Synergy Potential of Ursolic Acid-Based Hybrid Molecules

Background:

Ursolic acid (UA, 3β-hydroxy-urs-12-en-28-oic acid), a pentacyclic triterpenoid from various medicinal plants, has been blessed with proven biological effects, including anti-inflammatory, anticancer, antidiabetic, antioxidant and antibacterial, but its bioavailability and solubility limit its clinical application.

Objective:

Synthesis of UA-based hybrid molecules to explore their antibacterial and synergy potential in combination with azithromycin (AZT) for the treatment of multidrug-resistant (MDR) bacterial infections.

Methods:

Hybrid molecules of UA with menthol, eugenol, and nalidixic acid (NAL) along with some other ester derivatives were synthesized, and evaluated for their antibacterial and synergy potential in combination with AZT against the clinical isolate of Escherichia coli in terms of their minimum inhibitory concentration (MIC), fold reduction in MIC, fractional inhibitory concentration index (FICI) and type of interaction. In silico screening of pharmacokinetic parameters, docking affinity against efflux pump proteins AcrA, AcrB, and TolC was performed on the most potent derivative 7 (3-O-nalidixoyl UA).

Results:

Derivative 7 showed MIC of 62.5 µg/mL and a strong synergistic effect with AZT reducing the MIC of AZT from 100 to 0.19 µg/mL (512-fold reduction) against E. coli at a concentration of 12.5 µg/mL. Other derivatives neither showed antibacterial activity of their own (MIC > 1000 µg/mL) nor any significant synergistic interaction in combination with AZT. The in silico studies on 7 revealed improved druggability parameters over the parent UA and NAL.

Conclusion:

The findings highlight derivative 7 as strong synergistic agent in combination with AZT which may be further investigated to render its efficient use for the treatment of MDR bacterial infections.

Coumarin-1,2,3-triazole Hybrid Molecules: An Emerging Scaffold for Combating Drug Resistance

Undoubtedly, antibiotics have saved billions of lives, but lack of novel antibiotics, development of resistance mechanisms in almost all clinical isolates of bacteria, and recurrent infections caused by persistent bacteria hamper the successful treatment of the infections. Due to the widespread emergence of resistance, even the new families of anti-microbial agents have a short life expectancy. Drugs acting on a single target often lead to drug resistance and are associated with various side effects. For overcoming this problem, either multidrug therapy, or a single drug acting on multiple targets may be used. The latter is called 'hybrid molecules,' which are formed by clubbing two biologically active pharmacophores together, with or without an appropriate linker. In this rapidly evolving era, the development of natural product-based hybrid molecules may be a super-alternative to multidrug therapy, for combating drug resistance caused by various bacterial and fungal strains. Coumarins (benzopyran-2-one) are one of the earliest reported plant secondary metabolites having a clinically proven diverse range of pharmacological properties. On the other hand, 1,2,3-triazole is a common pharmacophore in many drugs responsible for polar interactions, improving the solubility and binding affinity to biomolecular targets. In this review, we discuss recent advances in Coumarin-1,2,3-triazole hybrids as potential anti-bacterial agents, aiming to provide a useful platform for the exploration of new leads with a broader spectrum, more effectiveness and less toxicity with multiple modes of action for the development of cost-effective and safer drugs in the future.

In vitro, in vivo and in silico Antihyperglycemic Activity of Some Semi-synthetic Phytol Derivatives

BACKGROUND

Due to the prevalence of type-2 diabetes across the globe, there is unmet need to explore new molecular targets for the development of cost-effective and safer antihyperglycemic agents.

OBJECTIVE

Structural modification of phytol and evaluation of in vitro, in vivo and in silico antihyperglycemic activity of derivatives establishing the preliminary structure activity relationship (SAR).

METHODS

The semi-synthetic derivatives of phytol were prepared following previously described methods. The antihyperglycemic potential was measured in vitro in terms of increase in 2-deoxyglucose (2-DG) uptake by L-6 rat skeletal muscle cells as well as in vivo in sucrose-loaded (SLM) and streptozotocin (STZ)-induced diabetic rat models. The blood glucose profile was measured at 30, 60, 90, 120, 180, 240, 300 and 1440 min post administration of sucrose in rats. The in silico docking was performed on peroxisome proliferator-activated receptor gamma (PPARγ) as anti-diabetic target along with absorption, distribution, metabolism, excretion and toxicity (ADMET) studies.

RESULTS

Nine semi-synthetic ester derivatives: acetyl (1), lauroyl (2), palmitoyl (3), pivaloyl (4), trans-crotonyl (5), benzoyl (6), m-anisoyl (7), 3,4,5-trimethoxy benzoyl (8) cinnamoyl (9) along with bromo derivative (10) of phytol were prepared. The derivatives 9, 8 and 2 caused 4.5, 3.2 and 2.7 times more in vitro uptake of 2-DG respectively than rosiglitazone (ROSI). The derivatives showed significant improvement on oral glucose tolerance both in SLM (29.6-21%) as well as STZ-induced diabetic (30.8-19.0%) rats. The in silico ADMET, docking studies showed non-toxicity and high binding affinity with PPARγ.

CONCLUSION

The potent antihyperglycemic activity with favorable pharmacokinetics supports phytol derivatives as suitable antidiabetic lead.

Novel Antiplasmodial Agents from Christia vespertilionis

The roots, leaves and stems of Christia vespertilionis were separately and successively extracted with methanol and aqueous-methanol (1:4, v/v) and were evaluated in vitro for their antiplasmodial potential against Plasmodium falciparum NF-54. The aqueous-methanolic stem (AS) extract was the most active (IC50 7.5 μg/mL) followed by the methanolic leaf (ML) extract (IC50 32.0 μg/mL). The in vivo antimalarial activity of the combined plant extract of C. vespertilionis was also assessed in P. berghei infected mice, which showed 87.8% suppression of parasitaemia as compared with complete suppression by chloroquine on day 8. Finally, detailed chemical investigation of C. vespertilionis resulted in the isolation and characterization of fifteen compounds (1–15), of which two (1 and 4) are being reported for the first time from nature. The novel compound 1 possesses potent antiplasmodial activity (IC50 = 9.0 μg/mL).

Novel antiplasmodial agents from Christia vespertilionis

The roots, leaves and stems of Christia vespertilionis were separately and successively extracted with methanol and aqueous-methanol (1:4, v/v) and were evaluated in vitro for their antiplasmodial potential against Plasmodium falciparum NF-54. The aqueous-methanolic stem (AS) extract was the most active (IC50 7.5 microg/mL) followed by the methanolic leaf (ML) extract (IC50 32.0 microg/mL). The in vivo antimalarial activity of the combined plant extract of C. vespertilionis was also assessed in P. berghei infected mice, which showed 87.8% suppression of parasitaemia as compared with complete suppression by chloroquine on day 8. Finally, detailed chemical investigation of C. vespertilionis resulted in the isolation and characterization of fifteen compounds (1-15), of which two (1 and 4) are being reported for the first time from nature. The novel compound 1 possesses potent antiplasmodial activity (IC50 = 9.0 microg/mL).

Antiplasmodial potential of extracts from two species of genus Blumea

CONTEXT

A number of Blumea (Asteraceae) species are being used in traditional Chinese and Indian folklore medicines to cure various diseases including cancer, fungal and bacterial infections.

OBJECTIVE

To evaluate the in vitro antiplasmodial potential and cytotoxicity of various extracts and fractions of B. membranacea DC and B. eriantha DC and high performance liquid chromatography (HPLC) chemical fingerprinting of their crude extracts.

MATERIALS AND METHODS

The aerial parts and roots of B. membranacea and B. eriantha were extracted with ethanol and the extracts were successively partitioned with n-hexane, ethyl acetate and n-butanol, which were later evaluated for their in vitro antiplasmodial activity against Plasmodium falciparum NF-54 and in vitro cytotoxicities against non-cancerous Vero cell line. HPLC chemical fingerprinting was performed on extracts of B. membranacea and B. eriantha.

RESULTS

The n-hexane (MA1), ethyl acetate (MA2) fractions of aerial parts and n-butanol (MR3) fraction of roots of B. membranacea showed IC50 values of 17.4, 19.0 and 3.3 µg/mL respectively, while the n-hexane (EA1), ethyl acetate (EA2) fractions of aerial parts and ethyl acetate (ER2) fraction of roots of B. eriantha showed IC50 values of 25.0, 26.5 and 15.6 µg/mL, respectively, against P. falciparum NF-54. All these fractions were non-toxic to Vero cells.

DISCUSSION AND CONCLUSION

Both B. membranacea and B. eriantha possesses a high degree of selective antiplasmodial activity (selectivity index up to >60) and hence, may find their use in antimalarial phytopharmaceuticals as well as in discovery of a safer and novel antimalarial lead.

Antihyperglycemic agents from Ammannia multiflora

The serial chromatographic separation of chloroform and n-butanol fractions of Ammannia multiflora resulted in the isolation and characterization of 4-hydroxy-alpha-tetralone (1) and 3,3'-(2R,5R)-tetrahydrofuran-2,5-diyldiphenol (ammaniol, 2). Compound 1 was chemically modified into six semi-synthetic acyl and aryl derivatives (1A - 1F). The isolated compounds 1 and 2 along with semi-synthetic derivatives 1A - 1F were evaluated for in vitro antihyperglycemic activity employing 2-deoxyglucose uptake by L-6 rat muscle cell lines. The results indicated that both the isolates, as well as derivatives (1A - 1F), have the property to stimulate glucose uptake. Ammaniol (2) increased glucose uptake significantly (64.8%), while one of the aryl derivatives of 1, 4-O-(3,4,5-trimethoxybenzoyl)-alpha-tetralone (1D), showed potent antihyperglycemic activity and increased glucose uptake by 94.6%, even more than rosiglitazone (88.8%). Further, since 1D possesses better antihyperglycemic activity than rosiglitazone (standard), this might be a new safer antidiabetic drug of herbal origin.

Antihyperglycemic agents from Ammannia multiflora

The serial chromatographic separation of chloroform and n-butanol fractions of Ammannia multiflora resulted in the isolation and characterization of 4-hydroxy-α-tetralone (1) and 3,3′-(2 R,5 R)-tetrahydrofuran-2,5-diyldiphenol (ammaniol, 2). Compound 1 was chemically modified into six semi-synthetic acyl and aryl derivatives (1A - 1F). The isolated compounds 1 and 2 along with semi-synthetic derivatives 1A - 1F were evaluated for in vitro antihyperglycemic activity employing 2-deoxyglucose uptake by L-6 rat muscle cell lines. The results indicated that both the isolates, as well as derivatives (1A - 1F), have the property to stimulate glucose uptake. Ammaniol (2) increased glucose uptake significantly (64.8%), while one of the aryl derivatives of 1, 4- O-(3,4,5-trimethoxybenzoyl)-α-tetralone (1D), showed potent antihyperglycemic activity and increased glucose uptake by 94.6%, even more than rosiglitazone (88.8%). Further, since 1D possesses better antihyperglycemic activity than rosiglitazone (standard), this might be a new safer antidiabetic drug of herbal origin.

Quantitative determination of bioactive 4-hydroxy-α-tetralone, tetralone-4-O-β-D-glucopyranoside and ellagic acid in Ammannia baccifera (Linn.) by reversed-phase high-performance liquid chromatography

Ammannia baccifera is an important component of various Chinese herbal formulations for which a rapid, simple, sensitive, gradient and reproducible reversed-phase high-performance liquid chromatographic method has been developed for the quantitative estimation of its bioactive constituents, 4-hydroxy-α-tetralone (4H), tetralone-4-O-β-D-glucopyranoside (T4) and ellagic acid (EA). The chromatographic separation of samples was performed on a Chromatopak Peerless C18 (250 × 4.6 mm i.d., 5 µm) column by gradient elution with 0.1% trifluoroacetic acid in water and methanol at a flow rate of 0.6 mL/min, a column temperature at 25°C and ultraviolet detection at λ 254 nm. The limit of detection (LOD) and limit of quantification (LOQ) were 1.51 and 5.06 µg/mL for EA, 0.70 and 2.33 µg/mL for T4 and 0.22 and 0.73 µg/mL for 4H, respectively. Good results were achieved with respect to linearity (r(2) > 0.999), repeatability (relative standard deviation ≤ 1.73%) and recovery (99.06-100.76%). The method was validated for linearity, accuracy, repeatability, LOQ and LOD. The method is simple, accurate and precise and was successfully applied to the analysis of these three analytes in five different leaf and root samples of A. baccifera; the method may be recommended for routine quality control analysis of various Chinese herbal formulations containing A. baccifera.

Bioenhancing and antimycobacterial agents from Ammannia multiflora

The methanolic extract of Ammannia multiflora (Lythraceae) showed significant bioenhancing activity with the antibiotic nalidixic acid. Bioassay-guided fractionation of MeOH extract resulted in the isolation of a novel compound, 2,5-bis-(3,3'-hydroxyaryl)tetrahydrofuran, named as ammaniol (5), along with 9 other known compounds (1-4, 6-10). Furthermore, compound 4-hydroxy- α-tetralone (1) was converted into five semisynthetic acyl derivatives, 1A-1E, which were evaluated along with compounds 1, 5, 6, 9, and 10 for their bioenhancing activity in combination with nalidixic acid against the two strains, CA8000 and DH5 α, of Escherichia coli. The results showed that the methanolic extract of A. multiflora and compounds 1 and 9 possessed significant bioenhancing activity and reduced the dose of nalidixic acid fourfold while compounds 5, 6, 10 and semisynthetic derivatives 1A- 1E reduced the dose of nalidixic acid twofold. Compound 5 was also tested for antimycobacterial activity against Mycobacterium H37Rv and was found to show moderate activity (MIC 25 µg/mL) against this pathogen.