aralia-saponin VII), 3-O-[beta-D-glucopyranosyl-(1-->3)-beta-D-glucopyranosyl-(1-->3)-[beta-D-glucopyranosyl-(1-->2)]-beta-D-glucopyranosyl]-caulophyllogenin 28-O-beta-D-glucopyranosyl ester (aralia-saponin VIII), 3-O-[beta-D-glucopyranosyl (1-->2)-[beta-D-glucopyranosyl(1-->3)]-alpha-L-arabinopyranosyl]-hederagenin 28-O-beta-D-glucopyranosyl ester (aralia-saponin IX), were isolated from the root bark of Aralia elata (Miq.) Seem., together with four known compounds. Their structures were determined on the basis of chemical and spectroscopic methods.

Bioactive oleanolic acid saponins and other constituents from the roots of Viguiera decurrens

The bisdesmoside oleanolic acid saponin, 3-0-(methyl-beta-D-glucuronopyranosiduronoate)-28-0-beta-D-glucopyranosyl-oleanolate along with nine known compounds (two diterpenic acids, one chromene, three triterpenes, one steroidal glycoside, and two monodesmoside oleanolic acid saponins), were obtained from Viguiera decurrens roots. The chemical structure of the bisdesmoside oleanolic saponin was determined by chemical and NMR spectral evidence. A mixture of monodesmoside saponins displayed cytotoxic activity against P388 and COLON cell lines (ED50= 2.3 and 3.6 microg/ml, respectively). Two of the known compounds showed insecticidal activity against the Mexican bean beetle larvae (Epilachna varivestis).

Structure-related inhibitory activity of oleanolic acid glycosides on gastric emptying in mice

We examined the effects of various oleanolic acid oligoglycosides obtained from traditional herbs on gastric emptying in non-nutrient meal- or nutrient meal-loaded mice. Test samples were given orally to fasted mice 0.5 h before loading of test meals. Oleanolic acid 3-O-monodesmosides [oleanolic acid 3-O-glucuronide (3, 12.5-50 mg/kg), momordin Ic (4, 25 and 50 mg/kg), momordin I (6, 12.5-50 mg/kg), and 28-O-deglucosyl-chikusetsusaponins IV (8, 12.5-50 mg/kg) and V (10, 50 mg/kg)] were found to show inhibitory effects on gastric emptying in 1.5% CMC-Na test meal-loaded mice. 4, 6, and 8 also inhibited gastric emptying in mice given 40% glucose test meal, milk test meal, and 60% ethanol test meal. 3 inhibited gastric emptying in mice given milk test meal or 60% ethanol test meal, but lacked significant inhibition in 40% glucose test meal-loaded mice. 10 (50 mg/kg) also slightly inhibited gastric emptying in milk test meal-loaded mice, but lacked the significant inhibition in mice given 40% glucose or 60% ethanol test meal. Whereas oleanolic acid 3,28-0-bisdesmosides [momordin IIc (5), chikusetsusaponins IV (7) and V (9)], oleanolic acid 28-O-monodesmoside [compound O (2)], and their common aglycon [oleanolic acid (1)] showed no such effects at dose of 50 mg/kg. 28-O-Deglucosyl-chikusetsusaponin V (10) showed a little inhibition in these experiments. These results indicate that both the 3-O-monodesmoside structure and 28-carboxyl group were confirmed to be essential for such activity, and the 28-ester glucoside moiety and 2'-O-beta-D-glucopyranoside moiety reduce the activity.

Mode of action of escins Ia and IIa and E,Z-senegin II on glucose absorption in gastrointestinal tract

We examined the mode of action of escins Ia (1) and IIa (2) and E,Z-senegin II (3) for the inhibitory effect on the increase in serum glucose levels in oral glucose-loaded rats. Although 1-3 inhibited the increase in serum glucose levels in oral glucose-loaded rats, these compounds did not lower serum glucose levels in normal or intraperitoneal glucose-loaded rats, or alloxan-induced diabetic mice. Furthermore, 1-3 suppressed gastric emptying in rats, and also inhibited glucose uptake in the rat small intestine in vitro. These results indicated that 1-3 given orally have neither insulin-like activity nor insulin-releasing activity. Compounds 1-3 inhibited glucose absorption by suppressing the transfer of glucose from the stomach to the small intestine and by inhibiting the glucose transport system at the small intestinal brush border.