Lihong Hu

Oleanolic acid and its derivatives: new inhibitor of protein tyrosine phosphatase 1B with cellular activities.

Protein tyrosine phosphatase 1B is a key factor in the negative regulation of insulin pathway and a promising target for treatment of diabetes and obesity. Herein, a series of competitive inhibitors were optimized from oleanolic acid, a natural triterpenoid identified against PTP1B by screening libraries of traditional Chinese medicinal herbs. Modifying at 3 and 28 positions, we obtained compound 13 with a K(i) of 130 nM, which exhibited good selectivity between other phosphatases involved in insulin pathway except T-cell protein tyrosine phosphatase. Further evaluation in cell models illustrated that the derivatives enhanced insulin receptor phosphorylation in CHO/hIR cells and also stimulated glucose uptake in L6 myotubes with or addition of without insulin.

Arctigenin effectively ameliorates memory impairment in Alzheimer's disease model mice targeting both β-amyloid production and clearance.

Alzheimers disease (AD) chiefly characterizes a progressively neurodegenerative disorder of the brain, and eventually leads to irreversible loss of intellectual abilities. The β-amyloid (Aβ)-induced neurodegeneration is believed to be the main pathological mechanism of AD, and Aβ production inhibition or its clearance promotion is one of the promising therapeutic strategies for anti-AD research. Here, we report that the natural product arctigenin from Arctium lappa (L.) can both inhibit Aβ production by suppressing β-site amyloid precursor protein cleavage enzyme 1 expression and promote Aβ clearance by enhancing autophagy through AKT/mTOR signaling inhibition and AMPK/Raptor pathway activation as investigated in cells and APP/PS1 transgenic AD model mice. Moreover, the results showing that treatment of arctigenin in mice highly decreased Aβ formation and senile plaques and efficiently ameliorated AD mouse memory impairment strongly highlight the potential of arctigenin in anti-AD drug discovery.

Biochemical characterization and inhibitor discovery of shikimate dehydrogenase from Helicobacter pylori

Shikimate dehydrogenase (SDH) is the fourth enzyme involved in the shikimate pathway. It catalyzes the NADPH‐dependent reduction of 3‐dehydroshikimate to shikimate, and has been developed as a promising target for the discovery of antimicrobial agent. In this report, we identified a new aroE gene encoding SDH from Helicobacter pylori strain SS1. The recombinant H. pylori shikimate dehydrogenase (HpSDH) was cloned, expressed, and purified in Escherichia coli system. The enzymatic characterization of HpSDH demonstrates its activity with kcat of 7.7 s−1 and Km of 0.148 mm toward shikimate, kcat of 7.1 s−1 and Km of 0.182 mm toward NADP, kcat of 5.2 s−1 and Km of 2.9 mm toward NAD. The optimum pH of the enzyme activity is between 8.0 and 9.0, and the optimum temperature is around 60 °C. Using high throughput screening against our laboratory chemical library, five compounds, curcumin (1), 3‐(2‐naphthyloxy)‐4‐oxo‐2‐(trifluoromethyl)‐4H‐chromen‐7‐yl 3‐chlorobenzoate (2), butyl 2‐{[3‐(2‐naphthyloxy)‐4‐oxo‐2‐(trifluoromethyl)‐4H‐chromen‐7‐yl]oxy}propanoate (3), 2‐({2‐[(2‐{[2‐(2,3‐dimethylanilino)‐2‐oxoethyl]sulfanyl}‐1,3‐benzothiazol‐6‐yl)amino]‐2‐oxoethyl}sulfanyl)‐N‐(2‐naphthyl)acetamide (4), and maesaquinone diacetate (5) were discovered as HpSDH inhibitors with IC50 values of 15.4, 3.9, 13.4, 2.9, and 3.5 µm, respectively. Further investigation indicates that compounds 1, 2, 3, and 5 demonstrate noncompetitive inhibition pattern, and compound 4 displays competitive inhibition pattern with respect to shikimate. Compounds 1, 4, and 5 display noncompetitive inhibition mode, and compounds 2 and 3 show competitive inhibition mode with respect to NADP. Antibacterial assays demonstrate that compounds 1, 2, and 5 can inhibit the growth of H. pylori with MIC of 16, 16, and 32 µg·mL−1, respectively. This current work is expected to favor better understanding the features of SDH and provide useful information for the development of novel antibiotics to treat H. pylori‐associated infection.

Three flavonoids targeting the beta-hydroxyacyl-acyl carrier protein dehydratase from Helicobacter pylori: crystal structure characterization with enzymatic inhibition assay

Flavonoids are the major functional components of many herbal and insect preparations and demonstrate varied pharmacological functions including antibacterial activity. Here by enzymatic assay and crystal structure analysis, we studied the inhibition of three flavonoids (quercetin, apigenin, and (S)‐sakuranetin) against the β‐hydroxyacyl‐acyl carrier protein dehydratase from Helicobacter pylori (HpFabZ). These three flavonoids are all competitive inhibitors against HpFabZ by either binding to the entrance of substrate tunnel B (binding model A) or plugging into the tunnel C near the catalytic residues (binding model B) mainly by hydrophobic interaction and hydrogen‐bond pattern. Surrounded by hydrophobic residues of HpFabZ at both positions of models A and B, the methoxy group at C‐7 of (S)‐sakuranetin seems to play an important role for the inhibitors binding to HpFabZ, partly responsible for the higher inhibitory activity of (S)‐sakuranetin than those of quercetin and apigenin against HpFabZ (IC50 in μM: (S)‐sakuranetin, 2.0 ± 0.1; quercetin: 39.3 ± 2.7; apigenin, 11.0 ± 2.5). Our work is expected to supply useful information for understanding the potential antibacterial mechanism of flavonoids.

Small molecules from natural sources, targeting signaling pathways in diabetes.

Diabetes mellitus (DM) is a metabolic disease caused by genetic or environmental factors. It has rendered a severe menace to the middle-aged and elderly, while there is still lack of efficient drugs against this disease. The pathogenic mechanism for DM is complex, and the complicated networks related to this disease involve distinct signaling pathways. Currently, discovery of potential modulators targeting these pathways has become a potent approach for anti-diabetic drug lead compound development. Compared with synthetic compounds, natural products provide inherent larger-scale structural diversity and have been the major resource of bioactive agents for new drug discovery. To date, more and more active components from plants or marine organisms have been reported to regulate diabetic pathophysiological signaling pathways and exhibit anti-diabetic activity. This review will summarize the regulation of natural small molecules on some key signaling pathways involved in DM. These pathways include insulin signaling pathway, carbohydrate metabolism pathway, the pathways involving insulin secretion and PPAR regulation, endoplasmic reticulum (ER) stress and inflammation related pathways and chromatin modification pathways.

Corosolic acid stimulates glucose uptake via enhancing insulin receptor phosphorylation

Corosolic acid, a triterpenoid compound widely existing in many traditional Chinese medicinal herbs, has been proved to have antidiabetic effects on animal experiments and clinical trials. However, the underlying mechanisms remain unknown. Here, we investigate its cellular effects and related signaling pathway. We demonstrate that it enhances glucose uptake in L6 myotubes and facilitates glucose transporter isoform 4 translocation in CHO/hIR cells. These actions are mediated by insulin pathway activation and can be blocked by phosphatidylinositol 3-kinase (PI(3) Kinase) inhibitor wortmannin. Furthermore, Corosolic acid inhibits the enzymatic activities of several diabetes-related non-receptor protein tyrosine phosphatases (PTPs) in vitro, such as PTP1B, T-cell-PTP, src homology phosphatase-1 and src homology phosphatase-2.

Thiamine hydrochloride (VB1): an efficient promoter for the one-pot synthesis of benzo[4,5]imidazo[1,2-a]pyrimidine and [1,2,4]triazolo[1,5-a]pyrimidine derivatives in water medium

A straightforward and general method has been developed for the synthesis of benzo[4,5]imidazo[1,2-a]pyrimidine and [1,2,4]triazolo[1,5-a]pyrimidine derivatives by simply combining 2-aminobenzimidazole or 3-amino-1,2,4-triazole, aldehyde, and β-dicarbonyl compound in the presence of a catalytic amount of thiamine hydrochloride (VB1). The advantages of this method are the use of an inexpensive and readily available catalyst, easy workup, improved yields, and the use of water as the solvent that is considered to be relatively environmentally benign.

An Approach to 3,6-Disubstituted 2,5-Dioxybenzoquinones via Two Sequential Suzuki Couplings. Three-Step Synthesis of Leucomelone

Two sequential Suzuki coupling reactions have been developed for efficient synthesis of synthetically and biologically important 3,6-disubstituted 2,5-dioxybenzoquinone architectures in a highly chemoselective controlled manner. The method serves as a key step in the total synthesis of leucomelone in three steps and in 61% overall yield.

Reversal of P-gp and MRP1-mediated multidrug resistance by H6, a gypenoside aglycon from Gynostemma pentaphyllum, in vincristine-resistant human oral cancer (KB/VCR) cells

Multidrug resistance (MDR) to anticancer drugs is a major obstacle to successful chemotherapy in the treatment of cancers. Identification of natural compounds capable of circumventing MDR with minimal adverse side effects is an attractive goal. Here, we found that H6, a gypenoside aglycon from Gynostemma pentaphyllum, displayed potent anti-MDR activity. Average resistant fold (RF) of H6 is 1.03 and 1.04 in KB/VCR and MCF-7/ADR cells compared to their parental cells. H6 alone ranging from 2 μmol/l to 40 μmol/l (μM) did not display a significant anti-proliferative effect on KB/VCR cells and other cells, while the compound at these concentrations enhanced the cytotoxicity of vincristine (VCR) to KB/VCR cells. H6 showed a significant synergistic effect in combination with VCR. By quantification of sub-G(1) fraction cells, H6 also enhanced the VCR-induced apoptosis in a dose-dependent manner. The short time treatment with H6 increased the intracellular accumulation of rhodamine 123 (Rho123) and 5(6)-carboxyfluorescein diacetate (CFDA) in KB/VCR cells. Further studies showed that H6 treatment resulted in the decrease of the RNA transcript level of P-glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1) and breast cancer resistance protein (BCRP). H6 inhibited the function of P-gp by stimulating P-gp ATPase activity and decreased MRP1 expression with a blockade of STAT3 phosphorylation. These findings suggest that H6, a multi-targets reversal agent with no significant toxic effect, may be a potential candidate to circumvent the P-gp and MRP1-mediated MDR.

Acetohydrazone: A Transient Directing Group for Arylation of Unactivated C(sp3)–H Bonds

A straightforward and efficient method has been developed for the synthesis of 2-benzylbenzaldehyde derivatives from 2-methylbenzaldehyde and iodobenzene via a C(sp(3))-H activation process. In the course of the activation reaction, acetohydrazone is formed between 2-benzylbenzaldehyde and acetohydrazine as a transient directing group. As a new kind of transient directing group, acetohydrazone exhibits a remarkable directing effect to give corresponding products in good to excellent yields.