Guang Xin

Haloemodin as novel antibacterial agent inhibiting DNA gyrase and bacterial topoisomerase I.

Drug-resistant bacterial infections and lack of available antibacterial agents in clinical practice are becoming serious risks to public health. We synthesized a new class of haloemodins by modifying a traditional Chinese medicine component, emodin. The novel haloemodin exerts strong inhibitory activity on bacterial topoisomerase I and DNA gyrase, and not on the topoisomerases of human origin. In principle, it shows remarkable antibacterial activities against laboratory and clinically isolated Gram-positive bacteria, including vancomycin-resistant Enterococcus faecium and methicillin-resistant Staphylococcus aureus. We further expanded its antibacterial spectrum into against Gram-negative bacteria with the assistance of polymyxin B nonapeptide, which helps haloemodin to penetrate through the bacterial outer membrane. Finally, the therapeutic effect of haloemodin in vivo was confirmed in curing S. aureus-induced keratitis on rabbit model. With distinctive structural difference from the antibiotics we used, the haloemodins are of value as promising antibacterial pharmacophore, especially for combat the infections caused by drug-resistant pathogens.

Anti-thrombosis effect of diosgenyl saponins in vitro and in vivo.

Thrombosis in coronary or cerebral arteries is the major cause of morbidity and mortality worldwide. Diosgenin and total steroidal saponins extracted from the rhizome of Dioscorea zingiberensis C.H. Wright are demonstrated to have anti-thrombotic activity. However, few studies describe the anti-thrombotic activity of the diosgenyl saponin monomer. In the present study, a simple and convenient method for the preparation of a new disaccharide saponin, diosgenyl β-D-galactopyranosyl-(1→4)-β-D-glucopyranoside (3), is described. We evaluated the anti-thrombotic effects of diosgenin and four diosgenyl saponins by measuring the bleeding time; the results showed that compound 3 exhibits outstanding efficiency in prolonging the bleeding time. Furthermore, we assessed whether compound 3 could alter platelet aggregation in vitro and in vivo. In addition, activated partial thromboplastin time (APTT), thrombin time (TT), prothrombin time (PT), coagulation factors and protection rate in mice were measured to evaluate the anti-thrombotic effect of compound 3. The results show that compound 3 inhibited platelet aggregation, prolonged APTT, inhibited factor VIII activities in rats, and increased the protection rate in mice in a dose-dependent manner. Taken together, these findings suggested that diosgenyl saponins, especially compound 3, had anti-thrombotic activity. It may execute anti-thrombotic activity through inhibiting factor VIII activities and platelet aggregation.

9,10-Dihydrophenanthrene derivatives and one 1,4-anthraquinone firstly isolated from Dioscorea zingiberensis C. H. Wright and their biological activities.

Two new phenanthrene derivatives, 2,5,7-trimethoxy-9,10-dihydrophenanthrene-1,4-dione (1) and 2,5,6-trihydroxy-3,4-dimethoxy-9,10-dihydrophenanthrene (3), one new anthracenedione, 2,5,7-trimethoxyanthracene-1,4-dione (2), together with two known 9,10-dihydrophenanthrenes (4-5) were isolated from the rhizomes of Dioscorea zingiberensis C. H. Wright. The structures of these new compounds were established based on extensive NMR spectroscopy. Several isolated compounds were evaluated for the inhibition against nitric oxide (NO) production in the lipopolysaccharide (LPS)-activated RAW 264.7 macrophage cell line, DPPH radical scavenging, and inhibitory activity on Free Fatty Acids (FFAs) induced triglyceride accumulation in HepG2 cells. Compound 2 exhibited moderate anti-inflammatory activity, compound 3 possessed comparable DPPH radical scavenging activity as Vitamin C, compounds 2 and 4 showed potent inhibitory activities on triglyceride accumulation.

Novel polyacetylenes from Coreopsis tinctoria Nutt.

Phytochemical investigation of the 95% EtOH extract of Coreopsis tinctoria Nutt. resulted in the isolation of two novel polyacetylenes, (2S)-(3Z,11E)-decadiene-5,7,9-triyne-1,2-diol (1) and (2R)-(3E,11Z)-decadiene-5,7,9-triyne-1,2-diol (2), together with two known polyacetylenes (3 and 4). The structures of these novel compounds were determined by extensive two-dimensional nuclear magnetic resonance, high-resolution mass spectrometry, and optical rotation. Compounds 1, 2, and 4 were evaluated for their anti-proliferative activities against C26 cell growth and inhibitory effects on the lipo-poly-saccharides-induced nitric oxide production using murine macrophage RAW 264.7 cells. However, compounds 1, 2, and 4 just showed weak activities.

Determination of deltonin in rat plasma by using HPLC–MS/MS and the application of this method in pharmacokinetic studies

Deltonin is a naturally occurring spirostanol glycoside from Dioscorea zingiberensis C.H. Wright, which is used in traditional Chinese medicine. It exerts strong cytotoxic effect on C26 cells, inhibits C26 derived-tumor growth, and prolongs the survival of tumor-bearing mice after its oral administration, indicating its potential for use as an anti-tumor drug. To investigate the pharmacokinetic profiles of deltonin, a rapid, sensitive, and simplified high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) assay was developed and validated for the determination of deltonin in rat plasma. After acetonitrile-mediated plasma protein precipitation, chromatographic separation of deltonin was achieved using a reversed phase Hypersil Gold column (150mm×2.1mm, 5μm), with gradient elution using 0.1% formic acid and acetonitrile. Thereafter, deltonin was quantified using MS/MS with electrospray ionization (ESI) in positive multiple reaction monitoring (MRM) mode. The flow rate of the mobile phase was 200μL/min, and the retention time was 9.03min for deltonin and 6.31min for the internal standard (IS: 20(S)-ginsenoside Rb1). The linear range of the calibration curve was 2-5000ng/mL (r(2)>0.99), and the limit of detection (LOD) was 0.46ng/mL. The intra- and inter-day accuracies ranged from -2.8% to 11.1% and precisions (RSD) were within 13.1%. Deltonin was found to be stable under short-term temperature conditions, post-preparative temperature conditions, and after 3 freeze-thaw cycles conditions. The validated method was successfully applied to a pharmacokinetic study in rats after oral administration of deltonin (50 and 100mg/kg). The pharmacokinetics is characterized by high apparent clearance (CL/F) and apparent volume of distribution (Vd/F).

d-galactose induces premature senescence of lens epithelial cells by disturbing autophagy flux and mitochondrial functions

Cataract is the leading cause of blindness with an estimated 16 million people affected worldwide. d-galactose (d-gal) is a reducing sugar that widely distributed in foodstuffs, and studies show that d-gal could promote cataract formation by damaging nature lens epithelial cells (LECs). However, the underlying mechanism is unclear. In our present study, d-gal resulted in premature senescence of LECs, which was confirmed by determining the β-galactosidase activity, cell proliferative potential and cell cycle distribution, though apoptosis of LECs was not observed. We also verified that d-gal induced the impairment of autophagy flux by measuring the expression of LC3II and P62. Meanwhile, we found that d-gal induced mitochondrial dysfunctions of LECs through increasing reactive oxygen species (ROS), reducing ATP synthesis and mitochondrial potential (MMP), enhancing the concentration of cytoplasm Ca2+ and permeability transition pore (mPTP) opening. Metformin, as a potential anti-aging agent, suppressed the senescence of LECs by restoring autophagy flux and mitochondria functions. Nevertheless, the antioxidant N-acetylcysteine (NAC) scavenged ROS significantly but was not efficient in preventing LECs from premature senescence. Our data suggests that restoring autophagy activity and improving mitochondrial functions may be a potential strategy for the prevention of LECs senescence-related cataract.

Synthesis, characterization, and biological studies of diosgenyl analogs

Abstract A series of diosgenyl analogs were prepared from diosgenin to evaluate their anticancer activity and antithrombotic property. Analog 4, which had a spiroketal structure with a 6-aminohexanoic acid residue, exhibited the highest potency against all five tumor cell lines. It significantly blocked tumor growth, induced cell apoptosis and autophagy, and regulated cellular calcium concentration, mitochondrial membrane potential, adenosine triphosphate, and cell cycle. In addition, fluorescence-tagged compounds indicated that the analogs could rapidly accumulate in the cytoplasm, but no specific localization in the nucleus of cancer cells was observed. Furthermore, preliminary structure–activity relationship studies demonstrated that spiroketal analogs exhibit better antithrombotic activity than furostanic analogs, which exhibit the opposite effect by promoting thrombosis. Our study indicates that compound 4 may be a promising anticancer drug candidate for cancer patients with thromboembolism.

The diosgenin prodrug nanoparticles with pH-responsive as a drug delivery system uniquely prevents thrombosis without increased bleeding risk

Thrombosis is the leading cause of death in patients with cardiovascular disease in the world. Current antithrombotic agent aspirin has serious side effects such as higher bleeding risk and serious gastrointestinal ulcers. Diosgenin reported in clinical research could prevent thrombosis without side effects. However, poor bioavailability and low knowledge on its molecular targets limit its clinical application. A novel prodrug with antithrombotic effect was prepared based on conjugating diosgenin derivatives to PEG with Schiff-base bond. The prodrug with long blood circulation time and satisfying safety could self-assemble into micelles in water. The prodrug micelles with pH-responsibility could targetedly release diosgenin in position of thrombus in vivo. The results indicate that the prodrug micelles without bleeding risk and histological damages prevent thrombosis by inhibiting platelet activation and apoptosis. Our studies demonstrate that the prodrug micelles could obviously enhance the efficacy in the prevention of arterial thrombus and venous thrombus than aspirin.

Chlorinated emodin as a natural antibacterial agent against drug-resistant bacteria through dual influence on bacterial cell membranes and DNA

The rise in infections caused by drug-resistant pathogens and a lack of effective medicines requires the discovery of new antibacterial agents. Naturally chlorinated emodin 1,3,8-trihydroxy-4-chloro-6-methyl-anthraquinone (CE) from fungi and lichens was found to markedly inhibit the growth of Gram-positive bacteria, especially common drug-resistant bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VRE). CE was confirmed to cause significant potassium leakage, cell membrane depolarization and damage to the selective permeability of cell membranes in bacterial cells, resulting in bacterial cell death. In addition, CE was shown to have a strong electrostatic interaction with bacterial DNA and induce DNA condensation. Thus, CE is a promising natural antibacterial pharmacophore against Gram-positive bacteria, especially common drug-resistant MRSA and VRE isolates, with a dual antibacterial mechanism that damages bacterial cell membranes and DNA.

Deoxyarbutin displays antitumour activity against melanoma in vitro and in vivo through a p38-mediated mitochondria associated apoptotic pathway

Deoxyarbutin (DeoxyArbutin, dA), a natural compound widely used in skin lighting, displayed selectively cytotoxicity in vitro. In the study, we found that dA significantly inhibited viability/proliferation of B16F10 melanoma cells, induced tumour cell arrest and apoptosis. Furthermore, dA triggered its pro-apoptosis through damaging the mitochondrial function (membrane potential loss, ATP depletion and ROS overload generation etc.) and activating caspase-9, PARP, caspase-3 and the phosphorylation of p38. Treatment with p38 agonist confirmed the involvement of p38 pathway triggered by dA in B16F10 cells. The in vivo finding also revealed that administration of dA significantly decreased the tumour volume and tumour metastasis in B16F10 xenograft model by inhibiting tumour proliferation and inducing tumour apoptosis. Importantly, the results indicated that dA was specific against tumour cell lines and had no observed systemic toxicity in vivo. Taken together, our study demonstrated that dA could combate tumour in vitro and in vivo by inhibiting the proliferation and metastasis of tumour via a p38-mediated mitochondria associated apoptotic pathway.