Antidiabetic principles of natural medicines. III. Structure-related inhibitory activity and action mode of oleanolic acid glycosides on hypoglycemic activity

Hypoglycemic effects of mountain caviar extract and inhibitory mechanism of saponins, including momordin Ic, on glucose absorption

Mountain caviar is a fruit of Kochia scoparia that contains momordin Ic as a major saponin constituent. Its extract (MCE) has been shown to suppress blood glucose elevations in the human oral glucose tolerance test (OGTT) as well as increases in blood glucose in OGTT, gastric emptying (GE), and glucose incorporation in the small intestine in rats. However, the effects of MCE and momordin Ic on glucose absorption in mice and these action mechanisms have not been examined for more than 2 decades. Therefore, we herein investigated the effects of MCE, its saponin fraction, and momordin Ic on blood glucose elevations in mice. Mouse blood glucose elevation tests were performed on carbohydrate-loaded mice. The mountain caviar saponin fraction significantly delayed blood glucose elevations in glucose-, sucrose-, and soluble starch-loaded mice. In glucose-loaded mice, the saponin fraction, MCE, and momordin Ic significantly suppressed rapid glucose elevations after glucose loading, but not sucrose loading. A mouse GE study was performed by loading with glucose and phenolphthalein solution. Momordin Ic and MCE strongly suppressed mouse GE. Intestinal glucose absorption was evaluated by the incorporation of 2-deoxyglucose (2-DG) into Caco-2 cell layers and mouse duodenum wall vesicles. The results obtained showed that momordin Ic inhibited the incorporation of 2-DG into Caco-2 cells and mouse duodenum vesicles. Collectively, these results suggest that MCE, particularly the principal saponin, momordin Ic, preferably suppressed glucose-induced blood glucose elevations and delayed carbohydrate-induced glucose elevations in mice. The underlying mechanism was found to involve the suppression of GE and intestinal glucose absorption.

Evaluation on the traditional safe use of Kochiae Fructus oriented by antioxidant properties and oral safety of its ethanolic extract

Kochiae Fructus (KF) is a traditional Chinese medicine, which has been used to delay aging and treat inflammation, such as rubella, eczema, cutaneous pruritus, etc. In order to fully understand the traditional medicinal value of KF, we evaluated the antioxidant properties and oral safety of its ethanolic extract. Considering flavonoids and phenolics in medicinal plants generally have strong antioxidant activity, we firstly detected the total flavonoids and phenolics contents of KFEE and its fractions. Secondly, we evaluated the antioxidant activities of KFEE and its fractions. Finally, we evaluated the oral safety of KFEE by the acute and 28-day subacute toxicities. The n-butanol fraction (ENBF) possessed the highest phenolics and flavonoids with values of 77.30 ± 3.17 mg gallic acid equivalents/g and 228.81 ± 7.56 mg rutin equivalents/g, respectively. The results of antioxidant tests showed that ENBF possessed potent antioxidant ability. Among them, the high antioxidation capacity observed in ENBF could be attributed to its rich content of flavonoids and phenolics. The results of toxicological studies showed that the LD50 value of KFEE was 6000 mg/kg BW, and the no observed adverse effect level (NOAEL) of KFEE was 600 mg/kg BW. According to the standards of the American Academy of Sciences for the classification of toxic substances, KFEE can be classified as practically non-toxic substance, which provided valuable evidence for the oral safety of KF as a natural aging delay medicine.

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.

Holistic Overview of the Phytoconstituents and Pharmacological Activities of Egyptian Riverhemp [Sesbania sesban (L.) Merr.]: A Review

Background: Sesbania sesban (L.) Merr. (Family: Fabaceae), commonly known as Egyptian riverhemp, is a well-known plant widely distributed through Egypt, the rest of Africa and Asia. S. sesban leaves have been traditionally used as an anthelmintic, demulcent, purgative, and anti-inflammatory agent in the treatment of eczema, in addition to its agricultural uses. Objective: The aim of this review is to present a comprehensive account of the isolated constituents from S. sesban leaves, along with the correlation between those constituents and the reported biological activities. Methods: This search was performed using SciFinder, Google, Google Scholar, and CrossRef websites using the following keywords: “ Sesbania sesban,” “ Sesbania aegyptiaca,” “Egyptian riverhemp,” “phytochemistry,” “phytochemical constituents,” “isolation,” “steroids,” “triterpenoids,” “saponins,” “coumarins,” “lipoidal contents,” “pharmacological properties,” “biological activities,” “therapeutic uses,” and “review.” Results: S. sesban leaves exhibited several therapeutic potentials such as antioxidant, antimicrobial, antiviral, anthelmintic, molluscicidal, antifertility, anti-inflammatory, antidiabetic, antihyperlipidemic, anticancer, antianxiety, and mosquito repellant properties. An updated chemical study of S. sesban leaves has provided a variety of essential metabolites belonging to different chemical classes including steroids, triterpenoids, saponins, flavonoids, coumarins, lipids, and other miscellaneous compounds. The correlations between biological activities and phytoconstituents are discussed. Conclusion: This article represents an updated comprehensive evaluation of the phytochemical and biological studies of S. sesban leaves.

Triterpenoids from Kochiae Fructus: Glucose Uptake in 3T3-L1 Adipocytes and α-Glucosidase Inhibition, In Silico Molecular Docking

In this study, three new triterpenes (1-3) and fourteen known triterpenoids (4-17) were isolated from the ethanol extract of Kochiae Fructus, and their structures were elucidated by analyzing UV, IR, HR-ESI-MS, 1D, and 2D NMR spectroscopic data. Among them, compounds 6, 8, and 11-17 were isolated for the first time from this plant. The screening results of the glucose uptake experiment indicated that compound 13 had a potent effect on glucose uptake in 3T3-L1 adipocytes at 20 μM. Meanwhile, compounds 3, 9 and 13 exhibited significant inhibitory activities against α-glucosidase, with IC₅₀ values of 23.50 ± 3.37, 4.29 ± 0.52, and 16.99 ± 2.70 µM, respectively, and their α-glucosidase inhibitory activities were reported for the first time. According to the enzyme kinetics using Lineweaver-Burk and Dixon plots, we found that compounds 3, 9 and 13 were α-glucosidase mixed-type inhibitors with K_i values of 56.86 ± 1.23, 48.88 ± 0.07 and 13.63 ± 0.42 μM, respectively. In silico molecular docking analysis showed that compounds 3 and 13 possessed superior binding capacities with α-glucosidase (3A4A AutoDock score: -4.99 and -4.63 kcal/mol). Whereas compound 9 showed +2.74 kcal/mol, which indicated compound 9 exerted the effect of inhibiting α-glucosidase activity by preferentially binding to the enzyme-substrate complex. As a result, compounds 3, 9 and 13 could have therapeutic potentials for type 2 diabetes mellitus, due to their potent hypoglycemic activities.

In Vitro & In Vivo Anti-Hyperglycemic Potential of Saponins Cake and Argan Oil from Argania spinosa

The Argan tree (Argania spinosa. L) is an evergreen tree endemic of southwestern Morocco. For centuries, various formulations have been used to treat several illnesses including diabetes. However, scientific results supporting these actions are needed. Hence, Argan fruit products (i.e., cake byproducts (saponins extract) and hand pressed Argan oil) were tested for their in-vitro anti-hyperglycemic activity, using α-glucosidase and α-amylase assays. The in-vivo anti-hyperglycemic activity was evaluated in a model of alloxan-induced diabetic mice. The diabetic animals were orally administered 100 mg/kg body weight of aqueous saponins cake extract and 3 mL/kg of Argan oil, respectively, to evaluate the anti-hyperglycemic effect. The blood glucose concentration and body weight of the experimental animals were monitored for 30 days. The chemical properties and composition of the Argan oil were assessed including acidity, peroxides, K232, K270, fatty acids, sterols, tocopherols, total polyphenols, and phenolic compounds. The saponins cake extract produced a significant reduction in blood glucose concentration in diabetic mice, which was better than the Argan oil. This decrease was equivalent to that detected in mice treated with metformin after 2–4 weeks. Moreover, the saponins cake extract showed a strong inhibitory action on α-amylase and α-glucosidase, which is also higher than that of Argan oil.

Kochiae Fructus, the Fruit of Common Potherb Kochia scoparia (L.) Schrad: A Review on Phytochemistry, Pharmacology, Toxicology, Quality Control, and Pharmacokinetics

Kochiae Fructus (KF) is the fruit of an annual potherb Kochia scoparia (Linn.) Schrad and has been traditionally used for the treatment of diseases in the skin, eyes, and urinary tract for thousands of years in China. Recent studies have showed its anti-inflammatory, antifungal, antiallergic, and antipruritogenic effects to clarify the mechanisms of these actions. Meanwhile, its other effects, such as anticancer, hypoglycemic, and hepatoprotective effects, also have been reported. The achievement of these therapeutic effects is contributed by its chemical constituents. A total of 153 compounds have been identified in KF, mainly including triterpenoids, flavonoids, carbohydrates, amino acids, organic acids, and essential oils. Momordin Ic is the representative triterpene glycoside compound, which is used as a phytochemical marker for the quality control of Kochiae Fructus. The research on toxicity is insufficient, and only one article reported that the LD₅₀ was 7.15 ± 0.03 g/kg for water extract of KF after oral administration in KM mice. In addition, the pharmacokinetic study was carried out on momordin Ic with linear pharmacokinetic characteristics. Above all, this review provides comprehensive information about Kochiae Fructus and may provide the theoretic foundation of its clinical application and further development.

Phytomedicinal relevance of South African Cucurbitaceae species and their safety assessment: A review

ETHNOPHARMACOLOGICAL RELEVANCE

South Africa has a very rich flora. Many of these species such as those in the Cucurbitaceae family are exploited as medicines for the treatment of various infections.

AIM OF THE REVIEW

The aim of the review was to synthesize the existing but scattered literature of some plant species in the Cucurbitaceae family used as sources of medicines in South Africa.

MATERIALS AND METHODS

A literature survey was carried out on the ethnopharmacology, phytochemistry, pharmacological relevance and safety assessment of the South African Cucurbitaceae used as medicines.

RESULTS

A total of 11 plants namely; Coccinia rehmannii Cogn., Cucumis africanus L.f., Cucumis anguria L. var. longaculeatus J.H.Kirkbr., Cucumis myriocarpus Naudin subsp. myriocarpus, Cucumis zeyheri Sond., Cucumis metuliferus E. Mey ex Naudin, Kedrostis nana (Lam) Cogn., Lagenaria siceraria (Molina) Standl., Momordica balsamina L., Momordica charantia L., and Momordica foetida Schumach. and Thonn were identified. Various traditional medicinal uses for these plants, from common ailments to life-threatening infections were reported. Biological activities including antidiabetic, antioxidant, antimicrobial, anticancer, anti-inflammatory and hepatoprotective were reported. However, some of the plants have not been investigated for some of the biological activities related to their traditional uses. In addition, most of the studies were carried out using non-standardized extracts. Thus, only a few studies on their bioactive constituents exist. Common compounds identified within the species are hydroxycinnamic and hydroxybenzoic acids such as sinapic, gallic, vanillic and salicylic acids; flavonoids such as naringenin, quercetin, kaempferol and rutin; fatty acids such as linoleic, palmitoleic, myristic and stearic acids; the saponin glycosides, momordicin alkaloids and cucurbitacins. However, most of these compounds have not been tested for biological activities. Cucurbitacins were implicated as a major class of toxic compounds present in the plants resulting in poisoning and death.

CONCLUSIONS

Adequate knowledge of the traditional use of these plants in medicine and the parts used are very important due to the presence of toxic substances and their wide usage. Proper screening of the safety of these plants and products derived from them calls for urgent attention.

Two new glycosides, farnesyl pentaglycoside and oleanane triglycoside from Lepisanthes rubiginosa, a mangrove plant collected from Thua Thien-Hue province, Vietnam

Phytochemical investigation of the leaves of Lepisanthes rubiginosa led to the isolation of two new glycosides, lepisantheside A (1) and lepisantheside B (2), together with two known compounds acutoside A (3) and 3-O-[β-D-xylopyranosyl-(1→3)-β-D-glucopyranosyl-]-oleanolic acid (4). Their structures were elucidated by means of spectroscopic methods (HR-ESI-MS, 1D and 2D NMR), and by comparison with the reported data. The cytotoxicity of compounds 1-4 against four human cancer cell lines (KB, HepG2, SK-LU-1 and MCF7) was evaluated. Compound 4 exhibited significant activity with IC₅₀ values of 9.57, 6.66, 6.97 and 18.32 µM, respectively, in comparison with the postive control ellipticine.

Exploring Antioxidant and Enzymes (A-Amylase and B-Glucosidase) Inhibitory Activity of Morinda lucida and Momordica charantia Leaves from Benin

BACKGROUND

Momordica charantia Linn. (Cucurbitaceae), the wild variety of bitter melon and Morinda lucida Benth (Rubiaceae) were commonly used as a popular folk medicine in Benin. This research focused to measure the antioxidant and enzyme inhibitory effects of M. charantia and M. lucida leaves and their antidiabetic activity.

METHODS

Antioxidant activities were evaluated by micro-dilution technique using DPPH free radical scavenging activity and β-carotene-linoleate bleaching assay. The α-amylase inhibition assay was carried out utilizing the 3,5-dinitrosalicylic acid procedure, while β-glucosidase inhibition assay was demonstrated using as substrate p-nitrophenyl-β-D-glucopyranoside (PNPG). HPLC-DAD analysis was realized using a high-performance liquid chromatography systems with diode-array detector, L-3000.

RESULTS

Chlorogenic acid, epicatechin, daidzein, rutin, naringin, quercetin, naringenin and genistein were identified as polyphenol compounds in the both plants extract. Dichloromethane and ethyl acetate extracts showed a good α-amylase inhibitory activity (56.46 ± 1.96% and 58.76 ± 2.74% respectively). M. lucida methanolic extract has shown IC₅₀ of 0.51 ± 0.01 mg/mL, which is the lowest for DPPH scavenging activity. M. lucida dichloromethane extract showed the highest inhibitory capacity of β-glucosidase activity (82.11. ± 2.15%).

CONCLUSION

These results justify some traditional medicinal uses of both plants. The purified fractions could be used in future formulations, possibly incorporated in functional foods to combat certain diseases.

Phytomedicines Used for Diabetes Mellitus in Ghana: A Systematic Search and Review of Preclinical and Clinical Evidence

Background

Available data indicate that diabetes mellitus leads to elevated cost of healthcare. This imposes a huge economic burden on households, societies, and nations. As a result many Ghanaians, especially rural folks, resort to the use of phytomedicine, which is relatively less expensive. This paper aims at obtaining information on plants used in Ghana to treat diabetes mellitus, gather and present evidence-based data available to support their uses and their mechanisms of action, and identify areas for future research.

Method

A catalogue of published textbooks, monographs, theses, and peer-reviewed articles of plants used in Ghanaian traditional medicine between 1987 and July 2018 for managing diabetes mellitus was obtained and used.

Results

The review identified 76 plant species belonging to 45 families that are used to manage diabetes mellitus. Leaves were the part of the plants frequently used for most preparation (63.8%) and were mostly used as decoctions. Majority of the plants belonged to the Euphorbiaceae, Lamiaceae, Asteraceae, and Apocynaceae families. Pharmacological data were available on 23 species that have undergone in vitro studies. Forty species have been studied using in vivo animal models. Only twelve plants and their bioactive compounds were found with data on both preclinical and clinical studies. The records further indicate that medicinal plants showing antidiabetic effects did so via biochemical mechanisms such as restitution of pancreatic β-cell function, improvement in insulin sensitivity by receptors, stimulating rate of insulin secretion, inhibition of liver gluconeogenesis, enhanced glucose absorption, and inhibition of G-6-Pase, α-amylase, and α-glucosidase activities.

Conclusion

This review contains information on medicinal plants used to manage diabetes mellitus, including their pharmacological properties and mechanisms of action as well as models used to investigate them. It also provides gaps that can form the basis for further investigations and development into useful medications for effective treatment of diabetes mellitus.

In vitro evaluation of the α-glucosidase inhibitory potential of methanolic extracts of traditionally used antidiabetic plants

BACKGROUND

Different plant parts of Roylea cinerea (D. Don) Baill. (Lamiaceae), Clematis grata Wall. (Ranunculaceae), Cornus capitata Wall. (Cornaceae) are traditionally used in the management of diabetes and various other diseases.

METHOD

The air-dried plant parts from different plants were coarsely powdered and macerated in methanol to obtain their crude extracts. The crude extracts were evaluated for their α-glucosidase inhibitory activity. On the basis of results obtained, the methanolic crude extract of Cornus capitata Wall. was further sequentially fractionated in hexane, diethyl ether, ethyl acetate, n-butanol. Fractions obtained were also evaluated for their α-glucosidase inhibitory potential. The kinetic study was performed using Lineweaver Burk plot to evaluate the type of inhibition. Furthermore, in silico analysis was also carried with active sites of the enzyme (PDB ID: 3WY1) using Autodock4.

RESULTS

Among all the plant extracts, Cornus capitata extract showed maximum inhibitory activity. Therefore its methanolic extract was further fractionated with the help of different solvents and the maximum activity was shown by the ethyl acetate fraction (IC50 50 μg/mL). Kinetic analysis indicated that Vmax and Km were increased indicating a competitive type of inhibition. In docking studies, among different constituents known in this plant, betulinic acid showed minimum binding energy (- 10.21 kcal/mol). The kinetic and docking studies have strengthened the observation made in the present study regarding the α-glucosidase inhibitory activity of Cornus capitata.

CONCLUSION

The study provided partial evidence for pharmacological basis regarding clinical applications of Cornus capitata in the treatment of diabetes suggesting it to be a suitable candidate for the treatment of postprandial hyperglycemia.

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.

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.

Synthesis and Evaluation of a Series of Oleanolic Acid Saponins as α-Glucosidase and α-Amylase Inhibitors

Sixteen naturally occurring oleanolic acid saponins and their derivatives were synthesized in an efficient and practical strategy, and their inhibitory activities against α-glucosidase and α-amylase were evaluated in vitro. Among all the compounds, 28-O-monoglucoside 8 exhibited remarkably potent inhibitory activity against α-glucosidase with an IC50 value of 87.3 µM, which was fivefold stronger than that of the antidiabetic acarbose. Based on the preliminary structure-activity relationships, for 28-O-monoglucosides, the presence of a terminal α-l-rhamnopyranosyl residue enhanced the α-glucosidase and α-amylase inhibitory activities. Furthermore, for 3,28-O-bidesmosides, sugar-substituted moieties attached to the C-3 and C-28 positions of the oleanolic acid scaffold are helpful to increase the inhibitory activities against α-amylase and α-glucosidase.

C-4 gem-dimethylated oleanes of Gymnema sylvestre and their pharmacological activities

Gymnema sylvestre R. Br., one of the most important medicinal plants of the Asclepiadaceae family, is a herb distributed throughout the World, predominantly in tropical countries. The plant, widely used for the treatment of diabetes and as a diuretic in Indian proprietary medicines, possesses beneficial digestive, anti-inflammatory, hypoglycemic and anti-helmentic effects. Furthermore, it is believed to be useful in the treatment of dyspepsia, constipation, jaundice, hemorrhoids, cardiopathy, asthma, bronchitis and leucoderma. A literature survey revealed that some other notable pharmacological activities of the plant such as anti-obesity, hypolipidemic, antimicrobial, free radical scavenging and anti-inflammatory properties have been proven too. This paper aims to summarize the chemical and pharmacological reports on a large group of C-4 gem-dimethylated pentacyclic triterpenoids from Gymnema sylvestre.

Traditional medicines in Africa: an appraisal of ten potent african medicinal plants

The use of medicinal plants as a fundamental component of the African traditional healthcare system is perhaps the oldest and the most assorted of all therapeutic systems. In many parts of rural Africa, traditional healers prescribing medicinal plants are the most easily accessible and affordable health resource available to the local community and at times the only therapy that subsists. Nonetheless, there is still a paucity of updated comprehensive compilation of promising medicinal plants from the African continent. The major focus of the present review is to provide an updated overview of 10 promising medicinal plants from the African biodiversity which have short- as well as long-term potential to be developed as future phytopharmaceuticals to treat and/or manage panoply of infectious and chronic conditions. In this endeavour, key scientific databases have been probed to investigate trends in the rapidly increasing number of scientific publications on African traditional medicinal plants. Within the framework of enhancing the significance of traditional African medicinal plants, aspects such as traditional use, phytochemical profile, in vitro, in vivo, and clinical studies and also future challenges pertaining to the use of these plants have been explored.

Dietary oleanolic acid mediates circadian clock gene expression in liver independently of diet and animal model but requires apolipoprotein A1

Oleanolic acid is a triterpene widely distributed throughout the plant kingdom and present in virgin olive oil at a concentration of 57 mg/kg. To test the hypotheses that its long-term administration could modify hepatic gene expression in several animal models and that this could be influenced by the presence of APOA1-containing high-density lipoproteins (HDLs), diets including 0.01% oleanolic acid were provided to Apoe- and Apoa1-deficient mice and F344 rats. Hepatic transcriptome was analyzed in Apoe-deficient mice fed long-term semipurified Western diets differing in the oleanolic acid content. Gene expression changes, confirmed by reverse transcriptase quantitative polymerase chain reaction, were sought for their implication in hepatic steatosis. To establish the effect of oleanolic acid independently of diet and animal model, male rats were fed chow diet with or without oleanolic acid, and to test the influence of HDL, Apoa1-deficient mice consuming the latter diet were used. In Apoe-deficient mice, oleanolic acid intake increased hepatic area occupied by lipid droplets with no change in oxidative stress. Bmal1 and the other core component of the circadian clock, Clock, together with Elovl3, Tubb2a and Cldn1 expressions, were significantly increased, while Amy2a5, Usp2, Per3 and Thrsp were significantly decreased in mice receiving the compound. Bmal1 and Cldn1 expressions were positively associated with lipid droplets. Increased Clock and Bmal1 expressions were also observed in rats, but not in Apoa1-deficient mice. The core liver clock components Clock-Bmal1 are a target of oleanolic acid in two animal models independently of the diets provided, and this compound requires APOA1-HDL for its hepatic action.

Evaluation of ethnomedical claim III: anti-hyperglycemic activities of Gongronema latifolium root and stem

BACKGROUND

The insulinotropic activity of the combined root and stem of Gongronema latifolium (Asclepiadaceae) was evaluated to justify its African ethnomedicinal use in the management of diabetes.

METHODS

A methanolic extract and its chromatographic fractions (A1 -A6 ) were tested for glucose-reducing and in vitro insulin-stimulating abilities using glucose-loaded rats and INS-1 cells, respectively. In vivo insulin-releasing activities for the significantly (P<0.05) active antihyperglycemic A5 and A6 and in vitro insulinotropic activity of the C1 fraction and its isolated constituents were also similarly determined.

RESULTS

The extract (100 mg/kg) had higher in vivo antihyperglycemic activity than the individual A1 -A6 , indicating a synergistic effect of the plant constituents. Higher in vivo insulin release in response to A5 (100 mg/kg) than A6 , agreed with their in vivo antihyperglycemic activities and confirmed insulin release as a mechanism of action of the plant. Compared with 5.6 mmol/L glucose (negative control), the extract and the A3 , A6 , and C1 (all at 100.0 μg/mL) elicited significantly higher in vitro insulin release that was similar to that of glibenclamide (1.0 μg/mL; P>0.05). Fraction C1 yielded a 1:1 mixture of α-amyrin and β-amyrin cinnamates (1a:1b), lupenyl cinnamate (2), lupenyl acetate (3), and two unidentified triterpenoids, Y and Z. The 1a:1b mixture (100.0 μg/mL) demonstrated the highest insulinotropic activity that was comparable (P>0.05) to that of glibenclamide (1.0 μg/mL).

CONCLUSIONS

The results confirm pancreatic activity as a mechanism underlying the antidiabetic action of G. latifolium and justify its ethnomedical use.

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.

LC-QTOF/MS metabolomic profiles in human plasma after a 5-week high dietary fiber intake

The objective was to investigate the alterations of plasma metabolome profiles to identify exposure and effect markers of dietary fiber intake. Subjects (n = 25) aged 58.6 (1.1) years (mean and SD) with a body mass index of 26.6 (0.5) kg/m(2) were given a high fiber (HF) and a low fiber (LF) diet, in a 5-week randomized controlled crossover intervention. The HF diet consisted of oat bran, rye bran, and sugar beet fiber incorporated into test food products, whereas the LF diet was made of equivalent food products to the HF diet, but without adding fibers. Blood plasma samples were collected at the start and end of each intervention period and analyzed by LC-QTOF/MS. In total, 6 features in positive mode and 14 features in negative mode were significantly different between the HF and the LF diet (p < 0.01, q < 0.05). Two markers, 2,6-dihydroxybenzoic acid and 2-aminophenol sulfate, were increased after HF diet, along with a tentatively identified saponin derived from oat avenacosides. The untargeted metabolomics approach enabled the identification of two new markers of dietary fiber intake in human plasma. Further studies will be needed to verify if these markers could serve as compliance markers of fiber intake.

Momordica charantia and its novel polypeptide regulate glucose homeostasis in mice via binding to insulin receptor

Momordica charantia (MC) has been used as an alternative therapy for diabetes mellitus. This study analyzed and elucidated therapeutic targets contributing to the hypoglycemic effect of aqueous extract of MC seeds (MCSE) by transcriptomic analysis. Protein ingredients aimed at the hypoglycemic target were further identified by proteomic, docking, and receptor-binding assays. The data showed that MSCE (1 g/kg) significantly lowered the blood glucose level in normal and diabetic mice. Moreover, MCSE primarily regulated the insulin signaling pathway in muscles and adipose tissues, suggesting that MCSE might target insulin receptor (IR), stimulate the IR-downstream pathway, and subsequently display hypoglycemic activity in mice. It was further revealed that inhibitor against trypsin (TI) of MC directly docked into IR and activated the kinase activity of IR in a dose-dependent manner. In conclusion, the findings suggested that MCSE regulated glucose metabolism mainly via the insulin signaling pathway. Moreover, TI was newly identified as a novel IR-binding protein of MC that triggered the insulin signaling pathway via binding to IR.

Effect of Gongronema latifolium on gastric emptying in healthy dogs

AIM: To investigate sonographically the effect of Gonogronema latifolium (G. latifolium) on gastric emptying of semi-solid meals in healthy dogs.

METHODS: In a randomized, placebo-controlled experiment, twenty-five clinically healthy dogs were randomly allotted into five groups of five dogs in each group. The placebo group served as the control, and the low, moderate and high dose groups ingested the methanolic leaf extract of G. latifolium in capsules at 100 mg/kg, 250 mg/kg and 500 mg/kg, respectively, while the prokinetic group ingested 0.5 mg/kg capsules of metoclopramide. After a 12-h fast, each group ingested its treatment capsules 30 min before the administration of a test meal. Measurements of gastric emptying and blood glucose levels were obtained 30 min before and immediately after the ingestion of the test meal and thereafter every 15 min for 4 h. This was followed by further measurements every 30 min for another 2 h.

RESULTS: The gastric emptying times of the placebo, low dose, moderate dose, high dose and prokinetic dose groups were 127.0 ± 8.2 min, 135.5 ± 3.7 min, 155.5 ± 3.9 min, 198.0 ± 5.3 min and 59.0 ± 2.5 min, respectively. Gastric emptying times of the moderate and high dose groups were significantly slower than in the placebo control group (155.5 ± 3.9 min, 198.0 ± 5.3 min vs 127.0 ± 8.2 min, P = 0.000). No significant difference in gastric emptying between the low dose and placebo control groups was noted (135.5 ± 3.7 min vs 127.0 ± 8.2 min, P = 0.072). Gastric emptying of the prokinetic group was significantly faster than that of the control group (59.0 ± 2.5 min vs 127.0 ± 8.2 min, P = 0.000). The hypoglycaemic effect of G. latifolium and gastric emptying were inversely related (r = -0.95, P = 0.000).

CONCLUSION: G. latifolium delays gastric emptying and lowers postprandial blood glucose in healthy dogs. It reduces the postprandial blood glucose by delaying gastric emptying.

Inhibitory effects of medicinal mushrooms on α-amylase and α-glucosidase - enzymes related to hyperglycemia

In Asia, medicinal mushrooms have been popularly used as folk medicine and functional foods. In this study, our aim was to examine the inhibitory effects of six medicinal mushrooms on key enzymes (α-amylase and α-glucosidase) related to hyperglycemia; chemical profiles of bioactive extracts were also examined. The results showed that the n-hexane extract of Coriolus versicolor had the strongest anti-α-amylase activity, while the n-hexane extract of Grifola frondosa showed the most potent anti-α-glucosidase activity. Compared with acarbose, the anti-α-amylase activity of all mushroom extracts was weaker, however a stronger anti-α-glucosidase activity was noted. GC-MS analysis showed that the magnitude of potency of inhibiting α-glucosidase activity varied with the levels of oleic acid and linoleic acid present in the extracts. These findings were consistent with the IC50 values of these free fatty acids on inhibiting α-glucosidase activity. Taken together, this study suggests that oleic acid and linoleic acid could have contributed to the potent anti-α-glucosidase activity of selected medicinal mushrooms.

Plant extracts of winter savory, purple coneflower, buckwheat and black elder activate PPAR-γ in COS-1 cells but do not lower blood glucose in Db/db mice in vivo

The aim of this study was to investigate possible blood glucose-lowering effects of plant extracts in vivo for which prior to this a peroxisome proliferator-activated receptor-γ activity in vitro was observed. The ability of extracts of winter savory, purple coneflower, buckwheat and black elder to dose-dependently activate peroxisome proliferator-activated receptor-γ was determined in a reporter gene assay in COS-1 cells. For evaluation of glucose-lowering effects in vivo, db/db mice were fed a diet containing either rosiglitazone (0.02 g/kg diet, positive control) or one of the plant extracts (0.1 and 1 g/kg diet) for four weeks. Apart from glucose, insulin, triacylglycerols, non-esterified fatty acids, cholesterol and adiponectin were determined in plasma. All plant extracts showed a dose-dependent peroxisome proliferator-activated receptor-γ-activating effect in vitro. In db/db mice none of the plant extracts exerted glucose-lowering effects at the used dosages compared to rosiglitazone. Non-esterified fatty acids, triacylglycerols, cholesterol, insulin and adiponectin in plasma were not altered by the plant extracts as well. Although dose-dependent peroxisome proliferator-activated receptor-γ activity could be shown in COS-1 cells, the experiments in db/db mice lacked to confirm any anti-diabetic effect of the plant extracts in vivo and emphasizes the importance of verifying cell culture data using an appropriate in vivo model.

Modulation of starch digestion for slow glucose release through "toggling" of activities of mucosal α-glucosidases

Starch digestion involves the breakdown by α-amylase to small linear and branched malto-oligosaccharides, which are in turn hydrolyzed to glucose by the mucosal α-glucosidases, maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI). MGAM and SI are anchored to the small intestinal brush-border epithelial cells, and each contains a catalytic N- and C-terminal subunit. All four subunits have α-1,4-exohydrolytic glucosidase activity, and the SI N-terminal subunit has an additional exo-debranching activity on the α-1,6-linkage. Inhibition of α-amylase and/or α-glucosidases is a strategy for treatment of type 2 diabetes. We illustrate here the concept of "toggling": differential inhibition of subunits to examine more refined control of glucogenesis of the α-amylolyzed starch malto-oligosaccharides with the aim of slow glucose delivery. Recombinant MGAM and SI subunits were individually assayed with α-amylolyzed waxy corn starch, consisting mainly of maltose, maltotriose, and branched α-limit dextrins, as substrate in the presence of four different inhibitors: acarbose and three sulfonium ion compounds. The IC(50) values show that the four α-glucosidase subunits could be differentially inhibited. The results support the prospect of controlling starch digestion rates to induce slow glucose release through the toggling of activities of the mucosal α-glucosidases by selective enzyme inhibition. This approach could also be used to probe associated metabolic diseases.

Antidiabetogenic oligostilbenoids and 3-ethyl-4-phenyl-3,4-dihydroisocoumarins from the bark of Shorea roxburghii

A methanol extract of the bark of Shorea roxburghii (Dipterocarpaceae) was found to inhibit plasma glucose elevation in sucrose-loaded mice. From the extract, three new 3-ethyl-4-phenyl-3,4-dihydroisocoumarins, 1'S-dihydrophayomphenol A(2) (1) and phayomphenols B(1) (2) and B(2) (3), were isolated together with 24 known compounds including 20 stilbenoids and oligostilbenoids. The structures of 1-3 were determined on the basis of their spectroscopic properties as well as of chemical evidences. Among the isolates, (-)-hopeaphenol (6), hemsleyanol D (8), (+)-α-viniferin (15), and (-)-balanocarpol (18) showed inhibitory activity against plasma glucose elevation in sucrose-loaded rats at doses of 100-200mg/kg, p.o. To clarify the mode of action of the antihyperglycemic property, effects of these oligostilbenoids on gastric emptying in mice, those on glucose uptake in isolated intestinal tissues as well as inhibitory activities against rat intestinal α-glucosidase and rat lens aldose reductase were examined.

Neuroprotective effect of Momordica charantia in global cerebral ischemia and reperfusion induced neuronal damage in diabetic mice

ETHNOPHARMACOLOGICAL RELEVANCE

Momordica charantia L. (Cucurbitaceae) fruits have been used traditionally for centuries, especially for treating diabetes and associated complications.

AIM OF THE STUDY

The present study was performed to evaluate neuroprotective effect of lyophilized M. charantia fruit juice against global cerebral ischemia and reperfusion induced neuronal injury in diabetic mice.

MATERIALS AND METHODS

Global cerebral ischemia induced by occluding both common carotid arteries for 10 min followed by 24 h reperfusion was used to induce neuronal injury. Ischemia-reperfusion induced neuronal injury was evaluated in terms of cerebral infarct size, generation of free radicals measured as thiobarbaturic acid reactive substances (TBARS), and neurological functions measured as short term memory and motor activity.

RESULTS

The cerebral oxidative stress and damage, and neurological deficits were dose dependently attenuated by pre-treatment with the lyophilized M. charantia juice (200-800 mg/kg, p.o., o.d.). Moreover, M. charantia also exhibited dose dependent antihyperglycemic activity in diabetic mice.

CONCLUSIONS

These results suggest that M. charantia has potent neuroprotective activity against global cerebral ischemia-reperfusion induced neuronal injury and consequent neurological deficits in diabetic mice.

Oleanolic Acid, a plant triterpenoid, significantly improves survival and function of islet allograft

BACKGROUND.: Oleanolic acid (OA) is a ubiquitous triterpenoid, with potent antioxidant and anti-inflammatory properties. Here, we tested whether these combined properties of OA can prevent nonimmunologic primary nonfunctioning and immunologic phenomena ascribed to graft rejection hence prolong islet allograft survival. METHODS.: Islet transplants were performed under kidney capsule of streptozotocin-induced diabetic C57BL/6 mice with BALB/c islets. Recipients were treated with 0.5 mg/day of OA intraperitoneally, and serum samples were collected once in 2 days and used for luminex, ELISA, and donor-specific antibody screening. Transplanted mice were killed at different time intervals to obtain splenocytes and kidney samples for ELISPOT, mixed leukocyte reaction, and immunohistochemical studies. RESULTS.: After transplantation, the decrement of blood glucose was significantly faster in mice receiving OA less than 2+/-1 days compared with untreated (4+/-2 days). OA prolonged survival of transplanted islets up to 23+/-3 days and reversed diabetes even with 250 islets. Treatment group showed increased serum interleukin (IL)-10 (twofold) and decreased inducible protein-10 and IL-4 (threefold) in luminex. Significantly reduced frequency of interferon-gamma (4.5-fold), IL-4 (3.5-fold), IL-2 (2.3-fold), and IL-17 (fourfold) producing T-cell populations were found in ELISPOT. OA-treated grafts had significant reduced and delayed infiltration of CD4+ and CD8+ T cells. OA also delayed donor-specific antibody generation up to 19 days after transplantation. Combined treatment with cyclosporine A, OA further prolonged the islet allograft survival to 34+/-3 days. CONCLUSIONS.: In conclusion, OA is an attractive, dietary nontoxic plant triterpenoid, which suppresses the production of proinflammatory cytokines and delays graft-specific immune responses to prolong islet allograft survival.