Oligonol promotes glucose uptake by modulating the insulin signaling pathway in insulin-resistant HepG2 cells via inhibiting protein tyrosine phosphatase 1B.

Insulin resistance and protein tyrosine phosphatase 1B (PTP1B) overexpression are strongly associated with type 2 diabetes mellitus (T2DM), which is characterized by defects in insulin signaling and glucose intolerance. In a previous study, we demonstrated oligonol inhibits PTP1B and α-glucosidase related to T2DM. In this study, we examined the molecular mechanisms underlying the anti-diabetic effects of oligonol in insulin-resistant HepG2 cells. Glucose uptake was assessed using a fluorescent glucose tracer, 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose, and the signaling pathway was investigated by western blotting. Oligonol significantly increased insulin-provoked glucose uptake and decreased PTP1B expression, followed by modulation of ERK phosphorylation. In addition, oligonol activated insulin receptor substrate 1 by reducing phosphorylation at serine 307 and increasing that at tyrosine 895, and enhanced the phosphorylations of Akt and phosphatidylinositol 3-kinase. Interestingly, it also reduced the expression of two key enzymes of gluconeogenesis (glucose 6-phosphatase and phosphoenolpyruvate carboxykinase), attenuated oxidative stress by scavenging/inhibiting peroxynitrite, and reactive oxygen species (ROS) generation, and augmented the expression of nuclear factor kappa B. These findings suggest oligonol improved the insulin sensitivity of insulin-resistant HepG2 cells by attenuating the insulin signaling blockade and modulating glucose uptake and production. Furthermore, oligonol attenuated ROS-related inflammation and prevented oxidative damage in our in vitro model of type 2 diabetes. These result indicate oligonol has promising potential as a treatment for T2DM.

Potential anti-cholinesterase and ß-site amyloid precursor protein cleaving enzyme 1 inhibitory activities of cornuside and gallotannins from Cornus officinalis fruits.

Cholinesterase (ChE) and ß-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitors are promising agents for the treatment of Alzheimer's disease (AD). In the present study, we examined the inhibitory activity of seven compounds isolated from the fruits of Cornus officinalis, cornuside, polymeric proanthocyanidins, 1,2,3-tri-O-galloyl-ß-D-glucose, 1,2,3,6-tetra-O-galloyl-ß-D-glucose, tellimagrandin I, tellimagrandin II, and isoterchebin, against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and BACE1. All of the compounds displayed concentration-dependent in vitro inhibitory activity toward the ChEs and BACE1. Among them, tellimagrandin II exhibited the best inhibitory activity toward ChEs, whereas the best BACE1 inhibitor was 1,2,3,6-tetra-O-galloyl-ß-D-glucose. Isoterchebin and polymeric proanthocyanidins were also significant ChE inhibitors. The kinetic and docking studies demonstrated that all compounds interacted with both the catalytic active sites and the peripheral anionic sites of the ChEs and BACE1. Tellimagrandin II, isoterchebin, and the polymeric proanthocyanidins exhibited concentration-dependent inhibition of peroxynitrite-mediated protein tyrosine nitration. In conclusion, we identified significant ChE and BACE1 inhibitors from Corni Fructus that could have value as new multi-targeted compounds for anti-AD agents.

Prunin is a highly potent flavonoid from Prunus davidiana stems that inhibits protein tyrosine phosphatase 1B and stimulates glucose uptake in insulin-resistant HepG2 cells.

Prunin is the main flavonoid in Prunus davidiana stems and improves hyperglycemia and hyperlipidemia in streptozotocin-induced diabetic rats. The aim of this study was to investigate the in vitro anti-diabetic potential of prunin via the inhibition of protein tyrosine phosphatase 1B (PTP1B), α-glucosidase, peroxynitrite (ONOO-)-mediated tyrosine nitration, and stimulation of glucose uptake in insulin-resistant hepatocytes. In addition, a molecular docking simulation was performed to predict specific prunin binding modes during PTP1B inhibition. Prunin showed strong inhibitory activity against PTP1B, with an IC50 value of 5.5 ± 0.29 µM, and significant inhibitory activity against α-glucosidase, with an IC50 value of 317 ± 2.12 µM. Moreover, a kinetics study revealed that prunin inhibited PTP1B (K i = 8.66) and α-glucosidase (K i = 189.56) with characteristics typical of competitive and mixed type inhibitors, respectively. Docking simulations showed that prunin selectively inhibited PTP1B by targeting its active site and exhibited good binding affinity, with a docking score of -9 kcal/mol. Furthermore, prunin exhibited dose-dependent inhibitory activity against ONOO--mediated tyrosine nitration and stimulated glucose uptake by decreasing PTP1B expression level in insulin-resistant HepG2 cells. These results indicate that prunin has significant potential as a selective PTP1B inhibitor and may possess anti-diabetic properties by improving insulin resistance.

Fucosterol activates the insulin signaling pathway in insulin resistant HepG2 cells via inhibiting PTP1B.

Insulin resistance is a characteristic feature of type 2 diabetes mellitus (T2DM) and is characterized by defects in insulin signaling. This study investigated the modulatory effects of fucosterol on the insulin signaling pathway in insulin-resistant HepG2 cells by inhibiting protein tyrosine phosphatase 1B (PTP1B). In addition, molecular docking simulation studies were performed to predict binding energies, the specific binding site of fucosterol to PTP1B, and to identify interacting residues using Autodock 4.2 software. Glucose uptake was determined using a fluorescent D-glucose analogue and the glucose tracer 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxyglucose, and the signaling pathway was detected by Western blot analysis. We found that fucosterol enhanced insulin-provoked glucose uptake and conjointly decreased PTP1B expression level in insulin-resistant HepG2 cells. Moreover, fucosterol significantly reduced insulin-stimulated serine (Ser307) phosphorylation of insulin receptor substrate 1 (IRS1) and increased phosphorylation of Akt, phosphatidylinositol-3-kinase, and extracellular signal- regulated kinase 1 at concentrations of 12.5, 25, and 50 µM in insulin-resistant HepG2 cells. Fucosterol inhibited caspase-3 activation and nuclear factor kappa B in insulin-resistant hepatocytes. These results suggest that fucosterol stimulates glucose uptake and improves insulin resistance by downregulating expression of PTP1B and activating the insulin signaling pathway. Thus, fucosterol has potential for development as an anti-diabetic agent.

Kinetics and molecular docking studies of loganin, morroniside and 7-O-galloyl-D-sedoheptulose derived from Corni fructus as cholinesterase and ß-secretase 1 inhibitors.

We evaluated the major active components isolated from Corni Fructus: loganin, morroniside, and 7-O-galloyl-D-sedoheptulose as inhibitors of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and ß-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) for use in Alzheimer's disease treatment. These compounds exhibited predominant cholinesterase (ChEs) inhibitory effects with IC50 values of 0.33, 3.95, and 10.50 ± 1.16 µM, respectively, for AChE, and 33.02, 37.78, and 87.94 ± 4.66 µM, respectively, for BChE. Kinetics studies revealed that loganin and 7-O-galloyl-D-sedoheptulose inhibited AChE with characteristics typical of mixed inhibitors, while morroniside was found to be a noncompetitive inhibitor against AChE and also exerted mixed BChE inhibitory activities. For BACE1, loganin showed noncompetitive type inhibitory effects, while morroniside and 7-O-galloyl-D-sedoheptulose were found to be mixed inhibitors. Furthermore, these compounds exhibited dose-dependent inhibitory activity with ONOO(-)-mediated protein tyrosine nitration. Molecular docking simulation of these compounds demonstrated negative binding energies for ChEs, and BACE1, indicating high affinity and tighter binding capacity for the active site of the enzyme. Loganin was the most potent inhibitor against both ChEs and BACE1. The data suggest that these compounds together can act as a triple inhibitor of AChE, BChE, and BACE1, providing a preventive and therapeutic strategy for Alzheimer's disease treatment.

Inhibitory evaluation of oligonol on α-glucosidase, protein tyrosine phosphatase 1B, cholinesterase, and ß-secretase 1 related to diabetes and Alzheimer's disease.

Oligonol is a low-molecular-weight form of polyphenol that is derived from lychee fruit extract and contains catechin-type monomers and oligomers of proanthocyanidins. This study investigates the anti-diabetic activities of oligonol via α-glucosidase and human recombinant protein tyrosine phosphatase 1B (PTP1B) assays, as well as its anti-Alzheimer activities by evaluating the ability of this compound to inhibit acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and ß-site amyloid precursor protein cleaving enzyme 1 (BACE1). Oligonol exhibited potent concentration-dependent anti-diabetic activities by inhibiting α-glucosidase and PTP1B with IC50 values of 23.14 µg/mL and 1.02 µg/mL, respectively. Moreover, a kinetics study revealed that oligonol inhibited α-glucosidase (K i = 22.36) and PTP1B (K i = 8.51) with characteristics typical of a mixed inhibitor. Oligonol also displayed potent concentration-dependent inhibitory activity against AChE and BChE with IC50 values of 4.34 µg/mL and 2.07 µg/mL, respectively. However, oligonol exhibited only marginal concentration-dependent BACE1 inhibitory activity with an IC50 value of 130.45 µg/mL. A kinetics study revealed mixed-type inhibition against AChE (K i = 4.65) and BACE1 (K i = 58.80), and noncompetitive-type inhibition against BChE (K i = 9.80). Furthermore, oligonol exhibited dose-dependent inhibitory activity against peroxynitrite (ONOO(-))-mediated protein tyrosine nitration. These results indicate that oligonol has strong preventative potential in diabetes mellitus and in Alzheimer's disease.