Inhibition of hepatic neoglucogenesis and glucose-6-phosphatase by quercetin 3-O-α(2″-galloyl)rhamnoside isolated fromBauhinia megalandra leaves

Phytochemical study and evaluation of cytotoxicity, mutagenicity, cell cycle kinetics and gene expression of Bauhinia holophylla (Bong.) Steud. in HepG2 cells in vitro

Bauhinia holophylla (Bong.) Steud. (Fabaceae) is a plant used in Brazilian folk medicine to treat diabetes and inflammation. This study evaluated the phytochemical properties, cytotoxic, apoptotic, mutagenic/antimutagenic effects and alterations in gene expression (RNAm) in HepG2 cells treated with the B. holophylla extract. The phytochemical profile highlight the presence of flavonoids isorhamentin and quercetin derivates. The MTT assay was used to evaluate the cytotoxicity of different concentrations for different treatment times. Three concentrations (7.5, 15, 30 µg/mL) were chosen for assessment of apoptosis (AO/EB), mutagenicity (micronucleus), and cell cycle kinetics (flow cytometry). Thereafter, the concentration of 7.5 µg/mL was chosen to evaluate the protective effects against DNA damage induced by benzo[a]pyrene (B[a]P). At concentrations higher than 7.5 µg/mL (between 10 and 50 µg/mL), the extract was cytotoxic, induced apoptosis, and caused antiproliferative effects. However, it did not induce micronucleus and a reduction of apoptotic and micronucleated cells was observed in treatments that included the extract and B[a]P. The protective effect is attributable to the presence of flavonoids, described as antioxidants, inhibitors of DNA adduct and activators of detoxifying enzymes. The results of the present study such as absence of cytotoxic and mutagenic effects and protective effects against known carcinogens suggest that B. holophylla has potential for use soon as herbal medicine.

The action of antidiabetic plants of the canadian james bay cree traditional pharmacopeia on key enzymes of hepatic glucose homeostasis

We determined the capacity of putative antidiabetic plants used by the Eastern James Bay Cree (Canada) to modulate key enzymes of gluconeogenesis and glycogen synthesis and key regulating kinases. Glucose-6-phosphatase (G6Pase) and glycogen synthase (GS) activities were assessed in cultured hepatocytes treated with crude extracts of seventeen plant species. Phosphorylation of AMP-dependent protein kinase (AMPK), Akt, and Glycogen synthase kinase-3 (GSK-3) were probed by Western blot. Seven of the seventeen plant extracts significantly decreased G6Pase activity, Abies balsamea and Picea glauca, exerting an effect similar to insulin. This action involved both Akt and AMPK phosphorylation. On the other hand, several plant extracts activated GS, Larix laricina and A. balsamea, far exceeding the action of insulin. We also found a significant correlation between GS stimulation and GSK-3 phosphorylation induced by plant extract treatments. In summary, three Cree plants stand out for marked effects on hepatic glucose homeostasis. P. glauca affects glucose production whereas L. laricina rather acts on glucose storage. However, A. balsamea has the most promising profile, simultaneously and powerfully reducing G6Pase and stimulating GS. Our studies thus confirm that the reduction of hepatic glucose production likely contributes to the therapeutic potential of several antidiabetic Cree traditional medicines.

Transcriptomic and metabonomic profiling reveal synergistic effects of quercetin and resveratrol supplementation in high fat diet fed mice

Dietary quercetin and resveratrol have been frequently used in treating various diseases, but the underlying mechanisms are not entirely clear. Here, we report combined transcriptomic and metabonomic profiling that showed that the combined supplementation with quercetin and resveratrol produced synergistic effects on a high-fat diet-induced metabolic phenotype in mice. Histological and phenotypic improvements in serum and hepatic total cholesterol, insulin, fasting blood glucose, and HbA1c were also observed in mice receiving combined quercetin and resveratrol supplementation. This combined quercetin and resveratrol supplementation resulted in significant restoration of gene sets in functional pathways of glucose/lipid metabolism, liver function, cardiovascular system, and inflammation/immunity, which were altered by high fat diet feeding. The integration of transcriptomic and metabonomic data indicated quercetin and resveratrol supplementation enhanced processes of glycolysis and fatty acid oxidation, as well as suppressed gluconeogenesis. These alterations discovered at both the transcriptional and metabolic levels highlight the significance of combined "omics" platforms for elucidating mechanistic pathways altered by dietary polyphenols, such as quercetin and resveratrol, in a synergistic manner.

Chemical composition and biological potential of plants from the genus Bauhinia

Plants of the genus Bauhinia (Fabaceae, Leguminosae), commonly known as cow's-paw or cow's hoof, are widely distributed in most tropical countries and have been used frequently in folk medicine to treat different kinds of pathologies, particularly diabetes, infections, as well as pain and inflammation. In recent years, interest in these plants has increased considerably throughout the world. The biological properties of different phytopreparations and pure metabolites have been investigated in numerous experimental in vivo and in vitro models. Although some contradicting evidence has been documented, in general, the results support the reported therapeutic properties, indicating that they are mainly due to the presence of flavonoids. This review summarizes the recent chemical and biological knowledge of plants of the genus Bauhinia.

The flavonoid silibinin decreases glucose-6-phosphate hydrolysis in perfused rat hepatocytes by an inhibitory effect on glucose-6-phosphatase

BACKGROUND/AIMS

The flavonoid silibinin has been reported to be beneficial in several hepatic disorders. Recent evidence also suggests that silibinin could be beneficial in the treatment of type 2 diabetes, owing to its anti-hyperglycemic properties. However, the mechanism(s) underlying these metabolic effects remains unknown.

METHODS

The effects of silibinin on liver gluconeogenesis were studied by titrating hepatocytes from starved rats with sub-saturating concentrations of various exogenous substrates in a perifusion system. Hepatocytes from fed rats were also used to investigate glycogenolysis from endogenous glycogen. The effect of silibinin on glucose-6-phosphatase kinetics was determined in intact and permeabilized rat liver microsomes.

RESULTS

Silibinin induced a dose-dependent inhibition of gluconeogenesis associated with a potent decrease in glucose-6-phosphate hydrolysis. This effect was demonstrated whatever the gluconeogenic substrates used, i.e. dihydroxyacetone, lactate/pyruvate, glycerol and fructose. In addition, silibinin decreased the glucagon-induced stimulation of both gluconeogenesis and glycogenolysis, this being associated with a reduction of glucose-6-phosphate hydrolysis. Silibinin inhibits glucose-6-phosphatase in rat liver microsomes in a concentration-dependent manner that could explain the decrease in glucose-6-phosphate hydrolysis seen in intact cells.

CONCLUSION

The inhibitory effect of silibinin on both hepatic glucose-6-phosphatase and gluconeogenesis suggests that its use may be interesting in treatment of type 2 diabetes.