Naphthofuroquinone derivatives show strong antimycobacterial activities against drug-resistant Mycobacteria.

Tuberculosis, one of the world's major health problems, has become more serious due to the emergence of multi-drug resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis (MTB). In this study, we performed three anti-MTB assays to evaluate the anti-mycobacterial activity of naphthofuroquinone derivatives against drug-resistant MTB. Among them, methyl 5-[2-(dimethylamino)ethoxy]-7,12-dioxo-7,12-dihydrodinaphtho[1,2-b:2',3'-d]furan-6-carboxylate (DFC2) exhibited strong anti-mycobacterial activity against MTB H37Ra, H37Rv and four drug-resistant MTB strains. The MIC of DFC2 ranged from 0.19-0.39 µg/ml to 0.78-1.56 µg/ml against all tested MTB strains. Moreover, DFC2 showed low cytotoxicity against fibroblast cells (L929) at concentrations 10-40-fold higher than their MICs. The IC50 value of DFC2 against L929 cells was 15.218 µg/ml. In addition, DFC2 reduced the number of intracellular M. tuberculosis in macrophages in a dose-dependent manner. Taken together, our results indicate DFC2 to be promising new candidate agents for the treatment of tuberculosis.

In vitro activity of (-)-deoxypergularinine, on its own and in combination with anti-tubercular drugs, against resistant strains of Mycobacterium tuberculosis.

BACKGROUND: The increasing incidence of multidrug-resistant tuberculosis (MDR-TB) infections has created a need for new effective drugs that also target extensively drug-resistant tuberculosis (XDR-TB) and/or augment the activities of existing drugs against tuberculosis. AIM: This study searched natural products for a new lead compound that targets MDR/XDR-TB. METHODS: An active compound was purified from the roots of Cynanchum atratum Bunge (Asclepiadaceae) after screening 1640 plant extracts, and its inhibitory effects against MDR/XDR strains and synergistic effects with existing anti-TB drugs were assessed using the resazurin, MGIT, and checkboard assays. RESULTS: (-)-Deoxypergularinine, purified from the roots of C. atratum, inhibited not only M. tuberculosis but also MDR/XDR strains. The minimum inhibitory concentrations (MICs) of (-)-deoxypergularinine for H37Ra, H37Rv, MDR, and XDR strains were all about 12.5 µg/ml. Moreover, combinations of (-)-deoxypergularinine with the first-line standard drugs rifampicin or isoniazid afforded six- and eight-fold reductions in drug MIC values, respectively, against strain H37Ra. CONCLUSIONS: (-)-Deoxypergularinine exerts anti-tubercular activities not only against normal tuberculosis strains but also MDR/XDR strains, and synergic effects with rifampicin and isoniazid for the H37Ra strain. The alkaloid may be valuable for targeting M/XDR M. tuberculosis.

Antimycobacterial activity of methanolic plant extract of Artemisia capillaris containing ursolic acid and hydroquinone against Mycobacterium tuberculosis.

OBJECTIVE: In order to protect against Mycobacterium tuberculosis (MTB) infection, novel drugs and new targets should be screened from the vast source of plants. We investigated the potentiality of the herbal plant of Artemisia capillaris extract (AC) against Mycobacterium tuberculosis. DESIGN: In this study, we isolated ursolic acid and hydroquinone by bio-activity guided fractionation from the methanol extracts of AC, and tested the inhibitory effects against several strains of MTB. Anti-mycobacterial evaluation of these compounds was carried out using the MGIT™ 960 and resazurin assay. Mycobacterial morphological changes due to the treatment of these compounds were further evaluated by Transmission electron microscopy (TEM). RESULTS: Ursolic acid (UA) and hydroquinone (HQ) inhibited the growth of both susceptible and resistant strains of M. tuberculosis. The MIC (minimum inhibitory concentration) values of both UA and HQ were 12.5 µg/ml against the susceptible strains of M. tuberculosis. Also both UA and HQ showed 12.5-25 µg/ml of MIC values against MDR/XDR MTB strains. However, against clinical strains of MTB, UA was found sensitive against those strains that are sensitive against both INH and RFP but resistant against those strains that are resistant to INH. On the other hand HQ was sensitive against all clinical strains. TEM image-analysis of the strain H37Ra after treatment with UA revealed cell wall lysis, whereas HQ-treated cells showed deformed cytoplasmic morphology. CONCLUSION: All these results indicate that AC extracts containing UA and HQ possess promising chemotherapeutic potency against MTB for future use.

Antifungal Activity and Action Mechanism of Histatin 5-Halocidin Hybrid Peptides against Candida ssp.

The candidacidal activity of histatin 5 is initiated through cell wall binding, followed by translocation and intracellular targeting, while the halocidin peptide exerts its activity by attacking the Candida cell membrane. To improve antimicrobial activities and to understand the killing mechanism of two peptides, six hybrid peptides were designed by conjugating histatin 5 and halocidin. A comparative approach was established to study the activity, salt tolerance, cell wall glucan binding assay, cytotoxicity, generation of ROS and killing kinetics. CD spectrometry was conducted to evaluate secondary structures of these hybrid peptides. Furthermore the cellular localization of hybrid peptides was investigated by confocal fluorescence microscopy. Of the six hybrid congeners, di-PH2, di-WP2 and HHP1 had stronger activities than other hybrid peptides against all tested Candida strains. The MIC values of these peptides were 1-2, 2-4 and 2-4 µg/ml, respectively. Moreover, none of the hybrid peptides was cytotoxic in the hemolytic assay and cell-based cytotoxicity assay. Confocal laser microscopy showed that di-PH2 and HHP1 were translocated into cytoplasm whereas di-WP2 was accumulated on surface of C. albicans to exert their candidacidal activity. All translocated peptides (Hst 5, P113, di-PH2) were capable of generating intracellular ROS except HHP1. Additionally, the KFH residues at C-terminal end of these peptides were assumed for core sequence for active translocation.

In vitro antituberculosis activity of diterpenoids from the Vietnamese medicinal plant Croton tonkinensis.

Diterpenoids from the Vietnamese medicinal plant Croton tonkinensis are rich in ent-kaurane, kaurane and the grayanane class and are valuable intermediate plant metabolites with different bioactivities. In this study, we report the antituberculosis activity of these diterpenoids against both susceptible and resistant strains of M. tuberculosis for the first time. All of the ent-kaurane, kaurane and grayanane diterpenoids showed high to moderate activity against Mycobacterium. The highest antituberculosis activity was observed for ent-1ß,7α,14ß-triacetoxykaur-16-en-15-one (cpp604), with MIC values of 0.78, 1.56 and 3.12-12.5 µg/ml against H37Ra, H37Rv and all other resistant strains of Mycobacterium tuberculosis examined. In addition, other ent-kaurane-type diterpenoids also showed very high activities against mycobacterium, including cpp609 (1.56 µg/ml), cpp610 (1.56 µg/ml), cpp601 (3.12-6.25 µg/ml), cpp602 (3.12-6.25 µg/ml), cpp607 (3.12-6.25 µg/ml) and cpp608 (3.12-6.25 µg/ml). From the structure-activity relationship, functional groups R3 and R5 of the ent-kaurane skeleton were found to modulate the antimycobacterial activity.

In vitro effect of ursolic acid on the inhibition of Mycobacterium tuberculosis and its cell wall mycolic acid.

Mycobacterium tuberculosis is a dangerous intracellular pathogen. In order to protect against mycobacterium infection, novel agents with anti-mycobacterial activity should be given emergency priority for evaluation. Ursolic acid (UA), a plant triterpenoid, shows promising bioactivities, including anti-mycobacterial potency. In this study, the action of UA against Mycobacterium tuberculosis H37Ra was evaluated, and the inhibitory concentration was found to range between 10 and 20 µg/ml in a resazurin assay and MGIT 960 instrument. The total mycolic acid in UA-treated H37Ra was detected and compared with INH-treated and non-treated bacterium by LC-MS/MS. Quantitative LC-MS/MS data confirmed that both UA and INH decreased mycolic acid biosynthesis in a dose-dependent manner. Thin-layer chromatogram (TLC) analysis showed that all mycolic acid subtypes were affected by UA treatment in the wild type but not in strains resistant to UA. Electron microscopy images also confirmed that UA treatment affected both H37Ra cell and intracellular content of H37Ra. Altogether, these data confirmed the promise of the inhibitory action of UA in mycolic acid, which might further delineate the mechanistic pathway of mycobacterial inhibition by UA.

Anti-Mycobacterial Activity of Tamoxifen Against Drug-Resistant and Intra-Macrophage Mycobacterium tuberculosis.

Recently, it has become a struggle to treat tuberculosis with the current commercial antituberculosis drugs because of the increasing emergence of multidrug-resistant (MDR) tuberculosis and extensively drug-resistant (XDR) tuberculosis. We evaluated here the antimycobacterial activity of tamoxifen, known as a synthetic anti-estrogen, against eight drug-sensitive or resistant strains of Mycobacterium tuberculosis (TB), and the active intracellular killing of tamoxifen on TB in macrophages. The results showed that tamoxifen had antituberculosis activity against drug-sensitive strains (MIC, 3.125-6.25 µg/ml) as well as drug-resistant strains (MIC, 6.25 to 12.5 µg/ml). In addition, tamoxifen profoundly decreased the number of intracellular TB in macrophages in a dose-dependent manner.