Enhancing effect of natural adjuvant, panduratin A, on antibacterial activity of colistin against multidrug-resistant Acinetobacter baumannii.

Colistin- and carbapenem-resistant Acinetobacter baumannii is a serious multidrug resistant (MDR) bacterium in clinical settings. Discovery of new antibacterial drugs against MDR is facing multiple challenges in drug development. Combination of known antibiotics with a robust adjuvant might be an alternative effective strategy for MDR treatment. In the study herein, we report an antibiotic adjuvant activity of a natural compound panduratin A from fingerroot (Boesenbergia rotunda) as a potent adjuvant to colistin. The present study investigated the antibiotic adjuvant effect of panduratin A against 10 colistin- and carbapenem-resistant A. baumannii. Antibacterial activities were tested by broth microdilution method. Biofilm assay was used to determine the efficacy of panduratin A in biofilm formation inhibition on two representative strains Aci46 and Aci44. Genomic and transcriptomic analyses of colistin- and carbapenem-resistant A. baumannii strains were used to identify potential resistance and tolerance mechanism in the bacteria. Panduratin A-colistin combination showed an increased effect on antibacterial in the A. baumannii. However, panduratin A did not improve the antibacterial activity of imipenem. In addition, panduratin A improves anti-biofilm activity of colistin against Aci44 and Aci46, the colistin- and carbapenem-resistant A. baumannii. Panduratin A markedly enhances bactericidal and anti-biofilm activity of colistin against colistin- resistant A. baumannii. Based on genome comparisons, single nucleotide polymorphism (SNP) patterns in six genes encoding biofilm and lipid A biosynthesis were shared in Aci44 and Aci46. In Aci44, we identified a partial sequence of pmrB encoding a polymyxin resistant component PmrB, whereas a full length of pmrB was observed in Aci46. RNA-seq analyses of Aci44 revealed that panduratin A-colistin combination induced expression of ribosomal proteins and oxidative stress response proteins, whereas iron transporter and MFS-type transporter systems were suppressed. Panduratin A-colistin combination could promote intracellular reactive oxygen species (ROS) accumulation could lead to the cidal effect on colistin-resistant A. baumannii. Combination of panduratin A and colistin showed a significant increase in colistin efficacy against colistin- resistant A. baumannii in comparison of colistin alone. Genomic comparison between Aci44 and Aci46 showed mutations and SNPs that might affect different phenotypes. Additionally, based on RNA-Seq, panduratin A-colistin combination could lead to ROS production and accumulation. These findings confirmed the potency of panduratin as colistin adjuvant against multidrug resistant A. baumannii.

Pyranonaphthoquinones and Naphthoquinones from the Stem Bark of Ventilago harmandiana and Their Anti-HIV-1 Activity.

Seven previously undescribed compounds, including five pyranonaphthoquinones (ventilanones L-P) and two naphthoquinones (ventilanones Q and R), along with 15 known compounds were isolated from the stem bark of Ventilago harmandiana (Rhamnaceae). The structures were established by extensive analysis of their spectroscopic data. The absolute configuration of ventilanone L was established from single crystal X-ray crystallographic analysis using Cu Kα radiation and from its electronic circular dichroism data. Anti-HIV-1 activity using a syncytium inhibition assay and the cytotoxic activities of some isolated compounds were evaluated. Compounds 12, 13, 15, and 16 showed activity against syncytium formation with half maximal effective concentration (EC50) values ranging from 9.9 to 47 µM (selectivity index (SI) 2.4-4.5).

Bioactive tetrahydrofuran lignans from roots, stems, leaves and twigs of Anogeissus rivularis.

Four previously undescribed tetrahydrofuran lignans, named anorisols A-D (1-4) and fourteen known compounds (5-18) were isolated from the roots, stems, leaves and twigs of Anogeissus rivularis. The chemical structures were elucidated on the basis of their spectroscopic data and by comparison with the literature data. The absolute configurations of 1-4 were established by comparison of the experimental ECD spectra with the calculated ECD spectra. Some isolated compounds were evaluated for their cytotoxic activity as well as anti-HIV-1 activity employing reverse transcriptase (RT) and syncytium reduction assays using the ΔTat/RevMC99 virus in 1A2 cell line systems. Compound 6 displayed the most potent activity in syncytium inhibition assay with effective concentration at 50% (EC50) value of 13.3 µM (SI >3.0). In the reverse transcriptase assay, compound 1 exhibited moderate activity with IC50 value of 213.9 µM.

Boesenmaxane Diterpenoids from Boesenbergia maxwellii.

Three new diterpenoids, boesenmaxanes A-C (1-3), with an unprecedented core skeleton consisting of an unusual C-C bond between C-12 and an exo-cyclic methylene C-13, were isolated from the rhizome extracts of Boesenbergia maxwellii. The structures were elucidated by analysis of spectroscopic and X-ray diffraction data. Electronic circular dichroism spectra were used to determine the absolute configuration. All the isolates were evaluated for their cytotoxic effects, anti-HIV activity, and antimicrobial activity. Boesenmaxanes A and C (1 and 3) showed significant inhibitory activity in the syncytium reduction assay, with EC50 values of 55.2 and 27.5 µM, respectively.

Anti-HIV-1 activities of constituents from the rhizomes of Boesenbergia thorelii.

A new lignan, thoreliin A (1), and a new bisnorlignan, thoreliin B (2), were isolated from a MeOH extract of the rhizomes of Boesenbergia thorelii. In addition, the known bisnorlignans 3 and 4, neolignan 5, phenylpropanoids 6-15, as well as benzenoids 18-21 were also obtained from the same source. The structures were elucidated based on their spectroscopic data. By single crystal X-ray analysis, the relative stereochemistry of 1 was confirmed. All isolated compounds were evaluated for anti-HIV-1 activities. Among them, thoreliin A (1) exhibited anti-HIV-1 activities on both HIV-1 reverse transcriptase (41.43% inhibition at 200 µg/mL) and syncytium reduction assays (EC50 20.6 µM, SI 3.7), while compounds 3-6, 9 and 11-21 showed anti-HIV-1 activity only in the anti-syncytium assay (EC50 6.6-454.1 µM, SI >1.32-7.75).

Anti-HIV and cytotoxic biphenyls, benzophenones and xanthones from stems, leaves and twigs of Garcinia speciosa.

Eleven previously undescribed compounds, including four benzophenones (garciosones A-D), four xanthones (garciosones E-H) and three biphenyls (garciosines A-C), along with eighteen known compounds were isolated from the stems, leaves and twigs of Garcinia speciosa Wall. (Clusiaceae). Their structures were established by extensive spectroscopic analysis. For garciosines A-C, the structures were confirmed by single crystal X-ray diffraction analysis. Most of the isolated compounds were evaluated for their cytotoxic activity and anti-HIV-1 activity using the syncytium inhibition assay and HIV-1 reverse transcriptase (RT) assay. The known compounds, 4,6,3',4'-tetrahydroxy-2-methoxybenzophenone and macluraxanthone, displayed significant cytotoxic activity with the ED50 in the range of 1.85-11.76 µM. 1,5-Dihydroxyxanthone exhibited the most potent anti-HIV activity against syncytium formation with EC50 < 17.13 µM (SI > 25.28) and 2-(3,3-dimethylallyl)-1,3,7-trihydroxyxanthone was the most active compound in the HIV-1 reverse transcriptase assay with IC50 value of 58.24 µM. Structure-activity relationship of some isolated compounds were also discussed.

Polycyclic polyprenylated acylphloroglucinols and biphenyl derivatives from the roots of Garcinia nuntasaenii Ngerns. & Suddee.

Seven previously undescribed compounds, including three polycyclic polyprenylated acylphloroglucinols (garcinuntins A-C), three biphenyl derivatives (garcinuntabiphenyls A-C) and a lanostane triterpene (garcinuntine), along with thirteen known compounds were isolated from the root of Garcinia nuntasaenii Ngerns. & Suddee. Their structures were elucidated on the basis of spectroscopic techniques. For garcinuntins A-C, the absolute configurations were confirmed by the combination of single X-ray crystallography and ECD calculations. Anti-HIV activity using anti-HIV-1 reverse transcriptase and syncytium inhibition assays, and cytotoxic activity against a panel of cultured mammalian cancer cell lines of isolated compounds were investigated.

Cytotoxic, antitopoisomerase IIα, and anti-HIV-1 activities of triterpenoids isolated from leaves and twigs of Gardenia carinata.

Eight new cycloartane triterpenoids (1-8), named carinatins A-H, and the known compounds secaubryolide (9) and dikamaliartane D (10) were isolated from the leaves and twigs of Gardenia carinata. Their structures were determined on the basis of spectroscopic methods. Cytotoxic, antitopoisomerase IIα, and anti-HIV-1 activities of compounds 1-7, 9, and 10 were investigated.

Purification and characterization of anti-HIV-1 protein from Canna indica L. leaves.

A novel 10 kDa protein with anti-HIV-1 reverse transcriptase (RT) inhibitory activity was isolated from leaves of Canna indica L. using a combination of native-PAGE and ammonium sulfate precipitation. HIV-1 and RT inhibitory activity was measured using a syncytium forming (deltaTat/Rev) MC99 virus in Tat/Rev transfected 1A2 cell line and ELISA technique, respectively. Edman N-terminal and internal amino acid sequence (using LC-MS-MS) determination revealed the 10 kDa Canna indica L. leaf protein as a putative plastocyanin. This is the first report of a plant plastocyanin with HIV-1 RT inhibitory property.

A new conjugated amide-dimer from the aerial parts of Piper submultinerve.

Bioassay-guided fractionation and purification of the aerial parts of Piper submultinerve led to the isolation of a new conjugated amide-dimer, submultinamide A (1), along with 11 known compounds. The structures were determined on the basis of spectroscopic methods. Among the tested compounds, pellitorine (2), guineensine (4), N-benzylcinnamide (6) and aristolactam BII (8) showed significant activities in the anti-syncytium assay using (ΔTat/Rev)MC99 virus and 1A2 cell line system, whereas 2 was most active (EC50 35.1 µM and selectivity index 4.7). In the HIV-1 reverse transcriptase assay, only 4 was active with IC50 50.8 µM.

DNA topoisomerase IIα inhibitory and anti-HIV-1 flavones from leaves and twigs of Gardenia carinata.

Four new flavones, 5,2'-dihydroxy-7,3',4',5'-tetramethoxyflavone (1), 5,2',5'-trihydroxy-7,3',4'-trimethoxyflavone (2), 5,7,2',5'-tetrahydroxy-6,3',4'-trimethoxyflavone (3) and 5,2',5'-trihydroxy-6,7,3',4'-tetramethoxyflavone (4), along with the known 5,3'-dihydroxy-6,7,4',5'-tetramethoxyflavone (5), 5,7,3',5'-tetrahydroxy-6,4'-dimethoxyflavone (6), syringaldehyde, vanillic acid and scopoletin were isolated from the leaves and twigs of Gardenia carinata (Rubiaceae). Their structures were determined by spectroscopic methods. Flavone 2 exhibited cytotoxic activity against P-388 and MCF-7 cell lines, while 3, 5 and 6 were active only in P-388 cell line. All active compounds were found to inhibit DNA topoisomerase IIα activity, which may be responsible for the observed cytotoxicity. Flavones 1-3, 5 and 6 also exhibited anti-HIV-1 activity in the anti-syncytium assay using (∆Tat/rev)MC99 virus and 1A2 cell line system; 2 was most potent. Only flavones 1 and 6 showed considerably activity against HIV-1 reverse transcriptase.

A new diarylheptanoid from the rhizomes of Zingiber mekongense.

A new diarylheptanoid, (3S,5S)-3,5-diacetoxy-1,7-bis(3,4,5-trimethoxyphenyl)heptane (1), together with the known docosyl trans-ferulate (2), (1S,2S,4S)-p-menthan-1,2,4-triol (3), 5αH-eudesmane-4α,11-diol (4), 5αH-eudesmane-4ß,11-diol (5), 4α,10ß-dihydroxy-1ßH,5αH-guaia-6-ene (guaianediol) (6), (+)-galanolactone (7), (E)-labda-8(17),12(13)-dien-15,16-olide (8), labda-8(17),13(14)-dien-15,16-olide (9), 3,5-dihydroxy-7,4'-dimethoxyflavone (10) and 3,5,3'-trihydroxy-7,4'-dimethoxyflavone (11) were isolated from the rhizomes of Zingiber mekongense. Their structures were determined by spectroscopic methods. The stereochemistry of 1 was proved through chemical conversion. Compounds 1, 4-7 and 9-11 exhibited anti-HIV-1 activities in the anti-syncytium assay using (∆Tat/rev)MC99 virus and 1A2 cell line system, while only compounds 7 and 11 were found active in the HIV-1 reverse transcriptase assay.

Anti-HIV-1 diterpenoids from leaves and twigs of Polyalthia sclerophylla.

Bioassay-guided fractionation and purification of the anti-HIV-1-active MeOH extract from the leaves and twigs of Polyalthia sclerophylla led to the isolation of two new compounds, ENT-kaur-sclerodimer ( 1) and cyclotucanol 3-palmitate ( 2), along with the known ENT-kaur-16-en-19-oic acid ( 3), 15 beta-hydroxy- ENT-kaur-16-en-19-oic acid ( 4), 15 beta-acetoxy- ENT-kaur-16-en-19-oic acid ( 5), 15-oxo- ENT-kaur-16-en-19-oic acid ( 6), 16 alpha,17-dihydroxy- ENT-kauran-19-oic acid ( 7), 16 alpha-hydroxy- ENT-kauran-19-oic acid (xylopic acid) ( 8), a pseudodimer (15 alpha-hydroxy- ENT-kaur-16-en-19-oic acid/17-hydroxy- ENT-kaur-15-en-19-oic acid) ( 9), ermanin, nicotiflorin, and allantoin. Among these isolates, compound 3 was the most active in both anti-syncytium (EC (50) 13.7 microg/mL and selectivity index 3.1) and HIV-1 reverse transcriptase (IC (50) 34.1 microg/mL) assays.

Dichapetalin-type triterpenoids and lignans from the aerial parts of Phyllanthus acutissima.

Chemical investigation of the aerial parts of Phyllanthus acutissima resulted in the isolation of five new dichapetalin-type triterpenoids, acutissimatriterpenes A-E ( 1- 5), and two new lignans, acutissimalignans A ( 6) and B ( 7), along with two known lignans and three known ellagic acid derivatives. The structures of 1- 7 were determined mainly on the basis of spectroscopic methods. The compounds obtained were evaluated for cytotoxic and anti-HIV-1 activities.

Anti HIV-1 flavonoid glycosides from Ochna integerrima.

Bioassay-guided fractionation of the anti-HIV-1 active EtOAc extract from leaves and twigs of Ochna integerrima led to the isolation of five new flavonoid glycosides 1 - 5, five known flavonoids 6 - 10, and two known flavonoid glycosides 11 and 12. Structures were determined based on spectroscopic analyses. 6- gamma, gamma-Dimethylallyldihydrokaempferol 7- O- beta-D-glucoside (1), 6-gamma, gamma-dimethylallylquercetin 7- O- beta- D-glucoside (3), 6-(3-hydroxy-3-methylbutyl)taxifolin 7- O- beta-D-glucoside (4), 6-(3-hydroxy-3-methylbutyl)quercetin 7- O-beta-D-glucoside (5), and 6-gamma, gamma-dimethylallyltaxifolin 7-O-beta-D-glucoside (11) showed anti-HIV-1 activities in the syncytium assay using the (Delta Tat/rev)MC99 virus and the 1A2 cell line system with EC(50) values ranging from 14.0 - 102.4 microg/mL. Furthermore, ochnaflavone 7''-O-methyl ether (7) and 2'', 3''-dihydroochnaflavone 7''-O-methyl ether (8) were very active; they exerted activities in the syncytium assay with EC(50) values of 2.0 and 0.9 microg/mL, respectively, and likewise inhibited HIV-1 reverse transcriptase (RT) with IC(50) values of 2.0 and 2.4 microg/mL, respectively.