Further isolation and identification of anti-diabetic principles from root bark of Myrianthus arboreus P. Beauv.: The ethyl acetate fraction contains bioactive phenolic compounds that improve liver cell glucose homeostasis

ETHNOPHARMACOLOGICAL RELEVANCE

We recently reported that ethanol extract of Myrianthus arboreus P. Beauv. root bark demonstrated antidiabetic activity by modulating hepatocyte glucose homeostasis. This activity was associated significantly to the ethyl acetate (EAc) fraction. The current study sought to identify the active compounds responsible of the antidiabetic effect of M. arboreus in the EAc fraction using bioassay-directed sub-fractionation.

MATERIALS AND METHODS

EAc fraction was sub-fractionated using Flash chromatography. Preparative HPLC was used to isolate the pure compounds. The structures of the isolated compounds were confirmed by analysis of NMR spectroscopic and mass spectrometric data. Hepatic (H4IIE, HepG2) cells were treated with maximum non-toxic concentrations of ethanol extract, its EAc fraction and isolated compounds thereof. Glucose-6-phosphatase (G6Pase) activity was measured using the glucose oxidase method. To measure glycogen synthase (GS) activity, radioactive assays were used. Phosphorylation of AMP-activated protein kinase (AMPK) and Glycogen Synthase Kinase-3 (GSK-3) were probed by Western blot.

RESULTS

Six sub-fractions were obtained, and the antidiabetic activity was found in two sub-fractions (SFE1 and SFE2). For the first time, two known C-glycosylflavone regio-isomers, isoorientin (1) and orientin (2) were detected and isolated from M. arboreus plant, especially from SFE2 as well as protocatechuic acid, 3,4-dihydroxybenzaldehyde (4), and chlorogenic acid isolated from SFE1. The compounds 1, 2, 4 were determined to decrease the activity of G6Pase by increasing AMPK phosphorylation and to stimulate GS through GSK-3 phosphorylation. Isoorientin which is one of the main compounds of EAc fraction, expressed the strongest effect in all bioassays, similar to that of the EAc fraction. A significant and linear correlation was found between the phosphorylation of AMPK and the activity of G6Pase modulated by all samples (R² = 0.54; p < 0.05). Similar to G6Pase assay, a correlation was determined between the capacity of M. arboreus extracts/fractions/compounds to stimulate GS activity and to phosphorylate GSK-3 (R² = 0.57, p < 0.01).

CONCLUSION

Results demonstrate that 1, 2, 4 are responsible, at least in part, for the antidiabetic activity of M. arboreus. These compounds can be used to ensure the quality and efficacy of M. arboreus antidiabetic preparations and standardize such preparations.

Bioactive Pentacyclic Triterpenes from the Root Bark Extract of Myrianthus arboreus, a Species Used Traditionally to Treat Type-2 Diabetes

Four new Δ¹² ursene-type pentacyclic triterpenes containing the trans-feruloyl moiety (1-4), along with ursolic acid (5), were isolated from a Myrianthus arboreus root bark ethanol extract, after bioassay-guided subfractionation of its hexane fraction. The structures of 1-4 were established on the basis of the results of standard spectroscopic analytical methods (IR, HRESIMS, GC-MS, 1D and 2D NMR). The compounds 3β- O- trans-feruloyl-2α,19α-dihydroxyurs-12-en-28-oic acid (1), 2α-acetoxy-3β- O- trans-feruloyl-19α-hydroxyurs-12-en-28-oic acid (3), and 5 were determined to decrease the activity of hepatocellular glucose-6-phosphatase (G6Pase) and to activate glycogen synthase (GS). Their action on G6Pase activity implicated both Akt and AMPK activation. In addition, these compounds were determined to stimulate GS via the phosphorylation of glycogen synthase kinase-3. Compound 3 showed the most potent effect in modulating glucose homeostasis in liver cells. This is the first comprehensive report on novel phytochemical components of the root bark extract of M. arboreus based on the isolation of the principles responsible for its antidiabetic effects.

Root bark extracts of Myrianthus arboreus P. Beauv. (Cecropiaceae) exhibit anti-diabetic potential by modulating hepatocyte glucose homeostasis

ETHNOPHARMACOLOGICAL RELEVANCE

Myrianthus arboreus P. Beauv. is a tropical tree used in African folk medicine, including for diabetes. However, little research has yet been conducted to support this ethnopharmacological use of this plant. The present study sought to determine the antidiabetic potential of root bark extracts through cell-based bioassays of liver and muscle glucose homeostasis.

MATERIALS AND METHODS

Four extracts were obtained from crude root bark powder: 1 aqueous (AQ), 2 ethanol (EtOH), 3 alkaloid enriched (Alk) (obtained from methanol extract) and 4 dichloromethane (Dic) extracts. Moreover, extract 2 was further separated into two fractions: 2.1 ethyl acetate (EAc) and 2.2 hexane (Hex). To assess the antidiabetic activity of the plant extracts, inhibition of glucose-6-phosphatase (G6Pase), stimulation of glycogen synthase (GS) and modulation of glucose uptake were determined in cultured H4IIE and HepG2 hepatocytes as well as C2C12 myocytes, respectively. Phosphorylation of three kinases, AMP-activated protein kinase (AMPK), Akt and Glycogen Synthase Kinase-3 (GSK-3) were probed by Western blot.

RESULTS

M. arboreus extracts/fractions did not stimulate glucose uptake in C2C12 cells albeit 2.2 (Hex) fraction showed a mild positive tendency. In contrast, extract 2 and its fractions as well as extract 3 were able to decrease hepatocyte G6Pase activity. Their effect on G6Pase activity involved both Akt and AMPK phosphorylation. No significant correlation was observed between activation of Akt and inhibition of G6Pase (R² = 0.50 p < 0.14), whereas that between stimulation of AMPK and inhibition of G6Pase was statistically significant (R² = 0.75 p < 0.05). On the other hand, extract 2, its fraction 2.2 and extract 3 were able to stimulate GS through GSK-3 phosphorylation. A high correlation was observed between the ability of M. arboreus extracts and fractions to phosphorylate GSK-3 and modulate GS activity (R²=0.81 p < 0.01). Extract 2 and its fraction 2.2 together with extract 3 were the only plant products to simultaneously and potently regulate G6Pase and GS, the key players of hepatic glucose homeostasis.

CONCLUSION

Overall, these data support the traditional antidiabetic uses of the root bark of M. arboreus.

Caffeic acid methyl and ethyl esters exert potential antidiabetic effects on glucose and lipid metabolism in cultured murine insulin-sensitive cells through mechanisms implicating activation of AMPK

CONTEXT

Caffeic acid methyl (CAME) and ethyl (CAEE) esters stimulate glucose uptake and AMP-activated protein kinase (AMPK) in C2C12 myocytes (ATCC^® CRL-1772^TM).

OBJECTIVE

Effects of CAME and CAEE were now assessed on myocyte glucose transporter GLUT4 activity and expression, on hepatic gluconeogenesis and on adipogenesis as well as major underlying signaling pathways.

MATERIALS AND METHODS

GLUT4 protein translocation was studied in L6 GLUT4myc cells, glucose-6-phospatase (G6Pase) in H4IIE hepatocytes and adipogenesis in 3T3-L1 adipocytes. Key modulators were measured using western immunoblot. Cells were treated for 18 h with either CAME or CAEE at various concentrations (12.5-100 μM).

RESULTS

Myocyte glucose uptake rose from 10.1 ± 0.5 to 18.7 ± 0.8 and 21.9 ± 1.0 pmol/min/mg protein in DMSO-, CAME- and CAEE-stimulated cells, respectively, similar to insulin (17.7 ± 1.2 pmol/min/mg protein), while GLUT4myc translocation increased significantly by 1.70 ± 0.18, by 1.73 ± 0.18- and by 1.95 ± 0.30-fold (relative to DMSO), following insulin, CAME and CAEE stimulation, respectively. CAME and CAEE suppressed hepatocyte G6Pase by 62.0 ± 6.9% and 62.7 ± 6.0% with IC₅₀ of 45.93 and 22.64 μM, respectively, comparable to insulin (70.7 ± 2.3% inhibition). Finally, CAME and CAEE almost abrogated adipogenesis (83.3 ± 7.2% and 97.3 ± 3.0% at 100 μM; IC₅₀ of 13.8 and 12.9 μM, respectively). The compounds inhibited adipogenic factors C/EBP-β and PPAR-γ and stimulated AMPK activity in the three cell-lines.

DISCUSSION AND CONCLUSIONS

CAME and CAEE exerted antidiabetic activities in insulin-responsive cells through insulin-independent mechanisms involving AMPK and adipogenic factors.

Phenolic compounds isolated from fermented blueberry juice decrease hepatocellular glucose output and enhance muscle glucose uptake in cultured murine and human cells

Background

We recently reported that blueberry juice fermented (FJ) with Serratia vaccinii bacterium has antidiabetic activities both in vivo and in vitro. The purpose of this project was to elucidate the effect of FJ on glucose homeostasis in liver and skeletal muscle cells and to identify active fractions/compounds responsible for this effect.

Methods

FJ was fractionated using standard chromatography procedures. Hepatic (H4IIE, HepG2) and skeletal muscle cells (C2C12) were treated with maximum non-toxic concentrations of FJ, fractions and isolated compounds thereof. Glucose-6-phosphatase (G6Pase) activity was measured using glucose oxidase method. To measure glucose uptake and glycogen synthase (GS) activity, radioactive assays were used.

Results

Fractionation of FJ yielded seven fractions. FJ and its phenolic fractions F2, F3-1 and F3-2 respectively inhibited G-6Pase by 31, 45, 51 and 26%; activated GS by 2.3-, 2.3-, 2.2- and 2-fold; and stimulated glucose uptake by 19, 25, 18 and 15%, as compared to DMSO vehicle control. Subfractionation of the active fractions yielded 4 compounds (catechol, chlorogenic, gallic and protocatechuic acid). Catechol, yielding the greatest bioactivity in G6Pase and glucose uptake assays, decreased G6Pase activity by 54%, increased GS by 2-fold and stimulated glucose uptake by 44% at 45.5 μM.

Conclusions

This study identifies novel potential antidiabetic compounds that can help standardize FJ.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-017-1650-2) contains supplementary material, which is available to authorized users.

Regulation of liver cell glucose homeostasis by dehydroabietic acid, abietic acid and squalene isolated from balsam fir (Abies balsamea (L.) Mill.) a plant of the Eastern James Bay Cree traditional pharmacopeia

In our previous study, Abies balsamea (L.) Mill., a plant used in Cree traditional medicine, had a strong effect on the regulation of glucose homeostasis in liver cells. This study aimed to isolate and identify its active constituents using a bioassay-guided fractionation approach as well as to elucidate their mechanism(s) of action. The effect of the crude extract and its constituents was evaluated on the activity of Glucose-6-Phosphatase (G6Pase) and Glycogen Synthase (GS) and phosphorylation of three kinases, AMP-activated protein kinase (AMPK), Akt and Glycogen Synthase Kinase-3 (GSK-3). Three compounds, abietic acid, dehydroabietic acid and squalene, were isolated from the most active fraction in the bioassays (hexane). The compounds were able to decrease the activity of G6Pase and to stimulate GS. Their effect on G6Pase activity involved both Akt and AMPK phosphorylation with significant correlations between insulin-dependent and -independent pathways and the bioassay. In addition, the compounds were able to stimulate GS through GSK-3 phosphorylation with a significant correlation between the signaling pathway and the bioassay. Dehydroabietic acid stood out for its strongest effect in all the experiments close to that of the crude extract. These compounds may have potential applications in the treatment of type 2 diabetes and insulin resistance.

The molecular basis of the antidiabetic action of quercetin in cultured skeletal muscle cells and hepatocytes

Background:

Quercetin is universally distributed in the plant kingdom and is the most abundant flavonoid in the human diet. In a previous study, we have reported that quercetin stimulated glucose uptake in cultured C2C12 skeletal muscle through an insulin-independent mechanism involving adenosine monophosphate-activated protein kinase (AMPK). AMPK is a key regulator of the whole body-energy homeostasis. In skeletal muscle, activation of AMPK increases glucose uptake through the stimulation of the glucose transporter GLUT4 translocation to the plasma membrane. In liver, AMPK decreases glucose production mainly through the downregulation of the key gluconeogenesis enzymes such as phosphoenolpyruvate carboxylase (PEPCK) and Glucose -6-phosphate (G6Pase).

Objective:

To study the effect of quercetin on glucose homeostasis in muscle and liver.

Materials and Methods:

L6 skeletal muscle cells, murine H4IIE and human HepG2 hepatocytes were treated with quercetin (50 μM) for 18 h.

Results:

An 18 h treatment with quercetin (50 μM) stimulated AMPK and increased GLUT4 translocation and protein content in cultured rat L6 skeletal muscle cells. On the other hand, we report that quercetin induced hepatic AMPK activation and inhibited G6pase in H4IIE hepatocytes. Finally, we have observed that quercetin exhibited a mild tendency to increase the activity of glycogen synthase (GS), the rate-limiting enzyme of glycogen synthesis, in HepG2 hepatocytes.

Conclusions:

Overall, these data demonstrate that quercetin positively influences glucose metabolism in the liver and skeletal muscle, and therefore appear to be a promising therapeutic candidate for the treatment of in type 2 diabetes.

Antidiabetic compounds from Sarracenia purpurea used traditionally by the Eeyou Istchee Cree First Nation

Through ethnobotanical surveys, the CIHR Team in Aboriginal Antidiabetic Medicines identified 17 boreal forest plants stemming from the pharmacopeia of the Cree First Nations of Eeyou Istchee (James Bay region of Northern Quebec) that were used traditionally against diabetes symptoms. The leaves of Sarracenia purpurea (pitcher plant), one of the identified Cree plants, exhibited marked antidiabetic activity in vitro by stimulating glucose uptake in C2C12 mouse muscle cells and by reducing glucose production in H4IIE rat liver cells. Fractionation guided by glucose uptake in C2C12 cells resulted in the isolation of 11 compounds from this plant extract, including a new phenolic glycoside, flavonoid glycosides, and iridoids. Compounds 6 (isorhamnetin-3-O-glucoside), 8 [kaempferol-3-O-(6″-caffeoylglucoside], and 11 (quercetin-3-O-galactoside) potentiated glucose uptake in vitro, which suggests they represent active principles of S. purpurea (EC(50) values of 18.5, 13.8, and 60.5 μM, respectively). This is the first report of potentiation of glucose uptake by compounds 6 and 8, while compound 11 (isolated from Vaccinium vitis) was previously shown to enhance glucose uptake. Treatment of H4IIE liver cells with the new compound 1, 6'-O-caffeoylgoodyeroside, decreased hepatic glucose production by reducing glucose-6-phosphatase enzymatic activity (IC(50) = 13.6 μM), which would contribute to lowering glycemia and to the antidiabetic potential of S. purpurea.